publicationDate,title,abstract,id
2017-09-29,Non-local Gilbert damping tensor within the torque-torque correlation model,"An essential property of magnetic devices is the relaxation rate in magnetic
switching which depends strongly on the damping in the magnetisation dynamics.
It was recently measured that damping depends on the magnetic texture and,
consequently, is a non-local quantity. The damping enters the
Landau-Lifshitz-Gilbert equation as the phenomenological Gilbert damping
parameter $\alpha$, that does not, in a straight forward formulation, account
for non-locality. Efforts were spent recently to obtain Gilbert damping from
first principles for magnons of wave vector $\mathbf{q}$. However, to the best
of our knowledge, there is no report about real space non-local Gilbert damping
$\alpha_{ij}$. Here, a torque-torque correlation model based on a tight binding
approach is applied to the bulk elemental itinerant magnets and it predicts
significant off-site Gilbert damping contributions, that could be also
negative. Supported by atomistic magnetisation dynamics simulations we reveal
the importance of the non-local Gilbert damping in atomistic magnetisation
dynamics. This study gives a deeper understanding of the dynamics of the
magnetic moments and dissipation processes in real magnetic materials. Ways of
manipulating non-local damping are explored, either by temperature, material's
doping or strain.",1709.10365v1
2016-02-23,Experimental Investigation of Temperature-Dependent Gilbert Damping in Permalloy Thin Films,"The Gilbert damping of ferromagnetic materials is arguably the most important
but least understood phenomenological parameter that dictates real-time
magnetization dynamics. Understanding the physical origin of the Gilbert
damping is highly relevant to developing future fast switching spintronics
devices such as magnetic sensors and magnetic random access memory. Here, we
report an experimental study of temperature-dependent Gilbert damping in
permalloy (Py) thin films of varying thicknesses by ferromagnetic resonance.
From the thickness dependence, two independent contributions to the Gilbert
damping are identified, namely bulk damping and surface damping. Of particular
interest, bulk damping decreases monotonically as the temperature decreases,
while surface damping shows an enhancement peak at the temperature of ~50 K.
These results provide an important insight to the physical origin of the
Gilbert damping in ultrathin magnetic films.",1602.07325v1
2019-02-22,Strongly Enhanced Gilbert Damping in 3d Transition Metal Ferromagnet Monolayers in Contact with Topological Insulator Bi2Se3,"Engineering Gilbert damping of ferromagnetic metal films is of great
importance to exploit and design spintronic devices that are operated with an
ultrahigh speed. Based on scattering theory of Gilbert damping, we extend the
torque method originally used in studies of magnetocrystalline anisotropy to
theoretically determine Gilbert dampings of ferromagnetic metals. This method
is utilized to investigate Gilbert dampings of 3d transition metal ferromagnet
iron, cobalt and nickel monolayers that are contacted by the prototypical
topological insulator Bi2Se3. Amazingly, we find that their Gilbert dampings
are strongly enhanced by about one order in magnitude, compared with dampings
of their bulks and free-standing monolayers, owing to the strong spin-orbit
coupling of Bi2Se3. Our work provides an attractive route to tailoring Gilbert
damping of ferromagnetic metallic films by putting them in contact with
topological insulators.",1902.08700v1
2018-08-20,Gilbert damping of [Co/Pd]n/Py multilayer thin films,"Understanding the Gilbert damping in exchange-coupled multilayer materials is
particularly important to develop future fast switching spintronics devices.
Here, we report an experimental investigation of temperature-dependent Gilbert
damping in [Co/Pd]n/Py multilayer films of varying the number of Co/Pd
repetitions by ferromagnetic resonance. The results demonstrate that three
independent contributions to the Gilbert damping are identified, namely the
intrinsic Gilbert damping, the inhomogeneous linewidth broadening and the
two-magnon scattering contribution. Of particular interest, the two-magnon
scattering intensity increases as the enlargement of number repetitions of
Co/Pd due to the larger pinning effect at the interface between Py and the
Co/Pd layers. The Gilbert damping increases monotonically as the temperature
decreases from 300K to 50K. Our findings open the door to comprehend the
physical origin of the Gilbert damping in ultrathin exchange-coupled multilayer
films.",1808.06515v2
2007-08-24,Enhancement of the Gilbert damping constant due to spin pumping in noncollinear ferromagnet/nonmagnet/ferromagnet trilayer systems,"We analyzed the enhancement of the Gilbert damping constant due to spin
pumping in non-collinear ferromagnet / non-magnet / ferromagnet trilayer
systems. We show that the Gilbert damping constant depends both on the
precession angle of the magnetization of the free layer and on the direction of
the magntization of the fixed layer. We find the condition to be satisfied to
realize strong enhancement of the Gilbert damping constant.",0708.3323v1
2017-06-14,Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order,"Half-metallicity and low magnetic damping are perpetually sought for in
spintronics materials and full Heusler alloys in this respect provide
outstanding properties. However, it is challenging to obtain the well-ordered
half-metallic phase in as-deposited full Heusler alloys thin films and theory
has struggled to establish a fundamentals understanding of the temperature
dependent Gilbert damping in these systems. Here we present a study of the
temperature dependent Gilbert damping of differently ordered as-deposited
Co2FeAl full Heusler alloy thin films. The sum of inter- and intraband electron
scattering in conjunction with the finite electron lifetime in Bloch states
govern the Gilbert damping for the well-ordered phase in contrast to the
damping of partially-ordered and disordered phases which is governed by
interband electronic scattering alone. These results, especially the ultralow
room temperature intrinsic damping observed for the well-ordered phase provide
new fundamental insights to the physical origin of the Gilbert damping in full
Heusler alloy thin films.",1706.04670v2
2023-11-27,Gilbert damping in two-dimensional metallic anti-ferromagnets,"A finite spin life-time of conduction electrons may dominate Gilbert damping
of two-dimensional metallic anti-ferromagnets or anti-ferromagnet/metal
heterostructures. We investigate the Gilbert damping tensor for a typical
low-energy model of a metallic anti-ferromagnet system with honeycomb magnetic
lattice and Rashba spin-orbit coupling for conduction electrons. We distinguish
three regimes of spin relaxation: exchange-dominated relaxation for weak
spin-orbit coupling strength, Elliot-Yafet relaxation for moderate spin-orbit
coupling, and Dyakonov-Perel relaxation for strong spin-orbit coupling. We
show, however, that the latter regime takes place only for the in-plane Gilbert
damping component. We also show that anisotropy of Gilbert damping persists for
any finite spin-orbit interaction strength provided we consider no spatial
variation of the N\'eel vector. Isotropic Gilbert damping is restored only if
the electron spin-orbit length is larger than the magnon wavelength. Our theory
applies to MnPS3 monolayer on Pt or to similar systems.",2311.16268v2
2008-07-31,Scattering Theory of Gilbert Damping,"The magnetization dynamics of a single domain ferromagnet in contact with a
thermal bath is studied by scattering theory. We recover the
Landau-Liftshitz-Gilbert equation and express the effective fields and Gilbert
damping tensor in terms of the scattering matrix. Dissipation of magnetic
energy equals energy current pumped out of the system by the time-dependent
magnetization, with separable spin-relaxation induced bulk and spin-pumping
generated interface contributions. In linear response, our scattering theory
for the Gilbert damping tensor is equivalent with the Kubo formalism.",0807.5009v1
2024-01-18,Real-space nonlocal Gilbert damping from exchange torque correlation applied to bulk ferromagnets and their surfaces,"In this work we present an ab initio scheme based on linear response theory
of exchange torque correlation, implemented into the real-space
Korringa-Kohn-Rostoker (RS-KKR) framework to calculate diagonal elements of the
atomic-site-dependent intrinsic Gilbert damping tensor. The method is first
applied to bcc iron and fcc cobalt bulk systems. Beside reproducing earlier
results from the literature for those bulk magnets, the effect of the lattice
compression is also studied for Fe bulk, and significant changes for the
Gilbert damping are found. Furthermore, (001)-oriented surfaces of Fe and Co
are also investigated. It is found that the on-site Gilbert damping increases
in the surface atomic layer and decreases in the subsurface layer, and
approaches the bulk value moving further inside the magnets. Realistic atomic
relaxation of the surface layers enhances the identified effects. The
first-neighbor damping parameters are extremely sensitive to the surface
relaxation. Despite their inhomogeneity caused by the surface, the transverse
Gilbert damping tensor components remain largely insensitive to the
magnetization direction.",2401.09938v2
2007-06-12,Gilbert and Landau-Lifshitz damping in the presense of spin-torque,"A recent article by Stiles et al. (cond-mat/0702020) argued in favor of the
Landau-Lifshitz damping term in the micromagnetic equations of motion over that
of the more commonly accepted Gilbert damping form. Much of their argument
revolved around spin-torque driven domain wall motion in narrow magnetic wires,
since the presence of spin-torques can more acutely draw a distinction between
the two forms of damping. In this article, the author uses simple arguments and
examples to offer an alternative point of view favoring Gilbert.",0706.1736v1
2008-04-04,Inhomogeneous Gilbert damping from impurities and electron-electron interactions,"We present a unified theory of magnetic damping in itinerant electron
ferromagnets at order $q^2$ including electron-electron interactions and
disorder scattering. We show that the Gilbert damping coefficient can be
expressed in terms of the spin conductivity, leading to a Matthiessen-type
formula in which disorder and interaction contributions are additive. In a weak
ferromagnet regime, electron-electron interactions lead to a strong enhancement
of the Gilbert damping.",0804.0820v2
2006-12-01,Gilbert damping and spin Coulomb drag in a magnetized electron liquid with spin-orbit interaction,"We present a microscopic calculation of the Gilbert damping constant for the
magnetization of a two-dimensional spin-polarized electron liquid in the
presence of intrinsic spin-orbit interaction. First we show that the Gilbert
constant can be expressed in terms of the auto-correlation function of the
spin-orbit induced torque. Then we specialize to the case of the Rashba
spin-orbit interaction and we show that the Gilbert constant in this model is
related to the spin-channel conductivity. This allows us to study the Gilbert
damping constant in different physical regimes, characterized by different
orderings of the relevant energy scales -- spin-orbit coupling, Zeeman
coupling, momentum relaxation rate, spin-momentum relaxation rate, spin
precession frequency -- and to discuss its behavior in various limits.
Particular attention is paid to electron-electron interaction effects,which
enter the spin conductivity and hence the Gilbert damping constant via the spin
Coulomb drag coefficient.",0612015v1
2021-01-07,Mechanisms behind large Gilbert damping anisotropies,"A method with which to calculate the Gilbert damping parameter from a
real-space electronic structure method is reported here. The anisotropy of the
Gilbert damping with respect to the magnetic moment direction and local
chemical environment is calculated for bulk and surfaces of Fe$_{50}$Co$_{50}$
alloys from first principles electronic structure in a real space formulation.
The size of the damping anisotropy for Fe$_{50}$Co$_{50}$ alloys is
demonstrated to be significant. Depending on details of the simulations, it
reaches a maximum-minimum damping ratio as high as 200%. Several microscopic
origins of the strongly enhanced Gilbert damping anisotropy have been examined,
where in particular interface/surface effects stand out, as do local
distortions of the crystal structure. Although theory does not reproduce the
experimentally reported high ratio of 400% [Phys. Rev. Lett. 122, 117203
(2019)], it nevertheless identifies microscopic mechanisms that can lead to
huge damping anisotropies.",2101.02794v2
2018-08-13,Gilbert damping phenomenology for two-sublattice magnets,"We present a systematic phenomenological description of Gilbert damping in
two-sublattice magnets. Our theory covers the full range of materials from
ferro- via ferri- to antiferromagnets. Following a Rayleigh dissipation
functional approach within a Lagrangian classical field formulation, the theory
captures intra- as well as cross-sublattice terms in the Gilbert damping,
parameterized by a 2$\times$2 matrix. When spin-pumping into an adjacent
conductor causes dissipation, we obtain the corresponding Gilbert damping
matrix in terms of the interfacial spin-mixing conductances. Our model
reproduces the experimentally observed enhancement of the ferromagnetic
resonance linewidth in a ferrimagnet close to its compensation temperature
without requiring an increased Gilbert parameter. It also predicts new
contributions to damping in an antiferromagnet and suggests the resonance
linewidths as a direct probe of the sublattice asymmetry, which may stem from
boundary or bulk.",1808.04385v2
2021-07-02,Anomalous Gilbert Damping and Duffing Features of the SFS {\boldmath $\varphi_0$} Josephson Junction,"We demonstrate unusual features of phase dynamics, IV-characteristics and
magnetization dynamics of the $\varphi_0$ Josephson junction at small values of
spin-orbit interaction, ratio of Josephson to magnetic energy and Gilbert
damping. In particular, an anomalous shift of the ferromagnetic resonance
frequency with an increase of Gilbert damping is found. The ferromagnetic
resonance curves show the Duffing oscillator behaviour, reflecting the
nonlinear nature of Landau-Lifshitz-Gilbert (LLG) equation. Based on the
numerical analysis of each term in LLG equation we obtained an approximated
equation demonstrated both damping effect and Duffing oscillator features. The
resulting Duffing equation incorporates the Gilbert damping in a special way
across the dissipative term and the restoring force. A resonance method for the
determination of spin-orbit interaction in noncentrosymmetric materials which
play the role of barrier in $\varphi_0$ junctions is proposed.",2107.00982v3
2023-03-07,Electrically tunable Gilbert damping in van der Waals heterostructures of two-dimensional ferromagnetic metals and ferroelectrics,"Tuning the Gilbert damping of ferromagnetic (FM) metals via a nonvolatile way
is of importance to exploit and design next-generation novel spintronic
devices. Through systematical first-principles calculations, we study the
magnetic properties of the van der Waals heterostructure of two-dimensional FM
metal CrTe2 and ferroelectric (FE) In2Te3 monolayers. The ferromagnetism of
CrTe2 is maintained in CrTe2/In2Te3 and its magnetic easy axis can be switched
from in-plane to out-of-plane by reversing the FE polarization of In2Te3.
Excitingly, we find that the Gilbert damping of CrTe2 is tunable when the FE
polarization of In2Te3 is reversed from upward to downward. By analyzing the
k-dependent contributions to the Gilbert damping, we unravel that such
tunability results from the changed intersections between the bands of CrTe2
and Fermi level on the reversal of the FE polarizations of In2Te3 in
CrTe2/In2Te3. Our work provides an appealing way to electrically tailor Gilbert
dampings of two-dimensional FM metals by contacting them with ferroelectrics.",2303.03852v1
2015-08-28,The inviscid limit for the Landau-Lifshitz-Gilbert equation in the critical Besov space,"We prove that in dimensions three and higher the Landau-Lifshitz- Gilbert
equation with small initial data in the critical Besov space is globally
wellposed in a uniform way with respect to the Gilbert damping parameter. Then
we show that the global solution converges to that of the Schrodinger maps in
the natural space as the Gilbert damping term vanishes. The proof is based on
some studies on the derivative Ginzburg-Landau equations.",1508.07118v3
2023-09-20,Evaluating Gilbert Damping in Magnetic Insulators from First Principles,"Magnetic damping has a significant impact on the performance of various
magnetic and spintronic devices, making it a long-standing focus of research.
The strength of magnetic damping is usually quantified by the Gilbert damping
constant in the Landau-Lifshitz-Gilbert equation. Here we propose a
first-principles based approach to evaluate the Gilbert damping constant
contributed by spin-lattice coupling in magnetic insulators. The approach
involves effective Hamiltonian models and spin-lattice dynamics simulations. As
a case study, we applied our method to Y$_3$Fe$_5$O$_{12}$, MnFe$_2$O$_4$ and
Cr$_2$O$_3$. Their damping constants were calculated to be $0.8\times10^{-4}$,
$0.2\times10^{-4}$, $2.2\times 10^{-4}$, respectively at a low temperature. The
results for Y$_3$Fe$_5$O$_{12}$ and Cr$_2$O$_3$ are in good agreement with
experimental measurements, while the discrepancy in MnFe$_2$O$_4$ can be
attributed to the inhomogeneity and small band gap in real samples. The
stronger damping observed in Cr$_2$O$_3$, compared to Y$_3$Fe$_5$O$_{12}$,
essentially results from its stronger spin-lattice coupling. In addition, we
confirmed a proportional relationship between damping constants and the
temperature difference of subsystems, which had been reported in previous
studies. These successful applications suggest that our approach serves as a
promising candidate for estimating the Gilbert damping constant in magnetic
insulators.",2309.11152v1
2019-06-25,Conductivity-Like Gilbert Damping due to Intraband Scattering in Epitaxial Iron,"Confirming the origin of Gilbert damping by experiment has remained a
challenge for many decades, even for simple ferromagnetic metals. In this
Letter, we experimentally identify Gilbert damping that increases with
decreasing electronic scattering in epitaxial thin films of pure Fe. This
observation of conductivity-like damping, which cannot be accounted for by
classical eddy current loss, is in excellent quantitative agreement with
theoretical predictions of Gilbert damping due to intraband scattering. Our
results resolve the longstanding question about a fundamental damping mechanism
and offer hints for engineering low-loss magnetic metals for cryogenic
spintronics and quantum devices.",1906.10326v2
2008-08-28,Gilbert Damping in Conducting Ferromagnets II: Model Tests of the Torque-Correlation Formula,"We report on a study of Gilbert damping due to particle-hole pair excitations
in conducting ferromagnets. We focus on a toy two-band model and on a four-band
spherical model which provides an approximate description of ferromagnetic
(Ga,Mn)As. These models are sufficiently simple that disorder-ladder-sum vertex
corrections to the long-wavelength spin-spin response function can be summed to
all orders. An important objective of this study is to assess the reliability
of practical approximate expressions which can be combined with electronic
structure calculations to estimate Gilbert damping in more complex systems.",0808.3923v1
2010-01-26,Effect of spin-conserving scattering on Gilbert damping in ferromagnetic semiconductors,"The Gilbert damping in ferromagnetic semiconductors is theoretically
investigated based on the $s$-$d$ model. In contrast to the situation in
metals, all the spin-conserving scattering in ferromagnetic semiconductors
supplies an additional spin relaxation channel due to the momentum dependent
effective magnetic field of the spin-orbit coupling, thereby modifies the
Gilbert damping. In the presence of a pure spin current, we predict a new
contribution due to the interplay of the anisotropic spin-orbit coupling and a
pure spin current.",1001.4576v1
2011-05-20,"Magnetization Dissipation in the Ferromagnetic Semiconductor (Ga,Mn)As","We compute the Gilbert damping in (Ga,Mn)As based on the scattering theory of
magnetization relaxation. The disorder scattering is included
non-perturbatively. In the clean limit, the spin-pumping from the localized
d-electrons to the itinerant holes dominates the relaxation processes. In the
diffusive regime, the breathing Fermi-surface effect is balanced by the effects
of interband scattering, which cause the Gilbert damping constant to saturate
at around 0.005. In small samples, the system shape induces a large anisotropy
in the Gilbert damping.",1105.4148v2
2008-12-17,Origin of intrinsic Gilbert damping,"The damping of magnetization, represented by the rate at which it relaxes to
equilibrium, is successfully modeled as a phenomenological extension in the
Landau-Lifschitz-Gilbert equation. This is the damping torque term known as
Gilbert damping and its direction is given by the vector product of the
magnetization and its time derivative. Here we derive the Gilbert term from
first principles by a non-relativistic expansion of the Dirac equation. We find
that the Gilbert term arises when one calculates the time evolution of the spin
observable in the presence of the full spin-orbital coupling terms, while
recognizing the relationship between the curl of the electric field and the
time varying magnetic induction.",0812.3184v2
2019-07-01,Magnon decay theory of Gilbert damping in metallic antiferromagnets,"Gilbert damping is a key property governing magnetization dynamics in ordered
magnets. We present a theoretical study of intrinsic Gilbert damping induced by
magnon decay in antiferromagnetic metals through $s$-$d$ exchange interaction.
Our theory delineates the qualitative features of damping in metallic
antiferromagnets owing to their bipartite nature, in addition to providing
analytic expressions for the damping parameters. Magnon-induced intraband
electron scattering is found to predominantly cause magnetization damping,
whereas the N\'eel field is found to be damped via disorder. Depending on the
conduction electron band structure, we predict that magnon-induced interband
electron scattering around band crossings may be exploited to engineer a strong
N\'eel field damping.",1907.01045v1
2022-11-24,Influence of non-local damping on magnon properties of ferromagnets,"We study the influence of non-local damping on magnon properties of Fe, Co,
Ni and Fe$_{1-x}$Co$_{x}$ ($x=30\%,50\%$) alloys. The Gilbert damping parameter
is typically considered as a local scalar both in experiment and in theoretical
modelling. However, recent works have revealed that Gilbert damping is a
non-local quantity that allows for energy dissipation between atomic sites.
With the Gilbert damping parameters calculated from a state-of-the-art
real-space electronic structure method, magnon lifetimes are evaluated from
spin dynamics and linear response, where a good agreement is found between
these two methods. It is found that non-local damping affects the magnon
lifetimes in different ways depending on the system. Specifically, we find that
in Fe, Co, and Ni the non-local damping decreases the magnon lifetimes, while
in $\rm Fe_{70}Co_{30}$ and Fe$_{50}$Co$_{50}$ an opposite, non-local damping
effect is observed, and our data show that it is much stronger in the former.",2211.13486v1
2010-02-26,Correlation Effects in the Stochastic Landau-Lifshitz-Gilbert Equation,"We analyze the Landau-Lifshitz-Gilbert equation when the precession motion of
the magnetic moments is additionally subjected to an uniaxial anisotropy and is
driven by a multiplicative coupled stochastic field with a finite correlation
time $\tau$. The mean value for the spin wave components offers that the
spin-wave dispersion relation and its damping is strongly influenced by the
deterministic Gilbert damping parameter $\alpha$, the strength of the
stochastic forces $D$ and its temporal range $\tau$. The spin-spin-correlation
function can be calculated in the low correlation time limit by deriving an
evolution equation for the joint probability function. The stability analysis
enables us to find the phase diagram within the $\alpha-D$ plane for different
values of $\tau$ where damped spin wave solutions are stable. Even for zero
deterministic Gilbert damping the magnons offer a finite lifetime. We detect a
parameter range where the deterministic and the stochastic damping mechanism
are able to compensate each other leading to undamped spin-waves. The onset is
characterized by a critical value of the correlation time. An enhancement of
$\tau$ leads to an increase of the oscillations of the correlation function.",1002.4958v1
2019-02-26,Enhanced Gilbert Damping in Re doped FeCo Films: A Combined Experimental and Theoretical Study,"The effects of rhenium doping in the range 0 to 10 atomic percent on the
static and dynamic magnetic properties of Fe65Co35 thin films have been studied
experimentally as well as with first principles electronic structure
calculations focusing on the change of the saturation magnetization and the
Gilbert damping parameter. Both experimental and theoretical results show that
the saturation magnetization decreases with increasing Re doping level, while
at the same time Gilbert damping parameter increases. The experimental low
temperature saturation magnetic induction exhibits a 29 percent decrease, from
2.31 T to 1.64 T, in the investigated doping concentration range, which is more
than predicted by the theoretical calculations. The room temperature value of
the damping parameter obtained from ferromagnetic resonance measurements,
correcting for extrinsic contributions to the damping, is for the undoped
sample 0.0027, which is close to the theoretically calculated Gilbert damping
parameter. With 10 atomic percent Re doping, the damping parameter increases to
0.0090, which is in good agreement with the theoretical value of 0.0073. The
increase in damping parameter with Re doping is explained by the increase in
density of states at Fermi level, mostly contributed by the spin-up channel of
Re. Moreover, both experimental and theoretical values for the damping
parameter are observed to be weakly decreasing with decreasing temperature.",1902.09896v1
2023-06-07,Helicity-dependent optical control of the magnetization state emerging from the Landau-Lifshitz-Gilbert equation,"It is well known that the Gilbert relaxation time of a magnetic moment scales
inversely with the magnitude of the externally applied field, H, and the
Gilbert damping, {\alpha}. Therefore, in ultrashort optical pulses, where H can
temporarily be extremely large, the Gilbert relaxation time can momentarily be
extremely short, reaching even picosecond timescales. Here we show that for
typical ultrashort pulses, the optical control of the magnetization emerges by
merely considering the optical magnetic field in the Landau-Lifshitz-Gilbert
(LLG) equation. Surprisingly, when circularly polarized optical pulses are
introduced to the LLG equation, an optically induced helicity-dependent torque
results. We find that the strength of the interaction is determined by
{\eta}={\alpha}{\gamma}H/f_opt, where f_opt and {\gamma} are the optical
frequency and gyromagnetic ratio. Our results illustrate the generality of the
LLG equation to the optical limit and the pivotal role of the Gilbert damping
in the general interaction between optical magnetic fields and spins in solids.",2306.04617v2
2018-04-03,Generalisation of Gilbert damping and magnetic inertia parameter as a series of higher-order relativistic terms,"The phenomenological Landau-Lifshitz-Gilbert (LLG) equation of motion remains
as the cornerstone of contemporary magnetisation dynamics studies, wherein the
Gilbert damping parameter has been attributed to first-order relativistic
effects. To include magnetic inertial effects the LLG equation has previously
been extended with a supplemental inertia term and the arising inertial
dynamics has been related to second-order relativistic effects. Here we start
from the relativistic Dirac equation and, performing a Foldy-Wouthuysen
transformation, derive a generalised Pauli spin Hamiltonian that contains
relativistic correction terms to any higher order. Using the Heisenberg
equation of spin motion we derive general relativistic expressions for the
tensorial Gilbert damping and magnetic inertia parameters, and show that these
tensors can be expressed as series of higher-order relativistic correction
terms. We further show that, in the case of a harmonic external driving field,
these series can be summed and we provide closed analytical expressions for the
Gilbert and inertial parameters that are functions of the frequency of the
driving field.",1804.09242v1
2016-08-02,Ferromagnetic Damping/Anti-damping in a Periodic 2D Helical surface; A Non-Equilibrium Keldysh Green Function Approach,"In this paper, we investigate theoretically the spin-orbit torque as well as
the Gilbert damping for a two band model of a 2D helical surface state with a
Ferromagnetic (FM) exchange coupling. We decompose the density matrix into the
Fermi sea and Fermi surface components and obtain their contributions to the
electronic transport as well as the spin-orbit torque (SOT). Furthermore, we
obtain the expression for the Gilbert damping due to the surface state of a 3D
Topological Insulator (TI) and predicted its dependence on the direction of the
magnetization precession axis.",1608.00984v2
2016-02-19,A systematic study of magnetodynamic properties at finite temperatures in doped permalloy from first principles calculations,"By means of first principles calculations, we have systematically
investigated how the magnetodynamic properties Gilbert damping, magnetization
and exchange stiffness are affected when permalloy (Py)
(Fe$_{0.19}$Ni$_{0.81}$) is doped with 4d or 5d transition metal impurities. We
find that the trends in the Gilbert damping can be understood from relatively
few basic parameters such as the density of states at the Fermi level, the
spin-orbit coupling and the impurity concentration. % The temperature
dependence of the Gilbert damping is found to be very weak which we relate to
the lack of intraband transitions in alloys. % Doping with $4d$ elements has no
major impact on the studied Gilbert damping, apart from diluting the host.
However, the $5d$ elements have a profound effect on the damping and allows it
to be tuned over a large interval while maintaining the magnetization and
exchange stiffness. % As regards spin stiffness, doping with early transition
metals results in considerable softening, whereas late transition metals have a
minor impact. % Our result agree well with earlier calculations where
available. In comparison to experiments, the computed Gilbert damping appears
slightly underestimated while the spin stiffness show good general agreement.",1602.06201v2
2002-11-01,Exploring dynamical magnetism with time-dependent density-functional theory: from spin fluctuations to Gilbert damping,"We use time-dependent spin-density-functional theory to study dynamical
magnetic phenomena. First, we recall that the local-spin-density approximation
(LSDA) fails to account correctly for magnetic fluctuations in the paramagnetic
state of iron and other itinerant ferromagnets. Next, we construct a
gradient-dependent density functional that does not suffer from this problem of
the LSDA. This functional is then used to derive, for the first time, the
phenomenological Gilbert equation of micromagnetics directly from
time-dependent density-functional theory. Limitations and extensions of Gilbert
damping are discussed on this basis, and some comparisons with phenomenological
theories and experiments are made.",0211021v1
2012-04-24,Nonlocal feedback in ferromagnetic resonance,"Ferromagnetic resonance in thin films is analyzed under the influence of
spatiotemporal feedback effects. The equation of motion for the magnetization
dynamics is nonlocal in both space and time and includes isotropic, anisotropic
and dipolar energy contributions as well as the conserved Gilbert- and the
non-conserved Bloch-damping. We derive an analytical expression for the
peak-to-peak linewidth. It consists of four separate parts originated by
Gilbert damping, Bloch-damping, a mixed Gilbert-Bloch component and a
contribution arising from retardation. In an intermediate frequency regime the
results are comparable with the commonly used Landau-Lifshitz-Gilbert theory
combined with two-magnon processes. Retardation effects together with Gilbert
damping lead to a linewidth the frequency dependence of which becomes strongly
nonlinear. The relevance and the applicability of our approach to ferromagnetic
resonance experiments is discussed.",1204.5342v1
2017-04-24,Spin injection into silicon detected by broadband ferromagnetic resonance spectroscopy,"We studied the spin injection in a NiFe(Py)/Si system using broadband
ferromagnetic resonance spectroscopy. The Gilbert damping parameter of the Py
layer on top of the Si channel was determined as a function of the Si doping
concentration and Py layer thickness. For fixed Py thickness we observed an
increase of the Gilbert damping parameter with decreasing resistivity of the Si
channel. For a fixed Si doping concentration we measured an increasing Gilbert
damping parameter for decreasing Py layer thickness. No increase of the Gilbert
damping parameter was found Py/Si samples with an insulating interlayer. We
attribute our observations to an enhanced spin injection into the
low-resistivity Si by spin pumping.",1704.07006v1
2019-11-07,Quantum Oscillations of Gilbert Damping in Ferromagnetic/Graphene Bilayer Systems,"We study the spin dynamics of a ferromagnetic insulator on which graphene is
placed. We show that the Gilbert damping is enhanced by the proximity exchange
coupling at the interface. The modulation of the Gilbert damping constant is
proportional to the product of the spin-up and spin-down densities of states of
graphene. Consequently, the Gilbert damping constant in a strong magnetic field
oscillates as a function of the external magnetic field that originates from
the Landau level structure of graphene. We find that a measurement of the
oscillation period enables the strength of the exchange coupling constant to be
determined. The results demonstrate in theory that the ferromagnetic resonance
measurements may be used to detect the spin resolved electronic structure of
the adjacent materials, which is critically important for future spin device
evaluations.",1911.02775v2
2021-03-11,Magnetoelastic Gilbert damping in magnetostrictive Fe$_{0.7}$Ga$_{0.3}$ thin films,"We report an enhanced magnetoelastic contribution to the Gilbert damping in
highly magnetostrictive Fe$_{0.7}$Ga$_{0.3}$ thin films. This effect is
mitigated for perpendicular-to-plane fields, leading to a large anisotropy of
the Gilbert damping in all of the films (up to a factor of 10 at room
temperature). These claims are supported by broadband measurements of the
ferromagnetic resonance linewidths over a range of temperatures (5 to 400 K),
which serve to elucidate the effect of both the magnetostriction and phonon
relaxation on the magnetoelastic Gilbert damping.",2103.07008v1
2022-01-27,Effect of vertex corrections on the enhancement of Gilbert damping in spin pumping into a two-dimensional electron gas,"We theoretically consider the effect of vertex correction on spin pumping
from a ferromagnetic insulator (FI) into a two-dimensional electron gas (2DEG)
in which the Rashba and Dresselhaus spin-orbit interactions coexist. The
Gilbert damping in the FI is enhanced by elastic spin-flipping or magnon
absorption. We show that the Gilbert damping due to elastic spin-flipping is
strongly enhanced by the vertex correction when the ratio of the two spin-orbit
interactions is near a special value at which the spin relaxation time diverges
while that due to magnon absorption shows only small modification. We also show
that the shift in the resonant frequency due to elastic spin-flipping is
strongly enhanced in a similar way as the Gilbert damping.",2201.11498v3
2016-02-22,Effects of Landau-Lifshitz-Gilbert damping on domain growth,"Domain patterns are simulated by the Landau-Lifshitz-Gilbert (LLG) equation
with an easy-axis anisotropy. If the Gilbert damping is removed from the LLG
equation, it merely describes the precession of magnetization with a
ferromagnetic interaction. However, even without the damping, domains that look
similar to those of scalar fields are formed, and they grow with time. It is
demonstrated that the damping has no significant effects on domain growth laws
and large-scale domain structure. In contrast, small-scale domain structure is
affected by the damping. The difference in small-scale structure arises from
energy dissipation due to the damping.",1602.06673v3
2018-06-13,Low magnetic damping of ferrimagnetic GdFeCo alloys,"We investigate the Gilbert damping parameter for rare earth (RE)-transition
metal (TM) ferrimagnets over a wide temperature range. Extracted from the
field-driven magnetic domain-wall mobility, the Gilbert damping parameter was
as low as 0.0072 and was almost constant across the angular momentum
compensation temperature, starkly contrasting previous predictions that the
Gilbert damping parameter should diverge at the angular momentum compensation
temperature due to vanishing total angular momentum. Thus, magnetic damping of
RE-TM ferrimagnets is not related to the total angular momentum but is
dominated by electron scattering at the Fermi level where the TM has a dominant
damping role.",1806.04881v1
2023-06-22,"Gilbert damping in metallic ferromagnets from Schwinger-Keldysh field theory: Intrinsically nonlocal and nonuniform, and made anisotropic by spin-orbit coupling","Understanding the origin of damping mechanisms in magnetization dynamics of
metallic ferromagnets is a fundamental problem for nonequilibrium many-body
physics of systems where quantum conduction electrons interact with localized
spins assumed to be governed by the classical Landau-Lifshitz-Gilbert (LLG)
equation. It is also of critical importance for applications, as damping
affects energy consumption and speed of spintronic and magnonic devices. Since
the 1970s, a variety of linear-response and scattering theory approaches have
been developed to produce widely used formulas for computation of
spatially-independent Gilbert scalar parameter as the magnitude of the Gilbert
damping term in the LLG equation. The largely unexploited for this purpose
Schwinger-Keldysh field theory (SKFT) offers additional possibilities, such as
to rigorously derive an extended LLG equation by integrating quantum electrons
out. Here we derive such equation whose Gilbert damping for metallic
ferromagnets is nonlocal, i.e., dependent on all localized spins at a given
time, and nonuniform, even if all localized spins are collinear and spin-orbit
coupling (SOC) is absent. This is in sharp contrast to standard lore, where
nonlocal damping is considered to emerge only if localized spins are
noncollinear; for such situations, direct comparison on the example of magnetic
domain wall shows that SKFT-derived nonlocal damping is an order of magnitude
larger than the previously considered one. Switching on SOC makes such nonlocal
damping anisotropic, in contrast to standard lore where SOC is usually
necessary to obtain nonzero Gilbert damping scalar parameter. Our analytical
formulas, with their nonlocality being more prominent in low spatial
dimensions, are fully corroborated by numerically exact quantum-classical
simulations.",2306.13013v4
2018-07-20,Another view on Gilbert damping in two-dimensional ferromagnets,"A keen interest towards technological implications of spin-orbit driven
magnetization dynamics requests a proper theoretical description, especially in
the context of a microscopic framework, to be developed. Indeed, magnetization
dynamics is so far approached within Landau-Lifshitz-Gilbert equation which
characterizes torques on magnetization on purely phenomenological grounds.
Particularly, spin-orbit coupling does not respect spin conservation, leading
thus to angular momentum transfer to lattice and damping as a result. This
mechanism is accounted by the Gilbert damping torque which describes relaxation
of the magnetization to equilibrium. In this study we work out a microscopic
Kubo-St\v{r}eda formula for the components of the Gilbert damping tensor and
apply the elaborated formalism to a two-dimensional Rashba ferromagnet in the
weak disorder limit. We show that an exact analytical expression corresponding
to the Gilbert damping parameter manifests linear dependence on the scattering
rate and retains the constant value up to room temperature when no vibrational
degrees of freedom are present in the system. We argue that the methodology
developed in this paper can be safely applied to bilayers made of non- and
ferromagnetic metals, e.g., CoPt.",1807.07897v2
2017-05-21,Dynamical depinning of chiral domain walls,"The domain wall depinning field represents the minimum magnetic field needed
to move a domain wall, typically pinned by samples' disorder or patterned
constrictions. Conventionally, such field is considered independent on the
Gilbert damping since it is assumed to be the field at which the Zeeman energy
equals the pinning energy barrier (both damping independent). Here, we analyse
numerically the domain wall depinning field as function of the Gilbert damping
in a system with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya
interaction. Contrary to expectations, we find that the depinning field depends
on the Gilbert damping and that it strongly decreases for small damping
parameters. We explain this dependence with a simple one-dimensional model and
we show that the reduction of the depinning field is related to the internal
domain wall dynamics, proportional to the Dzyaloshinskii-Moriya interaction,
and the finite size of the pinning barriers.",1705.07489v2
2019-01-07,Giant anisotropy of Gilbert damping in epitaxial CoFe films,"Tailoring Gilbert damping of metallic ferromagnetic thin films is one of the
central interests in spintronics applications. Here we report a giant Gilbert
damping anisotropy in epitaxial Co$_{50}$Fe$_{50}$ thin film with a
maximum-minimum damping ratio of 400 \%, determined by broadband spin-torque as
well as inductive ferromagnetic resonance. We conclude that the origin of this
damping anisotropy is the variation of the spin orbit coupling for different
magnetization orientations in the cubic lattice, which is further corroborate
from the magnitude of the anisotropic magnetoresistance in Co$_{50}$Fe$_{50}$.",1901.01941v1
2019-11-02,Tuning Non-Gilbert-type damping in FeGa films on MgO(001) via oblique deposition,"The ability to tailor the damping factor is essential for spintronic and
spin-torque applications. Here, we report an approach to manipulate the damping
factor of FeGa/MgO(001) films by oblique deposition. Owing to the defects at
the surface or interface in thin films, two-magnon scattering (TMS) acts as a
non-Gilbert damping mechanism in magnetization relaxation. In this work, the
contribution of TMS was characterized by in-plane angular dependent
ferromagnetic resonance (FMR). It is demonstrated that the intrinsic Gilbert
damping is isotropic and invariant, while the extrinsic mechanism related to
TMS is anisotropic and can be tuned by oblique deposition. Furthermore, the two
and fourfold TMS related to the uniaxial magnetic anisotropy (UMA) and
magnetocrystalline anisotropy were discussed. Our results open an avenue to
manipulate magnetization relaxation in spintronic devices.",1911.00728v1
2001-10-11,Enhanced Gilbert Damping in Thin Ferromagnetic Films,"Using a scattering matrix approach, the precession of the magnetization of a
ferromagnet is shown to transfer spins into adjacent normal metal layers. This
``pumping'' of spins slows down the precession corresponding to an enhanced
Gilbert damping factor in the Landau-Lifshitz equation. The damping is
expressed in terms of the scattering matrix of the ferromagnet-normal metal
interface, which is accessible to model and first-principles calculations. Our
estimates for permalloy thin films explain the trends observed in recent
experiments.",0110247v2
2002-02-11,Radiation Induced Landau-Lifshitz-Gilbert Damping in Ferromagnets,"The Landau-Lifshitz-Gilbert damping coefficient employed in the analysis of
spin wave ferromagnetic resonance is related to the electrical conductivity of
the sample. The changing magnetization (with time) radiates electromagnetic
fields. The electromagnetic energy is then absorbed by the sample and the
resulting heating effect describes magnetic dissipative damping. The
ferromagnetic resonance relaxation rate theoretically depends on the geometry
(shape and size) of the sample as well as temperature in agreement with
experiment.",0202181v1
2006-01-10,Voltage dependence of Landau-Lifshitz-Gilbert damping of a spin in a current driven tunnel junction,"We present a theory of Landau-Lifshitz-Gilbert damping $\alpha$ for a
localized spin ${\vec S}$ in the junction coupled to the conduction electrons
in both leads under an applied volatege $V$. We find the voltage dependence of
the damping term reflecting the energy dependence of the density of states. We
find the effect is linear in the voltage and cotrolled by particle-hole
asymmetry of the leads.",0601185v1
2015-02-06,Microscopic theory of Gilbert damping in metallic ferromagnets,"We present a microscopic theory for magnetization relaxation in metallic
ferromagnets of nanoscopic dimensions that is based on the dynamic spin
response matrix in the presence of spin-orbit coupling. Our approach allows the
calculation of the spin excitation damping rate even for perfectly crystalline
systems, where existing microscopic approaches fail. We demonstrate that the
relaxation properties are not completely determined by the transverse
susceptibility alone, and that the damping rate has a non-negligible frequency
dependence in experimentally relevant situations. Our results indicate that the
standard Landau-Lifshitz-Gilbert phenomenology is not always appropriate to
describe spin dynamics of metallic nanostructure in the presence of strong
spin-orbit coupling.",1502.02068v1
2018-05-03,"Exact Intrinsic Localized Excitation of an Anisotropic Ferromagnetic Spin Chain in External Magnetic Field with Gilbert Damping, Spin Current and PT-Symmetry","We obtain the exact one-spin intrinsic localized excitation in an anisotropic
Heisenberg ferromagnetic spin chain in a constant/variable external magnetic
field with Gilbert damping included. We also point out how an appropriate
magnitude spin current term in a spin transfer nano-oscillator (STNO) can
stabilize the tendency towards damping. Further, we show how this excitation
can be sustained in a recently suggested PT-symmetric magnetic nanostructure.
We also briefly consider more general spin excitations.",1805.01230v1
2011-09-22,Hole spin relaxation and coefficients in Landau-Lifshitz-Gilbert equation in ferromagnetic GaMnAs,"We investigate the temperature dependence of the coefficients in the
Landau-Lifshitz-Gilbert equation in ferromagnetic GaMnAs by employing the Zener
model. We first calculate the hole spin relaxation time based on the
microscopic kinetic equation. We find that the hole spin relaxation time is
typically several tens femtoseconds and can present a nonmonotonic temperature
dependence due to the variation of the interband spin mixing, influenced by the
temperature related Zeeman splitting. With the hole spin relaxation time, we
are able to calculate the coefficients in the Landau-Lifshitz-Gilbert equation,
such as the Gilbert damping, nonadiabatic spin torque, spin stiffness and
vertical spin stiffness coefficients. We find that the nonadiabatic spin torque
coefficient $\beta$ is around $0.1\sim 0.3$ at low temperature, which is
consistent with the experiment [Adam {\em et al.}, Phys. Rev. B {\bf 80},
193204 (2009)]. As the temperature increases, $\beta$ monotonically increases
and can exceed one in the vicinity of the Curie temperature. In the low
temperature regime with $\beta<1$, the Gilbert damping coefficient $\alpha$
increases with temperature, showing good agreement with the experiments [Sinova
{\em et al.}, Phys. Rev. B {\bf 69}, 085209 (2004); Khazen {\em et al.}, {\em
ibid.} {\bf 78}, 195210 (2008)]. Furthermore, we predict that $\alpha$
decreases with increasing temperature once $\beta>1$ near the Curie
temperature. We also find that the spin stiffness decreases with increasing
temperature, especially near the Curie temperature due to the modification of
the finite $\beta$. Similar to the Gilbert damping, the vertical spin stiffness
coefficient is also found to be nonmonotonically dependent on the temperature.",1109.4964v1
2011-04-08,Magnetization Dissipation in Ferromagnets from Scattering Theory,"The magnetization dynamics of ferromagnets are often formulated in terms of
the Landau-Lifshitz-Gilbert (LLG) equation. The reactive part of this equation
describes the response of the magnetization in terms of effective fields,
whereas the dissipative part is parameterized by the Gilbert damping tensor. We
formulate a scattering theory for the magnetization dynamics and map this
description on the linearized LLG equation by attaching electric contacts to
the ferromagnet. The reactive part can then be expressed in terms of the static
scattering matrix. The dissipative contribution to the low-frequency
magnetization dynamics can be described as an adiabatic energy pumping process
to the electronic subsystem by the time-dependent magnetization. The Gilbert
damping tensor depends on the time derivative of the scattering matrix as a
function of the magnetization direction. By the fluctuation-dissipation
theorem, the fluctuations of the effective fields can also be formulated in
terms of the quasistatic scattering matrix. The theory is formulated for
general magnetization textures and worked out for monodomain precessions and
domain wall motions. We prove that the Gilbert damping from scattering theory
is identical to the result obtained by the Kubo formalism.",1104.1625v1
2022-02-12,Generalization of the Landau-Lifshitz-Gilbert equation by multi-body contributions to Gilbert damping for non-collinear magnets,"We propose a systematic and sequential expansion of the
Landau-Lifshitz-Gilbert equation utilizing the dependence of the Gilbert
damping tensor on the angle between magnetic moments, which arises from
multi-body scattering processes. The tensor consists of a damping-like term and
a correction to the gyromagnetic ratio. Based on electronic structure theory,
both terms are shown to depend on e.g. the scalar, anisotropic, vector-chiral
and scalar-chiral products of magnetic moments: $\vec{e}_i\cdot\vec{e}_j$,
$(\vec{n}_{ij}\cdot\vec{e}_i)(\vec{n}_{ij}\cdot\vec{e}_j)$,
$\vec{n}_{ij}\cdot(\vec{e}_i\times\vec{e}_j)$, $(\vec{e}_i\cdot\vec{e}_j)^2$,
$\vec{e}_i\cdot(\vec{e}_j\times\vec{e}_k)$..., where some terms are subjected
to the spin-orbit field $\vec{n}_{ij}$ in first and second order. We explore
the magnitude of the different contributions using both the Alexander-Anderson
model and time-dependent density functional theory in magnetic adatoms and
dimers deposited on Au(111) surface.",2202.06154v1
2022-11-23,The fractional Landau-Lifshitz-Gilbert equation,"The dynamics of a magnetic moment or spin are of high interest to
applications in technology. Dissipation in these systems is therefore of
importance for improvement of efficiency of devices, such as the ones proposed
in spintronics. A large spin in a magnetic field is widely assumed to be
described by the Landau-Lifshitz-Gilbert (LLG) equation, which includes a
phenomenological Gilbert damping. Here, we couple a large spin to a bath and
derive a generic (non-)Ohmic damping term for the low-frequency range using a
Caldeira-Leggett model. This leads to a fractional LLG equation, where the
first-order derivative Gilbert damping is replaced by a fractional derivative
of order $s \ge 0$. We show that the parameter $s$ can be determined from a
ferromagnetic resonance experiment, where the resonance frequency and linewidth
no longer scale linearly with the effective field strength.",2211.12889v1
2018-05-04,Effective damping enhancement in noncollinear spin structures,"Damping mechanisms in magnetic systems determine the lifetime, diffusion and
transport properties of magnons, domain walls, magnetic vortices, and
skyrmions. Based on the phenomenological Landau-Lifshitz-Gilbert equation, here
the effective damping parameter in noncollinear magnetic systems is determined
describing the linewidth in resonance experiments or the decay parameter in
time-resolved measurements. It is shown how the effective damping can be
calculated from the elliptic polarization of magnons, arising due to the
noncollinear spin arrangement. It is concluded that the effective damping is
larger than the Gilbert damping, and it may significantly differ between
excitation modes. Numerical results for the effective damping are presented for
the localized magnons in isolated skyrmions, with parameters based on the
Pd/Fe/Ir(111) model-type system.",1805.01815v2
2023-12-14,"Nonlocal damping of spin waves in a magnetic insulator induced by normal, heavy, or altermagnetic metallic overlayer: a Schwinger-Keldysh field theory approach","Understanding spin wave (SW) damping, and how to control it to the point of
being able to amplify SW-mediated signals, is one of the key requirements to
bring the envisaged magnonic technologies to fruition. Even widely used
magnetic insulators with low magnetization damping in their bulk, such as
yttrium iron garnet, exhibit 100-fold increase in SW damping due to inevitable
contact with metallic layers in magnonic circuits, as observed in very recent
experiments [I. Bertelli et al., Adv. Quantum Technol. 4, 2100094 (2021)]
mapping SW damping in spatially-resolved fashion. Here, we provide microscopic
and rigorous understanding of wavevector-dependent SW damping using extended
Landau-Lifshitz-Gilbert equation with nonlocal damping tensor, instead of
conventional local scalar Gilbert damping, as derived from Schwinger-Keldysh
nonequilibrium quantum field theory. In this picture, the origin of nonlocal
magnetization damping and thereby induced wavevector-dependent SW damping is
interaction of localized magnetic moments of magnetic insulator with conduction
electrons from the examined three different types of metallic overlayers --
normal, heavy, and altermagnetic. Due to spin-split energy-momentum dispersion
of conduction electrons in the latter two cases, the nonlocal damping is
anisotropic in spin and space, and it can be dramatically reduced by changing
the relative orientation of the two layers when compared to the usage of normal
metal overlayer.",2312.09140v1
2017-03-20,Relativistic theory of magnetic inertia in ultrafast spin dynamics,"The influence of possible magnetic inertia effects has recently drawn
attention in ultrafast magnetization dynamics and switching. Here we derive
rigorously a description of inertia in the Landau-Lifshitz-Gilbert equation on
the basis of the Dirac-Kohn-Sham framework. Using the Foldy-Wouthuysen
transformation up to the order of $1/c^4$ gives the intrinsic inertia of a pure
system through the 2$^{\rm nd}$ order time-derivative of magnetization in the
dynamical equation of motion. Thus, the inertial damping $\mathcal{I}$ is a
higher order spin-orbit coupling effect, $\sim 1/c^4$, as compared to the
Gilbert damping $\Gamma$ that is of order $1/c^2$. Inertia is therefore
expected to play a role only on ultrashort timescales (sub-picoseconds). We
also show that the Gilbert damping and inertial damping are related to one
another through the imaginary and real parts of the magnetic susceptibility
tensor respectively.",1704.01559v1
2019-07-10,The superior role of the Gilbert damping on the signal-to-noise ratio in heat-assisted magnetic recording,"In magnetic recording the signal-to-noise ratio (SNR) is a good indicator for
the quality of written bits. However, a priori it is not clear which parameters
have the strongest influence on the SNR. In this work, we investigate the role
of the Gilbert damping on the SNR. Grains consisting of FePt like hard magnetic
material with two different grain sizes $d_1=5\,$nm and $d_2=7\,$nm are
considered and simulations of heat-assisted magnetic recording (HAMR) are
performed with the atomistic simulation program VAMPIRE. The simulations
display that the SNR saturates for damping constants larger or equal than 0.1.
Additionally, we can show that the Gilbert damping together with the bit length
have a major effect on the SNR whereas other write head and material parameters
only have a minor relevance on the SNR.",1907.04577v2
2019-10-24,Spin waves in ferromagnetic thin films,"A spin wave is the disturbance of intrinsic spin order in magnetic materials.
In this paper, a spin wave in the Landau-Lifshitz-Gilbert equation is obtained
based on the assumption that the spin wave maintains its shape while it
propagates at a constant velocity. Our main findings include: (1) in the
absence of Gilbert damping, the spin wave propagates at a constant velocity
with the increment proportional to the strength of the magnetic field; (2) in
the absence of magnetic field, at a given time the spin wave converges
exponentially fast to its initial profile as the damping parameter goes to zero
and in the long time the relaxation dynamics of the spin wave converges
exponentially fast to the easy-axis direction with the exponent proportional to
the damping parameter; (3) in the presence of both Gilbert damping and magnetic
field, the spin wave converges to the easy-axis direction exponentially fast at
a small timescale while propagates at a constant velocity beyond that. These
provides a comprehensive understanding of spin waves in ferromagnetic
materials.",1910.11200v1
2020-06-30,Negative Gilbert damping in cavity optomagnonics,"Exceptional point (EP) associated with the parity-time (PT) symmetry breaking
is receiving considerable recent attention by the broad physics community. By
introducing balanced gain and loss, it has been realized in photonic, acoustic,
and electronic structures. However, the observation of magnonic EP remains
elusive. The major challenge is to experimentally generate the negative Gilbert
damping, which was thought to be highly unlikely but is demanded by the PT
symmetry. In this work, we study the magneto-optical interaction of
circularly-polarized lasers with a submicron magnet placed in an optical
cavity. We show that the off-resonant coupling between the driving laser and
cavity photon in the far-blue detuning can induce the magnetic gain (or
negative damping) exactly of the Gilbert type. A hyperbolic-tangent function
ansatz is found to well describe the time-resolved spin switching as the
intrinsic magnetization dissipation is overcome. When the optically pumped
magnet interacts with a purely lossy one, we observe a phase transition from
the imbalanced to passive PT symmetries by varying the detuning coeffcient. Our
findings provide a feasible way to manipulate the sign of the magnetic damping
parameter and to realize the EP in cavity optomagnonics.",2006.16510v1
2017-11-20,Spin Pumping in Ion-beam Sputtered Co_{2}FeAl/Mo Bilayers:Interfacial Gilbert Damping,"The spin pumping mechanism and associated interfacial Gilbert damping are
demonstrated in ion-beam sputtered Co2FeAl (CFA) /Mo bilayer thin films
employing ferromagnetic resonance spectroscopy. The dependence of the net spin
current transportation on Mo layer thickness, 0 to 10 nm, and the enhancement
of the net effective Gilbert damping are reported. The experimental data has
been analyzed using spin pumping theory in terms of spin current pumped through
the ferromagnet /nonmagnetic metal interface to deduce the effective spin
mixing conductance and the spin-diffusion length, which are estimated to be
1.16(0.19)x10^19 m^-2 and 3.50(0.35)nm, respectively. The damping constant is
found to be 8.4(0.3)x10^-3 in the Mo(3.5nm) capped CFA(8nm) sample
corresponding to a ~42% enhancement of the original Gilbert damping
(6.0(0.3)x10^-3) in the uncapped CFA layer. This is further confirmed by
inserting a Cu dusting layer which reduces the spin transport across the CFA
/Mo interface. The Mo layer thickness dependent net spin current density is
found to lie in the range of 1-3 MAm^-2, which also provides additional
quantitative evidence of spin pumping in this bilayer thin film system.",1711.07455v1
2014-04-05,Gilbert damping in noncollinear ferromagnets,"The precession and damping of a collinear magnetization displaced from its
equilibrium are described by the Landau-Lifshitz-Gilbert equation. For a
noncollinear magnetization, it is not known how the damping should be
described. We use first-principles scattering theory to investigate the damping
in one-dimensional transverse domain walls (DWs) of the important ferromagnetic
alloy Ni$_{80}$Fe$_{20}$ and interpret the results in terms of phenomenological
models. The damping is found to depend not only on the magnetization texture
but also on the specific dynamic modes of Bloch and N\'eel DWs. Even in the
highly disordered Ni$_{80}$Fe$_{20}$ alloy, the damping is found to be
remarkably nonlocal.",1404.1488v2
2003-04-04,Dynamic exchange coupling and Gilbert damping in magnetic multilayers,"We theoretically study dynamic properties of thin ferromagnetic films in
contact with normal metals. Moving magnetizations cause a flow of spins into
adjacent conductors, which relax by spin flip, scatter back into the
ferromagnet, or are absorbed by another ferromagnet. Relaxation of spins
outside the moving magnetization enhances the overall damping of the
magnetization dynamics in accordance with the Gilbert phenomenology. Transfer
of spins between different ferromagnets by these nonequilibrium spin currents
leads to a long-ranged dynamic exchange interaction and novel collective
excitation modes. Our predictions agree well with recent
ferromagnetic-resonance experiments on ultrathin magnetic films.",0304116v1
2008-08-09,Gilbert Damping in Conducting Ferromagnets I: Kohn-Sham Theory and Atomic-Scale Inhomogeneity,"We derive an approximate expression for the Gilbert damping coefficient
\alpha_G of itinerant electron ferromagnets which is based on their description
in terms of spin-density-functional-theory (SDFT) and Kohn-Sham quasiparticle
orbitals. We argue for an expression in which the coupling of magnetization
fluctuations to particle-hole transitions is weighted by the spin-dependent
part of the theory's exchange-correlation potential, a quantity which has large
spatial variations on an atomic length scale. Our SDFT result for \alpha_G is
closely related to the previously proposed spin-torque correlation-function
expression.",0808.1373v1
2012-03-03,Scaling of intrinsic Gilbert damping with spin-orbital coupling strength,"We have experimentally and theoretically investigated the dependence of the
intrinsic Gilbert damping parameter $\alpha_0$ on the spin-orbital coupling
strength $\xi$ by using L1$_{\mathrm{0}}$ ordered
FePd$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$ ternary alloy films with perpendicular
magnetic anisotropy. With the time-resolved magneto-optical Kerr effect,
$\alpha_0$ is found to increase by more than a factor of ten when $x$ varies
from 0 to 1.0. Since changes of other leading parameters are found to be
neglected, the $\alpha_0$ has for the first time been proven to be proportional
to $\xi^2$.",1203.0607v1
2013-03-20,Spin-pumping and Enhanced Gilbert Damping in Thin Magnetic Insulator Films,"Precessing magnetization in a thin film magnetic insulator pumps spins into
adjacent metals; however, this phenomenon is not quantitatively understood. We
present a theory for the dependence of spin-pumping on the transverse mode
number and in-plane wave vector. For long-wavelength spin waves, the enhanced
Gilbert damping for the transverse mode volume waves is twice that of the
macrospin mode, and for surface modes, the enhancement can be ten or more times
stronger. Spin-pumping is negligible for short-wavelength exchange spin waves.
We corroborate our analytical theory with numerical calculations in agreement
with recent experimental results.",1303.4922v1
2022-06-10,Spin Pumping into Anisotropic Dirac Electrons,"We study spin pumping into an anisotropic Dirac electron system induced by
microwave irradiation to an adjacent ferromagnetic insulator theoretically. We
formulate the Gilbert damping enhancement due to the spin current flowing into
the Dirac electron system using second-order perturbation with respect to the
interfacial exchange coupling. As an illustration, we consider the anisotropic
Dirac system realized in bismuth to show that the Gilbert damping varies
according to the magnetization direction in the ferromagnetic insulator. Our
results indicate that this setup can provide helpful information on the
anisotropy of the Dirac electron system.",2206.04899v1
2023-03-02,Spin Pumping into Carbon Nanotubes,"We theoretically study spin pumping from a ferromagnetic insulator (FI) into
a carbon nanotube (CNT). By employing the bosonization method, we formulate the
Gilbert damping induced by the FI/CNT junction, which can be measured by
ferromagnetic resonance. We show that the increase in the Gilbert damping has a
temperature dependence characteristic of a Luttinger liquid and is highly
sensitive to the Luttinger parameter of the spin sector for a clean interface.
We also discuss the experimental relevance of our findings based on numerical
estimates, using realistic parameters.",2303.01343v2
2019-08-29,Enhancement of ultrafast demagnetization rate and Gilbert damping driven by femtosecond laser-induced spin currents in Fe81Ga19/Ir20Mn80 bilayers,"In spintronics applications, ultrafast spin dynamics have to be controlled at
femtosecond (fs) timescales via fs-laser radiation. At such ultrafast
timescales, the effect of the Gilbert damping factor {\alpha} on ultrafast
demagnetization time should be considered. In previous explorations for the
relationship between these two parameters, it was found that the theoretical
calculations based on the local spin-flip scattering model do not agree with
the experimental results. Here, we find that in Fe81Ga19(FeGa)/Ir20Mn80(IrMn)
bilayers, the unconventional IrMn thickness dependence of {\alpha} results from
the competition between spin currents pumped from the ferromagnetic (FM) FeGa
layer to the antiferromagnetic (AFM) IrMn layer and those pumped from the AFM
layer to the FM layer. More importantly, we establish a proportional
relationship between the change of the ultrafast demagnetization rate and the
enhancement of Gilbert damping induced by the spin currents via interfacial
spin chemical potential . Our work builds a bridge to connect the ultrafast
demagnetization time and Gilbert damping in ultrafast photo-induced spin
currents dominated systems, which not only explains the disagreement between
experimental and theoretical results in the relation of {\tau}_M with {\alpha},
but provides further insight into ultrafast spin dynamics as well.",1908.11084v1
2021-09-08,Room-Temperature Intrinsic and Extrinsic Damping in Polycrystalline Fe Thin Films,"We examine room-temperature magnetic relaxation in polycrystalline Fe films.
Out-of-plane ferromagnetic resonance (FMR) measurements reveal Gilbert damping
parameters of $\approx$ 0.0024 for Fe films with thicknesses of 4-25 nm,
regardless of their microstructural properties. The remarkable invariance with
film microstructure strongly suggests that intrinsic Gilbert damping in
polycrystalline metals at room temperature is a local property of nanoscale
crystal grains, with limited impact from grain boundaries and film roughness.
By contrast, the in-plane FMR linewidths of the Fe films exhibit distinct
nonlinear frequency dependences, indicating the presence of strong extrinsic
damping. To fit our in-plane FMR data, we have used a grain-to-grain two-magnon
scattering model with two types of correlation functions aimed at describing
the spatial distribution of inhomogeneities in the film. However, neither of
the two correlation functions is able to reproduce the experimental data
quantitatively with physically reasonable parameters. Our findings advance the
fundamental understanding of intrinsic Gilbert damping in structurally
disordered films, while demonstrating the need for a deeper examination of how
microstructural disorder governs extrinsic damping.",2109.03684v2
2006-06-09,Spin wave dynamics and the determination of intrinsic Gilbert damping in locally-excited Permalloy thin films,"Time-resolved scanning Kerr effect microscopy has been used to study
magnetization dynamics in Permalloy thin films excited by transient magnetic
pulses generated by a micrometer-scale transmission line structure. The results
are consistent with magnetostatic spin wave theory and are supported by
micromagnetic simulations. Magnetostatic volume and surface spin waves are
measured for the same specimen using different bias field orientations and can
be accurately calculated by k-space integrations over all excited plane wave
components. A single damping constant of Gilbert form is sufficient to describe
both scenarios. The nonuniform pulsed field plays a key role in the spin wave
dynamics, with its Fourier transform serving as a weighting function for the
participating modes. The intrinsic Gilbert damping parameter $\alpha$ is most
conveniently measured when the spin waves are effectively stationary.",0606235v3
2007-05-10,Effective temperature and Gilbert damping of a current-driven localized spin,"Starting from a model that consists of a semiclassical spin coupled to two
leads we present a microscopic derivation of the Langevin equation for the
direction of the spin. For slowly-changing direction it takes on the form of
the stochastic Landau-Lifschitz-Gilbert equation. We give expressions for the
Gilbert damping parameter and the strength of the fluctuations, including their
bias-voltage dependence. At nonzero bias-voltage the fluctuations and damping
are not related by the fluctuation-dissipation theorem. We find, however, that
in the low-frequency limit it is possible to introduce a voltage-dependent
effective temperature that characterizes the fluctuations in the direction of
the spin, and its transport-steady-state probability distribution function.",0705.1432v3
2012-11-15,Spin transport and tunable Gilbert damping in a single-molecule magnet junction,"We study time-dependent electronic and spin transport through an electronic
level connected to two leads and coupled with a single-molecule magnet via
exchange interaction. The molecular spin is treated as a classical variable and
precesses around an external magnetic field. We derive expressions for charge
and spin currents by means of the Keldysh non-equilibrium Green's functions
technique in linear order with respect to the time-dependent magnetic field
created by this precession. The coupling between the electronic spins and the
magnetization dynamics of the molecule creates inelastic tunneling processes
which contribute to the spin currents. The inelastic spin currents, in turn,
generate a spin-transfer torque acting on the molecular spin. This back-action
includes a contribution to the Gilbert damping and a modification of the
precession frequency. The Gilbert damping coefficient can be controlled by the
bias and gate voltages or via the external magnetic field and has a
non-monotonic dependence on the tunneling rates.",1211.3611v2
2014-12-05,Calculating linear response functions for finite temperatures on the basis of the alloy analogy model,"A scheme is presented that is based on the alloy analogy model and allows to
account for thermal lattice vibrations as well as spin fluctuations when
calculating response quantities in solids. Various models to deal with spin
fluctuations are discussed concerning their impact on the resulting temperature
dependent magnetic moment, longitudinal conductivity and Gilbert damping
parameter. It is demonstrated that using the Monte Carlo (MC) spin
configuration as an input, the alloy analogy model is capable to reproduce
results of MC simulations on the average magnetic moment within all spin
fluctuation models under discussion. On the other hand, response quantities are
much more sensitive to the spin fluctuation model. Separate calculations
accounting for either the thermal effect due to lattice vibrations or spin
fluctuations show their comparable contributions to the electrical conductivity
and Gilbert damping. However, comparison to results accounting for both thermal
effects demonstrate violation of Matthiessen's rule, showing the non-additive
effect of lattice vibrations and spin fluctuations. The results obtained for
bcc Fe and fcc Ni are compared with the experimental data, showing rather good
agreement for the temperature dependent electrical conductivity and Gilbert
damping parameter.",1412.1988v1
2015-10-13,Nonlocal torque operators in ab initio theory of the Gilbert damping in random ferromagnetic alloys,"We present an ab initio theory of the Gilbert damping in substitutionally
disordered ferromagnetic alloys. The theory rests on introduced nonlocal
torques which replace traditional local torque operators in the well-known
torque-correlation formula and which can be formulated within the atomic-sphere
approximation. The formalism is sketched in a simple tight-binding model and
worked out in detail in the relativistic tight-binding linear muffin-tin
orbital (TB-LMTO) method and the coherent potential approximation (CPA). The
resulting nonlocal torques are represented by nonrandom, non-site-diagonal and
spin-independent matrices, which simplifies the configuration averaging. The
CPA-vertex corrections play a crucial role for the internal consistency of the
theory and for its exact equivalence to other first-principles approaches based
on the random local torques. This equivalence is also illustrated by the
calculated Gilbert damping parameters for binary NiFe and FeCo random alloys,
for pure iron with a model atomic-level disorder, and for stoichiometric FePt
alloys with a varying degree of L10 atomic long-range order.",1510.03571v2
2016-12-07,Gilbert damping of magnetostatic modes in a yttrium iron garnet sphere,"The magnetostatic mode (MSM) spectrum of a 300$\mu$m diameter single
crystalline sphere of yttrium iron garnet is investigated using broadband
ferromagnetic resonance (FMR). The individual MSMs are identified via their
characteristic dispersion relations and the corresponding mode number tuples
$(nmr)$ are assigned. Taking FMR data over a broad frequency and magnetic field
range allows to analyze both the Gilbert damping parameter~$\alpha$ and the
inhomogeneous line broadening contribution to the total linewidth of the MSMs
separately. The linewidth analysis shows that all MSMs share the same Gilbert
damping parameter $\alpha=2.7(5) \times 10^{-5}$ irrespective of their mode
index. In contrast, the inhomogeneous line broadening shows a pronounced mode
dependence. This observation is modeled in terms of two-magnon scattering
processes of the MSMs into the spin-wave manifold, mediated by surface and
volume defects.",1612.02360v1
2018-05-29,Gilbert damping in non-collinear magnetic system,"The modification of the magnetization dissipation or Gilbert damping caused
by an inhomogeneous magnetic structure and expressed in terms of a wave vector
dependent tensor $\underline{\alpha}(\vec{q})$ is investigated by means of
linear response theory. A corresponding expression for
$\underline{\alpha}(\vec{q})$ in terms of the electronic Green function has
been developed giving in particular the leading contributions to the Gilbert
damping linear and quadratic in $q$. Numerical results for realistic systems
are presented that have been obtained by implementing the scheme within the
framework of the fully relativistic KKR (Korringa-Kohn-Rostoker) band structure
method. Using the multilayered system (Cu/Fe$_{1-x}$Co$_x$/Pt)$_n$ as an
example for systems without inversion symmetry we demonstrate the occurrence of
non-vanishing linear contributions. For the alloy system bcc Fe$_{1-x}$Co$_x$
having inversion symmetry, on the other hand, only the quadratic contribution
is non-zero. As it is shown, this quadratic contribution does not vanish even
if the spin-orbit coupling is suppressed, i.e.\ it is a direct consequence of
the non-collinear spin configuration.",1805.11468v1
2018-10-15,Localized spin waves in isolated $kπ$ skyrmions,"The localized magnon modes of isolated $k\pi$ skyrmions on a field-polarized
background are analyzed based on the Landau-Lifshitz-Gilbert equation within
the terms of an atomistic classical spin model, with system parameters based on
the Pd/Fe biatomic layer on Ir(111). For increasing skyrmion order $k$ a higher
number of excitation modes are found, including modes with nodes in the radial
eigenfunctions. It is shown that at low fields $2\pi$ and $3\pi$ skyrmions are
destroyed via a burst instability connected to a breathing mode, while $1\pi$
skyrmions undergo an elliptic instability. At high fields all $k\pi$ skyrmions
collapse due to the instability of a breathing mode. The effective damping
parameters of the spin waves are calculated in the low Gilbert damping limit,
and they are found to diverge in the case of the lowest-lying modes at the
burst and collapse instabilities, but not at the elliptic instability. It is
shown that the breathing modes of $k\pi$ skyrmions may become overdamped at
higher Gilbert damping values.",1810.06471v1
2018-10-24,Nearly isotropic spin-pumping related Gilbert damping in Pt/Ni$_{81}$Fe$_{19}$/Pt,"A recent theory by Chen and Zhang [Phys. Rev. Lett. 114, 126602 (2015)]
predicts strongly anisotropic damping due to interfacial spin-orbit coupling in
ultrathin magnetic films. Interfacial Gilbert-type relaxation, due to the spin
pumping effect, is predicted to be significantly larger for magnetization
oriented parallel to compared with perpendicular to the film plane. Here, we
have measured the anisotropy in the Pt/Ni$_{81}$Fe$_{19}$/Pt system via
variable-frequency, swept-field ferromagnetic resonance (FMR). We find a very
small anisotropy of enhanced Gilbert damping with sign opposite to the
prediction from the Rashba effect at the FM/Pt interface. The results are
contrary to the predicted anisotropy and suggest that a mechanism separate from
Rashba spin-orbit coupling causes the rapid onset of spin-current absorption in
Pt.",1810.10595v4
2019-11-08,Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet,"Giant Gilbert damping anisotropy is identified as a signature of strong
Rashba spin-orbit coupling in a two-dimensional antiferromagnet on a honeycomb
lattice. The phenomenon originates in spin-orbit induced splitting of
conduction electron subbands that strongly suppresses certain spin-flip
processes. As a result, the spin-orbit interaction is shown to support an
undamped non-equilibrium dynamical mode that corresponds to an ultrafast
in-plane N\'eel vector precession and a constant perpendicular-to-the-plane
magnetization. The phenomenon is illustrated on the basis of a two dimensional
$s$-$d$ like model. Spin-orbit torques and conductivity are also computed
microscopically for this model. Unlike Gilbert damping these quantities are
shown to reveal only a weak anisotropy that is limited to the semiconductor
regime corresponding to the Fermi energy staying in a close vicinity of
antiferromagnetic gap.",1911.03408v1
2005-05-10,Fluctuation-dissipation considerations and damping models for ferromagnetic materials,"The role of fluctuation-dissipation relations (theorems) for the
magnetization dynamics with Landau-Lifshitz-Gilbert and Bloch-Bloembergen
damping terms are discussed. We demonstrate that the use of the Callen-Welton
fluctuation-dissipation theorem that was proven for Hamiltonian systems can
give an inconsistent result for magnetic systems with dissipation.",0505259v1
2018-07-13,Gilbert damping of high anisotropy Co/Pt multilayers,"Using broadband ferromagnetic resonance, we measure the damping parameter of
[Co(5 \r{A})/Pt(3 \r{A})]${\times 6}$ multilayers whose growth was optimized to
maximize the perpendicular anisotropy. Structural characterizations indicate
abrupt interfaces essentially free of intermixing despite the miscible
character of Co and Pt. Gilbert damping parameters as low as 0.021 can be
obtained despite a magneto-crystalline anisotropy as large as
$10^6~\textrm{J/m}^3$. The inhomogeneous broadening accounts for part of the
ferromagnetic resonance linewidth, indicating some structural disorder leading
to a equivalent 20 mT of inhomogenity of the effective field. The unexpectedly
relatively low damping factor indicates that the presence of the Pt heavy metal
within the multilayer may not be detrimental to the damping provided that
intermixing is avoided at the Co/Pt interfaces.",1807.04977v1
2019-08-23,Damping enhancement in coherent ferrite/insulating-paramagnet bilayers,"High-quality epitaxial ferrites, such as low-damping MgAl-ferrite (MAFO), are
promising nanoscale building blocks for all-oxide heterostructures driven by
pure spin current. However, the impact of oxide interfaces on spin dynamics in
such heterostructures remains an open question. Here, we investigate the spin
dynamics and chemical and magnetic depth profiles of 15-nm-thick MAFO
coherently interfaced with an isostructural $\approx$1-8-nm-thick overlayer of
paramagnetic CoCr$_2$O$_4$ (CCO) as an all-oxide model system. Compared to MAFO
without an overlayer, effective Gilbert damping in MAFO/CCO is enhanced by a
factor of $>$3, irrespective of the CCO overlayer thickness. We attribute this
damping enhancement to spin scattering at the $\sim$1-nm-thick chemically
disordered layer at the MAFO/CCO interface, rather than spin pumping or
proximity-induced magnetism. Our results indicate that damping in ferrite-based
heterostructures is strongly influenced by interfacial chemical disorder, even
if the thickness of the disordered layer is a small fraction of the ferrite
thickness.",1908.08629v2
2021-05-08,A second-order numerical method for Landau-Lifshitz-Gilbert equation with large damping parameters,"A second order accurate numerical scheme is proposed and implemented for the
Landau-Lifshitz-Gilbert equation, which models magnetization dynamics in
ferromagnetic materials, with large damping parameters. The main advantages of
this method are associated with the following features: (1) It only solves
linear systems of equations with constant coefficients where fast solvers are
available, so that the numerical efficiency has been greatly improved, in
comparison with the existing Gauss-Seidel project method. (2) The second-order
accuracy in time is achieved, and it is unconditionally stable for large
damping parameters. Moreover, both the second-order accuracy and the great
efficiency improvement will be verified by several numerical examples in the 1D
and 3D simulations. In the presence of large damping parameters, it is observed
that this method is unconditionally stable and finds physically reasonable
structures while many existing methods have failed. For the domain wall
dynamics, the linear dependence of wall velocity with respect to the damping
parameter and the external magnetic field will be obtained through the reported
simulations.",2105.03576v1
2006-11-23,Analytical solutions for two-level systems with damping,"A method is proposed to transform any analytic solution of the Bloch equation
into an analytic solution of the Landau-Lifshitz-Gilbert equation. This allows
for the analytical description of the dynamics of a two level system with
damping. This method shows that damping turns the linear Schr\""{o}dinger
equation of a two-level system into a nonlinear Schr\""{o}dinger equation. As
applications, it is shown that damping has a relatively mild influence on
self-induced transparency but destroys dynamical localization.",0611238v1
2017-01-10,Magnetic properties in ultra-thin 3d transition metal alloys II: Experimental verification of quantitative theories of damping and spin-pumping,"A systematic experimental study of Gilbert damping is performed via
ferromagnetic resonance for the disordered crystalline binary 3d transition
metal alloys Ni-Co, Ni-Fe and Co-Fe over the full range of alloy compositions.
After accounting for inhomogeneous linewidth broadening, the damping shows
clear evidence of both interfacial damping enhancement (by spin pumping) and
radiative damping. We quantify these two extrinsic contributions and thereby
determine the intrinsic damping. The comparison of the intrinsic damping to
multiple theoretical calculations yields good qualitative and quantitative
agreement in most cases. Furthermore, the values of the damping obtained in
this study are in good agreement with a wide range of published experimental
and theoretical values. Additionally, we find a compositional dependence of the
spin mixing conductance.",1701.02475v1
2004-12-18,Fluctuations of the Magnetization in Thin Films due to Conduction Electrons,"A detailed analysis of damping and noise due to a {\it sd}-interaction in a
thin ferromagnetic film sandwiched between two large normal metal layers is
carried out. The magnetization is shown to obey in general a non-local equation
of motion which differs from the the Gilbert equation and is extended to the
non-adiabatic regime. To lowest order in the exchange interaction and in the
limit where the Gilbert equation applies, we show that the damping term is
enhanced due to interfacial effects but it also shows oscillations as a
function of the film thickness. The noise calculation is however carried out to
all orders in the exchange coupling constant. The ellipticity of the precession
of the magnetization is taken into account. The damping is shown to have a
Gilbert form only in the adiabatic limit while the relaxation time becomes
strongly dependent on the geometry of the thin film. It is also shown that the
induced noise characteristic of sd-exchange is inherently colored in character
and depends on the symmetry of the Hamiltonian of the magnetization in the
film. We show that the sd-noise can be represented in terms of an external
stochastic field which is white only in the adiabatic regime. The temperature
is also renormalized by the spin accumulation in the system. For large
intra-atomic exchange interactions, the Gilbert-Brown equation is no longer
valid.",0412510v1
2014-07-02,Spin Waves in Ferromagnetic Insulators Coupled via a Normal Metal,"Herein, we study the spin-wave dispersion and dissipation in a ferromagnetic
insulator--normal metal--ferromagnetic insulator system. Long-range dynamic
coupling because of spin pumping and spin transfer lead to collective magnetic
excitations in the two thin-film ferromagnets. In addition, the dynamic dipolar
field contributes to the interlayer coupling. By solving the
Landau-Lifshitz-Gilbert-Slonczewski equation for macrospin excitations and the
exchange-dipole volume as well as surface spin waves, we compute the effect of
the dynamic coupling on the resonance frequencies and linewidths of the various
modes. The long-wavelength modes may couple acoustically or optically. In the
absence of spin-memory loss in the normal metal, the spin-pumping-induced
Gilbert damping enhancement of the acoustic mode vanishes, whereas the optical
mode acquires a significant Gilbert damping enhancement, comparable to that of
a system attached to a perfect spin sink. The dynamic coupling is reduced for
short-wavelength spin waves, and there is no synchronization. For intermediate
wavelengths, the coupling can be increased by the dipolar field such that the
modes in the two ferromagnetic insulators can couple despite possible small
frequency asymmetries. The surface waves induced by an easy-axis surface
anisotropy exhibit much greater Gilbert damping enhancement. These modes also
may acoustically or optically couple, but they are unaffected by thickness
asymmetries.",1407.0635v1
2009-04-21,Tensor damping in metallic magnetic multilayers,"The mechanism of spin-pumping, described by Tserkovnyak et al., is formally
analyzed in the general case of a magnetic multilayer consisting of two or more
metallic ferromagnetic (FM) films separated by normal metal (NM) layers. It is
shown that the spin-pumping-induced dynamic coupling between FM layers modifies
the linearized Gilbert equations in a way that replaces the scalar Gilbert
damping constant with a nonlocal matrix of Cartesian damping tensors. The
latter are shown to be methodically calculable from a matrix algebra solution
of the Valet-Fert transport equations. As an example, explicit analytical
results are obtained for a 5-layer (spin-valve) of form NM/FM/NM'/FM/NM.
Comparisons with earlier well known results of Tserkovnyak et al. for the
related 3-layer FM/NM/FM indicate that the latter inadvertently hid the tensor
character of the damping, and instead singled out the diagonal element of the
local damping tensor along the axis normal to the plane of the two
magnetization vectors. For spin-valve devices of technological interest, the
influence of the tensor components of the damping on thermal noise or
spin-torque critical currents are strongly weighted by the relative magnitude
of the elements of the nonlocal, anisotropic stiffness-field tensor-matrix, and
for in-plane magnetized spin-valves are generally more sensitive to the
in-plane element of the damping tensor.",0904.3150v2
2023-12-20,An effective field theory of damped ferromagnetic systems,"Using the in-in formalism, we generalize the recently constructed
magnetoelastic EFT arXiv:2112.13873 [hep-th] to describe the damping dynamics
of ferromagnetic systems at long wavelengths. We find that the standard Gilbert
damping term naturally arises as the simplest leading-order symmetry-consistent
non-conservative contribution within the in-in framework. The EFT is easily
generalized to scenarios with anisotropy and inhomogeneity. In particular, we
find the classic Landau-Lifshitz damping term emerges when isotropy is broken
by a constant external background field. This provides a first principle
explanation for distinguishing the two types of damping dynamics that were
originally constructed phenomenologically. Furthermore, the EFT framework could
also incorporate intrinsic anisotropy of the material in a straightforward way
using the spurion method. For systems with inhomogeneity such as nontrivial
spin textures, we find that the leading order derivative correction yields the
generalized Gilbert damping equations that were found in condensed matter
literature. This shows that the EFT approach enables us to derive the form of
higher-derivative-order corrections in a systematic way. Lastly, using the
phonon-magnon coupling deduced in the magnetoelastic EFT, we are able to make a
prediction for the generic form of the phononic contribution to the damping
equation.",2312.13093v1
2015-10-07,"Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films","The half-metallic half-Heusler alloy NiMnSb is a promising candidate for
applications in spintronic devices due to its low magnetic damping and its rich
anisotropies. Here we use ferromagnetic resonance (FMR) measurements and
calculations from first principles to investigate how the composition of the
epitaxially grown NiMnSb influences the magnetodynamic properties of saturation
magnetization $M_S$, Gilbert damping $\alpha$, and exchange stiffness $A$.
$M_S$ and $A$ are shown to have a maximum for stoichiometric composition, while
the Gilbert damping is minimum. We find excellent quantitative agreement
between theory and experiment for $M_S$ and $\alpha$. The calculated $A$ shows
the same trend as the experimental data, but has a larger magnitude.
Additionally to the unique in-plane anisotropy of the material, these
tunabilities of the magnetodynamic properties can be taken advantage of when
employing NiMnSb films in magnonic devices.",1510.01894v1
2017-08-07,"Chiral damping, chiral gyromagnetism and current-induced torques in textured one-dimensional Rashba ferromagnets","We investigate Gilbert damping, spectroscopic gyromagnetic ratio and
current-induced torques in the one-dimensional Rashba model with an additional
noncollinear magnetic exchange field. We find that the Gilbert damping differs
between left-handed and right-handed N\'eel-type magnetic domain walls due to
the combination of spatial inversion asymmetry and spin-orbit interaction
(SOI), consistent with recent experimental observations of chiral damping.
Additionally, we find that also the spectroscopic $g$ factor differs between
left-handed and right-handed N\'eel-type domain walls, which we call chiral
gyromagnetism. We also investigate the gyromagnetic ratio in the Rashba model
with collinear magnetization, where we find that scattering corrections to the
$g$ factor vanish for zero SOI, become important for finite spin-orbit
coupling, and tend to stabilize the gyromagnetic ratio close to its
nonrelativistic value.",1708.02008v2
2017-09-14,Intrinsic Damping Phenomena from Quantum to Classical Magnets:An ab-initio Study of Gilbert Damping in Pt/Co Bilayer,"A fully quantum mechanical description of the precessional damping of Pt/Co
bilayer is presented in the framework of the Keldysh Green function approach
using {\it ab initio} electronic structure calculations. In contrast to
previous calculations of classical Gilbert damping ($\alpha_{GD}$), we
demonstrate that $\alpha_{GD}$ in the quantum case does not diverge in the
ballistic regime due to the finite size of the total spin, $S$. In the limit of
$S\rightarrow\infty$ we show that the formalism recovers the torque correlation
expression for $\alpha_{GD}$ which we decompose into spin-pumping and
spin-orbital torque correlation contributions. The formalism is generalized to
take into account a self consistently determined dephasing mechanism which
preserves the conservation laws and allows the investigation of the effect of
disorder. The dependence of $\alpha_{GD}$ on Pt thickness and disorder strength
is calculated and the spin diffusion length of Pt and spin mixing conductance
of the bilayer are determined and compared with experiments.",1709.04911v2
2018-04-02,Anisotropic Gilbert damping in perovskite La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ thin film,"The viscous Gilbert damping parameter governing magnetization dynamics is of
primary importance for various spintronics applications. Although, the damping
constant is believed to be anisotropic by theories. It is commonly treated as a
scalar due to lack of experimental evidence. Here, we present an elaborate
angle dependent broadband ferromagnetic resonance study of high quality
epitaxial La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films. Extrinsic effects are suppressed
and we show convincing evidence of anisotropic damping with twofold symmetry at
room temperature. The observed anisotropic relaxation is attributed to the
magnetization orientation dependence of the band structure. In addition, we
demonstrated that such anisotropy can be tailored by manipulating the stain.
This work provides new insights to understand the mechanism of magnetization
relaxation.",1804.00554v1
2006-02-03,Microscopic description of Landau-Lifshitz-Gilbert type equation based on the s-d model,"A Landau-Lifshitz-Gilbert type equation has been derived by using s-d model
in which the s-electron system is regarded as an environment coupled weakly
with the localized spins. Based on the irreducible linear response theory, we
show that the relaxation function of the s-electron spin leads to the Gilbert
type damping term which corresponds to the retarded resistance function in the
generalized Langevin equation. The Ohmic form of the Gilbert term stems from
the fact that the imaginary part of the response function (spin susceptibility)
of the itinerant electron system is proportional to the frequency (omega) in
the low omega region. It is confirmed that the Caldeira-Leggett theory based on
the path-integral approach gives the same result.",0602075v2
2014-09-08,Self-similar solutions of the one-dimensional Landau-Lifshitz-Gilbert equation,"We consider the one-dimensional Landau-Lifshitz-Gilbert (LLG) equation, a
model describing the dynamics for the spin in ferromagnetic materials. Our main
aim is the analytical study of the bi-parametric family of self-similar
solutions of this model. In the presence of damping, our construction provides
a family of global solutions of the LLG equation which are associated to a
discontinuous initial data of infinite (total) energy, and which are smooth and
have finite energy for all positive times. Special emphasis will be given to
the behaviour of this family of solutions with respect to the Gilbert damping
parameter.
  We would like to emphasize that our analysis also includes the study of
self-similar solutions of the Schr\""odinger map and the heat flow for harmonic
maps into the 2-sphere as special cases. In particular, the results presented
here recover some of the previously known results in the setting of the
1d-Schr\""odinger map equation.",1409.2340v1
2017-09-12,Green's function formalism for spin transport in metal-insulator-metal heterostructures,"We develop a Green's function formalism for spin transport through
heterostructures that contain metallic leads and insulating ferromagnets. While
this formalism in principle allows for the inclusion of various magnonic
interactions, we focus on Gilbert damping. As an application, we consider
ballistic spin transport by exchange magnons in a metal-insulator-metal
heterostructure with and without disorder. For the former case, we show that
the interplay between disorder and Gilbert damping leads to spin current
fluctuations. For the case without disorder, we obtain the dependence of the
transmitted spin current on the thickness of the ferromagnet. Moreover, we show
that the results of the Green's function formalism agree in the clean and
continuum limit with those obtained from the linearized stochastic
Landau-Lifshitz-Gilbert equation. The developed Green's function formalism is a
natural starting point for numerical studies of magnon transport in
heterostructures that contain normal metals and magnetic insulators.",1709.03775v1
2019-09-06,The interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films,"We report on broadband ferromagnetic resonance linewidth measurements
performed on epitaxial Heusler thin films. A large and anisotropic two-magnon
scattering linewidth broadening is observed for measurements with the
magnetization lying in the film plane, while linewidth measurements with the
magnetization saturated perpendicular to the sample plane reveal low Gilbert
damping constants of $(1.5\pm0.1)\times 10^{-3}$, $(1.8\pm0.2)\times 10^{-3}$,
and $<8\times 10^{-4}$ for Co$_2$MnSi/MgO, Co$_2$MnAl/MgO, and Co$_2$FeAl/MgO,
respectively. The in-plane measurements are fit to a model combining Gilbert
and two-magnon scattering contributions to the linewidth, revealing a
characteristic disorder lengthscale of 10-100 nm.",1909.02738v2
2010-02-17,Measurement of Gilbert damping parameters in nanoscale CPP-GMR spin-valves,"In-situ, device level measurement of thermal mag-noise spectral linewidths in
60nm diameter CPP-GMR spin-valve stacks of IrMn/ref/Cu/free, with reference and
free layer of similar CoFe/CoFeGe alloy, are used to simultaneously determine
the intrinsic Gilbert damping for both magnetic layers. It is shown that
careful alignment at a ""magic-angle"" between free and reference layer static
equilibrium magnetization can allow direct measurement of the broadband
intrinsic thermal spectra in the virtual absence of spin-torque effects which
otherwise grossly distort the spectral line shapes and require linewidth
extrapolations to zero current (which are nonetheless also shown to agree well
with the direct method). The experimental magic-angle spectra are shown to be
in good qualitative and quantitative agreement with both macrospin calculations
and micromagnetic eigenmode analysis. Despite similar composition and
thickness, it is repeatedly found that the IrMn exchange pinned reference layer
has ten times larger intrinsic Gilbert damping (alpha ~ 0.1) than that of the
free-layer (alpha ~ 0.01). It is argued that the large reference layer damping
results from strong, off -resonant coupling to to lossy modes of an IrMn/ref
couple, rather than commonly invoked two-magnon processes.",1002.3295v1
2018-09-28,Isotropic non-local Gilbert damping driven by spin currents in epitaxial Pd/Fe/MgO(001) films,"Although both theoretical predications and experimental observations
demonstrated that the damping factor is anisotropic at
ferromagnet/semiconductor interface with robust interfacial spin-orbit
coupling, it is not well understood whether non-local Gilbert damping driven by
spin currents in heavy metal/ferromagnetic metal (HM/FM) bilayers is
anisotropic or not. Here, we investigated the in-plane angular- and frequency-
dependence of magnetic relaxation of epitaxial Fe/MgO(001) films with different
capping layers of Pd and Cu. After disentangling the parasitic contributions,
such as two-magnon scattering (TMS), mosaicity, and field-dragging effect, we
unambiguously observed that both local and non-local Gilbert damping are
isotropic in Fe(001) plane, suggesting that the pure spin currents absorption
is independent of Fe magnetization orientation in the epitaxial Pd/Fe
heterostructure. First principles calculation reveals that the effective spin
mixing conductance of Pd/Fe interface is nearly invariant for different
magnetization directions in good agreement with the experimental observations.
These results offer a valuable insight into the transmission and absorption of
pure spin currents, and facilitate us to utilize next-generation spintronic
devices.",1809.11020v1
2004-09-24,Minimal field requirement in precessional magnetization switching,"We investigate the minimal field strength in precessional magnetization
switching using the Landau-Lifshitz-Gilbert equation in under-critically damped
systems. It is shown that precessional switching occurs when localized
trajectories in phase space become unlocalized upon application of field
pulses. By studying the evolution of the phase space, we obtain the analytical
expression of the critical switching field in the limit of small damping for a
magnetic object with biaxial anisotropy. We also calculate the switching times
for the zero damping situation. We show that applying field along the medium
axis is good for both small field and fast switching times.",0409671v1
2003-09-29,Damping rates of the atomic velocity in Sisyphus cooling,"We present a theoretical and experimental study of the damping process of the
atomic velocity in Sisyphus cooling. The relaxation rates of the atomic kinetic
temperature are determined for a 3D lin$\perp$lin optical lattice. We find that
the damping rates of the atomic temperature depend linearly on the optical
pumping rate, for a given depth of the potential wells. This is at variance
with the behavior of the friction coefficient as calculated from the spatial
diffusion coefficients within a model of Brownian motion. The origin of this
different behavior is identified by distinguishing the role of the trapped and
traveling atoms.",0309209v1
2011-11-04,Tunable magnetization relaxation in spin valves,"In spin values the damping parameters of the free layer are determined
non-locally by the entire magnetic configuration. In a dual spin valve
structure that comprises a free layer embedded between two pinned layers, the
spin pumping mechanism, in combination with the angular momentum conservation,
renders the tensor-like damping parameters tunable by varying the interfacial
and diffusive properties. Simulations based on the Landau-Lifshitz-Gilbert
phenomenology for a macrospin model are performed with the tensor-like damping
and the relaxation time of the free layer magnetization is found to be largely
dependent on while tunable through the magnetic configuration of the
source-drain magnetization.",1111.1219v1
2012-05-25,Spin wave amplification driven by heat flow: the role of damping and exchange interaction,"In this article we report on micromagnetic simulations performed on a
permalloy nanostructure in presence of a uniform thermal gradient. Our
numerical simulations show that heat flow is an effective mean to compensate
the damping, and that the gradients at which spin-wave amplification is
observed are experimentally accessible. In particular, we have studied the role
of the Gilbert damping parameter on spin-wave amplification.",1205.5650v2
2015-04-23,Magnetization damping in noncollinear spin valves with antiferromagnetic interlayer couplings,"We study the magnetic damping in the simplest of synthetic antiferromagnets,
i.e. antiferromagnetically exchange-coupled spin valves in which applied
magnetic fields tune the magnetic configuration to become noncollinear. We
formulate the dynamic exchange of spin currents in a noncollinear texture based
on the spindiffusion theory with quantum mechanical boundary conditions at the
ferrromagnet|normal-metal interfaces and derive the Landau-Lifshitz-Gilbert
equations coupled by the static interlayer non-local and the dynamic exchange
interactions. We predict non-collinearity-induced additional damping that can
be sensitively modulated by an applied magnetic field. The theoretical results
compare favorably with published experiments.",1504.06042v1
2016-05-05,Theory of magnon motive force in chiral ferromagnets,"We predict that magnon motive force can lead to temperature dependent,
nonlinear chiral damping in both conducting and insulating ferromagnets. We
estimate that this damping can significantly influence the motion of skyrmions
and domain walls at finite temperatures. We also find that in systems with low
Gilbert damping moving chiral magnetic textures and resulting magnon motive
forces can induce large spin and energy currents in the transverse direction.",1605.01694v2
2018-04-19,Damping of magnetization dynamics by phonon pumping,"We theoretically investigate pumping of phonons by the dynamics of a magnetic
film into a non-magnetic contact. The enhanced damping due to the loss of
energy and angular momentum shows interference patterns as a function of
resonance frequency and magnetic film thickness that cannot be described by
viscous (""Gilbert"") damping. The phonon pumping depends on magnetization
direction as well as geometrical and material parameters and is observable,
e.g., in thin films of yttrium iron garnet on a thick dielectric substrate.",1804.07080v2
2024-01-22,Damping-Enhanced Magnon Transmission,"The inevitable Gilbert damping in magnetization dynamics is usually regarded
as detrimental to spin transport. Here we demonstrate in a
ferromagnetic-insulator--normal-metal heterostructure that the strong momentum
dependence and chirality of the eddy-current-induced damping causes also
beneficial scattering properties. Here we show that a potential barrier that
reflects magnon wave packets becomes transparent in the presence of a metallic
cap layer, but only in one direction. We formulate the unidirectional
transmission in terms of a generalized group velocity with an imaginary
component and the magnon skin effect. This trick to turn presumably harmful
dissipation into useful functionalities should be useful for future quantum
magnonic devices.",2401.12022v1
2008-07-18,Current-induced dynamics of spiral magnet,"We study the dynamics of the spiral magnet under the charge current by
solving the Landau-Lifshitz-Gilbert equation numerically. In the steady state,
the current ${\vec j}$ induces (i) the parallel shift of the spiral pattern
with velocity $v=(\beta/\alpha)j$ ($\alpha$, $\beta$: the Gilbert damping
coefficients), (ii) the uniform magnetization $M$ parallel or anti-parallel to
the current depending on the chirality of the spiral and the ratio $\beta /
\alpha $, and (iii) the change in the wavenumber $k$ of the spiral. These are
analyzed by the continuum effective theory using the scaling argument, and the
various nonequilibrium phenomena such as the chaotic behavior and
current-induced annealing are also discussed.",0807.2901v1
2008-11-04,Amplitude-Phase Coupling in a Spin-Torque Nano-Oscillator,"The spin-torque nano-oscillator in the presence of thermal fluctuation is
described by the normal form of the Hopf bifurcation with an additive white
noise. By the application of the reduction method, the amplitude-phase coupling
factor, which has a significant effect on the power spectrum of the spin-torque
nano-oscillator, is calculated from the Landau-Lifshitz-Gilbert-Slonczewski
equation with the nonlinear Gilbert damping. The amplitude-phase coupling
factor exhibits a large variation depending on in-plane anisotropy under the
practical external fields.",0811.0425v1
2010-03-19,Dynamics of magnetization on the topological surface,"We investigate theoretically the dynamics of magnetization coupled to the
surface Dirac fermions of a three dimensional topological insulator, by
deriving the Landau-Lifshitz-Gilbert (LLG) equation in the presence of charge
current. Both the inverse spin-Galvanic effect and the Gilbert damping
coefficient $\alpha$ are related to the two-dimensional diagonal conductivity
$\sigma_{xx}$ of the Dirac fermion, while the Berry phase of the ferromagnetic
moment to the Hall conductivity $\sigma_{xy}$. The spin transfer torque and the
so-called $\beta$-terms are shown to be negligibly small. Anomalous behaviors
in various phenomena including the ferromagnetic resonance are predicted in
terms of this LLG equation.",1003.3769v1
2013-09-28,High-efficiency GHz frequency doubling without power threshold in thin-film Ni81Fe19,"We demonstrate efficient second-harmonic generation at moderate input power
for thin film Ni81Fe19 undergoing ferromagnetic resonance (FMR). Powers of the
generated second-harmonic are shown to be quadratic in input power, with an
upconversion ratio three orders of magnitude higher than that demonstrated in
ferrite. The second harmonic signal generated exhibits a significantly lower
linewidth than that predicted by low-power Gilbert damping, and is excited
without threshold. Results are in good agreement with an analytic, approximate
expansion of the Landau-Lifshitz-Gilbert (LLG) equation.",1309.7483v1
2016-06-30,Skyrmion dynamics in a chiral magnet driven by periodically varying spin currents,"In this work, we investigated the spin dynamics in a slab of chiral magnets
induced by an alternating (ac) spin current. Periodic trajectories of the
skyrmion in real space are discovered under the ac current as a result of the
Magnus and viscous forces, which originate from the Gilbert damping, the spin
transfer torque, and the $ \beta $-nonadiabatic torque effects. The results are
obtained by numerically solving the Landau-Lifshitz-Gilbert equation and can be
explained by the Thiele equation characterizing the skyrmion core motion.",1606.09326v2
2018-03-19,Dynamics of a Magnetic Needle Magnetometer: Sensitivity to Landau-Lifshitz-Gilbert Damping,"An analysis of a single-domain magnetic needle in the presence of an external
magnetic field ${\bf B}$ is carried out with the aim of achieving a high
precision magnetometer. We determine the uncertainty $\Delta B$ of such a
device due to Gilbert dissipation and the associated internal magnetic field
fluctuations that gives rise to diffusion of the magnetic needle axis direction
${\bf n}$ and the needle orbital angular momentum. The levitation of the
magnetic needle in a magnetic trap and its stability are also analyzed.",1803.10064v2
2020-08-27,Nutation Resonance in Ferromagnets,"The inertial dynamics of magnetization in a ferromagnet is investigated
theoretically. The analytically derived dynamic response upon microwave
excitation shows two peaks: ferromagnetic and nutation resonances. The exact
analytical expressions of frequency and linewidth of the magnetic nutation
resonance are deduced from the frequency dependent susceptibility determined by
the inertial Landau-Lifshitz-Gilbert equation. The study shows that the
dependence of nutation linewidth on the Gilbert precession damping has a
minimum, which becomes more expressive with increase of the applied magnetic
field.",2008.12221v3
2007-02-01,Adiabatic Domain Wall Motion and Landau-Lifshitz Damping,"Recent theory and measurements of the velocity of current-driven domain walls
in magnetic nanowires have re-opened the unresolved question of whether
Landau-Lifshitz damping or Gilbert damping provides the more natural
description of dissipative magnetization dynamics. In this paper, we argue that
(as in the past) experiment cannot distinguish the two, but that
Landau-Lifshitz damping nevertheless provides the most physically sensible
interpretation of the equation of motion. From this perspective, (i) adiabatic
spin-transfer torque dominates the dynamics with small corrections from
non-adiabatic effects; (ii) the damping always decreases the magnetic free
energy, and (iii) microscopic calculations of damping become consistent with
general statistical and thermodynamic considerations.",0702020v3
2009-04-09,Evaluating the locality of intrinsic precession damping in transition metals,"The Landau-Lifshitz-Gilbert damping parameter is typically assumed to be a
local quantity, independent of magnetic configuration. To test the validity of
this assumption we calculate the precession damping rate of small amplitude
non-uniform mode magnons in iron, cobalt, and nickel. At scattering rates
expected near and above room temperature, little change in the damping rate is
found as the magnon wavelength is decreased from infinity to a length shorter
than features probed in recent experiments. This result indicates that
non-local effects due to the presence of weakly non-uniform modes, expected in
real devices, should not appreciably affect the dynamic response of the element
at typical operating temperatures. Conversely, at scattering rates expected in
very pure samples around cryogenic temperatures, non-local effects result in an
order of magnitude decrease in damping rates for magnons with wavelengths
commensurate with domain wall widths. While this low temperature result is
likely of little practical importance, it provides an experimentally testable
prediction of the non-local contribution of the spin-orbit torque-correlation
model of precession damping. None of these results exhibit strong dependence on
the magnon propagation direction.",0904.1455v1
2018-02-15,Damping's effect on the magnetodynamics of spin Hall nano-oscillators,"We study the impact of spin wave damping ($\alpha$) on the auto-oscillation
properties of nano-constriction based spin Hall nano-oscillators (SHNOs). The
SHNOs are based on a 5 nm Pt layer interfaced to a 5 nm
Py$_{100-x-y}$Pt$_{x}$Ag$_{y}$ magnetic layer, where the Pt and Ag contents are
co-varied to keep the saturation magnetization constant (within 10 %), while
$\alpha$ varies close to a factor of three. We systematically investigate the
influence of the Gilbert damping on the magnetodynamics of these SHNOs by means
of electrical microwave measurements. Under the condition of a constant field,
the threshold current scales with the damping in the magnetic layer. The
threshold current as a function of field shows a parabolic-like behavior, which
we attribute to the evolution of the spatial profile of the auto-oscillation
mode. The signal linewidth is smaller for the high-damping materials in low
magnetic fields, although the lowest observed linewidth was measured for the
alloy with least damping.",1802.05548v1
2004-05-02,Spin Dynamics and Multiple Reflections in Ferromagnetic Film in Contact with Normal Metal Layers,"Spin dynamics of a metallic ferromagnetic film imbedded between normal metal
layers is studied using the spin-pumping theory of Tserkovnyak et al. [Phys.
Rev. Lett. 88, 117601 (2002)]. The scattering matrix for this structure is
obtained using a spin-dependent potential with quantum well in the
ferromagnetic region. Owing to multiple reflections in the well, the excess
Gilbert damping and the gyromagnetic ratio exhibit quantum oscillations as a
function of the thickness of the ferromagnetic film. The wavelength of the
oscillations is given by the depth of the quantum well. For iron film imbedded
between gold layers, the amplitude of the oscillations of the Gilbert damping
is in an order of magnitude agreement with the damping observed by Urban et al.
[Phys. Rev. Lett. 87, 217204 (2001)]. The results are compared with the linear
response theory of Mills [Phys. Rev. B 68, 0144419 (2003)].",0405020v1
2004-06-18,Spin pumping and magnetization dynamics in ferromagnet-Luttinger liquid junctions,"We study spin transport between a ferromagnet with time-dependent
magnetization and a conducting carbon nanotube or quantum wire, modeled as a
Luttinger liquid. The precession of the magnetization vector of the ferromagnet
due for instance to an outside applied magnetic field causes spin pumping into
an adjacent conductor. Conversely, the spin injection causes increased
magnetization damping in the ferromagnet. We find that, if the conductor
adjacent to the ferromagnet is a Luttinger liquid, spin pumping/damping is
suppressed by interactions, and the suppression has clear Luttinger liquid
power law temperature dependence. We apply our result to a few particular
setups. First we study the effective Landau-Lifshitz-Gilbert (LLG) coupled
equations for the magnetization vectors of the two ferromagnets in a FM-LL-FM
junction. Also, we compute the Gilbert damping for a FM-LL and a FM-LL-metal
junction.",0406437v1
2004-10-30,Dynamics of Domain Wall in a Biaxial Ferromagnet With Spin-torque,"The dynamics of the domain wall (DW) in a biaxial ferromagnet interacting
with a spin-polarized current are described by sine-gordon (SG) equation
coupled with Gilbert damping term in this paper. Within our frame-work of this
model, we obtain a threshold of the current in the motion of a single DW with
the perturbation theory on kink soliton solution to the corresponding
ferromagnetic system, and the threshold is shown to be dependent on the Gilbert
damping term. Also, the motion properties of the DW are discussed for the zero-
and nonzero-damping cases, which shows that our theory to describe the dynamics
of the DW are self-consistent.",0411005v3
2005-10-31,Time-Resolved Spin Torque Switching and Enhanced Damping in Py/Cu/Py Spin-Valve Nanopillars,"We report time-resolved measurements of current-induced reversal of a free
magnetic layer in Py/Cu/Py elliptical nanopillars at temperatures T = 4.2 K to
160 K. Comparison of the data to Landau-Lifshitz-Gilbert macrospin simulations
of the free layer switching yields numerical values for the spin torque and the
Gilbert damping parameters as functions of T. The damping is strongly
T-dependent, which we attribute to the antiferromagnetic pinning behavior of a
thin permalloy oxide layer around the perimeter of the free layer. This
adventitious antiferromagnetic pinning layer can have a major impact on spin
torque phenomena.",0510798v2
2006-09-18,General Form of Magnetization Damping: Magnetization dynamics of a spin system evolving nonadiabatically and out of equilibrium,"Using an effective Hamiltonian including the Zeeman and internal
interactions, we describe the quantum theory of magnetization dynamics when the
spin system evolves non-adiabatically and out of equilibrium. The
Lewis-Riesenfeld dynamical invariant method is employed along with the
Liouville-von Neumann equation for the density matrix. We derive a dynamical
equation for magnetization defined with respect to the density operator with a
general form of magnetization damping that involves the non-equilibrium
contribution in addition to the Landau-Lifshitz-Gilbert equation. Two special
cases of the radiation-spin interaction and the spin-spin exchange interaction
are considered. For the radiation-spin interaction, the damping term is shown
to be of the Gilbert type, while in the spin-spin exchange interaction case the
results depend on a coupled chain of correlation functions.",0609431v2
2010-12-25,Screw-pitch effect and velocity oscillation of domain-wall in ferromagnetic nanowire driven by spin-polarized current,"We investigate the dynamics of domain wall in ferromagnetic nanowire with
spin-transfer torque. The critical current condition is obtained analytically.
Below the critical current, we get the static domain wall solution which shows
that the spin-polarized current can't drive domain wall moving continuously. In
this case, the spin-transfer torque plays both the anti-precession and
anti-damping roles, which counteracts not only the spin-precession driven by
the effective field but also Gilbert damping to the moment. Above the critical
value, the dynamics of domain wall exhibits the novel screw-pitch effect
characterized by the temporal oscillation of domain wall velocity and width,
respectively. Both the theoretical analysis and numerical simulation
demonstrate that this novel phenomenon arise from the conjunctive action of
Gilbert-damping and spin-transfer torque. We also find that the roles of
spin-transfer torque are entirely contrary for the cases of below and above the
critical current.",1012.5473v1
2014-06-24,Interface enhancement of Gilbert damping from first-principles,"The enhancement of Gilbert damping observed for Ni80Fe20 (Py) films in
contact with the non-magnetic metals Cu, Pd, Ta and Pt, is quantitatively
reproduced using first-principles scattering theory. The ""spin-pumping"" theory
that qualitatively explains its dependence on the Py thickness is generalized
to include a number of factors known to be important for spin transport through
interfaces. Determining the parameters in this theory from first-principles
shows that interface spin-flipping makes an essential contribution to the
damping enhancement. Without it, a much shorter spin-flip diffusion length for
Pt would be needed than the value we calculate independently.",1406.6225v2
2015-09-06,Study of spin dynamics and damping on the magnetic nanowire arrays with various nanowire widths,"We investigate the spin dynamics including Gilbert damping in the
ferromagnetic nanowire arrays. We have measured the ferromagnetic resonance of
ferromagnetic nanowire arrays using vector-network analyzer ferromagnetic
resonance (VNA-FMR) and analyzed the results with the micromagnetic
simulations. We find excellent agreement between the experimental VNA-FMR
spectra and micromagnetic simulations result for various applied magnetic
fields. We find that the demagnetization factor for longitudinal conditions, Nz
(Ny) increases (decreases) as decreasing the nanowire width in the
micromagnetic simulations. For the transverse magnetic field, Nz (Ny) increases
(decreases) as increasing the nanowire width. We also find that the Gilbert
damping constant increases from 0.018 to 0.051 as the increasing nanowire width
for the transverse case, while it is almost constant as 0.021 for the
longitudinal case.",1509.01807v1
2016-03-25,Large spin pumping effect in antisymmetric precession of Ni$_{79}$Fe$_{21}$/Ru/Ni$_{79}$Fe$_{21}$,"In magnetic trilayer structures, a contribution to the Gilbert damping of
ferromagnetic resonance arises from spin currents pumped from one layer to
another. This contribution has been demonstrated for layers with weakly
coupled, separated resonances, where magnetization dynamics are excited
predominantly in one layer and the other layer acts as a spin sink. Here we
show that trilayer structures in which magnetizations are excited
simultaneously, antisymmetrically, show a spin-pumping effect roughly twice as
large. The antisymmetric (optical) mode of antiferromagnetically coupled
Ni$_{79}$Fe$_{21}$(8nm)/Ru/Ni$_{79}$Fe$_{21}$(8nm) trilayers shows a Gilbert
damping constant greater than that of the symmetric (acoustic) mode by an
amount as large as the intrinsic damping of Py ($\Delta
\alpha\simeq\textrm{0.006}$). The effect is shown equally in field-normal and
field-parallel to film plane geometries over 3-25 GHz. The results confirm a
prediction of the spin pumping model and have implications for the use of
synthetic antiferromagnets (SAF)-structures in GHz devices.",1603.07977v1
2016-07-18,Magnetic Skyrmion Transport in a Nanotrack With Spatially Varying Damping and Non-adiabatic Torque,"Reliable transport of magnetic skyrmions is required for any future
skyrmion-based information processing devices. Here we present a micromagnetic
study of the in-plane current-driven motion of a skyrmion in a ferromagnetic
nanotrack with spatially sinusoidally varying Gilbert damping and/or
non-adiabatic spin-transfer torque coefficients. It is found that the skyrmion
moves in a sinusoidal pattern as a result of the spatially varying Gilbert
damping and/or non-adiabatic spin-transfer torque in the nanotrack, which could
prevent the destruction of the skyrmion caused by the skyrmion Hall effect. The
results provide a guide for designing and developing the skyrmion transport
channel in skyrmion-based spintronic applications.",1607.04983v3
2016-10-21,Spin transport and dynamics in all-oxide perovskite La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$ bilayers probed by ferromagnetic resonance,"Thin films of perovskite oxides offer the possibility of combining emerging
concepts of strongly correlated electron phenomena and spin current in magnetic
devices. However, spin transport and magnetization dynamics in these complex
oxide materials are not well understood. Here, we experimentally quantify spin
transport parameters and magnetization damping in epitaxial perovskite
ferromagnet/paramagnet bilayers of La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$
(LSMO/SRO) by broadband ferromagnetic resonance spectroscopy. From the SRO
thickness dependence of Gilbert damping, we estimate a short spin diffusion
length of $\lesssim$1 nm in SRO and an interfacial spin-mixing conductance
comparable to other ferromagnet/paramagnetic-metal bilayers. Moreover, we find
that anisotropic non-Gilbert damping due to two-magnon scattering also
increases with the addition of SRO. Our results demonstrate LSMO/SRO as a
spin-source/spin-sink system that may be a foundation for examining
spin-current transport in various perovskite heterostructures.",1610.06661v1
2019-02-12,Ultra-low damping in lift-off structured yttrium iron garnet thin films,"We show that using maskless photolithography and the lift-off technique,
patterned yttrium iron garnet thin films possessing ultra-low Gilbert damping
can be accomplished. The films of 70 nm thickness were grown on (001)-oriented
gadolinium gallium garnet by means of pulsed laser deposition, and they exhibit
high crystalline quality, low surface roughness, and the effective
magnetization of 127 emu/cm3. The Gilbert damping parameter is as low as
5x10-4. The obtained structures have well-defined sharp edges which along with
good structural and magnetic film properties pave a path in the fabrication of
high-quality magnonic circuits and oxide-based spintronic devices.",1902.04605v1
2019-02-20,CoFeB/MgO/CoFeB structures with orthogonal easy axes: perpendicular anisotropy and damping,"We report on the Gilbert damping parameter $\alpha$, the effective
magnetization $4\pi M_{eff}$, and the asymmetry of the $g$-factor in
bottom-CoFeB(0.93~nm)/MgO(0.90--1.25~nm)/CoFeB(1.31~nm)-top as-deposited
systems.
  Magnetization of CoFeB layers exhibits a specific noncollinear configuration
with orthogonal easy axes and with $4\pi M_{eff}$ values of $+2.2$ kG and
$-2.3$ kG for the bottom and top layers, respectively. We show that $4\pi
M_{eff}$ depends on the asymmetry $g_\perp - g_\parallel$ of the $g$-factor
measured in the perpendicular and the in-plane directions revealing a highly
nonlinear relationship. In contrast, the Gilbert damping is practically the
same for both layers. Annealing of the films results in collinear easy axes
perpendicular to the plane for both layers. However, the linewidth is strongly
increased due to enhanced inhomogeneous broadening.",1902.07563v1
2021-06-28,Stability of a Magnetically Levitated Nanomagnet in Vacuum: Effects of Gas and Magnetization Damping,"In the absence of dissipation a non-rotating magnetic nanoparticle can be
stably levitated in a static magnetic field as a consequence of the spin origin
of its magnetization. Here we study the effects of dissipation on the stability
of the system, considering the interaction with the background gas and the
intrinsic Gilbert damping of magnetization dynamics. At large applied magnetic
fields we identify magnetization switching induced by Gilbert damping as the
key limiting factor for stable levitation. At low applied magnetic fields and
for small particle dimensions magnetization switching is prevented due to the
strong coupling of rotation and magnetization dynamics, and the stability is
mainly limited by the gas-induced dissipation. In the latter case, high vacuum
should be sufficient to extend stable levitation over experimentally relevant
timescales. Our results demonstrate the possibility to experimentally observe
the phenomenon of quantum spin stabilized magnetic levitation.",2106.14858v3
2021-10-31,Thermally induced all-optical ferromagnetic resonance in thin YIG films,"All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for local
detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert
damping or spin stiffness. In this work we demonstrate that the AO-FMR method
can be used in thin films of Yttrium Iron Garnet (YIG) if a metallic capping
layer (Au, Pt) is deposited on top of the film. Magnetization precession is
triggered by heating of the metallic layer with femtosecond laser pulses. The
heating modifies the magneto-crystalline anisotropy of the YIG film and shifts
the quasi-equilibrium orientation of magnetization, which results in
precessional magnetization dynamics. The laser-induced magnetization precession
corresponds to a uniform (Kittel) magnon mode, with the precession frequency
determined by the magnetic anisotropy of the material as well as the external
magnetic field, and the damping time set by a Gilbert damping parameter. The
AO-FMR method thus enables measuring local magnetic properties, with spatial
resolution given only by the laser spot size.",2111.00586v1
2024-01-01,Calculation of Gilbert damping and magnetic moment of inertia using torque-torque correlation model within ab initio Wannier framework,"Magnetization dynamics in magnetic materials are well described by the
modified semiclassical Landau-Lifshitz-Gilbert (LLG) equation, which includes
the magnetic damping $\alpha$ and the magnetic moment of inertia $\mathrm{I}$
tensors as key parameters. Both parameters are material-specific and physically
represent the time scales of damping of precession and nutation in
magnetization dynamics. $\alpha$ and $\mathrm{I}$ can be calculated quantum
mechanically within the framework of the torque-torque correlation model. The
quantities required for the calculation are torque matrix elements, the real
and imaginary parts of the Green's function and its derivatives. Here, we
calculate these parameters for the elemental magnets such as Fe, Co and Ni in
an ab initio framework using density functional theory and Wannier functions.
We also propose a method to calculate the torque matrix elements within the
Wannier framework. We demonstrate the effectiveness of the method by comparing
it with the experiments and the previous ab initio and empirical studies and
show its potential to improve our understanding of spin dynamics and to
facilitate the design of spintronic devices.",2401.00714v1
2017-12-20,Unifying ultrafast demagnetization and intrinsic Gilbert damping in Co/Ni bilayers with electronic relaxation near the Fermi surface,"The ability to controllably manipulate the laser-induced ultrafast magnetic
dynamics is a prerequisite for future high speed spintronic devices. The
optimization of devices requires the controllability of the ultrafast
demagnetization time, , and intrinsic Gilbert damping, . In previous attempts
to establish the relationship between and , the rare-earth doping of a
permalloy film with two different demagnetization mechanism is not a suitable
candidate. Here, we choose Co/Ni bilayers to investigate the relations between
and by means of time-resolved magneto-optical Kerr effect (TRMOKE) via
adjusting the thickness of the Ni layers, and obtain an approximately
proportional relation between these two parameters. The remarkable agreement
between TRMOKE experiment and the prediction of breathing Fermi-surface model
confirms that a large Elliott-Yafet spin-mixing parameter is relevant to the
strong spin-orbital coupling at the Co/Ni interface. More importantly, a
proportional relation between and in such metallic films or heterostructures
with electronic relaxation near Fermi surface suggests the local spin-flip
scattering domains the mechanism of ultrafast demagnetization, otherwise the
spin-current mechanism domains. It is an effective method to distinguish the
dominant contributions to ultrafast magnetic quenching in metallic
heterostructures by investigating both the ultrafast demagnetization time and
Gilbert damping simultaneously. Our work can open a novel avenue to manipulate
the magnitude and efficiency of Terahertz emission in metallic heterostructures
such as the perpendicular magnetic anisotropic Ta/Pt/Co/Ni/Pt/Ta multilayers,
and then it has an immediate implication of the design of high frequency
spintronic devices.",1712.07323v1
2008-05-22,Intrinsic and non-local Gilbert damping in polycrystalline nickel studied by Ti:Sapphire laser fs spectroscopy,"The use of femtosecond laser pulses generated by a Ti:Sapphire laser system
allows us to gain an insight into the magnetization dynamics on time scales
from sub-picosecond up to 1 ns directly in the time domain. This experimental
technique is used to excite a polycrystalline nickel (Ni) film optically and
probe the dynamics afterwards. Different spin wave modes (the Kittel mode,
perpendicular standing spin-wave modes (PSSW) and dipolar spin-wave modes
(Damon-Eshbach modes)) are identified as the Ni thickness is increased. The
Kittel mode allows determination of the Gilbert damping parameter alpha
extracted from the magnetization relaxation time tau_alpha. The non-local
damping by spin currents emitted into a non-magnetic metallic layer of vanadium
(V), palladium (Pd) and the rare earth dysprosium (Dy) are studied for
wedge-shaped Ni films 1 nm-30 nm. The damping parameter increases from
alpha=0.045 intrinsic for nickel to alpha>0.10 for the heavy materials, such as
Pd and Dy, for the thinnest Ni films below 10 nm thickness. Also, for the
thinnest reference Ni film thickness, an increased magnetic damping below 4 nm
is observed. The origin of this increase is discussed within the framework of
line broadening by locally different precessional frequencies within the laser
spot region.",0805.3495v1
2015-06-18,The absence of intraband scattering in a consistent theory of Gilbert damping in metallic ferromagnets,"Damping of magnetization dynamics in a ferromagnetic metal is usually
characterized by the Gilbert parameter alpha. Recent calculations of this
quantity, using a formula due to Kambersky, find that it is infinite for a
perfect crystal owing to an intraband scattering term which is of third order
in the spin-orbit parameter xi This surprising result conflicts with recent
work by Costa and Muniz who study damping numerically by direct calculation of
the dynamical transverse spin susceptibility in the presence of spin-orbit
coupling. We resolve this inconsistency by following the Costa-Muniz approach
for a slightly simplified model where it is possible to calculate alpha
analytically. We show that to second order in the spin-orbit parameter xi one
retrieves the Kambersky result for alpha, but to higher order one does not
obtain any divergent intraband terms. The present work goes beyond that of
Costa and Muniz by pointing out the necessity of including the effect of
long-range Coulomb interaction in calculating damping for large xi. A direct
derivation of the Kambersky formula is given which shows clearly the
restriction of its validity to second order in xi so that no intraband
scattering terms appear. This restriction has an important effect on the
damping over a substantial range of impurity content and temperature. The
experimental situation is discussed.",1506.05622v2
2020-02-07,"Engineering Co$_2$MnAl$_x$Si$_{1-x}$ Heusler compounds as a model system to correlate spin polarization, intrinsic Gilbert damping and ultrafast demagnetization","Engineering of magnetic materials for developing better spintronic
applications relies on the control of two key parameters: the spin polarization
and the Gilbert damping responsible for the spin angular momentum dissipation.
Both of them are expected to affect the ultrafast magnetization dynamics
occurring on the femtosecond time scale. Here, we use engineered Co2MnAlxSi1-x
Heusler compounds to adjust the degree of spin polarization P from 60 to 100%
and investigate how it correlates with the damping. We demonstrate
experimentally that the damping decreases when increasing the spin polarization
from 1.1 10-3 for Co2MnAl with 63% spin polarization to an ultra-low value of
4.10-4 for the half-metal magnet Co2MnSi. This allows us investigating the
relation between these two parameters and the ultrafast demagnetization time
characterizing the loss of magnetization occurring after femtosecond laser
pulse excitation. The demagnetization time is observed to be inversely
proportional to 1-P and as a consequence to the magnetic damping, which can be
attributed to the similarity of the spin angular momentum dissipation processes
responsible for these two effects. Altogether, our high quality Heusler
compounds allow controlling the band structure and therefore the channel for
spin angular momentum dissipation.",2002.02686v1
2006-08-22,Simulation of stress-impedance effects in low magnetostrictive films,"A theoretical study of stress-impedance effect based on the solution of
Landau-Lifsitz-Gilbert equation has been carried out. The results show that
stress impedance effects depend largely on several extrinsic (external bias
field, external frequency) and intrinsic (orientation and magnitude of uniaxial
anisotropy, damping) parameters.",0608488v1
2017-03-09,Material developments and domain wall based nanosecond-scale switching process in perpendicularly magnetized STT-MRAM cells,"We investigate the Gilbert damping and the magnetization switching of
perpendicularly magnetized FeCoB-based free layers embedded in tunnel junctions
adequate for spin-torque operated memories. We study the influence of the boron
content in MgO / FeCoB /Ta systems alloys on their Gilbert damping after
crystallization annealing. Increasing the boron content from 20 to 30\%
increases the crystallization temperature, thereby postponing the onset of
elemental diffusion within the free layer. This reduction of the interdiffusion
of the Ta atoms helps maintaining the Gilbert damping at a low level of 0.009
without any penalty on the anisotropy and the magneto-transport properties up
to the 400$^\circ$C annealing required in CMOS back-end of line processing. In
addition, we show that dual MgO free layers of composition
MgO/FeCoB/Ta/FeCoB/MgO have a substantially lower damping than their
MgO/FeCoB/Ta counterparts, reaching damping parameters as low as 0.0039 for a 3
\r{A} thick Tantalum spacer. This confirms that the dominant channel of damping
is the presence of Ta impurities within the FeCoB alloy. On optimized tunnel
junctions, we then study the duration of the switching events induced by
spin-transfer-torque. We focus on the sub-threshold thermally activated
switching in optimal applied field conditions. From the electrical signatures
of the switching, we infer that once the nucleation has occurred, the reversal
proceeds by a domain wall sweeping though the device at a few 10 m/s. The
smaller the device, the faster its switching. We present an analytical model to
account for our findings. The domain wall velocity is predicted to scale
linearly with the current for devices much larger than the wall width. The wall
velocity depends on the Bloch domain wall width, such that the devices with the
lowest exchange stiffness will be the ones that host the domain walls with the
slowest mobilities.",1703.03198v3
2018-07-31,"Comparative study of methodologies to compute the intrinsic Gilbert damping: interrelations, validity and physical consequences","Relaxation effects are of primary importance in the description of magnetic
excitations, leading to a myriad of methods addressing the phenomenological
damping parameters. In this work, we consider several well-established forms of
calculating the intrinsic Gilbert damping within a unified theoretical
framework, mapping out their connections and the approximations required to
derive each formula. This scheme enables a direct comparison of the different
methods on the same footing and a consistent evaluation of their range of
validity. Most methods lead to very similar results for the bulk ferromagnets
Fe, Co and Ni, due to the low spin-orbit interaction strength and the absence
of the spin pumping mechanism. The effects of inhomogeneities, temperature and
other sources of finite electronic lifetime are often accounted for by an
empirical broadening of the electronic energy levels. We show that the
contribution to the damping introduced by this broadening is additive, and so
can be extracted by comparing the results of the calculations performed with
and without spin-orbit interaction. Starting from simulated ferromagnetic
resonance spectra based on the underlying electronic structure, we
unambiguously demonstrate that the damping parameter obtained within the
constant broadening approximation diverges for three-dimensional bulk magnets
in the clean limit, while it remains finite for monolayers. Our work puts into
perspective the several methods available to describe and compute the Gilbert
damping, building a solid foundation for future investigations of magnetic
relaxation effects in any kind of material.",1807.11808v3
2002-07-30,Microscopic relaxation mechanisms and linear magnetization dynamics,"Linear magnetization dynamics in the presense of a thermal bath is analyzed
for two general classes of microscopic damping mechanisms. The resulting
stochastic differential equations are always in the form of a damped harmonic
oscillator driven by a thermal field. The damping term contains both the
interaction mechanisms and the symmetry of the magnetic system. Back
transformation from the oscillator coordinates to the magnetization variables
results in a macroscopic tensor form of damping that reflects the system
anisotropy. Scalar Landau-Lifshitz-Gilbert damping term is valid only for
systems with axial symmetry. Analysis of FMR linewith measurements versus
frequency, temperature, and film thickness in NiFe films shows good agreement
with a combination of slow-relaxing impurity and magnon-electron confluence
processes.",0207721v1
2006-10-10,Spin-transfer in an open ferromagnetic layer: from negative damping to effective temperature,"Spin-transfer is a typical spintronics effect that allows a ferromagnetic
layer to be switched by spin-injection. Most of the experimental results about
spin transfer are described on the basis of the Landau-Lifshitz-Gilbert
equation of the magnetization, in which additional current-dependent damping
factors are added, and can be positive or negative. The origin of the damping
can be investigated further by performing stochastic experiments, like one shot
relaxation experiments under spin-injection in the activation regime of the
magnetization. In this regime, the N\'eel-Brown activation law is observed
which leads to the introduction of a current-dependent effective temperature.
In order to justify the introduction of these counterintuitive parameters
(effective temperature and negative damping), a detailed thermokinetic analysis
of the different sub-systems involved is performed. We propose a thermokinetic
description of the different forms of energy exchanged between the electric and
the ferromagnetic sub-systems at a Normal/Ferromagnetic junction. The
corresponding Fokker Planck equations, including relaxations, are derived. The
damping coefficients are studied in terms of Onsager-Casimir transport
coefficients, with the help of the reciprocity relations. The effective
temperature is deduced in the activation regime.",0610264v1
2014-05-09,Magnetization dynamics and damping due to electron-phonon scattering in a ferrimagnetic exchange model,"We present a microscopic calculation of magnetization damping for a magnetic
""toy model."" The magnetic system consists of itinerant carriers coupled
antiferromagnetically to a dispersionless band of localized spins, and the
magnetization damping is due to coupling of the itinerant carriers to a phonon
bath in the presence of spin-orbit coupling. Using a mean-field approximation
for the kinetic exchange model and assuming the spin-orbit coupling to be of
the Rashba form, we derive Boltzmann scattering integrals for the distributions
and spin coherences in the case of an antiferromagnetic exchange splitting,
including a careful analysis of the connection between lifetime broadening and
the magnetic gap. For the Elliott-Yafet type itinerant spin dynamics we extract
dephasing and magnetization times T_1 and T_2 from initial conditions
corresponding to a tilt of the magnetization vector, and draw a comparison to
phenomenological equations such as the Landau-Lifshitz or the Gilbert damping.
We also analyze magnetization precession and damping for this system including
an anisotropy field and find a carrier mediated dephasing of the localized spin
via the mean-field coupling.",1405.2347v1
2015-11-13,Magnified Damping under Rashba Spin Orbit Coupling,"The spin orbit coupling spin torque consists of the field-like [REF: S.G. Tan
et al., arXiv:0705.3502, (2007).] and the damping-like terms [REF: H.
Kurebayashi et al., Nature Nanotechnology 9, 211 (2014).] that have been widely
studied for applications in magnetic memory. We focus, in this article, not on
the spin orbit effect producing the above spin torques, but on its magnifying
the damping constant of all field like spin torques. As first order precession
leads to second order damping, the Rashba constant is naturally co-opted,
producing a magnified field-like damping effect. The Landau-Liftshitz-Gilbert
equations are written separately for the local magnetization and the itinerant
spin, allowing the progression of magnetization to be self-consistently locked
to the spin.",1511.04227v1
2022-05-13,Precession dynamics of a small magnet with non-Markovian damping: Theoretical proposal for an experiment to determine the correlation time,"Recent advances in experimental techniques have made it possible to
manipulate and measure the magnetization dynamics on the femtosecond time scale
which is the same order as the correlation time of the bath degrees of freedom.
In the equations of motion of magnetization, the correlation of the bath is
represented by the non-Markovian damping. For development of the science and
technologies based on the ultrafast magnetization dynamics it is important to
understand how the magnetization dynamics depend on the correlation time. It is
also important to determine the correlation time experimentally. Here we study
the precession dynamics of a small magnet with the non-Markovian damping.
Extending the theoretical analysis of Miyazaki and Seki [J. Chem. Phys. 108,
7052 (1998)] we obtain analytical expressions of the precession angular
velocity and the effective damping constant for any values of the correlation
time under assumption of small Gilbert damping constant. We also propose a
possible experiment for determination of the correlation time.",2205.06399v1
2022-10-16,Magnetic damping anisotropy in the two-dimensional van der Waals material Fe$_3$GeTe$_2$ from first principles,"Magnetization relaxation in the two-dimensional itinerant ferromagnetic van
der Waals material Fe$_3$GeTe$_2$, below the Curie temperature, is
fundamentally important for applications to low-dimensional spintronics
devices. We use first-principles scattering theory to calculate the
temperature-dependent Gilbert damping for bulk and single-layer Fe$_3$GeTe$_2$.
The calculated damping frequency of bulk Fe$_3$GeTe$_2$ increases monotonically
with temperature because of the dominance of resistivitylike behavior. By
contrast, a very weak temperature dependence is found for the damping frequency
of a single layer, which is attributed to strong surface scattering in this
highly confined geometry. A systematic study of the damping anisotropy reveals
that orientational anisotropy is present in both bulk and single-layer
Fe3GeTe2. Rotational anisotropy is significant at low temperatures for both the
bulk and a single layer and is gradually diminished by temperature-induced
disorder. The rotational anisotropy can be significantly enhanced by up to 430%
in gated single-layer Fe$_3$GeTe$_2$.",2210.08429v1
2016-09-26,Relativistic theory of spin relaxation mechanisms in the Landau-Lifshitz-Gilbert equation of spin dynamics,"Starting from the Dirac-Kohn-Sham equation we derive the relativistic
equation of motion of spin angular momentum in a magnetic solid under an
external electromagnetic field. This equation of motion can be written in the
form of the well-known Landau-Lifshitz-Gilbert equation for a harmonic external
magnetic field, and leads to a more general magnetization dynamics equation for
a general time-dependent magnetic field. In both cases with an electronic
spin-relaxation term which stems from the spin-orbit interaction. We thus
rigorously derive, from fundamental principles, a general expression for the
anisotropic damping tensor which is shown to contain an isotropic Gilbert
contribution as well as an anisotropic Ising-like and a chiral,
Dzyaloshinskii-Moriya-like contribution. The expression for the spin relaxation
tensor comprises furthermore both electronic interband and intraband
transitions. We also show that when the externally applied electromagnetic
field possesses spin angular momentum, this will lead to an optical spin torque
exerted on the spin moment.",1609.07901v1
2002-11-22,Nonlinear microscopic relaxation of uniform magnetization precession,"Dynamic relaxation for nonlinear magnetization excitation is analyzed. For
direct processes, such as magnon-electron scattering and two-magnon scattering,
the relaxation rate is determined from the linear case simply by utilizing the
magnetization oscillation frequency for nonlinear excitation. For an indirect
process, such as slow-relaxing impurities, the analysis gives an additional
relaxation term proportional to the excitation level. In all cases the
effective magnetization damping is increased compared to
Landau-Lifshitz-Gilbert damping.",0211499v1
2005-10-11,Non-damping magnetization oscillations in a single-domain ferromagnet,"Non-damped oscillations of the magnetization vector of a ferromagnetic system
subject to a spin polarized current and an external magnetic field are studied
theoretically by solving the Landau-Lifshitz-Gilbert equation. It is shown that
the frequency and amplitude of such oscillations can be controlled by means of
an applied magnetic field and a spin current. The possibility of injection of
the oscillating spin current into a non-magnetic system is also discussed.",0510280v1
2007-03-27,Gauge Field Formulation of Adiabatic Spin Torques,"Previous calculation of spin torques for small-amplitude magnetization
dynamics around a uniformly magnetized state [J. Phys. Soc. Jpn. {\bf 75}
(2006) 113706] is extended here to the case of finite-amplitude dynamics. This
is achieved by introducing an `` adiabatic'' spin frame for conduction
electrons, and the associated SU(2) gauge field. In particular, the Gilbert
damping is shown to arise from the time variation of the spin-relaxation source
terms in this new frame, giving a new physical picture of the damping. The
present method will allow a `` first-principle'' derivation of spin torques
without any assumptions such as rotational symmetry in spin space.",0703705v1
2008-05-09,"Spin dynamics in (III,Mn)V ferromagnetic semiconductors: the role of correlations","We address the role of correlations between spin and charge degrees of
freedom on the dynamical properties of ferromagnetic systems governed by the
magnetic exchange interaction between itinerant and localized spins. For this
we introduce a general theory that treats quantum fluctuations beyond the
Random Phase Approximation based on a correlation expansion of the Green's
function equations of motion. We calculate the spin susceptibility, spin--wave
excitation spectrum, and magnetization precession damping. We find that
correlations strongly affect the magnitude and carrier concentration dependence
of the spin stiffness and magnetization Gilbert damping.",0805.1320v2
2010-01-16,Resonance Damping in Ferromagnets and Ferroelectrics,"The phenomenological equations of motion for the relaxation of ordered phases
of magnetized and polarized crystal phases can be developed in close analogy
with one another. For the case of magnetized systems, the driving magnetic
field intensity toward relaxation was developed by Gilbert. For the case of
polarized systems, the driving electric field intensity toward relaxation was
developed by Khalatnikov. The transport times for relaxation into thermal
equilibrium can be attributed to viscous sound wave damping via
magnetostriction for the magnetic case and electrostriction for the
polarization case.",1001.2845v1
2016-05-15,Propagation of Thermally Induced Magnonic Spin Currents,"The propagation of magnons in temperature gradients is investigated within
the framework of an atomistic spin model with the stochastic
Landau-Lifshitz-Gilbert equation as underlying equation of motion. We analyze
the magnon accumulation, the magnon temperature profile as well as the
propagation length of the excited magnons. The frequency distribution of the
generated magnons is investigated in order to derive an expression for the
influence of the anisotropy and the damping parameter on the magnon propagation
length. For soft ferromagnetic insulators with low damping a propagation length
in the range of some $\mu$m can be expected for exchange driven magnons.",1605.04543v1
2021-03-05,Universal spin wave damping in magnetic Weyl semimetals,"We analyze the decay of spin waves into Stoner excitations in magnetic Weyl
semimetals. The lifetime of a mode is found to have a universal dependence on
its frequency and momentum, and on a few parameters that characterize the
relativistic Weyl spectrum. At the same time, Gilbert damping by Weyl electrons
is absent. The decay rate of spin waves is calculated perturbatively using the
s-d model of itinerant Weyl or Dirac electrons coupled to local moments. We
show that many details of the Weyl spectrum, such as the momentum-space
locations, dispersions and sizes of the Weyl Fermi pockets, can be deduced
indirectly by probing the spin waves of local moments using inelastic neutron
scattering.",2103.03885v1
2023-02-17,Control of magnon-photon coupling by spin torque,"We demonstrate the influence of damping and field-like torques in the
magnon-photon coupling process by classically integrating the generalized
Landau-Lifshitz-Gilbert equation with RLC equation in which a phase correlation
between dynamic magnetization and microwave current through combined Amp\`ere
and Faraday effects are considered. We show that the gap between two hybridized
modes can be controlled in samples with damping parameter in the order of
$10^{-3}$ by changing the direction of the dc current density $J$ if a certain
threshold is reached. Our results suggest that an experimental realization of
the proposed magnon-photon coupling control mechanism is feasible in yttrium
iron garnet/Pt hybrid structures.",2302.08910v1
2017-03-21,Using rf voltage induced ferromagnetic resonance to study the spin-wave density of states and the Gilbert damping in perpendicularly magnetized disks,"We study how the shape of the spinwave resonance lines in rf-voltage induced
FMR can be used to extract the spinwave density of states and the damping
within the precessing layer in nanoscale tunnel junctions that possess
perpendicular anisotropy. We work with a field applied along the easy axis to
preserve the uniaxial symmetry of the system. We describe the set-up to study
the susceptibility contributions of the spin waves in the field-frequency
space. We then identify the maximum device size above which the spinwaves can
no longer be studied in isolation as the linewidths of their responses make
them overlap. The rf-voltage induced signal is the sum of two voltages that
have comparable magnitudes: a first voltage that originates from the transverse
susceptibility and rectification by magnetoresistance and a second voltage that
arises from the non-linear longitudinal susceptibility and the resultant
time-averaged change of the micromagnetic configuration. The transverse and
longitudinal susceptibility signals have different dc bias dependences such
that they can be separated by measuring how the device rectifies the rf voltage
at different dc bias voltages. The transverse and longitudinal susceptibility
signals have different lineshapes; their joint studies can yield the Gilbert
damping of the free layer of the device with a degree of confidence that
compares well with standard FMR. Our method is illustrated on FeCoB-based free
layers in which the individual spin-waves can be sufficiently resolved only for
disk diameters below 200 nm. The resonance line shapes on devices with 90 nm
diameters are consistent with a Gilbert damping of 0.011. This damping of 0.011
exceeds the value of 0.008 measured on the unpatterned films, which indicates
that device-level measurements are needed for a correct evaluation of
dissipation.",1703.07310v2
2015-11-16,Determination of intrinsic damping of perpendicularly magnetized ultrathin films from time resolved precessional magnetization measurements,"Magnetization dynamics are strongly influenced by damping. An effective
damping constant {\alpha}eff is often determined experimentally from the
spectral linewidth of the free induction decay of the magnetization after the
system is excited to its non-equilibrium state. Such an {\alpha}eff, however,
reflects both intrinsic damping as well as inhomogeneous broadening. In this
paper we compare measurements of the magnetization dynamics in ultrathin
non-epitaxial films having perpendicular magnetic anisotropy using two
different techniques, time-resolved magneto optical Kerr effect (TRMOKE) and
hybrid optical-electrical ferromagnetic resonance (OFMR). By using an external
magnetic field that is applied at very small angles to the film plane in the
TRMOKE studies, we develop an explicit closed-form analytical expression for
the TRMOKE spectral linewidth and show how this can be used to reliably extract
the intrinsic Gilbert damping constant. The damping constant determined in this
way is in excellent agreement with that determined from the OFMR method on the
same samples. Our studies indicate that the asymptotic high-field approach that
is often used in the TRMOKE method to distinguish the intrinsic damping from
the effective damping may result in significant error, because such high
external magnetic fields are required to make this approach valid that they are
out of reach. The error becomes larger the lower is the intrinsic damping
constant, and thus may account for the anomalously high damping constants that
are often reported in TRMOKE studies. In conventional ferromagnetic resonance
(FMR) studies, inhomogeneous contributions can be readily distinguished from
intrinsic damping contributions from the magnetic field dependence of the FMR
linewidth. Using the analogous approach, we show how reliable values of the
intrinsic damping can be extracted from TRMOKE.",1511.04802v1
2002-07-19,Gilbert Damping in Magnetic Multilayers,"We study the enhancement of the ferromagnetic relaxation rate in thin films
due to the adjacent normal metal layers. Using linear response theory, we
derive the dissipative torque produced by the s-d exchange interaction at the
ferromagnet-normal metal interface. For a slow precession, the enhancement of
Gilbert damping constant is proportional to the square of the s-d exchange
constant times the zero-frequency limit of the frequency derivative of the
local dynamic spin susceptibility of the normal metal at the interface.
Electron-electron interactions increase the relaxation rate by the Stoner
factor squared. We attribute the large anisotropic enhancements of the
relaxation rate observed recently in multilayers containing palladium to this
mechanism. For free electrons, the present theory compares favorably with
recent spin-pumping result of Tserkovnyak et al. [Phys. Rev. Lett.
\textbf{88},117601 (2002)].",0207471v1
2002-08-06,Spin pumping and magnetization dynamics in metallic multilayers,"We study the magnetization dynamics in thin ferromagnetic films and small
ferromagnetic particles in contact with paramagnetic conductors. A moving
magnetization vector causes \textquotedblleft pumping\textquotedblright of
spins into adjacent nonmagnetic layers. This spin transfer affects the
magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology.
The additional Gilbert damping is significant for small ferromagnets, when the
nonmagnetic layers efficiently relax the injected spins, but the effect is
reduced when a spin accumulation build-up in the normal metal opposes the spin
pumping. The damping enhancement is governed by (and, in turn, can be used to
measure) the mixing conductance or spin-torque parameter of the
ferromagnet--normal-metal interface. Our theoretical findings are confirmed by
agreement with recent experiments in a variety of multilayer systems.",0208091v2
2003-08-19,"Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors","We describe a theory of Mn local-moment magnetization relaxation due to p-d
kinetic-exchange coupling with the itinerant-spin subsystem in the
ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping
coefficient implied by this mechanism is calculated as a function of Mn moment
density, hole concentration, and quasiparticle lifetime. Comparison with
experimental ferromagnetic resonance data suggests that in annealed strongly
metallic samples, p-d coupling contributes significantly to the damping rate of
the magnetization precession at low temperatures. By combining the theoretical
Gilbert coefficient with the values of the magnetic anisotropy energy, we
estimate that the typical critical current for spin-transfer magnetization
switching in all-semiconductor trilayer devices can be as low as $\sim 10^{5}
{\rm A cm}^{-2}$.",0308386v3
2005-12-29,Current-induced magnetization dynamics in disordered itinerant ferromagnets,"Current-driven magnetization dynamics in ferromagnetic metals are studied in
a self-consistent adiabatic local-density approximation in the presence of
spin-conserving and spin-dephasing impurity scattering. Based on a quantum
kinetic equation, we derive Gilbert damping and spin-transfer torques entering
the Landau-Lifshitz equation to linear order in frequency and wave vector.
Gilbert damping and a current-driven dissipative torque scale identically and
compete, with the result that a steady current-driven domain-wall motion is
insensitive to spin dephasing in the limit of weak ferromagnetism. A uniform
magnetization is found to be much more stable against spin torques in the
itinerant than in the \textit{s}-\textit{d} model for ferromagnetism. A dynamic
spin-transfer torque reminiscent of the spin pumping in multilayers is
identified and shown to govern the current-induced domain-wall distortion.",0512715v4
2006-11-22,Magnetization damping in a local-density approximation,"The linear response of itinerant transition metal ferromagnets to transverse
magnetic fields is studied in a self-consistent adiabatic local-density
approximation. The susceptibility is calculated from a microscopic Hamiltonian,
including spin-conserving impurities, impurity induced spin-orbit interaction
and magnetic impurities using the Keldysh formalism. The Gilbert damping
constant in the Landau-Lifshitz-Gilbert equation is identified, parametrized by
an effective transverse spin dephasing rate, and is found to be inversely
proportional to the exchange splitting. Our result justify the phenomenological
treatment of transverse spin dephasing in the study of current-induced
magnetization dynamics in weak, itinerant ferromagnets by Tserkovnyak
\textit{et al.}. We show that neglect of gradient corrections in the
quasiclassical transport equations leads to incorrect results when the exchange
potential becomes of the order of the Fermi energy.",0611588v1
2007-08-03,Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles,"The shape of ferromagnetic resonance spectra of highly dispersed, chemically
disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution
of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline
anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the
LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional
to the particle magnetic moments determined from the Langevin analysis of the
magnetization isotherms. These novel features are explained by the scattering
of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the
spin-orbit coupling, while the sd-exchange can be ruled out. The large
saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the
dominance of an overdamped 1 meV e/h-pair which seems to originate from the
discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.",0708.0463v1
2008-05-01,Chaotic Spin Dynamics of a Long Nanomagnet Driven by a Current,"We study the spin dynamics of a long nanomagnet driven by an electrical
current. In the case of only DC current, the spin dynamics has a sophisticated
bifurcation diagram of attractors. One type of attractors is a weak chaos. On
the other hand, in the case of only AC current, the spin dynamics has a rather
simple bifurcation diagram of attractors. That is, for small Gilbert damping,
when the AC current is below a critical value, the attractor is a limit cycle;
above the critical value, the attractor is chaotic (turbulent). For normal
Gilbert damping, the attractor is always a limit cycle in the physically
interesting range of the AC current. We also developed a Melnikov integral
theory for a theoretical prediction on the occurrence of chaos. Our Melnikov
prediction seems performing quite well in the DC case. In the AC case, our
Melnikov prediction seems predicting transient chaos. The sustained chaotic
attractor seems to have extra support from parametric resonance leading to a
turbulent state.",0805.0147v1
2010-10-08,"A unified first-principles study of Gilbert damping, spin-flip diffusion and resistivity in transition metal alloys","Using a formulation of first-principles scattering theory that includes
disorder and spin-orbit coupling on an equal footing, we calculate the
resistivity $\rho$, spin flip diffusion length $l_{sf}$ and the Gilbert damping
parameter $\alpha$ for Ni$_{1-x}$Fe$_x$ substitutional alloys as a function of
$x$. For the technologically important Ni$_{80}$Fe$_{20}$ alloy, permalloy, we
calculate values of $\rho = 3.5 \pm 0.15$ $\mu$Ohm-cm, $l_{sf}=5.5 \pm 0.3$ nm,
and $\alpha= 0.0046 \pm 0.0001$ compared to experimental low-temperature values
in the range $4.2-4.8$ $\mu$Ohm-cm for $\rho$, $5.0-6.0$ nm for $l_{sf}$, and
$0.004-0.013$ for $\alpha$ indicating that the theoretical formalism captures
the most important contributions to these parameters.",1010.1626v3
2011-02-22,Ab-initio calculation of the Gilbert damping parameter via linear response formalism,"A Kubo-Greenwood-like equation for the Gilbert damping parameter $\alpha$ is
presented that is based on the linear response formalism. Its implementation
using the fully relativistic Korringa-Kohn-Rostoker (KKR) band structure method
in combination with Coherent Potential Approximation (CPA) alloy theory allows
it to be applied to a wide range of situations. This is demonstrated with
results obtained for the bcc alloy system Fe$_x$Co$_{1-x}$ as well as for a
series of alloys of permalloy with 5d transition metals.
  To account for the thermal displacements of atoms as a scattering mechanism,
an alloy-analogy model is introduced. The corresponding calculations for Ni
correctly describe the rapid change of $\alpha$ when small amounts of
substitutional Cu are introduced.",1102.4551v1
2012-07-28,Ultrafast optical control of magnetization in EuO thin films,"All-optical pump-probe detection of magnetization precession has been
performed for ferromagnetic EuO thin films at 10 K. We demonstrate that the
circularly-polarized light can be used to control the magnetization precession
on an ultrafast time scale. This takes place within the 100 fs duration of a
single laser pulse, through combined contribution from two nonthermal
photomagnetic effects, i.e., enhancement of the magnetization and an inverse
Faraday effect. From the magnetic field dependences of the frequency and the
Gilbert damping parameter, the intrinsic Gilbert damping coefficient is
evaluated to be {\alpha} \approx 3\times10^-3.",1207.6686v1
2012-08-07,Observation of Coherent Helimagnons and Gilbert damping in an Itinerant Magnet,"We study the magnetic excitations of itinerant helimagnets by applying
time-resolved optical spectroscopy to Fe0.8Co0.2Si. Optically excited
oscillations of the magnetization in the helical state are found to disperse to
lower frequency as the applied magnetic field is increased; the fingerprint of
collective modes unique to helimagnets, known as helimagnons. The use of
time-resolved spectroscopy allows us to address the fundamental magnetic
relaxation processes by directly measuring the Gilbert damping, revealing the
versatility of spin dynamics in chiral magnets. (*These authors contributed
equally to this work)",1208.1462v1
2012-11-02,Dynamic Spin Injection into Chemical Vapor Deposited Graphene,"We demonstrate dynamic spin injection into chemical vapor deposition (CVD)
grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic
resonance measurements at room temperature reveal a strong enhancement of the
Gilbert damping at the Py/graphene interface, exceeding that observed in even
Py/platinum interfaces. Similar results are also shown on Co/graphene layers.
This enhancement in the Gilbert damping is understood as the consequence of
spin pumping at the interface driven by magnetization dynamics. Our
observations suggest a strong enhancement of spin-orbit coupling in CVD
graphene, in agreement with earlier spin valve measurements.",1211.0492v1
2013-01-10,First-principles calculation of the Gilbert damping parameter via the linear response formalism with application to magnetic transition-metals and alloys,"A method for the calculations of the Gilbert damping parameter $\alpha$ is
presented, which based on the linear response formalism, has been implemented
within the fully relativistic Korringa-Kohn-Rostoker band structure method in
combination with the coherent potential approximation alloy theory. To account
for thermal displacements of atoms as a scattering mechanism, an alloy-analogy
model is introduced. This allows the determination of $\alpha$ for various
types of materials, such as elemental magnetic systems and ordered magnetic
compounds at finite temperature, as well as for disordered magnetic alloys at
$T = 0$ K and above. The effects of spin-orbit coupling, chemical and
temperature induced structural disorder are analyzed. Calculations have been
performed for the 3$d$ transition-metals bcc Fe, hcp Co, and fcc Ni, their
binary alloys bcc Fe$_{1-x}$Co$_{x}$, fcc Ni$_{1-x}$Fe$_x$, fcc
Ni$_{1-x}$Co$_x$ and bcc Fe$_{1-x}$V$_{x}$, and for 5d impurities in
transition-metal alloys. All results are in satisfying agreement with
experiment.",1301.2114v1
2013-08-01,Inverse Spin Hall Effect in nanometer-thick YIG/Pt system,"High quality nanometer-thick (20 nm, 7 nm and 4 nm) epitaxial YIG films have
been grown on GGG substrates using pulsed laser deposition. The Gilbert damping
coefficient for the 20 nm thick films is 2.3 x 10-4 which is the lowest value
reported for sub-micrometric thick films. We demonstrate Inverse spin Hall
effect (ISHE) detection of propagating spin waves using Pt. The amplitude and
the lineshape of the ISHE voltage correlate well to the increase of the Gilbert
damping when decreasing thickness of YIG. Spin Hall effect based
loss-compensation experiments have been conducted but no change in the
magnetization dynamics could be detected.",1308.0192v1
2014-01-24,Wavenumber-dependent Gilbert damping in metallic ferromagnets,"New terms to the dynamical equation of magnetization motion, associated with
spin transport, have been reported over the past several years. Each newly
identified term is thought to possess both a real and an imaginary effective
field leading to fieldlike and dampinglike torques on magnetization. Here we
show that three metallic ferromagnets possess an imaginary effective-field term
which mirrors the well-known real effective-field term associated with exchange
in spin waves. Using perpendicular standing spin wave resonance between 2-26
GHz, we evaluate the magnitude of the finite-wavenumber ($k$) dependent Gilbert
damping $\alpha$ in three typical device ferromagnets, Ni$_{79}$Fe$_{21}$, Co,
and Co$_{40}$Fe$_{40}$B$_{20}$, and demonstrate for the first time the presence
of a $k^2$ term as $\Delta\alpha=\Delta\alpha_0+A_{k}\cdot k^2$ in all three
metals. We interpret the new term as the continuum analog of spin pumping,
predicted recently, and show that its magnitude, $A_{k}$=0.07-0.1 nm$^2$, is
consistent with transverse spin relaxation lengths as measured by conventional
(interlayer) spin pumping.",1401.6467v2
2014-12-11,Deviation From the Landau-Lifshitz-Gilbert equation in the Inertial regime of the Magnetization,"We investigate in details the inertial dynamics of a uniform magnetization in
the ferromagnetic resonance (FMR) context. Analytical predictions and numerical
simulations of the complete equations within the Inertial
Landau-Lifshitz-Gilbert (ILLG) model are presented. In addition to the usual
precession resonance, the inertial model gives a second resonance peak
associated to the nutation dynamics provided that the damping is not too large.
The analytical resolution of the equations of motion yields both the precession
and nutation angular frequencies. They are function of the inertial dynamics
characteristic time $\tau$, the dimensionless damping $\alpha$ and the static
magnetic field $H$. A scaling function with respect to $\alpha\tau\gamma H$ is
found for the nutation angular frequency, also valid for the precession angular
frequency when $\alpha\tau\gamma H\gg 1$. Beyond the direct measurement of the
nutation resonance peak, we show that the inertial dynamics of the
magnetization has measurable effects on both the width and the angular
frequency of the precession resonance peak when varying the applied static
field. These predictions could be used to experimentally identify the inertial
dynamics of the magnetization proposed in the ILLG model.",1412.3783v1
2015-01-02,"Inertia, diffusion and dynamics of a driven skyrmion","Skyrmions recently discovered in chiral magnets are a promising candidate for
magnetic storage devices because of their topological stability, small size
($\sim 3-100$nm), and ultra-low threshold current density ($\sim
10^{6}$A/m$^2$) to drive their motion. However, the time-dependent dynamics has
hitherto been largely unexplored. Here we show, by combining the numerical
solution of the Landau-Lifshitz-Gilbert equation and the analysis of a
generalized Thiele's equation, that inertial effects are almost completely
absent in skyrmion dynamics driven by a time-dependent current. In contrast,
the response to time-dependent magnetic forces and thermal fluctuations depends
strongly on frequency and is described by a large effective mass and a (anti-)
damping depending on the acceleration of the skyrmion. Thermal diffusion is
strongly suppressed by the cyclotron motion and is proportional to the Gilbert
damping coefficient $\alpha$. This indicates that the skyrmion position is
stable, and its motion responds to the time-dependent current without delay or
retardation even if it is fast. These findings demonstrate the advantages of
skyrmions as information carriers.",1501.00444v1
2015-08-04,A Critical Analysis of the Feasibility of Pure Strain-Actuated Giant Magnetostrictive Nanoscale Memories,"Concepts for memories based on the manipulation of giant magnetostrictive
nanomagnets by stress pulses have garnered recent attention due to their
potential for ultra-low energy operation in the high storage density limit.
Here we discuss the feasibility of making such memories in light of the fact
that the Gilbert damping of such materials is typically quite high. We report
the results of numerical simulations for several classes of toggle precessional
and non-toggle dissipative magnetoelastic switching modes. Material candidates
for each of the several classes are analyzed and forms for the anisotropy
energy density and ranges of material parameters appropriate for each material
class are employed. Our study indicates that the Gilbert damping as well as the
anisotropy and demagnetization energies are all crucial for determining the
feasibility of magnetoelastic toggle-mode precessional switching schemes. The
roles of thermal stability and thermal fluctuations for stress-pulse switching
of giant magnetostrictive nanomagnets are also discussed in detail and are
shown to be important in the viability, design, and footprint of
magnetostrictive switching schemes.",1508.00629v2
2015-12-16,Parity-time symmetry breaking in magnetic systems,"The understanding of out-of-equilibrium physics, especially dynamic
instabilities and dynamic phase transitions, is one of the major challenges of
contemporary science, spanning the broadest wealth of research areas that range
from quantum optics to living organisms. Focusing on nonequilibrium dynamics of
an open dissipative spin system, we introduce a non-Hermitian Hamiltonian
approach, in which non-Hermiticity reflects dissipation and deviation from
equilibrium. The imaginary part of the proposed spin Hamiltonian describes the
effects of Gilbert damping and applied Slonczewski spin-transfer torque. In the
classical limit, our approach reproduces Landau-Lifshitz-Gilbert-Slonczewski
dynamics of a large macrospin. We reveal the spin-transfer torque-driven
parity-time symmetry-breaking phase transition corresponding to a transition
from precessional to exponentially damped spin dynamics. Micromagnetic
simulations for nanoscale ferromagnetic disks demonstrate the predicted effect.
Our findings can pave the way to a general quantitative description of
out-of-equilibrium phase transitions driven by spontaneous parity-time symmetry
breaking.",1512.05408v2
2017-01-11,The Cauchy problem for the Landau-Lifshitz-Gilbert equation in BMO and self-similar solutions,"We prove a global well-posedness result for the Landau-Lifshitz equation with
Gilbert damping provided that the BMO semi-norm of the initial data is small.
As a consequence, we deduce the existence of self-similar solutions in any
dimension. In the one-dimensional case, we characterize the self-similar
solutions associated with an initial data given by some ($\mathbb{S}^2$-valued)
step function and establish their stability. We also show the existence of
multiple solutions if the damping is strong enough. Our arguments rely on the
study of a dissipative quasilinear Schr\""odinger obtained via the stereographic
projection and techniques introduced by Koch and Tataru.",1701.03083v2
2017-01-27,Structural scale $q-$derivative and the LLG-Equation in a scenario with fractionality,"In the present contribution, we study the Landau-Lifshitz-Gilbert equation
with two versions of structural derivatives recently proposed: the scale
$q-$derivative in the non-extensive statistical mechanics and the axiomatic
metric derivative, which presents Mittag-Leffler functions as eigenfunctions.
The use of structural derivatives aims to take into account long-range forces,
possible non-manifest or hidden interactions and the dimensionality of space.
Having this purpose in mind, we build up an evolution operator and a deformed
version of the LLG equation. Damping in the oscillations naturally show up
without an explicit Gilbert damping term.",1701.08076v2
2018-10-17,Perpendicularly magnetized YIG films with small Gilbert damping constant and anomalous spin transport properties,"The Y3Fe5O12 (YIG) films with perpendicular magnetic anisotropy (PMA) have
recently attracted a great deal of attention for spintronics applications.
Here, we report the induced PMA in the ultrathin YIG films grown on
(Gd2.6Ca0.4)(Ga4.1Mg0.25Zr0.65)O12 (SGGG) substrates by epitaxial strain
without preprocessing. Reciprocal space mapping shows that the films are
lattice-matched to the substrates without strain relaxation. Through
ferromagnetic resonance and polarized neutron reflectometry measurements, we
find that these YIG films have ultra-low Gilbert damping constant with a
magnetic dead layer as thin as about 0.3 nm at the YIG/SGGG interfaces.
Moreover, the transport behavior of the Pt/YIG/SGGG films reveals an
enhancement of spin mixing conductance and a large non-monotonic magnetic field
dependence of anomalous Hall effect as compared with the Pt/YIG/Gd3Ga5O12 (GGG)
films. The non-monotonic anomalous Hall signal is extracted in the temperature
range from 150 to 350 K, which has been ascribed to the possible non-collinear
magnetic order at the Pt/YIG interface induced by uniaxial strain.",1810.07384v2
2019-03-07,Current-induced motion of twisted skyrmions,"Twisted skyrmions, whose helicity angles are different from that of Bloch
skyrmions and N\'eel skyrmions, have already been demonstrated in experiments
recently. In this work, we first contrast the magnetic structure and origin of
the twisted skyrmion with other three types of skyrmion including Bloch
skyrmion, N\'eel skyrmion and antiskyrmion. Following, we investigate the
dynamics of twisted skyrmions driven by the spin transfer toque (STT) and the
spin Hall effect (SHE) by using micromagnetic simulations. It is found that the
spin Hall angle of the twisted skyrmion is related to the dissipative force
tensor and the Gilbert damping both for the motions induced by the STT and the
SHE, especially for the SHE induced motion, the skyrmion Hall angle depends
substantially on the skyrmion helicity. At last, we demonstrate that the
trajectory of the twisted skyrmion can be controlled in a two dimensional plane
with a Gilbert damping gradient. Our results provide the understanding of
current-induced motion of twisted skyrmions, which may contribute to the
applications of skyrmion-based racetrack memories.",1903.02812v1
2019-07-03,Anisotropy of spin-transfer torques and Gilbert damping induced by Rashba coupling,"Spin-transfer torques (STT), Gilbert damping (GD), and effective spin
renormalization (ESR) are investigated microscopically in a 2D Rashba
ferromagnet with spin-independent Gaussian white-noise disorder. Rashba
spin-orbit coupling induced anisotropy of these phenomena is thoroughly
analysed. For the case of two partly filled spin subbands, a remarkable
relation between the anisotropic STT, GD, and ESR is established. In the
absence of magnetic field and other torques on magnetization, this relation
corresponds to a current-induced motion of a magnetic texture with the
classical drift velocity of conduction electrons. Finally, we compute spin
susceptibility of the system and generalize the notion of spin-polarized
current.",1907.02041v3
2020-08-14,Large enhancement of spin pumping due to the surface bound states in normal metal/superconductor structures,"We show that the spin pumping from ferromagnetic insulator into the adjacent
metallic spin sink can be strongly stimulated by the superconducting
correlations.
  The key physical mechanism responsible for this effect is the presence of
quasiparticle surface states at the ferromagnetic insulator/superconductor
interface. We consider the minimal model when these states appear because of
the suppressed pairing constant within the interfacial normal layer. For thin
normal layers we obtain a strongly peaked temperature dependence of the Gilbert
damping coefficient which has been recently observed in such systems. For
thicker normal layers the Gilbert damping monotonically increases down to the
temperatures much smaller than the critical one. The suggested model paves the
way to controlling the temperature dependence of the spin pumping by
fabricating hybrid normal metal/superconductor spin sinks.",2008.06253v1
2021-11-05,Giant oscillatory Gilbert damping in superconductor/ferromagnet/superconductor junctions,"Interfaces between materials with differently ordered phases present unique
opportunities for exotic physical properties, especially the interplay between
ferromagnetism and superconductivity in the ferromagnet/superconductor
heterostructures. The investigation of zero- and pi-junctions has been of
particular interest for both fundamental physical science and emerging
technologies. Here, we report the experimental observation of giant oscillatory
Gilbert damping in the superconducting Nb/NiFe/Nb junctions with respect to the
NiFe thickness. This observation suggests an unconventional spin pumping and
relaxation via zero-energy Andreev bound states that exist only in the
Nb/NiFe/Nb pi-junctions, but not in the Nb/NiFe/Nb zero-junctions. Our findings
could be important for further exploring the exotic physical properties of
ferromagnet/superconductor heterostructures, and potential applications of
ferromagnet pi-junctions in quantum computing, such as half-quantum flux
qubits.",2111.03233v1
2022-11-14,Magnetization Dynamics in Synthetic Antiferromagnets with Perpendicular Magnetic Anisotropy,"Understanding the rich physics of magnetization dynamics in perpendicular
synthetic antiferromagnets (p-SAFs) is crucial for developing next-generation
spintronic devices. In this work, we systematically investigate the
magnetization dynamics in p-SAFs combining time-resolved magneto-optical Kerr
effect (TR-MOKE) measurements with theoretical modeling. These model analyses,
based on a Landau-Lifshitz-Gilbert approach incorporating exchange coupling,
provide details about the magnetization dynamic characteristics including the
amplitudes, directions, and phases of the precession of p-SAFs under varying
magnetic fields. These model-predicted characteristics are in excellent
quantitative agreement with TR-MOKE measurements on an asymmetric p-SAF. We
further reveal the damping mechanisms of two procession modes co-existing in
the p-SAF and successfully identify individual contributions from different
sources, including Gilbert damping of each ferromagnetic layer, spin pumping,
and inhomogeneous broadening. Such a comprehensive understanding of
magnetization dynamics in p-SAFs, obtained by integrating high-fidelity TR-MOKE
measurements and theoretical modeling, can guide the design of p-SAF-based
architectures for spintronic applications.",2211.07744v2
2023-05-17,Material Parameters for Faster Ballistic Switching of an In-plane Magnetized Nanomagnet,"High-speed magnetization switching of a nanomagnet is necessary for faster
information processing. The ballistic switching by a pulsed magnetic filed is a
promising candidate for the high-speed switching. It is known that the
switching speed of the ballistic switching can be increased by increasing the
magnitude of the pulsed magnetic field. However it is difficult to generate a
strong and short magnetic field pulse in a small device. Here we explore
another direction to achieve the high-speed ballistic switching by designing
material parameters such as anisotropy constant, saturation magnetization, and
the Gilbert damping constant. We perform the macrospin simulations for the
ballistic switching of in-plane magnetized nano magnets with varying material
parameters. The results are analyzed based on the switching dynamics on the
energy density contour. We show that the pulse width required for the ballistic
switching can be reduced by increasing the magnetic anisotropy constant or by
decreasing the saturation magnetization. We also show that there exists an
optimal value of the Gilbert damping constant that minimizes the pulse width
required for the ballistic switching.",2305.10111v1
2023-05-23,Current-driven motion of magnetic topological defects in ferromagnetic superconductors,"Recent years have seen a number of instances where magnetism and
superconductivity intrinsically coexist. Our focus is on the case where
spin-triplet superconductivity arises out of ferromagnetism, and we make a
hydrodynamic analysis of the effect of a charge supercurrent on magnetic
topological defects like domain walls and merons. We find that the emergent
electromagnetic field that arises out of the superconducting order parameter
provides a description for not only the physical quantities such as the local
energy flux density and the interaction between current and defects but also
the energy dissipation through magnetic dynamics of the Gilbert damping, which
becomes more prominent compared to the normal state as superconductivity
attenuates the energy dissipation through the charge sector. In particular, we
reveal that the current-induced dynamics of domain walls and merons in the
presence of the Gilbert damping give rise to the nonsingular $4\pi$ and $2\pi$
phase slips, respectively, revealing the intertwined dynamics of spin and
charge degrees of freedom in ferromagnetic superconductors.",2305.13564v1
2023-07-03,Magnetic lump motion in saturated ferromagnetic films,"In this paper, we study in detail the nonlinear propagation of magnetic
soliton in a ferromagnetic film. The sample is magnetized to saturation by an
external field perpendicular to film plane. A new generalized (2+1)-dimensional
short-wave asymptotic model is derived. The bilinear-like forms of this
equation are constructed, and exact magnetic line soliton solutions are
exhibited. It is observed that a series of stable lumps can be generated by an
unstable magnetic soliton under Gaussian disturbance. Such magnetic lumps are
highly stable and can maintain their shapes and velocities during evolution or
collision. The interaction between lump and magnetic soliton, as well as
interaction between two lumps, are numerically investigated. We further discuss
the nonlinear motion of lumps in ferrites with Gilbert-damping and
inhomogeneous exchange effects. The results show that the Gilbert-damping
effects make the amplitude and velocity of the magnetic lump decay
exponentially during propagation. And the shock waves are generated from a lump
when quenching the strength of inhomogeneous exchange.",2307.00903v1
2005-03-24,Fast magnetization switching of Stoner particles: A nonlinear dynamics picture,"The magnetization reversal of Stoner particles is investigated from the point
of view of nonlinear dynamics within the Landau-Lifshitz-Gilbert formulation.
The following results are obtained. 1) We clarify that the so-called
Stoner-Wohlfarth (SW) limit becomes exact when damping constant is infinitely
large. Under the limit, the magnetization moves along the steepest energy
descent path. The minimal switching field is the one at which there is only one
stable fixed point in the system. 2) For a given magnetic anisotropy, there is
a critical value for the damping constant, above which the minimal switching
field is the same as that of the SW-limit. 3) We illustrate how fixed points
and their basins change under a field along different directions. This change
explains well why a non-parallel field gives a smaller minimal switching field
and a short switching time. 4) The field of a ballistic magnetization reversal
should be along certain direction window in the presence of energy dissipation.
The width of the window depends on both of the damping constant and the
magnetic anisotropy. The upper and lower bounds of the direction window
increase with the damping constant. The window width oscillates with the
damping constant for a given magnetic anisotropy. It is zero for both zero and
infinite damping. Thus, the perpendicular field configuration widely employed
in the current experiments is not the best one since the damping constant in a
real system is far from zero.",0503594v1
2003-02-17,Magnetization dynamics with a spin-transfer torque,"The magnetization reversal and dynamics of a spin valve pillar, whose lateral
size is 64$\times$64 nm$^2$, are studied by using micromagnetic simulation in
the presence of spin transfer torque. Spin torques display both characteristics
of magnetic damping (or anti-damping) and of an effective magnetic field. For a
steady-state current, both M-I and M-H hysteresis loops show unique features,
including multiple jumps, unusual plateaus and precessional states. These
states originate from the competition between the energy dissipation due to
Gilbert damping and the energy accumulation due to the spin torque supplied by
the spin current. The magnetic energy oscillates as a function of time even for
a steady-state current. For a pulsed current, the minimum width and amplitude
of the spin torque for achieving current-driven magnetization reversal are
quantitatively determined. The spin torque also shows very interesting thermal
activation that is fundamentally different from an ordinary damping effect.",0302337v1
2003-10-13,Domain wall mobility in nanowires: transverse versus vortex walls,"The motion of domain walls in ferromagnetic, cylindrical nanowires is
investigated numerically by solving the Landau-Lifshitz-Gilbert equation for a
classical spin model in which energy contributions from exchange, crystalline
anisotropy, dipole-dipole interaction, and a driving magnetic field are
considered. Depending on the diameter, either transverse domain walls or vortex
walls are found. The transverse domain wall is observed for diameters smaller
than the exchange length of the given material. Here, the system behaves
effectively one-dimensional and the domain wall mobility agrees with a result
derived for a one-dimensional wall by Slonczewski. For low damping the domain
wall mobility decreases with decreasing damping constant. With increasing
diameter, a crossover to a vortex wall sets in which enhances the domain wall
mobility drastically. For a vortex wall the domain wall mobility is described
by the Walker-formula, with a domain wall width depending on the diameter of
the wire. The main difference is the dependence on damping: for a vortex wall
the domain wall mobility can be drastically increased for small values of the
damping constant up to a factor of $1/\alpha^2$.",0310277v1
2013-10-29,Observational Study of Large Amplitude Longitudinal Oscillations in a Solar Filament,"On 20 August 2010 an energetic disturbance triggered damped large-amplitude
longitudinal (LAL) oscillations in almost an entire filament. In the present
work we analyze this periodic motion in the filament to characterize the
damping and restoring mechanism of the oscillation. Our method involves placing
slits along the axis of the filament at different angles with respect to the
spine of the filament, finding the angle at which the oscillation is clearest,
and fitting the resulting oscillation pattern to decaying sinusoidal and Bessel
functions. These functions represent the equations of motion of a pendulum
damped by mass accretion. With this method we determine the period and the
decaying time of the oscillation. Our preliminary results support the theory
presented by Luna and Karpen (2012) that the restoring force of LAL
oscillations is solar gravity in the tubes where the threads oscillate, and the
damping mechanism is the ongoing accumulation of mass onto the oscillating
threads. Following an earlier paper, we have determined the magnitude and
radius of curvature of the dipped magnetic flux tubes hosting a thread along
the filament, as well as the mass accretion rate of the filament threads, via
the fitted parameters.",1310.7657v1
2014-12-08,Magnetization Dynamics driven by Non-equilibrium Spin-Orbit Coupled Electron Gas,"The dynamics of magnetization coupled to an electron gas via s-d exchange
interaction is investigated by using density matrix technique. Our theory shows
that non-equilibrium spin accumulation induces a spin torque and the electron
bath leads to a damping of the magnetization. For the two-dimensional
magnetization thin film coupled to the electron gas with Rashba spin-orbit
coupling, the result for the spin-orbit torques is consistent with the previous
semi-classical theory. Our theory predicts a damping of the magnetization,
which is absent in the semi-classical theory. The magnitude of the damping due
to the electron bath is comparable to the intrinsic Gilbert damping and may be
important in describing the magnetization dynamics of the system.",1412.2479v1
2016-04-11,All-Optical Study of Tunable Ultrafast Spin Dynamics in [Co/Pd]-NiFe Systems: The Role of Spin-Twist Structure on Gilbert Damping,"We investigate optically induced ultrafast magnetization dynamics in [Co(0.5
nm)/Pd(1 nm)]x5/NiFe(t) exchange-spring samples with tilted perpendicular
magnetic anisotropy using a time-resolved magneto-optical Kerr effect
magnetometer. The competition between the out-of-plane anisotropy of the hard
layer, the in-plane anisotropy of the soft layer and the applied bias field
reorganizes the spins in the soft layer, which are modified further with the
variation in t. The spin-wave spectrum, the ultrafast demagnetization time, and
the extracted damping coefficient all depend on the spin distribution in the
soft layer, while the latter two also depend on the spin-orbit coupling between
the Co and Pd layers. The spin-wave spectra change from multimode to
single-mode as t increases. At the maximum field reached in this study, H=2.5
kOe, the damping shows a nonmonotonic dependence on t with a minimum at t=7.5
nm. For t<7.5 nm, intrinsic effects dominate, whereas for t>7.5 nm, extrinsic
effects govern the damping mechanisms.",1604.02998v1
2017-03-06,Damping dependence of spin-torque effects in thermally assisted magnetization reversal,"Thermal fluctuations of nanomagnets driven by spin-polarized currents are
treated via the Landau-Lifshitz-Gilbert equation as generalized to include both
the random thermal noise field and Slonczewski spin-transfer torque terms. The
magnetization reversal time of such a nanomagnet is then evaluated for wide
ranges of damping by using a method which generalizes the solution of the
so-called Kramers turnover problem for mechanical Brownian particles, thereby
bridging the very low damping and intermediate damping Kramers escape rates, to
the analogous magnetic turnover problem. The reversal time is then evaluated
for a nanomagnet with the free energy density given in the standard form of
superimposed easy-plane and in-plane easy-axis anisotropies with the dc bias
field along the easy axis.",1703.01879v5
2017-05-09,Low spin wave damping in the insulating chiral magnet Cu$_{2}$OSeO$_{3}$,"Chiral magnets with topologically nontrivial spin order such as Skyrmions
have generated enormous interest in both fundamental and applied sciences. We
report broadband microwave spectroscopy performed on the insulating chiral
ferrimagnet Cu$_{2}$OSeO$_{3}$. For the damping of magnetization dynamics we
find a remarkably small Gilbert damping parameter of about $1\times10^{-4}$ at
5 K. This value is only a factor of 4 larger than the one reported for the best
insulating ferrimagnet yttrium iron garnet. We detect a series of sharp
resonances and attribute them to confined spin waves in the mm-sized samples.
Considering the small damping, insulating chiral magnets turn out to be
promising candidates when exploring non-collinear spin structures for high
frequency applications.",1705.03416v1
2018-09-04,Separation of the two-magnon scattering contribution to damping for the determination of the spin mixing conductance,"We present angle dependent measurements of the damping properties of
epitaxial Fe layers with MgO, Al and Pt capping layers. Based on the
preferential distribution of lattice defects following the crystal symmetry, we
make use of a model of the defect density to separate the contribution of
two-magnon scattering to the damping from the isotropic contribution
originating in the spin pumping effect, the viscous Gilbert damping and the
magnetic proximity effect. The separation of the two-magnon contribution, which
depends strongly on the defect density, allows for the measurement of a value
of the effective spin mixing conductance which is closer to the value
exclusively due to spin pumping. The influence of the defect density for
bilayers systems due to the different capping layers and to the unavoidable
spread in defect density from sample to sample is thus removed. This shows the
potential of studying spin pumping phenomena in fully ordered systems in which
this separation is possible, contrary to polycrystalline or amorphous metallic
thin films.",1809.01042v1
2006-02-09,Magnetization damping in polycrystalline Co ultra-thin films: Evidence for non-local effects,"The magnetic properties and magnetization dynamics of polycrystalline
ultra-thin Co layers were investigated using a broadband ferromagnetic
resonance (FMR) technique at room temperature. A variable thickness (1 nm $\leq
t \leq$ 10 nm) Co layer is sandwiched between 10 nm thick Cu layers (10 nm Cu|
t Co|10 nm Cu), while materials in contact with the Cu outer interfaces are
varied to determine their influence on the magnetization damping. The resonance
field and the linewidth were studied for in-plane magnetic fields in field
swept experiments at a fixed frequency, from 4 to 25 GHz. The Co layers have a
lower magnetization density than the bulk, and an interface contribution to the
magnetic anisotropy normal to the film plane. The Gilbert damping, as
determined from the frequency dependence of the linewidth, increases with
decreasing Co layer thickness for films with outer Pt layers. This enhancement
is not observed in structures without Pt layers. The result can be understood
in terms of a non-local contribution to the damping due to spin pumping from Co
through the Cu layer and spin relaxation in Pt layers. Pt layers just 1.5 nm
thick are found to be sufficient to enhance the damping and thus act as
efficient ""spin-sinks"". In structures with Pt outer layers, this non-local
contribution to the damping becomes predominant when the Co layer is thinner
than 4 nm.",0602243v2
2020-04-09,Magnetic Damping in Epitaxial Fe Alloyed with Vanadium and Aluminum,"To develop low-moment, low-damping metallic ferromagnets for power-efficient
spintronic devices, it is crucial to understand how magnetic relaxation is
impacted by the addition of nonmagnetic elements. Here, we compare magnetic
relaxation in epitaxial Fe films alloyed with light nonmagnetic elements of V
and Al. FeV alloys exhibit lower intrinsic damping compared to pure Fe, reduced
by nearly a factor of 2, whereas damping in FeAl alloys increases with Al
content. Our experimental and computational results indicate that reducing the
density of states at the Fermi level, rather than the average atomic number,
has a more significant impact in lowering damping in Fe alloyed with light
elements. Moreover, FeV is confirmed to exhibit an intrinsic Gilbert damping
parameter of $\simeq$0.001, among the lowest ever reported for ferromagnetic
metals.",2004.04840v3
2014-05-19,"Comparison of micromagnetic parameters of ferromagnetic semiconductors (Ga,Mn)(As,P) and (Ga,Mn)As","We report on the determination of micromagnetic parameters of epilayers of
the ferromagnetic semiconductor (Ga,Mn)As, which has easy axis in the sample
plane, and (Ga,Mn)(As,P) which has easy axis perpendicular to the sample plane.
We use an optical analog of ferromagnetic resonance where the
laser-pulse-induced precession of magnetization is measured directly in the
time domain. By the analysis of a single set of pump-and-probe magneto-optical
data we determined the magnetic anisotropy fields, the spin stiffness and the
Gilbert damping constant in these two materials. We show that incorporation of
10% of phosphorus in (Ga,Mn)As with 6% of manganese leads not only to the
expected sign change of the perpendicular to plane anisotropy field but also to
an increase of the Gilbert damping and to a reduction of the spin stiffness.
The observed changes in the micromagnetic parameters upon incorporating P in
(Ga,Mn)As are consistent with the reduced hole density, conductivity, and Curie
temperature of the (Ga,Mn)(As,P) material. We report that the magnetization
precession damping is stronger for the n = 1 spin wave resonance mode than for
the n = 0 uniform magnetization precession mode.",1405.4677v1
2015-03-24,Spin dynamics and frequency dependence of magnetic damping study in soft ferromagnetic FeTaC film with a stripe domain structure,"Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key
factors for the free layer magnetization switching by spin transfer torque
technique in magnetic tunnel junction devices. The magnetization precessional
dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure
was explored in broad band frequency range by employing micro-strip
ferromagnetic resonance technique. The polar angular variation of resonance
field and linewidth at different frequencies have been analyzed numerically
using Landau-Lifshitz-Gilbert equation by taking into account the total free
energy density of the film. The numerically estimated parameters Land\'{e}
$g$-factor, PMA constant, and effective magnetization are found to be 2.1,
2$\times10^{5}$ erg/cm$^{3}$ and 7145 Oe, respectively. The frequency
dependence of Gilbert damping parameter ($\alpha$) is evaluated by considering
both intrinsic and extrinsic effects into the total linewidth analysis. The
value of $\alpha$ is found to be 0.006 at 10 GHz and it increases with
decreasing precessional frequency.",1503.07043v5
2016-05-22,Low Gilbert damping in Co2FeSi and Fe2CoSi films,"Thin highly textured Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si ($0 \leq$ x
$\leq 1$) films were prepared on MgO (001) substrates by magnetron
co-sputtering. The magneto-optic Kerr effect (MOKE) and ferromagnetic resonance
(FMR) measurements were used to investigate the composition dependence of the
magnetization, the magnetic anisotropy, the gyromagnetic ratio and the
relaxation of the films. The effective magnetization for the thin
Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films, determined by FMR measurements,
are consistent with the Slater Pauling prediction. Both MOKE and FMR
measurements reveal a pronounced fourfold anisotropy distribution for all
films. In addition we found a strong influence of the stoichiometry on the
anisotropy as the cubic anisotropy strongly increases with increasing Fe
concentration. The gyromagnetic ratio is only weakly dependent on the
composition. We find low Gilbert damping parameters for all films with values
down to $0.0012\pm0.00012$ for Fe$_{1.75}$Co$_{1.25}$Si. The effective damping
parameter for Co$_2$FeSi is found to be $0.0018\pm 0.0004$. We also find a
pronounced anisotropic relaxation, which indicates significant contributions of
two-magnon scattering processes that is strongest along the easy axes of the
films. This makes thin Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films ideal
materials for the application in STT-MRAM devices.",1605.06797v1
2017-09-21,Low Gilbert Damping Constant in Perpendicularly Magnetized W/CoFeB/MgO Films with High Thermal Stability,"Perpendicular magnetic materials with low damping constant and high thermal
stability have great potential for realizing high-density, non-volatile, and
low-power consumption spintronic devices, which can sustain operation
reliability for high processing temperatures. In this work, we study the
Gilbert damping constant ({\alpha}) of perpendicularly magnetized W/CoFeB/MgO
films with a high perpendicular magnetic anisotropy (PMA) and superb thermal
stability. The {\alpha} of these PMA films annealed at different temperatures
is determined via an all-optical Time-Resolved Magneto-Optical Kerr Effect
method. We find that {\alpha} of these W/CoFeB/MgO PMA films decreases with
increasing annealing temperature, reaches a minimum of {\alpha} = 0.016 at an
annealing temperature of 350 {\deg}C, and then increases to 0.024 after
post-annealing at 400 {\deg}C. The minimum {\alpha} observed at 350 {\deg}C is
rationalized by two competing effects as the annealing temperature becomes
higher: the enhanced crystallization of CoFeB and dead-layer growth occurring
at the two interfaces of the CoFeB layer. We further demonstrate that {\alpha}
of the 400 {\deg}C-annealed W/CoFeB/MgO film is comparable to that of a
reference Ta/CoFeB/MgO PMA film annealed at 300 {\deg}C, justifying the
enhanced thermal stability of the W-seeded CoFeB films.",1709.07483v1
2022-02-06,Enhancing Perpendicular Magnetic Anisotropy in Garnet Ferrimagnet by Interfacing with Few-Layer WTe2,"Engineering magnetic anisotropy in a ferro- or ferrimagnetic (FM) thin film
is crucial in spintronic device. One way to modify the magnetic anisotropy is
through the surface of the FM thin film. Here, we report the emergence of a
perpendicular magnetic anisotropy (PMA) induced by interfacial interactions in
a heterostructure comprised of a garnet ferrimagnet, Y3Fe5O12 (YIG), and the
low-symmetry, high spin orbit coupling (SOC) transition metal dichalcogenide,
WTe2. At the same time, we also observed an enhancement in Gilbert damping in
the WTe2 covered YIG area. Both the magnitude of interface-induced PMA and the
Gilbert damping enhancement have no observable WTe2 thickness dependence down
to single quadruple-layer, indicating that the interfacial interaction plays a
critical role. The ability of WTe2 to enhance the PMA in FM thin film, combined
with its previously reported capability to generate out-of-plane damping like
spin torque, makes it desirable for magnetic memory applications.",2202.02834v1
2018-10-25,Time-retarded damping and magnetic inertia in the Landau-Lifshitz-Gilbert equation self-consistently coupled to electronic time-dependent nonequilibrium Green functions,"The conventional Landau-Lifshitz-Gilbert (LLG) equation is a widely used tool
to describe dynamics of local magnetic moments, viewed as classical vectors of
fixed length, with their change assumed to take place simultaneously with the
cause. Here we demonstrate that recently developed [M. D. Petrovi\'{c} {\em et
al.}, {\tt arXiv:1802.05682}] self-consistent coupling of the LLG equation to
time-dependent quantum-mechanical description of electrons microscopically
generates time-retarded damping in the LLG equation described by a memory
kernel which is also spatially dependent. For sufficiently slow dynamics of
local magnetic moments, the memory kernel can be expanded to extract the
Gilbert damping (proportional to first time derivative of magnetization) and
magnetic inertia (proportional to second time derivative of magnetization)
terms whose parameters, however, are time-dependent in contrast to
time-independent parameters used in the conventional LLG equation. We use
examples of single or multiple magnetic moments precessing in an external
magnetic field, as well as field-driven motion of a magnetic domain wall (DW),
to quantify the difference in their time evolution computed from conventional
LLG equation vs. TDNEGF+LLG quantum-classical hybrid approach. The faster DW
motion predicted by TDNEGF+LLG approach reveals that important quantum effects,
stemming from finite amount of time which it takes for conduction electron spin
to react to the motion of classical local magnetic moments, are missing from
conventional classical micromagnetics simulations. We also demonstrate large
discrepancy between TDNEGF+LLG-computed numerically exact and, therefore,
nonperturbative result for charge current pumped by a moving DW and the same
quantity computed by perturbative spin motive force formula combined with the
conventional LLG equation.",1810.11016v2
2019-08-08,Annihilation of topological solitons in magnetism with spin wave burst finale: The role of nonequilibrium electrons causing nonlocal damping and spin pumping over ultrabroadband frequency range,"We not only reproduce burst of short-wavelength spin waves (SWs) observed in
recent experiment [S. Woo et al., Nat. Phys. 13, 448 (2017)] on
magnetic-field-driven annihilation of two magnetic domain walls (DWs) but,
furthermore, we predict that this setup additionally generates highly unusual}
pumping of electronic spin currents in the absence of any bias voltage. Prior
to the instant of annihilation, their power spectrum is ultrabroadband, so they
can be converted into rapidly changing in time charge currents, via the inverse
spin Hall effect, as a source of THz radiation of bandwidth $\simeq 27$ THz
where the lowest frequency is controlled by the applied magnetic field. The
spin pumping stems from time-dependent fields introduced into the quantum
Hamiltonian of electrons by the classical dynamics of localized magnetic
moments (LMMs) comprising the domains. The pumped currents carry spin-polarized
electrons which, in turn, exert backaction on LMMs in the form of nonlocal
damping which is more than twice as large as conventional local Gilbert
damping. The nonlocal damping can substantially modify the spectrum of emitted
SWs when compared to widely-used micromagnetic simulations where conduction
electrons are completely absent. Since we use fully microscopic (i.e.,
Hamiltonian-based) framework, self-consistently combining time-dependent
electronic nonequilibrium Green functions with the Landau-Lifshitz-Gilbert
equation, we also demonstrate that previously derived phenomenological formulas
miss ultrabroadband spin pumping while underestimating the magnitude of
nonlocal damping due to nonequilibrium electrons.",1908.03194v5
2006-06-05,Phenomenological theory of current driven exchange switching in ferromagnetic nanojunctions,"Phenomenological approach is developed in the theory of spin-valve type
ferromagnetic junctions to describe exchange switching by current flowing
perpendicular to interfaces. Forward and backward current switching effects are
described and they may be principally different in nature. Mobile electron
spins are considered as being free in all the contacting ferromagnetic layers.
Joint action of the following two current effects is investigated: the
nonequilibrium longitudinal spin-injection effective field and the transverse
spin-transfer surface torque. Dispersion relation for fluctuations is derived
and solved for a junction model having spatially localized spin transfer
torque: depth of the torque penetration into the free layer is assumed much
smaller than the total free layer thickness. Some critical value of the well
known Gilbert damping constant is established for the first time. Spin transfer
torque dominates in the instability threshold determination for small enough
damping constants, while the spin-injection effective field dominates for high
damping. Fine interplay between spin transfer torque and spin injection is
necessary to provide a hysteretic behavior of the resistance versus current
dependence. The state diagram building up shows the possibility of
non-stationary (time dependent) nonlinear states arising due to instability
development. Calculations lead to the instability rise time values of the order
of 0.1 ns. Spin wave resonance frequency spectrum softening occurs under the
current growing to the instability threshold. Magnetization fluctuations above
the threshold rise oscillating with time for low damping, but rise
aperiodically and much more rapid for high damping.",0606102v2
2015-07-29,Spin dynamics and relaxation in the classical-spin Kondo-impurity model beyond the Landau-Lifschitz-Gilbert equation,"The real-time dynamics of a classical spin in an external magnetic field and
locally exchange coupled to an extended one-dimensional system of
non-interacting conduction electrons is studied numerically. Retardation
effects in the coupled electron-spin dynamics are shown to be the source for
the relaxation of the spin in the magnetic field. Total energy and spin is
conserved in the non-adiabatic process. Approaching the new local ground state
is therefore accompanied by the emission of dispersive wave packets of
excitations carrying energy and spin and propagating through the lattice with
Fermi velocity. While the spin dynamics in the regime of strong exchange
coupling J is rather complex and governed by an emergent new time scale, the
motion of the spin for weak J is regular and qualitatively well described by
the Landau-Lifschitz-Gilbert (LLG) equation. Quantitatively, however, the full
quantum-classical hybrid dynamics differs from the LLG approach. This is
understood as a breakdown of weak-coupling perturbation theory in J in the
course of time. Furthermore, it is shown that the concept of the Gilbert
damping parameter is ill-defined for the case of a one-dimensional system.",1507.08227v2
2008-09-26,Damping and magnetic anisotropy of ferromagnetic GaMnAs thin films,"The magnetic properties of annealed, epitaxial Ga0.93Mn0.07As layers under
tensile and compressive stress have been investigated by X-band (9GHz) and
Q-band (35GHz) ferromagnetic resonance (FMR) spectroscopy. From the analysis of
the linewidths of the uniform mode spectra the FMR Gilbert damping factor
""alpha"" has been determined. At T=4K we obtain a minimum damping factor of
""alpha"" = 0.003 for the compressively stressed layer. Its value is not
isotropic. It has a minimum value for the easy axes orientations of the
magnetic field and increases with the measuring temperature. Its average value
is for both type of films of the order of 0.01 in spite of strong differences
in the inhomogeneous linewidth which vary between 20 Oe and 600 Oe for the
layers grown on GaAs and GaInAs substrates respectively.",0809.4644v2
2013-08-02,Spin pumping damping and magnetic proximity effect in Pd and Pt spin-sink layers,"We investigated the spin pumping damping contributed by paramagnetic layers
(Pd, Pt) in both direct and indirect contact with ferromagnetic
Ni$_{81}$Fe$_{19}$ films. We find a nearly linear dependence of the
interface-related Gilbert damping enhancement $\Delta\alpha$ on the heavy-metal
spin-sink layer thicknesses t$_\textrm{N}$ in direct-contact
Ni$_{81}$Fe$_{19}$/(Pd, Pt) junctions, whereas an exponential dependence is
observed when Ni$_{81}$Fe$_{19}$ and (Pd, Pt) are separated by \unit[3]{nm} Cu.
We attribute the quasi-linear thickness dependence to the presence of induced
moments in Pt, Pd near the interface with Ni$_{81}$Fe$_{19}$, quantified using
X-ray magnetic circular dichroism (XMCD) measurements. Our results show that
the scattering of pure spin current is configuration-dependent in these systems
and cannot be described by a single characteristic length.",1308.0450v2
2015-02-05,Nonlinear analysis of magnetization dynamics excited by spin Hall effect,"We investigate the possibility of exciting self-oscillation in a
perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear
analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-oscillation
state, the energy supplied by the spin torque during a precession on a constant
energy curve should equal the dissipation due to damping. Also, the current to
balance the spin torque and the damping torque in the self-oscillation state
should be larger than the critical current to destabilize the initial state. We
find that the second condition in the spin Hall system is not satisfied by
deriving analytical solutions of the energy supplied by the spin transfer
effect and the dissipation due to the damping from the nonlinear LLG equation.
This indicates that the self-oscillation of a perpendicular ferromagnet cannot
be excited solely by the spin Hall torque.",1502.01420v2
2015-03-04,Critical current destabilizing perpendicular magnetization by the spin Hall effect,"The critical current needed to destabilize the magnetization of a
perpendicular ferromagnet via the spin Hall effect is studied. Both the
dampinglike and fieldlike torques associated with the spin current generated by
the spin Hall effect is included in the Landau-Lifshitz-Gilbert equation to
model the system. In the absence of the fieldlike torque, the critical current
is independent of the damping constant and is much larger than that of
conventional spin torque switching of collinear magnetic systems, as in
magnetic tunnel junctions. With the fieldlike torque included, we find that the
critical current scales with the damping constant as $\alpha^{0}$ (i.e.,
damping independent),$\alpha$, and $\alpha^{1/2}$ depending on the sign of the
fieldlike torque and other parameters such as the external field. Numerical and
analytical results show that the critical current can be significantly reduced
when the fieldlike torque possesses the appropriate sign, i.e. when the
effective field associated with the fieldlike torque is pointing opposite to
the spin direction of the incoming electrons. These results provide a pathway
to reducing the current needed to switch magnetization using the spin Hall
effect.",1503.01478v2
2015-10-23,Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet,"Laser-induced magnetization precessional dynamics was investigated in
epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly
compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed,
the precession frequency for which exceeded 0.5 THz and originated from the
large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet.
The effective damping constant was approximately 0.03. The corresponding
effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable
to those of the similar Mn-Ga materials. The physical mechanisms for the
Gilbert damping and for the laser-induced excitation of the FMR mode were also
discussed in terms of the spin-orbit-induced damping and the laser-induced
ultrafast modulation of the magnetic anisotropy, respectively.",1510.06793v1
2017-04-11,CoFeAlB alloy with low damping and low magnetization for spin transfer torque switching,"We investigate the effect of Al doping on the magnetic properties of the
alloy CoFeB. Comparative measurements of the saturation magnetization, the
Gilbert damping parameter $\alpha$ and the exchange constant as a function of
the annealing temperature for CoFeB and CoFeAlB thin films are presented. Our
results reveal a strong reduction of the magnetization for CoFeAlB in
comparison to CoFeB. If the prepared CoFeAlB films are amorphous, the damping
parameter $\alpha$ is unaffected by the Al doping in comparison to the CoFeB
alloy. In contrast, in the case of a crystalline CoFeAlB film, $\alpha$ is
found to be reduced. Furthermore, the x-ray characterization and the evolution
of the exchange constant with the annealing temperature indicate a similar
crystallization process in both alloys. The data proves the suitability of
CoFeAlB for spin torque switching properties where a reduction of the switching
current in comparison with CoFeB is expected.",1704.03326v1
2018-09-25,"Theory of damping in magnetization dynamics, dispelling a myth and pointing a way forward","There is a widely-held belief amongst theoreticians that the Gilbert damping
parameter {\alpha} in magnetization dynamics is infinite for a pure metal at
T=0. The basic error leading to this belief is pointed out explicitly and the
various methods of calculation used are viewed in a unified way based on the
Lorentzian lineshape of ferromagnetic resonance spectra. A general torque
formula for {\alpha} is proposed as a good starting-point for treating
inhomogeneous materials such as alloys, compounds and layered structures. Local
spin density functional theory provides a simple physical picture, in terms of
a non-uniform precessional cone angle in ferromagnetic resonance, of how such
inhomogeneity contributes to the damping. In a complementary many-body theory
this contribution is given by a vertex correction to the torque-torque response
function.",1809.09429v1
2018-10-31,Anisotropic and controllable Gilbert-Bloch dissipation in spin valves,"Spin valves form a key building block in a wide range of spintronic concepts
and devices from magnetoresistive read heads to spin-transfer-torque
oscillators. We elucidate the dependence of the magnetic damping in the free
layer on the angle its equilibrium magnetization makes with that in the fixed
layer. The spin pumping-mediated damping is anisotropic and tensorial, with
Gilbert- and Bloch-like terms. Our investigation reveals a mechanism for tuning
the free layer damping in-situ from negligible to a large value via the
orientation of fixed layer magnetization, especially when the magnets are
electrically insulating. Furthermore, we expect the Bloch contribution that
emerges from the longitudinal spin accumulation in the non-magnetic spacer to
play an important role in a wide range of other phenomena in spin valves.",1811.00020v2
2019-07-27,Two improved Gauss-Seidel projection methods for Landau-Lifshitz-Gilbert equation,"In this paper, we present two improved Gauss-Seidel projection methods with
unconditional stability. The first method updates the gyromagnetic term and the
damping term simultaneously and follows by a projection step. The second method
introduces two sets of approximate solutions, where we update the gyromagnetic
term and the damping term simultaneously for one set of approximate solutions
and apply the projection step to the other set of approximate solutions in an
alternating manner. Compared to the original Gauss-Seidel projection method
which has to solve heat equations $7$ times at each time step, the improved
methods solve heat equations $5$ times and $3$ times, respectively. First-order
accuracy in time and second-order accuracy in space are verified by examples in
both 1D and 3D. In addition, unconditional stability with respect to both the
grid size and the damping parameter is confirmed numerically. Application of
both methods to a realistic material is also presented with hysteresis loops
and magnetization profiles. Compared with the original method, the recorded
running times suggest that savings of both methods are about $2/7$ and $4/7$
for the same accuracy requirement, respectively.",1907.11853v1
2020-10-01,Modeling coupled spin and lattice dynamics,"A unified model of molecular and atomistic spin dynamics is presented
enabling simulations both in microcanonical and canonical ensembles without the
necessity of additional phenomenological spin damping. Transfer of energy and
angular momentum between the lattice and the spin systems is achieved by a
coupling term based upon the spin-orbit interaction. The characteristic spectra
of the spin and phonon systems are analyzed for different coupling strength and
temperatures. The spin spectral density shows magnon modes together with the
uncorrelated noise induced by the coupling to the lattice. The effective
damping parameter is investigated showing an increase with both coupling
strength and temperature. The model paves the way to understanding magnetic
relaxation processes beyond the phenomenological approach of the Gilbert
damping and the dynamics of the energy transfer between lattice and spins.",2010.00642v1
2021-04-22,Impact of Fe$_{80}$B$_{20}$ insertion on the properties of dual-MgO perpendicular magnetic tunnel junctions,"We explore the impact of Fe80B20 inserted at both
Co$_{20}$Fe$_{80}$B$_{20}$/MgO interfaces of dual-MgO free layers (FLs) in
bottom-pinned magnetic tunnel junctions (MTJs). MTJ stacks are annealed for 30
min at 350 $^\circ$C and 400 $^\circ$C in a vacuum after film deposition.
Current-in-plane tunneling measurements are carried out to characterize
magnetotransport properties of the MTJs. Conventional magnetometry measurements
and ferromagnetic resonance are conducted to estimate the saturation
magnetization, the effective perpendicular anisotropy field and the Gilbert
damping of dual-MgO FLs as a function of the Fe$_{80}$B$_{20}$ thickness and
annealing temperatures. With ultrathin Fe$_{80}$B$_{20}$ (0.2 - 0.4 nm)
inserted, perpendicular magnetic anisotropy (PMA) of FLs increases with similar
tunnel magneto-resistance (TMR) and low damping values. As Fe$_{80}$B$_{20}$
layer thickness further increases (0.6 - 1.2 nm), both TMR and PMA degrade, and
damping increases dramatically. This study demonstrates a novel approach to
tune properties of MTJ stacks with dual-MgO FLs up to 400 $^\circ$C annealing,
which enables MTJ stacks for various applications.",2104.10918v1
2021-09-24,Damping in yttrium iron garnet film with an interface,"We report strong damping enhancement in a 200 nm thick yttrium iron garnet
(YIG) film due to spin inhomogeneity at the interface. The growth-induced thin
interfacial gadolinium iron garnet (GdIG) layer antiferromagnetically (AFM)
exchange couples with the rest of the YIG layer. The out-of-plane angular
variation of ferromagnetic resonance (FMR) linewidth $\Delta H$ reflects a
large inhomogeneous distribution of effective magnetization $\Delta 4 \pi
M_{eff}$ due to the presence of an exchange springlike moments arrangement in
YIG. We probe the spin inhomogeneity at the YIG-GdIG interface by performing an
in-plane angular variation of resonance field $H_{r}$, leading to a
unidirectional feature. The large extrinsic $\Delta 4\pi M_{eff}$ contribution,
apart from the inherent intrinsic Gilbert contribution, manifests enhanced
precessional damping in YIG film.",2109.12071v1
2003-09-11,Theory of Current-Induced Magnetization Precession,"We solve appropriate drift-diffusion and Landau-Lifshitz-Gilbert equations to
demonstrate that unpolarized current flow from a non-magnet into a ferromagnet
can produce a precession-type instability of the magnetization. The fundamental
origin of the instability is the difference in conductivity between majority
spins and minority spins in the ferromagnet. This leads to spin accumulation
and spin currents that carry angular momentum across the interface. The
component of this angular momentum perpendicular to the magnetization drives
precessional motion that is opposed by Gilbert damping. Neglecting magnetic
anisotropy and magnetostatics, our approximate analytic and exact numerical
solutions using realistic values for the material parameters show (for both
semi-infinite and thin film geometries) that a linear instability occurs when
both the current density and the excitation wave vector parallel to the
interface are neither too small nor too large. For many aspects of the problem,
the variation of the magnetization in the direction of the current flows makes
an important contribution.",0309289v1
2005-07-20,All-optical probe of precessional magnetization dynamics in exchange biased NiFe/FeMn bilayers,"An internal anisotropy pulse field is launched by an 8.3 ps short laser
excitation, which triggers precessional magnetization dynamics of a
polycrystalline NiFe/FeMn exchange bias system on the picosecond timescale. Due
to the excitation the unidirectional anisotropy and, thus, the exchange
coupling across the interface between the ferromagnetic and the
antiferromagnetic layer is reduced, leading to a fast reduction of the exchange
bias field and to a dramatic increase of the zero-field susceptibility. The
fast optical unpinning is followed by a slower recovery of the interfacial
exchange coupling dominated by spin-lattice and heat flow relaxation with a
time constant of the order of 160 ps. The measured picosecond time evolution of
the exchange decoupling and restoration is interpreted as an anisotropy pulse
field giving rise to fast precessional magnetization dynamics of the
ferromagnetic layer. The strength of the internal pulse field and even the
initial magnetization deflection direction from the equilibrium orientation can
be controlled by the absorbed photons. The dependence of the effective Gilbert
damping on both small and large angle precessional motion was studied, yielding
that both cases can be modeled with reasonable accuracy within the
Landau-Lifshitz and Gilbert framework.",0507475v1
2008-11-25,The quantum-mechanical basis of an extended Landau-Lifshitz-Gilbert equation for a current-carrying ferromagnetic wire,"An extended Landau-Lifshitz-Gilbert (LLG) equation is introduced to describe
the dynamics of inhomogeneous magnetization in a current-carrying wire. The
coefficients of all the terms in this equation are calculated
quantum-mechanically for a simple model which includes impurity scattering.
This is done by comparing the energies and lifetimes of a spin wave calculated
from the LLG equation and from the explicit model. Two terms are of particular
importance since they describe non-adiabatic spin-transfer torque and damping
processes which do not rely on spin-orbit coupling. It is shown that these
terms may have a significant influence on the velocity of a current-driven
domain wall and they become dominant in the case of a narrow wall.",0811.4118v1
2009-05-28,Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured ferromagnets,"We develop the hydrodynamical theory of collinear spin currents coupled to
magnetization dynamics in metallic ferromagnets. The collective spin density
couples to the spin current through a U(1) Berry-phase gauge field determined
by the local texture and dynamics of the magnetization. We determine
phenomenologically the dissipative corrections to the equation of motion for
the electronic current, which consist of a dissipative spin-motive force
generated by magnetization dynamics and a magnetic texture-dependent
resistivity tensor. The reciprocal dissipative, adiabatic spin torque on the
magnetic texture follows from the Onsager principle. We investigate the effects
of thermal fluctuations and find that electronic dynamics contribute to a
nonlocal Gilbert damping tensor in the Landau-Lifshitz-Gilbert equation for the
magnetization. Several simple examples, including magnetic vortices, helices,
and spirals, are analyzed in detail to demonstrate general principles.",0905.4544v2
2010-11-26,Dependence of nonlocal Gilbert damping on the ferromagnetic layer type in FM/Cu/Pt heterostructures,"We have measured the size effect in nonlocal Gilbert relaxation rate in
FM(t$_{FM}$) / Cu (5nm) [/ Pt (2nm)] / Al(2nm) heterostructures, FM = \{
Ni$_{81}$Fe$_{19}$, Co$_{60}$Fe$_{20}$B$_{20}$, pure Co\}. Common behavior is
observed for three FM layers, where the additional relaxation obeys both a
strict inverse power law dependence $\Delta G =K \:t^{n}$,
$n=-\textrm{1.04}\pm\textrm{0.06}$ and a similar magnitude
$K=\textrm{224}\pm\textrm{40 Mhz}\cdot\textrm{nm}$. As the tested FM layers
span an order of magnitude in spin diffusion length $\lambda_{SDL}$, the
results are in support of spin diffusion, rather than nonlocal resistivity, as
the origin of the effect.",1011.5868v1
2012-06-21,Fast domain wall propagation in uniaxial nanowires with transverse fields,"Under a magnetic field along its axis, domain wall motion in a uniaxial
nanowire is much slower than in the fully anisotropic case, typically by
several orders of magnitude (the square of the dimensionless Gilbert damping
parameter). However, with the addition of a magnetic field transverse to the
wire, this behaviour is dramatically reversed; up to a critical field strength,
analogous to the Walker breakdown field, domain walls in a uniaxial wire
propagate faster than in a fully anisotropic wire (without transverse field).
Beyond this critical field strength, precessional motion sets in, and the mean
velocity decreases. Our results are based on leading-order analytic
calculations of the velocity and critical field as well as numerical solutions
of the Landau-Lifshitz-Gilbert equation.",1206.4819v2
2013-03-05,"Angle-Dependent Spin-Wave Resonance Spectroscopy of (Ga,Mn)As Films","A modeling approach for standing spin-wave resonances based on a
finite-difference formulation of the Landau-Lifshitz-Gilbert equation is
presented. In contrast to a previous study [Bihler et al., Phys. Rev. B 79,
045205 (2009)], this formalism accounts for elliptical magnetization precession
and magnetic properties arbitrarily varying across the layer thickness,
including the magnetic anisotropy parameters, the exchange stiffness, the
Gilbert damping, and the saturation magnetization. To demonstrate the
usefulness of our modeling approach, we experimentally study a set of (Ga,Mn)As
samples grown by low-temperature molecular-beam epitaxy by means of
electrochemical capacitance-voltage measurements and angle-dependent standing
spin-wave resonance spectroscopy. By applying our modeling approach, the angle
dependence of the spin-wave resonance data can be reproduced in a simulation
with one set of simulation parameters for all external field orientations. We
find that the approximately linear gradient in the out-of-plane magnetic
anisotropy is related to a linear gradient in the hole concentrations of the
samples.",1303.1192v1
2013-04-26,Landau-Lifshitz theory of the longitudinal spin Seebeck effect,"Thermal-bias-induced spin angular momentum transfer between a paramagnetic
metal and ferromagnetic insulator is studied theoretically based on the
stochastic Landau-Lifshitz-Gilbert (LLG) phenomenology. Magnons in the
ferromagnet establish a nonequilibrium steady state by equilibrating with
phonons via bulk Gilbert damping and electrons in the paramagnet via spin
pumping, according to the fluctuation-dissipation theorem. Subthermal magnons
and the associated spin currents are treated classically, while the appropriate
quantum crossover is imposed on high-frequency magnetic fluctuations. We
identify several length scales in the ferromagnet, which govern qualitative
changes in the dependence of the thermally-induced spin current on the magnetic
film thickness.",1304.7295v2
2013-09-21,Patterns formation in axially symmetric Landau-Lifshitz-Gilbert-Slonczewski equations,"The Landau-Lifshitz-Gilbert-Slonczewski equation describes magnetization
dynamics in the presence of an applied field and a spin polarized current. In
the case of axial symmetry and with focus on one space dimension, we
investigate the emergence of space-time patterns in the form of wavetrains and
coherent structures, whose local wavenumber varies in space. A major part of
this study concerns existence and stability of wavetrains and of front- and
domain wall-type coherent structures whose profiles asymptote to wavetrains or
the constant up-/down-magnetizations. For certain polarization the Slonczewski
term can be removed which allows for a more complete charaterization, including
soliton-type solutions. Decisive for the solution structure is the polarization
parameter as well as size of anisotropy compared with the difference of field
intensity and current intensity normalized by the damping.",1309.5523v4
2014-02-27,On the longitudinal spin current induced by a temperature gradient in a ferromagnetic insulator,"Based on the solution of the stochastic Landau-Lifshitz-Gilbert equation
discretized for a ferromagnetic chain subject to a uniform temperature
gradient, we present a detailed numerical study of the spin dynamics with a
focus particularly on finite-size effects. We calculate and analyze the net
longitudinal spin current for various temperature gradients, chain lengths, and
external static magnetic fields. In addition, we model an interface formed by a
nonuniformly magnetized finite-size ferromagnetic insulator and a normal metal
and inspect the effects of enhanced Gilbert damping on the formation of the
space-dependent spin current within the chain. A particular aim of this study
is the inspection of the spin Seebeck effect beyond the linear response regime.
We find that within our model the microscopic mechanism of the spin Seebeck
current is the magnon accumulation effect quantified in terms of the exchange
spin torque. According to our results, this effect drives the spin Seebeck
current even in the absence of a deviation between the magnon and phonon
temperature profiles. Our theoretical findings are in line with the recently
observed experimental results by M. Agrawal et al., Phys. Rev. Lett. 111,
107204 (2013).",1402.6899v1
2015-01-19,Effect of Exchange Interaction on Magnetic Thermal Fluctuation and Spin Susceptibility,"The expression of the thermal fluctuation parameter in the stochastic
Landau-Lifshitz-Gilbert equation has been derived from a fundamental quantum
theory of spins and phonons, in which the exchange interaction between nearest
atoms has been included. Our studies show that the thermal fluctuation
decreases exponentially with increasing exchange interaction. The non-uniform
fluctuation of local spins make the spin susceptibility much different from the
result derived by the macro-spin model or single spin model. The related spin
susceptibility depends not only on the strength of exchange interaction, but
also on the lattice structure. The non-uniform fluctuation can lead to an extra
broadening of the resonance line width along with the broadening arisen from
the Gilbert damping.",1501.04503v2
2015-07-23,Nanomagnet coupled to quantum spin Hall edge: An adiabatic quantum motor,"The precessing magnetization of a magnetic islands coupled to a quantum spin
Hall edge pumps charge along the edge. Conversely, a bias voltage applied to
the edge makes the magnetization precess. We point out that this device
realizes an adiabatic quantum motor and discuss the efficiency of its operation
based on a scattering matrix approach akin to Landauer-B""uttiker theory.
Scattering theory provides a microscopic derivation of the
Landau-Lifshitz-Gilbert equation for the magnetization dynamics of the device,
including spin-transfer torque, Gilbert damping, and Langevin torque. We find
that the device can be viewed as a Thouless motor, attaining unit efficiency
when the chemical potential of the edge states falls into the
magnetization-induced gap. For more general parameters, we characterize the
device by means of a figure of merit analogous to the ZT value in
thermoelectrics.",1507.06505v2
2017-03-28,Temperature dependent magnetic damping of yttrium iron garnet spheres,"We investigate the temperature dependent microwave absorption spectrum of an
yttrium iron garnet sphere as a function of temperature (5 K to 300 K) and
frequency (3 GHz to 43.5 GHz). At temperatures above 100 K, the magnetic
resonance linewidth increases linearly with temperature and shows a
Gilbert-like linear frequency dependence. At lower temperatures, the
temperature dependence of the resonance linewidth at constant external magnetic
fields exhibits a characteristic peak which coincides with a non-Gilbert-like
frequency dependence. The complete temperature and frequency evolution of the
linewidth can be modeled by the phenomenology of slowly relaxing rare-earth
impurities and either the Kasuya-LeCraw mechanism or the scattering with
optical magnons. Furthermore, we extract the temperature dependence of the
saturation magnetization, the magnetic anisotropy and the g-factor.",1703.09444v2
2017-12-10,Magnetic field gradient driven dynamics of isolated skyrmions and antiskyrmions in frustrated magnets,"The study of skyrmion/antiskyrmion motion in magnetic materials is very
important in particular for the spintronics applications. In this work, we
study the dynamics of isolated skyrmions and antiskyrmions in frustrated
magnets driven by magnetic field gradient, using the Landau-Lifshitz-Gilbert
simulations on the frustrated classical Heisenberg model on the triangular
lattice. A Hall-like motion induced by the gradient is revealed in bulk system,
similar to that in the well-studied chiral magnets. More interestingly, our
work suggests that the lateral confinement in nano-stripes of the frustrated
system can completely suppress the Hall motion and significantly speed up the
motion along the gradient direction. The simulated results are well explained
by the Thiele theory. It is demonstrated that the acceleration of the motion is
mainly determined by the Gilbert damping constant, which provides useful
information for finding potential materials for skyrmion-based spintronics.",1712.03550v1
2018-02-28,Roles of chiral renormalization on magnetization dynamics in chiral magnets,"In metallic ferromagnets, the interaction between local magnetic moments and
conduction electrons renormalizes parameters of the Landau-Lifshitz-Gilbert
equation such as the gyromagnetic ratio and the Gilbert damping, and makes them
dependent on the magnetic configurations. Although the effects of the
renormalization for nonchiral ferromagnets are usually minor and hardly
detectable, we show that the renormalization does play a crucial role for
chiral magnets. Here the renormalization is chiral and as such we predict
experimentally identifiable effects on the phenomenology of magnetization
dynamics. In particular, our theory for the self-consistent magnetization
dynamics of chiral magnets allows for a concise interpretation of domain wall
creep motion. We also argue that the conventional creep theory of the domain
wall motion, which assumes Markovian dynamics, needs critical reexamination
since the gyromagnetic ratio makes the motion non-Markovian. The non-Markovian
nature of the domain wall dynamics is experimentally checkable by the chirality
of the renormalization.",1803.00017v2
2018-12-20,Laser Controlled Spin Dynamics of Ferromagnetic Thin Film from Femtosecond to Nanosecond Timescale,"Laser induced modulation of the magnetization dynamics occurring over various
time-scales have been unified here for a Ni80Fe20 thin film excited by
amplified femtosecond laser pulses. The weak correlation between
demagnetization time and pump fluence with substantial enhancement in
remagnetization time is demonstrated using three-temperature model considering
the temperatures of electron, spin and lattice. The picosecond magnetization
dynamics is modeled using the Landau-Lifshitz-Gilbert equation. With increasing
pump fluence the Gilbert damping parameter shows significant enhancement from
its intrinsic value due to increment in the ratio of electronic temperature to
Curie temperature within very short time scale. The precessional frequency
experiences noticeable red shift with increasing pump fluence. The changes in
the local magnetic properties due to accumulation and dissipation of thermal
energy within the probed volume are described by the evolution of temporal
chirp parameter in a comprehensive manner. A unification of ultrafast magnetic
processes and its control over broad timescale would enable the integration of
various magnetic processes in a single device and use one effect to control
another.",1812.08404v1
2019-03-13,Higher-order linearly implicit full discretization of the Landau--Lifshitz--Gilbert equation,"For the Landau--Lifshitz--Gilbert (LLG) equation of micromagnetics we study
linearly implicit backward difference formula (BDF) time discretizations up to
order $5$ combined with higher-order non-conforming finite element space
discretizations, which are based on the weak formulation due to Alouges but use
approximate tangent spaces that are defined by $L^2$-averaged instead of nodal
orthogonality constraints. We prove stability and optimal-order error bounds in
the situation of a sufficiently regular solution. For the BDF methods of orders
$3$ to~$5$, this requires %a mild time step restriction $\tau \leqslant ch$ and
that the damping parameter in the LLG equations be above a positive threshold;
this condition is not needed for the A-stable methods of orders $1$ and $2$,
for which furthermore a discrete energy inequality irrespective of solution
regularity is proved.",1903.05415v2
2019-12-01,Coarse-graining in micromagnetic simulations of dynamic hysteresis loops,"Micromagnetic simulations based on the stochastic Landau-Lifshitz-Gilbert
equation are used to calculate dynamic magnetic hysteresis loops relevant to
magnetic hyperthermia. With the goal to effectively simulate room-temperature
loops for large iron-oxide-based systems at relatively slow sweep rates on the
order of 1 Oe/ns or less, a previously derived renormalization group approach
for coarse-graining (Grinstein and Koch, Phys. Rev. Lett. 20, 207201, 2003) is
modified and applied to calculating loops for a magnetite nanorod. The nanorod
modelled is the building block for larger nanoparticles that were employed in
preclinical studies (Dennis et al., Nanotechnology 20, 395103, 2009). The
scaling algorithm is shown to produce nearly identical loops over several
decades in the model grain size. Sweep-rate scaling involving the Gilbert
damping parameter is also demonstrated to allow orders of magnitude speed-up of
the loop calculations.",1912.00310v3
2020-02-17,Self-similar shrinkers of the one-dimensional Landau-Lifshitz-Gilbert equation,"The main purpose of this paper is the analytical study of self-shrinker
solutions of the one-dimensional Landau-Lifshitz-Gilbert equation (LLG), a
model describing the dynamics for the spin in ferromagnetic materials. We show
that there is a unique smooth family of backward self-similar solutions to the
LLG equation, up to symmetries, and we establish their asymptotics. Moreover,
we obtain that in the presence of damping, the trajectories of the self-similar
profiles converge to great circles on the sphere $\mathbb{S}^2$, at an
exponential rate. In particular, the results presented in this paper provide
examples of blow-up in finite time, where the singularity develops due to rapid
oscillations forming limit circles.",2002.06858v2
2021-02-20,Fast magnetization reversal of a magnetic nanoparticle induced by cosine chirp microwave field pulse,"We investigate the magnetization reversal of single-domain magnetic
nanoparticle driven by the circularly polarized cosine chirp microwave pulse
(CCMP). The numerical findings, based on the Landau-Lifshitz-Gilbert equation,
reveal that the CCMP is by itself capable of driving fast and energy-efficient
magnetization reversal. The microwave field amplitude and initial frequency
required by a CCMP are much smaller than that of the linear down-chirp
microwave pulse. This is achieved as the frequency change of the CCMP closely
matches the frequency change of the magnetization precession which leads to an
efficient stimulated microwave energy absorption (emission) by (from) the
magnetic particle before (after) it crosses over the energy barrier. We further
find that the enhancement of easy-plane shape anisotropy significantly reduces
the required microwave amplitude and the initial frequency of CCMP. We also
find that there is an optimal Gilbert damping for fast magnetization reversal.
These findings may provide a pathway to realize the fast and low-cost memory
device.",2102.10394v2
2021-07-24,Electron-Phonon Scattering governs both Ultrafast and Precessional Magnetization Dynamics in Co-Fe Alloys,"Recent investigations have advanced the understanding of how
structure-property relationships in ferromagnetic metal alloys affect the
magnetization dynamics on nanosecond time-scales. A similar understanding for
magnetization dynamics on femto- to pico-second time-scales does not yet exist.
To address this, we perform time-resolved magneto optic Kerr effect (TRMOKE)
measurements of magnetization dynamics in Co-Fe alloys on femto- to nano-second
regimes. We show that Co-Fe compositions that exhibit low Gilbert damping
parameters also feature prolonged ultrafast demagnetization upon
photoexcitation. We analyze our experimental TR-MOKE data with the
three-temperature-model (3TM) and the Landau-Lifshitz-Gilbert equation. These
analyses reveal a strong compositional dependence of the dynamics across all
time-scales on the strength of electron-phonon interactions. Our findings are
beneficial to the spintronics and magnonics community, and will aid in the
quest for energy-efficient magnetic storage applications.",2107.11699v1
2022-09-07,Convergence analysis of an implicit finite difference method for the inertial Landau-Lifshitz-Gilbert equation,"The Landau-Lifshitz-Gilbert (LLG) equation is a widely used model for fast
magnetization dynamics in ferromagnetic materials. Recently, the inertial LLG
equation, which contains an inertial term, has been proposed to capture the
ultra-fast magnetization dynamics at the sub-picosecond timescale.
Mathematically, this generalized model contains the first temporal derivative
and a newly introduced second temporal derivative of magnetization.
Consequently, it produces extra difficulties in numerical analysis due to the
mixed hyperbolic-parabolic type of this equation with degeneracy. In this work,
we propose an implicit finite difference scheme based on the central difference
in both time and space. A fixed point iteration method is applied to solve the
implicit nonlinear system. With the help of a second order accurate constructed
solution, we provide a convergence analysis in $H^1$ for this numerical scheme,
in the $\ell^\infty (0, T; H_h^1)$ norm. It is shown that the proposed method
is second order accurate in both time and space, with unconditional stability
and a natural preservation of the magnetization length. In the hyperbolic
regime, significant damping wave behaviors of magnetization at a shorter
timescale are observed through numerical simulations.",2209.02914v2
2022-09-16,Pseudo-PT symmetric Dirac equation : effect of a new mean spin angular momentum operator on Gilbert damping,"The pseudo-PT symmetric Dirac equation is proposed and analyzed by using a
non-unitary Foldy-Wouthuysen transformations. A new spin operator PT symmetric
expectation value (called the mean spin operator) for an electron interacting
with a time-dependent electromagnetic field is obtained. We show that spin
magnetization - which is the quantity usually measured experimentally - is not
described by the standard spin operator but by this new mean spin operator to
properly describe magnetization dynamics in ferromagnetic materials and the
corresponding equation of motion is compatible with the phenomenological model
of the Landau-Lifshitz-Gilbert equation (LLG).",2209.07908v1
2022-11-15,Nonlinear sub-switching regime of magnetization dynamics in photo-magnetic garnets,"We analyze, both experimentally and numerically, the nonlinear regime of the
photo-induced coherent magnetization dynamics in cobalt-doped yttrium iron
garnet films. Photo-magnetic excitation with femtosecond laser pulses reveals a
strongly nonlinear response of the spin subsystem with a significant increase
of the effective Gilbert damping. By varying both laser fluence and the
external magnetic field, we show that this nonlinearity originates in the
anharmonicity of the magnetic energy landscape. We numerically map the
parameter workspace for the nonlinear photo-induced spin dynamics below the
photo-magnetic switching threshold. Corroborated by numerical simulations of
the Landau-Lifshitz-Gilbert equation, our results highlight the key role of the
cubic symmetry of the magnetic subsystem in reaching the nonlinear spin
precession regime. These findings expand the fundamental understanding of
laser-induced nonlinear spin dynamics as well as facilitate the development of
applied photo-magnetism.",2211.08048v2
2023-08-16,Discovery and regulation of chiral magnetic solitons: Exact solution from Landau-Lifshitz-Gilbert equation,"The Landau-Lifshitz-Gilbert (LLG) equation has emerged as a fundamental and
indispensable framework within the realm of magnetism. However, solving the LLG
equation, encompassing full nonlinearity amidst intricate complexities,
presents formidable challenges. In this context, we develop a precise mapping
through geometric representation, establishing a direct linkage between the LLG
equation and an integrable generalized nonlinear Schr\""odinger equation. This
novel mapping provides accessibility towards acquiring a great number of exact
spatiotemporal solutions. Notably, exact chiral magnetic solitons, critical for
stability and controllability in propagation with and without damping effects
are discovered. Our formulation provides exact solutions for the long-standing
fully nonlinear problem, facilitating practical control through spin current
injection in magnetic memory applications.",2308.08331v1
2002-12-05,Dynamic stiffness of spin valves,"The dynamics of the magnetic order parameters of
ferromagnet/normal-metal/ferromagnet spin valves and isolated ferromagnets may
be very different. We investigate the role of the nonequilibrium spin-current
exchange between the ferromagnets in the magnetization precession and
switching. We find a (low-temperature) critical current bias for a coherent
current-induced magnetization excitation in spin valves, which unifies and
generalizes previous ideas of Slonczewski and Berger. In the absence of an
applied bias, the effect of the spin transfer can be expressed as
magnetic--configuration-dependent Gilbert damping.",0212130v2
2005-01-13,Magnetization noise in magnetoelectronic nanostructures,"By scattering theory we show that spin current noise in normal electric
conductors in contact with nanoscale ferromagnets increases the magnetization
noise by means of a fluctuating spin-transfer torque. Johnson-Nyquist noise in
the spin current is related to the increased Gilbert damping due to spin
pumping, in accordance with the fluctuation-dissipation theorem. Spin current
shot noise in the presence of an applied bias is the dominant contribution to
the magnetization noise at low temperatures.",0501318v1
2005-01-27,Current-induced macrospin vs spin-wave excitations in spin valves,"The mode dependence of current-induced magnetic excitations in spin valves is
studied theoretically. The torque exerted on the magnetization by transverse
spin currents as well as the Gilbert damping constant are found to depend
strongly on the wave length of the excitation (spin wave). Analytic expressions
are presented for the critical currents that excite a selected spin wave. The
onset of macrospin (zero wavelength) vs finite wavelength instabilities depends
on the device parameters and the current direction, in agreement with recent
experimental findings.",0501672v3
2006-05-08,Microscopic Calculation of Spin Torques in Disordered Ferromagnets,"Effects of conduction electrons on magnetization dynamics, represented by
spin torques, are calculated microscopically in the first order in spatial
gradient and time derivative of magnetization. Special attention is paid to the
so-called $\beta$-term and the Gilbert damping, $\alpha$, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
(and spin-orbit) impurities. The obtained results such as $\alpha \ne \beta$
hold for localized as well as itinerant ferromagnetism.",0605186v1
2006-11-27,Microscopic Calculation of Spin Torques and Forces,"Spin torques, that is, effects of conduction electrons on magnetization
dynamics, are calculated microscopically in the first order in spatial gradient
and time derivative of magnetization. Special attention is paid to the
so-called \beta-term and the Gilbert damping, \alpha, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
impurities. Two types of forces that the electric/spin current exerts on
magnetization are identified based on a general formula relating the force to
the torque.",0611669v1
2007-10-15,Ferromagnetic resonance study of polycrystalline Fe_{1-x}V_x alloy thin films,"Ferromagnetic resonance has been used to study the magnetic properties and
magnetization dynamics of polycrystalline Fe$_{1-x}$V$_{x}$ alloy films with
$0\leq x < 0.7$. Films were produced by co-sputtering from separate Fe and V
targets, leading to a composition gradient across a Si substrate. FMR studies
were conducted at room temperature with a broadband coplanar waveguide at
frequencies up to 50 GHz using the flip-chip method. The effective
demagnetization field $4 \pi M_{\mathrm{eff}}$ and the Gilbert damping
parameter $\alpha$ have been determined as a function of V concentration. The
results are compared to those of epitaxial FeV films.",0710.2826v2
2008-10-25,The domain wall spin torque-meter,"We report the direct measurement of the non-adiabatic component of the
spin-torque in domain walls. Our method is independent of both the pinning of
the domain wall in the wire as well as of the Gilbert damping parameter. We
demonstrate that the ratio between the non-adiabatic and the adiabatic
components can be as high as 1, and explain this high value by the importance
of the spin-flip rate to the non-adiabatic torque. Besides their fundamental
significance these results open the way for applications by demonstrating a
significant increase of the spin torque efficiency.",0810.4633v1
2008-12-03,Observation of ferromagnetic resonance in strontium ruthenate (SrRuO3),"We report the observation of ferromagnetic resonance (FMR) in SrRuO3 using
the time-resolved magneto-optical Kerr effect. The FMR oscillations in the
time-domain appear in response to a sudden, optically induced change in the
direction of easy-axis anistropy. The high FMR frequency, 250 GHz, and large
Gilbert damping parameter, alpha ~ 1, are consistent with strong spin-orbit
coupling. We find that the parameters associated with the magnetization
dynamics, including alpha, have a non-monotonic temperature dependence,
suggestive of a link to the anomalous Hall effect.",0812.0832v1
2011-02-26,Dynamics of Skyrmion Crystals in Metallic Thin Films,"We study the collective dynamics of the Skyrmion crystal (SkX) in thin films
of ferromagnetic metals resulting from the nontrivial Skyrmion topology. We
show that the current-driven motion of the crystal reduces the topological Hall
effect and the Skyrmion trajectories bend away from the direction of the
electric current (the Skyrmion Hall effect). We find a new dissipation
mechanism in non-collinear spin textures that can lead to a much faster spin
relaxation than Gilbert damping, calculate the dispersion of phonons in the
SkX, and discuss effects of impurity pinning of Skyrmions.",1102.5384v2
2011-04-15,Lagrangian approach and dissipative magnetic systems,"A Lagrangian is introduced which includes the coupling between magnetic
moments $\mathbf{m}$ and the degrees of freedom $\boldsymbol{\sigma}$ of a
reservoir. In case the system-reservoir coupling breaks the time reversal
symmetry the magnetic moments perform a damped precession around an effective
field which is self-organized by the mutual interaction of the moments. The
resulting evolution equation has the form of the Landau-Lifshitz-Gilbert
equation. In case the bath variables are constant vector fields the moments
$\mathbf{m}$ fulfill the reversible Landau-Lifshitz equation. Applying
Noether's theorem we find conserved quantities under rotation in space and
within the configuration space of the moments.",1104.3002v1
2011-07-04,Minimization of the Switching Time of a Synthetic Free Layer in Thermally Assisted Spin Torque Switching,"We theoretically studied the thermally assisted spin torque switching of a
synthetic free layer and showed that the switching time is minimized if the
condition H_J=|H_s|/(2 alpha) is satisfied, where H_J, H_s and alpha are the
coupling field of two ferromagnetic layers, the amplitude of the spin torque,
and the Gilbert damping constant. We also showed that the coupling field of the
synthetic free layer can be determined from the resonance frequencies of the
spin-torque diode effect.",1107.0753v2
2012-09-14,Skyrmion Dynamics in Multiferroic Insulator,"Recent discovery of Skyrmion crystal phase in insulating multiferroic
compound Cu$_2$OSeO$_3$ calls for new ways and ideas to manipulate the
Skyrmions in the absence of spin transfer torque from the conduction electrons.
It is shown here that the position-dependent electric field, pointed along the
direction of the average induced dipole moment of the Skyrmion, can induce the
Hall motion of Skyrmion with its velocity orthogonal to the field gradient.
Finite Gilbert damping produces longitudinal motion. We find a rich variety of
resonance modes excited by a.c. electric field.",1209.3120v1
2013-03-12,Thermally excited spin waves in a nano-structure: thermal gradient vs. constant temperature,"Using micromagnetic simulations, we have investigated spin dynamics in a
nanostructure in the presence of thermal fluctuations. In particular, we have
studied the effects of a uniform temperature and of a uniform thermal gradient.
In both cases, the stochastic field leads to an increase of the precession
angle of the magnetization, and to a mild decreas of the linewidth of the
resonance peaks. Our results indicate that the Gilbert damping parameter plays
the role of control parameter for the amplification of spin waves.",1303.2895v1
2013-07-29,Theoretical Study of Spin-Torque Oscillator with Perpendicularly Magnetized Free Layer,"The magnetization dynamics of spin torque oscillator (STO) consisting of a
perpendicularly magnetized free layer and an in-plane magnetized pinned layer
was studied by solving the Landau-Lifshitz-Gilbert equation. We derived the
analytical formula of the relation between the current and the oscillation
frequency of the STO by analyzing the energy balance between the work done by
the spin torque and the energy dissipation due to the damping. We also found
that the field-like torque breaks the energy balance, and change the
oscillation frequency.",1307.7427v1
2014-06-10,Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance,"We show by vector network analyzer ferromagnetic resonance measurements that
low Gilbert damping {\alpha} down to 0.006 can be achieved in perpendicularly
magnetized MgO/CoFeB/MgO thin films with ultra-thin insertions of Ta in the
CoFeB layer. While increasing the number of Ta insertions allows thicker CoFeB
layers to remain perpendicular, the effective areal magnetic anisotropy does
not improve with more insertions, and also comes with an increase in {\alpha}.",1406.2491v2
2014-09-24,Dissipationless Multiferroic Magnonics,"We propose that the magnetoelectric effect in multiferroic insulators with
coplanar antiferromagnetic spiral order, such as BiFeO$_{3}$, enables
electrically controlled dissipationless magnonics. Applying an oscillating
electric field in these materials with frequency as low as household frequency
can activate Goldstone modes that manifests fast planar rotations of spins,
whose motion is not obstructed by crystalline anisotropy. Combining with spin
ejection mechanisms, such a fast planar rotation can deliver electricity at
room temperature over a distance of the magnetic domain, which is free from the
energy loss due to Gilbert damping.",1409.6900v2
2015-02-09,Large amplitude oscillation of magnetization in spin-torque oscillator stabilized by field-like torque,"Oscillation frequency of spin torque oscillator with a perpendicularly
magnetized free layer and an in-plane magnetized pinned layer is theoretically
investigated by taking into account the field-like torque. It is shown that the
field-like torque plays an important role in finding the balance between the
energy supplied by the spin torque and the dissipation due to the damping,
which results in a steady precession. The validity of the developed theory is
confirmed by performing numerical simulations based on the
Landau-Lifshitz-Gilbert equation.",1502.02699v1
2015-06-02,Current-Driven Motion of Magnetic Domain Wall with Many Bloch Lines,"The current-driven motion of a domain wall (DW) in a ferromagnet with many
Bloch lines (BLs) via the spin transfer torque is studied theoretically. It is
found that the motion of BLs changes the current-velocity ($j$-$v$)
characteristic dramatically. Especially, the critical current density to
overcome the pinning force is reduced by the factor of the Gilbert damping
coefficient $\alpha$ even compared with that of a skyrmion. This is in sharp
contrast to the case of magnetic field driven motion, where the existence of
BLs reduces the mobility of the DW.",1506.00723v1
2015-07-24,Boosting Domain Wall Propagation by Notches,"We report a counter-intuitive finding that notches in an otherwise
homogeneous magnetic nanowire can boost current-induced domain wall (DW)
propagation. DW motion in notch-modulated wires can be classified into three
phases: 1) A DW is pinned around a notch when the current density is below the
depinning current density. 2) DW propagation velocity is boosted by notches
above the depinning current density and when non-adiabatic spin-transfer torque
strength $\beta$ is smaller than the Gilbert damping constant $\alpha$. The
boost can be manyfold. 3) DW propagation velocity is hindered when $\beta >
\alpha$. The results are explained by using the Thiele equation.",1507.06748v1
2016-01-23,Nonlinear magnetization dynamics of antiferromagnetic spin resonance induced by intense terahertz magnetic field,"We report on the nonlinear magnetization dynamics of a HoFeO3 crystal induced
by a strong terahertz magnetic field resonantly enhanced with a split ring
resonator and measured with magneto-optical Kerr effect microscopy. The
terahertz magnetic field induces a large change (~40%) in the spontaneous
magnetization. The frequency of the antiferromagnetic resonance decreases in
proportion to the square of the magnetization change. A modified
Landau-Lifshitz-Gilbert equation with a phenomenological nonlinear damping term
quantitatively reproduced the nonlinear dynamics.",1601.06213v1
2017-08-11,Gradient expansion formalism for generic spin torques,"We propose a new quantum-mechanical formalism to calculate spin torques based
on the gradient expansion, which naturally involves spacetime gradients of the
magnetization and electromagnetic fields. We have no assumption in the
small-amplitude formalism or no difficulty in the SU($2$) gauge transformation
formalism. As a representative, we calculate the spin renormalization, Gilbert
damping, spin-transfer torque, and $\beta$-term in a three-dimensional
ferromagnetic metal with nonmagnetic and magnetic impurities being taken into
account within the self-consistent Born approximation. Our results serve as a
first-principles formalism for spin torques.",1708.03424v1
2019-06-03,Magnon-phonon interactions in magnetic insulators,"We address the theory of magnon-phonon interactions and compute the
corresponding quasi-particle and transport lifetimes in magnetic insulators
with focus on yttrium iron garnet at intermediate temperatures from anisotropy-
and exchange-mediated magnon-phonon interactions, the latter being derived from
the volume dependence of the Curie temperature. We find in general weak effects
of phonon scattering on magnon transport and the Gilbert damping of the
macrospin Kittel mode. The magnon transport lifetime differs from the
quasi-particle lifetime at shorter wavelengths.",1906.01042v1
2019-09-17,Microwave induced tunable subharmonic steps in superconductor-ferromagnet-superconductor Josephson junction,"We investigate the coupling between ferromagnet and superconducting phase
dynamics in superconductor-ferromagnet-superconductor Josephson junction. The
current-voltage characteristics of the junction demonstrate a pattern of
subharmonic current steps which forms a devil's staircase structure. We show
that a width of the steps becomes maximal at ferromagnetic resonance. Moreover,
we demonstrate that the structure of the steps and their widths can be tuned by
changing the frequency of the external magnetic field, ratio of Josephson to
magnetic energy, Gilbert damping and the junction size.",1909.08004v1
2019-09-19,Magnetization dynamics of the compensated ferrimagnet $Mn_{2}Ru_{x}Ga$,"Here we study both static and time-resolved dynamic magnetic properties of
the compensated ferrimagnet from room temperature down to 10K, thus crossing
the magnetic compensation temperature $T_{M}$. The behaviour is analysed with a
model of a simple collinear ferrimagnet with uniaxial anisotropy and
site-specific gyromagnetic ratios. We find a maximum zero-applied-field
resonance frequency of $\sim$160GHz and a low intrinsic Gilbert damping
$\alpha$$\sim$0.02, making it a very attractive candidate for various
spintronic applications.",1909.09085v1
2019-11-28,Transport properties of spin superfluids: comparing easy-plane ferro- and antiferromagnets,"We present a study on spin-superfluid transport based on an atomistic,
classical spin model. Easy-plane ferro- as well as antiferromagnets are
considered, which allows for a direct comparison of these two material classes
based on the same model assumptions. We find a spin-superfluid transport which
is robust against variations of the boundary conditions, thermal fluctuations,
and dissipation modeled via Gilbert damping. Though the spin accumulations is
smaller for antiferromagnets the range of the spin-superfluid transport turns
out to be identical for ferro- and antiferromagnets. Finally, we calculate and
explore the role of the driving frequency and especially the critical
frequency, where phase slips occur and the spin accumulation breaks down.",1911.12786v1
2020-01-17,Fermi Level Controlled Ultrafast Demagnetization Mechanism in Half-Metallic Heusler Alloy,"The electronic band structure-controlled ultrafast demagnetization mechanism
in Co2FexMn1-xSi Heusler alloy is underpinned by systematic variation of
composition. We find the spin-flip scattering rate controlled by spin density
of states at Fermi level is responsible for non-monotonic variation of
ultrafast demagnetization time ({\tau}M) with x with a maximum at x = 0.4.
Furthermore, Gilbert damping constant exhibits an inverse relationship with
{\tau}M due to the dominance of inter-band scattering mechanism. This
establishes a unified mechanism of ultrafast spin dynamics based on Fermi level
position.",2001.06217v1
2020-04-17,Collective coordinate study of spin wave emission from dynamic domain wall,"We study theoretically the spin wave emission from a moving domain wall in a
ferromagnet. Introducing a deformation mode describing a modulation of the wall
thickness in the collective coordinate description, we show that thickness
variation couples to the spin wave linearly and induces spin wave emission. The
dominant emitted spin wave turns out to be polarized in the out-of wall plane
($\phi$)-direction. The emission contributes to the Gilbert damping parameter
proportional to $\hbar\omega_\phi/K$, the ratio of the angular frequency
$\omega_\phi$ of $\phi$ and the easy-axis anisotropy energy $K$.",2004.08082v1
2021-03-10,Anisotropic superconducting spin transport at magnetic interfaces,"We present a theoretical investigation of anisotropic superconducting spin
transport at a magnetic interface between a p-wave superconductor and a
ferromagnetic insulator. Our formulation describes the ferromagnetic resonance
modulations due to spin current generation depending on spin-triplet Cooper
pair, including the frequency shift and enhanced Gilbert damping, in a unified
manner. We find that the Cooper pair symmetry is detectable from the
qualitative behavior of the ferromagnetic resonance modulation. Our theory
paves the way toward anisotropic superconducting spintronics.",2103.05871v3
2022-01-16,Ferromagnetic resonance modulation in $d$-wave superconductor/ferromagnetic insulator bilayer systems,"We investigate ferromagnetic resonance (FMR) modulation in $d$-wave
superconductor (SC)/ferromagnetic insulator (FI) bilayer systems theoretically.
The modulation of the Gilbert damping in these systems reflects the existence
of nodes in the $d$-wave SC and shows power-law decay characteristics within
the low-temperature and low-frequency limit. Our results indicate the
effectiveness of use of spin pumping as a probe technique to determine the
symmetry of unconventional SCs with high sensitivity for nanoscale thin films.",2201.06060v2
2022-09-28,Unidirectional magnetic coupling,"We show that interlayer Dzyaloshinskii-Moriya interaction in combination with
non-local Gilbert damping gives rise to unidirectional magnetic coupling. That
is, the coupling between two magnetic layers -- say the left and right layer --
is such that dynamics of the left layer leads to dynamics of the right layer,
but not vice versa. We discuss the implications of this result for the magnetic
susceptibility of a magnetic bilayer, electrically-actuated spin-current
transmission, and unidirectional spin-wave packet generation and propagation.
Our results may enable a route towards spin-current and spin-wave diodes and
further pave the way to design spintronic devices via reservoir engineering.",2209.14179v1
2023-08-11,Dynamical Majorana Ising spin response in a topological superconductor-magnet hybrid by microwave irradiation,"We study a dynamical spin response of surface Majorana modes in a topological
superconductor-magnet hybrid under microwave irradiation. We find a method to
toggle between dissipative and non-dissipative Majorana Ising spin dynamics by
adjusting the external magnetic field angle and the microwave frequency. This
reflects the topological nature of the Majorana modes, enhancing the Gilbert
damping of the magnet, thereby, providing a detection method for the Majorana
Ising spins. Our findings illuminate a magnetic probe for Majorana modes,
paving the path to innovative spin devices.",2308.05955v2
2006-10-04,On the dynamics of spin systems in the Landau-Lifshitz theory,"In the framework of the Landau-Lifshitz equations without any dissipation (an
approximation which may also be helpful for finite but weak Gilbert damping),
with all interactions included, for general ground states, geometries and
domain structures, and many types of effective fields the dynamics of the spin
precession around this ground state is considered.
  At first the precession is treated in the linear approximation. For the
eigenmodes of the precession one has a `rule of geometric mean' for the
eigenfrequencies. For the eigenmodes pseudo-orthogonality relations are
obtained, which reflect the gyrotropic and elliptic character of the spin
precession and differ from those known from the Schrodinger equation. Moreover,
pseudo-orthogonality relations are valid 'everywhere' (e.g., both in the outer
region and in the core region of a magnetic vortex).
  Then also some aspects of the nonlinear mode coupling with emphasis on
`confluence' and `splitting' processes of elementary magnetic spin-wave
excitations are considered. At the same time these processes contribute to the
Gilbert damping.
  There are thus essential differences to quantum mechanics, although at a
first glance one discovers many similarities. From the results one may also get
insights of why these systems are so complex that (although the essential
quantities depend only on the local values of the partially long-ranged
effective magnetic fields) practically only detailed experiments and computer
simulations make sense.",0610122v4
2016-04-26,First principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys,"Heusler alloys have been intensively studied due to the wide variety of
properties that they exhibit. One of these properties is of particular interest
for technological applications, i.e. the fact that some Heusler alloys are
half-metallic. In the following, a systematic study of the magnetic properties
of three different Heusler families $\textrm{Co}_2\textrm{Mn}\textrm{Z}$,
$\text{Co}_2\text{Fe}\text{Z}$ and $\textrm{Mn}_2\textrm{V}\textrm{Z}$ with
$\text{Z}=\left(\text{Al, Si, Ga, Ge}\right)$ is performed. A key aspect is the
determination of the Gilbert damping from first principles calculations, with
special focus on the role played by different approximations, the effect that
substitutional disorder and temperature effects. Heisenberg exchange
interactions and critical temperature for the alloys are also calculated as
well as magnon dispersion relations for representative systems, the
ferromagnetic $\textrm{Co}_2\textrm{Fe}\textrm{Si}$ and the ferrimagnetic
$\textrm{Mn}_2\textrm{V}\textrm{Al}$. Correlations effects beyond standard
density-functional theory are treated using both the local spin density
approximation including the Hubbard $U$ and the local spin density
approximation plus dynamical mean field theory approximation, which allows to
determine if dynamical self-energy corrections can remedy some of the
inconsistencies which were previously reported for these alloys.",1604.07552v1
2016-12-21,"Spin Pumping, Dissipation, and Direct and Alternating Inverse Spin Hall Effects in Magnetic Insulator-Normal Metal Bilayers","We theoretically consider the spin-wave mode- and wavelength-dependent
enhancement of the Gilbert damping in magnetic insulator--normal metal bilayers
due to spin pumping as well as the enhancement's relation to direct and
alternating inverse spin Hall voltages in the normal metal. In the
long-wavelength limit, including long-range dipole interactions, the ratio of
the enhancement for transverse volume modes to that of the macrospin mode is
equal to two. With an out-of-plane magnetization, this ratio decreases with
both an increasing surface anisotropic energy and mode number. If the surface
anisotropy induces a surface state, the enhancement can be an order of
magnitude larger than for to the macrospin. With an in-plane magnetization, the
induced dissipation enhancement can be understood by mapping the anisotropy
parameter to the out-of-plane case with anisotropy. For shorter wavelengths, we
compute the enhancement numerically and find good agreement with the analytical
results in the applicable limits. We also compute the induced direct- and
alternating-current inverse spin Hall voltages and relate these to the magnetic
energy stored in the ferromagnet. Because the magnitude of the direct spin Hall
voltage is a measure of spin dissipation, it is directly proportional to the
enhancement of Gilbert damping. The alternating spin Hall voltage exhibits a
similar in-plane wave-number dependence, and we demonstrate that it is greatest
for surface-localized modes.",1612.07020v2
2019-10-29,Perpendicular magnetic anisotropy in Pt/Co-based full Heusler alloy/MgO thin films structures,"Perpendicular magnetic anisotropy (PMA) in ultrathin magnetic structures is a
key ingredient for the development of electrically controlled spintronic
devices. Due to their relatively large spin-polarization, high Curie
temperature and low Gilbert damping the Co-based full Heusler alloys are of
special importance from a scientific and applications point of view. Here, we
study the mechanisms responsible for the PMA in Pt/Co-based full Heusler
alloy/MgO thin films structures. We show that the ultrathin Heusler films
exhibit strong PMA even in the absence of magnetic annealing. By means of
ferromagnetic resonance experiments, we demonstrate that the effective
magnetization shows a two-regime behavior depending on the thickness of the
Heusler layers. Using Auger spectroscopy measurements, we evidence
interdiffusion at the underlayer/Heusler interface and the formation of an
interfacial CoFe-rich layer which causes the two-regime behavior. In the case
of the ultrathin films, the interfacial CoFe-rich layer promotes the strong PMA
through the electronic hybridization of the metal alloy and oxygen orbitals
across the ferromagnet/MgO interface. In addition, the interfacial CoFe-rich
layer it is also generating an increase of the Gilbert damping for the
ultrathin films beyond the spin-pumping effect. Our results illustrate that the
strong PMA is not an intrinsic property of the Heusler/MgO interface but it is
actively influenced by the interdiffusion, which can be tuned by a proper
choice of the underlayer material, as we show for the case of the Pt, Ta and Cr
underlayers.",1910.13107v1
2020-10-15,Spin injection characteristics of Py/graphene/Pt by gigahertz and terahertz magnetization dynamics driven by femtosecond laser pulse,"Spin transport characteristics of graphene has been extensively studied so
far. The spin transport along c-axis is however reported by rather limited
number of papers. We have studied spin transport characteristics through
graphene along c-axis with permalloy(Py)/graphene(Gr)/Pt by gigahertz (GHz) and
terahertz (THz) magnetization dynamics driven by femtosecond laser pulses. The
relatively simple sample structure does not require electrodes on the sample.
The graphene layer was prepared by chemical vapor deposition and transferred on
Pt film. The quality of graphene layer was characterized by Raman microscopy.
Time resolved magneto-optical Kerr effect is used to characterize gigahertz
magnetization dynamics. Magnetization precession is clearly observed both for
Pt/Py and Pt/Gr/Py. The Gilbert damping constant of Pt/Py was 0.015, indicates
spin pumping effect from Py to Pt. The Gilbert damping constant of Pt/Gr/Py is
found to be 0.011, indicates spin injection is blocked by graphene layer. We
have also performed the measurement of THz emission for Pt/Py and Pt/Gr/Py.
While the THz emission is clearly observed for Pt/Py, a strong reduction of THz
emission is observed for Pt/Gr/Py. With these two different experiments, and
highly anisotropic resistivity of graphite, we conclude that the vertical spin
transport is strongly suppressed by the graphene layer.",2010.07694v1
2021-03-17,Spin injection efficiency at metallic interfaces probed by THz emission spectroscopy,"Terahertz (THz) spin-to-charge conversion has become an increasingly
important process for THz pulse generation and as a tool to probe ultrafast
spin interactions at magnetic interfaces. However, its relation to traditional,
steady state, ferromagnetic resonance techniques is poorly understood. Here we
investigate nanometric trilayers of Co/X/Pt (X=Ti, Au or Au0:85W0:15) as a
function of the 'X' layer thickness, where THz emission generated by the
inverse spin Hall effect is compared to the Gilbert damping of the
ferromagnetic resonance. Through the insertion of the 'X' layer we show that
the ultrafast spin current injected in the non-magnetic layer defines a direct
spin conductance, whereas the Gilbert damping leads to an effective spin
mixing-conductance of the trilayer. Importantly, we show that these two
parameters are connected to each other and that spin-memory losses can be
modeled via an effective Hamiltonian with Rashba fields. This work highlights
that magneto-circuits concepts can be successfully extended to ultrafast
spintronic devices, as well as enhancing the understanding of spin-to-charge
conversion processes through the complementarity between ultrafast THz
spectroscopy and steady state techniques.",2103.09557v1
2021-09-13,Control of magnetization dynamics by substrate orientation in YIG thin films,"Yttrium Iron Garnet (YIG) and bismuth (Bi) substituted YIG (Bi0.1Y2.9Fe5O12,
BYG) films are grown in-situ on single crystalline Gadolinium Gallium Garnet
(GGG) substrates [with (100) and (111) orientations] using pulsed laser
deposition (PLD) technique. As the orientation of the Bi-YIG film changes from
(100) to (111), the lattice constant is enhanced from 12.384 {\AA} to 12.401
{\AA} due to orientation dependent distribution of Bi3+ ions at dodecahedral
sites in the lattice cell. Atomic force microscopy (AFM) images show smooth
film surfaces with roughness 0.308 nm in Bi-YIG (111). The change in substrate
orientation leads to the modification of Gilbert damping which, in turn, gives
rise to the enhancement of ferromagnetic resonance (FMR) line width. The best
values of Gilbert damping are found to be (0.54)*10-4, for YIG (100) and
(6.27)*10-4, for Bi-YIG (111) oriented films. Angle variation measurements of
the Hr are also performed, that shows a four-fold symmetry for the resonance
field in the (100) grown film. In addition, the value of effective
magnetization (4{\pi}Meff) and extrinsic linewidth ({\Delta}H0) are observed to
be dependent on substrate orientation. Hence PLD growth can assist
single-crystalline YIG and BYG films with a perfect interface that can be used
for spintronics and related device applications.",2109.05901v1
2022-06-06,Probing spin dynamics of ultra-thin van der Waals magnets via photon-magnon coupling,"Layered van der Waals (vdW) magnets can maintain a magnetic order even down
to the single-layer regime and hold promise for integrated spintronic devices.
While the magnetic ground state of vdW magnets was extensively studied, key
parameters of spin dynamics, like the Gilbert damping, crucial for designing
ultra-fast spintronic devices, remains largely unexplored. Despite recent
studies by optical excitation and detection, achieving spin wave control with
microwaves is highly desirable, as modern integrated information technologies
predominantly are operated with these. The intrinsically small numbers of
spins, however, poses a major challenge to this.
  Here, we present a hybrid approach to detect spin dynamics mediated by
photon-magnon coupling between high-Q superconducting resonators and ultra-thin
flakes of Cr$_2$Ge$_2$Te$_6$ (CGT) as thin as 11\,nm. We test and benchmark our
technique with 23 individual CGT flakes and extract an upper limit for the
Gilbert damping parameter. These results are crucial in designing on-chip
integrated circuits using vdW magnets and offer prospects for probing spin
dynamics of monolayer vdW magnets.",2206.02460v2
2022-09-01,Growth parameters of Bi0.1Y2.9Fe5O12 thin films for high frequency applications,"The growth and characterization of Bismuth (Bi) substituted YIG (Bi-YIG,
Bi0.1Y2.9Fe5O12) thin films are reported. Pulsed laser deposited (PLD) films
with thicknesses ranging from 20 to 150 nm were grown on Gadolinium Gallium
Garnet substrates. Two substrate orientations of (100) and (111) were
considered. The enhanced distribution of Bi3+ ions at dodecahedral site along
(111) is observed to lead to an increment in lattice constant from 12.379
angstrom in (100) to 12.415 angstrom in (111) oriented films. Atomic force
microscopy images showed decreasing roughness with increasing film thickness.
Compared to (100) grown films, (111) oriented films showed an increase in
ferromagnetic resonance linewidth and consequent increase in Gilbert damping.
The lowest Gilbert damping values are found to be (1.06) * 10E-4 for (100) and
(2.30) * 10E-4 for (111) oriented films with thickness of 150 nm. The observed
values of extrinsic linewidth, effective magnetization, and anisotropic field
are related to thickness of the films and substrate orientation. In addition,
the in-plane angular variation established four-fold symmetry for the (100)
deposited films unlike the case of (111) deposited films. This study prescribes
growth conditions for PLD grown single-crystalline Bi-YIG films towards desired
high frequency and magneto-optical device applications.",2209.00558v1
2023-03-13,Experimental investigation of the effect of topological insulator on the magnetization dynamics of ferromagnetic metal: $BiSbTe_{1.5}Se_{1.5}$ and $Ni_{80}Fe_{20}$ heterostructure,"We have studied ferromagnetic metal/topological insulator bilayer system to
understand magnetization dynamics of ferromagnetic metal (FM) in contact with a
topological insulator (TI). At magnetic resonance condition, the precessing
magnetization in the metallic ferromagnet ($Ni_{80}Fe_{20}$) injects spin
current into the topological insulator ($BiSbTe_{1.5}Se_{1.5}$), a phenomenon
known as spin-pumping. Due to the spin pumping effect, fast relaxation in the
ferromagnet results in the broadening of ferromagnetic resonance linewidth
($\Delta H$). We evaluated the parameters like effective Gilbert damping
coefficient ($\alpha_{eff}$), spin-mixing conductance ($g_{eff}^{\uparrow
\downarrow}$) and spin current density ($j_S^0$) to confirm a successful spin
injection due to spin-pumping into the $BiSbTe_{1.5}Se_{1.5}$ layer. TIs embody
a spin-momentum locked surface state that span the bulk band-gap. It can act
differently to the FM magnetization than the other normal metals. To probe the
effect of topological surface state, a systematic low temperature study is
crucial as surface state of TI dominates at lower temperatures. The exponential
growth of $\Delta H$ for all different thickness combination of FM/TI bilayers
and effective Gilbert damping coefficient ($\alpha_{eff}$) with lowering
temperature confirms the prediction that spin chemical bias generated from
spin-pumping induces surface current in TI due to spin-momentum locking. The
hump-like feature of magnetic anisotropy field ($H_K$)of the bilayer around 60K
suggests that the decrease of interfacial in-plane magnetic anisotropy can
result from exchange coupling between the TI surface state and the local
moments of FM layer.",2303.07025v2
2017-02-27,Current Induced Damping of Nanosized Quantum Moments in the Presence of Spin-Orbit Interaction,"Motivated by the need to understand current-induced magnetization dynamics at
the nanoscale, we have developed a formalism, within the framework of Keldysh
Green function approach, to study the current-induced dynamics of a
ferromagnetic (FM) nanoisland overlayer on a spin-orbit-coupling (SOC) Rashba
plane. In contrast to the commonly employed classical micromagnetic LLG
simulations the magnetic moments of the FM are treated {\it quantum
mechanically}. We obtain the density matrix of the whole system consisting of
conduction electrons entangled with the local magnetic moments and calculate
the effective damping rate of the FM. We investigate two opposite limiting
regimes of FM dynamics: (1) The precessional regime where the magnetic
anisotropy energy (MAE) and precessional frequency are smaller than the
exchange interactions, and (2) The local spin-flip regime where the MAE and
precessional frequency are comparable to the exchange interactions. In the
former case, we show that due to the finite size of the FM domain, the
\textquotedblleft Gilbert damping\textquotedblright does not diverge in the
ballistic electron transport regime, in sharp contrast to Kambersky's breathing
Fermi surface theory for damping in metallic FMs. In the latter case, we show
that above a critical bias the excited conduction electrons can switch the
local spin moments resulting in demagnetization and reversal of the
magnetization. Furthermore, our calculations show that the bias-induced
antidamping efficiency in the local spin-flip regime is much higher than that
in the rotational excitation regime.",1702.08408v2
2018-12-18,Thermal gradient driven domain wall dynamics,"The issue of whether a thermal gradient acts like a magnetic field or an
electric current in the domain wall (DW) dynamics is investigated. Broadly
speaking, magnetization control knobs can be classified as energy-driving or
angular-momentum driving forces. DW propagation driven by a static magnetic
field is the best-known example of the former in which the DW speed is
proportional to the energy dissipation rate, and the current-driven DW motion
is an example of the latter. Here we show that DW propagation speed driven by a
thermal gradient can be fully explained as the angular momentum transfer
between thermally generated spin current and DW. We found DW-plane rotation
speed increases as DW width decreases. Both DW propagation speed along the wire
and DW-plane rotation speed around the wire decrease with the Gilbert damping.
These facts are consistent with the angular momentum transfer mechanism, but
are distinct from the energy dissipation mechanism. We further show that
magnonic spin-transfer torque (STT) generated by a thermal gradient has both
damping-like and field-like components. By analyzing DW propagation speed and
DW-plane rotation speed, the coefficient ( \b{eta}) of the field-like STT
arising from the non-adiabatic process, is obtained. It is found that \b{eta}
does not depend on the thermal gradient; increases with uniaxial anisotropy
K_(||) (thinner DW); and decreases with the damping, in agreement with the
physical picture that a larger damping or a thicker DW leads to a better
alignment between the spin-current polarization and the local magnetization, or
a better adiabaticity.",1812.07244v2
2021-06-16,Spin-Torque-driven Terahertz Auto Oscillations in Non-Collinear Coplanar Antiferromagnets,"We theoretically and numerically study the terahertz auto oscillations in
thin-film metallic non-collinear coplanar antiferromagnets (AFMs), such as
$\mathrm{Mn_{3}Sn}$ and $\mathrm{Mn_{3}Ir}$, under the effect of anti-damping
spin-torque with spin polarization perpendicular to the plane of the film. To
obtain the order parameter dynamics in these AFMs, we solve three
Landau-Lifshitz-Gilbert equations coupled by exchange interactions assuming
both single- and multi-domain (micromagnetics) dynamical processes. In the
limit of strong exchange interaction, the oscillatory dynamics of the order
parameter in these AFMs, which have opposite chiralities, could be mapped to
that of a linear damped-driven pendulum in the case of $\mathrm{Mn_{3}Sn}$, and
a non-linear damped-driven pendulum in case of $\mathrm{Mn_{3}Ir}$. The
theoretical framework allows us to identify the input current requirements as a
function of the material and geometry parameters for exciting an oscillatory
response. We also obtain a closed-form approximate solution of the oscillation
frequency for large input currents in case of both $\mathrm{Mn_{3}Ir}$ and
$\mathrm{Mn_{3}Sn}$. Our analytical predictions of threshold current and
oscillation frequency agree well with the numerical results and thus can be
used as compact models to design and optimize the auto oscillator. Employing a
circuit model, based on the principle of tunnel anisotropy magnetoresistance,
we present detailed models of the output power and efficiency versus
oscillation frequency of the auto oscillator. Finally, we explore the spiking
dynamics of two unidirectional as well as bidirectional coupled AFM oscillators
using non-linear damped-driven pendulum equations.",2106.08528v2
2023-01-30,Investigation of Ultrafast Demagnetization and Gilbert Damping and their Correlation in Different Ferromagnetic Thin Films Grown Under Identical Conditions,"Following the demonstration of laser-induced ultrafast demagnetization in
ferromagnetic nickel, several theoretical and phenomenological propositions
have sought to uncover its underlying physics. In this work we revisit the
three temperature model (3TM) and the microscopic three temperature model
(M3TM) to perform a comparative analysis of ultrafast demagnetization in
20-nm-thick cobalt, nickel and permalloy thin films measured using an
all-optical pump-probe technique. In addition to the ultrafast dynamics at the
femtosecond timescales, the nanosecond magnetization precession and damping are
recorded at various pump excitation fluences revealing a fluence-dependent
enhancement in both the demagnetization times and the damping factors. We
confirm that the Curie temperature to magnetic moment ratio of a given system
acts as a figure of merit for the demagnetization time, while the
demagnetization times and damping factors show an apparent sensitivity to the
density of states at the Fermi level for a given system. Further, from
numerical simulations of the ultrafast demagnetization based on both the 3TM
and the M3TM, we extract the reservoir coupling parameters that best reproduce
the experimental data and estimate the value of the spin flip scattering
probability for each system. We discuss how the fluence-dependence of
inter-reservoir coupling parameters so extracted may reflect a role played by
nonthermal electrons in the magnetization dynamics at low laser fluences.",2301.12797v1
2001-03-30,Thermal magnetization fluctuations in thin films and a new physical form for magnetization damping,"The effect of thermal fluctuations on a thin film magnetoresistive element
has been calculated. The technique involves adding to the basic spin dynamics a
general form of interaction with a thermal bath. For a general anisotropic
magnetic system the resulting equation can be written as a Langevin equation
for a harmonic oscillator. Our approach predicts two times smaller noise power
at low frequencies than the conventional stochastic Landau-Lifshitz-Gilbert
equation. It is shown that equivalent results can be obtained by introducing a
tensor phenomenological damping term to the gyromagnetic dynamics driven by a
thermal fluctuating field.",0103624v3
2004-02-03,First-principles study of magnetization relaxation enhancement and spin-transfer in thin magnetic films,"The interface-induced magnetization damping of thin ferromagnetic films in
contact with normal-metal layers is calculated from first principles for clean
and disordered Fe/Au and Co/Cu interfaces. Interference effects arising from
coherent scattering turn out to be very small, consistent with a very small
magnetic coherence length. Because the mixing conductances which govern the
spin transfer are to a good approximation real valued, the spin pumping can be
described by an increased Gilbert damping factor but an unmodified gyromagnetic
ratio. The results also confirm that the spin-current induced magnetization
torque is an interface effect.",0402088v2
2005-02-28,Magnetization dynamics of two interacting spins in an external magnetic field,"The longitudinal relaxation time of the magnetization of a system of two
exchange coupled spins subjected to a strong magnetic field is calculated
exactly by averaging the stochastic Gilbert-Landau-Lifshitz equation for the
magnetization, i.e., the Langevin equation of the process, over its
realizations so reducing the problem to a system of linear
differential-recurrence relations for the statistical moments (averaged
spherical harmonics). The system is solved in the frequency domain by matrix
continued fractions yielding the complete solution of the two-spin problem in
external fields for all values of the damping and barrier height parameters.
The magnetization relaxation time extracted from the exact solution is compared
with the inverse relaxation rate from Langer's theory of the decay of
metastable states, which yields in the high barrier and intermediate-to-high
damping limits the asymptotic behaviour of the greatest relaxation time.",0502661v2
2007-06-28,Coherent Magnetization Precession in GaMnAs induced by Ultrafast Optical Excitation,"We use femtosecond optical pulses to induce, control and monitor
magnetization precession in ferromagnetic Ga0.965Mn0.035As. At temperatures
below ~40 K we observe coherent oscillations of the local Mn spins, triggered
by an ultrafast photoinduced reorientation of the in-plane easy axis. The
amplitude saturation of the oscillations above a certain pump intensity
indicates that the easy axis remains unchanged above ~TC/2. We find that the
observed magnetization precession damping (Gilbert damping) is strongly
dependent on pump laser intensity, but largely independent on ambient
temperature. We provide a physical interpretation of the observed light-induced
collective Mn-spin relaxation and precession.",0706.4270v2
2008-02-14,Light-induced magnetization precession in GaMnAs,"We report dynamics of the transient polar Kerr rotation (KR) and of the
transient reflectivity induced by femtosecond laser pulses in ferromagnetic
(Ga,Mn)As with no external magnetic field applied. It is shown that the
measured KR signal consist of several different contributions, among which only
the oscillatory signal is directly connected with the ferromagnetic order in
(Ga,Mn)As. The origin of the light-induced magnetization precession is
discussed and the magnetization precession damping (Gilbert damping) is found
to be strongly influenced by annealing of the sample.",0802.2043v2
2008-09-17,Spin-transfer torque induced reversal in magnetic domains,"Using the complex stereographic variable representation for the macrospin,
from a study of the nonlinear dynamics underlying the generalized
Landau-Lifshitz(LL) equation with Gilbert damping, we show that the
spin-transfer torque is effectively equivalent to an applied magnetic field. We
study the macrospin switching on a Stoner particle due to spin-transfer torque
on application of a spin polarized current. We find that the switching due to
spin-transfer torque is a more effective alternative to switching by an applied
external field in the presence of damping. We demonstrate numerically that a
spin-polarized current in the form of a short pulse can be effectively employed
to achieve the desired macro-spin switching.",0809.2910v1
2009-12-30,Spin torque and critical currents for magnetic vortex nano-oscillator in nanopillars,"We calculated the main dynamic parameters of the spin polarized current
induced magnetic vortex oscillations in nanopillars, such as the range of
current density, where a vortex steady oscillations exist, the oscillation
frequency and orbit radius. We accounted for both the non-linear vortex
frequency and non-linear vortex damping. To describe the vortex excitations by
the spin polarized current we used a generalized Thiele approach to motion of
the vortex core as a collective coordinate. All the calculation results are
represented via the free layer sizes, saturation magnetization, Gilbert damping
and the degree of the spin polarization of the fixed layer. Predictions of the
developed model can be checked experimentally.",0912.5521v1
2010-10-01,Ferromagnetic resonance study of Co/Pd/Co/Ni multilayers with perpendicular anisotropy irradiated with Helium ions,"We present a ferromagnetic resonance (FMR) study of the effect of Helium ion
irradiation on the magnetic anisotropy, the linewidth and the Gilbert damping
of a Co/Ni multilayer coupled to Co/Pd bilayers. The perpendicular magnetic
anisotropy decreases linearly with He ion fluence, leading to a transition to
in-plane magnetization at a critical fluence of 5x10^{14} ions/cm^2. We find
that the damping is nearly independent of fluence but the FMR linewidth at
fixed frequency has a maximum near the critical fluence, indicating that the
inhomogeneous broadening of the FMR line is a non-monotonic function of the He
ion fluence. Based on an analysis of the angular dependence of the FMR
linewidth, the inhomogeneous broadening is associated with spatial variations
in the magnitude of the perpendicular magnetic anisotropy. These results
demonstrate that ion irradiation may be used to systematically modify the
magnetic anisotropy and distribution of magnetic anisotropy parameters of
Co/Pd/Co/Ni multilayers for applications and basic physics studies.",1010.0268v2
2010-11-23,Ultra-fast magnetisation rates within the Landau-Lifshitz-Bloch model,"The ultra-fast magnetisation relaxation rates during the laser-induced
magnetisation process are analyzed in terms of the Landau-Lifshitz-Bloch (LLB)
equation for different values of spin $S$. The LLB equation is equivalent in
the limit $S \rightarrow \infty$ to the atomistic Landau-Lifshitz-Gilbert (LLG)
Langevin dynamics and for $S=1/2$ to the M3TM model [B. Koopmans, {\em et al.}
Nature Mat. \textbf{9} (2010) 259]. Within the LLB model the ultra-fast
demagnetisation time ($\tau_{M}$) and the transverse damping ($\alpha_{\perp}$)
are parameterized by the intrinsic coupling-to-the-bath parameter $\lambda$,
defined by microscopic spin-flip rate. We show that for the phonon-mediated
Elliott-Yafet mechanism, $\lambda$ is proportional to the ratio between the
non-equilibrium phonon and electron temperatures.
  We investigate the influence of the finite spin number and the scattering
rate parameter $\lambda$ on the magnetisation relaxation rates. The relation
between the fs demagnetisation rate and the LLG damping, provided by the LLB
theory, is checked basing on the available experimental data. A good agreement
is obtained for Ni, Co and Gd favoring the idea that the same intrinsic
scattering process is acting on the femtosecond and nanosecond timescale.",1011.5054v1
2011-10-15,Atomistic spin dynamic method with both damping and moment of inertia effects included from first principles,"We consider spin dynamics for implementation in an atomistic framework and we
address the feasibility of capturing processes in the femtosecond regime by
inclusion of moment of inertia. In the spirit of an {\it s-d} -like interaction
between the magnetization and electron spin, we derive a generalized equation
of motion for the magnetization dynamics in the semi-classical limit, which is
non-local in both space and time. Using this result we retain a generalized
Landau-Lifshitz-Gilbert equation, also including the moment of inertia, and
demonstrate how the exchange interaction, damping, and moment of inertia, all
can be calculated from first principles.",1110.3387v2
2011-10-24,CoB/Ni-Based Multilayer Nanowire with High-Speed Domain Wall Motion under Low Current Control,"The spin-transfer torque motion of magnetic domain walls (DWs) in a
CoB/Ni-based nanowire driven by a low current density of
(1.12\pm0.8)\times10^{11} A m^{-2} has been observed indirectly by
magnetotransport measurements. A high DW velocity of 85\pm4 m/s at zero field
was measured at the threshold current density. Upon increasing the current
density to 2.6\times10^{11} A m^{-2}, the DW velocity increases to 197\pm16 m/s
before decreasing quickly in the high-current-density regime attributed to
nonadiabatic spin-transfer torque at a low damping factor and weak pinning. The
addition of B atoms to the Co layers decreased the magnitude of saturation
magnetization, Gilbert damping factor, and density of pinning sites, making the
CoB/Ni multilayer nanowire favorable for practical applications.",1110.5112v3
2012-09-17,Nonlinear emission of spin-wave caustics from an edge mode of a micro-structured Co2Mn0.6Fe0.4Si waveguide,"Magnetic Heusler materials with very low Gilbert damping are expected to show
novel magnonic transport phenomena. We report nonlinear generation of higher
harmonics leading to the emission of caustic spin-wave beams in a low-damping,
micro-structured Co2Mn0.6Fe0.4Si Heusler waveguide. The source for the higher
harmonic generation is a localized edge mode formed by the strongly
inhomogeneous field distribution at the edges of the spin-wave waveguide. The
radiation characteristics of the propagating caustic waves observed at twice
and three times the excitation frequency are described by an analytical
calculation based on the anisotropic dispersion of spin waves in a magnetic
thin film.",1209.3669v2
2013-07-10,"Scaling of spin Hall angle in 3d, 4d and 5d metals from Y3Fe5O12/metal spin pumping","Pure spin currents generated by spin pumping in ferromagnet/nonmagnet (FM/NM)
bilayers produce inverse spin Hall effect (ISHE) voltages in the NM, from which
spin pumping and transport characteristics of the NM can be extracted. Due to
its exceptionally low damping, Y3Fe5O12 (YIG) is an important and widely used
FM for microwave devices and ferromagnetic resonance (FMR) spin pumping. Here
we report systematic investigation of spin pumping from 20-nm thick YIG thin
films to a series of 3d, 4d and 5d normal metals (Cu, Ag, Ta, W, Pt and Au)
with various spin-orbit coupling strengths. From enhanced Gilbert damping
obtained from the frequency dependence of FMR linewidths and ISHE signals, the
spin Hall angles and YIG/NM interfacial spin mixing conductances are
quantitatively determined for these metals. The spin Hall angles largely vary
as the fourth power of the atomic number, corroborating the dominant role of
spin-orbit coupling across a broad range in the inverse spin Hall effect.",1307.2648v2
2013-11-25,Spin-wave excitation and propagation in microstructured waveguides of yttrium iron garnet (YIG)/Pt bilayers,"We present an experimental study of spin-wave excitation and propagation in
microstructured waveguides patterned from a 100 nm thick yttrium iron garnet
(YIG)/platinum (Pt) bilayer. The life time of the spin waves is found to be
more than an order of magnitude higher than in comparably sized metallic
structures despite the fact that the Pt capping enhances the Gilbert damping.
Utilizing microfocus Brillouin light scattering spectroscopy, we reveal the
spin-wave mode structure for different excitation frequencies. An exponential
spin-wave amplitude decay length of 31 {\mu}m is observed which is a
significant step towards low damping, insulator based micro-magnonics.",1311.6305v1
2014-10-02,Investigation of the temperature-dependence of ferromagnetic resonance and spin waves in Co2FeAl0.5Si0.5,"Co2FeAl0.5Si0.5 (CFAS) is a Heusler compound that is of interest for
spintronics applications, due to its high spin polarization and relatively low
Gilbert damping constant. In this study, the behavior of ferromagnetic
resonance as a function of temperature was investigated in CFAS, yielding a
decreasing trend of damping constant as the temperature was increased from 13
to 300 K. Furthermore, we studied spin waves in CFAS using both frequency
domain and time domain techniques, obtaining group velocities and attenuation
lengths as high as 26 km/s and 23.3 um, respectively, at room temperature.",1410.0439v1
2014-12-12,Spin waves in micro-structured yttrium iron garnet nanometer-thick films,"We investigated the spin-wave propagation in a micro-structured yttrium iron
garnet waveguide of $40$ nm thickness. Utilizing spatially-resolved Brillouin
light scattering microscopy, an exponential decay of the spin-wave amplitude of
$(10.06 \pm 0.83)$ $\mu$m was observed. This leads to an estimated Gilbert
damping constant of $\alpha=(8.79\pm 0.73)\times 10^{-4}$, which is larger than
damping values obtained through ferromagnetic resonance measurements in
unstructured films. The theoretically calculated spatial interference of
waveguide modes was compared to the spin-wave pattern observed experimentally
by means of Brillouin light scattering spectroscopy.",1412.4032v1
2016-04-16,A broadband Ferromagnetic Resonance dipper probe for magnetic damping measurements from 4.2 K to 300 K,"A dipper probe for broadband Ferromagnetic Resonance (FMR) operating from 4.2
K to room temperature is described. The apparatus is based on a 2-port
transmitted microwave signal measurement with a grounded coplanar waveguide.
The waveguide generates a microwave field and records the sample response. A
3-stage dipper design is adopted for fast and stable temperature control. The
temperature variation due to FMR is in the milli-Kelvin range at liquid helium
temperature. We also designed a novel FMR probe head with a spring-loaded
sample holder. Improved signal-to-noise ratio and stability compared to a
common FMR head are achieved. Using a superconducting vector magnet we
demonstrate Gilbert damping measurements on two thin film samples using a
vector network analyzer with frequency up to 26 GHz: 1) A Permalloy film of 5
nm thickness and 2) a CoFeB film of 1.5 nm thickness. Experiments were
performed with the applied magnetic field parallel and perpendicular to the
film plane.",1604.04688v1
2016-05-27,A reduced model for precessional switching of thin-film nanomagnets under the influence of spin-torque,"We study the magnetization dynamics of thin-film magnetic elements with
in-plane magnetization subject to a spin-current flowing perpendicular to the
film plane. We derive a reduced partial differential equation for the in-plane
magnetization angle in a weakly damped regime. We then apply this model to
study the experimentally relevant problem of switching of an elliptical element
when the spin-polarization has a component perpendicular to the film plane,
restricting the reduced model to a macrospin approximation. The macrospin
ordinary differential equation is treated analytically as a weakly damped
Hamiltonian system, and an orbit-averaging method is used to understand
transitions in solution behaviors in terms of a discrete dynamical system. The
predictions of our reduced model are compared to those of the full
Landau--Lifshitz--Gilbert--Slonczewski equation for a macrospin.",1605.08698v1
2016-06-21,Torsion Effects and LLG Equation,"Based on the non-relativistic regime of the Dirac equation coupled to a
torsion pseudo-vector, we study the dynamics of magnetization and how it is
affected by the presence of torsion. We consider that torsion interacting terms
in Dirac equation appear in two ways one of these is thhrough the covariant
derivative considering the spin connection and gauge magnetic field and the
other is through a non-minimal spin torsion coupling. We show within this
framework, that it is possible to obtain the most general Landau, Lifshitz and
Gilbert (LLG) equation including the torsion effects, where we refer to torsion
as a geometric field playing an important role in the spin coupling process. We
show that the torsion terms can give us two important landscapes in the
magnetization dynamics: one of them related with damping and the other related
with the screw dislocation that give us a global effect like a helix damping
sharped. These terms are responsible for changes in the magnetization
precession dynamics.",1606.06610v1
2016-07-05,Magnetic moment of inertia within the breathing model,"An essential property of magnetic devices is the relaxation rate in magnetic
switching which strongly depends on the energy dissipation and magnetic inertia
of the magnetization dynamics. Both parameters are commonly taken as a
phenomenological entities. However very recently, a large effort has been
dedicated to obtain Gilbert damping from first principles. In contrast, there
is no ab initio study that so far has reproduced measured data of magnetic
inertia in magnetic materials. In this letter, we present and elaborate on a
theoretical model for calculating the magnetic moment of inertia based on the
torque-torque correlation model. Particularly, the method has been applied to
bulk bcc Fe, fcc Co and fcc Ni in the framework of the tight-binding
approximation and the numerical values are comparable with recent experimental
measurements. The theoretical results elucidate the physical origin of the
moment of inertia based on the electronic structure. Even though the moment of
inertia and damping are produced by the spin-orbit coupling, our analysis shows
that they are caused by undergo different electronic structure mechanisms.",1607.01307v1
2016-10-14,Nambu mechanics for stochastic magnetization dynamics,"The Landau-Lifshitz-Gilbert (LLG) equation describes the dynamics of a damped
magnetization vector that can be understood as a generalization of Larmor spin
precession. The LLG equation cannot be deduced from the Hamiltonian framework,
by introducing a coupling to a usual bath, but requires the introduction of
additional constraints. It is shown that these constraints can be formulated
elegantly and consistently in the framework of dissipative Nambu mechanics.
This has many consequences for both the variational principle and for
topological aspects of hidden symmetries that control conserved quantities. We
particularly study how the damping terms of dissipative Nambu mechanics affect
the consistent interaction of magnetic systems with stochastic reservoirs and
derive a master equation for the magnetization. The proposals are supported by
numerical studies using symplectic integrators that preserve the topological
structure of Nambu equations. These results are compared to computations
performed by direct sampling of the stochastic equations and by using closure
assumptions for the moment equations, deduced from the master equation.",1610.04598v2
2017-01-31,"Lack of correlation between the spin mixing conductance and the ISHE-generated voltages in CoFeB/Pt,Ta bilayers","We investigate spin pumping phenomena in polycrystalline CoFeB/Pt and
CoFeB/Ta bilayers and the correlation between the effective spin mixing
conductance $g^{\uparrow\downarrow}_{\rm eff}$ and the obtained voltages
generated by the spin-to-charge current conversion via the inverse spin Hall
effect in the Pt and Ta layers. For this purpose we measure the in-plane
angular dependence of the generated voltages on the external static magnetic
field and we apply a model to separate the spin pumping signal from the one
generated by the spin rectification effect in the magnetic layer. Our results
reveal a dominating role of anomalous Hall effect for the spin rectification
effect with CoFeB and a lack of correlation between
$g^{\uparrow\downarrow}_{\rm eff}$ and inverse spin Hall voltages pointing to a
strong role of the magnetic proximity effect in Pt in understanding the
observed increased damping. This is additionally reflected on the presence of a
linear dependency of the Gilbert damping parameter on the Pt thickness.",1701.09110v1
2017-06-05,Consistent microscopic analysis of spin pumping effects,"We present a consistent microscopic study of spin pumping effects for both
metallic and insulating ferromagnets. As for metallic case, we present a simple
quantum mechanical picture of the effect as due to the electron spin flip as a
result of a nonadiabatic (off-diagonal) spin gauge field. The effect of
interface spin-orbit interaction is briefly discussed. We also carry out
field-theoretic calculation to discuss on the equal footing the spin current
generation and torque effects such as enhanced Gilbert damping constant and
shift of precession frequency both in metallic and insulating cases. For thick
ferromagnetic metal, our study reproduces results of previous theories such as
the correspondence between the dc component of the spin current and enhancement
of the damping. For thin metal and insulator, the relation turns out to be
modified. For the insulating case, driven locally by interface $sd$ exchange
interaction due to magnetic proximity effect, physical mechanism is distinct
from the metallic case. Further study of proximity effect and interface
spin-orbit interaction would be crucial to interpret experimental results in
particular for insulators.",1706.01185v1
2018-03-04,Optimization of Time-Resolved Magneto-optical Kerr Effect Signals for Magnetization Dynamics Measurements,"Recently magnetic storage and magnetic memory have shifted towards the use of
magnetic thin films with perpendicular magnetic anisotropy (PMA). Understanding
the magnetic damping in these materials is crucial, but normal Ferromagnetic
Resonance (FMR) measurements face some limitations. The desire to quantify the
damping in materials with PMA has resulted in the adoption of Time-Resolved
Magneto-optical Kerr Effect (TR-MOKE) measurements. In this paper, we discuss
the angle and field dependent signals in TR-MOKE, and utilize a numerical
algorithm based on the Landau-Lifshitz-Gilbert (LLG) equation to provide
information on the optimal conditions to run TR-MOKE measurements.",1803.01280v2
2018-05-04,Superparamagnetic Relaxation Driven by Colored Noise,"A theoretical investigation of magnetic relaxation processes in single domain
particles driven by colored noise is presented. Two approaches are considered;
the Landau-Lifshitz-Miyazaki-Seki equation, which is a Langevin dynamics model
based on the introduction of an Ornstein-Uhlenbeck correlated noise into the
Landau-Lifshitz-Gilbert equation and a Generalized Master Equation approach
whereby the ordinary Master Equation is modified through the introduction of an
explicit memory kernel. It is found that colored noise is likely to become
important for high anisotropy materials where the characteristic system time,
in this case the inverse Larmor precession frequency, becomes comparable to the
correlation time. When the escape time is much longer than the correlation
time, the relaxation profile of the spin has a similar exponential form to the
ordinary LLG equation, while for low barrier heights and intermediate damping,
for which the correlation time is a sizable fraction of the escape time, an
unusual bi-exponential decay is predicted as a characteristic of colored noise.
At very high damping and correlation times, the time profile of the spins
exhibits a more complicated, noisy trajectory.",1805.01776v2
2018-06-02,Ultra-low damping insulating magnetic thin films get perpendicular,"A magnetic material combining low losses and large Perpendicular Magnetic
Anisotropy (PMA) is still a missing brick in the magnonic and spintronic
fields. We report here on the growth of ultrathin Bismuth doped
Y$_{3}$Fe$_{5}$O$_{12}$ (BiYIG) films on Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) and
substituted GGG (sGGG) (111) oriented substrates. A fine tuning of the PMA is
obtained using both epitaxial strain and growth induced anisotropies. Both
spontaneously in-plane and out-of-plane magnetized thin films can be
elaborated. Ferromagnetic Resonance (FMR) measurements demonstrate the high
dynamic quality of these BiYIG ultrathin films, PMA films with Gilbert damping
values as low as 3 10$^{-4}$ and FMR linewidth of 0.3 mT at 8 GHz are achieved
even for films that do not exceed 30 nm in thickness. Moreover, we measure
Inverse Spin Hall Effect (ISHE) on Pt/BiYIG stacks showing that the magnetic
insulator$'$s surface is transparent to spin current making it appealing for
spintronic applications.",1806.00658v1
2018-06-12,"Dynamical and current-induced Dzyaloshinskii-Moriya interaction: Role for damping, gyromagnetism, and current-induced torques in noncollinear magnets","Both applied electric currents and magnetization dynamics modify the
Dzyaloshinskii-Moriya interaction (DMI), which we call current-induced DMI
(CIDMI) and dynamical DMI (DDMI), respectively. We report a theory of CIDMI and
DDMI. The inverse of CIDMI consists in charge pumping by a time-dependent
gradient of magnetization $\partial^2 M(r,t)/\partial r\partial t$, while the
inverse of DDMI describes the torque generated by $\partial^2 M(r,t)/\partial
r\partial t$. In noncollinear magnets CIDMI and DDMI depend on the local
magnetization direction. The resulting spatial gradients correspond to torques
that need to be included into the theories of Gilbert damping, gyromagnetism,
and current-induced torques (CITs) in order to satisfy the Onsager reciprocity
relations. CIDMI is related to the modification of orbital magnetism induced by
magnetization dynamics, which we call dynamical orbital magnetism (DOM), and
spatial gradients of DOM contribute to charge pumping. We present applications
of this formalism to the CITs and to the torque-torque correlation in textured
Rashba ferromagnets.",1806.04782v3
2018-10-11,"Propagating spin waves in nanometer-thick yttrium iron garnet films: Dependence on wave vector, magnetic field strength and angle","We present a comprehensive investigation of propagating spin waves in
nanometer-thick yttrium iron garnet (YIG) films. We use broadband spin-wave
spectroscopy with integrated coplanar waveguides (CPWs) and microstrip antennas
on top of continuous and patterned YIG films to characterize spin waves with
wave vectors up to 10 rad/$\mu$m. All films are grown by pulsed laser
deposition. From spin-wave transmission spectra, parameters such as the Gilbert
damping constant, spin-wave dispersion relation, group velocity, relaxation
time, and decay length are derived and their dependence on magnetic bias field
strength and angle is systematically gauged. For a 40-nm-thick YIG film, we
obtain a damping constant of $3.5 \times 10^{-4}$ and a maximum decay length of
1.2 mm. Our experiments reveal a strong variation of spin-wave parameters with
magnetic bias field and wave vector. Spin-wave properties change considerably
up to a magnetic bias field of about 30 mT and above a field angle of
$\theta_{H} = 20^{\circ}$, where $\theta_{H} = 0^{\circ}$ corresponds to the
Damon-Eshbach configuration.",1810.04973v1
2019-05-30,Predicting New Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy,"Perpendicular magnetic anisotropy (PMA) is a necessary condition for many
spintronic applications like spin-orbit torques switching, logic and memory
devices. An important class of magnetic insulators with low Gilbert damping at
room temperature are iron garnets, which only have a few PMA types such as
terbium and samarium iron garnet. More and stable PMA garnet options are
necessary for researchers to be able to investigate new spintronic phenomena.
In this study, we predict 20 new substrate/magnetic iron garnet film pairs with
stable PMA at room temperature. The effective anisotropy energies of 10
different garnet films that are lattice-matched to 5 different commercially
available garnet substrates have been calculated using shape, magnetoelastic
and magnetocrystalline anisotropy terms. Strain type, tensile or compressive
depending on substrate choice, as well as the sign and the magnitude of the
magnetostriction constants of garnets determine if a garnet film may possess
PMA. We show the conditions in which Samarium, Gadolinium, Terbium, Holmium,
Dysprosium and Thulium garnets may possess PMA on the investigated garnet
substrate types. Guidelines for obtaining garnet films with low damping are
presented. New PMA garnet films with tunable saturation moment and field may
improve spin-orbit torque memory and compensated magnonic thin film devices.",1905.13042v1
2019-07-17,Inhomogeneous domain walls in spintronic nanowires,"In case of a spin-polarized current, the magnetization dynamics in nanowires
are governed by the classical Landau-Lifschitz equation with Gilbert damping
term, augmented by a typically non-variational Slonczewski term. Taking axial
symmetry into account, we study the existence of domain wall type coherent
structure solutions, with focus on one space dimension and spin-polarization,
but our results also apply to vanishing spin-torque term. Using methods from
bifurcation theory for arbitrary constant applied fields, we prove the
existence of domain walls with non-trivial azimuthal profile, referred to as
inhomogeneous. We present an apparently new type of domain wall, referred to as
non-flat, whose approach of the axial magnetization has a certain oscillatory
character. Additionally, we present the leading order mechanism for the
parameter selection of flat and non-flat inhomogeneous domain walls for an
applied field below a threshold, which depends on anisotropy, damping, and
spin-transfer. Moreover, numerical continuation results of all these domain
wall solutions are presented.",1907.07470v2
2019-09-10,Spin Pumping from Permalloy into Uncompensated Antiferromagnetic Co doped Zinc Oxide,"Heterostructures of Co-doped ZnO and Permalloy were investigated for their
static and dynamic magnetic interaction. The highly Co-doped ZnO is
paramagentic at room temperature and becomes an uncompensated antiferromagnet
at low temperatures, showing a narrowly opened hysteresis and a vertical
exchange bias shift even in the absence of any ferromagnetic layer. At low
temperatures in combination with Permalloy an exchange bias is found causing a
horizontal as well as vertical shift of the hysteresis of the heterostructure
together with an increase in coercive field. Furthermore, an increase in the
Gilbert damping parameter at room temperature was found by multifrequency FMR
evidencing spin pumping. Temperature dependent FMR shows a maximum in magnetic
damping close to the magnetic phase transition. These measurements also
evidence the exchange bias interaction of Permalloy and long-range ordered
Co-O-Co structures in ZnO, that are barely detectable by SQUID due to the
shorter probing times in FMR.",1909.04362v3
2020-02-27,Ultrafast magnetization dynamics in half-metallic Co$_2$FeAl Heusler alloy,"We report on optically induced, ultrafast magnetization dynamics in the
Heusler alloy $\mathrm{Co_{2}FeAl}$, probed by time-resolved magneto-optical
Kerr effect. Experimental results are compared to results from electronic
structure theory and atomistic spin-dynamics simulations. Experimentally, we
find that the demagnetization time ($\tau_{M}$) in films of
$\mathrm{Co_{2}FeAl}$ is almost independent of varying structural order, and
that it is similar to that in elemental 3d ferromagnets. In contrast, the
slower process of magnetization recovery, specified by $\tau_{R}$, is found to
occur on picosecond time scales, and is demonstrated to correlate strongly with
the Gilbert damping parameter ($\alpha$). Our results show that
$\mathrm{Co_{2}FeAl}$ is unique, in that it is the first material that clearly
demonstrates the importance of the damping parameter in the remagnetization
process. Based on these results we argue that for $\mathrm{Co_{2}FeAl}$ the
remagnetization process is dominated by magnon dynamics, something which might
have general applicability.",2002.12255v1
2020-06-05,Controlling the nonlinear relaxation of quantized propagating magnons in nanodevices,"Relaxation of linear magnetization dynamics is well described by the viscous
Gilbert damping processes. However, for strong excitations, nonlinear damping
processes such as the decay via magnon-magnon interactions emerge and trigger
additional relaxation channels. Here, we use space- and time-resolved
microfocused Brillouin light scattering spectroscopy and micromagnetic
simulations to investigate the nonlinear relaxation of strongly driven
propagating spin waves in yttrium iron garnet nanoconduits. We show that the
nonlinear magnon relaxation in this highly quantized system possesses
intermodal features, i.e., magnons scatter to higher-order quantized modes
through a cascade of scattering events. We further show how to control such
intermodal dissipation processes by quantization of the magnon band in
single-mode devices, where this phenomenon approaches its fundamental limit.
Our study extends the knowledge about nonlinear propagating spin waves in
nanostructures which is essential for the construction of advanced spin-wave
elements as well as the realization of Bose-Einstein condensates in scaled
systems.",2006.03400v2
2021-05-16,Anatomy of inertial magnons in ferromagnets,"We analyze dispersion relations of magnons in ferromagnetic nanostructures
with uniaxial anisotropy taking into account inertial terms, i.e. magnetic
nutation. Inertial effects are parametrized by damping-independent parameter
$\beta$, which allows for an unambiguous discrimination of inertial effects
from Gilbert damping parameter $\alpha$. The analysis of magnon dispersion
relation shows its two branches are modified by the inertial effect, albeit in
different ways. The upper nutation branch starts at $\omega=1/ \beta$, the
lower branch coincides with FMR in the long-wavelength limit and deviates from
the zero-inertia parabolic dependence $\simeq\omega_{FMR}+Dk^2$ of the exchange
magnon. Taking a realistic experimental geometry of magnetic thin films,
nanowires and nanodiscs, magnon eigenfrequencies, eigenvectors and $Q$-factors
are found to depend on the shape anisotropy. The possibility of phase-matched
magneto-elastic excitation of nutation magnons is discussed and the condition
was found to depend on $\beta$, exchange stiffness $D$ and the acoustic
velocity.",2105.07376v1
2021-11-16,Ultrathin ferrimagnetic GdFeCo films with very low damping,"Ferromagnetic materials dominate as the magnetically active element in
spintronic devices, but come with drawbacks such as large stray fields, and low
operational frequencies. Compensated ferrimagnets provide an alternative as
they combine the ultrafast magnetization dynamics of antiferromagnets with a
ferromagnet-like spin-orbit-torque (SOT) behavior. However to use ferrimagnets
in spintronic devices their advantageous properties must be retained also in
ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1-x
thin films in the thickness range t = 2-20 nm were grown on high resistance
Si(100) substrates and studied using broadband ferromagnetic resonance
measurements at room temperature. By tuning their stoichiometry, a nearly
compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1-x ultrathin films
for the first time, with an effective magnetization of Meff = 0.02 T and a low
effective Gilbert damping constant of {\alpha} = 0.0078, comparable to the
lowest values reported so far in 30 nm films. These results show great promise
for the development of ultrafast and energy efficient ferrimagnetic spintronic
devices.",2111.08768v1
2021-11-30,First and second order magnetic anisotropy and damping of europium iron garnet under high strain,"Understanding and tailoring static and dynamic properties of magnetic
insulator thin films is important for spintronic device applications. Here, we
grow atomically flat epitaxial europium iron garnet (EuIG) thin films by pulsed
laser deposition on (111)-oriented garnet substrates with a range of lattice
parameters. By controlling the lattice mismatch between EuIG and the
substrates, we tune the strain in EuIG films from compressive to tensile
regime, which is characterized by X-ray diffraction. Using ferromagnetic
resonance, we find that in addition to the first-order perpendicular magnetic
anisotropy which depends linearly on the strain, there is a significant
second-order one that has a quadratic strain dependence. Inhomogeneous
linewidth of the ferromagnetic resonance increases notably with increasing
strain, while the Gilbert damping parameter remains nearly constant (~
2x10^-2). These results provide valuable insight into the spin dynamics in
ferrimagnetic insulators and useful guidance for material synthesis and
engineering of next-generation spintronics applications.",2111.15142v1
2022-10-01,Nonlinear features of the superconductor--ferromagnet--superconductor $\varphi_0$ Josephson junction in ferromagnetic resonance region,"We demonstrate the manifestations of the nonlinear features in magnetic
dynamics and IV-characteristics of the $\varphi_0$ Josephson junction in the
ferromagnetic resonance region. We show that at small values of system
parameters, namely, damping, spin-orbit interaction, and Josephson to magnetic
energy ratio, the magnetic dynamics is reduced to the dynamics of the scalar
Duffing oscillator, driven by the Josephson oscillations. The role of
increasing superconducting current in the resonance region is clarified.
Shifting of the ferromagnetic resonant frequency and the reversal of its
damping dependence due to nonlinearity are demonstrated by the full
Landau-Lifshitz-Gilbert-Josephson system of equations, and in its different
approximations. Finally, we demonstrate the negative differential resistance in
the IV--characteristics, and its correlation with the foldover effect.",2210.00366v1
2023-12-16,Spin-torque nano-oscillator based on two in-plane magnetized synthetic ferrimagnets,"We report the dynamic characterization of the spin-torque-driven in-plane
precession modes of a spin-torque nano-oscillator based on two different
synthetic ferrimagnets: a pinned one characterized by a strong RKKY interaction
which is exchange coupled to an antiferromagnetic layer; and a second one,
non-pinned characterized by weak RKKY coupling. The microwave properties
associated with the steady-state precession of both SyFs are characterized by
high spectral purity and power spectral density. However, frequency dispersion
diagrams of the damped and spin transfer torque modes reveal drastically
different dynamical behavior and microwave emission properties in both SyFs. In
particular, the weak coupling between the magnetic layers of the non-pinned SyF
raises discontinuous dispersion diagrams suggesting a strong influence of mode
crossing. An interpretation of the different dynamical features observed in the
damped and spin torque modes of both SyF systems was obtained by solving
simultaneously, in a macrospin approach, a linearized version of the
Landau-Lifshitz-Gilbert equation including the spin transfer torque term.",2312.10451v2
2013-08-17,Thickness and power dependence of the spin-pumping effect in Y3Fe5O12/Pt heterostructures measured by the inverse spin Hall effect,"The dependence of the spin-pumping effect on the yttrium iron garnet
(Y3Fe5O12, YIG) thickness detected by the inverse spin Hall effect (ISHE) has
been investigated quantitatively. Due to the spin-pumping effect driven by the
magnetization precession in the ferrimagnetic insulator YIG film a
spin-polarized electron current is injected into the Pt layer. This spin
current is transformed into electrical charge current by means of the ISHE. An
increase of the ISHE-voltage with increasing film thickness is observed and
compared to the theoretically expected behavior. The effective damping
parameter of the YIG/Pt samples is found to be enhanced with decreasing YIG
film thickness. The investigated samples exhibit a spin mixing conductance of
g=(7.43 \pm 0.36) \times 10^{18} m^{-2} and a spin Hall angle of theta_{ISHE} =
0.009 \pm 0.0008. Furthermore, the influence of nonlinear effects on the
generated voltage and on the Gilbert damping parameter at high excitation
powers are revealed. It is shown that for small YIG film thicknesses a
broadening of the linewidth due to nonlinear effects at high excitation powers
is suppressed because of a lack of nonlinear multi-magnon scattering channels.
We have found that the variation of the spin-pumping efficiency for thick YIG
samples exhibiting pronounced nonlinear effects is much smaller than the
nonlinear enhancement of the damping.",1308.3787v1
2020-05-28,Spintronics meets nonadiabatic molecular dynamics: Geometric spin torque and damping on noncollinear classical magnetism due to electronic open quantum system,"We analyze a quantum-classical hybrid system of steadily precessing slow
classical localized magnetic moments, forming a head-to-head domain wall,
embedded into an open quantum system of fast nonequilibrium electrons. The
electrons reside within a metallic wire connected to macroscopic reservoirs.
The model captures the essence of dynamical noncollinear and noncoplanar
magnetic textures in spintronics, while making it possible to obtain the exact
time-dependent nonequilibrium density matrix of electronic system and split it
into four contributions. The Fermi surface contribution generates dissipative
(or damping-like in spintronics terminology) spin torque on the moments, and
one of the two Fermi sea contributions generates geometric torque dominating in
the adiabatic regime. When the coupling to the reservoirs is reduced, the
geometric torque is the only nonzero contribution. Locally it has both
nondissipative (or field-like in spintronics terminology) and damping-like
components, but with the sum of latter being zero, which act as the
counterparts of geometric magnetism force and electronic friction in
nonadiabatic molecular dynamics. Such current-independent geometric torque is
absent from widely used micromagnetics or atomistic spin dynamics modeling of
magnetization dynamics based on the Landau-Lifshitz-Gilbert equation, where
previous analysis of Fermi surface-type torque has severely underestimated its
magnitude.",2005.14153v2
2020-09-29,Structural Phase Dependent Giant Interfacial Spin Transparency in W/CoFeB Thin Film Heterostructure,"Pure spin current has transfigured the energy-efficient spintronic devices
and it has the salient characteristic of transport of the spin angular
momentum. Spin pumping is a potent method to generate pure spin current and for
its increased efficiency high effective spin-mixing conductance (Geff) and
interfacial spin transparency (T) are essential. Here, a giant T is reported in
Sub/W(t)/Co20Fe60B20(d)/SiO2(2 nm) heterostructures in \beta-tungsten (\beta-W)
phase by employing all-optical time-resolved magneto-optical Kerr effect
technique. From the variation of Gilbert damping with W and CoFeB thicknesses,
the spin diffusion length of W and spin-mixing conductances are extracted.
Subsequently, T is derived as 0.81 \pm 0.03 for the \beta-W/CoFeB interface. A
sharp variation of Geff and T with W thickness is observed in consonance with
the thickness-dependent structural phase transition and resistivity of W. The
spin memory loss and two-magnon scattering effects are found to have negligible
contributions to damping modulation as opposed to spin pumping effect which is
reconfirmed from the invariance of damping with Cu spacer layer thickness
inserted between W and CoFeB. The observation of giant interfacial spin
transparency and its strong dependence on crystal structures of W will be
important for pure spin current based spin-orbitronic devices.",2009.14143v1
2023-12-31,Molecular Hybridization Induced Antidamping and Sizable Enhanced Spin-to-Charge Conversion in Co20Fe60B20/$β$-W/C60 Heterostructures,"Development of power efficient spintronics devices has been the compelling
need in the post-CMOS technology era. The effective tunability of
spin-orbit-coupling (SOC) in bulk and at the interfaces of hybrid materials
stacking is a prerequisite for scaling down the dimension and power consumption
of these devices. In this work, we demonstrate the strong chemisorption of C60
molecules when grown on the high SOC $\beta$-W layer. The parent CFB/$\beta$-W
bilayer exhibits large spin-to-charge interconversion efficiency, which can be
ascribed to the interfacial SOC observed at the Ferromagnet/Heavy metal
interface. Further, the adsorption of C60 molecules on $\beta$-W reduces the
effective Gilbert damping by $\sim$15% in the CFB/$\beta$-W/C60
heterostructures. The anti-damping is accompanied by a gigantic $\sim$115%
enhancement in the spin-pumping induced output voltage owing to the molecular
hybridization. The non-collinear Density Functional Theory calculations confirm
the long-range enhancement of SOC of $\beta$-W upon the chemisorption of C60
molecules, which in turn can also enhance the SOC at the CFB/$\beta$-W
interface in CFB/$\beta$-W/C60 heterostructures. The combined amplification of
bulk as well interfacial SOC upon molecular hybridization stabilizes the
anti-damping and enhanced spin-to-charge conversion, which can pave the way for
the fabrication of power efficient spintronics devices.",2401.00486v1
2002-04-25,Statics and Fast Dynamics of Nanomagnets with Vortex Structure,"Within the framework of the Landau-Lifshitz-Gilbert equation, using permalloy
parameters, we study the statics and dynamics of flat circular magnetic
nano-structures with an in-plane magnetic vortex configuration, putting
particular emphasis on the (planar) vorticity of the magnetic state and on the
(perpendicular) polarisation of the vortex center (which may be shifted with
respect to the center of the circle). These binary degrees of freedom can in
principle be used to manipulate two independent bits of information.
  Studying switching processes induced by in-plane and out-of plane field
pulses we find that it is possible to switch the vorticity of the magnetic dot
on a time scale of 40 ps in strong enough and short enough perpendicular
external field pulses (B_z^ext \approx 0.5 T, duration \approx 40 ps). But for
realistically small values of the Gilbert damping, only the vorticity can be
switched this fast, and it turns out that it is better to dismiss the center of
the circle totally, concentrating on flat 'nano-rings' with an inner radius R_1
and an outer radius R_2. On these 'nano-rings' the vortex state is more stable,
and with respect to the switching of the vorticity these structures have
similar properties as circular dots.",0204541v3
2007-03-15,Functional Keldysh Theory of Spin Torques,"We present a microscopic treatment of current-induced torques and thermal
fluctuations in itinerant ferromagnets based on a functional formulation of the
Keldysh formalism. We find that the nonequilibrium magnetization dynamics is
governed by a stochastic Landau-Lifschitz-Gilbert equation with spin transfer
torques. We calculate the Gilbert damping parameter $\alpha$ and the
non-adiabatic spin transfer torque parameter $\beta$ for a model ferromagnet.
We find that $\beta \neq \alpha$, in agreement with the results obtained using
imaginary-time methods of Kohno, Tatara and Shibata [J. Phys. Soc. Japan 75,
113706 (2006)]. We comment on the relationship between $s-d$ and
isotropic-Stoner toy models of ferromagnetism and more realistic
density-functional-theory models, and on the implications of these
relationships for predictions of the $\beta/\alpha$ ratio which plays a central
role in domain wall motion. Only for a single-parabolic-band isotropic-Stoner
model with an exchange splitting that is small compared to the Fermi energy
does $\beta/\alpha$ approach one. In addition, our microscopic formalism
incorporates naturally the fluctuations needed in a nonzero-temperature
description of the magnetization. We find that to first order in the applied
electric field, the usual form of thermal fluctuations via a phenomenological
stochastic magnetic field holds.",0703414v2
2010-10-04,Thermal fluctuation field for current-induced domain wall motion,"Current-induced domain wall motion in magnetic nanowires is affected by
thermal fluctuation. In order to account for this effect, the
Landau-Lifshitz-Gilbert equation includes a thermal fluctuation field and
literature often utilizes the fluctuation-dissipation theorem to characterize
statistical properties of the thermal fluctuation field. However, the theorem
is not applicable to the system under finite current since it is not in
equilibrium. To examine the effect of finite current on the thermal
fluctuation, we adopt the influence functional formalism developed by Feynman
and Vernon, which is known to be a useful tool to analyze effects of
dissipation and thermal fluctuation. For this purpose, we construct a quantum
mechanical effective Hamiltonian describing current-induced domain wall motion
by generalizing the Caldeira-Leggett description of quantum dissipation. We
find that even for the current-induced domain wall motion, the statistical
properties of the thermal noise is still described by the
fluctuation-dissipation theorem if the current density is sufficiently lower
than the intrinsic critical current density and thus the domain wall tilting
angle is sufficiently lower than pi/4. The relation between our result and a
recent result, which also addresses the thermal fluctuation, is discussed. We
also find interesting physical meanings of the Gilbert damping alpha and the
nonadiabaticy parameter beta; while alpha characterizes the coupling strength
between the magnetization dynamics (the domain wall motion in this paper) and
the thermal reservoir (or environment), beta characterizes the coupling
strength between the spin current and the thermal reservoir.",1010.0478v2
2015-06-03,Antidamping spin-orbit torque driven by spin-flip reflection mechanism on the surface of a topological insulator: A time-dependent nonequilibrium Green function approach,"Motivated by recent experiments observing spin-orbit torque (SOT) acting on
the magnetization $\vec{m}$ of a ferromagnetic (F) overlayer on the surface of
a three-dimensional topological insulator (TI), we investigate the origin of
the SOT and the magnetization dynamics in such systems. We predict that lateral
F/TI bilayers of finite length, sandwiched between two normal metal leads, will
generate a large antidamping-like SOT per very low charge current injected
parallel to the interface. The large values of antidamping-like SOT are {\it
spatially localized} around the transverse edges of the F overlayer. Our
analysis is based on adiabatic expansion (to first order in $\partial
\vec{m}/\partial t$) of time-dependent nonequilibrium Green functions (NEGFs),
describing electrons pushed out of equilibrium both by the applied bias voltage
and by the slow variation of a classical degree of freedom [such as
$\vec{m}(t)$]. From it we extract formulas for spin torque and charge pumping,
which show that they are reciprocal effects to each other, as well as Gilbert
damping in the presence of SO coupling. The NEGF-based formula for SOT
naturally splits into four components, determined by their behavior (even or
odd) under the time and bias voltage reversal. Their complex angular dependence
is delineated and employed within Landau-Lifshitz-Gilbert simulations of
magnetization dynamics in order to demonstrate capability of the predicted SOT
to efficiently switch $\vec{m}$ of a perpendicularly magnetized F overlayer.",1506.01303v3
2015-07-11,"Realization of the thermal equilibrium in inhomogeneous magnetic systems by the Landau-Lifshitz-Gilbert equation with stochastic noise, and its dynamical aspects","It is crucially important to investigate effects of temperature on magnetic
properties such as critical phenomena, nucleation, pinning, domain wall motion,
coercivity, etc. The Landau-Lifshitz-Gilbert (LLG) equation has been applied
extensively to study dynamics of magnetic properties. Approaches of Langevin
noises have been developed to introduce the temperature effect into the LLG
equation. To have the thermal equilibrium state (canonical distribution) as the
steady state, the system parameters must satisfy some condition known as the
fluctuation-dissipation relation. In inhomogeneous magnetic systems in which
spin magnitudes are different at sites, the condition requires that the ratio
between the amplitude of the random noise and the damping parameter depends on
the magnitude of the magnetic moment at each site. Focused on inhomogeneous
magnetic systems, we systematically showed agreement between the stationary
state of the stochastic LLG equation and the corresponding equilibrium state
obtained by Monte Carlo simulations in various magnetic systems including
dipole-dipole interactions. We demonstrated how violations of the condition
result in deviations from the true equilibrium state. We also studied the
characteristic features of the dynamics depending on the choice of the
parameter set. All the parameter sets satisfying the condition realize the same
stationary state (equilibrium state). In contrast, different choices of
parameter set cause seriously different relaxation processes. We show two
relaxation types, i.e., magnetization reversals with uniform rotation and with
nucleation.",1507.03075v1
2017-01-12,Dynamic coupling of ferromagnets via spin Hall magnetoresistance,"The synchronized magnetization dynamics in ferromagnets on a nonmagnetic
heavy metal caused by the spin Hall effect is investigated theoretically. The
direct and inverse spin Hall effects near the ferromagnetic/nonmagnetic
interface generate longitudinal and transverse electric currents. The
phenomenon is known as the spin Hall magnetoresistance effect, whose magnitude
depends on the magnetization direction in the ferromagnet due to the spin
transfer effect. When another ferromagnet is placed onto the same nonmagnet,
these currents are again converted to the spin current by the spin Hall effect
and excite the spin torque to this additional ferromagnet, resulting in the
excitation of the coupled motions of the magnetizations. The in-phase or
antiphase synchronization of the magnetization oscillations, depending on the
value of the Gilbert damping constant and the field-like torque strength, is
found in the transverse geometry by solving the Landau-Lifshitz-Gilbert
equation numerically. On the other hand, in addition to these synchronizations,
the synchronization having a phase difference of a quarter of a period is also
found in the longitudinal geometry. The analytical theory clarifying the
relation among the current, frequency, and phase difference is also developed,
where it is shown that the phase differences observed in the numerical
simulations correspond to that giving the fixed points of the energy supplied
by the coupling torque.",1701.03201v2
2018-10-16,Superfluid spin transport in ferro- and antiferromagnets,"This paper focuses on spin superfluid transport, observation of which was
recently reported in antiferromagnet Cr$_2$O$_3$ [Yuan et al., Sci. Adv. 4,
eaat1098 (2018)]. This paper analyzes the role of dissipation in transformation
of spin current injected with incoherent magnons to a superfluid spin current
near the interface where spin is injected. The Gilbert damping parameter in the
Landau-Lifshitz-Gilbert theory does not describe dissipation properly, and the
dissipation parameters are calculated from the Boltzmann equation for magnons
scattered by defects. The two-fluid theory is developed similar to the
two-fluid theory for superfluids. This theory shows that the influence of
temperature variation in bulk on the superfluid spin transport (bulk Seebeck
effect) is weak at low temperatures. The scenario that the results of Yuan et
al. are connected with the Seebeck effect at the interface between the spin
detector and the sample is also discussed.
  The Landau criterion for an antiferromagnet put in a magnetic field is
derived from the spectrum of collective spin modes. The Landau instability
starts in the gapped mode earlier than in the Goldstone gapless mode, in
contrast to easy-plane ferromagnets where the Goldstone mode becomes unstable.
The structure of the magnetic vortex in the geometry of the experiment is
determined. The vortex core has the skyrmion structure with finite
magnetization component normal to the magnetic field. This magnetization
creates stray magnetic fields around the exit point of the vortex line from the
sample, which can be used for experimental detection of vortices.",1810.07020v4
2020-02-20,Stoner-Wohlfarth switching of the condensate magnetization in a dipolar spinor gas and the metrology of excitation damping,"We consider quasi-one-dimensional dipolar spinor Bose-Einstein condensates in
the homogeneous-local-spin-orientation approximation, that is with
unidirectional local magnetization. By analytically calculating the exact
effective dipole-dipole interaction, we derive a Landau-Lifshitz-Gilbert
equation for the dissipative condensate magnetization dynamics, and show how it
leads to the Stoner-Wohlfarth model of a uni-axial ferro-magnetic particle,
where the latter model determines the stable magnetization patterns and
hysteresis curves for switching between them. For an external magnetic field
pointing along the axial, long direction, we analytically solve the
Landau-Lifshitz-Gilbert equation. The solution explicitly demonstrates that the
magnetic dipole-dipole interaction {\it accelerates} the dissipative dynamics
of the magnetic moment distribution and the associated dephasing of the
magnetic moment direction. Under suitable conditions, dephasing of the
magnetization direction due to dipole-dipole interactions occurs within time
scales up to two orders of magnitude smaller than the lifetime of currently
experimentally realized dipolar spinor condensates, e.g., produced with the
large magnetic-dipole-moment atoms ${}^{166} \textrm{Er}$. This enables
experimental access to the dissipation parameter $\Gamma$ in the
Gross-Pitaevski\v\i~mean-field equation, for a system currently lacking a
complete quantum kinetic treatment of dissipative processes and, in particular,
an experimental check of the commonly used assumption that $\Gamma$ is a single
scalar independent of spin indices.",2002.08723v2
2022-06-20,First-principles calculation of the parameters used by atomistic magnetic simulations,"While the ground state of magnetic materials is in general well described on
the basis of spin density functional theory (SDFT), the theoretical description
of finite-temperature and non-equilibrium properties require an extension
beyond the standard SDFT. Time-dependent SDFT (TD-SDFT), which give for example
access to dynamical properties are computationally very demanding and can
currently be hardly applied to complex solids. Here we focus on the alternative
approach based on the combination of a parameterized phenomenological spin
Hamiltonian and SDFT-based electronic structure calculations, giving access to
the dynamical and finite-temperature properties for example via spin-dynamics
simulations using the Landau-Lifshitz-Gilbert (LLG) equation or Monte Carlo
simulations. We present an overview on the various methods to calculate the
parameters of the various phenomenological Hamiltonians with an emphasis on the
KKR Green function method as one of the most flexible band structure methods
giving access to practically all relevant parameters. Concerning these, it is
crucial to account for the spin-orbit coupling (SOC) by performing relativistic
SDFT-based calculations as it plays a key role for magnetic anisotropy and
chiral exchange interactions represented by the DMI parameters in the spin
Hamiltonian. This concerns also the Gilbert damping parameters characterizing
magnetization dissipation in the LLG equation, chiral multispin interaction
parameters of the extended Heisenberg Hamiltonian, as well as spin-lattice
interaction parameters describing the interplay of spin and lattice dynamics
processes, for which an efficient computational scheme has been developed
recently by the present authors.",2206.09969v1
2023-09-25,Ultrafast Demagnetization through Femtosecond Generation of Non-thermal Magnons,"Ultrafast laser excitation of ferromagnetic metals gives rise to correlated,
highly non-equilibrium dynamics of electrons, spins and lattice, which are,
however, poorly described by the widely-used three-temperature model (3TM).
Here, we develop a fully ab-initio parameterized out-of-equilibrium theory
based on a quantum kinetic approach--termed (N+2) temperature model--that
describes magnon occupation dynamics due to electron-magnon scattering. We
apply this model to perform quantitative simulations on the ultrafast,
laser-induced generation of magnons in iron and demonstrate that on these
timescales the magnon distribution is non-thermal: predominantly high-energy
magnons are created, while the magnon occupation close to the center of the
Brillouin zone even decreases, due to a repopulation towards higher energy
states via a so-far-overlooked scattering term. We demonstrate that the simple
relation between magnetization and temperature computed at equilibrium does not
hold in the ultrafast regime and that the 3TM greatly overestimates the
demagnetization. The ensuing Gilbert damping becomes strongly magnon wavevector
dependent and requires a description beyond the conventional
Landau-Lifshitz-Gilbert spin dynamics. Our ab-initio-parameterized calculations
show that ultrafast generation of non-thermal magnons provides a sizable
demagnetization within 200fs in excellent comparison with experimentally
observed laser-induced demagnetizations. Our investigation emphasizes the
importance of non-thermal magnon excitations for the ultrafast demagnetization
process.",2309.14167v3
2023-12-12,Sliding Dynamics of Current-Driven Skyrmion Crystal and Helix in Chiral Magnets,"The skyrmion crystal (SkX) and helix (HL) phases, present in typical chiral
magnets, can each be considered as forms of density waves but with distinct
topologies. The SkX exhibits gyrodynamics analogous to electrons under a
magnetic field, while the HL state resembles topological trivial spin density
waves. However, unlike the charge density waves, the theoretical analysis of
the sliding motion of SkX and HL remains unclear, especially regarding the
similarities and differences in sliding dynamics between these two spin density
waves. In this work, we systematically explore the sliding dynamics of SkX and
HL in chiral magnets in the limit of large current density. We demonstrate that
the sliding dynamics of both SkX and HL can be unified within the same
theoretical framework as density waves, despite their distinct microscopic
orders. Furthermore, we highlight the significant role of gyrotropic sliding
induced by impurity effects in the SkX state, underscoring the impact of
nontrivial topology on the sliding motion of density waves. Our theoretical
analysis shows that the effect of impurity pinning is much stronger in HL
compared with SkX, i.e., $\chi^{SkX}/\chi^{HL}\sim \alpha^2$ ($\chi^{SkX}$,
$\chi^{HL}$: susceptibility to the impurity potential, $\alpha$ ($\ll 1$) is
the Gilbert damping). Moreover, the velocity correction is mostly in the
transverse direction to the current in SkX. These results are further
substantiated by realistic Landau-Lifshitz-Gilbert simulations.",2312.07116v2
2023-08-14,Temperature Evolution of Magnon Propagation Length in Tm$_3$Fe$_5$O$_{12}$ Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping,"The magnon propagation length ($\langle\xi\rangle$) of a ferro/ferrimagnet
(FM) is one of the key factors that controls the generation and propagation of
thermally-driven spin current in FM/heavy metal (HM) bilayer based
spincaloritronic devices. Theory predicts that for the FM layer,
$\langle\xi\rangle$ is inversely proportional to the Gilbert damping ($\alpha$)
and the square root of the effective magnetic anisotropy constant ($K_{\rm
eff}$). However, direct experimental evidence of this relationship is lacking.
To experimentally confirm this prediction, we employ a combination of
longitudinal spin Seebeck effect (LSSE), transverse susceptibility, and
ferromagnetic resonance experiments to investigate the temperature evolution of
$\langle\xi\rangle$ and establish its correlation with the effective magnetic
anisotropy field, $H_K^{\rm eff}$ ($\propto K_{\rm eff}$) and $\alpha$ in
Tm$_3$Fe$_5$O$_{12}$ (TmIG)/Pt bilayers. We observe concurrent drops in the
LSSE voltage and $\langle\xi\rangle$ below 200$^\circ$K in TmIG/Pt bilayers
regardless of TmIG film thickness and substrate choice and attribute it to the
noticeable increases in $H_K^{\rm eff}$ and $\alpha$ that occur within the same
temperature range. From the TmIG thickness dependence of the LSSE voltage, we
determined the temperature dependence of $\langle\xi\rangle$ and highlighted
its correlation with the temperature-dependent $H_K^{\rm eff}$ and $\alpha$ in
TmIG/Pt bilayers, which will be beneficial for the development of rare-earth
iron garnet-based efficient spincaloritronic nanodevices.",2308.07236v3
2014-01-08,Dynamic exchange via spin currents in acoustic and optical modes of ferromagnetic resonance in spin-valve structures,"Two ferromagnetic layers magnetically decoupled by a thick normal metal
spacer layer can be, nevertheless, dynamically coupled via spin currents
emitted by the spin-pump and absorbed through the spin-torque effects at the
neighboring interfaces. A decrease of damping in both layers due to a partial
compensation of the angular momentum leakage in each layer was previously
observed at the coincidence of the two ferromagnetic resonances. In case of
non-zero magnetic coupling, such a dynamic exchange will depend on the mutual
precession of the magnetic moments in the layers. A difference in the linewidth
of the resonance peaks is expected for the acoustic and optical regimes of
precession. However, the interlayer coupling hybridizes the resonance responses
of the layers and therefore can also change their linewidths. The interplay
between the two mechanisms has never been considered before. In the present
work, the joint influence of the hybridization and non-local damping on the
linewidth has been studied in weakly coupled NiFe/CoFe/Cu/CoFe/MnIr spin-valve
multilayers. It has been found that the dynamic exchange by spin currents is
different in the optical and acoustic modes, and this difference is dependent
on the interlayer coupling strength. In contrast to the acoustic precession
mode, the dynamic exchange in the optical mode works as an additional damping
source. A simulation in the framework of the Landau-Lifshitz-Gilbert formalism
for two ferromagnetic layers coupled magnetically and by spin currents has been
done to separate the effects of the non-local damping from the resonance modes
hybridization. In our samples both mechanisms bring about linewidth changes of
the same order of magnitude, but lead to a distinctly different angular
behavior. The obtained results are relevant for a broad class of coupled
magnetic multilayers with ballistic regime of the spin transport.",1401.1672v1
2020-08-29,Exploring a quantum-information-relevant magnonic material: Ultralow damping at low temperature in the organic ferrimagnet V[TCNE]x,"Quantum information science and engineering requires novel low-loss magnetic
materials for magnon-based quantum-coherent operations. The search for low-loss
magnetic materials, traditionally driven by applications in microwave
electronics near room-temperature, has gained additional constraints from the
need to operate at cryogenic temperatures for many applications in quantum
information science and technology. Whereas yttrium iron garnet (YIG) has been
the material of choice for decades, the emergence of molecule-based materials
with robust magnetism and ultra-low damping has opened new avenues for
exploration. Specifically, thin-films of vanadium tetracyanoethylene (V[TCNE]x)
can be patterned into the multiple, connected structures needed for hybrid
quantum elements and have shown room-temperature Gilbert damping ({\alpha} = 4
\times 10^-5) that rivals the intrinsic (bulk) damping otherwise seen only in
highly-polished YIG spheres (far more challenging to integrate into arrays).
Here, we present a comprehensive and systematic study of the low-temperature
magnetization dynamics for V[TCNE]x thin films, with implications for their
application in quantum systems. These studies reveal a temperature-driven,
strain-dependent magnetic anisotropy that compensates the thin-film shape
anisotropy, and the recovery of a magnetic resonance linewidth at 5 K that is
comparable to room-temperature values (roughly 2 G at 9.4 GHz). We can account
for these variations of the V[TCNE]x linewidth within the context of scattering
from very dilute paramagnetic impurities, and anticipate additional linewidth
narrowing as the temperature is further reduced.",2008.13061v3
2003-04-18,Elementary Excitations of Ferromagnetic Metal Nanoparticles,"We present a theory of the elementary spin excitations in transition metal
ferromagnet nanoparticles which achieves a unified and consistent quantum
description of both collective and quasiparticle physics. The theory starts by
recognizing the essential role played by spin-orbit interactions in determining
the energies of ferromagnetic resonances in the collective excitation spectrum
and the strength of their coupling to low-energy particle-hole excitations. We
argue that a crossover between Landau-damped ferromagnetic resonance and
pure-state collective magnetic excitations occurs as the number of atoms in
typical transition metal ferromagnet nanoparticles drops below approximately
$10^4$, approximately where the single-particle level spacing, $\delta$,
becomes larger than, $\sqrt{\alpha} E_{\rm res}$, where $E_{\rm res}$ is the
ferromagnetic resonance frequency and $\alpha$ is the Gilbert damping
parameter. We illustrate our ideas by studying the properties of semi-realistic
model Hamiltonians, which we solve numerically for nanoparticles containing
several hundred atoms. For small nanoparticles, we find one isolated
ferromagnetic resonance collective mode below the lowest particle-hole
excitation energy, at $E_{\rm res} \approx 0.1$ meV. The spectral weight of
this pure excitation nearly exhausts the transverse dynamical susceptibility
spectral weight. As $\delta$ approaches $\sqrt{\alpha} E_{\rm res}$, the
ferromagnetic collective excitation is more likely to couple strongly with
discrete particle-hole excitations. In this regime the distinction between the
two types of excitations blurs. We discuss the significance of this picture for
the interpretation of recent single-electron tunneling experiments.",0304427v1
2014-08-02,Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates,"We studied polycrystalline B2-type Co2FeAl (CFA) full-Heusler alloy based
magnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate.
Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a
flat surface were achieved using a MgO buffer layer. A tunnel magnetoresistance
(TMR) ratio up to 175% was obtained for an MTJ with a CFA/MgO/CoFe structure on
a 7.5-nm-thick MgO buffer. Spin-transfer torque induced magnetization switching
was achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a
switching layer. Using a thermal activation model, the intrinsic critical
current density (Jc0) was determined to be 8.2 x 10^6 A/cm^2, which is lower
than 2.9 x 10^7 A/cm^2, the value for epitaxial CFA-MTJs [Appl. Phys. Lett.
100, 182403 (2012)]. We found that the Gilbert damping constant evaluated using
ferromagnetic resonance measurements for the polycrystalline CFA film was
~0.015 and was almost independent of the CFA thickness (2~18 nm). The low Jc0
for the polycrystalline MTJ was mainly attributed to the low damping of the CFA
layer compared with the value in the epitaxial one (~0.04).",1408.0341v1
2018-02-20,Ultrafast magnetization dynamics in pure and doped Heusler and inverse Heusler alloys,"By using a multiscale approach based on first-principles density functional
theory combined with atomistic spin dynamics, we investigate the electronic
structure and magnetization dynamics of an inverse Heusler and a Heusler
compound and their alloys, i. e. Mn$_{2-x}Z_x$CoAl and Mn$_{2-x}Z_x$VAl, where
$Z$ = Mo, W, Os and Ru, respectively. A signature of the ferrimagnetic ordering
of Mn$_{2}$CoAl and Mn$_{2}$VAl Heusler alloys is reflected in the calculated
Heisenberg exchange constants. They decay very rapidly with the interatomic
distance and have short range, which is a consequence of the existence of the
finite gap in the minority spin band. The calculated Gilbert damping parameter
of both Mn$_2$CoAl and Mn$_2$VAl is high compared to other half-metals, but
interestingly in the particular case of the inverse Mn$_{2}$CoAl alloys and due
to the spin-gapless semiconducting property, the damping parameters decrease
with the doping concentration in clear contradiction to the general trend.
Atomistic spin dynamics simulations predict ultrafast magnetisation switching
in Mn$_{2}$CoAl and Mn$_{2}$VAl under the influence of an external magnetic
field, starting from a threshold field of $2\text{T}$. Our overall finding
extends with Heusler and inverse Heusler alloys, the class of materials that
exhibits laser induced magnetic switching.",1802.07195v1
2018-04-10,GONG Catalog of Solar Filament Oscillations Near Solar Maximum,"We have catalogued 196 filament oscillations from the GONG $H{\alpha}$
network data during several months near the maximum of solar cycle 24 (January
- June 2014). Selected examples from the catalog are described in detail, along
with our statistical analyses of all events. Oscillations were classified
according to their velocity amplitude: 106 small-amplitude oscillations (SAOs),
with velocities $<10\mathrm{\, km \; s^{-1}}$, and 90 large-amplitude
oscillations (LAOs), with velocities $>10\mathrm{\, km \; s^{-1}}$. Both SAOs
and LAOs are common, with one event of each class every two days on the visible
side of the Sun. For nearly half of the events we identified their apparent
trigger. The period distribution has a mean value of 58$\pm$15 min for both
types of oscillations. The distribution of the damping time per period peaks at
$\tau/P=1.75$ and $1.25$ for SAOs and LAOs respectively. We confirmed that LAO
damping rates depend nonlinearly on the oscillation velocity. The angle between
the direction of motion and the filament spine has a distribution centered at
$27^\circ$ for all filament types. This angle agrees with the observed
direction of filament-channel magnetic fields, indicating that most of the
catalogued events are longitudinal (i.e., undergo field-aligned motions). We
applied seismology to determine the average radius of curvature in the magnetic
dips, $R\approx89$ Mm, and the average minimum magnetic-field strength,
$B\approx16$ G. The catalog is available to the community online, and is
intended to be expanded to cover at least 1 solar cycle.",1804.03743v1
2018-10-16,Spin-wave-induced lateral temperature gradient in a YIG thin film/GGG system excited in an ESR cavity,"Lateral thermal gradient of an yttrium iron garnet (YIG) film under the
microwave application in the cavity of the electron spin resonance system (ESR)
was measured at room temperature by fabricating a Cu/Sb thermocouple onto it.
To date, thermal transport in YIG films caused by the Damon-Eshbach mode (DEM)
- the unidirectional spin-wave heat conveyer effect - was demonstrated only by
the excitation using coplanar waveguides. Here we show that effect exists even
under YIG excitation using the ESR cavity - tool often employed to realize spin
pumping. The temperature difference observed around the ferromagnetic resonance
(FMR) field under the 4 mW microwave power peaked at 13 mK. The observed
thermoelectric signal indicates the imbalance of the population between the
DEMs that propagate near the top and bottom surfaces of the YIG film. We
attribute the DEM population imbalance to the different magnetic damping near
the top and bottom YIG surfaces. Additionally, the spin wave dynamics of the
system were investigated using the micromagnetic simulations. The micromagnetic
simulations confirmed the existence of the DEM imbalance in the system with the
increased Gilbert damping at one of the YIG interfaces. The reported results
are indispensable for the quantitative estimation of the electromotive force in
the spin-charge conversion experiments using ESR cavities.",1810.06875v1
2019-11-21,Low damping and microstructural perfection of sub-40nm-thin yttrium iron garnet films grown by liquid phase epitaxy,"The field of magnon spintronics is experiencing an increasing interest in the
development of solutions for spin-wave-based data transport and processing
technologies that are complementary or alternative to modern CMOS
architectures. Nanometer-thin yttrium iron garnet (YIG) films have been the
gold standard for insulator-based spintronics to date, but a potential process
technology that can deliver perfect, homogeneous large-diameter films is still
lacking. We report that liquid phase epitaxy (LPE) enables the deposition of
nanometer-thin YIG films with low ferromagnetic resonance losses and
consistently high magnetic quality down to a thickness of 20 nm. The obtained
epitaxial films are characterized by an ideal stoichiometry and perfect film
lattices, which show neither significant compositional strain nor geometric
mosaicity, but sharp interfaces. Their magneto-static and dynamic behavior is
similar to that of single crystalline bulk YIG. We found, that the Gilbert
damping coefficient alpha is independent of the film thickness and close to 1 x
10-4, and that together with an inhomogeneous peak-to-peak linewidth broadening
of delta H0|| = 0.4 G, these values are among the lowest ever reported for YIG
films with a thickness smaller than 40 nm. These results suggest, that
nanometer-thin LPE films can be used to fabricate nano- and micro-scaled
circuits with the required quality for magnonic devices. The LPE technique is
easily scalable to YIG sample diameters of several inches.",1911.09400v1
2021-08-24,Shape anisotropy effect on magnetization reversal induced by linear down chirp pulse,"We investigate the influence of shape anisotropy on the magnetization
reversal of a single-domain magnetic nanoparticle driven by a circularly
polarized linear down-chirp microwave field pulse (DCMP). Based on the
Landau-Lifshitz-Gilbert equation, numerical results show that the three
controlling parameters of DCMP, namely, microwave amplitude, initial frequency
and chirp rate, decrease with the increase of shape anisotropy. For certain
shape anisotropy, the reversal time significantly reduces. These findings are
related to the competition of shape anisotropy and uniaxial magnetocrystalline
anisotropy and thus to the height of energy barrier which separates the two
stable states. The result of damping dependence of magnetization reversal
indicates that for a certain sample shape, there exists an optimal damping
situation at which magnetization is fastest. Moreover, it is also shown that
the required microwave field amplitude can be lowered by applying the
spin-polarized current simultaneously. The usage of an optimum combination of
both microwave field pulse and current is suggested to achieve cost efficiency
and faster switching. So these findings may provide the knowledge to fabricate
the shape of a single domain nanoparticle for the fast and power-efficient
magnetic data storage device.",2108.10965v2
2021-11-23,Resonant dynamics of skyrmion lattices in thin film multilayers: Localised modes and spin wave emission,"The spectral signatures of magnetic skyrmions under microwave field
excitation are of fundamental interest and can be an asset for high frequency
applications. These topological solitons can be tailored in multilayered thin
films, but the experimental observation of their spin wave dynamics remains
elusive, in particular due to large damping. Here, we study Pt/FeCoB/AlO$_x$
multilayers hosting dense and robust skyrmion lattices at room temperature with
Gilbert damping of $\sim 0.02$. We use magnetic force microscopy to
characterise their static magnetic phases and broadband ferromagnetic resonance
to probe their high frequency response. Micromagnetic simulations reproduce the
experiments with accuracy and allow us to identify distinct resonant modes
detected in the skyrmion lattice phase. Low ($<$ 2 GHz) and intermediate
frequency ($2-8$ GHz) modes involve excitations localised to skyrmion edges in
conjunction with precession of the uniform background magnetisation, while a
high frequency ($>$ 12 GHz) mode corresponds to in-phase skyrmion core
precession emitting spin waves into uniform background with wavelengths in the
50--80 nm range commensurate with the lattice structure. These findings could
be instrumental in the investigation of room temperature wave scattering and
the implementation of novel microwave processing schemes in reconfigurable
arrays of solitons.",2111.11797v2
2022-05-20,Effects of Crystalline Disorder on Interfacial and Magnetic Properties of Sputtered Topological Insulator/Ferromagnet Heterostructures,"Thin films of Topological insulators (TIs) coupled with ferromagnets (FMs)
are excellent candidates for energy-efficient spintronics devices. Here, the
effect of crystalline structural disorder of TI on interfacial and magnetic
properties of sputter-deposited TI/FM, Bi2Te3/Ni80Fe20, heterostructures is
reported. Ni and a smaller amount of Fe from Py was found to diffuse across the
interface and react with Bi2Te3. For highly crystalline c-axis oriented Bi2Te3
films, a giant enhancement in Gilbert damping is observed, accompanied by an
effective out-of-plane magnetic anisotropy and enhanced damping-like spin-orbit
torque (DL-SOT), possibly due to the topological surface states (TSS) of
Bi2Te3. Furthermore, a spontaneous exchange bias is observed in hysteresis loop
measurements at low temperatures. This is because of an antiferromagnetic
topological interfacial layer formed by reaction of the diffused Ni with Bi2Te3
which couples with the FM, Ni80Fe20. For increasing disorder of Bi2Te3, a
significant weakening of exchange interaction in the AFM interfacial layer is
found. These experimental results Abstract length is one paragraph.",2205.09913v1
2022-12-24,Anatomy of ultrafast quantitative magneto-acoustics in freestanding nickel thin films,"We revisit the quantitative analysis of the ultrafast magneto-acoustic
experiment in a freestanding nickel thin film by Kim and Bigot [1] by applying
our recently proposed approach of magnetic and acoustic eigenmodes
decomposition by Vernik et al. [2]. We show that the application of our
modeling to the analysis of time-resolved reflectivity measurements allows for
the determination of amplitudes and lifetimes of standing perpendicular
acoustic phonon resonances with unprecedented accuracy. The acoustic damping is
found to scale as $\propto\omega^2$ for frequencies up to 80~GHz and the peak
amplitudes reach $10^{-3}$. The experimentally measured magnetization dynamics
for different orientations of an external magnetic field agrees well with
numerical solutions of magneto-elastically driven magnon harmonic oscillators.
Symmetry-based selection rules for magnon-phonon interactions predicted by our
modeling approach allow for the unambiguous discrimination between spatially
uniform and non-uniform modes, as confirmed by comparing the resonantly
enhanced magneto-elastic dynamics simultaneously measured on opposite sides of
the film. Moreover, the separation of time scales for (early) rising and (late)
decreasing precession amplitudes provide access to magnetic (Gilbert) and
acoustic damping parameters in a single measurement.",2212.12673v1
2023-05-16,Non-Hermitian Casimir Effect of Magnons,"There has been a growing interest in non-Hermitian quantum mechanics. The key
concepts of quantum mechanics are quantum fluctuations. Quantum fluctuations of
quantum fields confined in a finite-size system induce the zero-point energy
shift. This quantum phenomenon, the Casimir effect, is one of the most striking
phenomena of quantum mechanics in the sense that there are no classical analogs
and has been attracting much attention beyond the hierarchy of energy scales,
ranging from elementary particle physics to condensed matter physics, together
with photonics. However, the non-Hermitian extension of the Casimir effect and
the application to spintronics have not yet been investigated enough, although
exploring energy sources and developing energy-efficient nanodevices are its
central issues. Here we fill this gap. By developing a magnonic analog of the
Casimir effect into non-Hermitian systems, we show that this non-Hermitian
Casimir effect of magnons is enhanced as the Gilbert damping constant (i.e.,
the energy dissipation rate) increases. When the damping constant exceeds a
critical value, the non-Hermitian Casimir effect of magnons exhibits an
oscillating behavior, including a beating one, as a function of the film
thickness and is characterized by the exceptional point. Our result suggests
that energy dissipation serves as a key ingredient of Casimir engineering.",2305.09231v1
2002-09-07,Neural network analysis of the magnetization reversal in magnetic dot arrays,"We simulated the remagnetization dynamics of the ultra-dense and ultra-thin
magnetic dot array system with dipole-dipole and exchange coupling
interactions. Within the proposed 2D XY superlattice model, the square dots are
modeled by the spatially modulated exchange-couplings. The dipole-dipole
interactions were approximated by the hierarchical sums and dynamics was
reduced to damping term of the Landau-Lifshitz-Gilbert equation. The simulation
of 40 000 spin system leads to nonequilibrium nonuniform configurations with
soliton-antisoliton pairs detected at intra-dot and inter-dot scales. The
classification of intra-dot magnetic configurations was performed using the
self-adaptive neural networks with varying number of neurons.",0209186v1
2005-04-06,Macrospin Models of Spin Transfer Dynamics,"The current-induced magnetization dynamics of a spin valve are studied using
a macrospin (single domain) approximation and numerical solutions of a
generalized Landau-Lifshitz-Gilbert equation. For the purpose of quantitative
comparison with experiment [Kiselev {\it et al.} Nature {\bf 425}, 380 (2003)],
we calculate the resistance and microwave power as a function of current and
external field including the effects of anisotropies, damping, spin-transfer
torque, thermal fluctuations, spin-pumping, and incomplete absorption of
transverse spin current. While many features of experiment appear in the
simulations, there are two significant discrepancies: the current dependence of
the precession frequency and the presence/absence of a microwave quiet magnetic
phase with a distinct magnetoresistance signature. Comparison is made with
micromagnetic simulations designed to model the same experiment.",0504142v1
2006-02-01,Mapping Monte Carlo to Langevin dynamics: A Fokker-Planck approach,"We propose a general method of using the Fokker-Planck equation (FPE) to link
the Monte-Carlo (MC) and the Langevin micromagnetic schemes. We derive the
drift and disusion FPE terms corresponding to the MC method and show that it is
analytically equivalent to the stochastic Landau-Lifshitz-Gilbert (LLG)
equation of Langevin-based micromagnetics. Subsequent results such as the time
quantification factor for the Metropolis MC method can be rigorously derived
from this mapping equivalence. The validity of the mapping is shown by the
close numerical convergence between the MC method and the LLG equation for the
case of a single magnetic particle as well as interacting arrays of particles.
We also found that our Metropolis MC is accurate for a large range of damping
factors $\alpha$, unlike previous time-quantified MC methods which break down
at low $\alpha$, where precessional motion dominates.",0602011v2
2006-04-21,Dynamic approach for micromagnetics close to the Curie temperature,"In conventional micromagnetism magnetic domain configurations are calculated
based on a continuum theory for the magnetization which is assumed to be of
constant length in time and space. Dynamics is usually described with the
Landau-Lifshitz-Gilbert (LLG) equation the stochastic variant of which includes
finite temperatures. Using simulation techniques with atomistic resolution we
show that this conventional micromagnetic approach fails for higher
temperatures since we find two effects which cannot be described in terms of
the LLG equation: i) an enhanced damping when approaching the Curie temperature
and, ii) a magnetization magnitude that is not constant in time. We show,
however, that both of these effects are naturally described by the
Landau-Lifshitz-Bloch equation which links the LLG equation with the theory of
critical phenomena and turns out to be a more realistic equation for
magnetization dynamics at elevated temperatures.",0604508v1
2007-02-20,Spin dynamics in a superconductor / ferromagnet proximity system,"The ferromagnetic resonance of thin sputtered Ni80Fe20 films grown on Nb is
measured. By varying the temperature and thickness of the Nb the role of the
superconductivity on the whole ferromagnetic layer in these heterostructures is
explored. The change in the spin transport properties below the superconducting
transition of the Nb is found to manifest itself in the Ni80Fe20 layer by a
sharpening in the resonance of the ferromagnet, or a decrease in the effective
Gilbert damping co-efficient. This dynamic proximity effect is in contrast to
low frequency studies in these systems, where the effect of the superconductor
is confined to a small region in the ferromagnet. We interpret this in terms of
the spin pumping model.",0702461v1
2007-02-21,"Domain wall mobility, stability and Walker breakdown in magnetic nanowires","We present an analytical calculation of the velocity of a single 180 degree
domain wall in a magnetic structure with reduced thickness and/or lateral
dimension under the combined action of an external applied magnetic field and
an electrical current. As for the case of field-induced domain wall propagation
in thick films, two motion regimes with different mobilities are obtained,
below and far above the so-called Walker field. Additionally, for the case of
current induced motion, a Walker-like current density threshold can be defined.
When the dimensions of the system become comparable to the domain wall width,
the threshold field and current density, stating the wall's internal structure
stability, are reduced by the same geometrical demagnetising factor which
accounts for the confinement. This points out the fact that the velocity
dependence over an extended field/current range and the knowledge of the Walker
breakdown are mandatory to draw conclusions about the phenomenological Gilbert
damping parameter tuning the magnetisation dynamics.",0702492v1
2001-01-09,Hysteresis in layered spring magnets,"This article addresses a problem of micromagnetics: the reversal of magnetic
moments in layered spring magnets. A one-dimensional model is used of a film
consisting of several atomic layers of a soft material on top of several atomic
layers of a hard material. Each atomic layer is taken to be uniformly
magnetized, and spatial inhomogeneities within an atomic layer are neglected.
The state of such a system is described by a chain of magnetic spin vectors.
Each spin vector behaves like a spinning top driven locally by the effective
magnetic field and subject to damping (Landau-Lifshitz-Gilbert equation). A
numerical integration scheme for the LLG equation is presented that is
unconditionally stable and preserves the magnitude of the magnetization vector
at all times. The results of numerical investigations for a bilayer in a
rotating in-plane magnetic field show hysteresis with a basic period of $2\pi$
at moderate fields and hysteresis with a basic period of $\pi$ at strong
fields.",0101077v1
2005-01-01,Equatorial and related non-equilibrium states in magnetization dynamics of ferromagnets: Generalization of Suhl's spin-wave instabilities,"We investigate the nonlinear dynamics underlying the evolution of a 2-D
nanoscale ferromagnetic film with uniaxial anisotropy in the presence of
perpendicular pumping. Considering the associated Landau-Lifshitz spin
evolution equation with Gilbert damping together with Maxwell equation for the
demagnetization field, we study the dynamics in terms of the stereographic
variable. We identify several new fixed points for suitable choice of external
field in a rotating frame of reference. In particular, we identify explicit
equatorial and related fixed points of the spin vector in the plane transverse
to the anisotropy axis when the pumping frequency coincides with the amplitude
of the static parallel field. We then study the linear stability of these novel
fixed points under homogeneous and spin wave perturbations and obtain a
generalized Suhl's instability criterion, giving the condition for exponential
growth of P-modes under spin wave perturbations. Two parameter phase diagrams
(in terms of amplitudes of static parallel and oscillatory perpendicular
magnetic fields) for stability are obtained, which differ qualitatively from
those for the conventional ferromagnetic resonance near thermal equilibrium and
are amenable to experimental tests.",0501002v2
2002-12-30,Stochastic resonance in periodic potentials: realization in a dissipative optical lattice,"We have observed the phenomenon of stochastic resonance on the Brillouin
propagation modes of a dissipative optical lattice. Such a mode has been
excited by applying a moving potential modulation with phase velocity equal to
the velocity of the mode. Its amplitude has been characterized by the
center-of-mass (CM) velocity of the atomic cloud. At Brillouin resonance, we
studied the CM-velocity as a function of the optical pumping rate at a given
depth of the potential wells. We have observed a resonant dependence of the CM
velocity on the optical pumping rate, corresponding to the noise strength. This
corresponds to the experimental observation of stochastic resonance in a
periodic potential in the low-damping regime.",0212156v1
2007-05-03,Planar spin-transfer device with a dynamic polarizer,"In planar nano-magnetic devices magnetization direction is kept close to a
given plane by the large easy-plane magnetic anisotropy, for example by the
shape anisotropy in a thin film. In this case magnetization shows effectively
in-plane dynamics with only one angle required for its description. Moreover,
the motion can become overdamped even for small values of Gilbert damping. We
derive the equations of effective in-plane dynamics in the presence of
spin-transfer torques. The simplifications achieved in the overdamped regime
allow to study systems with several dynamic magnetic pieces (``free layers'').
A transition from a spin-transfer device with a static polarizer to a device
with two equivalent magnets is observed. When the size difference between the
magnets is less than critical, the device does not exhibit switching, but goes
directly into the ``windmill'' precession state.",0705.0406v1
2007-05-03,Effective attraction induced by repulsive interaction in a spin-transfer system,"In magnetic systems with dominating easy-plane anisotropy the magnetization
can be described by an effective one dimensional equation for the in-plane
angle. Re-deriving this equation in the presence of spin-transfer torques, we
obtain a description that allows for a more intuitive understanding of
spintronic devices' operation and can serve as a tool for finding new dynamic
regimes. A surprising prediction is obtained for a planar ``spin-flip
transistor'': an unstable equilibrium point can be stabilized by a current
induced torque that further repels the system from that point. Stabilization by
repulsion happens due to the presence of dissipative environment and requires a
Gilbert damping constant that is large enough to ensure overdamped dynamics at
zero current.",0705.0508v1
2007-06-21,Spin pumping by a field-driven domain wall,"We calculate the charge current in a metallic ferromagnet to first order in
the time derivative of the magnetization direction. Irrespective of the
microscopic details, the result can be expressed in terms of the conductivities
of the majority and minority electrons and the non-adiabatic spin transfer
torque parameter $\beta$. The general expression is evaluated for the specific
case of a field-driven domain wall and for that case depends strongly on the
ratio of $\beta$ and the Gilbert damping constant. These results may provide an
experimental method to determine this ratio, which plays a crucial role for
current-driven domain-wall motion.",0706.3160v3
2007-09-18,Theory of current-driven magnetization dynamics in inhomogeneous ferromagnets,"We give a brief account of recent developments in the theoretical
understanding of the interaction between electric currents and inhomogeneous
ferromagnetic order parameters. We start by discussing the physical origin of
the spin torques responsible for this interaction and construct a
phenomenological description. We then consider the electric current-induced
ferromagnetic instability and domain-wall motion. Finally, we present a
microscopic justification of the phenomenological description of current-driven
magnetization dynamics, with particular emphasis on the dissipative terms, the
so-called Gilbert damping $\alpha$ and the $\beta$ component of the adiabatic
current-driven torque.",0709.2937v2
2008-02-12,Temperature dependent magnetization dynamics of magnetic nanoparticles,"Recent experimental and theoretical studies show that the switching behavior
of magnetic nanoparticles can be well controlled by external time-dependent
magnetic fields. In this work, we inspect theoretically the influence of the
temperature and the magnetic anisotropy on the spin-dynamics and the switching
properties of single domain magnetic nanoparticles (Stoner-particles). Our
theoretical tools are the Landau-Lifshitz-Gilbert equation extended as to deal
with finite temperatures within a Langevine framework. Physical quantities of
interest are the minimum field amplitudes required for switching and the
corresponding reversal times of the nanoparticle's magnetic moment. In
particular, we contrast the cases of static and time-dependent external fields
and analyze the influence of damping for a uniaxial and a cubic anisotropy.",0802.1740v1
2008-05-21,Non-equilibrium thermodynamic study of magnetization dynamics in the presence of spin-transfer torque,"The dynamics of magnetization in the presence of spin-transfer torque was
studied. We derived the equation for the motion of magnetization in the
presence of a spin current by using the local equilibrium assumption in
non-equilibrium thermodynamics. We show that, in the resultant equation, the
ratio of the Gilbert damping constant, $\alpha$, and the coefficient, $\beta$,
of the current-induced torque, called non-adiabatic torque, depends on the
relaxation time of the fluctuating field $\tau_{c}$. The equality
$\alpha=\beta$ holds when $\tau_c$ is very short compared to the time scale of
magnetization dynamics. We apply our theory to current-induced magnetization
reversal in magnetic multilayers and show that the switching time is a
decreasing function of $\tau_{c}$.",0805.3306v1
2008-06-28,Theory of spin magnetohydrodynamics,"We develop a phenomenological hydrodynamic theory of coherent magnetic
precession coupled to electric currents. Exchange interaction between electron
spin and collective magnetic texture produces two reciprocal effects:
spin-transfer torque on the magnetic order parameter and the Berry-phase gauge
field experienced by the itinerant electrons. The dissipative processes are
governed by three coefficients: the ohmic resistance, Gilbert damping of the
magnetization, and the ""beta coefficient"" describing viscous coupling between
magnetic dynamics and electric current, which stems from spin mistracking of
the magnetic order. We develop general magnetohydrodynamic equations and
discuss the net dissipation produced by the coupled dynamics. The latter in
particular allows us to determine a lower bound on the magnetic-texture
resistivity.",0806.4656v2
2008-09-25,The theory of magnetic field induced domain-wall propagation in magnetic nanowires,"A global picture of magnetic domain wall (DW) propagation in a nanowire
driven by a magnetic field is obtained: A static DW cannot exist in a
homogeneous magnetic nanowire when an external magnetic field is applied. Thus,
a DW must vary with time under a static magnetic field. A moving DW must
dissipate energy due to the Gilbert damping. As a result, the wire has to
release its Zeeman energy through the DW propagation along the field direction.
The DW propagation speed is proportional to the energy dissipation rate that is
determined by the DW structure. An oscillatory DW motion, either the precession
around the wire axis or the breath of DW width, should lead to the speed
oscillation.",0809.4311v1
2008-10-08,Transverse spin diffusion in ferromagnets,"We discuss the dissipative diffusion-type term of the form
$\mathbf{m}\times\nabla^2\partial_t\mathbf{m}$ in the phenomenological
Landau-Lifshitz equation of ferromagnetic precession, which describes enhanced
Gilbert damping of finite-momentum spin waves. This term arises physically from
itinerant-electron spin flows through a perturbed ferromagnetic configuration
and can be understood to originate in the ferromagnetic spin pumping in the
continuum limit. We develop a general phenomenology as well as provide
microscopic theory for the Stoner and s-d models of ferromagnetism, taking into
account disorder and electron-electron scattering. The latter is manifested in
our problem through the Coulomb drag between the spin bands. The spin diffusion
is identified in terms of the transverse spin conductivity, in analogy with the
Einstein relation in the kinetic theory.",0810.1340v2
2008-10-16,Interaction of reed and acoustic resonator in clarinetlike systems,"Sound emergence in clarinetlike instruments is investigated in terms of
instability of the static regime. Various models of reed-bore coupling are
considered, from the pioneering work of Wilson and Beavers [""Operating modes of
the clarinet"", J. Acoust. Soc. Am. 56, 653--658 (1974)] to more recent modeling
including viscothermal bore losses and vena contracta at the reed inlet. The
pressure threshold above which these models may oscillate as well as the
frequency of oscillation at threshold are calculated. In addition to Wilson and
Beavers' previous conclusions concerning the role of the reed damping in the
selection of the register the instrument will play on, the influence of the
reed motion induced flow is also emphasized, particularly its effect on playing
frequencies, contributing to reduce discrepancies between Wilson and Beavers'
experimental results and theory, despite discrepancies still remain concerning
the pressure threshold. Finally, analytical approximations of the oscillating
solution based on Fourier series expansion are obtained in the vicinity of the
threshold of oscillation. This allows to emphasize the conditions which
determine the nature of the bifurcation (direct or inverse) through which the
note may emerge, with therefore important consequences on the musical playing
performances.",0810.2870v1
2008-11-13,"Intrinsic Coupling between Current and Domain Wall Motion in (Ga,Mn)As","We consider current-induced domain wall motion and, the reciprocal process,
moving domain wall-induced current. The associated Onsager coefficients are
expressed in terms of scattering matrices. Uncommonly, in (Ga,Mn)As, the
effective Gilbert damping coefficient $\alpha_w$ and the effective out-of-plane
spin transfer torque parameter $\beta_w$ are dominated by spin-orbit
interaction in combination with scattering off the domain wall, and not
scattering off extrinsic impurities. Numerical calculations give $\alpha_w \sim
0.01$ and $\beta_w \sim 1$ in dirty (Ga,Mn)As. The extraordinary large
$\beta_w$ parameter allows experimental detection of current or voltage induced
by domain wall motion in (Ga,Mn)As.",0811.2235v2
2008-11-21,Spin Transfer Torque as a Non-Conservative Pseudo-Field,"In this paper we show that the spin transfer torque can be described by a
pseudo magnetic field, proportional to the magnetic moment of the itinerant
electrons that enters the Landau-Lifshitz-Gilbert equation in the same way as
other external or internal magnetic fields. However, unlike an ordinary
magnetic field, which is always conservative in nature, the spin torque induced
pseudo field may have both conservative and non-conservative components. We
further show that the magnetic moment of itinerant electrons develops an
out-of-plane component only at non-equilibrium and this component is
responsible for the Slonczewski type switching that acts against the damping
and is always non-conservative. On the other hand, the in-plane components of
the pseudo field exist both at equilibrium and out-of-equilibrium, and are
responsible for the field like term. For tunnel based devices, this term
results in lower switching current for anti-parallel (AP) to parallel (P)
switching compared to P to AP, even when the torque magnitudes are completely
symmetric with voltage.",0811.3472v1
2008-12-13,Non-Adiabatic Spin Transfer Torque in Real Materials,"The motion of simple domain walls and of more complex magnetic textures in
the presence of a transport current is described by the
Landau-Lifshitz-Slonczewski (LLS) equations. Predictions of the LLS equations
depend sensitively on the ratio between the dimensionless material parameter
$\beta$ which characterizes non-adiabatic spin-transfer torques and the Gilbert
damping parameter $\alpha$. This ratio has been variously estimated to be close
to 0, close to 1, and large compared to 1. By identifying $\beta$ as the
influence of a transport current on $\alpha$, we derive a concise, explicit and
relatively simple expression which relates $\beta$ to the band structure and
Bloch state lifetimes of a magnetic metal. Using this expression we demonstrate
that intrinsic spin-orbit interactions lead to intra-band contributions to
$\beta$ which are often dominant and can be (i) estimated with some confidence
and (ii) interpreted using the ""breathing Fermi surface"" model.",0812.2570v1
2009-05-01,Spin excitations in a monolayer scanned by a magnetic tip,"Energy dissipation via spin excitations is investigated for a hard
ferromagnetic tip scanning a soft magnetic monolayer. We use the classical
Heisenberg model with Landau-Lifshitz-Gilbert (LLG)-dynamics including a
stochastic field representing finite temperatures. The friction force depends
linearly on the velocity (provided it is small enough) for all temperatures.
For low temperatures, the corresponding friction coefficient is proportional to
the phenomenological damping constant of the LLG equation. This dependence is
lost at high temperatures, where the friction coefficient decreases
exponentially. These findings can be explained by properties of the spin
polarization cloud dragged along with the tip.",0905.0112v2
2009-05-29,Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy,"Transition metal ferromagnetic films with perpendicular magnetic anisotropy
(PMA) have ferromagnetic resonance (FMR) linewidths that are one order of
magnitude larger than soft magnetic materials, such as pure iron (Fe) and
permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate
the origin of the enhanced linewidth in Ni$|$Co multilayer films with PMA. The
FMR linewidth depends linearly on frequency for perpendicular applied fields
and increases significantly when the magnetization is rotated into the film
plane. Irradiation of the film with Helium ions decreases the PMA and the
distribution of PMA parameters. This leads to a great reduction of the FMR
linewidth for in-plane magnetization. These results suggest that fluctuations
in PMA lead to a large two magnon scattering contribution to the linewidth for
in-plane magnetization and establish that the Gilbert damping is enhanced in
such materials ($\alpha \approx 0.04$, compared to $\alpha \approx 0.002$ for
pure Fe).",0905.4779v2
2009-10-01,Spin motive forces and current fluctuations due to Brownian motion of domain walls,"We compute the power spectrum of the noise in the current due to spin motive
forces by a fluctuating domain wall. We find that the power spectrum of the
noise in the current is colored, and depends on the Gilbert damping, the spin
transfer torque parameter $\beta$, and the domain-wall pinning potential and
magnetic anisotropy. We also determine the average current induced by the
thermally-assisted motion of a domain wall that is driven by an external
magnetic field. Our results suggest that measuring the power spectrum of the
noise in the current in the presence of a domain wall may provide a new method
for characterizing the current-to-domain-wall coupling in the system.",0910.0163v1
2009-10-08,Fast domain wall propagation under an optimal field pulse in magnetic nanowires,"We investigate field-driven domain wall (DW) propagation in magnetic
nanowires in the framework of the Landau-Lifshitz-Gilbert equation. We propose
a new strategy to speed up the DW motion in a uniaxial magnetic nanowire by
using an optimal space-dependent field pulse synchronized with the DW
propagation. Depending on the damping parameter, the DW velocity can be
increased by about two orders of magnitude compared the standard case of a
static uniform field. Moreover, under the optimal field pulse, the change in
total magnetic energy in the nanowire is proportional to the DW velocity,
implying that rapid energy release is essential for fast DW propagation.",0910.1477v2
2009-11-24,Origin of adiabatic and non-adiabatic spin transfer torques in current-driven magnetic domain wall motion,"A consistent theory to describe the correlated dynamics of quantum mechanical
itinerant spins and semiclassical local magnetization is given. We consider the
itinerant spins as quantum mechanical operators, whereas local moments are
considered within classical Lagrangian formalism. By appropriately treating
fluctuation space spanned by basis functions, including a zero-mode wave
function, we construct coupled equations of motion for the collective
coordinate of the center-of-mass motion and the localized zero-mode coordinate
perpendicular to the domain wall plane. By solving them, we demonstrate that
the correlated dynamics is understood through a hierarchy of two time scales:
Boltzmann relaxation time when a non-adiabatic part of the spin-transfer torque
appears, and Gilbert damping time when adiabatic part comes up.",0911.4628v1
2010-01-26,Strategies and tolerances of spin transfer torque switching,"Schemes of switching nanomagnetic memories via the effect of spin torque with
various polarizations of injected electrons are studied. Simulations based on
macrospin and micromagnetic theories are performed and compared. We demonstrate
that switching with perpendicularly polarized current by short pulses and free
precession requires smaller time and energy than spin torque switching with
collinear in plane spin polarization; it is also found to be superior to other
kinds of memories. We study the tolerances of switching to the magnitude of
current and pulse duration. An increased Gilbert damping is found to improve
tolerances of perpendicular switching without increasing the threshold current,
unlike in plane switching.",1001.4578v1
2010-03-31,Magnonic Crystal with Two-Dimensional Periodicity as a Waveguide for Spin Waves,"We describe a simple method of including dissipation in the spin wave band
structure of a periodic ferromagnetic composite, by solving the Landau-Lifshitz
equation for the magnetization with the Gilbert damping term. We use this
approach to calculate the band structure of square and triangular arrays of Ni
nanocylinders embedded in an Fe host. The results show that there are certain
bands and special directions in the Brillouin zone where the spin wave lifetime
is increased by more than an order of magnitude above its average value. Thus,
it may be possible to generate spin waves in such composites decay especially
slowly, and propagate especially large distances, for certain frequencies and
directions in ${\bf k}$-space.",1003.6092v1
2010-07-20,Precessing vortices and antivortices in ferromagnetic elements,"A micromagnetic numerical study of the precessional motion of the vortex and
antivortex states in soft ferromagnetic circular nanodots is presented using
Landau-Lifshitz-Gilbert dynamics. For sufficiently small dot thickness and
diameter, the vortex state is metastable and spirals toward the center of the
dot when its initial displacement is smaller than a critical value. Otherwise,
the vortex spirals away from the center and eventually exits the dot which
remains in a state of in-plane magnetization (ground state). In contrast, the
antivortex is always unstable and performs damped precession resulting in
annihilation at the dot circumference. The vortex and antivortex frequencies of
precession are compared with the response expected on the basis of Thiele's
theory of collective coordinates. We also calculate the vortex restoring force
with an explicit account of the magnetostatic and exchange interaction on the
basis of the 'rigid' vortex and 'two-vortices side charges free' models and
show that neither model explains the vortex translation mode eigenfrequency for
nanodots of sufficiently small size.",1007.3508v1
2010-08-03,Determination of the spin-flip time in ferromagnetic SrRuO3 from time-resolved Kerr measurements,"We report time-resolved Kerr effect measurements of magnetization dynamics in
ferromagnetic SrRuO3. We observe that the demagnetization time slows
substantially at temperatures within 15K of the Curie temperature, which is ~
150K. We analyze the data with a phenomenological model that relates the
demagnetization time to the spin flip time. In agreement with our observations
the model yields a demagnetization time that is inversely proportional to T-Tc.
We also make a direct comparison of the spin flip rate and the Gilbert damping
coefficient showing that their ratio very close to kBTc, indicating a common
origin for these phenomena.",1008.0674v1
2010-10-07,Power optimization for domain wall motion in ferromagnetic nanowires,"The current mediated domain-wall dynamics in a thin ferromagnetic wire is
investigated. We derive the effective equations of motion of the domain wall.
They are used to study the possibility to optimize the power supplied by
electric current for the motion of domain walls in a nanowire. We show that a
certain resonant time-dependent current moving a domain wall can significantly
reduce the Joule heating in the wire, and thus it can lead to a novel proposal
for the most energy efficient memory devices. We discuss how Gilbert damping,
non-adiabatic spin transfer torque, and the presence of Dzyaloshinskii-Moriya
interaction can effect this power optimization.",1010.1537v1
2011-03-30,Spin motive forces due to magnetic vortices and domain walls,"We study spin motive forces, i.e, spin-dependent forces, and voltages induced
by time-dependent magnetization textures, for moving magnetic vortices and
domain walls. First, we consider the voltage generated by a one-dimensional
field-driven domain wall. Next, we perform detailed calculations on
field-driven vortex domain walls. We find that the results for the voltage as a
function of magnetic field differ between the one-dimensional and vortex domain
wall. For the experimentally relevant case of a vortex domain wall, the
dependence of voltage on field around Walker breakdown depends qualitatively on
the ratio of the so-called $\beta$-parameter to the Gilbert damping constant,
and thus provides a way to determine this ratio experimentally. We also
consider vortices on a magnetic disk in the presence of an AC magnetic field.
In this case, the phase difference between field and voltage on the edge is
determined by the $\beta$ parameter, providing another experimental method to
determine this quantity.",1103.5858v3
2011-07-04,Influence of randomness and retardation on the FMR-linewidth,"The theory predicts that the spin-wave lifetime $\tau_L$ and the linewidth of
ferromagnetic resonance $\Delta B$ can be governed by random fields and spatial
memory. To that aim the effective field around which the magnetic moments
perform a precession is superimposed by a stochastic time dependent magnetic
field with finite correlation time. The magnetization dynamics is altered by
inclusion of a spatial memory effect monitoring a non-local interaction of size
$\xi$. The underlying Landau-Lifshitz-Gilbert equation (LLG) is modified
accordingly. The stochastic LLG is equivalent to a Fokker-Planck equation which
enables to calculate the mean values of the magnetization vector. Within the
spin-wave approximation we present an analytical solution for the excitation
energy and its damping. The lifetime and the linewidth are analyzed depending
on the strength of the random field $D$ and its correlation time $\tau_c$ as
well as the retardation strength $\Gamma_0$ and the size $\xi$. Whereas
$\tau_L$ decreases with increasing $D$, retardation strength $\Gamma_0$ and
$\tau_c$, the lifetime is enhanced for growing width $\xi$ of the spatial
retardation kernel. In the same manner we calculate the experimentally
measurable linewidth $\Delta B$ is increased strongly when the correlation time
$\tau_c$ ranges in the nanosecond interval.",1107.0638v1
2011-11-18,Charge and Spin Transport in Magnetic Tunnel Junctions: Microscopic Theory,"We study the charge and spin currents passing through a magnetic tunnel
junction (MTJ) on the basis of a tight-binding model. The currents are
evaluated perturbatively with respect to the tunnel Hamiltonian. The charge
current has the form $A[\bm M_1(t)\times\dot{\bm M}_1(t)]\cdot\bm M_2+B\dot{\bm
M}_1(t)\cdot\bm M_2$, where $\bm M_1(t)$ and $\bm M_2$ denote the directions of
the magnetization in the free layer and fixed layer, respectively. The constant
$A$ vanishes when one or both layers are insulators, {while the constant $B$
disappears when both layers are insulators or the same ferromagnets.} The first
term in the expression for charge current represents dissipation driven by the
effective electric field induced by the dynamic magnetization. In addition,
from an investigation of the spin current, we obtain the microscopic expression
for the enhanced Gilbert damping constant $\varDelta \alpha$. We show that
$\varDelta\alpha$ is proportional to the tunnel conductance and depends on the
bias voltage.",1111.4295v2
2012-01-17,Magnetic vortex echoes: application to the study of arrays of magnetic nanostructures,"We propose the use of the gyrotropic motion of vortex cores in nanomagnets to
produce a magnetic echo, analogous to the spin echo in NMR. This echo occurs
when an array of nanomagnets, e.g., nanodisks, is magnetized with an in-plane
(xy) field, and after a time \tau a field pulse inverts the core magnetization;
the echo is a peak in M_{xy} at t=2\tau. Its relaxation times depend on the
inhomogeneity, on the interaction between the nanodots and on the Gilbert
damping constant \alpha. Its feasibility is demonstrated using micromagnetic
simulation. To illustrate an application of the echoes, we have determined the
inhomogeneity and measured the magnetic interaction in an array of nanodisks
separated by a distance d, finding a d^{-n} dependence, with n\approx 4.",1201.3553v1
2012-02-15,Current-induced motion of a transverse magnetic domain wall in the presence of spin Hall effect,"We theoretically study the current-induced dynamics of a transverse magnetic
domain wall in bi-layer nanowires consisting of a ferromagnet on top of a
nonmagnet having strong spin-orbit coupling. Domain wall dynamics is
characterized by two threshold current densities, $J_{th}^{WB}$ and
$J_{th}^{REV}$, where $J_{th}^{WB}$ is a threshold for the chirality switching
of the domain wall and $J_{th}^{REV}$ is another threshold for the reversed
domain wall motion caused by spin Hall effect. Domain walls with a certain
chirality may move opposite to the electron-flow direction with high speed in
the current range $J_{th}^{REV} < J < J_{th}^{WB}$ for the system designed to
satisfy the conditions $J_{th}^{WB} > J_{th}^{REV}$ and \alpha > \beta, where
\alpha is the Gilbert damping constant and \beta is the nonadiabaticity of spin
torque. Micromagnetic simulations confirm the validity of analytical results.",1202.3450v1
2012-04-23,Rotating skyrmion lattices by spin torques and field or temperature gradients,"Chiral magnets like MnSi form lattices of skyrmions, i.e. magnetic whirls,
which react sensitively to small electric currents j above a critical current
density jc. The interplay of these currents with tiny gradients of either the
magnetic field or the temperature can induce a rotation of the magnetic pattern
for j>jc. Either a rotation by a finite angle of up to 15 degree or -- for
larger gradients -- a continuous rotation with a finite angular velocity is
induced. We use Landau-Lifshitz-Gilbert equations extended by extra damping
terms in combination with a phenomenological treatment of pinning forces to
develop a theory of the relevant rotational torques. Experimental neutron
scattering data on the angular distribution of skyrmion lattices suggests that
continuously rotating domains are easy to obtain in the presence of remarkably
small currents and temperature gradients.",1204.5051v1
2012-07-09,Thermal vortex dynamics in thin circular ferromagnetic nanodisks,"The dynamics of gyrotropic vortex motion in a thin circular nanodisk of soft
ferromagnetic material is considered. The demagnetization field is calculated
using two-dimensional Green's functions for the thin film problem and fast
Fourier transforms. At zero temperature, the dynamics of the
Landau-Lifshitz-Gilbert equation is simulated using fourth order Runge-Kutta
integration. Pure vortex initial conditions at a desired position are obtained
with a Lagrange multipliers constraint. These methods give accurate estimates
of the vortex restoring force constant $k_F$ and gyrotropic frequency, showing
that the vortex core motion is described by the Thiele equation to very high
precision. At finite temperature, the second order Heun algorithm is applied to
the Langevin dynamical equation with thermal noise and damping. A spontaneous
gyrotropic motion takes place without the application of an external magnetic
field, driven only by thermal fluctuations. The statistics of the vortex radial
position and rotational velocity are described with Boltzmann distributions
determined by $k_F$ and by a vortex gyrotropic mass $m_G=G^2/k_F$,
respectively, where $G$ is the vortex gyrovector.",1207.2192v2
2013-02-19,Chirality Sensitive Domain Wall Motion in Spin-Orbit Coupled Ferromagnets,"Using the Lagrangian formalism, we solve analytically the equations of motion
for current-induced domain-wall dynamics in a ferromagnet with Rashba
spin-orbit coupling. An exact solution for the domain wall velocity is
provided, including the effect of non-equilibrium conduction electron
spin-density, Gilbert damping, and the Rashba interaction parameter. We
demonstrate explicitly that the influence of spin-orbit interaction can be
qualitatively different from the role of non-adiabatic spin-torque in the sense
that the former is sensitive to the chirality of the domain wall whereas the
latter is not: the domain wall velocity shows a reentrant behavior upon
changing the chirality of the domain wall. This could be used to experimentally
distinguish between the spin-orbit and non-adiabatic contribution to the wall
speed. A quantitative estimate for the attainable domain wall velocity is
given, based on an experimentally relevant set of parameters for the system.",1302.4744v1
2013-12-17,Control of the in-plane anisotropy in off-stoichiometric NiMnSb,"NiMnSb is a ferromagnetic half-metal which, because of its rich anisotropy
and very low Gilbert damping, is a promising candidate for applications in
information technologies. We have investigated the in-plane anisotropy
properties of thin, MBE-grown NiMnSb films as a function of their Mn
concentration. Using ferromagnetic resonance (FMR) to determine the uniaxial
and four-fold anisotropy fields, 2KU/Ms and 2K1/Ms, we find that a small
variation in composition is sufficient to change the film from primarily
four-fold to primarily uniaxial behavior, allowing for continuous tuning of the
anisotropy. This provides valuable flexibility in designing new device
geometries.",1312.4781v2
2014-05-09,Current-induced magnetization dynamics in two magnetic insulators separated by a normal metal,"We study the dynamics of spin valves consisting of two layers of magnetic
insulators separated by a normal metal in the macrospin model. A current
through the spacer generates a spin Hall current that can actuate the
magnetization via the spin-transfer torque. We derive expressions for the
effective Gilbert damping and the critical currents for the onset of
magnetization dynamics including the effects of spin pumping that can be tested
by ferromagnetic resonance experiments. The current generates an amplitude
asymmetry between the in-phase and out-of-phase modes. We briefly discuss
superlattices of metals and magnetic insulators.",1405.2267v1
2014-05-25,Spin Hall phenomenology of magnetic dynamics,"We study the role of spin-orbit interactions in the coupled magnetoelectric
dynamics of a ferromagnetic film coated with an electrical conductor. While the
main thrust of this work is phenomenological, several popular simple models are
considered microscopically in some detail, including Rashba and Dirac
two-dimensional electron gases coupled to a magnetic insulator, as well as a
diffusive spin Hall system. We focus on the long-wavelength magnetic dynamics
that experiences current-induced torques and produces fictitious electromotive
forces. Our phenomenology provides a suitable framework for analyzing
experiments on current-induced magnetic dynamics and reciprocal charge pumping,
including the effects of magnetoresistance and Gilbert-damping anisotropies,
without a need to resort to any microscopic considerations or modeling.
Finally, some remarks are made regarding the interplay of spin-orbit
interactions and magnetic textures.",1405.6354v2
2014-08-21,Brownian motion of massive skyrmions forced by spin polarized currents,"We report on the thermal effects on the motion of current-driven massive
magnetic skyrmions. The reduced equation for the motion of skyrmion has the
form of a stochastic generalized Thiele's equation. We propose an ansatz for
the magnetization texture of a non-rigid single skyrmion that depends linearly
with the velocity. By utilizing this ansatz it is is found that the mass of
skyrmion is closely related to intrinsic skyrmion parameters, such as Gilbert
damping, skyrmion-charge and dissipative force. We have found an exact
expression for the average drift velocity as well as the mean-square velocity
of the skyrmion. The longitudinal and transverse mobility of skyrmions for
small spin-velocity of electrons is also determined and found to be independent
of the skyrmion mass.",1408.4861v2
2014-11-11,Capturing of a Magnetic Skyrmion with a Hole,"Magnetic whirls in chiral magnets, so-called skyrmions, can be manipulated by
ultrasmall current densities. Here we study both analytically and numerically
the interactions of a single skyrmion in two dimensions with a small hole in
the magnetic layer. Results from micromagnetic simulations are in good
agreement with effective equations of motion obtained from a generalization of
the Thiele approach. Skyrmion-defect interactions are described by an effective
potential with both repulsive and attractive components. For small current
densities a previously pinned skyrmion stays pinned whereas an unpinned
skyrmion moves around the impurities and never gets captured. For higher
current densities, j_c1 < j < j_c2, however, single holes are able to capture
moving skyrmions. The maximal cross section is proportional to the skyrmion
radius and to Sqrt(alpha), where alpha is the Gilbert damping. For j > j_c2 all
skyrmions are depinned. Small changes of the magnetic field strongly change the
pinning properties, one can even reach a regime without pinning, j_c2=0. We
also show that a small density of holes can effectively accelerate the motion
of the skyrmion and introduce a Hall effect for the skyrmion.",1411.2857v1
2014-12-01,Dissipation due to pure spin-current generated by spin pumping,"Based on spin-dependent transport theory and thermodynamics, we develop a
generalized theory of the Joule heating in the presence of a spin current.
Along with the conventional Joule heating consisting of an electric current and
electrochemical potential, it is found that the spin current and spin
accumulation give an additional dissipation because the spin-dependent
scatterings inside bulk and ferromagnetic/nonmagnetic interface lead to a
change of entropy. The theory is applied to investigate the dissipation due to
pure spin-current generated by spin pumping across a
ferromagnetic/nonmagnetic/ferromagnetic multilayer. The dissipation arises from
an interface because the spin pumping is a transfer of both the spin angular
momentum and the energy from the ferromagnet to conduction electrons near the
interface. It is found that the dissipation is proportional to the enhancement
of the Gilbert damping constant by spin pumping.",1412.0688v1
2015-01-30,Head-to-Head Domain Wall Structures in Wide Permalloy Strips,"We analyze the equilibrium micromagnetic domain wall structures encountered
in Permalloy strips of a wide range of thicknesses and widths, with strip
widths up to several micrometers. By performing an extensive set of
micromagnetic simulations, we show that the equilibrium phase diagram of the
domain wall structures exhibits in addition to the previously found structures
(symmetric and asymmetric transverse walls, vortex wall) also double vortex and
triple vortex domain walls for large enough strip widths and thicknesses. Also
several metastable domain wall structures are found for wide and/or thick
strips. We discuss the details of the relaxation process from random
magnetization initial states towards the stable domain wall structure, and show
that our results are robust with respect to changes of e.g. the magnitude of
the Gilbert damping constant and details of the initial conditions.",1501.07731v1
2015-02-19,Characterization of spin relaxation anisotropy in Co using spin pumping,"Ferromagnets are believed to exhibit strongly anisotropic spin relaxation,
with relaxation lengths for spin longitudinal to magnetization significantly
longer than those for spin transverse to magnetization. Here we characterize
the anisotropy of spin relaxation in Co using the spin pumping contribution to
Gilbert damping in noncollinearly magnetized Py$_{1-x}$Cu$_{x}$/Cu/Co trilayer
structures. The static magnetization angle between Py$_{1-x}$Cu$_{x}$ and Co,
adjusted under field bias perpendicular to film planes, controls the
projections of longitudinal and transverse spin current pumped from
Py$_{1-x}$Cu$_{x}$ into Co. We find nearly isotropic absorption of pure spin
current in Co using this technique; fits to a diffusive transport model yield
the longitudinal spin relaxation length $< 2$ nm in Co. The longitudinal spin
relaxation lengths found are an order of magnitude smaller than those
determined by current-perpendicular-to-planes giant magnetoresistance
measurements, but comparable with transverse spin relaxation lengths in Co
determined by spin pumping.",1502.05687v3
2015-03-26,Thermophoresis of an Antiferromagnetic Soliton,"We study dynamics of an antiferromagnetic soliton under a temperature
gradient. To this end, we start by phenomenologically constructing the
stochastic Landau-Lifshitz-Gilbert equation for an antiferromagnet with the aid
of the fluctuation-dissipation theorem. We then derive the Langevin equation
for the soliton's center of mass by the collective coordinate approach. An
antiferromagentic soliton behaves as a classical massive particle immersed in a
viscous medium. By considering a thermodynamic ensemble of solitons, we obtain
the Fokker-Planck equation, from which we extract the average drift velocity of
a soliton. The diffusion coefficient is inversely proportional to a small
damping constant $\alpha$, which can yield a drift velocity of tens of m/s
under a temperature gradient of $1$ K/mm for a domain wall in an easy-axis
antiferromagnetic wire with $\alpha \sim 10^{-4}$.",1503.07854v2
2015-04-01,Multiscale modeling of ultrafast element-specific magnetization dynamics of ferromagnetic alloys,"A hierarchical multiscale approach to model the magnetization dynamics of
ferromagnetic ran- dom alloys is presented. First-principles calculations of
the Heisenberg exchange integrals are linked to atomistic spin models based
upon the stochastic Landau-Lifshitz-Gilbert (LLG) equation to calculate
temperature-dependent parameters (e.g., effective exchange interactions,
damping param- eters). These parameters are subsequently used in the
Landau-Lifshitz-Bloch (LLB) model for multi-sublattice magnets to calculate
numerically and analytically the ultrafast demagnetization times. The developed
multiscale method is applied here to FeNi (permalloy) as well as to copper-
doped FeNi alloys. We find that after an ultrafast heat pulse the Ni sublattice
demagnetizes faster than the Fe sublattice for the here-studied FeNi-based
alloys.",1504.00199v1
2015-05-04,High-topological-number magnetic skyrmions and topologically protected dissipative structure,"The magnetic skyrmion with the topological number of unity ($Q=1$) is a
well-known nanometric swirling spin structure in the nonlinear $\sigma$ model
with the Dzyaloshinskii-Moriya interaction. Here, we show that magnetic
skyrmion with the topological number of two ($Q=2$) can be created and
stabilized by applying vertical spin-polarized current though it cannot exist
as a static stable excitation. Magnetic skyrmion with $Q=2$ is a nonequilibrium
dynamic object, subsisting on a balance between the energy injection from the
current and the energy dissipation by the Gilbert damping. Once it is created,
it becomes a topologically protected object against fluctuations of various
variables including the injected current itself. Hence, we may call it a
topologically protected dissipative structure. We also elucidate the nucleation
and destruction mechanisms of the magnetic skyrmion with $Q=2$ by studying the
evolutions of the magnetization distribution, the topological charge density as
well as the energy density. Our results will be useful for the study of the
nontrivial topology of magnetic skyrmions with higher topological numbers.",1505.00522v2
2015-08-06,Large spin-wave bullet in a ferrimagnetic insulator driven by spin Hall effect,"Due to its transverse nature, spin Hall effects (SHE) provide the possibility
to excite and detect spin currents and magnetization dynamics even in magnetic
insulators. Magnetic insulators are outstanding materials for the investigation
of nonlinear phenomena and for novel low power spintronics applications because
of their extremely low Gilbert damping. Here, we report on the direct imaging
of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the
ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ based on the excitation and
detection by SHEs. The driven spin dynamics in Y$_3$Fe$_5$O$_{12}$ is directly
imaged by spatially-resolved microfocused Brillouin light scattering (BLS)
spectroscopy. Previously, ST-FMR experiments assumed a uniform precession
across the sample, which is not valid in our measurements. A strong spin-wave
localization in the center of the sample is observed indicating the formation
of a nonlinear, self-localized spin-wave `bullet'.",1508.01427v1
2015-12-02,Bose-Einstein Condensation of Magnons Pumped by the Bulk Spin Seebeck Effect,"We propose inducing Bose-Einstein condensation of magnons in a magnetic
insulator by a heat flow oriented toward its boundary. At a critical heat flux,
the oversaturated thermal gas of magnons accumulated at the boundary
precipitates the condensate, which then grows gradually as the thermal bias is
dialed up further. The thermal magnons thus pumped by the magnonic bulk (spin)
Seebeck effect must generally overcome both the local Gilbert damping
associated with the coherent magnetic dynamics as well as the radiative
spin-wave losses toward the magnetic bulk, in order to achieve the threshold of
condensation. We quantitatively estimate the requisite bias in the case of the
ferrimagnetic yttrium iron garnet, discuss different physical regimes of
condensation, and contrast it with the competing (so-called Doppler-shift) bulk
instability.",1512.00557v1
2016-01-10,"Interfacial Dzyaloshinskii-Moriya interaction, surface anisotropy energy,and spin pumping at spin orbit coupled Ir/Co interface","The interfacial Dzyaloshinskii-Moriya interaction (iDMI), surface anisotropy
energy, and spin pumping at the Ir/Co interface are experimentally investigated
by performing Brillouin light scattering. Contrary to previous reports, we
suggest that the sign of the iDMI at the Ir/Co interface is the same as in the
case of the Pt/Co interface. We also find that the magnitude of the iDMI energy
density is relatively smaller than in the case of the Pt/Co interface, despite
the large strong spin-orbit coupling (SOC) of Ir. The saturation magnetization
and the perpendicular magnetic anisotropy (PMA) energy are significantly
improved due to a strong SOC. Our findings suggest that an SOC in an Ir/Co
system behaves in different ways for iDMI and PMA. Finally, we determine the
spin pumping effect at the Ir/Co interface, and it increases the Gilbert
damping constant from 0.012 to 0.024 for 1.5 nmthick Co.",1601.02210v3
2016-02-23,Relaxation of a classical spin coupled to a strongly correlated electron system,"A classical spin which is antiferromagnetically coupled to a system of
strongly correlated conduction electrons is shown to exhibit unconventional
real-time dynamics which cannot be described by Gilbert damping. Depending on
the strength of the local Coulomb interaction, the two main electronic
dissipation channels, transport of excitations via correlated hopping and via
excitations of correlation-induced magnetic moments, become active on largely
different time scales. We demonstrate that this can lead to a prethermalization
scenario which so far has been observed in purely electronic systems only and
which is governed here by proximity to the divergent magnetic time scale in the
infinite-U limit.",1602.07317v2
2016-04-24,Coupled Spin-Light dynamics in Cavity Optomagnonics,"Experiments during the past two years have shown strong resonant
photon-magnon coupling in microwave cavities, while coupling in the optical
regime was demonstrated very recently for the first time. Unlike with
microwaves, the coupling in optical cavities is parametric, akin to
optomechanical systems. This line of research promises to evolve into a new
field of optomagnonics, aimed at the coherent manipulation of elementary
magnetic excitations by optical means. In this work we derive the microscopic
optomagnonic Hamiltonian. In the linear regime the system reduces to the
well-known optomechanical case, with remarkably large coupling. Going beyond
that, we study the optically induced nonlinear classical dynamics of a
macrospin. In the fast cavity regime we obtain an effective equation of motion
for the spin and show that the light field induces a dissipative term
reminiscent of Gilbert damping. The induced dissipation coefficient however can
change sign on the Bloch sphere, giving rise to self-sustained oscillations.
When the full dynamics of the system is considered, the system can enter a
chaotic regime by successive period doubling of the oscillations.",1604.07053v3
2016-05-12,Classical limit of Rabi nutations in spins of ferromagnets,"Rabi oscillations describe the interaction of a two-level system with a
rotating electromagnetic field. As such, they serve as the principle method for
manipulating quantum bits. By using a combination of femtosecond laser pulses
and microwave excitations, we have observed the classical form of Rabi
nutations in a ferromagnetic system whose equations of motion mirror the case
of a precessing quantum two-level system. Key to our experiments is the
selection of a subset of spins that is in resonance with the microwave
excitation and whose coherence time is thereby extended. Taking advantage of
Gilbert damping, the relaxation times are further increased such that
mode-locking takes place. The observation of such Rabi nutations is the first
step towards potential applications based on phase-coherent spin manipulation
in ferromagnets.",1605.03996v1
2016-05-21,Landau-Lifshitz theory of the magnon-drag thermopower,"Metallic ferromagnets subjected to a temperature gradient exhibit a magnonic
drag of the electric current. We address this problem by solving a stochastic
Landau-Lifshitz equation to calculate the magnon-drag thermopower. The
long-wavelength magnetic dynamics result in two contributions to the
electromotive force acting on electrons: (1) An adiabatic Berry-phase force
related to the solid angle subtended by the magnetic precession and (2) a
dissipative correction thereof, which is rooted microscopically in the
spin-dephasing scattering. The first contribution results in a net force
pushing the electrons towards the hot side, while the second contribution drags
electrons towards the cold side, i.e., in the direction of the magnonic drift.
The ratio between the two forces is proportional to the ratio between the
Gilbert damping coefficient $\alpha$ and the coefficient $\beta$ parametrizing
the dissipative contribution to the electromotive force.",1605.06578v1
2016-06-07,The temperature dependence of FeRh's transport properties,"The finite-temperature transport properties of FeRh compounds are
investigated by first-principles Density Functional Theory-based calculations.
The focus is on the behavior of the longitudinal resistivity with rising
temperature, which exhibits an abrupt decrease at the metamagnetic transition
point, $T = T_m$ between ferro- and antiferromagnetic phases. A detailed
electronic structure investigation for $T \geq 0$ K explains this feature and
demonstrates the important role of (i) the difference of the electronic
structure at the Fermi level between the two magnetically ordered states and
(ii) the different degree of thermally induced magnetic disorder in the
vicinity of $T_m$, giving different contributions to the resistivity. To
support these conclusions, we also describe the temperature dependence of the
spin-orbit induced anomalous Hall resistivity and Gilbert damping parameter.
For the various response quantities considered the impact of thermal lattice
vibrations and spin fluctuations on their temperature dependence is
investigated in detail. Comparison with corresponding experimental data finds
in general a very good agreement.",1606.02072v1
2016-09-05,Coarsening dynamics of topological defects in thin Permalloy films,"We study the dynamics of topological defects in the magnetic texture of
rectangular Permalloy thin film elements during relaxation from random
magnetization initial states. Our full micromagnetic simulations reveal complex
defect dynamics during relaxation towards the stable Landau closure domain
pattern, manifested as temporal power-law decay, with a system-size dependent
cut-off time, of various quantities. These include the energy density of the
system, and the number densities of the different kinds of topological defects
present in the system. The related power-law exponents assume non-trivial
values, and are found to be different for the different defect types. The
exponents are robust against a moderate increase in the Gilbert damping
constant and introduction of quenched structural disorder. We discuss details
of the processes allowed by conservation of the winding number of the defects,
underlying their complex coarsening dynamics.",1609.01094v1
2016-09-27,Anomalous Feedback and Negative Domain Wall Resistance,"Magnetic induction can be regarded as a negative feedback effect, where the
motive-force opposes the change of magnetic flux that generates the
motive-force. In artificial electromagnetics emerging from spintronics,
however, this is not necessarily the case. By studying the current-induced
domain wall dynamics in a cylindrical nanowire, we show that the spin
motive-force exerting on electrons can either oppose or support the applied
current that drives the domain wall. The switching into the anomalous feedback
regime occurs when the strength of the dissipative torque {\beta} is about
twice the value of the Gilbert damping constant {\alpha}. The anomalous
feedback manifests as a negative domain wall resistance, which has an analogy
with the water turbine.",1609.08250v1
2016-10-04,Magnetomechanical coupling and ferromagnetic resonance in magnetic nanoparticles,"We address the theory of the coupled lattice and magnetization dynamics of
freely suspended single-domain nanoparticles. Magnetic anisotropy generates
low-frequency satellite peaks in the microwave absorption spectrum and a
blueshift of the ferromagnetic resonance (FMR) frequency. The low-frequency
resonances are very sharp with maxima exceeding that of the FMR, because their
magnetic and mechanical precessions are locked, thereby suppressing Gilbert
damping. Magnetic nanoparticles can operate as nearly ideal motors that convert
electromagnetic into mechanical energy. The Barnett/Einstein-de Haas effect is
significant even in the absence of a net rotation.",1610.01072v2
2016-10-05,Finite-dimensional colored fluctuation-dissipation theorem for spin systems,"When nano-magnets are coupled to random external sources, their magnetization
becomes a random variable, whose properties are defined by an induced
probability density, that can be reconstructed from its moments, using the
Langevin equation, for mapping the noise to the dynamical degrees of freedom.
When the spin dynamics is discretized in time, a general
fluctuation-dissipation theorem, valid for non-Markovian noise, can be
established, even when zero modes are present. We discuss the subtleties that
arise, when Gilbert damping is present and the mapping between noise and spin
degrees of freedom is non--linear.",1610.01622v1
2017-03-31,Spin Seebeck effect in Y-type hexagonal ferrite thin films,"Spin Seebeck effect (SSE) has been investigated in thin films of two
Y-hexagonal ferrites Ba$_2$Zn$_{2}$Fe$_{12}$O$_{22}$ (Zn2Y) and
Ba$_2$Co$_{2}$Fe$_{12}$O$_{22}$ (Co2Y) deposited by a spin-coating method on
SrTiO$_3$(111) substrate. The selected hexagonal ferrites are both
ferrimagnetic with similar magnetic moments at room temperature and both
exhibit easy magnetization plane normal to $c$-axis. Despite that, SSE signal
was only observed for Zn2Y, whereas no significant SSE signal was detected for
Co2Y. We tentatively explain this different behavior by a presence of two
different magnetic ions in Co2Y, whose random distribution over octahedral
sites interferes the long range ordering and enhances the Gilbert damping
constant. The temperature dependence of SSE for Zn2Y was measured and analyzed
with regard to the heat flux and temperature gradient relevant to the SSE
signal.",1703.10903v1
2017-06-02,Power Loss for a Periodically Driven Ferromagnetic Nanoparticle in a Viscous Fluid: the Finite Anisotropy Aspects,"The joint magnetic and mechanical motion of a ferromagnetic nanoparticle in a
viscous fluid is considered within the dynamical approach. The equation based
on the total momentum conservation law is used for the description of the
mechanical rotation, while the modified Landau-Lifshitz-Gilbert equation is
utilized for the description of the internal magnetic dynamics. The exact
expressions for the particles trajectories and the power loss are obtained in
the linear approximation. The comparison with the results of other widespread
approaches, such as the model of fixed particle and the model of frozen
magnetic moment, is performed. It is established that in the small oscillations
mode the damping precession of the nanopartile magnetic moment is the main
channel of energy dissipation, but the motion of the nanoparticle easy axis can
significantly influence the value of the resulting power loss.",1706.00777v2
2017-06-07,Adiabatic and nonadiabatic spin torques induced by spin-triplet supercurrent,"We study spin transfer torques induced by a spin-triplet supercurrent in a
magnet with the superconducting proximity effect. By a perturbative approach,
we show that spin-triplet correlations realize new types of torques, which are
analogous to the adiabatic and non-adiabatic ($\beta$) torques, without
extrinsic spin-flip scattering. Remarkable advantages compared to conventional
spin-transfer torques are highlighted in domain wall manipulation. Oscillatory
motions of a domain wall do not occur for a small Gilbert damping, and the
threshold current density to drive its motion becomes zero in the absence of
extrinsic pinning potentials due to the nonadiabatic torque controlled by the
triplet correlations.",1706.02296v2
2017-06-26,Perpendicular magnetic anisotropy in insulating ferrimagnetic gadolinium iron garnet thin films,"We present experimental control of the magnetic anisotropy in a gadolinium
iron garnet (GdIG) thin film from in-plane to perpendicular anisotropy by
simply changing the sample temperature. The magnetic hysteresis loops obtained
by SQUID magnetometry measurements unambiguously reveal a change of the
magnetically easy axis from out-of-plane to in-plane depending on the sample
temperature. Additionally, we confirm these findings by the use of temperature
dependent broadband ferromagnetic resonance spectroscopy (FMR). In order to
determine the effective magnetization, we utilize the intrinsic advantage of
FMR spectroscopy which allows to determine the magnetic anisotropy independent
of the paramagnetic substrate, while magnetometry determines the combined
magnetic moment from film and substrate. This enables us to quantitatively
evaluate the anisotropy and the smooth transition from in-plane to
perpendicular magnetic anisotropy. Furthermore, we derive the temperature
dependent $g$-factor and the Gilbert damping of the GdIG thin film.",1706.08488v1
2017-09-07,Tunable spin pumping in exchange coupled magnetic trilayers,"Magnetic thin films at ferromagnetic resonance (FMR) leak angular momentum,
which may be absorbed by adjacent layers. This phenomenon, known as spin
pumping, is manifested by an increase in the resonance linewidth ($\Delta H$),
and the closely related Gilbert damping. Another effect of this transfer of
spin currents is a dynamical and long-range coupling that can drive two
magnetic layers into a collective precession when their FMR frequencies
coincide. A collective behavior is also found in magnetic trilayers with
interlayer exchange coupling (IEC). In this study we investigate the interplay
between IEC and spin pumping, using Co/Cu/Py pseudo-spin values. We employ
broadband FMR spectroscopy to explore both the frequency and coupling-strength
dependence of $\Delta H$. Our observations show that there exists a cut-off
frequency, set by the IEC strength, below which the precession is truly
collective and the spin pumping is suppressed. These results demonstrate that
it is possible to control the spin pumping efficiency by varying the frequency
or the interlayer exchange coupling.",1709.02295v1
2017-10-30,Probe of Spin Dynamics in Superconducting NbN Thin Films via Spin Pumping,"The emerging field of superconductor (SC) spintronics has attracted intensive
attentions recently. Many fantastic spin dependent properties in SC have been
discovered, including the observation of large magnetoresistance, long spin
lifetimes and the giant spin Hall effect in SC, as well as spin supercurrent in
Josephson junctions, etc. Regarding the spin dynamic in SC films, few studies
has been reported yet. Here, we report the investigation of the spin dynamics
in an s-wave superconducting NbN film via spin pumping from an adjacent
insulating ferromagnet GdN layer. A profound coherence peak of the Gilbert
damping is observed slightly below the superconducting critical temperature of
the NbN layer, which is consistent with recent theoretical studies. Our results
further indicate that spin pumping could be a powerful tool for investigating
the spin dynamics in 2D crystalline superconductors.",1710.10833v2
2017-11-17,Shot noise of charge and spin transport in a junction with a precessing molecular spin,"Magnetic molecules and nanomagnets can be used to influence the electronic
transport in mesoscopic junction. In a magnetic field the precessional motion
leads to resonances in the dc- and ac-transport properties of a nanocontact, in
which the electrons are coupled to the precession. Quantities like the
dc-conductance or the ac-response provide valuable information like the level
structure and the coupling parameters. Here, we address the current noise
properties of such contacts. This encompasses the charge current and
spin-torque shot noise, which both show a step-like behavior as functions of
bias voltage and magnetic field. The charge current noise shows pronounced dips
around the steps, which we trace back to interference effects of electron in
quasienergy levels coupled by the molecular spin precession. We show that some
components of the noise of the spin-torque currents are directly related to the
Gilbert damping and, hence, are experimentally accessible. Our results show
that the noise characteristics allow to investigate in more detail the
coherence of spin transport in contacts containing magnetic molecules.",1711.06759v2
2018-02-05,Cooper-Pair Spin Current in a Strontium Ruthenate Heterostructure,"It has been recognized that the condensation of spin-triplet Cooper pairs
requires not only the broken gauge symmetry but also the spin ordering as well.
One consequence of this is the possibility of the Cooper-pair spin current
analogous to the magnon spin current in magnetic insulators, the analogy also
extending to the existence of the Gilbert damping of the collective
spin-triplet dynamics. The recently fabricated heterostructure of the thin film
of the itinerant ferromagnet SrRuO3 on the bulk Sr2RuO4, the best-known
candidate material for the spin-triplet superconductor, offers a promising
platform for generating such spin current. We will show how such
heterostructure allows us to not only realize the long-range spin valve but
also electrically drive the collective spin mode of the spin-triplet order
parameter. Our proposal represents both a new realization of the spin
superfluidity and a transport signature of the spin-triplet superconductivity.",1802.01599v1
2018-02-07,Breaking the current density threshold in spin-orbit-torque magnetic random access memory,"Spin-orbit-torque magnetic random access memory (SOT-MRAM) is a promising
technology for the next generation of data storage devices. The main bottleneck
of this technology is the high reversal current density threshold. This
outstanding problem of SOT-MRAM is now solved by using a current density of
constant magnitude and varying flow direction that reduces the reversal current
density threshold by a factor of more than the Gilbert damping coefficient. The
Euler-Lagrange equation for the fastest magnetization reversal path and the
optimal current pulse are derived for an arbitrary magnetic cell. The
theoretical limit of minimal reversal current density and current density for a
GHz switching rate of the new reversal strategy for CoFeB/Ta SOT-MRAMs are
respectively of the order of $10^5$ A/cm$^2$ and $10^6$ A/cm$^2$ far below
$10^7$ A/cm$^2$ and $10^8$ A/cm$^2$ in the conventional strategy. Furthermore,
no external magnetic field is needed for a deterministic reversal in the new
strategy.",1802.02415v1
2018-02-12,Spin-orbit torque and spin pumping in YIG/Pt with interfacial insertion layers,"We experimentally investigate spin-orbit torque and spin pumping in
Y$_3$Fe$_5$O$_{12}$(YIG)/Pt bilayers with ultrathin insertion layers at the
interface. An insertion layer of Cu suppresses both spin-orbit torque and spin
pumping, whereas an insertion layer of Ni$_{80}$Fe$_{20}$ (permalloy, Py)
enhances them, in a quantitatively consistent manner with the reciprocity of
the two spin transmission processes. However, we observe a large enhancement of
Gilbert damping with the insertion of Py that cannot be accounted for solely by
spin pumping, suggesting significant spin-memory loss due to the interfacial
magnetic layer. Our findings indicate that the magnetization at the YIG-metal
interface strongly influences the transmission and depolarization of pure spin
current.",1802.03865v3
2018-06-01,Dirac-Surface-State Modulated Spin Dynamics in a Ferrimagnetic Insulator at Room Temperature,"This work demonstrates dramatically modified spin dynamics of magnetic
insulator (MI) by the spin-momentum locked Dirac surface states of the adjacent
topological insulator (TI) which can be harnessed for spintronic applications.
As the Bi-concentration x is systematically tuned in 5 nm thick (BixSb1-x)2Te3
TI film, the weight of the surface relative to bulk states peaks at x = 0.32
when the chemical potential approaches the Dirac point. At this concentration,
the Gilbert damping constant of the precessing magnetization in 10 nm thick
Y3Fe5O12 MI film in the MI/TI heterostructures is enhanced by an order of
magnitude, the largest among all concentrations. In addition, the MI acquires
additional strong magnetic anisotropy that favors the in-plane orientation with
similar Bi-concentration dependence. These extraordinary effects of the Dirac
surface states distinguish TI from other materials such as heavy metals in
modulating spin dynamics of the neighboring magnetic layer.",1806.00151v1
2018-08-23,Reduced thermal stability of antiferromagnetic nanostructures,"Antiferromagnetic materials hold promising prospects in novel types of
spintronics applications. Assessing the stability of antiferromagnetic
nanostructures against thermal excitations is a crucial aspect of designing
devices with a high information density. Here we use theoretical calculations
and numerical simulations to determine the mean switching time of
antiferromagnetic nanoparticles in the superparamagnetic limit. It is
demonstrated that the thermal stability is drastically reduced compared to
ferromagnetic particles in the limit of low Gilbert damping, attributed to the
exchange enhancement of the attempt frequencies. It is discussed how the system
parameters have to be engineered in order to optimize the switching rates in
antiferromagnetic nanoparticles.",1808.07665v3
2018-09-17,On the speed of domain walls in thin nanotubes: the transition from the linear to the magnonic regime,"Numerical simulations of domain wall propagation in thin nanotubes when an
external magnetic field is applied along the nanotube axis have shown an
unexpected behavior described as a transition from a linear to a magnonic
regime. As the applied magnetic field increases, the initial regime of linear
growth of the speed with the field is followed by a sudden change in slope
accompanied by the emission of spin waves. In this work an analytical formula
for the speed of the domain wall that explains this behavior is derived by
means of an asymptotic study of the Landau Lifshitz Gilbert equation for thin
nanotubes. We show that the dynamics can be reduced to a one dimensional
hyperbolic reaction diffusion equation, namely, the damped double Sine Gordon
equation, which shows the transition to the magnonic regime as the domain wall
speed approaches the speed of spin waves. This equation has been previously
found to describe domain wall propagation in weak ferromagnets with the
mobility proportional to the Dzyaloshinskii-Moriya interaction constant, for
Permalloy nanotubes the mobility is proportional to the nanotube radius.",1809.06278v3
2018-10-19,Magnon properties of random alloys,"We study magnon properties in terms of spin stiffness, Curie temperatures and
magnon spectrum of Fe-Ni, Co-Ni and Fe-Co random alloys using a combination of
electronic structure calculations and atomistic spin dynamics simulations.
Influence of the disorder are studied in detail by use of large supercells with
random atomic arrangement. It is found that disorder affects the magnon
spectrum in vastly different ways depending on the system. Specifically, it is
more pronounced in Fe-Ni alloys compared to Fe-Co alloys. In particular, the
magnon spectrum at room temperature in Permalloy (Fe$_{20}$Ni$_{80}$) is found
to be rather diffuse in a large energy interval while in Fe$_{75}$Co$_{25}$ it
forms sharp branches. Fe-Co alloys are very interesting from a technological
point of view due to the combination of large Curie temperatures and very low
calculated Gilbert damping of $\sim$0.0007 at room temperature for Co
concentrations around 20--30\%.",1810.08487v1
2018-11-09,Switching of biaxial synthetic antiferromagnets: a micromagentic study,"We simulate the switching behavior of nanoscale synthetic antiferromagnets
(SAFs), inspired by recent experimental progress in spin-orbit-torque switching
of crystal antiferromagnets. The SAF consists of two ferromagnetic thin films
with in-plane biaxial anisotropy and interlayer exchange coupling. Staggered
field-like Rashba spin-orbit torques from the opposite surfaces of the SAF
induce a canted net magnetization, which triggers an orthogonal torque that
drives 90$^\circ$ switching of the N\'eel vector. Such dynamics driven by the
field-like spin-orbit torque allows for faster switching with increased Gilbert
damping, without a significant detrimental increase of the threshold switching
current density. Our results point to the potential of SAFs as model systems,
based on simple ferromagnetic metals, to mimic antiferromagnetic device
physics.",1811.04094v2
2018-12-03,Microscopic theory of magnon-drag electron flow in ferromagnetic metals,"A temperature gradient applied to a ferromagnetic metal induces not only
independent flows of electrons and magnons but also drag currents because of
their mutual interaction. In this paper, we present a microscopic study of the
electron flow induced by the drag due to magnons. The analysis is based on the
$s$-$d$ model, which describes conduction electrons and magnons coupled via the
$s$-$d$ exchange interaction. Magnetic impurities are introduced in the
electron subsystem as a source of spin relaxation. The obtained magnon-drag
electron current is proportional to the entropy of magnons and to $\alpha -
\beta$ (more precisely, to $1 - \beta/\alpha$), where $\alpha$ is the Gilbert
damping constant and $\beta$ is the dissipative spin-transfer torque parameter.
This result almost coincides with the previous phenomenological result based on
the magnonic spin-motive forces, and consists of spin-transfer and
momentum-transfer contributions, but with a slight disagreement in the former.
The result is interpreted in terms of the nonequilibrium spin chemical
potential generated by nonequilibrium magnons.",1812.00720v1
2019-01-17,Spin transport parameters of NbN thin films characterised by spin pumping experiments,"We present measurements of ferromagnetic-resonance - driven spin pumping and
inverse spin-Hall effect in NbN/Y3Fe5O12 (YIG) bilayers. A clear enhancement of
the (effective) Gilbert damping constant of the thin-film YIG was observed due
to the presence of the NbN spin sink. By varying the NbN thickness and
employing spin-diffusion theory, we have estimated the room temperature values
of the spin diffusion length and the spin Hall angle in NbN to be 14 nm and
-1.1 10-2, respectively. Furthermore, we have determined the spin-mixing
conductance of the NbN/YIG interface to be 10 nm-2. The experimental
quantification of these spin transport parameters is an important step towards
the development of superconducting spintronic devices involving NbN thin films.",1901.05753v1
2019-02-12,Characterization of spin wave propagation in (111) YIG thin films with large anisotropy,"We report on long-range spin wave (SW) propagation in nanometer-thick yttrium
iron garnet (YIG) film with an ultralow Gilbert damping. The knowledge of a
wavenumber value $|\vec{k}|$ is essential for designing SW devices. Although
determining the wavenumber $|\vec{k}|$ in experiments like Brillouin light
scattering spectroscopy is straightforward, quantifying the wavenumber in
all-electrical experiments has not been widely commented upon so far. We
analyze magnetostatic spin wave (SW) propagation in YIG films in order to
determine the SW wavenumber $|\vec{k}|$ excited by the coplanar waveguide. We
show that it is crucial to consider the influence of magnetic anisotropy fields
present in YIG thin films for precise determination of SW wavenumber. With the
proposed methods we find that experimentally derived values of $|\vec{k}|$ are
in perfect agreement with that obtained from electromagnetic simulation only if
anisotropy fields are included.",1902.04608v1
2019-03-20,Nonlinear magnetization dynamics driven by strong terahertz fields,"We present a comprehensive experimental and numerical study of magnetization
dynamics triggered in a thin metallic film by single-cycle terahertz pulses of
$\sim20$ MV/m electric field amplitude and $\sim1$ ps duration. The
experimental dynamics is probed using the femtosecond magneto-optical Kerr
effect (MOKE), and it is reproduced numerically using macrospin simulations.
The magnetization dynamics can be decomposed in three distinct processes: a
coherent precession of the magnetization around the terahertz magnetic field,
an ultrafast demagnetization that suddenly changes the anisotropy of the film,
and a uniform precession around the equilibrium effective field that is relaxed
on the nanosecond time scale, consistent with a Gilbert damping process.
Macrospin simulations quantitatively reproduce the observed dynamics, and allow
us to predict that novel nonlinear magnetization dynamics regimes can be
attained with existing table-top terahertz sources.",1903.08395v2
2019-04-11,Measurement of spin mixing conductance in Ni$_{81}$Fe$_{19}$/$α$-W and Ni$_{81}$Fe$_{19}$/$β$-W heterostrucutures via ferromagnetic resonance,"We present measurements of interfacial Gilbert damping due to the spin
pumping effect in Ni$_{81}$Fe$_{19}$/W heterostructures. Measurements were
compared for heterostructures in which the crystallographic phase of W, either
$\alpha$(bcc)-W or $\beta$(A15)-W, was enriched through deposition conditions
and characterized using X-ray diffraction (XRD) and high-resolution
cross-sectional transmission electron microscopy (HR-XTEM). Single phase
Ni$_{81}$Fe$_{19}$/$\alpha$-W heterostructures could be realized, but
heterostructures with $\beta$-W were realized as mixed $\alpha$-$\beta$ phase.
The spin mixing conductances (SMC) for W at interfaces with Ni$_{81}$Fe$_{19}$
were found to be significantly lower than those for similarly heavy metals such
as Pd and Pt, but comparable to those for Ta, and independent of enrichment in
the $\beta$ phase.",1904.05950v2
2019-05-26,Influence of field-like torque in synchronization of spin torque oscillators,"The magnetization dynamics of two parallelly coupled spin torque oscillators,
destabilization of steady states and removal of multistability, are
investigated by taking into account the influence of field-like torque. It is
shown that the existence of such torque can cancel the effect of damping and
can, therefore, cause the oscillators to exhibit synchronized oscillations in
response to direct current. Further, our results show that the presence of
field-like torque enhances the power and Q-factor of the synchronized
oscillations. The validity of the above results is confirmed by numerical and
analytical studies based on the stochastic Landau-Lifshitz-Gilbert-Slonczewski
equation.",1905.10804v2
2019-05-30,Sub-nanosecond switching in a cryogenic spin-torque spin-valve memory element with a dilute permalloy free layer,"We present a study of the pulsed current switching characteristics of
spin-valve nanopillars with in-plane magnetized dilute permalloy and undiluted
permalloy free layers in the ballistic regime at low temperature. The dilute
permalloy free layer device switches much faster: the characteristic switching
time for a permalloy free (Ni0.83Fe0.17) layer device is 1.18 ns, while that
for a dilute permalloy ([Ni0.83Fe0.17]0.6Cu0.4) free layer device is 0.475 ns.
A ballistic macrospin model can capture the data trends with a reduced spin
torque asymmetry parameter, reduced spin polarization and increased Gilbert
damping for the dilute permalloy free layer relative to the permalloy devices.
Our study demonstrates that reducing the magnetization of the free layer
increases the switching speed while greatly reducing the switching energy and
shows a promising route toward even lower power magnetic memory devices
compatible with superconducting electronics.",1905.13262v1
2019-06-17,Controlling acoustic waves using magnetoelastic Fano resonances,"We propose and analyze theoretically a class of energy-efficient
magneto-elastic devices for analogue signal processing. The signals are carried
by transverse acoustic waves while the bias magnetic field controls their
scattering from a magneto-elastic slab. By tuning the bias field, one can alter
the resonant frequency at which the propagating acoustic waves hybridize with
the magnetic modes, and thereby control transmission and reflection
coefficients of the acoustic waves. The scattering coefficients exhibit
Breit-Wigner/Fano resonant behaviour akin to inelastic scattering in atomic and
nuclear physics. Employing oblique incidence geometry, one can effectively
enhance the strength of magnetoelastic coupling, and thus countermand the
magnetic losses due to the Gilbert damping. We apply our theory to discuss
potential benefits and issues in realistic systems and suggest further routes
to enhance performance of the proposed devices.",1906.07297v2
2019-07-05,Theory for shift current of bosons: Photogalvanic spin current in ferrimagnetic and antiferromagnetic insulators,"We theoretically study the optical generation of dc spin current (i.e., a
spin-current solar cell) in ordered antiferromagnetic and ferrimagnetic
insulators, motivated by a recent study on the laser-driven spinon spin current
in noncentrosymmetric quantum spin chains [H. Ishizuka and M. Sato, Phys. Rev.
Lett. 122, 197702 (2019)]. Using a non-linear response theory for magnons, we
analyze the dc spin current generated by a linearly-polarized electromagnetic
wave (typically, terahertz or gigahertz waves). Considering noncentrosymmetric
two-sublattice magnets as an example, we find a finite dc spin current
conductivity at $T=0$, where no thermally-excited magnons exist; this is in
contrast to the case of the spinon spin current, in which the optical
transition of the Fermi degenerate spinons plays an essential role. We find
that the dc spin-current conductivity is insensitive to the Gilbert damping,
i.e., it may be viewed as a shift current carried by bosonic particles
(magnons). Our estimate shows that an electric-field intensity of
$E\sim10^4-10^6$ V/cm is sufficient for an observable spin current. Our theory
indicates that the linearly-polarized electromagnetic wave generally produces a
dc spin current in noncentrosymmetric magnetic insulators.",1907.02734v1
2019-07-10,Temperature dependence of magnetic resonance in ferrimagnetic GdFeCo alloys,"We provide a macroscopic theory and experimental results for magnetic
resonances of antiferromagnetically-coupled ferrimagnets. Our theory, which
interpolates the dynamics of antiferromagnets and ferromagnets smoothly, can
describe ferrimagnetic resonances across the angular momentum compensation
point. We also present experimental results for spin-torque induced
ferrimagnetic resonance at several temperatures. The spectral analysis based on
our theory reveals that the Gilbert damping parameter, which has been
considered to be strongly temperature dependent, is insensitive to temperature.
We envision that our work will facilitate further investigation of
ferrimagnetic dynamics by providing a theoretical framework suitable for a
broad range of temperatures.",1907.04540v1
2019-07-11,Improving the Signal-to-noise Ratio for Heat-Assisted Magnetic Recording by Optimizing a High/Low Tc bilayer structure,"We optimize the recording medium for heat-assisted magnetic recording by
using a high/low $T_{\mathrm{c}}$ bilayer structure to reduce AC and DC noise.
Compared to a former work, small Gilbert damping $\alpha=0.02$ is considered
for the FePt like hard magnetic material. Atomistic simulations are performed
for a cylindrical recording grain with diameter $d=5\,$nm and height $h=8\,$nm.
Different soft magnetic material compositions are tested and the amount of hard
and soft magnetic material is optimized. The results show that for a soft
magnetic material with $\alpha_{\mathrm{SM}}=0.1$ and
$J_{ij,\mathrm{SM}}=7.72\times 10^{-21}\,$J/link a composition with $50\%$ hard
and $50\%$ soft magnetic material leads to the best results. Additionally, we
analyse how much the areal density can be improved by using the optimized
bilayer structure compared to the pure hard magnetic recording material. It
turns out that the optimized bilayer design allows an areal density that is
$1\,$Tb/in$^2$ higher than that of the pure hard magnetic material while
obtaining the same SNR.",1907.05027v1
2019-07-19,A cryogenic memory element based on an anomalous Josephson junction,"We propose a non-volatile memory element based on a lateral ferromagnetic
Josephson junction with spin-orbit coupling and out-of-plane magnetization. The
interplay between the latter and the intrinsic exchange field of the
ferromagnet leads to a magnetoelectric effect that couples the charge current
through the junction and its magnetization, such that by applying a current
pulse the direction of the magnetic moment in F can be switched. The two memory
states are encoded in the direction of the out-of-plane magnetization. With the
aim to determine the optimal working temperature for the memory element, we
explore the noise-induced effects on the averaged stationary magnetization by
taking into account thermal fluctuations affecting both the Josephson phase and
the magnetic moment dynamics. We investigate the switching process as a
function of intrinsic parameters of the ferromagnet, such as the Gilbert
damping and strength of the spin-orbit coupling, and proposed a non-destructive
readout scheme based on a dc-SQUID. Additionally, we analyze a way to protect
the memory state from external perturbations by voltage gating in systems with
a both linear-in-momentum Rashba and Dresselhaus spin-orbit coupling.",1907.08454v2
2019-07-23,Electron transport in high-entropy alloys: Al$_{x}$CrFeCoNi as a case study,"The high-entropy alloys Al$_{x}$CrFeCoNi exist over a broad range of Al
concentrations ($0 < x < 2$). With increasing Al content their structure is
changed from the fcc to bcc phase. We investigate the effect of such structural
changes on transport properties including the residual resistivity and the
anomalous Hall resistivity. We have performed a detailed comparison of the
first-principles simulations with available experimental data. We show that the
calculated residual resistivities for all studied alloy compositions are in a
fair agreement with available experimental data as concerns both the
resistivity values and concentration trends. We emphasize that a good agreement
with experiment was obtained also for the anomalous Hall resistivity. We have
completed study by estimation of the anisotropic magnetoresistance,
spin-disorder resistivity, and Gilbert damping. The obtained results prove that
the main scattering mechanism is due to the intrinsic chemical disorder whereas
the effect of spin polarization on the residual resistivity is appreciably
weaker.",1907.09731v1
2019-09-11,Chaos in nanomagnet via feedback current,"Nonlinear magnetization dynamics excited by spin-transfer effect with
feedback current is studied both numerically and analytically. The numerical
simulation of the Landau-Lifshitz-Gilbert equation indicates the positive
Lyapunov exponent for a certain range of the feedback rate, which identifies
the existence of chaos in a nanostructured ferromagnet. Transient behavior from
chaotic to steady oscillation is also observed in another range of the feedback
parameter. An analytical theory is also developed, which indicates the
appearance of multiple attractors in a phase space due to the feedback current.
An instantaneous imbalance between the spin-transfer torque and damping torque
causes a transition between the attractors, and results in the complex
dynamics.",1909.05315v2
2019-11-27,Ellipticity and Dissipation Effects in Magnon Spin Valves,"We consider alignment-dependent spin and heat transport across a magnon spin
valve in the tunneling regime, i.e., a junction consisting of two weakly
coupled ferromagnetic insulators. We determine the difference in spin and heat
conductance between the parallel and antiparallel configuration of the
magnetization direction. The dependence of these conductances on both the
Gilbert damping and ellipticity is studied. We find that both magnon
ellipticity and dissipation open channels for magnons to tunnel through in the
antiparallel configuration. Our results highlight an important difference
between electronic and magnon spin transport in spin-valve structures and may
be important for the development of devices based on magnetic insulators.",1911.12017v2
2020-03-24,Spin-transfer torque driven intrinsic localized spin excitations in the presence of field-like torque,"We study the existence of intrinsic localized one-spin excitation in the
Heisenberg one-dimensional ferromagnetic spin chain in the presence of
perpendicular and parallel external magnetic fields and current with
spin-transfer torque and field-like torque. The
Landau-Lifshitz-Gilbert-Slonczewski(LLGS) equation is exactly solved for the
one spin excitation in the absence of onsite anisotropy for the excitations of
spin with fields perpendicular and parallel to the chain. We show the removal
of damping in the spin excitations by appropriately introducing current and
also the enhancement of angular frequency of the oscillations due to field-like
torque in the case of both perpendicular and parallel field. The exactness of
the analytical results is verified by matching with numerical counterparts.
Further, we numerically confirm the existence of in-phase and anti-phase stable
synchronized oscillations for two spin-excitations in the presence of current
with perpendicular field and field-like torque.",2003.11023v2
2020-04-02,Stable solitons in a nearly PT-symmetric ferromagnet with spin-transfer torque,"We consider the Landau-Lifshitz equation for the spin torque oscillator - a
uniaxial ferromagnet in an external magnetic field with polarised spin current
driven through it. In the absence of the Gilbert damping, the equation turns
out to be PT-symmetric. We interpret the PT-symmetry as a balance between gain
and loss - and identify the gaining and losing modes. In the vicinity of the
bifurcation point of a uniform static state of magnetisation, the PT-symmetric
Landau-Lifshitz equation with a small dissipative perturbation reduces to a
nonlinear Schr\""odinger equation with a quadratic nonlinearity. The analysis of
the Schr\""odinger dynamics demonstrates that the spin torque oscillator
supports stable magnetic solitons. The PT near-symmetry is crucial for the
soliton stability: the addition of a finite dissipative term to the
Landau-Lifshitz equation destabilises all solitons that we have found.",2004.01245v2
2020-05-11,Manipulating 1-dimensinal skyrmion motion by external magnetic field gradient,"We have investigated an analytic formula of the 1-dimensional magnetic
skyrmion dynamics under external magnetic field gradient. We find excellent
agreement between the analytical model and micromagnetic simulation results for
various magnetic parameters such as the magnetic field gradient, Gilbert
damping constant. We also observe much faster velocity of the chiral domain
wall (DW) motion. The chiral DW is exist with smaller interfacial
Dzyaloshinskii-Moriya interaction energy density cases. These results provide
to develop efficient control of skyrmion for spintronic devices.",2005.05011v1
2020-07-08,Finite-frequency spin susceptibility and spin pumping in superconductors with spin-orbit relaxation,"Static spin susceptibility of superconductors with spin-orbit relaxation has
been calculated in the seminal work of A.A. Abrikosov and L.P. Gor'kov [Sov.
Phys. JETP, {\bf 15}, 752 (1962)]. Surprisingly the generalization of this
result to finite frequencies has not been done despite being quite important
for the modern topic of superconducting spintronics. The present paper fills
this gap by deriving the analytical expression for spin susceptibility. The
time-dependent spin response is shown to be captured by the quasiclassical
Eilenberger equation with collision integrals corresponding to the ordinary and
spin-orbit scattering. Using the developed formalism we study the linear spin
pumping effect between the ferromagnet and the adjacent superconducting film.
The consequences for understanding recent experiments demonstrating the
modification of Gilbert damping by the superconducting correlations are
discussed.",2007.04372v2
2020-07-16,Thermal noise effects on the magnetization switching of a ferromagnetic anomalous Josephson junction,"We discuss the effects of thermal noise on the magnetic response of a lateral
ferromagnetic Josephson junction with spin-orbit coupling and out-of-plane
magnetization. The direction of the magnetic moment in the ferromagnetic layer
can be inverted by using controlled current pulses. This phenomenon is due to
the magnetoelectric effect that couples the flowing charge current and the
magnetization of the ferromagnet. We investigate the magnetization reversal
effect versus intrinsic parameters of the ferromagnet, such as the Gilbert
damping and strength of the spin-orbit coupling. We estimate the magnetization
reversing time and find the optimal values of the parameters for fast
switching. With the aim of increasing the operation temperature we study the
effects induced by thermal fluctuations on the averaged stationary
magnetization, and find the conditions that make the system more robust against
noise.",2007.08414v3
2020-08-21,Integration and characterization of micron-sized YIG structures with very low Gilbert damping on arbitrary substrates,"We present a novel process that allows the transfer of monocrystalline
yttrium-iron-garnet microstructures onto virtually any kind of substrate. The
process is based on a recently developed method that allows the fabrication of
freestanding monocrystalline YIG bridges on gadolinium-gallium-garnet. Here the
bridges' spans are detached from the substrate by a dry etching process and
immersed in a watery solution. Using drop casting the immersed YIG platelets
can be transferred onto the substrate of choice, where the structures finally
can be reattached and thus be integrated into complex devices or experimental
geometries. Using time resolved scanning Kerr microscopy and inductively
measured ferromagnetic resonance we can demonstrate that the structures retain
their excellent magnetic quality. At room temperature we find a ferromagnetic
resonance linewidth of $\mu_0\Delta H_{HWHM}\approx 195\,\mu T$ and we were
even able to inductively measure magnon spectra on a single micron-sized
yttrium-iron-garnet platelet at a temperature of 5 K. The process is flexible
in terms of substrate material and shape of the structure. In the future this
approach will allow for new types of spin dynamics experiments up to now
unthinkable.",2008.09390v1
2020-09-01,Quantum Brownian Motion for Magnets,"Spin precession in magnetic materials is commonly modelled with the classical
phenomenological Landau-Lifshitz-Gilbert (LLG) equation. Based on a quantized
spin+environment Hamiltonian, we here derive a general spin operator equation
of motion that describes three-dimensional precession and damping and
consistently accounts for effects arising from memory, coloured noise and
quantum statistics. The LLG equation is recovered as its classical, Ohmic
approximation. We further introduce resonant Lorentzian system--reservoir
couplings that allow a systematic comparison of dynamics between Ohmic and
non--Ohmic regimes. Finally, we simulate the full non-Markovian dynamics of a
spin in the semi--classical limit. At low temperatures, our numerical results
demonstrate a characteristic reduction and flattening of the steady state spin
alignment with an external field, caused by the quantum statistics of the
environment. The results provide a powerful framework to explore general
three-dimensional dissipation in quantum thermodynamics.",2009.00600v2
2020-09-30,Quantum hydrodynamics of spin winding,"An easy-plane spin winding in a quantum spin chain can be treated as a
transport quantity, which propagates along the chain but has a finite lifetime
due to phase slips. In a hydrodynamic formulation for the winding dynamics, the
quantum continuity equation acquires a source term due to the transverse
vorticity flow. The latter reflects the phase slips and generally compromises
the global conservation law. A linear-response formalism for the nonlocal
winding transport then reduces to a Kubo response for the winding flow along
the spin chain, in conjunction with the parasitic vorticity flow transverse to
it. One-dimensional topological hydrodynamics can be recovered when the
vorticity flow is asymptotically small. Starting with a microscopic spin-chain
formulation, we focus on the asymptotic behavior of the winding transport based
on the renormalized sine-Gordon equation, incorporating phase slips as well as
Gilbert damping. A generic electrical device is proposed to manifest this
physics. We thus suggest winding conductivity as a tangible concept that can
characterize low-energy dynamics in a broad class of quantum magnets.",2010.00144v1
2020-11-29,Cross-sublattice Spin Pumping and Magnon Level Attraction in van der Waals Antiferromagnets,"We theoretically study spin pumping from a layered van der Waals
antiferromagnet in its canted ground state into an adjacent normal metal. We
find that the resulting dc spin pumping current bears contributions along all
spin directions. Our analysis allows for detecting intra- and cross-sublattice
spin-mixing conductances via measuring the two in-plane spin current
components. We further show that sublattice symmetry-breaking Gilbert damping
can be realized via interface engineering and induces a dissipative coupling
between the optical and acoustic magnon modes. This realizes magnon level
attraction and exceptional points in the system. Furthermore, the dissipative
coupling and cross-sublattice spin pumping contrive to produce an
unconventional spin current in the out-of-plane direction. Our findings provide
a route to extract the spin mixing conductance matrix and uncovers the unique
opportunities, such as level attraction, offered by van der Waals
antiferromagnet-normal metal hybrids.",2011.14314v1
2021-01-18,Topological electric driving of magnetization dynamics in insulators,"Established forms of electromagnetic coupling are usually conservative (in
insulators) or dissipative (in metals and semiconductors). Here we point out
the possibility of nondissipative electric driving of magnetization dynamics,
if the valence electronic states have nontrivial topology in the combined space
of crystal momentum and magnetization configuration. We provide a hybrid
insulator system to demonstrate that the topology-based nonconservative
electrical generalized force is capable of supporting sustained magnetization
motion in the presence of Gilbert damping, with quantized and steady energy
pumping into magnetization motion from the electric field. We also generalize
our results to magnetic textures, and discuss electric field induced
Dzyaloshinskii-Moriya interaction which can be nonconservative.",2101.07164v3
2021-02-07,Spinterface Induced Modification in Magnetic Properties in Co40Fe40B20/Fullerene Bilayers,"Organic semiconductor/ferromagnetic bilayer thin films can exhibit novel
properties due to the formation of the spinterface at the interface.
Buckminsterfullerene (C60) has been shown to exhibit ferromagnetism at the
interface when it is placed next to a ferromagnet (FM) such as Fe or Co.
Formation of spinterface occurs due to the orbital hybridization and spin
polarized charge transfer at the interface. In this work, we have demonstrated
that one can enhance the magnetic anisotropy of the low Gilbert damping alloy
CoFeB by introducing a C60 layer. We have shown that anisotropy increases by
increasing the thickness of C60 which might be a result of the formation of
spinterface. However, the magnetic domain structure remains same in the bilayer
samples as compared to the reference CoFeB film.",2102.03914v4
2021-02-15,Magnetodynamic properties of dipole-coupled 1D magnonic crystals,"Magnonic crystals are magnetic metamaterials, that provide a promising way to
manipulate magnetodynamic properties by controlling the geometry of the
patterned structures. Here, we study the magnetodynamic properties of 1D
magnonic crystals consisting of parallel NiFe strips with different strip
widths and separations. The strips couple via dipole-dipole interactions. As an
alternative to experiments and/or micromagnetic simulations, we investigate the
accuracy of a simple macrospin model. For the case of simple strips, a model
with a single free parameter to account for an overestimation of the
out-of-plane demagnetization of the magnonic lattice is described. By adjusting
this parameter a good fit with experimental as well as micromagnetic results is
obtained. Moreover, the Gilbert damping is found independent of the lattice
constant however the inhomogeneous linewidth broadening found to increase with
decreasing stripe separation.",2102.07712v2
2021-05-24,Spin pumping of two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interactions,"We theoretically consider spin pumping in a junction between a ferromagnetic
insulator (FI) and a two-dimensional electron gas (2DEG) in which the Rashba
and Dresselhaus spin-orbit interactions coexist. Using second-order
perturbation theory, we derive an increase in linewidth in the case of an
interfacial exchange coupling in a ferromagnetic resonance (FMR) experiment. We
clarify how the enhancement of Gilbert damping depends on the resonant
frequency and spin orientation of the FI. We show that this setup of an FMR
experiment can provide information on the spin texture of 2DEG at the Fermi
surface.",2105.11193v3
2021-08-05,Spin-transfer torque driven localized spin excitations in the presence of field-like torque,"We study the existence of localized one-spin excitation in the Heisenberg
one-dimensional ferromagnetic spin chain in the presence of perpendicular and
parallel external magnetic fields and current with spin-transfer torque and
field-like torque. The Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation is
exactly solved for the one spin excitation in the absence of onsite anisotropy
for the excitations of spin with fields perpendicular and parallel to the
chain. We show the removal of damping in the spin excitations by appropriately
introducing current and also the enhancement of angular frequency of the
oscillations due to field-like torque in the case of both perpendicular and
parallel field. The exactness of the analytical results is verified by matching
with numerical counterparts. Further, we numerically confirm the existence of
in-phase and anti-phase stable synchronized oscillations for two
spin-excitations in the presence of current with perpendicular field and
field-like torque. We also show that the one-spin excitation is stable against
thermal noise and gets only slightly modified against thermal fluctuations.",2108.02380v1
2021-09-07,Inertial spin dynamics in epitaxial cobalt films,"We investigate the spin dynamics driven by terahertz magnetic fields in
epitaxial thin films of cobalt in its three crystalline phases. The terahertz
magnetic field generates a torque on the magnetization which causes it to
precess for about 1 ps, with a sub-picosecond temporal lag from the driving
force. Then, the magnetization undergoes natural damped THz oscillations at a
frequency characteristic of the crystalline phase. We describe the experimental
observations solving the inertial Landau-Lifshitz-Gilbert equation. Using the
results from the relativistic theory of magnetic inertia, we find that the
angular momentum relaxation time $\eta$ is the only material parameter needed
to describe all the experimental evidence. Our experiments suggest a
proportionality between $\eta$ and the strength of the magneto-crystalline
anisotropy.",2109.03076v2
2021-09-26,Transition state dynamics of a driven magnetic free layer,"Magnetization switching in ferromagnetic structures is an important process
for technical applications such as data storage in spintronics, and therefore
the determination of the corresponding switching rates becomes essential. We
investigate a free-layer system in an oscillating external magnetic field
resulting in an additional torque on the spin. The magnetization dynamics
including inertial damping can be described by the phenomenological Gilbert
equation. The magnetization switching between the two stable orientations on
the sphere then requires the crossing of a potential region characterized by a
moving rank-1 saddle. We adopt and apply recent extensions of transition state
theory for driven systems to compute both the time-dependent and average
switching rates of the activated spin system in the saddle region.",2109.12605v1
2021-12-24,Skyrmion nucleation on the surface of a topological insulator,"Skyrmion nucleation induced by spin-transfer torques at an interface of a
topological insulator and a ferromagnetic insulator is investigated. Due to
strong spin-orbit coupling on a surface of topological insulators, which
enhances the effect of spin torques, efficient manipulation of skyrmions is
expected, and therefore, topological insulators could provide the ideal
platform to achieve high-performance skyrmionic devices. Using micromagnetic
simulations and energetics, we evaluate properties of the skyrmion nucleation
on a surface of topological insulators, such as nucleation time, critical
electric field, and skyrmion numbers. We show that the nucleation time is
inversely proportional to the applied electric field. We also identify the
Gilbert damping and temperature dependencies of the critical field.
Furthermore, we analytically evaluate the effect of the Dzyaloshinskii-Moriya
interaction and demonstrate that the temperature dependence can be explained by
the reduction of a magnon excitation gap due to the self-energy corrections.",2112.12967v2
2021-12-10,Enhanced Planar Antenna Efficiency Through Magnetic Thin-Films,"This work proposes to use magnetic material as the substrate of planar
antennas to overcome the platform effect caused by the conducting ground plane.
The upper bound of the radiation efficiency of an electric-current-driven
low-profile antenna is theoretically derived, which is inversely proportional
to the Gilbert damping factor of the magnetic material. Meanwhile, the
improvement of radiation due to the use of magnetic material is demonstrated by
a three-dimensional (3D) multiphysics and multiscale time-domain model. The
simulation results match the theoretical derivation, showing 25% radiation
efficiency from a planar antenna backed by a FeGaB thin film with 2.56 um
thickness. Furthermore, for conductive ferromagnetic materials, it is shown
that the eddy current loss can be well suppressed by laminating the thin film
into multiple layers. The radiation efficiency of the modeled antenna with a
conductive ferromagnetic substrate is improved from 2.2% to 11.8% by dividing
the substrate into 10 layers, with a ferromagnetic material fill factor of 93%.",2201.04932v1
2022-03-07,Ultrafast optical observation of spin-pumping induced dynamic exchange coupling in ferromagnetic semiconductor/metal bilayer,"Spin angular momentum transfer in magnetic bilayers offers the possibility of
ultrafast and low-loss operation for next-generation spintronic devices. We
report the field- and temperature- dependent measurements on the magnetization
precessions in Co$_2$FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr
effect (TRMOKE). Analysis of the effective Gilbert damping and phase shift
indicates a clear signature of an enhanced dynamic exchange coupling between
the two ferromagnetic (FM) layers due to the reinforced spin pumping at
resonance. The temperature dependence of the dynamic exchange-coupling reveals
a primary contribution from the ferromagnetism in (Ga,Mn)As.",2203.03225v2
2022-04-21,Transport theory for topological Josephson junctions with a Majorana qubit,"We construct a semiclassical theory for the transport of topological
junctions starting from a microscopic Hamiltonian that comprehensively includes
the interplay among the Majorana qubit, the Josephson phase, and the
dissipation process. With the path integral approach, we derive a set of
semiclassical equations of motion that can be used to calculate the time
evolution of the Josephson phase and the Majorana qubit. In the equations we
reveal rich dynamical phenomena such as the qubit induced charge pumping, the
effective spin-orbit torque, and the Gilbert damping. We demonstrate the
influence of these dynamical phenomena on the transport signatures of the
junction. We apply the theory to study the Shapiro steps of the junction, and
find the suppression of the first Shapiro step due to the dynamical feedback of
the Majorana qubit.",2204.09923v1
2022-04-22,A short-circuited coplanar waveguide for low-temperature single-port ferromagnetic resonance spectroscopy set-up to probe the magnetic properties of ferromagnetic thin films,"A coplanar waveguide shorted in one end is proposed, designed, and
implemented successfully to measure the properties of magnetic thin films as a
part of the vector network analyzer ferromagnetic resonance (VNA-FMR)
spectroscopy set-up. Its simple structure, potential applications and easy
installation inside the cryostat chamber made it advantageous especially for
low-temperature measurements. It provides a wide band of frequencies in the
gigahertz range essential for FMR measurements. Our spectroscopy set-up with
short-circuited coplanar waveguide has been used to extract Gilbert damping
coefficient and effective magnetization values for standard ferromagnetic thin
films like Py and Co. The thickness and temperature dependent studies of those
magnetic parameters have also been done here for the afore mentioned magnetic
samples.",2204.10596v2
2022-11-04,Derivation of Interacting Two-Qubit Dynamics from Spin-Boson Model,"We derive damping equations of motion for interacting two-spin states from a
spin-boson model in order to examine qubit dynamics in quantum computers. On
the basis of the composite operator method, we develop the Caldeira-Leggett
approach for open quantum systems so that the entanglement dynamics originated
from the two-spin correlation can be taken. We demonstrate numerical results
for time dependence on the two-spin dynamics. We find that the relaxation of
the total spin is described by a quantum version of the Landau-Lifshitz-Gilbert
equation for magnetic materials. We also find that a two-spin composite mode
keeps oscillation even after the total spin has been fully relaxed. We thus
conclude that the two-spin correlation due to the presence of the composite
mode is stable against dissipation. We consider the mechanism of why the
correlation is maintained.",2211.02490v1
2023-02-06,Global solutions of the Landau--Lifshitz--Baryakhtar equation,"The Landau--Lifshitz--Baryakhtar (LLBar) equation is a generalisation of the
Landau--Lifshitz--Gilbert and the Landau--Lifshitz--Bloch equations which takes
into account contributions from nonlocal damping and is valid at moderate
temperature below the Curie temperature. Therefore, it is used to explain some
discrepancies between the experimental observations and the known theories in
various problems on magnonics and magnetic domain-wall dynamics. In this paper,
the existence and uniqueness of global weak, strong, and regular solutions to
LLBar equation are proven. H\""older continuity of the solution is also
discussed.",2302.02556v3
2023-03-22,Twisted bilayer graphene reveals its flat bands under spin pumping,"The salient property of the electronic band structure of twisted bilayer
graphene (TBG), at the so-called magic angle (MA), is the emergence of flat
bands around the charge neutrality point. These bands are associated with the
observed superconducting phases and the correlated insulating states. Scanning
tunneling microscopy combined with angle resolved photoemission spectroscopy
are usually used to visualize the flatness of the band structure of TBG at the
MA. Here, we theoretically argue that spin pumping (SP) provides a direct probe
of the flat bands of TBG and an accurate determination of the MA. We consider a
junction separating a ferromagnetic insulator and a heterostructure of TBG
adjacent to a monolayer of a transition metal dichalcogenide. We show that the
Gilbert damping of the ferromagnetic resonance experiment, through this
junction, depends on the twist angle of TBG, and exhibits a sharp drop at the
MA. We discuss the experimental realization of our results which open the way
to a twist switchable spintronics in twisted van der Waals heterostructures.",2303.12380v2
2023-05-01,Coherent and incoherent magnons induced by strong ultrafast demagnetization in thin permalloy films,"Understanding spin dynamics on femto- and picosecond timescales offers new
opportunities for faster and more efficient spintronic devices. Here, we
experimentally investigate the coherent spin dynamics after ultrashort laser
excitation by time-resolved magneto optical Kerr effect (TR-MOKE) in thin
Ni80Fe20 films. We provide a detailed study of the magnetic field and pump
fluence dependence of the coherent precessional dynamics. We show that the
coherent precession lifetime increases with the applied external magnetic field
which cannot be understood by viscous Gilbert damping of the coherent magnons.
Instead, it can be explained by nonlinear magnon interactions and by the change
in the fraction of incoherent magnons. This interpretation is in agreement with
the observed trends of the coherent magnon amplitude and lifetime as a function
of the exciting laser fluence. Our results provide a new insight into the
magnetization relaxation processes in ferromagnetic thin films, which is of
great importance for further spintronic applications.",2305.00814v2
2023-07-15,Switching current distributions in ferromagnetic anomalous Josephson junctions,"We investigate the switching current distributions of ferromagnetic anomalous
Josephson junctions subjected to a linearly increasing bias current. Our study
uncovers a significant correlation between the position of the switching
current distributions and crucial system parameters, such as the strength of
the spin-orbit coupling and the Gilbert damping parameter. This indicates that
these parameters can be directly determined through experimental measurements.
By conducting a comprehensive analysis of the interplay among noise,
magnetization, phase dynamics, and the statistical properties of the switching
current distribution, we deepen our understanding of these intriguing cryogenic
spintronics devices. These findings hold potential for applications in the
field of quantum computing architectures and information processing
technologies.",2307.07751v2
2023-07-26,Oscillatory Edge Modes in Two Dimensional Spin-Torque Oscillator Arrays,"Spin torque oscillators (STOs) are dissipative magnetic systems that provide
a natural platform for exploring non-Hermitian phenomena. We theoretically
study a two-dimensional (2d) array of STOs and show that its dynamics can be
mapped to a 2d, non-Hermitian Su-Schrieffer-Heeger (SSH) model. We calculate
the energy spectrum and identify the one-dimensional (1d) edge states of our
model, corresponding to auto-oscillation of STOs on the boundary of the system
while the bulk oscillators do not activate. We show that tuning the Gilbert
damping, injected spin current, and coupling between STOs allows for exploring
the edge state properties under different parameter regimes. Furthermore, this
system admits 1d edge states with non-uniform probability density, and we
explore their properties in systems of different sizes. Additional symmetry
analysis indicates that these states are not topologically protected but are
nevertheless confined to the edge of the system, as the bulk is protected by
PT-symmetry. These results indicate that 2d arrays of STOs may be useful to
explore novel edge state behavior in dissipative systems.",2307.13876v1
2024-03-25,Detection of spin pumping free of rectification and thermal artefacts in molecular-based ferromagnetic insulator V[TCNE]x~2,"The molecular-based ferrimagnetic insulator V(TCNE)x has gained recent
interest for efficient spin-wave excitation due to its low Gilbert damping
ratio a=4E-5, and narrow ferromagnetic resonance linewidth f=1Oe. Here we
report a clean spin pumping signal detected on V(TCNE)x/metal bilayer
structures, free from spin rectification or thermal artifacts. On-chip coupling
of microwave power is achieved via a coplanar waveguide to measure the in-plane
angle-dependence of the inverse spin-Hall effect under ferromagnetic resonance
conditions with respect to a constant external magnetic field. A signature of
pure spin current from V(TCNE)x is observed in both platinum and permalloy
metal layers, demonstrating the utility of V(TCNE)x for magnon spintronics
studies in molecule/solid-state heterostructures.",2403.16429v2
2024-04-01,"Harnessing Interlayer Magnetic Coupling for Efficient, Field-Free Current-Induced Magnetization Switching in a Magnetic Insulator","Owing to the unique features of low Gilbert damping, long spin-diffusion
lengths and zero Ohmic losses, magnetic insulators are promising candidate
materials for next-generation spintronic applications. However, due to the
localized magnetic moments and the complex metal-oxide interface between
magnetic insulators and heavy metals, spin-functional Dzyaloshinskii-Moriya
interactions or spin Hall and Edelstein effects are weak, which diminishes the
performance of these typical building blocks for spintronic devices. Here, we
exploit the exchange coupling between metallic and insulating magnets for
efficient electrical manipulation of heavy metal/magnetic insulator
heterostructures. By inserting a thin Co layer, we enhance the spin-orbit
torque efficiency by more than 20 times, which significantly reduces the
switching current density. Moreover, we demonstrate field-free current-induced
magnetization switching caused by a symmetry-breaking non-collinear magnetic
texture. Our work launches magnetic insulators as an alternative platform for
low-power spintronic devices.",2404.00845v1
2005-07-15,A Theory of Physical Quantum Computation: The Quantum Computer Condition,"In this paper we present a new unified theoretical framework that describes
the full dynamics of quantum computation. Our formulation allows any questions
pertaining to the physical behavior of a quantum computer to be framed, and in
principle, answered. We refer to the central organizing principle developed in
this paper, on which our theoretical structure is based, as the *Quantum
Computer Condition* (QCC), a rigorous mathematical statement that connects the
irreversible dynamics of the quantum computing machine, with the reversible
operations that comprise the quantum computation intended to be carried out by
the quantum computing machine. Armed with the QCC, we derive a powerful result
that we call the *Encoding No-Go Theorem*. This theorem gives a precise
mathematical statement of the conditions under which fault-tolerant quantum
computation becomes impossible in the presence of dissipation and/or
decoherence. In connection with this theorem, we explicitly calculate a
universal critical damping value for fault-tolerant quantum computation. In
addition we show that the recently-discovered approach to quantum error
correction known as ""operator quantum error-correction"" (OQEC) is a special
case of our more general formulation. Our approach furnishes what we will refer
to as ""operator quantum fault-tolerance"" (OQFT). In particular, we show how the
QCC allows one to derive error thresholds for fault tolerance in a completely
general context. We prove the existence of solutions to a class of
time-dependent generalizations of the Lindblad equation. Using the QCC, we also
show that the seemingly different circuit, graph- (including cluster-) state,
and adiabatic paradigms for quantum computing are in fact all manifestations of
a single, universal paradigm for all physical quantum computation.",0507141v2
2018-12-22,Spin dynamics of $3d$ and $4d$ impurities embedded in prototypical topological insulators,"Topological insulators are insulating bulk materials hosting conducting
surface states. Their magnetic doping breaks time-reversal symmetry and
generates numerous interesting effects such as dissipationless transport.
Nonetheless, their dynamical properties are still poorly understood. Here, we
perform a systematic investigation of transverse spin excitations of $3d$ and
$4d$ single impurities embedded in two prototypical topological insulators
(Bi$_2$Te$_3$ and Bi$_2$Se$_3$). The impurity-induced states within the bulk
gap of the topological insulators are found to have a drastic impact on the
spin excitation spectra, resulting in very high lifetimes reaching up to
${microseconds}$. An intuitive picture of the spin dynamics is obtained by
mapping onto a generalized Landau-Lifshitz-Gilbert phenomenological model. The
first quantity extracted from this mapping procedure is the magnetic anisotropy
energy, which is then compared to the one provided by the magnetic force
theorem. This uncovers some difficulties encountered with the latter, which can
provide erroneous results for impurities with a high density of states at the
Fermi energy. Moreover, the Gilbert damping and nutation tensors are obtained.
The nutation effects can lead to a non-negligible shift in the spin excitation
resonance in the high-frequency regime. Finally, we study the impact of the
surface state on the spin dynamics, which may be severely altered due to the
repositioning of the impurity-induced state in comparison to the bulk case. Our
systematic investigation of this series of magnetic impurities sheds light on
their spin dynamics within topological insulators, with implications for
available and future experimental studies as, for instance, on the viability of
using such impurities for solid-state qubits.",1812.09596v1
2013-08-16,Quantum Gilbert-Varshamov Bound Through Symplectic Self-Orthogonal Codes,"It is well known that quantum codes can be constructed through classical
symplectic self-orthogonal codes. In this paper, we give a kind of
Gilbert-Varshamov bound for symplectic self-orthogonal codes first and then
obtain the Gilbert-Varshamov bound for quantum codes. The idea of obtaining the
Gilbert-Varshamov bound for symplectic self-orthogonal codes follows from
counting arguments.",1308.3578v1
2017-04-19,Refractive index of dense materials,"We show that applying the Lorentz-Lorenz transformation to the refractive
index of metals, semiconductors and insulators allows for a less empirical
modeling of this refractive index.",1704.05718v1
1998-10-01,Finite temperature dynamics of vortices in the two dimensional anisotropic Heisenberg model,"We study the effects of finite temperature on the dynamics of non-planar
vortices in the classical, two-dimensional anisotropic Heisenberg model with
XY- or easy-plane symmetry. To this end, we analyze a generalized
Landau-Lifshitz equation including additive white noise and Gilbert damping.
Using a collective variable theory with no adjustable parameters we derive an
equation of motion for the vortices with stochastic forces which are shown to
represent white noise with an effective diffusion constant linearly dependent
on temperature. We solve these stochastic equations of motion by means of a
Green's function formalism and obtain the mean vortex trajectory and its
variance. We find a non-standard time dependence for the variance of the
components perpendicular to the driving force. We compare the analytical
results with Langevin dynamics simulations and find a good agreement up to
temperatures of the order of 25% of the Kosterlitz-Thouless transition
temperature. Finally, we discuss the reasons why our approach is not
appropriate for higher temperatures as well as the discreteness effects
observed in the numerical simulations.",9810011v1
2004-07-21,A selfconsistent theory of current-induced switching of magnetization,"A selfconsistent theory of the current-induced switching of magnetization
using nonequilibrium Keldysh formalism is developed for a junction of two
ferromagnets separated by a nonmagnetic spacer. It is shown that the
spin-transfer torques responsible for current-induced switching of
magnetization can be calculated from first principles in a steady state when
the magnetization of the switching magnet is stationary. The spin-transfer
torque is expressed in terms of one-electron surface Green functions for the
junction cut into two independent parts by a cleavage plane immediately to the
left and right of the switching magnet. The surface Green functions are
calculated using a tight-binding Hamiltonian with parameters determined from a
fit to an {\it ab initio} band structure.This treatment yields the spin
transfer torques taking into account rigorously contributions from all the
parts of the junction. To calculate the hysteresis loops of resistance versus
current, and hence to determine the critical current for switching, the
microscopically calculated spin-transfer torques are used as an input into the
phenomenological Landau-Lifshitz equation with Gilbert damping. The present
calculations for Co/Cu/Co(111) show that the critical current for switching is
$\approx 10^7A/cm^2$, which is in good agreement with experiment.",0407562v2
2006-02-24,Magnetization dynamics in dysprosium orthoferrites via inverse Faraday effect,"The ultrafast non-thermal control of magnetization has recently become
feasible in canted antiferromagnets through photomagnetic instantaneous pulses
[A.V. Kimel {\it et al.}, Nature {\bf 435}, 655 (2005)]. In this experiment
circularly polarized femtosecond laser pulses set up a strong magnetic field
along the wave vector of the radiation through the inverse Faraday effect,
thereby exciting non-thermally the spin dynamics of dysprosium orthoferrites. A
theoretical study is performed by using a model for orthoferrites based on a
general form of free energy whose parameters are extracted from experimental
measurements. The magnetization dynamics is described by solving coupled
sublattice Landau-Lifshitz-Gilbert equations whose damping term is associated
with the scattering rate due to magnon-magnon interaction. Due to the inverse
Faraday effect and the non-thermal excitation, the effect of the laser is
simulated by magnetic field Gaussian pulses with temporal width of the order of
hundred femtoseconds. When the field is along the z-axis, a single resonance
mode of the magnetization is excited. The amplitude of the magnetization and
out-of-phase behavior of the oscillations for fields in z and -z directions are
in good agreement with the cited experiment. The analysis of the effect of the
temperature shows that magnon-magnon scattering mechanism affects the decay of
the oscillations on the picosecond scale. Finally, when the field pulse is
along the x-axis, another mode is excited, as observed in experiments. In this
case the comparison between theoretical and experimental results shows some
discrepancies whose origin is related to the role played by anisotropies in
orthoferrites.",0602593v1
2006-04-19,"Stress - and Magneto-Impedance in Co71-xFexCr7Si8B14 (x = 0, 2) amorphous ribbons","Systematic measurements of stress impedance (SI) and magneto-impedance (MI)
have been carried out using Co-rich amorphous ribbons of nominal composition
Co71-xFexCr7Si8B14 (x = 0, 2) at various excitation frequencies and bias fields
and at room temperature. The impedance, Z, for both the samples was found to be
very sensitive functions of applied tensile stress (up to 100MPa) exhibiting a
maximum SI ratio as much as 80% at low frequency ~ 0.1MHz. The nature of
variation of impedance, Z, changes with the excitation frequency especially at
higher frequencies in MHz region where it exhibits a peak. Magnetization
measurements were also performed to observe the effects of applied stress and
magnetization decreases with the application of stress confirming the negative
magnetostriction co-efficient of both the samples. Both the samples exhibited
negative magneto-impedance when the variation of Z is observed with the applied
bias magnetic field, H. Maximum MI ratio as large as 99% has been observed for
both the samples at low fields ~ 27Oe. The impedance as functions of applied
magnetic field, Z(H), decreases with the application of stress thus making the
MI curves broader. Based on the electromagnetic screening and magnetization
dynamics and incorporating the Gilbert and the Bloch-Bloembergen damping and
stress dependent anisotropy, the SI has been calculated and is found to
describe well the stress and field dependence of impedance of the two samples.",0604438v2
2010-05-25,"Structural, static and dynamic magnetic properties of CoMnGe thin films on a sapphire a-plane substrate","Magnetic properties of CoMnGe thin films of different thicknesses (13, 34,
55, 83, 100 and 200 nm), grown by RF sputtering at 400{\deg}C on single crystal
sapphire substrates, were studied using vibrating sample magnetometry (VSM) and
conventional or micro-strip line (MS) ferromagnetic resonance (FMR). Their
behavior is described assuming a magnetic energy density showing twofold and
fourfold in-plane anisotropies with some misalignment between their principal
directions. For all the samples, the easy axis of the fourfold anisotropy is
parallel to the c-axis of the substrate while the direction of the twofold
anisotropy easy axis varies from sample to sample and seems to be strongly
influenced by the growth conditions. Its direction is most probably monitored
by the slight unavoidable angle of miscut the Al2O3 substrate. The twofold
in-plane anisotropy field is almost temperature independent, in contrast with
the fourfold field which is a decreasing function of the temperature. Finally,
we study the frequency dependence of the observed line-width of the resonant
mode and we conclude to a typical Gilbert damping constant of 0.0065 for the
55-nm-thick film.",1005.4595v3
2011-06-22,Effect of spin diffusion on current generated by spin motive force,"Spin motive force is a spin-dependent force on conduction electrons induced
by magnetization dynamics. In order to examine its effects on magnetization
dynamics, it is indispensable to take into account spin accumulation, spin
diffusion, and spin-flip scattering since the spin motive force is in general
nonuniform. We examine the effects of all these on the way the spin motive
force generates the charge and spin currents in conventional situations, where
the conduction electron spin relaxation dynamics is much faster than the
magnetization dynamics. When the spin-dependent electric field is spatially
localized, which is common in experimental situations, we find that the
conservative part of the spin motive force is unable to generate the charge
current due to the cancelation effect by the diffusion current. We also find
that the spin current is a nonlocal function of the spin motive force and can
be effectively expressed in terms of nonlocal Gilbert damping tensor. It turns
out that any spin independent potential such as Coulomb potential does not
affect our principal results. At the last part of this paper, we apply our
theory to current-induced domain wall motion.",1106.4389v2
2011-07-11,Spin and charge transport induced by gauge fields in a ferromagnet,"We present a microscopic theory of spin-dependent motive force (""spin motive
force"") induced by magnetization dynamics in a conducting ferromagnet, by
taking account of spin relaxation of conduction electrons. The theory is
developed by calculating spin and charge transport driven by two kinds of gauge
fields; one is the ordinary electromagnetic field $A^{\rm em}_{\mu}$, and the
other is the effective gauge field $A^{z}_{\mu}$ induced by dynamical magnetic
texture. The latter acts in the spin channel and gives rise to a spin motive
force. It is found that the current induced as a linear response to
$A^{z}_{\mu}$ is not gauge-invariant in the presence of spin-flip processes.
This fact is intimately related to the non-conservation of spin via Onsager
reciprocity, so is robust, but indicates a theoretical inconsistency. This
problem is resolved by considering the time dependence of spin-relaxation
source terms in the ""rotated frame"", as in the previous study on Gilbert
damping [J. Phys. Soc. Jpn. {\bf 76}, 063710 (2007)]. This effect restores the
gauge invariance while keeping spin non-conservation. It also gives a
dissipative spin motive force expected as a reciprocal to the dissipative spin
torque (""$\beta$-term"").",1107.2165v3
2012-07-02,"Establishing micromagnetic parameters of ferromagnetic semiconductor (Ga,Mn)As","(Ga,Mn)As is at the forefront of research exploring the synergy of magnetism
with the physics and technology of semiconductors, and has led to discoveries
of new spin-dependent phenomena and functionalities applicable to a wide range
of material systems. Its recognition and utility as an ideal model material for
spintronics research has been undermined by the large scatter in reported
semiconducting doping trends and micromagnetic parameters. In this paper we
establish these basic material characteristics by individually optimizing the
highly non-equilibrium synthesis for each Mn-doping level and by simultaneously
determining all micromagnetic parameters from one set of magneto-optical
pump-and-probe measurements. Our (Ga,Mn)As thin-film epilayers, spannig the
wide range of accessible dopings, have sharp thermodynamic Curie point
singularities typical of uniform magnetic systems. The materials show
systematic trends of increasing magnetization, carrier density, and Curie
temperature (reaching 188 K) with increasing doping, and monotonous doping
dependence of the Gilbert damping constant of ~0.1-0.01 and the spin stiffness
of ~2-3 meVnm^2. These results render (Ga,Mn)As well controlled degenerate
semiconductor with basic magnetic characteristics comparable to common band
ferromagnets.",1207.0310v1
2013-03-14,Spin-torque effects in thermally assisted magnetization reversal: Method of statistical moments,"Thermal fluctuations of nanomagnets driven by spin-polarized currents are
treated via the Landau-Lifshitz-Gilbert equation generalized to include both
the random thermal noise field and the Slonczewski spin-transfer torque term.
By averaging this stochastic (Langevin) equation over its realizations, the
explicit infinite hierarchy of differential-recurrence relations for
statistical moments (averaged spherical harmonics) is derived for arbitrary
demagnetizing factors and magnetocrystalline anisotropy for the generic
nanopillar model of a spin-torque device comprising two ferromagnetic strata
representing the free and fixed layers and a nonmagnetic conducting spacer all
sandwiched between two ohmic contacts. The influence of thermal fluctuations
and spin-transfer torques on relevant switching characteristics, such as the
stationary magnetization, the magnetization reversal time, etc., is calculated
by solving the hierarchy for wide ranges of temperature, damping, external
magnetic field, and spin-polarized current indicating new spin-torque effects
in the thermally assisted magnetization reversal comprising several orders of
magnitude. In particular, a pronounced dependence of the switching
characteristics on the directions of the external magnetic field and the spin
polarization exists.",1303.3476v4
2013-05-03,"Co2 FeAl thin films grown on MgO substrates: Correlation between static, dynamic and structural properties","Co2FeAl (CFA) thin films with thickness varying from 10 nm to 115 nm have
been deposited on MgO(001) substrates by magnetron sputtering and then capped
by Ta or Cr layer. X-rays diffraction (XRD) revealed that the cubic $[001]$ CFA
axis is normal to the substrate and that all the CFA films exhibit full
epitaxial growth. The chemical order varies from the $B2$ phase to the $A2$
phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and
vibrating sample magnetometer measurements show that, depending on the field
orientation, one or two-step switchings occur. Moreover, the films present a
quadratic MOKE signal increasing with the CFA thickness, due to the increasing
chemical order. Ferromagnetic resonance, MOKE transverse bias initial inverse
susceptibility and torque (TBIIST) measurements reveal that the in-plane
anisotropy results from the superposition of a uniaxial and of a fourfold
symmetry term. The fourfold anisotropy is in accord with the crystal structure
of the samples and is correlated to the biaxial strain and to the chemical
order present in the films. In addition, a large negative perpendicular
uniaxial anisotropy is observed. Frequency and angular dependences of the FMR
linewidth show two magnon scattering and mosaicity contributions, which depend
on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found.",1305.0714v1
2013-06-19,"Asymmetric Ferromagnetic Resonance, Universal Walker Breakdown, and Counterflow Domain Wall Motion in the Presence of Multiple Spin-Orbit Torques","We study the motion of several types of domain wall profiles in spin-orbit
coupled magnetic nanowires and also the influence of spin-orbit interaction on
the ferromagnetic resonance of uniform magnetic films. We extend previous
studies by fully considering not only the field-like contribution from the
spin-orbit torque, but also the recently derived Slonczewski-like spin-orbit
torque. We show that the latter interaction affects both the domain wall
velocity and the Walker breakdown threshold non-trivially, which suggests that
it should be accounted in experimental data analysis. We find that the presence
of multiple spin-orbit torques may render the Walker breakdown to be universal
in the sense that the threshold is completely independent on the
material-dependent Gilbert damping, non-adiabaticity, and the chirality of the
domain wall. We also find that domain wall motion against the current injection
is sustained in the presence of multiple spin-orbit torques and that the wall
profile will determine the qualitative influence of these different types of
torques (e.g. field-like and Slonczewski-like). In addition, we consider a
uniform ferromagnetic layer under a current bias, and find that the resonance
frequency becomes asymmetric against the current direction in the presence of
Slonczewski-like spin-orbit coupling. This is in contrast with those cases
where such an interaction is absent, where the frequency is found to be
symmetric with respect to the current direction. This finding shows that
spin-orbit interactions may offer additional control over pumped and absorbed
energy in a ferromagnetic resonance setup by manipulating the injected current
direction.",1306.4680v1
2013-11-29,Magnon radiation by moving Abrikosov vortices in ferromagnetic superconductors and superconductor-ferromagnet multilayers,"In systems combining type-II superconductivity and magnetism the
non-stationary magnetic field of moving Abrikosov vortices may excite spin
waves, or magnons. This effect leads to the appearance of an additional damping
force acting on the vortices. By solving the London and Landau-Lifshitz-Gilbert
equations we calculate the magnetic moment induced force acting on vortices in
ferromagnetic superconductors and superconductor/ferromagnet superlattices. If
the vortices are driven by a dc force, magnon generation due to the Cherenkov
resonance starts as the vortex velocity exceeds some threshold value. For an
ideal vortex lattice this leads to an anisotropic contribution to the
resistivity and to the appearance of resonance peaks on the current voltage
characteristics. For a disordered vortex array the current will exhibit a
step-like increase at some critical voltage. If the vortices are driven by an
ac force with a frequency \omega, the interaction with magnetic moments will
lead to a frequency-dependent magnetic contribution \eta_M to the vortex
viscosity. If \omega is below the ferromagnetic resonance frequency \omega_F,
vortices acquire additional inertia. For \omega > \omega_F dissipation is
enhanced due to magnon generation. The viscosity \eta_M can be extracted from
the surface impedance of the ferromagnetic superconductor. Estimates of the
magnetic force acting on vortices for the U-based ferromagnetic superconductors
and cuprate/manganite superlattices are given.",1311.7620v1
2014-03-03,Observations and Implications of Large-Amplitude Longitudinal Oscillations in a Solar Filament,"On 20 August 2010 an energetic disturbance triggered large-amplitude
longitudinal oscillations in a nearby filament. The triggering mechanism
appears to be episodic jets connecting the energetic event with the filament
threads. In the present work we analyze this periodic motion in a large
fraction of the filament to characterize the underlying physics of the
oscillation as well as the filament properties. The results support our
previous theoretical conclusions that the restoring force of large-amplitude
longitudinal oscillations is solar gravity, and the damping mechanism is the
ongoing accumulation of mass onto the oscillating threads. Based on our
previous work, we used the fitted parameters to determine the magnitude and
radius of curvature of the dipped magnetic field along the filament, as well as
the mass accretion rate onto the filament threads. These derived properties are
nearly uniform along the filament, indicating a remarkable degree of
cohesiveness throughout the filament channel. Moreover, the estimated mass
accretion rate implies that the footpoint heating responsible for the thread
formation, according to the thermal nonequilibrium model, agrees with previous
coronal heating estimates. We estimate the magnitude of the energy released in
the nearby event by studying the dynamic response of the filament threads, and
discuss the implications of our study for filament structure and heating.",1403.0381v1
2015-01-16,Direct measurement of the magnetic anisotropy field in Mn--Ga and Mn--Co--Ga Heusler films,"The static and dynamic magnetic properties of tetragonally distorted Mn--Ga
based alloys were investigated. Static properties are determined in magnetic
fields up to 6.5~T using SQUID magnetometry. For the pure Mn$_{1.6}$Ga film,
the saturation magnetisation is 0.36~MA/m and the coercivity is 0.29~T. Partial
substitution of Mn by Co results in Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$. The
saturation magnetisation of those films drops to 0.2~MA/m and the coercivity is
increased to 1~T.
  Time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the
high-frequency dynamics of Mn--Ga. The ferromagnetic resonance frequency
extrapolated to zero-field is found to be 125~GHz with a Gilbert damping,
$\alpha$, of 0.019. The anisotropy field is determined from both SQUID and
TR-MOKE to be 4.5~T, corresponding to an effective anisotropy density of
0.81~MJ/m$^3$.
  Given the large anisotropy field of the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film,
pulsed magnetic fields up to 60~T are used to determine the field strength
required to saturate the film in the plane. For this, the extraordinary Hall
effect was employed as a probe of the local magnetisation. By integrating the
reconstructed in--plane magnetisation curve, the effective anisotropy energy
density for Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ is determined to be 1.23~MJ/m$^3$.",1501.03973v1
2015-06-02,Respective influence of in-plane and out-of-plane spin-transfer torques in magnetization switching of perpendicular magnetic tunnel junctions,"The relative contributions of in-plane (damping-like) and out-of-plane
(field-like) spin-transfer-torques in the magnetization switching of
out-of-plane magnetized magnetic tunnel junctions (pMTJ) has been theoretically
analyzed using the transformed Landau-Lifshitz (LL) equation with the STT
terms. It is demonstrated that in a pMTJ structure obeying macrospin dynamics,
the out-of-plane torque influences the precession frequency but it does not
contribute significantly to the STT switching process (in particular to the
switching time and switching current density), which is mostly determined by
the in-plane STT contribution. This conclusion is confirmed by finite
temperature and finite writing pulse macrospin simulations of the current-field
switching diagrams. It contrasts with the case of STT-switching in in-plane
magnetized MTJ in which the field-like term also influences the switching
critical current. This theoretical analysis was successfully applied to the
interpretation of voltage-field STT switching diagrams experimentally measured
on perpendicular MTJ pillars 36 nm in diameter, which exhibit macrospin-like
behavior. The physical nonequivalence of Landau and Gilbert dissipation terms
in presence of STT-induced dynamics is also discussed.",1506.00780v2
2015-08-28,Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching,"Electric-field modulation of magnetism in strain-mediated multiferroic
heterostructures is considered a promising scheme for enabling memory and
magnetic microwave devices with ultralow power consumption. However, it is not
well understood how electric-field-induced strain influences magnetic
relaxation, an important physical process for device applications. Here we
investigate resonant magnetization dynamics in ferromagnet/ferrolectric
multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct
strain states provided by electric-field-induced ferroelectric phase
transition. The strain not only modifies magnetic anisotropy but also magnetic
relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic
Gilbert damping by electric field, which is attributed to strain-induced tuning
of spin-orbit coupling. By contrast, a small but measurable change in extrinsic
linewidth broadening is attributed to inhomogeneous ferroelastic domain
switching during the phase transition of the PMN-PT substrate.",1508.07290v2
2016-04-05,Homodyne-detected ferromagnetic resonance of in-plane magnetized nano-contacts: composite spin wave resonances and their excitation mechanism,"This work provides a detailed investigation of the measured in-plane
field-swept homodyne-detected ferromagnetic resonance (FMR) spectra of an
extended Co/Cu/NiFe pseudo spin valve stack using a nanocontact (NC) geometry.
The magnetodynamics are generated by a pulse-modulated microwave current and
the resulting rectified dc mixing voltage, which appears across the NC at
resonance, is detected using a lock-in amplifier. Most notably, we find that
the measured spectra of the NiFe layer are composite in nature and highly
asymmetric, consistent with the broadband excitation of multiple modes.
Additionally, the data must be fit with two Lorentzian functions in order to
extract a reasonable value for the Gilbert damping of the NiFe. Aided by
micromagnetic simulations, we conclude that (i) for in-plane fields the rf
Oersted field in the vicinity of the NC plays the dominant role in generating
the observed spectra, (ii) in addition to the FMR mode, exchange dominated spin
waves are also generated, and (iii) the NC diameter sets the mean wavevector of
the exchange dominated spin wave, in good agreement with the dispersion
relation.",1604.01389v1
2016-08-29,Sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses,"Using liquid phase epitaxy (LPE) technique (111) yttrium iron garnet (YIG)
films with thicknesses of ~100 nm and surface roughnesses as low as 0.3 nm have
been grown as a basic material for spin-wave propagation experiments in
microstructured waveguides. The continuously strained films exhibit nearly
perfect crystallinity without significant mosaicity and with effective lattice
misfits of delta a(perpendicular)/a(substrate) ~10-4 and below. The
film/substrate interface is extremely sharp without broad interdiffusion layer
formation. All LPE films exhibit a nearly bulk-like saturation magnetization of
(1800+-20) Gs and an `easy cone' anisotropy type with extremely small in-plane
coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy
with a pronounced six-fold symmetry observed for saturation field <1.5 Oe. No
significant out-of-plane anisotropy is observed, but a weak dependence of the
effective magnetization on the lattice misfit is detected. The narrowest
ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is
the lowest value reported so far for YIG films of 100 nm thicknesses and below.
The Gilbert damping coefficient for investigated LPE films is estimated to be
close to 1 x 10-4.",1608.08043v1
2017-01-10,Motion of skyrmions in nanowires driven by magnonic momentum-transfer forces,"We study the motion of magnetic skyrmions in a nanowire induced by a
spin-wave current $J$ flowing out of a driving layer close to the edge of the
wire. By applying micromagnetic simulation and an analysis of the effective
Thiele equation, we find that the skyrmion trajectory is governed by an
interplay of both forces due to the magnon current and the wire boundary. The
skyrmion is attracted to the driving layer and is accelerated by the repulsive
force due to the wire boundary. We consider both cases of a driving
longitudinal and transverse to the nanowire, but a steady-state motion of the
skyrmion is only obtained for a transverse magnon current. For the latter case,
we find in the limit of low current densities $J$ the velocity-current relation
$v \sim J/\alpha$ where $v$ is the skyrmion velocity and $\alpha$ is the
Gilbert damping. For large $J$ in case of strong driving, the skyrmion is
pushed into the driving layer resulting in a drop of the skyrmion velocity and,
eventually, the destruction of the skyrmion.",1701.02430v2
2017-01-19,Ultrafast Electron-Lattice Coupling Dynamics in VO2 and V2O3 Thin Films,"Ultrafast optical pump - optical probe and optical pump - terahertz probe
spectroscopy were performed on vanadium dioxide (VO2) and vanadium sesquioxide
(V2O3) thin films over a wide temperature range. A comparison of the
experimental data from these two different techniques and two different
vanadium oxides, in particular a comparison of the electronic oscillations
generated by the photoinduced longitudinal acoustic modulation, reveals the
strong electron-phonon coupling that exists in the metallic state of both
materials. The low energy Drude response of V2O3 appears more susceptible than
VO2 to ultrafast strain control. Additionally, our results provide a
measurement of the temperature dependence of the sound velocity in both
systems, revealing a four- to fivefold increase in VO2 and a three- to fivefold
increase in V2O3 across the phase transition. Our data also confirm
observations of strong damping and phonon anharmonicity in the metallic phase
of VO2, and suggest that a similar phenomenon might be at play in the metallic
phase of V2O3. More generally, our simple table-top approach provides relevant
and detailed information about dynamical lattice properties of vanadium oxides,
opening the way to similar studies in other complex materials.",1701.05531v1
2017-02-21,All-optical Detection of Spin Hall Angle in W/CoFeB/SiO2 Heterostructures by Varying Tungsten Layer Thickness,"The development of advanced spintronics devices hinges on the efficient
generation and utilization of pure spin current. In materials with large
spin-orbit coupling, the spin Hall effect may convert charge current to pure
spin current and a large conversion efficiency, which is quantified by spin
Hall angle (SHA), is desirable for the realization of miniaturized and energy
efficient spintronic devices. Here, we report a giant SHA in beta-tungsten
(\b{eta}-W) thin films in Sub/W(t)/Co20Fe60B20(3 nm)/SiO2(2 nm)
heterostructures with variable W thickness. We employed an all-optical
time-resolved magneto-optical Kerr effect microscope for an unambiguous
determination of SHA using the principle of modulation of Gilbert damping of
the adjacent ferromagnetic layer by the spin-orbit torque from the W layer. A
non-monotonic variation of SHA with W layer thickness (t) is observed with a
maximum of about 0.4 at about t = 3 nm, followed by a sudden reduction to a
very low value at t = 6 nm. This variation of SHA with W-thickness correlates
well with the thickness dependent structural phase transition and resistivity
variation of W above the spin diffusion length of W, while below this length
the interfacial electronic effect at W/CoFeB influences the estimation of SHA.",1702.06258v1
2017-03-21,Annealing stability of magnetic tunnel junctions based on dual MgO free layers and [Co/Ni] based thin synthetic antiferromagnet fixed system,"We study the annealing stability of bottom-pinned perpendicularly magnetized
magnetic tunnel junctions based on dual MgO free layers and thin fixed systems
comprising a hard [Co/Ni] multilayer antiferromagnetically coupled to thin a Co
reference layer and a FeCoB polarizing layer. Using conventional magnetometry
and advanced broadband ferromagnetic resonance, we identify the properties of
each sub-unit of the magnetic tunnel junction and demonstrate that this
material option can ensure a satisfactory resilience to the 400$^\circ$C
thermal annealing needed in solid-state magnetic memory applications. The dual
MgO free layer possesses an anneal-robust 0.4 T effective anisotropy and
suffers only a minor increase of its Gilbert damping from 0.007 to 0.010 for
the toughest annealing conditions. Within the fixed system, the ferro-coupler
and texture-breaking TaFeCoB layer keeps an interlayer exchange above 0.8
mJ/m$^2$, while the Ru antiferrocoupler layer within the synthetic
antiferromagnet maintains a coupling above -0.5 mJ/m$^2$. These two strong
couplings maintain the overall functionality of the tunnel junction upon the
toughest annealing despite the gradual degradation of the thin Co layer
anisotropy that may reduce the operation margin in spin torque memory
applications. Based on these findings, we propose further optimization routes
for the next generation magnetic tunnel junctions.",1703.07154v1
2017-08-03,Evolution of the interfacial perpendicular magnetic anisotropy constant of the Co$_2$FeAl/MgO interface upon annealing,"We investigate thickness series of films of the Heusler alloy Co$_2$FeAl in
order to study the effect of annealing on the interface with a MgO layer and on
the bulk magnetic properties. Our results reveal that while the perpendicular
interface anisotropy constant $K^{\perp}_{\rm S}$ is zero for the as-deposited
samples, its value increases with annealing up to a value of $1.14\, \pm
\,0.07$~mJ/m$^2$ for the series annealed at 320$^{\rm o}$C and of $2.07\, \pm
\,0.7$~mJ/m$^2$ for the 450$^{\rm o}$C annealed series owing to a strong
modification of the interface during the thermal treatment. This large value
ensures a stabilization of a perpendicular magnetization orientation for a
thickness below 1.7~nm. The data additionally shows that the in-plane biaxial
anisotropy constant has a different evolution with thickness in as-deposited
and annealed systems. The Gilbert damping parameter $\alpha$ shows minima for
all series for a thickness of 40~nm and an absolute minimum value of
$2.8\pm0.1\cdot10^{-3}$. The thickness dependence is explained in terms of an
inhomogenous magnetization state generated by the interplay between the
different anisotropies of the system and by crystalline disorder.",1708.01126v2
2017-08-08,Spin-orbit-torque driven magnetoimpedance in Pt-layer/magnetic-ribbon heterostructures,"When a flow of electron passes through a paramagnetic layer with strong
spin-orbit-coupling such as platinum (Pt), a net spin current is produced via
spin Hall effect (SHE). This spin current can exert a torque on the
magnetization of an adjacent ferromagnetic layer which can be probed via
magnetization dynamic response, e.g. spin-torque ferromagnetic resonance
(ST-FMR). Nevertheless, that effect in lower frequency magnetization dynamic
regime (MHz) where skin effect occurs in high permeability ferromagnetic
conductors namely the magneto-impedance (MI) effect can be fundamentally
important which has not been studied so far. Here, by utilizing the MI effect
in magnetic-ribbon/Pt heterostructure with high magnetic permeability that
allows the ac current effectively confined at the skin depth of ~100 nm
thickness, the effect of spin-orbit-torque (SOT) induced by the SHE probed via
MI measurement is investigated. We observed a systematic MI frequency shift
that increases by increasing the applied current amplitude and thickness of the
Pt layer (varying from 0 nm to 20 nm). In addition, the role of Pt layer in
ribbon/Pt heterostructure is evaluated with ferromagnetic resonance (FMR)
effect representing standard Gilbert damping increase as the result of presence
of the SHE. Our results unveil the role of SOT in dynamic control of the
transverse magnetic permeability probed with impedance spectroscopy as useful
and valuable technique for detection of future SHE devices.",1708.02402v2
2017-12-20,Second-harmonic magnetic response characterizing magnetite-based colloid,"Nonlinear second-harmonic magnetic response (M2) was used to characterize an
aqueous colloidal solution of dextran-coated magnetite (Fe3O4) nanoparticles.
Data analysis with the formalism based on Gilbert-Landau-Lifshitz equation for
stochastic dynamics of superparamagnetic (SP) particles ensured extensive
quantifying of the system via a set of magnetic and magnetodynamic parameters,
such as the mean magnetic moment, the damping constant, the longitudinal
relaxation time, the magnetic anisotropy field and energy, and others. Combined
with transmission electron microscopy and dynamic light scattering, M2
technique allowed obtaining additional parameters, viz., the dextran-coating
thickness and the interparticle magnetic dipolar energy. Aggregated colloidal
nanoparticles were shown to be magnetically correlated inside the aggregate due
to magnetic dipole-dipole (d-d) coupling within the correlation radius ~50 nm.
With the d-d coupling account, the volume distribution of the aggregates
recovered from M2 measurements is well consistent with electron microscopy
results. From electron magnetic resonance, abrupt change of SP dynamics with
increasing external magnetic field was observed and explained. The presented
study exemplifies a novel M2-based procedure of comprehensive quantitative
characterization applicable for a wide variety of SP systems.",1712.07534v1
2018-02-09,Monocrystalline free standing 3D yttrium iron garnet magnon nano resonators,"Nano resonators in which mechanical vibrations and spin waves can be coupled
are an intriguing concept that can be used in quantum information processing to
transfer information between different states of excitation. Until now, the
fabrication of free standing magnetic nanostructures which host long lived spin
wave excitatons and may be suitable as mechanical resonators seemed elusive. We
demonstrate the fabrication of free standing monocrystalline yttrium iron
garnet (YIG) 3D nanoresonators with nearly ideal magnetic properties. The
freestanding 3D structures are obtained using a complex lithography process
including room temperature deposition and lift-off of amorphous YIG and
subsequent crystallization by annealing. The crystallization nucleates from the
substrate and propagates across the structure even around bends over distances
of several micrometers to form e.g. monocrystalline resonators as shown by
transmission electron microscopy. Spin wave excitations in individual
nanostructures are imaged by time resolved scanning Kerr microscopy. The narrow
linewidth of the magnetic excitations indicates a Gilbert damping constant of
only $\alpha = 2.6 \times 10^{-4}$ rivalling the best values obtained for
epitaxial YIG thin film material. The new fabrication process represents a leap
forward in magnonics and magnon mechanics as it provides 3D YIG structures of
unprecedented quality. At the same time it demonstrates a completely new route
towards the fabrication of free standing crystalline nano structures which may
be applicable also to other material systems.",1802.03176v2
2018-11-30,Dynamical precession of spin in the two-dimensional spin-orbit coupled systems,"We investigate the spin dynamics in the two-dimensional spin-orbit coupled
system subject to an in-plane ($x$-$y$ plane) constant electric field, which is
assumed to be turned on at the moment $t=0$. The equation of spin precession in
linear response to the switch-on of the electric field is derived in terms of
Heisenberg's equation by the perturbation method up to the first order of the
electric field. The dissipative effect, which is responsible for bringing the
dynamical response to an asymptotic result, is phenomenologically implemented
\`{a} la the Landau-Lifshitz-Gilbert equation by introducing damping terms upon
the equation of spin dynamics. Mediated by the dissipative effect, the
resulting spin dynamics asymptotes to a stationary state, where the spin and
the momentum-dependent effective magnetic field are aligned again and have
nonzero components in the out-of-plane ($z$) direction. In the linear response
regime, the asymptotic response obtained by the dynamical treatment is in full
agreement with the stationary response as calculated in the Kubo formula, which
is a time-independent approach treating the applied electric field as
completely time-independent. Our method provides a new perspective on the
connection between the dynamical and stationary responses.",1811.12626v2
2019-03-08,Spin-transfer torques for domain walls in antiferromagnetically coupled ferrimagnets,"Antiferromagnetic materials are outstanding candidates for next generation
spintronic applications, because their ultrafast spin dynamics makes it
possible to realize several orders of magnitude higher-speed devices than
conventional ferromagnetic materials1. Though spin-transfer torque (STT) is a
key for electrical control of spins as successfully demonstrated in
ferromagnetic spintronics, experimental understanding of STT in
antiferromagnets has been still lacking despite a number of pertinent
theoretical studies2-5. Here, we report experimental results on the effects of
STT on domain-wall (DW) motion in antiferromagnetically-coupled ferrimagnets.
We find that non-adiabatic STT acts like a staggered magnetic field and thus
can drive DWs effectively. Moreover, the non-adiabaticity parameter {\beta} of
STT is found to be significantly larger than the Gilbert damping parameter
{\alpha}, challenging our conventional understanding of the non-adiabatic STT
based on ferromagnets as well as leading to fast current-induced
antiferromagnetic DW motion. Our study will lead to further vigorous
exploration of STT for antiferromagnetic spin textures for fundamental physics
on spin-charge interaction as wells for efficient electrical control of
antiferromagnetic devices.",1903.03251v1
2019-03-26,Engineering of spin mixing conductance in Ru/FeCo/Ru interfaces: Effect of Re Doping,"We have deposited polycrystalline Re doped $(Fe_{65}Co_{35})_{100-x}Re_{x}$
(0 $\leq$ x $\leq$ 12.6 at\%) thin films grown under identical conditions and
sandwiched between thin layers of Ru in order to study the phenomenon of spin
pumping as a function of Re concentration. In-plane and out-of-plane
ferromagnetic resonance spectroscopy results show an enhancement of the Gilbert
damping with an increase in Re doping. We found evidence of an increase in the
real part of effective spin mixing conductance
[Re($g^{\uparrow\downarrow}_{eff}$)] with the increase in Re doping of 6.6
at\%, while a decrease is evident at higher Re doping. The increase in
Re($g^{\uparrow\downarrow}_{eff}$) can be linked to the Re doping induced
change of the interface electronic structure in the non-magnetic Ru layer and
the effect interfacial spin-orbit coupling has on the effective spin-mixing
conductance. The lowest and highest values of
Re($g^{\uparrow\downarrow}_{eff}$) are found to be 9.883(02) $nm^{-2}$ and
19.697(02) $nm^{-2}$ for 0 at\% and 6.6 at\% Re doping, respectively. The
saturation magnetization decreases with increasing Re doping, from 2.362(13) T
for the undoped film to 1.740(03) T for 12.6 at\% Re doping. This study opens a
new direction of tuning the spin-mixing conductance in magnetic
heterostructures by doping of the ferromagnetic layerr, which is essential for
the realization of energy efficient operation of spintronic devices.",1903.10966v2
2019-09-12,Spin Transport in Thick Insulating Antiferromagnetic Films,"Spin transport of magnonic excitations in uniaxial insulating
antiferromagnets (AFs) is investigated. In linear response to spin biasing and
a temperature gradient, the spin transport properties of
normal-metal--insulating antiferromagnet--normal-metal heterostructures are
calculated. We focus on the thick-film regime, where the AF is thicker than the
magnon equilibration length. This regime allows the use of a drift-diffusion
approach, which is opposed to the thin-film limit considered by Bender {\it et
al.} 2017, where a stochastic approach is justified. We obtain the temperature-
and thickness-dependence of the structural spin Seebeck coefficient
$\mathcal{S}$ and magnon conductance $\mathcal{G}$. In their evaluation we
incorporate effects from field- and temperature-dependent spin conserving
inter-magnon scattering processes. Furthermore, the interfacial spin transport
is studied by evaluating the contact magnon conductances in a microscopic model
that accounts for the sub-lattice symmetry breaking at the interface. We find
that while inter-magnon scattering does slightly suppress the spin Seebeck
effect, transport is generally unaffected, with the relevant spin decay length
being determined by non-magnon-conserving processes such as Gilbert damping. In
addition, we find that while the structural spin conductance may be enhanced
near the spin flip transition, it does not diverge due to spin impedance at the
normal metal|magnet interfaces.",1909.05881v2
2019-12-16,Spin-current manipulation of photoinduced magnetization dynamics in heavy metal / ferromagnet double layer based nanostructures,"Spin currents offer a way to control static and dynamic magnetic properties,
and therefore they are crucial for next-generation MRAM devices or spin-torque
oscillators. Manipulating the dynamics is especially interesting within the
context of photo-magnonics. In typical $3d$ transition metal ferromagnets like
CoFeB, the lifetime of light-induced magnetization dynamics is restricted to
about 1 ns, which e.g. strongly limits the opportunities to exploit the wave
nature in a magnonic crystal filtering device. Here, we investigate the
potential of spin-currents to increase the spin wave lifetime in a functional
bilayer system, consisting of a heavy metal (8 nm of $\beta$-Tantalum
(Platinum)) and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer
generates a transverse spin current when a lateral charge current passes
through the strip. Using time-resolved all-optical pump-probe spectroscopy, we
investigate how this spin current affects the magnetization dynamics in the
adjacent CoFeB layer. We observed a linear spin current manipulation of the
effective Gilbert damping parameter for the Kittel mode from which we were able
to determine the system's spin Hall angles. Furthermore, we measured a strong
influence of the spin current on a high-frequency mode. We interpret this mode
an an exchange dominated higher order spin-wave resonance. Thus we infer a
strong dependence of the exchange constant on the spin current.",1912.07728v1
2020-01-09,Role of longitudinal fluctuations in L$1_0$ FePt,"L$1_0$ FePt is a technologically important material for a range of novel data
storage applications. In the ordered FePt structure the normally non-magnetic
Pt ion acquires a magnetic moment, which depends on the local field originating
from the neighboring Fe atoms. In this work a model of FePt is constructed,
where the induced Pt moment is simulated by using combined longitudinal and
rotational spin dynamics. The model is parameterized to include a linear
variation of the moment with the exchange field, so that at the Pt site the
magnetic moment depends on the Fe ordering. The Curie temperature of FePt is
calculated and agrees well with similar models that incorporate the Pt dynamics
through an effective Fe-only Hamiltonian. By computing the dynamic correlation
function the anisotropy field and the Gilbert damping are extracted over a
range of temperatures. The anisotropy exhibits a power-law dependence with
temperature with exponent $n\approx2.1$. This agrees well with what observed
experimentally and it is obtained without including a two-ion anisotropy term
as in other approaches. Our work shows that incorporating longitudinal
fluctuations into spin dynamics calculations is crucial for understanding the
properties of materials with induced moments.",2001.03074v1
2020-05-07,Effect of interfacial oxidation layer in spin pumping experiments on Ni$_{80}$Fe$_{20}$/SrIrO$_3$ heterostructures,"SrIrO$_3$ with its large spin-orbit coupling and low charge conductivity has
emerged as a potential candidate for efficient spin-orbit torque magnetization
control in spintronic devices. We here report on the influence of an
interfacial oxide layer on spin pumping experiments in Ni$_{80}$Fe$_{20}$
(NiFe)/SrIrO$_3$ bilayer heterostructures. To investigate this scenario we have
carried out broadband ferromagnetic resonance (BBFMR) measurements, which
indicate the presence of an interfacial antiferromagnetic oxide layer. We
performed in-plane BBFMR experiments at cryogenic temperatures, which allowed
us to simultaneously study dynamic spin pumping properties (Gilbert damping)
and static magnetic properties (such as the effective magnetization and
magnetic anisotropy). The results for NiFe/SrIrO$_3$ bilayer thin films were
analyzed and compared to those from a NiFe/NbN/SrIrO$_3$ trilayer reference
sample, where a spin-transparent, ultra-thin NbN layer was inserted to prevent
oxidation of NiFe. At low temperatures, we observe substantial differences in
the magnetization dynamics parameters of these samples, which can be explained
by an antiferromagnetic interfacial layer in the NiFe/SrIrO$_3$ bilayers.",2005.03727v1
2020-05-28,Hard antinodal gap revealed by quantum oscillations in the pseudogap regime of underdoped high-$T_{\rm c}$ superconductors,"An understanding of the missing antinodal electronic excitations in the
pseudogap state is essential for uncovering the physics of the underdoped
cuprate high temperature superconductors. The majority of high temperature
experiments performed thus far, however, have been unable to discern whether
the antinodal states are rendered unobservable due to their damping, or whether
they vanish due to their gapping. Here we distinguish between these two
scenarios by using quantum oscillations to examine whether the small Fermi
surface pocket, found to occupy only 2% of the Brillouin zone in the underdoped
cuprates, exists in isolation against a majority of completely gapped density
of states spanning the antinodes, or whether it is thermodynamically coupled to
a background of ungapped antinodal states. We find that quantum oscillations
associated with the small Fermi surface pocket exhibit a signature sawtooth
waveform characteristic of an isolated two-dimensional Fermi surface pocket.
This finding reveals that the antinodal states are destroyed by a hard gap that
extends over the majority of the Brillouin zone, placing strong constraints on
a drastic underlying origin of quasiparticle disappearance over almost the
entire Brillouin zone in the pseudogap regime.",2005.14123v1
2020-06-01,Enhancement in Thermally Generated Spin Voltage at Pd/NiFe$_2$O$_4$ Interfaces by the Growth on Lattice-Matched Substrates,"Efficient spin injection from epitaxial ferrimagnetic NiFe$_2$O$_4$ thin
films into a Pd layer is demonstrated via spin Seebeck effect measurements in
the longitudinal geometry. The NiFe$_2$O$_4$ films (60 nm to 1 $\mu$m) are
grown by pulsed laser deposition on isostructural spinel MgAl$_2$O$_4$,
MgGa$_2$O$_4$, and CoGa$_2$O$_4$ substrates with lattice mismatch varying
between 3.2% and 0.2%. For the thinner films ($\leq$ 330 nm), an increase in
the spin Seebeck voltage is observed with decreasing lattice mismatch, which
correlates well with a decrease in the Gilbert damping parameter as determined
from ferromagnetic resonance measurements. High resolution transmission
electron microscopy studies indicate substantial decrease of antiphase boundary
and interface defects that cause strain-relaxation, i.e., misfit dislocations,
in the films with decreasing lattice mismatch. This highlights the importance
of reducing structural defects in spinel ferrites for efficient spin injection.
It is further shown that angle-dependent spin Seebeck effect measurements
provide a qualitative method to probe for in-plane magnetic anisotropies
present in the films.",2006.00777v1
2020-06-10,Study of magnetic interface and its effect in Fe/NiFe bilayers of alternating order,"We present a comprehensive study on the magnetization reversal in Fe/NiFe
bilayer system by alternating the order of the magnetic layers. All the samples
show growth-induced uniaxial magnetic anisotropy due to oblique angle
deposition technique. Strong interfacial exchange coupling between the Fe and
NiFe layers leads to the single-phase hysteresis loops in the bilayer system.
The strength of coupling being dependent on the interface changes upon
alternating the order of magnetic layers. The magnetic parameters such as
coercivity HC, and anisotropy field HK become almost doubled when NiFe layer is
grown over the Fe layers. This enhancement in the magnetic parameters is
primarily dependent on the increase of the thickness and magnetic moment of
Fe-NiFe interfacial layer as revealed from the polarized neutron reectivity
(PNR) data of the bilayer samples. The difference in the thickness and
magnetization of the Fe-NiFe interfacial layer indicates the modification of
the microstructure by alternating the order of the magnetic layers of the
bilayers. The interfacial magnetic moment increased by almost 18 % when NiFe
layer is grown over the Fe layer. In spite of the different values of
anisotropy fields and modified interfacial exchange coupling, the Gilbert
damping constant values of the ferromagnetic bilayers remain similar to single
NiFe layer.",2006.05756v1
2020-09-07,Spin pumping in d-wave superconductor/ferromagnet hybrids,"Spin-pumping across ferromagnet/superconductor (F/S) interfaces has attracted
much attention lately. Yet the focus has been mainly on s-wave
superconductors-based systems whereas (high-temperature) d-wave superconductors
such as YBa2Cu3O7-d (YBCO) have received scarce attention despite their
fundamental and technological interest. Here we use wideband ferromagnetic
resonance to study spin-pumping effects in bilayers that combine a soft
metallic Ni80Fe20 (Py) ferromagnet and YBCO. We evaluate the spin conductance
in YBCO by analyzing the magnetization dynamics in Py. We find that the Gilbert
damping exhibits a drastic drop as the heterostructures are cooled across the
normal-superconducting transition and then, depending on the S/F interface
morphology, either stays constant or shows a strong upturn. This unique
behavior is explained considering quasiparticle density of states at the YBCO
surface, and is a direct consequence of zero-gap nodes for particular
directions in the momentum space. Besides showing the fingerprint of d-wave
superconductivity in spin-pumping, our results demonstrate the potential of
high-temperature superconductors for fine tuning of the magnetization dynamics
in ferromagnets using k-space degrees of freedom of d-wave/F interfaces.",2009.03196v3
2020-09-22,Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy,"The control of pure spin currents carried by magnons in magnetic insulator
(MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of
great interest to spintronic technology as they can be used to carry, transport
and process information. Garnet films with PMA present labyrinth domain
magnetic structures that enrich the magnetization dynamics, and could be
employed in more efficient wave-based logic and memory computing devices. In
MI/NM bilayers, where NM being a normal metal providing a strong spin-orbit
coupling, the PMA benefits the spin-orbit torque (SOT) driven magnetization's
switching by lowering the needed current and rendering the process faster,
crucial for developing magnetic random-access memories (SOT-MRAM). In this
work, we investigated the magnetic anisotropies in thulium iron garnet (TIG)
films with PMA via ferromagnetic resonance measurements, followed by the
excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven
by microwaves and heat currents. TIG films presented a Gilbert damping constant
{\alpha}~0.01, with resonance fields above 3.5 kOe and half linewidths broader
than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through
TIG/Pt was observed as a micro-voltage generated at the edges of the Pt film.
The obtained spin Seebeck coefficient was 0.54 {\mu}V/K, confirming also the
high interfacial spin transparency.",2009.10299v1
2020-10-17,Multiscale modelling of magnetostatic effects on magnetic nanoparticles with application to hyperthermia,"We extend a renormalization group-based course-graining method for
micromagnetic simulations to include properly scaled magnetostatic
interactions. We apply the method in simulations of dynamic hysteresis loops at
clinically relevant sweep rates and at 310 K of iron oxide nanoparticles (NPs)
of the kind that have been used in preclinical studies of magnetic
hyperthermia. The coarse-graining method, along with a time scaling involving
sweep rate and Gilbert damping parameter, allow us to span length scales from
the unit cell to NPs approximately 50 nm in diameter with reasonable simulation
times. For both NPs and the nanorods composing them, we report effective
uniaxial anisotropy strengths and saturation magnetizations, which differ from
those of the bulk materials magnetite and maghemite of which they are made, on
account of the combined non-trivial effects of temperature, inter-rod exchange,
magnetostatic interactions and the degree of orientational order within the
nanorod composites. The effective parameters allow treating the NPs as single
macrospins, and we find for the test case of calculating loops for two aligned
NPs that using the dipole approximation is sufficient for distances beyond 1.5
times the NP diameter. We also present a study on relating integration time
step to micromagnetic cell size, finding that the optimal time step size scales
approximately linearly with cell volume.",2010.08848v1
2021-02-09,Unconventional quantum vortex matter state hosts quantum oscillations in the underdoped high-temperature cuprate superconductors,"A central question in the underdoped cuprates pertains to the nature of the
pseudogap ground state. A conventional metallic ground state of the pseudogap
region has been argued to host quantum oscillations upon destruction of the
superconducting order parameter by modest magnetic fields. Here we use low
applied measurement currents and millikelvin temperatures on ultra-pure single
crystals of underdoped YBa$_2$Cu$_3$O$_{6+x}$ to unearth an unconventional
quantum vortex matter ground state characterized by vanishing electrical
resistivity, magnetic hysteresis, and non-ohmic electrical transport
characteristics beyond the highest laboratory accessible static fields. A new
model of the pseudogap ground state is now required to explain quantum
oscillations that are hosted by the bulk quantum vortex matter state without
experiencing sizeable additional damping in the presence of a large maximum
superconducting gap; possibilities include a pair density wave.",2102.04927v2
2021-03-08,Emerging magnetic nutation,"Nutation has been recognized as of great significance for spintronics; but
justifying its presence has proven to be a hard problem. In this paper we show
that nutation can be understood as emerging from a systematic expansion of a
kernel that describes the history of the interaction of a magnetic moment with
a bath of colored noise. The parameter of the expansion is the ratio of the
colored noise timescale to the precession period. In the process we obtain the
Gilbert damping from the same expansion. We recover the known results, when the
coefficients of the two terms are proportional to one another, in the white
noise limit; and show how colored noise leads to situations where this simple
relation breaks down, but what replaces it can be understood by the appropriate
generalization of the fluctuation--dissipation theorem. Numerical simulations
of the stochastic equations support the analytic approach. In particular we
find that the equilibration time is about an order of magnitude longer than the
timescale set by the colored noise for a wide range of values of the latter and
we can identify the presence of nutation in the non-uniform way the
magnetization approaches equilibrium.",2103.04787v3
2021-03-11,Long-range spin transport on the surface of topological Dirac semimetal,"We theoretically propose the long-range spin transport mediated by the
gapless surface states of topological Dirac semimetal (TDSM). Low-dissipation
spin current is a building block of next-generation spintronics devices. While
conduction electrons in metals and spin waves in ferromagnetic insulators
(FMIs) are the major carriers of spin current, their propagation length is
inevitably limited due to the Joule heating or the Gilbert damping. In order to
suppress dissipation and realize long-range spin transport, we here make use of
the spin-helical surface states of TDSMs, such as $\mathrm{Cd_3 As_2}$ and
$\mathrm{Na_3 Bi}$, which are robust against disorder. Based on a junction of
two FMIs connected by a TDSM, we demonstrate that the magnetization dynamics in
one FMI induces a spin current on the TDSM surface flowing to the other FMI. By
both the analytical transport theory on the surface and the numerical
simulation of real-time evolution in the bulk, we find that the induced spin
current takes a universal semi-quantized value that is insensitive to the
microscopic coupling structure between the FMI and the TDSM. We show that this
surface spin current is robust against disorder over a long range, which
indicates that the TDSM surface serves as a promising system for realizing
spintronics devices.",2103.06519v1
2021-04-09,Spin diffusion length associated to out-of-plane resistivity of Pt thin films in spin pumping experiments,"We present a broadband ferromagnetic resonance study of the Gilbert damping
enhancement ($\Delta \alpha$) due to spin pumping in NiFe/Pt bilayers. The
bilayers, which have negligible interfacial spin memory loss, are studied as a
function of the Pt layer thickness ($t_{\text{Pt}}$) and temperature (100-293
K). Within the framework of diffusive spin pumping theory, we demonstrate that
Dyakonov-Perel (DP) or Elliot-Yaffet (EY) spin relaxation mechanisms acting
alone are incompatible with our observations. In contrast, if we consider that
the relation between spin relaxation characteristic time ($\tau_{\text{s}}$)
and momentum relaxation characteristic time ($\tau_{\text{p}}$) is determined
by a superposition of DP and EY mechanisms, the qualitative and quantitative
agreement with experimental results is excellent. Remarkably, we found that
$\tau_{\text{p}}$ must be determined by the out-of-plane electrical resistivity
($\rho$) of the Pt film and hence its spin diffusion length
($\lambda_{\text{Pt}}$) is independent of $t_{\text{Pt}}$. Our work settles the
controversy regarding the $t_{\text{Pt}}$ dependence of $\lambda_{\text{Pt}}$
by demonstrating its fundamental connection with $\rho$ considered along the
same direction of spin current flow. \end{abstract}",2104.04426v1
2021-05-05,Ni$_{80}$Fe$_{20}$ Nanotubes with Optimized Spintronic Functionalities Prepared by Atomic Layer Deposition,"Permalloy Ni$_{80}$Fe$_{20}$ is one of the key magnetic materials in the
field of magnonics. Its potential would be further unveiled if it could be
deposited in three dimensional (3D) architectures of sizes down to the
nanometer. Atomic Layer Deposition, ALD, is the technique of choice for
covering arbitrary shapes with homogeneous thin films. Early successes with
ferromagnetic materials include nickel and cobalt. Still, challenges in
depositing ferromagnetic alloys reside in the synthesis via decomposing the
consituent elements at the same temperature and homogeneously. We report
plasma-enhanced ALD to prepare permalloy Ni$_{80}$Fe$_{20}$ thin films and
nanotubes using nickelocene and iron(III) tert-butoxide as metal precursors,
water as the oxidant agent and an in-cycle plasma enhanced reduction step with
hydrogen. We have optimized the ALD cycle in terms of Ni:Fe atomic ratio and
functional properties. We obtained a Gilbert damping of 0.013, a resistivity of
28 $\mu\Omega$cm and an anisotropic magnetoresistance effect of 5.6 $\%$ in the
planar thin film geometry. We demonstrate that the process also works for
covering GaAs nanowires, resulting in permalloy nanotubes with high aspect
ratios and diameters of about 150 nm. Individual nanotubes were investigated in
terms of crystal phase, composition and spin-dynamic response by microfocused
Brillouin Light Scattering. Our results enable NiFe-based 3D spintronics and
magnonic devices in curved and complex topology operated in the GHz frequency
regime.",2105.01969v1
2021-06-23,Spin dynamics of itinerant electrons: local magnetic moment formation and Berry phase,"The state-of-the-art theoretical description of magnetic materials relies on
solving effective Heisenberg spin problems or their generalizations to
relativistic or multi-spin-interaction cases that explicitly assume the
presence of local magnetic moments in the system. We start with a general
interacting fermionic model that is often obtained in ab initio electronic
structure calculations and show that the corresponding spin problem can be
introduced even in the paramagnetic regime, which is characterized by a zero
average value of the magnetization. Further, we derive a physical criterion for
the formation of the local magnetic moment and confirm that the latter exists
already at high temperatures well above the transition to the ordered magnetic
state. The use of path-integral techniques allows us to disentangle spin and
electronic degrees of freedom and to carefully separate rotational dynamics of
the local magnetic moment from Higgs fluctuations of its absolute value. It
also allows us to accurately derive the topological Berry phase and relate it
to a physical bosonic variable that describes dynamics of the spin degrees of
freedom. As the result, we demonstrate that the equation of motion in the case
of a large magnetic moment takes a conventional Landau-Lifshitz form that
explicitly accounts for the Gilbert damping due to itinerant nature of the
original electronic model.",2106.12462v3
2021-11-20,Skyrmionics in correlated oxides,"While chiral magnets, metal-based magnetic multilayers, or Heusler compounds
have been considered as the material workhorses in the field of skyrmionics,
oxides are now emerging as promising alternatives, as they host special
correlations between the spin-orbital-charge-lattice degrees of freedom and/or
coupled ferroic order parameters. These interactions open new possibilities for
practically exploiting skyrmionics. In this article, we review the recent
advances in the observation and control of topological spin textures in various
oxide systems. We start with the discovery of skyrmions and related
quasiparticles in bulk and heterostructure ferromagnetic oxides. Next, we
emphasize the shortcomings of implementing ferromagnetic textures, which have
led to the recent explorations of ferrimagnetic and antiferromagnetic oxide
counterparts, with higher Curie temperatures, stray-field immunity, low Gilbert
damping, ultrafast magnetic dynamics, and/or absence of skyrmion deflection.
Then, we highlight the development of novel pathways to control the stability,
motion, and detection of topological textures using electric fields and
currents. Finally, we present the outstanding challenges that need to be
overcome to achieve all-electrical, nonvolatile, low-power oxide skyrmionic
devices.",2111.10562v2
2021-12-01,Unconditional well-posedness and IMEX improvement of a family of predictor-corrector methods in micromagnetics,"Recently, Kim & Wilkening (Convergence of a mass-lumped finite element method
for the Landau-Lifshitz equation, Quart. Appl. Math., 76, 383-405, 2018)
proposed two novel predictor-corrector methods for the Landau-Lifshitz-Gilbert
equation (LLG) in micromagnetics, which models the dynamics of the
magnetization in ferromagnetic materials. Both integrators are based on the
so-called Landau-Lifshitz form of LLG, use mass-lumped variational formulations
discretized by first-order finite elements, and only require the solution of
linear systems, despite the nonlinearity of LLG. The first(-order in time)
method combines a linear update with an explicit projection of an intermediate
approximation onto the unit sphere in order to fulfill the LLG-inherent
unit-length constraint at the discrete level. In the second(-order in time)
integrator, the projection step is replaced by a linear constraint-preserving
variational formulation. In this paper, we extend the analysis of the
integrators by proving unconditional well-posedness and by establishing a close
connection of the methods with other approaches available in the literature.
Moreover, the new analysis also provides a well-posed integrator for the
Schr\""odinger map equation (which is the limit case of LLG for vanishing
damping). Finally, we design an implicit-explicit strategy for the treatment of
the lower-order field contributions, which significantly reduces the
computational cost of the schemes, while preserving their theoretical
properties.",2112.00451v1
2021-12-21,Fast long-wavelength exchange spin waves in partially-compensated Ga:YIG,"Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing
attention from the perspective of novel magnon-based data processing
applications. For short wavelengths needed in small-scale devices, the group
velocity is directly proportional to the spin-wave exchange stiffness constant
$\lambda_\mathrm{ex}$. Using wave vector resolved Brillouin Light Scattering
(BLS) spectroscopy, we directly measure $\lambda_\mathrm{ex}$ in Ga-substituted
YIG thin films and show that it is about three times larger than for pure YIG.
Consequently, the spin-wave group velocity overcomes the one in pure YIG for
wavenumbers $k > 4$ rad/$\mu$m, and the ratio between the velocities reaches a
constant value of around 3.4 for all $k > 20$ rad/$\mu$m. As revealed by
vibrating-sample magnetometry (VSM) and ferromagnetic resonance (FMR)
spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert
damping ($\alpha < 10^{-3}$), a decreased saturation magnetization $\mu_0
M_\mathrm{S}~\approx~20~$mT and a pronounced out-of-plane uniaxial anisotropy
of about $\mu_0 H_{\textrm{u1}} \approx 95 $ mT which leads to an out-of-plane
easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport
for all wavelengths in nano-scale systems independently of dipolar effects.",2112.11348v1
2022-01-27,Magnon transport and thermoelectric effects in ultrathin Tm3Fe5O12/Pt nonlocal devices,"The possibility of electrically exciting and detecting magnon currents in
magnetic insulators has opened exciting perspectives for transporting spin
information in electronic devices. However, the role of the magnetic field and
the nonlocal thermal gradients on the magnon transport remain unclear. Here, by
performing nonlocal harmonic voltage measurements, we investigate magnon
transport in perpendicularly magnetized ultrathin Tm3Fe5O12 (TmIG) films
coupled to Pt electrodes. We show that the first harmonic nonlocal voltage
captures spin-driven magnon transport in TmIG, as expected, and the second
harmonic is dominated by thermoelectric voltages driven by current-induced
thermal gradients at the detector. The magnon diffusion length in TmIG is found
to be on the order of 0.3 {\mu}m at 0.5 T and gradually decays to 0.2 {\mu}m at
0.8 T, which we attribute to the suppression of the magnon relaxation time due
to the increase of the Gilbert damping with field. By performing current,
magnetic field, and distance dependent nonlocal and local measurements we
demonstrate that the second harmonic nonlocal voltage exhibits five
thermoelectric contributions, which originate from the nonlocal spin Seebeck
effect and the ordinary, planar, spin, and anomalous Nernst effects. Our work
provides a guide on how to disentangle magnon signals from diverse
thermoelectric voltages of spin and magnetic origin in nonlocal magnon devices,
and establish the scaling laws of the thermoelectric voltages in
metal/insulator bilayers.",2201.11353v1
2022-01-31,Tuning spin-orbit torques across the phase transition in VO$_2$/NiFe heterostructure,"The emergence of spin-orbit torques as a promising approach to
energy-efficient magnetic switching has generated large interest in material
systems with easily and fully tunable spin-orbit torques. Here, current-induced
spin-orbit torques in VO$_2$/NiFe heterostructures were investigated using
spin-torque ferromagnetic resonance, where the VO$_2$ layer undergoes a
prominent insulator-metal transition. A roughly two-fold increase in the
Gilbert damping parameter, $\alpha$, with temperature was attributed to the
change in the VO$_2$/NiFe interface spin absorption across the VO$_2$ phase
transition. More remarkably, a large modulation ($\pm$100%) and a sign change
of the current-induced spin-orbit torque across the VO$_2$ phase transition
suggest two competing spin-orbit torque generating mechanisms. The bulk spin
Hall effect in metallic VO$_2$, corroborated by our first-principles
calculation of spin Hall conductivity, $\sigma_{SH} \approx 10^4
\frac{\hbar}{e} \Omega^{-1} m^{-1}$, is verified as the main source of the
spin-orbit torque in the metallic phase. The self-induced/anomalous torque in
NiFe, of the opposite sign and a similar magnitude to the bulk spin Hall effect
in metallic VO$_2$, could be the other competing mechanism that dominates as
temperature decreases. For applications, the strong tunability of the torque
strength and direction opens a new route to tailor spin-orbit torques of
materials which undergo phase transitions for new device functionalities.",2201.12984v1
2022-02-03,Controlling spin pumping into superconducting Nb by proximity-induced spin-triplet Cooper pairs,"Proximity-induced long-range spin-triplet supercurrents, important for the
field of superconducting spintronics, are generated in
superconducting/ferromagnetic heterostructures when interfacial magnetic
inhomogeneities responsible for spin mixing and spin flip scattering are
present. The multilayer stack Nb/Cr/Fe/Cr/Nb has been shown to support such
exotic currents when fabricated into Josephson junction devices. However,
creating pure spin currents controllably in superconductors outside of the
Josephson junction architecture is a bottleneck to progress. Recently,
ferromagnetic resonance was proposed as a possible direction, the signature of
pure supercurrent creation being an enhancement of the Gilbert damping below
the superconducting critical temperature, but the necessary conditions are
still poorly established. Consistent with theoretical prediction, we
demonstrate conclusively that pumping pure spin currents into a superconductor
is only possible when conditions supporting proximity-induced spin-triplet
effects are satisfied. Our study is an important step forward for
superconducting pure spin current creation and manipulation, considerably
advancing the field of superconducting spintronics.",2202.01520v1
2022-06-17,Multiscale Modelling of the Antiferromagnet Mn2Au: From ab-initio to Micromagnetics,"Antiferromagnets (AFMs) are strong candidates for the future spintronic and
memory applications largely because of their inherently fast dynamics and lack
of stray fields, with Mn2Au being one of the most promising. For the numerical
modelling of magnetic material properties, it is common to use ab-initio
methods, atomistic models and micromagnetics. However, each method alone
describes the physics within certain limits. Multiscale methods bridging the
gap between these three approaches have been already proposed for ferromagnetic
materials. Here, we present a complete multiscale model of the AFM Mn2Au as an
exemplar material, starting with results from ab-initio methods going via
atomistic spin dynamics (ASD) to an AFM Landau-Lifshitz-Bloch (AFM-LLB) model.
Firstly, bulk is modelled using a classical spin Hamiltonian constructed based
on earlier first-principles calculations. Secondly, this spin model is used in
the stochastic Landau-Lifshitz-Gilbert (LLG) to calculate temperature-dependent
equilibrium properties, such as magnetization and magnetic susceptibilities.
Thirdly, the temperature dependent micromagnetic parameters are used in the
AFM-LLB. We validate our approach by comparing the ASD and AFM-LLB models for
three paradigmatic cases; (i) Damped magnetic oscillations, (ii) magnetization
dynamics following a heat pulse resembling pump-probe experiments, (iii)
magnetic domain wall motion under thermal gradients.",2206.08625v1
2022-10-29,Micromagnetic frequency-domain simulation methods for magnonic systems,"We present efficient numerical methods for the simulation of small
magnetization oscillations in three-dimensional micromagnetic systems.
Magnetization dynamics is described by the Landau-Lifshitz-Gilbert (LLG)
equation, linearized in the frequency domain around a generic equilibrium
configuration, and formulated in a special operator form that allows leveraging
large-scale techniques commonly used to evaluate the effective field in
time-domain micromagnetic simulations. By using this formulation, we derive
numerical algorithms to compute the free magnetization oscillations (i.e., spin
wave eigenmodes) as well as magnetization oscillations driven by ac
radio-frequency fields for arbitrarily shaped nanomagnets. Moreover,
semi-analytical perturbation techniques based on the computation of a reduced
set of eigenmodes are provided for fast evaluation of magnetization frequency
response and absorption spectra as a function of damping and ac field. We
present both finite difference and finite element implementations and
demonstrate their effectiveness on a test case. These techniques open the
possibility to study generic magnonic systems discretized with several hundred
thousand (or even millions) of computational cells in a reasonably short time.",2210.16564v3
2023-03-07,Magnon currents excited by the spin Seebeck effect in ferromagnetic EuS thin films,"A magnetic insulator is an ideal platform to propagate spin information by
exploiting magnon currents. However, until now, most studies have focused on
Y$_3$Fe$_5$O$_{12}$ (YIG) and a few other ferri- and antiferromagnetic
insulators, but not on pure ferromagnets. In this study, we demonstrate for the
first time that magnon currents can propagate in ferromagnetic insulating thin
films of EuS. By performing both local and non-local transport measurements in
18-nm-thick films of EuS using Pt electrodes, we detect magnon currents arising
from thermal generation by the spin Seebeck effect. By comparing the dependence
of the local and non-local signals with the temperature (< 30 K) and magnetic
field (< 9 T), we confirm the magnon transport origin of the non-local signal.
Finally, we extract the magnon diffusion length in the EuS film (~140 nm), a
short value in good correspondence with the large Gilbert damping measured in
the same film.",2303.03833v2
2023-04-01,A coupled magneto-structural continuum model for multiferroic $\mathrm{BiFeO}_3$,"A continuum approach to study magnetoelectric multiferroic $\mathrm{BiFeO}_3$
(BFO) is proposed. Our modeling effort marries the ferroelectric (FE) phase
field method and micromagnetic simulations in order to describe the entire
multiferroic order parameter sector (polarization, oxygen antiphase tilts,
strain, and magnetism) self-consistently on the same time and length scale. In
this paper, we discuss our choice of ferroelectric and magnetic energy terms
and demonstrate benchmarks against known behavior. We parameterize the lowest
order couplings of the structural distortions against previous predictions from
density functional theory calculations giving access to simulations of the FE
domain wall (DW) topology. This allows us to estimate the energetic hierarchy
and thicknesses of the numerous structural DWs. We then extend the model to the
canted antiferromagnetic order and demonstrate how the ferroelectric domain
boundaries influence the resulting magnetic DWs. We also highlight some
capabilities of this model by providing two examples relevant for applications.
We demonstrate spin wave transmission through the multiferroic domain
boundaries which identify rectification in qualitative agreement with recent
experimental observations. As a second example of application, we model
fully-dynamical magnetoelectric switching, where we find a sensitivity on the
Gilbert damping with respect to switching pathways. We envision that this
modeling effort will set the basis for further work on properties of arbitrary
3D nanostructures of BFO (and related multiferroics) at the mesoscale.",2304.00270v1
2023-04-19,Thickness-dependent magnetic properties in Pt[CoNi]n multilayers with perpendicular magnetic anisotropy,"We systematically investigated the Ni and Co thickness-dependent
perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain
structures, and magnetization dynamics of Pt(5 nm)/[Co(t_Co nm)/Ni(t_Ni
nm)]5/Pt(1 nm) multilayers by combining the four standard magnetic
characterization techniques. The magnetic-related hysteresis loops obtained
from the field-dependent magnetization M and anomalous Hall resistivity (AHR)
\r{ho}_xy found that the two serial multilayers with t_Co = 0.2 and 0.3 nm have
the optimum PMA coefficient K_U well as the highest coercivity H_C at the Ni
thickness t_Ni = 0.6 nm. Additionally, the magnetic domain structures obtained
by Magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the
thickness and K_U of the films. Furthermore, the thickness-dependent linewidth
of ferromagnetic resonance is inversely proportional to K_U and H_C, indicating
that inhomogeneous magnetic properties dominate the linewidth. However, the
intrinsic Gilbert damping constant determined by a linear fitting of
frequency-dependent linewidth does not depend on Ni thickness and K_U. Our
results could help promote the PMA [Co/Ni] multilayer applications in various
spintronic and spin-orbitronic devices.",2304.09366v1
2023-09-18,Coherent Tunneling and Strain Sensitivity of an All Heusler Alloy Magnetic Tunneling Junction: A First-Principles Study,"Half-metallic Co-based full Heusler alloys have captured considerable
attention of the researchers in the realm of spintronic applications, owing to
their remarkable characteristics such as exceptionally high spin polarization
at Fermi level, ultra-low Gilbert damping, and high Curie temperature. In this
comprehensive study, employing density functional theory, we delve into the
stability and electron transport properties of a magnetic tunneling junction
(MTJ) comprising a Co$_2$MnSb/HfIrSb interface. Utilizing a standard model
given by Julliere, we estimate the tunnel magnetoresistance (TMR) ratio of this
heterojunction under external electric field, revealing a significantly high
TMR ratio (500%) that remains almost unaltered for electric field magnitudes up
to 0.5 V/A. In-depth investigation of K-dependent majority spin transmissions
uncovers the occurrence of coherent tunneling for the Mn-Mn/Ir interface,
particularly when a spacer layer beyond a certain thickness is employed.
Additionally, we explore the impact of bi-axial strain on the MTJ by varying
the in-plane lattice constants between -4% and +4%. Our spin-dependent
transmission calculations demonstrate that the Mn-Mn/Ir interface manifests
strain-sensitive transmission properties under both compressive and tensile
strain, and yields a remarkable three-fold increase in majority spin
transmission under tensile strain conditions. These compelling outcomes place
the Co2MnSb/HfIrSb junction among the highly promising candidates for nanoscale
spintronic devices, emphasizing the potential significance of the system in the
advancement of the field.",2309.09755v1
2023-10-27,Effect of interfacial Dzyaloshinskii-Moriya interaction in spin dynamics of an Antiferromagnet coupled Ferromagnetic double-barrier Magnetic Tunnel Junction,"In this work, we have studied the spin dynamics of a synthethic
Antiferromagnet (SAFM)$|$Heavy Metal (HM)$|$Ferromagnet (FM) double barrier
magnetic tunnel junction (MTJ) in presence of Ruderman-Kittel-Kasuya-Yoside
interaction (RKKYI), interfacial Dzyaloshinskii-Moriya interaction (iDMI),
N\'eel field and Spin-Orbit Coupling (SOC) with different Spin Transfer Torque
(STT). We employ Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation to
investigate the AFM dynamics of the proposed system. We found that the system
exhibits a transition from regular to damped oscillations with the increase in
strength of STT for systems with weaker iDMI than RKKYI while display sustained
oscillatons for system having same order of iDMI and RKKYI. On the other hand
the iDMI dominating system exhibits self-similar but aperiodic patterns in
absence of N\'eel field. In the presence of N\'eel field, the RKKYI dominating
systems exhibit chaotic oscillations for low STT but display sustained
oscillation under moderate STT. Our results suggest that the decay time of
oscillations can be controlled via SOC. The system can works as an oscillator
for low SOC but display nonlinear characteristics with the rise in SOC for
systems having weaker iDMI than RKKYI while an opposite characteristic are
noticed for iDMI dominating systems. We found periodic oscillations under low
external magnetic field in RKKYI dominating systems while moderate field are
necessary for sustained oscillation in iDMI dominating systems. Moreover, the
system exhibits saddle-node bifurcation and chaos under moderate N\'eel field
and SOC with suitable iDMI and RKKYI. In addition, our results indicate that
the magnon lifetime can be enhanced by increasing the strength of iDMI for both
optical and acoustic modes.",2310.18175v1
2023-11-14,Berry curvature induced giant intrinsic spin-orbit torque in single layer magnetic Weyl semimetal thin films,"Topological quantum materials can exhibit unconventional surface states and
anomalous transport properties, but their applications to spintronic devices
are restricted as they require the growth of high-quality thin films with
bulk-like properties. Here, we study 10--30 nm thick epitaxial ferromagnetic
Co$_{\rm 2}$MnGa films with high structural order. Very high values of the
anomalous Hall conductivity, $\sigma_{\rm xy}=1.35\times10^{5}$ $\Omega^{-1}
m^{-1}$, and the anomalous Hall angle, $\theta_{\rm H}=15.8\%$, both comparable
to bulk values. We observe a dramatic crystalline orientation dependence of the
Gilbert damping constant of a factor of two and a giant intrinsic spin Hall
conductivity, $\mathit{\sigma_{\rm SHC}}=(6.08\pm 0.02)\times 10^{5}$
($\hbar/2e$) $\Omega^{-1} m^{-1}$, which is an order of magnitude higher than
literature values of single-layer Ni$_{\rm 80}$Fe$_{\rm 20}$, Ni, Co, Fe, and
multilayer Co$_{\rm 2}$MnGa stacks. Theoretical calculations of the intrinsic
spin Hall conductivity, originating from a strong Berry curvature, corroborate
the results and yield values comparable to the experiment. Our results open up
for the design of spintronic devices based on single layers of topological
quantum materials.",2311.08145v2
2023-12-26,All solution grown epitaxial magnonic crystal of thulium iron garnet thin film,"Magnonics has shown the immense potential of compatibility with CMOS devices
and the ability to be utilized in futuristic quantum computing. Therefore, the
magnonic crystals, both metallic and insulating, are under extensive
exploration. The presence of high spin-orbit interaction induced by the
presence of rare-earth elements in thulium iron garnet (TmIG) increases its
potential in magnonic applications. Previously, TmIG thin films were grown
using ultra-high vacuum-based techniques. Here, we present a cost-effective
solution-based approach that enables the excellent quality interface and
surface roughness of the epitaxial TmIG/GGG. The deposited TmIG (12.2 nm) thin
film's physical and spin dynamic properties are investigated in detail. The
confirmation of the epitaxy using X-ray diffraction in $\phi$-scan geometry
along with the X-ray reflectivity and atomic force for the thickness and
roughness analysis and topography, respectively. The epitaxial TmIG/GGG have
confirmed the perpendicular magnetic anisotropy utilizing the
polar-magneto-optic Kerr effect. Analyzing the ferromagnetic resonance study of
TmIG/GGG thin films provides the anisotropy constant K$_U$ = 20.6$\times$10$^3$
$\pm$ 0.2$\times$10$^3$ N/m$^2$ and the Gilbert damping parameter $\alpha$ =
0.0216 $\pm$ 0.0028. The experimental findings suggest that the
solution-processed TmIG/GGG thin films have the potential to be utilized in
device applications.",2312.15973v1
2024-03-01,Spin current control of magnetism,"Exploring novel strategies to manipulate the order parameter of magnetic
materials by electrical means is of great importance, not only for advancing
our understanding of fundamental magnetism, but also for unlocking potential
practical applications. A well-established concept to date uses gate voltages
to control magnetic properties, such as saturation magnetization, magnetic
anisotropies, coercive field, Curie temperature and Gilbert damping, by
modulating the charge carrier population within a capacitor structure. Note
that the induced carriers are non-spin-polarized, so the control via the
electric-field is independent of the direction of the magnetization. Here, we
show that the magnetocrystalline anisotropy (MCA) of ultrathin Fe films can be
reversibly modified by a spin current generated in Pt by the spin Hall effect.
The effect decreases with increasing Fe thickness, indicating that the origin
of the modification can be traced back to the interface. Uniquely, the change
in MCA due to the spin current depends not only on the polarity of the charge
current but also on the direction of magnetization, i.e. the change in MCA has
opposite sign when the direction of magnetization is reversed. The control of
magnetism by the spin current results from the modified exchange splitting of
majority- and minority-spin bands, and differs significantly from the
manipulation by gate voltages via a capacitor structure, providing a
functionality that was previously unavailable and could be useful in advanced
spintronic devices.",2403.00709v1
2005-01-02,Effect of dipolar interactions on the magnetization of a cubic array of nanomagnets,"We investigated the effect of intermolecular dipolar interactions on a cubic
3D ensemble of 5X5X4=100 nanomagnets, each with spin $S = 5$. We employed the
Landau-Lifshitz-Gilbert equation to solve for the magnetization $M(B)$ curves
for several values of the damping constant $\alpha$, the induction sweep rate,
the lattice constant $a$, the temperature $T$, and the magnetic anisotropy
field $H_A$. We find that the smaller the $\alpha$, the stronger the maximum
induction required to produce hysteresis. The shape of the hysteresis loops
also depends on the damping constant. We find further that the system
magnetizes and demagnetizes at decreasing magnetic field strengths with
decreasing sweep rates, resulting in smaller hysteresis loops. Variations of
$a$ within realistic values (1.5 nm - 2.5 nm) show that the dipolar interaction
plays an important role in the magnetic hysteresis by controlling the
relaxation process. The $T$ dependencies of $\alpha$ and of $M$ are presented
and discussed with regard to recent experimental data on nanomagnets. $H_A$
enhances the size of the hysteresis loops for external fields parallel to the
anisotropy axis, but decreases it for perpendicular external fields. Finally,
we reproduce and test an $M(B)$ curve for a 2D-system [M. Kayali and W. Saslow,
Phys. Rev. B {\bf 70}, 174404 (2004)]. We show that its hysteretic behavior is
only weakly dependent on the shape anisotropy field and the sweep rate, but
depends sensitively upon the dipolar interactions. Although in 3D systems,
dipole-dipole interactions generally diminish the hysteresis, in 2D systems,
they strongly enhance it. For both square 2D and rectangular 3D lattices with
${\bm B}||(\hat{\bm x}+\hat{\bm y})$, dipole-dipole interactions can cause
large jumps in the magnetization.",0501006v2
2019-03-07,"Uniaxial anisotropy, intrinsic and extrinsic damping in Co$_{2}$FeSi Heusler alloy thin films","Ferromagnetic resonance (FMR) technique has been used to study the
magnetization relaxation processes and magnetic anisotropy in two different
series of the Co2FeSi (CFS) Heusler alloy thin films, deposited on the Si(111)
substrate by UHV sputtering. While the CFS films of fixed (50 nm) thickness,
deposited at different substrate temperatures (TS) ranging from room
temperature (RT) to 600^C, constitute the series-I, the CFS films with
thickness t varying from 12 nm to 100 nm and deposited at 550^C make up the
series-II. In series-I, the CFS films deposited at TS = RT and 200^C are
completely amorphous, the one at TS = 300^C is partially crystalline, and those
at TS equal 450^C, 550^C and 600^C are completely crystalline with B2 order. By
contrast, all the CFS films in series-II are in the fully-developed B2
crystalline state. Irrespective of the strength of disorder and film thickness,
angular variation of the resonance field in the film plane unambiguously
establishes the presence of global in-plane uniaxial anisotropy. Angular
variation of the linewidth in the film plane reveals that, in the CFS thin
films of varying thickness, a crossover from the in-plane local four-fold
symmetry (cubic anisotropy) to local two-fold symmetry (uniaxial anisotropy)
occurs as t exceeds 50 nm. Gilbert damping parameter {\alpha} decreases
monotonously from 0.047 to 0.0078 with decreasing disorder strength (increasing
TS) and jumps from 0.008 for the CFS film with t = 50 nm to 0.024 for the film
with t equal 75 nm. Such variations of {\alpha} with TS and t are understood in
terms of the changes in the total (spin-up and spin-down) density of states at
the Fermi level caused by the disorder and film thickness.",1903.02976v1
2023-09-19,Impact of strain on the SOT-driven dynamics of thin film Mn$_3$Sn,"Mn$_3$Sn, a metallic antiferromagnet with an anti-chiral 120$^\circ$ spin
structure, generates intriguing magneto-transport signatures such as a large
anomalous Hall effect, spin-polarized current with novel symmetries, anomalous
Nernst effect, and magneto-optic Kerr effect. When grown epitaxially as
MgO(110)[001]$\parallel$ Mn$_3$Sn($0\bar{1}\bar{1}0$)[0001], Mn$_3$Sn
experiences a uniaxial tensile strain, which changes the bulk six-fold
anisotropy landscape to a perpendicular magnetic anisotropy with two stable
states. In this work, we investigate the field-assisted spin orbit-torque
(SOT)-driven response of the order parameter in single-domain Mn$_3$Sn with
uniaxial tensile strain. We find that for a non-zero external magnetic field,
the order parameter can be switched between the two stable states if the
magnitude of the input current is between two field-dependent critical
currents. Below the lower critical current, the order parameter exhibits a
stationary state in the vicinity of the initial stable state. On the other
hand, above the higher critical current, the order parameter shows oscillatory
dynamics which could be tuned from the 100's of megahertz to the gigahertz
range. We obtain approximate expressions of the two critical currents and find
them to agree very well with the numerical simulations for experimentally
relevant magnetic fields. We also obtain unified functional form of the
switching time versus the input current for different magnetic fields. Finally,
we show that for lower values of Gilbert damping ($\alpha \leq 2\times
10^{-3}$), the critical currents and the final steady states depend
significantly on the damping constant. The numerical and analytic results
presented in our work can be used by both theorists and experimentalists to
understand the SOT-driven order dynamics in PMA Mn$_3$Sn and design future
experiments and devices.",2309.10246v2
2008-12-31,Weak Solutions of the Stochastic Landau-Lifshitz-Gilbert Equation,"The Landau-Lifshitz-Gilbert equation perturbed by a multiplicative
space-dependent noise is considered for a ferromagnet filling a bounded
three-dimensional domain. We show the existence of weak martingale solutions
taking values in a sphere $\mathbb S^2$. The regularity of weak solutions is
also discussed. Some of the regularity results are new even for the
deterministic Landau-Lifshitz-Gilbert equation.",0901.0039v1
2023-09-08,Branching points in the planar Gilbert--Steiner problem have degree 3,"Gilbert--Steiner problem is a generalization of the Steiner tree problem on a
specific optimal mass transportation.
  We show that every branching point in a solution of the planar
Gilbert--Steiner problem has degree 3.",2309.04202v2
2007-02-23,Organization of the Modulopt collection of optimization problems in the Libopt environment -- Version 1.0,"This note describes how the optimization problems of the Modulopt collection
are organized within the Libopt environment. It is aimed at being a guide for
using and enriching this collection in this environment.",0702695v1
2005-10-17,"Comment on ""Operator Quantum Error Correction""","The attempt to equate operator quantum error correction (quant-ph/0504189v1)
with the quantum computer condition (quant-ph/0507141) in version two of
quant-ph/0504189 is shown to be invalid.",0510116v1
2007-09-17,H-Decompositions,"We show that for all graphs H of size n, the complete graph $K_{2n+1}$ has an
$H$-decomposition.",0709.2525v5
2008-10-06,Unsolvability of the isomorphism problem for [free abelian]-by-free groups,The isomorphism problem for [free abelian]-by-free groups is unsolvable.,0810.0935v2
2011-11-27,"Comment on ""Capturing correlations in chaotic diffusion by approximation methods""","This is a comment on [G. Knight and R. Klages, Phys. Rev. E 84, 041135
(2011); also available at arXiv:1107.5293v2 [math-ph]].",1111.6271v1
2014-01-11,Hashimoto transform for stochastic Landau-Lifshitz-Gilbert equation,"We show that Hashimoto transformation is applicable to the one dimensional
stochastic Landau-Lifshitz-Gilbert (LLG) equation and transforms it to the
stochastic generalized heat equation with nonlocal (in space) interaction.",1401.2520v1
2017-01-04,Non-linear Cyclic Codes that Attain the Gilbert-Varshamov Bound,"We prove that there exist non-linear binary cyclic codes that attain the
Gilbert-Varshamov bound.",1701.01043v1
2019-01-28,Conformal deformations preserving the Finslerian $R$-Einstein criterion,"Given a Finslerian metric $F$ on a $C^4$-manifold, conformal deformations of
$F$ preserving the $R$-Einstein criterion are presented. In particular, locally
conformal invariance between two Finslerian $R$-Einstein metrics is
characterized.",1902.00069v1
2022-04-07,How to design a network architecture using availability,"The best way to design a network is to take into account Availability values
and Capacity Planning. You already saw Availability expressed with numbers such
as 99.99%. The purpose of this document is to introduce the way to compute
Availability values using Reliability Block Diagrams.",2204.03311v1
2010-02-22,Transport and magnetization dynamics in a superconductor/single-molecule magnet/superconductor junction,"We study dc-transport and magnetization dynamics in a junction of arbitrary
transparency consisting of two spin-singlet superconducting leads connected via
a single classical spin precessing at the frequency $\Omega$. The presence of
the spin in the junction provides different transmission amplitudes for spin-up
and spin-down quasiparticles as well as a time-dependent spin-flip transmission
term. For a phase biased junction, we show that a steady-state superconducting
charge current flows through the junction and that an out-of-equilibrium
circularly polarized spin current, of frequency $\Omega$, is emitted in the
leads. Detailed understanding of the charge and spin currents is obtained in
the entire parameter range. In the adiabatic regime, $\hbar \Omega \ll 2\Delta$
where $\Delta$ is the superconducting gap, and for high transparencies of the
junction, a strong suppression of the current takes place around $\vp \approx
0$ due to an abrupt change in the occupation of the Andreev bound-states. At
higher values of the phase and/or precession frequency, extended
(quasi-particle like) states compete with the bound-states in order to carry
the current. Well below the superconducting transition, these results are shown
to be weakly affected by the back-action of the spin current on the dynamics of
the precessing spin. Indeed, we show that the Gilbert damping due to the
quasi-particle spin current is strongly suppressed at low-temperatures, which
goes along with a shift of the precession frequency due to the condensate. The
results obtained may be of interest for on-going experiments in the field of
molecular spintronics.",1002.3929v4
2013-06-18,"Baryons do trace dark matter 380,000 years after the big bang: Search for compensated isocurvature perturbations with WMAP 9-year data","Primordial isocurvature fluctuations between photons and either neutrinos or
non-relativistic species such as baryons or dark matter are known to be
sub-dominant to adiabatic fluctuations. Perturbations in the relative densities
of baryons and dark matter (known as compensated isocurvature perturbations, or
CIPs), however, are surprisingly poorly constrained. CIPs leave no imprint in
the cosmic microwave background (CMB) on observable scales, at least at linear
order in their amplitude and zeroth order in the amplitude of adiabatic
perturbations. It is thus not yet empirically known if baryons trace dark
matter at the surface of last scattering. If CIPs exist, they would spatially
modulate the Silk damping scale and acoustic horizon, causing distinct
fluctuations in the CMB temperature/polarization power spectra across the sky:
this effect is first order in both the CIP and adiabatic mode amplitudes. Here,
temperature data from the Wilkinson Microwave Anisotropy Probe (WMAP) are used
to conduct the first CMB-based observational search for CIPs, using
off-diagonal correlations and the CMB trispectrum. Reconstruction noise from
weak lensing and point sources is shown to be negligible for this data set. No
evidence for CIPs is observed, and a 95%-confidence upper limit of $1.1\times
10^{-2}$ is imposed to the amplitude of a scale-invariant CIP power spectrum.
This limit agrees with CIP sensitivity forecasts for WMAP, and is competitive
with smaller scale constraints from measurements of the baryon fraction in
galaxy clusters. It is shown that the root-mean-squared CIP amplitude on 5-100
degree scales is smaller than 0.07-0.17 (depending on the scale) at the
95%-confidence level. Temperature data from the Planck satellite will provide
an even more sensitive probe for the existence of CIPs, as will the upcoming
ACTPol and SPTPol experiments on smaller angular scales.",1306.4319v1
2015-05-29,Microscopic Theory for Coupled Atomistic Magnetization and Lattice Dynamics,"A coupled atomistic spin and lattice dynamics approach is developed which
merges the dynamics of these two degrees of freedom into a single set of
coupled equations of motion. The underlying microscopic model comprises local
exchange interactions between the electron spin and magnetic moment and the
local couplings between the electronic charge and lattice displacements. An
effective action for the spin and lattice variables is constructed in which the
interactions among the spin and lattice components are determined by the
underlying electronic structure. In this way, expressions are obtained for the
electronically mediated couplings between the spin and lattice degrees of
freedom, besides the well known inter-atomic force constants and spin-spin
interactions. These former susceptibilities provide an atomistic ab initio
description for the coupled spin and lattice dynamics. It is important to
notice that this theory is strictly bilinear in the spin and lattice variables
and provides a minimal model for the coupled dynamics of these subsystems and
that the two subsystems are treated on the same footing. Questions concerning
time-reversal and inversion symmetry are rigorously addressed and it is shown
how these aspects are absorbed in the tensor structure of the interaction
fields. By means of these results regarding the spin-lattice coupling, simple
explanations of ionic dimerization in double anti-ferromagnetic materials, as
well as, charge density waves induced by a non-uniform spin structure are
given. In the final parts, a set of coupled equations of motion for the
combined spin and lattice dynamics are constructed, which subsequently can be
reduced to a form which is analogous to the Landau-Lifshitz-Gilbert equations
for spin dynamics and damped driven mechanical oscillator for the ...",1505.08005v3
2016-04-28,Dynamics of skyrmionic states in confined helimagnetic nanostructures,"In confined helimagnetic nanostructures, skyrmionic states in the form of
incomplete and isolated skyrmion states can emerge as the ground state in
absence of both external magnetic field and magnetocrystalline anisotropy. In
this work, we study the dynamic properties (resonance frequencies and
corresponding eigenmodes) of skyrmionic states in thin film FeGe disk samples.
We employ two different methods in finite-element based micromagnetic
simulation: eigenvalue and ringdown method. The eigenvalue method allows us to
identify all resonance frequencies and corresponding eigenmodes that can exist
in the simulated system. However, using a particular experimentally feasible
excitation can excite only a limited set of eigenmodes. Because of that, we
perform ringdown simulations that resemble the experimental setup using both
in-plane and out-of-plane excitations. In addition, we report the nonlinear
dependence of resonance frequencies on the external magnetic bias field and
disk sample diameter and discuss the possible reversal mode of skyrmionic
states. We compare the power spectral densities of incomplete skyrmion and
isolated skyrmion states and observe several key differences that can
contribute to the experimental identification of the state present in the
sample. We measure the FeGe Gilbert damping, and using its value we determine
what eigenmodes can be expected to be observed in experiments. Finally, we show
that neglecting the demagnetisation energy contribution or ignoring the
magnetisation variation in the out-of-film direction - although not changing
the eigenmode's magnetisation dynamics significantly - changes their resonance
frequencies substantially. Apart from contributing to the understanding of
skyrmionic states physics, this systematic work can be used as a guide for the
experimental identification of skyrmionic states in confined helimagnetic
nanostructures.",1604.08347v2
2017-04-13,Low energy magnon dynamics and magneto-optics of the skyrmionic Mott insulator Cu$_2$OSeO$_3$,"In this work, we present a comprehensive study of the low energy optical
magnetic response of the skyrmionic Mott insulator Cu$_2$OSeO$_3$ via high
resolution time-domain THz spectroscopy. In zero field, a new magnetic
excitation not predicted by spin-wave theory with frequency $f$ = 2.03 THz is
observed and shown, with accompanying time-of-flight neutron scattering
experiments, to be a zone folded magnon from the $\mathrm{R}$ to
$\mathrm{\Gamma}$ points of the Brillouin zone. Highly sensitive polarimetry
experiments performed in weak magnetic fields, $\mu_0$H $<$ 200 mT, observe
Faraday and Kerr rotations which are proportional to the sample magnetization,
allowing for optical detection of the skyrmion phase and construction of a
magnetic phase diagram. From these measurements, we extract a critical exponent
of $\beta$ = 0.35 $\pm$ 0.04, in good agreement with the expected value for the
3D Heisenberg universality class of $\beta$ = 0.367. In large magnetic fields,
$\mu_0$H $>$ 5 T, we observe the magnetically active uniform mode of the
ferrimagnetic field polarized phase whose dynamics as a function of field and
temperature are studied. In addition to extracting a $g_\text{eff}$ = 2.08
$\pm$ 0.03, we observe the uniform mode to decay through a non-Gilbert damping
mechanism and to possesses a finite spontaneous decay rate, $\Gamma_0$
$\approx$ 25 GHz, in the zero temperature limit. Our observations are
attributed to Dzyaloshinkii-Moriya interactions, which have been proposed to be
exceptionally strong in Cu$_2$OSeO$_3$ and are expected to impact the low
energy magnetic response of such chiral magnets.",1704.04228v1
2017-08-25,Role of dimensional crossover on spin-orbit torque efficiency in magnetic insulator thin films,"Magnetic insulators (MIs) attract tremendous interest for spintronic
applications due to low Gilbert damping and absence of Ohmic loss. Magnetic
order of MIs can be manipulated and even switched by spin-orbit torques (SOTs)
generated through spin Hall effect and Rashba-Edelstein effect in heavy
metal/MI bilayers. SOTs on MIs are more intriguing than magnetic metals since
SOTs cannot be transferred to MIs through direct injection of electron spins.
Understanding of SOTs on MIs remains elusive, especially how SOTs scale with
the film thickness. Here, we observe the critical role of dimensionality on the
SOT efficiency by systematically studying the MI layer thickness dependent SOT
efficiency in tungsten/thulium iron garnet (W/TmIG) bilayers. We first show
that the TmIG thin film evolves from two-dimensional to three-dimensional
magnetic phase transitions as the thickness increases, due to the suppression
of long-wavelength thermal fluctuation. Then, we report the significant
enhancement of the measured SOT efficiency as the thickness increases. We
attribute this effect to the increase of the magnetic moment density in concert
with the suppression of thermal fluctuations. At last, we demonstrate the
current-induced SOT switching in the W/TmIG bilayers with a TmIG thickness up
to 15 nm. The switching current density is comparable with those of heavy
metal/ferromagnetic metal cases. Our findings shed light on the understanding
of SOTs in MIs, which is important for the future development of ultrathin
MI-based low-power spintronics.",1708.07584v2
2018-07-04,Phase Boundary Exchange Coupling in the Mixed Magnetic Phase Regime of a Pd-doped FeRh Epilayer,"Spin-wave resonance measurements were performed in the mixed magnetic phase
regime of a Pd-doped FeRh epilayer that appears as the first-order
ferromagnetic-antiferromagnetic phase transition takes place. It is seen that
the measured value of the exchange stiffness is suppressed throughout the
measurement range when compared to the expected value of the fully
ferromagnetic regime, extracted via the independent means of a measurement of
the Curie point, for only slight changes in the ferromagnetic volume fraction.
This behavior is attributed to the influence of the antiferromagnetic phase:
inspired by previous experiments that show ferromagnetism to be most persistent
at the surfaces and interfaces of FeRh thin films, we modelled the
antiferromagnetic phase as forming a thin layer in the middle of the epilayer
through which the two ferromagnetic layers are coupled up to a certain critical
thickness. The development of this exchange stiffness is then consistent with
that expected from the development of an exchange coupling across the magnetic
phase boundary, as a consequence of a thickness dependent phase transition
taking place in the antiferromagnetic regions and is supported by complimentary
computer simulations of atomistic spin-dynamics. The development of the Gilbert
damping parameter extracted from the ferromagnetic resonance investigations is
consistent with this picture.",1807.01615v6
2018-07-26,EPIC 246851721 b: A Tropical Jupiter Transiting a Rapidly Rotating Star in a Well-Aligned Orbit,"We report the discovery of EPIC 246851721 b, a ""tropical"" Jupiter in a
6.18-day orbit around the bright ($V=11.439$) star EPIC 246851721 (TYC
1283-739-1). We present a detailed analysis of the system using $K2$ and
ground-based photometry, radial velocities, Doppler tomography and adaptive
optics imaging. From our global models, we infer that the host star is a
rapidly rotating ($v \sin i = 74.92 $ km s$^{-1}$) F dwarf with
$T_\mathrm{eff}$ = 6202 K, $R_\star = 1.586 \ R_\odot$ and $M_\star= 1.317 \
M_\odot$. EPIC 246851721 b has a radius of $1.051 \pm 0.044 R_J$, and a mass of
3.0$^{+1.1}_{-1.2} M_J$ . Doppler tomography reveals an aligned spin-orbit
geometry, with a projected obliquity of $-1.47^{\circ\ +0.87}_{\ -0.86}$,
making EPIC 246851721 the fourth hottest star to host a Jovian planet with $P >
5$ days and a known obliquity. Using quasi-periodic signatures in its light
curve that appear to be spot modulations, we estimate the star's rotation
period, and thereby infer the true obliquity of the system to be $3.7^{\circ\
+3.7}_{\ -1.8}$. We argue that this near-zero obliquity is likely to be
primordial rather than a result of tidal damping. The host star also has a
bound stellar companion, a $0.4 \ M_\odot$ M dwarf at a projected separation of
2100 AU, but the companion is likely incapable of emplacing EPIC 246851721 b in
its current orbit via high eccentricity Kozai-Lidov migration.",1807.10298v2
2018-09-10,Magnetic properties and field-driven dynamics of chiral domain walls in epitaxial Pt/Co/Au$_x$Pt$_{1-x}$ trilayers,"Chiral domain walls in ultrathin perpendicularly magnetised layers have a
N\'{e}el structure stabilised by a Dzyaloshinskii-Moriya interaction (DMI) that
is generated at the interface between the ferromagnet and a heavy metal.
Different heavy metals are required above and below a ferromagnetic film in
order to generate the structural inversion asymmetry needed to ensure that the
DMI arising at the two interfaces does not cancel. Here we report on the
magnetic properties of epitaxial Pt/Co/Au$_x$Pt$_{1-x}$ trilayers grown by
sputtering onto sapphire substrates with 0.6 nm thick Co. As $x$ rises from 0
to 1 a structural inversion asymmetry is generated. We characterise the
epilayer structure with x-ray diffraction and cross-sectional transmission
electron microscopy, revealing (111) stacking. The saturation magnetization
falls as the proximity magnetisation in Pt is reduced, whilst the perpendicular
magnetic anisotropy $K_\mathrm{u}$ rises. The micromagnetic DMI strength $D$
was determined using the bubble expansion technique and also rises from a
negligible value when $x=0$ to $\sim 1$ mJ/m$^2$ for $x = 1$. The depinning
field at which field-driven domain wall motion crosses from the creep to the
depinning regime rises from $\sim 40$ to $\sim 70$ mT, attributed to greater
spatial fluctuations of the domain wall energy with increasing Au
concentration. Meanwhile, the increase in DMI causes the Walker field to rise
from $\sim 10$ to $\sim 280$ mT, meaning that only in the $x = 1$ sample is the
steady flow regime accessible. The full dependence of domain wall velocity on
driving field bears little resemblance to the prediction of a simple
one-dimensional model, but can be described very well using micromagnetic
simulations with a realistic model of disorder. These reveal a rise in Gilbert
damping as $x$ increases.",1809.03217v2
2019-09-06,Macrospin analysis of RF excitations within fully perpendicular magnetic tunnel junctions with second order easy-axis magnetic anisotropy contribution,"The conditions of field and voltage for inducing steady state excitations in
fully perpendicular magnetic tunnel junctions (pMTJs), adapted for memory
applications, were numerically investigated by the resolution of the
Landau-Lifshitz-Gilbert equation in the macrospin approach. Both damping-like
and the field-like spin transfer torque terms were taken into account in the
simulations, as well as the contribution of the second order uniaxial
anisotropy term (K2), which has been recently revealed in MgO-based pMTJs. An
in-plane applied magnetic field balances the out of plane symmetry of the pMTJ
and allows the signal detection. Using this model, we assessed the states of
the free layer magnetization as a function of strength of K2 and polar theta_H
angle of the applied field (varied from 90 to 60 deg.). There are two stable
states, with the magnetization in-plane or out of plane of the layer, and two
dynamic states with self-sustained oscillations, called in-plane precession
state (IPP) or out of plane precession state (OPP). The IPP mode, with
oscillation frequencies up to 7 GHz, appears only for positive voltages if
theta_H = 90 deg. However, it shows a more complex distribution when the field
is slightly tilted out of plane. The OPP mode is excited only if K2 is
considered and reaches a maximum oscillation frequency of 15 GHz. Large areas
of dynamic states with high frequencies are obtained for strong values of the
field-like torque and K2, when applying a slightly tilted external field toward
the out of plane direction. The non-zero temperature does not modify the phase
diagrams, but reduces drastically the power spectral density peak amplitudes.",1909.02926v1
2021-04-21,Atomic Layer Deposition of Yttrium Iron Garnet Thin Films for 3D Magnetic Structures,"A wide variety of new phenomena such as novel magnetization configurations
have been predicted to occur in three dimensional magnetic nanostructures.
However, the fabrication of such structures is often challenging due to the
specific shapes required, such as magnetic tubes and spirals. Furthermore, the
materials currently used to assemble these structures are predominantly
magnetic metals that do not allow to study the magnetic response of the system
separately from the electronic one. In the field of spintronics, the
prototypical material used for such experiments is the ferrimagnetic insulator
yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). YIG is one of the best
materials especially for magnonic studies due to its low Gilbert damping. Here,
we report the first successful fabrication of YIG thin films via atomic layer
deposition. To that end we utilize a supercycle approach based on the
combination of sub-nanometer thin layers of the binary systems Fe$_2$O$_3$ and
Y$_2$O$_3$ in the correct atomic ratio on Y$_3$Al$_5$O$_{12}$ substrates with a
subsequent annealing step. Our process is robust against typical growth-related
deviations, ensuring a good reproducibility. The ALD-YIG thin films exhibit a
good crystalline quality as well as magnetic properties comparable to other
deposition techniques. One of the outstanding characteristics of atomic layer
deposition is its ability to conformally coat arbitrarily-shaped substrates.
ALD hence is the ideal deposition technique to grant an extensive freedom in
choosing the shape of the magnetic system. The atomic layer deposition of YIG
enables the fabrication of novel three dimensional magnetic nanostructures,
which in turn can be utilized for experimentally investigating the phenomena
predicted in those structures.",2104.10293v2
2022-11-03,Skyrmion Jellyfish in Driven Chiral Magnets,"Chiral magnets can host topological particles known as skyrmions, which carry
an exactly quantised topological charge $Q=-1$. In the presence of an
oscillating magnetic field ${\bf B}_1(t)$, a single skyrmion embedded in a
ferromagnetic background will start to move with constant velocity ${\bf
v}_{\text{trans}}$. The mechanism behind this motion is similar to the one used
by a jellyfish when it swims through water. We show that the skyrmion's motion
is a universal phenomenon, arising in any magnetic system with translational
modes. By projecting the equation of motion onto the skyrmion's translational
modes and going to quadratic order in ${\bf B}_1(t)$, we obtain an analytical
expression for ${\bf v}_{\text{trans}}$ as a function of the system's linear
response. The linear response and consequently ${\bf v}_{\text{trans}}$ are
influenced by the skyrmion's internal modes and scattering states, as well as
by the ferromagnetic background's Kittel mode. The direction and speed of ${\bf
v}_{\text{trans}}$ can be controlled by changing the polarisation, frequency
and phase of the driving field ${\bf B}_1(t)$. For systems with small Gilbert
damping parameter $\alpha$, we identify two distinct physical mechanisms used
by the skyrmion to move. At low driving frequencies, the skyrmion's motion is
driven by friction, and $v_{\text{trans}}\sim\alpha$, whereas at higher
frequencies above the ferromagnetic gap, the skyrmion moves by magnon emission,
and $v_{\text{trans}}$ becomes independent of $\alpha$.",2211.01714v5
2023-04-05,Threshold current of field-free perpendicular magnetization switching using anomalous spin-orbit torque,"Spin-orbit torque (SOT) is a candidate technique in next generation magnetic
random-access memory (MRAM). Recently, experiments show that some material with
low-symmetric crystalline or magnetic structures can generate anomalous SOT
that has an out-of-plane component, which is crucial in switching perpendicular
magnetization of adjacent ferromagnetic (FM) layer in the field-free condition.
In this work, we analytically derive the threshold current of field-free
perpendicular magnetization switching using the anomalous SOT. And we
numerically calculate the track of the magnetic moment in a FM free layer when
an applied current is smaller and greater than the threshold current. After
that, we study the applied current dependence of the switching time and the
switching energy consumption, which shows the minimum energy consumption
decreases as out-of-plane torque proportion increases. Then we study the
dependences of the threshold current on anisotropy strength, out-of-plane
torque proportion, FM free layer thickness and Gilbert damping constant, and
the threshold current shows negative correlation with the out-of-plane torque
proportion and positive correlation with the other three parameters. Finally,
we demonstrate that when the applied current is smaller than the threshold
current, although it cannot switch the magnetization of FM free layer, it can
still equivalently add an effective exchange bias field H_{bias} on the FM free
layer. The H_{bias} is proportional to the applied current J_{SOT}, which
facilitates the determination of the anomalous SOT efficiency. This work helps
us to design new spintronic devices that favor field-free switching
perpendicular magnetization using the anomalous SOT, and provides a way to
adjust the exchange bias field, which is helpful in controlling FM layer
magnetization depinning.",2304.02248v2
2023-08-07,$\textit{In situ}$ electric-field control of ferromagnetic resonance in the low-loss organic-based ferrimagnet V[TCNE]$_{x\sim 2}$,"We demonstrate indirect electric-field control of ferromagnetic resonance
(FMR) in devices that integrate the low-loss, molecule-based, room-temperature
ferrimagnet vanadium tetracyanoethylene (V[TCNE]$_{x \sim 2}$) mechanically
coupled to PMN-PT piezoelectric transducers. Upon straining the V[TCNE]$_x$
films, the FMR frequency is tuned by more than 6 times the resonant linewidth
with no change in Gilbert damping for samples with $\alpha = 6.5 \times
10^{-5}$. We show this tuning effect is due to a strain-dependent magnetic
anisotropy in the films and find the magnetoelastic coefficient $|\lambda_S|
\sim (1 - 4.4)$ ppm, backed by theoretical predictions from DFT calculations
and magnetoelastic theory. Noting the rapidly expanding application space for
strain-tuned FMR, we define a new metric for magnetostrictive materials,
$\textit{magnetostrictive agility}$, given by the ratio of the magnetoelastic
coefficient to the FMR linewidth. This agility allows for a direct comparison
between magnetostrictive materials in terms of their comparative efficacy for
magnetoelectric applications requiring ultra-low loss magnetic resonance
modulated by strain. With this metric, we show V[TCNE]$_x$ is competitive with
other magnetostrictive materials including YIG and Terfenol-D. This combination
of ultra-narrow linewidth and magnetostriction in a system that can be directly
integrated into functional devices without requiring heterogeneous integration
in a thin-film geometry promises unprecedented functionality for electric-field
tuned microwave devices ranging from low-power, compact filters and circulators
to emerging applications in quantum information science and technology.",2308.03353v1
2023-08-18,Large thermo-spin effects in Heusler alloy based spin-gapless semiconductor thin films,"Recently, Heusler alloys-based spin gapless semiconductors (SGSs) with high
Curie temperature (TC) and sizeable spin polarization have emerged as potential
candidates for tunable spintronic applications. We report comprehensive
investigation of the temperature dependent ANE and intrinsic longitudinal spin
Seebeck effect (LSSE) in CoFeCrGa thin films grown on MgO substrates. Our
findings show the anomalous Nernst coefficient for the MgO/CoFeCrGa (95 nm)
film is $\cong 1.86$ micro V/K at room temperature which is nearly two orders
of magnitude higher than that of the bulk polycrystalline sample of CoFeCrGa (=
0.018 micro V/K) but comparable to that of the magnetic Weyl semimetal Co2MnGa
thin film (2-3 micro V/K). Furthermore, the LSSE coefficient for our
MgO/CoFeCrGa(95nm)/Pt(5nm) heterostructure is $\cong 20.5$ $\mu$V/K/$\Omega$ at
room temperature which is twice larger than that of the half-metallic
ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films ($\cong$ 20.5
$\mu$V/K/$\Omega$). We show that both ANE and LSSE coefficients follow
identical temperature dependences and exhibit a maximum at $\cong$ 225 K which
is understood as the combined effects of inelastic magnon scatterings and
reduced magnon population at low temperatures. Our analyses not only indicate
that the extrinsic skew scattering is the dominating mechanism for ANE in these
films but also provide critical insights into the functional form of the
observed temperature dependent LSSE at low temperatures. Furthermore, by
employing radio frequency transverse susceptibility and broadband ferromagnetic
resonance in combination with the LSSE measurements, we establish a correlation
among the observed LSSE signal, magnetic anisotropy and Gilbert damping of the
CoFeCrGa thin films, which will be beneficial for fabricating tunable and
highly efficient Heusler alloys based spincaloritronic nanodevices.",2308.09843v1
2017-07-28,Measurements of the Temperature and E-Mode Polarization of the CMB from 500 Square Degrees of SPTpol Data,"We present measurements of the $E$-mode polarization angular auto-power
spectrum ($EE$) and temperature-$E$-mode cross-power spectrum ($TE$) of the
cosmic microwave background (CMB) using 150 GHz data from three seasons of
SPTpol observations. We report the power spectra over the spherical harmonic
multipole range $50 < \ell \leq 8000$, and detect nine acoustic peaks in the
$EE$ spectrum with high signal-to-noise ratio. These measurements are the most
sensitive to date of the $EE$ and $TE$ power spectra at $\ell > 1050$ and $\ell
> 1475$, respectively. The observations cover 500 deg$^2$, a fivefold increase
in area compared to previous SPTpol analyses, which increases our sensitivity
to the photon diffusion damping tail of the CMB power spectra enabling tighter
constraints on \LCDM model extensions. After masking all sources with
unpolarized flux $>50$ mJy we place a 95% confidence upper limit on residual
polarized point-source power of $D_\ell = \ell(\ell+1)C_\ell/2\pi
<0.107\,\mu{\rm K}^2$ at $\ell=3000$, suggesting that the $EE$ damping tail
dominates foregrounds to at least $\ell = 4050$ with modest source masking. We
find that the SPTpol dataset is in mild tension with the $\Lambda CDM$ model
($2.1\,\sigma$), and different data splits prefer parameter values that differ
at the $\sim 1\,\sigma$ level. When fitting SPTpol data at $\ell < 1000$ we
find cosmological parameter constraints consistent with those for $Planck$
temperature. Including SPTpol data at $\ell > 1000$ results in a preference for
a higher value of the expansion rate ($H_0 = 71.3 \pm
2.1\,\mbox{km}\,s^{-1}\mbox{Mpc}^{-1}$ ) and a lower value for present-day
density fluctuations ($\sigma_8 = 0.77 \pm 0.02$).",1707.09353v3
2021-02-09,Binet's factorial series and extensions to Laplace transforms,"We investigate a generalization of Binet's factorial series in the parameter
$\alpha$ \[ \mu\left( z\right) =\sum_{m=1}^{\infty}\frac{b_{m}\left(
\alpha\right) }{\prod_{k=0}^{m-1}(z+\alpha+k)}% \] due to Gilbert, for the
Binet function \[ \mu\left( z\right) =\log\Gamma\left( z\right) -\left(
z-\frac{1} {2}\right) \log z+z-\frac{1}{2}\log\left( 2\pi\right) \] After a
review of the Binet function $\mu\left( z\right) $ and Gilbert's investigations
of $\mu\left( z\right) $, several properties of the Binet polynomials
$b_{m}\left( \alpha\right) $ are presented. We compare Gilbert's generalized
factorial series with Stirling's asymptotic expansion and demonstrate by a
numerical example that, with a same number of terms evaluated, the Gilbert
generalized factorial series with an optimized value of $\alpha$ can beat the
best possible accuracy of Stirling's expansion. Finally, we extend Binet's
method to factorial series of Laplace transforms.",2102.04891v7
2000-05-29,Entropy Production in a Persistent Random Walk,"We consider a one-dimensional persisent random walk viewed as a deterministic
process with a form of time reversal symmetry. Particle reservoirs placed at
both ends of the system induce a density current which drives the system out of
equilibrium. The phase space distribution is singular in the stationary state
and has a cumulative form expressed in terms of generalized Takagi functions.
The entropy production rate is computed using the coarse-graining formalism of
Gaspard, Gilbert and Dorfman. In the continuum limit, we show that the value of
the entropy production rate is independent of the coarse-graining and agrees
with the phenomenological entropy production rate of irreversible
thermodynamics.",0005063v1
2012-12-13,A convergent finite element approximation for the quasi-static Maxwell--Landau--Lifshitz--Gilbert equations,"We propose a $\theta$-linear scheme for the numerical solution of the
quasi-static Maxwell-Landau-Lifshitz-Gilbert (MLLG) equations. Despite the
strong nonlinearity of the Landau-Lifshitz-Gilbert equation, the proposed
method results in a linear system at each time step. We prove that as the time
and space steps tend to zero (with no further conditions when
$\theta\in(1/2,1]$), the finite element solutions converge weakly to a weak
solution of the MLLG equations. Numerical results are presented to show the
applicability of the method.",1212.3369v1
2013-09-28,Global Well-Posedness of the Landau-Lifshitz-Gilbert equation for initial data in Morrey space,"We establish the global well-posedness of the Landau-Lifshitz-Gilbert
equation in $\mathbb R^n$ for any initial data ${\bf m}_0\in H^1_*(\mathbb
R^n,\mathbb S^2)$ whose gradient belongs to the Morrey space $M^{2,2}(\mathbb
R^n)$ with small norm $\displaystyle\|\nabla {\bf m}_0\|_{M^{2,2}(\mathbb
R^n)}$. The method is based on priori estimates of a dissipative Schr\""odinger
equation of Ginzburg-Landau types obtained from the Landau-Lifshitz-Gilbert
equation by the moving frame technique.",1309.7426v1
2016-10-26,Iterated Gilbert Mosaics and Poisson Tropical Plane Curves,"We propose an iterated version of the Gilbert model, which results in a
sequence of random mosaics of the plane. We prove that under appropriate
scaling, this sequence of mosaics converges to that obtained by a classical
Poisson line process with explicit cylindrical measure. Our model arises from
considerations on tropical plane curves, which are zeros of random tropical
polynomials in two variables. In particular, the iterated Gilbert model
convergence allows one to derive a scaling limit for Poisson tropical plane
curves. Our work raises a number of open questions at the intersection of
stochastic and tropical geometry.",1610.08533v1
2017-05-29,Strong solvability of regularized stochastic Landau-Lifshitz-Gilbert equation,"We examine a stochastic Landau-Lifshitz-Gilbert equation based on an exchange
energy functional containing second-order derivatives of the unknown field.
Such regularizations are featured in advanced micromagnetic models recently
introduced in connection with nanoscale topological solitons. We show that, in
contrast to the classical stochastic Landau-Lifshitz-Gilbert equation based on
the Dirichlet energy alone, the regularized equation is solvable in the
stochastically strong sense. As a consequence it preserves the topology of the
initial data, almost surely.",1705.10184v1
2021-04-03,Improving the Gilbert-Varshamov Bound by Graph Spectral Method,"We improve Gilbert-Varshamov bound by graph spectral method. Gilbert graph
$G_{q,n,d}$ is a graph with all vectors in $\mathbb{F}_q^n$ as vertices where
two vertices are adjacent if their Hamming distance is less than $d$. In this
paper, we calculate the eigenvalues and eigenvectors of $G_{q,n,d}$ using the
properties of Cayley graph. The improved bound is associated with the minimum
eigenvalue of the graph. Finally we give an algorithm to calculate the bound
and linear codes which satisfy the bound.",2104.01403v3
2006-02-20,Fluctuation theorem applied to the Nosé-Hoover thermostated Lorentz gas,"We present numerical evidence supporting the validity of the Gallavotti-Cohen
Fluctuation Theorem applied to the driven Lorentz gas with Nos\'e-Hoover
thermostating. It is moreover argued that the asymptotic form of the
fluctuation formula is independent of the amplitude of the driving force, in
the limit where it is small.",0602458v1
1997-12-28,Model-independent $\tan β$ bounds in the MSSM,"We demonstrate, through the study of the one-loop effective potential in the
MSSM, the existence of fully model-independent lower and upper theoretical
bounds on $\tan \beta$. We give their general analytic form and illustrate some
of their implications.",9712529v1
2006-12-26,Very Light Gravitino Dark Matter,"We address the question of dark matter in the context of gauge mediated
supersymmetry breaking models. In contrast with mSUGRA scenarios, the messenger
of the susy breaking to the visible sector can play an important role allowing
a relic gravitino in the $\sim {keV}$ to $10 {MeV}$ mass range to account for
the cold dark matter in the Universe.",0612331v1
2004-09-15,Characterizing rigid simplicial actions on trees,"We extend Forester's rigidity theorem so as to give a complete
characterization of rigid group actions on trees (an action is rigid if it is
the only reduced action in its deformation space, in particular it is invariant
under automorphisms preserving the set of elliptic subgroups).",0409245v1
2005-12-14,Efficient Construction of Photonic Quantum Computational Clusters,"We demonstrate a method of creating photonic two-dimensional cluster states
that is considerably more efficient than previously proposed approaches. Our
method uses only local unitaries and type-I fusion operations. The increased
efficiency of our method compared to previously proposed constructions is
obtained by identifying and exploiting local equivalence properties inherent in
cluster states.",0512110v1
2007-10-26,The dark matter as a light gravitino,"We address the question of gravitino dark matter in the context of gauge
mediated supersymmetry breaking models. A special emphasis is put on the role
played by the MSSM singlet messenger in the case of SO(10) grand unification.",0710.5121v1
2008-03-05,Innovative Weak Formulation for The Landau-Lifshitz-Gilbert Equations,"A non-conventional finite element formalism is proposed to solve the dynamic
Landau-Lifshitz-Gilbert micromagnetic equations. Two bidimensional test
problems are treated to estimate the validity and the accuracy of this finite
element approach",0803.0599v1
2008-10-27,The profile of bubbling solutions of a class of fourth order geometric equations on 4-manifolds,"We study a class of fourth order geometric equations defined on a
4-dimensional compact Riemannian manifold which includes the Q-curvature
equation. We obtain sharp estimates on the difference near the blow-up points
between a bubbling sequence of solutions and the standard bubble.",0810.4879v1
2009-03-02,Asymptotic Improvement of the Binary Gilbert-Varshamov Bound on the Code Rate,"We compute the code parameters for binary linear codes obtained by greedy
constructing the parity check matrix. Then we show that these codes improve the
Gilbert-Varshamov (GV) bound on the code size and rate. This result counter
proves the conjecture on the asymptotical exactness of the binary GV bound.",0903.0302v2
2009-11-16,The Independent Chip Model and Risk Aversion,"We consider the Independent Chip Model (ICM) for expected value in poker
tournaments. Our first result is that participating in a fair bet with one
other player will always lower one's expected value under this model. Our
second result is that the expected value for players not participating in a
fair bet between two players always increases. We show that neither result
necessarily holds for a fair bet among three or more players.",0911.3100v1
2011-03-29,Statistical properties of $r$-adic processes and their connections to families of popular fractal curves,"Results concerning the statists of $r$-adic processes and their fractal
properties are reviewed. The connection between singular eigenstates of the
statistical evolution of such processes and popular fractal curves is
emphasized.",1103.5683v1
2011-05-09,Global Solvability of the Cauchy Problem for the Landau-Lifshitz-Gilbert Equation in Higher Dimensions,"We prove existence, uniqueness and asymptotics of global smooth solutions for
the Landau-Lifshitz-Gilbert equation in dimension $n \ge 3$, valid under a
smallness condition of initial gradients in the $L^n$ norm. The argument is
based on the method of moving frames that produces a covariant complex
Ginzburg-Landau equation, and a priori estimates that we obtain by the method
of weighted-in-time norms as introduced by Fujita and Kato.",1105.1597v1
2012-03-28,Fibonacci numbers in phyllotaxis : a simple model,"A simple model is presented which explains the occurrence of high order
Fibonacci number parastichies in asteracae flowers by two distinct steps. First
low order parastichies result from the fact that a new floret, at its
appearance is repelled by two former ones, then, in order to accommodate for
the increase of the radius, parastichies numbers have to evolve and can do it
only by applying the Fibonacci recurrence formula.",1203.6257v1
2014-02-19,Ordered groupoids and the holomorph of an inverse semigroup,"We present a construction for the holomorph of an inverse semigroup, derived
from the cartesian closed structure of the category of ordered groupoids. We
compare the holomorph with the monoid of mappings that preserve the ternary
heap operation on an inverse semigroup: for groups these two constructions
coincide. We present detailed calculations for semilattices of groups and for
the polycyclic monoids.",1402.4592v1
2014-11-01,Functorial Zeta Integrals,"The functional equation for nonarchimedean Rankin-Selberg local Euler factors
was proved by Jacquet, Piatetski-Shapiro, and Shalika in 1983. In this
expository note we translate the original proof into the purely functorial
language of parabolic induction-restriction of Bernstein-Zelevinsky. This new
language gives a clearer presentation of the ideas, and works over arbitrary
fields with characteristic not equal to the residue characteristic.",1411.0148v1
2016-02-17,Dispersion and Scaling Law of Dynamic Hysteresis Based on the Landau-Lifshitz-Gilbert Model,"Hysteresis dispersion under a varying external field Hex is investigated
through numerical simulations based on the Landau-Lifshitz-Gilbert (LLG)
equation, indicating the energy dissipation can be determined by W({\eta}) = A
(f, H0). A linear relation between area of hysteresis and magnitude of external
field is discovered. Evolution of hysteresis is also investigated under
oscillating external field.",1602.05375v1
2016-06-06,Proof of tightness of Varshamov - Gilbert bound for binary codes,"We prove tightness of right logarithmic asymptotic of Varshamov- Gilbert
bound for linear binary codes We find general asymptotic coding bound for
linear codes",1606.01592v5
2017-02-21,Cohomology and extensions of ordered groupoids,"We adapt and generalise results of Loganathan on the cohomology of inverse
semigroups to the cohomology of ordered groupoids. We then derive a five-term
exact sequence in cohomology from an extension of ordered groupoids, and show
that this sequence leads to a classification of extensions by a second
cohomology group. Our methods use structural ideas in cohomology as far as
possible, rather than computation with cocycles.",1702.06333v1
2017-05-11,Two Gilbert-Varshamov Type Existential Bounds for Asymmetric Quantum Error-Correcting Codes,"In this note we report two versions of Gilbert-Varshamov type existential
bounds for asymmetric quantum error-correcting codes.",1705.04087v2
2017-09-21,Self-Dual Codes better than the Gilbert--Varshamov bound,"We show that every self-orthogonal code over $\mathbb F_q$ of length $n$ can
be extended to a self-dual code, if there exists self-dual codes of length $n$.
Using a family of Galois towers of algebraic function fields we show that over
any nonprime field $\mathbb F_q$, with $q\geq 64$, except possibly $q=125$,
there are self-dual codes better than the asymptotic Gilbert--Varshamov bound.",1709.07221v1
2018-10-12,A convex approach to the Gilbert-Steiner problem,"We describe a convex relaxation for the Gilbert-Steiner problem both in $R^d$
and on manifolds, extending the framework proposed in [9], and we discuss its
sharpness by means of calibration type arguments. The minimization of the
resulting problem is then tackled numerically and we present results for an
extensive set of examples. In particular we are able to address the Steiner
tree problem on surfaces.",1810.05417v1
2018-11-09,Finslerian metrics locally conformally $R$-Einstein,"Let $R$ be the $hh$-curvature associated with the Chern connection or the
Cartan connection. Adopting the pulled-back tangent bundle approach to the
Finslerian Geometry, an intrinsic characterization of $R$-Einstein metrics is
given. Finslerian metrics which are locally conformally $R$-Einstein are
classified.",1811.04077v3
2019-02-05,Harmonic maps with prescribed singularities and applications in general relativity,"This paper presents a general existence and uniqueness result for harmonic
maps with prescribed singularities into non-positively curved targets, and
surveys a number of applications to general relativity. It is based on a talk
delivered by the author at The 11th Mathematical Society of Japan Seasonal
Institute, The Role of Metrics in the Theory of Partial Differential Equations.",1902.01576v2
2020-03-13,3D Stochastic Landau-Lifshitz-Gilbert Equations coupled with Maxwell's Equations with full energy,"We consider 3D stochastic Landau-Lifshitz-Gilbert equations coupled with the
Maxwell equations with the full energy. We have proved the existence and some
further regularities of the weak solution.",2003.06091v4
2021-12-09,Induced Semi-Riemannian structures on null submanifolds,"In this paper, we induce a semi-Riemannian metric on the $r$-null
submanifold. We establish the links between the null geometry and basics
invariants of the associated semi-Riemannian geometry on $r$-null submanifold
and semi-Riemannian constructed from a semi-Riemannian ambient.",2112.07348v1
2022-04-12,How to design a network architecture using capacity planning,"Building a network architecture must answer to organization needs, but also
to two major elements which are the need for dependability and performance. By
performance, we must understand the ability to meet an immediate need and the
ability to scale without reducing the performance of the whole as new elements
are added to the network infrastructure. This last point is covered by Capacity
Planning domain.",2204.05916v2
2022-07-31,Moduli of Representations of Skewed-Gentle Algebras,"We prove irreducible components of moduli spaces of semistable
representations of skewed-gentle algebras, and more generally, clannish
algebras, are isomorphic to products of projective spaces. This is achieved by
showing irreducible components of varieties of representations of clannish
algebras can be viewed as irreducible components of skewed-gentle algebras,
which we show are always normal. The main theorem generalizes an analogous
result for moduli of representations of special biserial algebras proven by
Carroll-Chindris-Kinser-Weyman.",2208.00336v1
2022-08-01,iOCR: Informed Optical Character Recognition for Election Ballot Tallies,"The purpose of this study is to explore the performance of Informed OCR or
iOCR. iOCR was developed with a spell correction algorithm to fix errors
introduced by conventional OCR for vote tabulation. The results found that the
iOCR system outperforms conventional OCR techniques.",2208.00865v1
2023-03-13,Adaptive mesh refinement for the Landau-Lifshitz-Gilbert equation,"We propose a new adaptive algorithm for the approximation of the
Landau-Lifshitz-Gilbert equation via a higher-order tangent plane scheme. We
show that the adaptive approximation satisfies an energy inequality and
demonstrate numerically, that the adaptive algorithm outperforms uniform
approaches.",2303.07463v1
2023-05-08,Evaluation of the Gilbert-Varshamov Bound using Multivariate Analytic Combinatorics,"Analytic combinatorics in several variables refers to a suite of tools that
provide sharp asymptotic estimates for certain combinatorial quantities. In
this paper, we apply these tools to determine the Gilbert-Varshamov (GV) bound
for the sticky insertion and the constrained-synthesis channel.",2305.04439v1
2023-12-11,Matrix Formulae and Skein Relations for Quasi-cluster Algebras,"In this paper, we give matrix formulae for non-orientable surfaces that
provide the Laurent expansion for quasi-cluster variables, generalizing the
orientable surface matrix formulae by Musiker-Williams. We additionally use our
matrix formulas to prove the skein relations for the elements in the
quasi-cluster algebra associated to curves on the non-orientable surface.",2312.06148v1
2009-08-12,Linear Fractionally Damped Oscillator,"In this paper the linearly damped oscillator equation is considered with the
damping term generalized to a Caputo fractional derivative. The order of the
derivative being considered is 0 less than or equal to nu which is less than or
equal to 1 . At the lower end, nu = 0, the equation represents an un-damped
oscillator and at the upper end, nu = 1, the ordinary linearly damped
oscillator equation is recovered. A solution is found analytically and a
comparison with the ordinary linearly damped oscillator is made. It is found
that there are nine distinct cases as opposed to the usual three for the
ordinary equation (damped, over-damped, and critically damped). For three of
these cases it is shown that the frequency of oscillation actually increases
with increasing damping order before eventually falling to the limiting value
given by the ordinary damped oscillator equation. For the other six cases the
behavior is as expected, the frequency of oscillation decreases with increasing
order of the derivative (damping term).",0908.1683v1
2004-05-06,On a theorem of Kac and Gilbert,"We prove a general operator theoretic result that asserts that many
multiplicity two selfadjoint operators have simple singular spectrum.",0405110v1
2011-01-05,Beating the Gilbert-Varshamov Bound for Online Channels,"In the online channel coding model, a sender wishes to communicate a message
to a receiver by transmitting a codeword x =(x_1,...,x_n) in {0,1}^n bit by bit
via a channel limited to at most pn corruptions. The channel is online in the
sense that at the ith step the channel decides whether to flip the ith bit or
not and its decision is based only on the bits transmitted so far, i.e.,
(x_1,...,x_i). This is in contrast to the classical adversarial channel in
which the corruption is chosen by a channel that has full knowledge on the sent
codeword x. The best known lower bound on the capacity of both the online
channel and the classical adversarial channel is the well-known
Gilbert-Varshamov bound. In this paper we prove a lower bound on the capacity
of the online channel which beats the Gilbert-Varshamov bound for any positive
p such that H(2p) < 0.5 (where H is the binary entropy function). To do so, we
prove that for any such p, a code chosen at random combined with the nearest
neighbor decoder achieves with high probability a rate strictly higher than the
Gilbert-Varshamov bound (for the online channel).",1101.1045v1
2014-11-25,From heavy-tailed Boolean models to scale-free Gilbert graphs,"Define the scale-free Gilbert graph based on a Boolean model with
heavy-tailed radius distribution on the $d$-dimensional torus by connecting two
centers of balls by an edge if at least one of the balls contains the center of
the other. We investigate two asymptotic properties of this graph as the size
of the torus tends to infinity. First, we determine the tail index associated
with the asymptotic distribution of the sum of all power-weighted incoming and
outgoing edge lengths at a randomly chosen vertex. Second, we study the
behavior of chemical distances on scale-free Gilbert graphs and show the
existence of different regimes depending on the tail index of the radius
distribution. Despite some similarities to long-range percolation and
ultra-small scale-free geometric networks, scale-free Gilbert graphs are
actually more closely related to fractal percolation and this connection gives
rise to different scaling limits. We also propose a modification of the graph,
where the total number of edges can be reduced substantially at the cost of
introducing a logarithmic factor in the chemical distances.",1411.6824v1
2016-03-16,Recent Results from SPLASH: Chemical Abundances and Kinematics of Andromeda's Stellar Halo,"Large scale surveys of Andromeda's resolved stellar populations have
revolutionized our view of this galaxy over the past decade. The combination of
large-scale, contiguous photometric surveys and pointed spectroscopic surveys
has been particularly powerful for discovering substructure and disentangling
the structural components of Andromeda. The SPLASH (Spectroscopic and
Photometric Landscape of Andromeda's Stellar Halo) survey consists of broad-
and narrow-band imaging and spectroscopy of red giant branch stars in lines of
sight ranging in distance from 2 kpc to more than 200 kpc from Andromeda's
center. The SPLASH data reveal a power-law surface brightness profile extending
to at least two-thirds of Andromeda's virial radius (Gilbert et al. 2012), a
metallicity gradient extending to at least 100 kpc from Andromeda's center
(Gilbert et al. 2014), and evidence of a significant population of heated disk
stars in Andromeda's inner halo (Dorman et al. 2013). We are also using the
velocity distribution of halo stars to measure the tangential motion of
Andromeda (Beaton et al., in prep).",1603.05160v1
2017-05-09,Gilbert's disc model with geostatistical marking,"We study a variant of Gilbert's disc model, in which discs are positioned at
the points of a Poisson process in $\mathbb{R}^2$ with radii determined by an
underlying stationary and ergodic random field
$\varphi:\mathbb{R}^2\to[0,\infty)$, independent of the Poisson process. When
the random field is independent of the point process one often talks about
'geostatistical marking'. We examine how typical properties of interest in
stochastic geometry and percolation theory, such as coverage probabilities and
the existence of long-range connections, differ between Gilbert's model with
radii given by some random field and Gilbert's model with radii assigned
independently, but with the same marginal distribution. Among our main
observations we find that complete coverage of $\mathbb{R}^2$ does not
necessarily happen simultaneously, and that the spatial dependence induced by
the random field may both increase as well as decrease the critical threshold
for percolation.",1705.03337v2
2019-01-30,Is the mailing Gilbert-Steiner problem convex?,"A convexification of the mailing version of the finite Gilbert problem for
optimal networks is introduced. It is ia convex functional on the set of
probability measures subject to the Wasserstein $p-$ metric. The minimizer of
this convex functional is a measure supported in a graph. If this graph is a
tree (i.e contains no cycles) then this tree is also a minimum of the
corresponding mailing Gilbert problem. A numerical algorithm for the
implementation of the convexified Gilbert-mailing problem is also suggested,
based on entropic regularization.",1901.10924v4
2019-11-06,Phase transitions for chase-escape models on Gilbert graphs,"We present results on phase transitions of local and global survival in a
two-species model on Gilbert graphs. At initial time there is an infection at
the origin that propagates on the Gilbert graph according to a continuous-time
nearest-neighbor interacting particle system. The Gilbert graph consists of
susceptible nodes and nodes of a second type, which we call white knights. The
infection can spread on susceptible nodes without restriction. If the infection
reaches a white knight, this white knight starts to spread on the set of
infected nodes according to the same mechanism, with a potentially different
rate, giving rise to a competition of chase and escape. We show
well-definedness of the model, isolate regimes of global survival and
extinction of the infection and present estimates on local survival. The proofs
rest on comparisons to the process on trees, percolation arguments and
finite-degree approximations of the underlying random graphs.",1911.02622v2
2019-12-13,Distance between Bound Entangled States from Unextendible Product Bases and Separable States,"We discuss the use of the Gilbert algorithm to tailor entanglement witnesses
for unextendibleproduct basis bound entangled states (UPB BE states). The
method relies on the fact that an optimalentanglement witness is given by a
plane perpendicular to a line between the reference state, entanglementof which
is to be witnessed, and its closest separable state (CSS). The Gilbert
algorithm finds anapproximation of CSS. In this article, we investigate if this
approximation can be good enough toyield a valid entanglement witness. We
compare witnesses found with Gilbert algorithm and those givenby
Bandyopadhyay-Ghosh-Roychowdhury (BGR) construction. This comparison allows us
to learnabout the amount of entanglement and we find a relationship between it
and a feature of the constructionof UPB BE states, namely the size of their
central tile. We show that in most studied cases, witnessesfound with the
Gilbert algorithm in this work are more optimal than ones obtained by
Bandyopadhyay,Ghosh, and Roychowdhury. This result implies the increased
tolerance to experimental imperfections ina realization of the state.",1912.06569v2
2020-10-16,Genome organization: experiments and modelling,"This is an introduction to the special issue Genome organization: experiments
and simulations, published in Chromosome Research, volume 25, issue 1 (2017).",2010.08464v1
2023-10-17,Sparse grid approximation of stochastic parabolic PDEs: The Landau--Lifshitz--Gilbert equation,"We show convergence rates for a sparse grid approximation of the distribution
of solutions of the stochastic Landau-Lifshitz-Gilbert equation. Beyond being a
frequently studied equation in engineering and physics, the stochastic
Landau-Lifshitz-Gilbert equation poses many interesting challenges that do not
appear simultaneously in previous works on uncertainty quantification: The
equation is strongly non-linear, time-dependent, and has a non-convex side
constraint. Moreover, the parametrization of the stochastic noise features
countably many unbounded parameters and low regularity compared to other
elliptic and parabolic problems studied in uncertainty quantification. We use a
novel technique to establish uniform holomorphic regularity of the
parameter-to-solution map based on a Gronwall-type estimate and the implicit
function theorem. This method is very general and based on a set of abstract
assumptions. Thus, it can be applied beyond the Landau-Lifshitz-Gilbert
equation as well. We demonstrate numerically the feasibility of approximating
with sparse grid and show a clear advantage of a multi-level sparse grid
scheme.",2310.11225v2
2024-04-04,Resolving Gilbert's Conjecture: Dimensional Dependencies in Hardy Spaces Valued in Clifford Modules,"This article provides a thorough investigation into Gilbert's Conjecture,
pertaining to Hardy spaces in the upper half-space valued in Clifford modules.
We explore the conjecture proposed by Gilbert in 1991, which seeks to extend
the classical principle of representing real $L^p$ functions on the real line
as boundary values of Hardy holomorphic functions to higher-dimensional
Euclidean spaces valued in any Clifford module. We present a complete
resolution to this conjecture, demonstrating that its validity is contingent
upon the dimension $n$, specifically holding true when \(n \not\equiv 6, 7 \mod
8\) and failing otherwise. The pivotal discovery that Gilbert's conjecture can
be reformulated as a set of algebraic conditions is underscored in this work.
To navigate these conditions, we employ a novel strategy that leverages the
octonions, revealing their instrumental role in addressing issues related to
Clifford modules and spinors. This innovative approach not only provides
explicit realization through the generalization of the Hilbert transform to the
Riesz transform but also establishes a significant advancement in the
understanding of Hardy spaces within higher dimensions.",2404.03478v1
1998-02-23,Shell Effects on Rotational Damping in Superdeformed Nuclei,"Damping of rotational motion in superdeformed Hg and Dy-region nuclei is
studied by means of cranked shell model diagonalization. It is shown that a
shell oscillation in single-particle alignments affects significantly
properties of rotational damping. Onset properties of damping and damping width
for Hg are quite different from those for Dy-region superdeformed nuclei.",9802065v1
2003-08-29,Influence of radiative damping on the optical-frequency susceptibility,"Motivated by recent discussions concerning the manner in which damping
appears in the electric polarizability, we show that (a) there is a dependence
of the nonresonant contribution on the damping and that (b) the damping enters
according to the ""opposite sign prescription."" We also discuss the related
question of how the damping rates in the polarizability are related to
energy-level decay rates.",0309001v1
2024-03-19,Weakly elliptic damping gives sharp decay,"We prove that weakly elliptic damping gives sharp energy decay for the
abstract damped wave semigroup, where the damping is not in the functional
calculus. In this case, there is no overdamping. We show applications in
linearised water waves and Kelvin--Voigt damping.",2403.13067v1
2015-05-15,Reliable Damping of Free Surface Waves in Numerical Simulations,"This paper generalizes existing approaches for free-surface wave damping via
momentum sinks for flow simulations based on the Navier-Stokes equations. It is
shown in 2D flow simulations that, to obtain reliable wave damping, the
coefficients in the damping functions must be adjusted to the wave parameters.
A scaling law for selecting these damping coefficients is presented, which
enables similarity of the damping in model- and full-scale. The influence of
the thickness of the damping layer, the wave steepness, the mesh fineness and
the choice of the damping coefficients are examined. An efficient approach for
estimating the optimal damping setup is presented. Results of 3D ship
resistance computations show that the scaling laws apply to such simulations as
well, so the damping coefficients should be adjusted for every simulation to
ensure convergence of the solution in both model and full scale. Finally,
practical recommendations for the setup of reliable damping in flow simulations
with regular and irregular free surface waves are given.",1505.04087v2
2019-02-25,Resonant absorption as a damping mechanism for the transverse oscillations of the coronal loops observed by SDO/AIA,"Solar coronal loops represent the variety of fast, intermediate, and slow
normal mode oscillations. In this study, the transverse oscillations of the
loops with a few-minutes period and also with damping caused by the resonant
absorption were analyzed using extreme ultraviolet (EUV) images of the Sun. We
employed the 171 $\AA$ data recorded by Solar Dynamic Observatory
(SDO)/Atmospheric Imaging Assembly (AIA) to analyze the parameters of coronal
loop oscillations such as period, damping time, loop length, and loop width.
For the loop observed on 11 October 2013, the period and the damping of this
loop are obtained to be 19 and 70 minutes, respectively. The damping quality,
the ratio of the damping time to the period, is computed about 3.6. The period
and damping time for the extracted loop recorded on 22 January 2013 are about
81 and 6.79 minutes, respectively. The damping quality is also computed as 12.
It can be concluded that the damping of the transverse oscillations of the
loops is in the strong damping regime, so resonant absorption would be the main
reason for the damping.",1902.09649v1
2013-05-21,Characterization and Synthesis of Rayleigh Damped Elastodynamic Networks,"We consider damped elastodynamic networks where the damping matrix is assumed
to be a non-negative linear combination of the stiffness and mass matrices
(also known as Rayleigh or proportional damping). We give here a
characterization of the frequency response of such networks. We also answer the
synthesis question for such networks, i.e., how to construct a Rayleigh damped
elastodynamic network with a given frequency response. Our analysis shows that
not all damped elastodynamic networks can be realized when the proportionality
constants between the damping matrix and the mass and stiffness matrices are
fixed.",1305.4961v1
2016-08-08,Damping Functions correct over-dissipation of the Smagorinsky Model,"This paper studies the time-averaged energy dissipation rate $\langle
\varepsilon_{SMD} (u)\rangle$ for the combination of the Smagorinsky model and
damping function. The Smagorinsky model is well known to over-damp. One common
correction is to include damping functions that reduce the effects of model
viscosity near walls. Mathematical analysis is given here that allows
evaluation of $\langle \varepsilon_{SMD} (u)\rangle $ for any damping function.
Moreover, the analysis motivates a modified van Driest damping. It is proven
that the combination of the Smagorinsky with this modified damping function
does not over dissipate and is also consistent with Kolmogorov phenomenology.",1608.02655v2
2012-01-27,Full and Half Gilbert Tessellations with Rectangular Cells,"We investigate the ray-length distributions for two different rectangular
versions of Gilbert's tessellation. In the full rectangular version, lines
extend either horizontally (with east- and west-growing rays) or vertically
(north- and south-growing rays) from seed points which form a Poisson point
process, each ray stopping when another ray is met. In the half rectangular
version, east and south growing rays do not interact with west and north rays.
For the half rectangular tessellation we compute analytically, via recursion, a
series expansion for the ray-length distribution, whilst for the full
rectangular version we develop an accurate simulation technique, based in part
on the stopping-set theory of Zuyev, to accomplish the same. We demonstrate the
remarkable fact that plots of the two distributions appear to be identical when
the intensity of seeds in the half model is twice that in the full model. Our
paper explores this coincidence mindful of the fact that, for one model, our
results are from a simulation (with inherent sampling error). We go on to
develop further analytic theory for the half-Gilbert model using stopping-set
ideas once again, with some novel features. Using our theory, we obtain exact
expressions for the first and second moment of ray length in the half-Gilbert
model. For all practical purposes, these results can be applied to the
full-Gilbert model as much better approximations than those provided by
Mackissack and Miles.",1201.5780v1
2021-06-08,On numerical aspects of parameter identification for the Landau-Lifshitz-Gilbert equation in Magnetic Particle Imaging,"The Landau-Lifshitz-Gilbert equation yields a mathematical model to describe
the evolution of the magnetization of a magnetic material, particularly in
response to an external applied magnetic field. It allows one to take into
account various physical effects, such as the exchange within the magnetic
material itself. In particular, the Landau-Lifshitz-Gilbert equation encodes
relaxation effects, i.e., it describes the time-delayed alignment of the
magnetization field with an external magnetic field. These relaxation effects
are an important aspect in magnetic particle imaging, particularly in the
calibration process. In this article, we address the data-driven modeling of
the system function in magnetic particle imaging, where the
Landau-Lifshitz-Gilbert equation serves as the basic tool to include relaxation
effects in the model. We formulate the respective parameter identification
problem both in the all-at-once and the reduced setting, present reconstruction
algorithms that yield a regularized solution and discuss numerical experiments.
Apart from that, we propose a practical numerical solver to the nonlinear
Landau-Lifshitz-Gilbert equation, not via the classical finite element method,
but through solving only linear PDEs in an inverse problem framework.",2106.07625v1
2000-09-11,Numerical Studies on Locally Damped Structures,"In the JLC/NLC X-band linear collider, it is essential to reduce the
long-range dipole wakefields in the accelerator structure to prevent beam break
up (BBU) and emittance degradation. The two methods of reducing the long-range
wakefields are detuning and damping. Detuning reduces the wakefields rapidly as
the dipole modes de-cohere but, with a finite number of modes, the wakefield
will grow again as the modes re-cohere. In contrast, damping suppresses the
wakefields at a longer distance. There are two principal damping schemes:
synchronous damping using HOM manifolds such as that used in the RDDS1
structure and local damping similar to that used in the CLIC structure. In a
locally damped scheme, one can obtain almost any Q value, however, the damping
can have significant effects on the accelerating mode. In this paper, we
present a medium local-damping scheme where the wakefields are controlled to
meet the BBU requirement while minimizing the degradations of the fundamental
rf parameters. We will address the load design and pulse heating issues
associated with the medium damping scheme.",0009039v1
2015-03-13,A one-step optimal energy decay formula for indirectly nonlinearly damped hyperbolic systems coupled by velocities,"In this paper, we consider the energy decay of a damped hyperbolic system of
wave-wave type which is coupled through the velocities. We are interested in
the asymptotic properties of the solutions of this system in the case of
indirect nonlinear damping, i.e. when only one equation is directly damped by a
nonlinear damping. We prove that the total energy of the whole system decays as
fast as the damped single equation. Moreover, we give a one-step general
explicit decay formula for arbitrary nonlinearity. Our results shows that the
damping properties are fully transferred from the damped equation to the
undamped one by the coupling in velocities, different from the case of
couplings through displacements as shown in \cite{AB01, ACK01, AB02, AL12} for
the linear damping case, and in \cite{AB07} for the nonlinear damping case. The
proofs of our results are based on multiplier techniques, weighted nonlinear
integral inequalities and the optimal-weight convexity method of \cite{AB05,
AB10}.",1503.04126v1
2015-08-21,Radiative damping in wave guide based FMR measured via analysis of perpendicular standing spin waves in sputtered Permalloy films,"The damping $\alpha$ of the spinwave resonances in 75 nm, 120 nm, and 200nm
-thick Permalloy films is measured via vector-network-analyzer
ferromagnetic-resonance (VNA-FMR) in the out-of-plane geometry. Inductive
coupling between the sample and the waveguide leads to an additional radiative
damping term. The radiative contribution to the over-all damping is determined
by measuring perpendicular standing spin waves (PSSWs) in the Permalloy films,
and the results are compared to a simple analytical model. The damping of the
PSSWs can be fully explained by three contributions to the damping: The
intrinsic damping, the eddy-current damping, and the radiative damping. No
other contributions were observed. Furthermore, a method to determine the
radiative damping in FMR measurements with a single resonance is suggested.",1508.05265v1
2022-09-28,Tunable nonlinear damping in parametric regime,"Nonlinear damping plays a significant role in several area of physics and it
is becoming increasingly important to understand its underlying mechanism.
However, microscopic origin of nonlinear damping is still a debatable topic.
Here, we probe and report nonlinear damping in a highly tunable MoS2 nano
mechanical drum resonator using electrical homodyne actuation and detection
technique. In our experiment, we achieve 2:1 internal resonance by tuning
resonance frequency and observe enhanced non-linear damping. We probe the
effect of non-linear damping by characterizing parametric gain. Geometry and
tunability of the device allow us to reduce the effect of other prominent
Duffing non-linearity to probe the non-linear damping effectively. The enhanced
non-linear damping in the vicinity of internal resonance is also observed in
direct drive, supporting possible origin of non-linear damping. Our experiment
demonstrates, a highly tunable 2D material based nanoresonator offers an
excellent platform to study the nonlinear physics and exploit nonlinear damping
in parametric regime.",2209.14120v1
2005-11-07,The Effects of Alfven Waves and Radiation Pressure in Dusty Winds of Late-Type Stars. II. Dust-Cyclotron Damping,"There are in the literature several theories to explain the mass loss in
stellar winds. In particular, for late-type stars, some authors have proposed a
wind model driven by an outward-directed flux of damped Alfven waves. The winds
of these stars present great amounts of dust particles that, if charged, can
give rise to new wave modes or modify the pre-existing ones. In this work, we
study how the dust can affect the propagation of Alfven waves in these winds
taking into account a specific damping mechanism, dust-cyclotron damping. This
damping affects the Alfven wave propagation near the dust-cyclotron frequency.
Hence, if we assume a dust size distribution, the damping occurs over a broad
band of wave frequencies. In this work, we present a model of Alfven
wave-driven winds using the dust-cyclotron damping mechanism. On the basis of
coronal holes in the Sun, which present a superradial expansion, our model also
assumes a diverging geometry for the magnetic field. Thus, the mass, momentum,
and energy equations are obtained and then solved in a self-consistent
approach. Our results of wind velocity and temperature profiles for a typical
K5 supergiant star shows compatibility with observations. We also show that,
considering the presence of charged dust particles, the wave flux is less
damped due to the dust-cyclotron damping than it would be if we consider some
other damping mechanisms studied in the literature, such as nonlinear damping,
resonant surface damping, and turbulent damping.",0511192v2
2013-09-11,Initial versus tangent stiffness-based Rayleigh damping in inelastic time history seismic analyses,"In the inelastic time history analyses of structures in seismic motion, part
of the seismic energy that is imparted to the structure is absorbed by the
inelastic structural model, and Rayleigh damping is commonly used in practice
as an additional energy dissipation source. It has been acknowledged that
Rayleigh damping models lack physical consistency and that, in turn, it must be
carefully used to avoid encountering unintended consequences as the appearance
of artificial damping. There are concerns raised by the mass proportional part
of Rayleigh damping, but they are not considered in this paper. As far as the
stiffness proportional part of Rayleigh damping is concerned, either the
initial structural stiffness or the updated tangent stiffness can be used. The
objective of this paper is to provide a comprehensive comparison of these two
types of Rayleigh damping models so that a practitioner (i) can objectively
choose the type of Rayleigh damping model that best fits her/his needs and (ii)
is provided with useful analytical tools to design Rayleigh damping model with
good control on the damping ratios throughout inelastic analysis. To that end,
a review of the literature dedicated to Rayleigh damping within these last two
decades is first presented; then, practical tools to control the modal damping
ratios throughout the time history analysis are developed; a simple example is
finally used to illustrate the differences resulting from the use of either
initial or tangent stiffness-based Rayleigh damping model.",1309.2741v1
2017-07-14,Damping of gravitational waves by matter,"We develop a unified description, via the Boltzmann equation, of damping of
gravitational waves by matter, incorporating collisions. We identify two
physically distinct damping mechanisms -- collisional and Landau damping. We
first consider damping in flat spacetime, and then generalize the results to
allow for cosmological expansion. In the first regime, maximal collisional
damping of a gravitational wave, independent of the details of the collisions
in the matter is, as we show, significant only when its wavelength is
comparable to the size of the horizon. Thus damping by intergalactic or
interstellar matter for all but primordial gravitational radiation can be
neglected. Although collisions in matter lead to a shear viscosity, they also
act to erase anisotropic stresses, thus suppressing the damping of
gravitational waves. Damping of primordial gravitational waves remains
possible. We generalize Weinberg's calculation of gravitational wave damping,
now including collisions and particles of finite mass, and interpret the
collisionless limit in terms of Landau damping. While Landau damping of
gravitational waves cannot occur in flat spacetime, the expansion of the
universe allows such damping by spreading the frequency of a gravitational wave
of given wavevector.",1707.05192v2
2024-03-13,The q-ary Gilbert-Varshamov bound can be improved for all but finitely many positive integers q,"For any positive integer $q\geq 2$ and any real number $\delta\in(0,1)$, let
$\alpha_q(n,\delta n)$ denote the maximum size of a subset of $\mathbb{Z}_q^n$
with minimum Hamming distance at least $\delta n$, where
$\mathbb{Z}_q=\{0,1,\dotsc,q-1\}$ and $n\in\mathbb{N}$. The asymptotic rate
function is defined by $ R_q(\delta) =
\limsup_{n\rightarrow\infty}\frac{1}{n}\log_q\alpha_q(n,\delta n).$ The famous
$q$-ary asymptotic Gilbert-Varshamov bound, obtained in the 1950s, states that
\[ R_q(\delta) \geq 1 -
\delta\log_q(q-1)-\delta\log_q\frac{1}{\delta}-(1-\delta)\log_q\frac{1}{1-\delta}
\stackrel{\mathrm{def}}{=}R_\mathrm{GV}(\delta,q) \] for all positive integers
$q\geq 2$ and $0<\delta<1-q^{-1}$. In the case that $q$ is an even power of a
prime with $q\geq 49$, the $q$-ary Gilbert-Varshamov bound was firstly improved
by using algebraic geometry codes in the works of Tsfasman, Vladut, and Zink
and of Ihara in the 1980s. These algebraic geometry codes have been modified to
improve the $q$-ary Gilbert-Varshamov bound $R_\mathrm{GV}(\delta,q)$ at a
specific tangent point $\delta=\delta_0\in (0,1)$ of the curve
$R_\mathrm{GV}(\delta,q)$ for each given integer $q\geq 46$. However, the
$q$-ary Gilbert-Varshamov bound $R_\mathrm{GV}(\delta,q)$ at $\delta=1/2$,
i.e., $R_\mathrm{GV}(1/2,q)$, remains the largest known lower bound of
$R_q(1/2)$ for infinitely many positive integers $q$ which is a generic prime
and which is a generic non-prime-power integer. In this paper, by using codes
from geometry of numbers introduced by Lenstra in the 1980s, we prove that the
$q$-ary Gilbert-Varshamov bound $R_\mathrm{GV}(\delta,q)$ with $\delta\in(0,1)$
can be improved for all but finitely many positive integers $q$. It is shown
that the growth defined by $\eta(\delta)=
\liminf_{q\rightarrow\infty}\frac{1}{\log q}\log[1-\delta-R_q(\delta)]^{-1}$
for every $\delta\in(0,1)$ has actually a nontrivial lower bound.",2403.08727v2
2002-06-27,Initial-amplitude dependence in weakly damped oscillators,"A pedagogically instructive experimental procedure is suggested for
distinguishing between different damping terms in a weakly damped oscillator,
which highclights the connection between non-linear damping and
initial-amplitude dependence. The most common damping terms such as contact
friction, air resistance, viscous drag, and electromagnetic damping have
velocity dependences of the form constant, v, or v^2. The corresponding energy
dependences of the form \sqrt{E}, E, or E\sqrt{E} in the energy loss equation
give rise to characteristic dependence of the amplitude decay slope on the
initial amplitude.",0206086v1
2006-05-22,The entanglement of damped noon-state and its performance in phase measurement,"The state evolution of the initial optical \textit{noon} state is
investigated. The residue entanglement of the state is calculated after it is
damped by amplitude and phase damping. The relative entropy of entanglement of
the damped state is exactly obtained. The performance of direct application of
the damped \textit{noon} state is compared with that of firstly distilling the
docoherence damped state then applying it in measurement.",0605184v1
2007-10-04,Channel-Adapted Quantum Error Correction for the Amplitude Damping Channel,"We consider error correction procedures designed specifically for the
amplitude damping channel. We analyze amplitude damping errors in the
stabilizer formalism. This analysis allows a generalization of the [4,1]
`approximate' amplitude damping code of quant-ph/9704002. We present this
generalization as a class of [2(M+1),M] codes and present quantum circuits for
encoding and recovery operations. We also present a [7,3] amplitude damping
code based on the classical Hamming code. All of these are stabilizer codes
whose encoding and recovery operations can be completely described with
Clifford group operations. Finally, we describe optimization options in which
recovery operations may be further adapted according to the damping probability
gamma.",0710.1052v1
2010-03-24,Dynamical shift condition for unequal mass black hole binaries,"Certain numerical frameworks used for the evolution of binary black holes
make use of a gamma driver, which includes a damping factor. Such simulations
typically use a constant value for damping. However, it has been found that
very specific values of the damping factor are needed for the calculation of
unequal mass binaries. We examine carefully the role this damping plays, and
provide two explicit, non-constant forms for the damping to be used with
mass-ratios further from one. Our analysis of the resultant waveforms compares
well against the constant damping case.",1003.4681v1
2011-11-30,Local phase damping of single qubits sets an upper bound on the phase damping rate of entangled states,"I derive an inequality in which the phase damping rates of single qubits set
an upper bound for the phase damping rate of entangled states of many qubits.
The derivation is based on two assumptions: first, that the phase damping can
be described by a dissipator in Lindblad form and, second, that the phase
damping preserves the population of qubit states in a given basis.",1111.7152v2
2012-05-11,Quantum dynamics of the damped harmonic oscillator,"The quantum theory of the damped harmonic oscillator has been a subject of
continual investigation since the 1930s. The obstacle to quantization created
by the dissipation of energy is usually dealt with by including a discrete set
of additional harmonic oscillators as a reservoir. But a discrete reservoir
cannot directly yield dynamics such as Ohmic damping (proportional to velocity)
of the oscillator of interest. By using a continuum of oscillators as a
reservoir, we canonically quantize the harmonic oscillator with Ohmic damping
and also with general damping behaviour. The dynamics of a damped oscillator is
determined by an arbitrary effective susceptibility that obeys Kramers-Kronig
relations. This approach offers an alternative description of nano-mechanical
oscillators and opto-mechanical systems.",1205.2545v1
2014-02-28,Escape rate for the power-law distribution in low-to-intermediate damping,"Escape rate in the low-to-intermediate damping connecting the low damping
with the intermediate damping is established for the power-law distribution on
the basis of flux over population theory. We extend the escape rate in the low
damping to the low-to-intermediate damping, and get an expression for the
power-law distribution. Then we apply the escape rate for the power-law
distribution to the experimental study of the excited-state isomerization, and
show a good agreement with the experimental value. The extra current and the
improvement of the absorbing boundary condition are discussed.",1402.7194v2
2015-03-21,On damping created by heterogeneous yielding in the numerical analysis of nonlinear reinforced concrete frame elements,"In the dynamic analysis of structural engineering systems, it is common
practice to introduce damping models to reproduce experimentally observed
features. These models, for instance Rayleigh damping, account for the damping
sources in the system altogether and often lack physical basis. We report on an
alternative path for reproducing damping coming from material nonlinear
response through the consideration of the heterogeneous character of material
mechanical properties. The parameterization of that heterogeneity is performed
through a stochastic model. It is shown that such a variability creates the
patterns in the concrete cyclic response that are classically regarded as
source of damping.",1503.07122v1
2016-01-20,Introduction to Landau Damping,"The mechanism of Landau damping is observed in various systems from plasma
oscillations to accelerators. Despite its widespread use, some confusion has
been created, partly because of the different mechanisms producing the damping
but also due to the mathematical subtleties treating the effects. In this
article the origin of Landau damping is demonstrated for the damping of plasma
oscillations. In the second part it is applied to the damping of coherent
oscillations in particle accelerators. The physical origin, the mathematical
treatment leading to the concept of stability diagrams and the applications are
discussed.",1601.05227v1
2018-07-25,Regularity and asymptotic behaviour for a damped plate-membrane transmission problem,"We consider a transmission problem where a structurally damped plate equation
is coupled with a damped or undamped wave equation by transmission conditions.
We show that exponential stability holds in the damped-damped situation and
polynomial stability (but no exponential stability) holds in the
damped-undamped case. Additionally, we show that the solutions first defined by
the weak formulation, in fact have higher Sobolev space regularity.",1807.09730v1
2021-08-04,Nonlinear fluid damping of elastically mounted pitching wings in quiescent water,"We experimentally study the nonlinear fluid damping of a rigid but
elastically mounted pitching wing in the absence of a freestream flow. The
dynamics of the elastic mount are simulated using a cyber-physical system. We
perturb the wing and measure the fluid damping coefficient from damped
oscillations over a large range of pitching frequencies, pitching amplitudes,
pivot locations and sweep angles. A universal fluid damping scaling is proposed
to incorporate all these parameters. Flow fields obtained using particle image
velocimetry are analyzed to explain the nonlinear behaviors of the fluid
damping.",2108.02090v1
2002-11-03,Damping of coupled phonon--plasmon modes,"The effect of free carriers on dispersion and damping of coupled
phonon-plasmon modes is considered in the long-wave approximation. The electron
and phonon scattering rate as well as Landau damping are taken into account.",0211040v1
2002-02-01,"On ""the authentic damping mechanism"" of the phonon damping model","Some general features of the phonon damping model are presented. It is
concluded that the fits performed within this model have no physical content.",0202006v1
2010-12-20,Global attractors for the one dimensional wave equation with displacement dependent damping,"We study the long-time behavior of solutions of the one dimensional wave
equation with nonlinear damping coefficient. We prove that if the damping
coefficient function is strictly positive near the origin then this equation
possesses a global attractor.",1012.4455v1
2018-01-28,Observations of excitation and damping of transversal oscillation in coronal loops by AIA/SDO,"The excitation and damping of transversal coronal loop oscillations and
quantitative relation between damping time, damping quality (damping time per
period), oscillation amplitude, dissipation mechanism and the wake phenomena
are investigated. The observed time series data with the \textit{Atmospheric
Imaging Assembly} (AIA) telescope on NASA's \textit{Solar Dynamics Observatory}
(SDO) satellite on 2015 March 2, consisting of 400 consecutive images with 12
seconds cadence in the 171 $ \rm{{\AA}}$ pass band is analyzed for evidence of
transversal oscillations along the coronal loops by Lomb-Scargle periodgram. In
this analysis signatures of transversal coronal loop oscillations that are
damped rapidly were found with dominant oscillation periods in the range of
$\rm{P=12.25-15.80}$ minutes. Also, damping times and damping qualities of
transversal coronal loop oscillations at dominant oscillation periods are
estimated in the range of $ \rm{\tau_d=11.76-21.46}$ minutes and $
\rm{\tau_d/P=0.86-1.49}$, respectively. The observational results of this
analysis show that damping qualities decrease slowly with increasing the
amplitude of oscillation, but periods of oscillations are not sensitive
function of amplitude of oscillations. The order of magnitude of the damping
qualities and damping times are in good agreement with previous findings and
the theoretical prediction for damping of kink mode oscillations by dissipation
mechanism. Furthermore, oscillation of loop segments attenuate with time
roughly as $t^{-\alpha}$ that magnitude values of $\alpha$ for 30 different
segments change from 0.51 to 0.75.",1801.09217v1
1999-11-16,Probing supernovae ejecta by Halpha damping wings,"It is predicted that H$\alpha$ emission line at the early nebular epoch of
type II-P supernovae may display robust observational effects of damping wings.
This is illustrated by Monte-Carlo simulations. The strength of damping wing
effects may be used to constrain parameters of the line-emitting zone. An
anomalous redshift, width and red wing of H$\alpha$ revealed by SN 1997D on day
150 are explained in terms of damping wing effects.",9911300v1
2009-01-23,Rheological Interpretation of Rayleigh Damping,"Damping is defined through various terms such as energy loss per cycle (for
cyclic tests), logarithmic decrement (for vibration tests), complex modulus,
rise-time or spectrum ratio (for wave propagation analysis), etc. For numerical
modeling purposes, another type of damping is frequently used : it is called
Rayleigh damping. It is a very convenient way of accounting for damping in
numerical models, although the physical or rheological meaning of this approach
is not clear. A rheological model is proposed to be related to classical
Rayleigh damping : it is a generalized Maxwell model with three parameters. For
moderate damping (<25%), this model perfectly coincide with Rayleigh damping
approach since internal friction has the same expression in both cases and
dispersive phenomena are negligible. This is illustrated by finite element
(Rayleigh damping) and analytical (generalized Maxwell model) results in a
simple one-dimensional case.",0901.3717v1
2009-05-20,"Eigenvalue asymptotics, inverse problems and a trace formula for the linear damped wave equation","We determine the general form of the asymptotics for Dirichlet eigenvalues of
the one-dimensional linear damped wave operator. As a consequence, we obtain
that given a spectrum corresponding to a constant damping term this determines
the damping term in a unique fashion. We also derive a trace formula for this
problem.",0905.3242v1
2015-05-06,Remarks on the asymptotic behavior of the solution of an abstract damped wave equation,"We study an abstract damped wave equation. We prove that the solution of the
damped wave equation becomes closer to the solution of a heat type equation as
time tend to infinity. As an application of our approach, we also study the
asymptotic behavior of the damped wave equation in Euclidean space under the
geometric control condition.",1505.01794v2
2017-01-18,Two types of spurious damping forces potentially modeled in numerical seismic nonlinear response history analysis,"The purpose of this paper is to provide practitioners with further insight
into spurious damping forces that can be generated in nonlinear seismic
response history analyses (RHA). The term 'spurious' is used to refer to
damping forces that are not present in an elastic system and appear as
nonlinearities develop: such damping forces are not necessarily intended and
appear as a result of modifications in the structural properties as it yields
or damages due to the seismic action. In this paper, two types of spurious
damping forces are characterized. Each type has often been treated separately
in the literature, but each has been qualified as 'spurious', somehow blurring
their differences. Consequently, in an effort to clarify the consequences of
choosing a particular viscous damping model for nonlinear RHA, this paper shows
that damping models that avoid spurious damping forces of one type do not
necessarily avoid damping forces of the other type.",1701.05092v1
2017-02-02,Exponential stability for a coupled system of damped-undamped plate equations,"We consider the transmission problem for a coupled system of undamped and
structurally damped plate equations in two sufficiently smooth and bounded
subdomains. It is shown that, independently of the size of the damped part, the
damping is strong enough to produce uniform exponential decay of the energy of
the coupled system.",1702.00637v1
2017-09-11,Comparison of damping mechanisms for transverse waves in solar coronal loops,"We present a method to assess the plausibility of alternative mechanisms to
explain the damping of magnetohydrodynamic (MHD) transverse waves in solar
coronal loops. The considered mechanisms are resonant absorption of kink waves
in the Alfv\'en continuum, phase-mixing of Alfv\'en waves, and wave leakage.
Our methods make use of Bayesian inference and model comparison techniques. We
first infer the values for the physical parameters that control the wave
damping, under the assumption of a particular mechanism, for typically observed
damping time-scales. Then, the computation of marginal likelihoods and Bayes
factors enable us to quantify the relative plausibility between the alternative
mechanisms. We find that, in general, the evidence is not large enough to
support a single particular damping mechanism as the most plausible one.
Resonant absorption and wave leakage offer the most probable explanations in
strong damping regimes, while phase mixing is the best candidate for
weak/moderate damping. When applied to a selection of 89 observed transverse
loop oscillations, with their corresponding measurements of damping times
scales and taking into account data uncertainties, we find that only in a few
cases positive evidence for a given damping mechanism is available.",1709.03347v1
2019-03-25,Distributed Inter-Area Oscillation Damping Control for Power Systems by Using Wind Generators and Load Aggregators,"This paper investigates the potential of wind turbine generators (WTGs) and
load aggregators (LAs) to provide supplementary damping control services for
low frequency inter-area oscillations (LFOs) through the additional distributed
damping control units (DCUs) proposed in their controllers. In order to provide
a scalable methodology for the increasing number of WTGs and LAs, a novel
distributed control framework is proposed to coordinate damping controllers.
Firstly, a distributed algorithm is designed to reconstruct the system Jacobian
matrix for each damping bus (buses with damping controllers). Thus, the
critical LFO can be identified locally at each damping bus by applying
eigen-analysis to the obtained system Jacobian matrix. Then, if the damping
ratio of the critical LFO is less than a preset threshold, the control
parameters of DCUs will be tuned in a distributed and coordinated manner to
improve the damping ratio and minimize the total control cost at the same time.
The proposed control framework is tested in a modified IEEE 39-bus test system.
The simulation results with and without the proposed control framework are
compared to demonstrate the effectiveness of the proposed framework.",1903.10135v1
2019-08-19,Spectral determinant for the damped wave equation on an interval,"We evaluate the spectral determinant for the damped wave equation on an
interval of length $T$ with Dirichlet boundary conditions, proving that it does
not depend on the damping. This is achieved by analysing the square of the
damped wave operator using the general result by Burghelea, Friedlander, and
Kappeler on the determinant for a differential operator with matrix
coefficients.",1908.06862v1
2020-10-12,Decays rates for Kelvin-Voigt damped wave equations II: the geometric control condition,"We study in this article decay rates for Kelvin-Voigt damped wave equations
under a geometric control condition. We prove that when the damping coefficient
is sufficiently smooth ($C^1$ vanishing nicely) we show that exponential decay
follows from geometric control conditions (see~\cite{BuCh, Te12} for similar
results under stronger assumptions on the damping function).",2010.05614v2
2020-12-05,On Periodical Damping Ratio of a Controlled Dynamical System with Parametric Resonances,"This report provides an interpretation on the periodically varying damping
ratio of a dynamical system with direct control of oscillation or vibration
damping. The principal parametric resonance of the system and a new type of
parametric resonance, named ""zero-th order"" parametric resonance, are
investigated by using the method of multiple scales to find approximate,
analytical solutions of the system, which provide an interpretation on such
damping variations.",2012.02932v1
2021-06-09,Grammage of cosmic rays in the proximity of supernova remnants embedded in a partially ionized medium,"We investigate the damping of Alfv\'en waves generated by the cosmic ray
resonant streaming instability in the context of the cosmic ray escape and
propagation in the proximity of supernova remnants. We consider ion-neutral
damping, turbulent damping and non linear Landau damping in the warm ionized
and warm neutral phases of the interstellar medium. For the ion-neutral
damping, up-to-date damping coefficients are used. We investigate in particular
whether the self-confinement of cosmic rays nearby sources can appreciably
affect the grammage. We show that the ion-neutral damping and the turbulent
damping effectively limit the residence time of cosmic rays in the source
proximity, so that the grammage accumulated near sources is found to be
negligible. Contrary to previous results, this also happens in the most extreme
scenario where ion-neutral damping is less effective, namely in a medium with
only neutral helium and fully ionized hydrogen. Therefore, the standard
picture, in which CR secondaries are produced during the whole time spent by
cosmic rays throughout the Galactic disk, need not to be deeply revisited.",2106.04948v1
2021-06-22,Sharp decay rate for the damped wave equation with convex-shaped damping,"We revisit the damped wave equation on two-dimensional torus where the damped
region does not satisfy the geometric control condition. We show that if the
damping vanishes as a H\""older function $|x|^{\beta}$, and in addition, the
boundary of the damped region is strictly convex, the wave is stable at rate
$t^{-1+\frac{2}{2\beta+7}}$, which is better than the known optimal decay rate
$t^{-1+\frac{1}{\beta+3}}$ for strip-shaped dampings of the same H\""older
regularity. Moreover, we show by example that the decay rate is optimal. This
illustrates the fact that the energy decay rate depends not only on the order
of vanishing of the damping, but also on the shape of the damped region. The
main ingredient of the proof is the averaging method (normal form reduction)
developed by Hitrick and Sj\""ostrand (\cite{Hi1}\cite{Sj}).",2106.11782v3
2021-08-09,Effect of stepwise adjustment of Damping factor upon PageRank,"The effect of adjusting damping factor {\alpha}, from a small initial value
{\alpha}0 to the final desired {\alpha}f value, upon then iterations needed for
PageRank computation is observed. Adjustment of the damping factor is done in
one or more steps. Results show no improvement in performance over a fixed
damping factor based PageRank.",2108.04150v1
2021-08-17,"Asymptotic behaviour of the wave equation with nonlocal weak damping, anti-damping and critical nonlinearity","In this paper we prove the existence of the global attractor for the wave
equation with nonlocal weak damping, nonlocal anti-damping and critical
nonlinearity.",2108.07395v2
2023-02-23,Buckling Metamaterials for Extreme Vibration Damping,"Damping mechanical resonances is a formidable challenge in an increasing
number of applications. Many of the passive damping methods rely on using low
stiffness dissipative elements, complex mechanical structures or electrical
systems, while active vibration damping systems typically add an additional
layer of complexity. However, in many cases, the reduced stiffness or
additional complexity and mass render these vibration damping methods
unfeasible. Here, we introduce a method for passive vibration damping by
allowing buckling of the primary load path, which sets an upper limit for
vibration transmission: the transmitted acceleration saturates at a maximum
value, no matter what the input acceleration is. This nonlinear mechanism leads
to an extreme damping coefficient tan delta ~0.23 in our metal
metamaterial|orders of magnitude larger than the linear damping of traditional
lightweight structural materials. We demonstrate this principle experimentally
and numerically in free-standing rubber and metal mechanical metamaterials over
a range of accelerations, and show that bi-directional buckling can further
improve its performance. Buckling metamaterials pave the way towards extreme
vibration damping without mass or stiffness penalty, and as such could be
applicable in a multitude of high-tech applications, including aerospace
structures, vehicles and sensitive instruments.",2302.11968v1
1997-11-20,Symmetric matrices and quantum codes,"This paper has been withdrawn since a Gilbert-Varshamov bound for general
quantum codes has already appeared in Ekert and Macchiavello, Prys. Rev. Lett.
77, p. 2585, and a Gilbert-Varshamov bound for stabilizer codes connected with
orthogonal geometry, or equivalently, with symmetric matrices as in this paper,
has been proved by Calredbank, Rains, Shor and Sloane, Phys. Rev. Lett. 78, p.
405. I would like to thank Robert Calderbank for pointing out these references
to me.",9711026v2
1994-06-09,Black Holes from Blue Spectra,"Blue primordial power spectra with a spectral index $n>1$ can lead to a
significant production of primordial black holes in the very early Universe.
The evaporation of these objects leads to a number of observational
consequences and a model independent upper limit of $n \approx 1.4$. In some
cases this limit is strengthened to $n=1.3$. Such limits may be employed to
define the boundary to the region of parameter space consistent with
generalized inflationary predictions. [To appear in Proceedings of the CASE
WESTERN CMB WORKSHOP, April 22-24 1994. Figures available on request from
J.H.Gilbert@qmw.ac.uk]",9406028v1
1995-06-14,Inversions in astronomy and the SOLA method,"This paper was presented at the Institute for Mathematics and its
Applications workshop ""Inverse problems in wave propagation"" and will appear in
the series IMA volumes (Springer). A brief overview of applications of
inversions within astronomy is presented and also an inventory of techniques
commonly in use. Most of this paper is focussed on the method of Subtractive
Optimally Localized Averages (SOLA) which is an adaptation of the Backus and
Gilbert method. This method was originally developed for use in helioseismology
where the Backus and Gilbert method is computationally too slow. Since then it
has also been applied to the problem of reverberation mapping of active
galactic nuclei and the differences between this inverse problem and the ones
of helioseismology are also discussed.",9506084v1
1997-11-11,No Need for MACHOS in the Halo,"A simple interpretation of the more than dozen microlensing events seen in
the direction of the LMC is a halo population of MACHOs which accounts for
about half of the mass of the Galaxy. Such an interpretation is not without its
problems, and we show that current microlensing data can, with some advantage,
be explained by dark components of the disk and spheroid, whose total mass is
only about 10% of the mass of the Galaxy.",9711110v1
2006-02-11,Likelihood Functions for Galaxy Cluster Surveys,"Galaxy cluster surveys offer great promise for measuring cosmological
parameters, but survey analysis methods have not been widely studied. Using
methods developed decades ago for galaxy clustering studies, it is shown that
nearly exact likelihood functions can be written down for galaxy cluster
surveys. The sparse sampling of the density field by galaxy clusters allows
simplifications that are not possible for galaxy surveys. An application to
counts in cells is explicitly tested using cluster catalogs from numerical
simulations and it is found that the calculated probability distributions are
very accurate at masses above several times 10^{14}h^{-1} solar masses at z=0
and lower masses at higher redshift.",0602251v3
2000-03-25,Thermokinetic approach of the generalized Landau-Lifshitz-Gilbert equation with spin polarized current,"In order to describe the recently observed effect of current induced
magnetization reversal in magnetic nanostructures, the thermokinetic theory is
applied to a metallic ferromagnet in contact with a reservoir of spin polarized
conduction electrons. The spin flip relaxation of the conduction electrons is
described thermodynamically as a chemical reaction. The diffusion equation of
the chemical potential (or the giant magnetoresistance) and the usual
Landau-Lifshitz-Gilbert (LLG) equation are derived from the entropy variation.
The expression of the conservation laws of the magnetic moments, including spin
dependent scattering processes, leads then to the generalized LLG equation with
spin polarized current. The equation is applied to the measurements obtained on
single magnetic Ni nanowires.",0003409v1
2004-05-26,Nonequilibrium Extension of the Landau-Lifshitz-Gilbert Equation for Magnetic Systems,"Using the invariant operator method for an effective Hamiltonian including
the radiation-spin interaction, we describe the quantum theory for
magnetization dynamics when the spin system evolves nonadiabatically and out of
equilibrium, $d \hat{\rho}/dt \neq 0$. It is shown that the vector parameter of
the invariant operator and the magnetization defined with respect to the
density operator, both satisfying the quantum Liouville equation, still obey
the Landau-Lifshitz-Gilbert equation.",0405599v1
2006-10-16,Properties of Codes with the Rank Metric,"In this paper, we study properties of rank metric codes in general and
maximum rank distance (MRD) codes in particular. For codes with the rank
metric, we first establish Gilbert and sphere-packing bounds, and then obtain
the asymptotic forms of these two bounds and the Singleton bound. Based on the
asymptotic bounds, we observe that asymptotically Gilbert-Varsharmov bound is
exceeded by MRD codes and sphere-packing bound cannot be attained. We also
establish bounds on the rank covering radius of maximal codes, and show that
all MRD codes are maximal codes and all the MRD codes known so far achieve the
maximum rank covering radius.",0610099v2
1994-08-26,On the Dirichlet problem for harmonic maps with prescribed singularities,"Let $\M$ be a classical Riemannian globally symmetric space of rank one and
non-compact type. We prove the existence and uniqueness of solutions to the
Dirichlet problem for harmonic maps into $\M$ with prescribed singularities
along a closed submanifold of the domain. This generalizes our previous work
where such maps into the hyperbolic plane were constructed. This problem, in
the case where $\M$ is the complex-hyperbolic plane, has applications to
equilibrium configurations of co-axially rotating charged black holes in
General Relativity.",9408005v1
1997-08-15,One-Loop Minimization Conditions in the Minimal Supersymmetric Standard Model,"We study, in the Minimal Supersymmetric Standard Model, the electroweak
symmetry breaking conditions obtained from the one-loop effective potential.
Novel model-independent lower and upper bounds on $\tan \beta$, involving the
other free parameters of the model, are inferred and determined analytically.
We discuss briefly some of the related issues and give an outlook for further
applications.",9708368v1
2004-05-31,On a Penrose Inequality with Charge,"We construct a time-symmetric asymptotically flat initial data set to the
Einstein-Maxwell Equations which satisfies the inequality: m - 1/2(R + Q^2/R) <
0, where m is the total mass, R=sqrt(A/4) is the area radius of the outermost
horizon and Q is the total charge. This yields a counter-example to a natural
extension of the Penrose Inequality to charged black holes.",0405602v3
2004-07-26,Automorphisms of free groups have asymptotically periodic dynamics,"We show that every automorphism $\alpha$ of a free group $F_k$ of finite rank
$k$ has {\it asymptotically periodic} dynamics on $F_k$ and its boundary
$\partial F_k$: there exists a positive power $\alpha^q$ such that every
element of the compactum $F_k \cup \partial F_k$ converges to a fixed point
under iteration of $\alpha^q$.",0407437v2
2004-12-30,The Construction of a Partially Regular Solution to the Landau-Lifshitz-Gilbert Equation in $\mathbb{R}^2$,"We establish a framework to construct a global solution in the space of
finite energy to a general form of the Landau-Lifshitz-Gilbert equation in
$\mathbb{R}^2$. Our characterization yields a partially regular solution,
smooth away from a 2-dimensional locally finite Hausdorff measure set. This
construction relies on approximation by discretization, using the special
geometry to express an equivalent system whose highest order terms are linear
and the translation of the machinery of linear estimates on the fundamental
solution from the continuous setting into the discrete setting. This method is
quite general and accommodates more general geometries involving targets that
are compact smooth hypersurfaces.",0412534v1
2002-01-13,Inverse Cascade Regime in Shell Models of 2-Dimensional Turbulence,"We consider shell models that display an inverse energy cascade similar to
2-dimensional turbulence (together with a direct cascade of an enstrophy-like
invariant). Previous attempts to construct such models ended negatively,
stating that shell models give rise to a ""quasi-equilibrium"" situation with
equipartition of the energy among the shells. We show analytically that the
quasi-equilibrium state predicts its own disappearance upon changing the model
parameters in favor of the establishment of an inverse cascade regime with K41
scaling. The latter regime is found where predicted, offering a useful model to
study inverse cascades.",0201020v1
2002-04-23,Algebraic decay in hierarchical graphs,"We study the algebraic decay of the survival probability in open hierarchical
graphs. We present a model of a persistent random walk on a hierarchical graph
and study the spectral properties of the Frobenius-Perron operator. Using a
perturbative scheme, we derive the exponent of the classical algebraic decay in
terms of two parameters of the model. One parameter defines the geometrical
relation between the length scales on the graph, and the other relates to the
probabilities for the random walker to go from one level of the hierarchy to
another. The scattering resonances of the corresponding hierarchical quantum
graphs are also studied. The width distribution shows the scaling behavior
$P(\Gamma) \sim 1/\Gamma$.",0204056v1
2004-03-11,Statistics of active vs. passive advections in magnetohydrodynamic turbulence,"Active turbulent advection is considered in the context of
magneto-hydrodynamics. In this case, an auxiliary passive field bears no
apparent connection to the active field. The scaling properties of the two
fields are different. In the framework of a shell model, we show that the
two-point structure function of the passive field has a unique zero mode,
characterizing the scaling of this field only. In other words, the existence of
statistical invariants for the decaying passive field carries no information on
the scaling properties of the active field.",0403017v1
2006-01-19,Drift of particles in self-similar systems and its Liouvillian interpretation,"We study the dynamics of classical particles in different classes of
spatially extended self-similar systems, consisting of (i) a self-similar
Lorentz billiard channel, (ii) a self-similar graph, and (iii) a master
equation. In all three systems the particles typically drift at constant
velocity and spread ballistically. These transport properties are analyzed in
terms of the spectral properties of the operator evolving the probability
densities. For systems (i) and (ii), we explain the drift from the properties
of the Pollicott-Ruelle resonance spectrum and corresponding eigenvectors",0601042v1
1997-11-20,Quantum self-dual codes and symmetric matrices,"This paper has been withdrawn since a Gilbert-Varshamov bound for general
quantum codes has already appeared in Ekert and Macchiavello, Prys. Rev. Lett.
77, p. 2585, and a Gilbert-Varshamov bound for stabilizer codes connected with
orthogonal geometry, or equivalently, with symmetric matrices as in this paper,
has been proved by Calredbank, Rains, Shor and Sloane, Phys. Rev. Lett. 78, p.
405. I would like to thank Robert Calderbank for pointing out these references
to me.",9711047v2
2001-06-06,Constraints on Eavesdropping on the BB84 Protocol,"An undetected eavesdropping attack must produce count rate statistics that
are indistinguishable from those that would arise in the absence of such an
attack. In principle this constraint should force a reduction in the amount of
information available to the eavesdropper. In this paper we illustrate, by
considering a particular class of eavesdropping attacks, how the general
analysis of this problem may proceed.",0106034v2
2007-09-14,A complete proof of The Graceful Tree Conjecture using the concept of Edge Degree,We show the Graceful Tree Conjecture holds.,0709.2201v9
2007-09-24,An extension of a result concerning convex geometric graphs,"We show a general result known as the Erdos_Sos Conjecture: if
$E(G)>{1/2}(k-1)n$ where $G$ has order $n$ then $G$ contains every tree of
order $k+1$ as a subgraph.",0709.3590v5
2008-06-13,Heat conduction and Fourier's law by consecutive local mixing and thermalization,"We present a first-principles study of heat conduction in a class of models
which exhibit a new multi-step local thermalization mechanism which gives rise
to Fourier's law. Local thermalization in our models occurs as the result of
binary collisions among locally confined gas particles. We explore the
conditions under which relaxation to local equilibrium, which involves no
energy exchange, takes place on time scales shorter than that of the binary
collisions which induce local thermalization. The role of this mechanism in
multi-phase material systems such as aerogels is discussed.",0806.2193v1
2009-08-05,Persistence effects in deterministic diffusion,"In systems which exhibit deterministic diffusion, the gross parameter
dependence of the diffusion coefficient can often be understood in terms of
random walk models. Provided the decay of correlations is fast enough, one can
ignore memory effects and approximate the diffusion coefficient according to
dimensional arguments. By successively including the effects of one and two
steps of memory on this approximation, we examine the effects of
``persistence'' on the diffusion coefficients of extended two-dimensional
billiard tables and show how to properly account for these effects, using walks
in which a particle undergoes jumps in different directions with probabilities
that depend on where they came from.",0908.0600v1
2009-08-10,Diffusion coefficients for multi-step persistent random walks on lattices,"We calculate the diffusion coefficients of persistent random walks on
lattices, where the direction of a walker at a given step depends on the memory
of a certain number of previous steps. In particular, we describe a simple
method which enables us to obtain explicit expressions for the diffusion
coefficients of walks with two-step memory on different classes of one-, two-
and higher-dimensional lattices.",0908.1271v1
2010-04-09,Strict inequalities of critical probabilities on Gilbert's continuum percolation graph,"Any infinite graph has site and bond percolation critical probabilities
satisfying $p_c^{site}\geq p_c^{bond}$. The strict version of this inequality
holds for many, but not all, infinite graphs.
  In this paper, the class of graphs for which the strict inequality holds is
extended to a continuum percolation model. In Gilbert's graph with
supercritical density on the Euclidean plane, there is almost surely a unique
infinite connected component. We show that on this component $p_c^{site} >
p_c^{bond}$. This also holds in higher dimensions.",1004.1596v2
2010-04-15,Rank of mapping tori and companion matrices,"Given $f$ in $GL(d,Z)$, it is decidable whether its mapping torus (the
semi-direct product of $Z^d$ with $Z$) may be generated by two elements or not;
if so, one can classify generating pairs up to Nielsen equivalence. If $f$ has
infinite order, the mapping torus of $f^n$ cannot be generated by two elements
for $n$ large enough; equivalently, $f^n$ is not conjugate to a companion
matrix in $GL(d,Z)$ if $n$ is large.",1004.2649v1
2010-04-30,Limit theory for planar Gilbert tessellations,"A Gilbert tessellation arises by letting linear segments (cracks) in the
plane unfold in time with constant speed, starting from a homogeneous Poisson
point process of germs in randomly chosen directions. Whenever a growing edge
hits an already existing one, it stops growing in this direction. The resulting
process tessellates the plane. The purpose of the present paper is to establish
law of large numbers, variance asymptotics and a central limit theorem for
geometric functionals of such tessellations. The main tool applied is the
stabilization theory for geometric functionals.",1005.0023v1
2010-06-24,Periodic solutions for the Landau-Lifshitz-Gilbert equation,"Ferromagnetic materials tend to develop very complex magnetization patterns
whose time evolution is modeled by the so-called Landau-Lifshitz-Gilbert
equation (LLG). In this paper, we construct time-periodic solutions for LLG in
the regime of soft and small ferromagnetic particles which satisfy a certain
shape condition. Roughly speaking, it is assumed that the length of the
particle is greater than its hight and its width. The approach is based on a
perturbation argument and the spectral analysis of the corresponding linearized
problem as well as the theory of sectorial operators.",1006.4765v1
2010-12-19,A counterexample to a Penrose inequality conjectured by Gibbons,"We show that the Brill-Lindquist initial data provides a counterexample to a
Riemannian Penrose inequality with charge conjectured by G. Gibbons. The
observation illustrates a sub-additive characteristic of the area radii for the
individual connected components of an outermost horizon as a lower bound of the
ADM mass.",1012.4190v2
2011-11-27,A two-stage approach to relaxation in billiard systems of locally confined hard spheres,"We consider the three-dimensional dynamics of systems of many interacting
hard spheres, each individually confined to a dispersive environment, and show
that the macroscopic limit of such systems is characterized by a coefficient of
heat conduction whose value reduces to a dimensional formula in the limit of
vanishingly small rate of interaction. It is argued that this limit arises from
an effective loss of memory. Similarities with the diffusion of a tagged
particle in binary mixtures are emphasized.",1111.6272v1
2012-01-12,Coil-helix transition in poly(L-glutamic acid) : Evidence for a 3-state non-cooperative process,"A careful analysis of measurements of circular dichroism of poly(L-glutamic
acid) (PGA) shows that the data can be very accurately described by introducing
a third state for the PGA configuration, in addition to the helix and coil
ones, and considering a simple equilibrium between these three states, without
cooperativity. The third state is more conspicuous when high molecular weight
polyethyleneglycol (PEG) is added. Excluded volume effects shown by differences
in presence of short and long PEG chains indicate a direct interaction of PEG
and PGA rather than an osmotic effect.",1201.2566v1
2012-03-20,Vortex dynamics in the presence of excess energy for the Landau-Lifschitz-Gilbert equation,"We study the Landau-Lifshitz-Gilbert equation for the dynamics of a magnetic
vortex system. We present a PDE-based method for proving vortex dynamics that
does not rely on strong well-preparedness of the initial data and allows for
instantaneous changes in the strength of the gyrovector force due to bubbling
events. The main tools are estimates of the Hodge decomposition of the
supercurrent and an analysis of the defect measure of weak convergence of the
stress energy tensor. Ginzburg-Landau equations with mixed dynamics in the
presence of excess energy are also discussed.",1203.4426v1
2012-12-22,Cumulative Distance Enumerators of Random Codes and their Thresholds,"Cumulative weight enumerators of random linear codes are introduced, their
asymptotic properties are studied, and very sharp thresholds are exhibited; as
a consequence, it is shown that the asymptotic Gilbert-Varshamov bound is a
very sharp threshold point for the density of the linear codes whose relative
distance is greater than a given positive number. For arbitrary random codes,
similar settings and results are exhibited; in particular, the very sharp
threshold point for the density of the codes whose relative distance is greater
than a given positive number is located at half the asymptotic
Gilbert-Varshamov bound.",1212.5679v1
2013-01-23,The Importance of Continuous Value Based Project Management in the Context of Requirements Engineering,"Despite several scientific achievements in the last years, there are still a
lot of IT projects that fail. Researchers found that one out of five
IT-projects run out of time, budget or value. Major reasons for this failure
are unexpected economic risk factors that emerge during the runtime of
projects. In order to be able to identify emerging risks early and to
counteract reasonably, financial methods for a continuous IT-project-steering
are necessary, which as of today to the best of our knowledge are missing
within scientific literature.",1301.5438v1
2013-04-08,On Automorphisms and Subtowers of an asymptotically optimal Tower of Function Fields,"In this article we investigate the automorphism group of an asymptotically
optimal tower of function fields introduced by Garcia and Stichtenoth. In
particular we provide a detailed description of the decomposition group of some
rational places. This group acts on the algebraic-geometric standard codes
obtained by the Garcia-Stichtenoth tower exceeding the Gilbert-Varshamov bound.
The fields fixed by the decomposition groups form an asymptotically optimal
non-Galois subtower, which has been first found by Bezerra and Garcia and
yields an improvement for computing codes above the Gilbert-Varshamov bound. In
this article we also describe its proportionality to the Garcia-Stichtenoth
tower and obtain new precise results on its rational places and their
Weierstra{\ss} semigroups.",1304.2145v1
2013-05-06,The Moment Generating function for ray lengths in the Half Gilbert Model with Rectangular Cells,"In the full rectangular version of Gilbert's tessellation lines extend either
horizontally (with east- and west--growing rays) or vertically (north- and
south--growing rays) from seed points which form a Poisson point process, each
ray stopping when another ray is met. In the half rectangular version, east and
south growing rays do not interact with west and north rays. Using techniques
developed in our previous paper, we derive an exact expression for the moment
generating function for the ray length distribution in the half rectangular
model.",1305.1289v1
2013-07-15,Degenerate transition pathways for screw dislocations: implications for migration,"In body-centred-cubic (bcc) metals migrating 1/2<111> screw dislocations
experience a periodic energy landscape with a triangular symmetry. Atomistic
simulations, such as those performed using the nudged-elastic-band (NEB)
method, generally predict a transition-pathway energy-barrier with a
double-hump; contradicting Ab Initio findings. Examining the trajectories
predicted by NEB for a particle in a Peierls energy landscape representative of
that obtained for a screw dislocation, reveals an unphysical anomaly caused by
the occurrence of monkey saddles in the landscape. The implications for motion
of screws with and without stress are discussed.",1307.3848v2
2013-08-17,The Riemannian Penrose Inequality with Charge for Multiple Black Holes,"We present a proof of the Riemannian Penrose inequality with charge $r\leq m
+ \sqrt{m^2-q^2}$, where $A=4\pi r^2$ is the area of the outermost apparent
horizon with possibly multiple connected components, $m$ is the total ADM mass,
and $q$ the total charge of a strongly asymptotically flat initial data set for
the Einstein-Maxwell equations, satisfying the charged dominant energy
condition, with no charged matter outside the horizon.",1308.3771v3
2013-08-23,Quotients and subgroups of Baumslag-Solitar groups,"We determine all generalized Baumslag-Solitar groups (finitely generated
groups acting on a tree with all stabilizers infinite cyclic) which are
quotients of a given Baumslag-Solitar group BS(m,n), and (when BS(m,n) is not
Hopfian) which of them also admit BS(m,n) as a quotient. We determine for which
values of r,s one may embed BS(r,s) into a given BS(m,n), and we characterize
finitely generated groups which embed into some BS(n,n).",1308.5122v2
2013-12-17,Limit theory for the Gilbert graph,"For a given homogeneous Poisson point process in $\mathbb{R}^d$ two points
are connected by an edge if their distance is bounded by a prescribed distance
parameter. The behaviour of the resulting random graph, the Gilbert graph or
random geometric graph, is investigated as the intensity of the Poisson point
process is increased and the distance parameter goes to zero. The asymptotic
expectation and covariance structure of a class of length-power functionals are
computed. Distributional limit theorems are derived that have a Gaussian, a
stable or a compound Poisson limiting distribution. Finally, concentration
inequalities are provided using a concentration inequality for the convex
distance.",1312.4861v2
2014-03-13,Fibrations of ordered groupoids and the factorization of ordered functors,"We investigate canonical factorizations of ordered functors of ordered
groupoids through star-surjective functors. Our main construction is a quotient
ordered groupoid, depending on an ordered version of the notion of normal
subgroupoid, that results is the factorization of an ordered functor as a
star-surjective functor followed by a star-injective functor. Any
star-injective functor possesses a universal factorization through a covering,
by Ehresmann's Maximum Enlargement Theorem. We also show that any ordered
functor has a canonical factorization through a functor with the ordered
homotopy lifting property.",1403.3254v2
2014-03-16,Interpolating local constants in families,"We extend the theory of local constants to l-adic families of representations
of GL_n(F) where F is a p-adic field with l not equal to p. We construct zeta
integrals and gamma factors for representations coming from the conjectural
""local Langlands correspondence in families"" of Emerton-Helm, proving a
rationality result and functional equation. We also construct a universal gamma
factor with coefficients in the integral Bernstein center.",1403.3914v2
2014-06-10,A thin-film limit in the Landau-Lifshitz-Gilbert equation relevant for the formation of Néel walls,"We consider an asymptotic regime for two-dimensional ferromagnetic films that
is consistent with the formation of transition layers (N\'eel walls). We first
establish compactness of S2-valued magnetizations in the energetic regime of
N\'eel walls and characterize the set of accumulation points. We then prove
that N\'eel walls are asymptotically the unique energy minimizing
configurations. We finally study the corresponding dynamical issues, namely the
compactness properties of the magnetizations under the flow of the
Landau-Lifshitz-Gilbert equation.",1406.2709v1
2014-08-02,Machta-Zwanzig regime of anomalous diffusion in infinite-horizon billiards,"We study diffusion on a periodic billiard table with infinite horizon in the
limit of narrow corridors. An effective trapping mechanism emerges according to
which the process can be modeled by a L\'evy walk combining
exponentially-distributed trapping times with free propagation along paths
whose precise probabilities we compute. This description yields an
approximation of the mean squared displacement of infinite-horizon billiards in
terms of two transport coefficients which generalizes to this anomalous regime
the Machta-Zwanzig approximation of normal diffusion in finite-horizon
billiards [Phys. Rev. Lett. 50, 1959 (1983)].",1408.0349v1
2014-12-11,Gamma factors of pairs and a local converse theorem in families,"We prove a GL(n)xGL(n-1) local converse theorem for l-adic families of smooth
representations of GL(n,F) where F is a finite extension of Q_p and l is
different from p. To do so, we also extend the theory of Rankin-Selberg
integrals, first introduced by Jacquet, Piatetski-Shapiro, and Shalika, to the
setting of families, continuing previous work of the author.",1412.3500v2
2015-05-28,A Geometric Interpretation of the Boolean Gilbert-Johnson-Keerthi Algorithm,"The Gilbert-Johnson-Keerthi (GJK) algorithm is an iterative improvement
technique for finding the minimum distance between two convex objects. It can
easily be extended to work with concave objects and return the pair of closest
points. [4] The key operation of GJK is testing whether a Voronoi region of a
simplex contains the origin or not. In this paper we show that, in the context
where one is interested only in the Boolean value of whether two convex objects
intersect, and not in the actual distance between them, the number of test
cases in GJK can be significantly reduced. This results in a simpler and more
efficient algorithm that can be used in many computational geometry
applications.",1505.07873v1
2016-01-29,Ordered groupoid quotients and congruences on inverse semigroups,"We introduce a preorder on an inverse semigroup $S$ associated to any normal
inverse subsemigroup $N$, that lies between the natural partial order and
Green's ${\mathscr J}$-relation. The corresponding equivalence relation
$\simeq_N$ is not necessarily a congruence on $S$, but the quotient set does
inherit a natural ordered groupoid structure. We show that this construction
permits the factorisation of any inverse semigroup homomorphism into a
composition of a quotient map and a star-injective functor, and that this
decomposition implies a classification of congruences on $S$. We give an
application to the congruence and certain normal inverse subsemigroups
associate to an inverse monoid presentation.",1601.08194v1
2016-08-16,Closed inverse subsemigroups of graph inverse semigroups,"As part of his study of representations of the polycylic monoids, M.V. Lawson
described all the closed inverse submonoids of a polycyclic monoid $P_n$ and
classified them up to conjugacy. We show that Lawson's description can be
extended to closed inverse subsemigroups of graph inverse semigroups. We then
apply B. Schein's theory of cosets in inverse semigroups to the closed inverse
subsemigroups of graph inverse semigroups: we give necessary and sufficient
conditions for a closed inverse subsemigroup of a graph inverse semigroup to
have finite index, and determine the value of the index when it is finite.",1608.04538v1
2016-10-11,Converse theorems and the local Langlands correspondence in families,"We prove a descent criterion for certain families of smooth representations
of GL_n(F) (F a p-adic field) in terms of the gamma factors of pairs
constructed in previous work of the second author. We then use this descent
criterion, together with a theory of gamma factors for families of
representations of the Weil group W_F (developed previously by both authors),
to prove a series of conjectures, due to the first author, that give a complete
description of the integral Bernstein center in terms of Galois theory and the
local Langlands correspondence. An immediate consequence is the conjectural
""local Langlands correspondence in families"" of Emerton and Helm.",1610.03277v1
2016-10-14,An alternative view on dissipation in turbulent flows,"An original experimental setup has been elaborated in order to get a better
view of turbulent flows in a von Karman geometry. The availability of a very
fast camera allowed to follow in time the evolution of the flows. A surprising
finding is that the development of smaller whorls ceases earlier than expected
and the aspect of the flows remains the same above Reynolds number of a few
thousand. This fact provides an explanation of the constancy of the reduced
dissipation in the same range without the need of singularity. Its cause could
be in relation with the same type of behavior observed in a rotating frame.",1610.05356v2
2017-03-02,Small Superposition Dimension and Active Set Construction for Multivariate Integration Under Modest Error Demand,"Constructing active sets is a key part of the Multivariate Decomposition
Method. An algorithm for constructing optimal or quasi-optimal active sets is
proposed in the paper. By numerical experiments, it is shown that the new
method can provide sets that are significantly smaller than the sets
constructed by the already existing method. The experiments also show that the
superposition dimension could surprisingly be very small, at most 3, when the
error demand is not smaller than $10^{-3}$ and the weights decay sufficiently
fast.",1703.00985v1
2017-03-03,Heat conduction and the nonequilibrium stationary states of stochastic energy exchange processes,"I revisit the exactly solvable Kipnis--Marchioro--Presutti model of heat
conduction [J. Stat. Phys. 27 65 (1982)] and describe, for one-dimensional
systems of arbitrary sizes whose ends are in contact with thermal baths at
different temperatures, a systematic characterization of their non-equilibrium
stationary states. These arguments avoid resorting to the analysis of a dual
process and yield a straightforward derivation of Fourier's law, as well as
higher-order static correlations, such as the covariant matrix. The
transposition of these results to families of gradient models generalizing the
KMP model is established and specific cases are examined.",1703.01240v1
2017-03-04,Algebraic geometry codes with complementary duals exceed the asymptotic Gilbert-Varshamov bound,"It was shown by Massey that linear complementary dual (LCD for short) codes
are asymptotically good. In 2004, Sendrier proved that LCD codes meet the
asymptotic Gilbert-Varshamov (GV for short) bound. Until now, the GV bound
still remains to be the best asymptotical lower bound for LCD codes. In this
paper, we show that an algebraic geometry code over a finite field of even
characteristic is equivalent to an LCD code and consequently there exists a
family of LCD codes that are equivalent to algebraic geometry codes and exceed
the asymptotical GV bound.",1703.01441v1
2017-03-17,A finite element approximation for the stochastic Landau--Lifshitz--Gilbert equation with multi-dimensional noise,"We propose an unconditionally convergent linear finite element scheme for the
stochastic Landau--Lifshitz--Gilbert (LLG) equation with multi-dimensional
noise. By using the Doss-Sussmann technique, we first transform the stochastic
LLG equation into a partial differential equation that depends on the solution
of the auxiliary equation for the diffusion part. The resulting equation has
solutions absolutely continuous with respect to time. We then propose a
convergent $\theta$-linear scheme for the numerical solution of the
reformulated equation. As a consequence, we are able to show the existence of
weak martingale solutions to the stochastic LLG equation.",1703.05901v1
2017-04-12,The homology of principally directed ordered groupoids,"We present some homological properties of a relation $\beta$ on ordered
groupoids that generalises the minimum group congruence for inverse semigroups.
When $\beta$ is a transitive relation on an ordered groupoid $G$, the quotient
$G / \beta$ is again an ordered groupoid, and construct a pair of adjoint
functors between the module categories of $G$ and of $G / \beta$. As a
consequence, we show that the homology of $G$ is completely determined by that
of $G / \beta$, generalising a result of Loganathan for inverse semigroups.",1704.03689v1
2017-06-15,Absence of correlations in the energy exchanges of an exactly solvable model of heat transport with many degrees of freedom,"A process based on the exactly solvable Kipnis--Marchioro--Presutti model of
heat conduction [J. Stat. Phys. 27 65 (1982)] is described whereby lattice
cells share their energies among many identical degrees of freedom while, in
each cell, only two of them are associated with energy exchanges connecting
neighbouring cells. It is shown that, up to dimensional constants, the heat
conductivity is half the interaction rate, regardless of the degrees of
freedom. Moreover, as this number becomes large, correlations between the
energy variables involved in the exchanges vanish. In this regime, the process
thus boils down to the time-evolution of the local temperatures which is
prescribed by the discrete heat equation.",1706.04849v1
2017-11-29,On the local converse theorem and the descent theorem in families,"We prove an analogue of Jacquet's conjecture on the local converse theorem
for \ell-adic families of co-Whittaker representations of GL_n(F), where F is a
finite extension of Q_p and \ell does not equal p. We also prove an analogue of
Jacquet's conjecture for a descent theorem, which asks for the smallest
collection of gamma factors determining the subring of definition of an
\ell-adic family. These two theorems are closely related to the local Langlands
correspondence in \ell-adic families.",1711.11159v1
2018-06-23,List Decodability of Symbol-Pair Codes,"We investigate the list decodability of symbol-pair codes in the present
paper. Firstly, we show that list decodability of every symbol-pair code does
not exceed the Gilbert-Varshamov bound. On the other hand, we are able to prove
that with high probability, a random symbol-pair code can be list decoded up to
the Gilbert-Varshamov bound. Our second result of this paper is to derive the
Johnson-type bound, i.e., a lower bound on list decoding radius in terms of
minimum distance. Finally, we present a list decoding algorithm of Reed-Solomon
codes beyond the Johnson-type bound.",1806.08992v1
2018-07-05,Volumetric performance capture from minimal camera viewpoints,"We present a convolutional autoencoder that enables high fidelity volumetric
reconstructions of human performance to be captured from multi-view video
comprising only a small set of camera views. Our method yields similar
end-to-end reconstruction error to that of a probabilistic visual hull computed
using significantly more (double or more) viewpoints. We use a deep prior
implicitly learned by the autoencoder trained over a dataset of view-ablated
multi-view video footage of a wide range of subjects and actions. This opens up
the possibility of high-end volumetric performance capture in on-set and
prosumer scenarios where time or cost prohibit a high witness camera count.",1807.01950v2
2018-10-26,Immobilization of convex bodies in $R^n$,"We extend to arbitrary finite $n$ the notion of immobilization of a convex
body $O$ in $R^n$ by a finite set of points $P$ in the boundary of $O$. Because
of its importance for this problem, necessary and sufficient conditions are
found for the immobilization of an $n$-simplex. A fairly complete geometric
description of these conditions is given: as $n$ increases from $n = 2$, some
qualitative difference in the nature of the sets $P$ emerges.",1810.11381v1
2019-01-14,Groupoids and the algebra of rewriting in group presentations,"Presentations of groups by rewriting systems (that is, by monoid
presentations), have been fruitfully studied by encoding the rewriting system
in a $2$--complex -- the Squier complex -- whose fundamental groupoid then
describes the derivation of consequences of the rewrite rules. We describe a
reduced form of the Squier complex, investigate the structure of its
fundamental groupoid, and show that key properties of the presentation are
still encoded in the reduced form.",1901.04348v1
2019-05-27,Tuning Free Rank-Sparse Bayesian Matrix and Tensor Completion with Global-Local Priors,"Matrix and tensor completion are frameworks for a wide range of problems,
including collaborative filtering, missing data, and image reconstruction.
Missing entries are estimated by leveraging an assumption that the matrix or
tensor is low-rank. Most existing Bayesian techniques encourage rank-sparsity
by modelling factorized matrices and tensors with Normal-Gamma priors. However,
the Horseshoe prior and other ""global-local"" formulations provide
tuning-parameter-free solutions which may better achieve simultaneous
rank-sparsity and missing-value recovery. We find these global-local priors
outperform commonly used alternatives in simulations and in a collaborative
filtering task predicting board game ratings.",1905.11496v1
2019-06-26,Fairness criteria through the lens of directed acyclic graphical models,"A substantial portion of the literature on fairness in algorithms proposes,
analyzes, and operationalizes simple formulaic criteria for assessing fairness.
Two of these criteria, Equalized Odds and Calibration by Group, have gained
significant attention for their simplicity and intuitive appeal, but also for
their incompatibility. This chapter provides a perspective on the meaning and
consequences of these and other fairness criteria using graphical models which
reveals Equalized Odds and related criteria to be ultimately misleading. An
assessment of various graphical models suggests that fairness criteria should
ultimately be case-specific and sensitive to the nature of the information the
algorithm processes.",1906.11333v1
2020-01-14,Neural Architecture Search for Deep Image Prior,"We present a neural architecture search (NAS) technique to enhance the
performance of unsupervised image de-noising, in-painting and super-resolution
under the recently proposed Deep Image Prior (DIP). We show that evolutionary
search can automatically optimize the encoder-decoder (E-D) structure and
meta-parameters of the DIP network, which serves as a content-specific prior to
regularize these single image restoration tasks. Our binary representation
encodes the design space for an asymmetric E-D network that typically converges
to yield a content-specific DIP within 10-20 generations using a population
size of 500. The optimized architectures consistently improve upon the visual
quality of classical DIP for a diverse range of photographic and artistic
content.",2001.04776v1
2020-07-18,Finslerian convolution metrics and their special classes,"Here, it is introduced a concept of convolution metric in Finslerian
Geometry. This convolution metric is a kind of function obtained by a given
mathematical operation between two Finslerian metrics. Some basic properties of
the Finslerian convolution metrics are studied. Then it is characterized
Finslerian convolution metrics which are of type Riemannian, Minkowskian as
well as Randers. Furthermore, some examples of the Finslerian convolutions are
given.",2007.14803v3
2020-09-14,What mathematical billiards teach us about statistical physics?,"We survey applications of the theory of hyperbolic (and to a lesser extent
non hyperbolic) billiards to some fundamental problems of statistical physics
and their mathematically rigorous derivations in the framework of classical
Hamiltonian systems.",2009.06284v2
2020-11-29,Applications of the Backus-Gilbert method to linear and some non linear equations,"We investigate the use of a functional analytical version of the
Backus-Gilbert Method as a reconstruction strategy to get specific information
about the solution of linear and slightly non-linear systems with Frech\'et
derivable operators. Some a priori error estimates are shown and tested for two
classes of problems: a nonlinear moment problem and a linear elliptic Cauchy
problem. For this second class of problems a special version of the
Green-formula is developed in order to analyze the involved adjoint equations.",2011.14407v1
2021-11-30,Global weak solutions for the Landau-Lifshitz-Gilbert-Vlasov-Maxwell system coupled via emergent electromagnetic fields,"Motivated by recent models of current driven magnetization dynamics, we
examine the coupling of the Landau-Lifshitz-Gilbert equation and classical
electron transport governed by the Vlasov-Maxwell system. The interaction is
based on space-time gyro-coupling in the form of emergent electromagnetic
fields of quantized helicity that add up to the conventional Maxwell fields. We
construct global weak solutions of the coupled system in the framework of
frustrated magnets with competing first and second order gradient interactions
known to host topological solitons such as magnetic skyrmions and hopfions.",2111.15482v1
2022-04-02,Introduction to the Artificial Intelligence that can be applied to the Network Automation Journey,"The computer network world is changing and the NetDevOps approach has brought
the dynamics of applications and systems into the field of communication
infrastructure. Businesses are changing and businesses are faced with
difficulties related to the diversity of hardware and software that make up
those infrastructures. The ""Intent-Based Networking - Concepts and Definitions""
document describes the different parts of the ecosystem that could be involved
in NetDevOps. The recognize, generate intent, translate and refine features
need a new way to implement algorithms. This is where artificial intelligence
comes in.",2204.00800v1
2022-05-24,Theory of the Energy Variance in a Quantum Bit,"We define a new quantum Hermitian operator (namely, the energy variance
operator) which is simply duplicated from the statistical definition of energy
variance in classical physics. Its expectation value yields the standard
deviation of the energy about the mean value of this latter. We show by use of
an exact Hamiltonian description that this standard deviation is due to the
high-frequeny energy oscillations which are usually discarded in the rotating
wave aproximation. We check the present theory by recovering the duration of an
abrupt quantum jump that has been described in a recent experiment.",2205.12763v1
2022-07-11,Quasilinear rough evolution equations,"We investigate the abstract Cauchy problem for a quasilinear parabolic
equation in a Banach space of the form \( du_t -L_t(u_t)u_t dt = N_t(u_t)dt +
F(u_t)\cdot d\mathbf X_t \), where \( \mathbf X\) is a \( \gamma\)-H\""older
rough path for \( \gamma\in(1/3,1/2)\). We explore the mild formulation that
combines functional analysis techniques and controlled rough paths theory which
entail the local well-posedness of such equations. We apply our results to the
stochastic Landau-Lifshitz-Gilbert and Shigesada-Kawasaki-Teramoto equation. In
this framework we obtain a random dynamical system associated to the
Landau-Lifshitz-Gilbert equation.",2207.04787v1
2022-08-01,A Pansiot-type subword complexity theorem for automorphisms of free groups,"Inspired by Pansiot's work on substitutions, we prove a similar theorem for
automorphisms of a free group F of finite rank: if a right-infinite word
represents an attracting fixed point of an automorphism of F, the subword
complexity of X is equivalent to n, n log log n, n log n, or n^2. The proof
uses combinatorial arguments analogue to Pansiot's as well as train tracks. We
also define the recurrence complexity of X, and we apply it to laminations. In
particular, we show that attracting laminations have complexity equivalent to
n, n log log n, n log n, or n^2 (to n if the automorphism is fully
irreducible).",2208.00676v1
2022-08-13,May the force be with you,"Modern methods in dimensionality reduction are dominated by nonlinear
attraction-repulsion force-based methods (this includes t-SNE, UMAP,
ForceAtlas2, LargeVis, and many more). The purpose of this paper is to
demonstrate that all such methods, by design, come with an additional feature
that is being automatically computed along the way, namely the vector field
associated with these forces. We show how this vector field gives additional
high-quality information and propose a general refinement strategy based on
ideas from Morse theory. The efficiency of these ideas is illustrated
specifically using t-SNE on synthetic and real-life data sets.",2208.06676v1
2022-10-26,Linearized frequency domain Landau-Lifshitz-Gilbert equation formulation,"We present a general finite element linearized Landau-Lifshitz-Gilbert
equation (LLGE) solver for magnetic systems under weak time-harmonic excitation
field. The linearized LLGE is obtained by assuming a small deviation around the
equilibrium state of the magnetic system. Inserting such expansion into LLGE
and keeping only first order terms gives the linearized LLGE, which gives a
frequency domain solution for the complex magnetization amplitudes under an
external time-harmonic applied field of a given frequency. We solve the linear
system with an iterative solver using generalized minimal residual method. We
construct a preconditioner matrix to effectively solve the linear system. The
validity, effectiveness, speed, and scalability of the linear solver are
demonstrated via numerical examples.",2210.14525v1
2022-11-10,Secure Aggregation Is Not All You Need: Mitigating Privacy Attacks with Noise Tolerance in Federated Learning,"Federated learning is a collaborative method that aims to preserve data
privacy while creating AI models. Current approaches to federated learning tend
to rely heavily on secure aggregation protocols to preserve data privacy.
However, to some degree, such protocols assume that the entity orchestrating
the federated learning process (i.e., the server) is not fully malicious or
dishonest. We investigate vulnerabilities to secure aggregation that could
arise if the server is fully malicious and attempts to obtain access to
private, potentially sensitive data. Furthermore, we provide a method to
further defend against such a malicious server, and demonstrate effectiveness
against known attacks that reconstruct data in a federated learning setting.",2211.06324v1
2022-12-22,Theory and construction of Quasi-Monte Carlo rules for option pricing and density estimation,"In this paper we propose and analyse a method for estimating three quantities
related to an Asian option: the fair price, the cumulative distribution
function, and the probability density. The method involves preintegration with
respect to one well chosen integration variable to obtain a smooth function of
the remaining variables, followed by the application of a tailored lattice
Quasi-Monte Carlo rule to integrate over the remaining variables.",2212.11493v2
2022-12-22,Novel Bottomonium Results,"We present the latest results from the use of the Backus-Gilbert method for
reconstructing the spectra of NRQCD bottomonium mesons using anisotropic
FASTSUM ensembles at non-zero temperature. We focus in particular on results
from the $\eta_b$, $\Upsilon$, $\chi_{b1}$ and $h_b$ generated from
Tikhonov-regularized Backus-Gilbert coefficient sets. We extend previous work
on the Laplace shifting theorem as a means of resolution improvement and
present new results from its use. We conclude with a discussion of the
limitations of the improvement routine and elucidate a connection with
Parisi-Lepage statistical scaling.",2212.12016v1
2022-12-30,Asymptotic stability of 2-domain walls for the Landau-Lifshitz-Gilbert equation in a nanowire with Dzyaloshinskii-Moriya interaction,"We consider a ferromagnetic nanowire, with an energy functional $E$ with
easy-axis in the direction $e_1$, and which takes into account the
Dzyaloshinskii-Moriya interaction. We consider configurations of the
magnetization which are perturbations of two well separated domain wall, and
study their evolution under the Landau-Lifshitz-Gilbert flow associated to E.
Our main result is that, if the two walls have opposite speed, these
configurations are asymptotically stable, up to gauges intrinsic to the
invariances of the energy $E$. Our analysis builds on the framework developed
in [4], taking advantage that it is amenable to space localisation.",2212.14589v1
2023-01-12,Time Domain Verification of Differential Transmission Line Modeling Methods,"The advantages and limitations of time-domain pseudo-random binary sequence
(PRBS) excitation methods for system identification of individual modes within
a multi-conductor transmission system are discussed. We develop the
modifications necessary to standard frequency-domain transmission-line models
to match time-domain experimental data from several types of transmission
systems. We show a variety of experimental results showing very good to
excellent agreement with our model's predictions, up to approximately 10 GHz.",2301.05281v1
2023-01-17,Power Supply Compensation for Capacitive Loads,"As ASIC supply voltages approach one volt, the source-impedance goals for
power distribution networks are driven ever lower as well. One approach to
achieving these goals is to add decoupling capacitors of various values until
the desired impedance profile is obtained. An unintended consequence of this
approach can be reduced power supply stability and even oscillation. In this
paper, we present a case study of a system design which encountered these
problems and we describe how these problems were resolved. Time-domain and
frequency-domain analysis techniques are discussed and measured data is
presented.",2301.09580v1
2023-01-17,Applications of Optimization Routines in Signal Integrity Analysis,"Signal integrity analysis often involves the development of design guidelines
through manual manipulation of circuit parameters and judicious interpretation
of results. Such an approach can result in significant effort and sub-optimal
conclusions. Optimization routines have been well proven to aid analysis across
a variety of common tasks. In addition, there are several non-traditional
applications where optimization can be useful. This paper begins by describing
the basics of optimization followed by two specific case studies where
non-traditional optimization provides significant improvements in both analysis
efficiency and channel performance.",2301.10157v1
2023-01-17,High Speed Parallel Signal Crosstalk Cancellation Concept,"High performance computing (HPC) systems make extensive use of high speed
electrical interconnects, in routing signals among processing elements, or
between processing elements and memory. Increasing bandwidth demands result in
high density, parallel I/O exposed to crosstalk due to tightly coupled
transmission lines. The crosstalk cancellation signaling concept discussed in
this paper utilizes the known, predictable theory of coupled transmission lines
to cancel crosstalk from neighboring traces with carefully chosen resistive
cross-terminations between them. Through simulation and analysis of practical
bus architectures, we explore the merits of crosstalk cancellation which could
be used in dense interconnect HPC (or other) applications.",2301.10170v1
2023-04-05,Elimination and Factorization,"If a matrix $A$ has rank $r$, then its row echelon form (from elimination)
contains the identity matrix in its first $r$ independent columns. How do we
\emph{interpret the matrix} $F$ that appears in the remaining columns of that
echelon form\,? $F$ multiplies those first $r$ independent columns of $A$ to
give its $n-r$ dependent columns. Then $F$ reveals bases for the row space and
the nullspace of the original matrix $A$. And $F$ is the key to the column-row
factorization $\boldsymbol{A}=\boldsymbol{CR}$.",2304.02659v1
2023-04-25,Jet: Multilevel Graph Partitioning on Graphics Processing Units,"The multilevel heuristic is the dominant strategy for high-quality sequential
and parallel graph partitioning. Partition refinement is a key step of
multilevel graph partitioning. In this work, we present Jet, a new parallel
algorithm for partition refinement specifically designed for Graphics
Processing Units (GPUs). We combine Jet with GPU-aware coarsening to develop a
$k$-way graph partitioner, the Jet partitioner. The new partitioner achieves
superior quality compared to state-of-the-art shared memory partitioners on a
large collection of test graphs.",2304.13194v2
2023-05-16,QHDL: a Low-Level Circuit Description Language for Quantum Computing,"This paper proposes a descriptive language called QHDL, akin to VHDL, to
program gate-based quantum computing systems. Unlike other popular quantum
programming languages, QHDL targets low-level quantum computing programming and
aims to provide a common framework for programming FPGAs and gate-based quantum
computing systems. The paper presents an initial implementation and design
principles of the QHDL framework, including a compiler and quantum computer
simulator. We discuss the challenges of low-level integration of streaming
models and quantum computing for programming FPGAs and gate-based quantum
computing systems.",2305.09419v1
2023-05-21,An Alternative Derivation of the Landau-Lifshitz-Gilbert Equation for Saturated Ferromagnets,"The Landau-Lifshitz-Gilbert equation for rigid and saturated ferromagnets is
derived using a two-continuum model constructed by H.F. Tiersten for elastic
and saturated ferromagnets. The relevant basic laws of physics are applied
systematically to the two continua or their combination. The exchange
interaction is introduced into the model through surface distributed magnetic
couples. This leads to a continuum theory with magnetization gradients in the
stored energy density. The saturation condition of the magnetization functions
as constraints on the energy density and has implications in the constitutive
relations.",2305.18232v1
2023-06-25,Gilbert's conjecture and A new way to octonionic analytic functions from the clifford analysis,"In this article we will give a affirmative answer to Gilbert's conjecture on
Hardy spaces of Clifford analytic functions in upper half-space of
$\mathbb{R}^8$. It depends on a explicit construction of Spinor space
$\mathcal{R}_8$ and Clifford algebra $Cl_8$ by octonion algbra. What's more ,
it gives us an associative way to octonionic analytic function theory. And the
similar question has been discussed in Octonionic Hardy space in upper-half
space, some classical results about octonionic analytic functions have been
reformulated, too.",2306.14164v1
2023-06-28,Stochastic Landau-Lifshitz-Gilbert equations for frustrated magnets under fluctuating currents,"We examine a stochastic Landau-Lifshitz-Gilbert equation for a frustrated
ferromagnet with competing first and second order exchange interactions exposed
to deterministic and random spin transfer torques in form of transport noise.
We prove the existence and pathwise uniqueness of weak martingale solutions in
the energy space. The result ensures the persistence of topological patterns,
occurring in such magnetic systems, under the influence of a fluctuating spin
current.",2306.15843v1
2023-07-28,"MDS, Hermitian Almost MDS, and Gilbert-Varshamov Quantum Codes from Generalized Monomial-Cartesian Codes","We construct new stabilizer quantum error-correcting codes from generalized
monomial-Cartesian codes. Our construction uses an explicitly defined twist
vector, and we present formulas for the minimum distance and dimension.
Generalized monomial-Cartesian codes arise from polynomials in $m$ variables.
When $m=1$ our codes are MDS, and when $m=2$ and our lower bound for the
minimum distance is $3$ the codes are at least Hermitian Almost MDS. For an
infinite family of parameters when $m=2$ we prove that our codes beat the
Gilbert-Varshamov bound. We also present many examples of our codes that are
better than any known code in the literature.",2307.15488v1
2023-09-06,Optimal Control of the 2D Landau-Lifshitz-Gilbert Equation with Control Energy in Effective Magnetic Field,"The optimal control of magnetization dynamics in a ferromagnetic sample at a
microscopic scale is studied. The dynamics of this model is governed by the
Landau-Lifshitz-Gilbert equation on a two-dimensional bounded domain with the
external magnetic field (the control) applied through the effective field. We
prove the global existence and uniqueness of a regular solution in $\mathbb
S^2$ under a smallness condition on control and initial data. We establish the
existence of optimal control and derive a first-order necessary optimality
condition using the Fr\'echet derivative of the control-to-state operator and
adjoint problem approach.",2309.02786v1
2023-09-22,Relaxed optimal control for the stochastic Landau-Lifshitz-Gilbert equation,"We consider the stochastic Landau-Lifshitz-Gilbert equation, perturbed by a
real-valued Wiener process. We add an external control to the effective field
as an attempt to drive the magnetization to a desired state and also to control
thermal fluctuations. We use the theory of Young measures to relax the given
control problem along with the associated cost. We consider a control operator
that can depend (possibly non-linearly) on both the control and the associated
solution. Moreover, we consider a fairly general associated cost functional
without any special convexity assumption. We use certain compactness arguments,
along with the Jakubowski version of the Skorohod Theorem to show that the
relaxed problem admits an optimal control.",2309.12556v1
2023-11-29,Bayesian interpretation of Backus-Gilbert methods,"The extraction of spectral densities from Euclidean correlators evaluated on
the lattice is an important problem, as these quantities encode physical
information on scattering amplitudes, finite-volume spectra, inclusive decay
rates, and transport coefficients. In this contribution, we show that the
Bayesian approach to this ""inverse"" problem, based on Gaussian processes, can
be reformulated in a way that yields a solution equivalent, up to statistical
uncertainties, to the one obtained in a Backus-Gilbert approach. After
discussing this equivalence, we point out its implications for a reliable
determination of spectral densities from lattice simulations.",2311.18125v1
2024-01-14,Multilevel Metamodels: A Novel Approach to Enhance Efficiency and Generalizability in Monte Carlo Simulation Studies,"Metamodels, or the regression analysis of Monte Carlo simulation (MCS)
results, provide a powerful tool to summarize MCS findings. However, an as of
yet unexplored approach is the use of multilevel metamodels (MLMM) that better
account for the dependent data structure of MCS results that arises from
fitting multiple models to the same simulated data set. In this study, we
articulate the theoretical rationale for the MLMM and illustrate how it can
dramatically improve efficiency over the traditional regression approach,
better account for complex MCS designs, and provide new insights into the
generalizability of MCS findings.",2401.07294v2
2024-02-29,Evaluating the Gilbert-Varshamov Bound for Constrained Systems,"We revisit the well-known Gilbert-Varshamov (GV) bound for constrained
systems. In 1991, Kolesnik and Krachkovsky showed that GV bound can be
determined via the solution of some optimization problem. Later, Marcus and
Roth (1992) modified the optimization problem and improved the GV bound in many
instances. In this work, we provide explicit numerical procedures to solve
these two optimization problems and hence, compute the bounds. We then show the
procedures can be further simplified when we plot the respective curves. In the
case where the graph presentation comprise a single state, we provide explicit
formulas for both bounds.",2402.18869v1
1992-06-18,Wormholes and Supersymmetry,"Revisions: reference added to: G. Gilbert, {\sl Nucl.Phys.} {\bf B328}, 159
(1989)",9206072v2
1993-05-26,Musings on Magnus,"The object of this paper is to describe a simple method for proving that
certain groups are residually torsion-free nilpotent, to describe some new
parafree groups and to raise some new problems in honour of the memory of
Wilhelm Magnus.",9305201v1
2001-10-17,Expected number of distinct part sizes in a random integer composition,"The asymptotics, as $n\to\infty$, for the expected number of distinct part
sizes in a random composition of an integer n is obtained.",0110189v1
2003-12-29,Non-hopfian relatively free groups,"To solve problems of Gilbert Baumslag and Hanna Neumann, posed in the 1960's,
we construct a nontrivial variety of groups all of whose noncyclic free groups
are non-hopfian.",0312491v1
2005-10-26,Winning rate in the full-information best choice problem,"Following a long-standing suggestion by Gilbert and Mosteller, we derive an
explicit formula for the asymptotic winning rate in the full-information
problem of the best choice.",0510568v3
2007-12-20,The dark matter as a light gravitino (II),"We address the question of gravitino dark matter in the context of gauge
mediated supersymmetry breaking models.",0712.3465v1
2014-02-25,Du-Hwang Characteristic Area: Catch-22,"The paper is devoted to description of two interconnected mistakes generated
by the gap in the Du and Hwang approach to Gilbert-Pollack Steiner ratio
conjecture.",1402.6079v1
2016-06-01,Existence of arbitrarily smooth solutions of the LLG equation in 3D with natural boundary conditions,"We prove that the Landau-Lifshitz-Gilbert equation in three space dimensions
with homogeneous Neumann boundary conditions admits arbitrarily smooth
solutions, given that the initial data is sufficiently close to a constant
function.",1606.00086v1
2018-10-28,Asymptotic Gilbert-Varshamov bound on Frequency Hopping Sequences,"Given a $q$-ary frequency hopping sequence set of length $n$ and size $M$
with Hamming correlation $H$, one can obtain a $q$-ary (nonlinear) cyclic code
of length $n$ and size $nM$ with Hamming distance $n-H$. Thus, every upper
bound on the size of a code from coding theory gives an upper bound on the size
of a frequency hopping sequence set. Indeed, all upper bounds from coding
theory have been converted to upper bounds on frequency hopping sequence sets
(\cite{Ding09}). On the other hand, a lower bound from coding theory does not
automatically produce a lower bound for frequency hopping sequence sets. In
particular, the most important lower bound--the Gilbert-Varshamov bound in
coding theory has not been transformed to frequency hopping sequence sets. The
purpose of this paper is to convert the Gilbert-Varshamov bound in coding
theory to frequency hopping sequence sets by establishing a connection between
a special family of cyclic codes (which are called hopping cyclic codes in this
paper) and frequency hopping sequence sets. We provide two proofs of the
Gilbert-Varshamov bound. One is based on probabilistic method that requires
advanced tool--martingale. This proof covers the whole rate region. The other
proof is purely elementary but only covers part of the rate region.",1810.11757v2
2020-05-26,Reidemeister Moves in Gauss Diagrams,"We provide a simple algorithm for recognizing and performing Reidemeister
moves in a Gauss diagram.",2005.12957v1
2021-05-26,Lee Weight for Nonbinary Quantum Error Correction,"We propose the quantum Lee weight for quantum errors, provide a
Gilbert-Varshamov type bound, and a code construction for the proposed weight.",2105.12354v1
2021-09-19,Compactness of isospectral conformal Finslerian metrics set on a 3-manifold,"Let F be a Finslerian metric on an n-dimensional closed manifold M. In this
work, we study problems about compactness of isospectral sets of conformal
Finslerian metrics when n=3.",2110.06338v2
2001-05-31,Lower bound for the quantum capacity of a discrete memoryless quantum channel,"We generalize the random coding argument of stabilizer codes and derive a
lower bound on the quantum capacity of an arbitrary discrete memoryless quantum
channel. For the depolarizing channel, our lower bound coincides with that
obtained by Bennett et al. We also slightly improve the quantum
Gilbert-Varshamov bound for general stabilizer codes, and establish an analogue
of the quantum Gilbert-Varshamov bound for linear stabilizer codes. Our proof
is restricted to the binary quantum channels, but its extension of to l-adic
channels is straightforward.",0105151v4
2007-08-30,Asymptotic improvement of the Gilbert-Varshamov bound for linear codes,"The Gilbert-Varshamov bound states that the maximum size A_2(n,d) of a binary
code of length n and minimum distance d satisfies A_2(n,d) >= 2^n/V(n,d-1)
where V(n,d) stands for the volume of a Hamming ball of radius d. Recently
Jiang and Vardy showed that for binary non-linear codes this bound can be
improved to A_2(n,d) >= cn2^n/V(n,d-1) for c a constant and d/n <= 0.499. In
this paper we show that certain asymptotic families of linear binary [n,n/2]
random double circulant codes satisfy the same improved Gilbert-Varshamov
bound.",0708.4164v1
2007-09-26,Finite Element Formalism for Micromagnetism,"The aim of this work is to present the details of the finite element approach
we developed for solving the Landau-Lifschitz-Gilbert equations in order to be
able to treat problems involving complex geometries. There are several
possibilities to solve the complex Landau-Lifschitz-Gilbert equations
numerically. Our method is based on a Galerkin-type finite element approach. We
start with the dynamic Landau-Lifschitz-Gilbert equations, the associated
boundary condition and the constraint on the magnetization norm. We derive the
weak form required by the finite element method. This weak form is afterwards
integrated on the domain of calculus. We compared the results obtained with our
finite element approach with the ones obtained by a finite difference method.
The results being in very good agreement, we can state that our approach is
well adapted for 2D micromagnetic systems.",0709.4153v1
2009-05-07,Heat transport in stochastic energy exchange models of locally confined hard spheres,"We study heat transport in a class of stochastic energy exchange systems that
characterize the interactions of networks of locally trapped hard spheres under
the assumption that neighbouring particles undergo rare binary collisions. Our
results provide an extension to three-dimensional dynamics of previous ones
applying to the dynamics of confined two-dimensional hard disks [Gaspard P &
Gilbert T On the derivation of Fourier's law in stochastic energy exchange
systems J Stat Mech (2008) P11021]. It is remarkable that the heat conductivity
is here again given by the frequency of energy exchanges. Moreover the
expression of the stochastic kernel which specifies the energy exchange
dynamics is simpler in this case and therefore allows for faster and more
extensive numerical computations.",0905.1051v1
2011-08-15,Hydrodynamics of self-alignment interactions with precession and derivation of the Landau-Lifschitz-Gilbert equation,"We consider a kinetic model of self-propelled particles with alignment
interaction and with precession about the alignment direction. We derive a
hydrodynamic system for the local density and velocity orientation of the
particles. The system consists of the conservative equation for the local
density and a non-conservative equation for the orientation. First, we assume
that the alignment interaction is purely local and derive a first order system.
However, we show that this system may lose its hyperbolicity. Under the
assumption of weakly non-local interaction, we derive diffusive corrections to
the first order system which lead to the combination of a heat flow of the
harmonic map and Landau-Lifschitz-Gilbert dynamics. In the particular case of
zero self-propelling speed, the resulting model reduces to the phenomenological
Landau-Lifschitz-Gilbert equations. Therefore the present theory provides a
kinetic formulation of classical micromagnetization models and spin dynamics.",1108.2951v1
2011-09-30,"Magnetization Dynamics, Gyromagnetic Relation, and Inertial Effects","The gyromagnetic relation - i.e. the proportionality between the angular
momentum $\vec L$ (defined by an inertial tensor) and the magnetization $\vec
M$ - is evidence of the intimate connections between the magnetic properties
and the inertial properties of ferromagnetic bodies. However, inertia is absent
from the dynamics of a magnetic dipole (the Landau-Lifshitz equation, the
Gilbert equation and the Bloch equation contain only the first derivative of
the magnetization with respect to time). In order to investigate this
paradoxical situation, the lagrangian approach (proposed originally by T. H.
Gilbert) is revisited keeping an arbitrary nonzero inertial tensor. A dynamic
equation generalized to the inertial regime is obtained. It is shown how both
the usual gyromagnetic relation and the well-known Landau-Lifshitz-Gilbert
equation are recovered at the kinetic limit, i.e. for time scales above the
relaxation time $\tau$ of the angular momentum.",1109.6782v1
2012-08-28,Decomposition of modified Landau-Lifshitz-Gilbert equation and corresponding analytic solutions,"The Suzuki-Trotter decomposition in general allows one to divide the equation
of motion of a dynamical system into smaller parts whose integration are easier
than the original equation. In this study, we first rewrite by employing
feasible approximations the modified Landau-Lifshitz-Gilbert equation for
localized spins in a suitable form for simulations using the Suzuki-Trotter
decomposition. Next we decompose the equation into parts and demonstrate that
the parts are classified into three groups, each of which can be solved
exactly. Since the modified Landau-Lifshitz-Gilbert equation from which we
start is in rather a general form, simulations of spin dynamics in various
systems accompanying only small numerical errors are possible.",1208.5545v1
2013-11-20,Asymptotic Improvement of the Gilbert-Varshamov Bound on the Size of Permutation Codes,"Given positive integers $n$ and $d$, let $M(n,d)$ denote the maximum size of
a permutation code of length $n$ and minimum Hamming distance $d$. The
Gilbert-Varshamov bound asserts that $M(n,d) \geq n!/V(n,d-1)$ where $V(n,d)$
is the volume of a Hamming sphere of radius $d$ in $\S_n$.
  Recently, Gao, Yang, and Ge showed that this bound can be improved by a
factor $\Omega(\log n)$, when $d$ is fixed and $n \to \infty$. Herein, we
consider the situation where the ratio $d/n$ is fixed and improve the
Gilbert-Varshamov bound by a factor that is \emph{linear in $n$}. That is, we
show that if $d/n < 0.5$, then $$ M(n,d)\geq cn\,\frac{n!}{V(n,d-1)} $$ where
$c$ is a positive constant that depends only on $d/n$. To establish this
result, we follow the method of Jiang and Vardy. Namely, we recast the problem
of bounding $M(n,d)$ into a graph-theoretic framework and prove that the
resulting graph is locally sparse.",1311.4925v1
2016-11-21,On the List-Decodability of Random Self-Orthogonal Codes,"In 2011, Guruswami-H{\aa}stad-Kopparty \cite{Gru} showed that the
list-decodability of random linear codes is as good as that of general random
codes. In the present paper, we further strengthen the result by showing that
the list-decodability of random {\it Euclidean self-orthogonal} codes is as
good as that of general random codes as well, i.e., achieves the classical
Gilbert-Varshamov bound. Specifically, we show that, for any fixed finite field
$\F_q$, error fraction $\delta\in (0,1-1/q)$ satisfying $1-H_q(\delta)\le
\frac12$ and small $\epsilon>0$, with high probability a random Euclidean
self-orthogonal code over $\F_q$ of rate $1-H_q(\delta)-\epsilon$ is $(\delta,
O(1/\epsilon))$-list-decodable. This generalizes the result of linear codes to
Euclidean self-orthogonal codes. In addition, we extend the result to list
decoding {\it symplectic dual-containing} codes by showing that the
list-decodability of random symplectic dual-containing codes achieves the
quantum Gilbert-Varshamov bound as well. This implies that list-decodability of
quantum stabilizer codes can achieve the quantum Gilbert-Varshamov bound.
  The counting argument on self-orthogonal codes is an important ingredient to
prove our result.",1611.06673v1
2017-11-29,Linear second-order IMEX-type integrator for the (eddy current) Landau-Lifshitz-Gilbert equation,"Combining ideas from [Alouges et al. (Numer. Math., 128, 2014)] and
[Praetorius et al. (Comput. Math. Appl., 2017)], we propose a numerical
algorithm for the integration of the nonlinear and time-dependent
Landau-Lifshitz-Gilbert (LLG) equation which is unconditionally convergent,
formally (almost) second-order in time, and requires only the solution of one
linear system per time-step. Only the exchange contribution is integrated
implicitly in time, while the lower-order contributions like the
computationally expensive stray field are treated explicitly in time. Then, we
extend the scheme to the coupled system of the Landau-Lifshitz-Gilbert equation
with the eddy current approximation of Maxwell equations (ELLG). Unlike
existing schemes for this system, the new integrator is unconditionally
convergent, (almost) second-order in time, and requires only the solution of
two linear systems per time-step.",1711.10715v1
2017-12-28,Subquadratic time encodable codes beating the Gilbert-Varshamov bound,"We construct explicit algebraic geometry codes built from the
Garcia-Stichtenoth function field tower beating the Gilbert-Varshamov bound for
alphabet sizes at least 192. Messages are identied with functions in certain
Riemann-Roch spaces associated with divisors supported on multiple places.
Encoding amounts to evaluating these functions at degree one places. By
exploiting algebraic structures particular to the Garcia-Stichtenoth tower, we
devise an intricate deterministic \omega/2 < 1.19 runtime exponent encoding and
1+\omega/2 < 2.19 expected runtime exponent randomized (unique and list)
decoding algorithms. Here \omega < 2.373 is the matrix multiplication exponent.
If \omega = 2, as widely believed, the encoding and decoding runtimes are
respectively nearly linear and nearly quadratic. Prior to this work, encoding
(resp. decoding) time of code families beating the Gilbert-Varshamov bound were
quadratic (resp. cubic) or worse.",1712.10052v2
2018-11-15,Hilbert-Schmidt distance and entanglement witnessing,"Gilbert proposed an algorithm for bounding the distance between a given point
and a convex set. In this article we apply the Gilbert's algorithm to get an
upper bound on the Hilbert-Schmidt distance between a given state and the set
of separable states. While Hilbert Schmidt Distance does not form a proper
entanglement measure, it can nevertheless be useful for witnessing
entanglement. We provide here a few methods based on the Gilbert's algorithm
that can reliably qualify a given state as strongly entangled or practically
separable, while being computationally efficient. The method also outputs
successively improved approximations to the Closest Separable State for the
given state. We demonstrate the efficacy of the method with examples.",1811.06599v3
2020-02-13,Age of Information with Gilbert-Elliot Servers and Samplers,"We study age of information in a status updating system that consists of a
single sampler, i.e., source node, that sends time-sensitive status updates to
a single monitor node through a server node. We first consider a Gilbert-Elliot
service profile at the server node. In this model, service times at the server
node follow a finite state Markov chain with two states: ${bad}$ state $b$ and
${good}$ state $g$ where the server is faster in state $g$. We determine the
time average age experienced by the monitor node and characterize the
age-optimal state transition matrix $P$ with and without an average cost
constraint on the service operation. Next, we consider a Gilbert-Elliot
sampling profile at the source. In this model, the interarrival times follow a
finite state Markov chain with two states: ${bad}$ state $b$ and ${good}$ state
$g$ where samples are more frequent in state $g$. We find the time average age
experienced by the monitor node and characterize the age-optimal state
transition matrix $P$.",2002.05711v1
2005-08-26,Damping of MHD turbulence in Solar Flares,"(Abridged) We describe the cascade of plasma waves or turbulence injected,
presumably by reconnection, at scales comparable to the size of a solar flare
loop to scales comparable to particle gyroradii, and evaluate their damping by
various mechanisms. We show that the classical viscous damping is unimportant
for magnetically dominated or low beta plasmas and the primary damping
mechanism is the collisionless damping by the background particles. We show
that the damping rate is proportional to the total random momentum density of
the particles. For solar flare conditions this means that in most flares,
except the very large ones, the damping is dominated by thermal background
electrons. For large flares one requires acceleration of essentially all
background electrons into a nonthermal distribution so that the accelerated
electrons can be important in the damping of the waves. In general, damping by
thermal or nonthermal protons is negligible compared to that of electrons
except for quasi-perpendicular propagating waves or for rare proton dominated
flares with strong nuclear gamma-ray line emission. Using the rate for damping
we determine the critical scale below which the damping becomes important and
the spectrum of the turbulence steepens. This critical scale, however, has
strong dependence on the angle of propagation with respect to the magnetic
field direction. The waves can cascade down to very small scales, such as the
gyroradii of the particles at small angles (quasi-parallel propagation) and
possibly near 90 degree (quasi-perpendicular propagation) giving rise to a
highly anisotropic spectral distribution.",0508567v1
2011-07-27,Constraint damping for the Z4c formulation of general relativity,"One possibility for avoiding constraint violation in numerical relativity
simulations adopting free-evolution schemes is to modify the continuum
evolution equations so that constraint violations are damped away. Gundlach et.
al. demonstrated that such a scheme damps low amplitude, high frequency
constraint violating modes exponentially for the Z4 formulation of General
Relativity. Here we analyze the effect of the damping scheme in numerical
applications on a conformal decomposition of Z4. After reproducing the
theoretically predicted damping rates of constraint violations in the linear
regime, we explore numerical solutions not covered by the theoretical analysis.
In particular we examine the effect of the damping scheme on low-frequency and
on high-amplitude perturbations of flat spacetime as well and on the long-term
dynamics of puncture and compact star initial data in the context of spherical
symmetry. We find that the damping scheme is effective provided that the
constraint violation is resolved on the numerical grid. On grid noise the
combination of artificial dissipation and damping helps to suppress constraint
violations. We find that care must be taken in choosing the damping parameter
in simulations of puncture black holes. Otherwise the damping scheme can cause
undesirable growth of the constraints, and even qualitatively incorrect
evolutions. In the numerical evolution of a compact static star we find that
the choice of the damping parameter is even more delicate, but may lead to a
small decrease of constraint violation. For a large range of values it results
in unphysical behavior.",1107.5539v2
1999-11-24,Damped Lyman alpha absorber and the faint end of the galaxy luminosity function at high redshift,"We combine predictions for several hierarchical cosmogonies with
observational evidence on damped Lyman alpha systems to establish a
correspondence between the high redshift galaxy population and the properties
of damped Lyman alpha systems. We assume that high redshift galaxies and damped
Lyman alpha systems are hosted by the same dark matter halos and require
consistency between the predicted halo space density, the rate of incidence and
the velocity width distribution of damped Lyman alpha systems, and the observed
galaxy luminosity function at the bright end. We arrive at the following
results: (1) predicted impact parameters between the damped absorption system
and the luminous part of the absorbing galaxy are expected to be very small
(0.3 - 1arcsec) for most galaxies; (2) luminosities of galaxies causing damped
absorption are generally fainter than m_R = 25 and damped Lyman alpha systems
are predicted to sample preferentially the outer regions of galaxies at the
faint end of the galaxy luminosity function at high redshift. Therefore, DLAS
should currently provide the best probe of the progenitors of normal
present-day galaxies.",9911447v1
2003-03-13,An explicit unconditionally stable numerical method for solving damped nonlinear Schrödinger equations with a focusing nonlinearity,"This paper introduces an extension of the time-splitting sine-spectral (TSSP)
method for solving damped focusing nonlinear Schr\""{o}dinger equations (NLS).
The method is explicit, unconditionally stable and time transversal invariant.
Moreover, it preserves the exact decay rate for the normalization of the wave
function if linear damping terms are added to the NLS. Extensive numerical
tests are presented for cubic focusing nonlinear Schr\""{o}dinger equations in
2d with a linear, cubic or a quintic damping term. Our numerical results show
that quintic or cubic damping always arrests blowup, while linear damping can
arrest blowup only when the damping parameter $\dt$ is larger than a threshold
value $\dt_{\rm th}$. We note that our method can also be applied to solve the
3d Gross-Pitaevskii equation with a quintic damping term to model the dynamics
of a collapsing and exploding Bose-Einstein condensate (BEC).",0303158v1
2004-11-03,Quantum probability applied to the damped harmonic oscillator,"In this introductory course we sketch the framework of quantum probability in
order to discuss open quantum systems, in particular the damped harmonic
oscillator.",0411024v1
2006-11-23,Path integrals and wavepacket evolution for damped mechanical systems,"Damped mechanical systems with various forms of damping are quantized using
the path integral formalism. In particular, we obtain the path integral kernel
for the linearly damped harmonic oscillator and a particle in a uniform
gravitational field with linearly or quadratically damped motion. In each case,
we study the evolution of Gaussian wavepackets and discuss the characteristic
features that help us distinguish between different types of damping. For
quadratic damping, we show that the action and equation of motion of such a
system has a connection with the zero dimensional version of a currently
popular scalar field theory. Furthermore we demonstrate that the equation of
motion (for quadratic damping) can be identified as a geodesic equation in a
fictitious two-dimensional space.",0611239v1
2007-07-05,Damping of bulk excitations over an elongated BEC - the role of radial modes,"We report the measurement of Beliaev damping of bulk excitations in cigar
shaped Bose Einstein condensates of atomic vapor. By using post selection,
excitation line shapes of the total population are compared with those of the
undamped excitations. We find that the damping depends on the initial
excitation energy of the decaying quasi particle, as well as on the excitation
momentum. We model the condensate as an infinite cylinder and calculate the
damping rates of the different radial modes. The derived damping rates are in
good agreement with the experimentally measured ones. The damping rates
strongly depend on the destructive interference between pathways for damping,
due to the quantum many-body nature of both excitation and damping products.",0707.0776v1
2008-09-22,Damping in 2D and 3D dilute Bose gases,"Damping in 2D and 3D dilute gases is investigated using both the
hydrodynamical approach and the Hartree-Fock-Bogoliubov (HFB) approximation .
We found that the both methods are good for the Beliaev damping at zero
temperature and Landau damping at very low temperature, however, at high
temperature, the hydrodynamical approach overestimates the Landau damping and
the HFB gives a better approximation. This result shows that the comparison of
the theoretical calculation using the hydrodynamical approach and the
experimental data for high temperature done by Vincent Liu (PRL {\bf21} 4056
(1997)) is not proper. For two-dimensional systems, we show that the Beliaev
damping rate is proportional to $k^3$ and the Landau damping rate is
proportional to $ T^2$ for low temperature and to $T$ for high temperature. We
also show that in two dimensions the hydrodynamical approach gives the same
result for zero temperature and for low temperature as HFB, but overestimates
the Landau damping for high temperature.",0809.3632v3
2008-12-08,Landau Damping and Alfven Eigenmodes of Neutron Star Torsion Oscillations,"Torsion oscillations of the neutron star crust are Landau damped by the
Alfven continuum in the bulk. For strong magnetic fields (in magnetars),
undamped Alfven eigenmodes appear.",0812.1570v1
2010-09-24,Spatial Damping of Propagating Kink Waves in Prominence Threads,"Transverse oscillations and propagating waves are frequently observed in
threads of solar prominences/filaments and have been interpreted as kink
magnetohydrodynamic (MHD) modes. We investigate the spatial damping of
propagating kink MHD waves in transversely nonuniform and partially ionized
prominence threads. Resonant absorption and ion-neutral collisions (Cowling's
diffusion) are the damping mechanisms taken into account. The dispersion
relation of resonant kink waves in a partially ionized magnetic flux tube is
numerically solved by considering prominence conditions. Analytical expressions
of the wavelength and damping length as functions of the kink mode frequency
are obtained in the Thin Tube and Thin Boundary approximations. For typically
reported periods of thread oscillations, resonant absorption is an efficient
mechanism for the kink mode spatial damping, while ion-neutral collisions have
a minor role. Cowling's diffusion dominates both the propagation and damping
for periods much shorter than those observed. Resonant absorption may explain
the observed spatial damping of kink waves in prominence threads. The
transverse inhomogeneity length scale of the threads can be estimated by
comparing the observed wavelengths and damping lengths with the theoretically
predicted values. However, the ignorance of the form of the density profile in
the transversely nonuniform layer introduces inaccuracies in the determination
of the inhomogeneity length scale.",1009.4871v1
2012-08-01,Artificial Neural Network Based Prediction of Optimal Pseudo-Damping and Meta-Damping in Oscillatory Fractional Order Dynamical Systems,"This paper investigates typical behaviors like damped oscillations in
fractional order (FO) dynamical systems. Such response occurs due to the
presence of, what is conceived as, pseudo-damping and meta-damping in some
special class of FO systems. Here, approximation of such damped oscillation in
FO systems with the conventional notion of integer order damping and time
constant has been carried out using Genetic Algorithm (GA). Next, a multilayer
feed-forward Artificial Neural Network (ANN) has been trained using the GA
based results to predict the optimal pseudo and meta-damping from knowledge of
the maximum order or number of terms in the FO dynamical system.",1208.0318v1
2012-08-27,Optimization of the damped quantum search,"The damped quantum search proposed in [A. Mizel, Phys. Rev. Lett., 102 150501
(2009)] was analyzed by calculating the highest possible probability of finding
the target state in each iteration. A new damping parameter that depends on the
number of iterations was obtained, this was compared to the critical damping
parameter for different values of target to database size ratio. The result
shows that the range of the new damping parameter as a function of the target
to database size ratio increases as the number of iterations is increased.
Furthermore, application of the new damping parameter per iteration on the
damped quantum search scheme shows a significant improvement on some target to
database size ratio (i.e. greater than or equal to 50% maximum percentage
difference) over the critically damped quantum search.",1208.5475v1
2013-04-03,Damping the zero-point energy of a harmonic oscillator,"The physics of quantum electromagnetism in an absorbing medium is that of a
field of damped harmonic oscillators. Yet until recently the damped harmonic
oscillator was not treated with the same kind of formalism used to describe
quantum electrodynamics in a arbitrary medium. Here we use the techniques of
macroscopic QED, based on the Huttner--Barnett reservoir, to describe the
quantum mechanics of a damped oscillator. We calculate the thermal and
zero-point energy of the oscillator for a range of damping values from zero to
infinity. While both the thermal and zero-point energies decrease with damping,
the energy stored in the oscillator at fixed temperature increases with
damping, an effect that may be experimentally observable. As the results follow
from canonical quantization, the uncertainty principle is valid for all damping
levels.",1304.0977v2
2015-05-28,Damping factors for head-tail modes at strong space charge,"This paper suggests how feedback and Landau damping can be taken into account
for transverse oscillations of bunched beam at strong space charge.",1505.07704v1
2015-06-18,Damping of MHD turbulence in partially ionized plasma: implications for cosmic ray propagation,"We study the damping from neutral-ion collisions of both incompressible and
compressible magnetohydrodynamic (MHD) turbulence in partially ionized medium.
We start from the linear analysis of MHD waves applying both single-fluid and
two-fluid treatments. The damping rates derived from the linear analysis are
then used in determining the damping scales of MHD turbulence. The physical
connection between the damping scale of MHD turbulence and cutoff boundary of
linear MHD waves is investigated. Our analytical results are shown to be
applicable in a variety of partially ionized interstellar medium (ISM) phases
and solar chromosphere. As a significant astrophysical utility, we introduce
damping effects to propagation of cosmic rays in partially ionized ISM. The
important role of turbulence damping in both transit-time damping and
gyroresonance is identified.",1506.05585v1
2016-02-04,Damping Evaluation for Free Vibration of Spherical Structures in Elastodynamic-Acoustic Interaction,"This paper discusses the free vibration of elastic spherical structures in
the presence of an externally unbounded acoustic medium. In this vibration,
damping associated with the radiation of energy from the confined solid medium
to the surrounding acoustic medium is observed. Evaluating the coupled system
response (solid displacement and acoustic pressure) and characterizing the
acoustic radiation damping in conjunction with the media properties are the
main objectives of this research. In this work, acoustic damping is
demonstrated for two problems: the thin spherical shell and the solid sphere.
The mathematical approach followed in solving these coupled problems is based
on the Laplace transform method. The linear under-damped harmonic oscillator is
the reference model for damping estimation. The damping evaluation is performed
in frequency as well as in time domains; both investigations lead to identical
damping factor expressions.",1604.06738v1
2017-09-05,Enhancement of space-charge induced damping due to reactive impedances for head-tail modes,"Landau damping of head-tail modes in bunches due to spreads in the tune shift
can be a deciding factor for beam stability. We demonstrate that the coherent
tune shifts due to reactive impedances can enhance the space-charge induced
damping and change the stability thresholds (here, a reactive impedance implies
the imaginary part of the impedance of both signs). For example, high damping
rates at strong space-charge, or damping of the $k=0$ mode, can be possible. It
is shown and explained, how the negative reactive impedances (causing negative
coherent tune shifts similarly to the effect of space-charge) can enhance the
Landau damping, while the positive coherent tune shifts have an opposite
effect. It is shown that the damping rate is a function of the coherent mode
position in the incoherent spectrum, in accordance with the concept of the
interaction of a collective mode with resonant particles. We present an
analytical model, which allows for quantitative predictions of damping
thresholds for different head-tail modes, for arbitrary space-charge and
coherent tune-shift conditions, as it is verified using particle tracking
simulations.",1709.01425v1
2018-05-21,Critical damping in nonviscously damped linear systems,"In structural dynamics, energy dissipative mechanisms with non-viscous
damping are characterized by their dependence on the time-history of the
response velocity, mathematically represented by convolution integrals
involving hereditary functions. Combination of damping parameters in the
dissipative model can lead the system to be overdamped in some (or all) modes.
In the domain of the damping parameters, the thresholds between induced
oscillatory and non--oscillatory motion are called critical damping surfaces
(or manifolds, since we can have a lot of parameters). In this paper a general
method to obtain critical damping surfaces for nonviscously damped systems is
proposed. The approach is based on transforming the algebraic equations which
defined implicitly the critical curves into a system of differential equations.
The derivations are validated with three numerical methods covering single and
multiple degree of freedom systems.",1805.08022v1
2018-11-01,Hereditary effects of exponentially damped oscillators with past histories,"Hereditary effects of exponentially damped oscillators with past histories
are considered in this paper. Nonviscously damped oscillators involve
hereditary damping forces which depend on time-histories of vibrating motions
via convolution integrals over exponentially decaying functions. As a result,
this kind of oscillators are said to have memory. In this work, initialization
for nonviscously damped oscillators is firstly proposed. Unlike the classical
viscously damped ones, information of the past history of response velocity is
necessary to fully determine the dynamic behaviors of nonviscously damped
oscillators. Then, initialization response of exponentially damped oscillators
is obtained to characterize the hereditary effects on the dynamic response. At
last, stability of initialization response is proved and the hereditary effects
are shown to gradually recede with increasing of time.",1811.00216v1
2019-08-01,The Temperature-dependent Damping of Propagating Slow Magnetoacoustic Waves,"The rapid damping of slow magnetoacoustic waves in the solar corona has been
extensively studied in previous years. Most studies suggest that thermal
conduction is a dominant contributor to this damping, albeit with a few
exceptions. Employing extreme-ultraviolet (EUV) imaging data from SDO/AIA, we
measure the damping lengths of propagating slow magnetoacoustic waves observed
in several fan-like loop structures using two independent methods. The
dependence of the damping length on temperature has been studied for the first
time. The results do not indicate any apparent decrease in damping length with
temperature, which is in contrast to the existing viewpoint. Comparing with the
corresponding theoretical values calculated from damping due to thermal
conduction, it is inferred that thermal conduction is suppressed in hotter
loops. An alternative interpretation that suggests thermal conduction is not
the dominant damping mechanism, even for short period waves in warm active
region loops, is also presented.",1908.00384v1
2019-10-14,Decay rates for the damped wave equation with finite regularity damping,"Decay rates for the energy of solutions of the damped wave equation on the
torus are studied. In particular, damping invariant in one direction and equal
to a sum of squares of nonnegative functions with a particular number of
derivatives of regularity is considered. For such damping energy decays at rate
$1/t^{2/3}$. If additional regularity is assumed the decay rate improves. When
such a damping is smooth the energy decays at $1/t^{4/5-\delta}$. The proof
uses a positive commutator argument and relies on a pseudodifferential calculus
for low regularity symbols.",1910.06372v3
2022-07-01,Seismic Response of Yielding Structures Coupled to Rocking Walls with Supplemental Damping,"Given that the coupling of a framing structure to a strong, rocking wall
enforces a first-mode response, this paper investigates the dynamic response of
a yielding single-degree-of-freedom oscillator coupled to a rocking wall with
supplemental damping (hysteretic or linear viscous) along its sides. The full
nonlinear equations of motion are derived, and the study presents an earthquake
response analysis in term of inelastic spectra. The study shows that for
structures with preyielding period T1<1.0 s the effect of supplemental damping
along the sides of the rocking wall is marginal even when large values of
damping are used. The study uncovers that occasionally the damped response
matches or exceeds the undamped response; however, when this happens, the
exceedance is marginal. The paper concludes that for yielding structures with
strength less than 10% of their weight the use of supplemental damping along
the sides of a rocking wall coupled to a yielding structure is not recommended.
The paper shows that supplemental damping along the sides of the rocking wall
may have some limited beneficial effects for structures with longer preyielding
periods (say T1>1.0 s). Nevertheless, no notable further response reduction is
observed when larger values of hysteretic or viscous damping are used.",2207.00641v1
2023-03-08,Material-Geometry Interplay in Damping of Biomimetic Scale Beams,"Biomimetic scale-covered substrates are architected meta-structures
exhibiting fascinating emergent nonlinearities via the geometry of collective
scales contacts. In spite of much progress in understanding their elastic
nonlinearity, their dissipative behavior arising from scales sliding is
relatively uninvestigated in the dynamic regime. Recently discovered is the
phenomena of viscous emergence, where dry Coulomb friction between scales can
lead to apparent viscous damping behavior of the overall multi-material
substrate. In contrast to this structural dissipation, material dissipation
common in many polymers has never been considered, especially synergestically
with geometrical factors. This is addressed here for the first time, where
material visco-elasticity is introduced via a simple Kelvin-Voigt model for
brevity and clarity. The results contrast the two damping sources in these
architectured systems: material viscoelasticity, and geometrical frictional
scales contact. It is discovered that although topically similar in effective
damping, viscoelsatic damping follows a different damping envelope than dry
friction, including starkly different effects on damping symmetry and specific
damping capacity.",2303.04920v1
1998-03-28,Landau damping and the echo effect in a confined Bose-Einstein condensate,"Low energy collective mode of a confined Bose-Einstein condensate should
demonstrate the echo effect in the regime of Landau damping. This echo is a
signature of reversible nature of Landau damping. General expression for the
echo profile is derived in the limit of small amplitudes of the external
pulses. Several universal features of the echo are found. The existence of echo
in other cases of reversible damping -- Fano effect and Caldeira-Leggett model
-- is emphasized. It is suggested to test reversible nature of the damping in
the atomic traps by conducting the echo experiment.",9803351v1
2000-07-10,Dephasing of Electrons on Helium by Collisions with Gas Atoms,"The damping of quantum effects in the transport properties of electrons
deposited on a surface of liquid helium is studied. It is found that due to
vertical motion of the helium vapour atoms the interference of paths of
duration $t$ is damped by a factor $\exp - (t/\tau_v)^3$. An expression is
derived for the weak-localization lineshape in the case that damping occurs by
a combination of processes with this type of cubic exponential damping and
processes with a simple exponential damping factor.",0007160v1
1997-10-07,Damping rate of plasmons and photons in a degenerate nonrelativistic plasma,"A calculation is presented of the plasmon and photon damping rates in a dense
nonrelativistic plasma at zero temperature, following the resummation program
of Braaten-Pisarski. At small soft momentum $k$, the damping is dominated by $3
\to 2$ scattering processes corresponding to double longitudinal Landau
damping. The dampings are proportional to $(\alpha/v_{F})^{3/2} k^2/m$, where
$v_{F}$ is the Fermi velocity.",9710260v1
2002-12-16,Influence of damping on the vanishing of the electro-optic effect in chiral isotropic media,"Using first principles, it is demonstrated that radiative damping alone
cannot lead to a nonvanishing electro-optic effect in a chiral isotropic
medium. This conclusion is in contrast with that obtained by a calculation in
which damping effects are included using the standard phenomenological model.
We show that these predictions differ because the phenomenological damping
equations are valid only in regions where the frequencies of the applied
electromagnetic fields are nearly resonant with the atomic transitions. We also
show that collisional damping can lead to a nonvanishing electrooptic effect,
but with a strength sufficiently weak that it is unlikely to be observable
under realistic laboratory conditions.",0212089v1
2005-08-28,Simultaneous amplitude and phase damping of a kind of Gaussian states and their separability,"We give out the time evolution solution of simultaneous amplitude and phase
damping for any continuous variable state. For the simultaneous amplitude and
phase damping of a wide class of two- mode entangled Gaussian states, two
analytical conditions of the separability are given. One is the sufficient
condition of separability. The other is the condition of PPT separability where
the Peres-Horodecki criterion is applied. Between the two conditions there may
exist bound entanglement. The simplest example is the simultaneous amplitude
and phase damping of a two-mode squeezed vacuum state. The damped state is
non-Gaussian.",0508209v2
2007-05-14,"Identification of the dominant precession damping mechanism in Fe, Co, and Ni by first-principles calculations","The Landau-Lifshitz equation reliably describes magnetization dynamics using
a phenomenological treatment of damping. This paper presents first-principles
calculations of the damping parameters for Fe, Co, and Ni that quantitatively
agree with existing ferromagnetic resonance measurements. This agreement
establishes the dominant damping mechanism for these systems and takes a
significant step toward predicting and tailoring the damping constants of new
materials.",0705.1990v1
2007-08-28,Ising Dynamics with Damping,"We show for the Ising model that is possible construct a discrete time
stochastic model analogous to the Langevin equation that incorporates an
arbitrary amount of damping. It is shown to give the correct equilibrium
statistics and is then used to investigate nonequilibrium phenomena, in
particular, magnetic avalanches. The value of damping can greatly alter the
shape of hysteresis loops, and for small damping and high disorder, the
morphology of large avalanches can be drastically effected. Small damping also
alters the size distribution of avalanches at criticality.",0708.3855v1
2008-02-08,On the scaling of the damping time for resonantly damped oscillations in coronal loops,"There is not as yet full agreement on the mechanism that causes the rapid
damping of the oscillations observed by TRACE in coronal loops. It has been
suggested that the variation of the observed values of the damping time as
function of the corresponding observed values of the period contains
information on the possible damping mechanism. The aim of this Letter is to
show that, for resonant absorption, this is definitely not the case unless
detailed a priori information on the individual loops is available.",0802.1143v1
2008-10-02,Critically damped quantum search,"Although measurement and unitary processes can accomplish any quantum
evolution in principle, thinking in terms of dissipation and damping can be
powerful. We propose a modification of Grover's algorithm in which the idea of
damping plays a natural role. Remarkably, we have found that there is a
critical damping value that divides between the quantum $O(\sqrt{N})$ and
classical O(N) search regimes. In addition, by allowing the damping to vary in
a fashion we describe, one obtains a fixed-point quantum search algorithm in
which ignorance of the number of targets increases the number of oracle queries
only by a factor of 1.5.",0810.0470v1
2009-07-01,Modal approximations to damped linear systems,"We consider a finite dimensional damped second order system and obtain
spectral inclusion theorems for the related quadratic eigenvalue problem. The
inclusion sets are the 'quasi Cassini ovals' which may greatly outperform
standard Gershgorin circles. As the unperturbed system we take a modally damped
part of the system; this includes the known proportionally damped models, but
may give much sharper estimates. These inclusions are then applied to derive
some easily calculable sufficient conditions for the overdampedness of a given
damped system.",0907.0167v1
2010-01-14,Multi-Error-Correcting Amplitude Damping Codes,"We construct new families of multi-error-correcting quantum codes for the
amplitude damping channel. Our key observation is that, with proper encoding,
two uses of the amplitude damping channel simulate a quantum erasure channel.
This allows us to use concatenated codes with quantum erasure-correcting codes
as outer codes for correcting multiple amplitude damping errors. Our new codes
are degenerate stabilizer codes and have parameters which are better than the
amplitude damping codes obtained by any previously known construction.",1001.2356v1
2011-09-05,Spectral theory of damped quantum chaotic systems,"We investigate the spectral distribution of the damped wave equation on a
compact Riemannian manifold, especially in the case of a metric of negative
curvature, for which the geodesic flow is Anosov. The main application is to
obtain conditions (in terms of the geodesic flow on $X$ and the damping
function) for which the energy of the waves decays exponentially fast, at least
for smooth enough initial data. We review various estimates for the high
frequency spectrum in terms of dynamically defined quantities, like the value
distribution of the time-averaged damping. We also present a new condition for
a spectral gap, depending on the set of minimally damped trajectories.",1109.0930v1
2012-06-07,From resolvent estimates to damped waves,"In this paper we show how to obtain decay estimates for the damped wave
equation on a compact manifold without geometric control via knowledge of the
dynamics near the un-damped set. We show that if replacing the damping term
with a higher-order \emph{complex absorbing potential} gives an operator
enjoying polynomial resolvent bounds on the real axis, then the ""resolvent""
associated to our damped problem enjoys bounds of the same order. It is known
that the necessary estimates with complex absorbing potential can also be
obtained via gluing from estimates for corresponding non-compact models.",1206.1565v1
2012-12-03,Inviscid limit of stochastic damped 2D Navier-Stokes equations,"We consider the inviscid limit of the stochastic damped 2D Navier- Stokes
equations. We prove that, when the viscosity vanishes, the stationary solution
of the stochastic damped Navier-Stokes equations converges to a stationary
solution of the stochastic damped Euler equation and that the rate of
dissipation of enstrophy converges to zero. In particular, this limit obeys an
enstrophy balance. The rates are computed with respect to a limit measure of
the unique invariant measure of the stochastic damped Navier-Stokes equations.",1212.0509v3
2014-01-13,NLSE for quantum plasmas with the radiation damping,"We consider contribution of the radiation damping in the quantum hydrodynamic
equations for spinless particles. We discuss possibility of obtaining of
corresponding non-linear Schrodinger equation (NLSE) for the macroscopic wave
function. We compare contribution of the radiation damping with weakly (or
semi-) relativistic effects appearing in the second order by v/c. The radiation
damping appears in the third order by v/c. So it might be smaller than weakly
relativistic effects, but it gives damping of the Langmuir waves which can be
considerable.",1401.2829v1
2014-09-26,An ultimate storage ring lattice with vertical emittance generated by damping wigglers,"We discuss the approach of generating round beams for ultimate storage rings
using vertical damping wigglers (with horizontal magnetic field). The vertical
damping wigglers provide damping and excite vertical emittance. This eliminates
the need to generate large linear coupling that is impractical with traditional
off-axis injection. We use a PEP-X compatible lattice to demonstrate the
approach. This lattice uses separate quadrupole and sextupole magnets with
realistic gradient strengths. Intrabeam scattering effects are calculated. The
horizontal and vertical emittances are 22.3 pm and 10.3 pm, respectively, for a
200 mA, 4.5 GeV beam, with a vertical damping wiggler of a total length of 90
meters, peak field of 1.5 T and wiggler period of 100 mm.",1409.7452v2
2016-08-14,Mechanical energy and mean equivalent viscous damping for SDOF fractional oscillators,"This paper addresses the total mechanical energy of a single degree of
freedom fractional oscillator. Based on the energy storage and dissipation
properties of the Caputo fractional derivatives, the expression for total
mechanical energy in the single degree of freedom fractional oscillator is
firstly presented. The energy regeneration due to the external exciting force
and the energy loss due to the fractional damping force during the vibratory
motion are analyzed. Furthermore, based on the mean energy dissipation of the
fractional damping element in steady-state vibration, a new concept of mean
equivalent viscous damping is suggested and the value of the damping
coefficient is evaluated.",1608.04071v1
2017-03-01,Behaviors of the energy of solutions of two coupled wave equations with nonlinear damping on a compact manifold with boundary,"In this paper we study the behaviors of the the energy of solutions of
coupled wave equations on a compact manifold with boundary in the case of
indirect nonlinear damping . Only one of the two equations is directly damped
by a localized nonlinear damping term. Under geometric conditions on both the
coupling and the damping regions we prove that the rate of decay of the energy
of smooth solutions of the system is determined from a first order differential
equation .",1703.00172v1
2017-06-02,Vanishing viscosity limit for global attractors for the damped Navier--Stokes system with stress free boundary conditions,"We consider the damped and driven Navier--Stokes system with stress free
boundary conditions and the damped Euler system in a bounded domain
$\Omega\subset\mathbf{R}^2$. We show that the damped Euler system has a
(strong) global attractor in~$H^1(\Omega)$. We also show that in the vanishing
viscosity limit the global attractors of the Navier--Stokes system converge in
the non-symmetric Hausdorff distance in $H^1(\Omega)$ to the the strong global
attractor of the limiting damped Euler system (whose solutions are not
necessarily unique).",1706.00607v1
2018-01-20,Long time dynamics for weakly damped nonlinear Klein-Gordon equations,"We continue our study of damped nonlinear Klein-Gordon equations. In our
previous work we considered fixed positive damping and proved a form of the
soliton resolution conjecture for radial solutions. In contrast, here we
consider damping which decreases in time to 0. In the class of radial data we
again establish soliton resolution provided the damping goes to 0 sufficiently
slowly. While our previous work relied on invariant manifold theory, here we
use the Lojasiewicz-Simon inequality applied to a suitable Lyapunov functional.",1801.06735v1
2018-02-28,Nonexistence of global solutions of wave equations with weak time-dependent damping and combined nonlinearity,"In our previous two works, we studied the blow-up and lifespan estimates for
damped wave equations with a power nonlinearity of the solution or its
derivative, with scattering damping independently. In this work, we are devoted
to establishing a similar result for a combined nonlinearity. Comparing to the
result of wave equation without damping, one can say that the scattering
damping has no influence.",1802.10273v1
2018-11-12,Choking non-local magnetic damping in exchange biased ferromagnets,"We investigated the temperature dependence of the magnetic damping in the
exchange biased Pt/ Fe50Mn50 /Fe20Ni80 /SiOx multilayers. In samples having a
strong exchange bias, we observed a drastic decrease of the magnetic damping of
the FeNi with increasing temperature up to the blocking temperature. The
results essentially indicate that the non-local enhancement of the magnetic
damping can be choked by the adjacent antiferromagnet and its temperature
dependent exchange bias. We also pointed out that such a strong temperature
dependent damping may be very beneficial for spintronic applications.",1811.04821v1
2019-05-23,Escaping Locally Optimal Decentralized Control Polices via Damping,"We study the evolution of locally optimal decentralized controllers with the
damping of the control system. Empirically it is shown that even for instances
with an exponential number of connected components, damping merges all local
solutions to the one global solution. We characterize the evolution of locally
optimal solutions with the notion of hemi-continuity and further derive
asymptotic properties of the objective function and of the locally optimal
controllers as the damping becomes large. Especially, we prove that with enough
damping, there is no spurious locally optimal controller with favorable control
structures. The convoluted behavior of the locally optimal trajectory is
illustrated with numerical examples.",1905.09915v1
2019-08-22,Some remarks on the asymptotic profile of solutions to structurally damped $σ$-evolution equations,"In this paper, we are interested in analyzing the asymptotic profiles of
solutions to the Cauchy problem for linear structurally damped
$\sigma$-evolution equations in $L^2$-sense. Depending on the parameters
$\sigma$ and $\delta$ we would like to not only indicate approximation formula
of solutions but also recognize the optimality of their decay rates as well in
the distinct cases of parabolic like damping and $\sigma$-evolution like
damping. Moreover, such results are also discussed when we mix these two kinds
of damping terms in a $\sigma$-evolution equation to investigate how each of
them affects the asymptotic profile of solutions.",1908.08492v1
2019-09-18,Global smooth solutions of the damped Boussinesq equations with a class of large initial data,"The global regularity problem concerning the inviscid Boussinesq equations
remains an open problem. In an attempt to understand this problem, we examine
the damped Boussinesq equations and study how damping affects the regularity of
solutions. In this paper, we consider the global existence to the damped
Boussinesq equations with a class of large initial data, whose $B^{s}_{p,r}$ or
$\dot{B}^{s}_{p,r}$ norms can be arbitrarily large. The idea is splitting the
linear Boussinesq equations from the damped Boussinesq equations, the
exponentially decaying solution of the former equations together with the
structure of the Boussinesq equations help us to obtain the global smooth
solutions.",1909.08360v1
2020-02-15,Asymptotic profile and optimal decay of solutions of some wave equations with logarithmic damping,"We introduce a new model of the nonlocal wave equations with a logarithmic
damping mechanism. We consider the Cauchy poroblem for the new model in the
whole space. We study the asymptotic profile and optimal decay and blowup rates
of solutions as time goes to infinity. The damping terms considered in this
paper is not studied so far, and in the low frequency parameters the damping is
rather weakly effective than that of well-studied fractional type of nonlocal
damping. In order to get the optimal estimates in time we meet the so-called
hypergeometric functions with special parameters.",2002.06319v1
2020-05-13,Weak Input to state estimates for 2D damped wave equations with localized and non-linear damping,"In this paper, we study input-to-state (ISS) issues for damped wave equations
with Dirichlet boundary conditions on a bounded domain of dimension two. The
damping term is assumed to be non-linear and localized to an open subset of the
domain. In a first step, we handle the undisturbed case as an extension of a
previous work, where stability results are given with a damping term active on
the full domain. Then, we address the case with disturbances and provide
input-to-state types of results.",2005.06206v3
2020-07-25,Decay for the Kelvin-Voigt damped wave equation: Piecewise smooth damping,"We study the energy decay rate of the Kelvin-Voigt damped wave equation with
piecewise smooth damping on the multi-dimensional domain. Under suitable
geometric assumptions on the support of the damping, we obtain the optimal
polynomial decay rate which turns out to be different from the one-dimensional
case studied in \cite{LR05}. This optimal decay rate is saturated by high
energy quasi-modes localised on geometric optics rays which hit the interface
along non orthogonal neither tangential directions. The proof uses
semi-classical analysis of boundary value problems.",2007.12994v2
2020-08-12,From Lieb-Thirring inequalities to spectral enclosures for the damped wave equation,"Using a correspondence between the spectrum of the damped wave equation and
non-self-adjoint Schroedinger operators, we derive various bounds on complex
eigenvalues of the former. In particular, we establish a sharp result that the
one-dimensional damped wave operator is similar to the undamped one provided
that the L^1 norm of the (possibly complex-valued) damping is less than 2. It
follows that these small dampings are spectrally undetectable.",2008.05176v1
2021-08-02,Wide-Area Damping Control for Interarea Oscillations in Power Grids Based on PMU Measurements,"In this paper, a phasor measurement unit (PMU)-based wide-area damping
control method is proposed to damp the interarea oscillations that threaten the
modern power system stability and security. Utilizing the synchronized PMU
data, the proposed almost model-free approach can achieve an effective damping
for the selected modes using a minimum number of synchronous generators.
Simulations are performed to show the validity of the proposed wide-area
damping control scheme.",2108.01193v1
2021-09-05,Regularity of the semigroups associated with some damped coupled elastic systems II: a nondegenerate fractional damping case,"In this paper, we examine regularity issues for two damped abstract elastic
systems; the damping and coupling involve fractional powers $\mu, \theta$, with
$0 \leq \mu , \theta \leq 1$, of the principal operators. The matrix defining
the coupling and damping is nondegenerate. This new work is a sequel to the
degenerate case that we discussed recently in \cite{kfl}. First, we prove that
for $1/2 \leq \mu , \theta \leq 1$, the underlying semigroup is analytic. Next,
we show that for $\min(\mu,\theta) \in (0,1/2)$, the semigroup is of certain
Gevrey classes. Finally, some examples of application are provided.",2109.02044v1
2021-09-28,A robust and efficient line search for self-consistent field iterations,"We propose a novel adaptive damping algorithm for the self-consistent field
(SCF) iterations of Kohn-Sham density-functional theory, using a backtracking
line search to automatically adjust the damping in each SCF step. This line
search is based on a theoretically sound, accurate and inexpensive model for
the energy as a function of the damping parameter. In contrast to usual damped
SCF schemes, the resulting algorithm is fully automatic and does not require
the user to select a damping. We successfully apply it to a wide range of
challenging systems, including elongated supercells, surfaces and
transition-metal alloys.",2109.14018v3
2021-11-17,Spectral asymptotics for the vectorial damped wave equation,"The eigenfrequencies associated to a scalar damped wave equation are known to
belong to a band parallel to the real axis. In [Sj{\""o}00] J. Sj{\""o}strand
showed that up to a set of density 0, the eigenfrequencies are confined in a
thinner band determined by the Birkhoff limits of the damping term. In this
article we show that this result is still true for a vectorial damped wave
equation. In this setting the Lyapunov exponents of the cocycle given by the
damping term play the role of the Birkhoff limits of the scalar setting.",2111.08982v1
2021-12-13,Rotons and their damping in elongated dipolar Bose-Einstein condensates,"We discuss finite temperature damping of rotons in elongated Bose-condensed
dipolar gases, which are in the Thomas-Fermi regime in the tightly confined
directions. The presence of many branches of excitations which can participate
in the damping process, is crucial for the Landau damping and results in
significant increase of the damping rate. It is found, however, that even
rotons with energies close to the roton gap may remain fairly stable in systems
with the roton gap as small as 1nK.",2112.06835v2
2022-03-03,Stability results of locally coupled wave equations with local Kelvin-Voigt damping: Cases when the supports of damping and coupling coefficients are disjoint,"In this paper, we study the direct/indirect stability of locally coupled wave
equations with local Kelvin-Voigt dampings/damping and by assuming that the
supports of the dampings and the coupling coefficients are disjoint. First, we
prove the well-posedness, strong stability, and polynomial stability for some
one dimensional coupled systems. Moreover, under some geometric control
condition, we prove the well-posedness and strong stability in the
multi-dimensional case.",2203.01632v1
2022-03-12,Asymptotic expansion of solutions to the wave equation with space-dependent damping,"We study the large time behavior of solutions to the wave equation with
space-dependent damping in an exterior domain. We show that if the damping is
effective, then the solution is asymptotically expanded in terms of solutions
of corresponding parabolic equations. The main idea to obtain the asymptotic
expansion is the decomposition of the solution of the damped wave equation into
the solution of the corresponding parabolic problem and the time derivative of
the solution of the damped wave equation with certain inhomogeneous term and
initial data. The estimate of the remainder term is an application of weighted
energy method with suitable supersolutions of the corresponding parabolic
problem.",2203.06360v1
2022-10-27,Sharp polynomial decay for polynomially singular damping on the torus,"We study energy decay rates for the damped wave equation with unbounded
damping, without the geometric control condition. Our main decay result is
sharp polynomial energy decay for polynomially controlled singular damping on
the torus. We also prove that for normally $L^p$-damping on compact manifolds,
the Schr\""odinger observability gives $p$-dependent polynomial decay, and
finite time extinction cannot occur. We show that polynomially controlled
singular damping on the circle gives exponential decay.",2210.15697v3
2023-09-26,Qualitative properties of solutions to a nonlinear transmission problem for an elastic Bresse beam,"We consider a nonlinear transmission problem for a Bresse beam, which
consists of two parts, damped and undamped. The mechanical damping in the
damped part is present in the shear angle equation only, and the damped part
may be of arbitrary positive length. We prove well-posedness of the
corresponding PDE system in energy space and establish existence of a regular
global attractor under certain conditions on nonlinearities and coefficients of
the damped part only. Moreover, we study singular limits of the problem when
$l\to 0$ or $l\to 0$ simultaneously with $k_i\to +\infty$ and perform numerical
modelling for these processes.",2309.15171v2
2023-09-27,Dispersion and damping of ion-acoustic waves in the plasma with a regularized kappa-distribution,"The dispersion and damping of ion-acoustic waves in the plasma with a
regularized kappa-distribution are studied. The generalized dispersion relation
and damping rate are derived, which both depend significantly on the parameters
alpha and kappa. The numerical analyses show that the wave frequency and the
damping rate of ion-acoustic waves in the plasma with the regularized
kappa-distribution are both generally less than those in the plasma with the
kappa-distribution, and if kappa is less than a value, the ion-acoustic waves
and their damping rate exist in the plasma with the regularized
kappa-distribution.",2309.15885v1
2023-11-16,Near-optimal Closed-loop Method via Lyapunov Damping for Convex Optimization,"We introduce an autonomous system with closed-loop damping for first-order
convex optimization. While, to this day, optimal rates of convergence are only
achieved by non-autonomous methods via open-loop damping (e.g., Nesterov's
algorithm), we show that our system is the first one featuring a closed-loop
damping while exhibiting a rate arbitrarily close to the optimal one. We do so
by coupling the damping and the speed of convergence of the system via a
well-chosen Lyapunov function. We then derive a practical first-order algorithm
called LYDIA by discretizing our system, and present numerical experiments
supporting our theoretical findings.",2311.10053v1
2024-02-05,Fractional damping induces resonant behavior in the Duffing oscillator,"The interaction between the fractional order parameter and the damping
parameter can play a relevant role for introducing different dynamical
behaviors in a physical system. Here, we study the Duffing oscillator with a
fractional damping term. Our findings show that for certain values of the
fractional order parameter, the damping parameter, and the forcing amplitude
high oscillations amplitude can be induced. This phenomenon is due to the
appearance of a resonance in the Duffing oscillator only when the damping term
is fractional.",2402.02940v1
2024-03-13,Impact of Decoherence on Average Correlation,"This article presents a comprehensive study of the impact of decoherence on
the average correlation for pure quantum states. We explore two primary
mechanisms of decoherence: phase damping and amplitude damping, each having
distinct effects on quantum systems. Phase damping, which describes the loss of
quantum coherence without energy loss, primarily affects the phase
relationships between the components of a quantum system while amplitude
damping involves energy dissipation and also affects the state's occupation
probabilities. We show that the average correlation follows a predictable
decaying pattern in both scenarios. Our analysis can be understood in the
context of quantum computing, by focusing on how phase damping influences the
entanglement and correlation between qubits, key factors in quantum
computational efficiency and error correction protocols.",2403.10551v1
1998-02-18,Damping rates of hot Giant Dipole Resonances,"The damping rate of hot giant dipole resonances (GDR) is investigated.
Besides Landau damping we consider collisions and density fluctuations as
contributions to the damping of GDR. Within the nonequilibrium Green's function
method we derive a non-Markovian kinetic equation. The linearization of the
latter one leads to complex dispersion relations. The complex solution provides
the centroid energy and the damping width of giant resonances. The experimental
damping widths are the full width half maximum (FWHM) and can be reproduced by
the full width of the structure function. Within simple finite size scaling we
give a relation between the minimal interaction strength which is required for
a collective oscillation and the clustersize. We investigate the damping of
giant dipole resonances within a Skyrme type of interaction. Different
collision integrals are compared with each other in order to incorporate
correlations. The inclusion of a conserving relaxation time approximation
allows to find the $T^2$-dependence of the damping rate with a temperature
known from the Fermi-liquid theory. However, memory effects turn out to be
essential for a proper treatment of the damping of collective modes. We derive
a Landau like formula for the one--particle relaxation time similar to the
damping of zero sound.",9802052v2
2015-12-11,Ultra-low magnetic damping of a metallic ferromagnet,"The phenomenology of magnetic damping is of critical importance for devices
that seek to exploit the electronic spin degree of freedom since damping
strongly affects the energy required and speed at which a device can operate.
However, theory has struggled to quantitatively predict the damping, even in
common ferromagnetic materials. This presents a challenge for a broad range of
applications in spintronics and spin-orbitronics that depend on materials and
structures with ultra-low damping. Such systems enable many experimental
investigations that further our theoretical understanding of numerous magnetic
phenomena such as damping and spin-transport mediated by chirality and the
Rashba effect. Despite this requirement, it is believed that achieving
ultra-low damping in metallic ferromagnets is limited due to the scattering of
magnons by the conduction electrons. However, we report on a binary alloy of Co
and Fe that overcomes this obstacle and exhibits a damping parameter
approaching 0.0001, which is comparable to values reported only for
ferrimagnetic insulators. We explain this phenomenon by a unique feature of the
bandstructure in this system: The density of states exhibits a sharp minimum at
the Fermi level at the same alloy concentration at which the minimum in the
magnetic damping is found. This discovery provides both a significant
fundamental understanding of damping mechanisms as well as a test of
theoretical predictions.",1512.03610v1
2020-05-12,Effective Viscous Damping Enables Morphological Computation in Legged Locomotion,"Muscle models and animal observations suggest that physical damping is
beneficial for stabilization. Still, only a few implementations of mechanical
damping exist in compliant robotic legged locomotion. It remains unclear how
physical damping can be exploited for locomotion tasks, while its advantages as
sensor-free, adaptive force- and negative work-producing actuators are
promising. In a simplified numerical leg model, we studied the energy
dissipation from viscous and Coulomb damping during vertical drops with
ground-level perturbations. A parallel spring-damper is engaged between
touch-down and mid-stance, and its damper auto-disengages during mid-stance and
takeoff. Our simulations indicate that an adjustable and viscous damper is
desired. In hardware we explored effective viscous damping and adjustability
and quantified the dissipated energy. We tested two mechanical, leg-mounted
damping mechanisms; a commercial hydraulic damper, and a custom-made pneumatic
damper. The pneumatic damper exploits a rolling diaphragm with an adjustable
orifice, minimizing Coulomb damping effects while permitting adjustable
resistance. Experimental results show that the leg-mounted, hydraulic damper
exhibits the most effective viscous damping. Adjusting the orifice setting did
not result in substantial changes of dissipated energy per drop, unlike
adjusting damping parameters in the numerical model. Consequently, we also
emphasize the importance of characterizing physical dampers during real legged
impacts to evaluate their effectiveness for compliant legged locomotion.",2005.05725v2
2022-02-10,Non-stationary Anderson acceleration with optimized damping,"Anderson acceleration (AA) has a long history of use and a strong recent
interest due to its potential ability to dramatically improve the linear
convergence of the fixed-point iteration. Most authors are simply using and
analyzing the stationary version of Anderson acceleration (sAA) with a constant
damping factor or without damping. Little attention has been paid to
nonstationary algorithms. However, damping can be useful and is sometimes
crucial for simulations in which the underlying fixed-point operator is not
globally contractive. The role of this damping factor has not been fully
understood. In the present work, we consider the non-stationary Anderson
acceleration algorithm with optimized damping (AAoptD) in each iteration to
further speed up linear and nonlinear iterations by applying one extra
inexpensive optimization. We analyze this procedure and develop an efficient
and inexpensive implementation scheme. We also show that, compared with the
stationary Anderson acceleration with fixed window size sAA(m), optimizing the
damping factors is related to dynamically packaging sAA(m) and sAA(1) in each
iteration (alternating window size $m$ is another direction of producing
non-stationary AA). Moreover, we show by extensive numerical experiments that
the proposed non-stationary Anderson acceleration with optimized damping
procedure often converges much faster than stationary AA with constant damping
or without damping.",2202.05295v1
2023-06-30,A finite element method to compute the damping rate of oscillating fluids inside microfluidic nozzles,"We introduce a finite element method for computing the damping rate of fluid
oscillations in nozzles of drop-on-demand (DoD) microfluidic devices. Accurate
knowledge of the damping rates for the least-damped oscillation modes following
droplet ejection is paramount for assessing jetting stability at higher jetting
frequencies, as ejection from a non-quiescent meniscus can result in deviations
from nominal droplet properties. Computational fluid dynamics (CFD) simulations
often struggle to accurately predict meniscus damping in the limit of low
viscosity and high surface tension. Moreover, their use in design loops aimed
at optimizing the nozzle geometry for stable jetting is slow and
computationally expensive. The faster alternative we adopt here is to compute
the damping rate directly from the eigenvalues of the linearized problem.
Starting from a variational formulation of the linearized governing equations,
we obtain a generalized eigenvalue problem for the oscillation modes, and
approximate its solutions with a finite element method that uses Taylor-Hood
elements. We solve the matrix eigenvalue problem with a sparse, parallelized
implementation of the Krylov-Schur algorithm. The spatial shape and temporal
evolution (angular frequency and damping rate) of the set of least-damped
oscillation modes are obtained in a matter of minutes, compared to days for a
CFD simulation. We verify that the method can reproduce an analytical benchmark
problem, and then determine numerical convergence rates on two examples with
axisymmetric geometry. We also prove that the method is free of spurious modes
with zero or positive damping rates. The method's ability to quickly generate
accurate estimates of fluid oscillation damping rates makes it suitable for
integration into design loops for prototyping microfluidic nozzles.",2307.00094v1
2023-07-05,Optimal damping of vibrating systems: dependence on initial conditions,"Common criteria used for measuring performance of vibrating systems have one
thing in common: they do not depend on initial conditions of the system. In
some cases it is assumed that the system has zero initial conditions, or some
kind of averaging is used to get rid of initial conditions. The aim of this
paper is to initiate rigorous study of the dependence of vibrating systems on
initial conditions in the setting of optimal damping problems. We show that,
based on the type of initial conditions, especially on the ratio of potential
and kinetic energy of the initial conditions, the vibrating system will have
quite different behavior and correspondingly the optimal damping coefficients
will be quite different. More precisely, for single degree of freedom systems
and the initial conditions with mostly potential energy, the optimal damping
coefficient will be in the under-damped regime, while in the case of the
predominant kinetic energy the optimal damping coefficient will be in the
over-damped regime. In fact, in the case of pure kinetic initial energy, the
optimal damping coefficient is $+\infty$! Qualitatively, we found the same
behavior in multi degree of freedom systems with mass proportional damping. We
also introduce a new method for determining the optimal damping of vibrating
systems, which takes into account the peculiarities of initial conditions and
the fact that, although in theory these systems asymptotically approach
equilibrium and never reach it exactly, in nature and in experiments they
effectively reach equilibrium in some finite time.",2307.02352v2
2024-01-18,Multithermal apparent damping of slow waves due to strands with a Gaussian temperature distribution,"Context. Slow waves in solar coronal loops are strongly damped. The current
theory of damping by thermal conduction cannot explain some observational
features.\n Aims. We investigate the propagation of slow waves in a coronal
loop built up from strands of different temperatures. \n Methods. We consider
the loop to have a multithermal, Gaussian temperature distribution. The
different propagation speeds in different strands lead to an multithermal
apparent damping of the wave, similar to observational phase mixing. We use an
analytical model to predict the damping length and propagation speed for the
slow waves, including in imaging with filter telescopes. \n Results. We compare
the damping length due to this multithermal apparent damping with damping due
to thermal conduction and find that the multithermal apparent damping is more
important for shorter period slow waves. We have found the influence of
instrument filters on the wave's propagation speed and damping. This allows us
to compare our analytical theory to forward models of numerical simulations. \n
Conclusions. We find that our analytical model matches the numerical
simulations very well. Moreover, we offer an outlook for using the slow wave
properties to infer the loop's thermal properties.",2401.09803v1
1996-06-07,Abundances at High Redshifts: the Chemical Enrichment History of Damped Lyman-alpha Galaxies,"Damped Lyman-alpha absorption systems found in the spectra of high redshift
quasars are believed to trace the interstellar gas in high redshift galaxies.
In this paper, we study the elemental abundances of C, N, O, Al, Si, S, Cr, Mn,
Fe, Ni, and Zn in a sample of 14 damped Lyman-alpha systems using high quality
echelle spectra of quasars obtained with the 10m Keck telescope. These
abundances are combined with similar measurements in the literature in order to
investigate the chemical evolution of damped Lyman-alpha galaxies in the
redshift range 0.7<z<4.4. Among the things investigated are: the metallicity
distribution of damped Lyman-alpha galaxy, its evolution with redshift (ie,
age-metallicity relation), the relative abundance patterns of the heavy metals
and implications for their nucleosynthetic origin, the effects of dust, the
nature of the star formation process in damped Lyman-alpha galaxies, and the
nature of damped Lyman-alpha galaxies themselves.",9606044v1
1998-07-17,Chaotic scattering on surfaces and collisional damping of collective modes,"The damping of hot giant dipole resonances is investigated. The contribution
of surface scattering is compared with the contribution from interparticle
collisions. A unified response function is presented which includes surface
damping as well as collisional damping. The surface damping enters the response
via the Lyapunov exponent and the collisional damping via the relaxation time.
The former is calculated for different shape deformations of quadrupole and
octupole type. The surface as well as the collisional contribution each
reproduce almost the experimental value, therefore we propose a proper
weighting between both contributions related to their relative occurrence due
to collision frequencies between particles and of particles with the surface.
We find that for low and high temperatures the collisional contribution
dominates whereas the surface damping is dominant around the temperatures
$\sqrt{3}/2\pi$ of the centroid energy.",9807185v4
2000-09-08,Probing High-Redshift Disks with Damped Lyman Alpha Systems,"Evidence is presented that the damped Lyman alpha absorption systems are the
high-redshift (z > 3) progenitors of galaxy disks. I discuss kinematic evidence
that the damped Lyman Alpha systems are rotating disks. I also discuss
implications of the lack of metal-poor damped Lyman alpha systems with line
width Delta v > 100 {\kms}. I then present new evidence stemming from
correlations between element-abundance ratios and [Fe/H], which connects damped
systems to the thick stellar disk of the Galaxy. I discuss the connections
between damped Lyman alpha systems and Lyman break galaxies, and how [CII] 158
micron emission from damped Lyman alpha systems discriminates among competing
theories of galaxy formation. ~",0009126v1
2006-09-10,Damping of Compressional MHD Waves In Quiescent Prominences and Prominence-Corona Transition Region (PCTR),"The effects of radiative losses due to Newtonian cooling and MHD turbulence
have been considered to examine the spatial damping of linear compressional
waves in quiescent prominences and prominence-corona transition region (PCTR).
The radiative losses give acceptable damping lengths for the slow mode wave for
the radiative relaxation time in the range (10-1000s). From prominence
seismology, the values of opacity and turbulent kinematic viscosity have been
inferred. It has been found that for a given value of radiative relaxation
time, the high frequency slow mode waves are highly damped. We have also
investigated the possible role of MHD turbulence in damping of MHD waves and
found a turbulent viscosity can re-produce the observed damping time and
damping length in prominences, especially in PCTR.",0609266v1
1997-10-14,Damping of low-energy excitations of a trapped Bose condensate at finite temperatures,"We present the theory of damping of low-energy excitations of a trapped Bose
condensate at finite temperatures, where the damping is provided by the
interaction of these excitations with the thermal excitations. We emphasize the
key role of stochastization in the behavior of the thermal excitations for
damping in non-spherical traps. The damping rates of the lowest excitations,
following from our theory, are in fair agreement with the data of recent JILA
and MIT experiments. The damping of quasiclassical excitations is determined by
the condensate boundary region, and the result for the damping rate is
drastically different from that in a spatially homogeneous gas.",9710128v3
2001-12-09,Soliton dynamics in damped and forced Boussinesq equations,"We investigate the dynamics of a lattice soliton on a monatomic chain in the
presence of damping and external forces. We consider Stokes and hydrodynamical
damping. In the quasi-continuum limit the discrete system leads to a damped and
forced Boussinesq equation. By using a multiple-scale perturbation expansion up
to second order in the framework of the quasi-continuum approach we derive a
general expression for the first-order velocity correction which improves
previous results. We compare the soliton position and shape predicted by the
theory with simulations carried out on the level of the monatomic chain system
as well as on the level of the quasi-continuum limit system. For this purpose
we restrict ourselves to specific examples, namely potentials with cubic and
quartic anharmonicities as well as the truncated Morse potential, without
taking into account external forces. For both types of damping we find a good
agreement with the numerical simulations both for the soliton position and for
the tail which appears at the rear of the soliton. Moreover we clarify why the
quasi-continuum approximation is better in the hydrodynamical damping case than
in the Stokes damping case.",0112148v1
2006-04-17,The Highly Damped Quasinormal Modes of $d$-dimensional Reissner-Nordstrom Black Holes in the Small Charge Limit,"We analyze in detail the highly damped quasinormal modes of $d$-dimensional
Reissner-Nordstr$\ddot{\rm{o}}$m black holes with small charge, paying
particular attention to the large but finite damping limit in which the
Schwarzschild results should be valid. In the infinite damping limit, we
confirm using different methods the results obtained previously in the
literature for higher dimensional Reissner-Nordstr$\ddot{\rm{o}}$m black holes.
Using a combination of analytic and numerical techniques we also calculate the
transition of the real part of the quasinormal mode frequency from the
Reissner-Nordstr$\ddot{\rm{o}}$m value for very large damping to the
Schwarzschild value of $\ln(3) T_{bh}$ for intermediate damping. The real
frequency does not interpolate smoothly between the two values. Instead there
is a critical value of the damping at which the topology of the
Stokes/anti-Stokes lines change, and the real part of the quasinormal mode
frequency dips to zero.",0604073v2
2005-02-16,Damping signatures in future neutrino oscillation experiments,"We discuss the phenomenology of damping signatures in the neutrino
oscillation probabilities, where either the oscillating terms or the
probabilities can be damped. This approach is a possibility for tests of
non-oscillation effects in future neutrino oscillation experiments, where we
mainly focus on reactor and long-baseline experiments. We extensively motivate
different damping signatures due to small corrections by neutrino decoherence,
neutrino decay, oscillations into sterile neutrinos, or other mechanisms, and
classify these signatures according to their energy (spectral) dependencies. We
demonstrate, at the example of short baseline reactor experiments, that damping
can severely alter the interpretation of results, e.g., it could fake a value
of $\sin(2\theta_{13})$ smaller than the one provided by Nature. In addition,
we demonstrate how a neutrino factory could constrain different damping models
with emphasis on how these different models could be distinguished, i.e., how
easily the actual non-oscillation effects could be identified. We find that the
damping models cluster in different categories, which can be much better
distinguished from each other than models within the same cluster.",0502147v2
1997-07-23,Riccati parameter modes from Newtonian free damping motion by supersymmetry,"We determine the class of damped modes \tilde{y} which are related to the
common free damping modes y by supersymmetry. They are obtained by employing
the factorization of Newton's differential equation of motion for the free
damped oscillator by means of the general solution of the corresponding Riccati
equation together with Witten's method of constructing the supersymmetric
partner operator. This procedure leads to one-parameter families of (transient)
modes for each of the three types of free damping, corresponding to a
particular type of %time-dependent angular frequency. %time-dependent,
antirestoring acceleration (adding up to the usual Hooke restoring
acceleration) of the form a(t)=\frac{2\gamma ^2}{(\gamma t+1)^{2}}\tilde{y},
where \gamma is the family parameter that has been chosen as the inverse of the
Riccati integration constant. In supersymmetric terms, they represent all those
one Riccati parameter damping modes having the same Newtonian free damping
partner mode",9707019v4
2000-08-22,Local and Fundamental Mode Coupler Damping of the Transverse Wakefield in RDDS1 Linacs,"In damping the wakefield generated by an electron beam traversing several
thousand X-band linacs in the NLC we utilise a Gaussian frequency distribution
of dipole modes to force the modes to deconstructively interfere, supplemented
with moderate damping achieved by coupling these modes to four attached
manifolds. Most of these modes are adequately damped by the manifolds. However,
the modes towards the high frequency end of the lower dipole band are not
adequately damped because the last few cells are, due to mechanical fabrication
requirements, not coupled to the manifolds. To mitigate this problem in the
present RDDS1 design, the output coupler for the accelerating mode has been
designed so as to also couple out those dipole modes which reach the output
coupler cell. In order to couple out both dipole mode polarizations, the output
coupler has four ports. We also report on the results of a study of the
benefits which can be achieved by supplementing manifold damping with local
damping for a limited number of cells at the downstream end of the structure.",0008211v1
2007-10-25,Damping of Condensate Oscillation of a Trapped Bose Gas in a One-Dimensional Optical Lattice at Finite Temperatures,"We study damping of a dipole oscillation in a Bose-Condensed gas in a
combined cigar-shaped harmonic trap and one-dimensional (1D) optical lattice
potential at finite temperatures. In order to include the effect of thermal
excitations in the radial direction, we derive a quasi-1D model of the
Gross-Pitaeavskii equation and the Bogoliubov equations. We use the Popov
approximation to calculate the temperature dependence of the condensate
fraction with varying lattice depth. We then calculate the Landau damping rate
of a dipole oscillation as a function of the lattice depth and temperature. The
damping rate increases with increasing lattice depth, which is consistent with
experimental observations. The magnitude of the damping rate is in reasonable
agreement with experimental data. We also find that the damping rate has a
strong temperature dependence, showing a sharp increase with increasing
temperature. Finally, we emphasize the importance of the radial thermal
excitations in both equilibrium properties and the Landau damping.",0710.4610v1
2008-01-03,Spin orbit precession damping in transition metal ferromagnets,"We provide a simple explanation, based on an effective field, for the
precession damping rate due to the spin-orbit interaction. Previous effective
field treatments of spin-orbit damping include only variations of the state
energies with respect to the magnetization direction, an effect referred to as
the breathing Fermi surface. Treating the interaction of the rotating spins
with the orbits as a perturbation, we include also changes in the state
populations in the effective field. In order to investigate the quantitative
differences between the damping rates of iron, cobalt, and nickel, we compute
the dependence of the damping rate on the density of states and the spin-orbit
parameter. There is a strong correlation between the density of states and the
damping rate. The intraband terms of the damping rate depend on the spin-orbit
parameter cubed while the interband terms are proportional to the spin-orbit
parameter squared. However, the spectrum of band gaps is also an important
quantity and does not appear to depend in a simple way on material parameters.",0801.0549v1
2009-02-03,Damping of filament thread oscillations: effect of the slow continuum,"Transverse oscillations of small amplitude are commonly seen in
high-resolution observations of filament threads, i.e. the fine-structures of
solar filaments/prominences, and are typically damped in a few periods. Kink
wave modes supported by the thread body offer a consistent explanation of these
observed oscillations. Among the proposed mechanisms to explain the kink mode
damping, resonant absorption in the Alfven continuum seems to be the most
efficient as it produces damping times of about 3 periods. However, for a
nonzero-beta plasma and typical prominence conditions, the kink mode is also
resonantly coupled to slow (or cusp) continuum modes, which could further
reduce the damping time. In this Letter, we explore for the first time both
analytically and numerically the effect of the slow continuum on the damping of
transverse thread oscillations. The thread model is composed of a homogeneous
and straight cylindrical plasma, an inhomogeneous transitional layer, and the
homogeneous coronal plasma. We find that the damping of the kink mode due to
the slow resonance is much less efficient than that due to the Alfven
resonance.",0902.0572v2
2010-11-23,Magnetohydrodynamic kink waves in two-dimensional non-uniform prominence threads,"We analyse the oscillatory properties of resonantly damped transverse kink
oscillations in two-dimensional prominence threads. The fine structures are
modelled as cylindrically symmetric magnetic flux tubes with a dense central
part with prominence plasma properties and an evacuated part, both surrounded
by coronal plasma. The equilibrium density is allowed to vary non-uniformly in
both the transverse and the longitudinal directions.We examine the influence of
longitudinal density structuring on periods, damping times, and damping rates
for transverse kink modes computed by numerically solving the linear resistive
magnetohydrodynamic (MHD) equations. The relevant parameters are the length of
the thread and the density in the evacuated part of the tube, two quantities
that are difficult to directly estimate from observations. We find that both of
them strongly influence the oscillatory periods and damping times, and to a
lesser extent the damping ratios. The analysis of the spatial distribution of
perturbations and of the energy flux into the resonances allows us to explain
the obtained damping times. Implications for prominence seismology, the physics
of resonantly damped kink modes in two-dimensional magnetic flux tubes, and the
heating of prominence plasmas are discussed.",1011.5175v2
2011-04-04,Plasmonic abilities of gold and silver spherical nanoantennas in terms of size dependent multipolar resonance frequencies and plasmon damping rates,"Absorbing and emitting optical properties of a spherical plasmonic
nanoantenna are described in terms of the size dependent resonance frequencies
and damping rates of the multipolar surface plasmons (SP). We provide the
plasmon size characteristics for gold and silver spherical particles up to the
large size retardation regime where the plasmon radiative damping is
significant. We underline the role of the radiation damping in comparison with
the energy dissipation damping in formation of receiving and transmitting
properties of a plasmonic particle. The size dependence of both: the multipolar
SP resonance frequencies and corresponding damping rates can be a convenient
tool in tailoring the characteristics of plasmonic nanoantennas for given
application. Such characteristics enable to control an operation frequency of a
plasmonic nanoantenna and to change the operation range from the spectrally
broad to spectrally narrow and vice versa. It is also possible to switch
between particle receiving (enhanced absorption) and emitting (enhanced
scattering) abilities. Changing the polarization geometry of observation it is
possible to effectively separate the dipole and the quadrupole plasmon
radiation from all the non-plasmonic contributions to the scattered light.
Keywords: surface plasmon (SP) resonance, plasmon damping rates, multipolar
plasmon",1104.0565v1
2011-11-16,Three-player quantum Kolkata restaurant problem under decoherence,"Effect of quantum decoherence in a three-player quantum Kolkata restaurant
problem is investigated using tripartite entangled qutrit states. Amplitude
damping, depolarizing, phase damping, trit-phase flip and phase flip channels
are considered to analyze the behaviour of players payoffs. It is seen that
Alice's payoff is heavily influenced by the amplitude damping channel as
compared to the depolarizing and flipping channels. However, for higher level
of decoherence, Alice's payoff is strongly affected by depolarizing noise.
Whereas the behaviour of phase damping channel is symmetrical around 50 %
decoherence. It is also seen that for maximum decoherence (p=1), the influence
of amplitude damping channel dominates over depolarizing and flipping channels.
Whereas, phase damping channel has no effect on the Alice's payoff. Therefore,
the problem becomes noiseless one at maximum decoherence in case of phase
damping channel. Furthermore, the Nash equilibrium of the problem does not
change under decoherence.",1111.3913v2
2012-07-27,The effect of non-uniform damping on flutter in axial flow and energy harvesting strategies,"The problem of energy harvesting from flutter instabilities in flexible
slender structures in axial flows is considered. In a recent study, we used a
reduced order theoretical model of such a system to demonstrate the feasibility
for harvesting energy from these structures. Following this preliminary study,
we now consider a continuous fluid-structure system. Energy harvesting is
modelled as strain-based damping and the slender structure under investigation
lies in a moderate fluid loading range, for which {the flexible structure} may
be destabilised by damping. The key goal of this work is to {analyse the effect
of damping distribution and intensity on the amount of energy harvested by the
system}. The numerical results {indeed} suggest that non-uniform damping
distributions may significantly improve the power harvesting capacity of the
system. For low damping levels, clustered dampers at the position of peak
curvature are shown to be optimal. Conversely for higher damping, harvesters
distributed over the whole structure are more effective.",1207.6484v1
2012-11-20,Damping rates of surface plasmons for particles of size from nano- to micrometers; reduction of the nonradiative decay,"Damping rates of multipolar, localized surface plasmons (SP) of gold and
silver nanospheres of radii up to $1000nm$ were found with the tools of
classical electrodynamics. The significant increase in damping rates followed
by noteworthy decrease for larger particles takes place along with substantial
red-shift of plasmon resonance frequencies as a function of particle size. We
also introduced interface damping into our modeling, which substantially
modifies the plasmon damping rates of smaller particles. We demonstrate
unexpected reduction of the multipolar SP damping rates in certain size ranges.
This effect can be explained by the suppression of the nonradiative decay
channel as a result of the lost competition with the radiative channel. We show
that experimental dipole damping rates [H. Baida, et al., Nano Lett. 9(10)
(2009) 3463, and C. S\""onnichsen, et al., Phys. Rev. Lett. 88 (2002) 077402],
and the resulting resonance quality factors can be described in a consistent
and straightforward way within our modeling extended to particle sizes still
unavailable experimentally.",1211.4781v1
2013-10-23,Landau damping in a collisionless dipolar Bose gas,"We present a theory for the Landau damping of low energy quasi-particles in a
collisionless, quasi-2D dipolar Bose gas and produce expressions for the
damping rate in uniform and non-uniform systems. Using simple energy-momentum
conservation arguments, we show that in the homogeneous system, the nature of
the low energy dispersion in a dipolar Bose gas severely inhibits Landau
damping of long wave-length excitations. For a gas with contact and dipolar
interactions, the damping rate for phonons tends to decrease with increasing
dipolar interactions; for strong dipole-dipole interactions, phonons are
virtually undamped over a broad range of temperature. The damping rate for
maxon-roton excitations is found to be significantly larger than the damping
rate for phonons.",1310.6386v1
2014-01-15,Damping of Terahertz Plasmons in Graphene Coupled with Surface Plasmons in Heavily-Doped Substrate,"Coupling of plasmons in graphene at terahert (THz) frequencies with surface
plasmons in a heavily-doped substrate is studied theoretically. We reveal that
a huge scattering rate may completely damp out the plasmons, so that proper
choices of material and geometrical parameters are essential to suppress the
coupling effect and to obtain the minimum damping rate in graphene. Even with
the doping concentration 10^{19} - 10^{20} cm^{-3} and the thickness of the
dielectric layer between graphene and the substrate 100 nm, which are typical
values in real graphene samples with a heavily-doped substrate, the increase in
the damping rate is not negligible in comparison with the
acoustic-phonon-limited damping rate. Dependence of the damping rate on
wavenumber, thicknesses of graphene-to-substrate and gate-to-graphene
separation, substrate doping concentration, and dielectric constants of
surrounding materials are investigated. It is shown that the damping rate can
be much reduced by the gate screening, which suppresses the field spread of the
graphene plasmons into the substrate.",1401.3396v1
2014-11-28,Non-equilibrium thermodynamics of damped Timoshenko and damped Bresse systems,"In this paper, we cast damped Timoshenko and damped Bresse systems into a
general framework for non-equilibrium thermodynamics, namely the GENERIC
(General Equation for Non-Equilibrium Reversible-Irreversible Coupling)
framework. The main ingredients of GENERIC consist of five building blocks: a
state space, a Poisson operator, a dissipative operator, an energy functional,
and an entropy functional. The GENERIC formulation of damped Timoshenko and
damped Bresse systems brings several benefits. First, it provides alternative
ways to derive thermodynamically consistent models of these systems by
construct- ing building blocks instead of invoking conservation laws and
constitutive relations. Second, it reveals clear physical and geometrical
structures of these systems, e.g., the role of the energy and the entropy as
the driving forces for the reversible and irreversible dynamics respectively.
Third, it allows us to introduce a new GENERIC model for damped Timoshenko
systems that is not existing in the literature.",1412.0038v2
2014-12-08,Bi-$\cal{PT}$ symmetry in nonlinearly damped dynamical systems and tailoring $\cal{PT}$ regions with position dependent loss-gain profiles,"We investigate the remarkable role of position dependent damping in
determining the parametric regions of symmetry breaking in nonlinear
$\cal{PT}$-symmetric systems. We illustrate the nature of $\cal{PT}$-symmetry
preservation and breaking with reference to a remarkable integrable scalar
nonlinear system. In the two dimensional cases of such position dependent
damped systems, we unveil the existence of a class of novel
bi-$\cal{PT}$-symmetric systems which have two fold $\cal{PT}$ symmetries. We
analyze the dynamics of these systems and show how symmetry breaking occurs,
that is whether the symmetry breaking of the two $\cal{PT}$ symmetries occurs
in pair or occurs one by one. The addition of linear damping in these
nonlinearly damped systems induces competition between the two types of
damping. This competition results in a $\cal{PT}$ phase transition in which the
$\cal{PT}$ symmetry is broken for lower loss/gain strength and is restored by
increasing the loss/gain strength. We also show that by properly designing the
form of the position dependent damping, we can tailor the $\cal{PT}$-symmetric
regions of the system.",1412.2574v3
2015-09-04,Damped transverse oscillations of interacting coronal loops,"Damped transverse oscillations of magnetic loops are routinely observed in
the solar corona. This phenomenon is interpreted as standing kink
magnetohydrodynamic waves, which are damped by resonant absorption owing to
plasma inhomogeneity across the magnetic field. The periods and damping times
of these oscillations can be used to probe the physical conditions of the
coronal medium. Some observations suggest that interaction between neighboring
oscillating loops in an active region may be important and can modify the
properties of the oscillations compared to those of an isolated loop. Here we
theoretically investigate resonantly damped transverse oscillations of
interacting non-uniform coronal loops. We provide a semi-analytic method, based
on the T-matrix theory of scattering, to compute the frequencies and damping
rates of collective oscillations of an arbitrary configuration of parallel
cylindrical loops. The effect of resonant damping is included in the T-matrix
scheme in the thin boundary approximation. Analytic and numerical results in
the specific case of two interacting loops are given as an application.",1509.01487v1
2015-09-14,Beliaev damping in quasi-2D dipolar condensates,"We study the effects of quasiparticle interactions in a quasi-two dimensional
(quasi-2D), zero-temperature Bose-Einstein condensate of dipolar atoms, which
can exhibit a roton-maxon feature in its quasiparticle spectrum. Our focus is
the Beliaev damping process, in which a quasiparticle collides with the
condensate and resonantly decays into a pair of quasiparticles. Remarkably, the
rate for this process exhibits a highly non-trivial dependence on the
quasiparticle momentum and the dipolar interaction strength. For weak
interactions, the low energy phonons experience no damping, and the higher
energy quasiparticles undergo anomalously weak damping. In contrast, the
Beliaev damping rates become anomalously large for stronger dipolar
interactions, as rotons become energetically accessible as final states.
Further, we find a qualitative anisotropy in the damping rates when the dipoles
are tilted off the axis of symmetry. Our study reveals the unconventional
nature of Beliaev damping in dipolar condensates, and has important
implications for ongoing studies of equilibrium and non-equilibrium dynamics in
these systems.",1509.04217v1
2015-12-08,Thermal energies of classical and quantum damped oscillators coupled to reservoirs,"We consider the global thermal state of classical and quantum harmonic
oscillators that interact with a reservoir. Ohmic damping of the oscillator can
be exactly treated with a 1D scalar field reservoir, whereas general non-Ohmic
damping is conveniently treated with a continuum reservoir of harmonic
oscillators. Using the diagonalized Hamiltonian of the total system, we
calculate a number of thermodynamic quantities for the damped oscillator: the
mean force internal energy, mean force free energy, and another internal energy
based on the free-oscillator Hamiltonian. The classical mean force energy is
equal to that of a free oscillator, for both Ohmic and non-Ohmic damping and no
matter how strong the coupling to the reservoir. In contrast, the quantum mean
force energy depends on the details of the damping and diverges for strictly
Ohmic damping. These results give additional insight into the steady-state
thermodynamics of open systems with arbitrarily strong coupling to a reservoir,
complementing results for energies derived within dynamical approaches (e.g.
master equations) in the weak-coupling regime.",1512.02551v2
2016-05-17,Simultaneous Identification of Damping Coefficient and Initial Value in PDEs from boundary measurement,"In this paper, the simultaneous identification of damping or anti-damping
coefficient and initial value for some PDEs is considered. An identification
algorithm is proposed based on the fact that the output of system happens to be
decomposed into a product of an exponential function and a periodic function.
The former contains information of the damping coefficient, while the latter
does not. The convergence and error analysis are also developed. Three
examples, namely an anti-stable wave equation with boundary anti-damping, the
Schr\""odinger equation with internal anti-damping, and two connected strings
with middle joint anti-damping, are investigated and demonstrated by numerical
simulations to show the effectiveness of the proposed algorithm.",1605.05063v1
2016-08-30,Optimal damping ratios of multi-axial perfectly matched layers for elastic-wave modeling in general anisotropic media,"The conventional Perfectly Matched Layer (PML) is unstable for certain kinds
of anisotropic media. This instability is intrinsic and independent of PML
formulation or implementation. The Multi-axial PML (MPML) removes such
instability using a nonzero damping coefficient in the direction parallel with
the interface between a PML and the investigated domain. The damping ratio of
MPML is the ratio between the damping coefficients along the directions
parallel with and perpendicular to the interface between a PML and the
investigated domain. No quantitative approach is available for obtaining these
damping ratios for general anisotropic media. We develop a quantitative
approach to determining optimal damping ratios to not only stabilize PMLs, but
also minimize the artificial reflections from MPMLs. Numerical tests based on
finite-difference method show that our new method can effectively provide a set
of optimal MPML damping ratios for elastic-wave propagation in 2D and 3D
general anisotropic media.",1608.08326v3
2016-10-10,A Five-Freedom Active Damping and Alignment Device Used in the Joule Balance,"Damping devices are necessary for suppressing the undesired coil motions in
the watt/joule balance. In this paper, an active electromagnetic damping
device, located outside the main magnet, is introduced in the joule balance
project. The presented damping device can be used in both dynamic and static
measurement modes. With the feedback from a detection system, five degrees of
freedom of the coil, i.e. the horizontal displacement $x$, $y$ and the rotation
angles $\theta_x$, $\theta_y$, $\theta_z$, can be controlled by the active
damping device. Hence, two functions, i.e. suppressing the undesired coil
motions and reducing the misalignment error, can be realized with this active
damping device. The principle, construction and performance of the proposed
active damping device are presented.",1610.02799v1
2016-10-01,The destabilizing effect of external damping: Singular flutter boundary for the Pfluger column with vanishing external dissipation,"Elastic structures loaded by nonconservative positional forces are prone to
instabilities induced by dissipation: it is well-known in fact that internal
viscous damping destabilizes the marginally stable Ziegler's pendulum and
Pfluger column (of which the Beck's column is a special case), two structures
loaded by a tangential follower force. The result is the so-called
'destabilization paradox', where the critical force for flutter instability
decreases by an order of magnitude when the coefficient of internal damping
becomes infinitesimally small. Until now external damping, such as that related
to air drag, is believed to provide only a stabilizing effect, as one would
intuitively expect. Contrary to this belief, it will be shown that the effect
of external damping is qualitatively the same as the effect of internal
damping, yielding a pronounced destabilization paradox. Previous results
relative to destabilization by external damping of the Ziegler's and Pfluger's
elastic structures are corrected in a definitive way leading to a new
understanding of the destabilizating role played by viscous terms.",1611.03886v1
2017-10-10,A four-field gyrofluid model with neoclassical effects for the study of the rotation velocity of magnetic islands in tokamaks,"A four-field system of equations which includes the neoclassical flow damping
effects and the lowest-order finite-Larmor-radius (FLR) corrections is deduced
from a system of gyrofluid equations. The FLR corrections to the poloidal flow
damping are calculated by solving a simplified version of the gyrokinetic
equation. This system of equations is applied to the study of a chain of freely
rotating magnetic islands in a tokamak, resulting from the nonlinear evolution
of a resistive tearing mode, to determine the islands rotation velocity
consistently with the fields radial profiles close to the resonant surface. The
island rotation velocity is determined by imposing the torque-balance
condition. The equations thus deduced are applied to the study of two different
collisional regimes, namely the weak-damping regime and the intermediate
damping regime. The equations reduce, in the weak damping regime, to a form
already obtained in previous works, while an additional term, containing the
lowest order FLR corrections to the poloidal flow damping, appears in the
intermediate damping regime. The numerical integration of the final system of
equations permits to determine the dependence of the island rotation velocity
on the plasma collisionality and the islands width compared to the ion Larmor
radius.",1710.03585v1
2017-10-13,Mode-Dependent Damping in Metallic Antiferromagnets Due to Inter-Sublattice Spin Pumping,"Damping in magnetization dynamics characterizes the dissipation of magnetic
energy and is essential for improving the performance of spintronics-based
devices. While the damping of ferromagnets has been well studied and can be
artificially controlled in practice, the damping parameters of
antiferromagnetic materials are nevertheless little known for their physical
mechanisms or numerical values. Here we calculate the damping parameters in
antiferromagnetic dynamics using the generalized scattering theory of
magnetization dissipation combined with the first-principles transport
computation. For the PtMn, IrMn, PdMn and FeMn metallic antiferromagnets, the
damping coefficient associated with the motion of magnetization ($\alpha_m$) is
one to three orders of magnitude larger than the other damping coefficient
associated with the variation of the N\'eel order ($\alpha_n$), in sharp
contrast to the assumptions made in the literature.",1710.04766v1
2017-12-04,Resonance oscillation of a damped driven simple pendulum,"The resonance characteristics of a driven damped harmonic oscillator are well
known. Unlike harmonic oscillators which are guided by parabolic potentials, a
simple pendulum oscillates under sinusoidal potentials. The problem of an
undamped pendulum has been investigated to a great extent. However, the
resonance characteristics of a driven damped pendulum have not been re- ported
so far due to the difficulty in solving the problem analytically. In the
present work we report the resonance characteristics of a driven damped
pendulum calculated numerically. The results are compared with the resonance
characteristics of a damped driven harmonic oscillator. The work can be of
pedagogic interest too as it reveals the richness of driven damped motion of a
simple pendulum in comparison to and how strikingly it differs from the motion
of a driven damped harmonic oscillator. We confine our work only to the
nonchaotic regime of pendulum motion.",1712.01032v1
2018-01-17,On Global Existence and Blow-up for Damped Stochastic Nonlinear Schrödinger Equation,"In this paper, we consider the well-posedness of the weakly damped stochastic
nonlinear Schr\""odinger(NLS) equation driven by multiplicative noise. First, we
show the global existence of the unique solution for the damped stochastic NLS
equation in critical case. Meanwhile, the exponential integrability of the
solution is proved, which implies the continuous dependence on the initial
data. Then, we analyze the effect of the damped term and noise on the blow-up
phenomenon. By modifying the associated energy, momentum and variance identity,
we deduce a sharp blow-up condition for damped stochastic NLS equation in
supercritical case. Moreover, we show that when the damped effect is large
enough, the damped effect can prevent the blow-up of the solution with high
probability.",1801.05630v1
2018-03-29,Giant resonant nonlinear damping in nanoscale ferromagnets,"Magnetic damping is a key metric for emerging technologies based on magnetic
nanoparticles, such as spin torque memory and high-resolution biomagnetic
imaging. Despite its importance, understanding of magnetic dissipation in
nanoscale ferromagnets remains elusive, and the damping is often treated as a
phenomenological constant. Here we report the discovery of a giant
frequency-dependent nonlinear damping that strongly alters the response of a
nanoscale ferromagnet to spin torque and microwave magnetic field. This novel
damping mechanism originates from three-magnon scattering that is strongly
enhanced by geometric confinement of magnons in the nanomagnet. We show that
the giant nonlinear damping can invert the effect of spin torque on a
nanomagnet leading to a surprising current-induced enhancement of damping by an
antidamping torque. Our work advances understanding of magnetic dynamics in
nanoscale ferromagnets and spin torque devices.",1803.10925v1
2018-05-16,Stabilization rates for the damped wave equation with Hölder-regular damping,"We study the decay rate of the energy of solutions to the damped wave
equation in a setup where the geometric control condition is violated. We
consider damping coefficients which are $0$ on a strip and vanish like
polynomials, $x^{\beta}$. We prove that the semigroup cannot be stable at rate
faster than $1/t^{(\beta+2)/(\beta+3)}$ by producing quasimodes of the
associated stationary damped wave equation. We also prove that the semigroup is
stable at rate at least as fast as $1/t^{(\beta+2)/(\beta+4)}$. These two
results establish an explicit relation between the rate of vanishing of the
damping and rate of decay of solutions. Our result partially generalizes a
decay result of Nonnemacher in which the damping is an indicator function on a
strip.",1805.06535v3
2019-03-01,Comprehensive Study of Neutrino-Dark Matter Mixed Damping,"Mixed damping is a physical effect that occurs when a heavy species is
coupled to a relativistic fluid which is itself free streaming. As a cross-case
between collisional damping and free-streaming, it is crucial in the context of
neutrino-dark matter interactions. In this work, we establish the parameter
space relevant for mixed damping, and we derive an analytical approximation for
the evolution of dark matter perturbations in the mixed damping regime to
illustrate the physical processes responsible for the suppression of
cosmological perturbations. Although extended Boltzmann codes implementing
neutrino-dark matter scattering terms automatically include mixed damping, this
effect has not been systematically studied. In order to obtain reliable
numerical results, it is mandatory to reconsider several aspects of
neutrino-dark matter interactions, such as the initial conditions, the
ultra-relativistic fluid approximation and high order multiple moments in the
neutrino distribution. Such a precise treatment ensures the correct assessment
of the relevance of mixed damping in neutrino-dark matter interactions.",1903.00540v2
2019-08-04,Efficient spin excitation via ultrafast damping-like torques in antiferromagnets,"Damping effects form the core of many emerging concepts for high-speed
spintronic applications. Important characteristics such as device switching
times and magnetic domain-wall velocities depend critically on the damping
rate. While the implications of spin damping for relaxation processes are
intensively studied, damping effects during impulsive spin excitations are
assumed to be negligible because of the shortness of the excitation process.
Herein, we show that, unlike in ferromagnets, ultrafast damping plays a crucial
role in antiferromagnets because of their strongly elliptical spin precession.
In time-resolved measurements, we find that ultrafast damping results in an
immediate spin canting along the short precession axis. The interplay between
antiferromagnetic exchange and magnetic anisotropy amplifies this canting by
several orders of magnitude towards large-amplitude modulations of the
antiferromagnetic order parameter. This leverage effect discloses a highly
efficient route towards the ultrafast manipulation of magnetism in
antiferromagnetic spintronics.",1908.01359v3
2019-10-31,Gyrokinetic investigation of the damping channels of Alfvén modes in ASDEX Upgrade,"The linear destabilization and nonlinear saturation of energetic-particle
driven Alfv\'enic instabilities in tokamaks strongly depend on the damping
channels. In this work, the collisionless damping mechanisms of Alfv\'enic
modes are investigated within a gyrokinetic framework, by means of global
simulations with the particle-in-cell code ORB5, and compared with the
eigenvalue code LIGKA and reduced models. In particular, the continuum damping
and the Landau damping (of ions and electrons) are considered. The electron
Landau damping is found to be dominant on the ion Landau damping for
experimentally relevant cases. As an application, the linear and nonlinear
dynamics of toroidicity induced Alfv\'en eigenmodes and energetic-particle
driven modes in ASDEX Upgrade is investigated theoretically and compared with
experimental measurements.",1910.14489v1
2020-03-13,Anharmonic phonon damping enhances the $T_c$ of BCS-type superconductors,"A theory of superconductivity is presented where the effect of anharmonicity,
as entailed in the acoustic, or optical, phonon damping, is explicitly
considered in the pairing mechanism. The gap equation is solved including
diffusive Akhiezer damping for longitudinal acoustic phonons or Klemens damping
for optical phonons, with a damping coefficient which, in either case, can be
directly related to the Gruneisen parameter and hence to the anharmonic
coefficients in the interatomic potential. The results show that the increase
of anharmonicity has a strikingly non-monotonic effect on the critical
temperature $T_{c}$. The optimal damping coefficient yielding maximum $T_c$ is
set by the velocity of the bosonic mediator. This theory may open up
unprecedented opportunities for material design where $T_{c}$ may be tuned via
the anharmonicity of the interatomic potential, and presents implications for
the superconductivity in the recently discovered hydrides, where anharmonicity
is very strong and for which the anharmonic damping is especially relevant.",2003.06220v2
2020-03-29,Stability results for an elastic-viscoelastic waves interaction systems with localized Kelvin-Voigt damping and with an internal or boundary time delay,"We investigate the stability of a one-dimensional wave equation with non
smooth localized internal viscoelastic damping of Kelvin-Voigt type and with
boundary or localized internal delay feedback. The main novelty in this paper
is that the Kelvin-Voigt and the delay damping are both localized via non
smooth coefficients. In the case that the Kelvin-Voigt damping is localized
faraway from the tip and the wave is subjected to a locally distributed
internal or boundary delay feedback, we prove that the energy of the system
decays polynomially of type t^{-4}. However, an exponential decay of the energy
of the system is established provided that the Kelvin-Voigt damping is
localized near a part of the boundary and a time delay damping acts on the
second boundary. While, when the Kelvin-Voigt and the internal delay damping
are both localized via non smooth coefficients near the tip, the energy of the
system decays polynomially of type t^{-4}. Frequency domain arguments combined
with piecewise multiplier techniques are employed.",2003.12967v1
2020-09-16,Fast convex optimization via inertial dynamics combining viscous and Hessian-driven damping with time rescaling,"In a Hilbert setting, we develop fast methods for convex unconstrained
optimization. We rely on the asymptotic behavior of an inertial system
combining geometric damping with temporal scaling. The convex function to
minimize enters the dynamic via its gradient. The dynamic includes three
coefficients varying with time, one is a viscous damping coefficient, the
second is attached to the Hessian-driven damping, the third is a time scaling
coefficient. We study the convergence rate of the values under general
conditions involving the damping and the time scale coefficients. The obtained
results are based on a new Lyapunov analysis and they encompass known results
on the subject. We pay particular attention to the case of an asymptotically
vanishing viscous damping, which is directly related to the accelerated
gradient method of Nesterov. The Hessian-driven damping significantly reduces
the oscillatory aspects. As a main result, we obtain an exponential rate of
convergence of values without assuming the strong convexity of the objective
function. The temporal discretization of these dynamics opens the gate to a
large class of inertial optimization algorithms.",2009.07620v1
2020-12-27,Quantum speed limit time in relativistic frame,"We investigate the roles of the relativistic effect on the speed of evolution
of a quantum system coupled with amplitude damping channels. We find that the
relativistic effect speed-up the quantum evolution to a uniform evolution speed
of open quantum systems for the damping parameter $p_{\tau}\lesssim
p_{\tau_{c0}}.$ Moreover, we point out a non-monotonic behavior of the quantum
speed limit time (QSLT) with acceleration in the damping limit
$p_{\tau_{c0}}\lesssim p_{\tau}\lesssim p_{\tau_{c1}},$ where the relativistic
effect first speed-up and then slow down the quantum evolution process of the
damped system. For the damping strength $p_{\tau_{c1}}\lesssim p_{\tau}$, we
observe a monotonic increasing behavior of QSLT, leads to slow down the quantum
evolution of the damped system. In addition, we examine the roles of the
relativistic effect on the speed limit time for a system coupled with the phase
damping channels.",2012.13859v2
2021-06-23,Regularization of central forces with damping in two and three-dimensions,"Regularization of damped motion under central forces in two and
three-dimensions are investigated and equivalent, undamped systems are
obtained. The dynamics of a particle moving in $\frac{1}{r}$ potential and
subjected to a damping force is shown to be regularized a la Levi-Civita. We
then generalize this regularization mapping to the case of damped motion in the
potential $r^{-\frac{2N}{N+1}}$. Further equation of motion of a damped Kepler
motion in 3-dimensions is mapped to an oscillator with inverted sextic
potential and couplings, in 4-dimensions using Kustaanheimo-Stiefel
regularization method. It is shown that the strength of the sextic potential is
given by the damping co-efficient of the Kepler motion. Using homogeneous
Hamiltonian formalism, we establish the mapping between the Hamiltonian of
these two models. Both in 2 and 3-dimensions, we show that the regularized
equation is non-linear, in contrast to undamped cases. Mapping of a particle
moving in a harmonic potential subjected to damping to an undamped system with
shifted frequency is then derived using Bohlin-Sudman transformation.",2106.12134v1
2021-07-06,Theory of vibrators with variable-order fractional forces,"In this paper, we present a theory of six classes of vibrators with
variable-order fractional forces of inertia, damping, and restoration. The
novelty and contributions of the present theory are reflected in six aspects.
1) Equivalent motion equations of those variable-order fractional vibrators are
proposed. 2) The analytical expressions of the effective mass, damping, and
stiffness of those variable-order fractional vibrators are presented. 3) The
asymptotic properties of the effective mass, damping, and stiffness of a class
of variable-order fractional vibrators are given. 4) The restricted effective
parameters (damping ratio, damping free natural frequency, damped natural
frequency, frequency ratio) of the variable-order fractional vibrators are put
forward. 5) We bring forward the analytical representations of the free
responses, the impulse responses, and the frequency transfer functions of those
variable-order fractional vibrators. 6) We propose a solution to an open
problem of how to mathematically explain the Rayleigh damping assumption based
on the present theory of variable-order fractional vibrations.",2107.02340v2
2021-08-15,Exponential stability of a damped beam-string-beam transmission problem,"We consider a beam-string-beam transmission problem, where two structurally
damped or undamped beams are coupled with a frictionally damped string by
transmission conditions. We show that for this type of structure, the
dissipation produced by the frictional part is strong enough to produce
exponential decay of the solution no matter how small is its size: for the
exponential stability in the damped-damped-damped situation we use energy
method and in the undamped-damped-undamped situation we use a frequency domain
method from the semigroups theory, which combines a contradiction argument with
the multiplier technique to carry out a special analysis for the resolvent.
Additionally, we show that the solution first defined by the weak formulation,
in fact, has higher Sobolev space regularity.",2108.06749v1
2021-09-10,Fourth-order dynamics of the damped harmonic oscillator,"It is shown that the classical damped harmonic oscillator belongs to the
family of fourth-order Pais-Uhlenbeck oscillators. It follows that the
solutions to the damped harmonic oscillator equation make the Pais-Uhlenbeck
action stationary. Two systematic approaches are given for deriving the
Pais-Uhlenbeck action from the damped harmonic oscillator equation, and it may
be possible to use these methods to identify stationary action principles for
other dissipative systems which do not conform to Hamilton's principle. It is
also shown that for every damped harmonic oscillator $x$, there exists a
two-parameter family of dual oscillators $y$ satisfying the Pais-Uhlenbeck
equation. The damped harmonic oscillator and any of its duals can be
interpreted as a system of two coupled oscillators with atypical spring
stiffnesses (not necessarily positive and real-valued). For overdamped systems,
the resulting coupled oscillators should be physically achievable and may have
engineering applications. Finally, a new physical interpretation is given for
the optimal damping ratio $\zeta=1/\sqrt{2}$ in control theory.",2109.06034v1
2022-01-13,Damping of Alfvén waves in MHD turbulence and implications for cosmic ray streaming instability and galactic winds,"Alfv\'{e}nic component of MHD turbulence damps Alfv\'{e}nic waves. The
consequences of this effect are important for many processes, from cosmic ray
(CR) propagation to launching outflows and winds in galaxies and other
magnetized systems. We discuss the differences in the damping of the streaming
instability by turbulence and the damping of a plane parallel wave. The former
takes place in the system of reference aligned with the local direction of
magnetic field along which CRs stream. The latter is in the reference frame of
the mean magnetic field and traditionally considered in plasma studies. We also
compare the turbulent damping of streaming instability with ion-neutral
collisional damping, which becomes the dominant damping effect at a
sufficiently low ionization fraction. Numerical testing and astrophysical
implications are also discussed.",2201.05168v1
2022-03-14,Investigation of nonlinear squeeze-film damping involving rarefied gas effect in micro-electro-mechanical-systems,"In this paper, the nonlinear squeeze-film damping (SFD) involving rarefied
gas effect in the micro-electro-mechanical-systems (MEMS) is investigated.
Considering the motion of structures (beam, cantilever, and membrane) in MEMS,
the dynamic response of structure will be influenced largely by the
squeeze-film damping. In the traditional model, a viscous damping assumption
that damping force is linear with moving velocity is used. As the nonlinear
damping phenomenon is observed for a micro-structure oscillating with a
high-velocity, this assumption is invalid and will generates error result for
predicting the response of micro-structure. In addition, due to the small size
of device and the low pressure of encapsulation, the gas in MEMS usually is
rarefied gas. Therefore, to correctly predict the damping force, the rarefied
gas effect must be considered. To study the nonlinear SFD phenomenon involving
the rarefied gas effect, a kinetic method, namely discrete unified gas kinetic
scheme (DUGKS), is introduced. And based on DUGKS, two solving methods, a
traditional decoupled method (Eulerian scheme) and a coupled framework
(arbitrary Lagrangian-Eulerian scheme), are adopted. With these two methods,
two basic motion forms, linear (perpendicular) and tilting motions of a rigid
micro-beam, are studied with forced and free oscillations.",2203.06902v1
2022-05-21,Noether symmetries and first integrals of damped harmonic oscillator,"Noether theorem establishes an interesting connection between symmetries of
the action integral and conservation laws of a dynamical system. The aim of the
present work is to classify the damped harmonic oscillator problem with respect
to Noether symmetries and to construct corresponding conservation laws for all
over-damped, under damped and critical damped cases. For each case we obtain
maximum five linearly independent group generators which provide related five
conserved quantities. Remarkably, after obtaining complete set of invariant
quantities we obtain analytical solutions for each case. In the current work,
we also introduce a new Lagrangian for the damped harmonic oscillator. Though
the form of this new Lagrangian and presented by Bateman are completely
different, yet it generates same set of Noether symmetries and conserved
quantities. So, this new form of Lagrangian we are presenting here may be
seriously interesting for the physicists. Moreover, we also find the Lie
algebras of Noether symmetries and point out some interesting aspects of
results related to Noether symmetries and first integrals of damped harmonic
oscillator which perhaps not reported in the earlier studies.",2205.10525v1
2023-01-31,The emergence of soft-glassy mechanics in simulated foams,"Several seemingly different soft materials, including foams, cells, and many
complex fluids, exhibit remarkably similar rheological properties and
microscopic dynamics, termed soft glassy mechanics. Here, we show that such
behavior emerges from a simple model of a damped ripening foam, for
sufficiently weak damping. In particular, we observe intermittent avalanchey
dynamics, bubble super-diffusion, and power-law rheology that vary as the
damping factor is changed. In the limit of weak damping, the dynamics are
determined by the tortuous low-lying portions of the energy landscape, as
described in a recent study. For strong damping the viscous stresses cause the
system configuration to evolve along higher energy paths, washing out
small-scale tortuosity and producing motion with an increasingly ballistic
character. Using a microrheological approach, the linear viscoelastic response
of the model can be efficiently calculated. This resembles the power-law
rheology expected for soft glassy mechanics, but unexpectedly, is only weakly
sensitive to the damping parameter. Lastly, we study the reported memory effect
in foams after large perturbations and find that the timescale of the memory
goes to zero as the damping parameter vanishes, suggesting that the effect is
due to viscous stress relaxation rather than slow structural changes stabilized
by the energy landscape.",2301.13400v1
2023-02-13,Thickness and temperature dependent damping in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ epitaxial films,"The damping of La0.67Sr0.33MnO3 (LSMO) epitaxial films as a function of
thickness at different temperatures was studied. The competition between two
scattering types (\r{ho}-like and {\sigma}-like) with entirely distinct
thickness and temperature dependencies resulted in complicated damping
behavior. The behavior of {\sigma}-like damping in LSMO films is consistent
with the behavior in magnetic metal films. However, because \r{ho}-like damping
is sensitive to the fine electron structure near the Fermi surface, the
distortion of the oxygen octahedra controlled by the film thickness is an
important factor in controlling the damping. Our study demonstrates that the
complexity of damping in LSMO epitaxial films is a consequence of
strong-correlation effects, which are characteristic of complex
transition-metal oxides.",2302.06099v3
2023-09-15,On the formation of singularities for the slightly supercritical NLS equation with nonlinear damping,"We consider the focusing, mass-supercritical NLS equation augmented with a
nonlinear damping term. We provide sufficient conditions on the nonlinearity
exponents and damping coefficients for finite-time blow-up. In particular,
singularities are formed for focusing and dissipative nonlinearities of the
same power, provided that the damping coefficient is sufficiently small. Our
result thus rigorously proves the non-regularizing effect of nonlinear damping
in the mass-supercritical case, which was suggested by previous numerical and
formal results.
  We show that, under our assumption, the damping term may be controlled in
such a way that the self-similar blow-up structure for the focusing NLS is
approximately retained even within the dissipative evolution. The nonlinear
damping contributes as a forcing term in the equation for the perturbation
around the self-similar profile, that may produce a growth over finite time
intervals. We estimate the error terms through a modulation analysis and a
careful control of the time evolution of total momentum and energy functionals.",2309.08281v1
1998-05-07,Discovery of z=0.0912 and z=0.2212 Damped Lyman-alpha Absorption Line Systems Toward the Quasar OI 363: Limits on the Nature of Damped Lyman-alpha Galaxies,"The discovery of a z_abs = 0.0912 damped Lyman-alpha absorption-line system
in the HST-FOS ultraviolet spectrum of the quasar OI 363 (0738+313) is
reported. This is the lowest redshift quasar damped Lyman-alpha system known.
Its neutral hydrogen column density is N(HI) = 1.5(+/- 0.2) E21 atoms/cm^2,
which easily exceeds the classical criterion for damped Lyman-alpha of N(HI)
greater than or equal to 2E20 atoms/cm^2. Remarkably, a z_abs = 0.2212 damped
system with N(HI) = 7.9(+/- 1.4) E20 atoms/cm^2 has also been discovered in the
same spectrum.
  In the past, the standard paradigm for damped Lyman-alpha systems has been
that they arise in galactic or protogalactic HI disks with low impact
parameters in luminous galaxies. However, WIYN imaging of the OI 363 field
shows that none of the galaxies visible in the vicinity of the quasar is a
luminous gas-rich spiral with low impact parameter, either at z = 0.0912 or z =
0.2212. Thus, these damped systems are among the clearest examples yet of cases
that are inconsistent with the standard damped Lyman-alpha - HI-disk paradigm.",9805093v1
2008-01-24,Attenuation of small-amplitude oscillations in a prominence-corona model with a transverse magnetic field,"Small-amplitude prominence oscillations are usually damped after a few
periods. We study the attenuation of non-adiabatic magnetoacoustic waves in a
slab prominence embedded in the coronal medium. We assume an equilibrium
configuration with a transverse magnetic field to the slab axis and investigate
wave damping by thermal conduction and radiative losses. The differential MHD
equations that govern linear slow and fast modes are numerically solved to
obtain the complex oscillatory frequency and the corresponding eigenfunctions.
We find that coronal thermal conduction and radiative losses from the
prominence plasma reveal as the most relevant damping mechanisms. Both
mechanisms govern together the attenuation of hybrid modes, whereas prominence
radiation is responsible for the damping of internal modes and coronal
conduction essentially dominates the attenuation of external modes. In
addition, the energy transfer between the prominence and the corona caused by
thermal conduction has a noticeable effect on the wave stability, radiative
losses from the prominence plasma being of paramount importance for the thermal
stability of fast modes. We conclude that slow modes are efficiently damped,
with damping times compatible with observations. On the contrary, fast modes
are less attenuated by non-adiabatic effects and their damping times are
several orders of magnitude larger than those observed. The presence of the
corona causes a decrease of the damping times with respect to those of an
isolated prominence slab, but its effect is still insufficient to obtain
damping times of the order of the period in the case of fast modes.",0801.3744v2
2010-04-26,Selective spatial damping of propagating kink waves due to resonant absorption,"There is observational evidence of propagating kink waves driven by
photospheric motions. These disturbances, interpreted as kink
magnetohydrodynamic (MHD) waves are attenuated as they propagate upwards in the
solar corona. In this paper we show that resonant absorption provides a simple
explanation to the spatial damping of these waves. Kink MHD waves are studied
using a cylindrical model of solar magnetic flux tubes which includes a
non-uniform layer at the tube boundary. Assuming that the frequency is real and
the longitudinal wavenumber complex, the damping length and damping per
wavelength produced by resonant absorption are analytically calculated. The
damping length of propagating kink waves due resonant absorption is a
monotonically decreasing function of frequency. For kink waves with low
frequencies the damping length is exactly inversely proportional to frequency
and we denote this as the TGV relation. When moving to high frequencies the TGV
relation continues to be an exceptionally good approximation of the actual
dependency of the damping length on frequency. This dependency means that
resonant absorption is selective as it favours low frequency waves and can
efficiently remove high frequency waves from a broad band spectrum of kink
waves. It is selective as the damping length is inversely proportional to
frequency so that the damping becomes more severe with increasing frequency.
This means that radial inhomogeneity can cause solar waveguides to be a natural
low-pass filter for broadband disturbances. Hence kink wave trains travelling
along, e.g., coronal loops, will have a greater proportion of the high
frequency components dissipated lower down in the atmosphere. This could have
important consequences with respect to the spatial distribution of wave heating
in the solar atmosphere.",1004.4468v1
2011-04-10,Spatial Damping of Propagating Kink Waves Due to Resonant Absorption: Effect of Background Flow,"Observations show the ubiquitous presence of propagating magnetohydrodynamic
(MHD) kink waves in the solar atmosphere. Waves and flows are often observed
simultaneously. Due to plasma inhomogeneity in the perpendicular direction to
the magnetic field, kink waves are spatially damped by resonant absorption. The
presence of flow may affect the wave spatial damping. Here, we investigate the
effect of longitudinal background flow on the propagation and spatial damping
of resonant kink waves in transversely nonuniform magnetic flux tubes. We
combine approximate analytical theory with numerical investigation. The
analytical theory uses the thin tube (TT) and thin boundary (TB) approximations
to obtain expressions for the wavelength and the damping length. Numerically,
we verify the previously obtained analytical expressions by means of the full
solution of the resistive MHD eigenvalue problem beyond the TT and TB
approximations. We find that the backward and forward propagating waves have
different wavelengths and are damped on length scales that are inversely
proportional to the frequency as in the static case. However, the factor of
proportionality depends on the characteristics of the flow, so that the damping
length differs from its static analogue. For slow, sub-Alfvenic flows the
backward propagating wave gets damped on a shorter length scale than in the
absence of flow, while for the forward propagating wave the damping length is
longer. The different properties of the waves depending on their direction of
propagation with respect to the background flow may be detected by the
observations and may be relevant for seismological applications.",1104.1791v1
2013-02-08,On the Damping-Induced Self-Recovery Phenomenon in Mechanical Systems with Several Unactuated Cyclic Variables,"The damping-induced self-recovery phenomenon refers to the fundamental
property of underactuated mechanical systems: if an unactuated cyclic variable
is under a viscous damping-like force and the system starts from rest, then the
cyclic variable will always move back to its initial condition as the actuated
variables come to stop. The regular momentum conservation phenomenon can be
viewed as the limit of the damping-induced self-recovery phenomenon in the
sense that the self-recovery phenomenon disappears as the damping goes to zero.
This paper generalizes the past result on damping-induced self-recovery for the
case of a single unactuated cyclic variable to the case of multiple unactuated
cyclic variables. We characterize a class of external forces that induce new
conserved quantities, which we call the damping-induced momenta. The
damping-induced momenta yield first-order asymptotically stable dynamics for
the unactuated cyclic variables under some conditions, thereby inducing the
self-recovery phenomenon. It is also shown that the viscous damping-like forces
impose bounds on the range of trajectories of the unactuated cyclic variables.
Two examples are presented to demonstrate the analytical discoveries: the
planar pendulum with gimbal actuators and the three-link planar manipulator on
a horizontal plane.",1302.2109v1
2016-07-06,Damping of Alfven waves by Turbulence and its Consequences: from Cosmic-Rays Streaming to Launching Winds,"This paper considers turbulent damping of Alfven waves in magnetized plasmas.
We identify two cases of damping, one related to damping of cosmic rays
streaming instability, the other related to damping of Alfven waves emitted by
a macroscopic wave source, e.g. stellar atmosphere. The physical difference
between the two cases is that in the former case the generated waves are
emitted in respect to the local direction of magnetic field, in the latter in
respect to the mean field. The scaling of damping is different in the two
cases. We the regimes of turbulence ranging from subAlfvenic to superAlfvenic
we obtain analytical expressions for the damping rates and define the ranges of
applicability of these expressions. Describing the damping of the streaming
instability, we find that for subAlfvenic turbulence the range of cosmic ray
energies influenced by weak turbulence is unproportionally large compared to
the range of scales that the weak turbulence is present. On the contrary, the
range of cosmic ray energies affected by strong Alfvenic turbulence is rather
limited. A number of astrophysical applications of the process ranging from
launching of stellar and galactic winds to propagation of cosmic rays in
galaxies and clusters of galaxies is considered. In particular, we discuss how
to reconcile the process of turbulent damping with the observed isotropy of the
Milky Way cosmic rays.",1607.02042v1
2018-01-18,Quantum Landau damping in dipolar Bose-Einstein condensates,"We consider Landau damping of elementary excitations in Bose-Einstein
condensates (BECs) with dipolar interactions. We discuss quantum and
quasi-classical regimes of Landau damping. We use a generalized wave-kinetic
description of BECs which, apart from the long range dipolar interactions, also
takes into account the quantum fluctuations and the finite energy corrections
to short-range interactions. Such a description is therefore more general than
the usual mean field approximation. The present wave-kinetic approach is well
suited for the study of kinetic effects in BECs, such as those associated with
Landau damping, atom trapping and turbulent diffusion. The inclusion of quantum
fluctuations and energy corrections change the dispersion relation and the
damping rates, leading to possible experimental signatures of these effects.
  Quantum Landau damping is described with generality, and particular examples
of dipole condensates in two and three dimensions are studied. The occurrence
of roton-maxon configurations, and their relevance to Landau damping is also
considered in detail, as well as the changes introduced by the three different
processes, associated with dipolar interactions, quantum fluctuations and
finite energy range collisions. The present approach is mainly based on a
linear perturbative procedure, but the nonlinear regime of Landau damping,
which includes atom trapping and atom diffusion, is also briefly discussed.",1801.06256v1
2020-05-31,Optimal decay rates of the compressible Euler equations with time-dependent damping in $\mathbb R^n$: (I) under-damping case,"This paper is concerned with the multi-dimensional compressible Euler
equations with time-dependent damping of the form
$-\frac{\mu}{(1+t)^\lambda}\rho\boldsymbol u$ in $\mathbb R^n$, where $n\ge2$,
$\mu>0$, and $\lambda\in[0,1)$. When $\lambda>0$ is bigger, the damping effect
time-asymptotically gets weaker, which is called under-damping. We show the
optimal decay estimates of the solutions such that $\|\partial_x^\alpha
(\rho-1)\|_{L^2(\mathbb R^n)}\approx
(1+t)^{-\frac{1+\lambda}{2}(\frac{n}{2}+|\alpha|)}$, and $\|\partial_x^\alpha
\boldsymbol u\|_{L^2(\mathbb R^n)}\approx
(1+t)^{-\frac{1+\lambda}{2}(\frac{n}{2}+|\alpha|)-\frac{1-\lambda}{2}}$, and
see how the under-damping effect influences the structure of the Euler system.
Different from the traditional view that the stronger damping usually makes the
solutions decaying faster, here surprisingly we recognize that the weaker
damping with $0\le\lambda<1$ enhances the faster decay for the solutions. The
adopted approach is the technical Fourier analysis and the Green function
method. The main difficulties caused by the time-dependent damping lie in
twofold: non-commutativity of the Fourier transform of the linearized operator
precludes explicit expression of the fundamental solution; time-dependent
evolution implies that the Green matrix $G(t,s)$ is not translation invariant,
i.e., $G(t,s)\ne G(t-s,0)$. We formulate the exact decay behavior of the Green
matrices $G(t,s)$ with respect to $t$ and $s$ for both linear wave equations
and linear hyperbolic system, and finally derive the optimal decay rates for
the nonlinear Euler system.",2006.00401v1
2022-08-17,Anti-parity-time symmetry hidden in a damping linear resonator,"Phase transition from the over-damping to under-damping states is a
ubiquitous phenomenon in physical systems. However, what kind of symmetry is
broken associated with this phase transition remains unclear. Here, we discover
that this phase transition is determined by an anti-parity-time
(anti-$\mathcal{PT}$) symmetry hidden in a single damping linear resonator,
which is significantly different from the conventional
anti-$\mathcal{PT}$-symmetric systems with two or more modes. We show that the
breaking of the anti-$\mathcal{PT}$ symmetry yields the phase transition from
the over-damping to under-damping states, with an exceptional point (EP)
corresponding to the critical-damping state. Moreover, we propose an
optomechanical scheme to show this anti-$\mathcal{PT}$ symmetry breaking by
using the optical spring effect in a quadratic optomechanical system. We also
suggest an optomechanical sensor with the sensitivity enhanced significantly
around the EPs for the anti-$\mathcal{PT}$ symmetry breaking. Our work unveils
the anti-$\mathcal{PT}$ symmetry hidden in damping oscillations and hence opens
up new possibilities for exploiting wide anti-$\mathcal{PT}$ symmetry
applications in single damping linear resonators.",2208.08187v2
1996-12-10,Collisional matter-phase damping in Bose-condensed gas,"Collisional damping of the excitations in a Bose-condensed gas is
investigated over the wide range of energies and temperatures. Numerical
results for the damping rate are presented and a number of asymptotic and
interpolating expressions for it are derived.",9612086v1
2001-11-29,Tensor form of magnetization damping,"A tensor form of phenomenological damping is derived for small magnetization
motions. This form reflects basic physical relaxation processes for a general
uniformly magnetized particle or film. Scalar Landau-Lifshitz damping is found
to occur only for two special cases of system symmetry.",0111566v1
1999-07-28,An effective relaxation-time approach to collisionless quark-gluon plasma,"We present an effective relaxation-time theory to study the collisionless
quark-gluon plasma. Applying this method we calculate the damping rate to be of
order $g^2T$ and find plasmon scattering is the damping mechanism. The damping
for the transverse mode is stronger than the longitudinal one.",9907526v1
1999-11-16,Dynamical resummation and damping in the O(N) model,"A general real-time formalism is developed to resum the self-energy operator
of broken symmetry scalar field theories in form of self-consistent gap
equations for the spectral function. The solution of the equations is
approximated with finite lifetime quasi-particles. In the Landau damping rates
viscosity terms, analogous to gauge theories, appear, what leads to a finite
damping rate for the long wavelength Goldstone modes.",9911374v1
1993-03-24,On the Quantizations of the Damped Systems,"Based on a simple observation that a classical second order differential
equation may be decomposed into a set of two first order equations, we
introduce a Hamiltonian framework to quantize the damped systems. In
particular, we analyze the system of a linear damped harmonic oscillator and
demonstrate that the time evolution of the Schr\""odinger equation is
unambiguously determined.",9303137v1
2006-01-09,Energy decay for damped wave equations on partially rectangular domains,"We consider the wave equation with a damping term on a partially rectangular
planar domain, assuming that the damping is concentrated close to the
non-rectangular part of the domain. Polynomial decay estimates for the energy
of the solution are established.",0601195v1
2002-06-07,Resonant states and classical damping,"Using Koopman's approach to classical dynamical systems we show that the
classical damping may be interpreted as appearance of resonant states of the
corresponding Koopman's operator. It turns out that simple classical damped
systems give rise to discrete complex spectra. Therefore, the corresponding
generalized eigenvectors may be interpreted as classical resonant states.",0206009v1
2004-03-12,Factorization of damped wave equations with cubic nonlinearities,"The recent factorization scheme that we introduced for nonlinear polynomial
ODEs in math-ph/0401040 is applied to the interesting case of damped wave
equations with cubic nonlinearities. Traveling kink solutions are possible in
the plane defined by the kink velocity versus the damping coefficient only
along hyperbolas that are plotted herein",0403022v1
2002-08-07,Toward a Universal Model of Damping--Modified Coulomb Friction,"A modification of Coulomb's law of friction uses a variable coefficient of
friction that depends on a power law in the energy of mechanical oscillation.
Through the use of three different exponents: 0, 1/2 and 1; all commonly
encountered non-viscous forms of damping are accommodated. The nonlinear model
appears to yield good agreement with experiment in cases of surface, internal,
and amplitude dependent damping.",0208025v1
2002-12-19,Trapped particle bounds on stimulated scatter in the large k/kD regime,"In the strongly damped regime, the convective gain rate for stimulated
scatter varies inversely with the plasma wave damping rate. Electron trapping
effects reduce the damping but also lead to loss of resonance for large enough
amplitude waves. This leads to a gain rate bound and corresponding optimum
scattered light frequency and plasma wave amplitude.",0212071v1
2003-02-03,Oscillator damping with more than one mechanism of internal friction dissipation,"The author's modified Coulomb damping model has been generalized to
accommodate internal friction that derives from several dissipation mechanisms
acting simultaneously. Because of its fundamental nonlinear nature, internal
friction damping causes the quality factor Q of an oscillator in free-decay to
change in time. Examples are given which demonstrate reasonable agreement
between theory and experiment.",0302003v1
2003-02-15,Anisotropic Internal Friction Damping,"The mechanical damping properties of sheet polaroid material have been
studied with a physical pendulum. The polaroid samples were placed under the
knife-edges of the pendulum, which was operated in free-decay at a period in
the vicinity of 10 s. With the edges oriented parallel to the direction of the
long molecular chains in the polaroid, it was found that the damping was more
than 10% smaller than when oriented perpendicular to the chains.",0302055v1
2006-08-07,Study of the Damped Pendulum,"Experiments on the oscillatory motion of a suspended bar magnet throws light
on the damping effects acting on the pendulum. The viscous drag offered by air
was found the be the main contributor for slowing the pendulum down. The nature
and magnitude of the damping effects were shown to be strongly dependent on the
amplitude.",0608071v1
1995-02-27,Quantum Oscillator with Kronig-Penney Excitation in Different Regimes of Damping,"There are discussed the exact solution of the time--dependent Schr\""{o}dinger
equation for a damped quantum oscillator subject to a periodical frequency
delta--kicks describing squeezed states which are expressed in terms of
Chebyshev polynomials. The cases of strong and weak damping are investigated in
the frame of Caldirola--Kanai model.",9502023v1
2007-03-12,Quantum estimation of a damping constant,"We discuss an interferometric approach to the estimation of quantum
mechanical damping. We study specific classes of entangled and separable probe
states consisting of superpositions of coherent states. Based on the assumption
of limited quantum resources we show that entanglement improves the estimation
of an unknown damping constant.",0703091v2
2008-11-07,Asymptotic stability of the wave equation on compact surfaces and locally distributed damping - A sharp result,"This paper is concerned with the study of the wave equation on compact
surfaces and locally distributed damping. We study the case where the damping
is effective in a well-chosen subset of arbitrarily small measure.",0811.1190v1
2008-11-07,Uniform Stabilization of the wave equation on compact surfaces and locally distributed damping,"This paper is concerned with the study of the wave equation on compact
surfaces and locally distributed damping. We study the case where the damping
is effective on the complement of visible umbilical sets.",0811.1204v1
2010-11-20,Enhanced damping of ion acoustic waves in dense plasmas,"A theory for the ion acoustic wave damping in dense plasmas and warm dense
matter, accounting for the Umklapp process, is presented. A higher decay rate
compared to the prediction from the Landau damping theory is predicted for
high-Z dense plasmas where the electron density ranges from $10^{21}$ to $
10^{24} \mathrm{cm^{-3}}$ and the electron temperature is moderately higher
than the Fermi energy.",1011.4607v1
2012-05-16,Enhanced coupling design of a detuned damped structure for clic,"The key feature of the improved coupling design in the Damped Detuned
Structure (DDS) is focused on the four manifolds. Rectangular geometry slots
and rectangular manifolds are used. This results in a significantly stronger
coupling to the manifolds compared to the previous design. We describe the new
design together with its wakefield damping properties.",1205.3590v1
2012-06-26,On the $L^{2}$-critical nonlinear Schrödinger Equation with a nonlinear damping,"We consider the Cauchy problem for the $L^{2}$-critical nonlinear
Schr\""{o}dinger equation with a nonlinear damping. According to the power of
the damping term, we prove the global existence or the existence of finite time
blowup dynamics with the log-log blow-up speed for $\|\nabla u(t)\|_{L^2}$.",1206.6082v4
2012-10-12,Semi-linear wave equations with effective damping,"We study the Cauchy problem for the semi-linear damped wave equation in any
space dimension. We assume that the time-dependent damping term is effective.
We prove the global existence of small energy data solutions in the
supercritical case.",1210.3493v1
2012-12-08,A note on the lifespan of solutions to the semilinear damped wave equation,"This paper concerns estimates of the lifespan of solutions to the semilinear
damped wave equation. We give upper estimates of the lifespan for the
semilinear damped wave equation with variable coefficients in all space
dimensions.",1212.1772v3
2012-12-10,Strongly damped wave equation with exponential nonlinearities,"In this paper, we study the initial boundary value problem for the two
dimensional strong damped wave equation with exponentially growing source and
damping terms. We first show the well-posedness of this problem and then prove
the existence of the global attractor in $(H_{0}^{1}(\Omega)\cap
L^{\infty}(\Omega))\times L^{2}(\Omega)$.",1212.2180v2
2013-10-27,Exponential decay of solutions for the plate equation with localized damping,"In this paper, we give positive answer to the open question raised in [E.
Zuazua, Exponential decay for the semilinear wave equation with localized
damping in unbounded domains. J. Math. Pures Appl., 70 (1991) 513--529] on the
exponential decay of solutions for the semilinear plate equation with localized
damping.",1310.7243v3
2014-03-07,Landau damping in Sobolev spaces for the Vlasov-HMF model,"We consider the Vlasov-HMF (Hamiltonian Mean-Field) model. We consider
solutions starting in a small Sobolev neighborhood of a spatially homogeneous
state satisfying a linearized stability criterion (Penrose criterion). We prove
that these solutions exhibit a scattering behavior to a modified state, which
implies a nonlinear Landau damping effect with polynomial rate of damping.",1403.1668v2
2015-03-30,Damping to prevent the blow-up of the Korteweg-de Vries equation,"We study the behavior of the solution of a generalized damped KdV equation
$u_t + u_x + u_{xxx} + u^p u_x + \mathscr{L}_{\gamma}(u)= 0$. We first state
results on the local well-posedness. Then when $p \geq 4$, conditions on
$\mathscr{L}_{\gamma}$ are given to prevent the blow-up of the solution.
Finally, we numerically build such sequences of damping.",1503.08559v1
2015-06-16,Fast energy decay for wave equations with variable damping coefficients in the 1-D half line,"We derive fast decay estimates of the total energy for wave equations with
localized variable damping coefficients, which are dealt with in the one
dimensional half line $(0,\infty)$. The variable damping coefficient vanishes
near the boundary $x = 0$, and is effective critically near spatial infinity $x
= \infty$.",1506.04851v1
2015-11-25,A Proposal of a Damping Term for the Relativistic Euler Equations,"We introduce a damping term for the special relativistic Euler equations in
$3$-D and show that the equations reduce to the non-relativistic damped Euler
equations in the Newtonian limit. We then write the equations as a symmetric
hyperbolic system for which local-in-time existence of smooth solutions can be
shown.",1511.08183v1
2016-01-27,Concatenated Codes for Amplitude Damping,"We discuss a method to construct quantum codes correcting amplitude damping
errors via code concatenation. The inner codes are chosen as asymmetric
Calderbank-Shor-Steane (CSS) codes. By concatenating with outer codes
correcting symmetric errors, many new codes with good parameters are found,
which are better than the amplitude damping codes obtained by any previously
known construction.",1601.07423v1
2016-03-29,Generalized damped Milne-Pinney equation and Chiellini method,"We adopt the Chiellini integrability method to find the solutions of various
generalizations of the damped Milne-Pinney equations. In particular, we find
the solution of the damped Ermakov-Painlev\'e II equation and generalized
dissipative Milne-Pinney equation.",1603.08747v2
2017-12-07,Damped wave equations on compact hyperbolic surfaces,"We prove exponential decay of energy for solutions of the damped wave
equation on compact hyperbolic surfaces with regular initial data as long as
the damping is nontrivial. The proof is based on a similar strategy as in
Dyatlov-Jin and in particular, uses the fractal uncertainty principle proved in
Bourgain-Dyatlov.",1712.02692v1
2018-03-20,Stability of the wave equations on a tree with local Kelvin-Voigt damping,"In this paper we study the stability problem of a tree of elastic strings
with local Kelvin-Voigt damping on some of the edges. Under the compatibility
condition of displacement and strain and continuity condition of damping
coefficients at the vertices of the tree, exponential/polynomial stability are
proved.",1803.07280v1
2018-09-10,Logarithmic Decay of a Wave Equation with Kelvin-Voigt Damping,"In this paper we analyze the long time behavior of a wave equation with local
Kelvin-Voigt Damping. Through introducing proper class symbol and
pseudo-differential calculus, we obtain a Carleman estimate, and then establish
an estimate on the corresponding resolvent operator. As a result, we show the
logarithmic decay rate for energy of the system without any geometric
assumption on the subdomain on which the damping is effective.",1809.03196v1
2018-11-07,Slow-dissipation limit of the harmonic oscillator with general power-law damping,"An approximate solution is presented for simple harmonic motion in the
presence of damping by a force which is a general power-law function of the
velocity. The approximation is shown to be quite robust, allowing for a simple
way to investigate amplitude decay in the presence of general types of weak,
nonlinear damping.",1811.02953v2
2019-09-25,Forced Coupled Duffing Oscillators with Nonlinear Damping: Resonance and Antiresonance,"In this work, we investigate resonance and antiresonance behaviour in forced
coupled Duffing oscillators with nonlinear damping. Further, we will analyse
the parameter dependence of the frequency response and stability. In the course
of all the analysis, emphasis shall be on how different damping mechanisms
contrast against each other.",1909.11390v1
2020-04-21,Damping rate limitations for transverse dampers in large hadron colliders,"The paper focuses on two issues important for design and operation of
bunch-by-bunch transverse damper in a very large hadron collider, where fast
damping is required to suppress beam instabilities and noise induced emittance
growth. The first issue is associated with kick variation along a bunch which
affects the damping of head-tail modes. The second issue is associated with
affect of damper noise on the instability threshold.",2004.10249v2
2021-02-01,Global existence for semilinear wave equations with scaling invariant damping in 3-D,"Global existence for small data Cauchy problem of semilinear wave equations
with scaling invariant damping in 3-D is established in this work, assuming
that the data are radial and the constant in front of the damping belongs to
$[1.5, 2)$. The proof is based on a weighted $L^2-L^2$ estimate for
inhomogeneous wave equation, which is established by interpolating between
energy estimate and Morawetz type estimate.",2102.00909v1
2021-08-17,Spectral enclosures for the damped elastic wave equation,"In this paper we investigate spectral properties of the damped elastic wave
equation. Deducing a correspondence between the eigenvalue problem of this
model and the one of Lam\'e operators with non self-adjoint perturbations, we
provide quantitative bounds on the location of the point spectrum in terms of
suitable norms of the damping coefficient.",2108.07676v1
2022-02-10,Stochastic optimal control for nonlinear damped network dynamics,"We present a stochastic optimal control problem for a tree network. The
dynamics of the network are governed by transport equations with a special
emphasis on the non-linear damping function. Demand profiles at the network
sinks are modelled by a stochastic differential equations. An explicit optimal
inflow into the network is determined and numerical simulations are presented
to show the effects for different choices of the non-linear damping.",2202.05114v1
2022-03-03,Conformal symmetry in damped Pais-Uhlenbeck oscillator,"Two Lagrangian formulations for describing of the damped harmonic oscillator
have been introduced by Bateman. For these models we construct higher
derivative generalization which enjoys the l-conformal Newton-Hooke symmetry.
The dynamics of generalized systems corresponds to the damped Pais-Uhlenbeck
oscillator for a particular choice of its frequencies.",2203.01651v1
2022-05-26,Ergodic results for the stochastic nonlinear Schrödinger equation with large damping,"We study the nonlinear Schr\""odinger equation with linear damping, i.e. a
zero order dissipation, and additive noise. Working in $R^d$ with d = 2 or d =
3, we prove the uniqueness of the invariant measure when the damping
coefficient is sufficiently large.",2205.13364v1
2022-10-31,An adaptive damped Newton method for strongly monotone and Lipschitz continuous operator equations,"We will consider the damped Newton method for strongly monotone and Lipschitz
continuous operator equations in a variational setting. We will provide a very
accessible justification why the undamped Newton method performs better than
its damped counterparts in a vicinity of a solution. Moreover, in the given
setting, an adaptive step-size strategy will be presented, which guarantees the
global convergence and favours an undamped update if admissible.",2210.17107v1
2022-11-19,Blow up and lifespan estimates for systems of semi-linear wave equations with damping and potential,"In this paper, we consider the semi-linear wave systems with
power-nonlinearities and a large class of space-dependent damping and
potential. We obtain the same blow-up regions and the lifespan estimates for
three types wave systems, compared with the systems without damping and
potential.",2211.10639v1
2023-08-10,Pathwise uniqueness for stochastic heat and damped equations with Hölder continuous drift,"In this paper, we prove pathwise uniqueness for stochastic differential
equations in infinite dimension. Under our assumptions, we are able to consider
the stochastic heat equation up to dimension $3$, the stochastic damped wave
equation in dimension $1$ and the stochastic Euler-Bernoulli damped beam
equation up to dimension $3$. We do not require that the so-called {\it
structure condition} holds true.",2308.05415v1
2023-10-30,Beliaev damping in Bose gas,"According to the Bogoliubov theory the low energy behaviour of the Bose gas
at zero temperature can be described by non-interacting bosonic quasiparticles
called phonons. In this work the damping rate of phonons at low momenta, the
so-called Beliaev damping, is explained and computed with simple arguments
involving the Fermi Golden Rule and Bogoliubov's quasiparticles.",2310.20070v1
2023-11-25,Energy scattering for the unsteady damped nonlinear Schrodinger equation,"We investigate the large time behavior of the solutions to the nonlinear
focusing Schr\""odinger equation with a time-dependent damping in the energy
sub-critical regime. Under non classical assumptions on the unsteady damping
term, we prove some scattering results in the energy space.",2311.14980v2
2017-10-18,Direct detection of metal-insulator phase transitions using the modified Backus-Gilbert method,"The detection of the (semi)metal-insulator phase transition can be extremely
difficult if the local order parameter which characterizes the ordered phase is
unknown.In some cases, it is even impossible to define a local order parameter:
the most prominent example of such system is the spin liquid state. This state
was proposed to exist in theHubbard model on the hexagonal lattice in a region
between the semimetal phase and the antiferromagnetic insulator phase. The
existence of this phase has been the subject of a long debate. In order to
detect these exotic phases we must use alternative methods to those used for
more familiar examples of spontaneous symmetry breaking. We have modified the
Backus-Gilbert method of analytic continuation which was previously used in the
calculation of the pion quasiparticle mass in lattice QCD. The modification of
the method consists of the introduction of the Tikhonov regularization scheme
which was used to treat the ill-conditioned kernel. This modified
Backus-Gilbert method is applied to the Euclidean propagators in momentum space
calculated using the hybridMonte Carlo algorithm. In this way, it is possible
to reconstruct the full dispersion relation and to estimate the mass gap, which
is a direct signal of the transition to the insulating state. We demonstrate
the utility of this method in our calculations for the Hubbard model on the
hexagonal lattice. We also apply the method to the metal-insulator phase
transition in the Hubbard-Coulomb model on the square lattice.",1710.06675v1
2019-01-29,Bounding the spectral gap for an elliptic eigenvalue problem with uniformly bounded stochastic coefficients,"A key quantity that occurs in the error analysis of several numerical methods
for eigenvalue problems is the distance between the eigenvalue of interest and
the next nearest eigenvalue. When we are interested in the smallest or
fundamental eigenvalue, we call this the spectral or fundamental gap. In a
recent manuscript [Gilbert et al., arXiv:1808.02639], the current authors,
together with Frances Kuo, studied an elliptic eigenvalue problem with
homogeneous Dirichlet boundary conditions, and with coefficients that depend on
an infinite number of uniformly distributed stochastic parameters. In this
setting, the eigenvalues, and in turn the eigenvalue gap, also depend on the
stochastic parameters. Hence, for a robust error analysis one needs to be able
to bound the gap over all possible realisations of the parameters, and because
the gap depends on infinitely-many random parameters, this is not trivial. This
short note presents, in a simplified setting, an important result that was
shown in the paper above. Namely, that, under certain decay assumptions on the
coefficient, the spectral gap of such a random elliptic eigenvalue problem can
be bounded away from 0, uniformly over the entire infinite-dimensional
parameter space.",1901.10470v1
2020-09-14,Bounds and Code Constructions for Partially Defect Memory Cells,"This paper considers coding for so-called partially stuck memory cells. Such
memory cells can only store partial information as some of their levels cannot
be used due to, e.g., wear out. First, we present a new code construction for
masking such partially stuck cells while additionally correcting errors. This
construction (for cells with $q >2$ levels) is achieved by generalizing an
existing masking-only construction in [1] (based on binary codes) to correct
errors as well. Compared to previous constructions in [2], our new construction
achieves larger rates for many sets of parameters. Second, we derive a
sphere-packing (any number of $u$ partially stuck cells) and a
Gilbert-Varshamov bound ($u<q$ partially stuck cells) for codes that can mask a
certain number of partially stuck cells and correct errors additionally. A
numerical comparison between the new bounds and our previous construction of
PSMCs for the case $u<q$ in [2] shows that our construction lies above the
Gilbert-Varshamov-like bound for several code parameters.",2009.06512v3
2020-10-02,Multilevel quasi-Monte Carlo for random elliptic eigenvalue problems I: Regularity and error analysis,"Stochastic PDE eigenvalue problems are useful models for quantifying the
uncertainty in several applications from the physical sciences and engineering,
e.g., structural vibration analysis, the criticality of a nuclear reactor or
photonic crystal structures. In this paper we present a multilevel quasi-Monte
Carlo (MLQMC) method for approximating the expectation of the minimal
eigenvalue of an elliptic eigenvalue problem with coefficients that are given
as a series expansion of countably-many stochastic parameters. The MLQMC
algorithm is based on a hierarchy of discretisations of the spatial domain and
truncations of the dimension of the stochastic parameter domain. To approximate
the expectations, randomly shifted lattice rules are employed. This paper is
primarily dedicated to giving a rigorous analysis of the error of this
algorithm. A key step in the error analysis requires bounds on the mixed
derivatives of the eigenfunction with respect to both the stochastic and
spatial variables simultaneously. Under stronger smoothness assumptions on the
parametric dependence, our analysis also extends to multilevel higher-order
quasi-Monte Carlo rules. An accompanying paper [Gilbert and Scheichl, 2022],
focusses on practical extensions of the MLQMC algorithm to improve efficiency,
and presents numerical results.",2010.01044v4
2021-03-05,Multilevel quasi-Monte Carlo for random elliptic eigenvalue problems II: Efficient algorithms and numerical results,"Stochastic PDE eigenvalue problems often arise in the field of uncertainty
quantification, whereby one seeks to quantify the uncertainty in an eigenvalue,
or its eigenfunction. In this paper we present an efficient multilevel
quasi-Monte Carlo (MLQMC) algorithm for computing the expectation of the
smallest eigenvalue of an elliptic eigenvalue problem with stochastic
coefficients. Each sample evaluation requires the solution of a PDE eigenvalue
problem, and so tackling this problem in practice is notoriously
computationally difficult. We speed up the approximation of this expectation in
four ways: we use a multilevel variance reduction scheme to spread the work
over a hierarchy of FE meshes and truncation dimensions; we use QMC methods to
efficiently compute the expectations on each level; we exploit the smoothness
in parameter space and reuse the eigenvector from a nearby QMC point to reduce
the number of iterations of the eigensolver; and we utilise a two-grid
discretisation scheme to obtain the eigenvalue on the fine mesh with a single
linear solve. The full error analysis of a basic MLQMC algorithm is given in
the companion paper [Gilbert and Scheichl, 2022], and so in this paper we focus
on how to further improve the efficiency and provide theoretical justification
for using nearby QMC points and two-grid methods. Numerical results are
presented that show the efficiency of our algorithm, and also show that the
four strategies we employ are complementary.",2103.03407v3
2002-02-21,Mechanisms of spin-polarized current-driven magnetization switching,"The mechanisms of the magnetization switching of magnetic multilayers driven
by a current are studied by including exchange interaction between local
moments and spin accumulation of conduction electrons. It is found that this
exchange interaction leads to two additional terms in the
Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both
terms are proportional to the transverse spin accumulation and have comparable
magnitudes.",0202363v1
2005-10-30,Domain instability during precessional magnetization reversal,"Spin wave equations in the non-equilibrium precessing state of a
ferromagnetic system are found. They show a spin-wave instability towards
growing domains of stable magnetization. Precession of the uniform
magnetization mode is described by the Landau Lifshitz equation with the
exponentially growing in time effective Gilbert dissipation constant that could
have both signs. On the developed stages of the domain instability a
non-stationary picture of domain chaos is observed.",0510817v1
1991-12-02,Perturbations of a Stringy Black Hole,"We extend the three dimensional stringy black hole of Horne and Horowitz to
four dimensions. After a brief discussion of the global properties of the
metric, we discuss the stability of the background with respect to small
perturbations, following the methods of Gilbert and of Chandrasekhar. The
potential for axial perturbations is found to be positive definite.",9112001v2
1996-05-06,Finitely presented subgroups of automatic groups and their isoperimetric functions,"We describe a general technique for embedding certain amalgamated products
into direct products. This technique provides us with a way of constructing a
host of finitely presented subgroups of automatic groups which are not even
asynchronously automatic. We can also arrange that such subgroups satisfy, at
best, an exponential isoperimetric inequality.",9605201v1
1999-07-22,Constructing Hyperbolic Manifolds,"In this paper we show how to obtain representations of Coxeter groups acting
on H^n to certain classical groups. We determine when the kernel of such a
representation is torsion-free and thus the quotient a hyperbolic n-manifold.",9907139v1
2002-02-06,Quaternionic equation for electromagnetic fields in inhomogeneous media,"We show that the Maxwell equations for arbitrary inhomogeneous media are
equivalent to a single quaternionic equation which can be considered as a
generalization of the Vekua equation for generalized analytic functions.",0202010v1
1996-02-29,Error Correction in Quantum Communication,"We show how procedures which can correct phase and amplitude errors can be
directly applied to correct errors due to quantum entanglement. We specify
general criteria for quantum error correction, introduce quantum versions of
the Hamming and the Gilbert-Varshamov bounds and comment on the practical
implementation of quantum codes.",9602022v1
2007-05-19,Log-periodic drift oscillations in self-similar billiards,"We study a particle moving at unit speed in a self-similar Lorentz billiard
channel; the latter consists of an infinite sequence of cells which are
identical in shape but growing exponentially in size, from left to right. We
present numerical computation of the drift term in this system and establish
the logarithmic periodicity of the corrections to the average drift.",0705.2790v1
2008-04-26,Asymptotic Bound on Binary Self-Orthogonal Codes,"We present two constructions for binary self-orthogonal codes. It turns out
that our constructions yield a constructive bound on binary self-orthogonal
codes. In particular, when the information rate R=1/2, by our constructive
lower bound, the relative minimum distance \delta\approx 0.0595 (for GV bound,
\delta\approx 0.110). Moreover, we have proved that the binary self-orthogonal
codes asymptotically achieve the Gilbert-Varshamov bound.",0804.4194v1
2008-11-14,Scott and Swarup's regular neighbourhood as a tree of cylinders,"Let G be a finitely presented group. Scott and Swarup have constructed a
canonical splitting of G which encloses all almost invariant sets over
virtually polycyclic subgroups of a given length. We give an alternative
construction of this regular neighbourhood, by showing that it is the tree of
cylinders of a JSJ splitting.",0811.2389v1
2009-05-04,Self-organized quantum transitions in a spin-electron coupled system,"We investigate quantum dynamics of the excited electronic states in the
double-exchange model at half-filling by solving coupled equations for the
quantum evolution of electrons and Landau-Lifshits-Gilbert equation for
classical spins. The non-adiabatic quantum transitions driving the relaxation
are coordinated through the self-organized space-time structure of the
electron/spin dynamics leading to a resonant precession analogous to the ESR
process.",0905.0311v1
2009-05-04,Oscillating Ponomarenko dynamo in the highly conducting limit,"This paper considers dynamo action in smooth helical flows in cylindrical
geometry, otherwise known as Ponomarenko dynamos, with periodic time
dependence. An asymptotic framework is developed that gives growth rates and
frequencies in the highly conducting limit of large magnetic Reynolds number,
when modes tend to be localized on resonant stream surfaces. This theory is
validated by means of numerical simulations.",0905.0415v1
2009-07-15,Barnett Effect in Thin Magnetic Films and Nanostructures,"The Barnett effect refers to the magnetization induced by rotation of a
demagnetized ferromagnet. We describe the location and stability of stationary
states in rotating nanostructures using the Landau-Lifshitz-Gilbert equation.
The conditions for an experimental observation of the Barnett effect in
different materials and sample geometries are discussed.",0907.2648v1
2009-12-24,Scenarios of Gravitino Dark Matter and their Cosmological and Particle Physics Implications,"I report on some scenarios where the gravitino is the dark matter and the
supersymmetry breaking mediated by a gauge sector.",0912.4885v1
2010-07-20,Factoring Permutation Matrices Into a Product of Tridiagonal Matrices,"Gilbert Strang posited that a permutation matrix of bandwidth $w$ can be
written as a product of $N < 2w$ permutation matrices of bandwidth 1. A proof
employing a greedy ``parallel bubblesort'' algorithm on the rows of the
permutation matrix is detailed and further points of interest are elaborated.",1007.3467v1
2011-05-26,Qu'est-ce qu'une espèce de structures? Genèse et description,"This is an overview (in french) of the Theory of Species for a general
audience. Basic notions are introduced in a non too technical manner, with an
explanation of why should one approach the notion of discrete structures in
this particular way.",1105.5406v1
2011-12-16,"Reply to the comment of T.Gilbert and D.P.Sanders on ""Capturing correlations in chaotic diffusion by approximation methods""","This is a reply to the comment by Gilbert and Sanders [arXiv:1111.6271
(2011)]. We point out that their comment is a follow-up of a previous
discussion which we briefly summarize before we refute their new criticism.",1112.3927v1
2012-03-24,A new look at finitely generated metabelian groups,"A group is metabelian if its commutator subgroup is abelian. For finitely
generated metabelian groups, classical commutative algebra, algebraic geometry
and geometric group theory, especially the latter two subjects, can be brought
to bear on their study. The object of this paper is to describe some of the new
ideas and open problems that arise.",1203.5431v1
2012-06-05,A convergent and precise finite element scheme for Landau-Lifschitz-Gilbert equation,"In this paper, we rigorously study an order 2 scheme that was previously
proposed by some of the authors. A slight modification is proposed that enables
us to prove the convergence of the scheme while simplifying in the same time
the inner iteration.",1206.0997v1
2013-01-20,Residual properties of groups defined by basic commutators,"In this paper we study the residual nilpotence of groups defined by basic
commutators. We prove that the so-called Hydra groups as well as certain of
their generalizations and quotients are, in the main, residually torsion-free
nilpotent. By way of contrast we give an example of a group defined by two
basic commutators which is not residually torsion-free nilpotent.",1301.4629v2
2013-03-21,Anisimov's Theorem for inverse semigroups,"The idempotent problem of a finitely generated inverse semigroup is the
formal language of all words over the generators representing idempotent
elements. This note proves that a finitely generated inverse semigroup with
regular idempotent problem is necessarily finite. This answers a question of
Gilbert and Noonan Heale, and establishes a generalisation to inverse
semigroups of Anisimov's Theorem for groups.",1303.5239v1
2013-10-13,Underwater Gas Expansion and Deflagration,"The underwater combustion of a propane-air mixture in an acrylic cylinder is
captured on video from multiple angles. This experiment is designed to provide
visual data and pressure time-histories for future CFD validation studies.",1310.3523v1
2013-11-14,The dimension of the leafwise reduced cohomology,"Geometric conditions are given so that the leafwise reduced cohomology is of
infinite dimension, specially for foliations with dense leaves on closed
manifolds. The main new definition involved is the intersection number of
subfoliations with ""appropriate coefficients"". The leafwise reduced cohomology
is also described for homogeneous foliations with dense leaves on closed
nilmanifolds.",1311.3518v1
2014-03-12,A semi-discrete scheme for the stochastic Landau-Lifshitz equation,"We propose a new convergent time semi-discrete scheme for the stochastic
Landau-Lifshitz-Gilbert equation. The scheme is only linearly implicit and does
not require the resolution of a nonlinear problem at each time step. Using a
martingale approach, we prove the convergence in law of the scheme up to a
subsequence.",1403.3016v1
2014-03-17,Quantum codes from affine variety codes and their subfield-subcodes,"We use affine variety codes and their subfield-subcodes for obtaining quantum
stabilizer codes via the CSS code construction. With this procedure, we get
codes with good parameters and a code whose parameters exceed the CSS quantum
Gilbert-Varshamov bound given by Feng and Ma.",1403.4060v2
2015-10-19,Decomposability of Finitely Generated Torsion-free Nilpotent Groups,"We describe an algorithm for deciding whether or not a given finitely
generated torsion-free nilpotent group is decomposable as the direct product of
nontrivial subgroups.",1510.05632v2
2016-02-27,On automatic subsets of the Gaussian integers,"Suppose that $a$ and $b$ are multiplicatively independent Gaussian integers,
that are both of modulus~$\geq \sqrt 5$. We prove that there exist a $X\subset
\mathbb Z[i]$ which is $a$-automatic but not $b$-automatic. This settles a
problem of Allouche, Cateland, Gilbert, Peitgen, Shallit, and Skordev.",1602.08579v3
2016-03-02,On self-dual double circulant codes,"Self-dual double circulant codes of odd dimension are shown to be dihedral in
even characteristic and consta-dihedral in odd characteristic. Exact counting
formulae are derived for them and used to show they contain families of codes
with relative distance satisfying a modified Gilbert-Varshamov bound.",1603.00762v1
2016-09-22,Manipulation of magnetic Skyrmions with a Scanning Tunneling Microscope,"The dynamics of a single magnetic Skyrmion in an atomic spin system under the
influence of Scanning Tunneling Microscope is investigated by computer
simulations solving the Landau-Lifshitz-Gilbert equation. Two possible
scenarios are described: manipulation with aid of a spin-polarized tunneling
current and by an electric field created by the scanning tunneling microscope.
The dynamics during the creation and annihilation process is studied and the
possibility to move single Skyrmions is showed.",1609.06797v1
2016-11-03,Quantile Reinforcement Learning,"In reinforcement learning, the standard criterion to evaluate policies in a
state is the expectation of (discounted) sum of rewards. However, this
criterion may not always be suitable, we consider an alternative criterion
based on the notion of quantiles. In the case of episodic reinforcement
learning problems, we propose an algorithm based on stochastic approximation
with two timescales. We evaluate our proposition on a simple model of the TV
show, Who wants to be a millionaire.",1611.00862v1
2017-01-30,Elementary equivalence vs commensurability for hyperbolic groups,"We study to what extent torsion-free (Gromov)-hyperbolic groups are
elementarily equivalent to their finite index subgroups. In particular, we
prove that a hyperbolic limit group either is a free product of cyclic groups
and surface groups, or admits infinitely many subgroups of finite index which
are pairwise non elementarily equivalent.",1701.08853v1
2017-08-01,Imaging from the Inside Out: Inverse Scattering with Photoactivated Internal Sources,"We propose a method to reconstruct the optical properties of a scattering
medium with subwavelength resolution. The method is based on the solution to
the inverse scattering problem with photoactivated internal sources. Numerical
simulations of three-dimensional structures demonstrate that a resolution of
approximately $\lambda/25$ is achievable.",1708.00128v1
2017-09-22,On self-dual four circulant codes,"Four circulant codes form a special class of $2$-generator, index $4$,
quasi-cyclic codes. Under some conditions on their generator matrices they can
be shown to be self-dual. Artin primitive root conjecture shows the existence
of an infinite subclass of these codes satisfying a modified Gilbert-Varshamov
bound.",1709.07548v1
2018-02-21,Enhanced global signal of neutral hydrogen due to excess radiation at cosmic dawn,"We revisit the global 21cm signal calculation incorporating a possible radio
background at early times, and find that the global 21cm signal shows a much
stronger absorption feature, which could enhance detection prospects for future
21 cm experiments. In light of recent reports of a possible low-frequency
excess radio background, we propose that detailed 21 cm calculations should
include a possible early radio background.",1802.07432v1
2019-03-22,Nonlinear Iterative Hard Thresholding for Inverse Scattering,"We consider the inverse scattering problem for sparse scatterers. An image
reconstruction algorithm is proposed that is based on a nonlinear
generalization of iterative hard thresholding. The convergence and error of the
method was analyzed by means of coherence estimates and compared to numerical
simulations.",1903.10875v1
2019-04-06,Phenomenological description of the dynamics of bipartite antiferromagnets in the limit of strong exchange,"The equation of motion of the staggered order parameter is derived in a
step-by-step manner from the coupled Landau-Lifshitz-Gilbert dynamics of
bipartite spin moments in the limit of strong antiferromagnetic exchange
coupling.",1904.03529v4
2019-04-19,Variational approximation of functionals defined on $1$-dimensional connected sets in $\mathbb{R}^n$,"In this paper we consider the Euclidean Steiner tree problem and, more
generally, (single sink) Gilbert--Steiner problems as prototypical examples of
variational problems involving 1-dimensional connected sets in $\mathbb{R}^n$.
Following the the analysis for the planar case presented in [4], we provide a
variational approximation through Ginzburg--Landau type energies proving a
$\Gamma$-convergence result for $n \geq 3$.",1904.09328v1
2020-03-02,Improved Gilbert-Varshamov Bound for Entanglement-Assisted Asymmetric Quantum Error Correction by Symplectic Orthogonality,"We propose and prove an existential theorem for entanglement-assisted
asymmetric quantum error correction. Then we demonstrate its superiority over
the conventional one.",2003.00668v2
2020-07-14,Competitively Pricing Parking in a Tree,"Motivated by demand-responsive parking pricing systems we consider
posted-price algorithms for the online metrical matching problem and the online
metrical searching problem in a tree metric. Our main result is a poly-log
competitive posted-price algorithm for online metrical searching.",2007.07294v2
2021-05-14,Very regular solution to Landau-Lifshitz system with spin-polarized transport,"In this paper, we provide a precise description of the compatibility
conditions for the initial data so that one can show the existence and
uniqueness of regular short-time solution to the Neumann initial-boundary
problem of a class of Landau-Lifshitz-Gilbert system with spin-polarized
transport, which is a strong nonlinear coupled parabolic system with non-local
energy.",2105.06616v1
2022-09-23,Limiting Distributions of Sums with Random Spectral Weights,"This paper studies the asymptotic properties of weighted sums of the form
$Z_n=\sum_{i=1}^n a_i X_i$, in which $X_1, X_2, \ldots, X_n$ are i.i.d.~random
variables and $a_1, a_2, \ldots, a_n$ correspond to either eigenvalues or
singular values in the classic Erd\H{o}s-R\'enyi-Gilbert model. In particular,
we prove central limit-type theorems for the sequences $n^{-1}Z_n$ with varying
conditions imposed on $X_1, X_2, \ldots, X_n$.",2209.11389v1
2023-09-16,Expansion of the Critical Intensity for the Random Connection Model,"We derive an asymptotic expansion for the critical percolation density of the
random connection model as the dimension of the encapsulating space tends to
infinity. We calculate rigorously the first expansion terms for the Gilbert
disk model, the hyper-cubic model, the Gaussian connection kernel, and a
coordinate-wise Cauchy kernel.",2309.08830v1
2024-03-14,Remarks on the rate of linear vortex symmetrization,"We reformulate results from the paper ``Linear vortex symmetrization: The
spectral density function"" by Ionescu and the author in simplified forms and
derive rigorously the bounds given in Bassom and Gilbert (J. Fluid Mech.,
1998), which provided interesting insights on the vortex symmetrization
phenomenon.",2403.09397v1
2003-10-29,Comparing Chemical Abundances of the Damped Lya Systems and Metal-Poor Stars,"I briefly draw comparisons between the fields of damped Lya and metal-poor
stellar abundances. In particular, I examine their complementary
age-metallicity relations and comparisons between the damped Lya and dwarf
galaxy abundance patterns. Regarding the latter, I describe a series of
problems concerning associating high z damped Lya systems with present-day
dwarfs.",0310850v1
2006-12-01,Stochastic excitation and damping of solar-type oscillations,"A review on acoustic mode damping and excitation in solar-type stars is
presented. Current models for linear damping rates are discussed in the light
of recent low-degree solar linewidth measurements with emphasis on the
frequency-dependence of damping rates of low-order modes. Recent developments
in stochastic excitation models are reviewed and tested against the latest
high-quality data of solar-like oscillations, such as from alpha Cen A, and
against results obtained from hydrodynamical simulations.",0612024v1
1997-08-11,A theoretical study on the damping of collective excitations in a Bose-Einstein condensate,"We study the damping of low-lying collective excitations of condensates in a
weakly interacting Bose gas model within the framework of imaginary time path
integral. A general expression of the damping rate has been obtained in the low
momentum limit for both the very low temperature regime and the higher
temperature regime. For the latter, the result is new and applicable to recent
experiments. Theoretical predictions for the damping rate are compared with the
experimental values.",9708080v3
1997-09-24,Damping in dilute Bose gases: a mean-field approach,"Damping in a dilute Bose gas is investigated using a mean-field approximation
which describes the coupled oscillations of condensate and non-condensate atoms
in the collisionless regime. Explicit results for both Landau and Beliaev
damping rates are given for non-uniform gases. In the case of uniform systems
we obtain results for the damping of phonons both at zero and finite
temperature. The isothermal compressibility of a uniform gas is also discussed.",9709259v1
2000-09-01,Damped Bogoliubov excitations of a condensate interacting with a static thermal cloud,"We calculate the damping of condensate collective excitations at finite
temperatures arising from the lack of equilibrium between the condensate and
thermal atoms. We neglect the non-condensate dynamics by fixing the thermal
cloud in static equilibrium. We derive a set of generalized Bogoliubov
equations for finite temperatures that contain an explicit damping term due to
collisional exchange of atoms between the two components. We have numerically
solved these Bogoliubov equations to obtain the temperature dependence of the
damping of the condensate modes in a harmonic trap. We compare these results
with our recent work based on the Thomas-Fermi approximation.",0009021v2
2000-11-20,Cavity assisted quasiparticle damping in a Bose-Einstein condensate,"We consider an atomic Bose-Einstein condensate held within an optical cavity
and interacting with laser fields. We show how the interaction of the cavity
mode with the condensate can cause energy due to excitations to be coupled to a
lossy cavity mode, which then decays, thus damping the condensate, how to
choose parameters for damping specific excitations, and how to target a range
of different excitations to potentially produce extremely cold condensates.",0011341v2
2002-12-16,The nonlinear damping of Bose-Einstein condensate oscillations at ultra-low temperatures,"We analyze the damping of the transverse breathing mode in an elongated trap
at ultralow temperatures. The damping occurs due to the parametric resonance
entailing the energy transfer to the longitudinal degrees of freedom. It is
found that the nonlinear coupling between the transverse and discrete
longitudinal modes can result in an anomalous behavior of the damping as a
function of time with the partially reversed pumping of the breathing mode. The
picture revealed explains the results observed in [16].",0212377v2
2004-08-27,Tunable magnetization damping in transition metal ternary alloys,"We show that magnetization damping in Permalloy, Ni80Fe20 (``Py''), can be
enhanced sufficiently to reduce post-switching magnetization precession to an
acceptable level by alloying with the transition metal osmium (Os). The damping
increases monotonically upon raising the Os-concentration in Py, at least up to
9% of Os. Other effects of alloying with Os are suppression of magnetization
and enhancement of in-plane anisotropy. Magnetization damping also increases
significantly upon alloying with the five other transition metals included in
this study (4d-elements: Nb, Ru, Rh; 5d-elements: Ta, Pt) but never as strongly
as with Os.",0408608v1
2005-03-06,Nonlinear damping in nanomechanical beam oscillator,"We investigate the impact of nonlinear damping on the dynamics of a
nanomechanical doubly clamped beam. The beam is driven into nonlinear regime
and the response is measured by a displacement detector. For data analysis we
introduce a nonlinear damping term to Duffing equation. The experiment shows
conclusively that accounting for nonlinear damping effects is needed for
correct modeling of the nanomechanical resonators under study.",0503130v2
2006-05-23,The origin of increase of damping in transition metals with rare earth impurities,"The damping due to rare earth impurities in transition metals is discussed in
the low concentration limit. It is shown that the increase in damping is mainly
due to the coupling of the orbital moments of the rare earth impurities and the
conduction $p$-electrons. It is shown that an itinerant picture for the host
transition ions is needed to reproduce the observed dependence of the damping
on the total angular moment of the rare earths.",0605583v1
2001-05-14,Simplified models of electromagnetic and gravitational radiation damping,"In previous work the authors analysed the global properties of an approximate
model of radiation damping for charged particles. This work is put into context
and related to the original motivation of understanding approximations used in
the study of gravitational radiation damping. It is examined to what extent the
results obtained previously depend on the particular model chosen. Comparisons
are made with other models for gravitational and electromagnetic fields. The
relation of the kinetic model for which theorems were proved to certain
many-particle models with radiation damping is exhibited.",0105045v1
1994-06-07,Damping Rate of a Yukawa Fermion at Finite Temperature,"The damping of a massless fermion coupled to a massless scalar particle at
finite temperature is considered using the Braaten-Pisarski resummation
technique. First the hard thermal loop diagrams of this theory are extracted
and effective Green's functions are constructed. Using these effective Green's
functions the damping rate of a soft Yukawa fermion is calculated. This rate
provides the most simple example for the damping of a soft particle. To leading
order it is proportional to $g^2T$, whereas the one of a hard fermion is of
higher order.",9406242v1
2006-05-02,Moduli decay in the hot early Universe,"We consider moduli fields interacting with thermalized relativistic matter.
We determine the temperature dependence of their damping rate and find it is
dominated by thermal effects in the high temperature regime, i.e. for
temperatures larger than their mass. For a simple scalar model the damping rate
is expressed through the known matter bulk viscosity. The high temperature
damping rate is always smaller than the Hubble rate, so that thermal effects
are not sufficient for solving the cosmological moduli problem.",0605030v2
2006-11-27,Inviscid limit for damped and driven incompressible Navier-Stokes equations in ${{\mathbb R}^2}$,"We consider the zero viscosity limit of long time averages of solutions of
damped and driven Navier-Stokes equations in ${\mathbb R}^2$. We prove that the
rate of dissipation of enstrophy vanishes. Stationary statistical solutions of
the damped and driven Navier-Stokes equations converge to renormalized
stationary statistical solutions of the damped and driven Euler equations.
These solutions obey the enstrophy balance.",0611782v1
2003-09-09,Traveling solitons in the damped driven nonlinear Schrödinger equation,"The well known effect of the linear damping on the moving nonlinear
Schr\""odinger soliton (even when there is a supply of energy via the spatially
homogeneous driving) is to quench its momentum to zero. Surprisingly, the zero
momentum does not necessarily mean zero velocity. We show that two or more
parametrically driven damped solitons can form a complex traveling with zero
momentum at a nonzero constant speed.
  All traveling complexes we have found so far, turned out to be unstable.
Thus, the parametric driving is capable of sustaining the uniform motion of
damped solitons, but some additional agent is required to stabilize it.",0309031v1
2001-11-25,The Landau Damping Effect and Complex-valued Nature of Physical Quantities,"Within the framework of the hypothesis offered by authors about
complex-valued nature of physical quantities, the effect of the Landau damping
has been explored with assumption that not only frequency can be a small
imaginary component but also a wave vector. The numerical solution of the
obtained dispersion equation testifies that uncollisional damping is
accompanied in a certain region of space by antidumping of waves, and in
particular situations antidumping may prevail over damping. It is possible that
this effect may explain the experimental difficulties connected with inhibition
of instabilities of plasma in the problem of controllable thermonuclear fusion.",0111176v1
2005-10-14,Nontrapping arrest of Langmuir wave damping near the threshold amplitude,"Evolution of a Langmuir wave is studied numerically for finite amplitudes
slightly above the threshold which separates damping from nondamping cases.
Arrest of linear damping is found to be a second-order effect due to ballistic
evolution of perturbations, resonant power transfer between field and
particles, and organization of phase space into a positive slope for the
average distribution function $f_{av}$ around the resonant wave phase speed
$v_\phi$. Near the threshold trapping in the wave potential does not arrest
damping or saturate the subsequent growth phase.",0510131v3
2000-06-22,Decoherence and Entanglement in Two-mode Squeezed Vacuum States,"I investigate the decoherence of two-mode squeezed vacuum states by analyzing
the relative entropy of entanglement. I consider two sources of decoherence:
(i) the phase damping and (ii) the amplitude damping due to the coupling to the
thermal environment. In particular, I give the exact value of the relative
entropy of entanglement for the phase damping model. For the amplitude damping
model, I give an upper bound for the relative entropy of entanglement, which
turns out to be a good approximation for the entanglement measure in usual
experimental situations.",0006100v1
2006-08-02,Damped Population Oscillation in a Spontaneously Decaying Two-Level Atom Coupled to a Monochromatic Field,"We investigate the time evolution of atomic population in a two-level atom
driven by a monochromatic radiation field, taking spontaneous emission into
account. The Rabi oscillation exhibits amplitude damping in time caused by
spontaneous emission. We show that the semiclassical master equation leads in
general to an overestimation of the damping rate and that a correct
quantitative description of the damped Rabi oscillation can thus be obtained
only with a full quantum mechanical theory.",0608020v1
2007-08-28,Linear frictional forces cause orbits to neither circularize nor precess,"For the undamped Kepler potential the lack of precession has historically
been understood in terms of the Runge-Lenz symmetry. For the damped Kepler
problem this result may be understood in terms of the generalization of Poisson
structure to damped systems suggested recently by Tarasov[1]. In this
generalized algebraic structure the orbit-averaged Runge-Lenz vector remains a
constant in the linearly damped Kepler problem to leading order in the damping
coe",0708.3827v3
2008-12-11,Frequency-dependent Drude damping in Casimir force calculations,"The Casimir force is calculated between Au thin films that are described by a
Drude model with a frequency dependent damping function. The model parameters
are obtained from available experimental data for Au thin films. Two cases are
considered; annealed and nonannealed films that have a different damping
function. Compared with the calculations using a Drude model with a constant
damping parameter, we observe changes in the Casimir force of a few percent.
This behavior is only observed in films of no more than 300 $\AA$ thick.",0812.2209v1
2008-12-18,Dipole Oscillations of a Fermi Gas in a Disordered Trap: Damping and Localization,"We theoretically study the dipole oscillations of an ideal Fermi gas in a
disordered trap. We show that even weak disorder induces strong damping of the
oscillations and we identify a metal-insulator crossover. For very weak
disorder, we show that damping results from a dephasing effect related to weak
random perturbations of the energy spectrum. For increasing disorder, we show
that the Fermi gas crosses over to an insulating regime characterized by
strong-damping due to the proliferation of localized states.",0812.3501v2
2009-03-11,Confronting the damping of the baryon acoustic oscillations with observation,"We investigate the damping of the baryon acoustic oscillations in the matter
power spectrum due to the quasinonlinear clustering and redshift-space
distortions by confronting the models with the observations of the Sloan
Digital Sky Survey luminous red galaxy sample. The chi-squared test suggests
that the observed power spectrum is better matched by models with the damping
of the baryon acoustic oscillations rather than the ones without the damping.",0903.1883v1
2009-04-10,Spectral deviations for the damped wave equation,"We prove a Weyl-type fractal upper bound for the spectrum of the damped wave
equation, on a negatively curved compact manifold. It is known that most of the
eigenvalues have an imaginary part close to the average of the damping
function. We count the number of eigenvalues in a given horizontal strip
deviating from this typical behaviour; the exponent that appears naturally is
the `entropy' that gives the deviation rate from the Birkhoff ergodic theorem
for the geodesic flow. A Weyl-type lower bound is still far from reach; but in
the particular case of arithmetic surfaces, and for a strong enough damping, we
can use the trace formula to prove a result going in this direction.",0904.1736v1
2009-10-26,Pressure Fronts in 1D Damped Nonlinear Lattices,"The propagation of pressure fronts (impact solutions) in 1D chains of atoms
coupled by anharmonic potentials between nearest neighbor and submitted to
damping forces preserving uniform motion, is investigated. Travelling fronts
between two regions at different uniform pressures are found numerically and
well approximate analytically. It is proven that there are three analytical
relations between the impact velocity, the compression, the front velocity and
the energy dissipation which only depend on the coupling potential and are
\textit{independent} of the damping. Such travelling front solutions cannot
exist without damping.",0910.4890v1
2009-11-05,Bloch oscillations in lattice potentials with controlled aperiodicity,"We numerically investigate the damping of Bloch oscillations in a
one-dimensional lattice potential whose translational symmetry is broken in a
systematic manner, either by making the potential bichromatic or by introducing
scatterers at distinct lattice sites. We find that the damping strongly depends
on the ratio of lattice constants in the bichromatic potential, and that even a
small concentration of scatterers can lead to strong damping. Moreover,
mean-field interactions are able to counteract aperiodicity-induced damping of
Bloch oscillations.",0911.1108v3
2010-01-12,Decoherence and damping in ideal gases,"The particle and current densities are shown to display damping and undergo
decoherence in ideal quantum gases. The damping is read off from the equations
of motion reminiscent of the Navier-Stokes equations and shows some formal
similarity with Landau damping. The decoherence leads to consistent density and
current histories with characteristic length and time scales given by the ideal
gas.",1001.1803v2
2010-05-14,The effect of spin magnetization in the damping of electron plasma oscillations,"The effect of spin of particles in the propagation of plasma waves is studied
using a semi-classical kinetic theory for a magnetized plasma. We focus in the
simple damping effects for the electrostatic wave modes besides Landau damping.
Without taking into account more quantum effects than spin contribution to
Vlasov's equation, we show that spin produces a new damping or instability
which is proportional to the zeroth order magnetization of the system. This
correction depends on the electromagnetic part of the wave which is coupled
with the spin vector.",1005.2573v1
2010-06-01,Recent Progress on a Manifold Damped and Detuned Structure for CLIC,"A damped detuned structure for the main X-band linacs of CLIC is being
investigated as an alternative design to the present baseline heavily damped
structure. In our earlier designs we studied detuned structures, operating at
11.994 GHz, with a range of dipole bandwidths in order to ensure the structure
satisfies beam dynamics and rf breakdown constraints. Here we report on the
development of a damped and detuned structure which satisfies both constraints.
Preparations for high power testing of the structure are also discussed",1006.0087v1
2010-07-21,Finite temperature damping of collective modes of a BCS-BEC crossover superfluid,"A new mechanism is proposed to explain the puzzling damping of collective
excitations, which was recently observed in the experiments of strongly
interacting Fermi gases below the superfluid critical temperature on the
fermionic (BCS) side of Feshbach resonance. Sound velocity, superfluid density
and damping rate are calculated with effective field theory. We find that a
dominant damping process is due to the interaction between superfluid phonons
and thermally excited fermionic quasiparticles, in contrast to the previously
proposed pair-breaking mechanism. Results from our effective model are compared
quantitatively with recent experimental findings, showing a good agreement.",1007.3694v2
2010-08-04,Confinement induced by fermion damping in three-dimensional QED,"The three-dimensional non-compact QED is known to exhibit weak confinement
when fermions acquire a finite mass via the mechanism of dynamical chiral
symmetry breaking. In this paper, we study the effect of fermion damping caused
by elastic scattering on the classical potential between fermions. By
calculating the vacuum polarization function that incorporates the fermion
damping effect, we show that fermion damping can induce a weak confinement even
when the fermions are massless and the chiral symmetry is not broken.",1008.0736v2
2011-06-22,Highly Damped Quasinormal Modes and the Small Scale Structure of Quantum Corrected Black Hole Exteriors,"Quasinormal modes provide valuable information about the structure of
spacetime outside a black hole. There is also a conjectured relationship
between the highly damped quasinormal modes and the semi-classical spectrum of
the horizon area/entropy. In this paper, we show that for spacetimes
characterized by more than one scale, the ""infinitely damped"" modes in
principle probe the structure of spacetime outside the horizon at the shortest
length scales. We demonstrate this with the calculation of the highly damped
quasinormal modes of the non-singular, single horizon, quantum corrected black
hole derived in [14].",1106.4357v1
2012-02-20,Simple Non-Markovian Microscopic Models for the Depolarizing Channel of a Single Qubit,"The archetypal one-qubit noisy channels ---depolarizing, phase-damping and
amplitude-damping channels--- describe both Markovian and non-Markovian
evolution. Simple microscopic models for the depolarizing channel, both
classical and quantum, are considered. Microscopic models which describe phase
damping and amplitude damping channels are briefly reviewed.",1202.4210v4
2012-05-11,On radiative damping in plasma-based accelerators,"Radiative damping in plasma-based electron accelerators is analyzed. The
electron dynamics under combined influence of the constant accelerating force
and the classical radiation reaction force is studied. It is shown that
electron acceleration cannot be limited by radiation reaction. If initially the
accelerating force was stronger than the radiation reaction force then the
electron acceleration is unlimited. Otherwise the electron is decelerated by
radiative damping up to a certain instant of time and then accelerated without
limits. Regardless of the initial conditions the infinite-time asymptotic
behavior of an electron is governed by self-similar solution providing
unlimited acceleration. The relative energy spread induced by the radiative
damping decreases with time in the infinite-time limit.",1205.2436v1
2012-06-14,Damping of optomechanical disks resonators vibrating in air,"We report on miniature GaAs disk optomechanical resonators vibrating in air
in the radiofrequency range. The flexural modes of the disks are studied by
scanning electron microscopy and optical interferometry, and correctly modeled
with the elasticity theory for annular plates. The mechanical damping is
systematically measured, and confronted with original analytical models for air
damping. Formulas are derived that correctly reproduce both the mechanical
modes and the damping behavior, and can serve as design tools for
optomechanical applications in fluidic environment.",1206.3032v1
2012-07-09,A Generalized Interpolation Inequality and its Application to the Stabilization of Damped Equations,"In this paper, we establish a generalized H{\""o}lder's or interpolation
inequality for weighted spaces in which the weights are non-necessarily
homogeneous. We apply it to the stabilization of some damped wave-like
evolution equations. This allows obtaining explicit decay rates for smooth
solutions for more general classes of damping operators. In particular, for
$1-d$ models, we can give an explicit decay estimate for pointwise damping
mechanisms supported on any strategic point.",1207.2030v2
2012-07-10,Conformation dependent damping and generalization of fluctuation-dissipation relation,"Damping on an object generally depends on its conformation (shape size etc.).
We consider the Langevin dynamics of a model system with a conformation
dependent damping and generalize the fluctuation dissipation relation to fit in
such a situation. We derive equilibrium distribution function for such a case
which converges to the standard Boltzmann form at the limit of uniform damping.
The results can have implications, in general, for barrier overcoming processes
where standard Boltzmann statistics is slow.",1207.2218v2
2012-10-30,On algebraic damping close to inhomogeneous Vlasov equilibria in multi-dimensional spaces,"We investigate the asymptotic damping of a perturbation around inhomogeneous
stable stationary states of the Vlasov equation in spatially multi-dimensional
systems. We show that branch singularities of the Fourier-Laplace transform of
the perturbation yield algebraic dampings. In two spatial dimensions, we
classify the singularities and compute the associated damping rate and
frequency. This 2D setting also applies to spherically symmetric
self-gravitating systems. We validate the theory using a toy model and an
advection equation associated with the isochrone model, a model of spherical
self-gravitating systems.",1210.8040v1
2013-04-07,Phenomenological model of anomalous magnon softening and damping in half-metallic manganites,"To describe anomalous zone-boundary softening and damping of magnons in
manganites we present a phenomenological two-fluid model containing
ferromagnetic Fermi-liquid and non-Fermi-liquid components. The Fermi-liquid
component accounts for softening of zone-boundary magnons and for the Landau
damping of magnons in the Stoner continuum arising at low frequencies due to
zero-point effects. Coupling of the Fermi-liquid and non-Fermi-liquid fluids
yields conventional long wavelength magnons damped due to their coupling with
longitudinal spin fluctuations.",1304.1983v1
2013-04-25,Determination of Transverse Density Structuring from Propagating MHD Waves in the Solar Atmosphere,"We present a Bayesian seismology inversion technique for propagating
magnetohydrodynamic (MHD) transverse waves observed in coronal waveguides. The
technique uses theoretical predictions for the spatial damping of propagating
kink waves in transversely inhomogeneous coronal waveguides. It combines wave
amplitude damping length scales along the waveguide with theoretical results
for resonantly damped propagating kink waves to infer the plasma density
variation across the oscillating structures. Provided the spatial dependence of
the velocity amplitude along the propagation direction is measured and the
existence of two different damping regimes is identified, the technique would
enable us to fully constrain the transverse density structuring, providing
estimates for the density contrast and its transverse inhomogeneity length
scale.",1304.6869v1
2013-07-08,Optimal decay rate of the bipolar Euler-Poisson system with damping in $\mathbb{R}^3$,"By rewriting a bipolar Euler-Poisson equations with damping into an Euler
equation with damping coupled with an Euler-Poisson equation with damping, and
using a new spectral analysis, we obtain the optimal decay results of the
solutions in $L^2$-norm, which improve theose in \cite{Li3, Wu3}. More
precisely, the velocities $u_1,u_2$ decay at the $L^2-$rate $(1+t)^{-{5}{4}}$,
which is faster than the normal $L^2-$rate $(1+t)^{-{3}{4}}$ for the Heat
equation and the Navier-Stokes equations. In addition, the disparity of two
densities $\rho_1-\rho_2$ and the disparity of two velocities $u_1-u_2$ decay
at the $L^2$-rate $(1+t)^{-2}$.",1307.2081v1
2013-07-27,Symmetry considerations on radiation damping,"It is well known that a direct Lagrangian description of radiation damping is
still missing. In this paper we will use a specific approach of this problem
which is the standard way to treat the radiation damping problem. The
objectives here are to construct: a N=2 supersymmetric extension for the model
describing the radiation damping on the noncommutative plane with electric and
magnetic interactions; a dualization analysis of the original action; the
supercharge algebra and the total Hamiltonian for the system.",1307.7319v1
2014-02-10,Damping of a nanocantilever by paramagnetic spins,"We compute damping of mechanical oscillations of a cantilever that contains
flipping paramagnetic spins. This kind of damping is mandated by the dynamics
of the total angular momentum, spin + mechanical. Rigorous expression for the
damping rate is derived in terms of measurable parameters. The effect of spins
on the quality factor of the cantilever can be significant in cantilevers of
small length that have large concentration of paramagnetic spins of atomic
and/or nuclear origin.",1402.2326v1
2014-02-20,Long-time behavior of solutions of a BBM equation with generalized damping,"We study the long-time behavior of the solution of a damped BBM equation $u_t
+ u_x - u_{xxt} + uu_x + \mathscr{L}_{\gamma}(u) = 0$. The proposed dampings
$\mathscr{L}_{\gamma}$ generalize standards ones, as parabolic
($\mathscr{L}_{\gamma}(u)=-\Delta u$) or weak damping
($\mathscr{L}_{\gamma}(u)=\gamma u$) and allows us to consider a greater range.
After establish the local well-posedness in the energy space, we investigate
some numerical properties.",1402.5009v1
2014-02-24,N=2 supersymmetric radiation damping problem on a noncommutative plane,"It is well known that a direct Lagrangian description of radiation damping is
still missing. In this paper a specific approach of this problem was used,
which is the standard way to treat the radiation damping problem. A $N=2$
supersymmetric extension for the model describing the radiation damping on the
noncommutative plane with electric and magnetic interactions was obtained. The
entire supercharge algebra and the total Hamiltonian for the system were
analyzed. Finally, noncommutativity features were introduced and its
consequences were explored..",1402.6996v1
2014-11-03,Renormalized solutions to the continuity equation with an integrable damping term,"We consider the continuity equation with a nonsmooth vector field and a
damping term. In their fundamental paper, DiPerna and Lions proved that, when
the damping term is bounded in space and time, the equation is well posed in
the class of distributional solutions and the solution is transported by
suitable characteristics of the vector field. In this paper, we prove existence
and uniqueness of renormalized solutions in the case of an integrable damping
term, employing a new logarithmic estimate inspired by analogous ideas of
Ambrosio, Lecumberry, and Maniglia, Crippa and De Lellis in the Lagrangian
case.",1411.0451v1
2015-02-07,Landau Damping in a Mixture of Bose and Fermi Superfluids,"We study the Landau damping in Bose-Fermi superfluid mixture at finite
temperature. We find that at low temperature, the Landau damping rate will be
exponentially suppressed at both the BCS side and the BEC side of Fermi
superfluid. The momentum dependence of the damping rate is obtained, and it is
quite different from the BCS side to the BEC side. The relations between our
result and collective mode experiment in the recently realized Bose-Fermi
superfluid mixture are also discussed.",1502.02116v1
2015-03-20,Applying a formula for generator redispatch to damp interarea oscillations using synchrophasors,"If an interarea oscillatory mode has insufficient damping, generator
redispatch can be used to improve its damping. We explain and apply a new
analytic formula for the modal sensitivity to rank the best pairs of generators
to redispatch. The formula requires some dynamic power system data and we show
how to obtain that data from synchrophasor measurements. The application of the
formula to damp interarea modes is explained and illustrated with interarea
modes of the New England 10-machine power system.",1503.06144v2
2016-01-21,Codeword Stabilized Quantum Codes for Asymmetric Channels,"We discuss a method to adapt the codeword stabilized (CWS) quantum code
framework to the problem of finding asymmetric quantum codes. We focus on the
corresponding Pauli error models for amplitude damping noise and phase damping
noise. In particular, we look at codes for Pauli error models that correct one
or two amplitude damping errors. Applying local Clifford operations on graph
states, we are able to exhaustively search for all possible codes up to length
$9$. With a similar method, we also look at codes for the Pauli error model
that detect a single amplitude error and detect multiple phase damping errors.
Many new codes with good parameters are found, including nonadditive codes and
degenerate codes.",1601.05763v1
2016-02-08,On Boundary Damped Inhomogeneous Timoshenko Beams and Related Problems,"We consider the model equations for the Timoshenko beam as a first order
system in the framework of evolutionary equations. The focus is on boundary
damping, which is implemented as a dynamic boundary condition. A change of
material laws allows to include a large class of cases of boundary damping. By
choosing a particular material law, it is shown that the first order approach
to Sturm-Liouville problems with boundary damping is also covered.",1602.02521v1
2016-02-13,Diffusion phenomena for the wave equation with space-dependent damping in an exterior domain,"In this paper, we consider the asymptotic behavior of solutions to the wave
equation with space-dependent damping in an exterior domain. We prove that when
the damping is effective, the solution is approximated by that of the
corresponding heat equation as time tends to infinity. Our proof is based on
semigroup estimates for the corresponding heat equation and weighted energy
estimates for the damped wave equation. The optimality of the decay late for
solutions is also established.",1602.04318v1
2016-02-29,Robust quantum state recovery from amplitude damping within a mixed states framework,"Due to the interaction with the environment, a quantum state is subjected to
decoherence which becomes one of the biggest problems for practical quantum
computation. Amplitude damping is one of the most important decoherence
processes. Here, we show that general two-qubit mixed states undergoing an
amplitude damping can be almost completely restored using a reversal procedure.
This reversal procedure through CNOT and Hadamard gates, could also protect the
entanglement of two-qubit mixed states, when it undergoes general amplitude
damping. Moreover, in the presence of uncertainty in the underlying system, we
propose a robust recovering method with optimal characteristics of the problem.",1602.08865v1
2016-05-23,Large time behaivor of global solutions to nonlinear wave equations with frictional and viscoelastic damping terms,"In this paper, we study the Cauchy problem for a nonlinear wave equation with
frictional and viscoelastic damping terms. As is pointed out by [8], in this
combination, the frictional damping term is dominant for the viscoelastic one
for the global dynamics of the linear equation. In this note we observe that if
the initial data is small, the frictional damping term is again dominant even
in the nonlinear equation case. In other words, our main result is diffusion
phenomena: the solution is approximated by the heat kernel with a suitable
constant. Our proof is based on several estimates for the corresponding linear
equations.",1605.07232v1
2016-07-21,Protecting and enhancing spin squeezing under decoherence using weak measurement,"We propose an efficient method to protect spin squeezing under the action of
amplitude-damping, depolarizing and phase-damping channels based on measurement
reversal from weak measurement, and consider an ensemble of N independent
spin-1/2 particles with exchange symmetry. We find that spin squeezing can be
enhanced greatly under three different decoherence channels and spin-squeezing
sudden death (SSSD) can be avoided undergoing amplitude damping and
phase-damping channels.",1607.06530v2
2016-09-05,Remarks on an elliptic problem arising in weighted energy estimates for wave equations with space-dependent damping term in an exterior domain,"This paper is concerned with weighted energy estimates and diffusion
phenomena for the initial-boundary problem of the wave equation with
space-dependent damping term in an exterior domain. In this analysis, an
elliptic problem was introduced by Todorova and Yordanov. This attempt was
quite useful when the coefficient of the damping term is radially symmetric. In
this paper, by modifying their elliptic problem, we establish weighted energy
estimates and diffusion phenomena even when the coefficient of the damping term
is not radially symmetric.",1609.01063v2
2016-11-16,Finite-orbit-width effects on the geodesic acoustic mode in the toroidally rotating tokamak plasma,"The Landau damping of geodesic acoustic mode (GAM) in a torodial rotating
tokamak plasma is analytically investigated by taking into account the
finite-orbit-width (FOW) resonance effect to the 3rd order. The analytical
result is shown to agree well with the numerical solution. The dependence of
the damping rate on the toroidal Mach number $M$ relies on $k_r \rho_i$. For
sufficiently small $k_r \rho_i$, the damping rate monotonically decreases with
$M$. For relatively large $k_r \rho_i$, the damping rate increases with $M$
until approaching the maximum and then decreases with $M$.",1611.05168v1
2017-03-09,Long-time dynamics of the strongly damped semilinear plate equation in $\mathbb{R}^{n}$,"We investigate the initial-value problem for the semilinear plate equation
containing localized strong damping, localized weak damping and nonlocal
nonlinearity. We prove that if nonnegative damping coefficients are strictly
positive almost everywhere in the exterior of some ball and the sum of these
coefficients is positive a.e. in $%
  \mathbb{R}
  ^{n}$, then the semigroup generated by the considered problem possesses a
global attractor in $H^{2}\left(
  \mathbb{R}
  ^{n}\right) \times L^{2}\left(
  \mathbb{R}
  ^{n}\right) $. We also establish boundedness of this attractor in $
H^{3}\left(
  \mathbb{R}
  ^{n}\right) \times H^{2}\left(
  \mathbb{R} ^{n}\right) $.",1703.03485v2
2017-04-21,The Effects of Rolling Deformation and Annealing Treatment on Damping Capacity of 1200 Aluminium Alloy,"Annealing treatment is an important step of rolling deformation that
contributes to microstructural evolution and leads to the significant changes
in damping capacity. Damping capacities were analyzed in the parallel to
rolling direction at 1 and 10 Hz respectively. It was found that severe plastic
deformation at 40 percent reduction has lower damping capacity compared to that
of 30 percent and 20 percent reductions respectively. The microstructural
results show that the grains of as rolled alloys were changed to almost
equiaxed structures after a rolling reduction at 40 percent reduction.",1704.07362v1
2017-07-12,Isolated resonances and nonlinear damping,"We analyze isolated resonance curves (IRCs) in a single-degree-of-freedom
system with nonlinear damping. The adopted procedure exploits singularity
theory in conjunction with the harmonic balance method. The analysis unveils a
geometrical connection between the topology of the damping force and IRCs.
Specifically, we demonstrate that extremas and zeros of the damping force
correspond to the appearance and merging of IRCs.",1707.03561v2
2017-07-25,Best exponential decay rate of energy for the vectorial damped wave equation,"The energy of solutions of the scalar damped wave equation decays uniformly
exponentially fast when the geometric control condition is satisfied. A theorem
of Lebeau [leb93] gives an expression of this exponential decay rate in terms
of the average value of the damping terms along geodesics and of the spectrum
of the infinitesimal generator of the equation. The aim of this text is to
generalize this result in the setting of a vectorial damped wave equation on a
Riemannian manifold with no boundary. We obtain an expression analogous to
Lebeau's one but new phenomena like high frequency overdamping arise in
comparison to the scalar setting. We also prove a necessary and sufficient
condition for the strong stabilization of the vectorial wave equation.",1707.07893v1
2017-08-20,Radiation Damping of a Polarizable Particle,"A polarizable body moving in an external electromagnetic field will slow
down. This effect is referred to as radiation damping and is analogous to
Doppler cooling in atomic physics. Using the principles of special relativity
we derive an expression for the radiation damping force and find that it solely
depends on the scattered power. The cooling of the particle's center-of-mass
motion is balanced by heating due to radiation pressure shot noise, giving rise
to an equilibrium that depends on the ratio of the field's frequency and the
particle's mass. While damping is of relativistic nature heating has it's roots
in quantum mechanics.",1708.06628v1
2017-09-13,Energy decay for the Klein-Gordon equation with highly oscillating damping,"We consider the free Klein-Gordon equation with periodic damping. We show on
this simple model that if the usual geometric condition holds then the decay of
the energy is uniform with respect to the oscillations of the damping, and in
particular the size of the derivatives do not play any role. We also show that
without geometric condition the polynomial decay of the energy is even slightly
better for a highly oscillating damping. To prove these estimates we provide a
parameter dependent version of well known results of semigroup theory.",1709.04197v1
2017-11-01,Analysis of A Splitting Scheme for Damped Stochastic Nonlinear Schrödinger Equation with Multiplicative Noise,"In this paper, we investigate the damped stochastic nonlinear
Schr\""odinger(NLS) equation with multiplicative noise and its splitting-based
approximation. When the damped effect is large enough, we prove that the
solutions of the damped stochastic NLS equation and the splitting scheme are
exponential stable and possess some exponential integrability.
  These properties lead that the strong order of the scheme is $\frac 12$ and
independent of time. Meanwhile, we analyze the regularity of the Kolmogorov
equation with respect to the equation. As a consequence, the weak order of the
scheme is shown to be twice the strong order and independent of time.",1711.00516v2
2017-12-31,Stabilization of the weakly coupled wave-plate system with one internal damping,"This paper is addressed to a stabilization problem of a system coupled by a
wave and a Euler-Bernoulli plate equation. Only one equation is supposed to be
damped. Under some assumption about the damping and the coupling terms, it is
shown that sufficiently smooth solutions of the system decay logarithmically at
infinity without any geometric conditions on the effective damping domain. The
proofs of these decay results rely on the interpolation inequalities for the
coupled elliptic-parabolic systems and make use of the estimate of the
resolvent operator for the coupled system. The main tools to derive the desired
interpolation inequalities are global Carleman estimates.",1801.00232v1
2018-05-10,Dynamics of coherence-induced state ordering under Markovian channels,"We study the dynamics of coherence-induced state ordering under incoherent
channels, particularly four specific Markovian channels: $-$ amplitude damping
channel, phase damping channel, depolarizing channel and bit flit channel for
single-qubit states. We show that the amplitude damping channel, phase damping
channel, and depolarizing channel do not change the coherence-induced state
ordering by $l_1$ norm of coherence, relative entropy of coherence, geometric
measure of coherence, and Tsallis relative $\alpha$-entropies, while the bit
flit channel does change for some special cases.",1805.03898v1
2018-08-19,Sharp lifespan estimates of blowup solutions to semilinear wave equations with time-dependent effective damping,"We consider the initial value problem for the semilinear wave equation with
time-dependent effective damping. The interest is the behavior of lifespan of
solutions in view of the asymptotic profile of the damping as $t\to \infty$.
The result of this paper is the sharp lifespan estimates of blowup solutions
for general time-dependent damping including threshold cases between effective
and overdamping.",1808.06189v2
2018-09-05,Damping estimates for oscillatory integral operators with real-analytic phases and its applications,"In this paper, we investigate sharp damping estimates for a class of one
dimensional oscillatory integral operators with real-analytic phases. By
establishing endpoint estimates for suitably damped oscillatory integral
operators, we are able to give a new proof of the sharp $L^p$ estimates which
have been proved by Xiao in Endpoint estimates for one-dimensional oscillatory
integral operators, \emph{Advances in Mathematics}, \textbf{316}, 255-291
(2017). The damping estimates obtained in this paper are of independent
interest.",1809.01298v2
2018-09-26,"Global Attractor For Weakly Damped, Forced Mkdv Equation Below Energy Space","We prove the existence of the global attractor in $ \dot H^s$, $s > 11/12$
for the weakly damped and forced mKdV on the one dimensional torus. The
existence of global attractor below the energy space has not been known, though
the global well-posedness below the energy space is established. We directly
apply the I-method to the damped and forced mKdV, because the Miura
transformation does not work for the mKdV with damping and forcing terms. We
need to make a close investigation into the trilinear estimates involving
resonant frequencies, which are different from the bilinear estimates
corresponding to the KdV.",1809.09787v1
2018-10-03,Damped Oscillator with delta-kicked frequency in probability representation of quantum mechanic,"We obtain the tomogram of squeezed correlated states of a quantum parametric
damped oscillator in an explicit form. We study the damping within the
framework of the Caldirola--Kanai model and chose the parametric excitation in
the form of a very short pulse simulated by a delta-kick of frequency; the
squeezing phenomenon is reviewed. The cases of strong and weak damping are
investigated.",1810.01672v1
2018-10-26,Drastic Reduction of Plasmon Damping in Two-Dimensional Electron Disks,"The plasmon damping has been investigated using resonant microwave absorption
of two-dimensional electrons in disks with different diameters. We have found
an unexpected drastic reduction of the plasmon damping in the regime of strong
retardation. This finding implies large delocalization of retarded plasmon
field outside the plane of the two-dimensional electron system. A universal
relation between the damping of plasmon polariton waves and retardation
parameter is reported.",1811.01040v1
2019-01-05,Cauchy problem for thermoelastic plate equations with different damping mechanisms,"In this paper we study Cauchy problem for thermoelastic plate equations with
friction or structural damping in $\mathbb{R}^n$, $n\geq1$, where the heat
conduction is modeled by Fourier's law. We explain some qualitative properties
of solutions influenced by different damping mechanisms. We show which damping
in the model has a dominant influence on smoothing effect, energy estimates,
$L^p-L^q$ estimates not necessary on the conjugate line, and on diffusion
phenomena. Moreover, we derive asymptotic profiles of solutions in a framework
of weighted $L^1$ data. In particular, sharp decay estimates for lower bound
and upper bound of solutions in the $\dot{H}^s$ norm ($s\geq0$) are shown.",1901.01423v2
2019-03-04,Damping of cosmological tensor modes in Horndeski theories after GW170817,"This paper investigates the propagation of cosmological gravitational waves
interacting with free-streaming neutrinos within the context of Horndeski
theories of gravity constrained by the detection of GW170817. We apply the
theory of cosmological perturbations to explicitly derive the
Einstein-Boltzmann equation for the damped propagation of first-order
transverse traceless gravitational waves. In contrast to general relativity, we
argue that modified gravity can give rise to non-vanishing free-streaming
damping effects during the cosmological matter dominated era. We also provide
an analytic formula for the main multipole order with which modified gravity
and free-streaming neutrinos damp the variety of tensor correlation functions
of the cosmic microwave background.",1903.01502v2
2019-04-24,On the Energy Decay Rate of the Fractional Wave Equation on $\mathbb{R}$ with Relatively Dense Damping,"We establish upper bounds for the decay rate of the energy of the damped
fractional wave equation when the averages of the damping coefficient on all
intervals of a fixed length are bounded below. If the power of the fractional
Laplacian, $s$, is between 0 and 2, the decay is polynomial. For $s \ge 2$, the
decay is exponential. Second, we show that our assumption on the damping is
necessary for the energy to decay exponentially.",1904.10946v3
2019-08-22,Damping of the Anderson-Bogolyubov mode by spin and mass imbalance in Fermi mixtures,"We study the temporally nonlocal contributions to the gradient expansion of
the pair fluctuation propagator for spin- and mass-imbalanced Fermi mixtures.
These terms are related to damping processes of sound-like
(Anderson-Bogolyubov) collective modes and are relevant for the structure of
the complex pole of the pair fluctuation propagator. We derive conditions under
which damping occurs even at zero temperature for large enough mismatch of the
Fermi surfaces. We compare our analytical results with numerically computed
damping rates of the Anderson-Bogolyubov mode.",1908.08559v2
2019-11-05,On the Smallness Condition in Linear Inviscid Damping: Monotonicity and Resonance Chains,"We consider the linearized Euler equations around a smooth, bilipschitz shear
profile $U(y)$ on $\mathbb{T}_L \times \mathbb{R}$. We construct an explicit
flow which exhibits linear inviscid damping for $L$ sufficiently small, but for
which damping fails if $L$ is large. In particular, similar to the instability
results for convex profiles for a shear flow being bilipschitz is not
sufficient for linear inviscid damping to hold. Instead of an eigenvalue-based
argument the underlying mechanism here is shown to be based on a new cascade of
resonances moving to higher and higher frequencies in $y$, which is distinct
from the echo chain mechanism in the nonlinear problem.",1911.02066v1
2020-01-02,On Echo Chains in Landau damping: Self-similar Solutions and Gevrey 3 as a Linear Stability Threshold,"We show that the linearized Vlasov-Poisson equations around self-similar
non-homogeneous states near zero contain the full plasma echo mechanism,
yielding Gevrey 3 as a critical stability class. Moreover, here Landau damping
may persist despite blow-up: We construct a critical Gevrey regularity class in
which the force field converges in $L^2$. Thus, on the one hand, the physical
phenomenon of Landau damping holds. On the other hand, the density diverges to
infinity in Sobolev regularity. Hence, ``strong damping'' cannot hold.",2001.00513v1
2020-01-21,Pseudospectra of the damped wave equation with unbounded damping,"We analyze pseudospectra of the generator of the damped wave equation with
unbounded damping. We show that the resolvent norm diverges as $\Re z \to -
\infty$. The highly non-normal character of the operator is a robust effect
preserved even when a strong potential is added. Consequently, spectral
instabilities and other related pseudospectral effects are present.",2001.07767v1
2020-02-09,The damped wave equation with singular damping,"We analyze the spectral properties and peculiar behavior of solutions of a
damped wave equation on a finite interval with a singular damping of the form
$\alpha/x$, $\alpha>0$. We establish the exponential stability of the semigroup
for all positive $\alpha$, and determine conditions for the spectrum to consist
of a finite number of eigenvalues. As a consequence, we fully characterize the
set of initial conditions for which there is extinction of solutions in finite
time. Finally, we propose two open problems related to extremal decay rates of
solutions.",2002.03440v1
2020-03-12,Optimal nonlinear damping control of second-order systems,"Novel nonlinear damping control is proposed for the second-order systems. The
proportional output feedback is combined with the damping term which is
quadratic to the output derivative and inverse to the set-point distance. The
global stability, passivity property, and convergence time and accuracy are
demonstrated. Also the control saturation case is explicitly analyzed. The
suggested nonlinear damping is denoted as optimal since requiring no design
additional parameters and ensuring a fast convergence, without transient
overshoots for a non-saturated and one transient overshoot for a saturated
control configuration.",2003.05670v3
2020-06-24,Stability of a star-shaped network with local Kelvin-Voigt damping and non-smooth coefficient at interface,"In this paper, we study the stability problem of a star-shaped network of
elastic strings with a local Kelvin-Voigt damping. Under the assumption that
the damping coefficients have some singularities near the transmission point,
we prove that the semigroup corresponding to the system is polynomially stable
and the decay rates depends on the speed of the degeneracy. This result
improves the decay rate of the semigroup associated to the system on an earlier
result of Z.~Liu and Q.~Zhang in \cite{LZ} involving the wave equation with
local Kelvin-Voigt damping and non-smooth coefficient at interface.",2006.14949v1
2020-11-06,A generalized finite element method for the strongly damped wave equation with rapidly varying data,"We propose a generalized finite element method for the strongly damped wave
equation with highly varying coefficients. The proposed method is based on the
localized orthogonal decomposition introduced and is designed to handle
independent variations in both the damping and the wave propagation speed
respectively. The method does so by automatically correcting for the damping in
the transient phase and for the propagation speed in the steady state phase.
Convergence of optimal order is proven in $L_2(H^1)$-norm, independent of the
derivatives of the coefficients. We present numerical examples that confirm the
theoretical findings.",2011.03311v1
2020-11-11,Reduction of back switching by large damping ferromagnetic material,"Recent studies on magnetization dynamics induced by spin-orbit torque have
revealed a weak dependence of the critical current for magnetization switching
on the damping constant of a ferromagnetic free layer. This study, however,
reveals that the damping constant nevertheless plays a key role in
magnetization switching induced by spin-orbit torque. An undesirable switching,
returning to an initial state, named as back switching, occurs in a ferromagnet
with an easy axis parallel to the current direction. Numerical and theoretical
analyses reveal that back switching is strongly suppressed when the damping
constant of the ferromagnet is large.",2011.05566v1
2020-12-28,Nonlinear modal analysis of nonconservative systems: Extension of the periodic motion concept,"As the motions of nonconservative autonomous systems are typically not
periodic, the definition of nonlinear modes as periodic motions cannot be
applied in the classical sense. In this paper, it is proposed 'make the motions
periodic' by introducing an additional damping term of appropriate sign and
magnitude. It is shown that this generalized definition is particularly suited
to reflect the periodic vibration behavior induced by harmonic external forcing
or negative linear damping. In a large range, the energy dependence of modal
frequency, damping ratio and stability is reproduced well. The limitation to
isolated or weakly-damped modes is discussed.",2101.00949v1
2021-02-28,Stability for an inverse source problem of the damped biharmonic plate equation,"This paper is concerned with the stability of the inverse source problem for
the damped biharmonic plate equation in three dimensions. The stability
estimate consists of the Lipschitz type data discrepancy and the high frequency
tail of the source function, where the latter decreases as the upper bound of
the frequency increases. The stability also shows exponential dependence on the
constant damping coefficient. The analysis employs Carleman estimates and time
decay estimates for the damped plate wave equation to obtain an exact
observability bound and depends on the study of the resonance-free region and
an upper bound of the resolvent of the biharmonic operator with respect to the
complex wavenumber.",2103.00461v1
2021-04-12,Lp-asymptotic stability of 1D damped wave equations with localized and linear damping,"In this paper, we study the $L^p$-asymptotic stability of the one-dimensional
linear damped wave equation with Dirichlet boundary conditions in $[0,1]$, with
$p\in (1,\infty)$. The damping term is assumed to be linear and localized to an
arbitrary open sub-interval of $[0,1]$. We prove that the semi-group
$(S_p(t))_{t\geq 0}$ associated with the previous equation is well-posed and
exponentially stable. The proof relies on the multiplier method and depends on
whether $p\geq 2$ or $1<p<2$.",2104.05679v1
2021-05-13,Sharp Polynomial Decay for Waves Damped from the Boundary in Cylindrical Waveguides,"We study the decay of global energy for the wave equation with H\""older
continuous damping placed on the $C^{1,1}$-boundary of compact and non-compact
waveguides with star-shaped cross-sections. We show there is sharp
$t^{-1/2}$-decay when the damping is uniformly bounded from below on the
cylindrical wall of product cylinders where the Geometric Control Condition is
violated. On non-product cylinders, we also show that there is $t^{-1/3}$-decay
when the damping is uniformly bounded from below on the cylindrical wall.",2105.06566v1
2021-06-02,Stabilisation of the generalised Rao-Nakra beam by partial viscous damping,"In this paper, we consider the stabilization of the generalized Rao-Nakra
beam equation, which consists of four wave equations for the longitudinal
displacements and the shear angle of the top and bottom layers and one
Euler-Bernoulli beam equation for the transversal displacement. Dissipative
mechanism are provided through viscous damping for two displacements. The
location of the viscous damping are divided into two groups, characterized by
whether both of the top and bottom layers are directly damped or otherwise.
Each group consists of three cases. We obtain the necessary and sufficient
conditions for the cases in group two to be strongly stable. Furthermore,
polynomial stability of certain orders are proved. The cases in group one are
left for future study",2106.01189v1
2021-09-01,Vibration damping platform for cavity quantum-electrodynamics experiments,"We present a mechanical platform with enhanced vibration damping properties
for cavity quantum-electrodynamics experiments. It is based on a composite
design that combines a soft, vibration-damping core with a rigid shell
maintaining optical alignment. It passively damps the vibrations generated by
piezoelectric actuators controlling the mirror positions. The mechanical
resonances of the platform, which lead to a length change of the cavity are
efficiently suppressed up to 100 kHz. Our platform is ultra-high vacuum
compatible and can be used in most applications, in particular where long
cavities and optical access to the cavity center are required.",2109.00439v1
2021-09-05,"Existence of a generalized polynomial attractor for the wave equation with nonlocal weak damping, anti-damping and critical nonlinearity","In this paper, we first establish a criterion based on contractive function
for the existence of polynomial attractors. This criterion only involves some
rather weak compactness associated with the repeated limit inferior and
requires no compactness, which makes it suitable for critical cases. Then by
this abstract theorem, we verify the existence of a polynomial attractor and
estimate its attractive speed for the wave equation with nonlocal weak damping,
anti-damping and critical nonlinearity.",2109.01967v2
2021-11-29,Stabilization of coupled wave equations with viscous damping on cylindrical and non-regular domains: Cases without the geometric control condition,"In this paper, we investigate the direct and indirect stability of locally
coupled wave equations with local viscous damping on cylindrical and
non-regular domains without any geometric control condition. If only one
equation is damped, we prove that the energy of our system decays polynomially
with the rate $t^{-\frac{1}{2}}$ if the two waves have the same speed of
propagation, and with rate $t^{-\frac{1}{3}}$ if the two waves do not propagate
at the same speed. Otherwise, in case of two damped equations, we prove a
polynomial energy decay rate of order $t^{-1}$.",2111.14554v1
2022-01-25,Linear pair creation damping of high frequency plasma oscillation,"We have studied the linear dispersion relation for Langmuir waves in plasmas
of very high density, based on the Dirac-Heisenberg-Wigner formalism. The
vacuum contribution to the physical observables leads to ultra-violet
divergences, that are removed by a charge renormalization. The remaining vacuum
contribution is small, and is in agreement with previously derived expressions
for the time-dependent vacuum polarization. The main new feature of the theory
is a damping mechanism similar to Landau damping, but where the plasmon energy
give rise to creation of electron-positron pairs. The dependence of the damping
rate (pair-creation rate) on wave-number, temperature, and density is analyzed.
Finally, the analytical results of linearized theory are compared.",2201.10370v1
2022-03-13,Continuum damping of topologically-protected edge modes at the boundary of a magnetized plasma,"Recent extension of the topological ideas to continuous systems with broken
time-reversal symmetry, such as magnetized plasmas, provides new insights into
the nature of scattering-free topologically-protected surface plasma waves
(TSPWs). We demonstrate a unique characteristic of TSPWs propagating above the
electron cyclotron frequency: their collisionless damping via coupling to the
continuum of resonant modes localized inside a smooth plasma-vacuum interface.
Damped TSPWs retain their unidirectional nature and robustness against
backscattering. When sheared magnetic field creates a boundary between damped
and undamped TSPWs, the two refract into each other without reflections",2203.06693v2
2022-04-21,On scattering and damping of Toroidal Alfven eigenmode by drift wave turbulence,"We demonstrate analytically that, in toroidal plasmas, scattering by drift
wave turbulence could lead to appreciable damping of toroidal Alfven eigenmodes
via generation of short-wavelength electron Landau damped kinetic Alfven waves.
A corresponding analytic expression of the damping rate is derived, and found
to be, typically, comparable to the linear drive by energetic particles. The
implications of this novel mechanism on the transport and heating processes in
burning plasmas are also discussed.",2204.09876v1
2022-10-30,Intrinsic polynomial squeezing for Balakrishnan-Taylor beam models,"We explore the energy decay properties related to a model in extensible beams
with the so-called energy damping. We investigate the influence of the
nonloncal damping coefficient in the stability of the model. We prove, for the
first time, that the corresponding energy functional is squeezed by
polynomial-like functions involving the power of the damping coefficient, which
arises intrinsically from the Balakrishnan-Taylor beam models. As a
consequence, it is shown that such models with nonlocal energy damping are
never exponentially stable in its essence.",2210.16931v1
2023-02-13,Damping of gravitational waves in f(R) gravity,"We study the damping of $f(R)$ gravitational waves by matter in flat
spacetime and in expanding universe. In the former case, we find that the
Landau damping of scalar mode in $f(R)$ theory exists, while that of the tensor
mode in general relativity does not; we also present the viscosity coefficients
and dispersion relations of the two modes. In the later case, we investigate
the evolution of tensor and scalar modes in Friedmann-Robertson-Walker (FRW)
cosmology with a matter distribution; by considering the case of $f(R)=R+\al
R^2$, we analysis the influence of parameter $\al$ on wave damping,and put
restrictions on its magnitude.",2302.06402v2
2023-07-11,Global smooth solution for the 3D generalized tropical climate model with partial viscosity and damping,"The three-dimensional generalized tropical climate model with partial
viscosity and damping is considered in this paper. Global well-posedness of
solutions of the three-dimensional generalized tropical climate model with
partial viscosity and damping is proved for $\alpha\geq\frac{3}{2}$ and
$\beta\geq4$. Global smooth solution of the three-dimensional generalized
tropical climate model with partial viscosity and damping is proved in
$H^s(\mathbb R^3)$ $(s>2)$ for $\alpha\geq\frac{3}{2}$ and $4\leq\beta\leq5$.",2307.05145v3
2023-08-07,Reconstruction of the initial data from the solutions of damped wave equations,"In this paper, we consider two types of damped wave equations: the weakly
damped equation and the strongly damped equation and show that the initial
velocity from the solution on the unit sphere. This inverse problem is related
to Photoacoustic Tomography (PAT), a hybrid medical imaging technique. PAT is
based on generating acoustic waves inside of an object of interest and one of
the mathematical problem in PAT is reconstructing the initial velocity from the
solution of the wave equation measured on the outside of object. Using the
spherical harmonics and spectral theorem, we demonstrate a way to recover the
initial velocity.",2308.03362v1
2023-09-26,Sharp conditions for exponential and non-exponential uniform stabilization of the time dependent damped wave equation,"It is classical that uniform stabilization of solutions to the damped wave
equation is equivalent to the geometric control condition The author previously
showed that, when the damping depends on time, a generalization of the
geometric control condition implies uniform stabilization at an exponential
rate. In this paper, it is shown that this generalization of the geometric
control condition is necessary for uniform stabilization at an exponential
rate. Furthermore, when the damping does not satisfy this generalization, and
has some additional structure, upper and lower bounds on non-exponential
uniform stabilization are computed. The qualitative behavior of these upper and
lower bounds coincide.",2309.15005v1
2023-10-19,The damped focusing cubic wave equation on a bounded domain,"For the focusing cubic wave equation on a compact Riemannian manifold of
dimension $3$, the dichotomy between global existence and blow-up for solutions
starting below the energy of the ground state is known since the work of Payne
and Sattinger. In the case of a damped equation, we prove that the dichotomy
between global existence and blow-up still holds. In particular, the damping
does not prevent blow-up. Assuming that the damping satisfies the geometric
control condition, we then prove that any global solution converges to a
stationary solution along a time sequence, and that global solutions below the
energy of the ground state can be stabilised, adapting the proof of a similar
result in the defocusing case.",2310.12644v2
2024-04-03,Damping Reveals Hidden Dimensions in Elastic Metastructures Through Induced Transparency,"Damping typically results in attenuation of vibrations and elastic wave
propagation in mechanical systems. Contrary to this conventional understanding,
we demonstrate experimentally and explain theoretically the revival of an
elastic wave transmitted through a periodic metastructure when a weak
non-Hermitian defect (damping mechanism) induces violation of time-reversal
symmetry. Damping alters the nature of the system's resonant modes, instigating
interference in the scattering field. This leads to transmission revival,
revealing the presence of hidden modes which are otherwise masked by the
symmetry. Our findings offer an innovative approach for designing
dissipation-driven switches and controllers and non-destructive structural
health monitoring systems.",2404.02979v1
1997-06-30,Damped Lyman Alpha Systems at High Redshift and Models of Protogalactic Disks,"We employ observationally determined intrinsic velocity widths and column
densities of damped Lyman-alpha systems at high redshift to investigate the
distribution of baryons in protogalaxies within the context of a standard cold
dark matter model. We proceed under the assumption that damped Lyman alpha
systems represent a population of cold, rotationally supported, protogalactic
disks and that the abundance of protogalactic halos is well approximated by a
cold dark matter model with critical density and vanishing cosmological
constant. Using conditional cross sections to observe a damped system with a
given velocity width and column density, we compare observationally inferred
velocity width and column density distributions to the corresponding
theoretically determined distributions for a variety of disk parameters and CDM
normalizations. In general, we find that the observations can not be reproduced
by the models for most disk parameters and CDM normalizations. Whereas the
column density distribution favors small disks with large neutral gas fraction,
the velocity width distribution favors large and thick disks with small neutral
gas fraction. The possible resolutions of this problem in the context of this
CDM model may be: (1) an increased contribution of rapidly rotating disks
within massive dark matter halos to damped Lyman-alpha absorption or (2) the
abandoning of simple disk models within this CDM model for damped Lyman-alpha
systems at high redshift. Here the first possibility may be achieved by
supposing that damped Lya system formation only occurs in halos with fairly
large circular velocities and the second possibility may result from a large
contribution of mergers and double-disks to damped Lya absorption at high
redshift.",9706290v1
2000-03-16,Non-existence of radiation damping of gravitational motions,"A rigorous, non-perturbative proof that there is no radiation damping of
gravitational motions.",0003230v1
2006-07-14,Lagrangian description of the radiation damping,"We present a Lagrangian formalism to the dissipative system of a charge
interacting with its own radiation field, which gives rise to the radiation
damping \cite{Heitler}, by the indirect representation doubling the phase-space
dimensions.",0607370v1
1994-05-17,Damping Rate of a Hard Photon in a Relativistic Plasma,"The damping rate of a hard photon in a hot relativistic QED and QCD plasma is
calculated using the resummation technique by Braaten and Pisarski.",9405309v1
1998-04-08,Evidence for xi- and t-dependent damping of the Pomeron Flux in the proton,"We show that a triple-Regge parametrization of inclusive single diffraction
agrees with the data in the following two domains: (a) xi > 0.03 at all t, (b)
|t| > 1 GeV^2 at all xi. Since the triple-Regge parametrization fails when
applied to the full xi-t range of the total single-diffractive cross section,
we conclude that damping occurs only at low-xi and low-|t|. We give a (``toy'')
parametrization of the damping factor, D(xi), valid at low-|t|, which describes
the diffractive differential cross-section (dsig/dt) data at the ISR and
roughly accounts for the observed s-dependence of diffractive total
cross-section up to Tevatron energies. However, an effective damping factor
calculated for the CDF fitted function for dsig/dxidt at sqrt(s} = 1800 GeV and
|t| = 0.05 GeV^2, suggests that, at fixed-xi, damping increases as s increases.
  We conjecture that, in the regions where the triple-Regge formalism describes
the data and there is no evidence of damping, factorization is valid and the
Pomeron-flux-factor may be universal. With the assumption that the observed
damping is due to multi-Pomeron exchange, our results imply that the recent UA8
demonstration that the effective Pomeron trajectory flattens for |t| > 1 GeV$^2
is evidence for the onset of the perturbative 2-gluon pomeron. Our damping
results may also shed some light on the self-consistency of recent measurements
of hard-diffractive jet production cross sections in the UA8, CDF and ZEUS
experiments.",9804257v1
2001-11-27,On the uniphase steady solutions of the nonlinear damped wave equation,"We study the steady uniphase and multiphase solutions of the discretized
nonlinear damped wave equation.Conditions for the stability abd instability of
the steady solutions are given;in the instability case the linear stable and
unstable associated manifolds are described.",0111281v1
2006-09-05,Damping estimates for oscillatory integral operators with finite type singularities,"We derive damping estimates and asymptotics of $L^p$ operator norms for
oscillatory integral operators with finite type singularities. The methods are
based on incorporating finite type conditions into $L^2$ almost orthogonality
technique of Cotlar-Stein.",0609145v1
2002-02-19,"On ""the authentic damping mechanism"" of the phonon damping model. II","This article continues a discussion raised in previous publications (LANL
preprint server, nucl-th/0202006 and nucl-th/0202020). I try to convince my
opponents that general arguments are not ""my case"" and may be applied to their
model.",0202058v1
1996-12-27,Coherent and trajectory-coherent states of a damped harmonic oscillator,"In this paper we construct the coherent and trajectory-coherent states of a
damped harmonic oscillator. We investigate the properties of this states.",9612051v2
2003-05-21,Probability representation of kinetic equation for open quantum system,"The tomographic probability distribution is used to decribe the kinetic
equations for open quantum systems. Damped oscillator is studied. Purity
parameter evolution for different damping regime is considered.",0305119v1
2007-08-09,The resonant damping of fast magnetohydrodynamic oscillations in a system of two coronal slabs,"Observations of transversal coronal loop oscillations very often show the
excitation and damping of oscillations in groups of coronal loops rather than
in individual and isolated structures. We present results on the oscillatory
properties (periods, damping rates, and spatial distribution of perturbations)
for resonantly damped oscillations in a system of two inhomogeneous coronal
slabs and compare them to the properties found in single slab loop models. A
system of two identical coronal loops is modeled, in Cartesian geometry, as
being composed by two density enhancements. The linear magnetohydrodynamic
(MHD) wave equations for oblique propagation of waves are solved and the
damping of the different solutions, due to the transversal inhomogeneity of the
density profile, is computed. The physics of the obtained results is analyzed
by an examination of the perturbed physical variables. We find that, due to the
interaction between the loops, the normal modes of oscillation present in a
single slab split into symmetric and antisymmetric oscillations when a system
of two identical slabs is considered. The frequencies of these solutions may
differ from the single slab results when the distance between the loops is of
the order of a few slab widths. Oblique propagation of waves weakens this
interaction, since solutions become more confined to the edges of the slabs.
The damping is strong for surface-like oscillations, while sausage body-like
solutions are unaffected. For some solutions, and small slab separations, the
damping in a system of two loops differs substantially from the damping of a
single loop.",0708.1251v1
2009-12-08,Exact Invariant Solutions for Generalized Invicid Burgers' Equation with Damping,"In this work we study the Lie group analysis of a generalized invicid
Burgers' equations with damping. Seven inequivalent classes of this generalized
equation were classified and many exact and transformed solutions were obtained
for each class.",0912.1631v1
2011-07-28,Creating quantum discord through local generalized amplitude damping,"We show that two qubits initially in completely classical state can create
quantum discord through a local generalized amplitude damping channel, but high
temperature will impede the creating of quantum discord.",1107.5670v1
2011-09-06,Damping of Alfven waves in solar partially ionized plasmas: effect of neutral helium in multi-fluid approach,"Chromospheric and prominence plasmas contain neutral atoms, which may change
the plasma dynamics through collision with ions. Most of the atoms are neutral
hydrogen, but a significant amount of neutral helium may also be present in the
plasma with a particular temperature. Damping of MHD waves due to ion collision
with neutral hydrogen is well studied, but the effects of neutral helium are
largely unknown. We aim to study the effect of neutral helium in the damping of
Alfven waves in solar partially ionized plasmas. We consider three-fluid
magnetohydrodynamic (MHD) approximation, where one component is
electron-proton-singly ionized helium and other two components are the neutral
hydrogen and neutral helium atoms. We derive the dispersion relation of linear
Alfven waves in isothermal and homogeneous plasma. Then we solve the dispersion
relation and derive the damping rates of Alfven waves for different plasma
parameters. The presence of neutral helium significantly enhances the damping
of Alfven waves compared to the damping due to neutral hydrogen at certain
values of plasma temperature (10000-40000 K) and ionization. Damping rates have
a peak near the ion-neutral collision frequency, but decrease for the higher
part of wave spectrum. Collision of ions with neutral helium atoms can be of
importance for the damping of Alfven waves in chromospheric spicules and in
prominence-corona transition regions.",1109.1154v1
2012-03-08,Damping rates of solar-like oscillations across the HR diagram. Theoretical calculations confronted to CoRoT and Kepler observations,"Space-borne missions CoRoT and {\it Kepler} are providing a rich harvest of
high-quality constraints on solar-like pulsators. Among the seismic parameters,
mode damping rates remains poorly understood and thus barely used to infer
physical properties of stars. Nevertheless, thanks to CoRoT and {\it Kepler}
space-crafts it is now possible to measure damping rates for hundreds of
main-sequence and thousands of red-giant stars with an unprecedented precision.
  By using a non-adiabatic pulsation code including a time-dependent convection
treatment, we compute damping rates for stellar models representative for
solar-like pulsators from the main-sequence to the red-giant phase. This allows
us to reproduce the observations of both CoRoT and {\it Kepler}, which
validates our modeling of mode damping rates and thus the underlying physical
mechanisms included in the modeling. Actually, by considering the perturbations
of turbulent pressure and entropy (including perturbation of the dissipation
rate of turbulent energy into heat) by the oscillation in our computation, we
succeed in reproducing the observed relation between damping rates and
effective temperature.
  Moreover, we discuss the physical reasons for mode damping rates to scale
with effective temperature, as observationally exhibited. Finally, this opens
the way for the use of mode damping rates to probe turbulent convection in
solar-like stars.",1203.1737v2
2012-09-14,Semi-linear structural damped waves,"We study the global existence of small data solutions for Cauchy problem for
the semi-linear structural damped wave equation with source term.",1209.3204v2
2012-10-25,Decay rates for the damped wave equation on the torus,"We address the decay rates of the energy for the damped wave equation when
the damping coefficient $b$ does not satisfy the Geometric Control Condition
(GCC). First, we give a link with the controllability of the associated
Schr\""odinger equation. We prove in an abstract setting that the observability
of the Schr\""odinger group implies that the semigroup associated to the damped
wave equation decays at rate $1/\sqrt{t}$ (which is a stronger rate than the
general logarithmic one predicted by the Lebeau Theorem).
  Second, we focus on the 2-dimensional torus. We prove that the best decay one
can expect is $1/t$, as soon as the damping region does not satisfy GCC.
Conversely, for smooth damping coefficients $b$, we show that the semigroup
decays at rate $1/t^{1-\eps}$, for all $\eps >0$. The proof relies on a second
microlocalization around trapped directions, and resolvent estimates.
  In the case where the damping coefficient is a characteristic function of a
strip (hence discontinuous), St\'{e}phane Nonnenmacher computes in an appendix
part of the spectrum of the associated damped wave operator, proving that the
semigroup cannot decay faster than $1/t^{2/3}$. In particular, our study shows
that the decay rate highly depends on the way $b$ vanishes.",1210.6879v1
2014-02-25,Asymptotic Profiles for wave equations with strong damping,"We consider the Cauchy problem in ${\bf R}^{n}$ for strongly damped wave
equations. We derive asymptotic profiles of these solutions with weighted
$L^{1,1}({\bf R}^{n})$ data by using a method introduced in [10].",1402.6073v1
2014-04-17,Exponential stability of the wave equation with memory and time delay,"We study the asymptotic behaviour of the wave equation with viscoelastic
damping in presence of a time-delayed damping. We prove exponential stability
if the amplitude of the time delay term is small enough.",1404.4456v1
2014-08-30,Marginalizing over the PageRank Damping Factor,"In this note, we show how to marginalize over the damping parameter of the
PageRank equation so as to obtain a parameter-free version known as TotalRank.
Our discussion is meant as a reference and intended to provide a guided tour
towards an interesting result that has applications in information retrieval
and classification.",1409.0104v1
2014-10-29,Blowup for the nonlinear Schrödinger equation with an inhomogeneous damping term in the $L^2$ critical case,"We consider the nonlinear Schr\""odinger equation with $L^2$-critical exponent
and an inhomogeneous damping term. By using the tools developed by Merle and
Raphael, we prove the existence of blowup phenomena in the energy space
$H^1(\mathbb{R})$.",1410.8011v1
2014-11-28,Landau damping,"Landau damping is calculated using real variables, clarifying the physical
mechanism.",1411.7793v1
2014-12-16,Linear Collisionless Landau Damping in Hilbert Space,"The equivalence between the Laplace transform [Landau L., J. Phys. USSR, 10
(1946), 25] and Hermite transform [Zocco and Schekochihin, Phys. Plasmas, 18,
102309 (2011)] solutions of the linear collisionless Landau damping problem is
proven.",1412.4913v1
2015-07-08,Calculation of continuum damping of Alfvén eigenmodes in 2D and 3D cases,"In ideal MHD, shear Alfv\'{e}n eigenmodes may experience dissipationless
damping due to resonant interaction with the shear Alfv\'{e}n continuum. This
continuum damping can make a significant contribution to the overall
growth/decay rate of shear Alfv\'{e}n eigenmodes, with consequent implications
for fast ion transport. One method for calculating continuum damping is to
solve the MHD eigenvalue problem over a suitable contour in the complex plane,
thereby satisfying the causality condition. Such an approach can be implemented
in three-dimensional ideal MHD codes which use the Galerkin method. Analytic
functions can be fitted to numerical data for equilibrium quantities in order
to determine the value of these quantities along the complex contour. This
approach requires less resolution than the established technique of calculating
damping as resistivity vanishes and is thus more computationally efficient. The
complex contour method has been applied to the three-dimensional finite element
ideal MHD code CKA . In this paper we discuss the application of the complex
contour technique to calculate the continuum damping of global modes in tokamak
as well as torsatron, W7X and H1-NF stellarator cases. To the authors'
knowledge these stellarator calculations represent the first calculation of
continuum damping for eigenmodes in fully three-dimensional equilibria. The
continuum damping of global modes in W7X and H1-NF stellarator configurations
investigated is found to depend sensitively on coupling to numerous poloidal
and toroidal harmonics.",1507.02072v1
2015-08-16,Jeans instability and hydrodynamic roots of Landau damping,"Landau damping of Langmuir waves is shown to have hydrodynamic roots, and, in
principle, might have been predicted (along with Langmuir waves) several
decades earlier, soon after Jeans (1902) paper appeared.",1508.03809v1
2015-12-07,"Damped and zero-damped quasinormal modes of charged, nearly extremal black holes","Despite recent progress, the complete understanding of the perturbations of
charged, rotating black holes as described by the Kerr-Newman metric remains an
open and fundamental problem in relativity. In this study, we explore the
existence of families of quasinormal modes of Kerr-Newman black holes whose
decay rates limit to zero at extremality, called zero-damped modes in past
studies. We review the nearly extremal and WKB approximation methods for
spin-weighted scalar fields (governed by the Dudley-Finley equation) and give
an accounting of the regimes where scalar zero-damped and damped modes exist.
Using Leaver's continued fraction method, we verify that these approximations
give accurate predictions for the frequencies in their regimes of validity. In
the nonrotating limit, we argue that gravito-electromagnetic perturbations of
nearly extremal Reissner-Nordstr\""{o}m black holes have zero-damped modes in
addition to the well-known spectrum of damped modes. We provide an analytic
formula for the frequencies of these modes, verify their existence using a
numerical search, and demonstrate the accuracy of our formula. These results,
along with recent numerical studies, point to the existence of a simple
universal equation for the frequencies of zero-damped gravito-electromagnetic
modes of Kerr-Newman black holes, whose precise form remains an open question.",1512.02247v2
2016-09-24,Recovering the damping rates of cyclotron damped plasma waves from simulation data,"Plasma waves with frequencies close to the particular gyrofrequencies of the
charged particles in the plasma lose energy due to cyclotron damping. We
briefly discuss the gyro-resonance of low frequency plasma waves and ions
particularly with regard to particle-in-cell (PiC) simulations. A setup is
outlined which uses artificially excited waves in the damped regime of the wave
mode's dispersion relation to track the damping of the wave's electromagnetic
fields. Extracting the damping rate directly from the field data in real or
Fourier space is an intricate and non-trivial task. We therefore present a
simple method of obtaining the damping rate {\Gamma} from the simulation data.
This method is described in detail, focusing on a step-by-step explanation of
the course of actions. In a first application to a test simulation we find that
the damping rates obtained from this simulation generally are in good agreement
with theoretical predictions. We then compare the results of one-, two- and
three-dimensional simulation setups and simulations with different physical
parameter sets.",1609.07646v2
2016-10-25,Quadratically damped oscillators with non-linear restoring force,"In this paper we qualitatively analyse quadratically damped oscillators with
non-linear restoring force. In particular, we obtain Hamiltonian structure and
analytical form of the energy functions.",1610.07821v1
2016-11-24,Longitudinal Stability Study for the FACET-II e+ Damping Ring,"This is an initial study of the longitudinal, single-bunch stability in the
proposed FACET-II e+ damping ring. It is preliminary because many vacuum
chamber objects of the ring have not yet been designed.",1611.08042v1
2017-08-25,On the entropy gain under the action of amplitude damping channel on qutrit,"After realising qutrit in the form of bipartite system we estimate from below
the entropy gain under the action of the amplitude damping channel.",1708.07710v1
2017-10-24,Demonstration of a switchable damping system to allow low-noise operation of high-Q low-mass suspension systems,"Low mass suspension systems with high-Q pendulum stages are used to enable
quantum radiation pressure noise limited experiments. Utilising multiple
pendulum stages with vertical blade springs and materials with high quality
factors provides attenuation of seismic and thermal noise, however damping of
these high-Q pendulum systems in multiple degrees of freedom is essential for
practical implementation. Viscous damping such as eddy-current damping can be
employed but introduces displacement noise from force noise due to thermal
fluctuations in the damping system. In this paper we demonstrate a passive
damping system with adjustable damping strength as a solution for this problem
that can be used for low mass suspension systems without adding additional
displacement noise in science mode. We show a reduction of the damping factor
by a factor of 8 on a test suspension and provide a general optimisation for
this system.",1710.08698v2
2017-11-30,Asymptotic for a second order evolution equation with vanishing damping term and Tikhonov regularization,"We investigate the asymptotic behavior of solutions to a second order
differential equation with vanishing damping term, convex potential and
regularizing Tikhonov term.",1711.11241v1
2018-10-04,Damping of slow surface sausage modes in photospheric waveguides,"There has been considerable interest in sausage modes in photospheric
waveguides like pores and sunspots, and slow surface sausage modes (SSSMs) have
been suggested to damp ufficiently rapidly to account for chromospheric
heating. Working in the framework of linear resistive magnetohydrodynamics, we
examine how efficient electric resistivity and resonant absorption in the cusp
continuum can be for damping SSSMs in a photospheric waveguide with equilibrium
parameters compatible with recent measurements of a photospheric pore. For
SSSMs with the measured wavelength, we find that the damping rate due to the
cusp resonance is substantially less strong than theoretically expected with
the thin-boundary approximation. The damping-time-to-period ratio ($\tau/P$) we
derive for standing modes, equivalent to the damping-length-to-wavelength ratio
for propagating modes given the extremely weak dispersion, can reach only $\sim
180$. However, the accepted values for electric resistivity ($\eta$) correspond
to a regime where both the cusp resonance and resistivity play a role. The
values for $\tau/P$ attained at the largest allowed $\eta$ may reach $\sim 30$.
We conclude that electric resistivity can be considerably more efficient than
the cusp resonance for damping SSSMs in the pore in question, and it needs to
be incorporated into future studies on the damping of SSSMs in photospheric
waveguides in general.",1810.02051v1
2018-10-20,Landau Damping in a weakly collisional regime,"In this paper, we consider the nonlinear Vlasov-Poisson equations in a weakly
collisional regime and study the linear Boltzmann collision operator. We prove
that Landau damping still occurs in this case.",1810.10955v1
2018-10-26,Energy regenerative damping in variable impedance actuators for long-term robotic deployment,"Energy efficiency is a crucial issue towards longterm deployment of compliant
robots in the real world. In the context of variable impedance actuators
(VIAs), one of the main focuses has been on improving energy efficiency through
reduction of energy consumption. However, the harvesting of dissipated energy
in such systems remains under-explored. This study proposes a novel variable
damping module design enabling energy regeneration in VIAs by exploiting the
regenerative braking effect of DC motors. The proposed damping module uses four
switches to combine regenerative and dynamic braking, in a hybrid approach that
enables energy regeneration without a reduction in the range of damping
achievable. A physical implementation on a simple VIA mechanism is presented in
which the regenerative properties of the proposed module are characterised and
compared against theoretical predictions. To investigate the role of variable
regenerative damping in terms of energy efficiency of longterm operation,
experiments are reported in which the VIA equipped with the proposed damping
module performs sequential reaching to a series of stochastic targets. The
results indicate that the combination of variable stiffness and variable
regenerative damping is preferable to achieve the optimal trade-off between
task performance and energy efficiency. Use of the latter results in a 25%
performance improvement on overall performance metrics (incorporating reaching
accuracy, settling time, energy consumption and regeneration), over comparable
schemes where either stiffness or damping are fixed.",1810.11246v3
2018-12-26,A class large solution of the 2D MHD equations with velocity and magnetic damping,"In this paper, we construct a class global large solution to the
two-dimensional MHD equations with damp terms in the nonhomogeneous Sobolev
framework.",1812.10310v2
2019-01-24,Generalization of Stokes-Einstein relation to coordinate dependent damping and diffusivity: An apparent conflict,"Brownian motion with coordinate dependent damping and diffusivity is
ubiquitous. Understanding equilibrium of a Brownian particle with coordinate
dependent diffusion and damping is a contentious area. In this paper, we
present an alternative approach based on already established methods to this
problem. We solve for the equilibrium distribution of the over-damped dynamics
using Kramers-Moyal expansion. We compare this with the over-damped limit of
the generalized Maxwell-Boltzmann distribution. We show that the equipartition
of energy helps recover the Stokes-Einstein relation at constant diffusivity
and damping of the homogeneous space. However, we also show that, there exists
no homogeneous limit of coordinate dependent diffusivity and damping with
respect to the applicability of Stokes-Einstein relation when it does not hold
locally. In the other scenario where the Stokes-Einstein relation holds
locally, one needs to impose a restriction on the local maximum velocity of the
Brownian particle to make the modified Maxwell-Boltzmann distribution coincide
with the modified Boltzmann distribution in the over-damped limit.",1901.08358v4
2019-02-19,Linear inviscid damping near monotone shear flows,"We give an elementary proof of sharp decay rates and the linear inviscid
damping near monotone shear flow in a periodic channel, first obtained in [14].
We shall also obtain the precise asymptotics of the solutions, measured in the
space $L^{\infty}$.",1902.06849v1
2019-04-18,Damping of Propagating Kink Waves in the Solar Corona,"Alfv\'enic waves have gained renewed interest since the existence of
ubiquitous propagating kink waves were discovered in the corona. {It has long
been suggested that Alfv\'enic} waves play an important role in coronal heating
and the acceleration of the solar wind. To this effect, it is imperative to
understand the mechanisms that enable their energy to be transferred to the
plasma. Mode conversion via resonant absorption is believed to be one of the
main mechanisms for kink wave damping, and is considered to play a key role in
the process of energy transfer. This study examines the damping of propagating
kink waves in quiescent coronal loops using the Coronal Multi-channel
Polarimeter (CoMP). A coherence-based method is used to track the Doppler
velocity signal of the waves, enabling us to investigate the spatial evolution
of velocity perturbations. The power ratio of outward to inward propagating
waves is used to estimate the associated damping lengths and quality factors.
To enable accurate estimates of these quantities, {we provide the first
derivation of a likelihood function suitable for fitting models to the ratio of
two power spectra obtained from discrete Fourier transforms. Maximum likelihood
estimation is used to fit an exponential damping model to the observed
variation in power ratio as a function of frequency.} We confirm earlier
indications that propagating kink waves are undergoing frequency dependent
damping. Additionally, we find that the rate of damping decreases, or
equivalently the damping length increases, for longer coronal loops that reach
higher in the corona.",1904.08834v1
2019-05-19,Finite time blow up for wave equations with strong damping in an exterior domain,"We consider the initial boundary value problem in exterior domain for
strongly damped wave equations with power type nonlinearity |u|^p. We will
establish blow-up results under some conditions on the initial data and the
exponent p.",1905.07782v1
2019-12-15,A result for nonexistence of global solutions to semi-linear structural damped wave model,"Main goal of this note is to give a result for nonexistence of global
solutions and determine the critical exponent as well to a semi-linear
structurally damped wave equation.",1912.07066v1
2020-09-23,Remark on the exponential decay of the solutions of the damped wave equation,"A condition which guaranties the exponential decay of the solutions of the
initial-boundary value problem for the damped wave equation is proved. A method
for the effective computability of the coefficient of exponential decay is also
presented.",2009.11244v1
2020-10-13,The Impact of Damping in Second-Order Dynamical Systems with Applications to Power Grid Stability,"We consider a broad class of second-order dynamical systems and study the
impact of damping as a system parameter on the stability, hyperbolicity, and
bifurcation in such systems. We prove a monotonic effect of damping on the
hyperbolicity of the equilibrium points of the corresponding first-order
system. This provides a rigorous formulation and theoretical justification for
the intuitive notion that damping increases stability. To establish this
result, we prove a matrix perturbation result for complex symmetric matrices
with positive semidefinite perturbations to their imaginary parts, which may be
of independent interest. Furthermore, we establish necessary and sufficient
conditions for the breakdown of hyperbolicity of the first-order system under
damping variations in terms of observability of a pair of matrices relating
damping, inertia, and Jacobian matrices, and propose sufficient conditions for
Hopf bifurcation resulting from such hyperbolicity breakdown. The developed
theory has significant applications in the stability of electric power systems,
which are one of the most complex and important engineering systems. In
particular, we characterize the impact of damping on the hyperbolicity of the
swing equation model which is the fundamental dynamical model of power systems,
and demonstrate Hopf bifurcations resulting from damping variations.",2010.06662v2
2020-10-26,Linear Predictive Coding for Acute Stress Prediction from Computer Mouse Movements,"Prior work demonstrated the potential of using the Linear Predictive Coding
(LPC) filter to approximate muscle stiffness and damping from computer mouse
movements to predict acute stress levels of users. Theoretically, muscle
stiffness and damping in the arm can be estimated using a mass-spring-damper
(MSD) biomechanical model. However, the damping frequency (i.e., stiffness) and
damping ratio values derived using LPC were not yet compared with those from a
theoretical MSD model. This work demonstrates that the damping frequency and
damping ratio from LPC are significantly correlated with those from an MSD
model, thus confirming the validity of using LPC to infer muscle stiffness and
damping. We also compare the stress level binary classification performance
using the values from LPC and MSD with each other and with neural network-based
baselines. We found comparable performance across all conditions demonstrating
LPC and MSD model-based stress prediction efficacy, especially for longer mouse
trajectories. Clinical relevance: This work demonstrates the validity of the
LPC filter to approximate muscle stiffness and damping and predict acute stress
from computer mouse movements.",2010.13836v3
2020-11-01,Sharp dimension estimates of the attractor of the damped 2D Euler-Bardina equations,"We prove existence of the global attractor of the damped and driven 2D
Euler--Bardina equations on the torus and give an explicit two-sided estimate
of its dimension that is sharp as $\alpha\to0^+$.",2011.00607v1
2021-03-30,Strong solution of 3D-NSE with exponential damping,"In this paper we prove the existence and uniqueness of strong solution of the
incompressible Navier-Stokes equations with damping $\alpha
(e^{\beta|u|^2}-1)u$.",2103.16707v1
2021-06-22,Choice of Damping Coefficient in Langevin Dynamics,"This article considers the application of Langevin dynamics to sampling and
investigates how to choose the damping parameter in Langevin dynamics for the
purpose of maximizing thoroughness of sampling. Also, it considers the
computation of measures of sampling thoroughness.",2106.11597v1
2021-09-27,Damping transition in an open generalized Aubry-André-Harper model,"We study the damping dynamics of the single-particle correlation for an open
system under periodic and aperiodic order, which is dominated by the Lindblad
master equation. In the absence of the aperiodic order, the Liouvillian
superoperator exhibits the non-Hermitian skin effect, which leads to
unidirectional damping dynamics, dubbed as ""chiral damping"". Due to the
non-Hermitian skin effect, the damping dynamics is boundary sensitive: The
long-time damping of such open systems is algebraic under periodic boundary
conditions but exponential under open boundary conditions. We reveal the phase
transition with the inclusion of the hopping amplitude modulation. By using the
spectral topology and a finite-size scaling analysis in the commensurate case,
we show there exists a phase transition of the skin effect with non-Bloch
anti-parity-time symmetry breaking. For the incommensurate case, we find richer
phases with the coexistence of the non-Hermitian skin effect and the Anderson
localization, which are separated by a generalized mobility edge. We reveal the
transition of the damping dynamics as a consequence of the phase transition.
Furthermore, we propose a possible scheme with ultracold atoms in a dissipative
momentum lattice to realize and detect the damping dynamics.",2109.12958v2
2022-01-20,Long Time Decay of Leray Solution of 3D-NSE With Exponential Damping,"We study the uniqueness, the continuity in $L^2$ and the large time decay for
the Leray solutions of the $3D$ incompressible Navier-Stokes equations with
nonlinear exponential damping term $a (e^{b |u|^{\bf 4}}-1)u$, ($a,b>0$).",2201.08292v1
2023-03-20,Nonlinear Damping and Field-aligned Flows of Propagating Shear Alfvén Waves with Braginskii Viscosity,"Braginskii MHD provides a more accurate description of many plasma
environments than classical MHD since it actively treats the stress tensor
using a closure derived from physical principles. Stress tensor effects
nonetheless remain relatively unexplored for solar MHD phenomena, especially in
nonlinear regimes. This paper analytically examines nonlinear damping and
longitudinal flows of propagating shear Alfv\'en waves. Most previous studies
of MHD waves in Braginskii MHD considered the strict linear limit of vanishing
wave perturbations. We show that those former linear results only apply to
Alfv\'en wave amplitudes in the corona that are so small as to be of little
interest, typically a wave energy less than $10^{-11}$ times the energy of the
background magnetic field. For observed wave amplitudes, the Braginskii viscous
dissipation of coronal Alfv\'en waves is nonlinear and a factor around $10^9$
stronger than predicted by the linear theory. Furthermore, the dominant damping
occurs through the parallel viscosity coefficient $\eta_0$, rather than the
perpendicular viscosity coefficient $\eta_2$ in the linearized solution. This
paper develops the nonlinear theory, showing that the wave energy density
decays with an envelope $(1+z/L_d)^{-1}$. The damping length $L_d$ exhibits an
optimal damping solution, beyond which greater viscosity leads to lower
dissipation as the viscous forces self-organise the longitudinal flow to
suppress damping. Although the nonlinear damping greatly exceeds the linear
damping, it remains negligible for many coronal applications.",2303.11128v1
2023-09-04,Joint Oscillation Damping and Inertia Provision Service for Converter-Interfaced Generation,"As renewable generation becomes more prevalent, traditional power systems
dominated by synchronous generators are transitioning to systems dominated by
converter-interfaced generation. These devices, with their weaker damping
capabilities and lower inertia, compromise the system's ability to withstand
disturbances, pose a threat to system stability, and lead to oscillations and
poor frequency response performance. While some new converter-interfaced
generations are capable of providing superior damping and fast frequency
control, there is a lack of effective measures to incentivize manufacturers to
adopt them. To address this gap, this paper defines the joint oscillation
damping and inertia provision services at the system level, seeking to
encourage converter-interfaced generation to provide enhanced damping and fast
frequency response capabilities. Our approach is anchored in a novel convex
parametric formulation that combines oscillation mode and frequency stability
constraints. These constraints ensure a sufficient damping ratio for all
oscillation modes and maintain transient frequency trajectories within
acceptable limits. They are designed to integrate smoothly into various
operational and planning optimization frameworks. Using this formulation, we
introduce a joint service for oscillation damping and inertia provision based
on a cost-minimization problem. This facilitates the optimal allocation of
damping and virtual inertia to converters, achieving both small-signal
stability and frequency stability. Furthermore, we investigate the economic
effects of introducing this service into a new ancillary service market,
assessing its impact on system operations and cost-efficiency. Numerical tests
highlight the service's efficacy in ensuring both small-signal stability and
frequency stability, and offer insights into potential economic benefits.",2309.01321v1
2024-01-09,Damping Separation of Finite Open Systems in Gravity-Related Experiments in the Free Molecular Flow Regime,"The residual gas damping of the test mass (TM) in the free molecular flow
regime is studied in the finite open systems for high-precision gravity-related
experiments. Through strict derivation, we separate the damping coefficients
for two finite open systems, i.e., the bi-plate system and the sensor core
system, into base damping and diffusion damping. This elucidates the
relationship between the free damping in the infinite gas volume and the
proximity damping in the constrained volume, unifies them into one microscopic
picture, and allows us to point out three pathways of energy dissipation in the
bi-plate gap. We also provide the conditions that need to be met to achieve
this separation. In applications, for space gravitational wave detection, our
results for the residual gas damping coefficient for the 4TM torsion balance
experiment is the closest one to the experimental and simulation data compared
to previous models. For the LISA mission, our estimation for residual gas
acceleration noise at the sensitive axis is consistent with the simulation
result, within about $5\%$ difference. In addition, in the test of the
gravitational inverse-square law, our results suggest that the constraint on
the distance between TM and the conducting membrane can be reduced by about
$28\%$.",2401.04808v1
2024-01-30,The Velocity-Space Signature of Transit-Time Damping,"Transit-time damping (TTD) is a process in which the magnetic mirror force --
induced by the parallel gradient of magnetic field strength -- interacts with
resonant plasma particles, leading to the collisionless damping of
electromagnetic waves and the resulting energization of those particles through
the perpendicular component of the electric field, $E_\perp$. In this study, we
utilize the recently developed field-particle correlation technique to analyze
gyrokinetic simulation data. This method enables the identification of the
velocity-space structure of the TTD energy transfer rate between waves and
particles during the damping of plasma turbulence. Our analysis reveals a
unique bipolar pattern of energy transfer in velocity space characteristic of
TTD. By identifying this pattern, we provide clear evidence of TTD's
significant role in the damping of strong plasma turbulence. Additionally, we
compare the TTD signature with that of Landau damping (LD). Although they both
produce a bipolar pattern of phase-space energy density loss and gain about the
parallel resonant velocity of the \Alfvenic waves, they are mediated by
different forces and exhibit different behaviors as $v_\perp \to 0$. We also
explore how the dominant damping mechanism varies with ion plasma beta
$\beta_i$, showing that TTD dominates over LD for $\beta_i > 1$. This work
deepens our understanding of the role of TTD in the damping of weakly
collisional plasma turbulence and paves the way to seek the signature of TTD
using in situ spacecraft observations of turbulence in space plasmas.",2401.16697v1
2024-03-04,How long will the quasar UV/optical flickering be damped?,"The UV/optical light curves of Active Galactic Nuclei (AGNs) are commonly
described by the Damped Random Walk (DRW) model. However, the physical
interpretation of the damping timescale, a key parameter in the DRW model,
remains unclear. Particularly, recent observations indicate a weak dependence
of the damping timescale upon both wavelength and accretion rate, clearly being
inconsistent with the accretion-disk theory. In this study, we investigate the
damping timescale in the framework of the Corona Heated Accretion disk
Reprocessing (CHAR) model, a physical model that describes AGN variability. We
find that while the CHAR model can reproduce the observed power spectral
densities of the 20-year light curves for 190 sources from \cite{Stone2022},
the observed damping timescale, as well as its weak dependence on wavelength,
can also be well recovered through fitting the mock light curves with DRW. We
further demonstrate that such weak dependence is artificial due to the effect
of inadequate durations of light curves, which leads to best-fitting damping
timescales lower than the intrinsic ones. After eliminating this effect, the
CHAR model indeed yields a strong dependence of the intrinsic damping timescale
on the bolometric luminosity and rest-frame wavelength. Our results highlight
the demand for sufficiently long light curves in AGN variability studies and
important applications of the CHAR model in such studies.",2403.01691v1
2005-04-18,Chemical Abundances in SFG and DLA,"We investigate the chemical abundances of local star-forming galaxies which
cause Damped Lyman Alpha lines. A metallicity versus redshift diagram is
constructed, on which the chemical abundances of low-redshift star-forming
galaxy populations are compared with those of high-redshift Damped Lyman Alpha
systems. We disucss two types of experiments on individual star-forming
galaxies. In the first, the Damped Lyman Alpha line is created against an
internal ultraviolet light source generated by a star-forming cluster or a
supernova explosion. In the second, the Damped Lyman Alpha line is seen against
a background Quasar. The metallicities measured from ionized gas in the
star-forming regions, and neutral gas in the Damped Lyman Alpha systems, are
compared with one another on a case-by-case basis. We highlight the occurrence
of the star-forming galaxy/Quasar pair SBS 1543+593/HS 1543+5921, where the
emission- and absorption-line derived abundances give the same result. We argue
that we therefore can in principle, interpret Damped Lyman Alpha system
metallicities as an extension of star-forming galaxy metallicities to higher
redshifts, supporting that gas-rich galaxies had lower chemical abundances when
the were younger.",0504389v2
1995-09-06,Fermi Liquid Damping and NMR Relaxation in Superconductors,"Electron collisions for a two dimensional Fermi liquid (FL) are shown to give
a quasiparticle damping with interesting frequency and temperature variations
in the BCS superconducting state. The spin susceptibility which determines the
structure of the damping is analyzed in the normal state for a Hubbard model
with a constant on--site Coulomb repulsion. This is then generalized to the
superconducting state by including coherence factors and self energy and vertex
corrections. Calculations of the NMR relaxation rate reveal that the FL damping
structure can reduce the Hebel--Slichter peak, in agreement with data on the
organic superconductor (MDT-TTF)$_2$AuI$_2$. However, the strongly suppressed
FL damping in the superconducting state does not eliminate the Hebel-Slichter
peak, and thus suggests that other mechanisms are needed to explain the NMR
data on (TMTSF)$_2$ClO$_4$, the BEDT organic compounds, and cuprate
superconductors. Predictions of the temperature variation of the damping and
the spin response are given over a wide frequency range as a guide to
experimental probes of the symmetry of the superconducting pairs.",9509028v1
1997-05-08,Topological asymmetry in the damping-pairing contribution of electron-boson scattering,"We make a harmonic analysis of the pairing and damping contribution of a
finite $k$ range isotropic electron-phonon (or other boson) scattering in an
anisotropic two-dimensional electronic system. We show that the pairing
contribution of the anisotropic part of the electronic system can be much
larger than its damping contribution enhancing significantly T_c. The higher is
the order of the harmonic of the electronic anisotropy, smaller is its damping
contribution and higher can be the asymmetry in its damping-pairing
contribution. This could explain the puzzle of a much broader quasiparticle
peak in the n-doped than in the p-doped cuprates, their smaller T_c's being
also attributed to larger damping effects.",9705071v1
2000-03-29,Damping of condensate collective modes due to equilibration with the non-condensate,"We consider the damping of condensate collective modes at finite temperatures
arising from lack of equilibrium between the condensate and the non-condensate
atoms, an effect that is ignored in the usual discussion of the collisionless
region. As a first approximation, we ignore the dynamics of the thermal cloud.
Our calculations should be applicable to collective modes of the condensate
which are oscillating out-of-phase with the thermal cloud. We obtain a
generalized Stringari equation of motion for the condensate at finite
temperatures, which includes a damping term associated with the fact that the
condensate is not in diffusive equilibrium with the static thermal cloud. This
inter-component collisional damping of the condensate modes is comparable in
magnitude to the Landau damping considered in the recent literature.",0003481v5
2006-06-27,Theoretical limit of the minimal magnetization switching field and the optimal field pulse for Stoner particles,"The theoretical limit of the minimal magnetization switching field and the
optimal field pulse design for uniaxial Stoner particles are investigated. Two
results are obtained. One is the existence of a theoretical limit of the
smallest magnetic field out of all possible designs. It is shown that the limit
is proportional to the damping constant in the weak damping regime and
approaches the Stoner-Wohlfarth (SW) limit at large damping. For a realistic
damping constant, this limit is more than ten times smaller than that of
so-called precessional magnetization reversal under a non-collinear static
field. The other is on the optimal field pulse design: If the magnitude of a
magnetic field does not change, but its direction can vary during a reversal
process, there is an optimal design that gives the shortest switching time. The
switching time depends on the field magnitude, damping constant, and magnetic
anisotropy. However, the optimal pulse shape depends only on the damping
constant.",0606681v1
2001-02-09,Magnetic effects on the viscous boundary layer damping of the r-modes in neutron stars,"This paper explores the effects that magnetic fields have on the viscous
boundary layers (VBLs) that can form in neutron stars at the crust-core
interface, and it investigates the VBL damping of the gravitational-radiation
driven r-mode instability. Approximate solutions to the magnetohydrodynamic
equations valid in the VBL are found for ordinary-fluid neutron stars. It is
shown that magnetic fields above 10^9 Gauss significantly change the structure
of the VBL, and that magnetic fields decrease the VBL damping time.
Furthermore, VBL damping completely suppresses the r-mode instability for B >=
10^{12} Gauss. Thus, magnetic fields will profoundly affect the VBL damping of
the r-mode instability in hot young pulsars (that are cool enough to have
formed a solid crust). One can speculate that magnetic fields can affect the
VBL damping of this instability in LMXBs and other cold old pulsars (if they
have sufficiently large internal fields).",0102042v1
2002-07-26,Landau damping of partially incoherent Langmuir waves,"It is shown that partial incoherence, in the form of stochastic phase noise,
of a Langmuir wave in an unmagnetized plasma gives rise to a Landau-type
damping. Starting from the Zakharov equations, which describe the nonlinear
interaction between Langmuir and ion-acoustic waves, a kinetic equation is
derived for the plasmons by introducing the Wigner-Moyal transform of the
complex Langmuir wave field. This equation is then used to analyze the
stability properties of small perturbations on a stationary solution consisting
of a constant amplitude wave with stochastic phase noise. The concomitant
dispersion relation exhibits the phenomenon of Landau-like damping. However,
this damping differs from the classical Landau damping in which a Langmuir
wave, interacting with the plasma electrons, loses energy. In the present
process, the damping is non-dissipative and is caused by the resonant
interaction between an instantaneously-produced disturbance, due to the
parametric interactions, and a partially incoherent Langmuir wave, which can be
considered as a quasi-particle composed of an ensemble of partially incoherent
plasmons.",0207050v1
2003-01-30,Dynamic effects of electromagnetic wave on a damped two-level atom,"We studied the dynamic effects of an electromagnetic(EM) wave with circular
polarization on a two-level damped atom. The results demonstrate interesting ac
Stark split of energy levels of damped atom. The split levels have different
energies and lifetimes, both of which depend on the interaction and the damping
rate of atom. When the frequency of the EM wave is tuned to satisfy the
resonance condition in the strong coupling limit, the transition probability
exhibits Rabi oscillation. Momentum transfer between atom and EM wave shows
similar properties as the transition probability under resonance condition. For
a damped atom interacting with EM field, there exists no longer stable state.
More importantly, if the angular frequency of the EM wave is tuned the same as
the atomic transition frequency and its amplitude is adjusted appropriately
according to the damping coefficients, we can prepare a particular 'Dressed
State' of the coupled system between atom and EM field and can keep the system
coherently in this 'Dressed state' for a very long time. This opens another way
to prepare coherent atomic states.",0301166v1
2007-12-18,"Spectroscopy of electronic defect states in Cu(In, Ga)(S, Se)$_2$-based heterojunctions and Schottky diodes under damp-heat exposure","The changes of defect characteristics induced by accelerated lifetime tests
on the heterostructure n-ZnO/i-ZnO/CdS/Cu(In, Ga)(S, Se)$_2$/Mo relevant for
photovoltaic energy conversion are investigated. We subject heterojunction and
Schottky devices to extended damp heat exposure at 85$^{\circ}$C ambient
temperature and 85% relative humidity for various time periods. In order to
understand the origin of the pronounced changes of the devices, we apply
current--voltage and capacitance--voltage measurements, admittance
spectroscopy, and deep-level transient spectroscopy. The fill factor and
open-circuit voltage of test devices are reduced after prolonged damp heat
treatment, leading to a reduced energy conversion efficiency. We observe the
presence of defect states in the vicinity of the CdS/chalcopyrite interface.
Their activation energy increases due to damp heat exposure, indicating a
reduced band bending at the Cu(In, Ga)(S, Se)$_2$ surface. The Fermi-level
pinning at the buffer/chalcopyrite interface, maintaining a high band bending
in as-grown cells, is lifted due to the damp-heat exposure. We also observe
changes in the bulk defect spectra due to the damp-heat treatment.",0712.2982v1
2008-05-07,Comparison Between Damping Coefficients of Measured Perforated Micromechanical Test Structures and Compact Models,"Measured damping coefficients of six different perforated micromechanical
test structures are compared with damping coefficients given by published
compact models. The motion of the perforated plates is almost translational,
the surface shape is rectangular, and the perforation is uniform validating the
assumptions made for compact models. In the structures, the perforation ratio
varies from 24% - 59%. The study of the structure shows that the
compressibility and inertia do not contribute to the damping at the frequencies
used (130kHz - 220kHz). The damping coefficients given by all four compact
models underestimate the measured damping coefficient by approximately 20%. The
reasons for this underestimation are discussed by studying the various flow
components in the models.",0805.0893v1
2009-01-26,Dispersion of Waves in Relativistic Plasmas with Isotropic Particle Distributions,"The dispersion laws of Langmuir and transverse waves are calculated in the
relativistic non-magnetized formalism for several isotropic particle
distributions: thermal, power-law, relativistic Lorentzian $\kappa,$ and hybrid
$\beta$. For Langmuir waves the parameters of superluminal undamped, subluminal
damped principal and higher modes are determined for a range of distribution
parameters. The undamped and principal damped modes are found to match
smoothly. Principal damped and second damped modes are found not to match
smoothly. The presence of maximum wavenumber is discovered above that no
longitudinal modes formally exist. The higher damped modes are discovered to be
qualitatively different for thermal and certain non-thermal distributions.
Consistently with the known results, the Landau damping is calculated to be
stronger for non-thermal power-law-like distributions. The dispersion law is
obtained for the single undamped transverse mode. The analytic results for the
simplest distributions are provided.",0901.4050v1
2009-03-28,Torsional waves propagation in an initially stressed dissipative cylinder,"The present paper has been framed to show the effect of damping on the
propagation of torsional waves in an initially stressed, dissipative,
incompressible cylinder of infinite length. A governing equation has been
formulated on Biot's incremental deformation theory. The velocities of
torsional waves are obtained as complex ones, in which real part gives the
phase velocity of propagation and corresponding imaginary part gives the
damping. The study reveals that the damping of the medium has strong effect in
the propagation of torsional wave. Since every medium has damping so it is more
realistic to use the damped wave equation instead of the undamped wave
equation. The study also shows that the velocity of propagation of such waves
depend on the presence of initial stress. The influences of damping and initial
stresses are shown separately.",0903.4896v1
2009-04-29,Atomistic theory for the damping of vibrational modes in mono-atomic gold chains,"We develop a computational method for evaluating the damping of vibrational
modes in mono-atomic metallic chains suspended between bulk crystals under
external strain. The damping is due to the coupling between the chain and
contact modes and the phonons in the bulk substrates. The geometry of the atoms
forming the contact is taken into account. The dynamical matrix is computed
with density functional theory in the atomic chain and the contacts using
finite atomic displacements, while an empirical method is employed for the bulk
substrate. As a specific example, we present results for the experimentally
realized case of gold chains in two different crystallographic directions. The
range of the computed damping rates confirm the estimates obtained by fits to
experimental data [Frederiksen et al., Phys. Rev. B, 75, 205413(R)(2007)]. Our
method indicates that an order-of-magnitude variation in the damping is
possible even for relatively small changes in the strain. Such detailed insight
is necessary for a quantitative analysis of damping in metallic atomic chains,
and in explaining the rich phenomenology seen in the experiments.",0904.4627v2
2009-12-20,A Kinetic Alfven wave cascade subject to collisionless damping cannot reach electron scales in the solar wind at 1 AU,"(Abridged) Turbulence in the solar wind is believed to generate an energy
cascade that is supported primarily by Alfv\'en waves or Alfv\'enic
fluctuations at MHD scales and by kinetic Alfv\'en waves (KAWs) at kinetic
scales $k_\perp \rho_i\gtrsim 1$. Linear Landau damping of KAWs increases with
increasing wavenumber and at some point the damping becomes so strong that the
energy cascade is completely dissipated. A model of the energy cascade process
that includes the effects of linear collisionless damping of KAWs and the
associated compounding of this damping throughout the cascade process is used
to determine the wavenumber where the energy cascade terminates. It is found
that this wavenumber occurs approximately when $|\gamma/\omega|\simeq 0.25$,
where $\omega(k)$ and $\gamma(k)$ are, respectively, the real frequency and
damping rate of KAWs and the ratio $\gamma/\omega$ is evaluated in the limit as
the propagation angle approaches 90 degrees relative to the direction of the
mean magnetic field.",0912.4026v2
2010-07-27,Alfvèn wave phase-mixing and damping in the ion cyclotron range of frequencies,"Aims. To determine the effect of the Hall term in the generalised Ohm's law
on the damping and phase mixing of Alfven waves in the ion cyclotron range of
frequencies in uniform and non-uniform equilibrium plasmas. Methods. Wave
damping in a uniform plasma is treated analytically, whilst a Lagrangian remap
code (Lare2d) is used to study Hall effects on damping and phase mixing in the
presence of an equilibrium density gradient. Results. The magnetic energy
associated with an initially Gaussian field perturbation in a uniform resistive
plasma is shown to decay algebraically at a rate that is unaffected by the Hall
term to leading order in k^2di^2 where k is wavenumber and di is ion skin
depth. A similar algebraic decay law applies to whistler perturbations in the
limit k^2di^2>>1. In a non-uniform plasma it is found that the
spatially-integrated damping rate due to phase mixing is lower in Hall MHD than
it is in MHD, but the reduction in the damping rate, which can be attributed to
the effects of wave dispersion, tends to zero in both the weak and strong phase
mixing limits.",1007.4752v2
2011-02-24,Environment-assisted quantum Minority games,"The effect of entanglement and correlated noise in a four-player quantum
Minority game is investigated. Different time correlated quantum memory
channels are considered to analyze the Nash equilibrium payoff of the 1st
player. It is seen that the Nash equilibrium payoff is substantially enhanced
due to the presence of correlated noise. The behaviour of damping channels
(amplitude damping and phase damping) is approximately similar. However,
bit-phase flip channel heavily influences the minority game as compared to
other channels in the presence of correlated noise. On the other hand, phase
flip channel has a symmetrical behaviour around 50% noise threshold. The
significant reduction in payoffs due to decoherence is well compensated due to
the presence of correlated noise. However, the Nash equilibrium of the game
does not change in the presence of noise. It is seen that in case of
generalized amplitude damping channel, entanglement plays a significant role at
lower level of decoherence. The channel has less dominant effects on the payoff
at higher values of decoherence. Furthermore, amplitude damping and generalized
amplitude damping channels have almost comparable effects at lower level of
decoherence $(p<0.5)$. Therefore, the game deserves careful study during its
implementation due to prominent role of noise for different channels.",1102.5056v2
2011-03-17,Viscous damping of r-modes: Large amplitude saturation,"We analyze the viscous damping of r-mode oscillations of compact stars,
taking into account non-linear viscous effects in the large-amplitude regime.
The qualitatively different cases of hadronic stars, strange quark stars, and
hybrid stars are studied. We calculate the viscous damping times of r-modes,
obtaining numerical results and also general approximate analytic expressions
that explicitly exhibit the dependence on the parameters that are relevant for
a future spindown evolution calculation. The strongly enhanced damping of large
amplitude oscillations leads to damping times that are considerably lower than
those obtained when the amplitude dependence of the viscosity is neglected.
Consequently, large-amplitude viscous damping competes with the gravitational
instability at all physical frequencies and could stop the r-mode growth in
case this is not done before by non-linear hydrodynamic mechanisms.",1103.3521v2
2011-05-01,"Viscous damping of nanobeam resonators: humidity, thermal noise and the paddling effect","The nanobeam resonator is the key mechanical component in the
nano-electromechanical system. In addition to its high frequency originating
from its low dimension, the performance is significantly influenced by the
circumstances, especially at nanoscale where a large surface area of the
material is exposed. Molecular dynamics simulations and theoretical analysis
are used for a quantitative prediction on the damping behavior, such as the
critical damping condition and lifetime, of nanobeam resonators that directly
maps the fluid-structure properties and interaction information into dynamical
behaviors. We show here how the humidity defines the critical damping condition
through viscous forces, marking the transition from under-damping to
over-damping regime at elevated humidity. Novel phenomena such as the thermal
fluctuation and paddling effects are also discussed.",1105.0139v1
2011-06-07,Damping by branching: a bioinspiration from trees,"Man-made slender structures are known to be sensitive to high levels of
vibration, due to their flexibility, which often cause irreversible damage. In
nature, trees repeatedly endure large amplitudes of motion, mostly caused by
strong climatic events, yet with minor or no damage in most cases. A new
damping mechanism inspired by the architecture of trees is here identified and
characterized in the simplest tree-like structure, a Y-shape branched
structure. Through analytical and numerical analyses of a simple
two-degree-of-freedom model, branching is shown to be the key ingredient in
this protective mechanism that we call damping-by-branching. It originates in
the geometrical nonlinearities so that it is specifically efficient to damp out
large amplitudes of motion. A more realistic model, using flexible beam
approximation, shows that the mechanism is robust. Finally, two bioinspired
architectures are analyzed, showing significant levels of damping achieved via
branching with typically 30% of the energy being dissipated in one oscillation.
This concept of damping-by-branching is of simple practical use in the design
of slender flexible structures.",1106.1283v1
2011-11-29,Dispersion and damping of potential surface waves in a degenerate plasma,"Potential (electrostatic) surface waves in plasma half-space with degenerate
electrons are studied using the quasi-classical mean-field kinetic model. The
wave spectrum and the collisionless damping rate are obtained numerically for a
wide range of wavelengths. In the limit of long wavelengths, the wave frequency
$\omega$ approaches the cold-plasma limit $\omega=\omega_p/\sqrt{2}$ with
$\omega_p$ being the plasma frequency, while at short wavelengths, the wave
spectrum asymptotically approaches the spectrum of zero-sound mode propagating
along the boundary. It is shown that the surface waves in this system remain
weakly damped at all wavelengths (in contrast to strongly damped surface waves
in Maxwellian electron plasmas), and the damping rate nonmonotonically depends
on the wavelength, with the maximum (yet small) damping occuring for surface
waves with wavelength of $\approx5\pi\lambda_{F}$, where $\lambda_{F}$ is the
Thomas-Fermi length.",1111.6723v1
2012-01-29,Smooth attractors of finite dimension for von Karman evolutions with nonlinear frictional damping localized in a boundary layer,"In this paper dynamic von Karman equations with localized interior damping
supported in a boundary collar are considered. Hadamard well-posedness for von
Karman plates with various types of nonlinear damping are well-known, and the
long-time behavior of nonlinear plates has been a topic of recent interest.
Since the von Karman plate system is of ""hyperbolic type"" with critical
nonlinearity (noncompact with respect to the phase space), this latter topic is
particularly challenging in the case of geometrically constrained and nonlinear
damping. In this paper we first show the existence of a compact global
attractor for finite-energy solutions, and we then prove that the attractor is
both smooth and finite dimensional. Thus, the hyperbolic-like flow is
stabilized asymptotically to a smooth and finite dimensional set.
  Key terms: dynamical systems, long-time behavior, global attractors,
nonlinear plates, nonlinear damping, localized damping",1201.6072v1
2012-06-15,Landau Damping in a Turbulent Setting,"To address the problem of Landau damping in kinetic turbulence, the forcing
of the linearized Vlasov equation by a stationary random source is considered.
It is found that the time-asymptotic density response is dominated by resonant
particle interactions that are synchronized with the source. The energy
consumption of this response is calculated, implying an effective damping rate,
which is the main result of this paper. Evaluating several cases, it is found
that the effective damping rate can differ from the Landau damping rate in
magnitude and also, remarkably, in sign. A limit is demonstrated in which the
density and current become phase-locked, which causes the effective damping to
be negligible; this potentially resolves an energy paradox that arises in the
application of critical balance to a kinetic turbulence cascade.",1206.3415v4
2012-07-17,Asymptotic Dynamics of a Class of Coupled Oscillators Driven by White Noises,"This paper is devoted to the study of the asymptotic dynamics of a class of
coupled second order oscillators driven by white noises. It is shown that any
system of such coupled oscillators with positive damping and coupling
coefficients possesses a global random attractor. Moreover, when the damping
and the coupling coefficients are sufficiently large, the global random
attractor is a one-dimensional random horizontal curve regardless of the
strength of the noises, and the system has a rotation number, which implies
that the oscillators in the system tend to oscillate with the same frequency
eventually and therefore the so called frequency locking is successful. The
results obtained in this paper generalize many existing results on the
asymptotic dynamics for a single second order noisy oscillator to systems of
coupled second order noisy oscillators. They show that coupled damped second
order oscillators with large damping have similar asymptotic dynamics as the
limiting coupled first order oscillators as the damping goes to infinite and
also that coupled damped second order oscillators have similar asymptotic
dynamics as their proper space continuous counterparts, which are of great
practical importance.",1207.3864v1
2013-10-29,Influence of sample geometry on inductive damping measurement methods,"We study the precession frequency and effective damping of patterned
permalloy thin films of different geometry using integrated inductive test
structures. The test structures consist of coplanar wave guides fabricated onto
patterned permalloy stripes of different geometry. The width, length and
position of the permalloy stripe with respect to the center conductor of the
wave guide are varied. The precession frequency and effective damping of the
different devices is derived by inductive measurements in time and frequency
domain in in-plane magnetic fields. While the precession frequencies do not
reveal a significant dependence on the sample geometry we find a decrease of
the measured damping with increasing width of the permalloy centered underneath
the center conductor of the coplanar wave guide. We attribute this effect to an
additional damping contribution due to inhomogeneous line broadening at the
edges of the permalloy stripes which does not contribute to the inductive
signal provided the permalloy stripe is wider than the center conductor.
Consequences for inductive determination of the effective damping using such
integrated reference samples are discussed.",1310.7817v1
2014-03-13,The best decay rate of the damped plate equation in a square,"In this paper we study the best decay rate of the solutions of a damped plate
equation in a square and with a homogeneous Dirichlet boundary conditions. We
show that the fastest decay rate is given by the supremum of the real part of
the spectrum of the infinitesimal generator of the underlying semigroup, if the
damping coefficient is in $L^\infty(\Omega).$ Moreover, we give some numerical
illustrations by spectral computation of the spectrum associated to the damped
plate equation. The numerical results obtained for various cases of damping are
in a good agreement with theoretical ones. Computation of the spectrum and
energy of discrete solution of damped plate show that the best decay rate is
given by spectral abscissa of numerical solution.",1403.3199v1
2014-04-02,Determination of the cross-field density structuring in coronal waveguides using the damping of transverse waves,"Time and spatial damping of transverse magnetohydrodynamic (MHD) kink
oscillations is a source of information on the cross-field variation of the
plasma density in coronal waveguides. We show that a probabilistic approach to
the problem of determining the density structuring from the observed damping of
transverse oscillations enables us to obtain information on the two parameters
that characterise the cross-field density profile. The inference is performed
by computing the marginal posterior distributions for density contrast and
transverse inhomo- geneity length-scale using Bayesian analysis and damping
ratios for transverse oscillations under the assumption that damping is
produced by resonant absorption. The obtained distributions show that, for
damping times of a few oscillatory periods, low density contrasts and short
inho- mogeneity length scales are more plausible in explaining observations.
This means that valuable information on the cross-field density profile can be
obtained even if the inversion problem, with two unknowns and one observable,
is a mathematically ill-posed problem.",1404.0584v1
2014-04-14,Distributed Approximate Message Passing for Compressed Sensing,"In this paper, an efficient distributed approach for implementing the
approximate message passing (AMP) algorithm, named distributed AMP (DAMP), is
developed for compressed sensing (CS) recovery in sensor networks with the
sparsity K unknown. In the proposed DAMP, distributed sensors do not have to
use or know the entire global sensing matrix, and the burden of computation and
storage for each sensor is reduced. To reduce communications among the sensors,
a new data query algorithm, called global computation for AMP (GCAMP), is
proposed. The proposed GCAMP based DAMP approach has exactly the same recovery
solution as the centralized AMP algorithm, which is proved theoretically in the
paper. The performance of the DAMP approach is evaluated in terms of the
communication cost saved by using GCAMP. For comparison purpose, thresholding
algorithm (TA), a well known distributed Top-K algorithm, is modified so that
it also leads to the same recovery solution as the centralized AMP. Numerical
results demonstrate that the GCAMP based DAMP outperforms the Modified TA based
DAMP, and reduces the communication cost significantly.",1404.3766v2
2014-12-17,The most metal-rich damped Lyman alpha systems at z>1.5 I: The Data,"We present HIRES observations for 30 damped Lyman alpha systems, selected on
the basis of their large metal column densities from previous, lower resolution
data. The measured metal column densities for Fe, Zn, S, Si, Cr, Mn, and Ni are
provided for these 30 systems. Combined with previously observed large metal
column density damped Lyman alpha systems, we present a sample of 44 damped
Lyman alpha systems observed with high resolution spectrographs (R~30000).
These damped Lyman alpha systems probe the most chemically evolved systems at
redshifts greater than 1.5. We discuss the context of our sample with the
general damped Lyman alpha population, demonstrating that we are probing the
top 10% of metal column densities with our sample. In a companion paper, we
will present an analysis of the sample's elemental abundances in the context of
galactic chemical enrichment.",1412.5491v1
2015-02-16,Role of nonlinear anisotropic damping in the magnetization dynamics of topological solitons,"The consequences of nonlinear anisotropic damping, driven by the presence of
Rashba spin-orbit coupling in thin ferromagnetic metals, are examined for the
dynamics of topological magnetic solitons such as domain walls, vortices, and
skyrmions. The damping is found to affect Bloch and N\'eel walls differently in
the steady state regime below Walker breakdown and leads to a monotonic
increase in the wall velocity above this transition for large values of the
Rashba coefficient. For vortices and skyrmions, a generalization of the damping
tensor within the Thiele formalism is presented. It is found that chiral
components of the damping affect vortex- and hedgehog-like skyrmions in
different ways, but the dominant effect is an overall increase in the
viscous-like damping.",1502.04695v2
2015-03-26,Transient nutations decay in diluted paramagnetic solids: a radiation damping mechanism,"Here, a theory of the intensity and concentration dependent damping of
nutation signals observed by Boscaino et al. (Phys. Rev B 48, 7077 (1993);
Phys. Rev. A 59, 4087 (1999)) and by others in various two-level spin systems
is proposed. It is shown that in diluted paramagnetic solids contribution of
dipole-dipole interaction to the nutation decay is negligibly small. We
elaborated a cavity loss (radiation damping) mechanism that explains the
intensity- and concentration dependence of the damping. It is shown that
instead of ordinary Bloch's transverse T2 and longitudinal T1 damping
parameters the decay of transverse and longitudinal spin components in nutation
process are described by one and the same intensity-, concentration-,
frequency- and time dependent damping parameter.",1503.07641v2
2015-08-17,Increased magnetic damping of a single domain wall and adjacent magnetic domains detected by spin torque diode in a nanostripe,"We use spin-torque resonance to probe simultaneously and separately the
dynamics of a magnetic domain wall and of magnetic domains in a nanostripe
magnetic tunnel junction. Thanks to the large associated resistance variations
we are able to analyze quantitatively the resonant properties of these single
nanoscale magnetic objects. In particular, we find that the magnetic damping of
both domains and domain walls is doubled compared to the damping value of their
host magnetic layer. We estimate the contributions to damping arising from
dipolar couplings between the different layers in the junction and from the
intralayer spin pumping effect. We find that they cannot explain the large
damping enhancement that we observe. We conclude that the measured increased
damping is intrinsic to large amplitudes excitations of spatially localized
modes or solitons such as vibrating or propagating domain walls",1508.04043v1
2016-04-27,Influence of nonlocal damping on the field-driven domain wall motion,"We derive the complete expression of nonlocal damping in noncollinear
magnetization due to the nonuniform spin current pumped by precessional
magnetization and incorporate it into a generalized Thiele equation to study
its effects on the dynamics of the transverse and vortex domain walls (DWs) in
ferromagnetic nanowires. We demonstrate that the transverse component of
nonlocal damping slows down the field-driven DW propagation and increases the
Walker breakdown field whereas it is neglected in many previous works in
literature. The experimentally measured DW mobility variation with the damping
tuned by doping with heavy rare-earth elements that had discrepancy from
micromagnetic simulation are now well understood with the nonlocal damping. Our
results suggest that the nonlocal damping should be properly included as a
prerequisite for quantitative studies of current-induced torques in
noncollinear magnetization.",1604.07971v2
2016-04-27,Damping of the Collective Amplitude Mode in Superconductors with Strong Electron-Phonon Coupling,"We study the effect of strong electron-phonon interactions on the damping of
the Higgs amplitude mode in superconductors by means of non-equilibrium
dynamical mean-field simulations of the Holstein model. In contrast to the BCS
dynamics, we find that the damping of the Higgs mode strongly depends on the
temperature, becoming faster as the systen approaches the transition
temperature. The damping at low temperatures is well described by a power-law,
while near the transition temperature the damping shows exponential-like
behavior. We explain this crossover by a temperature-dependent quasiparticle
lifetime caused by the strong electron- phonon coupling, which smears the
superconducting gap edge and makes the relaxation of the Higgs mode into
quasiparticles more efficient at elevated temperatures. We also reveal that the
phonon dynamics can soften the Higgs mode, which results in a slower damping.",1604.08073v2
2016-05-29,Damped Infinite Energy Solutions of the 3D Euler and Boussinesq Equations,"We revisit a family of infinite-energy solutions of the 3D incompressible
Euler equations proposed by Gibbon et al. [9] and shown to blowup in finite
time by Constantin [6]. By adding a damping term to the momentum equation we
examine how the damping coefficient can arrest this blowup. Further, we show
that similar infinite-energy solutions of the inviscid 3D Boussinesq system
with damping can develop a singularity in finite time as long as the damping
effects are insufficient to arrest the (undamped) 3D Euler blowup in the
associated damped 3D Euler system.",1605.08965v3
2016-06-14,Anomalous Damping of a Micro-electro-mechanical Oscillator in Superfluid $^3$He-B,"The mechanical resonance properties of a micro-electro-mechanical oscillator
with a gap of 1.25 $\mu$m was studied in superfluid $^3$He-B at various
pressures. The oscillator was driven in the linear damping regime where the
damping coefficient is independent of the oscillator velocity. The quality
factor of the oscillator remains low ($Q\approx 80$) down to 0.1 $T_c$, 4
orders of magnitude less than the intrinsic quality factor measured in vacuum
at 4 K. In addition to the Boltzmann temperature dependent contribution to the
damping, a damping proportional to temperature was found to dominate at low
temperatures. We propose a multiple scattering mechanism of the surface Andreev
bound states to be a possible cause for the anomalous damping.",1606.04483v2
2016-12-16,Dynamics of cohering and decohering power under Markovian channels,"In this paper, we investigate the cohering and decohering power for the
one-qubit Markovian channels with respect to coherence in terms of the
$l_{1}$-norm, the R$\acute{e}$nyi $\alpha$-relative entropy and the Tsallis
$\alpha$-relative entropy. In the case of $\alpha=2$, the cohering and
decohering power of the amplitude damping channel, the phase damping channel,
the depolarizing channel, and the flip channels under the three measures of
coherence are calculated analytically. The decohering power on the $x, y, z$
basis referring to the amplitude damping channel, the phase damping channel,
the flip channel for every measure we investigated is equal. This property also
happens in the cohering power of the phase damping channel, the depolarizing
channel, and the flip channels. However, the decohering power of the
depolarizing channel is independent to the reference basis, and the cohering
power of the amplitude damping channel on the $x, y$ basis is different to that
on the $z$ basis.",1612.05355v1
2017-01-19,Decoherence effects on multiplayer cooperative quantum games,"We study the behavior of cooperative multiplayer quantum games [35,36] in the
presence of decoherence using different quantum channels such as amplitude
damping, depolarizing and phase damping. It is seen that the outcomes of the
games for the two damping channels with maximum values of decoherence reduce to
same value. However, in comparison to phase damping channel, the payoffs of
cooperators are strongly damped under the influence\ amplitude damping channel
for\ the lower values of decoherence parameter. In the case of depolarizing
channel, the game is a no-payoff game irrespective of the degree of
entanglement in the initial state for the larger values of decoherence
parameter. The decoherence gets the cooperators worse off.",1701.05342v1
2017-07-30,Blow-up for semilinear damped wave equations with sub-Strauss exponent in the scattering case,"It is well-known that the critical exponent for semilinear damped wave
equations is Fujita exponent when the damping is effective. Lai, Takamura and
Wakasa in 2017 have obtained a blow-up result not only for super-Fujita
exponent but also for the one closely related to Strauss exponent when the
damping is scaling invariant and its constant is relatively small,which has
been recently extended by Ikeda and Sobajima. Introducing a multiplier for the
time-derivative of the spatial integral of unknown functions, we succeed in
employing the technics on the analysis for semilinear wave equations and
proving a blow-up result for semilinear damped wave equations with sub-Strauss
exponent when the damping is in the scattering range.",1707.09583v3
2017-10-09,Resonant absorption of surface sausage and surface kink modes under photospheric conditions,"We study the effect of resonant absorption of surface sausage and surface
kink modes under photospheric conditions where the slow surface sausage modes
undergo resonant damping in the slow continuum and the surface kink modes in
the slow and Alfv\'{e}n continua at the transitional layers. We use recently
derived analytical formulas to obtain the damping rate (time). By considering
linear density and linear pressure profiles for the transitional layers, we
show that resonant absorption in the slow continuum could be an efficient
mechanism for the wave damping of the slow surface sausage and slow surface
kink modes whilst the damping rate of the slow surface kink mode in the
Alfv\'{e}n continuum is weak. It is also found that the resonant damping of the
fast surface kink mode is much stronger than that of the slow surface kink
mode, showing a similar efficiency as under coronal conditions. It is worth to
notice that the slow body sausage and kink modes can also resonantly damp in
the slow continuum for those linear profiles.",1710.03350v2
2017-11-21,Nonexistence of global solutions of nonlinear wave equations with weak time-dependent damping related to Glassey conjecture,"This work is devoted to the nonexistence of global-in-time energy solutions
of nonlinear wave equation of derivative type with weak time-dependent damping
in the scattering and scale invariant range. By introducing some multipliers to
absorb the damping term, we succeed in establishing the same upper bound of the
lifespan for the scattering damping as the non-damped case, which is a part of
so-called Glassey conjecture on nonlinear wave equations. We also study an
upper bound of the lifespan for the scale invariant damping with the same
method.",1711.07591v2
2018-01-03,Stabilisation of wave equations on the torus with rough dampings,"For the damped wave equation on a compact manifold with {\em continuous}
dampings, the geometric control condition is necessary and sufficient for
{uniform} stabilisation. In this article, on the two dimensional torus, in the
special case where $a(x) = \sum\_{j=1}^N a\_j 1\_{x\in R\_j}$ ($R\_j$ are
polygons), we give a very simple necessary and sufficient geometric condition
for uniform stabilisation. We also propose a natural generalization of the
geometric control condition which makes sense for $L^\infty$ dampings. We show
that this condition is always necessary for uniform stabilisation (for any
compact (smooth) manifold and any $L^\infty$ damping), and we prove that it is
sufficient in our particular case on $\mathbb{T}^2$ (and for our particular
dampings).",1801.00983v2
2018-03-12,Optical Rotation of Levitated Spheres in High Vacuum,"A circularly polarized laser beam is used to levitate and control the
rotation of microspheres in high vacuum. At low pressure, rotation frequencies
as high as 6 MHz are observed for birefringent vaterite spheres, limited by
centrifugal stresses. Due to the extremely low damping in high vacuum,
controlled optical rotation of amorphous SiO$_2$ spheres is also observed at
rates above several MHz. At $10^{-7}$ mbar, a damping time of $6\times10^4$ s
is measured for a $10\ \mu$m diameter SiO$_2$ sphere. No additional damping
mechanisms are observed above gas damping, indicating that even longer damping
times may be possible with operation at lower pressure. The controlled optical
rotation of microspheres at MHz frequencies with low damping, including for
materials that are not intrinsically birefringent, provides a new tool for
performing precision measurements using optically levitated systems.",1803.04297v1
2018-03-23,A conservation law with spatially localized sublinear damping,"We consider a general conservation law on the circle, in the presence of a
sublinear damping. If the damping acts on the whole circle, then the solution
becomes identically zero in finite time, following the same mechanism as the
corresponding ordinary differential equation. When the damping acts only
locally in space, we show a dichotomy: if the flux function is not zero at the
origin, then the transport mechanism causes the extinction of the solution in
finite time, as in the first case. On the other hand, if zero is a
non-degenerate critical point of the flux function, then the solution becomes
extinct in finite time only inside the damping zone, decays algebraically
uniformly in space, and we exhibit a boundary layer, shrinking with time,
around the damping zone. Numerical illustrations show how similar phenomena may
be expected for other equations.",1803.08767v1
2019-03-06,Microwave magnon damping in YIG films at millikelvin temperatures,"Magnon systems used in quantum devices require low damping if coherence is to
be maintained. The ferrimagnetic electrical insulator yttrium iron garnet (YIG)
has low magnon damping at room temperature and is a strong candidate to host
microwave magnon excitations in future quantum devices. Monocrystalline YIG
films are typically grown on gadolinium gallium garnet (GGG) substrates. In
this work, comparative experiments made on YIG waveguides with and without GGG
substrates indicate that the material plays a significant role in increasing
the damping at low temperatures. Measurements reveal that damping due to
temperature-peak processes is dominant above 1 K. Damping behaviour that we
show can be attributed to coupling to two-level fluctuators (TLFs) is observed
below 1 K. Upon saturating the TLFs in the substrate-free YIG at 20 mK,
linewidths of 1.4 MHz are achievable: lower than those measured at room
temperature.",1903.02527v3
2019-09-21,Stability for coupled waves with locally disturbed Kelvin-Voigt damping,"We consider a coupled wave system with partial Kelvin-Voigt damping in the
interval (-1,1), where one wave is dissipative and the other does not. When the
damping is effective in the whole domain (-1,1) it was proven in H.Portillo
Oquendo and P.Sanez Pacheco, optimal decay for coupled waves with Kelvin-voigt
damping, Applied Mathematics Letters 67 (2017), 16-20. That the energy is
decreasing over the time with a rate equal to $t^{-\frac{1}{2}}$. In this
paper, using the frequency domain method we show the effect of the coupling and
the non smoothness of the damping coefficient on the energy decay. Actually, as
expected we show the lack of exponential stability, that the semigroup loses
speed and it decays polynomially with a slower rate then given in, H.Portillo
Oquendo and P.Sanez Pacheco, optimal decay for coupled waves with Kelvin-voigt
damping, Applied Mathematics Letters 67 (2017), 16-20, down to zero at least as
$t^{-\frac{1}{12}}$.",1909.09838v1
2020-05-15,Slow magnetosonic wave absorption by pressure induced ionization-recombination dissipation,"A new mechanisms for damping of slow magnetosonic waves (SMW) by pressure
induced oscillations of the ionization degree is proposed. An explicit formula
for the damping rate is quantitatively derived. Physical conditions where the
new mechanism will dominate are briefly discussed. The ionization-recombination
damping is frequency independent and has no hydrodynamic interpretation.
Roughly speaking large area of partially ionized plasma are damper for basses
of SMW while usual MHD mechanisms operate as a low pass filter. The derived
damping rate is proportional to the square of the sine between the constant
magnetic field and the wave-vector. Angular distribution of the spectral
density of SMW and Alfv\'en waves (AW) created by turbulent regions and passing
through large regions of partially ionized plasma is qualitatively considered.
The calculated damping rate is expressed by the electron impact cross section
of the hydrogen atom and in short all details of the proposed damping
mechanisms are well studied.",2005.07730v1
2020-06-30,Polynomial stabilization of non-smooth direct/indirect elastic/viscoelastic damping problem involving Bresse system,"We consider an elastic/viscoelastic transmission problem for the Bresse
system with fully Dirichlet or Dirichlet-Neumann-Neumann boundary conditions.
The physical model consists of three wave equations coupled in certain pattern.
The system is damped directly or indirectly by global or local Kelvin-Voigt
damping. Actually, the number of the dampings, their nature of distribution
(locally or globally) and the smoothness of the damping coefficient at the
interface play a crucial role in the type of the stabilization of the
corresponding semigroup. Indeed, using frequency domain approach combined with
multiplier techniques and the construction of a new multiplier function, we
establish different types of energy decay rate (see the table of stability
results below). Our results generalize and improve many earlier ones in the
literature and in particular some studies done on the Timoshenko system with
Kelvin-Voigt damping.",2006.16595v2
2020-07-02,Uniformly-Damped Binomial Filters: Five-percent Maximum Overshoot Optimal Response Design,"In this paper, the five-percent maximum overshoot design of uniformly-damped
binomial filters (transfer-functions) is introduced. First, the butterworth
filter response is represented as a damped-binomial filter response. To extend
the maximum-overshoot response of the second-order butterworth to higher
orders, the binomial theorem is extended to the uniformly-damped binomial
theorem. It is shown that the five-percent uniformly-damped binomial filter is
a compromise between the butterworth filter and the standard binomial filter,
with respect to the filter-approximation problem in the time and frequency
domain. Finally, this paper concludes that in applications of interest, such as
step-tracking, where both strong filtering and a fast, smooth
transient-response, with negligible overshoot are desired, the response of the
normalized five-percent uniformly-damped binomial form is a candidate
replacement for both the butterworth and standard binomial filter forms.",2007.00890v3
2020-09-17,Temperature Dependent Non-linear Damping in Palladium Nano-mechanical Resonators,"Advances in nano-fabrication techniques has made it feasible to observe
damping phenomena beyond the linear regime in nano-mechanical systems. In this
work, we report cubic non-linear damping in palladium nano-mechanical
resonators. Nano-scale palladium beams exposed to a $H_2$ atmosphere become
softer and display enhanced Duffing non-linearity as well as non-linear damping
at ultra low temperatures. The damping is highest at the lowest temperatures of
$\sim 110\: mK$ and decreases when warmed up-to $\sim 1\textrm{ }K$. We
experimentally demonstrate for the first time a temperature dependent
non-linear damping in a nano-mechanical system below 1 K. It is consistent with
a predicted two phonon mediated non-linear Akhiezer scenario for ballistic
phonons with mean free path comparable to the beam thickness. This opens up new
possibilities to engineer non-linear phenomena at low temperatures.",2009.08324v1
2020-09-22,Sharp exponential decay rates for anisotropically damped waves,"In this article, we study energy decay of the damped wave equation on compact
Riemannian manifolds where the damping coefficient is anisotropic and modeled
by a pseudodifferential operator of order zero. We prove that the energy of
solutions decays at an exponential rate if and only if the damping coefficient
satisfies an anisotropic analogue of the classical geometric control condition,
along with a unique continuation hypothesis. Furthermore, we compute an
explicit formula for the optimal decay rate in terms of the spectral abscissa
and the long-time averages of the principal symbol of the damping over
geodesics, in analogy to the work of Lebeau for the isotropic case. We also
construct genuinely anisotropic dampings which satisfy our hypotheses on the
flat torus.",2009.10832v2
2020-12-25,Information constraint in open quantum systems,"We propose an effect called information constraint which is characterized by
the existence of different decay rates of signal strengths propagating along
opposite directions. It is an intrinsic property of a type of open quantum
system, which does not rely on boundary conditions. We define the value of
information constraint ($I_C$) as the ratio of different decay rates and derive
the analytical representation of $I_C$ for general quadratic Lindbladian
systems. Based on information constraint, we can provide a simple and elegant
explanation of chiral and helical damping, and get the local maximum points of
relative particle number for the periodical boundary system, consistent with
numerical calculations. Inspired by information constraint, we propose and
prove the correspondence between edge modes and damping modes. A new damping
mode called Dirac damping is constructed, and chiral/helical damping can be
regarded as a special case of Dirac damping.",2012.13583v3
2021-04-29,Non-linear damping of standing kink waves computed with Elsasser variables,"In a previous paper, we computed the energy density and the non-linear energy
cascade rate for transverse kink waves using Elsasser variables. In this paper,
we focus on the standing kink waves, which are impulsively excited in coronal
loops by external perturbations. We present an analytical calculation to
compute the damping time due to the non-linear development of the
Kelvin-Helmholtz instability. The main result is that the damping time is
inversely proportional to the oscillation amplitude. We compare the damping
times from our formula with the results of numerical simulations and
observations. In both cases we find a reasonably good match. The comparison
with the simulations show that the non-linear damping dominates in the high
amplitude regime, while the low amplitude regime shows damping by resonant
absorption. In the comparison with the observations, we find a power law
inversely proportional to the amplitude $\eta^{-1}$ as an outer envelope for
our Monte Carlo data points.",2104.14331v1
2021-05-31,Revisiting the Plasmon Radiation Damping of Gold Nanorods,"Noble metal nanoparticles have been utilized for a vast amount of optical
applications. For the applications that used metal nanoparticles as nanosensors
and optical labeling, larger radiation damping is preferred (higher optical
signal). To get a deeper knowledge about the radiation damping of noble metal
nanoparticles, we used gold nanorods with different geometry factors (aspect
ratios) as the model system to study. We investigated theoretically how the
radiation damping of a nanorod depends on the material, and shape of the
particle. Surprisingly, a simple analytical equation describes radiation
damping very accurately and allow to disentangle the maximal radiation damping
parameter for gold nanorod with resonance energy E_res around 1.81 eV (685 nm).
We found very good agreement with theoretical predictions and experimental data
obtained by single-particle spectroscopy. Our results and approaches may pave
the way for designing and optimizing gold nanostructure with higher optical
signal and better sensing performance.",2105.14873v1
2021-06-23,Bayesian evidence for a nonlinear damping model for coronal loop oscillations,"Recent observational and theoretical studies indicate that the damping of
solar coronal loop oscillations depends on the oscillation amplitude. We
consider two mechanisms, linear resonant absorption and a nonlinear damping
model. We confront theoretical predictions from these models with observed data
in the plane of observables defined by the damping ratio and the oscillation
amplitude. The structure of the Bayesian evidence in this plane displays a
clear separation between the regions where each model is more plausible
relative to the other. There is qualitative agreement between the regions of
high marginal likelihood and Bayes factor for the nonlinear damping model and
the arrangement of observed data. A quantitative application to 101 loop
oscillation cases observed with SDO/AIA results in the marginal likelihood for
the nonlinear model being larger in the majority of them. The cases with
conclusive evidence for the nonlinear damping model outnumber considerably
those in favor of linear resonant absorption.",2106.12243v1
2021-07-13,Convergence of iterates for first-order optimization algorithms with inertia and Hessian driven damping,"In a Hilbert space setting, for convex optimization, we show the convergence
of the iterates to optimal solutions for a class of accelerated first-order
algorithms. They can be interpreted as discrete temporal versions of an
inertial dynamic involving both viscous damping and Hessian-driven damping. The
asymptotically vanishing viscous damping is linked to the accelerated gradient
method of Nesterov while the Hessian driven damping makes it possible to
significantly attenuate the oscillations. By treating the Hessian-driven
damping as the time derivative of the gradient term, this gives, in discretized
form, first-order algorithms. These results complement the previous work of the
authors where it was shown the fast convergence of the values, and the fast
convergence towards zero of the gradients.",2107.05943v1
2021-12-13,Effect of interfacial damping on high-frequency surface wave resonance on a nanostrip-bonded substrate,"Since surface acoustic waves (SAW) are often generated on substrates to which
nanostrips are periodically attached, it is very important to consider the
effect of interface between the deposited strip and the substrate surface,
which is an unavoidable issue in manufacturing. In this paper, we propose a
theoretical model that takes into account the interface damping and calculate
the dispersion relationships both for frequency and attenuation of SAW
resonance. This results show that the interface damping has an insignificant
effect on resonance frequency, but, interestingly, attenuation of the SAW can
decrease significantly in the high frequency region as the interface damping
increases. Using picosecond ultrasound spectroscopy, we confirm the validity of
our theory; the experimental results show similar trends both for resonant
frequency and attenuation in the SAW resonance. Furthermore, the resonant
behavior of the SAW is simulated using the finite element method, and the
intrinsic cause of interface damping on the vibrating system is discussed.
These findings strongly indicate the necessity of considering interfacial
damping in the design of SAW devices.",2112.06367v1
2021-12-13,Cosmic ray streaming in the turbulent interstellar medium,"We study the streaming instability of GeV$-100~$GeV cosmic rays (CRs) and its
damping in the turbulent interstellar medium (ISM). We find that the damping of
streaming instability is dominated by ion-neutral collisional damping in weakly
ionized molecular clouds, turbulent damping in the highly ionized warm medium,
and nonlinear Landau damping in the Galactic halo. Only in the Galactic halo,
is the streaming speed of CRs close to the Alfv\'{e}n speed. Alfv\'{e}nic
turbulence plays an important role in both suppressing the streaming
instability and regulating the diffusion of streaming CRs via magnetic field
line tangling, with the effective mean free path of streaming CRs in the
observer frame determined by the Alfv\'{e}nic scale in super-Alfv\'{e}nic
turbulence. The resulting diffusion coefficient is sensitive to Alfv\'{e}n Mach
number, which has a large range of values in the multi-phase ISM.
Super-Alfv\'{e}nic turbulence contributes to additional confinement of
streaming CRs, irrespective of the dominant damping mechanism.",2112.06941v2
2022-05-27,Scalar field damping at high temperatures,"The motion of a scalar field that interacts with a hot plasma, like the
inflaton during reheating, is damped, which is a dissipative process. At high
temperatures the damping can be described by a local term in the effective
equation of motion. The damping coefficient is sensitive to multiple
scattering. In the loop expansion its computation would require an all-order
resummation. Instead we solve an effective Boltzmann equation, similarly to the
computation of transport coefficients. For an interaction with another scalar
field we obtain a simple relation between the damping coefficient and the bulk
viscosity, so that one can make use of known results for the latter. The
numerical prefactor of the damping coefficient turns out to be rather large, of
order $ 10 ^ 4 $.",2205.14166v2
2022-09-13,Latest results from the DAMPE space mission,"The DArk Matter Particle Explorer (DAMPE) is a space-based particle detector
launched on December 17th, 2015 from the Jiuquan Satellite Launch Center
(China). The main goals of the DAMPE mission are the study of galactic cosmic
rays (CR), the electron-positron energy spectrum, gamma-ray astronomy, and
indirect dark matter search. Among its sub-detectors, the deep calorimeter
makes DAMPE able to measure electrons and gamma-ray spectra up to 10 TeV, and
CR nuclei spectra up to hundreds of TeV, with unprecedented energy resolution.
This high-energy region is important in order to search for electron-positron
sources, for dark matter signatures in space, and to clarify CR acceleration
and propagation mechanisms inside our galaxy. A general overview of the DAMPE
experiment will be presented in this work, along with its main results and
ongoing activities.",2209.06014v1
2022-10-25,Microscopic structure of electromagnetic whistler wave damping by kinetic mechanisms in hot magnetized Vlasov plasmas,"The kinetic damping mechanism of low frequency transverse perturbations
propagating parallel to the magnetic field in a magnetized warm electron plasma
is simulated by means of electromagnetic (EM) Vlasov simulations. The
short-time-scale damping of the electron magnetohydrodynamic whistler
perturbations and underlying physics of finite electron temperature effect on
its real frequency are recovered rather deterministically, and analyzed. The
damping arises from an interplay between a global (prevailing over entire
phase-space) and the more familiar resonant-electron-specific kinetic damping
mechanisms, both of which preserve entropy but operate distinctly by leaving
their characteristic signatures on an initially coherent finite amplitude
modification of the warm electron equilibrium distribution. The net damping
results from a deterministic thermalization, or phase-mixing process, largely
supplementing the resonant acceleration of electrons at shorter time scales,
relevant to short-lived turbulent EM fluctuations. A kinetic model for the
evolving initial transverse EM perturbation is presented and applied to
signatures of the whistler wave phase-mixing process in simulations.",2210.13764v1
2022-12-02,Equivalence between the energy decay of fractional damped Klein-Gordon equations and geometric conditions for damping coefficients,"We consider damped $s$-fractional Klein--Gordon equations on $\mathbb{R}^d$,
where $s$ denotes the order of the fractional Laplacian. In the one-dimensional
case $d = 1$, Green (2020) established that the exponential decay for $s \geq
2$ and the polynomial decay of order $s/(4-2s)$ hold if and only if the damping
coefficient function satisfies the so-called geometric control condition. In
this note, we show that the $o(1)$ energy decay is also equivalent to these
conditions in the case $d=1$. Furthermore, we extend this result to the
higher-dimensional case: the logarithmic decay, the $o(1)$ decay, and the
thickness of the damping coefficient are equivalent for $s \geq 2$. In
addition, we also prove that the exponential decay holds for $0 < s < 2$ if and
only if the damping coefficient function has a positive lower bound, so in
particular, we cannot expect the exponential decay under the geometric control
condition.",2212.01029v4
2023-01-13,An artificially-damped Fourier method for dispersive evolution equations,"Computing solutions to partial differential equations using the fast Fourier
transform can lead to unwanted oscillatory behavior. Due to the periodic nature
of the discrete Fourier transform, waves that leave the computational domain on
one side reappear on the other and for dispersive equations these are typically
high-velocity, high-frequency waves. However, the fast Fourier transform is a
very efficient numerical tool and it is important to find a way to damp these
oscillations so that this transform can still be used. In this paper, we
accurately model solutions to four nonlinear partial differential equations on
an infinite domain by considering a finite interval and implementing two
damping methods outside of that interval: one that solves the heat equation and
one that simulates rapid exponential decay. Heat equation-based damping is best
suited for small-amplitude, high-frequency oscillations while exponential decay
is used to damp traveling waves and high-amplitude oscillations. We demonstrate
significant improvements in the runtime of well-studied numerical methods when
adding in the damping method.",2301.05789v1
2023-03-07,Stabilization of the wave equation on larger-dimension tori with rough dampings,"This paper deals with uniform stabilization of the damped wave equation. When
the manifold is compact and the damping is continuous, the geometric control
condition is known to be necessary and sufficient. In the case where the
damping is a sum of characteristic functions of polygons on a two-dimensional
torus, a result by Burq-G\'erard states that stabilization occurs if and only
if every geodesic intersects the interior of the damped region or razes damped
polygons on both sides. We give a natural generalization of their result to a
sufficient condition on tori of any dimension $d \geq 3$. In some particular
cases, we show that this sufficient condition can be weakened.",2303.03733v4
2023-07-10,The Characteristic Shape of Damping Wings During Reionization,"Spectroscopic analysis of Ly$\alpha$ damping wings of bright sources at $z>6$
is a promising way to measure the reionization history of the universe.
However, the theoretical interpretation of the damping wings is challenging due
to the inhomogeneous nature of the reionization process and the proximity
effect of bright sources. In this Letter, we analyze the damping wings arising
from the neutral patches in the radiative transfer cosmological simulation
suite Cosmic Reionization on Computers (CROC). We find that the damping wing
profile remains a tight function of volume-weighted neutral fraction $\left<
x_{\rm HI} \right>_{\rm v}$, especially when $\left< x_{\rm HI} \right>_{\rm
v}>0.5$, despite the patchy nature of reionization and the proximity effect.
This small scatter indicates that with a well-measured damping wing profile, we
could constrain the volume-weighted neutral fraction as precise as $\Delta
\left< x_{\rm HI} \right>_{\rm v} \lesssim 0.1$ in the first half of
reionization.",2307.04797v1
2023-07-17,Dissipation in solids under oscillatory shear: Role of damping scheme and sample thickness,"We study dissipation as a function of sample thickness in solids under global
oscillatory shear applied to the top layer of the sample. Two types of damping
mechanism are considered: Langevin and Dissipative Particle Dynamics (DPD). In
the regime of low driving frequency, and under strain-controlled conditions, we
observe that for Langevin damping, dissipation increases with sample thickness,
while for DPD damping, it decreases. Under force-controlled conditions,
dissipation increases with sample thickness for both damping schemes. These
results can be physically understood by treating the solid as a one-dimensional
harmonic chain in the quasi-static limit, for which explicit equations (scaling
relations) describing dissipation as a function of chain length (sample
thickness) are provided. The consequences of these results, in particular
regarding the choice of damping scheme in computer simulations, are discussed.",2307.08413v1
2023-08-17,A low-rank algorithm for strongly damped wave equations with visco-elastic damping and mass terms,"Damped wave equations have been used in many real-world fields. In this
paper, we study a low-rank solution of the strongly damped wave equation with
the damping term, visco-elastic damping term and mass term. Firstly, a
second-order finite difference method is employed for spatial discretization.
Then, we receive a second-order matrix differential system. Next, we transform
it into an equivalent first-order matrix differential system, and split the
transformed system into three subproblems. Applying a Strang splitting to these
subproblems and combining a dynamical low-rank approach, we obtain a low-rank
algorithm. Numerical experiments are reported to demonstrate that the proposed
low-rank algorithm is robust and accurate, and has second-order convergence
rate in time.",2308.08888v2
2023-10-30,Optimal backward uniqueness and polynomial stability of second order equations with unbounded damping,"For general second order evolution equations, we prove an optimal condition
on the degree of unboundedness of the damping, that rules out finite-time
extinction. We show that control estimates give energy decay rates that
explicitly depend on the degree of unboundedness, and establish a dilation
method to turn existing control estimates for one propagator into those for
another in the functional calculus. As corollaries, we prove Schr\""odinger
observability gives decay for unbounded damping, weak monotonicity in damping,
and quantitative unique continuation and optimal propagation for fractional
Laplacians. As applications, we establish a variety of novel and explicit
energy decay results to systems with unbounded damping, including singular
damping, linearised gravity water waves and Euler--Bernoulli plates.",2310.19911v1
2024-03-12,"Modulational instability of nonuniformly damped, broad-banded waves: applications to waves in sea-ice","This paper sets out to explore the modulational (or Benjamin-Feir)
instability of a monochromatic wave propagating in the presence of damping such
as that induced by sea-ice on the ocean surface. The fundamental wave motion is
modelled using the spatial Zakharov equation, to which either uniform or
non-uniform (frequency dependent) damping is added. By means of mode truncation
the spatial analogue of the classical Benjamin-Feir instability can be studied
analytically using dynamical systems techniques. The formulation readily yields
the free surface envelope, giving insight into the physical implications of
damping on the modulational instability. The evolution of an initially unstable
mode is also studied numerically by integrating the damped, spatial Zakharov
equation, in order to complement the analytical theory. This sheds light on the
effects of damping on spectral broadening arising from this instability.",2403.07425v1
1994-05-12,Black Hole Relics and Inflation: Limits on Blue Perturbation Spectra,"Blue primordial power spectra have spectral index $n>1$ and arise naturally
in the recently proposed hybrid inflationary scenario. An observational upper
limit on {\em n} is derived by normalizing the spectrum at the quadrupole scale
and considering the possible overproduction of Planck mass relics formed in the
final stage of primordial black hole evaporation. In the inflationary Universe
with the maximum reheating temperature compatible with the observed quadrupole
anisotropy, the upper limit is $n=1.4$, but it is slightly weaker for lower
reheat temperatures. This limit applies over 57 decades of mass and is
therefore insensitive to cosmic variance and any gravitational wave
contribution to the quadrupole anisotropy. It is also independent of the dark
matter content of the Universe and therefore the bias parameter. In some
circumstances, there may be an extended dust-like phase between the end of
inflation and reheating. In this case, primordial black holes form more
abundantly and the upper limit is $n=1.3$.",9405027v1
1995-02-01,Spectra and Statistics of Cosmic String Perturbations on the Microwave Background: A Monte Carlo Approach,"Using Monte Carlo simulations of perturbations induced by cosmic strings on
the microwave background, we demonstrate the scale invariance of string
fluctuation patterns. By comparing string-induced fluctuation patterns with
gaussian random phase ones, we show that the non-gaussian signatures of the
string patterns are detectable by tests based on the moments of the
distributions only for angular scales smaller than a few arcminutes and for
maps based on the gradient of temperature fluctuations. However, we find that
tests of the gaussianity of the moments fail when we include a reasonable
amount of instrumental noise in a pattern. Signal to noise ratios of $3.3$ or
greater completely suppress a string pattern's non-gaussian features even at
the highest resolutions.",9502004v2
1999-04-16,The Sunyaev-Zeldovich Effect as Microwave Foreground and Probe of Cosmology,"The Sunyaev-Zel'dovich (SZ) effect from clusters of galaxies should yield a
significant signal in cosmic microwave background(CMB) experiments at small
angular scales ($\ell \ga 1000$). Experiments with sufficient frequency
coverage should be able to remove much of this signal in order to recover the
primary anisotropy. The SZ signal is interesting in its own right; the
amplitude and angular dependence are sensitive to both cosmology and the
evolution of the gas. Combining CMB measurements with planned non-targeted SZ
surveys could isolate the cosmological effects, providing CMB experiments with
a low-redshift test of cosmology as a consistency check. Improvements in the
determination of the angular diameter distance as a function of redshift from
SZ and X-ray observations of a large sample of clusters will also provide a
probe of cosmology.",9904220v1
2000-12-05,Near-IR Spectroscopy and Population Synthesis of Super Star Clusters in NGC 1569,"We present H- and K-band NIRSPEC spectroscopy of super star clusters (SSCs)
in the irregular starburst galaxy NGC 1569, obtained at the Keck Observatory.
We fit these photospheric spectra to NextGen model atmospheres to obtain
effective spectral types of clusters, and find that the information in both H-
and K-band spectra is necessary to remove degeneracy in the fits. The light of
SSC B is unambiguously dominated by K0 supergiants (T_eff=4400 +- 100 K, log
g=0.5 +- 0.5). The double cluster SSC A has higher T_eff (G5) and less tightly
constrained surface gravity (log g=1.3 +- 1.3), consistent with a mixed stellar
population dominated by blue Wolf-Rayet stars and red supergiants. We predict
the time evolution of infrared spectra of SSCs using Starburst99 population
synthesis models coupled with empirical stellar spectral libraries (at solar
metallicity). The resulting model sequence allows us to assign ages of 15-18
Myr for SSC B and 18-21 Myr for SSC A.",0012089v1
2001-05-14,Understanding Cluster Gas Evolution and Fine-Scale CMB Anisotropy with Deep Sunyaev-Zel'dovich Effect Surveys,"We investigate the impact of gas evolution on the expected yields from deep
Sunyaev-Zel'dovich (SZ) effect surveys as well as on the expected SZ effect
contribution to fine scale anisotropy in the Cosmic Microwave Background. The
approximate yields from SZ effect surveys are remarkably insensitive to gas
evolution, even though the observable properties of the resulting clusters can
be markedly different. The CMB angular power spectrum at high multipoles due to
the SZ effect from clusters is quite sensitive to gas evolution. We show that
moderate resolution SZ effect imaging of clusters found in deep SZ effect
surveys should allow a good understanding of gas evolution in galaxy clusters,
independent of the details of the nature of the gas evolution. Such an
understanding will be necessary before precise cosmological constraints can be
set from yields of large cluster surveys.",0105229v1
2001-05-22,"Constraints on Omega_m, Omega_L, and Sigma_8, from Galaxy Cluster Redshift Distributions","We show that the counts of galaxy clusters in future deep cluster surveys can
place strong constraints on the matter density, Omega_m, the vacuum energy
density, Omega_L, and the normalization of the matter power spectrum, sigma_8.
Degeneracies between these parameters are different from those in studies of
either high--redshift type Ia Supernovae (SNe), or cosmic microwave background
(CMB) anisotropies. Using a mass threshold for cluster detection expected to be
typical for upcoming SZE surveys, we find that constraints on Omega_m and
sigma_8 at the level of roughly 5% or better can be expected, assuming redshift
information is known at least to z=0.5 and in the absence of significant
systematic errors. Without information past this redshift, Omega_L is
constrained to 25%. With complete redshift information, deep (M_{lim}=
10^{14}h^{-1}{M_sun}), relatively small solid angle (roughly 12 {deg}^2)
surveys can further constrain Omega_L to an accuracy of 15%, while large solid
angle surveys with ground-based large-format bolometer arrays could measure
Omega_L to a precision of 4% or better.",0105396v2
2002-05-27,Radio Point Sources and the Thermal SZ Power Spectrum,"Radio point sources are strongly correlated with clusters of galaxies, so a
significant fraction of the thermal Sunyaev-Zel'dovich (SZ) effect signal could
be affected by point source contamination. Based on empirical estimates of the
radio galaxy population, it is shown that the rms temperature fluctuations of
the thermal SZ effect could be underestimated by as much as 30% at an observing
frequency of 30 GHz at l>1000. The effect is larger at higher multipoles. If
the recent report of excess power at small angular scales is to be explained by
the thermal SZ effect, then radio point sources at an observing frequency of 30
GHz must be a surprisingly weak contaminant of the SZ effect for low-mass
clusters.",0205467v2
2002-07-29,Measuring Cluster Peculiar Velocities and Temperatures at cm and mm Wavelengths,"We present a detailed investigation of issues related to the measurement of
peculiar velocities and temperatures using Sunyaev-Zel'dovich (SZ) effects. We
estimate the accuracy to which peculiar velocities and gas temperatures of
distant galaxy clusters could be measured. With uK sensitivity on arcminute
scales at several frequencies it will be possible to measure peculiar
velocities to an accuracy of about 130 km/s and gas temperatures to better than
1 keV. The limiting factor for the accuracy of the measured peculiar velocity
is the presence of bulk motions within the galaxy cluster, even for apparently
relaxed clusters. The accuracy of the temperature is mainly limited by noise.
These results are independent of redshift. Such constraints can best be
achieved with only three frequencies: one in the Rayleigh-Jeans region (<40
GHz), one near 150 GHz, and the third at 300 GHz or higher. Measurements at the
null of the thermal SZ effect are of marginal utility, other than as a
foreground/background monitor.",0207600v2
2002-07-29,CMB-Normalized Predictions for Sunyaev-Zel'dovich effect fluctuations,"We predict the level of small-scale anisotropy in the cosmic microwave
background (CMB) due to the Sunyaev--Zel'dovich (SZ) effect for the ensemble of
cosmological models that are consistent with current measurements of
large-scale CMB anisotropy. We argue that the recently reported detections of
the small-scale (arcminutes) CMB anisotropy are only marginally consistent with
being the SZ effect when cosmological models are calibrated to the existing
primary CMB data on large scales. The discrepancy is at more than 2-2.5 sigma,
and is mainly due to a lower sigma_8 <0.8 favored by the primary CMB and a
higher sigma_8 > 1 favored by the SZ effect. A degeneracy between the optical
depth to Thomson scattering and the CMB-derived value of sigma_8 suggests that
the discrepancy is reduced if the universe was reionized very early, at a
redshift of about 25.",0207633v1
2002-08-08,Cosmology with the Sunyaev-Zel'dovich Effect,"The Sunyaev-Zel'dovich effect (SZE) provides a unique way to map the
large-scale structure of the universe as traced by massive clusters of
galaxies. As a spectral distortion of the cosmic microwave background, the SZE
is insensitive to the redshift of the galaxy cluster, making it well-suited for
studies of clusters at all redshifts, and especially at reasonably high
redshifts (z > 1) where the abundance of clusters is critically dependent on
the underlying cosmology. Recent high signal-to-noise detections of the SZE
have enabled interesting constraints on the Hubble constant and the matter
density of the universe using small samples of galaxy clusters. Upcoming SZE
surveys are expected to find hundreds to thousands of new galaxy clusters, with
a mass selection function that is remarkably uniform with redshift. In this
review we provide an overview of the SZE and its use for cosmological studies
with emphasis on the cosmology that can, in principle, be extracted from SZE
survey yields. We discuss the observational and theoretical challenges that
must be met before precise cosmological constraints can be extracted from the
survey yields.",0208192v1
2002-09-25,External Shear in Quadruply Imaged Lens Systems,"We use publicly available N-body simulations and semi-analytic models of
galaxy formation to estimate the levels of external shear due to structure near
the lens in gravitational lens systems. We also describe two selection effects,
specific to four-image systems, that enhance the probability of observing
systems to have higher external shear. Ignoring additional contributions from
""cosmic shear"" and assuming that lens galaxies are not significantly flattened,
we find that the mean shear at the position of a quadruple lens galaxy is 0.11,
the rms shear is roughly 0.15, and there is roughly a 45% likelihood of
external shear greater than 0.1. This is much larger than previous estimates
and in good agreement with typical measured external shear. The higher shear
primarily stems from the tendency of early-type galaxies, which are the
majority of lenses, to reside in overdense regions.",0209532v2
2003-05-21,A Method for Mapping the Temperature Profile of X-ray Clusters Through Radio Observations,"Many of the most luminous extragalactic radio sources are located at the
centers of X-ray clusters, and so their radiation must be scattered by the
surrounding hot gas. We show that radio observations of the highly-polarized
scattered radiation (which depends on the electron density distribution) in
combination with the thermal Sunyaev-Zeldovich effect (which measures the
electron pressure distribution), can be used to determine the radial profile of
the electron temperature within the host cluster. The sensitivity levels
expected from current instruments will allow radio measurements of
mass-weighted cluster temperature profiles to better than roughly 1 keV
accuracy, as long as the central radio source is steady over several million
years. Variable or beamed sources will leave observable signatures in the
scattered emission. For clusters with a central point source brighter than
about 1 mJy, the scattered polarization signal is stronger than competing
effects due to the cosmic microwave background.",0305417v1
2006-09-26,Reconstructing the Thomson Optical Depth due to Patchy Reionization with 21-cm Fluctuation Maps,"Large fluctuations in the electron column density can occur during the
reionization process. We investigate the possibility of deriving the electron
density fluctuations through detailed mapping of the redshifted 21-cm emission
from the neutral medium during reionization. We find that the
electron-scattering optical depth and 21-cm differential brightness temperature
are strongly anti-correlated, allowing optical depth estimates based entirely
on redshifted 21-cm measurements. This should help isolate the CMB polarization
fluctuations that are due to reionization, allowing both cleaning of the patchy
reionization polarization signal as a contaminating source of confusion to
other signals and a measurement of the primordial quadrupole that would be
measured at various locations in the universe at the epoch of reionization.
This latter application in principle allows mapping of the primordial density
field at z~1100 over a large fraction of the Hubble volume.",0609689v2
1998-07-06,Field Driven Thermostated System : A Non-Linear Multi-Baker Map,"In this paper, we discuss a simple model for a field driven, thermostated
random walk that is constructed by a suitable generalization of a multi-baker
map. The map is a usual multi-baker, but perturbed by a thermostated external
field that has many of the properties of the fields used in systems with
Gaussian thermostats. For small values of the driving field, the map is
hyperbolic and has a unique SRB measure that we solve analytically to first
order in the field parameter. We then compute the positive and negative
Lyapunov exponents to second order and discuss their relation to the transport
properties. For higher values of the parameter, this system becomes
non-hyperbolic and posseses an attractive fixed point.",9807011v2
2006-01-19,Fluctuation theorem for constrained equilibrium systems,"We discuss the fluctuation properties of equilibrium chaotic systems with
constraints such as iso-kinetic and Nos\'e-Hoover thermostats. Although the
dynamics of these systems does not typically preserve phase-space volumes, the
average phase-space contraction rate vanishes, so that the stationary states
are smooth. Nevertheless finite-time averages of the phase-space contraction
rate have non-trivial fluctuations which we show satisfy a simple version of
the Gallavotti-Cohen fluctuation theorem, complementary to the usual
fluctuation theorem for non-equilibrium stationary states, and appropriate to
constrained equilibrium states. Moreover we show these fluctuations are
distributed according to a Gaussian curve for long-enough times. Three
different systems are considered here, namely (i) a fluid composed of particles
interacting with Lennard-Jones potentials; (ii) a harmonic oscillator with
Nos\'e-Hoover thermostatting; (iii) a simple hyperbolic two-dimensional map.",0601435v1
2003-06-12,ATLAS Data Challenge 1,"In 2002 the ATLAS experiment started a series of Data Challenges (DC) of
which the goals are the validation of the Computing Model, of the complete
software suite, of the data model, and to ensure the correctness of the
technical choices to be made. A major feature of the first Data Challenge (DC1)
was the preparation and the deployment of the software required for the
production of large event samples for the High Level Trigger (HLT) and physics
communities, and the production of those samples as a world-wide distributed
activity. The first phase of DC1 was run during summer 2002, and involved 39
institutes in 18 countries. More than 10 million physics events and 30 million
single particle events were fully simulated. Over a period of about 40 calendar
days 71000 CPU-days were used producing 30 Tbytes of data in about 35000
partitions. In the second phase the next processing step was performed with the
participation of 56 institutes in 21 countries (~ 4000 processors used in
parallel). The basic elements of the ATLAS Monte Carlo production system are
described. We also present how the software suite was validated and the
participating sites were certified. These productions were already partly
performed by using different flavours of Grid middleware at ~ 20 sites.",0306052v1
2004-06-21,Long Nonbinary Codes Exceeding the Gilbert - Varshamov Bound for any Fixed Distance,"Let A(q,n,d) denote the maximum size of a q-ary code of length n and distance
d. We study the minimum asymptotic redundancy \rho(q,n,d)=n-log_q A(q,n,d) as n
grows while q and d are fixed. For any d and q<=d-1, long algebraic codes are
designed that improve on the BCH codes and have the lowest asymptotic
redundancy \rho(q,n,d) <= ((d-3)+1/(d-2)) log_q n known to date. Prior to this
work, codes of fixed distance that asymptotically surpass BCH codes and the
Gilbert-Varshamov bound were designed only for distances 4,5 and 6.",0406039v3
2006-08-19,Algorithmic linear dimension reduction in the l_1 norm for sparse vectors,"This paper develops a new method for recovering m-sparse signals that is
simultaneously uniform and quick. We present a reconstruction algorithm whose
run time, O(m log^2(m) log^2(d)), is sublinear in the length d of the signal.
The reconstruction error is within a logarithmic factor (in m) of the optimal
m-term approximation error in l_1. In particular, the algorithm recovers
m-sparse signals perfectly and noisy signals are recovered with polylogarithmic
distortion. Our algorithm makes O(m log^2 (d)) measurements, which is within a
logarithmic factor of optimal. We also present a small-space implementation of
the algorithm. These sketching techniques and the corresponding reconstruction
algorithms provide an algorithmic dimension reduction in the l_1 norm. In
particular, vectors of support m in dimension d can be linearly embedded into
O(m log^2 d) dimensions with polylogarithmic distortion. We can reconstruct a
vector from its low-dimensional sketch in time O(m log^2(m) log^2(d)).
Furthermore, this reconstruction is stable and robust under small
perturbations.",0608079v1
2007-03-06,LIBOPT - An environment for testing solvers on heterogeneous collections of problems - Version 1.0,"The Libopt environment is both a methodology and a set of tools that can be
used for testing, comparing, and profiling solvers on problems belonging to
various collections. These collections can be heterogeneous in the sense that
their problems can have common features that differ from one collection to the
other. Libopt brings a unified view on this composite world by offering, for
example, the possibility to run any solver on any problem compatible with it,
using the same Unix/Linux command. The environment also provides tools for
comparing the results obtained by solvers on a specified set of problems. Most
of the scripts going with the Libopt environment have been written in Perl.",0703025v1
1995-09-19,Harmonic Maps with Prescribed Singularities on Unbounded Domains,"The Einstein/Abelian-Yang-Mills Equations reduce in the stationary and
axially symmetric case to a harmonic map with prescribed singularities
$\p\colon\R^3\sm\Sigma\to\H^{k+1}_\C$ into the $(k+1)$-dimensional complex
hyperbolic space. In this paper, we prove the existence and uniqueness of
harmonic maps with prescribed singularities $\p\colon\R^n\sm\Sigma\to\H$, where
$\Sigma$ is an unbounded smooth closed submanifold of $\R^n$ of codimension at
least $2$, and $\H$ is a real, complex, or quaternionic hyperbolic space. As a
corollary, we prove the existence of solutions to the reduced stationary and
axially symmetric Einstein/Abelian-Yang-Mills Equations.",9509003v1
1994-12-12,N-Black Hole Stationary and Axially Symmetric Solutions of the Einstein-Maxwell Equations,"The Einstein/Maxwell equations reduce in the stationary and axially symmetric
case to a harmonic map with prescribed singularities phi: R^3\Sigma -> H^2_C,
where Sigma is a subset of the axis of symmetry, and H^2_C is the complex
hyperbolic plane. Motivated by this problem, we prove the existence and
uniqueness of harmonic maps with prescribed singularities phi: R^n\Sigma -> H,
where Sigma is a submanifold of R^n of co-dimension at least 2, and H is a
classical Riemannian globally symmetric space of noncompact type and rank one.
This result, when applied to the black hole problem, yields solutions which can
be interpreted as equilibrium configurations of multiple co-axially rotating
charged black holes held apart by singular struts.",9412036v2
1997-11-17,Novel Electroweak Symmetry Breaking Conditions From Quantum Effects In The MSSM,"We present, in the context of the Minimal Supersymmetric Standard Model, a
detailed one-loop analytic study of the minimization conditions of the
effective potential in the Higgs sector.
  Special emphasis is put on the role played by $Str M^4$ in the determination
of the electroweak symmetry breaking conditions, where first and second order
derivatives of the effective potential are systematically taken into account.
Novel, necessary (and sufficient in the Higgs sector) model-independent
constraints, are thus obtained analytically, leading to new theoretical lower
and upper bounds on $\tan \beta$. Although fully model-independent, these
bounds are found to be much more restrictive than the existing model-dependent
ones! A first illustration is given in the context of a SUGRA-GUT motivated
scenario.",9711356v1
1999-01-08,On the fourth adjoint Contractions of divisorial and fiber types,"In this paper, we will list up all the cases for the ray contractions of
divisorial and fiber types for smooth projective varieties of dimension five.
These are obtained as a corollary from the lists of n-dimensional k-th adjoint
contractions f: X -> Y of the same types for k=1,2,3 and 4 (n> or =5). The
lists for k=1,2 and 3 have previously been obtained in [Na], Proposition 1.2
and Theorem 1.3. The main task will be to have such a list for k=4, where one
case in the list fails to show that a positive-dimensional general fiber F of f
is irreducible when n>5. This assertion will, however, be proven when n=5 with
an essential aid of 3-dimensional Minimal Model Program in [Mo2]. (We do not
show the existence of cases.)",9901033v2
2004-04-19,Asymptotic Improvement of the Gilbert-Varshamov Bound on the Size of Binary Codes,"Given positive integers $n$ and $d$, let $A_2(n,d)$ denote the maximum size
of a binary code of length $n$ and minimum distance $d$. The well-known
Gilbert-Varshamov bound asserts that $A_2(n,d) \geq 2^n/V(n,d-1)$, where
$V(n,d) = \sum_{i=0}^{d} {n \choose i}$ is the volume of a Hamming sphere of
radius $d$. We show that, in fact, there exists a positive constant $c$ such
that $$ A_2(n,d) \geq c \frac{2^n}{V(n,d-1)} \log_2 V(n,d-1) $$ whenever $d/n
\le 0.499$. The result follows by recasting the Gilbert- Varshamov bound into a
graph-theoretic framework and using the fact that the corresponding graph is
locally sparse. Generalizations and extensions of this result are briefly
discussed.",0404325v1
2005-11-03,On the automorphism group of generalized Baumslag-Solitar groups,"A generalized Baumslag-Solitar group (GBS group) is a finitely generated
group $G$ which acts on a tree with all edge and vertex stabilizers infinite
cyclic. We show that Out(G) either contains non-abelian free groups or is
virtually nilpotent of class at most 2. It has torsion only at finitely many
primes.
  One may decide algorithmically whether Out(G) is virtually nilpotent or not.
If it is, one may decide whether it is virtually abelian, or finitely
generated. The isomorphism problem is solvable among GBS groups with Out(G)
virtually nilpotent.
  If $G$ is unimodular (virtually $F_n \times Z$), then Out(G) is commensurable
with a semi-direct product $Z^k \rtimes Out(H)$ with $H$ virtually free.",0511083v1
2001-07-08,Statistically Preserved Structures in Shell Models of Passive Scalar Advection,"It was conjectured recently that Statiscally Preserved Structures underlie
the statistical physics of turbulent transport processes. We analyze here in
detail the time-dependent (non compact) linear operator that governs the
dynamics of correlation functions in the case of shell models of passive scalar
advection. The problem is generic in the sense that the driving velocity field
is neither Gaussian nor $\delta$-correlated in time. We show how to naturally
discuss the dynamics in terms of an effective compact operator that displays
""zero modes"" which determine the anomalous scaling of the correlation
functions. Since shell models have neither Lagrangian structure nor ""shape
dynamics"" this example differs significantly from standard passive scalar
advection. Nevertheless with the necessary modifications the generality and
efficacy of the concept of Statistically Preserved Structures are further
exemplified. In passing we point out a bonus of the present approach, in
providing analytic predictions for the time-dependent correlation functions in
decaying turbulent transport.",0107016v1
2001-11-13,Statistically Preserved Structures and Anomalous Scaling in Turbulent Active Scalar Advection,"The anomalous scaling of correlation functions in the turbulent statistics of
active scalars (like temperature in turbulent convection) is understood in
terms of an auxiliary passive scalar which is advected by the same turbulent
velocity field. While the odd-order correlation functions of the active and
passive fields differ, we propose that the even-order correlation functions are
the same to leading order (up to a trivial multiplicative factor). The leading
correlation functions are statistically preserved structures of the passive
scalar decaying problem, and therefore universality of the scaling exponents of
the even-order correlations of the active scalar is demonstrated.",0111030v1
2003-03-27,On the parametric dependences of a class of non-linear singular maps,"We discuss a two-parameter family of maps that generalize piecewise linear,
expanding maps of the circle. One parameter measures the effect of a
non-linearity which bends the branches of the linear map. The second parameter
rotates points by a fixed angle. For small values of the nonlinearity
parameter, we compute the invariant measure and show that it has a singular
density to first order in the nonlinearity parameter. Its Fourier modes have
forms similar to the Weierstrass function. We discuss the consequences of this
singularity on the Lyapunov exponents and on the transport properties of the
corresponding multibaker map. For larger non-linearities, the map becomes
non-hyperbolic and exhibits a series of period-adding bifurcations.",0303062v1
2001-06-06,The Secrecy Capacity of Practical Quantum Cryptography,"Quantum cryptography has attracted much recent attention due to its potential
for providing secret communications that cannot be decrypted by any amount of
computational effort. This is the first analysis of the secrecy of a practical
implementation of the BB84 protocol that simultaneously takes into account and
presents the {\it full} set of complete analytical expressions for effects due
to the presence of pulses containing multiple photons in the attenuated output
of the laser, the finite length of individual blocks of key material, losses
due to error correction, privacy amplification, continuous authentication,
errors in polarization detection, the efficiency of the detectors, and
attenuation processes in the transmission medium. The analysis addresses
eavesdropping attacks on individual photons rather than collective attacks in
general. Of particular importance is the first derivation of the necessary and
sufficient amount of privacy amplification compression to ensure secrecy
against the loss of key material which occurs when an eavesdropper makes
optimized individual attacks on pulses containing multiple photons. It is shown
that only a fraction of the information in the multiple photon pulses is
actually lost to the eavesdropper.",0106033v1
2005-11-17,"Quantum Computer Condition: Stability, Classical Computation and Norms","The Quantum Computer Condition (QCC) provides a rigorous and completely
general framework for carrying out analyses of questions pertaining to
fault-tolerance in quantum computers. In this paper we apply the QCC to the
problem of fluctuations and systematic errors in the values of characteristic
parameters in realistic systems. We show that fault-tolerant quantum
computation is possible despite variations in these parameters. We also use the
QCC to explicitly show that reliable classical computation can be carried out
using as input the results of fault-tolerant, but imperfect, quantum
computation. Finally, we consider the advantages and disadvantages of the
superoperator and diamond norms in connection with application of the QCC to
various quantum information-theoretic problems.",0511177v1
2006-12-19,On the use of photonic N00N states for practical quantum interferometry,"The performance of photonic $N00N$ states, propagating in an attenuating
medium, is analyzed with respect to phase estimation. It is shown that, for
$N00N$ states propagating through a lossy medium, the Heisenberg limit is never
achieved. It is also shown that, for a given value of $N$, a signal comprised
of an attenuated separable state of $N$ photons will actually produce a better
phase estimate than will a signal comprised of an equally attenuated $N00N$
state, unless the transmittance of the medium is very high. This is a
consequence of the need to utilize measurement operators appropriate to the
different signal states. The result is that, for most practical applications in
realistic scenarios with attenuation, the resolution of $N00N$ state-based
phase estimation not only does not achieve the Heisenberg Limit, but is
actually worse than the Standard Quantum Limit. It is demonstrated that this
performance deficit becomes more pronounced as the number, $N$, of photons in
the signal increases.",0612156v1
2007-05-22,Analysis of evidence of Mars life,"Gillevinia straata, the scientific name [1, 2] recognizing the first
extraterrestrial living form ever nomenclated, as well as the existence of a
new biological kingdom, Jakobia, in a new biosphere -Marciana- of what now has
become the living system Solaria, is grounded on old evidence reinterpreted in
the light of newly acquired facts. The present exposition provides a summary
overview of all these grounds, outlined here as follows. A more detailed paper
is being prepared for publication.",0705.3176v3
2007-06-26,Feedback in the Antennae Galaxies (NGC 4038/9): I. High-Resolution Infrared Spectroscopy of Winds from Super Star Clusters,"We present high-resolution (R ~ 24,600) near-IR spectroscopy of the youngest
super star clusters (SSCs) in the prototypical starburst merger, the Antennae
Galaxies. These SSCs are young (3-7 Myr old) and massive (10^5 - 10^7 M_sun for
a Kroupa IMF) and their spectra are characterized by broad, extended Br-gamma
emission, so we refer to them as emission-line clusters (ELCs) to distinguish
them from older SSCs. The Brgamma lines of most ELCs have supersonic widths
(60-110 km/s FWHM) and non-Gaussian wings whose velocities exceed the clusters'
escape velocities. This high-velocity unbound gas is flowing out in winds that
are powered by the clusters' massive O and W-R stars over the course of at
least several crossing times. The large sizes of some ELCs relative to those of
older SSCs may be due to expansion caused by these outflows; many of the ELCs
may not survive as bound stellar systems, but rather dissipate rapidly into the
field population. The observed tendency of older ELCs to be more compact than
young ones is consistent with the preferential survival of the most
concentrated clusters at a given age.",0706.3935v1
2007-06-29,Reliable Final Computational Results from Faulty Quantum Computation,"In this paper we extend both standard fault tolerance theory and Kitaev's
model for quantum computation, combining them so as to yield quantitative
results that reveal the interplay between the two. Our analysis establishes a
methodology that allows us to quantitatively determine design parameters for a
quantum computer, the values of which ensure that an overall computation of
interest yields a correct *final result* with some prescribed probability of
success, as opposed to merely ensuring that the desired *final quantum state*
is obtained. As a specific example of the practical application of our
approach, we explicitly calculate the number of levels of error correction
concatenation needed to achieve a correct final result for the overall
computation with some prescribed success probability. Since our methodology
allows one to determine parameters required in order to achieve the correct
final result for the overall quantum computation, as opposed to merely ensuring
that the desired final quantum state is produced, our method enables the
determination of complete quantum computational resource requirements
associated to the actual solution of practical problems.",0707.0008v1
2007-08-24,Quantum Sensor Miniaturization,"The classical bound on image resolution defined by the Rayleigh limit can be
beaten by exploiting the properties of quantum mechanical entanglement. If
entangled photons are used as signal states, the best possible resolution is
instead given by the Heisenberg limit, an improvement proportional to the
number of entangled photons in the signal. In this paper we present a novel
application of entanglement by showing that the resolution obtained by an
imaging system utilizing separable photons can be achieved by an imaging system
making use of entangled photons, but with the advantage of a smaller aperture,
thus resulting in a smaller and lighter system. This can be especially valuable
in satellite imaging where weight and size play a vital role.",0708.3403v1
2007-09-02,A Universal Operator Theoretic Framework for Quantum Fault Tolerance,"In this paper we introduce a universal operator theoretic framework for
quantum fault tolerance. This incorporates a top-down approach that implements
a system-level criterion based on specification of the full system dynamics,
applied at every level of error correction concatenation. This leads to more
accurate determinations of error thresholds than could previously be obtained.
This is demonstrated both formally and with an explicit numerical example. The
basis for our approach is the Quantum Computer Condition (QCC), an inequality
governing the evolution of a quantum computer. We show that all known coding
schemes are actually special cases of the QCC. We demonstrate this by
introducing a new, operator theoretic form of entanglement assisted quantum
error correction, which incorporates as special cases all known error
correcting protocols, and is itself a special case of the QCC.",0709.0128v3
2007-10-25,Ordering in red abalone nacre,"Red abalone nacre is an intensely studied biomineral, and yet its formation
mechanism remains poorly understood. Here we report quantitative measurements
probing the degree of order of the aragonite tablets in nacre, and show that
order develops over a distance of about 50 microns. These observations indicate
that the orientational order of aragonite tablets in nacre is established
gradually and dynamically, and we show that a model of controlled assembly
based on suppression of the crystal growth rate along a specific direction,
when growth is confined in a layered structure, yields a tablet pattern
consistent with those revealed by detailed experimental measurements. This work
provides strong evidence that the organism s control of crystal orientation in
nacre occurs via regulation of crystal nucleation and growth as opposed to
direct templation or heteroepitaxial growth on organic molecules on the organic
matrix sheets.",0710.4573v1
2007-11-01,Interaction effects in mixed-valent Kondo insulators,"We study theoretically the class of mixed-valent Kondo insulators, employing
a recently developed local moment approach to heavy Fermion systems using the
asymmetric periodic Anderson model (PAM). Novel features in spectra and
transport, observable experimentally but lying outside the scope of the
symmetric PAM or the Kondo lattice model, emerge naturally within the present
theory. We argue in particular that a shoulder-like feature in the optical
conductivity, that is distinct from the usual mid-infrared or direct gap peak
and has been observed experimentally in mixed-valent compounds such as
CeOs4Sb12 and YbAl3, is of intrinsic origin. Detailed comparison is made
between the resultant theory and transport/optical experiments on the
filled-skutterudite compound CeOs4Sb12, and good agreement is obtained.",0711.0121v1
2008-01-31,Counting growth types of automorphisms of free groups,"Given an automorphism of a free group $F_n$, we consider the following
invariants: $e$ is the number of exponential strata (an upper bound for the
number of different exponential growth rates of conjugacy classes); $d$ is the
maximal degree of polynomial growth of conjugacy classes; $R$ is the rank of
the fixed subgroup. We determine precisely which triples $(e,d,R)$ may be
realized by an automorphism of $F_n$. In particular, the inequality $e\le
(3n-2)/4}$ (due to Levitt-Lustig) always holds. In an appendix, we show that
any conjugacy class grows like a polynomial times an exponential under
iteration of the automorphism.",0801.4844v2
2008-02-29,Heat conduction and Fourier's law in a class of many particle dispersing billiards,"We consider the motion of many confined billiard balls in interaction and
discuss their transport and chaotic properties. In spite of the absence of mass
transport, due to confinement, energy transport can take place through binary
collisions between neighbouring particles. We explore the conditions under
which relaxation to local equilibrium occurs on time scales much shorter than
that of binary collisions, which characterize the transport of energy, and
subsequent relaxation to local thermal equilibrium. Starting from the
pseudo-Liouville equation for the time evolution of phase-space distributions,
we derive a master equation which governs the energy exchange between the
system constituents. We thus obtain analytical results relating the transport
coefficient of thermal conductivity to the frequency of collision events and
compute these quantities. We also provide estimates of the Lyapunov exponents
and Kolmogorov-Sinai entropy under the assumption of scale separation. The
validity of our results is confirmed by extensive numerical studies.",0802.4455v3
2008-04-29,Combining geometry and combinatorics: A unified approach to sparse signal recovery,"There are two main algorithmic approaches to sparse signal recovery:
geometric and combinatorial. The geometric approach starts with a geometric
constraint on the measurement matrix and then uses linear programming to decode
information about the signal from its measurements. The combinatorial approach
constructs the measurement matrix and a combinatorial decoding algorithm to
match. We present a unified approach to these two classes of sparse signal
recovery algorithms.
  The unifying elements are the adjacency matrices of high-quality unbalanced
expanders. We generalize the notion of Restricted Isometry Property (RIP),
crucial to compressed sensing results for signal recovery, from the Euclidean
norm to the l_p norm for p about 1, and then show that unbalanced expanders are
essentially equivalent to RIP-p matrices.
  From known deterministic constructions for such matrices, we obtain new
deterministic measurement matrix constructions and algorithms for signal
recovery which, compared to previous deterministic algorithms, are superior in
either the number of measurements or in noise tolerance.",0804.4666v1
2008-08-08,Heat conductivity from molecular chaos hypothesis in locally confined billiard systems,"We study the transport properties of a large class of locally confined
Hamiltonian systems, in which neighboring particles interact through hard core
elastic collisions. When these collisions become rare and the systems large, we
derive a Boltzmann-like equation for the evolution of the probability
densities. We solve this equation in the linear regime and compute the heat
conductivity from a Green-Kubo formula. The validity of our approach is
demonstated by comparing our predictions to the results of numerical
simulations performed on a new class of high-dimensional defocusing chaotic
billiards.",0808.1179v2
2008-09-23,On the derivation of Fourier's law in stochastic energy exchange systems,"We present a detailed derivation of Fourier's law in a class of stochastic
energy exchange systems that naturally characterize two-dimensional mechanical
systems of locally confined particles in interaction. The stochastic systems
consist of an array of energy variables which can be partially exchanged among
nearest neighbours at variable rates. We provide two independent derivations of
the thermal conductivity and prove this quantity is identical to the frequency
of energy exchanges. The first derivation relies on the diffusion of the
Helfand moment, which is determined solely by static averages. The second
approach relies on a gradient expansion of the probability measure around a
non-equilibrium stationary state. The linear part of the heat current is
determined by local thermal equilibrium distributions which solve a
Boltzmann-like equation. A numerical scheme is presented with computations of
the conductivity along our two methods. The results are in excellent agreement
with our theory.",0809.3967v2
2008-10-19,Coding Theorems for Repeat Multiple Accumulate Codes,"In this paper the ensemble of codes formed by a serial concatenation of a
repetition code with multiple accumulators connected through random
interleavers is considered. Based on finite length weight enumerators for these
codes, asymptotic expressions for the minimum distance and an arbitrary number
of accumulators larger than one are derived using the uniform interleaver
approach. In accordance with earlier results in the literature, it is first
shown that the minimum distance of repeat-accumulate codes can grow, at best,
sublinearly with block length. Then, for repeat-accumulate-accumulate codes and
rates of 1/3 or less, it is proved that these codes exhibit asymptotically
linear distance growth with block length, where the gap to the
Gilbert-Varshamov bound can be made vanishingly small by increasing the number
of accumulators beyond two. In order to address larger rates, random puncturing
of a low-rate mother code is introduced. It is shown that in this case the
resulting ensemble of repeat-accumulate-accumulate codes asymptotically
achieves linear distance growth close to the Gilbert-Varshamov bound. This
holds even for very high rate codes.",0810.3422v1
2008-12-09,Statistical properties of time-reversible triangular maps of the square,"Time reversal symmetric triangular maps of the unit square are introduced
with the property that the time evolution of one of their two variables is
determined by a piecewise expanding map of the unit interval. We study their
statistical properties and establish the conditions under which their
equilibrium measures have a product structure, i.e. factorises in a symmetric
form. When these conditions are not verified, the equilibrium measure does not
have a product form and therefore provides additional information on the
statistical properties of theses maps. This is the case of anti-symmetric cusp
maps, which have an intermittent fixed point and yet have uniform invariant
measures on the unit interval. We construct the invariant density of the
corresponding two-dimensional triangular map and prove that it exhibits a
singularity at the intermittent fixed point.",0812.1648v1
2009-03-20,Fractality of the non-equilibrium stationary states of open volume-preserving systems: I. Tagged particle diffusion,"Deterministic diffusive systems such as the periodic Lorentz gas, multi-baker
map, as well as spatially periodic systems of interacting particles, have
non-equilibrium stationary states with fractal properties when put in contact
with particle reservoirs at their boundaries. We study the macroscopic limits
of these systems and establish a correspondence between the thermodynamics of
the macroscopic diffusion process and the fractality of the stationary states
that characterize the phase-space statistics. In particular the entropy
production rate is recovered from first principles using a formalism due to
Gaspard [J. Stat. Phys. 88, 1215 (1997)]. This article is the first of two; the
second article considers the influence of a uniform external field on such
systems.",0903.3476v1
2009-03-20,Fractality of the non-equilibrium stationary states of open volume-preserving systems: II. Galton boards,"Galton boards are models of deterministic diffusion in a uniform external
field, akin to driven periodic Lorentz gases, here considered in the absence of
dissipation mechanism. Assuming a cylindrical geometry with axis along the
direction of the external field, the two-dimensional board becomes a model for
one-dimensional mass transport along the direction of the external field. This
is a purely diffusive process which admits fractal non-equilibrium stationary
states under flux boundary conditions. Analytical results are obtained for the
statistics of multi-baker maps modeling such a non-uniform diffusion process. A
correspondence is established between the local phase-space statistics and
their macroscopic counter-parts. The fractality of the invariant state is shown
to be responsible for the positiveness of the entropy production rate.",0903.3849v1
2009-07-23,On Possible Variation in the Cosmological Baryon Fraction,"The fraction of matter that is in the form of baryons or dark matter could
have spatial fluctuations in the form of baryon-dark matter isocurvature
fluctuations. We use big bang nucleosynthesis calculations compared with
observed light element abundances as well as galaxy cluster gas fractions to
constrain cosmological variations in the baryon fraction. Light element
abundances constrain spatial variations to be less than 26-27%, while a sample
of ""relaxed"" galaxy clusters shows spatial variations in gas fractions less
than 8%. Larger spatial variations could cause differential screening of the
primary cosmic microwave background anisotropies, leading to asymmetries in the
fluctuations and ease some tension with the halo-star 7Li abundance.
Fluctuations within our allowed bounds can lead to ""B-mode"" CMB polarization
anisotropies at a non-negligible level.",0907.3919v2
2009-08-28,Chaos in cylindrical stadium billiards via a generic nonlinear mechanism,"We describe conditions under which higher-dimensional billiard models in
bounded, convex regions are fully chaotic, generalizing the Bunimovich stadium
to dimensions above two. An example is a three-dimensional stadium bounded by a
cylinder and several planes; the combination of these elements may give rise to
defocusing, allowing large chaotic regions in phase space. By studying families
of marginally-stable periodic orbits that populate the residual part of phase
space, we identify conditions under which a nonlinear instability mechanism
arises in their vicinity. For particular geometries, this mechanism rather
induces stable nonlinear oscillations, including in the form of
whispering-gallery modes.",0908.4243v2
2009-09-23,The Gilbert Arborescence Problem,"We investigate the problem of designing a minimum cost flow network
interconnecting n sources and a single sink, each with known locations in a
normed space and with associated flow demands. The network may contain any
finite number of additional unprescribed nodes from the space; these are known
as the Steiner points. For concave increasing cost functions, a minimum cost
network of this sort has a tree topology, and hence can be called a Minimum
Gilbert Arborescence (MGA). We characterise the local topological structure of
Steiner points in MGAs, showing, in particular, that for a wide range of
metrics, and for some typical real-world cost-functions, the degree of each
Steiner point is 3.",0909.4270v2
2010-08-12,Magnetization dynamics in the inertial regime: nutation predicted at short time scales,"The dynamical equation of the magnetization has been reconsidered with
enlarging the phase space of the ferromagnetic degrees of freedom to the
angular momentum. The generalized Landau-Lifshitz-Gilbert equation that
includes inertial terms, and the corresponding Fokker-Planck equation, are then
derived in the framework of mesoscopic non-equilibrium thermodynamics theory. A
typical relaxation time $\tau$ is introduced describing the relaxation of the
magnetization acceleration from the inertial regime towards the precession
regime defined by a constant Larmor frequency. For time scales larger than
$\tau$, the usual Gilbert equation is recovered. For time scales below $\tau$,
nutation and related inertial effects are predicted. The inertial regime offers
new opportunities for the implementation of ultrafast magnetization switching
in magnetic devices.",1008.2177v1
2010-09-20,Diffusive properties of persistent walks on cubic lattices with application to periodic Lorentz gases,"We calculate the diffusion coefficients of persistent random walks on cubic
and hypercubic lattices, where the direction of a walker at a given step
depends on the memory of one or two previous steps. These results are then
applied to study a billiard model, namely a three-dimensional periodic Lorentz
gas. The geometry of the model is studied in order to find the regimes in which
it exhibits normal diffusion. In this regime, we calculate numerically the
transition probabilities between cells to compare the persistent random-walk
approximation with simulation results for the diffusion coefficient.",1009.3922v1
2010-11-03,Existence of vertical spin stiffness in Landau-Lifshitz-Gilbert equation in ferromagnetic semiconductors,"We calculate the magnetization torque due to the spin polarization of the
itinerant electrons by deriving the kinetic spin Bloch equations based on the
$s$-$d$ model. We find that the first-order gradient of the magnetization
inhomogeneity gives rise to the current-induced torques, which are consistent
to the previous works. At the second-order gradient, we find an effective
magnetic field perpendicular to the spin stiffness filed. This field is
proportional to the nonadiabatic parameter $\beta$. We show that this vertical
spin stiffness term can significantly modify the domain-wall structure in
ferromagnetic semiconductors and hence should be included in the
Landau-Lifshitz-Gilbert equation in studying the magnetization dynamics.",1011.0871v1
2011-01-05,The Fascinating World of Landau-Lifshitz-Gilbert Equation: An Overview,"The Landau-Lifshitz-Gilbert (LLG) equation is a fascinating nonlinear
evolution equation both from mathematical and physical points of view. It is
related to the dynamics of several important physical systems such as
ferromagnets, vortex filaments, moving space curves, etc. and has intimate
connections with many of the well known integrable soliton equations, including
nonlinear Schr\""odinger and sine-Gordon equations. It can admit very many
dynamical structures including spin waves, elliptic function waves, solitons,
dromions, vortices, spatio-temporal patterns, chaos, etc. depending on the
physical and spin dimensions and the nature of interactions. An exciting recent
development is that the spin torque effect in nanoferromagnets is described by
a generalization of the LLG equation which forms a basic dynamical equation in
the field of spintronics. This article will briefly review these developments
as a tribute to Robin Bullough who was a great admirer of the LLG equation.",1101.1005v1
2011-02-05,Graph Theory,"This is a replacement paper. There are 6 chapters. The first two chapters are
introductory. The third chapter is on extremal graph theory. The fourth chapter
is about algebra in graph theory. The fifth chapter is focused on algorithms.
The third section of the fifth chapter deals with computable time. The sixth
chapter has sections on probability and enumeration.",1102.1087v11
2011-04-28,The High-Redshift Neutral Hydrogen Signature of an Anisotropic Matter Power Spectrum,"An anisotropic power spectrum will have a clear signature in the 21cm
radiation from high-redshift hydrogen. We calculate the expected power spectrum
of the intensity fluctuations in neutral hydrogen from before the epoch of
reionization, and predict the accuracy to which future experiments could
constrain a quadrupole anisotropy in the power spectrum. We find that the
Square Kilometer Array will have marginal detection abilities for this signal
at z~17 if the process of reionization has not yet started; reionization could
enhance the detectability substantially. Pushing to higher redshifts and higher
sensitivity will allow highly precise (percent level) measurements of
anisotropy.",1104.5403v3
2011-06-30,A generalisation of the Gilbert-Varshamov bound and its asymptotic evaluation,"The Gilbert-Varshamov (GV) lower bound on the maximum cardinality of a q-ary
code of length n with minimum Hamming distance at least d can be obtained by
application of Turan's theorem to the graph with vertex set {0,1,..,q-1}^n in
which two vertices are joined if and only if their Hamming distance is at least
d. We generalize the GV bound by applying Turan's theorem to the graph with
vertex set C^n, where C is a q-ary code of length m and two vertices are joined
if and only if their Hamming distance at least d. We asymptotically evaluate
the resulting bound for n-> \infty and d \delta mn for fixed \delta > 0, and
derive conditions on the distance distribution of C that are necessary and
sufficient for the asymptotic generalized bound to beat the asymptotic GV
bound. By invoking the Delsarte inequalities, we conclude that no improvement
on the asymptotic GV bound is obtained. By using a sharpening of Turan's
theorem due to Caro and Wei, we improve on our bound. It is undecided if there
exists a code C for which the improved bound can beat the asymptotic GV bound.",1106.6206v1
2011-07-17,Probabilistic Methods on Erdos Problems,"The paper reviews and tries to describe the reference set method, which is a
method of combinatorial optimization that gives upper bounds on parameters.",1107.3279v17
2011-09-12,Externally-driven transmission and collisions of domain walls in ferromagnetic wires,"Analytical multi-domain solutions to the dynamical (Landau-Lifshitz-Gilbert)
equation of a one-dimensional ferromagnet including an external magnetic field
and spin-polarized electric current are found using the Hirota bilinearization
method. A standard approach to solve the Landau-Lifshitz equation (without the
Gilbert term) is modified in order to treat the dissipative dynamics. I
establish the relations between the spin interaction parameters (the constants
of exchange, anisotropy, dissipation, external-field intensity, and
electric-current intensity) and the domain-wall parameters (width and velocity)
and compare them to the results of the Walker approximation and micromagnetic
simulations. The domain-wall motion driven by a longitudinal external field is
analyzed with especial relevance to the field-induced collision of two domain
walls. I determine the result of such a collision (which is found to be the
elastic one) on the domain-wall parameters below and above the Walker breakdown
(in weak- and strong-field regimes). Single-domain-wall dynamics in the
presence of an external transverse field is studied with relevance to the
challenge of increasing the domain-wall velocity below the breakdown.",1109.2465v1
2011-10-19,Current-induced switching in transport through anisotropic magnetic molecules,"Anisotropic single-molecule magnets may be thought of as molecular switches,
with possible applications to molecular spintronics. In this paper, we consider
current-induced switching in single-molecule junctions containing an
anisotropic magnetic molecule. We assume that the carriers interact with the
magnetic molecule through the exchange interaction and focus on the regime of
high currents in which the molecular spin dynamics is slow compared to the time
which the electrons spend on the molecule. In this limit, the molecular spin
obeys a non-equilibrium Langevin equation which takes the form of a generalized
Landau-Lifshitz-Gilbert equation and which we derive microscopically by means
of a non-equilibrium Born-Oppenheimer approximation. We exploit this Langevin
equation to identify the relevant switching mechanisms and to derive the
current-induced switching rates. As a byproduct, we also derive S-matrix
expressions for the various torques entering into the Landau-Lifshitz-Gilbert
equation which generalize previous expressions in the literature to
non-equilibrium situations.",1110.4270v2
2011-10-27,"George Augustus Linhart - as a ""widely unknown"" thermodynamicist","The name of George Augustus Linhart is in fact ""widely unknown"". In effect,
he was a Viennese-born USA-American physicist-chemist, partially associated
with the Gilbert Newton Lewis' school of thermodynamics at the University of
California in Berkeley. As a lone small boy, he had arrived (from Austria via
Hamburg) at New York in 1896, but was officially USA-naturalized only in 1912.
He was able to pick up English in the streets of New York and Philadelphia,
when occasionally working as a waiter and/or as a tailor - just to somehow
survive. But, nonetheless, he could successfully graduate a high school in
about one year - and then went to the universities for his further education.
After obtaining his BS from the University of Pennsylvania, he could manage
getting both MA and then PhD from the Yale University, Kent Chemical
Laboratory. George Augustus Linhart was afterwards definitely able to
successfully work out the true foundations of thermodynamics and could thus
outdistance many famous thermodynamicists of his time and even the later ones.
Linhart's view of the Second Law of Thermodynamics was and is extremely
fruitful. The interconnection of Linhart's ideas with those of Gilbert Newton
Lewis, as well as with the modern standpoints are discussed here in detail.",1110.6352v1
2012-03-29,Power Allocation over Two Identical Gilbert-Elliott Channels,"We study the problem of power allocation over two identical Gilbert-Elliot
communication channels. Our goal is to maximize the expected discounted number
of bits transmitted over an infinite time horizon. This is achieved by choosing
among three possible strategies: (1) betting on channel 1 by allocating all the
power to this channel, which results in high data rate if channel 1 happens to
be in good state, and zero bits transmitted if channel 1 is in bad state (even
if channel 2 is in good state) (2) betting on channel 2 by allocating all the
power to the second channel, and (3) a balanced strategy whereby each channel
is allocated half the total power, with the effect that each channel can
transmit a low data rate if it is in good state. We assume that each channel's
state is only revealed upon transmission of data on that channel. We model this
problem as a partially observable Markov decision processes (MDP), and derive
key threshold properties of the optimal policy. Further, we show that by
formulating and solving a relevant linear program the thresholds can be
determined numerically when system parameters are known.",1203.6630v2
2012-04-11,A short note on spin pumping theory with Landau-Lifshitz-Gilbert equation under quantum fluctuation; necessity for quantization of localized spin,"We would like to point out the blind spots of the approach combining the spin
pumping theory proposed by Tserkovnyak et al. with the Landau-Lifshitz-Gilbert
equation; this method has been widely used for interpreting vast experimental
results. The essence of the spin pumping effect is the quantum fluctuation.
Thus, localized spin degrees of freedom should be quantized, i.e. be treated as
magnons not as classical variables. Consequently, the precessing ferromagnet
can be regarded as a magnon battery. This point of view will be useful for
further progress of spintronics.",1204.2339v1
2012-05-22,Signature of Phase Transitions in the Disordered Quantum Spin Hall State From the Entanglement Spectrum,"Of the available classes of insulators which have been shown to contain
topologically non-trivial properties one of the most important is class AII,
which contains systems that possess time-reversal symmetry $T$ with $T^2=-1.$
This class has been the subject of significant attention as it encompasses
non-trivial Z$_2$ topological insulators such as the quantum spin Hall (QSH)
state and the 3D strong topological insulator. One of the defining properties
of this system is the robustness of the state under the addition of disorder
that preserves $T.$ In this letter, we explore the phase diagram of the
disordered QSH state as a function of disorder strength and chemical potential
by examining the entanglement spectrum for disordered class AII symplectic
systems. As for the case of the $T$ breaking Chern insulator we show that there
is a correspondence between the level-spacing statistics of the Hamiltonian and
that of the level spacing statistics of the entanglement spectrum. We observe a
feature in the statistics of the entanglement spectrum that aids the
identification of delocalized states and consequently critical energies across
which phase transitions occur.",1205.5071v1
2012-07-03,The unusual smoothness of the extragalactic unresolved radio background,"If the radio background is coming from cosmological sources, there should be
some amount of clustering due to the large scale structure in the universe.
Simple models for the expected clustering combined with the recent measurement
by ARCADE-2 of the mean extragalactic temperature lead to predicted clustering
levels that are substantially above upper limits from searches for anisotropy
on arcminute scales using ATCA and the VLA. The rms temperature variations in
the cosmic radio background appear to be more than a factor of 10 smaller (in
temperature) than the fluctuations in the cosmic infrared background. It is
therefore extremely unlikely that this background comes from galaxies, galaxy
clusters, or any sources that trace dark matter halos at z<5, unless typical
sources are smooth on arcminute scales, requiring typical sizes of several Mpc.",1207.0856v1
2012-10-12,Optimal Power Allocation Policy over Two Identical Gilbert-Elliott Channels,"We study the fundamental problem of optimal power allocation over two
identical Gilbert-Elliott (Binary Markov) communication channels. Our goal is
to maximize the expected discounted number of bits transmitted over an infinite
time span by judiciously choosing one of the four actions for each time slot:
1) allocating power equally to both channels, 2) allocating all the power to
channel 1, 3) allocating all the power to channel 2, and 4) allocating no power
to any of the channels. As the channel state is unknown when power allocation
decision is made, we model this problem as a partially observable Markov
decision process(POMDP), and derive the optimal policy which gives the optimal
action to take under different possible channel states. Two different
structures of the optimal policy are derived analytically and verified by
linear programming simulation. We also illustrate how to construct the optimal
policy by the combination of threshold calculation and linear programming
simulation once system parameters are known.",1210.3609v1
2013-03-16,A convergent linear finite element scheme for the Maxwell-Landau-Lifshitz-Gilbert equation,"We consider a lowest-order finite element discretization of the nonlinear
system of Maxwell's and Landau-Lifshitz-Gilbert equations (MLLG). Two
algorithms are proposed to numerically solve this problem, both of which only
require the solution of at most two linear systems per timestep. One of the
algorithms is fully decoupled in the sense that each timestep consists of the
sequential computation of the magnetization and afterwards the magnetic and
electric field. Under some mild assumptions on the effective field, we show
that both algorithms converge towards weak solutions of the MLLG system.
Numerical experiments for a micromagnetic benchmark problem demonstrate the
performance of the proposed algorithms.",1303.4009v1
2013-03-17,On the Landau-Lifshitz-Gilbert equation with magnetostriction,"To describe and simulate dynamic micromagnetic phenomena, we consider a
coupled system of the nonlinear Landau-Lifshitz-Gilbert equation and the
conservation of momentum equation. This coupling allows to include
magnetostrictive effects into the simulations. Existence of weak solutions has
recently been shown in [Carbout et al. 2011]. In our contribution, we give an
alternate proof which additionally provides an effective numerical integrator.
The latter is based on lowest-order finite elements in space and a
linear-implicit Euler time-stepping. Despite the nonlinearity, only two linear
systems have to be solved per timestep, and the integrator fully decouples both
equations. Finally, we prove unconditional convergence---at least of a
subsequence---towards, and hence existence of, a weak solution of the coupled
system, as timestep size and spatial mesh-size tend to zero. Numerical
experiments conclude the work and shed new light on the existence of blow-up in
micromagnetic simulations.",1303.4060v2
2013-03-27,Optimal Power Allocation over Multiple Identical Gilbert-Elliott Channels,"We study the fundamental problem of power allocation over multiple
Gilbert-Elliott communication channels. In a communication system with time
varying channel qualities, it is important to allocate the limited transmission
power to channels that will be in good state. However, it is very challenging
to do so because channel states are usually unknown when the power allocation
decision is made. In this paper, we derive an optimal power allocation policy
that can maximize the expected discounted number of bits transmitted over an
infinite time span by allocating the transmission power only to those channels
that are believed to be good in the coming time slot. We use the concept belief
to represent the probability that a channel will be good and derive an optimal
power allocation policy that establishes a mapping from the channel belief to
an allocation decision.
  Specifically, we first model this problem as a partially observable Markov
decision processes (POMDP), and analytically investigate the structure of the
optimal policy. Then a simple threshold-based policy is derived for a
three-channel communication system. By formulating and solving a linear
programming formulation of this power allocation problem, we further verified
the derived structure of the optimal policy.",1303.6771v1
2013-04-29,Generalized Baumslag-Solitar groups: rank and finite index subgroups,"A generalized Baumslag-Solitar (GBS) group is a finitely generated group
acting on a tree with infinite cyclic edge and vertex stabilizers. We show how
to determine effectively the rank (minimal cardinality of a generating set) of
a GBS group; as a consequence, one can compute the rank of the mapping torus of
a finite order outer automorphism of a free group $F_n$. We also show that the
rank of a finite index subgroup of a GBS group G cannot be smaller than the
rank of G. We determine which GBS groups are large (some finite index subgroup
maps onto $F_2$), and we solve the commensurability problem (deciding whether
two groups have isomorphic finite index subgroups) in a particular family of
GBS groups.",1304.7582v2
2013-06-02,On the Riemannian Penrose inequality with charge and the cosmic censorship conjecture,"We note an area-charge inequality orignially due to Gibbons: if the outermost
horizon $S$ in an asymptotically flat electrovacuum initial data set is
connected then $|q|\leq r$, where $q$ is the total charge and $r=\sqrt{A/4\pi}$
is the area radius of $S$. A consequence of this inequality is that for
connected black holes the following lower bound on the area holds: $r\geq
m-\sqrt{m^2-q^2}$. In conjunction with the upper bound $r\leq m +
\sqrt{m^2-q^2}$ which is expected to hold always, this implies the natural
generalization of the Riemannian Penrose inequality: $m\geq 1/2(r+q^2/r)$.",1306.0206v3
2013-08-19,A finite element approximation for the stochastic Landau-Lifshitz-Gilbert equation,"The stochastic Landau--Lifshitz--Gilbert (LLG) equation describes the
behaviour of the magnetization under the influence of the effective field
consisting of random fluctuations. We first reformulate the equation into an
equation the unknown of which is differentiable with respect to the time
variable. We then propose a convergent $\theta$-linear scheme for the numerical
solution of the reformulated equation. As a consequence, we show the existence
of weak martingale solutions to the stochastic LLG equation. A salient feature
of this scheme is that it does not involve a nonlinear system, and that no
condition on time and space steps is required when $\theta\in(\frac{1}{2},1]$.
Numerical results are presented to show the applicability of the method.",1308.3912v2
2014-01-14,Constructions of Pure Asymmetric Quantum Alternant Codes Based on Subclasses of Alternant Codes,"In this paper, we construct asymmetric quantum error-correcting codes(AQCs)
based on subclasses of Alternant codes. Firstly, We propose a new subclass of
Alternant codes which can attain the classical Gilbert-Varshamov bound to
construct AQCs. It is shown that when $d_x=2$, $Z$-parts of the AQCs can attain
the classical Gilbert-Varshamov bound. Then we construct AQCs based on a famous
subclass of Alternant codes called Goppa codes. As an illustrative example, we
get three $[[55,6,19/4]],[[55,10,19/3]],[[55,15,19/2]]$ AQCs from the well
known $[55,16,19]$ binary Goppa code. At last, we get asymptotically good
binary expansions of asymmetric quantum GRS codes, which are quantum
generalizations of Retter's classical results. All the AQCs constructed in this
paper are pure.",1401.3215v2
2014-03-19,Numerical integration of the stochastic Landau-Lifshitz-Gilbert equation in generic time-discretisation schemes,"We introduce a numerical method to integrate the stochastic
Landau-Lifshitz-Gilbert equation in spherical coordinates for generic
discretization schemes. This method conserves the magnetization modulus and
ensures the approach to equilibrium under the expected conditions. We test the
algorithm on a benchmark problem: the dynamics of a uniformly magnetized
ellipsoid. We investigate the influence of various parameters, and in
particular, we analyze the efficiency of the numerical integration, in terms of
the number of steps needed to reach a chosen long time with a given accuracy.",1403.4822v2
2014-05-05,Measuring logarithmic corrections to normal diffusion in infinite-horizon billiards,"We perform numerical measurements of the moments of the position of a tracer
particle in a two-dimensional periodic billiard model (Lorentz gas) with
infinite corridors. This model is known to exhibit a weak form of
super-diffusion, in the sense that there is a logarithmic correction to the
linear growth in time of the mean-squared displacement. We show numerically
that this expected asymptotic behavior is easily overwhelmed by the subleading
linear growth throughout the time-range accessible to numerical simulations. We
compare our simulations to the known analytical results for the variance of the
anomalously-rescaled limiting normal distributions.",1405.0975v2
2014-05-12,Efficient Energy-minimization in Finite-Difference Micromagnetics: Speeding up Hysteresis Computations,"We implement an efficient energy-minimization algorithm for finite-difference
micromagnetics that proofs especially useful for the computation of hysteresis
loops. Compared to results obtained by time integration of the
Landau-Lifshitz-Gilbert equation, a speedup of up to two orders of magnitude is
gained. The method is implemented in a finite-difference code running on CPUs
as well as GPUs. This setup enables us to compute accurate hysteresis loops of
large systems with a reasonable computational effort. As a benchmark we solve
the {\mu}Mag Standard Problem #1 with a high spatial resolution and compare the
results to the solution of the Landau-Lifshitz-Gilbert equation in terms of
accuracy and computing time.",1405.2728v3
2014-07-01,Transport properties of Lévy walks: an analysis in terms of multistate processes,"Continuous time random walks combining diffusive and ballistic regimes are
introduced to describe a class of L\'evy walks on lattices. By including
exponentially-distributed waiting times separating the successive jump events
of a walker, we are led to a description of such L\'evy walks in terms of
multistate processes whose time-evolution is shown to obey a set of coupled
delay differential equations. Using simple arguments, we obtain asymptotic
solutions to these equations and rederive the scaling laws for the mean squared
displacement of such processes. Our calculation includes the computation of all
relevant transport coefficients in terms of the parameters of the models.",1407.0227v2
2014-07-26,Magnetization reversal condition for a nanomagnet within a rotating magnetic field,"The reversal condition of magnetization in a nanomagnet under the effect of
rotating magnetic field generated by a microwave is theoretically studied based
on the Landau-Lifshitz-Gilbert equation. In a rotating frame, the microwave
produces a dc magnetic field pointing in the reversed direction, which
energetically stabilizes the reversed state. We find that the microwave
simultaneously produces a torque preventing the reversal. It is pointed out
that this torque leads to a jump in the reversal field with respect to the
frequency. We derive the equations determining the reversal fields in both the
low- and high-frequency regions from the energy balance equation. The
validities of the formulas are confirmed by a comparison with the numerical
simulation of the Landau-Lifshitz-Gilbert equation.",1407.7095v1
2014-09-17,Aharonov-Bohm Oscillations in a Quasi-Ballistic 3D Topological Insulator Nanowire,"In three-dimensional topological insulators (3D TI) nanowires, transport
occurs via gapless surface states where the spin is fixed perpendicular to the
momentum[1-6]. Carriers encircling the surface thus acquire a \pi Berry phase,
which is predicted to open up a gap in the lowest-energy 1D surface subband.
Inserting a magnetic flux ({\Phi}) of h/2e through the nanowire should cancel
the Berry phase and restore the gapless 1D mode[7-8]. However, this signature
has been missing in transport experiments reported to date[9-11]. Here, we
report measurements of mechanically-exfoliated 3D TI nanowires which exhibit
Aharonov-Bohm oscillations consistent with topological surface transport. The
use of low-doped, quasi-ballistic devices allows us to observe a minimum
conductance at {\Phi} = 0 and a maximum conductance reaching e^2/h at {\Phi} =
h/2e near the lowest subband (i.e. the Dirac point), as well as the carrier
density dependence of the transport.",1409.5095v1
2014-10-13,[$α$/Fe] Abundances of Four Outer M 31 Halo Stars,"We present alpha element to iron abundance ratios, [$\alpha$/Fe], for four
stars in the outer stellar halo of the Andromeda Galaxy (M 31). The stars were
identified as high-likelihood field halo stars by Gilbert et al. (2012) and lie
at projected distances between 70 and 140 kpc from M 31's center. These are the
first alpha abundances measured for a halo star in a galaxy beyond the Milky
Way. The stars range in metallicity between [Fe/H]= -2.2 and [Fe/H]= -1.4. The
sample's average [$\alpha$/Fe] ratio is +0.20+/-0.20. The best-fit average
value is elevated above solar which is consistent with rapid chemical
enrichment from Type II supernovae. The mean [$\alpha$/Fe] ratio of our M31
outer halo sample agrees (within the uncertainties) with that of Milky Way
inner/outer halo stars that have a comparable range of [Fe/H].",1410.3475v1
2014-11-05,Kalman Filtering over Gilbert-Elliott Channels: Stability Conditions and the Critical Curve,"This paper investigates the stability of Kalman filtering over
Gilbert-Elliott channels where random packet drop follows a time-homogeneous
two-state Markov chain whose state transition is determined by a pair of
failure and recovery rates. First of all, we establish a relaxed condition
guaranteeing peak-covariance stability described by an inequality in terms of
the spectral radius of the system matrix and transition probabilities of the
Markov chain. We further show that that condition can be interpreted using a
linear matrix inequality feasibility problem. Next, we prove that the
peak-covariance stability implies mean-square stability, if the system matrix
has no defective eigenvalues on the unit circle. This connection between the
two stability notions holds for any random packet drop process. We prove that
there exists a critical curve in the failure-recovery rate plane, below which
the Kalman filter is mean-square stable and no longer mean-square stable above,
via a coupling method in stochastic processes. Finally, a lower bound for this
critical failure rate is obtained making use of the relationship we establish
between the two stability criteria, based on an approximate relaxation of the
system matrix.",1411.1217v1
2015-01-21,Lévy walks on lattices as multi-state processes,"Continuous-time random walks combining diffusive scattering and ballistic
propagation on lattices model a class of L\'evy walks. The assumption that
transitions in the scattering phase occur with exponentially-distributed
waiting times leads to a description of the process in terms of multiple
states, whose distributions evolve according to a set of delay differential
equations, amenable to analytic treatment. We obtain an exact expression of the
mean squared displacement associated with such processes and discuss the
emergence of asymptotic scaling laws in regimes of diffusive and superdiffusive
(subballistic) transport, emphasizing, in the latter case, the effect of
initial conditions on the transport coefficients. Of particular interest is the
case of rare ballistic propagation, in which case a regime of superdiffusion
may lurk underneath one of normal diffusion.",1501.05216v1
2015-01-31,Bases and Structure Constants of Generalized Splines with Integer Coefficients on Cycles,"An integer generalized spline is a set of vertex labels on an edge-labeled
graph that satisfy the condition that if two vertices are joined by an edge,
the vertex labels are congruent modulo the edge label. Foundational work on
these objects comes from Gilbert, Polster, and Tymoczko, who generalize ideas
from geometry/topology (equivariant cohomology rings) and algebra (algebraic
splines) to develop the notion of generalized splines. Gilbert, Polster, and
Tymoczko prove that the ring of splines on a graph can be decomposed in terms
of splines on its subgraphs (in particular, on trees and cycles), and then
fully analyze splines on trees. Following Handschy-Melnick-Reinders and Rose,
we analyze splines on cycles, in our case integer generalized splines. The
primary goal of this paper is to establish two new bases for the module of
integer generalized splines on cycles: the triangulation basis and the King
basis. Unlike bases in previous work, we are able to characterize each basis
element completely in terms of the edge labels of the underlying cycle. As an
application we explicitly construct the multiplication table for the ring of
integer generalized splines in terms of the King basis.",1502.00176v1
2015-03-02,An Anisotropic Landau-Lifschitz-Gilbert model of dissipation in qubits,"We derive a microscopic model for dissipative dynamics in a system of
mutually interacting qubits coupled to a thermal bath that generalises the
dissipative model of Landau-Lifschitz-Gilbert to the case of anisotropic bath
couplings. We show that the dissipation acts to bias the quantum trajectories
towards a reduced phase space. This model applies to a system of
superconducting flux qubits whose coupling to the environment is necessarily
anisotropic. We study the model in the context of the D-Wave computing device
and show that the form of environmental coupling in this case produces dynamics
that are closely related to several models proposed on phenomenological
grounds.",1503.00651v2
2015-03-25,Optimising the neutron environment of Radiation Portal Monitors: a computational optimisation study,"Efficient and reliable detection of radiological or nuclear threats is a
crucial part of national and international efforts to prevent terrorist
activities. Radiation Portal Monitors (RPMs), which are deployed worldwide, are
intended to interdict smuggled fissile material by detecting emissions of
neutrons and gamma rays. However, considering the range and variety of threat
sources, vehicular and shielding scenarios, and that only a small signature is
present, it is important that the design of the RPMs allows these signatures to
be accurately differentiated from the environmental background. Using
Monte-Carlo neutron-transport simulations of a model helium-3 detector system
we have conducted a parameter study to identify the optimum combination of
detector shielding and collimation that maximises the sensitivity of RPMs.
These structures, which could be simply and cost-effectively added to existing
RPMs, can improve the detector response by more than a factor of two relative
to an unmodified, bare design. Furthermore, optimisation of the air gap
surrounding the helium tubes also improves detector efficiency.",1503.07346v1
2015-06-29,Energy spectra of primary knock-on atoms under neutron irradiation,"Materials subjected to neutron irradiation will suffer from a build-up of
damage caused by the displacement cascades initiated by nuclear reactions.
Previously, the main ""measure"" of this damage accumulation has been through the
displacements per atom (dpa) index. There are known limitations associated with
the dpa quantity and its domain of application and therefore this paper
describes a more rigorous methodology to calculate the primary atomic recoil
events (often called the primary knock-on atoms or PKAs) that lead to cascade
damage events as a function of energy and recoiling species for any simulated
or measured neutron irradiation scenario. Via examples of fusion relevant
materials, it is shown that the PKA spectra can be complex, involving many
different recoiling species, potentially differing in both proton and neutron
number from the original target nuclei, including high energy recoils of light
emitted particles such as alpha-particles and protons. The variations in PKA
spectra as a function of time, neutron field, and material are explored.
Example PKA spectra are applied to radiation damage quantification using the
binary collision approximation and stochastic cluster dynamics, and the results
from these different approaches are discussed and compared.",1506.08554v1
2015-08-25,Direct Visualization of Memory Effects in Artificial Spin Ice,"We experimentally demonstrate that arrays of interacting nanoscale
ferromagnetic islands, known as artificial spin ice, develop reproducible
microstates upon cycling an applied magnetic field. The onset of this memory
effect is determined by the strength of the applied field relative to the array
coercivity. Specifically, when the applied field strength is almost exactly
equal to the array coercivity, several training cycles are required before the
array achieves a nearly completely repeatable microstate, whereas when the
applied field strength is stronger or weaker than the array coercivity, a
repeatable microstate is achieved after the first minor loop. We show through
experiment and simulation that this memory exhibited by artificial spin ice is
due to a ratchet effect on interacting, magnetically-charged defects in the
island moment configuration and to the complexity of the network of strings of
reversed moments that forms during magnetization reversal.",1508.06330v1
2015-10-21,On the limiting Markov process of energy exchanges in a rarely interacting ball-piston gas,"We analyse the process of energy exchanges generated by the elastic
collisions between a point-particle, confined to a two-dimensional cell with
convex boundaries, and a `piston', i.e. a line-segment, which moves back and
forth along a one-dimensional interval partially intersecting the cell. This
model can be considered as the elementary building block of a spatially
extended high-dimensional billiard modeling heat transport in a class of hybrid
materials exhibiting the kinetics of gases and spatial structure of solids.
Using heuristic arguments and numerical analysis, we argue that, in a regime of
rare interactions, the billiard process converges to a Markov jump process for
the energy exchanges and obtain the expression of its generator.",1510.06408v2
2015-10-29,Deligne--Langlands gamma factors in families,"Let F be a p-adic field, W_F its absolute Weil group, and let k be an
algebraically closed field of prime characteristic l different from p. Attached
to any l-adic representation of W_F are local epsilon- and L-factors. There are
natural notions of families of l-adic representations of W_F, such as the
theory of Galois deformations or, more generally, families over arbitrary
Noetherian W(k)-algebras. However, the epsilon and L-factors do not interpolate
well in such families. In this paper it is shown that the gamma factor, which
is the product of the epsilon factor with a ratio of L-factors, interpolates
over such families.",1510.08743v3
2015-11-01,Verification of commercial motor performance for WEAVE at the William Herschel Telescope,"WEAVE is a 1000-fiber multi-object spectroscopic facility for the 4.2~m
William Herschel Telescope. It will feature a double-headed pick-and-place
fiber positioning robot comprising commercially available robotic axes. This
paper presents results on the performance of these axes, obtained by testing a
prototype system in the laboratory. Positioning accuracy is found to be better
than the manufacturer's published values for the tested cases, indicating that
the requirement for a maximum positioning error of 8.0~microns is achievable.
Field reconfiguration times well within the planned 60 minute observation
window are shown to be likely when individual axis movements are combined in an
efficient way.",1511.00202v1
2015-11-02,Learning from history: Adaptive calibration of 'tilting spine' fiber positioners,"This paper discusses a new approach for determining the calibration
parameters of independently-actuated optical fibers in multi-object
astronomical fiber positioning systems. This work comes from the development of
a new type of piezoelectric motor intended to enhance the 'tilting spine' fiber
positioning technology originally created by the Australian Astronomical
Observatory. Testing has shown that the motor's performance can vary depending
on the fiber's location within its accessible field, meaning that an individual
fiber is difficult calibrate with a one-time routine. Better performance has
resulted from constantly updating calibration parameters based on the observed
movements of the fiber during normal closed-loop positioning. Over time,
location-specific historical data is amassed that can be used to better predict
the results of a future fiber movement. This is similar to a technique
previously proposed by the Australian Astronomical Observatory, but with the
addition of location-specific learning. Results from a prototype system are
presented, showing a significant reduction in overall positioning error when
using this new approach.",1511.00737v1
2016-06-23,Echidna Mark II: one giant leap for 'tilting spine' fibre positioning technology,"The Australian Astronomical Observatory's 'tilting spine' fibre positioning
technology has been redeveloped to provide superior performance in a smaller
package. The new design offers demonstrated closed-loop positioning errors of
2.8 {\mu}m RMS in only five moves (~10 s excluding metrology overheads) and an
improved capacity for open-loop tracking during observations. Tilt-induced
throughput losses have been halved by lengthening spines while maintaining
excellent accuracy. New low-voltage multilayer piezo actuator technology has
reduced a spine's peak drive amplitude from ~150 V to <10 V, simplifying the
control electronics design, reducing the system's overall size, and improving
modularity. Every spine is now a truly independent unit with a dedicated drive
circuit and no restrictions on the timing or direction of fibre motion.",1606.07305v1
2016-08-15,Inverse subsemigroups of finite index in finitely generated inverse semigroups,"The index of a subgroup of a group counts the number of cosets of that
subgroup. A subgroup of finite index often shares structural properties with
the group, and the existence of a subgroup of finite index with some particular
property can therefore imply useful structural information for the overgroup. A
developed theory of cosets in inverse semigroups exists, originally due to
Schein: it is defined only for closed inverse subsemigroups, and the structural
correspondences between an inverse semigroup and a closed inverse subsemigroup
of finite index are weaker than in the group case. Nevertheless, many aspects
of this theory are of interest, and some of them are addressed in this paper.
We study the basic theory of cosets in inverse semigroups, including an index
formula for chains of subgroups and an analogue of M. Hall's Theorem on
counting subgroups of finite index in finitely generated groups. We then look
in detail at the connection between the following properties of a closed
inverse submonoid of an inverse monoid: having finite index; being a
recognisable subset; being a rational subset; being finitely generated (as a
closed inverse submonoid). A remarkable result of Margolis and Meakin shows
that these properties are equivalent for closed inverse submonoids of free
inverse monoids.",1608.04254v1
2016-10-03,Magnetic microscopy and simulation of strain-mediated control of magnetization in Ni/PMN-PT nanostructures,"Strain-mediated thin film multiferroics comprising
piezoelectric/ferromagnetic heterostructures enable the electrical manipulation
of magnetization with much greater efficiency than other methods; however, the
investigation of nanostructures fabricated from these materials is limited.
Here we characterize ferromagnetic Ni nanostructures grown on a ferroelectric
PMN-PT substrate using scanning electron microscopy with polarization analysis
(SEMPA) and micromagnetic simulations. The magnetization of the Ni
nanostructures can be controlled with a combination of sample geometry and
applied electric field, which strains the ferroelectric substrate and changes
the magnetization via magnetoelastic coupling. We evaluate two types of
simulations of ferromagnetic nanostructures on strained ferroelectric
substrates: conventional micromagnetic simulations including a simple uniaxial
strain, and coupled micromagnetic-elastodynamic simulations. Both simulations
qualitatively capture the response of the magnetization changes produced by the
applied strain, with the coupled solution providing more accurate
representation.",1610.00746v1
2016-10-17,Formalising Real Numbers in Homotopy Type Theory,"Cauchy reals can be defined as a quotient of Cauchy sequences of rationals.
The limit of a Cauchy sequence of Cauchy reals is defined through lifting it to
a sequence of Cauchy sequences of rationals. This lifting requires the axiom of
countable choice or excluded middle, neither of which is available in homotopy
type theory. To address this, the Univalent Foundations Program uses a higher
inductive-inductive type to define the Cauchy reals as the free Cauchy complete
metric space generated by the rationals. We generalize this construction to
define the free Cauchy complete metric space generated by an arbitrary metric
space. This forms a monad in the category of metric spaces with Lipschitz
functions. When applied to the rationals it defines the Cauchy reals. Finally,
we can use Altenkirch and Danielson (2016)'s partiality monad to define a
semi-decision procedure comparing a real number and a rational number.
  The entire construction has been formalized in the Coq proof assistant. It is
available at https://github.com/SkySkimmer/HoTTClasses/tree/CPP2017 .",1610.05072v2
2016-11-04,The flow and evolution of ice-sucrose crystal mushes,"We study the rheology of suspensions of ice crystals at moderate to high
volume fractions in a sucrose solution in which they are partially soluble; a
model system for a wide class of crystal mushes or slurries. Under step changes
in shear rate, the viscosity changes to a new `relaxed' value over several
minutes, in a manner well fitted by a single exponential. The behavior of the
relaxed viscosity is power-law shear thinning with shear rate, with an exponent
of $-1.76 \pm 0.25$, so that shear stress falls with increasing shear rate. On
longer timescales, the crystals ripen (leading to a falling viscosity) so that
the mean radius increases with time to the power $0.14 \pm 0.07$. We speculate
that this unusually small exponent is due to the interaction of classical
ripening dynamics with abrasion or breakup under flow. We compare the
rheological behavior to mechanistic models based on flow-induced aggregation
and breakup of crystal clusters, finding that the exponents can be predicted
from liquid phase sintering and breakup by brittle fracture.",1611.01365v1
2016-11-08,Convergence of an implicit-explicit midpoint scheme for computational micromagnetics,"Based on lowest-order finite elements in space, we consider the numerical
integration of the Landau-Lifschitz-Gilbert equation (LLG). The dynamics of LLG
is driven by the so-called effective field which usually consists of the
exchange field, the external field, and lower-order contributions such as the
stray field. The latter requires the solution of an additional partial
differential equation in full space. Following Bartels and Prohl (2006)
(Convergence of an implicit finite element method for the
Landau-Lifschitz-Gilbert equation. SIAM J. Numer. Anal. 44), we employ the
implicit midpoint rule to treat the exchange field. However, in order to treat
the lower-order terms effectively, we combine the midpoint rule with an
explicit Adams-Bashforth scheme. The resulting integrator is formally of
second-order in time, and we prove unconditional convergence towards a weak
solution of LLG. Numerical experiments underpin the theoretical findings.",1611.02465v2
2016-11-17,Dynamical contribution to the heat conductivity in stochastic energy exchanges of locally confined gases,"We present a systematic computation of the heat conductivity of the Markov
jump process modeling the energy exchanges in an array of locally confined hard
spheres at the conduction threshold. Based on a variational formula [Sasada M.
2016, {\it Thermal conductivity for stochastic energy exchange models},
arXiv:1611.08866], explicit upper bounds on the conductivity are derived, which
exhibit a rapid power-law convergence towards an asymptotic value. We thereby
conclude that the ratio of the heat conductivity to the energy exchange
frequency deviates from its static contribution by a small negative correction,
its dynamic contribution, evaluated to be $-0.000\,373$ in dimensionless units.
This prediction is corroborated by kinetic Monte Carlo simulations which were
substantially improved compared to earlier results.",1611.05809v3
2016-11-27,Thermal conductivity for stochastic energy exchange models,"We consider a class of stochastic models for energy transport and study
relations between the thermal conductivity and some static observables, such as
the static conductivity, which is defined as the contribution of static
correlations in Green-Kubo formula. The class of models is a generalization of
two specific models derived by Gaspard and Gilbert as mesoscopic dynamics of
energies for two-dimensional and three-dimensional locally confined hard-discs.
They claim some equalities hold between the thermal conductivity and several
static observables and also conjecture that these equations are universal in
the sense that they hold for mesoscopic dynamics of energies for confined
particles interacting through hard-core collisions. In this paper, we give
sufficient and necessary conditions for these equalities to hold in the class
we introduce. In particular, we prove that the equality between the thermal
conductivity and other static observables holds if and only if the model obeys
the gradient condition. Since the gradient condition does not hold for models
derived by Gaspard and Gilbert, our result implies a part of their claim is
incorrect.",1611.08866v1
2016-12-07,Spatial heterogeneity of W transmutation in a fusion device,"Accurately quantifying the transmutation rate of tungsten (W) under neutron
irradiation is a necessary requirement in the assessment of its performance as
an armour material in a fusion power plant. The usual approach of calculating
average responses, assuming large, homogenised material volumes, is
insufficient to capture the full complexity of the transmutation picture in the
context of a realistic fusion power plant design, particularly for rhenium (Re)
production from W. Combined neutron transport and inventory simulations for
representative {\it spatially heterogeneous} models of a fusion power plant
show that the production rate of Re is strongly influenced by the local spatial
environment. Localised variation in neutron moderation (slowing down) due to
structural steel and coolant, particularly water, can dramatically increase Re
production because of the huge cross sections of giant resolved resonances in
the neutron-capture reaction of \(^{186}\)W at low neutron energies.
Calculations using cross section data corrected for temperature (Doppler)
effects suggest that temperature may have a relatively lesser influence on
transmutation rates.",1612.03892v1
2017-01-20,Structure of optimal strategies for remote estimation over Gilbert-Elliott channel with feedback,"We investigate remote estimation over a Gilbert-Elliot channel with feedback.
We assume that the channel state is observed by the receiver and fed back to
the transmitter with one unit delay. In addition, the transmitter gets ACK/NACK
feedback for successful/unsuccessful transmission. Using ideas from team
theory, we establish the structure of optimal transmission and estimation
strategies and identify a dynamic program to determine optimal strategies with
that structure. We then consider first-order autoregressive sources where the
noise process has unimodal and symmetric distribution. Using ideas from
majorization theory, we show that the optimal transmission strategy has a
threshold structure and the optimal estimation strategy is Kalman-like.",1701.05943v1
2017-02-04,Fabrication of Atomically Precise Nanopores in Hexagonal Boron Nitride,"We demonstrate the fabrication of individual nanopores in hexagonal boron
nitride (hBN) with atomically precise control of the pore size. Previous
methods of pore production in other 2D materials create pores of irregular
geometry with imprecise diameters. By taking advantage of the preferential
growth of boron vacancies in hBN under electron beam irradiation, we are able
to observe the pore growth via transmission electron microscopy, and terminate
the process when the pore has reached its desired size. Careful control of beam
conditions allows us to nucleate and grow individual triangular and hexagonal
pores with diameters ranging from subnanometer to 6nm over a large area of
suspended hBN using a conventional TEM. These nanopores could find application
in molecular sensing, DNA sequencing, water desalination, and molecular
separation. Furthermore, the chemical edge-groups along the hBN pores can be
made entirely nitrogen terminated or faceted with boron-terminated edges,
opening avenues for tailored functionalization and extending the applications
of these hBN nanopores.",1702.01220v1
2017-02-10,A finite element approximation for the stochastic Maxwell--Landau--Lifshitz--Gilbert system,"The stochastic Landau--Lifshitz--Gilbert (LLG) equation coupled with the
Maxwell equations (the so called stochastic MLLG system) describes the creation
of domain walls and vortices (fundamental objects for the novel nanostructured
magnetic memories). We first reformulate the stochastic LLG equation into an
equation with time-differentiable solutions. We then propose a convergent
$\theta$-linear scheme to approximate the solutions of the reformulated system.
As a consequence, we prove convergence of the approximate solutions, with no or
minor conditions on time and space steps (depending on the value of $\theta$).
Hence, we prove the existence of weak martingale solutions of the stochastic
MLLG system. Numerical results are presented to show applicability of the
method.",1702.03027v1
2017-03-07,The extrapolated explicit midpoint scheme for variable order and step size controlled integration of the Landau-Lifschitz-Gilbert equation,"A practical and efficient scheme for the higher order integration of the
Landau-Lifschitz-Gilbert (LLG) equation is presented. The method is based on
extrapolation of the two-step explicit midpoint rule and incorporates adaptive
time step and order selection. We make use of a piecewise time-linear stray
field approximation to reduce the necessary work per time step. The
approximation to the interpolated operator is embedded into the extrapolation
process to keep in step with the hierarchic order structure of the scheme. We
verify the approach by means of numerical experiments on a standardized NIST
problem and compare with a higher order embedded Runge-Kutta formula. The
efficiency of the presented approach increases when the stray field computation
takes a larger portion of the costs for the effective field evaluation.",1703.02479v1
2017-09-06,Adaptively time stepping the stochastic Landau-Lifshitz-Gilbert equation at nonzero temperature: implementation and validation in MuMax3,"Thermal fluctuations play an increasingly important role in micromagnetic
research relevant for various biomedical and other technological applications.
Until now, it was deemed necessary to use a time stepping algorithm with a
fixed time step in order to perform micromagnetic simulations at nonzero
temperatures. However, Berkov and Gorn have shown that the drift term which
generally appears when solving stochastic differential equations can only
influence the length of the magnetization. This quantity is however fixed in
the case of the stochastic Landau-Lifshitz-Gilbert equation. In this paper, we
exploit this fact to straightforwardly extend existing high order solvers with
an adaptive time stepping algorithm. We implemented the presented methods in
the freely available GPU-accelerated micromagnetic software package MuMax3 and
used it to extensively validate the presented methods. Next to the advantage of
having control over the error tolerance, we report a twenty fold speedup
without a loss of accuracy, when using the presented methods as compared to the
hereto best practice of using Heun's solver with a small fixed time step.",1709.01682v1
2017-09-18,Growth-Induced In-Plane Uniaxial Anisotropy in V$_{2}$O$_{3}$/Ni Films,"We report on a strain-induced and temperature dependent uniaxial anisotropy
in V$_{2}$O$_{3}$/Ni hybrid thin films, manifested through the interfacial
strain and sample microstructure, and its consequences on the angular dependent
magnetization reversal. X-ray diffraction and reciprocal space maps identify
the in-plane crystalline axes of the V$_{2}$O$_{3}$; atomic force and scanning
electron microscopy reveal oriented rips in the film microstructure.
Quasi-static magnetometry and dynamic ferromagnetic resonance measurements
identify a uniaxial magnetic easy axis along the rips. Comparison with films
grown on sapphire without rips shows a combined contribution from strain and
microstructure in the V$_{2}$O$_{3}$/Ni films. Magnetization reversal
characteristics captured by angular-dependent first order reversal curve
measurements indicate a strong domain wall pinning along the direction
orthogonal to the rips, inducing an angular-dependent change in the reversal
mechanism. The resultant anisotropy is tunable with temperature and is most
pronounced at room temperature, which is beneficial for potential device
applications.",1709.06100v1
2018-05-07,Generalized Random Gilbert-Varshamov Codes,"We introduce a random coding technique for transmission over discrete
memoryless channels, reminiscent of the basic construction attaining the
Gilbert-Varshamov bound for codes in Hamming spaces. The code construction is
based on drawing codewords recursively from a fixed type class, in such a way
that a newly generated codeword must be at a certain minimum distance from all
previously chosen codewords, according to some generic distance function. We
derive an achievable error exponent for this construction, and prove its
tightness with respect to the ensemble average. We show that the exponent
recovers the Csisz\'{a}r and K{\""o}rner exponent as a special case, which is
known to be at least as high as both the random-coding and expurgated
exponents, and we establish the optimality of certain choices of the distance
function. In addition, for additive distances and decoding metrics, we present
an equivalent dual expression, along with a generalization to infinite
alphabets via cost-constrained random coding.",1805.02515v2
2018-07-04,Deep Autoencoder for Combined Human Pose Estimation and body Model Upscaling,"We present a method for simultaneously estimating 3D human pose and body
shape from a sparse set of wide-baseline camera views. We train a symmetric
convolutional autoencoder with a dual loss that enforces learning of a latent
representation that encodes skeletal joint positions, and at the same time
learns a deep representation of volumetric body shape. We harness the latter to
up-scale input volumetric data by a factor of $4 \times$, whilst recovering a
3D estimate of joint positions with equal or greater accuracy than the state of
the art. Inference runs in real-time (25 fps) and has the potential for passive
human behaviour monitoring where there is a requirement for high fidelity
estimation of human body shape and pose.",1807.01511v1
2018-10-08,Hiding the weights -- CBC black box algorithms with a guaranteed error bound,"The component-by-component (CBC) algorithm is a method for constructing good
generating vectors for lattice rules for the efficient computation of
high-dimensional integrals in the ""weighted"" function space setting introduced
by Sloan and Wo\'zniakowski. The ""weights"" that define such spaces are needed
as inputs into the CBC algorithm, and so a natural question is, for a given
problem how does one choose the weights? This paper introduces two new CBC
algorithms which, given bounds on the mixed first derivatives of the integrand,
produce a randomly shifted lattice rule with a guaranteed bound on the
root-mean-square error. This alleviates the need for the user to specify the
weights. We deal with ""product weights"" and ""product and order dependent (POD)
weights"". Numerical tables compare the two algorithms under various assumed
bounds on the mixed first derivatives, and provide rigorous upper bounds on the
root-mean-square integration error.",1810.03394v1
2018-10-11,Alternative Stacking Sequences in Hexagonal Boron Nitride,"The relative orientation of successive sheets, i.e. the stacking sequence, in
layered two-dimensional materials is central to the electronic, thermal, and
mechanical properties of the material. Often different stacking sequences have
comparable cohesive energy, leading to alternative stable crystal structures.
Here we theoretically and experimentally explore different stacking sequences
in the van der Waals bonded material hexagonal boron nitride (h-BN). We examine
the total energy, electronic bandgap, and dielectric response tensor for five
distinct high symmetry stacking sequences for both bulk and bilayer forms of
h-BN. Two sequences, the generally assumed AA' sequence and the relatively
unknown (for h-BN) AB (Bernal) sequence, are predicted to have comparably low
energy. We present a scalable modified chemical vapor deposition method that
produces large flakes of virtually pure AB stacked h-BN; this new material
complements the generally available AA' stacked h-BN.",1810.04814v1
2018-10-17,Unified theory of magnetization dynamics with relativistic and nonrelativistic spin torques,"Spin torques play a crucial role in operative properties of modern spintronic
devices. To study current-driven magnetization dynamics, spin-torque terms
providing the action of spin-polarized currents have previously often been
added in a phenomenological way to the Landau-Lifshitz-Gilbert equation
describing the local spin dynamics, yet without derivation from fundamental
principles. Here, starting from the Dirac-Kohn-Sham theory and incorporating
nonlocal spin transport we rigorously derive the various spin-torque terms that
appear in current-driven magnetization dynamics. In particular we obtain an
extended magnetization dynamics equation that precisely contains the
nonrelativistic adiabatic and relativistic nonadiabatic spin-transfer torques
(STTs) of the Berger and Zhang-Li forms as well as relativistic spin-orbit
torques (SOTs). We derive in addition a previously unnoticed relativistic
spin-torque term and moreover show that the various obtained spin-torque terms
do not appear in the same mathematical form in both the Landau-Lifshitz and
Landau-Lifshitz-Gilbert equations of spin dynamics.",1810.07438v1
2018-10-23,Resource-Constrained Simultaneous Detection and Labeling of Objects in High-Resolution Satellite Images,"We describe a strategy for detection and classification of man-made objects
in large high-resolution satellite photos under computational resource
constraints. We detect and classify candidate objects by using five pipelines
of convolutional neural network processing (CNN), run in parallel. Each
pipeline has its own unique strategy for fine tunning parameters, proposal
region filtering, and dealing with image scales. The conflicting region
proposals are merged based on region confidence and not just based on overlap
areas, which improves the quality of the final bounding-box regions selected.
We demonstrate this strategy using the recent xView challenge, which is a
complex benchmark with more than 1,100 high-resolution images, spanning 800,000
aerial objects around the world covering a total area of 1,400 square
kilometers at 0.3 meter ground sample distance. To tackle the
resource-constrained problem posed by the xView challenge, where inferences are
restricted to be on CPU with 8GB memory limit, we used lightweight CNN's
trained with the single shot detector algorithm. Our approach was competitive
on sequestered sets; it was ranked third.",1810.10110v1
2018-11-01,"Ludometrics: Luck, and How to Measure It","Game theory is the study of tractable games which may be used to model more
complex systems. Board games, video games and sports, however, are intractable
by design, so ""ludological"" theories about these games as complex phenomena
should be grounded in empiricism. A first ""ludometric"" concern is the empirical
measurement of the amount of luck in various games. We argue against a narrow
view of luck which includes only factors outside any player's control, and
advocate for a holistic definition of luck as complementary to the variation in
effective skill within a population of players. We introduce two metrics for
luck in a game for a given population - one information theoretical, and one
Bayesian, and discuss the estimation of these metrics using sparse,
high-dimensional regression techniques. Finally, we apply these techniques to
compare the amount of luck between various professional sports, between Chess
and Go, and between two hobby board games: Race for the Galaxy and Seasons.",1811.00673v1
2019-01-28,Topology and Observables of the Non-Hermitian Chern Insulator,"Topology plays a central role in nearly all disciplines of physics, yet its
applications have so far been restricted to closed, lossless systems in
thermodynamic equilibrium. Given that many physical systems are open and may
include gain and loss mechanisms, there is an eminent need to reexamine
topology within the context of non-Hermitian theories that describe open, lossy
systems. The recent generalization of the Chern number to non-Hermitian
Hamiltonians initiated this reexamination; however, there is so far no
established connection between a non-Hermitian topological invariant and the
quantization of an observable. In this work, we show that no such relationship
exists between the Chern number of non-Hermitian bands and the quantization of
the Hall conductivity. Using field theoretical techniques, we calculate the
longitudinal and Hall conductivities of a non-Hermitian Hamiltonian with a
finite Chern number to explicitly demonstrate the physics of a non-quantized
Hall conductivity despite an invariable Chern number. These results demonstrate
that the Chern number does not provide a physically meaningful classification
of non-Hermitian Hamiltonians.",1901.09961v2
2019-03-25,Deep Shape from Polarization,"This paper makes a first attempt to bring the Shape from Polarization (SfP)
problem to the realm of deep learning. The previous state-of-the-art methods
for SfP have been purely physics-based. We see value in these principled
models, and blend these physical models as priors into a neural network
architecture. This proposed approach achieves results that exceed the previous
state-of-the-art on a challenging dataset we introduce. This dataset consists
of polarization images taken over a range of object textures, paints, and
lighting conditions. We report that our proposed method achieves the lowest
test error on each tested condition in our dataset, showing the value of
blending data-driven and physics-driven approaches.",1903.10210v2
2019-04-30,The algebra of rewriting for presentations of inverse monoids,"We describe a formalism, using groupoids, for the study of rewriting for
presentations of inverse monoids, that is based on the Squier complex
construction for monoid presentations. We introduce the class of pseudoregular
groupoids, an example of which now arises as the fundamental groupoid of our
version of the Squier complex. A further key ingredient is the factorisation of
the presentation map from a free inverse monoid as the composition of an
idempotent pure map and an idempotent separating map. The relation module of a
presentation is then defined as the abelianised kernel of this idempotent
separating map. We then use the properties of idempotent separating maps to
derive a free presentation of the relation module. The construction of its
kernel - the module of identities - uses further facts about pseudoregular
groupoids.",1904.13135v1
2019-05-31,Characterizing the mod-$\ell$ local Langlands correspondence by nilpotent gamma factors,"Let $F$ be a $p$-adic field and choose $k$ an algebraic closure of
$\mathbb{F}_{\ell}$, with $\ell$ different from $p$. We define ``nilpotent
lifts'' of irreducible generic $k$-representations of $GL_n(F)$, which take
coefficients in Artin local $k$-algebras. We show that an irreducible generic
$\ell$-modular representation $\pi$ of $GL_n(F)$ is uniquely determined by its
collection of Rankin--Selberg gamma factors $\gamma(\pi\times
\widetilde{\tau},X,\psi)$ as $\widetilde{\tau}$ varies over nilpotent lifts of
irreducible generic $k$-representations $\tau$ of $GL_t(F)$ for $t=1,\dots,
\lfloor \frac{n}{2}\rfloor$. This gives a characterization of the mod-$\ell$
local Langlands correspondence in terms of gamma factors, assuming it can be
extended to a surjective local Langlands correspondence on nilpotent lifts.",1905.13487v2
2019-07-18,"The homology of groups, profinite completions, and echoes of Gilbert Baumslag","We present novel constructions concerning the homology of finitely generated
groups. Each construction draws on ideas of Gilbert Baumslag. There is a
finitely presented acyclic group $U$ such that $U$ has no proper subgroups of
finite index and every finitely presented group can be embedded in $U$. There
is no algorithm that can determine whether or not a finitely presentable
subgroup of a residually finite, biautomatic group is perfect. For every
recursively presented abelian group $A$ there exists a pair of groups
$i:P_A\hookrightarrow G_A$ such that $i$ induces an isomorphism of profinite
completions, where $G_A$ is a torsion-free biautomatic group that is residually
finite and superperfect, while $P_A$ is a finitely generated group with
$H_2(P_A,\mathbb{Z})\cong A$.",1907.08072v2
2019-08-08,Semantic Estimation of 3D Body Shape and Pose using Minimal Cameras,"We aim to simultaneously estimate the 3D articulated pose and high fidelity
volumetric occupancy of human performance, from multiple viewpoint video (MVV)
with as few as two views. We use a multi-channel symmetric 3D convolutional
encoder-decoder with a dual loss to enforce the learning of a latent embedding
that enables inference of skeletal joint positions and a volumetric
reconstruction of the performance. The inference is regularised via a prior
learned over a dataset of view-ablated multi-view video footage of a wide range
of subjects and actions, and show this to generalise well across unseen
subjects and actions. We demonstrate improved reconstruction accuracy and lower
pose estimation error relative to prior work on two MVV performance capture
datasets: Human 3.6M and TotalCapture.",1908.03030v2
2019-09-06,The universal unramified module for GL(n) and the Ihara conjecture,"Let $F$ be a finite extension of $\mathbb{Q}_p$. Let $W(k)$ denote the Witt
vectors of an algebraically closed field $k$ of characteristic $\ell$ different
from $p$ and $2$, and let $\mathcal{Z}$ be the spherical Hecke algebra for
$GL_n(F)$ over $W(k)$. Given a Hecke character $\lambda:\mathcal{Z}\to R$,
where $R$ is an arbitrary $W(k)$-algebra, we introduce the universal unramified
module $\mathcal{M}_{\lambda,R}$. We show $\mathcal{M}_{\lambda,R}$ embeds in
its Whittaker space and is flat over $R$, resolving a conjecture of Lazarus. It
follows that $\mathcal{M}_{\lambda,k}$ has the same semisimplification as any
unramified principle series with Hecke character $\lambda$.
  In the setting of mod-$\ell$ automorphic forms, Clozel, Harris, and Taylor
formulate a conjectural analogue of Ihara's lemma. It predicts that every
irreducible submodule of a certain cyclic module $V$ of mod-$\ell$ automorphic
forms is generic. Our result on the Whittaker model of
$\mathcal{M}_{\lambda,k}$ reduces the Ihara conjecture to the statement that
$V$ is generic.",1909.02709v3
2019-10-10,Weak-strong uniqueness for the Landau-Lifshitz-Gilbert equation in micromagnetics,"We consider the time-dependent Landau-Lifshitz-Gilbert equation. We prove
that each weak solution coincides with the (unique) strong solution, as long as
the latter exists in time. Unlike available results in the literature, our
analysis also includes the physically relevant lower-order terms like Zeeman
contribution, anisotropy, stray field, and the Dzyaloshinskii-Moriya
interaction (which accounts for the emergence of magnetic Skyrmions). Moreover,
our proof gives a template on how to approach weak-strong uniqueness for even
more complicated problems, where LLG is (nonlinearly) coupled to other
(nonlinear) PDE systems.",1910.04630v2
2019-11-20,Hard Choices in Artificial Intelligence: Addressing Normative Uncertainty through Sociotechnical Commitments,"As AI systems become prevalent in high stakes domains such as surveillance
and healthcare, researchers now examine how to design and implement them in a
safe manner. However, the potential harms caused by systems to stakeholders in
complex social contexts and how to address these remains unclear. In this
paper, we explain the inherent normative uncertainty in debates about the
safety of AI systems. We then address this as a problem of vagueness by
examining its place in the design, training, and deployment stages of AI system
development. We adopt Ruth Chang's theory of intuitive comparability to
illustrate the dilemmas that manifest at each stage. We then discuss how
stakeholders can navigate these dilemmas by incorporating distinct forms of
dissent into the development pipeline, drawing on Elizabeth Anderson's work on
the epistemic powers of democratic institutions. We outline a framework of
sociotechnical commitments to formal, substantive and discursive challenges
that address normative uncertainty across stakeholders, and propose the
cultivation of related virtues by those responsible for development.",1911.09005v1
2019-11-22,Asymmetric entanglement-assisted quantum error-correcting codes and BCH codes,"The concept of asymmetric entanglement-assisted quantum error-correcting code
(asymmetric EAQECC) is introduced in this article. Codes of this type take
advantage of the asymmetry in quantum errors since phase-shift errors are more
probable than qudit-flip errors. Moreover, they use pre-shared entanglement
between encoder and decoder to simplify the theory of quantum error correction
and increase the communication capacity. Thus, asymmetric EAQECCs can be
constructed from any pair of classical linear codes over an arbitrary field.
Their parameters are described and a Gilbert-Varshamov bound is presented.
Explicit parameters of asymmetric EAQECCs from BCH codes are computed and
examples exceeding the introduced Gilbert-Varshamov bound are shown.",1911.10031v2
2019-12-16,Nanosecond-timescale development of Faraday rotation in an ultracold gas,"When a gas of ultracold atoms is suddenly illuminated by light that is nearly
resonant with an atomic transition, the atoms cannot respond instantaneously.
This non-instantaneous response means the gas is initially more transparent to
the applied light than in steady-state. The timescale associated with the
development of light absorption is set by the atomic excited state lifetime.
Similarly, the index of refraction in the gas also requires time to reach a
steady-state value, but the development of the associated phase response is
expected to be slower than absorption effects. Faraday rotation is one
manifestation of differing indices of refraction for orthogonal circular light
polarization components. We have performed experiments measuring the
time-dependent development of polarization rotation in an ultracold gas
subjected to a magnetic field. Our measurements match theoretical predictions
based on solving optical Bloch equations. We are able to identify how
parameters such as steady-state optical thickness and applied magnetic field
strength influence the development of Faraday rotation.",1912.07553v1
2020-01-31,An efficient automated data analytics approach to large scale computational comparative linguistics,"This research project aimed to overcome the challenge of analysing human
language relationships, facilitate the grouping of languages and formation of
genealogical relationship between them by developing automated comparison
techniques. Techniques were based on the phonetic representation of certain key
words and concept. Example word sets included numbers 1-10 (curated), large
database of numbers 1-10 and sheep counting numbers 1-10 (other sources),
colours (curated), basic words (curated).
  To enable comparison within the sets the measure of Edit distance was
calculated based on Levenshtein distance metric. This metric between two
strings is the minimum number of single-character edits, operations including:
insertions, deletions or substitutions. To explore which words exhibit more or
less variation, which words are more preserved and examine how languages could
be grouped based on linguistic distances within sets, several data analytics
techniques were involved. Those included density evaluation, hierarchical
clustering, silhouette, mean, standard deviation and Bhattacharya coefficient
calculations. These techniques lead to the development of a workflow which was
later implemented by combining Unix shell scripts, a developed R package and
SWI Prolog. This proved to be computationally efficient and permitted the fast
exploration of large language sets and their analysis.",2001.11899v1
2020-03-24,An information theoretic framework for classifying exoplanetary system architectures,"We propose several descriptive measures to characterize the arrangements of
planetary masses, periods, and mutual inclinations within exoplanetary systems.
These measures are based in complexity theory and capture the global,
system-level trends of each architecture. Our approach considers all planets in
a system simultaneously, facilitating both intra-system and inter-system
analysis. We find that based on these measures, Kepler's high-multiplicity
($N\geq3$) systems can be explained if most systems belong to a single
intrinsic population, with a subset of high-multiplicity systems ($\sim20\%$)
hosting additional, undetected planets intermediate in period between the known
planets. We confirm prior findings that planets within a system tend to be
roughly the same size and approximately coplanar. We find that forward modeling
has not yet reproduced the high degree of spacing similarity (in log-period)
actually seen in the Kepler data. Although our classification scheme was
developed using compact Kepler multis as a test sample, our methods can be
immediately applied to any other population of exoplanetary systems. We apply
this classification scheme to (1) quantify the similarity between systems, (2)
resolve observational biases from physical trends, and (3) identify which
systems to search for additional planets and where to look for these planets.",2003.11098v1
2020-05-14,On the Performance Analysis of Streaming Codes over the Gilbert-Elliott Channel,"The Gilbert-Elliot (GE) channel is a commonly-accepted model for packet
erasures in networks. Streaming codes are a class of packet-level erasure codes
designed to provide reliable communication over the GE channel. The design of a
streaming code may be viewed as a two-step process. In the first, a more
tractable, delay-constrained sliding window (DCSW) channel model is considered
as a proxy to the GE channel. The streaming code is then designed to reliably
recover from all erasures introduced by the DCSW channel model. Simulation is
typically used to evaluate the performance of the streaming code over the
original GE channel, as analytic performance evaluation is challenging. In the
present paper, we take an important first step towards analytical performance
evaluation. Recognizing that most, efficient constructions of a streaming code
are based on the diagonal embedding or horizontal embedding of scalar block
codes within a packet stream, this paper provides upper and lower bounds on the
block-erasure probability of the underlying scalar block code when operated
over the GE channel.",2005.06921v2
2020-08-25,Differentiating a Tensor Language,"How does one compile derivatives of tensor programs, such that the resulting
code is purely functional (hence easier to optimize and parallelize) and
provably efficient relative to the original program? We show that naively
differentiating tensor code---as done in popular systems like Tensorflow and
PyTorch---can cause asymptotic slowdowns in pathological cases, violating the
Cheap Gradients Principle. However, all existing automatic differentiation
methods that guarantee this principle (for variable size data) do so by relying
on += mutation through aliases/pointers---which complicates downstream
optimization. We provide the first purely functional, provably efficient,
adjoint/reverse-mode derivatives of array/tensor code by explicitly accounting
for sparsity. We do this by focusing on the indicator function from Iverson's
APL. We also introduce a new ""Tensor SSA"" normal form and a new derivation of
reverse-mode automatic differentiation based on the universal property of
inner-products.",2008.11256v1
2020-09-14,Moduli of Langlands Parameters,"Let $F$ be a nonarchimedean local field of residue characteristic $p$, let
$\hat{G}$ be a split reductive group over $\mathbb{Z}[1/p]$ with an action of
$W_F$, and let $^LG$ denote the semidirect product $\hat{G}\rtimes W_F$. We
construct a moduli space of Langlands parameters $W_F \to {^LG}$, and show that
it is locally of finite type and flat over $\mathbb{Z}[1/p]$, and that it is a
reduced local complete intersection. We give parameterizations of the connected
components and the irreducible components of the geometric fibers of this
space, and parameterizations of the connected components of the total space
over $\overline{\mathbb{Z}}[1/p]$ (under mild hypotheses) and over
$\overline{\mathbb{Z}}_{\ell}$ for $\ell\neq p$. In each case, we show
precisely how each connected component identifies with the ""principal""
connected component attached to a smaller split reductive group scheme. Finally
we study the GIT quotient of this space by $\hat{G}$ and give a complete
description of its fibers up to homeomorphism, and a complete description of
its ring of functions after inverting an explicit finite set of primes
depending only on $^LG$.",2009.06708v3
2020-09-30,Spin-diffusion model for micromagnetics in the limit of long times,"In this paper, we consider spin-diffusion Landau-Lifshitz-Gilbert equations
(SDLLG), which consist of the time-dependent Landau-Lifshitz-Gilbert (LLG)
equation coupled with a time-dependent diffusion equation for the electron spin
accumulation. The model takes into account the diffusion process of the spin
accumulation in the magnetization dynamics of ferromagnetic multilayers. We
prove that in the limit of long times, the system reduces to simpler equations
in which the LLG equation is coupled to a nonlinear and nonlocal steady-state
equation, referred to as SLLG. As a by-product, the existence of global weak
solutions to the SLLG equation is obtained. Moreover, we prove weak-strong
uniqueness of solutions of SLLG, i.e., all weak solutions coincide with the
(unique) strong solution as long as the latter exists in time. The results
provide a solid mathematical ground to the qualitative behavior originally
predicted by Zhang, Levy, and Fert in [Physical Review Letters 88 (2002)] in
ferromagnetic multilayers.",2009.14534v1
2020-12-20,Reconstructing phase-resolved hysteresis loops from first-order reversal curves,"The first order reversal curve (FORC) method is a magnetometry based
technique used to capture nanoscale magnetic phase separation and interactions
with macroscopic measurements using minor hysteresis loop analysis. This makes
the FORC technique a powerful tool in the analysis of complex systems which
cannot be effectively probed using localized techniques. However, recovering
quantitative details about the identified phases which can be compared to
traditionally measured metrics remains an enigmatic challenge. We demonstrate a
technique to reconstruct phase-resolved magnetic hysteresis loops by
selectively integrating the measured FORC distribution. From these minor loops,
the traditional metrics - including the coercivity and saturation field, and
the remanent and saturation magnetization - can be determined. In order to
perform this analysis, special consideration must be paid to the accurate
quantitative management of the so-called reversible features. This technique is
demonstrated on three representative materials systems, high anisotropy FeCuPt
thin-films, Fe nanodots, and SmCo/Fe exchange spring magnet films, and shows
excellent agreement with the direct measured major loop, as well as the phase
separated loops.",2012.11041v1
2021-01-13,Self-organization in the one-dimensional Landau-Lifshitz-Gilbert-Slonczewski equation with non-uniform anisotropy fields,"In magnetic films driven by spin-polarized currents, the
perpendicular-to-plane anisotropy is equivalent to breaking the time
translation symmetry, i.e., to a parametric pumping. In this work, we
numerically study those current-driven magnets via the
Landau-Lifshitz-Gilbert-Slonczewski equation in one spatial dimension. We
consider a space-dependent anisotropy field in the parametric-like regime. The
anisotropy profile is antisymmetric to the middle point of the system. We find
several dissipative states and dynamical behavior and focus on localized
patterns that undergo oscillatory and phase instabilities. Using numerical
simulations, we characterize the localized states' bifurcations and present the
corresponding diagram of phases.",2101.05263v1
2021-01-20,Global Optimization of the Mean First Passage Time for Narrow Capture Problems in Elliptic Domains,"Narrow escape and narrow capture problems which describe the average times
required to stop the motion of a randomly travelling particle within a domain
have applications in various areas of science. While for general domains, it is
known how the escape time decreases with the increase of the trap sizes, for
some specific 2D and 3D domains, higher-order asymptotic formulas have been
established, providing the dependence of the escape time on the sizes and
locations of the traps. Such results allow the use of global optimization to
seek trap arrangements that minimize average escape times. In a recent paper
\cite{iyaniwura2021optimization}, an explicit size- and trap location-dependent
expansion of the average mean first passage time (MFPT) in a 2D elliptic domain
was derived. The goal of this work is to systematically seek global minima of
MFPT for $1\leq N\leq 50$ traps in elliptic domains using global optimization
techniques, and compare the corresponding putative optimal trap arrangements
for different values of the domain eccentricity. Further, an asymptotic formula
the for the average MFPT in elliptic domains with $N$ circular traps of
arbitrary sizes is derived, and sample optimal configurations involving
non-equal traps are computed.",2101.08368v2
2021-02-03,Bounds and Genericity of Sum-Rank-Metric Codes,"We derive simplified sphere-packing and Gilbert--Varshamov bounds for codes
in the sum-rank metric, which can be computed more efficiently than previous
ones. They give rise to asymptotic bounds that cover the asymptotic setting
that has not yet been considered in the literature: families of sum-rank-metric
codes whose block size grows in the code length. We also provide two genericity
results: we show that random linear codes achieve almost the sum-rank-metric
Gilbert--Varshamov bound with high probability. Furthermore, we derive bounds
on the probability that a random linear code attains the sum-rank-metric
Singleton bound, showing that for large enough extension fields, almost all
linear codes achieve it.",2102.02244v3
2021-03-01,A pathwise stochastic Landau-Lifshitz-Gilbert equation with application to large deviations,"Using a rough path formulation, we investigate existence, uniqueness and
regularity for the stochastic Landau-Lifshitz-Gilbert equation with
Stratonovich noise on the one dimensional torus. As a main result we show the
continuity of the so-called It\^o-Lyons map in the energy spaces
$L^\infty(0,T;H^k)\cap L^2(0,T;H^{k+1})$ for any $k\ge1$. The proof proceeds in
two steps. First, based on an energy estimate in the aforementioned space
together with a compactness argument we prove existence of a unique solution,
implying the continuous dependence in a weaker norm. This is then strengthened
in the second step where the continuity in the optimal norm is established
through an application of the rough Gronwall lemma. Our approach is direct and
does not rely on any transformation formula, which permits to treat
multidimensional noise. As an easy consequence we then deduce a Wong-Zakai type
result, a large deviation principle for the solution and a support theorem.",2103.00926v1
2021-03-17,Numerical analysis of the Landau-Lifshitz-Gilbert equation with inertial effects,"We consider the numerical approximation of the inertial
Landau-Lifshitz-Gilbert equation (iLLG), which describes the dynamics of the
magnetization in ferromagnetic materials at subpicosecond time scales. We
propose and analyze two fully discrete numerical schemes: The first method is
based on a reformulation of the problem as a linear constrained variational
formulation for the linear velocity. The second method exploits a reformulation
of the problem as a first order system in time for the magnetization and the
angular momentum. Both schemes are implicit, based on first-order finite
elements, and generate approximations satisfying the unit-length constraint of
iLLG at the vertices of the underlying mesh. For both methods, we prove
convergence of the approximations towards a weak solution of the problem.
Numerical experiments validate the theoretical results and show the
applicability of the methods for the simulation of ultrafast magnetic
processes.",2103.09888v2
2021-07-12,Human-like Relational Models for Activity Recognition in Video,"Video activity recognition by deep neural networks is impressive for many
classes. However, it falls short of human performance, especially for
challenging to discriminate activities. Humans differentiate these complex
activities by recognising critical spatio-temporal relations among explicitly
recognised objects and parts, for example, an object entering the aperture of a
container. Deep neural networks can struggle to learn such critical
relationships effectively. Therefore we propose a more human-like approach to
activity recognition, which interprets a video in sequential temporal phases
and extracts specific relationships among objects and hands in those phases.
Random forest classifiers are learnt from these extracted relationships. We
apply the method to a challenging subset of the something-something dataset and
achieve a more robust performance against neural network baselines on
challenging activities.",2107.05319v2
2021-08-17,Small-misorientation toughness in biominerals evolved convergently,"The hardest materials in living organisms are biologically grown crystalline
minerals, or biominerals, which are also incredibly fracture-tough. Biomineral
mesostructure includes size, shape, spatial arrangement, and crystal
orientation of crystallites, observable at the mesoscale (10 nanometer - 10
micron). Here we show that diverse biominerals, including nacre and prisms from
mollusk shells, coral skeletons, and tunicate spicules have different
mesostructures, but they converged to similar, small (<30 degrees)
misorientations of adjacent crystals at the mesoscale. We show that such small
misorientations are an effective toughening mechanism. Combining
Polarization-dependent Imaging Contrast (PIC) mapping of mesostructures and
Molecular Dynamics (MD) simulations of misoriented bicrystals, we reveal here
that small misorientations toughen bicrystals, thus explaining why they evolved
independently but convergently: preventing fracture is a clear evolutionary
advantage for diverse organisms.",2108.07877v1
2021-08-19,Evidence for a liquid precursor to biomineral formation,"The crystals in animal biominerals such as sea urchin spines, mollusk shells,
and coral skeletons, form by attachment of amorphous particles that
subsequently crystallize. Do these solid amorphous precursor particles have
liquid precursors? Polymer-induced liquid precursors (PILP), or prenucleation
clusters coalescing into a liquid precursor to calcium carbonate
crystallization have been observed extensively in synthetic systems. Molecular
dynamics simulations also predict liquid-liquid phase separation. However,
evidence for liquid precursors in natural biominerals remains elusive. Here we
present Scanning or PhotoEmission Electron Microscopy (SEM, PEEM) evidence
consistent with a dense liquid-like precursor in regenerating sea urchin
spines. The observed precursor originates in tissue and ultimately transforms
into a single crystal of calcite (CaCO3) with complex stereom morphology.",2108.08429v1
2021-08-22,Factors Enhancing E-Government Service Gaps in a Developing Country Context,"Globally, the discourse of e-government has gathered momentum in public
service delivery. No country has been left untouched in the implementation of
e-government. Several government departments and agencies are now using
information and communication technology (ICTs) to deliver government services
and information to citizens, other government departments, and businesses.
However, most of the government departments have not provided all of their
services electronically or at least the most important ones. Thus, this creates
a phenomenon of e-government service gaps. The objective of this study was to
investigate the contextual factors enhancing e-government service gaps in a
developing country. To achieve this aim, the TOE framework was employed
together with a qualitative case study to guide data collection and analysis.
The data was collected through semi-structured interviews from government
employees who are involved in the implementation of e-government services in
Zimbabwe as well as from citizens and businesses. Eleven (11) factors were
identified and grouped under the TOE framework. This research contributes
significantly to the implementation and utilisation of e-government services in
Zimbabwe. The study also contributes to providing a strong theoretical
understanding of the factors that enhance e-government service gaps explored in
the research model.",2108.09803v1
2021-09-23,Cyclically presented groups as Labelled Oriented Graph groups,"We use results concerning the Smith forms of circulant matrices to identify
when cyclically presented groups have free abelianisation and so can be
Labelled Oriented Graph (LOG) groups. We generalize a theorem of Odoni and
Cremona to show that for a fixed defining word, whose corresponding representer
polynomial has an irreducible factor that is not cyclotomic and not equal to
$\pm t$, there are at most finitely many $n$ for which the corresponding
$n$-generator cyclically presented group has free abelianisation. We classify
when Campbell and Robertson's generalized Fibonacci groups $H(r,n,s)$ are LOG
groups and when the Sieradski groups are LOG groups. We prove that amongst
Johnson and Mawdesley's groups of Fibonacci type, the only ones that can be LOG
groups are Gilbert-Howie groups $H(n,m)$. We conjecture that if a Gilbert-Howie
group is a LOG group, then it is a Sieradski group, and prove this in certain
cases (in particular, for fixed $m$, the conjecture can only be false for
finitely many $n$). We obtain necessary conditions for a cyclically presented
group to be a connected LOG group in terms of the representer polynomial and
apply them to the Prishchepov groups.",2109.11463v1
2021-12-03,Spectral reconstruction in NRQCD via the Backus-Gilbert method,"We present progress results from the FASTSUM collaboration's programme to
determine the spectrum of the bottomonium system as a function of temperature
using a variety of approaches. In this contribution, the Backus Gilbert method
is used to reconstruct spectral functions from NRQCD meson correlator data from
FASTSUM's anisotropic ensembles at nonzero temperature. We focus in particular
on the resolving power of the method, providing a demonstration of how the
underlying resolution functions can be probed by exploiting the Laplacian
nature of the NRQCD kernel. We conclude with estimates of the bottomonium
ground state mass and widths at nonzero temperature.",2112.02075v2
2021-12-23,Energy minimizing maps with prescribed singularities and Gilbert-Steiner optimal networks,"We investigate the relation between energy minimizing maps valued into
spheres having topological singularities at given points and optimal networks
connecting them (e.g. Steiner trees, Gilbert-Steiner irrigation networks). We
show the equivalence of the corresponding variational problems, interpreting in
particular the branched optimal transport problem as a homological Plateau
problem for rectifiable currents with values in a suitable normed group. This
generalizes the pioneering work by Brezis, Coron and Lieb [10].",2112.12511v4
2022-02-02,Asymptotic stability of precessing domain walls for the Landau-Lifshitz-Gilbert equation in a nanowire with Dzyaloshinskii-Moriya interaction,"We consider a ferromagnetic nanowire and we focus on an asymptotic regime
where the Dzyaloshinskii-Moriya interaction is taken into account. First we
prove a dimension reduction result via $\Gamma$-convergence that determines a
limit functional $E$ defined for maps $m:\mathbb{R}\to \mathbb{S}^2$ in the
direction $e_1$ of the nanowire. The energy functional $E$ is invariant under
translations in $e_1$ and rotations about the axis $e_1$. We fully classify the
critical points of finite energy $E$ when a transition between $-e_1$ and $e_1$
is imposed; these transition layers are called (static) domain walls. The
evolution of a domain wall by the Landau-Lifshitz-Gilbert equation associated
to $E$ under the effect of an applied magnetic field $h(t)e_1$ depending on the
time variable $t$ gives rise to the so-called precessing domain wall. Our main
result proves the asymptotic stability of precessing domain walls for small $h$
in $L^\infty([0, +\infty))$ and small $H^1(\mathbb{R})$ perturbations of the
static domain wall, up to a gauge which is intrinsic to invariances of the
functional $E$.",2202.01005v1
2022-02-14,The Higgs Boson Mass as Fundamental Parameter of the Minimal Supersymmetric Standard Model,"In the Minimal Supersymmetric Standard Model (MSSM) the mass of the lightest
neutral Higgs boson is determined by the supersymmetric parameters. In the
$m_h$MSSM the precisely measured Higgs boson replaces the trilinear coupling
$A_t$ as input parameter. Expressions are derived to extract $A_t$ in a
semi-analytical form as a function of the light Higgs boson (pole) mass. An
algorithm is developed and implemented at two--loop precision, generalizable to
higher orders, to perform this inversion consistently. The result of the
algorithm, implemented in the SuSpect spectrum calculator, is illustrated on a
parameter set compatible with LHC measurements.",2202.06919v2
2022-02-15,Coding and Bounds for Partially Defective Memory Cells,"This paper considers coding for so-called partially stuck (defect) memory
cells. Such memory cells can only store partial information as some of their
levels cannot be used fully due to, e.g., wearout. First, we present new
constructions that are able to mask $u$ partially stuck cells while correcting
at the same time $t$ random errors. The process of ""masking"" determines a word
whose entries coincide with writable levels at the (partially) stuck cells. For
$u>1$ and alphabet size $q>2$, our new constructions improve upon the required
redundancy of known constructions for $t=0$, and require less redundancy for
masking partially stuck cells than former works required for masking fully
stuck cells (which cannot store any information). Second, we show that treating
some of the partially stuck cells as erroneous cells can decrease the required
redundancy for some parameters. Lastly, we derive Singleton-like,
sphere-packing-like, and Gilbert--Varshamov-like bounds. Numerical comparisons
state that our constructions match the Gilbert--Varshamov-like bounds for
several code parameters, e.g., BCH codes that contain all-one word by our first
construction.",2202.07541v1
2022-03-24,Multi-platform Process Flow Models and Algorithms for Extraction and Documentation of Digital Forensic Evidence from Mobile Devices,"The increasing need for the examination of evidence from mobile and portable
gadgets increases the essential need to establish dependable measures for the
investigation of these gadgets. Many differences exist while detailing the
requirement for the examination of each gadget, to help detectives and
examiners in guaranteeing that of any kind piece of evidence extracted/
collected from any mobile devices is well documented and the outcomes can be
repeatable, a reliable and well-documented investigation process must be
implemented if the results of the examination are to be repeatable and
defensible in courts of law. In this paper we developed a generic process flow
model for the extraction of digital evidence in mobile devices running on
android, Windows, iOs and Blackberry operating system. The research adopted
survey approach and extensive literature review a s means to collect data. The
models developed were validate through expert opinion. Results of this work can
guide solution developers in ensuring standardization of evidence extraction
tools for mobile devices.",2203.13258v1
2022-06-07,Implicit biases in transit models using stellar pseudo-density,"The transit technique is responsible for the majority of exoplanet
discoveries to date. Characterizing these planets involves careful modeling of
their transit profiles. A common technique involves expressing the transit
duration using a density-like parameter, $\tilde{\rho}$, often called the
""circular density."" Most notably, the Kepler project -- the largest analysis of
transit lightcurves to date -- adopted a linear prior on $\tilde{\rho}$. Here,
we show that such a prior biases measurements of impact parameter, $b$, due to
the non-linear relationship between $\tilde{\rho}$ and transit duration. This
bias slightly favors low values ($b \lesssim 0.3$) and strongly disfavors high
values ($b \gtrsim 0.7$) unless transit signal-to-noise ratio is sufficient to
provide an independent constraint on $b$, a criterion that is not satisfied for
the majority of Kepler planets. Planet-to-star radius ratio, $r$, is also
biased due to $r{-}b$ covariance. Consequently, the median Kepler DR25 target
suffers a $1.6\%$ systematic underestimate of $r$. We present a techniques for
correcting these biases and for avoiding them in the first place.",2206.03432v1
2022-06-22,Homogenization of the Landau-Lifshitz-Gilbert equation with natural boundary condition,"The full Landau-Lifshitz-Gilbert equation with periodic material coefficients
and natural boundary condition is employed to model the magnetization dynamics
in composite ferromagnets. In this work, we establish the convergence between
the homogenized solution and the original solution via a Lax equivalence
theorem kind of argument. There are a few technical difficulties, including: 1)
it is proven the classic choice of corrector to homogenization cannot provide
the convergence result in the $H^1$ norm; 2) a boundary layer is induced due to
the natural boundary condition; 3) the presence of stray field give rise to a
multiscale potential problem. To keep the convergence rates near the boundary,
we introduce the Neumann corrector with a high-order modification. Estimates on
singular integral for disturbed functions and boundary layer are deduced, to
conduct consistency analysis of stray field. Furthermore, inspired by length
conservation of magnetization, we choose proper correctors in specific
geometric space. These, together with a uniform $W^{1,6}$ estimate on original
solution, provide the convergence rates in the $H^1$ sense.",2206.10948v1
2022-09-12,GenLoco: Generalized Locomotion Controllers for Quadrupedal Robots,"Recent years have seen a surge in commercially-available and affordable
quadrupedal robots, with many of these platforms being actively used in
research and industry. As the availability of legged robots grows, so does the
need for controllers that enable these robots to perform useful skills.
However, most learning-based frameworks for controller development focus on
training robot-specific controllers, a process that needs to be repeated for
every new robot. In this work, we introduce a framework for training
generalized locomotion (GenLoco) controllers for quadrupedal robots. Our
framework synthesizes general-purpose locomotion controllers that can be
deployed on a large variety of quadrupedal robots with similar morphologies. We
present a simple but effective morphology randomization method that
procedurally generates a diverse set of simulated robots for training. We show
that by training a controller on this large set of simulated robots, our models
acquire more general control strategies that can be directly transferred to
novel simulated and real-world robots with diverse morphologies, which were not
observed during training.",2209.05309v1
2022-10-11,Element-Specific First Order Reversal Curves Measured by Magnetic Transmission X-ray Microscopy,"The first order reversal curve (FORC) method is a macroscopic measurement
technique which can be used to extract quantitative, microscopic properties of
hysteretic systems. Using magnetic transmission X-ray microscopy (MTXM), local
element-specific FORC measurements are performed on a 20 nm thick film of CoTb.
The FORCs measured with microscopy reveal a step-by-step domain evolution under
the magnetic field cycling protocol, and provide a direct visualization of the
mechanistic interpretation of FORC diagrams. They are compared with
magnetometry FORCs and show good quantitative agreement. Furthermore, the high
spatial resolution and element-specific sensitivity of MTXM provide new
capabilities to measure FORCs on small regions or specific phases within
multicomponent systems, including buried layers in heterostructures. The
ability to perform FORCs on very small features is demonstrated with the
MTXM-FORC measurement of a rectangular microstructure with vortex-like Landau
structures. This work demonstrates the confluence of two uniquely powerful
techniques to achieve quantitative insight into nanoscale magnetic behavior.",2210.05739v1
2022-11-08,Landau-Lifshitz-Gilbert equations: Controllability by Low Modes Forcing for deterministic version and Support Theorems for Stochastic version,"In this article, we study the controllability issues of the
Landau-Lifshitz-Gilbert Equations (LLGEs), accompanied with non-zero exchange
energy only, in an interval in one spatial dimension with Neumann boundary
conditions. The paper is of twofold. In the first part of the paper, we study
the controllability issues of the LLGEs. The control force acting here is
degenerate i.e., it acts through a few numbers of low mode frequencies. We
exploit the Fourier series expansion of the solution. We borrow methods of
differential geometric control theory (Lie bracket generating property) to
establish the global controllability of the finite-dimensional Galerkin
approximations of LLGEs. We show $L^2$ approximate controllability of the full
system. In the second part, we consider the LLGEs with lower-dimensional
degenerate random forcing (finite-dimensional Brownian motions) and study
support theorems.",2211.04204v1
2022-11-18,Knowledge Graph Refinement based on Triplet BERT-Networks,"Knowledge graph embedding techniques are widely used for knowledge graph
refinement tasks such as graph completion and triple classification. These
techniques aim at embedding the entities and relations of a Knowledge Graph
(KG) in a low dimensional continuous feature space. This paper adopts a
transformer-based triplet network creating an embedding space that clusters the
information about an entity or relation in the KG. It creates textual sequences
from facts and fine-tunes a triplet network of pre-trained transformer-based
language models. It adheres to an evaluation paradigm that relies on an
efficient spatial semantic search technique. We show that this evaluation
protocol is more adapted to a few-shot setting for the relation prediction
task. Our proposed GilBERT method is evaluated on triplet classification and
relation prediction tasks on multiple well-known benchmark knowledge graphs
such as FB13, WN11, and FB15K. We show that GilBERT achieves better or
comparable results to the state-of-the-art performance on these two refinement
tasks.",2211.10460v1
2022-11-22,Generalized Random Gilbert-Varshamov Codes: Typical Error Exponent and Concentration Properties,"We find the exact typical error exponent of constant composition generalized
random Gilbert-Varshamov (RGV) codes over DMCs channels with generalized
likelihood decoding. We show that the typical error exponent of the RGV
ensemble is equal to the expurgated error exponent, provided that the RGV
codebook parameters are chosen appropriately. We also prove that the random
coding exponent converges in probability to the typical error exponent, and the
corresponding non-asymptotic concentration rates are derived. Our results show
that the decay rate of the lower tail is exponential while that of the upper
tail is double exponential above the expurgated error exponent. The explicit
dependence of the decay rates on the RGV distance functions is characterized.",2211.12238v1
2023-01-05,Improved Gilbert-Varshamov bounds for hopping cyclic codes and optical orthogonal codes,"Hopping cyclic codes (HCCs) are (non-linear) cyclic codes with the additional
property that the $n$ cyclic shifts of every given codeword are all distinct,
where $n$ is the code length. Constant weight binary hopping cyclic codes are
also known as optical orthogonal codes (OOCs). HCCs and OOCs have various
practical applications and have been studied extensively over the years.
  The main concern of this paper is to present improved Gilbert-Varshamov type
lower bounds for these codes, when the minimum distance is bounded below by a
linear factor of the code length. For HCCs, we improve the previously best
known lower bound of Niu, Xing, and Yuan by a linear factor of the code length.
For OOCs, we improve the previously best known lower bound of Chung, Salehi,
and Wei, and Yang and Fuja by a quadratic factor of the code length. As
by-products, we also provide improved lower bounds for frequency hopping
sequences sets and error-correcting weakly mutually uncorrelated codes. Our
proofs are based on tools from probability theory and graph theory, in
particular the McDiarmid's inequality on the concentration of Lipschitz
functions and the independence number of locally sparse graphs.",2301.02042v1
2023-01-11,Thou Shalt not Pick all Items if Thou are First: of Strategyproof and Fair Picking Sequences,"When allocating indivisible items to agents, it is known that the only
strategyproof mechanisms that satisfy a set of rather mild conditions are
constrained serial dictatorships: given a fixed order over agents, at each step
the designated agent chooses a given number of items (depending on her position
in the sequence). With these rules, also known as non-interleaving picking
sequences, agents who come earlier in the sequence have a larger choice of
items. However, this advantage can be compensated by a higher number of items
received by those who come later. How to balance priority in the sequence and
number of items received is a nontrivial question. We use a previous model,
parameterized by a mapping from ranks to scores, a social welfare functional,
and a distribution over preference profiles. For several meaningful choices of
parameters, we show that the optimal sequence can be computed in polynomial
time. Last, we give a simple procedure for eliciting scoring vectors and we
study the impact of the assignment from agents to positions on the ex-post
social welfare.",2301.06086v1
2023-01-17,Comparison of Optical and Electrical Links for Highly-Interconnected Systems,"As data rates for multi-gigabit serial interfaces within multi-node compute
systems approach and exceed 10 Gigabits per second (Gbps), board-to-board and
chip-to-chip optical signaling solutions become more attractive, particularly
for longer (e.g. 50-100 cm) links. The transition to optical signaling will
potentially allow new high performance compute (HPC) system architectures that
benefit from characteristics unique to optical links.
  To examine these characteristics, we built and tested several optical
demonstration vehicles; one based on dense wavelength division multiplexing
(DWDM), and others based on multiple point-to-point links carried across
multimode fibers. All test vehicles were constructed to evaluate applicability
to a multi-node compute system. Test results, combined with data from recent
research efforts are summarized and compared to equivalent electrical links and
the advantages and design characteristics unique to optical signaling are
identified.",2301.10169v1
2023-01-17,PWB Manufacturing Variability Effects on High Speed SerDes Links: Statistical Insights from Thousands of 4-Port SParameter Measurements,"Variability analysis is important in successfully deploying multi-gigabit
backplane printed wiring boards (PWBs) with growing numbers of high-speed
SerDes links. We discuss the need for large sample sizes to obtain accurate
variability estimates of SI metrics (eye height, phase skew, etc).
  Using a dataset of 11,961 S-parameters, we demonstrate statistical techniques
to extract accurate estimates of PWB SI performance variations. We cite
numerical examples illustrating how these variations may contribute to
underestimated or overestimated design criteria, causing unnecessary design
expense. Tabular summaries of performance variation and key findings of broad
interest to the general SI community are highlighted.",2301.10176v1
2023-01-17,"A Zero Sum Signaling Method for High Speed, Dense Parallel Bus Communications","Complex digital systems such as high performance computers (HPCs) make
extensive use of high-speed electrical interconnects, in routing signals among
processing elements, or between processing elements and memory. Despite
increases in serializer/deserializer (SerDes) and memory interface speeds,
there is demand for higher bandwidth busses in constrained physical spaces
which still mitigate simultaneous switching noise (SSN). The concept of zero
sum signaling utilizes coding across a data bus to allow the use of
single-ended buffers while still mitigating SSN, thereby reducing the number of
physical channels (e.g. circuit board traces) by nearly a factor of two when
compared with traditional differential signaling. Through simulation and
analysis of practical (non-ideal) data bus and power delivery network
architectures, we demonstrate the feasibility of zero sum signaling and compare
performance with that of traditional (single-ended and differential) methods.",2302.05427v1
2023-03-20,Dynamic Documentation for AI Systems,"AI documentation is a rapidly-growing channel for coordinating the design of
AI technologies with policies for transparency and accessibility. Calls to
standardize and enact documentation of algorithmic harms and impacts are now
commonplace. However, documentation standards for AI remain inchoate, and fail
to match the capabilities and social effects of increasingly impactful
architectures such as Large Language Models (LLMs). In this paper, we show the
limits of present documentation protocols, and argue for dynamic documentation
as a new paradigm for understanding and evaluating AI systems. We first review
canonical approaches to system documentation outside the context of AI,
focusing on the complex history of Environmental Impact Statements (EISs). We
next compare critical elements of the EIS framework to present challenges with
algorithmic documentation, which have inherited the limitations of EISs without
incorporating their strengths. These challenges are specifically illustrated
through the growing popularity of Model Cards and two case studies of
algorithmic impact assessment in China and Canada. Finally, we evaluate more
recent proposals, including Reward Reports, as potential components of fully
dynamic AI documentation protocols.",2303.10854v1
2023-01-17,"56 Gbps PCB Design Strategies for Clean, Low-Skew Channels","Although next generation (>28 Gbps) SerDes standards have been contemplated
for several years, it has not been clear whether PCB structures supporting 56
Gbps NRZ will be feasible and practical. In this paper, we assess a number of
specific PCB design strategies (related to pin-field breakouts, via stubs, and
fiber weave skew) both through simulation and through measurement of a wide
range of structures on a PCB test vehicle. We demonstrate that conventional
approaches in many cases will not be sufficient, but that modest
(manufacturable) design changes can enable low-skew 56 Gbps NRZ channels having
acceptable insertion and return loss.",2304.01909v1
2023-01-17,Inverting the SerDes Link Design Flow Process,"The traditional SerDes link simulation process begins with the extraction of
printed circuit board (PCB) physical stripline and via models, followed by
channel modeling and link simulation. We invert this simulation flow by first
creating link performance curves across an array of hypothetical channels
defined with specially-developed, high level, equation-based models; limited
physical extraction is later undertaken to relate PCB channel implementation to
these performance curves. These curves allow us to determine the system-level
SerDes channel requirements and to become better informed in choosing PCB
technologies for lower cost and easier manufacturability. The inverted modeling
process is very efficient, allowing for the rapid identification and avoidance
of problematic channel topologies and the study of other potentially useful
channel designs.",2304.01911v1
2023-01-17,Plated-Through-Hole Via Design Specifications for 112G Serial Links,"An earlier study of a high layer-count test board using plated-through-hole
(PTH) vias and a limited quantity of laser vias was shown to be capable of
supporting 112 Gb/s PAM-4 links (or equivalent signaling having 28 GHz
(Nyquist) bandwidth). This original board design was then rebuilt using a
different fabricator, and the test results revealed a significant decrease in
the bandwidth of the vias. These results led to the development of a set of
design specifications that PCB vendors can easily validate, which will ensure
that the use of high layer-count boards with PTH technology are viable for
emerging 112 Gb/s PAM-4 links.",2304.01913v1
2023-04-18,Sample-and-Hold Safety with Control Barrier Functions,"A common assumption on the deployment of safeguarding controllers on the
digital platform is that high sampling frequency translates to a small
violation of safety. This paper investigates and formalizes this assumption
through the lens of Input-to-State Safety. From this perspective, and
leveraging control barrier functions (CBFs), we propose an alternative solution
for maintaining safety of sample-and-hold controlled systems without any
violation to the original safe set. Our approach centers around modulating the
sampled control input in order to guarantee a more robust safety condition. We
analyze both the time-triggered and the event-triggered sample-and-hold
implementations, including the characterization of sampling frequency
requirements and trigger conditions. We demonstrate the effectiveness of our
approach in the context of adaptive cruise control through simulations.",2304.08685v2
2023-01-17,Efficient Circuit-Level Implementation of Knuth-Based Balanced and Nearly-Balanced Codes,"Coding schemes are often used in high-speed processor-processor or
processor-memory busses in digital systems. In particular, we have introduced
(in a 2012 DesignCon paper) a zero sum (ZS) signaling method which uses
balanced or nearly-balanced coding to reduce simultaneous switching noise (SSN)
in a single-ended bus to a level comparable to that of differential signaling.
While several balanced coding schemes are known, few papers exist that describe
the necessary digital hardware implementations of (known) balanced coding
schemes, and no algorithms had previously been developed for nearly-balanced
coding. In this work, we extend a known balanced coding scheme to accommodate
nearly-balanced coding and demonstrate a range of coding and decoding circuits
through synthesis in 65 nm CMOS. These hardware implementations have minimal
impact on the energy efficiency and area when compared to current
serializer/deserializers (SerDes) at clock rates which would support SerDes
integration.",2304.13497v1
2023-01-17,Capacitor Optimization in Power Distribution Networks Using Numerical Computation Techniques,"This paper presents a power distribution network (PDN) decoupling capacitor
optimization application with three primary goals: reduction of solution times
for large networks, development of flexible network scoring routines, and a
concentration strictly on achieving the best network performance. Example
optimizations are performed using broadband models of a printed circuit board
(PCB), a chip-package, on-die networks, and candidate capacitors. A novel
worst-case time-domain optimization technique is presented as an alternative to
the traditional frequency-domain approach. The trade-offs and criteria for
scoring the computed network are presented. The output is a recommended set of
capacitors which can then be applied to the product design.",2305.01540v1
2023-05-26,Sphaleron rate from a modified Backus-Gilbert inversion method,"We compute the sphaleron rate in quenched QCD for a temperature $T \simeq
1.24~T_c$ from the inversion of the Euclidean lattice time correlator of the
topological charge density. We explore and compare two different strategies:
one follows a new approach proposed in this study and consists in extracting
the rate from finite lattice spacing correlators, and then in taking the
continuum limit at fixed smoothing radius followed by a zero-smoothing
extrapolation; the other follows the traditional approach of extracting the
rate after performing such double extrapolation directly on the correlator. In
both cases the rate is obtained from a recently-proposed modification of the
standard Backus-Gilbert procedure. The two strategies lead to compatible
estimates within errors, which are then compared to previous results in the
literature at the same or similar temperatures; the new strategy permits to
obtain improved results, in terms of statistical and systematic uncertainties.",2305.17120v2
2023-07-21,Visibility graph-based covariance functions for scalable spatial analysis in nonconvex domains,"We present a new method for constructing valid covariance functions of
Gaussian processes over irregular nonconvex spatial domains such as water
bodies, where the geodesic distance agrees with the Euclidean distance only for
some pairs of points. Standard covariance functions based on geodesic distances
are not positive definite on such domains. Using a visibility graph on the
domain, we use the graphical method of ""covariance selection"" to propose a
class of covariance functions that preserve Euclidean-based covariances between
points that are connected through the domain. The proposed method preserves the
partially Euclidean nature of the intrinsic geometry on the domain while
maintaining validity (positive definiteness) and marginal stationarity over the
entire parameter space, properties which are not always fulfilled by existing
approaches to construct covariance functions on nonconvex domains. We provide
useful approximations to improve computational efficiency, resulting in a
scalable algorithm. We evaluate the performance of competing state-of-the-art
methods using simulation studies on a contrived nonconvex domain. The method is
applied to data regarding acidity levels in the Chesapeake Bay, showing its
potential for ecological monitoring in real-world spatial applications on
irregular domains.",2307.11941v2
2023-08-23,Consistency of common spatial estimators under spatial confounding,"This paper addresses the asymptotic performance of popular spatial regression
estimators on the task of estimating the effect of an exposure on an outcome in
the presence of an unmeasured spatially-structured confounder. This setting is
often referred to as ""spatial confounding."" We consider spline models, Gaussian
processes (GP), generalized least squares (GLS), and restricted spatial
regression (RSR) under two data generation processes: one where the confounder
is a fixed effect and one where it is a random effect. The literature on
spatial confounding is confusing and contradictory, and our results correct and
clarify several misunderstandings. We first show that, like an unadjusted OLS
estimator, RSR is asymptotically biased under any spatial confounding scenario.
We then prove a novel result on the consistency of the GLS estimator under
spatial confounding. We finally prove that estimators like GLS, GP, and
splines, that are consistent under confounding by a fixed effect will also be
consistent under confounding by a random effect. We conclude that, contrary to
much of the recent literature on spatial confounding, traditional estimators
based on partially linear models are amenable to estimating effects in the
presence of spatial confounding. We support our theoretical arguments with
simulation studies.",2308.12181v1
2023-09-19,Stochastic control of the Landau-Lifshitz-Gilbert equation,"We consider the stochastic Landau-Lifshitz-Gilbert equation in dimension 1. A
control process is added to the effective field. We show the existence of a
weak martingale solution for the resulting controlled equation. The proof uses
the classical Faedo-Galerkin approximation, along with the Jakubowski version
of the Skorohod Theorem. We then show pathwise uniqueness for the obtained
solution, which is then coupled with the theory of Yamada and Watanabe to give
the existence of a unique strong solution. We then show, using some semigroup
techniques that the obtained solution satisfies the maximum regularity. We then
show the existence of an optimal control. A main ingredient of the proof is
using the compact embedding of a space into itself, albeit with the weak
topology.",2309.10260v1
2023-10-13,Unified framework of the microscopic Landau-Lifshitz-Gilbert equation and its application to Skyrmion dynamics,"The Landau-Lifshitz-Gilbert (LLG) equation is widely used to describe
magnetization dynamics. We develop a unified framework of the microscopic LLG
equation based on the nonequilibrium Green's function formalism. We present a
unified treatment for expressing the microscopic LLG equation in several
limiting cases, including the adiabatic, inertial, and nonadiabatic limits with
respect to the precession frequency for a magnetization with fixed magnitude,
as well as the spatial adiabatic limit for the magnetization with slow
variation in both its magnitude and direction. The coefficients of those terms
in the microscopic LLG equation are explicitly expressed in terms of
nonequilibrium Green's functions. As a concrete example, this microscopic
theory is applied to simulate the dynamics of a magnetic Skyrmion driven by
quantum parametric pumping. Our work provides a practical formalism of the
microscopic LLG equation for exploring magnetization dynamics.",2310.08807v1
2023-10-18,Parallel-in-Time Integration of the Landau-Lifshitz-Gilbert Equation with the Parallel Full Approximation Scheme in Space and Time,"Speeding up computationally expensive problems, such as numerical simulations
of large micromagnetic systems, requires efficient use of parallel computing
infrastructures. While parallelism across space is commonly exploited in
micromagnetics, this strategy performs poorly once a minimum number of degrees
of freedom per core is reached. We use magnum.pi, a finite-element
micromagnetic simulation software, to investigate the Parallel Full
Approximation Scheme in Space and Time (PFASST) as a space- and time-parallel
solver for the Landau-Lifshitz-Gilbert equation (LLG). Numerical experiments
show that PFASST enables efficient parallel-in-time integration of the LLG,
significantly improving the speedup gained from using a given number of cores
as well as allowing the code to scale beyond spatial limits.",2310.11819v1
2023-12-29,Chebyshev and Backus-Gilbert reconstruction for inclusive semileptonic $B_{(s)}$-meson decays from Lattice QCD,"We present a study on the nonperturbative calculation of observables for
inclusive semileptonic decays of $B_{(s)}$ mesons using lattice QCD. We focus
on the comparison of two different methods to analyse the lattice data of
Euclidean correlation functions, specifically Chebyshev and Backus-Gilbert
approaches. This type of computation may eventually provide new insight into
the long-standing tension between the inclusive and exclusive determinations of
the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements $|V_{cb}|$ and $|V_{ub}|$.
We report the results from a pilot lattice computation for the decay $B_s
\rightarrow X_c \, l\nu_l$, where the valence quark masses are approximately
tuned to their physical values using the relativistic-heavy quark action for
the $b$ quark and the domain-wall formalism for the other valence quarks. We
address the computation of the total decay rate as well as leptonic and
hadronic moments, discussing similarities and differences between the two
analysis techniques.",2312.17401v1
2024-02-22,Gilbert-Varshamov Bound for Codes in $L_1$ Metric using Multivariate Analytic Combinatorics,"Analytic combinatorics in several variables refers to a suite of tools that
provide sharp asymptotic estimates for certain combinatorial quantities. In
this paper, we apply these tools to determine the Gilbert--Varshamov lower
bound on the rate of optimal codes in $L_1$ metric. Several different code
spaces are analyzed, including the simplex and the hypercube in $\mathbb{Z^n}$,
all of which are inspired by concrete data storage and transmission models such
as the sticky insertion channel, the permutation channel, the adjacent
transposition (bit-shift) channel, the multilevel flash memory channel, etc.",2402.14712v1
2024-02-28,Embodied Supervision: Haptic Display of Automation Command to Improve Supervisory Performance,"A human operator using a manual control interface has ready access to their
own command signal, both by efference copy and proprioception. In contrast, a
human supervisor typically relies on visual information alone. We propose
supplying a supervisor with a copy of the operators command signal,
hypothesizing improved performance, especially when that copy is provided
through haptic display. We experimentally compared haptic with visual access to
the command signal, quantifying the performance of N equals 10 participants
attempting to determine which of three reference signals was being tracked by
an operator. Results indicate an improved accuracy in identifying the tracked
target when haptic display was available relative to visual display alone. We
conjecture the benefit follows from the relationship of haptics to the
supervisor's own experience, perhaps muscle memory, as an operator.",2402.18707v1
2024-03-14,Quantum analog of Landau-Lifshitz-Gilbert dynamics,"The Landau-Lifshitz-Gilbert (LLG) and Landau-Lifshitz (LL) equations play an
essential role for describing the dynamics of magnetization in solids. While a
quantum analog of the LL dynamics has been proposed in [Phys. Rev. Lett. 110,
147201 (2013)], the corresponding quantum version of LLG remains unknown. Here,
we propose such a quantum LLG equation that inherently conserves purity of the
quantum state. We examine the quantum LLG dynamics of a dimer consisting of two
interacting spin-1/2 particles. Our analysis reveals that, in the case of
ferromagnetic coupling, the evolution of initially uncorrelated spins mirrors
the classical LLG dynamics. However, in the antiferromagnetic scenario, we
observe pronounced deviations from classical behavior, underscoring the unique
dynamics of becoming a spinless state, which is non-locally correlated.
Moreover, when considering spins that are initially correlated, our study
uncovers an unusual form of transient quantum correlation dynamics, which
differ significantly from what is typically seen in open quantum systems.",2403.09255v1
2024-03-15,Identification and estimation of mediational effects of longitudinal modified treatment policies,"We demonstrate a comprehensive semiparametric approach to causal mediation
analysis, addressing the complexities inherent in settings with longitudinal
and continuous treatments, confounders, and mediators. Our methodology utilizes
a nonparametric structural equation model and a cross-fitted sequential
regression technique based on doubly robust pseudo-outcomes, yielding an
efficient, asymptotically normal estimator without relying on restrictive
parametric modeling assumptions. We are motivated by a recent scientific
controversy regarding the effects of invasive mechanical ventilation (IMV) on
the survival of COVID-19 patients, considering acute kidney injury (AKI) as a
mediating factor. We highlight the possibility of ""inconsistent mediation,"" in
which the direct and indirect effects of the exposure operate in opposite
directions. We discuss the significance of mediation analysis for scientific
understanding and its potential utility in treatment decisions.",2403.09928v1
2024-03-22,Two-scale Analysis for Multiscale Landau-Lifshitz-Gilbert Equation: Theory and Numerical Methods,"This paper discusses the theory and numerical method of two-scale analysis
for the multiscale Landau-Lifshitz-Gilbert equation in composite ferromagnetic
materials. The novelty of this work can be summarized in three aspects:
Firstly, the more realistic and complex model is considered, including the
effects of the exchange field, anisotropy field, stray field, and external
magnetic field. The explicit convergence orders in the $H^1$ norm between the
classical solution and the two-scale solution are obtained. Secondly, we
propose a robust numerical framework, which is employed in several
comprehensive experiments to validate the convergence results for the Periodic
and Neumann problems. Thirdly, we design an improved implicit numerical scheme
to reduce the required number of iterations and relaxes the constraints on the
time step size, which can significantly improve computational efficiency.
Specifically, the projection and the expansion methods are given to overcome
the inherent non-consistency in the initial data between the multiscale problem
and homogenized problem.",2403.14957v1
2020-11-30,Role of Compressive Viscosity and Thermal Conductivity on the Damping of Slow Waves in the Coronal Loops With and Without Heating-Cooling Imbalance,"In the present paper, we derive a new dispersion relation for slow
magnetoacoustic waves invoking the effect of thermal conductivity, compressive
viscosity, radiation and unknown heating term along with the consideration of
heating cooling imbalance from linearized MHD equations. We solve the general
dispersion relation to understand role of compressive viscosity and thermal
conductivity in damping of the slow waves in coronal loops with and without
heating cooling imbalance. We have analyzed wave damping for the range of loop
length $L$=50-500 Mm, temperature $T$=5-30 MK, and density
$\rho$=10$^{-11}$-10$^{-9}$ kg m$^{-3}$. It was found that inclusion of
compressive viscosity along with thermal conductivity significantly enhances
the damping of fundamental mode oscillations in shorter (e.g., $L$=50 Mm) and
super-hot ($T>$10 MK) loops. However, role of the viscosity in damping is
insignificant in longer (e.g., $L$=500 Mm) and hot loops (T$\leq$10 MK) where,
instead, thermal conductivity along with the presence of heating cooling
imbalance plays a dominant role. For the shorter loops at the super-hot regime
of the temperature, increment in loop density substantially enhances damping of
the fundamental modes due to thermal conductivity when the viscosity is absent,
however, when the compressive viscosity is added the increase in density
substantially weakens damping. Thermal conductivity alone is found to play a
dominant role in longer loops at lower temperatures (T$\leq$10 MK), while
compressive viscosity dominates in damping at super-hot temperatures ($T>$10
MK) in shorter loops. The predicted scaling law between damping time ($\tau$)
and wave period ($P$) is found to better match to observed SUMER oscillations
when heating cooling imbalance is taken into account in addition to thermal
conductivity and compressive viscosity for the damping of the fundamental slow
mode oscillations.",2011.14519v2
1993-06-22,Weakly Damped Modes in Star Clusters and Galaxies,"A perturber may excite a coherent mode in a star cluster or galaxy. If the
stellar system is stable, it is commonly assumed that such a mode will be
strongly damped and therefore of little practical consequence other than
redistributing momentum and energy deposited by the perturber. This paper
demonstrates that this assumption is false; weakly damped modes exist and may
persist long enough to have observable consequences. To do this, a method for
investigating the dispersion relation for spherical stellar systems and for
locating weakly damped modes in particular is developed and applied to King
models of varying concentration. This leads to the following remarkable result:
King models exhibit {\it very} weakly damped $m=1$ modes over a wide range of
concentration ($0.67\le c\le1.5$ have been examined). The predicted damping
time is tens to hundreds of crossing times. This mode causes the peak density
to shift from and slowly revolve about the initial center. The existence of the
mode is supported by n-body simulation. Higher order modes and possible
astronomical consequences are discussed. Weakly damped modes, for example, may
provide a natural explanation for observed discrepancies between density and
kinematic centers in galaxies, the location of velocity cusps due to massive
black holes, and $m=1$ disturbances of disks embedded in massive halos.
Gravitational shocking may excite the $m=1$ mode in globular clusters, which
could modify their subsequent evolution and displace the positions of exotic
remnants.",9306020v1
1997-12-03,On the Evolution of Damped Lyman Alpha Systems to Galactic Disks,"The mean metallicity of the thick disk of the Galaxy is 0.5 dex higher than
that of the damped Lyman alpha systems. This has been interpreted to argue that
stars in the former do not arise out of gas in the latter. Using new
metallicity and H I column-density data we show the metal-rich damped systems
do contain sufficient baryons at the thick-disk metallicity to account for the
stellar masses of thick disks. Comparing our kinematic data with the
metallicities we show that damped Lyman alpha systems exhibiting the largest
profile velocity widths span a narrow range of high metallicities, while
systems with small velocity widths span a wider range of metallicities. This is
naturally explained by passage of the damped Lyman alpha sightlines through
rapidly rotating disks with negative radial gradients in metallicity. The
systematically lower N(H I) of systems with high velocity widths indicates (a)
the gaseous disks have centrally located holes, and (b) an apparent
inconsistency with the protogalactic clump model for damped Lyman alpha
systems. The higher metallicity of systems with low N(H I) further implies that
stars rather than gas dominate the baryonic content of the most metal-rich
damped systems.",9712050v1
1998-10-23,Chemical Abundances of the Damped Lya Systems at z>1.5,"We present chemical abundance measurements for 19 damped lya systems observed
with HIRES on the 10m W.M. Keck Telescope. Our principal goal is to investigate
the abundance patterns of the damped systems and thereby determine the
underlying physical processes which dominate their chemical evolution. We place
particular emphasis on gauging the relative importance of two complementary
effects often invoked to explain the damped lya abundances: (1) nucleosynthetic
enrichment from Type II supernovae and (2) an ISM-like dust depletion pattern.
  Similar to the principal results of Lu et al. (1996), our observations lend
support both for dust depletion and Type II SN enrichment. Specifically, the
observed overabundance of Zn/Fe and underabundance of Ni/Fe relative to solar
abundances suggest significant dust depletion within the damped lya systems.
Meanwhile, the relative abundances of Al, Si, and Cr vs. Fe are consistent with
both dust depletion and Type II supernova enrichment. Our measurements of Ti/Fe
and the Mn/Fe measurements from Lu et al. (1996), however, cannot be explained
by dust depletion and indicate an underlying Type II SN pattern. Finally, the
observed values of [S/Fe] are inconsistent with the combined effects of dust
depletion and the nucleosynthetic yields expected for Type II supernovae. This
last result emphasizes the need for another physical process to explain the
damped lya abundance patterns.
  We also examine the metallicity of the damped lya systems both with respect
to Zn/H and Fe/H. Our results confirm previous surveys by Pettini and
collaborators, i.e., [<Zn/H>] = -1.15 +/- 0.15 dex. [abridged]",9810381v1
2002-04-03,The role of damped Alfven waves on magnetospheric accretion models of young stars,"We examine the role of Alfven wave damping in heating the plasma in the
magnetic funnels of magnetospheric accretion models of young stars. We study
four different damping mechanisms of the Alfven waves: nonlinear, turbulent,
viscous-resistive and collisional. Two different possible origins for the
Alfven waves are discussed: 1) Alfven waves generated at the surface of the
star by the shock produced by the infalling matter; and 2) Alfven waves
generated locally in the funnel by the Kelvin-Helmholtz instability. We find
that, in general, the damping lengths are smaller than the tube length. Since
thermal conduction in the tube is not efficient, Alfven waves generated only at
the star's surface cannot heat the tube to the temperatures necessary to fit
the observations. Only for very low frequency Alfven waves ~10^{-5} the ion
cyclotron frequency, is the viscous-resistive damping length greater than the
tube length. In this case, the Alfven waves produced at the surface of the star
are able to heat the whole tube. Otherwise, local production of Alfven waves is
required to explain the observations. The turbulence level is calculated for
different frequencies for optically thin and thick media. We find that
turbulent velocities varies greatly for different damping mechanisms, reaching
\~100 km s^{-1} for the collisional damping of small frequency waves.",0204056v1
2009-09-19,Resonantly Damped Kink Magnetohydrodynamic Waves in a Partially Ionized Filament Thread,"Transverse oscillations of solar filament and prominence threads have been
frequently reported. These oscillations have the common features of being of
short period (2-10 min) and being damped after a few periods. Kink
magnetohydrodynamic (MHD) wave modes have been proposed as responsible for the
observed oscillations, whereas resonant absorption in the Alfven continuum and
ion-neutral collisions are the best candidates to be the damping mechanisms.
Here, we study both analytically and numerically the time damping of kink MHD
waves in a cylindrical, partially ionized filament thread embedded in a coronal
environment. The thread model is composed of a straight and thin, homogeneous
filament plasma, with a transverse inhomogeneous transitional layer where the
plasma physical properties vary continuously from filament to coronal
conditions. The magnetic field is homogeneous and parallel to the thread axis.
We find that the kink mode is efficiently damped by resonant absorption for
typical wavelengths of filament oscillations, the damping times being
compatible with the observations. Partial ionization does not affect the
process of resonant absorption, and the filament plasma ionization degree is
only important for the damping for wavelengths much shorter than those
observed. To our knowledge, this is the first time that the phenomenon of
resonant absorption is studied in a partially ionized plasma.",0909.3599v1
2009-10-15,Time damping of non-adiabatic magnetohydrodynamic waves in a partially ionized prominence plasma: Effect of helium,"Prominences are partially ionized, magnetized plasmas embedded in the solar
corona. Damped oscillations and propagating waves are commonly observed. These
oscillations have been interpreted in terms of magnetohydrodynamic (MHD) waves.
Ion-neutral collisions and non-adiabatic effects (radiation losses and thermal
conduction) have been proposed as damping mechanisms. We study the effect of
the presence of helium on the time damping of non-adiabatic MHD waves in a
plasma composed by electrons, protons, neutral hydrogen, neutral helium (He I),
and singly ionized helium (He II) in the single-fluid approximation. The
dispersion relation of linear non-adiabatic MHD waves in a homogeneous,
unbounded, and partially ionized prominence medium is derived. The period and
the damping time of Alfven, slow, fast, and thermal waves are computed. A
parametric study of the ratio of the damping time to the period with respect to
the helium abundance is performed. The efficiency of ion-neutral collisions as
well as thermal conduction is increased by the presence of helium. However, if
realistic abundances of helium in prominences (~10%) are considered, this
effect has a minor influence on the wave damping. The presence of helium can be
safely neglected in studies of MHD waves in partially ionized prominence
plasmas.",0910.2883v1
2009-12-21,The effect of longitudinal flow on resonantly damped kink oscillations,"The most promising mechanism acting towards damping the kink oscillations of
coronal loops is resonant absorption. In this context most of previous studies
neglected the effect of the obvious equilibrium flow along magnetic field
lines. The flows are in general sub-Alfv\'enic and hence comparatively slow.
Here we investigate the effect of an equilibrium flow on the resonant
absorption of linear kink MHD waves in a cylindrical magnetic flux tube with
the aim of determining the changes in the frequency of the forward and backward
propagating waves and in the modification of the damping times due to the flow.
A loop model with both the density and the longitudinal flow changing in the
radial direction is considered. We use the thin tube thin boundary (TTTB)
approximation in order to calculate the damping rates. The full resistive
eigenvalue problem is also solved without assuming the TTTB approximation.
Using the small ratio of flow and Alfv\'en speeds we derive simple analytical
expressions to the damping rate. The analytical expressions are in good
agreement with the resistive eigenmode calculations. Under typical coronal
conditions the effect of the flow on the damped kink oscillations is small when
the characteristic scale of the density layer is similar or smaller than the
characteristic width of the velocity layer. However, in the opposite situation
the damping rates can be significantly altered, specially for the backward
propagating wave which is undamped while the forward wave is overdamped.",0912.4136v1
2010-07-12,Seismology of Standing Kink Oscillations of Solar Prominence Fine Structures,"We investigate standing kink magnetohydrodynamic (MHD) oscillations in a
prominence fine structure modeled as a straight and cylindrical magnetic tube
only partially filled with the prominence material, and with its ends fixed at
two rigid walls representing the solar photosphere. The prominence plasma is
partially ionized and a transverse inhomogeneous transitional layer is included
between the prominence thread and the coronal medium. Thus, ion-neutral
collisions and resonant absorption are the considered damping mechanisms.
Approximate analytical expressions of the period, the damping time, and their
ratio are derived for the fundamental mode in the thin tube and thin boundary
approximations. We find that the dominant damping mechanism is resonant
absorption, which provides damping ratios in agreement with the observations,
whereas ion-neutral collisions are irrelevant for the damping. The values of
the damping ratio are independent of both the prominence thread length and its
position within the magnetic tube, and coincide with the values for a tube
fully filled with the prominence plasma. The implications of our results in the
context of the MHD seismology technique are discussed, pointing out that the
reported short-period (2 - 10 min) and short-wavelength (700 - 8,000 km) thread
oscillations may not be consistent with a standing mode interpretation and
could be related to propagating waves. Finally, we show that the inversion of
some prominence physical parameters, e.g., Alfv\'en speed, magnetic field
strength, transverse inhomogeneity length-scale, etc., is possible using
observationally determined values of the period and damping time of the
oscillations along with the analytical approximations of these quantities.",1007.1959v2
2012-10-30,Mode- and size-dependent Landau-Lifshitz damping in magnetic nanostructures: Evidence for non-local damping,"We demonstrate a strong dependence of the effective damping on the nanomagnet
size and the particular spin-wave mode that can be explained by the theory of
intralayer transverse-spin-pumping. The effective Landau-Lifshitz damping is
measured optically in individual, isolated nanomagnets as small as 100 nm. The
measurements are accomplished by use of a novel heterodyne magneto-optical
microwave microscope with unprecedented sensitivity. Experimental data reveal
multiple standing spin-wave modes that we identify by use of micromagnetic
modeling as having either localized or delocalized character, described
generically as end- and center-modes. The damping parameter of the two modes
depends on both the size of the nanomagnet as well as the particular spin-wave
mode that is excited, with values that are enhanced by as much as 40% relative
to that measured for an extended film. Contrary to expectations based on the ad
hoc consideration of lithography-induced edge damage, the damping for the
end-mode decreases as the size of the nanomagnet decreases. The data agree with
the theory for damping caused by the flow of intralayer transverse
spin-currents driven by the magnetization curvature. These results have serious
implications for the performance of nanoscale spintronic devices such as
spin-torque-transfer magnetic random access memory.",1210.8118v3
2012-11-21,Kinetic theory of surface plasmon polariton in semiconductor nanowires,"Based on the semiclassical model Hamiltonian of the surface plasmon polariton
and the nonequilibrium Green-function approach, we present a microscopic
kinetic theory to study the influence of the electron scattering on the
dynamics of the surface plasmon polariton in semiconductor nanowires. The
damping of the surface plasmon polariton originates from the resonant
absorption by the electrons (Landau damping), and the corresponding damping
exhibits size-dependent oscillations and distinct temperature dependence
without any scattering. The scattering influences the damping by introducing a
broadening and a shifting to the resonance. To demonstrate this, we investigate
the damping of the surface plasmon polariton in InAs nanowires in the presence
of the electron-impurity, electron-phonon and electron-electron Coulomb
scatterings. The main effect of the electron-impurity and electron-phonon
scatterings is to introduce a broadening, whereas the electron-electron Coulomb
scattering can not only cause a broadening, but also introduce a shifting to
the resonance. For InAs nanowires under investigation, the broadening due to
the electron-phonon scattering dominates. As a result, the scattering has a
pronounced influence on the damping of the surface plasmon polariton: The
size-dependent oscillations are smeared out and the temperature dependence is
also suppressed in the presence of the scattering. These results demonstrate
the the important role of the scattering on the surface plasmon polariton
damping in semiconductor nanowires.",1211.5055v2
2013-11-12,Damping filter method for obtaining spatially localized solutions,"Spatially localized structures are key components of turbulence and other
spatio-temporally chaotic systems. From a dynamical systems viewpoint, it is
desirable to obtain corresponding exact solutions, though their existence is
not guaranteed. A damping filter method is introduced to obtain variously
localized solutions, and adopted into two typical cases. This method introduces
a spatially selective damping effect to make a good guess at the exact
solution, and we can obtain an exact solution through a continuation with the
damping amplitude. First target is a steady solution to Swift-Hohenberg
equation, which is a representative of bi-stable systems in which localized
solutions coexist, and a model for span-wisely localized cases. Not only
solutions belonging to the well-known snaking branches but also those belonging
to an isolated branch known as ""isolas"" are found with a continuation paths
between them in phase space extended with the damping amplitude. This indicates
that this spatially selective excitation mechanism has an advantage in
searching spatially localized solutions. Second target is a spatially localized
traveling-wave solution to Kuramoto-Sivashinsky equation, which is a model for
stream-wisely localized cases. Since the spatially selective damping effect
breaks Galilean and translational invariances, the propagation velocity cannot
be determined uniquely while the damping is active, and a singularity arises
when these invariances are recovered. We demonstrate that this singularity can
be avoided by imposing a simple condition, and a localized traveling-wave
solution is obtained with a specific propagation speed.",1311.2792v2
2014-09-19,Highly confined low-loss plasmons in graphene-boron nitride heterostructures,"Graphene plasmons were predicted to possess ultra-strong field confinement
and very low damping at the same time, enabling new classes of devices for deep
subwavelength metamaterials, single-photon nonlinearities, extraordinarily
strong light-matter interactions and nano-optoelectronic switches. While all of
these great prospects require low damping, thus far strong plasmon damping was
observed, with both impurity scattering and many-body effects in graphene
proposed as possible explanations. With the advent of van der Waals
heterostructures, new methods have been developed to integrate graphene with
other atomically flat materials. In this letter we exploit near-field
microscopy to image propagating plasmons in high quality graphene encapsulated
between two films of hexagonal boron nitride (h-BN). We determine dispersion
and particularly plasmon damping in real space. We find unprecedented low
plasmon damping combined with strong field confinement, and identify the main
damping channels as intrinsic thermal phonons in the graphene and dielectric
losses in the h-BN. The observation and in-depth understanding of low plasmon
damping is the key for the development of graphene nano-photonic and
nano-optoelectronic devices.",1409.5674v1
2015-09-02,Energy Dependence of Synchrotron X-Ray Rims in Tycho's Supernova Remnant,"Several young supernova remnants exhibit thin X-ray bright rims of
synchrotron radiation at their forward shocks. Thin rims require strong
magnetic field amplification beyond simple shock compression if rim widths are
only limited by electron energy losses. But, magnetic field damping behind the
shock could produce similarly thin rims with less extreme field amplification.
Variation of rim width with energy may thus discriminate between competing
influences on rim widths. We measured rim widths around Tycho's supernova
remnant in 5 energy bands using an archival 750 ks Chandra observation. Rims
narrow with increasing energy and are well described by either loss-limited or
damped scenarios, so X-ray rim width-energy dependence does not uniquely
specify a model. But, radio counterparts to thin rims are not loss-limited and
better reflect magnetic field structure. Joint radio and X-ray modeling favors
magnetic damping in Tycho's SNR with damping lengths ~1--5% of remnant radius
and magnetic field strengths ~50--400 $\mu$G assuming Bohm diffusion. X-ray rim
widths are ~1% of remnant radius, somewhat smaller than inferred damping
lengths. Electron energy losses are important in all models of X-ray rims,
suggesting that the distinction between loss-limited and damped models is
blurred in soft X-rays. All loss-limited and damping models require magnetic
fields $\gtrsim$ 20 $\mu$G, affirming the necessity of magnetic field
amplification beyond simple compression.",1509.00877v1
2016-02-02,Forward Modelling of Propagating Slow Waves in Coronal Loops and Their Frequency-Dependent Damping,"Propagating slow waves in coronal loops exhibit a damping which depends upon
the frequency of the waves. In this study we aim to investigate the
relationship of the damping length (L$_d$) with the frequency of the
propagating wave. We present a 3-D coronal loop model with uniform density and
temperature and investigate the frequency dependent damping mechanism for the
four chosen wave periods. We include the thermal conduction to damp the waves
as they propagate through the loop. The numerical model output has been forward
modelled to generate synthetic images of SDO/AIA 171 \r{A} and 193 \r{A}
channels. The use of forward modelling, which incorporates the atomic emission
properties into the intensity images, allows us to directly compare our results
with the real observations. The results show that the damping lengths vary
linearly with the periods. We also measure the contributions of the emission
properties on the damping lengths by using density values from the simulation.
In addition to that} we have also calculated the theoretical dependence of
L$_d$ with wave periods and showed that it is consistent with the results we
obtained from the numerical modelling and earlier observations.",1602.00787v1
2016-05-11,Damping of prominence longitudinal oscillations due to mass accretion,"We study the damping of longitudinal oscillations of a prominence thread
caused by the mass accretion. In this model we considered a thin curved
magnetic tube filled with the plasma. The parts of the tube at the two sides of
the thread are filled with hot rarefied plasma. We assume that there are flows
of rarefied plasma toward the thread caused by the plasma evaporation at the
magnetic tube footpoints. Our main assumption is that the hot plasma is
instantaneously accommodated by the thread when it arrives at the thread, and
its temperature and density become equal to those of the thread. Then we derive
the system of ordinary differential equations describing the thread dynamics.
We consider linear and nonlinear oscillation. The nonlinearity reduces the
damping time, however this reduction is small. The damping time is inversely
proportional to the accretion rate. We also obtain that the oscillation periods
decrease with time. However even for the largest initial oscillation amplitude
considered in our article the period reduction does not exceed 20%. We conclude
that the mass accretion can damp the motion of the threads rapidly. Thus, this
mechanism can explain the observed strong damping of large-amplitude
longitudinal oscillations. In addition, the damping time can be used to
determine the mass accretion rate and indirectly the coronal heating.",1605.03376v1
2016-11-17,Inductive detection of field-like and damping-like AC inverse spin-orbit torques in ferromagnet/normal metal bilayers,"Functional spintronic devices rely on spin-charge interconversion effects,
such as the reciprocal processes of electric field-driven spin torque and
magnetization dynamics-driven spin and charge flow. Both damping-like and
field-like spin-orbit torques have been observed in the forward process of
current-driven spin torque and damping-like inverse spin-orbit torque has been
well-studied via spin pumping into heavy metal layers. Here we demonstrate that
established microwave transmission spectroscopy of ferromagnet/normal metal
bilayers under ferromagnetic resonance can be used to inductively detect the AC
charge currents driven by the inverse spin-charge conversion processes. This
technique relies on vector network analyzer ferromagnetic resonance (VNA-FMR)
measurements. We show that in addition to the commonly-extracted spectroscopic
information, VNA-FMR measurements can be used to quantify the magnitude and
phase of all AC charge currents in the sample, including those due to spin
pumping and spin-charge conversion. Our findings reveal that
Ni$_{80}$Fe$_{20}$/Pt bilayers exhibit both damping-like and field-like inverse
spin-orbit torques. While the magnitudes of both the damping-like and
field-like inverse spin-orbit torque are of comparable scale to prior reported
values for similar material systems, we observed a significant dependence of
the damping-like magnitude on the order of deposition. This suggests interface
quality plays an important role in the overall strength of the damping-like
spin-to-charge conversion.",1611.05798v2
2016-12-30,Spectroscopic evidence of Alfvén wave damping in the off-limb solar corona,"We investigate off-limb active region and quiet Sun corona using
spectroscopic data. Active region is clearly visible in several spectral lines
formed in the temperature range of 1.1--2.8 MK. We derive electron number
density using line ratio method, and non-thermal velocity in the off-limb
region up to the distance of 140 Mm. We compare density scale heights derived
from several spectral line pairs with expected scale heights as per hydrostatic
equilibrium model. Using several isolated and unblended spectral line profiles,
we estimate non-thermal velocities in active region and quiet Sun. Non-thermal
velocities obtained from warm lines in active region first show increase and
later show either decrease or almost constant value with height in the far
off-limb region, whereas hot lines show consistent decrease. However, in the
quiet Sun region, non-thermal velocities obtained from various spectral lines
show either gradual decrease or remain almost constant with height. Using these
obtained parameters, we further calculate Alfv\'en wave energy flux in the both
active and quiet Sun regions. We find significant decrease in wave energy
fluxes with height, and hence provide evidence of Alfv\'en wave damping.
Furthermore, we derive damping lengths of Alfv\'en waves in the both regions
and find them to be in the range of 25-170 Mm. Different damping lengths
obtained at different temperatures may be explained as either possible
temperature dependent damping or measurements obtained in different coronal
structures formed at different temperatures along the line-of-sight.
Temperature dependent damping may suggest some role of thermal conduction in
the damping of Alfv\'en waves in the lower corona.",1612.09551v2
2017-01-04,Controlling plasmon modes and damping in buckled two-dimensional material open systems,"Full ranges of both hybrid plasmon-mode dispersions and their damping are
studied systematically by our recently developed mean-field theory in open
systems involving a conducting substrate and a two-dimensional (2D) material
with a buckled honeycomb lattice, such as silicene, germanene, and a group
\rom{4} dichalcogenide as well. In this hybrid system, the single plasmon mode
for a free-standing 2D layer is split into one acoustic-like and one
optical-like mode, leading to a dramatic change in the damping of plasmon
modes. In comparison with gapped graphene, critical features associated with
plasmon modes and damping in silicene and molybdenum disulfide are found with
various spin-orbit and lattice asymmetry energy bandgaps, doping types and
levels, and coupling strengths between 2D materials and the conducting
substrate. The obtained damping dependence on both spin and valley degrees of
freedom is expected to facilitate measuring the open-system dielectric property
and the spin-orbit coupling strength of individual 2D materials. The unique
linear dispersion of the acoustic-like plasmon mode introduces additional
damping from the intraband particle-hole modes which is absent for a
free-standing 2D material layer, and the use of molybdenum disulfide with a
large bandgap simultaneously suppresses the strong damping from the interband
particle-hole modes.",1701.01084v1
2017-04-05,Stimulated Brillouin scattering behaviors in different species ignition hohlraum plasmas in high-temperature and high-density region,"The presence of multiple ion species can add additional branches to the IAW
dispersion relation and change the Landau damping significantly. Different IAW
modes excited by stimulated Brillouin scattering (SBS) and different SBS
behaviors in several typical ignition hohlraum plasmas in the high-temperature
and high-density region have been researched by Vlasov-Maxwell simulation. The
slow mode in HeH or CH plasmas is the least damped mode and will be excited in
SBS, while the fast mode in AuB plasmas is the least damped mode and will be
excited in SBS. Due to strong Landau damping, the SBS in H or HeH plasmas is
strong convective instability, while the SBS in AuB plasmas is absolute
instability due to the weak Landau damping. However, although the SBS in CH
plasmas is weak convective instability in the linear theory, the SBS will
transform into absolute instability due to decreasing linear Landau damping by
particles trapping. These results give a detail research of the IAW modes
excitation and the properties of SBS in different species plasmas, thus
providing the possibility of controlling SBS by increasing the linear Landau
damping of the IAW by changing ion species.",1704.02317v1
2017-06-29,Resonant Absorption of Axisymmetric Modes in Twisted Magnetic Flux Tubes,"It has been shown recently that magnetic twist and axisymmetric MHD modes are
ubiquitous in the solar atmosphere and therefore, the study of resonant
absorption for these modes have become a pressing issue as it can have
important consequences for heating magnetic flux tubes in the solar atmosphere
and the observed damping. In this investigation, for the first time, we
calculate the damping rate for axisymmetric MHD waves in weakly twisted
magnetic flux tubes. Our aim is to investigate the impact of resonant damping
of these modes for solar atmospheric conditions. This analytical study is based
on an idealized configuration of a straight magnetic flux tube with a weak
magnetic twist inside as well as outside the tube. By implementing the
conservation laws derived by \cite{Sakurai:1991aa} and the analytic solutions
for weakly twisted flux tubes obtained recently by \cite{Giagkiozis:2015apj},
we derive a dispersion relation for resonantly damped axisymmetric modes in the
spectrum of the Alfv\'{e}n continuum. We also obtain an insightful analytical
expression for the damping rate in the long wavelength limit. Furthermore, it
shown that both the longitudinal magnetic field and the density, which are
allowed to vary continuously in the inhomogeneous layer, have a significant
impact on the damping time. Given the conditions in the solar atmosphere,
resonantly damped axisymmetric modes are highly likely to be ubiquitous and
play an important role in energy dissipation.
  We also suggest that given the character of these waves, it is likely that
they have already been observed in the guise of Alfv\'{e}n waves.",1706.09665v1
2017-08-16,Damping of an oscillating scalar field indirectly coupled to a thermal bath,"The damping process of a homogeneous oscillating scalar field that indirectly
interacts with a thermal bath through a mediator field is investigated over a
wide range of model parameters. We consider two types of mediator fields, those
that can decay to the thermal bath and those that are individually stable but
pair annihilate. The former case has been extensively studied in the literature
by treating the damping as a local effect after integrating out the assumed
close-to-equilibrium mediator field. The same approach does not apply if the
mediator field is stable and freezes out of equilibrium. To account for the
latter case, we adopt a non-local description of damping that is only
meaningful when we consider full half-oscillations of the field being damped.
The damping rates of the oscillating scalar field and the corresponding heating
rate of the thermal bath in all bulk parameter regions are calculated in both
cases, corroborating previous results in the direct decay case. Using the
obtained results, the time it takes for the amplitude of the scalar field to be
substantially damped is estimated.",1708.04865v2
2018-04-20,A Weakly Nonlinear Model for the Damping of Resonantly Forced Density Waves in Dense Planetary Rings,"In this paper we address the stability of resonantly forced density waves in
dense planetary rings.
  Already by Goldreich & Tremaine (1978) it has been argued that density waves
might be unstable, depending on the relationship between the ring's viscosity
and the surface mass density.
  In the recent paper Schmidt et al. (2016) we have pointed out that when -
within a fluid description of the ring dynamics - the criterion for viscous
overstability is satisfied, forced spiral density waves become unstable as
well.
  In this case, linear theory fails to describe the damping, but nonlinearity
of the underlying equations guarantees a finite amplitude and eventually a
damping of the wave.
  We apply the multiple scale formalism to derive a weakly nonlinear damping
relation from a hydrodynamical model.
  This relation describes the resonant excitation and nonlinear viscous damping
of spiral density waves in a vertically integrated fluid disk with density
dependent transport coefficients.
  The model consistently predicts density waves to be (linearly) unstable in a
ring region where the conditions for viscous overstability are met.
  Sufficiently far away from the Lindblad resonance, the surface mass density
perturbation is predicted to saturate to a constant value due to nonlinear
viscous damping.
  The wave's damping lengths of the model depend on certain input parameters,
such as the distance to the threshold for viscous overstability in parameter
space and the ground state surface mass density.",1804.07674v1
2018-09-14,Continuous and discrete damping reduction for systems with quadratic interaction,"We study the connection between Lagrangian and Hamiltonian descriptions of
closed/open dynamics, for a collection of particles with quadratic interaction
(closed system) and a sub-collection of particles with linear damping (open
system). We consider both continuous and discrete versions of mechanics. We
define the Damping Reduction as the mapping from the equations of motion of the
closed system to those of the open one. As variational instruments for the
obtention of these equations we use the Hamilton's principle (closed dynamics)
and Lagrange-d'Alembert principle (open dynamics). We establish the
commutativity of the branches Legendre transform + Damping Reduction and
Damping Reduction+Legendre transform, where the Legendre transform is the usual
mapping between Lagrangian and Hamiltonian mechanics. At a discrete level, this
commutativity provides interesting insight about the resulting integrators.
More concretely, Discrete Damping Reduction yields particular numerical schemes
for linearly damped systems which are not symplectic anymore, but preserve some
of the features of their symplectic counterparts from which they proceed (for
instance the semi-implicitness in some cases). The theoretical results are
illustrated with the examples of the heat bath and transmission lines. In the
latter case some simulations are displayed, showing a better performance of the
integrators with variational origin.",1809.05532v1
2019-03-02,Complex Stiffness Model of Physical Human-Robot Interaction: Implications for Control of Performance Augmentation Exoskeletons,"Human joint dynamic stiffness plays an important role in the stability of
performance augmentation exoskeletons. In this paper, we consider a new
frequency domain model of the human joint dynamics which features a complex
value stiffness. This complex stiffness consists of a real stiffness and a
hysteretic damping. We use it to explain the dynamic behaviors of the human
connected to the exoskeleton, in particular the observed non-zero low frequency
phase shift and the near constant damping ratio of the resonant as stiffness
and inertia vary. We validate this concept by experimenting with an elbow-joint
exoskeleton testbed on a subject while modifying joint stiffness behavior,
exoskeleton inertia, and strength augmentation gains. We compare three
different models of elbow-joint dynamic stiffness: a model with real stiffness,
viscous damping and inertia, a model with complex stiffness and inertia, and a
model combining the previous two models. Our results show that the hysteretic
damping term improves modeling accuracy, using a statistical F-test. Moreover
this improvement is statistically more significant than using classical viscous
damping term. In addition, we experimentally observe a linear relationship
between the hysteretic damping and the real part of the stiffness which allows
us to simplify the complex stiffness model as a 1-parameter system. Ultimately,
we design a fractional order controller to demonstrate how human hysteretic
damping behavior can be exploited to improve strength amplification performance
while maintaining stability.",1903.00704v4
2020-05-31,Optimal decay rates of the compressible Euler equations with time-dependent damping in $\mathbb R^n$: (II) over-damping case,"This paper is concerned with the multi-dimensional compressible Euler
equations with time-dependent over-damping of the form
$-\frac{\mu}{(1+t)^\lambda}\rho\boldsymbol u$ in $\mathbb R^n$, where $n\ge2$,
$\mu>0$, and $\lambda\in[-1,0)$. This continues our previous work dealing with
the under-damping case for $\lambda\in[0,1)$. We show the optimal decay
estimates of the solutions such that for $\lambda\in(-1,0)$ and $n\ge2$,
$\|\rho-1\|_{L^2(\mathbb R^n)}\approx(1+t)^{-\frac{1+\lambda}{4}n}$ and
$\|\boldsymbol u\|_{L^2(\mathbb R^n)}\approx
(1+t)^{-\frac{1+\lambda}{4}n-\frac{1-\lambda}{2}}$, which indicates that a
stronger damping gives rise to solutions decaying optimally slower. For the
critical case of $\lambda=-1$, we prove the optimal logarithmical decay of the
perturbation of density for the damped Euler equations such that
$\|\rho-1\|_{L^2(\mathbb R^n)}\approx |\ln(e+t)|^{-\frac{n}{4}}$ and
$\|\boldsymbol u\|_{L^2(\mathbb R^n)}\approx
(1+t)^{-1}\cdot|\ln(e+t)|^{-\frac{n}{4}-\frac{1}{2}}$ for $n\ge7$. The
over-damping effect reduces the decay rates of the solutions to be slow, which
causes us some technical difficulty in obtaining the optimal decay rates by the
Fourier analysis method and the Green function method. Here, we propose a new
idea to overcome such a difficulty by artfully combining the Green function
method and the time-weighted energy method.",2006.00403v1
2020-07-07,Nonlinear viscoelastic isolation for seismic vibration mitigation,"The aim of this paper is to assess the effectiveness of nonlinear
viscoelastic damping in controlling base-excited vibrations. Specifically, the
focus is on investigating the robustness of the nonlinear base isolation
performance in controlling the system response due to a wide set of possible
excitation spectra. The dynamic model is derived to study a simple structure
whose base isolation is provided via a Rubber-Layer Roller Bearing (RLRB)
(rigid cylinders rolling on rigid plates with highly damping rubber coatings)
equipped with a nonlinear cubic spring, thus presenting both nonlinear damping
and stiffness. We found that, under periodic loading, due to the non-monotonic
bell-shaped viscoelastic damping arising from the viscoelastic rolling
contacts, different dynamic regimes occur mostly depending on whether the
damping peak is overcome or not. Interestingly, in the former case, poorly
damped self-excited vibrations may be triggered by the steep damping decrease.
Moreover, in order to investigate the robustness of the isolation performance,
we consider a set of real seismic excitations, showing that tuned nonlinear
RLRB provide loads isolation in a wider range of excitation spectra, compared
to generic linear isolators. This is peculiarly suited for applications (such
as seismic and failure engineering) in which the specific excitation spectrum
is unknown a priori, and blind design on statistical data has to be employed.",2007.04378v1
2021-01-20,Damped perturbations in stellar systems: Genuine modes and Landau-damped waves,"This research was stimulated by the recent studies of damping solutions in
dynamically stable spherical stellar systems. Using the simplest model of the
homogeneous stellar medium, we discuss nontrivial features of stellar systems.
Taking them into account will make it possible to correctly interpret the
results obtained earlier and will help to set up decisive numerical experiments
in the future. In particular, we compare the initial value problem versus the
eigenvalue problem. It turns out that in the unstable regime, the Landau-damped
waves can be represented as a superposition of van Kampen modes {\it plus} a
discrete damped mode, usually ignored in the stability study. This mode is a
solution complex conjugate to the unstable Jeans mode. In contrast, the
Landau-damped waves are not genuine modes: in modes, eigenfunctions depend on
time as $\exp (-{\rm i} \omega t)$, while the waves do not have eigenfunctions
on the real $v$-axis at all. However, `eigenfunctions' on the complex
$v$-contours do exist. Deviations from the Landau damping are common and can be
due to singularities or cut-off of the initial perturbation above some fixed
value in the velocity space.",2101.08287v2
2021-03-10,Dynamical Pose Estimation,"We study the problem of aligning two sets of 3D geometric primitives given
known correspondences. Our first contribution is to show that this primitive
alignment framework unifies five perception problems including point cloud
registration, primitive (mesh) registration, category-level 3D registration,
absolution pose estimation (APE), and category-level APE. Our second
contribution is to propose DynAMical Pose estimation (DAMP), the first general
and practical algorithm to solve primitive alignment problem by simulating
rigid body dynamics arising from virtual springs and damping, where the springs
span the shortest distances between corresponding primitives. We evaluate DAMP
in simulated and real datasets across all five problems, and demonstrate (i)
DAMP always converges to the globally optimal solution in the first three
problems with 3D-3D correspondences; (ii) although DAMP sometimes converges to
suboptimal solutions in the last two problems with 2D-3D correspondences, using
a scheme for escaping local minima, DAMP always succeeds. Our third
contribution is to demystify the surprising empirical performance of DAMP and
formally prove a global convergence result in the case of point cloud
registration by charactering local stability of the equilibrium points of the
underlying dynamical system.",2103.06182v3
2021-04-13,Apparent nonlinear damping triggered by quantum fluctuations,"Nonlinear damping, the change in damping rate with the amplitude of
oscillations plays an important role in many electrical, mechanical and even
biological oscillators. In novel technologies such as carbon nanotubes,
graphene membranes or superconducting resonators, the origin of nonlinear
damping is sometimes unclear. This presents a problem, as the damping rate is a
key figure of merit in the application of these systems to extremely precise
sensors or quantum computers. Through measurements of a superconducting
resonator, we show that from the interplay of quantum fluctuations and the
nonlinearity of a Josephson junction emerges a power-dependence in the
resonator response which closely resembles nonlinear damping. The phenomenon
can be understood and visualized through the flow of quasi-probability in phase
space where it reveals itself as dephasing. Crucially, the effect is not
restricted to superconducting circuits: we expect that quantum fluctuations or
other sources of noise give rise to apparent nonlinear damping in systems with
a similar conservative nonlinearity, such as nano-mechanical oscillators or
even macroscopic systems.",2104.06464v2
2023-07-26,Improving frequency response with synthetic damping available from fleets of distributed energy resources,"With the increasing use of renewable generation in power systems, responsive
resources will be necessary to support primary frequency control in future
low-inertia/under-damped power systems. Flexible loads can provide
fast-frequency response services if coordinated effectively. However, practical
implementations of such synthetic damping services require both effective local
sensing and control at the device level and an ability to accurately estimate
online and predict the available synthetic damping from a fleet. In addition,
the inherent trade-off between a fleet being available for fast frequency
response while providing other ancillary services needs to be characterized. In
this context, the manuscript presents a novel, fully decentralized,
packet-based controller for diverse flexible loads that dynamically prioritizes
and interrupts loads to engender synthetic damping suitable for primary
frequency control. Moreover, the packet-based control methodology is shown to
accurately characterize the available synthetic damping in real-time, which is
useful to aggregators and system operators. Furthermore, spectral analysis of
historical frequency regulation data is used to produce a probabilistic bound
on the expected available synthetic damping for primary frequency control from
a fleet and the trade-off from concurrently providing secondary frequency
control services. Finally, numerical simulation on IEEE test networks
demonstrates the effectiveness of the proposed methodology.",2307.14498v1
2023-12-11,Possible Contamination of the Intergalactic Medium Damping Wing in ULAS J1342+0928 by Proximate Damped Ly$α$ Absorption,"The red damping wing from neutral hydrogen in the intergalactic medium is a
smoking-gun signal of ongoing reionization. One potential contaminant of the
intergalactic damping wing signal is dense gas associated with foreground
galaxies, which can give rise to proximate damped Ly$\alpha$ absorbers. The
Ly$\alpha$ imprint of such absorbers on background quasars is indistinguishable
from the intergalactic medium within the uncertainty of the intrinsic quasar
continuum, and their abundance at $z\gtrsim7$ is unknown. Here we show that the
complex of low-ionization metal absorption systems recently discovered by deep
JWST/NIRSpec observations in the foreground of the $z=7.54$ quasar
ULAS~J1342$+$0928 can potentially reproduce the quasar's spectral profile close
to rest-frame Ly$\alpha$ without invoking a substantial contribution from the
intergalactic medium, but only if the absorbing gas is extremely metal-poor
($[{\rm O}/{\rm H}]\sim-3.5$). Such a low oxygen abundance has never been
observed in a damped Ly$\alpha$ absorber at any redshift, but this possibility
still complicates the interpretation of the spectrum. Our analysis highlights
the need for deep spectroscopy of high-redshift quasars with JWST or ELT to
""purify"" damping wing quasar samples, an exercise which is impossible for much
fainter objects like galaxies.",2312.06747v1
2024-02-13,Forecasts for Constraining Lorentz-violating Damping of Gravitational Waves from Compact Binary Inspirals,"Violation of Lorentz symmetry can result in two distinct effects in the
propagation of the gravitational waves (GWs). One is a modified dispersion
relation and another is a frequency-dependent damping of GWs. While the former
has been extensively studied in the literature, in this paper we concentrate on
the frequency-dependent damping effect that arises from several specific
Lorentz-violating theories, such as spatial covariant gravities,
Ho\v{r}ava-Lifshitz gravities, etc. This Lorentz-violating damping effect
changes the damping rate of GWs at different frequencies and leads to an
amplitude correction to the GW waveform of compact binary inspiral systems.
With this modified waveform, we then use the Fisher information matrix to
investigate the prospects of constraining the Lorentz-violating damping effect
with GW observations. We consider both ground-based and space-based GW
detectors, including the advanced LIGO, Einstein Telescope, Cosmic Explorer
(CE), Taiji, TianQin, and LISA. Our results indicate that the ground-based
detectors in general give tighter constraints than those from the space-based
detectors. Among the considered three ground-based detectors, CE can give the
tightest constraints on the Lorentz-violating damping effect, which improves
the current constraint from LIGO-Virgo-KAGRA events by about 8 times.",2402.08240v1
2024-03-13,Thermal Hall effect incorporating magnon damping in localized spin systems,"We propose a theory for thermal Hall transport mediated by magnons to address
the impact of their damping resulting from magnon-magnon interactions in
insulating magnets. This phenomenon is anticipated to be particularly
significant in systems characterized by strong quantum fluctuations,
exemplified by spin-1/2 systems. Employing a nonlinear flavor-wave theory, we
analyze a general model for localized electron systems and develop a
formulation for thermal conductivity based on a perturbation theory, utilizing
bosonic Green's functions with a nonzero self-energy. We derive the expression
of the thermal Hall conductivity incorporating magnon damping. To demonstrate
the applicability of the obtained representation, we adopt it to two $S=1/2$
quantum spin models on a honeycomb lattice. In calculations for these systems,
we make use of the self-consistent imaginary Dyson equation approach at finite
temperatures for evaluating the magnon damping rate. In both systems, the
thermal Hall conductivity is diminished due to the introduction of magnon
damping over a wide temperature range. This effect arises due to the smearing
of magnon spectra with nonzero Berry curvatures. We also discuss the relation
to the damping of chiral edge modes of magnons. Our formulation can be applied
to various localized electron systems as we begin with a general Hamiltonian
for these systems. Our findings shed light on a new aspect of topological
magnonics emergent from many-body effects and will stimulate further
investigations on the impact of magnon damping on topological phenomena.",2403.08478v1
2024-04-02,A recipe for eccentricity and inclination damping for partial gap opening planets in 3D disks,"In a previous paper we showed that, like the migration speed, the
eccentricity damping efficiency is modulated linearly by the depth of the
partial gap a planet carves in the disk surface density profile, resulting in
less efficient $e$-damping compared to the prescription commonly used in
population synthesis works. Here, we extend our analysis to 3D, refining our
$e$-damping formula and studying how the inclination damping efficiency is also
affected. We perform high resolution 3D locally isothermal hydrodynamical
simulations of planets with varying masses embedded in disks with varying
aspect ratios and viscosities. We extract the gap profile and orbital damping
timescales for fixed eccentricities and inclinations up to the disk scale
height. The limit in gap depths below which vortices appear, in the
low-viscosity case, happens roughly at the transition between classical type-I
and type-II migration regimes. The orbital damping timescales can be described
by two linear trends with a break around gap depths $\sim80\%$ and with slopes
and intercepts depending on the eccentricity and inclination. These trends are
understood on physical grounds and are reproduced by simple fitting formulas
whose error is within the typically uncertainty of type-I torque formulas.
Thus, our recipes for the gap depth and orbital damping efficiencies yield a
simple description for planet-disk interactions to use in N-body codes in the
case of partial gap opening planets that is consistent with high-resolution 3D
hydro-simulations. Finally, we show examples of how our novel orbital damping
prescription can affect the outcome of population synthesis experiments.",2404.02247v1
2009-08-21,Surface Alfven Wave Damping in a 3D Simulation of the Solar Wind,"Here we investigate the contribution of surface Alfven wave damping to the
heating of the solar wind in minima conditions. These waves are present in
regions of strong inhomogeneities in density or magnetic field (e. g., the
border between open and closed magnetic field lines). Using a 3-dimensional
Magnetohydrodynamics (MHD) model, we calculate the surface Alfven wave damping
contribution between 1-4 solar radii, the region of interest for both
acceleration and coronal heating. We consider waves with frequencies lower than
those that are damped in the chromosphere and on the order of those dominating
the heliosphere. In the region between open and closed field lines, within a
few solar radii of the surface, no other major source of damping has been
suggested for the low frequency waves we consider here. This work is the first
to study surface Alfven waves in a 3D environment without assuming a priori a
geometry of field lines or magnetic and density profiles. We determine that
waves with frequencies >2.8x10^-4 Hz are damped between 1-4 solar radii. In
quiet sun regions, surface Alfven waves are damped at further distances
compared to active regions, thus carrying additional wave energy into the
corona. We compare the surface Alfven wave contribution to the heating by a
variable polytropic index and find that it an order of magnitude larger than
needed for quiet sun regions. For active regions the contribution to the
heating is twenty percent. As it has been argued that a variable gamma acts as
turbulence, our results indicate that surface Alfven wave damping is comparable
to turbulence in the lower corona. This damping mechanism should be included
self consistently as an energy driver for the wind in global MHD models.",0908.3146v1
2014-03-19,The effects of time-dependent dissipation on the basins of attraction for the pendulum with oscillating support,"We consider a pendulum with vertically oscillating support and time-dependent
damping coefficient which varies until reaching a finite final value. The sizes
of the corresponding basins of attraction are found to depend strongly on the
full evolution of the dissipation. In order to predict the behaviour of the
system, it is essential to understand how the sizes of the basins of attraction
for constant dissipation depend on the damping coefficient. For values of the
parameters in the perturbation regime, we characterise analytically the
conditions under which the attractors exist and study numerically how the sizes
of their basins of attraction depend on the damping coefficient. Away from the
perturbation regime, a numerical study of the attractors and the corresponding
basins of attraction for different constant values of the damping coefficient
produces a much more involved scenario: changing the magnitude of the
dissipation causes some attractors to disappear either leaving no trace or
producing new attractors by bifurcation, such as period doubling and
saddle-node bifurcation. For an initially non-constant damping coefficient,
both increasing and decreasing to some finite final value, we numerically
observe that, when the damping coefficient varies slowly from a finite initial
value to a different final value, without changing the set of attractors, the
slower the variation the closer the sizes of the basins of attraction are to
those they have for constant damping coefficient fixed at the initial value. If
during the variation of the damping coefficient attractors appear or disappear,
remarkable additional phenomena may occur. For instance, a fixed point
asymptotically may attract the entire phase space, up to a zero measure set,
even though no attractor with such a property exists for any value of the
damping coefficient between the extreme values.",1403.4996v1
2017-11-21,Determination of spin Hall effect and spin diffusion length of Pt from self-consistent fitting of damping enhancement and inverse spin-orbit torque measurements,"Understanding the evolution of spin-orbit torque (SOT) with increasing
heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical
for the development of magnetic memory based on SOT. However, several
experiments have revealed an apparent discrepancy between damping enhancement
and damping-like SOT regarding their dependence on NM thickness. Here, using
linewidth and phase-resolved amplitude analysis of vector network analyzer
ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract
damping enhancement and both field-like and damping-like inverse SOT in
Ni$_{80}$Fe$_{20}$/Pt bilayers as a function of Pt thickness. By enforcing an
interpretation of the data which satisfies Onsager reciprocity, we find that
both the damping enhancement and damping-like inverse SOT can be described by a
single spin diffusion length ($\approx$ 4 nm), and that we can separate the
spin pumping and spin memory loss (SML) contributions to the total damping.
This analysis indicates that less than 40% of the angular momentum pumped by
FMR through the Ni$_{80}$Fe$_{20}$/Pt interface is transported as spin current
into the Pt. On account of the SML and corresponding reduction in total spin
current available for spin-charge transduction in the Pt, we determine the Pt
spin Hall conductivity ($\sigma_\mathrm{SH} = (2.36 \pm 0.04)\times10^6
\Omega^{-1} \mathrm{m}^{-1}$) and bulk spin Hall angle
($\theta_\mathrm{SH}=0.387 \pm0.008$) to be larger than commonly-cited values.
These results suggest that Pt can be an extremely useful source of SOT if the
FM/NM interface can be engineered to minimize SML. Lastly, we find that
self-consistent fitting of the damping and SOT data is best achieved by a model
with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such
that both the spin diffusion length and spin Hall conductivity are proportional
to the Pt charge conductivity.",1711.07654v2
2019-09-19,"Nonlinear energy loss in the oscillations of coated and uncoated bubbles: Role of thermal, radiation damping and encapsulating shell at various excitation pressures","A simple generalized model (GM) for coated bubbles accounting for the effect
of compressibility of the liquid is presented. The GM was then coupled with
nonlinear ODEs that account for the thermal effects. Starting with mass and
momentum conservation equations for a bubbly liquid and using the GM, nonlinear
pressure dependent terms were derived for energy dissipation due to thermal
damping (Td), radiation damping (Rd) and dissipation due to the viscosity of
liquid (Ld) and coating (Cd). The dissipated energies were solved for uncoated
and coated 2- 20 $\mu m$ bubbles over a frequency range of $0.25f_r-2.5f_r$
($f_r$ is the bubble resonance) and for various acoustic pressures
(1kPa-300kPa). Thermal effects were examined for air and C3F8 gas cores in each
case. For uncoated bubbles with an air gas core and a diameter larger than 4
$\mu m$, thermal damping is the strongest damping factor. When pressure
increases, the contributions of Rd grow faster and become the dominant damping
mechanism for pressure dependent resonance frequencies (e.g. fundamental and
super harmonic resonances). For coated bubbles, Cd is the strongest damping
mechanism. As pressure increases Rd contributes more to damping compared to Ld
and Td. In case of air bubbles, as pressure increases, the linear thermal model
largely deviates from the nonlinear model and accurate modeling requires
inclusion of the full thermal model. However, for coated C3F8 bubbles of
diameter 1-8 $\mu m$, typically used in medical ultrasound, thermal effects
maybe neglected even at higher pressures. We show that the scattering to
damping ratio (STDR), a measure of the effectiveness of the bubble as contrast
agent, is pressure dependent and can be maximized for specific frequency ranges
and pressures.",1909.08793v1
2020-11-20,The effect of magnetic field on the damping of slow waves in the solar corona,"Slow magnetoacoustic waves are routinely observed in astrophysical plasma
systems such as the solar corona. As a slow wave propagates through a plasma,
it modifies the equilibrium quantities of density, temperature, and magnetic
field. In the corona and other plasma systems, the thermal equilibrium is
comprised of a balance between continuous heating and cooling processes, the
magnitudes of which vary with density, temperature and magnetic field. Thus the
wave may induce a misbalance between these competing processes. Its back
reaction on the wave has been shown to lead to dispersion, and amplification or
damping, of the wave. In this work the importance of the effect of magnetic
field in the rapid damping of slow waves in the solar corona by heating/cooling
misbalance is evaluated and compared to the effects of thermal conduction. The
two timescales characterising the effect of misbalance are derived and
calculated for plasma systems with a range of typical coronal conditions. The
predicted damping times of slow waves from thermal misbalance in the solar
corona are found to be of the order of 10-100 minutes, coinciding with the wave
periods and damping times observed. Moreover the slow wave damping by thermal
misbalance is found to be comparable to the damping by field-aligned thermal
conduction. We show that in the infinite field limit, the wave dynamics is
insensitive to the dependence of the heating function on the magnetic field,
and this approximation is found to be valid in the corona so long as the
magnetic field strength is greater than 10G for quiescent loops and plumes and
100G for hot and dense loops. In summary thermal misbalance may damp slow
magnetoacoustic waves rapidly in much of the corona, and its inclusion in our
understanding of slow mode damping may resolve discrepancies between
observations and theory relying on compressive viscosity and thermal conduction
alone.",2011.10437v1
1997-11-25,Abundances of Heavy Elements and CO Molecules in High Redshift Damped Lyman-alpha Galaxies,"Damped Lyman-alpha systems seen in spectra of background quasars are
generally thought to represent high redshift counterparts of present-day
galaxies. We summarize observations of heavy element abundances in damped
Lyman-alpha systems. The results of a systematic search for CO and C II*
absorption in 17 damped Lyman-alpha systems are also presented using
observations obtained with the 10m Keck telescopes. The latter provides a
useful constraint on the expected strength of [C II] 158 micron emission from
damped Lyman-alpha galaxies. It is hoped that these results will be useful for
planning future radio to millimeter wave observations of high redshift galaxies
using next generation instruments which are now being built.",9711298v1
1997-12-05,Magnetohydrodynamics in the Early Universe and the Damping of Non-linear Alfven Waves,"The evolution and viscous damping of cosmic magnetic fields in the early
universe, is analysed. Using the fact that the fluid, electromagnetic, and
shear viscous energy-momentum tensors are all conformally invariant, the
evolution is transformed from the expanding universe setting into that in flat
spacetime. Particular attention is paid to the evolution of nonlinear Alfven
modes. For a small enough magnetic field, which satisfies our observational
constraints, these wave modes either oscillate negligibly or, when they do
oscillate, become overdamped. Hence they do not suffer Silk damping on galactic
and subgalactic scales. The smallest scale which survives damping depends on
the field strength and is of order a dimensionless Alfven velocity times the
usual baryon-photon Silk damping scale. After recombination, nonlinear effects
can convert the Alfven mode into compressional, gravitationally unstable waves
and seed cosmic structures if the cosmic magnetic field is sufficiently strong.",9712083v1
2001-08-09,Are Simulations of CDM Consistent with Galactic-Scale Observations at High Redshift?,"We compare new observations on the kinematic characteristics of the damped
Lya systems against results from numerical SPH simulations to test the
predictions of hierarchical galaxy formation. This exercise is particularly
motivated by recent numerical results on the cross-section of damped Lya
systems. Our analysis focuses on the velocity widths of ~50 low-ion absorption
profiles from our sample of z>1.5 damped Lya systems. The results indicate that
current numerical simulations fail to match the damped Lya observations at high
confidence levels (>99.9%). Although we do not believe that our results present
an insurmountable challenge to the paradigm of hierarchical cosmology, the
damped Lya observations suggest that current numerical SPH simulations overlook
an integral aspect of galaxy formation.",0108154v1
2003-03-19,Distinct Abundance Patterns in Multiple Damped Ly-alpha Galaxies: Evidence for Truncated Star Formation?,"(abridged) Following our previous work on metal abundances of a double damped
Ly-alpha system with a line-of-sight separation ~2000 km/s (Ellison & Lopez
2001), we present VLT UVES abundances of 3 new systems spanning a total of
\~6000 km/s at z~2.5 toward the southern QSO CTQ247. These abundances are
supplemented with echelle observations of another `double' damped Ly-alpha
system in the literature. We propose a definition in terms of velocity shift of
the sub-class 'multiple damped Ly-alpha system', which is motivated by its
possible connection with large-scale structure. We find that the abundance
ratio alpha/Fe is systematically low in multiple systems compared with single
systems, and with a small scatter. The same behavior is found in 2 more single
DLA systems taken from the literature that show evidence of belonging to a
galaxy group. After a careful investigation of possible sources of systematic
errors, we conclude that the low alpha/Fe ratios in multiple DLAs have a
nucleosynthetic origin. We suggest that they could be explained by reduced star
formation in multiple damped Ly-alpha systems, possibly due to environmental
effects.",0303441v1
2003-05-16,New Damped Lya Metallicities from ESI Spectroscopy of Five Palomar Sky Survey Quasars,"This paper presents chemical abundance measurements for 12 new z>3 damped Lya
systems discovered toward five quasars from the Palomar Sky Survey. We
determine HI column densities from profile fits to the observed damped Lya
profiles and measure ionic column densities and limits for all observed
metal-line transitions. This dataset, acquired with the Echellette Spectrograph
and Imager on the KeckII telescope, adds to the rapidly growing database of
damped Lya abundances. It will impact studies of chemical evolution in the
early universe and help identify candidates for detailed follow-up observations
with echelle spectrographs. We report the discovery of the first quasar
sightline with four cosmologically distinct damped Lya systems.",0305313v1
2006-07-06,Ekman layer damping of r-modes revisited,"We investigate the damping of neutron star r-modes due to the presence of a
viscous boundary (Ekman) layer at the interface between the crust and the core.
Our study is motivated by the possibility that the gravitational-wave driven
instability of the inertial r-modes may become active in rapidly spinning
neutron stars, eg. in low-mass X-ray binaries, and the fact that a viscous
Ekman layer at the core-crust interface provides an efficient damping mechanism
for these oscillations. We review various approaches to the problem and carry
out an analytic calculation of the effects due to the Ekman layer for a rigid
crust. Our analytic estimates support previous numerical results, and provide
further insight into the intricacies of the problem. We add to previous work by
discussing the effect that compressibility and composition stratification have
on the boundary layer damping. We show that, while stratification is
unimportant for the r-mode problem, composition suppresses the damping rate by
about a factor of two (depending on the detailed equation of state).",0607105v2
1997-11-05,Hydrodynamic damping in trapped Bose gases,"Griffin, Wu and Stringari have derived the hydrodynamic equations of a
trapped dilute Bose gas above the Bose-Einstein transition temperature. We give
the extension which includes hydrodynamic damping, following the classic work
of Uehling and Uhlenbeck based on the Chapman-Enskog procedure. Our final
result is a closed equation for the velocity fluctuations $\delta v$ which
includes the hydrodynamic damping due to the shear viscosity $\eta$ and the
thermal conductivity $\kappa$. Following Kavoulakis, Pethick and Smith, we
introduce a spatial cutoff in our linearized equations when the density is so
low that the hydrodynamic description breaks down. Explicit expressions are
given for $\eta$ and $\kappa$, which are position-dependent through dependence
on the local fugacity when one includes the effect of quantum degeneracy of the
trapped gas. We also discuss a trapped Bose-condensed gas, generalizing the
work of Zaremba, Griffin and Nikuni to include hydrodynamic damping due to the
(non-condensate) normal fluid.",9711036v4
1998-05-01,Finite Temperature Perturbation Theory for a Spatially Inhomogeneous Bose-condensed Gas,"We develop a finite temperature perturbation theory (beyond the mean field)
for a Bose-condensed gas and calculate temperature-dependent damping rates and
energy shifts for Bogolyubov excitations of any energy. The theory is
generalized for the case of excitations in a spatially inhomogeneous (trapped)
Bose-condensed gas, where we emphasize the principal importance of
inhomogeneouty of the condensate density profile and develop the method of
calculating the self-energy functions. The use of the theory is demonstrated by
calculating the damping rates and energy shifts of low-energy quasiclassical
excitations, i.e. the quasiclassical excitations with energies much smaller
than the mean field interaction between particles. In this case the boundary
region of the condensate plays a crucial role, and the result for the damping
rates and energy shifts is completely different from that in spatially
homogeneous gases. We also analyze the frequency shifts and damping of sound
waves in cylindrical Bose condensates and discuss the role of damping in the
recent MIT experiment on the sound propagation.",9805015v2
2003-10-18,Experiment and Dynamic Simulations of Radiation Damping of Laser-polarized liquid 129Xe at low magnetic field in a flow system,"Radiation damping is generally observed when the sample with high spin
concentration and high gyro-magnetic ratio is placed in a high magnetic field.
However, we firstly observed liquid state 129Xe radiation damping using
laser-enhanced nuclear polarization at low magnetic field in a flow system in
which the polarization enhancement factor for the liquid state 129Xe was
estimated to be 5000, and furthermore theoretically simulated the envelopes of
the 129Xe FID and spectral lineshape in the presence of both relaxation and
radiation damping with different pulse flip angles and ratios of T2*/Trd. The
radiation damping time constant Trd of 5 ms was derived based on the
simulations. The reasons of depolarization and the further possible
improvements were also discussed.",0310435v1
2004-03-25,XMCD characterization of rare-earth dopants in Ni$_{81}$Fe$_{19}$(50nm): microscopic basis of engineered damping,"We present direct evidence for the contribution of local orbital moments to
the damping of magnetization precession in magnetic thin films. Using x-ray
magnetic circular dichroism (XMCD) characterization of rare-earth (RE)
M$_{4,5}$ edges in Ni$_{81}$Fe$_{19}$ doped with $<$ 2% Gd and Tb, we show that
the enhancement of GHz precessional relaxation is accompanied by a significant
orbital moment fraction on the RE site. Tb impurities, which enhance the
Landau-Lifshitz(-Gilbert) LL(-G) damping $\lambda(\alpha)$, show a spin to
orbital number ratio of 1.5$\pm$0.3; Gd impurities, which have no effect on
damping, show a spin to orbital number ratio of zero within experimental error.
The results indicate that the dopant-based control of magnetization damping in
RE-doped ferromagnets is an atomistic effect, arising from spin-lattice
coupling, and thus scalable to nanometer dimensions.",0403627v1
2005-02-08,Landau Damping of Spin Waves in Trapped Boltzmann Gases,"A semiclassical method is used to study Landau damping of transverse
pseudo-spin waves in harmonically trapped ultracold gases in the collisionless
Boltzmann limit. In this approach, the time evolution of a spin is calculated
numerically as it travels in a classical orbit through a spatially dependent
mean field. This method reproduces the Landau damping results for spin-waves in
unbounded systems obtained with a dielectric formalism. In trapped systems, the
simulations indicate that Landau damping occurs for a given spin-wave mode
because of resonant phase space trajectories in which spins are ""kicked out"" of
the mode (in spin space). A perturbative analysis of the resonant and nearly
resonant trajectories gives the Landau damping rate, which is calculated for
the dipole and quadrupole modes as a function of the interaction strength. The
results are compared to a numerical solution of the kinetic equation by Nikuni
et al.",0502189v1
2005-06-01,Landau damping of Bogoliubov excitations in optical lattices at finite temperature,"We study the damping of Bogoliubov excitations in an optical lattice at
finite temperatures. For simplicity, we consider a Bose-Hubbard tight-binding
model and limit our analysis to the lowest excitation band. We use the Popov
approximation to calculate the temperature dependence of the number of
condensate atoms $n^{\rm c 0}(T)$ in each lattice well. We calculate the Landau
damping of a Bogoliubov excitation in an optical lattice due to coupling to a
thermal cloud of excitations. While most of the paper concentrates on 1D
optical lattices, we also briefly present results for 2D and 3D lattices. For
energy conservation to be satisfied, we find that the excitations in the
collision process must exhibit anomalous dispersion ({\it i.e.} the excitation
energy must bend upward at low momentum), as also exhibited by phonons in
superfluid $^4\rm{He}$. This leads to the sudden disappearance of all damping
processes in $D$-dimensional simple cubic optical lattice when $U n^{\rm c
0}\ge 6DJ$, where $U$ is the on-site interaction, and $J$ is the hopping matrix
element. Beliaev damping in a 1D optical lattice is briefly discussed.",0506016v1
2006-06-15,Landau damping: instability mechanism of superfluid Bose gases moving in optical lattices,"We investigate Landau damping of Bogoliubov excitations in a dilute Bose gas
moving in an optical lattice at finite temperatures. Using a 1D tight-binding
model, we explicitly obtain the Landau damping rate, the sign of which
determines the stability of the condensate. We find that the sign changes at a
certain condensate velocity, which is exactly the same as the critical velocity
determined by the Landau criterion of superfluidity. This coincidence of the
critical velocities reveals the microscopic mechanism of the Landau
instability. This instability mechanism is also consistent with the recent
experiment suggesting that a thermal cloud plays a crucial role in breakdown of
superfluids, since the thermal cloud is also vital in the Landau damping
process. We also examine the possibility of simultaneous disappearance of all
damping processes.",0606398v2
1996-11-25,Damping rates of hard momentum particles in a cold ultrarelativistic plasma,"We compute the damping rates of one-particle excitations in a cold
ultrarelativistic plasma to leading order in the coupling constant e for three
types of interaction: Yukawa coupling to a massless scalar boson, QED and QCD.
Damping rates of charged particles in QED and QCD are of order e^3 mu, while
damping rates of other particles are of order e^4 mu or e^4 mu log(1/e). We
find that the damping rate of an electron or of a quark is constant far from
the Fermi surface, and decreases linearly with the excitation energy close to
the Fermi surface. This unusual behavior is attributed to the long-range
magnetic interactions.",9611415v2
1999-09-24,Gauge Invariance of Nonlinear Landau Damping Rate of Bose Excitations in Quark-Gluon Plasma,"On the basis of the approximate dynamical equations describing the behavior
of quark-gluon plasma (QGP) in the semiclassical limit and Yang-Mills equation,
the kinetic equation for longitudinal waves (plasmons) is obtained. With the
Ward identities the gauge invariance of obtained nonlinear Landau damping rate
is proved. The physical mechanisms defining nonlinear scattering of a plasmon
by QGP particles are analyzed. The problem on a connection of nonlinear Landau
damping rate of longitudinal oscillations with damping rate, obtained in the
framework of hard thermal loops approximation, is considered. It is shown that
the gauge-dependent part of nonlinear Landau damping rate for the plasmons with
zero momentum vanishes on mass-shell.",9909505v1
2005-07-16,Sharp estimates for the number of degrees of freedom for the damped-driven 2D Navier--Stokes equations,"We derive upper bounds for the number of asymptotic degrees (determining
modes and nodes) of freedom for the two-dimensional Navier--Stokes system and
Navier-Stokes system with damping. In the first case we obtain the previously
known estimates in an explicit form, which are larger than the fractal
dimension of the global attractor. However, for the Navier--Stokes system with
damping our estimates for the number of the determining modes and nodes are
comparable to the sharp estimates for the fractal dimension of the global
attractor. Our investigation of the damped-driven 2D Navier--Stokes system is
inspired by the Stommel--Charney barotropic model of ocean circulation where
the damping represents the Rayleigh friction. We remark that our results
equally apply to the Stommel--Charney model.",0507327v1
2006-12-04,A singular perturbation approach for choosing PageRank damping factor,"The choice of the PageRank damping factor is not evident. The Google's choice
for the value c=0.85 was a compromise between the true reflection of the Web
structure and numerical efficiency. However, the Markov random walk on the
original Web Graph does not reflect the importance of the pages because it
absorbs in dead ends. Thus, the damping factor is needed not only for speeding
up the computations but also for establishing a fair ranking of pages. In this
paper, we propose new criteria for choosing the damping factor, based on the
ergodic structure of the Web Graph and probability flows. Specifically, we
require that the core component receives a fair share of the PageRank mass.
Using singular perturbation approach we conclude that the value c=0.85 is too
high and suggest that the damping factor should be chosen around 1/2. As a
by-product, we describe the ergodic structure of the OUT component of the Web
Graph in detail. Our analytical results are confirmed by experiments on two
large samples of the Web Graph.",0612079v1
1998-10-26,Microscopic Structure of Rotational Damping,"The damping of collective rotational motion is studied microscopically,
making use of shell model calculations based on the cranked Nilsson deformed
mean-field and on residual two-body interactions, and focusing on the shape of
the gamma-gamma correlation spectra and on its systematic behavior. It is shown
that the spectral shape is directly related to the damping width of collective
rotation, \Gammarot, and to the spreading width of many-particle many-hole
configurations, \Gammamu. The rotational damping width is affected by the shell
structure, and is very sensitive to the position of the Fermi surface, besides
mass number, spin and deformation. This produces a rich variety of features in
the rotational damping phenomena.",9810066v1
2004-07-25,Rotational damping in a multi-$j$ shell particles-rotor model,"The damping of collective rotational motion is investigated by means of
particles-rotor model in which the angular momentum coupling is treated exactly
and the valence nucleons are in a multi-$j$ shell mean-field. It is found that
the onset energy of rotational damping is around 1.1 MeV above yrast line, and
the number of states which form rotational band structure is thus limited. The
number of calculated rotational bands around 30 at a given angular momentum
agrees qualitatively with experimental data. The onset of rotational damping
takes place gradually as a function of excitation energy. It is shown that the
pairing correlation between valence nucleons has a significant effect on the
appearance of rotational damping.",0407089v3
2001-07-19,Manifold Damping of Transverse Wakefields in High Phase Advance Traveling Wave Structures and Local Damping of Dipole Wakefields in Standing Wave Accelerators,"Operating the SLAC/KEK DDS (Damped Detuned Structure) X-band linacs at high
gradients (in excess of 70MV/m) has recently been found to be limited by the
accelerator structures breaking down and as a consequence severe damage occurs
to the cells which makes the structures inoperable. A series of recent
experiments at SLAC indicates that arcing in the structures is significantly
reduced if the group velocity of the accelerating mode is reduced and
additionally it has been discovered that reducing the length of the
accelerating structure also limits the number and intensity of breakdown events
[1]. However, in designing new accelerating structures care must be taken to
ensure that the beam-induced transverse wakefields do not cause the beam to
become unstable. Here, we report on damping transverse wakefields in two
different short structures: a 90cm traveling wave structure in which the
wakefield is coupled out to four attached manifolds and secondly, in a standing
wave structure in which a limited number of cells heavily damp down the
wakefield.
  [1] C. Adolphsen, ROAA003, this conf.",0107048v1
2002-06-28,Manifold Damping Of Wakefields In High Phase Advance Linacs For The NLC,"Earlier RDDS (Rounded Damped Detuned Structures) [1,2], designed, fabricated
and tested at SLAC, in collaboration with KEK, have been shown to damp
wakefields successfully. However, electrical breakdown has been found to occur
in these structures and this makes them inoperable at the desired gradient.
Recent results [3] indicate that lowering the group velocity of the
accelerating mode reduces electrical breakdown events. In order to preserve the
filling time of each structure a high synchronous phase advance (150 degrees as
opposed to 120 used in previous NLC designs) has been chosen. Here, damping of
the wakefield is analyzed. Manifold damping and interleaving of structure cell
frequencies is discussed. These wakefields impose alignment tolerances on the
cells and on the structure as a whole. Tolerance calculations are performed and
these are compared with analytic estimations.",0206090v1
2006-06-30,Nonlinear Damping of the LC Circuit using Anti-parallel Diodes,"We investigate a simple variation of the series RLC circuit in which
anti-parallel diodes replace the resistor. This results in a damped harmonic
oscillator with a nonlinear damping term that is maximal at zero current and
decreases with an inverse current relation for currents far from zero. A set of
nonlinear differential equations for the oscillator circuit is derived and
integrated numerically for comparison with circuit measurements. The agreement
is very good for both the transient and steady-state responses. Unlike the
standard RLC circuit, the behavior of this circuit is amplitude dependent. In
particular for the transient response the oscillator makes a transition from
under-damped to over-damped behavior, and for the driven oscillator the
resonance response becomes sharper and stronger as drive source amplitude
increases. The equipment is inexpensive and common to upper level physics labs.",0606261v1
1995-11-11,A New Look at the Landau's Theory of Spreading and Damping of Waves in Collisionless Plasmas,"The theory of plasma waves and Landau damping in Maxwellian plasmas, Landau's
``rule of pass around poles'' include doubtful statements, particularly related
to an artificial ``constructing'' of the dispersion equation, what should allow
the possibility of its solution otherwise not existing at all, and the
possibility of analytical continuations of corresponding very specific ruptured
functions in the one-dimensional Laplace transformation, used by Landau, what
is the base of his theory.
  We represent, as an accessible variant, a more general alternative theory
based on a two-dimensional Laplace transformation, leading to an asymptotical
in time and space solution as a complicated superposition of coupled damping
and {\em non-damping \/} plane waves and oscillations with different dispersion
laws for every constituent mode. This theory naturally and very simply explains
paradoxes of the phenomenon of plasma echo. We propose for discussion a new
ideology of plasma waves (both electron and ion-acoustic waves) qualitatively
different from the traditional theory of Landau damping for non-collisional as
well as for low-collisional plasmas.",9511001v1
2001-07-27,Quantum limits of cold damping with optomechanical coupling,"Thermal noise of a mirror can be reduced by cold damping. The displacement is
measured with a high-finesse cavity and controlled with the radiation pressure
of a modulated light beam. We establish the general quantum limits of noise in
cold damping mechanisms and we show that the optomechanical system allows to
reach these limits. Displacement noise can be arbitrarily reduced in a narrow
frequency band. In a wide-band analysis we show that thermal fluctuations are
reduced as with classical damping whereas quantum zero-point fluctuations are
left unchanged. The only limit of cold damping is then due to zero-point energy
of the mirror",0107138v2
2005-05-20,A symmetric treatment of damped harmonic oscillator in extended phase space,"Extended phase space (EPS) formulation of quantum statistical mechanics
treats the ordinary phase space coordinates on the same footing and thereby
permits the definite the canonical momenta conjugate to these coordinates . The
extended lagrangian and extended hamiltonian are defined in EPS by the same
procedure as one does for ordinary lagrangian and hamiltonian. The combination
of ordinary phase space and their conjugate momenta exhibits the evolution of
particles and their mirror images together. The resultant evolution equation in
EPS for a damped harmonic oscillator, is such that the energy dissipated by the
actual oscillator is absorbed in the same rate by the image oscillator leaving
the whole system as a conservative system. We use the EPS formalism to obtain
the dual hamiltonian of a damped harmonic oscillator, first proposed by
Batemann, by a simple extended canonical transformations in the extended phase
space. The extended canonical transformations are capable of converting the
damped system of actual and image oscillators to an undamped one, and transform
the evolution equation into a simple form. The resultant equation is solved and
the eigenvalues and eigenfunctions for damped oscillator and its mirror image
are obtained. The results are in agreement with those obtained by Bateman. At
last, the uncertainty relation are examined for above system.",0505147v1
2007-08-28,Pattern formation in the damped Nikolaevskiy equation,"The Nikolaevskiy equation has been proposed as a model for seismic waves,
electroconvection and weak turbulence; we show that it can also be used to
model transverse instabilities of fronts. This equation possesses a large-scale
""Goldstone"" mode that significantly influences the stability of spatially
periodic steady solutions; indeed, all such solutions are unstable at onset,
and the equation exhibits so-called soft-mode turbulence. In many applications,
a weak damping of this neutral mode will be present, and we study the influence
of this damping on solutions to the Nikolaevskiy equation. We examine the
transition to the usual Eckhaus instability as the damping of the large-scale
mode is increased, through numerical calculation and weakly nonlinear analysis.
The latter is accomplished using asymptotically consistent systems of coupled
amplitude equations. We find that there is a critical value of the damping
below which (for a given value of the supercriticality parameter) all periodic
steady states are unstable. The last solutions to lose stability lie in a cusp
close to the left-hand side of the marginal stability curve.",0708.3735v1
2008-01-12,Strong and weak coupling limits in optics of quantum well excitons,"A transition between the strong (coherent) and weak (incoherent) coupling
limits of resonant interaction between quantum well (QW) excitons and bulk
photons is analyzed and quantified as a function of the incoherent damping rate
caused by exciton-phonon and exciton-exciton scattering. For confined QW
polaritons, a second, anomalous, damping-induced dispersion branch arises and
develops with increasing damping. In this case, the strong-weak coupling
transition is attributed to a critical damping rate, when the intersection of
the normal and damping-induced dispersion branches occurs. For the radiative
states of QW excitons, i.e., for radiative QW polaritons, the transition is
described as a qualitative change of the photoluminescence spectrum at grazing
angles along the QW structure. Furthermore, we show that the radiative
corrections to the QW exciton states with in-plane wavevector approaching the
photon cone are universally scaled by an energy parameter rather than diverge.
The strong-weak coupling transition rates are also proportional to the same
energy parameter. The numerical evaluations are given for a GaAs single quantum
well with realistic parameters.",0801.1895v2
2008-01-22,Damped Bloch Oscillations of Bose-Einstein Condensates in Disordered Potential Gradients,"We investigate both experimentally and theoretically disorder induced damping
of Bloch oscillations of Bose-Einstein condensates in optical lattices. The
spatially inhomogeneous force responsible for the damping is realised by a
combination of a disordered optical and a magnetic gradient potential. We show
that the inhomogeneity of this force results in a broadening of the
quasimomentum spectrum, which in turn causes damping of the centre-of-mass
oscillation. We quantitatively compare the obtained damping rates to the
simulations using the Gross-Pitaevskii equation. Our results are relevant for
high precision experiments on very small forces, which require the observation
of a large number of oscillation cycles.",0801.3437v2
2008-02-26,"Fractional Langevin Equation: Over-Damped, Under-Damped and Critical Behaviors","The dynamical phase diagram of the fractional Langevin equation is
investigated for harmonically bound particle. It is shown that critical
exponents mark dynamical transitions in the behavior of the system. Four
different critical exponents are found. (i) $\alpha_c=0.402\pm 0.002$ marks a
transition to a non-monotonic under-damped phase, (ii) $\alpha_R=0.441...$
marks a transition to a resonance phase when an external oscillating field
drives the system, (iii) $\alpha_{\chi_1}=0.527...$ and (iv)
$\alpha_{\chi_2}=0.707...$ marks transition to a double peak phase of the
""loss"" when such an oscillating field present. As a physical explanation we
present a cage effect, where the medium induces an elastic type of friction.
Phase diagrams describing over-damped, under-damped regimes, motion and
resonances, show behaviors different from normal.",0802.3777v1
2008-04-26,Vibrational modes of metal nanoshells and bimetallic core-shell nanoparticles,"We study theoretically spectrum of radial vibrational modes in composite
metal nanostructures such as bimetallic core-shell particles and metal
nanoshells with dielectric core in an environment. We calculate frequencies and
damping rates of fundamental (breathing) modes for these nanostructures along
with those of two higher-order modes. For metal nanoshells, we find that the
breathing mode frequency is always lower than the one for solid particles of
the same size, while the damping is higher and increases with reduction of the
shell thickness. We identify two regimes that can be characterized as weakly
damped and overdamped vibrations in the presence of external medium. For
bimetalllic particles, we find periodic dependence of frequency and damping
rate on the shell thickness with period determined by mode number. For both
types of nanostructures, the frequency of higher modes is nearly independent of
the environment, while the damping rate shows strong sensitivity to outside
medium.",0804.4249v2
2008-09-26,Damping of the baryon acoustic oscillations in the matter power spectrum as a probe of the growth factor,"We investigate the damping of the baryon acoustic oscillations (BAO)
signature in the matter power spectrum due to the quasi-nonlinear clustering of
density perturbations. On the basis of the third order perturbation theory, we
construct a fitting formula of the damping in an analytic way. This
demonstrates that the damping is closely related with the growth factor and the
amplitude of the matter power spectrum. Then, we investigate the feasibility of
constraining the growth factor through a measurement of the damping of the BAO
signature. An extension of our formula including higher order corrections of
density perturbations is also discussed.",0809.4538v2
2008-10-07,Corotational Damping of Diskoseismic C-modes in Black Hole Accretion Discs,"Diskoseismic c-modes in accretion discs have been invoked to explain
low-frequency variabilities observed in black-hole X-ray binaries. These modes
are trapped in the inner-most region of the disc and have frequencies much
lower than the rotation frequency at the disc inner radius. We show that
because the trapped waves can tunnel through the evanescent barrier to the
corotational wave zone, the c-modes are damped due to wave absorption at the
corotation resonance. We calculate the corotational damping rates of various
c-modes using the WKB approximation. The damping rate varies widely depending
on the mode frequency, the black hole spin parameter and the disc sound speed,
and is generally much less than 10% of the mode frequency. A sufficiently
strong excitation mechanism is needed to overcome this corotational damping and
make the mode observable.",0810.1299v3
2008-10-10,Non-standard conserved Hamiltonian structures in dissipative/damped systems : Nonlinear generalizations of damped harmonic oscillator,"In this paper we point out the existence of a remarkable nonlocal
transformation between the damped harmonic oscillator and a modified Emden type
nonlinear oscillator equation with linear forcing, $\ddot{x}+\alpha
x\dot{x}+\beta x^3+\gamma x=0,$ which preserves the form of the time
independent integral, conservative Hamiltonian and the equation of motion.
Generalizing this transformation we prove the existence of non-standard
conservative Hamiltonian structure for a general class of damped nonlinear
oscillators including Li\'enard type systems. Further, using the above
Hamiltonian structure for a specific example namely the generalized modified
Emden equation $\ddot{x}+\alpha x^q\dot{x}+\beta x^{2q+1}=0$, where $\alpha$,
$\beta$ and $q$ are arbitrary parameters, the general solution is obtained
through appropriate canonical transformations. We also present the conservative
Hamiltonian structure of the damped Mathews-Lakshmanan oscillator equation. The
associated Lagrangian description for all the above systems is also briefly
discussed.",0810.1819v2
2008-11-05,R-matrix inner-shell electron-impact excitation of Fe$^{15+}$ including Auger-plus-radiation damping,"We present results for the inner-shell electron-impact excitation of
Fe$^{15+}$ using the intermediate-coupling frame transformation {\it R}-matrix
approach in which Auger-plus-radiation damping has been included. The target
and close-coupling expansions are both taken to be the 134 levels belonging to
the configurations ${\rm 2s^22p^63}l$, ${\rm 2s^22p^53s3}l$, ${\rm
2s^22p^53p^2}$ and ${\rm 2s^22p^53p3d}$. The comparison of Maxwell-averaged
effective collision strengths with and without damping shows that the damping
reduction is about 30-40% for many transitions at low temperatures, but up to
80% for a few transitions. As a consequence, the results of previous Dirac
$R$-matrix calculations (Aggarwal and Keenan, 2008) overestimate the effective
collision strengths due to their omission of Auger-plus-radiation damping.",0811.0750v1
2009-03-11,An alternate design for CLIC main linac wakefield suppression,"The present design of the main accelerating structure for CLIC is based on
heavy damping (WDS) with a Q of ~10. The wakefield suppression in this case
entails locating the damping materials in relatively close proximity to the
accelerating cells. Herein we present an alternate design for the main
accelerating structures. We detune the lowest dipole band by prescribing a
Gaussian distribution to the cell parameters and consider moderate damping
Q~500 to prevent the recoherence of the modes; in this case the damping
materials can be located at an extended distance from the accelerating
structure. The procedure to achieve a well-damped wakefield is described.
Results are presented elucidating the various designs including the current one
which is being developed to incorporate r.f. breakdown, pulse surface heating
and beam dynamics constraints.",0903.1935v1
2009-04-17,Revealing Sub-Surface Vibrational Modes by Atom-Resolved Damping Force Spectroscopy,"We propose to use the damping signal of an oscillating cantilever in dynamic
atomic force microscopy as a noninvasive tool to study the vibrational
structure of the substrate. We present atomically resolved maps of damping in
carbon nanotube peapods, capable of identifying the location and packing of
enclosed Dy@C82 molecules as well as local excitations of vibrational modes
inside nanotubes of different diameter. We elucidate the physical origin of
damping in a microscopic model and provide quantitative interpretation of the
observations by calculating the vibrational spectrum and damping of Dy@C82
inside nanotubes with different diameters using ab initio total energy and
molecular dynamics calculations.",0904.2666v1
2009-08-04,Time domain detection of pulsed spin torque damping reduction,"Combining multiple ultrafast spin torque impulses with a 5 nanosecond
duration pulse for damping reduction, we observe time-domain precession which
evolves from an initial 1 ns duration transient with changing precessional
amplitude to constant amplitude oscillations persisting for over 2 ns. These
results are consistent with relaxation of the transient trajectories to a
stable orbit with nearly zero damping. We find that in order to observe
complete damping cancellation and the transient behavior in a time domain
sampling measurement, a short duration, fast rise-time pulse is required to
cancel damping without significant trajectory dephasing.",0908.0481v1
2009-10-02,Damping of a nanomechanical oscillator strongly coupled to a quantum dot,"We present theoretical and experimental results on the mechanical damping of
an atomic force microscope cantilever strongly coupled to a self-assembled InAs
quantum dot. When the cantilever oscillation amplitude is large, its motion
dominates the charge dynamics of the dot which in turn leads to nonlinear,
amplitude-dependent damping of the cantilever. We observe highly asymmetric
lineshapes of Coulomb blockade peaks in the damping that reflect the degeneracy
of energy levels on the dot, in excellent agreement with our strong coupling
theory. Furthermore, we predict that excited state spectroscopy is possible by
studying the damping versus oscillation amplitude, in analogy to varying the
amplitude of an ac gate voltage.",0910.0308v1
2010-01-27,The spatial damping of magnetohydrodynamic waves in a flowing partially ionised prominence plasma,"Solar prominences are partially ionised plasmas displaying flows and
oscillations. These oscillations show time and spatial damping and, commonly,
have been explained in terms of magnetohydrodynamic (MHD) waves. We study the
spatial damping of linear non-adiabatic MHD waves in a flowing partially
ionised plasma, having prominence-like physical properties. We consider single
fluid equations for a partially ionised hydrogen plasma including in the energy
equation optically thin radiation, thermal conduction by electrons and
neutrals, and heating. Keeping the frequency real and fixed, we have solved the
obtained dispersion relations for the complex wavenumber, k, and have analysed
the behaviour of the damping length, wavelength and the ratio of the damping
length to the wavelength, versus period, for Alfven, fast, slow and thermal
waves.",1001.4962v1
2010-03-04,Internal dissipation of a polymer,"The dynamics of flexible polymer molecules are often assumed to be governed
by hydrodynamics of the solvent. However there is considerable evidence that
internal dissipation of a polymer contributes as well. Here we investigate the
dynamics of a single chain in the absence of solvent to characterize the nature
of this internal friction. We model the chains as freely hinged but with
localized bond angles and 3-fold symmetric dihedral angles. We show that the
damping is close but not identical to Kelvin damping, which depends on the
first temporal and second spatial derivative of monomer position. With no
internal potential between monomers, the magnitude of the damping is small for
long wavelengths and weakly damped oscillatory time dependent behavior is seen
for a large range of spatial modes. When the size of the internal potential is
increased, such oscillations persist, but the damping becomes larger. However
underdamped motion is present even with quite strong dihedral barriers for long
enough wavelengths.",1003.0944v2
2010-05-26,Indirect Evidence for Lévy Walks in Squeeze Film Damping,"Molecular flow gas damping of mechanical motion in confined geometries, and
its associated noise, is important in a variety of fields, including precision
measurement, gravitational wave detection, and MEMS devices. We used two
torsion balance instruments to measure the strength and distance-dependence of
`squeeze film' damping. Measured quality factors derived from free decay of
oscillation are consistent with gas particle superdiffusion in L\'evy walks and
inconsistent with those expected from traditional Gaussian random walk particle
motion. The distance-dependence of squeeze film damping observed in our
experiments is in agreement with a parameter-free Monte Carlo simulation. The
squeeze film damping of the motion of a plate suspended a distance d away from
a parallel surface scales with a fractional power between 1/d and 1/d^2.",1005.4926v2
2010-05-28,Gravitational wave asteroseismology with fast rotating neutron stars,"We investigate damping and growth times of the f-mode for rapidly rotating
stars and a variety of different polytropic equations of state in the Cowling
approximation. We discuss the differences in the eigenfunctions of co- and
counterrotating modes and compute the damping times of the f-mode for several
EoS and all rotation rates up to the Kepler-limit. This is the first study of
the damping/growth time of this type of oscillations for fast rotating neutron
stars in a general relativistic framework. We use these frequencies and
damping/growth times to create robust empirical formulae which can be used for
gravitational wave asteroseismology. The estimation of the damping/growth time
is based on the quadrupole formula and our results agree very well with
Newtonian ones in the appropriate limit.",1005.5228v3
2010-06-09,Synchrotron oscillation damping due to beam-beam collisions,"In DA{\Phi}NE, the Frascati e+/e- collider, the crab waist collision scheme
has been successfully implemented in 2008 and 2009. During the collision
operations for Siddharta experiment, an unusual synchrotron damping effect has
been observed. Indeed, with the longitudinal feedback switched off, the
positron beam becomes unstable with beam currents in the order of 200-300 mA.
The longitudinal instability is damped by bringing the positron beam in
collision with a high current electron beam (~2A). Besides, we have observed a
shift of \approx 600Hz in the residual synchrotron sidebands. Precise
measurements have been performed by using both a commercial spectrum analyzer
and the diagnostics capabilities of the DA{\Phi}NE longitudinal bunch-by-bunch
feedback. This damping effect has been observed in DA{\Phi}NE for the first
time during collisions with the crab waist scheme. Our explanation is that beam
collisions with a large crossing angle produce a longitudinal tune shift and a
longitudinal tune spread, providing Landau damping of synchrotron oscillations.",1006.1783v1
2010-06-30,Landau Damping of Baryon Structure Formation in the Post Reionization Epoch,"It has been suggested by Chen and Lai that the proper description of the
large scale structure formation of the universe in the post-reionization era,
which is conventionally characterized via gas hydrodynamics, should include the
plasma collective effects in the formulation. Specifically, it is the combined
pressure from the baryon thermal motions and the residual long-range
electrostatic potentials resulted from the imperfect Debye shielding, that
fights against the gravitational collapse. As a result, at small-scales the
baryons would oscillate at the ion-acoustic, instead of the conventional
neutral acoustic, frequency. In this paper we extend and improve the Chen-Lai
formulation with the attention to the Landau damping of the ion-acoustic
oscillations. Since T_e \sim T_i in the post-reionization era, the ion acoustic
oscillations would inevitably suffer the Landau damping which severely
suppresses the baryon density spectrum in the regimes of intermediate and high
wavenumber k. To describe this Landau-damping phenomenon more appropriately, we
find it necessary to modify the filtering wavenumber k_f in our analysis. It
would be interesting if our predicted Landau damping of the ion-acoustic
oscillations can be observed at high redshifts.",1006.5777v1
2010-07-12,Passive damping of beam vibrations through distributed electric networks and piezoelectric transducers: prototype design and experimental validation,"The aim of this work is two-fold: to design devices for passive electric
damping of structural vibrations by distributed piezoelectric transducers and
electric networks, and to experimentally validate the effectiveness of such a
damping concept. Two different electric networks are employed, namely a purely
resistive network and an inductive-resistive one. The presented devices can be
considered as distributed versions of the well-known resistive and resonant
shunt of a single piezoelectric transducer. The technicalfeasibility and
damping effectiveness of the proposed novel devices are assessed through the
construction of an experimental prototype. Experimental results are shown to be
in very good agreement with theoretical predictions. It is proved that the
presented technique allows for a substantial reduction in the inductances used
when compared with those required by the single resonant shunted transducer. In
particular, it is shown that the required inductance decreases when the number
of piezoelectric elements is increased. The electric networks are optimized in
order to reduce forced vibrations close to the first resonance frequency.
Nevertheless, the damping effectiveness for higher modes is experimentally
proved. As well as specific results, fundamental theoretical and experimental
considerations for passive distributed vibration control are provided.",1007.1863v1
2010-07-23,Highly-damped quasi-normal frequencies for piecewise Eckart potentials,"Highly-damped quasi-normal frequencies are very often of the form omega_n =
(offset) + i n (gap). We investigate the genericity of this phenomenon by
considering a model potential that is piecewise Eckart (piecewise
Poeschl-Teller), and developing an analytic ""quantization condition"" for the
highly-damped quasi-normal frequencies. We find that this omega_n = (offset) +
i n (gap) behaviour is generic but not universal, with the controlling feature
being whether or not the ratio of the rates of exponential falloff in the two
asymptotic directions is a rational number. These observations are of direct
relevance to any physical situation where highly-damped quasi-normal modes
(damped modes) are important --- in particular (but not limited to) to black
hole physics, both theoretical and observational.",1007.4039v2
2010-09-23,Asymptotic Spectrum of Kerr Black Holes in the Small Angular Momentum Limit,"We study analytically the highly damped quasinormal modes of Kerr black holes
in the small angular momentum limit. To check the previous analytic
calculations in the literature, which use a combination of radial and tortoise
coordinates, we reproduce all the results using the radial coordinate only.
According to the earlier calculations, the real part of the highly damped
quasinormal mode frequency of Kerr black holes approaches zero in the limit
where the angular momentum goes to zero. This result is not consistent with the
Schwarzschild limit where the real part of the highly damped quasinormal mode
frequency is equal to c^3 ln(3)/(8 pi G M). In this paper, our calculations
suggest that the highly damped quasinormal modes of Kerr black holes in the
zero angular momentum limit make a continuous transition from the Kerr value to
the Schwarzschild value. We explore the nature of this transition using a
combination of analytical and numerical techniques. Finally, we calculate the
highly damped quasinormal modes of the extremal case in which the topology of
Stokes/anti-Stokes lines takes a different form.",1009.4632v2
2010-12-31,Exact Tkachenko modes and their damping in the vortex lattice regime of rapidly rotating bosons,"We have found an exact analytical solution of the Bogoliubov-de Gennes
equations for the Tkachenko modes of the vortex lattice in the lowest Landau
level (LLL) in the thermodynamic limit at any momenta and calculated their
damping rates. At finite temperatures both Beliaev and Landau damping leads to
momentum independent damping rates in the low-energy limit, which shows that at
sufficiently low energies Tkachenko modes become strongly damped. We then found
that the mean square fluctuations of the density grow logarithmically at large
distances, which indicates that the state is ordered in the vortex lattice only
on a finite (although exponentially large) distance scale and introduces a
low-momentum cut-off. Using this circumstance we showed that at finite
temperatures the one-body density matrix undergoes an exponential decay at
large distances.",1101.0269v1
2011-01-20,Decoherence and entanglement degradation of a qubit-qutrit system in non-inertial frames,"We study the effect of decoherence on a qubit-qutrit system under the
influence of global, local and multilocal decoherence in non-inertial frames.
We show that the entanglement sudden death can be avoided in non-inertial
frames in the presence of amplitude damping, depolarizing and phase damping
channels. However, degradation of entanglement is seen due to Unruh effect. It
is shown that for lower level of decoherence, the depolarizing channel degrades
the entanglement more heavily as compared to the amplitude damping and phase
damping channels. However, for higher values of decoherence parameters,
amplitude damping channel heavily degrades the entanglement of the hybrid
system. Further more, no ESD is seen for any value of Rob's acceleration.",1101.3986v1
2011-06-23,Ratchet effect on a relativistic particle driven by external forces,"We study the ratchet effect of a damped relativistic particle driven by both
asymmetric temporal bi-harmonic and time-periodic piecewise constant forces.
This system can be formally solved for any external force, providing the
ratchet velocity as a non-linear functional of the driving force. This allows
us to explicitly illustrate the functional Taylor expansion formalism recently
proposed for this kind of systems. The Taylor expansion reveals particularly
useful to obtain the shape of the current when the force is periodic, piecewise
constant. We also illustrate the somewhat counterintuitive effect that
introducing damping may induce a ratchet effect. When the force is symmetric
under time-reversal and the system is undamped, under symmetry principles no
ratchet effect is possible. In this situation increasing damping generates a
ratchet current which, upon increasing the damping coefficient eventually
reaches a maximum and decreases toward zero. We argue that this effect is not
specific of this example and should appear in any ratchet system with tunable
damping driven by a time-reversible external force.",1106.4861v1
2011-07-17,Nonlinear-damping continuation of the nonlinear Schrödinger equation - a numerical study,"We study the nonlinear-damping continuation of singular solutions of the
critical and supercritical NLS. Our simulations suggest that for generic
initial conditions that lead to collapse in the undamped NLS, the solution of
the weakly-damped NLS $$
i\psi_t(t,\X)+\Delta\psi+|\psi|^{p-1}\psi+i\delta|\psi|^{q-1}\psi=0,\qquad0<\delta
\ll 1, $$ is highly asymmetric with respect to the singularity time, and the
post-collapse defocusing velocity of the singular core goes to infinity as the
damping coefficient $\delta$ goes to zero. In the special case of the
minimal-power blowup solutions of the critical NLS, the continuation is a
minimal-power solution with a higher (but finite) defocusing velocity, whose
magnitude increases monotonically with the nonlinear damping exponent $q$.",1107.3281v1
2011-10-05,Radiation damping in pulsed Gaussian beams,"We consider the effects of radiation damping on the electron dynamics in a
Gaussian beam model of a laser field. For high intensities, i.e. with
dimensionless intensity a0 \gg 1, it is found that the dynamics divide into
three regimes. For low energy electrons (low initial {\gamma}-factor,
{\gamma}0) the radiation damping effects are negligible. At higher energies,
but still at 2{\gamma}0 < a0, the damping alters the final displacement and the
net energy change of the electron. For 2{\gamma}0 > a0 one is in a regime of
radiation reaction induced electron capture. This capture is found to be stable
with respect to the spatial properties of the electron beam and results in a
significant energy loss of the electrons. In this regime the plane wave model
of the laser field provides a good description of the dynamics, whereas for
lower energies the Gaussian beam and plane wave models differ significantly.
Finally the dynamics are considered for the case of an XFEL field. It is found
that the significantly lower intensities of such fields inhibits the damping
effects.",1110.0996v1
2012-03-28,Analysis of the absorbing layers for the weakly-compressible lattice Boltzmann schemes,"It has been demonstrated that Lattice Boltzmann schemes (LBSs) are very
efficient for Computational AeroAcoustics (CAA). In order to handle the issue
of absorbing acoustic boundary conditions for LBS, three kinds of damping terms
are proposed and added into the right hand sides of the governing equations of
LBS. From the classical theory, these terms play an important role to absorb
and minimize the acoustic wave reflections from computational boundaries.
Meanwhile, the corresponding macroscopic equations with the damping terms are
recovered for analyzing the macroscopic behaviors of the these damping terms
and determining the critical absorbing strength. Further, in order to detect
the dissipation and dispersion behaviors, the linearized LBS with the damping
terms is derived and analyzed. The dispersive and dissipative properties are
explored in the wave-number spaces via the Von Neumann analysis. The related
damping strength critical values and the optimal absorbing term are addressed.
Finally, some benchmark problems are implemented to assess the theoretical
results.",1203.6350v1
2012-04-11,Formation of bremsstrahlung in an absorptive QED/QCD medium,"The radiative energy loss of a relativistic charge in a dense, absorptive
medium can be affected significantly by damping phenomena. The effect is more
pronounced for large energies of the charge and/or large damping of the
radiation. This can be understood in terms of a competition between the
formation time of bremsstrahlung and a damping time scale. We discuss this
competition in detail for the absorptive QED and QCD medium, focusing on the
case in which the mass of the charge is large compared to the in-medium mass of
the radiation quanta. We identify the regions in energy and parameter space, in
which either coherence or damping effects are of major importance for the
radiative energy loss spectrum. We show that damping phenomena can lead to a
stronger suppression of the spectrum than coherence effects.",1204.2469v2
2012-06-05,Existence and exponential stability of a damped wave equation with dynamic boundary conditions and a delay term,"In this paper we consider a multi-dimensional wave equation with dynamic
boundary conditions related to the Kelvin-Voigt damping and a delay term acting
on the boundary. If the weight of the delay term in the feedback is less than
the weight of the term without delay or if it is greater under an assumption
between the damping factor, and the difference of the two weights, we prove the
global existence of the solutions. Under the same assumptions, the exponential
stability of the system is proved using an appropriate Lyapunov functional.
More precisely, we show that even when the weight of the delay is greater than
the weight of the damping in the boundary conditions, the strong damping term
still provides exponential stability for the system.",1206.1010v1
2012-08-27,Analysis of the damped quantum search and its application to the one-dimensional Ising system,"An analysis on the damped quantum search by exploring the rate at which the
target state is obtained. The results were compared with that of the classical
search since the standard Grover's algorithm does not give a convergent result
if the number of target state is unknown. For a large number of target states,
the classical and the damped quantum search give a similar result. However, for
intermediate values of the target size the damped quantum search gives a higher
probability of success than the classical search. Furthermore, we also made an
analysis on the average number of iterations needed to obtain at least one of
the target states. As the number of target states is reduced, the damped
quantum search gives a better result than the classical search. The results
coincide if the size of target state is comparable to the size of the sample.",1208.5509v1
2012-10-20,Radiative damping of surface plasmon resonance in spheroidal metallic nanoparticle embedded in a dielectric medium,"The local field approach and kinetic equation method is applied to calculate
the surface plasmon radiative damping in a spheroidal metal nanoparticle
embedded in any dielectric media. The radiative damping of the surface plasmon
resonance as a function of the particle radius, shape, dielectric constant of
the surrounding medium and the light frequency is studied in detail. It is
found that the radiative damping grows quadratically with the particle radius
and oscillates with altering both the particle size and the dielectric constant
of a surrounding medium. Much attention is paid to the electron
surface-scattering contribution to the plasmon decay. All calculations of the
radiative damping are illustrated by examples on the Au and Na nanoparticles.",1210.5647v1
2012-11-11,Dissipation in relativistic superfluid neutron stars,"We analyze damping of oscillations of general relativistic superfluid neutron
stars. To this aim we extend the method of decoupling of superfluid and normal
oscillation modes first suggested in [Gusakov & Kantor PRD 83, 081304(R)
(2011)]. All calculations are made self-consistently within the finite
temperature superfluid hydrodynamics. The general analytic formulas are derived
for damping times due to the shear and bulk viscosities. These formulas
describe both normal and superfluid neutron stars and are valid for oscillation
modes of arbitrary multipolarity. We show that: (i) use of the ordinary
one-fluid hydrodynamics is a good approximation, for most of the stellar
temperatures, if one is interested in calculation of the damping times of
normal f-modes; (ii) for radial and p-modes such an approximation is poor;
(iii) the temperature dependence of damping times undergoes a set of rapid
changes associated with resonance coupling of neighboring oscillation modes.
The latter effect can substantially accelerate viscous damping of normal modes
in certain stages of neutron-star thermal evolution.",1211.2452v1
2013-03-07,Universal damping behavior of dipole oscillations of one-dimensional ultracold gases induced by quantum phase slips,"We study superflow decay via quantum phase slips in trapped one-dimensional
(1D) quantum gases through dipole oscillations induced by sudden displacement
of the trapping potential. We find the relation between the damping rate of the
dipole oscillation $G$ and the phase-slip nucleation rate $\Gamma$ as $G\propto
\Gamma/v$, where $v$ is the flow velocity. This relation allows us to show that
damping of 1D Bose gases in optical lattices, which has been extensively
studied in experiment, is due to quantum phase slips. It is also found that the
damping rate versus the flow velocity obeys the scaling formula for an impurity
potential even in the absence of an explicit impurity. We suggest that the
damping rate at a finite temperature exhibits a universal crossover behavior
upon changing the flow velocity.",1303.1616v1
2013-07-16,Blow-up of solutions to the one-dimensional semilinear wave equation with damping depending on time and space variables,"In this paper, we give a small data blow-up result for the one-dimensional
semilinear wave equation with damping depending on time and space variables. We
show that if the damping term can be regarded as perturbation, that is,
non-effective damping in a certain sense, then the solution blows up in finite
time for any power of nonlinearity. This gives an affirmative answer for the
conjecture that the critical exponent agrees with that of the wave equation
when the damping is non-effective in one space dimension.",1307.4260v2
2013-11-12,Landau damping: paraproducts and Gevrey regularity,"We give a new, simpler, proof of nonlinear Landau damping on T^d in
Gevrey-1/s regularity (s > 1/3) which matches the regularity requirement
predicted by the formal analysis of Mouhot and Villani in the original proof of
Landau damping [Acta Mathematica 2011]. Our proof combines in a novel way ideas
from the original proof of Landau damping and the proof of inviscid damping in
2D Euler [arXiv:1306.5028]. As in the work on 2D Euler, we use paraproduct
decompositions and controlled regularity loss to replace the Newton iteration
scheme employed in the original proof. We perform time-response estimates
adapted from the original proof to control the plasma echoes and couple them to
energy estimates on the distribution function in the style of the work on 2D
Euler.",1311.2870v1
2014-02-07,One-dimensional random attractor and rotation number of the stochastic damped sine-Gordon equation,"This paper is devoted to the study of the asymptotic dynamics of the
stochastic damped sine-Gordon equation with homogeneous Neumann boundary
condition. It is shown that for any positive damping and diffusion
coefficients, the equation possesses a random attractor, and when the damping
and diffusion coefficients are sufficiently large, the random attractor is a
one-dimensional random horizontal curve regardless of the strength of noise.
Hence its dynamics is not chaotic. It is also shown that the equation has a
rotation number provided that the damping and diffusion coefficients are
sufficiently large, which implies that the solutions tend to oscillate with the
same frequency eventually and the so called frequency locking is successful.",1402.1787v1
2014-02-26,Comparison of methods for numerical calculation of continuum damping,"Continuum resonance damping is an important factor in determining the
stability of certain global modes in fusion plasmas. A number of analytic and
numerical approaches have been developed to compute this damping, particularly
in the case of the toroidicity-induced shear Alfv\'en eigenmode. This paper
compares results obtained using an analytical perturbative approach with those
found using resistive and complex contour numerical approaches. It is found
that the perturbative method does not provide accurate agreement with reliable
numerical methods for the range of parameters examined. This discrepancy exists
even in the limit where damping approaches zero. When the perturbative
technique is implemented using a standard finite element method, the damping
estimate fails to converge with radial grid resolution. The finite elements
used cannot accurately represent the eigenmode in the region of the continuum
resonance, regardless of the number of radial grid points used.",1402.6389v1
2014-05-16,Quantum corrections to nonlinear ion acoustic wave with Landau damping,"Quantum corrections to nonlinear ion acoustic wave with Landau damping have
been computed using Wigner equation approach. The dynamical equation governing
the time development of nonlinear ion acoustic wave with semiclassical quantum
corrections is shown to have the form of higher KdV equation which has higher
order nonlinear terms coming from quantum corrections, with the usual classical
and quantum corrected Landau damping integral terms.
  The conservation of total number of ions is shown from the evolution
equation. The decay rate of KdV solitary wave amplitude due to presence of
Landau damping terms has been calculated assuming the Landau damping parameter
$\alpha_1 = \sqrt{{m_e}/{m_i}}$ to be of the same order of the quantum
parameter $Q = {\hbar^2}/({24 m^2 c^2_{s} L^2})$. The amplitude is shown to
decay very slowly with time as determined by the quantum factor $ Q$.",1405.4107v1
2014-05-19,Mesh Size and Damped Edge Effects in Micromagnetic Spin Wave Simulation,"We have studied the dependence of spin wave dispersion on the characteristics
of the mesh used in a finite element micromagnetic simulation. It is shown that
the dispersion curve has a cut off at a frequency which is analytically
predictable. The frequency depends on the average mesh length used for the
simulation. Based on this, a recipe to effectively obtain the dispersion
relation has been suggested. In a separate study, spin wave reflections are
absorbed by introducing highly damped edges in the device. However, an abrupt
change in the damping parameter causes reflections. We compare damping profiles
and identify an exponential damping profile as causing significantly less
reflections.",1405.4615v2
2014-07-08,Fourier-Hermite spectral representation for the Vlasov-Poisson system in the weakly collisional limit,"We study Landau damping in the 1+1D Vlasov-Poisson system using a
Fourier-Hermite spectral representation. We describe the propagation of free
energy in phase space using forwards and backwards propagating Hermite modes
recently developed for gyrokinetics [Schekochihin et al. (2014)]. The change in
the electric field corresponds to the net Hermite flux via a free energy
evolution equation. In linear Landau damping, decay in the electric field
corresponds to forward propagating Hermite modes; in nonlinear damping, the
initial decay is followed by a growth phase characterised by the generation of
backwards propagating Hermite modes by the nonlinear term. The free energy
content of the backwards propagating modes increases exponentially until
balancing that of the forward propagating modes. Thereafter there is no
systematic net Hermite flux, so the electric field cannot decay and the
nonlinearity effectively suppresses Landau damping. These simulations are
performed using the fully-spectral 5D gyrokinetics code SpectroGK [Parker et
al. 2014], modified to solve the 1+1D Vlasov-Poisson system. This captures
Landau damping via an iterated L\'enard-Bernstein collision operator or via
Hou-Li filtering in velocity space. Therefore the code is applicable even in
regimes where phase-mixing and filamentation are dominant.",1407.1932v1
2014-08-15,Linear hyperbolic equations with time-dependent propagation speed and strong damping,"We consider a second order linear equation with a time-dependent coefficient
c(t) in front of the ""elastic"" operator. For these equations it is well-known
that a higher space-regularity of initial data compensates a lower
time-regularity of c(t).
  In this paper we investigate the influence of a strong dissipation, namely a
friction term which depends on a power of the elastic operator.
  What we discover is a threshold effect. When the exponent of the elastic
operator in the friction term is greater than 1/2, the damping prevails and the
equation behaves as if the coefficient c(t) were constant. When the exponent is
less than 1/2, the time-regularity of c(t) comes into play. If c(t) is regular
enough, once again the damping prevails. On the contrary, when c(t) is not
regular enough the damping might be ineffective, and there are examples in
which the dissipative equation behaves as the non-dissipative one. As expected,
the stronger is the damping, the lower is the time-regularity threshold.
  We also provide counterexamples showing the optimality of our results.",1408.3499v1
2014-08-14,Particle Dynamics in Damped Nonlinear Quadrupole Ion Traps,"We examine the motions of particles in quadrupole ion traps as a function of
damping and trapping forces, including cases where nonlinear damping or
nonlinearities in the electric field geometry play significant roles. In the
absence of nonlinearities, particles are either damped to the trap center or
ejected, while their addition brings about a rich spectrum of stable closed
particle trajectories. In three-dimensional (3D) quadrupole traps, the extended
orbits are typically confined to the trap axis, and for this case we present a
1D analysis of the relevant equation of motion. We follow this with an analysis
of 2D quadrupole traps that frequently show diamond-shaped closed orbits. For
both the 1D and 2D cases we present experimental observations of the calculated
trajectories in microparticle ion traps. We also report the discovery of a new
collective behavior in damped 2D microparticle ion traps, where particles
spontaneously assemble into a remarkable knot of overlapping, corotating
diamond orbits, self-stabilized by air currents arising from the particle
motion.",1409.6262v1
2015-01-03,Finite-Parameters Feedback Control for Stabilizing Damped Nonlinear Wave Equations,"In this paper we introduce a finite-parameters feedback control algorithm for
stabilizing solutions of various classes of damped nonlinear wave equations.
Specifically, stabilization the zero steady state solution of initial boundary
value problems for nonlinear weakly and strongly damped wave equations,
nonlinear wave equation with nonlinear damping term and some related nonlinear
wave equations, introducing a feedback control terms that employ parameters,
such as, finitely many Fourier modes, finitely many volume elements and
finitely many nodal observables and controllers. In addition, we also establish
the stabilization of the zero steady state solution to initial boundary value
problem for the damped nonlinear wave equation with a controller acting in a
proper subdomain. Notably, the feedback controllers proposed here can be
equally applied for stabilizing other solutions of the underlying equations.",1501.00556v1
2015-06-26,A Universal Damping Mechanism of Quantum Vibrations in Deep Sub-Barrier Fusion Reactions,"We demonstrate the damping of quantum octupole vibrations near the touching
point when two colliding nuclei approach each other in the mass-asymmetric
$^{208}$Pb + $^{16}$O system, for which the strong fusion hindrance was clearly
observed. We, for the first time, apply the random-phase approximation method
to the heavy-mass asymmetric di-nuclear system to calculate the transition
strength $B$(E3) as a function of the center-of-mass distance. The obtained
$B$(E3) strengths are substantially damped near the touching point, because the
single-particle wave functions of the two nuclei strongly mix with each other
and a neck is formed. The energy-weighted sums of $B$(E3) are also strongly
correlated with the damping factor which is phenomenologically introduced in
the standard coupled-channel calculations to reproduce the fusion hindrance.
This strongly indicates that the damping of the quantum vibrations universally
occurs in the deep sub-barrier fusion reactions.",1506.07963v1
2015-07-28,Phenomenology of chiral damping in noncentrosymmetric magnets,"A phenomenology of magnetic chiral damping is proposed in the context of
magnetic materials lacking inversion symmetry breaking. We show that the
magnetic damping tensor adopts a general form that accounts for a component
linear in magnetization gradient in the form of Lifshitz invariants. We propose
different microscopic mechanisms that can produce such a damping in
ferromagnetic metals, among which spin pumping in the presence of anomalous
Hall effect and an effective ""$s$-$d$"" Dzyaloshinskii-Moriya antisymmetric
exchange. The implication of this chiral damping in terms of domain wall motion
is investigated in the flow and creep regimes. These predictions have major
importance in the context of field- and current-driven texture motion in
noncentrosymmetric (ferro-, ferri-, antiferro-)magnets, not limited to metals.",1507.07762v1
2015-08-06,"Phenomenological description of the nonlocal magnetization relaxation in magnonics, spintronics, and domain-wall dynamics","A phenomenological equation called Landau-Lifshitz-Baryakhtar (LLBar)
equation, which could be viewed as the combination of Landau-Lifshitz (LL)
equation and an extra ""exchange damping"" term, was derived by Baryakhtar using
Onsager's relations. We interpret the origin of this ""exchange damping"" as
nonlocal damping by linking it to the spin current pumping. The LLBar equation
is investigated numerically and analytically for the spin wave decay and domain
wall motion. Our results show that the lifetime and propagation length of
short-wavelength magnons in the presence of nonlocal damping could be much
smaller than those given by LL equation. Furthermore, we find that both the
domain wall mobility and the Walker breakdown field are strongly influenced by
the nonlocal damping.",1508.01478v1
2016-01-05,Vlasov Simulations of Electron-Ion Collision Effects on Damping of Electron Plasma Waves,"Collisional effects can play an essential role in the dynamics of plasma
waves by setting a minimum damping rate and by interfering with wave-particle
resonances. Kinetic simulations of the effects of electron-ion pitch angle
scattering on Electron Plasma Waves (EPWs) are presented here. In particular,
the effects of such collisions on the frequency and damping of small-amplitude
EPWs for a range of collision rates and wave phase velocities are computed and
compared with theory. Both the Vlasov simulations and linear kinetic theory
find the direct contribution of electron-ion collisions to wave damping is
about a factor of two smaller than is obtained from linearized fluid theory. To
our knowledge, this simple result has not been published before.
  Simulations have been carried out using a grid-based (Vlasov) approach, based
on a high-order conservative finite difference method for discretizing the
Fokker-Planck equation describing the evolution of the electron distribution
function. Details of the implementation of the collision operator within this
framework are presented. Such a grid-based approach, which is not subject to
numerical noise, is of particular interest for the accurate measurements of the
wave damping rates.",1601.01002v1
2016-02-13,The effect of orbital damping during planet migration on the Inclination and Eccentricity Distributions of Neptune Trojans,"We explore planetary migration scenarios for formation of high inclination
Neptune Trojans (NTs) and how they are affected by the planetary migration of
Neptune and Uranus. If Neptune and Uranus's eccentricity and inclination were
damped during planetary migration, then their eccentricities and inclinations
were higher prior and during migration than their current values. Using test
particle integrations we study the stability of primordial NTs, objects that
were initially Trojans with Neptune prior to migration. We also study
Trans-Neptunian objects captured into resonance with Neptune and becoming NTs
during planet migration. We find that most primordial NTs were unstable and
lost if eccentricity and inclination damping took place during planetary
migration. With damping, secular resonances with Neptune can increase a low
eccentricity and inclination population of Trans-Neptunian objects increasing
the probability that they are captured into 1:1 resonance with Neptune,
becoming high inclination NTs. We suggest that the resonant trapping scenario
is a promising and more effective mechanism explaining the origin of NTs that
is particularly effective if Uranus and Neptune experienced eccentricity and
inclination damping during planetary migration.",1602.04303v1
2016-03-08,Damping of the Higgs and Nambu-Goldstone modes of superfluid Bose gases at finite temperatures,"We study collective modes of superfluid Bose gases in optical lattices at
commensurate fillings. We focus on the vicinity of the quantum phase transition
to the Mott insulator, where there exists the Higgs amplitude mode in addition
to the Nambu-Goldstone phase mode associated with the spontaneous U(1) symmetry
breaking. We analyze finite-temperature effects on the damping of the
collective modes by using an effective spin-1 model and the field theoretical
methods based on the finite-temperature Green's function. We calculate the
damping rates up to 1-loop order and evaluate them analytically and
numerically. We show that the damping rate of the Higgs mode increases with
increasing the temperature but it remains underdamped up to a typical
temperature achieved in experiments. Moreover, we find that the Nambu-Goldstone
mode attenuates via a Landau damping process resulting from interactions with
the Higgs mode and it can be overdamped at the typical temperature in a certain
parameter region.",1603.02395v1
2016-04-12,Offline software for the DAMPE experiment,"A software system has been developed for the DArk Matter Particle Explorer
(DAMPE) mission, a satellite-based experiment. The DAMPE software is mainly
written in C++ and steered using Python script. This article presents an
overview of the DAMPE offline software, including the major architecture design
and specific implementation for simulation, calibration and reconstruction. The
whole system has been successfully applied to DAMPE data analysis, based on
which some results from simulation and beam test experiments are obtained and
presented.",1604.03219v6
2016-04-18,Stabilization of Damped Waves on Spheres and Zoll Surfaces of Revolution,"We study the strong stabilization of wave equations on some sphere-like
manifolds, with rough damping terms which do not satisfy the geometric control
condition posed by Rauch-Taylor and Bardos-Lebeau-Rauch. We begin with an
unpublished result of G. Lebeau, which states that on S^d , the indicator
function of the upper hemisphere strongly stabilizes the damped wave equation,
even though the equators, which are geodesics contained in the boundary of the
upper hemisphere, do not enter the damping region. Then we extend this result
on dimension 2, to Zoll surfaces of revolution, whose geometry is similar to
that of S^2 . In particular, geometric objects such as the equator, and the
hemi-surfaces are well defined. Our result states that the indicator function
of the upper hemi-surface strongly stabilizes the damped wave equation, even
though the equator, as a geodesic, does not enter the upper hemi-surface
either.",1604.05218v2
2016-07-25,Damping of parametrically excited magnons in the presence of the longitudinal spin Seebeck effect,"The impact of the longitudinal spin Seebeck effect (LSSE) on the magnon
damping in magnetic-insulator/nonmagnetic-metal bilayers was recently discussed
in several reports. However, results of those experiments can be blurred by
multimode excitation within the measured linewidth. In order to avoid possible
intermodal interference, we investigated the damping of a single magnon group
in a platinum covered Yttrium Iron Garnet (YIG) film by measurement of the
threshold of its parametric excitation. Both dipolar and exchange spin-wave
branches were probed. It turned out that the LSSE-related modification of
spin-wave damping in a micrometer-thick YIG film is too weak to be observed in
the entire range of experimentally accessible wavevectors. At the same time,
the change in the mean temperature of the YIG layer, which can appear by
applying a temperature gradient, strongly modifies the damping value.",1607.07274v1
2016-07-27,Frequency dispersion of small-amplitude capillary waves in viscous fluids,"This work presents a detailed study of the dispersion of capillary waves with
small amplitude in viscous fluids using an analytically derived solution to the
initial value problem of a small-amplitude capillary wave as well as direct
numerical simulation. A rational parametrization for the dispersion of
capillary waves in the underdamped regime is proposed, including predictions
for the wavenumber of critical damping based on a harmonic oscillator model.
The scaling resulting from this parametrization leads to a self-similar
solution of the frequency dispersion of capillary waves that covers the entire
underdamped regime, which allows an accurate evaluation of the frequency at a
given wavenumber, irrespective of the fluid properties. This similarity also
reveals characteristic features of capillary waves, for instance that critical
damping occurs when the characteristic timescales of dispersive and dissipative
mechanisms are balanced. In addition, the presented results suggest that the
widely adopted hydrodynamic theory for damped capillary waves does not
accurately predict the dispersion when viscous damping is significant and a new
definition of the damping rate, which provides consistent accuracy in the
underdamped regime, is presented.",1607.08266v1
2016-10-18,On the stability of the Bresse system with frictional damping,"In this paper, we consider the Bresse system with frictional damping terms
and prove some optimal decay results for the $L^2$-norm of the solution and its
higher order derivatives. In fact, if we consider just one damping term acting
on the second equation of the solution, we show that the solution does not
decay at all. On the other hand, by considering one damping term alone acting
on the third equation, we show that this damping term is strong enough to
stabilize the whole system. In this case, we found a completely new stability
number that depends on the parameters in the system.
  In addition, we prove the optimality of the results by using eigenvalues
expansions. Our obtained results have been proved under some assumptions on the
wave speeds of the three equations in the Bresse system.",1610.05500v2
2017-01-12,Blow-up for semilinear wave equations with the scale invariant damping and super-Fujita exponent,"The blow-up for semilinear wave equations with the scale invariant damping
has been well-studied for sub-Fujita exponent. However, for super-Fujita
exponent, there is only one blow-up result which is obtained in 2014 by
Wakasugi in the case of non-effective damping. In this paper we extend his
result in two aspects by showing that: (I) the blow-up will happen for bigger
exponent, which is closely related to the Strauss exponent, the critical number
for non-damped semilinear wave equations; (II) such a blow-up result is
established for a wider range of the constant than the known non-effective one
in the damping term.",1701.03232v3
2017-02-17,Transition of multi-diffusive states in a biased periodic potential,"We study a frequency-dependent damping model of hyper-diffusion within the
generalized Langevin equation. The model allows for the colored noise defined
by its spectral density, assumed to be proportional to $\omega^{\delta-1}$ at
low frequencies with $0<\delta<1$ (sub-Ohmic damping) or $1<\delta<2$
(super-Ohmic damping), where the frequency-dependent damping is deduced from
the noise by means of the fluctuation-dissipation theorem. It is shown that for
super-Ohmic damping and certain parameters, the diffusive process of the
particle in a titled periodic potential undergos sequentially four
time-regimes: thermalization, hyper-diffusion, collapse and asymptotical
restoration. For analysing transition phenomenon of multi-diffusive states, we
demonstrate that the first exist time of the particle escaping from the locked
state into the running state abides by an exponential distribution. The concept
of equivalent velocity trap is introduced in the present model, moreover,
reformation of ballistic diffusive system is also considered as a marginal
situation, however there does not exhibit the collapsed state of diffusion.",1702.05370v1
2017-09-27,Wave turbulence in vibrating plates : the effect of damping,"The effect of damping in the wave turbulence regime for thin vibrating plates
is studied. An experimental method, allowing measurements of dissipation in the
system at all scales, is first introduced. Practical experimental devices for
increasing the dissipation are used. The main observable consequence of
increasing the damping is a significant modification in the slope of the power
spectral density, so that the observed power laws are not in a pure inertial
regime. However, the system still displays a turbulent behavior with a cut-off
frequency that is determined by the injected power which does not depend on
damping. By using the measured damping power-law in numerical simulations,
similar conclusions are drawn out.",1709.09438v1
2017-11-02,Vibration Damping of Carbon Nanotube Assembly Materials,"Vibration reduction is of great importance in various engineering
applications, and a material that exhibits good vibration damping along with
high strength and modulus has become more and more vital. Owing to the superior
mechanical property of carbon nanotube (CNT), new types of vibration damping
material can be developed. This paper presents recent advancements, including
our progresses, in the development of high-damping macroscopic CNT assembly
materials, such as forests, gels, films, and fibers. In these assemblies,
structural deformation of CNTs, zipping and unzipping at CNT connection nodes,
strengthening and welding of the nodes, and sliding between CNTs or CNT bundles
are playing important roles in determining the viscoelasticity, and elasticity
as well. Towards the damping enhancement, strategies for micro-structure and
interface design are also discussed.",1711.00623v1
2017-12-05,Dark Matter Annihilation from Nearby Ultra-compact Micro Halos to Explain the Tentative Excess at ~1.4 TeV in DAMPE data,"The tentative 1.4 TeV excess in the $e^+e^-$ spectrum measured by The DArk
Matter Particle Explorer (DAMPE) motivates the possible existence of one or
more local dark matter concentrated regions. In particular, Ultra-compact Micro
Halos (UCMHs) seeded by large density perturbations in the early universe,
allocated within ~0.3 kpc from the solar system, could provide the potential
source of electrons and positrons produced from dark matter annihilation,
enough to explain the DAMPE signal. Here we consider a UCMH with density
profile assuming radial in-fall and explore the preferred halo parameters to
explain the 1.4 TeV ""DAMPE excess"". We find that typical parameter space of
UCMHs can easily explain the ""DAMPE excess"" with usual thermal-averaged
annihilation cross section of WIMP. The fraction of dark matter stored in such
UCMHs in the Galactic-scale halo can be reduced to as small as $O(10^{-5})$,
well within the current cosmological and astrophysical constraints.",1712.01724v2
2017-12-21,A new charge reconstruction algorithm for the DAMPE silicon microstrip detector,"The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within the Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). The Silicon-Tungsten Tracker (STK), which is composed
of 768 singled-sided silicon microstrip detectors, is one of the four
subdetectors in DAMPE, providing track reconstruction and charge identification
for relativistic charged particles. The charge response of DAMPE silicon
microstrip detectors is complicated, depending on the incident angle and impact
position. A new charge reconstruction algorithm for the DAMPE silicon
microstrip detector is introduced in this paper. This algorithm can correct the
complicated charge response, and was proved applicable by the ion test beam.",1712.08011v1
2018-01-23,The dominancy of damping like torque for the current induced magnetization switching in Pt/Co/W multilayers,"Two classes of spin-orbit coupling (SOC) mechanisms have been considered as
candidate sources for the spin orbit torque (SOT): the spin Hall Effect (SHE)
in heavy metals with strong SOC and the Rashba effect arising from broken
inversion symmetry at material surfaces and interfaces. In this work, we have
investigated the SOT in perpendicularly magnetized Pt/Co/W films, which is
compared with the results in Pt/Co/AlOx films. Theoretically, in the case of
the asymmetric structure of trilayers with opposite sign of spin Hall angle,
both damping like torque and field like torque due to the SHE and the Rashba
effect will be enhanced. Using the harmonic measurements, we have characterized
the effective fields corresponding to the damping like torque and the field
like torque, but we have found the dominancy of damping like torque in the
Pt/Co/W films. It is much different from the results in the Pt/Co/AlOx films,
in which both the damping like torque and the field like torque are strong.",1801.07408v1
2018-02-20,The damped wave equation with unbounded damping,"We analyze new phenomena arising in linear damped wave equations on unbounded
domains when the damping is allowed to become unbounded at infinity. We prove
the generation of a contraction semigroup, study the relation between the
spectra of the semigroup generator and the associated quadratic operator
function, the convergence of non-real eigenvalues in the asymptotic regime of
diverging damping on a subdomain, and we investigate the appearance of
essential spectrum on the negative real axis. We further show that the presence
of the latter prevents exponential estimates for the semigroup and turns out to
be a robust effect that cannot be easily canceled by adding a positive
potential. These analytic results are illustrated by examples.",1802.07026v1
2018-04-06,Exponential Integrators Preserving Local Conservation Laws of PDEs with Time-Dependent Damping/Driving Forces,"Structure-preserving algorithms for solving conservative PDEs with added
linear dissipation are generalized to systems with time-dependent
damping/driving terms. This study is motivated by several PDE models of
physical phenomena, such as Korteweg-de Vries, Klein-Gordon, Schr\""{o}dinger,
and Camassa-Holm equations, all with damping/driving terms and time-dependent
coefficients. Since key features of the PDEs under consideration are described
by local conservation laws, which are independent of the boundary conditions,
the proposed (second-order in time) discretizations are developed with the
intent of preserving those local conservation laws. The methods are
respectively applied to a damped-driven nonlinear Schr\""{o}dinger equation and
a damped Camassa-Holm equation. Numerical experiments illustrate the
structure-preserving properties of the methods, as well as favorable results
over other competitive schemes.",1804.02266v1
2018-05-29,Enhancing precision of damping rate by PT symmetric Hamiltonian,"We utilize quantum Fisher information to investigate the damping parameter
precision of a dissipative qubit. PT symmetric non-Hermitian Hamiltonian is
used to enhance the parameter precision in two models: one is direct PT
symmetric quantum feedback; the other is that the damping rate is encoded into
a effective PT symmetric non-Hermitian Hamiltonian conditioned on the absence
of decay events. We find that compared with the case without feedback and with
Hermitian quantum feedback, direct PT symmetric non-Hermitan quantum feedback
can obtain better precision of damping rate. And in the second model the result
shows that the uncertainty of damping rate can be close to 0 at the exceptional
point. We also obtain that non-maximal multiparticle entanglement can improve
the precision to reach Heisenberg limit.",1805.11216v1
2018-05-31,Damping Effect on PageRank Distribution,"This work extends the personalized PageRank model invented by Brin and Page
to a family of PageRank models with various damping schemes. The goal with
increased model variety is to capture or recognize a larger number of types of
network activities, phenomena and propagation patterns. The response in
PageRank distribution to variation in damping mechanism is then characterized
analytically, and further estimated quantitatively on 6 large real-world link
graphs. The study leads to new observation and empirical findings. It is found
that the difference in the pattern of PageRank vector responding to parameter
variation by each model among the 6 graphs is relatively smaller than the
difference among 3 particular models used in the study on each of the graphs.
This suggests the utility of model variety for differentiating network
activities and propagation patterns. The quantitative analysis of the damping
mechanisms over multiple damping models and parameters is facilitated by a
highly efficient algorithm, which calculates all PageRank vectors at once via a
commonly shared, spectrally invariant subspace. The spectral space is found to
be of low dimension for each of the real-world graphs.",1806.00127v1
2018-08-10,Relativistic charge solitons created due to nonlinear Landau damping: A candidate for explaining coherent radio emission in pulsars,"A potential resolution for the generation of coherent radio emission in
pulsar plasma is the existence of relativistic charge solitons, which are
solutions of nonlinear Schr\""{o}dinger equation (NLSE). In an earlier study,
Melikidze et al. (2000) investigated the nature of these charge solitons;
however, their analysis ignored the effect of nonlinear Landau damping, which
is inherent in the derivation of the NLSE in the pulsar pair plasma. In this
paper we include the effect of nonlinear Landau damping and obtain solutions of
the NLSE by applying a suitable numerical scheme. We find that for reasonable
parameters of the cubic nonlinearity and nonlinear Landau damping, soliton-like
intense pulses emerge from an initial disordered state of Langmuir waves and
subsequently propagate stably over sufficiently long times, during which they
are capable of exciting the coherent curvature radiation in pulsars. We
emphasize that this emergence of {\em stable} intense solitons from a
disordered state does not occur in a purely cubic NLSE; thus, it is {\em
caused} by the nonlinear Landau damping.",1808.03657v1
2018-11-21,Super Damping of Mechanical Vibrations,"We report the phenomenon of coherent super decay, where a linear sum of
several damped oscillators can collectively decay much faster than the
individual ones in the first stage, followed by stagnating ones after more than
90 percent of the energy has already been dissipated. The parameters of the
damped oscillators for CSD are determined by the process of response function
decomposition, which is to use several slow decay response functions to
approximate the response function of a fast decay reference resonator. Evidence
established in experiments and in finite element simulations not only strongly
supported the numerical investigations, but also uncovered an unexplored region
of the tuned mass damper parameter space where TMDs with total mass less than
0.2 percent of a primary free body can damp its first resonance up to a damping
ratio of 4.6 percent. Our findings also shed light onto the intriguing
underline connections between complex functions with different singular points.",1811.08621v2
2018-11-29,Flowing fibers as a proxy of turbulence statistics,"The flapping states of a flexible fiber fully coupled to a three-dimensional
turbulent flow are investigated via state-of-the-art numerical methods. Two
distinct flapping regimes are predicted by the phenomenological theory recently
proposed by Rosti et al. [Phys. Rev. Lett. 121, 044501, 2018]: the under-damped
regime, where the elasticity strongly affects the fiber dynamics, and the
over-damped regime, where the elastic effects are strongly inhibited. In both
cases we can identify a critical value of the bending rigidity of the fiber by
a resonance condition, which further provides a distinction between different
flapping behaviors, especially in the under-damped case. We validate the theory
by means of direct numerical simulations and find that, both for the
over-damped regime and for the under-damped one, fibers are effectively slaved
to the turbulent fluctuations and can therefore be used as a proxy to measure
various two-point statistics of turbulence. Finally, we show that this holds
true also in the case of a passive fiber, without any feedback force on the
fluid.",1811.12023v2
2018-11-29,The Lugiato-Lefever equation with nonlinear damping caused by two photon absorption,"In this paper we investigate the effect of nonlinear damping on the
Lugiato-Lefever equation $$ \i \partial_t a = -(\i-\zeta) a - da_{xx}
-(1+\i\kappa)|a|^2a +\i f $$ on the torus or the real line. For the case of the
torus it is shown that for small nonlinear damping $\kappa>0$ stationary
spatially periodic solutions exist on branches that bifurcate from constant
solutions whereas all nonconstant solutions disappear when the damping
parameter $\kappa$ exceeds a critical value. These results apply both for
normal ($d<0$) and anomalous ($d>0$) dispersion. For the case of the real line
we show by the Implicit Function Theorem that for small nonlinear damping
$\kappa>0$ and large detuning $\zeta\gg 1$ and large forcing $f\gg 1$ strongly
localized, bright solitary stationary solutions exists in the case of anomalous
dispersion $d>0$. These results are achieved by using techniques from
bifurcation and continuation theory and by proving a convergence result for
solutions of the time-dependent Lugiato-Lefever equation.",1811.12200v3
2018-11-26,Linear Theory of Electron-Plasma Waves at Arbitrary Collisionality,"The dynamics of electron-plasma waves are described at arbitrary
collisionality by considering the full Coulomb collision operator. The
description is based on a Hermite-Laguerre decomposition of the velocity
dependence of the electron distribution function. The damping rate, frequency,
and eigenmode spectrum of electron-plasma waves are found as functions of the
collision frequency and wavelength. A comparison is made between the
collisionless Landau damping limit, the Lenard-Bernstein and Dougherty
collision operators, and the electron-ion collision operator, finding large
deviations in the damping rates and eigenmode spectra. A purely damped entropy
mode, characteristic of a plasma where pitch-angle scattering effects are
dominant with respect to collisionless effects, is shown to emerge numerically,
and its dispersion relation is analytically derived. It is shown that such a
mode is absent when simplified collision operators are used, and that
like-particle collisions strongly influence the damping rate of the entropy
mode.",1811.12855v2
2019-01-17,"Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures","We investigate the effect of capping layer (CAP) on the interfacial magnetic
anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
HfOx, or TaN). At room temperature (RT) the CAP materials influence the
effective magnitude of K_S, which is associated with a formation of interfacial
magnetic oxides. The dynamical dissipation parameters of Co are considerably
influenced by the CAP (especially MgO) while those of Py are not. This is
possibly due to an extra magnetic damping via spin-pumping process across the
Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
interfacial CoO. It is also observed that both anti-damping and field-like SOT
efficiencies vary marginally with the CAP in the thickness ranges we examined.
Our results reveal the crucial role of interfacial oxides on the perpendicular
magnetic anisotropy, magnetic damping, and SOTs.",1901.05777v1
2019-05-31,The amplitude of solar p-mode oscillations from three-dimensional convection simulations,"The amplitude of solar p-mode oscillations is governed by stochastic
excitation and mode damping, both of which take place in the surface convection
zone. However, the time-dependent, turbulent nature of convection makes it
difficult to self-consistently study excitation and damping processes through
the use of traditional one-dimensional hydrostatic models. To this end, we
carried out \textit{ab initio} three-dimensional, hydrodynamical numerical
simulations of the solar atmosphere to investigate how p-modes are driven and
dissipated in the Sun. The description of surface convection in the simulations
is free from the tuneable parameters typically adopted in traditional
one-dimensional models. Mode excitation and damping rates are computed based on
analytical expressions whose ingredients are evaluated directly from the
three-dimensional model. With excitation and damping rates both available, we
estimate the theoretical oscillation amplitude and frequency of maximum power,
$\nu_{\max}$, for the Sun. We compare our numerical results with helioseismic
observations, finding encouraging agreement between the two. The numerical
method presented here provides a novel way to investigate the physical
processes responsible for mode driving and damping, and should be valid for all
solar-type oscillating stars.",1905.13397v2
2019-10-03,Many-body collision contributions to electron momentum damping rates in a plasma influenced by electron strong coupling,"Experimental studies of electron-ion collision rates in an ultracold neutral
plasma (UNP) can be conducted through measuring the rate of electron plasma
oscillation damping. For sufficiently cold and dense conditions where strong
coupling influences are important, the measured damping rate was faster by 37\%
than theoretical expectations [W. Chen, C. Witte, and J. Roberts, Phys. Rev. E
\textbf{96}, 013203 (2017)]. We have conducted a series of numerical
simulations to isolate the primary source of this difference. By analyzing the
distribution of electron velocity changes due to collisions in a molecular
dynamics simulation, examining the trajectory of electrons with high deflection
angle in such simulations, and examining the oscillation damping rate while
varying the ratio of two-body to three-body electron-ion collision rates, we
have found that the difference is consistent with the effect due to many-body
collisions leading to bound electrons. This has implications for other
electron-ion collision related transport properties in addition to electron
oscillation damping.",1910.01707v1
2019-10-18,Escape of a forced-damped particle from weakly nonlinear truncated potential well,"Escape from a potential well is an extreme example of transient behavior. We
consider the escape of the harmonically forced particle under viscous damping
from the benchmark truncated weakly nonlinear potential well. Main attention is
paid to most interesting case of primary 1:1 resonance. The treatment is based
on multiple-scales analysis and exploration of the slow-flow dynamics. Contrary
to Hamiltonian case described in earlier works, in the case with damping the
slow-flow equations are not integrable. However, if the damping is small
enough, it is possible to analyze the perturbed slow-flow equations. The effect
of the damping on the escape threshold is evaluated in the explicit analytic
form. Somewhat unexpectedly, the escape mechanisms in terms of the slow flow
are substantially different for the linear and weakly nonlinear cases.",1910.08545v1
2019-10-24,Topological damping Rashba spin orbit torque in ballistic magnetic domain walls,"Rashba spin orbit torque derived from the broken inversion symmetry at
ferromagnet/heavy metal interfaces has potential application in spintronic
devices. In conventional description of the precessional and damping components
of the Rashba spin orbit torque in magnetization textures, the decomposition
coefficients are assumed to be independent of the topology of the underlying
structure. Contrary to this common wisdom, for Schr\""{o}dinger electrons
trespassing ballistically across a magnetic domain wall, we found that the
decomposition coefficient of the damping component is determined by the
topology of the domain wall. The resultant damping Rashba spin orbit torque is
protected by the topology of the underlying magnetic domain wall and robust
against small deviations from the ideal domain wall profile. Our identification
of a topological damping Rashba spin orbit torque component in magnetic domain
walls will help to understand experiments on current driven domain wall motion
in ferromagnet/heavy metal systems with broken inversion symmetry and to
facilitate its utilization in innovative device designs.",1910.10977v2
2019-11-13,Dipole oscillations of fermionic superfluids along the BEC-BCS crossover in disordered potentials,"We investigate dipole oscillations of ultracold Fermi gases along the BEC-BCS
crossover through disordered potentials. We observe a disorder-induced damping
of oscillations as well as a change of the fundamental Kohn-mode frequency. The
measurement results are compared to numerical density matrix renormalization
group calculations as well as to a three-dimensional simulation of
non-interacting fermions. Experimentally, we find a disorder-dependent damping,
which grows approximately with the second power of the disorder strength.
Moreover, we observe experimentally a change of oscillation frequency which
deviates from the expected behavior of a damped harmonic oscillator on a
percent level. While this behavior is qualitatively expected from the
theoretical models used, quantitatively the experimental observations show a
significantly stronger effect than predicted by theory. Furthermore, while the
frequency shift seems to scale differently with interaction strength in the BEC
versus BCS regime, the damping coefficient apparently decreases with the
strength of interaction, but not with the sign, which changes for BEC and BCS
type Fermi gases. This is surprising, as the dominant damping mechanisms are
expected to be different in the two regimes.",1911.05638v1
2020-02-07,Model of damping and anisotropy at elevated temperatures: application to granular FePt films,"Understanding the damping mechanism in finite size systems and its dependence
on temperature is a critical step in the development of magnetic
nanotechnologies. In this work, nano-sized materials are modeled via atomistic
spin dynamics, the damping parameter being extracted from Ferromagnetic
Resonance (FMR) simulations applied for FePt systems, generally used for
heat-assisted magnetic recording media (HAMR). We find that the damping
increases rapidly close to Tc and the effect is enhanced with decreasing system
size, which is ascribed to scattering at the grain boundaries. Additionally,
FMR methods provide the temperature dependence of both damping and the
anisotropy, important for the development of HAMR. Semi-analytical calculations
show that, in the presence of a grain size distribution, the FMR linewidth can
decrease close to the Curie temperature due to a loss of inhomogeneous line
broadening. Although FePt has been used in this study, the results presented in
the current work are general and valid for any ferromagnetic material.",2002.02865v1
2020-04-06,Damping-like Torque in Monolayer 1T-TaS$_2$,"A damping-like spin orbit torque (SOT) is a prerequisite for ultralow power
spin logic devices. Here, we report on the damping-like SOT in just one
monolayer of the conducting transition metal dichalcogenide (TMD) TaS$_2$
interfaced with a NiFe (Py) ferromagnetic layer. The charge-spin conversion
efficiency is found to be 0.25$\pm$0.03 and the spin Hall conductivity (2.63
$\times$ 10$^5$ $\frac{\hbar}{2e}$ $\Omega^{-1}$ m$^{-1}$) is found to be
superior to values reported for other TMDs. The origin of this large
damping-like SOT can be found in the interfacial properties of the TaS$_2$/Py
heterostructure, and the experimental findings are complemented by the results
from density functional theory calculations. The dominance of damping-like
torque demonstrated in our study provides a promising path for designing next
generation conducting TMD based low-powered quantum memory devices.",2004.02649v1
2020-05-15,Calibration and performance of the neutron detector onboard of the DAMPE mission,"The DArk Matter Particle Explorer (DAMPE), one of the four space-based
scientific missions within the framework of the Strategic Pioneer Program on
Space Science of the Chinese Academy of Sciences, has been successfully
launched on Dec. 17th 2015 from Jiuquan launch center. One of the most
important scientific goals of DAMPE is to search for the evidence of dark
matter indirectly by measuring the spectrum of high energy cosmic-ray
electrons. The neutron detector, one of the four sub-payloads of DAMPE, is
designed to distinguish high energy electrons from hadron background by
measuring the secondary neutrons produced in the shower. In this paper, a
comprehensive introduction of the neutron detector is presented, including the
design, the calibration and the performance. The analysis with simulated data
and flight data indicates a powerful proton rejection capability of the neutron
detector, which plays an essential role for TeV electron identification of
DAMPE.",2005.07828v1
2020-05-16,Simultaneous observation of anti-damping and inverse spin Hall effect in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayer system,"Manganites have shown potential in spintronics because they exhibit high spin
polarization. Here, by ferromagnetic resonance we have studied the damping
properties of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayers which are prepared by
oxide molecular beam epitaxy. The damping coefficient ($\alpha$) of
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) single layer is found to be 0.0104.
However the LSMO/Pt bilayers exhibit decrease in $\alpha$ with increase in Pt
thickness. This decrease in the value of $\alpha$ is probably due to high
anti-damping like torque. Further, we have investigated the angle dependent
inverse spin Hall effect (ISHE) to quantify the spin pumping voltage from other
spin rectification effects such as anomalous Hall effect and anisotropic
magnetoresistance. We have observed high spin pumping voltage ($\sim$~20 $ \mu
V$). The results indicate that both anti-damping and spin pumping phenomena are
occuring simultaneously.",2005.07848v3
2020-07-16,Linearized wave-damping structure of Vlasov-Poisson in $\mathbb R^3$,"In this paper we study the linearized Vlasov-Poisson equation for localized
disturbances of an infinite, homogeneous Maxwellian background distribution in
$\mathbb R^3_x \times \mathbb R^3_v$. In contrast with the confined case
$\mathbb T^d _x \times \mathbb R_v ^d$, or the unconfined case $\mathbb R^d_x
\times \mathbb R^d_v$ with screening, the dynamics of the disturbance are not
scattering towards free transport as $t \to \pm \infty$: we show that the
electric field decomposes into a very weakly-damped Klein-Gordon-type evolution
for long waves and a Landau-damped evolution. The Klein-Gordon-type waves
solve, to leading order, the compressible Euler-Poisson equations linearized
about a constant density state, despite the fact that our model is
collisionless, i.e. there is no trend to local or global thermalization of the
distribution function in strong topologies. We prove dispersive estimates on
the Klein-Gordon part of the dynamics. The Landau damping part of the electric
field decays faster than free transport at low frequencies and damps as in the
confined case at high frequencies; in fact, it decays at the same rate as in
the screened case. As such, neither contribution to the electric field behaves
as in the vacuum case.",2007.08580v1
2020-07-25,Using a Lindbladian approach to model decoherence in two coupled nuclear spins via correlated phase-damping and amplitude damping noise channels,"In this work, we studied the relaxation dynamics of coherences of different
order present in a system of two coupled nuclear spins. We used a previously
designed model for intrinsic noise present in such systems which considers the
Lindblad master equation for Markovian relaxation. We experimentally created
zero-, single- and double- quantum coherences in several two-spin systems and
performed a complete state tomography and computed state fidelity. We
experimentally measured the decay of zero- and double- quantum coherences in
these systems. The experimental data fitted well to a model that considers the
main noise channels to be a correlated phase damping channel acting
simultaneously on both spins in conjunction with a generalized amplitude
damping channel acting independently on both spins. The differential relaxation
of multiple-quantum coherences can be ascribed to the action of a correlated
phase damping channel acting simultaneously on both the spins.",2007.12972v1
2020-09-29,The effects of nonlinear damping on degenerate parametric amplification,"This paper considers the dynamic response of a single degree of freedom
system with nonlinear stiffness and nonlinear damping that is subjected to both
resonant direct excitation and resonant parametric excitation, with a general
phase between the two. This generalizes and expands on previous studies of
nonlinear effects on parametric amplification, notably by including the effects
of nonlinear damping, which is commonly observed in a large variety of systems,
including micro- and nano-scale resonators. Using the method of averaging, a
thorough parameter study is carried out that describes the effects of the
amplitudes and relative phase of the two forms of excitation. The effects of
nonlinear damping on the parametric gain are first derived. The transitions
among various topological forms of the frequency response curves, which can
include isolae, dual peaks, and loops, are determined, and bifurcation analyses
in parameter spaces of interest are carried out. In general, these results
provide a complete picture of the system response and allow one to select drive
conditions of interest that avoid bistability while providing maximum amplitude
gain, maximum phase sensitivity, or a flat resonant peak, in systems with
nonlinear damping.",2009.14284v2
2020-11-10,Damped oscillators within the general theory of Casimir and van der Waals forces,"It is demonstrated that the general theory of Casimir and van der Waals
forces describes the interaction-induced equilibrium thermodynamic potentials
of the damped harmonic oscillator bilinearly coupled to the environment. An
extended model for a damped oscillator is suggested along the lines of the
general theory of Casimir and van der Waals forces, and the corresponding
thermodynamic quantities obtained. While the original model involves a heat
bath consisting of a large number of free oscillators having infinitesimal
damping functions, the extended model allows any generally admissible frequency
and temperature dependent dissipative susceptibilities of the heat bath
constituents, influenced by the additional dissipative environmental channels
that are not directly linked to the system oscillator. Consequently, the
results obtained are applicable to the frequency and temperature dependent
damping function of the system oscillator.",2011.04960v2
2020-11-16,Technology to Counter Online Flaming Based on the Frequency-Dependent Damping Coefficient in the Oscillation Model,"Online social networks, which are remarkably active, often experience
explosive user dynamics such as online flaming, which can significantly impact
the real world. However, countermeasures based on social analyses of the
individuals causing flaming are too slow to be effective because of the
rapidity with which the influence of online user dynamics propagates. A
countermeasure technology for the flaming phenomena based on the oscillation
model, which describes online user dynamics, has been proposed; it is an
immediate solution as it does not depend on social analyses of individuals.
Conventional countermeasures based on the oscillation model assume that the
damping coefficient is a constant regardless of the eigenfrequency. This
assumption is, however, problematic as the damping coefficients are, in
general, inherently frequency-dependent; the theory underlying the dependence
is being elucidated. This paper discusses a design method that uses the damping
coefficient to prevent flaming under general conditions considering the
frequency-dependence of the damping coefficient and proposes a countermeasure
technology for the flaming phenomena.",2011.08117v1
2021-01-03,The effect of flow on resonant absorption of slow MHD waves in magnetic flux tubes,"In this paper, we study kink and sausage oscillations in the presence of
longitudinal background flow. We study resonant absorption of the kink and
sausage modes in the slow continuum under magnetic pore conditions in the
presence of flow. we determine the dispersion relation then solve it
numerically, and find the frequencies and damping rates of the slow kink and
sausage surface modes. We also, obtain analytical solution for the damping rate
of the slow surface mode in the long wavelength limit. We show that in the
presence of plasma flow, resonance absorption can result in strong damping for
forward waves and can be considered as an efficient mechanism to justify the
extremely rapid damping of slow surface sausage waves observed in magnetic
pores. Also, the plasma flow reduces the efficiency of resonance absorption to
damp backward waves. Furthermore, for the pore conditions, the resonance
instability is avoided in our model.",2101.02064v1
2021-02-01,Blow-up and lifespan estimates for a damped wave equation in the Einstein-de Sitter spacetime with nonlinearity of derivative type,"In this article, we investigate the blow-up for local solutions to a
semilinear wave equation in the generalized Einstein - de Sitter spacetime with
nonlinearity of derivative type. More precisely, we consider a semilinear
damped wave equation with a time-dependent and not summable speed of
propagation and with a time-dependent coefficient for the linear damping term
with critical decay rate. We prove in this work that the results obtained in a
previous work, where the damping coefficient takes two particular values $0$ or
$2$, can be extended for any positive damping coefficient. In the blow-up case,
the upper bound of the exponent of the nonlinear term is given, and the
lifespan estimate of the global existence time is derived as well.",2102.01137v2
2021-02-02,Analysis of Lower Hybrid Drift Waves in Kappa Distributions over Solar Atmosphere,"Kappa distributions and with loss cone features have been frequently observed
with flares emissions with the signatures of Lower hybrid waves. We have
analysed the plasma with Kappa distributions and with loss cone features for
the drift wave instabilities in perpendicular propagation for Large flare and
Normal flare and Coronal condition . While analysing the growth/damping rate,
we understand that the growth of propagation of EM waves increases with kappa
distribution index for all the three cases. In comparing the propagation large
flare shows lesser growth in compared with the normal and the coronal plasmas.
When added the loss cone features to Kappa distributions, we find that the
damping of EM wave propagation takes place. The damping rate EM waves is
increases with perpendicular temperature and loss cone index l, in all the
three cases but damping is very high for large flare and then normal in
comparision with coronal condition. This shows that the lower hybrid damping
may be the source of coronal heating.",2102.01323v1
2021-02-25,Regularity and stability of the semigroup associated with some interacting elastic systems I: A degenerate damping case,"In this paper, we examine regularity and stability issues for two damped
abstract elastic systems. The damping involves the average velocity and a
fractional power $\theta$, with $\theta$ in $[-1,1]$, of the principal
operator. The matrix operator defining the damping mechanism for the coupled
system is degenerate. First, we prove that for $\theta$ in $(1/2,1]$, the
underlying semigroup is not analytic, but is differentiable for $\theta$ in
$(0,1)$; this is in sharp contrast with known results for a single similarly
damped elastic system, where the semigroup is analytic for $\theta$ in
$[1/2,1]$; this shows that the degeneracy dominates the dynamics of the
interacting systems, preventing analyticity in that range. Next, we show that
for $\theta$ in $(0,1/2]$, the semigroup is of certain Gevrey classes. Finally,
we show that the semigroup decays exponentially for $\theta$ in $[0,1]$, and
polynomially for $\theta$ in $[-1,0)$. To prove our results, we use the
frequency domain method, which relies on resolvent estimates. Optimality of our
resolvent estimates is also established. Several examples of application are
provided.",2102.13217v4
2021-03-05,Existence and congruence of global attractors for damped and forced integrable and nonintegrable discrete nonlinear Schrödinger equations,"We study two damped and forced discrete nonlinear Schr\""odinger equations on
the one-dimensional infinite lattice. Without damping and forcing they are
represented by the integrable Ablowitz-Ladik equation (AL) featuring non-local
cubic nonlinear terms, and its standard (nonintegrable) counterpart with local
cubic nonlinear terms (DNLS). The global existence of a unique solution to the
initial value problem for both, the damped and forced AL and DNLS, is proven.
It is further shown that for sufficiently close initial data, their
corresponding solutions stay close for all times. Concerning the asymptotic
behaviour of the solutions to the damped and forced AL and DNLS, for the former
a sufficient condition for the existence of a restricted global attractor is
established while it is shown that the latter possesses a global attractor.
Finally, we prove the congruence of the restricted global AL attractor and the
DNLS attractor for dynamics ensuing from initial data contained in an
appropriate bounded subset in a Banach space.",2103.03533v1
2021-05-17,Dissipation of Oscillation Energy and Distribution of Damping Power in a Multimachine Power System: A Small-signal Analysis,"This paper revisits the concept of damping torque in a multimachine power
system and its relation to the dissipation of oscillation energy in synchronous
machine windings. As a multimachine extension of an existing result on a
single-machine-infinite-bus (SMIB) system, we show that the total damping power
for a mode stemming from the interaction of electromagnetic torques and rotor
speeds is equal to the sum of average power dissipations in the generator
windings corresponding to the modal oscillation. Further, counter-intuitive to
the SMIB result, we demonstrate that, although the equality holds on an
aggregate, such is not the case for individual machines in an interconnected
system. To that end, distribution factors are derived for expressing the
average damping power of each generator as a linear combination of average
powers of modal energy dissipation in the windings of all machines in the
system. These factors represent the distribution of damping power in a
multimachine system. The results are validated on IEEE 4-machine and 16-machine
test systems.",2105.07618v2
2021-06-04,Imaging spin-wave damping underneath metals using electron spins in diamond,"Spin waves in magnetic insulators are low-damping signal carriers that could
enable a new generation of spintronic devices. The excitation, control, and
detection of spin waves by metal electrodes is crucial for interfacing these
devices to electrical circuits. It is therefore important to understand
metal-induced damping of spin-wave transport, but characterizing this process
requires access to the underlying magnetic films. Here we show that spins in
diamond enable imaging of spin waves that propagate underneath metals in
magnetic insulators, and then use this capability to reveal a 100-fold increase
in spin-wave damping. By analyzing spin-wave-induced currents in the metal, we
derive an effective damping parameter that matches these observations well. We
furthermore detect buried scattering centers, highlighting the technique's
power for assessing spintronic device quality. Our results open new avenues for
studying metal - spin-wave interaction and provide access to interfacial
processes such as spin-wave injection via the spin-Hall effect.",2106.02508v2
2021-06-04,Inherent Non-Linear Damping in Resonators with Inertia Amplification,"Inertia amplification is a mechanism coupling degrees of freedom within a
vibrating structure. Its goal is to achieve an apparent high dynamic mass and,
accordingly, a low resonance frequency. Such structures have been described for
use in locally resonant metamaterials and phononic crystals to lower the
starting frequency of a band gap without adding mass to the system. This study
shows that any non-linear kinematic coupling between translational or
rotational vibrations leads to the appearance of amplitude-dependent damping.
The analytical derivation of the equation of motion of a resonator with inertia
amplification creates insight in the damping process, and shows that the
vibration damping increases with its amplitude. The theoretical study is
validated by experimental evidence from two types of inertia-amplification
resonators. Finally, the importance of amplitude-dependent damping is
illustrated when the structure is used as a tuned mass damper for a cantilever
beam.",2106.02576v2
2021-06-30,On the effect of perturbations in first-order optimization methods with inertia and Hessian driven damping,"Second-order continuous-time dissipative dynamical systems with viscous and
Hessian driven damping have inspired effective first-order algorithms for
solving convex optimization problems. While preserving the fast convergence
properties of the Nesterov-type acceleration, the Hessian driven damping makes
it possible to significantly attenuate the oscillations. To study the stability
of these algorithms with respect to perturbations, we analyze the behaviour of
the corresponding continuous systems when the gradient computation is subject
to exogenous additive errors. We provide a quantitative analysis of the
asymptotic behaviour of two types of systems, those with implicit and explicit
Hessian driven damping. We consider convex, strongly convex, and non-smooth
objective functions defined on a real Hilbert space and show that, depending on
the formulation, different integrability conditions on the perturbations are
sufficient to maintain the convergence rates of the systems. We highlight the
differences between the implicit and explicit Hessian damping, and in
particular point out that the assumptions on the objective and perturbations
needed in the implicit case are more stringent than in the explicit case.",2106.16159v2
2021-07-13,A new approach to the quantization of the damped harmonic oscillator,"In this paper, a new approach for constructing Lagrangians for driven and
undriven linearly damped systems is proposed, by introducing a redefined time
coordinate and an associated coordinate transformation to ensure that the
resulting Lagrangian satisfies the Helmholtz conditions. The approach is
applied to canonically quantize the damped harmonic oscillator and although it
predicts an energy spectrum that decays at the same rate to previous models,
unlike those approaches it recovers the classical critical damping condition,
which determines transitions between energy eigenstates, and is therefore
consistent with the correspondence principle. It is also demonstrated how to
apply the procedure to a driven damped harmonic oscillator.",2107.05827v3
2021-10-26,Theory of sound attenuation in amorphous solids from nonaffine motions,"We present a theoretical derivation of acoustic phonon damping in amorphous
solids based on the nonaffine response formalism for the viscoelasticity of
amorphous solids. The analytical theory takes into account the nonaffine
displacements in transverse waves and is able to predict both the ubiquitous
low-energy diffusive damping $\sim k^{2}$, as well as a novel contribution to
the Rayleigh damping $\sim k^{4}$ at higher wavevectors and the crossover
between the two regimes observed experimentally. The coefficient of the
diffusive term is proportional to the microscopic viscous (Langevin-type)
damping in particle motion (which arises from anharmonicity), and to the
nonaffine correction to the static shear modulus, whereas the Rayleigh damping
emerges in the limit of low anharmonicity, consistent with previous
observations and macroscopic models. Importantly, the $k^4$ Rayleigh
contribution derived here does not arise from harmonic disorder or elastic
heterogeneity effects and it is the dominant mechanism for sound attenuation in
amorphous solids as recently suggested by molecular simulations.",2110.13446v2
2021-11-21,Energy Transport in 1-Dimensional Oscillator Arrays With Hysteretic Damping,"Energy transport in 1-dimensional oscillator arrays has been extensively
studied to date in the conservative case, as well as under weak viscous
damping. When driven at one end by a sinusoidal force, such arrays are known to
exhibit the phenomenon of supratransmission, i.e. a sudden energy surge above a
critical driving amplitude. In this paper, we study 1-dimensional oscillator
chains in the presence of hysteretic damping, and include nonlinear stiffness
forces that are important for many materials at high energies. We first employ
Reid's model of local hysteretic damping, and then study a new model of nearest
neighbor dependent hysteretic damping to compare their supratransmission and
wave packet spreading properties in a deterministic as well as stochastic
setting. The results have important quantitative differences, which should be
helpful when comparing the merits of the two models in specific engineering
applications.",2111.10816v3
2021-12-15,An Innovative Transverse Emittance Cooling Technique using a Laser-Plasma Wiggler,"We propose an innovative beam cooling scheme based on laser driven plasma
wakefields to address the challenge of high luminosity generation for a future
linear collider. For linear colliders, beam cooling is realised by means of
damping rings equipped with wiggler magnets and accelerating cavities. This
scheme ensures systematic reduction of phase space volume through synchrotron
radiation emission whilst compensating for longitudinal momentum loss via an
accelerating cavity. In this paper, the concept of a plasma wiggler and its
effective model analogous to a magnetic wiggler are introduced; relation of
plasma wiggler characteristics with damping properties are demonstrated;
underpinning particle-in-cell simulations for laser propagation optimisation
are presented. The oscillation of transverse wakefields and resulting
sinusoidal probe beam trajectory are numerically demonstrated. The formation of
an order of magnitude larger effective wiggler field compared to conventional
wigglers is successfully illustrated. Potential damping ring designs on the
basis of this novel plasma-based technology are presented and performance in
terms of damping times and footprint was compared to an existing conventional
damping ring design.",2112.08163v1
2021-12-21,ISS-Based Robustness to Various Neglected Damping Mechanisms for the 1-D Wave PDE,"This paper is devoted to the study of the robustness properties of the 1-D
wave equation for an elastic vibrating string under four different damping
mechanisms that are usually neglected in the study of the wave equation: (i)
friction with the surrounding medium of the string (or viscous damping), (ii)
thermoelastic phenomena (or thermal damping), (iii) internal friction of the
string (or Kelvin-Voigt damping), and (iv) friction at the free end of the
string (the so-called passive damper). The passive damper is also the simplest
boundary feedback law that guarantees exponential stability for the string. We
study robustness with respect to distributed inputs and boundary disturbances
in the context of Input-to-State Stability (ISS). By constructing appropriate
ISS Lyapunov functionals, we prove the ISS property expressed in various
spatial norms.",2112.11287v1
2022-01-20,Derivation of the linear Boltzmann equation from the damped quantum Lorentz gas with a general scatterer configuration,"It is a fundamental problem in mathematical physics to derive macroscopic
transport equations from microscopic models. In this paper we derive the linear
Boltzmann equation in the low-density limit of a damped quantum Lorentz gas for
a large class of deterministic and random scatterer configurations. Previously
this result was known only for the single-scatterer problem on the flat torus,
and for uniformly random scatterer configurations where no damping is required.
The damping is critical in establishing convergence -- in the absence of
damping the limiting behaviour depends on the exact configuration under
consideration, and indeed, the linear Boltzmann equation is not expected to
appear for periodic and other highly ordered configurations.",2201.08229v2
2022-01-22,Effect of MagneticField on the Damping Behavior of a Ferrofluid based Damper,"This paper is an extension of our earlier work where we had reported a proof
of concept for a ferrofluid based damper. The damper used ferrofluid as damping
medium and it was seen that damping efficiency of the damper changes on
application of magnetic field. The present paper deals with a systematic study
of the effect of magnetic field on the damping efficiency of the damper.
Results of these studies are reported. It is seen that damping ratio varies
linearly with magnetic field ({\zeta} / H = 0.028 per kG) for magnetic field in
range of 0.0 to 4.5 kG. It may be mentioned that ferrofluid is different from
magnetorheological fluid even though both of them are magnetic field-responsive
fluids. The ferrofluid-dampers are better suited than MR Fluid-dampers for
their use in automobiles.",2201.09027v1
2022-01-28,Machine learning-based method of calorimeter saturation correction for helium flux analysis with DAMPE experiment,"DAMPE is a space-borne experiment for the measurement of the cosmic-ray
fluxes at energies up to around 100 TeV per nucleon. At energies above several
tens of TeV, the electronics of DAMPE calorimeter would saturate, leaving
certain bars with no energy recorded. In the present work we discuss the
application of machine learning techniques for the treatment of DAMPE data, to
compensate the calorimeter energy lost by saturation.",2201.12185v3
2022-03-10,Accelerated gradient methods combining Tikhonov regularization with geometric damping driven by the Hessian,"In a Hilbert setting, for convex differentiable optimization, we consider
accelerated gradient dynamics combining Tikhonov regularization with
Hessian-driven damping. The Tikhonov regularization parameter is assumed to
tend to zero as time tends to infinity, which preserves equilibria. The
presence of the Tikhonov regularization term induces a strong convexity
property which vanishes asymptotically. To take advantage of the exponential
convergence rates attached to the heavy ball method in the strongly convex
case, we consider the inertial dynamic where the viscous damping coefficient is
taken proportional to the square root of the Tikhonov regularization parameter,
and therefore also converges towards zero. Moreover, the dynamic involves a
geometric damping which is driven by the Hessian of the function to be
minimized, which induces a significant attenuation of the oscillations. Under
an appropriate tuning of the parameters, based on Lyapunov's analysis, we show
that the trajectories have at the same time several remarkable properties: they
provide fast convergence of values, fast convergence of gradients towards zero,
and strong convergence to the minimum norm minimizer. This study extends a
previous paper by the authors where similar issues were examined but without
the presence of Hessian driven damping.",2203.05457v2
2022-04-01,On the Importance of High-Frequency Damping in High-Order Conservative Finite-Difference Schemes for Viscous Fluxes,"This paper discusses the importance of high-frequency damping in high-order
conservative finite-difference schemes for viscous terms in the Navier-Stokes
equations. Investigating nonlinear instability encountered in a high-resolution
viscous shock-tube simulation, we have discovered that a modification to the
viscous scheme rather than the inviscid scheme resolves a problem with spurious
oscillations around shocks. The modification introduces a term responsible for
high-frequency damping that is missing in a conservative high-order viscous
scheme. The importance of damping has been known for schemes designed for
unstructured grids. However, it has not been recognized well in very high-order
difference schemes, especially in conservative difference schemes. Here, we
discuss how it is easily missed in a conservative scheme and how to improve
such schemes by a suitably designed damping term.",2204.00393v1
2022-06-20,Stability and Damping in the Disks of Massive Galaxies,"After their initial formation, disk galaxies are observed to be rotationally
stable over periods of >6 Gyr, implying that any large velocity disturbances of
stars and gas clouds are damped rapidly on the timescale of their rotation.
However, it is also known that despite this damping, there must be a degree of
random local motion to stabilize the orbits against degenerate collapse. A
mechanism for such damping is proposed by a combination of inter-stellar
gravitational interactions, and interactions with the Oort clouds and exo-Oort
objects associated with each star. Analysis of the gravitational interactions
between two stars is a three-body problem, because the stars are also in orbit
round the large virtual mass of the galaxy. These mechanisms may produce rapid
damping of large perturbations within a time period that is short on the scale
of observational look-back time, but long on the scale of the disk rotational
period for stars with small perturbations. This mechanism may also account for
the locally observed mean perturbations in the Milky Way of 8-15~km/s for
younger stars and 20-30~km/s for older stars.",2206.09671v2
2022-08-25,The Effect of Frequency Droop Damping on System Parameters and Battery Sizing During Load Change Condition,"Inverter-based resources (IBR) have been widely studied for their advantages
on the current power systems. This increase in the penetration of renewable
energy has raised some concerns about the stability of the existing grid.
Historically, power systems are dominated by synchronous generators that can
easily react to system instability due to high inertia and damping
characteristics. However, with IBR, the control of the inverter plays a crucial
role in contributing to the system stability and enhancing the functionality of
the inverters. One of these novel control methods is droop control. Droop
characteristics are used to control voltage, frequency, and active and reactive
power. This paper presents the impact of frequency droop damping on system
frequency, real power, and the rate of change of frequency with distributed
energy resources. Also, battery sizing is suggested based on the results. The
results also show the need for optimal selection for the frequency droop
damping to fulfill the appropriate battery size in terms of cost and
performance. The simulations are carried out in an electromagnetic transient
program (EMTP)",2208.12291v1
2022-09-15,Superfluid $^4$He as a rigorous test bench for different damping models in nanoelectromechanical resonators,"We have used nanoelectromechanical resonators to probe superfluid $^4$He at
different temperature regimes, spanning over four orders of magnitude in
damping. These regimes are characterized by the mechanisms which provide the
dominant contributions to damping and the shift of the resonance frequency:
tunneling two level systems at the lowest temperatures, ballistic phonons and
rotons at few hundred mK, and laminar drag in the two-fluid regime below the
superfluid transition temperature as well as in the normal fluid. Immersing the
nanoelectromechanical resonators in fluid increases their effective mass
substantially, decreasing their resonance frequency. Dissipationless superflow
gives rise to a unique possibility to dramatically change the mechanical
resonance frequency in situ, allowing rigorous tests on different damping
models in mechanical resonators. We apply this method to characterize tunneling
two-level system losses and magnetomotive damping in the devices.",2209.07229v2
2022-11-08,On the injection scale of the turbulence in the partially ionized very local interstellar medium,"The cascade of magnetohydrodynamic (MHD) turbulence is subject to ion-neutral
collisional damping and neutral viscous damping in the partially ionized
interstellar medium. By examining the damping effects in the warm and partially
ionized local interstellar medium, we find that the interstellar turbulence is
damped by neutral viscosity at $\sim 261$ au and cannot account for the
turbulent magnetic fluctuations detected by Voyager 1 and 2. The MHD turbulence
measured by Voyager in the very local interstellar medium (VLISM) should be
locally injected in the regime where ions are decoupled from neutrals for its
cascade to survive the damping effects. With the imposed ion-neutral decoupling
condition, and the strong turbulence condition for the observed Kolmogorov
magnetic energy spectrum, we find that the turbulence in the VLISM is
sub-Alfv\'{e}nic, and its largest possible injection scale is $\sim 194$ au.",2211.04496v1
2022-12-11,"The overtone level spacing of a black hole quasinormal frequencies: a fingerprint of a local $SL(2,\mathbb{R})$ symmetry","The imaginary part of the quasinormal frequencies spectrum for a static and
spherically symmetric black hole is analytically known to be equally spaced,
both for the highly damped and the weakly damped families of quasinormal modes.
Some interesting attempts have been made in the last twenty years to understand
in simple ways this level spacing for the only case of highly damped
quasinormal frequencies. Here, we show that the overtone level spacing, for
both the highly damped and weakly damped families of quasinormal modes, can
simply be understood as a fingerprint of a hidden local $SL(2,\mathbb{R})$
symmetry, near different regions of the black hole spacetime, i.e. the
near-horizon and the near-photon sphere regions.",2212.05538v1
2022-12-15,Formation of shifted shock for the 3D compressible Euler equations with time-dependent damping,"In this paper, we show the shock formation to the compressible Euler
equations with time-dependent damping $\frac{a\p u}{(1+t)^{\lam}}$ in three
spatial dimensions without any symmetry conditions. It's well-known that for
$\lam>1$, the damping is too weak to prevent the shock formation for suitably
large data. However, the classical results only showed the finite existence of
the solution. Follow the work by D.Christodoulou in\cite{christodoulou2007},
starting from the initial isentropic and irrotational short pulse data, we show
the formation of shock is characterized by the collapse of the characteristic
hypersurfaces and the vanishing of the inverse foliation density function
$\mu$, at which the first derivatives of the velocity and the density blow up,
and the lifespan $T_{\ast}(a,\lam)$ is exponentially large. Moreover, the
damping effect will shift the time of shock formation $T_{\ast}$. The methods
in the paper can also be extended to the Euler equations with general
time-decay damping.",2212.07828v1
2023-01-15,Damped-driven system of bouncing droplets leading to deterministic diffusive behavior,"Damped-driven systems are ubiquitous in science, however the damping and
driving mechanisms are often quite convoluted. This manuscript presents an
experimental and theoretical investigation of a fluidic droplet on a vertically
vibrating fluid bath as a damped-driven system. We study a fluidic droplet in
an annular cavity with the fluid bath forced above the Faraday wave threshold.
We model the droplet as a kinematic point particle in air and as inelastic
collisions during impact with the bath. In both experiments and the model the
droplet is observed to chaotically change velocity with a Gaussian
distribution. Finally, the statistical distributions from experiments and
theory are analyzed. Incredibly, this simple deterministic interaction of
damping and driving of the droplet leads to more complex Brownian-like and
Levy-like behavior.",2301.06041v2
2023-03-01,Generation of intraparticle quantum correlations in amplitude damping channel and its robustness,"Quantum correlations between two or more different degrees of freedom of the
same particle is sometimes referred to as intraparticle entanglement. In this
work, we study these intra-particle correlations between two different degrees
of freedom under various decoherence channels viz. amplitude damping,
depolarising and phase damping channels. We observe a unique feature of the
amplitude damping channel, wherein entanglement is shown to arise starting from
separable states. In case of non maximally entangled input states, in addition
to entanglement sudden death, the creation of entanglement is also observed,
having an asymptotic decay over a long time. These counter-intuitive behaviours
arise due to the subtle interplay of channel and input state parameters, and
are not seen for interparticle entanglement without consideration of
non-Markovian noise. It is also not observed for maximally entangled input
states. Furthermore, investigation of entanglement evolution in phase damping
and depolarizing channels shows its robustness against decoherence as compared
to interparticle entanglement.",2303.01238v1
2023-03-16,Quantum Brownian Motion in the Caldeira-Leggett Model with a Damped Environment,"We model a quantum system coupled to an environment of damped harmonic
oscillators by following the approach of Caldeira-Leggett and adopting the
Caldirola-Kanai Lagrangian for the bath oscillators. In deriving the master
equation of the quantum system of interest (a particle in a general potential),
we show that the potential is modified non-trivially by a new inverted harmonic
oscillator term, induced by the damping of the bath oscillators. We analyze
numerically the case of a particle in a double-well potential, and find that
this modification changes both the rate of decoherence at short times and the
well-transfer probability at longer times. We also identify a simple rescaling
condition that keeps the potential fixed despite changes in the environmental
damping. Here, the increase of environmental damping leads to a slowing of
decoherence.",2303.09516v1
2023-03-22,A Numerical Study of Landau Damping with PETSc-PIC,"We present a study of the standard plasma physics test, Landau damping, using
the Particle-In-Cell (PIC) algorithm. The Landau damping phenomenon consists of
the damping of small oscillations in plasmas without collisions. In the PIC
method, a hybrid discretization is constructed with a grid of finitely
supported basis functions to represent the electric, magnetic and/or
gravitational fields, and a distribution of delta functions to represent the
particle field. Approximations to the dispersion relation are found to be
inadequate in accurately calculating values for the electric field frequency
and damping rate when parameters of the physical system, such as the plasma
frequency or thermal velocity, are varied. We present a full derivation and
numerical solution for the dispersion relation, and verify the PETSC-PIC
numerical solutions to the Vlasov-Poisson for a large range of wave numbers and
charge densities.",2303.12620v1
2023-04-07,Shifted shock formation for the 3D compressible Euler equations with damping and variation of the vorticity,"In this paper, we consider the shock formation problem for the
3-dimensional(3D) compressible Euler equations with damping inspired by the
work \cite{BSV3Dfulleuler}. It will be shown that for a class of large data,
the damping can not prevent the formation of point shock, and the damping
effect shifts the shock time and the wave amplitude while the shock location
and the blow up direction remain the same with the information of this point
shock being computed explicitly. Moreover, the vorticity is concentrated in the
non-blow-up direction, which varies exponentially due to the damping effect.
Our proof is based on the estimates for the modulated self-similar variables
and lower bounds for the Lagrangian trajectories.",2304.03506v2
2023-07-05,Bayesian evidence for two slow-wave damping models in hot coronal loops,"We compute the evidence in favour of two models, one based on field-aligned
thermal conduction alone and another that includes thermal misbalance as well,
in explaining the damping of slow magneto-acoustic waves in hot coronal loops.
Our analysis is based on the computation of the marginal likelihood and the
Bayes factor for the two damping models. We quantify their merit in explaining
the apparent relationship between slow mode periods and damping times, measured
with SOHO/SUMER in a set of hot coronal loops. The results indicate evidence in
favour of the model with thermal misbalance in the majority of the sample, with
a small population of loops for which thermal conduction alone is more
plausible. The apparent possibility of two different regimes of slow-wave
damping, if due to differences between the loops of host active regions and/or
the photospheric dynamics, may help with revealing the coronal heating
mechanism.",2307.02439v1
2023-07-24,From characteristic functions to multivariate distribution functions and European option prices by the damped COS method,"We provide a unified framework for the computation of the distribution
function and the computation of prices of financial options from the
characteristic function of some density by the COS method. The classical COS
method is numerically very efficient in one-dimension but cannot deal very well
with certain financial options in general dimensions. Therefore, we introduce
the damped COS method which can handle a large class of integrands very
efficiently. We prove the convergence of the (damped) COS method and study its
order of convergence. The (damped) COS method converges exponentially if the
characteristic function decays exponentially. To apply the (damped) COS method,
one has to specify two parameters: a truncation range for the multivariate
density and the number of terms to approximate the truncated density by a
cosine series. We provide an explicit formula for the truncation range and an
implicit formula for the number of terms. Numerical experiments up to five
dimensions confirm the theoretical results.",2307.12843v6
2023-07-26,A Nonlinear Damped Metamaterial: Wideband Attenuation with Nonlinear Bandgap and Modal Dissipation,"In this paper, we incorporate the effect of nonlinear damping with the
concept of locally resonant metamaterials to enable vibration attenuation
beyond the conventional bandgap range. The proposed design combines a linear
host cantilever beam and periodically distributed inertia amplifiers as
nonlinear local resonators. The geometric nonlinearity induced by the inertia
amplifiers causes an amplitude-dependent nonlinear damping effect. Through the
implementation of both modal superposition and numerical harmonic methods the
finite nonlinear metamaterial is accurately modelled. The resulting nonlinear
frequency response reveals the bandgap is both amplitude-dependent and
broadened. Furthermore, the modal frequencies are also attenuated due to the
nonlinear damping effect. The theoretical results are validated experimentally.
By embedding the nonlinear damping effect into locally resonant metamaterials,
wideband attenuation of the proposed metamaterial is achieved, which opens new
possibilities for versatile metamaterials beyond the limit of their linear
counterparts.",2307.14165v2
2023-07-28,Premature jump-down mimicks nonlinear damping in nanoresonators,"Recent experiments on nano-resonators in a bistable regime use the
`jump-down' point between states to infer mechanical properties of the membrane
or a load, but often suggest the presence of some nonlinear damping. Motivated
by such experiments, we develop a mechanical model of a membrane subject to a
uniform, oscillatory load and linear damping. We solve this model numerically
and compare its jump-down behaviour with standard asymptotic predictions for a
one-dimensional Duffing oscillator with strain stiffening. We show that the
axisymmetric, but spatially-varying, problem can be mapped to the Duffing
problem with coefficients determined rationally from the model's Partial
Differential Equations. However, we also show that jump-down happens earlier
than expected (i.e.~at lower frequency, and with a smaller oscillation
amplitude). Although this premature jump-down is often interpreted as the
signature of a nonlinear damping in experiments, its appearance in numerical
simulations with only linear damping suggests instead that indicate that the
limitations of asymptotic results may, at least sometimes, be the cause. We
therefore suggest that care should be exercised in interpreting the results of
nano-resonator experiments.",2307.15656v1
2023-09-22,Long time energy averages and a lower resolvent estimate for damped waves,"We consider the damped wave equation on a compact manifold. We propose
different ways of measuring decay of the energy (time averages of lower energy
levels, decay for frequency localized data...) and exhibit links with resolvent
estimates on the imaginary axis. As an application we prove a universal
logarithmic lower resolvent bound on the imaginary axis for the damped wave
operator when the Geometric Control Condition (GCC) is not satisfied. This is
to be compared to the uniform boundedness of the resolvent on that set when GCC
holds. The proofs rely on (i) various (re-)formulations of the damped wave
equation as a conservative hyperbolic part perturbed by a lower order damping
term;(ii) a ""Plancherel-in-time"" argument as in classical proofs of the
Gearhart-Huang-Pr{\""u}ss theorem; and (iii) an idea of Bony-Burq-Ramond of
propagating a coherent state along an undamped trajectory up to Ehrenfest time.",2309.12709v1
2023-10-11,Damping Density of an Absorptive Shoebox Room Derived from the Image-Source Method,"The image-source method is widely applied to compute room impulse responses
(RIRs) of shoebox rooms with arbitrary absorption. However, with increasing RIR
lengths, the number of image sources grows rapidly, leading to slow
computation. In this paper, we derive a closed-form expression for the damping
density, which characterizes the overall multi-slope energy decay. The
omnidirectional energy decay over time is directly derived from the damping
density. The resulting energy decay model accurately matches the late
reverberation simulated via the image-source method. The proposed model allows
the fast stochastic synthesis of late reverberation by shaping noise with the
energy envelope. Simulations of various wall damping coefficients demonstrate
the model's accuracy. The proposed model consistently outperforms the energy
decay prediction accuracy compared to a state-of-the-art approximation method.
The paper elaborates on the proposed damping density's applicability to
modeling multi-sloped sound energy decay, predicting reverberation time in
non-diffuse sound fields, and fast frequency-dependent RIR synthesis.",2310.07363v1
2023-10-14,Exploring Damping Effect of Inner Control Loops for Grid-Forming VSCs,"This paper presents an analytical approach to explore the damping effect of
inner loops on grid-forming converters. First, an impedance model is proposed
to characterize the behaviors of inner loops, thereby illustrating their
influence on output impedance shaping. Then, based on the impedance
representation, the complex torque coefficient method is employed to assess the
contribution of inner loops to system damping. The interactions among inner
loops, outer loops, and the ac grid are analyzed. It reveals that inner loops
shape the electrical damping torque coefficient and consequently influence both
synchronous and sub-synchronous oscillation modes. The virtual admittance and
current control-based inner-loop scheme is employed to illustrate the proposed
analytical approach. The case study comprises the analysis of impedance
profiles, the analysis of damping torque contributed by inner loops under
various grid strengths, and the comparison between dq-frame and
{\alpha}\b{eta}-frame realizations of inner loops. Finally, simulation and
experimental tests collaborate with theoretical approaches and findings.",2310.09660v1
2023-10-24,Frictional weakening of a granular sheared layer due to viscous rolling revealed by Discrete Element Modeling,"Considering a 3D sheared granular layer modeled with discrete elements, it is
well known the rolling resistance significantly influences the mechanical
behavior. Even if the rolling resistance role has been deeply investigated as
it is commonly used to represent the the roughness of the grains and the
interparticle locking, the role of rolling viscous damping coefficient has been
largely overlooked so far. This parameter is rarely used or only to dissipate
the energy and to converge numerically. This paper revisits the physical role
of those coefficients with a parametric study of the rolling friction and the
rolling damping for a sheared layer at different shear speeds and different
confinement pressures. It has been observed that the damping coefficient
induces a frictional weakening. Hence, competition between the rolling
resistance and the rolling damping occurs. Angular resistance aims to avoid
grains rolling, decreasing the difference between the angular velocities of
grains. Whereas, angular damping acts in the opposite, avoiding a change in the
difference between the angular velocities of grains. In consequence, grains
keep rolling and the sample strength decreases. This effect must be considered
to not overestimate the frictional response of a granular layer.",2310.15945v1
2023-12-12,Coordination of Damping Controllers: A Data-Informed Approach for Adaptability,"This work proposes a data-informed approach for an adaptable coordination of
damping controllers. The novel concept of coordination is based on minimizing
the Total Action, a single metric that measures the system's dynamic response
post-disturbance. This is a performance measure based on the physics of the
power system, which encapsulates the oscillation energy related to synchronous
generators. Deep learning theory is used to propose a Total Action function
approximator, which captures the relationship between the system wide-area
measurements, the status of damping controllers, and the conditions of the
disturbance. By commissioning the switching status (on/off) of damping
controllers in real-time, the oscillation energy is reduced, enhancing the
power system stability. The concept is tested in the Western North America
Power System (wNAPS) and compared with a model-based approach for the
coordination of damping controllers. The data-informed coordination outperforms
the model-based approach, demonstrating exceptional adaptability and
performance to handle multi-modal events. The proposed scheme shows outstanding
reductions in low-frequency oscillations even under various operating
conditions, fault locations, and time delay considerations.",2312.07739v1
2024-01-26,Efficient Control of Magnetization Dynamics Via W/CuO$_\text{x}$ Interface,"Magnetization dynamics, which determine the speed of magnetization switching
and spin information propagation, play a central role in modern spintronics.
Gaining its control will satisfy the different needs of various spintronic
devices. In this work, we demonstrate that the surface oxidized Cu
(CuO$_\text{x}$) can be employed for the tunability of magnetization dynamics
of ferromagnet (FM)/heavy metal (HM) bilayer system. The capping CuO$_\text{x}$
layer in CoFeB/W/CuO$_\text{x}$ trilayer reduces the magnetic damping value in
comparison with the CoFeB/W bilayer. The magnetic damping even becomes lower
than that of the CoFeB/CuO$_\text{x}$ by ~ 16% inferring the stabilization of
anti-damping phenomena. Further, the reduction in damping is accompanied by a
very small reduction in the spin pumping-induced output DC voltage in the
CoFeB/W/CuO$_\text{x}$ trilayer. The simultaneous observation of anti-damping
and spin-to-charge conversion can be attributed to the orbital Rashba effect
observed at the HM/CuO$_\text{x}$ interface. Our experimental findings
illustrate that the cost-effective CuO$_\text{x}$ can be employed as an
integral part of modern spintronics devices owing to its rich underneath
spin-orbital physics.",2401.14708v1
2024-02-08,The stability analysis based on viscous theory of Faraday waves in Hele-Shaw cells,"The linear instability of Faraday waves in Hele-Shaw cells is investigated
with consideration of the viscosity of fluids after gap-averaging the governing
equations due to the damping from two lateral walls and the dynamic behavior of
contact angle. A new hydrodynamic model is thus derived and solved
semi-analytically. The contribution of viscosity to critical acceleration
amplitude is slight compared to other factors associated with dissipation, and
the potential flow theory is sufficient to describe onset based on the present
study, but the rotational component of velocity can change the timing of onset
largely, which paradoxically comes from the viscosity. The model degenerates
into a novel damped Mathieu equation if the viscosity is dropped with two
damping terms referring to the gap-averaged damping and dissipation from
dynamic contact angle, respectively. The former increases when the gap size
decreases, and the latter grows as frequency rises. When it comes to the
dispersion relation of Faraday waves, an unusual detuning emerges due to the
imaginary part of the gap-averaged damping.",2402.05505v2
2024-02-09,Damping of density oscillations from bulk viscosity in quark matter,"We study the damping of density oscillations in the quark matter phase that
might occur in compact stars. To this end we compute the bulk viscosity and the
associated damping time in three-flavor quark matter, considering both
nonleptonic and semileptonic electroweak processes. We use two different
equations of state of quark matter, more precisely, the MIT bag model and
perturbative QCD, including the leading order corrections in the strong
coupling constant. We analyze the dependence of our results on the density,
temperature and value of strange quark mass in each case. We then find that the
maximum of the bulk viscosity is in the range of temperature from 0.01 to 0.1
MeV for frequencies around 1 kHz, while the associated minimal damping times of
the density oscillations at those temperatures might be in the range of few to
hundreds milliseconds. Our results suggest that bulk viscous damping might be
relevant in the post-merger phase after the collision of two neutron stars if
deconfined matter is achieved in the process.",2402.06595v1
2003-08-05,Reliability of Calderbank-Shor-Steane Codes and Security of Quantum Key Distribution,"After Mayers (1996, 2001) gave a proof of the security of the
Bennett-Brassard 1984 (BB84) quantum key distribution protocol, Shor and
Preskill (2000) made a remarkable observation that a Calderbank-Shor-Steane
(CSS) code had been implicitly used in the BB84 protocol, and suggested its
security could be proven by bounding the fidelity, say F(n), of the
incorporated CSS code of length n in the form 1-F(n) <= exp[-n E+o(n)] for some
positive number E. This work presents such a number E=E(R) as a function of the
rate of a code R, and a threshold R' such that E(R)>0 whenever R < R', which is
larger than the achievable rate based on the Gilbert-Varshamov bound that is
essentially due to Shor and Preskill (2000). The codes in the present work are
robust against fluctuations of channel parameters, which fact is needed to
establish the security rigorously and was not proved for rates above the
Gilbert-Varshamov rate before in the literature. As a byproduct, the security
of a modified BB84 protocol against any joint (coherent) attacks is proved
quantitatively.",0308029v6
2011-07-13,(In-)Stability of Singular Equivariant Solutions to the Landau-Lifshitz-Gilbert Equation,"In this paper we use formal asymptotic arguments to understand the stability
proper- ties of equivariant solutions to the Landau-Lifshitz-Gilbert model for
ferromagnets. We also analyze both the harmonic map heatflow and Schrodinger
map flow limit cases. All asymptotic results are verified by detailed numerical
experiments, as well as a robust topological argument. The key result of this
paper is that blowup solutions to these problems are co-dimension one and hence
both unstable and non-generic. Solutions permitted to deviate from radial
symmetry remain global for all time but may, for suitable initial data,
approach arbitrarily close to blowup. A careful asymptotic analysis of
solutions near blowup shows that finite-time blowup corresponds to a saddle
fixed point in a low dimensional dynamical system. Radial symmetry precludes
motion anywhere but on the stable manifold towards blowup. A similar scenario
emerges in the equivariant setting: blowup is unstable. To be more precise,
blowup is co-dimension one both within the equivariant symmetry class and in
the unrestricted class of initial data. The value of the parameter in the
Landau-Lifshitz-Gilbert equation plays a very subdued role in the analysis of
equivariant blowup, leading to identical blowup rates and spatial scales for
all parameter values. One notable exception is the angle between solution in
inner scale (which bubbles off) and outer scale (which remains), which does
depend on parameter values. Analyzing near-blowup solutions, we find that in
the inner scale these solution quickly rotate over an angle {\pi}. As a
consequence, for the blowup solution it is natural to consider a continuation
scenario after blowup where one immediately re-attaches a sphere (thus
restoring the energy lost in blowup), yet rotated over an angle {\pi}. This
continuation is natural since it leads to continuous dependence on initial
data.",1107.2620v1
1996-09-10,The Damping Tail of CMB Anisotropies,"By decomposing the damping tail of CMB anisotropies into a series of transfer
functions representing individual physical effects, we provide ingredients that
will aid in the reconstruction of the cosmological model from small-scale CMB
anisotropy data. We accurately calibrate the model-independent effects of
diffusion and reionization damping which provide potentially the most robust
information on the background cosmology. Removing these effects, we uncover
model-dependent processes such as the acoustic peak modulation and
gravitational enhancement that can help distinguish between alternate models of
structure formation and provide windows into the evolution of fluctuations at
various stages in their growth.",9609079v1
1997-09-16,Lyman-alpha emission as a tool to study high redshift damped systems,"We report a quantitative study of the escape of Lyman-alpha photons from an
inhomogeneous optically thick medium that mimics the structure of damped
Lyman-alpha absorbers. Modeling the optically thick disk with 3 components
(massive stars and HII regions, dust, and neutral hydrogen), we study the
resulting emission line profile that may arise near the extended damped
absorption profile.",9709150v1
1997-10-17,The chemical evolution of galaxies causing damped Ly$α$ absorption,"We have compiled all available data on chemical abundances in damped Lyman
alpha absorption systems for comparison with results from our combined chemical
and spectrophotometric galaxy evolution models. Preliminary results from
chemically consistent calculations are in agreement with observations of damped
Ly$\alpha$ systems.",9710193v1
1998-01-26,Are Damped Lyman alpha Systems Rotating Disks ?,"We report on high spectral resolution observations of five damped Lyman alpha
systems whose line velocity profiles and abundances are analyzed. By combining
these data with information from the literature, we study the kinematics of the
low and high ionization phases of damped systems and discuss the possibility
that part of the motions is due to rotation.",9801243v1
2001-10-29,Damping of inhomogeneities in neutralino dark matter,"The lightest supersymmetric particle, most likely the neutralino, might
account for a large fraction of dark matter in the Universe. We show that the
primordial spectrum of density fluctuations in neutralino cold dark matter
(CDM) has a sharp cut-off due to two damping mechanisms: collisional damping
during the kinetic decoupling of the neutralinos at O(10 MeV) and free
streaming after last scattering of neutralinos. The cut-off in the primordial
spectrum defines a minimal mass for CDM objects in hierarchical structure
formation. For typical neutralino and sfermion masses the first gravitationally
bound neutralino clouds have masses above 10^(-6) M_\odot.",0110601v1
2002-08-03,Adiabatic Index of Dense Matter and Damping of Neutron Star Pulsations,"The adiabatic index Gamma_1 for perturbations of dense matter is studied
under various physical conditions which can prevail in neutron star cores. The
dependence of Gamma_1 on the composition of matter (in particular, on the
presence of hyperons), on the stellar pulsation amplitude, and on the baryon
superfluidity is analyzed. Timescales of damping of stellar pulsations are
estimated at different compositions, temperatures, and pulsation amplitudes.
Damping of pulsations by bulk viscosity in the neutron-star cores can prevent
the stars to pulsate with relative amplitudes > (1-15)% (depending on the
composition of matter).",0208078v1
2003-01-07,Damping of Neutron Star Shear Modes by Superfluid Friction,"The forced motion of superfluid vortices in shear oscillations of rotating
solid neutron star matter produces damping of the mode. A simple model of the
unpinning and repinning processes is described, with numerical calculations of
the consequent energy decay times. These are of the order of 1 s or more for
typical anomalous X-ray pulsars but become very short for the general
population of radio pulsars. The superfluid friction processes considered here
may also be significant for the damping of r-modes in rapidly rotating neutron
stars.",0301112v1
2005-04-25,Radiative Effect on Particle Acceleration via Relativistic Electromagnetic Expansion,"The radiation damping effect on the diamagnetic relativistic pulse
accelerator (DRPA) is studied in two-and-half dimensional Particle-in-Cell
(PIC) simulation with magnetized electron-positron plasmas. Self-consistently
solved radiation damping force converts particle energy to radiation energy.
The DRPA is still robust with radiation, and the Lorentz factor of the most
high energy particles reach more than two thousand before they decouple from
the electromagnetic pulse. Resulted emitted power from the pulse front is lower
in the radiative case than the estimation from the non-radiative case due to
the radiation damping. The emitted radiation is strongly linearly polarized and
peaked within few degrees from the direction of Poynting flux.",0504561v1
1999-05-06,Collective and chaotic motion in self-bound many-body systems,"We investigate the interplay of collective and chaotic motion in a classical
self-bound N-body system with two-body interactions. This system displays a
hierarchy of three well separated time scales that govern the onset of chaos,
damping of collective motion and equilibration. Comparison with a mean-field
problem shows that damping is mainly due to dephasing. The Lyapunov exponent,
damping and equilibration rates depend mildly on the system size N.",9905007v2
1997-05-12,Damping of Oscillations in Layer-by-Layer Growth,"We present a theory for the damping of layer-by-layer growth oscillations in
molecular beam epitaxy. The surface becomes rough on distances larger than a
layer coherence length which is substantially larger than the diffusion length.
The damping time can be calculated by a comparison of the competing roughening
and smoothening mechanisms. The dependence on the growth conditions,
temperature and deposition rate, is characterized by a power law. The
theoretical results are confirmed by computer simulations.",9705100v1
1999-09-17,Thermoelastic Damping in Micro- and Nano-Mechanical Systems,"The importance of thermoelastic damping as a fundamental dissipation
mechanism for small-scale mechanical resonators is evaluated in light of recent
efforts to design high-Q micrometer- and nanometer-scale electro-mechanical
systems (MEMS and NEMS). The equations of linear thermoelasticity are used to
give a simple derivation for thermoelastic damping of small flexural vibrations
in thin beams. It is shown that Zener's well-known approximation by a
Lorentzian with a single thermal relaxation time slightly deviates from the
exact expression.",9909271v1
2000-10-01,Super-Radiance and the Unstable Photon Oscillator,"If the damping of a simple harmonic oscillator from a thermally random force
is sufficiently strong, then the oscillator may become unstable. For a photon
oscillator (radiatively damped by electric dipole moments), the instability
leads to a low temperature Hepp-Lieb-Preparata super-radiant phase transition.
The stable oscillator regime is described by the free energy of the
conventional Casimir effect. The unstable (strongly damped) oscillator has a
free energy corresponding to Dicke super-radiance.",0010013v1
2001-08-07,Non-damped Acoustic Plasmon and Superconductivity in Single Wall Carbon Nanotubes,"We show that non-damped acoustic plasmons exist in single wall carbon
nanotubes (SWCNT) and propose that the non-damped acoustic plasmons may mediate
electron-electron attraction and result in superconductivity in the SWCNT. The
superconducting transition temperature Tc for the SWCNT (3,3) obtained by this
mechanism agrees with the recent experimental result (Z. K. Tang et al, Science
292, 2462(2001)). We also show that it is possible to get higher Tc up to 99 K
by doping the SWCNT (5,5).",0108124v2
2001-12-16,The Damping of the Bose-Condensate Oscillations in a Trap at Zero Temperature,"We discuss an existence of the damping for the radial condensate oscillations
in a cylindric trap at zero temperature. The damping is a result of the
parametric resonance leading to energy transfer from the coherent condensate
oscillations to the longitudinal sound waves within a finite frequency
interval. The parametric resonance is due to the oscillations of the sound
velocity. The triggering amplitudes at zero temperature are associated with the
zero-point oscillations.",0112292v1
2002-06-13,Beliaev damping of quasi-particles in a Bose-Einstein condensate,"We report a measurement of the suppression of collisions of quasi-particles
with ground state atoms within a Bose-Einstein condensate at low momentum.
These collisions correspond to Beliaev damping of the excitations, in the
previously unexplored regime of the continuous quasi-particle energy spectrum.
We use a hydrodynamic simulation of the expansion dynamics, with the Beliaev
damping cross-section, in order to confirm the assumptions of our analysis.",0206234v1
2002-06-28,Accidental suppression of Landau damping of the transverse breathing mode in elongated Bose-Einstein condensates,"We study transverse radial oscillations of an elongated Bose-Einstein
condensate using finite temperature simulations, in the context of a recent
experiment at ENS. We demonstrate the existence of a mode corresponding to an
in-phase collective oscillation of both the condensate and thermal cloud.
Excitation of this mode accounts for the very small damping rate observed
experimentally, and we find excellent quantitative agreement between experiment
and theory. In contrast to other condensate modes, interatomic collisions are
found to be the dominant damping mechanism in this case.",0206582v1
2004-04-19,Nonlinear response of superparamagnets with finite damping: an analytical approach,"The strongly damping-dependent nonlinear dynamical response of classical
superparamagnets is investigated by means of an analytical approach. Using
rigorous balance equations for the spin occupation numbers a simple approximate
expression is derived for the nonlinear susceptibility. The results are in good
agreement with those obtained from the exact (continued-fraction) solution of
the Fokker-Planck equation. The formula obtained could be of assistance in the
modelling of the experimental data and the determination of the damping
coefficient in superparamagnets.",0404445v1
2005-03-03,Collapse of thermal activation in moderately damped Josephson junctions,"We study switching current statistics in different moderately damped
Josephson junctions: a paradoxical collapse of the thermal activation with
increasing temperature is reported and explained by interplay of two
conflicting consequences of thermal fluctuations, which can both assist in
premature escape and help in retrapping back into the stationary state. We
analyze the influence of dissipation on the thermal escape by tuning the
damping parameter with a gate voltage, magnetic field, temperature and an
in-situ capacitor.",0503067v1
2006-03-13,Universal features of the defect-induced damping of lattice vibrations,"It is shown that any defect gives an Ohmic contribution to the damping of any
normal mode of the crystal lattice with nonzero wavevector which does not
vanish at zero temperature. This explains the large phason damping observed at
low temperatures in incommensurate phases, and might be a key factor to
understand the linear-in-$T$ specific heat observed in a number of real
dielectrics at low enough temperatures.",0603343v2
2006-04-25,Spin Precession and Avalanches,"In many magnetic materials, spin dynamics at short times are dominated by
precessional motion as damping is relatively small. In the limit of no damping
and no thermal noise, we show that for a large enough initial instability, an
avalanche can transition to an ergodic phase where the state is equivalent to
one at finite temperature, often above that for ferromagnetic ordering. This
dynamical nucleation phenomenon is analyzed theoretically. For small finite
damping the high temperature growth front becomes spread out over a large
region. The implications for real materials are discussed.",0604563v1
2007-02-11,Non-Markovian coherence dynamics of driven spin boson model: damped quantum beat or large amplitude coherence oscillation,"The dynamics of driven spin boson model is studied analytically by means of
the perturbation approach based on a unitary transformation. We gave the
analytical expression for the population difference and coherence of the two
level system. The results show that in the weak driven case, the population
difference present damped coherent oscillation (single or double frequency) and
the frequencies depend on the initial state. The coherence exhibit damped
oscillation with Rabi frequency. When driven field is strong enough, the
population difference exhibit undamped large-amplitude coherent oscillation.
The results easily return to the two extreme cases without dissipation or
without periodic driven.",0702268v1
2005-05-10,Highly Damped Quasinormal Modes of Generic Single Horizon Black Holes,"We calculate analytically the highly damped quasinormal mode spectra of
generic single-horizon black holes using the rigorous WKB techniques of
Andersson and Howls\cite{Andersson}. We thereby provide a firm foundation for
previous analysis, and point out some of their possible limitations. The
numerical coefficient in the real part of the highly damped frequency is
generically determined by the behavior of coupling of the perturbation to the
gravitational field near the origin, as expressed in tortoise coordinates. This
fact makes it difficult to understand how the famous $ln(3)$ could be related
to the quantum gravitational microstates near the horizon.",0505044v1
2006-05-01,Stability and quasinormal modes of the massive scalar field around Kerr black holes,"We find quasinormal spectrum of the massive scalar field in the background of
the Kerr black holes. We show that all found modes are damped under the
quasinormal modes boundary conditions when $\mu M$ is not large, thereby
implying stability of the massive scalar field. This complements the region of
stability determined by the Beyer inequality for large masses of the field. We
show that, similar to the case of a non-rotating black holes, the massive term
of the scalar field does not contribute in the regime of high damping. Thereby,
the high damping asymptotic should be the same as for the massless scalar
field.",0605013v1
1992-04-06,Comment on ``High Temperature Fermion Propagator -- Resummation and Gauge Dependence of the Damping Rate'',"Baier et al. have reported the damping rate of long-wavelength fermionic
excitations in high-temperature QED and QCD to be gauge-fixing-dependent even
within the resummation scheme due to Braaten and Pisarski. It is shown that
this problem is caused by the singular nature of the on-shell expansion of the
fermion self-energy in the infra-red. Its regularization reveals that the
alleged gauge dependence pertains to the residue rather than the pole of the
fermion propagator, so that in particular the damping constant comes out
gauge-independent, as it should.",9204210v1
1993-02-09,Damping rates for moving particles in hot QCD,"Using a program of perturbative resummation I compute the damping rates for
fields at nonzero spatial momentum to leading order in weak coupling in hot
$QCD$. Sum rules for spectral densities are used to simplify the calculations.
For massless fields the damping rate has an apparent logarithmic divergence in
the infrared limit, which is cut off by the screening of static magnetic fields
(``magnetic mass''). This demonstrates how at high temperature even
perturbative quantities are sensitive to nonperturbative phenomenon.",9302242v1
1994-04-21,Is \lq\lq Heavy Quark Damping Rate Puzzle'' in Hot QCD Really the Puzzle?,"Within the framework of perturbative resummation scheme of Pisarski and
Braaten, the decay- or damping-rate of a moving heavy quark (muon) to leading
order in weak coupling in hot QCD (QED) is examined. Although, as is well
known, the conventionally-defined damping rate diverges logarithmically at the
infrared limit, shown is that no such divergence appears in the physically
measurable decay rate. The cancellation occurs between the contribution from
the \lq\lq real'' decay diagram and the contribution from the diagrams with
\lq\lq thermal radiative correction''.",9404318v1
1996-01-12,Damping Rate of a Scalar Particle in Hot Scalar QED,"In contrast to the damping of partons in a quark-gluon plasma, the damping of
a scalar particle in a hot scalar QED plasma can be calculated to leading order
for the whole momentum range using the Braaten-Pisarski method. In this way the
evolution of the logarithmic infrared singularity caused by the exchange of a
transverse photon from soft to hard momenta can be studied.",9601254v1
1996-09-17,Damping Rate of Quasiparticles in Degenerate Ultrarelativistic Plasmas,"We compute the damping rate of a fermion in a dense relativistic plasma at
zero temperature. Just above the Fermi sea, the damping rate is dominated by
the exchange of soft magnetic photons (or gluons in QCD) and is proportional to
$(E-\mu)$, where E is the fermion energy and $\mu$ the chemical potential. We
also compute the contribution of soft electric photons and of hard photons. As
in the nonrelativistic case, the contribution of longitudinal photons is
proportional to $(E-\mu)^2$, and is thus non leading in the relativistic case.",9609369v1
1997-05-28,Classical Statistical Mechanics and Landau Damping,"We study the retarded response function in scalar $\phi^4$-theory at finite
temperature. We find that in the high-temperature limit the imaginary part of
the self-energy is given by the classical theory to leading order in the
coupling. In particular the plasmon damping rate is a purely classical effect
to leading order, as shown by Aarts and Smit. The dominant contribution to
Landau damping is given by the propagation of classical fields in a heat bath
of non-interacting fields.",9705452v1
1997-12-01,A potential infrared problem with the damping rates for gluons with soft momentum in hot QCD,"We calculate the damping rate $\gamma_l$ for longitudinal gluons with zero
momentum in finite high temperature QCD and show that some of its contributing
terms are infrared divergent. This is in contrast with the expectation that
this damping rate is to be equal to the corresponding one $\gamma_t$ for
transverse gluons which is known to be finite. Our calculation was motivated by
the fact that similar divergent terms occur when we calculated in a previous
work $\gamma_t$ to order $ p^2$, p being the momentum of the gluon. After we
present our results, we briefly discuss them.",9712210v1
1998-04-21,The Plasmon Damping Rate for T -> T_C,"The plasmon damping rate in scalar field theory is computed close to the
critical temperature. It is shown that the divergent result obtained in
perturbation theory is a consequence of neglecting the thermal renormalization
of the coupling. Taking this effect into account, a vanishing damping rate is
obtained, leading to the critical slowing down of the equilibration process.",9804351v2
1998-10-06,Self-consistent Study on Color Transport in the Quark Gluon Plasma at Finite Chemical Potential,"We calculate the relaxation time self-consistently to study the damping of
collective color modes and the color conductivity in a QGP by deriving
self-consistent equations for the damping rates of gluons and quarks to leading
order QCD by TFD including a chemical potential for quarks. We show that the
damping rates are not sensitive to the chemical potential whereas color
conductivity is enhanced considerably.",9810256v1
1999-02-19,The problem of nonlinear Landau damping in quark-gluon plasma,"On the basis of the semiclassical equations for quark-gluon plasma (QGP) and
Yang-Mills equation, the generalized kinetic equation for waves with regard to
its interaction is obtained. The physical mechanisms defining nonlinear
scattering of a plasmon by QGP particles are analysed. The problem on a
connection of nonlinear Landau damping rate of longitudinal oscillation with
damping rate, obtained on the basis of hard thermal loops approximation, is
considered.",9902397v2
1999-07-21,A Slavnov-Taylor identity and equality of damping rates for static transverse and longitudinal gluons in hot QCD,"A Slavnov-Taylor identity is derived for the gluon polarization tensor in hot
QCD. We evaluate its implications for damping of gluonic modes in the plasma.
Applying the identity to next to the leading order in hard-thermal-loop
resummed perturbation theory, we derive the expected equality of damping rates
for static transverse and longitudinal (soft) gluons. This is of interest also
in view of deviating recent reports of $\gamma_t(p=0)\neq\gamma_l(p=0)$ based
on a direct calculation of $\gamma_l(p=0)$.",9907439v1
2000-09-15,Fermion Damping Rate Effects in Cold Dense Matter,"We review the non-Fermi or marginal liquid behavior of a relativistic QED
plasma. In this medium a quasiparticle has a damping rate that depends linearly
on the distance between its energy and the Fermi surface. We stress that this
dependence is due to the long-range character of the magnetic interactions in
the medium. Finally, we study how the quark damping rate modifies the gap
equation of color superconductivity, reducing the value of the gap at the Fermi
surface.",0009182v1
2001-07-19,Photon Damping Caused by Electron-Positron Pair Production in a Strong Magnetic Field,"Damping of an electromagnetic wave in a strong magnetic field is analyzed in
the kinematic region near the threshold of electron-positron pair production.
Damping of the electromagnetic field is shown to be noticeably nonexponential
in this region. The resulting width of the photon $\gamma \to e^+ e^-$ decay is
considerably smaller than previously known results.",0107217v1
2004-09-27,Damping of electromagnetic waves due to electron-positron pair production,"The problem of the backreaction during the process of electron-positron pair
production by a circularly polarized electromagnetic wave propagating in a
plasma is investigated. A model based on the relativistic Boltzmann-Vlasov
equation with a source term corresponding to the Schwinger formula for the pair
creation rate is used. The damping of the wave, the nonlinear up-shift of its
frequency due to the plasma density increase and the effect of the damping on
the wave polarization and on the background plasma acceleration are
investigated as a function of the wave amplitude.",0409301v1
2005-10-25,Infrared behavior of the dispersion relations in high-temperature scalar QED,"We investigate the infrared properties of the next-to-leading-order
dispersion relations in scalar quantum electrodynamics at high temperature in
the context of hard-thermal-loop perturbation theory. Specifically, we
determine the damping rate and the energy for scalars with ultrasoft momenta.
We show by explicit calculations that an early external-momentum expansion,
before the Matsubara sum is performed, gives exactly the same result as a late
one. The damping rate is obtained up to fourth order included in the ultrasoft
momentum and the energy up to second order. The damping rate is found sensitive
in the infrared whereas the energy not.",0510330v1
2006-11-09,Lepton asymmetry in the primordial gravitational wave spectrum,"Effects of neutrino free streaming is evaluated on the primordial spectrum of
gravitational radiation taking both neutrino chemical potential and masses into
account. The former or the lepton asymmetry induces two competitive effects,
namely, to increase anisotropic pressure, which damps the gravitational wave
more, and to delay the matter-radiation equality time, which reduces the
damping. The latter effect is more prominent and a large lepton asymmetry would
reduce the damping. We may thereby be able to measure the magnitude of lepton
asymmetry from the primordial gravitational wave spectrum.",0611121v1
2005-03-17,A New Approach to Canonical Quantization of the Radiation Damping,"Inspired in some works about quantization of dissipative systems, in
particular of the damped harmonic oscillator\cite{MB,RB,12}, we consider the
dissipative system of a charge interacting with its own radiation, which
originates the radiation damping (RD). Using the indirect Lagrangian
representation we obtained a Lagrangian formalism with a Chern-Simons-like
term. A Hamiltonian analysis is also done, what leads to the quantization of
the system.",0503135v1
2003-09-15,Eigenfrequencies and expansions for damped wave equations,"We study eigenfrequencies and propagator expansions for damped wave equations
on compact manifolds. Under the assumption of geometric control, the propagator
is shown to admit an expansion in terms of finitely many eigenmodes near the
real axis, with an error term exponentially decaying in time. In the presence
of a nondegenerate elliptic closed geodesic not meeting the support of the
damping coefficient, we show that there exists a sequence of eigenfrequencies
converging rapidly to the real axis. In the case of Zoll manifolds, we show
that the propagator can be expanded in terms of clusters of the
eigenfrequencies in the entire spectral band.",0309250v1
2004-06-02,Instability results for the damped wave equation in unbounded domains,"We extend some previous results for the damped wave equation in bounded
domains in Euclidean spaces to the unbounded case. In particular, we show that
if the damping term is of the form $\alpha a$ with bounded $a$ taking on
negative values on a set of positive measure, then there will always exist
unbounded solutions for sufficiently large positive $\alpha$.
  In order to prove these results, we generalize some existing results on the
asymptotic behaviour of eigencurves of one-parameter families of Schrodinger
operators to the unbounded case, which we believe to be of interest in their
own right.",0406041v1
1997-07-20,Effects of gluon damping rate on the viscosity coefficient of the quark-gluon plasma at finite chemical potential,"By considering the Debye screening and damping rate of gluons, the viscosity
coefficient of the quark-gluon plasma was evaluated via real-time finite
temperature QCD in the relaxation time approximation at finite temperature and
chemical potential . The results show that both the damping rate and the
chemical potential cause considerable enhancements to the viscosity coefficient
of hot dense quark-gluon plasma.",9707033v1
2002-12-11,Rotational Damping and Compound Formation in Warm Rotating Nuclei,"The rotational damping width \Gamma_{rot} and the compound damping width
\Gamma_{comp} are two fundamental quantities that characterize rapidly rotating
compound nuclei having finite thermal excitation energy. A two-component
structure in the strength function of consecutive E2 transitions reflects the
two widths, and it causes characteristic features in the double and triple
gamma-ray spectra. We discuss a new method to extract experimentally values of
\Gamma_{rot} and \Gamma_{comp}. The first preliminary result of this method is
presented.",0212050v1
2003-07-27,Chaos and rotational damping in particle-rotor model,"The onset of chaos and the mechanism of rotational damping are studied in an
exactly soluble particle-rotor model. It is shown that the degree of chaoticity
as inferred from the statistical measures is closely related to the onset of
rotational damping obtained using the model Hamiltonian.",0307104v2
1997-07-10,Supersymmetric partner chirping of Newtonian free damping,"We connect the classical free damping cases by means of Rosner's construction
in supersymmetric quantum mechanics. Starting with the critical damping, one
can obtain in the underdamping case a chirping of instantaneous physical
frequency \omega ^{2}(t) \propto \omega_{u}^{2}sech^2(\omega_{u}t), whereas in
the overdamped case the ""chirping"" is of the (unphysical) type \omega
^{2}(t)\propto\omega_{o}^{2}sec^{2}(\omega_{o}t), where \omega_{u}$ and
$\omega_{o} are the underdamped and overdamped frequency parameters,
respectively",9707012v4
2000-04-10,Ermakov-Lewis angles for one-parameter supersymmetric families of Newtonian free damping modes,"We apply the Ermakov-Lewis procedure to the one-parameter damped modes
\tilde{y} recently introduced by Rosu and Reyes, which are related to the
common Newtonian free damping modes y by the general Riccati solution [H.C.
Rosu and M. Reyes, Phys. Rev. E 57, 4850 (1998), physics/9707019]. In
particular, we calculate and plot the angle quantities of this approach that
can help to distinguish these modes from the common y modes",0004014v4
2002-10-29,Model of Internal Friction Damping in Solids,"A model for harmonic oscillator damping due to the internal friction of
solids has been developed, based on considerations of a long period pendulum.
The assumption of a complex elastic modulus to describe stress-strain
hysteresis in the support structure of the pendulum yields an expression for
the figure of merit Q that agrees with many experiments involving material
damping. As such, the approximations of this linear model stand in contrast
with common theory.",0210121v1
2003-06-11,Nonlinear Damping of the 'Linear' Pendulum,"This study shows that typical pendulum dynamics is far from the simple
equation of motion presented in textbooks. A reasonably complete damping model
must use nonlinear terms in addition to the common linear viscous expression.
In some cases a nonlinear substitute for assumed linear damping may be more
appropriate. Even for exceptional cases where all nonlinearity may be ignored,
it is shown that viscous dissipation involves subtleties that can lead to huge
errors when ignored.",0306081v1
2003-07-02,Harmonic Oscillator Potential to describe Internal Dissipation,"Assuming that a constant potential energy function has meaning for a
dissipated harmonic oscillator, then an important issue is the time dependence
of the turning points. Turning point studies demonstrate that the common model
of external (viscous) damping fails to properly describe those many systems
where structural (internal friction) damping is the most important source of
dissipation. For internal friction damping, the better model of potential
energy is one in which the function is not stationary.",0307016v1
2004-08-19,Beyond the Linear Damping Model for Mechanical Harmonic Oscillators,"The steady state motion of a folded pendulum has been studied using
frequencies of drive that are mainly below the natural (resonance) frequency of
the instrument. Although the free-decay of this mechanical oscillator appears
textbook exponential, the steady state behavior of the instrument for
sub-resonance drive can be remarkably complex. Although the response cannot be
explained by linear damping models, the general features can be understood with
the nonlinear, modified Coulomb damping model developed by the author.",0408091v1
1998-01-28,Phenomenological damping in trapped atomic Bose-Einstein condensates,"The method of phenomenological damping developed by Pitaevskii for
superfluidity near the $\lambda$ point is simulated numerically for the case of
a dilute, alkali, inhomogeneous Bose-condensed gas near absolute zero. We study
several features of this method in describing the damping of excitations in a
Bose-Einstein condensate. In addition, we show that the method may be employed
to obtain numerically accurate ground states for a variety of trap potentials.",9801064v1
1998-04-06,Optimal quantum codes for preventing collective amplitude damping,"Collective decoherence is possible if the departure between quantum bits is
smaller than the effective wave length of the noise field. Collectivity in the
decoherence helps us to devise more efficient quantum codes. We present a class
of optimal quantum codes for preventing collective amplitude damping to a
reservoir at zero temperature. It is shown that two qubits are enough to
protect one bit quantum information, and approximately $L+ 1/2 \log_2((\pi
L)/2)$ qubits are enough to protect $L$ qubit information when $L$ is large.
For preventing collective amplitude damping, these codes are much more
efficient than the previously-discovered quantum error correcting or avoiding
codes.",9804014v1
2000-01-12,Antibunching effect of the radiation field in a microcavity with a mirror undergoing heavily damping oscillation,"The interaction between the radiation field in a microcavity with a mirror
undergoing damping oscillation is investigated. Under the heavily damping
cases, the mirror variables are adiabatically eliminated.
  The the stationary conditions of the system are discussed. The small
fluctuation approximation around steady values is applied to analysis the
antibunching effect of the cavity field. The antibunching condition is given
under two limit cases.",0001036v1
2000-03-29,Disagreement between correlations of quantum mechanics and stochastic electrodynamics in the damped parametric oscillator,"Intracavity and external third order correlations in the damped nondegenerate
parametric oscillator are calculated for quantum mechanics and stochastic
electrodynamics (SED), a semiclassical theory. The two theories yield greatly
different results, with the correlations of quantum mechanics being cubic in
the system's nonlinear coupling constant and those of SED being linear in the
same constant. In particular, differences between the two theories are present
in at least a mesoscopic regime. They also exist when realistic damping is
included. Such differences illustrate distinctions between quantum mechanics
and a hidden variable theory for continuous variables.",0003131v1
2002-02-15,Decoherence of Quantum Damped Oscillators,"Quantum dissipation is studied within two model oscillators, the
Caldirola-Kanai (CK) oscillator as an open system with one degree of freedom
and the Bateman-Feshbach-Tikochinsky (BFT) oscillator as a closed system with
two degrees of freedom. Though these oscillators describe the same classical
damped motion, the CK oscillator retains the quantum coherence, whereas the
damped subsystem of the BFT oscillator exhibits both quantum decoherence and
classical correlation. Furthermore the amplified subsystem of the BFT
oscillator shows the same degree of quantum decohernce and classical
correlation.",0202089v1
2002-12-05,Time correlated quantum amplitude damping channel,"We analyze the problem of sending classical information through qubit
channels where successive uses of the channel are correlated. This work extends
the analysis of C. Macchiavello and G. M. Palma to the case of a non-Pauli
channel - the amplitude damping channel. Using the channel description outlined
in S. Daffer, et al, we derive the correlated amplitude damping channel. We
obtain a similar result to C. Macchiavello and G. M. Palma, that is, that under
certain conditions on the degree of channel memory, the use of entangled input
signals may enhance the information transmission compared to the use of product
input signals.",0212032v1
2005-06-01,Quantum damped oscillator I: dissipation and resonances,"Quantization of a damped harmonic oscillator leads to so called Bateman's
dual system. The corresponding Bateman's Hamiltonian, being a self-adjoint
operator, displays the discrete family of complex eigenvalues. We show that
they correspond to the poles of energy eigenvectors and the corresponding
resolvent operator when continued to the complex energy plane. Therefore, the
corresponding generalized eigenvectors may be interpreted as resonant states
which are responsible for the irreversible quantum dynamics of a damped
harmonic oscillator.",0506007v1
2005-10-19,The damped harmonic oscillator in deformation quantization,"We propose a new approach to the quantization of the damped harmonic
oscillator in the framework of deformation quantization. The quantization is
performed in the Schr\""{o}dinger picture by a star-product induced by a
modified ""Poisson bracket"". We determine the eigenstates in the damped regime
and compute the transition probability between states of the undamped harmonic
oscillator after the system was submitted to dissipation.",0510150v1
2006-04-28,The characteristic function of optical evolution,"The master equation of quantum optical density operator is transformed to the
equation of characteristic function. The parametric amplification and amplitude
damping as well as the phase damping are considered. The solution for the most
general initial quantum state is obtained for parametric amplification and
amplitude damping. The purity of one mode Gaussian system and the entanglement
of two mode Gaussian system are studied.",0604208v4
2007-01-13,Wave-particle duality in the damped harmonic oscillator,"Quantization of the damped harmonic oscillator is taken as leitmotiv to
gently introduce elements of quantum probability theory for physicists. To this
end, we take (graduate) students in physics as entry level and explain the
physical intuition and motivation behind the, sometimes overwhelming, math
machinery of quantum probability theory.
  The main text starts with the quantization of the (undamped) harmonic
oscillator from the Heisenberg and Schroedinger point of view. We show how both
treatments are special instances of a quantum probabilistic quantization
procedure: the second quantization functor. We then apply the second
quantization functor to the damped harmonic oscillator and interpret the
quantum dynamics of the position and energy operator as stochastic processes.",0701082v1
2007-04-11,Time dependence of joint entropy of oscillating quantum systems,"The time dependent entropy (or Leipnik's entropy) of harmonic and damped
harmonic oscillators is extensively investigated by using time dependent wave
function obtained by the Feynman path integral method. Our results for simple
harmonic oscillator are in agrement with the literature. However, the joint
entropy of damped harmonic oscillator shows remarkable discontinuity with time
for certain values of damping factor. According to the results, the envelop of
the joint entropy curve increases with time monotonically. This results is the
general properties of the envelop of the joint entropy curve for quantum
systems.",0704.1370v3
2007-06-30,The squeezed generalized amplitude damping channel,"Squeezing of a thermal bath introduces new features absent in an open quantum
system interacting with an uncorrelated (zero squeezing) thermal bath. The
resulting dynamics, governed by a Lindblad-type evolution, extends the concept
of a generalized amplitude damping channel, which corresponds to a dissipative
interaction with a purely thermal bath. Here we present the Kraus
representation of this map, which we call the squeezed generalized amplitude
damping channel. As an application of this channel to quantum information, we
study the classical capacity of this channel.",0707.0059v2
2007-07-09,Memory in a nonlocally damped oscillator,"We analyze the new equation of motion for the damped oscillator. It differs
from the standard one by a damping term which is nonlocal in time and hence it
gives rise to a system with memory. Both classical and quantum analysis is
performed. The characteristic feature of this nonlocal system is that it breaks
local composition low for the classical Hamiltonian dynamics and the
corresponding quantum propagator.",0707.1199v2
2007-07-20,Dynamics of Bloch Oscillations in Disordered Lattice Potentials,"We present a detailed analysis of the dynamics of Bloch oscillations of
Bose-Einstein condensates in disordered lattice potentials. Due to the disorder
and the interparticle interactions these oscillations undergo a dephasing,
reflected in a damping of the center of mass oscillations, which should be
observable under realistic experimental conditions. The interplay between
interactions and disorder is far from trivial, ranging from an
interaction-enhanced damping due to modulational instability for strong
interactions, to an interaction-reduced damping due to a dynamical screening of
the disorder potential.",0707.3131v1
2007-09-14,Damping of field-induced chemical potential oscillations in ideal two-band compensated metals,"The field and temperature dependence of the de Haas-van Alphen oscillations
spectrum is studied for an ideal two-dimensional compensated metal. It is shown
that the chemical potential oscillations, involved in the frequency
combinations observed in the case of uncompensated orbits, are strongly damped
and can even be suppressed when the effective masses of the electron- and
hole-type orbits are the same. When magnetic breakdown between bands occurs,
this damping is even more pronounced and the Lifshits-Kosevich formalism
accounts for the data in a wide field range.",0709.2223v2
2007-09-14,Update on Ion Studies,"The effect of ions has received one of the highest priorities in R&D for the
damping rings of the International Linear Collider(ILC). It is detrimental to
the performance of the electron damping ring. In this note, an update
concerning the ion studies for the ILC damping ring is given. We investigate
the gap role and irregular fill pattern in the ring.The ion density reduction
in different fills is calculated analytically. Simulation results are also
presented.",0709.2248v1
2007-10-03,Stability of a Nonlinear Axially Moving String With the Kelvin-Voigt Damping,"In this paper, a nonlinear axially moving string with the Kelvin-Voigt
damping is considered. It is proved that the string is stable, i.e., its
transversal displacement converges to zero when the axial speed of the string
is less than a certain critical value. The proof is established by showing that
a Lyapunov function corresponding to the string decays to zero exponentially.
It is also shown that the string displacement is bounded when a bounded
distributed force is applied to it transversally. Furthermore, a few open
problems regarding the stability and stabilization of strings with the
Kelvin-Voigt damping are stated.",0710.0872v1
2007-10-15,General Solution of the Quantum Damped Harmonic Oscillator,"In this paper the general solution of the quantum damped harmonic oscillator
is given.",0710.2724v4
2008-02-21,Identification of Test Structures for Reduced Order Modeling of the Squeeze Film Damping in Mems,"In this study the dynamic behaviour of perforated microplates oscillating
under the effect of squeeze film damping is analyzed. A numerical approach is
adopted to predict the effects of damping and stiffness transferred from the
surrounding ambient air to oscillating structures ; the effect of hole's cross
section and plate's extension is observed. Results obtained by F.E.M. models
are compared with experimental measurements performed by an optical
interferometric microscope.",0802.3076v1
2008-03-14,Current-induced noise and damping in non-uniform ferromagnets,"In the presence of spatial variation of the magnetization direction, electric
current noise causes a fluctuating spin-transfer torque that increases the
fluctuations of the ferromagnetic order parameter. By the
fluctuation-dissipation theorem, the equilibrium fluctuations are related to
the magnetization damping, which in non-uniform ferromagnets acquires a
nonlocal tensor structure. In biased ferromagnets, shot noise can become the
dominant contribution to the magnetization noise at low temperatures.
Considering spin spirals as a simple example, we show that the current-induced
noise and damping is significant.",0803.2175v1
2008-04-23,Ion acoustic waves in the plasma with the power-law q-distribution in nonextensive statistics,"We investigate the dispersion relation and Landau damping of ion acoustic
waves in the collisionless magnetic-field-free plasma if it is described by the
nonextensive q-distributions of Tsallis statistics. We show that the increased
numbers of superthermal particles and low velocity particles can explain the
strengthened and weakened modes of Landau damping, respectively, with the
q-distribution. When the ion temperature is equal to the electron temperature,
the weakly damped waves are found to be the distributions with small values of
q.",0804.3732v1
2008-07-23,Tunneling-induced damping of phase coherence revivals in deep optical lattices,"We consider phase coherence collapse and revival in deep optical lattices,
and calculate within the Bose-Hubbard model the revival amplitude damping
incurred by a finite tunneling coupling of the lattice wells (after sweeping
from the superfluid to the Mott phase). Deriving scaling laws for the
corresponding decay of first-order coherence revival in terms of filling
factor, final lattice depth, and number of tunneling coupling partners, we
estimate whether revival-damping related to tunneling between sites can be or
even has already been observed in experiment.",0807.3627v2
2008-07-31,Generalized Theory of Landau Damping,"Collisionless damping of electrical waves in plasma is investigated in the
frame of the classical formulation of the problem. The new principle of
regularization of the singular integral is used. The exact solution of the
corresponding dispersion equation is obtained. The results of calculations lead
to existence of discrete spectrum of frequencies and discrete spectrum of
dispersion curves. Analytical results are in good coincidence with results of
direct mathematical experiments. Key words: Foundations of the theory of
transport processes and statistical physics; Boltzmann physical kinetics;
damping of plasma waves, linear theory of wave`s propagation PACS: 67.55.Fa,
67.55.Hc",0807.5007v1
2008-08-05,"Radiation damping, noncommutativity and duality","In this work, our main objective is to construct a N=2 supersymmetric
extension of the nonrelativistic $(2+1)$-dimensional model describing the
radiation damping on the noncommutative plane with scalar (electric) and vector
(magnetic) interactions by the N=2 superfield technique. We also introduce a
dual equivalent action to the radiation damping one using the Noether
procedure.",0808.0694v2
2008-10-06,Local existence and exponential growth for a semilinear damped wave equation with dynamic boundary conditions,"In this paper we consider a multi-dimensional damped semiliear wave equation
with dynamic boundary conditions, related to the Kelvin-Voigt damping. We
firstly prove the local existence by using the Faedo-Galerkin approximations
combined with a contraction mapping theorem. Secondly, the exponential growth
of the energy and the $L^p$ norm of the solution is presented.",0810.1013v1
2008-11-20,An explanation for the pseudogap of high-temperature superconductors based on quantum optics,"We first explain the pseudogap of high-temperature superconductivity based on
an approach of quantum optics. After introducing a damping factor for the
lifetime $\tau$ of quasiparticles, the superconducting dome is naturally
produced, and the pseudogap is the consequence of pairing with damped
coherence. We derive a new expression of Ginzburg-Landau free energy density,
in which a six-order term due to decoherence damping effect is included.
Without invoking any microscopic pairing mechanism, this approach provides a
simple universal equation of second-order phase transition, which can be
reduced to two well-known empirical scaling equations: the superconducting dome
Presland-Tallon equation, and the normal-state pseudogap crossover temperature
$T^{*}$ line.",0811.3262v1
2008-12-18,Exponential decay for solutions to semilinear damped wave equation,"This paper is concerned with decay estimate of solutions to the semilinear
wave equation with strong damping in a bounded domain. Introducing an
appropriate Lyaponuv function, we prove that when the damping is linear, we can
find initial data, for which the solution decays exponentially. This result
improves an early one in an article of Gazzola and Squassina.",0812.3637v3
2009-05-27,Difference between penetration and damping lengths in photonic crystal mirrors,"Different mirror geometries in two-dimensional photonic crystal slabs are
studied with fully-vectorial calculations. We compare their optical properties
and, in particular, we show that, for heterostructure mirrors, the penetration
length associated with the delay induced by distributed reflection is not
correlated to the characteristic damping length of the electromagnetic energy
distribution in the mirror. This unexpected result evidences that the usual
trade-off between short damping lengths and large penetration lengths that is
classically encountered in distributed Bragg reflectors can be overcome with
carefully designed photonic crystal structures.",0905.4449v2
2009-06-01,Exponential Decay Rates for the Damped Korteweg-de Vries Type Equation,"The exponential decay rate of $L^2-$norm related to the Korteweg-de Vries
equation with localized damping posed on whole real line will be established.
In addition, by using classical arguments we determine the $H^1-$norm of the
solution associated to Korteweg-de Vries equation with damping in whole domain,
can not have a decay property for an arbitrary initial data.",0906.0285v2
2009-07-02,Damping and decoherence of a nanomechanical resonator due to a few two level systems,"We consider a quantum model of a nanomechanical flexing beam resonator
interacting with a bath comprising a few damped tunneling two level systems
(TLS's). In contrast with a resonator interacting bilinearly with an ohmic free
oscillator bath (modeling clamping loss, for example), the mechanical resonator
damping is amplitude dependent, while the decoherence of quantum superpositions
of mechanical position states depends only weakly on their spatial separation.",0907.0431v1
2009-07-29,High performance single-error-correcting quantum codes for amplitude damping,"We construct families of high performance quantum amplitude damping codes.
All of our codes are nonadditive and most modestly outperform the best possible
additive codes in terms of encoded dimension. One family is built from
nonlinear error-correcting codes for classical asymmetric channels, with which
we systematically construct quantum amplitude damping codes with parameters
better than any prior construction known for any block length n > 7 except
n=2^r-1. We generalize this construction to employ classical codes over GF(3)
with which we numerically obtain better performing codes up to length 14.
Because the resulting codes are of the codeword stabilized (CWS) type, easy
encoding and decoding circuits are available.",0907.5149v1
2009-10-12,Suppression of Landau damping via electron band gap,"The pondermotive potential in the X-ray Raman compression can generate an
electron band gap which suppresses the Landau damping. The regime is identified
where a Langmuir wave can be driven without damping in the stimulated Raman
compression. It is shown that the partial wave breaking and the frequency
detuning due to the trapped particles would be greatly reduced.",0910.2196v3
2009-10-27,Rabi type oscillations in damped single 2D-quantum dot,"We present a quantized model of harmonically confined dot atom with inherent
damping in the presence of a transverse magnetic field. The model leads to a
non hermitian Hamiltonian in real coordinate. We have analytically studied the
effects that damping has on the Rabi type oscillations of the system. The model
explains the decoherence of Rabi oscillation in a Josephson Junction.",0910.5184v1
2009-12-16,Toward a dynamical shift condition for unequal mass black hole binary simulations,"Moving puncture simulations of black hole binaries rely on a specific gauge
choice that leads to approximately stationary coordinates near each black hole.
Part of the shift condition is a damping parameter, which has to be properly
chosen for stable evolutions. However, a constant damping parameter does not
account for the difference in mass in unequal mass binaries. We introduce a
position dependent shift damping that addresses this problem. Although the
coordinates change, the changes in the extracted gravitational waves are small.",0912.3125v1
2010-03-08,A single-ion nonlinear mechanical oscillator,"We study the steady state motion of a single trapped ion oscillator driven to
the nonlinear regime. Damping is achieved via Doppler laser-cooling. The ion
motion is found to be well described by the Duffing oscillator model with an
additional nonlinear damping term. We demonstrate a unique ability of tuning
both the linear as well as the nonlinear damping coefficients by controlling
the cooling laser parameters. Our observations open a way for the investigation
of nonlinear dynamics on the quantum-to-classical interface as well as
mechanical noise squeezing in laser-cooling dynamics.",1003.1577v1
2010-03-09,Damping of Nanomechanical Resonators,"We study the transverse oscillatory modes of nanomechanical silicon nitride
strings under high tensile stress as a function of geometry and mode index m <=
9. Reproducing all observed resonance frequencies with classical elastic theory
we extract the relevant elastic constants. Based on the oscillatory local
strain we successfully predict the observed mode-dependent damping with a
single frequency independent fit parameter. Our model clarifies the role of
tensile stress on damping and hints at the underlying microscopic mechanisms.",1003.1868v1
2010-03-24,Global attractors for strongly damped wave equations with displacement dependent damping and nonlinear source term of critical exponent,"In this paper the long time behaviour of the solutions of 3-D strongly damped
wave equation is studied. It is shown that the semigroup generated by this
equation possesses a global attractor in H_{0}^{1}(\Omega)\times L_{2}(\Omega)
and then it is proved that this global attractor is a bounded subset of
H^{2}(\Omega)\times H^{2}(\Omega) and also a global attractor in
H^{2}(\Omega)\cap H_{0}^{1}(\Omega)\times H_{0}^{1}(\Omega).",1003.4760v3
2010-04-12,Entanglement properties of optical coherent states under amplitude damping,"Through concurrence, we characterize the entanglement properties of optical
coherent-state qubits subject to an amplitude damping channel. We investigate
the distillation capabilities of known error correcting codes and obtain upper
bounds on the entanglement depending on the non-orthogonality of the coherent
states and the channel damping parameter. This work provides a first, full
quantitative analysis of these photon-loss codes which are naturally
reminiscent of the standard qubit codes against Pauli errors.",1004.1931v2
2010-05-20,Nonclassical phase-space trajectories for the damped harmonic quantum oscillator,"The phase-space path-integral approach to the damped harmonic oscillator is
analyzed beyond the Markovian approximation. It is found that pairs of
nonclassical trajectories contribute to the path-integral representation of the
Wigner propagating function. Due to the linearity of the problem, the sum
coordinate of a pair still satisfies the classical equation of motion.
Furthermore, it is shown that the broadening of the Wigner propagating function
of the damped oscillator arises due to the time-nonlocal interaction mediated
by the heat bath.",1005.3839v1
2010-06-09,Self frequency-locking of a chain of oscillators,"The paper studies the vibrational modes of a slightly damped uniform chain,
with n masses coupled by elastic forces. It will be shown that, for certain
lengths of the chain, that is for certain values of n, the damping of one of
the masses at a specific position in the chain is able to constrain the
vibration of the system to oscillate at a specific frequency. The damped mass
turns out to be a node of the chain, subdividing it in two parts. This node can
be considered as the synchronization element of the two subchains. As a
consequence the oscillating system of n-masses is self-locking to the
synchronized frequency of its subchains.",1006.1722v1
2010-08-20,First principles quasiparticle damping rates in bulk lead,"First principles calculations of the damping rates (inverse inelastic
lifetimes) of low energy quasiparticles in bulk Pb are presented. Damping rates
are obtained both for excited electrons and holes with energies up to 8 eV on a
set of k vectors throughout the Brillouin zone (BZ). Strong localization
effects in the calculated lifetimes are found. Averaged over the BZ inelastic
lifetimes versus quasiparticle energy are reported as well. In addition, the
effect of the spin-orbit induced splitting in the band structure on the
calculated lifetimes in Pb is investigated.",1008.3415v1
2010-12-07,Turbulence damping as a measure of the flow dimensionality,"The dimensionality of turbulence in fluid layers determines their properties.
We study electromagnetically driven flows in finite depth fluid layers and show
that eddy viscosity, which appears as a result of three-dimensional motions,
leads to increased bottom damping. The anomaly coefficient, which characterizes
the deviation of damping from the one derived using a quasi-two-dimensional
model, can be used as a measure of the flow dimensionality. Experiments in
turbulent layers show that when the anomaly coefficient becomes high, the
turbulent inverse energy cascade is suppressed. In the opposite limit
turbulence can self-organize into a coherent flow.",1012.1371v1
2011-03-18,Single File Diffusion of particles with long ranged interactions: damping and finite size effects,"We study the Single File Diffusion (SFD) of a cyclic chain of particles that
cannot cross each other, in a thermal bath, with long ranged interactions, and
arbitrary damping. We present simulations that exhibit new behaviors
specifically associated to systems of small number of particles and to small
damping. In order to understand those results, we present an original analysis
based on the decomposition of the particles motion in the normal modes of the
chain. Our model explains all dynamic regimes observed in our simulations, and
provides convincing estimates of the crossover times between those regimes.",1103.3642v1
2011-04-21,Spin Damping Monopole,"We present theoretical evidence that a magnetic monopole emerges in dynamic
magnetic systems in the presence of the spin-orbit interaction. The monopole
field is expressed in terms of spin damping associated with magnetization
dynamics. We demonstrate that the observation of this spin damping monopole is
accomplished electrically using Ampere's law for monopole current. Our
discovery suggests the integration of monopoles into electronics, namely,
monopolotronics.",1104.4215v2
2011-08-16,Long time dynamics for forced and weakly damped KdV on the torus,"The forced and weakly damped Korteweg-de Vries (KdV) equation with periodic
boundary conditions is considered. Starting from $L^2$ and mean-zero initial
data we prove that the solution decomposes into two parts; a linear one which
decays to zero as time goes to infinity and a nonlinear one which always
belongs to a smoother space. As a corollary we prove that all solutions are
attracted by a ball in $H^s$, $s\in(0,1)$, whose radius depends only on $s$,
the $L^2$ norm of the forcing term and the damping parameter. This gives a new
proof for the existence of a smooth global attractor and provides quantitative
information on the size of the attractor set in $H^s$.",1108.3358v1
2011-10-12,Acceleration Control in Nonlinear Vibrating Systems based on Damped Least Squares,"A discrete time control algorithm using the damped least squares is
introduced for acceleration and energy exchange controls in nonlinear vibrating
systems. It is shown that the damping constant of least squares and sampling
time step of the controller must be inversely related to insure that vanishing
the time step has little effect on the results. The algorithm is illustrated on
two linearly coupled Duffing oscillators near the 1:1 internal resonance. In
particular, it is shown that varying the dissipation ratio of one of the two
oscillators can significantly suppress the nonlinear beat phenomenon.",1110.2811v2
2011-10-17,Normal Mode Expansion of Damped Coupled Oscillators in 3 dimensions,"In this paper, I aim to study free oscillations of a system of oscillators in
more than one dimensions in the absence of damping. The basic approach lies in
decoupling the motion in the individual perpendicular directions. Once the
equations are decoupled, the existent techniques of Normal mode expansion for
1-dimensional oscillators are used to solve for the equations of motion. I also
study the motion of a driven system of oscillators in higher dimensions in the
presence of a velocity dependent damping force.",1110.3773v1
2011-10-25,Distinguishing mesoscopic quantum superpositions from statistical mixtures in periodically shaken double wells,"For Bose-Einstein condensates in double wells, N-particle Rabi-like
oscillations often seem to be damped. Far from being a decoherence effect, the
apparent damping can indicate the emergence of quantum superpositions in the
many-particle quantum dynamics. However, in an experiment it would be difficult
to distinguish the apparent damping from decoherence effects. The present paper
suggests using controlled periodic shaking to quasi-instantaneously switch the
sign of an effective Hamiltonian, thus implementing an `echo' technique which
distinguishes quantum superpositions from statistical mixtures. The scheme for
the effective time-reversal is tested by numerically solving the time-dependent
N-particle Schrodinger equation.",1110.5444v1
2011-11-23,Wave Propagation And Landau-Type Damping In Liquids,"Intermolecular forces are modeled by means of a modified Lennard-Jones
potential, introducing a distance of minimum approach, and the effect of
intermolecular interactions is accounted for with a self consistent field of
the Vlasov type. A Vlasov equation is then written and used to investigate the
propagation of perturbations in a liquid. A dispersion relation is obtained and
an effect of damping, analogous to what is known in plasmas as ""Landau
damping"", is found to take place.",1111.5519v3
2011-11-25,Radiation Damping for Speeding-up NMR Applications,"We demonstrate theoretically and numerically how to control the NMR
relaxation rate after application of the standard spin echo technique. Using
radiation damping, we return the nuclear magnetization to its equilibrium state
during a time interval that is negligible compared to the relaxation time. We
obtain an estimate for optimal radiation damping which is consistent with our
numerical simulations.",1111.7060v1
2011-12-09,Perturbed damped pendulum: finding periodic solutions,"Using the damped pendulum system we introduce the averaging method to study
the periodic solutions of a dynamical system with small perturbation. We
provide sufficient conditions for the existence of periodic solutions with
small amplitude of the non--linear perturbed damped pendulum. The averaging
theory provides a useful means to study dynamical systems, accessible to Master
and PhD students.",1112.2129v2
2011-12-28,The role of damping for the driven anharmonic quantum oscillator,"For the model of a linearly driven quantum anharmonic oscillator, the role of
damping is investigated. We compare the position of the stable points in phase
space obtained from a classical analysis to the result of a quantum mechanical
analysis. The solution of the full master equation shows that the stable points
behave qualitatively similar to the classical solution but with small
modifications. Both the quantum effects and additional effects of temperature
can be described by renormalizing the damping.",1112.6119v1
2012-01-03,Creating and studying ion acoustic waves in ultracold neutral plasmas,"We excite ion acoustic waves in ultracold neutral plasmas by imprinting
density modulations during plasma creation. Laser-induced fluorescence is used
to observe the density and velocity perturbations created by the waves. The
effect of expansion of the plasma on the evolution of the wave amplitude is
described by treating the wave action as an adiabatic invariant. After
accounting for this effect, we determine that the waves are weakly damped, but
the damping is significantly faster than expected for Landau damping.",1201.0786v1
2012-01-05,Damped bead on a rotating circular hoop - a bifurcation zoo,"The evergreen problem of a bead on a rotating hoop shows a multitude of
bifurcations when the bead moves with friction. This motion is studied for
different values of the damping coefficient and rotational speeds of the hoop.
Phase portraits and trajectories corresponding to all different modes of motion
of the bead are presented. They illustrate the rich dynamics associated with
this simple system. For some range of values of the damping coefficient and
rotational speeds of the hoop, linear stability analysis of the equilibrium
points is inadequate to classify their nature. A technique involving
transformation of coordinates and order of magnitude arguments is presented to
examine such cases. This may provide a general framework to investigate other
complex systems.",1201.1218v1
2012-02-24,Small data global existence for the semilinear wave equation with space-time dependent damping,"In this paper we consider the critical exponent problem for the semilinear
wave equation with space-time dependent damping. When the damping is effective,
it is expected that the critical exponent agrees with that of only space
dependent coefficient case. We shall prove that there exists a unique global
solution for small data if the power of nonlinearity is larger than the
expected exponent. Moreover, we do not assume that the data are compactly
supported. However, it is still open whether there exists a blow-up solution if
the power of nonlinearity is smaller than the expected exponent.",1202.5379v1
2012-03-11,Magnetic damping of a carbon nanotube NEMS resonator,"A suspended, doubly clamped single wall carbon nanotube is characterized at
cryogenic temperatures. We observe specific switching effects in dc-current
spectroscopy of the embedded quantum dot. These have been identified previously
as nano-electromechanical self-excitation of the system, where positive
feedback from single electron tunneling drives mechanical motion. A magnetic
field suppresses this effect, by providing an additional damping mechanism.
This is modeled by eddy current damping, and confirmed by measuring the
resonance quality factor of the rf-driven nano-electromechanical resonator in
an increasing magnetic field.",1203.2319v2
2012-03-21,Approximate rogue wave solutions of the forced and damped Nonlinear Schrödinger equation for water waves,"We consider the effect of the wind and the dissipation on the nonlinear
stages of the modulational instability. By applying a suitable transformation,
we map the forced/damped Nonlinear Schr\""odinger (NLS) equation into the
standard NLS with constant coefficients. The transformation is valid as long as
|{\Gamma}t| \ll 1, with {\Gamma} the growth/damping rate of the waves due to
the wind/dissipation. Approximate rogue wave solutions of the equation are
presented and discussed. The results shed some lights on the effects of wind
and dissipation on the formation of rogue waves.",1203.4735v1
2012-04-02,Random Symmetry Breaking and Freezing in Chaotic Networks,"Parameter space of a driven damped oscillator in a double well potential
presents either a chaotic trajectory with sign oscillating amplitude or a
non-chaotic trajectory with a fixed sign amplitude. A network of such delay
coupled damped oscillators is shown to present chaotic dynamics while the
amplitude sign of each damped oscillator is randomly frozen. This phenomenon of
random broken global symmetry of the network simultaneously with random
freezing of each degree of freedom is accompanied by the existence of
exponentially many randomly frozen chaotic attractors with the ize of the
network. Results are exemplified by a network of modified Duffing oscillators
with infinite ange pseudo-inverse delayed interactions.",1204.0528v1
2012-04-04,Nonlinear Damping in Graphene Resonators,"Based on a continuum mechanical model for single-layer graphene we propose
and analyze a microscopic mechanism for dissipation in nanoelectromechanical
graphene resonators. We find that coupling between flexural modes and in-plane
phonons leads to linear and nonlinear damping of out-of-plane vibrations. By
tuning external parameters such as bias and ac voltages, one can cross over
from a linear to a nonlinear-damping dominated regime. We discuss the behavior
of the effective quality factor in this context.",1204.0911v2
2012-05-22,Heavy quark damping rate in hot viscous QCD plasma,"We derive an expression for the heavy quark damping rate in hot quark gluon
plasma in presence of flow. Here all the bath particles here are out of
equilibrium due to the existence of non-zero velocity gradient. The magnetic
sector shows similar infrared divergences even after hard thermal loop
corrections as one encounters in case of non-viscous plasma. We estimate the
first order correction in ($\eta/s$) for heavy quark damping rate due to the
non-zero viscosity of the QCD plasma.",1205.4895v3
2012-07-24,Quantum capacity of an amplitude-damping channel with memory,"We calculate the quantum capacity of an amplitude-damping channel with time
correlated Markov noise, for two channel uses. Our results show that memory of
the channel increases it's ability to transmit quantum information
significantly. We analyze and compare our findings with earlier numerical
results on amplitude-damping channel with memory. An upper bound on the amount
of quantum information transmitted over the channel in presence of memory, for
an arbitrary number of channel uses is also presented.",1207.5612v3
2012-08-21,Protecting quantum entanglement from amplitude damping,"Quantum entanglement is a critical resource for quantum information and
quantum computation. However, entanglement of a quantum system is subjected to
change due to the interaction with the environment. One typical result of the
interaction is the amplitude damping that usually results in the reduction of
the entanglement. Here we propose a protocol to protect quantum entanglement
from the amplitude damping by applying Hadamard and CNOT gates. As opposed to
some recently studied methods, the scheme presented here does not require weak
measurement in the reversal process, leading to a faster recovery of
entanglement. We propose a possible experimental implementation based on linear
optical system.",1208.4187v2
2012-10-03,Exact solutions for discrete breathers in forced-damped chain,"Exact solutions for symmetric discrete breathers (DBs) are obtained in
forced-damped linear chain with on-site vibro-impact constraints. The damping
is related to inelastic impacts; the forcing may be chosen from broad class of
periodic antisymmetric functions. Global conditions for existence and stability
of the DB are established. Some unusual phenomena, like non-monotonous
dependence of the stability boundary on the forcing amplitude, are revealed
analytically for the full system and illustrated numerically for small periodic
lattices.",1210.1085v1
2012-12-18,Using the mobile phone acceleration sensor in Physics experiments: free and damped harmonic oscillations,"The mobile acceleration sensor has been used to in Physics experiments on
free and damped oscillations. Results for the period, frequency, spring
constant and damping constant match very well to measurements obtained by other
methods. The Accelerometer Monitor application for Android has been used to get
the outputs of the sensor. Perspectives for the Physics laboratory have also
been discussed.",1212.4403v1
2012-12-20,How long-range interactions tune the damping in compact stars,"Long-range interactions lead to non-Fermi liquid effects in dense matter. We
show that, in contrast to other material properties, their effect on the bulk
viscosity of quark matter is significant since they shift its resonant maximum
and can thereby change the viscosity by many orders of magnitude. This is of
importance for the damping of oscillations of compact stars, like in particular
unstable r-modes, and the quest to detect signatures of deconfined matter in
astrophysical observations. We find that, in contrast to neutron stars with
standard damping mechanisms, compact stars that contain ungapped quark matter
are consistent with the observed data on low mass x-ray binaries.",1212.5242v1
2013-02-12,Impact of gluon damping on heavy-quark quenching,"In this conference contribution, we discuss the influence of
gluon-bremsstrahlung damping in hot, absorptive QCD matter on the heavy-quark
radiation spectra. Within our Monte-Carlo implementation for the description of
the heavy-quark in-medium propagation we demonstrate that as a consequence of
gluon damping the quenching of heavy quarks becomes significantly affected at
higher transverse momenta.",1302.2934v1
2013-03-12,On nonlinear Schrodinger type equations with nonlinear damping,"We consider equations of nonlinear Schrodinger type augmented by nonlinear
damping terms. We show that nonlinear damping prevents finite time blow-up in
several situations, which we describe. We also prove that the presence of a
quadratic confinement in all spatial directions drives the solution of our
model to zero for large time. In the case without external potential we prove
that the solution may not go to zero for large time due to (non-trivial)
scattering.",1303.3033v2
2013-06-15,A formula for damping interarea oscillations with generator redispatch,"We derive a new formula for the sensitivity of electromechanical oscillation
damping with respect to generator redispatch. The formula could lead to some
combination of observations, computations and heuristics to more effectively
damp interarea oscillations.",1306.3590v2
2013-07-24,Eigenvalue asymptotics for the damped wave equation on metric graphs,"We consider the linear damped wave equation on finite metric graphs and
analyse its spectral properties with an emphasis on the asymptotic behaviour of
eigenvalues. In the case of equilateral graphs and standard coupling conditions
we show that there is only a finite number of high-frequency abscissas, whose
location is solely determined by the averages of the damping terms on each
edge. We further describe some of the possible behaviour when the edge lengths
are no longer necessarily equal but remain commensurate.",1307.6377v3
2013-08-03,Hadamard well-posedness for a hyperbolic equation of viscoelasticity with supercritical sources and damping,"Presented here is a study of a viscoelastic wave equation with supercritical
source and damping terms. We employ the theory of monotone operators and
nonlinear semigroups, combined with energy methods to establish the existence
of a unique local weak solution. In addition, it is shown that the solution
depends continuously on the initial data and is global provided the damping
dominates the source in an appropriate sense.",1308.0720v2
2013-10-14,Signatures of two-level defects in the temperature-dependent damping of nanomechanical silicon nitride resonators,"The damping rates of high quality factor nanomechanical resonators are well
beyond intrinsic limits. Here, we explore the underlying microscopic loss
mechanisms by investigating the temperature-dependent damping of the
fundamental and third harmonic transverse flexural mode of a doubly clamped
silicon nitride string. It exhibits characteristic maxima reminiscent of
two-level defects typical for amorphous materials. Coupling to those defects
relaxes the momentum selection rules, allowing energy transfer from discrete
long wavelength resonator modes to the high frequency phonon environment.",1310.3671v1
2013-10-25,Quenched decoherence in qubit dynamics due to strong amplitude-damping noise,"We study non-perturbatively the time evolution of a qubit subject to
amplitude-damping noise. We show that at strong coupling the qubit decoherence
can be quenched owing to large environment feedbacks, such that the qubit can
evolve coherently even in the long-time limit. As an application, we show that
for a quantum channel that consists of two independent qubits subject to
uncorrelated local amplitude-damping noises, it can maintain at strong coupling
finite entanglement and better than classical teleportation fidelity at long
times.",1310.6843v2
2013-11-16,Shear viscosity due to the Landau damping from quark-pion interaction,"We have calculated the shear viscosity coefficient $\eta$ of the strongly
interacting matter in the relaxation time approximation, where a quasi particle
description of quarks with its dynamical mass is considered from NJL model. Due
to the thermodynamic scattering of quarks with pseudo scalar type condensate
(i.e. pion), a non zero Landau damping will be acquired by the propagating
quarks. This Landau damping may be obtained from the Landau cut contribution of
the in-medium self-energy of quark-pion loop, which is evaluated in the
framework of real-time thermal field theory.",1311.4070v1
2013-12-19,Cyclotron dynamics of interacting bosons in artificial magnetic fields,"We study theoretically quantum dynamics of interacting bosons in artificial
magnetic fields as engineered in recent ultracold atomic experiments, where
quantum cyclotron orbital motion has been observed. With exact numerical
simulations and perturbative analyses, we find that interactions induce damping
in the cyclotron motion. The damping time is found to be dependent on
interaction and tunneling strengths monotonically, while its dependence on
magnetic flux is non-monotonic. Sufficiently strong interactions would render
bosons dynamically localized inhibiting the cyclotron motion. The damping
predicted by us can be construed as an interaction-induced quantum decoherence
of the cyclotron motion.",1312.5747v2
2014-01-11,Damping in two component Bose gas,"We investigate the Landau and Baliaev damping of the collective modes in a
two-component Bose gas using the mean-field approximation. We show that due to
the two body atom-atom interaction, oscillations of each component is coupled
to the thermal excitations of the other component which gives rise to creation
or destruction of the elementary excitations that can take place in the two
separate components.In addition we find that the damping is also enhanced due
to inter-component coupling.",1401.2537v1
2014-03-24,Existence Results for Some Damped Second-Order Volterra Integro-Differential Equations,"In this paper we make a subtle use of operator theory techniques and the
well-known Schauder fixed-point principle to establish the existence of
pseudo-almost automorphic solutions to some second-order damped
integro-differential equations with pseudo-almost automorphic coefficients. In
order to illustrate our main results, we will study the existence of
pseudo-almost automorphic solutions to a structurally damped plate-like
boundary value problem.",1403.5955v1
2014-04-25,The time singular limit for a fourth-order damped wave equation for MEMS,"We consider a free boundary problem modeling electrostatic
microelectromechanical systems. The model consists of a fourth-order damped
wave equation for the elastic plate displacement which is coupled to an
elliptic equation for the electrostatic potential. We first review some recent
results on existence and non-existence of steady-states as well as on local and
global well-posedness of the dynamical problem, the main focus being on the
possible touchdown behavior of the elastic plate. We then investigate the
behavior of the solutions in the time singular limit when the ratio between
inertial and damping effects tends to zero.",1404.6342v1
2014-05-12,A note on a strongly damped wave equation with fast growing nonlinearities,"A strongly damped wave equation including the displacement depending
nonlinear damping term and nonlinear interaction function is considered. The
main aim of the note is to show that under the standard dissipativity
restrictions on the nonlinearities involved the initial boundary value problem
for the considered equation is globally well-posed in the class of sufficiently
regular solutions and the semigroup generated by the problem possesses a global
attractor in the corresponding phase space. These results are obtained for the
nonlinearities of an arbitrary polynomial growth and without the assumption
that the considered problem has a global Lyapunov function.",1405.2707v1
2014-06-03,Optimal Estimation of a Classical Force with a Damped Oscillator in the non-Markovian Bath,"We solve the optimal quantum limit of probing a classical force exactly by a
damped oscillator initially prepared in the factorized squeezed state. The
memory effects of the thermal bath on the oscillator evolution are
investigated. We show that the optimal force sensitivity obtained by the
quantum estimation theory approaches to zero for the non-Markovian bath,
whereas approaches to a finite non-zero value for the Markovian bath as the
energy of the damped oscillator goes to infinity.",1406.0658v1
2014-08-09,Local existence results for the Westervelt equation with nonlinear damping and Neumann as well as absorbing boundary conditions,"We investigate the Westervelt equation with several versions of nonlinear
damping and lower order damping terms and Neumann as well as absorbing boundary
conditions. We prove local in time existence of weak solutions under the
assumption that the initial and boundary data are sufficiently small.
Additionally, we prove local well-posedness in the case of spatially varying
$L^{\infty}$ coefficients, a model relevant in high intensity focused
ultrasound (HIFU) applications.",1408.2160v1
2014-08-11,Characterization and suppression techniques for degree of radiation damping in inversion recovery measurements,"Radiation damping (RD) has been shown to affect T1 measurement in inversion
recovery experiments. In this work, we demonstrate that the extent of RD
depends upon the T1 of the sample. RD difference spectroscopy (RADDSY) is used
to characterize the severity of RD, while gradient inversion recovery (GIR) is
used for RD suppression in T1 measurements. At 9.4 T, for the radiation damping
characteristic time (Trd) of 50 ms, these investigations show non-negligible RD
effects for T1 values greater than Trd, with severe distortions for T1 longer
than about 150 ms, showing reasonable agreement with the predicted Trd. We also
report a discrepancy between published expressions for the characteristic RD
time.",1408.2457v2
2014-09-28,Spin-electron acoustic waves: The Landau damping and ion contribution in the spectrum,"Separated spin-up and spin-down quantum kinetics is derived for more detailed
research of the spin-electron acoustic waves. Kinetic theory allows to obtain
spectrum of the spin-electron acoustic waves including effects of occupation of
quantum states more accurately than quantum hydrodynamics. We apply quantum
kinetic to calculate the Landau damping of the spin-electron acoustic waves. We
have considered contribution of ions dynamics in the spin-electron acoustic
wave spectrum. We obtain contribution of ions in the Landau damping in
temperature regime of classic ions. Kinetic analysis for ion-acoustic, zero
sound, and Langmuir waves at separated spin-up and spin-down electron dynamics
is presented as well.",1409.7885v1
2014-10-05,Ultimate limit of field confinement by surface plasmon polaritons,"We show that electric field confinement in surface plasmon polaritons
propagating at the metal/dielectric interfaces enhances the loss due to Landau
damping and which effectively limits the degree of confinement itself. We prove
that Landau damping and associated with it surface collision damping follow
directly from Lindhard formula for the dielectric constant of free electron gas
Furthermore, we demonstrate that even if all the conventional loss mechanisms,
caused by phonons, electron-electron, and interface roughness scattering, were
eliminated, the maximum attainable degree of confinement and the loss
accompanying it would not change significantly compared to the best existing
plasmonic materials, such as silver.",1410.1226v1
2014-10-15,Quasiparticle Damping of Surface Waves in Superfluid $^3$He and $^4$He,"Oscillations on free surface of superfluids at the inviscid limit are damped
by quasiparticle scattering. We have studied this effect in both superfluids
$^3$He and $^4$He deep below the respective critical temperatures. Surface
oscillators offer several benefits over immersed mechanical oscillators
traditionally used for similar purposes. Damping is modeled as specular
scattering of ballistic quasiparticles from the moving free surface. The model
is in reasonable agreement with our measurements for superfluid $^4$He but
significant deviation is found for $^3$He.",1410.4071v1
2014-12-22,Long time behavior for a semilinear hyperbolic equation with asymtotically vanishing damping term and convex potential,"We investigate the asymptotic behavior, as t goes to infinity, for a
semilinear hyperbolic equation with asymptotically smal dissipation and convex
potential. We prove that if the damping term behaves like K/t^\alpha for t
large enough, k>0 and 0</alpha<1 then every global solution converges weakly to
an equilibrium point. This result is a positive answer to a question left open
in the paper [A. Cabot and P. Frankel, Asymptotics for some semilinear
hyperbolic equation with non-autonomous damping. J. Differential Equations 252
(2012) 294-322.]",1412.7008v1
2015-03-03,Large Deviations for the Langevin equation with strong damping,"We study large deviations in the Langevin dynamics, with damping of order
$\e^{-1}$ and noise of order $1$, as $\e\downarrow 0$. The damping coefficient
is assumed to be state dependent. We proceed first with a change of time and
then, we use a weak convergence approach to large deviations and their
equivalent formulation in terms of the Laplace principle, to determine the good
action functional.
  Some applications of these results to the exit problem from a domain and to
the wave front propagation for a suitable class of reaction diffusion equations
are considered.",1503.01027v1
2015-03-14,Stabilization of the nonlinear damped wave equation via linear weak observability,"We consider the problem of energy decay rates for nonlinearly damped abstract
infinite dimensional systems. We prove sharp, simple and quasi-optimal energy
decay rates through an indirect method, namely a weak observability estimate
for the corresponding undamped system. One of the main advantage of these
results is that they allow to combine the optimal-weight convexity method of
Alabau-Boussouira and a methodology of Ammari-Tucsnak for weak stabilization by
observability. Our results extend to nonlinearly damped systems, those of
Ammari and Tucsnak. At the end, we give an appendix on the weak stabilization
of linear evolution systems.",1503.04356v1
2015-06-02,"On the the wave equation with hyperbolic dynamical boundary conditions, interior and boundary damping and source","The aim of the paper is to study local Hadamard well-posedness for wave
equation with an hyperbolic dynamical boundary condition, internal and/or
boundary damping and sources for initial data in the natural energy space.
Moreover the regularity of solutions is studied. Finally a dynamical system is
generated when sources are at most linear at infinity, or they are dominated by
the damping terms.",1506.00910v4
2015-06-15,Tautochrone in the damped cycloidal pendulum,"The tautochrone on a cycloid curve is usually considered without drag force.
In this work, we investigate the motion of a damped cycloidal pendulum under
presence of a drag force. Using the Lagrange formulation, and considering
linear dependence with velocity for damping force, we found the dynamics of the
system to remain tautochrone. This dictates the possibility for studying the
tautochrone experimentally, e.g. the cycloidal pendulum in water or oil.",1506.04943v2
2015-07-04,Comments on turbulence theory by Qian and by Edwards and McComb,"We reexamine Liouville equation based turbulence theories proposed by Qian
{[}Phys. Fluids \textbf{26}, 2098 (1983){]} and Edwards and McComb {[}J. Phys.
A: Math. Gen. \textbf{2}, 157 (1969){]}, which are compatible with Kolmogorov
spectrum. These theories obtained identical equation for spectral density
$q(k)$ and different results for damping coefficient. Qian proposed variational
approach and Edwards and McComb proposed maximal entropy principle to obtain
equation for the damping coefficient. We show that assumptions used in these
theories to obtain damping coefficient correspond to unphysical conditions.",1507.01124v1
2015-08-24,Scaling variables and asymptotic profiles for the semilinear damped wave equation with variable coefficients,"We study the asymptotic behavior of solutions for the semilinear damped wave
equation with variable coefficients. We prove that if the damping is effective,
and the nonlinearity and other lower order terms can be regarded as
perturbations, then the solution is approximated by the scaled Gaussian of the
corresponding linear parabolic problem. The proof is based on the scaling
variables and energy estimates.",1508.05778v3
2015-10-01,Impact of surface collisions on enhancement and quenching of the luminescence near the metal nanoparticles,"The fact that surface-induced damping rate of surface plasmon polaritons
(SPPs) in metal nanoparticles increases with the decrease of particle size is
well known. We show that this rate also increases with the degree of the mode
confinement, hence damping of the higher order nonradiative SPP modes in
spherical particles is greatly enhanced relative to damping of the fundamental
(dipole) SPP mode. Since higher order modes are the ones responsible for
quenching of luminescence in the vicinity of metal surfaces, the degree of
quenching increases resulting in a substantial decrease in the amount of
attainable enhancement of the luminescence",1510.00321v1
2015-10-22,On numerical Landau damping for splitting methods applied to the Vlasov-HMF model,"We consider time discretizations of the Vlasov-HMF (Hamiltonian Mean-Field)
equation based on splitting methods between the linear and non-linear parts. We
consider solutions starting in a small Sobolev neighborhood of a spatially
homogeneous state satisfying a linearized stability criterion (Penrose
criterion). We prove that the numerical solutions exhibit a scattering behavior
to a modified state, which implies a nonlinear Landau damping effect with
polynomial rate of damping. Moreover, we prove that the modified state is close
to the continuous one and provide error estimates with respect to the time
stepsize.",1510.06555v1
2015-11-02,Asymptotic decomposition for nonlinear damped Klein-Gordon equations,"In this paper, we proved that if the solution to damped focusing Klein-Gordon
equations is global forward in time, then it will decouple into a finite number
of equilibrium points with different shifts from the origin. The core
ingredient of our proof is the existence of the ""concentration-compact
attractor"" which yields a finite number of profiles. Using damping effect, we
can prove all the profiles are equilibrium points.",1511.00437v3
2015-11-11,Contact Stiffness and Damping of Liquid Films in Dynamic Atomic Force Microscopy,"Small-amplitude dynamic atomic force microscopy (dynamic-AFM) in a simple
nonpolar liquid was studied through molecular dynamics simulations. We find
that within linear dynamics regime, the contact stiffness and damping of the
confined film exhibit the similar solvation force oscillations, and they are
generally out-of-phase. For the solidified film with integer monolayer
thickness, further compression of the film before layering transition leads to
higher stiffness and lower damping. We find that molecular diffusion in the
solidified film was nevertheless enhanced due to the mechanical excitation of
AFM tip.",1511.03580v1
2015-11-13,Nonlinear Radiation Damping of Nuclear Spin Waves and Magnetoelastic Waves in Antiferromagnets,"Parallel pumping of nuclear spin waves in antiferromagnetic CsMnF3 at liquid
helium temperatures and magnetoelastic waves in antiferromagnetic FeBO3 at
liquid nitrogen temperature in a helical resonator was studied. It was found
that the absorbed microwave power is approximately equal to the irradiated
power from the sample and that the main restriction mechanism of absortption in
both cases is defined by the nonlinear radiation damping predicted about two
decades ago. We believe that the nonlinear radiation damping is a common
feature of parallel pumping technique of all normal magnetic excitations and it
can be detected by purposeful experiments.",1511.04396v1
2016-03-01,Damped vacuum states of light,"We consider one-dimensional propagation of quantum light in the presence of a
block of material, with a full account of dispersion and absorption. The
electromagnetic zero-point energy for some frequencies is damped (suppressed)
by the block below the free-space value, while for other frequencies it is
increased. We also calculate the regularized (Casimir) zero-point energy at
each frequency and find that it too is damped below the free-space value (zero)
for some frequencies. The total Casimir energy is positive.",1603.00233v2
2016-04-18,Parameter Estimation of Gaussian-Damped Sinusoids from a Geometric Perspective,"The five parameter gaussian damped sinusoid equation is a reasonable model
for betatron motion with chromatic decoherence of the proton bunch centroid
signal in the ring at the Spallation Neutron Source. A geometric method for
efficiently fitting this equation to the turn by turn signals to extract the
betatron tune and damping constant will be presented. This method separates the
parameters into global and local parameters and allows the use of vector
arithmetic to eliminate the local parameters from the parameter search space.
Furthermore, this method is easily generalized to reduce the parameter search
space for a larger class of problems.",1604.05167v1
2016-04-20,Landau damping in finite regularity for unconfined systems with screened interactions,"We prove Landau damping for the collisionless Vlasov equation with a class of
$L^1$ interaction potentials (including the physical case of screened Coulomb
interactions) on $\mathbb R^3_x \times \mathbb R^3_v$ for localized
disturbances of an infinite, homogeneous background. Unlike the confined case
$\mathbb T^3_x \times \mathbb R_v^3$, results are obtained for initial data in
Sobolev spaces (as well as Gevrey and analytic classes). For spatial
frequencies bounded away from zero, the Landau damping of the density is
similar to the confined case. The finite regularity is possible due to an
additional dispersive mechanism available on $\mathbb R_x^3$ which reduces the
strength of the plasma echo resonance.",1604.05783v1
2016-04-26,Trigonometric Splines for Oscillator Simulation,"We investigate the effects of numerical damping for oscillator simulation
with spline methods. Numerical damping results in an artificial loss of energy
and leads therefore to unreliable results in the simulation of autonomous
systems, as e.g.\ oscillators. We show that the negative effects of numerical
damping can be eliminated by the use of trigonometric splines. This will be in
particular important for spline based adaptive methods.",1604.07607v1
2016-07-13,Optimal decay rate for the wave equation on a square with constant damping on a strip,"We consider the damped wave equation with Dirichlet boundary conditions on
the unit square. We assume the damping to be a characteristic function of a
strip. We prove the exact $t^{-4/3}$-decay rate for the energy of classical
solutions. This answers a question of Anantharaman and L\'eautaud (2014).",1607.03633v2
2016-08-29,"Stochastic 3D Navier-Stokes equations with nonlinear damping: martingale solution, strong solution and small time large deviation principles","In this paper, by using classical Faedo-Galerkin approximation and
compactness method, the existence of martingale solutions for the stochastic 3D
Navier-Stokes equations with nonlinear damping is obtained. The existence and
uniqueness of strong solution are proved for $\beta > 3$ with any $\alpha>0$
and $\alpha \geq \frac12$ as $\beta = 3$. Meanwhile, a small time large
deviation principle for the stochastic 3D Navier-Stokes equation with damping
is proved for $\beta > 3$ with any $\alpha>0$ and $\alpha \geq \frac12$ as
$\beta = 3$.",1608.07996v1
2016-09-05,Estimates of lifespan and blow-up rates for the wave equation with a time-dependent damping and a power-type nonlinearity,"We study blow-up behavior of solutions for the Cauchy problem of the
semilinear wave equation with time-dependent damping. When the damping is
effective, and the nonlinearity is subcritical, we show the blow-up rates and
the sharp lifespan estimates of solutions. Upper estimates are proved by an ODE
argument, and lower estimates are given by a method of scaling variables.",1609.01035v2
2016-09-06,Numerical Convergence Rate for a Diffusive Limit of Hyperbolic Systems: p-System with Damping,"This paper deals with diffusive limit of the p-system with damping and its
approximation by an Asymptotic Preserving (AP) Finite Volume scheme. Provided
the system is endowed with an entropy-entropy flux pair, we give the
convergence rate of classical solutions of the p-system with damping towards
the smooth solutions of the porous media equation using a relative entropy
method. Adopting a semi-discrete scheme, we establish that the convergence rate
is preserved by the approximated solutions. Several numerical experiments
illustrate the relevance of this result.",1609.01436v1
2016-09-20,Global existence and asymptotic behavior of solutions to the Euler equations with time-dependent damping,"We study the isentropic Euler equations with time-dependent damping, given by
$\frac{\mu}{(1+t)^\lambda}\rho u$. Here, $\lambda,\mu$ are two non-negative
constants to describe the decay rate of damping with respect to time. We will
investigate the global existence and asymptotic behavior of small data
solutions to the Euler equations when $0<\lambda<1,0<\mu$ in multi-dimensions
$n\geq 1$. The asymptotic behavior will coincide with the one that obtained by
many authors in the case $\lambda=0$. We will also show that the solution can
only decay polynomially in time while in the three dimensions, the vorticity
will decay exponentially fast.",1609.06286v1
2016-11-08,Emulated Inertia and Damping of Converter-Interfaced Power Source,"Converter-interfaced power sources (CIPSs), like wind turbine and energy
storage, can be switched to the inertia emulation mode when the detected
frequency deviation exceeds a pre-designed threshold, i.e. dead band, to
support the frequency response of a power grid. This letter proposes an
approach to derive the emulated inertia and damping from a CIPS based on the
linearized model of the CIPS and the power grid, where the grid is represented
by an equivalent single machine. The emulated inertia and damping can be
explicitly expressed in time and turn out to be time-dependent.",1611.02698v1
2016-12-09,Ornstein-Uhlenbeck Process with Fluctuating Damping,"This paper studies Langevin equation with random damping due to
multiplicative noise and its solution. Two types of multiplicative noise,
namely the dichotomous noise and fractional Gaussian noise are considered.
Their solutions are obtained explicitly, with the expressions of the mean and
covariance determined explicitly. Properties of the mean and covariance of the
Ornstein-Uhlenbeck process with random damping, in particular the asymptotic
behavior, are studied. The effect of the multiplicative noise on the stability
property of the resulting processes is investigated.",1612.03013v3
2016-12-20,Symmetry group classification and optimal reduction of a class of damped Timoshenko beam system with a nonlinear rotational moment,"We consider a nonlinear Timoshenko system of partial differential equations
(PDEs) with a frictional damping term in rotation angle. The nonlinearity is
due to the arbitrary dependence on the rotation moment. A Lie symmetry group
classification of the arbitrary function of rotation moment is presented. An
optimal system of one-dimensional subalgebras of the nonlinear damped
Timoshenko system is derived for all the non-linear cases. All possible
invariant variables of the optimal systems for the three non-linear cases are
presented. The corresponding reduced systems of ordinary differential equations
(ODEs) are also provided.",1612.06775v1
2017-03-14,Landau damping in the multiscale Vlasov theory,"Vlasov kinetic theory is extended by adopting an extra one particle
distribution function as an additional state variable characterizing the
micro-turbulence internal structure. The extended Vlasov equation keeps the
reversibility, the Hamiltonian structure, and the entropy conservation of the
original Vlasov equation. In the setting of the extended Vlasov theory we then
argue that the Fokker-Planck type damping in the velocity dependence of the
extra distribution function induces the Landau damping. The same type of
extension is made also in the setting of fluid mechanics.",1703.04577v2
2017-03-15,Energy decay and diffusion phenomenon for the asymptotically periodic damped wave equation,"We prove local and global energy decay for the asymptotically periodic damped
wave equation on the Euclidean space. Since the behavior of high frequencies is
already mostly understood, this paper is mainly about the contribution of low
frequencies. We show in particular that the damped wave behaves like a solution
of a heat equation which depends on the H-limit of the metric and the mean
value of the absorption index.",1703.05112v1
2017-04-03,Linear inviscid damping and vorticity depletion for shear flows,"In this paper, we prove the linear damping for the 2-D Euler equations around
a class of shear flows under the assumption that the linearized operator has no
embedding eigenvalues. For the symmetric flows, we obtain the explicit decay
estimates of the velocity, which is the same as one for monotone shear flows.
We confirm a new dynamical phenomena found by Bouchet and Morita: the depletion
of the vorticity at the stationary streamlines, which could be viewed as a new
mechanism leading to the damping for the base flows with stationary
streamlines.",1704.00428v1
2017-04-25,Diffusion phenomena for the wave equation with space-dependent damping term growing at infinity,"In this paper, we study the asymptotic behavior of solutions to the wave
equation with damping depending on the space variable and growing at the
spatial infinity. We prove that the solution is approximated by that of the
corresponding heat equation as time tends to infinity. The proof is based on
semigroup estimates for the corresponding heat equation and weighted energy
estimates for the damped wave equation. To construct a suitable weight function
for the energy estimates, we study a certain elliptic problem.",1704.07650v1
2017-06-05,Mixed finite elements for global tide models with nonlinear damping,"We study mixed finite element methods for the rotating shallow water
equations with linearized momentum terms but nonlinear drag. By means of an
equivalent second-order formulation, we prove long-time stability of the system
without energy accumulation. We also give rates of damping in unforced systems
and various continuous dependence results on initial conditions and forcing
terms. \emph{A priori} error estimates for the momentum and free surface
elevation are given in $L^2$ as well as for the time derivative and divergence
of the momentum. Numerical results confirm the theoretical results regarding
both energy damping and convergence rates.",1706.01352v1
2017-06-13,Uniform energy decay for wave equations with unbounded damping coefficients,"We consider the Cauchy problem for wave equations with unbounded damping
coefficients in the whole space. For a general class of unbounded damping
coefficients, we derive uniform total energy decay estimates together with a
unique existence result of a weak solution. In this case we never impose strong
assumptions such as compactness of the support of the initial data. This means
that we never rely on the finite propagation speed property of the solution,
and we try to deal with an essential unbounded coefficient case.",1706.03942v1
2017-06-15,Fractional Driven Damped Oscillator,"The resonances associated with a fractional damped oscillator which is driven
by an oscillatory external force are studied. It is shown that such resonances
can be manipulated by tuning up either the coefficient of the fractional
damping or the order of the corresponding fractional derivatives.",1706.08596v1
2017-07-11,Stability of partially locked states in the Kuramoto model through Landau damping with Sobolev regularity,"The Kuramoto model is a mean-field model for the synchronisation behaviour of
oscillators, which exhibits Landau damping. In a recent work, the nonlinear
stability of a class of spatially inhomogeneous stationary states was shown
under the assumption of analytic regularity. This paper proves the nonlinear
Landau damping under the assumption of Sobolev regularity. The weaker
regularity required the construction of a different more robust bootstrap
argument, which focuses on the nonlinear Volterra equation of the order
parameter.",1707.03475v2
2017-08-27,Global well-posedness for the semilinear wave equation with time dependent damping in the overdamping case,"We study global existence of solutions to the Cauchy problem for the wave
equation with time-dependent damping and a power nonlinearity in the
overdamping case. We prove the global well-posedness for small data in the
energy space for the whole energy-subcritical case. This result implies that
small data blow-up does not occur in the overdamping case, different from the
other cases, i.e. effective or non-effective damping.",1708.08044v2
2017-09-04,A note on the blowup of scale invariant damping wave equation with sub-Strauss exponent,"We concern the blow up problem to the scale invariant damping wave equations
with sub-Strauss exponent. This problem has been studied by Lai, Takamura and
Wakasa (\cite{Lai17}) and Ikeda and Sobajima \cite{Ikedapre} recently. In
present paper, we extend the blowup exponent from $p_F(n)\leq p<p_S(n+2\mu)$ to
$1<p<p_S(n+\mu)$ without small restriction on $\mu$. Moreover, the upper bound
of lifespan is derived with uniform estimate $T(\varepsilon)\leq
C\varepsilon^{-2p(p-1)/\gamma(p,n+2\mu)}$. This result extends the blowup
result of semilinear wave equation and shows the wave-like behavior of scale
invariant damping wave equation's solution even with large $\mu>1$.",1709.00866v2
2017-09-13,Life-span of blowup solutions to semilinear wave equation with space-dependent critical damping,"This paper is concerned with the blowup phenomena for initial value problem
of semilinear wave equation with critical space-dependent damping term
(DW:$V$). The main result of the present paper is to give a solution of the
problem and to provide a sharp estimate for lifespan for such a solution when
$\frac{N}{N-1}<p\leq p_S(N+V_0)$, where $p_S(N)$ is the Strauss exponent for
(DW:$0$). The main idea of the proof is due to the technique of test functions
for (DW:$0$) originated by Zhou--Han (2014, MR3169791). Moreover, we find a new
threshold value $V_0=\frac{(N-1)^2}{N+1}$ for the coefficient of critical and
singular damping $|x|^{-1}$.",1709.04401v1
2017-09-24,Suppression of Recurrence in the Hermite-Spectral Method for Transport Equations,"We study the unphysical recurrence phenomenon arising in the numerical
simulation of the transport equations using Hermite-spectral method. From a
mathematical point of view, the suppression of this numerical artifact with
filters is theoretically analyzed for two types of transport equations. It is
rigorously proven that all the non-constant modes are damped exponentially by
the filters in both models, and formally shown that the filter does not affect
the damping rate of the electric energy in the linear Landau damping problem.
Numerical tests are performed to show the effect of the filters.",1709.08194v1
2017-11-01,Life-Span of Semilinear Wave Equations with Scale-invariant Damping: Critical Strauss Exponent Case,"The blow up problem of the semilinear scale-invariant damping wave equation
with critical Strauss type exponent is investigated. The life span is shown to
be: $T(\varepsilon)\leq C\exp(\varepsilon^{-2p(p-1)})$ when $p=p_S(n+\mu)$ for
$0<\mu<\frac{n^2+n+2}{n+2}$. This result completes our previous study
\cite{Tu-Lin} on the sub-Strauss type exponent $p<p_S(n+\mu)$. Our novelty is
to construct the suitable test function from the modified Bessel function. This
approach might be also applied to the other type damping wave equations.",1711.00223v1
2017-11-14,Spin-Noise and Damping in Individual Metallic Ferromagnetic Nanoparticles,"We introduce a highly sensitive and relatively simple technique to observe
magnetization motion in single Ni nanoparticles, based on charge sensing by
electron tunneling at millikelvin temperature. Sequential electron tunneling
via the nanoparticle drives nonequilibrium magnetization dynamics, which
induces an effective charge noise that we measure in real time. In the free
spin diffusion regime, where the electrons and magnetization are in detailed
balance, we observe that magnetic damping time exhibits a peak with the
magnetic field, with a record long damping time of $\simeq 10$~ms.",1711.05142v1
2017-12-04,Graviton-mediated dark matter model explanation the DAMPE electron excess and search at $e^+e^-$ colliders,"The very recent result of the DAMPE cosmic ray spectrum of electrons shows a
narrow bump above the background at around 1.4 TeV. We attempt to explain the
DAMPE electron excess in a simplified Kaluza-Klein graviton-mediated dark
matter model, in which the graviton only interacts with leptons and dark
matter. The related phenomenological discussions are given and this simplified
graviton-mediated dark matter model has the potential to be cross-tested in
future lepton collider experiments.",1712.01143v1
2017-12-13,On nonlinear damped wave equations for positive operators. I. Discrete spectrum,"In this paper we study a Cauchy problem for the nonlinear damped wave
equations for a general positive operator with discrete spectrum. We derive the
exponential in time decay of solutions to the linear problem with decay rate
depending on the interplay between the bottom of the operator's spectrum and
the mass term. Consequently, we prove global in time well-posedness results for
semilinear and for more general nonlinear equations with small data. Examples
are given for nonlinear damped wave equations for the harmonic oscillator, for
the twisted Laplacian (Landau Hamiltonian), and for the Laplacians on compact
manifolds.",1712.05009v1
2018-03-14,Damped Newton's Method on Riemannian Manifolds,"A damped Newton's method to find a singularity of a vector field in
Riemannian setting is presented with global convergence study. It is ensured
that the sequence generated by the proposed method reduces to a sequence
generated by the Riemannian version of the classical Newton's method after a
finite number of iterations, consequently its convergence rate is
superlinear/quadratic. Moreover, numerical experiments illustrate that the
damped Newton's method has better performance than Newton's method in number of
iteration and computational time.",1803.05126v2
2018-05-29,Asymptotic profile of solutions for strongly damped Klein-Gordon equations,"We consider the Cauchy problem in the whole space for strongly damped
Klein-Gordon equations. We derive asymptotic profles of solutions with weighted
initial data by a simple method introduced by R. Ikehata. The obtained results
show that the wave effect will be weak because of the mass term, especially in
the low dimensional case (n = 1,2) as compared with the strongly damped wave
equations without mass term (m = 0), so the most interesting topic in this
paper is the n = 1,2 cases.",1805.11975v1
2018-06-08,"Brownian motion of magnetic domain walls and skyrmions, and their diffusion constants","Extended numerical simulations enable to ascertain the diffusive behavior at
finite temperatures of chiral walls and skyrmions in ultra-thin model Co layers
exhibiting symmetric - Heisenberg - as well as antisymmetric -
Dzyaloshinskii-Moriya - exchange interactions. The Brownian motion of walls and
skyrmions is shown to obey markedly different diffusion laws as a function of
the damping parameter. Topology related skyrmion diffusion suppression with
vanishing damping parameter, albeit already documented, is shown to be
restricted to ultra-small skyrmion sizes or, equivalently, to ultra-low damping
coefficients, possibly hampering observation.",1806.03172v1
2018-06-18,Damped second order flow applied to image denoising,"In this paper, we introduce a new image denoising model: the damped flow
(DF), which is a second order nonlinear evolution equation associated with a
class of energy functionals of image. The existence, uniqueness and
regularization property of DF are proven. For the numerical implementation,
based on the St\""{o}rmer-Verlet method, a discrete damped flow, SV-DDF, is
developed. The convergence of SV-DDF is studied as well. Several numerical
experiments, as well as a comparison with other methods, are provided to
demonstrate the feasibility and effectiveness of the SV-DDF.",1806.06732v2
2018-07-10,Cyclotron Damping along an Uniform Magnetic Field,"We prove cyclotron damping for the collisionless Vlasov-Maxwell equations on
$\mathbb{T}_{x}^{3}\times\mathbb{R}_{v}^{3}$ under the assumptions that the
electric induction is zero and $(\mathcal{\mathbf{PSC}})$ holds. It is a
crucial step to solve the stability problem of the Vlasov-Maxwell equations.
Our proof is based on a new dynamical system of the plasma particles,
originating from Faraday Law of Electromagnetic induction and Lenz's Law. On
the basis of it, we use the improved Newton iteration scheme to show the
damping mechanism.",1807.05254v3
2018-07-17,On the blow-up for critical semilinear wave equations with damping in the scattering case,"We consider the Cauchy problem for semilinear wave equations with variable
coefficients and time-dependent scattering damping in $\mathbf{R}^n$, where
$n\geq 2$. It is expected that the critical exponent will be Strauss' number
$p_0(n)$, which is also the one for semilinear wave equations without damping
terms. Lai and Takamura (2018) have obtained the blow-up part, together with
the upper bound of lifespan, in the sub-critical case $p<p_0(n)$. In this
paper, we extend their results to the critical case $p=p_0(n)$. The proof is
based on Wakasa and Yordanov (2018), which concerns the blow-up and upper bound
of lifespan for critical semilinear wave equations with variable coefficients.",1807.06164v1
2018-08-22,Radiation Damping of a Yang-Mills Particle Revisited,"The problem of a color-charged point particle interacting with a four
dimensional Yang-Mills gauge theory is revisited. The radiation damping is
obtained inspired in the Dirac's computation. The difficulties in the
non-abelian case were solved by using an ansatz for the Li\'enard-Wiechert
potentials, already used in the literature for finding solutions to the
Yang-Mills equations. Three non-trivial examples of radiation damping for the
non-abelian particle are discussed in detail.",1808.07533v2
2018-08-28,Enhancement of zonal flow damping due to resonant magnetic perturbations in the background of an equilibrium $E \times B$ sheared flow,"Using a parametric interaction formalism, we show that the equilibrium
sheared rotation can enhance the zonal flow damping effect found in Ref. [M.
Leconte and P.H. Diamond, \emph{Phys. Plasmas} 19, 055903 (2012)]. This
additional damping contribution is proportional to $(L_s/L_V)^2 \times \delta
B_r^2 / B^2$, where $L_s/L_V$ is the ratio of magnetic shear length to the
scale-length of equilibrium $E \times B$ flow shear, and $\delta B_r / B$ is
the amplitude of the external magnetic perturbation normalized to the
background magnetic field.",1808.09110v1
2018-08-30,Optimal indirect stability of a weakly damped elastic abstract system of second order equations coupled by velocities,"In this paper, by means of the Riesz basis approach, we study the stability
of a weakly damped system of two second order evolution equations coupled
through the velocities. If the fractional order damping becomes viscous and the
waves propagate with equal speeds, we prove exponential stability of the system
and, otherwise, we establish an optimal polynomial decay rate. Finally, we
provide some illustrative examples.",1808.10256v1
2018-09-10,Linear inviscid damping for the $β$-plane equation,"In this paper, we study the linear inviscid damping for the linearized
$\beta$-plane equation around shear flows. We develop a new method to give the
explicit decay rate of the velocity for a class of monotone shear flows. This
method is based on the space-time estimate and the vector field method in sprit
of the wave equation. For general shear flows including the Sinus flow, we also
prove the linear damping by establishing the limiting absorption principle,
which is based on the compactness method introduced by Wei-Zhang-Zhao in
\cite{WZZ2}. The main difficulty is that the Rayleigh-Kuo equation has more
singular points due to the Coriolis effects so that the compactness argument
becomes more involved and delicate.",1809.03065v1
2018-10-14,Critical exponent for nonlinear damped wave equations with non-negative potential in 3D,"We are studying possible interaction of damping coefficients in the
subprincipal part of the linear 3D wave equation and their impact on the
critical exponent of the corresponding nonlinear Cauchy problem with small
initial data. The main new phenomena is that certain relation between these
coefficients may cause very strong jump of the critical Strauss exponent in 3D
to the critical 5D Strauss exponent for the wave equation without damping
coefficients.",1810.05956v1
2018-10-23,Perfect absorption of water waves by linear or nonlinear critical coupling,"We report on experiments of perfect absorption for surface gravity waves
impinging a wall structured by a subwavelength resonator. By tuning the
geometry of the resonator, a balance is achieved between the radiation damping
and the intrinsic viscous damping, resulting in perfect absorption by critical
coupling. Besides, it is shown that the resistance of the resonator, hence the
intrinsic damping, can be controlled by the wave amplitude, which provides a
way for perfect absorption tuned by nonlinear mechanisms. The perfect absorber
that we propose, without moving parts or added material, is simple, robust and
it presents a deeply subwavelength ratio wavelength/size $\simeq 18$.",1810.09884v1
2018-12-16,Damping of sound waves by bulk viscosity in reacting gases,"The very long standing problem of sound waves propagation in fluids is
reexamined. In particular, from the analysis of the wave damping in reacting
gases following the work of Einsten \citep{Ein}, it is found that the damping
due to the chemical reactions occurs nonetheless the second (bulk) viscosity
introduced by Landau \& Lifshitz \citep{LL86} is zero. The simple but important
case of a recombining Hydrogen plasma is examined.",1812.06478v1
2019-02-27,Forward Discretely Self-Similar Solutions of the MHD Equations and the Viscoelastic Navier-Stokes Equations with Damping,"In this paper, we prove the existence of forward discretely self-similar
solutions to the MHD equations and the viscoelastic Navier-Stokes equations
with damping with large weak $L^3$ initial data. The same proving techniques
are also applied to construct self-similar solutions to the MHD equations and
the viscoelastic Navier-Stokes equations with damping with large weak $L^3$
initial data. This approach is based on [Z. Bradshaw and T.-P. Tsai, Ann. Henri
Poincar'{e}, vol. 18, no. 3, 1095-1119, 2017].",1902.10771v3
2019-03-11,The effect of magnetic twist on resonant absorption of slow sausage waves in magnetic flux tubes,"Observations show that twisted magnetic flux tubes are present throughout the
sun's atmosphere. The main aim of this work is to obtain the damping rate of
sausage modes in the presence of magnetic twist. Using the connection formulae
obtained by Sakurai et al. (1991), we investigate resonant absorption of the
sausage modes in the slow continuum under photosphere conditions. We derive the
dispersion relation and solve it numerically and consequently obtain the
frequencies and damping rates of the slow surface sausage modes. We conclude
that the magnetic twist can result in strong damping in comparison with the
untwisted case.",1903.04171v1
2019-03-14,Endpoint Strichartz estimate for the damped wave equation and its application,"Recently, the Strichartz estimates for the damped wave equation was obtained
by the first author except for the wave endpoint case. In the present paper, we
give the Strichartz estimate in the wave endpoint case. We slightly modify the
argument of Keel--Tao. Moreover, we apply the endpoint Strichartz estimate to
the unconditional uniqueness for the energy critical nonlinear damped wave
equation. This problem seems not to be solvable as the perturbation of the wave
equation.",1903.05891v2
2019-04-02,Linear inviscid damping in Gevrey spaces,"We prove linear inviscid damping near a general class of monotone shear flows
in a finite channel, in Gevrey spaces. It is an essential step towards proving
nonlinear inviscid damping for general shear flows that are not close to the
Couette flow, which is a major open problem in 2d Euler equations.",1904.01188v2
2019-04-16,Damping modes of harmonic oscillator in open quantum systems,"Through a set of generators that preserves the hermiticity and trace of
density matrices, we analyze the damping of harmonic oscillator in open quantum
systems into four modes, distinguished by their specific effects on the
covariance matrix of position and momentum of the oscillator. The damping modes
could either cause exponential decay to the initial covariance matrix or shift
its components. They have to act together properly in actual dynamics to ensure
that the generalized uncertainty relation is satisfied. We use a few quantum
master equations to illustrate the results.",1904.07452v2
2019-05-20,Stabilization of two strongly coupled hyperbolic equations in exterior domains,"In this paper we study the behavior of the total energy and the $L^2$-norm of
solutions of two coupled hyperbolic equations by velocities in exterior
domains. Only one of the two equations is directly damped by a localized
damping term. We show that, when the damping set contains the coupling one and
the coupling term is effective at infinity and on captive region, then the
total energy decays uniformly and the $L^2$-norm of smooth solutions is
bounded. In the case of two Klein-Gordon equations with equal speeds we deduce
an exponential decay of the energy.",1905.08370v1
2019-06-02,Mixed control of vibrational systems,"We consider new performance measures for vibrational systems based on the
$H_2$ norm of linear time invariant systems. New measures will be used as an
optimization criterion for the optimal damping of vibrational systems. We
consider both theoretical and concrete cases in order to show how new measures
stack up against the standard measures. The quality and advantages of new
measures as well as the behaviour of optimal damping positions and
corresponding damping viscosities are illustrated in numerical experiments.",1906.00503v1
2019-06-27,Comments on the linear modified Poisson-Boltzmann equation in electrolyte solution theory,"Three analytic results are proposed for a linear form of the modified
Poisson-Boltzmann equation in the theory of bulk electrolytes. Comparison is
also made with the mean spherical approximation results. The linear theories
predict a transition of the mean electrostatic potential from a
Debye-H\""{u}ckel type damped exponential to a damped oscillatory behaviour as
the electrolyte concentration increases beyond a critical value. The screening
length decreases with increasing concentration when the mean electrostatic
potential is damped oscillatory. A comparison is made with one set of recent
experimental screening results for aqueous NaCl electrolytes.",1906.11584v1
2019-09-19,Growth rate and gain of stimulated Brillouin scattering considering nonlinear Landau damping due to particle trapping,"Growth rate and gain of SBS considering the reduced Landau damping due to
particle trapping has been proposed to predict the growth and average level of
SBS reflectivity. Due to particle trapping, the reduced Landau damping has been
taken used of to calculate the gain of SBS, which will make the simulation data
of SBS average reflectivity be consistent to the Tang model better. This work
will solve the pending questions in laser-plasma interaction and have wide
applications in parametric instabilities.",1909.11606v1
2019-11-26,Pullback Attractors for a Critical Degenerate Wave Equation with Time-dependent Damping,"The aim of this paper is to analyze the long-time dynamical behavior of the
solution for a degenerate wave equation with time-dependent damping term
$\partial_{tt}u + \beta(t)\partial_tu = \mathcal{L}u(x,t) + f(u)$ on a bounded
domain $\Omega\subset\mathbb{R}^N$ with Dirichlet boundary conditions. Under
some restrictions on $\beta(t)$ and critical growth restrictions on the
nonlinear term $f$, we will prove the local and global well-posedness of the
solution and derive the existence of a pullback attractor for the process
associated with the degenerate damped hyperbolic problem.",1911.11432v1
2019-12-18,Blow-up criteria for linearly damped nonlinear Schrödinger equations,"We consider the Cauchy problem for linearly damped nonlinear Schr\""odinger
equations
  \[ i\partial_t u + \Delta u + i a u= \pm |u|^\alpha u, \quad (t,x) \in
[0,\infty) \times \mathbb{R}^N, \] where $a>0$ and $\alpha>0$. We prove the
global existence and scattering for a sufficiently large damping parameter in
the energy-critical case. We also prove the existence of finite time blow-up
$H^1$ solutions to the focusing problem in the mass-critical and
mass-supercritical cases.",1912.08752v2
2020-01-17,Bounding the Classical Capacity of Multilevel Damping Quantum Channels,"A recent method to certify the classical capacity of quantum communication
channels is applied for general damping channels in finite dimension. The
method compares the mutual information obtained by coding on the computational
and a Fourier basis, which can be obtained by just two local measurement
settings and classical optimization. The results for large representative
classes of different damping structures are presented.",2001.06486v2
2020-01-27,Robustness of polynomial stability of damped wave equations,"In this paper we present new results on the preservation of polynomial
stability of damped wave equations under addition of perturbing terms. We in
particular introduce sufficient conditions for the stability of perturbed
two-dimensional wave equations on rectangular domains, a one-dimensional weakly
damped Webster's equation, and a wave equation with an acoustic boundary
condition. In the case of Webster's equation, we use our results to compute
explicit numerical bounds that guarantee the polynomial stability of the
perturbed equation.",2001.10033v3
2020-02-09,Fujita modified exponent for scale invariant damped semilinear wave equations,"The aim of this paper is to prove a blow up result of the solution for a
semilinear scale invariant damped wave equation under a suitable decay
condition on radial initial data. The admissible range for the power of the
nonlinear term depends both on the damping coefficient and on the pointwise
decay order of the initial data. In addition we give an upper bound estimate
for the lifespan of the solution, in terms of the power of the nonlinearity,
size and growth of initial data.",2002.03418v2
2020-02-16,Blow up results for semi-linear structural damped wave model with nonlinear memory,"This article is to study the nonexistence of global solutions to semi-linear
structurally damped wave equation with nonlinear memory in $\R^n$ for any space
dimensions $n\ge 1$ and for the initial arbitrarily small data being subject to
the positivity assumption. We intend to apply the method of a modified test
function to establish blow-up results and to overcome some difficulties as well
caused by the well-known fractional Laplacian $(-\Delta)^{\sigma/2}$ in
structural damping terms.",2002.06582v1
2020-03-04,Existence and uniqueness of solutions to the damped Navier-Stokes equations with Navier boundary conditions for three dimensional incompressible fluid,"In this article, we study the solutions of the damped Navier--Stokes equation
with Navier boundary condition in a bounded domain $\Omega$ in $\mathbb{R}^3$
with smooth boundary. The existence of the solutions is global with the damped
term $\vartheta |u|^{\beta-1}u, \vartheta >0.$ The regularity and uniqueness of
solutions with Navier boundary condition is also studied. This extends the
existing results in literature.",2003.01903v1
2020-04-22,Logarithmic stabilization of an acoustic system with a damping term of Brinkman type,"We study the problem of stabilization for the acoustic system with a
spatially distributed damping. Without imposing any hypotheses on the
structural properties of the damping term, we identify logarithmic decay of
solutions with growing time. Logarithmic decay rate is shown by using a
frequency domain method and combines a contradiction argument with the
multiplier technique and a new Carleman estimate to carry out a special
analysis for the resolvent.",2004.10669v1
2020-05-24,A transmission problem for the Timoshenko system with one local Kelvin-Voigt damping and non-smooth coefficient at the interface,"In this paper, we study the indirect stability of Timoshenko system with
local or global Kelvin-Voigt damping, under fully Dirichlet or mixed boundary
conditions. Unlike the results of H. L. Zhao, K. S. Liu, and C. G. Zhang and of
X. Tian and Q. Zhang, in this paper, we consider the Timoshenko system with
only one locally or globally distributed Kelvin-Voigt damping. Indeed, we prove
that the energy of the system decays polynomially and that the obtained decay
rate is in some sense optimal. The method is based on the frequency domain
approach combining with multiplier method.",2005.12756v1
2020-06-09,Lifespan of solutions to a damped fourth-order wave equation with logarithmic nonlinearity,"This paper is devoted to the lifespan of solutions to a damped fourth-order
wave equation with logarithmic nonlinearity $$u_{tt}+\Delta^2u-\Delta
u-\omega\Delta u_t+\alpha(t)u_t=|u|^{p-2}u\ln|u|.$$ Finite time blow-up
criteria for solutions at both lower and high initial energy levels are
established, and an upper bound for the blow-up time is given for each case.
Moreover, by constructing a new auxiliary functional and making full use of the
strong damping term, a lower bound for the blow-up time is also derived.",2006.05006v1
2020-07-05,Oscillation of damped second order quasilinear wave equations with mixed arguments,"Following the previous work [1], we investigate the impact of damping on the
oscillation of smooth solutions to some kind of quasilinear wave equations with
Robin and Dirichlet boundary condition. By using generalized Riccati
transformation and technical inequality method, we give some sufficient
conditions to guarantee the oscillation of all smooth solutions. From the
results, we conclude that positive damping can ``hold back"" oscillation. At
last, some examples are presented to confirm our main results.",2007.02284v1
2020-07-08,A competition on blow-up for semilinear wave equations with scale-invariant damping and nonlinear memory term,"In this paper, we investigate blow-up of solutions to semilinear wave
equations with scale-invariant damping and nonlinear memory term in
$\mathbb{R}^n$, which can be represented by the Riemann-Liouville fractional
integral of order $1-\gamma$ with $\gamma\in(0,1)$. Our main interest is to
study mixed influence from damping term and the memory kernel on blow-up
conditions for the power of nonlinearity, by using test function method or
generalized Kato's type lemma. We find a new competition, particularly for the
small value of $\gamma$, on the blow-up range between the effective case and
the non-effective case.",2007.03954v2
2020-08-02,Quantum capacity analysis of multi-level amplitude damping channels,"The set of Multi-level Amplitude Damping (MAD) quantum channels is introduced
as a generalization of the standard qubit Amplitude Damping Channel to quantum
systems of finite dimension $d$. In the special case of $d=3$, by exploiting
degradability, data-processing inequalities, and channel isomorphism, we
compute the associated quantum and private classical capacities for a rather
wide class of maps, extending the set of solvable models known so far. We
proceed then to the evaluation of the entanglement assisted, quantum and
classical, capacities.",2008.00477v3
2020-08-11,An inverse spectral problem for a damped wave operator,"This paper proposes a new and efficient numerical algorithm for recovering
the damping coefficient from the spectrum of a damped wave operator, which is a
classical Borg-Levinson inverse spectral problem. The algorithm is based on
inverting a sequence of trace formulas, which are deduced by a recursive
formula, bridging geometrical and spectrum information explicitly in terms of
Fredholm integral equations. Numerical examples are presented to illustrate the
efficiency of the proposed algorithm.",2008.04523v1
2020-08-17,Asymptotic profiles and singular limits for the viscoelastic damped wave equation with memory of type I,"In this paper, we are interested in the Cauchy problem for the viscoelastic
damped wave equation with memory of type I. By applying WKB analysis and
Fourier analysis, we explain the memory's influence on dissipative structures
and asymptotic profiles of solutions to the model with weighted $L^1$ initial
data. Furthermore, concerning standard energy and the solution itself, we
establish singular limit relations between the Moore-Gibson-Thompson equation
with memory and the viscoelastic damped wave equation with memory.",2008.07151v1
2020-08-18,A class of Finite difference Methods for solving inhomogeneous damped wave equations,"In this paper, a class of finite difference numerical techniques is presented
to solve the second-order linear inhomogeneous damped wave equation. The
consistency, stability, and convergences of these numerical schemes are
discussed. The results obtained are compared to the exact solution, ordinary
explicit, implicit finite difference methods, and the fourth-order compact
method (FOCM). The general idea of these methods is developed by using the
C0-semigroups operator theory. We also showed that the stability region for the
explicit finite difference scheme depends on the damping coefficient.",2008.08043v2
2020-09-10,Blow-up results for semilinear damped wave equations in Einstein-de Sitter spacetime,"We prove by using an iteration argument some blow-up results for a semilinear
damped wave equation in generalized Einstein-de Sitter spacetime with a
time-dependent coefficient for the damping term and power nonlinearity. Then,
we conjecture an expression for the critical exponent due to the main blow-up
results, which is consistent with many special cases of the considered model
and provides a natural generalization of Strauss exponent. In the critical
case, we consider a non-autonomous and parameter-dependent Cauchy problem for a
linear ODE of second-order, whose explicit solutions are determined by means of
special functions' theory.",2009.05372v1
2020-09-11,Asymptotic profiles for a wave equation with parameter dependent logarithmic damping,"We study a nonlocal wave equation with logarithmic damping which is rather
weak in the low frequency zone as compared with frequently studied strong
damping case. We consider the Cauchy problem for this model in the whole space
and we study the asymptotic profile and optimal estimates of the solutions and
the total energy as time goes to infinity in L^{2}-sense. In that case some
results on hypergeometric functions are useful.",2009.06395v1
2020-09-17,Sensitivity of steady states in a degenerately-damped stochastic Lorenz system,"We study stability of solutions for a randomly driven and degenerately damped
version of the Lorenz '63 model. Specifically, we prove that when damping is
absent in one of the temperature components, the system possesses a unique
invariant probability measure if and only if noise acts on the convection
variable. On the other hand, if there is a positive growth term on the vertical
temperature profile, we prove that there is no normalizable invariant state.
Our approach relies on the derivation and analysis of non-trivial Lyapunov
functions which ensure positive recurrence or null-recurrence/transience of the
dynamics.",2009.08429v1
2021-01-23,Oscillation time and damping coefficients in a nonlinear pendulum,"We establish a relationship between the normalized damping coefficients and
the time that takes a nonlinear pendulum to complete one oscillation starting
from an initial position with vanishing velocity. We establish some conditions
on the nonlinear restitution force so that this oscillation time does not
depend monotonically on the viscosity damping coefficient.",2101.09400v2
2021-02-20,Lifespan estimates for semilinear wave equations with space dependent damping and potential,"In this work, we investigate the influence of general damping and potential
terms on the blow-up and lifespan estimates for energy solutions to power-type
semilinear wave equations. The space-dependent damping and potential functions
are assumed to be critical or short range, spherically symmetric perturbation.
The blow up results and the upper bound of lifespan estimates are obtained by
the so-called test function method. The key ingredient is to construct special
positive solutions to the linear dual problem with the desired asymptotic
behavior, which is reduced, in turn, to constructing solutions to certain
elliptic ""eigenvalue"" problems.",2102.10257v1
2021-02-24,Attractors for locally damped Bresse systems and a unique continuation property,"This paper is devoted to Bresse systems, a robust model for circular beams,
given by a set of three coupled wave equations. The main objective is to
establish the existence of global attractors for dynamics of semilinear
problems with localized damping. In order to deal with localized damping a
unique continuation property (UCP) is needed. Therefore we also provide a
suitable UCP for Bresse systems. Our strategy is to set the problem in a
Riemannian geometry framework and see the system as a single equation with
different Riemann metrics. Then we perform Carleman-type estimates to get our
result.",2102.12025v1
2021-03-09,Global weak solution of 3D-NSE with exponential damping,"In this paper we prove the global existence of incompressible Navier-Stokes
equations with damping $\alpha (e^{\beta |u|^2}-1)u$, where we use Friedrich
method and some new tools. The delicate problem in the construction of a global
solution, is the passage to the limit in exponential nonlinear term. To solve
this problem, we use a polynomial approximation of the damping part and a new
type of interpolation between $L^\infty(\mathbb{R}^+,L^2(\mathbb{R}^3))$ and
the space of functions $f$ such that $(e^{\beta|f|^2}-1)|f|^2\in
L^1(\mathbb{R}^3)$. Fourier analysis and standard techniques are used.",2103.05388v1
2021-05-03,Enhanced and unenhanced dampings of Kolmogorov flow,"In the present study, Kolmogorov flow represents the stationary sinusoidal
solution $(\sin y,0)$ to a two-dimensional spatially periodic Navier-Stokes
system, driven by an external force. This system admits the additional
non-stationary solution $(\sin y,0)+e^{-\nu t} (\sin y,0)$, which tends
exponentially to the Kolmogorov flow at the minimum decay rate determined by
the viscosity $\nu$. Enhanced damping or enhanced dissipation of the problem is
obtained by presenting higher decay rate for the difference between a solution
and the non-stationary basic solution. Moreover, for the understanding of the
metastability problem in an explicit manner, a variety of exact solutions are
presented to show enhanced and unenhanced dampings.",2105.00730v2
2021-05-06,On Linear Damping Around Inhomogeneous Stationary States of the Vlasov-HMF Model,"We study the dynamics of perturbations around an inhomogeneous stationary
state of the Vlasov-HMF (Hamiltonian Mean-Field) model, satisfying a linearized
stability criterion (Penrose criterion). We consider solutions of the
linearized equation around the steady state, and prove the algebraic decay in
time of the Fourier modes of their density. We prove moreover that these
solutions exhibit a scattering behavior to a modified state, implying a linear
Landau damping effect with an algebraic rate of damping.",2105.02484v1
2021-05-31,Blowup of Solutions to a Damped Euler Equation with Homogeneous Three-Point Boundary Condition,"It has been established that solutions to the inviscid Proudman-Johnson
equation subject to a homogeneous three-point boundary condition can develop
singularities in finite time. In this paper, we consider the possibility of
singularity formation in solutions of the generalized, inviscid
Proudman-Johnson equation with damping subject to the same homogeneous
three-point boundary condition. In particular, we derive conditions the initial
data must satisfy in order for solutions to blowup in finite time with either
bounded or unbounded smooth damping term.",2106.00068v1
2021-06-16,Sharp upper and lower bounds of the attractor dimension for 3D damped Euler-Bardina equations,"The dependence of the fractal dimension of global attractors for the damped
3D Euler--Bardina equations on the regularization parameter $\alpha>0$ and
Ekman damping coefficient $\gamma>0$ is studied. We present explicit upper
bounds for this dimension for the case of the whole space, periodic boundary
conditions, and the case of bounded domain with Dirichlet boundary conditions.
The sharpness of these estimates when $\alpha\to0$ and $\gamma\to0$ (which
corresponds in the limit to the classical Euler equations) is demonstrated on
the 3D Kolmogorov flows on a torus.",2106.09077v1
2021-06-23,Damping of the Franz-Keldysh oscillations in the presence of disorder,"Franz-Keldysh oscillations of the optical absorption in the presence of
short-range disorder are studied theoretically. The magnitude of the effect
depends on the relation between the mean-free path in a zero field and the
distance between the turning points in electric field. Damping of the
Franz-Keldysh oscillations by the disorder develops at high absorption
frequency. Effect of damping is amplified by the fact that, that electron and
hole are most sensitive to the disorder near the turning points. This is
because, near the turning points, velocities of electron and hole turn to zero.",2106.12691v1
2021-06-25,Perturbed primal-dual dynamics with damping and time scaling coefficients for affine constrained convex optimization problems,"In Hilbert space, we propose a family of primal-dual dynamical system for
affine constrained convex optimization problem. Several damping coefficients,
time scaling coefficients, and perturbation terms are thus considered. By
constructing the energy functions, we investigate the convergence rates with
different choices of the damping coefficients and time scaling coefficients.
Our results extend the inertial dynamical approaches for unconstrained convex
optimization problems to affine constrained convex optimization problems.",2106.13702v1
2021-07-01,Event-triggering mechanism to damp the linear wave equation,"This paper aims at proposing a sufficient matrix inequality condition to
carry out the global exponential stability of the wave equation under an
event-triggering mechanism that updates a damping source term. The damping is
distributed in the whole space but sampled in time. The wellposedness of the
closed-loop event-triggered control system is shown. Furthermore, the avoidance
of Zeno behavior is ensured provided that the initial data are more regular.
The interest of the results is drawn through some numerical simulations.",2107.00292v1
2022-01-28,Quantum metrology with a non-linear kicked Mach-Zehnder interferometer,"We study the sensitivity of a Mach-Zehnder interferometer that contains in
addition to the phase shifter a non-linear element. By including both elements
in a cavity or a loop that the light transverses many times, a non-linear
kicked version of the interferometer arises. We study its sensitivity as
function of the phase shift, the kicking strength, the maximally reached
average number of photons, and damping due to photon loss for an initial
coherent state. We find that for vanishing damping Heisenberg-limited scaling
of the sensitivity arises if squeezing dominates the total photon number. For
small to moderate damping rates the non-linear kicks can considerably increase
the sensitivity as measured by the quantum Fisher information per unit time.",2201.12255v1
2022-02-27,The time asymptotic expansion for the compressible Euler equations with time-dependent damping,"In this paper, we study the compressible Euler equations with time-dependent
damping $-\frac{1}{(1+t)^{\lambda}}\rho u$. We propose a time asymptotic
expansion around the self-similar solution of the generalized porous media
equation (GPME) and rigorously justify this expansion as $\lambda \in
(\frac17,1)$. In other word, instead of the self-similar solution of GPME, the
expansion is the best asymptotic profile of the solution to the compressible
Euler equations with time-dependent damping.",2202.13385v1
2022-03-12,Stability for nonlinear wave motions damped by time-dependent frictions,"We are concerned with the dynamical behavior of solutions to semilinear wave
systems with time-varying damping and nonconvex force potential. Our result
shows that the dynamical behavior of solution is asymptotically stable without
any bifurcation and chaos. And it is a sharp condition on the damping
coefficient for the solution to converge to some equilibrium. To illustrate our
theoretical results, we provide some numerical simulations for dissipative
sine-Gordon equation and dissipative Klein-Gordon equation.",2203.06312v1
2022-03-30,A Toy Model for Damped Water Waves,"We consider a toy model for a damped water waves system in a domain $\Omega_t
\subset \mathbb{T} \times \mathbb{R}$. The toy model is based on the
paradifferential water waves equation derived in the work of
Alazard-Burq-Zuily. The form of damping we utilize we utilize is a modified
sponge layer proposed for the three-dimensional water waves system by Clamond,
et. al. We show that, in the case of small Cauchy data, solutions to the toy
model exhibit a quadratic lifespan. This is done via proving energy estimates
with the energy being constructed from appropriately chosen vector fields.",2203.16645v1
2022-05-10,Global attractor for the weakly damped forced Kawahara equation on the torus,"We study the long time behaviour of solutions for the weakly damped forced
Kawahara equation on the torus. More precisely, we prove the existence of a
global attractor in $L^2$, to which as time passes all solutions draw closer.
In fact, we show that the global attractor turns out to lie in a smoother space
$H^2$ and be bounded therein. Further, we give an upper bound of the size of
the attractor in $H^2$ that depends only on the damping parameter and the norm
of the forcing term.",2205.04642v1
2022-06-07,"Decay property of solutions to the wave equation with space-dependent damping, absorbing nonlinearity, and polynomially decaying data","We study the large time behavior of solutions to the semilinear wave equation
with space-dependent damping and absorbing nonlinearity in the whole space or
exterior domains. Our result shows how the amplitude of the damping
coefficient, the power of the nonlinearity, and the decay rate of the initial
data at the spatial infinity determine the decay rates of the energy and the
$L^2$-norm of the solution. In Appendix, we also give a survey of basic results
on the local and global existence of solutions and the properties of weight
functions used in the energy method.",2206.03218v2
2022-10-24,The time asymptotic expansion for the compressible Euler equations with damping,"In 1992, Hsiao and Liu \cite{Hsiao-Liu-1} firstly showed that the solution to
the compressible Euler equations with damping time-asymptotically converges to
the diffusion wave $(\bar v, \bar u)$ of the porous media equation. In
\cite{Geng-Huang-Jin-Wu}, we proposed a time-asymptotic expansion around the
diffusion wave $(\bar v, \bar u)$, which is a better asymptotic profile than
$(\bar v, \bar u)$. In this paper, we rigorously justify the time-asymptotic
expansion by the approximate Green function method and the energy estimates.
Moreover, the large time behavior of the solution to compressible Euler
equations with damping is accurately characterized by the time asymptotic
expansion.",2210.13157v1
2022-12-18,Exponential decay of solutions of damped wave equations in one dimensional space in the $L^p$ framework for various boundary conditions,"We establish the decay of the solutions of the damped wave equations in one
dimensional space for the Dirichlet, Neumann, and dynamic boundary conditions
where the damping coefficient is a function of space and time. The analysis is
based on the study of the corresponding hyperbolic systems associated with the
Riemann invariants. The key ingredient in the study of these systems is the use
of the internal dissipation energy to estimate the difference of solutions with
their mean values in an average sense.",2212.09164v1
2023-02-09,A remark on the logarithmic decay of the damped wave and Schrödinger equations on a compact Riemannian manifold,"In this paper we consider a compact Riemannian manifold (M, g) of class C 1
$\cap$ W 2,$\infty$ and the damped wave or Schr\""odinger equations on M , under
the action of a damping function a = a(x). We establish the following fact: if
the measure of the set {x $\in$ M ; a(x) = 0} is strictly positive, then the
decay in time of the associated energy is at least logarithmic.",2302.04498v1
2023-03-02,Using vibrating wire in non-linear regime as a thermometer in superfluid $^3$He-B,"Vibrating wires are common temperature probes in $^3$He experiments. By
measuring mechanical resonance of a wire driven by AC current in magnetic field
one can directly obtain temperature-dependent viscous damping. This is easy to
do in a linear regime where wire velocity is small enough and damping force is
proportional to velocity. At lowest temperatures in superfluid $^3$He-B a
strong non-linear damping appears and linear regime shrinks to a very small
velocity range. Expanding measurements to the non-linear area can significantly
improve sensitivity. In this note I describe some technical details useful for
analyzing such temperature measurements.",2303.01189v1
2023-04-06,A turbulent study for a damped Navier-Stokes equation: turbulence and problems,"In this article we consider a damped version of the incompressible
Navier-Stokes equations in the whole three-dimensional space with a
divergence-free and time-independent external force. Within the framework of a
well-prepared force and with a particular choice of the damping parameter, when
the Grashof numbers are large enough, we are able to prove some estimates from
below and from above between the fluid characteristic velocity and the energy
dissipation rate according to the Kolmogorov dissipation law. Precisely, our
main contribution concerns the estimate from below which is not often studied
in the existing literature. Moreover, we address some remarks which open the
door to a deep discussion on the validity of this theory of turbulence.",2304.03134v1
2023-05-03,Lyapunov functions for linear damped wave equations in one-dimensional space with dynamic boundary conditions,"We establish the exponential decay of the solutions of the damped wave
equations in one-dimensional space where the damping coefficient is a
nowhere-vanishing function of space. The considered PDE is associated with
several dynamic boundary conditions, also referred to as Wentzell/Ventzel
boundary conditions in the literature. The analysis is based on the
determination of appropriate Lyapunov functions and some further analysis. This
result is associated with a regulation problem inspired by a real experiment
with a proportional-integral control. Some numerical simulations and additional
results on closed wave equations are also provided.",2305.01969v2
2023-05-13,Global existence for a 3D Tropical Climate Model with damping and small initial data in $\dot H^{1/2}(\mathbb{R}^3)$,"We consider a 3D Tropical Climate Model with damping terms in the equation of
the barotropic mode $u$ and in the equation of the first baroclinic mode $v$ of
the velocity. The equation for the temperature $\theta$ is free from dampings.
We prove global existence in time for this system assuming the initial data
$(u_0, v_0,\theta_0)$ small, in terms of the homogeneous space $\dot
H^{1/2}(\mathbb{R}^3)$.",2305.07964v1
2023-06-21,The effect of singularities and damping on the spectra of photonic crystals,"Understanding the dispersive properties of photonic crystals is a fundamental
and well-studied problem. However, the introduction of singular permittivities
and damping complicates the otherwise straightforward theory. In this paper, we
study photonic crystals with a Drude-Lorentz model for the permittivity,
motivated by halide perovskites. We demonstrate how the introduction of
singularities and damping affects the spectral band structure and show how to
interpret the notion of a ""band gap"" in this setting. We present explicit
solutions for a one-dimensional model and show how integral operators can be
used to handle multi-dimensional systems.",2306.12254v1
2023-07-12,Asymptotic behavior of solutions to the Cauchy problem for 1-D p-system with space dependent damping,"We consider the Cauchy problem for one-dimensional p-system with damping of
space-dependent coefficient. This system models the compressible flow through
porous media in the Lagrangean coordinate. Our concern is an asymptotic
behavior of solutions, which is expected to be the diffusion wave based on the
Darcy law. To show this expectation, the problem is reformulated to the Cauchy
problem for the second order quasilinear hyperbolic equation with space
dependent damping, which is analyzed by the energy method.",2307.05865v1
2023-07-12,Parabolic-elliptic Keller-Segel's system,"We study on the whole space R d the compressible Euler system with damping
coupled to the Poisson equation when the damping coefficient tends towards
infinity. We first prove a result of global existence for the Euler-Poisson
system in the case where the damping is large enough, then, in a second step,
we rigorously justify the passage to the limit to the parabolic-elliptic
Keller-Segel after performing a diffusive rescaling, and get an explicit
convergence rate. The overall study is carried out in 'critical' Besov spaces,
in the spirit of the recent survey [16] by R. Danchin devoted to partially
dissipative systems.",2307.05981v1
2023-07-25,Asymptotic behavior and life-span estimates for the damped inhomogeneous nonlinear Schrödinger equation,"We are interested in the behavior of solutions to the damped inhomogeneous
nonlinear Schr\""odinger equation $ i\partial_tu+\Delta
u+\mu|x|^{-b}|u|^{\alpha}u+iau=0$, $\mu \in\mathbb{C} $, $b>0$, $a \in
\mathbb{C}$ such that $\Re \textit{e}(a) \geq 0$, $\alpha>0$. We establish
lower and upper bound estimates of the life-span. In particular for $a\geq 0$,
we obtain explicit values $a_*,\; a^*$ such that if $a<a_*$ then blow up
occurs, while for $a>a^*,$ global existence holds. Also, we prove scattering
results with precise decay rates for large damping. Some of the results are new
even for $b=0.$",2307.13495v1
2023-07-26,On nonlinear Landau damping and Gevrey regularity,"In this article we study the problem of nonlinear Landau damping for the
Vlasov-Poisson equations on the torus. As our main result we show that for
perturbations initially of size $\epsilon>0$ and time intervals
$(0,\epsilon^{-N})$ one obtains nonlinear stability in regularity classes
larger than Gevrey $3$, uniformly in $\epsilon$. As a complementary result we
construct families of Sobolev regular initial data which exhibit nonlinear
Landau damping. Our proof is based on the methods of Grenier, Nguyen and
Rodnianski.",2307.14271v1
2023-08-18,Damping for fractional wave equations and applications to water waves,"Motivated by numerically modeling surface waves for inviscid Euler equations,
we analyze linear models for damped water waves and establish decay properties
for the energy for sufficiently regular initial configurations. Our findings
give the explicit decay rates for the energy, but do not address
reflection/transmission of waves at the interface of the damping. Still for a
subset of the models considered, this represents the first result proving the
decay of the energy of the surface wave models.",2308.09288v1
2023-08-30,Optimal decay for one-dimensional damped wave equations with potentials via a variant of Nash inequality,"The optimality of decay properties of the one-dimensional damped wave
equations with potentials belonging to a certain class is discussed. The
typical ingredient is a variant of Nash inequality which involves an invariant
measure for the corresponding Schr\""odinger semigroup. This enables us to find
a sharp decay estimate from above. Moreover, the use of a test function method
with the Nash-type inequality provides the decay estimate from below. The
diffusion phenomena for the damped wave equations with potentials are also
considered.",2308.15680v1
2023-09-15,Explicit solutions and linear inviscid damping in the Euler-Boussinesq equation near a stratified Couette flow in the periodic strip,"This short note provides explicit solutions to the linearized Boussinesq
equations around the stably stratified Couette flow posed on
$\mathbb{T}\times\mathbb{R}$. We consider the long-time behavior of such
solutions and prove inviscid damping of the perturbed density and velocity
field for any positive Richardson number, with optimal rates. The explicit
solution is obtained through the limiting absorption principle whereas the
inviscid damping is proved using oscillatory integral methods.",2309.08419v2
2023-09-21,Beyond Qubits : An Extensive Noise Analysis for Qutrit Quantum Teleportation,"The four quantum noises Bit Flip, Phase Flip, Depolarization, and Amplitude
Damping as well as any potential combinations of them are examined in this
papers investigation of quantum teleportation using qutrit states. Among the
above mentioned noises, we observed phase flip has highest fidelity. Compared
to uncorrelated Amplitude Damping, we find that correlated Amplitude Damping
performs two times better. Finally, we agreed that, for better fidelity, it is
preferable to provide the same noise in channel state if noise is unavoidable.",2309.12163v1
2023-12-22,Soliton resolution for the energy critical damped wave equations in the radial case,"We consider energy-critical damped wave equation \begin{equation*}
\partial_{tt}u-\Delta u+\alpha \partial_t u=\left|u\right|^{\frac{4}{D-2}}u
\end{equation*} with radial initial data in dimensions $D\geq 4$. The equation
has a nontrivial radial stationary solution $W$, called the ground state, which
is unique up to sign and scale. We prove that any bounded energy norm solution
behaves asymptotically as a superposition of the modulated ground states and a
radiation term. In the global case, particularly, the solution converges to a
pure multi-bubble due to the damping effect.",2401.04115v2
2024-02-18,Sharp lifespan estimate for the compressible Euler system with critical time-dependent damping in $\R^2$,"This paper concerns the long time existence to the smooth solutions of the
compressible Euler system with critical time dependent damping in $\R^2$. We
establish the sharp lifespan estimate from below, with respect to the small
parameter of the initial perturbation. For this end, the vector fields
$\widehat{Z}$ (defined below) are used instead of the usual one $Z$, to get
better decay for the linear error terms. This idea may also apply to the long
time behavior study of nonlinear wave equations with time-dependent damping.",2402.11516v1
2024-02-28,Linear inviscid damping in the presence of an embedding eigenvalue,"In this paper, we investigate the long-time dynamics of the linearized 2-D
Euler equations around a hyperbolic tangent flow $(\tanh y,0)$. A key
difference compared to previous results is that the linearized operator has an
embedding eigenvalue, which has a significant impact on the dynamics of the
linearized system. For the first mode, the dynamics consists of there parts:
non-decay part related to the eigenspace associated with the embedding
eigenvalue, slow decay part due to the resolvent singularity, and fast decay
part related to the inviscid damping. For higher modes, the dynamics is similar
to the inviscid damping phenomena in the case without embedding eigenvalues.",2402.18229v1
2024-03-19,Improved decay results for micropolar flows with nonlinear damping,"We examine the long-time behavior of solutions (and their derivatives) to the
micropolar equations with nonlinear velocity damping. Additionally, we get a
speed-up gain of $ t^{1/2} $ for the angular velocity, consistent with
established findings for classic micropolar flows lacking nonlinear damping.
Consequently, we also obtain a sharper result regarding the asymptotic
stability of the micro-rotational velocity $\ww(\cdot,t)$. Related results of
independent interest are also included.",2403.12885v1
2024-03-26,On a class of nonautonomous quasilinear systems with general time-gradually-degenerate damping,"In this paper, we study two systems with a time-variable coefficient and
general time-gradually-degenerate damping. More explicitly, we construct the
Riemann solutions to the time-variable coefficient Zeldovich approximation and
time-variable coefficient pressureless gas systems both with general
time-gradually-degenerate damping. Applying the method of similar variables and
nonlinear viscosity, we obtain classical Riemann solutions and delta shock wave
solutions.",2403.17732v1
1994-05-02,Damped Lyman Alpha Systems vs. Cold + Hot Dark Matter,"Although the Cold + Hot Dark Matter (CHDM) cosmology provides perhaps the
best fit of any model to all the available data at the current epoch, CHDM
produces structure at relatively low redshifts and thus could be ruled out if
there were evidence for formation of massive objects at high redshifts. Damped
Ly$\alpha$ systems are abundant in quasar absorption spectra and thus provide
possibly the most significant evidence for early structure formation, and thus
perhaps the most stringent constraint on CHDM. Using the numbers of halos in
N-body simulations to normalize Press-Schechter estimates of the number
densities of protogalaxies as a function of redshift, we find that CHDM with
$\Omega_c/\Omega_\nu/\Omega_b = 0.6/0.3/0.1$ is compatible with the damped
Ly$\alpha$ data at $\le 2.5$, but that it is probably incompatible with the
limited $z>3$ damped Ly$\alpha$ data. The situation is uncertain because there
is very little data for $z>3$, and also it is unclear whether all damped
Ly$\alpha$ systems are associated with collapsed protogalaxies. The predictions
of CHDM are quite sensitive to the hot (neutrino) fraction, and we find that
$\Omega_c/\Omega_\nu/\Omega_b = 0.675/0.25/0.075$ is compatible even with the
$z>3$ data. This corresponds to lowering the neutrino mass from 6.8 to 5.7 eV,
for $H_0=50\kmsMpc$. In CHDM, the higher redshift damped Ly$\alpha$ systems are
predicted to have lower masses, which can be checked by measuring the velocity
widths of the associated metal line systems.",9405003v1
1995-03-24,High Redshift Lyman Limit and Damped Lyman-Alpha Absorbers,"We have obtained high signal:to:noise optical spectroscopy at 5\AA\
resolution of 27 quasars from the APM z$>$4 quasar survey. The spectra have
been analyzed to create new samples of high redshift Lyman-limit and damped
Lyman-$\alpha$ absorbers. These data have been combined with published data
sets in a study of the redshift evolution and the column density distribution
function for absorbers with $\log$N(HI)$\ge17.5$, over the redshift range 0.01
$<$ z $<$ 5. The main results are: \begin{itemize} \item Lyman limit systems:
The data are well fit by a power law $N(z) = N_0(1 + z)^{\gamma}$ for the
number density per unit redshift. For the first time intrinsic evolution is
detected in the product of the absorption cross-section and comoving spatial
number density for an $\Omega = 1$ Universe. We find $\gamma = 1.55$ ($\gamma =
0.5$ for no evolution) and $N_0 = 0.27$ with $>$99.7\% confidence limits for
$\gamma$ of 0.82 \& 2.37. \item Damped \lya systems: The APM QSOs provide a
substantial increase in the redshift path available for damped surveys for
$z>3$. Eleven candidate and three confirmed damped Ly$\alpha$ absorption
systems, have been identified in the APM QSO spectra covering the redshift
range $2.8\le z \le 4.4$ (11 with $z>3.5$). Combining the APM survey confirmed
and candidate damped \lya absorbers with previous surveys, we find evidence for
a turnover at z$\sim$3 or a flattening at z$\sim$2 in the cosmological mass
density of neutral gas, $\Omega_g$. \end{itemize} The Lyman limit survey
results are published in Storrie-Lombardi, et~al., 1994, ApJ, 427, L13. Here we
describe the results for the DLA population of absorbers.",9503089v1
1997-05-15,Cosmological Constraints from High-Redshift Damped Lyman-Alpha Systems,"Any viable cosmological model must produce enough structure at early epochs
to explain the amount of gas associated with high-redshift damped Ly$\alpha$
systems. We study the evolution of damped Ly$\alpha$ systems at redshifts $z\ge
2$ in cold dark matter (CDM) and cold+hot dark matter (CDM+HDM) models using
both N-body and hydrodynamic simulations. Our approach incorporates the effects
of gas dynamics, and we find that all earlier estimates which assumed that all
the baryons in dark matter halos would contribute to damped Ly$\alpha$
absorption have overestimated the column density distribution $f(N)$ and the
fraction of neutral dense gas $\Omega_g$ in damped Ly$\alpha$ systems. The
differences are driven by ionization of hydrogen in the outskirts of galactic
halos and by gaseous dissipation near the halo centers, and they tend to
exacerbate the problem of late galaxy formation in CDM+HDM models. We only
include systems up to the highest observed column density $N\sim 10^{21.8}$
cm$^{-2}$ in the estimation of $\Omega_g$ for a fair comparison with data. If
the observed $f(N)$ and $\Omega_g$ inferred from a small number of confirmed
and candidate absorbers are robust, the amount of gas in damped Ly$\alpha$
systems at high redshifts in the $\Omega_\nu=0.2$ CDM+HDM model falls well
below the observations.",9705113v1
2001-01-03,Galactic Chemical Abundances at z>3 I: First Results from the Echellette Spectrograph and Imager,"We present the first results from an ongoing survey to discover and measure
the metallicity of z>3 damped Lya systems with the Echellette Spectrograph and
Imager (ESI) on the Keck II telescope. Our motivation arises from a recent
study on the damped Lya systems suggesting only mild evolution in the cosmic
metallicity from z~2 to 4. The Echellette Spectrograph and Imager, which
provides two complementary spectroscopic modes, is the ideal instrument for a
z>3 damped Lya survey. We describe our observing strategy and report on the
discovery and analysis of 5 new z>3 damped Lya systems acquired in a single
night of observing. These observations further support the principal
conclusions of the previous study: (1) the cosmic metallicity in neutral gas
inferred from the damped Lya systems does not evolve significantly from z~2 to
4; (2) the unweighted metallicity exhibits a statistically significant decrease
with increasing redshift; and (3) not a single damped Lya system has a
metallicity below [Fe/H]=-3. We discuss the implications of these results and
comment on recent theoretical studies which attempt to explain the
observations.",0101029v1
2002-01-17,Self-shielding Effects on the Column Density Distribution of Damped Lyman Alpha Systems,"We calculate the column density distribution of damped Lyman alpha systems,
modeled as spherical isothermal gaseous halos ionized by the external cosmic
background. The effects of self-shielding introduce a hump in this
distribution, at a column density N_{HI} \sim 1.6x10^{17} X^{-1} cm^{-2}, where
X is the neutral fraction at the radius where self-shielding starts being
important. The most recent compilation of the column density distribution by
Storrie-Lombardi & Wolfe shows marginal evidence for the detection of this
feature due to self-shielding, suggesting a value X \sim 10^{-3}. Assuming a
photoionization rate \Gamma \sim 10^{-12} s^{-1} from the external ionizing
background, the radius where self-shielding occurs is inferred to be about
3.8kpc. If damped Lyman alpha systems consist of a clumpy medium, this should
be interpreted as the typical size of the gas clumps in the region where they
become self-shielding. Clumps of this size with typical column densities N_H
\sim 3x10^{20} cm^{-2} would be in hydrostatic equilibrium at the
characteristic photoionization temperature \sim 10^4 K if they do not contain
dark matter. Since this size is similar to the overall radius of damped \lya
systems in Cold Dark Matter models, where all halos are assumed to contain
similar gas clouds producing damped absorbers, this suggests that the gas in
damped absorbers is in fact not highly clumped.",0201275v2
2002-04-30,Two-phase equilibrium and molecular hydrogen formation in damped Lyman-alpha systems,"Molecular hydrogen is quite underabundant in damped Lyman-alpha systems at
high redshift, when compared to the interstellar medium near the Sun. This has
been interpreted as implying that the gas in damped Lyman-alpha systems is
warm. like the nearby neutral intercloud medium, rather than cool, as in the
clouds which give rise to most H I absorption in the Milky Way. Other lines of
evidence suggest that the gas in damped Lyman-alpha systems -- in whole or part
-- is actually cool; spectroscopy of neutral and ionized carbon, discussed
here, shows that the damped Lyman-alpha systems observed at lower redshift z
$<$ 2.3 are largely cool, while those seen at z $>$ 2.8 are warm (though not
devoid of H2). To interpret the observations of carbon and hydrogen we
constructed detailed numerical models of H2 formation under the conditions of
two-phase thermal equilibrium, like those which account for conditions near the
Sun, but with varying metallicity, dust-gas ratio, $etc$. We find that the low
metallicity of damped Lyman-alpha systems is enough to suppress H2 formation by
many orders of magnitude even in cool diffuse clouds, as long as the ambient
optical/uv radiation field is not too small. For very low metallicity and under
the most diffuse conditions, H2 formation will be dominated by slow gas-phase
processes not involving grains, and a minimum molecular fraction in the range
$10^{-8}-10^{-7}$ is expected.",0204515v1
2003-05-12,Ordinary and Viscosity-Damped MHD Turbulence,"We compare the properties of ordinary strong magnetohydrodynamic (MHD)
turbulence in a strongly magnetized medium with the recently discovered
viscosity-damped regime. We focus on energy spectra, anisotropy, and
intermittency. Our most surprising conclusion is that in ordinary strong MHD
turbulence the velocity and magnetic fields show different high-order structure
function scalings. Moreover this scaling depends on whether the intermittency
is viewed in a global or local system of reference. This reconciles seemingly
contradictory earlier results. On the other hand, the intermittency scaling for
viscosity-damped turbulence is very different, and difficult to understand in
terms of the usual phenomenological models for intermittency in turbulence. Our
remaining results are in reasonable agreement with expectations. First, we find
that our high resolution simulations for ordinary MHD turbulence show that the
energy spectra are {\it compatible} with a Kolmogorov spectrum, while
viscosity-damped turbulence shows a shallow $k^{-1}$ spectrum for the magnetic
fluctuations. Second, a new numerical technique confirms that ordinary MHD
turbulence exhibits Goldreich-Sridhar type anisotropy, while viscosity-damped
MHD turbulence shows extremely anisotropic eddy structures. Finally, we show
that many properties of incompressible turbulence for both the ordinary and
viscosity-damped regimes carry over to the case of compressible turbulence.",0305212v2
2003-09-17,Observational Tests of Damping by Resonant Absorption in Coronal Loop Oscillations,"One of the proposed damping mechanisms of coronal (transverse) loop
oscillations in the kink-mode is resonant absorption as a result of the Alfven
speed variation at the outer boundary of coronal loops. Analytical expressions
for the period and damping time exist for loop models with thin non-uniform
boundaries. Here we measure the thickness of the non-uniform layer in
oscillating loops for 11 events, by forward-fitting of the cross-sectional
density profile and line-of-sight integration to the cross-sectional fluxes
observed with TRACE 171 A. This way we model the internal and external electron
density of the coronal plasma in oscillating loops. This allows us to test the
theoretically predicted damping rates for thin boundaries as function of the
density ratio. We find that the density ratio predicted by the damping time is
higher than the density ratio estimated from the background fluxes. The lower
densities modeled from the background fluxes are likely to be a consequence of
the neglected hotter plasma that is not detected with the TRACE 171 A filter.
Taking these correction into account, resonant absorption predicts damping
times of kink-mode oscillations that are commensurable with the observed ones
and provides a new diagnostic of the density contrast of oscillating loops.",0309470v1
2005-03-01,Metal Abundances in a Damped Lyman-alpha System Along Two Lines of Sight at z=0.93,"We study metal abundances in the z=0.9313 damped Lya system observed in the
two lines-of-sight, A and B, toward the gravitationally-lensed double QSO
HE0512-3329. Spatially resolved STIS spectra constrain the neutral-gas column
density to be LogN(HI)=20.5 in both Aand B. UVES spectra (spectral resolution
FWHM=9.8 km/s) show, in contrast, significant line-of-sight differences in the
column densities of MnII and FeII; these are not due to observational
systematics. We find that [Mn/H]=-1.44 and [Fe/H]=-1.52 in damped Lya system A,
while [Mn/H]=-0.98 and [Fe/H]>-1.32, and possibly as high as [Fe/H] approx. -1
in damped Lya system B. A careful assessment of possible systematic errors
leads us to conclude that these transverse differences are significant at a 5
sigma level or greater. Although nucleosynthesis effects may also be at play,
we favor differential dust-depletion as the main mechanism producing the
observed abundance gradient. The transverse separation is 5 kpc at the redshift
of the absorber, which is also likely to be the lensing galaxy. The derived
abundances therefore probe two opposite sides of a single galaxy hosting both
damped Lya systems. This is the first time firm abundance constraints have been
obtained for a single damped system probed by two lines-of-sight. The
significance of this finding for the cosmic evolution of metals is discussed.",0503026v1
2000-08-26,Adsorbate aggregation and relaxation of low-frequency vibrations,"We present a study of resonant vibrational coupling between adsorbates and an
elastic substrate at low macroscopic coverages. In the first part of the paper
we consider the situation when adsorbates form aggregates with high local
coverage. Based upon our previously published theory, we derive formulas
describing the damping rate of adsorbate vibrations for two cases of such
aggregation: (i) adsorbates attached to step edges and (ii) adsorbates forming
two-dimensional islands. We have shown that damping is governed by local
coverage. Particularly, for a wide range of resonant frequencies, the damping
rate of adsorbates forming well separated islands is described by the damping
rate formula for a periodic overlayer with the coverage equal to the local
coverage in the island. The second part of the paper is devoted to facilitating
the evaluation of damping rates for a disordered overlayer. The formula
describing the damping rate involves the parameter $\beta$ which is related to
the local density of phonon states at the substrate surface and does not allow
a closed-form representation. For substrates of isotropic and cubic symmetries,
we have developed a good analytical approximation to this parameter. For a vast
majority of cubic substrates the difference between the analytical
approximation and numerical calculation does not exceed 4%.",0008389v1
2004-10-26,Mean-field treatment of the damping of the oscillations of a 1D Bose gas in an optical lattice,"We present a theoretical treatment of the surprisingly large damping observed
recently in one-dimensional Bose-Einstein atomic condensates in optical
lattices. We show that time-dependent Hartree-Fock-Bogoliubov (HFB)
calculations can describe qualitatively the main features of the damping
observed over a range of lattice depths. We also derive a formula of the
fluctuation-dissipation type for the damping, based on a picture in which the
coherent motion of the condensate atoms is disrupted as they try to flow
through the random local potential created by the irregular motion of
noncondensate atoms. We expect this irregular motion to result from the
well-known dynamical instability exhibited by the mean-field theory for these
systems. When parameters for the characteristic strength and correlation times
of the fluctuations, obtained from the HFB calculations, are substituted in the
damping formula, we find very good agreement with the experimentally-observed
damping, as long as the lattice is shallow enough for the fraction of atoms in
the Mott insulator phase to be negligible. We also include, for completeness,
the results of other calculations based on the Gutzwiller ansatz, which appear
to work better for the deeper lattices.",0410677v4
1998-10-16,Fermion Damping in a Fermion-Scalar Plasma,"In this article we study the dynamics of fermions in a fermion-scalar plasma.
We begin by obtaining the effective in-medium Dirac equation in real time which
is fully renormalized and causal and leads to the initial value problem. For a
heavy scalar we find the novel result that the decay of the scalar into fermion
pairs in the medium leads to damping of the fermionic excitations and their
in-medium propagation as quasiparticles. That is, the fermions acquire a width
due to the decay of the heavier scalar in the medium. We find the damping rate
to lowest order in the Yukawa coupling for arbitrary values of scalar and
fermion masses, temperature and fermion momentum. An all-order expression for
the damping rate in terms of the exact quasiparticle wave functions is
established. A kinetic Boltzmann approach to the relaxation of the fermionic
distribution function confirms the damping of fermionic excitations as a
consequence of the induced decay of heavy scalars in the medium. A
linearization of the Boltzmann equation near equilibrium clearly displays the
relationship between the damping rate of fermionic mean fields and the fermion
interaction rate to lowest order in the Yukawa coupling directly in real time.",9810393v2
2006-01-06,Wave energy localization by self-focusing in large molecular structures: a damped stochastic discrete nonlinear Schroedinger equation model,"Wave self-focusing in molecular systems subject to thermal effects, such as
thin molecular films and long biomolecules, can be modeled by stochastic
versions of the Discrete Self-Trapping equation of Eilbeck, Lomdahl and Scott,
and this can be approximated by continuum limits in the form of stochastic
nonlinear Schroedinger equations.
  Previous studies directed at the SNLS approximations have indicated that the
self-focusing of wave energy to highly localized states can be inhibited by
phase noise (modeling thermal effects) and can be restored by phase damping
(modeling heat radiation).
  We show that the continuum limit is probably ill-posed in the presence of
spatially uncorrelated noise, at least with little or no damping, so that
discrete models need to be addressed directly. Also, as has been noted by other
authors, omission of damping produces highly unphysical results.
  Numerical results are presented for the first time for the discrete models
including the highly nonlinear damping term, and new numerical methods are
introduced for this purpose. Previous conjectures are in general confirmed, and
the damping is shown to strongly stabilize the highly localized states of the
discrete models. It appears that the previously noted inhibition of nonlinear
wave phenomena by noise is an artifact of modeling that includes the effects of
heat, but not of heat loss.",0601017v1
2007-11-15,Effect of the steady flow on spatial damping of small-amplitude prominence oscillations,"Aims. Taking account of steady flow in solar prominences, we study its
effects on spatial damping of small-amplitude non-adiabatic magnetoacoustic
waves in a homogeneous, isothermal, and unbounded prominence plasma. Methods.
We model the typical feature of observed damped oscillatory motion in
prominences, removing the adiabaticity assumption through thermal conduction,
radiation and heating. Invoking steady flow in MHD equations, we linearise them
under small-amplitude approximation and obtain a new general dispersion
relation for linear non-adiabatic magnetoacoustic waves in prominences Results.
The presence of steady flow breaks the symmetry of forward and backward
propagating MHD wave modes in prominences. The steady flow has dramatic
influence on the propagation and damping of magnetoacoustic and thermal waves.
Depending upon the direction and strength of flow the magnetoacoustic and
thermal modes can show both the features of wave amplification and damping. At
the wave period of 5 min where the photospheric power is maximum, the slow mode
shows wave amplification. However, in the absence of steady flow the slow mode
wave shows damping. Conclusions. For the wave period between 5 min and 15 min,
the amplification length for slow mode, in the case of prominence regime 1.1,
varies between 3.4*10^11 m to 2*10^12 m. Dramatic influence of steady flow on
small-amplitude prominence oscillations is likely to play an important role in
both wave detection and prominence seismology.",0711.2353v1
2008-02-07,Cascade and Damping of Alfvén-Cyclotron Fluctuations: Application to Solar Wind Turbulence Spectrum,"With the diffusion approximation, we study the cascade and damping of
Alfv\'{e}n-cyclotron fluctuations in solar plasmas numerically. Motivated by
wave-wave couplings and nonlinear effects, we test several forms of the
diffusion tensor. For a general locally anisotropic and inhomogeneous diffusion
tensor in the wave vector space, the turbulence spectrum in the inertial range
can be fitted with power-laws with the power-law index varying with the wave
propagation direction. For several locally isotropic but inhomogeneous
diffusion coefficients, the steady-state turbulence spectra are nearly
isotropic in the absence of damping and can be fitted by a single power-law
function. However, the energy flux is strongly polarized due to the
inhomogeneity that leads to an anisotropic cascade. Including the anisotropic
thermal damping, the turbulence spectrum cuts off at the wave numbers, where
the damping rates become comparable to the cascade rates. The combined
anisotropic effects of cascade and damping make this cutoff wave number
dependent on the wave propagation direction, and the propagation direction
integrated turbulence spectrum resembles a broken power-law, which cuts off at
the maximum of the cutoff wave numbers or the $^4$He cyclotron frequency.
Taking into account the Doppler effects, the model can naturally reproduce the
broken power-law wave spectra observed in the solar wind and predicts that a
higher break frequency is aways accompanied with a greater spectral index
change that may be caused by the increase of the Alfv\'{e}n Mach number, the
reciprocal of the plasma beta, and/or the angle between the solar wind velocity
and the mean magnetic field. These predictions can be tested by future
observations.",0802.0910v1
2011-04-13,Evolution of inclined planets in three-dimensional radiative discs,"While planets in the solar system only have a low inclination with respect to
the ecliptic there is mounting evidence that in extrasolar systems the
inclination can be very high, at least for close-in planets. One process to
alter the inclination of a planet is through planet-disc interactions. Recent
simulations considering radiative transport have shown that the evolution of
migration and eccentricity can strongly depend on the thermodynamic state of
the disc. We extend previous studies to investigate the planet-disc
interactions of fixed and moving planets on inclined and eccentric orbits. We
also analyse the effect of the disc's thermodynamic properties on the orbital
evolution of embedded planets in detail. The protoplanetary disc is modelled as
a viscous gas where the internally produced dissipation is transported by
radiation. For locally isothermal discs, we confirm previous results and find
inclination damping and inward migration for planetary cores. For low
inclinations i < 2 H/r, the damping is exponential, while di/dt is proportional
to i^-2 for larger i. For radiative discs, the planetary migration is very
limited, as long as their inclination exceeds a certain threshold. If the
inclination is damped below this threshold, planetary cores with a mass up to
approximately 33 Earth masses start to migrate outwards, while larger cores
migrate inwards right from the start. The inclination is damped for all
analysed planet masses. In a viscous disc an initial inclination of embedded
planets will be damped for all planet masses. This damping occurs on timescales
that are shorter than the migration time. If the inclination lies beneath a
certain threshold, the outward migration in radiative discs is not handicapped.
Outward migration is strongest for circular and non-inclined orbits.",1104.2408v1
2011-07-12,Mode conversion of radiatively damped magnetogravity waves in the solar chromosphere,"Modelling of adiabatic gravity wave propagation in the solar atmosphere
showed that mode conversion to field guided acoustic waves or Alfv\'en waves
was possible in the presence of highly inclined magnetic fields. This work aims
to extend the previous adiabatic study, exploring the consequences of radiative
damping on the propagation and mode conversion of gravity waves in the solar
atmosphere. We model gravity waves in a VAL-C atmosphere, subject to a uniform,
and arbitrarily orientated magnetic field, using the Newton cooling
approximation for radiatively damped propagation. The results indicate that the
mode conversion pathways identified in the adiabatic study are maintained in
the presence of damping. The wave energy fluxes are highly sensitive to the
form of the height dependence of the radiative damping time. While simulations
starting from 0.2 Mm result in modest flux attenuation compared to the
adiabatic results, short damping times expected in the low photosphere
effectively suppress gravity waves in simulations starting at the base of the
photosphere. It is difficult to reconcile our results and observations of
propagating gravity waves with significant energy flux at photospheric heights
unless they are generated in situ, and even then, why they are observed to be
propagating as low as 70 km where gravity waves should be radiatively
overdamped.",1107.2208v1
2013-09-23,Phonon-mediated damping of mechanical vibrations in a finite atomic chain coupled to an outer environment,"We study phonon-mediated damping of mechanical vibrations in a finite
quantum-mechanical atomic-chain model. Our study is motivated by the quest to
understand the quality factors (Q) of nanomechanical resonators and
nanoelectromechanical systems (NEMS), as well as actual experiments with
suspended atomic chains and molecular junctions. We consider a finite atomic
chain which is coupled to a zero-temperature outer environment, modeled as two
additional semi-infinite chains, thus inducing ""clamping-losses"". Weak coupling
to the outer environment ensures that the clamping losses are small, and that
the initially discrete nature of the phonon spectrum is approximately
maintained. We then consider a phonon damping process known as ""Landau-Rumer
damping"", where phonons in the excited mode of vibration decay into other modes
through anharmonic phonon-phonon interaction. The approximately discrete nature
of the phonon spectrum leads to sharp nonmonotonic changes in Q as parameters
are varied, and to the appearance of resonances in the damping. The latter
correspond to the existence of decay processes where the participating phonons
approximately conserve energy. We explore means to control the damping by
changing either the number of atoms in the chains or the ratio between the
longitudinal and transverse speeds of sound, thereby suggesting future
experiments to observe this resonance-like behavior.",1309.5772v1
2014-04-01,Stellar dynamics in gas: The role of gas damping,"In this paper, we consider how gas damping affects the dynamical evolution of
gas-embedded star clusters. Using a simple three-component (i.e. one gas and
two stellar components) model, we compare the rates of mass segregation due to
two-body relaxation, accretion from the interstellar medium, and gas dynamical
friction in both the supersonic and subsonic regimes. Using observational data
in the literature, we apply our analytic predictions to two different
astrophysical environments, namely galactic nuclei and young open star
clusters. Our analytic results are then tested using numerical simulations
performed with the NBSymple code, modified by an additional deceleration term
to model the damping effects of the gas.
  The results of our simulations are in reasonable agreement with our analytic
predictions, and demonstrate that gas damping can significantly accelerate the
rate of mass segregation. A stable state of approximate energy equilibrium
cannot be achieved in our model if gas damping is present, even if Spitzer's
Criterion is satisfied. This instability drives the continued dynamical
decoupling and subsequent ejection (and/or collisions) of the more massive
population. Unlike two-body relaxation, gas damping causes overall cluster
contraction, reducing both the core and half-mass radii. If the cluster is mass
segregated (and/or the gas density is highest at the cluster centre), the
latter contracts faster than the former, accelerating the rate of core
collapse.",1404.0379v1
2014-04-26,Landau damping effects on dust-acoustic solitary waves in a dusty negative-ion plasma,"The nonlinear theory of dust-acoustic waves (DAWs) with Landau damping is
studied in an unmagnetized dusty negative-ion plasma in the extreme conditions
when the free electrons are absent. The cold massive charged dusts are
described by fluid equations, whereas the two-species of ions (positive and
negative) are described by the kinetic Vlasov equations. A Korteweg de-Vries
(KdV) equation with Landau damping, governing the dynamics of weakly nonlinear
and weakly dispersive DAWs, is derived following Ott and Sudan [Phys. Fluids
{\bf 12}, 2388 (1969)]. It is shown that for some typical laboratory and space
plasmas, the Landau damping (and the nonlinear) effects are more pronounced
than the finite Debye length (dispersive) effects for which the KdV soliton
theory is not applicable to DAWs in dusty pair-ion plasmas. The properties of
the linear phase velocity, solitary wave amplitudes (in presence and absence of
the Landau damping) as well as the Landau damping rate are studied with the
effects of the positive ion to dust density ratio $(\mu_{pd})$ as well as the
ratios of positive to negative ion temperatures $(\sigma)$ and masses $(m)$.",1404.6623v3
2015-03-31,Damping of Confined Excitations Modes of 1D Condensates in an Optical Lattice,"We study the damping of the collective excitations of Bose-Einstein
condensates in a harmonic trap potential loaded in an optical lattice. In the
presence of a confining potential the system is non-homogeneous and the
collective excitations are characterized by a set of discrete confined
phonon-like excitations. We derive a general convenient analytical description
for the damping rate, which takes into account, the trapping potential and the
optical lattice, for the Landau and Beliaev processes at any temperature, $T$.
At high temperature or weak spatial confinement, we show that both mechanisms
display linear dependence on $T$. In the quantum limit, we found that the
Landau damping is exponentially suppressed at low temperatures and the total
damping is independent of $T$. Our theoretical predictions for the damping rate
under thermal regime is in completely correspondence with the experimental
values reported for 1D condensate of sodium atoms. We show that the laser
intensity can tune the collision process, allowing a \textit{resonant effect}
for the condensate lifetime. Also, we study the influence of the attractive or
repulsive non-linear terms on the decay rate of the collective excitations. A
general expression of the renormalized Goldstone frequency has been obtained as
a function of the 1D non-linear self-interaction parameter, laser intensity and
temperature.",1503.08884v2
2015-08-06,On the spatial scales of wave heating in the solar chromosphere,"Dissipation of magnetohydrodynamic (MHD) wave energy has been proposed as a
viable heating mechanism in the solar chromospheric plasma. Here, we use a
simplified one-dimensional model of the chromosphere to theoretically
investigate the physical processes and the spatial scales that are required for
the efficient dissipation of Alfv\'en waves and slow magnetoacoustic waves. We
consider the governing equations for a partially ionized hydrogen-helium plasma
in the single-fluid MHD approximation and include realistic wave damping
mechanisms that may operate in the chromosphere, namely Ohmic and ambipolar
magnetic diffusion, viscosity, thermal conduction, and radiative losses. We
perform an analytic local study in the limit of small amplitudes to
approximately derive the lengthscales for critical damping and efficient
dissipation of MHD wave energy. We find that the critical dissipation
lengthscale for Alfv\'en waves depends strongly on the magnetic field strength
and ranges from 10~m to 1~km for realistic field strengths. The damping of
Alfv\'en waves is dominated by Ohmic diffusion for weak magnetic field and low
heights in the chromosphere, and by ambipolar diffusion for strong magnetic
field and medium/large heights in the chromosphere. Conversely, the damping of
slow magnetoacoustic waves is less efficient, and spatial scales shorter than
10~m are required for critical damping. Thermal conduction and viscosity govern
the damping of slow magnetoacoustic waves and play an equally important role at
all heights. These results indicate that the spatial scales at which strong
wave heating may work in the chromosphere are currently unresolved by
observations.",1508.01497v1
2015-11-11,A statistical study of decaying kink oscillations detected using SDO/AIA,"Despite intensive studies of kink oscillations of coronal loops in the last
decade, a large scale statistically significant investigation of the
oscillation parameters has not been made using data from the Solar Dynamics
Observatory (SDO).
  We carry out a statistical study of kink oscillations using Extreme
Ultra-Violet (EUV) imaging data from a previously compiled catalogue.
  We analysed 58 kink oscillation events observed by the Atmospheric Imaging
Assembly (AIA) onboard SDO during its first four years of operation
(2010-2014). Parameters of the oscillations, including the initial apparent
amplitude, period, length of the oscillating loop, and damping are studied for
120 individual loop oscillations.
  Analysis of the initial loop displacement and oscillation amplitude leads to
the conclusion that the initial loop displacement prescribes the initial
amplitude of oscillation in general. The period is found to scale with the loop
length, and a linear fit of the data cloud gives a kink speed of Ck
=(1330+/-50) km s-1 . The main body of the data corresponds to kink speeds in
the range Ck =(800-3300) km s-1. Measurements of 52 exponential damping times
were made, and it was noted that at least 22 of the damping profiles may be
better approximated by a combination of non-exponential and exponential
profiles, rather than a purely exponential damping envelope. There are an
additional 10 cases where the profile appears to be purely non-exponential, and
no damping time was measured. A scaling of the exponential damping time with
the period is found, following the previously established linear scaling
between these two parameters.",1511.03558v1
2016-03-01,A comparative study of protocols for secure quantum communication under noisy environment: single-qubit-based protocols versus entangled-state-based protocols,"The effect of noise on various protocols of secure quantum communication has
been studied. Specifically, we have investigated the effect of amplitude
damping, phase damping, squeezed generalized amplitude damping, Pauli type as
well as various collective noise models on the protocols of quantum key
distribution, quantum key agreement,quantum secure direct quantum communication
and quantum dialogue. From each type of protocol of secure quantum
communication, we have chosen two protocols for our comparative study; one
based on single qubit states and the other one on entangled states. The
comparative study reported here has revealed that single-qubit-based schemes
are generally found to perform better in the presence of amplitude damping,
phase damping, squeezed generalized amplitude damping noises, while
entanglement-based protocols turn out to be preferable in the presence of
collective noises. It is also observed that the effect of noise entirely
depends upon the number of rounds of quantum communication involved in a scheme
of quantum communication. Further, it is observed that squeezing, a completely
quantum mechanical resource present in the squeezed generalized amplitude
channel, can be used in a beneficial way as it may yield higher fidelity
compared to the corresponding zero squeezing case.",1603.00178v1
2016-11-17,A stable partitioned FSI algorithm for rigid bodies and incompressible flow. Part I: Model problem analysis,"A stable partitioned algorithm is developed for fluid-structure interaction
(FSI) problems involving viscous incompressible flow and rigid bodies. This
{\em added-mass partitioned} (AMP) algorithm remains stable, without
sub-iterations, for light and even zero mass rigid bodies when added-mass and
viscous added-damping effects are large. The scheme is based on a generalized
Robin interface condition for the fluid pressure that includes terms involving
the linear acceleration and angular acceleration of the rigid body. Added-mass
effects are handled in the Robin condition by inclusion of a boundary integral
term that depends on the pressure. Added-damping effects due to the viscous
shear forces on the body are treated by inclusion of added-damping tensors that
are derived through a linearization of the integrals defining the force and
torque. Added-damping effects may be important at low Reynolds number, or, for
example, in the case of a rotating cylinder or rotating sphere when the
rotational moments of inertia are small. In this first part of a two-part
series, the properties of the AMP scheme are motivated and evaluated through
the development and analysis of some model problems. The analysis shows when
and why the traditional partitioned scheme becomes unstable due to either
added-mass or added-damping effects. The analysis also identifies the proper
form of the added-damping which depends on the discrete time-step and the
grid-spacing normal to the rigid body. The results of the analysis are
confirmed with numerical simulations that also demonstrate a second-order
accurate implementation of the AMP scheme.",1611.05711v1
2017-01-30,Torsional Alfvén resonances as an efficient damping mechanism for non-radial oscillations in red giant stars,"Stars are self-gravitating fluids in which pressure, buoyancy, rotation and
magnetic fields provide the restoring forces for global modes of oscillation.
Pressure and buoyancy energetically dominate, while rotation and magnetism are
generally assumed to be weak perturbations and often ignored. However,
observations of anomalously weak dipole mode amplitudes in red giant stars
suggest that a substantial fraction of these are subject to an additional
source of damping localised to their core region, with indirect evidence
pointing to the role of a deeply buried magnetic field. It is also known that
in many instances the gravity-mode character of affected modes is preserved,
but so far no effective damping mechanism has been proposed that accommodates
this aspect. Here we present such a mechanism, which damps the oscillations of
stars harbouring magnetised cores via resonant interactions with standing
Alfv\'en modes of high harmonic index. The damping rates produced by this
mechanism are quantitatively on par with those associated with turbulent
convection, and in the range required to explain observations, for realistic
stellar models and magnetic field strengths. Our results suggest that magnetic
fields can provide an efficient means of damping stellar oscillations without
needing to disrupt the internal structure of the modes, and lay the groundwork
for an extension of the theory of global stellar oscillations that incorporates
these effects.",1701.08771v1
2018-03-30,Damping of gravitational waves in a viscous Universe and its implication for dark matter self-interactions,"It is well known that a gravitational wave (GW) experiences the damping
effect when it propagates in a fluid with nonzero shear viscosity. In this
paper, we propose a new method to constrain the GW damping rate and thus the
fluid shear viscosity. By defining the effective distance which incorporates
damping effects, we can transform the GW strain expression in a viscous
Universe into the same form as that in a perfect fluid. Therefore, the
constraints of the luminosity distances from the observed GW events by LIGO and
Virgo can be directly applied to the effective distances in our formalism. We
exploit the lognormal likelihoods for the available GW effective distances and
a Gaussian likelihood for the luminosity distance inferred from the
electromagnetic radiation observation of the binary neutron star merger event
GW170817. Our fittings show no obvious damping effects in the current GW data,
and the upper limit on the damping rate with the combined data is $6.75 \times
10^{-4}\,{\rm Mpc}^{-1}$ at 95\% confidence level. By assuming that the dark
matter self-scatterings are efficient enough for the hydrodynamic description
to be valid, we find that a GW event from its source at a luminosity distance
$D\gtrsim 10^4\;\rm Mpc$ can be used to put a constraint on the dark matter
self-interactions.",1803.11397v1
2018-05-29,Basic microscopic plasma physics from N-body mechanics,"Computing is not understanding. This is exemplified by the multiple and
discordant interpretations of Landau damping still present after seventy years.
For long deemed impossible, the mechanical N-body description of this damping,
not only enables its rigorous and simple calculation, but makes unequivocal and
intuitive its interpretation as the synchronization of almost resonant passing
particles. This synchronization justifies mechanically why a single formula
applies to both Landau growth and damping. As to the electrostatic potential,
the phase mixing of many beam modes produces Landau damping, but it is
unexpectedly essential for Landau growth too. Moreover, collisions play an
essential role in collisionless plasmas. In particular, Debye shielding results
from a cooperative dynamical self-organization process, where ""collisional""
deflections due to a given electron diminish the apparent number of charges
about it. The finite value of exponentiation rates due to collisions is crucial
for the equivalent of the van Kampen phase mixing to occur in the N-body
system. The N-body approach incorporates spontaneous emission naturally, whose
compound effect with Landau damping drives a thermalization of Langmuir waves.
O'Neil's damping with trapping typical of initially large enough Langmuir waves
results from a phase transition. As to collisional transport, there is a smooth
connection between impact parameters where the two-body Rutherford picture is
correct, and those where a collective description is mandatory. The N-body
approach reveals two important features of the Vlasovian limit: it is singular
and it corresponds to a renormalized description of the actual N-body dynamics.",1805.11408v2
2018-08-22,"Constructing a boosted, spinning black hole in the damped harmonic gauge","The damped harmonic gauge is important for numerical relativity computations
based on the generalized harmonic formulation of Einstein's equations, and is
used to reduce coordinate distortions near binary black hole mergers. However,
currently there is no prescription to construct quasiequilibrium binary black
hole initial data in this gauge. Instead, initial data are typically
constructed using a superposition of two boosted analytic single black hole
solutions as free data in the solution of the constraint equations. Then, a
smooth time-dependent gauge transformation is done early in the evolution to
move into the damped harmonic gauge. Using this strategy to produce initial
data in damped harmonic gauge would require the solution of a single black hole
in this gauge, which is not known analytically. In this work we construct a
single boosted, spinning, equilibrium BH in damped harmonic coordinates as a
regular time-independent coordinate transformation from Kerr-Schild
coordinates. To do this, we derive and solve a set of 4 coupled, nonlinear,
elliptic equations for this transformation, with appropriate boundary
conditions. This solution can now be used in the construction of damped
harmonic initial data for binary black holes.",1808.07490v3
2018-12-13,Neutrino damping in a fermion and scalar background,"We consider the propagation of a neutrino in a background composed of a
scalar particle and a fermion using a simple model for the coupling of the form
$\lambda\bar f_R\nu_L\phi$. In the presence of these interactions there can be
damping terms in the neutrino effective potential and index of refraction. We
calculate the imaginary part of the neutrino self-energy in this case, from
which the damping terms are determined. The results are useful in the context
of Dark Matter-neutrino interaction models in which the scalar and/or fermion
constitute the dark-matter. The corresponding formulas for models in which the
scalar particle couples to two neutrinos via a coupling of the form
$\lambda^{(\nu\nu\phi)}\bar\nu^c_R\nu_L\phi$ are then obtained as a special
case, which can be important also in the context of neutrino collective
oscillations in a supernova and in the Early Universe hot plasma before
neutrino decoupling. A particular feature of our results is that the damping
term in a $\nu\phi$ background is independent of the antineutrino-neutrino
asymmetry in the background. Therefore, the relative importance of the damping
term may be more significant if the neutrino-antineutrino asymmetry in the
background is small, because the leading $Z$-exchange and $\phi$-exchange
contributions to the effective potential, which are proportional to the
neutrino-antineutrino asymmetry, are suppressed in that case, while the damping
term is not.",1812.05672v2
2019-04-25,High Spin-Wave Propagation Length Consistent with Low Damping in a Metallic Ferromagnet,"We report ultra-low intrinsic magnetic damping in
Co$_{\text{25}}$Fe$_{\text{75}}$ heterostructures, reaching the low $10^{-4}$
regime at room temperature. By using a broadband ferromagnetic resonance
technique, we extracted the dynamic magnetic properties of several
Co$_{\text{25}}$Fe$_{\text{75}}$-based heterostructures with varying
ferromagnetic layer thickness. By estimating the eddy current contribution to
damping, measuring radiative damping and spin pumping effects, we found the
intrinsic damping of a 26\,nm thick sample to be $$\alpha_{\mathrm{0}} \lesssim
3.18\times10^{-4}$. Furthermore, using Brillouin light scattering microscopy we
measured spin-wave propagation lengths of up to $(21\pm1)\,\mathrm{\mu m}$ in a
26 nm thick Co$_{\text{25}}$Fe$_{\text{75}}$ heterostructure at room
temperature, which is in excellent agreement with the measured damping.",1904.11321v3
2019-11-02,Soft contribution to the damping rate of a hard photon in a weakly magnetized hot medium,"We consider weakly magnetized hot QED plasma comprising electrons and
positrons. There are three distinct dispersive (longitudinal and two
transverse) modes of a photon in a thermo-magnetic medium. At lowest order in
coupling constant, photon is damped in this medium via Compton scattering and
pair creation process. We evaluate the damping rate of hard photon by
calculating the imaginary part of the each transverse dispersive modes in a
thermo-magnetic QED medium. We note that one of the fermions in the loop of
one-loop photon self-energy is considered as soft and the other one is hard.
Considering the resummed fermion propagator in a weakly magnetized medium for
the soft fermion and the Schwinger propagator for hard fermion, we calculate
the soft contribution to the damping rate of hard photon. In weak field
approximation the thermal and thermo-magnetic contributions to damping rate get
separated out for each transverse dispersive mode. The total damping rate for
each dispersive mode in presence of magnetic field is found to be reduced than
that of the thermal one. This formalism can easily be extended to QCD plasma.",1911.00744v2
2020-09-25,Temperature dependence of the damping parameter in the ferrimagnet Gd$_3$Fe$_5$O$_{12}$,"The damping parameter ${\alpha}_{\text{FM}}$ in ferrimagnets defined
according to the conventional practice for ferromagnets is known to be strongly
temperature dependent and diverge at the angular momentum compensation
temperature, where the net angular momentum vanishes. However, recent
theoretical and experimental developments on ferrimagnetic metals suggest that
the damping parameter can be defined in such a way, which we denote by
${\alpha}_{\text{FiM}}$, that it is free of the diverging anomaly at the
angular momentum compensation point and is little dependent on temperature. To
further understand the temperature dependence of the damping parameter in
ferrimagnets, we analyze several data sets from literature for a ferrimagnetic
insulator, gadolinium iron garnet, by using the two different definitions of
the damping parameter. Using two methods to estimate the individual sublattice
magnetizations, which yield results consistent with each other, we found that
in all the used data sets, the damping parameter ${\alpha}_{\text{FiM}}$ does
not increase at the angular compensation temperature and shows no anomaly
whereas the conventionally defined ${\alpha}_{\text{FM}}$ is strongly dependent
on the temperature.",2009.12073v2
2020-09-25,A Complex Stiffness Human Impedance Model with Customizable Exoskeleton Control,"The natural impedance, or dynamic relationship between force and motion, of a
human operator can determine the stability of exoskeletons that use
interaction-torque feedback to amplify human strength. While human impedance is
typically modelled as a linear system, our experiments on a single-joint
exoskeleton testbed involving 10 human subjects show evidence of nonlinear
behavior: a low-frequency asymptotic phase for the dynamic stiffness of the
human that is different than the expected zero, and an unexpectedly consistent
damping ratio as the stiffness and inertia vary. To explain these observations,
this paper considers a new frequency-domain model of the human joint dynamics
featuring complex value stiffness comprising a real stiffness term and a
hysteretic damping term. Using a statistical F-test we show that the hysteretic
damping term is not only significant but is even more significant than the
linear damping term. Further analysis reveals a linear trend linking hysteretic
damping and the real part of the stiffness, which allows us to simplify the
complex stiffness model down to a 1-parameter system. Then, we introduce and
demonstrate a customizable fractional-order controller that exploits this
hysteretic damping behavior to improve strength amplification bandwidth while
maintaining stability, and explore a tuning approach which ensures that this
stability property is robust to muscle co-contraction for each individual.",2009.12446v1
2020-11-26,On the stabilization of breather-type solutions of the damped higher order nonlinear Schrödinger equation,"Spatially periodic breather solutions (SPBs) of the nonlinear Schr\""o\-dinger
(NLS) equation are frequently used to model rogue waves and are typically
unstable. In this paper we study the effects of dissipation and higher order
nonlinearities on the stabilization of both single and multi-mode SPBs in the
framework of a damped higher order NLS (HONLS) equation. We observe the onset
of novel instabilities associated with the development of critical states which
result from symmetry breaking in the damped HONLS system. We broaden the
Floquet characterization of instabilities of solutions of the NLS equation,
using an even 3-phase solution of the NLS as an example, to show instabilities
are associated with degenerate complex elements of both the periodic and
continuous Floquet spectrum. As a result the Floquet criteria for the
stabilization of a solution of the damped HONLS centers around the elimination
of all complex degenerate elements of the spectrum. For an initial SPB with a
given mode structure, a perturbation analysis shows that for short time only
the complex double points associated with resonant modes split under the damped
HONLS while those associated with nonresonant modes remain effectively closed.
The corresponding damped HONLS numerical experiments corroborate that
instabilities associated with nonresonant modes persist on a longer time scale
than the instabilities associated with resonant modes.",2011.13334v1
2020-12-22,Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators,"The linear collisionless damping of zonal flows is calculated for
quasi-symmetric stellarator equilibria in flux-tube, flux-surface, and
full-volume geometry. Equilibria are studied from the quasi-helical symmetry
configuration of the Helically Symmetric eXperiment (HSX), a broken symmetry
configuration of HSX, and the quasi-axial symmetry geometry of the National
Compact Stellarator eXperiment (NCSX). Zonal flow oscillations and long-time
damping affect the zonal flow evolution, and the zonal flow residual goes to
zero for small radial wavenumber. The oscillation frequency and damping rate
depend on the bounce-averaged radial particle drift in accordance with theory.
While each flux tube on a flux surface is unique, several different flux tubes
in HSX or NCSX can reproduce the zonal flow damping from a flux-surface
calculation given an adequate parallel extent. The flux-surface or flux-tube
calculations can accurately reproduce the full-volume long-time residual for
moderate $k_x$, but the oscillation and damping time scales are longer in local
representations, particularly for small $k_x$ approaching the system size.",2012.12213v2
2020-12-31,Damping of slow surface kink modes in solar photospheric waveguides modeled by one-dimensional inhomogeneities,"Given the recent interest in magnetohydrodynamic (MHD) waves in pores and
sunspot umbrae, we examine the damping of slow surface kink modes (SSKMs) by
modeling solar photospheric waveguides with a cylindrical inhomogeneity
comprising a uniform interior, a uniform exterior, and a continuous transition
layer (TL) in between. Performing an eigen-mode analysis in linear, resistive,
gravity-free MHD, our approach is idealized in that, among other things, our
equilibrium is structured only in the radial direction. We can nonetheless
address two damping mechanisms simultaneously, one being the Ohmic resistivity,
and the other being the resonant absorption of SSKMs in the cusp and
Alfv$\acute{\rm e}$n continua. We find that the relative importance of the two
mechanisms depends sensitively on the magnetic Reynolds number ($R_{\rm m}$).
Resonant absorption is the sole damping mechanism for realistically large
values of $R_{\rm m}$, and the cusp resonance in general dominates the
Alfv$\acute{\rm e}$n one unless the axial wavenumbers are at the lower end of
the observationally relevant range. We also find that the thin-boundary
approximation holds only when the TL-width-to-radius ratios are much smaller
than nominally expected. The Ohmic resistivity is far more important for
realistically small $R_{\rm m}$. Even in this case, SSKMs are only marginally
damped, with damping-time-to-period-ratios reaching $\sim 10$ in the parameter
range we examine.",2012.15426v1
2021-02-24,Finding the mechanism of wave energy flux damping in solar pores using numerical simulations,"Context. Solar magnetic pores are, due to their concentrated magnetic fields,
suitable guides for magnetoacoustic waves. Recent observations have shown that
propagating energy flux in pores is subject to strong damping with height;
however, the reason is still unclear. Aims. We investigate possible damping
mechanisms numerically to explain the observations. Methods. We performed 2D
numerical magnetohydrodynamic (MHD) simulations, starting from an equilibrium
model of a single pore inspired by the observed properties. Energy was inserted
into the bottom of the domain via different vertical drivers with a period of
30s. Simulations were performed with both ideal MHD and non-ideal effects.
Results. While the analysis of the energy flux for ideal and non-ideal MHD
simulations with a plane driver cannot reproduce the observed damping, the
numerically predicted damping for a localized driver closely corresponds with
the observations. The strong damping in simulations with localized driver was
caused by two geometric effects, geometric spreading due to diverging field
lines and lateral wave leakage.",2102.12420v1
2022-04-08,Damped Strichartz estimates and the incompressible Euler--Maxwell system,"Euler--Maxwell systems describe the dynamics of inviscid plasmas. In this
work, we consider an incompressible two-dimensional version of such systems and
prove the existence and uniqueness of global weak solutions, uniformly with
respect to the speed of light $c\in (c_0,\infty)$, for some threshold value
$c_0>0$ depending only on the initial data. In particular, the condition
$c>c_0$ ensures that the velocity of the plasma nowhere exceeds the speed of
light and allows us to analyze the singular regime $c\to\infty$.
  The functional setting for the fluid velocity lies in the framework of
Yudovich's solutions of the two-dimensional Euler equations, whereas the
analysis of the electromagnetic field hinges upon the refined interactions
between the damping and dispersive phenomena in Maxwell's equations in the
whole space. This analysis is enabled by the new development of a robust
abstract method allowing us to incorporate the damping effect into a variety of
existing estimates. The use of this method is illustrated by the derivation of
damped Strichartz estimates (including endpoint cases) for several dispersive
systems (including the wave and Schr\""odinger equations), as well as damped
maximal regularity estimates for the heat equation. The ensuing damped
Strichartz estimates supersede previously existing results on the same systems.",2204.04277v3
2022-05-11,A new look at the frequency-dependent damping of slow-mode waves in the solar corona,"Being directly observed in the Doppler shift and imaging data and indirectly
as quasi-periodic pulsations in solar and stellar flares, slow magnetoacoustic
waves offer an important seismological tool for probing many vital parameters
of the coronal plasma. A recently understood active nature of the solar corona
for magnetoacoustic waves, manifested through the phenomenon of wave-induced
thermal misbalance, led to the identification of new natural mechanisms for the
interpretation of observed properties of waves. A frequency-dependent damping
of slow waves in various coronal plasma structures remains an open question, as
traditional wave damping theories fail to match observations. We demonstrate
that accounting for the back-reaction caused by thermal misbalance on the wave
dynamics leads to a modification of the relationship between the damping time
and oscillation period of standing slow waves, prescribed by the linear theory.
The modified relationship is not of a power-law form and has the equilibrium
plasma conditions and properties of the coronal heating/cooling processes as
free parameters. It is shown to readily explain the observed scaling of the
damping time with period of standing slow waves in hot coronal loops.
Functional forms of the unknown coronal heating process, consistent with the
observed frequency-dependent damping, are seismologically revealed.",2205.05346v1
2022-12-13,The Effect of Internal Damping on Locomotion in Frictional Environments,"The gaits of undulating animals arise from a complex interaction of their
central nervous system, muscle, connective tissue, bone, and environment. As a
simplifying assumption, many previous studies have often assumed that
sufficient internal force is available to produce observed kinematics, thus not
focusing on quantifying the interconnection between muscle effort, body shape,
and external reaction forces. This interplay, however, is critical to
locomotion performance in crawling animals, especially when accompanied by body
viscoelasticity. Moreover, in bio-inspired robotic applications, the body's
internal damping is indeed a parameter that the designer can tune. Still, the
effect of internal damping is not well understood. This study explores how
internal damping affects the locomotion performance of a crawler with a
continuous, visco-elastic, nonlinear beam model. Crawler muscle actuation is
modeled as a traveling wave of bending moment propagating posteriorly along the
body. Consistent with the friction properties of the scales of snakes and
limbless lizards, environmental forces are modeled using anisotropic Coulomb
friction. It is found that by varying the crawler body's internal damping, the
crawler's performance can be altered, and distinct gaits could be achieved,
including changing the net locomotion direction from forward to back. We will
discuss this forward and backward control and identify the optimal internal
damping for peak crawling speed.",2212.06290v1
2023-01-19,Inverse Problems of Identifying the Unknown Transverse Shear Force in the Euler-Bernoulli Beam with Kelvin-Voigt Damping,"In this paper, we study the inverse problems of determining the unknown
transverse shear force $g(t)$ in a system governed by the damped
Euler-Bernoulli equation $\rho(x)u_{tt}+\mu(x)u_t+ (r(x)u_{xx})_{xx}+
(\kappa(x)u_{xxt})_{xx}=0, ~(x,t)\in (0,\ell)\times(0,T],$ subject to the
boundary conditions $u(0,t) =0$, $u_{x}(0,t)=0$,
$\left[r(x)u_{xx}+\kappa(x)u_{xxt}\right]_{x=\ell} =0$,
$-\left[\big(r(x)u_{xx}+\kappa(x)u_{xxt}\big)_{x}\right]_{x=\ell}=g(t)$, $t\in
[0,T]$, from the measured deflection $\nu(t):=u(\ell,t)$, $t \in [0,T]$, and
from the bending moment $\omega(t):=-\left(
r(0)u_{xx}(0,t)+\kappa(0)u_{xxt}(0,t) \right)$, $t \in [0,T]$, where the terms
$(\kappa(x)u_{xxt})_{xx}$ and $\mu(x)u_t$ account for the Kelvin-Voigt damping
and external damping, respectively.
  The main purpose of this study is to analyze the Kelvin-Voigt damping effect
on determining the unknown transverse shear force (boundary input) through the
given boundary measurements. The inverse problems are transformed into
minimization problems for Tikhonov functionals, and it is shown that the
regularized functionals admit unique solutions for the inverse problems. By
suitable regularity on the admissible class of shear force $g(t),$ we prove
that these functionals are Fr\'echet differentiable, and the derivatives are
expressed through the solutions of corresponding adjoint problems posed with
measured data as boundary data associated with the direct problem. The
solvability of these adjoint problems is obtained under the minimal regularity
of the boundary data $g(t)$, which turns out to be the regularizing effect of
the Kelvin-Voigt damping in the direct problem.",2301.07931v1
2023-03-28,Escape Kinetics of an Underdamped Colloidal Particle from a Cavity through Narrow Pores,"It is often desirable to know the controlling mechanism of survival
probability of nano - or microscale particles in small cavities such as, e.g.,
confined submicron particles in fiber beds of high-efficiency filter media or
ions/small molecules in confined cellular structures. Here we address this
issue based on numerical study of the escape kinetics of inertial Brownian
colloidal particles from various types of cavities with single and multiple
pores. We consider both the situations of strong and weak viscous damping. Our
simulation results show that as long as the thermal length is larger than the
cavity size the mean exit time remains insensitive to the medium viscous
damping. On further increasing damping strength, a linear relation between
escape rate and damping strength emerges gradually. This result is in sharp
contrast to the energy barrier crossing dynamics where the escape rate exhibits
a turnover behavior as a function of the damping strength. Moreover, in the
ballistic regime, the exit rate is directly proportional to the pore width and
the thermal velocity. All these attributes are insensitive to the cavity as
well as the pore structures. Further, we show that the effects of pore
structure variation on the escape kinetics are conspicuously different in the
low damping regimes compared to the overdamped situation. Apart from direct
applications in biology and nanotechnology, our simulation results can
potentially be used to understand diffusion of living or artificial micro/nano
objects, such as bacteria, virus, Janus Particle etc. where memory effects play
dictating roles.",2303.16092v1
2023-06-05,Damping of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere,"Oscillations are abundant in the solar corona. Coronal loop oscillations are
typically studied using highly idealised models of magnetic flux tubes. In
order to improve our understanding of coronal oscillations, it is necessary to
consider the effect of realistic magnetic field topology and density
structuring. We analyse the damping of coronal oscillations using a
self-consistent 3D radiation-MHD simulation of the solar atmosphere spanning
from the convection zone into the corona, the associated oscillation
dissipation and heating, and finally the physical processes responsible for the
damping and dissipation. The simulated corona formed in such a model does not
depend on any prior assumptions about the shape of the coronal loops. We find
that the bundle of magnetic loops shows damped transverse oscillations in
response to perturbations in two separate instances with oscillation periods of
177 s and 191 s, velocity amplitudes of 10 km/s and 16 km/s and damping times
of 176 s and 198 s, respectively. The coronal oscillations lead to the
development of velocity shear in the simulated corona resulting in the
formation of vortices seen in the velocity field caused by the Kelvin-Helmholtz
instability, contributing to the damping and dissipation of the transverse
oscillations. The oscillation parameters and evolution observed are in line
with the values typically seen in observations of coronal loop oscillations.
The dynamic evolution of the coronal loop bundle suggests the models of
monolithic and static coronal loops with constant lengths might need to be
re-evaluated by relaxing the assumption of highly idealised waveguides.",2306.02770v1
2023-08-22,Investigating the characteristic shape and scatter of intergalactic damping wings during reionization,"Ly$\alpha$ damping wings in the spectra of bright objects at high redshift
are a useful probe of the ionization state of the intergalactic medium during
the reionization epoch. It has recently been noted that, despite the
inhomogeneous nature of reionization, these damping wings have a characteristic
shape which is a strong function of the volume-weighted average neutral
hydrogen fraction of the intergalactic medium. We present here a closer
examination of this finding using a simulation of patchy reionization from the
Sherwood-Relics simulation suite. We show that the characteristic shape and
scatter of the damping wings are determined by the average neutral hydrogen
density along the line of sight, weighted by its contribution to the optical
depth producing the damping wing. We find that there is a redshift dependence
in the characteristic shape due to the expansion of the Universe. Finally, we
show that it is possible to differentiate between the shapes of damping wings
in galaxies and young (or faint) quasars at different points in the
reionization history at large velocity offsets from the point where the
transmission first reaches zero.",2308.11709v1
2023-10-02,Characterizing the Velocity-Space Signature of Electron Landau Damping,"Plasma turbulence plays a critical role in the transport of energy from
large-scale magnetic fields and plasma flows to small scales, where the
dissipated turbulent energy ultimately leads to heating of the plasma species.
A major goal of the broader heliophysics community is to identify the physical
mechanisms responsible for the dissipation of the turbulence and to quantify
the consequent rate of plasma heating. One of the mechanisms proposed to damp
turbulent fluctuations in weakly collisional space and astrophysical plasmas is
electron Landau damping. The velocity-space signature of electron energization
by Landau damping can be identified using the recently developed field-particle
correlation technique. Here, we perform a suite of gyrokinetic turbulence
simulations with ion plasma beta values of 0.01, 0.1, 1, and 10 and use the
field-particle correlation technique to characterize the features of the
velocity-space signatures of electron Landau damping in turbulent plasma
conditions consistent with those observed in the solar wind and planetary
magnetospheres. We identify the key features of the velocity-space signatures
of electron Landau damping as a function of varying plasma \beta_i to provide a
critical framework for interpreting the results of field-particle correlation
analysis of in situ spacecraft observations of plasma turbulence.",2310.01242v2
2023-10-07,OEDG: Oscillation-eliminating discontinuous Galerkin method for hyperbolic conservation laws,"Controlling spurious oscillations is crucial for designing reliable numerical
schemes for hyperbolic conservation laws. This paper proposes a novel, robust,
and efficient oscillation-eliminating discontinuous Galerkin (OEDG) method on
general meshes, motivated by the damping technique in [Lu, Liu, and Shu, SIAM
J. Numer. Anal., 59:1299-1324, 2021]. The OEDG method incorporates an OE
procedure after each Runge-Kutta stage, devised by alternately evolving
conventional semidiscrete DG scheme and a damping equation. A novel damping
operator is carefully designed to possess scale-invariant and
evolution-invariant properties. We rigorously prove optimal error estimates of
the fully discrete OEDG method for linear scalar conservation laws. This might
be the first generic fully-discrete error estimates for nonlinear DG schemes
with automatic oscillation control mechanism. The OEDG method exhibits many
notable advantages. It effectively eliminates spurious oscillations for
challenging problems across various scales and wave speeds, without
problem-specific parameters. It obviates the need for characteristic
decomposition in hyperbolic systems. It retains key properties of conventional
DG method, such as conservation, optimal convergence rates, and
superconvergence. Moreover, it remains stable under normal CFL condition. The
OE procedure is non-intrusive, facilitating integration into existing DG codes
as an independent module. Its implementation is easy and efficient, involving
only simple multiplications of modal coefficients by scalars. The OEDG approach
provides new insights into the damping mechanism for oscillation control. It
reveals the role of damping operator as a modal filter and establishes close
relations between the damping and spectral viscosity techniques. Extensive
numerical results confirm the theoretical analysis and validate the
effectiveness and advantages of the OEDG method.",2310.04807v1
2023-12-07,Probing levitodynamics with multi-stochastic forces and the simple applications on the dark matter detection in optical levitation experiment,"If the terrestrial environment is permeated by dark matter, the levitation
experiences damping forces and fluctuations attributed to dark matter. This
paper investigates levitodynamics with multiple stochastic forces, including
thermal drag, photon recoil, feedback, etc., assuming that all of these forces
adhere to the fluctuation-dissipation theorem. The ratio of total damping to
the stochastic damping coefficient distinguishes the levitodynamics from cases
involving only one single stochastic force. The heating and cooling processes
are formulated to determine the limits of temperature change. All sources of
stochastic forces are comprehensively examined, revealing that dark matter
collisions cannot be treated analogously to fluid dynamics. Additionally, a
meticulous analysis is presented, elucidating the intricate relationship
between the fundamental transfer cross-section and the macroscopic transfer
cross-section. While the dark damping coefficient is suppressed by the mass of
the levitated particle, scattering can be coherently enhanced based on the
scale of the component microscopic particle, the atomic form factor, and the
static structure factor. Hence, dark damping holds the potential to provide
valuable insights into the detection of the macroscopic strength of fundamental
particles. We propose experimental procedures for levitation and employ linear
estimation to extract the dark damping coefficient. Utilizing current
levitation results, we demonstrate that the fundamental transfer cross section
of dark matter can be of the order $\sigma^{\rm D}_{T}\lsim {\cal
O}(10^{-26})\rm cm^2$.",2312.04202v2
2024-01-23,Damped kink motions in a system of two solar coronal tubes with elliptic cross-sections,"This study is motivated by observations of coordinated transverse
displacements in neighboring solar active region loops, addressing specifically
how the behavior of kink motions in straight two-tube equilibria is impacted by
tube interactions and tube cross-sectional shapes.We work with linear, ideal,
pressureless magnetohydrodynamics. Axially standing kink motions are examined
as an initial value problem for transversely structured equilibria involving
two identical, field-aligned, density-enhanced tubes with elliptic
cross-sections (elliptic tubes). Continuously nonuniform layers are implemented
around both tube boundaries. We numerically follow the system response to
external velocity drivers, largely focusing on the quasi-mode stage of internal
flows to derive the pertinent periods and damping times. The periods and
damping times we derive for two-circular-tube setups justify available modal
results found with the T-matrix approach. Regardless of cross-sectional shapes,
our nonuniform layers feature the development of small-scale shears and energy
accumulation around Alf\'ven resonances, indicative of resonant absorption and
phase-mixing. As with two-circular-tube systems, our configurational symmetries
make it still possible to classify lower-order kink motions by the polarization
and symmetric properties of the internal flows; hence such mode labels as $S_x$
and $A_x$. However, the periods and damping times for two-elliptic-tube setups
further depend on cross-sectional aspect ratios, with $A_x$ motions
occasionally damped less rapidly than $S_x$ motions. We find uncertainties up
to $\sim 20\%$ ($\sim 50\%$) for the axial Alfven time (the inhomogeneity
lengthscale) if the periods (damping times) computed for two-elliptic-tube
setups are seismologically inverted with canonical theories for isolated
circular tubes.",2401.12885v2
1995-02-08,The Chemical Evolution of Damped Lyman Alpha Galaxies,"Measurements of element abundances in damped Lyman alpha systems are
providing new means to investigate the chemical evolution of galaxies,
particularly at early times. We review progress in this area, concentrating on
recent efforts to extend the range of existing surveys to both higher and lower
redshifts.",9502047v1
1996-01-19,The Chemical Enrichment History of Damped Lyman-alpha Galaxies,"Studies of damped Lyman-alpha absorption systems in quasar spectra are
yielding very interesting results regarding the chemical evolution of these
galaxies. We present some preliminary results from such a program.",9601098v1
1997-01-30,Initial Chemical Enrichment in Galaxies,"We present evidence that damped Lyman-alpha galaxies detected in spectra of
quasars may not have started forming stars until the redshift z~3. If damped
Lyman-alpha absorbers are the progenitors of disk galaxies, then the above
result may indicate that star formation in galactic disks first began at z~3.",9701241v1
1997-10-24,The N/Si Abundance Ratio in Fifteen Damped Lyman-alpha Galaxies: Implications for the Origin of Nitrogen,"Galactic chemical evolution model calculations indicate that there should be
considerable scatter in the observed N/O ratios at a fixed metallicity (O/H)
for galaxies with very low metallicities due to the delayed release of primary
N from intermediate mass stars relative to that of O from short-lived massive
stars. Moreover, the scatter should increase progressively toward decreasing
metallicity. Such effects have not been convincingly demonstrated by
observations of H II regions in nearby metal-poor galaxies, raising doubts
about the time-delay model of primary N production. Pettini et al and Lipman et
al realized the utility of high-redshift damped Lyman-alpha galaxies for
gaining further insights into the origin of N and discussed abundances in three
damped Lyman-alpha galaxies. Since abundance measurements for O are generally
unavailable for damped Lyman-alpha galaxies, they used N/Si or N/S in place of
N/O under the reasonable assumption that the abundance ratios O/Si and O/S are
the same as solar in damped Lyman-alpha galaxies. We discuss observations of
heavy element abundances in 15 high-redshift (z>2) damped Lyman-alpha galaxies,
many of which have metallicities comparable to or lower than the lowest
metallicity galaxy known locally (I Zw 18). We find that the N/Si ratios in
damped Lyman-alpha galaxies exhibit a very large scatter (about 1 dex) at
[Si/H]~-2 and there is some indication that the scatter increases toward
decreasing metallicity. Considerations of various sources of uncertainties
suggest that they are not likely the main causes of the large scatter. These
results thus provide strong support for the time-delay model of primary N
production in intermediate mass stars if, indeed, O/Si=solar in damped
Lyman-alpha galaxies.",9710266v2
2001-06-05,On Nonlinear Alfvén Waves Generated by Cosmic Ray Streaming Instability,"Nonlinear damping of parallel propagating Alfv\'en waves in high-$\beta$
plasma is considered. Trapping of thermal ions and Coulomb collisions are taken
into account. Saturated damping rate is calculated. Applications are made for
cosmic ray propagation in the Galaxy.",0106078v1
2001-10-15,The UCSD HIRES/KeckI Damped Lya Abundance Database: II. The Implications,"We present a comprehensive analysis of the damped Lya abundance database
presented in the first paper of this series. This database provides a
homogeneous set of abundance measurements for many elements including Si, Cr,
Ni, Zn, Fe, Al, S, Co, O, and Ar from 38 damped Lya systems with z > 1.5. With
little exception, these damped Llya systems exhibit very similar relative
abundances. There is no significant correlation in X/Fe with [Fe/H] metallicity
and the dispersion in X/Fe is small at all metallicity.
  We search the database for trends indicative of dust depletion and in a few
cases find strong evidence. Specifically, we identify a correlation between
[Si/Ti] and [Zn/Fe] which is unambiguous evidence for depletion.
  We present a discussion on the nucleosynthetic history of the damped Lya
systems by focusing on abundance patterns which are minimally affected by dust
depletion. We find [Si/Fe] -> +0.25 dex as [Zn/Fe] -> 0 and that the [Si/Fe]
values exhibit a plateau of ~+0.3 dex at [Si/H] < -1.5 dex. Together these
trends indicate significant alpha-enrichment in the damped Lya systems at low
metallicity, an interpretation further supported by the observed O/Fe, S/Fe and
Ar/Fe ratios. We also discuss Fe-peak nucleosynthesis and the odd-even effect.
  To assess the impact of dust obscuration, we present estimates of the
dust-to-gas ratios for the damped Lya sightlines and crudely calculate dust
extinction corrections. The distribution of extinction corrections suggests the
effects of dust obscuration are minimal and that the population of 'missing'
damped systems has physical characteristics similar to the observed sample.
  We update our investigation on the chemical evolution of the early universe
in neutral gas. [significantly abridged]",0110351v1
2005-09-05,"Comment on ""Damping of Tensor Modes in Cosmology""","We provide an analytic solution to the short wave length limit of the
integro-differential equation describing the damping of the tensor modes of
gravitational waves.",0509096v2
1997-02-12,Crossover from coherent to incoherent dynamics in damped quantum systems,"The destruction of quantum coherence by environmental influences is
investigated taking the damped harmonic oscillator and the dissipative
two-state system as prototypical examples. It is shown that the location of the
coherent-incoherent transition depends to a large degree on the dynamical
quantity under consideration.",9702115v1
1998-06-05,Dielectric formalism and damping of collective modes in trapped Bose-Einstein condensed gases,"We present the general dielectric formalism for Bose-Einstein condensed
systems in external potential at finite temperatures. On the basis of a model
arising within this framework as a first approximation in an intermediate
temperature region for large condensate we calculate the damping of low-energy
excitations in the collisionless regime.",9806079v1
1999-05-27,Do correlations create an energy gap in electronic bilayers? Critical analysis of different approaches,"This paper investigates the effect of correlations in electronic bilayers on
the longitudinal collective mode structure. We employ the dielectric
permeability constructed by means of the classical theory of moments. It is
shown that the neglection of damping processes overestimates the role of
correlations. We conclude that the correct account of damping processes leads
to an absence of an energy gap.",9905405v1
1999-11-16,Damping of low-energy excitations of a Bose-condensed gas in the hydrodynamic regime,"We develop a theory to describe the damping of elementary excitations of a
Bose-condensed gas in the hydrodynamic regime for the thermal cloud. We discuss
second sound in a spatially homogeneous gas and the lowest excitations of a
trapped condensate.",9911238v2
2002-04-18,"Faraday patterns in Bose-Einstein condensates. Amplitude equation for rolls in the parametrically driven, damped Gross-Pitaevskii equation","The parametrically driven, damped Gross-Pitaevskii equation, which models
Bose-Einstein condensates in which the interatomic s-wave scattering length is
modulated in time, is shown to support spatially modulated states in the form
of rolls. A Landau equation with broken phase symmetry is derived, which
governs the dynamics of the roll amplitude.",0204406v1
2002-11-14,Sound damping in ferrofluids: Magnetically enhanced compressional viscosity,"The damping of sound waves in magnetized ferrofluids is investigated and
shown to be considerably higher than in the non-magnetized case. This fact may
be interpreted as a field-enhanced, effective compressional viscosity -- in
analogy to the ubiquitous field-enhanced shear viscosity that is known to be
the reason for many unusual behavior of ferrofluids under shear.",0211297v1
2003-10-23,Input and output in damped quantum systems III: Formulation of damped systems driven by Fermion fields,"A comprehensive input-output theory is developed for Fermionic input fields.
Quantum stochastic differential equations are developed in both the Ito and
Stratonovich forms. The major technical issue is the development of a formalism
which takes account of anticommutation relations between the Fermionic driving
field and those system operators which can change the number of Fermions within
the system.",0310542v1
2004-01-12,Nonexponential motional damping of impurity atoms in Bose-Einstein condensates,"We demonstrate that the damping of the motion of an impurity atom injected at
a supercritical velocity into a Bose-Einstein condensate can exhibit
appreciable deviation from the exponential law on time scales of $10^{-5}$ s.",0401172v1
2005-02-21,Two Transitions in the Damping of a Unitary Fermi Gas,"We measure the temperature dependence of the radial breathing mode in an
optically trapped, strongly-interacting Fermi gas of $^6$Li, just above the
center of a broad Feshbach resonance. The frequency remains close to the
unitary hydrodynamic value, while the damping rate reveals transitions at two
well-separated temperatures, consistent with the existence of atom pairs above
a superfluid transition.",0502507v1
1994-07-04,Cat States and Single Runs for the Damped Harmonic Oscillator,"We discuss the fate of initial states of the cat type for the damped harmonic
oscillator, mostly employing a linear version of the stochastic Schr\""odinger
equation. We also comment on how such cat states might be prepared and on the
relation of single realizations of the noise to single runs of experiments.",9407001v1
2000-10-27,Damping and the Hartree Ensemble Approximation,"We study a Hartree ensemble approximation for real-time dynamics in the toy
model of 1+1 dimensional scalar field theory. Damping behavior seen in
numerical simulations is compared with analytical predictions based on
perturbation theory in the original (non-Hartree-approximated) model.",0010054v1
1995-03-21,APPLICATIONS OF HIGH-TEMPERATURE FIELD THEORY TO HEAVY-ION COLLISIONS,"A recent development in finite temperature field theory, the so-called
Braaten-Pisarski method, and its application to properties of a quark-gluon
plasma, possibly formed in relativistic heavy ion collisions, are reviewed. In
particular parton damping rates, the energy loss of energetic partons,
thermalization times, viscosity, and production and damping rates of hard
photons are discussed.",9503400v1
1996-03-19,Damping Rate and Lyapunov Exponent of a Higgs Field at High Temperature,"The damping rate of a Higgs field at zero momentum is calculated using the
Braaten-Pisarski method and compared to the Lyapunov exponent of the classical
SU(2) Yang-Mills Higgs system.",9603339v1
1997-04-30,Comments on the Erhan-Schlein model of damping the pomeron flux at small x-pomeron,"We explore the theoretical and experimental consequences of a model proposed
by Samim Erhan and Peter Schlein for unitarizing the diffractive amplitude by
damping the pomeron flux at small x-pomeron and conclude that the model is
unphysical and contradicts well established experimental data.",9704454v1
1998-03-26,The Nonlinear Spatial Damping Rate in QGP,"The derivative expansion method has been used to solve the semiclassical
kinetic equations of quark-gluon plasma (QGP). The nonlinear spatial damping
rate, the imaginary part of the wave vector, for the longitudinal secondary
color waves in the long wavelength limit has been calculated numerically.",9803455v1
2006-07-27,Long-Time Asymptotic Behavior of Dissipative Boussinesq System,"In this paper, we study various dissipative mechanics associated with the
Boussinesq systems which model two-dimensional small amplitude long wavelength
water waves. We will show that the decay rate for the damped one-directional
model equations, such as the KdV and BBM equations, holds for some of the
damped Boussinesq systems which model two-directional waves.",0607708v1
2006-12-27,Stochastic inertial manifolds for damped wave equations,"In this paper, stochastic inertial manifold for damped wave equations
subjected to additive white noise is constructed by the Lyapunov-Perron method.
It is proved that when the intensity of noise tends to zero the stochastic
inertial manifold converges to its deterministic counterpart almost surely.",0612774v1
2007-01-19,On the Domain of Analyticity and Small Scales for the Solutions of the Damped-driven 2D Navier-Stokes Equations,"We obtain a logarithmically sharp estimate for the space-analyticity radius
of the solutions of the damped-driven 2D Navier-Stokes equations with periodic
boundary conditions and relate this to the small scales in this system. This
system is inspired by the Stommel--Charney barotropic ocean circulation model.",0701530v1
2002-09-04,Wigner function for damped systems,"Both classical and quantum damped systems give rise to complex spectra and
corresponding resonant states. We investigate how resonant states, which do not
belong to the Hilbert space, fit the phase space formulation of quantum
mechanics. It turns out that one may construct out of a pair of resonant states
an analog of the stationary Wigner function.",0209008v1
2004-12-14,Two-Ion Dusty Plasma Waves and Landau Damping,"The paper analyses the properties of dusty plasmas in the extreme conditions
when the free electrons are absent. The nonlinear Korteveg de Vries equation
with a nonlocal (integral) term in a small parameter approximation is derived.
The conditions are determined when the integral term is essential hence the
Landau damping of two-ion-dusty plasma waves is substantial.",0412033v1
2002-10-16,Dependence of Nuclear Level Density on Vibrational State Damping,"The response function approach is proposed to include vibrational state in
calculation of level density. The calculations show rather strong dependence of
level density on the relaxation times of collective state damping.",0210048v1
1999-02-09,One-Dimensional Motion of Sommerfeld Sphere in Potential Hole in Classical Electrodynamics: Inside the Hole,"Equation of motion of Sommerfeld sphere in the one-dimensional potential
hole, produced by two equal charges on some distance from each other, is
numerically investigated. Two types of solutions are found: (i) damping
oscillations, (ii) oscillations without damping (radiationless motion).
Solutions with growing amplitude (""climbing-up-the-wall solution"") for chosen
initial conditions were not founded.",9902018v3
2000-03-23,The Hawking-Unruh Temperature and Damping in a Linear Focusing Channel,"The Hawking-Unruh effective temperature, hbar a* / 2 pi c k, due to quantum
fluctuations in the radiation of an accelerated charged-particle beam can be
used to show that transverse oscillations of the beam in a practical linear
focusing channel damp to the quantum-mechanical limit. A comparison is made
between this behavior and that of beams in a wiggler.",0003061v1
2003-06-17,Ruchhardt Oscillator Decay- Thermodynamic basis for Hysteretic Damping,"Using thermodynamic arguments based on the ideal gas law, it is shown that
hysteretic (also called structural) damping is the natural form of energy
dissipation for this classic oscillator that is used to measure the ratio of
heat capacities for a gas.",0306136v1
2005-08-25,Rutherford scattering with radiation damping,"We study the effect of radiation damping on the classical scattering of
charged particles. Using a perturbation method based on the Runge-Lenz vector,
we calculate radiative corrections to the Rutherford cross section, and the
corresponding energy and angular momentum losses.",0508186v2
2006-01-18,Expressions for frictional and conservative force combinations within the dissipative Lagrange-Hamilton formalism,"Dissipative Lagrangians and Hamiltonians having Coulomb, viscous and
quadratic damping,together with gravitational and elastic terms are presented
for a formalism that preserves the Hamiltonian as a constant of the motion.
Their derivations are also shown. The resulting L's and H's may prove useful in
exploring new types of damped quantum systems.",0601133v1
1997-03-27,Macroscopic quantum damping in SQUID rings,"The measurement process is introduced in the dynamics of Josephson devices
exhibiting quantum behaviour in a macroscopic degree of freedom. The
measurement is shown to give rise to a dynamical damping mechanism whose
experimental observability could be relevant to understand decoherence in
macroscopic quantum systems.",9703052v1
2005-07-19,Radiation reaction and quantum damped harmonic oscillator,"By taking a Klein-Gordon field as the environment of an harmonic oscillator
and using a new method for dealing with quantum dissipative systems (minimal
coupling method), the quantum dynamics and radiation reaction for a quantum
damped harmonic oscillator investigated. Applying perturbation method, some
transition probabilities indicating the way energy flows between oscillator,
reservoir and quantum vacuum, obtained",0507179v1
2005-08-18,Density operator and entropy of the damped quantum harmonic oscillator,"The expression for the density operator of the damped harmonic oscillator is
derived from the master equation in the framework of the Lindblad theory for
open quantum systems. Then the von Neumann entropy and effective temperature of
the system are obtained. The entropy for a state characterized by a Wigner
distribution function which is Gaussian in form is found to depend only on the
variance of the distribution function.",0508141v1
2006-03-03,On the damping of the angular momentum of three harmonic oscillators,"In the frame of the Lindblad theory of open quantum systems, the system of
three uncoupled harmonic oscillators with opening operators linear in the
coordinates and momenta of the considered system is analyzed. The damping of
the angular momentum and of its projection is obtained.",0603029v1
2006-10-10,Simultaneous amplification and non-symmetric amplitude damping of two-mode Gaussian state,"The evolution of two-mode Gaussian state under symmetric amplification,
non-symmetric damping and thermal noise is studied. The time dependent solution
of the state characteristic function is obtained. The separability criterions
are given for the final state of weak amplification as well as strong
amplification.",0610070v1
2007-10-13,The separability of tripartite Gaussian state with amplification and amplitude damping,"Tripartite three mode Gaussian state undergoes parametric amplification and
amplitude damping as well as thermal noise is studied. In the case of a state
totally symmetrically interacting with the environment, the time dependent
correlation matrix of the state in evolution is given. The conditions for fully
separability and fully entanglement of the final tripartite three mode Gaussian
state are worked out.",0710.2570v1
2007-12-16,Nonadditive quantum error correcting codes adapted to the ampltitude damping channel,"A family of high rate quantum error correcting codes adapted to the amplitude
damping channel is presented. These codes are nonadditive and exploit
self-complementarity structure to correct all first-order errors. Their rates
can be higher than 1/2. The recovery operations of these codes can be generated
by a simple algorithm and have a projection nature, which makes them
potentially easy to implement.",0712.2586v1
2007-12-22,Chaos in an intermittently driven damped oscillator,"We observe chaotic dynamics in a damped linear oscillator, which is driven
only at certain regions of phase space. Both deterministic and random drives
are studied. The dynamics is characterized using standard techniques of
nonlinear dynamics. Interchanging roles of determinism and stochasticity is
also considered.",0712.3827v2
2008-03-01,Well-posedness of the IBVP for 2-D Euler Equations with Damping,"In this paper we focus on the initial-boundary value problem of the 2-D
isentropic Euler equations with damping. We prove the global-in-time existence
of classical solution to the initial-boundary value problem by the method of
energy estimates.",0803.0039v1
2008-03-27,Shear viscosity of degenerate electron matter,"We calculate the partial electron shear viscosity $\eta_{ee}$ limited by
electron-electron collisions in a strongly degenerate electron gas taking into
account the Landau damping of transverse plasmons. The Landau damping strongly
suppresses $\eta_{ee}$ in the domain of ultrarelativistic degenerate electrons
and modifies its %asymptotic temperature behavior. The efficiency of the
electron shear viscosity in the cores of white dwarfs and envelopes of neutron
stars is analyzed.",0803.3893v1
2008-04-09,Stationary Oscillations in a Damped Wave Equation from Isospectral Bessel Functions,"Using the isospectral partners of the Bessel functions derived by Reyes et
al., we find, on one hand, that these functions show non-typical supersymmetric
(SUSY) behavior and, on the other, that the isospectral partner of the
classical wave equation is equivalent to that of a damped system whose
oscillations do not vanish in time, but show a non-harmonic shape.",0804.1510v1
2008-06-03,Simulation study of fast ion instability in the ILC damping ring and PETRA III,"The fast ion instability is simulated in different gas pressures and fill
patterns for the damping ring of the International Linear Collider (ILC) and
PETRA III respectively. Beam size variation due to beta function and dispersion
function change is taken into account. Feedback is also applied in the
simulation.",0806.0529v1
2008-08-01,Damped wave equations with dynamic boundary conditions,"We discuss several classes of linear second order initial-boundary value
problems, where damping terms appear in the main wave equation as well as in
the dynamic boundary condition. We investigate their well-posedness and
describe some qualitative properties of their solutions, including boundedness,
stability, or almost periodicity. In particular, we are able to characterize
the analyticity of certain $C_0$-semigroups associated to such problems.
Applications to several problems on domains and networks are shown.",0808.0213v1
2008-12-17,The damping of gravitational waves in dust,"We examine a simple model of interaction of gravitational waves with matter
(primarily represented by dust). The aim is to investigate a possible damping
effect on the intensity of gravitational wave when passing through media. This
might be important for gravitational wave astronomy when the sources are
obscured by dust or molecular clouds.",0812.3336v1
2009-05-24,Computer assisted proof of the existence of homoclinic tangency for the Henon map and for the forced-damped pendulum,"We present a topological method for the efficient computer assisted
verification of the existence of the homoclinic tangency which unfolds
generically in a one-parameter family of planar maps. The method has been
applied to the Henon map and the forced damped pendulum ODE.",0905.3924v1
2009-08-15,"Antigravitation, Dark Energy, Dark Matter - Alternative Solution","Collisional damping of gravitational waves in the Newtonian matter is
investigated. The generalized theory of Landau damping is applied to the
gravitational physical systems in the context of the plasma gravitational
analogy.",0908.2180v3
2009-08-31,A comment about the existence of a weak solution for a non linear wave equation damped propagation,"We give a proof for the existence of a weak solution on the initial-value
problem of a non-linear damped propagation",0909.0052v2
2009-09-15,Quantum Parrondo's games under decoherence,"We study the effect of quantum noise on history dependent quantum Parrondo's
games by taking into account different noise channels. Our calculations show
that entanglement can play a crucial role in quantum Parrondo's games. It is
seen that for the maximally entangled initial state in the presence of
decoherence, the quantum phases strongly influence the payoffs for various
sequences of the game. The effect of amplitude damping channel leads to winning
payoffs. Whereas the depolarizing and phase damping channels lead to the losing
payoffs. In case of amplitude damping channel, the payoffs are enhanced in the
presence of decoherence for the sequence AAB. This is because the quantum
phases interfere constructively which leads to the quantum enhancement of the
payoffs in comparison to the undecohered case. It is also seen that the quantum
phase angles damp the payoffs significantly in the presence of decoherence.
Furthermore, it is seen that for multiple games of sequence AAB, under the
influence of amplitude damping channel, the game still remains a winning game.
However, the quantum enhancement reduces in comparison to the single game of
sequence AAB because of the destructive interference of phase dependent terms.
In case of depolarizing channel, the game becomes a loosing game. It is seen
that for the game sequence B the game is loosing one and the behavior of
sequences B and BB is similar for amplitude damping and depolarizing channels.
In addition, the repeated games of A are only influenced by the amplitude
damping channel and the game remains a losing game. Furthermore, it is also
seen that for any sequence when played in series, the phase damping channel
does not influence the game.",0909.2897v2
2009-10-01,Global attractor for weakly damped Nonlinear Schrödinger equations in $L^2(\R)$,"We prove that the weakly damped nonlinear Schr\""odinger flow in
$L^2(\mathbb{R})$ provides a dynamical system which possesses a global
attractor. The proof relies on the continuity of the Schr\""odinger flow for the
weak topology in $L^2(\R)$.",0910.0172v1
2009-12-11,"Waves, damped wave and observation","We consider the wave equation in a bounded domain (eventually convex). Two
kinds of inequality are described when occurs trapped ray. Applications to
control theory are given. First, we link such kind of estimate with the damped
wave equation and its decay rate. Next, we describe the design of an
approximate control function by an iterative time reversal method.",0912.2202v1
2010-01-01,Exponential Energy Decay for Damped Klein-Gordon Equation with Nonlinearities of Arbitrary Growth,"We derive a uniform exponential decay of the total energy for the nonlinear
Klein-Gordon equation with a damping around spatial infinity in the whole space
or in the exterior of a star shaped obstacle.",1001.0209v1
2010-03-10,"Covariant Constitutive Relations, Landau Damping and Non-stationary Inhomogeneous Plasmas","Models of covariant linear electromagnetic constitutive relations are
formulated that have wide applicability to the computation of susceptibility
tensors for dispersive and inhomogeneous media. A perturbative framework is
used to derive a linear constitutive relation for a globally neutral plasma
enabling one to describe in this context a generalized Landau damping mechanism
for non-stationary inhomogeneous plasma states.",1003.2062v1
2010-03-28,Damped wave dynamics for a complex Ginzburg-Landau equation with low dissipation,"We consider a complex Ginzburg-Landau equation, corresponding to a
Gross-Pitaevskii equation with a small dissipation term. We study an asymptotic
regime for long-wave perturbations of constant maps of modulus one. We show
that such solutions never vanish and we derive a damped wave dynamics for the
perturbation.",1003.5375v1
2010-06-16,Hysteresis effects in Bose-Einstein condensates,"Here, we consider damped two-components Bose-Einstein condensates with
many-body interactions. We show that, when the external trapping potential has
a double-well shape and when the nonlinear coupling factors are modulated in
time, hysteresis effects may appear under some circumstances. Such hysteresis
phenomena are a result of the joint contribution between the appearance of
saddle node bifurcations and damping effect.",1006.3240v1
2010-09-25,Different Network Topologies for Distributed Electric Damping of Beam Vibrations,"In this work passive electric damping of structural vibrations by distributed
piezoelectric transducers and electric networks is analyzed. Different
distributed electric controllers are examined as finite degrees of freedom
systems and their performances are compared. Modal reduction is used to
optimize the electric parameters",1009.5001v1
2010-12-27,The Relativistic kinetics of gravitational waves collisional damping in hot Universe,"The article is a translation of authors paper printed earlier in the
inaccessible edition and summarizing the results of research of gravitational
waves damping problem in the cosmologic plasma due to the different
interactions of elementary particles.",1012.5582v1
2011-01-14,Blowup for the Damped $L^{2}$-Critical Nonlinear Schrödinger Equation,"We consider the Cauchy problem for the $L^{2}$-critical damped nonlinear
Schr\""odinger equation. We prove existence and stability of finite time blowup
dynamics with the log-log blow-up speed for $\|\nabla u(t)\|_{L^2}$.",1101.2763v3
2011-02-05,Partial regularity of weak solutions of the viscoelastic Navier-Stokes equations with damping,"We prove an analog of the Caffarelli-Kohn-Nirenberg theorem for weak
solutions of a system of PDE that model a viscoelastic fluid in the presence of
an energy damping mechanism. The system was recently introduced as a possible
method of establishing the global in time existence of weak solutions of the
well known Oldroyd system.",1102.1112v1
2011-02-21,The One Dimensional Damped Forced Harmonic Oscillator Revisited,"In this paper we give a general solution to the problem of the damped
harmonic oscillator under the influence of an arbitrary time-dependent external
force. We employ simple methods accessible for beginners and useful for
undergraduate students and professors in an introductory course of mechanics.",1102.4112v1
2011-03-18,"Soliton complexity in the damped-driven nonlinear Schrödinger equation: stationary, periodic, quasiperiodic complexes","Stationary and oscillatory bound states, or complexes, of the damped-driven
solitons are numerically path-followed in the parameter space. We compile a
chart of the two-soliton attractors, complementing the one-soliton attractor
chart.",1103.3607v1
2011-09-27,Exponential energy decay of solutions for a system of viscoelastic wave equations of Kirchhoff type with strong damping,"The initial boundary value problem for a system of viscoelastic wave
equations of Kirchhoff type with strong damping is considered. We prove that,
under suitable assumptions on relaxation functions and certain initial data,
the decay rate of the solutions energy is exponential.",1109.5921v1
2011-11-20,Null controllability of the structurally damped wave equation with moving point control,"We investigate the internal controllability of the wave equation with
structural damping on the one dimensional torus. We assume that the control is
acting on a moving point or on a moving small interval with a constant
velocity. We prove that the null controllability holds in some suitable Sobolev
space and after a fixed positive time independent of the initial conditions.",1111.4655v1
2011-12-04,On the Apparent Superluminal Motion of a Damped Gaussian Pulse,"Alicki has demonstrated that a travelling Gaussian pulse subject to damping
is indistinguishable from an undamped pulse moving with greater speed; such an
effect could create the illusion of a pulse moving faster than light. In this
note, an alternative derivation of the same result is presented. However, it is
unlikely that this particular illusion could explain the superluminal
neutrino-velocities reported by OPERA.",1112.1324v1
2011-12-28,Photon Damping in One-Loop HTL Perturbation Theory,"We determine the damping rates of slow-moving photons in next-to-leading
order hard-thermal-loop perturbation of massless QED. We find both longitudinal
and transverse rates finite, positive, and equal at zero momentum. Various
divergences, light-cone and at specific momenta, but not infrared, appear and
cancel systematically.",1112.6065v2
2012-04-06,Late time evolution of the gravitational wave damping in the early Universe,"An analytical solution for time evolution of the gravitational wave damping
in the early Universe due to freely streaming neutrinos is found in the late
time regime. The solution is represented by a convergent series of spherical
Bessel functions of even order and was possible with the help of a new compact
formula for the convolution of spherical Bessel functions of integer order.",1204.1384v2
2012-05-30,Beam Dynamics Studies for the CLIC Main Linac,"The implications of long-range wakefields on the beam quality are
investigated through a detailed beam dynamics study. Injection offsets are
considered and the resulting emittance dilution recorded, including systematic
sources of error. These simulations have been conducted for damped and detuned
structures (DDS) and for waveguide damped structures-both for the CLIC
collider.",1205.6623v2
2012-07-31,Energy decay rates for solutions of the wave equations with nonlinear damping in exterior domain,"In this paper we study the behaviors of the energy of solutions of the wave
equations with localized nonlinear damping in exterior domains.",1207.7336v3
2012-11-02,A modified test function method for damped waves,"In this paper we use a modified test function method to derive nonexistence
results for the semilinear wave equation with time-dependent speed and damping.
The obtained critical exponent is the same exponent of some recent results on
global existence of small data solution.",1211.0453v1
2012-12-15,Damping and Pseudo-fermions,"After a short abstract introduction on the time evolution driven by non
self-adjoint hamiltonians, we show how the recently introduced concept of {\em
pseudo-fermion} can be used in the description of damping in finite dimensional
quantum systems, and we compare the results deduced adopting the Schr\""odinger
and the Heisenberg representations.",1212.3663v1
2013-01-14,On estimating the output entropy of a tensor product of the quantum phase-damping channel with an arbitrary channel,"We obtained the estimation from below for the output entropy of a tensor
product of the quantum phase-damping channel with an arbitrary channel. It is
shown that from this estimation immediately follows that the strong
superadditivity of the output entropy holds for this channel as well as for the
quantum depolarizing channel.",1301.2886v1
2013-06-10,Smooth attractors for the quintic wave equations with fractional damping,"Dissipative wave equations with critical quintic nonlinearity and damping
term involving the fractional Laplacian are considered. The additional
regularity of energy solutions is established by constructing the new
Lyapunov-type functional and based on this, the global well-posedness and
dissipativity of the energy solutions as well as the existence of a smooth
global and exponential attractors of finite Hausdorff and fractal dimension is
verified.",1306.2294v1
2013-07-20,Entanglement-assisted capacities of time-correlated amplitude-damping channel,"We calculate the information capacities of a time-correlated
amplitude-damping channel, provided the sender and receiver share prior
entanglement. Our analytical results show that the noisy channel with zero
capacity can transmit information if it has finite memory. The capacities
increase as the memory increases attaining maximum value for perfect memory
channel.",1307.5403v1
2013-07-23,Comment on Damping Force in the Transit-time Method of Optical Stochastic Cooling,"In this brief report we pointed at mistake in paper A. Zholents, Damping
Force in the Transit-Time Method of Optical Stochastic Cooling, PRLST. Mar 1,
2012. 2 pp. Published in Phys.Rev.ST Accel. Beams 15 (2012) 032801.",1307.6185v1
2013-08-23,Stability results for second-order evolution equations with switching time-delay,"We consider second-order evolution equations in an abstract setting with
intermittently delayed/ not-delayed damping. We give sufficient conditions for
asymptotic and exponential stability, improving and generalising our previous
results from [19]. In particular, under suitable conditions, we can consider
unbounded damping operators. Some concrete examples are finally presented.",1308.5100v1
2013-09-10,Convergence of global solutions for some classes of nonlinear damped wave equations,"We consider the asymptotic behavior of the soltion to the wave equation with
time-dependent damping and analytic nonlinearity. Our main goal is to prove the
convergence of a global solution to an equilibrium as time goes to infinity by
means of a suitable Lojasiewicz-Simon type inequality.",1309.2364v1
2013-09-13,On diffusion phenomena for the linear wave equation with space-dependent damping,"In this paper, we prove the diffusion phenomenon for the linear wave equation
with space-dependent damping. We prove that the asymptotic profile of the
solution is given by a solution of the corresponding heat equation in the
$L^2$-sense.",1309.3377v1
2013-09-19,Compressible Euler equation with damping on Torus in arbitrary dimensions,"We study the exponential stability of constant steady state of isentropic
compressible Euler equation with damping on $\mathbb T^n$. The local existence
of solutions is based on semigroup theory and some commutator estimates. We
propose a new method instead of energy estimates to study the stability, which
works equally well for any spatial dimensions.",1309.5059v3
2013-10-28,Large deviations for a damped telegraph process,"In this paper we consider a slight generalization of the damped telegraph
process in Di Crescenzo and Martinucci (2010). We prove a large deviation
principle for this process and an asymptotic result for its level crossing
probabilities (as the level goes to infinity). Finally we compare our results
with the analogous well-known results for the standard telegraph process.",1310.7332v1
2013-10-29,Blow-up for the wave equation with nonlinear source and boundary damping terms,"The paper deals with blow--up for the solutions of wave equation with
nonlinear source and nonlinear boudary damping terms, posed in a bounded and
regular domain. The initial data are posed in the energy space. The aim of the
paper is to improve previous blow-up results concerning the problem.",1310.7734v1
2013-11-24,Global small solution to the 2D MHD system with a velocity damping term,"This paper studies the global well-posedness of the incompressible
magnetohydrodynamic (MHD) system with a velocity damping term. We establish the
global existence and uniqueness of smooth solutions when the initial data is
close to an equilibrium state. In addition, explicit large-time decay rates for
various Sobolev norms of the solutions are also given.",1311.6185v1
2014-08-25,Asymptotic behavior of global entropy solutions for nonstrictly hyperbolic systems with linear damping,"In this paper we investigate the large time behavior of the global weak
entropy solutions to the symmetric Keyftiz-Kranzer system with linear damping.
It is proved that as t tends to infinite the entropy solutions tend to zero in
the L p norm",1408.5856v1
2014-08-26,Stability of an abstract-wave equation with delay and a Kelvin-Voigt damping,"In this paper we consider a stabilization problem for the abstract-wave
equation with delay. We prove an exponential stability result for appropriate
damping coefficient. The proof of the main result is based on a
frequency-domain approach.",1408.6261v2
2015-02-02,"Spontaneous toroidal rotation, anomalous radial particle flux, and the electron-ion asymmetric anomalous viscous damping","AA spontaneous toroidal rotation due to the electron-ion asymmetric anomalous
viscous damping and the turbulent radial particle flux has been found, which
explains the experimental observation of the anomalous toroidal momentum source
in the edge of a tokamak plasma.",1502.00499v3
2015-03-06,Concentration Of Laplace Eigenfunctions And Stabilization Of Weakly Damped Wave Equation,"- In this article, we prove some universal bounds on the speed of
concentration on small (frequency-dependent) neighborhoods of submanifolds of L
2-norms of quasi modes for Laplace operators on compact manifolds. We deduce
new results on the rate of decay of weakly damped wave equations.
R{\'e}sum{\'e}.",1503.02058v1
2015-03-11,Upper bounds for the attractor dimension of damped Navier-Stokes equations in $\mathbb R^2$,"We consider finite energy solutions for the damped and driven two-dimensional
Navier--Stokes equations in the plane and show that the corresponding dynamical
system possesses a global attractor. We obtain upper bounds for its fractal
dimension when the forcing term belongs to the whole scale of homogeneous
Sobolev spaces from -1 to 1",1503.03415v1
2015-03-18,Laplace Eigenfunctions And Damped Wave Equation Ii: Product Manifolds,"- The purpose of this article is to study possible concentrations of
eigenfunc-tions of Laplace operators (or more generally quasi-modes) on product
manifolds. We show that the approach of the first author and Zworski [10, 11]
applies (modulo rescalling) and deduce new stabilization results for weakly
damped wave equations which extend to product manifolds previous results by
Leautaud-Lerner [12] obtained for products of tori.",1503.05513v1
2015-10-14,The General Solution to Vlasov Equation and Linear Landau Damping,"A general solution to linearized Vlasov equation for an electron
electrostatic wave in a homogeneous unmagnetized plasma is derived. The
quasi-linear diffusion coefficient resulting from this solution is a continuous
function of omega in contrast to that derived from the traditional Vlasov
treatment. The general solution is also equivalent to the Landau treatment of
the plasma normal oscillations, and hence leads to the well-known Landau
damping.",1510.03949v1
2016-01-13,Non uniform decay of the energy of some dissipative evolution systems,"In this paper we consider second order evolution equations with bounded
damping. We give a characterization of a non uniform decay for the damped
problem using a kind of observability estimate for the associated undamped
problem.",1601.03373v1
2016-01-27,Forward self-similar solutions to the viscoelastic Navier-Stokes equation with damping,"Motivated by \cite{JS}, we prove that there exists a global, forward
self-similar solution to the viscoelastic Navier-Stokes equation with damping,
that is smooth for $t>0$, for any initial data that is homogeneous of degree
$-1$.",1601.07478v1
2016-03-14,Phase speed and frequency-dependent damping of longitudinal intensity oscillations in coronal loop structures observed with AIA/SDO,"Longitudinal intensity oscillations along coronal loops that are interpreted
as signatures of magneto-acoustic waves are observed frequently in different
coronal structures. The aim of this paper is to estimate the physical
parameters of the slow waves and the quantitative dependence of these
parameters on their frequencies in the solar corona loops that are situated
above active regions with the Atmospheric Imaging Assembly (AIA) onboard Solar
Dynamic Observatory (SDO). The observed data on 2012-Feb-12, consisting of 300
images with an interval of 24 seconds in the 171 $\rm{\AA}$ and 193 $\rm{\AA}$
passbands is analyzed for evidence of propagating features as slow waves along
the loop structures. Signatures of longitudinal intensity oscillations that are
damped rapidly as they travel along the loop structures were found, with
periods in the range of a few minutes to few tens of minutes. Also, the
projected (apparent) phase speeds, projected damping lengths, damping times and
damping qualities of filtered intensities centred on the dominant frequencies
are measured in the range of $\rm{C_s}\simeq 38-79~ \rm {km~s^{-1}}$,
$\rm{L_d}\simeq 23-68 ~\rm{Mm }$, $\rm{\tau_d}\simeq 7- 21 ~\rm {min}$ and
$\rm{\tau_d/P}\simeq 0.34- 0.77$, respectively. The theoretical and
observational results of this study indicate that the damping times and damping
lengths increase with increasing the oscillation periods, and are highly
sensitive function of oscillation period, but the projected speeds and the
damping qualities are not very sensitive to the oscillation periods.
Furthermore, the magnitude values of physical parameters are in good agreement
with the prediction of the theoretical dispersion relations of high-frequency
MHD waves ($>1.1~ \rm{mHz}$) in a coronal plasma with electron number density
in the range of $\rm{n_e}\simeq 10^{7} - 10^{12} ~\rm{cm^{-3}}$.",1603.04207v1
2016-04-27,Critical exponent for nonlinear wave equations with frictional and viscoelastic damping terms,"In this paper, we study the Cauchy problem for a nonlinear wave equation with
frictional and viscoelastic damping terms. Our aim is to obtain the threshold,
to classify the global existence of solution for small data or the finite time
blow-up pf the solution, with respect to the growth order of the nonlinearity.",1604.08265v1
2016-05-19,On circular flows: linear stability and damping,"In this article we establish linear inviscid damping with optimal decay rates
around 2D Taylor-Couette flow and similar monotone flows in an annular domain
$B_{r_{2}}(0) \setminus B_{r_{1}}(0) \subset \mathbb{R}^{2}$. Following recent
results by Wei, Zhang and Zhao, we establish stability in weighted norms, which
allow for a singularity formation at the boundary, and additional provide a
description of the blow-up behavior.",1605.05959v1
2016-08-04,Resonance Damping of the THz-frequency Transverse Acoustic Phonon in the Relaxor Ferroelectric KTa1-xNbxO3,"The damping ($\Gamma_a$) of the transverse acoustic (TA) phonon in single
crystals of the relaxor $KTa_{1-x}Nb_xO_3$ with x=0.15-0.17 was studied by
means of high resolution inelastic cold neutron scattering near the (200) B.Z.
point where diffuse scattering is absent, although it is present near (110). In
a wide range of temperatures centered on the phase transition, T=195K-108K, the
TA phonon width (damping) exhibits a step increase around momentum q=0.07, goes
through a shallow maximum at q=0.09-0.12 and remains high up to the highest
momentum studied of q=0.16. These experimental results are explained in terms
of a resonant interaction between the TA phonon and the collective or
correlated reorientation through tunneling of the off-center Nb+5 ions. The
observed TA damping is successfully reproduced in a simple model that includes
an interaction between the TA phonon and a dispersionless localized mode (LM)
with frequency $\omega_L$ and damping $\Gamma_L$ ($\Gamma_L < \omega_L$),
itself coupled to the transverse optic (TO) mode. Maximum damping of the TA
phonon occurs when its frequency $\omega_a \approx{\omega_L}$. $\omega_L$ and
$\Gamma_L$ are moderately dependent on temperature but the oscillator strength,
$M_2$, of the resonant damping exhibits a strong maximum in the range
$T\sim{150 K-120 K}$ in which neutron diffuse scattering near the (110) B.Z.
point is also maximum and the dielectric susceptibility exhibits the relaxor
behavior. The maximum value of M appears to be due to the increasing number of
polar nanodomains. In support of the proposed model, the observed value of
$\omega_L$ is found to be similar to the estimate previously obtained by
Girshberg and Yacoby. Alternatively, the TA phonon damping can be successfully
fitted in the framework of an empirical Havriliak - Negami (HN) relaxation
model that includes a strong resonance-like transient contribution.",1608.01591v1
2016-08-26,Cheillini integrability and quadratically damped oscillators,"In this paper a new approach to study an equation of the Lienard type with a
strong quadratic damping is proposed based on Jacobi's last multiplier and
Cheillini's integrability condition. We obtain a closed form solution of the
transcendental characteristic equation of the Lienard type equation using the
Lambert W-function.",1608.07377v1
2016-11-27,Nonlinear Wave Equation with Damping: Periodic Forcing and Non-Resonant Solutions to the Kuznetsov Equation,"Existence of non-resonant solutions of time-periodic type are established for
the Kuznetsov equation with a periodic forcing term. The equation is considered
in a three-dimensional whole-space, half-space and bounded domain, and with
both non-homogeneous Dirichlet and Neumann boundary values. A method based on
Lp estimates of the corresponding linearization, namely the wave equation with
Kelvin-Voigt damping, is employed.",1611.08883v1
2017-02-02,Stationary solutions for stochastic damped Navier-Stokes equations in $\mathbb R^d$,"We consider the stochastic damped Navier-Stokes equations in $\mathbb R^d$
($d=2,3$), assuming as in our previous work [4] that the covariance of the
noise is not too regular, so It\^o calculus cannot be applied in the space of
finite energy vector fields. We prove the existence of an invariant measure
when $d=2$ and of a stationary solution when $d=3$.",1702.00697v1
2017-03-08,Moderate deviations for the Langevin equation with strong damping,"In this paper, we establish a moderate deviations principle for the Langevin
dynamics with strong damping. The weak convergence approach plays an important
role in the proof.",1703.03033v3
2017-03-17,Damping in a Superconducting Mechanical Resonator,"We study a mechanical resonator made of aluminum near the normal to super
conductivity phase transition. A sharp drop in the rate of mechanical damping
is observed below the critical temperature. The experimental results are
compared with predictions based on the Bardeen Cooper Schrieffer theory of
superconductivity and a fair agreement is obtained.",1703.05912v1
2017-03-27,On the $L^{2}$-critical nonlinear Schrodinger equation with an inhomogeneous damping term,"We consider the $L^2$-critical nonlinear Schrodinger equation with an
inhomogeneous damping term. We prove that there exists an initial data such
that the corresponding solution is global in $H^1(R^d)$ and we give the minimal
time of the blow up for some initial data.",1703.09101v1
2017-06-22,Asymptotic profile of solutions for some wave equations with very strong structural damping,"We consider the Cauchy problem in R^n for some types of damped wave
equations. We derive asymptotic profiles of solutions with weighted
L^{1,1}(R^n) initial data by employing a simple method introduced by the first
author. The obtained results will include regularity loss type estimates, which
are essentially new in this kind of equations.",1706.07174v1
2017-08-11,Global existence of a diffusion limit with damping for the compressible radiative Euler system coupled to an electromagnetic field,"We study the Cauchy problem for a system of equations corresponding to a
singular limit of radiative hydrodynamics, namely the 3D radiative compressible
Euler system coupled to an electromagnetic field through the MHD approximation.
Assuming the presence of damping together with suitable smallness hypotheses
for the data, we prove that this problem admits a unique global smooth
solution.",1708.03681v1
2017-08-21,A remark on the critical exponent for the semilinear damped wave equation on the half-space,"In this short notice, we prove the non-existence of global solutions to the
semilinear damped wave equation on the half-space, and we determine the
critical exponent for any space dimension.",1708.06429v1
2017-08-24,Nonlinear network dynamics for interconnected micro-grids,"This paper deals with transient stability in interconnected micro-grids. The
main contribution involves i) robust classification of transient dynamics for
different intervals of the micro-grid parameters (synchronization, inertia, and
damping); ii) exploration of the analogies with consensus dynamics and bounds
on the damping coefficient separating underdamped and overdamped dynamics iii)
the extension to the case of disturbed measurements due to hackering or
parameter uncertainties.",1708.07296v1
2017-12-04,Radiative seesaw models linking to dark matter candidates inspired by the DAMPE excess,"We propose two possibilities to explain an excess of electron/positron flux
around 1.4 TeV recently reported by Dark Matter Explore (DAMPE) in the
framework of radiative seesaw models where one of them provides a fermionic
dark matter candidate, and the other one provides a bosonic dark matter
candidate. We also show unique features of both models regarding neutrino mass
structure.",1712.00941v1
2018-01-06,Multiscale analysis of semilinear damped stochastic wave equations,"In this paper we proceed with the multiscale analysis of semilinear damped
stochastic wave motions. The analysis is made by combining the well-known sigma
convergence method with its stochastic counterpart, associated to some
compactness results such as the Prokhorov and Skorokhod theorems. We derive the
equivalent model, which is of the same type as the micro-model.",1801.02036v1
2018-07-06,Global existence for the 3-D semilinear damped wave equations in the scattering case,"We study the global existence of solutions to semilinear damped wave
equations in the scattering case with derivative power-type nonlinearity on
(1+3) dimensional nontrapping asymptotically Euclidean manifolds. The main idea
is to exploit local energy estimate, together with local existence to convert
the parameter $\mu$ to small one.",1807.02403v1
2018-09-22,Asymptotic behavior of solutions to 3D incompressible Navier-Stokes equations with damping,"In this paper, we study the upper bound of the time decay rate of solutions
to the Navier-Stokes equations and generalized Navier-Stokes equations with
damping term $|u|^{\beta-1}u$ ($\beta>1$) in $\mathbb{R}^3$.",1809.08394v2
2018-10-22,Optimal leading term of solutions to wave equations with strong damping terms,"We analyze the asymptotic behavior of solutions to wave equations with strong
damping terms. If the initial data belong to suitable weighted $L^1$ spaces,
lower bounds for the difference between the solutions and the leading terms in
the Fourier space are obtained, which implies the optimality of expanding
methods and some estimates proposed in this paper.",1810.09114v1
2018-10-29,Apples with Apples comparison of 3+1 conformal numerical relativity schemes,"This paper contains a comprehensive comparison catalog of `Apples with
Apples' tests for the BSSNOK, CCZ4 and Z4c numerical relativity schemes, with
and without constraint damping terms for the latter two. We use basic numerical
methods and reach the same level of accuracy as existing results in the
literature. We find that the best behaving scheme is generically CCZ4 with
constraint damping terms.",1810.12346v1
2018-11-07,Statistical complexity of the quasiperiodical damped systems,"We consider the concept of statistical complexity to write the
quasiperiodical damped systems applying the snapshot attractors. This allows us
to understand the behaviour of these dynamical systems by the probability
distribution of the time series making a difference between the regular, random
and structural complexity on finite measurements. We interpreted the
statistical complexity on snapshot attractor and determined it on the
quasiperiodical forced pendulum.",1811.02958v1
2018-12-13,Rapid exponential stabilization of a 1-D transmission wave equation with in-domain anti-damping,"We consider the problem of pointwise stabilization of a one-dimensional wave
equation with an internal spatially varying anti-damping term. We design a
feedback law based on the backstepping method and prove exponential stability
of the closed-loop system with a desired decay rate.",1812.11035v1
2019-01-20,Stationary Solutions of Damped Stochastic 2-dimensional Euler's Equation,"Existence of stationary point vortices solution to the damped and
stochastically driven Euler's equation on the two dimensional torus is proved,
by taking limits of solutions with finitely many vortices. A central limit
scaling is used to show in a similar manner the existence of stationary
solutions with white noise marginals.",1901.06744v1
2019-03-13,Solar $p$-mode damping rates: insight from a 3D hydrodynamical simulation,"Space-borne missions CoRoT and Kepler have provided a rich harvest of
high-quality photometric data for solar-like pulsators. It is now possible to
measure damping rates for hundreds of main-sequence and thousands of red-giant.
However, among the seismic parameters, mode damping rates remain poorly
understood and thus barely used for inferring the physical properties of stars.
Previous approaches to model mode damping rates were based on mixing-length
theory or a Reynolds-stress approach to model turbulent convection. While able
to grasp the main physics of the problem, those approaches are of little help
to provide quantitative estimates as well as a definitive answer on the
relative contribution of each physical mechanism. Our aim is thus to assess the
ability of 3D hydrodynamical simulations to infer the physical mechanisms
responsible for damping of solar-like oscillations. To this end, a solar
high-spatial resolution and long-duration hydrodynamical 3D simulation computed
with the ANTARES code allows probing the coupling between turbulent convection
and the normal modes of the simulated box. Indeed, normal modes of the
simulation experience realistic driving and damping in the super-adiabatic
layers of the simulation. Therefore, investigating the properties of the normal
modes in the simulation provides a unique insight into the mode physics. We
demonstrate that such an approach provides constraints on the solar damping
rates and is able to disentangle the relative contribution related to the
perturbation of the turbulent pressure, the gas pressure, the radiative flux,
and the convective flux contributions. Finally, we conclude that using the
normal modes of a 3D numerical simulation is possible and is potentially able
to unveil the respective role of the different physical mechanisms responsible
for mode damping provided the time-duration of the simulation is long enough.",1903.05479v1
2019-04-15,Carleman estimate for an adjoint of a damped beam equation and an application to null controllability,"In this article we consider a control problem of a linear Euler-Bernoulli
damped beam equation with potential in dimension one with periodic boundary
conditions. We derive a new Carleman estimate for an adjoint of the equation
under consideration. Then using a well known duality argument we obtain
explicitly the control function which can be used to drive the solution
trajectory of the control problem to zero state.",1904.07038v1
2019-05-01,Dissipative structure and diffusion phenomena for doubly dissipative elastic waves in two space dimensions,"In this paper we study the Cauchy problem for doubly dissipative elastic
waves in two space dimensions, where the damping terms consist of two different
friction or structural damping. We derive energy estimates and diffusion
phenomena with different assumptions on initial data. Particularly, we find the
dominant influence on diffusion phenomena by introducing a new threshold of
diffusion structure.",1905.00257v1
2019-06-21,Unique determination of the damping coefficient in the wave equation using point source and receiver data,"In this article, we consider the inverse problems of determining the damping
coefficient appearing in the wave equation. We prove the unique determination
of the coefficient from the data coming from a single coincident
source-receiver pair. Since our problem is under-determined, so some extra
assumption on the coefficient is required to prove the uniqueness.",1906.08987v1
2019-07-12,Non-Existence of Periodic Orbits for Forced-Damped Potential Systems in Bounded Domains,"We prove Lr-estimates on periodic solutions of periodically-forced,
linearly-damped mechanical systems with polynomially-bounded potentials. The
estimates are applied to obtain a non-existence result of periodic solutions in
bounded domains, depending on an upper bound on the gradient of the potential.
The results are illustrated on examples.",1907.05778v1
2019-09-02,On the inclusion of damping terms in the hyperbolic MBO algorithm,"The hyperbolic MBO is a threshold dynamic algorithm which approximates
interfacial motion by hyperbolic mean curvature flow. We introduce a
generalization of this algorithm for imparting damping terms onto the equation
of motion. We also construct corresponding numerical methods, and perform
numerical tests. We also use our results to show that the generalized
hyperbolic MBO is able to approximate motion by the standard mean curvature
flow.",1909.00552v1
2019-09-07,Lindblad dynamics of the damped and forced quantum harmonic oscillator: General solution,"The quantum dynamics of a damped and forced harmonic oscillator described by
a Lindblad master equation is analyzed. The master equation is converted into a
matrix-vector representation and the resulting non-Hermitian Schr\""odinger
equation is solved by Lie-algebraic techniques allowing the construction of the
general solution for the density operator.",1909.03206v1
2019-10-17,Modified different nonlinearities for weakly coupled systems of semilinear effectively damped waves with different time-dependent coefficients in the dissipation terms,"We prove the global existence of small data solution in all space dimension
for weakly coupled systems of semi-linear effectively damped wave, with
different time-dependent coefficients in the dissipation terms. Moreover,
nonlinearity terms $ f(t,u) $ and $ g(t,v) $ satisfying some properties of the
parabolic equation. We study the problem in several classes of regularity.",1910.07731v1
2019-11-01,Convergence of a damped Newton's method for discrete Monge-Ampere functions with a prescribed asymptotic cone,"We prove the convergence of a damped Newton's method for the nonlinear system
resulting from a discretization of the second boundary value problem for the
Monge-Ampere equation. The boundary condition is enforced through the use of
the notion of asymptotic cone. The differential operator is discretized based
on a partial discrete analogue of the subdifferential.",1911.00260v2
2019-12-17,"Comment on ""On the Origin of Frictional Energy Dissipation""","In their interesting study (Ref. [1]) Hu et al have shown that for a simple
""harmonium"" solid model the slip-induced motion of surface atoms is close to
critically damped. This result is in fact well known from studies of
vibrational damping of atoms and molecules at surfaces. However, for real
practical cases the situation may be much more complex and the conclusions of
Hu et al invalid.",1912.07799v1
2020-01-23,Nonlinear inviscid damping for a class of monotone shear flows in finite channel,"We prove the nonlinear inviscid damping for a class of monotone shear flows
in $T\times [0,1]$ for initial perturbation in Gevrey-$1/s$($s>2$) class with
compact support. The main idea of the proof is to use the wave operator of a
slightly modified Rayleigh operator in a well chosen coordinate system.",2001.08564v1
2020-02-26,Bistability in the dissipative quantum systems I: Damped and driven nonlinear oscillator,"We revisit quantum dynamics of the damped and driven nonlinear oscillator. In
the classical case this system has two stationary solutions (the limit cycles)
in the certain parameter region, which is the origin of the celebrated
bistability phenomenon. The quantum-classical correspondence for the oscillator
dynamics is discussed in details.",2002.11373v1
2020-04-08,Scattering and asymptotic order for the wave equations with the scale-invariant damping and mass,"We consider the linear wave equation with the time-dependent scale-invariant
damping and mass. We also treat the corresponding equation with the energy
critical nonlinearity. Our aim is to show that the solution scatters to a
modified linear wave solution and to obtain its asymptotic order.",2004.03832v2
2020-04-24,Infinite energy solutions for weakly damped quintic wave equations in $\mathbb{R}^3$,"The paper gives a comprehensive study of infinite-energy solutions and their
long-time behavior for semi-linear weakly damped wave equations in
$\mathbb{R}^3$ with quintic nonlinearities. This study includes global
well-posedness of the so-called Shatah-Struwe solutions, their dissipativity,
the existence of a locally compact global attractors (in the uniformly local
phase spaces) and their extra regularity.",2004.11864v1
2020-07-30,Delta shock solution to the generalized one-dimensional zero-pressure gas dynamics system with linear damping,"In this paper, we propose a time-dependent viscous system and by using the
vanishing viscosity method we show the existence of delta shock solution for a
particular $2 \times 2$ system of conservation laws with linear damping.",2007.15184v2
2020-08-06,On global attractors for 2D damped driven nonlinear Schrödinger equations,"Well-posedness and global attractor are established for 2D damped driven
nonlinear Schr\""odinger equation with almost periodic pumping in a bounded
region. The key role is played by a novel application of the energy equation.",2008.02741v1
2020-08-30,Influence of dissipation on extreme oscillations of a forced anharmonic oscillator,"Dynamics of a periodically forced anharmonic oscillator (AO) with cubic
nonlinearity, linear damping, and nonlinear damping, is studied. To begin with,
the authors examine the dynamics of an AO. Due to this symmetric nature, the
system has two neutrally stable elliptic equilibrium points in positive and
negative potential-wells. Hence, the unforced system can exhibit both
single-well and double-well periodic oscillations depending on the initial
conditions. Next, the authors include nonlinear damping into the system. Then,
the symmetry of the system is broken instantly and the stability of the two
elliptic points is altered to result in stable focus and unstable focus in the
positive and negative potential-wells, respectively. Consequently, the system
is dual-natured and is either non-dissipative or dissipative, depending on
location in the phase space. Furthermore, when one includes a periodic external
forcing with suitable parameter values into the nonlinearly damped AO system
and starts to increase the damping strength, the symmetry of the system is not
broken right away, but it occurs after the damping reaches a threshold value.
As a result, the system undergoes a transition from double-well chaotic
oscillations to single-well chaos mediated through extreme events (EEs).
Furthermore, it is found that the large-amplitude oscillations developed in the
system are completely eliminated if one incorporates linear damping into the
system. The numerically calculated results are in good agreement with the
theoretically obtained results on the basis of Melnikov's function. Further, it
is demonstrated that when one includes linear damping into the system, this
system has a dissipative nature throughout the entire phase space of the
system. This is believed to be the key to the elimination of EEs.",2008.13172v1
2020-09-16,Exponential decay for semilinear wave equations with viscoelastic damping and delay feedback,"In this paper we study a class of semilinear wave type equations with
viscoelastic damping and delay feedback with time variable coefficient. By
combining semigroup arguments, careful energy estimates and an iterative
approach we are able to prove, under suitable assumptions, a well-posedness
result and an exponential decay estimate for solutions corresponding to small
initial data. This extends and concludes the analysis initiated in [16] and
then developed in [13, 17].",2009.07777v1
2020-09-18,Vanishing viscosity limit for Riemann solutions to a $2 \times 2$ hyperbolic system with linear damping,"In this paper, we propose a time-dependent viscous system and by using the
vanishing viscosity method we show the existence of %delta shock solution
solutions for the Riemann problem to a particular $2 \times 2$ system of
conservation laws with linear damping.",2009.09041v1
2020-11-28,A Smoluchowski-Kramers approximation for an infinite dimensional system with state-dependent damping,"We study the validity of a Smoluchowski-Kramers approximation for a class of
wave equations in a bounded domain of $\mathbb{R}^n$ subject to a
state-dependent damping and perturbed by a multiplicative noise. We prove that
in the small mass limit the solution converges to the solution of a stochastic
quasilinear parabolic equation where a noise-induced extra drift is created.",2011.14236v2
2020-12-13,Uniform Stabilization of the Petrovsky-Wave Nonlinear coupled system with strong damping,"This paper concerns the well-posedness and uniform stabilization of the
Petrovsky-Wave Nonlinear coupled system with strong damping. Existence of
global weak solutions for this problem is established by using the Galerkin
method. Meanwhile, under a clever use of the multiplier method, we estimate the
total energy decay rate.",2012.07109v3
2021-03-24,"On the long-time statistical behavior of smooth solutions of the weakly damped, stochastically-driven KdV equation","This paper considers the damped periodic Korteweg-de Vries (KdV) equation in
the presence of a white-in-time and spatially smooth stochastic source term and
studies the long-time behavior of solutions. We show that the integrals of
motion for KdV can be exploited to prove regularity and ergodic properties of
invariant measures for damped stochastic KdV. First, by considering non-trivial
modifications of the integrals of motion, we establish Lyapunov structure by
proving that moments of Sobolev norms of solutions at all orders of regularity
are bounded globally-in-time; existence of invariant measures follows as an
immediate consequence. Next, we prove a weak Foias-Prodi type estimate for
damped stochastic KdV, for which the synchronization occurs in expected value.
This estimate plays a crucial role throughout our subsequent analysis. As a
first novel application, we combine the Foias-Prodi estimate with the Lyapunov
structure to establish that invariant measures are supported on $C^\infty$
functions provided that the external driving forces belong to $C^\infty$. We
then establish ergodic properties of invariant measures, treating the regimes
of arbitrary damping and large damping separately. For arbitrary damping, we
demonstrate that the framework of `asymptotic coupling' can be implemented for
a compact proof of uniqueness of the invariant measure provided that
sufficiently many directions in phase space are stochastically forced. Our
proof is paradigmatic for SPDEs for which a weak Foias-Prodi type property
holds. Lastly, for large damping, we establish the existence of a spectral gap
with respect to a Wasserstein-like distance, and exponential mixing and
uniqueness of the invariant measure follows.",2103.12942v2
2021-04-21,On absorbing set for 3D Maxwell--Schrödinger damped driven equations in bounded region,"We consider the 3D damped driven Maxwell--Schr\""odinger equations in a
bounded region under suitable boundary conditions. We establish new a priori
estimates, which provide the existence of global finite energy weak solutions
and bounded absorbing set. The proofs rely on the Sobolev type estimates for
magnetic Schr\""odinger operator.",2104.10723v1
2021-06-23,Pitt inequality for the linear structurally damped $σ$-evolution equations,"This work is devoted to improve the time decay estimates for the solution and
some of its derivatives of the linear structurally damped $\sigma$-evolution
equations. The Pitt inequality is the main tool provided that the initial data
lies in some weighted spaces.",2106.12342v1
2021-07-22,Dimension estimates for the attractor of the regularized damped Euler equations on the sphere,"We prove existence of the global attractor of the damped and driven
Euler--Bardina equations on the 2D sphere and on arbitrary domains on the
sphere
  and give explicit estimates of its fractal dimension in terms of the physical
parameters.",2107.10779v1
2021-09-22,State-space representation of Matérn and Damped Simple Harmonic Oscillator Gaussian processes,"Gaussian processes (GPs) are used widely in the analysis of astronomical time
series. GPs with rational spectral densities have state-space representations
which allow O(n) evaluation of the likelihood. We calculate analytic state
space representations for the damped simple harmonic oscillator and the
Mat\'ern 1/2, 3/2 and 5/2 processes.",2109.10685v1
2021-10-10,Global existence of solutions for semilinear damped wave equations with variable coefficients,"We consider the Cauchy problem for the damped wave equations with variable
coefficients a(x) having power type nonlinearity |u|^p. We discuss the global
existence of solutions for small initial data and investigate the relation
between the range of a(x) and the order p.",2110.04718v2
2021-10-21,Stability properties of dissipative evolution equations with nonautonomous and nonlinear damping,"In this paper, we obtain some stability results of (abstract) dissipative
evolution equations with a nonautonomous and nonlinear damping using the
exponential stability of the retrograde problem with a linear and autonomous
feedback and a comparison principle. We then illustrate our abstract statements
for different concrete examples, where new results are achieved. In a
preliminary step, we prove some well-posedness results for some nonlinear and
nonautonomous evolution equations.",2110.11122v1
2021-11-23,Logistic damping effect in chemotaxis models with density-suppressed motility,"This paper is concerned with a parabolic-elliptic chemotaxis model with
density-suppressed motility and general logistic source in an $n$-dimensional
smooth bounded domain with Neumann boundary conditions. Under the minimal
conditions for the density-suppressed motility function, we explore how strong
the logistic damping can warrant the global boundedness of solutions, and
further establish the asymptotic behavior of solutions on top of the
conditions.",2111.11669v1
2022-01-04,Global existence and decay estimates for a viscoelastic plate equation with nonlinear damping and logarithmic nonlinearity,"In this article, we consider a viscoelastic plate equation with a logarithmic
nonlinearity in the presence of nonlinear frictional damping term. Using the
the Faedo-Galerkin method we establish the global existence of the solution of
the problem and we also prove few general decay rate results.",2201.00983v1
2022-01-20,Long Time Decay of Leray Solution of 3D-NSE With Damping,"In \cite{CJ}, the authors show that the Cauchy problem of the Navier-Stokes
equations with damping $\alpha|u|^{\beta-1}u(\alpha>0,\;\beta\geq1)$ has global
weak solutions in $L^2(\R^3)$. In this paper, we prove the uniqueness, the
continuity in $L^2$ for $\beta>3$, also the large time decay is proved for
$\beta\geq\frac{10}3$. Fourier analysis and standard techniques are used.",2201.08427v1
2022-02-20,On a non local non-homogeneous fractional Timoshenko system with frictional and viscoelastic damping terms,"We are devoted to the study of a nonhomogeneous time-fractional Timoshenko
system with frictional and viscoelastic damping terms. We are concerned with
the well-posedness of the given problem. The approach relies on some
functional-analysis tools, operator theory, a prori estimates, and density
arguments.",2202.09879v1
2022-04-05,Large time behavior of solutions to nonlinear beam equations,"In this note we analyze the large time behavior of solutions to a class of
initial/boundary problems involving a damped nonlinear beam equation. We show
that under mild conditions on the damping term of the equation of motions the
solutions of the dynamical problem converge to the solution of the stationary
problem. We also show that this convergence is exponential.",2204.02151v1
2022-05-09,Energy asymptotics for the strongly damped Klein-Gordon equation,"We consider the strongly damped Klein Gordon equation for defocusing
nonlinearity and we study the asymptotic behaviour of the energy for periodic
solutions. We prove first the exponential decay to zero for zero mean
solutions. Then, we characterize the limit of the energy, when the time tends
to infinity, for solutions with small enough initial data and we finally prove
that such limit is not necessary zero.",2205.04205v1
2022-06-07,Asymptotic study of Leray Solution of 3D-NSE With Exponential Damping,"We study the uniqueness, the continuity in $L^2$ and the large time decay for
the Leray solutions of the $3D$ incompressible Navier-Stokes equations with the
nonlinear exponential damping term $a (e^{b |u|^{\bf 2}}-1)u$, ($a,b>0$)
studied by the second author in \cite{J1}.",2206.03138v1
2022-06-25,"Decay estimate in a viscoelastic plate equation with past history, nonlinear damping, and logarithmic nonlinearity","In this article, we consider a viscoelastic plate equation with past history,
nonlinear damping, and logarithmic nonlinearity. We prove explicit and general
decay rate results of the solution to the viscoelastic plate equation with past
history. Convex properties, logarithmic inequalities, and generalised Young's
inequality are mainly used to prove the decay estimate.",2206.12561v1
2022-06-30,Effect of a viscous fluid shell on the propagation of gravitational waves,"In this paper we show that there are circumstances in which the damping of
gravitational waves (GWs) propagating through a viscous fluid can be highly
significant; in particular, this applies to Core Collapse Supernovae (CCSNe).
In previous work, we used linearized perturbations on a fixed background within
the Bondi-Sachs formalism, to determine the effect of a dust shell on GW
propagation. Here, we start with the (previously found) velocity field of the
matter, and use it to determine the shear tensor of the fluid flow. Then, for a
viscous fluid, the energy dissipated is calculated, leading to an equation for
GW damping. It is found that the damping effect agrees with previous results
when the wavelength $\lambda$ is much smaller than the radius $r_i$ of the
matter shell; but if $\lambda\gg r_i$, then the damping effect is greatly
increased.
  Next, the paper discusses an astrophysical application, CCSNe. There are
several different physical processes that generate GWs, and many models have
been presented in the literature. The damping effect thus needs to be evaluated
with each of the parameters $\lambda,r_i$ and the coefficient of shear
viscosity $\eta$, having a range of values. It is found that in most cases
there will be significant damping, and in some cases that it is almost
complete.
  We also consider the effect of viscous damping on primordial gravitational
waves (pGWs) generated during inflation in the early Universe. Two cases are
investigated where the wavelength is either much shorter than the shell radii
or much longer; we find that there are conditions that will produce significant
damping, to the extent that the waves would not be detectable.",2206.15103v2
2022-09-07,Blow up and lifespan estimates for systems of semi-linear wave equations with dampings and potentials,"In this paper, we consider the semi-linear wave systems with
power-nonlinearities and space-dependent dampings and potentials. We obtain the
blow-up regions for three types wave systems as well as the lifespan estimates.",2209.02920v1
2022-12-04,Inverse problem of recovering the time-dependent damping and nonlinear terms for wave equations,"In this paper, we consider the inverse boundary problems of recovering the
time-dependent nonlinearity and damping term for a semilinear wave equation on
a Riemannian manifold. The Carleman estimate and the construction of Gaussian
beams together with the higher order linearization are respectively used to
derive the uniqueness results of recovering the coefficients.",2212.01815v2
2022-12-14,Gevrey regularity for the Euler-Bernoulli beam equation with localized structural damping,"We study a Euler-Bernoulli beam equation with localized discontinuous
structural damping. As our main result, we prove that the associated
$C_0$-semigroup $(S(t))_{t\geq0}$ is of Gevrey class $\delta>24$ for $t>0$,
hence immediately differentiable. Moreover, we show that $(S(t))_{t\geq0}$ is
exponentially stable.",2212.07110v1
2022-12-28,On extended lifespan for 1d damped wave equation,"In this manuscript, a sharp lifespan estimate of solutions to semilinear
classical damped wave equation is investigated in one dimensional case, when
the sum of initial position and speed is $0$ pointwisely. Especially, an
extension of lifespan is shown in this case. Moreover, existence of some global
solutions are obtained by a direct computation.",2212.13845v1
2023-02-06,Uniform stabilization of an acoustic system,"We study the problem of stabilization for the acoustic system with a
spatially distributed damping. With imposing hypothesis on the structural
properties of the damping term, we identify exponential decay of solutions with
growing time.",2302.02726v1
2023-04-23,Decay rates for a variable-coefficient wave equation with nonlinear time-dependent damping,"In this paper, a class of variable-coefficient wave equations equipped with
time-dependent damping and the nonlinear source is considered. We show that the
total energy of the system decays to zero with an explicit and precise decay
rate estimate under different assumptions on the feedback with the help of the
method of weighted energy integral.",2304.11522v1
2023-05-22,Fast energy decay for wave equation with a monotone potential and an effective damping,"We consider the total energy decay of the Cauchy problem for wave equations
with a potential and an effective damping. We treat it in the whole
one-dimensional Euclidean space. Fast energy decay is established with the help
of potential. The proofs of main results rely on a multiplier method and
modified techniques adopted in [8].",2305.12666v1
2023-08-03,Blow-up for semilinear wave equations with damping and potential in high dimensional Schwarzschild spacetime,"In this work, we study the blow up results to power-type semilinear wave
equation in the high dimensional Schwarzschild spacetime, with damping and
potential terms. We can obtain the upper bound estimates of lifespan without
the assumption that the support of the initial date should be far away from the
black hole.",2308.01691v1
2023-08-22,Lifespan estimates for 1d damped wave equation with zero moment initial data,"In this manuscript, a sharp lifespan estimate of solutions to semilinear
classical damped wave equation is investigated in one dimensional case when the
Fourier 0th moment of sum of initial position and speed is $0$. Especially, it
is shown that the behavior of lifespan changes with $p=3/2$ with respect to the
size of the initial data.",2308.11113v1
2023-09-01,Damped Euler system with attractive Riesz interaction forces,"We consider the barotropic Euler equations with pairwise attractive Riesz
interactions and linear velocity damping in the periodic domain. We establish
the global-in-time well-posedness theory for the system near an equilibrium
state. We also analyze the large-time behavior of solutions showing the
exponential rate of convergence toward the equilibrium state as time goes to
infinity.",2309.00210v1
2023-10-02,The damped wave equation and associated polymer,"Considering the damped wave equation with a Gaussian noise $F$ where $F$ is
white in time and has a covariance function depending on spatial variables, we
will see that this equation has a mild solution which is stationary in time
$t$. We define a weakly self-avoiding polymer with intrinsic length $J$
associated to this SPDE. Our main result is that the polymer has an effective
radius of approximately $J^{5/3}$.",2310.01631v1
2023-10-17,Indirect boundary stabilization for weakly coupled degenerate wave equations under fractional damping,"In this paper, we consider the well-posedness and stability of a
one-dimensional system of degenerate wave equations coupled via zero order
terms with one boundary fractional damping acting on one end only. We prove
optimal polynomial energy decay rate of order $1/t^{(3-\tau)}$. The method is
based on the frequency domain approach combined with multiplier technique.",2310.11174v1
2024-03-11,Uniform estimates for solutions of nonlinear focusing damped wave equations,"For a damped wave (or Klein-Gordon) equation on a bounded domain, with a
focusing power-like nonlinearity satisfying some growth conditions, we prove
that a global solution is bounded in the energy space, uniformly in time. Our
result applies in particular to the case of a cubic equation on a bounded
domain of dimension 3.",2403.06541v1
1995-10-27,A modified R1 X R1 method for helioseismic rotation inversions,"We present an efficient method for two dimensional inversions for the solar
rotation rate using the Subtractive Optimally Localized Averages (SOLA) method
and a modification of the R1 X R1 technique proposed by Sekii (1993). The SOLA
method is based on explicit construction of averaging kernels similar to the
Backus-Gilbert method. The versatility and reliability of the SOLA method in
reproducing a target form for the averaging kernel, in combination with the
idea of the R1 X R1 decomposition, results in a computationally very efficient
inversion algorithm. This is particularly important for full 2-D inversions of
helioseismic data in which the number of modes runs into at least tens of
thousands.",9510143v1
1997-10-22,Globular Cluster Microlensing: Globular Clusters as Microlensing Targets,"We investigate the possibility of using globular clusters as targets for
microlensing searches. Such searches will be challenging and require more
powerful telescopes than now employed, but are feasible in the 0 future.
Although expected event rates are low, we show that the wide variety of lines
of sight to globular clusters greatly enhances the ability to distinguish
between halo models using microlensing observations as compared to LMC/SMC
observations alone.",9710251v1
2002-12-17,An Intrinsic Baldwin Effect in the H-beta Broad Emission Line in the Spectrum of NGC 5548,"We investigate the possibility of an intrinsic Baldwin Effect (i.e.,nonlinear
emission-line response to continuum variations) in the broad H-beta emission
line of the active galaxy NGC 5548 using cross-correlation techniques to remove
light travel-time effects from the data. We find a nonlinear relationship
between the H-beta emission line and continuum fluxes that is in good agreement
with theoretical predictions. We suggest that similar analysis of multiple
lines might provide a useful diagnostic of physical conditions in the
broad-line region.",0212379v1
2002-12-28,Detecting supersymmetric dark matter in M31 with CELESTE ?,"It is widely believed that dark matter exists within galaxies and clusters of
galaxies. Under the assumption that this dark matter is composed of the
lightest, stable supersymmetric particle, assumed to be the neutralino, the
feasibility of its indirect detection via observations of a diffuse gamma-ray
signal due to neutralino annihilation within M31 is examined.",0212560v1
2003-03-18,Model-Independent Reionization Observables in the CMB,"We represent the reionization history of the universe as a free function in
redshift and study the potential for its extraction from CMB polarization
spectra. From a principal component analysis, we show that the ionization
history information is contained in 5 modes, resembling low-order Fourier modes
in redshift space. The amplitude of these modes represent a compact description
of the observable properties of reionization in the CMB, easily predicted given
a model for the ionization fraction. Measurement of these modes can ultimately
constrain the total optical depth, or equivalently the initial amplitude of
fluctuations to the 1% level regardless of the true model for reionization.",0303400v1
2006-05-08,Discovery of an Extended Halo of Metal-poor Stars in the Andromeda Spiral Galaxy,This paper has been withdrawn. Please see astro-ph/0502366.,0605172v3
1995-01-02,Dynamics of homogeneous magnetizations in strong transverse driving fields,"Spatially homogeneous solutions of the Landau--Lifshitz--Gilbert equation are
analysed. The conservative as well as the dissipative case is considered
explicitly. For the linearly polarized driven Hamiltonian system we apply
canonical perturbation theory to uncover the main resonances as well as the
global phase space structure. In the case of circularly polarized driven
dissipative motion we present the complete bifurcation diagram including
bifurcations up to codimension three.",9501002v1
2000-09-18,Electronic properties of the degenerate Hubbard Model : A dynamical mean field approach,"We have investigated electronic properties of the degenerate multi-orbital
Hubbard model, in the limit of large spatial dimension. A new local model,
including a doubly degenerate strongly correlated site has been introduced and
solved in the framework of the non-crossing approximation (NCA). Mott-Hubbard
transitions have been examined in details, including the calculation of Coulomb
repulsion critical values and electronic densities of states for any regime of
parameters.",0009253v1
2001-01-11,Theoretical and Experimental Approach to Spin Dynamics in Thin Magnetic Films,"The Landau-Lifshitz (L-L) equation describing the time dependence of the
magnetisation vector is numerically integrated fully without any simplifying
assumptions in the time domain and the magnetisation time series obtained is
Fourier transformed (FFT) to yield the permeability spectrum up to 10 GHz. The
non linear results are compared to the experimental results obtained on
magnetic amorphous thin films of Co-Zr, Co-Zr-Re. We analyse our results with
the frequency response obtained directly from the Landau-Lifshitz equation as
well as with the second order Gilbert frequency response.",0101154v1
2004-08-13,Finite lattice size effect in the ground state phase diagram of quasi-two-dimensional magnetic dipolar dots array with perpendicular anisotropy,"A prototype Hamiltonian for the generic patterned magnetic structures, of
dipolar interaction with perpendicular anisotropy, is investigated within the
finite-size framework by Landau-Lifshift-Gilbert classical spin dynamics.
Modifications on the ground state phase diagram are discussed with an emphasis
on the disappearance of continuous degeneracy in the ground state of in-plane
phase due to the finite lattice size effect. The symmetry-governed ground state
evolution upon the lattice size increase provides a critical insight into the
systematic transition to the infinite extreme.",0408324v1
2004-10-01,Current-spin coupling for ferromagnetic domain walls in fine wires,"The coupling between a current and a domain wall is examined. In the presence
of a finite current and the absence of a potential which breaks the
translational symmetry, there is a perfect transfer of angular momentum from
the conduction electrons to the wall. As a result, the ground state is in
uniform motion. This remains the case when relaxation is accounted for. This is
described by, appropriately modified, Landau-Lifshitz-Gilbert equations.",0410035v1
2004-12-17,Hysteresis loops of magnetic thin films with perpendicular anisotropy,"We model the magnetization of quasi two-dimensional systems with easy
perpendicular (z-)axis anisotropy upon change of external magnetic field along
z. The model is derived from the Landau-Lifshitz-Gilbert equation for
magnetization evolution, written in closed form in terms of the z component of
the magnetization only. The model includes--in addition to the external
field--magnetic exchange, dipolar interactions and structural disorder. The
phase diagram in the disorder/interaction strength plane is presented, and the
different qualitative regimes are analyzed. The results compare very well with
observed experimental hysteresis loops and spatial magnetization patterns, as
for instance for the case of Co-Pt multilayers.",0412461v1
2006-01-11,Relaxing-Precessional Magnetization Switching,"A new way of magnetization switching employing both the spin-transfer torque
and the torque by a magnetic field is proposed. The solution of the
Landau-Lifshitz-Gilbert equation shows that the dynamics of the magnetization
in the initial stage of the switching is similar to that in the precessional
switching, while that in the final stage is rather similar to the relaxing
switching. We call the present method the relaxing-precessional switching. It
offers a faster and lower-power-consuming way of switching than the relaxing
switching and a more controllable way than the precessional switching.",0601227v1
2006-04-01,Magnetization reversal through synchronization with a microwave,"Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a
circularly-polarized microwave can reverse the magnetization of a Stoner
particle through synchronization. In comparison with magnetization reversal
induced by a static magnetic field, it can be shown that when a proper
microwave frequency is used the minimal switching field is much smaller than
that of precessional magnetization reversal. A microwave needs only to overcome
the energy dissipation of a Stoner particle in order to reverse magnetization
unlike the conventional method with a static magnetic field where the switching
field must be of the order of magnetic anisotropy.",0604013v1
2006-05-25,Time Quantified Monte Carlo Algorithm for Interacting Spin Array Micromagnetic Dynamics,"In this paper, we reexamine the validity of using time quantified Monte Carlo
(TQMC) method [Phys. Rev. Lett. 84, 163 (2000); Phys. Rev. Lett. 96, 067208
(2006)] in simulating the stochastic dynamics of interacting magnetic
nanoparticles. The Fokker-Planck coefficients corresponding to both TQMC and
Langevin dynamical equation (Landau-Lifshitz-Gilbert, LLG) are derived and
compared in the presence of interparticle interactions. The time quantification
factor is obtained and justified. Numerical verification is shown by using TQMC
and Langevin methods in analyzing spin-wave dispersion in a linear array of
magnetic nanoparticles.",0605621v1
2006-06-26,Self Consistent NEGF-LLG Model for Spin-Torque Based Devices,"We present here a self consistent solution of quantum transport, using the
Non Equilibrium Green's Function (NEGF) method, and magnetization dynamics,
using the Landau-Lifshitz-Gilbert (LLG) formulation. We have applied this model
to study current induced magnetic switching due to `spin torque' in a device
where the electronic transport is ballistic and the free magnetic layer is
sandwiched between two anti-parallel ferromagnetic contacts. The device shows
clear hysteretic current-voltage characteristics, at room temperature, with a
sharp transition between the bistable states and hence can be used as a
non-volatile memory. We show that the proposed design may allow reducing the
switching current by an order of magnitude.",0606648v2
2006-07-25,Thermally-Assisted Current-Driven Domain Wall Motion,"Starting from the stochastic Landau-Lifschitz-Gilbert equation, we derive
Langevin equations that describe the nonzero-temperature dynamics of a rigid
domain wall. We derive an expression for the average drift velocity of the
domain wall as a function of the applied current, and find qualitative
agreement with recent magnetic semiconductor experiments. Our model implies
that at any nonzero temperature the average domain-wall velocity initially
varies linearly with current, even in the absence of non-adiabatic spin
torques.",0607663v1
2006-09-08,Large cone angle magnetization precession of an individual nanomagnet with dc electrical detection,"We demonstrate on-chip resonant driving of large cone-angle magnetization
precession of an individual nanoscale permalloy element. Strong driving is
realized by locating the element in close proximity to the shorted end of a
coplanar strip waveguide, which generates a microwave magnetic field. We used a
microwave frequency modulation method to accurately measure resonant changes of
the dc anisotropic magnetoresistance. Precession cone angles up to $9^{0}$ are
determined with better than one degree of resolution. The resonance peak shape
is well-described by the Landau-Lifshitz-Gilbert equation.",0609190v1
2006-12-30,Low relaxation rate in a low-Z alloy of iron,"The longest relaxation time and sharpest frequency content in ferromagnetic
precession is determined by the intrinsic (Gilbert) relaxation rate \emph{$G$}.
For many years, pure iron (Fe) has had the lowest known value of $G=\textrm{57
Mhz}$ for all pure ferromagnetic metals or binary alloys. We show that an
epitaxial iron alloy with vanadium (V) possesses values of $G$ which are
significantly reduced, to 35$\pm$5 Mhz at 27% V. The result can be understood
as the role of spin-orbit coupling in generating relaxation, reduced through
the atomic number $Z$.",0701004v1
2004-09-07,Distance properties of expander codes,"We study the minimum distance of codes defined on bipartite graphs. Weight
spectrum and the minimum distance of a random ensemble of such codes are
computed. It is shown that if the vertex codes have minimum distance $\ge 3$,
the overall code is asymptotically good, and sometimes meets the
Gilbert-Varshamov bound.
  Constructive families of expander codes are presented whose minimum distance
asymptotically exceeds the product bound for all code rates between 0 and 1.",0409010v1
1996-06-11,Radiative corrections to $e^+e^-\to H^+ H^-$,"We study the 1-loop corrections to the charged Higgs production both in the
Minimal Supersymmetric Standard Model (MSSM) and in a more general type II
two-Higgs-doublet model (THDM-II). We consider the full set of corrections
(including soft photon contributions as well as box diagrams), and define a
parametrization that allows a comparison between the two models. Besides the
soft photon radiation there can be prominent model-dependent effects.",9606300v1
1997-05-15,Analytic constraints from electroweak symmetry breaking in the MSSM,"We report on how a straightforward (albeit technically involved) analytic
study of the 1-loop effective potential in the Minimal Supersymmetric Standard
Model, modifies the usual electroweak symmetry breaking conditions involving
$\tan \beta$ and the other free parameters of the model. The study implies new
constraints which (in contrast with the existing ones like $1 \leq \tan \beta
\leq m_t/m_b$) are fully model-independent and exclude more restrictively a
region around $\tan \beta \sim 1$. Further results of this study will be only
touched upon here.",9705330v1
1998-10-01,Extracting chargino/neutralino mass parameters from physical observables,"I report on two papers, hep-ph/9806279 and hep-ph/9807336, where
complementary strategies are proposed for the determination of the
chargino/neutralino sector parameters, $M_1, M_2, \mu $ and $\tan \beta$, from
the knowledge of some physical observables. This determination and the
occurrence of possible ambiguities are studied as far as possible analytically
within the context of the unconstrained MSSM, assuming however no CP-violation.",9810214v1
1999-12-28,Associated H$^{-}$ W$^{+}$ Production in High Energy $e^+e^-$ Collisions,"We study the associated production of charged Higgs bosons with $W$ gauge
bosons in high energy $e^+ e^-$ collisions at the one loop level. We present
the analytical results and give a detailed discussion for the total cross
section predicted in the context of a general Two Higgs Doublet Model (THDM).",9912527v2
2001-03-25,"Comment on ``Infrared Fixed Point Structure in Minimal Supersymmetric Standard Model with Baryon and Lepton Number Violation""","We reconsider the Infrared Quasi Fixed Points which were studied recently in
the literature in the context of the Baryon and Lepton number violating Minimal
Supersymmetric Standard Model (hep-ph/0011274). The complete analysis requires
further care and reveals more structure than what was previously shown. The
formalism we develop here is quite general, and can be readily applied to a
large class of models.",0103270v1
1991-11-21,"""the Instability of String-Theoretic Black Holes""","It is demonstrated that static, charged, spherically--symmetric black holes
in string theory are classically and catastrophically unstable to linearized
perturbations in four dimensions, and moreover that unstable modes appear for
arbitrarily small positive values of the charge. This catastrophic classical
instability dominates and is distinct from much smaller and less significant
effects such as possible quantum mechanical evaporation. The classical
instability of the string--theoretic black hole contrasts sharply with the
situation which obtains for the Reissner--Nordstr\""om black hole of general
relativity, which has been shown by Chandrasekhar to be perfectly stable to
linearized perturbations at the event horizon.",9111042v1
1997-12-09,The combinatorics of biased riffle shuffles,"This paper studies biased riffle shuffles, first defined by Diaconis, Fill,
and Pitman. These shuffles generalize the well-studied Gilbert-Shannon-Reeds
shuffle and convolve nicely. An upper bound is given for the time for these
shuffles to converge to the uniform distribution; this matches lower bounds of
Lalley. A careful version of a bijection of Gessel leads to a generating
function for cycle structure after one of these shuffles and gives new results
about descents in random permutations. Results are also obtained about the
inversion and descent structure of a permutation after one of these shuffles.",9712240v1
2000-08-16,Homotopies and automorphisms of crossed modules of groupoids,"We give a detailed description of the structure of the actor 2-crossed module
related to the automorphisms of a crossed module of groupoids. This generalises
work of Brown and Gilbert for the case of crossed modules of groups, and part
of this is needed for work on 2-dimensional holonomy to be developed elsewhere
(see math.DG/0009082).",0008117v2
2005-06-14,Transitive and Self-dual Codes Attaining the Tsfasman-Vladut-Zink Bound,"We introduce - as a generalization of cyclic codes - the notion of transitive
codes, and we show that the class of transitive codes is asymptotically good.
Even more, transitive codes attain the Tsfasman-Vladut-Zink bound over F_q, for
all aquares q=l^2. We also show that self-orthogonal and self-dual codes attain
the Tsfasman-Vladut-Zink bound, thus improving previous results about self-dual
codes attaining the Gilbert-Varshamov bound. The main tool is a new
asymptotically optimal tower (E_n) of function fields over F_q where all
extensions E_n/E_0 are Galois.",0506264v1
2005-09-01,Counting unlabelled toroidal graphs with no K33-subdivisions,"We provide a description of unlabelled enumeration techniques, with complete
proofs, for graphs that can be canonically obtained by substituting 2-pole
networks for the edges of core graphs. Using structure theorems for toroidal
and projective-planar graphs containing no K33-subdivisions, we apply these
techniques to obtain their unlabelled enumeration.",0509004v2
2006-05-19,Deformation spaces of trees,"Let G be a finitely generated group. Two simplicial G-trees are said to be in
the same deformation space if they have the same elliptic subgroups (if H fixes
a point in one tree, it also does in the other). Examples include
Culler-Vogtmann's outer space, and spaces of JSJ decompositions. We discuss
what features are common to trees in a given deformation space, how to pass
from one tree to all other trees in its deformation space, and the topology of
deformation spaces. In particular, we prove that all deformation spaces are
contractible complexes.",0605545v2
1999-10-12,"Uniform spectral properties of one-dimensional quasicrystals, III. $α$-continuity","We study the spectral properties of discrete one-dimensional Schr\""odinger
operators with Sturmian potentials. It is shown that the point spectrum is
always empty. Moreover, for rotation numbers with bounded density, we establish
purely $\alpha$-continuous spectrum, uniformly for all phases. The proofs rely
on the unique decomposition property of Sturmian potentials, a
mass-reproduction technique based upon a Gordon-type argument, and on the
Jitomirskaya-Last extension of the Gilbert-Pearson theory of subordinacy.",9910017v1
2003-08-18,Vector Coherent States on Clifford algebras,"The well-known canonical coherent states are expressed as an infinite series
in powers of a complex number $z$ together with a positive sequence of real
numbers $\rho(m)=m$. In this article, in analogy with the canonical coherent
states, we present a class of vector coherent states by replacing the complex
variable $z$ by a real Clifford matrix. We also present another class of vector
coherent states by simultaneously replacing $z$ by a real Clifford matrix and
$\rho(m)$ by a real matrix. As examples, we present vector coherent states on
quaternions and octonions with their real matrix representations.",0308020v2
2000-07-10,Fractal Dimensions of the Hydrodynamic Modes of Diffusion,"We consider the time-dependent statistical distributions of diffusive
processes in relaxation to a stationary state for simple, two dimensional
chaotic models based upon random walks on a line. We show that the cumulative
functions of the hydrodynamic modes of diffusion form fractal curves in the
complex plane, with a Hausdorff dimension larger than one. In the limit of
vanishing wavenumber, we derive a simple expression of the diffusion
coefficient in terms of this Hausdorff dimension and the positive Lyapunov
exponent of the chaotic model.",0007008v1
2000-10-06,The Fractality of the Hydrodynamic Modes of Diffusion,"Transport by normal diffusion can be decomposed into the so-called
hydrodynamic modes which relax exponentially toward the equilibrium state. In
chaotic systems with two degrees of freedom, the fine scale structure of these
hydrodynamic modes is singular and fractal. We characterize them by their
Hausdorff dimension which is given in terms of Ruelle's topological pressure.
For long-wavelength modes, we derive a striking relation between the Hausdorff
dimension, the diffusion coefficient, and the positive Lyapunov exponent of the
system. This relation is tested numerically on two chaotic systems exhibiting
diffusion, both periodic Lorentz gases, one with hard repulsive forces, the
other with attractive, Yukawa forces. The agreement of the data with the theory
is excellent.",0010017v1
2007-01-12,Non-equilibrium Lorentz gas on a curved space,"The periodic Lorentz gas with external field and iso-kinetic thermostat is
equivalent, by conformal transformation, to a billiard with expanding
phase-space and slightly distorted scatterers, for which the trajectories are
straight lines. A further time rescaling allows to keep the speed constant in
that new geometry. In the hyperbolic regime, the stationary state of this
billiard is characterized by a phase-space contraction rate, equal to that of
the iso-kinetic Lorentz gas. In contrast to the iso-kinetic Lorentz gas where
phase-space contraction occurs in the bulk, the phase-space contraction rate
here takes place at the periodic boundaries.",0701024v1
1998-05-29,Atom cooling and trapping by disorder,"We demonstrate the possibility of three-dimensional cooling of neutral atoms
by illuminating them with two counterpropagating laser beams of mutually
orthogonal linear polarization, where one of the lasers is a speckle field,
i.e. a highly disordered but stationary coherent light field. This
configuration gives rise to atom cooling in the transverse plane via a Sisyphus
cooling mechanism similar to the one known in standard two-dimensional optical
lattices formed by several plane laser waves. However, striking differences
occur in the spatial diffusion coefficients as well as in local properties of
the trapped atoms.",9805037v1
2006-02-23,Equivalence of two mathematical forms for the bound angular momentum of the electromagnetic field,"It is shown that the mathematical form, obtained in a recent paper, for the
angular momentum of the electromagnetic field in the vicinity of electric
charge is equivalent to another form obtained previously by Cohen-Tannoudji,
Dupont-Roc and Gilbert. In this version of the paper an improved derivation is
given.",0602157v3
2006-10-13,Senescence Can Explain Microbial Persistence,"It has been known for many years that small fractions of persister cells
resist killing in many bacterial colony-antimicrobial confrontations. These
persisters are not believed to be mutants. Rather it has been hypothesized that
they are phenotypic variants. Current models allow cells to switch in and out
of the persister phenotype. Here we suggest a different explanation, namely
senescence, for persister formation. Using a mathematical model including age
structure, we show that senescence provides a natural explanation for
persister-related phenomena including the observations that persister fraction
depends on growth phase in batch culture and dilution rate in continuous
culture.",0610026v1
2002-12-30,Dark propagation modes in optical lattices,"We examine the stimulated light scattering onto the propagation modes of a
dissipative optical lattice. We show that two different pump-probe
configurations may lead to the excitation, via different mechanisms, of the
same mode. We found that in one configuration the scattering on the propagation
mode results in a resonance in the probe transmission spectrum while in the
other configuration no modification of the scattering spectrum occurs, i.e. the
mode is dark. A theoretical explanation of this behaviour is provided.",0212157v1
2003-09-29,Phase-control of directed diffusion in a symmetric optical lattice,"We demonstrate the phenomenon of directed diffusion in a symmetric periodic
potential. This has been realized with cold atoms in a one-dimensional
dissipative optical lattice. The stochastic process of optical pumping leads to
a diffusive dynamics of the atoms through the periodic structure, while a
zero-mean force which breaks the temporal symmetry of the system is applied by
phase-modulating one of the lattice beams. The atoms are set into directed
motion as a result of the breaking of the temporal symmetry of the system.",0309208v1
2003-09-29,Synchronization of Hamiltonian motion and dissipative effects in optical lattices: Evidence for a stochastic resonance,"We theoretically study the influence of the noise strength on the excitation
of the Brillouin propagation modes in a dissipative optical lattice. We show
that the excitation has a resonant behavior for a specific amount of noise
corresponding to the precise synchronization of the Hamiltonian motion on the
optical potential surfaces and the dissipative effects associated with optical
pumping in the lattice. This corresponds to the phenomenon of stochastic
resonance. Our results are obtained by numerical simulations and correspond to
the analysis of microscopic quantities (atomic spatial distributions) as well
as macroscopic quantities (enhancement of spatial diffusion and pump-probe
spectra). We also present a simple analytical model in excellent agreement with
the simulations.",0309210v1
2006-06-23,Playing Quantum Physics Jeopardy with zero-energy eigenstates,"We describe an example of an exact, quantitative Jeopardy-type quantum
mechanics problem. This problem type is based on the conditions in
one-dimensional quantum systems that allow an energy eigenstate for the
infinite square well to have zero curvature and zero energy when suitable Dirac
delta functions are added. This condition and its solution are not often
discussed in quantum mechanics texts and have interesting pedagogical
consequences.",0606196v1
2006-10-18,Subsystem Codes,"We investigate various aspects of operator quantum error-correcting codes or,
as we prefer to call them, subsystem codes. We give various methods to derive
subsystem codes from classical codes. We give a proof for the existence of
subsystem codes using a counting argument similar to the quantum
Gilbert-Varshamov bound. We derive linear programming bounds and other upper
bounds. We answer the question whether or not there exist
[[n,n-2d+2,r>0,d]]<sub>q</sub> subsystem codes. Finally, we compare stabilizer
and subsystem codes with respect to the required number of syndrome qudits.",0610153v1
2007-05-14,The dynamical response to the node defect in thermally activated remagnetization of magnetic dot array,"The influence of nonmagnetic central node defect on dynamical properties of
regular square-shaped 5 x 5 segment of magnetic dot array under the thermal
activation is investigated via computer simulations. Using stochastic
Landau-Lifshitz-Gilbert equation we simulate hysteresis and relaxation
processes. The remarkable quantitative and qualitative differences between
magnetic dot arrays with nonmagnetic central node defect and magnetic dot
arrays without defects have been found.",0705.1889v1
2007-05-18,Steady-state conduction in self-similar billiards,"The self-similar Lorentz billiard channel is a spatially extended
deterministic dynamical system which consists of an infinite one-dimensional
sequence of cells whose sizes increase monotonically according to their
indices. This special geometry induces a nonequilibrium stationary state with
particles flowing steadily from the small to the large scales. The
corresponding invariant measure has fractal properties reflected by the
phase-space contraction rate of the dynamics restricted to a single cell with
appropriate boundary conditions. In the near-equilibrium limit, we find
numerical agreement between this quantity and the entropy production rate as
specified by thermodynamics.",0705.2758v1
2007-06-04,Generation of microwave radiation in planar spin-transfer devices,"Current induced precession states in spin-transfer devices are studied in the
case of large easy plane anisotropy (present in most experimental setups). It
is shown that the effective one-dimensional planar description provides a
simple qualitative understanding of the emergence and evolution of such states.
Switching boundaries are found analytically for the collinear device and the
spin-flip transistor. The latter can generate microwave oscillations at zero
external magnetic field without either special functional form of spin-transfer
torque, or ``field-like'' terms, if Gilbert constant corresponds to the
overdamped planar regime.",0706.0529v1
2007-12-26,Mass and angular-momentum inequalities for axi-symmetric initial data sets. II. Angular-momentum,"We extend the validity of Dain's angular-momentum inequality to maximal,
asymptotically flat, initial data sets on a simply connected manifold with
several asymptotically flat ends which are invariant under a U(1) action and
which admit a twist potential.",0712.4064v2
2008-01-28,TER: A Robot for Remote Ultrasonic Examination: Experimental Evaluations,"This chapter:
  o Motivates the clinical use of robotic tele-echography
  o Introduces the TER system
  o Describes technical and clinical evaluations performed with TER",0801.4355v1
2008-03-14,Spin-torque shot noise in magnetic tunnel junctions,"Spin polarized current may transfer angular momentum to a ferromagnet,
resulting in a spin-torque phenomenon. At the same time the shot noise,
associated with the current, leads to a non-equilibrium stochastic force acting
on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert
equation for a magnetization of a ''free'' ferromagnetic layer in contact with
a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and
show that the non-equilibrium noise yields to a non-monotonous dependence of
the precession spectrum linewidth on the current.",0803.2101v1
2008-04-07,Paired Orbitals for Different Spins equations,"Eigenvalue-type equations for Lowdin-Amos-Hall spin-paired (corresponding)
orbitals are developed to provide an alternative to the standard spin-polarized
Hartree-Fock or Kohn-Sham equations. Obtained equations are non-canonical
unrestricted Hartree-Fock-type equations in which non-canonical orbitals are
fixed to be biorthogonal spin-paired orbitals. To derive paired orbitals for
different spins (PODS) equations there has been applied Adams-Gilbert
localizing operator approach. PODS equations are especially useful for
treatment of the broken-symmetry solutions for antiferromagnetic materials.",0804.0967v1
2008-04-26,Spin-torque oscillator based on tilted magnetization of the fixed layer,"The spin torque oscillator (STO), where the magnetization of the fixed layer
is tilted out of the film plane, is capable of strong microwave signal
generation in zero magnetic field. Through numerical simulations of the
Landau-Lifshitz-Gilbert-Slonczewski equations, within a macro-spin
approximation, we study the microwave signal generation as a function of drive
current for two realistic tilt angles. The tilt magnetization of the fixed
layer can be achieved by using a material with high out-of-plane
magnetocrystalline anisotropy, such as L10 FePt.",0804.4213v1
2008-07-11,Superconductivity up to 29 K in SrFe2As2 and BaFe2As2 at high pressures,"We report the discovery of superconductivity at high pressure in SrFe2As2 and
BaFe2As2. The superconducting transition temperatures are up to 27 K in
SrFe2As2 and 29 K in BaFe2As2, making these the highest pressure-induced
superconducting materials discovered thus far.",0807.1896v2
2008-07-14,An Adaptive Entanglement Distillation Scheme Using Quantum Low Density Parity Check Codes,"Quantum low density parity check (QLDPC) codes are useful primitives for
quantum information processing because they can be encoded and decoded
efficiently. Besides, the error correcting capability of a few QLDPC codes
exceeds the quantum Gilbert-Varshamov bound. Here, we report a numerical
performance analysis of an adaptive entanglement distillation scheme using
QLDPC codes. In particular, we find that the expected yield of our adaptive
distillation scheme to combat depolarization errors exceed that of Leung and
Shor whenever the error probability is less than about 0.07 or greater than
about 0.28. This finding illustrates the effectiveness of using QLDPC codes in
entanglement distillation.",0807.2122v1
2008-07-16,Analytical solution of the equation of motion for a rigid domain wall in a magnetic material with perpendicular anisotropy,"This paper reports the solution of the equation of motion for a domain wall
in a magnetic material which exhibits high magneto-crystalline anisotropy.
Starting from the Landau-Lifschitz-Gilbert equation for field-induced motion,
we solve the equation to give an analytical expression, which specifies the
domain wall position as a function of time. Taking parameters from a Co/Pt
multilayer system, we find good quantitative agreement between calculated and
experimentally determined wall velocities, and show that high field uniform
wall motion occurs when wall rigidity is assumed.",0807.2604v3
2008-07-16,A graphical extension for the Windows version of the Parallel Finite Element Micromagnetics Package (MagParExt),"In the current paper we present a graphical user interface useful for
settings input parameter of the Windows precompiled binaries for the Parallel
Finite Element Micromagnetics Package (MagPar). The Package is used for
magnetization dynamics analysis on a base of the Landau-Lifshitz-Gilbert (LLG)
equation. In an available version of the MagPar package there are several text
files which control simulations. Presented here graphical extension (MagParExt)
enables easy preparation of input and output data, stored in text files, and
additionally, direct and fast creation of figures obtained from dependencies
between simulated physical quantities.",0807.2655v1
2008-08-17,Attempt frequency of magnetization in nanomagnets with thin-film geometry,"Solving the stochastic Landau-Lifshitz-Gilbert equation numerically, we
investigate the effect of the potential landscape on the attempt frequency of
magnetization in nanomagnets with the thin-film geometry. Numerical estimates
of the attempt frequency are analyzed in comparison with theoretical
predictions from the Fokker-Planck equation for the Neel-Brown model. It is
found that for a nanomagnet with the thin-film geometry, theoretically
predicted values for the universal case are in excellent agreement with
numerical estimates.",0808.2281v1
2008-08-30,Path integral study of the role of correlation in exchange coupling of spins in double quantum dots and optical lattices,"We explore exchange coupling of a pair of spins in a double dot and in an
optical lattice. Our algorithm uses the frequency of exchanges in a bosonic
path integral, evaluated with Monte Carlo. This algorithm is simple enough to
be a ""black box"" calculator, yet gives insights into the role of correlation
through two-particle probability densities, visualization of instantons, and
pair correlation functions. We map the problem to Hubbard model and see that
exchange and correlation renormalize the effective parameters, dramatically
lowering U at larger separations.",0809.0038v1
2008-09-16,Stochastic dynamics of magnetization in a ferromagnetic nanoparticle out of equilibrium,"We consider a small metallic particle (quantum dot) where ferromagnetism
arises as a consequence of Stoner instability. When the particle is connected
to electrodes, exchange of electrons between the particle and the electrodes
leads to a temperature- and bias-driven Brownian motion of the direction of the
particle magnetization. Under certain conditions this Brownian motion is
described by the stochastic Landau-Lifshitz-Gilbert equation. As an example of
its application, we calculate the frequency-dependent magnetic susceptibility
of the particle in a constant external magnetic field, which is relevant for
ferromagnetic resonance measurements.",0809.2611v1
2008-12-09,On densest packings of equal balls of $\rb^{n}$ and Marcinkiewicz spaces,"We investigate, by ""a la Marcinkiewicz"" techniques applied to the
(asymptotic) density function, how dense systems of equal spheres of $\rb^{n},
n \geq 1,$ can be partitioned at infinity in order to allow the computation of
their density as a true limit and not a limsup. The density of a packing of
equal balls is the norm 1 of the characteristic function of the systems of
balls in the sense of Marcinkiewicz. Existence Theorems for densest sphere
packings and completely saturated sphere packings of maximal density are given
new direct proofs.",0812.1720v1
2009-01-26,Bioprotectant glassforming solutions confined in porous silicon nanocapillaries,"Glycerol and trehalose-glycerol binary solutions are glass-forming liquids
with remarkable bioprotectant properties. In this paper, we address the effects
of confining of these solutions in straight channels of diameter D=8 nm formed
by porous silicon. Neutron diffraction and incoherent quasielastic neutron
scattering are used to reveal the different effects of nanoconfinement and
addition of trehalose on the intermolecular structure and molecular dynamics of
the liquid and glassy phases, on a nanosecond timescale.",0901.3994v1
2009-02-12,Computing equations for residually free groups,"We show that there is no algorithm deciding whether the maximal residually
free quotient of a given finitely presented group is finitely presentable or
not.
  Given a finitely generated subgroup G of a finite product of limit groups, we
discuss the possibility of finding an explicit set of defining equations (i.e.
of expressing G as the maximal residually free quotient of an explicit finitely
presented group).",0902.2119v2
2009-03-06,Simulation of current-induced microwave oscillation in geometrically confined domain wall,"We studied magnetization dynamics of a geometrically confined domain wall
under dc current by solving simultaneously the Landau-Lifshitz-Gilbert equation
and diffusion equation for spin accumulation. We showed that the oscillation
motion of the domain wall is driven by the spin-transfer torque and the dc
current is converted to the ac voltage signal. The results means that the
geometrically confined domain wall is applicable as a source of microwave
oscillator.",0903.1151v1
2009-04-05,Projective Space Codes for the Injection Metric,"In the context of error control in random linear network coding, it is useful
to construct codes that comprise well-separated collections of subspaces of a
vector space over a finite field. In this paper, the metric used is the
so-called ""injection distance"", introduced by Silva and Kschischang. A
Gilbert-Varshamov bound for such codes is derived. Using the code-construction
framework of Etzion and Silberstein, new non-constant-dimension codes are
constructed; these codes contain more codewords than comparable codes designed
for the subspace metric.",0904.0813v2
2009-05-28,Hamilton cycles in random geometric graphs,"We prove that, in the Gilbert model for a random geometric graph, almost
every graph becomes Hamiltonian exactly when it first becomes 2-connected. This
answers a question of Penrose. We also show that in the k-nearest neighbor
model, there is a constant \kappa\ such that almost every \kappa-connected
graph has a Hamilton cycle.",0905.4650v2
2009-06-25,Nonlinear Schroedinger-Poisson Theory for Quantum-Dot Helium,"We use a nonlinear Schroedinger-Poisson equation to describe two interacting
electrons with opposite spins confined in a parabolic potential, a quantum dot.
We propose an effective form of the Poisson equation taking into account the
dimensional mismatch of the two-dimensional electronic system and the
three-dimensional electrostatics. The results agree with earlier numerical
calculations performed in a large basis of two-body states and provide a simple
model for continuous quantum-classical transition with increasing nonlinearity.
Specific intriguing properties due to eigenstate non-orthogonality are
emphasized.",0906.4650v1
2009-06-29,Performance of Magnetic Quantum Cellular Automata and Limitations due to Thermal Noise,"Operation parameters of magnetic quantum cellular automata are evaluated for
the purposes of reliable logic operation. The dynamics of the nanomagnets is
simulated via the Landau-Lifshitz-Gilbert equations with a stochastic magnetic
field corresponding to thermal fluctuations. It is found that in the macrospin
approximation the switching speed does not change under scaling of both size
and distances between nanomagnets. Thermal fluctuations put a limitation on the
size of nanomagnets, since the gate error rate becomes excessive for
nanomagnets smaller than 200nm at room temperature.",0906.5172v1
2009-09-15,Critical current density for spin transfer torque switching with composite free layer structure,"Critical current density of composite free layer (CFL) in magnetic tunneling
junction is investigated. CFL consists of two exchange coupled ferromagnetic
layers, where the coupling is parallel or anti-parallel. Instability condition
of the CFL under the spin transfer torque, which is related with critical
current density, is obtained by analytic spin wave excitation model and
confirmed by macro-spin Landau-Lifshitz-Gilbert equation. The critical current
densities for the coupled two identical layers are investigated with various
coupling strengths, and spin transfer torque efficiencies.",0909.2711v1
2009-09-25,Tunable steady-state domain wall oscillator with perpendicular magnetic anisotropy,"We theoretically study domain wall oscillations upon the injection of a dc
current through a geometrically constrained wire with perpendicular magnetic
anisotropy. The oscillation frequency spectrum can be tuned by the injected
current density, but additionally by the application of an external magnetic
field independent of the power. The results of analytical calculations are
supported by micromagnetic simulations based on the Landau-Lifshitz-Gilbert
equation. The simple concept of our localized steady-state oscillator might
prove useful as a nanoscale microwave generator with possible applications in
telecommunication or for rf-assisted writing in magnetic hard drives.",0909.4733v1
2009-10-13,Dipolar field effect on microwave oscillation in a domain wall spin-valve,"We examined dipolar field effects on the microwave generation in the domain
wall spin-valve by solving simultaneously the Landau-Lifshitz-Gilbert and
Zhang-Levy-Fert diffusion equations. By numerically analyzing dipolar field
dependence, we showed that the microwave generation needs the dipole-dipole
interaction for a 180$^\circ$ domain wall and the amplitude of the microwave
voltage signal depends strongly on the exchange length. In order to design a
microwave generator using the domain wall spin-valve with high efficiency, we
propose that the materials with short exchange length are preferred.",0910.2280v1
2009-10-30,Dissipative dynamics of magnetic solitons in metals,"Soliton dynamics in spin-textured metals generate electrical currents, which
produce backaction through spin torques. We modify the Landau-Lifshitz-Gilbert
equation and the corresponding solitonic equations of motion to include such
higher-order texture effects. We also find a quasistatic equation for the
induced electrochemical potential, which needs to be solved for
self-consistently, in the incompressible limit. As an example, we consider the
orbital motion of a vortex in a point-contact spin valve, and discuss
modifications of orbit radius, frequency, and dissipation power.",0910.5912v2
2009-11-16,"JSJ decompositions: definitions, existence, uniqueness. I: The JSJ deformation space","This paper and its companion arXiv:1002.4564 have been replaced by
arXiv:1602.05139.
  We give a general simple definition of JSJ decompositions by means of a
universal maximality property. The JSJ decomposition should not be viewed as a
tree (which is not uniquely defined) but as a canonical deformation space of
trees. We prove that JSJ decompositions of finitely presented groups always
exist, without any assumption on edge groups. Many examples are given.",0911.3173v3
2010-02-15,Domain wall motion in ferromagnetic nanowires driven by arbitrary time-dependent fields: An exact result,"We address the dynamics of magnetic domain walls in ferromagnetic nanowires
under the influence of external time-dependent magnetic fields. We report a new
exact spatiotemporal solution of the Landau-Lifshitz-Gilbert equation for the
case of soft ferromagnetic wires and nanostructures with uniaxial anisotropy.
The solution holds for applied fields with arbitrary strength and time
dependence. We further extend this solution to applied fields slowly varying in
space and to multiple domain walls.",1002.2913v1
2010-05-24,SN2010U -- a Luminous Nova in NGC 4214,"The luminosity, light curve, post--maximum spectrum, and lack of a progenitor
on deep pre-outburst images suggest that SN 2010U was a luminous, fast nova.
Its outburst magnitude is consistent with that for a fast nova using the
Maximum Magnitude-Rate of Decline relationship for classical novae.",1005.4356v1
2010-06-11,Highly Parallel Sparse Matrix-Matrix Multiplication,"Generalized sparse matrix-matrix multiplication is a key primitive for many
high performance graph algorithms as well as some linear solvers such as
multigrid. We present the first parallel algorithms that achieve increasing
speedups for an unbounded number of processors. Our algorithms are based on
two-dimensional block distribution of sparse matrices where serial sections use
a novel hypersparse kernel for scalability. We give a state-of-the-art MPI
implementation of one of our algorithms. Our experiments show scaling up to
thousands of processors on a variety of test scenarios.",1006.2183v1
2010-06-24,Boundary regularity for minimizers of the micromagnetic energy functional,"Motivated by the construction of time-periodic solutions for the
three-dimensional Landau-Lifshitz-Gilbert equation in the case of soft and
small ferromagnetic particles, we investigate the regularity properties of
minimizers of the micromagnetic energy functional at the boundary. In
particular, we show that minimizers are regular provided the volume of the
particle is sufficiently small. The approach uses a reflection construction at
the boundary and an adaption of the well-known regularity theory for minimizing
harmonic maps into spheres.",1006.4766v1
2010-06-24,Time-periodic Néel wall motions,"In thin ferromagnetic films, the predominance of the magnetic shape
anisotropy leads to in-plane magnetizations. The simplest domain wall in this
geometry is the one-dimensional Neel wall that connects two magnetizations of
opposite sign by a planar 180 degree rotation. In this paper, we perturb the
static Neel wall profile in order to construct time-periodic Neel wall motions
governed by to the Landau-Lifshitz-Gilbert equation. Our construction works
within a certain parameter regime and requires the restriction to external
magnetic fields with small amplitudes and suitable time averages.",1006.4768v1
2010-06-30,Supercurrent-Induced Magnetization Dynamics,"We investigate supercurrent-induced magnetization dynamics in a Josephson
junction with two misaligned ferromagnetic layers, and demonstrate a variety of
effects by solving numerically the Landau-Lifshitz-Gilbert equation. In
particular, we demonstrate the possibility to obtain supercurrent-induced
magnetization switching for an experimentally feasible set of parameters, and
clarify the favorable condition for the realization of magnetization reversal.
These results constitute a superconducting analogue to conventional
current-induced magnetization dynamics and indicate how spin-triplet
supercurrents may be utilized for practical purposes in spintronics.",1007.0004v1
2010-07-09,Polarization and magnetization dynamics of a field-driven multiferroic structure,"We consider a multiferroic chain with a linear magnetoelectric coupling
induced by the electrostatic screening at the ferroelectric/ferromagnet
interface. We study theoretically the dynamic ferroelectric and magnetic
response to external magnetic and electric fields by utilizing an approach
based on coupled Landau- Khalatnikov and finite-temperature
Landau-Lifshitz-Gilbert equations. Additionally, we compare with Monte Carlo
calculations. It is demonstrated that for material parameters corresponding to
BaTiO3/Fe the polarization and the magnetization are controllable by external
magnetic and electric fields respectively.",1007.1543v1
2010-07-11,Factorization of banded permutations,"We consider the factorization of permutations into bandwidth 1 permutations,
which are products of mutually nonadjacent simple transpositions. We exhibit an
upper bound on the minimal number of such factors and thus prove a conjecture
of Gilbert Strang: a banded permutation of bandwidth $w$ can be represented as
the product of at most $2w-1$ permutations of bandwidth 1. An analogous result
holds also for infinite and cyclically banded permutations.",1007.1760v2
2010-07-14,Nonlinear interference in a mean-field quantum model,"Using similar nonlinear stationary mean-field models for Bose-Einstein
Condensation of cold atoms and interacting electrons in a Quantum Dot, we
propose to describe the original many-particle ground state as a one-particle
statistical mixed state of the nonlinear eigenstates whose weights are provided
by the eigenstate non-orthogonality. We search for physical grounds in the
interpretation of our two main results, namely, quantum-classical nonlinear
transition and interference between nonlinear eigenstates.",1007.2408v1
2011-01-17,Steiner Ratio for Manifolds,"The Steiner ratio characterizes the greatest possible deviation of the length
of a minimal spanning tree from the length of the minimal Steiner tree. In this
paper, estimates of the Steiner ratio on Riemannian manifolds are obtained. As
a corollary, the Steiner ratio for flat tori, flat Klein bottles, and
projective plane of constant positive curvature are computed. Steiner ratio -
Steiner problem - Gilbert--Pollack conjecture - surfaces of constant curvature",1101.3144v1
2011-02-04,Current-induced dynamics of composite free layer with antiferromagnetic interlayer exchange coupling,"Current-induced dynamics in spin valves including composite free layer with
antiferromagnetic interlayer exchange coupling is studied theoretically within
the diffusive transport regime. We show that current-induced dynamics of a
synthetic antiferromagnet is significantly different from dynamics of a
synthetic ferrimagnet. From macrospin simulations we obtain conditions for
switching the composite free layer, as well as for appearance of various
self-sustained dynamical modes. Numerical simulations are compared with simple
analytical models of critical current based on linearized
Landau-Lifshitz-Gilbert equation.",1102.1028v2
2011-04-01,Spin waves cause non-linear friction,"Energy dissipation is studied for a hard magnetic tip that scans a soft
magnetic substrate. The dynamics of the atomic moments are simulated by solving
the Landau-Lifshitz-Gilbert (LLG) equation numerically. The local energy
currents are analysed for the case of a Heisenberg spin chain taken as
substrate. This leads to an explanation for the velocity dependence of the
friction force: The non-linear contribution for high velocities can be
attributed to a spin wave front pushed by the tip along the substrate.",1104.0197v2
2011-05-31,Upper and Lower Bounds on the Minimum Distance of Expander Codes,"The minimum distance of expander codes over GF(q) is studied. A new upper
bound on the minimum distance of expander codes is derived. The bound is shown
to lie under the Varshamov-Gilbert (VG) bound while q >= 32. Lower bounds on
the minimum distance of some families of expander codes are obtained. A lower
bound on the minimum distance of low-density parity-check (LDPC) codes with a
Reed--Solomon constituent code over GF(q) is obtained. The bound is shown to be
very close to the VG bound and to lie above the upper bound for expander codes.",1105.6224v1
2011-06-28,Stability of precessing domain walls in ferromagnetic nanowires,"We show that recently reported precessing solution of Landau-Lifshitz-Gilbert
equations in ferromagnetic nanowires is stable under small perturbations of
initial data, applied field and anisotropy constant. Linear stability is
established analytically, while nonlinear stability is verified numerically.",1106.5808v2
2011-07-01,Current induced magnetization reversal on the surface of a topological insulator,"We study dynamics of the magnetization coupled to the surface Dirac fermions
of a three di- mensional topological insulator. By solving the
Landau-Lifshitz-Gilbert equation in the presence of charge current, we find
current induced magnetization dynamics and discuss the possibility of mag-
netization reversal. The torque from the current injection depends on the
transmission probability through the ferromagnet and shows nontrivial
dependence on the exchange coupling. The mag- netization dynamics is a direct
manifestation of the inverse spin-galvanic effect and hence another ferromagnet
is unnecessary to induce spin transfer torque in contrast to the conventional
setup.",1107.0116v1
2011-08-05,Thermoelectric detection of ferromagnetic resonance of a nanoscale ferromagnet,"We present thermoelectric measurements of the heat dissipated due to
ferromagnetic resonance of a Permalloy strip. A microwave magnetic field,
produced by an on-chip coplanar strip waveguide, is used to drive the
magnetization precession. The generated heat is detected via Seebeck
measurements on a thermocouple connected to the ferromagnet. The observed
resonance peak shape is in agreement with the Landau-Lifshitz-Gilbert equation
and is compared with thermoelectric finite element modeling. Unlike other
methods, this technique is not restricted to electrically conductive media and
is therefore also applicable to for instance ferromagnetic insulators.",1108.1286v1
2011-08-31,Effects of Fermion Flavor on Exciton Condensation in Double Layer Systems,"We use fermionic path integral quantum Monte Carlo to study the effects of
fermion flavor on the physical properties of dipolar exciton condensates in
double layer systems. We find that by including spin in the system weakens the
effective interlayer interaction strength, yet this has very little effect on
the Kosterlitz-Thouless transition temperature. We further find that, to obtain
the correct description of screening, it is necessary to account for
correlation in both the interlayer and intralayer interactions. We show that
while the excitonic binding cannot completely surpress screening by additional
fermion flavors, their screening effectiveness is reduced leading to a much
higher transition temperatures than predicted with large-N analysis.",1108.6107v1
2011-09-30,An ultrafast image recovery and recognition system implemented with nanomagnets possessing biaxial magnetocrystalline anisotropy,"A circular magnetic disk with biaxial magnetocrystalline anisotropy has four
stable magnetization states which can be used to encode a pixel's shade in a
black/gray/white image. By solving the Landau-Lifshitz- Gilbert equation, we
show that if moderate noise deflects the magnetization slightly from a stable
state, it always returns to the original state, thereby automatically
de-noising the corrupted image. The same system can compare a noisy input image
with a stored image and make a matching decision using magneto-tunneling
junctions. These tasks are executed at ultrahigh speeds (~2 ns for a
512\times512 pixel image).",1109.6932v1
2011-11-10,Magnonic band structure of a two-dimensional magnetic superlattice,"The frequencies and linewidths of spin waves in a two-dimensional periodic
superlattice of magnetic materials are found, using the Landau-Lifshitz-Gilbert
equations. The form of the exchange field from a surface-torque-free boundary
between magnetic materials is derived, and magnetic-material combinations are
identified which produce gaps in the magnonic spectrum across the entire
superlattice Brillouin zone for hexagonal and square-symmetry superlattices.",1111.2506v1
2011-11-29,Supercurrent induced domain wall motion,"We study the dynamics of a magnetic domain wall, inserted in, or juxtaposed
to, a conventional superconductor, via the passage of a spin polarized current
through a FSF junction. Solving the Landau-Lifshitz-Gilbert equation of motion
for the magnetic moments we calculate the velocity of the domain wall and
compare it with the case of a FNF junction. We find that in several regimes the
domain wall velocity is larger when it is driven by a supercurrent.",1111.6751v1
2011-12-02,The Main Diagonal of a Permutation Matrix,"By counting 1's in the ""right half"" of $2w$ consecutive rows, we locate the
main diagonal of any doubly infinite permutation matrix with bandwidth $w$.
Then the matrix can be correctly centered and factored into block-diagonal
permutation matrices. Part II of the paper discusses the same questions for the
much larger class of band-dominated matrices. The main diagonal is determined
by the Fredholm index of a singly infinite submatrix. Thus the main diagonal is
determined ""at infinity"" in general, but from only $2w$ rows for banded
permutations.",1112.0582v2
2011-12-11,Stability of the Greedy Algorithm on the Circle,"We consider a single-server system with service stations in each point of the
circle. Customers arrive after exponential times at uniformly-distributed
locations. The server moves at finite speed and adopts a greedy routing
mechanism. It was conjectured by Coffman and Gilbert in~1987 that the service
rate exceeding the arrival rate is a sufficient condition for the system to be
positive recurrent, for any value of the speed. In this paper we show that the
conjecture holds true.",1112.2389v3
2011-12-12,Riffle shuffles with biased cuts,"The well-known Gilbert-Shannon-Reeds model for riffle shuffles assumes that
the cards are initially cut 'about in half' and then riffled together. We
analyze a natural variant where the initial cut is biased. Extending results of
Fulman (1998), we show a sharp cutoff in separation and L-infinity distances.
This analysis is possible due to the close connection between shuffling and
quasisymmetric functions along with some complex analysis of a generating
function.",1112.2650v1
2011-12-15,Solutions of the Fully Compressible Semi-Geostrophic System,"The fully compressible semi-geostrophic system is widely used in the
modelling of large-scale atmospheric flows. In this paper, we prove rigorously
the existence of weak Lagrangian solutions of this system, formulated in the
original physical coordinates. In addition, we provide an alternative proof of
the earlier result on the existence of weak solutions of this system expressed
in the so-called geostrophic, or dual, coordinates. The proofs are based on the
optimal transport formulation of the problem and on recent general results
concerning transport problems posed in the Wasserstein space of probability
measures.",1112.3553v2
2012-01-23,Micromagnetic Simulations for Spin Transfer Torque in Magnetic Multilayers,"We investigate the spin transfer torque (STT) in the magnetic multilayer
structures with micromagnetic simulations. We implement the STT contribution
for the magnetic multilayer structures in addition to the
Landau-Lifshitz-Gilbert (LLG) micromagnetic simulators. Not only the Sloncewski
STT term, the zero, first, and second order field- like terms are also
considered, and the effects of the Oersted field by the current are addressed.
We determine the switching current densities of the free layer with the
exchange biased synthetic ferrimagnetic reference layers for various cases.",1201.4707v1
2012-01-26,Pseudospin Transfer Torques in Semiconductor Electron Bilayers,"We use self-consistent quantum transport theory to investigate the influence
of electron-electron interactions on interlayer transport in semiconductor
electron bilayers in the absence of an external magnetic field. We conclude
that, even though spontaneous pseudospin order does not occur at zero field,
interaction-enhanced quasiparticle tunneling amplitudes and pseudospin transfer
torques do alter tunneling I-V characteristics, and can lead to time-dependent
response to a dc bias voltage.",1201.5569v2
2012-03-03,Skyrmion Generation by Current,"Skyrmions, once a hypothesized field-theoretical object believed to describe
the nature of elementary particles, became common sightings in recent years
among several non-centrosymmetric metallic ferromagnets. For more practical
applications of Skyrmionic matter as carriers of information, thus realizing
the prospect of ""Skyrmionics"", it is necessary to have the means to create and
manipulate Skyrmions individually. We show through extensive simulation of the
Landau-Lifshitz-Gilbert equation that a circulating current imparted to the
metallic chiral ferromagnetic system can create isolated Skyrmionic spin
texture without the aid of external magnetic field.",1203.0638v1
2012-04-25,Numerical Study on Spin Torque Switching in Thermally Activated Region,"We studied the spin torque switching of the single free layer in the
thermally activated region by numerically solving the Landau-Lifshitz-Gilbert
equation. We found that the temperature dependence of the switching time of the
in-plane magnetized system is nonlinear, which means $b \neq 1$. Here, $b$ is
the exponent of the current term in the switching rate formula and has been
widely assumed to be unity. This result enables us to evaluate the thermal
stability of spintronics devices.",1204.5596v2
2012-07-13,Theory of current-driven motion of Skyrmions and spirals in helical magnets,"We study theoretically the dynamics of the spin textures, i.e., Skyrmion
crystal (SkX) and spiral structure (SS), in two-dimensional helical magnets
under external current. By numerically solving the Landau-Lifshitz-Gilbert
equation, it is found that (i) the critical current density of the motion is
much lower for SkX compared with SS in agreement with the recent experiment,
(ii) there is no intrinsic pinning effect for SkX and the deformation of the
internal structure of Skyrmion reduces the pinning effect dramatically, (iii)
the Bragg intensity of SkX shows strong time-dependence as can be observed by
neutron scattering experiment.",1207.3224v1
2012-07-19,Solar Orbiter: Exploring the Sun-heliosphere connection,"The heliosphere represents a uniquely accessible domain of space, where
fundamental physical processes common to solar, astrophysical and laboratory
plasmas can be studied under conditions impossible to reproduce on Earth and
unfeasible to observe from astronomical distances. Solar Orbiter, the first
mission of ESA's Cosmic Vision 2015-2025 programme, will address the central
question of heliophysics: How does the Sun create and control the heliosphere?
In this paper, we present the scientific goals of the mission and provide an
overview of the mission implementation.",1207.4579v2
2012-07-19,Harnessing the modulation instability spectrum in optical fibers with a periodic dispersion landscape,"We report the experimental demonstration of modulation instability process
assisted by a dispersion grating in an optical fiber. A simple analytical model
is developed to further analyze and explain the complex dynamics of this
process, showing that each of the multiple spectral components grows thanks to
a quasi phase-matching mechanism inherent to the periodicity of the waveguide
parameters. This model is confirmed by numerical simulations and it is
successfully used to tailor the multi-peak modulation instability spectrum
shape. These theoretical predictions are confirmed by experiments.",1207.4667v1
2012-08-11,Lexicodes over Rings,"In this paper, we consider the construction of linear lexicodes over finite
chain rings by using a $B$-ordering over these rings and a selection criterion.
% and a greedy Algorithm. As examples we give lexicodes over $\mathbb{Z}_4$ and
$\mathbb{F}_2+u\mathbb{F}_2$. %First, greedy algorithms are presented to
construct %lexicodes using a multiplicative property. Then, greedy algorithms
%are given for the case when the selection criteria is not %multiplicative such
as the minimum distance constraint. It is shown that this construction produces
many optimal codes over rings and also good binary codes. Some of these codes
meet the Gilbert bound. We also obtain optimal self-dual codes, in particular
the octacode.",1208.2361v2
2012-09-07,Self-sustained current oscillations in spin-blockaded quantum dots,"Self-sustained current oscillation observed in spin-blockaded double quantum
dots is explained as a consequence of periodic motion of dynamically polarized
nuclear spins (along a limit cycle) in the spin-blockaded regime under an
external magnetic field and a spin-transfer torque. It is shown, based on the
Landau-Lifshtz-Gilbert equation, that a sequence of semistable limit cycle,
Hopf and homoclinic bifurcations occurs as the external field is tuned. The
divergent period near the homoclinic bifurcation explains well why the period
in the experiment is so long and varies by many orders of magnitudes.",1209.1548v1
2012-10-04,All Spin Nano-magnetic State Elements,"We propose an all spin state element to enable all spin state machines using
spin currents and nanomagnets. We demonstrate via numerical simulations the
operation of a state element a critical building block for synchronous,
sequential logic computation. The numerical models encompass
Landau-Lifshitz-Gilbert (LLG) nanomagnet dynamics with stochastic models and
vector spin-transport in metallic magnetic and non-magnetic channels. Combined
with all spin combinatorial logic, the state elements can enable synchronous
and asynchronous computing elements.",1210.1613v1
2012-11-02,Effect of Spin Torque on Magnetization Switching Speed Having Nonuniform Spin Distribution,"We study the influence of the spin torque, which depends on the space and
time derivative of magnetization, on magnetization reversal time in a
ferromagnetic fine particle. The spin torque operates to dissipate the angular
momentum of the magnetization precession, and the torque increases in a spin
vortex structure. We calculate the magnetization reversal time under a DC
magnetic field using the Landau-Lifshitz-Gilbert equation containing a spin
torque term. We found that the spin torque changes the magnetization switching
speed significantly during the reversal process by maintaining a spin vortex in
an intermediate state.",1211.0360v1
2013-01-14,magnum.fe: A micromagnetic finite-element simulation code based on FEniCS,"We have developed a finite-element micromagnetic simulation code based on the
FEniCS package called magnum.fe. Here we describe the numerical methods that
are applied as well as their implementation with FEniCS. We apply a
transformation method for the solution of the demagnetization-field problem. A
semi-implicit weak formulation is used for the integration of the
Landau-Lifshitz-Gilbert equation. Numerical experiments show the validity of
simulation results. magnum.fe is open source and well documented. The broad
feature range of the FEniCS package makes magnum.fe a good choice for the
implementation of novel micromagnetic finite-element algorithms.",1301.3061v2
2013-02-04,Control of dissipation in superconducting films by magnetic stray fields,"Hybrid superconducting/magnetic nanostructures on Si substrates have been
built with identical physical dimensions but different magnetic configurations.
By constructing arrays based on Co-dots with in-plane, out-of-plane, and vortex
state magnetic configurations, the stray fields are systematically tuned.
Dissipation in the mixed state of superconductors can be decreased (increased)
by several orders of magnitude by decreasing (increasing) the stray magnetic
fields. Furthermore, ordering of the stray fields over the entire array helps
to suppress dissipation and enhance commensurability effects increasing the
number of dissipation minima.",1302.0680v1
2013-02-09,Lower bounds on the minimum distance of long codes in the Lee metric,"The Gilbert type bound for codes in the title is reviewed, both for small and
large alphabets. Constructive lower bounds better than these existential bounds
are derived from geometric codes, either over Fp or Fp2 ; or over even degree
extensions of Fp: In the latter case the approach is concatena- tion with a
good code for the Hamming metric as outer code and a short code for the Lee
metric as an inner code. In the former case lower bounds on the minimum Lee
distance are derived by algebraic geometric arguments inspired by results of
Wu, Kuijper, Udaya (2007).",1302.2246v1
2013-03-04,Mansuripur's Paradox,"A recent article claims that the Lorentz force law is incompatible with
special relativity. We discuss the ""paradox"" on which this claim is based. The
resolution depends on whether one assumes a ""Gilbert"" model for the magnetic
dipole (separated monopoles) or the standard ""Ampere"" model (current loop). The
former was presented in these pages many years ago; the latter requires the
inclusion of ""hidden momentum.""",1303.0732v2
2013-04-09,Instability of Walker Propagating Domain Wall in Magnetic Nanowires,"Stability of the well-known Walker propagating domain wall (DW) solution of
the Landau-Lifshitz-Gilbert equation is analytically investigated.
Surprisingly, the Walker's rigid body propagating DW mode is not stable against
the spin wave/wavepacket emission. In the low field region only stern spin
waves are emitted while both stern and bow waves are generated under high
fields. In a high enough field, but below the Walker breakdown field, the
Walker solution could be convective/absolute unstable if the transverse
magnetic anisotropy is larger than a critical value, corresponding to a
significant modification of the DW profile and DW propagating speed.",1304.2439v1
2013-04-26,Maximizing Spin Torque Diode Voltage by Optimizing Magnetization Alignment,"The optimum condition of the magnetization alignment to maximize the spin
torque diode voltage is derived by solving the Landau-Lifshitz-Gilbert
equation. We show that the optimized diode voltage can be one order of
magnitude larger than that of the conventional alignment where the easy axes of
the free and the pinned layers are parallel. These analytical predictions are
confirmed by numerical simulations.",1304.7079v1
2013-05-23,Residual properties of automorphism groups of (relatively) hyperbolic groups,"We show that Out(G) is residually finite if G is a one-ended group that is
hyperbolic relative to virtually polycyclic subgroups. More generally, if G is
one-ended and hyperbolic relative to proper residually finite subgroups, the
group of outer automorphisms preserving the peripheral structure is residually
finite. We also show that Out(G) is virtually p-residually finite for every
prime p if G is one-ended and toral relatively hyperbolic, or infinitely-ended
and virtually p-residually finite.",1305.5403v3
2013-05-25,Thermally-Assisted Spin-Transfer Torque Dynamics in Energy Space,"We consider the general Landau-Lifshitz-Gilbert theory underlying the
magnetization dynamics of a macrospin magnet subject to spin-torque effects and
thermal fluctuations. Thermally activated dynamical properties are analyzed by
averaging the full magnetization equations over constant- energy orbits. After
averaging, all the relevant dynamical scenarios are a function of the ratio
between hard and easy axis anisotropies. We derive analytically the range of
currents for which limit cycles exist and discuss the regimes in which the
constant energy orbit averaging technique is applicable.",1305.5945v2
2013-06-10,Imperfect Construction of Microclusters,"Microclusters are the basic building blocks used to construct cluster states
capable of supporting fault-tolerant quantum computation. In this paper, we
explore the consequences of errors on microcluster construction using two error
models. To quantify the effect of the errors we calculate the fidelity of the
constructed microclusters and the fidelity with which two such microclusters
can be fused together. Such simulations are vital for gauging the capability of
an experimental system to achieve fault tolerance.",1306.2202v1
2013-06-19,Weyl Phases in Point-Group Symmetric Superconductors,"We study superconductivity in a Weyl semimetal with broken time-reversal
symmetry and stabilized by a point-group symmetry. The resulting
superconducting phase is characterized by topologically protected bulk nodes
and surface states with Fermi arcs. The topological invariant governing the
system is calculated using changes in eigenvalues of the point-group operator
along high-symmetry momentum lines. We show that this invariant is determined
by the Fermi surface topology of the Weyl semimetal. We discuss the effect of
surface orientation and $C_4$-breaking strain as possible experimental
consequences.",1306.4696v1
2013-06-21,The Polarization Signature of Local Bulk Flows,"A large peculiar velocity of the intergalactic medium produces a Doppler
shift of the cosmic microwave background with a frequency-dependent quadrupole
term. This quadrupole will act as a source for polarization of the cosmic
microwave background, creating a large-scale polarization anisotropy if the
bulk flow is local and coherent on large scales. In the case where we are near
the center of the moving region, the polarization signal is a pure quadrupole.
We show that the signal is small, but detectable with future experiments for
bulk flows as large as some recent reports.",1306.5248v3
2013-07-21,Rigidity in the Positive Mass Theorem with Charge,"In this paper we show how a natural coupling of the Dirac equation with the
generalized Jang equation, leads to a proof of the rigidity statement in the
positive mass theorem with charge, without the maximal slicing condition,
provided a solution to the coupled system exists.",1307.5499v4
2014-01-08,Tri-Dirac Surface Modes in Topological Superconductors,"We propose a new type of topological surface modes having cubic dispersion in
three-dimensional topological superconductors. Lower order dispersions are
prohibited by the threefold rotational symmetry and time-reversal symmetry.
Cooper pairing in the bulk changes sign under improper rotations, akin
to$^{3}$He-B. The surface manifestations are a divergent surface density of
states at the Fermi level and isospins that rotate three times as they circle
the origin in momentum space. We propose that Heusler alloys with band
inversion are candidate materials to harbor the novel topological
superconductivity.",1401.1823v1
2014-01-09,Automated Code Generation for Lattice Quantum Chromodynamics and beyond,"We present here our ongoing work on a Domain Specific Language which aims to
simplify Monte-Carlo simulations and measurements in the domain of Lattice
Quantum Chromodynamics. The tool-chain, called Qiral, is used to produce
high-performance OpenMP C code from LaTeX sources. We discuss conceptual issues
and details of implementation and optimization. The comparison of the
performance of the generated code to the well-established simulation software
is also made.",1401.2039v1
2014-01-13,Effect of Dzyaloshinskii Moriya interaction on magnetic vortex,"The effect of the Dzyaloshinskii Moriya interaction on the vortex in magnetic
microdisk was investigated by micro magnetic simulation based on the Landau
Lifshitz Gilbert equation. Our results show that the DM interaction modifies
the size of the vortex core, and also induces an out of plane magnetization
component at the edge and inside the disk. The DM interaction can destabilizes
one vortex handedness, generate a bias field to the vortex core and couple the
vortex polarity and chirality. This DM-interaction-induced coupling can
therefore provide a new way to control vortex polarity and chirality.",1401.3292v1
2014-01-31,Self-Oscillation in Spin Torque Oscillator Stabilized by Field-like Torque,"The self-oscillation of the magnetization in a spin torque oscillator (STO)
with a perpendicularly magnetized free layer and an in-plane magnetized pinned
layer in the absence of an applied magnetic field was studied by numerically
solving the Landau-Lifshitz-Gilbert equation. It was pointed out that
field-like torque was necessary to realize stable self-oscillation in this type
of STO at zero field. The numerical simulation at finite temperature showed
that the presence of the field-like torque led to a high power with a
relatively high oscillation frequency.",1401.8088v2
2014-02-05,Spin-polarized transport in ferromagnetic multilayers: An unconditionally convergent FEM integrator,"We propose and analyze a decoupled time-marching scheme for the coupling of
the Landau-Lifshitz-Gilbert equation with a quasilinear diffusion equation for
the spin accumulation. This model describes the interplay of magnetization and
electron spin accumulation in magnetic and non-magnetic multilayer structures.
Despite the strong nonlinearity of the overall PDE system, the proposed
integrator requires only the solution of two linear systems per time-step.
Unconditional convergence of the integrator towards weak solutions is proved.",1402.0983v2
2014-02-12,An efficient algorithm for the entropy rate of a hidden Markov model with unambiguous symbols,"We demonstrate an efficient formula to compute the entropy rate $H(\mu)$ of a
hidden Markov process with $q$ output symbols where at least one symbol is
unambiguously received. Using an approximation to $H(\mu)$ to the first $N$
terms we give a $O(Nq^3$) algorithm to compute the entropy rate of the hidden
Markov model. We use the algorithm to estimate the entropy rate when the
parameters of the hidden Markov model are unknown.In the case of $q =2$ the
process is the output of the Z-channel and we use this fact to give bounds on
the capacity of the Gilbert channel.",1402.2733v2
2014-03-24,Skyrmionic spin Seebeck effect via dissipative thermomagnonic torques,"We derive thermomagnonic torque and its ""$\beta$-type"" dissipative correction
from the stochastic Landau-Lifshitz-Gilbert equation. The ""$\beta$-type""
dissipative correction describes viscous coupling between magnetic dynamics and
magnonic current and it stems from spin mistracking of the magnetic order. We
show that thermomagnonic torque is important for describing temperature
gradient induced motion of skyrmions in helical magnets while dissipative
correction plays an essential role in generating transverse Magnus force. We
propose to detect such skyrmionic motion by employing the transverse spin
Seebeck effect geometry.",1403.6160v2
2014-04-18,"Sparse Approximation, List Decoding, and Uncertainty Principles","We consider list versions of sparse approximation problems, where unlike the
existing results in sparse approximation that consider situations with unique
solutions, we are interested in multiple solutions. We introduce these problems
and present the first combinatorial results on the output list size. These
generalize and enhance some of the existing results on threshold phenomenon and
uncertainty principles in sparse approximations. Our definitions and results
are inspired by similar results in list decoding. We also present lower bound
examples that bolster our results and show they are of the appropriate size.",1404.5190v2
2014-04-25,Linewidth of Power Spectrum Originated from Thermal Noise in Spin Torque Oscillator,"A theoretical formula of the linewidth caused by the thermal activation in a
spin torque oscillator with a perpendicularly magnetized free layer and an
in-plane magnetized pinned layer was developed by solving the stochastic
Landau-Lifshitz-Gilbert equation in the energy-phase representation. It is
shown that the linewidth can be suppressed down to 0.1 MHz by applying a large
current (10 mA for typical material parameters). A quality factor larger than
10^{4} is predicted in the large current limit, which is two orders of
magnitude larger than the recently observed experimental value.",1404.6558v1
2014-08-11,An optimal irrigation network with infinitely many branching points,"The Gilbert-Steiner problem is a mass transportation problem, where the cost
of the transportation depends on the network used to move the mass and it is
proportional to a certain power of the ""flow"". In this paper, we introduce a
new formulation of the problem, which turns it into the minimization of a
convex functional in a class of currents with coefficients in a group. This
framework allows us to define calibrations, which can be used to prove the
optimality of concrete configurations. We apply this technique to prove the
optimality of a certain irrigation network, having the topological property
mentioned in the title.",1408.2406v1
2014-09-04,Integer Generalized Splines on Cycles,"Let G be a graph whose edges are labeled by positive integers. Label each
vertex with an integer and suppose if two vertices are joined by an edge, the
vertex labels are congruent to each other modulo the edge label. The set of
vertex labels satisfying this condition is called a generalized spline.
Gilbert, Polster, and Tymoczko recently defined generalized splines based on
work on polynomial splines by Billera, Rose, Haas, Goresky-Kottwitz-Machperson,
and many others. We focus on generalized splines on $n$-cycles. We construct a
particularly nice basis for the module of splines on $n$-cycles. As an
application, we construct generalized splines on star graphs, wheel graphs, and
complete graphs.",1409.1481v1
2014-09-10,Proof of the Riemannian Penrose Inequality with Charge for Multiple Black Holes,"We present a proof of the Riemannian Penrose inequality with charge in the
context of asymptotically flat initial data sets for the Einstein-Maxwell
equations, having possibly multiple black holes with no charged matter outside
the horizon, and satisfying the relevant dominant energy condition. The proof
is based on a generalization of Hubert Bray's conformal flow of metrics adapted
to this setting.",1409.3271v2
2014-09-15,Enhanced synchronization in an array of spin torque nano oscillators in the presence of oscillating external magnetic field,"We demonstrate that the synchronization of an array of electrically coupled
spin torque nano-oscillators (STNO) modelled by
Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation can be enhanced appreciably
in the presence of a common external microwave magnetic field. The applied
microwave magnetic field stabilizes and enhances the regions of synchronization
in the parameter space of our analysis, where the oscillators are exhibiting
synchronized oscillations thereby emitting improved microwave power. To
characterize the synchronized oscillations we have calculated the locking range
in the domain of external source frequency.",1409.4384v2
2014-10-19,Extensions of the Charged Riemannian Penrose Inequality,"In this paper we investigate the extension of the charged Riemannian Penrose
inequality to the case where charges are present outside the horizon. We prove
a positive result when the charge densities are compactly supported, and
present a counterexample when the charges extend to infinity. We also discuss
additional extensions to other matter models.",1410.5027v2
2014-10-23,Quantum spin dynamics,"The classical Landau-Lifshitz equation has been derived from quantum
mechanics. Starting point is the assumption of a non-Hermitian Hamilton
operator to take the energy dissipation into account. The corresponding quantum
mechanical time dependent Schr\""odinger, Liouville and Heisenberg equation have
been described and the similarities and differences between classical and
quantum mechanical spin dynamics have been discussed. Furthermore, a time
dependent Schr\""odinger equation corresponding to the classical
Landau-Lifshitz-Gilbert equation and two ways to include temperature into the
quantum mechanical spin dynamics have been proposed.",1410.6383v1
2014-12-04,Role of Magnetic Field in Self-Oscillation of Nanomagnet Excited by Spin Torque,"The critical current of the self-oscillation of spin torque oscillator (STO)
consisting of a perpendicularly magnetized free layer and an in-plane
magnetized pinned layer was studied by solving the Landau-Lifshitz-Gilbert
(LLG) equation. We found that the critical current diverged at certain field
directions, indicating that the self-oscillation does not occur at these
directions. It was also found that the sign of the critical current changed
depending on the applied field direction.",1412.1532v1
2015-01-30,Memory functions of magnetic skyrmions,"Magnetic skyrmion, a swirling spin texture, in chiral magnets is
characterized by (i) nano-scale size ($\sim$1nm -- 100nm), (ii) topological
stability, and (iii) gyro-dynamics. These features are shown to be advantageous
for (a) high-density data-storage, (b) nonvolatile memory, and (c) ultra-low
current and energy cost manipulation, respectively. By the numerical
simulations of Landau-Lifshitz-Gilbert equation, the elementary functions of
skyrmions are demonstrated aiming at the design principles of skyrmionic memory
devices.",1501.07650v1
2015-02-14,Energy dissipation in single-domain ferromagnetic nanoparticles: Dynamical approach,"We study, both analytically and numerically, the phenomenon of energy
dissipation in single-domain ferromagnetic nanoparticles driven by an
alternating magnetic field. Our interest is focused on the power loss resulting
from the Landau-Lifshitz-Gilbert equation, which describes the precessional
motion of the nanoparticle magnetic moment. We determine the power loss as a
function of the field amplitude and frequency and analyze its dependence on
different regimes of forced precession induced by circularly and linearly
polarized magnetic fields. The conditions to maximize the nanoparticle heating
are also analyzed.",1502.04222v1
2015-02-23,The Positive Mass Theorem for Multiple Rotating Charged Black Holes,"In this paper a lower bound for the ADM mass is given in terms of the angular
momenta and charges of black holes present in axisymmetric initial data sets
for the Einstein-Maxwell equations. This generalizes the mass-angular
momentum-charge inequality obtained by Chrusciel and Costa to the case of
multiple black holes. We also weaken the hypotheses used in the proof of this
result for single black holes, and establish the associated rigidity statement.",1502.06290v2
2015-02-24,An Upper Bound on the Minimum Distance of LDPC Codes over GF(q),"In [1] a syndrome counting based upper bound on the minimum distance of
regular binary LDPC codes is given. In this paper we extend the bound to the
case of irregular and generalized LDPC codes over GF(q). The comparison to the
lower bound for LDPC codes over GF(q) and to the upper bound for non-binary
codes is done. The new bound is shown to lie under the Gilbert-Varshamov bound
at high rates.",1502.06874v1
2015-03-16,Impact of Current on Static and Kinetic Depinning Fields of Domain Wall in Ferromagnetic Nanostrip,"The impact of current on static and kinetic depinning fields of a domain wall
in an one dimensional ferromagnetic nanostrip is investigated by solving the
Landau-Lifshitz-Gilbert equation with adiabatic and non-adiabatic spin-transfer
torques analytically and numerically. The results show that in the absence of
current, the static depinning field is greater than the kinetic depinning field
and both the depinning fields decrease by the increase of current applied in a
direction opposite to the direction of the applied field. Both the depinning
fields can also be tuned by the current to make them equal.",1503.04553v1
2015-04-17,Critical analysis and remedy of switching failures in straintronic logic using Bennett clocking in the presence of thermal fluctuations,"Straintronic logic is a promising platform for beyond Moore's law computing.
Using Bennett clocking mechanism, information can propagate through an array of
strain-mediated multiferroic nanomagnets exploiting the dipolar coupling
between the magnets without having to physically interconnect them. Here we
perform a critical analysis of switching failures, i.e., error in information
propagation due to thermal fluctuations through a chain of such straintronic
devices. We solved stochastic Landau-Lifshitz-Gilbert equation considering
room-temperature thermal perturbations and show that magnetization switching
may fail due to inherent magnetization dynamics accompanied by thermally
broadened switching delay distribution. Avenues available to circumvent such
issue are proposed.",1504.04618v1
2015-06-18,Landauer limit of energy dissipation in a magnetostrictive particle,"According to Landauer's principle, a minimum amount of energy proportional to
temperature must be dissipated during the erasure of a classical bit of
information compensating the entropy loss, thereby linking the information and
thermodynamics. Here we show that the Landauer limit of energy dissipation is
achievable in a shape-anisotropic single-domain magnetostrictive nanomagnet
having two mutually anti-parallel degenerate magnetization states that store a
bit of information. We model the magnetization dynamics using stochastic
Landau-Lifshitz-Gilbert equation in the presence of thermal fluctuations and
show that on average the Landauer bound is satisfied, i.e., it accords to the
generalized Landauer's principle for small systems with stochastic
fluctuations.",1506.07897v1
2015-06-29,Pseudo-Spin Based Dynamical Model for Polarisation Switching in Ferroelectrics,"A microscopic view of the response of the electric dipoles to a dynamic
external field in a ferroelectric (FE) chain has been studied by two spin
dynamics methods. One is the prominent micromagnetic approach, and the other is
the micromagnetic approach with a variable size of the pseudo-spin. The energy
stored in the ferroelectric chain is described by the transverse Ising model
(TIM) with electric pseudo-spins. The simulations are based on a modified
Landau-Lifshitz-Gilbert (LLG) equation which is precession free. The results
obtained are shown and compared with the result supplemented by
Landau-Devonshire (L-D) theory in the Appendix.",1506.08500v2
2015-07-13,Explicit Construction of AG Codes from Generalized Hermitian Curves,"We present multi-point algebraic geometric codes overstepping the
Gilbert-Varshamov bound. The construction is based on the generalized Hermitian
curve introduced by A. Bassa, P. Beelen, A. Garcia, and H. Stichtenoth. These
codes are described in detail by constrcting a generator matrix. It turns out
that these codes have nice properties similar to those of Hermitian codes. It
is shown that the duals are also such codes and an explicit formula is given.",1507.03418v1
2015-07-22,Reflexive insensitive modal logics,"We analyze a class of modal logics rendered insensitive to reflexivity by way
of a modification to the semantic definition of the modal operator. We explore
the extent to which these logics can be characterized, and prove a general
completeness theorem on the basis of a translation between normal modal logics
and their reflexive-insensitive counterparts. Lastly, we provide a sufficient
semantic condition describing when a similarly general soundness result is also
available.",1507.06113v1
2015-08-24,Spin Dynamics Simulation of the Magneto-Electric Effect in a Composite Multiferroic Chain,"A composite multiferroic chain with an interfacial linear magneto-electric
coupling is used to study the magnetic and electric responses to an external
magnetic or electric field. The simulation uses continuous spin dynamics
through the Landau-Lifshitz-Gilbert equations of the magnetic spin and the
electric pseudo-spin. The results demonstrate an accurate description of the
distribution of the magnetisation and polarisation are induced by applied
electric and magnetic field, respectively.",1508.05693v1
2015-10-16,Reaction diffusion dynamics and the Schryer-Walker solution for domain walls of the Landau-Lifshitz-Gilbert equation,"We study the dynamics of the equation obtained by Schryer and Walker for the
motion of domain walls. The reduced equation is a reaction diffusion equation
for the angle between the applied field and the magnetization vector. If the
hard axis anisotropy $K_d$ is much larger than the easy axis anisotropy $K_u$,
there is a range of applied fields where the dynamics does not select the
Schryer-Walker solution. We give analytic expressions for the speed of the
domain wall in this regime and the conditions for its existence.",1510.04927v1
2015-11-06,Dynamic Response in a Finite Size Composite Multiferroic Thin Film,"Composite multiferroics, heterostructures of ferromagnetic (FM) and
ferroelectric (FE) materials, are characterized by a remarkable magnetoelectric
effect at the interface. Previous work has supported the ferromagnetic
structure with magnetic spins and the ferroelectric with pseudospins which act
as electric dipoles in a microscopic model, coupled with a magnetoelectric
interaction [J. Appl. Phys. 118, 124109 (2015)]. In this work, by solving the
stochastic Landau-Lifshitz-Gilbert equation, the electric-field-induced
magnetization switching in a twisted boundary condition has been studied, and a
behavior of domain wall in the ferromagnetic structure is discussed.",1511.01982v2
2015-12-18,Existence of travelling-wave solutions representing domain wall motion in a thin ferromagnetic nanowire,"We study the dynamics of a domain wall under the influence of applied
magnetic fields in a one-dimensional ferromagnetic nanowire, governed by the
Landau--Lifshitz--Gilbert equation. Existence of travelling-wave solutions
close to two known static solutions is proven using
implicit-function-theorem-type arguments.",1512.06016v2
2016-01-18,On Simultaneous Percolation with Two Disk Types,"In this paper we consider the simultaneous percolation of two Gilbert disk
models. The two models are connected through excluding disks, which prevent
elements of the second model to be in the vicinity of the first model. Under
these assumptions we characterize the region of densities in which the two
models both have a unique infinite connected component. The motivation for this
work is the co-existence of two cognitive radio networks.",1601.04471v2
2016-01-22,Toward a New Microscopic Framework for Kondo Lattice Materials,"Understanding the emergence and subsequent behavior of heavy electrons in
Kondo lattice materials is one of the grand challenges in condensed matter
physics. In this perspective we review the progress that has been made during
the past decade and suggest some directions for future research. Our focus will
be on developing a new microscopic framework that incorporates the basic
concepts that emerge from a phenomenological description of the key
experimental findings.",1601.06050v1
2016-02-01,The Eddy Current-LLG Equations-Part I: FEM-BEM Coupling,"We analyse a numerical method for the coupled system of the eddy current
equations in $\mathbb{R}^3$ with the Landau-Lifshitz-Gilbert equation in a
bounded domain. The unbounded domain is discretised by means of
finite-element/boundary-element coupling. Even though the considered problem is
strongly nonlinear, the numerical approach is constructed such that only two
linear systems per time step have to be solved. In this first part of the
paper, we prove unconditional weak convergence (of a subsequence) of the
finite-element solutions towards a weak solution. A priori error estimates will
be presented in the second part.",1602.00744v1
2016-02-01,The Eddy Current--LLG Equations: FEM-BEM Coupling and A Priori Error Estimates,"We analyze a numerical method for the coupled system of the eddy current
equations in $\mathbb{R}^3$ with the Landau-Lifshitz-Gilbert equation in a
bounded domain. The unbounded domain is discretized by means of
finite-element/boundary-element coupling. Even though the considered problem is
strongly nonlinear, the numerical approach is constructed such that only two
linear systems per time step have to be solved. We prove unconditional weak
convergence (of a subsequence) of the finite-element solutions towards a weak
solution. We establish a priori error estimates if a sufficiently smooth strong
solution exists. Numerical experiments underlining the theoretical results are
presented.",1602.00745v2
2016-02-24,Partial Category Actions on Sets and Topological Spaces,"We introduce (continuous) partial category actions on sets (topological
spaces) and show that each such action admits a universal globalization.
Thereby, we obtain a simultaneous generalization of corresponding results for
groups, by Kellendonk and Lawson, and for monoids, by Megrelishvili and
Schroder. We apply this result to the special case of partial groupoid actions
where we obtain a sharpening of a result by Gilbert, concerning ordered
groupoids, in the sense that mediating functions between universal
globalizations always are injective.",1602.07541v4
2016-05-20,Interlayer interaction in multilayer CoPt/Co structures,"We report a study of interlayer exchange interaction in multilayer CoPt/Co
structures consisting of periodic CoPt multilayer film with an ""easy axis""
anisotropy and thick Co layer with an ""easy plane"" anisotropy separated by Pt
spacer with variable thickness. The magnetooptical Kerr effect (MOKE) and
ferromagnetic resonance (FMR) measurements show up the essentially
non-collinear state of magnetic moments of the layers and strong exchange
coupling between CoPt and Co subsystems. The estimation of effective anisotropy
and exchange coupling in a simple model based on the Landau-Lifshitz-Gilbert
equation describing magnetization dynamics was performed.",1605.06468v1
2016-06-02,On self-dual double negacirculant codes,"Double negacirculant (DN) codes are the analogues in odd characteristic of
double circulant codes. Self-dual DN codes of odd dimension are shown to be
consta-dihedral. Exact counting formulae are derived for DN codes. The special
class of length a power of two is studied by means of Dickson polynomials, and
is shown to contain families of codes with relative distances satisfying a
modified Gilbert-Varshamov bound.",1606.00815v1
2016-07-12,Tailoring the topological details of the magnetic skyrmion by the spin configuration at the edges,"The magnetic skyrmion structure can be formed in the chiral magnets (CMs)
with strong Dzyaloshinskii-Moriya interactions. In this work, we propose a way
of artificially tailoring the topological details of the skyrmion such as its
radial and whirling symmetric patterns by external magnetic fields besieging
the CM slab. As long as the boundary magnetic fields are strong enough to fix
the boundary ferromagnetism, the attained skyrmion profile is stable over time.
The dynamics of spins is considered by numerically solving the non-equilibrium
Landau-Lifshitz-Gilbert equation.",1607.03268v2
2016-09-07,Entanglement manipulation by a magnetic pulse in Gd3N@C80 endohedral metallofullerenes on a Cu(001) surface,"In this paper we present result of theoretical calculation of entanglement
within a spin structure of Gd3N@C80 under the in uence of rectangular impulses.
Research is conducted using general spin Hamiltonian within SSNQ (spin system
of N-qubits). Calculation of entanglement with variable impulse is performed
using the time-dependent Landau-Lifshitz-Gilbert equation with spin-spin
correlation function. We show that long rectangular impulse (t=850ps) can be
used for maintaining of entanglement value. This allows us to offer a new
algorithm which can be used to reduce the challenge of decoherence to logical
scheme optimization.",1609.01959v1
2016-09-10,Optical tomography on graphs,"We present an algorithm for solving inverse problems on graphs analogous to
those arising in diffuse optical tomography for continuous media. In
particular, we formulate and analyze a discrete version of the inverse Born
series, proving estimates characterizing the domain of convergence,
approximation errors, and stability of our approach. We also present a
modification which allows additional information on the structure of the
potential to be incorporated, facilitating recovery for a broader class of
problems.",1609.03041v1
2016-09-30,Interaction Between a Domain Wall and Spin Supercurrent in Easy-cone Magnets,"A domain wall and spin supercurrent can coexist in magnets with easy-cone
anisotropy owing to simultaneous spontaneous breaking of Z$_2$ and U(1)
symmetries. Their interaction is theoretically investigated in quasi
one-dimensional ferromagnets within the Landau-Lifshitz-Gilbert phenomenology.
Specifically, we show that spin supercurrent can exert the torque on a domain
wall and thereby drive it. We also show, as a reciprocal phenomenon, a
field-induced motion of a domain wall can generate spin supercurrent.",1610.00034v1
2016-10-04,A Local Inverse Formula and a Factorization,"When a matrix has a banded inverse there is a remarkable formula that quickly
computes that inverse, using only local information in the original matrix.
This local inverse formula holds more generally, for matrices with sparsity
patterns that are examples of chordal graphs or perfect eliminators. The
formula has a long history going back at least as far as the completion problem
for covariance matrices with missing data. Maximum entropy estimates,
log-determinants, rank conditions, the Nullity Theorem and wavelets are all
closely related, and the formula has found wide applications in machine
learning and graphical models. We describe that local inverse and explain how
it can be understood as a matrix factorization.",1610.01230v1
2016-10-10,Parametric frequency mixing in the magneto-elastically driven FMR-oscillator,"We demonstrate the nonlinear frequency conversion of ferromagnetic resonance
(FMR) frequency by optically excited elastic waves in a thin metallic film on
dielectric substrates. Time-resolved probing of the magnetization directly
witnesses magneto-elastically driven second harmonic generation, sum- and
difference frequency mixing from two distinct frequencies, as well as
parametric downconversion of each individual drive frequency. Starting from the
Landau-Lifshitz-Gilbert equations, we derive an analytical equation of an
elastically driven nonlinear parametric oscillator and show that frequency
mixing is dominated by the parametric modulation of FMR frequency.",1610.02926v1
2016-11-05,Magnonic analog of relativistic Zitterbewegung in an antiferromagnetic spin chain,"We theoretically investigate the spin wave (magnon) excitations in a
classical antiferromagnetic spin chain with easy-axis anisotropy. We obtain a
Dirac-like equation by linearizing the Landau- Lifshitz-Gilbert equation in
this antiferromagnetic system, in contrast to the ferromagnetic system in which
a Schr\""{o}dinger equation is derived. The Hamiltonian operator in the
Dirac-like equation is a pseudo-Hermitian. We compute and demonstrate the
relativistic Zitterbewegung (trembling motion) in the antiferromagnetic spin
chain by measuring the expectation values of the wave packet position.",1611.01512v2
2016-11-15,The norm of the Fourier transform on compact or discrete abelian groups,"We calculate the norm of the Fourier operator from $L^p(X)$ to $L^q(\hat{X})$
when $X$ is an infinite locally compact abelian group that is, furthermore,
compact or discrete. This subsumes the sharp Hausdorff-Young inequality on such
groups. In particular, we identify the region in $(p,q)$-space where the norm
is infinite, generalizing a result of Fournier, and setting up a contrast with
the case of finite abelian groups, where the norm was determined by Gilbert and
Rzeszotnik. As an application, uncertainty principles on such groups expressed
in terms of R\'enyi entropies are discussed.",1611.04692v1
2016-12-01,Optimizing Quantiles in Preference-based Markov Decision Processes,"In the Markov decision process model, policies are usually evaluated by
expected cumulative rewards. As this decision criterion is not always suitable,
we propose in this paper an algorithm for computing a policy optimal for the
quantile criterion. Both finite and infinite horizons are considered. Finally
we experimentally evaluate our approach on random MDPs and on a data center
control problem.",1612.00094v1
2017-02-02,Magnon Condensation and Spin Superfluidity,"We consider the phenomenon of Bose-Einstein condensation of quasi-equilibrium
magnons which leads to a spin superfluidity, the coherent quantum transfer of
magnetization in magnetic materials. These phenomena are beyond the classical
Landau-Lifshitz-Gilbert paradigm. The critical conditions for excited magnon
density for ferro- and antiferromagnets, bulk and thin films are estimated and
discussed. The BEC should occur in the antiferromagnetic hematite at much lower
excited magnon density compared to the ferromagnetic YIG.",1702.00846v2
2017-02-09,Transient spin dynamics in a single-molecule magnet,"We explore the limitations and validity of semi-classically formulated spin
equations of motion. Using a single-molecule magnet as a test model, we employ
three qualitatively different approximation schemes. From a microscopic model,
we derive a generalized spin equation of motion in which the parameters have a
non-local time-dependence. This dynamical equation is simplified to the
Landau-Lifshitz-Gilbert equation with i) time-dependent, and ii)
time-independent parameters. We show that transient dynamics is essentially
non-existing in the latter approximation, while the former breaks down in the
regime of strong coupling between the spin and the itinerant electrons.",1702.02820v2
2017-03-05,On the VC-Dimension of Binary Codes,"We investigate the asymptotic rates of length-$n$ binary codes with
VC-dimension at most $dn$ and minimum distance at least $\delta n$. Two upper
bounds are obtained, one as a simple corollary of a result by Haussler and the
other via a shortening approach combining Sauer-Shelah lemma and the linear
programming bound. Two lower bounds are given using Gilbert-Varshamov type
arguments over constant-weight and Markov-type sets.",1703.01586v2
2017-03-09,Long quasi-polycyclic $t-$CIS codes,"We study complementary information set codes of length $tn$ and dimension $n$
of order $t$ called ($t-$CIS code for short). Quasi-cyclic and quasi-twisted
$t$-CIS codes are enumerated by using their concatenated structure. Asymptotic
existence results are derived for one-generator and have co-index $n$ by
Artin's conjecture for quasi cyclic and special case for quasi twisted. This
shows that there are infinite families of long QC and QT $t$-CIS codes with
relative distance satisfying a modified Varshamov-Gilbert bound for rate $1/t$
codes.
  Similar results are defined for the new and more general class of
quasi-polycyclic codes introduced recently by Berger and Amrani.",1703.03109v1
2017-09-05,On the Lagrangian branched transport model and the equivalence with its Eulerian formulation,"First we present two classical models of Branched Transport: the Lagrangian
model introduced by Bernot, Caselles, Morel, Maddalena, Solimini, and the
Eulerian model introduced by Xia. An emphasis is put on the Lagrangian model,
for which we give a complete proof of existence of minimizers in a
--hopefully-- simplified manner. We also treat in detail some
$\sigma$-finiteness and rectifiability issues to yield rigorously the energy
formula connecting the irrigation cost I$\alpha$ to the Gilbert Energy
E$\alpha$. Our main purpose is to use this energy formula and exploit a Smirnov
decomposition of vector flows, which was proved via the Dacorogna-Moser
approach by Santambrogio, to establish the equivalence between the Lagrangian
and Eulerian models.",1709.01414v1
2017-09-09,On Low-Risk Heavy Hitters and Sparse Recovery Schemes,"We study the heavy hitters and related sparse recovery problems in the
low-failure probability regime. This regime is not well-understood, and has
only been studied for non-adaptive schemes. The main previous work is one on
sparse recovery by Gilbert et al.(ICALP'13). We recognize an error in their
analysis, improve their results, and contribute new non-adaptive and adaptive
sparse recovery algorithms, as well as provide upper and lower bounds for the
heavy hitters problem with low failure probability.",1709.02919v3
2017-10-30,Lattice calculation of hadronic tensor of the nucleon,"We report an attempt to calculate the deep inelastic scattering structure
functions from the hadronic tensor calculated on the lattice. We used the
Backus-Gilbert reconstruction method to address the inverse Laplace
transformation for the analytic continuation from the Euclidean to the
Minkowski space.",1710.11145v1
2017-10-31,TF Boosted Trees: A scalable TensorFlow based framework for gradient boosting,"TF Boosted Trees (TFBT) is a new open-sourced frame-work for the distributed
training of gradient boosted trees. It is based on TensorFlow, and its
distinguishing features include a novel architecture, automatic loss
differentiation, layer-by-layer boosting that results in smaller ensembles and
faster prediction, principled multi-class handling, and a number of
regularization techniques to prevent overfitting.",1710.11555v1
2017-11-08,Micromagnetic simulation study of a disordered model for one-dimensional granular perovskite manganite oxide nanostructures,"Chemical techniques are an efficient method to synthesize one-dimensional
perovskite manganite oxide nanostructures with a granular morphology, that is,
formed by arrays of monodomain magnetic nanoparticles. Integrating the
stochastic Landau-Lifshitz-Gilbert equation, we simulate the dynamics of a
simple disordered model for such materials that only takes into account the
morphological characteristics of their nanograins. We show that it is possible
to describe reasonably well experimental hysteresis loops reported in the
literature for single La_0.67Ca_0.33MnO_3 nanotubes and powders of these
nanostructures, simulating small systems consisting of only 100 nanoparticles.",1711.03159v2
2017-11-21,Construction of asymptotically good locally repairable codes via automorphism groups of function fields,"Locally repairable codes have been investigated extensively in recent years
due to practical application in distributed storage as well as theoretical
interest. However, not much work on asymptotical behavior of locally repairable
codes has been done until now. In particular, there is a little result on
constructive lower bound on asymptotical behavior of locally repairable codes.
In this paper, we extend the construction given in \cite{BTV17} via
automorphism groups of function field towers. The main advantage of our
construction is to allow more flexibility of locality. Furthermore, we show
that the Gilbert-Varshamov type bound on locally repairable codes can be
improved for all sufficiently large alphabet size $q$.",1711.07703v1
2017-11-21,Stability of axisymmetric chiral skyrmions,"We examine topological solitons in a minimal variational model for a chiral
magnet, so-called chiral skyrmions. In the regime of large background fields,
we prove linear stability of axisymmetric chiral skyrmions under arbitrary
perturbations in the energy space, a long-standing open question in physics
literature. Moreover, we show strict local minimality of axisymmetric chiral
skyrmions and nearby existence of moving soliton solution for the
Landau-Lifshitz-Gilbert equation driven by a small spin transfer torque.",1711.07717v1
2017-12-13,Mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers,"A mutual synchronization of spin-torque oscillators coupled through current
injection is studied theoretically. Models of electrical coupling in parallel
and series circuits are proposed. Solving the Landau-Lifshitz-Gilbert equation,
excitation of in-phase or antiphase synchronization, depending on the ways the
oscillators are connected, is found. It is also found from both analytical and
numerical calculations that the current-frequency relations for both parallel
and series circuits are the same as that for a single spin-torque oscillator.",1712.04591v1
2018-01-25,Pharmacokinetics Simulations for Studying Correlates of Prevention Efficacy of Passive HIV-1 Antibody Prophylaxis in the Antibody Mediated Prevention (AMP) Study,"A key objective in two phase 2b AMP clinical trials of VRC01 is to evaluate
whether drug concentration over time, as estimated by non-linear mixed effects
pharmacokinetics (PK) models, is associated with HIV infection rate. We
conducted a simulation study of marker sampling designs, and evaluated the
effect of study adherence and sub-cohort sample size on PK model estimates in
multiple-dose studies. With m=120, even under low adherence (about half of
study visits missing per participant), reasonably unbiased and consistent
estimates of most fixed and random effect terms were obtained. Coarsened marker
sampling schedules were also studied.",1801.08626v1
2018-03-30,Nanostructured Ceramic Oxides with a Slow Crack Growth Resistance Close to Covalent Materials,"Oxide ceramics are sensitive to slow crack growth because adsorption of water
can take place at the crack tip, leading to a strong decrease of the surface
energy in humid (or air) conditions. This is a major drawback concerning
demanding, long-term applications such as orthopaedic implants. Here we show
that a specific nanostructuration of ceramic oxides can lead to a crack
resistance never reached before, similar to that of covalent ceramics.",1804.01393v1
2018-05-30,Quantum Annealed Criticality,"Experimentally there exist many materials with first-order phase transitions
at finite temperature that display quantum criticality. Classically a
strain-energy density coupling is known to drive first-order transitions in
compressible systems, and here we generalize this Larkin-Pikin mechanism to the
quantum case. We show that if the T=0 system lies above its upper critical
dimension, the line of first-order transitions can end in a quantum annealed
critical point where zero-point fluctuations restore the underlying criticality
of the order parameter.",1805.11771v1
2018-08-03,A thermally driven spin-transfer-torque system far from equilibrium: enhancement of the thermoelectric current via pumping current,"We consider a small itinerant ferromagnet exposed to an external magnetic
field and strongly driven by a thermally induced spin current. For this model,
we derive the quasi-classical equations of motion for the magnetization where
the effects of a dynamical non-equilibrium distribution function are taken into
account self-consistently. We obtain the Landau-Lifshitz-Gilbert equation
supplemented by a spin-transfer torque term of Slonczewski form. We identify a
regime of persistent precessions in which we find an enhancement of the
thermoelectric current by the pumping current.",1808.01192v1
2018-09-12,But How Does It Work in Theory? Linear SVM with Random Features,"We prove that, under low noise assumptions, the support vector machine with
$N\ll m$ random features (RFSVM) can achieve the learning rate faster than
$O(1/\sqrt{m})$ on a training set with $m$ samples when an optimized feature
map is used. Our work extends the previous fast rate analysis of random
features method from least square loss to 0-1 loss. We also show that the
reweighted feature selection method, which approximates the optimized feature
map, helps improve the performance of RFSVM in experiments on a synthetic data
set.",1809.04481v3
2018-09-22,"Optimizing a Generalized Gini Index in Stable Marriage Problems: NP-Hardness, Approximation and a Polynomial Time Special Case","This paper deals with fairness in stable marriage problems. The idea studied
here is to achieve fairness thanks to a Generalized Gini Index (GGI), a
well-known criterion in inequality measurement, that includes both the
egalitarian and utilitarian criteria as special cases. We show that determining
a stable marriage optimizing a GGI criterion of agents' disutilities is an
NP-hard problem. We then provide a polynomial time 2-approximation algorithm in
the general case, as well as an exact algorithm which is polynomial time in the
case of a constant number of non-zero weights parametrizing the GGI criterion.",1809.08453v1
2018-10-17,Out-of-plane auto-oscillation in spin Hall oscillator with additional polarizer,"The theoretical investigation on magnetization dynamics excited by the spin
Hall effect in metallic multilayers having two ferromagnets is discussed. The
relaxation of the transverse spin in one ferromagnet enables us to manipulate
the direction of the spin-transfer torque excited in another ferromagnet,
although the spin-polarization originally generated by the spin Hall effect is
geometrically fixed. Solving the Landau-Lifshitz-Gilbert-Slonczewski equation,
the possibility to excite an out-of-plane auto-oscillation of an in-plane
magnetized ferromagnet is presented. An application to magnetic recording using
microwave-assisted magnetization reversal is also discussed.",1810.07831v1
2018-11-23,Most Graphs are Knotted,"We present four models for a random graph and show that, in each case, the
probability that a graph is intrinsically knotted goes to one as the number of
vertices increases. We also argue that, for $k \geq 18$, most graphs of order
$k$ are intrinsically knotted and, for $k \geq 2n+9$, most of order $k$ are not
$n$-apex. We observe that $p(n) = 1/n$ is the threshold for intrinsic knotting
and linking in Gilbert's model.",1811.09726v1
2018-12-13,Entanglement-assisted quantum error-correcting codes over arbitrary finite fields,"We prove that the known formulae for computing the optimal number of
maximally entangled pairs required for entanglement-assisted quantum
error-correcting codes (EAQECCs) over the binary field hold for codes over
arbitrary finite fields as well. We also give a Gilbert-Varshamov bound for
EAQECCs and constructions of EAQECCs coming from punctured self-orthogonal
linear codes which are valid for any finite field.",1812.05312v4
2019-01-23,Coupled dynamics of magnetizations in spin-Hall oscillators via spin current injection,"An array of spin torque oscillators (STOs) for practical applications such as
pattern recognition was recently proposed, where several STOs are connected by
a common nonmagnet. In this structure, in addition to the electric and/or
magnetic interactions proposed in previous works, the STOs are spontaneously
coupled to each other through the nonmagnetic connector, due to the injection
of spin current. Solving the Landau-Lifshitz-Gilbert equation numerically for
such system consisting of three STOs driven by the spin Hall effect, it is
found that both in-phase and antiphase synchronization of the STOs can be
achieved by adjusting the current density and appropriate distance between the
oscillators.",1901.07669v1
2019-01-28,A Multi-parameter regression model for interval censored survival data,"We develop flexible multi-parameter regression survival models for interval
censored survival data arising in longitudinal prospective studies and
longitudinal randomised controlled clinical trials. A multi-parameter Weibull
regression survival model, which is wholly parametric, and has non-proportional
hazards, is the main focus of the paper. We describe the basic model, develop
the interval-censored likelihood and extend the model to include gamma frailty
and a dispersion model. We evaluate the models by means of a simulation study
and a detailed re-analysis of data from the Signal Tandmobiel$^{\circledR}$
study. The results demonstrate that the multi-parameter regression model with
frailty is computationally efficient and provides an excellent fit to the data.",1901.09634v1
2019-02-15,Stochastic homogenization of the Landau-Lifshitz-Gilbert equation,"Following the ideas of V. V. Zhikov and A. L. Pyatnitski, and more precisely
the stochastic two-scale convergence, this paper establishes a homogenization
theorem in a stochastic setting for two nonlinear equations : the equation of
harmonic maps into the sphere and the Landau-Lifschitz equation. These
equations have strong nonlinear features, in particular, in general their
solutions are not unique.",1902.05743v1
2019-03-06,Cluster multipole dynamics in non-collinear antiferromagnets,"A systematic framework to investigate spin dynamics in non-collinear
antiferromagnet is proposed. Taking Mn$_3$Sn as a representative example, we
derive an effective low energy model based on the multipole expansion of the
magnetic structure, and investigate the uniform precession and the domain wall
dynamics. We show that the solution for the effective model accurately
reproduces the numerical calculation of the Landau-Lifshitz-Gilbert equations.
Our results indicate that Mn$_3$Sn has preferable properties for applications
to a racetrack memory and a spin torque oscillator, and thus, is a promising
candidate for new devices by using the multipole degrees of freedom.",1903.02259v1
2019-03-22,Learning magnetization dynamics,"Deep neural networks are used to model the magnetization dynamics in magnetic
thin film elements. The magnetic states of a thin film element can be
represented in a low dimensional space. With convolutional autoencoders a
compression ratio of 1024:1 was achieved. Time integration can be performed in
the latent space with a second network which was trained by solutions of the
Landau-Lifshitz-Gilbert equation. Thus the magnetic response to an external
field can be computed quickly.",1903.09499v1
2019-04-01,Synchrony breakdown and noise-induced oscillation death in ensembles of serially connected spin-torque oscillators,"We consider collective dynamics in the ensemble of serially connected
spin-torque oscillators governed by the Landau-Lifshitz-Gilbert-Slonczewski
magnetization equation. Proximity to homoclinicity hampers synchronization of
spin-torque oscillators: when the synchronous ensemble experiences the
homoclinic bifurcation, the Floquet multiplier, responsible for the temporal
evolution of small deviations from the ensemble mean, diverges. Depending on
the configuration of the contour, sufficiently strong common noise, exemplified
by stochastic oscillations of the current through the circuit, may suppress
precession of the magnetic field for all oscillators. We derive the explicit
expression for the threshold amplitude of noise, enabling this suppression.",1904.00897v1
2019-04-21,Global classical solutions to an evolutionary model for magnetoelasticity,"In this paper, we first prove the local-in-time existence of the evolutionary
model for magnetoelasticity with finite initial energy by employing the
nonlinear iterative approach given in \cite{Jiang-Luo-2019-SIAM} to deal with
the geometric constraint $M \in \mathbb{S}^{d-1}$ in the
Landau-Lifshitz-Gilbert (LLG) equation. Inspired by
\cite{Lin-Liu-Zhang-CPAM2005, Lin-Zhang-2008-CPAM}, we reformulate the
evolutionary model for magnetoelasticity with vanishing external magnetic field
$H_{ext}$, so that a further dissipative term will be sought from the elastic
stress. We thereby justify the global well-posedness to the evolutionary model
for magnetoelasticity with zero external magnetic field under small size of
initial data.",1904.09531v1
2019-06-21,Thermal Collapse of a Skyrmion,"Thermal collapse of an isolated skyrmion on a two-dimensional spin lattice
has been investigated. The method is based upon solution of the system of
stochastic Landau-Lifshitz-Gilbert equations for up $10^4$ spins. Recently
developed pulse-noise algorithm has been used for the stochastic component of
the equations. The collapse rate follows the Arrhenius law. Analytical formulas
derived within a continuous spin-field model support numerically-obtained
values of the energy barrier and the pre-exponential factor, and their
dependence on the magnetic field. Our findings agree with experiments, as well
as with recent numerical results obtained by other methods.",1906.09132v3
2019-06-23,"Random subgroups, automorphisms, splittings","We show that, if $H$ is a random subgroup of a finitely generated free group
$F_k$, only inner automorphisms of $F_k$ may leave $H$ invariant. A similar
result holds for random subgroups of toral relatively hyperbolic groups, more
generally of groups which are hyperbolic relative to slender subgroups. These
results follow from non-existence of splittings over slender groups which are
relative to a random group element. Random subgroups are defined using random
walks or balls in a Cayley tree of $F_k$.",1906.09654v1
2019-07-28,Polarization of the Cosmic Infrared Background Fluctuations,"The cosmic infrared background (CIB) is slightly polarized. Polarization
directions of individual galaxies could be aligned with tidal fields around
galaxies, resulting in nonzero CIB polarization. We use a linear intrinsic
alignment model to theoretically predict angular correlations of the CIB
polarization fluctuations and find that electriclike and curl-like ($B$-mode)
polarization modes are equally generated with power four orders of magnitude
less than its intensity. The CIB $B$-mode signal is negligible and not a
concerning foreground for the inflationary $B$-mode searches at nominal
frequencies for cosmic microwave background measurements, but could be detected
at submillimetre wavelengths by future space missions.",1907.12085v1
2019-08-05,Constructive asymptotic bounds of locally repairable codes via function fields,"Locally repairable codes have been investigated extensively in recent years
due to practical applications in distributed and cloud storage systems.
However, there are few asymptotical constructions of locally repairable codes
in the literature. In this paper, we provide an explicit asymptotic
construction of locally repairable codes over arbitrary finite fields from
local expansions of functions at a rational place. This construction gives a
Tsfasman-Vladut-Zink type bound for locally repairable codes. Its main
advantage is that there are no constraints on both locality and alphabet size.
Furthermore, we show that the Gilbert-Varshamov type bound on locally
repairable codes over non-prime finite fields can be exceeded for sufficiently
large alphabet size.",1908.01471v1
2019-10-25,Application-Layer Coding with Intermittent Feedback under Delay and Duty-Cycle Constraints,"We propose two application-layer coding schemes for delay-constrained
point-to-point packet communications with restrictions on the transmitter's
maximum duty-cycle. The schemes operate over GF(2) and utilize intermittently
available receiver feedback for erasure correction. Applications that will
benefit from the proposed schemes include wireless sensor networks in which
energy-constrained sensors must deliver readings to a gateway within a
deadline. Simulation results for independent Bernoulli erasure channels,
Gilbert-Elliott channels, and Long Range (LoRa) communications demonstrate
orders-of-magnitude reductions in the delivery failure rate as compared to
feedback-assisted repetition redundancy and a blind coding scheme that does not
utilize feedback.",1910.11700v2
2019-10-28,Dissipative solutions to a system for the flow of magnetoviscoelastic materials,"We address the question of global in time existence of solutions to a
magnetoviscoelastic system with general initial data. We show that the notion
of dissipative solutions allows to prove such an existence in two and three
dimensions. This extends an earlier result for the viscoelastic subsystem to
the setting which includes the magnetization vector and its evolution in terms
of a Landau-Lifshitz-Gilbert equation.",1910.12751v2
2019-12-09,Multi-reference protocol for (auto)ionization spectra: application to molecules,"We present the application of the spherically averaged continuum model to the
evaluation of molecular photoelectron and resonant Auger electron spectra. In
this model, the continuum wave function is obtained in a numerically efficient
way by solving the radial Schr\""odinger equation with a spherically averaged
molecular potential. Different approximations to the Auger transition matrix
element and, in particular, the one-center approximation are thoroughly tested
against experimental data for the CH$_4$, O$_2$, NO$_2$, and pyrimidine
molecules. In general, this approach appears to estimate the shape of the
photoelectron and autoionization spectra as well as the total Auger decay rates
with reasonable accuracy, allowing for the interpretation of experimental
results.",1912.04139v1
2020-01-25,Phase estimation of spin-torque oscillator by nonlinear spin-torque diode effect,"A theoretical analysis is developed on spin-torque diode effect in nonlinear
region. An analytical solution of the diode voltage generated from spin-torque
oscillator by the rectification of an alternating current is derived. The diode
voltage is revealed to depend nonlinearly on the phase difference between the
oscillator and the alternating current. The validity of the analytical
prediction is confirmed by numerical simulation of the Landau-Lifshitz-Gilbert
equation. The results indicate that the spin-torque diode effect is useful to
evaluate the phase of a spin-torque oscillator in forced synchronization state.",2001.09247v1
2020-04-06,Frequency enhancement and power tunability in tilted polarizer spin-torque nano oscillator,"In the absence of an applied magnetic field, a spin-torque nano
oscillator(STNO) with a tilted polarizer is studied using numerical simulation
of the associated Landau-Lifshitz-Gilbert-Slonczewski equation. We find
considerable enhancement of frequency by tilting the polarizer out-of-plane
appropriately. Also, we observe improved tunability of frequency of
oscillations from 15 GHz to 75 GHz and increment in the power spectral density
by current and tilt angle. In addition, our findings and insights pave a simple
way for nanoscale level microwave generators to be implemented.",2004.02659v1
2020-05-11,Perspective on Metallic Antiferromagnets,"Antiferromagnet materials have recently gained renewed interest due to their
possible use in spintronics technologies, where spin transport is the
foundation of their functionalities. In that respect metallic antiferromagnets
are of particular interest, since they enable complex interplays between
electronic charge transport, spin, optical, and magnetization dynamics. Here we
review phenomena where the metallic conductivity provides unique perspectives
for the practical use and fundamental properties of antiferromagnetic
materials.",2005.05247v1
2020-07-09,Enumerating alternating matrix spaces over finite fields with explicit coordinates,"We initiate the study of enumerating linear subspaces of alternating matrices
over finite fields with explicit coordinates. We postulate that this study can
be viewed as a linear algebraic analogue of the classical topic of enumerating
labelled graphs. To support this viewpoint, we present q-analogues of Gilbert's
formula for enumerating connected graphs (Can. J. Math., 1956), and Read's
formula for enumerating c-colored graphs (Can. J. Math., 1960). We also develop
an analogue of Riddell's formula relating the exponential generating function
of graphs with that of connected graphs (Riddell's PhD thesis, 1951), building
on Eulerian generating functions developed by Srinivasan (Discrete Math.,
2006).",2007.05108v1
2020-08-06,"On Passivity, Feedback Passivity, And Feedback Passivity Over Erasure Network: A Piecewise Affine Approximation Approach","In this paper, we deal with the problem of passivity and feedback
passification of smooth discrete-time nonlinear systems by considering their
piecewise affine approximations. Sufficient conditions are derived for
passivity and feedback passivity. These results are then extended to systems
that operate over Gilbert-Elliott type communication channels. As a special
case, results for feedback passivity of piecewise affine systems over a lossy
channel are also derived.",2008.02748v1
2020-08-20,Hyperbolic groups of Fibonacci type and T(5) cyclically presented groups,"Building on previous results concerning hyperbolicity of groups of Fibonacci
type, we give an almost complete classification of the (non-elementary)
hyperbolic groups within this class. We are unable to determine the
hyperbolicity status of precisely two groups, namely the Gilbert-Howie groups
H(9,4), H(9,7). We show that if H(9,4) is torsion-free then it is not
hyperbolic. We consider the class of T(5) cyclically presented groups and
classify the (non-elementary) hyperbolic groups and show that the Tits
alternative holds.",2008.08986v2
2020-10-13,Mechanistic Modelling of Chromatin Folding to Understand Function,"Experimental approaches have been applied to address questions in
understanding three-dimensional chromatin organisation and function. As
datasets increase in size and complexity, it becomes a challenge to reach a
mechanistic interpretation of experimental results. Polymer simulations and
mechanistic modelling have been applied to explain experimental observations,
and the links to different aspects of genome function. Here, we provide a guide
for biologists, explaining different simulation approaches and the contexts in
which they have been used.",2010.06413v1
2020-12-05,Dual Regularized Optimal Transport,"In this paper, we present a new formulation of unbalanced optimal transport
called Dual Regularized Optimal Transport (DROT). We argue that regularizing
the dual formulation of optimal transport results in a version of unbalanced
optimal transport that leads to sparse solutions and that gives us control over
mass creation and destruction. We build intuition behind such control and
present theoretical properties of the solutions to DROT. We demonstrate that
due to recent advances in optimization techniques, we can feasibly solve such a
formulation at large scales and present extensive experimental evidence for
this formulation and its solution.",2012.03126v1
2020-12-20,Achieving positive rates with predetermined dictionaries,"In the first part of the paper we consider binary input channels that are not
necessarily stationary and show how positive rates can be achieved using codes
constrained to be within predetermined dictionaries. We use a
Gilbert-Varshamov-like argument to obtain the desired rate achieving codes.
Next we study the corresponding problem for channels with arbitrary alphabets
and use conflict-set decoding to show that if the dictionaries are contained
within nice sets, then positive rates are achievable.",2012.10897v1
2020-12-25,Colossal stability of antiferromagnetically exchange coupled nanomagnets,"Bistable nanomagnets store a binary bit of information. Exchange coupled
nanomagnets can increase the thermal stability at low dimensions. Here we show
that the antiferromagnetically (AFM) coupled nanomagnets can be highly stable
at low dimensions than that of the ferromagnetically (FM) coupled nanomagnets.
By solving stochastic Landau-Lifshitz-Gilbert equation of magnetization
dynamics at room temperature, we analyze the stability of the exchange coupled
nanomagnets in the presence of correlated, uncorrelated, and anti-correlated
noise. The results show that the correlated noise can make the stability of the
AFM coupled nanomagnets very high. Such finding will lead to very high-density
non-volatile storage and logic devices in our future information processing
systems.",2012.13590v1
2021-03-08,Cutoff for the Asymmetric Riffle Shuffle,"In the Gilbert-Shannon-Reeds shuffle, a deck of $N$ cards is cut into two
approximately equal parts which are then riffled uniformly at random. Bayer and
Diaconis famously showed that this Markov chain undergoes cutoff in total
variation after $\frac{3\log(N)}{2 \log(2)}$ shuffles. We establish cutoff for
the more general asymmetric riffle shuffles in which one cuts the deck into
differently sized parts before riffling. The value of the cutoff point confirms
a conjecture of Lalley from 2000. Some appealing consequences are that
asymmetry always slows mixing and that total variation mixing is strictly
faster than separation and $L^{\infty}$ mixing.",2103.05068v3
2021-03-24,Information Freshness Analysis of Slotted ALOHA in Gilbert-Elliot Channels,"This letter analyzes a class of information freshness metrics for large IoT
systems in which terminals employ slotted ALOHA to access a common channel.
Considering a Gilbert- Elliot channel model, information freshness is evaluated
through a penalty function that follows a power law of the time elapsed since
the last received update, in contrast with the linear growth of age of
information. By means of a signal flow graph analysis of Markov processes, we
provide exact closed form expressions for the average penalty and for the peak
penalty violation probability.",2103.13346v2
2021-04-30,Micromagnetic modeling of magnon coherent states in a nonuniform magnetic field,"The study of the dynamics of magnetically ordered states in strong excitation
through micromagnetic modeling has become relevant due to the observation of
magnon Bose condensation. In particular, the question has arisen about the
possibility of describing the coherent quantum state by the quasi-classical
Landau-Lifshitz-Gilbert equations. We performed micromagnetic simulations of
magnetization precession with a high angle of deviation in an out-of-plane
nonuniform dc field. Our results confirm the formation of coherent magnon state
under conditions of high excitation. This coherent state extends over long
distances and described by a spatially inhomogeneous amplitude and a
homogeneous precession phase.",2104.14804v1
2021-07-07,Superconducting Magnets,"Superconductivity allows to construct and operate magnets at field values
beyond 2 Tesla, the practical limitation of normal-conducting magnets
exploiting ferro-magnetism. The field of superconducting magnets is dominated
by the field generated in the coil. The stored energy and the electromagnetic
forces generated by the coil are the main challenges to be overcome in the
design of these magnets. For further reading you may consult the following
books: [1], [2], [3], [4] or the proceedings of two specialized CAS courses:
[5] and [6].",2107.03177v1
2021-08-14,An Experimental-Design Perspective on Population Genetic Variation,"We consider the hypothesis that Evolution promotes population-wide genome
patterns that, under randomization, ensures the External Validity of
adaptations across population members. An adaptation is Externally Valid (EV)
if its effect holds under a wide range of population genetic variations. A
prediction following the hypothesis is that pairwise base substitutions in
segregating regions must be 'random' as in Erdos-Renyi-Gilbert random graphs,
but with edge probabilities derived from Experimental-Design concepts. We
demonstrate these probabilities, and consequent mutation rates, in the
full-genomes of 2504 humans, 1135 flowering plants, 1170 flies, 453 domestic
sheep and 1223 brown rats.",2108.06580v1
2021-12-14,Extending the team with a project-specific bot,"While every other software team is adopting off-the-shelf bots to automate
everyday tasks, the Coq team has made a different choice by developing and
maintaining a project-specific bot from the ground up. In this article, we
describe the reasons for this choice, what kind of automation this has allowed
us to implement, how the many features of this custom bot have evolved based on
internal feedback, and the technology and architecture choices that have made
it possible.",2112.07365v1
2021-12-29,Multi-Adversarial Safety Analysis for Autonomous Vehicles,"This work in progress considers reachability-based safety analysis in the
domain of autonomous driving in multi-agent systems. We formulate the safety
problem for a car following scenario as a differential game and study how
different modelling strategies yield very different behaviors regardless of the
validity of the strategies in other scenarios. Given the nature of real-life
driving scenarios, we propose a modeling strategy in our formulation that
accounts for subtle interactions between agents, and compare its Hamiltonian
results to other baselines. Our formulation encourages reduction of
conservativeness in Hamilton-Jacobi safety analysis to provide better safety
guarantees during navigation.",2112.14344v1
2022-01-26,Analyzing Ta-Shma's Code via the Expander Mixing Lemma,"Random walks in expander graphs and their various derandomizations (e.g.,
replacement/zigzag product) are invaluable tools from pseudorandomness.
Recently, Ta-Shma used s-wide replacement walks in his breakthrough
construction of a binary linear code almost matching the Gilbert-Varshamov
bound (STOC 2017). Ta-Shma's original analysis was entirely linear algebraic,
and subsequent developments have inherited this viewpoint. In this work, we
rederive Ta-Shma's analysis from a combinatorial point of view using repeated
application of the expander mixing lemma. We hope that this alternate
perspective will yield a better understanding of Ta-Shma's construction. As an
additional application of our techniques, we give an alternate proof of the
expander hitting set lemma.",2201.11166v1
2022-02-15,Further Collapses in TFNP,"We show $\textsf{EOPL}=\textsf{PLS}\cap\textsf{PPAD}$. Here the class
$\textsf{EOPL}$ consists of all total search problems that reduce to the
End-of-Potential-Line problem, which was introduced in the works by Hubacek and
Yogev (SICOMP 2020) and Fearnley et al. (JCSS 2020). In particular, our result
yields a new simpler proof of the breakthrough collapse
$\textsf{CLS}=\textsf{PLS}\cap\textsf{PPAD}$ by Fearnley et al. (STOC 2021). We
also prove a companion result $\textsf{SOPL}=\textsf{PLS}\cap\textsf{PPADS}$,
where $\textsf{SOPL}$ is the class associated with the Sink-of-Potential-Line
problem.",2202.07761v2
2022-03-19,A proposed test of quantum mechanics with three connected atomic clock transitions,"We consider possible extensions to quantum mechanics proposed by Steven
Weinberg, and re-analyze his prediction of a new test based upon three atomic
clocks in the same atom. We propose realistic experimental systems where this
hypothesis can be tested. Two systems already set limits on deviations from
quantum mechanics, while with another system, one would be able to search for
new physics at the limit of sensitivity of the best atomic clocks.",2203.10269v3
2022-06-14,Generalized graph splines and the Universal Difference Property,"We study the generalized graph splines introduced by Gilbert, Tymoczko, and
Viel and focus on an attribute known as the Universal Difference Property
(UDP). We prove that paths, trees, and cycles satisfy UDP. We explore UDP on
graphs pasted at a single vertex and use Pr\""ufer domains to illustrate that
not every edge labeled graph satisfies UDP. We show that UDP must hold for any
edge labeled graph over a ring $R$ if and only if $R$ is a Pr\""ufer domain.
Lastly, we prove that UDP is preserved by isomorphisms of edge labeled graphs.",2206.06981v2
2022-08-04,Total stability and Auslander-Reiten theory for Dynkin quivers,"This paper concerns stability functions for Dynkin quivers, in the generality
introduced by Rudakov. We show that relatively few inequalities need to be
satisfied for a stability function to be totally stable (i.e. to make every
indecomposable stable). Namely, a stability function $\mu$ is totally stable if
and only if $\mu(\tau V) < \mu(V)$ for every almost split sequences $0 \to \tau
V \to E \to V \to 0$ where $E$ is indecomposable. These can be visualized as
those sequences around the ""border"" of the Auslander-Reiten quiver.",2208.02445v1
2022-09-09,Magnetization dynamics and reversal of two-dimensional magnets,"Micromagnetics simulation based on the classical Landau-Lifshitz-Gilbert
(LLG) equation has long been a powerful method for modeling magnetization
dynamics and reversal of three-dimensional (3D) magnets. For two-dimensional
(2D) magnets, the magnetization reversal always accompanies the collapse of the
magnetization even at low temperatures due to intrinsic strong spin
fluctuation. We propose a micromagnetic theory that explicitly takes into
account the rapid demagnetization and remagnetization dynamics of 2D magnets
during magnetization reversal. We apply the theory to a single-domain magnet to
illustrate fundamental differences in magnetization trajectories and reversal
times for 2D and 3D magnets.",2209.04483v1
2022-11-06,Two-Qutrit entanglement: 56-years old algorithm challenges machine learning,"Classifying states as entangled or separable is a highly challenging task,
while it is also one of the foundations of quantum information processing
theory. This task is higly nontrivial even for relatively simple cases, such as
two-qutrit Bell-diagonal states, i.e., mixture of nine mutually orthogonal
maximally entangled states. In this article we apply the Gilbert algorithm to
revise previously obtained results for this class. In particular we use
``cartography of entanglement'' to argue that most states left in [Hiesmayr, B.
C. {\em Scientific Reports} {\bf 11}, 19739 (2021)] as unknown to be entangled
or separable are most likely indeed separable, or very weakly entangled. The
presented technique can find endless applications in more general cases.",2211.03213v1
2022-12-07,Quantitative CLTs on the Poisson space via Skorohod estimates and $p$-Poincaré inequalities,"We establish new explicit bounds on the Gaussian approximation of Poisson
functionals based on novel estimates of moments of Skorohod integrals.
Combining these with the Malliavin-Stein method, we derive bounds in the
Wasserstein and Kolmogorov distances whose application requires minimal moment
assumptions on add-one cost operators $\unicode{x2014}$ thereby extending the
results from (Last, Peccati and Schulte, 2016). Our applications include a CLT
for the Online Nearest Neighbour graph, whose validity was conjectured in
(Wade, 2009; Penrose and Wade, 2009). We also apply our techniques to derive
quantitative CLTs for edge functionals of the Gilbert graph, of the $k$-Nearest
Neighbour graph and of the Radial Spanning Tree, both in cases where
qualitative CLTs are known and unknown.",2212.03782v1
2022-12-19,Bounds on Mixed Codes with Finite Alphabets,"Mixed codes, which are error-correcting codes in the Cartesian product of
different-sized spaces, model degrading storage systems well. While such codes
have previously been studied for their algebraic properties (e.g., existence of
perfect codes) or in the case of unbounded alphabet sizes, we focus on the case
of finite alphabets, and generalize the Gilbert-Varshamov, sphere-packing,
Elias-Bassalygo, and first linear programming bounds to that setting. In the
latter case, our proof is also the first for the non-symmetric mono-alphabetic
$q$-ary case using Navon and Samorodnitsky's Fourier-analytic approach.",2212.09314v1
2023-02-17,Codes Correcting Burst and Arbitrary Erasures for Reliable and Low-Latency Communication,"Motivated by modern network communication applications which require low
latency, we study codes that correct erasures with low decoding delay. We
provide a simple explicit construction that yields convolutional codes that can
correct both burst and arbitrary erasures under a maximum decoding delay
constraint $T$. Our proposed code has efficient encoding/decoding algorithms
and requires a field size that is linear in $T$. We study the performance of
our code over the Gilbert-Elliot channel; our simulation results show
significant performance gains over low-delay codes existing in the literature.",2302.08644v1
2023-03-10,On the coherence of one-relator groups and their group algebras,"We prove that one-relator groups are coherent, solving a well-known problem
of Gilbert Baumslag. Our proof strategy is readily applicable to many classes
of groups of cohomological dimension two. We show that fundamental groups of
two-complexes with non-positive immersions are homologically coherent, we show
that groups with staggered presentations and many Coxeter groups are coherent
and we show that group algebras over fields of characteristic zero of groups
with reducible presentations without proper powers are coherent.",2303.05976v3
2023-03-15,Algebraic Geometry codes in the sum-rank metric,"We introduce the first geometric construction of codes in the sum-rank
metric, which we called linearized Algebraic Geometry codes, using quotients of
the ring of Ore polynomials with coefficients in the function field of an
algebraic curve. We study the parameters of these codes and give lower bounds
for their dimension and minimum distance. Our codes exhibit quite good
parameters, respecting a similar bound to Goppa's bound for Algebraic Geometry
codes in the Hamming metric. Furthermore, our construction yields codes
asymptotically better than the sum-rank version of the Gilbert-Varshamov bound.",2303.08903v2
2023-05-11,Linear Codes with Prescribed Hull Dimension and Minimum Distance,"The hull of a linear code (i.e., a finite field vector space)~\({\mathcal
C}\) is defined to be the vector space formed by the intersection
of~\({\mathcal C}\) with its dual~\({\mathcal C}^{\perp}.\) Constructing vector
spaces with a specified hull dimension has important applications and it is
therefore of interest to study minimum distance properties of such spaces. In
this paper, we use the probabilistic method to obtain spaces with a given hull
dimension and minimum distance and also derive Gilbert-Varshamov type
sufficient conditions for their existence.",2305.07140v1
2023-05-18,Bounds on Size of Homopolymer Free Codes,"For any given alphabet of size $q$, a Homopolymer Free code (HF code) refers
to an $(n, M, d)_q$ code of length $n$, size $M$ and minimum Hamming distance
$d$, where all the codewords are homopolymer free sequences. For any given
alphabet, this work provides upper and lower bounds on the maximum size of any
HF code using Sphere Packing bound and Gilbert-Varshamov bound. Further, upper
and lower bounds on the maximum size of HF codes for various HF code families
are calculated. Also, as a specific case, upper and lower bounds are obtained
on the maximum size of homopolymer free DNA codes.",2305.10741v1
2023-05-31,Codes from Goppa codes,"On a Goppa code whose structure polynomial has coefficients in the symbol
field, the Frobenius acts. Its fixed codewords form a subcode. Deleting the
naturally occurred redundance, we obtain a new code. It is proved that these
new codes approach the Gilbert-Varshamov bound. It is also proved that these
codes can be decoded within $O(n^2(\logn)^a)$ operations in the symbol field,
which is usually much small than the location field, where $n$ is the codeword
length, and $a$ a constant determined by the polynomial factorization
algorithm.",2305.19565v5
2023-06-08,A Macroscopic Theory of Saturated Ferromagnetic Conductors,"A phenomenological theory of rigid and saturated ferromagnetic conductors is
constructed from a four-continuum model consisting of a rigid lattice
continuum, a bound charge continuum for polarization, a circulating current
continuum for magnetization, and a free charge continuum for electrical
conduction. The basic laws of physics are applied to the four continua. Thermal
couplings and the related dissipative effects are also included. The theory
includes the Landau-Lifshitz-Gilbert equation as one of a system of
simultaneous equations.",2306.11525v1
2023-07-02,Unveiling Stable One-dimensional Magnetic Solitons in Magnetic Bilayers,"We propose a novel model which efficiently describes the magnetization
dynamics in a magnetic bilayer system. By applying a particular gauge
transformation to the Landau-Lifshitz-Gilbert (LLG) equation, we successfully
convert the model into an exactly integrable framework. Thus the obtained
analytical solutions allows us to predict a 1D magnetic soliton pair existed by
tunning the thickness of the spacing layer between the two ferrimagnetic
layers. The decoupling-unlocking-locking transition of soliton motion is
determined at various interaction intensitiy. Our results have implications for
the manipulation of magnetic solitons and the design of magnetic soliton-based
logic devices.",2307.00471v1
2023-07-21,Thermomechanics of ferri-antiferromagnetic phase transition in finitely-strained rocks towards paleomagnetism,"The thermodynamic model of visco-elastic deformable magnetic materials at
finite strains is formulated in a fully Eulerian way in rates with the aim to
describe thermoremanent paleomagnetism in crustal rocks. The Landau theory
applied to a ferro-to-para-magnetic phase transition, the gradient theory for
magnetization (leading to exchange energy) with general mechanically dependent
coefficient, hysteresis in magnetization evolution by Gilbert equation
involving objective corotational time derivative of magnetization, and
demagnetizing field are considered in the model. The Jeffreys viscoelastic
rheology is used with temperature-dependent creep to model solidification or
melting transition. The model complies with energy conservation and the
Clausius-Duhem entropy inequality.",2307.11826v2
2023-09-22,Characterizing Smooth Safety Filters via the Implicit Function Theorem,"Optimization-based safety filters, such as control barrier function (CBF)
based quadratic programs (QPs), have demonstrated success in controlling
autonomous systems to achieve complex goals. These CBF-QPs can be shown to be
continuous, but are generally not smooth, let alone continuously
differentiable. In this paper, we present a general characterization of smooth
safety filters -- smooth controllers that guarantee safety in a minimally
invasive fashion -- based on the Implicit Function Theorem. This
characterization leads to families of smooth universal formulas for
safety-critical controllers that quantify the conservatism of the resulting
safety filter, the utility of which is demonstrated through illustrative
examples.",2309.12614v1
2023-09-23,Sphaleron rate from lattice QCD,"We compute the sphaleron rate on the lattice from the inversion of the
Euclidean time correlators of the topological charge density, performing also
controlled continuum and zero-smoothing extrapolations. The correlator
inversion is performed by means of a recently-proposed modification of the
Backus-Gilbert method.",2309.13327v1
2023-09-23,"CA-PCA: Manifold Dimension Estimation, Adapted for Curvature","The success of algorithms in the analysis of high-dimensional data is often
attributed to the manifold hypothesis, which supposes that this data lie on or
near a manifold of much lower dimension. It is often useful to determine or
estimate the dimension of this manifold before performing dimension reduction,
for instance. Existing methods for dimension estimation are calibrated using a
flat unit ball. In this paper, we develop CA-PCA, a version of local PCA based
instead on a calibration of a quadratic embedding, acknowledging the curvature
of the underlying manifold. Numerous careful experiments show that this
adaptation improves the estimator in a wide range of settings.",2309.13478v1
2023-11-13,Dedukti: a Logical Framework based on the $λ$$Π$-Calculus Modulo Theory,"Dedukti is a Logical Framework based on the $\lambda$$\Pi$-Calculus Modulo
Theory. We show that many theories can be expressed in Dedukti: constructive
and classical predicate logic, Simple type theory, programming languages, Pure
type systems, the Calculus of inductive constructions with universes, etc. and
that permits to used it to check large libraries of proofs developed in other
proof systems: Zenon, iProver, FoCaLiZe, HOL Light, and Matita.",2311.07185v1
2023-12-24,Sphaleron rate as an inverse problem: a novel lattice approach,"We compute the sphaleron rate on the lattice. We adopt a novel strategy based
on the extraction of the spectral density via a modified version of the
Backus-Gilbert method from finite-lattice-spacing and finite-smoothing-radius
Euclidean topological charge density correlators. The physical sphaleron rate
is computed by performing controlled continuum limit and zero-smoothing
extrapolations both in pure gauge and, for the first time, in full QCD.",2312.15468v1
1999-12-17,Expectations For an Interferometric Sunyaev-Zel'dovich Effect Survey for Galaxy Clusters,"Non-targeted surveys for galaxy clusters using the Sunyaev-Zel'dovich effect
(SZE) will yield valuable information on both cosmology and evolution of the
intra-cluster medium (ICM). The redshift distribution of detected clusters will
constrain cosmology, while the properties of the discovered clusters will be
important for studies of the ICM and galaxy formation. Estimating survey yields
requires a detailed model for both cluster properties and the survey strategy.
We address this by making mock observations of galaxy clusters in cosmological
hydrodynamical simulations. The mock observatory consists of an interferometric
array of ten 2.5 m diameter telescopes, operating at a central frequency of 30
GHz with a bandwidth of 8 GHz. We find that clusters with a mass above $2.5
\times 10^{14} h_{50}^{-1} M_\odot$ will be detected at any redshift, with the
exact limit showing a very modest redshift dependence. Using a Press-Schechter
prescription for evolving the number densities of clusters with redshift, we
determine that such a survey should find hundreds of galaxy clusters per year,
many at high redshifts and relatively low mass -- an important regime uniquely
accessible to SZE surveys. Currently favored cosmological models predict
roughly 25 clusters per square degree.",9912364v2
2000-02-17,K-Band Spectroscopy of an Obscured Massive Stellar Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC,"We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039)
with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the
vicinity of the southern nucleus (NGC 4039) in 0.39"" seeing in K-band using
NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the
near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the
highest surface brightness peak in the mid-IR (12-18 um) ISO image presented by
Mirabel et al (1998). We obtained high signal-to-noise 2.03-2.45 um spectra of
the nucleus and the obscured star cluster at R = 1900.
  The cluster is very young (age ~ 4 Myr), massive (M ~ 16E6 M_sun), and
compact (density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius),
assuming a Salpeter IMF (0.1-100 M_sun). Its hot stars have a radiation field
characterized by T_eff ~ 39,000 K, and they ionize a compact HII region with
n_e ~ 10^4 cm^(-3). The stars are deeply embedded in gas and dust (A_V = 9-10
mag), and their strong FUV field powers a clumpy photodissociation region with
densities n_H > 10^5 cm^(-3) on scales of ~ 200 pc, radiating L{H_2 1-0 S(1)}=
9600 L_sun.",0002357v1
2003-02-20,The Reionization History at High Redshifts II: Estimating the Optical Depth to Thomson Scattering from CMB Polarization,"In light of the recent inference of a high optical depth to Thomson
scattering, tau, from the WMAP data we investigate the effects of extended
periods of partial ionization and ask if the value of tau inferred by assuming
a single sharp transition is an unbiased estimate. We construct and consider
several representative ionization models and evaluate their signatures in the
CMB. If tau is estimated with a single sharp transition we show that there can
be a significant bias in the derived value (and therefore a bias in sigma8 as
well). For WMAP noise levels the bias in tau is smaller than the statistical
uncertainty, but for Planck or a cosmic variance limited experiment the tau
bias could be much larger than the statistical uncertainties. This bias can be
reduced in the ionization models we consider by fitting a slightly more
complicated ionization history, such as a two-step ionization process. Assuming
this two-step process we find the Planck satellite can simultaneously determine
the initial redshift of reionization to +-2 and tau to +-0.01 Uncertainty about
the ionization history appears to provide a limit of about 0.005 on how well
tau can be estimated from CMB polarization data, much better than expected from
WMAP but significantly worse than expected from cosmic-variance limits.",0302404v2
2007-02-27,The Sunyaev-Zeldovich Background,"The cosmic background due to the Sunyaev-Zeldovich (SZ) effect is expected to
be the largest signal at mm and cm wavelengths at a resolution of a few
arcminutes. We investigate some simple statistics of SZ maps and their scaling
with the normalization of the matter power spectrum, sigma_8, as well as the
effects of the unknown physics of the intracluster medium on these statistics.
We show that the SZ background provides a significant background for SZ cluster
searches, with the onset of confusion occurring around 10^{14} h^{-1} solar
masses in a cosmology-dependent way, where confusion is defined as typical
errors in recovered flux larger than 20%. The confusion limit, corresponds to
the mass at which there are roughly ten clusters per square degree, with this
number nearly independent of cosmology and cluster gas physics. Typical errors
grow quickly as lower mass objects are included in the catalog.
  We also point out that there is nothing in particular about the rms of the
filtered map that makes it especially well-suited for capturing aspects of the
SZ effect, and other indicators of the one-point SZ probability distribution
function are at least as well suited for the task. For example, the full width
at half maximum of the one point probability distribution has a field-to-field
scatter that is about 60% that of the rms.
  The simplest statistics of SZ maps are largely unaffected by cluster physics
such aspreheating, although the impact of preheating is clear by eye in the
maps.Studies aimed at learning about the physics of the intracluster medium
will apparently require more specialized statistical indicators.",0702727v1
1998-01-23,An Analytical Construction of the SRB Measures for Baker-type Maps,"For a class of dynamical systems, called the axiom-A systems, Sinai, Ruelle
and Bowen showed the existence of an invariant measure (SRB measure) weakly
attracting the temporal average of any initial distribution that is absolutely
continuous with respect to the Lebesgue measure. Recently, the SRB measures
were found to be related to the nonequilibrium stationary state distribution
functions for thermostated or open systems. Inspite of the importance of these
SRB measures, it is difficult to handle them analytically because they are
often singular functions. In this article, for three kinds of Baker-type maps,
the SRB measures are analytically constructed with the aid of a functional
equation, which was proposed by de Rham in order to deal with a class of
singular functions. We first briefly review the properties of singular
functions including those of de Rham. Then, the Baker-type maps are described,
one of which is non-conservative but time reversible, the second has a
Cantor-like invariant set, and the third is a model of a simple chemical
reaction $R \leftrightarrow I \leftrightarrow P$. For the second example, the
cases with and without escape are considered. For the last example, we consider
the reaction processes in a closed system and in an open system under a flux
boundary condition. In all cases, we show that the evolution equation of the
distribution functions partially integrated over the unstable direction is very
similar to de Rham's functional equation and, employing this analogy, we
explicitly construct the SRB measures.",9801031v2
1998-04-08,Entropy Production : From Open Volume Preserving to Dissipative Systems,"We generalize Gaspard's method for computing the \epsilon-entropy production
rate in Hamiltonian systems to dissipative systems with attractors considered
earlier by T\'el, Vollmer, and Breymann. This approach leads to a natural
definition of a coarse grained Gibbs entropy which is extensive, and which can
be expressed in terms of the SRB measures and volumes of the coarse graining
sets which cover the attractor. One can also study the entropy and entropy
production as functions of the degree of resolution of the coarse graining
process, and examine the limit as the coarse graining size approaches zero. We
show that this definition of the Gibbs entropy leads to a positive rate of
irreversible entropy production for reversible dissipative systems. We apply
the method to the case of a two dimensional map, based upon a model considered
by Vollmer, T\'el and Breymann, that is a deterministic version of a
biased-random walk. We treat both volume preserving and dissipative versions of
the basic map, and make a comparison between the two cases. We discuss the
\epsilon-entropy production rate as a function of the size of the coarse
graining cells for these biased-random walks and, for an open system with flux
boundary conditions, show regions of exponential growth and decay of the rate
of entropy production as the size of the cells decreases. This work describes
in some detail the relation between the results of Gaspard, those of T\'el,
Vollmer and Breymann, and those of Ruelle, on entropy production in various
systems described by Anosov or Anosov-like maps.",9804009v2
1998-07-23,A priori bounds for co-dimension one isometric embeddings,"We prove a priori bounds for the trace of the second fundamental form of a
$C^4$ isometric embedding into $R^{n+1}$ of a metric $g$ of non-negative
sectional curvature on $S^n$, in terms of the scalar curvature, and the
diameter of $g$. These estimates give a bound on the extrinsic geometry in
terms of intrinsic quantities. They generalize estimates originally obtained by
Weyl for the case $n=2$ and positive curvature, and then by P. Guan and the
first author for non-negative curvature and $n=2$. Using $C^{2,\alpha}$
interior estimates of Evans and Krylov for concave fully nonlinear elliptic
partial differential equations, these bounds allow us to obtain the following
convergence theorem: For any $\epsilon>0$, the set of metrics of non-negative
sectional curvature and scalar curvature bounded below by $\epsilon$ which are
isometrically embedable in Euclidean space $R^{n+1}$ is closed in the H\""older
space $C^{4,\alpha}$, $0<\alpha<1$. These results are obtained in an effort to
understand the following higher dimensional version of the Weyl embedding
problem which we propose: \emph{Suppose that $g$ is a smooth metric of
non-negative sectional curvature and positive scalar curvature on \S^n$ which
is locally isometrically embeddable in $R^{n+1}$. Does $(S^n,g)$ then admit a
smooth global isometric embedding into $R^{n+1}$?}",9807130v1
2002-07-02,Active and Passive Fields in Turbulent Transport: the Role of Statistically Preserved Structures,"We have recently proposed that the statistics of active fields (which affect
the velocity field itself) in well-developed turbulence are also dominated by
the Statistically Preserved Structures of auxiliary passive fields which are
advected by the same velocity field. The Statistically Preserved Structures are
eigenmodes of eigenvalue 1 of an appropriate propagator of the decaying
(unforced) passive field, or equivalently, the zero modes of a related
operator. In this paper we investigate further this surprising finding via two
examples, one akin to turbulent convection in which the temperature is the
active scalar, and the other akin to magneto-hydrodynamics in which the
magnetic field is the active vector. In the first example, all the even
correlation functions of the active and passive fields exhibit identical
scaling behavior. The second example appears at first sight to be a
counter-example: the statistical objects of the active and passive fields have
entirely different scaling exponents. We demonstrate nevertheless that the
Statistically Preserved Structures of the passive vector dominate again the
statistics of the active field, except that due to a dynamical conservation law
the amplitude of the leading zero mode cancels exactly. The active vector is
then dominated by the sub-leading zero mode of the passive vector. Our work
thus suggests that the statistical properties of active fields in turbulence
can be understood with the same generality as those of passive fields.",0207005v1
2001-06-07,"Secrecy, Computational Loads and Rates in Practical Quantum Cryptography","A number of questions associated with practical implementations of quantum
cryptography systems having to do with unconditional secrecy, computational
loads and effective secrecy rates in the presence of perfect and imperfect
sources are discussed. The different types of unconditional secrecy, and their
relationship to general communications security, are discussed in the context
of quantum cryptography. In order to actually carry out a quantum cryptography
protocol it is necessary that sufficient computational resources be available
to perform the various processing steps, such as sifting, error correction,
privacy amplification and authentication. We display the full computer machine
instruction requirements needed to support a practical quantum cryptography
implementation. We carry out a numerical comparison of system performance
characteristics for implementations that make use of either weak coherent
sources of light or perfect single photon sources, for eavesdroppers making
individual attacks on the quantum channel characterized by different levels of
technological capability. We find that, while in some circumstances it is best
to employ perfect single photon sources, in other situations it is preferable
to utilize weak coherent sources. In either case the secrecy level of the final
shared cipher is identical, with the relevant distinguishing figure-of-merit
being the effective throughput rate.",0106043v2
2001-08-02,Privacy Amplification in Quantum Key Distribution: Pointwise Bound versus Average Bound,"In order to be practically useful, quantum cryptography must not only provide
a guarantee of secrecy, but it must provide this guarantee with a useful,
sufficiently large throughput value. The standard result of generalized privacy
amplification yields an upper bound only on the average value of the mutual
information available to an eavesdropper. Unfortunately this result by itself
is inadequate for cryptographic applications. A naive application of the
standard result leads one to incorrectly conclude that an acceptable upper
bound on the mutual information has been achieved. It is the pointwise value of
the bound on the mutual information, associated with the use of some specific
hash function, that corresponds to actual implementations. We provide a fully
rigorous mathematical derivation that shows how to obtain a cryptographically
acceptable upper bound on the actual, pointwise value of the mutual
information. Unlike the bound on the average mutual information, the value of
the upper bound on the pointwise mutual information and the number of bits by
which the secret key is compressed are specified by two different parameters,
and the actual realization of the bound in the pointwise case is necessarily
associated with a specific failure probability. The constraints amongst these
parameters, and the effect of their values on the system throughput, have not
been previously analyzed. We show that the necessary shortening of the key
dictated by the cryptographically correct, pointwise bound, can still produce
viable throughput rates that will be useful in practice.",0108013v1
2008-03-27,Assessing surrogate endpoints in vaccine trials with case-cohort sampling and the Cox model,"Assessing immune responses to study vaccines as surrogates of protection
plays a central role in vaccine clinical trials. Motivated by three ongoing or
pending HIV vaccine efficacy trials, we consider such surrogate endpoint
assessment in a randomized placebo-controlled trial with case-cohort sampling
of immune responses and a time to event endpoint. Based on the principal
surrogate definition under the principal stratification framework proposed by
Frangakis and Rubin [Biometrics 58 (2002) 21--29] and adapted by Gilbert and
Hudgens (2006), we introduce estimands that measure the value of an immune
response as a surrogate of protection in the context of the Cox proportional
hazards model. The estimands are not identified because the immune response to
vaccine is not measured in placebo recipients. We formulate the problem as a
Cox model with missing covariates, and employ novel trial designs for
predicting the missing immune responses and thereby identifying the estimands.
The first design utilizes information from baseline predictors of the immune
response, and bridges their relationship in the vaccine recipients to the
placebo recipients. The second design provides a validation set for the
unmeasured immune responses of uninfected placebo recipients by immunizing them
with the study vaccine after trial closeout. A maximum estimated likelihood
approach is proposed for estimation of the parameters. Simulated data examples
are given to evaluate the proposed designs and study their properties.",0803.3919v1
2008-06-13,The Formation and Evolution of Massive Stellar Clusters in IC 4662,"We present a multiwavelength study of the formation of massive stellar
clusters, their emergence from cocoons of gas and dust, and their feedback on
surrounding matter. Using data that span from radio to optical wavelengths,
including Spitzer and Hubble ACS observations, we examine the population of
young star clusters in the central starburst region of the irregular Wolf-Rayet
galaxy IC 4662. We model the radio-to-IR spectral energy distributions of
embedded clusters to determine the properties of their HII regions and dust
cocoons (sizes, masses, densities, temperatures), and use near-IR and optical
data with mid-IR spectroscopy to constrain the properties of the embedded
clusters themselves (mass, age, extinction, excitation, abundance). The two
massive star-formation regions in IC 4662 are excited by stellar populations
with ages of ~ 4 million years and masses of ~ 3 x 10^5 M_sun (assuming a
Kroupa IMF). They have high excitation and sub-solar abundances, and they may
actually be comprised of several massive clusters rather than the single
monolithic massive compact objects known as Super Star Clusters (SSCs). Mid-IR
spectra reveal that these clusters have very high extinctions, A_V ~ 20-25 mag,
and that the dust in IC 4662 is well-mixed with the emitting gas, not in a
foreground screen.",0806.2302v1
2009-01-28,Searching for Main-Belt Comets Using the Canada-France-Hawaii Telescope Legacy Survey,"The Canada-France-Hawaii Telescope Legacy Survey, specifically the Very Wide
segment of data, is used to search for possible main-belt comets. In the first
data set, 952 separate objects with asteroidal orbits within the main-belt are
examined using a three-level technique. First, the full-width-half-maximum of
each object is compared to stars of similar magnitude, to look for evidence of
a coma. Second, the brightness profiles of each object are compared with three
stars of the same magnitude, which are nearby on the image to ensure any
extended profile is not due to imaging variations. Finally, the star profiles
are subtracted from the asteroid profile and the residuals are compared with
the background using an unpaired T-test. No objects in this survey show
evidence of cometary activity. The second survey includes 11438 objects in the
main-belt, which are examined visually. One object, an unknown comet, is found
to show cometary activity. Its motion is consistent with being a main-belt
asteroid, but the observed arc is too short for a definitive orbit calculation.
No other body in this survey shows evidence of cometary activity. Upper limits
of the number of weakly and strongly active main-belt comets are derived to be
630+/-77 and 87+/-28, respectively. These limits are consistent with those
expected from asteroid collisions. In addition, data extracted from the
Canada-France-Hawaii Telescope image archive of main-belt comet 176P/LINEAR is
presented.",0901.4511v1
2009-10-02,Spectroscopic Observations of New Oort Cloud Comet 2006 VZ13 and Four Other Comets,"Spectral data are presented for comets 2006 VZ13 (LINEAR), 2006 K4 (NEAT),
2006 OF2 (Broughton), 2P/Encke, and 93P/Lovas I, obtained with the Cerro-Tololo
Inter-American Observatory 1.5-m telescope in August 2007. Comet 2006 VZ13 is a
new Oort cloud comet and shows strong lines of CN (3880 angstroms), the Swan
band sequence for C_2 (4740, 5160, and 5630 angstroms), C_3 (4056 angstroms),
and other faint species. Lines are also identified in the spectra of the other
comets. Flux measurements of the CN, C_2 (Delta v = +1,0), and C_3 lines are
recorded for each comet and production rates and ratios are derived. When
considering the comets as a group, there is a correlation of C_2 and C_3
production with CN, but there is no conclusive evidence that the production
rate ratios depend on heliocentric distance. The continuum is also measured,
and the dust production and dust-to-gas ratios are calculated. There is a
general trend, for the group of comets, between the dust-to-gas ratio and
heliocentric distance, but it does not depend on dynamical age or class. Comet
2006 VZ13 is determined to be in the carbon-depleted (or Tempel 1 type) class.",0910.0416v1
2009-12-01,Approximate Sparse Recovery: Optimizing Time and Measurements,"An approximate sparse recovery system consists of parameters $k,N$, an
$m$-by-$N$ measurement matrix, $\Phi$, and a decoding algorithm, $\mathcal{D}$.
Given a vector, $x$, the system approximates $x$ by $\widehat x
=\mathcal{D}(\Phi x)$, which must satisfy $\| \widehat x - x\|_2\le C \|x -
x_k\|_2$, where $x_k$ denotes the optimal $k$-term approximation to $x$. For
each vector $x$, the system must succeed with probability at least 3/4. Among
the goals in designing such systems are minimizing the number $m$ of
measurements and the runtime of the decoding algorithm, $\mathcal{D}$.
  In this paper, we give a system with $m=O(k \log(N/k))$
measurements--matching a lower bound, up to a constant factor--and decoding
time $O(k\log^c N)$, matching a lower bound up to $\log(N)$ factors.
  We also consider the encode time (i.e., the time to multiply $\Phi$ by $x$),
the time to update measurements (i.e., the time to multiply $\Phi$ by a
1-sparse $x$), and the robustness and stability of the algorithm (adding noise
before and after the measurements). Our encode and update times are optimal up
to $\log(N)$ factors.",0912.0229v1
2010-04-07,Concatenated quantum codes can attain the quantum Gilbert-Varshamov bound,"A family of quantum codes of increasing block length with positive rate is
asymptotically good if the ratio of its distance to its block length approaches
a positive constant. The asymptotic quantum Gilbert-Varshamov (GV) bound states
that there exist $q$-ary quantum codes of sufficiently long block length $N$
having fixed rate $R$ with distance at least $N H^{-1}_{q^2}((1-R)/2)$, where
$H_{q^2}$ is the $q^2$-ary entropy function. For $q < 7$, only random quantum
codes are known to asymptotically attain the quantum GV bound. However, random
codes have little structure. In this paper, we generalize the classical result
of Thommesen to the quantum case, thereby demonstrating the existence of
concatenated quantum codes that can asymptotically attain the quantum GV bound.
The outer codes are quantum generalized Reed-Solomon codes, and the inner codes
are random independently chosen stabilizer codes, where the rates of the inner
and outer codes lie in a specified feasible region.",1004.1127v6
2010-09-02,Stable and unstable regimes in higher-dimensional convex billiards with cylindrical shape,"We introduce a class of convex, higher-dimensional billiard models which
generalise stadium billiards. These models correspond to the free motion of a
point-particle in a region bounded by cylinders cut by planes. They are
motivated by models of particles interacting via a string-type mechanism, and
confined by hard walls. The combination of these elements may give rise to a
defocusing mechanism, similar to that in two dimensions, which allows large
chaotic regions in phase space. The remaining part of phase space is associated
with marginally stable behaviour. In fact periodic orbits in these systems
generically come in continuous parametric families, sociated with a pair of
parabolic eigen-directions: the periodic orbits are unstable in the presence of
a defocusing mechanism, but marginally stable otherwise. By performing the
stability analysis of families of periodic orbits at a nonlinear level, we
establish the conditions under which families are nonlinearly stable or
unstable. As a result, we identify regions in the parameter space of the models
which admit non-linearly stable oscillations in the form of whispering gallery
modes. Where no families of periodic orbits are stable, the billiards are
completely chaotic, i.e.\ the Lyapunov exponents of the billiard map are
non-zero.",1009.0337v1
2011-08-29,"Magnetization Dynamics, Throughput and Energy Dissipation in a Universal Multiferroic Nanomagnetic Logic Gate with Fan-in and Fan-out","The switching dynamics of a multiferroic nanomagnetic NAND gate with
fan-in/fan-out is simulated by solving the Landau-Lifshitz-Gilbert (LLG)
equation while neglecting thermal fluctuation effects. The gate and logic wires
are implemented with dipole-coupled 2-phase (magnetostrictive/piezoelectric)
multiferroic elements that are clocked with electrostatic potentials of ~50 mV
applied to the piezoelectric layer generating 10 MPa stress in the
magnetostrictive layers for switching. We show that a pipeline bit throughput
rate of ~ 0.5 GHz is achievable with proper magnet layout and sinusoidal
four-phase clocking. The gate operation is completed in 2 ns with a latency of
4 ns. The total (internal + external) energy dissipated for a single gate
operation at this throughput rate is found to be only ~ 1000 kT in the gate and
~3000 kT in the 12-magnet array comprising two input and two output wires for
fan-in and fan-out. This makes it respectively 3 and 5 orders of magnitude more
energy-efficient than complementary-metal-oxide-semiconductor-transistor (CMOS)
based and spin-transfer-torque-driven nanomagnet based NAND gates. Finally, we
show that the dissipation in the external clocking circuit can always be
reduced asymptotically to zero using increasingly slow adiabatic clocking, such
as by designing the RC time constant to be 3 orders of magnitude smaller than
the clocking period. However, the internal dissipation in the device must
remain and cannot be eliminated if we want to perform fault-tolerant classical
computing.
  Keywords: Nanomagnetic logic, multiferroics, straintronics and spintronics,
Landau-Lifshitz-Gilbert equation.",1108.5758v1
2011-09-15,Stato evolutivo delle stelle della Cintura di Orione ed implicazioni archeoastronomiche,"In the present work it is evaluated the evolutionary state of the Orion Belt
stars, an asterism very important for the ancient Egyptians, finding that, when
the pyramids were built, the brightness of the three stars of the Belt was
practically the same as today. This not trivial result has important
implications in the framework of the so-called Orion Correlation Theory, a
controversial theory proposed by Bauval and Gilbert (1994), according to which
a perfect coincidence would exist between the disposition of the three stars of
the Orion Belt and that of the main Giza pyramids, so that the latter would
represent the monumental reproduction on the ground of that important asterism.
  ----
  Nel presente lavoro viene determinato lo stato evolutivo delle stelle della
Cintura di Orione, ricavando che, all'epoca della costruzione delle piramidi,
la luminosita' delle tre stelle della Cintura era di fatto uguale a quella
odierna. Tale non banale risultato riveste una importanza fondamentale
nell'ambito della verifica della controversa Teoria della Correlazione di
Orione proposta da Bauval e Gilbert nel 1994, secondo la quale esisterebbe una
perfetta coincidenza tra la disposizione delle tre stelle della Cintura e
quella delle tre piramidi nella piana di Giza.",1109.3284v2
2012-07-31,Surface Acoustic Wave-Driven Ferromagnetic Resonance in Nickel Thin Films: Theory and Experiment,"We present an extensive experimental and theoretical study of surface
acoustic wave-driven ferromagnetic resonance. In a first modeling approach
based on the Landau-Lifshitz-Gilbert equation, we derive expressions for the
magnetization dynamics upon magnetoelastic driving that are used to calculate
the absorbed microwave power upon magnetic resonance as well as the spin
current density generated by the precessing magnetization in the vicinity of a
ferromagnet/normal metal interface. In a second modeling approach, we deal with
the backaction of the magnetization dynamics on the elastic wave by solving the
elastic wave equation and the Landau-Lifshitz-Gilbert equation
selfconsistently, obtaining analytical solutions for the acoustic wave phase
shift and attenuation. We compare both modeling approaches with the complex
forward transmission of a LiNbO$_3$/Ni surface acoustic wave hybrid device
recorded experimentally as a function of the external magnetic field
orientation and magnitude, rotating the field within three different planes and
employing three different surface acoustic wave frequencies. We find
quantitative agreement of the experimentally observed power absorption and
surface acoustic wave phase shift with our modeling predictions using one set
of parameters for all field configurations and frequencies.",1208.0001v1
2012-09-27,Vortex Lattices in the Superconducting Phases of Doped Topological Insulators and Heterostructures,"Majorana fermions are predicted to play a crucial role in condensed matter
realizations of topological quantum computation. These heretofore undiscovered
quasiparticles have been predicted to exist at the cores of vortex excitations
in topological superconductors and in heterostructures of superconductors and
materials with strong spin-orbit coupling. In this work we examine topological
insulators with bulk s-wave superconductivity in the presence of a
vortex-lattice generated by a perpendicular magnetic field. Using
self-consistent Bogoliubov-de Gennes, calculations we confirm that beyond the
semi-classical, weak-pairing limit that the Majorana vortex states appear as
the chemical potential is tuned from either side of the band edge so long as
the density of states is sufficient for superconductivity to form. Further, we
demonstrate that the previously predicted vortex phase transition survives
beyond the semi-classical limit. At chemical potential values smaller than the
critical chemical potential, the vortex lattice modes hybridize within the top
and bottom surfaces giving rise to a dispersive low-energy mid-gap band. As the
chemical potential is increased, the Majorana states become more localized
within a single surface but spread into the bulk toward the opposite surface.
Eventually, when the chemical potential is sufficiently high in the bulk bands,
the Majorana modes can tunnel between surfaces and eventually a critical point
is reached at which modes on opposite surfaces can freely tunnel and annihilate
leading to the topological phase transition previously studied in the work of
Hosur et al.",1209.6373v1
2013-04-23,L2/L2-foreach sparse recovery with low risk,"In this paper, we consider the ""foreach"" sparse recovery problem with failure
probability $p$. The goal of which is to design a distribution over $m \times
N$ matrices $\Phi$ and a decoding algorithm $\algo$ such that for every
$\vx\in\R^N$, we have the following error guarantee with probability at least
$1-p$ \[\|\vx-\algo(\Phi\vx)\|_2\le C\|\vx-\vx_k\|_2,\] where $C$ is a constant
(ideally arbitrarily close to 1) and $\vx_k$ is the best $k$-sparse
approximation of $\vx$.
  Much of the sparse recovery or compressive sensing literature has focused on
the case of either $p = 0$ or $p = \Omega(1)$. We initiate the study of this
problem for the entire range of failure probability. Our two main results are
as follows: \begin{enumerate} \item We prove a lower bound on $m$, the number
measurements, of $\Omega(k\log(n/k)+\log(1/p))$ for $2^{-\Theta(N)}\le p <1$.
Cohen, Dahmen, and DeVore \cite{CDD2007:NearOptimall2l2} prove that this bound
is tight. \item We prove nearly matching upper bounds for \textit{sub-linear}
time decoding. Previous such results addressed only $p = \Omega(1)$.
\end{enumerate}
  Our results and techniques lead to the following corollaries: (i) the first
ever sub-linear time decoding $\lolo$ ""forall"" sparse recovery system that
requires a $\log^{\gamma}{N}$ extra factor (for some $\gamma<1$) over the
optimal $O(k\log(N/k))$ number of measurements, and (ii) extensions of Gilbert
et al. \cite{GHRSW12:SimpleSignals} results for information-theoretically
bounded adversaries.",1304.6232v1
2013-11-28,"Starbugs: all-singing, all-dancing fibre positioning robots","Starbugs are miniature piezoelectric 'walking' robots with the ability to
simultaneously position many optical fibres across a telescope's focal plane.
Their simple design incorporates two piezoceramic tubes to form a pair of
concentric 'legs' capable of taking individual steps of a few microns, yet with
the capacity to move a payload several millimetres per second. The Australian
Astronomical Observatory has developed this technology to enable fast and
accurate field reconfigurations without the inherent limitations of more
traditional positioning techniques, such as the 'pick and place' robotic arm.
We report on our recent successes in demonstrating Starbug technology, driven
principally by R&D efforts for the planned MANIFEST (many instrument
fibre-system) facility for the Giant Magellan Telescope. Significant
performance gains have resulted from improvements to the Starbug system,
including i) the use of a vacuum to attach Starbugs to the underside of a
transparent field plate, ii) optimisation of the control electronics, iii) a
simplified mechanical design with high sensitivity piezo actuators, and iv) the
construction of a dedicated laboratory 'test rig'. A method of reliably
rotating Starbugs in steps of several arcminutes has also been devised, which
integrates with the pre-existing x-y movement directions and offers greater
flexibility while positioning. We present measured performance data from a
prototype system of 10 Starbugs under full (closed-loop control), at field
plate angles of 0-90 degrees.",1311.7371v1
2014-02-05,Magnetization dynamics: path-integral formalism for the stochastic Landau-Lifshitz-Gilbert equation,"We construct a path-integral representation of the generating functional for
the dissipative dynamics of a classical magnetic moment as described by the
stochastic generalization of the Landau-Lifshitz-Gilbert equation proposed by
Brown, with the possible addition of spin-torque terms. In the process of
constructing this functional in the Cartesian coordinate system, we critically
revisit this stochastic equation. We present it in a form that accommodates for
any discretization scheme thanks to the inclusion of a drift term. The
generalized equation ensures the conservation of the magnetization modulus and
the approach to the Gibbs-Boltzmann equilibrium in the absence of non-potential
and time-dependent forces. The drift term vanishes only if the mid-point
Stratonovich prescription is used. We next reset the problem in the more
natural spherical coordinate system. We show that the noise transforms
non-trivially to spherical coordinates acquiring a non-vanishing mean value in
this coordinate system, a fact that has been often overlooked in the
literature. We next construct the generating functional formalism in this
system of coordinates for any discretization prescription. The functional
formalism in Cartesian or spherical coordinates should serve as a starting
point to study different aspects of the out-of-equilibrium dynamics of magnets.
Extensions to colored noise, micro-magnetism and disordered problems are
straightforward.",1402.1200v2
2014-10-17,The fixed irreducible bridge ensemble for self-avoiding walks,"We define a new ensemble for self-avoiding walks in the upper half-plane, the
fixed irredicible bridge ensemble, by considering self-avoiding walks in the
upper half-plane up to their $n$-th bridge height, $Y_n$, and scaling the walk
by $1/Y_n$ to obtain a curve in the unit strip, and then taking $n\to\infty$.
We then conjecture a relationship between this ensemble to $\SLE$ in the unit
strip from $0$ to a fixed point along the upper boundary of the strip,
integrated over the conjectured exit density of self-avoiding walk spanning a
strip in the scaling limit. We conjecture that there exists a positive constant
$\sigma$ such that $n^{-\sigma}Y_n$ converges in distribution to that of a
stable random variable as $n\to\infty$. Then the conjectured relationship
between the fixed irreducible bridge scaling limit and $\SLE$ can be described
as follows: If one takes a SAW considered up to $Y_n$ and scales by $1/Y_n$ and
then weights the walk by $Y_n$ to an appropriate power, then in the limit
$n\to\infty$, one should obtain a curve from the scaling limit of the
self-avoiding walk spanning the unit strip. In addition to a heuristic
derivation, we provide numerical evidence to support the conjecture and give
estimates for the boundary scaling exponent.",1410.4796v1
2014-11-20,Type II Seesaw Higgsology and LEP/LHC constraints,"In the {\sl type II seesaw} model, if spontaneous violation of the lepton
number conservation prevails over that of explicit violation, a rich Higgs
sector phenomenology is expected to arise with light scalar states having mixed
charged-fermiophobic/neutrinophilic properties. We study the constraints on
these light CP-even ($h^0$) and CP-odd ($A^0$) states from LEP exclusion
limits, combined with the so far established limits and properties of the
$125-126$~GeV ${\cal H}$ boson discovered at the LHC. We show that, apart from
a fine-tuned region of the parameter space, masses in the $\sim 44$ to $80$ GeV
range escape from the LEP limits if the vacuum expectation value of the Higgs
triplet is $\lesssim {\cal O}(10^{-3})$GeV, that is comfortably in the region
for 'natural' generation of Majorana neutrino masses within this model. In the
lower part of the scalar mass spectrum the decay channels ${\cal H} \to h^0
h^0, A^0 A^0$ lead predominantly to heavy flavor plus missing energy or to
totally invisible Higgs decays, mimicking dark matter signatures without a dark
matter candidate. Exclusion limits at the percent level of these
(semi-)invisible decay channels would be needed, together with stringent bounds
on the (doubly-)charged states, to constrain significantly this scenario. We
also revisit complementary constraints from ${\cal H} \to \gamma \gamma$ and
${\cal H} \to Z \gamma$ channels on the (doubly)charged scalar sector of the
model, pinpointing non-sensitivity regions, and carry out a likeliness study
for the theoretically allowed couplings in the scalar potential.",1411.5645v1
2015-01-11,Epidemic Threshold of an SIS Model in Dynamic Switching Networks,"In this paper, we analyze dynamic switching networks, wherein the networks
switch arbitrarily among a set of topologies. For this class of dynamic
networks, we derive an epidemic threshold, considering the SIS epidemic model.
First, an epidemic probabilistic model is developed assuming independence
between states of nodes. We identify the conditions under which the epidemic
dies out by linearizing the underlying dynamical system and analyzing its
asymptotic stability around the origin. The concept of joint spectral radius is
then used to derive the epidemic threshold, which is later validated using
several networks (Watts-Strogatz, Barabasi-Albert, MIT reality mining graphs,
Regular, and Gilbert). A simplified version of the epidemic threshold is
proposed for undirected networks. Moreover, in the case of static networks, the
derived epidemic threshold is shown to match conventional analytical results.
Then, analytical results for the epidemic threshold of dynamic networksare
proved to be applicable to periodic networks. For dynamic regular networks, we
demonstrate that the epidemic threshold is identical to the epidemic threshold
for static regular networks. An upper bound for the epidemic spread probability
in dynamic Gilbert networks is also derived and verified using simulation.",1501.02472v2
2015-04-29,Entropy measures as geometrical tools in the study of cosmology,"Classical chaos is often characterized as exponential divergence of nearby
trajectories. In many interesting cases these trajectories can be identified
with geodesic curves. We define here the entropy by $S = \ln \chi (x)$ with
$\chi(x)$ being the distance between two nearby geodesics. We derive an
equation for the entropy which by transformation to a Ricatti-type equation
becomes similar to the Jacobi equation. We further show that the geodesic
equation for a null geodesic in a double warped space time leads to the same
entropy equation. By applying a Robertson-Walker metric for a flat
three-dimensional Euclidian space expanding as a function of time, we again
reach the entropy equation stressing the connection between the chosen entropy
measure and time. We finally turn to the Raychaudhuri equation for expansion,
which also is a Ricatti equation similar to the transformed entropy equation.
Those Ricatti-type equations have solutions of the same form as the Jacobi
equation. The Raychaudhuri equation can be transformed to a harmonic oscillator
equation, and it has been shown that the geodesic deviation equation of Jacobi
is essentially equivalent to that of a harmonic oscillator. The Raychaudhuri
equations are strong geometrical tools in the study of General Relativity and
Cosmology. We suggest a refined entropy measure applicable in Cosmology and
defined by the average deviation of the geodesics in a congruence.",1504.07855v2
2015-06-24,Ebb: A DSL for Physical Simulation on CPUs and GPUs,"Designing programming environments for physical simulation is challenging
because simulations rely on diverse algorithms and geometric domains. These
challenges are compounded when we try to run efficiently on heterogeneous
parallel architectures. We present Ebb, a domain-specific language (DSL) for
simulation, that runs efficiently on both CPUs and GPUs. Unlike previous DSLs,
Ebb uses a three-layer architecture to separate (1) simulation code, (2)
definition of data structures for geometric domains, and (3) runtimes
supporting parallel architectures. Different geometric domains are implemented
as libraries that use a common, unified, relational data model. By structuring
the simulation framework in this way, programmers implementing simulations can
focus on the physics and algorithms for each simulation without worrying about
their implementation on parallel computers. Because the geometric domain
libraries are all implemented using a common runtime based on relations, new
geometric domains can be added as needed, without specifying the details of
memory management, mapping to different parallel architectures, or having to
expand the runtime's interface.
  We evaluate Ebb by comparing it to several widely used simulations,
demonstrating comparable performance to hand-written GPU code where available,
and surpassing existing CPU performance optimizations by up to 9$\times$ when
no GPU code exists.",1506.07577v3
2016-04-27,Scoping of material response under DEMO neutron irradiation: comparison with fission and influence of nuclear library selection,"Predictions of material activation inventories will be a key input to
virtually all aspects of the operation, safety and environmental assessment of
future fusion nuclear plants. Additionally, the neutron-induced transmutation
(change) of material composition (inventory) with time, and the creation and
evolution of configurational damage from atomic displacements, require precise
quantification because they can lead to significant changes in material
properties, and thus influence reactor-component lifetime. A comprehensive
scoping study has been performed to quantify the activation, transmutation
(depletion and build-up) and immediate damage response under neutron
irradiation for all naturally occurring elements from hydrogen to bismuth. The
resulting database provides a global picture of the response of a material,
covering the majority of nuclear technological space, but focussing
specifically on typical conditions expected for a demonstration fusion power
plant (DEMO). Results from fusion are compared against typical fission
conditions for selected fusion relevant materials, demonstrating that the
latter cannot be relied upon to give accurate scalable experimental predictions
of material response in a future fusion reactor. Results from different nuclear
data libraries are also compared, highlighting the variations and deficiencies.",1604.08496v1
2016-05-23,Beyond the Interface Limit: Structural and Magnetic Depth Profiles of Voltage-Controlled Magneto-Ionic Heterostructures,"Electric-field control of magnetism provides a promising route towards
ultralow power information storage and sensor technologies. The effects of
magneto-ionic motion have so far been prominently featured in the direct
modification of interface chemical and physical characteristics. Here we
demonstrate magnetoelectric coupling moderated by voltage-driven oxygen
migration beyond the interface limit in relatively thick AlOx/GdOx/Co (15 nm)
films. Oxygen migration and its ramifications on the Co magnetization are
quantitatively mapped with polarized neutron reflectometry under thermal and
electro-thermal conditionings. The depth-resolved profiles uniquely identify
interfacial and bulk behaviors and a semi-reversible suppression and recovery
of the magnetization. Magnetometry measurements show that the conditioning
changes the microstructure so as to disrupt long-range ferromagnetic ordering,
resulting in an additional magnetically soft phase. X-ray spectroscopy confirms
electric field induced changes in the Co oxidation state but not in the Gd,
suggesting that the GdOx transmits oxygen but does not source or sink it. These
results together provide crucial insight into controlling magnetic
heterostructures via magneto-ionic motion, not only at the interface, but also
throughout the bulk of the films.",1605.07209v1
2016-06-02,RankSign: an efficient signature algorithm based on the rank metric,"In this paper we propose a new approach to code-based signatures that makes
use in particular of rank metric codes. When the classical approach consists in
finding the unique preimage of a syndrome through a decoding algorithm, we
propose to introduce the notion of mixed decoding of erasures and errors for
building signature schemes. In that case the difficult problem becomes, as is
the case in lattice-based cryptography, finding a preimage of weight above the
Gilbert-Varshamov bound (case where many solutions occur) rather than finding a
unique preimage of weight below the Gilbert-Varshamov bound. The paper
describes RankSign: a new signature algorithm for the rank metric based on a
new mixed algorithm for decoding erasures and errors for the recently
introduced Low Rank Parity Check (LRPC) codes. We explain how it is possible
(depending on choices of parameters) to obtain a full decoding algorithm which
is able to find a preimage of reasonable rank weight for any random syndrome
with a very strong probability. We study the semantic security of our signature
algorithm and show how it is possible to reduce the unforgeability to direct
attacks on the public matrix, so that no information leaks through signatures.
Finally, we give several examples of parameters for our scheme, some of which
with public key of size $11,520$ bits and signature of size $1728$ bits.
Moreover the scheme can be very fast for small base fields.",1606.00629v2
2016-09-09,Image and Video Mining through Online Learning,"Within the field of image and video recognition, the traditional approach is
a dataset split into fixed training and test partitions. However, the labelling
of the training set is time-consuming, especially as datasets grow in size and
complexity. Furthermore, this approach is not applicable to the home user, who
wants to intuitively group their media without tirelessly labelling the
content. Our interactive approach is able to iteratively cluster classes of
images and video. Our approach is based around the concept of an image
signature which, unlike a standard bag of words model, can express
co-occurrence statistics as well as symbol frequency. We efficiently compute
metric distances between signatures despite their inherent high dimensionality
and provide discriminative feature selection, to allow common and distinctive
elements to be identified from a small set of user labelled examples. These
elements are then accentuated in the image signature to increase similarity
between examples and pull correct classes together. By repeating this process
in an online learning framework, the accuracy of similarity increases
dramatically despite labelling only a few training examples. To demonstrate
that the approach is agnostic to media type and features used, we evaluate on
three image datasets (15 scene, Caltech101 and FG-NET), a mixed text and image
dataset (ImageTag), a dataset used in active learning (Iris) and on three
action recognition datasets (UCF11, KTH and Hollywood2). On the UCF11 video
dataset, the accuracy is 86.7% despite using only 90 labelled examples from a
dataset of over 1200 videos, instead of the standard 1122 training videos. The
approach is both scalable and efficient, with a single iteration over the full
UCF11 dataset of around 1200 videos taking approximately 1 minute on a standard
desktop machine.",1609.02770v2
2016-11-17,Stashing the stops in multijet events at the LHC,"While the presence of a light stop is increasingly disfavored by the
experimental limits set on R-parity conserving scenarios, the naturalness of
supersymmetry could still be safely concealed in the more challenging final
states predicted by the existence of non-null R-parity violating couplings.
Although R-parity violating signatures are extensively looked for at the Large
Hadron Collider, these searches always assume 100\% branching ratios for the
direct decays of supersymmetric particles into Standard Model ones. In this
paper we scrutinize the implications of relaxing this assumption by focusing on
one motivated scenario where the lightest stop is heavier than a chargino and a
neutralino. Considering a class of R-parity baryon number violating couplings,
we show on general grounds that while the direct decay of the stop into
Standard Model particles is dominant for large values of these couplings,
smaller values give rise, instead, to the dominance of a plethora of longer
decay chains and richer final states that have not yet been analyzed at the
LHC, thus weakening the impact of the present experimental stop mass limits. We
characterize the case for R-parity baryon number violating couplings in the
$10^{-7} - 10^{-1}$ range, in two different benchmark points scenarios within
the model-independent setting of the low-energy phenomenological Minimal
Supersymmetric Standard Model. We identify the different relevant experimental
signatures, estimate the corresponding proton--proton cross sections at
$\sqrt{s}=14$ TeV and discuss signal versus background issues.",1611.05850v2
2017-02-18,Inf-sup stable finite-element methods for the Landau--Lifshitz--Gilbert and harmonic map heat flow equation,"In this paper we propose and analyze a finite element method for both the
harmonic map heat and Landau--Lifshitz--Gilbert equation, the time variable
remaining continuous. Our starting point is to set out a unified saddle point
approach for both problems in order to impose the unit sphere constraint at the
nodes since the only polynomial function satisfying the unit sphere constraint
everywhere are constants. A proper inf-sup condition is proved for the Lagrange
multiplier leading to the well-posedness of the unified formulation. \emph{A
priori} energy estimates are shown for the proposed method.
  When time integrations are combined with the saddle point finite element
approximation some extra elaborations are required in order to ensure both
\emph{a priori} energy estimates for the director or magnetization vector
depending on the model and an inf-sup condition for the Lagrange multiplier.
This is due to the fact that the unit length at the nodes is not satisfied in
general when a time integration is performed. We will carry out a linear Euler
time-stepping method and a non-linear Crank--Nicolson method. The latter is
solved by using the former as a non-linear solver.",1702.05588v2
2017-06-15,Generalized Voltage-based State-Space Modelling of Modular Multilevel Converters with Constant Equilibrium in Steady-State,"This paper demonstrates that the sum and difference of the upper and lower
arm voltages are suitable variables for deriving a generalized state-space
model of an MMC which settles at a constant equilibrium in steady-state
operation, while including the internal voltage and current dynamics. The
presented modelling approach allows for separating the multiple frequency
components appearing within the MMC as a first step of the model derivation, to
avoid variables containing multiple frequency components in steady-state. On
this basis, it is shown that Park transformations at three different
frequencies ($+\omega$, $-2\omega$ and $+3\omega$) can be applied for deriving
a model formulation where all state-variables will settle at constant values in
steady-state, corresponding to an equilibrium point of the model. The resulting
model is accurately capturing the internal current and voltage dynamics of a
three-phase MMC, independently from how the control system is implemented. The
main advantage of this model formulation is that it can be linearised, allowing
for eigenvalue-based analysis of the MMC dynamics. Furthermore, the model can
be utilized for control system design by multi-variable methods requiring any
stable equilibrium to be defined by a fixed operating point. Time-domain
simulations in comparison to an established average model of the MMC, as well
as results from a detailed simulation model of an MMC with 400 sub-modules per
arm, are presented as verification of the validity and accuracy of the
developed model.",1706.04959v1
2017-11-07,Global Properties of M31's Stellar Halo from the SPLASH Survey: III. Measuring the Stellar Velocity Dispersion Profile,"We present the velocity dispersion of red giant branch (RGB) stars in M31's
halo, derived by modeling the line of sight velocity distribution of over 5000
stars in 50 fields spread throughout M31's stellar halo. The dataset was
obtained as part of the SPLASH (Spectroscopic and Photometric Landscape of
Andromeda's Stellar Halo) Survey, and covers projected radii of 9 to 175 kpc
from M31's center. All major structural components along the line of sight in
both the Milky Way (MW) and M31 are incorporated in a Gaussian Mixture Model,
including all previously identified M31 tidal debris features in the observed
fields. The probability an individual star is a constituent of M31 or the MW,
based on a set of empirical photometric and spectroscopic diagnostics, is
included as a prior probability in the mixture model. The velocity dispersion
of stars in M31's halo is found to decrease only mildly with projected radius,
from 108 km/s in the innermost radial bin (8.2 to 14.1 kpc) to $\sim 80$ to 90
km/s at projected radii of $\sim 40$ to 130 kpc, and can be parameterized with
a power-law of slope $-0.12\pm 0.05$. The quoted uncertainty on the power-law
slope reflects only the precision of the method, although other sources of
uncertainty we consider contribute negligibly to the overall error budget.",1711.02700v1
2017-12-19,Efficient implementations of the Multivariate Decomposition Method for approximating infinite-variate integrals,"In this paper we focus on efficient implementations of the Multivariate
Decomposition Method (MDM) for approximating integrals of $\infty$-variate
functions. Such $\infty$-variate integrals occur for example as expectations in
uncertainty quantification. Starting with the anchored decomposition $f =
\sum_{\mathfrak{u}\subset\mathbb{N}} f_\mathfrak{u}$, where the sum is over all
finite subsets of $\mathbb{N}$ and each $f_\mathfrak{u}$ depends only on the
variables $x_j$ with $j\in\mathfrak{u}$, our MDM algorithm approximates the
integral of $f$ by first truncating the sum to some `active set' and then
approximating the integral of the remaining functions $f_\mathfrak{u}$
term-by-term using Smolyak or (randomized) quasi-Monte Carlo (QMC) quadratures.
The anchored decomposition allows us to compute $f_\mathfrak{u}$ explicitly by
function evaluations of $f$. Given the specification of the active set and
theoretically derived parameters of the quadrature rules, we exploit structures
in both the formula for computing $f_\mathfrak{u}$ and the quadrature rules to
develop computationally efficient strategies to implement the MDM in various
scenarios. In particular, we avoid repeated function evaluations at the same
point. We provide numerical results for a test function to demonstrate the
effectiveness of the algorithm.",1712.06782v3
2018-05-24,Impact of thermal fluctuations on transport in antiferromagnetic semimetals,"Recent demonstrations on manipulating antiferromagnetic (AF) order have
triggered a growing interest in antiferromagnetic metal (AFM), and potential
high-density spintronic applications demand further improvements in the
anisotropic magnetoresistance (AMR). The antiferromagnetic semimetals (AFS) are
newly discovered materials that possess massless Dirac fermions that are
protected by the crystalline symmetries. In this material, a reorientation of
the AF order may break the underlying symmetries and induce a finite energy
gap. As such, the possible phase transition from the semimetallic to insulating
phase gives us a choice for a wide range of resistance ensuring a large AMR. To
further understand the robustness of the phase transition, we study thermal
fluctuations of the AF order in AFS at a finite temperature. For macroscopic
samples, we find that the thermal fluctuations effectively decrease the
magnitude of the AF order by renormalizing the effective Hamiltonian. Our
finding suggests that the insulating phase exhibits a gap narrowing at elevated
temperatures, which leads to a substantial decrease in AMR. We also examine
spatially correlated thermal fluctuations for microscopic samples by solving
the microscopic Landau-Lifshitz-Gilbert equation finding a qualitative
difference of the gap narrowing in the insulating phase. For both cases, the
semimetallic phase shows a minimal change in its transmission spectrum
illustrating the robustness of the symmetry protected states in AFS. Our
finding may serve as a guideline for estimating and maximizing AMR of the AFS
samples at elevated temperatures.",1805.09826v1
2018-05-29,An exact solution for choosing the largest measurement from a sample drawn from an uniform distribution,"In ""Recognizing the Maximum of a Sequence"", Gilbert and Mosteller analyze a
full information game where n measurements from an uniform distribution are
drawn and a player (knowing n) must decide at each draw whether or not to
choose that draw. The goal is to maximize the probability of choosing the draw
that corresponds to the maximum of the sample. In their calculations of the
optimal strategy, the optimal probability and the asymptotic probability, they
assume that after a draw x the probability that the next i numbers are all
smaller than x is $x^i$; but this fails to recognize that continuing the game
(not choosing a draw because it is lower than a cutoff and waiting for the next
draw) conditions the distribution of the following i numbers such that their
expected maximum is higher then i/(i+1). The problem is now redefined with each
draw leading to a win, a false positive loss, a false negative loss and a
continuation. An exact formula for these probabilities is deduced, both for the
general case of n-1 different indifference numbers (assuming 0 as the last
cutoff) and the particular case of the same indifference number for all cutoffs
but the last. An approximation is found that preserves the main characteristics
of the optimal solution (slow decay of win probability, quick decay of false
positives and linear decay of false negatives). This new solution and the
original Gilbert and Mosteller formula are compared against simulations, and
their asymptotic behavior is studied.",1805.11556v1
2018-06-28,From clusters to queries: exploiting uncertainty in the modularity landscape of complex networks,"Uncovering latent community structure in complex networks is a field that has
received an enormous amount of attention. Unfortunately, whilst potentially
very powerful, unsupervised methods for uncovering labels based on topology
alone has been shown to suffer from several difficulties. For example, the
search space for many module extraction approaches, such as the modularity
maximisation algorithm, appears to be extremely glassy, with many high valued
solutions that lack any real similarity to one another. However, in this paper
we argue that this is not a flaw with the modularity maximisation algorithm
but, rather, information that can be used to aid the context specific
classification of functional relationships between vertices. Formally, we
present an approach for generating a high value modularity consensus space for
a network, based on the ensemble space of locally optimal modular partitions.
We then use this approach to uncover latent relationships, given small query
sets. The methods developed in this paper are applied to biological and social
datasets with ground-truth label data, using a small number of examples used as
seed sets to uncover relationships. When tested on both real and synthetic
datasets our method is shown to achieve high levels of classification accuracy
in a context specific manner, with results comparable to random walk with
restart methods.",1806.10904v1
2018-07-05,Veloce Rosso: Australia's new precision radial velocity spectrograph,"Veloce is an ultra-stable fibre-fed R4 echelle spectrograph for the 3.9 m
Anglo-Australian Telescope. The first channel to be commissioned, Veloce
'Rosso', utilises multiple low-cost design innovations to obtain Doppler
velocities for Sun-like and M-dwarf stars at <1 m/s precision. The spectrograph
has an asymmetric white-pupil format with a 100-mm beam diameter, delivering
R>75,000 spectra over a 580-950 nm range for the Rosso channel. Simultaneous
calibration is provided by a single-mode pulsed laser frequency comb in tandem
with a traditional arc lamp. A bundle of 19 object fibres provides a 2.4"" field
of view for full sampling of stellar targets from the AAT site. Veloce is
housed in dual environmental enclosures that maintain positive air pressure at
a stability of +/-0.3 mbar, with a thermal stability of +/-0.01 K on the
optical bench. We present a technical overview and early performance data from
Australia's next major spectroscopic machine.",1807.01938v1
2018-07-19,Generalized Metric Repair on Graphs,"Many modern data analysis algorithms either assume that or are considerably
more efficient if the distances between the data points satisfy a metric. These
algorithms include metric learning, clustering, and dimensionality reduction.
Because real data sets are noisy, the similarity measures often fail to satisfy
a metric. For this reason, Gilbert and Jain [11] and Fan, et al. [8] introduce
the closely related problems of $\textit{sparse metric repair}$ and
$\textit{metric violation distance}$. The goal of each problem is to repair as
few distances as possible to ensure that the distances between the data points
satisfy a metric. We generalize these problems so as to no longer require all
the distances between the data points. That is, we consider a weighted graph
$G$ with corrupted weights w and our goal is to find the smallest number of
modifications to the weights so that the resulting weighted graph distances
satisfy a metric. This problem is a natural generalization of the sparse metric
repair problem and is more flexible as it takes into account different
relationships amongst the input data points. As in previous work, we
distinguish amongst the types of repairs permitted (decrease, increase, and
general repairs). We focus on the increase and general versions and establish
hardness results and show the inherent combinatorial structure of the problem.
We then show that if we restrict to the case when $G$ is a chordal graph, then
the problem is fixed parameter tractable. We also present several classes of
approximation algorithms. These include and improve upon previous metric repair
algorithms for the special case when $G = K_n$",1807.07619v1
2018-10-17,Precipitating Ordered Skyrmion Lattices from Helical Spaghetti,"Magnetic skyrmions have been the focus of intense research due to their
potential applications in ultra-high density data and logic technologies, as
well as for the unique physics arising from their antisymmetric exchange term
and topological protections. In this work we prepare a chiral jammed state in
chemically disordered (Fe, Co)Si consisting of a combination of
randomly-oriented magnetic helices, labyrinth domains, rotationally disordered
skyrmion lattices and/or isolated skyrmions. Using small angle neutron
scattering, (SANS) we demonstrate a symmetry-breaking magnetic field sequence
which disentangles the jammed state, resulting in an ordered, oriented skyrmion
lattice. The same field sequence was performed on a sample of powdered Cu2OSeO3
and again yields an ordered, oriented skyrmion lattice, despite relatively
non-interacting nature of the grains. Micromagnetic simulations confirm the
promotion of a preferred skyrmion lattice orientation after field treatment,
independent of the initial configuration, suggesting this effect may be
universally applicable. Energetics extracted from the simulations suggest that
approaching a magnetic hard axis causes the moments to diverge away from the
magnetic field, increasing the Dzyaloshinskii-Moriya energy, followed
subsequently by a lattice re-orientation. The ability to facilitate an emergent
ordered magnetic lattice with long-range orientation in a variety of materials
despite overwhelming internal disorder enables the study of skyrmions even in
imperfect powdered or polycrystalline systems and greatly improves the ability
to rapidly screen candidate skyrmion materials.",1810.07631v1
2018-11-09,Post-randomization Biomarker Effect Modification in an HIV Vaccine Clinical Trial,"While the HVTN 505 trial showed no overall efficacy of the tested vaccine to
prevent HIV infection over placebo, previous studies, biological theories, and
the finding that immune response markers strongly correlated with infection in
vaccine recipients generated the hypothesis that a qualitative interaction
occurred. This hypothesis can be assessed with statistical methods for studying
treatment effect modification by an intermediate response variable (i.e.,
principal stratification effect modification (PSEM) methods). However,
available PSEM methods make untestable structural risk assumptions, such that
assumption-lean versions of PSEM methods are needed in order to surpass the
high bar of evidence to demonstrate a qualitative interaction. Fortunately, the
survivor average causal effect (SACE) literature is replete with
assumption-lean methods that can be readily adapted to the PSEM application for
the special case of a binary intermediate response variable. We map this
adaptation, opening up a host of new PSEM methods for a binary intermediate
variable measured via two-phase sampling, for a dichotomous or failure time
final outcome and including or excluding the SACE monotonicity assumption. The
new methods support that the vaccine partially protected vaccine recipients
with a high polyfunctional CD8+ T cell response, an important new insight for
the HIV vaccine field.",1811.03930v1
2019-03-22,Natural reward as the fundamental macroevolutionary force,"Darwin's theory of evolution by natural selection does not predict long-term
progress or advancement, nor does it provide a useful way to define or
understand these concepts. Nevertheless, the history of life is marked by major
trends that appear progressive, and seemingly more advanced forms of life have
appeared. To reconcile theory and fact, evolutionists have proposed novel
theories that extend natural selection to levels and time frames not justified
by the original structure of Darwin's theory. To extend evolutionary theory
without violating the most basic tenets of Darwinism, I here identify a
separate struggle and an alternative evolutionary force. Owing to the abundant
free energy in our universe, there is a struggle for supremacy that naturally
rewards those that are first to invent novelties that allow exploitation of
untapped resources. This natural reward comes in form of a temporary monopoly,
which is granted to those who win a competitive race to innovate. By analogy to
human economies, natural selection plays the role of nature's inventor,
gradually fashioning inventions to the situation at hand, while natural reward
plays the role of nature's entrepreneur, choosing which inventions to first
disseminate to large markets. Natural reward leads to progress through a
process of invention-conquest macroevolution, in which the dual forces of
natural selection and natural reward create and disseminate major innovations.
Over vast time frames, natural reward drives the advancement of life by a
process of extinction-replacement megaevolution that releases constraints on
progress and increases the innovativeness of life.",1903.09567v1
2019-07-15,Entanglement-assisted Quantum Codes from Algebraic Geometry Codes,"Quantum error correcting codes play the role of suppressing noise and
decoherence in quantum systems by introducing redundancy. Some strategies can
be used to improve the parameters of these codes. For example, entanglement can
provide a way for quantum error correcting codes to achieve higher rates than
the one obtained via the traditional stabilizer formalism. Such codes are
called entanglement-assisted quantum (QUENTA) codes. In this paper, we use
algebraic geometry codes to construct several families of QUENTA codes via the
Euclidean and the Hermitian construction. Two of the families created have
maximal entanglement and have quantum Singleton defect equal to zero or one.
Comparing the other families with the codes with the respective quantum
Gilbert-Varshamov bound, we show that our codes have a rate that surpasses that
bound. At the end, asymptotically good towers of linear complementary dual
codes are used to obtain asymptotically good families of maximal entanglement
QUENTA codes. Furthermore, a simple comparison with the quantum
Gilbert-Varshamov bound demonstrates that using our construction it is possible
to create an asymptotically family of QUENTA codes that exceeds this bound.",1907.06357v2
2019-09-06,Parameter identification for the Landau-Lifshitz-Gilbert equation in Magnetic Particle Imaging,"Magnetic particle imaging (MPI) is a tracer-based technique for medical
imaging where the tracer consists of ironoxide nanoparticles. The key idea is
to measure the particle response to a temporally changing external magnetic
field to compute the spatial concentration of the tracer inside the object. A
decent mathematical model demands for a data-driven computation of the system
function which does not only describe the measurement geometry but also encodes
the interaction of the particles with the external magnetic field. The physical
model of this interaction is given by the Landau-Lifshitz-Gilbert (LLG)
equation. The determination of the system function can be seen as an inverse
problem of its own which can be interpreted as a calibration problem for MPI.
In this contribution the calibration problem is formulated as an inverse
parameter identification problem for the LLG equation. We give a detailed
analysis of the direct as well as the inverse problem in an all-at-once as well
as in a reduced setting. The analytical results yield a deeper understanding of
inverse problems connected to the LLG equation and provide a starting point for
the development of robust numerical solution methods in MPI.",1909.02912v1
2019-11-06,Automated Left Ventricle Dimension Measurement in 2D Cardiac Ultrasound via an Anatomically Meaningful CNN Approach,"Two-dimensional echocardiography (2DE) measurements of left ventricle (LV)
dimensions are highly significant markers of several cardiovascular diseases.
These measurements are often used in clinical care despite suffering from large
variability between observers. This variability is due to the challenging
nature of accurately finding the correct temporal and spatial location of
measurement endpoints in ultrasound images. These images often contain fuzzy
boundaries and varying reflection patterns between frames. In this work, we
present a convolutional neural network (CNN) based approach to automate 2DE LV
measurements. Treating the problem as a landmark detection problem, we propose
a modified U-Net CNN architecture to generate heatmaps of likely coordinate
locations. To improve the network performance we use anatomically meaningful
heatmaps as labels and train with a multi-component loss function. Our network
achieves 13.4%, 6%, and 10.8% mean percent error on intraventricular septum
(IVS), LV internal dimension (LVID), and LV posterior wall (LVPW) measurements
respectively. The design outperforms other networks and matches or approaches
intra-analyser expert error.",1911.02448v1
2019-11-12,Linear-mode avalanche photodiode arrays for low-noise near-infrared imaging in space,"Astronomical observations often require the detection of faint signals in the
presence of noise, and the near-infrared regime is no exception. In particular,
where the application has short exposure time constraints, we are frequently
and unavoidably limited by the read noise of a system. A recent and
revolutionary development in detector technology is that of linear-mode
avalanche photodiode (LmAPD) arrays. By the introduction of a signal
multiplication region within the device, effective read noise can be reduced to
<0.2 e-, enabling the detection of very small signals at frame rates of up to 1
kHz. This is already impacting ground-based astronomy in high-speed
applications such as wavefront sensing and fringe tracking, but has not yet
been exploited for scientific space missions. We present the current status of
a collaboration with Leonardo MW - creators of the 'SAPHIRA' LmAPD array - as
we work towards the first in-orbit demonstration of a SAPHIRA device in 'Emu',
a hosted payload on the International Space Station. The Emu mission will fully
benefit from the 'noiseless' gains offered by LmAPD technology as it produces a
time delay integration photometric sky survey at 1.4 microns, using compact
readout electronics developed at the Australian National University. This is
just one example of a use case that could not be achieved with conventional
infrared sensors.",1911.04684v1
2020-03-17,Maximizing Influence-based Group Shapley Centrality,"One key problem in network analysis is the so-called influence maximization
problem, which consists in finding a set $S$ of at most $k$ seed users, in a
social network, maximizing the spread of information from $S$. This paper
studies a related but slightly different problem: We want to find a set $S$ of
at most $k$ seed users that maximizes the spread of information, when $S$ is
added to an already pre-existing - but unknown - set of seed users $T$. We
consider such scenario to be very realistic. Assume a central entity wants to
spread a piece of news, while having a budget to influence $k$ users. This
central authority may know that some users are already aware of the information
and are going to spread it anyhow. The identity of these users being however
completely unknown. We model this optimization problem using the Group Shapley
value, a well-founded concept from cooperative game theory. While the standard
influence maximization problem is easy to approximate within a factor
$1-1/e-\epsilon$ for any $\epsilon>0$, assuming common computational complexity
conjectures, we obtain strong hardness of approximation results for the problem
at hand in this paper. Maybe most prominently, we show that it cannot be
approximated within $1/n^{o(1)}$ under the Gap Exponential Time Hypothesis.
Hence, it is unlikely to achieve anything better than a polynomial factor
approximation. Nevertheless, we show that a greedy algorithm can achieve a
factor of $\frac{1-1/e}{k}-\epsilon$ for any $\epsilon>0$, showing that not all
is lost in settings where $k$ is bounded.",2003.07966v1
2020-04-24,Single-electron operation of a silicon-CMOS 2x2 quantum dot array with integrated charge sensing,"The advanced nanoscale integration available in silicon complementary
metal-oxide-semiconductor (CMOS) technology provides a key motivation for its
use in spin-based quantum computing applications. Initial demonstrations of
quantum dot formation and spin blockade in CMOS foundry-compatible devices are
encouraging, but results are yet to match the control of individual electrons
demonstrated in university-fabricated multi-gate designs. We show here that the
charge state of quantum dots formed in a CMOS nanowire device can be sensed by
using floating gates to electrostatically couple it to a remote single electron
transistor (SET) formed in an adjacent nanowire. By biasing the nanowire and
gates of the remote SET with respect to the nanowire hosting the quantum dots,
we controllably form ancillary quantum dots under the floating gates, thus
enabling the demonstration of independent control over charge transitions in a
quadruple (2x2) quantum dot array. This device overcomes the limitations
associated with measurements based on tunnelling transport through the dots and
permits the sensing of all charge transitions, down to the last electron in
each dot. We use effective mass theory to investigate the necessary
optimization of the device parameters in order to achieve the tunnel rates
required for spin-based quantum computation.",2004.11558v1
2020-08-22,Measurement of magnetic fields using the voltage generated by a vibrating wire,"A vibrating wire may be used as an instrument with a variety of applications,
one of which is the measurement of magnetic fields. Often, the magnetic fields
are determined by measuring the amplitude of the wire vibration under the
action of a Lorentz force. Though generally adequate, this approach may be
inconvenient in certain circumstances. One of these occurs when it is necessary
to measure the amplitude of high-frequency vibration, as the amplitude is
expected to decrease linearly with frequency, and thus becomes harder to
measure. Another example may be found in situations where the sensor must
operate over a wide range of vibration frequencies. In this case the sensor
will be unresponsive to specific frequencies of wire vibration, which are
determined by the placement of the sensor. This means that for the instrument
to be robust, the sensor must be precisely mobile, or multiple sensors must be
used.
  Here a technique which may be used to supplement the displacement sensor is
described. This technique makes use of the voltage generated by the motion of
the wire in the magnetic field under measurement. It is predicted that the
technique may be more suitable for measurements requiring high frequency
vibration, and is sensitive to all frequencies of vibration. Measurements of a
magnetic field obtained using this technique are compared to those found using
only a displacement sensor, and the benefits and drawbacks of the technique are
discussed.",2008.09898v1
2020-11-25,Domain wall motion in axially symmetric spintronic nanowires,"This article is concerned with the dynamics of magnetic domain walls (DWs) in
nanowires as solutions to the classical Landau-Lifschitz-Gilbert equation
augmented by a typically non-variational Slonczewski term for spin-torque
effects. Taking applied field and spin-polarization as the primary parameters,
we study dynamic stability as well as selection mechanisms analytically and
numerically in an axially symmetric setting. Concerning the stability of the
DWs' asymptotic states, we distinguish the bistable (both stable) and the
monostable (one unstable, one stable) parameter regime. In the bistable regime,
we extend known stability results of an explicit family of precessing solutions
and identify a relation of applied field and spin-polarization for standing
DWs. We verify that this family is convectively unstable into the monostable
regime, thus forming so-called pushed fronts, before turning absolutely
unstable. In the monostable regime, we present explicit formulas for the
so-called absolute spectrum of more general matrix operators. This allows us to
relate translation and rotation symmetries to the position of the singularities
of the pointwise Green's function. Thereby, we determine the linear selection
mechanism for the asymptotic velocity and frequency of DWs and corroborate
these by long-time numerical simulations. All these results include the axially
symmetric Landau-Lifschitz-Gilbert equation.",2012.01343v1
2020-12-08,Sparse Correspondence Analysis for Contingency Tables,"Since the introduction of the lasso in regression, various sparse methods
have been developed in an unsupervised context like sparse principal component
analysis (s-PCA), sparse canonical correlation analysis (s-CCA) and sparse
singular value decomposition (s-SVD). These sparse methods combine feature
selection and dimension reduction. One advantage of s-PCA is to simplify the
interpretation of the (pseudo) principal components since each one is expressed
as a linear combination of a small number of variables. The disadvantages lie
on the one hand in the difficulty of choosing the number of non-zero
coefficients in the absence of a well established criterion and on the other
hand in the loss of orthogonality for the components and/or the loadings. In
this paper we propose sparse variants of correspondence analysis (CA)for large
contingency tables like documents-terms matrices used in text mining, together
with pPMD, a deation technique derived from projected deflation in s-PCA. We
use the fact that CA is a double weighted PCA (for rows and columns) or a
weighted SVD, as well as a canonical correlation analysis of indicator
variables. Applying s-CCA or s-SVD allows to sparsify both rows and columns
weights. The user may tune the level of sparsity of rows and columns and
optimize it according to some criterium, and even decide that no sparsity is
needed for rows (or columns) by relaxing one sparsity constraint. The latter is
equivalent to apply s-PCA to matrices of row (or column) profiles.",2012.04271v1
2020-12-27,Vacuum Stability Conditions for Higgs Potentials with $SU(2)_L$ Triplets,"Tree-level dynamical stability of scalar field potentials in renormalizable
theories can in principle be expressed in terms of positivity conditions on
quartic polynomial structures. However, these conditions cannot always be cast
in a fully analytical resolved form, involving only the couplings and being
valid for all field directions. In this paper we consider such forms in three
physically motivated models involving $SU(2)$ triplet scalar fields: the
Type-II seesaw model, the Georgi-Machacek model, and a generalized two-triplet
model. A detailed analysis of the latter model allows to establish the full set
of necessary and sufficient boundedness from below conditions. These can serve
as a guide, together with unitarity and vacuum structure constraints, for
consistent phenomenological (tree-level) studies. They also provide a seed for
improved loop-level conditions, and encompass in particular the leading ones
for the more specific Georgi-Machacek case. Incidentally, we present complete
proofs of various properties and also derive general positivity conditions on
quartic polynomials that are equivalent but much simpler than the ones used in
the literature.",2012.13947v2
2021-03-25,Phases of Small Worlds: A Mean Field Formulation,"A network is said to have the properties of a small world if a suitably
defined average distance between any two nodes is proportional to the logarithm
of the number of nodes, $N$. In this paper, we present a novel derivation of
the small-world property for Gilbert-Erd\""os-Renyi random networks. We employ a
mean field approximation that permits the analytic derivation of the
distribution of shortest paths that exhibits logarithmic scaling away from the
phase transition, inferable via a suitably interpreted order parameter. We
begin by framing the problem in generality with a formal generating functional
for undirected weighted random graphs with arbitrary disorder, recovering the
result that the free energy associated with an ensemble of Gilbert graphs
corresponds to a system of non-interacting fermions identified with the edge
states. We then present a mean field solution for this model and extend it to
more general realizations of network randomness. For a two family class of
stochastic block models that we refer to as dimorphic networks, which allow for
links within the different families to be drawn from two independent discrete
probability distributions, we find the mean field approximation maps onto a
spin chain combinatorial problem and again yields useful approximate analytic
expressions for mean path lengths. Dimorophic networks exhibit a richer phase
structure, where distinct small world regimes separate in analogy to the
spinodal decomposition of a fluid. We find that is it possible to induce small
world behavior in sub-networks that by themselves would not be in the
small-world regime.",2103.14001v2
2021-05-04,Evaluating Metrics for Standardized Benchmarking of Remote Presence Systems,"To reduce the need for business-related air travel and its associated energy
consumption and carbon footprint, the U.S. Department of Energy's ARPA-E is
supporting a research project called SCOTTIE - Systematic Communication
Objectives and Telecommunications Technology Investigations and Evaluations.
SCOTTIE tests virtual and augmented reality platforms in a functional
comparison with face-to-face (FtF) interactions to derive travel replacement
thresholds for common industrial training scenarios. The primary goal of Study
1 is to match the communication effectiveness and learning outcomes obtained
from a FtF control using virtual reality (VR) training scenarios in which a
local expert with physical equipment trains a remote apprentice without
physical equipment immediately present. This application scenario is
commonplace in industrial settings where access to expensive equipment and
materials is limited and a number of apprentices must travel to a central
location in order to undergo training. Supplying an empirically validated
virtual training alternative constitutes a readily adoptable use-case for
businesses looking to reduce time and monetary expenditures associated with
travel. The technology used for three different virtual presence technologies
was strategically selected for feasibility, relatively low cost, business
relevance, and potential for impact through transition. The authors suggest
that the results of this study might generalize to the challenge of virtual
conferences.",2105.01772v1
2021-07-12,Partially Concatenated Calderbank-Shor-Steane Codes Achieving the Quantum Gilbert-Varshamov Bound Asymptotically,"In this paper, we utilize a concatenation scheme to construct new families of
quantum error correction codes achieving the quantum Gilbert-Varshamov (GV)
bound asymptotically. We concatenate alternant codes with any linear code
achieving the classical GV bound to construct Calderbank-Shor-Steane (CSS)
codes. We show that the concatenated code can achieve the quantum GV bound
asymptotically and can approach the Hashing bound for asymmetric Pauli
channels. By combing Steane's enlargement construction of CSS codes, we derive
a family of enlarged stabilizer codes achieving the quantum GV bound for
enlarged CSS codes asymptotically. As applications, we derive two families of
fast encodable and decodable CSS codes with parameters
$\mathscr{Q}_1=[[N,\Omega(\sqrt{N}),\Omega( \sqrt{N})]],$ and
$\mathscr{Q}_2=[[N,\Omega(N/\log N),\Omega(N/\log N)/\Omega(\log N)]].$ We show
that $\mathscr{Q}_1$ can be encoded very efficiently by circuits of size $O(N)$
and depth $O(\sqrt{N})$. For an input error syndrome, $\mathscr{Q}_1$ can
correct any adversarial error of weight up to half the minimum distance bound
in $O(N)$ time. $\mathscr{Q}_1$ can also be decoded in parallel in
$O(\sqrt{N})$ time by using $O(\sqrt{N})$ classical processors. For an input
error syndrome, we proved that $\mathscr{Q}_2$ can correct a linear number of
${X}$-errors with high probability and an almost linear number of ${Z}$-errors
in $O(N )$ time. Moreover, $\mathscr{Q}_2$ can be decoded in parallel in
$O(\log(N))$ time by using $O(N)$ classical processors.",2107.05174v2
2021-07-12,Assessment of Immune Correlates of Protection via Controlled Vaccine Efficacy and Controlled Risk,"Immune correlates of protection (CoPs) are immunologic biomarkers accepted as
a surrogate for an infectious disease clinical endpoint and thus can be used
for traditional or provisional vaccine approval. To study CoPs in randomized,
placebo-controlled trials, correlates of risk (CoRs) are first assessed in
vaccine recipients. This analysis does not assess causation, as a CoR may fail
to be a CoP. We propose a causal CoP analysis that estimates the controlled
vaccine efficacy curve across biomarker levels $s$, $CVE(s)$, equal to one
minus the ratio of the controlled-risk curve $r_C(s)$ at $s$ and placebo risk,
where $r_C(s)$ is causal risk if all participants are assigned vaccine and the
biomarker is set to $s$. The criterion for a useful CoP is wide variability of
$CVE(s)$ in $s$. Moreover, estimation of $r_C(s)$ is of interest in itself,
especially in studies without a placebo arm. For estimation of $r_C(s)$,
measured confounders can be adjusted for by any regression method that
accommodates missing biomarkers, to which we add sensitivity analysis to
quantify robustness of CoP evidence to unmeasured confounding. Application to
two harmonized phase 3 trials supports that 50% neutralizing antibody titer has
value as a controlled vaccine efficacy CoP for virologically confirmed dengue
(VCD): in CYD14 the point estimate (95% confidence interval) for $CVE(s)$
accounting for measured confounders and building in conservative margin for
unmeasured confounding increases from 29.6% (95% CI 3.5 to 45.9) at titer 1:36
to 78.5% (95% CI 67.9 to 86.8) at titer 1:1200; these estimates are 17.4% (95%
CI -14.4 to 36.5) and 84.5% (95% CI 79.6 to 89.1) for CYD15.",2107.05734v1
2021-07-23,"Efficient nonparametric estimation of the covariate-adjusted threshold-response function, a support-restricted stochastic intervention","Identifying a biomarker or treatment-dose threshold that marks a specified
level of risk is an important problem, especially in clinical trials. This
risk, viewed as a function of thresholds and possibly adjusted for covariates,
we call the threshold-response function. Extending the work of Donovan, Hudgens
and Gilbert (2019), we propose a nonparametric efficient estimator for the
covariate-adjusted threshold-response function, which utilizes machine learning
and Targeted Minimum-Loss Estimation (TMLE). We additionally propose a more
general estimator, based on sequential regression, that also applies when there
is outcome missingness. We show that the threshold-response for a given
threshold may be viewed as the expected outcome under a stochastic intervention
where all participants are given a treatment dose above the threshold. We prove
the estimator is efficient and characterize its asymptotic distribution. A
method to construct simultaneous 95% confidence bands for the
threshold-response function and its inverse is given. Furthermore, we discuss
how to adjust our estimator when the treatment or biomarker is
missing-at-random, as is the case in clinical trials with biased sampling
designs, using inverse-probability-weighting. The methods are assessed in a
diverse set of simulation settings with rare outcomes and cumulative
case-control sampling. The methods are employed to estimate neutralizing
antibody thresholds for virologically confirmed dengue risk in the CYD14 and
CYD15 dengue vaccine trials.",2107.11459v2
2021-10-15,The radio SZ effect as a probe of the cosmological radio background,"If there is a substantial cosmological radio background, there should be a
radio Sunyaev-Zeldovich (SZ) effect that goes along with it. The radio
background Comptonization leads to a slight photon excess at all wavelengths,
while Comptonization of the CMB at low frequencies leads to a decrement. For
levels of the radio background consistent with observations, these effects
cancel each other around $\nu\simeq 735~$MHz, with an excess at lower
frequencies and a decrement at higher frequencies. Assuming a purely
cosmological origin of the observed ARCADE radio excess, at $\nu \lesssim
20\,{\rm GHz}$ the signal scales as $\Delta T / T_{\rm CMB}\simeq 2\,y\left[
(\nu/735\,{\rm MHz})^{-2.59}-1\right]$ with frequency and the Compton-$y$
parameter of the cluster. For a typical cluster, the total radio SZ signal is
at the level of $\Delta T\simeq 1\,{\rm mK}$ around the null, with a steep
scaling towards radio frequencies. This is above current raw sensitivity limits
for many radio facilities at these wavelengths, providing a unique way to
confirm the cosmological origin of the ARCADE excess and probe its properties
(e.g., redshift dependence and isotropy). We also give an expression to compute
the radio-analogue of the kinematic SZ effect, highlighting that this might
provide a new tool to probe large-scale velocity fields and the cosmic
evolution of the radio background.",2110.08373v1
2021-10-20,No Transits of Proxima Centauri Planets in High-Cadence TESS Data,"Proxima Centauri is our nearest stellar neighbor and one of the most
well-studied stars in the sky. In 2016, a planetary companion was detected
through radial velocity measurements. Proxima Centauri b has a minimum mass of
1.3 Earth masses and orbits with a period of 11.2 days at 0.05 AU from its
stellar host, and resides within the star's Habitable Zone. While recent work
has shown that Proxima Centauri b likely does not transit, given the value of
potential atmospheric observations via transmission spectroscopy of the closest
possible Habitable Zone planet, we reevaluate the possibility that Proxima
Centauri b is a transiting exoplanet using data from the Transiting Exoplanet
Survey Satellite (TESS). We use three sectors (Sectors 11, 12, and 38 at
2-minute cadence) of observations from TESS to search for planets. Proxima
Centauri is an extremely active M5.5 star, emitting frequent white-light
flares; we employ a novel method that includes modeling the stellar activity in
our planet search algorithm. We do not detect any planet signals. We injected
synthetic transiting planets into the TESS and use this analysis to show that
Proxima Centauri b cannot be a transiting exoplanet with a radius larger than
0.4 R$_\oplus$. Moreover, we show that it is unlikely that any Habitable Zone
planets larger than Mars transit Proxima Centauri.",2110.10702v2
2021-12-20,Analysis of preintegration followed by quasi-Monte Carlo integration for distribution functions and densities,"In this paper, we analyse a method for approximating the distribution
function and density of a random variable that depends in a non-trivial way on
a possibly high number of independent random variables, each with support on
the whole real line. Starting with the integral formulations of the
distribution and density, the method involves smoothing the original integrand
by preintegration with respect to one suitably chosen variable, and then
applying a suitable quasi-Monte Carlo (QMC) method to compute the integral of
the resulting smoother function. Interpolation is then used to reconstruct the
distribution or density on an interval. The preintegration technique is a
special case of conditional sampling, a method that has previously been applied
to a wide range of problems in statistics and computational finance. In
particular, the pointwise approximation studied in this work is a specific case
of the conditional density estimator previously considered in L'Ecuyer et al.,
arXiv:1906.04607. Our theory provides a rigorous regularity analysis of the
preintegrated function, which is then used to show that the errors of the
pointwise and interpolated estimators can both achieve nearly first-order
convergence. Numerical results support the theory.",2112.10308v5
2021-12-21,Exponential decay of intersection volume with applications on list-decodability and Gilbert-Varshamov type bound,"We give some natural sufficient conditions for balls in a metric space to
have small intersection. Roughly speaking, this happens when the metric space
is (i) expanding and (ii) well-spread, and (iii) a certain random variable on
the boundary of a ball has a small tail. As applications, we show that the
volume of intersection of balls in Hamming, Johnson spaces and symmetric groups
decay exponentially as their centers drift apart. To verify condition (iii), we
prove some large deviation inequalities `on a slice' for functions with
Lipschitz conditions.
  We then use these estimates on intersection volumes to
  $\bullet$ obtain a sharp lower bound on list-decodability of random $q$-ary
codes, confirming a conjecture of Li and Wootters; and
  $\bullet$ improve the classical bound of Levenshtein from 1971 on constant
weight codes by a factor linear in dimension, resolving a problem raised by
Jiang and Vardy.
  Our probabilistic point of view also offers a unified framework to obtain
improvements on other Gilbert--Varshamov type bounds, giving conceptually
simple and calculation-free proofs for $q$-ary codes, permutation codes, and
spherical codes. Another consequence is a counting result on the number of
codes, showing ampleness of large codes.",2112.11274v2
2021-12-22,Preintegration is not smoothing when monotonicity fails,"Preintegration is a technique for high-dimensional integration over
$d$-dimensional Euclidean space, which is designed to reduce an integral whose
integrand contains kinks or jumps to a $(d-1)$-dimensional integral of a smooth
function. The resulting smoothness allows efficient evaluation of the
$(d-1)$-dimensional integral by a Quasi-Monte Carlo or Sparse Grid method. The
technique is similar to conditional sampling in statistical contexts, but the
intention is different: in conditional sampling the aim is to reduce the
variance, rather than to achieve smoothness. Preintegration involves an initial
integration with respect to one well chosen real-valued variable. Griebel, Kuo,
Sloan [Math. Comp. 82 (2013), 383--400] and Griewank, Kuo, Le\""ovey, Sloan [J.
Comput. Appl. Maths. 344 (2018), 259--274] showed that the resulting
$(d-1)$-dimensional integrand is indeed smooth under appropriate conditions,
including a key assumption -- the integrand of the smooth function underlying
the kink or jump is strictly monotone with respect to the chosen special
variable when all other variables are held fixed. The question addressed in
this paper is whether this monotonicity property with respect to one well
chosen variable is necessary. We show here that the answer is essentially yes,
in the sense that without this property the resulting $(d-1)$-dimensional
integrand is generally not smooth, having square-root or other singularities.",2112.11621v1
2021-12-30,A causal inference framework for spatial confounding,"Recently, addressing spatial confounding has become a major topic in spatial
statistics. However, the literature has provided conflicting definitions, and
many proposed definitions do not address the issue of confounding as it is
understood in causal inference. We define spatial confounding as the existence
of an unmeasured causal confounder with a spatial structure. We present a
causal inference framework for nonparametric identification of the causal
effect of a continuous exposure on an outcome in the presence of spatial
confounding. We propose double machine learning (DML), a procedure in which
flexible models are used to regress both the exposure and outcome variables on
confounders to arrive at a causal estimator with favorable robustness
properties and convergence rates, and we prove that this approach is consistent
and asymptotically normal under spatial dependence. As far as we are aware,
this is the first approach to spatial confounding that does not rely on
restrictive parametric assumptions (such as linearity, effect homogeneity, or
Gaussianity) for both identification and estimation. We demonstrate the
advantages of the DML approach analytically and in simulations. We apply our
methods and reasoning to a study of the effect of fine particulate matter
exposure during pregnancy on birthweight in California.",2112.14946v7
2022-01-20,Accurate modeling of grazing transits using umbrella sampling,"Grazing transits present a special problem for statistical studies of
exoplanets. Even though grazing planetary orbits are rare (due to geometric
selection effects), for many low to moderate signal-to-noise cases, a
significant fraction of the posterior distribution is nonetheless consistent
with a grazing geometry. A failure to accurately model grazing transits can
therefore lead to biased inferences even for cases where the planet is not
actually on a grazing trajectory. With recent advances in stellar
characterization, the limiting factor for many scientific applications is now
the quality of available transit fits themselves, and so the time is ripe to
revisit the transit fitting problem. In this paper, we model exoplanet transits
using a novel application of umbrella sampling and a geometry-dependent
parameter basis that minimizes covariances between transit parameters. Our
technique splits the transit fitting problem into independent Monte Carlo
sampling runs for the grazing, non-grazing, and transition regions of the
parameter space, which we then recombine into a single joint posterior
probability distribution using a robust weighting scheme. Our method can be
trivially parallelized and so requires no increase in the wall clock time
needed for computations. Most importantly, our method produces accurate
estimates of exoplanet properties for both grazing and non-grazing orbits,
yielding more robust results than standard methods for many common star-planet
configurations.",2201.08350v1
2022-04-22,Reward Reports for Reinforcement Learning,"Building systems that are good for society in the face of complex societal
effects requires a dynamic approach. Recent approaches to machine learning (ML)
documentation have demonstrated the promise of discursive frameworks for
deliberation about these complexities. However, these developments have been
grounded in a static ML paradigm, leaving the role of feedback and
post-deployment performance unexamined. Meanwhile, recent work in reinforcement
learning has shown that the effects of feedback and optimization objectives on
system behavior can be wide-ranging and unpredictable. In this paper we sketch
a framework for documenting deployed and iteratively updated learning systems,
which we call Reward Reports. Taking inspiration from various contributions to
the technical literature on reinforcement learning, we outline Reward Reports
as living documents that track updates to design choices and assumptions behind
what a particular automated system is optimizing for. They are intended to
track dynamic phenomena arising from system deployment, rather than merely
static properties of models or data. After presenting the elements of a Reward
Report, we discuss a concrete example: Meta's BlenderBot 3 chatbot. Several
others for game-playing (DeepMind's MuZero), content recommendation
(MovieLens), and traffic control (Project Flow) are included in the appendix.",2204.10817v3
2022-05-29,Generalized Stochastic Matching,"In this paper, we generalize the recently studied Stochastic Matching problem
to more accurately model a significant medical process, kidney exchange, and
several other applications. Up until now the Stochastic Matching problem that
has been studied was as follows: given a graph G = (V, E), each edge is
included in the realized sub-graph of G mutually independently with probability
p_e, and the goal is to find a degree-bounded sub-graph Q of G that has an
expected maximum matching that approximates the expected maximum matching of
the realized sub-graph. This model does not account for possibilities of vertex
dropouts, which can be found in several applications, e.g. in kidney exchange
when donors or patients opt out of the exchange process as well as in online
freelancing and online dating when online profiles are found to be faked. Thus,
we will study a more generalized model of Stochastic Matching in which vertices
and edges are both realized independently with some probabilities p_v, p_e,
respectively, which more accurately fits important applications than the
previously studied model.
  We will discuss the first algorithms and analysis for this generalization of
the Stochastic Matching model and prove that they achieve good approximation
ratios. In particular, we show that the approximation factor of a natural
algorithm for this problem is at least $0.6568$ in unweighted graphs, and $1/2
+ \epsilon$ in weighted graphs for some constant $\epsilon > 0$. We further
improve our result for unweighted graphs to $2/3$ using edge degree constrained
subgraphs (EDCS).",2205.14717v1
2022-07-25,Spin-transfer and spin-orbit torques in the Landau-Lifshitz-Gilbert equation,"Dynamic simulations of spin-transfer and spin-orbit torques are increasingly
important for a wide range of spintronic devices including magnetic random
access memory, spin-torque nano-oscillators and electrical switching of
antiferromagnets. Here we present a computationally efficient method for the
implementation of spin-transfer and spin-orbit torques within the
Landau-Lifshitz-Gilbert equation used in micromagnetic and atomistic
simulations. We consolidate and simplify the varying terminology of different
kinds of torques into a physical action and physical origin that clearly shows
the common action of spin torques while separating their different physical
origins. Our formalism introduces the spin torque as an effective magnetic
field, greatly simplifying the numerical implementation and aiding the
interpretation of results. The strength of the effective spin torque field
unifies the action of the spin torque and subsumes the details of experimental
effects such as interface resistance and spin Hall angle into a simple
transferable number between numerical simulations. We present a series of
numerical tests demonstrating the mechanics of generalised spin torques in a
range of spintronic devices. This revised approach to modelling spin-torque
effects in numerical simulations enables faster simulations and a more direct
way of interpreting the results, and thus it is also suitable to be used in
direct comparisons with experimental measurements or in a modelling tool that
takes experimental values as input.",2207.12071v2
2022-08-03,On ergodic invariant measures for the stochastic Landau-Lifschitz-Gilbert equation in 1D,"We establish existence of an ergodic invariant measure on
$H^1(D,\mathbb{R}^3)\cap L^2(D,\mathbb{S}^2)$ for the stochastic
Landau-Lifschitz-Gilbert equation on a bounded one dimensional interval $D$.
The conclusion is achieved by employing the classical Krylov-Bogoliubov
theorem. In contrast to other equations, verifying the hypothesis of the
Krylov-Bogoliubov theorem is not a standard procedure. We employ rough paths
theory to show that the semigroup associated to the equation has the Feller
property in $H^1(D,\mathbb{R}^3)\cap L^2(D,\mathbb{S}^2)$. It does not seem
possible to achieve the same conclusion by the classical Stratonovich calculus.
On the other hand, we employ the classical Stratonovich calculus to prove the
tightness hypothesis. The Krein-Milman theorem implies existence of an ergodic
invariant measure. In case of spatially constant noise, we show that there
exists a unique Gibbs invariant measure and we establish the qualitative
behaviour of the unique stationary solution. In absence of the anisotropic
energy and for a spatially constant noise, we are able to provide a path-wise
long time behaviour result: in particular, every solution synchronises with a
spherical Brownian motion and it is recurrent for large times",2208.02136v2
2023-01-25,"The Benchmark M Dwarf Eclipsing Binary CM Draconis With TESS: Spots, Flares and Ultra-Precise Parameters","A gold standard for the study of M dwarfs is the eclipsing binary CM
Draconis. It is rare because it is bright ($J_{\rm mag}=8.5$) and contains twin
fully convective stars on an almost perfectly edge-on orbit. Both masses and
radii were previously measured to better than $1\%$ precision, amongst the best
known. We use 15 sectors of data from the Transiting Exoplanet Survey Satellite
(TESS) to show that CM Draconis is the gift that keeps on giving. Our paper has
three main components. First, we present updated parameters, with radii and
masses constrained to previously unheard of precisions of $\approx 0.06\%$ and
$\approx 0.12\%$, respectively. Second, we discover strong and variable spot
modulation, suggestive of spot clustering and an activity cycle on the order of
$\approx 4$ years. Third, we discover 163 flares. We find a relationship
between the spot modulation and flare rate, with flares more likely to occur
when the stars appear brighter. This may be due to a positive correlation
between flares and the occurrence of bright spots (plages). The flare rate is
surprisingly not reduced during eclipse, but one flare may show evidence of
being occulted. We suggest the flares may be preferentially polar, which has
positive implications for the habitability of planets orbiting M dwarfs.",2301.10858v2
2023-02-23,Beyond Bias and Compliance: Towards Individual Agency and Plurality of Ethics in AI,"AI ethics is an emerging field with multiple, competing narratives about how
to best solve the problem of building human values into machines. Two major
approaches are focused on bias and compliance, respectively. But neither of
these ideas fully encompasses ethics: using moral principles to decide how to
act in a particular situation. Our method posits that the way data is labeled
plays an essential role in the way AI behaves, and therefore in the ethics of
machines themselves. The argument combines a fundamental insight from ethics
(i.e. that ethics is about values) with our practical experience building and
scaling machine learning systems. We want to build AI that is actually ethical
by first addressing foundational concerns: how to build good systems, how to
define what is good in relation to system architecture, and who should provide
that definition.
  Building ethical AI creates a foundation of trust between a company and the
users of that platform. But this trust is unjustified unless users experience
the direct value of ethical AI. Until users have real control over how
algorithms behave, something is missing in current AI solutions. This causes
massive distrust in AI, and apathy towards AI ethics solutions. The scope of
this paper is to propose an alternative path that allows for the plurality of
values and the freedom of individual expression. Both are essential for
realizing true moral character.",2302.12149v1
2023-04-03,Three-Dimensional Structure of Hybrid Magnetic Skyrmions Determined by Neutron Scattering,"Magnetic skyrmions are topologically protected chiral spin textures which
present opportunities for next-generation magnetic data storage and logic
information technologies. The topology of these structures originates in the
geometric configuration of the magnetic spins - more generally described as the
structure. While the skyrmion structure is most often depicted using a 2D
projection of the three-dimensional structure, recent works have emphasized the
role of all three dimensions in determining the topology and their response to
external stimuli. In this work, grazing-incidence small-angle neutron
scattering and polarized neutron reflectometry are used to determine the
three-dimensional structure of hybrid skyrmions. The structure of the hybrid
skyrmions, which includes a combination of N\'eel-like and Bloch-like
components along their length, is expected to significantly contribute to their
notable stability, which includes ambient conditions. To interpret the neutron
scattering data, micromagnetic simulations of the hybrid skyrmions were
performed, and the corresponding diffraction patterns were determined using a
Born approximation transformation. The converged magnetic profile reveals the
magnetic structure along with the skyrmion depth profile, including the
thickness of the Bloch and N\'eel segments and the diameter of the core.",2304.01369v2
2023-05-18,Towards Intersectional Moderation: An Alternative Model of Moderation Built on Care and Power,"Shortcomings of current models of moderation have driven policy makers,
scholars, and technologists to speculate about alternative models of content
moderation. While alternative models provide hope for the future of online
spaces, they can fail without proper scaffolding. Community moderators are
routinely confronted with similar issues and have therefore found creative ways
to navigate these challenges. Learning more about the decisions these
moderators make, the challenges they face, and where they are successful can
provide valuable insight into how to ensure alternative moderation models are
successful.
  In this study, I perform a collaborative ethnography with moderators of
r/AskHistorians, a community that uses an alternative moderation model,
highlighting the importance of accounting for power in moderation. Drawing from
Black feminist theory, I call this ""intersectional moderation."" I focus on
three controversies emblematic of r/AskHistorians' alternative model of
moderation: a disagreement over a moderation decision; a collaboration to fight
racism on Reddit; and a period of intense turmoil and its impact on policy.
Through this evidence I show how volunteer moderators navigated multiple layers
of power through care work. To ensure the successful implementation of
intersectional moderation, I argue that designers should support
decision-making processes and policy makers should account for the impact of
the sociotechnical systems in which moderators work.",2305.11250v1
2023-06-08,Environmental Considerations in the age of Space Exploration: the Conservation and Protection of Non-Earth Environments,"This document is an abbreviated version of the law review, led by Alexander
Q. Gilbert, entitled: ""Major Federal Actions Significantly Affecting the
Quality of the Space Environment: Applying NEPA to Federal and Federally
Authorized Outer Space Activities."" Here, we discuss the future of the space
environment, and how it is increasingly becoming a human environment with
regard to continued robotic and human presence in orbit, planned and proposed
robotic and human presence on bodies such as the Moon and Mars, planned space
mining projects, the increase use of low-Earth orbit for communications
satellites, and other human uses of space. As such, we must evaluate and
protect these environments just as we do on Earth. In order to prioritize
mitigating threat of contamination, avoiding conflict, and promoting
sustainability in space, all to ensure that actors maintain equal and safe
access to space, we propose applying the National Environmental Policy Act, or
NEPA, to space missions. We put forward three examples of environmental best
practices for those involved in space missions to consider: adopting
precautionary and communicative structure to before, during, and after missions
taking place off-world, environmental impact statements, and transparency in
tools that may impact the environment (including radioisotope power sources,
plans in case of vehicle loss or loss of trajectory, and others). For
additional discussion related to potential space applications of NEPA, NEPA's
statutory text, and NEPA's relation to space law and judicial precedent for
space, we recommend reading the full law review.",2306.05594v1
2023-07-13,Accurate and efficient photo-eccentric transit modeling,"A planet's orbital eccentricity is fundamental to understanding the present
dynamical state of a system and is a relic of its formation history. There is
high scientific value in measuring eccentricities of Kepler and TESS planets
given the sheer size of these samples and the diversity of their planetary
systems. However, Kepler and TESS lightcurves typically only permit robust
determinations of planet-to-star radius ratio $r$, orbital period $P$, and
transit mid-point $t_0$. Three other orbital properties, including impact
parameter $b$, eccentricity $e$, and argument of periastron $\omega$, are more
challenging to measure because they are all encoded in the lightcurve through
subtle effects on a single observable -- the transit duration $T_{14}$. In
Gilbert, MacDougall, & Petigura (2022), we showed that a five-parameter transit
description $\{P, t_0, r, b, T_{14}\}$ naturally yields unbiased measurements
of $r$ and $b$. Here, we build upon our previous work and introduce an accurate
and efficient prescription to measure $e$ and $\omega$. We validate this
approach through a suite of injection-and-recovery experiments. Our method
agrees with previous approaches that use a seven-parameter transit description
$\{P, t_0, r, b, \rho_\star, e, \omega\}$ which explicitly fits the
eccentricity vector and mean stellar density. The five-parameter method is
simpler than the seven-parameter method and is ""future-proof"" in that posterior
samples can be quickly reweighted (via importance sampling) to accommodate
updated priors and updated stellar properties. This method thus circumvents the
need for an expensive reanalysis of the raw photometry, offering a streamlined
path toward large-scale population analyses of eccentricity from transit
surveys.",2307.07070v1
2023-09-01,"A decoupled, convergent and fully linear algorithm for the Landau--Lifshitz--Gilbert equation with magnetoelastic effects","We consider the coupled system of the Landau--Lifshitz--Gilbert equation and
the conservation of linear momentum law to describe magnetic processes in
ferromagnetic materials including magnetoelastic effects in the small-strain
regime. For this nonlinear system of time-dependent partial differential
equations, we present a decoupled integrator based on first-order finite
elements in space and an implicit one-step method in time. We prove
unconditional convergence of the sequence of discrete approximations towards a
weak solution of the system as the mesh size and the time-step size go to zero.
Compared to previous numerical works on this problem, for our method, we prove
a discrete energy law that mimics that of the continuous problem and, passing
to the limit, yields an energy inequality satisfied by weak solutions.
Moreover, our method does not employ a nodal projection to impose the unit
length constraint on the discrete magnetisation, so that the stability of the
method does not require weakly acute meshes. Furthermore, our integrator and
its analysis hold for a more general setting, including body forces and
traction, as well as a more general representation of the magnetostrain.
Numerical experiments underpin the theory and showcase the applicability of the
scheme for the simulation of the dynamical processes involving magnetoelastic
materials at submicrometer length scales.",2309.00605v2
2023-11-09,Skyrmion-Excited Spin Wave Fractal Network,"Magnetic skyrmions exhibit unique, technologically relevant pseudo-particle
behaviors which arise from their topological protection, including
well-defined, three-dimensional dynamic modes that occur at microwave
frequencies. During dynamic excitation, spin waves are ejected into the
interstitial regions between skyrmions, creating the magnetic equivalent of a
turbulent sea. However, since the spin waves in these systems have a
well-defined length scale, and the skyrmions are on an ordered lattice, ordered
structures from spin wave interference can precipitate from the chaos. This
work uses small angle neutron scattering (SANS) to capture the dynamics in
hybrid skyrmions and investigate the spin wave structure. Performing
simultaneous ferromagnetic resonance and SANS, the diffraction pattern shows a
large increase in low-angle scattering intensity which is present only in the
resonance condition. This scattering pattern is best fit using a mass fractal
model, which suggests the spin waves form a long-range fractal network. The
fractal structure is constructed of fundamental units with a size that encodes
the spin wave emissions and are constrained by the skyrmion lattice. These
results offer critical insights into the nanoscale dynamics of skyrmions,
identify a new dynamic spin wave fractal structure, and demonstrates SANS as a
unique tool to probe high-speed dynamics.",2311.05469v1
2023-12-08,Analysis of the magnetization control problem for the 2D evolutionary Landau-Lifshitz-Gilbert equation,"The magnetization control problem for the Landau-Lifshitz-Gilbert (LLG)
equation $m_t= m \times (\Delta m +u)- m \times (m \times (\Delta m +u)),\
(x,t) \in \Omega\times (0,T] $ with zero Neumann boundary data on a
two-dimensional bounded domain $\Omega$ is studied when the control energy $u$
is applied on the effective field. First, we show the existence of a weak
solution, and the magnetization vector field $m$ satisfies an energy
inequality. If a weak solution $m$ obeys the condition that $\nabla m\in
L^4(0,T;L^4(\Omega)),$ then we show that it is a regular solution. The
classical cost functional is modified by incorporating
$L^4(0,T;L^4(\Omega))$-norm of $\nabla m$ so that a rigorous study of the
optimal control problem is established. Then, we justified the existence of an
optimal control and derived first-order necessary optimality conditions using
an adjoint problem approach. We have established the continuous dependency and
Fr\'echet differentiability of the control-to-state and control-to-costate
operators and shown the Lipschitz continuity of their Fr\'echet derivatives.
Using these postulates, we derived a local second-order sufficient optimality
condition when a control belongs to a critical cone. Finally, we also obtain
another remarkable global optimality condition posed only in terms of the
adjoint state associated with the control problem.",2312.05165v1
2024-01-05,Solutions to the Landau-Lifshitz-Gilbert equation in the frequency space: Discretization schemes for the dynamic-matrix approach,"The dynamic matrix method addresses the Landau-Lifshitz-Gilbert (LLG)
equation in the frequency domain by transforming it into an eigenproblem.
Subsequent numerical solutions are derived from the eigenvalues and
eigenvectors of the dynamic matrix. In this work we explore discretization
methods needed to obtain a matrix representation of the dynamic operator, a
fundamental counterpart of the dynamic matrix. Our approach opens a new set of
linear algebra tools for the dynamic matrix method and expose the
approximations and limitations intrinsic to it. Moreover, our discretization
algorithms can be applied to various discretization schemes, extending beyond
micromagnetism problems. We present some application examples, including a
technique to obtain the dynamic matrix directly from the magnetic free energy
function of an ensemble of macrospins, and an algorithmic method to calculate
numerical micromagnetic kernels, including plane wave kernels. We also show how
to exploit symmetries and reduce the numerical size of micromagnetic
dynamic-matrix problems by a change of basis. This procedure significantly
reduces the size of the dynamic matrix by several orders of magnitude while
maintaining high numerical precision. Additionally, we calculate analytical
approximations for the dispersion relations in magnonic crystals. This work
contributes to the understanding of the current magnetization dynamics methods,
and could help the development and formulations of novel analytical and
numerical methods for solving the LLG equation within the frequency domain.",2401.02933v2
1995-10-27,Radiation Damping and Quantum Excitation for Longitudinal Charged Particle Dynamics in the Thermal Wave Model,"On the basis of the recently proposed {\it Thermal Wave Model (TWM) for
particle beams}, we give a description of the longitudinal charge particle
dynamics in circular accelerating machines by taking into account both
radiation damping and quantum excitation (stochastic effect), in presence of a
RF potential well. The longitudinal dynamics is governed by a 1-D
Schr\""{o}dinger-like equation for a complex wave function whose squared modulus
gives the longitudinal bunch density profile. In this framework, the
appropriate {\it r.m.s. emittance} scaling law, due to the damping effect, is
naturally recovered, and the asymptotic equilibrium condition for the bunch
length, due to the competition between quantum excitation (QE) and radiation
damping (RD), is found. This result opens the possibility to apply the TWM,
already tested for protons, to electrons, for which QE and RD are very
important.",9510004v1
1994-02-04,Constraints on Models of Galaxy Formation from the Evolution of Damped Ly$α$ Absorption Systems,"There is accumulating observational evidence suggesting that damped
Ly$\alpha$ absorption systems systems are the progenitors of present-day spiral
galaxies. We use the observed properties of these systems to place constraints
on the history of star formation in galactic disks, and on cosmological
theories of structure formation in the universe. We show that the observed
increase in $\Omega_{HI}$ contributed by damped Ly$\alpha$ systems at high
redshift implies that star formation must have been considerably less efficient
in the past. We also show that the data can constrain cosmological models in
which structure forms at late epochs. A mixed dark matter (MDM) model with
$\Omega_{\nu}=0.3$ is unable to reproduce the mass densities of cold gas seen
at high redshift, even in the absence of any star formation. We show that at
redshifts greater than 3, this model predicts that the total baryonic mass
contained in dark matter halos with circular velocities $V_c > 35$ km s$^{-1}$
is less than the observed mass of HI in damped systems. At these redshifts, the
photo-ionizing background would prevent gas from dissipating and collapsing to
form high column density systems in halos smaller than 35 km s$^{-1}$. MDM
models are thus ruled out by the observations.",9402015v1
1999-02-11,The HI Column Density Distribution Function at z=0: the Connection to Damped Ly alpha Statistics,"We present a measurement of the HI column density distribution function,
f(N), at the present epoch for column densities log N > 20 cm^-2. These high
column densities compare to those measured in damped Ly alpha lines seen in
absorption against background quasars. Although observationally rare, it
appears that the bulk of the neutral gas in the Universe is associated with
these damped Ly alpha systems. In order to obtain a good anchor point at z=0 we
determine f(N) in the local Universe by using 21cm synthesis observations of a
complete sample of spiral galaxies. We show that f(N) for damped Ly alpha
systems has changed significantly from high z to the present and that change is
greatest for the highest column densities. The measurements indicate that low
surface brightness galaxies make a minor contribution to the cross section for
HI, especially for log N > 21^-2.",9902171v1
2000-10-27,Planetary Torques as the Viscosity of Protoplanetary Disks,"We revisit the idea that density-wave wakes of planets drive accretion in
protostellar disks. The effects of many small planets can be represented as a
viscosity if the wakes damp locally, but the viscosity is proportional to the
damping length. Damping occurs mainly by shocks even for earth-mass planets.
The excitation of the wake follows from standard linear theory including the
torque cutoff. We use this as input to an approximate but quantitative
nonlinear theory based on Burger's equation for the subsequent propagation and
shock. Shock damping is indeed local but weakly so. If all metals in a
minimum-mass solar nebula are invested in planets of a few earth masses each,
dimensionless viscosities [alpha] of order dex(-4) to dex(-3) result. We
compare this with observational constraints. Such small planets would have
escaped detection in radial-velocity surveys and could be ubiquitous. If so,
then the similarity of the observed lifetime of T Tauri disks to the
theoretical timescale for assembling a rocky planet may be fate rather than
coincidence.",0010576v1
2000-12-27,Constraining Dark Matter candidates from structure formation,"We show that collisional damping of adiabatic primordial fluctuations yields
constraints on the possible range of mass and interaction rates of Dark Matter
particles. Our analysis relies on a general classification of Dark Matter
candidates, that we establish independently of any specific particle theory or
model. From a relation between the collisional damping scale and the Dark
Matter interaction rate, we find that Dark Matter candidates must have
cross-sections at decoupling smaller than $ 10^{-33} \frac{m_{dm}}{1 MeV} cm^2$
with photons and $10^{-37} \frac{m_{dm}}{1 MeV} cm^2$ with neutrinos, to
explain the observed primordial structures of $10^9$ Solar mass. These damping
constraints are particularly relevant for Warm Dark Matter candidates. They
also leave open less known regions of parameter space corresponding to
particles having rather high interaction rates with other species than
neutrinos and photons.",0012504v2
2001-07-26,The Contribution of HI-Rich Galaxies to the Damped Absorber Population at z=0,"We present a study of HI-rich galaxies in the local universe selected from
blind emission-line surveys. These galaxies represent the emission-line
counterparts of local damped Lyman-alpha systems. We find that the HI
cross-section of galaxies is drawn from a large range of galaxy masses below
M_star, 66% of the area comes from galaxies in the range 8.5 < Log M_star <
9.7. Both because of the low mass galaxy contribution, and because of the range
of galaxy types and luminosities at any given HI mass, the galaxies
contributing to the HI cross-section are not exclusively L_star spirals, as is
often expected. The optical and near infrared counterparts of these galaxies
cover a range of types (from spirals to irregulars), luminosities (from L_star
to <0.01 L_star), and surface brightnesses. The range of optical and near
infrared properties as well as the kinematics for this population are
consistent with the properties for the low-z damped Lyman-alpha absorbers. We
also show that the number of HI-rich galaxies in the local universe does not
preclude evolution of the low-z damped absorber population, but it is
consistent with no evolution.",0107495v1
2003-11-17,Cosmic Ray Scattering by Compressible Magnetohydrodynamic Turbulence,"Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call
for substantial revisions in the picture of cosmic ray transport. In this paper
we use recently obtained scaling laws for MHD modes to calculate the scattering
frequency for cosmic rays in the ISM. We consider gyroresonance with MHD modes
(Alfvenic, slow and fast) and transit-time damping (TTD) by fast modes. We
provide calculations of cosmic ray scattering for various phases of
interstellar medium with realistic interstellar turbulence driving that is
consistent with the velocity dispersions observed in diffuse gas. We account
for the turbulence cutoff arising from both collisional and collisionless
damping. We obtain analytical expressions for diffusion coefficients that enter
Fokker-Planck equation describing cosmic ray evolution. We calculate the
scattering rate and parallel spatial diffusion coefficients of cosmic rays for
both Alfvenic and fast modes. We conclude that fast modes provides the dominant
contribution to cosmic ray scattering for the typical interstellar conditions
in spite of the fact that fast modes are subjected to damping. We show that the
efficiency of the scattering depends on the plasma beta since it determines the
damping of the fast modes. We also show that the streaming instability is
modified in the presence of turbulence.",0311369v1
2003-11-17,Wave damping by MHD turbulence and its effect upon cosmic ray propagation in the ISM,"Cosmic rays scatter off magnetic irregularities (Alfven waves) with which
they are resonant, that is waves of wavelength comparable to their gyroradii.
These waves may be generated either by the cosmic rays themselves, if they
stream faster than the Alfven speed, or by sources of MHD turbulence. Waves
excited by streaming cosmic rays are ideally shaped for scattering, whereas the
scattering efficiency of MHD turbulence is severely diminished by its
anisotropy. We show that MHD turbulence has an indirect effect on cosmic ray
propagation by acting as a damping mechanism for cosmic ray generated waves.
The hot (``coronal'') phase of the interstellar medium is the best candidate
location for cosmic ray confinement by scattering from self-generated waves. We
relate the streaming velocity of cosmic rays to the rate of turbulent
dissipation in this medium, for the case in which turbulent damping is the
dominant damping mechanism. We conclude that cosmic rays with up to 10^2 GeV
could not stream much faster than the Alfven speed, but that 10^6 GeV cosmic
rays would stream unimpeded by self-generated waves unless the coronal gas were
remarkably turbulence-free.",0311400v1
2004-10-25,Constraints on Dark Matter interactions from structure formation: Damping lengths,"(Shortened) Weakly Interacting Massive Particles are often said to be the
best Dark Matter candidates. Studies have shown however that rather large Dark
Matter-photon or Dark Matter-baryon interactions could be allowed by cosmology.
Here we address the question of the role of the Dark Matter interactions in
more detail to determine at which extent Dark Matter has to be necessarily
weakly interacting. To this purpose, we compute the collisional damping (and
free-streaming) lengths of generic interacting Dark Matter candidates and
compare them to the scale of the smallest primordial structures known to exist
in the Universe. We obtain necessary conditions that any candidate must
satisfy. We point out the existence of new Dark Matter scenarios and exhibit
new damping regimes. For example, an interacting candidate may bear a similar
damping than that of collisionless Warm Dark Matter particles. The main
difference is due to the Dark Matter coupling to interacting (or even
freely-propagating) species. Our approach yields a general classification of
Dark Matter candidates which extends the definitions of the usual Cold, Warm
and Hot Dark Matter scenarios when interactions, weak or strong, are
considered.",0410591v1
2005-10-10,Collisional dissipation of Alfvén waves in a partially ionised solar chromosphere,"Certain regions of the solar atmosphere are at sufficiently low temperatures
to be only partially ionised. The lower chromosphere contains neutral atoms,
the existence of which greatly increases the efficiency of the damping of waves
due to collisional friction momentum transfer. More specifically the Cowling
conductivity can be up to 12 orders of magnitude smaller than the Spitzer
value, so that the main damping mechanism in this region is due to the
collisions between neutrals and positive ions. Using values for the gas density
and temperature as functions of height taken from the VAL C model of the quiet
Sun, an estimate is made for the dependance of the Cowling conductivity on
height and strength of magnetic field. Using both analytic and numerical
approaches the passage of Alfven waves over a wide spectrum through this
partially ionised region is investigated. Estimates of the efficiency of this
region in the damping of Alfven waves are made and compared for both
approaches. We find that Alfven waves with frequencies above 0.6Hz are
completely damped and frequencies below 0.01 Hz unaffected.",0510265v1
2006-04-10,The Nearby Damped Lyman-alpha Absorber SBS 1543+593: A Large HI Envelope in a Gas-Rich Galaxy Group,"We present a Very Large Array (VLA) HI 21cm map and optical observations of
the region around one of the nearest damped Lyman-alpha absorbers beyond the
local group, SBS 1543+593. Two previously uncataloged galaxies have been
discovered and a redshift has been determined for a third. All three of these
galaxies are at the redshift of SBS 1543+593 and are ~185 kpc from the damped
Lyman-alpha absorber. We discuss the HI and optical properties of SBS 1543+593
and its newly identified neighbors. Both SBS 1543+593 and Dwarf 1 have baryonic
components that are dominated by neutral gas -- unusual for damped Lyman-alpha
absorbers for which only ~5% of the HI cross-section originates in such
strongly gas-dominated systems. What remains unknown is whether low mass
gas-rich groups are common surrounding gas-rich galaxies in the local universe
and whether the low star-formation rate in these systems is indicative of a
young system or a stable, slowly evolving system. We discuss these evolutionary
scenarios and future prospects for answering these questions.",0604220v1
2006-08-02,SINS of Viscosity Damped Turbulence,"The problems with explaining the Small Ionized and Neutral Structures (SINS)
appealing to turbulence stem from inefficiency of the Kolmogorov cascade in
creating large fluctuations at sufficiently small scales. However, other types
of cascades are possible. When magnetic turbulence in a fluid with viscosity
that is much larger than resistivity gets to a viscous damping scale, the
turbulence does not vanish. Instead, it gets into a different new regime.
Viscosity-damped turbulence produces fluctuations on the small scales. Magnetic
fields sheared by turbulent motions by eddies not damped by turbulence create
small scale filaments that are confined by the external plasma pressure. This
creates small scale density fluctuations. In addition, extended current sheets
create even stronger density gradients that accompany field reversals in the
plane perpendicular to mean magnetic field. Those can be responsible for the
SINS formation. This scenario is applicable to partially ionized gas. More
studies of reconnection in the viscosity dominated regime are necessary to
understand better the extend to which the magnetic reversals can compress the
gas.",0608046v3
1998-01-13,Comparative Study of the Adiabatic Evolution of a Nonlinear Damped Oscillator and an Hamiltonian Generalized Nonlinear Oscillator,"In this paper we study to what extent the canonical equivalence and the
identity of the geometric phases of dissipative and conservative linear
oscillators, established in a preceeding paper, can be generalized to nonlinear
ones. Considering first the 1-D quartic generalized oscillator we determine, by
means of a perturbative time dependent technic of reduction to normal forms,
the canonical transformations which lead to the adiabatic invariant of the
system and to the first order non linear correction to its Hannay angle. Then,
applying the same transformations to the 1-D quartic damped oscillator we show
that this oscillator is canonically equivalent to the linear generalized
harmonic oscillator for finite values of the damping parameter (which implies
no correction to the linear Hannay angle) whereas, in an appropriate weak
damping limit, it becomes equivalent to the quartic generalized oscillator
(which implies a non linear correction to this angle) .",9801017v1
1995-03-20,Quasiparticle damping in two-dimensional superconductors with unconventional pairing.,"We calculate the damping of excitations due to four-fermionic interaction in
the case of two-dimensional superconductor with nodes in the spectrum. At zero
temperature and low frequencies it reveals gapless $\omega^3$ behavior at the
nodal points. With the frequency increasing the crossover to the normal-state
regimes appears. At high frequencies the damping strongly depends on details of
a normal-state spectrum parametrization. Two important particular cases such as
the models of almost free and tight-binding electrons are studied explicitly
and the characteristic scales are expressed through the model-free parameters
of the spectrum at the nodal points. The possibility of crossover in
temperature dependence of damping in the superconducting phase is discussed.",9503112v1
1996-01-09,Relaxation of Collective Excitations in LJ-13 Cluster,"We have performed classical molecular dynamics simulation of $Ar_{13}$
cluster to study the behavior of collective excitations. In the solid ``phase''
of the cluster, the collective oscillation of the monopole mode can be well
fitted to a damped harmonic oscillator. The parameters of the equivalent damped
harmonic oscillator-- the damping coefficient, spring constant, time period of
oscillation and the mass of the oscillator -- all show a sharp change in
behavior at a kinetic temperature of about $7.0^oK$. This marks yet another
characteristic temperature of the system, a temperature $T_s$ below which
collective excitations are very stable, and at higher temperatures the single
particle excitations cause the damping of the collective oscillations. We argue
that so long as the cluster remains confined within the global potential energy
minimum the collective excitations do not decay; and once the cluster comes out
of this well, the local potential energy minima pockets act as single particle
excitation channels in destroying the collective motion. The effect is manifest
in almost all the physical observables of the cluster.",9601026v2
1997-10-14,Damping of Hydrodynamic Modes in a Trapped Bose Gas above the Bose-Einstein Transition Temperature,"We calculate the damping of low-lying collective modes of a trapped Bose gas
in the hydrodynamic regime, and show that this comes solely from the shear
viscosity, since the contributions from bulk viscosity and thermal conduction
vanish. The hydrodynamic expression for the damping diverges due to the failure
of hydrodynamics in the outer parts of the cloud, and we take this into account
by a physically motivated cutoff procedure. Our analysis of available
experimental data indicates that higher densities than have yet been achieved
are necessary for investigating hydrodynamic modes above the Bose-Einstein
transition temperature.",9710130v2
1997-12-24,Thermal dephasing and the echo effect in a confined Bose-Einstein condensate,"It is shown that thermal fluctuations of the normal component induce
dephasing -- reversible damping of the low energy collective modes of a
confined Bose-Einstein condensate. The dephasing rate is calculated for the
isotropic oscillator trap, where Landau damping is expected to be suppressed.
This rate is characterized by a steep temperature dependence, and it is weakly
amplitude dependent.
  In the limit of large numbers of bosons forming the condensate, the rate
approaches zero. However, for the numbers employed by the JILA group, the
calculated value of the rate is close to the experimental one. We suggest that
a reversible nature of the damping caused by the thermal dephasing in the
isotropic trap can be tested by the echo effect. A reversible nature of Landau
damping is also discussed, and a possibility of observing the echo effect in an
anisotropic trap is considered as well. The parameters of the echo are
calculated in the weak echo limit for the isotropic trap. Results of the
numerical simulations of the echo are also presented.",9712287v1
1998-09-29,Numerical test of the damping time of layer-by-layer growth on stochastic models,"We perform Monte Carlo simulations on stochastic models such as the
Wolf-Villain (WV) model and the Family model in a modified version to measure
mean separation $\ell$ between islands in submonolayer regime and damping time
$\tilde t$ of layer-by-layer growth oscillations on one dimension. The
stochastic models are modified, allowing diffusion within interval $r$ upon
deposited. It is found numerically that the mean separation and the damping
time depend on the diffusion interval $r$, leading to that the damping time is
related to the mean separation as ${\tilde t} \sim \ell^{4/3}$ for the WV model
and ${\tilde t} \sim \ell^2$ for the Family model. The numerical results are in
excellent agreement with recent theoretical predictions.",9809382v1
2000-01-10,Enhanced vortex damping by eddy currents in superconductor-semiconduc tor hybrids,"An enhancement of vortex-motion damping in thin Pb/In superconducting films
is obtained through coupling to an adjacent two-dimensional electron gas formed
in a modulation-doped GaAs/AlGaAs heterostructure. This effect is observed by
monitoring the power dissipation at the superconductor in the vortex state
while increasing the density of the electron gas using a gate voltage.
Quantitative agreement is found with calculations based on a viscous model of
vortex damping which considers generation of eddy currents in the electron gas
by moving flux lines. In the regime of filamentary and channel vortex flow,
eddy-current damping leads to striking dissipation breakdown due to stopping of
entire vortex channels.",0001123v1
2000-10-11,The experimental observation of Beliaev damping in a Bose condensed gas,"We report the first experimental observation of Beliaev damping of a
collective excitation in a Bose-condensed gas. Beliaev damping is not predicted
by the Gross-Pitaevskii equation and so this is one of the few experiments that
tests BEC theory beyond the mean field approximation. Measurements of the
amplitude of a high frequency scissors mode, show that the Beliaev process
transfers energy to a lower lying mode and then back and forth between these
modes. These characteristics are quite distinct from those of Landau damping,
which leads to a monotonic decrease in amplitude. To enhance the Beliaev
process we adjusted the geometry of the magnetic trapping potential to give a
frequency ratio of 2 to 1 between two of the scissors modes of the condensate.
The ratios of the trap oscillation frequencies $\omega_y / \omega_x$ and
$\omega_z / \omega_x$ were changed independently, so that we could investigate
the resonant coupling over a range of conditions.",0010157v1
2001-06-18,AC induced damping of a fluxon in long Josephson junction,"We present a theoretical and experimental study of Josephson vortex (fluxon)
moving in the presence of spatially homogeneous dc and ac bias currents. By
mapping this problem to the problem of calculating the current-voltage
characteristic of a small Josephson junction, we derive the dependence of the
average fluxon velocity on the dc bias current. In particular we find that the
low frequency ac bias current results in an additional nonlinear damping of
fluxon motion. Such ac induced damping crucially depends on the intrinsic
damping parameter and increases drastically as this parameter is reduced. We
find a good agreement of the analysis with both the direct numerical
simulations and the experimentally measured current-voltage characteristics of
a long annular Josephson junction with one trapped fluxon.",0106337v1
2002-03-20,Microscopic nonequilibrium dynamics of an inhomogeneous Bose gas beyond the Born approximation,"Using the prescription of the nonequilibrium statistical operator method, we
derive a non-Markovian generalization to the kinetic theory described by Walser
{\sl et al.} [Phys. Rev. A {\bf 59}, 3878 (1999)]. Quasi-particle damping and
effects arising from the finite duration of a collision are introduced to
include terms beyond the Born approximation. Such a self-consistent theory is
shown to conserve energy to second order in the interaction strength, even in
the Markov limit. This kinetic theory is applied to a simple model of a Bose
gas confined in a spherical trap to study the full real-time evolution towards
equilibrium. A modified form for the damping function, is seen to strongly
improve the energy conservation. Based on a linear response calculation, we
predict the damping rates and frequencies of the collective excitations. We
demonstrate the emergence of differing time scales for damping and
equilibration.",0203415v1
2003-05-12,Landau damping in trapped Bose-condensed gases,"We study Landau damping in dilute Bose-Einstein condensed gases in both
spherical and prolate ellipsoidal harmonic traps. We solve the Bogoliubov
equations for the mode spectrum in both of these cases, and calculate the
damping by summing over transitions between excited quasiparticle states. The
results for the spherical case are compared to those obtained in the
Hartree-Fock approximation, where the excitations take on a single-particle
character, and excellent agreement between the two approaches is found. We have
also taken the semiclassical limit of the Hartree-Fock approximation and obtain
a novel expression for the Landau damping rate involving the time dependent
self-diffusion function of the thermal cloud. As a final approach, we study the
decay of a condensate mode by making use of dynamical simulations in which both
the condensate and thermal cloud are evolved explicitly as a function of time.
A detailed comparison of all these methods over a wide range of sample sizes
and trap geometries is presented.",0305251v1
2003-05-27,Damped finite-time-singularity driven by noise,"We consider the combined influence of linear damping and noise on a dynamical
finite-time-singularity model for a single degree of freedom. We find that the
noise effectively resolves the finite-time-singularity and replaces it by a
first-passage-time or absorbing state distribution with a peak at the
singularity and a long time tail. The damping introduces a characteristic
cross-over time. In the early time regime the probability distribution and
first-passage-time distribution show a power law behavior with scaling exponent
depending on the ratio of the non linear coupling strength to the noise
strength. In the late time regime the behavior is controlled by the damping.
The study might be of relevance in the context of hydrodynamics on a nanometer
scale, in material physics, and in biophysics.",0305630v1
2003-06-05,On Surface Plasmon Damping in Metallic Nanoparticles,"Two possible mechanisms of surface plasmon (SP) oscillations damping in
metallic nanoparticles (MNPs), not connected with electron-phonon interaction
are investigated theoretically: a) the radiation damping of SP, b) resonant
coupling of SP oscillations with electronic transitions in matrix. It is shown
that the radiation damping rate is proportional to the number of electrons in
MNP and therefore this channel of energy outflow from MNP becomes essential for
relatively large particles. The investigation of second mechanism shows that
the rate of SP oscillations energy leakage from MNP dos not depend on particle
size and is fully determined by the optical characteristics of the matrix. It
is demonstrated that for very small MNPs of 3-5 nm size, where the strong 3D
size quantization effect suppresses the electron-phonon interaction, the
resonance coupling in certain cases provides an effective energy outflow.",0306123v1
2003-09-11,Frequency and damping of hydrodynamic modes in a trapped Bose-condensed gas,"Recently it was shown that the Landau-Khalatnikov two-fluid hydrodynamics
describes the collision-dominated region of a trapped Bose condensate
interacting with a thermal cloud. We use these equations to discuss the low
frequency hydrodynamic collective modes in a trapped Bose gas at finite
temperatures. We derive a variational expressions based on these equations for
both the frequency and damping of collective modes. A new feature is our use of
frequency-dependent transport coefficients, which produce a natural cutoff by
eliminating the collisionless low-density tail of the thermal cloud. Above the
superfluid transition, our expression for the damping in trapped inhomogeneous
gases is analogous to the result first obtained by Landau and Lifshitz for
uniform classical fluids. We also use the moment method to discuss the
crossover from the collisionless to the hydrodynamic region. Recent data for
the monopole-quadrupole mode in the hydrodynamic region of a trapped gas of
metastable $^4$He is discussed. We also present calculations for the damping of
the analogous $m=0$ monopole-quadrupole condensate mode in the superfluid
phase.",0309269v1
2003-11-13,Damping of Bogoliubov Excitations in Optical Lattices,"Extending recent work to finite temperatures, we calculate the Landau damping
of a Bogoliubov excitation in an optical lattice, due to coupling to a thermal
cloud of such excitations. For simplicity, we consider a 1D Bose-Hubbard model
and restrict ourselves to the first energy band. For energy conservation to be
satisfied, the excitations in the collision processes must exhibit ``anomalous
dispersion'', analogous to phonons in superfluid $^4\rm{He}$. This leads to the
disappearance of all damping processes when $U n^{\rm c 0}\ge 6t$, where $U$ is
the on-site interaction, $t$ is the hopping matrix element and $n^{\rm c 0}(T)$
is the number of condensate atoms at a lattice site. This phenomenon also
occurs in 2D and 3D optical lattices. The disappearance of Beliaev damping
above a threshold wavevector is noted.",0311321v1
2004-09-22,Symmetry breaking in driven and strongly damped pendulum,"We examine the conditions for appearance of symmetry breaking bifurcation in
damped and periodically driven pendulum in the case of strong damping. We show
that symmetry breaking, unlike other nonlinear phenomena, can exist at high
dissipation. We prove that symmetry breaking phases exist between phases of
symmetric normal and symmetric inverted oscillations. We find that symmetry
broken solutions occupy a sufficiently smaller region of pendulum's parameter
space in comparison to the statements made in earlier considerations [McDonald
and Plischke, Phys. Rev. B 27 (1983) 201]. Our research on symmetry breaking in
a strongly damped pendulum is relevant to an understanding of phenomena of
dynamic symmetry breaking and rectification in a pure ac driven semiconductor
superlattices.",0409572v1
2004-10-19,Strongly inhibited transport of a 1D Bose gas in a lattice,"We report the observation of strongly damped dipole oscillations of a quantum
degenerate 1D atomic Bose gas in a combined harmonic and optical lattice
potential. Damping is significant for very shallow axial lattices (0.25 photon
recoil energies), and increases dramatically with increasing lattice depth,
such that the gas becomes nearly immobile for times an order of magnitude
longer than the single-particle tunneling time. Surprisingly, we see no
broadening of the atomic quasimomentum distribution after damped motion. Recent
theoretical work suggests that quantum fluctuations can strongly damp dipole
oscillations of 1D atomic Bose gas, providing a possible explanation for our
observations.",0410491v3
2005-08-10,Collective oscillations of a quasi one dimensional Bose condensate under damping,"Influence of the damping on collective oscillations of a one-dimensional
trapped Bose gas in the mean field regime has been studied. Using the
phenomenological damping approach developed by L.P. Pitaevskii, modified
variational equations for the parameters of the condensate wave function is
derived. Analytical expressions for the condensate parameters in equilibrium
state have been obtained. Bistability in nonlinear oscillations of the
condensate under periodic variations of the trap potential is predicted. The
predictions of the modified variational approach are confirmed by full
numerical simulations of the 1D GP equation with the damping.",0508262v1
2005-08-11,Influence of layer defects on the damping in ferroelectric thin films,"A Green's function technique for a modified Ising model in a transverse field
is applied, which allows to calculate the damping of the elementary excitations
and the phase transition temperature of ferroelectric thin films with
structural defects. Based on an analytical expression for the damping function,
we analyze its dependence on temperature, film thickness and interaction
strength numerically. The results demonstrate that defect layers in
ferroelectric thin films, layers with impurities or vacancies as well as layers
with dislocations are able to induce a strong increase of the damping due to
different exchange interactions within the defect layers. The results are in
good agreement with experimental data for thin ferroelectric films with
different thickness.",0508287v1
2007-02-23,Parametric Resonance of Optically Trapped Aerosols,"The Brownian dynamics of an optically trapped water droplet are investigated
across the transition from over to under-damped oscillations. The spectrum of
position fluctuations evolves from a Lorentzian shape typical of over-damped
systems (beads in liquid solvents), to a damped harmonic oscillator spectrum
showing a resonance peak. In this later under-damped regime, we excite
parametric resonance by periodically modulating the trapping power at twice the
resonant frequency. The power spectra of position fluctuations are in excellent
agreement with the obtained analytical solutions of a parametrically modulated
Langevin equation.",0702557v1
2007-03-22,Spin-Torque Ferromagnetic Resonance Measurements of Damping in Nanomagnets,"We measure the magnetic damping parameter a in thin film CoFeB and permalloy
(Py) nanomagnets at room temperature using ferromagnetic resonance driven by
microwave frequency spin-transfer torque. We obtain $\alpha_{CoFeB} = 0.014 \pm
0.003$ and $\alpha_{Py}=0.010 \pm 0.002$, values comparable to measurements for
extended thin films, but significantly less than the effective damping
determined previously for similar nanomagnets by fits to time-domain studies of
large-angle magnetic excitations and magnetic reversal. The greater damping
found for the large amplitude nanomagnet dynamics is attributed to the
nonlinear excitation of non-uniform magnetic modes.",0703577v1
2007-02-28,Numerical Model For Vibration Damping Resulting From the First Order Phase Transformations,"A numerical model is constructed for modelling macroscale damping effects
induced by the first order martensite phase transformations in a shape memory
alloy rod. The model is constructed on the basis of the modified
Landau-Ginzburg theory that couples nonlinear mechanical and thermal fields.
The free energy function for the model is constructed as a double well function
at low temperature, such that the external energy can be absorbed during the
phase transformation and converted into thermal form. The Chebyshev spectral
methods are employed together with backward differentiation for the numerical
analysis of the problem. Computational experiments performed for different
vibration energies demonstrate the importance of taking into account damping
effects induced by phase transformations.",0702172v1
2005-04-22,Constraint damping in the Z4 formulation and harmonic gauge,"We show that by adding suitable lower-order terms to the Z4 formulation of
the Einstein equations, all constraint violations except constant modes are
damped. This makes the Z4 formulation a particularly simple example of a
lambda-system as suggested by Brodbeck et al. We also show that the Einstein
equations in harmonic coordinates can be obtained from the Z4 formulation by a
change of variables that leaves the implied constraint evolution system
unchanged. Therefore the same method can be used to damp all constraints in the
Einstein equations in harmonic gauge.",0504114v2
2005-07-05,Universality of Highly Damped Quasinormal Modes for Single Horizon Black Holes,"It has been suggested that the highly damped quasinormal modes of black holes
provide information about the microscopic quantum gravitational states
underlying black hole entropy. This interpretation requires the form of the
highly damped quasinormal mode frequency to be universally of the form:
$\hbar\omega_R = \ln(l)kT_{BH}$, where $l$ is an integer, and $T_{BH}$ is the
black hole temperature. We summarize the results of an analysis of the highly
damped quasinormal modes for a large class of single horizon, asymptotically
flat black holes.",0507019v1
2005-09-07,Massive vector field perturbations in the Schwarzschild background: stability and quasinormal spectrum,"We consider the perturbations of the massive vector field around
Schwarzschild black hole, (generally, with non-vanishing $\Lambda$ - term). The
monopole massive vector perturbation equations can be reduced to a single
wave-like equation. We have proved the stability against these perturbations
and investigated the quasinormal spectrum. The quasinormal behaviour for
Schwarzschild black hole is quite unexpected: the fundamental mode and all
higher overtones shows totally different dependence on the mass of the field
$m$: as $m$ is increasing, the damping rate of the fundamental mode is
decreasing, what results in appearing of the infinitely long living modes,
while, on contrary, damping rate of all higher overtones are increasing, and
their real oscillation frequencies gradually go to tiny values. Thereby, for
all higher overtones, almost non-oscillatory, damping modes can exist. In the
limit of asymptotically high damping, $Re \omega$ goes to $ln3/(8 \pi M)$,
while imaginary part shows equidistant behaviour with spacing $Im \omega_{n+1}-
Im \omega_{n}=i/4M$. In addition, we have found quasinormal spectrum of massive
vector field for Schwarzschild-anti-de Sitter black hole.",0509026v3
2006-11-27,The Mystery of the Asymptotic Quasinormal Modes of Gauss-Bonnet Black Holes,"We analyze the quasinormal modes of $D$-dimensional Schwarzschild black holes
with the Gauss-Bonnet correction in the large damping limit and show that
standard analytic techniques cannot be applied in a straightforward manner to
the case of infinite damping. However, by using a combination of analytic and
numeric techniques we are able to calculate the quasinormal mode frequencies in
a range where the damping is large but finite. We show that for this damping
region the famous $\ln(3)$ appears in the real part of the quasinormal mode
frequency. In our calculations, the Gauss-Bonnet coupling, $\alpha$, is taken
to be much smaller than the parameter $\mu$, which is related to the black hole
mass.",0611139v1
1995-09-22,Damping rate of neutrinos in the singlet Majoron model,"The damping rate and free path of neutrinos in the singlet Majoron model have
been calculated including both finite temperature and symmetry breaking
effects. The behaviour of right- and left-handed fermions are found inherently
different. While the damping rates of the left-handed leptons are essentially
model independent, e.g. directly applicable to the Standard Model, for the
right-handed particles the rates are crucially sensitive to parameters of the
scalar sector. In general, the damping rates are fairly large. The possibility
of the right-handed neutrinos to penetrate deep into the broken phase in the
electroweak phase transition still remains, however, for some parts of
parameter space.",9509359v1
1996-09-25,The hot baryon violation rate is $O(α_W^5 T^4)$,"The rate per unit volume for anomalous electroweak baryon number violation at
high temperatures, in the symmetric phase, has been estimated in the literature
to be $O(\alpha_W^4 T^4)$ based on simple scaling arguments. We argue that
damping effects in the plasma suppress the rate by an extra power of $\alpha_W$
to give $O(\alpha_W^5 T^4)$. We show how to understand this effect in a variety
of ways ranging from an effective description of the long-distance modes
responsible for baryon number violation, to a microscopic picture of the
short-distance modes responsible for damping. In particular, we resolve an old
controversy as to whether damping effects are relevant. Finally, we argue that
similar damping effects should occur in numerical simulations of the rate in
classical thermal field theory on a spatial lattice, and we point out a
potential problem with simulations in the literature that have not found such
an effect.",9609481v1
2001-03-29,Phase transition dynamics in the hot Abelian Higgs model,"We present a detailed numerical study of the equilibrium and non-equilibrium
dynamics of the phase transition in the finite-temperature Abelian Higgs model.
Our simulations use classical equations of motion both with and without
hard-thermal-loop corrections, which take into account the leading quantum
effects. From the equilibrium real-time correlators, we determine the Landau
damping rate, the plasmon frequency and the plasmon damping rate. We also find
that, close to the phase transition, the static magnetic field correlator shows
power-law magnetic screening at long distances. The information about the
damping rates allows us to derive a quantitative prediction for the number
density of topological defects formed in a phase transition. We test this
prediction in a non-equilibrium simulation and show that the relevant time
scale for defect formation is given by the Landau damping rate.",0103311v1
1996-04-12,Onset of Rotational Damping in Superdeformed Nuclei,"We discuss damping of the collective rotational motion in $A\sim 150$
superdeformed nuclei by means of a shell model combining the cranked Nilsson
mean-filed and the surface-delta two-body residual force. It is shown that,
because of the shell structure associated with the superdeformed mean-field,
onset energy of the rotational damping becomes $E_x \sim 2-3 $ MeV above yrast
line, which is much higher than in normal deformed nuclei. The mechanism of the
shell structure effect is investigated through detailed analysis of level
densities in superdeformed nuclei. It is predicted the onset of damping varies
in different supedeformed nuclei along with variation in the single-particle
structure at the Fermi surface.",9604015v1
2001-09-12,The damping width of giant dipole resonances of cold and hot nuclei: a macroscopic model,"A phenomenological macroscopic model of the Giant Dipole Resonance (GDR)
damping width of cold- and hot-nuclei with ground-state spherical and
near-spherical shapes is developed. The model is based on a generalized Fermi
Liquid model which takes into account the nuclear surface dynamics. The
temperature dependence of the GDR damping width is accounted for in terms of
surface- and volume-components. Parameter-free expressions for the damping
width and the effective deformation are obtained. The model is validated with
GDR measurements of the following nuclides, $^{39,40}$K, $^{42}$Ca, $^{45}$Sc,
$^{59,63}$Cu, $^{109-120}$Sn,$^{147}$Eu, $^{194}$Hg, and $^{208}$Pb, and is
compared with the predictions of other models.",0109034v1
2006-01-31,Small damping approach in Fermi-liquid theory,"The validity of small damping approximation (SDA) for the quasi-classical
description of the averaged properties of nuclei at high temperatures is
studied within the framework of collisional kinetic theory. The isoscalar
collective quadrupole vibrations in hot nuclei are considered. We show that the
extension of the SDA, by accounting for the damping of the distribution
function $\delta f$ in the collision integral reduces the rate of variation
with temperature of the Fermi surface distortion effects. The damping of the
$\delta f$ in the collision integral increases significantly the collisional
width of the giant quadrupole resonance (GQR) for small enough values of the
relaxation time. The temperature dependence of the eigenenergy of the GQR
becomes much more weaker than in the corresponding SDA case.",0601094v1
2001-11-05,Damping of transversal plasma-electron oscillations and waves in low-collision electron-ion plasmas,"Previously developed method for finding asymptotic solutions of Vlasov
equations using two-dimensional (in coordinate x and time t) Laplace transform
is here applied to consider transversal oscillations and waves in low-collision
quasi-neutral (n_i \simeq n_e) Maxwellian electron-ion plasmas. We obtain two
branches of electron waves: the ubiquitous one of high-frequency and
high-velocity oscillations and the unusual low-velocity one. Taking into
account Coulomb collisions in the limit m_e << m_i, \bar{v_i} << \bar{v_e}, and
T_e m_e << T_i m_i results in expressions for transversal plasma-electron
oscillation/wave decrements with a damping of the low-velocity electron branch
\sim n_i^{1/3}/\bar{v}_e^{4/3}, where n_i is the ion density and \bar{v}_e is
the mean electron velocity. It ought to rehabilitate Vlasov principal value
prescription for relevant integrals, but to supplement it with representation
of an asymptotical solution as a sum of exponents (not a single one).
""Non-damping"" kinematical waves in low-collision plasma transform in the
damping ones at reasonably chosen iteration process.",0111014v3
2002-03-13,Enhanced radiative ion cooling,"Enhanced radiative cooling of ion beams in storage rings and Robinson's
damping criterion are discussed.",0203036v1
2003-05-24,Impact of the Wiggler Coherent Synchrotron Radiation Impedance on the Beam Instability,"Coherent Synchrotron Radiation (CSR) can play an important role by not only
increasing the energy spread and emittance of a beam, but also leading to a
potential instability. Previous studies of the CSR induced longitudinal
instability were carried out for the CSR impedance due to dipole magnets.
However, many storage rings include long wigglers where a large fraction of the
synchrotron radiation is emitted. This includes high-luminosity factories such
as DAPHNE, PEP-II, KEK-B, and CESR-C as well as the damping rings of future
linear colliders. In this paper, the instability due to the CSR impedance from
a wiggler is studied assuming a large wiggler parameter $K$. The primary
consideration is a low frequency microwave-like instability, which arises near
the pipe cut-off frequency. Detailed results are presented on the growth rate
and threshold for the damping rings of several linear collider designs.
Finally, the optimization of the relative fraction of damping due to the
wiggler systems is discussed for the damping rings.",0305107v1
2004-09-13,Landau damping in thin films irradiated by a strong laser field,"The rate of linear collisionless damping (Landau damping) in a classical
electron gas confined to a heated ionized thin film is calculated. The general
expression for the imaginary part of the dielectric tensor in terms of the
parameters of the single-particle self-consistent electron potential is
obtained. For the case of a deep rectangular well, it is explicitly calculated
as a function of the electron temperature in the two limiting cases of specular
and diffuse reflection of the electrons from the boundary of the
self-consistent potential. For realistic experimental parameters, the
contribution of Landau damping to the heating of the electron subsystem is
estimated. It is shown that for films with a thickness below about 100 nm and
for moderate laser intensities it may be comparable with or even dominate over
electron-ion collisions and inner ionization.",0409062v1
1996-06-24,Quantum damping of position due to energy measurements,"Quantum theory for measurements of energy is introduced and its consequences
for the average position of monitored dynamical systems are analyzed. It turns
out that energy measurements lead to a localization of the expectation values
of other observables. This is manifested, in the case of position, as a damping
of the motion without classical analogue. Quantum damping of position for an
atom bouncing on a reflecting surface in presence of a homogeneous
gravitational field is dealt in detail and the connection with an experiment
already performed in the classical regime is studied. We show that quantum
damping is testable provided that the same measurement strength obtained in the
experimental verification of the quantum Zeno effect in atomic spectroscopy [W.
M. Itano et al., Phys. Rev. A {\bf 41}, 2295 (1990)] is made available.",9606024v1
2006-12-17,Influence of a classical homogeneous gravitational field on dissipative dynamics of the Jaynes-Cummings model with phase damping,"In this paper, we study the dissipative dynamics of the Jaynes-Cummings model
with phase damping in the presence of a classical homogeneous gravitational
field. The model consists of a moving two-level atom simultaneously exposed to
the gravitational field and a single-mode traveling radiation field in the
presence of the phase damping. We present a quantum treatment of the internal
and external dynamics of the atom based on an alternative su(2) dynamical
algebraic structure. By making use of the super-operator technique, we obtain
the solution of the master equation for the density operator of the quantum
system, under the Markovian approximation. Assuming that initially the
radiation field is prepared in a Glauber coherent state and the two-level atom
is in the excited state, we investigate the influence of gravity on the
temporal evolution of collapses and revivals of the atomic population
inversion, atomic dipole squeezing, atomic momentum diffusion, photon counting
statistics and quadrature squeezing of the radiation field in the presence of
phase damping.",0612143v2
2007-04-25,Theory of weakly damped free-surface flows: a new formulation based on potential flow solutions,"Several theories for weakly damped free-surface flows have been formulated.
In this paper we use the linear approximation to the Navier-Stokes equations to
derive a new set of equations for potential flow which include dissipation due
to viscosity. A viscous correction is added not only to the irrotational
pressure (Bernoulli's equation), but also to the kinematic boundary condition.
The nonlinear Schr\""odinger (NLS) equation that one can derive from the new set
of equations to describe the modulations of weakly nonlinear, weakly damped
deep-water gravity waves turns out to be the classical damped version of the
NLS equation that has been used by many authors without rigorous justification.",0704.3352v1
2007-05-25,The Secular Evolution of a Close Ring-Satellite System: The Excitation of Spiral Bending Waves at a Nearby Gap Edge,"The secular perturbations exerted by an inclined satellite orbiting in a gap
in a broad planetary ring tends to excite the inclinations of the nearby ring
particles, and the ring's self-gravity can allow that disturbance to propagate
away in the form of a spiral bending wave. The amplitude of this spiral bending
wave is determined, as well as the wavelength, which shrinks as the waves
propagate outwards due to the effects of the central planet's oblateness. The
excitation of these bending waves also damps the satellite's inclination I.
This secular I damping is also compared to the inclination excitation that is
due to the satellite's many other vertical resonances in the ring, and the
condition for inclination damping is determined. The secular I damping is
likely responsible for confining the orbits of Saturn's two known gap-embedded
moons, Pan and Daphnis, to the ring plane.",0705.3797v1
2007-06-15,Anticorrelation between temperature and fluctuations in moderately damped Josephson junctions,"We study the influence of dissipation on the switching current statistics of
moderately damped Josephson junctions. Different types of both low- and high-
$T_c$ junctions with controlled damping are studied. The damping parameter of
the junctions is tuned in a wide range by changing temperature, magnetic field,
gate voltage, introducing a ferromagnetic layer or in-situ capacitive shunting.
A paradoxical collapse of switching current fluctuations occurs with increasing
$T$ in all studied junctions. The phenomenon critically depends on dissipation
in the junction and is explained by interplay of two counteracting consequences
of thermal fluctuations, which on the one hand assist in premature switching
into the resistive state and on the other hand help in retrapping back to the
superconducting state. This is one of the rare examples of anticorrelation
between temperature and fluctuation amplitude of a physically measurable
quantity.",0706.2248v1
2007-08-06,Collisionless damping of electron waves in non-Maxwellian plasma,"In this paper we have criticized the so-called Landau damping theory. We have
analyzed solutions of the standard dispersion equations for longitudinal
(electric) and transversal (electromagnetic and electron) waves in
half-infinite slab of the uniform collisionless plasmas with non-Maxwellian and
Maxwellian-like electron energy distribution functions. One considered the most
typical cases of both the delta-function type distribution function (the plasma
stream with monochromatic electrons) and distribution functions, different from
Maxwellian ones as with a surplus as well as with a shortage in the Maxwellian
distribution function tail. It is shown that there are present for the
considered cases both collisionless damping and also non-damping electron waves
even in the case of non-Maxwellian distribution function.",0708.0748v5
2007-08-14,Preliminary Results on Vibration Damping Properties of Nanoscale-Reinforced Composite Materials,"The focus in this paper is an analysis of existing state of the arts directed
toward the development of the next generation of vibration damping systems. The
research work concentrates on an investigation related to
nanoparticles/fibres/tubes-reinforced materials and coatings dynamic
characterization and modeling of the fundamental phenomena that control
relationships between structure and damping/mechanical properties of the
materials. We simulated composite materials using finite element and mesh free
methods, using a hollow shell representation of the individual nanotube/fiber.
Results of the research work will provide a platform for the development of
nanoparticle-reinforced damping materials that are light-weight, vibration and
shock resistant. The outcome of the research work is expected to have
wide-ranging technical benefits with direct relevance to industry in areas of
transportation (aerospace, automotive, rail), electronics and civil
infrastructure development.",0708.1821v1
2007-08-18,Non-Riemannian geometrical asymmetrical damping stresses on the Lagrange instability of shear flows,"It is shown that the physical interpretation of Elie Cartan three-dimensional
space torsion as couple asymmetric stress, has the effect of damping,
previously Riemannian unstable Couette planar shear flow, leading to stability
of the flow in the Lagrangean sense. Actually, since the flow speed is
inversely proportional to torsion, it has the effect of causing a damping in
the planar flow atenuating the instability effect. In this sense we may say
that Cartan torsion induces shear viscous asymmetric stresses in the fluid,
which are able to damp the instability of the flow. The stability of the flow
is computed from the sectional curvature in non-Riemannian three-dimensional
manifold. Marginal stability is asssumed by making the sectional non-Riemannian
curvature zero, which allows us to determine the speeds of flows able to induce
this stability. The ideas discussed here show that torsion plays the
geometrical role of magnetic field in hydromagnetic instability of Couette
flows recently investigated by Bonnano and Urpin (PRE, (2007,in press) can be
extended and applied to plastic flows with microstructure defects. Recently
Riemannian asymmetric stresses in magnetohydrodynamics (MHD) have been
considered by Billig (2004).",0708.2467v1
2007-12-07,State transition of a non-Ohmic damping system in a corrugated plane,"Anomalous transport of a particle subjected to non-Ohmic damping of the power
$\delta$ in a tilted periodic potential is investigated via Monte Carlo
simulation of generalized Langevin equation. It is found that the system
exhibits two relative motion modes: the locking state and the running state.
Under the surrounding of sub-Ohmic damping ($0<\delta<1$), the particle should
transfer into a running state from a locking state only when local minima of
the potential vanish; hence the particle occurs a synchronization oscillation
in its mean displacement and mean square displacement (MSD). In particular, the
two motion modes are allowed to coexist in the case of super-Ohmic damping
($1<\delta<2$) for moderate driving forces, namely, where exists double centers
in the velocity distribution. This induces the particle having faster
diffusion, i.e., its MSD reads $<\Delta x^2(t)> = 2D^{(\delta)}_{eff}
t^{\delta_{eff}}$. Our result shows that the effective power index
$\delta_{\textmd{eff}}$ can be enhanced and is a nonmonotonic function of the
temperature and the driving force. The mixture effect of the two motion modes
also leads to a breakdown of hysteresis loop of the mobility.",0712.1070v1
2007-12-25,The damped Pinney equation and its applications to dissipative quantum mechanics,"The work considers the damped Pinney equation, defined as the model arising
when a linear in velocity damping term is included in the Pinney equation. In
the general case the resulting equation does not admit Lie point symmetries or
is reducible to a simpler form by any obvious coordinate transformation. In
this context the method of Kuzmak-Luke is applied to derive a perturbation
solution, for weak damping and slow time-dependence of the frequency function.
The perturbative and numerical solutions are shown to be in good agreement. The
results are applied to examine the time-evolution of Gaussian shaped
wave-functions in the Kostin formulation of dissipative quantum mechanics.",0712.4083v3
2008-01-01,Non-linear equations for electron waves in Maxwellian low-collision ion-electron plasmas,"The before described general principles and methodology of calculating
electron wave propagation in homogeneous isotropic half-infinity slab of
Maxwellian plasma with indefinite but in principal value sense taken integrals
in characteristic equations, and the use of 2D Laplace transform method are
applied to an evaluation of collision damping decrements of plane electron
longitudinal and transverse waves. Damping decrement tends to infinity when the
wave frequency tends to electron Langmuir frequency from above values. We
considered recurrent relations for amplitudes of the overtones which form in
their sum the all solution of the plasma wave non-linear equations including
collision damping and quadratic (non-linear) terms. Collisionless damping at
frequencies more the Langmuir one is possible only in non-Maxwellian plasmas.",0801.0286v2
2008-02-22,Radiative Damping and Functional Differential Equations,"We propose a general technique to solve the classical many-body problem with
radiative damping. We modify the short-distance structure of Maxwell
electrodynamics. This allows us to avoid runaway solutions as if we had a
covariant model of extended particles. The resulting equations of motion are
functional differential equations (FDEs) rather than ordinary differential
equations. Using recently developed numerical techniques for stiff FDEs, we
solve these equations for the one-body central force problem with radiative
damping with a view to benchmark our new approach. Our results indicate that
locally the magnitude of radiation damping may be well approximated by the
standard third-order expression but the global properties of our solutions are
dramatically different. We comment on the two body problem and applications to
quantum field theory and quantum mechanics.",0802.3390v2
2008-04-24,Analytic approximate seismology of transversely oscillating coronal loops,"We present an analytic approximate seismic inversion scheme for damped
transverse coronal loop oscillations based on the thin tube and thin boundary
approximation for computing the period and the damping time. Asymptotic
expressions for the period and damping rate are used to illustrate the process
of seismological inversion in a simple and easy to follow manner. The inversion
procedure is formulated in terms of two simple functions, which are given by
simple closed expressions. The analytic seismic inversion shows that an
infinite amount of 1-dimensional equilibrium models can reproduce the observed
periods and damping times. It predicts a specific range of allowable values for
the Alfven travel time and lower bounds for the density contrast and the
inhomogeneity length scale. When the results of the present analytic seismic
inversion are compared with those of a previous numerical inversion, excellent
agreement is found up to the point that the analytic seismic inversion emerges
as a tool for validating results of numerical inversions. Actually it helped us
to identify and correct inaccuracies in a previous numerical investigation.",0804.3877v1
2008-10-21,On Wigner functions and a damped star product in dissipative phase-space quantum mechanics,"Dito and Turrubiates recently introduced an interesting model of the
dissipative quantum mechanics of a damped harmonic oscillator in phase space.
Its key ingredient is a non-Hermitian deformation of the Moyal star product
with the damping constant as deformation parameter. We compare the
Dito-Turrubiates scheme with phase-space quantum mechanics (or deformation
quantization) based on other star products, and extend it to incorporate Wigner
functions. The deformed (or damped) star product is related to a complex
Hamiltonian, and so necessitates a modified equation of motion involving
complex conjugation. We find that with this change the Wigner function
satisfies the classical equation of motion. This seems appropriate since
non-dissipative systems with quadratic Hamiltonians share this property.",0810.3893v1
2009-01-08,Grand-mother clocks and quiet lasers,"Galileo noted in the 16th century that the period of oscillation of a
pendulum is almost independent of the amplitude. However, such a pendulum is
damped by air friction. The latter may be viewed as resulting from air
molecules getting in contact with the pendulum. It follows that air friction,
not only damps the oscillation, but also introduces randomness. In the
so-called ``grand-mother'' clock, discovered by Huygens in the 18th century,
damping is compensated for, on the average, by an escapement mechanism driven
by a falling weight. The purpose of this paper is to show that such a clock is,
in its idealized form, a quiet oscillator. By ``quiet'' we mean that in spite
of the randomness introduced by damping, the dissipated power (viewed as the
oscillator output) does not fluctuate slowly. Comparison is made with quiet
laser oscillators discovered theoretically in 1984. Because the input power
does not fluctuate in both the mechanical oscillator and the quiet laser
oscillator, the output power does not fluctuate at small Fourier frequencies,
irrespectively of the detailed mechanisms involved.",0901.0983v1
2009-01-15,Interaction of fast charged projectiles with two-dimensional electron gas: Interaction and disorder effects,"The results of a theoretical investigation on the stopping power of ions
moving in a disordered two-dimensional degenerate electron gas are presented.
The stopping power for an ion is calculated employing linear response theory
using the dielectric function approach. The disorder, which leads to a damping
of plasmons and quasiparticles in the electron gas, is taken into account
through a relaxation time approximation in the linear response function. The
stopping power for an ion is calculated in both the low- and high-velocity
limits. In order to highlight the effects of damping we present a comparison of
our analytical and numerical results, in the case of point-like ions, obtained
for a non-zero damping with those for a vanishing damping. It is shown that the
equipartition sum rule first formulated by Lindhard and Winther for
three-dimensional degenerate electron gas does not necessarily hold in
two-dimensions. We have generalized this rule introducing an effective
dielectric function. In addition some new results for two-dimensional
interacting electron gas have been obtained. In this case the
exchange-correlation interactions of electrons are considered via
local-field-corrected dielectric function.",0901.2249v1
2009-02-01,Non-Markovian Analysis of the Phase Damped Jaynes-Cummings Model in the Presence of a Classical Homogeneous Gravitational Field,"In this paper, the non-Markovian dissipative dynamics of the phase damped
Jaynes-Cummings model in the presence of a classical homogeneous gravitational
field will be analyzed. The model consists of a moving two-level atom
simultaneously exposed to the gravitational field and a single-mode traveling
radiation field in the presence of a non-Markovian phase damping mechanism.
First, the non-Markovian master equation for the reduced density operator of
the system in terms of a Hamiltonian describing the atom-field interaction in
the presence of a homogeneous gravitational field will be presented. Then, the
super-operator technique will be generalized and an exact solution of the
non-Markovian master equation will be obtained. Assuming that initially the
radiation field is prepared in a Glauber coherent state and the two-level atom
is in the excited state, the non-Markovian effects on the temporal evolution of
collapses and revivals of the atomic population inversion and photon counting
statistics of the radiation field in the presence of both the phase damping and
a homogeneous gravitational field will be investigated.",0902.0114v1
2009-05-04,Models of Damped Oscillators in Quantum Mechanics,"We consider several models of the damped oscillators in nonrelativistic
quantum mechanics in a framework of a general approach to the dynamics of the
time-dependent Schroedinger equation with variable quadratic Hamiltonians. The
Green functions are explicitly found in terms of elementary functions and the
corresponding gauge transformations are discussed. The factorization technique
is applied to the case of a shifted harmonic oscillator. The time-evolution of
the expectation values of the energy related operators is determined for two
models of the quantum damped oscillators under consideration. The classical
equations of motion for the damped oscillations are derived for the
corresponding expectation values of the position operator.",0905.0507v6
2009-05-28,Resonant Nonlinear Damping of Quantized Spin Waves in Ferromagnetic Nanowires,"We use spin torque ferromagnetic resonance to measure the spectral properties
of dipole-exchange spin waves in permalloy nanowires. Our measurements reveal
that geometric confinement has a profound effect on the damping of spin waves
in the nanowire geometry. The damping parameter of the lowest-energy quantized
spin wave mode depends on applied magnetic field in a resonant way and exhibits
a maximum at a field that increases with decreasing nanowire width. This
enhancement of damping originates from a nonlinear resonant three-magnon
confluence process allowed at a particular bias field value determined by
quantization of the spin wave spectrum in the nanowire geometry.",0905.4699v2
2009-06-01,Effect of Decoherence in Ekert-Protocol,"We have examined the effect of the decoherence in the Ekert91 quantum
cryptographic protocol. In order to explore this issue we have introduced two
major decoherences, the depolarizing channel and the generalized amplitude
damping, between the singlet source and one of the legitimate users. It is
shown that the depolarizing channel disentangles the quantum channel more
easily than the generalized amplitude damping. This fact indicates that the
Ekert protocol is more robust to the generalized amplitude damping. We also
have computed the Bell inequality to check the robustness or weakness of the
Ekert91 protocol. Computation of the Bell inequality also confirms the
robustness of the Ekert91 protocol to the generalized amplitude damping
compared to the depolarizing channel.",0906.0233v1
2009-08-05,Surface plasmon lifetime in metal nanoshells,"The lifetime of localized surface plasmon plays an important role in many
aspects of plasmonics and its applications. In small metal nanostructures, the
dominant mechanism restricting plasmon lifetime is size-dependent Landau
damping. We performed quantum-mechanical calculations of Landau damping for the
bright surface plasmon mode in a metal nanoshell. In contrast to the
conventional model based on the electron surface scattering, we found that the
damping rate decreases as the nanoshell thickness is reduced. The origin of
this behavior is traced to the spatial distribution of plasmon local field
inside the metal shell. We also found that, due to interference of electron
scattering amplitudes from nanoshell's two metal surfaces, the damping rate
exhibits pronounced quantum beats with changing shell thickness.",0908.0647v3
2009-08-12,Coarse Grained Simulations of a Small Peptide: Effects of Finite Damping and Hydrodynamic Interactions,"In the coarse grained Brownian Dynamics simulation method the many solvent
molecules are replaced by random thermal kicks and an effective friction acting
on the particles of interest. For Brownian Dynamics the friction has to be so
strong that the particles' velocities are damped much faster than the duration
of an integration timestep. Here we show that this conceptual limit can be
dropped with an analytic integration of the equations of damped motion. In the
resulting Langevin integration scheme our recently proposed approximate form of
the hydrodynamic interactions between the particles can be incorparated
conveniently, leading to a fast multi-particle propagation scheme, which
captures more of the short-time and short-range solvent effects than standard
BD. Comparing the dynamics of a bead-spring model of a short peptide, we
recommend to run simulations of small biological molecules with the Langevin
type finite damping and to include the hydrodynamic interactions.",0908.1685v1
2009-09-01,Quantum Stackelberg duopoly in the presence of correlated noise,"We study the influence of entanglement and correlated noise using correlated
amplitude damping, depolarizing and phase damping channels on the quantum
Stackelberg duopoly. Our investigations show that under the action of amplitude
damping channel a critical point exists for unentangled initial state as well,
at which firms get equal payoffs. The game becomes a follower advantage game
when the channel is highly decohered. Two critical points corresponding to two
values of the entanglement angle are found in the presence of correlated noise.
Within the range of these limits of entanglement angle, the game is follower
advantage game. In case of depolarizing channel, the payoffs of the two firms
are strongly influenced by the memory parameter. The presence of quantum memory
ensures the existence of Nash equilibrium for the entire range of decoherence
and entanglement parameters for both the channels. A local maximum in the
payoffs is observed which vanishes as the channel correlation increases.
Moreover, under the influence of depolarizing channel, the game is always a
leader advantage game. Furthermore, it is seen that phase damping channel does
not effect the outcome of the game.",0909.0063v2
2009-09-04,Second sound dipole mode in a partially Bose-Einstein condensed gas,"We study the second sound dipole mode in a partially Bose-Einstein condensed
gas. This mode is excited by spatially separating and releasing the
center-of-mass of the Bose-Einstein condensate (BEC) with respect to the
thermal cloud, after which the equilibration is observed. The oscillation
frequency and the damping rate of this mode is studied for different harmonic
confinements and temperatures. The measured damping rates close to the
collisionless regime are found to be in good agreement with Landau damping. For
increasing hydrodynamicity of the cloud we observe an increase of the damping.",0909.0886v1
2009-12-30,Finite dimensional attractor for a composite system of wave/plate equations with localised damping,"The long-term behaviour of solutions to a model for acoustic-structure
interactions is addressed; the system is comprised of coupled semilinear wave
(3D) and plate equations with nonlinear damping and critical sources. The
questions of interest are: existence of a global attractor for the dynamics
generated by this composite system, as well as dimensionality and regularity of
the attractor. A distinct and challenging feature of the problem is the
geometrically restricted dissipation on the wave component of the system. It is
shown that the existence of a global attractor of finite fractal dimension --
established in a previous work by Bucci, Chueshov and Lasiecka (Comm. Pure
Appl. Anal., 2007) only in the presence of full interior acoustic damping --
holds even in the case of localised dissipation. This nontrivial generalization
is inspired by and consistent with the recent advances in the study of wave
equations with nonlinear localised damping.",0912.5464v2
2010-02-12,Features of ion acoustic waves in collisional plasmas,"The effects of friction on the ion acoustic (IA) wave in fully and partially
ionized plasmas are studied. In a quasi-neutral electron-ion plasma the
friction between the two species cancels out exactly and the wave propagates
without any damping. If the Poisson equation is used instead of the
quasi-neutrality, however, the IA wave is damped and the damping is dispersive.
In a partially ionized plasma, the collisions with the neutrals modify the IA
wave beyond recognition. For a low density of neutrals the mode is damped. Upon
increasing the neutral density, the mode becomes first evanescent and then
reappears for a still larger number of neutrals. A similar behavior is obtained
by varying the mode wave-length. The explanation for this behavior is given. In
an inhomogeneous plasma placed in an external magnetic field, and for
magnetized electrons and un-magnetized ions, the IA mode propagates in any
direction and in this case the collisions make it growing on the account of the
energy stored in the density gradient. The growth rate is angle dependent. A
comparison with the collision-less kinetic density gradient driven IA
instability is also given.",1002.2502v1
2010-02-18,Damping mechanisms for oscillations in solar prominences,"Small amplitude oscillations are a commonly observed feature in
prominences/filaments. These oscillations appear to be of local nature, are
associated to the fine structure of prominence plasmas, and simultaneous flows
and counterflows are also present. The existing observational evidence reveals
that small amplitude oscillations, after excited, are damped in short spatial
and temporal scales by some as yet not well determined physical mechanism(s).
Commonly, these oscillations have been interpreted in terms of linear
magnetohydrodynamic (MHD) waves, and this paper reviews the theoretical damping
mechanisms that have been recently put forward in order to explain the observed
attenuation scales. These mechanisms include thermal effects, through
non-adiabatic processes, mass flows, resonant damping in non-uniform media, and
partial ionization effects. The relevance of each mechanism is assessed by
comparing the spatial and time scales produced by each of them with those
obtained from observations. Also, the application of the latest theoretical
results to perform prominence seismology is discussed, aiming to determine
physical parameters in prominence plasmas that are difficult to measure by
direct means.",1002.3489v2
2010-03-07,Theory of plasmon decay in dense plasmas and warm dense matter,"The decay of the Langmuir waves in dense plasmas is not accurately predicted
by the prevalent Landau damping theory. A dielectric function theory is
introduced, predicting much higher damping than the Landau damping theory. This
strong damping is in better agreement with the experimentally observed data in
metals. It is shown that the strong plasmon decay leads to the existence of a
parameter regime where the backward Raman scattering is unstable while the
forward Raman scattering is stable. This regime may be used to create intense
x-ray pulses, by means of the the backward Raman compression. The optimal pulse
duration and intensity is estimated.",1003.1523v2
2010-03-16,Justification of the symmetric damping model of the dynamical Casimir effect in a cavity with a semiconductor mirror,"A ""microscopic"" justification of the ""symmetric damping"" model of a quantum
oscillator with time-dependent frequency and time-dependent damping is given.
This model is used to predict results of experiments on simulating the
dynamical Casimir effect in a cavity with a photo-excited semiconductor mirror.
It is shown that the most general bilinear time-dependent coupling of a
selected oscillator (field mode) to a bath of harmonic oscillators results in
two equal friction coefficients for the both quadratures, provided all the
coupling coefficients are proportional to a single arbitrary function of time
whose duration is much shorter than the periods of all oscillators. The choice
of coupling in the rotating wave approximation form leads to the ""mimimum
noise"" model of the quantum damped oscillator, introduced earlier in a pure
phenomenological way.",1003.3061v2
2010-04-12,Dissipative Transport of a Bose-Einstein Condensate,"We investigate the effects of impurities, either correlated disorder or a
single Gaussian defect, on the collective dipole motion of a Bose-Einstein
condensate of $^7$Li in an optical trap. We find that this motion is damped at
a rate dependent on the impurity strength, condensate center-of-mass velocity,
and interatomic interactions. Damping in the Thomas-Fermi regime depends
universally on the disordered potential strength scaled to the condensate
chemical potential and the condensate velocity scaled to the peak speed of
sound. The damping rate is comparatively small in the weakly interacting
regime, and the damping in this case is accompanied by strong condensate
fragmentation. \textit{In situ} and time-of-flight images of the atomic cloud
provide evidence that this fragmentation is driven by dark soliton formation.",1004.1891v2
2010-05-23,Constraining phases of quark matter with studies of r-mode damping in neutron stars,"The r-mode instability in rotating compact stars is used to constrain the
phase of matter at high density. The color-flavor-locked phase with kaon
condensation (CFL-K0) and without (CFL) is considered in the temperature range
10^8K < T <10^{11} K. While the bulk viscosity in either phase is only
effective at damping the r-mode at temperatures T > 10^{11} K, the shear
viscosity in the CFL-K0 phase is the only effective damping agent all the way
down to temperatures T > 10^8 K characteristic of cooling neutron stars.
However, it cannot keep the star from becoming unstable to gravitational wave
emission for rotation frequencies f ~ 56-11 Hz at T ~ 10^8-10^9 K. Stars
composed almost entirely of CFL or CFL-K0 matter are ruled out by observation
of rapidly rotating neutron stars, indicating that dissipation at the
quark-hadron interface or nuclear crust interface must play a key role in
damping the instability.",1005.4161v1
2010-07-07,Observational evidence of resonantly damped propagating kink waves in the solar corona,"In this Letter we establish clear evidence for the resonant absorption
damping mechanism by analyzing observational data from the novel Coronal
Multi-Channel Polarimeter (CoMP). This instrument has established that in the
solar corona there are ubiquitous propagating low amplitude ($\approx$1 km
s$^{-1}$) Alfv\'{e}nic waves with a wide range of frequencies. Realistically
interpreting these waves as the kink mode from magnetohydrodynamic (MHD) wave
theory, they should exhibit a frequency dependent damping length due to
resonant absorption, governed by the TGV relation showing that transversal
plasma inhomogeneity in coronal magnetic flux tubes causes them to act as
natural low-pass filters. It is found that observed frequency dependence on
damping length (up to about 8 mHz) can be explained by the kink wave
interpretation and furthermore, the spatially averaged equilibrium parameter
describing the length scale of transverse plasma density inhomogeneity over a
system of coronal loops is consistent with the range of values estimated from
TRACE observations of standing kink modes.",1007.1080v1
2010-07-12,Variable damping and coherence in a high-density magnon gas,"We report on the fast relaxation behavior of a high-density magnon gas
created by a parametric amplification process. The magnon gas is probed using
the technique of spin-wave packet recovery by parallel parametric pumping.
Experimental results show a damping behavior which is in disagreement with both
the standard model of exponential decay and with earlier observations of
non-linear damping. In particular, the inherent magnon damping is found to
depend upon the presence of the parametric pumping field. A phenomenological
model which accounts for the dephasing of the earlier injected magnons is in
good agreement with the experimental data.",1007.1895v3
2010-07-21,A low-power circuit for piezoelectric vibration control by synchronized switching on voltage sources,"In the paper, a vibration damping system powered by harvested energy with
implementation of the so-called SSDV (synchronized switch damping on voltage
source) technique is designed and investigated. In the semi-passive approach,
the piezoelectric element is intermittently switched from open-circuit to
specific impedance synchronously with the structural vibration. Due to this
switching procedure, a phase difference appears between the strain induced by
vibration and the resulting voltage, thus creating energy dissipation. By
supplying the energy collected from the piezoelectric materials to the
switching circuit, a new low-power device using the SSDV technique is proposed.
Compared with the original self-powered SSDI (synchronized switch damping on
inductor), such a device can significantly improve its performance of vibration
control. Its effectiveness in the single-mode resonant damping of a composite
beam is validated by the experimental results.",1007.3596v1
2010-10-24,Long-time dynamics in plate models with strong nonlinear damping,"We study long-time dynamics of a class of abstract second order in time
evolution equations in a Hilbert space with the damping term depending both on
displacement and velocity. This damping represents the nonlinear strong
dissipation phenomenon perturbed with relatively compact terms. Our main result
states the existence of a compact finite dimensional attractor. We study
properties of this attractor. We also establish the existence of a fractal
exponential attractor and give the conditions that guarantee the existence of a
finite number of determining functionals. In the case when the set of
equilibria is finite and hyperbolic we show that every trajectory is attracted
by some equilibrium with exponential rate. Our arguments involve a recently
developed method based on the ""compensated"" compactness and quasi-stability
estimates. As an application we consider the nonlinear Kirchhoff, Karman and
Berger plate models with different types of boundary conditions and strong
damping terms. Our results can be also applied to the nonlinear wave equations.",1010.4991v1
2010-11-05,"Effects of Turbulence, Eccentricity Damping, and Migration Rate on the Capture of Planets into Mean Motion Resonance","Pairs of migrating extrasolar planets often lock into mean motion resonance
as they drift inward. This paper studies the convergent migration of giant
planets (driven by a circumstellar disk) and determines the probability that
they are captured into mean motion resonance. The probability that such planets
enter resonance depends on the type of resonance, the migration rate, the
eccentricity damping rate, and the amplitude of the turbulent fluctuations.
This problem is studied both through direct integrations of the full 3-body
problem, and via semi-analytic model equations. In general, the probability of
resonance decreases with increasing migration rate, and with increasing levels
of turbulence, but increases with eccentricity damping. Previous work has shown
that the distributions of orbital elements (eccentricity and semimajor axis)
for observed extrasolar planets can be reproduced by migration models with
multiple planets. However, these results depend on resonance locking, and this
study shows that entry into -- and maintenance of -- mean motion resonance
depends sensitively on migration rate, eccentricity damping, and turbulence.",1011.1486v1
2010-11-21,Quasi-normal frequencies: Semi-analytic results for highly damped modes,"Black hole highly-damped quasi-normal frequencies (QNFs) are very often of
the form (offset)} + i n (gap). We have investigated the genericity of this
phenomenon for the Schwarzschild--deSitter (SdS) black hole by considering a
model potential that is piecewise Eckart (piecewise Poeschl-Teller), and
developing an analytic ``quantization condition'' for the highly-damped
quasi-normal frequencies. We find that the (offset) + i n(gap) behaviour is
common but not universal, with the controlling feature being whether or not the
ratio of the surface gravities is a rational number. We furthermore observed
that the relation between rational ratios of surface gravities and periodicity
of QNFs is very generic, and also occurs within different analytic approaches
applied to various types of black hole spacetimes. These observations are of
direct relevance to any physical situation where highly-damped quasi-normal
modes are important.",1011.4634v1
2011-03-08,Application of Explicit Symplectic Algorithms to Integration of Damping Oscillators,"In this paper an approach is outlined. With this approach some explicit
algorithms can be applied to solve the initial value problem of $n-$dimensional
damped oscillators. This approach is based upon following structure: for any
non-conservative classical mechanical system and arbitrary initial conditions,
there exists a conservative system; both systems share one and only one common
phase curve; and, the value of the Hamiltonian of the conservative system is,
up to an additive constant, equal to the total energy of the non-conservative
system on the aforementioned phase curve, the constant depending on the initial
conditions. A key way applying explicit symplectic algorithms to damping
oscillators is that by the Newton-Laplace principle the nonconservative force
can be reasonably assumed to be equal to a function of a component of
generalized coordinates $q_i$ along a phase curve, such that the damping force
can be represented as a function analogous to an elastic restoring force
numerically in advance. Two numerical examples are given to demonstrate the
good characteristics of the algorithms.",1103.1455v1
2011-03-09,Nonlinear damping in mechanical resonators based on graphene and carbon nanotubes,"Carbon nanotubes and graphene allow fabricating outstanding nanomechanical
resonators. They hold promise for various scientific and technological
applications, including sensing of mass, force, and charge, as well as the
study of quantum phenomena at the mesoscopic scale. Here, we have discovered
that the dynamics of nanotube and graphene resonators is in fact highly exotic.
We propose an unprecedented scenario where mechanical dissipation is entirely
determined by nonlinear damping. As a striking consequence, the quality factor
Q strongly depends on the amplitude of the motion. This scenario is radically
different from that of other resonators, whose dissipation is dominated by a
linear damping term. We believe that the difference stems from the reduced
dimensionality of carbon nanotubes and graphene. Besides, we exploit the
nonlinear nature of the damping to improve the figure of merit of
nanotube/graphene resonators.",1103.1788v1
2011-05-03,Entanglement in a Bipartite Gaussian State,"To examine the loss of entanglement in a two-particle Gaussian system, we
couple it to an environment and use the Non-Rotating Wave master equation to
study the system's dynamics. We also present a derivation of this equation. We
consider two different types of evolution. Under free evolution we find that
entanglement is lost quickly between the particles. When a harmonic potential
is added between the particles, two very different behaviours can be observed,
namely in the over and under-damped cases respectively, where the strength of
the damping is determined by how large the coupling to the bath is with respect
to the frequency of the potential. In the over-damped case, we find that the
entanglement vanishes at even shorter times than it does in the free evolution.
In the (very) under-damped case, we observe that the entanglement does not
vanish. Instead it oscillates towards a stable value.",1105.0564v1
2011-06-15,Plasma damping effects on the radiative energy loss of relativistic particles,"The energy loss of a relativistic charge undergoing multiple scatterings
while traversing an infinite, polarizable and absorptive plasma is
investigated. Polarization and damping mechanisms in the medium are
phenomenologically modelled by a complex index of refraction. Apart from the
known Ter-Mikaelian effect related to the dielectric polarization of matter, we
find an additional, substantial reduction of the energy loss due to damping of
radiation. The observed effect is more prominent for larger damping and/or
larger energy of the charge. A conceivable analog of this phenomenon in QCD
could influence the study of jet quenching phenomena in ultra-relativistic
heavy-ion collisions at RHIC and LHC.",1106.2856v3
2011-09-12,Reduction of compressibility and parallel transfer by Landau damping in turbulent magnetized plasmas,"Three-dimensional numerical simulations of decaying turbulence in a
magnetized plasma are performed using a so-called FLR-Landau fluid model which
incorporates linear Landau damping and finite Larmor radius (FLR) corrections.
It is shown that compared to simulations of compressible Hall-MHD, linear
Landau damping is responsible for significant damping of magnetosonic waves,
which is consistent with the linear kinetic theory. Compressibility of the
fluid and parallel energy cascade along the ambient magnetic field are also
significantly inhibited when the beta parameter is not too small. In contrast
with Hall-MHD, the FLR-Landau fluid model can therefore correctly describe
turbulence in collisionless plasmas such as the solar wind, providing an
interpretation for its nearly incompressible behavior.",1109.2636v1
2011-09-24,Existence of weak solutions for the generalized Navier-Stokes equations with damping,"In this work we consider the generalized Navier-Stoke equations with the
presence of a damping term in the momentum equation. % The problem studied here
derives from the set of equations which govern the isothermal flow of
incompressible, homogeneous and non-Newtonian fluids. % For the generalized
Navier-Stokes problem with damping, we prove the existence of weak solutions by
using regularization techniques, the theory of monotone operators and
compactness arguments together with the local decomposition of the pressure and
the Lipschitz-truncation method. The existence result proved here holds for any
$q>\frac{2N}{N+2}$ and any $\sigma>1$, where $q$ is the exponent of the
diffusion term and $\sigma$ is the exponent which characterizes the damping
term.",1109.5217v1
2011-11-14,New Electrodynamics of Pulsars,"We have recently proposed that Force-Free Electrodynamics (FFE) does not
apply to pulsars -- pulsars should be described by the high-conductivity limit
of Strong-Field Electrodynamics (SFE), which predicts an order-unity damping of
the Poynting flux, while FFE postulates zero damping. The strong damping result
has not been accepted by several pulsar experts, who claim that FFE basically
works and the Poynting flux damping can be arbitrarily small.
  Here we consider a thought experiment -- cylindrical periodic pulsar. We show
that FFE is incapable of describing this object, while SFE predictions are
physically plausible. The intrinsic breakdown of FFE should mean that the FFE
description of the singular current layer (the only region of magnetosphere
where FFE and the high-conductivity SFE differ) is incorrect. Then the
high-conductivity SFE should be the right theory for real pulsars too, and the
pure-FFE description of pulsars should be discarded.",1111.3377v1
2011-12-20,Dynamics of DNA breathing in the Peyrard-Bishop model with damping and external force,"The impact of damping effect and external forces to the DNA breathing is
investigated within the Peyrard-Bishop model. In in the continuum limit, the
dynamics of the breathing of DNA is described by the forced-damped nonlinear
Schrodinger equation and studied by means of variational method. The analytical
solutions are obtained for special cases. It is shown that the breather
propagation is decelerated in the presence of damping factor without the
external force, while the envelope velocity and the amplitude increase
significantly with the presence of external force. It is particularly found
that the higher harmonic terms are enhanced when the periodic force is applied.
It is finally argued that the external force accelerates the DNA breathing.",1112.4715v1
2012-01-31,Parametric amplification and self-oscillation in a nanotube mechanical resonator,"A hallmark of mechanical resonators made from a single nanotube is that the
resonance frequency can be widely tuned. Here, we take advantage of this
property to realize parametric amplification and self-oscillation. The gain of
the parametric amplification can be as high as 18.2 dB and tends to saturate at
high parametric pumping due to nonlinear damping. These measurements allow us
to determine the coefficient of the linear damping force. The corresponding
damping rate is lower than the one obtained from the lineshape of the resonance
(without pumping), supporting the recently reported scenario that describes
damping in nanotube resonators by a nonlinear force. The possibility to combine
nanotube resonant mechanics and parametric amplification holds promise for
future ultra-low force sensing experiments.",1201.6557v1
2012-02-22,Radiation Damping in the Photoionization of Fe^{14+},"A theoretical investigation of photoabsorption and photoionization of
Fe^{14+} extending beyond an earlier frame transformation R-matrix
implementation is performed using a fully-correlated, Breit-Pauli R-matrix
formulation including both fine-structure splitting of strongly-bound
resonances and radiation damping. The radiation damping of $2p\rightarrow nd$
resonances gives rise to a resonant photoionization cross section that is
significantly lower than the total photoabsorption cross section. Furthermore,
the radiation-damped photoionization cross section is found to be in good
agreement with recent experimental results once a global shift in energy of
$\approx -3.5$ eV is applied. These findings have important implications.
Firstly, the presently available synchrotron experimental data are applicable
only to photoionization processes and not to photoabsorption; the latter is
required in opacity calculations. Secondly, our computed cross section, for
which the L-shell ionization threshold is aligned with the NIST value, shows a
series of $2p \rightarrow nd$ Rydberg resonances that are uniformly 3-4 eV
higher in energy than the corresponding experimental profiles, indicating that
the L-shell threshold energy values currently recommended by NIST are likely in
error.",1202.4800v1
2012-02-29,Present status of development of damping ring extraction kicker system for CLIC,"The CLIC damping rings will produce ultra-low emittance beam, with high bunch
charge, necessary for the luminosity performance of the collider. To limit the
beam emittance blow-up due to oscillations, the pulse power modulators for the
damping ring kickers must provide extremely flat, high-voltage pulses:
specifications call for a 160 ns duration and a flattop of 12.5 kV, 250 A, with
a combined ripple and droop of not more than \pm0.02 %. The stripline design is
also extremely challenging: the field for the damping ring kicker system must
be homogenous to within \pm0.01 % over a 1 mm radius, and low beam coupling
impedance is required. The solid-state modulator, the inductive adder, is a
very promising approach to meeting the demanding specifications for the field
pulse ripple and droop. This paper describes the initial design of the
inductive adder and the striplines of the kicker system.",1202.6527v1
2012-04-03,Inhomogeneity of the phase space of the damped harmonic oscillator under Levy noise,"The damped harmonic oscillator under symmetric L\'{e}vy white noise shows
inhomogeneous phase space, which is in contrast to the homogeneous one of the
same oscillator under the Gaussian white noise, as shown in a recent paper [I.
M. Sokolov, W. Ebeling, and B. Dybiec, Phys. Rev. E \textbf{83}, 041118
(2011)]. The inhomogeneity of the phase space shows certain correlation between
the coordinate and the velocity of the damped oscillator under symmetric
L\'{e}vy white noise. In the present work we further explore the physical
origin of these distinguished features and find that it is due to the
combination of the damped effect and heavy tail of the noise. We demonstrate
directly this in the reduced coordinate $\tilde{x}$ versus velocity $\tilde{v}$
plots and identify the physics of the anti-association of the coordinate and
velocity.",1204.0593v2
2012-06-20,Metadamping: An emergent phenomenon in dissipative metamaterials,"We theoretically demonstrate the concept of metadamping in dissipative
metamaterials. We consider an infinite mass-spring chain with repeated local
resonators and a statically equivalent periodic chain whose wave propagation
characteristics are based on Bragg scattering. For each system we introduce
identical viscous damping (dashpot) elements and compare the damping ratio
associated with all Bloch modes. We find that the locally resonant metamaterial
exhibits higher dissipation overall which indicates a damping emergence
phenomena due to the presence of local resonance. We conclude our investigation
by quantifying the degree of emergent damping as a function of the long-wave
speed of sound in the medium or the static stiffness.",1206.4577v2
2012-07-12,Spin Damping in an RF Atomic Magnetometer,"Under negative feedback, the quality factor Q of a radio-frequency
magnetometer can be decreased by more than two orders of magnitude, so that any
initial perturbation of the polarized spin system can be rapidly damped,
preparing the magnetometer for detection of the desired signal. We find that
noise is also suppressed under such spin-damping, with a characteristic
spectral response corresponding to the type of noise; therefore magnetic,
photon-shot, and spin-projection noise can be measured distinctly. While the
suppression of resonant photon-shot noise implies the closed-loop production of
polarization-squeezed light, the suppression of resonant spin-projection noise
does not imply spin-squeezing, rather simply the broadening of the noise
spectrum with Q. Furthermore, the application of spin-damping during
phase-sensitive detection suppresses both signal and noise in such a way as to
increase the sensitivity bandwidth. We demonstrate a three-fold increase in the
magnetometer's bandwidth while maintaining 0.3 fT/\surdHz sensitivity.",1207.2842v1
2012-07-12,Damping of phase fluctuations in superfluid Bose gases,"Using Popov's hydrodynamic approach we derive an effective Euclidean action
for the long-wavelength phase fluctuations of superfluid Bose gases in D
dimensions. We then use this action to calculate the damping of phase
fluctuations at zero temperature as a function of D. For D >1 and wavevectors |
k | << 2 mc (where m is the mass of the bosons and c is the sound velocity) we
find that the damping in units of the phonon energy E_k = c | k | is to leading
order gamma_k / E_k = A_D (k_0^D / 2 pi rho) (| k | / k_0)^{2 D -2}, where rho
is the boson density and k_0 =2 mc is the inverse healing length. For D -> 1
the numerical coefficient A_D vanishes and the damping is proportional to an
additional power of |k | /k_0; a self-consistent calculation yields in this
case gamma_k / E_k = 1.32 (k_0 / 2 pi rho)^{1/2} |k | / k_0. In one dimension,
we also calculate the entire spectral function of phase fluctuations.",1207.3002v3
2012-08-27,The properties of non-thermal X-ray filaments in young supernova remnants,"Context. Young supernova remnants (SNRs) exhibit narrow filaments of
non-thermal X-ray emission whose widths can be limited either by electron
energy losses or damping of the magnetic field. Aims. We want to investigate
whether or not different models of these filaments can be observationally
tested. Methods. Using observational parameters of four historical remnants, we
calculate the filament profiles and compare the spectra of the filaments with
those of the total non-thermal emission. For that purpose, we solve an
one-dimensional stationary transport equation for the isotropic differential
number density of the electrons. Results. We find that the difference between
the spectra of filament and total non-thermal emission above 1 keV is more
pronounced in the damping model than in the energy-loss model. Conclusions. A
considerable damping of the magnetic field can result in an observable
difference between the spectra of filament and total non-thermal emission, thus
potentially permitting an observational discrimination between the energy-loss
model and the damping model of the X-ray filaments.",1208.5322v1
2012-09-10,Mid-infrared plasmons in scaled graphene nanostructures,"Plasmonics takes advantage of the collective response of electrons to
electromagnetic waves, enabling dramatic scaling of optical devices beyond the
diffraction limit. Here, we demonstrate the mid-infrared (4 to 15 microns)
plasmons in deeply scaled graphene nanostructures down to 50 nm, more than 100
times smaller than the on-resonance light wavelength in free space. We reveal,
for the first time, the crucial damping channels of graphene plasmons via its
intrinsic optical phonons and scattering from the edges. A plasmon lifetime of
20 femto-seconds and smaller is observed, when damping through the emission of
an optical phonon is allowed. Furthermore, the surface polar phonons in SiO2
substrate underneath the graphene nanostructures lead to a significantly
modified plasmon dispersion and damping, in contrast to a non-polar
diamond-like-carbon (DLC) substrate. Much reduced damping is realized when the
plasmon resonance frequencies are close to the polar phonon frequencies. Our
study paves the way for applications of graphene in plasmonic waveguides,
modulators and detectors in an unprecedentedly broad wavelength range from
sub-terahertz to mid-infrared.",1209.1984v1
2012-11-05,No asymptotically highly damped quasi-normal modes without horizons?,"We explore the question of what happens with the asymptotically highly damped
quasi-normal modes ($\ell$ fixed, $|\omega_{I}|\to\infty$) when the underlying
spacetime has no event horizons. We consider the characteristic oscillations of
a scalar field in a large class of asymptotically flat spherically symmetric
static spacetimes without (absolute) horizons, such that the class accommodates
the cases that are known to be of some sort of physical interest. The question
of the asymptotic quasi-normal modes in such spacetimes is relevant to
elucidate the connection between the behavior of the asymptotic quasi-normal
modes and the quantum properties of event horizons, as put forward in some
recent important conjectures. We prove for a large class of asymptotically flat
spacetimes without horizons that the scalar field asymptotically highly damped
modes do not exist. This provides in our view additional evidence that there is
indeed a close link between the asymptotically highly damped modes and the
existence of spacetime horizons (and their properties).",1211.1046v2
2012-11-21,Chaotic saddles in nonlinear modulational interactions in a plasma,"A nonlinear model of modulational processes in the subsonic regime involving
a linearly unstable wave and two linearly damped waves with different damping
rates in a plasma is studied numerically. We compute the maximum Lyapunov
exponent as a function of the damping rates in a two-parameter space, and
identify shrimp-shaped self-similar structures in the parameter space. By
varying the damping rate of the low-frequency wave, we construct bifurcation
diagrams and focus on a saddle-node bifurcation and an interior crisis
associated with a periodic window. We detect chaotic saddles and their stable
and unstable manifolds, and demonstrate how the connection between two chaotic
saddles via coupling unstable periodic orbits can result in a crisis-induced
intermittency. The relevance of this work for the understanding of modulational
processes observed in plasmas and fluids is discussed.",1211.5070v1
2012-12-18,Thermal activation at moderate-to-high and high damping: finite barrier effects and force spectroscopy,"We study the thermal escape problem in the moderate-to-high and high damping
regime of a system with a parabolic barrier. We present a formula that matches
our numerical results accounting for finite barrier effects, and compare it
with previous works. We also show results for the full damping range. We
quantitatively study some aspects on the relation between mean first passage
time and the definition of a escape rate. To finish we apply our results and
considerations in the framework of force spectroscopy problems. We study the
differences on the predictions using the different theories and discuss the
role of $\gamma \dot{F}$ as the relevant parameter at high damping.",1212.4290v2
2013-01-18,Interfacial roughening in non-ideal fluids: Dynamic scaling in the weak- and strong-damping regime,"Interfacial roughening denotes the nonequilibrium process by which an
initially flat interface reaches its equilibrium state, characterized by the
presence of thermally excited capillary waves. Roughening of fluid interfaces
has been first analyzed by Flekkoy and Rothman [Phys. Rev. Lett. 75, 260
(1995)], where the dynamic scaling exponents in the weakly damped case in two
dimensions were found to agree with the Kardar-Parisi-Zhang universality class.
We extend this work by taking into account also the strong-damping regime and
perform extensive fluctuating hydrodynamics simulations in two dimensions using
the Lattice Boltzmann method. We show that the dynamic scaling behavior is
different in the weakly and strongly damped case.",1301.4468v2
2013-02-02,Achieving the Quantum Ground State of a Mechanical Oscillator using a Bose-Einstein Condensate with Back-Action and Cold Damping feedback schemes,"We present a detailed study to show the possibility of approaching the
quantum ground-state of a hybrid optomechanical quantum device formed by a
Bose-Einstein condensate (BEC) confined inside a high-finesse optical cavity
with an oscillatory end mirror. Cooling is achieved using two experimentally
realizable schemes: back-action cooling and cold damping quantum feedback
cooling. In both the schemes, we found that increasing the two body atom-atom
interaction brings the mechanical oscillator to its quantum ground state. It
has been observed that back-action cooling is more effective in the good cavity
limit while the cold damping cooling scheme is more relevant in the bad cavity
limit. It is also shown that in the cold damping scheme, the device is more
efficient in the presence of BEC than in the absence of BEC.",1302.0339v1
2013-02-27,Resonantly damped oscillations of elliptically shaped stratified emerging coronal loops,"The effects of both elliptical shape and stage of emergence of the coronal
loop on the resonant absorption of standing kink oscillations are studied. To
do so, a typical coronal loop is modeled as a zero-beta longitudinally
stratified cylindrical magnetic flux tube. We developed the connection formulae
for the resonant absorption of standing transversal oscillations of a coronal
loop with an elliptical shape, at various stages of its emergence. Using the
connection formulae, the dispersion relation is derived and solved numerically
to obtain the frequencies and damping rates of the fundamental and
first-overtone kink modes. Our numerical results show that both the elliptical
shape and stage of emergence of the loop alter the frequencies and damping
rates of the tube as well as the ratio of frequencies of the fundamental and
its first-overtone modes. However, the ratio of the oscillation frequency to
the damping rate is not affected by the tube shape and stage of its emergence
and also is independent of the density stratification parameter.",1302.6884v1
2013-02-28,Damping of Quantum Vibrations Revealed in Deep Sub-barrier Fusion,"We demonstrate that when two colliding nuclei approach each other, their
quantum vibrations are damped near the touching point. We show that this
damping is responsible for the fusion hindrance phenomena measured in the deep
sub-barrier fusion reactions. To show those, we for the first time apply the
random-phase-approximation (RPA) method to the two-body $^{16}$O + $^{16}$O and
$^{40}$Ca + $^{40}$Ca systems. We calculate the octupole transition strengths
for the two nuclei adiabatically approaching each other. The calculated
transition strength drastically decreases near the touching point, strongly
suggesting the vanishing of the quantum couplings between the relative motion
and the vibrational intrinsic degrees of freedom of each nucleus. Based on this
picture, we also calculate the fusion cross section for the $^{40}$Ca +
$^{40}$Ca system using the coupled-channel method with the damping factor
simulating the vanishing of the couplings. The calculated results reproduce
well the experimental data, indicating that the smooth transition from the
sudden to adiabatic processes indeed occurs in the deep sub-barrier fusion
reactions.",1302.7115v2
2013-03-14,Microwave-assisted switching of a nanomagnet: analytical determination of the optimal microwave field,"We analytically determine the optimal microwave field that allows for the
magnetization reversal of a nanomagnet modeled as a macrospin. This is done by
minimizing the total injected energy. The results are in good agreement with
the fields obtained numerically using the optimal control theory. For typical
values of the damping parameter, a weak microwave field is sufficient to induce
switching through a resonant process. The optimal field is orthogonal to the
magnetization direction at any time and modulated both in amplitude and
frequency. The dependence of the pulse shape on the applied field and damping
parameter is interpreted. The total injected energy is found to be
proportionnal to the energy barrier between the initial state and the saddle
point and to the damping parameter. This result may be used as a means for
probing the damping parameter in real nanoparticles.",1303.3501v4
2013-04-05,Nonlocal Gravity: Damping of Linearized Gravitational Waves,"In nonlocal general relativity, linearized gravitational waves are damped as
they propagate from the source to the receiver in the Minkowski vacuum.
Nonlocal gravity is a generalization of Einstein's theory of gravitation in
which nonlocality is due to the gravitational memory of past events. That
nonlocal gravity is dissipative is demonstrated in this paper within certain
approximation schemes. The gravitational memory drag leads to the decay of the
amplitude of gravitational waves given by the exponential damping factor exp
(-t/\tau), where $\tau$ depends on the kernel of nonlocal gravity. The damping
time $\tau$ is estimated for gravitational waves of current observational
interest and is found to be of the order of, or longer than, the age of the
universe.",1304.1769v1
2013-07-29,Damping of Primordial Gravitational Waves from Generalized Sources,"It has been shown that a cosmological background with an anisotropic stress
tensor, appropriate for a free streaming thermal neutrino background, can damp
primordial gravitational waves after they enter the horizon, and can thus
affect the CMB B-mode polarization signature due to such tensor modes. Here we
generalize this result, and examine the sensitivity of this effect to non-zero
neutrino masses, extra neutrino species, and also a possible relativistic
background of axions from axion strings. In particular, additional neutrinos
with cosmologically interesting neutrino masses at the O(1) eV level will
noticeably reduce damping compared to massless neutrinos for gravitational wave
modes with $k\tau_0 \approx 100-200$, where $\tau_0 \approx 2/H_0$ and $H_0$ is
the present Hubble parameter, while an axion background would produce a
phase-dependent damping distinct from that produced by neutrinos.",1307.7571v1
2013-08-08,Small global solutions to the damped two-dimensional Boussinesq equations,"The two-dimensional (2D) incompressible Euler equations have been thoroughly
investigated and the resolution of the global (in time) existence and
uniqueness issue is currently in a satisfactory status. In contrast, the global
regularity problem concerning the 2D inviscid Boussinesq equations remains
widely open. In an attempt to understand this problem, we examine the damped 2D
Boussinesq equations and study how damping affects the regularity of solutions.
Since the damping effect is insufficient in overcoming the difficulty due to
the ""vortex stretching"", we seek unique global small solutions and the efforts
have been mainly devoted to minimizing the smallness assumption. By positioning
the solutions in a suitable functional setting (more precisely the homogeneous
Besov space $\mathring{B}^1_{\infty,1}$), we are able to obtain a unique global
solution under a minimal smallness assumption.",1308.1723v1
2013-08-21,Approximate quantum error correction for generalized amplitude damping errors,"We present analytic estimates of the performances of various approximate
quantum error correction schemes for the generalized amplitude damping (GAD)
qubit channel. Specifically, we consider both stabilizer and nonadditive
quantum codes. The performance of such error-correcting schemes is quantified
by means of the entanglement fidelity as a function of the damping probability
and the non-zero environmental temperature. The recovery scheme employed
throughout our work applies, in principle, to arbitrary quantum codes and is
the analogue of the perfect Knill-Laflamme recovery scheme adapted to the
approximate quantum error correction framework for the GAD error model. We also
analytically recover and/or clarify some previously known numerical results in
the limiting case of vanishing temperature of the environment, the well-known
traditional amplitude damping channel. In addition, our study suggests that
degenerate stabilizer codes and self-complementary nonadditive codes are
especially suitable for the error correction of the GAD noise model. Finally,
comparing the properly normalized entanglement fidelities of the best
performant stabilizer and nonadditive codes characterized by the same length,
we show that nonadditive codes outperform stabilizer codes not only in terms of
encoded dimension but also in terms of entanglement fidelity.",1308.4582v2
2013-11-01,Kinetic theory of acoustic-like modes in nonextensive pair plasmas,"The low-frequency acoustic-like modes in a pair plasma (electron-positron or
pair-ion) is studied by employing a kinetic theory model based on the Vlasov
and Poisson's equation with emphasizing the Tsallis's nonextensive statistics.
The possibility of the acoustic-like modes and their properties in both fully
symmetric and temperature-asymmetric cases are examined by studying the
dispersion relation, Landau damping and instability of modes. The resultant
dispersion relation in this study is compatible with the acoustic branch of the
experimental data [W. Oohara, D. Date, and R. Hatakeyama, Phys. Rev. Lett. 95,
175003 (2005)], in which the electrostatic waves have been examined in a pure
pair-ion plasma. Particularly, our study reveals that the occurrence of growing
or damped acoustic-like modes depends strongly on the nonextensivity of the
system as a measure for describing the long-range Coulombic interactions and
correlations in the plasma. The mechanism that leads to the unstable modes lies
in the heart of the nonextensive formalism yet, the mechanism of damping is the
same developed by Landau. Furthermore, the solutions of acoustic-like waves in
an equilibrium Maxwellian pair plasma are recovered in the extensive limit
($q\rightarrow1$), where the acoustic modes have only the Landau damping and no
growth.",1311.0193v1
2013-11-29,Exploring viscous damping in undergraduate Physics laboratory using electromagnetically coupled oscillators,"We design a low-cost, electromagnetically coupled, simple harmonic oscillator
and demonstrate free, damped and forced oscillations in an under-graduate (UG)
Physics laboratory. It consists of a spring-magnet system that can oscillate
inside a cylinder around which copper coils are wound. Such demonstrations can
compliment the traditional way in which a Waves & Oscillations course is taught
and offers a richer pedagogical experience for students. We also show that with
minimal modifications, it can be used to probe the magnitude of viscous damping
forces in liquids by analyzing the oscillations of an immersed magnet. Finally,
we propose some student activities to explore non-linear damping effects and
their characterization using this apparatus.",1311.7489v1
2013-12-18,Radiative damping and synchronization in a graphene-based terahertz emitter,"We investigate the collective electron dynamics in a recently proposed
graphene-based terahertz emitter under the influence of the radiative damping
effect, which is included self-consistently in a molecular dynamics approach.
We show that under appropriate conditions synchronization of the dynamics of
single electrons takes place, leading to a rise of the oscillating component of
the charge current. The synchronization time depends dramatically on the
applied dc electric field and electron scattering rate, and is roughly
inversely proportional to the radiative damping rate that is determined by the
carrier concentration and the geometrical parameters of the device. The
emission spectra in the synchronized state, determined by the oscillating
current component, are analyzed. The effective generation of higher harmonics
for large values of the radiative damping strength is demonstrated.",1312.5193v1
2014-01-20,Analysis of mean cluster size in directed compact percolation near a damp wall,"We investigate the behaviour of the mean size of directed compact percolation
clusters near a damp wall in the low-density region, where sites in the bulk
are wet (occupied) with probability $p$ while sites on the wall are wet with
probability $p_w$. Methods used to find the exact solution for the dry case
($p_w=0$) and the wet case ($p_w=1$) turn out to be inadequate for the damp
case. Instead we use a series expansion for the $p_w=2p$ case to obtain a
second order inhomogeneous differential equation satisfied by the mean size,
which exhibits a critical exponent $\gamma=2$, in common with the wet wall
result. For the more general case of $p_w=rp$, with $r$ rational, we use a
modular arithmetic method of finding ODEs and obtain a fourth order homogeneous
ODE satisfied by the series. The ODE is expressed exactly in terms of $r$. We
find that in the damp region $0<r<2$ the critical exponent $\gamma^{\rm
damp}=1$, in common with the dry wall result.",1401.4793v1
2014-02-13,On the Convergence of Approximate Message Passing with Arbitrary Matrices,"Approximate message passing (AMP) methods and their variants have attracted
considerable recent attention for the problem of estimating a random vector
$\mathbf{x}$ observed through a linear transform $\mathbf{A}$. In the case of
large i.i.d. zero-mean Gaussian $\mathbf{A}$, the methods exhibit fast
convergence with precise analytic characterizations on the algorithm behavior.
However, the convergence of AMP under general transforms $\mathbf{A}$ is not
fully understood. In this paper, we provide sufficient conditions for the
convergence of a damped version of the generalized AMP (GAMP) algorithm in the
case of quadratic cost functions (i.e., Gaussian likelihood and prior). It is
shown that, with sufficient damping, the algorithm is guaranteed to converge,
although the amount of damping grows with peak-to-average ratio of the squared
singular values of the transforms $\mathbf{A}$. This result explains the good
performance of AMP on i.i.d. Gaussian transforms $\mathbf{A}$, but also their
difficulties with ill-conditioned or non-zero-mean transforms $\mathbf{A}$. A
related sufficient condition is then derived for the local stability of the
damped GAMP method under general cost functions, assuming certain strict
convexity conditions.",1402.3210v3
2014-03-28,Strichartz estimates and smooth attractors for a sub-quintic wave equation with fractional damping in bounded domains,"The work is devoted to Dirichlet problem for sub-quintic semi-linear wave
equation with damping damping term of the form $(-\Delta)^\alpha\partial_t u$,
$\alpha\in(0,\frac{1}{2})$, in bounded smooth domains of $\Bbb R^3$. It appears
that to prove well-posedness and develop smooth attractor theory for the
problem we need additional regularity of the solutions, which does not follow
from the energy estimate. Considering the original problem as perturbation of
the linear one the task is reduced to derivation of Strichartz type estimate
for the linear wave equation with fractional damping, which is the main feature
of the work. Existence of smooth exponential attractor for the natural
dynamical system associated with the problem is also established.",1403.7476v1
2014-05-12,Global Existence and Nonlinear Diffusion of Classical Solutions to Non-Isentropic Euler Equations with Damping in Bounded Domain,"We considered classical solutions to the initial boundary value problem for
non-isentropic compressible Euler equations with damping in multi-dimensions.
We obtained global a priori estimates and global existence results of classical
solutions to both non-isentropic Euler equations with damping and their
nonlinear diffusion equations under small data assumption. We proved the
pressure and velocity decay exponentially to constants, while the entropy and
density can not approach constants. Finally, we proved the pressure and
velocity of the non-isentropic Euler equations with damping converge
exponentially to those of their nonlinear diffusion equations when the time
goes to infinity.",1405.2842v3
2014-05-16,Damping of Confined Modes in a Ferromagnetic Thin Insulating Film: Angular Momentum Transfer Across a Nanoscale Field-defined Interface,"We observe a dependence of the damping of a confined mode of precessing
ferromagnetic magnetization on the size of the mode. The micron-scale mode is
created within an extended, unpatterned YIG film by means of the intense local
dipolar field of a micromagnetic tip. We find that damping of the confined mode
scales like the surface-to-volume ratio of the mode, indicating an interfacial
damping effect (similar to spin pumping) due to the transfer of angular
momentum from the confined mode to the spin sink of ferromagnetic material in
the surrounding film. Though unexpected for insulating systems, the measured
intralayer spin-mixing conductance $g_{\uparrow \downarrow} = 5.3 \times
10^{19} {\rm m}^{-2}$ demonstrates efficient intralayer angular momentum
transfer.",1405.4203v2
2014-06-03,Persistently damped transport on a network of circles,"In this paper we address the exponential stability of a system of transport
equations with intermittent damping on a network of $N \geq 2$ circles
intersecting at a single point $O$. The $N$ equations are coupled through a
linear mixing of their values at $O$, described by a matrix $M$. The activity
of the intermittent damping is determined by persistently exciting signals, all
belonging to a fixed class. The main result is that, under suitable hypotheses
on $M$ and on the rationality of the ratios between the lengths of the circles,
such a system is exponentially stable, uniformly with respect to the
persistently exciting signals. The proof relies on an explicit formula for the
solutions of this system, which allows one to track down the effects of the
intermittent damping.",1406.0731v4
2014-06-06,Damping of quasiparticles in a Bose-Einstein condensate coupled to an optical cavity,"We present a general theory for calculating the damping rate of elementary
density wave excitations in a Bose-Einstein condensate strongly coupled to a
single radiation field mode of an optical cavity. Thereby we give a detailed
derivation of the huge resonant enhancement in the Beliaev damping of a density
wave mode, predicted recently by K\'onya et al., Phys.~Rev.~A 89, 051601(R)
(2014). The given density-wave mode constitutes the polariton-like soft mode of
the self-organization phase transition. The resonant enhancement takes place,
both in the normal and ordered phases, outside the critical region. We show
that the large damping rate is accompanied by a significant frequency shift of
this polariton mode. Going beyond the Born-Markov approximation and determining
the poles of the retarded Green's function of the polariton, we reveal a strong
coupling between the polariton and a collective mode in the phonon bath formed
by the other density wave modes.",1406.1669v1
2014-08-18,Kirchhoff equations with strong damping,"We consider Kirchhoff equations with strong damping, namely with a friction
term which depends on a power of the ""elastic"" operator. We address local and
global existence of solutions in two different regimes depending on the
exponent in the friction term.
  When the exponent is greater than 1/2, the dissipation prevails, and we
obtain global existence in the energy space assuming only degenerate
hyperbolicity and continuity of the nonlinear term. When the exponent is less
than 1/2, we assume strict hyperbolicity and we consider a phase space
depending on the continuity modulus of the nonlinear term and on the exponent
in the damping. In this phase space we prove local existence, and global
existence if initial data are small enough.
  The regularity we assume both on initial data and on the nonlinear term is
weaker than in the classical results for Kirchhoff equations with standard
damping.
  Proofs exploit some recent sharp results for the linearized equation and
suitably defined interpolation spaces.",1408.3908v1
2014-08-28,A convergent method for linear half-space kinetic equations,"We give a unified proof for the well-posedness of a class of linear
half-space equations with general incoming data and construct a Galerkin method
to numerically resolve this type of equations in a systematic way. Our main
strategy in both analysis and numerics includes three steps: adding damping
terms to the original half-space equation, using an inf-sup argument and
even-odd decomposition to establish the well-posedness of the damped equation,
and then recovering solutions to the original half-space equation. The proposed
numerical methods for the damped equation is shown to be quasi-optimal and the
numerical error of approximations to the original equation is controlled by
that of the damped equation. This efficient solution to the half-space problem
is useful for kinetic-fluid coupling simulations.",1408.6630v4
2014-09-02,Damping effects in hole-doped graphene: the relaxation-time approximation,"The dynamical conductivity of interacting multiband electronic systems
derived in Ref.[1] is shown to be consistent with the general form of the Ward
identity. Using the semiphenomenological form of this conductivity formula, we
have demonstrated that the relaxation-time approximation can be used to
describe the damping effects in weakly interacting multiband systems only if
local charge conservation in the system and gauge invariance of the response
theory are properly treated. Such a gauge-invariant response theory is
illustrated on the common tight-binding model for conduction electrons in
hole-doped graphene. The model predicts two distinctly resolved maxima in the
energy-loss-function spectra. The first one corresponds to the intraband
plasmons (usually called the Dirac plasmons). On the other hand, the second
maximum ($\pi$ plasmon structure) is simply a consequence of the van Hove
singularity in the single-electron density of states. The dc resistivity and
the real part of the dynamical conductivity are found to be well described by
the relaxation-time approximation, but only in the parametric space in which
the damping is dominated by the direct scattering processes. The ballistic
transport and the damping of Dirac plasmons are thus the questions that require
abandoning the relaxation-time approximation.",1409.0621v1
2014-10-13,Relaxation damping in oscillating contacts,"If a contact of two purely elastic bodies with no sliding (infinite
coefficient of friction) is subjected to superimposed oscillations in the
normal and tangential directions, then a specific damping appears, that is not
dependent on friction or dissipation in the material. We call this effect
""relaxation damping"". The rate of energy dissipation due to relaxation damping
is calculated in a closed analytic form for arbitrary axially-symmetric
contacts. In the case of equal frequency of normal and tangential oscillations,
the dissipated energy per cycle is proportional to the square of the amplitude
of tangential oscillation and to the absolute value of the amplitude of normal
oscillation, and is dependent on the phase shift between both oscillations. In
the case of low frequency tangential motion with superimposed high frequency
normal oscillations, the system acts as a tunable linear damper. Generalization
of the results for macroscopically planar, randomly rough surfaces is
discussed.",1410.3238v1
2014-11-13,Maximal correlation between flavor entanglement and oscillation damping due to localization effects,"Localization effects and quantum decoherence driven by the mass-eigenstate
wave packet propagation are shown to support a statistical correlation between
quantum entanglement and damped oscillations in the scenario of three-flavor
quantum mixing for neutrinos. Once the mass-eigenstates that support flavor
oscillations are identified as three-{\em qubit} modes, a decoherence scale can
be extracted from correlation quantifiers, namely the entanglement of formation
and the logarithmic negativity. Such a decoherence scale is compared with the
coherence length of damped oscillations. Damping signatures exhibited by flavor
transition probabilities as an effective averaging of the oscillating terms are
then explained as owing to loss of entanglement between mass modes involved in
the relativistic propagation.",1411.3634v1
2015-01-20,Damping of long wavelength collective modes in spinor Bose-Fermi mixtures,"Using an effective field theory we describe the low energy bosonic
excitations in a three dimensional ultra-cold mixture of spin-1 bosons and
spin-1/2 fermions. We establish an interesting fermionic excitation induced
generic damping of the usual undamped long wavelength bosonic collective
Goldstone modes. Two states with bosons forming either a ferromagnetic or polar
superfluid are studied. The linear dispersion of the bosonic Bogoliubov
excitations is preserved with a renormalized sound velocity. For the polar
superfluid we find both gapless modes (density and spin) are damped, whereas in
the ferromagnetic superfluid we find the density (spin) mode is (not) damped.
We argue quite generally that this holds for any mixture of bosons and fermions
that are coupled through at least a density-density interaction. We discuss the
implications of our many-body interaction results for experiments on Bose-Fermi
mixtures.",1501.05015v2
2015-01-27,Non-linear fluctuation effects in dynamics of freely suspended film,"Long-scale dynamic fluctuation phenomena in freely suspended films is
analyzed. We consider isotropic films that, say, can be pulled from bulk
smectic A liquid crystals. The key feature of such objects is possibility of
bending deformations of the film. The bending (also known as flexular) mode
turns out to be anomalously weakly attenuated. In the harmonic approximation
there is no viscous-like damping of the bending mode, proportional to q^2 (q is
the wave vector of the mode), since it is forbidden by the rotational symmetry.
Therefore the bending mode is strongly affected by non-linear dynamic
fluctuation effects. We calculate the dominant fluctuation contributions to the
damping of the bending mode due to its coupling to the in-plane viscous mode,
that restores the viscous-like q^2 damping of the bending mode. Our
calculations are performed in the framework of the perturbation theory where
the coupling of the modes is assumed to be small, then the bending mode damping
is relatively weak. We discuss our results in the context of existing
experiments and numeric simulations of the freely suspended films and propose
possible experimental observations of our predictions.",1501.06703v1
2015-01-30,Intrinsic Damping of Collective Spin Modes in a Two-Dimensional Fermi Liquid with Spin-Orbit Coupling,"A Fermi liquid with spin-orbit coupling (SOC) is expected to support a new
kind of collective modes: oscillations of magnetization in the absence of the
magnetic field. We show that these modes are damped by the electron-electron
interaction even in the limit of an infinitely long wavelength (q = 0). The
linewidth of the collective mode is on the order of {\Delta}^2=E_F , where
{\Delta} is a characteristic spin-orbit energy splitting and E_F is the Fermi
energy. Such damping is in a stark contrast to known damping mechanisms of both
charge and spin collective modes in the absence of SOC, all of which disappear
at q = 0, and arises because none of the components of total spin is conserved
in the presence of SOC.",1502.00027v1
2015-02-01,Nonlocal Damping of Helimagnets in One-Dimensional Interacting Electron Systems,"We investigate the magnetization relaxation of a one-dimensional helimagnetic
system coupled to interacting itinerant electrons. The relaxation is assumed to
result from the emission of plasmons, the elementary excitations of the
one-dimensional interacting electron system, caused by slow changes of the
magnetization profile. This dissipation mechanism leads to a highly nonlocal
form of magnetization damping that is strongly dependent on the
electron-electron interaction. Forward scattering processes lead to a spatially
constant damping kernel, while backscattering processes produce a spatially
oscillating contribution. Due to the nonlocal damping, the thermal fluctuations
become spatially correlated over the entire system. We estimate the
characteristic magnetization relaxation times for magnetic quantum wires and
nuclear helimagnets.",1502.00268v2
2015-07-21,Onboard Calibration Circuit for the Front-end Electronics of DAMPE BGO Calorimeter,"An onboard calibration circuit has been designed for the front-end
electronics (FEE) of DAMPE BGO Calorimeter. It is mainly composed of a 12 bit
DAC, an operation amplifier and an analog switch. Test results showed that a
dynamic range of 0 ~ 30 pC with a precision of 5 fC was achieved, which meets
the requirements of the front-end electronics. Furthermore, it is used to test
the trigger function of the FEEs. The calibration circuit has been implemented
and verified by all the environmental tests for both Qualification Model and
Flight Model of DAMPE. The DAMPE satellite will be launched at the end of 2015
and the calibration circuit will perform onboard calibration in space.",1507.05862v1
2015-07-30,Reservoir interactions during Bose-Einstein condensation: modified critical scaling in the Kibble-Zurek mechanism of defect formation,"As a test of the Kibble-Zurek mechanism (KZM) of defect formation, we
simulate the Bose-Einstein condensation transition in a toroidally confined
Bose gas using the stochastic projected Gross-Pitaevskii equation (SPGPE), with
and without the energy-damping reservoir interaction. Energy-damping alters the
scaling of the winding number distribution with the quench time - a departure
from the universal KZM theory that relies on equilibrium critical exponents.
Numerical values are obtained for the correlation-length critical exponent
$\nu$ and the dynamical critical exponent $z$ for each variant of reservoir
interaction theory. The energy-damping reservoir interactions cause significant
modification of the dynamical critical exponent of the phase transition, whilst
preserving the essential KZM critical scaling behavior. Comparison of numerical
and analytical two-point correlation functions further illustrates the effect
of energy damping on the correlation length during freeze out.",1507.08357v1
2015-08-23,Melnikov chaos in a modified Rayleigh-Duffing oscillator with $ φ^6$ potential,"The chaotic behavior of the modified Rayleigh-Duffing oscillator with $
\phi^6$ potential and external excitation which modeles ship rolling motions
are investigated both analytically and numerically. Melnikov method is applied
and the conditions for the existence of homoclinic and heteroclinic chaos are
obtained. The effects of nonlinear damping on roll motion of ships are analyzed
in detail. As it is known, nonlinear roll damping is a very important parameter
in estimating ship reponses. The predictions are tested numerical simulations
based on the basin of attraction. We conclude that certains quadratic damping
effects are contrary to cubic damping effect.",1508.05664v1
2015-09-23,Quantum Error-Correcting Codes for Qudit Amplitude Damping,"Traditional quantum error-correcting codes are designed for the depolarizing
channel modeled by generalized Pauli errors occurring with equal probability.
Amplitude damping channels model, in general, the decay process of a multilevel
atom or energy dissipation of a bosonic system at zero temperature. We discuss
quantum error-correcting codes adapted to amplitude damping channels for higher
dimensional systems (qudits). For multi-level atoms, we consider a natural kind
of decay process, and for bosonic systems,we consider the qudit amplitude
damping channel obtained by truncating the Fock basis of the bosonic modes to a
certain maximum occupation number. We construct families of
single-error-correcting quantum codes that can be used for both cases. Our
codes have larger code dimensions than the previously known
single-error-correcting codes of the same lengths. Additionally, we present
families of multi-error correcting codes for these two channels, as well as
generalizations of our construction technique to error-correcting codes for the
qutrit $V$ and $\Lambda$ channels.",1509.06829v1
2015-10-09,Determining form and data assimilation algorithm for weakly damped and driven Korteweg-de Vries equaton- Fourier modes case,"We show that the global attractor of a weakly damped and driven Korteweg-de
Vries equation (KdV) is embedded in the long-time dynamics of an ordinary
differential equation called a determining form. In particular, there is a
one-to-one identification of the trajectories in the global attractor of the
damped and driven KdV and the steady state solutions of the determining form.
Moreover, we analyze a data assimilation algorithm (down-scaling) for the
weakly damped and driven KdV. We show that given a certain number of low
Fourier modes of a reference solution of the KdV equation, the algorithm
recovers the full reference solution at an exponential rate in time.",1510.02730v1
2015-10-27,Remarks on 1-D Euler Equations with Time-Decayed Damping,"We study the 1-d isentropic Euler equations with time-decayed damping
\begin{equation} \left\{ \begin{aligned} &\partial_t \rho+\partial_x(\rho u)=0,
\\ &\partial_t(\rho u)+ \partial_x(\rho
u^2)+\partial_xp(\rho)=-\frac{\mu}{1+t}\rho u,\\
&\rho|_{t=0}=1+\varepsilon\rho_0(x),u|_{t=0}=\varepsilon u_0(x). \end{aligned}
\right. \nonumber \end{equation}
  This work is inspired by a recent work of F. Hou, I. Witt and H.C. Yin
\cite{Hou01}. In \cite{Hou01}, they proved a global existence and blow-up
result of 3-d irrotational Euler flow with time-dependent damping. In the 1-d
case, we will prove a different result when the damping decays of order $-1$
with respect to the time $t$. More precisely, when $\mu>2$, we prove the global
existence of the 1-d Euler system. While when $0\leq\mu\leq2 $, we will prove
the blow up of $C^1$ solutions.",1510.08115v1
2016-01-04,Generalized Bloch's theorem for viscous metamaterials: Dispersion and effective properties based on frequencies and wavenumbers that are simultaneously complex,"It is common for dispersion curves of damped periodic materials to be based
on real frequencies versus complex wavenumbers or, conversely, real wavenumbers
versus complex frequencies. The former condition corresponds to harmonic wave
motion where a driving frequency is prescribed and where attenuation due to
dissipation takes place only in space alongside spatial attenuation due to
Bragg scattering. The latter condition, on the other hand, relates to free wave
motion admitting attenuation due to energy loss only in time while spatial
attenuation due to Bragg scattering also takes place. Here, we develop an
algorithm for 1D systems that provides dispersion curves for damped free wave
motion based on frequencies and wavenumbers that are permitted to be
simultaneously complex. This represents a generalized application of Bloch's
theorem and produces a dispersion band structure that fully describes all
attenuation mechanisms, in space and in time. The algorithm is applied to a
viscously damped mass-in-mass metamaterial exhibiting local resonance. A
frequency-dependent effective mass for this damped infinite chain is also
obtained.",1601.00683v1
2016-02-05,Protecting entanglement from correlated amplitude damping channel using weak measurement and quantum measurement reversal,"Based on the quantum technique of weak measurement, we propose a scheme to
protect the entanglement from correlated amplitude damping decoherence. In
contrast to the results of memoryless amplitude damping channel, we show that
the memory effects play a significant role in the suppression of entanglement
sudden death and protection of entanglement under severe decoherence. Moreover,
we find that the initial entanglement could be drastically amplified by the
combination of weak measurement and quantum measurement reversal even under the
correlated amplitude damping channel. The underlying mechanism can be
attributed to the probabilistic nature of weak measurements.",1602.01998v1
2016-03-10,Stability Analysis of Networked Systems Containing Damped and Undamped Nodes,"This paper answers the question if a qualitatively heterogeneous passive
networked system containing damped and undamped nodes shows consensus in the
output of the nodes in the long run. While a standard Lyapunov analysis shows
that the damped nodes will always converge to a steady-state value, the
convergence of the undamped nodes is much more delicate and depends on the
parameter values of the network as well as on the topology of the graph. A
complete stability analysis is presented based on an eigenvector analysis
involving the mass values and the topology of both the original graph and the
reduced graph obtained by a Kron reduction that eliminates the damped nodes.",1603.03477v1
2016-04-29,Nonlinear Landau damping of wave envelopes in a quantum plasma,"The nonlinear theory of Landau damping of electrostatic wave envelopes (WEs)
is revisited in a quantum electron-positron (EP) pair plasma. Starting from a
Wigner-Moyal equation coupled to the Poisson equation and applying the multiple
scale technique, we derive a nonlinear Schr{\""o}dinger (NLS) equation which
governs the evolution of electrostatic WEs. It is shown that the coefficients
of the NLS equation, including the nonlocal nonlinear term, which appears due
to the resonant particles having group velocity of the WEs, are significantly
modified by the particle dispersion. The effects of the quantum parameter $H$
(the ratio of the plasmon energy to the thermal energy densities), associated
with the particle dispersion, are examined on the Landau damping rate of
carrier waves, as well as on the modulational instability of WEs. It is found
that the Landau damping rate and the decay rate of the solitary wave amplitude
are greatly reduced compared to their classical values $(H=0)$.",1604.08751v4
2016-05-02,Three types of nonlinear resonances,"We analyse different types of nonlinear resonances in a weakly damped Duffing
oscillator using bifurcation theory techniques. In addition to (i) odd
subharmonic resonances found on the primary branch of symmetric periodic
solutions with the forcing frequency and (ii) even subharmonic resonances due
to symmetry-broken periodic solutions that bifurcate off the primary branch and
also oscillate at the forcing frequency, we uncover (iii) novel resonance type
due to isolas of periodic solutions that are not connected to the primary
branch. These occur between odd and even resonances, oscillate at a fraction of
the forcing frequency, and give rise to a complicated resonance `curve' with
disconnected elements and high degree of multistability. We use bifurcation
continuation to compute resonance tongues in the plane of the forcing frequency
vs. the forcing amplitude for different but fixed values of the damping rate.
In this way, we demonstrate that identified here isolated resonances explain
the intriguing structure of ""patchy tongues"" observed for week damping and link
it to a seemingly unrelated phenomenon of ""bifurcation superstructure""
described for moderate damping.",1605.00858v2
2016-07-21,The Noisy Oscillator : Random Mass and Random Damping,"The problem of a linear damped noisy oscillator is treated in the presence of
two multiplicative sources of noise which imply a random mass and random
damping. The additive noise and the noise in the damping are responsible for an
influx of energy to the oscillator and its dissipation to the surrounding
environment. A random mass implies that the surrounding molecules not only
collide with the oscillator but may also adhere to it, thereby changing its
mass. We present general formulas for the first two moments and address the
question of mean and energetic stabilities. The phenomenon of stochastic
resonance, i.e. the expansion due to the noise of a system response to an
external periodic signal, is considered for separate and joint action of two
sources of noise and their characteristics.",1607.06289v2
2016-08-09,Optomechanical damping of a nanomembrane inside an optical ring cavity,"We experimentally and theoretically investigate mechanical nanooscillators
coupled to the light in an optical ring resonator made of dielectric mirrors.
We identify an optomechanical damping mechanism that is fundamentally different
to the well known cooling in standing wave cavities. While, in a standing wave
cavity the mechanical oscillation shifts the resonance frequency of the cavity
in a ring resonator the frequency does not change. Instead the position of the
nodes is shifted with the mechanical excursion. We derive the damping rates and
test the results experimentally with a silicon-nitride nanomembrane. It turns
out that scattering from small imperfections of the dielectric mirror coatings
has to be taken into account to explain the value of the measured damping rate.
We extend our theoretical model and regard a second reflector in the cavity
that captures the effects of mirror back scattering. This model can be used to
also describe the situation of two membranes that both interact with the cavity
fields. This may be interesting for future work on synchronization of distant
oscillators that are coupled by intracavity light fields.",1608.02799v1
2016-08-11,Decay of geodesic acoustic modes due to the combined action of phase mixing and Landau damping,"Geodesic acoustic modes (GAMs) are oscillations of the electric field whose
importance in tokamak plasmas is due to their role in the regulation of
turbulence. The linear collisionless damping of GAMs is investigated here by
means of analytical theory and numerical simulations with the global
gyrokinetic particle-in-cell code ORB5. The combined effect of the phase mixing
and Landau damping is found to quickly redistribute the GAM energy in
phase-space, due to the synergy of the finite orbit width of the passing ions
and the cascade in wave number given by the phase mixing. When plasma
parameters characteristic of realistic tokamak profiles are considered, the GAM
decay time is found to be an order of magnitude lower than the decay due to the
Landau damping alone, and in some cases of the same order of magnitude of the
characteristic GAM drive time due to the nonlinear interaction with an ITG
mode. In particular, the radial mode structure evolution in time is
investigated here and reproduced quantitatively by means of a dedicated initial
value code and diagnostics.",1608.03447v1
2016-09-06,JRSP of three-particle state via three tripartite GHZ class in quantum noisy channels,"We present a scheme for joint remote state preparation (JRSP) of
three-particle state via three tripartite Greenberger-Horne-Zeilinger (GHZ)
entangled states as the quantum channel linking the parties. We use eight-qubit
mutually orthogonal basis vector as measurement point of departure. The
likelihood of success for this scheme has been found to be $1/8$. However, by
putting some special cases into consideration, the chances can be ameliorated
to $1/4$ and $1$. The effects of amplitude-damping noise, phase-damping noise
and depolarizing noise on this scheme have been scrutinized and the analytical
derivations of fidelities for the quantum noisy channels have been presented.
We found that for $0.55\leq\eta\leq1$, the states conveyed through depolarizing
channel lose more information than phase-damping channel while the information
loss through amplitude damping channel is most minimal.",1609.01538v3
2016-09-22,Damping of nonlinear standing kink oscillations: a numerical study,"We aim to study the standing fundamental kink mode of coronal loops in the
nonlinear regime, investigating the changes in energy evolution in the
cross-section and oscillation amplitude of the loop which are related to
nonlinear effects, in particular to the development of the Kelvin-Helmholtz
instability (KHI). We run idea, high-resolution three-dimensional (3D)
magnetohydrodynamics (MHD) simulations, studying the influence of the initial
velocity amplitude and the inhomogeneous layer thickness. We model the coronal
loop as a straight, homogeneous magnetic flux tube with an outer inhomogeneous
layer, embedded in a straight, homogeneous magnetic field. We find that, for
low amplitudes which do not allow for the KHI to develop during the simulated
time, the damping time agrees with the theory of resonant absorption. However,
for higher amplitudes, the presence of KHI around the oscillating loop can
alter the loop's evolution, resulting in a significantly faster damping than
predicted by the linear theory in some cases. This questions the accuracy of
seismological methods applied to observed damping profiles, based on linear
theory.",1609.06883v1
2016-09-28,Nonlinear damping and dephasing in nanomechanical systems,"We present a microscopic theory of nonlinear damping and dephasing of
low-frequency eigenmodes in nano- and micro-mechanical systems. The mechanism
of the both effects is scattering of thermally excited vibrational modes off
the considered eigenmode. The scattering is accompanied by energy transfer of
$2\hbar\omega_0$ for nonlinear damping and is quasieleastic for dephasing. We
develop a formalism that allows studying both spatially uniform systems and
systems with a strong nonuniformity, which is smooth on the typical wavelength
of thermal modes but not their mean free path. The formalism accounts for the
decay of thermal modes, which plays a major role in the nonlinear damping and
dephasing. We identify the nonlinear analogs of the Landau-Rumer,
thermoelastic, and Akhiezer mechanisms and find the dependence of the
relaxation parameters on the temperature and the geometry of a system.",1609.08714v1
2016-09-24,Parametric Landau damping of space charge modes,"Landau damping is the mechanism of plasma and beam stabilization; it arises
through energy transfer from collective modes to the incoherent motion of
resonant particles. Normally this resonance requires the resonant particle's
frequency to match the collective mode frequency. We have identified an
important new damping mechanism, {\it parametric Landau damping}, which is
driven by the modulation of the mode-particle interaction. This reveals new
possibilities for stability control through manipulation of both particle and
mode-particle coupling spectra. We demonstrate the existence of parametric
Landau damping in a simulation of transverse coherent modes of bunched
accelerator beams with space charge.",1609.09393v3
2016-12-13,Continuous-variable entanglement generated with a hybrid PT-symmetric system,"We study a proposal of generating macroscopic continuous-variable
entanglement with two coupled waveguides respectively carrying optical damping
and optical gain. Moreover, a squeezing element is added into one or both
waveguides. We show that quantum noise effect existing in the process is
essential to the degree of the generated entanglement. It will totally
eliminate the entanglement in the setup of adding the squeezing element into
the waveguide filled with optical damping material, but will not completely
damp the entanglement to zero in the other configurations of having the
squeezing element in the gain medium or in both gain and damping medium. The
degree of the generated continuous-variable entanglement is irrelevant to the
intensities of the input light in coherent states. Moreover, the relations
between the entanglement and system parameters are illustrated in terms of the
dynamical evolutions of the created continuous-variable entanglement.",1612.03996v2
2017-01-08,Decentralized Robust Control for Damping Inter-area Oscillations in Power Systems,"As power systems become more and more interconnected, the inter-area
oscillations has become a serious factor limiting large power transfer among
different areas. Underdamped (Undamped) inter-area oscillations may cause
system breakup and even lead to large-scale blackout. Traditional damping
controllers include Power System Stabilizer (PSS) and Flexible AC Transmission
System (FACTS) controller, which adds additional damping to the inter-area
oscillation modes by affecting the real power in an indirect manner. However,
the effectiveness of these controllers is restricted to the neighborhood of a
prescribed set of operating conditions. In this paper, decentralized robust
controllers are developed to improve the damping ratios of the inter-area
oscillation modes by directly affecting the real power through the turbine
governing system. The proposed control strategy requires only local signals and
is robust to the variations in operation condition and system topology. The
effectiveness of the proposed robust controllers is illustrated by detailed
case studies on two different test systems.",1701.02036v1
2017-01-18,Ion beam test results of the Plastic Scintillator Detector of DAMPE,"The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). DAMPE can detect electrons, photons and ions in a
wide energy range (5 GeV to 10 TeV) and ions up to iron (100GeV to 100 TeV).
Plastic Scintillator Detector (PSD) is one of the four payloads in DAMPE,
providing e/{\gamma} separation and charge identification up to Iron. An ion
beam test was carried out for the Qualification Model of PSD in CERN with
40GeV/u Argon primary beams. The Birk's saturation and charge resolution of PSD
were investigated.",1701.04947v2
2017-01-18,DAMPE space mission: first data,"The DAMPE (DArk Matter Particle Explorer) satellite was launched on December
17, 2015 and started its data taking operation a few days later.
  DAMPE has a large geometric factor ($\sim~0.3\ m^2\ sr$) and provides good
tracking, calorimetric and charge measurements for electrons, gammas rays and
nuclei. This will allow precise measurement of cosmic ray spectra from tens of
$GeV$ up to about $100\ TeV$. In particular, the energy region between $1-100\
TeV$ will be explored with higher precision compared to previous experiments.
The various subdetectors allow an efficient identification of the electron
signal over the large (mainly proton-induced) background. As a result, the
all-electron spectrum will be measured with excellent resolution from few $GeV$
up to few $TeV$, thus giving the opportunity to identify possible contribution
of nearby sources. A report on the mission goals and status is presented,
together with the on-orbit detector performance and the first data coming from
space.",1701.05046v1
2017-01-25,Control Allocation for Wide Area Coordinated Damping,"In this work, a modal-based sparse control allocation (CA) is proposed for
coordinated and fault-tolerant wide-area damping controllers (WADCs). In our
proposed method, the supervisory CA only communicates with necessary actuators
to achieve the required damping performance and in case of actuator failures
(e.g., due to loss of communication or scheduling), capabilities of the
remaining actuators are fully used before the nominal performance is degraded.
This method offers the advantages of modular design where WADC is initially
designed to achieve satisfactory damping without the detailed knowledge of
actuators. In the next step, CA is designed to manage actuator failures and
limitations without the need to redesign the nominal WADC. The proposed
approach is applied to a modified $286$-bus Western Electricity Coordinating
Council (WECC) system to verify the feasibility on a complex power system.
Simulation results indicate the effectiveness of the proposed method in
coordinating multiple actuators and building resiliency.",1701.07456v1
2017-03-22,Direct Measurement of Kramers Turnover with a Levitated Nanoparticle,"Understanding the thermally activated escape from a metastable state is at
the heart of important phenomena such as the folding dynamics of proteins, the
kinetics of chemical reactions or the stability of mechanical systems. In 1940
Kramers calculated escape rates both in the high damping and the low damping
regime and suggested that the rate must have a maximum for intermediate
damping. This phenomenon, today known as the Kramers turnover, has triggered
important theoretical and numerical studies. However, to date there is no
direct and quantitative experimental verification of this turnover. Using a
nanoparticle trapped in a bi-stable optical potential we experimentally measure
the nanoparticle's transition rates for variable damping and directly resolve
the Kramers turnover. Our measurements are in agreement with an analytical
model that is free of adjustable parameters.",1703.07699v2
2017-04-03,Suppression of plasma echoes and Landau damping in Sobolev spaces by weak collisions in a Vlasov-Fokker-Planck equation,"In this paper, we study Landau damping in the weakly collisional limit of a
Vlasov-Fokker-Planck equation with nonlinear collisions in the phase-space
$(x,v) \in \mathbb T_x^n \times \mathbb R^n_v$. The goal is four-fold: (A) to
understand how collisions suppress plasma echoes and enable Landau damping in
agreement with linearized theory in Sobolev spaces, (B) to understand how phase
mixing accelerates collisional relaxation, (C) to understand better how the
plasma returns to global equilibrium during Landau damping, and (D) to rule out
that collision-driven nonlinear instabilities dominate. We give an estimate for
the scaling law between Knudsen number and the maximal size of the perturbation
necessary for linear theory to be accurate in Sobolev regularity. We conjecture
this scaling to be sharp (up to logarithmic corrections) due to potential
nonlinear echoes in the collisionless model.",1704.00425v2
2017-04-14,Impulse-Based Hybrid Motion Control,"The impulse-based discrete feedback control has been proposed in previous
work for the second-order motion systems with damping uncertainties. The
sate-dependent discrete impulse action takes place at zero crossing of one of
both states, either relative position or velocity. In this paper, the proposed
control method is extended to a general hybrid motion control form. We are
using the paradigm of hybrid system modeling while explicitly specifying the
state trajectories each time the continuous system state hits the guards that
triggers impulsive control actions. The conditions for a stable convergence to
zero equilibrium are derived in relation to the control parameters, while
requiring only the upper bound of damping uncertainties to be known. Numerical
examples are shown for an underdamped closed-loop dynamics with oscillating
transients, an upper bounded time-varying positive system damping, and system
with an additional Coulomb friction damping.",1704.04372v5
2017-04-19,Reliable channel-adapted error correction: Bacon-Shor code recovery from amplitude damping,"We construct two simple error correction schemes adapted to amplitude damping
noise for Bacon-Shor codes and investigate their prospects for fault-tolerant
implementation. Both consist solely of Clifford gates and require far fewer
qubits, relative to the standard method, to achieve correction to a desired
order in the damping rate. The first, employing one-bit teleportation and
single-qubit measurements, needs only one fourth as many physical qubits, while
the second, using just stabilizer measurements and Pauli corrections, needs
only half. We show that existing fault-tolerance methods can be employed for
the latter, while the former can be made to avoid potential catastrophic errors
and can easily cope with damping faults in ancilla qubits.",1704.05857v1
2017-04-30,Comparison of dynamic mechanical properties of non-superheated and superheated A357 alloys,"The influence of superheat treatment on the microstructure and dynamic
mechanical properties of A357 alloys has been investigated. The study of
microstructure was performed by the optical microscope. Dynamic mechanical
properties (storage modulus, loss modulus, and damping capacity) were measured
by the dynamic mechanical analyzer (DMA). Microstructure showed coarser and
angular eutectic Si particles with larger {\alpha}-Al dendrites in the
non-superheated A357 alloy. In contrast, finer and rounded eutectic Si
particles together with smaller and preferred oriented {\alpha}-Al dendrites
have been observed in the superheated A357 alloy. Dynamic mechanical properties
showed an increasing trend of loss modulus and damping capacity meanwhile a
decreasing trend of storage modulus at elevated temperatures for superheated
and non-superheated A357 alloys. The high damping capacity of superheated A357
has been ascribed to the grain boundary damping at elevated temperatures.",1705.00350v1
2017-05-19,Improving two - qubit state teleportation affected by amplitude damping noise based on choosing appropriate quantum channel,"We consider two qubit teleportation via quantum channel affected by amplitude
damping noise. Addressing the same problem, X. Hu, Y. Gu, Q. Gong and G. Guo
[Phys. Rev. A 81, 054302, (2010)] recently showed that in presence of noise,
subjecting more qubits in quantum channel to amplitude damping can increase the
fidelity of teleportation protocol. However, in this paper, by making some
adjustments on quantum channel, we obtain teleportation fidelity which is even
higher than one in the case of X. Hu et al. Moreover, our strategy is simpler
than quantum distillation and compared to using weak measurement, it is
deterministic. Furthermore, explicit analysis of fidelity is provided, we show
that in general, choosing appropriate quantum channel enhances the ability of
teleportation better and negates the fact that more amplitude damping noise
more quality.",1705.07064v2
2017-05-27,Charge reconstruction study of the DAMPE Silicon-Tungsten Tracker with ion beams,"The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). DAMPE can detect electrons, photons in a wide energy
range (5 GeV to 10 TeV) and ions up to iron (100GeV to 100 TeV).
Silicon-Tungsten Tracker (STK) is one of the four subdetectors in DAMPE,
providing photon-electron conversion, track reconstruction and charge
identification for ions. Ion beam test was carried out in CERN with 60GeV/u
Lead primary beams. Charge reconstruction and charge resolution of STK
detectors were investigated.",1705.09791v1
2017-06-09,Effect of oxygen plasma on nanomechanical silicon nitride resonators,"Precise control of tensile stress and intrinsic damping is crucial for the
optimal design of nanomechanical systems for sensor applications and quantum
optomechanics in particular. In this letter we study the in uence of oxygen
plasma on the tensile stress and intrinsic damping of nanomechanical silicon
nitride resonators. Oxygen plasma treatments are common steps in micro and
nanofabrication. We show that oxygen plasma of only a few minutes oxidizes the
silicon nitride surface, creating several nanometer thick silicon dioxide
layers with a compressive stress of 1.30(16)GPa. Such oxide layers can cause a
reduction of the e ective tensile stress of a 50 nm thick stoichiometric
silicon nitride membrane by almost 50%. Additionally, intrinsic damping
linearly increases with the silicon dioxide lm thickness. An oxide layer of
1.5nm grown in just 10s in a 50W oxygen plasma almost doubled the intrinsic
damping. The oxide surface layer can be e ciently removed in bu ered HF.",1706.02957v1
2017-06-11,Absorbing boundary layers for spin wave micromagnetics,"Micromagnetic simulations are used to investigate the effects of different
absorbing boundary layers (ABLs) on spin waves (SWs) reflected from the edges
of a magnetic nano-structure. We define the conditions that a suitable ABL must
fulfill and compare the performance of abrupt, linear, polynomial and tan
hyperbolic damping profiles in the ABL. We first consider normal incidence in a
permalloy stripe and propose a transmission line model to quantify reflections
and calculate the loss introduced into the stripe due to the ABL. We find that
a parabolic damping profile absorbs the SW energy efficiently and has a low
reflection coefficient, thus performing much better than the commonly used
abrupt damping profile. We then investigated SWs that are obliquely incident at
26.6, 45 and 63.4 degrees on the edge of a yttrium-iron-garnet film. The
parabolic damping profile again performs efficiently by showing a high SW
energy transfer to the ABL and a low reflected SW amplitude.",1706.03325v1
2017-07-03,Quantum behaviour of pumped and damped triangular Bose Hubbard systems,"We propose and analyse analogs of optical cavities for atoms using three-well
Bose-Hubbard models with pumping and losses. We consider triangular
configurations. With one well pumped and one damped, we find that both the
mean-field dynamics and the quantum statistics show a quantitative dependence
on the choice of damped well. The systems we analyse remain far from
equilibrium, preserving good coherence between the wells in the steady-state.
We find quadrature squeezing and mode entanglement for some parameter regimes
and demonstrate that the trimer with pumping and damping at the same well is
the stronger option for producing non-classical states. Due to recent
experimental advances, it should be possible to demonstrate the effects we
investigate and predict.",1707.01000v1
2017-07-06,Damping optimization of parameter dependent mechanical systems by rational interpolation,"We consider an optimization problem related to semi-active damping of
vibrating systems. The main problem is to determine the best damping matrix
able to minimize influence of the input on the output of the system. We use a
minimization criteria based on the $\mathcal{H}_2$ system norm.
  The objective function is non-convex and the associated optimization problem
typically requires a large number of objective function evaluations. We propose
an optimization approach that calculates `interpolatory' reduced order models,
allowing for significant acceleration of the optimization process.
  In our approach, we use parametric model reduction (PMOR) based on the
Iterative Rational Krylov Algorithm, which ensures good approximations relative
to the $\mathcal{H}_2$ system norm, aligning well with the underlying damping
design objectives. For the parameter sampling that occurs within each PMOR
cycle, we consider approaches with predetermined sampling and approaches using
adaptive sampling, and each of these approaches may be combined with three
possible strategies for internal reduction. In order to preserve important
system properties, we maintain second-order structure, which through the use of
modal coordinates, allows for very efficient implementation.
  The methodology proposed here provides a significant acceleration of the
optimization process; the gain in efficiency is illustrated in numerical
experiments.",1707.01789v1
2017-07-08,Nonlinear dynamics of damped DNA systems with long-range interactions,"We investigate the nonlinear dynamics of a damped Peyrard-Bishop DNA model
taking into account long-range interactions with distance dependence |l|^-s on
the elastic coupling constant between different DNA base pairs. Considering
both Stokes and long-range hydrodynamical damping forces, we use the discrete
difference operator technique and show in the short wavelength modes that the
lattice equation can be governed by the complex Ginzburg-Landau equation. We
found analytically that the technique leads to the correct expression for the
breather soliton parameters. We found that the viscosity makes the amplitude of
the breather to damp out. We compare the approximate analytic results with
numerical simulations for the value s = 3 (dipole-dipole interactions).",1707.02425v1
2017-08-05,Dynamic Sensitivity Study of MEMS Capacitive Acceleration Transducer Based on Analytical Squeeze Film Damping and Mechanical Thermoelasticity Approaches,"The dynamic behavior of a capacitive micro-electro-mechanical (MEMS)
accelerometer is evaluated by using a theoretical approach which makes use of a
squeeze film damping (SFD) model and ideal gas approach. The study investigates
the performance of the device as a function of the temperature, from 228 K to
398 K, and pressure, from 20 to 1000 Pa, observing the damping gas trapped
inside de mechanical transducer. Thermoelastic properties of the silicon bulk
are considered for the entire range of temperature. The damping gases
considered are Air, Helium and Argon. The global behavior of the system is
evaluated considering the electro-mechanical sensitivity (SEM) as the main
figure of merit in frequency domain. The results show the behavior of the main
mechanism losses of SFD, as well as the dynamic sensitivity of the MEMS
transducer system, and are in good agreement with experimental dynamic results
behavior.",1708.01812v1
2017-09-01,Scaling of the Rashba spin-orbit torque in magnetic domain walls,"Spin-orbit torque in magnetic domain walls was investigated by solving the
Pauli-Schr\""{o}dinger equation for the itinerant electrons. The Rashba
interaction considered is derived from the violation of inversion symmetry at
interfaces between ferromagnets and heavy metals. In equilibrium, the Rashba
spin-orbit interaction gives rise to a torque corresponding to the
Dzyaloshinskii-Moriya interaction. When there is a current flowing, the
spin-orbit torque experienced by the itinerant electrons in short domain walls
has both field-like and damping-like components. However, when the domain wall
width is increased, the damping-like component, which is the counterpart of the
non-adiabatic spin transfer torque, decreases rapidly at the domain wall
center. In contrast to the non-adiabatic spin transfer torque, the damping-like
spin-orbit torque does not approach to zero far away from the domain wall
center, even in the adiabatic limit. The scattering of spin-up and spin-down
wave functions, which is caused by the Rashba spin-orbit interaction and the
spatial variation of magnetization profile in the domain wall, gives rise to
the finite damping-like spin-orbit torque.",1709.00187v3
2017-09-12,Temperature effects on MIPs in the BGO calorimeters of DAMPE,"In this paper, we presented a study of temperature effects on BGO
calorimeters using proton MIP's collected in the first year operation of DAMPE.
By directly comparing MIP calibration constants used by DAMPE data production
pipe line, we found an experimental relation between temperature and signal
amplitudes of each BGO bar: a general deviation of -1.162%/$^{\circ}$C,and
-0.47%/$^{\circ}$C to -1.60%/$^{\circ}$C statistically for each detector
element. During 2016, DAMPE's temperature changed by about 7 degrees due to
solar elevation angle and the corresponding energy scale bias is about 8%. By
frequent MIP calibration operation, this kind of bias is eliminated to an
acceptable value.",1709.03735v2
2017-09-28,Universal and approximate relations for the gravitational-wave damping timescale of $f$-modes in neutron stars,"Existing estimates of the gravitational-wave damping timescale of the
dominant quadrupole oscillation mode in the case of rapidly rotating stars are
based on using a Newtonian estimate for the energy of the mode, in combination
with the lowest-order post-Newtonian quadrupole formula for estimating the
gravitational-wave luminosity. We investigate a number of other choices for
estimating the gravitational-wave damping timescale in the nonrotating limit
and construct a highly accurate, empirically corrected formula that has a
maximum relative error of only 3% with respect to the perturbative result in
full general relativity. The expressions involved are sufficiently general to
be extended to the case of rapidly rotating stars. We also present a new
higher-order empirical relation for the gravitational-wave damping timescale of
quadrupole oscillations that is accurate in the whole range of expected values
for the compactness of neutron stars, without the need for involving the moment
of inertia.",1709.10067v2
2017-10-09,Time-dependent propagation speed vs strong damping for degenerate linear hyperbolic equations,"We consider a degenerate abstract wave equation with a time-dependent
propagation speed. We investigate the influence of a strong dissipation, namely
a friction term that depends on a power of the elastic operator.
  We discover a threshold effect. If the propagation speed is regular enough,
then the damping prevails, and therefore the initial value problem is
well-posed in Sobolev spaces. Solutions also exhibit a regularizing effect
analogous to parabolic problems. As expected, the stronger is the damping, the
lower is the required regularity.
  On the contrary, if the propagation speed is not regular enough, there are
examples where the damping is ineffective, and the dissipative equation behaves
as the non-dissipative one.",1710.03602v1
2017-10-17,Entropic uncertainty relation under quantum channels with memory,"Recently, Xu et al. [Phys. Rev. A 86, 012113(2012)] explored the behavior of
the entropic uncertainty relation under the influence of local unital and
nonunital noisy channels for a class of Bell-diagonal states. We here reform
their results and investigate the entropic uncertainty relation under the
influence of unital and nonunital noisy channels with memory. Different types
of noisy channels with memory, such as amplitude damping channel(nonunitary),
phase-damping and depolarizing channels(unitary) have been taken into account.
Some analytical or numerical results are presented. The effect of channels with
memory on dynamics of the entropic uncertainties (or their lower bounds) has
been discussed in detail. Compare with previous results, our results show that,
the entropic uncertainties (or their lower bounds) subjecting to amplitude
damping channel with memory will be reduced at first and then be lifted with
the memory coefficient of channel $\mu$ increasing, however they will be only
reduced under phase-damping and depolarizing channels with memory. Especially,
in the limit of $\mu\rightarrow1$, the entropic uncertainties (or their lower
bounds) could be well protected and immune to decoherence of channle. Moreover,
the mechanism behind these phenomena are also explored by using the purity of
state.",1710.06344v1
2017-10-31,Improving mechanical sensor performance through larger damping,"Mechanical resonances are used in a wide variety of devices; from smart phone
accelerometers to computer clocks and from wireless communication filters to
atomic force microscope sensors. Frequency stability, a critical performance
metric, is generally assumed to be tantamount to resonance quality factor (the
inverse of the linewidth and of the damping). Here we show that frequency
stability of resonant nanomechanical sensors can generally be made independent
of quality factor. At high bandwidths, we show that quality factor reduction is
completely mitigated by increases in signal to noise ratio. At low bandwidths,
strikingly, increased damping leads to better stability and sensor resolution,
with improvement proportional to damping. We confirm the findings by
demonstrating temperature resolution of 50 \mu K at 200 Hz bandwidth. These
results open the door for high performance ultrasensitive resonant sensors in
gaseous or liquid environments, single cell nanocalorimetry, nanoscale gas
chromatography, and atmospheric pressure nanoscale mass spectrometry.",1710.11280v1
2017-11-30,The electron-flavored Z'-portal dark matter and the DAMPE cosmic ray excess,"The DAMPE experiment has recently reported strong indications for the
existence of an excess of high-energy electrons and positrons. If interpreted
in terms of the annihilation of dark matter, the DAMPE result restricts the
dark matter mass and possible annihilation channels to a few case. In this
paper we explain the DAMPE result with the electron-flavored $Z^\prime$-portal
fermionic dark matter. We show that the Dirac dark matter scenario is promising
to explain the excess via the process $\bar \chi \chi \to\mathbf{Z}'\to \bar e
e$. The reduced annihilation cross section is limited in a range of
$10^{-26}\sim 10^{-24}~{\rm cm^3 s^{-1}}$ to interpret the excess.",1711.11182v2
2017-12-04,DAMPE Electron-Positron Excess in Leptophilic $Z'$ model,"Recently the DArk Matter Particle Explorer (DAMPE) has reported an excess in
the electron-positron flux of the cosmic rays which is interpreted as a dark
matter particle with the mass about $1.5$ TeV. We come up with a leptophilic
$Z'$ scenario including a Dirac fermion dark matter candidate which beside
explaining the observed DAMPE excess, is able to pass various
experimental/observational constraints including the relic density value from
the WMAP/Planck, the invisible Higgs decay bound at the LHC, the LEP bounds in
electron-positron scattering, the muon anomalous magnetic moment constraint,
Fermi-LAT data, and finally the direct detection experiment limits from the
XENON1t/LUX. By computing the electron-positron flux produced from a dark
matter with the mass about $1.5$ TeV we show that the model predicts the peak
observed by the DAMPE.",1712.01239v4
2017-12-06,Confronting the DAMPE Excess with the Scotogenic Type-II Seesaw Model,"The DArk Matter Particle Explorer (DAMPE) has observed a tentative peak at
$E\sim1.4~\TeV$ in the cosmic-ray electron spectrum. In this paper, we
interpret this excess in the scotogenic type-II seesaw model. This model
extends the canonical type-II seesaw model with dark matter (DM) candidates and
a loop-induced vacuum expectation value of the triplet scalars, $v_\Delta$,
resulting in small neutrino masses naturally even for TeV scale triplet
scalars. Assuming a nearby DM subhalo, the DAMPE excess can be explained by DM
annihilating into a pair of triplet scalars which subsequently decay to charged
lepton final states. Spectrum fitting of the DAMPE excess indicates it
potentially favors the inverted neutrino mass hierarchy. We also discuss how to
evade associated neutrino flux in our model.",1712.02021v3
2018-02-28,Beliaev Damping in Spin-$\frac{1}{2}$ Interacting Bosons with Spin-Orbit Coupling,"Beliaev damping provides one of the most important mechanisms for dissipation
of quasiparticles through beyond-mean-field effects at zero temperature. Here
we present the first analytical result of Beliaev damping in low-energy
excitations of spin-$\frac{1}{2}$ interacting bosons with equal Rashba and
Dresslhaus spin-orbit couplings. We identify novel features of Beliaev decay
rate due to spin-orbit coupling, in particular, it shows explicit dependence on
the spin-density interaction and diverges at the interaction-modified phase
boundary between the zero-momentum and plane-wave phases. This represents a
manifestation of the effect of spin-orbit coupling in the beyond-mean-field
regime, which by breaking Galilean invariance couples excitations in the
density- and spin-channels. By describing the Beliaev damping in terms of the
observable dynamic structure factors, our results allow direct experimental
access within current facilities.",1802.10295v1
2018-03-03,Universal stabilization of single-qubit states using a tunable coupler,"We theoretically analyze a scheme for fast stabilization of arbitrary qubit
states with high fidelities, extending a protocol recently demonstrated
experimentally [Lu et al., Phys. Rev. Lett. 119, 150502 (2017)]. That
experiment utilized red and blue sideband transitions in a system composed of a
fluxonium qubit, a low-Q LC-oscillator, and a coupler enabling us to tune the
interaction between them. Under parametric modulations of the coupling
strength, the qubit can be steered into any desired pure or mixed single-qubit
state. For realistic circuit parameters, we predict that stabilization can be
achieved within 100 ns. By varying the ratio between the oscillator's damping
rate and the effective qubit-oscillator coupling strength, we can switch
between under-damped, critically-damped, and over-damped stabilization and find
optimal working points. We further analyze the effect of thermal fluctuations
and show that the stabilization scheme remains robust for realistic
temperatures.",1803.01079v3
2018-04-15,Reevaluation of radiation reaction and consequences for light-matter interactions at the nanoscale,"In the context of electromagnetism and nonlinear optical interactions damping
is generally introduced as a phenomenological, viscous term that dissipates
energy, proportional to the temporal derivative of the polarization. Here, we
follow the radiation reaction method presented in [G. W. Ford and R. F.
O'Connell, Phys. Lett. A, 157, 217 (1991)], which applies to non-relativistic
electrons of finite size, to introduce an explicit reaction force in the
Newtonian equation of motion, and derive a hydrodynamic equation that offers
new insight on the influence of damping in generic plasmas, metal-based and/or
dielectric structures. In these settings, we find new damping-dependent linear
and nonlinear source terms that suggest the damping coefficient is proportional
to the local charge density, and nonlocal contributions that stem from the
spatial derivative of the magnetic field and discuss the conditions that could
modify both linear and nonlinear electromagnetic responses.",1804.05369v1
2018-04-30,Wave-like blow-up for semilinear wave equations with scattering damping and negative mass term,"In this paper we establish blow-up results and lifespan estimates for
semilinear wave equations with scattering damping and negative mass term for
subcritical power, which is the same as that of the corresponding problem
without mass term, and also the same as that of the corresponding problem
without both damping and mass term. For this purpose, we have to use the
comparison argument twice, due to the damping and mass term, in additional to a
key multiplier. Finally, we get the desired results by an iteration argument.",1804.11073v3
2018-05-22,Uniqueness of the Cauchy datum for the tempered-in-time response and conductivity operator of a plasma,"We study the linear Vlasov equation with a given electric field $E \in
\mathcal{S}$, where $\mathcal{S}$ is the space of Schwartz functions. The
associated damped partial differential equation has a unique tempered solution,
which fixes the needed Cauchy datum. This tempered solution then converges to
the causal solution of the linear Vlasov equation when the damping parameter
goes to zero. This result allows us to define the plasma conductivity operator
$\sigma$, which gives the current density $j = \sigma (E)$ induced by the
electric field $E$. We prove that $\sigma$ is continuous from $\mathcal{S}$ to
its dual $\mathcal{S}^\prime$. We can treat rigorously the case of uniform
non-magnetized non-relativistic plasma (linear Landau damping) and the case of
uniform magnetized relativistic plasma (cyclotron damping). In both cases, we
demonstrate that the main part of the conductivity operator is a
pseudo-differential operator and we give its expression rigorously. This
matches the formal results widely used in the theoretical physics community.",1805.08733v3
2018-05-26,Stabilization for the wave equation with singular Kelvin-Voigt damping,"We consider the wave equation with Kelvin-Voigt damping in a bounded domain.
The exponential stability result proposed by Liu and Rao or T\'ebou for that
system assumes that the damping is localized in a neighborhood of the whole or
a part of the boundary under some consideration. In this paper we propose to
deal with this geometrical condition by considering a singular Kelvin-Voigt
damping which is localized faraway from the boundary. In this particular case
it was proved by Liu and Liu the lack of the uniform decay of the energy.
However, we show that the energy of the wave equation decreases logarithmically
to zero as time goes to infinity. Our method is based on the frequency domain
method. The main feature of our contribution is to write the resolvent problem
as a transmission system to which we apply a specific Carleman estimate.",1805.10430v1
2018-06-01,"Fluctuation-damping of isolated, oscillating Bose-Einstein condensates","Experiments on the nonequilibrium dynamics of an isolated Bose-Einstein
condensate (BEC) in a magnetic double-well trap exhibit a puzzling divergence:
While some show dissipation-free Josephson oscillations, others find strong
damping. Such damping in isolated BECs cannot be understood on the level of the
coherent Gross-Pitaevskii dynamics. Using the Keldysh functional-integral
formalism, we describe the time-dependent system dynamics by means of a
multi-mode BEC coupled to fluctuations (single-particle excitations) beyond the
Gross-Pitaevskii saddle point. We find that the Josephson oscillations excite
an excess of fluctuations when the effective Josephson frequency,
$\tilde{\omega}_J$, is in resonance with the effective fluctuation energy,
$\tilde{\varepsilon}_m$, where both, $\tilde{\omega}_J$ and
$\tilde{\varepsilon}_m$, are strongly renormalized with respect to their
noninteracting values. Evaluating and using the model parameters for the
respective experiments describes quantitatively the presence or absence of
damping.",1806.00376v2
2018-06-05,Decoherence assisted spin squeezing generation in superposition of tripartite GHZ and W states,"In the present paper, we study spin squeezing under decoherence in the
superposition of tripartite maximally entangled GHZ and W states. Here we use
amplitude damping, phase damping and depolarisation channel. We have
investigated the dynamics of spin squeezing with the interplay of superposition
and decoherence parameters with different directions of the mean spin vector.
We have found the mixture of GHZ and W states is robust against spin squeezing
generation for amplitude damping and phase damping channels for certain
directions of the mean spin vector. However, the depolarisation channel
performs well for spin squeezing generation and generates permanent spin
squeezing in the superposition of GHZ and W states.",1806.01730v1
2018-07-31,Dark Matter Particle Explorer observations of high-energy cosmic ray electrons plus positrons and their physical implications,"The DArk Matter Particle Explorer (DAMPE) is a satellite-borne, high-energy
particle and $\gamma$-ray detector, which is dedicated to indirectly detecting
particle dark matter and studying high-energy astrophysics. The first results
about precise measurement of the cosmic ray electron plus positron spectrum
between 25 GeV and 4.6 TeV were published recently. The DAMPE spectrum reveals
an interesting spectral softening around $0.9$ TeV and a tentative peak around
$1.4$ TeV. These results have inspired extensive discussion. The detector of
DAMPE, the data analysis, and the first results are introduced. In particular,
the physical interpretations of the DAMPE data are reviewed.",1807.11638v1
2018-08-08,A Hybrid Dynamic-regenerative Damping Scheme for Energy Regeneration in Variable Impedance Actuators,"Increasing research efforts have been made to improve the energy efficiency
of variable impedance actuators (VIAs) through reduction of energy consumption.
However, the harvesting of dissipated energy in such systems remains
underexplored. This study proposes a novel variable damping module design
enabling energy regeneration in VIAs by exploiting the regenerative braking
effect of DC motors. The proposed damping module uses four switches to combine
regenerative and dynamic braking, in a hybrid approach that enables energy
regeneration without reduction in the range of damping achievable. Numerical
simulations and a physical experiment are presented in which the proposed
module shows an optimal trade-off between task performance and energy
efficiency.",1808.03143v1
2018-08-15,$L^1$ estimates for oscillating integrals and their applications to semi-linear models with $σ$-evolution like structural damping,"The present paper is a continuation of our recent paper \cite{DaoReissig}. We
will consider the following Cauchy problems for semi-linear structurally damped
$\sigma$-evolution models: \begin{equation*} u_{tt}+ (-\Delta)^\sigma u+ \mu
(-\Delta)^\delta u_t = f(u,u_t),\, u(0,x)= u_0(x),\, u_t(0,x)=u_1(x)
\end{equation*} with $\sigma \ge 1$, $\mu>0$ and $\delta \in
(\frac{\sigma}{2},\sigma]$. Our aim is to study two main models including
$\sigma$-evolution models with structural damping $\delta \in
(\frac{\sigma}{2},\sigma)$ and those with visco-elastic damping
$\delta=\sigma$. Here the function $f(u,u_t)$ stands for power nonlinearities
$|u|^{p}$ and $|u_t|^{p}$ with a given number $p>1$. We are interested in
investigating the global (in time) existence of small data solutions to the
above semi-linear models from suitable spaces basing on $L^q$ space by assuming
additional $L^{m}$ regularity on the initial data, with $q\in (1,\infty)$ and
$m\in [1,q)$.",1808.05484v2
2018-09-26,Permutation-invariant constant-excitation quantum codes for amplitude damping,"The increasing interest in using quantum error correcting codes in practical
devices has heightened the need for designing quantum error correcting codes
that can correct against specialized errors, such as that of amplitude damping
errors which model photon loss. Although considerable research has been devoted
to quantum error correcting codes for amplitude damping, not so much attention
has been paid to having these codes simultaneously lie within the decoherence
free subspace of their underlying physical system. One common physical system
comprises of quantum harmonic oscillators, and constant-excitation quantum
codes can be naturally stabilized within them. The purpose of this paper is to
give constant-excitation quantum codes that not only correct amplitude damping
errors, but are also immune against permutations of their underlying modes. To
construct such quantum codes, we use the nullspace of a specially constructed
matrix based on integer partitions.",1809.09801v4
2018-09-30,Critical behavior of the damping rate of GHz acoustic phonons in SrTiO3 at the antiferrodistortive phase transition measured by time- and frequency-resolved Brillouin scattering,"We determine the temperature dependent damping rate of longitudinal acoustic
phonons in SrTiO3 using frequency domain Brillouin scattering and time domain
Brillouin scattering. We investigate samples with (La,Sr)MnO3 and SrRuO3
capping layers, which result in compressive or tensile strain at the layer -
substrate interface, respectively. The different strain states lead to dif-
ferent domain structures in SrTiO3 that extend into the bulk of the SrTiO3
substrates and strongly affect the phonon propagation. Our experiments show
that the damping rate of acoustic phonons in the interfacial STO layer depends
strongly on the sample temperature and strain induced do- main structure. We
also show that the damping rate as function of temperature exhibits a critical
behavior close to the cubic-to-tetragonal phase transition of SrTiO3.",1810.00381v1
2018-12-04,Atmospheric oscillations provide simultaneous measurement of neutron star mass and radius,"Neutron stars with near-Eddington observable luminosities were shown to
harbor levitating atmospheres, suspended above their surface. We report a new
method to simultaneously measure the mass and radius of a neutron star based on
oscillations of such atmospheres. In this paper, we present an analytic
derivation of a family of relativistic, oscillatory, spherically symmetric
eigenmodes of the optically and geometrically thin levitating atmospheres,
including the damping effects induced by the radiation drag. We discover
characteristic maxima in the frequencies of the damped oscillations and show
that using the frequency maxima, one can estimate mass and radius of the
neutron star, given the observed frequency and the corresponding luminosity of
the star during the X-ray burst. Thus, our model provides a new way to probe
the stellar parameters. We also show that the ratio of any two undamped
eigenfrequencies depends only on the adiabatic index of the atmosphere, while
for the damped eigenfrequencies, this ratio varies with the luminosity. The
damping coefficient is independent of the mode number of the oscillations.
Signatures of these atmospheres' dynamics will be reflected in the source's
X-ray light curves.",1812.01299v2
2018-12-04,Spin transport in a magnetic insulator with zero effective damping,"Applications based on spin currents strongly profit from the control and
reduction of their effective damping and their transport properties. We here
experimentally observe magnon mediated transport of spin (angular) momentum
through a 13.4 nm thin yttrium iron garnet film with full control of the
magnetic damping via spin-orbit torque. Above a critical spin-orbit torque, the
fully compensated damping manifests itself as an increase of magnon
conductivity by almost two orders of magnitude. We compare our results to
theoretical expectations based on recently predicted current induced magnon
condensates and discuss other possible origins of the observed critical
behaviour.",1812.01334v3
2019-01-10,Data-Driven Online Optimization for Enhancing Power System Oscillation Damping,"This paper reports an initial work on power system oscillation damping
improvement using a data-driven online optimization method. An online
oscillation damping optimization mod-el is proposed and formulated in a form
solvable by the data-driven method. Key issues in the online optimization
procedures, including the damping sensitivity identification method, its
compatibility with the dispatch plans, as well as other practical issues in
real large-scale system are discussed. Simulation results based on the 2-area
4-machine system, and the NETS-NYPS 68-bus system verify the feasibility and
efficiency of the proposed method. The results also show the capability of the
proposed method to bridge the gap between online data analysis and complex
optimization for power system dynamics.",1901.03167v2
2019-01-13,Nonexistence of global solutions for a weakly coupled system of semilinear damped wave equations in the scattering case with mixed nonlinear terms,"In this paper we consider the blow-up of solutions to a weakly coupled system
of semilinear damped wave equations in the scattering case with nonlinearities
of mixed type, namely, in one equation a power nonlinearity and in the other a
semilinear term of derivative type. The proof of the blow-up results is based
on an iteration argument. As expected, due to the assumptions on the
coefficients of the damping terms, we find as critical curve in the p-q plane
for the pair of exponents (p,q) in the nonlinear terms the same one found by
Hidano-Yokoyama and, recently, by Ikeda-Sobajima-Wakasa for the weakly coupled
system of semilinear wave equations with the same kind of nonlinearities. In
the critical and not-damped case we provide a different approach from the test
function method applied by Ikeda-Sobajima-Wakasa to prove the blow-up of the
solution on the critical curve, improving in some cases the upper bound
estimate for the lifespan. More precisely, we combine an iteration argument
with the so-called slicing method to show the blow-up dynamic of a weighted
version of the functionals used in the subcritical case.",1901.04038v1
2019-01-15,Continuum damping effects in nuclear collisions associated with twisted boundary conditions,"The time-dependent Skyrme Hartree-Fock calculations have been performed to
study $^{24}$Mg +$^{24}$Mg collisions. The twisted boundary conditions, which
can avoid finite box-size effects of the employed 3D coordinate space, have
been implemented. The prolate deformed $^{24}$Mg has been set to different
orientations to study vibrations and rotations of the compound nucleus
$^{48}$Cr. Our time evolution results show continuum damping effects associated
with the twist-averaged boundary condition play a persistent role after the
fusion stage. In particular, a rotational damping in continuum is presented in
calculations of both twist-averaged and absorbing boundary conditions, in which
damping widths can be clearly extracted. It is unusual that the rotating
compound nucleus in continuum evolves towards spherical but still has a
considerable angular momentum.",1901.04736v2
2019-03-03,Spin wave damping in periodic and quasiperiodic magnonic structures,"We investigated the lifetime of spin wave eigenmodes in periodic and
quasiperiodic sequences of Py and Co wires. Those materials differ
significantly in damping coefficients, therefore, the spatial distribution of
the mode amplitude within the structure is important for the lifetime of
collective spin wave excitations. Modes of the lower frequencies prefer to
concentrate in Py wires, because of the lower FMR frequency for this material.
This inhomogeneous distribution of amplitude of modes (with lower amplitude in
material of higher damping and with higher amplitude in material of lower
damping) is preferable for extending the lifetime of the collective excitations
beyond the volume average of lifetimes for solid materials. We established the
relation between the profile of the mode and its lifetime for periodic and
quasiperiodic structures. We performed also the comparative studies in order to
find the differences resulting from complexity of the structure and enhancement
of localization in quasiperiodic system on the lifetime of spin waves.",1903.00856v1
2019-03-07,Investigating optically-excited THz standing spin waves using noncollinear magnetic bilayers,"We investigate optically excited THz standing spin waves in noncollinear
magnetic bilayers. Using femtosecond laser-pulse excitation, a spin current is
generated in the first ferromagnetic (FM) layer, and flows through a conductive
spacer layer to be injected into the second (transverse) FM layer, where it
exerts a spin-transfer torque on the magnetization and excites higher-order
standing spin waves. We show that the noncollinear magnetic bilayer is a
convenient tool that allows easy excitation of THz spin waves, and can be used
to investigate the dispersion and thereby the spin wave stiffness parameter in
the thin-film regime. This is experimentally demonstrated using wedge-shaped Co
and CoB (absorption) layers. Furthermore, the damping of these THz spin waves
is investigated, showing a strong increase of the damping with decreasing
absorption layer thickness, much stronger than expected from interface spin
pumping effects. Additionally, a previously unseen sudden decrease in the
damping for the thinnest films is observed. A model for the additional damping
contribution incorporating both these observations is proposed.",1903.02802v1
2019-03-14,An analog simulation experiment to study free oscillations of a damped simple pendulum,"The characteristics of drive-free oscillations of a damped simple pendulum
under sinusoidal potential force field differ from those of the damped harmonic
oscillations. The frequency of oscillation of a large amplitude simple pendulum
decreases with increasing amplitude. Many prototype mechanical simple pendulum
have been fabricated with precision and studied earlier in view of introducing
them in undergraduate physics laboratories. However, fabrication and
maintenance of such mechanical pendulum require special skill. In this work, we
set up an analog electronic simulation experiment to serve the purpose of
studying the force-free oscillations of a damped simple pendulum. We present
the details of the setup and some typical results of our experiment. The
experiment is simple enough to implement in undergraduate physics laboratories.",1903.06162v1
2019-03-15,Frictional Damping in Biomimetic Scale Beam Oscillations,"Stiff scales adorn the exterior surfaces of fishes, snakes, and many
reptiles. They provide protection from external piercing attacks and control
over global deformation behavior to aid locomotion, slithering, and swimming
across a wide range of environmental condition. In this letter, we investigate
the dynamic behavior of biomimetic scale substrates for further understanding
the origins of the nonlinearity that involve various aspect of scales
interaction, sliding kinematics, interfacial friction, and their combination.
Particularly, we study the vibrational characteristics through an analytical
model and numerical investigations for the case of a simply supported scale
covered beam. Our results reveal for the first time that biomimetic scale beams
exhibit viscous damping behavior even when only Coulomb friction is postulated
for free vibrations. We anticipate and quantify the anisotropy in the damping
behavior with respect to curvature. We also find that unlike static pure
bending where friction increases bending stiffness, a corresponding increase in
natural frequency for the dynamic case does not arise for simply supported
beam. Since both scale geometry, distribution and interfacial properties can be
easily tailored, our study indicates a biomimetic strategy to design
exceptional synthetic materials with tailorable damping behavior.",1903.06819v1
2019-04-08,Damping control in viscoelastic beam dynamics,"Viscoelasticity plays a key role in many practical applications and in
different reasearch fields, such as in seals, sliding-rolling contacts and
crack propagation. In all these contexts, a proper knowledge of the
viscoelastic modulus is very important. However, the experimental
characterization of the frequency dependent modulus, carried out through
different standard procedures, still presents some complexities, then possible
alternative approaches are desirable. For example, the experimental
investigation of viscoelastic beam dynamics would be challenging, especially
for the intrinsic simplicity of this kind of test. This is why, a deep
understanding of damping mechanisms in viscoelastic beams results to be a quite
important task to better predict their dynamics. With the aim to enlighten
damping properties in such structures, an analytical study of the transversal
vibrations of a viscoelastic beam is presented in this paper. Some
dimensionless parameters are defined, depending on the material properties and
the beam geometry, which enable to shrewdly design the beam dynamics. In this
way, by properly tuning such disclosed parameters, for example the
dimensionless beam length or a chosen material, it is possible to enhance or
suppress some resonant peaks, one at a time or more simultaneously. This is a
remarkable possibility to efficiently control damping in these structures, and
the results presented in this paper may help in elucidating experimental
procedures for the characterization of viscoelastic materials.",1904.03875v1
2019-04-28,On the Kolmogorov dissipation law in a damped Navier-Stokes equation,"We consider here the Navier-Stokes equations in $\mathbb{R}^{3}$ with a
stationary, divergence-free external force and with an additional damping term
that depends on two parameters. We first study the well-posedness of weak
solutions for these equations and then, for a particular set of the damping
parameters, we will obtain an upper and lower control for the energy
dissipation rate $\varepsilon$ according to the Kolmogorov K41 theory. However,
although the behavior of weak solutions corresponds to the K41 theory, we will
show that in some specific cases the damping term introduced in the
Navier-Stokes equations could annihilate the turbulence even though the Grashof
number (which are equivalent to the Reynolds number) are large.",1904.12382v1
2019-04-23,Entanglement sudden death and birth effects in two qubits maximally entangled mixed states under quantum channels,"In the present article, the robustness of entanglement in two qubits
maximally entangled mixed states (MEME) have been studied under quantum
decoherence channels. Here we consider bit flip, phase flip, bit-phase-flip,
amplitude damping, phase damping and depolarization channels. To quantify the
entanglement, the concurrence has been used as an entanglement measure. During
this study interesting results have been found for sudden death and birth of
entanglement under bit flip and bit-phase-flip channels. While amplitude
damping channel produces entanglement sudden death and does not allow re-birth
of entanglement. On the other hand, two qubits MEMS exhibit the robust
character against the phase flip, phase damping and depolarization channels.
The elegant behavior of all the quantum channels have been investigated with
varying parameter of quantum state MEMS in different cases.",1904.12630v2
2019-05-23,Strauss exponent for semilinear wave equations with scattering space dependent damping,"It is believed or conjectured that the semilinear wave equations with
scattering space dependent damping admit the Strauss critical exponent, see
Ikehata-Todorova-Yordanov \cite{ITY}(the bottom in page 2) and
Nishihara-Sobajima-Wakasugi \cite{N2}(conjecture iii in page 4). In this work,
we are devoted to showing the conjecture is true at least when the decay rate
of the space dependent variable coefficients before the damping is larger than
2. Also, if the nonlinear term depends only on the derivative of the solution,
we may prove the upper bound of the lifespan is the same as that of the
solution of the corresponding problem without damping. This shows in another
way the \lq\lq hyperbolicity"" of the equation.",1905.09445v2
2019-05-24,Multicomponent Dark Matter in the Light of CALET and DAMPE,"In the light of the latest measurements on the total $e^+ + e^-$ flux by
CALET and DAMPE experiments, we revisit the multicomponent leptonically
decaying dark matter (DM) explanations to the cosmic-ray electron/positron
excesses observed previously. Especially, we use the single and
double-component DM models to explore the compatibility of the AMS-02 positron
fraction with the new CALET or DAMPE data. It turns out that neither single nor
double-component DM models are able to fit the AMS-02 positron fraction and
DAMPE total $e^+ + e^-$ flux data simultaneously. On the other hand, for the
combined AMS-02 and CALET dataset, both the single and double-component DM
models can provide reasonable fits. If we further take into the diffuse
$\gamma$-ray constraints from Fermi-LAT, only the double-component DM models
are allowed.",1905.10136v3
2019-05-30,Quantum dynamical speedup in correlated noisy channels,"The maximal evolution speed of a quantum system can be represented by quantum
speed limit time (QSLT).We investigate QSLT of a two-qubit system passing
through a correlated channel (amplitude damping, phase damping, and
depolarizing).By adjusting the correlation parameter of channel and the initial
entanglement,a method to accelerate the evolution speed of the system for some
specific channels is proposed.It is shown that, in amplitude damping channel
and depolarizing channel,QSLT may be shortened in some cases by increasing
correlation parameter of the channel and initial entanglement, which are in
sharp contrast to phase damping channel.In particular, under depolarizing
channels, the transition from no-speedup evolution to speedup evolution for the
system can be realized by changing correlation strength of the channel.",1905.12911v3
2019-07-01,Probing superfluid $^4\mathrm{He}$ with high-frequency nanomechanical resonators down to $\mathrm{mK}$ temperatures,"Superfluids, such as superfluid $^3\mathrm{He}$ and $^4\mathrm{He}$, exhibit
a broad range of quantum phenomena and excitations which are unique to these
systems. Nanoscale mechanical resonators are sensitive and versatile force
detectors with the ability to operate over many orders of magnitude in damping.
Using nanomechanical-doubly clamped beams of extremely high quality factors
($Q>10^6$), we probe superfluid $^4\mathrm{He}$ from the superfluid transition
temperature down to $\mathrm{mK}$ temperatures at frequencies up to $11.6 \,
\mathrm{MHz}$. Our studies show that nanobeam damping is dominated by
hydrodynamic viscosity of the normal component of $^4\mathrm{He}$ above
$1\,\mathrm{K}$. In the temperature range $0.3-0.8\,\mathrm{K}$, the ballistic
quasiparticles (phonons and rotons) determine the beams' behavior. At lower
temperatures, damping saturates and is determined either by magnetomotive
losses or acoustic emission into helium. It is remarkable that all these
distinct regimes can be extracted with just a single device, despite damping
changing over six orders of magnitude.",1907.00970v1
2019-07-10,Determination of the damping co-efficient of electrons in optically transparent glasses at the true resonance frequency in the ultraviolet from an analysis of the Lorentz-Maxwell model of dispersion,"The Lorentz-Maxwell model of dispersion of light has been analyzed in this
paper to determine the true resonance frequency in the ultraviolet for the
electrons in optically transparent glasses and the damping coefficient at this
frequency. For this we needed the refractive indices of glass in the optical
frequency range. We argue that the true resonance condition in the absorption
region prevails when the frequency at which the absorption coefficient is
maximum is the same as the frequency at which the average energy per cycle of
the electrons is also a maximum. We have simultaneously solved the two
equations obtained from the two maxima conditions numerically to arrive at a
unique solution for the true resonance frequency and the damping coefficient at
this frequency. Assuming the damping coefficient to be constant over a small
frequency range in the absorption region, we have determined the frequencies at
which the extinction coefficient and the reflectance are maxima. These
frequencies match very well with the published data for silica glasses
available from the literature.",1907.04499v1
2019-07-15,Asymptotic profiles of solutions for regularity-loss type generalized thermoelastic plate equations and their applications,"In this paper, we consider generalized thermoelastic plate equations with
Fourier's law of heat conduction. By introducing a threshold for decay
properties of regularity-loss, we investigate decay estimates of solutions
with/without regularity-loss in a framework of weighted $L^1$ spaces.
Furthermore, asymptotic profiles of solutions are obtained by using
representations of solutions in the Fourier space, which are derived by
employing WKB analysis. Next, we study generalized thermoelastic plate
equations with additional structural damping, and analysis the influence of
structural damping on decay properties and asymptotic profiles of solutions. We
find that the regularity-loss structure is destroyed by structural damping.
Finally, we give some applications of our results on thermoelastic plate
equations and damped Moore-Gibson-Thompson equation.",1907.06344v1
2019-07-21,Critical Thresholds in One Dimensional Damped Euler-Poisson Systems,"This paper is concerned with the critical threshold phenomenon for one
dimensional damped, pressureless Euler-Poisson equations with electric force
induced by a constant background, originally studied in [S. Engelberg and H.
Liu and E. Tadmor, Indiana Univ. Math. J., 50:109--157, 2001]. A simple
transformation is used to linearize the characteristic system of equations,
which allows us to study the geometrical structure of critical threshold curves
for three damping cases: overdamped, underdamped and borderline damped through
phase plane analysis. We also derive the explicit form of these critical
curves. These sharp results state that if the initial data is within the
threshold region, the solution will remain smooth for all time, otherwise it
will have a finite time breakdown. Finally, we apply these general results to
identify critical thresholds for a non-local system subjected to initial data
on the whole line.",1907.09039v1
2019-07-23,Ignatyuk damping factor: A semiclassical formula,"Data on nuclear level densities extracted from transmission data or gamma
energy spectrum store the basic statistical information about nuclei at various
temperatures. Generally this extracted data goes through model fitting using
computer codes like CASCADE. However, recently established semiclassical
methods involving no adjustable parameters to determine the level density
parameter for magic and semi-magic nuclei give a good agreement with the
experimental values. One of the popular ways to paramaterize the level density
parameter which includes the shell effects and its damping was given by
Ignatyuk. This damping factor is usually fitted from the experimental data on
nuclear level density and it comes around 0.05 $MeV^{-1}$. In this work we
calculate the Ignatyuk damping factor for various nuclei using semiclassical
methods.",1907.09770v1
2019-08-13,Dynamics of Riemann waves with sharp measure-controlled damping,"This paper is concerned with locally damped semilinear wave equations defined
on compact Riemannian manifolds with boundary. We present a construction of
measure-controlled damping regions which are sharp in the sense that their
summed interior and boundary measures are arbitrarily small. The construction
of this class of open sets is purely geometric and allows us to prove a new
observability inequality in terms of potential energy rather than the usual one
with kinetic energy. A unique continuation property is also proved. Then, in
three-dimension spaces, we establish the existence of finite dimensional smooth
global attractors for a class of wave equations with nonlinear damping and
forces with critical Sobolev growth. In addition, by means of an obstacle
control condition, we show that our class of measure-controlled regions
satisfies the well-known geometric control condition (GCC). Therefore, many of
known results for the stabilization of wave equations hold true in the present
context.",1908.04814v1
2019-08-15,Sharp polynomial decay rates for the damped wave equation with Hölder-like damping,"We study decay rates for the energy of solutions of the damped wave equation
on the torus. We consider dampings invariant in one direction and bounded above
and below by multiples of $x^{\beta}$ near the boundary of the support and show
decay at rate $1/t^{\frac{\beta+2}{\beta+3}}$. In the case where $W$ vanishes
exactly like $x^{\beta}$ this result is optimal by work of the second author.
The proof uses a version of the Morawetz multiplier method.",1908.05631v3
2019-08-26,Revisiting the Coulomb-Damped Harmonic Oscillator,"The force of dry friction is studied extensively in introductory physics but
its effect on oscillations is hardly ever mentioned. Instead, to provide a
mathematically tractable introduction to damping, virtually all authors adopt a
viscous resistive force. While exposure to linear damping is of paramount
importance to the student of physics, the omission of Coulomb damping might
have a negative impact on the way the students conceive of the subject. In the
paper, we propose to approximate the action of Coulomb friction on a harmonic
oscillator by a sinusoidal resistive force whose amplitude is the model's only
free parameter. We seek the value of this parameter that yields the best fit
and obtain a closed-form analytic solution, which is shown to nicely fit the
numerical one.",1908.10363v1
2019-09-21,Resonant absorption of kink oscillations in coronal flux tubes with continuous magnetic twist,"There are observational evidences for the existence of twisted magnetic field
in the solar corona. Here, we have investigated resonant damping of the
magnetohydrodynamic (MHD) kink waves in magnetic flux tubes. A realistic model
of the tube with continuous magnetic twist and radially inhomogeneous density
profile has been considered. We have obtained the dispersion relation of the
kink wave using the solution to the linear MHD equations outside the density
inhomogeneity and the appropriate connection formula to the solutions across
the thin transitional boundary layer. The dependence of the oscillation
frequency and damping rate of the waves on the twist parameter and longitudinal
wavenumber has been investigated. For the flux tube parameters considered in
this paper, we obtain rapid damping of the kink waves comparable to the
observations. In order to justify this rapid damping, depending on the sign of
the azimuthal kink mode number, $m=+1$ or $m=-1$, the background magnetic field
must have left handed or right handed twisted profile, respectively. For the
model considered here, the resonant absorption occurs only when the twist
parameter is in a range specified by the density contrast.",1909.09787v1
2019-10-22,Controlled nonlinear magnetic damping in spin-Hall nano-devices,"Large-amplitude magnetization dynamics is substantially more complex compared
to the low-amplitude linear regime, due to the inevitable emergence of
nonlinearities. One of the fundamental nonlinear phenomena is the nonlinear
damping enhancement, which imposes strict limitations on the operation and
efficiency of magnetic nanodevices. In particular, nonlinear damping prevents
excitation of coherent magnetization auto-oscillations driven by the injection
of spin current into spatially extended magnetic regions. Here, we propose and
experimentally demonstrate that nonlinear damping can be controlled by the
ellipticity of magnetization precession. By balancing different contributions
to anisotropy, we minimize the ellipticity and achieve coherent magnetization
oscillations driven by spatially extended spin current injection into a
microscopic magnetic disk. Our results provide a novel route for the
implementation of efficient active spintronic and magnonic devices driven by
spin current.",1910.09801v1
2019-10-24,The lifespan of solutions of semilinear wave equations with the scale-invariant damping in two space dimensions,"In this paper, we study the initial value problem for semilinear wave
equations with the time-dependent and scale-invariant damping in two
dimensions. Similarly to the one dimensional case by Kato, Takamura and Wakasa
in 2019, we obtain the lifespan estimates of the solution for a special
constant in the damping term, which are classified by total integral of the sum
of the initial position and speed. The key fact is that, only in two space
dimensions, such a special constant in the damping term is a threshold between
""wave-like"" domain and ""heat-like"" domain. As a result, we obtain a new type of
estimate especially for the critical exponent.",1910.11692v2
2019-11-05,Exceptional points in dissipatively coupled spin dynamics,"We theoretically investigate dynamics of classical spins exchange-coupled
through an isotropic medium. The coupling is treated at the adiabatic level of
the medium's response, which mediates a first-order in frequency dissipative
interaction along with an instantaneous Heisenberg exchange. The resultant
damped spin precession yields exceptional points (EPs) in the coupled spin
dynamics, which should be experimentally accessible with the existing magnetic
heterostructures. In particular, we show that an EP is naturally approached in
an antiferromagnetic dimer by controlling local damping, while the same is
achieved by tuning the dissipative coupling between spins in the ferromagnetic
case. Extending our treatment to one-dimensional spin chains, we show how EPs
can emerge within the magnonic Brillouin zone by tuning the dissipative
properties. The critical point, at which an EP pair emerges out of the
Brillouin zone center, realizes a gapless Weyl point in the magnon spectrum.
Tuning damping beyond this critical point produces synchronization (level
attraction) of magnon modes over a finite range of momenta, both in ferro- and
antiferromagnetic cases. We thus establish that damped magnons can generically
yield singular points in their band structure, close to which their kinematic
properties, such as group velocity, become extremely sensitive to the control
parameters.",1911.01619v2
2019-11-08,Influence of Sensor Feedback Limitations on Power Oscillation Damping and Transient Stability,"Fundamental sensor feedback limitations for improving rotor angle stability
using local frequency or phase angle measurement are derived. Using a
two-machine power system model, it is shown that improved damping of inter-area
oscillations must come at the cost of reduced transient stability margins,
regardless of the control design method. The control limitations stem from that
the excitation of an inter-area mode by external disturbances cannot be
estimated with certainty using local frequency information. The results are
validated on a modified Kundur four-machine two-area test system where the
active power is modulated on an embedded high-voltage dc link. Damping control
using local phase angle measurements, unavoidably leads to an increased rotor
angle deviation following certain load disturbances. For a highly stressed
system, it is shown that this may lead to transient instability. The
limitations derived in the paper may motivate the need for wide-area
measurements in power oscillation damping control.",1911.03342v3
2019-11-12,Non-uniform Stability of Damped Contraction Semigroups,"We investigate the stability properties of strongly continuous semigroups
generated by operators of the form $A-BB^\ast$, where $A$ is a generator of a
contraction semigroup and $B$ is a possibly unbounded operator. Such systems
arise naturally in the study of hyperbolic partial differential equations with
damping on the boundary or inside the spatial domain. As our main results we
present general sufficient conditions for non-uniform stability of the
semigroup generated by $A-BB^\ast$ in terms of selected observability-type
conditions of the pair $(B^\ast,A)$. We apply the abstract results to obtain
rates of energy decay in one-dimensional and two-dimensional wave equations, a
damped fractional Klein--Gordon equation and a weakly damped beam equation.",1911.04804v3
2020-01-31,Dynamo in weakly collisional nonmagnetized plasmas impeded by Landau damping of magnetic fields,"We perform fully kinetic simulations of flows known to produce dynamo in
magnetohydrodynamics (MHD), considering scenarios with low Reynolds number and
high magnetic Prandtl number, relevant for galaxy cluster scale fluctuation
dynamos. We find that Landau damping on the electrons leads to a rapid decay of
magnetic perturbations, impeding the dynamo. This collisionless damping process
operates on spatial scales where electrons are nonmagnetized, reducing the
range of scales where the magnetic field grows in high magnetic Prandtl number
fluctuation dynamos. When electrons are not magnetized down to the resistive
scale, the magnetic energy spectrum is expected to be limited by the scale
corresponding to magnetic Landau damping or, if smaller, the electron
gyroradius scale, instead of the resistive scale. In simulations we thus
observe decaying magnetic fields where resistive MHD would predict a dynamo.",2001.11929v2
2020-03-05,Sound propagation and quantum limited damping in a two-dimensional Fermi gas,"Strongly interacting two-dimensional Fermi systems are one of the great
remaining challenges in many-body physics due to the interplay of strong local
correlations and enhanced long-range fluctuations. Here, we probe the
thermodynamic and transport properties of a 2D Fermi gas across the BEC-BCS
crossover by studying the propagation and damping of sound modes. We excite
particle currents by imprinting a phase step onto homogeneous Fermi gases
trapped in a box potential and extract the speed of sound from the frequency of
the resulting density oscillations. We measure the speed of sound across the
BEC-BCS crossover and compare the resulting dynamic measurement of the equation
of state both to a static measurement based on recording density profiles and
to Quantum Monte Carlo calculations and find reasonable agreement between all
three. We also measure the damping of the sound mode, which is determined by
the shear and bulk viscosities as well as the thermal conductivity of the gas.
We find that the damping is minimal in the strongly interacting regime and the
diffusivity approaches the universal quantum bound $\hbar/m$ of a perfect
fluid.",2003.02713v1
2020-03-09,Proof-of-principle direct measurement of Landau damping strength at the Large Hadron Collider with an anti-damper,"Landau damping is an essential mechanism for ensuring collective beam
stability in particle accelerators. Precise knowledge of how strong Landau
damping is, is key to making accurate predictions on beam stability for
state-of-the-art high energy colliders. In this paper we demonstrate an
experimental procedure that would allow quantifying the strength of Landau
damping and the limits of beam stability using an active transverse feedback as
a controllable source of beam coupling impedance. In a proof-of-principle test
performed at the Large Hadron Collider stability diagrams for a range of Landau
Octupole strengths have been measured. In the future, the procedure could
become an accurate way of measuring stability diagrams throughout the machine
cycle.",2003.04383v1
2020-03-19,An inverse-system method for identification of damping rate functions in non-Markovian quantum systems,"Identification of complicated quantum environments lies in the core of
quantum engineering, which systematically constructs an environment model with
the aim of accurate control of quantum systems. In this paper, we present an
inverse-system method to identify damping rate functions which describe
non-Markovian environments in time-convolution-less master equations. To access
information on the environment, we couple a finite-level quantum system to the
environment and measure time traces of local observables of the system. By
using sufficient measurement results, an algorithm is designed, which can
simultaneously estimate multiple damping rate functions for different
dissipative channels. Further, we show that identifiability for the damping
rate functions corresponds to the invertibility of the system and a necessary
condition for identifiability is also given. The effectiveness of our method is
shown in examples of an atom and three-spin-chain non-Markovian systems.",2003.08617v1
2020-04-23,Damping of gravitational waves in 2-2-holes,"A 2-2-hole is an explicit realization of a horizonless object that can still
very closely resemble a BH. An ordinary relativistic gas can serve as the
matter source for the 2-2-hole solution of quadratic gravity, and this leads to
a calculable area-law entropy. Here we show that it also leads to an estimate
of the damping of a gravitational wave as it travels to the center of the
2-2-hole and back out again. We identify two frequency dependent effects that
greatly diminish the damping. Spinning 2-2-hole solutions are not known, but we
are still able to consider some spin dependent effects. The frequency and spin
dependence of the damping helps to determine the possible echo resonance signal
from the rotating remnants of merger events. It also controls the fate of the
ergoregion instability.",2004.11285v3
2020-05-04,Plasmon damping in electronically open systems,"Rapid progress in electrically-controlled plasmonics in solids poses a
question about effects of electronic reservoirs on the properties of plasmons.
We find that plasmons in electronically open systems [i.e. in (semi)conductors
connected to leads] are prone to an additional damping due to charge carrier
penetration into contacts and subsequent thermalization. We develop a theory of
such lead-induced damping based on kinetic equation with self-consistent
electric field, supplemented by microscopic carrier transport at the
interfaces. The lifetime of plasmon in electronically open ballistic system
appears to be finite, order of conductor length divided by carrier Fermi
(thermal) velocity. The reflection loss of plasmon incident on the contact of
semi-conductor and perfectly conducting metal also appears to be finite, order
of Fermi velocity divided by wave phase velocity. Recent experiments on
plasmon-assisted photodetection are discussed in light of the proposed
lead-induced damping phenomenon.",2005.01680v1
2020-05-06,Helical damping and anomalous critical non-Hermitian skin effect,"Non-Hermitian skin effect and critical skin effect are unique features of
non-Hermitian systems. In this Letter, we study an open system with its
dynamics of single-particle correlation function effectively dominated by a
non-Hermitian damping matrix, which exhibits $\mathbb{Z}_2$ skin effect, and
uncover the existence of a novel phenomenon of helical damping. When adding
perturbations that break anomalous time reversal symmetry to the system, the
critical skin effect occurs, which causes the disappearance of the helical
damping in the thermodynamic limit although it can exist in small size systems.
We also demonstrate the existence of anomalous critical skin effect when we
couple two identical systems with $\mathbb{Z}_2$ skin effect. With the help of
non-Bloch band theory, we unveil that the change of generalized Brillouin zone
equation is the necessary condition of critical skin effect.",2005.02617v1
2020-05-16,Gravitational Landau Damping for massive scalar modes,"We establish the possibility of Landau damping for gravitational scalar waves
which propagate in a non-collisional gas of particles. In particular, under the
hypothesis of homogeneity and isotropy, we describe the medium at the
equilibrium with a J\""uttner-Maxwell distribution, and we analytically
determine the damping rate from the Vlasov equation. We find that damping
occurs only if the phase velocity of the wave is subluminal throughout the
propagation within the medium. Finally, we investigate relativistic media in
cosmological settings by adopting numerical techniques.",2005.08010v4
2020-05-21,"On Strong Feller Property, Exponential Ergodicity and Large Deviations Principle for Stochastic Damping Hamiltonian Systems with State-Dependent Switching","This work focuses on a class of stochastic damping Hamiltonian systems with
state-dependent switching, where the switching process has a countably infinite
state space. After establishing the existence and uniqueness of a global weak
solution via the martingale approach under very mild conditions, the paper next
proves the strong Feller property for regime-switching stochastic damping
Hamiltonian systems by the killing technique together with some resolvent and
transition probability identities. The commonly used continuity assumption for
the switching rates $q_{kl}(\cdot)$ in the literature is relaxed to
measurability in this paper. Finally the paper provides sufficient conditions
for exponential ergodicity and large deviations principle for regime-switching
stochastic damping Hamiltonian systems. Several examples on regime-switching
van der Pol and (overdamped) Langevin systems are studied in detail for
illustration.",2005.10730v1
2020-06-09,Logarithmic decay for damped hypoelliptic wave and Schr{ö}dinger equations,"We consider damped wave (resp. Schr{\""o}dinger and plate) equations driven by
a hypoelliptic ""sum of squares"" operator L on a compact manifold and a damping
function b(x). We assume the Chow-Rashevski-H{\""o}rmander condition at rank k
(at most k Lie brackets needed to span the tangent space) together with
analyticity of M and the coefficients of L. We prove decay of the energy at
rate $log(t)^{-1/k}$ (resp. $log(t)^{-2/k}$ ) for data in the domain of the
generator of the associated group. We show that this decay is optimal on a
family of Grushin-type operators. This result follows from a perturbative
argument (of independent interest) showing, in a general abstract setting, that
quantitative approximate observability/controllability results for wave-type
equations imply a priori decay rates for associated damped wave,
Schr{\""o}dinger and plate equations. The adapted quantitative approximate
observability/controllability theorem for hypoelliptic waves is obtained by the
authors in [LL19, LL17].",2006.05122v1
2020-06-14,Bulk Viscous Damping of Density Oscillations in Neutron Star Mergers,"In this paper, we discuss the damping of density oscillations in dense
nuclear matter in the temperature range relevant to neutron star mergers. This
damping is due to bulk viscosity arising from the weak interaction ``Urca''
processes of neutron decay and electron capture. The nuclear matter is modelled
in the relativistic density functional approach. The bulk viscosity reaches a
resonant maximum close to the neutrino trapping temperature, then drops rapidly
as temperature rises into the range where neutrinos are trapped in neutron
stars. We investigate the bulk viscous dissipation timescales in a post-merger
object and identify regimes where these timescales are as short as the
characteristic timescale $\sim$10 ms, and, therefore, might affect the
evolution of the post-merger object. Our analysis indicates that bulk viscous
damping would be important at not too high temperatures of the order of a few
MeV and densities up to a few times saturation density.",2006.07975v2
2020-06-15,Exact solutions of a damped harmonic oscillator in a time dependent noncommutative space,"In this paper we have obtained the exact eigenstates of a two dimensional
damped harmonic oscillator in time dependent noncommutative space. It has been
observed that for some specific choices of the damping factor and the time
dependent frequency of the oscillator, there exists interesting solutions of
the time dependent noncommutative parameters following from the solutions of
the Ermakov-Pinney equation. Further, these solutions enable us to get exact
analytic forms for the phase which relates the eigenstates of the Hamiltonian
with the eigenstates of the Lewis invariant. We then obtain expressions for the
matrix elements of the coordinate operators raised to a finite arbitrary power.
From these general results we then compute the expectation value of the
Hamiltonian. The expectation values of the energy are found to vary with time
for different solutions of the Ermakov-Pinney equation corresponding to
different choices of the damping factor and the time dependent frequency of the
oscillator.",2006.08611v1
2020-06-16,Enhancing nonlinear damping by parametric-direct internal resonance,"Mechanical sources of nonlinear damping play a central role in modern
physics, from solid-state physics to thermodynamics. The microscopic theory of
mechanical dissipation [M. I . Dykman, M. A. Krivoglaz, Physica Status Solidi
(b) 68, 111 (1975)] suggests that nonlinear damping of a resonant mode can be
strongly enhanced when it is coupled to a vibration mode that is close to twice
its resonance frequency. To date, no experimental evidence of this enhancement
has been realized. In this letter, we experimentally show that nanoresonators
driven into parametric-direct internal resonance provide supporting evidence
for the microscopic theory of nonlinear dissipation. By regulating the drive
level, we tune the parametric resonance of a graphene nanodrum over a range of
40-70 MHz to reach successive two-to-one internal resonances, leading to a
nearly two-fold increase of the nonlinear damping. Our study opens up an
exciting route towards utilizing modal interactions and parametric resonance to
realize resonators with engineered nonlinear dissipation over wide frequency
range.",2006.09364v3
2020-06-22,Blow-up for wave equation with the scale-invariant damping and combined nonlinearities,"In this article, we study the blow-up of the damped wave equation in the
\textit{scale-invariant case} and in the presence of two nonlinearities. More
precisely, we consider the following equation: $$u_{tt}-\Delta
u+\frac{\mu}{1+t}u_t=|u_t|^p+|u|^q, \quad \mbox{in}\ \R^N\times[0,\infty), $$
with small initial data.\\ For $\mu < \frac{N(q-1)}{2}$ and $\mu \in (0,
\mu_*)$, where $\mu_*>0$ is depending on the nonlinearties' powers and the
space dimension ($\mu_*$ satisfies $(q-1)\left((N+2\mu_*-1)p-2\right) = 4$), we
prove that the wave equation, in this case, behaves like the one without
dissipation ($\mu =0$). Our result completes the previous studies in the case
where the dissipation is given by $\frac{\mu}{(1+t)^\beta}u_t; \ \beta >1$
(\cite{LT3}), where, contrary to what we obtain in the present work, the effect
of the damping is not significant in the dynamics. Interestingly, in our case,
the influence of the damping term $\frac{\mu}{1+t}u_t$ is important.",2006.12600v1
2020-07-10,Decentralized Frequency Control using Packet-based Energy Coordination,"This paper presents a novel frequency-responsive control scheme for
demand-side resources, such as electric water heaters. A frequency-dependent
control law is designed to provide damping from distributed energy resources
(DERs) in a fully decentralized fashion. This local control policy represents a
frequency-dependent threshold for each DER that ensures that the aggregate
response provides damping during frequency deviations. The proposed
decentralized policy is based on an adaptation of a packet-based DER
coordination scheme where each device send requests for energy access (also
called an ""energy packet"") to an aggregator. The number of previously accepted
active packets can then be used a-priori to form an online estimate of the
aggregate damping capability of the DER fleet in a dynamic power system. A
simple two-area power system is used to illustrate and validate performance of
the decentralized control policy and the accuracy of the online damping
estimating for a fleet of 400,000 DERs.",2007.05624v1
2020-07-30,Origin of micron-scale propagation lengths of heat-carrying acoustic excitations in amorphous silicon,"The heat-carrying acoustic excitations of amorphous silicon are of interest
because their mean free paths may approach micron scales at room temperature.
Despite extensive investigation, the origin of the weak acoustic damping in the
heat-carrying frequencies remains a topic of debate. Here, we report
measurements of the thermal conductivity mean free path accumulation function
in amorphous silicon thin films from 60 - 315 K using transient grating
spectroscopy. With additional picosecond acoustics measurements and considering
the known frequency-dependencies of damping mechanisms in glasses, we
reconstruct the mean free paths from $\sim 0.1-3$ THz. The mean free paths are
independent of temperature and exhibit a Rayleigh scattering trend over most of
this frequency range. The observed trend is inconsistent with the predictions
of numerical studies based on normal mode analysis but agrees with diverse
measurements on other glasses. The micron-scale MFPs in amorphous Si arise from
the absence of anharmonic or two-level system damping in the sub-THz
frequencies, leading to heat-carrying acoustic excitations with
room-temperature damping comparable to that of other glasses at cryogenic
temperatures.",2007.15777v2
2020-08-06,Quantum sensing of open systems: Estimation of damping constants and temperature,"We determine quantum precision limits for estimation of damping constants and
temperature of lossy bosonic channels. A direct application would be the use of
light for estimation of the absorption and the temperature of a transparent
slab. Analytic lower bounds are obtained for the uncertainty in the estimation,
through a purification procedure that replaces the master equation description
by a unitary evolution involving the system and ad hoc environments. For zero
temperature, Fock states are shown to lead to the minimal uncertainty in the
estimation of damping, with boson-counting being the best measurement
procedure. In both damping and temperature estimates, sequential
pre-thermalization measurements, through a stream of single bosons, may lead to
huge gain in precision.",2008.02728v1
2020-08-07,Quantifying the evidence for resonant damping of coronal waves with foot-point wave power asymmetry,"We use Coronal Multi-channel Polarimeter (CoMP) observations of propagating
waves in the solar corona and Bayesian analysis to assess the evidence of
models with resonant damping and foot-point wave power asymmetries. Two nested
models are considered. The reduced model considers resonant damping as the sole
cause of the measured discrepancy between outward and inward wave power. The
larger model contemplates an extra source of asymmetry with origin at the
foot-points. We first compute probability distributions of parameters
conditional on the models and the observed data. The obtained constraints are
then used to calculate the evidence for each model in view of data. We find
that we need to consider the larger model to explain CoMP data and to
accurately infer the damping ratio, hence, to better assess the possible
contribution of the waves to coronal heating.",2008.03004v1
2020-08-22,Sound damping in frictionless granular materials: The interplay between configurational disorder and inelasticity,"We numerically investigate sound damping in a model of granular materials in
two dimensions. We simulate evolution of standing waves in disordered
frictionless disks and analyze their damped oscillations by velocity
autocorrelation functions and power spectra. We control the strength of
inelastic interactions between the disks in contact to examine the effect of
energy dissipation on sound characteristics of disordered systems. Increasing
the strength of inelastic interactions, we find that (i) sound softening
vanishes and (ii) sound attenuation due to configurational disorder, i.e. the
Rayleigh scattering at low frequencies and disorder-induced broadening at high
frequencies, is completely dominated by the energy dissipation. Our findings
suggest that sound damping in granular media is determined by the interplay
between elastic heterogeneities and inelastic interactions.",2008.09760v1
2020-09-27,Squeezed comb states,"Continuous-variable codes are an expedient solution for quantum information
processing and quantum communication involving optical networks. Here we
characterize the squeezed comb, a finite superposition of equidistant squeezed
coherent states on a line, and its properties as a continuous-variable encoding
choice for a logical qubit. The squeezed comb is a realistic approximation to
the ideal code proposed by Gottesman, Kitaev, and Preskill [Phys. Rev. A 64,
012310 (2001)], which is fully protected against errors caused by the
paradigmatic types of quantum noise in continuous-variable systems: damping and
diffusion. This is no longer the case for the code space of finite squeezed
combs, and noise robustness depends crucially on the encoding parameters. We
analyze finite squeezed comb states in phase space, highlighting their
complicated interference features and characterizing their dynamics when
exposed to amplitude damping and Gaussian diffusion noise processes. We find
that squeezed comb state are more suitable and less error-prone when exposed to
damping, which speaks against standard error correction strategies that employ
linear amplification to convert damping into easier-to-describe isotropic
diffusion noise.",2009.12888v2
2020-11-16,Switchable Damping for a One-Particle Oscillator,"The possibility to switch the damping rate for a one-electron oscillator is
demonstrated, for an electron that oscillates along the magnetic field axis in
a Penning trap. Strong axial damping can be switched on to allow this
oscillation to be used for quantum nondemolition detection of the cyclotron and
spin quantum state of the electron. Weak axial damping can be switched on to
circumvent the backaction of the detection motion that has limited past
measurements. The newly developed switch will reduce the linewidth of the
cyclotron transition of one-electron by two orders of magnitude.",2011.08136v2
2020-11-15,A Random Matrix Theory Approach to Damping in Deep Learning,"We conjecture that the inherent difference in generalisation between adaptive
and non-adaptive gradient methods in deep learning stems from the increased
estimation noise in the flattest directions of the true loss surface. We
demonstrate that typical schedules used for adaptive methods (with low
numerical stability or damping constants) serve to bias relative movement
towards flat directions relative to sharp directions, effectively amplifying
the noise-to-signal ratio and harming generalisation. We further demonstrate
that the numerical damping constant used in these methods can be decomposed
into a learning rate reduction and linear shrinkage of the estimated curvature
matrix. We then demonstrate significant generalisation improvements by
increasing the shrinkage coefficient, closing the generalisation gap entirely
in both logistic regression and several deep neural network experiments.
Extending this line further, we develop a novel random matrix theory based
damping learner for second order optimiser inspired by linear shrinkage
estimation. We experimentally demonstrate our learner to be very insensitive to
the initialised value and to allow for extremely fast convergence in
conjunction with continued stable training and competitive generalisation.",2011.08181v5
2020-11-17,Challenging an experimental nonlinear modal analysis method with a new strongly friction-damped structure,"In this work, we show that a recently proposed method for experimental
nonlinear modal analysis based on the extended periodic motion concept is well
suited to extract modal properties for strongly nonlinear systems (i.e. in the
presence of large frequency shifts, high and nonlinear damping, changes of the
mode shape, and higher harmonics). To this end, we design a new test rig that
exhibits a large extent of friction-induced damping (modal damping ratio up to
15 %) and frequency shift by 36 %. The specimen, called RubBeR, is a
cantilevered beam under the influence of dry friction, ranging from full stick
to mainly sliding. With the specimen's design, the measurements are well
repeatable for a system subjected to dry frictional force. Then, we apply the
method to the specimen and show that single-point excitation is sufficient to
track the modal properties even though the deflection shape changes with
amplitude. Computed frequency responses using a single nonlinear-modal
oscillator with the identified modal properties agree well with measured
reference curves of different excitation levels, indicating the modal
properties' significance and accuracy.",2011.08527v1
2020-11-27,Thermal damping of Weak Magnetosonic Turbulence in the Interstellar Medium,"We present a generic mechanism for the thermal damping of compressive waves
in the interstellar medium (ISM), occurring due to radiative cooling. We solve
for the dispersion relation of magnetosonic waves in a two-fluid (ion-neutral)
system in which density- and temperature-dependent heating and cooling
mechanisms are present. We use this dispersion relation, in addition to an
analytic approximation for the nonlinear turbulent cascade, to model
dissipation of weak magnetosonic turbulence. We show that in some ISM
conditions, the cutoff wavelength for magnetosonic turbulence becomes tens to
hundreds of times larger when the thermal damping is added to the regular
ion-neutral damping. We also run numerical simulations which confirm that this
effect has a dramatic impact on cascade of compressive wave modes.",2011.13879v3
2021-02-10,WAMS-Based Model-Free Wide-Area Damping Control by Voltage Source Converters,"In this paper, a novel model-free wide-area damping control (WADC) method is
proposed, which can achieve full decoupling of modes and damp multiple critical
inter-area oscillations simultaneously using grid-connected voltage source
converters (VSCs). The proposed method is purely measurement based and requires
no knowledge of the network topology and the dynamic model parameters. Hence,
the designed controller using VSCs can update the control signals online as the
system operating condition varies. Numerical studies in the modified IEEE
68-bus system with grid-connected VSCs show that the proposed method can
estimate the system dynamic model accurately and can damp inter-area
oscillations effectively under different working conditions and network
topologies.",2102.05494v1
2021-04-08,Fast optimization of viscosities for frequency-weighted damping of second-order systems,"We consider frequency-weighted damping optimization for vibrating systems
described by a second-order differential equation. The goal is to determine
viscosity values such that eigenvalues are kept away from certain undesirable
areas on the imaginary axis. To this end, we present two complementary
techniques. First, we propose new frameworks using nonsmooth constrained
optimization problems, whose solutions both damp undesirable frequency bands
and maintain stability of the system. These frameworks also allow us to weight
which frequency bands are the most important to damp. Second, we also propose a
fast new eigensolver for the structured quadratic eigenvalue problems that
appear in such vibrating systems. In order to be efficient, our new eigensolver
exploits special properties of diagonal-plus-rank-one complex symmetric
matrices, which we leverage by showing how each quadratic eigenvalue problem
can be transformed into a short sequence of such linear eigenvalue problems.
The result is an eigensolver that is substantially faster than standard
techniques. By combining this new solver with our new optimization frameworks,
we obtain our overall algorithm for fast computation of optimal viscosities.
The efficiency and performance of our new methods are verified and illustrated
on several numerical examples.",2104.04035v1
2021-04-09,"Nonexistence result for the generalized Tricomi equation with the scale-invariant damping, mass term and time derivative nonlinearity","In this article, we consider the damped wave equation in the
\textit{scale-invariant case} with time-dependent speed of propagation, mass
term and time derivative nonlinearity. More precisely, we study the blow-up of
the solutions to the following equation: $$ (E) \quad u_{tt}-t^{2m}\Delta
u+\frac{\mu}{t}u_t+\frac{\nu^2}{t^2}u=|u_t|^p, \quad \mbox{in}\
\mathbb{R}^N\times[1,\infty), $$ that we associate with small initial data.
Assuming some assumptions on the mass and damping coefficients, $\nu$ and
$\mu>0$, respectively, that the blow-up region and the lifespan bound of the
solution of $(E)$ remain the same as the ones obtained for the case without
mass, {\it i.e.} $\nu=0$ in $(E)$. The latter case constitutes, in fact, a
shift of the dimension $N$ by $\frac{\mu}{1+m}$ compared to the problem without
damping and mass. Finally, we think that the new bound for $p$ is a serious
candidate to the critical exponent which characterizes the threshold between
the blow-up and the global existence regions.",2104.04393v2
2021-04-12,Slow periodic oscillation without radiation damping: New evolution laws for rate and state friction,"The dynamics of sliding friction is mainly governed by the frictional force.
Previous studies have shown that the laboratory-scale friction is well
described by an empirical law stated in terms of the slip velocity and the
state variable. The state variable represents the detailed physicochemical
state of the sliding interface. Despite some theoretical attempts to derive
this friction law, there has been no unique equation for time evolution of the
state variable. Major equations known to date have their own merits and
drawbacks. To shed light on this problem from a new aspect, here we investigate
the feasibility of periodic motion without the help of radiation damping.
Assuming a patch on which the slip velocity is perturbed from the rest of the
sliding interface, we prove analytically that three major evolution laws fail
to reproduce stable periodic motion without radiation damping. Furthermore, we
propose two new evolution equations that can produce stable periodic motion
without radiation damping. These two equations are scrutinized from the
viewpoint of experimental validity and the relevance to slow earthquakes.",2104.05398v2
2021-04-27,Absence of a boson peak in anharmonic phonon models with Akhiezer-type damping,"In a recent article M. Baggioli and A. Zaccone (Phys. Rev. Lett. {\bf 112},
145501 (2019)) claimed that an anharmonic damping, leading to a sound
attenuation proportional to $\omega^2$ (Akhiezer-type damping) would imply a
boson peak, i.e.\ a maximum in the vibrational density of states, divided by
the frequency squared (reduced density of states). This would apply both to
glasses and crystals.Here we show that this is not the case. In a
mathematically correct treatment of the model the reduced density of states
monotonously decreases, i.e.\ there is no boson peak. We further show that the
formula for the would-be boson peak, presented by the authors, corresponds to a
very short one-dimensional damped oscillator system. The peaks they show
correspond to resonances, which vanish in the thermodynamic limit.",2104.13076v1
2021-05-03,Damping and polarization rates in near equilibrium state,"The collision terms in spin transport theory are analyzed in Kadanoff-Baym
formalism for systems close to equilibrium. The non-equilibrium fluctuations in
spin distribution include both damping and polarization, with the latter
arising from the exchange between orbital and spin angular momenta. The damping
and polarization rates or the relaxation times are expressed in terms of
various Dirac components of the self-energy. Unlike the usually used
Anderson-Witting relaxation time approximation assuming a single time scale for
different degrees of freedom, the polarization effect is induced by the thermal
vorticity and its time scale of thermalization is different from the damping.
The numerical calculation in the Nambu--Jona-Lasinio model shows that, charge
is thermalized earlier and spin is thermalized later.",2105.00915v1
2021-06-07,Voltage-control of damping constant in magnetic-insulator/topological-insulator bilayers,"The magnetic damping constant is a critical parameter for magnetization
dynamics and the efficiency of memory devices and magnon transport. Therefore,
its manipulation by electric fields is crucial in spintronics. Here, we
theoretically demonstrate the voltage-control of magnetic damping in ferro- and
ferrimagnetic-insulator (FI)/topological-insulator (TI) bilayers. Assuming a
capacitor-like setup, we formulate an effective dissipation torque induced by
spin-charge pumping at the FI/TI interface as a function of an applied voltage.
By using realistic material parameters, we find that the effective damping for
a FI with 10nm thickness can be tuned by one order of magnitude under the
voltage with 0.25V. Also, we provide perspectives on the voltage-induced
modulation of the magnon spin transport on proximity-coupled FIs.",2106.03332v1
2021-05-14,Exact solution of damped harmonic oscillator with a magnetic field in a time dependent noncommutative space,"In this paper we have obtained the exact eigenstates of a two dimensional
damped harmonic oscillator in the presence of an external magnetic field
varying with respect to time in time dependent noncommutative space. It has
been observed that for some specific choices of the damping factor, the time
dependent frequency of the oscillator and the time dependent external magnetic
field, there exists interesting solutions of the time dependent noncommutative
parameters following from the solutions of the Ermakov-Pinney equation.
Further, these solutions enable us to get exact analytic forms for the phase
which relates the eigenstates of the Hamiltonian with the eigenstates of the
Lewis invariant. Then we compute the expectation value of the Hamiltonian. The
expectation values of the energy are found to vary with time for different
solutions of the Ermakov-Pinney equation corresponding to different choices of
the damping factor, the time dependent frequency of the oscillator and the time
dependent applied magnetic field. We also compare our results with those in the
absence of the magnetic field obtained earlier.",2106.05182v1
2021-06-21,Self-stabilization of light sails by damped internal degrees of freedom,"We consider the motion of a light sail that is accelerated by a powerful
laser beam. We derive the equations of motion for two proof-of-concept sail
designs with damped internal degrees of freedom. Using linear stability
analysis we show that perturbations of the sail movement in all lateral degrees
of freedom can be damped passively. This analysis also shows complicated
behaviour akin to that associated with exceptional points in PT-symmetric
systems in optics and quantum mechanics. The excess heat that is produced by
the damping mechanism is likely to be substantially smaller than the expected
heating due to the partial absorption of the incident laser beam by the sail.",2106.10961v1
2021-07-14,Determining the source of phase noise: Response of a driven Duffing oscillator to low-frequency damping and resonance frequency fluctuations,"We present an analytical calculation of the response of a driven Duffing
oscillator to low-frequency fluctuations in the resonance frequency and
damping. We find that fluctuations in these parameters manifest themselves
distinctively, allowing them to be distinguished. In the strongly nonlinear
regime, amplitude and phase noise due to resonance frequency fluctuations and
amplitude noise due to damping fluctuations are strongly attenuated, while the
transduction of damping fluctuations into phase noise remains of order $1$. We
show that this can be seen by comparing the relative strengths of the amplitude
fluctuations to the fluctuations in the quadrature components, and suggest that
this provides a means to determine the source of low-frequency noise in a
driven Duffing oscillator.",2107.06879v1
2021-07-27,Spin transport-induced damping of coherent THz spin dynamics in iron,"We study the damping of perpendicular standing spin-waves (PSSWs) in
ultrathin Fe films at frequencies up to 2.4 THz. The PSSWs are excited by
optically generated ultrashort spin current pulses, and probed optically in the
time domain. Analyzing the wavenumber and thickness dependence of the damping,
we demonstrate that at sufficiently large wave vectors $k$ the damping is
dominated by spin transport effects scaling with k^4 and limiting the frequency
range of observable PSSWs. Although this contribution is known to originate in
the spin diffusion, we argue that at moderate and large k a more general
description is necessary and develop a model where the 'transverse spin mean
free path' is the a key parameter, and estimate it to be ~0.5 nm.",2107.12812v2
2021-07-29,A N-dimensional elastic\viscoelastic transmission problem with Kelvin-Voigt damping and non smooth coefficient at the interface,"We investigate the stabilization of a multidimensional system of coupled wave
equations with only one Kelvin Voigt damping. Using a unique continuation
result based on a Carleman estimate and a general criteria of Arendt Batty, we
prove the strong stability of the system in the absence of the compactness of
the resolvent without any geometric condition. Then, using a spectral analysis,
we prove the non uniform stability of the system. Further, using frequency
domain approach combined with a multiplier technique, we establish some
polynomial stability results by considering different geometric conditions on
the coupling and damping domains. In addition, we establish two polynomial
energy decay rates of the system on a square domain where the damping and the
coupling are localized in a vertical strip.",2107.13785v1
2021-09-03,Stabilization of the damped plate equation under general boundary conditions,"We consider a damped plate equation on an open bounded subset of R^d, or a
smooth manifold, with boundary, along with general boundary operators
fulfilling the Lopatinskii-Sapiro condition. The damping term acts on a region
without imposing a geometrical condition. We derive a resolvent estimate for
the generator of the damped plate semigroup that yields a logarithmic decay of
the energy of the solution to the plate equation. The resolvent estimate is a
consequence of a Carleman inequality obtained for the bi-Laplace operator
involving a spectral parameter under the considered boundary conditions. The
derivation goes first though microlocal estimates, then local estimates, and
finally a global estimate.",2109.01521v2
2021-09-07,Fluid energy cascade rate and kinetic damping: new insight from 3D Landau-fluid simulations,"Using an exact law for incompressible Hall magnetohydrodynamics (HMHD)
turbulence, the energy cascade rate is computed from three-dimensional HMHD-CGL
(bi-adiabatic ions and isothermal electrons) and Landau fluid (LF) numerical
simulations that feature different intensities of Landau damping over a broad
range of wavenumbers, typically $0.05\lesssim k_\perp d_i \lesssim100$. Using
three sets of cross-scale simulations where turbulence is initiated at large,
medium and small scales, the ability of the fluid energy cascade to ""sense"" the
kinetic Landau damping at different scales is tested. The cascade rate
estimated from the exact law and the dissipation calculated directly from the
simulation are shown to reflect the role of Landau damping in dissipating
energy at all scales, with an emphasis on the kinetic ones. This result
provides new prospects on using exact laws for simplified fluid models to
analyze dissipation in kinetic simulations and spacecraft observations, and new
insights into theoretical description of collisionless magnetized plasmas.",2109.03123v2
2021-09-24,Effect of nonlocal transformations on the linearizability and exact solvability of the nonlinear generalized modified Emden type equations,"The nonlinear generalized modified Emden type equations (GMEE) are known to
be linearizable into simple harmonic oscillator (HO) or damped harmonic
oscillators (DHO) via some nonlocal transformations. Hereby, we show that the
structure of the nonlocal transformation and the linearizability into HO or DHO
determine the nature/structure of the dynamical forces involved (hence,
determine the structure of the dynamical equation). Yet, a reverse engineering
strategy is used so that the exact solutions of the emerging GMEE are
nonlocally transformed to find the exact solutions of the HO and DHO dynamical
equations. Consequently, whilst the exact solution for the HO remains a
textbook one, the exact solution for the DHO (never reported elsewhere, to the
best of our knowledge) turns out to be manifestly the most explicit and general
solution that offers consistency and comprehensive coverage for the associated
under-damping, critical-damping, and over-damping cases (i.e., no complex
settings for the coordinates and/or the velocities are eminent/feasible).
Moreover, for all emerging dynamical system, we report illustrative figures for
each solution as well as the corresponding phase-space trajectories as they
evolve in time.",2109.12059v1
2021-12-27,Trajectory attractors for 3D damped Euler equations and their approximation,"We study the global attractors for the damped 3D Euler--Bardina equations
with the regularization parameter $\alpha>0$ and Ekman damping coefficient
$\gamma>0$ endowed with periodic boundary conditions as well as their damped
Euler limit $\alpha\to0$. We prove that despite the possible non-uniqueness of
solutions of the limit Euler system and even the non-existence of such
solutions in the distributional sense, the limit dynamics of the corresponding
dissipative solutions introduced by P.\,Lions can be described in terms of
attractors of the properly constructed trajectory dynamical system. Moreover,
the convergence of the attractors $\Cal A(\alpha)$ of the regularized system to
the limit trajectory attractor $\Cal A(0)$ as $\alpha\to0$ is also established
in terms of the upper semicontinuity in the properly defined functional space.",2112.13691v1
2022-01-12,Implicit Bias of MSE Gradient Optimization in Underparameterized Neural Networks,"We study the dynamics of a neural network in function space when optimizing
the mean squared error via gradient flow. We show that in the
underparameterized regime the network learns eigenfunctions of an integral
operator $T_{K^\infty}$ determined by the Neural Tangent Kernel (NTK) at rates
corresponding to their eigenvalues. For example, for uniformly distributed data
on the sphere $S^{d - 1}$ and rotation invariant weight distributions, the
eigenfunctions of $T_{K^\infty}$ are the spherical harmonics. Our results can
be understood as describing a spectral bias in the underparameterized regime.
The proofs use the concept of ""Damped Deviations"", where deviations of the NTK
matter less for eigendirections with large eigenvalues due to the occurence of
a damping factor. Aside from the underparameterized regime, the damped
deviations point-of-view can be used to track the dynamics of the empirical
risk in the overparameterized setting, allowing us to extend certain results in
the literature. We conclude that damped deviations offers a simple and unifying
perspective of the dynamics when optimizing the squared error.",2201.04738v1
2022-01-19,Variance-Reduced Stochastic Quasi-Newton Methods for Decentralized Learning: Part II,"In Part I of this work, we have proposed a general framework of decentralized
stochastic quasi-Newton methods, which converge linearly to the optimal
solution under the assumption that the local Hessian inverse approximations
have bounded positive eigenvalues. In Part II, we specify two fully
decentralized stochastic quasi-Newton methods, damped regularized
limited-memory DFP (Davidon-Fletcher-Powell) and damped limited-memory BFGS
(Broyden-Fletcher-Goldfarb-Shanno), to locally construct such Hessian inverse
approximations without extra sampling or communication. Both of the methods use
a fixed moving window of $M$ past local gradient approximations and local
decision variables to adaptively construct positive definite Hessian inverse
approximations with bounded eigenvalues, satisfying the assumption in Part I
for the linear convergence. For the proposed damped regularized limited-memory
DFP, a regularization term is added to improve the performance. For the
proposed damped limited-memory BFGS, a two-loop recursion is applied, leading
to low storage and computation complexity. Numerical experiments demonstrate
that the proposed quasi-Newton methods are much faster than the existing
decentralized stochastic first-order algorithms.",2201.07733v1
2022-01-19,Active tuning of plasmon damping via light induced magnetism,"Circularly polarized optical excitation of plasmonic nanostructures causes
coherent circulating motion of their electrons, which in turn, gives rise to
strong optically induced magnetization - a phenomenon known as the inverse
Faraday effect (IFE). In this study we report how the IFE also significantly
decreases plasmon damping. By modulating the optical polarization state
incident on achiral plasmonic nanostructures from linear to circular, we
observe reversible increases of reflectance by 78% as well as simultaneous
increases of optical field concentration by 35.7% under 10^9 W/m^2 continuous
wave (CW) optical excitation. These signatures of decreased plasmon damping
were also monitored in the presence of an externally applied magnetic field
(0.2 T). The combined interactions allow an estimate of the light-induced
magnetization, which corresponds to an effective magnetic field of ~1.3 T
during circularly polarized CW excitation (10^9 W/m^2). We rationalize the
observed decreases in plasmon damping in terms of the Lorentz forces acting on
the circulating electron trajectories. Our results outline strategies for
actively modulating intrinsic losses in the metal, and thereby, the optical
mode quality and field concentration via opto-magnetic effects encoded in the
polarization state of incident light.",2201.07842v1
2022-03-02,Simplified Stability Assessment of Power Systems with Variable-Delay Wide-Area Damping Control,"Power electronic devices such as HVDC and FACTS can be used to improve the
damping of poorly damped inter-area modes in large power systems. This involves
the use of wide-area feedback signals, which are transmitted via communication
networks. The performance of the closed-loop system is strongly influenced by
the delay associated with wide-area signals. The random nature of this delay
introduces a switched linear system model. The stability assessment of such a
system requires linear matrix inequality based approaches. This makes the
stability analysis more complicated as the system size increases. To address
this challenge, this paper proposes a delay-processing strategy that simplifies
the modelling and analysis in discrete-domain. In contrast to the existing
stability assessment techniques, the proposed approach is advantageous because
the stability, as well as damping performance, can be accurately predicted by a
simplified analysis. The proposed methodology is verified with a case study on
the 2-area 4-machine power system with a series compensated tie-line. The
results are found to be in accordance with the predictions of the proposed
simplified analysis.",2203.01362v1
2022-03-03,Forward-modulated damping estimates and nonlocalized stability of periodic Lugiato-Lefever wave,"In an interesting recent analysis, Haragus-Johnson-Perkins-de Rijk have shown
modulational stability under localized perturbations of steady periodic
solutions of the Lugiato-Lefever equation (LLE), in the process pointing out a
difficulty in obtaining standard ""nonlinear damping estimates"" on modulated
perturbation variables to control regularity of solutions. Here, we point out
that in place of standard ""inverse-modulated"" damping estimates, one can
alternatively carry out a damping estimate on the ""forward-modulated""
perturbation, noting that norms of forward- and inverse-modulated variables are
equivalent modulo absorbable errors, thus recovering the classical argument
structure of Johnson-Noble-Rodrigues-Zumbrun for parabolic systems. This
observation seems of general use in situations of delicate regularity.
  Applied in the context of (LLE) it gives the stronger result of stability and
asymptotic behavior with respect to nonlocalized perturbations.",2203.01770v3
2022-03-31,Observing Particle Energization above the Nyquist Frequency: An Application of the Field-Particle Correlation Technique,"The field-particle correlation technique utilizes single-point measurements
to uncover signatures of various particle energization mechanisms in turbulent
space plasmas. The signature of Landau damping by electrons has been found in
both simulations and observations from Earth's magnetosheath using this
technique, but instrumental limitations of spacecraft sampling rates present a
challenge to discovering the full extent of the presence of Landau damping in
the solar wind. Theory predicts that field-particle correlations can recover
velocity-space energization signatures even from data that is undersampled with
respect to the characteristic frequencies at which the wave damping occurs. To
test this hypothesis, we perform a high-resoluation gyrokinetic simulation of
space plasma turbulence, confirm that it contains signatures of electron Landau
damping, and then systematically reduce the time resolution of the data to
identify the point at which the signatures become impossible to recover. We
find results in support of our theoretical prediction and look for a rule of
thumb that can be compared with the measurement capabilities of spacecraft
missions to inform the process of applying field-particle correlations to low
time resolution data.",2204.00104v1
2022-04-06,A Potential Based Quantization Procedure of the Damped Oscillator,"Nowadays, two of the most prospering fields of physics are quantum computing
and spintronics. In both, the loss of information and dissipation plays a
crucial role. In the present work we formulate the quantization of the
dissipative oscillator, which aids understanding of the above mentioned, and
creates a theoretical frame to overcome these issues in the future. Based on
the Lagrangian framework of the damped spring system, the canonically
conjugated pairs and the Hamiltonian of the system are obtained, by which the
quantization procedure can be started and consistently applied. As a result,
the damping quantum wave equation of the dissipative oscillator is deduced, by
which an exact damping wave solution of this equation is obtained.
Consequently, we arrive at such an irreversible quantum theory by which the
quantum losses can be described.",2204.02893v2
2022-04-19,Role of shape anisotropy on thermal gradient-driven domain wall dynamics in magnetic nanowires,"We investigate the magnetic domain wall (DW) dynamics in uniaxial/biaxial
nanowires under a thermal gradient (TG). The findings reveal that the DW
propagates toward the hotter region in both nanowires. The main physics of such
observations is the magnonic angular momentum transfer to the DW. The hard
(shape) anisotropy exists in biaxial nanowire, which contributes an additional
torque, hence DW speed is larger than that in uniaxial nanowire. With lower
damping, the DW velocity is smaller and DW velocity increases with damping
which is opposite to usual expectation. To explain this, it is predicted that
there is a probability to form the standing spin-waves (which do not carry net
energy/momentum) together with travelling spin-waves if the propagation length
of thermally-generated spin-waves is larger than the nanowire length. For
larger-damping, DW decreases with damping since the magnon propagation length
decreases. Therefore, the above findings might be useful in realizing the
spintronic (racetrack memory) devices.",2204.09101v2
2022-04-25,Energy decay estimates for the wave equation with supercritical nonlinear damping,"We consider a damped wave equation in a bounded domain. The damping is
nonlinear and is homogeneous with degree p -- 1 with p > 2. First, we show that
the energy of the strong solution in the supercritical case decays as a
negative power of t; the rate of decay is the same as in the subcritical or
critical cases, provided that the space dimension does not exceed ten. Next,
relying on a new differential inequality, we show that if the initial
displacement is further required to lie in L p , then the energy of the
corresponding weak solution decays logarithmically in the supercritical case.
Those new results complement those in the literature and open an important
breach in the unknown land of super-critical damping mechanisms.",2204.11494v1
2022-05-07,Proposal for a Damping-Ring-Free Electron Injector for Future Linear Colliders,"The current designs of future electron-positron linear colliders incorporate
large and complex damping rings to produce asymmetric beams for beamstrahlung
suppression. Here we present the design of an electron injector capable of
delivering flat electron beams with phase-space partition comparable to the
electron-beam parameters produced downstream of the damping ring in the
proposed international linear collider (ILC) design. Our design does not employ
a damping ring but is instead based on cross-plane phase-space-manipulation
techniques. The performance of the proposed configuration, its sensitivity to
jitter along with its impact on spin-polarization is investigated. The proposed
paradigm could be adapted to other linear collider concepts under consideration
and offers a path toward significant cost and complexity reduction.",2205.03736v1
2022-06-02,Optimal Control of the 3D Damped Navier-Stokes-Voigt Equations with Control Constraints,"In this paper, we consider the 3D Navier-Stokes-Voigt (NSV) equations with
nonlinear damping $|u|^{r-1}u, r\in[1,\infty)$ in bounded and space-periodic
domains. We formulate an optimal control problem of minimizing the curl of the
velocity field in the energy norm subject to the flow velocity satisfying the
damped NSV equation with a distributed control force. The control also needs to
obey box-type constraints. For any $r\geq 1,$ the existence and uniqueness of a
weak solution is discussed when the domain $\Omega$ is periodic/bounded in
$\mathbb R^3$ while a unique strong solution is obtained in the case of
space-periodic boundary conditions. We prove the existence of an optimal pair
for the control problem. Using the classical adjoint problem approach, we show
that the optimal control satisfies a first-order necessary optimality condition
given by a variational inequality. Since the optimal control problem is
non-convex, we obtain a second-order sufficient optimality condition showing
that an admissible control is locally optimal. Further, we derive optimality
conditions in terms of adjoint state defined with respect to the growth of the
damping term for a global optimal control.",2206.00988v2
2022-06-05,Stationary measures for stochastic differential equations with degenerate damping,"A variety of physical phenomena involve the nonlinear transfer of energy from
weakly damped modes subjected to external forcing to other modes which are more
heavily damped. In this work we explore this in (finite-dimensional) stochastic
differential equations in $\mathbb R^n$ with a quadratic, conservative
nonlinearity $B(x,x)$ and a linear damping term $-Ax$ which is degenerate in
the sense that $\mathrm{ker} A \neq \emptyset$. We investigate sufficient
conditions to deduce the existence of a stationary measure for the associated
Markov semigroups. Existence of such measures is straightforward if $A$ is full
rank, but otherwise, energy could potentially accumulate in $\mathrm{ker} A$
and lead to almost-surely unbounded trajectories, making the existence of
stationary measures impossible. We give a relatively simple and general
sufficient condition based on time-averaged coercivity estimates along
trajectories in neighborhoods of $\mathrm{ker} A$ and many examples where such
estimates can be made.",2206.02240v1
2022-06-17,Resolvent estimates for the one-dimensional damped wave equation with unbounded damping,"We study the generator $G$ of the one-dimensional damped wave equation with
unbounded damping. We show that the norm of the corresponding resolvent
operator, $\| (G - \lambda)^{-1} \|$, is approximately constant as $|\lambda|
\to +\infty$ on vertical strips of bounded width contained in the closure of
the left-hand side complex semi-plane, $\overline{\mathbb{C}}_{-} := \{\lambda
\in \mathbb{C}: \operatorname{Re} \lambda \le 0\}$. Our proof rests on a
precise asymptotic analysis of the norm of the inverse of $T(\lambda)$, the
quadratic operator associated with $G$.",2206.08820v2
2022-07-13,Energy decay for the time dependent damped wave equation,"Energy decay is established for the damped wave equation on compact
Riemannian manifolds where the damping coefficient is allowed to depend on
time. Using a time dependent observability inequality, it is shown that the
energy of solutions decays at an exponential rate if the damping coefficient
satisfies a time dependent analogue of the classical geometric control
condition. Existing time dependent observability inequalities are improved by
removing technical assumptions on the permitted initial data.",2207.06260v4
2022-08-04,Lp-asymptotic stability of 1D damped wave equations with localized and nonlinear damping,"In this paper, we study the $L^p$-asymptotic stability with $p\in (1,\infty)$
of the one-dimensional nonlinear damped wave equation with a localized damping
and Dirichlet boundary conditions in a bounded domain $(0,1)$. We start by
addressing the well-posedness problem. We prove the existence and the
uniqueness of weak solutions for $p\in [2,\infty)$ and the existence and the
uniqueness of strong solutions for all $p\in [1,\infty)$. The proofs rely on
the well-posedness already proved in the $L^\infty$ framework by [4] combined
with a density argument. Then we prove that the energy of strong solutions
decays exponentially to zero. The proof relies on the multiplier method
combined with the work that has been done in the linear case in [8].",2208.02779v1
2022-08-07,"Damping of neutrino oscillations, decoherence and the lengths of neutrino wave packets","Spatial separation of the wave packets (WPs) of neutrino mass eigenstates
leads to decoherence and damping of neutrino oscillations. Damping can also be
caused by finite energy resolution of neutrino detectors or, in the case of
experiments with radioactive neutrino sources, by finite width of the emitted
neutrino line. We study in detail these two types of damping effects using
reactor neutrino experiments and experiments with radioactive $^{51}$Cr source
as examples. We demonstrate that the effects of decoherence by WP separation
can always be incorporated into a modification of the energy resolution
function of the detector and so are intimately entangled with it. We estimate
for the first time the lengths $\sigma_x$ of WPs of reactor neutrinos and
neutrinos from a radioactive $^{51}$Cr source. The obtained values, $\sigma_x =
(2\times 10^{-5} - 1.4\times 10^{-4})$ cm, are at least six orders of magnitude
larger than the currently available experimental lower bounds. We conclude that
effects of decoherence by WP separation cannot be probed in reactor and
radioactive source experiments.",2208.03736v2
2022-08-23,Fate of exceptional points in the presence of nonlinearities,"The non-Hermitian dynamics of open systems deal with how intricate coherent
effects of a closed system intertwine with the impact of coupling to an
environment. The system-environment dynamics can then lead to so-called
exceptional points, which are the open-system marker of phase transitions,
i.e., the closing of spectral gaps in the complex spectrum. Even in the
ubiquitous example of the damped harmonic oscillator, the dissipative
environment can lead to an exceptional point, separating between under-damped
and over-damped dynamics at a point of critical damping. Here, we examine the
fate of this exceptional point in the presence of strong correlations, i.e.,
for a nonlinear oscillator. By employing a functional renormalization group
approach, we identify non-perturbative regimes of this model where the
nonlinearity makes the system more robust against the influence of dissipation
and can remove the exceptional point altogether. The melting of the exceptional
point occurs above a critical nonlinearity threshold. Interestingly, the
exceptional point melts faster with increasing temperatures, showing a
surprising flow to coherent dynamics when coupled to a warm environment.",2208.11205v2
2022-09-10,"Data-driven, multi-moment fluid modeling of Landau damping","Deriving governing equations of complex physical systems based on first
principles can be quite challenging when there are certain unknown terms and
hidden physical mechanisms in the systems. In this work, we apply a deep
learning architecture to learn fluid partial differential equations (PDEs) of a
plasma system based on the data acquired from a fully kinetic model. The
learned multi-moment fluid PDEs are demonstrated to incorporate kinetic effects
such as Landau damping. Based on the learned fluid closure, the data-driven,
multi-moment fluid modeling can well reproduce all the physical quantities
derived from the fully kinetic model. The calculated damping rate of Landau
damping is consistent with both the fully kinetic simulation and the linear
theory. The data-driven fluid modeling of PDEs for complex physical systems may
be applied to improve fluid closure and reduce the computational cost of
multi-scale modeling of global systems.",2209.04726v1
2022-09-25,Formation of the cosmic-ray halo: The role of nonlinear Landau damping,"We present a nonlinear model of self-consistent Galactic halo, where the
processes of cosmic ray (CR) propagation and excitation/damping of MHD waves
are included. The MHD-turbulence, which prevents CR escape from the Galaxy, is
entirely generated by the resonant streaming instability. The key mechanism
controlling the halo size is the nonlinear Landau (NL) damping, which
suppresses the amplitude of MHD fluctuations and, thus, makes the halo larger.
The equilibrium turbulence spectrum is determined by a balance of CR excitation
and NL damping, which sets the regions of diffusive and advective propagation
of CRs. The boundary $z_{cr}(E)$ between the two regions is the halo size,
which slowly increases with the energy. For the vertical magnetic field of
$\sim 1~\mu G$, we estimate $z_{cr} \sim 1$ kpc for GeV protons. The derived
proton spectrum is in a good agreement with observational data.",2209.12302v1
2022-10-10,Finite time extinction for a critically damped Schr{ö}dinger equation with a sublinear nonlinearity,"This paper completes some previous studies by several authors on the finite
time extinction for nonlinear Schr{\""o}dinger equation when the nonlinear
damping term corresponds to the limit cases of some ``saturating non-Kerr law''
$F(|u|^2)u=\frac{a}{\varepsilon+(|u|^2)^\alpha}u,$ with $a\in\mathbb{C},$
$\varepsilon\geqslant0,$ $2\alpha=(1-m)$ and $m\in[0,1).$ Here we consider the
sublinear case $0<m<1$ with a critical damped coefficient: $a\in\mathbb{C}$ is
assumed to be in the set $D(m)=\big\{z\in\mathbb{C}; \; \mathrm{Im}(z)>0 \text{
and } 2\sqrt{m}\mathrm{Im}(z)=(1-m)\mathrm{Re}(z)\big\}.$ Among other things,
we know that this damping coefficient is critical, for instance, in order to
obtain the monotonicity of the associated operator (see the paper by Liskevich
and Perel'muter [16] and the more recent study by Cialdea and Maz'ya [14]). The
finite time extinction of solutions is proved by a suitable energy method after
obtaining appropiate a priori estimates. Most of the results apply to
non-necessarily bounded spatial domains.",2210.04493v4
2022-10-14,Landau damping for gravitational waves in parity-violating theories,"We discuss how tensor polarizations of gravitational waves can suffer Landau
damping in the presence of velocity birefringence, when parity symmetry is
explicitly broken. In particular, we analyze the role of the Nieh-Yan and
Chern-Simons terms in modified theories of gravity, showing how the
gravitational perturbation in collisionless media can be characterized by a
subluminal phase velocity, circumventing the well-known results of General
Relativity and allowing for the appearance of the kinematic damping. We
investigate in detail the connection between the thermodynamic properties of
the medium, such as temperature and mass of the particles interacting with the
gravitational wave, and the parameters ruling the parity violating terms of the
models. In this respect, we outline how the dispersion relations can give rise
in each model to different regions of the wavenumber space, where the phase
velocity is subluminal, superluminal or does not exist. Quantitative estimates
on the considered models indicate that the phenomenon of Landau damping is not
detectable given the sensitivity of present-day instruments.",2210.07673v2
2022-10-25,Formation of shifted shock for the 3D compressible Euler equations with damping,"In this paper, we show the shock formation of the solutions to the
3-dimensional (3D) compressible isentropic and irrotational Euler equations
with damping for the initial short pulse data which was first introduced by
D.Christodoulou\cite{christodoulou2007}. Due to the damping effect, the
largeness of the initial data is necessary for the shock formation and we will
work on the class of large data (in energy sense). Similar to the undamped
case, the formation of shock is characterized by the collapse of the
characteristic hypersurfaces and the vanishing of the inverse foliation density
function $\mu$, at which the first derivatives of the velocity and the density
blow up. However, the damping effect changes the asymptotic behavior of the
inverse foliation density function $\mu$ and then shifts the time of shock
formation compared with the undamped case. The methods in the paper can also be
extended to a class of $3D$ quasilinear wave equations for the short pulse
initial data.",2210.13796v1
2022-10-30,Dynamics of a class of extensible beams with degenerate and non-degenerate nonlocal damping,"This work is concerned with new results on long-time dynamics of a class of
hyperbolic evolution equations related to extensible beams with three
distinguished nonlocal nonlinear damping terms. In the first possibly
degenerate case, the results feature the existence of a family of compact
global attractors and a thickness estimate for their Kolmogorov's
$\varepsilon$-entropy. Then, in the non-degenerate context, the structure of
the helpful nonlocal damping leads to the existence of finite-dimensional
compact global and exponential attractors. Lastly, in a degenerate and critical
framework, it is proved the existence of a bounded closed global attractor but
not compact. To the proofs, we provide several new technical results by means
of refined estimates that open up perspectives for a new branch of nonlinearly
damped problems.",2210.16851v1
2022-11-11,Nonlinear fractional damped wave equation on compact Lie groups,"In this paper, we deal with the initial value fractional damped wave equation
on $G$, a compact Lie group, with power-type nonlinearity. The aim of this
manuscript is twofold. First, using the Fourier analysis on compact Lie groups,
we prove a local in-time existence result in the energy space for the
fractional damped wave equation on $G$. Moreover, a finite time blow-up result
is established under certain conditions on the initial data. In the next part
of the paper, we consider fractional wave equation with lower order terms, that
is, damping and mass with the same power type nonlinearity on compact Lie
groups, and prove the global in-time existence of small data solutions in the
energy evolution space.",2211.06155v1
2022-11-16,Controlling the motional quality factor of a diamagnetically levitated graphite plate,"Researchers seek methods to levitate matter for a wide variety of purposes,
ranging from exploring fundamental problems in science, through to developing
new sensors and mechanical actuators. Many levitation techniques require active
driving and most can only be applied to objects smaller than a few micrometers.
Diamagnetic levitation has the strong advantage of being the only form of
levitation which is passive, requiring no energy input, while also supporting
massive objects. Known diamagnetic materials which are electrical insulators
are only weakly diamagnetic, and require large magnetic field gradients to
levitate. Strong diamagnetic materials which are electrical conductors, such as
graphite, exhibit eddy damping, restricting motional freedom and reducing their
potential for sensing applications. In this work we describe a method to
engineer the eddy damping while retaining the force characteristics provided by
the diamagnetic material. We study, both experimentally and theoretically, the
motional damping of a magnetically levitated graphite plate in high vacuum and
demonstrate that one can control the eddy damping by patterning the plate with
through-slots which interrupt the eddy currents. We find we can control the
motional quality factor over a wide range with excellent agreement between the
experiment and numerical simulations.",2211.08764v1
2022-12-03,Strong On-Chip Microwave Photon-Magnon Coupling Using Ultra-low Damping Epitaxial Y3Fe5O12 Films at 2 Kelvin,"Y3Fe5O12 is arguably the best magnetic material for magnonic quantum
information science (QIS) because of its extremely low damping. We report
ultralow damping at 2 K in epitaxial Y3Fe5O12 thin films grown on a diamagnetic
Y3Sc2Ga3O12 substrate that contains no rare-earth elements. Using these
ultralow damping YIG films, we demonstrate for the first time strong coupling
between magnons in patterned YIG thin films and microwave photons in a
superconducting Nb resonator. This result paves the road towards scalable
hybrid quantum systems that integrate superconducting microwave resonators, YIG
film magnon conduits, and superconducting qubits into on-chip QIS devices.",2212.01708v1
2022-12-21,Fractional damping effects on the transient dynamics of the Duffing oscillator,"We consider the nonlinear Duffing oscillator in presence of fractional
damping which is characteristic in different physical situations. The system is
studied with a smaller and larger damping parameter value, that we call the
underdamped and overdamped regimes. In both we have studied the relation
between the fractional parameter, the amplitude of the oscillations and the
times to reach the asymptotic behavior, called asymptotic times. In the
overdamped regime, the study shows that, also here, there are oscillations for
fractional order derivatives and their amplitudes and asymptotic times can
suddenly change for small variations of the fractional parameter. In addition,
in this latter regime, a resonant-like behavior can take place for suitable
values of the parameters of the system. These results are corroborated by
calculating the corresponding Q-factor. We expect that these results can be
useful for a better understanding of fractional dynamics and its possible
applications as in modeling different kind of materials that normally need
complicated damping terms.",2212.11023v1
2023-01-02,Fast convex optimization via closed-loop time scaling of gradient dynamics,"In a Hilbert setting, for convex differentiable optimization, we develop a
general framework for adaptive accelerated gradient methods. They are based on
damped inertial dynamics where the coefficients are designed in a closed-loop
way. Specifically, the damping is a feedback control of the velocity, or of the
gradient of the objective function. For this, we develop a closed-loop version
of the time scaling and averaging technique introduced by the authors. We thus
obtain autonomous inertial dynamics which involve vanishing viscous damping and
implicit Hessian driven damping. By simply using the convergence rates for the
continuous steepest descent and Jensen's inequality, without the need for
further Lyapunov analysis, we show that the trajectories have several
remarkable properties at once: they ensure fast convergence of values, fast
convergence of the gradients towards zero, and they converge to optimal
solutions. Our approach leads to parallel algorithmic results, that we study in
the case of proximal algorithms. These are among the very first general results
of this type obtained using autonomous dynamics.",2301.00701v1
2023-01-19,Damped harmonic oscillator revisited: the fastest route to equilibrium,"Theoretically, solutions of the damped harmonic oscillator asymptotically
approach equilibrium, i.e., the zero energy state, without ever reaching it
exactly, and the critically damped solution approaches equilibrium faster than
the underdamped or the overdamped solution. Experimentally, the systems
described with this model reach equilibrium when the system's energy has
dropped below some threshold corresponding to the energy resolution of the
measuring apparatus. We show that one can (almost) always find an optimal
underdamped solution that will reach this energy threshold sooner than all
other underdamped solutions, as well as the critically damped solution, no
matter how small this threshold is. We also comment on one exception to this
for a particular type of initial conditions, when a specific overdamped
solution reaches the equilibrium state sooner than all other solutions. We
confirm some of our findings experimentally.",2301.08222v2
2023-01-22,Boundary stabilization of a vibrating string with variable length,"We study small vibrations of a string with time-dependent length $\ell(t)$
and boundary damping. The vibrations are described by a 1-d wave equation in an
interval with one moving endpoint at a speed $\ell'(t)$ slower than the speed
of propagation of the wave c=1. With no damping, the energy of the solution
decays if the interval is expanding and increases if the interval is shrinking.
The energy decays faster when the interval is expanding and a constant damping
is applied at the moving end. However, to ensure the energy decay in a
shrinking interval, the damping factor $\eta$ must be close enough to the
optimal value $\eta=1$, corresponding to the transparent condition. In all
cases, we establish lower and upper estimates for the energy with explicit
constants.",2301.09086v1
2023-02-24,Asymptotic behaviour of the semidiscrete FE approximations to weakly damped wave equations with minimal smoothness on initial data,"Exponential decay estimates of a general linear weakly damped wave equation
are studied with decay rate lying in a range. Based on the $C^0$-conforming
finite element method to discretize spatial variables keeping temporal variable
continuous, a semidiscrete system is analysed, and uniform decay estimates are
derived with precisely the same decay rate as in the continuous case. Optimal
error estimates with minimal smoothness assumptions on the initial data are
established, which preserve exponential decay rate, and for a 2D problem, the
maximum error bound is also proved. The present analysis is then generalized to
include the problems with non-homogeneous forcing function, space-dependent
damping, and problems with compensator. It is observed that decay rates are
improved with large viscous damping and compensator. Finally, some numerical
experiments are performed to validate the theoretical results established in
this paper.",2302.12476v1
2023-02-27,Nonlinear acoustic imaging with damping,"In this paper, we consider an inverse problem for a nonlinear wave equation
with a damping term and a general nonlinear term. This problem arises in
nonlinear acoustic imaging and has applications in medical imaging and other
fields. The propagation of ultrasound waves can be modeled by a quasilinear
wave equation with a damping term. We show the boundary measurements encoded in
the Dirichlet-to-Neumann map (DN map) determine the damping term and the
nonlinearity at the same time. In a more general setting, we consider a
quasilinear wave equation with a one-form (a first-order term) and a general
nonlinear term. We prove the one-form and the nonlinearity can be determined
from the DN map, up to a gauge transformation, under some assumptions.",2302.14174v1
2023-04-11,Sizable suppression of magnon Hall effect by magnon damping in Cr$_2$Ge$_2$Te$_6$,"Two-dimensional (2D) Heisenberg honeycomb ferromagnets are expected to have
interesting topological magnon effects as their magnon dispersion can have
Dirac points. The Dirac points are gapped with finite second nearest neighbor
Dzyaloshinskii-Moriya interaction, providing nontrivial Berry curvature with
finite magnon Hall effect. Yet, it is unknown how the topological properties
are affected by magnon damping. We report the thermal Hall effect in
Cr$_2$Ge$_2$Te$_6$, an insulating 2D honeycomb ferromagnet with a large Dirac
magnon gap and significant magnon damping. Interestingly, the thermal Hall
conductivity in Cr$_2$Ge$_2$Te$_6$ shows the coexisting phonon and magnon
contributions. Using an empirical two-component model, we successfully estimate
the magnon contribution separate from the phonon part, revealing that the
magnon Hall conductivity was 20 times smaller than the theoretical calculation.
Finally, we suggest that such considerable suppression in the magnon Hall
conductivity is due to the magnon damping effect in Cr$_2$Ge$_2$Te$_6$.",2304.04922v1
2023-04-22,Video analysis of the damped oscillations of Pohl's pendulum,"In this paper problems that arose with the introduction of distance learning
in physics at the Technical University of Sofia due to the COVID-19 pandemic
and the imposition of video recording of laboratory exercises are indicated. It
was found that the video for the ''Damped Mechanical Oscillations'' exercise
provides enough information for a more detailed and in-depth analysis of the
studied phenomenon compared to the standard way of capturing the data. The
Video Editor program was used to view the video frame by frame and statistical
processing - non-linear regression - was performed with the recorded data. The
laboratory results are compared with the theoretical function, the parameters
of which are optimized as a result of the specified processing. A theoretical
model of the damped oscillation is described and the dependence of the damping
coefficient on the current through the electromagnetic brake is theoretically
investigated.",2304.11390v1
2023-05-22,Semi-active damping optimization of vibrational systems using the reduced basis method,"In this article, we consider vibrational systems with semi-active damping
that are described by a second-order model. In order to minimize the influence
of external inputs to the system response, we are optimizing some damping
values. As minimization criterion, we evaluate the energy response, that is the
$\cH_2$-norm of the corresponding transfer function of the system. Computing
the energy response includes solving Lyapunov equations for different damping
parameters. Hence, the minimization process leads to high computational costs
if the system is of large dimension. We present two techniques that reduce the
optimization problem by applying the reduced basis method to the corresponding
parametric Lyapunov equations. In the first method, we determine a reduced
solution space on which the Lyapunov equations and hence the resulting energy
response values are computed approximately in a reasonable time. The second
method includes the reduced basis method in the minimization process. To
evaluate the quality of the approximations, we introduce error estimators that
evaluate the error in the controllability Gramians and the energy response.
Finally, we illustrate the advantages of our methods by applying them to two
different examples.",2305.12946v1
2023-06-01,A combined volume penalization / selective frequency damping approach for immersed boundary methods: application to moving geometries,"This work extends, to moving geometries, the immersed boundary method based
on volume penalization and selective frequency damping approach [J. Kou, E.
Ferrer, A combined volume penalization/selective frequency damping approach for
immersed boundary methods applied to high-order schemes, Journal of
Computational Physics (2023)]. To do so, the numerical solution inside the
solid is decomposed into a predefined movement and an oscillatory part
(spurious waves), where the latter is damped by an SFD approach combined with
volume penalization. We challenge the method with two cases. First, a new
manufactured solution problem is proposed to show that the method can recover
high-order accuracy. Second, we validate the methodology by simulating the
laminar flow past a moving cylinder, where improved accuracy of the combined
method is reported.",2306.00504v1
2023-06-09,Damped nonlinear Schrödinger equation with Stark effect,"We study the $L^2$-critical damped NLS with a Stark potential. We prove that
the threshold for global existence and finite time blowup of this equation is
given by $\|Q\|_2$, where $Q$ is the unique positive radial solution of $\Delta
Q + |Q|^{4/d} Q = Q$ in $H^1(\mathbb{R}^d)$. Moreover, in any small
neighborhood of $Q$, there exists an initial data $u_0$ above the ground state
such that the solution flow admits the log-log blowup speed. This verifies the
structural stability for the ``$\log$-$\log$ law'' associated to the NLS
mechanism under the perturbation by a damping term and a Stark potential. The
proof of our main theorem is based on the Avron-Herbst formula and the
analogous result for the unperturbed damped NLS.",2306.05931v1
2023-06-19,New Perspectives and Systematic Approaches for Analyzing Negative Damping-Induced Sustained Oscillation,"Sustained oscillations (SOs) are commonly observed in systems dominated by
converters. Under specific conditions, even though the origin of SOs can be
identified through negative damping modes using conventional linear analysis,
utilizing the describing function to compute harmonic amplitude and frequency
remains incomplete. This is because a) it can not cover the cases where hard
limits are not triggered, and b) it can not provide a complete trajectory for
authentic linear analysis to confirm the presence of SO. Hence, two analytical
methods are proposed by returning to the essential principle of harmonic
balance. a) A dedicated approach is proposed to solving steady-state harmonics
via Newton-Raphson iteration with carefully chosen initial values. The method
encompasses all potential hard limit triggered cases. b) By employing extended
multiharmonic linearization theory and considering loop impedance, an authentic
linear analysis of SO is conducted. The analysis indicates that the initial
negative damping modes transform into multiple positive damping modes as SO
develops. Simulation validations are performed on a two-level voltage source
converter using both PSCAD and RT-LAB. Additionally, valuable insights into the
work are addressed considering the modularity and scalability of the proposed
methods.",2306.10839v2
2023-06-24,Numerical approximation of the invariant distribution for a class of stochastic damped wave equations,"We study a class of stochastic semilinear damped wave equations driven by
additive Wiener noise. Owing to the damping term, under appropriate conditions
on the nonlinearity, the solution admits a unique invariant distribution. We
apply semi-discrete and fully-discrete methods in order to approximate this
invariant distribution, using a spectral Galerkin method and an exponential
Euler integrator for spatial and temporal discretization respectively. We prove
that the considered numerical schemes also admit unique invariant
distributions, and we prove error estimates between the approximate and exact
invariant distributions, with identification of the orders of convergence. To
the best of our knowledge this is the first result in the literature concerning
numerical approximation of invariant distributions for stochastic damped wave
equations.",2306.13998v1
2023-07-31,Estimation of Power in the Controlled Quantum Teleportation through the Witness Operator,"Controlled quantum teleportation (CQT) can be considered as a variant of
quantum teleportation in which three parties are involved where one party acts
as the controller. The usability of the CQT scheme depends on two types of
fidelities viz. conditioned fidelity and non-conditioned fidelity. The
difference between these fidelities may be termed as power of the controller
and it plays a vital role in the CQT scheme. Thus, our aim is to estimate the
power of the controller in such a way so that its estimated value can be
obtained in an experiment. To achieve our goal, we have constructed a witness
operator and have shown that its expected value may be used in the estimation
of the lower bound of the power of the controller. Furthermore, we have shown
that it is possible to make the standard W state useful in the CQT scheme if
one of its qubits either passes through the amplitude damping channel or the
phase damping channel. We have also shown that the phase damping channel
performs better than the amplitude damping channel in the sense of generating
more power of the controller in the CQT scheme.",2307.16574v1
2023-08-03,Triple-Spherical Bessel Function Integrals with Exponential and Gaussian Damping: Towards an Analytic N-Point Correlation Function Covariance Model,"Spherical Bessel functions appear commonly in many areas of physics wherein
there is both translation and rotation invariance, and often integrals over
products of several arise. Thus, analytic evaluation of such integrals with
different weighting functions (which appear as toy models of a given physical
observable, such as the galaxy power spectrum) is useful. Here we present a
generalization of a recursion-based method for evaluating such integrals. It
gives relatively simple closed-form results in terms of Legendre functions (for
the exponentially-damped case) and Gamma, incomplete Gamma functions, and
hypergeometric functions (for the Gaussian-damped case). We also present a new,
non-recursive method to evaluate integrals of products of spherical Bessel
functions with Gaussian damping in terms of incomplete Gamma functions and
hypergeometric functions.",2308.01955v2
2023-08-28,Quantized damped transversal single particle mechanical waves,"In information transfer, the dissipation of a signal may have crucial
importance. The feasibility of reconstructing the distorted signal also depends
on this. That is why the study of quantized dissipative transversal single
particle mechanical waves may have an important role. It may be true,
particularly on the nanoscale in the case of signal distortion, loss, or
restoration. Based on the damped oscillator quantum description, we generalize
the canonical quantization procedure for the transversal waves. Furthermore, we
deduce the related damped wave equation and the state function. We point out
the two kinds of solutions of the wave equation. One involves the well-known
spreading solution superposed with the oscillation, in which the loss of
information is complete. The other is the Airy function solution, which is
non-spreading, so there is information loss only due to oscillation damping.
However, the structure of the wavefront remains unchanged. Thus, this result
allows signal reconstruction, which is important in restoring the lost
information.",2308.14820v1
2023-11-15,Integrated Local Energy Decay for Damped Magnetic Wave Equations on Stationary Space-Times,"We establish local energy decay for damped magnetic wave equations on
stationary, asymptotically flat space-times subject to the geometric control
condition. More specifically, we allow for the addition of time-independent
magnetic and scalar potentials, which negatively affect energy coercivity and
may add in unwieldy spectral effects. By asserting the non-existence of
eigenvalues in the lower half-plane and resonances on the real line, we are
able to apply spectral theory from the work of Metcalfe, Sterbenz, and Tataru
and combine with a generalization of prior work by the present author to extend
the latter work and establish local energy decay, under one additional symmetry
hypothesis. Namely, we assume that either the imaginary part of the magnetic
potentials are uniformly small or, more interestingly and novelly, that the
damping term is the dominant principal term in the skew-adjoint part of the
damped wave operator within the region where the metric perturbation from that
of Minkowski space is permitted to be large. We also obtain an energy dichotomy
if we do not prohibit non-zero real resonances. In order to make the structure
of the argument more cohesive, we contextualize the present work within
requisite existing theory.",2311.08628v1
2023-11-15,Applications of $L^p-L^q$ estimates for solutions to semi-linear $σ$-evolution equations with general double damping,"In this paper, we would like to study the linear Cauchy problems for
semi-linear $\sigma$-evolution models with mixing a parabolic like damping term
corresponding to $\sigma_1 \in [0,\sigma/2)$ and a $\sigma$-evolution like
damping corresponding to $\sigma_2 \in (\sigma/2,\sigma]$. The main goals are
on the one hand to conclude some estimates for solutions and their derivatives
in $L^q$ setting, with any $q\in [1,\infty]$, by developing the theory of
modified Bessel functions effectively to control oscillating integrals
appearing the solution representation formula in a competition between these
two kinds of damping. On the other hand, we are going to prove the global (in
time) existence of small data Sobolev solutions in the treatment of the
corresponding semi-linear equations by applying $(L^{m}\cap L^{q})- L^{q}$ and
$L^{q}- L^{q}$ estimates, with $q\in (1,\infty)$ and $m\in [1,q)$, from the
linear models. Finally, some further generalizations will be discussed in the
end of this paper.",2311.09085v1
2023-11-23,"Friction of a driven chain: Role of momentum conservation, Goldstone and radiation modes","We analytically study friction and dissipation of a driven bead in a 1D
harmonic chain, and analyze the role of internal damping mechanism as well as
chain length. Specifically, we investigate Dissipative Particle Dynamics and
Langevin Dynamics, as paradigmatic examples that do and do not display
translational symmetry, with distinct results: For identical parameters, the
friction forces can differ by many orders of magnitude. For slow driving, a
Goldstone mode traverses the entire system, resulting in friction of the driven
bead that grows arbitrarily large (Langevin) or gets arbitrarily small
(Dissipative Particle Dynamics) with system size. For a long chain, the
friction for DPD is shown to be bound, while it shows a singularity (i.e. can
be arbitrarily large) for Langevin damping. For long underdamped chains, a
radiation mode is recovered in either case, with friction independent of
damping mechanism. For medium length chains, the chain shows the expected
resonant behavior. At the resonance, friction is non-analytic in damping
parameter $\gamma$, depending on it as $\gamma^{-1}$. Generally, no zero
frequency bulk friction coefficient can be determined, as the limits of small
frequency and infinite chain length do not commute, and we discuss the regimes
where ""simple"" macroscopic friction occurs.",2311.14075v1
2023-12-07,Generalized Damping Torque Analysis of Ultra-Low Frequency Oscillation in the Jerk Space,"Ultra low frequency oscillation (ULFO) is significantly threatening the power
system stability. Its unstable mechanism is mostly studied via generalized
damping torque analysis method (GDTA). However, the analysis still adopts the
framework established for low frequency oscillation. Hence, this letter
proposes a GDTA approach in the jerk space for ULFO. A multi-information
variable is constructed to transform the system into a new state space, where
it is found that the jerk dynamics of the turbine-generator cascaded system is
a second-order differential equation. Benefiting from this characteristic, we
propose a new form for GDTA using jerk dynamics, which is established in the
frequency-frequency acceleration phase space. Then, analytical expressions of
all damping torque are provided. Finally, test results verified the proposed
theoretical results. The negative damping mechanism is revealed, and parameter
adjustment measures are concluded.",2312.04148v1
2023-12-08,Selective damping of plasmons in coupled two-dimensional systems by Coulomb drag,"The Coulomb drag is a many-body effect observed in proximized low-dimensional
systems. It appears as emergence of voltage in one of them upon passage of bias
current in another. The magnitude of drag voltage can be strongly affected by
exchange of plasmonic excitations between the layers; however, the reverse
effect of Coulomb drag on properties of plasmons has not been studied. Here, we
study the plasmon spectra and damping in parallel two-dimensional systems in
the presence of Coulomb drag. We find that Coulomb drag leads to selective
damping of one of the two fundamental plasma modes of a coupled bilayer. For
identical electron doping of both layers, the drag suppresses the acoustic
plasma mode; while for symmetric electron-hole doping of the coupled pair, the
drag suppresses the optical plasma mode. The selective damping can be observed
both for propagating modes in extended bilayers and for localized plasmons in
bilayers confined by source and drain contacts. The discussed effect may
provide access to the strength of Coulomb interaction in 2d electron systems
from various optical and microwave scattering experiments.",2312.05097v1
2023-12-13,Geometrical Interpretation of Neutrino Oscillation with decay,"The geometrical representation of two-flavor neutrino oscillation represents
the neutrino's flavor eigenstate as a magnetic moment-like vector that evolves
around a magnetic field-like vector that depicts the Hamiltonian of the system.
In the present work, we demonstrate the geometrical interpretation of neutrino
in a vacuum in the presence of decay, which transforms this circular trajectory
of neutrino into a helical track that effectively makes the neutrino system
mimic a classical damped driven oscillator. We show that in the absence of the
phase factor $\xi$ in the decay Hamiltonian, the neutrino exactly behaves like
the system of nuclear magnetic resonance(NMR); however, the inclusion of the
phase part introduces a $CP$ violation, which makes the system deviate from
NMR. Finally, we make a qualitative discussion on under-damped,
critically-damped, and over-damped scenarios geometrically by three different
diagrams. In the end, we make a comparative study of geometrical picturization
in vacuum, matter, and decay, which extrapolates the understanding of the
geometrical representation of neutrino oscillation in a more straightforward
way.",2312.08178v1
2023-12-14,Smoluchowski-Kramers diffusion approximation for systems of stochastic damped wave equations with non-constant friction,"We consider systems of damped wave equations with a state-dependent damping
coefficient and perturbed by a Gaussian multiplicative noise. Initially, we
investigate their well-posedness, under quite general conditions on the
friction. Subsequently, we study the validity of the so-called
Smoluchowski-Kramers diffusion approximation. We show that, under more
stringent conditions on the friction, in the small-mass limit the solution of
the system of stochastic damped wave equations converges to the solution of a
system of stochastic quasi-linear parabolic equations. In this convergence, an
additional drift emerges as a result of the interaction between the noise and
the state-dependent friction. The identification of this limit is achieved by
using a suitable generalization of the classical method of perturbed test
functions, tailored to the current infinite dimensional setting.",2312.08925v1
2023-12-28,Cause-effect relationship between model parameters and damping performance of hydraulic shock absorbers,"Despite long-term research and development of modern shock absorbers, the
effect of variations of several crucial material and model parameters still
remains dubious. The goal of this work is therefore a study of the changes of
shock absorber dynamics with respect to typical parameter ranges in a realistic
model. We study the impact of shim properties, as well as geometric features
such as discharge coefficients and bleed orifice cross section. We derive
cause-effect relationships by nonlinear parameter fitting of the differential
equations of the model and show digressive and progressive quadratic damping
curves for shim number and thickness, sharp exponential curves for discharge
coefficients, and leakage width, as well as a linear decrease of damping
properties with bleed orifice area. Temperature increase affecting material
properties, such as density and viscosity of the mineral oil, is found to have
a mostly linear relationship with damping and pressure losses. Our results are
not only significant for the general understanding of shock absorber dynamics,
but also serve as a guidance for the development of specific models by
following the proposed methodology.",2312.17175v1
2024-01-01,Magnon Damping Minimum and Logarithmic Scaling in a Kondo-Heisenberg Model,"Recently, an anomalous temperature evolution of spin wave excitations has
been observed in a van der Waals metallic ferromagnet Fe$_3$GeTe$_2$ (FGT) [S.
Bao, et al., Phys. Rev. X 12, 011022 (2022)], whose theoretical understanding
yet remains elusive. Here we study the spin dynamics of a ferromagnetic
Kondo-Heisenberg lattice model at finite temperature, and propose a mechanism
of magnon damping that explains the intriguing experimental results. In
particular, we find the magnon damping rate $\gamma(T)$ firstly decreases as
temperature lowers, due to the reduced magnon-magnon scatterings. It then
reaches a minimum at $T_{\rm d}^*$, and rises up again following a logarithmic
scaling $\gamma(T) \sim \ln{(T_0/T)}$ (with $T_0$ a constant) for $T < T_{\rm
d}^*$, which can be attributed to electron-magnon scatterings of spin-flip
type. Moreover, we obtain the phase diagram containing the ferromagnetic and
Kondo insulator phases by varying the Kondo coupling, which may be relevant for
experiments on pressured FGT. The presence of a magnon damping minimum and
logarithmic scaling at low temperature indicates the emergence of the Kondo
effect reflected in the collective excitations of local moments in a Kondo
lattice system.",2401.00758v1
2024-01-04,Simplified Information Geometry Approach for Massive MIMO-OFDM Channel Estimation -- Part II: Convergence Analysis,"In Part II of this two-part paper, we prove the convergence of the simplified
information geometry approach (SIGA) proposed in Part I. For a general Bayesian
inference problem, we first show that the iteration of the common second-order
natural parameter (SONP) is separated from that of the common first-order
natural parameter (FONP). Hence, the convergence of the common SONP can be
checked independently. We show that with the initialization satisfying a
specific but large range, the common SONP is convergent regardless of the value
of the damping factor. For the common FONP, we establish a sufficient condition
of its convergence and prove that the convergence of the common FONP relies on
the spectral radius of a particular matrix related to the damping factor. We
give the range of the damping factor that guarantees the convergence in the
worst case. Further, we determine the range of the damping factor for massive
MIMO-OFDM channel estimation by using the specific properties of the
measurement matrices. Simulation results are provided to confirm the
theoretical results.",2401.02037v1
2024-01-04,A Pure Integral-Type PLL with a Damping Branch to Enhance the Stability of Grid-Tied Inverter under Weak Grids,"In a phase-locked loop (PLL) synchronized inverter, due to the strong
nonlinear coupling between the PLL's parame-ters and the operation power angle,
the equivalent damping coefficient will quickly deteriorate while the power
angle is close to 90{\deg} under an ultra-weak grid, which causes the
synchronous instability. To address this issue, in this letter, a pure
integral-type phase-locked loop (IPLL) with a damping branch is proposed to
replace the traditional PI-type PLL. The equivalent damping coefficient of an
IPLL-synchronized inverter is decoupled with the steady-state power angle. As a
result, the IPLL-synchronized inverter can stably operate under an ultra-weak
grid when the equilibrium point exists. Finally, time-domain simulation results
verify the effectiveness and correctness of the proposed IPLL.",2401.02202v1
2024-01-05,Solving convex optimization problems via a second order dynamical system with implicit Hessian damping and Tikhonov regularization,"This paper deals with a second order dynamical system with a Tikhonov
regularization term in connection to the minimization problem of a convex
Fr\'echet differentiable function. The fact that beside the asymptotically
vanishing damping we also consider an implicit Hessian driven damping in the
dynamical system under study allows us, via straightforward explicit
discretization, to obtain inertial algorithms of gradient type. We show that
the value of the objective function in a generated trajectory converges rapidly
to the global minimum of the objective function and depending the Tikhonov
regularization parameter the generated trajectory converges weakly to a
minimizer of the objective function or the generated trajectory converges
strongly to the element of minimal norm from the $\argmin$ set of the objective
function. We also obtain the fast convergence of the velocities towards zero
and some integral estimates. Our analysis reveals that the Tikhonov
regularization parameter and the damping parameters are strongly correlated,
there is a setting of the parameters that separates the cases when weak
convergence of the trajectories to a minimizer and strong convergence of the
trajectories to the minimal norm minimizer can be obtained.",2401.02676v1
2024-01-16,"Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron","Hybrid magnonic quantum systems have drawn increased attention in recent
years for coherent quantum information processing, but too large magnetic
damping is a persistent concern when metallic magnets are used. Their intrinsic
damping is largely determined by electron-magnon scattering induced by
spin-orbit interactions. In the low scattering limit, damping is dominated by
intra-band electronic transitions, which has been theoretically shown to be
proportional to the electronic density of states at the Fermi level. In this
work, we focus on body-centered-cubic iron as a paradigmatic ferromagnetic
material. We comprehensively study its electronic structure using
first-principles density functional theory simulations and account for finite
lattice temperature, boron (B) doping, and structure amorphization. Our results
indicate that temperature induced atomic disorder and amorphous atomic
geometries only have a minor influence. Instead, boron doping noticeably
decreases the density of states near the Fermi level with an optimal doping
level of 6.25%. In addition, we show that this reduction varies significantly
for different atomic geometries and report that the highest reduction
correlates with a large magnetization of the material. This may suggest
materials growth under external magnetic fields as a route to explore in
experiment.",2401.08076v1
2024-01-16,Waves in strong centrifugal filed: dissipative gas,"In the fast rotating gas (with the velocity typical for Iguassu gas
centrifuge) three families of linear waves exist with different polarizations
and law of dispersion. The energy of the waves is basically concentrated at the
axis of rotation in the rarefied region. Therefore these waves decay on the
distance comparable with the wavelength. There is only one type of waves
propagating strictly along the axis of rotation with the law of dispersion
similar to ordinary acoustic waves. These waves are interested for the physics
of gas centrifuges. The energy density of these waves concentrates at the wall
of the rotor. These waves have weak damping due to the molecular viscosity and
heat conductivity. The damping coefficient is determined for this type of waves
by numerical calculations. Analytical approximations for the damping
coefficient is defined as well. At the parameters typical for the Iguassu
centrifuge the damping is defined by interaction of the waves with the rotor
wall.",2401.08240v1
2024-01-19,Upper bound of the lifespan of the solution to the nonlinear fractional wave equations with time-dependent damping,"In this paper, we study the Cauchy problem of the nonlinear wave equation
with fractional Laplacian and time-dependent damping. Firstly, we derive the
weighted Sobolev estimate of the solution operators for the linear wave
equation with the damping of constant coefficient, and prove the local
existence and uniqueness in the weighted Sobolev space for the power-type
nonlinearity and $b(t)\in L^\infty$, by the contraction mapping principle.
Secondly, we consider the case of the source nonlinearity $f(u)\approx |u|^p$.
In the subcritical and critical cases $1<p\leq p_c=1+\frac \sigma N$, based on
the blow-up result on the ordinary differential inequality, we could prove the
blow-up of the solution and obtain the upper bound of the lifespan. And the
upper bound of the lifespan in the critical case is independent on the
coefficient of the time-dependent damping and is completely new even if the
classical case $b(t)=1$.",2401.10552v1
2024-03-13,Effects of wave damping and finite perpendicular scale on three-dimensional Alfvén wave parametric decay in low-beta plasmas,"Shear Alfven wave parametric decay instability (PDI) provides a potential
path toward significant wave dissipation and plasma heating. However,
fundamental questions regarding how PDI is excited in a realistic
three-dimensional (3D) open system and how critically the finite perpendicular
wave scale -- as found in both the laboratory and space plasmas -- affects the
excitation remain poorly understood. Here, we present the first 3D,
open-boundary, hybrid kinetic-fluid simulations of kinetic Alfven wave PDI in
low-beta plasmas. Key findings are that the PDI excitation is strongly limited
by the wave damping present, including electron-ion collisional damping
(represented by a constant resistivity) and geometrical attenuation associated
with the finite-scale Alfven wave, and ion Landau damping of the child acoustic
wave. The perpendicular wave scale alone, however, plays no discernible role,
with different wave scales exhibiting similar instability growth. These
findings are corroborated by theoretical analysis and estimates. The new
understanding of 3D kinetic Alfven wave PDI physics is essential for laboratory
study of the basic plasma process and may also help evaluate the relevance/role
of PDI in low-beta space plasmas.",2403.08179v1
2024-03-19,Polarization Dynamics in Paramagnet of Charged Quark-Gluon Plasma,"It is commonly understood that the strong magnetic field produced in heavy
ion collisions is short-lived. The electric conductivity of the quark-gluon
plasma is unable to significantly extend the life time of magnetic field. We
propose an alternative scenario to achieve this: with finite baryon density and
spin polarization by the initial magnetic field, the quark-gluon plasma behaves
as a paramagnet, which may continue to polarize quark after fading of initial
magnetic field. We confirm this picture by calculations in both quantum
electrodynamics and quantum chromodynamics. In the former case, we find a
splitting in the damping rates of probe fermion with opposite spin component
along the magnetic field with the splitting parametrically small than the
average damping rate. In the latter case, we find a similar splitting in the
damping rates of probe quark with opposite spin components along the magnetic
field. The splitting is parametrically comparable to the average damping rate,
providing an efficient way of polarizing strange quarks by the quark-gluon
plasma paramagnet consisting of light quarks.",2403.12615v1
2024-03-25,Radiation damping of a Rayleigh scatterer illuminated by a plane wave,"We investigate the radiation damping experienced by a dielectric spherical
particle when it is illuminated by an electromagnetic plane wave within the
Rayleigh regime. We derive the equivalent electric dipole of the moving
particle and subsequently calculate the electromagnetic force acting on it from
two different approaches. In the first approach, we calculate the force from
the integration of stress tensor and field momentum. In the second one, we
calculate the force directly from the integration of the force density. Our
derivations reveal that the damping coefficient is equal to $6P_{scat}/mc^2$
along the propagation direction, whereas it is $P_{scat}/mc^2$ along
perpendicular directions. Here, $P_{scat}$ denotes the power scattered by the
particle, and $mc^2$ represents the particle's mass energy. The radiation
damping derived in this study sets upper limits on the quality factor of
optically levitated objects and ensures the existence of a steady-state
solution of the particle's dynamics.",2403.16618v1
2006-04-14,The UCSD Radio-Selected Quasar Survey for Damped Lyman alpha System,"As large optical quasar surveys for damped Lya become a reality and the study
of star forming gas in the early Universe achieves statistical robustness, it
is now vital to identify and quantify the sources of systematic error. Because
the nature of optically-selected quasar surveys makes them vulnerable to dust
obscuration, we have undertaken a radio-selected quasar survey for damped Lya
systems to address this bias. We present the definition and results of this
survey. We then combine our sample with the CORALS dataset to investigate the
HI column density distribution function f(N) of damped Lya systems toward
radio-selected quasars. We find that f(N) is well fit by a power-law f(N) = k_1
N^alpha_1, with log k_1 = 22.90 and alpha_1 = -2.18. This power-law is in
excellent agreement with that of optically-selected samples at low N(HI), an
important yet expected result given that obscuration should have negligible
effect at these gas columns. However, because of the relatively small size of
the radio-selected sample, 26 damped Lya systems in 119 quasars, f(N) is not
well constrained at large N(HI) and the first moment of the HI distribution
function, Omega_g, is, strictly speaking, a lower limit. The power-law is steep
enough, however, that extrapolating it to higher column densities implies only
a modest, logarithmic increase in Omega_g. The radio-selected value of Omega_g
= 1.15 x 10^-3, agrees well with the results of optically-selected surveys.
While our results indicate that dust obscuration is likely not a major issue
for surveys of damped Lya systems, we estimate that a radio-selected sample of
approximately 100 damped Lya systems will be required to obtain the precision
necessary to absolutely confirm an absence of dust bias.",0604334v1
2012-04-12,Evidence of Gunn-Peterson damping wings in high-z quasar spectra: strengthening the case for incomplete reionization,"The spectra of several high-redshift (z>6) quasars have shown evidence for a
Gunn-Peterson (GP) damping wing, indicating a substantial mean neutral hydrogen
fraction (x_HI > 0.03) in the z ~ 6 intergalactic medium (IGM). However,
previous analyses assumed that the IGM was uniformly ionized outside of the
quasar's HII region. Here we relax this assumption and model patchy
reionization scenarios for a range of IGM and quasar parameters. We quantify
the impact of these differences on the inferred x_HI, by fitting the spectra of
three quasars: SDSS J1148+5251 (z=6.419), J1030+0524 (z=6.308), and J1623+3112
(z=6.247). We find that the best-fit values of x_HI in the patchy models agree
well with the uniform case. More importantly, we confirm that the observed
spectra favor the presence of a GP damping wing, with peak likelihoods
decreasing by factors of > few - 10 when the spectra are modeled without a
damping wing. We also find that the Ly alpha absorption spectra, by themselves,
cannot distinguish the damping wing in a relatively neutral IGM from a damping
wing in a highly ionized IGM, caused either by an isolated neutral patch, or by
a damped Ly alpha absorber (DLA). However, neutral patches in a highly ionized
universe (x_HI < 0.01), and DLAs with the large required column densities (N_HI
> few x 10^{20} cm^{-2}) are both rare. As a result, when we include reasonable
prior probabilities for the line of sight (LOS) to intercept either a neutral
patch or a DLA at the required distance of ~ 40-60 comoving Mpc away from the
quasar, we find strong lower limits on the neutral fraction in the IGM, x_HI >
0.1 (at 95% confidence). This strengthens earlier claims that a substantial
global fraction of hydrogen in the z~6 IGM is in neutral form.",1204.2838v2
2013-05-31,Highly inclined and eccentric massive planets I: Planet-disc interactions,"In the Solar System, planets have a small inclination with respect to the
equatorial plane of the Sun, but there is evidence that in extrasolar systems
the inclination can be very high. This spin-orbit misalignment is unexpected,
as planets form in a protoplanetary disc supposedly aligned with the stellar
spin. Planet-planet interactions are supposed to lead to a mutual inclination,
but the effects of the protoplanetary disc are still unknown. We investigate
therefore planet-disc interactions for planets above 1M_Jup. We check the
influence of the inclination i, eccentricity e, and mass M_p of the planet. We
perform 3D numerical simulations of protoplanetary discs with embedded
high-mass planets. We provide damping formulae for i and e as a function of i,
e, and M_p that fit the numerical data. For highly inclined massive planets,
the gap opening is reduced, and the damping of i occurs on time-scales of the
order of 10^-4 deg/yr M_disc/(0.01 M_star) with the damping of e on a smaller
time-scale. While the inclination of low planetary masses (<5M_Jup) is always
damped, large planetary masses with large i can undergo a Kozai-cycle with the
disc. These Kozai-cycles are damped in time. Eccentricity is generally damped,
except for very massive planets (M_p = 5M_Jup) where eccentricity can increase
for low inclinations. The dynamics tends to a final state: planets end up in
midplane and can then, over time, increase their eccentricity as a result of
interactions with the disc. The interactions with the disc lead to damping of i
and e after a scattering event of high-mass planets. If i is sufficiently
reduced, the eccentricity can be pumped up because of interactions with the
disc. If the planet is scattered to high inclination, it can undergo a
Kozai-cycle with the disc that makes it hard to predict the exact movement of
the planet and its orbital parameters at the dispersal of the disc.",1305.7330v1
2014-10-20,Frequency-dependent attenuation and elasticity in unconsolidated earth materials: effect of damping,"We use the Discrete Element Method (DEM) to understand the underlying
attenuation mechanism in granular media, with special applicability to the
measurements of the so-called effective mass developed earlier. We consider
that the particles interact via Hertz-Mindlin elastic contact forces and that
the damping is describable as a force proportional to the velocity difference
of contacting grains. We determine the behavior of the complex-valued normal
mode frequencies using 1) DEM, 2) direct diagonalization of the relevant
matrix, and 3) a numerical search for the zeros of the relevant determinant.
All three methods are in strong agreement with each other. The real and the
imaginary parts of each normal mode frequency characterize the elastic and the
dissipative properties, respectively, of the granular medium. We demonstrate
that, as the interparticle damping, $\xi$, increases, the normal modes exhibit
nearly circular trajectories in the complex frequency plane and that for a
given value of $\xi$ they all lie on or near a circle of radius $R$ centered on
the point $-iR$ in the complex plane, where $R\propto 1/\xi$. We show that each
normal mode becomes critically damped at a value of the damping parameter $\xi
\approx 1/\omega_n^0$, where $\omega_n^0$ is the (real-valued) frequency when
there is no damping. The strong indication is that these conclusions carry over
to the properties of real granular media whose dissipation is dominated by the
relative motion of contacting grains. For example, compressional or shear waves
in unconsolidated dry sediments can be expected to become overdamped beyond a
critical frequency, depending upon the strength of the intergranular damping
constant.",1410.5484v2
2020-08-05,Fast optimization via inertial dynamics with closed-loop damping,"In a Hilbert space $H$, in order to develop fast optimization methods, we
analyze the asymptotic behavior, as time $t$ tends to infinity, of inertial
continuous dynamics where the damping acts as a closed-loop control. The
function $f: H \to R$ to be minimized (not necessarily convex) enters the
dynamic through it gradient, which is assumed to be Lipschitz continuous on the
bounded subsets of $H$. This gives autonomous dynamical systems with nonlinear
damping and nonlinear driving force. We first consider the case where the
damping term $\partial \phi (\dot{x}(t))$ acts as a closed-loop control of the
velocity. The damping potential $\phi : H \to [0,+\infty)$ is a convex
continuous function which achieves its minimum at the origin. We show the
existence and uniqueness of a global solution to the associated Cauchy problem.
Then, we analyze the asymptotic convergence properties of the generated
trajectories generated. We use techniques from optimization, control theory,
and PDE's: Lyapunov analysis based on the decreasing property of an energy-like
function, quasi-gradient and Kurdyka-Lojasiewicz theory, monotone operator
theory for wave-like equations. Convergence rates are obtained based on the
geometric properties of the data $f$ and $\phi$. When $f$ is strongly convex,
we give general conditions which provide exponential convergence rates. Then,
we extend the results to the case where an additional Hessian-driven damping
enters the dynamic, which reduces the oscillations. Finally, we consider an
inertial system involving jointly the velocity $\dot{x}(t)$ and the gradient
$\nabla f(x(t))$. In addition to its original results, this work surveys the
numerous works devoted in recent years to the interaction between continuous
damped inertial dynamics and numerical algorithms for optimization, with the
emphasis on autonomous systems, closed-loop adaptive procedures, and
convergence rates.",2008.02261v3
2023-01-10,Cosmic Ray Drag and Damping of Compressive Turbulence,"While it is well-known that cosmic rays (CRs) can gain energy from turbulence
via second order Fermi acceleration, how this energy transfer affects the
turbulent cascade remains largely unexplored. Here, we show that damping and
steepening of the compressive turbulent power spectrum are expected once the
damping time $t_{\rm damp} \sim \rho v^{2}/\dot{E}_{\rm CR} \propto E_{\rm
CR}^{-1}$ becomes comparable to the turbulent cascade time. Magnetohydrodynamic
(MHD) simulations of stirred compressive turbulence in a gas-CR fluid with
diffusive CR transport show clear imprints of CR-induced damping, saturating at
$\dot{E}_{\rm CR} \sim \tilde{\epsilon}$, where $\tilde{\epsilon}$ is the
turbulent energy input rate. In that case, almost all the energy in large scale
motions is absorbed by CRs and does not cascade down to grid scale. Through a
Hodge-Helmholtz decomposition, we confirm that purely compressive forcing can
generate significant solenoidal motions, and we find preferential CR damping of
the compressive component in simulations with diffusion and streaming,
rendering small-scale turbulence largely solenoidal, with implications for
thermal instability and proposed resonant scattering of $E > 300$ GeV CRs by
fast modes. When CR transport is streaming dominated, CRs also damp large scale
motions, with kinetic energy reduced by up to to an order of magnitude in
realistic $E_{\rm CR} \sim E_{\rm g}$ scenarios, but turbulence (with a reduced
amplitude) still cascades down to small scales with the same power spectrum.
Such large scale damping implies that turbulent velocities obtained from the
observed velocity dispersion may significantly underestimate turbulent forcing
rates, i.e. $\tilde{\epsilon} \gg \rho v^{3}/L$.",2301.04156v2
2024-02-12,"Relaxation of weakly collisional plasma: continuous spectra, Landau eigenmodes, and transition from the collisionless to the fluid limit","The relaxation of a weakly collisional plasma is described by the
Boltzmann-Poisson equations with the Lenard-Bernstein collision operator. We
perform a perturbative analysis of these equations, and obtain, for the first
time, exact analytic solutions, enabling definitive resolutions to
long-standing controversies regarding the impact of weak collisions on
continuous spectra and Landau eigenmodes. Unlike some previous studies, we
retain both damping and diffusion terms in the collision operator. We find that
the linear response is a temporal convolution of a continuum that depends on
the continuous velocities of particles, and discrete normal modes that
encapsulate coherent oscillations. The normal modes are exponentially damped
over time due to collective effects (Landau damping) as well as collisional
dissipation. The continuum is also damped by collisions but somewhat
differently. Up to a collision time, which is the inverse of the collision
frequency $\nu_{\mathrm{c}}$, the continuum decay is driven by velocity
diffusion and occurs super-exponentially over a timescale $\sim
\nu^{-1/3}_{\mathrm{c}}$. After a collision time, however, the continuum decay
is driven by the collisional damping of particle velocities and diffusion of
their positions, and occurs exponentially over a timescale $\sim
\nu_{\mathrm{c}}$. This hitherto unknown, slow exponential decay causes
perturbations to damp the most on scales comparable to the mean free path, but
very slowly on larger scales, which establishes the local thermal equilibrium,
the essence of the fluid limit. The long-term decay of the response is driven
by the normal modes on scales smaller than the mean free path, but, on larger
scales, is governed by the slowly decaying continuum and the least damped
normal mode. Our analysis firmly establishes a long-sought connection between
the collisionless and fluid limits of weakly collisional plasmas.",2402.07992v1
1995-09-21,Damped Lyman-alpha and Lyman Limit Absorbers in the Cold Dark Matter Model,"We study the formation of damped \lya and Lyman limit absorbers in a
hierarchical clustering scenario using a gas dynamical simulation of an $\Omega
= 1$, cold dark matter universe. In the simulation, these high column density
systems are associated with forming galaxies. Damped \lya absorption, $N_{HI}
\simgt 10^{20.2}\cm^{-2}$, arises along lines of sight that pass near the
centers of relatively massive, dense protogalaxies. Lyman limit absorption,
$10^{17}\cm^{-2} \simlt N_{HI} \simlt 10^{20.2}\cm^{-2}$, develops on lines of
sight that pass through the outer parts of such objects or near the centers of
smaller protogalaxies. The number of Lyman limit systems is less than observed,
while the number of damped \lya systems is quite close to the observed
abundance. Damped absorbers are typically $\sim 10$ kpc in radius, but the
population has a large total cross section because the systems are much more
numerous than present day $L_*$ galaxies. Our results demonstrate that high
column density systems like those observed arise naturally in a hierarchical
theory of galaxy formation and that it is now possible to study these absorbers
directly from numerical simulations.",9509106v1
1995-09-21,Nonlinear Damping of Oscillations in Tidal-Capture Binaries,"We calculate the damping of quadrupole f and low order g modes (primary
modes) by nonlinear coupling to other modes of the star. This damping is orders
of magnitude more rapid than direct radiative damping when the primary
amplitude is large, as in tidal capture.
  Primary modes destabilize high degree g-modes of half their frequency
(daughter modes) by 3-mode coupling in radiative zones. In sunlike stars, the
growth time $\equiv\eta^{-1}\approx 4 E_{0,42}^{-1/2}$ days, where $E_{0,42}$
is the initial energy of the primary mode in units of $10^{42}~$erg, and of
order $10^{10}E_{0,42}^{5/4}$ daughters are unstable. The growth rate is
approximately equal to the angular frequency of the primary mode times its
dimensionless radial amplitude, $\delta R/R_*\approx 0.002E_{0,42}^{1/2}$.
Although the daughter modes are limited by their own nonlinearities,
collectively they absorb most of the primary mode's energy after a time $\sim
10\eta^{-1}$ provided $E_{0}> 10^{40}~\mbox{erg}$. In fact nonlinear mode
interaction may be the dominant damping process if $E_0\gtrsim
10^{37}~\mbox{erg}$.
  Our results have application to tidally captured main sequence globular
cluster stars of mass $\ge 0.5 M_{\sun}$; the tidal energy is dissipated in the
radiative core of the star in about a month, which is less than the initial
orbital period.",9509112v1
1997-08-12,Spectroscopy of PKS 0528-260: New Limits on CO Absorption and Emission,"We have obtained a moderate resolution spectrum of the quasar PKS 0528-250
with the Red Channel Spectrograph on the Multiple Mirror Telescope (MMT) in
order to study a damped Lyman alpha absorption line system at z = 2.8115.
  We obtain a new upper limit for the CO column density for the z = 2.8108
velocity component in the z = 2.8115 damped Lyman alpha system. The ionization
of different species in this component rules out a quasar spectral energy
distribution (SED) as the ionization field,and implies an ultraviolet radiation
field intensity a few times that of the Milky Way value. The estimated total
number density is n(H) about 20 cm^{-3}. The physical size for the z = 2.8108
component implied by these models is about 40 parsecs. The ionization of
different species also suggests a structure with a hot intercloud medium
associated with a H I cloud in this component, that is, most low ionized ions
are from the cold medium where photoionization and photodissociation dominates.
The highly ionized species may be from the intercloud medium where collisional
ionization dominates. We also present newly identified Ni II absorption lines
in the z = 2.1408 and z = 2.8115 damped Ly$\alpha$ systems. The derived
depletion of nickel by dust confirms previous results that the dust-to-gas
ratio in these two damped Lyman alpha systems is about 10% of the Milky Way
ratio. Millimeter wavelength observations obtained at the NRAO 12 meter
telescope provide new upper limits on CO (3-2) emission in the z = 2.8115
damped Lyman alpha system.",9708104v1
1998-11-04,GMRT Observations of Low z Damped Lyman-alpha Absorbers,"We present Giant Metrewave Radio Telescope (GMRT) observations of redshifted
HI 21cm absorption in two low redshift (z=0.2212, z=0.0912) damped Lyman-alpha
systems seen towards the gigahertz peaked source OI 363 (z_em = 0.630). The
object at z=0.0912 is the lowest redshift damped Lyman-alpha system known to
date. Ground based imaging (Rao & Turnshek, 1998) shows that at neither
redshift is there a large spiral galaxy at low impact parameter to the line of
sight to OI 363, in contradiction with the suggestion that these systems are
large proto-disks.
  Since OI 363 is a highly compact, core dominated source, the covering factor
of the HI gas is likely to be unity. Nonetheless, the spin temperatures derived
from the 21cm optical depth (and using the N_HI measured from HST spectra, Rao
& Turnshek, 1998) are high, viz. 1120 +/- 200 K and 825 +/- 110 K for the high
and low redshift systems respectively. These values are considerably higher
than typical values (100 - 200 K) measured in our Galaxy and Andromeda and are,
in fact, similar to those obtained in high redshift damped Lyman-alpha systems.
Our observations hence suggest that evolutionary effects may not be crucial in
understanding the difference in derived spin temperature values between local
spiral disks and high redshift damped Lyman-alpha systems.",9811068v1
2002-01-25,Galaxies Associated with z~4 Damped Lya Systems: I. Imaging and Photometric Selection,"This paper describes the acquisition and analysis of imaging data for the
identification of galaxies associated with z~4 damped Lya systems. We present
deep BRI images of three fields known to contain four z~4 damped systems. We
discuss the reduction and calibration of the data, detail the color criteria
used to identify z~4 galaxies, and present a photometric redshift analysis to
complement the color selection. We have found no galaxy candidates closer to
the QSO than 7'' which could be responsible for the damped Lya systems.
Assuming that at least one of the galaxies is not directly beneath the QSO, we
set an upper limit on this damped Lya system of L < L*/4. Finally, we have
established a web site to release these imaging data to the public.",0201417v2
2002-02-25,Eccentricity Evolution for Planets in Gaseous Disks,"We investigate the hypothesis that interactions between a giant planet and
the disk from which it forms promote eccentricity growth. These interactions
are concentrated at discrete Lindblad and corotation resonances. Interactions
at principal Lindblad resonances cause the planet's orbit to migrate and open a
gap in the disk if the planet is sufficiently massive. Those at first order
Lindblad and corotation resonances change the planet's orbital eccentricity.
Eccentricity is excited by interactions at external Lindblad resonances which
are located on the opposite side of corotation from the planet, and damped by
co-orbital Lindblad resonances which overlap the planet's orbit. If the planet
clears a gap in the disk, the rate of eccentricity damping by co-orbital
Lindblad resonances is reduced. Density gradients associated with the gap
activate eccentricity damping by corotation resonances at a rate which
initially marginally exceeds that of eccentricity excitation by external
Lindblad resonances. But the corotation torque drives a mass flux which reduces
the density gradient near the resonance. Sufficient partial saturation of
corotation resonances can tip the balance in favor of eccentricity excitation.
A minimal initial eccentricity of a few percent is required to overcome viscous
diffusion which acts to unsaturate corotation resonances by reestablishing the
large scale density gradient. Thus eccentricity growth is a finite amplitude
instability. Formally, interactions at the apsidal resonance, which is a
special kind of co-orbital Lindblad resonance, appears to damp eccentricity
faster than external Lindblad resonances can excite it. However, apsidal waves
have such long wavelengths that they do not propagate in protoplanetary disks.
This reduces eccentricity damping by the apsidal resonance to a modest level.",0202462v1
2003-07-23,Dusty Molecular Cloud Collapse in the Presence of Alfvén Waves,"It has been shown that magnetic fields play an important role in the
stability of molecular clouds, mainly perpendicularly to the field direction.
However, in the parallel direction the stability is a serious problem still to
be explained. Interstellar turbulence may allow the generation of Alfv\'en
waves that propagate through the clouds in the magnetic field direction. These
regions also present great amounts of dust particles which can give rise to new
wave modes, or modify the pre-existing ones. The dust-cyclotron damping affects
the Alfv\'en wave propagation near the dust- cyclotron frequency. On the other
hand, the clouds present different grain sizes, which carry different charges.
In this sense, a dust particle distribution has several dust-cyclotron
frequencies and it will affect a broad band of wave frequencies. In this case,
the energy transfer to the gas is more efficient than in the case where the
ion-cyclotron damping is considered alone. This effect becomes more important
if a power law spectrum is considered for the wave energy flux, since the major
part of the energy is concentrated in low-frequency waves. In this work we
calculate the dust- cyclotron damping in a dusty and magnetized dwarf molecular
cloud, as well as determine the changes in the Alfv\'en wave flux. Then, we use
these results to study the gravitational stability of the cloud. We show that,
considering the presence of charged dust particles, the wave flux is rapidly
damped due to dust-cyclotron damping. Then the wave pressure acts in a small
length scale, and cannot explain the observable cloud sizes, but can explain
the existence of small and dense cores.",0307411v1
2005-02-28,Thermal Evolution of a Pulsating Neutron Star,"We have derived a set of equations to describe the thermal evolution of a
neutron star which undergoes small-amplitude radial pulsations. We have taken
into account, in the frame of the General Theory of Relativity, the pulsation
damping due to the bulk and shear viscosity and the accompanying heating of the
star. The neutrino emission of a pulsating non-superfluid star and its heating
due to the bulk viscosity are calculated assuming that both processes are
determined by the non-equilibrium modified Urca process. Analytical and
numerical solutions to the set of equations of the stellar evolution are
obtained for linear and strongly non-linear deviations from beta-equilibrium.
It is shown that a pulsating star may be heated to very high temperatures,
while the pulsations damp very slowly with time (a power law damping for
100-1000 years), as long as the damping is determined by the bulk viscosity.
The contribution of the shear viscosity to the damping becomes important in a
rather cool star with a low pulsation energy.",0502583v2
2005-05-02,Collisionless Damping of Fast MHD Waves in Magneto-rotational Winds,"We propose collisionless damping of fast MHD waves as an important mechanism
for the heating and acceleration of winds from rotating stars. Stellar rotation
causes magnetic field lines anchored at the surface to form a spiral pattern
and magneto-rotational winds can be driven. If the structure is a magnetically
dominated, fast MHD waves generated at the surface can propagate almost
radially outward and cross the field lines. The propagating waves undergo
collisionless damping owing to interactions with particles surfing on magnetic
mirrors that are formed by the waves themselves. The damping is especially
effective where the angle between the wave propagation and the field lines
becomes moderately large ($\sim 20$ to $80^{\circ}$). The angle tends naturally
to increase into this range because the field in magneto-rotational winds
develops an increasingly large azimuthal component. The dissipation of the wave
energy produces heating and acceleration of the outflow. We show using
specified wind structures that this damping process can be important in both
solar-type stars and massive stars that have moderately large rotation rates.
This mechanism can play a role in coronae of young solar-type stars which are
rapidly rotating and show X-ray luminosities much larger than the sun. The
mechanism could also be important for producing the extended X-ray emitting
regions inferred to exist in massive stars of spectral type middle B and later.",0505013v5
2006-08-05,The nature of damped Lyman alpha and sub-damped Lyman alpha absorbers,"We present arguments based on the measured abundances in individual damped
Lyman alpha systems (DLAs) and sub-damped Lyman alpha systems (sub-DLAs), and
also the average abundances inferred in large samples of QSO absorption line
systems, to suggest that the amount of dust in intervening QSO absorbers is
small and is not responsible for missing many QSOs in magnitude limited QSO
surveys. While we can not totally rule out a bimodal dust distribution with a
population of very dusty, metal rich, absorbers which push the background QSOs
below the observational threshold of current optical spectroscopic studies,
based upon the current samples it appears that the metallicity in QSO absorbers
decreases with increase in H I column densities beyond 10^{19} cm^{-2}. Thus
the sub-DLA population is more metal rich than the DLAs, a trend which may
possibly extend to the non-damped Lyman limit systems (NDLLS). Based on the
recently discovered mass-metallicity relation for galaxies, we suggest that
most sub-DLAs and possibly NDLLS, are associated with massive spiral/elliptical
galaxies while most DLAs are associated with low mass galaxies. The sub-DLA
galaxies will then contribute a larger fraction of total mass (stellar and ISM)
and therefore metals, to the cosmic budget, specially at low redshifts, as
compared to the DLAs.",0608127v2
2007-02-12,The Ucsd/Keck Damped Lya Abundance Database: A Decade of High Resolution Spectroscopy,"We publish the Keck/HIRES and Keck/ESI spectra that we have obtained during
the first 10 years of Keck observatory operations. Our full sample includes 42
HIRES spectra and 39 ESI spectra along 65 unique sightlines providing abundance
measurements on ~85 damped Lya systems. The normalized data can be downloaded
from the journal or from our supporting website:
http://www.ucolick.org/~xavier/DLA/. The database includes all of the
sightlines that have been included in our papers on the chemical abundances,
kinematics, and metallicities of the damped Lya systems. This data has also
been used to argue for variations in the fine-structure constant. We present
new chemical abundance measurements for 10 damped Lya systems and a summary
table of high-resolution metallicity measurements (including values from the
literature) for 153 damped Lya systems at z>1.6. We caution, however, that this
metallicity sample (and all previous ones) is biased to higher N(HI) values
than a random sample.",0702325v1
1998-06-30,Structure and Spin Dynamics of La$_{0.85}$Sr$_{0.15}$MnO$_3$,"Neutron scattering has been used to study the structure and spin dynamics of
La$_{0.85}$Sr$_{0.15}$MnO$_3$. The magnetic structure of this system is
ferromagnetic below T_C = 235 K. We see anomalies in the Bragg peak intensities
and new superlattice peaks consistent with the onset of a spin-canted phase
below T_{CA} = 205 K, which appears to be associated with a gap at q = (0, 0,
0.5) in the spin-wave spectrum. Anomalies in the lattice parameters indicate a
concomitant lattice distortion. The long-wavelength magnetic excitations are
found to be conventional spin waves, with a gapless (< 0.02 meV) isotropic
dispersion relation $E = Dq^2$. The spin stiffness constant D has a $T^{5/2}$
dependence at low T, and the damping at small q follows $q^4T^{2}$. An
anomalously strong quasielastic component, however, develops at small wave
vector above 200 K and dominates the fluctuation spectrum as T -> T_C. At
larger q, on the other hand, the magnetic excitations become heavily damped at
low temperatures, indicating that spin waves in this regime are not eigenstates
of the system, while raising the temperature dramatically increases the
damping. The strength of the spin-wave damping also depends strongly on the
symmetry direction in the crystal. These anomalous damping effects are likely
due to the itinerant character of the $e_g$ electrons.",9806381v1
1999-02-01,Damping Rates and Mean Free Paths of Soft Fermion Collective Excitations in a Hot Fermion-Gauge-Scalar Theory,"We study the transport coefficients, damping rates and mean free paths of
soft fermion collective excitations in a hot fermion-gauge-scalar plasma with
the goal of understanding the main physical mechanisms that determine transport
of chirality in scenarios of non-local electroweak baryogenesis. The focus is
on identifying the different transport coefficients for the different branches
of soft collective excitations of the fermion spectrum. These branches
correspond to collective excitations with opposite ratios of chirality to
helicity and different dispersion relations. By combining results from the hard
thermal loop (HTL) resummation program with a novel mechanism of fermion
damping through heavy scalar decay, we obtain a robust description of the
different damping rates and mean free paths for the soft collective excitations
to leading order in HTL and lowest order in the Yukawa coupling. The space-time
evolution of wave packets of collective excitations unambiguously reveals the
respective mean free paths. We find that whereas both the gauge and scalar
contribution to the damping rates are different for the different branches, the
difference of mean free paths for both branches is mainly determined by the
decay of the heavy scalar into a hard fermion and a soft collective excitation.
We argue that these mechanisms are robust and are therefore relevant for
non-local scenarios of baryogenesis either in the Standard Model or extensions
thereof.",9902218v2
2002-08-29,Some notes on ideology of waves in plasmas,"Our last three papers provide an occasion to make some brief notes on
ideology of waves in plasmas and to rehabilitate Vlasov prescription to
calculate relevant logarithmically divergent integrals in the principal value
sense. In this approach asymptotical solutions of plasma oscillations are
selected according to self-consistent boundary physical conditions. Landau
damping is absent in this case by definition. Boundary electrical field
together with conditions of absence of unphysical backward and kinematical
waves define single-valued dependence of boundary distribution function on
electron velocity \vec{v} in the case of transversal waves and on the surface
break of the normal electrical field in the case of longitudinal oscillations.
We have proposed physically more justified modified iteration procedure of
collisional damping calculation and demonstrated some results of damping
decrements calculations in a low-collision electron-ion plasma. Dispersion
smearing of both longitudinal and transversal high-frequency waves, for which
the smearing decrement \delta_x is proportional to
\Delta\omega/(\omega\sqrt{\omega^2-\omega_L^2}), might be the main cause of
waves amplitude damping in collisionless plasmas imitating Landau damping.",0208098v7
2004-11-26,Open quantum systems,"The damping of the harmonic oscillator is studied in the framework of the
Lindblad theory for open quantum systems. A generalization of the fundamental
constraints on quantum mechanical diffusion coefficients which appear in the
master equation for the damped quantum oscillator is presented; the
Schr\""odinger, Heisenberg and Weyl-Wigner-Moyal representations of the Lindblad
equation are given explicitly. On the basis of these representations it is
shown that various master equations for the damped quantum oscillator used in
the literature are particular cases of the Lindblad equation and that not all
of these equations are satisfying the constraints on quantum mechanical
diffusion coefficients. The master equation is transformed into Fokker-Planck
equations for quasiprobability distributions and a comparative study is made
for the Glauber $P$ representation, the antinormal ordering $Q$ representation
and the Wigner $W$ representation. The density matrix is represented via a
generating function, which is obtained by solving a time-dependent linear
partial differential equation derived from the master equation. The damped
harmonic oscillator is applied for the description of the charge equilibration
mode observed in deep inelastic reactions. For a system consisting of two
harmonic oscillators the time dependence of expectation values, Wigner function
and Weyl operator are obtained and discussed. In addition models for the
damping of the angular momentum are studied. Using this theory to the quantum
tunneling through the nuclear barrier, besides Gamow's transitions with energy
conservation, additional transitions with energy loss, are found. When this
theory is used to the resonant atom-field interaction, new optical equations
describing the coupling through the environment are obtained.",0411189v1
2006-02-17,Damped quantum harmonic oscillator,"In the framework of the Lindblad theory for open quantum systems the damping
of the harmonic oscillator is studied. A generalization of the fundamental
constraints on quantum mechanical diffusion coefficients which appear in the
master equation for the damped quantum oscillator is presented; the
Schr\""odinger and Heisenberg representations of the Lindblad equation are given
explicitly. On the basis of these representations it is shown that various
master equations for the damped quantum oscillator used in the literature are
particular cases of the Lindblad equation and that the majority of these
equations are not satisfying the constraints on quantum mechanical diffusion
coefficients. Analytical expressions for the first two moments of coordinate
and momentum are also obtained by using the characteristic function of the
Lindblad master equation. The master equation is transformed into Fokker-Planck
equations for quasiprobability distributions. A comparative study is made for
the Glauber $P$ representation, the antinormal ordering $Q$ representation and
the Wigner $W$ representation. It is proven that the variances for the damped
harmonic oscillator found with these representations are the same. By solving
the Fokker-Planck equations in the steady state, it is shown that the
quasiprobability distributions are two-dimensional Gaussians with widths
determined by the diffusion coefficients. The density matrix is represented via
a generating function, which is obtained by solving a time-dependent linear
partial differential equation derived from the master equation. Illustrative
examples for specific initial conditions of the density matrix are provided.",0602149v1
2007-04-12,The effect of the solar corona on the attenuation of small-amplitude prominence oscillations. I. Longitudinal magnetic field,"Context. One of the typical features shown by observations of solar
prominence oscillations is that they are damped in time and that the values of
the damping times are usually between one and three times the corresponding
oscillatory period. However, the mechanism responsible for the attenuation is
still not well-known. Aims. Thermal conduction, optically thin or thick
radiation and heating are taken into account in the energy equation, and their
role on the attenuation of prominence oscillations is evaluated. Methods. The
dispersion relation for linear non-adiabatic magnetoacoustic waves is derived
considering an equilibrium made of a prominence plasma slab embedded in an
unbounded corona. The magnetic field is orientated along the direction parallel
to the slab axis and has the same strength in all regions. By solving the
dispersion relation for a fixed wavenumber, a complex oscillatory frequency is
obtained, and the period and the damping time are computed. Results. The effect
of conduction and radiation losses is different for each magnetoacoustic mode
and depends on the wavenumber. In the observed range of wavelengths the
internal slow mode is attenuated by radiation from the prominence plasma, the
fast mode by the combination of prominence radiation and coronal conduction and
the external slow mode by coronal conduction. The consideration of the external
corona is of paramount importance in the case of the fast and external slow
modes, whereas it does not affect the internal slow modes at all. Conclusions.
Non-adiabatic effects are efficient damping mechanisms for magnetoacoustic
modes, and the values of the obtained damping times are compatible with those
observed.",0704.1566v2
2007-10-01,Lyman-alpha Damping Wing Constraints on Inhomogeneous Reionization,"One well-known way to constrain the hydrogen neutral fraction, x_H, of the
high-redshift intergalactic medium (IGM) is through the shape of the red
damping wing of the Lya absorption line. We examine this method's effectiveness
in light of recent models showing that the IGM neutral fraction is highly
inhomogeneous on large scales during reionization. Using both analytic models
and ""semi-numeric"" simulations, we show that the ""picket-fence"" absorption
typical in reionization models introduces both scatter and a systematic bias to
the measurement of x_H. In particular, we show that simple fits to the damping
wing tend to overestimate the true neutral fraction in a partially ionized
universe, with a fractional error of ~ 30% near the middle of reionization.
This bias is generic to any inhomogeneous model. However, the bias is reduced
and can even underestimate x_H if the observational sample only probes a subset
of the entire halo population, such as quasars with large HII regions. We also
find that the damping wing absorption profile is generally steeper than one
would naively expect in a homogeneously ionized universe. The profile steepens
and the sightline-to-sightline scatter increases as reionization progresses. Of
course, the bias and scatter also depend on x_H and so can, at least in
principle, be used to constrain it. Damping wing constraints must therefore be
interpreted by comparison to theoretical models of inhomogeneous reionization.",0710.0371v1
2008-02-11,Eccentricity of masing disks in Active Galactic Nuclei,"Observations of Keplerian disks of masers in NCG 4258 and other Seyfert
galaxies can be used to obtain geometric distance estimates and derive the
Hubble constant. The ultimate precision of such measurements could be limited
by uncertainties in the disk geometry. Using a time-dependent linear theory
model, we study the evolution of a thin initially eccentric disk under
conditions appropriate to sub-pc scales in Active Galactic Nuclei. The
evolution is controlled by a combination of differential precession driven by
the disk potential and propagating eccentricity waves that are damped by
viscosity. A simple estimate yields a circularization timescale of
approximately 10 Myr at 0.1 pc. Numerical solutions for the eccentricity
evolution confirm that damping commences on this timescale, but show that the
subsequent decay rate of the eccentricity depends upon the uncertain strength
of viscous damping of eccentricity. If eccentricity waves are important further
decay of the eccentricity can be slow, with full circularization requiring up
to 50 Myr for disks at radii of 0.1 pc to 0.2 pc. Observationally, this implies
that it is plausible that enough time has elapsed for the eccentricity of
masing disks to have been substantially damped, but that it may not be
justified to assume vanishing eccentricity. We predict that during the damping
phase the pericenter of the eccentric orbits describes a moderately tightly
wound spiral with radius.",0802.1524v1
2008-02-20,The Effect of Charon's Tidal Damping on the Orbits of Pluto's Three Moons,"Pluto's recently discovered minor moons, Nix and Hydra, have almost circular
orbits, and are nearly coplanar with Charon, Pluto's major moon. This is
surprising because tidal interactions with Pluto are too weak to damp their
eccentricities. We consider an alternative possibility: that Nix and Hydra
circularize their orbits by exciting Charon's eccentricity via secular
interactions, and Charon in turn damps its own eccentricity by tidal
interaction with Pluto. The timescale for this process can be less than the age
of the Solar System, for plausible tidal parameters and moon masses. However,
as we show numerically and analytically, the effects of the 2:1 and 3:1
resonant forcing terms between Nix and Charon complicate this picture. In the
presence of Charon's tidal damping, the 2:1 term forces Nix to migrate outward
and the 3:1 term changes the eccentricity damping rate, sometimes leading to
eccentricity growth. We conclude that this mechanism probably does not explain
Nix and Hydra's current orbits. Instead, we suggest that they were formed
in-situ with low eccentricities.
  We also show that an upper limit on Nix's migration speed sets a lower limit
on Pluto-Charon's tidal circularization timescale of >10^5 yrs. Moreover,
Hydra's observed proper eccentricity may be explained by the 3:2 forcing by
Nix.",0802.2939v1
2008-03-18,Non-adiabatic magnetohydrodynamic waves in a cylindrical prominence thread with mass flow,"High-resolution observations show that oscillations and waves in prominence
threads are common and that they are attenuated in a few periods. In addition,
observers have also reported the presence of material flows in such prominence
fine-structures. Here we investigate the time damping of non-leaky oscillations
supported by a homogeneous cylindrical prominence thread embedded in an
unbounded corona and with a steady mass flow. Thermal conduction and radiative
losses are taken into account as damping mechanisms, and the effect of these
non-ideal effects and the steady flow on the attenuation of oscillations is
assessed. We solve the general dispersion relation for linear, non-adiabatic
magnetoacoustic and thermal waves supported by the model, and find that slow
and thermal modes are efficiently attenuated by non-adiabatic mechanisms. On
the contrary, fast kink modes are much less affected and their damping times
are much larger than those observed. The presence of flow has no effect on the
damping of slow and thermal waves, whereas fast kink waves are more (less)
attenuated when they propagate parallel (anti-parallel) to the flow direction.
Although the presence of steady mass flows improves the efficiency of
non-adiabatic mechanisms on the attenuation of transverse, kink oscillations
for parallel propagation to the flow, its effect is still not enough to obtain
damping times compatible with observations.",0803.2600v2
2008-07-28,"Thermal fluctuations in moderately damped Josephson junctions: Multiple escape and retrapping, switching- and return-current distributions and hysteresis","A crossover at a temperature T* in the temperature dependence of the width s
of the distribution of switching currents of moderately damped Josephson
junctions has been reported in a number of recent publications, with positive
ds/dT and IV characteristics associated with underdamped behaviour for lower
temperatures T<T*, and negative ds/dT and IV characteristics resembling
overdamped behaviour for higher temperatures T>T*. We have investigated in
detail the behaviour of Josephson junctions around the temperature T* by using
Monte Carlo simulations including retrapping from the running state into the
supercurrent state as given by the model of Ben-Jacob et al. We develop
discussion of the important role of multiple escape and retrapping events in
the moderate-damping regime, in particular considering the behaviour in the
region close to T*. We show that the behaviour is more fully understood by
considering two crossover temperatures, and that the shape of the distribution
and s(T) around T*, as well as at lower T<T*, are largely determined by the
shape of the conventional thermally activated switching distribution. We show
that the characteristic temperatures T* are not unique for a particular
Josephson junction, but have some dependence on the ramp rate of the applied
bias current. We also consider hysteresis in moderately damped Josephson
junctions and discuss the less commonly measured distribution of return
currents for a decreasing current ramp. We find that some hysteresis should be
expected to persist above T* and we highlight the importance, even well below
T*, of accounting properly for thermal fluctuations when determining the
damping parameter Q.",0807.4502v1
2009-02-26,Viscous propagation of mass flow variability in accretion discs,"We study mass flow rate through a disc resulting from a varying mass supply
rate. Variable mass supply rate occurs, e.g., during disc state transitions,
and in interacting eccentric binaries. It is, however, damped by the viscosity
of the disc. Here, we calculate this damping in detail. We derive an analytical
description of the propagation of the flow rate using the solution of
Lynden-Bell & Pringle, in which the disc is assumed to extend to infinity. In
particular, we derive the accretion-rate Green's function, and its Fourier
transform, which gives the fractional damping at a given variability frequency.
We then compare this model to that of a finite disc with the mass supply at its
outer edge. We find significant differences with respect to the infinite disc
solution, which we find to overestimate the viscous damping. In particular, the
asymptotic form of the Green's function is power-law for the infinite disc and
exponential for the finite one. We then find a simple fitting form for the
latter, and also calculate its Fourier transform. In general, the damping
becomes very strong when the viscous time at the outer edge of the disc becomes
longer than the modulation time scale. We apply our results to a number of
astrophysical systems. We find the effect is much stronger in low-mass X-ray
binaries, where the disc size is comparable to that of the Roche lobe, than in
high-mass binaries, where the wind-fed disc can have a much smaller size.",0902.4530v2
2010-04-09,Oscillations of weakly viscous conducting liquid drops in a strong magnetic field,"We analyse small-amplitude oscillations of a weakly viscous electrically
conducting liquid drop in a strong uniform DC magnetic field. An asymptotic
solution is obtained showing that the magnetic field does not affect the shape
eigenmodes, which remain the spherical harmonics as in the non-magnetic case.
Strong magnetic field, however, constrains the liquid flow associated with the
oscillations and, thus, reduces the oscillation frequencies by increasing
effective inertia of the liquid. In such a field, liquid oscillates in a
two-dimensional (2D) way as solid columns aligned with the field. Two types of
oscillations are possible: longitudinal and transversal to the field. Such
oscillations are weakly damped by a strong magnetic field - the stronger the
field, the weaker the damping, except for the axisymmetric transversal and
inherently 2D modes. The former are overdamped because of being incompatible
with the incompressibility constraint, whereas the latter are not affected at
all because of being naturally invariant along the field. Since the magnetic
damping for all other modes decreases inversely with the square of the field
strength, viscous damping may become important in a sufficiently strong
magnetic field. The viscous damping is found analytically by a simple energy
dissipation approach which is shown for the longitudinal modes to be equivalent
to a much more complicated eigenvalue perturbation technique. This study
provides a theoretical basis for the development of new measurement methods of
surface tension, viscosity and the electrical conductivity of liquid metals
using the oscillating drop technique in a strong superimposed DC magnetic
field.",1004.1548v2
2011-02-03,Damping of Electron Density Structures and Implications for Interstellar Scintillation,"The forms of electron density structures in kinetic Alfven wave turbulence
are studied in connection with scintillation. The focus is on small scales $L
\sim 10^8-10^{10}$ cm where the Kinetic Alfv\'en wave (KAW) regime is active in
the interstellar medium. MHD turbulence converts to a KAW cascade, starting at
10 times the ion gyroradius and continuing to smaller scales. These scales are
inferred to dominate scintillation in the theory of Boldyrev et al. From
numerical solutions of a decaying kinetic Alfv\'en wave turbulence model,
structure morphology reveals two types of localized structures, filaments and
sheets, and shows that they arise in different regimes of resistive and
diffusive damping. Minimal resistive damping yields localized current filaments
that form out of Gaussian-distributed initial conditions. When resistive
damping is large relative to diffusive damping, sheet-like structures form. In
the filamentary regime, each filament is associated with a non-localized
magnetic and density structure, circularly symmetric in cross section. Density
and magnetic fields have Gaussian statistics (as inferred from Gaussian-valued
kurtosis) while density gradients are strongly non-Gaussian, more so than
current. This enhancement of non-Gaussian statistics in a derivative field is
expected since gradient operations enhance small-scale fluctuations. The
enhancement of density gradient kurtosis over current kurtosis is not obvious,
yet it suggests that modest fluctuation levels in electron density may yield
large scintillation events during pulsar signal propagation in the interstellar
medium. In the sheet regime the same statistical observations hold, despite the
absence of localized filamentary structures. Probability density functions are
constructed from statistical ensembles in both regimes, showing clear formation
of long, highly non-Gaussian tails.",1102.0810v2
2011-09-28,"Different dimensionality trends in the Landau damping of magnons in iron, cobalt and nickel: time dependent density functional study","We study the Landau damping of ferromagnetic magnons in Fe, Co, and Ni as the
dimensionality of the system is reduced from three to two. We resort to the
\textit{ab initio} linear response time dependent density functional theory in
the adiabatic local spin density approximation. The numerical scheme is based
on the Korringa-Kohn-Rostoker Green's function method. The key points of the
theoretical approach and the implementation are discussed. We investigate the
transition metals in three different forms: bulk phases, free-standing thin
films and thin films supported on a nonmagnetic substrate. We demonstrate that
the dimensionality trends in Fe and Ni are opposite: in Fe the transition from
bulk bcc crystal to Fe/Cu(100) film reduces the damping whereas in Ni/Cu(100)
film the attenuation increases compared to bulk fcc Ni. In Co, the strength of
the damping depends relatively weakly on the sample dimensionality. We explain
the difference in the trends on the basis of the underlying electronic
structure. The influence of the substrate on the spin-wave damping is analyzed
by employing Landau maps representing wave-vector resolved spectral density of
the Stoner excitations.",1109.6217v2
2011-10-06,Dissipative and conservative nonlinearity in carbon nanotube and graphene mechanical resonators,"Graphene and carbon nanotubes represent the ultimate size limit of one and
two-dimensional nanoelectromechanical resonators. Because of their reduced
dimensionality, graphene and carbon nanotubes display unusual mechanical
behavior; in particular, their dynamics is highly nonlinear. Here, we review
several types of nonlinear behavior in resonators made from nanotubes and
graphene. We first discuss an unprecedented scenario where damping is described
by a nonlinear force. This scenario is supported by several experimental facts:
(i) the quality factor varies with the amplitude of the motion as a power law
whose exponent coincides with the value predicted by the nonlinear damping
model, (ii) hysteretic behavior (of the motional amplitude as a function of
driving frequency) is absent in some of our resonators even for large driving
forces, as expected when nonlinear damping forces are large, and (iii) when we
quantify the linear damping force (by performing parametric excitation
measurements) we find that it is significantly smaller than the nonlinear
damping force. We then review parametric excitation measurements, an
alternative actuation method which is based on nonlinear dynamics. Finally, we
discuss experiments where the mechanical motion is coupled to electron
transport through a nanotube. The coupling can be made so strong that the
associated force acting on the nanotube becomes highly nonlinear with
displacement and velocity. Overall, graphene and nanotube resonators hold
promise for future studies on classical and quantum nonlinear dynamics.",1110.1234v1
2012-06-02,Slow Mode Oscillations and Damping of Hot Solar Coronal Loops,"The effect of temperature inhomogeneity on the periods, their ratios
(fundamental vs. first overtone), and the damping times of the standing slow
modes in gravitationally stratified solar coronal loops are studied. The
effects of optically thin radiation, compressive viscosity, and thermal
conduction are considered. The linearized one-dimensional magnetohydrodynamic
(MHD) equations (under low-$\beta$ condition) were reduced to a fourth--order
ordinary differential equation for the perturbed velocity. The numerical
results indicate that the periods of non-isothermal loops (i.e. temperature
increases from the loop base to apex) are smaller compared to those of
isothermal loops. In the presence of radiation, viscosity, and thermal
conduction, an increase in the temperature gradient is followed by a monotonic
decrease in the periods (compared with the isothermal case), while the period
ratio turns out to be a sensitive function of the gradient of the temperature
and the loop lengths. We verify that radiative dissipation is not a main
cooling mechanism of both isothermal and non-isothermal hot coronal loops and
has a small effect on the periods. Thermal conduction and compressive viscosity
are primary mechanisms in the damping of slow modes of the hot coronal loops.
The periods and damping times in the presence of compressive viscosity and/or
thermal conduction dissipation are consistent with the observed data in
specific cases. By tuning the dissipation parameters, the periods and the
damping times could be made consistent with the observations in more general
cases.",1206.0366v1
2012-09-15,Damped kink oscillations of flowing prominence threads,"Transverse oscillations of thin threads in solar prominences are frequently
reported in high-resolution observations. Two typical features of the
observations are that the oscillations are damped in time and that simultaneous
mass flows along the threads are detected. Flows cause the dense threads to
move along the prominence magnetic structure while the threads are oscillating.
The oscillations have been interpreted in terms of standing magnetohydrodynamic
(MHD) kink waves of the magnetic flux tubes which support the threads. The
damping is most likely due to resonant absorption caused by plasma
inhomogeneity. The technique of seismology uses the observations combined with
MHD wave theory to estimate prominence physical parameters. This paper presents
a theoretical study of the joint effect of flow and resonant absorption on the
amplitude of standing kink waves in prominence threads. We find that flow and
resonant absorption can either be competing effects on the amplitude or both
can contribute to damp the oscillations depending on the instantaneous position
of the thread within the prominence magnetic structure. The amplitude profile
deviates from the classic exponential profile of resonantly damped kink waves
in static flux tubes. Flow also introduces a progressive shift of the
oscillation period compared to the static case, although this effect is in
general of minor importance. We test the robustness of seismological estimates
by using synthetic data aiming to mimic real observations. The effect of the
thread flow can significantly affect the estimation of the transverse
inhomogeneity length scale. The presence of random background noise adds
uncertainty to this estimation. Caution needs to be paid to the seismological
estimates that do not take the influence of flow into account.",1209.3382v1
2013-04-13,Parametric survey of longitudinal prominence oscillation simulations,"It is found that both microflare-sized impulsive heating at one leg of the
loop and a suddenly imposed velocity perturbation can propel the prominence to
oscillate along the magnetic dip. An extensive parameter survey results in a
scaling law, showing that the period of the oscillation, which weakly depends
on the length and height of the prominence, and the amplitude of the
perturbations, scales with $\sqrt{R/g_\odot}$, where $R$ represents the
curvature radius of the dip, and $g_\odot$ is the gravitational acceleration of
the Sun. This is consistent with the linear theory of a pendulum, which implies
that the field-aligned component of gravity is the main restoring force for the
prominence longitudinal oscillations, as confirmed by the force analysis.
However, the gas pressure gradient becomes non-negligible for short
prominences. The oscillation damps with time in the presence of non-adiabatic
processes. Compared to heat conduction, the radiative cooling is the dominant
factor leading to the damping. A scaling law for the damping timescale is
derived, i.e., $\tau\sim l^{1.63} D^{0.66}w^{-1.21}v_{0}^{-0.30}$, showing
strong dependence on the prominence length $l$, the geometry of the magnetic
dip (characterized by the depth $D$ and the width $w$), and the velocity
perturbation amplitude $v_0$. The larger the amplitude, the faster the
oscillation damps. It is also found that mass drainage significantly reduces
the damping timescale when the perturbation is too strong.",1304.3798v1
2013-06-08,Observation of a Berry phase anti-damping spin-orbit torque,"Recent observations of current-induced magnetization switching at
ferromagnet/normal-conductor interfaces have important consequences for future
magnetic memory technology. In one interpretation, the switching originates
from carriers with spin-dependent scattering giving rise to a relativistic
anti-damping spin-orbit torque (SOT) in structures with broken space-inversion
symmetry. The alternative interpretation combines the relativistic spin Hall
effect (SHE), making the normal-conductor an injector of a spin-current, with
the non-relativistic spin-transfer torque (STT) in the ferromagnet. Remarkably,
the SHE in these experiments originates from the Berry phase effect in the band
structure of a clean crystal and the anti-damping STT is also based on a
disorder-independent transfer of spin from carriers to magnetization. Here we
report the observation of an anti-damping SOT stemming from an analogous Berry
phase effect to the SHE. The SOT alone can therefore induce magnetization
dynamics based on a scattering-independent principle. The ferromagnetic
semiconductor (Ga,Mn)As we use has a broken space-inversion symmetry in the
crystal. This allows us to consider a bare ferromagnetic element which
eliminates by design any SHE related contribution to the spin torque. We
provide an intuitive picture of the Berry phase origin of the anti-damping SOT
and a microscopic modeling of measured data.",1306.1893v1
2013-08-20,Stringent constraints on the H I spin temperature in two z > 3 Damped Lyman-alpha systems from redshifted 21 cm absorption studies,"Physical properties of Damped Lyman-alpha absorbers and their evolution are
closely related to galaxy formation and evolution theories, and have important
cosmological implications. H I 21 cm absorption study is one useful way of
measuring the temperature of these systems. In this work, very strong
constraints on the temperature of two Damped Lyman-alpha absorbers at z > 3 are
derived from low radio frequency observations. The H I spin temperature is
found to be greater than 2000 K for both the absorbers. The high spin
temperature of these high-redshift systems is in agreement with the trend found
in a compilation of temperatures for other Damped Lyman-alpha absorbers. We
also argue that the temperature - metallicity relation, reported earlier in the
literature, is unlikely to be a spurious line of sight effect, and that the
redshift evolution of the spin temperature does not arises due to a selection
effect. All of these are consistent with a redshift evolution of the warm gas
fraction in Damped Lyman-alpha systems.",1308.4410v1
2013-09-26,Non-Landau damping of magnetic excitations in systems with localized and itinerant electrons,"We discuss the form of the damping of magnetic excitations in a metal near a
ferromagnetic instability. The paramagnon theory predicts that the damping term
should have the form $\Omega/\Gamma (q)$ with $\Gamma (q) \propto q$ (the
Landau damping). However, the experiments on uranium metallic compounds UGe$_2$
and UCoGe showed that $\Gamma (q)$ tends to a constant value at vanishing $q$.
A non-zero $\Gamma (0)$ is impossible in systems with one type of carriers
(either localized or itinerant) because it would violate the spin conservation.
It has been conjectured recently that a non-zero $\Gamma (q)$ in UGe$_2$ and
UCoGe may be due to the presence of both localized and itinerant electrons in
these materials, with ferromagnetism involving predominantly localized spins.
We present microscopic analysis of the damping of near-critical localized
excitations due to interaction with itinerant carriers. We show explicitly how
the presence of two types of electrons breaks the cancellation between the
contributions to $\Gamma (0)$ from self-energy and vertex correction insertions
into the spin polarization bubble and discuss the special role of the
Aslamazov-Larkin processes. We show that $\Gamma (0)$ increases with $T$ both
in the paramagnetic and ferromagnetic regions, but in-between it has a peak at
$T_c$. We compare our theory with the available experimental data.",1309.7065v3
2014-06-16,Design of the Readout Electronics for the Qualification Model of DAMPE BGO Calorimeter,"The DAMPE (DArk Matter Particle Explorer) is a scientific satellite being
developed in China, aimed at cosmic ray study, gamma ray astronomy, and
searching for the clue of dark matter particles, with a planned mission period
of more than 3 years and an orbit altitude of about 500 km. The BGO
Calorimeter, which consists of 308 BGO (Bismuth Germanate Oxid) crystal bars,
616 PMTs (photomultiplier tubes) and 1848 dynode signals, has approximately 32
radiation lengths. It is a crucial sub-detector of the DAMPE payload, with the
functions of precisely measuring the energy of cosmic particles from 5 GeV to
10TeV, distinguishing positrons/electrons and gamma rays from hadron
background, and providing trigger information for the whole DAMPE payload. The
dynamic range for a single BGO crystal is about 2?105 and there are 1848
detector signals in total. To build such an instrument in space, the major
design challenges for the readout electronics come from the large dynamic
range, the high integrity inside the very compact structure, the strict power
supply budget and the long term reliability to survive the hush environment
during launch and in orbit. Currently the DAMPE mission is in the end of QM
(Qualification Model) stage. This paper presents a detailed description of the
readout electronics for the BGO calorimeter.",1406.3886v1
2014-11-24,Damping of liquid sloshing by foams,"When a container is set in motion, the free surface of the liquid starts to
oscillate or slosh. Such effects can be observed when a glass of water is
handled carelessly and the fluid sloshes or even spills over the rims of the
container. However, beer does not slosh as readily as water, which suggests
that foam could be used to damp sloshing. In this work, we study experimentally
the effect on sloshing of a liquid foam placed on top of a liquid bath. We
generate a monodisperse two-dimensional liquid foam in a rectangular container
and track the motion of the foam. The influence of the foam on the sloshing
dynamics is experimentally characterized: only a few layers of bubbles are
sufficient to significantly damp the oscillations. We rationalize our
experimental findings with a model that describes the foam contribution to the
damping coefficient through viscous dissipation on the walls of the container.
Then we extend our study to confined three-dimensional liquid foam and observe
that the behavior of 2D and confined 3D systems are very similar. Thus we
conclude that only the bubbles close to the walls have a significant impact on
the dissipation of energy. The possibility to damp liquid sloshing using foam
is promising in numerous industrial applications such as the transport of
liquefied gas in tankers or for propellants in rocket engines.",1411.6542v2
2015-04-16,Attenuation of short strongly nonlinear stress pulses in dissipative granular chains,"Attenuation of short, strongly nonlinear stress pulses in chains of spheres
and cylinders was investigated experimentally and numerically for two ratios of
their masses keeping their contacts identical. The chain with mass ratio 0.98
supports solitary waves and another one (with mass ratio 0.55) supports
nonstationary pulses which preserve their identity only on relatively short
distances, but attenuate on longer distances because of radiation of small
amplitude tails generated by oscillating small mass particles. Pulse
attenuation in experiments in the chain with mass ratio 0.55 was faster at the
same number of the particles from the entrance than in the chain with mass
ratio 0.98. It is in quantitative agreement with results of numerical
calculations with effective damping coefficient 6 kg/s. This level of damping
was critical for eliminating the gap openings between particles in the system
with mass ratio 0.55 present at lower or no damping. However with increase of
dissipation numerical results show that the chain with mass ratio 0.98 provides
faster attenuation than chain with mass ratio 0.55 due to the fact that the
former system supports the narrower pulse with the larger difference between
velocities of neighboring particles. The investigated chains demonstrated
different wave structure at zero dissipation and at intermediate damping
coefficients and the similar behavior at large damping.",1504.04344v1
2015-04-17,Chiral damping of magnetic domain walls,"Structural symmetry breaking in magnetic materials is responsible for a
variety of outstanding physical phenomena. Examples range from the existence of
multiferroics, to current induced spin orbit torques (SOT) and the formation of
topological magnetic structures. In this letter we bring into light a novel
effect of the structural inversion asymmetry (SIA): a chiral damping mechanism.
This phenomenon is evidenced by measuring the field driven domain wall (DW)
motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. The
difficulty in evidencing the chiral damping is that the ensuing DW dynamics
exhibit identical spatial symmetry to those expected from the
Dzyaloshinskii-Moriya interaction (DMI). Despite this fundamental resemblance,
the two scenarios are differentiated by their time reversal properties: while
DMI is a conservative effect that can be modeled by an effective field, the
chiral damping is purely dissipative and has no influence on the equilibrium
magnetic texture. When the DW motion is modulated by an in-plane magnetic
field, it reveals the structure of the internal fields experienced by the DWs,
allowing to distinguish the physical mechanism. The observation of the chiral
damping, not only enriches the spectrum of physical phenomena engendered by the
SIA, but since it can coexists with DMI it is essential for conceiving DW and
skyrmion devices.",1504.04411v1
2015-07-28,Spatial damping of propagating sausage waves in coronal cylinders,"Sausage modes are important in coronal seismology. Spatially damped
propagating sausage waves were recently observed in the solar atmosphere. We
examine how wave leakage influences the spatial damping of sausage waves
propagating along coronal structures modeled by a cylindrical density
enhancement embedded in a uniform magnetic field. Working in the framework of
cold magnetohydrodynamics, we solve the dispersion relation (DR) governing
sausage waves for complex-valued longitudinal wavenumber $k$ at given real
angular frequencies $\omega$. For validation purposes, we also provide
analytical approximations to the DR in the low-frequency limit and in the
vicinity of $\omega_{\rm c}$, the critical angular frequency separating trapped
from leaky waves. In contrast to the standing case, propagating sausage waves
are allowed for $\omega$ much lower than $\omega_{\rm c}$. However, while able
to direct their energy upwards, these low-frequency waves are subject to
substantial spatial attenuation. The spatial damping length shows little
dependence on the density contrast between the cylinder and its surroundings,
and depends only weakly on frequency. This spatial damping length is of the
order of the cylinder radius for $\omega \lesssim 1.5 v_{\rm Ai}/a$, where $a$
and $v_{\rm Ai}$ are the cylinder radius and the Alfv\'en speed in the
cylinder, respectively. We conclude that if a coronal cylinder is perturbed by
symmetric boundary drivers (e.g., granular motions) with a broadband spectrum,
wave leakage efficiently filters out the low-frequency components.",1507.07724v1
2015-10-19,On the branching of the quasinormal resonances of near-extremal Kerr black holes,"It has recently been shown by Yang. et. al. [Phys. Rev. D {\bf 87}, 041502(R)
(2013)] that rotating Kerr black holes are characterized by two distinct sets
of quasinormal resonances. These two families of quasinormal resonances display
qualitatively different asymptotic behaviors in the extremal ($a/M\to 1$)
black-hole limit: The zero-damping modes (ZDMs) are characterized by relaxation
times which tend to infinity in the extremal black-hole limit ($\Im\omega\to 0$
as $a/M\to 1$), whereas the damped modes (DMs) are characterized by non-zero
damping rates ($\Im\omega\to$ finite-values as $a/M\to 1$). In this paper we
refute the claim made by Yang et. al. that co-rotating DMs of near-extremal
black holes are restricted to the limited range $0\leq
\mu\lesssim\mu_{\text{c}}\approx 0.74$, where $\mu\equiv m/l$ is the
dimensionless ratio between the azimuthal harmonic index $m$ and the spheroidal
harmonic index $l$ of the perturbation mode. In particular, we use an
analytical formula originally derived by Detweiler in order to prove the
existence of DMs (damped quasinormal resonances which are characterized by
finite $\Im\omega$ values in the $a/M\to 1$ limit) of near-extremal black holes
in the $\mu>\mu_{\text{c}}$ regime, the regime which was claimed by Yang et.
al. not to contain damped modes. We show that these co-rotating DMs (in the
regime $\mu>\mu_{\text{c}}$) are expected to characterize the resonance spectra
of rapidly-rotating (near-extremal) black holes with $a/M\gtrsim 1-10^{-9}$.",1510.05604v1
2016-02-16,Damping and power spectra of quasi-periodic intensity disturbances above a solar polar coronal hole,"We study intensity disturbances above a solar polar coronal hole seen in the
AIA 171 \AA\ and 193 \AA\ passbands, aiming to provide more insights into their
physical nature. The damping and power spectra of the intensity disturbances
with frequencies from 0.07 mHz to 10.5 mHz are investigated. The damping of the
intensity disturbances tends to be stronger at lower frequencies, and their
damping behavior below 980"" (for comparison, the limb is at 945"") is different
from what happens above. No significant difference is found between the damping
of the intensity disturbances in the AIA 171 \AA\ and that in the AIA 193 \AA.
The indices of the power spectra of the intensity disturbances are found to be
slightly smaller in the AIA 171 \AA\ than in the AIA 193 \AA, but the
difference is within one sigma deviation. An additional enhanced component is
present in the power spectra in a period range of 8--40 minutes at lower
heights. While the power spectra of spicule is highly correlated with its
associated intensity disturbance, it suggests that the power spectra of the
intensity disturbances might be a mixture of spicules and wave activities. We
suggest that each intensity disturbance in the polar coronal hole is possibly a
series of independent slow magnetoacoustic waves triggered by spicular
activities.",1602.04883v1
2016-04-20,Nonlinear wave damping due to multi-plasmon resonances,"For short wavelengths, it is well known that the linearized Wigner-Moyal
equation predicts wave damping due to wave-particle interaction, where the
resonant velocity shifted from the phase velocity by a velocity $v_q = \hbar
k/2m$. Here $\hbar$ is the reduced Planck constant, $k$ is the wavenumber and
$m$ is the electron mass. Going beyond linear theory, we find additional
resonances with velocity shifts $n v_q$, $n = 2, 3, \ldots$, giving rise to a
new wave-damping mechanism that we term \emph{multi-plasmon damping}, as it can
be seen as the simultaneous absorption (or emission) of multiple plasmon
quanta. Naturally this wave damping is not present in classical plasmas. For a
temperature well below the Fermi temperature, if the linear ($n = 1$) resonant
velocity is outside the Fermi sphere, the number of linearly resonant particles
is exponentially small, while the multi-plasmon resonances can be located in
the bulk of the distribution. We derive sets of evolution equations for the
case of two-plasmon and three-plasmon resonances for Langmuir waves in the
simplest case of a fully degenerate plasma. By solving these equations
numerically for a range of wave-numbers we find the corresponding damping
rates, and we compare them to results from linear theory to estimate the
applicability. Finally, we discuss the effects due to a finite temperature.",1604.05983v2
2016-05-09,Storage-ring Electron Cooler for Relativistic Ion Beams,"Application of electron cooling at ion energies above a few GeV has been
limited due to reduction of electron cooling efficiency with energy and
difficulty in producing and accelerating a high-current high-quality electron
beam. A high-current storage-ring electron cooler offers a solution to both of
these problems by maintaining high cooling beam quality through
naturally-occurring synchrotron radiation damping of the electron beam.
However, the range of ion energies where storage-ring electron cooling can be
used has been limited by low electron beam damping rates at low ion energies
and high equilibrium electron energy spread at high ion energies. This paper
reports a development of a storage ring based cooler consisting of two sections
with significantly different energies: the cooling and damping sections. The
electron energy and other parameters in the cooling section are adjusted for
optimum cooling of a stored ion beam. The beam parameters in the damping
section are adjusted for optimum damping of the electron beam. The necessary
energy difference is provided by an energy recovering SRF structure. A
prototype linear optics of such storage-ring cooler and initial tracking
simulations are presented and some potential issues such as coherent
synchrotron radiation and beam break up are discussed.",1605.02594v1
2016-07-06,Measuring Collisionless Damping in Heliospheric Plasmas using Field-Particle Correlations,"An innovative field-particle correlation technique is proposed that uses
single-point measurements of the electromagnetic fields and particle velocity
distribution functions to investigate the net transfer of energy from fields to
particles associated with the collisionless damping of turbulent fluctuations
in weakly collisional plasmas, such as the solar wind. In addition to providing
a direct estimate of the local rate of energy transfer between fields and
particles, it provides vital new information about the distribution of that
energy transfer in velocity space. This velocity-space signature can
potentially be used to identify the dominant collisionless mechanism
responsible for the damping of turbulent fluctuations in the solar wind. The
application of this novel field-particle correlation technique is illustrated
using the simplified case of the Landau damping of Langmuir waves in an
electrostatic 1D-1V Vlasov-Poisson plasma, showing that the procedure both
estimates the local rate of energy transfer from the electrostatic field to the
electrons and indicates the resonant nature of this interaction. Modifications
of the technique to enable single-point spacecraft measurements of fields and
particles to diagnose the collisionless damping of turbulent fluctuations in
the solar wind are discussed, yielding a method with the potential to transform
our ability to maximize the scientific return from current and upcoming
spacecraft missions, such as the Magnetospheric Multiscale (MMS) and Solar
Probe Plus missions.",1607.01738v1
2016-07-22,Excitation of nonlinear ion acoustic waves in CH plasmas,"Excitation of nonlinear ion acoustic wave (IAW) by an external electric field
is demonstrated by Vlasov simulation. The frequency calculated by the
dispersion relation with no damping is verified much closer to the resonance
frequency of the small-amplitude nonlinear IAW than that calculated by the
linear dispersion relation. When the wave number $ k\lambda_{De} $ increases,
the linear Landau damping of the fast mode (its phase velocity is greater than
any ion's thermal velocity) increases obviously in the region of $ T_i/T_e <
0.2 $ in which the fast mode is weakly damped mode. As a result, the deviation
between the frequency calculated by the linear dispersion relation and that by
the dispersion relation with no damping becomes larger with $k\lambda_{De}$
increasing. When $k\lambda_{De}$ is not large, such as $k\lambda_{De}=0.1, 0.3,
0.5$, the nonlinear IAW can be excited by the driver with the linear frequency
of the modes. However, when $k\lambda_{De}$ is large, such as
$k\lambda_{De}=0.7$, the linear frequency can not be applied to exciting the
nonlinear IAW, while the frequency calculated by the dispersion relation with
no damping can be applied to exciting the nonlinear IAW.",1607.06598v1
2016-11-17,A stable partitioned FSI algorithm for rigid bodies and incompressible flow. Part II: General formulation,"A stable partitioned algorithm is developed for fluid-structure interaction
(FSI) problems involving viscous incompressible flow and rigid bodies. This
{\em added-mass partitioned} (AMP) algorithm remains stable, without
sub-iterations, for light and even zero mass rigid bodies when added-mass and
viscous added-damping effects are large. The scheme is based on a generalized
Robin interface condition for the fluid pressure that includes terms involving
the linear acceleration and angular acceleration of the rigid body. Added mass
effects are handled in the Robin condition by inclusion of a boundary integral
term that depends on the pressure. Added-damping effects due to the viscous
shear forces on the body are treated by inclusion of added-damping tensors that
are derived through a linearization of the integrals defining the force and
torque. Added-damping effects may be important at low Reynolds number, or, for
example, in the case of a rotating cylinder or rotating sphere when the
rotational moments of inertia are small. In this second part of a two-part
series, the general formulation of the AMP scheme is presented including the
form of the AMP interface conditions and added-damping tensors for general
geometries. A fully second-order accurate implementation of the AMP scheme is
developed in two dimensions based on a fractional-step method for the
incompressible Navier-Stokes equations using finite difference methods and
overlapping grids to handle the moving geometry. The numerical scheme is
verified on a number of difficult benchmark problems.",1611.05703v2
2017-03-01,The Plastic Scintillator Detector at DAMPE,"he DArk Matter Particle Explorer (DAMPE) is a general purposed
satellite-borne high energy $\gamma-$ray and cosmic ray detector, and among the
scientific objectives of DAMPE are the searches for the origin of cosmic rays
and an understanding of Dark Matter particles. As one of the four detectors in
DAMPE, the Plastic Scintillator Detector (PSD) plays an important role in the
particle charge measurement and the photons/electrons separation. The PSD has
82 modules, each consists of a long organic plastic scintillator bar and two
PMTs at both ends for readout, in two layers and covers an overall active area
larger than 82 cm $\times$ 82 cm. It can identify the charge states for
relativistic ions from H to Fe, and the detector efficiency for Z=1 particles
can reach 0.9999. The PSD has been successfully launched with DAMPE on Dec. 17,
2015. In this paper, the design, the assembly, the qualification tests of the
PSD and some of the performance measured on the ground have been described in
detail.",1703.00098v1
2017-03-22,Observation of a strong coupling effect on electron-ion collisions in ultracold plasmas,"Ultracold plasmas (UCP) provide a well-controlled system for studying
multiple aspects in plasma physics that include collisions and strong coupling
effects. By applying a short electric field pulse to a UCP, a plasma electron
center-of-mass (CM) oscillation can be initiated. In accessible parameter
ranges, the damping rate of this oscillation is determined by the electron-ion
collision rate. We performed measurements of the oscillation damping rate with
such parameters and compared the measured rates to both a molecular dynamic
(MD) simulation that includes strong coupling effects and to Monte-Carlo
collisional operator simulation designed to predict the damping rate including
only weak coupling considerations. We found agreement between experimentally
measured damping rate and the MD result. This agreement did require including
the influence of a previously unreported UCP heating mechanism whereby the
presence of a DC electric field during ionization increased the electron
temperature, but estimations and simulations indicate that such a heating
mechanism should be present for our parameters. The measured damping rate at
our coldest electron temperature conditions was much faster than the weak
coupling prediction obtained from the Monte-Carlo operator simulation, which
indicates the presence of significant strong coupling influence. The density
averaged electron strong coupling parameter $\Gamma$ measured at our coldest
electron temperature conditions was 0.35.",1703.07852v2
2017-04-18,Critical pairing fluctuations in the normal state of a superconductor: pseudogap and quasi-particle damping,"We study the effect of critical pairing fluctuations on the electronic
properties in the normal state of a clean superconductor in three dimensions.
Using a functional renormalization group approach to take the non-Gaussian
nature of critical fluctuations into account, we show microscopically that in
the BCS regime, where the inverse coherence length is much smaller than the
Fermi wavevector, critical pairing fluctuations give rise to a non-analytic
contribution to the quasi-particle damping of order $ T_c \sqrt{Gi} \ln ( 80 /
Gi )$, where the Ginzburg-Levanyuk number $Gi$ is a dimensionless measure for
the width of the critical region. As a consequence, there is a temperature
window above $T_c$ where the quasiparticle damping due to critical pairing
fluctuations can be larger than the usual $T^2$-Fermi liquid damping due to
non-critical scattering processes. On the other hand, in the strong coupling
regime where $Gi$ is of order unity, we find that the quasiparticle damping due
to critical pairing fluctuations is proportional to the temperature. Moreover,
we show that in the vicinity of the critical temperature $T_c$ the electronic
density of states exhibits a fluctuation-induced pseudogap. We also use
functional renormalization group methods to derive and classify various types
of processes induced by the pairing interaction in Fermi systems close to the
superconducting instability.",1704.05282v2
2017-05-29,Probing decoherence in plasmonic waveguides in the quantum regime,"We experimentally investigate the decoherence of single surface plasmon
polaritons in metal stripe waveguides. In our study we use a Mach-Zehnder
configuration previously considered for measuring decoherence in atomic,
electronic and photonic systems. By placing waveguides of different length in
one arm we are able to measure the amplitude damping time T_1 = 1.90 +/- 0.01 x
10^-14 s, pure phase damping time T_2^* = 11.19 +/- 4.89 x 10^-14 s and total
phase damping time T_2 = 2.83 +/- 0.32 x 10^-14 s. We find that decoherence is
mainly due to amplitude damping and thus loss arising from inelastic electron
and photon scattering plays the most important role in the decoherence of
plasmonic waveguides in the quantum regime. However, pure phase damping is not
completely negligible. The results will be useful in the design of plasmonic
waveguide systems for carrying out phase-sensitive quantum applications, such
as quantum sensing. The probing techniques developed may also be applied to
other plasmonic nanostructures, such as those used as nanoantennas, as unit
cells in metamaterials and as nanotraps for cold atoms.",1705.10344v2
2017-07-21,Spatially Localized Particle Energization by Landau Damping in Current Sheets Produced by Strong Alfven Wave Collisions,"Understanding the removal of energy from turbulent fluctuations in a
magnetized plasma and the consequent energization of the constituent plasma
particles is a major goal of heliophysics and astrophysics. Previous work has
shown that nonlinear interactions among counterpropagating Alfven waves---or
Alfven wave collisions---are the fundamental building block of astrophysical
plasma turbulence and naturally generate current sheets in the strongly
nonlinear limit. A nonlinear gyrokinetic simulation of a strong Alfven wave
collision is used to examine the damping of the electromagnetic fluctuations
and the associated energization of particles that occurs in self-consistently
generated current sheets. A simple model explains the flow of energy due to the
collisionless damping and the associated particle energization, as well as the
subsequent thermalization of the particle energy by collisions. The net
particle energization by the parallel electric field is shown to be spatially
intermittent, and the nonlinear evolution is essential in enabling that spatial
non-uniformity. Using the recently developed field-particle correlation
technique, we show that particles resonant with the Alfven waves in the
simulation dominate the energy transfer, demonstrating conclusively that Landau
damping plays a key role in the spatially intermittent damping of the
electromagnetic fluctuations and consequent energization of the particles in
this strongly nonlinear simulation.",1708.00757v1
2017-10-30,Enhancement of intrinsic magnetic damping in defect-free epitaxial Fe3O4 thin films,"We have investigated the magnetic damping of precessional spin dynamics in
defect-controlled epitaxial grown Fe$_3$O$_4$(111)/Yttria-stabilized Zirconia
(YSZ) nanoscale films by all-optical pump-probe measurements. The intrinsic
damping constant of the defect-free Fe$_3$O$_4$ film is found to be strikingly
larger than that of the as-grown Fe$_3$O$_4$ film with structural defects. We
demonstrate that the population of the first-order perpendicular standing spin
wave (PSSW) mode, which is exclusively observed in the defect-free film under
sufficiently high external magnetic fields, leads to the enhancement of the
magnetic damping of the uniform precession (Kittel) mode. We propose a physical
picture in which the PSSW mode acts as an additional channel for the extra
energy dissipation of the Kittel mode. The energy transfer from Kittel mode to
PSSW mode increases as in-plane magnetization precession becomes more uniform,
resulting in the unique intrinsic magnetic damping enhancement in the
defect-free Fe$_3$O$_4$ film.",1710.10938v2
2018-05-26,Critical collapse of ultra-relativistic fluids: damping or growth of aspherical deformations,"We perform fully nonlinear numerical simulations to study aspherical
deformations of the critical self-similar solution in the gravitational
collapse of ultra-relativistic fluids. Adopting a perturbative calculation,
Gundlach predicted that these perturbations behave like damped or growing
oscillations, with the frequency and damping (or growth) rates depending on the
equation of state. We consider a number of different equations of state and
degrees of asphericity and find very good agreement with the findings of
Gundlach for polar $\ell = 2$ modes. For sufficiently soft equations of state,
the modes are damped, meaning that, in the limit of perfect fine-tuning, the
spherically symmetric critical solution is recovered. We find that the degree
of asphericity has at most a small effect on the frequency and damping
parameter, or on the critical exponents in the power-law scalings. Our findings
also confirm, for the first time, Gundlach's prediction that the $\ell = 2$
modes become unstable for sufficiently stiff equations of state. In this regime
the spherically symmetric self-similar solution can no longer be recovered by
fine-tuning to the black-hole threshold, and one can no longer expect power-law
scaling to hold to arbitrarily small scales.",1805.10442v1
2018-06-19,Non-linear Relaxation of Interacting Bosons Coherently Driven on a Narrow Optical Transition,"We study the dynamics of a two-component Bose-Einstein condensate (BEC) of
$^{174}$Yb atoms coherently driven on a narrow optical transition. The
excitation transfers the BEC to a superposition of states with different
internal and momentum quantum numbers. We observe a crossover with decreasing
driving strength between a regime of damped oscillations, where coherent
driving prevails, and an incoherent regime, where relaxation takes over.
Several relaxation mechanisms are involved: inelastic losses involving two
excited atoms, leading to a non-exponential decay of populations; Doppler
broadening due to the finite momentum width of the BEC and inhomogeneous
elastic interactions, both leading to dephasing and to damping of the
oscillations. We compare our observations to a two-component Gross-Pitaevskii
(GP) model that fully includes these effects. For small or moderate densities,
the damping of the oscillations is mostly due to Doppler broadening. In this
regime, we find excellent agreement between the model and the experimental
results. For higher densities, the role of interactions increases and so does
the damping rate of the oscillations. The damping in the GP model is less
pronounced than in the experiment, possibly a hint for many-body effects not
captured by the mean-field description.",1806.07210v2
2018-10-16,The Solution to the Differential Equation with Linear Damping describing a Physical Systems governed by a Cubic Energy Potential,"An analytical solution to the nonlinear differential equation describing the
equation of motion of a particle moving in an unforced physical system with
linear damping, governed by a cubic potential well, is presented in terms of
the Jacobi elliptic functions. In the attractive region of the potential the
system becomes an anharmonic damped oscillator, however with asymmetric
displacement. An expression for the period of oscillation is derived, which for
a nonlinear damped system is time dependent, and in particular it contains a
quartic root of an exponentially decaying term in the denominator. Initially
the period is longer as compared to that of a linear oscillator, however
gradually it decreases to that of a linear damped oscillator.
  Transforming the undamped nonlinear differential equation into the
differential equation describing orbital motion of planets, the perihelion
advance of Mercury can be estimated to 42.98 arcseconds/century, close to
present day observations of 43.1 arcseconds/century.
  Some familiarity with the Jacobi elliptic functions is required, in
particular with respect to the differential behavior of these functions,
however, they are standard functions of advanced mathematical computer algebra
tools. The expression derived for the solution to the nonlinear physical
system, and in particular the expression for the period of oscillation, is
useful for an accurate evaluation of experiments in introductory and advanced
physics labs, but also of interest for specialists working with nonlinear
phenomena governed by the cubic potential well.",1810.10336v1
2019-01-10,Damping and softening of transverse acoustic phonons in colossal magnetoresistive La$_{0.7}$Ca$_{0.3}$MnO$_3$ and La$_{0.7}$Sr$_{0.3}$MnO$_3$,"Neutron spectroscopy is used to probe transverse acoustic phonons near the
(2, 2, 0) Bragg position in colossal magnetoresistive La0.7Ca0.3MnO3 and
La0.7Sr0.3MnO3. Upon warming to temperatures near Tc = 257 K the phonon peaks
in La0.7Ca0.3MnO3 soften and damp significantly with the phonon half width at
half maximum approaching 2.5 meV for phonons at a reduced wave vector of q =
(0.2, 0.2, 0). Concurrently a quasielastic component develops that dominates
the spectrum near the polaron position at high temperatures. This quasielastic
scattering is ~5 times more intense near Tc than in La0.7Sr0.3MnO3 despite
comparable structural distortions in the two. The damping becomes more
significant near the polaron position with a temperature dependence similar to
that of polaron structural distortions. An applied magnetic field of 9.5 T only
partially reverses the damping and quasielastic component, despite smaller
fields being sufficient to drive the colossal magnetoresistive effect. The
phonon energy, on the other hand, is unaffected by field. The damping in
La0.7Sr0.3MnO3 near Tc at a reduced wave vector of q = (0.25, 0.25, 0) is
significantly smaller but displays a similar trend with an applied magnetic
field.",1901.03394v1
2019-03-13,Inference of magnetic field strength and density from damped transverse coronal waves,"A classic application of coronal seismology uses transverse oscillations of
waveguides to obtain estimates of the magnetic field strength. The procedure
requires information on the density of the structures. Often, it ignores the
damping of the oscillations. We computed marginal posteriors for parameters
such as the waveguide density; the density contrast; the transverse
inhomogeneity length-scale; and the magnetic field strength, under the
assumption that the oscillations can be modelled as standing
magnetohydrodynamic (MHD) kink modes damped by resonant absorption. Our results
show that the magnetic field strength can be properly inferred, even if the
densities inside and outside the structure are largely unknown. Incorporating
observational estimates of plasma density further constrains the obtained
posteriors. The amount of information one is willing to include (a priori) for
the density and the density contrast influences their corresponding posteriors,
but very little the inferred magnetic field strength. The decision to include
or leave out the information on the damping and the damping time-scales have a
minimal impact on the obtained magnetic field strength. In contrast to the
classic method which provides with numerical estimates with error bars or
possible ranges of variation for the magnetic field strength, Bayesian methods
offer the full distribution of plausibility over the considered range of
possible values. The methods are applied to available datasets of observed
transverse loop oscillations, can be extended to prominence fine structures or
chromospheric spicules and implemented to propagating waves in addition to
standing oscillations.",1903.05437v1
2019-03-14,A metal-poor damped Ly-alpha system at redshift 6.4,"We identify a strong Ly-alpha damping wing profile in the spectrum of the
quasar P183+05 at z=6.4386. Given the detection of several narrow metal
absorption lines at z=6.40392, the most likely explanation for the absorption
profile is that it is due to a damped Ly-alpha system. However, in order to
match the data a contribution of an intergalactic medium 5-38% neutral or
additional weaker absorbers near the quasar is also required. The absorption
system presented here is the most distant damped Ly-alpha system currently
known. We estimate an HI column density ($10^{20.68\pm0.25}\,$cm$^{-2}$),
metallicity ([O/H]$=-2.92\pm 0.32$), and relative chemical abundances of a
system consistent with a low-mass galaxy during the first Gyr of the universe.
This object is among the most metal-poor damped Ly-alpha systems known and,
even though it is observed only ~850 Myr after the big bang, its relative
abundances do not show signatures of chemical enrichment by Population III
stars.",1903.06186v2
2019-04-30,DmpIRFs and DmpST: DAMPE Instrument Response Functions and Science Tools for Gamma-Ray Data Analysis,"GeV gamma ray is an important observation target of DArk Matter Particle
Explorer (DAMPE) for indirect dark matter searching and high energy
astrophysics. We present in this work a set of accurate instrument response
functions of DAMPE (DmpIRFs) including the effective area, point-spread
function and energy dispersion that are crucial for the gamma-ray data analysis
based on the high statistics simulation data. A dedicated software named DmpST
is developed to facilitate the scientific analyses of DAMPE gamma-ray data.
Considering the limited number of photons and the angular resolution of DAMPE,
the maximum likelihood method is adopted in the DmpST to better disentangle
different source components. The basic mathematics and the framework regarding
this software are also introduced in this paper.",1904.13098v1
2019-05-14,Fractional damping through restricted calculus of variations,"We deliver a novel approach towards the variational description of Lagrangian
mechanical systems subject to fractional damping by establishing a restricted
Hamilton's principle. Fractional damping is a particular instance of non-local
(in time) damping, which is ubiquitous in mechanical engineering applications.
The restricted Hamilton's principle relies on including fractional derivatives
to the state space, the doubling of curves (which implies an extra mirror
system) and the restriction of the class of varied curves. We will obtain the
correct dynamics, and will show rigorously that the extra mirror dynamics is
nothing but the main one in reversed time; thus, the restricted Hamilton's
principle is not adding extra physics to the original system. The price to pay,
on the other hand, is that the fractional damped dynamics is only a sufficient
condition for the extremals of the action. In addition, we proceed to
discretise the new principle. This discretisation provides a set of numerical
integrators for the continuous dynamics that we denote Fractional Variational
Integrators (FVIs). The discrete dynamics is obtained upon the same
ingredients, say doubling of discrete curves and restriction of the discrete
variations. We display the performance of the FVIs, which have local truncation
order 1, in two examples. As other integrators with variational origin, for
instance those generated by the discrete Lagrange-d'Alembert principle, they
show a superior performance tracking the dissipative energy, in opposition to
direct (order 1) discretisations of the dissipative equations, such as explicit
and implicit Euler schemes.",1905.05608v1
2019-05-22,Ultra-low magnetic damping in Co 2 Mn-based Heusler compounds: promising materials for spintronic,"The prediction of ultra-low magnetic damping in Co 2 MnZ Heusler half-metal
thin-film magnets is explored in this study and the damping response is shown
to be linked to the underlying electronic properties. By substituting the Z
elements in high crystalline quality films (Co 2 MnZ with Z=Si, Ge, Sn, Al, Ga,
Sb), electronic properties such as the minority spin band gap, Fermi energy
position in the gap and spin polarization can be tuned and the consequence on
magnetization dynamics analyzed. The experimental results allow us to directly
explore the interplay of spin polarization, spin gap, Fermi energy position and
the magnetic damping obtained in these films, together with ab initio
calculation predictions. The ultra-low magnetic damping coefficients measured
in the range 4.1 10-4-9 10-4 for Co 2 MnSi, Ge, Sn, Sb are the lowest values
obtained on a conductive layer and offers a clear experimental demonstration of
theoretical predictions on Half-Metal Magnetic Heusler compounds and a pathway
for future materials design.",1905.08987v1
2019-07-16,Damping of slow magnetoacoustic oscillations by the misbalance between heating and cooling processes in the solar corona,"Rapidly decaying slow magnetoacoustic waves are regularly observed in the
solar coronal structures, offering a promising tool for a seismological
diagnostics of the coronal plasma, including its thermodynamical properties.
The effect of damping of standing slow magnetoacoustic oscillations in the
solar coronal loops is investigated accounting for the field-aligned thermal
conductivity and a wave-induced misbalance between radiative cooling and some
unspecified heating rates. The non-adiabatic terms were allowed to be
arbitrarily large, corresponding to the observed values. The thermal
conductivity was taken in its classical form, and a power-law dependence of the
heating function on the density and temperature was assumed. The analysis was
conducted in the linear regime and in the infinite magnetic field
approximation. The wave dynamics is found to be highly sensitive to the
characteristic time scales of the thermal misbalance. Depending on certain
values of the misbalance time scales three regimes of the wave evolution were
identified, namely the regime of a suppressed damping, enhanced damping where
the damping rate drops down to the observational values, and acoustic
over-stability. The specific regime is determined by the dependences of the
radiative cooling and heating functions on thermodynamical parameters of the
plasma in the vicinity of the perturbed thermal equilibrium. The comparison of
the observed and theoretically derived decay times and oscillation periods
allows us to constrain the coronal heating function. For typical coronal
parameters, the observed properties of standing slow magnetoacoustic
oscillations could be readily reproduced with a reasonable choice of the
heating function.",1907.07051v1
2019-07-29,Breather arrest in a chain of damped oscillators with Hertzian contact,"We explore breather propagation in the damped oscillatory chain with
essentially nonlinear (non-linearizable) nearest-neighbour coupling.
Combination of the damping and the substantially nonlinear coupling leads to
rather unusual two-stage pattern of the breather propagation. The first stage
occurs at finite fragment of the chain and is characterized by power-law decay
of the breather amplitude. The second stage is characterized by extremely small
breather amplitudes that decay hyper-exponentially with the site number. Thus,
practically, one can speak about finite penetration depth of the breather. This
phenomenon is referred to as breather arrest (BA). As particular example, we
explore the chain with Hertzian contacts. Dependencies of the breather
penetration depth on the initial excitation and on the damping coefficient on
the breather penetration depth obey power laws. The results are rationalized by
considering beating responses in a system of two damped linear oscillators with
strongly nonlinear (non-linearizable) coupling. Initial excitation of one of
these oscillators leads to strictly finite number of beating cycles. Then, the
beating cycle in this simplified system is associated with the passage of the
discrete breather between the neighbouring sites in the chain. Somewhat
surprisingly, this simplified model reliably predicts main quantitative
features of the breather arrest in the chain, including the exponents in
numerically observed power laws.",1907.12462v1
2019-08-22,Influence of structure and cation distribution on magnetic anisotropy and damping in Zn/Al doped nickel ferrites,"An in-depth analysis of Zn/Al doped nickel ferrites grown by reactive
magnetron sputtering is relevant due to their promising characteristics for
applications in spintronics. The material is insulating and ferromagnetic at
room temperature with an additional low magnetic damping. By studying the
complex interplay between strain and cation distribution their impact on the
magnetic properties, i.e. anisotropy, damping and g-factor is unravelled. In
particular, a strong influence of the lattice site occupation of
Ni$^{2+}_{\text{Td}}$ and cation coordination of Fe$^{2+}_{\text{Oh}}$ on the
intrinsic damping is found. Furthermore, the critical role of the incorporation
of Zn$^{2+}$ and Al$^{3+}$ is evidenced by comparison with a sample of altered
composition. Especially, the dopant Zn$^{2+}$ is evidenced as a tuning factor
for Ni$^{2+}_{\text{Td}}$ and therefore unquenched orbital moments directly
controlling the g-factor. A strain-independent reduction of the magnetic
anisotropy and damping by adapting the cation distribution is demonstrated.",1908.08257v3
2019-09-11,Critical corrections to formulations of nonlinear energy dissipation of ultrasonically excited bubbles and a unifying parameter to asses and enhance bubble activity in applications,"Nonlinear oscillations of bubbles can significantly increase the attenuation
of the host media. Optimization of bubble related applications needs a
realistic estimation of the medium attenuation and bubble activity. A correct
estimation of the wave attenuation in bubbly media requires an accurate
estimation of the power dissipated by nonlinear oscillations of bubbles.
Pioneering work of Louisnard \cite{1} meticulously derived the nonlinear energy
terms for viscous and thermal damping; however, radiation damping arising from
the compressibility of the liquid was neglected. Jamshidi $\&$ Brenner \cite{2}
have considered the effects of the compressibility of the liquid and showed
that damping due to radiation becomes the most significant factor at pressures
above the blake threshold. Despite the improvement in their formulation;
however, the radiation damping term estimates non-physical values for some
frequency and pressure regions including near resonance oscillations. Thus, the
new terms arising from the compressibility of the liquid needs critical
assessment. In this work, we provide critical corrections to the present
formulations. Importance of the new corrections are highlighted by the
scattering to damping ratio (STDR). We then introduce a unifying parameter to
assess the efficacy of applications; this parameter is defined as the
multiplication of maximum scattered pressure by STDR.",1909.04864v1
2019-09-14,Measurement-Based Wide-Area Damping of Inter-Area Oscillations based on MIMO Identification,"Interconnected power grid exhibits oscillatory response after a disturbance
in the system. One such type of oscillations, the inter-area oscillations has
the oscillation frequency in the range of 0.1 to 1 Hz. The damping of
inter-area oscillations is difficult with local controllers, but it can be
achieved using a Wide Area Damping Controller (WADC). For effective control,
the input to the WADC should be the most observable signal and the WADC output
should be sent to the most controllable generator. This paper presents a
measurement-based novel algorithm for multi-input-multi-output (MIMO) transfer
function identification of the power system based on optimization to estimate
such oscillation frequencies. Based on the MIMO transfer function the optimal
control loop for WADC is estimated. The WADC design is based on the discrete
linear quadratic regulator (DLQR) and Kalman filtering for damping of
inter-area oscillations. Since the MIMO identification is based on actual
measurements, the proposed method can accurately monitor changes in the power
grid whereas the conventional methods are based on small-signal analysis of a
linearized model which does not consider changing operating conditions. The
overall algorithm is implemented and validated on a RTDS/RSCAD and MATLAB
real-time co-simulation platform using two-area and IEEE 39 bus power system
models.",1909.06687v1
2019-12-09,Analytical solution of linearized equations of the Morris-Lecar neuron model at large constant stimulation,"The classical biophysical Morris-Lecar model of neuronal excitability
predicts that upon stimulation of the neuron with a sufficiently large constant
depolarizing current there exists a finite interval of the current values where
periodic spike generation occurs. Above the upper boundary of this interval,
there is four-stage damping of the spike amplitude: 1) minor primary damping,
which reflects a typical transient to stationary dynamic state, 2) plateau of
nearly undamped periodic oscillations, 3) strong damping, and 4) reaching a
constant asymptotic value of the neuron potential. We have shown that in the
vicinity of the asymptote the Morris-Lecar equations can be reduced to the
standard equation for exponentially damped harmonic oscillations. Importantly,
all coefficients of this equation can be explicitly expressed through
parameters of the original Morris-Lecar model, enabling direct comparison of
the numerical and analytical solutions for the neuron potential dynamics at
later stages of the spike amplitude damping.",1912.04083v4
2020-03-16,Spin-orbit torques originating from bulk and interface in Pt-based structures,"We investigated spin-orbit torques in prototypical Pt-based spintronic
devices. We found that, in Pt/Ni and Pt/Fe bilayers, the damping-like torque
efficiency depends on the thickness of the Pt layer. We also found that the
damping-like torque efficiency is almost identical in the Pt/Ni and Pt/Fe
bilayers despite the stronger spin memory loss at the Pt/Fe interface. These
results suggest that although the dominant source of the damping-like torque is
the bulk spin Hall effect in the Pt layer, a sizable damping-like torque is
generated by the interface in the Pt/Fe bilayer due to the stronger interfacial
spin-orbit coupling. In contrast to the damping-like torque, whose magnitude
and sign are almost identical in the Pt/Ni and Pt/Fe bilayers, the field-like
torque strongly depends on the choice of the ferromagnetic layer. The sign of
the field-like torque originating from the bulk spin Hall effect in the Pt
layer is opposite between the Pt/Ni and Pt/Fe bilayers, which can be attributed
to the opposite sign of the imaginary part of the spin-mixing conductance.
These results demonstrate that the spin-orbit torques are quite sensitive to
the electronic structure of the FM layer.",2003.07271v2
2020-03-23,Heat-like and wave-like lifespan estimates for solutions of semilinear damped wave equations via a Kato's type lemma,"In this paper we study several semilinear damped wave equations with
""subcritical"" nonlinearities, focusing on demonstrating lifespan estimates for
energy solutions. Our main concern is on equations with scale-invariant damping
and mass. Under different assumptions imposed on the initial data, lifespan
estimates from above are clearly showed. The key fact is that we find
""transition surfaces"", which distinguish lifespan estimates between ""wave-like""
and ""heat-like"" behaviours. Moreover we conjecture that the lifespan estimates
on the ""transition surfaces"" can be logarithmically improved. As direct
consequences, we reorganize the blow-up results and lifespan estimates for the
massless case in which the ""transition surfaces"" degenerate to ""transition
curves"". Furthermore, we obtain improved lifespan estimates in one space
dimension, comparing to the known results. We also study semilinear wave
equations with the scattering damping and negative mass term, and find that if
the decay rate of the mass term equals to 2, the lifespan estimate is the same
as one special case of the equations with the scale-invariant damping and
positive mass. The main strategy of the proof consists of a Kato's type lemma
in integral form, which is established by iteration argument.",2003.10578v1
2020-09-03,Dynamics of magnetic collective modes in the square and triangular lattice Mott insulators at finite temperature,"We study the equilibrium dynamics of magnetic moments in the Mott insulating
phase of the Hubbard model on the square and triangular lattice. We rewrite the
Hubbard interaction in terms of an auxiliary vector field and use a recently
developed Langevin scheme to study its dynamics. A thermal `noise', derivable
approximately from the Keldysh formalism, allows us to study the effect of
finite temperature. At strong coupling, $U \gg t$, where $U$ is the local
repulsion and $t$ the nearest neighbour hopping, our results reproduce the well
known dynamics of the nearest neighbour Heisenberg model with exchange $J \sim
{\cal O}(t^2/U)$. These include crossover from weakly damped dispersive modes
at temperature $T \ll J$ to strong damping at $T \sim {\cal O}(J)$, and
diffusive dynamics at $T \gg J$. The crossover temperatures are naturally
proportional to $J$. To highlight the progressive deviation from Heisenberg
physics as $U/t$ reduces we compute an effective exchange scale $J_{eff}(U)$
from the low temperature spin wave velocity. We discover two features in the
dynamical behaviour with decreasing $U/t$: (i)~the low temperature dispersion
deviates from the Heisenberg result, as expected, due to longer range and
multispin interactions, and (ii)~the crossovers between weak damping, strong
damping, and diffusion take place at noticeably lower values of $T/J_{eff}$. We
relate this to enhanced mode coupling, in particular to thermal amplitude
fluctuations, at weaker $U/t$. A comparison of the square and triangular
lattice reveals the additional effect of geometric frustration on damping.",2009.01833v2
2020-09-15,Classification of the mechanisms of wave energy dissipation in the nonlinear oscillations of coated and uncoated bubbles,"Acoustic waves are dissipated when they pass through bubbly media.
Dissipation by bubbles takes place through thermal damping (Td), radiation
damping (Rd) and damping due to the friction of the liquid (Ld) and friction of
the coating (Cd). Knowledge of the contributions of the Td, Rd, Ld and Cd
during nonlinear bubble oscillations will help in optimizing bubble and
ultrasound exposure parameters for the relevant applications by maximizing a
desirable parameter. In this work we investigate the mechanisms of dissipation
in bubble oscillations and their contribution to the total damping (Wtotal) in
various nonlinear regimes. By using bifurcation analysis, we have classified
nonlinear dynamics of bubbles that are sonicated with their 3rd superharmonic
(SuH) and 2nd SuH resonance frequency (fr), pressure dependent resonance
frequency (PDfr), fr, subharmonic (SH) resonance (fsh=2fr), pressure dependent
SH resonance (PDfsh) and 1/3 order SH resonance. The corresponding Td, Rd, Ld,
Cd, Wtotal, scattering to dissipation ratio (STDR), maximum wall velocity and
maximum back-scattered pressure from non-destructive oscillations of bubbles
were calculated and analyzed using the bifurcation diagrams. We classified
different regimes of dissipation and provided parameter regions in which a
particular parameter of interest (e.g. Rd) can be enhanced. Afterwards enhanced
bubble activity is linked to some relevant applications in ultrasound. This
paper represents the first comprehensive analysis of the nonlinear oscillations
regimes and the corresponding damping mechanisms.",2009.07380v1
2020-11-18,The effect of redshift degeneracy and the damping effect of viscous medium on the information extracted from gravitational wave signals,"Considering the cosmological redshift $z_c$ , the mass of GW source extracted
from GW signal is $1+z_c$ times larger than its intrinsic value, and distance
between detector and GW source should be regarded as luminosity distance.
However, besides cosmological redshift, there are other kinds of redshifts
should be considered, which is actually ignored, in the analysis of GW data,
such as Doppler redshift and gravitational redshift, so the parameters
extracted from GW may deviate from their intrinsic values. Another factor that
may affect GW is the viscous medium in propagation path of GW, which may damp
the GW with a damping rate of $16{\pi}G{\eta}$. Some studies indicate dark
matter may interact with each other, thus dark matter may be the origin of
viscosity of cosmic medium. Then the GW may be rapidly damped by the viscous
medium that is made of dark matter, such as dark matter ""mini-spike"" around
intermediate mass black hole. In this article, we mainly discuss how Doppler
and gravitational redshift, together with the damping effect of viscous medium,
affect the information, such as the mass and redshift of GW source, extracted
from GW signals.",2011.09169v2
2020-12-28,On the Efficacy of Friction Damping in the Presence of Nonlinear Modal Interactions,"This work addresses friction-induced modal interactions in jointed
structures, and their effects on the passive mitigation of vibrations by means
of friction damping. Under the condition of (nearly) commensurable natural
frequencies, the nonlinear character of friction can cause so-called nonlinear
modal interactions. If harmonic forcing near the natural frequency of a
specific mode is applied, for instance, another mode may be excited due to
nonlinear energy transfer and thus contribute considerably to the vibration
response. We investigate how this phenomenon affects the performance of
friction damping. To this end, we study the steady-state, periodic forced
vibrations of a system of two beams connected via a local mechanical friction
joint. The system can be tuned to continuously adjust the ratio between the
first two natural frequencies in the range around the $1:3$ internal resonance,
in order to trigger or suppress the emergence of modal interactions. Due to the
re-distribution of the vibration energy, the vibration level can in fact be
reduced in certain situations. However, in other situations, the multi-harmonic
character of the vibration has detrimental effects on the effective damping
provided by the friction joint. The resulting response level can be
significantly larger than in the absence of modal interactions. Moreover, it is
shown that the vibration behavior is highly sensitive in the neighborhood of
internal resonances. It is thus concluded that the condition of internal
resonance should be avoided in the design of friction-damped systems.",2101.03232v1
2021-06-30,Origin of Nonlinear Damping due to Mode Coupling in Auto-Oscillatory Modes Strongly Driven by Spin-Orbit Torque,"We investigate the physical origin of nonlinear damping due to mode coupling
between several auto-oscillatory modes driven by spin-orbit torque in
constricted Py/Pt heterostructures by examining the dependence of
auto-oscillation on temperature and applied field orientation. We observe a
transition in the nonlinear damping of the auto-oscillation modes extracted
from the total oscillation power as a function of drive current, which
coincides with the onset of power redistribution amongst several modes and the
crossover from linewidth narrowing to linewidth broadening in all individual
modes. This indicates the activation of another relaxation process by nonlinear
magnon-magnon scattering within the modes. We also find that both nonlinear
damping and threshold current in the mode-interaction damping regime at high
drive current after transition are temperature independent, suggesting that the
mode coupling occurs dominantly through a non-thermal magnon scattering process
via a dipole or exchange interaction rather than thermally excited
magnon-mediated scattering. This finding presents a promising pathway to
overcome the current limitations of efficiently controlling the interaction
between two highly nonlinear magnetic oscillators to prevent mode crosstalk or
inter-mode energy transfer and deepens understanding of complex nonlinear spin
dynamics in multimode spin wave systems.",2107.00150v2
2021-07-15,On the long-time behavior for a damped Navier-Stokes-Bardina model,"In this paper, we consider a damped Navier-Stokes-Bardina model posed on the
whole three-dimensional. These equations have an important physical motivation
and they arise from some oceanic model. From the mathematical point of view,
they write down as the well-know Navier-Stokes equations with an additional
nonlocal operator in their nonlinear transport term, and moreover, with an
additional damping term depending of a parameter $\beta>0$. We study first the
existence and uniqueness of global in time weak solutions in the energy space.
Thereafter, our main objective is to describe the long time behavior of these
solutions. For this, we use some tools in the theory of dynamical systems to
prove the existence of a global attractor, which is a compact subset in the
energy space attracting all the weak solutions when the time goes to infinity.
Moreover, we derive an upper bound for the fractal dimension of the global
attractor associated to these equations.
  Finally, we find a range of values for the damping parameter $\beta>0$, where
we are able to give an acutely description of the internal structure of the
global attractor. More precisely, we prove that the global attractor only
contains the stationary (time-independing) solution of the damped
Navier-Stokes-Bardina equations.",2107.07070v2
2021-07-17,Plasmon-Exciton Coupling Effect on Plasmon Damping,"Plasmon decay via the surface or interface is a critical process for
practical energy conversion and plasmonic catalysis. However, the relationship
between plasmon damping and the coupling between the plasmon and 2D materials
is still unclear. The spectral splitting due to plasmon-exciton interaction
impedes the conventional single-particle method to evaluate the plasmon damping
rate by the spectral linewidth directly. Here, we investigated the interaction
between a single gold nanorod (GNR) and 2D materials using the single-particle
spectroscopy method assisted with in situ nanomanipulation technique by
comparing scattering intensity and linewidth together. Our approach allows us
to indisputably identify that the plasmon-exciton coupling in the GNR-WSe2
hybrid would induce plasmon damping. We can also isolate the contribution
between the charge transfer channel and resonant energy transfer channel for
the plasmon decay in the GNR-graphene hybrid by comparing that with thin hBN
layers as an intermediate medium to block the charge transfer. We find out that
the contact layer between the GNR and 2D materials contributes most of the
interfacial plasmon damping. These findings contribute to a deep understanding
of interfacial excitonic effects on the plasmon and 2D materials hybrid.",2107.08230v1
2021-10-12,Outflows in the presence of cosmic rays and waves with cooling,"Plasma outflow from a gravitational potential well with cosmic rays and
self-excited Alfv\'en waves with cooling and wave damping is studied in the
hydrodynamics regime. We study outflows in the presence of cosmic ray and
Alfv\'en waves including the effect of cooling and wave damping. We seek
physically allowable steady-state subsonic-supersonic transonic solutions. We
adopted a multi-fluid hydrodynamical model for the cosmic ray plasma system.
Thermal plasma, cosmic rays, and self-excited Alfv\'en waves are treated as
fluids. Interactions such as cosmic-ray streaming instability, cooling, and
wave damping were fully taken into account. We considered one-dimensional
geometry and explored steady-state solutions. The model is reduced to a set of
ordinary differential equations, which we solved for subsonic-supersonic
transonic solutions with given boundary conditions at the base of the
gravitational potential well. We find that physically allowable
subsonic-supersonic transonic solutions exist for a wide range of parameters.
We studied the three-fluid system (considering only forward-propagating
Alfv\'en waves) in detail. We examined the cases with and without cosmic ray
diffusion separately. Comparisons of solutions with and without cooling and
with and without wave damping for the same set of boundary conditions (on
density, pressures of thermal gas, cosmic rays and waves) are presented. We
also present the interesting case of a four-fluid system (both forward- and
backward-propagating Alfv\'en waves are included), highlighting the intriguing
relation between different components.",2110.06170v1
2021-11-19,Finite time extinction for a class of damped Schr{ö}dinger equations with a singular saturated nonlinearity,"We present some sharper finite extinction time results for solutions of a
class of damped nonlinear Schr{\""o}dinger equations when the nonlinear damping
term corresponds to the limit cases of some ``saturating non-Kerr law''
$F(|u|^2)u=\frac{a}{\varepsilon+(|u|^2)^\alpha}u,$ with $a\in\mathbb{C},$
$\varepsilon\geqslant0,$ $2\alpha=(1-m)$ and $m\in[0,1).$ To carry out the
improvement of previous results in the literature we present in this paper a
careful revision of the existence and regularity of weak solutions under very
general assumptions on the data. We prove that the problem can be solved in the
very general framework of the maximal monotone operators theory, even under a
lack of regularity of the damping term. This allows us to consider, among other
things, the singular case $m=0.$ We replace the above approximation of the
damping term by a different one which keeps the monotonicity for any
$\varepsilon\geqslant0$. We prove that, when $m=0,$ the finite extinction time
of the solution arises for merely bounded right hand side data $f(t,x).$ This
is specially useful in the applications in which the Schr{\""o}dinger equation
is coupled with some other functions satisfying some additional equations.",2111.10136v2
2022-01-26,Effect of Chiral Damping on the dynamics of chiral domain walls and skyrmions,"Friction plays an essential role in most physical processes that we
experience in our everyday life. Examples range from our ability to walk or
swim, to setting boundaries of speed and fuel efficiency of moving vehicles. In
magnetic systems, the displacement of chiral domain walls (DW) and skyrmions
(SK) by Spin Orbit Torques (SOT), is also prone to friction. Chiral damping,
the dissipative counterpart of the Dzyaloshinskii Moriya Interaction (DMI),
plays a central role in these dynamics. Despite experimental observation, and
numerous theoretical studies confirming its existence, the influence of chiral
damping on DW and SK dynamics has remained elusive due to the difficulty of
discriminating from DMI. Here we unveil the effect that chiral damping has on
the flow motion of DWs and SKs driven by current and magnetic field. We use a
static in-plane field to lift the chiral degeneracy. As the in-plane field is
increased, the chiral asymmetry changes sign. When considered separately,
neither DMI nor chiral damping can explain the sign reversal of the asymmetry,
which we prove to be the result of their competing effects. Finally, numerical
modelling unveils the non-linear nature of chiral dissipation and its critical
role for the stabilization of moving SKs.",2201.10742v1
2022-01-27,A Study on Monte Carlo simulation of the radiation environment above GeV at the DAMPE orbit,"The Dark Matter Particle Explorer (DAMPE) has been undergoing a stable
on-orbit operation for more than 6 years and acquired observation of over 11
billion events. And a better understanding of the overall radiation environment
on the DAMPE orbit is crucial for both simulation data production and flight
data analysis. In this work, we study the radiation environment at the low
Earth orbit and develop a simulation software package using the framework of
ATMNC3, in which state-of-the-art full 3D models of the Earth's atmospheric and
magnetic-field configurations is integrated. We consider in our Monte Carlo
procedure event-by-event propagation of the cosmic rays in the geomagnetic
field and their interaction with the Earth's atmosphere, focusing on the
particles above GeV that are able to trigger the DAMPE data acquisition system.
We compare the simulation results with the cosmic-ray electrons and positrons
(CREs) flux measurements made by DAMPE. The overall agreement on both the
spectral and angular distribution of the CREs flux demonstrates that our
simulation is well established. Our software package could be of more general
usage for the simulation of the radiation environment at the low Earth orbit of
various altitudes.",2201.11364v1
2022-05-10,Nonlinear damping quantification from phase-resonant tests under base excitation,"The present work addresses the experimental identification of
amplitude-dependent modal parameters (modal frequency, damping ratio, Fourier
coefficients of periodic modal oscillation). Phase-resonant testing has emerged
as an important method for this task, as it substantially reduces the amount of
data required for the identification compared to conventional
frequency-response testing at different excitation/response levels. In the case
of shaker-stinger excitation, the applied excitation force is commonly measured
in order to quantify the amplitude-dependent modal damping ratio from the
phase-resonant test data. In the case of base excitation, however, the applied
excitation force is challenging or impossible to measure. In this work we
develop an original method for damping quantification from phase-resonant
tests. It relies solely on response measurement; it avoids the need to resort
to force measurement. The key idea is to estimate the power provided by the
distributed inertia force imposed by the base motion. We develop both a
model-free and a model-based variant of the method. We validate the developed
method first in virtual experiments of a friction-damped and a geometrically
nonlinear system, and then in a physical experiment involving a thin beam
clamped at both ends via bolted joints. We conclude that the method is highly
robust and provides high accuracy already for a reasonable number of sensors.",2205.04735v1
2022-06-08,Motion control with optimal nonlinear damping: from theory to experiment,"Optimal nonlinear damping control was recently introduced for the
second-order SISO systems, showing some advantages over a classical PD feedback
controller. This paper summarizes the main theoretical developments and
properties of the optimal nonlinear damping controller and demonstrates, for
the first time, its practical experimental evaluation. An extended analysis and
application to more realistic (than solely the double-integrator) motion
systems are also given in the theoretical part of the paper. As comparative
linear feedback controller, a PD one is taken, with the single tunable gain and
direct compensation of the plant time constant. The second, namely
experimental, part of the paper includes the voice-coil drive system with
relatively high level of the process and measurement noise, for which the
standard linear model is first identified in frequency domain. The linear
approximation by two-parameters model forms the basis for designing the PD
reference controller, which fixed feedback gain is the same as for the optimal
nonlinear damping control. A robust sliding-mode based differentiator is used
in both controllers for a reliable velocity estimation required for the
feedback. The reference PD and the proposed optimal nonlinear damping
controller, both with the same single design parameter, are compared
experimentally with respect to trajectory tracking and disturbance rejection.",2206.03802v2
2022-09-22,Neutrino Fast Flavor Pendulum. Part 2: Collisional Damping,"In compact astrophysical objects, the neutrino density can be so high that
neutrino-neutrino refraction can lead to fast flavor conversion of the kind
$\nu_e \bar\nu_e \leftrightarrow \nu_x \bar\nu_x$ with $x=\mu,\tau$, depending
on the neutrino angle distribution. Previously, we have shown that in a
homogeneous, axisymmetric two-flavor system, these collective solutions evolve
in analogy to a gyroscopic pendulum. In flavor space, its deviation from the
weak-interaction direction is quantified by a variable $\cos\vartheta$ that
moves between $+1$ and $\cos\vartheta_{\rm min}$, the latter following from a
linear mode analysis. As a next step, we include collisional damping of flavor
coherence, assuming a common damping rate $\Gamma$ for all modes. Empirically
we find that the damped pendular motion reaches an asymptotic level of pair
conversion $f=A+(1-A)\cos\vartheta_{\rm min}$ (numerically $A\simeq 0.370$)
that does not depend on details of the angular distribution (except for fixing
$\cos\vartheta_{\rm min}$), the initial seed, nor $\Gamma$. On the other hand,
even a small asymmetry between the neutrino and antineutrino damping rates
strongly changes this picture and can even enable flavor instabilities in
otherwise stable systems.",2209.11235v3
2022-10-12,Second order two-species systems with nonlocal interactions: existence and large damping limits,"We study the mathematical theory of second order systems with two species,
arising in the dynamics of interacting particles subject to linear damping, to
nonlocal forces and to external ones, and resulting into a nonlocal version of
the compressible Euler system with linear damping. Our results are limited to
the $1$ space dimensional case but allow for initial data taken in a
Wasserstein space of probability measures. We first consider the case of smooth
nonlocal interaction potentials, not subject to any symmetry condition, and
prove existence and uniqueness. The concept of solutions relies on a stickiness
condition in case of collisions, in the spirit of previous works in the
literature. The result uses concepts from classical Hilbert space theory of
gradient flows (cf. Brezis [7]) and a trick used in [4]. We then consider a
large-time and large-damping scaled version of our system and prove convergence
to solutions to the corresponding first order system. Finally, we consider the
case of Newtonian potentials -- subject to symmetry of the cross-interaction
potentials -- and external convex potentials. After showing existence in the
sticky particles framework in the spirit of [4], we prove convergence for large
times towards Dirac delta solutions for the two densities. All the results
share a common technical framework in that solutions are considered in a
Lagrangian framework, which allows to estimate the behavior of solutions via
$L^2$ estimates of the pseudo-inverse variables corresponding to the two
densities. In particular, due to this technique, the large-damping result holds
under a rather weak condition on the initial data, which does not require
well-prepared initial velocities. We complement the results with numerical
simulations.",2210.06162v1
2022-10-12,Stability of the Néel quantum critical point in the presence of Dirac fermions,"We investigate the stability of the N\'eel quantum critical point of
two-dimensional quantum antiferromagnets, described by a non-linear $\sigma$
model (NL$\sigma$M), in the presence of a Kondo coupling to $N_f$ flavours of
two-component Dirac fermion fields. The long-wavelength order parameter
fluctuations are subject to Landau damping by electronic particle-hole
fluctuations. Using momentum-shell RG, we demonstrate that the Landau damping
is weakly irrelevant at the N\'eel quantum critical point, despite the fact
that the corresponding self-energy correction dominates over the quadratic
gradient terms in the IR limit. In the ordered phase, the Landau damping
increases under the RG, indicative of damped spin-wave excitations. Although
the Kondo coupling is weakly relevant, sufficiently strong Landau damping
renders the N\'eel quantum critical point quasi-stable for $N_f\ge 4$ and
thermodynamically stable for $N_f<4$. In the latter case, we identify a new
multi-critical point which describes the transition between the N\'eel critical
and Kondo run-away regimes. The symmetry breaking at this fixed point results
in the opening of a gap in the Dirac fermion spectrum. Approaching the
multi-critical point from the disordered phase, the fermionic quasiparticle
residue vanishes, giving rise to non-Fermi-liquid behavior.",2210.06577v3
2022-11-13,Damping analysis of Floating Offshore Wind Turbine (FOWT): a new control strategy reducing the platform vibrations,"In this paper, the coupled dynamics of the floating platform and the WTG
rotor is analysed. In particular, the damping is explicitly derived from the
coupled equations of rotor and floating platform. The analysis of the damping
leads to the study of the instability phenomena and it derives the explicit
conditions that lead to the Non Minimum Phase Zero (NMPZ). Two NMPZs, one
related to the rotor dynamics and the other one to the platform pitch dynamics,
are analysed. The latter is a novelty and it is analysed in this work,
providing the community of an explicit condition for its verification. The
domain of the instability of the platform is explicitly derived from the
coupled system of equations. In the second part of the paper, from the analysis
of the damping of the floating platform, a new strategy for the control of
FOWTs is proposed. This strategy allows one to impose to the controller an
explicit level of damping in the platform pitch motion without changing the
period of platform pitching. Finally the new strategy is compared to the one
without compensation by performing aero-hydro-servo-elastic numerical
simulations of the UMaine IEA15MW FOWT. Generated power, movements, blade pitch
and tower base fatigue are compared showing that the new control strategy can
reduce fatigue in the structure without affecting the power production.",2211.10362v1
2022-11-22,Universal Dynamics of Damped-Driven Systems: The Logistic Map as a Normal Form for Energy Balance,"Damped-driven systems are ubiquitous in engineering and science. Despite the
diversity of physical processes observed in a broad range of applications, the
underlying instabilities observed in practice have a universal characterization
which is determined by the overall gain and loss curves of a given system. The
universal behavior of damped-driven systems can be understood from a
geometrical description of the energy balance with a minimal number of
assumptions. The assumptions on the energy dynamics are as follows: the energy
increases monotonically as a function of increasing gain, and the losses become
increasingly larger with increasing energy, i.e. there are many routes for
dissipation in the system for large input energy. The intersection of the gain
and loss curves define an energy balanced solution. By constructing an
iterative map between the loss and gain curves, the dynamics can be shown to be
homeomorphic to the logistic map, which exhibits a period doubling cascade to
chaos. Indeed, the loss and gain curves allow for a geometrical description of
the dynamics through a simple Verhulst diagram (cobweb plot). Thus irrespective
of the physics and its complexities, this simple geometrical description
dictates the universal set of logistic map instabilities that arise in complex
damped-driven systems. More broadly, damped-driven systems are a class of
non-equilibrium pattern forming systems which have a canonical set of
instabilities that are manifest in practice.",2211.11748v1
2023-01-23,Optimal Inter-area Oscillation Damping Control: A Transfer Deep Reinforcement Learning Approach with Switching Control Strategy,"Wide-area damping control for inter-area oscillation (IAO) is critical to
modern power systems. The recent breakthroughs in deep learning and the broad
deployment of phasor measurement units (PMU) promote the development of
datadriven IAO damping controllers. In this paper, the damping control of IAOs
is modeled as a Markov Decision Process (MDP) and solved by the proposed Deep
Deterministic Policy Gradient (DDPG) based deep reinforcement learning (DRL)
approach. The proposed approach optimizes the eigenvalue distribution of the
system, which determines the IAO modes in nature. The eigenvalues are evaluated
by the data-driven method called dynamic mode decomposition. For a given power
system, only a subset of generators selected by participation factors needs to
be controlled, alleviating the control and computing burdens. A Switching
Control Strategy (SCS) is introduced to improve the transient response of IAOs.
Numerical simulations of the IEEE-39 New England power grid model validate the
effectiveness and advanced performance of the proposed approach as well as its
robustness against communication delays. In addition, we demonstrate the
transfer ability of the DRL model trained on the linearized power grid model to
provide effective IAO damping control in the non-linear power grid model
environment.",2301.09321v1
2023-03-15,Blow-up and decay for a class of variable coefficient wave equation with nonlinear damping and logarithmic source,"In this paper, we consider the long time behavior for the solution of a class
of variable coefficient wave equation with nonlinear damping and logarithmic
source. The existence and uniqueness of local weak solution can be obtained by
using the Galerkin method and contraction mapping principle. However, the long
time behavior of the solution is usually complicated and it depends on the
balance mechanism between the damping and source terms. When the damping
exponent $(p+1)$ (see assumption (H3)) is greater than the source term exponent
$(q-1)$ (see equation (1.1)), namely, $p+2>q$, we obtain the global existence
and accurate decay rates of the energy for the weak solutions with any initial
data. Moreover, whether the weak solution exists globally or blows up in finite
time, it is closely related to the initial data. In the framework of modified
potential well theory, we construct the stable and unstable sets (see (2.8))
for the initial data. For the initial data belonging to the stable set, we
prove that the weak solution exists globally and has similar decay rates as the
previous results. For $p+2<q$ and the initial data belonging to the unstable
set, we prove that the weak solution blows up in finite time for a little
special damping $g(u_{t})=|u_{t}|^{p}u_{t}$.",2303.08629v1
2023-04-13,Centralised Multimode Power Oscillation Damping Controller for Photovoltaic Plants with Communication Delay Compensation,"Low-frequency oscillations are an inherent phenomena in transmission networks
and renewable energy plants should be configured to damp them. Commonly, a
centralised controller is used in PV plants to coordinate PV generators via
communication channels. However, the communication systems of PV plants
introduce delays of a stochastic nature that degrade the performance of
centralised control algorithms. Therefore, controllers for oscillation damping
may not operate correctly unless the communication channel characteristics are
not considered and compensated. In this paper, a centralised controller is
proposed for the oscillation damping that uses a PV plant with all the
realistic effects of communication channels taken into consideration. The
communication channels are modelled based on measurements taken in a laboratory
environment. The controller is designed to damp several modes of oscillation by
using the open-loop phase shift compensation. Theoretical developments were
validated in a laboratory using four converters acting as two PV inverters, a
battery and a STATCOM. A real-time processing platform was used to implement
the centralised controller and to deploy the communication infrastructure.
Experimental results show the communication channels impose severe restrictions
on the performance of centralised POD controllers, highlighting the importance
of their accurate modelling and consideration during the controller design
stage.",2304.06415v1
2023-05-09,Glassy heat capacity from overdamped phasons and a hypothetical phason-induced superconductivity in incommensurate structures,"Phasons are collective low-energy modes that appear in disparate condensed
matter systems such as quasicrystals, incommensurate structures, fluctuating
charge density waves, and Moir\'e superlattices. They share several
similarities with acoustic phonon modes, but they are not protected by any
exact translational symmetry. As a consequence, they are subject to a
wavevector independent damping, and they develop a finite pinning frequency,
which destroy their acoustic linearly propagating dispersion. Under a few and
simple well-motivated assumptions, we compute the phason density of states, and
we derive the phason heat capacity as a function of the temperature. Finally,
imagining a hypothetical s-wave pairing channel with electrons, we compute the
critical temperature $T_c$ of the corresponding superconducting state as a
function of phason damping using the Eliashberg formalism. We find that for
large phason damping, the heat capacity is linear in temperature, showing a
distinctive glass-like behavior. Additionally, we observe that the phason
damping can strongly enhance the effective Eliashberg coupling, and we reveal a
sharp non-monotonic dependence of the superconducting temperature $T_c$ on the
phason damping, with a maximum located at the underdamped to overdamped
crossover scale. Our simple computations confirm the potential role of
overdamped modes in explaining the glassy properties of incommensurate
structures, but also in possibly inducing strongly-coupled superconductivity
therein, and enhancing the corresponding $T_c$.",2305.05407v2
2023-07-12,Exponential stability of damped Euler-Bernoulli beam controlled by boundary springs and dampers,"In this paper, the vibration model of an elastic beam, governed by the damped
Euler-Bernoulli equation
$\rho(x)u_{tt}+\mu(x)u_{t}$$+\left(r(x)u_{xx}\right)_{xx}=0$, subject to the
clamped boundary conditions $u(0,t)=u_x(0,t)=0$ at $x=0$, and the boundary
conditions $\left(-r(x)u_{xx}\right)_{x=\ell}=k_r u_x(\ell,t)+k_a
u_{xt}(\ell,t)$, $\left(-\left(r(x)u_{xx}\right)_{x}\right )_{x=\ell}$$=- k_d
u(\ell,t)-k_v u_{t}(\ell,t)$ at $x=\ell$, is analyzed. The boundary conditions
at $x=\ell$ correspond to linear combinations of damping moments caused by
rotation and angular velocity and also, of forces caused by displacement and
velocity, respectively. The system stability analysis based on well-known
Lyapunov approach is developed. Under the natural assumptions guaranteeing the
existence of a regular weak solution, uniform exponential decay estimate for
the energy of the system is derived. The decay rate constant in this estimate
depends only on the physical and geometric parameters of the beam, including
the viscous external damping coefficient $\mu(x) \ge 0$, and the boundary
springs $k_r,k_d \ge 0$ and dampers $k_a,k_v \ge 0$. Some numerical examples
are given to illustrate the role of the damping coefficient and the boundary
dampers.",2307.06170v2
2023-08-03,Flavor-wave theory with quasiparticle damping at finite temperatures: Application to chiral edge modes in the Kitaev model,"We propose a theoretical framework to investigate elementary excitations at
finite temperatures within a localized electron model that describes the
interactions between multiple degrees of freedom, such as quantum spin models
and Kugel-Khomskii models. Thus far, their excitation structures have been
mainly examined using the linear flavor-wave theory, an SU($N$) generalization
of the linear spin-wave theory. These techniques introduce noninteracting
bosonic quasiparticles as elementary excitations from the ground state, thereby
elucidating numerous physical phenomena, including excitation spectra and
transport properties characterized by topologically nontrivial band structures.
Nevertheless, the interactions between quasiparticles cannot be ignored in
systems exemplified by $S=1/2$ quantum spin models, where strong quantum
fluctuations are present. Recent studies have investigated the effects of
quasiparticle damping at zero temperature in such models. In our study,
extending this approach to the flavor-wave theory for general localized
electron models, we construct a comprehensive method to calculate excitation
spectra with the quasiparticle damping at finite temperatures. We apply our
method to the Kitaev model under magnetic fields, a typical example of models
with topologically nontrivial magnon bands. Our calculations reveal that chiral
edge modes undergo significant damping in weak magnetic fields, amplifying the
damping rate by the temperature increase. This effect is caused by collisions
with thermally excited quasiparticles. Since our approach starts from a general
Hamiltonian, it will be widely applicable to other localized systems, such as
spin-orbital coupled systems derived from multi-orbital Hubbard models in the
strong correlation limit.",2308.01711v1
2024-02-13,Investigating the Effect of Noise on the Training Performance of Hybrid Quantum Neural Networks,"In this paper, we conduct a comprehensively analyze the influence of
different quantum noise gates, including Phase Flip, Bit Flip, Phase Damping,
Amplitude Damping, and the Depolarizing Channel, on the performance of HyQNNs.
Our results reveal distinct and significant effects on HyQNNs training and
validation accuracies across different probabilities of noise. For instance,
the Phase Flip gate introduces phase errors, and we observe that HyQNNs exhibit
resilience at higher probability (p = 1.0), adapting effectively to consistent
noise patterns, whereas at intermediate probabilities, the performance
declines. Bit Flip errors, represented by the PauliX gate, impact HyQNNs in a
similar way to that Phase Flip error gate. The HyQNNs, can adapt such kind of
errors at maximum probability (p = 1.0). Unlike Phase and Bit Flip error gates,
Phase Damping and Amplitude Damping gates disrupt quantum information, with
HyQNNs demonstrating resilience at lower probabilities but facing challenges at
higher probabilities. Amplitude Damping error gate, in particular, poses
efficiency and accuracy issues at higher probabilities however with lowest
probability (p = 0.1),it has the least effect and the HyQNNs, however not very
effectively, but still tends to learn. The Depolarizing Channel proves most
detrimental to HyQNNs performance, with limited or no training improvements.
There was no training potential observed regardless of the probability of this
noise gate. These findings underscore the critical need for advanced quantum
error mitigation and resilience strategies in the design and training of
HyQNNs, especially in environments prone to depolarizing noise. This paper
quantitatively investigate that understanding the impact of quantum noise gates
is essential for harnessing the full potential of quantum computing in
practical applications.",2402.08523v1
2024-03-03,Magnonic $\varphi$ Josephson Junctions and Synchronized Precession,"There has been a growing interest in non-Hermitian physics. One of its main
goals is to engineer dissipation and to explore ensuing functionality. In
magnonics, the effect of dissipation due to local damping on magnon transport
has been explored. However, the effects of non-local damping on the magnonic
analog of the Josephson effect remain missing, despite that non-local damping
is inevitable and has been playing a central role in magnonics. Here, we
uncover theoretically that a surprisingly rich dynamics can emerge in magnetic
junctions due to intrinsic non-local damping, using analytical and numerical
methods. In particular, under microwave pumping, we show that coherent spin
precession in the right and left insulating ferromagnet (FM) of the junction
becomes synchronized by non-local damping and thereby a magnonic analog of the
$\varphi$ Josephson junction emerges, where $\varphi$ stands here for the
relative precession phase of right and left FM in the stationary limit.
Remarkably, $\varphi$ decreases monotonically from $ \pi$ to $\pi/2$ as the
magnon-magnon interaction, arising from spin anisotropies, increases. Moreover,
we also find a magnonic diode effect giving rise to rectification of magnon
currents. Our predictions are readily testable with current device and
measurement technologies at room temperatures.",2403.01625v1
1997-01-17,Evidence for Rotation in the Galaxy at z=3.15 Responsible for a Damped Lyman-alpha Absorption System in the Spectrum of Q2233+1310,"Proof of the existence of a significant population of normal disk galaxies at
redshift z>2 would have profound implications for theories of structure
formation and evolution. We present evidence based on Keck HIRES observations
that the damped Lyman-alpha absorber at z=3.15 toward the quasar Q2233+1310 may
well be such an example. Djorgovski et al have recently detected the
Lyman-alpha emission from the absorber, which we assume is at the systemic
redshift of the absorbing galaxy. By examining the profiles of the metal
absorption lines arising from the absorbing galaxy in relation to its systemic
redshift, we find strong kinematical evidence for rotation. Therefore the
absorber is likely to be a disk galaxy. The inferred circular velocity for the
galaxy is >200 km/s. With a separation of ~17 kpc between the galaxy and the
quasar sightline, the implied dynamic mass for the galaxy is >1.6x10(11) solar
mass. The metallicity of the galaxy is found to be [Fe/H]=-1.4, typical of
damped Lyman-alpha galaxies at such redshifts. However, in another damped
galactic rotation is evident. In the latter case, the damped Lyman-alpha
absorber occurs near the background quasar in redshift so its properties may be
influenced by the background quasar. These represent the only two cases at
present for which the technique used here may be applied. Future applications
of the same technique to a large sample of damped Lyman-alpha galaxies may
allow us to determine if a significant population of disk galaxies already
existed only a few billion years after the Big Bang.",9701116v2
1997-04-11,The Metallicity of High Redshift Galaxies: The Abundance of Zinc in 34 Damped Lyman Alpha Systems from z = 0.7 to 3.4,"We report new observations of ZnII and CrII absorption lines in 10 damped
\lya systems (DLAs), mostly at redshift $z_{abs} \simgt 2.5$ . By combining
these results with those from our earlier survey (Pettini et al. 1994) and
other recent data, we construct a sample of 34 measurements (or upper limits)
of the Zn abundance relative to hydrogen [Zn/H]; the sample includes more than
one third of the total number of DLAs known.
  The plot of the abundance of Zn as a function of redshift reinforces the two
main findings of our previous study. (1) Damped \lya systems are mostly
metal-poor, at all redshifts sampled; the column density weighted mean for the
whole data set is [Zn/H] $= -1.13 \pm 0.38$ (on a logarithmic scale), or
approximately 1/13 of solar. (2) There is a large spread, by up to two orders
of magnitude, in the metallicities we measure at essentially the same
redshifts. We propose that damped \lya systems are drawn from a varied
population of galaxies of different morphological types and at different stages
of chemical evolution, supporting the idea of a protracted epoch of galaxy
formation.
  At redshifts $z \simgt 2$ the typical metallicity of the damped \lya systems
is in agreement with expectations based on the consumption of HI gas implied by
the recent measurements of $\Omega_{DLA}$ by Storrie-Lombardi et al. (1996a),
and with the metal ejection rates in the universe at these epochs deduced by
Madau (1996) from the ultraviolet luminosities of high redshift galaxies
revealed by deep imaging surveys. There are indications in our data for an
increase in the mean metallicity of the damped \lya systems from $z > 3$ to
$\approx 2$, consistent with the rise in the comoving star formation rate
indicated by the relative numbers of $U$ and $B$ drop-outs in the Hubble Deep
Field. Although such comparisons are still tentative, it appears that these
different avenues for exploring the early evolution of galaxies give a broadly
consistent picture.",9704102v1
1997-04-17,On the Kinematics of the Damped Lyman Alpha Protogalaxies,"We present the first results of an ongoing program to investigate the
kinematic characteristics of high redshift damped lya systems. Because damped
lya systems are widely believed to be the progenitors of current massive
galaxies, an analysis of their kinematic history allows a direct test of galaxy
formation scenarios.
  We have collected a kinematically unbiased sample of 17 high S/N ratio, high
resolution damped lya spectra taken with HIRES on the 10m W.M. Keck Telescope.
Our study focuses on the unsaturated, low-ion transitions of these systems
which reveal their kinematic traits. The profiles exhibit a nearly uniform
distribution of velocity widths ranging from 20 - 200 km/s and a relatively
high degree of asymmetry. In an attempt to explain these characteristics, we
introduce several physical models, which have previously been attributed to
damped lya systems, including rapidly rotating cold disks, slowly rotating hot
disks, massive isothermal halos, and a hydrodynamic spherical accretion model.
  Using standard Monte Carlo techniques, we run sightlines through these model
systems to derive simulated low-ion profiles. Comparing statistical measures of
the simulated profiles with the observed profiles, we determine that the
rapidly rotating cold disk model is the only tested model consistent with the
data at high confidence levels. A Relative Likelihood Test of the rapidly
rotating cold disk model indicates the disks must have large rotation speeds; v
> 180 km/s at the 99% c.l. In turn, we demonstrate that the Cold Dark Matter
Model, as developed by Kauffmann (1996), is inconsistent with the damped lya
data at very high c.l. This is because the CDM Model does not predict a large
enough fraction of rapidly rotating disks at z approx 2.5.",9704169v2
2000-11-20,H-alpha Imaging with HST+NICMOS of An Elusive Damped Ly-alpha Cloud at z=0.6,"Despite previous intensive ground-based imaging and spectroscopic campaigns
and wide-band HST imaging of the z=0.927 QSO 3C336 field, the galaxy that hosts
the damped Ly-alpha system along this line-of-sight has eluded detection. We
present a deep narrow-band H-alpha image of the field of this z=0.656 damped
Ly-alpha absorber, obtained through the F108N filter of NICMOS 1 onboard the
Hubble Space Telescope. The goal of this project was to detect any H-alpha
emission 10 times closer than previous studies to unveil the damped absorber.
We do not detect H-alpha emission between 0.05'' and 6'' (0.24 and 30 $h^{-1}$
kpc) from the QSO, with a 3-sigma flux limit of $3.70 \times 10^{-17} h^{-2}$
erg/s/cm^2 for an unresolved source, corresponding to a star formation rate
(SFR) of $0.3 h^{-2}$ M_sun/yr. This leads to a 3-sigma upper limit of 0.15
M_sun/yr/kpc^2 on the SFR density, or a maximum SFR of 1.87 M_sun/yr assuming a
disk of 4 kpc in diameter. This result adds to the number of low redshift
damped Ly-alpha absorbers that are not associated with the central regions of
Milky-Way-like disks. Damped Ly-alpha absorption can arise from high density
concentrations in a variety of galactic environments including some that,
despite their high local HI densities, are not conducive to widespread star
formation.",0011374v2
2005-08-17,The SDSS Damped Lya Survey: Data Release 3,"We present the results from a damped Lya survey of the Sloan Digital Sky
Survey, Data Release 3 based on over 500 new damped Lya systems at z>2.2. We
measure the HI column density distribution f(N) and its zeroth and first
moments (the incidence l(X) and gas mass-density O_dla of damped Lya systems,
respectively) as a function of redshift. The key results include: (1) the f(N)
distribution is well fit by a Gamma-function with `break' column density log
N_g=10^21.5 and `faint-end' slope alpha=-1.8; (2) the shape of the f(N)
distributions do not show evolution with redshift; (3) l(X) and O_dla decrease
by 35% and 50% during ~1Gyr between redshift z=[3.,3.5] to z=[2.2,2.5]; and (4)
l(X) and O_dla in the lowest SDSS redshift bin (z=2.2) are consistent with the
current values. We investigate systematic errors in damped Lya analysis and
identify only one important effect: we measure 40 +/- 20% higher O_dla values
toward a subset of brighter quasars than toward a faint subset. This effect
runs contrary to the bias associated with dust obscuration and suggests that
gravitational lensing may be important. Comparing the results against models of
galaxy formation, we find all of the models significantly underpredict l(X) at
z=3 and only SPH models with significant feedback may reproduce O_dla at high
redshift. We argue that the Lyman limit systems contribute ~1/3 of the
universe's HI atoms at all redshifts z=2 to 5 and that the f(N) distribution
for N(HI)<10^20 has an inflection with slope >-1. We advocate a new mass
density definition -- the mass density of predominantly neutral gas O_neut --
to be contrasted with the mass density of gas associated with HI atoms. We
contend the damped Lya systems contribute >80% of O_neut at all redshifts and
therefore are the main reservoirs for star formation. [abridged]",0508361v1
2010-03-11,Damping of MHD turbulence in partially ionized gas and the observed difference of velocities of neutrals and ions,"Theoretical and observational studies on the turbulence of the interstellar
medium developed fast in the past decades. The theory of supersonic magnetized
turbulence, as well as the understanding of projection effects of observed
quantities, are still in progress. In this work we explore the characterization
of the turbulent cascade and its damping from observational spectral line
profiles. We address the difference of ion and neutral velocities by clarifying
the nature of the turbulence damping in the partially ionized. We provide
theoretical arguments in favor of the explanation of the larger Doppler
broadening of lines arising from neutral species compared to ions as arising
from the turbulence damping of ions at larger scales. Also, we compute a number
of MHD numerical simulations for different turbulent regimes and explicit
turbulent damping, and compare both the 3-dimensional distributions of velocity
and the synthetic line profile distributions. From the numerical simulations,
we place constraints on the precision with which one can measure the 3D
dispersion depending on the turbulence sonic Mach number. We show that no
universal correspondence between the 3D velocity dispersions measured in the
turbulent volume and minima of the 2D velocity dispersions available through
observations exist. For instance, for subsonic turbulence the correspondence is
poor at scales much smaller than the turbulence injection scale, while for
supersonic turbulence the correspondence is poor for the scales comparable with
the injection scale. We provide a physical explanation of the existence of such
a 2D-3D correspondence and discuss the uncertainties in evaluating the damping
scale of ions that can be obtained from observations. However, we show that the
statistics of velocity dispersion from observed line profiles can provide the
spectral index and the energy transfer rate of turbulence. Also, comparing two
similar simulations with different viscous coefficients it was possible to
constrain the turbulent cut-off scale. This may especially prove useful since
it is believed that ambipolar diffusion may be one of the dominant dissipative
mechanism in star-forming regions. In this case, the determination of the
ambipolar diffusion scale may be used as a complementary method for the
determination of magnetic field intensity in collapsing cores. We discuss the
implications of our findings in terms of a new approach to magnetic field
measurement proposed by Li & Houde (2008).",1003.2346v1
2011-09-07,Weakly collisional Landau damping and three-dimensional Bernstein-Greene-Kruskal modes: New results on old problems,"Landau damping and Bernstein-Greene-Kruskal (BGK) modes are among the most
fundamental concepts in plasma physics. While the former describes the
surprising damping of linear plasma waves in a collisionless plasma, the latter
describes exact undamped nonlinear solutions of the Vlasov equation. There does
exist a relationship between the two: Landau damping can be described as the
phase-mixing of undamped eigenmodes, the so-called Case-Van Kampen modes, which
can be viewed as BGK modes in the linear limit. While these concepts have been
around for a long time, unexpected new results are still being discovered. For
Landau damping, we show that the textbook picture of phase-mixing is altered
profoundly in the presence of collision. In particular, the continuous spectrum
of Case-Van Kampen modes is eliminated and replaced by a discrete spectrum,
even in the limit of zero collision. Furthermore, we show that these discrete
eigenmodes form a complete set of solutions. Landau-damped solutions are then
recovered as true eigenmodes (which they are not in the collisionless theory).
For BGK modes, our interest is motivated by recent discoveries of electrostatic
solitary waves in magnetospheric plasmas. While one-dimensional BGK theory is
quite mature, there appear to be no exact three-dimensional solutions in the
literature (except for the limiting case when the magnetic field is
sufficiently strong so that one can apply the guiding-center approximation). We
show, in fact, that two- and three-dimensional solutions that depend only on
energy do not exist. However, if solutions depend on both energy and angular
momentum, we can construct exact three-dimensional solutions for the
unmagnetized case, and two-dimensional solutions for the case with a finite
magnetic field. The latter are shown to be exact, fully electromagnetic
solutions of the steady-state Vlasov-Poisson-Amp\`ere system.",1109.1353v1
2012-11-06,Torsional Alfvén waves in solar partially ionized plasma: effects of neutral helium and stratification,"Ion-neutral collisions may lead to the damping of Alfven waves in
chromospheric and prominence plasmas. Neutral helium atoms enhance the damping
in certain temperature interval, where the ratio of neutral helium and neutral
hydrogen atoms is increased. Therefore, the height-dependence of ionization
degrees of hydrogen and helium may influence the damping rate of Alfven waves.
We aim to study the effect of neutral helium in the damping of Alfven waves in
stratified partially ionized plasma of the solar chromosphere. We consider a
magnetic flux tube, which is expanded up to 1000 km height and then becomes
vertical due to merging with neighboring tubes, and study the dynamics of
linear torsional Alfven waves in the presence of neutral hydrogen and neutral
helium atoms. We start with three-fluid description of plasma and consequently
derive single-fluid magnetohydrodynamic (MHD) equations for torsional Alfven
waves. Thin flux tube approximation allows to obtain the dispersion relation of
the waves in the lower part of tubes, while the spatial dependence of
steady-state Alfven waves is governed by Bessel type equation in the upper part
of tubes. Consecutive derivation of single-fluid MHD equations results in a new
Cowling diffusion coefficient in the presence of neutral helium which is
different from previously used one. We found that shorter-period (< 5 s)
torsional Alfven waves damp quickly in the chromospheric network due to
ion-neutral collision. On the other hand, longer-period (> 5 s) waves do not
reach the transition region as they become evanescent at lower heights in the
network cores. Propagation of torsional Alfven waves through the chromosphere
into the solar corona should be considered with caution: low-frequency waves
are evanescent due to the stratification, while high-frequency waves are damped
due to ion neutral collisions.",1211.1348v2
2013-05-16,Application of vibration-transit theory to distinct dynamic response for a monatomic liquid,"We examine the distinct part of the density autocorrelation function Fd(q,t),
also called the intermediate scattering function, from the point of view of the
vibration-transit (V-T) theory of monatomic liquid dynamics. A similar study
has been reported for the self part, and we study the self and distinct parts
separately because their damping processes are not simply related. We begin
with the perfect vibrational system, which provides precise definitions of the
liquid correlations, and provides the vibrational approximation Fdvib(q,t) at
all q and t. Two independent liquid correlations are defined, motional and
structural, and these are decorrelated sequentially, with a crossover time
tc(q). This is done by two independent decorrelation processes: the first,
vibrational dephasing, is naturally present in Fdvib(q,t) and operates to damp
the motional correlation; the second, transit-induced decorrelation, is invoked
to enhance the damping of motional correlation, and then to damp the structural
correlation. A microscopic model is made for the ""transit drift"", the averaged
transit motion that damps motional correlation on 0 < t < tc(q). Following the
previously developed self-decorrelation theory, a microscopic model is also
made for the ""transit random walk,"" which damps the structural correlation on t
> tc(q). The complete model incorporates a property common to both self and
distinct decorrelation: simple exponential decay following a delay period,
where the delay is tc(q, the time required for the random walk to emerge from
the drift. Our final result is an accurate expression for Fd(q,t) for all q
through the first peak in Sd(q). The theory is calibrated and tested using
molecular dynamics (MD) calculations for liquid Na at 395K; however, the theory
itself does not depend on MD, and we consider other means for calibrating it.",1305.3954v2
2013-09-16,Two-atom system as a nano-antenna for mode switching and light routing,"We determine how a system composed of two nonidentical two-level atoms with
different resonance frequencies and different damping rates could work as a
nano-antenna for controlled mode switching and light routing. We calculate the
angular distribution of the emitted field detected in a far-field zone of the
system including the direct interatomic interactions and arbitrary linear
dimensions of the system. The calculation is carried out in terms of the
symmetric and antisymmetric modes of the two atom system. We find that as long
as the atoms are identical, the emission cannot be switched between the
symmetric and antisymmetric modes. The switching may occur when the atoms are
non-identical and the emission can then be routed to different modes by
changing the relative ratio of the atomic frequencies, or damping rates or by a
proper tuning of the laser frequency to the atomic resonance frequencies. It is
shown that in the case of atoms of different resonance frequencies but equal
damping rates, the light routing is independent of the frequency of the driving
laser field. It depends only on the sign of the detuning between the atomic
resonance frequencies. In the case of atoms of different damping rates, the
emission can be switched between different modes by changing the laser
frequency from the blue to red detuned from the atomic resonance. The effect of
the interatomic interactions is also considered and it is found that in the
case of unequal resonance frequencies of the atoms, the interactions slightly
modify the visibility of the intensity pattern. The case of unequal damping
rates of the atoms is affected rather more drastically, the light routing
becoming asymmetric under the dipole-dipole interaction with the enhanced
intensities of the modes turned towards the atom of smaller damping rate.",1309.3924v1
2015-04-01,Landau damping of Gardner solitons in a dusty bi-ion plasma,"The effects of linear Landau damping on the nonlinear propagation of
dust-acoustic solitary waves (DASWs) are studied in a collisionless
unmagnetized dusty plasma with two species of positive ions. The extremely
massive, micron-seized, cold and negatively charged dust particles are
described by fluid equations, whereas the two species of positive ions, namely
the cold (heavy) and hot (light) ions are described by the kinetic Vlasov
equations. Following Ott and Sudan [Phys. Fluids {\bf 12}, 2388 (1969)], and by
considering lower and higher-order perturbations, the evolution of DASWs with
Landau damping is shown to be governed by Korteweg-de Vries (KdV), modified KdV
(mKdV) or Gardner (KdV-mKdV)-like equations. The properties of the phase
velocity and the Landau damping rate of DASWs are studied for different values
of the ratios of the temperatures $(\sigma)$ and the number densities $(\mu)$
of hot and cold ions as well the cold to hot ion mass ratio $m$. The
distinctive features of the decay rates of the amplitudes of the KdV, mKdV and
Gardner solitons with a small effect of Landau damping are also studied in
different parameter regimes. It is found that the Gardner soliton points to
lower wave amplitudes than the KdV and mKdV solitons. The results may be useful
for understanding the localization of solitary pulses and associated wave
damping (collisionless) in laboratory and space plasmas (e.g., the F-ring of
Saturn) in which the number density of free electrons is much smaller than that
of ions and the heavy, micron seized dust grains are highly charged.",1504.00089v2
2017-07-18,Explanations of the DAMPE high energy electron/positron spectrum in the dark matter annihilation and pulsar scenarios,"Many studies have shown that either the nearby astrophysical source or dark
matter (DM) annihilation/decay is required to explain the origin of high energy
cosmic ray (CR) $e^\pm$, which are measured by many experiments, such as PAMELA
and AMS-02. Recently, the Dark Matter Particle Explorer (DAMPE) collaboration
has reported its first result of the total CR $e^\pm$ spectrum from $25
\,\mathrm{GeV}$ to $4.6 \,\mathrm{TeV}$ with high precision. In this work, we
study the DM annihilation and pulsar interpretations of the DAMPE high energy
$e^\pm$ spectrum. In the DM scenario, the leptonic annihilation channels to
$\tau^+\tau^-$, $4\mu$, $4\tau$, and mixed charged lepton final states can well
fit the DAMPE result, while the $\mu^+\mu^-$ channel has been excluded. In
addition, we find that the mixed charged leptons channel would lead to a sharp
drop at $\sim$ $\mathrm{TeV}$. However, these DM explanations are almost
excluded by the observations of gamma-ray and CMB, unless some complicated DM
models are introduced. In the pulsar scenario, we analyze 21 nearby known
pulsars and assume that one of them is the primary source of high energy CR
$e^\pm$.Considering the constraint from the Fermi-LAT observation of the
$e^\pm$ anisotropy, we find that two pulsars are possible to explain the DAMPE
data. Our results show that it is difficult to distinguish between the DM
annihilation and single pulsar explanations of high energy $e^\pm$ with the
current DAMPE result.",1707.05664v2
2018-06-27,In-flight performance of the DAMPE silicon tracker,"DAMPE (DArk Matter Particle Explorer) is a spaceborne high-energy cosmic ray
and gamma-ray detector, successfully launched in December 2015. It is designed
to probe astroparticle physics in the broad energy range from few GeV to 100
TeV. The scientific goals of DAMPE include the identification of possible
signatures of Dark Matter annihilation or decay, the study of the origin and
propagation mechanisms of cosmic-ray particles, and gamma-ray astronomy. DAMPE
consists of four sub-detectors: a plastic scintillator strip detector, a
Silicon-Tungsten tracKer-converter (STK), a BGO calorimeter and a neutron
detector. The STK is composed of six double layers of single-sided silicon
micro-strip detectors interleaved with three layers of tungsten for photon
conversions into electron-positron pairs. The STK is a crucial component of
DAMPE, allowing to determine the direction of incoming photons, to reconstruct
tracks of cosmic rays and to estimate their absolute charge (Z). We present the
in-flight performance of the STK based on two years of in-flight DAMPE data,
which includes the noise behavior, signal response, thermal and mechanical
stability, alignment and position resolution.",1806.10355v1
2018-10-30,Effect of Landau damping on ion acoustic solitary waves in a multi-species collisionless unmagnetized plasma consisting of nonthermal and isothermal electrons,"A Korteweg-de Vries (KdV) equation including the effect of Landau damping is
derived to study the propagation of weakly nonlinear and weakly dispersive ion
acoustic waves in a collisionless unmagnetized plasma consisting of warm
adiabatic ions and two different species of electrons at different
temperatures. The hotter energetic electron species follows the nonthermal
velocity distribution of Cairns et al. [Geophys. Res. Lett. 22, 2709 (1995)]
whereas the cooler electron species obeys the Boltzmann distribution. It is
found that the coefficient of the nonlinear term of this KdV like evolution
equation vanishes along different family of curves in different parameter
planes. In this context, a modified KdV (MKdV) equation including the effect of
Landau damping effectively describes the nonlinear behaviour of ion acoustic
waves. It has also been observed that the coefficients of the nonlinear terms
of the KdV and MKdV like evolution equations including the effect of Landau
damping, are simultaneously equal to zero along a family of curves in the
parameter plane. In this situation, we have derived a further modified KdV
(FMKdV) equation including the effect of Landau damping to describe the
nonlinear behaviour of ion acoustic waves. In fact, different modified KdV like
evolution equations including the effect of Landau damping have been derived to
describe the nonlinear behaviour of ion acoustic waves in different region of
parameter space. The method of Ott & Sudan [Phys. Fluids 12, 2388 (1969)] has
been applied to obtain the solitary wave solution of the evolution equation
having the nonlinear term $(\phi^{(1)})^{r}\frac{\partial \phi^{(1)}}{\partial
\xi}$, where $\phi^{(1)}$ is the first order perturbed electrostatic potential
and $r =1,2,3$. We have found that the amplitude of the solitary wave solution
decreases with time for all $r =1,2,3$.",1810.12739v1
2019-03-28,Improving convergence of volume penalised fluid-solid interactions,"We analyse and improve the volume-penalty method, a simple and versatile way
to model objects in fluid flows. The volume-penalty method is a kind of
fictitious-domain method that approximates no-slip boundary conditions with
rapid linear damping inside the object. The method can then simulate complex,
moving objects in general numerical solvers without specialised algorithms or
boundary-conforming grids. Volume penalisation pays for this simplicity by
introducing an equation-level error, the $\textit{model error}$, that is
related to the damping time $\eta \ll 1$. While the model error has been proven
to vanish as the damping time tends to zero, previous work suggests convergence
at a slow rate of $\mathcal{O}(\eta^{1/2})$. The stiffness of the damping
implies conventional volume penalisation only achieves first order numerical
accuracy. We analyse the volume-penalty method using multiple-scales
matched-asymptotics with a signed-distance coordinate system valid for
arbitrary smooth geometries. We show the dominant model error stems from a
displacement length that is proportional to a Reynolds number $\text{Re}$
dependent boundary layer of size $\mathcal{O}(\eta^{1/2}\text{Re}^{-1/2})$. The
relative size of the displacement length and damping time leads to multiple
error regimes. Our key finding derives a simple smoothing prescription for the
damping that eliminates the displacement length and reduces the model error to
$\mathcal{O}(\eta)$ in all regimes. This translates to second order numerical
accuracy. We validate our findings in several comprehensive benchmark problems
and finally combine Richardson extrapolation of the model error with our
correction to further improve convergence to $\mathcal{O}(\eta^{2})$.",1903.11914v4
2019-06-12,Study of Alfven Eigenmodes stability in plasma with multiple NBI driven energetic particle specie,"The aim of this study is to analyze the destabilization of Alfven Eigenmodes
(AE) by multiple energetic particles (EP) species in DIII-D and LHD discharges.
We use the reduced MHD equations to describe the linear evolution of the
poloidal flux and the toroidal component of the vorticity in a full 3D system,
coupled with equations of density and parallel velocity moments for the
energetic particles species, including the effect of the acoustic modes,
diamagnetic currents and helical couplings. We add the Landau damping and
resonant destabilization effects using a closure relation. The simulations with
multiple NBI lines show three different regimes: the non damped regime where
the multi beam AEs growth rate is larger compared to the growth rate of the AEs
destabilized by the individual NBI lines, the interaction regime where the
multi beam AEs growth rate is smaller than the single NBI AEs and the damped
regime where the AEs are suppressed. Operations in the damped regime requires
EP species with different density profile flatness or gradient locations. In
addition, the AEs growth rate in the interaction regime is further reduced if
the combined NBI lines have similar beam temperatures and the beta of the NBI
line with flatter EP density profile increases. Then, optimization trends are
identified in DIII-D high poloidal beta and LHD low density / magnetic field
discharges with multiple NBI lines as well as the configuration requirements to
operate in the damped and interaction regimes. DIII-D simulations show a
decrease of the n=2 to 6 AEs growth rate and n=1 AE are stabilized in the LHD
case. The helical coupling effects in LHD simulations lead to a transition from
the interaction to the damped regime of the n=2,-8,12 helical family.",1906.05701v1
2019-11-05,Observation of Nanoscale Opto-Mechanical Molecular Damping; Origin of Spectroscopic Contrast in Photo Induced Force Microscopy,"We experimentally investigated the contrast mechanism of infrared
photoinduced force microscopy (PiFM) for recording vibrational resonances.
Extensive experiments have demonstrated that spectroscopic contrast in PiFM is
mediated by opto-mechanical damping of the cantilever oscillation as the
optical wavelength is scanned through optical resonance. To our knowledge, this
is the first time opto-mechanical damping has been observed in the AFM. We
hypothesize that this damping force is a consequence of the dissipative
interaction between the sample and the vibrating tip; the modulated light
source in PiFM modulates the effective damping constant of the 2nd eigenmode of
the cantilever which in turn generate side-band signals producing the PiFM
signal at the 1st eigenmode. A series of experiments have eliminated other
mechanisms of contrast. By tracking the frequency shift of the PiFM signal at
the 1st cantilever eigenmode as the excitation wavenumber is tuned through a
mid-infrared absorption band, we showed that the near-field optical interaction
is attractive. By using a vibrating piezoelectric crystal to mimic sample
thermal expansion in a PiFM operating in mixing mode, we determined that the
minimum thermal expansion our system can detect is 30 pm limited by system
noise. We have confirmed that van der Waal mediated thermal-expansion forces
have negligible effect on PiFM signals by detecting the resonant response of a
4-methylbenzenethiol mono molecular layer deposited on template-stripped gold,
where thermal expansion was expected to be < 3 pm, i.e., 10 times lower than
our system noise level. Finally, the basic theory for dissipative tip-sample
interactions was introduced to model the photoinduced opto-mechanical damping.
Theoretical simulations are in excellent agreement with experiment.",1911.05190v1
2020-06-08,Stochastic re-acceleration and magnetic-field damping in Tycho's supernova remnant,"A number of studies suggest that shock acceleration with particle feedback
and very efficient magnetic-field amplification combined with Alfv\'{e}nic
drift are needed to explain the rather soft radio spectrum and the narrow rims
observed for Tycho's SNR. We show that the broadband spectrum of Tycho's SNR
can alternatively be well explained when accounting for stochastic acceleration
as a secondary process. The re-acceleration of particles in the turbulent
region immediately downstream of the shock should be efficient enough to impact
particle spectra over several decades in energy. The so-called Alfv\'{e}nic
drift and particle feedback on the shock structure are not required in this
scenario. Additionally, we investigate whether synchrotron losses or
magnetic-field damping play a more profound role in the formation of the
non-thermal filaments. We solve the full particle transport equation in
test-particle mode using hydrodynamic simulations of the SNR plasma flow. The
background magnetic field is either computed from the induction equation or
follows analytic profiles, depending on the model considered. Fast-mode waves
in the downstream region provide the diffusion of particles in momentum space.
We show that the broadband spectrum of Tycho can be well explained if
magnetic-field damping and stochastic re-acceleration of particles are taken
into account. Although not as efficient as standard DSA, stochastic
acceleration leaves its imprint on the particle spectra, which is especially
notable in the emission at radio wavelengths. We find a lower limit for the
post-shock magnetic-field strength $\sim330\,\mathrm{\mu G}$, implying
efficient amplification even for the magnetic-field damping scenario. For the
formation of the filaments in the radio range magnetic-field damping is
necessary, while the X-ray filaments are shaped by both the synchrotron losses
and magnetic-field damping.",2006.04832v1
2021-02-23,Influence of Ion-Neutral Damping on the Cosmic-Ray Streaming Instability: Magnetohydrodynamic Particle-in-cell Simulations,"We explore the physics of the gyro-resonant cosmic ray streaming instability
(CRSI) including the effects of ion-neutral (IN) damping. This is the main
damping mechanism in (partially-ionized) atomic and molecular gas, which are
the primary components of the interstellar medium (ISM) by mass. Limitation of
CRSI by IN damping is important in setting the amplitude of Alfv\'en waves that
scatter cosmic rays and control galactic-scale transport. Our study employs the
MHD-PIC hybrid fluid-kinetic numerical technique to follow linear growth as
well as post-linear and saturation phases. During the linear phase of the
instability -- where simulations and analytical theory are in good agreement --
IN damping prevents wave growth at small and large wavelengths, with the
unstable bandwidth lower for higher ion-neutral collision rate $\nu_{\rm in}$.
Purely MHD effects during the post-linear phase extend the wave spectrum
towards larger $k$. In the saturated state, the cosmic ray distribution evolves
toward greater isotropy (lower streaming velocity) by scattering off of Alv\'en
waves excited by the instability. In the absence of low-$k$ waves, CRs with
sufficiently high momentum are not isotropized. The maximum wave amplitude and
rate of isotropization of the distribution function decreases at higher
$\nu_{\rm in}$. When the IN damping rate approaches the maximum growth rate of
CSRI, wave growth and isotropization is suppressed. Implications of our results
for CR transport in partially ionized ISM phases are discussed.",2102.11878v3
2022-06-17,Quantum Dynamics of Magnetic Skyrmions: Consistent Path Integral Formulation,"We present a path integral formalism for the intrinsic quantum dynamics of
magnetic skyrmions coupled to a thermal background of magnetic fluctuations.
Upon promoting the skyrmion's collective coordinate $\boldsymbol{R}$ to a
dynamic variable and integrating out the magnonic heat bath, we derive the
generalized equation of motion for $\boldsymbol{R}$ with a non-local damping
term that describes a steady-state skyrmion dynamics at finite temperatures.
Being essentially temperature dependent, the intrinsic damping is shown to
originate from the coupling of thermally activated magnon modes to the
adiabatic potential driven by a rigid skyrmion motion, which can be regarded as
another manifestation of emergent electrodynamics inherent to topological
magnetic textures. We further argue that the diagonal components of the damping
term act as the source of dissipation and inertia, while its off-diagonal
components modify the gyrotropic motion of a magnetic skyrmion. By means of
numerical calculations for the lattice spin model of chiral ferromagnets, we
study the temperature behavior of the intrinsic damping as a function of
magnetic field in periodic and confined geometries. The intrinsic damping is
demonstrated to be highly non-local, revealing its quantum-mechanical nature,
that becomes more pronounced with increasing temperature. At high temperatures
when the magnon occupation factors are large, the intrinsic damping is shown to
yield a modified Thiele's equation with the additional non-local dissipative
and mass terms that exhibit an almost linear temperature behavior. Our results
provide a microscopic background for semiclassical magnetization dynamics and
establish a framework for understanding spin caloritronics effects in
topological magnetic textures.",2206.08532v2
2024-02-05,Revisiting the role of cosmic-ray driven Alfvén waves in pre-existing magnetohydrodynamic turbulence. I. Turbulent damping rates and feedback on background fluctuations,"Alfv\'en waves (AWs) excited by the cosmic-ray (CR) streaming instability
(CRSI) are a fundamental ingredient for CR confinement. The effectiveness of
self-confinement relies on a balance between CRSI growth rate and damping
mechanisms acting on quasi-parallel AWs excited by CRs. One relevant mechanism
is the so-called turbulent damping, in which an AW packet injected in
pre-existing turbulence undergoes a cascade process due to its nonlinear
interaction with fluctuations of the background. The turbulent damping of an AW
packet in pre-existing magnetohydrodynamic turbulence is re-examined, revised,
and extended to include most-recent theories of MHD turbulence that account for
dynamic alignment and reconnection-mediated regime. The case in which the role
of feedback of CR-driven AWs on pre-existing turbulence is important will also
be discussed. Particular attention is given to the nonlinearity parameter
$\chi^w$ that estimates the strength of nonlinear interaction between CR-driven
AWs and background fluctuations. We point out the difference between $\chi^w$
and $\chi^z$ that instead describes the strength of nonlinear interactions
between pre-existing fluctuations. When $\chi^w$ is properly taken into
account, one finds that (i) the turbulent damping rate of quasi-parallel AWs in
anisotropic turbulence depends on the background-fluctuations' amplitude to the
third power, hence is strongly suppressed, and (ii) the dependence on the AW's
wavelength (and thus on the CR gyro-radius from which it is excited) is
different from what has been previously obtained. Finally, (iii) when dynamic
alignment of cascading fluctuations and the possibility of a
reconnection-mediated range is included in the picture, the turbulent damping
rate exhibits novel regimes and breaks. Finally, a criterion for CR-feedback is
derived and simple phenomenological models of CR-modified turbulent scaling are
provided.",2402.02901v1
2006-10-24,Logical contradictions of Landau damping,"Landau damping/growing at boundary condition of excitation of a harmonic wave
in collisionless ion-electron-neutrals plasma contradicts to the law of energy
conservation of a wave damping/growing in space. There is also no criterion of
a choice either damping or growing solution in difference from always
non-damping in the direction of propagation Vlasov waves. Variety of other
incongruities as consequence of Landau damping is specified also. Absence of
explicit positivity and finiteness of wave solutions for electron distribution
function near singularity point leads to need of imposing additional cutting
off constraints with resulting positivity and finiteness of the electron
distribution function at the singularity points and finiteness of the complex
dispersion integral. Landau damping as a real physical phenomenon of
collisionless damping does not exist. A relation is established for the real
dispersion equation with real waves (see Appendices 2,4) between the averaged
over period wave damping decrement and the collisional energy-exchange term of
kinetic equation. Collisionless Vlasov-Landau damping is explained finally by
the usual wrong use of nonlinearly complex wave functions leading to complex
dispersion equation. All used solution of the complex dispersion equation for
the simultaneously existing collisionless both exponentially damping and
growing nonlinear complex waves is entirely, quantitatively and in its logical
sense, different from the solution of initially real dispersion equation for
real either damping or growing waves and should be discarded (see Appendices
2,4,5,6). Collisionless damping is caused by unreasonable use of wave functions
with complex frequency or complex wave number leading to complex dispersion
relation with unphysical binomial virtual complex roots. Thus finding roots of
the complex dispersion equation has only abstract mathematical interest.",0610220v67
1999-12-17,Infrared Spectroscopy of a Massive Obscured Star Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC,"We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039)
with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the
vicinity of the southern nucleus (NGC 4039) in 0.39"" seeing in K-band using
NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the
near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the
highest surface brightness peak in the mid-IR (12-18 micron) ISO image
presented by Mirabel et al. (1998). We obtained high signal-to-noise 2.03 -
2.45 micron spectra of the nucleus and the obscured star cluster at R ~ 1900.
  The cluster is very young (4 Myr old), massive (16e6 M_sun), and compact
(density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius), assuming a
Salpeter IMF (0.1 - 100 M_sun). Its hot stars have a radiation field
characterized by T_eff ~ 39,000 K, and they ionize a compact H II region with
n_e ~ 1e4 cm^(-3). The stars are deeply embedded in gas and dust (A_V ~ 9-10
mag), and their strong FUV field powers a clumpy photodissociation region with
densities n_H >= 1e5 cm^(-3) on scales of up to 200 pc, radiating L[H_2 1-0
S(1)] = 9600 L_sun.",9912369v1
2000-09-07,Practical Quantum Cryptography: A Comprehensive Analysis (Part One),"We perform a comprehensive analysis of practical quantum cryptography (QC)
systems implemented in actual physical environments via either free-space or
fiber-optic cable quantum channels for ground-ground, ground-satellite,
air-satellite and satellite-satellite links. (1) We obtain universal
expressions for the effective secrecy capacity and rate for QC systems taking
into account three important attacks on individual quantum bits, including
explicit closed-form expressions for the requisite amount of privacy
amplification. Our analysis also includes the explicit calculation in detail of
the total cost in bits of continuous authentication, thereby obtaining new
results for actual ciphers of finite length. (2) We perform for the first time
a detailed, explicit analysis of all systems losses due to propagation, errors,
noise, etc. as appropriate to both optical fiber cable- and satellite
communications-based implementations of QC. (3) We calculate for the first time
all system load costs associated to classical communication and computational
constraints that are ancillary to, but essential for carrying out, the pure QC
protocol itself. (4) We introduce an extended family of generalizations of the
Bennett-Brassard (BB84) QC protocol that equally provide unconditional secrecy
but allow for the possibility of optimizing throughput rates against specific
cryptanalytic attacks. (5) We obtain universal predictions for maximal rates
that can be achieved with practical system designs under realistic
environmental conditions. (6) We propose a specific QC system design that
includes the use of a novel method of high-speed photon detection that may be
able to achieve very high throughput rates for actual implementations in
realistic environments.",0009027v5
2009-08-07,The Dominance of Metal-Rich Streams in Stellar Halos: A Comparison Between Substructure in M31 and Lambda-CDM Models,"Extensive photometric and spectroscopic surveys of the Andromeda galaxy (M31)
have discovered tidal debris features throughout M31's stellar halo. We present
stellar kinematics and metallicities in fields with identified substructure
from our on-going SPLASH survey of M31 red giant branch stars with the DEIMOS
spectrograph on the Keck II 10-m telescope. Radial velocity criteria are used
to isolate members of the kinematically-cold substructures. The substructures
are shown to be metal-rich relative to the rest of the dynamically hot stellar
population in the fields in which they are found. We calculate the mean
metallicity and average surface brightness of the various kinematical
components in each field, and show that, on average, higher surface brightness
features tend to be more metal-rich than lower surface brightness features.
Simulations of stellar halo formation via accretion in a cosmological context
are used to illustrate that the observed trend can be explained as a natural
consequence of the observed dwarf galaxy mass-metallicity relation. A
significant spread in metallicity at a given surface brightness is seen in the
data; we show that this is due to time effects, namely the variation in the
time since accretion of the tidal streams' progenitor onto the host halo. We
show that in this theoretical framework a relationship between the
alpha-enhancement and surface brightness of tidal streams is expected, which
arises from the varying times of accretion of the progenitor satellites onto
the host halo. Thus, measurements of the alpha-enrichment, metallicity, and
surface brightness of tidal debris can be used to reconstruct the luminosity
and time of accretion onto the host halo of the progenitors of tidal streams.",0908.1111v1
2009-09-25,The SPLASH Survey: A Spectroscopic Portrait of Andromeda's Giant Southern Stream,"The giant southern stream (GSS) is the most prominent tidal debris feature in
M31's stellar halo. The GSS is composed of a relatively metal-rich, high
surface-brightness ""core"" and a lower metallicity, lower surface brightness
""envelope."" We present Keck/DEIMOS spectroscopy of red giant stars in six
fields in the vicinity of M31's GSS and one field on Stream C, an arc-like
feature on M31's SE minor axis at R=60 kpc. Several GSS-related findings and
measurements are presented here. We present the innermost kinematical detection
of the GSS core to date (R=17 kpc). This field also contains the continuation
of a second kinematically cold component originally seen in a GSS core field at
R=21 kpc. The velocity gradients of the GSS and the second component in the
combined data set are parallel over a radial range of 7 kpc, suggesting a
possible bifurcation in the line-of-sight velocities of GSS stars. We also
present the first kinematical detection of substructure in the GSS envelope.
Using kinematically identified samples, we show that the envelope debris has a
~0.7 dex lower mean photometric metallicity and possibly higher intrinsic
velocity dispersion than the GSS core. The GSS is also identified in the field
of the M31 dSph satellite And I; the GSS in this field has a metallicity
distribution identical to that of the GSS core. We confirm the presence of two
kinematically cold components in Stream C, and measure intrinsic velocity
dispersions of ~10 and ~4 km/s. This compilation of the kinematical (mean
velocity, intrinsic velocity dispersion) and chemical properties of stars in
the GSS core and envelope, coupled with published surface brightness
measurements and wide-area star-count maps, will improve constraints on the
orbit and internal structure of the dwarf satellite progenitor.",0909.4540v1
2011-05-28,Transmission Control of Two-User Slotted ALOHA Over Gilbert-Elliott Channel: Stability and Delay Analysis,"In this paper, we consider the problem of calculating the stability region
and average delay of two user slotted ALOHA over a Gilbert-Elliott channel,
where users have channel state information and adapt their transmission
probabilities according to the channel state. Each channel has two states,
namely, the 'good' and 'bad' states. In the 'bad' state, the channel is assumed
to be in deep fade and the transmission fails with probability one, while in
the 'good' state, there is some positive success probability. We calculate the
Stability region with and without Multipacket Reception capability as well as
the average delay without MPR. Our results show that the stability region of
the controlled S-ALOHA is always a superset of the stability region of
uncontrolled S-ALOHA. Moreover, if the channel tends to be in the 'bad' state
for long proportion of time, then the stability region is a convex Polyhedron
strictly containing the TDMA stability region and the optimal transmission
strategy is to transmit with probability one whenever the nodes have packets
and it is shown that this strategy is delay optimal. On the other hand, if the
channel tends to be in the 'good' state more often, then the stability region
is bounded by a convex curve and is strict subset of the TDMA stability region.
We also show that enhancing the physical layer by allowing MPR capability can
significantly enhance the performance while simplifying the MAC Layer design by
the lack of the need of scheduling under some conditions. Furthermore, it is
shown that transmission control not only allows handling higher stable arrival
rates but also leads to lower delay for the same arrival rate compared with
ordinary S-ALOHA.",1105.5676v2
2012-10-11,Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile,"We present the surface brightness profile of M31's stellar halo out to a
projected radius of 175 kpc. The surface brightness estimates are based on
confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS
spectroscopic observations. A set of empirical spectroscopic and photometric
M31 membership diagnostics is used to identify and reject foreground and
background contaminants. This enables us to trace the stellar halo of M31 to
larger projected distances and fainter surface brightnesses than previous
photometric studies. The surface brightness profile of M31's halo follows a
power-law with index -2.2 +/- 0.2 and extends to a projected distance of at
least ~175 kpc (~ 2/3 of M31's virial radius), with no evidence of a downward
break at large radii. The best-fit elliptical isophotes have b/a=0.94 with the
major axis of the halo aligned along the minor axis of M31's disk, consistent
with a prolate halo, although the data are also consistent with M31's halo
having spherical symmetry. The fact that tidal debris features are
kinematically cold is used to identify substructure in the spectroscopic fields
out to projected radii of 90 kpc, and investigate the effect of this
substructure on the surface brightness profile. The scatter in the surface
brightness profile is reduced when kinematically identified tidal debris
features in M31 are statistically subtracted; the remaining profile indicates a
comparatively diffuse stellar component to M31's stellar halo exists to large
distances. Beyond 90 kpc, kinematically cold tidal debris features can not be
identified due to small number statistics; nevertheless, the significant
field-to-field variation in surface brightness beyond 90 kpc suggests that the
outermost region of M31's halo is also comprised to a significant degree of
stars stripped from accreted objects.",1210.3362v2
2014-09-12,Global Properties of M31's Stellar Halo from the SPLASH Survey: II. Metallicity Profile,"We present the metallicity distribution of red giant branch (RGB) stars in
M31's stellar halo, derived from photometric metallicity estimates for over
1500 spectroscopically confirmed RGB halo stars. The stellar sample comes from
38 halo fields observed with the Keck/DEIMOS spectrograph, ranging from 9 to
175 kpc in projected distance from M31's center, and includes 52 confirmed M31
halo stars beyond 100 kpc. While a wide range of metallicities is seen
throughout the halo, the metal-rich peak of the metallicity distribution
function becomes significantly less prominent with increasing radius. The
metallicity profile of M31's stellar halo shows a continuous gradient from 9 to
~100 kpc, with a magnitude of -0.01 dex/kpc. The stellar velocity distributions
in each field are used to identify stars that are likely associated with tidal
debris features. The removal of tidal debris features does not significantly
alter the metallicity gradient in M31's halo: a gradient is maintained in
fields spanning 10 to 90 kpc. We analyze the halo metallicity profile, as well
as the relative metallicities of stars associated with tidal debris features
and the underlying halo population, in the context of current simulations of
stellar halo formation. We argue that the large scale gradient in M31's halo
implies M31 accreted at least one relatively massive progenitor in the past,
while the field to field variation seen in the metallicity profile indicates
that multiple smaller progenitors are likely to have contributed substantially
to M31's outer halo.",1409.3843v1
2016-07-15,Solving the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation for monodomain nanomagnets : A survey and analysis of numerical techniques,"The stochastic Landau-Lifshitz-Gilbert-Slonczewski (s-LLGS) equation is
widely used to study the temporal evolution of the macrospin subject to spin
torque and thermal noise. The numerical simulation of the s-LLGS equation
requires an appropriate choice of stochastic calculus and numerical integration
scheme. In this paper, we comprehensively evaluate the accuracy and complexity
of various numerical techniques to solve the s-LLGS equation. We focus on
implicit midpoint, Heun, and Euler-Heun methods that converge to the
Stratonovich solution of the s-LLGS equation. By performing numerical tests for
both strong (path-wise) and weak (statistical) convergence, we quantify the
accuracy of various numerical schemes used to solve the s-LLGS equation. We
demonstrate a new method intended to solve Stochastic Differential Equations
(SDEs) with small noise (RK4-Heun), and test its capability to handle the
s-LLGS equation. We also discuss the circuit implementation of nanomagnets for
large-scale SPICE-based simulations. We evaluate the efficacy of SPICE in
handling the stochastic dynamics of the multiplicative noise in the s-LLGS
equation. Numerical schemes such as Euler and Gear, typically used by
SPICE-based circuit simulators do not yield the expected outcome when solving
the Stratonovich s-LLGS equation. While the trapezoidal method in SPICE does
solve for the Stratonovich solution, its accuracy is limited by the minimum
time step of integration in SPICE. We implement the s-LLGS equation in both its
cartesian and spherical coordinates form in SPICE and compare the stability and
accuracy of the two implementations. The results in this paper will serve as
guidelines for researchers to understand the tradeoffs between accuracy and
complexity of various numerical methods and the choice of appropriate calculus
to solve the s-LLGS equation.",1607.04596v4
2016-11-30,Low Energy Supergravity Revisited (I),"General forms of the K\""ahler and superpotenials that lead to consistent low
energy broken Supersymmetry originating from $N=1$ Supergravity have been
classified and used for model building since more than three decades. We point
out the incompleteness of this classification when hidden sector vacuum
expectation values are of the order of the Planck mass. Focusing in this paper
mainly on the case of minimal K\""ahler potential, we adopt a rigorous approach
that retrieves on the one hand the known forms, and demonstrate on the other
hand the existence of a whole set of new forms for the superpotential of which
we give a complete classification. The latter forms involve a new type of
chiral superfields having the unusual property of belonging neither to the
hidden sector nor to the conventional observable sector. Comparing the obtained
forms with the conventional ones, we argue how new possibilities for model
building can arise, and discuss the gravity mediation of soft as well as
additional hard (but parametrically small) Supersymmetry breaking, in the
presence of the new type of chiral superfields. In the simplest case, we study
the vacuum structure, characterize the masses and couplings of the scalar
components to the hidden and observable sectors and discuss briefly the
physical role they could play. In the generic case, we estimate the magnitude
and possible consequences of the hard breaking of Supersymmetry in terms of the
interplay between hidden and visible sectors mass scales.",1611.10327v2
2018-08-08,Analysis of quasi-Monte Carlo methods for elliptic eigenvalue problems with stochastic coefficients,"We consider the forward problem of uncertainty quantification for the
generalised Dirichlet eigenvalue problem for a coercive second order partial
differential operator with random coefficients, motivated by problems in
structural mechanics, photonic crystals and neutron diffusion. The PDE
coefficients are assumed to be uniformly bounded random fields, represented as
infinite series parametrised by uniformly distributed i.i.d. random variables.
The expectation of the fundamental eigenvalue of this problem is computed by
(a) truncating the infinite series which define the coefficients; (b)
approximating the resulting truncated problem using lowest order conforming
finite elements and a sparse matrix eigenvalue solver; and (c) approximating
the resulting finite (but high dimensional) integral by a randomly shifted
quasi-Monte Carlo lattice rule, with specially chosen generating vector. We
prove error estimates for the combined error, which depend on the truncation
dimension $s$, the finite element mesh diameter $h$, and the number of
quasi-Monte Carlo samples $N$. Under suitable regularity assumptions, our
bounds are of the particular form $\mathcal{O}(h^2+N^{-1+\delta})$, where
$\delta>0$ is arbitrary and the hidden constant is independent of the
truncation dimension, which needs to grow as $h\to 0$ and $N\to\infty$.
Although the eigenvalue problem is nonlinear, which means it is generally
considered harder than the analogous source problem, in almost all cases we
obtain error bounds that converge at the same rate as the corresponding rate
for the source problem. The proof involves a detailed study of the regularity
of the fundamental eigenvalue as a function of the random parameters. As a key
intermediate result in the analysis, we prove that the spectral gap (between
the fundamental and the second eigenvalues) is uniformly positive over all
realisations of the random problem.",1808.02639v3
2018-09-24,Ionic Tuning of Cobaltites at the Nanoscale,"Control of materials through custom design of ionic distributions represents
a powerful new approach to develop future technologies ranging from spintronic
logic and memory devices to energy storage. Perovskites have shown particular
promise for ionic devices due to their high ion mobility and sensitivity to
chemical stoichiometry. In this work, we demonstrate a solid-state approach to
control of ionic distributions in (La,Sr)CoO$_{3}$ thin films. Depositing a Gd
capping layer on the perovskite film, oxygen is controllably extracted from the
structure, up-to 0.5 O/u.c. throughout the entire 36 nm thickness. Commensurate
with the oxygen extraction, the Co valence state and saturation magnetization
show a smooth continuous variation. In contrast, magnetoresistance measurements
show no-change in the magnetic anisotropy and a rapid increase in the
resistivity over the same range of oxygen stoichiometry. These results suggest
significant phase separation, with metallic ferromagnetic regions and
oxygen-deficient, insulating, non-ferromagnetic regions, forming percolated
networks. Indeed, X-ray diffraction identifies oxygen-vacancy ordering,
including transformation to a brownmillerite crystal structure. The unexpected
transformation to the brownmillerite phase at ambient temperature is further
confirmed by high-resolution scanning transmission electron microscopy which
shows significant structural - and correspondingly chemical - phase separation.
This work demonstrates room-temperature ionic control of magnetism, electrical
resistivity, and crystalline structure in a 36 nm thick film, presenting new
opportunities for ionic devices that leverage multiple material
functionalities.",1809.08728v1
2019-04-10,The Convergence of Iterative Delegations in Liquid Democracy in a Social Network,"Liquid democracy is a collective decision making paradigm which lies between
direct and representative democracy. One of its main features is that voters
can delegate their votes in a transitive manner such that: A delegates to B and
B delegates to C leads to A indirectly delegates to C. These delegations can be
effectively empowered by implementing liquid democracy in a social network, so
that voters can delegate their votes to any of their neighbors in the network.
However, it is uncertain that such a delegation process will lead to a stable
state where all voters are satisfied with the people representing them. We
study the stability (w.r.t. voters preferences) of the delegation process in
liquid democracy and model it as a game in which the players are the voters and
the strategies are their possible delegations. We answer several questions on
the equilibria of this process in any social network or in social networks that
correspond to restricted types of graphs.
  We show that a Nash-equilibrium may not exist, and that it is even
NP-complete to decide whether one exists or not. This holds even if the social
network is a complete graph or a bounded degree graph. We further show that
this existence problem is W[1]-hard w.r.t. the treewidth of the social network.
Besides these hardness results, we demonstrate that an equilibrium always
exists whatever the preferences of the voters iff the social network is a tree.
We design a dynamic programming procedure to determine some desirable
equilibria (e.g., minimizing the dissatisfaction of the voters) in polynomial
time for tree social networks. Lastly, we study the convergence of delegation
dynamics. Unfortunately, when an equilibrium exists, we show that a best
response dynamics may not converge, even if the social network is a path or a
complete graph.",1904.05775v2
2019-06-20,Ongoing Vaccine and Monoclonal Antibody HIV Prevention Efficacy Trials and Considerations for Sequel Efficacy Trial Designs,"Four randomized placebo-controlled efficacy trials of a candidate vaccine or
passively infused monoclonal antibody for prevention of HIV-1 infection are
underway (HVTN 702 in South African men and women; HVTN 705 in sub-Saharan
African women; HVTN 703/HPTN 081 in sub-Saharan African women; HVTN 704/HPTN
085 in U.S., Peruvian, Brazilian, and Swiss men or transgender persons who have
sex with men). Several challenges are posed to the optimal design of the sequel
efficacy trials, including: (1) how to account for the evolving mosaic of
effective prevention interventions that may be part of the trial design or
standard of prevention; (2) how to define viable and optimal sequel trial
designs depending on the primary efficacy results and secondary 'correlates of
protection' results of each of the ongoing trials; and (3) how to define the
primary objective of sequel efficacy trials if HIV-1 incidence is expected to
be very low in all study arms such that a standard trial design has a steep
opportunity cost. After summarizing the ongoing trials, I discuss statistical
science considerations for sequel efficacy trial designs, both generally and
specifically to each trial listed above. One conclusion is that the results of
'correlates of protection' analyses, which ascertain how different host
immunological markers and HIV-1 viral features impact HIV-1 risk and prevention
efficacy, have an important influence on sequel trial design. This influence is
especially relevant for the monoclonal antibody trials because of the focused
pre-trial hypothesis that potency and coverage of serum neutralization
constitutes a surrogate endpoint for HIV-1 infection... (see manuscript for the
full abstract)",1906.08409v1
2019-08-12,Elemental Abundances in M31: First Alpha and Iron Abundance Measurements in M31's Giant Stellar Stream,"We present the first measurements of [Fe/H] and [$\alpha$/Fe] abundances,
obtained using spectral synthesis modeling, for red giant branch stars in M31's
giant stellar stream. The spectroscopic observations, obtained at a projected
distance of 17 kpc from M31's center, yielded 61 stars with [Fe/H]
measurements, including 21 stars with [$\alpha$/Fe] measurements, from 112
targets identified as M31 stars. The [Fe/H] measurements confirm the
expectation from photometric metallicity estimates that stars in this region of
M31's halo are relatively metal-rich compared to stars in the MW's inner halo:
more than half the stars in the field, including those not associated with
kinematically identified substructure, have [Fe/H] abundances $> -1.0$. The
stars in this field are $\alpha$-enhanced at lower metallicities, while
[$\alpha$/Fe] decreases with increasing [Fe/H] above metallicities of [Fe/H]
$\gtrsim -0.9$. Three kinematical components have been previously identified in
this field: the giant stellar stream, a second kinematically cold feature of
unknown origin, and M31's kinematically hot halo. We compare probabilistic
[Fe/H] and [$\alpha$/Fe] distribution functions for each of the components. The
giant stellar stream and the second kinematically cold feature have very
similar abundance distributions, while the halo component is more metal-poor.
Although the current sample sizes are small, a comparison of the abundances of
stars in the giant stellar stream field with abundances of M31 halo and dSph
stars from the literature indicate that the progenitor of the stream was likely
more massive, and experienced a higher efficiency of star formation, than M31's
existing dSphs or the dEs NGC147 and NGC185.",1908.04429v1
2019-08-21,Generalized Metric Repair on Graphs,"Many modern data analysis algorithms either assume or are considerably more
efficient if the distances between the data points satisfy a metric. These
algorithms include metric learning, clustering, and dimension reduction. As
real data sets are noisy, distances often fail to satisfy a metric. For this
reason, Gilbert and Jain and Fan et al. introduced the closely related sparse
metric repair and metric violation distance problems. The goal of these
problems is to repair as few distances as possible to ensure they satisfy a
metric. Three variants were considered, one admitting a polynomial time
algorithm. The other variants were shown to be APX-hard, and an
$O(OPT^{1/3})$-approximation was given, where $OPT$ is the optimal solution
size.
  In this paper, we generalize these problems to no longer consider all
distances between the data points. That is, we consider a weighted graph $G$
with corrupted weights $w$, and our goal is to find the smallest number of
weight modifications so that the resulting weighted graph distances satisfy a
metric. This is a natural generalization and is more flexible as it takes into
account different relationships among the data points. As in previous work, we
distinguish among the types of repairs permitted and focus on the increase only
and general versions. We demonstrate the inherent combinatorial structure of
the problem, and give an approximation-preserving reduction from MULTICUT.
Conversely, we show that for any fixed constant $\varsigma$, for the large
class of $\varsigma$-chordal graphs, the problems are fixed parameter
tractable. Call a cycle broken if it contains an edge whose weight is larger
than the sum of all its other edges, and call the amount of this difference its
deficit. We present approximation algorithms, one which depends on the maximum
number of edges in a broken cycle, and one which depends on the number of
distinct deficit values.",1908.08411v1
2019-09-19,Parameterized Complexity of Manipulating Sequential Allocation,"The sequential allocation protocol is a simple and popular mechanism to
allocate indivisible goods, in which the agents take turns to pick the items
according to a predefined sequence. While this protocol is not strategy-proof,
it has been shown recently that finding a successful manipulation for an agent
is an NP-hard problem (Aziz et al., 2017). Conversely, it is also known that
finding an optimal manipulation can be solved in polynomial time in a few
cases: if there are only two agents or if the manipulator has a binary or a
lexicographic utility function. In this work, we take a parameterized approach
to provide several new complexity results on this manipulation problem. More
precisely, we give a complete picture of its parameterized complexity w.r.t.
the following three parameters: the number $n$ of agents, the number $\mu(a_1)$
of times the manipulator $a_1$ picks in the picking sequence, and the maximum
range $\mathtt{rg}^{\max}$ of an item. This third parameter is a correlation
measure on the preference rankings of the agents. In particular, we show that
the problem of finding an optimal manipulation can be solved in polynomial time
if $n$ or $\mu(a_1)$ is a constant, and that it is fixed-parameter tractable
w.r.t. $\mathtt{rg}^{\max}$ and $n+\mu(a_1)$. Interestingly enough, we show
that w.r.t. the single parameters $n$ and $\mu(a_1)$ it is W[1]-hard. Moreover,
we provide an integer program and a dynamic programming scheme to solve the
manipulation problem and we show that a single manipulator can increase the
utility of her bundle by a multiplicative factor which is at most 2.",1909.08920v4
2019-11-06,Doppler Spectrum Classification with CNNs via Heatmap Location Encoding and a Multi-head Output Layer,"Spectral Doppler measurements are an important part of the standard
echocardiographic examination. These measurements give important insight into
myocardial motion and blood flow providing clinicians with parameters for
diagnostic decision making. Many of these measurements can currently be
performed automatically with high accuracy, increasing the efficiency of the
diagnostic pipeline. However, full automation is not yet available because the
user must manually select which measurement should be performed on each image.
In this work we develop a convolutional neural network (CNN) to automatically
classify cardiac Doppler spectra into measurement classes. We show how the
multi-modal information in each spectral Doppler recording can be combined
using a meta parameter post-processing mapping scheme and heatmaps to encode
coordinate locations. Additionally, we experiment with several state-of-the-art
network architectures to examine the tradeoff between accuracy and memory usage
for resource-constrained environments. Finally, we propose a confidence metric
using the values in the last fully connected layer of the network. We analyze
example images that fall outside of our proposed classes to show our confidence
metric can prevent many misclassifications. Our algorithm achieves 96% accuracy
on a test set drawn from a separate clinical site, indicating that the proposed
method is suitable for clinical adoption and enabling a fully automatic
pipeline from acquisition to Doppler spectrum measurements.",1911.02407v2
2020-01-02,"The Effect of Treatment-Related Deaths and ""Sticky"" Diagnoses on Recorded Prostate Cancer Mortality","Background: Although recorded cancer mortality should include both deaths
from cancer and deaths from cancer treatment, there is evidence suggesting that
the measure may be incomplete. To investigate the completeness of recorded
prostate cancer mortality, we compared other-cause (non-prostate cancer)
mortality in men found and not found to have prostate cancer following a needle
biopsy.
  Methods: We linked Medicare claims data to SEER data to analyze survival in
the population of men aged 65+ enrolled in Medicare who resided in a SEER area
and received a needle biopsy in 1993-2001. We compared other-cause mortality in
men found to have prostate cancer (n=53,462) to that in men not found to have
prostate cancer (n=103,659).
  Results: The age-race adjusted other-cause mortality rate was 471 per 10,000
person-years in men found to have prostate cancer vs. 468 per 10,000 in men not
found to have prostate cancer (RR = 1.01;95% CI:0.98-1.03). The effect was
modified, however, by age. The RR declined in a stepwise fashion from 1.08 (95%
CI:1.03-1.14) in men age 65-69 to 0.89 (95% CI:0.83-0.95) in men age 85 and
older. If the excess (or deficit) in other-cause mortality were added to the
recorded prostate cancer mortality, prostate cancer mortality would rise 23% in
the youngest age group (from 90 to 111 per 10,000) and would fall 30% in the
oldest age group (from 551 to 388 per 10,000).
  Conclusion: Although recorded prostate cancer mortality appears to be an
accurate measure overall, it systematically underestimates the mortality
associated with prostate cancer diagnosis and treatment in younger men and
overestimates it in the very old. We surmise that in younger men
treatment-related deaths are incompletely captured in recorded prostate cancer
mortality, while in older men the diagnosis ""sticks""-- once diagnosed, they are
more likely to be said to have died from the disease.",2001.00492v1
2020-06-09,Elemental Abundances in M31: Iron and Alpha Element Abundances in M31's Outer Halo,"We present [Fe/H] and [$\alpha$/Fe] abundances, derived using spectral
synthesis techniques, for stars in M31's outer stellar halo. The 21 [Fe/H]
measurements and 7 [$\alpha$/Fe] measurements are drawn from fields ranging
from 43 to 165 kpc in projected distance from M31. We combine our measurements
with existing literature measurements, and compare the resulting sample of 23
stars with [Fe/H] and 9 stars with [$\alpha$/Fe] measurements in M31's outer
halo with [$\alpha$/Fe] and [Fe/H] measurements, also derived from spectral
synthesis, in M31's inner stellar halo ($r < $26 kpc) and dSph galaxies. The
stars in M31's outer halo have [$\alpha$/Fe] patterns that are consistent with
the largest of M31's dSph satellites (And I and And VII). These abundances
provide tentative evidence that the [$\alpha$/Fe] abundances of stars in M31's
outer halo are more similar to the abundances of Milky Way halo stars than to
the abundances of stars in M31's inner halo. We also compare the spectral
synthesis-based [Fe/H] measurements of stars in M31's halo with previous
photometric [Fe/H] estimates, as a function of projected distance from M31. The
spectral synthesis-based [Fe/H] measurements are consistent with a large-scale
metallicity gradient previously observed in M31's stellar halo to projected
distances as large as 100 kpc.",2006.05430v1
2020-11-11,Unique Decoding of Explicit $ε$-balanced Codes Near the Gilbert-Varshamov Bound,"The Gilbert-Varshamov bound (non-constructively) establishes the existence of
binary codes of distance $1/2 -\epsilon$ and rate $\Omega(\epsilon^2)$ (where
an upper bound of $O(\epsilon^2\log(1/\epsilon))$ is known). Ta-Shma [STOC
2017] gave an explicit construction of $\epsilon$-balanced binary codes, where
any two distinct codewords are at a distance between $1/2 -\epsilon/2$ and
$1/2+\epsilon/2$, achieving a near optimal rate of
$\Omega(\epsilon^{2+\beta})$, where $\beta \to 0$ as $\epsilon \to 0$.
  We develop unique and list decoding algorithms for (essentially) the family
of codes constructed by Ta-Shma. We prove the following results for
$\epsilon$-balanced codes with block length $N$ and rate
$\Omega(\epsilon^{2+\beta})$ in this family:
  - For all $\epsilon, \beta > 0$ there are explicit codes which can be
uniquely decoded up to an error of half the minimum distance in time
$N^{O_{\epsilon, \beta}(1)}$.
  - For any fixed constant $\beta$ independent of $\epsilon$, there is an
explicit construction of codes which can be uniquely decoded up to an error of
half the minimum distance in time $(\log(1/\epsilon))^{O(1)} \cdot
N^{O_\beta(1)}$.
  - For any $\epsilon > 0$, there are explicit $\epsilon$-balanced codes with
rate $\Omega(\epsilon^{2+\beta})$ which can be list decoded up to error $1/2 -
\epsilon'$ in time $N^{O_{\epsilon,\epsilon',\beta}(1)}$, where $\epsilon',
\beta \to 0$ as $\epsilon \to 0$.
  The starting point of our algorithms is the list decoding framework from Alev
et al. [SODA 2020], which uses the Sum-of-Squares SDP hierarchy. The rates
obtained there were quasipolynomial in $\epsilon$. Here, we show how to
overcome the far from optimal rates of this framework obtaining unique decoding
algorithms for explicit binary codes of near optimal rate. These codes are
based on simple modifications of Ta-Shma's construction.",2011.05500v1
2021-03-30,Equivalence between Sobolev spaces of first-order dominating mixed smoothness and unanchored ANOVA spaces on $\mathbb{R}^d$,"We prove that a variant of the classical Sobolev space of first-order
dominating mixed smoothness is equivalent (under a certain condition) to the
unanchored ANOVA space on $\mathbb{R}^d$, for $d \geq 1$. Both spaces are
Hilbert spaces involving weight functions, which determine the behaviour as
different variables tend to $\pm \infty$, and weight parameters, which
represent the influence of different subsets of variables. The unanchored ANOVA
space on $\mathbb{R}^d$ was initially introduced by Nichols & Kuo in 2014 to
analyse the error of quasi-Monte Carlo (QMC) approximations for integrals on
unbounded domains; whereas the classical Sobolev space of dominating mixed
smoothness was used as the setting in a series of papers by Griebel, Kuo &
Sloan on the smoothing effect of integration, in an effort to develop a
rigorous theory on why QMC methods work so well for certain non-smooth
integrands with kinks or jumps coming from option pricing problems. In this
same setting, Griewank, Kuo, Le\""ovey & Sloan in 2018 subsequently extended
these ideas by developing a practical smoothing by preintegration technique to
approximate integrals of such functions with kinks or jumps.
  We first prove the equivalence in one dimension (itself a non-trivial task),
before following a similar, but more complicated, strategy to prove the
equivalence for general dimensions. As a consequence of this equivalence, we
analyse applying QMC combined with a preintegration step to approximate the
fair price of an Asian option, and prove that the error of such an
approximation using $N$ points converges at a rate close to $1/N$.",2103.16075v3
2021-06-13,Advantages of a semi-implicit scheme over a fully implicit scheme for Landau-Lifshitz-Gilbert equation,"Magnetization dynamics in magnetic materials is modeled by the
Landau-Lifshitz-Gilbert (LLG) equation. In the LLG equation, the length of
magnetization is conserved and the system energy is dissipative. Implicit and
semi-implicit schemes have been used in micromagnetics simulations due to their
unconditional numerical stability. In more details, implicit schemes preserve
the properties of the LLG equation, but solve a nonlinear system of equations
per time step. In contrast, semi-implicit schemes only solve a linear system of
equations, while additional operations are needed to preserve the length of
magnetization. It still remains unclear which one shall be used if both
implicit and semi-implicit schemes are available. In this work, using the
implicit Crank-Nicolson (ICN) scheme as a benchmark, we propose to make this
implicit scheme semi-implicit. It can be proved that both schemes are
second-order accurate in space and time. For the unique solvability of
nonlinear systems of equations in the ICN scheme, we require that the temporal
step size scales quadratically with the spatial mesh size. It is numerically
verified that the convergence of the nonlinear solver becomes slower for larger
temporal step size and multiple magnetization profiles are obtained for
different initial guesses. The linear systems of equations in the semi-implicit
CN (SICN) scheme are unconditionally uniquely solvable, and the condition that
the temporal step size scales linearly with the spatial mesh size is needed in
the convergence of the SICN scheme. In terms of numerical efficiency, the SICN
scheme achieves the same accuracy as the ICN scheme with less computational
time. Based on these results, we conclude that a semi-implicit scheme is
superior to its implicit analog both theoretically and numerically, and we
recommend the semi-implicit scheme in micromagnetics simulations if both
methods are available.",2106.06936v1
2021-08-06,A second-order semi-implicit method for the inertial Landau-Lifshitz-Gilbert equation,"Recent theoretical and experimental advances show that the inertia of
magnetization emerges at sub-picoseconds and contributes to the ultrafast
magnetization dynamics which cannot be captured intrinsically by the LLG
equation. Therefore, as a generalization, the inertial Landau-Lifshitz-Gilbert
(iLLG) equation is proposed to model the ultrafast magnetization dynamics.
Mathematically, the LLG equation is a nonlinear system of parabolic type with
(possible) degeneracy. However, the iLLG equation is a nonlinear system of
mixed hyperbolic-parabolic type with degeneracy, and exhibits more complicated
structures. It behaves like a hyperbolic system at the sub-picosecond scale
while behaves like a parabolic system at larger timescales. Such hybrid
behaviors impose additional difficulties on designing numerical methods for the
iLLG equation. In this work, we propose a second-order semi-implicit scheme to
solve the iLLG equation. The second temporal derivative of magnetization is
approximated by the standard centered difference scheme and the first
derivative is approximated by the midpoint scheme involving three time steps.
The nonlinear terms are treated semi-implicitly using one-sided interpolation
with the second-order accuracy. At each step, the unconditionally unique
solvability of the unsymmetric linear system of equations in the proposed
method is proved with a detailed discussion on the condition number.
Numerically, the second-order accuracy in both time and space is verified.
Using the proposed method, the inertial effect of ferromagnetics is observed in
micromagnetics simulations at small timescales, in consistency with the
hyperbolic property of the model at sub-picoseconds. For long time simulations,
the results of the iLLG model are in nice agreements with those of the LLG
model, in consistency with the parabolic feature of the iLLG model at larger
timescales.",2108.03060v1
2021-09-08,"Flares, Rotation, and Planets of the AU Mic System from TESS Observations","AU Mic is a young ($\sim$24 Myr), pre-Main Sequence M~dwarf star that was
observed in the first month of science observations of the Transiting Exoplanet
Survey Satellite (TESS) and re-observed two years later. This target has
photometric variability from a variety of sources that is readily apparent in
the TESS light curves; spots induce modulation in the light curve, flares are
present throughout (manifesting as sharp rises with slow exponential decay
phases), and transits of AU Mic b may be seen by eye as dips in the light
curve. We present a combined analysis of both TESS Sector 1 and Sector 27 AU
Mic light curves including the new 20-second cadence data from TESS Year 3. We
compare flare rates between both observations and analyze the spot evolution,
showing that the activity levels increase slightly from Sector 1 to Sector 27.
Furthermore, the 20-second data collection allows us to detect more flares,
smaller flares, and better resolve flare morphology in white light as compared
to the 2-minute data collection mode. We also refine the parameters for AU Mic
b by fitting three additional transits of AU Mic b from Sector 27 using a model
that includes stellar activity. We show that the transits exhibit clear transit
timing variations (TTVs) with an amplitude of $\sim$80 seconds. We also detect
three transits of a 2.8 $R_\oplus$ planet, AU Mic c, which has a period of
18.86 days.",2109.03924v1
2021-10-29,The TREX Survey: Kinematical Complexity Throughout M33's Stellar Disk and Evidence for a Stellar Halo,"We present initial results from a large spectroscopic survey of stars
throughout M33's stellar disk. We analyze a sample of 1667 red giant branch
(RGB) stars extending to projected distances of $\sim 11$ kpc from M33's center
($\sim 18$ kpc, or $\sim 10$ scale lengths, in the plane of the disk). The
line-of-sight velocities of RGB stars show the presence of two kinematical
components. One component is consistent with rotation in the plane of M33's HI
disk and has a velocity dispersion ($\sim 19$ km s$^{-1}$) consistent with that
observed in a comparison sample of younger stars, while the second component
has a significantly higher velocity dispersion. A two-component fit to the RGB
velocity distribution finds that the high dispersion component has a velocity
dispersion of $59.3^{+2.6}_{-2.5}$ km s$^{-1}$ and rotates very slowly in the
plane of the disk (consistent with no rotation at the $<1.5\sigma$ level),
which favors interpreting it as a stellar halo rather than a thick disk
population. A spatial analysis indicates that the fraction of RGB stars in the
high-velocity-dispersion component decreases with increasing radius over the
range covered by the spectroscopic sample. Our spectroscopic sample establishes
that a significant high-velocity-dispersion component is present in M33's RGB
population from near M33's center to at least the radius where M33's HI disk
begins to warp at 30$'$ ($\sim 7.5$ kpc) in the plane of the disk. This is the
first detection and spatial characterization of a kinematically hot stellar
component throughout M33's inner regions.",2110.15773v1
2021-11-23,Magnetism in Metastable and Annealed Compositionally Complex Alloys,"Compositionally complex materials (CCMs) present a potential paradigm shift
in the design of magnetic materials. These alloys exhibit long-range structural
order coupled with limited or no chemical order. As a result, extreme local
environments exist with a large opposing magnetic energy term, which can
manifest large changes in the magnetic behavior. In the current work, the
magnetic properties of (Cr, Mn, Fe, Ni) alloys are presented. These materials
were prepared by room-temperature combinatorial sputtering, resulting in a
range of compositions with a single BCC structural phase and no chemical
ordering. The combinatorial growth technique allows CCMs to be prepared outside
of their thermodynamically stable phase, enabling the exploration of otherwise
inaccessible order. The mixed ferromagnetic and antiferromagnetic interactions
in these alloys causes frustrated magnetic behavior, which results in an
extremely low coercivity (<1 mT), which increases rapidly at 50 K. At low
temperatures, the coercivity achieves values of nearly 500 mT, which is
comparable to some high-anisotropy magnetic materials. Commensurate with the
divergent coercivity is an atypical drop in the temperature dependent
magnetization. These effects are explained by a mixed magnetic phase model,
consisting of ferro-, antiferro , and frustrated magnetic regions, and are
rationalized by simulations. A machine-learning algorithm is employed to
visualize the parameter space and inform the development of subsequent
compositions. Annealing the samples at 600 {\deg}C orders the sample, more-than
doubling the Curie temperature and increasing the saturation magnetization by
as much as 5x. Simultaneously, the large coercivities are suppressed, resulting
in magnetic behavior that is largely temperature independent over a range of
350 K.",2111.12188v1
2021-11-23,Controlling magnetic configuration in soft-hard bilayers probed by polarized neutron reflectometry,"Hard/soft magnetic bilayer thin films have been widely used in data storage
technologies and permanent magnet applications. The magnetic configuration and
response to temperatures and magnetic fields in these heterostructures are
considered to be highly dependent on the interfacial coupling. However, the
intrinsic properties of each of the layers, such as the saturation
magnetization and layer thickness, also strongly influence the magnetic
configuration. Changing these parameters provides an effective method to tailor
magnetic properties in composite magnets. Here, we use polarized neutron
reflectometry (PNR) to experimentally probe the interfacial magnetic
configurations in hard/soft bilayer thin films: L10-FePt/A1-FePt, [Co/Pd]
/CoPd, [Co/Pt] /FeNi and L10-FePt/Fe, which all have a perpendicular magnetic
anisotropy in the hard layer. These films were designed with different soft and
hard layer thicknesses (t_soft and t_hard) and saturation magnetization
(M_s^soft and M_s^hard), respectively. The influences of an in-plane magnetic
field (H_ip) and temperature (T) are also studied using a L10 FePt/A1-FePt
bilayer sample. Comparing the PNR results to micromagnetic simulations reveals
that the interfacial magnetic configuration is highly dependent on t_soft,
M_s^soft and the external factors (H_ip and T), and has a relatively weak
dependence on t_hard and M_s^hard. Key among these results, for thin t_soft,
the hard and soft layers are rigidly coupled in the out-of-plane direction,
then undergo a transition to relax in-plane. This transition can be delayed to
larger t_soft by decreasing M_s^soft. Understanding the influence of these
parameters on the magnetic configuration is critical to designing functional
composite magnets for applications.",2111.12191v1
2022-01-18,On-demand electrical control of spin qubits,"Once called a ""classically non-describable two-valuedness"" by Pauli , the
electron spin is a natural resource for long-lived quantum information since it
is mostly impervious to electric fluctuations and can be replicated in large
arrays using silicon quantum dots, which offer high-fidelity control.
Paradoxically, one of the most convenient control strategies is the integration
of nanoscale magnets to artificially enhance the coupling between spins and
electric field, which in turn hampers the spin's noise immunity and adds
architectural complexity. Here we demonstrate a technique that enables a
\emph{switchable} interaction between spins and orbital motion of electrons in
silicon quantum dots, without the presence of a micromagnet. The naturally weak
effects of the relativistic spin-orbit interaction in silicon are enhanced by
more than three orders of magnitude by controlling the energy quantisation of
electrons in the nanostructure, enhancing the orbital motion. Fast electrical
control is demonstrated in multiple devices and electronic configurations,
highlighting the utility of the technique. Using the electrical drive we
achieve coherence time $T_{2,{\rm Hahn}}\approx50 \mu$s, fast single-qubit
gates with ${T_{\pi/2}=3}$ ns and gate fidelities of 99.93 % probed by
randomised benchmarking. The higher gate speeds and better compatibility with
CMOS manufacturing enabled by on-demand electric control improve the prospects
for realising scalable silicon quantum processors.",2201.06679v2
2022-04-28,Anti-microbial properties of a multi-component alloy,"High traffic touch surfaces such as doorknobs, countertops, and handrails can
be transmission points for the spread of pathogens, emphasizing the need to
develop materials that actively self-sanitize. Metals are frequently used for
these surfaces due to their durability, but many metals also possess
antimicrobial properties which function through a variety of mechanisms. This
work investigates metallic alloys comprised of several bioactive metals with
the target of achieving broad-spectrum, rapid bioactivity through synergistic
activity. An entropy-motivated stabilization paradigm is proposed to prepare
scalable alloys of copper, silver, nickel and cobalt. Using combinatorial
sputtering, thin-film alloys were prepared on 100 mm wafers with 50%
compositional grading of each element across the wafer. The films were then
annealed and investigated for alloy stability. Bioactivity testing was
performed on both the as-grown alloys and the annealed films using four
microorganisms -- Phi6, MS2, Bacillus subtilis and Escherichia coli -- as
surrogates for human viral and bacterial pathogens. Testing showed that after
30 s of contact with some of the test alloys, Phi6, an enveloped,
single-stranded RNA bacteriophage that serves as a SARS-CoV 2 surrogate, was
reduced up to 6.9 orders of magnitude (>99.9999%). Additionally, the
non-enveloped, double-stranded DNA bacteriophage MS2, and the Gram-negative E.
coli and Gram-positive B. subtilis bacterial strains showed a 5.0, 6.4, and 5.7
log reduction in activity after 30, 20 and 10 minutes, respectively.
Bioactivity in the alloy samples showed a strong dependence on the composition,
with the log reduction scaling directly with the Cu content. Concentration of
Cu by phase separation after annealing improved activity in some of the
samples. The results motivate a variety of themes which can be leveraged to
design ideal bioactive surfaces.",2205.00886v1
2022-05-11,Models of Advance Recording Systems: A Multi-timescale Micromagnetic code for granular thin film magnetic recording systems,"Micromagnetic modelling provides the ability to simulate large magnetic
systems accurately without the computational cost limitation imposed by
atomistic modelling. Through micromagnetic modelling it is possible to simulate
systems consisting of thousands of grains over a time range of nanoseconds to
years, depending upon the solver used. Here we present the creation and release
of an open-source multi-timescale micromagnetic code combining three key
solvers: Landau-Lifshitz-Gilbert; Landau-Lifshitz-Bloch; Kinetic Monte Carlo.
This code, called MARS (Models of Advanced Recording Systems), is capable of
accurately simulating the magnetisation dynamics in large and structurally
complex single- and multi-layered granular systems. The short timescale
simulations are achieved for systems far from and close to the Curie point via
the implemented Landau-Lifshitz-Gilbert and Landau-Lifshitz-Bloch solvers
respectively. This enables read/write simulations for general perpendicular
magnetic recording and also state of the art heat assisted magnetic recording
(HAMR). The long timescale behaviour is simulated via the Kinetic Monte Carlo
solver, enabling investigations into signal-to-noise ratio and data longevity.
The combination of these solvers opens up the possibility of multi-timescale
simulations within a single software package. For example the entire HAMR
process from initial data writing and data read back to long term data storage
is possible via a single simulation using MARS. The use of atomistic
parameterisation for the material input of MARS enables highly accurate
material descriptions which provide a bridge between atomistic simulation and
real world experimentation. Thus MARS is capable of performing simulations for
all aspects of recording media research and development. This ranges from
material characterisation and optimisation to system design and implementation.",2205.05263v1
2022-10-11,Finite-time singularity formations for the Landau-Lifshitz-Gilbert equation in dimension two,"We construct finite time blow-up solutions to the Landau-Lifshitz-Gilbert
equation (LLG) from ${\mathbb R}^2$ into $S^2$ \begin{equation*} \begin{cases}
u_t= a(\Delta u+|\nabla u|^2u) -b u\wedge \Delta u &\ \mbox{ in }\ {\mathbb
R}^2\times(0,T), u(\cdot,0) = u_0\in S^2 &\ \mbox{ in }\ {\mathbb R}^2,
\end{cases} \end{equation*} where $a^2+b^2=1,~a > 0,~ b\in {\mathbb R}$. Given
any prescribed $N$ points in $\mathbb{R}^2$ and small $T>0$, we prove that
there exists regular initial data such that the solution blows up precisely at
these points at finite time $t=T$, taking around each point the profile of
sharply scaled degree 1 harmonic map with the type II blow-up speed
\begin{equation*} \| \nabla u\|_{L^\infty } \sim \frac{|\ln(T-t)|^2}{ T-t } \
\mbox{ as } \ t\to T. \end{equation*} The proof is based on the {\em parabolic
inner-outer gluing method}, developed in \cite{17HMF} for Harmonic Map Flow
(HMF). However, a direct consequence of the presence of dispersion is the {\em
lack of maximum principle} for suitable quantities, which makes the analysis
more delicate even at the linearized level. To overcome this difficulty, we
make use of two key technical ingredients: first, for the inner problem we
employ the tool of {\em distorted Fourier transform}, as developed by Krieger,
Miao, Schlag and Tataru \cite{Krieger09Duke,KMS20WM}. Second, the linear theory
for the outer problem is achieved by means of the sub-Gaussian estimate for the
fundamental solution of parabolic system in non-divergence form with
coefficients of Dini mean oscillation in space ($\mathsf{DMO_x}$), which was
proved by Dong, Kim and Lee \cite{dong22-non-divergence} recently.",2210.05800v1
2023-01-03,Measuring Physical and Electrical Parameters in Free-Living Subjects: Motivating an Instrument to Characterize Analytes of Clinical Importance in Blood Samples,"Significance: A path is described to increase the sensitivity and accuracy of
body-worn devices used to monitor patient health. This path supports improved
health management. A wavelength-choice algorithm developed at Mayo demonstrates
that critical biochemical analytes can be assessed using accurate optical
absorption curves over a wide range of wavelengths. Aim: Combine the
requirements for monitoring cardio/electrical, movement, activity, gait,
tremor, and critical biochemical analytes including hemoglobin makeup in the
context of body-worn sensors. Use the data needed to characterize clinically
important analytes in blood samples to drive instrument requirements. Approach:
Using data and knowledge gained over previously separate research threads, some
providing currently usable results from more than eighty years back, determine
analyte characteristics needed to design sensitive and accurate multiuse
measurement and recording units. Results: Strategies for wavelength selection
are detailed. Fine-grained, broad-spectrum measurement of multiple analytes
transmission, absorption, and anisotropic scattering are needed.
Post-Beer-Lambert, using the propagation of error from small variations, and
utility functions that include costs and systemic error sources, improved
measurements can be performed. Conclusions: The Mayo Double-Integrating Sphere
Spectrophotometer (referred hereafter as MDISS), as described in the companion
report arXiv:2212.08763, produces the data necessary for optimal component
choice. These data can provide for robust enhancement of the sensitivity, cost,
and accuracy of body-worn medical sensors. Keywords: Bio-Analyte,
Spectrophotometry, Body-worn monitor, Propagation of error, Double-Integrating
Sphere, Mt. Everest medical measurements, O2SAT
  Please see also arXiv:2212.08763",2301.00938v2
2023-01-09,"A Second Earth-Sized Planet in the Habitable Zone of the M Dwarf, TOI-700","We report the discovery of TOI-700 e, a 0.95 R$_\oplus$ planet residing in
the Optimistic Habitable Zone (HZ) of its host star. This discovery was enabled
by multiple years of monitoring from NASA's Transiting Exoplanet Survey
Satellite (TESS) mission. The host star, TOI-700 (TIC 150428135), is a nearby
(31.1 pc), inactive, M2.5 dwarf ($V_{mag} = 13.15$). TOI-700 is already known
to host three planets, including the small, HZ planet, TOI-700 d. The new
planet has an orbital period of 27.8 days and, based on its radius (0.95
R$_\oplus$), it is likely rocky. TOI-700 was observed for 21 sectors over Years
1 and 3 of the TESS mission, including 10 sectors at 20-second cadence in Year
3. Using this full set of TESS data and additional follow-up observations, we
identify, validate, and characterize TOI-700 e. This discovery adds another
world to the short list of small, HZ planets transiting nearby and bright host
stars. Such systems, where the stars are bright enough that follow-up
observations are possible to constrain planet masses and atmospheres using
current and future facilities, are incredibly valuable. The presence of
multiple small, HZ planets makes this system even more enticing for follow-up
observations.",2301.03617v1
2023-01-17,Introduction to Non-Invasive Current Estimation (NICE),"It is notoriously difficult to measure instantaneous supply current to a
device such as an ASIC, FPGA, or CPU without also affecting the instantaneous
supply voltage and compromising the operation of the device [21]. For decades
designers have relied on rough estimates of dynamic load currents that
stimulate a designed Power Delivery Network (PDN). The consequences of
inaccurate load-current characterization can range from excessive PDN cost and
lengthened development schedules to poor performance or functional failure.
This paper will introduce and describe a method to precisely determine
timedomain current waveforms from a pair of measured timedomain voltage
waveforms. This NonInvasive Current Estimation (NICE) method is based on
established twoport network theory along with component and board modeling
techniques that have been validated through measurements on demonstrative
circuits. This paper will show that the NICE method works for any transient
event that can be captured on a digital oscilloscope. Limitations of the method
and underlying measurements are noted where appropriate. The method is applied
to a simple PDN with an arbitrary load, and the NICE-derived current waveform
is verified against an independent measurement by sense resistor. With careful
component and board modeling, it is possible to calculate current waveforms
with a root mean square error of less than five percent compared to the
reference measurement. Current transients that were previously difficult or
impossible to characterize by any means can now be calculated and displayed
within seconds of an oscilloscope-trigger event by using NICE. ASIC and FPGA
manufacturers can now compute the startup current for their device and publish
the actual waveform, or provide a piecewiselinear SPICE model (PWL source) to
facilitate design and testing of the regulator and PDN required to support
their device.",2301.10237v1
2023-02-08,"Weighted Edit Distance Computation: Strings, Trees and Dyck","Given two strings of length $n$ over alphabet $\Sigma$, and an upper bound
$k$ on their edit distance, the algorithm of Myers (Algorithmica'86) and Landau
and Vishkin (JCSS'88) computes the unweighted string edit distance in
$\mathcal{O}(n+k^2)$ time. Till date, it remains the fastest algorithm for
exact edit distance computation, and it is optimal under the Strong Exponential
Hypothesis (STOC'15). Over the years, this result has inspired many
developments, including fast approximation algorithms for string edit distance
as well as similar $\tilde{\mathcal{O}}(n+$poly$(k))$-time algorithms for
generalizations to tree and Dyck edit distances. Surprisingly, all these
results hold only for unweighted instances.
  While unweighted edit distance is theoretically fundamental, almost all
real-world applications require weighted edit distance, where different weights
are assigned to different edit operations and may vary with the characters
being edited. Given a weight function $w: \Sigma \cup \{\varepsilon \}\times
\Sigma \cup \{\varepsilon \} \rightarrow \mathbb{R}_{\ge 0}$ (such that
$w(a,a)=0$ and $w(a,b)\ge 1$ for all $a,b\in \Sigma \cup \{\varepsilon\}$ with
$a\ne b$), the goal is to find an alignment that minimizes the total weight of
edits. Except for the vanilla $\mathcal{O}(n^2)$-time dynamic-programming
algorithm and its almost trivial $\mathcal{O}(nk)$-time implementation, none of
the aforementioned developments on the unweighted edit distance apply to the
weighted variant. In this paper, we propose the first
$\mathcal{O}(n+$poly$(k))$-time algorithm that computes weighted string edit
distance exactly, thus bridging a fundamental gap between our understanding of
unweighted and weighted edit distance. We then generalize this result to
weighted tree and Dyck edit distances, which lead to a deterministic algorithm
that improves upon the previous work for unweighted tree edit distance.",2302.04229v1
2023-03-07,Multilevel Monte Carlo methods for stochastic convection-diffusion eigenvalue problems,"We develop new multilevel Monte Carlo (MLMC) methods to estimate the
expectation of the smallest eigenvalue of a stochastic convection-diffusion
operator with random coefficients. The MLMC method is based on a sequence of
finite element (FE) discretizations of the eigenvalue problem on a hierarchy of
increasingly finer meshes. For the discretized, algebraic eigenproblems we use
both the Rayleigh quotient (RQ) iteration and implicitly restarted Arnoldi
(IRA), providing an analysis of the cost in each case. By studying the variance
on each level and adapting classical FE error bounds to the stochastic setting,
we are able to bound the total error of our MLMC estimator and provide a
complexity analysis. As expected, the complexity bound for our MLMC estimator
is superior to plain Monte Carlo. To improve the efficiency of the MLMC
further, we exploit the hierarchy of meshes and use coarser approximations as
starting values for the eigensolvers on finer ones. To improve the stability of
the MLMC method for convection-dominated problems, we employ two additional
strategies. First, we consider the streamline upwind Petrov--Galerkin
formulation of the discrete eigenvalue problem, which allows us to start the
MLMC method on coarser meshes than is possible with standard FEs. Second, we
apply a homotopy method to add stability to the eigensolver for each sample.
Finally, we present a multilevel quasi-Monte Carlo method that replaces Monte
Carlo with a quasi-Monte Carlo (QMC) rule on each level. Due to the faster
convergence of QMC, this improves the overall complexity. We provide detailed
numerical results comparing our different strategies to demonstrate the
practical feasibility of the MLMC method in different use cases. The results
support our complexity analysis and further demonstrate the superiority over
plain Monte Carlo in all cases.",2303.03673v2
2023-03-09,Zonostrophic instabilities in magnetohydrodynamic Kolmogorov flow,"This paper concerns the stability of Kolmogorov flow u = (0, sin x) in the
infinite (x,y)-plane. A mean magnetic field of strength B0 is introduced and
the MHD linear stability problem studied for modes with wave-number k in the
y-direction, and Bloch wavenumber l in the x-direction. The parameters
governing the problem are Reynolds number 1/nu, magnetic Prandtl number P, and
dimensionless magnetic field strength B0. The mean magnetic field can be taken
to have an arbitrary direction in the (x,y)-plane and a mean x-directed flow U0
can be incorporated.
  First the paper considers Kolmogorov flow with y-directed mean magnetic
field, referred to as vertical. Taking l=0, the suppression of the pure
hydrodynamic instability is observed with increasing field strength B0. A
branch of strong-field instabilities occurs for magnetic Prandtl number P less
than unity, as found by A.E. Fraser, I.G. Cresser and P. Garaud (J. Fluid Mech.
949, A43, 2022). Analytical results using eigenvalue perturbation theory in the
limit k->0 support the numerics for both weak- and strong-field instabilities,
and originate in the coupling of large-scale modes with x-wavenumber n=0, to
smaller-scale modes.
  The paper considers the case of horizontal or x-directed mean magnetic field.
The unperturbed state consists of steady, wavey magnetic field lines. As the
magnetic field is increased, the purely hydrodynamic instability is suppressed
again, but for stronger fields a new branch of instabilities appears. Allowing
a non-zero Bloch wavenumber l allows further instability, and in some
circumstances when the system is hydrodynamically stable, arbitrarily weak
magnetic fields can give growing modes. Numerical results are presented
together with eigenvalue perturbation theory in the limits k,l->0. The theory
gives analytical approximations for growth rates and thresholds in good
agreement with those computed.",2303.05212v1
2023-03-30,Fate of entanglement in magnetism under Lindbladian or non-Markovian dynamics and conditions for their transition to Landau-Lifshitz-Gilbert classical dynamics,"It is commonly assumed in spintronics and magnonics that localized spins
within antiferromagnets are in the N\'{e}el ground state (GS), as well as that
such state evolves, when pushed out of equilibrium by current or external
fields, according to the Landau-Lifshitz-Gilbert (LLG) equation viewing
localized spins as classical vectors of fixed length. On the other hand, the
true GS of antiferromagnets is highly entangled, as confirmed by very recent
neutron scattering experiments witnessing their entanglement. Although GS of
ferromagnets is always unentangled, their magnonic low-energy excitation are
superpositions of many-body spin states and, therefore, entangled. In this
study, we initialize quantum Heisenberg ferro- or antiferromagnetic chains
hosing localized spins $S=1/2$, $S=1$ or $S=5/2$ into unentangled pure state
and then evolve them by quantum master equations (QMEs) of Lindblad or
non-Markovian type, derived by coupling localized spins to a bosonic bath (such
as due to phonons) or by using additional ``reaction coordinate'' in the latter
case. The time evolution is initiated by applying an external magnetic field,
and entanglement of time-evolving {\em mixed} quantum states is monitored by
computing its logarithmic negativity. We find that non-Markovian dynamics
maintains some degree of entanglement, which shrinks the length of the vector
of spin expectation values, thereby making the LLG equation inapplicable.
Conversely, Lindbladian (i.e., Markovian) dynamics ensures that entanglement
goes to zero, thereby enabling quantum-to-classical (i.e., to LLG) transition
in all cases -- $S=1/2$, $S=1$ and $S=5/2$ ferromagnet or $S=5/2$
antiferromagnet -- {\em except} for $S=1/2$ and $S=1$ antiferromagnet. We also
investigate the stability of entangled antiferromagnetic GS upon suddenly
coupling it to the bosonic bath.",2303.17596v3
2024-02-07,"Item-Level Heterogeneous Treatment Effects of Selective Serotonin Reuptake Inhibitors (SSRIs) on Depression: Implications for Inference, Generalizability, and Identification","In analysis of randomized controlled trials (RCTs) with patient-reported
outcome measures (PROMs), Item Response Theory (IRT) models that allow for
heterogeneity in the treatment effect at the item level merit consideration.
These models for ``item-level heterogeneous treatment effects'' (IL-HTE) can
provide more accurate statistical inference, allow researchers to better
generalize their results, and resolve critical identification problems in the
estimation of interaction effects. In this study, we extend the IL-HTE model to
polytomous data and apply the model to determine how the effect of selective
serotonin reuptake inhibitors (SSRIs) on depression varies across the items on
a depression rating scale. We first conduct a Monte Carlo simulation study to
assess the performance of the polytomous IL-HTE model under a range of
conditions. We then apply the IL-HTE model to item-level data from 28 RCTs
measuring the effect of SSRIs on depression using the 17-item Hamilton
Depression Rating Scale (HDRS-17) and estimate potential heterogeneity by
subscale (HDRS-6). Our results show that the IL-HTE model provides more
accurate statistical inference, allows for generalizability of results to
out-of-sample items, and resolves identification problems in the estimation of
interaction effects. Our empirical application shows that while the average
effect of SSRIs on depression is beneficial (i.e., negative) and statistically
significant, there is substantial IL-HTE, with estimates of the standard
deviation of item-level effects nearly as large as the average effect. We show
that this substantial IL-HTE is driven primarily by systematically larger
effects on the HDRS-6 subscale items. The IL-HTE model has the potential to
provide new insights for the inference, generalizability, and identification of
treatment effects in clinical trials using patient reported outcome measures.",2402.04487v1
1995-02-16,Lyman alpha Emission from High-Redshift Galaxies,"We summarise the results of a deep search for Lyman alpha emission from
star-forming regions associated with damped Lyman alpha absorption systems and
conclude that the Lyman alpha luminosity of high redshift galaxies is generally
less than 10^(42) erg/s . We also present a newly discovered case, in the field
of the QSO Q2059-360, where the emission is unusually strong, possibly because
the damped system is close in redshift to the QSO.",9502076v1
1995-10-12,Limits on diffusive shock acceleration in dense and incompletely ionised media,"The limits imposed on diffusive shock acceleration by upstream ion-neutral
Alfven wave damping, and by ionisation and Coulomb losses of low energy
particles, are calculated. Analytic solutions are given for the steady upstream
wave excitation problem with ion-neutral damping and the resulting escaping
upstream flux calculated. The time dependent problem is discussed and numerical
solutions presented. Finally the significance of these results for possible
observational tests of shock acceleration in supernova remnants is discussed.",9510066v2
1995-11-28,Damping of GRR instability by direct URCA reactions,"The role of direct URCA reactions in damping of the gravitational radiation
driven instability is discussed. The temperature at which bulk viscosity
suppresses completely this instability is calculated.
  The results are obtained analytically using recent calculations performed in
the case of bulk viscosity due to the modified URCA processes (Lindblom 1995;
Yoshida & Eriguchi 1995).
  The bulk viscosity caused by direct URCA reactions is found to reduce
significantly the region of temperatures and rotation frequencies where a
neutron star is subject to GRR instability.",9511136v1
1997-10-31,Abundances in Damped Lyman-alpha Systems and Chemical Evolution of High Redshift Galaxies,"Recent abundance measurements in damped Lyman-alpha galaxies, supplemented
with unpublished Keck observations, are discussed. The metallicity distribution
with cosmic time is examined for clues about the degree of enrichment, the
onset of initial star formation, and the nature of the galxies. The relative
abundances of the elements are compared with the abundnce pattern in Galactic
halo stars and in the Sun, taking into account of the effects of dust
depletion, in order to gain insight into the stellar processes and the time
scales by which the enrichment occurred.",9710370v1
1998-05-08,Exploring the Damped Lyman-alpha Clouds with AXAF,"The High Energy Transmission Grating (HETG) Spectrometer on the Advanced
X-ray Astrophysics Facility (AXAF) (scheduled for launch in August, 1998) will
provide a new tool for the study of absorption in the X-ray spectra of high
redshift quasars due to the material along the line of sight. In this paper we
try to explore the possibility of using AXAF HETG to detect resonance
absorption lines from the Damped Lyman-alpha (DLA) clouds.",9805110v1
1998-05-28,Photon Damping of Waves in Accretion Disks,"MHD turbulence is generally believed to have two important functions in
accretion disks: it transports angular momentum outward, and the energy in its
shortest wavelength modes is dissipated into the heat that the disks radiate.
In this paper we examine a pair of mechanisms which may play an important role
in regulating the amplitude and spectrum of this turbulence: photon diffusion
and viscosity. We demonstrate that in radiation pressure-dominated disks,
photon damping of compressive MHD waves is so rapid that it likely dominates
all other dissipation mechanisms.",9805358v1
1998-06-11,Damping of differential rotation in neutron stars,"We derive the transport relaxation times for quasiparticle-vortex scattering
processes via nuclear force, relevant for the damping of differential rotation
of superfluids in the quantum liquid core of a neutron star. The proton
scattering off the neutron vortices provides the dominant resistive force on
the vortex lattice at all relevant temperatures in the phase where neutrons
only are in the paired state. If protons are superconducting, a small fraction
of hyperons and resonances in the normal state would be the dominant source of
friction on neutron and proton vortex lattices at the core temperatures $T\ge
10^{7}$ K.",9806156v1
1999-03-10,Elemental abundances at early times: the nature of Damped Lyman-alpha systems,"The distribution of element abundances with redshift in Damped Ly-alpha (DLA)
systems can be adequately reproduced by the same model reproducing the halo and
disk components of the Milky Way Galaxy at different galactocentric distances:
DLA systems are well represented by normal spiral galaxies in their early
evolutionary stages.",9903150v1
1999-07-26,"Are Damped Ly-alpha Systems Large, Galactic Disks ?","The hypothesis that the Damped Ly-alpha systems (DLAs) are large, galactic
disks (Milky Way sized) is tested by confronting predictions of models of the
formation and evolution of (large) disk galaxies with observations, in
particular the Zinc abundance distribution with neutral hydrogen column density
found for DLAs. A pronounced mismatch is found strongly hinting that the
majority of DLAs may not be large, galactic disks.",9907349v1
1999-08-26,Oscillator Strengths and Damping Constants for Atomic Lines in the J and H Bands,"We have built a line list in the near-infrared J and H bands (1.00-1.34,
1.49-1.80 um) by gathering a series of laboratory and computed line lists.
Oscillator strengths and damping constants were computed or obtained by fitting
the solar spectrum.
  The line list presented in this paper is, to our knowledge, the most complete
one now available, and supersedes previous lists.",9908296v1
1999-11-25,Probing Solar Convection,"In the solar convection zone acoustic waves are scattered by turbulent sound
speed fluctuations. In this paper the scattering of waves by convective cells
is treated using Rytov's technique. Particular care is taken to include
diffraction effects which are important especially for high-degree modes that
are confined to the surface layers of the Sun. The scattering leads to damping
of the waves and causes a phase shift. Damping manifests itself in the width of
the spectral peak of p-mode eigenfrequencies. The contribution of scattering to
the line widths is estimated and the sensitivity of the results on the assumed
spectrum of the turbulence is studied. Finally the theoretical predictions are
compared with recently measured line widths of high-degree modes.",9911469v1
1999-12-14,The Gas Reservoir for present day Galaxies : Damped Ly-alpha Absorption Systems,"We present results from an ongoing search for galaxy counterparts of a
subgroup of Quasar Absorption Line Systems called Damped Ly-alpha Absorbers
(DLAs). DLAs have several characteristics that make them essential in the
process of understanding how galaxies formed in the early universe and evolved
to the galaxies we see today in the local universe.
  Finally we compare DLAs with recent findings of a population of starforming
galaxies at high redshifts, so called Lyman-break galaxies.",9912268v1
2000-06-22,Nuclear Reaction Rates in a Plasma: The Effect of Highly Damped Modes,"The fluctuation-dissipation theorem is used to evaluate the screening factor
of nuclear reactions due to the electromagnetic fluctuations in a plasma. We
show that the commonly used Saltpeter factor is obtained if only fluctuations
near the plasma eigenfrequency are assumed to be important (\omega \sim
\omega_{pe}\ll T (\hbar=k_{B}=1)). By taking into account all the fluctuations,
the highly damped ones, with \omega >\omega_{pe}, as well as those with
\omega\leq\omega_{pe}, we find that nuclear reaction rates are higher than
those obtained using the Saltpeter factor, for many interesting plasmas.",0006326v1
2000-09-06,The Cosmological Evolution of Quasar Damped Lyman-Alpha Systems,"We present results from an efficient, non-traditional survey to discover
damped Lyman-alpha (DLA) absorption-line systems with neutral hydrogen column
densities N(HI)>2x10^{20} atoms cm^{-2} and redshifts z<1.65. Contrary to
previous studies at higher redshift that showed a decrease in the cosmological
mass density of neutral gas in DLA absorbers, Omega_{DLA}, with time, our
results indicate that Omega_{DLA} is consistent with remaining constant from
redshifts z \approx 4 to z \approx 0.5. There is no evidence that Omega_{DLA}
is approaching the value at z=0. Other interesting results from the survey are
also presented.",0009098v1
2001-01-13,Measuring Feedback in Damped Lyman Alpha Systems,"We measure feedback (heating rates) in damped Lyman alpha systems from the
cooling rate of the neutral gas. Since cooling occurs through [C II] 158 micron
emission, we infer cooling from C II^{*} 1335.7 absorption lines detected with
HIRES on the Keck I telescope. The inferred heating rates are about 30 times
lower than for the Galaxy ISM. At z = 2.8, the implied star formation rate per
unit area is 10^{-2.4+-0.3} solar masses per kpc^{2} per year, and the the star
formation rate per unit comoving volume is 10^{-0.8+-0.2} solar masses per
Mpc^{3} per year. This is the first measurement of star formation rates in
objects likely to be the progenitors of current galaxies.",0101218v1
2001-04-18,The First Detection of Cobalt in a Damped Lyman Alpha System,"We present the first ever detection of Cobalt in a Damped Lyman Alpha system
(DLA) at z = 1.92. In addition to providing important clues to the star
formation history of these high redshift galaxies, we discuss how studying the
Co abundance in DLAs may also help to constrain models of stellar
nucleosynthesis in a regime not probed by Galactic stars.",0104301v1
2001-05-09,Nuclear reaction rates and energy in stellar plasmas : The effect of highly damped modes,"The effects of the highly damped modes in the energy and reaction rates in a
plasma are discussed. These modes, with wavenumbers $k \gg k_{D}$, even being
only weakly excited, with less than $k_{B}T$ per mode, make a significant
contribution to the energy and screening in a plasma. When the de Broglie
wavelength is much less than the distance of closest approach of thermal
electrons, a classical analysis of the plasma can",0105153v1
2001-07-03,The HI Content and Extent of Low Surface Brightness Galaxies - Could LSB Galaxies be Responsible for Damped Ly-alpha Absorption?,"Low surface brightness galaxies, those galaxies with a central surface
brightness at least one magnitude fainter than the night sky, are often not
included in discussions of extragalactic gas at z < 0.1. In this paper we
review many of the properties of low surface brightness galaxies, including
recent studies which indicate low surface brightness systems may contribute far
more to the local HI luminosity function than previously thought. Additionally,
we use the known (HI) gas properties of low surface brightness galaxies to
consider their possible contribution to nearby damped Lyman-alpha absorbers.",0107064v1
2001-09-10,H_2 molecules in damped systems,"Damped Lyman alpha systems seen in the spectra of high-z QSOs arise in
high-density neutral gas in which molecular hydrogen (H_2) should be
conspicuous. Systematic searches to detect the H_2 lines redshifted into the
Lyman alpha forest at <3400\AA are now possible thanks to the unique
capabilities of UVES on the VLT. Here we summarise the present status of our on
going programme to search for H_2 in DLAs, discuss the physical conditions in
the systems where H_2 is detected and the implications of non-detections.",0109155v1
2001-10-23,A scaling law of interstellar depletions as a tool for abundance studies of Damped Ly alpha systems,"An analytical expression is presented that allows dust depletions to be
estimated in different types of interstellar environments, including Damped Ly
alpha systems. The expression is a scaling law of a reference depletion pattern
and takes into account the possibility that the dust chemical composition may
vary as a function of the dust-to-metals ratio and of the intrinsic abundances
of the medium. Preliminary tests and applications of the proposed scaling law
are briefly reported.",0110499v1
2002-09-23,Outflows in Galaxies and Damped Ly-alpha System,"Although quasar absorbers, and in particular Damped Lyman-alpha systems
(DLAs) have proven a valuable tool to study the early Universe, their exact
nature is so far poorly constrained. It has been suggested that outflows in
galaxies might account for at least part of the DLA population. Observational
evidences and models in support of this hypothesis are reviewed, including
recent observations of Lyman Break Galaxies (LBGs). Observational
counter-arguments and theoretical limitations are also given. Finally,
implications of such a model for the environment of galaxies at high-redshifts
are discussed.",0209463v1
2004-03-15,The Damping Wing of the Gunn-Peterson Absorption and Lyman-Alpha Emitters in the Pre-Reionization Era,"We use a numerical simulation of cosmological reionization to estimate the
likelihood of detecting Lyman-alpha emitting galaxies during the
pre-reionization era. We show that it is possible to find galaxies even at z~9
that are barely affected by the dumping wing of the Gunn-Peterson absorption
from the neutral IGM outside of their HII regions. The damping wing becomes
rapidly more significant at z>9, but even at z>10 is it not inconceivable
(although quite hard) to see a Lyman-alpha emission line from a star-forming
galaxy.",0403345v1
2005-05-28,Cosmic ray transport in MHD turbulence,"Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call
for revisions in the picture of cosmic ray transport. In this paper we use
recently obtained scaling laws for MHD modes to obtain the scattering frequency
for cosmic rays. We account for the turbulence cutoff arising from both
collisional and collisionless damping. We obtain the scattering rate and show
that fast modes provide the dominant contribution to cosmic ray scattering for
the typical interstellar conditions in spite of the fact that fast modes are
subjected to damping. We determine how the efficiency of the scattering depends
on the characteristics of ionized media, e.g. plasma $\beta$. We show that
streaming instability is suppressed by the ambient MHD turbulence.",0505575v1
2005-06-09,Phantom damping of matter perturbations,"Cosmological scaling solutions are particularly important in solving the
coincidence problem of dark energy. We derive the equations of sub-Hubble
linear matter perturbations for a general scalar-field Lagrangian--including
quintessence, tachyon, dilatonic ghost condensate and k-essence--and solve them
analytically for scaling solutions. We find that matter perturbations are
always damped if a phantom field is coupled to dark matter and identify the
cases in which the gravitational potential is constant. This provides an
interesting possibility to place stringent observational constraints on scaling
dark energy models.",0506222v1
2005-06-22,A Damped Ly-alpha Absorption-line System in an Apparent Void at Redshift 2.38,"We study the contents of an apparent void in the distribution of Ly-alpha
emitting galaxies at redshift 2.38. We show that this void is not empty, but
contains a damped Ly-alpha absorption-line system, seen in absorption against
background QSO 2138-4427. Imaging does not reveal any galaxy associated with
this absorption-line system, but it contains metals (Fe/H ~ -1.3), and its
large velocity range (~ 180 km/s) implies a significant mass.",0506525v1
2005-08-08,Fluorescence in damp air and comments on the radiative life time,"Photon yields in damp air excited by an electron using a Sr90 $\beta$ source
are compared withthose in dry air. Water vapors considerably reduce the yields,
however, a further study is needed to evaluate the effects on the energy
estimation of ultrahigh-energy cosmic rays. The relation of fluorescence
efficiency to the life time of de-excitation by radiation is discussed.",0508183v1
2006-08-17,Electron thermal conductivity owing to collisions between degenerate electrons,"We calculate the thermal conductivity of electrons produced by
electron-electron Coulomb scattering in a strongly degenerate electron gas
taking into account the Landau damping of transverse plasmons. The Landau
damping strongly reduces this conductivity in the domain of ultrarelativistic
electrons at temperatures below the electron plasma temperature. In the inner
crust of a neutron star at temperatures T < 1e7 K this thermal conductivity
completely dominates over the electron conductivity due to electron-ion
(electron-phonon) scattering and becomes competitive with the the electron
conductivity due to scattering of electrons by impurity ions.",0608371v1
2006-09-19,"Dust, Metals and Diffuse Interstellar Bands in Damped Lyman Alpha Systems","Although damped Lyman alpha (DLA) systems are usually considered metal-poor,
it has been suggested that this could be due to observational bias against
metal-enriched absorbers. I review recent surveys to quantify the particular
issue of dust obscuration bias and demonstrate that there is currently no
compelling observational evidence to support a widespread effect due to
extinction. On the other hand, a small sub-set of DLAs may be metal-rich and I
review some recent observations of these metal-rich absorbers and the detection
of diffuse interstellar bands in one DLA at z ~ 0.5.",0609530v1
2006-11-08,Comments on Viscous Damping of Non-Adiabatic MHD Waves in an Unbounded Solar Coronal Plasma by Kumar and Kumar,"Considering thermal conduction, compressive viscosity and optically thin
radiation as damping mechanisms for MHD waves, we derive a six-order general
dispersion relation. We point out a fundamental flaw in the derivation of
five-order dispersion relation by Kumar and Kumar (2006) who adopt as a basis
vector. The correct definition of the motion in the x-z plane (2-D vector
space) stems from the two independent variables, namely .",0611252v2
2007-01-10,Non-gaussianity in fluctuations from warm inflation,"The scalar mode density perturbations in a the warm inflationary scenario are
analysed with a view to predicting the amount of non-gaussianity produced by
this scenario. The analysis assumes that the inflaton evolution is strongly
damped by the radiation, with damping terms that are temperature independent.
Entropy fluctuations during warm inflation play a crucial role in generating
non-gaussianity and result in a distinctive signal which should be observable
by the Planck satellite.",0701302v2
1998-05-22,WKB for a damped spin,"The master equation for a damped spin well known from the theory of
superradiance, is written as a finite-difference equation and solved by a
WKB-like method. The propagator thus obtained looks like the van Vleck
propagator of a certain classical Hamiltonian system with one degree of
freedom. A new interpretation is provided of the temporal broadening of
initially sharp probability distributions as the analogue of the spreading of
the quantum mechanical wave packet.",9805018v1
1998-11-04,Cascades of energy and helicity in the GOY shell model of turbulence,"The effect of extreme hyperviscous damping, $\nu k_n^p, p=\infty$ is studied
numerically in the GOY shell model of turbulence. It has resently been
demonstrated [Leveque and She, Phys. Rev. Lett, 75,2690 (1995)] that the
inertial range scaling in the GOY model is non-universal and depending on the
viscous damping. The present study shows that the deviation from Kolmogorov
scaling is due to the cascade of the second inviscid invariant. This invariant
is non-positive definite and in this sense analogous to the helicity of 3D
turbulent flow.",9811009v1
1994-02-04,Effects of Disorder in a Dilute Bose Gas,"We discuss the effects of a weak random external potential on the properties
of the dilute Bose gas at zero temperature. The results recently obtained by
Huang and Meng for the depletion of the condensate and of the superfluid
density are recovered. Results for the shift of the velocity of sound as well
as for its damping due to collisions with the external field are presented. The
damping of phonons is calculated also for dense superfluids. (submitted to
Phys.Rev.B)",9402015v1
1995-02-10,The influence of structure disorder on mean atomic momentum fluctuations and a spin-wave spectrum,"The relation between atomic momenta fluctuations and density fluctuations is
obtained in frames of mean-field approximation. Using two-time temperature
Green functions within Tyablikov approximation the equations for spin
excitation energy and damping are obtained. The asymptotics of energy and
damping in the long-wave limit are investigated and the anomalous behaviour of
spin-wave stiffness constant is discussed.",9502042v1
1997-02-13,"Comment on ""Collective Excitations of a Bose-Einstein Condensate in a Magnetic Trap""","We calculate the damping rate of collective excitations for a nearly pure
Bose-Einstein condensate regarding the recent experiments in MIT [M.-O. Mews et
al, Phys. Rev. Lett. 77, 988 (1996)]. The decay time of collective excitations
obtained in our theoretical calculations agrees well with their experimental
result. We argue that the damping of collective excitations is due to thermal
contributions rather than interactions between collective modes.",9702122v1
1997-08-14,Landau damping in dilute Bose gases,"Landau damping in weakly interacting Bose gases is investigated by means of
perturbation theory. Our approach points out the crucial role played by
Bose-Einstein condensation and yields an explicit expression for the decay rate
of elementary excitations in both uniform and non uniform gases. Systematic
results are derived for the phonon width in homogeneous gases interacting with
repulsive forces. Special attention is given to the low and high temperature
regimes.",9708104v1
1997-11-07,Coulomb suppression of NMR coherence peak in fullerene superconductors,"The suppressed NMR coherence peak in the fullerene superconductors is
explained in terms of the dampings in the superconducting state induced by the
Coulomb interaction between conduction electrons. The Coulomb interaction,
modelled in terms of the onsite Hubbard repulsion, is incorporated into the
Eliashberg theory of superconductivity with its frequency dependence considered
self-consistently at all temperatures. The vertex correction is also included
via the method of Nambu. The frequency dependent Coulomb interaction induces
the substantial dampings in the superconducting state and, consequently,
suppresses the anticipated NMR coherence peak of fullerene superconductors as
found experimentally.",9711060v2
1997-12-09,The Sound of Sonoluminescence,"We consider an air bubble in water under conditions of single bubble
sonoluminescence (SBSL) and evaluate the emitted sound field nonperturbatively
for subsonic gas-liquid interface motion. Sound emission being the dominant
damping mechanism, we also implement the nonperturbative sound damping in the
Rayleigh-Plesset equation for the interface motion. We evaluate numerically the
sound pulse emitted during bubble collapse and compare the nonperturbative and
perturbative results, showing that the usual perturbative description leads to
an overestimate of the maximal surface velocity and maximal sound pressure. The
radius vs. time relation for a full SBSL cycle remains deceptively unaffected.",9712097v1
1998-07-02,Linear systems with adiabatic fluctuations,"We consider a dynamical system subjected to weak but adiabatically slow
fluctuations of external origin. Based on the ``adiabatic following''
approximation we carry out an expansion in \alpha/|\mu|, where \alpha is the
strength of fluctuations and 1/|\mu| refers to the time scale of evolution of
the unperturbed system to obtain a linear differential equation for the average
solution. The theory is applied to the problems of a damped harmonic oscillator
and diffusion in a turbulent fluid. The result is the realization of
`renormalized' diffusion constant or damping constant for the respective
problems. The applicability of the method has been critically analyzed.",9807031v1
1998-12-02,Vortex lattice melting and the damping of the dHvA oscillations in the mixed state,"Phase fluctuations in the superconducting order parameter, which are
responsible for the melting of the Abrikosov vortex lattice below the mean
field $H_{c2}$, are shown to dramatically enhance the scattering of
quasi-particles by the fluctuating pair potential, thus leading to enhanced
damping of the dHvA oscillations in the liquid mixed state. This effect is
shown to quantitatively account for the detailed field dependence of the dHvA
amplitude observed recently in the mixed state of a Quasi 2D organic SC.",9812040v1
1999-01-19,Damping of Growth Oscillations,"Computer simulations and scaling theory are used to investigate the damping
of oscillations during epitaxial growth on high-symmetry surfaces. The
crossover from smooth to rough growth takes place after the deposition of
(D/F)^\delta monolayers, where D and F are the surface diffusion constant and
the deposition rate, respectively, and the exponent \delta=2/3 on a
two-dimensional surface. At the transition, layer-by-layer growth becomes
desynchronized on distances larger than a layer coherence length proportional
l^2, where l is a typical distance between two-dimensional islands in the
submonolayer region of growth.",9901178v1
1999-06-15,Temperature-induced resonances and Landau damping of collective modes in Bose-Einstein condensed gases in spherical traps,"Interaction between collective monopole oscillations of a trapped
Bose-Einstein condensate and thermal excitations is investigated by means of
perturbation theory. We assume spherical symmetry to calculate the matrix
elements by solving the linearized Gross-Pitaevskii equations. We use them to
study the resonances of the condensate induced by temperature when an external
perturbation of the trapping frequency is applied and to calculate the Landau
damping of the oscillations.",9906214v1
1999-08-03,Kinetic Theory of Collective Modes in Atomic Clouds above the Bose-Einstein Transition Temperature,"We calculate frequencies and damping rates of the lowest collective modes of
a dilute Bose gas confined in an anisotropic trapping potential above the
Bose-Einstein transition temperature. From the Boltzmann equation with a
simplified collision integral we derive a general dispersion relation that
interpolates between the collisionless and hydrodynamic regimes. In the case of
axially symmetric traps we obtain explicit expressions for the frequencies and
damping rates of the lowest modes in terms of a phenomenological collision
time. Our results are compared with microscopic calculations and experiments.",9908043v1
1999-09-01,Normal Fermi Liquid Behavior of Quasiholes in the Spin-Polaron Model for Copper Oxides,"Based on the t-J model and the self-consistent Born approximation, the
damping of quasiparticle hole states near the Fermi surface is calculated in a
low doping regime. Renormalization of spin-wave excitations due to hole doping
is taken into account. The damping is shown to be described by a familiar form
$\text{Im}\Sigma({\bf k}^{\prime},\epsilon)\propto (\epsilon^{2}/
\epsilon_{F})\ln(\epsilon/ \epsilon_{F})$ characteristic of the 2-dimensional
Fermi liquid, in contrast with the earlier statement reported by Li and Gong
[Phys. Rev. B {\bf 51}, 6343 (1995)] on the marginal Fermi liquid behavior of
quasiholes.",9909020v1
1999-12-01,Impurity relaxation mechanism for dynamic magnetization reversal in a single domain grain,"The interaction of coherent magnetization rotation with a system of two-level
impurities is studied. Two different, but not contradictory mechanisms, the
`slow-relaxing ion' and the `fast-relaxing ion' are utilized to derive a system
of integro-differential equations for the magnetization. In the case that the
impurity relaxation rate is much greater than the magnetization precession
frequency, these equations can be written in the form of the Landau-Lifshitz
equation with damping. Thus the damping parameter can be directly calculated
from these microscopic impurity relaxation processes.",9912014v1
2000-02-16,Dissipative dynamics of Bose condensates in optical cavities,"We study the zero temperature dynamics of Bose-Einstein condensates in driven
high-quality optical cavities in the limit of large atom-field detuning. We
calculate the stationary ground state and the spectrum of coupled atom and
field mode excitations for standing wave cavities as well as for travelling
wave cavities. Finite cavity response times lead to damping or controlled
amplification of these excitations. Analytic solutions in the Lamb-Dicke
expansion are in good agreement with numerical results for the full problem and
show that oscillation frequencies and the corresponding damping rates are
qualitatively different for the two cases.",0002247v1
2000-03-27,Effect of memory and dynamical chaos in long Josephson junctions,"A long Josephson junction in a constant external magnetic field and in the
presence of a dc bias current is investigated. It is shown that the system,
simulated by the sine-Gorgon equation, ""remembers"" a rapidly damping initial
perturbation and final asymptotic states are determined exactly with this
perturbation. Numerical solving of the boundary sine-Gordon problem and
calculations of Lyapunov indices show that this system has a memory even when
it is in a state of dynamical chaos, i.e., dynamical chaos does not destroy
initial information having a character of rapidly damping perturbation.",0003421v1
2000-09-13,Oscillations of the superconducting order parameter in a ferromagnet,"Planar tunneling spectroscopy reveals damped oscillations of the
superconducting order parameter induced into a ferromagnetic thin film by the
proximity effect. The oscillations are due to the finite momentum transfer
provided to Cooper pairs by the splitting of the spin up and down bands in the
ferromagnet. As a consequence, for negative values of the superconducting order
parameter the tunneling spectra are capsized (""$\pi$-state""). The oscillations'
damping and period are set by the same length scale, which depends on the spin
polarization.",0009192v1
2000-09-29,Damping and revivals of collective oscillations in a finite-temperature model of trapped Bose-Einstein condensation,"We utilize a two-gas model to simulate collective oscillations of a
Bose-Einstein condensate at finite temperatures. The condensate is described
using a generalized Gross-Pitaevskii equation, which is coupled to a thermal
cloud modelled by a Monte Carlo algorithm. This allows us to include the
collective dynamics of both the condensed and non-condensed components
self-consistently. We simulate quadrupolar excitations, and measure the damping
rate and frequency as a function of temperature. We also observe revivals in
condensate oscillations at high temperatures, and in the thermal cloud at low
temperature. Extensions of the model to include non-equilibrium effects and
describe more complex phenomena are discussed.",0009468v1
2001-04-18,Effective rate equations for the over-damped motion in fluctuating potentials,"We discuss physical and mathematical aspects of the over-damped motion of a
Brownian particle in fluctuating potentials. It is shown that such a system can
be described quantitatively by fluctuating rates if the potential fluctuations
are slow compared to relaxation within the minima of the potential, and if the
position of the minima does not fluctuate. Effective rates can be calculated;
they describe the long-time dynamics of the system. Furthermore, we show the
existence of a stationary solution of the Fokker-Planck equation that describes
the motion within the fluctuating potential under some general conditions. We
also show that a stationary solution of the rate equations with fluctuating
rates exists.",0104330v1
2001-09-05,Spin Excitations in a Fermi Gas of Atoms,"We have experimentally investigated a spin excitation in a quantum degenerate
Fermi gas of atoms. In the hydrodynamic regime the damping time of the
collective excitation is used to probe the quantum behavior of the gas. At
temperatures below the Fermi temperature we measure up to a factor of 2
reduction in the excitation damping time. In addition we observe a strong
excitation energy dependence for this quantum statistical effect.",0109098v2
2001-10-09,Freezing of a Stripe Liquid,"The existence of a stripe-liquid phase in a layered nickelate,
La(1.725)Sr(0.275)NiO(4), is demonstrated through neutron scattering
measurements. We show that incommensurate magnetic fluctuations evolve
continuously through the charge-ordering temperature, although an abrupt
decrease in the effective damping energy is observed on cooling through the
transition. The energy and momentum dependence of the magnetic scattering are
parametrized with a damped-harmonic-oscillator model describing overdamped
spin-waves in the antiferromagnetic domains defined instantaneously by charge
stripes.",0110191v2
2001-12-13,Magnon softening and damping in the ferromagnetic manganites due to orbital correlations,"We present a theory for spin excitations in ferromagnetic metallic manganites
and demonstrate that orbital fluctuations have strong effects on the magnon
dynamics in the case these compounds are close to a transition to an orbital
ordered state. In particular we show that the scattering of the spin
excitations by low-lying orbital modes with cubic symmetry causes both the
magnon softening and damping observed experimentally.",0112252v2
2002-01-16,Quantum Spin dynamics of the Bilayer Ferromagnet La(1.2)Sr(1.8)Mn2O7,"We construct a theory of spin wave excitations in the bilayer manganite
La(1.2)Sr(1.8)Mn2O7 based on the simplest possible double-exchange model, but
including leading quantum corrections to the spin wave dispersion and damping.
Comparison is made with recent inelastic neutron scattering experiments. We
find that quantum effects account for some part of the measured damping of spin
waves, but cannot by themselves explain the observed softening of spin waves at
the zone boundary. Furthermore a doping dependence of the total spin wave
dispersion and the optical spin wave gap is predicted.",0201269v1
2002-02-21,Dynamics of a Bose-Einstein condensate at finite temperature in an atomoptical coherence filter,"The macroscopic coherent tunneling through the barriers of a periodic
potential is used as an atomoptical filter to separate the condensate and the
thermal components of a $^{87}$Rb mixed cloud. We condense in the combined
potential of a laser standing-wave superimposed on the axis of a cigar-shape
magnetic trap and induce condensate dipole oscillation in the presence of a
static thermal component. The oscillation is damped due to interaction with the
thermal fraction and we investigate the role played by the periodic potential
in the damping process.",0202369v1
2002-03-11,A Damping of the de Haas-van Alphen Oscillations in the superconducting state,"Deploying a recently developed semiclassical theory of quasiparticles in the
superconducting state we study the de Haas-van Alphen effect. We find that the
oscillations have the same frequency as in the normal state but their amplitude
is reduced. We find an analytic formulae for this damping which is due to
tunnelling between semiclassical quasiparticle orbits comprising both
particle-like and hole-like segments. The quantitative predictions of the
theory are consistent with the available data.",0203224v1
2002-03-26,Measurement induced quantum-classical transition,"A model of an electrical point contact coupled to a mechanical system
(oscillator) is studied to simulate the dephasing effect of measurement on a
quantum system. The problem is solved at zero temperature under conditions of
strong non-equilibrium in the measurement apparatus. For linear coupling
between the oscillator and tunneling electrons, it is found that the oscillator
dynamics becomes damped, with the effective temperature determined by the
voltage drop across the junction. It is demonstrated that both the quantum
heating and the quantum damping of the oscillator manifest themselves in the
current-voltage characteristic of the point contact.",0203521v3
2002-07-04,Fluctuations and correlations in hexagonal optical patterns,"We analyze the influence of noise in transverse hexagonal patterns in
nonlinear Kerr cavities. The near field fluctuations are determined by the
neutrally stable Goldstone modes associated to translational invariance and by
the weakly damped soft modes. However these modes do not contribute to the far
field intensity fluctuations which are dominated by damped perturbations with
the same wave vectors than the pattern. We find strong correlations between the
intensity fluctuations of any arbitrary pair of wave vectors of the pattern.
Correlation between pairs forming 120 degrees is larger than between pairs
forming 180 degrees, contrary to what a naive interpretation of emission in
terms of twin photons would suggest.",0207127v2
2002-09-19,Damping of long-wavelength collective excitations in quasi-onedimensional Fermi liquids,"The imaginary part of the exchange-correlation kernel in the longitudinal
current-current response function of a quasi-onedimensional Fermi liquid is
evaluated by an approximate decoupling in the equation of motion for the
current density, which accounts for processes of excitation of two
particle-hole pairs. The two-pair spectrum determines the intrinsic damping
rate of long-wavelength collective density fluctuations, which is calculated
and contrasted with a result previously obtained for a clean Luttinger liquid.",0209455v1
2002-11-05,Magnetic fluctuations and resonant peak in cuprates: a microscopic theory,"The theory for the dynamical spin susceptibility within the t-J model is
developed, as relevant for the resonant magnetic peak and normal-state magnetic
response in superconducting (SC) cuprates. The analysis is based on the
equations of motion for spins and the memory-function presentation of magnetic
response where the main damping of the low-energy spin collective mode comes
from the decay into fermionic degrees of freedom. It is shown that the damping
function at low doping is closely related to the c-axis optical conductivity.
The analysis reproduces doping-dependent features of the resonant magnetic
scattering.",0211090v1
2002-11-20,Damping of Nodal Fermions Caused by a Dissipative Mode,"Using a $d_{x^2 - y^2}$ superconductor in 2+1 dimensions we show that the
Nambu Goldstone fluctuations are replaced by dissipative excitations. We find
that the nodal quasi-particles damping is caused by the strong dissipative
excitations near the nodal points. As a result we find that the scattering
rates are linear in frequency and not cubic as predicted in the literature for
the ``d'' wave superconductors. Our results explain the recent angle resolved
photoemission spectroscopy and optical conductivity in the BSCCO high $T_c$
compounds.",0211440v1
2003-05-27,Dynamics of a classical gas including dissipative and mean field effects,"By means of a scaling ansatz, we investigate an approximated solution of the
Boltzmann-Vlasov equation for a classical gas. Within this framework, we derive
the frequencies and the damping of the collective oscillations of a
harmonically trapped gas and we investigate its expansion after release of the
trap. The method is well suited to studying the collisional effects taking
place in the system and in particular to discussing the crossover between the
hydrodynamic and the collisionless regimes. An explicit link between the
relaxation times relevant for the damping of the collective oscillations and
for the expansion is established.",0305624v1
2003-07-21,Chaotic scattering of a quantum particle weakly coupled to a very complicated background,"Effect of a complicated many-body environment is analyzed on the chaotic
motion of a quantum particle in a mesoscopic ballistic structure. The dephasing
and absorption phenomena are treated on the same footing in the framework of a
model which is free of the ambiguities inherent to earlier models. The
single-particle doorway resonance states excited via an external channel are
damped not only because of the escape onto such channels but also due to
ulterior population of long-lived background states, the resulting internal
damping being uniquely characterized by the spreading width. On the other hand,
the formation of the fine-structure resonances strongly enhances the delay time
fluctuations thus broadening the delay time distribution.",0307496v1
2003-09-24,Landau Damping in a 2D Electron Gas with Imposed Quantum Grid,"Dielectric properties of semiconductor substrate with imposed two dimensional
(2D) periodic grid of quantum wires or nanotubes (quantum crossbars, QCB) are
studied. It is shown that a capacitive contact between QCB and semiconductor
substrate does not destroy the Luttinger liquid character of the long wave QCB
excitations. However, the dielectric losses of a substrate surface are
drastically modified due to diffraction processes on the QCB superlattice.
QCB-substrate interaction results in additional Landau damping regions of the
substrate plasmons. Their existence, form and the density of losses are
strongly sensitive to the QCB lattice constant.",0309546v2
2003-11-21,Self-stabilised fractality of sea-coasts through damped erosion,"Erosion of rocky coasts spontaneously creates irregular seashores. But the
geometrical irregularity, in turn, damps the sea-waves, decreasing the average
wave amplitude. There may then exist a mutual self-stabilisation of the waves
amplitude together with the irregular morphology of the coast. A simple model
of such stabilisation is studied. It leads, through a complex dynamics of the
earth-sea interface, to the appearance of a stationary fractal seacoast with
dimension close to 4/3. Fractal geometry plays here the role of a morphological
attractor directly related to percolation geometry.",0311509v1
2003-12-10,Exciton-LO-phonon dynamics in InAs/GaAs quantum dots: Effects of zone-edge phonon damping,"The dynamics of an exciton-LO-phonon system after an ultrafast optical
excitation in an InAs/GaAs quantum dot is studied theoretically. Influence of
anharmonic phonon damping and its interplay with the phonon dispersion is
analyzed. The signatures of the zone-edge decay process in the absorption
spectrum and time evolution are highlighted, providing a possible way of
experimental investigation on phonon anharmonicity effects.",0312256v2
2004-01-13,Vortex waves and the onset of turbulence in $^3$He-B,"In a recent experiment Finne et al. discovered an intrinsic condition for the
onset of quantum turbulence in $^3$He-B, that q=alpha/(1-alpha')<1, where alpha
and alpha' are mutual friction parameters. The authors argued that this
condition corresponds to Kelvin waves which are marginally damped, so for q>1
Kelvin waves cannot grow in amplitude and trigger vortex reconnections and
turbulence. By analysing both axisymmetric and non-axisymmetric modes of
oscillations of a rotating superfluid, we confirm that in the long axial
wavelength limit the simple condition q=1 is indeed the crossover between
damped and propagating Kelvin waves.",0401212v1
2004-01-28,Long lived acoustic vibrational modes of an embedded nanoparticle,"Classical continuum elastic calculations show that the acoustic vibrational
modes of an embedded nanoparticle can be lightly damped even when the
longitudinal plane wave acoustic impedances $Z_o=\rho v_L$ of the nanoparticle
and the matrix are the same. It is not necessary for the matrix to be less
dense or softer than the nanoparticle in order to have long lived vibrational
modes. Continuum boundary conditions do not always accurately reflect the
microscropic nature of the interface between nanoparticle and matrix, and a
multi-layer model of the interface reveals the possibility of additional
reduction of mode damping.",0401579v2
2004-07-20,Dynamics of a trapped ultracold two-dimensional atomic gas,"This article is devoted to the study of two-dimensional Bose gases
harmonically confined. We first summarize their equilibrium properties. For
such a gas above the critical temperature, we also derive the frequencies and
the damping of the collective oscillations and we investigate its expansion
after releasing of the trap. The method is well suited to study the collisional
effects taking place in the system and in particular to discuss the crossover
between the hydrodynamic and the collisionless regimes. We establish the link
between the relaxation times relevant for the damping of the collective
oscillations and for the time-of-flight expansion. We also evaluate the
collision rate and its relationship with the relaxation time.",0407522v1
2004-12-06,Thermal wave packets induced by attosecond laser pulses,"In this paper the dynamics of the interaction of attosecond laser pulses with
matter is investigated. It will be shown that the master equation: modified
Klein-Gordon equation describes the propagation of the heatons. Heatons are the
thermal wave packets. When the duration of the laser pulsees \delta t is of the
order of attosecond the heaton-thermal wave packets are nondispersive objects.
For \delta t \to \infty, the heatons are damped with damping factor of the
order of relaxation time for thermal processes.
  Key words: Temperature fields; Attosecond laser pulses; Heatons; Modified
Klein-Gordon equation.",0412126v1
2005-04-12,Nonlinear response and discrete breather excitation in driven micro-mechanical cantilever arrays,"We explain the origin of the generation of discrete breathers (DBs) in
experiments on damped and driven micromechanical cantilever arrays (M.Sato et
al. Phys. Rev. Lett. {\bf 90}, 044102, 2003). Using the concept of the
nonlinear response manifold (NLRM) we provide a systematic way to find the
optimal parameter regime in damped and driven lattices where DBs exist. Our
results show that DBs appear via a new instability of the NLRM different from
the anticipated modulational instability (MI) known for conservative systems.
We present several ways of exciting DBs, and compare also to experimental
studies of exciting and destroying DBs in antiferromagnetic layered systems.",0504298v1
2005-05-14,Monopole Oscillations and Dampings in Boson and Fermion Mixture in the Time-Dependent Gross-Pitaevskii and Vlasov Equations,"We construct a dynamical model for the time evolution of the boson-fermion
coexistence system. The dynamics of bosons and fermions are formulated with the
time-dependent Gross-Pitaevsky equation and the Vlasov equation. We thus study
the monopole oscillation in the bose-fermi mixture. We find that large damping
exists for fermion oscillations in the mixed system even at zero temperature.",0505357v1
2005-10-13,Superconducting Flywheel Model for Energy Storage Applications,"In order to explore the complexity and diversity of the flywheels' dynamics,
we have developed the real-physics computer model of a universal mechanical
rotor. Due to an arbitrary external force concept, the model can be adjusted to
operate identical to the real experimental prototype. Taking the high-speed
magnetic rotor on superconducting bearings as the prototype, the law for the
energy loss in real high temperature superconducting bearings has been derived.
Varying the laws of damping and elasticity in the system, we have found a way
to effectively damp the parasitic resonances and minimize the loss of energy
storage.",0510346v1
2005-11-05,Ratchet Effect in Magnetization Reversal of Stoner Particles,"A new strategy is proposed aimed at substantially reducing the minimal
magnetization switching field for a Stoner particle. Unlike the normal method
of applying a static magnetic field which must be larger than the magnetic
anisotropy, a much weaker field, proportional to the damping constant in the
weak damping regime, can be used to switch the magnetization from one state to
another if the field is along the motion of the magnetization. The concept is
to constantly supply energy to the particle from the time-dependent magnetic
field to allow the particle to climb over the potential barrier between the
initial and the target states.",0511135v1
2005-12-03,Apparent vibrational side-bands in pi-conjugated systems: the case of distyrylbenzene,"The photoluminescence (PL) spectra of dilute solution and single crystals of
distyrylbenzene show unique temperature dependent vibronic structures. The
characteristic single frequency progression at high temperatures is modulated
by a low frequency progression series at low temperatures. None of the series
side band modes corresponds to any of the distyrylbenzene Raman frequencies. We
explain these PL properties using a time dependent model with temperature
dependent damping, in which the many-mode system is effectively transformed to
two- and then to a single ""apparent"" mode as damping increases.",0512067v1
2006-05-26,Thermo-Plasma Polariton within Scaling Theory of Single-Layer Graphene,"Electrodynamics of single-layer graphene is studied in the scaling regime. At
any finite temperature, there is a weakly damped collective thermo-plasma
polariton mode whose dispersion and wavelength dependent damping is determined
analytically. The electric and magnetic fields associated with this mode decay
exponentially in the direction perpendicular to the graphene layer, but unlike
the surface plasma polariton modes of metals, the decay length and the mode
frequency are strongly temperature dependent. This may lead to new ways of
generation and manipulation of these modes.",0605642v1
2006-12-18,Shear viscosity and damping for a Fermi gas in the unitarity limit,"The shear viscosity of a two-component Fermi gas in the normal phase is
calculated as a function of temperature in the unitarity limit, taking into
account strong-coupling effects that give rise to a pseudogap in the spectral
density for single-particle excitations. The results indicate that recent
measurements of the damping of collective modes in trapped atomic clouds can be
understood in terms of hydrodynamics, with a decay rate given by the viscosity
integrated over an effective volume of the cloud.",0612460v2
2007-02-07,Damping of antiferromagnetic spin waves by valence fluctuations in the double layer perovskite YBaFe2O5,"Inelastic neutron scattering experiments show that spin dynamics in the
charge ordered insulating ground state of the double-layer perovskite YBaFe2O5
is well described in terms of eg superexchange interactions. Above the Verwey
transition at TV = 308 K, t2g double exchange-type conduction within
antiferromagnetic FeO2--BaO--FeO2 double layers proceeds by an electron hopping
process that requires a spin flip of the five-fold coordinated Fe ions, costing
an energy 5<J>S^2 of approximately 0.1 eV. The hopping process disrupts
near-neighbor spin correlations, leading to massive damping of zone-boundary
spin waves.",0702181v1
2007-02-20,Spin Drag and Spin-Charge Separation in Cold Fermi Gases,"Low-energy spin and charge excitations of one-dimensional interacting
fermions are completely decoupled and propagate with different velocities.
These modes however can decay due to several possible mechanisms. In this paper
we expose a new facet of spin-charge separation: not only the speeds but also
the damping rates of spin and charge excitations are different. While the
propagation of long-wavelength charge excitations is essentially ballistic,
spin propagation is intrinsically damped and diffusive. We suggest that cold
Fermi gases trapped inside a tight atomic waveguide offer the opportunity to
measure the spin-drag relaxation rate that controls the broadening of a spin
packet.",0702466v1
1996-07-23,Quasinormal modes of nearly extreme Reissner-Nordstrom black holes,"We present detailed calculations of the quasinormal modes of
Reissner-Nordstrom black holes. While the first few, slowly damped, modes
depend on the charge of the black hole in a relatively simple way, we find that
the rapidly damped modes show several peculiar features. The higher modes
generally spiral into the value for the extreme black hole as the charge
increases. We also discuss the possible existence of a purely imaginary mode
for the Schwarzschild black hole: Our data suggest that there is a quasinormal
mode that limits to $\omega M = -2i$ as $Q\to 0$.",9607054v1
1996-08-22,Gravitational Ionization: A Chaotic Net in the Kepler System,"The long term nonlinear dynamics of a Keplerian binary system under the
combined influences of gravitational radiation damping and external tidal
perturbations is analyzed. Gravitational radiation reaction leads the binary
system towards eventual collapse, while the external periodic perturbations
could lead to the ionization of the system via Arnold diffusion. When these two
opposing tendencies nearly balance each other, interesting chaotic behavior
occurs that is briefly studied in this paper. It is possible to show that
periodic orbits can exist in this system for sufficiently small damping.
Moreover, we employ the method of averaging to investigate the phenomenon of
capture into resonance.",9608054v1
1999-11-11,Inertial Control of the VIRGO Superattenuator,"The VIRGO superattenuator (SA) is effective in depressing the seismic noise
below the thermal noise level above 4 Hz. On the other hand, the residual
mirror motion associated to the SA normal modes can saturate the dynamics of
the interferometer locking system. This motion is reduced implementing a
wideband (DC-5 Hz) multidimensional control (the so called inertial damping)
which makes use of both accelerometers and position sensors and of a DSP
system. Feedback forces are exerted by coil-magnet actuators on the top of the
inverted pendulum. The inertial damping is successful in reducing the mirror
motion within the requirements. The results are presented.",9911044v1
2002-04-29,Schwarzschild black holes and propagation of electromagnetic and gravitational waves,"Disturbing of a spacetime geometry may result in the appearance of an
oscillating and damped radiation - the so-called quasinormal modes. Their
periods of oscillations and damping coefficients carry unique information about
the mass and the angular momentum, that would allow one to identify the source
of the gravitational field. In this talk we present recent bounds on the
diffused energy, applicable to the Schwarzschild spacetime, that give also
rough estimates of the energy of excited quasinormal modes.",0204086v1
2002-10-30,Massive charged scalar field in a Reissner-Nordstrom black hole background: quasinormal ringing,"We compute characteristic (quasinormal) frequencies corresponding to decay of
a massive charged scalar field in a Reissner-Nordstrom black hole background.
It proves that, contrary to the behavior at very late times, at the stage of
quasinormal ringing the neutral perturbations will damp slower than the charged
ones. In the limit of the extremal black hole the damping rate of charged and
neutral perturbations coincides. Possible connection of this with the critical
collapse in a massive scalar electrodynamics is discussed.",0210105v3
2003-03-20,Dirac Quasi-Normal Modes in Schwarzschild Black Hole Spacetimes,"We evaluate both the massless and the massive Dirac quasi-normal mode
frequencies in the Schwarzschild black hole spacetime using the WKB
approximation. For the massless case, we find that, similar to those for the
integral spin fields, the real parts of the frequencies increase with the
angular momentum number $\kappa$, while the imaginary parts or the dampings
increase with the mode number $n$ for fixed $\kappa$. For the massive case, the
oscillation frequencies increase with the mass $m$ of the field, while the
dampings decrease. Fields with higher masses will therefore decay more slowly.",0303078v1
2003-07-31,Effects of electrical charging on the mechanical Q of a fused silica disk,"We report on the effects of an electrical charge on mechanical loss of a
fused silica disk. A degradation of Q was seen that correlated with charge on
the surface of the sample. We examine a number of models for charge damping,
including eddy current damping and loss due to polarization. We conclude that
rubbing friction between the sample and a piece of dust attracted by the
charged sample is the most likely explanation for the observed loss.",0308001v1
2004-09-15,Rippled Cosmological Dark Matter from Damped Oscillating Newton Constant,"Let the reciprocal Newton 'constant' be an apparently non-dynamical
Brans-Dicke scalar field damped oscillating towards its General Relativistic
VEV. We show, without introducing additional matter fields or dust, that the
corresponding cosmological evolution averagely resembles, in the Jordan frame,
the familiar dark radiation -> dark matter -> dark energy domination sequence.
The fingerprints of our theory are fine ripples, hopefully testable, in the FRW
scale factor; they die away at the General Relativity limit. The possibility
that the Brans-Dicke scalar also serves as the inflaton is favorably examined.",0409059v2
2004-10-06,Thermoelastic-damping noise from sapphire mirrors in a fundamental-noise-limited interferometer,"We report the first high-precision interferometer using large sapphire
mirrors, and we present the first direct, broadband measurements of the
fundamental thermal noise in these mirrors. Our results agree well with the
thermoelastic-damping noise predictions of Braginsky, et al. [Phys. Lett. A
264, 1(1999)] and Cerdonio, et al.[Phys. Rev. D 63, 082003 (2001)], which have
been used to predict the astrophysical reach of advanced interferometric
gravitational wave detectors.",0410028v1
2004-10-28,Gravitational waves from neutron stars described by modern EOS,"The frequencies and damping times of neutron star (and quark star)
oscillations have been computed using the most recent equations of state
available in the literature. We find that some of the empirical relations that
connect the frequencies and damping times of the modes to the mass and radius
of the star, and that were previously derived in the literature need to be
modified.",0410140v1
2005-06-08,Resonant growth of stellar oscillations by incident gravitational waves,"Stellar oscillation under the combined influences of incident gravitational
wave and radiation loss is studied in a simple toy model. The star is
approximated as a uniform density ellipsoid in the Newtonian gravity including
radiation damping through quadrupole formula. The time evolution of the
oscillation is significantly controlled by the incident wave amplitude $h$,
frequency $\nu$ and damping time $\tau$. If a combination $ h \nu \tau $
exceeds a threshold value, which depends on the resonance mode, the resonant
growth is realized.",0506047v1
2006-11-28,Massive scalar field quasinormal modes of a Schwarzschild black hole surrounded by quintessence,"We present the quasinormal frequencies of the massive scalar field in the
background of a Schwarzchild black hole surrounded by quintessence with the
third-order WKB method. The mass of the scalar field $u$ plays an important
role in studying the quasinormal frequencies, the real part of the frequencies
increases linearly as mass $u$ increases, while the imaginary part in absolute
value decreases linearly which leads to damping more slowly and the frequencies
having a limited value. Moreover, owing to the presence of the quintessence,
the massive scalar field damps more slowly.",0611146v2
1992-09-24,Non-Abelian Boltzmann Equation for Mixing and Decoherence,"We consider particle oscillations and their damping in second-quantized form.
We find that the damping or ""decoherence"" may be described by a Boltzmann-like
collision integral with ""non-abelian blocking factors"" (fermions). Earlier
results are generalized in that the momentum degrees of freedom are included
and that the mixing equations become intrinsically non-linear at high
densities.",9209276v1
1993-06-03,The heavy fermion damping rate puzzle,": We examine again the problem of the damping rate of a moving heavy fermion
in a hot plasma within the resummed perturbative theory of Pisarski and
Braaten. The ansatz for its evaluation which relates it to the imaginary part
of the fermion propagator pole in the framework of a self-consistent approach
is critically analyzed. As already pointed out by various authors, the only way
to define the rate is through additional implementation of magnetic screening.
We show in detail how the ansatz works in this case and where we disagree with
other authors. We conclude that the self-consistent approach is not
satisfactory.",9306219v1
1993-09-03,Damping Rate of a Fermion in a Medium,"We examine the relation between the damping rate of a massless, chiral
fermion that propagates in a medium, and the rate $\Gamma$ of approach to
equilibrium. It is proven that these quantities are equal, by showing that they
are given by the same formula in terms of the imaginary part of the self-energy
evaluated at the energy of the propagating fermion mode. This result is valid
provided $\Gamma$ is defined by using the appropriate wave functions of the
mode.",9309225v2
1994-03-22,On the Damping Rate of a Fast Fermion in Hot QED,"The self-consistent determination of the damping rate of a fast moving
fermion in a hot QED plasma is reexamined. We argue how a detailed
investigation of the analytic properties of the retarded fermion Green's
function motivated by the cutting rules at finite temperature may resolve
ambiguities related to the proper definition of the mass-shell condition.",9403335v1
1994-09-12,Fermion damping rate in a hot medium,"In principle every excitation acquires a finite lifetime in a hot system.
This nonzero spectral width is calculated self-consistently for massive
fermions coupled to massless scalar, vector and pseudoscalar bosons. It is
shown that the self-consistent summation of the corresponding Fock diagram for
fermions eliminates all infrared divergences although the bosons are not
screened at all. Our solutions for the fermion damping rate are analytical in
the coupling constant, but not analytical in the temperature parameter around
T=0.",9409280v2
1994-09-22,Lyapunov Exponent and Plasmon Damping Rate in Nonabelian Gauge Theories,"We explain why the maximal positive Lyapunov exponent of classical SU($N$)
gauge theory coincides with (twice) the damping rate of a plasmon at rest in
the leading order of thermal gauge theory. [This is a substantially revised and
expanded version of the manuscript.]",9409392v2
1994-12-20,Baryogenesis and damping in nonminimal electroweak models,"We study the effect of damping on the generation of baryon asymmetry of the
Universe in the standard model of the eletroweak theory with simple extensions
of the Higgs sector. The propagation of quarks of masses up to about 5 GeV are
considered, taking into account their markedly different dispersion relations
due to interaction with the hot electroweak plasma. It is argued that the
contribution of the b quark can be comparable to that of the t quark calculated
earlier.",9412330v1
1998-10-07,Classical Kinetic Theory of Landau Damping for Self-interacting Scalar Fields in the Broken Phase,"The classical kinetic theory of one-component self-interacting scalar fields
is formulated in the broken symmetry phase and applied to the phenomenon of
Landau damping. The domain of validity of the classical approach is found by
comparing with the result of a 1-loop quantum calculation.",9810278v2
1999-08-02,Plasma wave instabilities induced by neutrinos,"Quantum field theory is applied to study the interaction of an electron
plasma with an intense neutrino flux. A connection is established between the
field theory results and classical kinetic theory. The dispersion relation and
damping rate of the plasma longitudinal waves are derived in the presence of
neutrinos. It is shown that Supernova neutrinos are never collimated enough to
cause non-linear effects associated with a neutrino resonance. They only induce
neutrino Landau damping, linearly proportional to the neutrino flux and
$G_{\mathrm{F}}^{2}$.",9908206v2
1999-09-27,Radiation Damping at a Bubble Wall,"The first order phase transition proceeds via nucleation and growth of true
vacuum bubbles. When charged particles collide with the bubble they could
radiate electromagnetic wave. We show that, due to an energy loss of the
particles by the radiation, the damping pressure acting on the bubble wall
depends on the velocity of the wall even in a thermal equilibrium state.",9909521v1
1999-10-08,Lifetime of Collective Isospin Rotations of a Quantum Meson Field,"We calculate the lifetime of the collective isospin rotating solutions which
have been found recently in the case a quantum N-component meson field with
exact O(N) symmetry. For this purpose we take into account the small breaking
of the O(N) symmetry associated to the non vanishing mass of the pion. This
term induces a coupling between collective rotations and intrinsic meson
excitations. We evaluate the associated damping time in the framework of linear
response theory. We find damping times of the order of 100 fm/c, i.e.
substantially longer than reaction times.",9910276v1
2000-02-08,Finite pion width effects on the rho-meson and di-lepton spectra,"Within a field theoretical model where all damping width effects are treated
self-consistently we study the changes of the spectral properties of rho-mesons
due to the finite damping width of the pions in dense hadronic matter at finite
temperature. The corresponding effects in the di-lepton yields are presented.
Some problems concerning the self consistent treatment of vector or gauge
bosons are discussed.",0002087v1
2000-08-31,Damping of very soft moving quarks in high-temperature QCD,"We determine the analytic expression of the damping rates for very soft
moving quarks in an expansion to second order in powers of their momentum in
the context of QCD at high temperature. The calculation is performed using the
hard-thermal-loop-summed perturbation scheme. We describe the range of validity
of the expansion and make a comparison with other calculations, particularly
those using a magnetic mass as a shield from infrared sensitivity. We discuss
the possible occurrence of infrared divergences in our results and argue that
they are due to magnetic sensitivity.",0008335v1
2000-09-27,Damping of the HERA effect in DIS?,"The drastic rise of the proton structure function F_2(x,Q^2) when the
Bj\""orken variable x decreases, seen at HERA for a large span of Q^2, negative
values for the 4-momentum transfer, may be damped when Q^2 increases beyond
several hundreds GeV^2. A new data analysis and a comparison with recent models
for the proton structure function is proposed to discuss this phenomenon in
terms of the derivative \partial ln F_2(x,Q^2)/\partial ln(1/x).",0009313v2
2001-12-13,Time evolution in linear response: Boltzmann equations and beyond,"In this work a perturbative linear response analysis is performed for the
time evolution of the quasi-conserved charge of a scalar field. One can find
two regimes, one follows exponential damping, where the damping rate is shown
to come from quantum Boltzmann equations. The other regime (coming from
multiparticle cuts and products of them) decays as power law. The most
important, non-oscillating contribution in our model comes from a 4-particle
intermediate state and decays as 1/t^3. These results may have relevance for
instance in the context of lepton number violation in the Early Universe.",0112188v1
2002-04-26,Oscillation damping of chiral string loops,"Chiral cosmic string loop tends to the stationary (vorton) configuration due
to the energy loss into the gravitational and electromagnetic radiation. We
describe the asymptotic behaviour of near stationary chiral loops and their
fading to vortons. General limits on the gravitational and electromagnetic
energy losses by near stationary chiral loops are found. For these loops we
estimate the oscillation damping time. We present solvable examples of
gravitational radiation energy loss by some chiral loop configurations. The
analytical dependence of string energy with time is found in the case of the
chiral ring with small amplitude radial oscillations.",0204304v1
2002-09-21,Infrared Sensitivity in Damping Rate for Very Soft Moving Fermions in Finite Temperature QED,"We calculate the fermion damping rate to second order in powers of the
external momentum $p$ in the context of QED at finite temperature using the
hard-thermal-loop (HTL) summation scheme. We find that the coefficient of order
$p^{2}$ is divergent in the infrared whereas the two others are finite. This
result suggests that the htl-based pertubation is infrared sensitive at
next-to-leading order.",0209246v1
2004-02-06,Critical Behavior of Damping Rate for Plasmon with Finite Momentum in φ^4 Theory,"Applying thermal renormalization group (TRG) equations to $\phi^4$ theory
with spontaneous breaking symmetry, we investigate the critical behavior of the
damping rate for the plasmons with finite momentum at the symmetry-restoring
phase transition. From the TRG equation the IR cutoff provided by the external
momentum leads to that the momentum-dependent coupling constant stops running
in the critical region. As the result, the critical slowing down phenomenon
reflecting the inherently IR effect doesn't take place at the critical point
for the plasmon with finite external momentum.",0402069v2
2005-11-22,Ultrasoft Quark Damping in Hot QCD,"We determine the quark damping rates in the context of next-to-leading order
hard-thermal-loop summed perturbation of high-temperature QCD where weak
coupling is assumed. The quarks are ultrasoft. Three types of divergent
behavior are encountered: infrared, light-cone and at specific points
determined by the gluon energies. The infrared divergence persists and is
logarithmic whereas the two others are circumvented.",0511258v1
2006-03-10,Numerical Approach to Multi Dimensional Phase Transitions,"We present an algorithm to analyze numerically the bounce solution of
first-order phase transitions. Our approach is well suited to treat phase
transitions with several fields. The algorithm consists of two parts. In the
first part the bounce solution without damping is determined, in which case
energy is conserved. In the second part the continuation to the physically
relevant case with damping is performed. The presented approach is numerically
stable and easily implemented.",0603081v2
1994-06-22,Damped quantum harmonic oscillator: density operator and related quantities,"A closed expression for the density operator of the damped harmonic
oscillator is extracted from the master equation based on the Lindblad theory
for open quantum systems. The entropy and effective temperature of the system
are subsequently calculated and their temporal behaviour is surveyed by showing
how these quantities relax to their equilibrium values. The entropy for a state
characterized by a Wigner distribution function which is Gaussian in form is
found to depend only on the variance of the distribution function.",9406142v1
1997-05-09,Radiation Damping of a BPS Monopole; an Implication to S-duality,"The radiation reaction of a BPS monopole in the presence of incident
electromagnetic waves as well as massless Higgs waves is analyzed classically.
The reactive forces are compared to those of $W$ boson that is interpreted as a
dual partner of the BPS monopole. It is shown that the damping of acceleration
is dual to each other, while in the case of finite size effects the duality is
broken explicitly. Their implications on the duality are discussed.",9705059v2
1997-07-02,The Asymptotic Method Developed from Weak Turbulent Theory and the Nonlinear Permeability and Damping Rate in QGP,"With asymptotic method developed from weak turbulent theory, the kinetic
equations for QGP are expanded in fluctuation field potential $A^T_\mu $.
Considering the second-order and third-order currents, we derive the nonlinear
permeability tensor function from Yang-Mills field equation, and find that the
third-order current is more important in turbulent theory. The nonlinear
permeability formulae for longitudinal color oscillations show that the
non-Abelian effects are more important than the Abelian-like effects. To
compare with other works, we give the numerical result of the damping rate for
the modes with zero wave vector.",9707052v1
2005-04-07,Continuous area spectrum in regular black hole,"We investigate highly damped quasinormal modes of regular black hole coupled
to nonlinear electrodynamics. Using the WKB approximation combined with
complex-integration technique, we show that the real part of the frequency
disappears in the highly damped limit. If we use the Bohr's correspondence
principle, the area spectrum of this black hole is continuous. We discuss its
implication in the loop quantum gravity.",0504059v2
2005-05-16,Supersymmetrization of the Radiation Damping,"We construct a supersymmetrized version of the model to the radiation damping
\cite{03} introduced by the present authors \cite{ACWF}. We dicuss its
symmetries and the corresponding conserved Noether charges. It is shown this
supersymmetric version provides a supersymmetric generalization of the Galilei
algebra obtained in \cite{ACWF}. We have shown that the supersymmetric action
can be splited into dynamically independent external and internal sectors.",0505142v1
1999-08-16,Topological Entropy and epsilon-Entropy for Damped Hyperbolic Equations,"We study damped hyperbolic equations on the infinite line. We show that on
the global attracting set $G$ the $\epsilon$-entropy (per unit length) exists
in the topology of $W^{1,\infty}$. We also show that the topological entropy
per unit length of $G$ exists. These results are shown using two main
techniques: Bounds in bounded domains in position space and for large momenta,
and a novel submultiplicativity argument in $W^{1,\infty}$.",9908080v1
2003-11-28,Uniform stability of damped nonlinear vibrations of an elastic string,"Here we are concerned about uniform stability of damped nonlinear transverse
vibrations of an elastic string fixed at its two ends. The vibrations governed
by nonlinear integro-differential equation of Kirchoff type, is shown to
possess energy uniformly bounded by exponentially decaying function of time.
The result is achieved by considering an energy-like Lyapunov functional for
the system.",0311527v1
2005-07-06,On stability and stabilization of elastic systems by time-variant feedback,"We study a class of elastic systems described by a (hyperbolic) partial
differential equation. Our working example is the equation of a vibrating
string subject to linear disturbance. The main goal is to establish conditions
for stabilization and asymptotic stabilization by applying a fast oscillating
control to the string. In the first situation studied we assume that system is
subject to a damping force; next we consider the system without damping. We
extend the tools of high-order averaging and of chronological calculus for
studying stability of this distributed parameter system.",0507123v1
2006-01-13,Attractors for damped hyperbolic equations on arbitrary unbounded domains,"We prove existence of global attractors for damped hyperbolic equations of
the form $$\aligned \eps u_{tt}+\alpha(x) u_t+\beta(x)u- \sum_{ij}(a_{ij}(x)
u_{x_j})_{x_i}&=f(x,u),\quad x\in \Omega, t\in[0,\infty[, u(x,t)&=0,\quad x\in
\partial \Omega, t\in[,\infty[.\endaligned$$ on an unbounded domain $\Omega$,
without smoothness assumptions on $\beta(\cdot)$, $a_{ij}(\cdot)$, $f(\cdot,u)$
and $\partial\Omega$, and $f(x,\cdot)$ having critical or subcritical growth.",0601319v3
2007-02-07,Finite time blow-up results for the damped wave equations with arbitrary initial energy in an inhomogeneous medium,"In this paper we consider the long time behavior of solutions of the initial
value problem for the damped wave equation of the form \begin{eqnarray*}
u_{tt}-\rho(x)^{-1}\Delta u+u_t+m^2u=f(u) \end{eqnarray*} with some $\rho(x)$
and $f(u)$ on the whole space $\R^n$ ($n\geq 3$).
  For the low initial energy case, which is the non-positive initial energy,
based on concavity argument we prove the blow up result. As for the high
initial energy case, we give out sufficient conditions of the initial datum
such that the corresponding solution blows up in finite time.",0702190v1
2007-03-09,Analyticity and Riesz basis property of semigroups associated to damped vibrations,"Second order equations of the form $z'' + A_0 z + D z'=0$ in an abstract
Hilbert space are considered. Such equations are often used as a model for
transverse motions of thin beams in the presence of damping. We derive various
properties of the operator matrix $A$ associated with the second order problem
above. We develop sufficient conditions for analyticity of the associated
semigroup and for the existence of a Riesz basis consisting of eigenvectors and
associated vectors of $A$ in the phase space.",0703247v1
2007-03-21,Existence and asymptotic behavior of $C^1$ solutions to the multidimensional compressible Euler equations with damping,"In this paper, the existence and asymptotic behavior of $C^1$ solutions to
the multidimensional compressible Euler equations with damping on the framework
of Besov space are considered. We weaken the regularity requirement of the
initial data, and improve the well-posedness results of Sideris-Thomases-Wang
(Comm.P.D.E. 28 (2003) 953). The global existence lies on a crucial a-priori
estimate which is proved by the spectral localization method. The main analytic
tools are the Littlewood-Paley decomposition and Bony's para-product formula.",0703621v1
2000-12-22,The Vlasov-Poisson system with radiation damping,"We set up and analyze a model of radiation damping within the framework of
continuum mechanics, inspired by a model of post-Newtonian hydrodynamics due to
Blanchet, Damour and Schaefer. In order to simplify the problem as much as
possible we replace the gravitational field by the electromagnetic field and
the fluid by kinetic theory. We prove that the resulting system has a
well-posed Cauchy problem globally in time for general initial data and in all
solutions the fields decay to zero at late times. In particular, this means
that the model is free from the runaway solutions which frequently occur in
descriptions of radiation reaction.",0012041v1
2003-01-17,Quantum mechanics of damped systems,"We show that the quantization of a simple damped system leads to a
self-adjoint Hamiltonian with a family of complex generalized eigenvalues. It
turns out that they correspond to the poles of energy eigenvectors when
continued to the complex energy plane. Therefore, the corresponding generalized
eigenvectors may be interpreted as resonant states. We show that resonant
states are responsible for the irreversible quantum dynamics of our simple
model.",0301024v3
2003-07-23,Quantum Mechanics of Damped Systems II. Damping and Parabolic Potential Barrier,"We investigate the resonant states for the parabolic potential barrier known
also as inverted or reversed oscillator. They correspond to the poles of
meromorphic continuation of the resolvent operator to the complex energy plane.
As a byproduct we establish an interesting relation between parabolic cylinder
functions (representing energy eigenfunctions of our system) and a class of
Gel'fand distributions used in our recent paper.",0307047v1
2001-07-02,Pattern formation and localization in the forced-damped FPU lattice,"We study spatial pattern formation and energy localization in the dynamics of
an anharmonic chain with quadratic and quartic intersite potential subject to
an optical, sinusoidally oscillating field and a weak damping. The
zone-boundary mode is stable and locked to the driving field below a critical
forcing that we determine analytically using an approximate model which
describes mode interactions. Above such a forcing, a standing modulated wave
forms for driving frequencies below the band-edge, while a ``multibreather''
state develops at higher frequencies. Of the former, we give an explicit
approximate analytical expression which compares well with numerical data. At
higher forcing space-time chaotic patterns are observed.",0107002v1
2003-06-16,On the influence of noise on chaos in nearly Hamiltonian systems,"The simultaneous influence of small damping and white noise on Hamiltonian
systems with chaotic motion is studied on the model of periodically kicked
rotor. In the region of parameters where damping alone turns the motion into
regular, the level of noise that can restore the chaos is studied. This
restoration is created by two mechanisms: by fluctuation induced transfer of
the phase trajectory to domains of local instability, that can be described by
the averaging of the local instability index, and by destabilization of motion
within the islands of stability by fluctuation induced parametric modulation of
the stability matrix, that can be described by the methods developed in the
theory of Anderson localization in one-dimensional systems.",0306024v1
2003-07-30,Faraday Wave Pattern Selection Via Multi-Frequency Forcing,"We use symmetry considerations to investigate how damped modes affect pattern
selection in multi-frequency forced Faraday waves. We classify and tabulate the
most important damped modes and determine how the corresponding resonant triad
interactions depend on the forcing parameters. The relative phase of the
forcing terms may be used to enhance or suppress the nonlinear interactions. We
compare our predictions with numerical results and discuss their implications
for recent experiments. Our results suggest how to design multi-frequency
forcing functions that favor chosen patterns in the lab.",0307056v1
2004-10-11,Nodal two-dimensional solitons in nonlinear parametric resonance,"The parametrically driven damped nonlinear Schr\""odinger equation serves as
an amplitude equation for a variety of resonantly forced oscillatory systems on
the plane. In this note, we consider its nodal soliton solutions. We show that
although the nodal solitons are stable against radially-symmetric perturbations
for sufficiently large damping coefficients, they are always unstable to
azimuthal perturbations. The corresponding break-up scenarios are studied using
direct numerical simulations. Typically, the nodal solutions break into
symmetric ""necklaces"" of stable nodeless solitons.",0410012v1
2004-10-21,Stabilization mechanism for two-dimensional solitons in nonlinear parametric resonance,"We consider a simple model system supporting stable solitons in two
dimensions. The system is the parametrically driven damped nonlinear
Schr\""odinger equation, and the soliton stabilises for sufficiently strong
damping. The purpose of this note is to elucidate the stabilisation mechanism;
we do this by reducing the partial differential equation to a
finite-dimensional dynamical system. Our conclusion is that the negative
feedback loop occurs via the enslaving of the soliton's phase, locked to the
driver, to its amplitude and width.",0410044v1
2006-01-14,Vibration of the Duffing Oscillator: Effect of Fractional Damping,"We have applied the Melnikov criterion to examine a global homoclinic
bifurcation and transition to chaos in a case of the Duffing system with
nonlinear fractional damping and external excitation.
  Using perturbation methods we have found a critical forcing amplitude above
which the system may behave chaotically.
  The results have been verified by numerical simulations using standard
nonlinear tools as
  Poincare maps and a Lyapunov exponent. Above the critical Melnikov amplitude
$\mu_c$, which is the sufficient condition of a global homoclinic bifurcation,
we have observed the region with a transient chaotic motion.",0601033v1
2006-10-22,Response of a Magneto-Rheological Fluid Damper Subjected to Periodic Forcing in a High Frequency Limit,"We explored vibrations of a single-degree of freedom oscillator with a
magneto-rheological damper subjected to kinematic excitations. Using fast and
slow scales decoupling procedure we derived an effective damping coefficient in
the limit of high frequency excitation. Damping characteristics, as functions
of velocity, change considerably especially by terminating the singular
non-smoothness points. This effect was more transparent for a larger control
parameter which was defined as the product of the excitation amplitude and its
frequency.",0610055v1
2006-11-02,Solitons in strongly driven discrete nonlinear Schrödinger-type models,"Discrete solitons in the Ablowitz-Ladik (AL) and discrete nonlinear
Schr\""odinger (DNLS) equations with damping and strong rapid drive are
investigated. The averaged equations have the forms of the parametric AL and
DNLS equations. A new type of parametric bright discrete soliton and cnoidal
waves are found and the stability properties are analyzed. The analytical
predictions of the perturbed inverse scattering transform are confirmed by the
numerical simulations of the AL and DNLS equations with rapidly varying drive
and damping.",0611004v1
2006-11-26,On the Lagrangian and Hamiltonian description of the damped linear harmonic oscillator,"Using the modified Prelle- Singer approach, we point out that explicit time
independent first integrals can be identified for the damped linear harmonic
oscillator in different parameter regimes. Using these constants of motion, an
appropriate Lagrangian and Hamiltonian formalism is developed and the resultant
canonical equations are shown to lead to the standard dynamical description.
Suitable canonical transformations to standard Hamiltonian forms are also
obtained. It is also shown that a possible quantum mechanical description can
be developed either in the coordinate or momentum representations using the
Hamiltonian forms.",0611048v1
1992-12-14,Microscopic Origin of Quantum Chaos in Rotational Damping,"The rotational spectrum of $^{168}$Yb is calculated diagonalizing different
effective interactions within the basis of unperturbed rotational bands
provided by the cranked shell model. A transition between order and chaos
taking place in the energy region between 1 and 2 MeV above the yrast line is
observed, associated with the onset of rotational damping. It can be related to
the higher multipole components of the force acting among the unperturbed
rotational bands.",9212005v1
1996-12-17,Damping mechanisms of the Delta resonance in nuclei,"The damping mechanisms of the Delta(1232) resonance in nuclei are studied by
analyzing the quasi-free decay reactions 12C(pi+,pi+ p)11B and 12C(3He,t pi+
p)11B and the 2p emission reactions 12C(pi+,pp)10B and 12C(3He,t pp)10B. The
coincidence cross sections are calculated within the framework of the
isobar-hole model. It is found that the 2p emission process induced by the
decay of the Delta resonance in the nucleus can be consistently described by a
pi+rho+g' model for the Delta+N -> N+N decay interaction.",9612046v1
1997-11-08,Cooperative damping mechanism of the resonance in the nuclear photoabsorption,"We propose a resonance damping mechanism to explain the disappearance of the
peaks around the position of the resonances higher than the $\Delta$ resonance
in the nuclear photoabsorption. This phenomenon is understood by taking into
account the cooperative effect of the collision broadening of $\Delta$ and
$N^{*}$, the pion distortion and the interference in the two-pion
photoproduction processes in the nuclear medium.",9711017v4
1998-05-27,Collisional Damping of Nuclear Collective Vibrations in a Non-Markovian Transport Approach,"A detailed derivation of the collisional widths of collective vibrations is
presented in both quantal and semi-classical frameworks by considering the
linearized limits of the extended TDHF and the BUU model with a non-Markovian
binary collision term. Damping widths of giant dipole and giant quadrupole
excitations are calculated by employing an effective Skyrme force, and the
results are compared with GDR measurements in Lead and Tin nuclei at finite
temperature.",9805050v1
1999-07-06,Probing the width of compound states with rotational gamma rays,"The intrinsic width of (multiparticle-multihole) compound states is an
elusive quantity, of difficult direct access, as it is masked by damping
mechanisms which control the collective response of nuclei. Through microscopic
cranked shell model calculations, it is found that the strength function
associated with two-dimensional gamma-coincidence spectra arising from
rotational transitions between states lying at energies >1 MeV above the yrast
line, exhibits a two-component structure controlled by the rotational (wide
component) and compound (narrow component) damping width. This last component
is found to be directly related to the width of the multiparticle-multihole
autocorrelation function.",9907016v1
1999-07-09,Color plasma oscillation in strangelets,"The dispersion relation and damping rate of longitudinal color plasmons in
finite strange quark matter (strangelets) are evaluated in the limits of weak
coupling, low temperature, and long wavelength. The property of the QCD vacuum
surrounding a strangelet makes the frequency of the plasmons nearly the same as
the color plasma frequency of bulk matter. The plasmons are damped by their
coupling with individual excitations of particle-hole pairs of quarks, of which
the energy levels are discretized by the boundary. For strangelets of
macroscopic size, the lifetime of the plasmons is found to be proportional to
the size, as in the case of the usual plasma oscillations in metal
nanoparticles.",9907039v1
1999-09-21,On the Collisional Damping of Giant Dipole Resonance,"Collisional damping widths of giant dipole excitations are calculated in
Thomas-Fermi approximation by employing the microscopic in-medium
cross-sections of Li and Machleidt and the phenomenological Gogny force. The
results obtained in both calculations compare well, but account for about
25-35% of the observed widths in $^{120}Sn$ and $^{208}Pb$ at finite
temperatures.",9909057v1
2000-01-09,Strongly damped nuclear collisions: zero or first sound ?,"The relaxation of the collective quadrupole motion in the initial stage of a
central heavy ion collision at beam energies $E_{lab}=5\div20$ AMeV is studied
within a microscopic kinetic transport model. The damping rate is shown to be a
non-monotonic function of E_{lab} for a given pair of colliding nuclei. This
fact is interpreted as a manifestation of the zero-to-first sound transition in
a finite nuclear system.",0001016v1
2002-11-18,Collision damping in the pi 3He -> d'N reaction near the threshold,"We present a simple quantum mechanical model exploiting the optical potential
approach for the description of collision damping in the reaction pi 3He -> d'N
near the threshold, which recently has been measured at TRIUMF. The influence
of the open d'N -> NNN channel is taken into account. It leads to a suppression
factor of about ten in the d' survival probability. Applications of the method
to other reactions are outlined.",0211050v1
2003-03-14,Pion damping width from SU(2) x SU(2) NJL model,"Within the framework of the NJL model, we investigate the modification of the
pion damping width in a hot pion gas for temperatures ranging from 0 to 180
MeV. The pion is found to broaden noticeably at T > 60 MeV. Near the chiral
phase transition T ~ 180 MeV, the pion width is saturated and amounts to 70
MeV. The main contribution to the width comes from pion-pion collisions. Other
contributions are found negligibly small.",0303034v1
2004-06-09,Damped collective motion of isolated many body systems within a variational approach to functional integrals,"Two improvements with respect to previous formulations are presented for the
calculation of the partition function $\mathcal{Z}$ of small, isolated and
interacting many body systems. By including anharmonicities and employing a
variational approach quantum effects can be treated even at very low
temperatures. A method is proposed of how to include collisional damping.
Finally, our approach is applied to the calculation of the decay rate of
metastable systems.",0406025v1
2004-07-26,Damped collective motion of many body systems: A variational approach to the quantal decay rate,"We address the problem of collective motion across a barrier like encountered
in fission. A formula for the quantal decay rate is derived which bases on a
recently developed variational approach for functional integrals. This formula
can be applied to low temperatures that have not been accessible within the
former PSPA type approach. To account for damping of collective motion one
particle Green functions are dressed with appropriate self-energies.",0407092v2
1997-11-15,Fluctuational phase-flip transitions in parametrically pumped oscillators,"We analyze the rates of noise-induced transitions between period-two
attractors. The model investigated is an underdamped oscillator parametrically
driven by a field at nearly twice the oscillator eigenfrequency. The activation
energy of the transitions is analyzed as a function of the frequency detuning
and field amplitude scaled by the damping and nonlinearity parameters of the
oscillator. The parameter ranges where the system is bi- and tristable are
investigated. Explicit results are obtained in the limit of small damping (or
strong driving), and near bifurcation points.",9711014v1
1999-05-31,Collisionless Damping of Low-Frequency Magnetosonic Pulses in a Two-Ion-Species Plasma,"Low-frequency mangnetosonic pulses in a two-ion-species plasma are studied
theoretically and by simulation with a one-dimensional electromagnetic
simulation code based on a three-fluid model, with particular attention to the
dynamics of minority heavy ions. It is found that heavy ions can gain some
energy from the pulses. Because of this energy transfer, the pulses are damped
even if the plasma is collisionless and pulse propagation is perpendicular to
the magnetic field.",9905059v1
2000-10-17,Bunch Length Measurements at the ATF Damping Ring in April 2000,"This report presents bunch length and energy spread measurements performed in
April 2000 at the ATF Damping Ring, at KEK. Measurements were performed with
the beam on and then off the linear (difference) coupling resonance. Due to
strong intra-beam scattering in the ATF ring, the results depended strongly on
the coupling.",0010043v1
2000-12-21,Phase transition in the collisionless regime for wave-particle interaction,"Gibbs statistical mechanics is derived for the Hamiltonian system coupling
self-consistently a wave to N particles. This identifies Landau damping with a
regime where a second order phase transition occurs. For nonequilibrium initial
data with warm particles, a critical initial wave intensity is found: above it,
thermodynamics predicts a finite wave amplitude in the limit of infinite N;
below it, the equilibrium amplitude vanishes. Simulations support these
predictions providing new insight on the long-time nonlinear fate of the wave
due to Landau damping in plasmas.",0012053v1
2001-09-25,Creep and Mechanical Oscillator Damping,"Although ""friction"" is included in many models of oscillator damping,
including viscous ones applied to the pendulum; they ""miss the mark"" with
regard to a conceptual understanding of the mechanisms responsible for energy
loss. The theory of the present paper corrects some of these misunderstandings
by considering the influence of internal friction which derives from the
structural members of the oscillator through secondary rather than primary
creep. The simple model properly describes the variation of Q with frequency.",0109067v1
2001-11-06,Electromagnetic induction and damping - quantitative experiments using PC interface,"A bar magnet, attached to an oscillating system, passes through a coil
periodically, generating a series of emf pulses. A novel method is described
for the quantitative verification of Faraday's law which eliminates all errors
associated with angular measurements, thereby revealing delicate features of
the underlying mechanics. When electromagnetic damping is activated by
short-circuiting the coil, a distinctly linear decay of oscillation amplitude
is surprisingly observed. A quantitative analysis reveals an interesting
interplay of the electromagnetic and mechanical time scales.",0111016v1
2003-08-31,Effects of Bulk Viscosity in Non-linear Bubble Dynamics,"The non-linear bubble dynamics equations in a compressible liquid have been
modified considering the effects of compressibility of both the liquid and the
gas at the bubble interface. A new bubble boundary equation has been derived,
which includes a new term resulted from the liquid bulk viscosity effects. The
influence of this term has been numerically investigated considering the
effects of water vapor and chemical reactions on the bubble evolution. The
results clearly indicate that the new term has an important damping role at the
collapse, so that its consideration decreases the amplitude of the bubble
rebounds after the collapse. This damping feature is more remarkable for higher
deriving pressures.",0309012v1
2004-04-30,"On violation of the Robinson's damping criterion and enhanced cooling of ion, electron and muon beams in storage rings","Limits of applicability of the Robinson's damping criterion and the problem
of enhanced cooling of particle beams in storage rings beyond the criterion are
discussed.",0404142v6
2004-12-28,"Electron Bernstein waves in spherical tokamak plasmas with ""magnetic wells""","In addition to traditional regimes with monotonously increasing magnetic
field, regimes with ""magnetic wells"" also occur in spherical tokamaks (STs).
The magnetic field profile inversion modifies significantly the whole picture
of the wave propagation and damping. Since the magnetic wells may become quite
common with further improvement of ST performance, analysis of such
configurations is of interest for assessment of EBW plasma heating an CD
perspectives. In this paper the basic features of the EBWs propagation and
damping for the second cyclotron harmonic in a slab model are considered.",0412173v1
2005-02-10,Modulational instabilities in Josephson oscillations of elongated coupled condensates,"We study the Josephson oscillations of two coupled elongated condensates.
Linearized calculations show that the oscillating mode uniform over the length
of the condensates (uniform Josephson mode) is unstable : modes of non zero
longitudinal momentum grow exponentially. In the limit of strong atom
interactions, we give scaling laws for the instability time constant and
unstable wave vectors. Beyond the linearized approach, numerical calculations
show a damped recurrence behavior : the energy in the Josephson mode presents
damped oscillations. Finally, we derive conditions on the confinement of the
condensates to prevent instabilities.",0502050v3
2005-08-16,Creep-Enhanced Low-Frequency Sensitivity of Seismometers,"The frequency response of a seismometer is typically assumed to be the
textbook case of a viscous damped, simple harmonic oscillator. Real mechanical
oscillators are not ideal, and the damping at low frequencies, due to internal
friction, is presently too poorly understood to describe from first principles.
Even if the low-level motions were smooth (which they are not), the mean
position of a seismic mass changes because of creep and creep recovery. This
article shows that secondary creep can actually serve to increase the
sensitivity of a seismometer at low frequencies.",0508105v1
2006-06-22,Looking for a time independent Hamiltonian of a dynamical system,"In this paper we introduce a method for finding a time independent
Hamiltonian of a given dynamical system by canonoid transformation. We also
find a condition that the system should satisfy to have an equivalent time
independent formulation. We study the example of damped oscillator and give the
new time independent Hamiltonian for it, which has the property of tending to
the standard Hamiltonian of the harmonic oscillator as damping goes to zero.",0606197v2
1996-02-27,Effects of Loss and Decoherence on a Simple Quantum Computer,"We investigate the impact of loss (amplitude damping) and decoherence (phase
damping) on the performance of a simple quantum computer which solves the
one-bit Deutsch problem. The components of this machine are beamsplitters and
nonlinear optical Kerr cells, but errors primarily originate from the latter.
We develop models to describe the effect of these errors on a quantum optical
Fredkin gate. The results are used to analyze possible error correction
strategies in a complete quantum computer. We find that errors due to loss can
be avoided perfectly by appropriate design techniques, while decoherence can be
partially dealt with using projective error correction.",9602018v1
1996-11-25,The Quantum state diffusion model and the driven damped nonlinear oscillator,"We consider a driven damped anharmonic oscillator which classically leads to
a bistable steady state and to hysteresis. The quantum counterpart for this
system has an exact analytical solution in the steady state which does not
display any bistability or hysteresis. We use quantum state diffusion theory to
describe this system and to provide a new perspective on the lack of hysteresis
in the quantum regime so as to study in detail the quantum to classical
transition. The analysis is also relevant to measurements of a single
periodically driven electron in a Penning trap where hysteresis has been
observed.",9611044v1
1997-12-02,Prevention of dissipation with two particles,"An error prevention procedure based on two-particle encoding is proposed for
protecting an arbitrary unknown quantum state from dissipation, such as phase
damping and amplitude damping. The schemes, which exhibits manifestation of the
quantum Zeno effect, is effective whether quantum bits are decohered
independently or cooperatively. We derive the working condition of the scheme
and argue that this procedure has feasible practical implementation.",9712005v1
1998-02-23,Caldirola-Kanai Oscillator in Classical Formulation of Quantum Mechanics,"The quadrature distribution for the quantum damped oscillator is introduced
in the framework of the formulation of quantum mechanics based on the
tomography scheme. The probability distribution for the coherent and Fock
states of the damped oscillator is expressed explicitly in terms of Gaussian
and Hermite polynomials, correspondingly.",9802057v1
1999-03-22,Decoherence - Fluctuation Relation and Measurement Noise,"We discuss fluctuations in the measurement process and how these fluctuations
are related to the dissipational parameter characterising quantum damping or
decoherence. On the example of the measuring current of the variable-barrier or
QPC problem we show there is an extra noise or fluctuation connected with the
possible different outcomes of a measurement. This noise has an enhanced short
time component which could be interpreted as due to ``telegraph noise'' or
``wavefunction collapses''. Furthermore the parameter giving the the strength
of this noise is related to the parameter giving the rate of damping or
decoherence.",9903072v1
1999-07-27,Nonclassical correlations in damped N-solitons,"The quantum statistics of damped higher-order optical solitons are analyzed
numerically, using cumulant-expansion techniques in Gaussian approximation. A
detailed analysis of nonclassical properties in both the time and the frequency
domain is given, with special emphasis on the role of absorption. Highly
nonclassical broadband spectral correlation is predicted.",9907090v2
2001-01-08,Cavity-damping-induced transitions in a driven atom-cavity system,"We investigate the fluorescence spectrum of a two-level atom in a cavity when
the atom is driven by a classical field. We show that forbidden dipole
transitions in the Jaynes-Cummings Ladder structure are induced in the presence
of the cavity damping, which deteriorates the degree of otherwise perfect
destructive interference among the transition channels. With the larger cavity
decay, these transitions are more enhanced.",0101036v1
2001-06-09,Squeezing enhancement by damping in a driven atom-cavity system,"In a driven atom-cavity coupled system in which the two-level atom is driven
by a classical field, the cavity mode which should be in a coherent state in
the absence of its reservoir, can be squeezed by coupling to its reservoir. The
squeezing effect is enhanced as the damping rate of the cavity is increased to
some extent.",0106054v1
2001-08-01,Decoherence-induced wave packet splitting,"We provide an intuitive interpretation of the optical Stern-Gerlach effect
(OSGE) in the dressed-state point of view. We also analyze the effect of atomic
damping in an experiment on the OSGE. We show that the atomic damping also
causes the wave packet splitting, in a non-mechanical fashion, as opposed to
the coherent process that is mechanical.",0108005v1
2001-08-11,A Canonical Approach to the Quantization of the Damped Harmonic Oscillator,"We provide a new canonical approach for studying the quantum mechanical
damped harmonic oscillator based on the doubling of degrees of freedom
approach. Explicit expressions for Lagrangians of the elementary modes of the
problem, characterising both forward and backward time propagations are given.
  A Hamiltonian analysis, showing the equivalence with the Lagrangian approach,
is also done. Based on this Hamiltonian analysis, the quantization of the model
is discussed.",0108055v2
2002-05-09,Implementation of quantum maps by programmable quantum processors,"A quantum processor is a device with a data register and a program register.
The input to the program register determines the operation, which is a
completely positive linear map, that will be performed on the state in the data
register. We develop a mathematical description for these devices, and apply it
to several different examples of processors. The problem of finding a processor
that will be able to implement a given set of mappings is also examined, and it
is shown that while it is possible to design a finite processor to realize the
phase-damping channel, it is not possible to do so for the amplitude-damping
channel.",0205050v1
2002-08-28,Damped Quantum Interference using Stochastic Calculus,"It is shown how the phase-damping master equation, either in Markovian and
nonMarkovian regimes, can be obtained as an averaged random unitary evolution.
This, apart from offering a common mathematical setup for both regimes, enables
us to solve this equation in a straightforward manner just by solving the
Schrodinger equation and taking the stochastic expectation value of its
solutions after an adequate modification. Using the linear entropy as a figure
of merit (basically the loss of quantum coherence) the distinction of four
kinds of environments is suggested.",0208176v1
2002-10-31,Quantum Markov Channels for Qubits,"We examine stochastic maps in the context of quantum optics. Making use of
the master equation, the damping basis, and the Bloch picture we calculate a
non-unital, completely positive, trace-preserving map with unequal damping
eigenvalues. This results in what we call the squeezed vacuum channel. A
geometrical picture of the effect of stochastic noise on the set of pure state
qubit density operators is provided. Finally, we study the capacity of the
squeezed vacuum channel to transmit quantum information and to distribute EPR
states.",0211001v1
2003-01-17,Concurrence and foliations induced by some 1-qubit channels,"We start with a short introduction to the roof concept. An elementary
discussion of phase-damping channels shows the role of anti-linear operators in
representing their concurrence. A general expression for some concurrences is
derived. We apply it to 1-qubit channels of length two, getting induced
foliations of the state space, the optimal decompositions, and the entropy of a
state with respect to these channels. For amplitude-damping channels one
obtains an expression for the Holevo capacity allowing for easy numerical
calculations.",0301088v1
2003-05-19,Statistical Effects in the Multistream Model for Quantum Plasmas,"A statistical multistream description of quantum plasmas is formulated, using
the Wigner-Poisson system as dynamical equations. A linear stability analysis
of this system is carried out, and it is shown that a Landau-like damping of
plane wave perturbations occurs due to the broadening of the background Wigner
function that arises as a consequence of statistical variations of the wave
function phase. The Landau-like damping is shown to suppress instabilities of
the one- and two-stream type.",0305102v1
2003-06-28,Misbelief and misunderstandings on the non--Markovian dynamics of a damped harmonic oscillator,"We use the exact solution for the damped harmonic oscillator to discuss some
relevant aspects of its open dynamics often mislead or misunderstood. We
compare two different approximations both referred to as Rotating Wave
Approximation. Using a specific example, we clarify some issues related to
non--Markovian dynamics, non--Lindblad type dynamics, and positivity of the
density matrix.",0306193v3
2003-11-26,Effective damping in the Raman cooling of trapped ions,"We present a method of treating the interaction of a single three-level ion
with two laser beams. The idea is to apply a unitary transformation such that
the exact transformed Hamiltonian has one of the three levels decoupled for all
values of the detunings. When one takes into account damping, the evolution of
the system is governed by a master equation usually obtained via adiabatic
approximation under the assumption of far-detuned lasers. To go around the
drawbacks of this technique, we use the same unitary transformation to get an
effective master equation.",0311183v1
2004-06-20,Entanglement-assisted classical information capacity of the amplitude damping channel,"In this paper, we calculate the entanglement-assisted classical information
capacity of amplitude damping channel and compare it with the particular mutual
information which is considered as the entanglement-assisted classical
information capacity of this channel in Ref. 6. It is shown that the difference
between them is very small. In addition, we point out that using partial
symmetry and concavity of mutual information derived from dense coding scheme
one can simplify the calculation of entanglement-assisted classical information
capacities for non-unitary-covariant quantum noisy channels.",0406140v1
2004-08-13,Decoherence versus Dynamical Casimir Effect,"By means of two simple examples: phase and amplitude damping, the impact of
decoherence on the dynamical Casimir effect is investigated. Even without
dissipating energy (i.e., pure phase damping), the amount of created particles
can be diminished significantly via the coupling to the environment (reservoir
theory) inducing decoherence. For a simple microscopic model, it is
demonstrated that spontaneous decays within the medium generate those problems
-- Rabi oscillations are far more advantageous in that respect. These findings
are particularly relevant in view of a recently proposed experimental
verification of the dynamical Casimir effect. PACS: 42.50.Lc, 03.65.Yz,
03.70.+k, 42.50.Dv.",0408087v2
2004-10-11,Quantizing the damped harmonic oscillator,"We consider the Fermi quantization of the classical damped harmonic
oscillator (dho). In past work on the subject, authors double the phase space
of the dho in order to close the system at each moment in time. For an
infinite-dimensional phase space, this method requires one to construct a
representation of the CAR algebra for each time. We show that unitary dilation
of the contraction semigroup governing the dynamics of the system is a logical
extension of the doubling procedure, and it allows one to avoid the
mathematical difficulties encountered with the previous method.",0410078v1
2004-11-18,Drastic effects of damping mechanisms on the third-order optical nonlinearity,"We have investigated the optical response of superradiant atoms, which
undergoes three different damping mechanisms: radiative dissipation
($\gamma_r$), dephasing ($\gamma_d$), and nonradiative dissipation
($\gamma_n$). Whereas the roles of $\gamma_d$ and $\gamma_n$ are equivalent in
the linear susceptibility, the third-order nonlinear susceptibility drastically
depends on the ratio of $\gamma_d$ and $\gamma_n$: When $\gamma_d \ll
\gamma_n$, the third-order susceptibility is essentially that of a single atom.
Contrarily, in the opposite case of $\gamma_d \gg \gamma_n$, the third-order
susceptibility suffers the size-enhancement effect and becomes proportional to
the system size.",0411129v1
2005-01-19,Stabilizing an atom laser using spatially selective pumping and feedback,"We perform a comprehensive study of stability of a pumped atom laser in the
presence of pumping, damping and outcoupling. We also introduce a realistic
feedback scheme to improve stability by extracting energy from the condensate
and determine its effectiveness. We find that while the feedback scheme is
highly efficient in reducing condensate fluctuations, it usually does not alter
the stability class of a particular set of pumping, damping and outcoupling
parameters.",0501101v1
2005-06-11,Quantum damped oscillator II: Bateman's Hamiltonian vs. 2D Parabolic Potential Barrier,"We show that quantum Bateman's system which arises in the quantization of a
damped harmonic oscillator is equivalent to a quantum problem with 2D parabolic
potential barrier known also as 2D inverted isotropic oscillator. It turns out
that this system displays the family of complex eigenvalues corresponding to
the poles of analytical continuation of the resolvent operator to the complex
energy plane. It is shown that this representation is more suitable than the
hyperbolic one used recently by Blasone and Jizba.",0506091v1
2005-06-27,Entanglement of pair cat states and teleportation,"The entanglement of pair cat states in the phase damping channel is studied
by employing the relative entropy of entanglement. It is shown that the pair
cat states can always be distillable in the phase damping channel. Furthermore,
we analyze the fidelity of teleportation for the pair cat states by using joint
measurements of the photon-number sum and phase difference.",0506217v1
2005-07-21,Entanglement versus mixedness for coupled qubits under a phase damping channel,"Quantification of entanglement against mixing is given for a system of
coupled qubits under a phase damping channel. A family of pure initial joint
states is defined, ranging from pure separable states to maximally entangled
state. An ordering of entanglement measures is given for well defined initial
state amount of entanglement.",0507212v2
2005-10-20,Overdamping by weakly coupled environments,"A quantum system weakly interacting with a fast environment usually undergoes
a relaxation with complex frequencies whose imaginary parts are damping rates
quadratic in the coupling to the environment, in accord with Fermi's ``Golden
Rule''. We show for various models (spin damped by harmonic-oscillator or
random-matrix baths, quantum diffusion, quantum Brownian motion) that upon
increasing the coupling up to a critical value still small enough to allow for
weak-coupling Markovian master equations, a new relaxation regime can occur. In
that regime, complex frequencies lose their real parts such that the process
becomes overdamped. Our results call into question the standard belief that
overdamping is exclusively a strong coupling feature.",0510164v1
2006-06-07,"Comment on ""Optimum Quantum Error Recovery using Semidefinite Programming""","In a recent paper ([1]=quant-ph/0606035) it is shown how the optimal recovery
operation in an error correction scheme can be considered as a semidefinite
program. As a possible future improvement it is noted that still better error
correction might be obtained by optimizing the encoding as well. In this note
we present the result of such an improvement, specifically for the four-bit
correction of an amplitude damping channel considered in [1]. We get a strict
improvement for almost all values of the damping parameter. The method (and the
computer code) is taken from our earlier study of such correction schemes
(quant-ph/0307138).",0606059v1
2006-09-19,Quantum master equations from classical Lagrangians with two stochastic forces,"We show how a large family of master equations, describing quantum Brownian
motion of a harmonic oscillator with translationally invariant damping, can be
derived within a phenomenological approach, based on the assumption that an
environment can be simulated by two classical stochastic forces. This family is
determined by three time-dependent correlation functions (besides the frequency
and damping coefficients), and it includes as special cases the known master
equations, whose dissipative part is bilinear with respect to the operators of
coordinate and momentum.",0609144v3
2006-10-16,Local noise can enhance entanglement teleportation,"Recently we have considered two-qubit teleportation via mixed states of four
qubits and defined the generalized singlet fraction. For single-qubit
teleportation, Badziag {\em et al.} [Phys. Rev. A {\bf 62}, 012311 (2000)] and
Bandyopadhyay [Phys. Rev. A {\bf 65}, 022302 (2002)] have obtained a family of
entangled two-qubit mixed states whose teleportation fidelity can be enhanced
by subjecting one of the qubits to dissipative interaction with the environment
via an amplitude damping channel. Here, we show that a dissipative interaction
with the local environment via a pair of time-correlated amplitude damping
channels can enhance fidelity of entanglement teleportation for a class of
entangled four-qubit mixed states. Interestingly, we find that this enhancement
corresponds to an enhancement in the quantum discord for some states.",0610125v1
2006-11-24,High fidelity transfer of an arbitrary quantum state between harmonic oscillators,"It is shown that by switching a specific time-dependent interaction between a
harmonic oscillator and a transmission line (a waveguide, an optical fiber,
etc.) the quantum state of the oscillator can be transferred into that of
another oscillator coupled to the distant other end of the line, with a
fidelity that is independent of the initial state of both oscillators. For a
transfer time $T$, the fidelity approaches 1 exponentially in $\gamma T$ where
$\gamma$ is a characteristic damping rate. Hence, a good fidelity is achieved
even for a transfer time of a few damping times. Some implementations are
discussed.",0611249v1
2006-12-05,Quantum Brownian motion and the second law of thermodynamics,"We consider a single harmonic oscillator coupled to a bath at zero
temperature. As is well known, the oscillator then has a higher average energy
than that given by its ground state. Here we show analytically that for a
damping model with arbitrarily discrete distribution of bath modes and damping
models with continuous distributions of bath modes with cut-off frequencies,
this excess energy is less than the work needed to couple the system to the
bath, therefore, the quantum second law is not violated. On the other hand, the
second law may be violated for bath modes without cut-off frequencies, which
are, however, physically unrealistic models.",0612038v1
2007-05-08,Minimal qudit code for a qubit in the phase-damping channel,"Using the stabilizer formalism we construct the minimal code into a
D-dimensional Hilbert space (qudit) to protect a qubit against phase damping.
The effectiveness of this code is then studied by means of input-output
fidelity.",0705.1099v3
2007-05-10,Anomalous Diffusion of particles with inertia in external potentials,"Recently a new type of Kramers-Fokker-Planck Equation has been proposed [R.
Friedrich et al. Phys. Rev. Lett. {\bf 96}, 230601 (2006)] describing anomalous
diffusion in external potentials. In the present paper the explicit cases of a
harmonic potential and a velocity-dependend damping are incorporated. Exact
relations for moments for these cases are presented and the asymptotic
behaviour for long times is discussed. Interestingly the bounding potential and
the additional damping by itself lead to a subdiffussive behaviour, while
acting together the particle becomes localized for long times.",0705.1480v1
2007-05-31,Stability of Solutions to Damped Equations with Negative Stiffness,"This article concerns the stability of a model for mass-spring systems with
positive damping and negative stiness. It is well known that when the
coefficients are frozen in time the system is unstable. Here we find conditions
on the variable cofficients to prove stability. In particular, we disprove the
believe that if the eigenvalues of the system change slowly in time the system
remains unstable. We extend some of our results for nonlinear systems.",0705.4670v1
2007-06-13,Polymers in a vacuum,"In a variety of situations, isolated polymer molecules are found in a vacuum
and here we examine their properties. Angular momentum conservation is shown to
significantly alter the average size of a chain and its conservation is only
broken slowly by thermal radiation. The time autocorrelation for monomer
position oscillates with a characteristic time proportional to chain length.
The oscillations and damping are analyzed in detail. Short range repulsive
interactions suppress oscillations and speed up relaxation but stretched chains
still show damped oscillatory time correlations.",0706.2001v1
2007-07-15,Enhancement of Carrier Mobility in Semiconductor Nanostructures by Dielectric Engineering,"We propose a technique for achieving large improvements in carrier mobilities
in 2- and 1-dimensional semiconductor nanostructures by modifying their
dielectric environments. We show that by coating the nanostructures with
high-$\kappa$ dielectrics, scattering from Coulombic impurities can be strongly
damped. Though screening is also weakened, the damping of Coulombic scattering
is much larger, and the resulting improvement in mobilities of carriers can be
as much as an order of magnitude for thin 2D semiconductor membranes, and more
for semiconductor nanowires.",0707.2244v1
2007-07-23,Causal vs. Noncausal Description of Nonlinear Wave Mixing; Resolving the Damping-Sign Controversy,"Frequency-domain nonlinear wave mixing processes may be described either
using response functions whereby the signal is generated after all interactions
with the incoming fields, or in terms of scattering amplitudes where all fields
are treated symetrically with no specific time ordering. Closed Green's
function expressions derived for the two types of signals have different
analytical properties. The recent controversy regarding the sign of radiative
damping in the linear (Kramers Heisenberg) formula is put in a broader context.",0707.3458v1
2007-07-27,Excitation of spin dynamics by spin-polarized current in vortex state disks,"A spin-polarized current with the polarization perpendicular to the plane of
a vortex-state disk results in renormalization of the effective damping for a
given magnetization mode, and the effective damping becomes zero if the current
exceeds a threshold value. The lowest threshold current corresponds to the
lowest frequency vortex gyroscopic mode. For larger values of the current the
dynamic magnetization state is characterized by precession of the vortex around
the dot center with non-small amplitude and higher frequency.",0707.4128v1
2007-09-11,Frequency and damping of the Scissors Mode of a Fermi gas,"We calculate the frequency and damping of the scissors mode in a classical
gas as a function of temperature and coupling strength. Our results show good
agreement with the main features observed in recent measurements of the
scissors mode in an ultracold gas of $^6$Li atoms. The comparison between
theory and experiment involves no fitting parameters and thus allows an
identification of non-classical effects at and near the unitarity limit.",0709.1617v2
2007-09-14,Strong collisionless damping of the low-velocity branch of electromagnetic wave in plasmas with Maxwellian-like electron velocity distribution function,"After approximate replacing of Maxwellian distribution exponent with the
rational polynomial fraction we have obtained precise analytical expression for
and calculated the principal value of logarithmically divergent integral in the
electron wave dispersion equation. At the same time our calculations have shown
the presence of strong collisionless damping of the electromagnetic
low-velocity (electron) wave in plasmas with Maxwellian-like electron velocity
distribution function at some small, of the order of several per cents,
differences from Maxwellian distribution in the main region of large electron
densities, however due to the differences in the distribution tail, where
electron density itself is negligibly small.",0709.2206v1
2007-09-14,"Plasmons, plasminos and Landau damping in a quasiparticle model of the quark-gluon plasma","A phenomenological quasiparticle model is surveyed for 2+1 quark flavors and
compared with recent lattice QCD results. Emphasis is devoted to the effects of
plasmons, plasminos and Landau damping. It is shown that thermodynamic bulk
quantities, known at zero chemical potential, can uniquely be mapped towards
nonzero chemical potential by means of a thermodynamic consistency condition
and a stationarity condition.",0709.2262v2
2007-10-04,Activation of additional energy dissipation processes in the magnetization dynamics of epitaxial chromium dioxide films,"The precessional magnetization dynamics of a chromium dioxide$(100)$ film is
examined in an all-optical pump-probe setup. The frequency dependence on the
external field is used to extract the uniaxial in-plane anisotropy constant.
The damping shows a strong dependence on the frequency, but also on the laser
pump fluency, which is revealed as an important experiment parameter in this
work: above a certain threshold further channels of energy dissipation open and
the damping increases discontinuously. This behavior might stem from spin-wave
instabilities.",0710.0986v2
2007-10-24,Spin dynamics of a trapped spin-1 Bose Gas above the Bose-Einstein transition temperature,"We study collective spin oscillations in a spin-1 Bose gas above the
Bose-Einstein transition temperature. Starting from the Heisenberg equation of
motion, we derive a kinetic equation describing the dynamics of a thermal gas
with the spin-1 degree of freedom. Applying the moment method to the kinetic
equation, we study spin-wave collective modes with dipole symmetry. The dipole
modes in the spin-1 system are found to be classified into the three type of
modes. The frequency and damping rate are obtained as functions of the peak
density. The damping rate is characterized by three relaxation times associated
with collisions.",0710.4419v2
2007-11-19,Nonlinear mode conversion in monodomain magnetic squares,"Modifications of spatial distributions of dynamic magnetization corresponding
to spinwave eigenmodes of magnetic squares subjected to a strong microwave
excitation field have been studied experimentally and theoretically. We show
that an increase of the excitation power leads to a nonlinear generation of
long-wavelength spatial harmonics caused by the nonlinear cross coupling
between the eigenmodes. The analysis of the experimental data shows that this
process is mainly governed by the action of the nonlinear spin-wave damping.
This conclusion is further supported by the numerical calculations based on the
complex Ginzburg-Landau equation phenomenologically taking into account the
nonlinear damping.",0711.2872v1
2007-12-18,Weibel Instabilities in Dense Quantum Plasmas,"The quantum effect on the Weibel instability in an unmagnetized plasma is
presented. Our analysis shows that the quantum effect tends to stabilize the
Weibel instability in the hydrodynamic regime, whereas it produces a new
oscillatory instability in the kinetic regime. A novel effect the quantum
damping, which is associated with the Landau damping, is disclosed. The new
quantum Weibel instability may be responsible for the generation of
non-stationary magnetic fields in compact astrophysical objects as well as in
the forthcoming intense laser-solid density plasma experiments.",0712.2874v1
2008-01-18,A qualitative perspective on the dynamics of a single-Cooper-pair box with a phase-damped cavity,"In a recent paper Dajka, et.al., [J. Phys. A \textbf{40}, F879 (2007)]
predicted that some composite systems can be entangled forever even if coupled
with a thermal bath. We analyze the transient entanglement of a
single-Cooper-pair box biased by a classical voltage and irradiated by a
quantized field and find the unusual feature that the phase-damped cavity can
lead to a long-lived entanglement. The results show an asymptotic value of the
idempotency defect (concurrence) which embodies coherence loss (entanglement
survival), independent of the interaction development by dependent critically
on environment.",0801.2905v2
2008-02-28,Current driven spin-wave instability triggered by the anomalous Hall effect,"We studied the effect of strong electric current on spin waves interacting
relativistically with the current. The spin-wave spectrum is calculated at
arbitrary direction of the wave vector. It is shown that the alternating Hall
current generated by the alternating magnetic moment of the spin waves, reduces
the spin-wave damping. At strong enough unpolarized dc current the damping
changes sign, and the spin-wave amplitude starts to increase exponentially fast
with time. The critical current for the spin-wave instability is determined
mainly by the anomalous Hall effect, and can be much smaller than that for the
spin-torque mechanism of instability.",0802.4150v1
2008-03-31,Spectral Modeling of Magnetohydrodynamic Turbulent Flows,"We present a dynamical spectral model for Large Eddy Simulation of the
incompressible magnetohydrodynamic (MHD) equations based on the Eddy Damped
Quasi Normal Markovian approximation. This model extends classical spectral
Large Eddy Simulations for the Navier-Stokes equations to incorporate general
(non Kolmogorovian) spectra as well as eddy noise. We derive the model for MHD
and show that introducing a new eddy-damping time for the dynamics of spectral
tensors in the absence of equipartition between the velocity and magnetic
fields leads to better agreement with direct numerical simulations, an
important point for dynamo computations.",0803.4499v1
2008-04-10,Trapped Phase-Segregated Bose-Fermi Mixtures and their Collective Excitations,"Recent progress in the field of ultracold gases has allowed the creation of
phase-segregated Bose-Fermi systems. We present a theoretical study of their
collective excitations at zero temperature. As the fraction of fermion to boson
particle number increases, the collective mode frequencies take values between
those for a fully bosonic and those for a fully fermionic cloud, with damping
in the intermediate region. This damping is caused by fermions which are
resonantly driven at the interface.",0804.1759v2
2008-04-14,Size dependence of multipolar plasmon resonance frequencies and damping rates in simple metal spherical nanoparticles,"Multipolar plasmon oscillation frequencies and corresponding damping rates
for nanospheres formed of the simplest free-electron metals are studied. The
possibility of controlling plasmon features by choosing the size and dielectric
properties of the sphere surroundings is discussed. Optical properties of the
studied metals are described within the Drude-Sommerfeld model of the
dielectric function with effective parameters acounting for the contribution of
conduction electrons and of interband transitions. No approximation is made in
respect of the size of a particle; plasmon size characteristics are described
rigorously. The results of our experiment on sodium nanodroplets [1] are
compared with the oscillation frequency size dependence of dipole and
quadrupole plasmon.",0804.2156v1
2008-06-05,Thermally Assisted Spin Hall Effect,"The spin polarized charge transport is systematically analyzed as a thermally
driven stochastic process. The approach is based on Kramers' equation
describing the semiclassical motion under the inclusion of stochastic and
damping forces. Due to the relativistic spin-orbit coupling the damping
experiences a relativistic correction leading to an additional contribution
within the spin Hall conductivity. A further contribution to the conductivity
is originated from the averaged underlying crystal potential, the mean value of
which depends significantly on the electric field. We derive an exact
expression for the electrical conductivity. All corrections are estimated in
lowest order of a relativistic approach and in the linear response regime.",0806.0948v1
2008-06-13,General Solution of the Quantum Damped Harmonic Oscillator II : Some Examples,"In the preceding paper (arXiv : 0710.2724 [quant-ph]) we have constructed the
general solution for the master equation of quantum damped harmonic oscillator,
which is given by the complicated infinite series in the operator algebra
level. In this paper we give the explicit and compact forms to solutions
(density operators) for some initial values. In particular, the compact one for
the initial value based on a coherent state is given, which has not been given
as far as we know. Moreover, some related problems are presented.",0806.2169v1
2008-08-27,Entanglement dynamics of two-qubit system in different types of noisy channels,"In this paper, we study entanglement dynamics of a two-qubit extended
Werner-like state locally interacting with independent noisy channels, i.e.,
amplitude damping, phase damping and depolarizing channels. We show that the
purity of initial entangled state has direct impacts on the entanglement
robustness in each noisy channel. That is, if the initial entangled state is
prepared in mixed instead of pure form, the state may exhibit entanglement
sudden death (ESD) and/or be decreased for the critical probability at which
the entanglement disappear.",0808.3690v1
2008-09-01,Heatons induced by attosecond laser pulses,"In this paper the dynamics of the interaction of attosecond laser pulses with
matter is investigated. It will be shown that the master equation: modified
Klein-Gordon equation describes the propagation of the heatons. Heatons are the
thermal wave packets. When the duration of the laser pulses is of the order of
attosecond the heaton thermal wave packets are nondispersive objects. For
infinite time the heatons are damped with damping factor of the order of
relaxation time for thermal processes.",0809.0204v1
2008-10-09,Heat conduction in 2D strongly-coupled dusty plasmas,"We perform non-equilibrium simulations to study heat conduction in
two-dimensional strongly coupled dusty plasmas. Temperature gradients are
established by heating one part of the otherwise equilibrium system to a higher
temperature. Heat conductivity is measured directly from the stationary
temperature profile and heat flux. Particular attention is paid to the
influence of damping effect on the heat conduction. It is found that the heat
conductivity increases with the decrease of the damping rate, while its
magnitude agrees with previous experimental measurement.",0810.1623v2
2008-10-21,Structurally damped plate and wave equations with random point force in arbitrary space dimensions,"In this paper we consider structurally damped plate and wave equations with
point and distributed random forces. In order to treat space dimensions more
than one, we work in the setting of $L^q$--spaces with (possibly small)
$q\in(1,2)$. We establish existence, uniqueness and regularity of mild and weak
solutions to the stochastic equations employing recent theory for stochastic
evolution equations in UMD Banach spaces.",0810.3898v2
2008-11-05,Spectral function and quasi-particle damping of interacting bosons in two dimensions,"We employ the functional renormalization group to study dynamical properties
of the two-dimensional Bose gas. Our approach is free of infrared divergences,
which plague the usual diagrammatic approaches, and is consistent with the
exact Nepomnyashchy identity, which states that the anomalous self-energy
vanishes at zero frequency and momentum. We recover the correct infrared
behavior of the propagators and present explicit results for the spectral
line-shape, from which we extract the quasi-particle dispersion and damping.",0811.0624v2
2008-11-13,Existence of weak solutions to the Cauchy problem of a semilinear wave equation with supercritical interior source and damping,"In this paper we show existence of finite energy solutions for the Cauchy
problem associated with a semilinear wave equation with interior damping and
supercritical source terms. The main contribution consists in dealing with
super-supercritical source terms (terms of the order of $|u|^p$ with $p\geq 5$
in $n=3$ dimensions), an open and highly recognized problem in the literature
on nonlinear wave equations.",0811.2151v1
2008-11-17,Asymptotic stability and blow up for a semilinear damped wave equation with dynamic boundary conditions,"In this paper we consider a multi-dimensional wave equation with dynamic
boundary conditions, related to the Kelvin-Voigt damping. Global existence and
asymptotic stability of solutions starting in a stable set are proved. Blow up
for solutions of the problem with linear dynamic boundary conditions with
initial data in the unstable set is also obtained.",0811.2783v3
2008-11-19,Weyl laws for partially open quantum maps,"We study a toy model for ""partially open"" wave-mechanical system, like for
instance a dielectric micro-cavity, in the semiclassical limit where ray
dynamics is applicable. Our model is a quantized map on the 2-dimensional
torus, with an additional damping at each time step, resulting in a subunitary
propagator, or ""damped quantum map"". We obtain analogues of Weyl's laws for
such maps in the semiclassical limit, and draw some more precise estimates when
the classical dynamic is chaotic.",0811.3134v2
2008-12-16,A picogram and nanometer scale photonic crystal opto-mechanical cavity,"We describe the design, fabrication, and measurement of a cavity
opto-mechanical system consisting of two nanobeams of silicon nitride in the
near-field of each other, forming a so-called ""zipper"" cavity. A photonic
crystal patterning is applied to the nanobeams to localize optical and
mechanical energy to the same cubic-micron-scale volume. The picrogram-scale
mass of the structure, along with the strong per-photon optical gradient force,
results in a giant optical spring effect. In addition, a novel damping regime
is explored in which the small heat capacity of the zipper cavity results in
blue-detuned opto-mechanical damping.",0812.2953v1
2009-02-03,Freezing of spin dynamics in underdoped cuprates,"The Mori's memory function approach to spin dynamics in doped
antiferromagnetic insulator combined with the assumption of temperature
independent static spin correlations and constant collective mode damping leads
to w/T scaling in a broad range. The theory involving a nonuniversal scaling
parameter is used to analyze recent inelastic neutron scattering results for
underdoped cuprates. Adopting modified damping function also the emerging
central peak in low-doped cuprates at low temperatures can be explained within
the same framework.",0902.0546v1
2009-02-12,"Discrete breathers in a forced-damped array of coupled pendula: Modeling, Computation and Experiment","In this work, we present a mechanical example of an experimental realization
of a stability reversal between on-site and inter-site centered localized
modes. A corresponding realization of a vanishing of the Peierls-Nabarro
barrier allows for an experimentally observed enhanced mobility of the
localized modes near the reversal point. These features are supported by
detailed numerical computations of the stability and mobility of the discrete
breathers in this system of forced and damped coupled pendula. Furthermore,
additional exotic features of the relevant model, such as dark breathers are
briefly discussed.",0902.2129v1
2009-03-08,Enhancement of transmission rates in quantum memory channels with damping,"We consider the transfer of quantum information down a single-mode quantum
transmission line. Such quantum channel is modeled as a damped harmonic
oscillator, the interaction between the information carriers -a train of N
qubits- and the oscillator being of the Jaynes-Cummings kind. Memory effects
appear if the state of the oscillator is not reset after each channel use. We
show that the setup without resetting is convenient in order to increase the
transmission rates, both for the transfer of quantum and classical private
information. Our results can be applied to the micromaser.",0903.1424v1
2009-03-15,A variational approach to strongly damped wave equations,"We discuss a Hilbert space method that allows to prove analytical
well-posedness of a class of linear strongly damped wave equations. The main
technical tool is a perturbation lemma for sesquilinear forms, which seems to
be new. In most common linear cases we can furthermore apply a recent result
due to Crouzeix--Haase, thus extending several known results and obtaining
optimal analyticity angle.",0903.2599v2
2009-03-30,Damping of Exciton Rabi Rotations by Acoustic Phonons in Optically Excited InGaAs/GaAs Quantum Dots,"We report experimental evidence identifying acoustic phonons as the principal
source of the excitation-induced-dephasing (EID) responsible for the intensity
damping of quantum dot excitonic Rabi rotations. The rate of EID is extracted
from temperature dependent Rabi rotation measurements of the ground-state
excitonic transition, and is found to be in close quantitative agreement with
an acoustic-phonon model.",0903.5278v2
2009-05-13,Landau damping,"In this note we present the main results from the recent work
hal-00376547/arXiv:0904.2760, which for the first time establish Landau damping
in a nonlinear context.",0905.2167v2
2009-05-13,Amortissement Landau,"Dans cette note nous pr\'esentons les principaux r\'esultats du r\'ecent
travail hal-00376547/arXiv:0904.2760, o\`u le ph\'enom\`ene d'amortissement
Landau est pour la premi\`ere fois \'etabli dans un contexte non lin\'eaire.
  -----
  In this note we present the main results from the recent work hal-00376547 /
arXiv:0904.2760, which for the first time establish Landau damping in a
nonlinear context.",0905.2168v2
2009-06-27,Effect of Bohm potential on a charged gas,"Bohm's interpretation of Quantum Mechanics leads to the derivation of a
Quantum Kinetic Equation (QKE): in the present work, propagation of waves in
charged quantum gases is investigated starting from this QKE. Dispersion
relations are derived for fully and weakly degenerate fermions and bosons
(these latter above critical temperature), and the differences underlined. Use
of a kinetic equation permits investigation of ""Landau-type"" damping: it is
found that the presence of damping in fermion gases is dependent upon the
degree of degeneracy, whereas it is always present in boson gases. In fully
degenerate fermions a phenomenon appears that is akin to the ""zero sound""
propagation.",0906.5061v1
2009-07-14,Quantum Monty Hall problem under decoherence,"We study the effect of decoherence on quantum Monty Hall problem under the
influence of amplitude damping, depolarizing and dephasing channels. It is
shown that under the effect of decoherence, there is a Nash equilibrium of the
game in case of depolarizing channel for Alice's quantum strategy. Where as in
case of dephasing noise, the game is not influenced by the quantum channel. For
amplitude damping channel, the Bob's payoffs are found symmetrical with maximum
at p=0.5 against his classical strategy. However, it is worth-mentioning that
in case of depolarizing channel, Bob's classical strategy remains always
dominant against any choice of Alice's strategy.",0907.2293v1
2009-08-31,Rigorous Theory of Optical Trapping by an Optical Vortex Beam,"We propose a rigorous theory for the optical trapping by optical vortices,
which is emerging as an important tool to trap mesoscopic particles. The common
perception is that the trapping is solely due to the gradient force, and may be
characterized by three real force constants. However, we show that the optical
vortex trap can exhibit complex force constants, implying that the trapping
must be stabilized by ambient damping. At different damping levels, particle
shows remarkably different dynamics, such as stable trapping, periodic and
aperiodic orbital motions.",0908.4504v1
2009-09-11,Energy decay for the damped wave equation under a pressure condition,"We establish the presence of a spectral gap near the real axis for the damped
wave equation on a manifold with negative curvature. This results holds under a
dynamical condition expressed by the negativity of a topological pressure with
respect to the geodesic flow. As an application, we show an exponential decay
of the energy for all initial data sufficiently regular. This decay is governed
by the imaginary part of a finite number of eigenvalues close to the real axis.",0909.2093v1
2009-09-12,Signature of smooth transition from diabatic to adiabatic states in heavy-ion fusion reactions at deep subbarrier energies,"We propose a novel extension of the standard coupled-channels framework for
heavy-ion reactions in order to analyze fusion reactions at deep subbarrier
incident energies. This extension simulates a smooth transition between the
diabatic two-body and the adiabatic one-body states. To this end, we damp
gradually the off-diagonal part of the coupling potential, for which the
position of the onset of the damping varies for each eigen channel. We show
that this model accounts well for the steep falloff of the fusion cross
sections for the $^{16}$O+$^{208}$Pb, $^{64}$Ni+$^{64}$Ni, and
$^{58}$Ni+$^{58}$Ni reactions.",0909.2298v1
2009-10-05,Construction of quasi-periodic response solutions in forced strongly dissipative systems,"We consider a class of ordinary differential equations describing
one-dimensional quasiperiodically forced systems in the presence of large
damping. We give a fully constructive proof of the existence of response
solutions, that is quasi-periodic solutions which have the same frequency
vector as the forcing. This requires dealing with a degenerate implicit
function equation: we prove that the latter has a unique solution, which can be
explicitly determined. As a by-product we obtain an explicit estimate of the
minimal size of the damping coefficient.",0910.0746v1
2009-10-14,Plasmon-phonon Strongly-Coupled Mode in Epitaxial Graphene,"We report the dispersion measurements, using angle-resolved reflection
electron-energy-loss-spectroscopy (AREELS), on two-dimensional (2D) plasmons in
single and multilayer graphene which couple strongly to surface optical phonon
(FK phonon) modes of silicon carbide substrate. The coupled modes show discrete
dispersion behaviors in the single and bilayer graphene. With increasing
graphene layers on SiC(0001), a transition from plasmon-like dispersion to
phonon-like dispersion is observed. For plasmon-like modes, the dispersion is
strongly damped by electron-hole pair excitations at entering single-particle
continuum, while phonon-like mode is undamped. In the region free of coupling,
the graphene 2D plasmon exhibits acoustic behavior with linear dispersion with
slope and damping determined by the Fermi surface topology.",0910.2735v1
2009-10-23,Collective Enhancement and Suppression of Excitation Decay in Optical Lattices,"We calculate radiative lifetimes of collective electronic excitations of
atoms in an infinite one dimensional lattice. The translational symmetry along
the lattice restricts the photon wave vector component parallel to the lattice
to the exciton wave number and thus the possible emission directions. The
resulting radiation damping rate and emission pattern of the exciton strongly
deviates from independent atom. For some wave numbers and polarizations the
excitons superradiantly decay very fast, while other excitons show zero
radiation damping rate and form propagating meta-stable excitations. Such
states could be directly coupled via tailored evanescent fields from a nearby
fiber.",0910.4501v1
2009-10-24,Global Attractor for Weakly Damped Forced KdV Equation in Low Regularity on T,"In this paper we consider the long time behavior of the weakly damped, forced
Korteweg-de Vries equation in the Sololev spaces of the negative indices in the
periodic case. We prove that the solutions are uniformly bounded in
$\dot{H}^s(\T)$ for $s>-\dfrac{1}{2}$. Moreover, we show that the solution-map
possesses a global attractor in $\dot{H}^s(\T)$ for $s>-\dfrac{1}{2}$, which is
a compact set in $H^{s+3}(\T)$.",0910.4652v1
2009-10-24,Two bodies gravitational system with variable mass and damping-antidamping effect due to star wind,"We study two-bodies gravitational problem where the mass of one of the bodies
varies and suffers a damping-antidamping effect due to star wind during its
motion. A constant of motion, a Lagrangian and a Hamiltonian are given for the
radial motion of the system, and the period of the body is studied using the
constant of motion of the system. An application to the comet motion is given,
using the comet Halley as an example.",0910.4684v2
2009-11-12,A new perspective on supersymmetric inflation,"We consider supersymmetric inflation with the hybrid-type potential. In the
absence of the symmetry that forbids Hubble-induced mass terms, the inflaton
mass will be as large as the Hubble scale during inflation. We consider
gravitational decay of the trigger field as the least decay mode and find that
the damping caused by the dissipation can dominate the friction of the inflaton
when the heavy trigger field is coupled to the inflaton. The dissipative
damping provides a solution to the traditional $\eta$ problem without
introducing additional symmetry and interactions. Considering the spatial
inhomogeneities of the dissipative coefficient, we find that modulated
inflation (modulation of the inflaton velocity) can create significant
curvature perturbations.",0911.2350v1
2009-12-15,Distillability sudden death in qutrit-qutrit systems under amplitude damping,"Recently it has been discovered that certain two-qutrit entangled states
interacting with global and/or multi-local decoherence undergo distillability
sudden death (DSD). We investigate this phenomenon for qutrit-qutrit systems
interacting with statistically independent zero-temperature reservoirs. We show
that certain initially prepared free-entangled states become bound-entangled in
a finite time due to the action of Markovian dissipative environment. Moreover,
in contrast with local dephasing, simple local unitary transformations can
completely avoid distillability sudden death under amplitude damping.",0912.2868v1
2009-12-15,Global Controllability of Multidimensional Rigid Body by Few Torques,"We study global controllability of 'rotating' multidimensional rigid body
(MRB) controlled by application of few torques. Study by methods of geometric
control requires analysis of algebraic structure introduced by the quadratic
term of Euler-Frahm equation. We discuss problems, which arise in the course of
this analysis, and establish several global controllability criteria for damped
and non damped cases.",0912.2900v1
2010-02-05,Damping Effect of Electromagnetic Radiation and Time-Dependent Schrodinger Equation,"The inexactness of the time-dependent Schr\""odinger equation of a charged
particle in an external electromagnetic field is discussed in terms of the
damping effect of the radiation. A possible improvement is to add a nonlinear
term representing this effect to the linear Schr\""odinger equation. Conditions
for the nonlinear term are investigated and it is demonstrated that the
obtained nonlinear Schr\""odinger equation may present state evolutions similar
to the wave-function reduction and transitions between stationary states.",1002.1116v3
2010-02-05,Uniform stabilization in weighted Sobolev spaces for the KdV equation posed on the half-line,"Studied here is the large-time behavior of solutions of the Korteweg-de Vries
equation posed on the right half-line under the effect of a localized damping.
Assuming as in \cite{linares-pazoto} that the damping is active on a set
$(a_0,+\infty)$ with $a_0>0$, we establish the exponential decay of the
solutions in the weighted spaces $L^2((x+1)^mdx)$ for $m\in \N ^*$ and
$L^2(e^{2bx}dx)$ for $b>0$ by a Lyapunov approach. The decay of the spatial
derivatives of the solution is also derived.",1002.1127v1
2010-03-28,Giant magnetic broadening of ferromagnetic resonance in a GMR Co/Ag/Co/Gd quadlayer,"Both magnetic-resonance damping and the giant magnetoresistance effect have
been predicted to be strongly affected by the local density of states in thin
ferromagnetic films. We employ the antiferromagnetic coupling between Co and Gd
to provide a spontaneous change from parallel to antiparallel alignment of two
Co films. A sharp increase in magnetic damping accompanies the change from
parallel to antiparallel alignment, analogous to resistivity changes in giant
magnetoresistance.",1003.5344v1
2010-04-04,Quantum information reclaiming after amplitude damping,"We investigate the quantum information reclaim from the environment after
amplitude damping has occurred. In particular we address the question of
optimal measurement on the environment to perform the best possible correction
on two and three dimensional quantum systems. Depending on the dimension we
show that the entanglement fidelity (the measure quantifying the correction
performance) is or is not the same for all possible measurements and uncover
the optimal measurement leading to the maximum entanglement fidelity.",1004.0497v1
2010-04-09,Validity of Landauer's principle in the quantum regime,"We demonstrate the validity of Landauer's erasure principle in the strong
coupling quantum regime by treating the system-reservoir interaction in a
consistent way. We show that the initial coupling to the reservoir modifies
both energy and entropy of the system and provide explicit expressions for the
latter in the case of a damped quantum harmonic oscillator. These contributions
are related to the Hamiltonian of mean force and dominate in the strong damping
limit. They need therefore to be fully taken into account in any
low-temperature thermodynamic analysis of quantum systems.",1004.1599v1
2010-04-22,Critical exponent for damped wave equations with nonlinear memory,"We consider the Cauchy problem in $\mathbb{R}^n,$ $n\geq 1,$ for a semilinear
damped wave equation with nonlinear memory. Global existence and asymptotic
behavior as $t\rightarrow\infty$ of small data solutions have been established
in the case when $1\leq n\leq3.$ Moreover, we derive a blow-up result under
some positive data in any dimensional space.",1004.3850v4
2010-04-26,Entanglement of a two-particle Gaussian state interacting with a heat bath,"The effect of a thermal reservoir is investigated on a bipartite Gaussian
state. We derive a pre-Lindblad master equation in the non-rotating wave
approximation for the system. We then solve the master equation for a bipartite
harmonic oscillator Hamiltonian with entangled initial state. We show that for
strong damping the loss of entanglement is the same as for freely evolving
particles. However, if the damping is small, the entanglement is shown to
oscillate and eventually tend to a constant nonzero value.",1004.4515v2
2010-04-27,Radiation Damping in a Non-Abelian Strongly-Coupled Gauge Theory,"We study a `dressed' or `composite' quark in strongly-coupled N=4
super-Yang-Mills (SYM), making use of the AdS/CFT correspondence. We show that
the standard string dynamics nicely captures the physics of the quark and its
surrounding quantum non-Abelian field configuration, making it possible to
derive a relativistic equation of motion that incorporates the effects of
radiation damping. From this equation one can deduce a non-standard dispersion
relation for the composite quark, as well as a Lorentz covariant formula for
its rate of radiation.",1004.4912v1
2010-05-21,Quantization of the Damped Harmonic Oscillator Revisited,"We return to the description of the damped harmonic oscillator by means of a
closed quantum theory with a general assessment of previous works, in
particular the Bateman-Caldirola-Kanai model and a new model recently proposed
by one of the authors. We show the local equivalence between the two models and
argue that latter has better high energy behavior and is naturally connected to
existing open-quantum-systems approaches.",1005.4096v1
2010-06-09,Dispersion and damping of two-dimensional dust acoustic waves: Theory and Simulation,"A two-dimensional generalized hydrodynamics (GH) model is developed to study
the full spectrum of both longitudinal and transverse dust acoustic waves (DAW)
in strongly coupled complex (dusty) plasmas, with memory-function-formalism
being implemented to enforce high-frequency sum rules. Results are compared
with earlier theories (such as quasi-localized charge approximation and its
extended version) and with a self-consistent Brownian dynamics simulation. It
is found that the GH approach provides good account, not only for dispersion
relations, but also for damping rates of the DAW modes in a wide range of
coupling strengths, an issue hitherto not fully addressed for dusty plasmas.",1006.1799v1
2010-07-01,Finite time extinction by nonlinear damping for Schrodinger equation,"We consider the Schrodinger equation on a compact manifold, in the presence
of a nonlinear damping term, which is homogeneous and sublinear. For initial
data in the energy space, we construct a weak solution, defined for all
positive time, which is shown to be unique. In the one-dimensional case, we
show that it becomes zero in finite time. In the two and three-dimensional
cases, we prove the same result under the assumption of extra regularity on the
initial datum.",1007.0077v2
2010-07-07,Spin drag Hall effect in a rotating Bose mixture,"We show that in a rotating two-component Bose mixture, the spin drag between
the two different spin species shows a Hall effect. This spin drag Hall effect
can be observed experimentally by studying the out-of-phase dipole mode of the
mixture. We determine the damping of this mode due to spin drag as a function
of temperature. We find that due to Bose stimulation there is a strong
enhancement of the damping for temperatures close to the critical temperature
for Bose-Einstein condensation.",1007.1088v1
2010-08-30,Synthesis of electrical networks interconnecting PZT actuators to damp mechanical vibrations,"This paper proves that it is possible to damp mechanical vibrations of some
beam frames by means of piezoelectric actuators interconnected via passive
networks. We create a kind of electromechanical wave guide where the electrical
velocity group equals the mechanical one thus enabling an electromechanical
energy transfer. Numerical simulations are presented which prove the technical
feasibility of proposed device",1008.5112v1
2010-09-09,The Damped String Problem Revisited,"We revisit the damped string equation on a compact interval with a variety of
boundary conditions and derive an infinite sequence of trace formulas
associated with it, employing methods familiar from supersymmetric quantum
mechanics. We also derive completeness and Riesz basis results (with
parentheses) for the associated root functions under less smoothness
assumptions on the coefficients than usual, using operator theoretic methods
(rather than detailed eigenvalue and root function asymptotics) only.",1009.1858v1
2010-09-15,Anomalous High-Energy Spin Excitations in La2CuO4,"Inelastic neutron scattering is used to investigate the collective magnetic
excitations of the high-temperature superconductor parent antiferromagnet
La2CuO4. We find that while the lower energy excitations are well described by
spin-wave theory, including one- and two-magnon scattering processes, the
high-energy spin waves are strongly damped near the (1/2,0) position in
reciprocal space and merge into a momentum dependent continuum. This anomalous
damping indicates the decay of spin waves into other excitations, possibly
unbound spinon pairs.",1009.2915v1
2010-10-05,Damping of dHvA oscillations and vortex-lattice disorder in the peak-effect region of strong type-II superconductors,"The phenomenon of magnetic quantum oscillations in the superconducting state
poses several questions that still defy satisfactory answers. A key
controversial issue concerns the additional damping observed in the vortex
state. Here, we show results of \mu SR, dHvA, and SQUID magnetization
measurements on borocarbide superconductors, indicating that a sharp drop
observed in the dHvA amplitude just below H_{c2} is correlated with enhanced
disorder of the vortex lattice in the peak-effect region, which significantly
enhances quasiparticle scattering by the pair potential.",1010.0929v1
2010-10-21,Classical behavior of strongly correlated Fermi systems near a quantum critical point. Transport properties,"The low-temperature kinetics of the strongly correlated electron liquid
inhabiting a solid is analyzed. It is demonstrated that a softly damped branch
of transverse zero sound emerges when several bands cross the Fermi surface
simultaneously near a quantum critical point at which the density of states
diverges. Suppression of the damping of this branch occurs due to a mechanism
analogous to that affecting the phonon mode in solids at room temperature,
giving rise to a classical regime of transport at extremely low temperatures in
the strongly correlated Fermi system.",1010.4547v1
2010-10-26,Open Quantum Systems in Noninertial Frames,"We study the effects of decoherence on the entanglement generated by Unruh
effect in noninertial frames by using bit flip, phase damping and depolarizing
channels. It is shown that decoherence strongly influences the initial state
entanglement. The entanglement sudden death can happens irrespective of the
acceleration of the noninertial frame under the action of phase flip and phase
damping channels. It is investigated that an early sudden death happens for
large acceleration under the depolarizing environment. Moreover, the
entanglement increases for a highly decohered phase flip channel.",1010.5395v1
2010-11-17,Faint Resonantly Scattered Lyman Alpha Emission from the Absorption Troughs of Damped Lyman Alpha Systems at z ~ 3,"We demonstrate that the Lyman alpha emission in the absorption troughs of a
large sample of stacked damped Lyman alpha absorption systems (DLAS) presented
by Rahmani et al (2010) is consistent with the spectral profiles and
luminosities of a recently detected population of faint Lyman alpha emitters at
z ~ 3. This result supports the suggestion that the faint emitters are to be
identified with the host galaxies of DLAS at these redshifts.",1011.4061v1
2010-12-19,Quantum damping of Fermi-Pasta-Ulam revivals in ultracold Bose gases,"We propose an experimental scheme for studying the Fermi-Pasta-Ulam (FPU)
phenomenon in a quantum mechanical regime using ultracold atoms. Specifically,
we suggest and analyze a setup of one-dimensional Bose gases confined into an
optical lattice. The strength of quantum fluctuations is controlled by tuning
the number of atoms per lattice sites (filling factor). By simulating the
real-time dynamics of the Bose-Hubbard model by means of the exact numerical
method of time-evolving block decimation, we investigate the effects of quantum
fluctuations on the FPU recurrence and show that strong quantum fluctuations
cause significant damping of the FPU oscillation.",1012.4159v1
2010-12-21,Pullback attractors for a singularly nonautonomous plate equation,"We consider the family of singularly nonautonomous plate equation with
structural damping \[ u_{tt} + a(t,x)u_{t} + (- \Delta) u_{t} + (-\Delta)^{2} u
+ \lambda u = f(u), \] in a bounded domain $\Omega \subset \R^n$, with Navier
boundary conditions. When the nonlinearity $f$ is dissipative we show that this
problem is globally well posed in $H^2_0(\Omega) \times L^2(\Omega)$ and has a
family of pullback attractors which is upper-semicontinuous under small
perturbations of the damping $a$.",1012.4749v1
2010-12-30,On rotational solutions for elliptically excited pendulum,"The author considers the planar rotational motion of the mathematical
pendulum with its pivot oscillating both vertically and horizontally, so the
trajectory of the pivot is an ellipse close to a circle. The analysis is based
on the exact rotational solutions in the case of circular pivot trajectory and
zero gravity. The conditions for existence and stability of such solutions are
derived. Assuming that the amplitudes of excitations are not small while the
pivot trajectory has small ellipticity the approximate solutions are found both
for high and small linear damping. Comparison between approximate and numerical
solutions is made for different values of the damping parameter.",1101.0062v1
2011-01-28,Entanglement between two atoms in a damping Jaynes-Cummings model,"The entanglement between two atoms in a damping Jaynes-Cummings model is
investigated with different decay coefficients of the atoms from the upper
level to other levels under detuning between the atomic frequency and the
quantized light field frequency. The results indicate that the larger the decay
coefficient is, the more quickly the entanglement decays. The detuning enhances
the entanglement's average value at long times. More importantly, the results
show that the so-called sudden death effect can be avoided by enhancing the
detuning or the decay coefficient.",1101.5522v1
2011-03-10,Laser-like vibrational instability in rectifying molecular conductors,"We study the damping of molecular vibrations due to electron-hole pair
excitations in donor-acceptor(D-A) type molecular rectifiers. At finite voltage
additional non-equilibrium electron-hole pair excitations involving both
electrodes become possible, and contribute to the stimulated emission and
absorption of phonons. We point out a generic mechanism for D-A molecules,
where the stimulated emission can dominate beyond a certain voltage due to
inverted position of the D and A quantum resonances. This leads to
current-driven amplification (negative damping) of the phonons similar to
laser-action. We investigate the effect in realistic molecular rectifier
structures using first principles calculations.",1103.1990v1
2011-03-11,Spin Transport in Polaronic and Superfluid Fermi Gases,"We present measurements of spin transport in ultracold gases of fermionic
lithium-6 in a mixture of two spin states at a Feshbach resonance. In
particular, we study the spin dipole mode, where the two spin components are
displaced from each other against a harmonic restoring force. We prepare a
highly-imbalanced, or polaronic, spin mixture with a spin dipole excitation and
observe strong, unitarity limited damping of the spin dipole mode. In gases
with small spin imbalance, below the Pauli limit for superfluidity, we observe
strongly damped spin flow despite the presence of a superfluid core.",1103.2337v1
2011-03-14,Tidal Evolution of a Secularly Interacting Planetary System,"In a multi-planet system, a gradual change in one planet's semi-major axis
will affect the eccentricities of all the planets, as angular momentum is
distributed via secular interactions. If tidal dissipation in the planet is the
cause of the change in semi-major axis, it also damps that planet's
eccentricity, which in turn also contributes to the evolution of all the
eccentricities. Formulae quantifying the combined effects on the whole system
due to semi-major axis changes, as well as eccentricity damping, are derived
here for a two-planet system. The CoRoT 7 system is considered as an example.",1103.2794v1
2011-03-30,Damping in quantum love affairs,"In a series of recent papers we have used an operatorial technique to
describe stock markets and, in a different context, {\em love affairs} and
their time evolutions. The strategy proposed so far does not allow any dumping
effect. In this short note we show how, within the same framework, a strictly
non periodic or quasi-periodic effect can be introduced in the model by
describing in some details a linear Alice-Bob love relation with damping.",1103.5907v1
2011-04-03,Spatially confined Bloch oscillations in semiconductor superlattices,"In a semiconductor superlattice with long scattering times, damping of Bloch
oscillations due to scattering is so small that convective nonlinearities may
compensate it and Bloch oscillations persist even in the hydrodynamic regime.
In this case, numerical solutions show that there are stable Bloch oscillations
confined to a region near the collector with inhomogeneous field, charge,
current density and energy density profiles. These Bloch oscillations disappear
when damping due to inelastic collisions becomes sufficiently strong.",1104.0429v2
2011-04-06,Relativistic magnetic reconnection at X-type neutral points,"Relativistic effects in the oscillatory damping of magnetic disturbances near
two-dimensional X-points are investigated. By taking into account displacement
current, we study new features of extremely magnetized systems, in which the
Alfv\'en velocity is almost the speed of light. The frequencies of the
least-damped mode are calculated using linearized relativistic MHD equations
for wide ranges of the Lundquist number S and the magnetization parameter
$\sigma$. These timescales approach constant values in the large resistive
limit: the oscillation time becomes a few times the light crossing time,
irrespective of $\sigma$, and the decay time is proportional to $\sigma$ and
therefore is longer for a highly magnetized system.",1104.1003v1
2011-04-06,Observed damping of the slow magnetoacoustic mode,"Spectroscopic and stereoscopic imaging observations of slow magnetoacoustic
wave propagation within a coronal loop are investigated to determine the decay
length scale of the slow magnetoacoustic mode in three dimensions and the
density profile within the loop system. The slow wave is found to have an
e-folding decay length scale of $20,000^{+4000}_{-3000}$km with a uniform
density profile along the loop base. These observations place quantitive
constraints on the modelling of wave propagation within coronal loops.
Theoretical forward modelling suggests that magnetic field line divergence is
the dominant damping factor and thermal conduction is insufficient, given the
observed parameters of the coronal loop temperature, density and wave mode
period.",1104.1100v1
2011-04-17,Stochastic Wave Equations with Nonlinear Damping and Source Terms,"In this paper, we discuss an initial boundary value problem for the
stochastic wave equation involving the nonlinear damping term $|u_t|^{q-2}u_t$
and a source term of the type $|u|^{p-2}u$. We firstly establish the local
existence and uniqueness of solution by the Galerkin approximation method and
show that the solution is global for $q\geq p$. Secondly, by an appropriate
energy inequality, the local solution of the stochastic equations will blow up
with positive probability or explosive in energy sense for $p>q$.",1104.3279v2
2011-05-07,Cooperative scattering measurement of coherence in a spatially modulated Bose gas,"Correlations of a Bose gas released from an optical lattice are measured
using superradiant scattering. Conditions are chosen so that after initial
incident light pumping at the Bragg angle for diffraction, due to matter wave
amplification and mode competition, superradiant scattering into the Bragg
diffracted mode is preponderant. A temporal analysis of the superradiant
scattering gain reveals periodical oscillations and damping due to the initial
lack of coherence between lattice sites. Such damping is used for
characterizing first order spatial correlations in our system with a precision
of one lattice period.",1105.1425v1
2011-06-09,Hamiltonian of mean force for damped quantum systems,"We consider a quantum system linearly coupled to a reservoir of harmonic
oscillators. For finite coupling strengths, the stationary distribution of the
damped system is not of the Gibbs form, in contrast to standard thermodynamics.
With the help of the quantum Hamiltonian of mean force, we quantify this
deviation exactly for a harmonic oscillator and provide approximations in the
limit of high and low temperatures, and weak and strong couplings. Moreover, in
the semiclassical regime, we use the quantum Smoluchowski equation to obtain
results valid for any potential. We, finally, give a physical interpretation of
the deviation in terms of the initial system-reservoir coupling.",1106.1775v1
2011-06-17,Current effect on magnetization oscillations in a ferromagnet - antiferromagnet junction,"Spin-polarized current effect is studied on the static and dynamic
magnetization of the antiferromagnet in a ferromagnet - antiferromagnet
junction. The macrospin approximation is generalized to antiferromagnets.
Canted antiferromagnetic configuration and resulting magnetic moment are
induced by an external magnetic field. The resonance frequency and damping are
calculated, as well as the threshold current density corresponding to
instability appearance. A possibility is shown of generating low-damping
magnetization oscillations in terahertz range. The fluctuation effect is
discussed on the canted antiferromagnetic configuration.",1106.3519v1
2011-06-23,Dissipation evidence for the quantum damped harmonic oscillator via pseudo-bosons,"It is known that a self-adjoint, time-independent hamiltonian can be defined
for the quantum damped harmonic oscillator. We show here that the two vacua
naturally associated to this operator, when expressed in terms of
pseudo-bosonic lowering and raising operators, appear to be non
square-integrable. This fact is interpreted as the evidence of the dissipation
effect of the classical oscillator at a purely quantum level.",1106.4638v1
2011-07-15,"Aspects of General Relativity: Pseudo-Finsler extensions, Quasi-normal frequencies and Multiplication of tensorial distributions","This thesis is based on three different projects, all of them are directly
linked to the classical general theory of relativity, but they might have
consequences for quantum gravity as well. The first chapter deals with
pseudo-Finsler geometric extensions of the classical theory, these being ways
of naturally representing high-energy Lorentz symmetry violations. The second
chapter deals with the problem of highly damped quasi-normal modes related to
different types of black hole spacetimes. Besides the astrophysical meaning of
the quasi-normal modes, there are conjectures about the link between the highly
damped modes and black hole thermodynamics. The third chapter is related to the
topic of multiplication of tensorial distributions.",1107.2978v1
2011-08-08,"Synchrotron radiation damping, intrabeam scattering and beam-beam simulations for HE-LHC","The proposed High-Energy LHC project presents an unusual combination of
strong synchrotron radiation (SR) damping and intrabeam scattering (IBS), which
is not seen in present-day hadron colliders. The subject of investigation
reported in this paper was the simulation of beam-beam effect for the HE-LHC
parameters. Parameters of SR and IBS are calculated, and the luminosity
evolution is simulated in the absence of beambeam interaction. Then, a
weak-strong numerical simulation is used to predict the effect of beam-beam
interaction on particle losses and emittance evolution.",1108.1644v1
2011-09-08,On the attenuation coefficient of monomode periodic waveguides,"It is widely accepted that, on ensemble average, the transmission T of guided
modes decays exponentially with the waveguide length L due to small
imperfections, leading to the important figure of merit defined as the
attenuation-rate coefficient alpha = -<ln(T)>/L. In this letter, we evidence
that the exponential-damping law is not valid in general for periodic monomode
waveguides, especially as the group velocity decreases. This result that
contradicts common beliefs and experimental practices aiming at measuring alpha
is supported by a theoretical study of light transport in the limit of very
small imperfections, and by numerical results obtained for two waveguide
geometries that offer contrasted damping behaviours.",1109.1642v1
2011-09-09,Delocalization of slowly damped eigenmodes on Anosov manifolds,"We look at the properties of high frequency eigenmodes for the damped wave
equation on a compact manifold with an Anosov geodesic flow. We study
eigenmodes with spectral parameters which are asymptotically close enough to
the real axis. We prove that such modes cannot be completely localized on
subsets satisfying a condition of negative topological pressure. As an
application, one can deduce the existence of a ""strip"" of logarithmic size
without eigenvalues below the real axis under this dynamical assumption on the
set of undamped trajectories.",1109.1909v2
2011-10-18,Life times and chirality of spin-waves in antiferromagnetic and ferromagnetic FeRh: time depedent density functional theory perspective,"The study of the spin excitations in antiferromagnetic (AFM) and
ferromagnetic (FM) phases of FeRh is reported. We demonstrate that although the
Fe atomic moments are well defined there is a number of important phenomena
absent in the Heisenberg description: Landau damping of spin waves, large Rh
moments induced by the AFM magnons, the formation of the optical magnons
terminated by Stoner excitations. We relate the properties of the spin-wave
damping to the features of the Stoner continuum and compare the chirality of
the spin excitations in AFM, FM and paramagnetic (PM) systems.",1110.3913v1
2011-10-21,Environment-Assisted Error Correction of Single-Qubit Phase Damping,"Open quantum system dynamics of random unitary type may in principle be fully
undone. Closely following the scheme of environment-assisted error correction
proposed by Gregoratti and Werner [M. Gregoratti and R. F. Werner, J. Mod. Opt.
50(6), 915-933 (2003)], we explicitly carry out all steps needed to invert a
phase-damping error on a single qubit. Furthermore, we extend the scheme to a
mixed-state environment. Surprisingly, we find cases for which the uncorrected
state is closer to the desired state than any of the corrected ones.",1110.4806v1
2011-11-01,Damping of tensor modes in inflation,"We discuss the damping of tensor modes due to anisotropic stress in
inflation. The effect is negligible in standard inflation and may be
significantly large in inflation models that involve drastic production of
free-streaming particles.",1111.0295v3
2011-11-04,Global uniform asymptotic stabilization and k-exponential trajectory tracking of underactuated surface ships with non-diagonal inertia/damping matrices,"In this work, we investigate the state stabilization and trajectory tracking
problems of underactuated surface ships with full state model of having
non-diagonal inertia and damping matrices. By combining the novel state
transformations, the direct Lyapunov approach, and the nonlinear time-varying
tools, the stabilization and the trajectory tracking controllers are developed
respectively guaranteeing global uniform asymptotic convergence of the state to
the desired set point and global exponential convergence to the desired
reference trajectory via mild persistent exciting conditions. Simulation
examples are given to illustrate the effectiveness of the proposed control
schemes.",1111.1029v1
2011-11-08,The entropy of large black holes in loop quantum gravity: A combinatorics/analysis approach,"The issue of a possible damping of the entropy periodicity for large black
holes in Loop Quantum Gravity is highly debated. Using a combinatorics/analysis
approach, we give strong arguments in favor of this damping, at least for
prescriptions where the projection constraint is not fully implemented. This
means that black holes in loop gravity exhibit an asymptotic Bekenstein-Hawking
behavior, provided that a consistent choice of the Immirzi constant is made.",1111.1975v1
2011-11-15,Finite Size Effects of the Surface States in a Lattice Model of Topological Insulator,"Energy gap and wave function in thin films of topological insulator is
studied, based on tight--binding model. It is revealed that thickness
dependence of the magnitude of energy gap is composed of damping and
oscillation. The damped behavior originates from the presence of gapless
surface Dirac cone in the infinite thickness limit. On the other hand, the
oscillatory behavior stems from electronic properties in the thin thickness
limit.",1111.3528v2
2011-11-23,Pumping the eccentricity of exoplanets by tidal effect,"Planets close to their host stars are believed to undergo significant tidal
interactions, leading to a progressive damping of the orbital eccentricity.
Here we show that, when the orbit of the planet is excited by an outer
companion, tidal effects combined with gravitational interactions may give rise
to a secular increasing drift on the eccentricity. As long as this secular
drift counterbalances the damping effect, the eccentricity can increase to high
values. This mechanism may explain why some of the moderate close-in exoplanets
are observed with substantial eccentricity values.",1111.5486v1
2011-11-30,Shear viscosity and damping of collective modes in a two-dimensional Fermi gas,"We compute the shear viscosity of a two dimensional Fermi gas interacting via
a short range potential with scattering length $a_{2d}$ in kinetic theory. We
find that kinetic theory predicts that the shear viscosity to entropy density
ratio of a strongly interacting two dimensional gas is comparable to that of
the three dimensional unitary gas. We use our results to compute the damping of
collective modes in a trapped Fermi gas, and compare to experimental data
recently obtained in E. Vogt et al., arXiv:1111.1173.",1111.7242v2
2011-12-13,Drastically suppressing the error of ballistic readout of qubits,"The thermal jitter of transmission of magnetic flux quanta in long Josephson
junctions is studied. While for large-to-critical damping and small values of
bias current the physically obvious dependence of the jitter versus length
$\sigma\sim\sqrt{L}$ is confirmed, for small damping starting from the
experimentally relevant $\alpha=0.03$ and below strong deviation from
$\sigma\sim\sqrt{L}$ is observed, up to nearly complete independence of the
jitter versus length, which is exciting from fundamental point of view, but
also intriguing from the point of view of possible applications.",1112.2805v1
2011-12-15,Diffusion-Induced Oscillations of Extended Defects,"From a simple model for the driven motion of a planar interface under the
influence of a diffusion field we derive a damped nonlinear oscillator equation
for the interface position. Inside an unstable regime, where the damping term
is negative, we find limit-cycle solutions, describing an oscillatory
propagation of the interface. In case of a growing solidification front this
offers a transparent scenario for the formation of solute bands in binary
alloys, and, taking into account the Mullins-Sekerka instability, of banded
structures.",1112.3669v1
2011-12-31,Stability of cnoidal waves in the parametrically driven nonlinear Schrödinger equation,"The parametrically driven, damped nonlinear Schr\""odinger equation has two
cn- and two dn-wave solutions. We show that one pair of the cn and dn solutions
is unstable for any combination of the driver's strength, dissipation
coefficient and spatial period of the wave; this instability is against
periodic perturbations. The second dn-wave solution is shown to be unstable
against antiperiodic perturbations --- in a certain region of the parameter
space. We also consider quasiperiodic perturbations with long modulation
wavelength, in the limit where the driving strength is only weakly exceeding
the damping coefficient.",1201.0263v1
2012-01-03,Dynamics of DNA Bubble in Viscous Medium,"The damping effect to the DNA bubble is investigated within the
Peyrard-Bishop model. In the continuum limit, the dynamics of the bubble of DNA
is described by the damped nonlinear Schrodinger equation and studied by means
of variational method. It is shown that the propagation of solitary wave
pattern is not vanishing in a non-viscous system. Inversely, the solitary wave
vanishes soon as the viscous force is introduced.",1201.0689v2
2012-01-18,Magnetohydrodynamic Waves in Partially Ionized Prominence Plasmas,"Prominences or filaments are cool clouds of partially ionized plasma living
in the solar corona. Ground- and space-based observations have confirmed the
presence of oscillatory motions in prominences and they have been interpreted
in terms of magnetohydrodynamic (MHD) waves. Existing observational evidence
points out that these oscillatory motions are damped in short spatial and
temporal scales by some still not well known physical mechanism(s). Since
prominences are partially ionized plasmas, a potential mechanism able to damp
these oscillations could be ion-neutral collisions. Here, we will review the
work done on the effects of partial ionization on MHD waves in prominence
plasmas.",1201.3752v1
2012-01-26,Inhomogeneous spin diffusion in traps with cold atoms,"The spin diffusion and damped oscillations are studied in the collision of
two spin polarized clouds of cold atoms with resonant interactions. The strong
density dependence of the diffusion coefficient leads to inhomogeneous spin
diffusion that changes from central to surface spin flow as the temperature
increases. The inhomogeneity and the smaller finite trap size significantly
reduce the spin diffusion rate at low temperatures. The resulting spin
diffusion rates, spin drag and initial damped oscillations are compatible with
measurements at low to high temperatures for resonant attractive interactions
but are incompatible with a metastable ferromagnetic phase.",1201.5526v2
2012-01-30,Volatility-dependent damping of evaporation-driven Bénard-Marangoni instability,"The interface between a pure liquid and its vapor is usually close to
saturation temperature, hence strongly hindering any thermocapillary flow. In
contrast, when the gas phase contains an inert gas such as air,
surface-tension-driven convection is easily observed. We here reconcile these
two facts by studying the corresponding crossover experimentally, as a function
of a new dimensionless number quantifying the degree of damping of interfacial
temperature fluctuations. Critical conditions are in convincing agreement with
a simple nonlocal one-sided model, in quite a range of evaporation rates.",1201.6334v1
2012-02-18,Dynamics of multi-modes maximum entangled coherent state over amplitude damping channel,"The dynamics of maximum entangled coherent state travels through an amplitude
damping channel is investigated. For small values of the transmissivity rate
the travelling state is very fragile to this noise channel, where it suffers
from the phase flip error with high probability. The entanglement decays
smoothly for larger values of the transmissivity rate and speedily for smaller
values of this rate. As the number of modes increases, the travelling state
over this noise channel loses its entanglement hastily. The odd and even states
vanish at the same value of the field intensity.",1202.4089v1
2012-03-02,Damping-Antidamping Effect on Comets Motion,"We make an observation about Galilean transformation on a 1-D mass variable
systems which leads us to the right way to deal with mass variable systems.
Then using this observation, we study two-bodies gravitational problem where
the mass of one of the bodies varies and suffers a damping-antidamping effect
due to star wind during its motion. For this system, a constant of motion, a
Lagrangian and a Hamiltonian are given for the radial motion, and the period of
the body is studied using the constant of motion of the system. Our theoretical
results are applied to Halley's comet.",1203.0495v2
2012-03-03,Necessary and sufficient conditions of freezing phenomena of quantum discord under phase damping,"We investigate the freezing phenomenon of quantum discord occurring in phase
damping noise processes. By relating the expression of the time variation of
the discord to the convex function of relative entropy, we obtain the necessary
and sufficient conditions of the phenomenon for standard Bell-diagonal states.
These conditions are applicable also to the phenomenon occurring in a
non-Markovian dephasing process. Moreover, we show that the same condition and
phenomenon coincide in a new sort of Bell-diagonal states beyond the standard
form.",1203.0650v3
2012-03-06,Universal anomalous diffusion of weakly damped particles,"We show that anomalous diffusion arises in two different models for the
motion of randomly forced and weakly damped particles: one is a generalisation
of the Ornstein-Uhlenbeck process with a random force which depends on position
as well as time, the other is a generalisation of the Chandrasekhar-Rosenbluth
model of stellar dynamics, encompassing non-Coulombic potentials. We show that
both models exhibit anomalous diffusion of position $x$ and momentum $p$ with
the same exponents: $<x^2> \sim C_x t^2$ and $<p^2> \sim C_p t^{2/5}$. We are
able to determine the prefactors $C_x$, $C_p$ analytically.",1203.1354v1
2012-03-09,Collective Light Emission of a Finite Size Atomic Chain,"Radiative properties of collective electronic states in a one dimensional
atomic chain are investigated. Radiative corrections are included with
emphasize put on the effect of the chain size through the dependence on both
the number of atoms and the lattice constant. The damping rates of collective
states are calculated in considering radiative effects for different values of
the lattice constant relative to the atomic transition wave length. Especially
the symmetric state damping rate as a function of the number of the atoms is
derived. The emission pattern off a finite linear chain is also presented. The
results can be adopted for any chain of active material, e.g., a chain of
semiconductor quantum dots or organic molecules on a linear matrix.",1203.2094v1
2012-03-13,Monopoles in ferromagnetic metals,"The aim of this short review is to give an introduction to monopoles and to
present theoretical derivation of two particular monopoles in ferromagnetic
metals, a hedgehog monopole and a spin damping monopole. Spin damping monopoles
can be generated in simple systems such as a junction of a ferromagnet and a
heavy element with strong spin-orbit interaction such as Pt. This monopole is
essential in coupling electronics with magnetism, and is thus expected to play
an essential role in spintronics.",1203.2709v1
2012-03-16,Report from KEK (High gradient study results from Nextef),"Most up-to-date high gradient test of the CLIC prototype structures as of
September 2011 is described in this report. The ""T24"" undamped structure showed
fast processing time, still-decreasing breakdown rate and its breakdown rate
was estimated to be as low as the CLIC requirement. The ""TD24"" damped structure
showed not so excellent high gradient performance as undamped ""T24"" but the
characteristics was much improved than the damped ""TD18"" structure with higher
magnetic field. Further R&D is needed and we present some of the present
efforts at KEK.",1203.3626v1
2012-03-30,Energy decay rates for solutions of the wave equation with linear damping in exterior domain,"In this paper we study the behavior of the energy of solutions of the wave
equation with localized damping in exterior domain. We assume that the damper
is positive at infinity. Under the Geometric Control Condition of Bardos et al
(1992), we prove that: 1) The total energy decay like O(1/t) and L^2-norm is
bounded for the solutions with initial data in (H_{0}^{1},L^{2}). 2) The total
energy and the square of the L^2-norm, repectively, decay like O(1/t^{2}) and
O(1/t) for a kind of the weighted initial data.",1203.6780v4
2012-04-03,Modification in Silling's Peridynamic Formulation of Elasticity Theory for Discontinuities and Long-Range Forces,"We suggest modified version of Silling's peridynamic equation of motion
within the framework of Silling's peridynamics formulation (J. Mech. Phys.
Solids {\bf 48}, pp.175-209, 2000) of elasticity theory. The modified equation
contains an additional damping force term. This term can eliminate artificial
oscillations in displacement field at large values of time as predicted by
Silling's peridynamic equation.",1204.0612v2
2012-04-06,Experimental signatures of the quantum-classical transition in a nanomechanical oscillator modeled as a damped driven double-well problem,"We demonstrate robust and reliable signatures for the transition from quantum
to classical behavior in the position probability distribution of a damped
double-well system using the Qunatum State Diffusion approach to open quantum
systems. We argue that these signatures are within experimental reach, for
example in a doubly-clamped nanomechanical beam.",1204.1397v1
2012-05-31,The impact of fill patterns on the fast ion instability in the ILC damping ring,"The ions produced via collisional ionization of the residual gas molecules in
vacuum pipe with the circulating electron beam have deleterious effect on the
beam properties and may become a limiting factor for the machine's performance.
For the electron damping ring of the International Linear Collider (ILC), the
ion instability is noticeable due to the ultra-low beam emittance with many
bunches operation. In this paper, the different beam fill patterns are
investigated and their effects on the fast ion instability are discussed. The
simulations show that the mini train fill patterns can reduce the growth of the
fast ion instability significantly.",1205.6977v1
2012-06-11,Damping and decoherence of Fock states in a nanomechanical resonator due to two level systems,"We numerically investigate the decay of initial quantum Fock states and their
superpositions for a mechanical resonator mode coupled to an environment
comprising interacting, damped tunneling two level system (TLS) defects. The
cases of one, three, and six near resonant, interacting TLS's are considered in
turn and it is found that the resonator displays Ohmic bath like decay behavior
with as few as three TLS's.",1206.2200v1
2012-07-13,Magnetic relaxation in bilayers of yttrium iron garnet/platinum due to the dynamic coupling at the interface,"We show that in ferromagnetic (FM)/normal metal (NM) bilayers the dynamic
coupling at the interface transfers an additional magnetic relaxation from the
heavily damped motion of the conduction electron spins in the NM layer to the
FM spins. While the FM relaxation rates due to two-magnon scattering and spin
pumping decrease rapidly with increasing FM film thickness, the damping due to
the dynamic coupling does not depend on the FM film thickness. The proposed
mechanism explains the very large broadening of ferromagnetic resonance lines
in thick films of yttrium iron garnet after deposition of a Pt layer.",1207.3330v1
2012-07-23,Quantum interference induced by initial system-environment correlations,"We investigate the quantum interference induced by a relative phase in the
correlated initial state of a system which consists in a two-level atom
interacting with a damped mode of the radiation field. We show that the initial
relative phase has significant effects on both the evolution of the atomic
excited-state population and the information flow between the atom and the
reservoir, as quantified by the trace distance. Furthermore, by considering two
two-level atoms interacting with a common damped mode of the radiation field,
we highlight how initial relative phases can affect the subsequent entanglement
dynamics.",1207.5474v1
2012-07-31,An analytic description of the damping of gravitational waves by free streaming neutrinos,"We provide an analytic solution to the general wavelength
integro-differential equation describing the damping of tensor modes of
gravitational waves due to free streaming neutrinos in the early universe. Our
result is expressed as a series of spherical Bessel functions whose
coefficients are functions of the reduced wave number $Q$.",1207.7285v4
2012-08-21,Dancing bunches as Van Kampen modes,"Van Kampen modes are eigen-modes of Jeans-Vlasov equation. Their spectrum
consists of continuous and, possibly, discrete parts. Onset of a discrete van
Kampen mode means emergence of a coherent mode without any Landau damping;
thus, even a tiny couple-bunch wake is sufficient to drive instability.
Longitudinal instabilities observed at Tevatron, RHIC and SPS can be explained
as loss of Landau damping (LLD), which is shown here to happen at fairly low
impedances. For repulsive wakes and single-harmonic RF, LLD is found to be
extremely sensitive to steepness of the bunch distribution function at small
amplitudes. Based on that, a method of beam stabilization is suggested.",1208.4338v1
2012-08-22,Polynomial stabilization of some dissipative hyperbolic systems,"We study the problem of stabilization for the acoustic system with a
spatially distributed damping. Imposing various hypotheses on the structural
properties of the damping term, we identify either exponential or polynomial
decay of solutions with growing time. Expo- nential decay rate is shown by
means of a time domain approach, reducing the problem to an observability
inequality to be verified for solutions of the associated conservative problem.
In addition, we show a polynomial stabilization result, where the proof uses a
frequency domain method and combines a contradiction argument with the
multiplier technique to carry out a special analysis for the resolvent.",1208.4485v1
2012-09-07,Quantum Damped Harmonic Oscillator,"In this chapter we treat the quantum damped harmonic oscillator, and study
mathematical structure of the model, and construct general solution with any
initial condition, and give a quantum counterpart in the case of taking
coherent state as an initial condition.
  This is a simple and good model of Quantum Mechanics with dissipation which
is important to understand real world, and readers will get a powerful weapon
for Quantum Physics.",1209.1437v1
2012-10-08,"Comment on ""Thermal fluctuations of magnetic nanoparticles"" [arXiv:1209.0298]","We comment on some misleading and biased statements appearing in the
manuscript arXiv:1209.0298 (""Thermal fluctuations of magnetic nanoparticles"")
about the use of the damped Landau-Lifshitz equation and the kinetic Langer
theory for the calculation of the relaxation rate of magnetic nanoclusters. We
reiterate simple scientific arguments, part of which is well known to the whole
community, demonstrating that the authors' criticisms are unfounded and that
they overstate the issue of damping in the Landau-Lifshitz equation with no
unanimous experimental evidence.",1210.2436v1
2012-10-10,Phonon momentum and damping of mechanical resonators,"The concept of physical momentum associated to phonons in a crystal,
complemented with some fundamental reasoning, implies measurable effects in
crystals even at a macroscopic scale. We show that, in close analogy with the
transfer of momentum in the kinetic theory of gases, physical momentum carried
by of phonons couples the thermal and the velocity field in a vibrating
crystal. Therefore an heat flow applied to a vibrating crystal can sustain or
damp the oscillation, depending on the interplay between the temperature and
the velocity gradient. We derive the general equations of this effect and show
that its experimental confirmation is within reach of current technology.",1210.2847v1
2012-10-12,HTS wiggler concept for a damping ring,"Magnetic design proposed for a damping ring (DR) is based on second
generation HTS cabling technology applied to the DC windings with a yoke and
mu-metal-shimmed pole to achieve ~2T high-quality field within a 86 mm gap and
32-40 cm period. Low levels of current densities (~90-100A/mm2) provide a
robust, reliable operation of the wiggler at higher heat loads, up to LN2
temperatures with long leads, enhanced flexibility for the cryostats and
infrastructure in harsh radiation environment, and reduced failure rate
compared to the baseline SC ILC DR wiggler design at very competitive cost.",1210.3648v1
2012-10-23,Dynamic response of open cell dry foams,"We study the mechanical response of an open cell dry foam subjected to
periodic forcing using experiments and theory. Using the measurements of the
static and dynamic stress-strain relationship, we derive an over-damped model
of the foam, as a set of infinitesimal non-linear springs, where the damping
term depends on the local foam strain. We then analyse the properties of the
foam when subjected to large amplitudes periodic stresses and determine the
conditions for which the foam becomes optimally absorbing.",1210.6229v1
2012-10-31,Quantum discord of Bell cat-states under amplitude damping,"The evolution of pairwise quantum correlations of Bell cat-states under
amplitude damping is examined using the concept of quantum discord which goes
beyond entanglement. A closed expression of the quantum discord is explicitly
derived. We used of the Koashi-Winter relation. A relation which facilitates
the optimization process of the conditional entropy. We also discuss the
temporal evolution of bipartite quantum correlations under a dephasing channel
and compare the behaviors of quantum discord and entanglement whose properties
are characterized through the concurrence.",1210.8309v1
2012-10-31,Upsilon suppression in PbPb collisions at the LHC,"We suggest that the combined effect of screening, gluon-induced dissociation,
collisional damping, and reduced feed-down explains most of the sequential
suppression of Upsilon(nS) states that has been observed in PbPb relative to pp
collisions at sqrt(s_NN) = 2.76 TeV. The suppression is thus a clear, albeit
indirect, indication for the presence of a QGP. The Upsilon(1S) ground state
suppression is essentially due to reduced feed-down, collisional damping and
gluodissociation, whereas screening prevails for the suppression of the excited
states.",1210.8366v2
2012-11-04,The Threshold between Effective and Noneffective Damping for Semilinear Waves,"In this paper we study the global existence of small data solutions to the
Cauchy problem for the semilinear wave equation with scale-invariant damping.
We obtain estimates for the solution and its energy with the same decay rate of
the linear problem. We extend our results to a model with polynomial speed of
propagation and to a model with an exponential speed of propagation.",1211.0731v2
2012-11-10,Heavy quark quenching from RHIC to LHC and the consequences of gluon damping,"In this contribution to the Quark Matter 2012 conference, we study whether
energy loss models established for RHIC energies to describe the quenching of
heavy quarks can be applied at LHC with the same success. We also benefit from
the larger $p_T$-range accessible at this accelerator to test the impact of
gluon damping on observables such as the nuclear modification factor.",1211.2281v1
2012-11-13,Critical exponent for the semilinear wave equation with scale invariant damping,"In this paper we consider the critical exponent problem for the semilinear
damped wave equation with time-dependent coefficients. We treat the scale
invariant cases. In this case the asymptotic behavior of the solution is very
delicate and the size of coefficient plays an essential role. We shall prove
that if the power of the nonlinearity is greater than the Fujita exponent, then
there exists a unique global solution with small data, provided that the size
of the coefficient is sufficiently large. We shall also prove some blow-up
results even in the case that the coefficient is sufficiently small.",1211.2900v1
2012-11-30,Local feedback stabilisation to a non-stationary solution for a damped non-linear wave equation,"We study a damped semi-linear wave equation in a bounded domain with smooth
boundary. It is proved that any sufficiently smooth solution can be stabilised
locally by a finite-dimensional feedback control supported by a given open
subset satisfying a geometric condition. The proof is based on an investigation
of the linearised equation, for which we construct a stabilising control
satisfying the required properties. We next prove that the same control
stabilises locally the non-linear problem.",1211.7202v1
2012-12-06,The physics of business cycles and inflation,"We analyse four consecutive cycles observed in the USA for employment and
inflation. They are driven by three oil price shocks and an intended interest
rate shock. Non-linear coupling between the rate equations for consumer
products as prey and consumers as predators provides the required instability,
but its natural damping is too high for spontaneous cycles. Extending the
Lotka-Volterra equations with a small term for collective anticipation yields a
second analytic solution without damping. It predicts the base period, phase
shifts, and the sensitivity to shocks for all six cyclic variables correctly.",1212.1282v1
2012-12-13,CMB Distortions from Damping of Acoustic Waves Produced by Cosmic Strings,"We study diffusion damping of acoustic waves in the photon-baryon fluid due
to cosmic strings, and calculate the induced $\mu$- and $y$-type spectral
distortions of the cosmic microwave background. For cosmic strings with tension
within current bounds, their contribution to the spectral distortions is
subdominant compared to the distortions from primordial density perturbations.",1212.3283v2
2013-01-21,Asymptotic parabolicity for strongly damped wave equations,"For $S$ a positive selfadjoint operator on a Hilbert space, \[
\frac{d^2u}{dt}(t) + 2 F(S)\frac{du}{dt}(t) + S^2u(t)=0 \] describes a class of
wave equations with strong friction or damping if $F$ is a positive Borel
function. Under suitable hypotheses, it is shown that \[ u(t)=v(t)+ w(t) \]
where $v$ satisfies \[ 2F(S)\frac{dv}{dt}(t)+ S^2v(t)=0 \] and \[
\frac{w(t)}{\|v(t)\|} \rightarrow 0, \; \text{as} \; t \rightarrow +\infty. \]
The required initial condition $v(0)$ is given in a canonical way in terms of
$u(0)$, $u'(0)$.",1301.4979v1
2013-02-04,Gravity waves on the surface of topological superfluid 3He-B,"We have observed waves on the free surface of 3He-B sample at temperatures
below 0.2mK. The waves are excited by vibrations of the cryostat and detected
by coupling the surface to the Bose-Einstein condensate of magnon
quasiparticles in the superfluid. The two lowest gravity-wave modes in our
cylindrical container are identified. Damping of the waves increases with
temperature linearly with the density of thermal quasiparticles, as expected.
Additionally finite damping of the waves in the zero-temperature limit and
enhancement of magnetic relaxation of magnon condensates by the surface waves
are observed. We discuss whether the latter effects may be related to Majorana
fermions bound to the surface of the topological superfluid.",1302.0764v1
2013-02-12,On the fractional damped oscillators and fractional forced oscillators,"In this paper, we use the fractional calculus to discuss the fractional
mechanics, where the time derivative is replaced with the fractional derivative
of order $\nu$. We deal with the motion of a body in a resisting medium where
the retarding force is assumed to be proportional to the fractional velocity
which is obtained by acting the fractional derivative on the position. The
fractional harmonic oscillator problem, fractional damped oscillator problem
and fractional forced oscillator problem are also studied.",1302.2847v1
2013-02-25,Optimal damping algorithm for unrestricted Hartree-Fock calculations,"We have developed a couple of optimal damping algorithms (ODAs) for
unrestricted Hartree-Fock (UHF) calculations of open-shell molecular systems. A
series of equations were derived for both concurrent and alternate
constructions of alpha- and beta-Fock matrices in the integral-direct
self-consistent-field (SCF) procedure. Several test calculations were performed
to check the convergence behaviors. It was shown that the concurrent algorithm
provides better performance than does the alternate one.",1302.6099v1
2013-03-08,Entanglement of Open Quantum Systems in Noninertial Frames,"We study the effects of decoherence on the entanglement generated by Unruh
effect in accelerated frames by using various combinations of an amplitude
damping channel, a phase damping channel and a depolarizing channel in the form
of multilocal and collective environments. Using concurrence as entanglement
quantifier, we show that the occurrence of entanglement sudden death (ESD)
depends on different combinations of the channels. The ESD can be avoided under
a particular configuration of the channels. We show that the channels can be
used to distinguish between a moving and a stationary frame.",1303.2034v1
2013-03-21,Glued trees algorithm under phase damping,"We study the behaviour of the glued trees algorithm described by Childs et
al. in [STOC `03, Proc. 35th ACM Symposium on Theory of Computing (2004) 59]
under decoherence. We consider a discrete time reformulation of the continuous
time quantum walk protocol and apply a phase damping channel to the coin state,
investigating the effect of such a mechanism on the probability of the walker
appearing on the target vertex of the graph. We pay particular attention to any
potential advantage coming from the use of weak decoherence for the spreading
of the walk across the glued trees graph.",1303.5319v2
2013-04-04,Pais-Uhlenbeck Oscillator with a Benign Friction Force,"It is shown that the Pais-Uhlenbeck oscillator with damping, considered by
Nesterenko, is a special case of a more general oscillator that has not only a
first order, but also a third order friction term. If the corresponding damping
constants, \alpha\ and \beta, are both positive and below certain critical
values, then the system is stable. In particular, if \alpha = - \beta, then we
have the unstable Nesterenko's oscillator",1304.1325v2
2013-05-13,Guaranteed convergence of the Kohn-Sham equations,"A sufficiently damped iteration of the Kohn-Sham equations with the exact
functional is proven to always converge to the true ground-state density,
regardless of the initial density or the strength of electron correlation, for
finite Coulomb systems. We numerically implement the exact functional for
one-dimensional continuum systems and demonstrate convergence of the damped KS
algorithm. More strongly correlated systems converge more slowly.",1305.2967v2
2013-06-25,Decoherence effects in the quantum qubit flip game using Markovian approximation,"We are considering a quantum version of the penny flip game, whose
implementation is influenced by the environment that causes decoherence of the
system. In order to model the decoherence we assume Markovian approximation of
open quantum system dynamics. We focus our attention on the phase damping,
amplitude damping and amplitude raising channels. Our results show that the
Pauli strategy is no longer a Nash equilibrium under decoherence. We attempt to
optimize the players' control pulses in the aforementioned setup to allow them
to achieve higher probability of winning the game compared to the Pauli
strategy.",1306.5957v1
2013-07-06,The 3-dimensional oscillon equation,"On a bounded three-dimensional smooth domain, we consider the generalized
oscillon equation with Dirichlet boundary conditions, with time-dependent
damping and time-dependent squared speed of propagation. Under structural
assumptions on the damping and the speed of propagation, which include the
relevant physical case of reheating phase of inflation, we establish the
existence of a pullback global attractor of optimal regularity, and
finite-dimensionality of the kernel sections.",1307.1777v1
2013-07-17,Functional inequalities on path space over a non-compact Riemannian manifold,"We prove the existence of the O-U Dirichlet form and the damped O-U Dirichlet
form on path space over a general non-compact Riemannian manifold which is
complete and stochastically complete. We show a weighted log-Sobolev inequality
for the O-U Dirichlet form and the (standard) log-Sobolev inequality for the
damped O-U Dirichlet form. In particular, the Poincar\'e inequality (and the
super Poincar\'e inequality) can be established for the O-U Dirichlet form on
path space over a class of Riemannian manifolds with unbounded Ricci
curvatures. Moreover, we construct a large class of quasi-regular local
Dirichlet forms with unbounded random diffusion coefficients on the path space
over a general non-compact manifold.",1307.4482v2
2013-08-30,"A conservative, skew-symmetric Finite Difference Scheme for the compressible Navier--Stokes Equations","We present a fully conservative, skew-symmetric finite difference scheme on
transformed grids. The skew-symmetry preserves the kinetic energy by first
principles, simultaneously avoiding a central instability mechanism and
numerical damping. In contrast to other skew-symmetric schemes no special
averaging procedures are needed. Instead, the scheme builds purely on
point-wise operations and derivatives. Any explicit and central derivative can
be used, permitting high order and great freedom to optimize the scheme
otherwise. This also allows the simple adaption of existing finite difference
schemes to improve their stability and damping properties.",1308.6672v1
2013-09-09,Classical and quantum capacities of a fully correlated amplitude damping channel,"We study information transmission over a fully correlated amplitude damping
channel acting on two qubits. We derive the single-shot classical channel
capacity and show that entanglement is needed to achieve the channel best
performance. We discuss the degradability properties of the channel and
evaluate the quantum capacity for any value of the noise parameter. We finally
compute the entanglement-assisted classical channel capacity.",1309.2219v3
2013-09-13,Polarization hydrodynamics in a one-dimensional polariton condensate,"We study the hydrodynamics of a nonresonantly-pumped polariton condensate in
a quasi-one-dimensional quantum wire taking into account the spin degree of
freedom. We clarify the relevance of the Landau criterion for superfluidity in
this dissipative two-component system. Two Cherenkov-like critical velocities
are identified corresponding to the opening of different channels of radiation:
one of (damped) density fluctuations and another of (weakly damped)
polarization fluctuations. We determine the drag force exerted onto an external
obstacle and propose experimentally measurable consequences of the specific
features of the fluctuations of polarization.",1309.3494v1
2013-09-26,Imperfect geometric control and overdamping for the damped wave equation,"We consider the damped wave equation on a manifold with imperfect geometric
control. We show the sub-exponential energy decay estimate in
\cite{Chr-NC-erratum} is optimal in the case of one hyperbolic periodic
geodesic. We show if the equation is overdamped, then the energy decays
exponentially. Finally we show if the equation is overdamped but geometric
control fails for one hyperbolic periodic geodesic, then nevertheless the
energy decays exponentially.",1309.6967v1
2013-10-01,Scalar filed evolution and area spectrum for Lovelock-AdS black holes,"We study the modes of evolution of massless scalar fields in the
asymptotically AdS spacetime surrounding maximally symmetric black holes of
large and intermediate size in the Lovelock model. It is observed that all
modes are purely damped at higher orders. Also, the rate of damping is seen to
be independent of order at higher dimensions. The asymptotic form of these
frequencies for the case of large black holes is found analytically. Finally,
the area spectrum for such black holes is found from these asymptotic modes.",1310.0159v2
2013-10-16,Perturbative quantum damping of cosmological expansion,"Perturbative quantum gravity in the framework of the Schwinger-Keldysh
formalism is applied to compute lowest-order corrections to the actual
expansion of the Universe described in terms of the spatially flat
Friedman-Lematre-Robertson-Walker solution. The classical metric is
approximated by a third order polynomial perturbation around the Minkowski
metric. It is shown that the quantum contribution to the classical expansion,
although extremely small, has damping properties (quantum friction), i.e. it
slows down the expansion.",1310.4308v2
2013-10-27,Loss of non-Gaussianity for damped photon-subtracted thermal states,"We investigate non-Gaussianity properties for a set of classical one-mode
states obtained by subtracting photons from a thermal state. Three
distance-type degrees of non-Gaussianity used for these states are shown to
have a monotonic behaviour with respect to their mean photon number. Decaying
of their non-Gaussianity under damping is found to be consistently described by
the distance-type measures considered here. We also compare the dissipative
evolution of non-Gaussianity when starting from $M$-photon-subtracted and
$M$-photon-added thermal states",1310.7229v1
2013-10-27,Landau damping effects and evolutions of energy spread in small isochronous ring,"This paper presents the Landau damping effects on the microwave instability
of a coasting long bunch in an isochronous ring due to finite energy spread and
emittance. Our two-dimensional (2D) dispersion relation gives more accurate
predictions of the microwave instability growth rates of short-wavelength
perturbations than the conventional 1D formula. The long-term evolution of
energy spread is also studied by measurements and simulations.",1310.7253v3
2013-10-28,Robustness of multiparticle entanglement: specific entanglement classes and random states,"We investigate the robustness of genuine multiparticle entanglement under
decoherence. We consider different kinds of entangled three- and four-qubit
states as well as random pure states. For amplitude damping noise, we find that
the W-type states are most robust, while other states are not more robust than
generic states. For phase damping noise the GHZ state is the most robust state,
and for depolarizing noise several states are significantly more robust than
random states.",1310.7336v2
2013-11-22,Complexity of the minimum-time damping of a physical pendulum,"We study the minimum-time damping of a physical pendulum by means of a
bounded control. In the similar problem for a linear oscillator each optimal
trajectory possesses a finite number of control switchings from the maximal to
the minimal value. If one considers simultaneously all optimal trajectories
with any initial state, the number of switchings can be arbitrary large. We
show that for the nonlinear pendulum there is a uniform bound for the switching
number for all optimal trajectories. We find asymptotics for this bound as the
control amplitude goes to zero.",1311.5729v1
2013-12-16,Local Energy Decay for the Damped Wave Equation,"We prove local energy decay for the damped wave equation on R^d. The problem
which we consider is given by a long range metric perturbation of the Euclidean
Laplacian with a short range absorption index. Under a geometric control
assumption on the dissipation we obtain an almost optimal polynomial decay for
the energy in suitable weighted spaces. The proof relies on uniform estimates
for the corresponding ""resolvent"", both for low and high frequencies. These
estimates are given by an improved dissipative version of Mourre's commutators
method.",1312.4483v1
2013-12-23,Photonic tuning of quasi-particle decay in a superfluid,"We show that the damping rate of elementary excitations of hybrid systems
close to a phase transition can undergo a remarkable resonance like enhancement
before mode softening takes place. In particular, we consider the friction of a
collective density wave in a homogeneous superfluid of weakly interacting
bosonic atoms coupled to the electromagnetic field of a single mode optical
resonator. Here the Beliaev damping can thus be controlled by an external laser
drive and be enhanced by several orders of magnitude.",1312.6719v1
2014-01-04,Entanglement and quantum teleportation via decohered tripartite entangled states,"The entanglement behavior of two classes of multi-qubit system, GHZ and GHZ
like states passing through a generalized amplitude damping channel is
discussed. Despite this channel causes degradation of the entangled properties
and consequently their abilities to perform quantum teleportation, one can
always improve the lower values of the entanglement and the fidelity of the
teleportrd state by controlling on Bell measurements, analyzer angle and
channel's strength. Using GHZ-like state within a generalized amplitude damping
channel is much better than using the normal GHZ-state, where the decay rate of
entanglement and the fidelity of the teleported states are smaller than those
depicted for GHZ state.",1401.0796v1
2014-02-11,New approach for Damping in a squeezed bath and its time evolution through Complete Class of Gaussian Quasi-distributions,"By virtue of the thermal entangled states representation of density operator
and using dissipative interaction picture we solve the master equation of a
driven damped harmonic oscillator in a squeezed bath. We show that the
essential part of the dynamics can be expressed by the convolution of initial
Wigner function with a special kind of normalized Gaussian in phase space and
relate the dynamics with the change of Gaussian ordering of density operator.",1402.2545v1
2014-02-11,New approach for solving master equations of density operator for the Jaynes Cummings Model with Cavity Damping,"By introducing thermal entangled state representation which can map master
equations of density operator in quantum statistics as state vector evolution
equations and using dissipative interaction picture we solve the master
equation of J-C model with cavity damping. In addition we derive the Wigner
function for density operator when the atom is initially in the up state and
the cavity mode is in coherent state.",1402.2556v1
2014-02-19,Superfluid Bloch dynamics in an incommensurate lattice,"We investigate the interplay of disorder and interactions in the accelerated
transport of a Bose-Einstein condensate through an incommensurate optical
lattice. We show that interactions can effectively cancel the damping of Bloch
oscillations due to the disordered potential and we provide a simple model to
qualitatively capture this screening effect. We find that the characteristic
interaction energy, above which interactions and disorder cooperate to enhance,
rather than reduce, the damping of Bloch oscillations, coincides with the
average disorder depth. This is consistent with results of a mean-field
simulation.",1402.4830v1
2014-02-21,Weakly damped acoustic plasmon mode in transition metal dichalcogenides with Zeeman splitting,"We analyze the effect of a strong Zeeman field on the spectrum of collective
excitations of monolayer transition metal dichalcogenides. The combination of
the Dresselhaus type spin orbit coupling and an external Zeeman field result in
the lifting of the valley degeneracy in the valence band of these crystals. We
show that this lifting of the valley degeneracy manifests in the appearance of
an additional plasmon mode with linear in wavenumber dispersion along with the
standard square root in wavenumber mode. Despite this novel mode being subject
to the Landau damping, it corresponds to a well defined quasiparticle peak in
the spectral function of the electron gas.",1402.5274v1
2014-04-18,"On the Instability and Critical Damping Conditions, $kτ= 1/e$ and $kτ= π/2$ of the equation $\dotθ = -k θ(t-τ)$","In this note, I show that it is possible to use elementary mathematics,
instead of the machinery of Lambert function, Laplace Transform, or numerics,
to derive the instability condition, $k \tau = \pi/2$, and the critical damping
condition, $k\tau = 1/e$, for the time-delayed equation $\dot{\theta} = -k
\theta(t-\tau)$. I hope it will be useful for the new comers to this equation,
and perhaps even to the experts if this is a simpler method compared to other
versions.",1404.4763v1
2014-04-22,Nonlinear-damped Duffing oscillators having finite time dynamics,"A class of modified Duffing oscillator differential equations, having
nonlinear damping forces, are shown to have finite time dynamics, i.e., the
solutions oscillate with only a finite number of cycles, and, thereafter, the
motion is zero. The relevance of this feature is briefly discussed in
relationship to the mathematical modeling, analysis, and estimation of
parameters for the vibrations of carbon nano-tubes and graphene sheets, and
macroscopic beams and plates.",1404.5596v1
2014-05-01,On the collapse of trial solutions for a damped-driven non-linear Schrödinger equation,"We consider the focusing 2D non-linear Schr\""odinger equation, perturbed by a
damping term, and driven by multiplicative noise. We show that a physically
motivated trial solution does not collapse for any admissible initial condition
although the exponent of the non-linearity is critical. Our method is based on
the construction of a global solution to a singular stochastic Hamiltonian
system used to connect trial solution and Schr\""odinger equation.",1405.0151v3
2014-05-02,Dynamic phase diagram of dc-pumped magnon condensates,"We study the effects of nonlinear dynamics and damping by phonons on a system
of interacting electronically pumped magnons in a ferromagnet. The nonlinear
effects are crucial for constructing the dynamic phase diagram, which describes
how ""swasing"" and Bose-Einstein condensation emerge out of the
quasiequilibrated thermal cloud of magnons. We analyze the system in the
presence of magnon damping and interactions, demonstrating the continuous onset
of stable condensates as well as hysteretic transitions.",1405.0522v1
2014-05-05,Finite time extinction for nonlinear Schrodinger equation in 1D and 2D,"We consider a nonlinear Schrodinger equation with power nonlinearity, either
on a compact manifold without boundary, or on the whole space in the presence
of harmonic confinement, in space dimension one and two. Up to introducing an
extra superlinear damping to prevent finite time blow up, we show that the
presence of a sublinear damping always leads to finite time extinction of the
solution in 1D, and that the same phenomenon is present in the case of small
mass initial data in 2D.",1405.0995v1
2014-05-16,Investigation of Power-Law Damping/Dissipative Forces,"The properties of a one space-dimension, one particle dynamical system under
the influence of a purely dissipative force are investigated. Assuming this
force depends only on the velocity, it is demonstrated, in contrast to the case
of linear damping, that there exist dissipative forces for which the particle
\textquotedblleft stops"" in a finite time. It is also shown, by an explicit
example, that other dissipative forces exist such that they produce dynamics in
which the particle achieves zero velocity only after an infinite distance has
been traveled. Possible applications of these results to more complex
situations are discussed.",1405.4062v1
2014-06-02,"Nonlinear coupler operating on Werner-like states - entanglement creation, its enhancement and preservation","We discuss a model of two nonlinear Kerr-like oscillators, mutually coupled
and excited by parametric process. We show that the system's evolution,
starting from Werner-like states, remains closed within a small set of two-mode
n-photon states the system, and pure two-qubit entangled state can be
generated. For some initial Werner-like states delayed entanglement generation
can be observed. We investigate the influence of two damping mechanisms on the
system's evolution. We show that for the both cases, the entanglement can
survive despite the presence of damping, and the effects of sudden entanglement
death and its rebirth can appear in the system.",1406.0414v1
2014-06-10,A determining form for the damped driven Nonlinear Schrödinger Equation- Fourier modes case,"In this paper we show that the global attractor of the 1D damped, driven,
nonlinear Schr\""odinger equation (NLS) is embedded in the long-time dynamics of
a determining form. The determining form is an ordinary differential equation
in a space of trajectories $X=C_b^1(\mathbb{R}, P_mH^2)$ where $P_m$ is the
$L^2$-projector onto the span of the first $m$ Fourier modes. There is a
one-to-one identification with the trajectories in the global attractor of the
NLS and the steady states of the determining form. We also give an improved
estimate for the number of the determining modes.",1406.2626v1
2014-08-20,Initial Layer and Relaxation Limit of Non-Isentropic Compressible Euler Equations with Damping,"In this paper, we study the relaxation limit of the relaxing Cauchy problem
for non-isentropic compressible Euler equations with damping in
multi-dimensions. We prove that the velocity of the relaxing equations
converges weakly to that of the relaxed equations, while other variables of the
relaxing equations converges strongly to the corresponding variables of the
relaxed equations. We show that as relaxation time approaches 0, there exists
an initial layer for the ill-prepared data, the convergence of the velocity is
strong outside the layer; while there is no initial layer for the well-prepared
data, the convergence of the velocity is strong near t=0.",1408.4784v1
2014-08-26,Exponential decay for the damped wave equation in unbounded domains,"We study the decay of the semigroup generated by the damped wave equation in
an unbounded domain. We first prove under the natural geometric control
condition the exponential decay of the semigroup. Then we prove under a weaker
condition the logarithmic decay of the solutions (assuming that the initial
data are smoother). As corollaries, we obtain several extensions of previous
results of stabilisation and control.",1408.6054v2
2014-10-03,Relaxation of regularity for the Westervelt equation by nonlinear damping with application in acoustic-acoustic and elastic-acoustic coupling,"In this paper we show local (and partially global) in time existence for the
Westervelt equation with several versions of nonlinear damping. This enables us
to prove well-posedness with spatially varying $L_\infty$-coefficients, which
includes the situation of interface coupling between linear and nonlinear
acoustics as well as between linear elasticity and nonlinear acoustics, as
relevant, e.g., in high intensity focused ultrasound (HIFU) applications.",1410.0797v1
2014-10-13,Vortex gyration mediated by spin waves driven by an out-of-plane oscillating magnetic field,"In this letter we address the vortex core dynamics involved in gyration
excitation and damping change by out-of-plane oscillating magnetic fields. When
the vortex core is at rest under the effect of in-plane bias magnetic fields,
the spin waves excited by the perpendicular magnetic field can induce obvious
vortex gyration. When simultaneously excite spin waves and vortex gyrotropic
motion, the gyration damping changes. Analysis of the system energy allows us
to explain the origin of the spin-wave-mediated vortex gyration.",1410.3230v1
2014-10-23,Non-equilibrium thermodynamics approach to open quantum systems,"Open quantum systems are studied from the thermodynamical point of view
unifying the principle of maximum informational entropy and the hypothesis of
relaxation times hierarchy. The result of the unification is a non-Markovian
and local in time master equation that provides a direct connection of
dynamical and thermodynamical properties of open quantum systems. The power of
the approach is illustrated with the application to the damped harmonic
oscillator and the damped driven two-level system resulting in analytical
expressions for the non-Markovian and non-equilibrium entropy and inverse
temperature.",1410.6312v2
2014-10-27,Linear Inviscid Damping for Monotone Shear Flows,"In this article, we prove linear stability, scattering and inviscid damping
with optimal decay rates for the linearized 2D Euler equations around a large
class of strictly monotone shear flows, $(U(y),0)$, in a periodic channel under
Sobolev perturbations. Here, we consider the settings of both an infinite
periodic channel of period $L$, $\mathbb{T}_{L}\times \mathbb{R}$, as well as a
finite periodic channel, $\mathbb{T}_{L} \times [0,1]$, with impermeable walls.
The latter setting is shown to not only be technically more challenging, but to
exhibit qualitatively different behavior due to boundary effects.",1410.7341v2
2014-11-08,Damping of liquid sloshing by foams: from everyday observations to liquid transport,"We perform experiments on the sloshing dynamics of liquids in a rectangular
container submitted to an impulse. We show that when foam is placed on top of
the liquid the oscillations of the free interface are significantly damped. The
ability to reduce sloshing and associated splashing could find applications in
numerous industrial processes involving liquid transport.",1411.2123v1
2014-11-17,A geometric mesh smoothing algorithm related to damped oscillations,"We introduce a smoothing algorithm for triangle, quadrilateral, tetrahedral
and hexahedral meshes whose centerpiece is a simple geometric triangle
transformation. The first part focuses on the mathematical properties of the
element transformation. In particular, the transformation gives rise directly
to a continuous model given by a system of coupled damped oscillations. Derived
from this physical model, adaptive parameters are introduced and their benefits
presented. The second part discusses the mesh smoothing algorithm based on the
element transformation and its numerical performance on example meshes.",1411.4390v3
2014-12-05,Exponential dephasing of oscillators in the Kinetic Kuramoto Model,"We study the kinetic Kuramoto model for coupled oscillators with coupling
constant below the synchronization threshold. We manage to prove that, for any
analytic initial datum, if the interaction is small enough, the order parameter
of the model vanishes exponentially fast, and the solution is asymptotically
described by a free flow. This behavior is similar to the phenomenon of Landau
damping in plasma physics. In the proof we use a combination of techniques from
Landau damping and from abstract Cauchy-Kowalewskaya theorem.",1412.1923v1
2014-12-23,Selftrapping triggered by losses in cavity QED,"In a coupled cavity QED network model, we study the transition from a
localized super fluid like state to a delocalized Mott insulator like state,
triggered by losses. Without cavity losses, the transition never takes place.
Further, if one measures the quantum correlations between the polaritons via
the negativity, we find a critical cavity damping constant, above which the
negativity displays a single peak in the same time region where the transition
takes place. Additionally, we identify two regions in the parameter space,
where below the critical damping, oscillations of the initial localized state
are observed along with a multipeaked negativity, while above the critical
value, the oscillations die out and the transition is witnessed by a neat
single peaked negativity.",1412.7495v1
2015-01-07,Two-photon lasing by a superconducting qubit,"We study the response of a magnetic-field-driven superconducting qubit
strongly coupled to a superconducting coplanar waveguide resonator. We observed
a strong amplification/damping of a probing signal at different resonance
points corresponding to a one and two-photon emission/absorption. The sign of
the detuning between the qubit frequency and the probe determines whether
amplification or damping is observed. The larger blue detuned driving leads to
two-photon lasing while the larger red detuning cools the resonator. Our
experimental results are in good agreement with the theoretical model of qubit
lasing and cooling at the Rabi frequency.",1501.01543v1
2015-02-02,Enhanced oscillation lifetime of a Bose-Einstein condensate in the 3D/1D crossover,"We have measured the damped motion of a trapped Bose-Einstein condensate,
oscillating with respect to a thermal cloud. The cigar-shaped trapping
potential provides enough transverse confinement that the dynamics of the
system are intermediate between three-dimensional and one-dimensional. We find
that oscillations persist for longer than expected for a three-dimensional gas.
We attribute this to the suppressed occupation of transverse momentum states,
which are essential for damping.",1502.00430v2
2015-02-03,Nonequilibrium dynamics of an ultracold dipolar gas,"We study the relaxation and damping dynamics of an ultracold, but not quantum
degenerate, gas consisting of dipolar particles. These simulations are
performed using a direct simulation Monte Carlo method and employing the highly
anisotropic differential cross section of dipoles in the Wigner threshold
regime. We find that both cross-dimensional relaxation and damping of breathing
modes occur at rates that are strongly dependent on the orientation of the
dipole moments relative to the trap axis. The relaxation simulations are in
excellent agreement with recent experimental results in erbium. The results
direct our interest toward a less explored regime in dipolar gases where
interactions are dominated by collision processes rather than mean-field
interactions.",1502.00960v1
2015-02-01,"On the Stability of Cylindrical Tangential Discontinuity, Generation and Damping of Helical Waves","Stability of cylindrical interface between two ideal incompressible fluids,
including the magnetic field, surface tension and gravitational field is
studied in linear approximation. We found that helical waves arising both in
plasma comet tails and on the vertical cylindrical water jet in the air are
described by the same dispersion equation where the comet tail magnetic field
plays the same stabilizing role as surface tension for water jet. Hence they
represent the same phenomenon of Kelvin-Helmholtz instability. Thus helical
waves in comet tails and astrophysical jets may be simulated in the laboratory.
The resonance nature of the Kelvin- instability damping is demonstrated.",1502.00989v1
2015-03-04,On the Lewis-Riesenfeld (Dodonov-Man'ko) invariant method,"We revise the Lewis-Riesenfeld invariant method for solving the quantum
time-dependent harmonic oscillator in light of the Quantum Arnold
Transformation previously introduced and its recent generalization to the
Quantum Arnold-Ermakov-Pinney Transformation. We prove that both methods are
equivalent and show the advantages of the Quantum Arnold-Ermakov-Pinney
transformation over the Lewis-Riesenfeld invariant method. We show that, in the
quantum time-dependent and damped harmonic oscillator, the invariant proposed
by Dodonov & Man'ko is more suitable and provide some examples to illustrate
it, focusing on the damped case.",1503.01371v1
2015-03-06,On the strongly damped wave equation with constraint,"A weak formulation for the so-called ""semilinear strongly damped wave
equation with constraint"" is introduced and a corresponding notion of solution
is defined. The main idea in this approach consists in the use of duality
techniques in Sobolev-Bochner spaces, aimed at providing a suitable
""relaxation"" of the constraint term. A global in time existence result is
proved under the natural condition that the initial data have finite ""physical""
energy.",1503.01911v1
2015-03-23,Spin-Orbit Torques in Two-Dimensional Rashba Ferromagnets,"Magnetization dynamics in single-domain ferromagnets can be triggered by
charge current if spin-orbit coupling is sufficiently strong. We apply
functional Keldysh theory to investigate Rashba spin-orbit torques in metallic
two-dimensional ferromagnets. A reactive, anti-damping-like spin-orbit torque
as well as a dissipative, field-like torque are calculated microscopically, to
the leading order in the spin-orbit interaction strength. By calculating the
first vertex correction we show that the intrinsic anti-damping-like torque
vanishes unless the scattering rates are spin-dependent.",1503.06872v2
2015-04-18,Global Dirichlet Heat Kernel Estimates for Symmetric Lévy Processes in Half-space,"In this paper, we derive explicit sharp two-sided estimates for the Dirichlet
heat kernels of a large class of symmetric (but not necessarily rotationally
symmetric) L\'evy processes on half spaces for all $t>0$. These L\'evy
processes may or may not have Gaussian component. When L\'evy density is
comparable to a decreasing function with damping exponent $\beta$,our estimate
is explicit in terms of the distance to the boundary, the L\'evy exponent and
the damping exponent $\beta$ of L\'evy density.",1504.04673v2
2015-05-05,The transition from the classical to the quantum regime in nonlinear Landau damping,"Starting from the Wigner-Moyal equation coupled to Poisson's equation, a
simplified set of equations describing nonlinear Landau damping of Langmuir
waves is derived. This system is studied numerically, with a particular focus
on the transition from the classical to the quantum regime. In the quantum
regime several new features are found. This includes a quantum modified bounce
frequency, and the discovery that bounce-like amplitude oscillations can take
place even in the absence of trapped particles. The implications of our results
are discussed.",1505.01381v1
2015-05-08,The amplification of weak measurements under quantum noise,"The influence of outside quantum noises on the amplification of weak
measurements is investigated. Three typical quantum noises are discussed. The
maximum values of the pointer's shifts decrease sharply with the strength of
the depolarizing channel and phase damping. In order to obtain significant
amplified signals, the preselection quantum systems must be kept away from the
two quantum noises. Interestingly, the amplification effect is immune to the
amplitude damping noise.",1505.01911v1
2015-05-27,Local energy decay and smoothing effect for the damped Schr{ö}dinger equation,"We prove the local energy decay and the smoothing effect for the damped
Schr{\""o}dinger equation on R^d. The self-adjoint part is a Laplacian
associated to a long-range perturbation of the flat metric. The proofs are
based on uniform resolvent estimates obtained by the dissipative Mourre method.
All the results depend on the strength of the dissipation which we consider.",1505.07200v1
2015-05-27,Logarithmic stability in determining a boundary coefficient in an ibvp for the wave equation,"In [2] we introduced a method combining together an observability inequality
and a spectral decomposition to get a logarithmic stability estimate for the
inverse problem of determining both the potential and the damping coefficient
in a dissipative wave equation from boundary measurements. The present work
deals with an adaptation of that method to obtain a logarithmic stability
estimate for the inverse problem of determining a boundary damping coefficient
from boundary measurements. As in our preceding work, the different boundary
measurements are generated by varying one of the initial conditions.",1505.07248v1
2015-06-01,Local decay for the damped wave equation in the energy space,"We improve a previous result about the local energy decay for the damped wave
equation on R^d. The problem is governed by a Laplacian associated with a long
range perturbation of the flat metric and a short range absorption index. Our
purpose is to recover the decay O(t^{--d+$\epsilon$}) in the weighted energy
spaces. The proof is based on uniform resolvent estimates, given by an improved
version of the dissipative Mourre theory. In particular we have to prove the
limiting absorption principle for the powers of the resolvent with inserted
weights.",1506.00377v1
2015-06-03,Giant Phonon Anomaly associated with Superconducting Fluctuations in the Pseudogap Phase of Cuprates,"The opening of the pseudogap in underdoped cuprates breaks up the Fermi
surface, which may lead to a breakup of the d-wave order parameter into two
subband amplitudes and a low energy Leggett mode due to phase fluctuations
between them. This causes a large increase in the temperature range of
superconducting fluctuations with an overdamped Leggett mode. Almost resonant
scattering of inter-subband phonons to a state with a pair of Leggett modes
causes anomalously strong damping. In the ordered state, the Leggett mode
develops a finite energy, suppressing the anomalous phonon damping but leading
to an anomaly in the phonon dispersion.",1506.01258v1
2015-06-06,On higher regularity for the Westervelt equation with strong nonlinear damping,"We show higher interior regularity for the Westervelt equation with strong
nonlinear damping term of the $q$-Laplace type. Secondly, we investigate an
interface coupling problem for these models, which arise, e.g., in the context
of medical applications of high intensity focused ultrasound in the treatment
of kidney stones. We show that the solution to the coupled problem exhibits
piecewise $H^2$ regularity in space, provided that the gradient of the acoustic
pressure is essentially bounded in space and time on the whole domain. This
result is of importance in numerical approximations of the present problem, as
well as in gradient based algorithms for finding the optimal shape of the
focusing acoustic lens in lithotripsy.",1506.02125v1
2015-06-08,Intermode-coupling modulation in the fermion-boson model: heating effects in the BCS regime,"Heating induced by an oscillating modulation of the interaction strength in
an atomic Fermion pair condensate is analyzed. The coupled fermion-boson model,
generalized by incorporating a time-dependent intermode coupling through a
magnetic Feshbach resonance, is applied. The dynamics is analytically
characterized in a perturbative scheme. The results account for experimental
findings which have uncovered a damped and delayed response of the condensate
to the modulation. The delay is due to the variation of the quasiparticle
energies and the subsequent relaxation of the condensate. The detected damping
results from the excitations induced by a nonadiabatic modulation: for driving
frequencies larger than twice the pairing gap, quasiparticles are generated,
and, consequently, heating sets in.",1506.02612v1
2015-06-22,N-body description of Debye shielding and Landau damping,"This paper brings further insight into the recently published N-body
description of Debye shielding and Landau damping [Escande D F, Elskens Y and
Doveil F 2014 Plasma Phys. Control. Fusion 57 025017]. Its fundamental equation
for the electrostatic potential is derived in a simpler and more rigorous way.
Various physical consequences of the new approach are discussed, and this
approach is compared with the seminal one by Pines and Bohm [Pines D and Bohm D
1952 Phys. Rev. 85 338--353].",1506.06468v2
2015-07-23,Millisecond newly born pulsars as efficient accelerators of electrons,"The newly born millisecond pulsars are investigated as possible energy
sources for creating ultra-high energy electrons. The transfer of energy from
the star rotation to high energy electrons takes place through the Landau
damping of centrifugally driven (via a two stream instability) electrostatic
Langmuir waves. Generated in the bulk magnetosphere plasma, such waves grow to
high amplitudes, and then damp, very effectively, on relativistic electrons
driving them to even higher energies. We show that the rate of transfer of
energy is so efficient that no energy losses might affect the mechanism of
particle acceleration; the electrons might achieve energies of the order of
10^{18}eV for parameters characteristic of a young star.",1507.06415v1
2015-07-28,Stability of solutions to nonlinear wave equations with switching time-delay,"In this paper we study well-posedness and asymptotic stability for a class of
nonlinear second-order evolution equations with intermittent delay damping.
More precisely, a delay feedback and an undelayed one act alternately in time.
We show that, under suitable conditions on the feedback operators, asymptotic
stability results are available. Concrete examples included in our setting are
illustrated. We give also stability results for an abstract model with
alternate positive-negative damping, without delay.",1507.07787v1
2015-08-10,Theory of the strongly-damped quantum harmonic oscillator,"We analyse the properties of a strongly-damped quantum harmonic oscillator by
means of an exact diagonalisation of the full Hamiltonian, including both the
oscillator and the reservoir degrees of freedom to which it is coupled. Many of
the properties of the oscillator, including its steady-state properties and
entanglement with the reservoir can be understood and quantified in terms of a
simple probability density, which we may associate with the ground-state
frequency spectrum of the oscillator.",1508.02442v1
2015-08-20,Bump-on-tail instability of twisted excitations in rotating cold atomic clouds,"We develop a kinetic theory for twisted density waves (phonons), carrying a
finite amount of orbital angular momentum, in large magneto optical traps,
where the collective processes due to the exchange of scattered photons are
considered. Explicit expressions for the dispersion relation and for the
kinetic (Landau) damping are derived and contributions from the orbital angular
momentum are discussed. We show that for rotating clouds, exhibiting
ring-shaped structures, phonons carrying orbital angular momentum can cross the
instability threshold and grow out of noise, while the usual plane wave
solutions are kinetically damped.",1508.05127v1
2015-09-30,Approximation of Invariant Measure for Damped Stochastic Nonlinear Schrödinger Equation via an Ergodic Numerical Scheme,"In order to inherit numerically the ergodicity of the damped stochastic
nonlinear Schr\""odinger equation with additive noise, we propose a fully
discrete scheme, whose spatial direction is based on spectral Galerkin method
and temporal direction is based on a modification of the implicit Euler scheme.
We not only prove the unique ergodicity of the numerical solutions of both
spatial semi-discretization and full discretization, but also present error
estimations on invariant measures, which gives order $2$ in spatial direction
and order ${\frac12}$ in temporal direction.",1509.09148v2
2015-10-02,Cavity and HOM Coupler Design for CEPC,"In this paper we will show a cavity and higher order mode (HOM) coupler
designing scheme for the Circular Electron-Positron Collider (CEPC) main ring.
The cavity radio frequency (RF) design parameters are showed in this paper. The
HOM power is calculated based on the beam parameters in the Preliminary
Conceptual Design Report (Pre-CDR). The damping results of the higher order
modes (HOMs) and same order modes (SOMs) show that they are reached the damping
requirements for beam stability.",1510.00467v1
2015-11-08,Upper semicontinuity of pullback attractors for damped wave equations,"In this paper, we study the upper semicontinuity of pullback attractors for a
strongly damped wave equation. In particular, under some proper assumptions, we
prove that, the pullback attractor $\{A_\varepsilon(t)\}_{t\in\mathbb R}$} of
Eq.(1.1) with $\varepsilon\in[0,1]$ satisfies that for any $[a,b]\subset\mathbb
R$ and $\varepsilon_0\in[0,1]$, $\lim_{\varepsilon\to\varepsilon_0}
\sup_{t\in[a,b]} \mathrm{dist}_{H_0^1\times L^2} (A_\varepsilon(t),
A_{\varepsilon_0}(t))=0$, and $\cup_{t\in[a,b]} \cup_{\varepsilon\in[0,1]}
A_\varepsilon(t)$ is precompact in $H_0^1 (\Omega) \times L^2(\Omega)$.",1511.02481v2
2015-11-12,"Strong trajectory and global $\mathbf{W^{1,p}}$-attractors for the damped-driven Euler system in $\mathbb R^2$","We consider the damped and driven two-dimensional Euler equations in the
plane with weak solutions having finite energy and enstrophy. We show that
these (possibly non-unique) solutions satisfy the energy and enstrophy
equality. It is shown that this system has a strong global and a strong
trajectory attractor in the Sobolev space $H^1$. A similar result on the strong
attraction holds in the spaces $H^1\cap\{u:\ \|\mathrm{curl}
u\|_{L^p}<\infty\}$ for $p\ge2$.",1511.03873v1
2015-11-14,Infinite energy solutions for critical wave equation with fractional damping in unbounded domains,"This work is devoted to infinite-energy solutions of semi-linear wave
equations in unbounded smooth domains of $\mathbb{R}^3$ with fractional damping
of the form $(-\Delta_x+1)^\frac{1}{2}\partial_t u$. The work extends
previously known results for bounded domains in finite energy case.
Furthermore, well-posedness and existence of locally-compact smooth attractors
for the critical quintic non-linearity are obtained under less restrictive
assumptions on non-linearity, relaxing some artificial technical conditions
used before. This is achieved by virtue of new type Lyapunov functional that
allows to establish extra space-time regularity of solutions of Strichartz
type.",1511.04592v1
2015-11-14,Parametric resonance induced chaos in magnetic damped driven pendulum,"A damped driven pendulum with a magnetic driving force, appearing from a
solenoid, where ac current flows is considered. The solenoid acts on the
magnet, which is located at the free end of the pendulum. In this system, the
existence and interrelation of chaos and parametric resonance is theoretically
examined. Derived analytical results are supported by numerical simulations and
conducted experiments.",1511.04593v2
2015-11-19,Periodic damping gives polynomial energy decay,"Let $u$ solve the damped Klein--Gordon equation $$ \big( \partial_t^2-\sum
\partial_{x_j}^2 +m \text{Id} +\gamma(x) \partial_t \big) u=0 $$ on
$\mathbb{R}^n$ with $m>0$ and $\gamma\geq 0$ bounded below on a $2 \pi
\mathbb{Z}^n$-invariant open set by a positive constant. We show that the
energy of the solution $u$ decays at a polynomial rate. This is proved via a
periodic observability estimate on $\mathbb{R}^n.$",1511.06144v5
2015-12-03,Evidence for the role of normal-state electrons in nanoelectromechanical damping mechanisms at very low temperatures,"We report on experiments performed at low temperatures on aluminum covered
silicon nanoelectromechanical resonators. The substantial difference observed
between the mechanical dissipation in the normal and superconducting states
measured within the same device unambiguously demonstrates the importance of
normal-state electrons in the damping mechanism. The dissipative component
becomes vanishingly small at very low temperatures in the superconducting
state, leading to exceptional values for the quality factor of such small
silicon structures. A critical discussion is given within the framework of the
standard tunneling model.",1512.01036v1
2015-12-31,Nonlinear stochastic evolution equations of second order with damping,"Convergence of a full discretization of a second order stochastic evolution
equation with nonlinear damping is shown and thus existence of a solution is
established. The discretization scheme combines an implicit time stepping
scheme with an internal approximation. Uniqueness is proved as well.",1512.09260v2
2016-01-18,Stabilizing the Long-time Behavior of the Navier-Stokes Equations and Damped Euler Systems by Fast Oscillating Forces,"The paper studies the issue of stability of solutions to the Navier-Stokes
and damped Euler systems in periodic boxes. We show that under action of fast
oscillating-in- time external forces all two dimensional regular solutions
converge to a time periodic flow. Unexpectedly, effects of stabilization can be
also obtained for systems with stationary forces with large total momentum
(average of the velocity). Thanks to the Galilean transformation and space
boundary conditions, the stationary force changes into one with time
oscillations. In the three dimensional case we show an analogical result for
weak solutions to the Navier- Stokes equations.",1601.04612v1
2016-01-27,Design of a large dynamic range readout unit for the PSD detector of DAMPE,"A large dynamic range is required by the Plastic Scintillator Detector (PSD)
of DArk Matter Paricle Explorer (DAMPE), and a double-dynode readout has been
developed. To verify this design, a prototype detector module has been
constructed and tested with cosmic rays and heavy ion beams. The results match
with the estimation and the readout unit could easily cover the required
dynamic range.",1601.07234v1
2016-02-09,Engineering and Suppression of Decoherence in Two Qubit Systems,"In this work, two experimentally feasible methods of decoherence
engineering-one based on the application of stochastic classical kicks and the
other based on temporally randomized pulse sequences are combined. A different
coupling interaction is proposed, which leads to amplitude damping as compared
to existing methods which model phase damping, utilizing the $zz$ coupling
interaction. The decoherence process on combining the stochastic kick method
and the randomized pulse sequence method and the effectiveness of dynamical
decoupling under these coupling interactions are analyzed. Finally, a
counter-intuitive result where decoherence is suppressed in the presence of two
noise sources under certain resonant conditions is presented.",1602.03026v1
2016-02-10,Attractors for the strongly damped wave equation with $p$-Laplacian,"This paper is concerned with the initial boundary value problem for one
dimensional strongly damped wave equation involving $p$-Laplacian. For $p>2$,
we establish the existence of weak local attractors for this problem in
$W_{0}^{1,p}(0,1)\times L^{2}(0,1)$. Under restriction $2<p<4$, we prove that
the semigroup, generated by the considered problem, possesses a strong global
attractor in $W_{0}^{1,p}(0,1)\times L^{2}(0,1)$ and this attractor is a
bounded subset of $W^{1,\infty }(0,1)\times W^{1,\infty }(0,1)$.",1602.03339v3
2016-02-11,Renormalization Group Study of a Fragile Fermi liquid in $1+ε$ dimensions,"We present a calculation of the low energy Greens function in $1+\epsilon$
dimensions using the method of extended poor man's scaling, developed here. We
compute the wave function renormalization $Z(\omega)$ and also the decay rate
near the Fermi energy. Despite the lack of $\omega^2$ damping characteristic of
3-dimensional Fermi liquids, we show that quasiparticles do exist in
$1+\epsilon$ dimensions, in the sense that the quasiparticle weight $Z$ is
finite and that the damping rate is smaller than the energy. We explicitly
compute the crossover from this behavior to a 1-dimensional type
Tomonaga-Luttinger liquid behavior at higher energies.",1602.03613v2
2016-02-20,Movement of time-delayed hot spots in Euclidean space,"We investigate the shape of the solution of the Cauchy problem for the damped
wave equation. In particular, we study the existence, location and number of
spatial maximizers of the solution. Studying the shape of the solution of the
damped wave equation, we prepare a decomposed form of the solution into the
heat part and the wave part. Moreover, as its another application, we give
$L^p$-$L^q$ estimates of the solution.",1602.06376v1
2016-03-04,Optical realization of the dissipative quantum oscillator,"An optical realization of the damped quantum oscillator, based on transverse
light dynamics in an optical resonator with slowly-moving mirrors, is
theoretically suggested. The optical resonator setting provides a simple
implementation of the time-dependent Caldirola-Kanai Hamiltonian of the
dissipative quantum oscillator, and enables to visualize the effects of damped
oscillations in the classical (ray optics) limit and wave packet collapse in
the quantum (wave optics) regime.",1603.01364v1
2016-03-08,Modifications of the Lifshitz-Kosevich formula in two-dimensional Dirac systems,"Starting from the Luttinger-Ward functional we derive an expression for the
oscillatory part of the grand potential of a two dimensional Dirac system in a
magnetic field. We perform the computation for the clean and the disordered
system, and we study the effect of electron-electron interactions on the
oscillations. Unlike in the two dimensional electron gas (2DEG), a finite
temperature and impurity scattering also affects the oscillation frequency.
Furthermore, we find that in graphene, compared to the 2DEG, additional
interaction induced damping effects occur: to two-loop order electron-electron
interactions do lead to an additional damping factor in the amplitude of the
Lifshitz-Kosevich-formula.",1603.02559v1
2016-03-23,Landau damping for the linearized Vlasov Poisson equation in a weakly collisional regime,"In this paper, we consider the linearized Vlasov-Poisson equation around an
homogeneous Maxwellian equilibrium in a weakly collisional regime: there is a
parameter $\eps$ in front of the collision operator which will tend to $0$.
Moreover, we study two cases of collision operators, linear Boltzmann and
Fokker-Planck. We prove a result of Landau damping for those equations in
Sobolev spaces uniformly with respect to the collision parameter $\eps$ as it
goes to $0$.",1603.07219v2
2016-04-14,Higher order asymptotic expansions to the solutions for a nonlinear damped wave equation,"We study the Cauchy problem for a nonlinear damped wave equation. Under
suitable assumptions for the nonlinearity and the initial data, we obtain the
global solution which satisfies weighted $L^1$ and $L^\infty$ estimates.
Furthermore, we establish the higher order asymptotic expansion of the
solution. This means that we construct the nonlinear approximation of the
global solution with respect to the weight of the data. Our proof is based on
the approximation formula of the linear solution, which is given in [36], and
the nonlinear approximation theory for a nonlinear parabolic equation developed
by [18].",1604.04100v1
2016-04-18,On the pressureless damped Euler-Poisson equations with non-local forces: Critical thresholds and large-time behavior,"We analyse the one-dimensional pressureless Euler-Poisson equations with a
linear damping and non-local interaction forces. These equations are relevant
for modelling collective behavior in mathematical biology. We provide a sharp
threshold between the supercritical region with finite-time breakdown and the
subcritical region with global-in-time existence of the classical solution. We
derive an explicit form of solution in Lagrangian coordinates which enables us
to study the time-asymptotic behavior of classical solutions with the initial
data in the subcritical region.",1604.05229v1
2016-04-20,Reconstruction for multiwave imaging in attenuating media with large damping coefficient,"In this article we study the reconstruction problem in TAT/PAT on an
attenuating media. Namely, we prove a reconstruction procedure of the initial
condition for the damped wave equation via Neumann series that works for
arbitrary large smooth attenuation coefficients extending the result of Homan
in [1]. We also illustrate the theoretical result by including some numerical
experiments at the end of the paper.",1604.06068v3
2016-04-27,Temperature Dependence Calibration and Correction of the DAMPE BGO Electromagnetic Calorimeter,"A BGO electromagnetic calorimeter (ECAL) is built for the DArk Matter
Particle Explorer (DAMPE) mission. The effect of temperature on the BGO ECAL
was investigated with a thermal vacuum experiment. The light output of a BGO
crystal depends on temperature significantly. The temperature coefficient of
each BGO crystal bar has been calibrated, and a correction method is also
presented in this paper.",1604.08060v1
2016-05-24,Non-existence for fractionally damped fractional differential problems,"In this paper, we are concerned with a fractional differential inequality
containing a lower order fractional derivative and a polynomial source term in
the right hand side. A non-existence of non-trivial global solutions result is
proved in an appropriate space by means of the test-function method. The range
of blow up is found to depend only on the lower order derivative. This is in
line with the well-known fact for an internally weakly damped wave equation
that solutions will converge to solutions of the parabolic part.",1605.07432v1
2016-05-31,On the Benjamin-Bona-Mahony equation with a localized damping,"We introduce several mechanisms to dissipate the energy in the
Benjamin-Bona-Mahony (BBM) equation. We consider either a distributed
(localized) feedback law, or a boundary feedback law. In each case, we prove
the global wellposedness of the system and the convergence towards a solution
of the BBM equation which is null on a band. If the Unique Continuation
Property holds for the BBM equation, this implies that the origin is
asymp-totically stable for the damped BBM equation.",1605.09574v1
2016-06-03,Microscopic derivation of the one qubit Kraus operators for amplitude and phase damping,"This article presents microscopic derivation of the Kraus operators for (the
generalized) amplitude and phase damping process. Derivation is based on the
recently developed method [Andersson et al, J. Mod.Opt. 54, 1695 (2007)] which
concerns finite dimensional systems (e.g. qubit). The form of these operators
is usually estimated without insight into the microscopic details of the
dynamics. The behavior of the qubit dynamics is simulated and depicted via
Bloch sphere change.",1606.01145v1
2016-06-08,Energy Decay in a Wave Guide with Dissipation at Infinity,"We prove local and global energy decay for the wave equation in a wave guide
with damping at infinity. More precisely, the absorption index is assumed to
converge slowly to a positive constant, and we obtain the diffusive phenomenon
typical for the contribution of low frequencies when the damping is effective
at infinity. On the other hand, the usual Geometric Control Condition is not
necessarily satisfied so we may have a loss of regularity for the contribution
of high frequencies. Since our results are new even in the Euclidean space, we
also state a similar result in this case.",1606.02549v2
2016-06-29,Damped Topological Magnons in the Kagomé-Lattice Ferromagnets,"We demonstrate that interactions can substantially undermine the
free-particle description of magnons in ferromagnets on geometrically
frustrated lattices. The anharmonic coupling, facilitated by the
Dzyaloshinskii-Moriya interaction, and a highly-degenerate two-magnon continuum
yield a strong, non-perturbative damping of the high-energy magnon modes. We
provide a detailed account of the effect for the $S=1/2$ ferromagnet on the
kagom\'e lattice and propose further experiments.",1606.09249v3
2016-07-06,Asymptotic profiles of solutions for structural damped wave equations,"In this paper, we obtain several asymptotic profiles of solutions to the
Cauchy problem for structurally damped wave equations $\partial_{t}^{2} u -
\Delta u + \nu (-\Delta)^{\sigma} \partial_{t} u=0$, where $\nu >0$ and $0<
\sigma \le1$. Our result is the approximation formula of the solution by a
constant multiple of a special function as $t \to \infty$, which states that
the asymptotic profiles of the solutions are classified into $5$ patterns
depending on the values $\nu$ and $\sigma$.",1607.01839v1
2016-08-01,Landau-Khalatnikov phonon damping in strongly interacting Fermi gases,"We derive the phonon damping rate due to the four-phonon Landau-Khalatnikov
process in low temperature strongly interacting Fermi gases using quantum
hydrodynamics, correcting and extending the original calculation of Landau and
Khalatnikov [ZhETF, 19 (1949) 637]. Our predictions can be tested in
state-of-the-art experiments with cold atomic gases in the collisionless
regime.",1608.00402v3
2016-08-17,New mechanism of acceleration of particles by stellar black holes,"In this paper we study efficiency of particle acceleration in the
magnetospheres of stellar mass black holes. For this purpose we consider the
linearized set of the Euler equation, continuity equation and Poisson equation
respectively. After introducing the varying relativistic centrifugal force, we
show that the charge separation undergoes the parametric instability, leading
to generation of centrifugally excited Langmuir waves. It is shown that these
waves, via the Langmuir collapse damp by means of the Landau damping, as a
result energy transfers to particles accelerating them to energies of the order
of $10^{16}$eV.",1608.04889v1
2016-09-20,H{ö}lder stability in determining the potential and the damping coefficient in a wave equation,"We improve the preceding results obtained by the first and the second authors
in [3]. They concern the stability issue of the inverse problem that consists
in determining the potential and the damping coefficient in a wave equation
from an initial-to-boundary operator. We partially modify the arguments in [3]
to show that actually we have H{\""o}lder stability instead of logarithmic
stability.",1609.06102v1
2016-10-09,Beam halo study on ATF damping ring,"Halo distribution is a key topic for background study. This paper has
developed an analytical method to give an estimation of ATF beam halo
distribution. The equilibrium particle distribution of the beam tail in the ATF
damping ring is calculated analytically with different emittance and different
vacuum degree. The analytical results agree the measurements very well. This is
a general method which can be applied to any electron rings.",1610.02624v1
2016-10-11,"Damping of hard excitations in strongly coupled $\mathcal N\,{=}\,4$ plasma","The damping of high momentum excitations in strongly coupled maximally
supersymmetric Yang-Mills plasma is studied. Previous calculations of the
asymptotic behavior of the quasinormal mode spectrum are extended and
clarified. We confirm that subleading corrections to the lightlike dispersion
relation $\omega({\bf q}) = |{\bf q}|$ have a universal $|{\bf q}|^{-1/3}$
form. Sufficiently narrow, weak planar shocks may be viewed as coherent
superpositions of short wavelength quasinormal modes. The attenuation and
evolution in profile of narrow planar shocks are examined as an application of
our results.",1610.03491v1
2016-10-24,Assessing the quantumness of a damped two-level system,"We perform a detailed analysis of the nonclassical properties of a damped
two-level system. We compute and compare three different criteria of
quantumness, the $l_1$-norm of coherence, the Leggett- Garg inequality and a
quantum witness based on the no-signaling in time condition. We show that all
three quantum indicators decay exponentially in time as a result of the
coupling to the thermal reservoir. We further demonstrate that the
corresponding characteristic times are identical and given by the coherence
half-life. These results quantify how violations of Leggett-Garg inequalities
and nonzero values of the quantum witness are connected to the coherence of the
two-level system.",1610.07626v1
2016-10-26,Restoring genuine tripartite entanglement under local amplitude damping,"We investigate the possibility to restore genuine tripartite entanglement
under local amplitude damping. We show that it is possible to protect genuine
entanglement using CNOT and Hadamard gates. We analyze several ordering of such
recovery operations. We find that for recovery operations applied after
exposing qubits to decoherence, there is no enhancement in lifetime of genuine
entanglement. Actual retrieval of entanglement is only possible when reversal
scheme is applied before and after the decoherence process. We find that
retrieval of entanglement for mixture of $|\widetilde{W}\rangle$ state with
white noise is more evident than the respective mixture of $|W\rangle$ state.
We also find the retrieval of entanglement for similar mixture of $|GHZ\rangle$
state as well.",1610.08280v1
2016-10-27,Linear Inviscid Damping for Couette Flow in Stratified Fluid,"We study the inviscid damping of Couette flow with an exponentially
stratified density. The optimal decay rates of the velocity field and the
density are obtained for general perturbations with minimal regularity. For
Boussinesq approximation model, the decay rates we get are consistent with the
previous results in the literature. We also study the decay rates for the full
Euler equations of stratified fluids, which were not studied before. For both
models, the decay rates depend on the Richardson number in a very similar way.
Besides, we also study the dispersive decay due to the exponential
stratification when there is no shear.",1610.08924v2
2016-11-01,On the penalty stabilization mechanism for upwind discontinuous Galerkin formulations of first order hyperbolic systems,"Penalty fluxes are dissipative numerical fluxes for high order discontinuous
Galerkin (DG) methods which depend on a penalization parameter. We investigate
the dependence of the spectra of high order DG discretizations on this
parameter, and show that as its value increases, the spectra of the DG
discretization splits into two disjoint sets of eigenvalues. One set converges
to the eigenvalues of a conforming discretization, while the other set
corresponds to spurious eigenvalues which are damped proportionally to the
parameter. Numerical experiments also demonstrate that undamped spurious modes
present in both in the limit of zero and large penalization parameters are
damped for moderate values of the upwind parameter.",1611.00102v2
2016-11-26,Landau damping of surface plasmons in metal nanostructures,"We develop a quantum-mechanical theory for Landau damping of surface plasmons
in metal nanostructures larger that the characteristic length for nonlocal
effects. We show that the electron surface scattering, which facilitates
plasmon decay in small nanostructures, can be incorporated into the metal
dielectric function on par with phonon and impurity scattering. The derived
surface scattering rate is determined by the plasmon local field polarization
relative to the metal-dielectric interface and is highly sensitive to the
system geometry. We illustrate our model by providing analytical results for
surface scattering rate in some common shape nanostructures.",1611.08670v3
2016-11-27,Convergence in probability of an ergodic and conformal multi-symplectic numerical scheme for a damped stochastic NLS equation,"In this paper, we investigate the convergence order in probability of a novel
ergodic numerical scheme for damped stochastic nonlinear Schr\""{o}dinger
equation with an additive noise. Theoretical analysis shows that our scheme is
of order one in probability under appropriate assumptions for the initial value
and noise. Meanwhile, we show that our scheme possesses the unique ergodicity
and preserves the discrete conformal multi-symplectic conservation law.
Numerical experiments are given to show the longtime behavior of the discrete
charge and the time average of the numerical solution, and to test the
convergence order, which verify our theoretical results.",1611.08778v1
2016-12-27,Wiggler for CESR operation at 2 GeV,"For low energy operation strategy we advocate utilization of many short
wigglers in contrast with single long wiggler. This allows begin to operate
very naturally with few strong field wigglers giving necessary damping time on
expense of energy spread. By adding more and more wigglers in the ring, as
these wigglers are manufactured and tuned, the field in the wigglers will be
decreased, keeping necessary damping. This strategy allows the mostly effective
operation of CESR with minimum down time. This also gives flexibility in
operation in wider energy scale without non-reversible modifications.",1612.09227v1
2017-01-30,Energy Transport Property of Charged Particles with Time-Dependent Damping Force via Manifold-Based Analysis Approach,"This paper deals with the energy transport properties of charged particles
with time-dependent damping force. Based on the proposed nonlinear
dimensionless mapping,the stability and dynamical evolution of the particle
system is analyzed with the help of manifold-based analysis approach.It has
been found that the particle system possesses two types of energy asymptotic
behaviors. More significantly, the underlying mechanism of an ""energy barrier""
is uncovered,i.e., one generalized invariant spanning curve emerges in the
dissipative particle system. These results will be useful to enrich the energy
transport behavior knowledge of the particle system.",1701.08762v1
2017-02-22,Integration by parts of some non-adapted vector field from Malliavin's lifting approach,"In this paper we propose a lift of vector field $X$ on a Riemannian manifold
$M$ to a vector field $\tilde{X}$ on the curved Cameron-Martin space
$H\left(M\right)$ named orthogonal lift. The construction of this lift is based
on a least square spirit with respect to a metric on $H(M)$ reflecting the
damping effect of Ricci curvature. Its stochastic extension gives rise to a
non-adapted Cameron-Martin vector field on $W_o(M)$. In particular, if
$M=\mathbb{R}^d$ with Euclidean metric, then the damp disappears and the lift
reduces to the well-known Malliavin's lift. We establish an integration by
parts formula for these first order differential operators.",1702.06741v1
2017-02-23,The sharp lifespan estimate for semilinear damped wave equation with Fujita critical power in high dimensions,"This paper is concerned about the lifespan estimate to the Cauchy problem of
semilinear damped wave equations with the Fujita critical exponent in high
dimensions$(n\geq 4)$. We establish the sharp upper bound of the lifespan in
the following form \begin{equation}\nonumber\\ \begin{aligned}
T(\varepsilon)\leq \exp(C\varepsilon^{-\frac 2n}), \end{aligned} \end{equation}
by using the heat kernel as the test function.",1702.07073v2
2017-03-09,Off resonance coupling between a cavity mode and an ensemble of driven spins,"We study the interaction between a superconducting cavity and a spin
ensemble. The response of a cavity mode is monitored while simultaneously the
spins are driven at a frequency close to their Larmor frequency, which is tuned
to a value much higher than the cavity resonance. We experimentally find that
the effective damping rate of the cavity mode is shifted by the driven spins.
The measured shift in the damping rate is attributed to the retarded response
of the cavity mode to the driven spins. The experimental results are compared
with theoretical predictions and fair agreement is found.",1703.03311v1
2017-03-10,Negative Landau damping in bilayer graphene,"We theoretically demonstrate that a system formed by two coupled graphene
sheets enables a negative damping regime wherein graphene plasmons are pumped
by a DC current. This effect is triggered by electrons drifting through one of
the graphene sheets and leads to the spontaneous light emission (spasing) and
wave instabilities in the mid-infrared range. It is shown that there is a deep
link between the drift-induced instabilities and wave instabilities in moving
media, as both result from the hybridization of oscillators with oppositely
signed frequencies. With a thickness of few nanometers and wide spectral
tunability, the proposed structure may find interesting applications in
nanophotonic circuitry as an on-chip light source.",1703.03623v1
2017-03-10,Effects on the CMB from magnetic field dissipation before recombination,"Magnetic fields present before decoupling are damped due to radiative
viscosity. This energy injection affects the thermal and ionization history of
the cosmic plasma. The implications for the CMB anisotropies and polarization
are investigated for different parameter choices of a non helical stochastic
magnetic field. Assuming a Gaussian smoothing scale determined by the magnetic
damping wave number at recombination it is found that magnetic fields with
present day strength less than 0.1 nG and negative magnetic spectral indices
have a sizeable effect on the CMB temperature anisotropies and polarization.",1703.03650v1
2017-03-28,(1+1) Newton-Hooke Group for the Simple and Damped Harmonic Oscillator,"It is demonstrated that, in the framework of the orbit method, a simple and
damped harmonic oscillators are indistinguishable at the level of an abstract
Lie algebra. This opens a possibility for treating the dissipative systems
within the orbit method. In depth analysis of the coadjoint orbits of the
$(1+1)$ dimensional Newton-Hooke group are presented. Further, it is argued
that the physical interpretation is carried by a specific realisation of the
Lie algebra of smooth functions on a phase space rather than by an abstract Lie
algebra.",1703.09583v2
2017-04-09,Controllability of the Strongly Damped Impulsive Semilinear Wave Equation with Memory and Delay,"This article is devoted to study the interior approximated controllability of
the strongly damped semilinear wave equation with memory, impulses and delay
terms. The problem is challenging since the state equation contains memory and
impulsive terms yielding to potential unbounded control sequences steering the
system to a neighborhood of the final state, thus fixed point theorems cannot
be used directly. As alternative, the A.E Bashirov and et al. techniques are
applied and together with the delay allow the control solution to be directed
to fixed curve in a short time interval and achieve our result.",1704.02561v1
2017-04-12,Damping parametric instabilities in future gravitational wave detectors by means of electrostatic actuators,"It has been suggested that the next generation of interferometric
gravitational wave detectors may observe spontaneously excited parametric
oscillatory instabilities. We present a method of actively suppressing any such
instability through application of electrostatic forces to the interferometers'
test masses. Using numerical methods we quantify the actuation force required
to damp candidate instabilities and find that such forces are readily
achievable. Our predictions are subsequently verified experimentally using
prototype Advanced LIGO hardware, conclusively demonstrating the effectiveness
of our approach.",1704.03587v1
2017-04-28,Cross-damping effects in 1S-3S spectroscopy of hydrogen and deuterium,"We calculate the cross-damping frequency shift of a laser-induced two-photon
transition monitored through decay fluorescence, by adapting the analogy with
Raman scattering developed by Amaro et al. [P. Amaro et al., PRA 92, 022514
(2015)]. We apply this method to estimate the frequency shift of the 1S-3S
transition in hydrogen and deuterium. Taking into account our experimental
conditions, we find a frequency shift of less than 1 kHz, that is smaller than
our current statistical uncertainty.",1704.09003v1
2017-05-15,Damping self-forces and Asymptotic Symmetries,"Energy conservation in radiating processes requires, at the classical level,
to take into account damping forces on the sources. These forces can be
represented in terms of asymptotic data and lead to charges defined as
integrals over the asymptotic boundary. For scattering processes these charges,
in case of zero radiated energy, are conserved and encode the information about
the sub-leading soft theorems and matching conditions. The QED version of the
self forces is associated with the dependence of the differential cross section
on the infrared resolution scale.",1705.05297v2
2017-05-17,Exact Model Reduction for Damped-Forced Nonlinear Beams: An Infinite-Dimensional Analysis,"We use invariant manifold results on Banach spaces to conclude the existence
of spectral submanifolds (SSMs) in a class of nonlinear, externally forced beam
oscillations. SSMs are the smoothest nonlinear extensions of spectral subspaces
of the linearized beam equation. Reduction of the governing PDE to SSMs
provides an explicit low-dimensional model which captures the correct
asymptotics of the full, infinite-dimensional dynamics. Our approach is general
enough to admit extensions to other types of continuum vibrations. The
model-reduction procedure we employ also gives guidelines for a mathematically
self-consistent modeling of damping in PDEs describing structural vibrations.",1705.06133v1
2017-06-26,Weighted energy estimates for wave equation with space-dependent damping term for slowly decaying initial data,"This paper is concerned with weighted energy estimates for solutions to wave
equation $\partial_t^2u-\Delta u + a(x)\partial_tu=0$ with space-dependent
damping term $a(x)=|x|^{-\alpha}$ $(\alpha\in [0,1))$ in an exterior domain
$\Omega$ having a smooth boundary. The main result asserts that the weighted
energy estimates with weight function like polymonials are given and these
decay rate are almost sharp, even when the initial data do not have compact
support in $\Omega$. The crucial idea is to use special solution of $\partial_t
u=|x|^{\alpha}\Delta u$ including Kummer's confluent hypergeometric functions.",1706.08311v1
2017-08-09,Global well-posedness for the 2D Boussinesq equations with a velocity damping term,"In this paper, we prove global well-posedness of smooth solutions to the
two-dimensional incompressible Boussinesq equations with only a velocity
damping term when the initial data is close to an nontrivial equilibrium state
$(0,x_2)$. As a by-product, under this equilibrium state, our result gives a
positive answer to the question proposed by [ACWX] (see P.3597).",1708.02695v4
2017-08-18,Second sound in systems of one-dimensional fermions,"We study sound in Galilean invariant systems of one-dimensional fermions. At
low temperatures, we find a broad range of frequencies in which in addition to
the waves of density there is a second sound corresponding to ballistic
propagation of heat in the system. The damping of the second sound mode is
weak, provided the frequency is large compared to a relaxation rate that is
exponentially small at low temperatures. At lower frequencies the second sound
mode is damped, and the propagation of heat is diffusive.",1708.05733v2
2017-08-21,Equilibrium of a Brownian particle with coordinate dependent diffusivity and damping: Generalized Boltzmann distribution,"Fick's law for coordinate dependent diffusivity is derived. Corresponding
diffusion current in the presence of coordinate dependent diffusivity is
consistent with the form as given by Kramers-Moyal expansion. We have obtained
the equilibrium solution of the corresponding Smoluchowski equation. The
equilibrium distribution is a generalization of the Boltzmann distribution.
This generalized Boltzmann distribution involves an effective potential which
is a function of coordinate dependent diffusivity. We discuss various
implications of the existence of this generalized Boltzmann distribution for
equilibrium of systems with coordinate dependent diffusivity and damping.",1708.06132v5
2017-08-21,Global small solutions of 3D incompressible Oldroyd-B model without damping mechanism,"In this paper, we prove the global existence of small smooth solutions to the
three-dimensional incompressible Oldroyd-B model without damping on the stress
tensor. The main difficulty is the lack of full dissipation in stress tensor.
To overcome it, we construct some time-weighted energies based on the special
coupled structure of system. Such type energies show the partial dissipation of
stress tensor and the strongly full dissipation of velocity. In the view of
treating ""nonlinear term"" as a ""linear term"", we also apply this result to 3D
incompressible viscoelastic system with Hookean elasticity and then prove the
global existence of small solutions without the physical assumption (div-curl
structure) as previous works.",1708.06172v2
2017-10-13,$L^2$ asymptotic profiles of solutions to linear damped wave equations,"In this paper we obtain higher order asymptotic profilles of solutions to the
Cauchy problem of the linear damped wave equation in $\textbf{R}^n$
\begin{equation*} u_{tt}-\Delta u+u_t=0, \qquad u(0,x)=u_0(x), \quad
u_t(0,x)=u_1(x), \end{equation*} where $n\in\textbf{N}$ and $u_0$, $u_1\in
L^2(\textbf{R}^n)$. Established hyperbolic part of asymptotic expansion seems
to be new in the sense that the order of the expansion of the hyperbolic part
depends on the spatial dimension.",1710.04870v1
2017-11-06,Linear inviscid damping and enhanced dissipation for the Kolmogorov flow,"In this paper, we prove the linear inviscid damping and voticity depletion
phenomena for the linearized Euler equations around the Kolmogorov flow. These
results confirm Bouchet and Morita's predictions based on numerical analysis.
By using the wave operator method introduced by Li, Wei and Zhang, we solve
Beck and Wayne's conjecture on the optimal enhanced dissipation rate for the
2-D linearized Navier-Stokes equations around the bar state called Kolmogorov
flow. The same dissipation rate is proved for the Navier-Stokes equations if
the initial velocity is included in a basin of attraction of the Kolmogorov
flow with the size of $\nu^{\frac 23+}$, here $\nu$ is the viscosity
coefficient.",1711.01822v1
2017-11-27,Statistical mechanics of Landau damping,"Landau damping is the tendency of solutions to the Vlasov equation towards
spatially homogeneous distribution functions. The distribution functions
however approach the spatially homogeneous manifold only weakly, and Boltzmann
entropy is not changed by Vlasov equation. On the other hand, density and
kinetic energy density, which are integrals of the distribution function,
approach spatially homogeneous states strongly, which is accompanied by growth
of the hydrodynamic entropy. Such a behavior can be seen when Vlasov equation
is reduced to the evolution equations for density and kinetic energy density by
means of the Ehrenfest reduction.",1711.10022v1
2017-11-29,Lepton-portal Dark Matter in Hidden Valley model and the DAMPE recent results,"We study the recent $e^\pm$ cosmic ray excess reported by DAMPE in a Hidden
Valley Model with lepton-portal dark matter. We find the electron-portal can
account for the excess well and satisfy the DM relic density and direct
detection bounds, while electron+muon/electron+muon+tau-portal suffers from
strong constraints from lepton flavor violating observables, such as $\mu \to 3
e$. We also discuss possible collider signatures of our model, both at the LHC
and a future 100 TeV hadron collider.",1711.11058v3
2017-11-30,"Radiative Dirac neutrino mass, DAMPE dark matter and leptogenesis","We explain the electron-positron excess reported by the DAMPE collaboration
recently in a radiative Dirac seesaw model where a dark $U(1)_X$ gauge symmetry
can (i) forbid the tree-level Yukawa couplings of three right-handed neutrinos
to the standard model lepton and Higgs doublets, (ii) predict the existence of
three dark fermions for the gauge anomaly cancellation, (iii) mediate a
testable scattering of the lightest dark fermion off the nucleons. Our model
can also accommodate a successful leptogenesis to generate the cosmic baryon
asymmetry.",1711.11333v2
2017-12-13,Sub-logistic source can prevent blow-up in the 2D minimal Keller-Segel chemotaxis system,"It is well-known that the Neumann initial-boundary value problem for the
minimal-chemotaxis-logistic system in a 2D bounded smooth domain has no blow-up
for any choice of parameters. Here, for a large class of kinetic terms
including sub-logistic sources, we show that the corresponding 2D Neumann
initial-boundary value problems do not possess any blow-up. This illustrates a
new phenomenon that even a class of sub-logistic sources can prevent blow-up
for the 2D problem, indicating that logistic damping is not the weakest damping
to guarantee uniform-in-time boundedness for the 2D minimal Keller-Segel
chemotaxis model.",1712.04739v1
2017-12-16,Convergence to Equilibrium in Wasserstein distance for damped Euler equations with interaction forces,"We develop tools to construct Lyapunov functionals on the space of
probability measures in order to investigate the convergence to global
equilibrium of a damped Euler system under the influence of external and
interaction potential forces with respect to the 2-Wasserstein distance. We
also discuss the overdamped limit to a nonlocal equation used in the modelling
of granular media with respect to the 2-Wasserstein distance, and provide
rigorous proofs for particular examples in one spatial dimension.",1712.05923v2
2017-12-27,Normal-mode-based analysis of electron plasma waves with second-order Hermitian formalism,"The classic problem of the dynamic evolution of Langmuir electron waves in a
collisionless plasma and their Landau damping is cast as a second-order,
self-adjoint problem with a continuum spectrum of real and positive squared
frequencies. The corresponding complete basis of singular normal modes is
obtained, along with their orthogonality relation. This yields easily the
general expression of the time-reversal-invariant solution for any
initial-value problem. An example is given for a specific initial condition
that illustrates the Landau damping of the macroscopic moments of the
perturbation.",1712.09682v1
2018-01-19,Discontinuous energy shaping control of the Chaplygin sleigh,"In this paper we present an energy shaping control law for set-point
regulation of the Chaplygin sleigh. It is well known that nonholonomic
mechanical systems cannot be asymptotically stabilised using smooth control
laws as they do no satisfy Brockett's necessary condition for smooth
stabilisation. Here, we propose a discontinuous control law that can be seen as
a potential energy shaping and damping injection controller. The proposed
controller is shown to be robust against the parameters of both the inertia
matrix and the damping structure of the open-loop system.",1801.06278v1
2018-01-19,Robust integral action of port-Hamiltonian systems,"Interconnection and damping assignment, passivity-based control (IDA-PBC) has
proven to be a successful control technique for the stabilisation of many
nonlinear systems. In this paper, we propose a method to robustify a system
which has been stabilised using IDA-PBC with respect to constant, matched
disturbances via the addition of integral action. The proposed controller
extends previous work on the topic by being robust against the damping of the
system, a quantity which may not be known in many applications.",1801.06279v1
2018-01-19,A study of Landau damping with random initial inputs,"For the Vlasov-Poisson equation with random uncertain initial data, we prove
that the Landau damping solution given by the deterministic counterpart
(Caglioti and Maffei, {\it J. Stat. Phys.}, 92:301-323, 1998) depends smoothly
on the random variable if the time asymptotic profile does, under the
smoothness and smallness assumptions similar to the deterministic case. The
main idea is to generalize the deterministic contraction argument to more
complicated function spaces to estimate derivatives in space, velocity and
random variables. This result suggests that the random space regularity can
persist in long-time even in time-reversible nonlinear kinetic equations.",1801.06304v1
2018-01-31,Smoluchowski-Kramers approximation for the damped stochastic wave equation with multiplicative noise in any spatial dimension,"We show that the solutions to the damped stochastic wave equation converge
pathwise to the solution of a stochastic heat equation. This is called the
Smoluchowski-Kramers approximation. Cerrai and Freidlin have previously
demonstrated that this result holds in the cases where the system is exposed to
additive noise in any spatial dimension or when the system is exposed to
multiplicative noise and the spatial dimension is one. The current paper proves
that the Smoluchowski-Kramers approximation is valid in any spatial dimension
when the system is exposed to multiplicative noise.",1801.10538v1
2018-02-26,Controllability and observability for non-autonomous evolution equations: the averaged Hautus test,"We consider the observability problem for non-autonomous evolution systems
(i.e., the operators governing the system depend on time). We introduce an
averaged Hautus condition and prove that for skew-adjoint operators it
characterizes exact observability. Next, we extend this to more general class
of operators under a growth condition on the associated evolution family. We
give an application to the Schr\""odinger equation with time dependent potential
and the damped wave equation with a time dependent damping coefficient.",1802.09224v1
2018-02-28,Global-in-time Stability of 2D MHD boundary Layer in the Prandtl-Hartmann Regime,"In this paper, we prove global existence of solutions with analytic
regularity to the 2D MHD boundary layer equations in the mixed Prandtl and
Hartmann regime derived by formal multi-scale expansion in \cite{GP}. The
analysis shows that the combined effect of the magnetic diffusivity and
transveral magnetic field on the boundary leads to a linear damping on the
tangential velocity field near the boundary. And this damping effect yields the
global in time analytic norm estimate in the tangential space variable on the
perturbation of the classical steady Hartmann profile.",1802.10494v3
2018-02-28,Modal approach to the controllability problem of distributed parameter systems with damping,"This paper is devoted to the controllability analysis of a class of linear
control systems in a Hilbert space. It is proposed to use the minimum energy
controls of a reduced lumped parameter system for solving the infinite
dimensional steering problem approximately. Sufficient conditions of the
approximate controllability are formulated for a modal representation of a
flexible structure with small damping.",1803.00129v1
2018-03-14,Study of Quantum Walk over a Square Lattice,"Quantum random walk finds application in efficient quantum algorithms as well
as in quantum network theory. Here we study the mixing time of a discrete
quantum walk over a square lattice in presence percolation and decoherence. We
consider bit-flip and phase damping noise, and evaluate the instantaneous
mixing time for both the cases. Using numerical analysis we show that in case
of phase damping noise probability distribution of walker's position is
sufficiently close to the uniform distribution after infinite time. However,
during the action of bit-flip noise, even after infinite time the total
variation distance between the two probability distributions is large enough.",1803.05152v1
2018-03-15,Improving the capacity of quantum dense coding by weak measurement and reversal measurement,"A protocol of quantum dense coding protection of two qubits is proposed in
amplitude damping (AD) channel using weak measurement and reversal measurement.
It is found that the capacity of quantum dense coding under the weak
measurement and reversal measurement is always greater than that without weak
measurement and reversal measurement. When the protocol is applied, for the AD
channels with different damping coefficient, the result reflects that quantum
entanglement can be protected and quantum dense coding becomes successful.",1803.05678v1
2018-04-10,Motion of a superconducting loop in an inhomogeneous magnetic field: a didactic experiment,"We present an experiment conductive to an understanding of both Faraday's law
and the properties of the superconducting state. It consists in the analysis of
the motion of a superconducting loop moving under the influence of gravity in
an inhomogeneous horizontal magnetic field. Gravity, conservation of magnetic
flux, and friction combine to give damped harmonic oscillations. The measured
frequency of oscillation and the damping constant as a function of the magnetic
field strength (the only free parameter) are in good agreement with the
theoretical model.",1804.03553v1
2018-05-08,Optomechanical damping as the origin of sideband asymmetry,"Sideband asymmetry in cavity optomechanics has been explained by particle
creation and annihilation processes, which bestow an amplitude proportional to
'n+1' and 'n' excitations to each of the respective sidebands. We discuss the
issues with this as well as other interpretations, such as quantum backaction
and noise interference, and show that the asymmetry is due to the
optomechanical damping caused by the probe and the cooling lasers instead.",1805.02952v4
2018-05-11,On the asymptotic stability of stratified solutions for the 2D Boussinesq equations with a velocity damping term,"We consider the 2D Boussinesq equations with a velocity damping term in a
strip $\mathbb{T}\times[-1,1]$, with impermeable walls. In this physical
scenario, where the \textit{Boussinesq approximation} is accurate when
density/temperature variations are small, our main result is the asymptotic
stability for a specific type of perturbations of a stratified solution. To
prove this result, we use a suitably weighted energy space combined with linear
decay, Duhamel's formula and ""bootstrap"" arguments.",1805.05179v2
2018-06-30,A linearized and conservative Fourier pseudo-spectral method for the damped nonlinear Schrödinger equation in three dimensions,"In this paper, we propose a linearized Fourier pseudo-spectral method, which
preserves the total mass and energy conservation laws, for the damped nonlinear
Schr\""{o}dinger equation in three dimensions. With the aid of the semi-norm
equivalence between the Fourier pseudo-spectral method and the finite
difference method, an optimal $L^2$-error estimate for the proposed method
without any restriction on the grid ratio is established by analyzing the real
and imaginary parts of the error function. Numerical results are addressed to
confirm our theoretical analysis.",1807.00091v3
2018-07-11,Global existence and blow-up for semilinear damped wave equations in three space dimensions,"We consider initial value problem for semilinear damped wave equations in
three space dimensions. We show the small data global existence for the problem
without the spherically symmetric assumption and obtain the sharp lifespan of
the solutions. This paper is devoted to a proof of the Takamura's conjecture on
the lifespan of solutions.",1807.04327v3
2018-07-18,B-field induced mixing between Langmuir waves and axions,"We present an analytic study of the dispersion relation for an isotropic
magnetized plasma interacting with axions. We provide a quantitative picture of
the electromagnetic plasma oscillations in both the ultrarelativistic and
nonrelativistic regimes and considering both non-degenerate and degenerate
media, accounting for the dispersion curves as a function of the plasma
temperature and the ratio of the plasma phase velocity to the characteristic
velocity of particles. We include the modifications on the Landau damping of
plasma waves induced by the presence of the axion field, and we comment on the
effects of damping on subluminal plasma oscillations.",1807.06828v2
2018-07-26,Moment conditions and lower bounds in expanding solutions of wave equations with double damping terms,"In this report we obtain higher order asymptotic expansions of solutions to
wave equations with frictional and viscoelastic damping terms. Although the
diffusion phenomena are dominant, differences between the solutions we deal
with and those of heat equations can be seen by comparing the second order
expansions of them. In order to analyze such effects we consider the weighted
L1 initial data. We also give some lower bounds which show the optimality of
obtained expansions.",1807.10020v1
2018-08-16,Continuity of the set equilibria of non-autonomous damped wave equations with terms concentrating on the boundary,"In this paper we are interested in the behavior of the solutions of
non-autonomous damped wave equations when some reaction terms are concentrated
in a neighborhood of the boundary and this neighborhood shrinks to boundary as
a parameter \varepsilon goes to zero. We prove the conti- nuity of the set
equilibria of these equations. Moreover, if an equilibrium solution of the
limit problem is hyperbolic, then we show that the per- turbed equation has one
and only one equilibrium solution nearby.",1808.05667v1
2018-08-30,Protecting temporal correlations of two-qubit states using quantum channels with memory,"Quantum temporal correlations exhibited by violations of Leggett-Garg
Inequality (LGI) and Temporal Steering Inequality (TSI) are in general found to
be non-increasing under decoherence channels when probed on two-qubit pure
entangled states. We study the action of decoherence channels, such as
amplitude damping, phase-damping and depolarising channels when partial memory
is introduced in a way such that two consecutive uses of the channels are
time-correlated. We show that temporal correlations demonstrated by violations
of the above temporal inequalities can be protected against decoherence using
the effect of memory.",1808.10345v1
2018-09-17,Global existence for weakly coupled systems of semi-linear structurally damped $σ$-evolution models with different power nonlinearities,"In this paper, we study the Cauchy problems for weakly coupled systems of
semi-linear structurally damped $\sigma$-evolution models with different power
nonlinearities. By assuming additional $L^m$ regularity on the initial data,
with $m \in [1,2)$, we use $(L^m \cap L^2)- L^2$ and $L^2- L^2$ estimates for
solutions to the corresponding linear Cauchy problems to prove the global (in
time) existence of small data Sobolev solutions to the weakly coupled systems
of semi-linear models from suitable function spaces.",1809.06744v2
2018-09-25,On the energy decay rates for the 1D damped fractional Klein-Gordon equation,"We consider the fractional Klein-Gordon equation in one spatial dimension,
subjected to a damping coefficient, which is non-trivial and periodic, or more
generally strictly positive on a periodic set. We show that the energy of the
solution decays at the polynomial rate $O(t^{-\frac{s}{4-2s}})$ for $0< s<2 $
and at some exponential rate when $s\geq 2$. Our approach is based on the
asymptotic theory of $C_0$ semigroups in which one can relate the decay rate of
the energy in terms of the resolvent growth of the semigroup generator. The
main technical result is a new observability estimate for the fractional
Laplacian, which may be of independent interest.",1809.09531v1
2018-10-15,Global well-posedness in the critical Besov spaces for the incompressible Oldroyd-B model without damping mechanism,"We prove the global well-posedness in the critical Besov spaces for the
incompressible Oldroyd-B model without damping mechanism on the stress tensor
in $\mathbb{R}^d$ for the small initial data. Our proof is based on the
observation that the behaviors of Green's matrix to the system of
$\big(u,(-\Delta)^{-\frac12}\mathbb{P}\nabla\cdot\tau\big)$ as well as the
effects of $\tau$ change from the low frequencies to the high frequencies and
the construction of the appropriate energies in different frequencies.",1810.06171v1
2018-10-18,Global solutions to the $n$-dimensional incompressible Oldroyd-B model without damping mechanism,"The present work is dedicated to the global solutions to the incompressible
Oldroyd-B model without damping on the stress tensor in $\mathbb{R}^n(n=2,3)$.
This result allows to construct global solutions for a class of highly
oscillating initial velocity. The proof uses the special structure of the
system. Moreover, our theorem extends the previous result by Zhu [19] and
covers the recent result by Chen and Hao [4].",1810.08048v3
2018-10-30,Global well-posedness for nonlinear wave equations with supercritical source and damping terms,"We prove the global well-posedness of weak solutions for nonlinear wave
equations with supercritical source and damping terms on a three-dimensional
torus $\mathbb T^3$ of the prototype \begin{align*} &u_{tt}-\Delta
u+|u_t|^{m-1}u_t=|u|^{p-1}u, \;\; (x,t) \in \mathbb T^3 \times \mathbb R^+ ;
\notag\\ &u(0)=u_0 \in H^1(\mathbb T^3)\cap L^{m+1}(\mathbb T^3), \;\;
u_t(0)=u_1\in L^2(\mathbb T^3), \end{align*} where $1\leq p\leq \min\{
\frac{2}{3} m + \frac{5}{3} , m \}$. Notably, $p$ is allowed to be larger than
$6$.",1810.12476v1
2018-11-02,Nonlinear Damped Timoshenko Systems with Second Sound - Global Existence and Exponential Stability,"In this paper, we consider nonlinear thermoelastic systems of Timoshenko type
in a one-dimensional bounded domain. The system has two dissipative mechanisms
being present in the equation for transverse displacement and rotation angle -
a frictional damping and a dissipation through hyperbolic heat conduction
modelled by Cattaneo's law, respectively. The global existence of small, smooth
solutions and the exponential stability in linear and nonlinear cases are
established.",1811.01128v1
2018-11-14,Quantum witness of a damped qubit with generalized measurements,"We evaluate the quantum witness based on the no-signaling-in-time condition
of a damped two-level system for nonselective generalized measurements of
varying strength. We explicitly compute its dependence on the measurement
strength for a generic example. We find a vanishing derivative for weak
measurements and an infinite derivative in the limit of projective
measurements. The quantum witness is hence mostly insensitive to the strength
of the measurement in the weak measurement regime and displays a singular,
extremely sensitive dependence for strong measurements. We finally relate this
behavior to that of the measurement disturbance defined in terms of the
fidelity between pre-measurement and post-measurement states.",1811.06013v1
2018-12-11,Blow up of solutions to semilinear non-autonomous wave equations under Robin boundary conditions,"The problem of blow up of solutions to the initial boundary value problem for
non-autonomous semilinear wave equation with damping and accelerating terms
under the Robin boundary condition is studied. Sufficient conditions of blow up
in a finite time of solutions to semilinear damped wave equations with
arbitrary large initial energy are obtained. A result on blow up of solutions
with negative initial energy of semilinear second order wave equation with
accelerating term is also obtained.",1812.04595v1
2018-12-23,Global existence of weak solutions for strongly damped wave equations with nonlinear boundary conditions and balanced potentials,"We demonstrate the global existence of weak solutions to a class of
semilinear strongly damped wave equations possessing nonlinear hyperbolic
dynamic boundary conditions. Our work assumes $(-\Delta_W)^\theta \partial_tu$
with $\theta\in[\frac{1}{2},1)$ and where $\Delta_W$ is the Wentzell-Laplacian.
Hence, the associated linear operator admits a compact resolvent. A balance
condition is assumed to hold between the nonlinearity defined on the interior
of the domain and the nonlinearity on the boundary. This allows for arbitrary
(supercritical) polynomial growth on each potential, as well as mixed
dissipative/anti-dissipative behavior. Moreover, the nonlinear function defined
on the interior of the domain is assumed to be only $C^0$.",1812.09781v1
2018-12-24,Cold Damping of an Optically Levitated Nanoparticle to micro-Kelvin Temperatures,"We implement a cold damping scheme to cool one mode of the center-of-mass
motion of an optically levitated nanoparticle in ultrahigh vacuum from room
temperature to a record-low temperature of 100 micro-Kelvin. The measured
temperature dependence on feedback gain and thermal decoherence rate is in
excellent agreement with a parameter-free model. We determine the
imprecision-backaction product for our system and provide a roadmap towards
ground-state cooling of optically levitated nanoparticles.",1812.09875v1
2019-01-18,Decay of semilinear damped wave equations:cases without geometric control condition,"We consider the semilinear damped wave equation $\partial_{tt}^2
u(x,t)+\gamma(x)\partial_t u(x,t)=\Delta u(x,t)-\alpha u(x,t)-f(x,u(x,t))$. In
this article, we obtain the first results concerning the stabilization of this
semilinear equation in cases where $\gamma$ does not satisfy the geometric
control condition. When some of the geodesic rays are trapped, the
stabilization of the linear semigroup is semi-uniform in the sense that
$\|e^{At}A^{-1}\|\leq h(t)$ for some function $h$ with $h(t)\rightarrow 0$ when
$t\rightarrow +\infty$. We provide general tools to deal with the semilinear
stabilization problem in the case where $h(t)$ has a sufficiently fast decay.",1901.06169v1
2019-02-04,Non-Markovian Effects on Overdamped Systems,"We study the consequences of adopting the memory dependent, non-Markovian,
physics with the memory-less over-damped approximation usually employed to
investigate Brownian particles. Due to the finite correlation time scale
associated with the noise, the stationary behavior of the system is not
described by the Boltzmann-Gibbs statistics. However, the presence of a very
weak external white noise can be used to regularize the equilibrium properties.
Surprisingly, the coupling to another bath effectively restores the dynamical
aspects missed by the over-damped treatment.",1902.01356v1
2019-02-06,Stability analysis of a 1D wave equation with a nonmonotone distributed damping,"This paper is concerned with the asymptotic stability analysis of a one
dimensional wave equation subject to a nonmonotone distributed damping. A
well-posedness result is provided together with a precise characterization of
the asymptotic behavior of the trajectories of the system under consideration.
The well-posedness is proved in the nonstandard L p functional spaces, with p
$\in$ [2, $\infty$], and relies mostly on some results collected in Haraux
(2009). The asymptotic behavior analysis is based on an attractivity result on
a specific infinite-dimensional linear time-variant system.",1902.02050v1
2019-02-13,"Comment on ""Quantization of the damped harmonic oscillator"" [Serhan et al, J. Math. Phys. 59, 082105 (2018)]","A recent paper [J. Math. Phys. {\bf 59}, 082105 (2018)] constructs a
Hamiltonian for the (dissipative) damped harmonic oscillator. We point out that
non-Hermiticity of this Hamiltonian has been ignored to find real discrete
eigenvalues which are actually non-real. We emphasize that non-Hermiticity in
Hamiltonian is crucial and it is a quantal signature of dissipation.",1902.04895v1
2019-02-15,Memory effects teleportation of quantum Fisher information under decoherence,"We have investigated how memory effects on the teleportation of quantum
Fisher information(QFI) for a single qubit system using a class of X-states as
resources influenced by decoherence channels with memory, including amplitude
damping, phase-damping and depolarizing channels. Resort to the definition of
QFI, we first derive the explicit analytical results of teleportation of QFI
with respect to weight parameter $\theta$ and phase parameter $\phi$ under the
decoherence channels. Component percentages, the teleportation of QFI for a
two-qubit entanglement system has also been addressed. The remarkable
similarities and differences among these two situations are also analyzed in
detail and some significant results are presented.",1902.05668v1
2019-02-23,Uniform decay rates for a suspension bridge with locally distributed nonlinear damping,"We study a nonlocal evolution equation modeling the deformation of a bridge,
either a footbridge or a suspension bridge. Contrarily to the previous
literature we prove the asymptotic stability of the considered model with a
minimum amount of damping which represents less cost of material. The result is
also numerically proved.",1902.09963v1
2019-03-01,Spectra of the Dissipative Spin Chain,"This paper generalizes the (0+1)-dimensional spin-boson problem to the
corresponding (1+1)-dimensional version. Monte Carlo simulation is used to find
the phase diagram and imaginary time correlation function. The real frequency
spectrum is recovered by the newly developed P\'ade regression analytic
continuation method. We find that, as dissipation strength $\alpha$ is
increased, the sharp quasi-particle spectrum is broadened and the peak
frequency is lower. According to the behavior of the low frequency spectrum, we
classify the dynamical phase into three different regions: weakly damped,
linear $k$-edge, and strongly damped.",1903.00567v1
2019-03-17,Sensing Kondo correlations in a suspended carbon nanotube mechanical resonator with spin-orbit coupling,"We study electron mechanical coupling in a suspended carbon nanotube (CNT)
quantum dot device. Electron spin couples to the flexural vibration mode due to
spin-orbit coupling in the electron tunneling processes. In the weak coupling
limit, i.e. electron-vibration coupling is much smaller than the electron
energy scale, the damping and resonant frequency shift of the CNT resonator can
be obtained by calculating the dynamical spin susceptibility. We find that
strong spin-flip scattering processes in Kondo regime significantly affect the
mechanical motion of the carbon nanotube: Kondo effect induces strong damping
and frequency shift of the CNT resonator.",1903.07049v1
2019-03-27,Lifespan of semilinear generalized Tricomi equation with Strauss type exponent,"In this paper, we consider the blow-up problem of semilinear generalized
Tricomi equation. Two blow-up results with lifespan upper bound are obtained
under subcritical and critical Strauss type exponent. In the subcritical case,
the proof is based on the test function method and the iteration argument. In
the critical case, an iteration procedure with the slicing method is employed.
This approach has been successfully applied to the critical case of semilinear
wave equation with perturbed Laplacian or the damped wave equation of
scattering damping case. The present work gives its application to the
generalized Tricomi equation.",1903.11351v2
2019-04-01,A remark on semi-linear damped $σ$-evolution equations with a modulus of continuity term in nonlinearity,"In this article, we indicate that under suitable assumptions of a modulus of
continuity we obtain either the global (in time) existence of small data
Sobolev solutions or the blow-up result of local (in time) Sobolev solutions to
semi-linear damped $\sigma$-evolution equations with a modulus of continuity
term in nonlinearity.",1904.00698v3
2019-04-05,Critical regularity of nonlinearities in semilinear classical damped wave equations,"In this paper we consider the Cauchy problem for the semilinear damped wave
equation
  $u_{tt}-\Delta u + u_t = h(u);\qquad u(0;x) = f(x); \quad u_t(0;x) = g(x);$
  where $h(s) = |s|^{1+2/n}\mu(|s|)$. Here n is the space dimension and $\mu$
is a modulus of continuity. Our goal is to obtain sharp conditions on $\mu$ to
obtain a threshold between global (in time) existence of small data solutions
(stability of the zerosolution) and blow-up behavior even of small data
solutions.",1904.02939v1
2019-04-29,Origin of the DAMPE 1.4 TeV peak,"Recent accurate measurements of cosmic ray electron flux by the Dark Matter
Particle Explorer (DAMPE) reveal a sharp peak structure near 1.4 TeV, which is
difficult to explain by standard astrophysical processes. In this letter, we
propose a simple model that the enhanced dark matter annihilation via the
$e^+e^-$ channel and with the thermal relic annihilation cross section around
the current nearest black hole (A0620-00) can satisfactorily account for the
sharp peak structure. The predicted dark matter mass is $\sim 1.5-3$ TeV.",1904.12418v1
2019-05-07,Decay estimate for the solution of the evolutionary damped $p$-Laplace equation,"In this note, we study the asymptotic behavior, as $t$ tends to infinity, of
the solution $u$ to the evolutionary damped $p$-Laplace equation
\begin{equation*}
  u_{tt}+a\, u_t =\Delta_p u \end{equation*}
  with Dirichlet boundary values. Let $u^*$ denote the stationary solution with
same boundary values, then the $W^{1,p}$-norm of $u(t) - u^{*}$ decays for
large $t$ like $t^{-\frac{1}{(p-1)p}}$, in the degenerate case $ p > 2$.",1905.03597v2
2019-05-10,Asymptotic profiles for damped plate equations with rotational inertia terms,"We consider the Cauchy problem for plate equations with rotational inertia
and frictional damping terms. We will derive asymptotic profiles of the
solution in L^2-sense as time goes to infinity in the case when the initial
data have high and low regularity, respectively. Especially, in the low
regularity case of the initial data one encounters the regularity-loss
structure of the solutions, and the analysis is more delicate. We employ the
so-called Fourier splitting method combined with the explicit expression of the
solutions (high frequency estimates) and the method due to Ikehata (low
frequency estimates).",1905.04012v1
2019-05-20,Small perturbations for a Duffing-like evolution equation involving non-commuting operators,"We consider an abstract evolution equation with linear damping, a nonlinear
term of Duffing type, and a small forcing term. The abstract problem is
inspired by some models for damped oscillations of a beam subject to external
loads or magnetic fields, and shaken by a transversal force.
  The main feature is that very natural choices of the boundary conditions lead
to equations whose linear part involves two operators that do not commute.
  We extend to this setting the results that are known in the commutative case,
namely that for asymptotically small forcing terms all solutions are eventually
close to the three equilibrium points of the unforced equation, two stable and
one unstable.",1905.07942v1
2019-05-30,A study of coherence based measure of quantumness in (non) Markovian channels,"We make a detailed analysis of quantumness for various quantum noise
channels, both Markovian and non-Markovian. The noise channels considered
include dephasing channels like random telegraph noise, non-Markovian dephasing
and phase damping, as well as the non-dephasing channels such as generalized
amplitude damping and Unruh channels. We make use of a recently introduced
witness for quantumness based on the square $l_1$ norm of coherence. It is
found that the increase in the degree of non-Markovianity increases the
quantumness of the channel.",1905.12872v1
2019-05-30,Stabilization for vibrating plate with singular structural damping,"We consider the dynamic elasticity equation, modeled by the Euler-Bernoulli
plate equation, with a locally distributed singular structural (or viscoelastic
) damping in a boundary domain. Using a frequency domain method combined, based
on the Burq's result, combined with an estimate of Carleman type we provide
precise decay estimate showing that the energy of the system decays
logarithmically as the type goes to the infinity.",1905.13089v1
2019-06-12,A no-go result for the quantum damped harmonic oscillator,"In this letter we show that it is not possible to set up a canonical
quantization for the damped harmonic oscillator using the Bateman lagrangian.
In particular, we prove that no square integrable vacuum exists for the {\em
natural} ladder operators of the system, and that the only vacua can be found
as distributions. This implies that the procedure proposed by some authors is
only formally correct, and requires a much deeper analysis to be made rigorous.",1906.05121v2
2019-06-26,Mismatched Estimation of Polynomially Damped Signals,"In this work, we consider the problem of estimating the parameters of
polynomially damped sinusoidal signals, commonly encountered in, for instance,
spectroscopy. Generally, finding the parameter values of such signals
constitutes a high-dimensional problem, often further complicated by not
knowing the number of signal components or their specific signal structures. In
order to alleviate the computational burden, we herein propose a mismatched
estimation procedure using simplified, approximate signal models. Despite the
approximation, we show that such a procedure is expected to yield predictable
results, allowing for statistically and computationally efficient estimates of
the signal parameters.",1906.11113v1
2019-06-27,Temperature-Dependent Lifetimes of Low-Frequency Adsorbate Modes from Non-Equilibrium Molecular Dynamics Simulations,"We present calculations on the damping of a low-frequency adsorbate mode on a
metal surface, namely the frustrated translation of Na on Cu(100). For the
first time, vibrational lifetimes of excited adlayers are extracted from
non-equilibrium molecular dynamics calculations accounting for both the
phononic and the electronic dissipation channels. The relative contributions of
the two damping mechanisms, which we show to be additive, are found to disagree
with textbook predictions. A simple model based on separable harmonic and
anharmonic contributions is able to semi-quantitatively reproduce the
temperature dependence of the computed lifetimes.",1906.11776v1
2019-07-10,Formal expansions in stochastic model for wave turbulence 1: kinetic limit,"We consider the damped/driver (modified) cubic NLS equation on a large torus
with a properly scaled forcing and dissipation, and decompose its solutions to
formal series in the amplitude. We study the second order truncation of this
series and prove that when the amplitude goes to zero and the torus' size goes
to infinity the energy spectrum of the truncated solutions becomes close to a
solution of the damped/driven wave kinetic equation. Next we discuss higher
order truncations of the series.",1907.04531v4
2019-07-22,Thresholds for low regularity solutions to wave equations with structural damping,"We study the asymptotic behavior of solutions to wave equations with a
structural damping term \[ u_{tt}-\Delta u+\Delta^2 u_t=0, \qquad
u(0,x)=u_0(x), \,\,\, u_t(0,x)=u_1(x), \] in the whole space. New thresholds
are reported in this paper that indicate which of the diffusion wave property
and the non-diffusive structure dominates in low regularity cases. We develop
to that end the previous author's research in 2019 where they have proposed a
threshold that expresses whether the parabolic-like property or the wave-like
property strongly appears in the solution to some regularity-loss type
dissipative wave equation.",1907.09299v1
2019-08-03,Lindblad dynamics of the damped and forced quantum harmonic oscillator,"The quantum dynamics of a damped and forced harmonic oscillator is
investigated in terms of a Lindblad master equation. Elementary algebraic
techniques are employed allowing for example to analyze the long time behavior,
i.e. the quantum limit cycle. The time evolution of various expectation values
is obtained in closed form as well as the entropy and the Husimi phase space
distribution. We also discuss the related description in terms of a
non-Hermitian Hamiltonian.",1908.01187v2
2019-08-07,Decay estimates for the linear damped wave equation on the Heisenberg group,"This paper is devoted to the derivation of $L^2$ - $L^2$ decay estimates for
the solution of the homogeneous linear damped wave equation on the Heisenberg
group $\mathbf{H}_n$, for its time derivative and for its horizontal gradient.
Moreover, we consider the improvement of these estimates when further
$L^1(\mathbf{H}_n)$ regularity is required for the Cauchy data. Our approach
will rely strongly on the group Fourier transform of $\mathbf{H}_n$ and on the
properties of the Hermite functions that form a maximal orthonormal system for
$L^2(\mathbb{R}^n)$ of eigenfunctions of the harmonic oscillator.",1908.02657v1
2019-08-08,Critical exponent of Fujita-type for the semilinear damped wave equation on the Heisenberg group with power nonlinearity,"In this paper, we consider the Cauchy problem for the semilinear damped wave
equation on the Heisenberg group with power nonlinearity. We prove that the
critical exponent is the Fujita exponent $p_{\mathrm{Fuj}}(\mathscr{Q}) = 1+2 /
\mathscr{Q}$, where $\mathscr{Q}$ is the homogeneous dimension of the
Heisenberg group. On the one hand, we will prove the global existence of small
data solutions for $p >p_{\mathrm{Fuj}}(\mathscr{Q})$ in an exponential
weighted energy space. On the other hand, a blow-up result for $1 < p \leq
p_{\mathrm{Fuj}}(\mathscr{Q})$ under certain integral sign assumptions for the
Cauchy data by using the test function method.",1908.02989v1
2019-09-01,Invariant measures for stochastic damped 2D Euler equations,"We study the two-dimensional Euler equations, damped by a linear term and
driven by an additive noise. The existence of weak solutions has already been
studied; pathwise uniqueness is known for solutions that have vorticity in
$L^\infty$. In this paper, we prove the Markov property and then the existence
of an invariant measure in the space $L^\infty$ by means of a
Krylov-Bogoliubov's type method, working with the weak$\star$ and the bounded
weak$\star$ topologies in $L^\infty$.",1909.00424v2
2019-09-03,A blow-up result for semi-linear structurally damped $σ$-evolution equations,"We would like to prove a blow-up result for semi-linear structurally damped
$\sigma$-evolution equations, where $\sigma \ge 1$ and $\delta\in [0,\sigma)$
are assumed to be any fractional numbers. To deal with the fractional Laplacian
operators $(-\Delta)^\sigma$ and $(-\Delta)^\delta$ as well-known non-local
operators, in general, it seems difficult to apply the standard test function
method directly. For this reason, in this paper we shall construct new test
functions to overcome this difficulty.",1909.01181v1
2019-09-09,Action Functional for a Particle with Damping,"In this brief report we discuss the action functional of a particle with
damping, showing that it can be obtained from the dissipative equation of
motion through a modification which makes the new dissipative equation
invariant for time reversal symmetry. This action functional is exactly the
effective action of Caldeira-Leggett model but, in our approach, it is derived
without the assumption that the particle is weakly coupled to a bath of
infinite harmonic oscillators.",1909.03694v2
2019-09-11,Remark on global existence of solutions to the 1D compressible Euler equation with time-dependent damping,"In this paper, we consider the 1D compressible Euler equation with the
damping coefficient $\lambda/(1+t)^{\mu}$. Under the assumption that $0\leq \mu
<1$ and $\lambda >0$ or $\mu=1$ and $\lambda > 2$, we prove that solutions
exist globally in time, if initial data are small $C^1$ perturbation near
constant states. In particular, we remove the conditions on the limit
$\lim_{|x| \rightarrow \infty} (u (0,x), v (0,x))$, assumed in previous
results.",1909.05683v1
2019-09-11,Equilibrium radiation in a plasma medium with spatial and frequency dispersion,"Examination of equilibrium radiation in plasma media shows that the spectral
energy distribution of such radiation is different from the Planck equilibrium
radiation. Using the approach of quantum electrodynamics the general relation
for the spectral energy density of equilibrium radiation in a system of charged
particles is found. The obtained result takes into account the influence of
plasma on equilibrium radiation through the explicit transverse dielectric
permittivity which takes into account spatial and frequency dispersion, as well
as the finite collisional damping. For the limiting case of an infinitesimal
damping the result coincides with the known expression.",1909.08056v1
2019-10-14,Blow-up of solutions to semilinear strongly damped wave equations with different nonlinear terms in an exterior domain,"In this paper, we consider the initial boundary value problem in an exterior
domain for semilinear strongly damped wave equations with power nonlinear term
of the derivative-type $|u_t|^q$ or the mixed-type $|u|^p+|u_t|^q$, where
$p,q>1$. On one hand, employing the Banach fixed-point theorem we prove local
(in time) existence of mild solutions. On the other hand, under some conditions
for initial data and the exponents of power nonlinear terms, the blow-up
results are derived by applying the test function method.",1910.05981v1
2019-11-03,Linear Inviscid Damping in Sobolev and Gevrey Spaces,"In a recent article Jia established linear inviscid damping in Gevrey
regularity for compactly supported Gevrey regular shear flows in a finite
channel, which is of great interest in view of existing nonlinear results. In
this article we provide an alternative very short proof of stability in Gevrey
regularity as a consequence of stability in high Sobolev regularity. Here, we
consider both the setting of a finite channel with compactly supported
perturbations and of an infinite channel without this restriction. Furthermore,
we consider the setting where perturbations vanish only of finite order.",1911.00880v1
2019-11-03,A global existence result for two-dimensional semilinear strongly damped wave equation with mixed nonlinearity in an exterior domain,"We study two-dimensional semilinear strongly damped wave equation with mixed
nonlinearity $|u|^p+|u_t|^q$ in an exterior domain, where $p,q>1$. Assuming the
smallness of initial data in exponentially weighted spaces and some conditions
on powers of nonlinearity, we prove global (in time) existence of small data
energy solution with suitable higher regularity by using a weighted energy
method.",1911.00899v1
2019-11-05,Critical exponent for a weakly coupled system of semi-linear $σ$-evolution equations with frictional damping,"We are interested in studying the Cauchy problem for a weakly coupled system
of semi-linear $\sigma$-evolution equations with frictional damping. The main
purpose of this paper is two-fold. We would like to not only prove the global
(in time) existence of small data energy solutions but also indicate the
blow-up result for Sobolev solutions when $\sigma$ is assumed to be any
fractional number.",1911.01946v1
2019-11-11,Existence and nonexistence of global solutions for a structurally damped wave system with power nonlinearities,"Our interest itself of this paper is strongly inspired from an open problem
in the paper [1] published by D'Abbicco. In this article, we would like to
study the Cauchy problem for a weakly coupled system of semi-linear
structurally damped wave equations. Main goal is to find the threshold, which
classifies the global (in time) existence of small data solutions or the
nonexistence of global solutions under the growth condition of the
nonlinearities.",1911.04412v1
2019-11-15,Some $L^1$-$L^1$ estimates for solutions to visco-elastic damped $σ$-evolution models,"This note is to conclude $L^1-L^1$ estimates for solutions to the following
Cauchy problem for visco-elastic damped $\sigma$-evolution models:
\begin{equation} \begin{cases} u_{tt}+ (-\Delta)^\sigma u+ (-\Delta)^\sigma u_t
= 0, &\quad x\in \mathbb{R}^n,\, t \ge 0, \\ u(0,x)= u_0(x),\quad
u_t(0,x)=u_1(x), &\quad x\in \mathbb{R}^n, \label{pt1.1} \end{cases}
\end{equation} where $\sigma> 1$, in all space dimensions $n\ge 1$.",1911.06563v1
2019-11-22,Long-time asymptotics for a coupled thermoelastic plate-membrane system,"In this paper we consider a transmission problem for a system of a
thermoelastic plate with (or without) rotational inertia term coupled with a
membrane with different variants of damping for the plate and/or the membrane.
We prove well-posedness of the problem and higher regularity of the solution
and study the asymptotic behaviour of the solution, depending on the damping
and on the presence of the rotational term.",1911.10161v1
2019-11-28,Tikhonov regularization of a second order dynamical system with Hessian driven damping,"We investigate the asymptotic properties of the trajectories generated by a
second-order dynamical system with Hessian driven damping and a Tikhonov
regularization term in connection with the minimization of a smooth convex
function in Hilbert spaces. We obtain fast convergence results for the function
values along the trajectories. The Tikhonov regularization term enables the
derivation of strong convergence results of the trajectory to the minimizer of
the objective function of minimum norm.",1911.12845v2
2019-12-15,"Negative mobility, sliding and delocalization for stochastic networks","We consider prototype configurations for quasi-one-dimensional stochastic
networks that exhibit negative mobility, meaning that current decreases or even
reversed as the bias is increased. We then explore the implications of
disorder. In particular we ask whether lower and upper bias thresholds restrict
the possibility to witness non-zero current (sliding and anti-sliding
transitions respectively), and whether a delocalization effect manifest itself
(crossover from over-damped to under-damped relaxation). In the latter context
detailed analysis of the relaxation spectrum as a function of the bias is
provided for both on-chain and off-chain disorder.",1912.07059v2
2019-12-23,On a damped Szego equation (with an appendix in collaboration with Christian Klein),"We investigate how damping the lowest Fourier mode modifies the dynamics of
the cubic Szeg{\""o} equation. We show that there is a nonempty open subset of
initial data generating trajec-tories with high Sobolev norms tending to
infinity. In addition, we give a complete picture of this phenomenon on a
reduced phase space of dimension 6. An appendix is devoted to numerical
simulations supporting the generalisation of this picture to more general
initial data.",1912.10933v1
2020-01-29,The long time behavior and the rate of convergence of symplectic convex algorithms obtained via splitting discretizations of inertial damping systems,"In this paper we propose new numerical algorithms in the setting of
unconstrained optimization problems and we study the rate of convergence in the
iterates of the objective function. Furthermore, our algorithms are based upon
splitting and symplectic methods and they preserve the energy properties of the
inherent continuous dynamical system that contains a Hessian perturbation. At
the same time, we show that Nesterov gradient method is equivalent to a
Lie-Trotter splitting applied to a Hessian driven damping system. Finally, some
numerical experiments are presented in order to validate the theoretical
results.",2001.10831v2
2020-02-05,Long-time asymptotics of the one-dimensional damped nonlinear Klein-Gordon equation,"For the one-dimensional nonlinear damped Klein-Gordon equation \[
\partial_{t}^{2}u+2\alpha\partial_{t}u-\partial_{x}^{2}u+u-|u|^{p-1}u=0 \quad
\mbox{on $\mathbb{R}\times\mathbb{R}$,}\] with $\alpha>0$ and $p>2$, we prove
that any global finite energy solution either converges to $0$ or behaves
asymptotically as $t\to \infty$ as the sum of $K\geq 1$ decoupled solitary
waves. In the multi-soliton case $K\geq 2$, the solitary waves have alternate
signs and their distances are of order $\log t$.",2002.01826v1
2020-02-11,Distributional Solutions of the Damped Wave Equation,"This work presents results on solutions of the one-dimensional damped wave
equation, also called telegrapher's equation, when the initial conditions are
general distributions, not only functions. We make a complete deduction of its
fundamental solutions, both for positive and negative times. To obtain them we
use only self-similarity arguments and distributional calculus, making no use
of Fourier or Laplace transforms. We next use these fundamental solutions to
prove both the existence and the uniqueness of solutions to the distributional
initial value problem. As applications we recover the semigroup property for
initial data in classical function spaces and also the probability distribution
function for a certain financial model of evolution of prices.",2002.04249v2
2020-02-13,Description of the wavevector dispersion of surface plasmon-phonon-polaritons,"We reported here the results of the calculations of wavevector dispersion of
oscillations frequencies, $\omega'(k)$, and damping $\omega''(k)$ of the
surface plasmon phonon polaritons (\mbox{SPPhP}) for the heavy-doped GaN
sample. We showed that $\omega'(k)$- dependence consists of the three branches
with the specific anticrossing behavior due to the interaction of surface
plasmon polariton (SPP) with surface phonon polariton(SPhP). The strong
renormalization of the damping $\omega''(k)$ in the vicinity of the
anticrossing region was found. The obtained dispersions of the $\omega'(k)$ and
$\omega''(k)$ were applied for the analytical analysis of exact electrodynamic
simulation of the resonant behavior of the reflectivity spectrum of the n-GaN
grating.",2002.05473v1
2020-03-20,The Cauchy problem of the semilinear second order evolution equation with fractional Laplacian and damping,"In the present paper, we prove time decay estimates of solutions in weighted
Sobolev spaces to the second order evolution equation with fractional Laplacian
and damping for data in Besov spaces. Our estimates generalize the estimates
obtained in the previous studies. The second aim of this article is to apply
these estimates to prove small data global well-posedness for the Cauchy
problem of the equation with power nonlinearities. Especially, the estimates
obtained in this paper enable us to treat more general conditions on the
nonlinearities and the spatial dimension than the results in the previous
studies.",2003.09239v1
2020-03-31,Time-Asymptotics of Physical Vacuum Free Boundaries for Compressible Inviscid Flows with Damping,"In this paper, we prove the leading term of time-asymptotics of the moving
vacuum boundary for compressible inviscid flows with damping to be that for
Barenblatt self-similar solutions to the corresponding porous media equations
obtained by simplifying momentum equations via Darcy's law plus the possible
shift due to the movement of the center of mass, in the one-dimensional and
three-dimensional spherically symmetric motions, respectively. This gives a
complete description of the large time asymptotic behavior of solutions to the
corresponding vacuum free boundary problems. The results obtained in this paper
are the first ones concerning the large time asymptotics of physical vacuum
boundaries for compressible inviscid fluids, to the best of our knowledge.",2003.14072v2
2020-04-13,Landau damping for analytic and Gevrey data,"In this paper, we give an elementary proof of the nonlinear Landau damping
for the Vlasov-Poisson system near Penrose stable equilibria on the torus
$\mathbb{T}^d \times \mathbb{R}^d$ that was first obtained by Mouhot and
Villani in \cite{MV} for analytic data and subsequently extended by Bedrossian,
Masmoudi, and Mouhot \cite{BMM} for Gevrey-$\gamma$ data,
$\gamma\in(\frac13,1]$. Our proof relies on simple pointwise resolvent
estimates and a standard nonlinear bootstrap analysis, using an ad-hoc family
of analytic and Gevrey-$\gamma$ norms.",2004.05979v3
2020-04-16,Strichartz estimates for mixed homogeneous surfaces in three dimensions,"We obtain sharp mixed norm Strichartz estimates associated to mixed
homogeneous surfaces in $\mathbb{R}^3$. Both cases with and without a damping
factor are considered. In the case when a damping factor is considered our
results yield a wide generalization of a result of Carbery, Kenig, and Ziesler
[CKZ13]. The approach we use is to first classify all possible singularities
locally, after which one can tackle the problem by appropriately modifying the
methods from the paper of Ginibre and Velo [GV92], and by using the recently
developed methods by Ikromov and M\""uller [IM16].",2004.07751v1
2020-04-17,Critical exponent for semi-linear structurally damped wave equation of derivative type,"Main purpose of this paper is to study the following semi-linear structurally
damped wave equation with nonlinearity of derivative type: $$u_{tt}- \Delta u+
\mu(-\Delta)^{\sigma/2} u_t= |u_t|^p,\quad u(0,x)= u_0(x),\quad
u_t(0,x)=u_1(x),$$ with $\mu>0$, $n\geq1$, $\sigma \in (0,2]$ and $p>1$. In
particular, we are going to prove the non-existence of global weak solutions by
using a new test function and suitable sign assumptions on the initial data in
both the subcritical case and the critical case.",2004.08486v2
2020-04-29,Exponential decay for damped Klein-Gordon equations on asymptotically cylindrical and conic manifolds,"We study the decay of the global energy for the damped Klein-Gordon equation
on non-compact manifolds with finitely many cylindrical and subconic ends up to
bounded perturbation. We prove that under the Geometric Control Condition, the
decay is exponential, and that under the weaker Network Control Condition, the
decay is logarithmic, by developing the global Carleman estimate with multiple
weights.",2004.13894v2
2020-05-06,Zero-dimensional models for gravitational and scalar QED decoherence,"We investigate the dynamics of two quantum mechanical oscillator system-bath
toy models obtained by truncating to zero spatial dimensions linearized gravity
coupled to a massive scalar field and scalar QED. The scalar-gravity toy model
maps onto the phase damped oscillator, while the scalar QED toy model
approximately maps onto an oscillator system subject to two-photon damping. The
toy models provide potentially useful insights into solving for open system
quantum dynamics relevant to the full scalar QED and weak gravitational field
systems, in particular operational probes of the decoherence for initial scalar
field system superposition states.",2005.02554v2
2020-05-16,On the asymptotic stability of wave equations coupled by velocities of anti-symmetric type,"In this paper, we study the asymptotic stability of two wave equations
coupled by velocities of anti-symmetric type via only one damping. We adopt the
frequency domain method to prove that the system with smooth initial data is
logarithmically stable, provided that the coupling domain and the damping
domain intersect each other. Moreover, we show, by an example, that this
geometric assumption of the intersection is necessary for 1-D case.",2005.07977v2
2020-05-27,On the blow-up of solutions to semilinear damped wave equations with power nonlinearity in compact Lie groups,"In this note, we prove a blow-up result for the semilinear damped wave
equation in a compact Lie group with power nonlinearity $|u|^p$ for any $p>1$,
under suitable integral sign assumptions for the initial data, by using an
iteration argument. A byproduct of this method is the upper bound estimate for
the lifespan of a local in time solution. As a preliminary result, a local (in
time) existence result is proved in the energy space via Fourier analysis on
compact Lie groups.",2005.13479v2
2020-06-13,On the well-posedness of the damped time-harmonic Galbrun equation and the equations of stellar oscillations,"We study the time-harmonic Galbrun equation describing the propagation of
sound in the presence of a steady background flow. With additional rotational
and gravitational terms these equations are also fundamental in helio- and
asteroseismology as a model for stellar oscillations. For a simple damping
model we prove well-posedness of these equations, i.e. uniqueness, existence,
and stability of solutions under mild conditions on the parameters (essentially
subsonic flows). The main tool of our analysis is a generalized Helmholtz
decomposition.",2006.07658v1
2020-06-22,Prediction of short time qubit readout via measurement of the next quantum jump of a coupled damped driven harmonic oscillator,"The dynamics of the next quantum jump for a qubit [two level system] coupled
to a readout resonator [damped driven harmonic oscillator] is calculated. A
quantum mechanical treatment of readout resonator reveals non exponential short
time behavior which could facilitate detection of the state of the qubit faster
than the resonator lifetime.",2006.11950v1
2020-07-08,The interplay of critical regularity of nonlinearities in a weakly coupled system of semi-linear damped wave equations,"We would like to study a weakly coupled system of semi-linear classical
damped wave equations with moduli of continuity in nonlinearities whose powers
belong to the critical curve in the $p-q$ plane. The main goal of this paper is
to find out the sharp conditions of these moduli of continuity which classify
between global (in time) existence of small data solutions and finite time
blow-up of solutions.",2007.04157v1
2020-07-09,Semi-uniform stability of operator semigroups and energy decay of damped waves,"Only in the last fifteen years or so has the notion of semi-uniform
stability, which lies between exponential stability and strong stability,
become part of the asymptotic theory of $C_0$-semigroups. It now lies at the
very heart of modern semigroup theory. After briefly reviewing the notions of
exponential and strong stability, we present an overview of some of the best
known (and often optimal) abstract results on semi-uniform stability. We go on
to indicate briefly how these results can be applied to obtain (sometimes
optimal) rates of energy decay for certain damped second-order Cauchy problems.",2007.04711v1
2020-07-10,Quasi-periodic travelling waves for a class of damped beams on rectangular tori,"This article concerns a class of beam equations with damping on rectangular
tori. When the generators satisfy certain relationship, by excluding some value
of two model parameters, we prove that such models admit small amplitude
quasi-periodic travelling wave solutions with two frequencies, which are
continuations of two rotating wave solutions with one frequency. This result
holds not only for an isotropic torus, but also for an anisotropic torus. The
proof is mainly based on a Lyapunov--Schmidt reduction together with the
implicit function theorem.",2007.05154v1
2020-07-24,A Framework to Control Inter-Area Oscillations with Local Measurement,"Inter-area oscillations in power system limit of power transfer capability
though tie-lines. For stable operation, wide-area power system stabilizers are
deployed to provide sufficient damping. However, as the feedback is through a
communication network, it brings challenges such as additional communication
layer and cybersecurity issues. To address this, a framework for synthesizing
remote signal from local measurement as feedback in the wide-area power system
stabilizer is proposed. The remote signal is synthesized using different
variants of observers in a case study of two-area benchmark system. The
proposed framework can improve the damping of inter-area oscillations for
static output feedback controller. The presented framework should help to
design attack-resilient controller design in smart grid.",2007.12426v1
2020-07-24,Convergence Rates of Inertial Primal-Dual Dynamical Methods for Separable Convex Optimization Problems,"In this paper, we propose a second-order continuous primal-dual dynamical
system with time-dependent positive damping terms for a separable convex
optimization problem with linear equality constraints. By the Lyapunov function
approach, we investigate asymptotic properties of the proposed dynamical system
as the time $t\to+\infty$. The convergence rates are derived for different
choices of the damping coefficients. We also show that the obtained results are
robust under external perturbations.",2007.12428v1
2020-08-17,Dynamics of spatially indistinguishable particles and entanglement protection,"We provide a general framework which allows one to obtain the dynamics of $N$
noninteracting spatially indistinguishable particles locally coupled to
separated environments. The approach is universal, being valid for both bosons
and fermions and for any type of system-environment interaction. It is then
applied to study the dynamics of two identical qubits under paradigmatic
Markovian noises, such as phase damping, depolarizing and amplitude damping. We
find that spatial indistinguishability of identical qubits is a controllable
intrinsic property of the system which protects quantum entanglement against
detrimental noise.",2008.07471v1
2020-09-02,Discriminating qubit amplitude damping channels,"We address the issue of the discrimination between two-qubit amplitude
damping channels by exploring several strategies. For the single-shot, we show
that the excited state does not always give the optimal input, and that side
entanglement assistance has limited benefit. On the contrary, feedback
assistance from the environment is more beneficial. For the two-shot, we prove
the in-utility of entangled inputs. Then focusing on individual (local)
measurements, we find the optimal adaptive strategy.",2009.01000v3
2020-09-03,Asymptotic behavior of 2D stably stratified fluids with a damping term in the velocity equation,"This article is concerned with the asymptotic behavior of the two-dimensional
inviscid Boussinesq equations with a damping term in the velocity equation.
Precisely, we provide the time-decay rates of the smooth solutions to that
system. The key ingredient is a careful analysis of the Green kernel of the
linearized problem in Fourier space, combined with bilinear estimates and
interpolation inequalities for handling the nonlinearity.",2009.01578v2
2020-08-05,The perturbational stability of the Schr$\ddot{o}$dinger equation,"By using the Wigner transform, it is shown that the nonlinear
Schr$\ddot{\textmd{o}}$dinger equation can be described, in phase space, by a
kinetic theory similar to the Vlasov equation which is used for describing a
classical collisionless plasma. In this paper we mainly show Landau damping in
the quantum sense, namely,quantum Landau damping exists for the Wigner-Poisson
system. At the same time, we also prove the existence and the stability of the
nonlinear Schr$\ddot{\textmd{o}}$dinger equation under the quantum stability
assumption.",2009.09855v1
2020-10-12,Long time behavior of solutions for a damped Benjamin-Ono equation,"We consider the Benjamin-Ono equation on the torus with an additional damping
term on the smallest Fourier modes (cos and sin). We first prove global
well-posedness of this equation in $L^2_{r,0}(\mathbb{T})$. Then, we describe
the weak limit points of the trajectories in $L^2_{r,0}(\mathbb{T})$ when time
goes to infinity, and show that these weak limit points are strong limit
points. Finally, we prove the boundedness of higher-order Sobolev norms for
this equation. Our key tool is the Birkhoff map for the Benjamin-Ono equation,
that we use as an adapted nonlinear Fourier transform.",2010.05520v1
2020-10-18,Classical limit of quantum mechanics for damped driven oscillatory systems: Quantum-classical correspondence,"The investigation of quantum-classical correspondence may lead to gain a
deeper understanding of the classical limit of quantum theory. We develop a
quantum formalism on the basis of a linear-invariant theorem, which gives an
exact quantum-classical correspondence for damped oscillatory systems that are
perturbed by an arbitrary force. Within our formalism, the quantum trajectory
and expectation values of quantum observables are precisely coincide with their
classical counterparts in the case where we remove the global quantum constant
h from their quantum results. In particular, we illustrate the correspondence
of the quantum energy with the classical one in detail.",2010.08971v1
2020-10-21,Initial boundary value problem for a strongly damped wave equation with a general nonlinearity,"In this paper, a strongly damped semilinear wave equation with a general
nonlinearity is considered. With the help of a newly constructed auxiliary
functional and the concavity argument, a general finite time blow-up criterion
is established for this problem. Furthermore, the lifespan of the weak solution
is estimated from both above and below. This partially extends some results
obtained in recent literatures and sheds some light on the similar effect of
power type nonlinearity and logarithmic nonlinearity on finite time blow-up of
solutions to such problems.",2010.10696v1
2020-10-21,MRI Image Recovery using Damped Denoising Vector AMP,"Motivated by image recovery in magnetic resonance imaging (MRI), we propose a
new approach to solving linear inverse problems based on iteratively calling a
deep neural-network, sometimes referred to as plug-and-play recovery. Our
approach is based on the vector approximate message passing (VAMP) algorithm,
which is known for mean-squared error (MSE)-optimal recovery under certain
conditions. The forward operator in MRI, however, does not satisfy these
conditions, and thus we design new damping and initialization schemes to help
VAMP. The resulting DD-VAMP++ algorithm is shown to outperform existing
algorithms in convergence speed and accuracy when recovering images from the
fastMRI database for the practical case of Cartesian sampling.",2010.11321v1
2020-11-05,Mathematical modelling of an unstable bent flow using the selective frequency damping method,"The selective frequency damping method was applied to a bent flow. The method
was used in an adaptive formulation. The most dangerous frequency was
determined by solving an eigenvalue problem. It was found that one of the
patterns, steady-state or pulsating, may exist at some relatively high Reynolds
numbers. The periodic flow occurs due to the instability of the steady-state
flow. This numerical method is easy to use but requires a great deal of time
for calculations.",2011.02646v1
2020-11-04,"The ""Dark disk"" model in the light of DAMPE experiment","There are a lot of models considering the Dark Matter (DM) to be the origin
of cosmic ray (CR) positron excess. However, they face an obstacle in the form
of gamma-rays. Simple DM models tend to overproduce gamma-rays, leading to
contradiction with isotropic gamma-ray background (IGRB). The <<dark disk>>
model has been proposed to alleviate this contradiction. This work considers
results of DAMPE experiment in the framework of the disk model. It is obtained
that such a framework allows improving data fit considerably.",2011.04425v2
2020-12-15,On the stability of Bresse system with one discontinuous local internal Kelvin-Voigt damping on the axial force,"In this paper, we investigate the stabilization of a linear Bresse system
with one discontinuous local internal viscoelastic damping of Kelvin-Voigt type
acting on the axial force, under fully Dirichlet boundary conditions. First,
using a general criteria of Arendt-Batty, we prove the strong stability of our
system. Finally, using a frequency domain approach combined with the multiplier
method, we prove that the energy of our system decays polynomially with
different rates.",2012.08219v1
2020-12-28,An efficient method for approximating resonance curves of weakly-damped nonlinear mechanical systems,"A method is presented for tracing the locus of a specific peak in the
frequency response under variation of a parameter. It is applicable to
periodic, steady-state vibrations of harmonically forced nonlinear mechanical
systems. It operates in the frequency domain and its central idea is to assume
a constant phase lag between forcing and response. The method is validated for
a two-degree-of-freedom oscillator with cubic spring and a bladed disk with
shroud contact. The method provides superior computational efficiency, but is
limited to weakly-damped systems. Finally, the capability to reveal isolated
solution branches is highlighted.",2012.14458v1
2021-01-16,Convergence of non-autonomous attractors for subquintic weakly damped wave equation,"We study the non-autonomous weakly damped wave equation with subquintic
growth condition on the nonlinearity. Our main focus is the class of
Shatah--Struwe solutions, which satisfy the Strichartz estimates and are
coincide with the class of solutions obtained by the Galerkin method. For this
class we show the existence and smoothness of pullback, uniform, and cocycle
attractors and the relations between them. We also prove that these
non-autonomous attractors converge upper-semicontinuously to the global
attractor for the limit autonomous problem if the time-dependent nonlinearity
tends to time independent function in an appropriate way.",2101.06523v1
2021-01-20,A Damped Newton Algorithm for Generated Jacobian Equations,"Generated Jacobian Equations have been introduced by Trudinger [Disc. cont.
dyn. sys (2014), pp. 1663-1681] as a generalization of Monge-Amp{\`e}re
equations arising in optimal transport. In this paper, we introduce and study a
damped Newton algorithm for solving these equations in the semi-discrete
setting, meaning that one of the two measures involved in the problem is
finitely supported and the other one is absolutely continuous. We also present
a numerical application of this algorithm to the near-field parallel refractor
problem arising in non-imaging problems.",2101.08080v1
2021-02-04,Global existence results for semi-linear structurally damped wave equations with nonlinear convection,"In this paper, we consider the Cauchy problem for semi-linear wave equations
with structural damping term $\nu (-\Delta)^2 u_t$, where $\nu >0$ is a
constant. As being mentioned in [8,10], the linear principal part brings both
the diffusion phenomenon and the regularity loss of solutions. This implies
that, for the nonlinear problems, the choice of solution spaces plays an
important role to obtain global solutions with sharp decay properties in time.
Our main purpose of this paper is to prove the global (in time) existence of
solutions for the small data and their decay properties for the supercritical
nonlinearities.",2102.02445v2
2021-02-14,Suppression of singularities of solutions of the Euler-Poisson system with density-dependent damping,"We find a sharp condition on the density-dependent coefficient of damping of
a one-dimensional repulsive Euler-Poisson system, which makes it possible to
suppress the formation of singularities in the solution of the Cauchy problem
with arbitrary smooth data. In the context of plasma physics, this means the
possibility of suppressing the breakdown of arbitrary oscillations of cold
plasma.",2102.07176v2
2021-02-15,"Piezoelectric beam with magnetic effect, time-varying delay and time-varying weights","The main result of this work is to obtain the exponential decay of the
solutions of a piezoelectric beam model with magnetic effect and delay term.
The dampings are inserted into the equation of longitudinal displacement. The
terms of damping, whose weight associated with them varies over time, are of
the friction type, and one of them has delay. This work will also address the
issue of existence and uniqueness of solution for the model.",2102.07538v1
2021-02-23,Effects of ground-state correlations on damping of giant dipole resonaces in $LS$ closed shell nuclei,"The effects of ground-state correlations on the damping of isovector giant
dipole resonances in $LS$ closed shell nuclei $^{16}$O and $^{40}$Ca are
studied using extended random-phase-approximation (RPA) approaches derived from
the time-dependent density-matrix theory. It is pointed out that unconventional
two-body amplitudes of one particle--three hole and three particle--one hole
types which are neglected in most extended RPA theories play an important role
in the fragmentation of isovector dipole strength.",2102.11505v2
2021-02-28,The influence of the physical coefficients of a Bresse system with one singular local viscous damping in the longitudinal displacement on its stabilization,"In this paper, we investigate the stabilization of a linear Bresse system
with one singular local frictional damping acting in the longitudinal
displacement, under fully Dirichlet boundary conditions. First, we prove the
strong stability of our system. Next, using a frequency domain approach
combined with the multiplier method, we establish the exponential stability of
the solution if and only if the three waves have the same speed of propagation.
On the contrary, we prove that the energy of our system decays polynomially
with rates $t^{-1}$ or $t^{-\frac{1}{2}}$.",2103.00628v2
2021-03-01,On a damped nonlinear beam equation,"In this note we analyze the large time behavior of solutions to an
initial/boundary problem involving a damped nonlinear beam equation. We show
that under physically realistic conditions on the nonlinear terms in the
equation of motion the energy is a decreasing function of time and solutions
converge to a stationary solution with respect to a desirable norm.",2103.00969v3
2021-03-23,Fast convergence of dynamical ADMM via time scaling of damped inertial dynamics,"In this paper, we propose in a Hilbertian setting a second-order
time-continuous dynamic system with fast convergence guarantees to solve
structured convex minimization problems with an affine constraint. The system
is associated with the augmented Lagrangian formulation of the minimization
problem. The corresponding dynamics brings into play three general time-varying
parameters, each with specific properties, and which are respectively
associated with viscous damping, extrapolation and temporal scaling. By
appropriately adjusting these parameters, we develop a Lyapunov analysis which
provides fast convergence properties of the values and of the feasibility gap.
These results will naturally pave the way for developing corresponding
accelerated ADMM algorithms, obtained by temporal discretization.",2103.12675v1
2021-03-29,Comparison between the Cauchy problem and the scattering problem for the Landau damping in the Vlasov-HMF equation,"We analyze the analytic Landau damping problem for the Vlasov-HMF equation,
by fixing the asymptotic behavior of the solution. We use a new method for this
""scattering problem"", closer to the one used for the Cauchy problem. In this
way we are able to compare the two results, emphasizing the different influence
of the plasma echoes in the two approaches. In particular, we prove a
non-perturbative result for the scattering problem.",2103.15932v2
2021-04-06,Realising Einstein's mirror: Optomechanical damping with a thermal photon gas,"In 1909 Einstein described the thermalization of a mirror within a blackbody
cavity by collisions with thermal photons. While the time to thermalize the
motion of even a microscale or nanoscale object is so long that it is not
feasible, we show that it is using the high intensity light from an amplified
thermal light source with a well-defined chemical potential. We predict damping
of the center-of mass motion due to this effect on times scales of seconds for
small optomechanical systems, such as levitated nanoparticles, allowing
experimental observation.",2104.02708v2
2021-04-12,The pressureless damped Euler-Riesz equations,"In this paper, we analyze the pressureless damped Euler-Riesz equations posed
in either $\mathbb{R}^d$ or $\mathbb{T}^d$. We construct the global-in-time
existence and uniqueness of classical solutions for the system around a
constant background state. We also establish large-time behaviors of classical
solutions showing the solutions towards the equilibrium as time goes to
infinity. For the whole space case, we first show the algebraic decay rate of
solutions under additional assumptions on the initial data compared to the
existence theory. We then refine the argument to have the exponential decay
rate of convergence even in the whole space. In the case of the periodic
domain, without any further regularity assumptions on the initial data, we
provide the exponential convergence of solutions.",2104.05153v1
2021-04-12,Fractional time stepping and adjoint based gradient computation in an inverse problem for a fractionally damped wave equation,"In this paper we consider the inverse problem of identifying the initial data
in a fractionally damped wave equation from time trace measurements on a
surface, as relevant in photoacoustic or thermoacoustic tomography. We derive
and analyze a time stepping method for the numerical solution of the
corresponding forward problem. Moreover, to efficiently obtain reconstructions
by minimizing a Tikhonov regularization functional (or alternatively, by
computing the MAP estimator in a Bayesian approach), we develop an adjoint
based scheme for gradient computation. Numerical reconstructions in two space
dimensions illustrate the performance of the devised methods.",2104.05577v1
2021-04-15,Explaining Neptune's Eccentricity,"Early migration damped Neptune's eccentricity. Here, we assume that the
damped value was much smaller than the value observed today, and show that the
closest flyby of $\sim 0.1 \; \mathrm{M_{\odot}}$ star over $\sim 4.5
\mathrm{\; Gyr}$ in the field, at a distance of $\sim 10^3 \mathrm{\; AU}$
would explain the value of Neptune's eccentricity observed today.",2104.07672v3
2021-04-17,Lifespan estimates for wave equations with damping and potential posed on asymptotically Euclidean manifolds,"In this work, we investigate the problem of finite time blow up as well as
the upper bound estimates of lifespan for solutions to small-amplitude
semilinear wave equations with time dependent damping and potential, and mixed
nonlinearities $c_1 |u_t|^p+c_2 |u|^q$, posed on asymptotically Euclidean
manifolds, which is related to both the Strauss conjecture and the Glassey
conjecture.",2104.08497v2
2021-05-20,On the the critical exponent for the semilinear Euler-Poisson-Darboux-Tricomi equation with power nonlinearity,"In this note, we derive a blow-up result for a semilinear generalized Tricomi
equation with damping and mass terms having time-dependent coefficients. We
consider these coefficients with critical decay rates. Due to this threshold
nature of the time-dependent coefficients (both for the damping and for the
mass), the multiplicative constants appearing in these lower-order terms
strongly influence the value of the critical exponent, determining a
competition between a Fujita-type exponent and a Strauss-type exponent.",2105.09879v2
2021-06-02,Convergent dynamics of optimal nonlinear damping control,"Following Demidovich's concept and definition of convergent systems, we
analyze the optimal nonlinear damping control, recently proposed [1] for the
second-order systems. Targeting the problem of output regulation,
correspondingly tracking of $\mathcal{C}^1$-trajectories, it is shown that all
solutions of the control system are globally uniformly asymptotically stable.
The existence of the unique limit solution in the origin of the control error
and its time derivative coordinates are shown in the sense of Demidovich's
convergent dynamics. Explanative numerical examples are also provided along
with analysis.",2106.00962v1
2021-06-26,Role of Dissipation on the Stability of a Parametrically Driven Quantum Harmonic Oscillator,"We study the dissipative dynamics of a single quantum harmonic oscillator
subjected to a parametric driving with in an effective Hamiltonian approach.
Using Liouville von Neumann approach, we show that the time evolution of a
parametrically driven dissipative quantum oscillator has a strong connection
with the classical damped Mathieu equation. Based on the numerical analysis of
the Monodromy matrix, we demonstrate that the dynamical instability generated
by the parametric driving are reduced by the effect of dissipation. Further, we
obtain a closed relationship between the localization of the Wigner function
and the stability of the damped Mathieu equation.",2106.14018v1
2021-07-11,Space-time arithmetic quasi-periodic homogenization for damped wave equations,"This paper is concerned with space-time homogenization problems for damped
wave equations with spatially periodic oscillating elliptic coefficients and
temporally (arithmetic) quasi-periodic oscillating viscosity coefficients. Main
results consist of a homogenization theorem, qualitative properties of
homogenized matrices which appear in homogenized equations and a corrector
result for gradients of solutions. In particular, homogenized equations and
cell problems will turn out to deeply depend on the quasi-periodicity as well
as the log ratio of spatial and temporal periods of the coefficients. Even
types of equations will change depending on the log ratio and
quasi-periodicity. Proofs of the main results are based on a (very weak)
space-time two-scale convergence theory.",2107.04966v1
2021-07-29,Global existence for damped $σ$-evolution equations with nonlocal nonlinearity,"In this research, we would like to study the global (in time) existence of
small data solutions to the following damped $\sigma$-evolution equations with
nonlocal (in space) nonlinearity: \begin{equation*}
\partial_{t}^{2}u+(-\Delta)^{\sigma}u+\partial_{t}u+(-\Delta)^{\sigma}\partial_{t}u=I_{\alpha}(|u|^{p}),
\ \ t>0, \ \ x\in \mathbb{R}^{n}, \end{equation*} where $\sigma\geq1$, $p>1$
and $I_{\alpha}$ is the Riesz potential of power nonlinearity $|u|^{p}$ for any
$\alpha\in (0,n)$. More precisely, by using the $(L^{m}\cap L^{2})-L^{2}$ and
$L^{2}-L^{2}$ linear estimates, where $m\in[1,2]$, we show the new influence of
the parameter $\alpha$ on the admissible ranges of the exponent $p$.",2107.13924v1
2021-08-17,Estimate of the attractive velocity of attractors for some dynamical systems,"In this paper, we first prove an abstract theorem on the existence of
polynomial attractors and the concrete estimate of their attractive velocity
for infinite-dimensional dynamical systems, then apply this theorem to a class
of wave equations with nonlocal weak damping and anti-damping in case that the
nonlinear term~$f$~is of subcritical growth.",2108.07410v4
2021-08-27,Distributed Mirror Descent Algorithm with Bregman Damping for Nonsmooth Constrained Optimization,"To solve distributed optimization efficiently with various constraints and
nonsmooth functions, we propose a distributed mirror descent algorithm with
embedded Bregman damping, as a generalization of conventional distributed
projection-based algorithms. In fact, our continuous-time algorithm well
inherits good capabilities of mirror descent approaches to rapidly compute
explicit solutions to the problems with some specific constraint structures.
Moreover, we rigorously prove the convergence of our algorithm, along with the
boundedness of the trajectory and the accuracy of the solution.",2108.12136v1
2021-08-27,Non relativistic and ultra relativistic limits in 2d stochastic nonlinear damped Klein-Gordon equation,"We study the non relativistic and ultra relativistic limits in the
two-dimensional nonlinear damped Klein-Gordon equation driven by a space-time
white noise on the torus. In order to take the limits, it is crucial to clarify
the parameter dependence in the estimates of solution. In this paper we present
two methods to confirm this parameter dependence. One is the classical, simple
energy method. Another is the method via Strichartz estimates.",2108.12183v4
2021-09-08,The isothermal limit for the compressible Euler equations with damping,"We consider the isothermal Euler system with damping. We rigorously show the
convergence of Barenblatt solutions towards a limit Gaussian profile in the
isothermal limit $\gamma$ $\rightarrow$ 1, and we explicitly compute the
propagation and the behavior of Gaussian initial data. We then show the weak L
1 convergence of the density as well as the asymptotic behavior of its first
and second moments. Contents 1. Introduction 1 2. Assumptions and main results
3 3. The limit $\gamma$ $\rightarrow$ 1 of Barenblatt's solutions 6 4. Gaussian
solutions 9 5. Evolution of certain quantities 10 6. Convergence 15 7.
Conclusion 17 References 17",2109.03590v1
2021-11-01,Strong solution of modified 3D-Navier-stockes equations,"In this paper we study the incompressible Navier-Stokes equations with
logarithme damping {\alpha} log(e + |u|2)|u|2u, where we used new methods, new
tools and Fourier analysis",2111.00859v2
2021-11-02,Blow-up of solutions to semilinear wave equations with a time-dependent strong damping,"The paper investigates a class of a semilinear wave equation with
time-dependent damping term ($-\frac{1}{{(1+t)}^{\beta}}\Delta u_t$) and a
nonlinearity $|u|^p$. We will show the influence of the the parameter $\beta$
in the blow-up results under some hypothesis on the initial data and the
exponent $p$ by using the test function method. We also study the local
existence in time of mild solution in the energy space $H^1(\mathbb{R}^n)\times
L^2(\mathbb{R}^n)$.",2111.01433v1
2021-11-02,Around plane waves solutions of the Schr{ö}dinger-Langevin equation,"We consider the logarithmic Schr{\""o}dinger equations with damping, also
called Schr{\""o}dinger-Langevin equation. On a periodic domain, this equation
possesses plane wave solutions that are explicit. We prove that these solutions
are asymptotically stable in Sobolev regularity. In the case without damping,
we prove that for almost all value of the nonlinear parameter, these solutions
are stable in high Sobolev regularity for arbitrary long times when the
solution is close to a plane wave. We also show and discuss numerical
experiments illustrating our results.",2111.01487v1
2021-11-11,Stabilization for Euler-Bernoulli beam equation with a local degenerated Kelvin-Voigt damping,"We consider the Euler-Bernoulli beam equation with a local Kelvin-Voigt
dissipation type in the interval $(-1,1)$. The coefficient damping is only
effective in $(0,1)$ and is degenerating near the $0$ point with a speed at
least equal to $x^{\alpha}$ where $\alpha\in(0,5)$. We prove that the semigroup
corresponding to the system is polynomially stable and the decay rate depends
on the degeneracy speed $\alpha$.",2111.06431v1
2021-11-12,GCGE: A Package for Solving Large Scale Eigenvalue Problems by Parallel Block Damping Inverse Power Method,"We propose an eigensolver and the corresponding package, GCGE, for solving
large scale eigenvalue problems. This method is the combination of damping
idea, subspace projection method and inverse power method with dynamic shifts.
To reduce the dimensions of projection subspaces, a moving mechanism is
developed when the number of desired eigenpairs is large. The numerical
methods, implementing techniques and the structure of the package are
presented. Plenty of numerical results are provided to demonstrate the
efficiency, stability and scalability of the concerned eigensolver and the
package GCGE for computing many eigenpairs of large symmetric matrices arising
from applications.",2111.06552v1
2021-11-25,Continuity and topological structural stability for nonautonomous random attractors,"In this work, we study continuity and topological structural stability of
attractors for nonautonomous random differential equations obtained by small
bounded random perturbations of autonomous semilinear problems. First, we study
existence and permanence of unstable sets of hyperbolic solutions. Then, we use
this to establish lower semicontinuity of nonautonomous random attractors and
to show that the gradient structure persists under nonautonomous random
perturbations. Finally, we apply the abstract results in a stochastic
differential equation and in a damped wave equation with a perturbation on the
damping.",2111.13006v1
2021-11-30,Determining damping terms in fractional wave equations,"This paper deals with the inverse problem of recovering an arbitrary number
of fractional damping terms in a wave equation. We develop several approaches
on uniqueness and reconstruction, some of them relying on Tauberian theorems on
the relation between the asymptotics of solutions in time and Laplace domain.
Also the possibility of additionally recovering space dependent coefficients or
initial data is discussed. The resulting methods for reconstructing
coefficients and fractional orders in these terms are tested numerically.
Additionally, we provide an analysis of the forward problem, a multiterm
fractional wave equation.",2112.00080v2
2021-12-20,Dense Coding Capacity in Correlated Noisy Channels with Weak Measurement,"Capacity of dense coding via correlated noisy channel is greater than that in
uncorrelated noisy channel. It is shown that weak measurement and reversal
measurement can make further effort to improve quantum dense coding capacity in
correlated amplitude damping channel, but this effort is very small in
correlated phase damping channel and correlated depolarizing channel.",2112.10346v1
2021-12-22,Low-frequency squeezing spectrum of a laser drivenpolar quantum emitter,"It was shown by a study of the incoherent part of the low-frequency resonance
fluorescence spectrum of the polar quantum emitter driven by semiclassical
external laser field and damped by non-squeezed vacuum reservoir that the
emitted fluorescence field is squeezed to some degree nevertheless. As was also
found, a higher degree of squeezing could, in principle, be achieved by damping
the emitter by squeezed vacuum reservoir.",2112.11809v1
2022-01-13,Cavity optomechanics in a fiber cavity: the role of stimulated Brillouin scattering,"We study the role of stimulated Brillouin scattering in a fiber cavity by
numerical simulations and a simple theoretical model and find good agreement
between experiment, simulation and theory. We also investigate an
optomechanical system based on a fiber cavity in the presence on the nonlinear
Brillouin scattering. Using simulation and theory, we show that this hybrid
optomechanical system increases optomechanical damping for low mechanical
resonance frequencies in the unresolved sideband regime. Furthermore, optimal
damping occurs for blue detuning in stark contrast to standard optomechanics.
We investigate whether this hybrid optomechanical system is capable cooling a
mechanical oscillator to the quantum ground state.",2201.04987v1
2022-01-20,Vacuum and singularity formation for compressible Euler equations with time-dependent damping,"In this paper, vacuum and singularity formation are considered for
compressible Euler equations with time-dependent damping. For $1<\gamma\leq 3$,
by constructing some new control functions ingeniously, we obtain the lower
bounds estimates on density for arbitrary classical solutions. Basing on these
lower estimates, we succeed in proving the singular formation theorem for all
$\lambda$, which was open in [1] for some cases.Moreover, the singularity
formation of the compressible Euler equations when $\gamma=3$ is investigated,
too.",2201.07957v1
2022-01-22,Absorption of charged particles in Perfectly-Matched-Layers by optimal damping of the deposited current,"Perfectly-Matched Layers (PML) are widely used in Particle-In-Cell
simulations, in order to absorb electromagnetic waves that propagate out of the
simulation domain. However, when charged particles cross the interface between
the simulation domain and the PMLs, a number of numerical artifacts can arise.
In order to mitigate these artifacts, we introduce a new PML algorithm whereby
the current deposited by the macroparticles in the PML is damped by an
analytically-derived, optimal coefficient. The benefits of this new algorithm
is illustrated in practical simulations.",2201.09084v2
2022-03-19,The Equilibrium Temperature of Planets on Eccentric Orbits: Time Scales and Averages,"From estimates of the near-surface heat capacity of planets it is shown that
the thermal time scale is larger than the orbital period in the presence of a
global ocean that is well-mixed to a depth of 100 m, or of an atmosphere with a
pressure of several tens of bars. As a consequence, the temperature
fluctuations of such planets on eccentric orbits are damped. The average
temperature should be calculated by taking the temporal mean of the irradiation
over an orbit, which increases with $1/\sqrt{1-e^2}$. This conclusion is
independent of the orbital distance and valid for Sun-like stars; the damping
is even stronger for low-mass main sequence hosts.",2203.11723v1
2022-03-31,Long-time dynamical behavior for a piezoelectric system with magnetic effect and nonlinear dampings,"This paper is concerned with the long-time dynamical behavior of a
piezoelectric system with magnetic effect, which has nonlinear damping terms
and external forces with a parameter. At first, we use the nonlinear semigroup
theory to prove the well-posedness of solutions. Then, we investigate the
properties of global attractors and the existence of exponential attractors.
Finally, the upper semicontinuity of global attractors has been investigated.",2203.16736v1
2022-04-04,Exponential ergodicity for damping Hamiltonian dynamics with state-dependent and non-local collisions,"In this paper, we investigate the exponential ergodicity in a
Wasserstein-type distance for a damping Hamiltonian dynamics with
state-dependent and non-local collisions, which indeed is a special case of
piecewise deterministic Markov processes while is very popular in numerous
modelling situations including stochastic algorithms. The approach adopted in
this work is based on a combination of the refined basic coupling and the
refined reflection coupling for non-local operators. In a certain sense, the
main result developed in the present paper is a continuation of the counterpart
in \cite{BW2022} on exponential ergodicity of stochastic Hamiltonian systems
with L\'evy noises and a complement of \cite{BA} upon exponential ergodicity
for Andersen dynamics with constant jump rate functions.",2204.01372v1
2022-04-08,Effect of Tamm surface states on hot electron generation and Landau damping in nanostructures metal-semiconductor,"The hot electron generation in plasmonic nanoparticles is the key to
efficient plasmonic photocatalysis. In the paper, we study theoretically for
the first time the effect of Tamm states (TSs) at the interface
metal-semiconductor on hot electron generation and Landau damping (LD) in metal
nanoparticles. TSs can lead to resonant hot electron generation and to the LD
rate enhanced by several times. The resonant hot electron generation is
reinforced by the transition absorption due to the jump of the permittivity at
the metal-semiconductor interface.",2204.04021v1
2022-04-11,Certified Reduced Basis Method for the Damped Wave Equations on Networks,"In this paper we present a reduced basis method which yields
structure-preservation and a tight a posteriori error bound for the simulation
of the damped wave equations on networks. The error bound is based on the
exponential decay of the energy inside the system and therefore allows for
sharp bounds without the need of regularization parameters. The fast
convergence of the reduced solution to the truth solution as well as the
tightness of the error bound are verified numerically using an academic network
as example.",2204.05010v1
2022-04-27,Spectrum of the wave equation with Dirac damping on a non-compact star graph,"We consider the wave equation on non-compact star graphs, subject to a
distributional damping defined through a Robin-type vertex condition with
complex coupling. It is shown that the non-self-adjoint generator of the
evolution problem admits an abrupt change in its spectral properties for a
special coupling related to the number of graph edges. As an application, we
show that the evolution problem is highly unstable for the critical couplings.
The relationship with the Dirac equation in non-relativistic quantum mechanics
is also mentioned.",2204.12747v1
2022-04-27,Dependence on the thermodynamic state of self-diffusion of pseudo hard-spheres,"Self-diffusion, $D$, in a system of particles that interact with a pseudo
hard sphere potential is analyzed. Coupling with a solvent is represented by a
Langevin thermostat, characterized by the damping time $t_d$. The hypotheses
that $D=D_0 \varphi$ is proposed, where $D_0$ is the small concentration
diffusivity and $\varphi$ is a thermodynamic function that represents the
effects of interactions as concentration is increased. Molecular dynamics
simulations show that different values of the noise intensity modify $D_0$ but
do not modify $\varphi$. This result is consistent with the assumption that
$\varphi$ is a thermodynamic function, since the thermodynamic state is not
modified by the presence of damping and noise.",2204.12969v1
2022-04-29,Plasmon damping rates in Coulomb-coupled two-dimensional layers in a heterostructure,"The Coulomb excitations of charge density oscillation are calculated for a
double-layer heterostructure. Specifically, we consider two-dimensional (2D)
layers of silicene and graphene on a substrate. From the obtained surface
response function, we calculated the plasmon dispersion relations which
demonstrate the way in which the Coulomb coupling renormalizes the plasmon
frequencies. Additionally, we present a novel result for the damping rates of
the plasmons in this Coulomb coupled heterostructure and compare these results
as the separation between layers is varied.",2205.00053v1
2022-05-08,A regularity criterion for a 3D tropical climate model with damping,"In this paper we deal with the 3D tropical climate model with damping terms
in the equation of the barotropic mode $u$ and in the equation of the first
baroclinic mode $v$ of the velocity, and we establish a regularity criterion
for this system thanks to which the local smooth solution $(u, v, \theta)$ can
actually be extended globally in time.",2205.03841v3
2022-06-04,Radiation backreaction in axion electrodynamics,"Energy-momentum conservation of classical axion-electrodynamics is carefully
analyzed in the Hamiltonian formulation of the theory. The term responsible for
the energy transfer between the electromagnetic and the axion sectors is
identified. As a special application the axion-to-light Primakoff-process in
the background of a static magnetic field is worked out and the radiative
self-damping of the axion oscillations is characterized quantitatively. The
damping time turns out comparable to the age of the Universe in the preferred
axion mass range.",2206.02052v1
2022-06-07,Strong attractors for weakly damped quintic wave equation in bounded domains,"In this paper, we study the longtime dynamics for the weakly damped wave
equation with quintic non-linearity in a bounded smooth domain of
$\mathbb{R}^3.$ Based on the Strichartz estimates for the case of bounded
domains, we establish the existence of a strong global attractor in the phase
space $H^2(\Omega)\cap H^1_0(\Omega)\times H^1_0(\Omega)$. Moreover, the finite
fractal dimension of the attractor is also shown with the help of the
quasi-stable estimation.",2206.03158v1
2022-06-07,Long-time dynamics of the wave equation with nonlocal weak damping and sup-cubic nonlinearity in 3-D domains,"In this paper, we study the long-time dynamics for the wave equation with
nonlocal weak damping and sup-cubic nonlinearity in a bounded smooth domain of
$\mathbb{R}^3.$ Based on the Strichartz estimates for the case of bounded
domains, we first prove the global well-posedness of the Shatah-Struwe
solutions. Then we establish the existence of the global attractor for the
Shatah-Struwe solution semigroup by the method of contractive function.
Finally, we verify the existence of a polynomial attractor for this semigroup.",2206.03163v1
2022-06-17,On energy-stable and high order finite element methods for the wave equation in heterogeneous media with perfectly matched layers,"This paper presents a stable finite element approximation for the acoustic
wave equation on second-order form, with perfectly matched layers (PML) at the
boundaries. Energy estimates are derived for varying PML damping for both the
discrete and the continuous case. Moreover, a priori error estimates are
derived for constant PML damping. Most of the analysis is performed in Laplace
space. Numerical experiments in physical space validate the theoretical
results.",2206.08507v1
2022-06-20,Harmonic Oscillators of Mathematical Biology: Many Faces of a Predator-Prey Model,"We show that a number of models in virus dynamics, epidemiology and plant
biology can be presented as ``damped"" versions of the Lotka-Volterra
predator-prey model, by analogy to the damped harmonic oscillator. The analogy
deepens with the use of Lyapunov functions, which allow us to characterize
their dynamics and even make some estimates.",2206.09561v1
2022-06-21,Phase-covariant mixtures of non-unital qubit maps,"We analyze convex combinations of non-unital qubit maps that are
phase-covariant. In particular, we consider the behavior of maps that combine
amplitude damping, inverse amplitude damping, and pure dephasing. We show that
mixing non-unital channels can result in restoring the unitality, whereas
mixing commutative maps can lead to non-commutativity. For the convex
combinations of Markovian semigroups, we prove that classical uncertainties
cannot break quantum Markovianity. Moreover, contrary to the Pauli channel
case, the semigroup can be recovered only by mixing two other semigroups.",2206.10742v1
2022-07-01,Stabilization results of a Lorenz piezoelectric beam with partial viscous dampings,"In this paper, we investigate the stabilization of a one-dimensional Lorenz
piezoelectric (Stretching system) with partial viscous dampings. First, by
using Lorenz gauge conditions, we reformulate our system to achieve the
existence and uniqueness of the solution. Next, by using General criteria of
Arendt-Batty, we prove the strong stability in different cases. Finally, we
prove that it is sufficient to control the stretching of the center-line of the
beam in x-direction to achieve the exponential stability. Numerical results are
also presented to validate our theoretical result.",2207.00488v1
2022-07-06,Quantum Decomposition Algorithm For Master Equations of Stochastic Processes: The Damped Spin Case,"We introduce a quantum decomposition algorithm (QDA) that decomposes the
problem $\frac{\partial \rho}{\partial t}=\mathcal{L}\rho=\lambda \rho$ into a
summation of eigenvalues times phase-space variables. One interesting feature
of QDA stems from its ability to simulate damped spin systems by means of pure
quantum harmonic oscillators adjusted with the eigenvalues of the original
eigenvalue problem. We test the proposed algorithm in the case of undriven
qubit with spontaneous emission and dephasing.",2207.02755v3
2022-07-25,Geometric modelling of polycrystalline materials: Laguerre tessellations and periodic semi-discrete optimal transport,"In this paper we describe a fast algorithm for generating periodic RVEs of
polycrystalline materials. In particular, we use the damped Newton method from
semi-discrete optimal transport theory to generate 3D periodic Laguerre
tessellations (or power diagrams) with cells of given volumes. Complex,
polydisperse RVEs with up to 100,000 grains of prescribed volumes can be
created in a few minutes on a standard laptop. The damped Newton method relies
on the Hessian of the objective function, which we derive by extending recent
results in semi-discrete optimal transport theory to the periodic setting.",2207.12036v1
2022-07-27,Subsonic time-periodic solution to compressible Euler equations with damping in a bounded domain,"In this paper, we consider the one-dimensional isentropic compressible Euler
equations with linear damping $\beta(t,x)\rho u$ in a bounded domain, which can
be used to describe the process of compressible flows through a porous
medium.~And the model is imposed a dissipative subsonic time-periodic boundary
condition.~Our main results reveal that the time-periodic boundary can trigger
a unique subsonic time-periodic smooth solution which is stable under small
perturbations on initial data. Moreover, the time-periodic solution possesses
higher regularity and stability provided a higher regular boundary condition.",2207.13433v1
2022-09-10,Landau damping on the torus for the Vlasov-Poisson system with massless electrons,"This paper studies the nonlinear Landau damping on the torus $\mathbb{T}^d$
for the Vlasov-Poisson system with massless electrons (VPME). We consider
solutions with analytic or Gevrey ($\gamma > 1/3$) initial data, close to a
homogeneous equilibrium satisfying a Penrose stability condition. We show that
for such solutions, the corresponding density and force field decay
exponentially fast as time goes to infinity. This work extends the results for
Vlasov-Poisson on the torus to the case of ions and, more generally, to
arbitrary analytic nonlinear couplings.",2209.04676v2
2022-09-25,Polynomial mixing of a stochastic wave equation with dissipative damping,"We study the long time statistics of a class of semi--linear wave equations
modeling the motions of a particle suspended in continuous media while being
subjected to random perturbations via an additive Gaussian noise. By comparison
with the nonlinear reaction settings, of which the solutions are known to
possess geometric ergodicity, we find that, under the impact of nonlinear
dissipative damping, the mixing rate is at least polynomial of any order. This
relies on a combination of Lyapunov conditions, the contracting property of the
Markov transition semigroup as well as the notion of $d$--small sets.",2209.12151v2
2022-09-30,A Lyapunov approach for the exponential stability of a damped Timoshenko beam,"In this technical note, we consider the stability properties of a viscously
damped Timoshenko beam equation with spatially varying parameters. With the
help of the port-Hamiltonian framework, we first prove the existence of
solutions and show, by an appropriate Lyapunov function, that the system is
exponentially stable and has an explicit decay rate. The explicit exponential
bound is computed for an illustrative example of which we provide some
numerical simulations.",2209.15281v1
2022-11-01,Well-posedness and strong attractors for a beam model with degenerate nonlocal strong damping,"This paper is devoted to initial-boundary value problem of an extensible beam
equation with degenerate nonlocal energy damping in
$\Omega\subset\mathbb{R}^n$: $u_{tt}-\kappa\Delta u+\Delta^2u-\gamma(\Vert
\Delta u\Vert^2+\Vert u_t\Vert^2)^q\Delta u_t+f(u)=0$. We prove the global
existence and uniqueness of weak solutions, which gives a positive answer to an
open question in [24]. Moreover, we establish the existence of a strong
attractor for the corresponding weak solution semigroup, where the ``strong""
means that the compactness and attractiveness of the attractor are in the
topology of a stronger space $\mathcal{H}_{\frac{1}{q}}$.",2211.00287v3
2022-11-18,Energy decay estimates for an axially travelling string damped at one end,"We study the small vibrations of an axially travelling string with a
dashpoint damping at one end. The string is modelled by a wave equation in a
time-dependent interval with two endpoints moving at a constant speed $v$. For
the undamped case, we obtain a conserved functional equivalent to the energy of
the solution. We derive precise upper and lower estimates for the exponential
decay of the energy with explicit constants. These estimates do not seem to be
reported in the literature even for the non-travelling case $v=0$.",2211.10537v1
2022-12-01,The viscous damping of three dimensional spherical gas bubble inside unbounded compressible liquid,"The present paper considers a homogeneous bubble inside an unbounded
polytropic compressible liquid with viscosity. The system is governed by the
Navier-Stokes equation with free boundary which is determined by the kinematic
and dynamic boundary conditions on the bubble-liquid interface. The global
existence of solution is proved, and the $\dot{H}^1$ asymptotic stability of
the spherical equilibrium in terms of viscous damping together with a explicit
decay rate is given in bare energy methods.",2212.00299v1
2022-12-27,Stabilization of the Kawahara-Kadomtsev-Petviashvili equation with time-delayed feedback,"Results of stabilization for the higher order of the Kadomtsev-Petviashvili
equation are presented in this manuscript. Precisely, we prove with two
different approaches that under the presence of a damping mechanism and an
internal delay term (anti-damping) the solutions of the
Kawahara-Kadomtsev-Petviashvili equation are locally and globally exponentially
stable. The main novelty is that we present the optimal constant, as well as
the minimal time, that ensures that the energy associated with this system goes
to zero exponentially.",2212.13552v1
2023-02-23,Hopf-Like Bifurcation in a Wave Equation at a Removable Singularity,"It is shown that a one-dimensional damped wave equation with an odd time
derivative nonlinearity exhibits small amplitude bifurcating time periodic
solutions, when the bifurcation parameter is the linear damping coefficient is
positive and accumulates to zero. The upshot is that the singularity of the
linearized operator at criticality which stems from the well known small
divisor problem for the wave operator, is entirely removed without the need to
exclude parameters via Diophantine conditions, nor the use of accelerated
convergence schemes. Only the contraction mapping principle is used.",2302.12092v2
2023-03-11,Control estimates for 0th order pseudodifferential operators,"We introduce the control conditions for 0th order pseudodifferential
operators $\mathbf{P}$ whose real parts satisfy the Morse--Smale dynamical
condition. We obtain microlocal control estimates under the control conditions.
As a result, we show that there are no singular profiles in the solution to the
evolution equation $(i\partial_t-\mathbf{P})u=f$ when $\mathbf{P}$ has a
damping term that satisfies the control condition and $f\in C^{\infty}$. This
is motivated by the study of a microlocal model for the damped internal waves.",2303.06443v2
2023-03-24,Exponential decay estimates for semilinear wave-type equations with time-dependent time delay,"In this paper, we analyze a semilinear damped second order evolution equation
with time-dependent time delay and time-dependent delay feedback coefficient.
The nonlinear term satisfies a local Lipschitz continuity assumption. Under
appropriate conditions, we prove well-posedness and exponential stability of
our model for small initial data. Our arguments combine a Lyapunov functional
approach with some continuity arguments. Moreover, as an application of our
abstract results, the damped wave equation with a source term and delay
feedback is analyzed.",2303.14208v1
2023-03-25,Existence and regularity of global attractors for a Kirchhoff wave equation with strong damping and memory,"This paper is concerned with the existence and regularity of global attractor
$\mathcal A$ for a Kirchhoff wave equation with strong damping and memory in
the weighted time-dependent spaces $\mathcal H$ and $\mathcal H^{1}$,
respectively. In order to obtain the existence of $\mathcal A$, we mainly use
the energy method in the priori estimations, and then verify the asymptotic
compactness of the semigroup by the method of contraction function. Finally, by
decomposing the weak solutions into two parts and some elaborate calculations,
we prove the regularity of $\mathcal A$.",2303.14387v1
2023-03-27,Linear Landau damping for a two-species Vlasov-Poisson system for electrons and ions,"This paper concerns the linear Landau damping for the two species
Vlasov-Poisson system for ions and electrons near Penrose stable equilibria.
The result is an extension of the result on the one species Vlasov-Poisson
equation by Mouhout and Villani. Different from their work we do not describe
the ions as a background species but as a species which is also described by a
separate Vlasov equation. We show an exponential decay of the electric energy
for the linearised system near Penrose stable equilibria.",2303.14981v2
2023-03-28,Role of intersublattice exchange interaction on ultrafast longitudinal and transverse magnetization dynamics in Permalloy,"We report about element specific measurements of ultrafast demagnetization
and magnetization precession damping in Permalloy (Py) thin films.
Magnetization dynamics induced by optical pump at $1.5$eV is probed
simultaneously at the $M_{2,3}$ edges of Ni and Fe with High order Harmonics
for moderate demagnetization rates (less than $50$%). The role of the
intersublattice exchange interaction on both longitudinal and transverse
dynamics is analyzed with a Landau Lifshitz Bloch description of
ferromagnetically coupled Fe and Ni sublattices. It is shown that the
intersublattice exchange interaction governs the dissipation during
demagnetization as well as precession damping of the magnetization vector.",2303.15837v1
2023-03-31,Polynomial Mixing for a Weakly Damped Stochastic Nonlinear Schrödinger Equation,"This paper is devoted to proving the polynomial mixing for a weakly damped
stochastic nonlinear Schr\""{o}dinger equation with additive noise on a 1D
bounded domain. The noise is white in time and smooth in space. We consider
both focusing and defocusing nonlinearities, respectively, with exponents of
the nonlinearity $\sigma\in[0,2)$ and $\sigma\in[0,\infty)$ and prove the
polynomial mixing which implies the uniqueness of the invariant measure by
using a coupling method.",2303.18082v1
2023-04-19,Inviscid damping of monotone shear flows for 2D inhomogeneous Euler equation with non-constant density in a finite channel,"We prove the nonlinear inviscid damping for a class of monotone shear flows
with non-constant background density for the two-dimensional ideal
inhomogeneous fluids in $\mathbb{T}\times [0,1]$ when the initial perturbation
is in Gevrey-$\frac{1}{s}$ ($\frac{1}{2}<s<1$) class with compact support.",2304.09841v2
2023-05-07,Nonexistence of global weak solutions to semilinear wave equations involving time-dependent structural damping terms,"We consider a semilinear wave equation involving a time-dependent structural
damping term of the form
$\displaystyle\frac{1}{{(1+t)}^{\beta}}(-\Delta)^{\sigma/2} u_t$. Our results
show the influence of the parameters $\beta,\sigma$ on the nonexistence of
global weak solutions under assumptions on the given system data.",2305.04278v1
2023-05-15,Blow-up phenomena for a class of extensible beam equations,"In this paper, we investigate the initial boundary value problem of the
following nonlinear extensible beam equation with nonlinear damping term $$u_{t
t}+\Delta^2 u-M\left(\|\nabla u\|^2\right) \Delta u-\Delta
u_t+\left|u_t\right|^{r-1} u_t=|u|^{p-1} u$$ which was considered by Yang et
al. (Advanced Nonlinear Studies 2022; 22:436-468). We consider the problem with
the nonlinear damping and establish the finite time blow-up of the solution for
the initial data at arbitrary high energy level, including the estimate lower
and upper bounds of the blowup time. The result provides some affirmative
answer to the open problems given in (Advanced Nonlinear Studies 2022;
22:436-468).",2305.08398v1
2023-06-08,Vanishing of long time average p-enstrophy dissipation rate in the inviscid limit of the 2D damped Navier-Stokes equations,"In 2007, Constantin and Ramos proved a result on the vanishing long time
average enstrophy dissipation rate in the inviscid limit of the 2D damped
Navier-Stokes equations. In this work, we prove a generalization of this for
the p-enstrophy, sequences of distributions of initial data and sequences of
strongly converging right-hand sides. We simplify their approach by working
with invariant measures on the global attractors which can be characterized via
bounded complete solution trajectories. Then, working on the level of
trajectories allows us to directly employ some recent results on strong
convergence of the vorticity in the inviscid limit.",2306.05081v1
2023-06-13,Stability of asymptotically Hamiltonian systems with damped oscillatory and stochastic perturbations,"A class of asymptotically autonomous systems on the plane with oscillatory
coefficients is considered. It is assumed that the limiting system is
Hamiltonian with a stable equilibrium. The effect of damped multiplicative
stochastic perturbations of white noise type on the stability of the system is
discussed. It is shown that different long-term asymptotic regimes for
solutions are admissible in the system and the stochastic stability of the
equilibrium depends on the realized regime. In particular, we show that stable
phase locking is possible in the system due to decaying stochastic
perturbations. The proposed analysis is based on a combination of the averaging
technique and the construction of stochastic Lyapunov functions.",2306.07694v1
2023-06-16,Algorithm MGB to solve highly nonlinear elliptic PDEs in $\tilde{O}(n)$ FLOPS,"We introduce Algorithm MGB (Multi Grid Barrier) for solving highly nonlinear
convex Euler-Lagrange equations. This class of problems includes many highly
nonlinear partial differential equations, such as $p$-Laplacians. We prove
that, if certain regularity hypotheses are satisfied, then our algorithm
converges in $\tilde{O}(1)$ damped Newton iterations, or $\tilde{O}(n)$ FLOPS,
where the tilde indicates that we neglect some polylogarithmic terms. This the
first algorithm whose running time is proven optimal in the big-$\tilde{O}$
sense. Previous algorithms for the $p$-Laplacian required $\tilde{O}(\sqrt{n})$
damped Newton iterations or more.",2306.10183v1
2023-06-28,Global solutions and blow-up for the wave equation with variable coefficients: II. boundary supercritical source,"In this paper, we consider the wave equation with variable coefficients and
boundary damping and supercritical source terms. The goal of this work is
devoted to prove the local and global existence, and classify decay rate of
energy depending on the growth near zero on the damping term. Moreover, we
prove the blow-up of the weak solution with positive initial energy as well as
nonpositive initial energy.",2306.15897v4
2023-07-24,On the stability of a double porous elastic system with visco-porous dampings,"In this paper we consider a one dimensional elastic system with double
porosity structure and with frictional damping in both porous equations. We
introduce two stability numbers $\chi_{0}$ and $\chi_{1}$ and prove that the
solution of the system decays exponentially provided that $\chi_{0}=0$ and
$\chi_{1}\neq0.$ Otherwise, we prove the lack of exponential decay. Our results
improve the results of \cite{Bazarra} and \cite{Nemsi}.",2307.12690v1
2023-07-27,Best Ulam constants for damped linear oscillators with variable coefficients,"This study uses an associated Riccati equation to study the Ulam stability of
non-autonomous linear differential vector equations that model the damped
linear oscillator. In particular, the best (minimal) Ulam constants for these
non-autonomous linear differential vector equations are derived. These robust
results apply to vector equations with solutions that blow up in finite time,
as well as to vector equations with solutions that exist globally on
$(-\infty,\infty)$. Illustrative, non-trivial examples are presented,
highlighting the main results.",2307.15103v1
2023-07-29,An inverse problem for the fractionally damped wave equation,"We consider an inverse problem for a Westervelt type nonlinear wave equation
with fractional damping. This equation arises in nonlinear acoustic imaging,
and we show the forward problem is locally well-posed. We prove that the smooth
coefficient of the nonlinearity can be uniquely determined, based on the
knowledge of the source-to-solution map and a priori knowledge of the
coefficient in an arbitrarily small subset of the domain. Our approach relies
on a second order linearization as well as the unique continuation property of
the spectral fractional Laplacian.",2307.16065v1
2023-08-02,Blow-up and lifespan estimate for the generalized tricomi equation with the scale-invariant damping and time derivative nonlinearity on exterior domain,"The article is devoted to investigating the initial boundary value problem
for the damped wave equation in the scale-invariant case with time-dependent
speed of propagation on the exterior domain. By presenting suitable multipliers
and applying the test-function technique, we study the blow-up and the lifespan
of the solutions to the problem with derivative-type nonlinearity
  $ \d u_{tt}-t^{2m}\Delta u+\frac{\mu}{t}u_t=|u_t|^p, \quad \mbox{in}\
\Omega^{c}\times[1,\infty),$ that we associate with appropriate small initial
data.",2308.01272v2
2023-08-03,Gravitational Wave Heating,"It was shown in previous work that when a gravitational wave (GW) passes
through a viscous shell of matter the magnitude of the GW will be damped and
there are astrohysical circumstances in which the damping is almost complete.
The energy transfer from the GWs to the fluid will increase its temperature. We
construct a model for this process and obtain an expression for the temperature
distribution inside the shell in terms of spherical harmonics. Further, it is
shown that this effect is astrophysically significant: a model problem is
constructed for which the temperature increase is of order $10^6{}^\circ$K.",2308.01615v2
2023-08-08,Stabilization of piezoelectric beam with Coleman-Gurtin or Gurtin-Pipkin thermal law and under Lorenz gauge condition,"In this paper, we present the analysis of stability for a piezoelectric beam
subject to a thermal law (Coleman-Gurtin or Gurtin-Pipkin thermal law) adding
some viscous damping mechanism to the electric field in $x-$direction and
$z-$direction, and we discuss several cases. Then, there is no need to control
the electrical field components in $x$-direction and $z-$ direction to
establish an exponential decay of solutions when the beam is subjected to a
Coleman-Gurtin law, otherwise a polynomial stability is established with
Gurtin-Pipkin thermal law in case when the electrical field components are
damped.",2308.04231v2
2023-08-11,Well-posedness and global attractor for wave equation with nonlinear damping and super-cubic nonlinearity,"In the paper, we study the semilinear wave equation involving the nonlinear
damping $g(u_t) $ and nonlinearity $f(u)$. Under the wider ranges of exponents
of $g$ and $f$, the well-posedness of the weak solution is achieved by
establishing a priori space-time estimates. Then, the existence of the global
attractor in the naturally phase space $H^1_0(\Omega)\times L^2(\Omega)$ is
obtained. Moreover, we prove that the global attrator is regular, that is, the
global attractor is a bounded subset of $(H^2(\Omega)\cap H^1_0(\Omega))\times
H^1_0(\Omega)$.",2308.06208v1
2023-08-16,Stability for degenerate wave equations with drift under simultaneous degenerate damping,"In this paper we study the stability of two different problems. The first one
is a one-dimensional degenerate wave equation with degenerate damping,
incorporating a drift term and a leading operator in non-divergence form. In
the second problem we consider a system that couples degenerate and
non-degenerate wave equations, connected through transmission, and subject to a
single dissipation law at the boundary of the non-degenerate equation. In both
scenarios, we derive exponential stability results.",2308.08645v3
2023-09-02,Existence and nonexistence of global solutions for time-dependent damped NLS equations,"We investigate the Cauchy problem for the nonlinear Schr\""odinger equation
with a time-dependent linear damping term. Under non standard assumptions on
the loss dissipation, we prove the blow-up in the inter-critical regime, and
the global existence in the energy subcritical case. Our results generalize and
improve the ones in [9, 11, 21].",2309.00849v1
2023-09-04,On the small-mass limit for stationary solutions of stochastic wave equations with state dependent friction,"We investigate the convergence, in the small mass limit, of the stationary
solutions of a class of stochastic damped wave equations, where the friction
coefficient depends on the state and the noisy perturbation if of
multiplicative type. We show that the Smoluchowski-Kramers approximation that
has been previously shown to be true in any fixed time interval, is still valid
in the long time regime. Namely we prove that the first marginals of any
sequence of stationary solutions for the damped wave equation converge to the
unique invariant measure of the limiting stochastic quasilinear parabolic
equation. The convergence is proved with respect to the Wasserstein distance
associated with the $H^{-1}$ norm.",2309.01549v1
2023-09-09,Finite-dimensionality of attractors for wave equations with degenerate nonlocal damping,"In this paper we study the fractal dimension of global attractors for a class
of wave equations with (single-point) degenerate nonlocal damping. Both the
equation and its linearization degenerate into linear wave equations at the
degenerate point and the usual approaches to bound the dimension of the
entirety of attractors do not work directly. Instead, we develop a new process
concerning the dimension near the degenerate point individually and show the
finite dimensionality of the attractor.",2309.04712v2
2023-09-19,The Raman gap and collisional absorption,"One of the long-standing puzzles observed in many laser-plasma experiments is
the gap in the Raman backscattering spectrum. This gap is characterized by the
absence of backscattered light between some critical wavelength and twice the
incident laser wavelength. The latter is associated with the absolute Raman
instability from the quarter-critical density surface. Supported by
particle-in-cell (PIC) simulations, it is suggested that the gap can result
from the collisional damping of the backscattered light. A linear analysis of
the competition between the Raman growth rate and the damping rate in a
non-homogenous plasma predicts the gap's existence and width as a function of
the system's parameters. The theory is compared with the PIC simulations and
past experiments.",2309.10366v1
2023-09-21,Inverse problems for a quasilinear strongly damped wave equation arising in nonlinear acoustics,"We consider inverse problems for a Westervelt equation with a strong damping
and a time-dependent potential $q$. We first prove that all boundary
measurements, including the initial data, final data, and the lateral boundary
measurements, uniquely determine $q$ and the nonlinear coefficient $\beta$. The
proof is based on complex geometric optics construction and the approach
proposed by Isakov. Further, by considering fundamental solutions supported in
a half-space constructed by H\""ormander, we prove that with vanishing initial
conditions the Dirichlet-to-Neumann map determines $q$ and $\beta$.",2309.11775v1
2023-09-28,On inverse problems for a strongly damped wave equation on compact manifolds,"We consider a strongly damped wave equation on compact manifolds, both with
and without boundaries, and formulate the corresponding inverse problems. For
closed manifolds, we prove that the metric can be uniquely determined, up to an
isometry, from the knowledge of the source-to-solution map. Similarly, for
manifolds with boundaries, we prove that the metric can be uniquely determined,
up to an isometry, from partial knowledge of the Dirichlet-to-Neumann map. The
key point is to retrieve the spectral information of the Laplace-Beltrami
operator, from the Laplace transform of the measurements. Further we show that
the metric can be determined up to an isometry, using a single measurement in
both scenarios.",2309.16182v1
2023-10-10,Emerging Spin-Orbit Torques in Low Dimensional Dirac Materials,"We report a theoretical description of novel spin-orbit torque components
emerging in two-dimensional Dirac materials with broken inversion symmetry. In
contrast to usual metallic interfaces where field-like and damping-like torque
components are competing, we find that an intrinsic damping-like torque which
derives from all Fermi-sea electrons can be simultaneously enhanced along with
the field-like component. Additionally, hitherto overlooked torque components
unique to Dirac materials, emerge from the coupling between spin and pseudospin
degrees of freedom. These torques are found to be resilient to disorder and
could enhance the magnetic switching performance of nearby magnets.",2310.06447v1
2023-10-22,The residual flow in well-optimized stellarators,"The gyrokinetic theory of the residual flow, in the electrostatic limit, is
revisited, with optimized stellarators in mind. We consider general initial
conditions for the problem, and identify cases that lead to a non-zonal
residual electrostatic potential, i.e. one having a significant component that
varies within a flux surface. We investigate the behavior of the ``intermediate
residual'' in stellarators, a measure of the flow that remains after geodesic
acoustic modes have damped away, but before the action of the slower damping
that is caused by unconfined particle orbits. The case of a quasi-isodynamic
stellarator is identified as having a particularly large such residual, owing
to the small orbit width achieved by optimization.",2310.14218v1
2023-10-26,Efficient Numerical Algorithm for Large-Scale Damped Natural Gradient Descent,"We propose a new algorithm for efficiently solving the damped Fisher matrix
in large-scale scenarios where the number of parameters significantly exceeds
the number of available samples. This problem is fundamental for natural
gradient descent and stochastic reconfiguration. Our algorithm is based on
Cholesky decomposition and is generally applicable. Benchmark results show that
the algorithm is significantly faster than existing methods.",2310.17556v1
2023-11-09,Exponential convergence to steady-states for trajectories of a damped dynamical system modelling adhesive strings,"We study the global well-posedness and asymptotic behavior for a semilinear
damped wave equation with Neumann boundary conditions, modelling a
one-dimensional linearly elastic body interacting with a rigid substrate
through an adhesive material. The key feature of of the problem is that the
interplay between the nonlinear force and the boundary conditions allows for a
continuous set of equilibrium points. We prove an exponential rate of
convergence for the solution towards a (uniquely determined) equilibrium point.",2311.05295v1
2023-11-29,On the exponential stability of uniformly damped wave equations,"We study damped wave propagation problems phrased as abstract evolution
equations in Hilbert spaces. Under some general assumptions, including a
natural compatibility condition for initial values, we establish exponential
decay estimates for all mild solutions using the language and tools of Hilbert
complexes. This framework turns out strong enough to conduct our analysis but
also general enough to include a number of interesting examples. Some of these
are briefly discussed. By a slight modification of the main arguments, we also
obtain corresponding decay results for numerical approximations obtained by
compatible discretization strategies.",2311.18084v1
2023-12-01,Semilinear wave inequalities with double damping and potential terms on Riemannian Manifolds,"We study a semilinear wave inequality with double damping on a complete
noncompact Riemannian manifold. The considered problem involves a potential
function $V$ depending on the space variable in front of the power nonlinearity
and an inhomogeneous term $W$ depending on both time and space variables.
Namely, we establish sufficient conditions for the nonexistence of weak
solutions in both cases: $W\equiv 0$ and $W\not\equiv 0$. The obtained
conditions depend on the parameters of the problem as well as the geometry of
the manifold. Some special cases of manifolds, and of $V$ and $W$ are discussed
in detail.",2312.00617v1
2023-12-29,On damping a control system of arbitrary order with global aftereffect on a tree,"We study a problem of damping a control system described by
functional-differential equations of natural order $n$ and neutral type with
non-smooth complex coefficients on an arbitrary tree with global delay. The
latter means that the delay propagates through internal vertices of the tree.
Minimization of the energy functional of the system leads to a variational
problem. We establish its equivalence to a certain self-adjoint boundary value
problem on the tree for equations of order $2n$ with nonlocal quasi-derivatives
and multidirectional shifts of the argument, as well as Kirchhoff-type
conditions emerging at the internal vertices. The unique solvability of both
problems is proved.",2312.17592v1
2024-01-11,Weak collision effect on nonlinear Landau damping for the Vlasov-Poisson-Fokker-Planck system,"We investigate the impact of weak collisions on Landau damping in the
Vlasov-Poisson-Fokker-Planck system on a torus, specifically focusing on its
proximity to a Maxwellian distribution. In the case where the Gevrey index
satisfies $\frac{1}{s}<3$, we establish the global stability and enhanced
dissipation of small initial data, which remain unaffected by the small
diffusion coefficient $\nu$. For Gevrey index $\frac{1}{s}\ge3$, we prove the
global stability and enhanced dissipation of initial data, whose size is on the
order of $O(\nu^a)$ for any $a>\frac{1-3s}{3-3s}$. Our analysis provides
insights into the effects of phase mixing, enhanced dissipation, and plasma
echoes.",2401.05601v3
2024-01-23,Revisit on global existence of solutions for semilinear damped wave equations in $\mathbb{R}^N$ with noncompactly supported initial data,"In this note, we study the Cauchy problem of the semilinear damped wave
equation and our aim is the small data global existence for noncompactly
supported initial data. For this problem, Ikehata and Tanizawa [5] introduced
the energy method with the exponential-type weight function $e^{|x|^2/(1+t)}$,
which is the so-called Ikehata--Todorova--Yordanov type weight. In this note,
we suggest another weight function of the form $(1+|x|^2/(1+t))^{\lambda}$,
which allows us to treat polynomially decaying initial data and give a simpler
proof than the previous studies treating such initial data.",2401.12530v1
2024-01-24,Eigenmode analysis of the damped Jaynes-Cummings model,"The generating functions for density matrix elements of the Jaynes-Cummings
model with cavity damping are analysed in terms of their eigenmodes, which are
characterised by a specific temporal behaviour. These eigenmodes are shown to
be proportional to particular generalised hypergeometric functions. The
relative weights of these eigenmodes in the generating functions are determined
by the initial conditions of the model. These weights are found by deriving
orthogonality relations involving adjoint modes. In an example it is shown how
the time-dependent density matrix elements and the related factorial moments
can be extracted from the eigenmode decompositions of the generating functions.",2401.13348v1
2024-02-15,A comprehensive modelling and experimental approach for damped oscillations in U-tubes via Easy JavaScript Simulations,"In recent years, science simulations have become popular among educators due
to their educational usefulness, availability, and potential for increasing the
students' knowledge on scientific topics. In this paper, we introduce the
implementation of a user-friendly simulation based on Easy Java/JavaScript
Simulations (EJS) to study the problem of damped oscillations in U-tubes.
Furthermore, we illustrate various advantages associated with the capabilities
of EJS in terms of design and usability in order to encourage teachers to use
it as an educational supplement to physics laboratories.",2402.09866v1
2024-02-21,Hybrid Multi-Directional Quantum Communication Protocol,"The way a new type of state called a hybrid state, which contains more than
one degree of freedom, is used in many practical applications of quantum
communication tasks with lesser amount of resources. Similarly, our aim is here
to perform multi-quantum communication tasks in a protocol to approach quantum
information in multipurpose and multi-directional. We propose a hybrid
multi-directional six-party scheme of implementing quantum teleportation and
joint remote state preparation under the supervision of a controller via a
multi-qubit entangled state as a quantum channel with 100% success probability.
Moreover, we analytically derive the average fidelities of this hybrid scheme
under the amplitude-damping and the phase-damping noise.",2402.14043v1
2024-03-19,Damped energy-norm a posteriori error estimates for fully discrete approximations of the wave equation using C2-reconstructions,"We derive a posteriori error estimates for the the scalar wave equation
discretized in space by continuous finite elements and in time by the explicit
leapfrog scheme. Our analysis combines the idea of invoking extra
time-regularity for the right-hand side, as previously introduced in the space
semi-discrete setting, with a novel, piecewise quartic, globally
twice-differentiable time-reconstruction of the fully discrete solution. Our
main results show that the proposed estimator is reliable and efficient in a
damped energy norm. These properties are illustrated in a series of numerical
examples.",2403.12954v1
1995-02-09,A linear thermohaline oscillator driven by stochastic atmospheric forcing,"The interdecadal variability of a stochastically forced four-box model of the
oceanic meridional thermohaline circulation (THC) is described and compared to
the THC variability in the coupled ocean-atmosphere GCM of Delworth, Manabe,
and Stouffer (1993). The box model is placed in a linearly stable thermally
dominant mean state under mixed boundary conditions. A linear stability
analysis of this state reveals one damped oscillatory THC mode in addition to
purely damped modes. The variability of the model under a moderate amount of
stochastic forcing, meant to emulate the random variability of the atmosphere
affecting the coupled model's interdecadal THC variability, is studied. A
linear interpretation, in which the damped oscillatory mode is of primary
importance, is sufficient for understanding the mechanism accounting for the
stochastically forced variability. Direct comparison of the variability in the
box model and coupled GCM reveals common qualitative aspects. Such a comparison
supports, although does not verify, the hypothesis that the coupled model's THC
variability can be interpreted as the result of atmospheric weather exciting a
linear damped oscillatory THC mode.",9502002v2
1993-09-30,The metal systems in Q0000--2619 at high resolution,"We have obtained high, 11 and 14 \kms, and medium, 40 and 53 \kms, resolution
spectra of the $z_{em} = 4.11$ quasar Q0000--2619 covering the range 4400 \AA\
to 9265 \AA . We identify nine metal absorption systems, of which four were
previously known. A fifth previously suggested system at $z_{abs} \approx
3.409$ (Turnshek et al~ 1991) is ruled out by our data. Two of the eight
systems for which the \lya~ line is in the observable range have a damped \lya~
line. Six of the nine systems show evidence for complex sub--component
structure. At our resolution and S/N we identify a total of 21 sub--components
in the nine systems. Five of the nine systems (11 of the 21 components) fall
within the $\pm 5000$ \kms~ range of the emission redshift, and are hence
classified as \zae~ absorbers. For the two damped systems we find metal
abundances of $\leq 1$% and $\leq 8$% of solar values at redshifts of 3.0541
and 3.3901 respectively. These upper limits are consistent with what would be
expected from previous determinations at lower redshifts, and our data are
hence compatible with earlier conclusions that no evidence is yet found for
chemical evolution of intervening damped and Lyman limit absorbers. For the
\zae~ systems we found indications of metallicities comparable to, and even in
excess of solar values. These much higher values compared to the damped
systems, are in favour of the intrinsic hypothesis for these systems.",9309053v1
1994-12-27,The z=0.8596 Damped Lyman Alpha Absorbing Galaxy Toward PKS 0454+039,"We present {\it Hubble Space Telescope} and ground--based data on the
$z_{abs}=0.8596$ metal line absorption system along the line of sight to PKS
0454+0356. The system is a moderate redshift damped Lyman alpha system, with
${\rm N(HI)}=(5.7\pm0.3)\times10^{20}$~cm$^{-2}$ as measured from the {\it
Faint Object Spectrograph} spectrum. We also present ground--based images which
we use to identify the galaxy which most probably gives rise to the damped
system; the most likely candidate is relatively underluminous by QSO absorber
standards ($M_B \sim -19.0$ for $q_0=0.5$ and $H_0=50$ \kms Mpc$^{-1}$), and
lies $\sim 8.5h^{-1}$ kpc in projection from the QSO sightline. Ground--based
measurements of Zn~II, Cr~II, and Fe~II absorption lines from this system allow
us to infer abundances of [Zn/H]=$-1.1$, [Cr/H]=$-1.2$, and [Fe/H]=$-1.2$,
indicating overall metallicity similar to damped systems at $z >2$, and that
the depletion of Cr and Fe onto dust grains may be even {\it less} important
than in many of the high redshift systems of comparable metallicity. Limits
previously placed on the 21-cm optical depth in the $z=0.8596$ system, together
with our new N(H~I) measurement, suggest a very high spin temperature for the
H~I, $T_S >> 580$ K.",9412093v2
1995-05-17,GRAVITATIONAL LENSING OF QUASARS BY THEIR DAMPED LYMAN-ALPHA ABSORBERS,"Damped Lyman-alpha absorbers are believed to be associated with galactic
disks. We show that gravitational lensing can therefore affect the statistics
of these systems. First, the magnification bias due to lensing raises faint
QSOs above a given magnitude threshold and thereby enhances the probability for
observing damped absorption systems. Second, the bending of light rays from the
source effectively limits the minimum impact parameter of the line-of-sight
relative to the center of the absorber, thus providing an upper cut-off to the
observed neutral hydrogen (HI) column density. The combination of these effects
yields a pronounced peak in the observed abundance of absorbers with high
column densities (>2*10^{21} cm^{-2}) and low redshifts (z<1). The inferred
value of the cosmological density parameter of neutral hydrogen, Omega_{HI},
increases with increasing redshift and luminosity of the sources even if the
true HI density remains constant. This trend resembles the observed evolution
of Omega_{HI}(z). Damped Lyman-alpha absorbers with column densities >10^{21}
cm^{-2} and redshifts 0.5<z<1 are reliable flags for lensed QSOs with a close
pair of images separated by 0.3 arcsec. Detection of these gravitational
lensing signatures with the Hubble Space Telescope can be used to constrain the
depth of the absorber potential-wells and the cosmological constant.",9505078v1
1996-08-22,APM z>4 QSO Survey: Distribution and Evolution of High Column Density HI Absorbers,"Eleven candidate damped Lya absorption systems were identified in 27 spectra
of the quasars from the APM z>4 survey covering the redshift range
2.8<z(abs)<4.4 (8 with z(abs)>3.5). High resolution echelle spectra (0.8A FWHM)
have been obtained for three quasars, including 2 of the highest redshift
objects in the survey. Two damped systems have confirmed HI column densities of
N(HI) >= 10^20.3 atoms cm^-2, with a third falling just below this threshold.
We have discovered the highest redshift damped Lya absorber known at z=4.383 in
QSO BR1202-0725. The APM QSOs provide a substantial increase in the redshift
path available for damped surveys for z>3. We combine this high redshift sample
with other quasar samples covering the redshift range 0.008 < z < 4.7 to study
the redshift evolution and the column density distribution function for
absorbers with log N(HI)>=17.2. In the HI column density distribution
f(N)=kN^-beta we find evidence for breaks in the power law, flattening for
17.2< log N(HI)<21 and steepening for log N(HI)>21.2. The column density
distribution function for the data with log N(HI)>=20.3 is better fit with the
form f(N)=(f*/N*)(N/N*)^-beta exp(-N/N*). Significant redshift evolution in the
number density per unit redshift is evident in the higher column density
systems with an apparent decline in N(z) for z>3.5.",9608146v1
1997-05-16,Testing Cosmological Models Against the Abundance of Damped Lyman-Alpha Absorbers,"We calculate the number of damped Lyman-alpha absorbers expected in various
popular cosmological models as a function of redshift and compare our
predictions with observed abundances. The Press-Schechter formalism is used to
obtain the distribution of halos with circular velocity in different
cosmologies, and we calibrate the relation between circular velocity and
absorption cross-section using detailed gas dynamical simulations of a
``standard'' cold dark matter (CDM) model. Because of this calibration, our
approach makes more realistic assumptions about the absorption properties of
collapsed objects than previous, analytic calculations of the damped
Lyman-alpha abundance. CDM models with Omega_0=1, H_0=50, baryon density
Omega_b=0.05, and scale-invariant primeval fluctuations reproduce the observed
incidence and redshift evolution of damped Lyman-alpha absorption to within
observational uncertainty, for both COBE normalization (sigma_8=1.2) and a
lower normalization (sigma_8=0.7) that better matches the observed cluster
abundance at z=0. A tilted (n=0.8, sigma_8=0.7) CDM model tends to underproduce
absorption, especially at z=4. With COBE normalization, a CDM model with
Omega_0=0.4, Omega_{Lambda}=0.6 gives an acceptable fit to the observed
absorption; an open CDM model is marginally acceptable if Omega_0 is at least
0.4 and strongly inconsistent with the z=4 data if Omega_0=0.3. Mixed dark
matter models tend not to produce sufficient absorption, being roughly
comparable to tilted CDM models if Omega_{nu} = 0.2 and failing drastically if
Omega_{nu} = 0.3.",9705118v1
1997-05-28,Zinc and Chromium Abundances in a Third Damped Lyman alpha System at Intermediate Redshift,"We have determined the metallicity of the $z_{abs} = 1.0093$ damped Lyman
alpha system in the bright QSO EX 0302-223; this is only the third such
measurement at redshifts $z \simlt 1$. Unlike the previous two cases, we find
that the abundance of Zn is only a factor of $\sim 2$ lower than in the
Galactic interstellar medium today and is entirely compatible with the typical
metallicity of stars in the Milky Way disk at a look-back time of 9.5 Gyrs.
Although the galaxy responsible for producing the absorption system has yet to
be positively identified, our observations show that galaxies on a chemical
evolution path similar to that of the Milky Way do contribute to the damped
Lyman alpha population at intermediate redshifts. Cr is 2.5 times less abundant
than Zn, presumably because of depletion onto dust; however, the degree of
depletion is less severe than in diffuse interstellar clouds in the disk of our
Galaxy and in the Magellanic Clouds. Evidently, the interstellar environment in
damped Lyman alpha galaxies is less conducive to the formation and survival of
dust grains (and molecular hydrogen), but the physical processes at the root of
this effect have yet to be clarified.",9705222v1
1998-11-18,The Closest Damped Lyman Alpha System,"A difficulty of studying damped Lyman alpha systems is that they are distant,
so one knows little about the interstellar medium of the galaxy. Here we report
upon a damped Lyman alpha system in the nearby galaxy NGC 4203, which is so
close (v_helio = 1117 km/s) and bright (B_o = 11.62) that its HI disk has been
mapped. The absorption lines are detected against Ton 1480, which lies only
1.9' (12 h_50 kpc) from the center of NGC 4203. Observations were obtained with
the Faint Object Spectrograph on HST (G270H grating) over the 2222-3277
Angstrom region with 200 km/s resolution. Low ionization lines of Fe, Mn, and
Mg were detected, leading to metallicities of -2.29, < -0.68, and > -2.4, which
are typical of other damped Lyman alpha systems, but well below the stellar
metallicity of this type of galaxy. Most notably, the velocity of the lines is
1160 +- 10 km/s, which is identical to the HI rotational velocity of 1170 km/s
at that location in NGC 4203, supporting the view that these absorption line
systems can be associated with the rotating disks of galaxies. In addition, the
line widths of the Mg lines give an upper limit to the velocity dispersion of
167 km/s, to the 99% confidence level.",9811274v1
1999-07-29,Ionized Gas in Damped Lyman-alpha Systems and Its Effects on Elemental Abundance Studies,"Recent high-resolution observations of metal absorption lines in
high-redshift damped Ly-alpha systems have shown that Al III, a tracer of
moderately-ionized gas, very often has a velocity structure indistinguishable
from that of low-ionization gas. Regions of ionized and neutral hydrogen in
these systems are likely cospatial. The higher-ionization Si IV and C IV
absorption shows a much weaker or non-existent correlation with the low
ionization material, implying that the regions traced by Al III are
photoionized by a soft (stellar) spectrum, by a hard (power law) spectrum with
a very low ionization parameter, or a combination of both. We discuss the
ionization of the damped Ly-alpha systems and use photoionization equilibrium
models to make quantitative estimates of its effects on abundance studies in
these systems. We show that ionization effects may be large enough to account
for the observed dispersion in absolute metal abundances in damped Ly-alpha
systems, causing systematically higher abundances in lower column density
systems. The observed Si^+/Fe^+ and Zn^+/Cr^+ ratios may systematically
overestimate the intrinsic Si/Fe and Zn/Cr ratios, respectively, if ionized gas
is present in these systems, thereby mimicking the effects of alpha-element
enrichment or dust depletion.",9907428v1
1999-11-09,Detection of Warm and Cold Phases of the Neutral ISM in a Damped Ly-alpha Absorber,"We present a detailed study of the HI 21cm absorption system at z=0.0912
towards the radio quasar B0738+313. The uncommonly narrow main absorption line
and weak secondary line are resolved for the first time. In addition we find it
necessary to add a third, broader shallow component to obtain a good fit to the
spectrum. Although the harmonic mean spin temperature calculated by comparison
of the 21cm lines to the damped Ly-alpha line is T_s = 775 K, the thermal
kinetic temperatures of the two narrow components, calculated from their
widths, are much lower: T_k \leq 297 and \leq 103 K respectively. This is the
first case of a redshifted absorption system for which T_k is measured to be
less than T_s. We discuss this result in the context of a two phase gas model,
in which the damped Ly-alpha gas is sensitive to a significant neutral column
density of warm phase gas as well as the cold phase gas of the narrow 21cm
lines. The third component is interpreted as representing the warm phase gas
with with T_k \leq 5050 K. The combined column density of the three 21cm
components is approximately equal to that derived from fits to the damped
Ly-alpha line.",9911142v1
2000-06-01,Crust-core coupling and r-mode damping in neutron stars: a toy model,"R-modes in neutron stars with crusts are damped by viscous friction at the
crust-core boundary. The magnitude of this damping, evaluated by Bildsten and
Ushomirsky (BU) under the assumption of a perfectly rigid crust, sets the
maximum spin frequency for a neutron star spun up by accretion in a Low-Mass
X-ray binary (LMXB). In this paper we explore the mechanical coupling between
the core r-modes and the elastic crust, using a toy model of a constant density
neutron star with a constant shear modulus crust. We find that, at spin
frequencies in excess of ~50 Hz, the r-modes strongly penetrate the crust. This
reduces the relative motion (slippage) between the crust and the core compared
to the rigid crust limit. We therefore revise down, by as much as a factor of
10^2-10^3, the damping rate computed by BU, significantly reducing the maximal
possible spin frequency of neutron star with a solid crust. The dependence of
the crust-core slippage on the spin frequency is complicated, and is very
sensitive to the physical thickness of the crust. If the crust is sufficiently
thick, the curve of the critical spin frequency for the onset of the r-mode
instability becomes multi-valued for some temperatures; this is related to the
avoided crossings between the r-mode and the higher-order torsional modes in
the crust. The critical frequencies are comparable to the observed spins of
neutron stars in LMXBs and millisecond pulsars.",0006028v1
2001-03-23,First Investigation of the Clustering Environment of Damped Lyman Alpha Absorbers at z=4,"We report the first observations of the clustering environment of damped
Lyman alpha absorption systems at z=4. Color selection and photometric
redshifts were used to select 44 candidate Lyman-break galaxies brighter than
I_AB=25.5 from deep BRI images of the 35 sq. arcmin field containing the quasar
BR 0951-04. Multislit spectroscopy of 35 candidate galaxies was performed and 8
of these candidates have been confirmed as z>3.5 Lyman-break galaxies. With
only BRI photometry, the photometric redshifts are quite accurate for the
spectroscopically confirmed galaxies but have a high rate of misclassification
due to color degeneracies between Lyman-break galaxies and low-redshift
ellipticals. Both of the z>3.5 galaxies found within 15'' of the quasar
line-of-sight appear to be causing absorption systems in the quasar spectrum.
We use a battery of statistical tests to look for clustering in the redshift
histogram of the z>3.5 galaxies but do not find measurable clustering of these
Lyman-break galaxies with the damped Lyman alpha absorbers. With a larger
sample of galaxies, our method should determine the cross-correlation between
these objects, which probes the bias and hence the mass of the damped Lyman
alpha absorbers.",0103387v2
2002-11-11,Damped Lyman alpha systems and galaxy formation models - II. High ions and Lyman limit systems,"We investigate a model for the high-ionization state gas associated with
observed damped Lyman-alpha systems, based on a semi-analytic model of galaxy
formation set within the paradigm of hierarchical structure formation. In our
model, the hot gas in halos and sub-halos gives rise to CIV absorption, while
the low-ionization state gas is associated with the cold gas in galaxies. The
model matches the distribution of CIV column densities and leads naturally to
kinematic properties that are in good agreement with the data.
  We examine the contribution of both hot and cold gas to sub-damped systems
and suggest that the properties of these systems can be used as an important
test of the model. We expect that sub-DLA systems will generally be composed of
a single gas disk and thus predict that they should have markedly different
kinematics than the damped systems.
  Finally, we find that hot halo gas produces less than one third of Lyman
limit systems at redshift three. We model the contribution of mini-halos (halos
with virial velocities < 35 km/s) to Lyman limit systems and find that they may
contain as much gas as is observed in these systems. However, if we adopt
realistic models of the gas density distribution we find that these systems are
not a significant source of Lyman limit absorption. Instead we suggest that
uncollapsed gas outside of virialized halos is responsible for most of the
Lyman limit systems at high redshift.",0211231v1
2003-05-16,The Age-Metallicity Relation of the Universe in Neutral Gas: The First 100 Damped Lya Systems,"We present accurate metallicity measurements for 121 damped Lya systems at
0.5<z<5 including ~50 new measurements from our recently published Echellette
Spectrograph and Imager surveys. This dataset is analysed to determine the
age-metallicity relation of neutral gas in the universe. Contrary to previous
datasets this sample shows statistically significant evolution in the mean
metallicity. The best linear fit rate to metallicity vs. redshift is -0.26 +/-
0.07 dex corresponding to approximately a factor of 2 every Gyr at z=3. The DLA
continue to maintain a floor in metallicity of ~1/700 solar independent of
observational effects. This metallicity threshold limits the prevalence of
primordial gas in high redshift galaxies and stresses the correspondence
between damped systems and star formation (i.e. galaxy formation). This floor
is significantly offset from the metallicity of the Lya forest and therefore we
consider it to be more related to active star formation within these galaxies
than scenarios of enrichment in the very early universe. Finally, we comment on
an apparent 'missing metals problem': the mean metallicity of the damped
systems is ~10x lower than the value expected from their observed star
formation history. This problem is evident in current theoretical treatments of
chemical evolution and galaxy formation; it may indicate a serious flaw in our
understanding of the interplay between star formation and metal production.",0305314v1
2003-09-24,WIMP matter power spectra and small scale power generation,"Dark Matter (DM) is generally assumed to be massive, cold and collisionless
from the structure formation point of view. A more correct statement however is
that DM indeed experiences collisional damping, but on a scale which is
supposed to be too small to be relevant for structure formation. The aim of
this paper is to present a Cold (although ``collisional'') Dark Matter particle
whose matter power spectrum is damped and see whether it is distinguishable
from standard candidates. To achieve this purpose, we calculate the collisional
damping and free-streaming scales of neutralinos and non conventional
candidates (say light particles heavier than ~1 MeV but lighter than O(10)
GeV). The latter can be considered as Cold Dark Matter (CDM) particles in the
sense that they become non relativistic before their thermal decoupling epoch.
Unlike neutralinos, however, their linear matter power spectrum can be damped
on scales of ~ 10^3 Msol due to their interactions. Since these scales are of
cosmological interest for structure formation, we perform a series of numerical
simulations to obtain the corresponding non linear matter power spectra
P(k)_{nl} at the present epoch. We show that because of small scale
regeneration, they all resemble each other at low redshifts, i.e. become very
similar to a typical CDM matter power spectrum on all but the smallest scales.
Therefore, even if lensing measurements at redshift below unity were to yield a
P(k)_{nl} consistent with CDM models, this would not constitute a sufficiently
robust evidence in favour of the neutralino to rule out alternative DM
candidates.",0309652v1
2004-03-16,The SDSS Damped Lya Survey: Data Release 1,"We present the results from an automated search for damped Lya (DLA) systems
in the quasar spectra of Data Release 1 from the Sloan Digital Sky Survey
(SDSS-DR1). At z~2.5, this homogeneous dataset has greater statistical
significance than the previous two decades of research. We derive a statistical
sample of 71 damped Lya systems (>50 previously unpublished) at z>2.1 and
measure HI column densities directly from the SDSS spectra. The number of DLA
systems per unit redshift is consistent with previous measurements and we
expect our survey has >95% completeness. We examine the cosmological baryonic
mass density of neutral gas Omega_g inferred from the damped Lya systems from
the SDSS-DR1 survey and a combined sample drawn from the literature. Contrary
to previous results, the Omega_g values do not require a significant correction
from Lyman limit systems at any redshift. We also find that the Omega_g values
for the SDSS-DR1 sample do not decline at high redshift and the combined sample
shows a (statistically insignificant) decrease only at z>4. Future data
releases from SDSS will provide the definitive survey of DLA systems at z~2.5
and will significantly reduce the uncertainty in Omega_g at higher redshift.",0403391v2
2006-06-28,Neutral gas density in Damped Lyman Alpha systems,"We estimate the intrinsic neutral gas density in Damped Lyman Alpha systems
($\Omega_{HI}^{(DLA)}$) in the redshift range $ 2.2 \lesssim z \lesssim 5$ from
the DLA SDSS DR_3 sample of optically selected quasars. We take into account
self-consistently the obscuration on background quasars due to the dust present
in Damped Lyman Alpha systems. We model the column density and redshift
distribution of these systems by using both a non-parametric and a parametric
approach. Under conservative assumptions on the dust content of Damped Lyman
$\alpha$ systems, we show that selection effects lead to underestimating the
intrinsic neutral gas density by at least $15\%$ with respect to the observed
neutral gas density. Over the redshift range $[2.2;5.5]$ we find
$\Omega_{HI}^{(DLA)}=0.97^{+0.08+0.28}_{-0.06-0.15} \cdot 10^{-3}$, where the
first set of error bars gives the $1\sigma$ random errors and the second set
gives the modeling uncertainty dependent on the fraction of metals in dust -
from 0\% to 50\%. This value compares with
$\Omega_{HI}^{(DLA)}=0.82^{+0.05}_{-0.05}$ ($1\sigma$ error bars), which is
obtained when no correction for dust is introduced. In the model with half of
the metals mass in dust we cannot constraint $\Omega_{HI}^{(DLA)}$ at a
confidence level higher than $90\%$. In this case there is indeed a probability
of about $10\%$ that the intrinsic column density distribution of DLA systems
is a power law $f(N_{HI}) \propto 1/N_{HI}^{~1.95}$. In contrast, with $25 \%$
of the metals in dust - the most realistic estimate - a power law is ruled out
at $99.5\%$ of confidence level.",0606693v1
2006-09-06,Sun-as-a-star observations: evidence for degree dependence of changes in damping of low-l p modes along the solar cycle,"We use 9.5-yr of BiSON Sun-as-a-star data to search for dependence of
solar-cycle parameter changes on the angular degree, l, of the data. The nature
of the Sun-as-a-star observations is such that for changes measured at fixed
frequency, or for changes averaged across the same range in frequency, any l
dependence present carries information on the latitudinal distribution of the
agent (i.e., the activity) responsible for those changes. We split the 9.5-yr
timeseries into contiguous 108-d pieces, and determine mean changes in the
damping of, power in, and energy supplied to the modes through the solar cycle.
We also apply a careful correction to account for the deleterious effects of
the ground-based BiSON window function on the results. From our full analysis
we obtain a marginally significant result for the damping parameter, where the
mean change is found to be weakest at l=0. The other parameters show hints of
some dependence in l. Our main conclusion is that the mean fractional
solar-cycle change in the l=0 damping rates is approximately 50 % smaller than
was previously assumed. It had been common practice to use an average over all
low-l modes; our downward revision of the radial-mode value has implications
for comparisons with models of the global solar cycle changes, which are
usually based on a spherically symmetric geometry.",0609156v2
1997-08-12,Coherence in the Quasi-Particle 'Scattering' by the Vortex Lattice in Pure Type-II Superconductors,"The effect of quasi-particle (QP) 'scattering' by the vortex lattice on the
de-Haas van-Alphen oscillations in a pure type-II superconductor is
investigated within mean field,asymptotic perturbation theory. Using a 2D
electron gas model it is shown that, due to a strict phase coherence in the
many-particle correlation functions, the 'scattering' effect in the asymptotic
limit ($\sqrt{E_F/\hbar\omega_c}\gg 1$) is much weaker than what is predicted
by the random vortex lattice model proposed by Maki and Stephen, which destroys
this coherence . The coherent many particle configuration is a collinear array
of many particle coordinates, localized within a spatial region with size of
the order of the magnetic length. The amplitude of the magnetization
oscillations is sharply damped just below $% H_{c2}$ because of strong
$180^{\circ}$ out of phase magnetic oscillations in the superconducting
condensation energy ,which tend to cancel the normal electron oscillations.
Within the ideal 2D model used it is found, however, that because of the
relative smallness of the quartic and higher order terms in the expansion, the
oscillations amplitude at lower fields does not really damp to zero, but only
reverses sign and remains virtually undamped well below $H_{c2}$. This
conclusion may be changed if disorder in the vortex lattice, or vortex lines
motion will be taken into account. The reduced QP 'scattering' effect may be
responsible for the apparent crossover from a strong damping of the dHvA
oscillations just below $H_{c2}$ to a weaker damping at lower fields observed
experimentally in several 3D superconductors.",9708088v1
1999-08-27,Electron Correlations in an Electron Bilayer at Finite Temperature: Landau Damping of the Acoustic Plasmon,"We report angle-resolved Raman scattering observations of the temperature
dependent Landau damping of the acoustic plasmon in an electron bilayer system
realised in a GaAs double quantum well structure. Corresponding calculations of
the charge-density excitation spectrum of the electron bilayer using forms of
the random phase approximation (RPA), and the static local field formalism of
Singwi, Tosi, Land and Sj\""{o}lander (STLS) extended to incorporate non-zero
electron temperature $T_{\rm e}$ and phenomenological damping, are also
presented. The STLS calculations include details of the temperature dependence
of the intra- and inter-layer local field factors and pair-correlation
functions. Good agreement between experiment and the various theories is
obtained for the acoustic plasmon energy and damping for $T_{\rm e} \lesssim
T_{\rm F}/2$, the Fermi temperature. However, contrary to current expectations,
all of the calculations show significant departures from our experimental data
for $T_{\rm e} \gtrsim T_{\rm F}/2$. From this, we go on to demonstrate
unambiguously that real local field factors fail to provide a physically
accurate description of exchange correlation behaviour in low dimensional
electron gases. Our results suggest instead that one must resort to a
{\em{dynamical}} local field theory, characterised by a {\em{complex}} field
factor to provide a more accurate description.",9908408v1
2000-10-02,"Comment on ""Magnetic Breakdown at High Fields: Semiclassical and Quantum Treatments""","We comment on the study of the spin-damping factor on the de Haas-van Alphen
(dHvA) discussed by Han et al. (Phys. Rev. Lett. 85, 1500 (2000)).",0010018v1
2002-03-11,Shubnikov - de Haas effect in the quantum vortex liquid state of the organic superconductor $κ$-(BEDT-TTF)$_{2}$Cu(NCS)$_{2}$,"We report the Shubnikov-de Haas (SdH) oscillations observed in the vortex
liquid state of the quasi two dimensional organic superconductor
$\kappa$-(BEDT-TTF)$_{2}$Cu(NCS)$_{2}$. The SdH oscillations can be observed
down to about 5 T at 0.5 K, where the flux flow resistivity becomes as small as
about 30 % of the normal state value. Below the upper critical field $H_{\rm
c2}$ of about 7 T, the additional damping of the SdH oscillation amplitude
appears, as well as that of the de Haas-van Alphen (dHvA) oscillations, with
respect to the normal state one which is described with the standard
Lifshitz-Kosevich formula. The magnitude of the additional damping near $H_{\rm
c2}$ is the same with that observed in the dHvA oscillations and well explained
by the theoretical predictions in consideration of fluctuations in the thermal
vortex liquid state. In the quantum fluctuation region at lower temperature,
however, only SdH effect shows the stronger damping than that of the dHvA
oscillations. The different magnetic field dependence of the additional damping
of the oscillation amplitude between the SdH and dHvA effects is discussed in
connection with the effect of the transport current on the short-range order of
vortices in the quantum vortex slush state reported at the same temperature and
magnetic field region.",0203228v2
2003-03-13,Vibrational sidebands and dissipative tunneling in molecular transistors,"Transport through molecular devices with strong coupling to a single
vibrational mode is considered in the case where the vibration is damped by
coupling to the environment. We focus on the weak tunneling limit, for which a
rate equation approach is valid. The role of the environment can be
characterized by a frictional damping term $\mysig(\omega)$ and corresponding
frequency shift. We consider a molecule that is attached to a substrate,
leading to frequency-dependent frictional damping of the single oscillator mode
of the molecule, and compare it to a reference model with frequency-independent
damping featuring a constant quality factor $Q$. For large values of $Q$, the
transport is governed by tunneling between displaced oscillator states giving
rise to the well-known series of the Frank-Condon steps, while at small $Q$,
there is a crossover to the classical regime with an energy gap given by the
classical displacement energy. Using realistic values for the elastic
properties of the substrate and the size of the molecule, we calculate $I$-$V$
curves and find qualitative agreement between our theory and recent experiments
on $C_{60}$ single-molecule devices.",0303236v3
2004-09-03,Weyl equation for temperature fields induced by attosecond laser pulses,"In this paper the Weyl equation for temperature field induced by laser beam
interaction with matter is proposed and solved. Depending on the scattering
mechanism the temperature field oscillate or is damped.
  Key words: Thermal processes, Weyl equation",0409076v1
2004-12-08,Spectroscopy of a driven solid-state qubit coupled to a structured environment,"We study the asymptotic dynamics of a driven spin-boson system where the
environment is formed by a broadened localized mode. Upon exploiting an exact
mapping, an equivalent formulation of the problem in terms of a quantum
two-state system (qubit) coupled to a harmonic oscillator which is itself
Ohmically damped, is found. We calculate the asymptotic population difference
of the two states in two complementary parameter regimes. For weak damping and
low temperature, a perturbative Floquet-Born-Markovian master equation for the
qubit-oscillator system can be solved. We find multi-photon resonances
corresponding to transitions in the coupled quantum system and calculate their
line-shape analytically. In the complementary parameter regime of strong
damping and/or high temperatures, non-perturbative real-time path integral
techniques yield analytic results for the resonance line shape. In both
regimes, we find very good agreement with exact results obtained from a
numerical real-time path-integral approach. Finally, we show for the case of
strong detuning between qubit and oscillator that the width of the $n$-photon
resonance scales with the $n$-th Bessel function of the driving strength in the
weak-damping regime.",0412194v2
1995-03-08,A NEW NUMERICAL APPROACH TO THE OSCILLATION MODES OF RELATIVISTIC STARS,"The oscillation modes of a simple polytropic stellar model are studied. Using
a new numerical approach (based on integration for complex coordinates) to the
problem for the stellar exterior we have computed the eigenfrequencies of the
highly damped w-modes. The results obtained agree well with recent ones of
Leins, Nollert and Soffel (1993) Specifically, we are able to explain why
several modes in this regime of the complex frequency plane could not be
identified within the WKB approach of Kokkotas and Schutz (1992). Furthermore,
we have established that the ``kink'' that was a prominent feature of the
spectra of Kokkotas and Schutz, but did not appear in the results of Leins {\em
et al.}, was a numerical artefact. Using our new numerical code we are also
able to compute, for the first time, several of the slowly damped (p) modes for
the considered stellar models. For very compact stars we find, somewhat
surprisingly, that the damping of these modes does not decrease monotonically
as one proceeds to higher oscillation frequencies. The existence of low-order
modes that damp away much faster than anticipated may have implications for
questions regarding stellar stability and the lifetime of gravitational-wave
sources. The present results illustrate the accuracy and reliability of the
complex-coordinate method and indicate that the method could prove to be of
great use also in problems involving rotating stars. There is no apparent
reason why the complex-coordinate approach should not extend to rotating stars,
whereas it is accepted that all previous methods will fail to do so.",9503014v1
1998-01-29,"On the gravitational, dilatonic and axionic radiative damping of cosmic strings","We study the radiation reaction on cosmic strings due to the emission of
dilatonic, gravitational and axionic waves. After verifying the (on average)
conservative nature of the time-symmetric self-interactions, we concentrate on
the finite radiation damping force associated with the half-retarded minus
half-advanced ``reactive'' fields. We revisit a recent proposal of using a
``local back reaction approximation'' for the reactive fields. Using
dimensional continuation as convenient technical tool, we find, contrary to
previous claims, that this proposal leads to antidamping in the case of the
axionic field, and to zero (integrated) damping in the case of the
gravitational field. One gets normal positive damping only in the case of the
dilatonic field. We propose to use a suitably modified version of the local
dilatonic radiation reaction as a substitute for the exact (non-local)
gravitational radiation reaction. The incorporation of such a local
approximation to gravitational radiation reaction should allow one to complete,
in a computationally non-intensive way, string network simulations and to give
better estimates of the amount and spectrum of gravitational radiation emitted
by a cosmologically evolving network of massive strings.",9801105v3
2004-10-15,A Nonlinear Coupling Network to Simulate the Development of the r-mode Instablility in Neutron Stars II. Dynamics,"Two mechanisms for nonlinear mode saturation of the r-mode in neutron stars
have been suggested: the parametric instability mechanism involving a small
number of modes and the formation of a nearly continuous Kolmogorov-type
cascade. Using a network of oscillators constructed from the eigenmodes of a
perfect fluid incompressible star, we investigate the transition between the
two regimes numerically. Our network includes the 4995 inertial modes up to n<=
30 with 146,998 direct couplings to the r-mode and 1,306,999 couplings with
detuning< 0.002 (out of a total of approximately 10^9 possible couplings).
  The lowest parametric instability thresholds for a range of temperatures are
calculated and it is found that the r-mode becomes unstable to modes with
13<n<15. In the undriven, undamped, Hamiltonian version of the network the rate
to achieve equipartition is found to be amplitude dependent, reminiscent of the
Fermi-Pasta-Ulam problem. More realistic models driven unstable by
gravitational radiation and damped by shear viscosity are explored next. A
range of damping rates, corresponding to temperatures 10^6K to 10^9K, is
considered. Exponential growth of the r-mode is found to cease at small
amplitudes, approximately 10^-4. For strongly damped, low temperature models, a
few modes dominate the dynamics. The behavior of the r-mode is complicated, but
its amplitude is still no larger than about 10^-4 on average. For high
temperature, weakly damped models the r-mode feeds energy into a sea of
oscillators that achieve approximate equipartition. In this case the r-mode
amplitude settles to a value for which the rate to achieve equipartition is
approximately the linear instability growth rate.",0410072v1
1997-02-20,Numerical study of plasmon properties in the SU(2)-Higgs model,"Using the (effective) classical approximation, we compute numerically
time-dependent correlation functions in the SU(2)-Higgs model around the
electroweak phase transition, for $m_H \approx m_W$. The parameters of the
classical model have been determined previously by the dimensional reduction
relations for time-independent correlators. The $H$ and $W$ correlation
functions correspond to gauge invariant fields. They show damped oscillatory
behavior from which we extract frequencies $\om$ and damping rates $\gm$. In
the Higgs phase the damping rates have roughly the values obtained in analytic
calculations in the quantum theory. In the plasma phase (where analytic
estimates for gauge invariant fields are not available), the damping rate
associated with $H$ is an order of magnitude larger than in the Higgs phase,
while the $W$ correlator appears to be overdamped, with a small rate. The
frequency $\om_H$ shows a clear dip at the transition. The results are
approximately independent of the lattice spacing, but this appears to be
compatible with the lattice spacing dependence expected from perturbation
theory.",9702017v2
2001-01-16,Nonlinear Landau damping of a plasmino in the quark-gluon plasma,"On the basis of the Blaizot-Iancu equations, which are a local formulation of
the hard thermal loop (HTL) equations of motion for soft fluctuating quark and
gluon fields and their induced sources, the coupled kinetic equations for
plasminos and plasmons are obtained. The equality of matrix elements for
nonlinear scattering of a plasmino by hard particles in covariant and temporal
gauges is established by using effective Ward identities. The model problem of
the interaction of two infinitely narrow packets with fermion and boson quantum
numbers is considered. The kinematical relations between wave vectors of the
plasmino and plasmon are derived, when the effective pumping over of the plasma
excitation energy from the fermion branch of plasma excitations to the boson
branch and vice versa occur. The expression for the nonlinear Landau damping
rate of a plasmino at rest is found, and a comparison with a plasmino damping
constant obtained within the framework of the hard thermal loop approximation
is made. The nonlinear Landau damping rate for normal quark excitations is
shown to diverge like $1/\sqrt{q^2}$ near the light cone where $q$ is a
four-momentum of excitations, and the improved Blaizot-Iancu equations removing
this divergence are proposed.",0101167v2
2003-12-15,Nonequilibrium pion dynamics near the critical point in a constituent quark model,"We study static and dynamical critical phenomena of chiral symmetry breaking
in a two-flavor Nambu--Jona-Lasinio constituent quark model. We obtain the
low-energy effective action for scalar and pseudoscalar degrees of freedom to
lowest order in quark loops and to quadratic order in the meson fluctuations
around the mean field. The \emph{static} limit of critical phenomena is shown
to be described by a Ginzburg-Landau effective action including \emph{spatial}
gradients. Hence \emph{static} critical phenomena is described by the
universality class of the O(4) Heisenberg ferromagnet. \emph{Dynamical}
critical phenomena is studied by obtaining the equations of motion for pion
fluctuations. We find that for $T<T_c$ the are stable long-wavelength pion
excitations with dispersion relation $\omega_{\pi}(k)=k$ described by isolated
pion poles. The residue of the pion pole vanishes near $T_c$ as $Z \propto
1/|\ln(1-T/T_c)|$ and long-wavelength fluctuations are damped out by Landau
damping on a time scale $t_\mathrm{rel}(k)\propto 1/k$, reflecting
\emph{critical slowing down} of pion fluctuations near the critical point. At
the critical point, the pion propagator features mass shell logarithmic
divergences which we conjecture to be the harbinger of a (large) dynamical
anomalous dimension. We find that while the \emph{classical spinodal} line
coincides with that of the Ginzburg-Landau theory, the growth rate of
long-wavelength spinodal fluctuations has a richer wavelength dependence as a
consequence of Landau damping. We argue that Landau damping prevents a
\emph{local} low energy effective action in terms of a derivative expansion in
real time.",0312185v2
2001-11-16,Resonances and superlattice pattern stabilization in two-frequency forced Faraday waves,"We investigate the role weakly damped modes play in the selection of Faraday
wave patterns forced with rationally-related frequency components m*omega and
n*omega. We use symmetry considerations to argue for the special importance of
the weakly damped modes oscillating with twice the frequency of the critical
mode, and those oscillating primarily with the ""difference frequency""
|n-m|*omega and the ""sum frequency"" (n+m)*omega. We then perform a weakly
nonlinear analysis using equations of Zhang and Vinals (1997, J. Fluid Mech.
336) which apply to small-amplitude waves on weakly inviscid, semi-infinite
fluid layers. For weak damping and forcing and one-dimensional waves, we
perform a perturbation expansion through fourth order which yields analytical
expressions for onset parameters and the cubic bifurcation coefficient that
determines wave amplitude as a function of forcing near onset. For stronger
damping and forcing we numerically compute these same parameters, as well as
the cubic cross-coupling coefficient for competing waves travelling at an angle
theta relative to each other. The resonance effects predicted by symmetry are
borne out in the perturbation results for one spatial dimension, and are
supported by the numerical results in two dimensions. The difference frequency
resonance plays a key role in stabilizing superlattice patterns of the SL-I
type observed by Kudrolli, Pier and Gollub (1998, Physica D 123).",0111039v2
2002-02-01,Time Domain Computation of a Nonlinear Nonlocal Cochlear Model with Applications to Multitone Interaction in Hearing,"A nonlinear nonlocal cochlear model of the transmission line type is studied
in order to capture the multitone interactions and resulting tonal suppression
effects. The model can serve as a module for voice signal processing, it is a
one dimensional (in space) damped dispersive nonlinear PDE based on mechanics
and phenomenology of hearing. It describes the motion of basilar membrane (BM)
in the cochlea driven by input pressure waves. Both elastic damping and
selective longitudinal fluid damping are present. The former is nonlinear and
nonlocal in BM displacement, and plays a key role in capturing tonal
interactions. The latter is active only near the exit boundary (helicotrema),
and is built in to damp out the remaining long waves. The initial boundary
value problem is numerically solved with a semi-implicit second order finite
difference method. Solutions reach a multi-frequency quasi-steady state.
Numerical results are shown on two tone suppression from both high-frequency
and low-frequency sides, consistent with known behavior of two tone
suppression. Suppression effects among three tones are demonstrated by showing
how the response magnitudes of the fixed two tones are reduced as we vary the
third tone in frequency and amplitude. We observe qualitative agreement of our
model solutions with existing cat auditory neural data. The model is thus
simple and efficient as a processing tool for voice signals.",0202004v3
2003-12-22,Intermittency is a consequence of turbulent transport in nonlinear systems,"Intermittent high-amplitude structures emerge in a damped and driven discrete
nonlinear Schroedinger equation whose solutions transport both energy and
particles from sources to sinks. These coherent structures are necessary for
any solution that has statistically stationary transport properties.",0312059v1
2004-06-17,Multi-frequency control of Faraday wave patterns,"We show how pattern formation in Faraday waves may be manipulated by varying
the harmonic content of the periodic forcing function. Our approach relies on
the crucial influence of resonant triad interactions coupling pairs of critical
standing wave modes with damped, spatio-temporally resonant modes. Under the
assumption of weak damping and forcing, we perform a symmetry-based analysis
that reveals the damped modes most relevant for pattern selection, and how the
strength of the corresponding triad interactions depends on the forcing
frequencies, amplitudes, and phases. In many cases, the further assumption of
Hamiltonian structure in the inviscid limit determines whether the given triad
interaction has an enhancing or suppressing effect on related patterns.
Surprisingly, even for forcing functions with arbitrarily many frequency
components, there are at most five frequencies that affect each of the
important triad interactions at leading order. The relative phases of those
forcing components play a key role, sometimes making the difference between an
enhancing and suppressing effect. In numerical examples, we examine the
validity of our results for larger values of the damping and forcing. Finally,
we apply our findings to one-dimensional periodic patterns obtained with
impulsive forcing and to two-dimensional superlattice patterns and
quasipatterns obtained with multi-frequency forcing.",0406034v1
1997-01-22,Shell Model for Warm Rotating Nuclei,"In order to provide a microscopic description of levels and E2 transitions in
rapidly rotating nuclei with internal excitation energy up to a few MeV, use is
made of a shell model which combines the cranked Nilsson mean-field and the
residual surface delta two-body force. The damping of collective rotational
motion is investigated in the case of a typical rare-earth nucleus, namely \Yb.
It is found that rotational damping sets in at around 0.8 MeV above the yrast
line, and the levels which form rotational band structures are thus limited. We
predict at a given rotational frequency existence of about 30 rotational bands
of various lengths, in overall agreement with the experimental findings. The
onset of the rotational damping proceeds quite gradually as a function of the
internal excitation energy. The transition region extends up to around 2 MeV
above yrast and it is characterized by the presence of scars of discrete
rotational bands which extend over few spin values and stand out among the
damped transitions, and by a two-component profile in the $E_\gamma -E_\gamma$
correlation. The important role played by the high-multipole components of the
two-body residual interaction is emphasized.",9701044v1
2005-04-21,Enhanced optical cooling of particle beams in storage rings,"The problem of enhanced optical cooling (EOC) of particle beams in storage
rings beyond the Robinson's damping criterion is discussed.",0504145v1
2005-10-21,Non-contact atomic force microscopy: Stability criterion and dynamical responses of the shift of frequency and damping signal,"The aim of this article is to provide a complete analysis of the behavior of
a noncontact atomic force microscope (NC-AFM). We start with a review of the
equations of motion of a tip interacting with a surface in which the stability
conditions are first revisited for tapping mode. Adding the equations of
automatic gain control (AGC), which insures constant amplitude of the
oscillations in the NC-AFM, to the equations of motion of the tip, a new
analytical stability criterion that involves proportional and integral gains of
AGC is deduced. Stationary solutions for the shift of frequency and for the
damping signal are obtained. Special attention is paid to the damping signal in
order to clarify its physical origin. The theoretical results are then compared
to those given by a virtual machine. The virtual machine is a set of equations
solved numerically without any approximation. The virtual machine is of great
help in understanding the dynamical behavior of the NC-AFM as images are
recorded. Transient responses of the shift in frequency and of the damping
signal are discussed in relation to the values of proportional and integral
gains of AGC.",0510192v1
1999-06-09,Quantum dynamics of a damped deformed oscillator,"The interaction of a quantum deformed oscillator with the environment is
studied deriving a master equation whose form strongly depends on the type of
deformation.",9906031v1
2006-06-15,Purity and decoherence in the theory of a damped harmonic oscillator,"For the generalized master equations derived by Karrlein and Grabert for the
microscopic model of a damped harmonic oscillator, the conditions for purity of
states are written, in particular for different initial conditions and
different types of damping, including Ohmic, Drude and weak coupling cases,
Agarwal and Weidlich-Haake models. It is shown that the states which remain
pure are the squeezed states with constant in time variances. For pure states,
the generalized nonlinear Schr\"" odinger-type equations corresponding to these
master equations are also obtained. Then the condition for purity of states of
a damped harmonic oscillator is considered in the framework of Lindblad theory
for open quantum systems. For a special choice of the environment coefficients,
the correlated coherent states with constant variances and covariance are shown
to be the only states which remain pure all the time during the evolution of
the considered system. In Karrlein-Grabert and Lindblad models, as well as in
the considered particular models, the expressions of the rate of entropy
production is written and it is shown that the states which preserve their
purity in time are also the states which minimize the entropy production and,
therefore, they are the most stable ones under evolution in the presence of the
environment and play an important role in the description of decoherence
phenomenon.",0606134v1
2007-04-29,Long Term Evolution of Magnetic Turbulence in Relativistic Collisionless Shocks: Electron-Positron Plasmas,"We study the long term evolution of magnetic fields generated by a
collisionless relativistic $e^+e^-$ shock which is initially unmagnetized. Our
2D particle-in-cell numerical simulations show that downstream of such a
Weibel-mediated shock, particle distributions are close to isotropic,
relativistic Maxwellians, and the magnetic turbulence is highly intermittent
spatially, with the non-propagating magnetic fields forming relatively isolated
regions with transverse dimension $\sim 10-20$ skin depths. These structures
decay in amplitude, with little sign of downstream merging. The fields start
with magnetic energy density $\sim (0.1-0.2)$ of the upstream kinetic energy
within the shock transition, but rapid downstream decay drives the fields to
much smaller values, below $10^{-3}$ of equipartition after $10^3$ skin depths.
  In an attempt to construct a theory that follows field decay to these smaller
values, we explore the hypothesis that the observed damping is a variant of
Landau damping in an unmagnetized plasma. The model is based on the small value
of the downstream magnetic energy density, which suggests that particle orbits
are only weakly perturbed from straight line motion, if the turbulence is
homogeneous. Using linear kinetic theory applied to electromagnetic fields in
an isotropic, relativistic Maxwellian plasma, we find a simple analytic form
for the damping rates, $\gamma_k$, in two and three dimensions for small
amplitude, subluminous electromagnetic fields. We find that magnetic energy
does damp due to phase mixing of current carrying particles as $(\omega_p
t)^{-q}$ with $q \sim 1$. (abridged)",0704.3832v2
2007-06-21,Production of a sterile species via active-sterile mixing: an exactly solvable model,"The production of a sterile species via active-sterile mixing in a thermal
medium is studied in an exactly solvable model. The \emph{exact} time evolution
of the sterile distribution function is determined by the dispersion relations
and damping rates $\Gamma_{1,2}$ for the quasiparticle modes. These depend on
$\wtg = \Gamma_{aa}/2\Delta E$, with $\Gamma_{aa}$ the interaction rate of the
active species in absence of mixing and $\Delta E$ the oscillation frequency in
the medium without damping. $\wtg \ll1,\wtg \gg 1$ describe the weak and strong
damping limits respectively. For $\wtg\ll1$, $\Gamma_1 = \Gamma_{aa}\cos^2\tm ;
\Gamma_{2}=\Gamma_{aa}\sin^2\tm$ where $\tm$ is the mixing angle in the medium
and the sterile distribution function \emph{does not} obey a simple rate
equation. For $\wtg \gg 1$, $\Gamma_1= \Gamma_{aa}$ and $\Gamma_2 = \Gamma_{aa}
\sin^22\tm/4\wtg^2$, is the sterile production rate. In this regime sterile
production is suppressed and the oscillation frequency \emph{vanishes} at an
MSW resonance, with a breakdown of adiabaticity. These are consequences of
quantum Zeno suppression. For active neutrinos with standard model interactions
the strong damping limit is \emph{only} available near an MSW resonance
\emph{if} $\sin\theta \lesssim \alpha_w$ with $\theta$ the vacuum mixing angle.
The full set of quantum kinetic equations for sterile production for arbitrary
$\wtg$ are obtained from the quantum master equation. Cosmological resonant
sterile neutrino production is quantum Zeno suppressed relieving potential
uncertainties associated with the QCD phase transition.",0706.3167v2
2007-08-02,Eccentricity evolution of giant planet orbits due to circumstellar disk torques,"The extrasolar planets discovered to date possess unexpected orbital
elements. Most orbit their host stars with larger eccentricities and smaller
semi-major axes than similarly sized planets in our own solar system do. It is
generally agreed that the interaction between giant planets and circumstellar
disks (Type II migration) drives these planets inward to small radii, but the
effect of these same disks on orbital eccentricity, e, is controversial.
Several recent analytic calculations suggest that disk-planet interactions can
excite eccentricity, while numerical studies generally produce eccentricity
damping. This paper addresses this controversy using a quasi-analytic approach,
drawing on several preceding analytic studies. This work refines the current
treatment of eccentricity evolution by removing several approximations from the
calculation of disk torques. We encounter neither uniform damping nor uniform
excitation of orbital eccentricity, but rather a function de/dt that varies in
both sign and magnitude depending on eccentricity and other solar system
properties. Most significantly, we find that for every combination of disk and
planet properties investigated herein, corotation torques produce negative
values of de/dt for some range in e within the interval [0.1, 0.5]. If
corotation torques are saturated, this region of eccentricity damping
disappears, and excitation occurs on a short timescale of less than 0.08 Myr.
Thus, our study does not produce eccentricity excitation on a timescale of a
few Myr -- we obtain either eccentricity excitation on a short time scale, or
eccentricity damping on a longer time scale. Finally, we discuss the
implications of this result for producing the observed range in extrasolar
planet eccentricity.",0708.0335v1
2007-10-10,HE 0515-4414 - an unusual sub-damped Ly alpha system revisited,"Using STIS and VLT UVES observations we have examined the ionization,
abundances, and differential dust depletion of metals, the kinematic structure,
and the physical conditions in the molecular hydrogen-bearing sub-damped Ly
alpha system toward HE 0515-4414 at z = 1.15. The velocity interval of
associated metal lines extends for 700 km/s. In addition, saturated H I
absorption is detected in the blue damping wing of the main component. The
column density ratios of associated Al II, Al III, and Fe II lines indicate
that the absorbing material is ionized. 19 of in total 31 detected metal line
components are formed within peripheral H II regions, while only 12 components
are associated with the predominantly neutral main absorber. For the main
absorber the observed abundance ratios of refractory elements to Zn range from
Galactic warm disk [Si/Zn] = - 0.40, [Fe/Zn] = -1.10 to halo-like and
essentially undepleted patterns. The dust-corrected metal abundances indicate a
nucleosynthetic odd-even effect and might imply an anomalous depletion of Si
relative to Fe for two components, but otherwise do correspond to solar ratios.
The intrinsic average metallicity is almost solar [Fe/H] = -0.08, whereas the
uncorrected average is [Zn/H] = -0.38. The ion abundances in the periphery
conform with solar element composition. The detection of H II as well as the
large variation in dust depletion for this sight line raises the question
whether in future studies of damped Ly alpha systems ionization and depletion
effects have to be considered in further detail. Ionization effects, for
instance, may pretend an enrichment of alpha elements. An empirical recipe for
detecting H II regions is provided.",0710.3560v1
2008-06-05,Viscous damping of r-mode oscillations in compact stars with quark matter,"We determine characteristic timescales for the viscous damping of r-mode
oscillations in rapidly rotating compact stars that contain quark matter. We
present results for the color-flavor-locked (CFL) phase of dense quark matter,
in which the up, down and strange quarks are gapped, as well as the normal
(ungapped) quark phase. While the ungapped quark phase supports a temperature
window between 10^8 K and 5x10^9 K where the r-mode is damped even for rapid
rotation, the r-mode in a rapidly rotating pure CFL star is not damped in the
temperature range 10^10 K - 10^11 K. Rotating hybrid stars with quark matter
cores display an instability window whose width is determined by the amount of
quark matter present, and they can have large spin frequencies outside this
window. Except at high temperatures T > 10^10 K, the presence of a quark phase
allows for larger critical frequencies and smaller spin-periods compared to
rotating neutron stars. If low-mass X-ray binaries contain a large amount of
ungapped or CFL quark matter, then our estimates of the r-mode instability
suggest that there should be a population of rapidly rotating binaries at
frequencies greater than 1000 Hz which have not yet been observed.",0806.1005v2
2008-06-09,Relaxation Time and Relaxation Function of Quark-Gluon Plasma with Lattice QCD,"We propose a method which enables a QCD-based calculation of a relaxation
time for a dissipative current in the causal and dissipative hydrodynamic
equation derived by Israel and Stewart. We point out that the Israel-Stewart
equation is not unique as a causal and dissipative hydrodynamic equation, and
the form of the causal and dissipative hydrodynamic equation is determined by
the shape of a spectral function reflecting the properties of elementary
excitations in the system we consider. Our method utilizes a relaxation
function, which can be calculated from QCD using the linear response theory. We
show that the relaxation function can be derived from a spectral function for a
microscopic representation of the dissipative current. We also show that the
Israel-Stewart equation is acceptable only as long as the calculated relaxation
function is approximated well by a exponentially damping function, and the
relaxation time can be obtained as its damping time constant. Taking a
baryon-number dissipative current of a plasma consisting of charm quarks and
gluons as a simple example, we present the first calculation of the relaxation
function with use of the spectral function derived employing the quenched
lattice QCD together with the maximum entropy method. The calculated relaxation
function shows a strongly-oscillation damping behaviour due to the charmed
vector hadron $J/\Psi$ surviving above the deconfinement phase transition
temperature in QCD. This result suggests that the applicability of the
Israel-Stewart equation to the baryon-number dissipative current of the charm
quark-gluon plasma is quite doubtful. We present an idea for the improvement of
the Israel-Stewart equation by deriving the hydrodynamic equation consistent
with the strongly-oscillation damping relaxation function.",0806.1481v1
2008-06-18,Imaging method for interface rheological characterization,"The present work investigates free damped oscillations of an oil drop in
water after its release from a capillary tube. Both pure heptane drops and
diluted crude oil drops are considered (in the second case the interface is
covered by amphiphilic species, natural components of crude oil). Shadowgraph
images of the drops are taken by means of a high speed camera and the drop
contour is detected by image processing. The axisymmetric drop shape is then
decomposed into spherical harmonics, which constitute the eigenmodes of
oscillations predicted by the Rayleigh-Lamb theory. Time evolution of each mode
is then obtained. The frequency and the damping rate of the principal mode
(n=2) are accurately determined and compared with theoretical values for an
immobile clean drop oscillating around spherical shape. For pure heptane drops,
theoretical value of the frequency agrees well with experiments whereas the
damping rate is significantly underestimated by theory. The experimental
results clearly show that the different modes are coupled. Energy is thus
transfered from mode n=2 to n=3, which probably explains the observed
enhancement of the damping rate. The effect of the interface viscoelastic
behaviour, induced by adsorbed amphiphilic species on the free oscillations was
examined. No significant effect was observed in the experiments conditions
(small amplitude oscillations and moderate aging).",0806.3030v1
2008-06-27,Klein - Gordon equation for market wealth operations,"In this paper the modified Klein - Gordon equation for market processes is
proposed and solved. It is argued that the oscillations in market propagate
with the light velocity. The initial pulse in the market is damped and for very
large time diffused according to the Fourier law.",0806.4466v1
2008-10-22,"Mean Motion Resonances in Extrasolar Planetary Systems with Turbulence, Interactions, and Damping","This paper continues previous work on the effects of turbulence on mean
motion resonances in extrasolar planetary systems. Turbulence is expected to
arise in the disks that form planets, and these fluctuations act to compromise
resonant configurations. This paper extends previous work by considering how
interactions between the planets and possible damping effects imposed by the
disk affect the outcomes. These physical processes are studied using three
approaches: numerical integrations of the 3-body problem with additional
forcing due to turbulence, model equations that reduce the problem to
stochastically driven oscillators, and Fokker-Planck equations that describe
the time evolution of an ensemble of systems. With this combined approach, we
elucidate the physics of how turbulence can remove extrasolar planetary systems
from mean motion resonance. As expected, systems with sufficiently large
damping (dissipation) can maintain resonance, in spite of turbulent forcing. In
the absence of strong damping, ensembles of these systems exhibit two regimes
of behavior, where the fraction of the bound states decreases as a power-law or
as an exponential. Both types of behavior can be understood through the model
developed herein. For systems with weak interactions between planets, the model
reduces to a stochastic pendulum, and the fraction of bound states decreases as
a power-law. For highly interactive systems, the dynamics are more complicated
and the fraction of bound states decreases exponentially. We show how planetary
interactions lead to drift terms in the Fokker-Planck equation and account for
this exponential behavior. In addition to clarifying the physical processes
involved, this paper strengthens the finding that turbulence implies that mean
motions resonances should be rare.",0810.4076v1
2009-01-11,On the derivation of structural models with general thermomechanical prestress,"The vibrating behaviour of thin structures is affected by prestress states.
Hence, the effects of thermal prestress are important research subjects in view
of ambient vibration monitoring of civil structures. The interaction between
prestress, geometrically non-linear behaviour, as well as damping and its
coupling with the aforementioned phenomena has to be taken into account for a
comprehensive understanding of the structural behaviour. Since the literature
on this subject lacks a clear procedure to derive models of thin prestressed
and damped structures from 3D continuum mechanics, this paper presents a new
derivation of models for thin structures accounting for generic prestress,
moderate rotations and viscous damping. Although inspired by classical
approaches, the proposed procedure is quite different, because of (i) the
definition of a modified Hu-Washizu (H-W) functional, accounting for stress
constraints associated with Lagrange multipliers, in order to derive
lower-dimensional models in a convenient way; (ii) an original definition of a
(mechanical and thermal) strain measure and a rotation measure enabling one to
identify the main terms in the strain energy and to derive a cascade of
lower-dimensional models (iii) a new definition of ""strain-rotation domains""
providing a clear interpretation of the classical assumptions of ""small
perturbations"" and ""small strains and moderate rotations""; (iv) the
introduction of a pseudo-potential with stress constraints to account for
viscous damping. The proposed procedure is applied to thin beams.",0901.1446v1
2009-04-17,On Landau damping,"Going beyond the linearized study has been a longstanding problem in the
theory of Landau damping. In this paper we establish exponential Landau damping
in analytic regularity. The damping phenomenon is reinterpreted in terms of
transfer of regularity between kinetic and spatial variables, rather than
exchanges of energy; phase mixing is the driving mechanism. The analysis
involves new families of analytic norms, measuring regularity by comparison
with solutions of the free transport equation; new functional inequalities; a
control of nonlinear echoes; sharp scattering estimates; and a Newton
approximation scheme. Our results hold for any potential no more singular than
Coulomb or Newton interaction; the limit cases are included with specific
technical effort. As a side result, the stability of homogeneous equilibria of
the nonlinear Vlasov equation is established under sharp assumptions. We point
out the strong analogy with the KAM theory, and discuss physical implications.",0904.2760v5
2009-07-27,Parameter exploration of optically trapped liquid aerosols,"When studying the motion of optically trapped particles on the $\mu s$ time
scale, in low viscous media such as air, inertia cannot be neglected.
Resolution of unusual and interesting behaviour not seen in colloidal trapping
experiments is possible. In attempt to explain the phenomena we use power
spectral methods to perform a parameter study of the Brownian motion of
optically trapped liquid aerosol droplets concentrated around the critically
damped regime. We present evidence that the system is suitably described by a
simple harmonic oscillator model which must include a description of
Fax\'{e}n's correction, but not necessarily frequency dependent hydrodynamic
corrections to Stokes' law. We also provide results describing how the system
behaves under several variables and discuss the difficulty in decoupling the
parameters responsible for the observed behaviour. We show that due to the
relatively low dynamic viscosity and high trap stiffness it is easy to transfer
between over- and under-damped motion by experimentally altering either trap
stiffness or damping. Our results suggest stable aerosol trapping may be
achieved in under-damped conditions, but the onset of deleterious optical
forces at high trapping powers prevents the probing of the upper stability
limits due to Brownian motion.",0907.4582v2
2009-10-09,One-way coupled Van der Pol system,"The equation of the Van der Pol oscillator, being characterized by a
dissipative term, is non-Lagrangian. Appending an additional degree of freedom
we bring the equation in the frame of action principle and thus introduce a
one-way coupled system. As with the Van der Pol oscillator, the coupled system
also involves only one parameter that controls the dynamics. The response
system is described by a linear differential equation coupled nonlinearly to
the drive system. In the linear approximation the equations of our coupled
system coincide with those of the Bateman dual system (a pair of damped and
anti-damped harmonic oscillators). The critical point of damped and anti-damped
oscillators are stable and unstable for all physical values of the frictional
coefficient $\mu$. Contrarily, the critical points of the drive- (Van der Pol)
and response systems depend crucially on the values of $\mu$. These points are
unstable for $\mu > 0$ while the critical point of the drive system is stable
and that of the response system is unstable for $\mu < 0$. The one-way coupled
system exhibits bifurcations which are different from those of the uncoupled
Van der Pol oscillator. Our system is chaotic and we observe phase
synchronization in the regime of dynamic chaos only for small values of $\mu$.",0910.1700v1
2010-06-19,On the saturation amplitude of the f-mode instability,"We investigate strong nonlinear damping effects which occur during high
amplitude oscillations of neutron stars, and the gravitational waves they
produce. For this, we use a general relativistic nonlinear hydrodynamics code
in conjunction with a fixed spacetime (Cowling approximation) and a polytropic
equation of state (EOS). Gravitational waves are estimated using the quadrupole
formula. Our main interest are l=m=2 f modes subject to the CFS (Chandrasekhar,
Friedman, Schutz) instability, but we also investigate axisymmetric and
quasiradial modes. We study various models to determine the influence of
rotation rate and EOS. We find that axisymmetric oscillations at high
amplitudes are predominantly damped by shock formation, while the
nonaxisymmetric f modes are mainly damped by wave breaking and, for rapidly
rotating models, coupling to nonaxisymmetric inertial modes. From the observed
nonlinear damping, we derive upper limits for the saturation amplitude of
CFS-unstable f modes. Finally, we estimate that the corresponding gravitational
waves for an oscillation amplitude at the upper limit should be detectable with
the advanced LIGO and VIRGO interferometers at distances above 10 MPc. This
strongly depends on the stellar model, in particular on the mode frequency.",1006.3885v2
2010-07-06,Magneto-elastic oscillations and the damping of crustal shear modes in magnetars,"In a realistic model of magneto-elastic oscillations in magnetars, we find
that crustal shear oscillations, often invoked as an explanation of
quasi-periodic oscillations (QPOs) seen after giant flares in soft gamma-ray
repeaters (SGRs), are damped by resonant absorption on timescales of at most
0.2s, for a lower limit on the dipole magnetic field strength of 5 x 10^13 G.
At higher magnetic field strengths (typical in magnetars) the damping timescale
is even shorter, as anticipated by earlier toy-models. We have investigated a
range of equations of state and masses and if magnetars are dominated by a
dipole magnetic field, our findings exclude torsional shear oscillations of the
crust from explaining the observed low-frequency QPOs. In contrast, we find
that the Alfv\'en QPO model is a viable explanation of observed QPOs, if the
dipole magnetic field strength exceeds a minimum strength of about several
times 10^14 G to 10^15 G. Then, Alfv\'en QPOs are no longer confined to the
fluid core, but completely dominate in the crust region and have a maximum
amplitude at the surface of the star.",1007.0856v2
2010-08-16,Orbital evolution of eccentric planets in radiative discs,"With an average eccentricity of about 0.29, the eccentricity distribution of
extrasolar planets is markedly different from the solar system. Among other
scenarios considered, it has been proposed that eccentricity may grow through
planet-disc interaction. Recently, it has been noticed that the thermodynamical
state of the disc can significantly influence the migration properties of
growing protoplanets. However, the evolution of planetary eccentricity in
radiative discs has not been considered yet. In this paper we study the
evolution of planets on eccentric orbits that are embedded in a
three-dimensional viscous disc and analyse the disc's effect on the orbital
evolution of the planet. We use the three-dimensional hydrodynamical code
NIRVANA that includes full tensor viscosity and implicit radiation transport in
the flux-limited diffusion approximation. The code uses the FARGO-algorithm to
speed up the simulations. First we measure the torque and power exerted on the
planet by the disc for fixed orbits, and then we let the planet start with
initial eccentricity and evolve it in the disc. For locally isothermal we
confirm previous results and find eccentricity damping and inward migration for
planetary cores. In the case of radiative discs, the planets experience an
inward migration as long as its eccentricity lies above a certain threshold.
After the damping of eccentricity cores with masses below 33 Earthmasses begin
to migrate outward in radiative discs, while higher mass cores always migrate
inward. For all planetary masses studied (up to 200 Earthmasses) we find
eccentricity damping. In viscous discs the orbital eccentricity of embedded
planets is damped during the evolution independent of the mass. Hence,
planet-disc interaction does not seem to be a viable mechanism to explain the
observed high eccentricity of exoplanets.",1008.2656v1
2010-11-02,A Carbon-enhanced Metal-poor Damped Lyman alpha System: Probing Gas from Population III Nucleosynthesis?,"We present high resolution observations of an extremely metal-poor damped
Lyman-alpha system, at z_abs = 2.3400972 in the spectrum of the QSO J0035-0918,
exhibiting an abundance pattern consistent with model predictions for the
supernova yields of Population III stars. Specifically, this DLA has [Fe/H] =
-3.04, shows a clear `odd-even' effect, and is C-rich with [C/Fe] = +1.53, a
factor of about 20 greater than reported in any other damped Lyman-alpha
system. In analogy to the carbon-enhanced metal-poor stars in the Galactic halo
(with [C/Fe] > +1.0), this is the first reported case of a carbon-enhanced
damped Lyman-alpha system. We determine an upper limit to the mass of 12C,
M(12C) < 200 solar masses, which depends on the unknown gas density n(H); if
n(H) > 1 atom per cubic cm (which is quite likely for this DLA given its low
velocity dispersion), then M(12C) < 2 solar masses, consistent with pollution
by only a few prior supernovae. We speculate that DLAs such as the one reported
here may represent the `missing link' between the yields of Pop III stars and
their later incorporation in the class of carbon-enhanced metal-poor stars
which show no enhancement of neutron-capture elements (CEMP-no stars).",1011.0733v2
2010-11-08,Exponential stabilization without geometric control,"We present examples of exponential stabilization for the damped wave equation
on a compact manifold in situations where the geometric control condition is
not satisfied. This follows from a dynamical argument involving a topological
pressure on a suitable uncontrolled set.",1011.1699v1
2010-11-11,Damping of longitudinal magneto-acoustic oscillations in slowly varying coronal plasma,"We investigate the propagation of MHD waves in a homogenous, magnetized
plasma in a weakly stratified atmosphere, representing hot coronal loops. In
most of earlier studies a time-independent equilibrium is considered. Here we
abandon this restriction and allow the equilibrium to develop as function of
time. In particular, the background plasma is assumed to be cooling due to
thermal conduction. The cooling is assumed to be on a time scale greater than
the characteristic travel times of the perturbations. We investigate the
influence of cooling of the background plasma on the properties of
magneto-acoustic waves. The MHD equations are reduced to a 1-D system modelling
magneto-acoustic modes progressing along a dynamically cooling coronal loop. A
time dependent dispersion relation which describes the propagation of the
magneto-acoustic waves is derived by using the WKB theory. An analytic solution
for the time-dependent amplitude of waves is obtained and the method of
characteristics is used to find an approximate analytical solution. Numerical
calculations are applied to the analytically derived solutions to obtain
further insight into the behavior of the MHD waves in a system with variable,
time-dependent background. The results show that there is a strong damping of
MHD waves that can be linked to the widely observed damping of hot coronal loop
oscillations. The damping also appears to be independent of position along the
loop. Studies of MHD wave behaviour in time-dependent background seem to be a
fundamental and very important next step in developing MHD wave theory
applicable to a wide range in solar physics.",1011.2617v1
2010-12-17,Optimal switching of a nanomagnet assisted by microwaves,"We develop an efficient and general method for optimizing the microwave field
that achieves magnetization switching with a smaller static field. This method
is based on optimal control and renders an exact solution for the 3D microwave
field that triggers the switching of a nanomagnet with a given anisotropy and
in an oblique static field. Applying this technique to the particular case of
uniaxial anisotropy, we show that the optimal microwave field, that achieves
switching with minimal absorbed energy, is modulated both in frequency and in
magnitude. Its role is to drive the magnetization from the metastable
equilibrium position towards the saddle point and then damping induces the
relaxation to the stable equilibrium position. For the pumping to be efficient,
the microwave field frequency must match at the early stage of the switching
process the proper precession frequency of the magnetization, which depends on
the magnitude and direction of the static field. We investigate the effect of
the static field (in amplitude and direction) and of damping on the
characteristics of the microwave field. We have computed the switching curves
in the presence of the optimal microwave field. The results are in qualitative
agreement with micro-SQUID experiments on isolated nanoclusters. The strong
dependence of the microwave field and that of the switching curve on the
damping parameter may be useful in probing damping in various nanoclusters.",1012.3901v1
2010-12-22,PageRank for ranking authors in co-citation networks,"Google's PageRank has created a new synergy to information retrieval for a
better ranking of Web pages. It ranks documents depending on the topology of
the graphs and the weights of the nodes. PageRank has significantly advanced
the field of information retrieval and keeps Google ahead of competitors in the
search engine market. It has been deployed in bibliometrics to evaluate
research impact, yet few of these studies focus on the important impact of the
damping factor (d) for ranking purposes. This paper studies how varied damping
factors in the PageRank algorithm can provide additional insight into the
ranking of authors in an author co-citation network. Furthermore, we propose
weighted PageRank algorithms. We select 108 most highly cited authors in the
information retrieval (IR) area from the 1970s to 2008 to form the author
co-citation network. We calculate the ranks of these 108 authors based on
PageRank with damping factor ranging from 0.05 to 0.95. In order to test the
relationship between these different measures, we compare PageRank and weighted
PageRank results with the citation ranking, h-index, and centrality measures.
We found that in our author co-citation network, citation rank is highly
correlated with PageRank's with different damping factors and also with
different PageRank algorithms; citation rank and PageRank are not significantly
correlated with centrality measures; and h-index is not significantly
correlated with centrality measures.",1012.4872v1
2011-01-20,Magnetohydrodynamic waves in solar partially ionized plasmas: two-fluid approach,"We derive the dynamics of magnetohydrodynamic waves in two-fluid partially
ionized plasmas and to compare the results with those obtained under
single-fluid description. Two-fluid magnetohydrodynamic equations are used,
where ion-electron plasma and neutral particles are considered as separate
fluids. Dispersion relations of linear magnetohydrodynamic waves are derived
for simplest case of homogeneous medium. Frequencies and damping rates of waves
are obtained for different parameters of background plasma. We found that two-
and single-fluid descriptions give similar results for low frequency waves.
However, the dynamics of MHD waves in two-fluid approach is significantly
changed when the wave frequency becomes comparable or higher than ion-neutral
collision frequency. Alfven and fast magneto-acoustic waves attain their
maximum damping rate at particular frequencies (for example, the peak frequency
equals 2.5 ion-neutral collision frequency for 50 % of neutral Hydrogen) in
wave spectrum. The damping rates are reduced for higher frequency waves. The
new mode of slow magneto-acoustic wave appears for higher frequency branch,
which is connected to neutral hydrogen fluid. The single-fluid approach
perfectly deals with slow processes in partially ionized plasmas, but fails for
time-scales smaller than ion-neutral collision time. Therefore, two-fluid
approximation should be used for the description of relatively fast processes.
Some results of single-fluid description, for example the damping of
high-frequency Alfven waves in the solar chromosphere due to ion-neutral
collisions, should be revised in future.",1101.3913v1
2011-08-25,Characterizing Multi-planet Systems with Classical Secular Theory,"Classical secular theory can be a powerful tool to describe the qualitative
character of multi-planet systems and offer insight into their histories. The
eigenmodes of the secular behavior, rather than current orbital elements, can
help identify tidal effects, early planet-planet scattering, and dynamical
coupling among the planets, for systems in which mean-motion resonances do not
play a role. Although tidal damping can result in aligned major axes after all
but one eigenmode have damped away, such alignment may simply be fortuitous. An
example of this is 55 Cancri (orbital solution of Fischer et al., 2008) where
multiple eigenmodes remain undamped. Various solutions for 55 Cancri are
compared, showing differing dynamical groupings, with implications for the
coupling of eccentricities and for the partitioning of damping among the
planets. Solutions for orbits that include expectations of past tidal evolution
with observational data, must take into account which eigenmodes should be
damped, rather than expecting particular eccentricities to be near zero.
Classical secular theory is only accurate for low eccentricity values, but
comparison with other results suggests that it can yield useful qualitative
descriptions of behavior even for moderately large eccentricity values, and may
have advantages for revealing underlying physical processes and, as large
numbers of new systems are discovered, for triage to identify where more
comprehensive dynamical studies should have priority.",1108.5149v2
2011-09-12,Nonlinear spectroscopy of superconducting anharmonic resonators,"We formulate a model for the steady state response of a nonlinear quantum
oscillator structure, such as those used in a variety of superconducting qubit
experiments, when excited by a steady, but not necessarily small, ac tone. We
show that this model can be derived directly from a circuit description of some
recent qubit experiments in which the state of the qubit is read out directly,
without a SQUID magnetometer. The excitation profile has a rich structure
depending on the detuning of the tone from the small-signal resonant frequency,
on the degree of damping, and on the excitation amplitude. We explore two
regions in detail: First, at high damping there is a trough in the excitation
response as a function of detuning, near where the classical Duffing
bifurcation occurs. This trough has been understood as a classical interference
between two metastable responses with opposite phase. We use Wigner function
studies to show that while this picture is roughly correct, there are also more
quantum mechanical aspects to this feature. Second, at low damping we study the
emergence of sharp, discrete spectral features from a continuum response. We
show that these the structures, associated with discrete transitions between
different excited-state eigenstates of the oscillator, provide an interesting
example of a quantum Fano resonance. The trough in the Fano response evolves
continuously from the ""classical"" trough at high damping.",1109.2490v1
2011-11-09,Stabilization by switching control methods,"In this paper we consider some stabilization problems for the wave equation
with switching. We prove exponential stability results for appropriate damping
coefficients. The proof of the main results is based on D'Alembert formula and
some energy estimates.",1111.2171v1
2012-04-09,The Kato Smoothing Effect for Regularized Schrödinger Equations in Exterior Domains,"We prove, under the exterior geometric control condition, the Kato smoothing
effect for solutions of an inhomogenous and damped Schr\""odinger equation on
exterior domains.",1204.1904v1
2012-04-26,Well-posedness and long time behavior in nonlinear dissipative hyperbolic-like evolutions with critical exponents,"These lectures present the analysis of stability and control of long time
behavior of PDE models described by nonlinear evolutions of hyperbolic type.
Specific examples of the models under consideration include: (i) nonlinear
systems of dynamic elasticity: von Karman systems, Berger's equations,
Kirchhoff - Boussinesq equations, nonlinear waves (ii) nonlinear flow -
structure and fluid - structure interactions, (iii) and nonlinear
thermo-elasticity. A characteristic feature of the models under consideration
is criticality or super-criticality of sources (with respect to Sobolev's
embeddings) along with super-criticality of damping mechanisms which, in
addition, may be also geometrically constrained.
  Our aim is to present several methods relying on cancelations, harmonic
analysis and geometric analysis, which enable to handle criticality and also
super-criticality in both sources and the damping of the underlined nonlinear
PDE. It turns out that if carefully analyzed the nonlinearity can be taken
""advantage of"" in order to produce implementable damping mechanism.
  Another goal of these lectures is the understanding of control mechanisms
which are geometrically constrained. The final task boils down to showing that
appropriately damped system is ""quasi-stable"" in the sense that any two
trajectories approach each other exponentially fast up to a compact term which
can grow in time. Showing this property- formulated as quasi-stability estimate
-is the key and technically demanding issue that requires suitable tools. These
include: weighted energy inequalities, compensated compactness, Carleman's
estimates and some elements of microlocal analysis.",1204.5864v1
2012-06-15,"Comment on ""Anisotropic Critical Magnetic Fluctuations in the Ferromagnetic Superconductor UCoGe""","We have presented the potential explanation of nonvanishing at q=0 Landau
damping measured experimentally in ferromagnetic compounds UGe2 and UCoGe based
on possible intersection of the Fermi sheets corresponding different bands.",1206.3468v1
2012-06-21,Interaction between an Isotropic Nanoparticle and Drifting Electrons in a Quantum Well,"A hybrid system composed of an isotropic nanoparticle and a semiconductor
heterostructure with a quantum well has been considered. The nanoparticle is
supposed to be polarizable in an external electric field. A theoretical model
of the hybrid system is substantiated and formulated. Exact solutions of the
model equations are obtained. The frequencies of charge oscillations in the
hybrid system and their damping owing to the dipole--plasmon interaction are
found, the damping mechanism being similar to that of Landau damping. The
space-time behavior of concentration perturbations in the two-dimensional
electron gas is analyzed, and the polarization oscillations of a nanoparticle
are studied. The induced polarization of a nanoparticle at nonzero electron
drift velocities is found to have a complicated dynamics. In particular, the
polarization vector circulates along elliptic trajectories for two of three
frequency dispersion branches. If the electric current flows through the
quantum well due to an applied electric field, the damping of oscillations in
the hybrid system is replaced by their growth in time, which corresponds to the
electric instability of the system. New phenomena in hybrid systems can be used
to excite the emission of nanoparticles by an electric current and to
electrically stimulate the emission in the terahertz spectral range.",1206.4782v1
2012-10-02,Coherence and Stimulated Emission in the Tavis-Cummings Model: A Quantum Description of the Free Induction Signal and Radiation Damping in Magnetic Resonance,"We numerically solve the Liouville equation for the Tavis Cummings model of
multiple spins coupled to a lossless single mode cavity, starting from an
initial condition with small numbers of fully polarized spins tipped by a
specified angle, and the cavity in its ground Fock state. Time evolution of the
magnetizations and cavity states, following small to medium nutation by a
classical field, yields a microscopic quantum mechanical picture of radiation
damping in magnetic resonance, and the formation of the free induction signal,
that is, the transfer of Zeeman energy, via spin coherence, to cavity
coherence. Although the motion of the Bloch vector is nonclassical, our quantum
description is related to the macroscopic picture of NMR reception, by showing
the close relationship between the usual radiation damping constant, and the
quantum mechanical Rabi nutation frequency (as enhanced by cavity coupling and
stimulated emission.) That is, each is the product, of a nutation rate per
oscillator current, and a current. Although the current in the damping constant
is explicitly limited by cavity losses, which do not enter the formula for the
Rabi frequency, we nonetheless show (in an appendix) how these losses can be
introduced into our problem by means of a master equation. Numerical solution
of the classical Bloch-Kirchhoff equations reinforces the conclusion that the
strength of the free induction",1210.0868v2
2012-10-11,Experimental estimations of viscoelastic properties of multilayer damped plates in broad-band frequency range,"Regarding lightweighting structures for aeronautics, automotive or
construction applications, the level of performance of solutions proposed in
terms of damping and isolation is fundamental. Hence multilayered plate appears
as an interesting answer if damping performances are properly optimized. In
this paper, a novel modal analysis method (Ege et al, JSV 325 (4-5), 2009) is
used to identify viscoelastic properties (loss factors, Young's modulus) of
""polyethylene thermoplastic / aluminum"" bilayer plates. The thermoplastic is
chosen for its high loss factors and relative low mass. The experimental method
consists in a high-resolution technique (ESPRIT algorithm) which allows precise
estimations of the viscoelastic properties even in frequency domains with high
modal overlap (high damping or modal density). Experimental loss factors
estimated from impact hammer excitations on the free-free plates highly
corresponds with two theoretical estimations. In the first model (Guyader &
Lesueur, JSV 58(1), 1978) the calculation is based on multilayered plates
equations and use wave propagation analysis ; in the second one (Laulagnet &
Guyader, JASA 96(1), 1994) the thickness deformation solving Navier's equations
is allowed. Results on several plates with several thicknesses of
thermoplastics are given and compared with the models, demonstrating the
validity of the approach.",1210.3333v3
2012-11-02,Damping of mechanical vibrations by free electrons in metallic nanoresonators,"We investigate the effect of free electrons on the quality factor (Q) of a
metallic nanomechanical resonator in the form of a thin elastic beam. The
flexural and longitudinal modes of the beam are modeled using thin beam
elasticity theory, and simple perturbation theory is used to calculate the rate
at which an externally excited vibration mode decays due to its interaction
with free electrons. We find that electron-phonon interaction significantly
affects the Q of longitudinal modes, and may also be of significance to the
damping of flexural modes in otherwise high-Q beams. The finite geometry of the
beam is manifested in two important ways. Its finite length breaks translation
invariance along the beam and introduces an imperfect momentum conservation law
in place of the exact law. Its finite width imposes a quantization of the
electronic states that introduces a temperature scale for which there exists a
crossover from a high-temperature macroscopic regime, where electron-phonon
damping behaves as if the electrons were in the bulk, to a low-temperature
mesoscopic regime, where damping is dominated by just a few dissipation
channels and exhibits sharp non-monotonic changes as parameters are varied.
This suggests a novel scheme for probing the electronic spectrum of a nanoscale
device by measuring the Q of its mechanical vibrations.",1211.0450v1
2013-01-14,Two-qubit mixed states more entangled than pure states: Comparison of the relative entropy of entanglement for a given nonlocality,"Amplitude damping changes entangled pure states into usually less-entangled
mixed states. We show, however, that even local amplitude damping of one or two
qubits can result in mixed states more entangled than pure states if one
compares the relative entropy of entanglement (REE) for a given degree of the
Bell-Clauser-Horne-Shimony-Holt inequality violation (referred to as
nonlocality). By applying Monte-Carlo simulations, we find the maximally
entangled mixed states and show that they are likely to be optimal by checking
the Karush-Kuhn-Tucker conditions, which generalize the method of Lagrange
multipliers for this nonlinear optimization problem. We show that the REE for
mixed states can exceed that of pure states if the nonlocality is in the range
(0,0.82) and the maximal difference between these REEs is 0.4. A former
comparison [Phys. Rev. A 78, 052308 (2008)] of the REE for a given negativity
showed analogous property but the corresponding maximal difference in the REEs
is one-order smaller (i.e., 0.039) and the negativity range is (0,0.53) only.
For appropriate comparison, we normalized the nonlocality measure to be equal
to the standard entanglement measures, including the negativity, for arbitrary
two-qubit pure states. We also analyze the influence of the phase-damping
channel on the entanglement of the initially pure states. We show that the
minimum of the REE for a given nonlocality can be achieved by this channel,
contrary to the amplitude damping channel.",1301.2969v2
2013-07-02,The ESO UVES Advanced Data Products Quasar Sample - I. Dataset and New N_HI Measurements of Damped Absorbers,"We present here a dataset of quasars observed with the Ultraviolet Visual
Echelle Spectrograph (UVES) on the VLT and available in the ESO UVES Advanced
Data Products archive. The sample is made up of a total of 250 high resolution
quasar spectra with emission redshifts ranging from 0.191 < z_em <6.311. The
total UVES exposure time of this dataset is 1560 hours. Thanks to the high
resolution of UVES spectra, it is possible to unambiguously measure the column
density of absorbers with damping wings, down to N_HI > 10^{19} cm^{-2}, which
constitutes the sub-damped Lya absorber (sub-DLA) threshold. Within the
wavelength coverage of our UVES data, we find 150 damped Lya systems
(DLAs)/sub-DLAs in the range 1.5 < z_abs < 4.7. Of these 150, 93 are DLAs and
57 are sub-DLAs. An extensive search in the literature indicates that 6 of
these DLAs and 13 of these sub-DLAs have their N_HI measured for the first
time. Among them, 10 are new identifications as DLAs/sub-DLAs. For each of
these systems, we obtain an accurate measurement of the HI column density and
the absorber's redshift in the range 1.7 < z_abs < 4.2 by implementing a Voigt
profile-fitting algorithm. These absorbers are further confirmed thanks to the
detection of associated metal lines and/or lines from members of the Lyman
series. In our data, a few quasars' lines-of-sight are rich. An interesting
example is towards QSO J0133+0400 (z_em = 4.154) with six DLAs and sub-DLAs
reported.",1307.0678v2
2013-08-23,Stabilization of second-order evolution equations with time delay,"We consider second-order evolution equations in an abstract setting with
damping and time delay and give sufficient conditions ensuring exponential
stability. Our abstract framework is then applied to the wave equation, the
elasticity system and the Petrovsky system.",1308.5106v1
2013-09-21,Bottomonium suppression at $\sqrt{s_{NN}}=2.76$ TeV using model based on color screening and gluonic dissociation with collisional damping,"We present a model to explain the bottomonium suppression in Pb+Pb collisions
at mid rapidity obtained from Large Hadron Collider (LHC) energy,
$\sqrt{s_{NN}}=2.76$ TeV. The model consists of two decoupled mechanisms
namely, color screening during bottomonium production followed by gluon induced
dissociation along with collisional damping. The quasi-particle model (QPM) is
used as equation of state (EOS) for the Quark-Gluon Plasma (QGP) medium. The
feed-down from higher $\Upsilon$ states, such as $\Upsilon(1P)$, $\Upsilon(2S)$
and $\Upsilon(2P)$, dilated formation times for bottomonium states and viscous
effect of QGP medium are other ingredients included in the current formulation.
We further assume that the QGP is expanding according to (1+1)-dimensional
Bjorken's boost invariant scaling law. The net suppression (in terms of $p_T$
integrated survival probability) for bottomonium states at mid rapidity is
obtained as a function of centrality and the result is then compared both
quantitatively and qualitatively with the recent LHC experimental data in the
mid rapidity region recently published by CMS collaboration. We find that the
current model, based on the Debye color screening plus gluonic dissociation
along with collisional damping, better describes the centrality dependence of
bottomonium suppression at LHC energy as compared to color screening model
alone.
  \vskip 0.5cm
  {\nd \it Keywords} : Color screening, Gluonic dissociation, Collisional
damping, Survival probability {\nd \it PACS numbers} : 12.38.Mh, 12.38.Gc,
25.75.Nq, 24.10.Pa",1309.5467v2
2013-10-20,Nonequilibrium stationary state for a damped rotator,"Perturbative construction of the nonequilibrium steady state of a rotator
under a stochastic forcing while subject to torque and friction",1310.5379v1
2013-11-07,Spin-Orbit Torques and Anisotropic Magnetization Damping in Skyrmion Crystals,"The length scale of the magnetization gradients in chiral magnets is
determined by the relativistic Dzyaloshinskii-Moriya interaction. Thus, even
conventional spin-transfer torques are controlled by the relativistic
spin-orbit coupling in these systems, and additional relativistic corrections
to the current-induced torques and magnetization damping become important for a
complete understanding of the current-driven magnetization dynamics. We
theoretically study the effects of reactive and dissipative homogeneous
spin-orbit torques and anisotropic damping on the current-driven skyrmion
dynamics in cubic chiral magnets. Our results demonstrate that spin-orbit
torques play a significant role in the current-induced skyrmion velocity. The
dissipative spin-orbit torque generates a relativistic Magnus force on the
skyrmions, whereas the reactive spin-orbit torque yields a correction to both
the drift velocity along the current direction and the transverse velocity
associated with the Magnus force. The spin-orbit torque corrections to the
velocity scale linearly with the skyrmion size, which is inversely proportional
to the spin-orbit coupling. Consequently, the reactive spin-orbit torque
correction can be the same order of magnitude as the non-relativistic
contribution. More importantly, the dissipative spin-orbit torque can be the
dominant force that causes a deflected motion of the skyrmions if the torque
exhibits a linear or quadratic relationship with the spin-orbit coupling. In
addition, we demonstrate that the skyrmion velocity is determined by
anisotropic magnetization damping parameters governed by the skyrmion size.",1311.1778v1
2013-11-13,Recent progress in attractors for quintic wave equations,"We report on new results concerning the global well-posedness, dissipativity
and attractors of the damped quintic wave equations in bounded domains of R^3.",1311.3290v1
2014-01-19,Analytical Solution of Mathieu Equation,"The general solution of the homogeneous damped Mathieu equation in the
analytical form, allowing its practical using in many applications, including
superconductivity studies, without numerical calculations has been found.",1401.5348v1
2014-06-10,Wigner's Space-time Symmetries based on the Two-by-two Matrices of the Damped Harmonic Oscillators and the Poincaré Sphere,"The second-order differential equation for a damped harmonic oscillator can
be converted to two coupled first-order equations, with two two-by-two matrices
leading to the group $Sp(2)$. It is shown that this oscillator system contains
the essential features of Wigner's little groups dictating the internal
space-time symmetries of particles in the Lorentz-covariant world. The little
groups are the subgroups of the Lorentz group whose transformations leave the
four-momentum of a given particle invariant. It is shown that the damping modes
of the oscillator correspond to the little groups for massive and
imaginary-mass particles respectively. When the system makes the transition
from the oscillation to damping mode, it corresponds to the little group for
massless particles. Rotations around the momentum leave the four-momentum
invariant. This degree of freedom extends the $Sp(2)$ symmetry to that of
$SL(2,c)$ corresponding to the Lorentz group applicable to the four-dimensional
Minkowski space. The Poincar\'e sphere contains the $SL(2,c)$ symmetry. In
addition, it has a non-Lorentzian parameter allowing us to reduce the mass
continuously to zero. It is thus possible to construct the little group for
massless particles from that of the massive particle by reducing its mass to
zero. Spin-1/2 particles and spin-1 particles are discussed in detail.",1406.2403v1
2014-06-11,Quantum critical metals in $4-ε$ dimensions,"We study the quantum theory of a Fermi surface coupled to a gapless boson
scalar in $D=4-\epsilon$ spacetime dimensions as a simple model for non-Fermi
liquids (NFL) near a quantum phase transition. Our analysis takes into account
the full backreaction from Landau damping of the boson, and obtains an RG flow
that proceeds through three distinct stages. Above the scale of Landau damping
the Fermi velocity flows to zero, while the coupling evolves according to its
classical dimension. Once damping becomes important, its backreaction leads to
a crossover regime where dynamic and static damping effects compete and the
fermion self-energy does not respect scaling. Below this crossover and having
tuned the boson to criticality, the theory flows to a $z=3$ scalar interacting
with a NFL. By increasing the number of bosonic flavors, the phase diagram near
the quantum critical point interpolates between a superconducting dome fully
covering the NFL behavior, and a phase where NFL effects become important
first, before the onset of superconductivity. A generic prediction of the
theory is that the Fermi velocity and quasiparticle residue vanish with a
power-law $\omega^\epsilon$ as the fixed point is approached. These features
may be useful for understanding some of the phenomenology of high $T_c$
materials in a systematic $\epsilon$--expansion.",1406.3029v2
2014-10-15,A comparison of weak-turbulence and PIC simulations of weak electron-beam plasma interaction,"Quasilinear theory has long been used to treat the problem of a weak electron
beam interacting with plasma and generating Langmuir waves. Its extension to
weak-turbulence theory treats resonant interactions of these Langmuir waves
with other plasma wave modes, in particular ion-sound waves. These are strongly
damped in plasma of equal ion and electron temperatures, as sometimes seen in,
for example, the solar corona and wind. Weak turbulence theory is derived in
the weak damping limit, with a term describing ion-sound wave damping then
added. In this paper we use the EPOCH particle-in-cell code to numerically test
weak turbulence theory for a range of electron-ion temperature ratios. We find
that in the cold ion limit the results agree well, but increasing ion
temperature the three-wave resonance becomes broadened in proportion to the
ion-sound wave damping rate. This may be important in, for example, the theory
of solar radio bursts, where the spectrum of Langmuir waves is critical.
Additionally we establish lower limits on the number of simulation particles
needed to accurately reproduce the electron and wave distributions in their
saturated states, and to reproduce their intermediate states and time
evolution.",1410.4046v2
2015-03-31,Existence of the global attractor for the plate equation with nonlocal nonlinearity in R^{n},"We consider Cauchy problem for the semilinear plate equation with nonlocal
nonlinearity. Under mild conditions on the damping coefficient, we prove that
the semigroup generated by this problem possesses a global attractor.",1503.09123v1
2015-05-07,Theory for Bose-Einstein condensation of light in nano-fabricated semiconductor microcavities,"We construct a theory for Bose-Einstein condensation of light in
nano-fabricated semiconductor microcavities. We model the semiconductor by one
conduction and one valence band which consist of electrons and holes that
interact via a Coulomb interaction. Moreover, we incorporate screening effects
by using a contact interaction with the scattering length for a Yukawa
potential and describe in this manner the crossover from exciton gas to
electron-hole plasma as we increase the excitation level of the semiconductor.
We then show that the dynamics of the light in the microcavities is damped due
to the coupling to the semiconductor. Furthermore, we demonstrate that on the
electron-hole plasma side of the crossover, which is relevant for the
Bose-Einstein condensation of light, this damping can be described by a single
dimensionless damping parameter that depends on the external pumping.
Hereafter, we propose to probe the superfluidity of light in these
nano-fabricated semiconductor microcavities by making use of the differences in
the response in the normal or superfluid phase to a sudden rotation of the
trap. In particular, we determine frequencies and damping of the scissors modes
that are excited in this manner. Moreover, we show that a distinct signature of
the dynamical Casimir effect can be observed in the density-density
correlations of the excited light fluid.",1505.01732v2
2015-08-21,Which verification qubits perform best for secure communication in noisy channel?,"In secure quantum communication protocols, a set of single qubits prepared
using 2 or more mutually unbiased bases or a set of $n$-qubit ($n\geq2$)
entangled states of a particular form are usually used to form a verification
string which is subsequently used to detect traces of eavesdropping. The qubits
that form a verification string are referred to as decoy qubits, and there
exists a large set of different quantum states that can be used as decoy
qubits. In the absence of noise, any choice of decoy qubits provides equivalent
security. In this paper, we examine such equivalence for noisy environment
(e.g., in amplitude damping, phase damping, collective dephasing and collective
rotation noise channels) by comparing the decoy-qubit assisted schemes of
secure quantum communication that use single qubit states as decoy qubits with
the schemes that use entangled states as decoy qubits. Our study reveals that
the single qubit assisted scheme perform better in some noisy environments,
while some entangled qubits assisted schemes perform better in other noisy
environments. Specifically, single qubits assisted schemes perform better in
amplitude damping and phase damping noisy channels, whereas a few
Bell-state-based decoy schemes are found to perform better in the presence of
the collective noise. Thus, if the kind of noise present in a communication
channel (i.e., the characteristics of the channel) is known or measured, then
the present study can provide the best choice of decoy qubits required for
implementation of schemes of secure quantum communication through that channel.",1508.05237v1
2015-08-30,Spin-transfer torque based damping control of parametrically excited spin waves in a magnetic insulator,"The damping of spin waves parametrically excited in the magnetic insulator
Yttrium Iron Garnet (YIG) is controlled by a dc current passed through an
adjacent normal-metal film. The experiment is performed on a macroscopically
sized YIG(100nm)/Pt(10nm) bilayer of 4x2 mm^2 lateral dimensions. The spin-wave
relaxation frequency is determined via the threshold of the parametric
instability measured by Brillouin light scattering (BLS) spectroscopy. The
application of a dc current to the Pt film leads to the formation of a
spin-polarized electron current normal to the film plane due to the spin Hall
effect (SHE). This spin current exerts a spin transfer torque (STT) in the YIG
film and, thus, changes the spin-wave damping. Depending on the polarity of the
applied dc current with respect to the magnetization direction, the damping can
be increased or decreased. The magnitude of its variation is proportional to
the applied current. A variation in the relaxation frequency of +/-7.5% is
achieved for an applied dc current density of 5*10^10 A/m^2.",1508.07517v1
2015-09-08,Model comparison for the density structure across solar coronal waveguides,"The spatial variation of physical quantities, such as the mass density,
across solar atmospheric waveguides governs the timescales and spatial scales
for wave damping and energy dissipation. The direct measurement of the spatial
distribution of density, however, is difficult and indirect seismology
inversion methods have been suggested as an alternative. We applied Bayesian
inference, model comparison, and model-averaging techniques to the inference of
the cross-field density structuring in solar magnetic waveguides using
information on periods and damping times for resonantly damped
magnetohydrodynamic (MHD) transverse kink oscillations. Three commonly employed
alternative profiles were used to model the variation of the mass density
across the waveguide boundary. Parameter inference enabled us to obtain
information on physical quantities such as the Alfv\'en travel time, the
density contrast, and the transverse inhomogeneity length scale. The inference
results from alternative density models were compared and their differences
quantified. Then, the relative plausibility of the considered models was
assessed by performing model comparison. Our results indicate that the evidence
in favor of any of the three models is minimal, unless the oscillations are
strongly damped. In such a circumstance, the application of model-averaging
techniques enables the computation of an evidence-weighted inference that takes
into account the plausibility of each model in the calculation of a combined
inversion for the unknown physical parameters.",1509.02340v1
2015-09-15,Resonance vibration of impact oscillator with biharmonic excitation,"We consider a damped impact oscillator subject to the action of a biharmonic
force. The conditions for the existence and stability of almost periodic
resonance solutions are investigated.",1509.05381v1
2015-11-08,On 2d incompressible Euler equations with partial damping,"We consider various questions about the 2d incompressible Navier-Stokes and
Euler equations on a torus when dissipation is removed from or added to some of
the Fourier modes.",1511.02530v1
2015-12-11,The Ping Pong Pendulum,"Many damped mechanical systems oscillate with increasing frequency as the
amplitude decreases. One popular example is Euler's Disk, where the point of
contact rotates with increasing rapidity as the energy is dissipated. We study
a simple mechanical pendulum that exhibits this behaviour.",1512.03700v1
2016-01-26,Fast convex optimization via inertial dynamics with Hessian driven damping,"We first study the fast minimization properties of the trajectories of the
second-order evolution equation $$\ddot{x}(t) + \frac{\alpha}{t} \dot{x}(t) +
\beta \nabla^2 \Phi (x(t))\dot{x} (t) + \nabla \Phi (x(t)) = 0,$$ where
$\Phi:\mathcal H\to\mathbb R$ is a smooth convex function acting on a real
Hilbert space $\mathcal H$, and $\alpha$, $\beta$ are positive parameters. This
inertial system combines an isotropic viscous damping which vanishes
asymptotically, and a geometrical Hessian driven damping, which makes it
naturally related to Newton's and Levenberg-Marquardt methods. For $\alpha\geq
3$, $\beta >0$, along any trajectory, fast convergence of the values
$$\Phi(x(t))- \min_{\mathcal H}\Phi =\mathcal O\left(t^{-2}\right)$$ is
obtained, together with rapid convergence of the gradients $\nabla\Phi(x(t))$
to zero. For $\alpha>3$, just assuming that $\Phi$ has minimizers, we show that
any trajectory converges weakly to a minimizer of $\Phi$, and $
\Phi(x(t))-\min_{\mathcal H}\Phi = o(t^{-2})$. Strong convergence is
established in various practical situations. For the strongly convex case,
convergence can be arbitrarily fast depending on the choice of $\alpha$. More
precisely, we have $\Phi(x(t))- \min_{\mathcal H}\Phi = \mathcal
O(t^{-\frac{2}{3}\alpha})$. We extend the results to the case of a general
proper lower-semicontinuous convex function $\Phi : \mathcal H \rightarrow
\mathbb R \cup \{+\infty \}$. This is based on the fact that the inertial
dynamic with Hessian driven damping can be written as a first-order system in
time and space. By explicit-implicit time discretization, this opens a gate to
new $-$ possibly more rapid $-$ inertial algorithms, expanding the field of
FISTA methods for convex structured optimization problems.",1601.07113v1
2016-03-28,Stabilization of gravity water waves,"This paper is devoted to the stabilization of the incompressible Euler
equation with free surface. We study the damping of two-dimensional gravity
waves by an absorbing beach where the water-wave energy is dissipated by using
the variations of the external pressure.",1603.08541v1
2016-06-14,Precession Relaxation of Viscoelastic Oblate Rotators,"Perturbations of all sorts destabilise the rotation of a small body and leave
it in a non-principal spin state. In such a state, the body experiences
alternating stresses generated by the inertial forces. This yields nutation
relaxation, i.e., evolution of the spin towards the principal rotation about
the maximal-inertia axis. Knowledge of the timescales needed to damp the
nutation is crucial in studies of small bodies' dynamics. In the literature
hitherto, nutation relaxation has always been described with aid of an
empirical quality factor $\,Q\,$ introduced to parameterise the energy
dissipation rate.
  Among the drawbacks of this approach was its inability to describe the
dependence of the relaxation rate upon the current nutation angle. This
inability stemmed from our lack of knowledge of the quality factor's dependence
on the forcing frequency. In this article, we derive our description of
nutation damping directly from the rheological law obeyed by the material. This
renders us the nutation damping rate as a function of the current nutation
angle, as well as of the shape and the rheological parameters of the body. In
contradistinction from the approach based on an empirical $\,Q\,$-factor, our
development gives a zero damping rate in the spherical-shape limit. Our method
is generic and applicable to any shape and to any linear rheological law.
However, to simplify the developments, here we consider a dynamically oblate
rotator with a Maxwell rheology.",1606.04559v3
2016-09-07,Quasi-stability and Exponential Attractors for A Non-Gradient System---Applications to Piston-Theoretic Plates with Internal Damping,"We consider a nonlinear (Berger or Von Karman) clamped plate model with a
{\em piston-theoretic} right hand side---which include non-dissipative,
non-conservative lower order terms. The model arises in aeroelasticity when a
panel is immersed in a high velocity linear potential flow; in this case the
effect of the flow can be captured by a dynamic pressure term written in terms
of the material derivative of the plate's displacement. The effect of
fully-supported internal damping is studied for both Berger and von Karman
dynamics. The non-dissipative nature of the dynamics preclude the use of strong
tools such as backward-in-time smallness of velocities and finiteness of the
dissipation integral. Modern quasi-stability techniques are utilized to show
the existence of compact global attractors and generalized fractal exponential
attractors. Specific results depending on the size of the damping parameter and
the nonlinearity in force. For the Berger plate, in the presence of large
damping, the existence of a proper global attractor (whose fractal dimension is
finite in the state space) is shown via a decomposition of the nonlinear
dynamics. This leads to the construction of a compact set upon which
quasi-stability theory can be implemented. Numerical investigations for
appropriate 1-D models are presented which explore and support the abstract
results presented herein.",1609.02211v1
2016-10-26,On the region of attraction of phase-locked states for swing equations on connected graphs with inhomogeneous dampings,"We consider the synchronization problem of swing equations, a second-order
Kuramoto-type model, on connected networks with inhomogeneous dampings. This
was largely motivated by its relevance to the dynamics of power grids. We focus
on the estimate of the region of attraction of synchronous states which is a
central problem in the transient stability of power grids. In the recent
literature, D\""{o}rfler, Chertkov, and Bullo [Proc. Natl. Acad. Sci. USA, 110
(2013), pp. 2005-2010] found a condition for the synchronization in smart
grids. They pointed out that the region of attraction is an important unsolved
problem. In [SIAM J. Control Optim., 52 (2014), pp. 2482-2511], only a special
case was considered where the oscillators have homogeneous dampings and the
underlying graph has a diameter less than or equal to 2. There the analysis
heavily relies on these assumptions; however, they are too strict compared to
the real power networks. In this paper, we continue the study and derive an
estimate on the region of attraction of phase-locked states for lossless power
grids on connected graphs with inhomogeneous dampings. Our main strategy is
based on the gradient-like formulation and energy estimate. We refine the
assumptions by constructing a new energy functional which enables us to
consider such general settings.",1610.08437v1
2016-10-31,A quest for new physics inside the neutron,"The lecture presents an overview of the quest for the new physics in low
energy neutron phenomena. In addition to the traditional topics the quantum
damping of $n$ $\bar{n}$ oscillations is discussed.",1610.10046v1
2016-11-28,First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO,"Interferometric gravitational wave detectors operate with high optical power
in their arms in order to achieve high shot-noise limited strain sensitivity. A
significant limitation to increasing the optical power is the phenomenon of
three-mode parametric instabilities, in which the laser field in the arm
cavities is scattered into higher order optical modes by acoustic modes of the
cavity mirrors. The optical modes can further drive the acoustic modes via
radiation pressure, potentially producing an exponential buildup. One proposed
technique to stabilize parametric instability is active damping of acoustic
modes. We report here the first demonstration of damping a parametrically
unstable mode using active feedback forces on the cavity mirror. A 15,538 Hz
mode that grew exponentially with a time constant of 182 sec was damped using
electro-static actuation, with a resulting decay time constant of 23 sec. An
average control force of 0.03 nNrms was required to maintain the acoustic mode
at its minimum amplitude.",1611.08997v1
2016-12-19,Improving the efficiency of joint remote state preparation in noisy environment with weak measurement,"Quantum secure communication provides a new way for protecting the security
of information. As an important component of quantum secure communication,
remote state preparation (RSP) can securely transmit a quantum state from a
sender to a remote receiver. The existence of quantum noise severely affects
the security and reliability of quantum communication system. In this paper, we
study the method for improving the efficiency of joint RSP (JRSP) subjected to
noise with the help of weak measurement and its reversal measurement. Taking a
GHZ based deterministic JRSP as an example, we utilize the technique of weak
measurement and its reversal to suppress the effect of the amplitude-damping
noise firstly. Our study shows that the fidelity of the output state can be
improved in the amplitude-damping noise. We also study the effect of weak
measurement and its reversal in other three types of noise usually encountered
in real-world, namely, the bit-flip, phase-flip (phase-damping) and
depolarizing noise. Our results show that the weak measurement has no effect
for suppressing the bit-flip and phase-flip (phase-damping) noise, while has
slight effect for suppressing the depolarizing noise. Our study is suitable for
JRSP and RSP, and will be helpful for improving the efficiency of multiparticle
entanglement based quantum secure communication in real implementation.",1612.06020v1
2017-03-21,Evidence for structural damping in a high-stress silicon nitride nanobeam and its implications for quantum optomechanics,"We resolve the thermal motion of a high-stress silicon nitride nanobeam at
frequencies far below its fundamental flexural resonance (3.4 MHz) using
cavity-enhanced optical interferometry. Over two decades, the displacement
spectrum is well-modeled by that of a damped harmonic oscillator driven by a
$1/f$ thermal force, suggesting that the loss angle of the beam material is
frequency-independent. The inferred loss angle at 3.4 MHz, $\phi = 4.5\cdot
10^{-6}$, agrees well with the quality factor ($Q$) of the fundamental beam
mode ($\phi = Q^{-1}$). In conjunction with $Q$ measurements made on higher
order flexural modes, and accounting for the mode dependence of stress-induced
loss dilution, we find that the intrinsic (undiluted) loss angle of the beam
changes by less than a factor of 2 between 50 kHz and 50 MHz. We discuss the
impact of such ""structural damping"" on experiments in quantum optomechanics, in
which the thermal force acting on a mechanical oscillator coupled to an optical
cavity is overwhelmed by radiation pressure shot noise. As an illustration, we
show that structural damping reduces the bandwidth of ponderomotive squeezing.",1703.07134v2
2017-03-29,"Comment on ""Spreading widths of giant resonances in spherical nuclei: damped transient response"" by Severyukhin et al. [arXiv:1703.05710]","We argue whether physics of universal approach of Severyukhin et al.
[arXiv:1703.05710] is approved.",1703.10003v1
2017-05-16,Propagation of transition fronts in nonlinear chains with non-degenerate on-site potentials,"We address the problem of a front propagation in chains with a bi-stable
nondegenerate on-site potential and a nonlinear gradient coupling. For a
generic nonlinear coupling, one encounters a special regime of transitions,
characterized by extremely narrow fronts, far supersonic velocities of
propagation and long waves in the oscillatory tail. This regime can be
qualitatively associated with a shock wave. The front propagation can be
described with the help of a simple reduced-order model; the latter delivers a
kinetic law, which is almost not sensitive to fine details of the on-site
potential. Besides, it is possible to predict all main characteristics of the
transition front, including its shape and frequency and amplitude of the
oscillatory tail. The numerical results are in a good agreement with the
analytical predictions. The suggested approach allows one to consider the
effects of an external pre-load and on-site damping. When the damping is
moderate, the analysis remains in the frame of the reduced-order model. It is
possible to consider the solution for the front propagating in the damped chain
as a perturbation of the undamped dynamics. This approach yield reasonable
predictions. When the damping is high, the transition front enters a completely
different asymptotic regime. The gradient nonlinearity generically turns
negligible, and the propagating front converges to the exact solution obtained
from a simple linear continuous model.",1705.05555v1
2017-08-16,The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere,"High spatial and temporal resolution images of a sunspot, obtained
simultaneously in multiple optical and UV wavelengths, are employed to study
the propagation and damping characteristics of slow magnetoacoustic waves up to
transition region heights. Power spectra are generated from intensity
oscillations in sunspot umbra, across multiple atmospheric heights, for
frequencies up to a few hundred mHz. It is observed that the power spectra
display a power-law dependence over the entire frequency range, with a
significant enhancement around 5.5 mHz found for the chromospheric channels.
The phase-difference spectra reveal a cutoff frequency near 3 mHz, up to which
the oscillations are evanescent, while those with higher frequencies propagate
upwards. The power-law index appears to increase with atmospheric height. Also,
shorter damping lengths are observed for oscillations with higher frequencies
suggesting frequency-dependent damping. Using the relative amplitudes of the
5.5 mHz (3 minute) oscillations, we estimate the energy flux at different
heights, which seems to decay gradually from the photosphere, in agreement with
recent numerical simulations. Furthermore, a comparison of power spectra across
the umbral radius highlights an enhancement of high-frequency waves near the
umbral center, which does not seem to be related to magnetic field inclination
angle effects.",1708.04835v1
2017-08-29,Spin wave damping arising from phase coexistence below $T_c$ in colossal magnetoresistive La$_{0.7}$Ca$_{0.3}$MnO$_3$,"While the spin dynamics of La$_{0.7}$Ca$_{0.3}$MnO$_3$ in the ferromagnetic
phase are known to be unconventional, previous measurements have yielded
contradictory results regarding the damping of spin wave excitations. Neutron
spectroscopy measurements on a sample with a transition temperature of
$T_c$=257 K, higher than most single crystals, unambiguously reveal an
anomalous increase in spin wave damping for excitations approaching the
Brillouin zone boundary along the [$100$] direction that cannot be explained as
an artifact due to a noninteracting phonon branch. Spin waves throughout the
($HK0$) plane display a common trend where the spin wave damping is dependent
upon the excitation energy, increasing for energies above roughly 15 meV and
reaching a full width at half maximum of at least 20 meV. The results are
consistent with a model of intrinsic spatial inhomogeneity with phase separated
regions approximately 18 {\AA} in size persisting over a large range of
temperatures below $T_c$.",1708.08960v2
2017-09-08,Topological and Graph-coloring Conditions on the Parameter-independent Stability of Second-order Networked Systems,"In this paper, we study parameter-independent stability in qualitatively
heterogeneous passive networked systems containing damped and undamped nodes.
Given the graph topology and a set of damped nodes, we ask if output consensus
is achieved for all system parameter values. For given parameter values, an
eigenspace analysis is used to determine output consensus. The extension to
parameter-independent stability is characterized by a coloring problem, named
the richly balanced coloring (RBC) problem. The RBC problem asks if all nodes
of the graph can be colored red, blue and black in such a way that (i) every
damped node is black, (ii) every black node has blue neighbors if and only if
it has red neighbors, and (iii) not all nodes in the graph are black. Such a
colored graph is referred to as a richly balanced colored graph.
Parameter-independent stability is guaranteed if there does not exist a richly
balanced coloring. The RBC problem is shown to cover another well-known graph
coloring scheme known as zero forcing sets. That is, if the damped nodes form a
zero forcing set in the graph, then a richly balanced coloring does not exist
and thus, parameter-independent stability is guaranteed. However, the full
equivalence of zero forcing sets and parameter-independent stability holds only
true for tree graphs. For more general graphs with few fundamental cycles an
algorithm, named chord node coloring, is proposed that significantly
outperforms a brute-force search for solving the NP-complete RBC problem.",1709.02629v1
2017-10-11,Collisional damping rates for plasma waves,"The distinction between the plasma dynamics dominated by collisional
transport versus collective processes has never been rigorously addressed until
recently. A recent paper [Yoon et al., Phys. Rev. E 93, 033203 (2016)]
formulates for the first time, a unified kinetic theory in which collective
processes and collisional dynamics are systematically incorporated from first
principles. One of the outcomes of such a formalism is the rigorous derivation
of collisional damping rates for Langmuir and ion-acoustic waves, which can be
contrasted to the heuristic customary approach. However, the results are given
only in formal mathematical expressions. The present Brief Communication
numerically evaluates the rigorous collisional damping rates by considering the
case of plasma particles with Maxwellian velocity distribution function so as
to assess the consequence of the rigorous formalism in a quantitative manner.
Comparison with the heuristic (""Spitzer"") formula shows that the accurate
damping rates are much lower in magnitude than the conventional expression,
which implies that the traditional approach over-estimates the importance of
attenuation of plasma waves by collisional relaxation process. Such a finding
may have a wide applicability ranging from laboratory to space and
astrophysical plasmas.",1710.03874v1
2017-10-20,Tidal dissipation in rotating fluid bodies: the presence of a magnetic field,"We investigate effects of the presence of a magnetic field on tidal
dissipation in rotating fluid bodies. We consider a simplified model consisting
of a rigid core and a fluid envelope, permeated by a background magnetic field
(either a dipolar field or a uniform axial field). The wavelike tidal responses
in the fluid layer are in the form of magnetic-Coriolis waves, which are
restored by both the Coriolis force and the Lorentz force. Energy dissipation
occurs through viscous damping and Ohmic damping of these waves. Our numerical
results show that the tidal dissipation can be dominated by Ohmic damping even
with a weak magnetic field. The presence of a magnetic field smooths out the
complicated frequency-dependence of the dissipation rate, and broadens the
frequency spectrum of the dissipation rate, depending on the strength of the
background magnetic field. However, the frequency-averaged dissipation is
independent of the strength and structure of the magnetic field, and of the
dissipative parameters, in the approximation that the wave-like response is
driven only by the Coriolis force acting on the non-wavelike tidal flow.
Indeed, the frequency-averaged dissipation quantity is in good agreement with
previous analytical results in the absence of magnetic fields. Our results
suggest that the frequency-averaged tidal dissipation of the wavelike
perturbations is insensitive to detailed damping mechanisms and dissipative
properties.",1710.07690v2
2017-11-30,"Implications of dark matter cascade decay from DAMPE, HESS, Fermi-LAT and AMS02 data","Recent high-energy cosmic $e^\pm$ measurement from the DArk Matter Particle
Explorer (DAMPE) satellite confirms the deviation of total cosmic ray electron
spectrum above 700-900 GeV from a simple power law. In this paper we
demonstrate that the cascade decay of dark matter (DM) can account for DAMPE's
TeV $e^+e^-$ spectrum. We select the least constraint DM decay channel into
four muons as the benchmark scenario, and perform an analysis with propagation
variance in both DM signal and the Milky Way's electron background. The
best-fit of the model is obtained for joint DAMPE, Fermi-Large Area Telescope
(Fermi-LAT), High Energy Stereoscopic System (HESS), high energy electron data
sets, and with an $\mathcal{O}(10^{26})$ second decay lifetime, which is
consistent with existing gamma ray and cosmic microwave background limits. We
compare the spectral difference between the cascade decay of typical
final-state channels. The least constrained $4\mu$ channels give good fits to
the electron spectrum's TeV scale down-turn, yet their low energy spectrum has
tension with sub-TeV positron data from AMS02. We also consider a three-step
cascade decay into eight muons, and also a gamma-ray constrained $4\mu,4b$
mixed channel, to demonstrate that a further softened cascade decay signal
would be required for the agreement with all the data sets.",1712.00370v3
2017-12-04,"Scalar dark matter, Type II Seesaw and the DAMPE cosmic ray $e^+ + e^-$ excess","The DArk Matter Particle Explorer (DAMPE) has reported a measurement of the
flux of high energy cosmic ray electrons plus positrons (CREs) in the energy
range between $25$ GeV and $4.6$ TeV. With unprecedented high energy
resolution, the DAMPE data exhibit an excess of the CREs flux at an energy of
around $1.4$ TeV. In this letter, we discuss how the observed excess can be
understood in a minimal framework where the Standard Model (SM) is supplemented
by a stable SM singlet scalar as dark matter (DM) and type II seesaw for
generating the neutrino mass matrix. In our framework, a pair of DM particles
annihilates into a pair of the SM SU(2) triplet scalars ($\Delta$s) in type II
seesaw, and the subsequent $\Delta$ decays create the primary source of the
excessive CREs around $1.4$ TeV. The lepton flavor structure of the primary
source of CREs has a direct relationship with the neutrino oscillation data. We
find that the DM interpretation of the DAMPE excess determines the pattern of
neutrino mass spectrum to be the inverted hierarchy type, taking into account
the constraints from the Fermi-LAT observations of dwarf spheroidal galaxies.",1712.00869v2
2017-12-07,Nonlinear growth of structure in cosmologies with damped matter fluctuations,"We investigate the nonlinear evolution of structure in variants of the
standard cosmological model which display damped density fluctuations relative
to cold dark matter (e.g. in which cold dark matter is replaced by warm or
interacting DM). Using N-body simulations, we address the question of how much
information is retained from different scales in the initial linear power
spectrum following the nonlinear growth of structure. We run a suite of N-body
simulations with different initial linear matter power spectra to show that,
once the system undergoes nonlinear evolution, the shape of the linear power
spectrum at high wavenumbers does not affect the non-linear power spectrum,
while it still matters for the halo mass function. Indeed, we find that linear
power spectra which differ from one another only at wavenumbers larger than
their half-mode wavenumber give rise to (almost) identical nonlinear power
spectra at late times, regardless of the fact that they originate from
different models with damped fluctuations. On the other hand, the halo mass
function is more sensitive to the form of the linear power spectrum. Exploiting
this result, we propose a two parameter model of the transfer function in
generic damped scenarios, and show that this parametrisation works as well as
the standard three parameter models for the scales on which the linear spectrum
is relevant.",1712.02742v2
2017-12-11,DAMPE excess from decaying right-handed neutrino dark matter,"The flux of high-energy cosmic-ray electrons plus positrons recently measured
by the DArk Matter Particle Explorer (DAMPE) exhibits a tentative peak excess
at an energy of around $1.4$ TeV. In this paper, we consider the minimal gauged
$U(1)_{B-L}$ model with a right-handed neutrino (RHN) dark matter (DM) and
interpret the DAMPE peak with a late-time decay of the RHN DM into $e^\pm
W^\mp$. We find that a DM lifetime $\tau_{DM} \sim 10^{28}$ s can fit the DAMPE
peak with a DM mass $m_{DM}=3$ TeV. This favored lifetime is close to the
current bound on it by Fermi-LAT, our decaying RHN DM can be tested once the
measurement of cosmic gamma ray flux is improved. The RHN DM communicates with
the Standard Model particles through the $U(1)_{B-L}$ gauge boson ($Z^\prime$
boson), and its thermal relic abundance is controlled by only three free
parameters: $m_{DM}$, the $U(1)_{B-L}$ gauge coupling ($\alpha_{BL}$), and the
$Z^\prime$ boson mass ($m_{Z^\prime}$). For $m_{DM}=3$ TeV, the rest of the
parameters are restricted to be $m_{Z^\prime}\simeq 6$ TeV and $0.00807 \leq
\alpha_{BL} \leq 0.0149$, in order to reproduce the observed DM relic density
and to avoid the Landau pole for the running $\alpha_{BL}$ below the Planck
scale. This allowed region will be tested by the search for a $Z^\prime$ boson
resonance at the future Large Hadron Collider.",1712.03652v3
2017-12-11,A Statistical Study on The Frequency-Dependent Damping of Slow-mode Waves in Polar Plumes and Interplumes,"We perform a statistical study on the frequency-dependent damping of slow
waves propagating along polar plumes and interplumes in the solar corona.
Analysis of a large sample of extreme ultraviolet (EUV) imaging data with high
spatial and temporal resolutions obtained from AIA/SDO suggests an inverse
power-law dependence of the damping length on the periodicity of slow waves
(i.e., the shorter period oscillations exhibit longer damping lengths), in
agreement with the previous case studies. Similar behavior is observed in both
plume and interplume regions studied in AIA 171 \AA\ and AIA 193 \AA\
passbands. It is found that the short-period (2--6 min) waves are relatively
more abundant than their long period (7--30 min) counterparts in contrast to
the general belief that the polar regions are dominated by the longer-period
slow waves. We also derived the slope of the power spectra ($\mathrm{\alpha}$,
the power-law index) statistically to better understand the characteristics of
turbulence present in the region. It is found that the $\mathrm{\alpha}$ values
and their distributions are similar in both plume and interplume structures
across the two AIA passbands. At the same time, the spread of these
distributions also indicates the complexity of the underlying turbulence
mechanism.",1712.03673v1
2018-02-18,On energy stable discontinuous Galerkin spectral element approximations of the perfectly matched layer for the wave equation,"We develop a provably energy stable discontinuous Galerkin spectral element
method (DGSEM) approximation of the perfectly matched layer (PML) for the three
and two space dimensional (3D and 2D) linear acoustic wave equations, in first
order form, subject to well-posed linear boundary conditions. First, using the
well-known complex coordinate stretching, we derive an efficient un-split modal
PML for the 3D acoustic wave equation. Second, we prove asymptotic stability of
the continuous PML by deriving energy estimates in the Laplace space, for the
3D PML in a heterogeneous acoustic medium, assuming piece-wise constant PML
damping. Third, we develop a DGSEM for the wave equation using physically
motivated numerical flux, with penalty weights, which are compatible with all
well-posed, internal and external, boundary conditions. When the PML damping
vanishes, by construction, our choice of penalty parameters yield an upwind
scheme and a discrete energy estimate analogous to the continuous energy
estimate. Fourth, to ensure numerical stability when PML damping is present, it
is necessary to systematically extend the numerical numerical fluxes, and the
inter-element and boundary procedures, to the PML auxiliary differential
equations. This is critical for deriving discrete energy estimates analogous to
the continuous energy estimates. Finally, we propose a procedure to compute PML
damping coefficients such that the PML error converges to zero, at the optimal
convergence rate of the underlying numerical method. Numerical experiments are
presented in 2D and 3D corroborating the theoretical results.",1802.06388v1
2018-08-05,"Dispersion, damping, and intensity of spin excitations in the single-layer (Bi,Pb)$_{2}$(Sr,La)$_{2}$CuO$_{6+δ}$ cuprate superconductor family","Using Cu-$L_3$ edge resonant inelastic x-ray scattering (RIXS) we measured
the dispersion and damping of spin excitations (magnons and paramagnons) in the
high-$T_\mathrm{c}$ superconductor (Bi,Pb)$_{2}$(Sr,La)$_{2}$CuO$_{6+\delta}$
(Bi2201), for a large doping range across the phase diagram ($0.03\lesssim
p\lesssim0.21$). Selected measurements with full polarization analysis
unambiguously demonstrate the spin-flip character of these excitations, even in
the overdoped sample. We find that the undamped frequencies increase slightly
with doping for all accessible momenta, while the damping grows rapidly, faster
in the (0,0)$\rightarrow$(0.5,0.5) nodal direction than in the
(0,0)$\rightarrow$(0.5,0) antinodal direction. We compare the experimental
results to numerically exact determinant quantum Monte Carlo (DQMC)
calculations that provide the spin dynamical structure factor
$S(\textbf{Q},\omega)$ of the three-band Hubbard model. The theory reproduces
well the momentum and doping dependence of the dispersions and spectral weights
of magnetic excitations. These results provide compelling evidence that
paramagnons, although increasingly damped, persist across the superconducting
dome of the cuprate phase diagram; this implies that long range
antiferromagnetic correlations are quickly washed away, while short range
magnetic interactions are little affected by doping.",1808.01682v1
2018-09-19,Critical exponent for the semilinear wave equations with a damping increasing in the far field,"We consider the Cauchy problem of the semilinear wave equation with a damping
term \begin{align*}
  u_{tt} - \Delta u + c(t,x) u_t = |u|^p, \quad (t,x)\in (0,\infty)\times
\mathbb{R}^N,\quad
  u(0,x) = \varepsilon u_0(x), \ u_t(0,x) = \varepsilon u_1(x), \quad x\in
\mathbb{R}^N, \end{align*} where $p>1$ and the coefficient of the damping term
has the form \begin{align*}
  c(t,x) = a_0 (1+|x|^2)^{-\alpha/2} (1+t)^{-\beta} \end{align*} with some $a_0
> 0$, $\alpha < 0$, $\beta \in (-1, 1]$. In particular, we mainly consider the
cases $ \alpha < 0, \beta =0$ or $\alpha < 0, \beta = 1$, which imply $\alpha +
\beta < 1$, namely, the damping is spatially increasing and effective. Our aim
is to prove that the critical exponent is given by $ p = 1+
\frac{2}{N-\alpha}$. This shows that the critical exponent is the same as that
of the corresponding parabolic equation $c(t,x) v_t - \Delta v = |v|^p$. The
global existence part is proved by a weighted energy estimates with an
exponential-type weight function and a special case of the
Caffarelli-Kohn-Nirenberg inequality. The blow-up part is proved by a
test-function method introduced by Ikeda and Sobajima (arXiv:1710.06780v1). We
also give an upper estimate of the lifespan.",1809.06994v1
2018-10-16,Dark matter gets DAMPE,"The DArk Matter Particle Explorer (DAMPE) recently reported an excess of
electrons/positrons above expected background fluxes even when a double
power-law background spectrum is assumed. Several dark matter models that
involve TeV-scale leptophilic WIMPs have been suggested in the literature to
account for this excess. All of these models are associated with the presence
of a nearby dark matter clump/over-density.
  In this work we set out to explore how current constraints from observational
data impact the suggested parameter space for a dark matter explanation of the
DAMPE excess, as well as make projections of the capacity of LOFAR and the
up-coming SKA to observe indirect radio emissions from the nearby dark matter
over-density.
  We show that LOFAR is incapable of probing the parameter space for DAMPE
excess models, unless the dark matter clump is in the form of an ultra-compact
mini halo. Fermi-LAT limits on dark matter annihilation are unable to probe
these models in all cases. Limits derived from diffuse Coma cluster radio
emission can probe a substantial portion of the parameter space and muon
neutrino limits inferred from galactic centre gamma-ray fluxes heavily restrict
muon coupling for the proposed WIMPs. The SKA is shown to able to fully probe
the parameter space of all the studied models using indirect emissions from the
local dark matter over-density.",1810.07176v2
2018-11-15,Damping rate of a fermion in ultradegenerate chiral matter,"We compute the damping rate of a fermion propagating in a chiral plasma when
there is an imbalance between the densities of left- and right-handed fermions,
after generalizing the hard thermal loop resummation techniques for these
systems. In the ultradegenerate limit, for very high energies the damping rate
of this external fermion approaches a constant value. Closer to the two Fermi
surfaces, however, we find that the rate depends on both the energy and the
chirality of the fermion, being higher for the predominant chirality. This
comes out as a result of its scattering with the particles of the plasma,
mediated by the exchange of Landau damped photons. In particular, we find that
the chiral imbalance is responsible for a different propagation of the left and
right circular polarised transverse modes of the photon, and that a chiral
fermion interacts differently with these two transverse modes. We argue that
spontaneous radiation of energetic fermions is kinematically forbidden, and
discuss the time regime where our computation is valid.",1811.06394v3
2018-12-16,Nonlinear Dynamics of Spherical Shells Buckling under Step Pressure,"Dynamic buckling is addressed for complete elastic spherical shells subject
to a rapidly applied step in external pressure. Insights from the perspective
of nonlinear dynamics reveal essential mathematical features of the buckling
phenomena. To capture the strong buckling imperfection-sensitivity, initial
geometric imperfections in the form of an axisymmetric dimple at each pole are
introduced. Dynamic buckling under the step pressure is related to the
quasi-static buckling pressure. Both loadings produce catastrophic collapse of
the shell for conditions in which the pressure is prescribed. Damping plays an
important role in dynamic buckling because of the time-dependent nonlinear
interaction among modes, particularly the interaction between the spherically
symmetric 'breathing' mode and the buckling mode. In this paper we argue that
the precise frequency dependence of the damping does not matter as most of the
damping happens at a single frequency (the breathing frequency). In general,
there is not a unique step pressure threshold separating responses associated
with buckling from those that do not buckle. Instead there exists a cascade of
buckling thresholds, dependent on the damping and level of imperfection,
separating pressures for which buckling occurs from those for which it does not
occur. For shells with small and moderately small imperfections the dynamic
step buckling pressure can be substantially below the quasi-static buckling
pressure.",1812.06526v2
2019-01-09,Turbulent dynamo in a weakly ionized medium,"The small-scale turbulent dynamo is an important process contributing to the
cosmic magnetization. In partially ionized astrophysical plasmas, the dynamo
growth of magnetic energy strongly depends on the coupling state between ions
and neutrals and the ion-neutral collisional damping effect. A new damping
stage of turbulent dynamo in a weakly ionized medium was theoretically
predicted by Xu \& Lazarian (2016). By carrying out a 3D two-fluid dynamo
simulation, here we for the first time numerically confirmed the physical
conditions and the linear-in-time growth of magnetic field strength of the
damping stage of dynamo. The dynamo-amplified magnetic field has a
characteristic length as the damping scale, which increases with time and can
reach the injection scale of turbulence after around eight largest
eddy-turnover times given sufficiently low ionization fraction and weak initial
magnetic field. Due to the weak coupling between ions and neutrals, most
turbulent energy carried by neutrals cannot be converted to the magnetic
energy, resulting in a relatively weak magnetic field at the end of dynamo.
This result has important implications for the growth of magnetic fields in the
partially ionized interstellar medium and shock acceleration of Galactic cosmic
rays.",1901.02893v1
2019-01-25,Quantum speed limit time for correlated quantum channel,"Memory effects play a fundamental role in the dynamics of open quantum
systems. There exist two different views on memory for quantum noises. In the
first view, the quantum channel has memory when there exist correlations
between successive uses of the channels on a sequence of quantum systems. These
types of channels are also known as correlated quantum channels. In the second
view, memory effects result from correlations which are created during the
quantum evolution. In this work we will consider the first view and study the
quantum speed limit time for a correlated quantum channel. Quantum speed limit
time is the bound on the minimal time which is needed for a quantum system to
evolve from an initial state to desired states. The quantum evolution is fast
if the quantum speed limit time is short. In this work, we will study the
quantum speed limit time for some correlated unital and correlated non-unital
channels. As an example for unital channels we choose correlated dephasing
colored noise. We also consider the correlated amplitude damping and correlated
squeezed generalized amplitude damping channels as the examples for non-unital
channels. It will be shown that the quantum speed limit time for correlated
pure dephasing colored noise is increased by increasing correlation strength,
while for correlated amplitude damping and correlated squeezed generalized
amplitude damping channels quantum speed limit time is decreased by increasing
correlation strength.",1901.08917v4
2019-02-17,Finite-size effects on sound damping in stable computer glasses,"In this brief note we comment on the recent results presented in
arXiv:1812.08736v1",1902.06225v1
2019-05-04,A class of second-order geometric quasilinear hyperbolic PDEs and their application in imaging science,"In this paper, we study damped second-order dynamics, which are quasilinear
hyperbolic partial differential equations (PDEs). This is inspired by the
recent development of second-order damping systems for accelerating energy
decay of gradient flows. We concentrate on two equations: one is a damped
second-order total variation flow, which is primarily motivated by the
application of image denoising; the other is a damped second-order mean
curvature flow for level sets of scalar functions, which is related to a
non-convex variational model capable of correcting displacement errors in image
data (e.g. dejittering). For the former equation, we prove the existence and
uniqueness of the solution. For the latter, we draw a connection between the
equation and some second-order geometric PDEs evolving the hypersurfaces which
are described by level sets of scalar functions, and show the existence and
uniqueness of the solution for a regularized version of the equation. The
latter is used in our algorithmic development. A general algorithm for
numerical discretization of the two nonlinear PDEs is proposed and analyzed.
Its efficiency is demonstrated by various numerical examples, where simulations
on the behavior of solutions of the new equations and comparisons with
first-order flows are also documented.",1905.01457v2
2019-07-08,Single-spectrum prediction of kurtosis of water waves in a non-conservative model,"We study statistical properties after a sudden episode of wind for water
waves propagating in one direction. A wave with random initial conditions is
propagated using a forced-damped higher order Nonlinear Schr\""odinger equation
(NLS). During the wind episode, the wave action increases, the spectrum
broadens, the spectral mean shifts up and the Benjamin-Feir index (BFI) and the
kurtosis increase. Conversely, after the wind episode, the opposite occurs for
each quantity. The kurtosis of the wave height distribution is considered the
main parameter that can indicate whether rogue waves are likely to occur in a
sea state, and the BFI is often mentioned as a means to predict the kurtosis.
However, we find that while there is indeed a quadratic relation between these
two, this relationship is dependent on the details of the forcing and damping.
Instead, a simple and robust quadratic relation does exist between the kurtosis
and the bandwidth. This could allow for a single-spectrum assessment of the
likelihood of rogue waves in a given sea state. In addition, as the kurtosis
depends strongly on the damping and forcing coefficients, by combining the
bandwidth measurement with the damping coefficient, the evolution of the
kurtosis after the wind episode can be predicted.",1907.03490v1
2019-08-20,Synthetic Extreme-ultraviolet Emissions Modulated by Leaky Fast Sausage Modes in Solar Active Region Loops,"We study the extreme-ultraviolet (EUV) emissions modulated by leaky fast
sausage modes (FSMs) in solar active region loops and examine their
observational signatures via spectrometers like EIS. After computing fluid
variables of leaky FSMs with MHD simulations, we forward-model the intensity
and spectral properties of the Fe X 185~\AA~and Fe XII 195~\AA~lines by
incorporating non-equilibrium ionization (NEI) in the computations of the
relevant ionic fractions. The damping times derived from the intensity
variations are then compared with the wave values, namely the damping times
directly found from our MHD simulations. Our results show that in the
equilibrium ionization cases, the density variations and the intensity
variations can be either in phase or in anti-phase, depending on the loop
temperature. NEI considerably impacts the intensity variations but has only
marginal effects on the derived Doppler velocity or Doppler width. We find that
the damping time derived from the intensity can largely reflect the wave
damping time if the loop temperature is not drastically different from the
nominal formation temperature of the corresponding emission line. These results
are helpful for understanding the modulations to the EUV emissions by leaky
FSMs and hence helpful for identifying FSMs in solar active region loops.",1908.07131v1
2019-10-24,Frequency criteria for exponential stability,"We discuss some frequency-domain criteria for the exponential stability of
nonlinear feedback systems based on dissipativity theory. Applications are
given to convergence rates for certain perturbations of the damped harmonic
oscillator.",1910.10855v2
2019-11-05,IW And-Type State in IM Eridani,"IW And stars are a recently recognized group of dwarf novae which are
characterized by a repeated sequence of brightening from a standstill-like
phase with damping oscillations followed by a deep dip. Kimura et al. (2019)
recently proposed a model based on thermal-viscous disk instability in a tilted
disk to reproduce the IW And-type characteristics. IM Eri experienced the IW
And-type phase in 2018 and we recorded three cycles of the (damping)
oscillation phase terminated by brightening. We identified two periods during
the IW And-type state: 4-5 d small-amplitude (often damping) oscillations and a
34-43 d long cycle. This behavior is typical for an IW And-type star. The
object gradually brightened within the long cycle before the next brightening
which terminated the (damping) oscillation phase. This observation agrees with
the increasing disk mass during the long cycle predicted by a model of
thermal-viscous disk instability in a tilted disk (Kimura et al. 2019). We,
however, did not succeed in detecting negative superhumps, which are considered
to be the signature of a tilted disk.",1911.01587v1
2019-11-28,Magnon damping in the zigzag phase of the Kitaev-Heisenberg-$Γ$ model on a honeycomb lattice,"We calculate magnon dispersions and damping in the Kitaev-Heisenberg model
with an off-diagonal exchange $\Gamma$ and isotropic third-nearest-neighbor
interaction $J_3$ on a honeycomb lattice. This model is relevant to a
description of the magnetic properties of iridium oxides $\alpha$-Li$_2$IrO$_3$
and Na$_2$IrO$_3$, and Ru-based materials such as $\alpha$-RuCl$_3$. We use an
unconventional parametrization of the spin-wave expansion, in which each
Holstein-Primakoff boson is represented by two conjugate hermitian operators.
This approach gives us an advantage over the conventional one in identifying
parameter regimes where calculations can be performed analytically. Focusing on
the parameter regime with the zigzag spin pattern in the ground state that is
consistent with experiments, we demonstrate that one such region is $\Gamma =
K>0$, where $K$ is the Kitaev coupling. Within our approach we are able to
obtain explicit analytical expressions for magnon energies and eigenstates and
go beyond the standard linear spin-wave theory approximation by calculating
magnon damping and demonstrating its role in the dynamical structure factor. We
show that the magnon damping effects in both Born and self-consistent
approximations are very significant, underscoring the importance of non-linear
magnon coupling in interpreting broad features in the neutron-scattering
spectra.",1911.12829v2
2019-12-10,A Stochastic Quasi-Newton Method for Large-Scale Nonconvex Optimization with Applications,"This paper proposes a novel stochastic version of damped and regularized BFGS
method for addressing the above problems.",1912.04456v1
2019-12-27,Ultralow mechanical damping with Meissner-levitated ferromagnetic microparticles,"Levitated nanoparticles and microparticles are excellent candidates for the
realization of extremely isolated mechanical systems, with a huge potential
impact in sensing applications and in quantum physics. Magnetic levitation
based on static fields is a particularly interesting approach, due to the
unique property of being completely passive and compatible with low
temperatures. Here, we show experimentally that micromagnets levitated above
type-I superconductors feature very low damping at low frequency and low
temperature. In our experiment, we detect 5 out of 6 rigid-body mechanical
modes of a levitated ferromagnetic microsphere, using a dc SQUID
(Superconducting Quantum Interference Device) with a single pick-up coil. The
measured frequencies are in agreement with a finite element simulation based on
ideal Meissner effect. For two specific modes we find further substantial
agreement with analytical predictions based on the image method. We measure
damping times $\tau$ exceeding $10^4$ s and quality factors $Q$ beyond $10^7$,
improving by $2-3$ orders of magnitude over previous experiments based on the
same principle. We investigate the possible residual loss mechanisms besides
gas collisions, and argue that much longer damping time can be achieved with
further effort and optimization. Our results open the way towards the
development of ultrasensitive magnetomechanical sensors with potential
applications to magnetometry and gravimetry, as well as to fundamental and
quantum physics.",1912.12252v3
2020-01-22,Wide Area Measurement System-based Low Frequency Oscillation Damping Control through Reinforcement Learning,"Ensuring the stability of power systems is gaining more attraction today than
ever before, due to the rapid growth of uncertainties in load and renewable
energy penetration. Lately, wide area measurement system-based centralized
controlling techniques started providing a more flexible and robust control to
keep the system stable. But, such a modernization of control philosophy faces
pressing challenges due to the irregularities in delays of long-distance
communication channels and response of equipment to control actions. Therefore,
we propose an innovative approach that can revolutionize the control strategy
for damping down low frequency oscillations in transmission systems. Proposed
method is enriched with a potential of overcoming the challenges of
communication delays and other non-linearities in wide area damping control by
leveraging the capability of the reinforcement learning technique. Such a
technique has a unique characteristic to learn on diverse scenarios and
operating conditions by exploring the environment and devising an optimal
control action policy by implementing policy gradient method. Our detailed
analysis and systematically designed numerical validation prove the
feasibility, scalability and interpretability of the carefully modelled
low-frequency oscillation damping controller so that stability is ensured even
with the uncertainties of load and generation are on the rise.",2001.07829v1
2020-02-13,Semi-realistic tight-binding model for spin-orbit torques,"We compute the spin-orbit torque in a transition metal heterostructure using
Slater-Koster parameterization in the two-center tight-binding approximation
and accounting for d-orbitals only. In this method, the spin-orbit coupling is
modeled within Russel-Saunders scheme, which enables us to treat interfacial
and bulk spin-orbit transport on equal footing. The two components of the
spin-orbit torque, dissipative (damping-like) and reactive (field-like), are
computed within Kubo linear response theory. By systematically studying their
thickness and angular dependence, we were able to accurately characterize these
components beyond the traditional ""inverse spin galvanic"" and ""spin Hall""
effects. Whereas the conventional field-like torque is purely interfacial, we
unambiguously demonstrate that the conventional the damping-like torque
possesses both an interfacial and a bulk contribution. In addition, both
field-like and damping-like torques display substantial angular dependence with
strikingly different thickness behavior. While the planar contribution of the
field-like torque decreases smoothly with the nonmagnetic metal thickness, the
planar contribution of the damping-like torque increases dramatically with the
nonmagnetic metal thickness. Finally, we investigate the self-torque exerted on
the ferromagnet when the spin-orbit coupling of the nonmagnetic metal is turned
off. Our results suggest that the spin accumulation that builds up inside the
ferromagnet can be large enough to induce magnetic excitations.",2002.05533v1
2020-02-14,"One-dimensional wave equation with set-valued boundary damping: well-posedness, asymptotic stability, and decay rates","This paper is concerned with the analysis of a one dimensional wave equation
$z_{tt}-z_{xx}=0$ on $[0,1]$ with a Dirichlet condition at $x=0$ and a damping
acting at $x=1$ which takes the form $(z_t(t,1),-z_x(t,1))\in\Sigma$ for every
$t\geq 0$, where $\Sigma$ is a given subset of $\mathbb R^2$. The study is
performed within an $L^p$ functional framework, $p\in [1, +\infty]$. We aim at
determining conditions on $\Sigma$ ensuring existence and uniqueness of
solutions of that wave equation as well as strong stability and uniform global
asymptotic stability of its solutions. In the latter case, we also study the
decay rates of the solutions and their optimality. We first establish a
one-to-one correspondence between the solutions of that wave equation and the
iterated sequences of a discrete-time dynamical system in terms of which we
investigate the above mentioned issues. This enables us to provide a simple
necessary and sufficient condition on $\Sigma$ ensuring existence and
uniqueness of solutions of the wave equation as well as an efficient strategy
for determining optimal decay rates when $\Sigma$ verifies a generalized sector
condition. As an application, we solve two conjectures stated in the
literature, the first one seeking a specific optimal decay rate and the second
one associated with a saturation type of damping. In case the boundary damping
is subject to perturbations, we derive sharp results regarding asymptotic
perturbation rejection and input-to-state issues.",2002.06186v3
2020-03-30,Optimal absorption of acoustical waves by a boundary,"In the aim to find the simplest and most efficient shape of a noise absorbing
wall to dissipate the acoustical energy of a sound wave, we consider a
frequency model described by the Helmholtz equation with a damping on the
boundary. The well-posedness of the model is shown in a class of domains with
d-set boundaries (N -- 1 $\le$ d < N). We introduce a class of admissible
Lipschitz boundaries, in which an optimal shape of the wall exists in the
following sense: We prove the existence of a Radon measure on this shape,
greater than or equal to the usual Lebesgue measure, for which the
corresponding solution of the Helmholtz problem realizes the infimum of the
acoustic energy defined with the Lebesgue measure on the boundary. If this
Radon measure coincides with the Lebesgue measure, the corresponding solution
realizes the minimum of the energy. For a fixed porous material, considered as
an acoustic absorbent, we derive the damping parameters of its boundary from
the corresponding time-dependent problem described by the damped wave equation
(damping in volume).",2003.13250v2
2020-04-24,Suppression of the longitudinal coupled bunch instability in DA$Φ$NE in collisions with a crossing angle,"In DAFNE, the Frascati $e^+e^-$ collider operating since 1998, an innovative
collision scheme, the crab waist, has been successfully implemented during the
years 2008-09. During operations for the Siddharta experiment an unusual
synchrotron oscillation damping effect induced by beam-beam collisions has been
observed. Indeed, when the longitudinal feedback is off, the positron beam
becomes unstable with currents above 200-300 mA due to coupled bunch
instability. The longitudinal instability is damped by colliding the positron
beam with a high current electron beam (of the order of 2 A). A shift of about
-600 Hz in the residual synchrotron sidebands is observed. Precise measurements
have been performed by using both a commercial spectrum analyzer and the
diagnostic capabilities of the longitudinal bunch-by-bunch feedback. The
damping effect has been observed in DAFNE for the first time during collisions
with the crab waist scheme. Our explanation, based both on theoretical
consideration and modeling simulation, is that beam collisions with a large
crossing angle produce longitudinal tune shift and spread, providing Landau
damping of synchrotron oscillations.",2004.11902v1
2020-05-08,Separatrix crossing and symmetry breaking in NLSE-like systems due to forcing and damping,"We theoretically and experimentally examine the effect of forcing and damping
on systems that can be described by the nonlinear Schr\""odinger equation
(NLSE), by making use of the phase-space predictions of the three-wave
truncation of the spectrum. In the latter, only the fundamental frequency and
the upper and lower sidebands are retained. Plane wave solutions to the NLSE
exhibit modulation instability (MI) within a frequency band determined by a
linear stability analysis. For modulation frequencies inside the MI-band, we
experimentally demonstrate that forcing and damping cause a separatrix crossing
during the evolution. Our experiments are performed on deep water waves, which
are better described by the higher-order NLSE, the Dysthe equation. We
therefore extend our analysis to this system. However, our conclusions are
general. When the system is damped by the viscosity of the water, it is pulled
outside the separatrix, which in the real space corresponds to a phase-shift of
the envelope and therefore doubles the period of the Fermi-Pasta-Ulam-Tsingou
recurrence cycle. When the system is forced by the wind, it is pulled inside
the separatrix. Furthermore, for modulation frequencies outside the
conventional MI-band, we experimentally demonstrate that contrary to the linear
prediction, we do observe a growth and decay cycle of the plane-wave
modulation. Finally, we give a theoretical demonstration that forcing the NLSE
system can induce symmetry breaking during the evolution.",2005.03931v1
2020-05-13,Damping of a micro-electromechanical oscillator in turbulent superfluid $^4$He: A novel probe of quantized vorticity in the ultra-low temperature regime,"We report a comprehensive investigation of the effects of quantum turbulence
and quantized vorticity in superfluid $^4$He on the motion of a
micro-electromechanical systems (MEMS) resonator. We find that the MEMS is
uniquely sensitive to quantum turbulence present in the fluid. To generate
turbulence in the fluid, a quartz tuning fork (TF) is placed in proximity to
the MEMS and driven at large amplitude. We observe that at low velocity, the
MEMS is damped by the turbulence, and that above a critical velocity, $v_c
\simeq 5\,$mm\,s$^{-1}$, the turbulent damping is greatly reduced. We find that
above $v_c$, the damping of the MEMS is reduced further for increasing
velocity, indicating a velocity dependent coupling between the surface of the
MEMS and the quantized vortices constituting the turbulence. We propose a model
of the interaction between vortices in the fluid and the surface of the MEMS.
The sensitivity of these devices to a small number of vortices and the almost
unlimited customization of MEMS open the door to a more complete understanding
of the interaction between quantized vortices and oscillating structures, which
in turn provides a new route for the investigation of the dynamics of single
vortices.",2005.06570v1
2020-06-10,Online PMU-Based Wide-Area Damping Control for Multiple Inter-Area Modes,"This paper presents a new phasor measurement unit (PMU)-based wide-area
damping control (WADC) method to suppress the critical inter-area modes of
large-scale power systems. Modal participation factors, estimated by a
practically model-free system identification approach, are used to select the
most suitable synchronous generators for control through the proposed WADC
algorithm. It is shown that multiple inter-area modes can be sufficiently
damped by the proposed approach without affecting the rest of the modes, while
only a few machines are needed to perform the control. The proposed technique
is applied to the IEEE 68-bus and the IEEE 145-bus systems, including the test
cases with PMU measurement noise and with missing PMUs. The simulation results
clearly demonstrate the good adaptivity of the control strategy subjected to
network model changes, its effective damping performance comparing to power
system stabilizers (PSSs), and its great potential for near real-time
implementation.",2006.05651v1
2020-06-14,A general formulation for the magnetic oscillations in two dimensional systems,"We develop a general formalism for the magnetic oscillations (MO) in two
dimensional (2D) systems. We consider general 2D Landau levels, which may
depend on other variable or indices, besides the perpendicular magnetic field.
In the ground state, we obtain expressions for the MO phase and amplitude. From
this we use a Fourier expansion to write the MO, with the first term being a
sawtooth oscillation. We also consider the effects of finite temperature,
impurities or lattice imperfections, assuming a general broadening of the
Landau levels. We develop two methods for describing these damping effects in
the MO. One in terms of the occupancy of the Landau levels, the other in terms
of reduction factors, which results in a generalization of the
Lifshits-Kosevich (LK) formula. We show that the first approach is particularly
useful at very low damping, when only the states close to the Fermi energy are
excited. In contrast, the LK formula may be more convenient at higher damping,
when only few terms are needed in its harmonic expansion. We compare different
damping situations, showing how the MO are broadened in each case. The general
formulation presented allows to relate the properties of the MO with those of
the 2D systems.",2006.07944v2
2020-07-19,Global existence and convergence to the modified Barenblatt solution for the compressible Euler equations with physical vacuum and time-dependent damping,"In this paper, the smooth solution of the physical vacuum problem for the one
dimensional compressible Euler equations with time-dependent damping is
considered. Near the vacuum boundary, the sound speed is $C^{1/2}$-H\""{o}lder
continuous. The coefficient of the damping depends on time, given by this form
$\frac{\mu}{(1+t)^\lambda}$, $\lambda$, $\mu>0$, which decays by order
$-\lambda$ in time. Under the assumption that $0<\lambda<1$, $0<\mu$ or
$\lambda=1$, $2<\mu$, we will prove the global existence of smooth solutions
and convergence to the modified Barenblatt solution of the related porous media
equation with time-dependent dissipation and the same total mass when the
initial data of the Euler equations is a small perturbation of that of the
Barenblatt solution. The pointwise convergence rates of the density, velocity
and the expanding rate of the physical vacuum boundary are also given. The
proof is based on space-time weighted energy estimates, elliptic estimates and
Hardy inequality in the Lagrangian coordinates. Our result is an extension of
that in Luo-Zeng [Comm. Pure Appl. Math. 69 (2016), no. 7, 1354-1396], where
the authors considered the physical vacuum free boundary problem of the
compressible Euler equations with constant-coefficient damping.",2007.14802v2
2020-08-03,Improvement on the blow-up of the wave equation with the scale-invariant damping and combined nonlinearities,"We consider in this article the damped wave equation, in the
\textit{scale-invariant case} with combined two nonlinearities, which reads as
follows: \begin{displaymath} \d (E) \hspace{1cm} u_{tt}-\Delta
u+\frac{\mu}{1+t}u_t=|u_t|^p+|u|^q, \quad \mbox{in}\ \R^N\times[0,\infty),
\end{displaymath} with small initial data.\\ Compared to our previous work
\cite{Our}, we show in this article that the first hypothesis on the damping
coefficient $\mu$, namely $\mu < \frac{N(q-1)}{2}$, can be removed, and the
second one can be extended from $(0, \mu_*/2)$ to $(0, \mu_*)$ where $\mu_*>0$
is solution of $(q-1)\left((N+\mu_*-1)p-2\right) = 4$. Indeed, owing to a
better understanding of the influence of the damping term in the global
dynamics of the solution, we think that this new interval for $\mu$ describe
better the threshold between the blow-up and the global existence regions.
Moreover, taking advantage of the techniques employed in the problem $(E)$, we
also improve the result in \cite{LT2,Palmieri} in relationship with the Glassey
conjecture for the solution of $(E)$ but without the nonlinear term $|u|^q$.
More precisely, we extend the blow-up region from $p \in (1, p_G(N+\sigma)]$,
where $\sigma$ is given by \eqref{sigma} below, to $p \in (1, p_G(N+\mu)]$
giving thus a better estimate of the lifespan in this case.",2008.02109v3
2020-08-26,Quantum Lifshitz points and fluctuation-induced first-order phase transitions in imbalanced Fermi mixtures,"We perform a detailed analysis of the phase transition between the uniform
superfluid and normal phases in spin- and mass-imbalanced Fermi mixtures. At
mean-field level we demonstrate that at temperature $T\to 0$ the gradient term
in the effective action can be tuned to zero for experimentally relevant sets
of parameters, thus providing an avenue to realize a quantum Lifshitz point. We
subsequently analyze damping processes affecting the order-parameter field
across the phase transition. We show that, in the low energy limit, Landau
damping occurs only in the symmetry-broken phase and affects exclusively the
longitudinal component of the order-parameter field. It is however unavoidably
present in the immediate vicinity of the phase transition at temperature $T=0$.
We subsequently perform a renormalization-group analysis of the system in a
situation, where, at mean-field level, the quantum phase transition is second
order (and not multicritical). We find that, at $T$ sufficiently low, including
the Landau damping term in a form derived from the microscopic action
destabilizes the renormalization group flow towards the Wilson-Fisher fixed
point. This signals a possible tendency to drive the transition weakly
first-order by the coupling between the order-parameter fluctuations and
fermionic excitations effectively captured by the Landau damping contribution
to the order-parameter action.",2008.11782v1
2020-09-10,Electron Landau Damping of Kinetic Alfvén Waves in Simulated Magnetosheath Turbulence,"Turbulence is thought to play a role in the heating of the solar wind plasma,
though many questions remain to be solved regarding the exact nature of the
mechanisms driving this process in the heliosphere. In particular, the physics
of the collisionless interactions between particles and turbulent
electromagnetic fields in the kinetic dissipation range of the turbulent
cascade remains incompletely understood. A recent analysis of an interval of
Magnetosphere Multiscale (MMS) observations has used the field-particle
correlation technique to demonstrate that electron Landau damping is involved
in the dissipation of turbulence in the Earth's magnetosheath. Motivated by
this discovery, we perform a high-resolution gyrokinetic numerical simulation
of the turbulence in the MMS interval to investigate the role of electron
Landau damping in the dissipation of turbulent energy. We employ the
field-particle correlation technique on our simulation data, compare our
results to the known velocity-space signatures of Landau damping outside the
dissipation range, and evaluate the net electron energization. We find
qualitative agreement between the numerical and observational results for some
key aspects of the energization and speculate on the nature of disagreements in
light of experimental factors, such as differences in resolution, and of
developing insights into the nature of field-particle interactions in the
presence of dispersive kinetic Alfv\'en waves.",2009.05010v1
2020-11-09,Plasmon energy losses in shear bands of metallic glass,"Shear bands resulting from plastic deformation in cold-rolled
Al$_{88}$Y$_{7}$Fe$_{5}$ metallic glass were observed to display alternating
density changes along their propagation direction. Electron-energy loss
spectroscopy (EELS) was used to investigate the volume plasmon energy losses in
and around shear bands. Energy shifts of the peak centre and changes in the
peak width (FWHM) reflecting the damping were precisely determined within an
accuracy of a few meV using an open source python module (Hyperspy) to fit the
shapes of the plasmon and zero-loss peaks with Lorentzian functions. The
maximum bulk plasmon energy shifts were calculated for the bright and dark
shear band segments relative to the matrix to be about 38 and 14 meV,
respectively. The damping was observed to be larger for the denser regions. The
analysis presented here suggests that the changes in the plasmons are caused by
two contributions: (i) Variable damping in the shear band segments due to
changes in the medium-range order (MRO). This affects the static structure
factor S(k), which, in turn, leads to either reduced or increased damping
according to the Ziman-Baym formula. (ii) The ionic density and the effective
electron mass appearing in the zero-momentum plasmon frequency formula
$E_p(q=0)$ are coupled and give rise to small variations in the plasmon energy.
The model predicts plasmon energy shifts in the order of meV.",2011.04396v3
2020-11-16,Thresholds for loss of Landau damping in longitudinal plane,"Landau damping mechanism plays a crucial role in providing single-bunch
stability in LHC, High-Luminosity LHC, other existing as well as previous and
future (like FCC) circular hadron accelerators. In this paper, the thresholds
for the loss of Landau damping (LLD) in the longitudinal plane are derived
analytically using the Lebedev matrix equation (1968) and the concept of the
emerged van Kampen modes (1983). We have found that for the commonly-used
particle distribution functions from a binomial family, the LLD threshold
vanishes in the presence of the constant inductive impedance Im$Z/k$ above
transition energy. Thus, the effect of the cutoff frequency or the resonant
frequency of a broad-band impedance on beam dynamics is studied in detail. The
findings are confirmed by direct numerical solutions of the Lebedev equation as
well as using the Oide-Yokoya method (1990). Moreover, the characteristics,
which are important for beam operation, as the amplitude of residual
oscillations and the damping time after a kick (or injection errors) are
considered both above and below the threshold. Dependence of the threshold on
particle distribution in the longitudinal phase space is also analyzed,
including some special cases with a non-zero threshold for Im$Z/k = const$. All
main results are confirmed by macro-particle simulations and consistent with
available beam measurements in the LHC.",2011.07985v1
2020-12-04,Quantum Circuits for Collective Amplitude Damping in Two-Qubit Systems,"Quantum computers have now appeared in our society and are utilized for the
investigation of science and engineering. At present, they have been built as
intermediate-size computers containing about fifty qubits and are weak against
noise effects. Hence, they are called noisy-intermediate scale quantum devices.
In order to accomplish efficient quantum computation with using these machines,
a key issue is going to be the coherent control of individual and collective
quantum noises. In this work, we focus on a latter type and investigate
formulations of the collective quantum noises represented as quantum circuits.
To simplify our discussions and make them concrete, we analyze collective
amplitude damping processes in two-qubit systems. As verifications of our
formalisms and the quantum circuits, we demonstrate digital quantum simulations
of the collective amplitude damping by examining six different initial
conditions with varying the number of execution of an overall operation for our
quantum simulations. We observe that our results show good numerical matching
with the solution of quantum master equation for the two-qubit systems as we
increase such a number. In addition, we explain the essence of the way to
extend our formalisms to analyze the collective amplitude damping in larger
qubit systems. These results pave the way for establishing systematic
approaches to control the quantum noises and designing large-scale quantum
computers.",2012.02410v1
2020-12-10,Dimensional analysis of spring-wing systems reveals performance metrics for resonant flapping-wing flight,"Flapping-wing insects, birds, and robots are thought to offset the high power
cost of oscillatory wing motion by using elastic elements for energy storage
and return. Insects possess highly resilient elastic regions in their flight
anatomy that may enable high dynamic efficiency. However, recent experiments
highlight losses due to damping in the insect thorax that could reduce the
benefit of those elastic elements. We performed experiments on, and simulations
of a dynamically-scaled robophysical flapping model with an elastic element and
biologically-relevant structural damping to elucidate the roles of body
mechanics, aerodynamics, and actuation in spring-wing energetics. We measured
oscillatory flapping wing dynamics and energetics subject to a range of
actuation parameters, system inertia, and spring elasticity. To generalize
these results, we derive the non-dimensional spring-wing equation of motion and
present variables that describe the resonance properties of flapping systems:
$N$, a measure of the relative influence of inertia and aerodynamics, and
$\hat{K}$, the reduced stiffness. We show that internal damping scales with
$N$, revealing that dynamic efficiency monotonically decreases with increasing
$N$. Based on these results, we introduce a general framework for understanding
the roles of internal damping, aerodynamic and inertial forces, and elastic
structures within all spring-wing systems.",2012.05428v1
2021-01-22,Measurements and analysis of response function of cold atoms in optical molasses,"We report our experimental measurements and theoretical analysis of the
position response function of a cloud of cold atoms residing in the viscous
medium of an optical molasses and confined by a magneto-optical trap (MOT). We
measure the position response function by applying a transient homogeneous
magnetic field as a perturbing force. We observe a transition from a damped
oscillatory motion to an over-damped relaxation, stemming from a competition
between the viscous drag provided by the optical molasses and the restoring
force of the MOT. Our observations are in both qualitative and quantitative
agreement with the predictions of a theoretical model based on the Langevin
equation. As a consistency check, and as a prototype for future experiments, we
also study the free diffusive spreading of the atomic cloud in our optical
molasses with the confining magnetic field of the MOT turned off. We find that
the measured value of the diffusion coefficient agrees with the value predicted
by our Langevin model, using the damping coefficient. The damping coefficient
was deduced from our measurements of the position response function at the same
temperature.",2101.09118v2
2021-03-11,Nontrivial damping of quantum many-body dynamics,"Understanding how the dynamics of a given quantum system with many degrees of
freedom is altered by the presence of a generic perturbation is a notoriously
difficult question. Recent works predict that, in the overwhelming majority of
cases, the unperturbed dynamics is just damped by a simple function, e.g.,
exponentially as expected from Fermi's golden rule. While these predictions
rely on random-matrix arguments and typicality, they can only be verified for a
specific physical situation by comparing to the actual solution or measurement.
Crucially, it also remains unclear how frequent and under which conditions
counterexamples to the typical behavior occur. In this work, we discuss this
question from the perspective of projection-operator techniques, where
exponential damping of a density matrix occurs in the interaction picture but
not necessarily in the Schr\""odinger picture. We show that a nontrivial damping
in the Schr\""odinger picture can emerge if the dynamics in the unperturbed
system possesses rich features, for instance due to the presence of strong
interactions. This suggestion has consequences for the time dependence of
correlation functions. We substantiate our theoretical arguments by large-scale
numerical simulations of charge transport in the extended Fermi-Hubbard chain,
where the nearest-neighbor interactions are treated as a perturbation to the
integrable reference system.",2103.06646v2
2021-03-24,"Multimode piezoelectric shunt damping of thin plates with arrays of separately shunted patches, method, and experimental validation","Two-dimensional thin plates are widely used in many applications. Shunt
damping is a promising way for the attenuation of vibration of these
electromechanical systems. It enables a compact vibration damping method
without adding significant mass and volumetric occupancy. Analyzing the
dynamics of such electromechanical systems requires precise modeling tools that
properly consider the coupling between the piezoelectric elements and the host
structure. Although the concept of shunt damping has been studied extensively
in the literature, most of the studies do not provide a formulation for
modeling the multiple piezoelectric patches that are scattered on the host
structure and shunted separately. This paper presents a methodology and a
formulation for separately shunted piezoelectric patches for achieving higher
performance on vibration attenuation. The Rayleigh-Ritz method is used for
performing modal analysis and obtaining the frequency response functions of the
electro-mechanical system. The developed model includes mass and stiffness
contribution of the piezoelectric patches as well as the electromechanical
coupling effect. In this study, the piezoelectric patches are shunted via
separate electrical circuits and compared with the ones those are shunted via
interconnected electrical circuits. For verification, system-level finite
element simulations are performed in ANSYS software and compared with the
analytical model results. An experimental setup is also built to validate the
performance of the separately shunted piezoelectric patches. The effectiveness
of the method is investigated for a broader range of frequencies and it was
shown that separately shunted piezoelectric patches are more effective compared
to connected for a wide range of frequencies.",2103.13179v1
2021-03-29,Nonequilibrium Dynamics of the Chiral Quark Condensate under a Strong Magnetic Field,"Strong magnetic fields impact quantum-chromodynamics (QCD) properties in
several situations; examples include the early universe, magnetars, and
heavy-ion collisions. These examples share a common trait: time evolution. A
prominent QCD property impacted by a strong magnetic field is the quark
condensate, an approximate order parameter of the QCD transition between a
high-temperature quark-gluon phase and a low-temperature hadronic phase. We use
the linear sigma model with quarks to address the quark condensate time
evolution under a strong magnetic field. We use the closed time path formalism
of nonequilibrium quantum field theory to integrate out the quarks and obtain a
mean-field Langevin equation for the condensate. The Langevin equation features
dissipation and noise kernels controlled by a damping coefficient. We compute
the damping coefficient for magnetic field and temperature values achieved in
peripheral relativistic heavy-ion collisions and solve the Langevin equation
for a temperature quench scenario. The magnetic field changes the dissipation
and noise pattern by increasing the damping coefficient compared to the
zero-field case. An increased damping coefficient increases fluctuations and
time scales controlling condensate's short-time evolution, a feature that can
impact hadron formation at the QCD transition. The formalism developed here can
be extended to include other order parameters, hydrodynamic modes, and system's
expansion to address magnetic field effects in complex settings as heavy-ion
collisions, the early universe, and magnetars.",2103.15665v1
2021-04-09,Taming the pinch singularities in the two-loop neutrino self-energy in a medium,"We consider the calculation of the thermal self-energy of a neutrino that
propagates in a medium composed of fermions and scalars interacting via a
Yukawa-type coupling, in the case that the neutri no energy is much larger than
the fermion and scalar masses, as well as the temperature and chemical
potentials of the background. In this kinematic regime the one-loop
contribution to the imaginary part of the self-energy is negligible. We
consider the two-loop contribution and we encounter the so-called pinch
singularities which are known to arise in higher loop self-energy calculations
in Thermal Field Theory. With a judicious use of the properties and
parametrizations of the thermal propagators the singularities are treated
effectively and actually disappear. From the imaginary part of the self-energy,
we obtain a precise formula for the damping matrix expressed in terms of
integrals over the background particle distributions. The formulas predict a
specific dependence of the damping terms on the neutrino energy, depending on
the background conditions. For guidance to estimating the effects in specific
contexts, we compute the damping terms for several limiting cases of the
momentum distribution functions of the background particles. We discuss briefly
the connection between the results of our calculations for the damping matrix
and the decoherence effects described in terms of the Lindblad equation.",2104.04459v2
2021-06-20,Life-cycle assessment for flutter probability of a long-span suspension bridge based on field monitoring data,"Assessment of structural safety status is of paramount importance for
existing bridges, where accurate evaluation of flutter probability is essential
for long-span bridges. In current engineering practice, at the design stage,
flutter critical wind speed is usually estimated by the wind tunnel test, which
is sensitive to modal frequencies and damping ratios. After construction,
structural properties of existing structures will change with time due to
various factors, such as structural deteriorations and periodic environments.
The structural dynamic properties, such as modal frequencies and damping
ratios, cannot be considered as the same values as the initial ones, and the
deteriorations should be included when estimating the life-cycle flutter
probability. This paper proposes an evaluation framework to assess the
life-cycle flutter probability of long-span bridges considering the
deteriorations of structural properties, based on field monitoring data. The
Bayesian approach is employed for modal identification of a suspension bridge
with the main span of 1650 m, and the field monitoring data during 2010-2015 is
analyzed to determine the deterioration functions of modal frequencies and
damping ratios, as well as their inter-seasonal fluctuations. According to the
historical trend, the long-term structural properties can be predicted, and the
probability distributions of flutter critical wind speed for each year in the
long term are calculated. Consequently, the life-cycle flutter probability is
estimated, based on the predicted modal frequencies and damping ratios.",2106.10694v1
2021-07-17,Theoretical and numerical study of vibrational resonance in a damped softening Duffing oscillator,"We study the possibility of occurrence of vibrational resonance in a
softening Duffing oscillator in the underdamped and overdamped cases both
theoretically as well as numerically. The oscillator is driven by two periodic
forces. Numerically we find that in the underdamped case two oscillatory
solutions are obtained in a limited range of the parameters considered (damping
coefficient and amplitude of the high frequency force) for a fixed frequency
and amplitude of the low frequency periodic force depending on the initial
conditions. These solutions have distinct response amplitude to the low
frequency force. When damping is gradually increased, only one oscillatory
solution is observed. Vibrational resonance is observed in both the regions of
oscillation. The analytical approximation yields only one oscillatory solution
for all damping values. Analytically, the peak in the area bounded by the phase
portrait as a function of the amplitude of the high frequency force is
connected to vibrational resonance. Also, the values of the frequency of the
low frequency forcing and the amplitude of the high frequency forcing at which
vibrational resonance is found to occur are obtained. In the overdamped case,
vibrational resonance is not observed for the softening Duffing oscillator thus
showing a marked contrast to the overdamped bistable oscillator",2107.08302v1
2021-07-28,Optimal gamma-ray selections for monochromatic line searches with DAMPE,"The DArk Matter Particle Explorer (DAMPE) is a space high-energy cosmic-ray
detector covering a wide energy band with a high energy resolution. One of the
key scientific goals of DAMPE is to carry out indirect detection of dark matter
by searching for high-energy gamma-ray line structure. To promote the
sensitivity of gamma-ray line search with DAMPE, it is crucial to improve the
acceptance and energy resolution of gamma-ray photons. In this paper, we
quantitatively prove that the photon sample with the largest ratio of
acceptance to energy resolution is optimal for line search. We therefore
develop a line-search sample specifically optimized for the line search.
Meanwhile, in order to increase the statistics, we also selected the so called
BGO-only photons that convert into $e^+e^-$ pairs only in the BGO calorimeter.
The standard, the line-search, and the BGO-only photon samples are then tested
for line search individually and collectively. The results show that a
significantly improved limit could be obtained from an appropriate combination
of the date sets, and the increase is about 20\% for the highest case compared
with using the standard sample only.",2107.13208v2
2021-07-28,Magnetic field induced asymmetric splitting of the output signal,"In this paper we have investigated the dynamics of a damped harmonic
oscillator in the presence of an electromagnetic field. The transients for the
two dimensional harmonic oscillator imply about the modulation of the frequency
of the oscillator by the velocity dependent non conservative force from an
applied magnetic field. Except a special condition, the motion is in general
quasi periodic nature even in the absence of damping. Another interesting
finding is that the magnetic field may induce an asymmetric splitting of the
spectrum of the output signal with two peaks in the case of a driven damped two
dimensional harmonic oscillator. One more additional peak may appear for the
three dimensional case. In some cases the spectrum may have similarity with the
Normal Zeeman Effect. At the same time one may observe to appear the anti
resonance phenomenon even for the driven damped cyclotron motion where the
system with the purely non conservative force fields is driven by an electric
field. Finally, our calculation exhibits how the magnetic field can modulate
the phase difference (between input and output signals) and the efficiency like
quantity of the energy storing process. Thus the present study might be
applicable in the areas related to the refractive index, the barrier crossing
dynamics and autonomous stochastic resonance, respectively.",2107.13305v1
2021-07-28,Evolution of a Mode of Oscillation Within Turbulent Accretion Disks,"We investigate the effects of subsonic turbulence on a normal mode of
oscillation [a possible origin of the high-frequency quasi-periodic
oscillations (HFQPOs) within some black hole accretion disks]. We consider
perturbations of a time-dependent background (steady state disk plus
turbulence), obtaining an oscillator equation with stochastic damping, (mildly)
nonlinear restoring, and stochastic driving forces. The (long-term) mean values
of our turbulent functions vanish. In particular, turbulence does not damp the
oscillation modes, so `turbulent viscosity' is not operative. However, the
frequency components of the turbulent driving force near that of the mode can
produce significant changes in the amplitude of the mode. Even with an
additional (phenomenological constant) source of damping, this leads to an
eventual `blowout' (onset of effects of nonlinearity) if the turbulence is
sufficiently strong or the damping constant is sufficiently small. The
infrequent large increases in the energy of the mode could be related to the
observed low duty cycles of the HFQPOs. The width of the peak in the power
spectral density (PSD) is proportional to the amount of nonlinearity. A
comparison with observed continuum PSDs indicates the conditions required for
visibility of the mode.",2107.13546v1
2021-07-31,Oscillating scalar dissipating in a medium,"We study how oscillations of a scalar field condensate are damped due to
dissipative effects in a thermal medium. Our starting point is a non-linear and
non-local condensate equation of motion descending from a 2PI-resummed
effective action derived in the Schwinger-Keldysh formalism appropriate for
non-equilibrium quantum field theory. We solve this non-local equation by means
of multiple-scale perturbation theory appropriate for time-dependent systems,
obtaining approximate analytic solutions valid for very long times. The
non-linear effects lead to power-law damping of oscillations, that at late
times transition to exponentially damped ones characteristic for linear
systems. These solutions describe the evolution very well, as we demonstrate
numerically in a number of examples. We then approximate the non-local equation
of motion by a Markovianised one, resolving the ambiguities appearing in the
process, and solve it utilizing the same methods to find the very same leading
approximate solution. This comparison justifies the use of Markovian equations
at leading order. The standard time-dependent perturbation theory in comparison
is not capable of describing the non-linear condensate evolution beyond the
early time regime of negligible damping. The macroscopic evolution of the
condensate is interpreted in terms of microphysical particle processes. Our
results have implications for the quantitative description of the decay of
cosmological scalar fields in the early Universe, and may also be applied to
other physical systems.",2108.00254v1
2021-08-02,Large-amplitude longitudinal oscillations in solar prominences simulated with different resolutions,"Large-amplitude longitudinal oscillations (LALOs) in solar prominences have
been widely studied in the last decades. However, their damping and
amplification mechanisms are not well understood. In this study, we investigate
the attenuation and amplification of LALOs using high-resolution numerical
simulations with progressively increasing spatial resolutions. We performed
time-dependent numerical simulations of LALOs using the 2D magnetic
configuration that contains a dipped region. After the prominence mass loading
in the magnetic dips, we triggered LALOs by perturbing the prominence mass
along the magnetic field. We performed the experiments with four values of
spatial resolution. In the simulations with the highest resolution, the period
shows a good agreement with the pendulum model. The convergence experiment
revealed that the damping time saturates at the bottom prominence region with
improving the resolution, indicating the existence of a physical reason for the
damping of oscillations. At the prominence top, the oscillations are amplified
during the first minutes and then are slowly attenuated. The characteristic
time suggests more significant amplification in the experiments with the
highest spatial resolution. The analysis revealed that the energy exchange
between the bottom and top prominence regions is responsible for the
attenuation and amplification of LALOs. The high-resolution experiments are
crucial for the study of the periods and the damping mechanism of LALOs. The
period agrees with the pendulum model only when using high enough spatial
resolution. The results suggest that numerical diffusion in simulations with
insufficient spatial resolution can hide important physical mechanisms, such as
amplification of oscillations.",2108.01143v1
2021-08-05,Complexity analysis of quantum teleportation via different entangled channels in the presence of noise,"Quantum communication is one of the hot topics in quantum computing, where
teleportation of a quantum state has a slight edge and gained significant
attention from researchers. A large number of teleportation schemes have
already been introduced so far. Here, we compare the teleportation of a single
qubit message among different entangled channels such as the two-qubit Bell
channel, three-qubit GHZ channel, two- and three-qubit cluster states, the
highly entangled five-qubit Brown \emph{et al.} state and the six-qubit Borras
\emph{et al.} state. We calculate and compare the quantum costs in each of the
cases. Furthermore, we study the effects of six noise models, namely bit-flip
noise, phase-flip noise, bit-phase flip noise, amplitude damping, phase damping
and the depolarizing error that may affect the communication channel used for
the teleportation. An investigation on the variation of the initial state's
fidelity with respect to the teleported state in the presence of the noise
model is performed. A visual representation of the variation of fidelity for
various values of the noise parameter $\eta$ is done through a graph plot. It
is observed that as the value of noise parameter in the range $\eta \in
[0,0.5]$, the fidelity decreases in all the entangled channels under all the
noise models. After that, in the Bell channel, GHZ channel and three-qubit
cluster state channel, the fidelity shows an upward trend under all the noise
models. However, in the other three channels, the fidelity substantially
decreases in the case of amplitude damping, phase damping and depolarizing
noise, and even it reaches zero for $\eta = 1$ in Brown \emph{et al.} and
Borras \emph{et al.} channels.",2108.02641v1
2021-08-06,Noncontact friction: Role of phonon damping and its nonuniversality,"While obtaining theoretical predictions for dissipation during sliding motion
is a difficult task, one regime that allows for analytical results is the
so-called noncontact regime, where a probe is weakly interacting with the
surface over which it moves. Studying this regime for a model crystal, we
extend previously obtained analytical results and confirm them quantitatively
via particle based computer simulations. Accessing the subtle regime of weak
coupling in simulations is possible via use of Green-Kubo relations. The
analysis allows to extract and compare the two paradigmatic mechanisms that
have been found to lead to dissipation: phonon radiation, prevailing even in a
purely elastic solid, and phonon damping, e.g., caused by viscous motion of
crystal atoms. While phonon radiation is dominant at large probe-surface
distances, phonon damping dominates at small distances. Phonon radiation is
furthermore a pairwise additive phenomenon so that the dissipation due to
interaction with different parts (areas) of the surface adds up. This additive
scaling results from a general one-to-one mapping between the mean
probe-surface force and the friction due to phonon radiation, irrespective of
the nature of the underlying pair interaction. In contrast, phonon damping is
strongly nonadditive, and no such general relation exists. We show that for
certain cases, the dissipation can even {\it decrease} with increasing surface
area the probe interacts with. The above properties, which are rooted in the
spatial correlations of surface fluctuations, are expected to have important
consequences when interpreting experimental measurements, as well as scaling
with system size.",2108.03025v3
2021-09-14,Design of a HOM-Damped 166.6 MHz Compact Quarter-Wave beta=1 Superconducting Cavity for High Energy Photon Source,"Superconducting cavities with low RF frequencies and heavy damping of higher
order modes (HOM) are desired for the main accelerator of High Energy Photon
Source (HEPS), a 6 GeV synchrotron light source promising ultralow emittance
currently under construction in Beijing. A compact 166.6 MHz superconducting
cavity was proposed adopting a quarter-wave beta=1 geometry. Based on the
successful development of a proof-of-principle cavity, a HOM-damped 166.6 MHz
compact superconducting cavity was subsequently designed. A ferrite damper was
installed on the beam pipe to reduce HOM impedance below the stringent
threshold of coupled-bunch instabilities. Being compact, RF field heating on
the cavity vacuum seal was carefully examined against quenching the NbTi
flange. The cavity was later dressed with a helium vessel and the tuning
mechanism was also realized. Excellent RF and mechanical properties were
eventually achieved. Finally, the two-cavity string was designed to ensure
smooth transitions among components and proper shielding of synchrotron light.
This paper presents a complete design of a fully dressed HOM-damped
low-frequency beta=1 superconducting cavity for HEPS.",2109.06560v1
2021-11-13,Effects of microplastics and surfactants on surface roughness of water waves,"In this paper, we study the flow physics underlying the recently developed
remote sensing capability of detecting oceanic microplastics, which is based on
the measurable surface roughness reduction induced by the presence of
microplastics on the ocean surface. In particular, we are interested in whether
this roughness reduction is caused by the microplastics as floating particles,
or by the surfactants which follow similar transport paths as microplastics.
For this purpose, we experimentally test the effects of floating particles and
surfactants on surface roughness, quantified by the mean square slope (MSS),
with waves generated by a mechanical wave maker or by wind. For microplastics,
we find that their effect on wave energy and MSS critically depends on the
surface area fraction of coverage, irrespective of the particle sizes in the
test range. The damping by particles is observed only for fractions above
$O(5-10\%)$, which is much higher than the realistic ocean condition. For
surfactants, their damping effect on mechanically generated irregular waves
generally increases with the concentration of surfactants, but no optimal
concentration corresponding to maximum damping is observed, in contrast to
previous studies based on monochromatic waves. In wind-wave experiments, the
presence of surfactants suppresses the wave generation, due to the combined
effects of reduced wind shear stress and increased wave damping. For the same
wind speed, the wind stress is identified to depend on the concentration of
surfactants with a power-law relation. The implications of these findings to
remote sensing are discussed.",2111.07021v1
2021-11-15,"Convergence Analysis of A Second-order Accurate, Linear Numerical Scheme for The Landau-Lifshitz Equation with Large Damping Parameters","A second order accurate, linear numerical method is analyzed for the
Landau-Lifshitz equation with large damping parameters. This equation describes
the dynamics of magnetization, with a non-convexity constraint of unit length
of the magnetization. The numerical method is based on the second-order
backward differentiation formula in time, combined with an implicit treatment
of the linear diffusion term and explicit extrapolation for the nonlinear
terms. Afterward, a projection step is applied to normalize the numerical
solution at a point-wise level. This numerical scheme has shown extensive
advantages in the practical computations for the physical model with large
damping parameters, which comes from the fact that only a linear system with
constant coefficients (independent of both time and the updated magnetization)
needs to be solved at each time step, and has greatly improved the numerical
efficiency. Meanwhile, a theoretical analysis for this linear numerical scheme
has not been available. In this paper, we provide a rigorous error estimate of
the numerical scheme, in the discrete $\ell^{\infty}(0,T; \ell^2) \cap
\ell^2(0,T; H_h^1)$ norm, under suitable regularity assumptions and reasonable
ratio between the time step-size and the spatial mesh-size. In particular, the
projection operation is nonlinear, and a stability estimate for the projection
step turns out to be highly challenging. Such a stability estimate is derived
in details, which will play an essential role in the convergence analysis for
the numerical scheme, if the damping parameter is greater than 3.",2111.07537v1
2021-11-17,United Nation Security Council in Quantum World: Experimental Realization of Quantum Anonymous Veto Protocols using IBM Quantum Computer,"United Nation (UN) security council has fifteen members, out of which five
permanent members of the council can use their veto power against any
unfavorable decision taken by the council. In certain situation, a member using
right to veto may prefer to remain anonymous. This need leads to the
requirement of the protocols for anonymous veto which can be viewed as a
special type of voting. Recently, a few protocols for quantum anonymous veto
have been designed which clearly show quantum advantages in ensuring anonymity
of the veto. However, none of the efficient protocols for quantum anonymous
veto have yet been experimentally realized. Here, we implement 2 of those
protocols for quantum anonymous veto using an IBM quantum computer named IBMQ
Casablanca and different quantum resources like Bell, GHZ and cluster states.
In this set of proof-of-principle experiments, it's observed that using the
present technology, a protocol for quantum anonymous veto can be realized
experimentally if the number of people who can veto remains small as in the
case of UN council. Further, it's observed that Bell state based protocol
implemented here performs better than the GHZ/cluster state based
implementation of the other protocol in an ideal scenario as well as in
presence of different types of noise (amplitude damping, phase damping,
depolarizing and bit-flip noise). In addition, it's observed that based on
diminishing impact on fidelity, different noise models studied here can be
ordered in ascending order as phase damping, amplitude damping, depolarizing,
bit-flip.",2111.09028v1
2021-12-03,The Importance of Electron Landau Damping for the Dissipation of Turbulent Energy in Terrestrial Magnetosheath Plasma,"Heliospheric plasma turbulence plays a key role in transferring the energy of
large-scale magnetic field and plasma flow fluctuations to smaller scales where
the energy can be dissipated, ultimately leading to plasma heating.
High-quality measurements of electromagnetic fields and electron velocity
distributions by the Magnetospheric Multiscale (MMS) mission in Earth's
magnetosheath present a unique opportunity to characterize plasma turbulence
and to determine the mechanisms responsible for its dissipation. We apply the
field-particle correlation technique to a set of twenty MMS magnetosheath
intervals to identify the dissipation mechanism and quantify the dissipation
rate. It is found that 95% of the intervals have velocity-space signatures of
electron Landau damping that are quantitatively consistent with linear kinetic
theory for the collisionless damping of kinetic Alfv\'en waves. About 75% of
the intervals contain asymmetric signatures, indicating a local imbalance of
kinetic Alfv\'en wave energy flux in one direction along the magnetic field
than the other. About one third of the intervals have an electron energization
rate with the same order-of-magnitude as the estimated turbulent cascade rate,
suggesting that electron Landau damping plays a significant, and sometimes
dominant, role in the dissipation of the turbulent energy in these
magnetosheath intervals.",2112.02171v1
2022-01-01,Extremely strong DLAs at high redshift: Gas cooling and H$_2$ formation,"We present a spectroscopic investigation with VLT/X-shooter of seven
candidate extremely strong damped Lyman-$\alpha$ absorption systems (ESDLAs,
$N(\text{HI})\ge 5\times 10^{21}$ cm$^{-2}$) observed along quasar sightlines.
We confirm the extremely high column densities, albeit slightly (0.1~dex) lower
than the original ESDLA definition for four systems. We measured low-ionisation
metal abundances and dust extinction for all systems. For two systems we also
found strong associated H$_2$ absorption $\log
N(\text{H$_2$)[cm$^{-2}$]}=18.16\pm0.03$ and $19.28\pm0.06$ at $z=3.26$ and
$2.25$ towards J2205+1021 and J2359+1354, respectively), while for the
remaining five we measured conservative upper limits on the H$_2$ column
densities of typically $\log N(\text{H$_2$)[cm$^{-2}$]}<17.3$. The increased
H$_2$ detection rate ($10-55$% at 68% confidence level) at high HI column
density compared to the overall damped Lyman-$\alpha$ population ($\sim 5-10$%)
confirms previous works. We find that these seven ESDLAs have similar observed
properties as those previously studied towards quasars and gamma-ray burst
afterglows, suggesting they probe inner regions of galaxies. We use the
abundance of ionised carbon in excited fine-structure level to calculate the
cooling rates through the CII $\lambda$158$\mu$m emission, and compare them
with the cooling rates from damped Lyman-$\alpha$ systems in the literature. We
find that the cooling rates distribution of ESDLAs also presents the same
bimodality as previously observed for the general (mostly lower HI column
density) damped Lyman-$\alpha$ population.",2201.00245v1
2022-01-05,Stability of the discrete time-crystalline order in spin-optomechanical and open cavity QED systems,"Discrete time crystals (DTC) have been demonstrated experimentally in several
different quantum systems in the past few years. Spin couplings and cavity
losses have been shown to play crucial roles for realizing DTC order in open
many-body systems out of equilibrium. Recently, it has been proposed that
eternal and transient DTC can be present with an open Floquet setup in the
thermodynamic limit and in the deep quantum regime with few qubits,
respectively. In this work, we consider the effects of spin damping and spin
dephasing on the DTC order in spin-optomechanical and open cavity systems in
which the spins can be all-to-all coupled. In the thermodynamic limit, it is
shown that the existence of dephasing can destroy the coherence of the system
and finally lead the system to its trivial steady state. Without dephasing,
eternal DTC is displayed in the weak damping regime, which may be destroyed by
increasing the all-to-all spin coupling or the spin damping. By contrast, the
all-to-all coupling is constructive to the DTC in the moderate damping regime.
We also focus on a model which can be experimentally realized by a suspended
hexagonal boron nitride (hBN) membrane with a few spin color centers under
microwave drive and Floquet magnetic field. Signatures of transient DTC
behavior are demonstrated in both weak and moderate dissipation regimes without
spin dephasing. Relevant experimental parameters are also discussed for
realizing transient DTC order in such an hBN optomechanical system.",2201.01568v2
2022-01-20,Sharp resolvent estimate for the Baouendi-Grushin operator and applications,"In this article we study the semiclassical resolvent estimate for the
non-selfadjoint Baouendi-Grushin operator on the two-dimensional torus
$\mathbb{T}^2=\mathbb{R}^2/(2\pi\mathbb{Z})^2$ with H\""older dampings. The
operator is subelliptic degenerating along the vertical direction at $x=0$. We
exhibit three different situations:
  (i) the damping region verifies the geometric control condition with respect
to both the non-degenerate Hamiltonian flow and the vertical subelliptic flow;
  (ii) the undamped region contains a horizontal strip;
  (iii) the undamped part is a line. In all of these situations, we obtain
sharp resolvent estimates. Consequently, we prove the optimal energy decay rate
for the associated damped waved equations. For (i) and (iii), our results are
in sharp contrast to the Laplace resolvent since the optimal bound is governed
by the quasimodes in the subelliptic regime. While for (ii), the optimality is
governed by the quasimodes in the elliptic regime, and the optimal energy decay
rate is the same as for the classical damped wave equation on $\mathbb{T}^2$.
  Our analysis contains the study of adapted two-microlocal semiclassical
measures, construction of quasimodes and refined Birkhoff normal-form
reductions in different regions of the phase-space. Of independent interest, we
also obtain the propagation theorem for semiclassical measures of quasimodes
microlocalized in the subelliptic regime.",2201.08189v2
2022-02-24,Coherence of ion cyclotron resonance for damping ion cyclotron waves in space plasmas,"Ion cyclotron resonance is one of the fundamental energy conversion processes
through field-particle interaction in collisionless plasmas. However, the key
evidence for ion cyclotron resonance (i.e., the coherence between
electromagnetic fields and the ion phase space density) and the resulting
damping of ion cyclotron waves (ICWs) has not yet been directly observed.
Investigating the high-quality measurements of space plasmas by the
Magnetospheric Multiscale (MMS) satellites, we find that both the wave
electromagnetic field vectors and the bulk velocity of the disturbed ion
velocity distribution rotate around the background magnetic field. Moreover, we
find that the absolute gyro-phase angle difference between the center of the
fluctuations in the ion velocity distribution functions and the wave electric
field vectors falls in the range of (0, 90) degrees, consistent with the
ongoing energy conversion from wave-fields to particles. By invoking plasma
kinetic theory, we demonstrate that the field-particle correlation for the
damping ion cyclotron waves in our theoretical model matches well with our
observations. Furthermore, the wave electric field vectors ($\delta
\mathbf{E'}_{\mathrm {wave,\perp}}$), the ion current density ($\delta
\mathbf{J}_\mathrm {i,\perp}$) and the energy transfer rate ($\delta
\mathbf{J}_\mathrm {i,\perp}\cdot \delta \mathbf{E'}_{\mathrm {wave,\perp}}$)
exhibit quasi-periodic oscillations, and the integrated work done by the
electromagnetic field on the ions are positive, indicates that ions are mainly
energized by the perpendicular component of the electric field via cyclotron
resonance. Therefore, our combined analysis of MMS observations and kinetic
theory provides direct, thorough, and comprehensive evidence for ICW damping in
space plasmas.",2202.11967v1
2022-03-15,Search for gamma-ray line signals around the black hole at the galactic center with DAMPE observation,"The adiabatic growth of a black hole (BH) may enhance the dark matter (DM)
density surrounding it, causing a spike in the DM density profile. The spike
around the supermassive BH at the center of the Milky Way may lead to a
dramatic enhancement of the gamma-ray flux of DM annihilation from the galactic
center (GC). In this work, we analyze the gamma-ray data of the innermost
region (i.e., the inner 1$^\circ$) of the GC to search for potential line-like
signals from the BH spike. Such line-like signals could be generated in the
process of DM particles annihilating into double photons. We adopt the
gamma-ray data from the Dark Matter Particle Explorer (DAMPE). Although the
DAMPE has a much smaller effective area than the Fermi-LAT, the gamma-ray line
search can benefit from its unprecedented high energy resolution. No
significant line-like signals are found in our analysis. We derive upper limits
on the cross section of the annihilation based on this non-detection. We find
that despite the DAMPE's small effective area for photon detection, we can
still place strong constraints on the cross section ($\left<\sigma
v\right>\lesssim10^{-27}\,{\rm cm^3\,s^{-1}}$) in the spike scenario due to the
very bright model-expected flux from the spike. Our results indicate that
either DM does not annihilate primarily through the $\gamma\gamma$ channel in
the mass range we considered or no sharp density spike is present at the GC.",2203.08078v1
2022-03-15,Optimal Damping with Hierarchical Adaptive Quadrature for Efficient Fourier Pricing of Multi-Asset Options in Lévy Models,"Efficiently pricing multi-asset options is a challenging problem in
quantitative finance. When the characteristic function is available,
Fourier-based methods are competitive compared to alternative techniques
because the integrand in the frequency space often has a higher regularity than
that in the physical space. However, when designing a numerical quadrature
method for most Fourier pricing approaches, two key aspects affecting the
numerical complexity should be carefully considered: (i) the choice of damping
parameters that ensure integrability and control the regularity class of the
integrand and (ii) the effective treatment of high dimensionality. We propose
an efficient numerical method for pricing European multi-asset options based on
two complementary ideas to address these challenges. First, we smooth the
Fourier integrand via an optimized choice of the damping parameters based on a
proposed optimization rule. Second, we employ sparsification and
dimension-adaptivity techniques to accelerate the convergence of the quadrature
in high dimensions. The extensive numerical study on basket and rainbow options
under the multivariate geometric Brownian motion and some L\'evy models
demonstrates the advantages of adaptivity and the damping rule on the numerical
complexity of quadrature methods. Moreover, for the tested two-asset examples,
the proposed approach outperforms the COS method in terms of computational
time. Finally, we show significant speed-up compared to the Monte Carlo method
for up to six dimensions.",2203.08196v4
2022-03-25,Nonlinear damped spatially periodic breathers and the emergence of soliton-like rogue waves,"The spatially periodic breather solutions (SPBs) of the nonlinear
Schr\""odinger equation, prominent in modeling rogue waves, are unstable. In
this paper we numerically investigate the effects of nonlinear dissipation and
higher order nonlinearities on the routes to stability of the SPBs in the
framework of the nonlinear damped higher order nonlinear Schr\""odinger
(NLD-HONLS) equation. The initial data used in the experiments are generated by
evaluating exact SPB solutions at time $T_0$. The number of instabilities of
the background Stokes wave and the damping strength are varied. The Floquet
spectral theory of the NLS equation is used to interpret and provide a
characterization of the perturbed dynamics in terms of nearby solutions of the
NLS equation. Significantly, as $T_0$ is varied, tiny bands of complex spectrum
are observed to pinch off in the Floquet decomposition of the NLD-HONLS data,
reflecting the breakup of the SPB into a waveform that is close to either a one
or two ""soliton-like"" structure. For wide ranges of $T_0$, i.e. for solutions
initialized in the early to middle stage of the development of the MI, all
rogue waves are observed to occur when the spectrum is close to a one or two
soliton-like state. When the solutions are initialized as the MI is saturating,
rogue waves also can occur after the spectrum has left a soliton-like state.
Other novel features arise due to nonlinear damping: enhanced asymmetry, two
timescales in the evolution of the spectrum and a delay in the growth of
instabilities due to frequency downshifting.",2203.13488v2
2022-03-25,Investigating the effect of noise channels on the quality of unitary t-designs,"Unitary t-designs have a wide variety of applications in quantum information
theory, such as quantum data encryption and randomised benchmarking. However,
experimental realisations of t-designs are subject to noise. Here we
investigate the effect of noise channels on the quality of single-qubit
t-designs. The noise channels we study are bit flips, phase flips, bit and
phase flips, phase damping, amplitude damping, and depolarising noise. We
consider two noise models: the first has noise applied before the t-design
unitary operations, while the second has noise applied after the unitary
operations. We show that the single-qubit 1-design is affected only by
amplitude damping, while numeric results obtained for the 2-, 3-, 4-, and
5-designs suggest that a 2t-design is significantly more sensitive to noise
than a (2t-1)-design and that, with the exception of amplitude damping, a
(2t+1)-design is as sensitive to noise as a 2t-design. Numeric results also
reveal substantial variations in sensitivity to noise throughout the Bloch
sphere. In particular, t-designs appear to be most sensitive to noise when
acting on pure states and least sensitive to noise for the maximally mixed
state. For depolarising noise, we show that our two noise models are
equivalent, and for the other noise channels, numeric results obtained for the
model where noise is applied after the unitaries reflect the transformation of
the noise channel into a depolarising channel, an effect exploited in
randomised benchmarking with 2-designs.",2203.13771v2
2022-04-25,Geometrical aspects of contact mechanical systems and field theories,"Many important theories in modern physics can be stated using differential
geometry. Symplectic geometry is the natural framework to deal with autonomous
Hamiltonian mechanics. This admits several generalizations for nonautonomous
systems, both regular and singular. Some of these extensions are the subject of
this thesis.
  Recently there has been a growing interest in studying dissipative mechanical
systems from a geometric perspective using contact geometry. In this thesis we
review what has been done in this topic and go deeper, studying symmetries and
dissipated quantities of contact systems, and developing the Skinner-Rusk
formalism for these systems.
  With regard to classical field theory, we introduce the notion of
k-precosymplectic manifold and use it to give a geometric description of
singular nonautonomous field theories. We also devise a constraint algorithm
for these systems.
  Field theories with damping are described through a modification of the De
Donder-Weyl Hamiltonian field theory. This is achieved by combining contact
geometry and k-symplectic structures, resulting in the k-contact formalism. We
introduce two notions of dissipation laws, generalizing the concept of
dissipated quantity. These developments are also applied to Lagrangian field
theory. The Skinner-Rusk formulation for k-contact systems is described in
detail and we show how to recover the Lagrangian and Hamiltonian formalisms
from it.
  Throughout the thesis we present several examples in mechanics and field
theory. The most remarkable mechanical examples are the damped harmonic
oscillator, the motion in a gravitational field with friction, the parachute
equation and the damped simple pendulum. In field theory, we study the damped
vibrating string, the Burgers' equation, the Klein-Gordon equation and its
relation with the telegrapher's equation, and the Maxwell's equations with
dissipation.",2204.11537v1
2022-06-20,Swinging a playground swing: torque controls for inducing sustained oscillations,"Models of a playground swing have been studied since the 1960s. However, in
most of them, the position of the swinger is controlled directly. This
simplifies the problem but hides the mechanics of torques applied to keep the
swing moving in a regular pattern. This article studies these mechanics. Two
models of a swing with torques as controls that we consider are identical to
popular models of modern robotics: the Acrobot and reaction wheel pendulum.
However, the control task of sustaining the swing's regular oscillations by a
static feedback control is new and challenging, especially when damping in the
joint connecting the swing to the frame is considered. We develop two types of
controls to accomplish this task. One works for small damping and is based on
linearizing the undamped system by a suitable preliminary feedback control. The
other works for large damping. In the steady state, the resulting closed-loop
system describes a harmonically driven damped pendulum (a simple system known
for its complex behavior), including chaotic motion for some parameter values.
To address such complexities, we build free parameters into the controls, then
adjust them based on simulations to avoid chaos and achieve regular
oscillations that are seen on playgrounds.",2206.09579v1
2022-07-01,Frequency beating and damping of breathing oscillations of a harmonically trapped one-dimensional quasicondensate,"We study the breathing (monopole) oscillations and their damping in a
harmonically trapped one-dimensional (1D) Bose gas in the quasicondensate
regime using a finite-temperature classical field approach. By characterising
the oscillations via the dynamics of the density profile's rms width over long
time, we find that the rms width displays beating of two distinct frequencies.
This means that 1D Bose gas oscillates not at a single breathing mode
frequency, as found in previous studies, but as a superposition of two distinct
breathing modes, one oscillating at frequency close to $\simeq\!\sqrt{3}\omega$
and the other at $\simeq\!2\omega$, where $\omega$ is the trap frequency. The
breathing mode at $\sim\!\sqrt{3}\omega$ dominates the beating at lower
temperatures, deep in the quasicondensate regime, and can be attributed to the
oscillations of the bulk of the density distribution comprised of particles
populating low-energy, highly-occupied states. The breathing mode at
$\simeq\!2\omega$, on the other hand, dominates the beating at higher
temperatures, close to the nearly ideal, degenerate Bose gas regime, and is
attributed to the oscillations of the tails of the density distribution
comprised of thermal particles in higher energy states. The two breathing modes
have distinct damping rates, with the damping rate of the bulk component being
approximately four times larger than that of the tails component.",2207.00209v2
2022-07-29,Coordinated control in multi-terminal VSC-HVDC systems to improve transient stability: Impact on electromechanical-oscillation damping,"Multi-terminal high-voltage Direct Current technology based on Voltage-Source
Converter stations (VSC-MTDC) is expected to be one of the most important
contributors to the future of electric power systems. In fact, among other
features, it has already been shown how this technology can contribute to
improve transient stability in power systems by the use of supplementary
controllers. Along this line, this paper will investigate in detail how these
supplementary controllers may affect electromechanical oscillations, by means
of small-signal stability analysis. The paper analyses two control strategies
based on the modulation of active-power injections (P-WAF) and reactive-power
injections (Q-WAF) in the VSC stations. Both control strategies use global
signals of the frequencies of the VSC-MTDC system and they presented
significant improvements on transient stability. The paper will provide
guidelines for the design of these type of controllers to improve both, large-
and small-disturbance angle stability. Small-signal stability techniques (in
Matlab) will be used to assess electromechanical-oscillation damping, while
non-linear time domain simulation (in PSS/E) will be used to confirm the
results. Results will be illustrated in Nordic32A test system with an embedded
VSC-MTDC system. The paper analyses the impact of the controller gains and
communication latency on electromechanical-oscillation damping. The main
conclusion of the paper is that transient-stability-tailored supplementary
controllers in VSC-MTDC systems can be tuned to damp inter-area oscillations
too, maintaining their effectiveness for transient-stability improvement.",2208.00083v1
2022-08-04,Thermoelastic Damping in MEMS Gyroscopes at High Frequencies,"Microelectromechanical systems (MEMS) gyroscopes are widely used, e.g. in
modern automotive and consumer applications, and require signal stability and
accuracy in rather harsh environmental conditions. In many use cases, device
reliability must be guaranteed under large external loads at high frequencies.
The sensitivity of the sensor to such external loads depends strongly on the
damping, or rather quality factor, of the high frequency mechanical modes of
the structure. In this paper, we investigate the influence of thermoelastic
damping on several high frequency modes by comparing finite element simulations
with measurements of the quality factor in an application-relevant temperature
range. We measure the quality factors over different temperatures in vacuum, to
extract the relevant thermoelastic material parameters of the polycrystalline
MEMS device. Our simulation results show a good agreement with the measured
quantities, therefore proving the applicability of our method for predictive
purposes in the MEMS design process. Overall, we are able to uniquely identify
the thermoelastic effects and show their significance for the damping of the
high frequency modes of an industrial MEMS gyroscope. Our approach is generic
and therefore easily applicable to any mechanical structure with many possible
applications in nano- and micromechanical systems.",2208.02591v2
2022-08-02,Motion of a parametrically driven damped coplanar double pendulum,"We present the results of linear stability of a damped coplanar double
pendulum and its non-linear motion, when the point of suspension is vibrated
sinusoidally in the vertical direction with amplitude $a$ and frequency $\omega
$. A double pendulum has two pairs of Floquet multipliers, which have been
calculated for various driving parameters. We have considered the stability of
a double pendulum when it is in any of its possible stationary states: (i) both
pendulums are either vertically downward or upward and (ii) one pendulum is
downward, and the other is upward. The damping is considered to be
velocity-dependent, and the driving frequency is taken in a wide range. A
double pendulum excited from its stable state shows both periodic and chaotic
motion. The periodic motion about its pivot may be either oscillatory or
rotational. The periodic swings of a driven double pendulum may be either
harmonic or subharmonic for lower values of $a$. The limit cycles corresponding
to the normal mode oscillations of a double pendulum of two equal masses are
squeezed into a line in its configuration space. For unequal masses, the
pendulum shows multi-period swings for smaller values of $a$ and damping, while
chaotic swings or rotational motion at relatively higher values of $a$. The
parametric driving may lead to stabilization of a partially or fully inverted
double pendulum.",2208.03292v2
2022-08-09,Simultaneous measurements of unstable and stable Alfvén Eigenmodes in JET,"In this paper, we report the novel experimental observation of both unstable
and stable Toroidicity-induced Alfv\'en Eigenmodes (TAEs) measured
simultaneously in a JET tokamak plasma. The three-ion-heating scheme
(D-DNBI-3He) is employed to accelerate deuterons to MeV energies, thereby
destabilizing TAEs with toroidal mode numbers n = 3-5, each decreasing in mode
amplitude. At the same time, the Alfv\'en Eigenmode Active Diagnostic
resonantly excites a stable n = 6 TAE with total normalized damping rate
$-\gamma/\omega_0 \approx$ 1%-4%. Hybrid kinetic-MHD modeling with codes NOVA-K
and MEGA both find eigenmodes with similar frequencies, mode structures, and
radial locations as in experiment. NOVA-K demonstrates good agreement with the
n = 3, 4, and 6 TAEs, matching the damping rate of the n = 6 mode within
uncertainties and identifying radiative damping as the dominant contribution.
Improved agreement is found with MEGA for all modes: the unstable n = 3-5 and
stable n = 2, 6 modes, with the latter two stabilized by higher intrinsic
damping and lower fast ion drive, respectively. While some discrepancies remain
to be resolved, this unique validation effort gives us confidence in TAE
stability predictions for future fusion devices.",2208.05052v1
2022-09-24,Deep Attentive Belief Propagation: Integrating Reasoning and Learning for Solving Constraint Optimization Problems,"Belief Propagation (BP) is an important message-passing algorithm for various
reasoning tasks over graphical models, including solving the Constraint
Optimization Problems (COPs). It has been shown that BP can achieve
state-of-the-art performance on various benchmarks by mixing old and new
messages before sending the new one, i.e., damping. However, existing methods
of tuning a static damping factor for BP not only are laborious but also harm
their performance. Moreover, existing BP algorithms treat each variable node's
neighbors equally when composing a new message, which also limits their
exploration ability. To address these issues, we seamlessly integrate BP, Gated
Recurrent Units (GRUs), and Graph Attention Networks (GATs) within the
message-passing framework to reason about dynamic weights and damping factors
for composing new BP messages. Our model, Deep Attentive Belief Propagation
(DABP), takes the factor graph and the BP messages in each iteration as the
input and infers the optimal weights and damping factors through GRUs and GATs,
followed by a multi-head attention layer. Furthermore, unlike existing
neural-based BP variants, we propose a novel self-supervised learning algorithm
for DABP with a smoothed solution cost, which does not require expensive
training labels and also avoids the common out-of-distribution issue through
efficient online learning. Extensive experiments show that our model
significantly outperforms state-of-the-art baselines.",2209.12000v1
2022-12-01,Slack-based tunable damping leads to a trade-off between robustness and efficiency in legged locomotion,"Animals run robustly in diverse terrain. This locomotion robustness is
puzzling because axon conduction velocity is limited to a few ten meters per
second. If reflex loops deliver sensory information with significant delays,
one would expect a destabilizing effect on sensorimotor control. Hence, an
alternative explanation describes a hierarchical structure of low-level
adaptive mechanics and high-level sensorimotor control to help mitigate the
effects of transmission delays. Motivated by the concept of an adaptive
mechanism triggering an immediate response, we developed a tunable physical
damper system. Our mechanism combines a tendon with adjustable slackness
connected to a physical damper. The slack damper allows adjustment of damping
force, onset timing, effective stroke, and energy dissipation. We characterize
the slack damper mechanism mounted to a legged robot controlled in open-loop
mode. The robot hops vertically and planar over varying terrains and
perturbations. During forward hopping, slack-based damping improves faster
perturbation recovery (up to 170%) at higher energetic cost (27%). The tunable
slack mechanism auto-engages the damper during perturbations, leading to a
perturbation-trigger damping, improving robustness at minimum energetic cost.
With the results from the slack damper mechanism, we propose a new functional
interpretation of animals' redundant muscle tendons as tunable dampers.",2212.00475v1
2022-12-22,Spin wave dispersion of ultra-low damping hematite ($α\text{-Fe}_2\text{O}_3$) at GHz frequencies,"Low magnetic damping and high group velocity of spin waves (SWs) or magnons
are two crucial parameters for functional magnonic devices. Magnonics research
on signal processing and wave-based computation at GHz frequencies focussed on
the artificial ferrimagnetic garnet Y$_3$Fe$_5$O$_{12}$ (YIG) so far. We report
on spin-wave spectroscopy studies performed on the natural mineral hematite
($\alpha\text{-Fe}_2\text{O}_3$) which is a canted antiferromagnet. By means of
broadband GHz spectroscopy and inelastic light scattering, we determine a
damping coefficient of $1.1\times10^{-5}$ and magnon group velocities of a few
10 km/s, respectively, at room temperature. Covering a large regime of wave
vectors up to $k\approx 24~{\rm rad}/\mu$m, we find the exchange stiffness
length to be relatively short and only about 1 \r{A}. In a small magnetic field
of 30 mT, the decay length of SWs is estimated to be 1.1 cm similar to the best
YIG. Still, inelastic light scattering provides surprisingly broad and partly
asymmetric resonance peaks. Their characteristic shape is induced by the large
group velocities, low damping and distribution of incident angles inside the
laser beam. Our results promote hematite as an alternative and sustainable
basis for magnonic devices with fast speeds and low losses based on a stable
natural mineral.",2212.11887v2
2023-01-19,Magnetoreological spring as element of vibration control system of dynamicly active equipment for biofuel production,"The development of vibration protection systems that ensure efficiency and
safety in the operation of process equipment and pipelines is one of the main
tasks of controlling the dynamic state of machines. One of the effective
methods of vibration isolation of the equipment of these installations is the
use of vibration mounts. Today, both passive and active methods of
extinguishing are actively used. The combination of two methods of damping will
ensure the stability and adaptability of vibration protection systems to the
operating conditions of process equipment. The paper presents and investigates
the device of a hybrid vibration support, including a magnetorheological
spring, as an element of vibration damping. A distinctive feature of the
vibration mount is an extended range of performance and reduced wear rate of
the components. An analysis of the damping characteristics of a hybrid
vibration support in passive and active modes of operation is presented. A
simulation model of the vibration support under consideration has been
developed in the MATLAB Simulink simulation environment using the PIB
controller. The simulation results indicate the effectiveness of the use of
vibration damping systems with a magnetorheological spring in conjunction with
various technological equipment.",2301.07911v1
2023-02-19,Collective Quantum Approach to Surface Plasmon Resonance Effect,"In this research we present a theory of the surface plasmon resonance (SPR)
effect based on the dual length-scale driven damped collective quantum
oscillations of the spill-out electrons in plasmonic material surface. The
metallic electron excitations are modeled using the Hermitian effective
Schr\""{o}dinger-Poisson system, whereas, the spill-out electron excitations are
modeled via the damped non-Hermitian effective Schr\""{o}dinger-Poisson system
adapted appropriately at the metal-vacuum interface. It is shows that, when
driven by external field, the system behaves like the driven damped oscillator
in wavenumber domain, quite analogous to the driven damped mechanical
oscillation in frequency domain, leading to the collective surface spill-out
electron excitation resonance. In this model the resonance occurs when the
wavenumber of the driving pseudoforce matches that of the surface plasmon
excitations which can be either due to single-electrons or collective effects.
Current theory of SPR is based on longitudinal electrostatic excitations of the
surface electrons, instead of the polariton excitation parallel to the
metal-dielectric or metal-vacuum surface. Current theory may also be extended
to use for the localized surface plasmon resonance (LSPR) in nanometer sized
metallic surfaces in non-planar geometry. A new equation of state (EoS) for the
plasmon electron number density in quantum plasmas is obtained which limits the
plasmonic effects in high-density low-temperature electron gas regime, due to
small transition probability of electrons to the plasmon energy band.",2302.13974v1
2023-03-01,Evolution of the eccentricity and inclination of low-mass planets subjected to thermal forces: a numerical study,"By means of three dimensional, high resolution hydrodynamical simulations we
study the orbital evolution of weakly eccentric or inclined low-mass
protoplanets embedded in gaseous discs subject to thermal diffusion. We
consider both non-luminous planets, and planets that also experience the
radiative feedback from their own luminosity. We compare our results to
previous analytical work, and find that thermal forces (the contribution to the
disc's force arising from thermal effects) match those predicted by linear
theory within $\sim 20$%. When the planet's luminosity exceeds a threshold
found to be within $10$% of that predicted by linear theory, its eccentricity
and inclination grow exponentially, whereas these quantities undergo a strong
damping below this threshold. In this regime of low luminosity indeed, thermal
diffusion cools the surroundings of the planet and allows gas to accumulate in
its vicinity. It is the dynamics of this gas excess that contributes to damp
eccentricity and inclination. The damping rates obtained can be up to $h^{-1}$
times larger than those due to the resonant interaction with the disc, where
$h$ is the disc's aspect ratio. This suggests that models that incorporate
planet-disc interactions using well-known formulae based on resonant
wave-launching to describe the evolution of eccentricity and inclination
underestimate the damping action of the disc on the eccentricity and
inclination of low-mass planets by an order of magnitude.",2303.00867v1
2023-03-13,Discriminative sEMG-based features to assess damping ability and interpret activation patterns in lower-limb muscles of ACLR athletes,"Objective: The main goal of the athletes who undergo anterior cruciate
ligament reconstruction (ACLR) surgery is a successful return-to-sport. At this
stage, identifying muscular deficits becomes important. Hence, in this study,
three discriminative features based on surface electromyographic signals (sEMG)
acquired in a dynamic protocol are introduced to assess the damping ability and
interpret activation patterns in lower-limb muscles of ACLR athletes. Methods:
The features include the median frequency of the power spectrum density (PSD),
the relative percentage of the equivalent damping or equivalent stiffness
derived from the median frequency, and the energy of the signals in the
time-frequency plane of the pseudo-Wigner-Ville distribution (PWVD). To
evaluate the features, 11 healthy and 11 ACLR athletes (6 months
post-reconstruction surgery) were recruited to acquire the sEMG signals from
the medial and the lateral parts of the hamstrings, quadriceps, and
gastrocnemius muscles in pre- and post-fatigue single-leg landings. Results: A
significant damping deficiency is observed in the hamstring muscles of ACLR
athletes by evaluating the proposed features. This deficiency indicates that
more attention should be paid to this muscle of ACLR athletes in
pre-return-to-sport rehabilitations. Conclusion: The quality of
electromyography-based pre-return-to-sport assessments on ACLR subjects depends
on the sEMG acquisition protocol, as well as the type and nature of the
extracted features. Hence, combinatorial application of both energy-based
features (derived from the PWVD) and power-based features (derived from the
PSD) could facilitate the assessment process by providing additional
biomechanical information regarding the behavior of the muscles surrounding the
knee.",2303.06954v1
2023-03-28,Search for damped oscillating structures from charged pion electromagnetic form factor data,"The damped oscillating structures recently revealed by a three parametric
formula from the proton ``effective'' form factor data extracted of the
measured total cross section $\sigma^{bare}_{tot}(e^+e^-\to p\bar p)$ still
seem to have an unknown origin. The conjectures of their direct manifestation
of the quark-gluon structure of the proton indicate that they are not specific
only of the proton and neutron, but they have to be one's own, similar to other
hadrons.
  Therefore, the oscillatory structures from the charged pion electromagnetic
form factor timelike data, extracted of the process $e^+e^-\to \pi^+ \pi^-$ are
investigated by using the same procedure as in the case of the proton.
  The analysis shows the appearance of the oscillating structures in the
description of the charged pion electromagnetic form factor timelike data by
three parametric formula with a rather large value of $\chi^2/ndf$, while the
description of the data by the physically well-founded Unitary and Analytic
model has not revealed any damped oscillating structures.
  From the obtained result on the most simple object of strong interactions,
one can conclude that damped oscillating structures received from the
``effective'' proton form factor data are probably generated by a utilization
of the improper three parametric formula which does not describe these data
with sufficient precision.",2303.16681v1
2023-05-15,Landau damping and the survival threshold,"In this paper, we establish the large time asymptotic behavior of solutions
to the linearized Vlasov-Poisson system near general spatially homogenous
equilibria $\mu(\frac12|v|^2)$ with connected support on the whole space
$\RR^3_x \times \RR^3_v$, including those that are non-monotone. The problem
can be solved completely mode by mode for each spatial wave number, and their
longtime dynamics is intimately tied to the ``survival threshold'' of wave
numbers computed by $$\kappa_0^2 = 4\pi \int_0^\Upsilon \frac{u^2\mu(\frac12
u^2)}{\Upsilon^2-u^2} \;du$$ where $\Upsilon$ is the maximal speed of particle
velocities. It is shown that purely oscillatory electric fields exist and obey
a Klein-Gordon's type dispersion relation for wave numbers below the threshold,
thus confirming the existence of Langmuir's oscillatory waves known in the
physical literature. At the threshold, the phase velocity of these oscillatory
waves enters the range of admissible particle velocities, namely there are
particles that move at the same propagation speed of the waves. It is this
exact resonant interaction between particles and the oscillatory fields that
causes the waves to be damped, classically known as Landau damping. Landau's
law of decay is explicitly computed and is sensitive to the decaying rate of
the background equilibria. The faster it decays at the maximal velocity, the
weaker Landau damping is. Beyond the threshold, the electric fields are a
perturbation of those generated by the free transport dynamics and thus decay
rapidly fast due to the phase mixing mechanism.",2305.08672v1
2023-06-04,Large Dynamical Tide Amplitudes from Small Kicks at Pericenter,"The effect of dynamical tide ``kicks"" on eccentric binary orbits is
considered using the orbital mapping method. It is demonstrated that when mode
damping is negligible the mode amplitude will generically grow in time for all
values of orbital eccentricity and semi-major axis, even for small kicks
outside the regime exhibiting diffusive growth. The origin of the small-kick
growth is the change in kick size from orbit to orbit, an effect quadratic in
the mode amplitude. When damping of the mode is included, the growth is shut
off when the damping time is shorter than the growth time. Hence, in practice,
kicks of sufficient size and long mode damping times are required for
interesting levels of growth to occur. Application to the circularization of
hot Jupiters is discussed. Previous investigations found that diffusive growth
of the planetary f-mode in the large-kick regime would lead to rapid orbital
shrinkage, but upon exiting the diffusive regime at $e \sim 0.9$ the theory
would predict a large population of highly eccentric orbits. Simulations
presented here show that subsequent orbital evolution relying on the small-kick
regime may further decrease the eccentricity to $e \sim 0.2$ on timescales much
less than the Gyrs ages of these systems.",2306.02382v1
2023-06-16,Damping of MHD Turbulence in A Partially Ionized Medium,"The coupling state between ions and neutrals in the interstellar medium plays
a key role in the dynamics of magnetohydrodynamic (MHD) turbulence, but is
challenging to study numerically. In this work, we investigate the damping of
MHD turbulence in a partially ionized medium using 3D two-fluid (ions+neutrals)
simulations generated with the AthenaK code. Specifically, we examine the
velocity, density, and magnetic field statistics of the two-fluid MHD
turbulence in different regimes of neutral-ion coupling. Our results
demonstrate that when ions and neutrals are strongly coupled, the velocity
statistics resemble those of single-fluid MHD turbulence. Both the velocity
structures and kinetic energy spectra of ions and neutrals are similar, while
their density structures can be significantly different. With an excess of
small-scale sharp density fluctuations in ions, the density spectrum in ions is
shallower than that of neutrals. When ions and neutrals are weakly coupled, the
turbulence in ions is more severely damped due to the ion-neutral collisional
friction than that in neutrals, resulting in a steep kinetic energy spectrum
and density spectrum in ions compared to the Kolmogorov spectrum. We also find
that the magnetic energy spectrum basically follows the shape of the kinetic
energy spectrum of ions, irrespective of the coupling regime. In addition, we
find large density fluctuations in ions and neutrals and thus spatially
inhomogeneous ionization fractions. As a result, the neutral-ion decoupling and
damping of MHD turbulence take place over a range of length scales.",2306.10010v2
2023-07-24,BGO quenching effect on spectral measurements of cosmic-ray nuclei in DAMPE experiment,"The Dark Matter Particle Explorer (DAMPE) is a satellite-borne detector
designed to measure high energy cosmic-rays and $\gamma$-rays. As a key
sub-detector of DAMPE, the Bismuth Germanium Oxide (BGO) imaging calorimeter is
utilized to measure the particle energy with a high resolution. The nonlinear
fluorescence response of BGO for large ionization energy deposition, known as
the quenching effect, results in an under-estimate of the energy measurement
for cosmic-ray nuclei. In this paper, various models are employed to
characterize the BGO quenching factors obtained from the experimental data of
DAMPE. Applying the proper quenching model in the detector simulation process,
we investigate the tuned energy responses for various nuclei and compare the
results based on two different simulation softwares, i.e. GEANT4 and FLUKA. The
BGO quenching effect results in a decrease of the measured energy by
approximately $2.5\%$ ($5.7 \%$) for carbon (iron) at $\sim$10 GeV/n and $<1\%$
above 1 TeV/n, respectively. Accordingly, the correction of the BGO quenching
effect leads to an increase of the low-energy flux measurement of cosmic-ray
nuclei.",2307.12629v1
2023-08-04,"Interplay of space charge, intrabeam scattering and synchrotron radiation in the Compact Linear Collider damping rings","Future ultra-low emittance rings for electron/positron colliders requiring
extremely high beam brightness can be limited by collective effects. In this
paper, the interplay of effects such as synchrotron radiation, intra-beam
scattering (IBS) and space charge in the vicinity of excited betatron
resonances is assessed. In this respect, two algorithms were developed to
simulate IBS and synchrotron radiation effects and integrated in the PyORBIT
tracking code, to be combined with its widely used space charge module. The
impact of these effects on the achievable beam parameters of the Compact Linear
Collider (CLIC) Damping Rings was studied, showing that synchrotron radiation
damping mitigates the adverse effects of IBS and space charge induced resonance
crossing. The studies include also a full dynamic simulation of the CLIC
damping ring cycle starting from the injection beam parameters. It is
demonstrated that a careful working point choice is necessary, in order to
accommodate the transition from a non-linear lattice induced detuning to a
space-charge dominated one and thereby avoid excessive losses and emittance
growth generated in the vicinity of strong resonances.",2308.02196v3
2023-08-04,Nonlinear wave damping by Kelvin-Helmholtz instability induced turbulence,"Magnetohydrodynamic kink waves naturally form as a consequence of
perturbations to a structured medium, for example transverse oscillations of
coronal loops. Linear theory has provided many insights in the evolution of
linear oscillations, and results from these models are often applied to infer
information about the solar corona from observed wave periods and damping
times. However, simulations show that nonlinear kink waves can host the
Kelvin-Helmholtz instability (KHi) which subsequently creates turbulence in the
loop, dynamics which are beyond linear models. In this paper we investigate the
evolution of KHi-induced turbulence on the surface of a flux tube where a
non-linear fundamental kink-mode has been excited. We control our numerical
experiment so that we induce the KHi without exciting resonant absorption. We
find two stages in the KHi turbulence dynamics. In the first stage, we show
that the classic model of a KHi turbulent layer growing $\propto t$is
applicable. We adapt this model to make accurate predictions for damping of the
oscillation and turbulent heating as a consequence of the KHi dynamics. In the
second stage, the now dominant turbulent motions are undergoing decay. We find
that the classic model of energy decay proportional to $t^{-2}$ approximately
holds and provides an accurate prediction of the heating in this phase. Our
results show that we can develop simple models for the turbulent evolution of a
non-linear kink wave, but the damping profiles produced are distinct from those
of linear theory that are commonly used to confront theory and observations.",2308.02217v2
2023-08-10,JWST observations of galaxy damping wings during reionization interpreted with cosmological simulations,"Spectra of the highest redshift galaxies taken with JWST are now allowing us
to see into the heart of the reionization epoch. Many of these observed
galaxies exhibit strong damping wing absorption redward of their Lyman-$\alpha$
emission. These observations have been used to measure the redshift evolution
of the neutral fraction of the intergalactic medium and sizes of ionized
bubbles. However, these estimates have been made using a simple analytic model
for the intergalactic damping wing. We explore the recent observations with
models of inhomogeneous reionization from the Sherwood-Relics simulation suite.
We carry out a comparison between the damping wings calculated from the
simulations and from the analytic model. We find that although the agreement is
good on the red side of the Lyman-$\alpha$ emission, there is a discrepancy on
the blue side due to residual neutral hydrogen present in the simulations,
which saturates the intergalactic absorption. For this reason, we find that it
is difficult to reproduce the claimed observations of large bubble sizes at z ~
7, which are driven by a detection of transmitted flux blueward of the
Lyman-$\alpha$ emission. We suggest instead that the observations can be
explained by a model with smaller ionized bubbles and larger intrinsic
Lyman-$\alpha$ emission from the host galaxy.",2308.05800v1
2023-08-23,Dynamics of pinned quantized vortices in superfluid $^4$He in a microelectromechanical oscillator,"We numerically studied the vortex dynamics at zero temperature in superfluid
$^4$He confined between two parallel rough solid boundaries, one of which
oscillates in a shear mode. This study was motivated by the experimental work
by Barquist $et$ $al.$ which employed a microelectromechanical systems (MEMS)
oscillator operating in superfluid $^4$He at a near-zero temperature. Their
experiments suggest that the motion of the MEMS oscillator is damped by
quantized vortices. In our study, we postulated that this damping effect was
closely associated with vortex pinning phenomena and developed pinning models.
Our primary objective is to understand the vortex dynamics in the presence of
pinning and to provide insight into the experimental observations regarding the
damping mechanism. We confirmed that Kelvin waves were excited in the pinned
vortices when the oscillation frequency of the solid boundary matched with the
mode frequency of the Kelvin wave. Additionally, we examined the formation and
evolution of vortex tangles between the boundaries. The vortex tangle was
suppressed in the presence of pinning, while the absence of pinning allowed to
form well developed vortex tangle resulting in turbulence. Finally, by
evaluating the tension of pinned vortices we extracted the damping force acting
on the solid boundaries.",2308.11942v2
2023-12-29,Modeling polyelectrolyte hydration from a multi scale polarizable pseudo particle solvent coarse grained approach,"We investigate the reliability of simulations of polyelectrolyte systems in
aqueous environments, simulations that are performed using an efficient multi
scale coarse grained polarizable pseudo-particle particle approach, denoted as
pppl, to model the solvent water, whereas the solutes are modeled using a
polarizable all atom force field. We focus our study on issues tied to two key
parameters of the pppl approach, namely the extension of the solvent domain SD
at the close vicinity of a solute (domain in which each solvent particle
corresponds to a single water molecule) and the magnitude of solute/solvent
short range polarization damping effects. To this end we built a new pppl
models from which we simulate NaCl aqueous solutions at the molar concentration
scale. We also re investigate the hydration of a hydrophobic polyelectrolyte
polymer that we showed in an earlier study [J Chem Phys, 114903 (155) 2021] to
evolve towards a counter intuitive globular form surrounded by a spherical
counter ion cloud along pppl-based simulations. Strong short range damping is
pivotal to simulate NaCl aqueous solutions. The extension of the domain SD (as
well as short range damping) has a weak effect on the conformation of the
polymer, but it plays a pivotal role to compute accurate solute/solvent
interaction energies. In all our results lead us to recommend to simulate
polyelectrolyte polymers as dissolved alone in pppl fluids (i.e. without
explicitly accounting for their counter ions) to investigate their behavior at
infinite dilution conditions, and to systematically consider strong
solute/solvent polarization short range damping to model charged species.",2312.17580v1
2024-02-19,Global existence for non-homogeneous incompressible inviscid fluids in presence of Ekman pumping,"In this paper, we study the global solvability of the density-dependent
incompressible Euler equations, supplemented with a damping term of the form $
\mathfrak{D}_{\alpha}^{\gamma}(\rho, u) = \alpha \rho^{\gamma} u $, where
$\alpha>0$ and $ \gamma \in \{0,1\} $. To some extent, this system can be seen
as a simplified model describing the mean dynamics in the ocean; from this
perspective, the damping term can be interpreted as a term encoding the effects
of the celebrated Ekman pumping in the system.
  On the one hand, in the general case of space dimension $d\geq 2$, we
establish global well-posedness in the Besov spaces framework, under a
non-linear smallness condition involving the size of the initial velocity field
$u_0$, of the initial non-homogeneity $\rho_0-1$ and of the damping coefficient
$\alpha$. On the other hand, in the specific situation of planar motions and
damping term with $\gamma=1$, we exhibit a second smallness condition implying
global existence, which in particular yields global well-posedness for
arbitrarily large initial velocity fields, provided the initial density
variations $\rho_0-1$ are small enough. The formulated smallness conditions
rely only on the endpoint Besov norm $B^1_{\infty,1}$ of the initial datum,
whereas, as a byproduct of our analysis, we derive exponential decay of the
velocity field and of the pressure gradient in the high regularity norms
$B^s_{p,r}$.",2402.12592v1
2024-02-20,The Fundamental Parameters of Astrophysical Plasma Turbulence and its Dissipation: Nonrelativistic Limit,"A specific set of dimensionless plasma and turbulence parameters is
introduced to characterize the nature of turbulence and its dissipation in
weakly collisional space and astrophysical plasmas. Key considerations are
discussed for the development of predictive models of the turbulent plasma
heating that characterize the partitioning of dissipated turbulent energy
between the ion and electron species and between the perpendicular and parallel
degrees of freedom for each species. Identifying the kinetic physical
mechanisms that govern the damping of the turbulent fluctuations is a critical
first step in constructing such turbulent heating models. A set of ten general
plasma and turbulence parameters are defined, and reasonable approximations
along with the exploitation of existing scaling theories for
magnetohydrodynamic turbulence are used to reduce this general set of ten
parameters to just three parameters in the isotropic temperature case. A
critical step forward in this study is to identify the dependence of all of the
proposed kinetic mechanisms for turbulent damping in terms of the same set of
fundamental plasma and turbulence parameters. Analytical estimations of the
scaling of each damping mechanism on these fundamental parameters are
presented, and this information is synthesized to produce the first phase
diagram for the turbulent damping mechanisms as a function of driving scale and
ion plasma beta.",2402.12829v1
2024-03-06,Universality of pseudo-Goldstone damping near critical points,"Recently, in studies of holographic models and hydrodynamics with spontaneous
breaking of approximate symmetries, it has been proposed that the damping of
pseudo-Goldstone modes at finite temperatures is universally constrained in the
way that $\Omega_{\varphi}/m_{\varphi}^2\simeq D_{\varphi}$ in the broken
phase, where $\Omega_{\varphi}$ and $m_{\varphi} $ are the relaxation rate at
zero wavenumber and the mass of pseudo-Goldstones, $D_{\varphi}$ is the
Goldstone diffusivity in the limit of purely spontaneous breaking. In this
paper, we investigate the pseudo-Goldstone damping in a purely relaxational
O($N$) model by performing the functional renormalization group calculations at
the full quantum and stochastic level within the Schwinger-Keldysh formalism.
We find that, away from the critical temperature, the proposed relation is
always valid. When the temperature is very close to the critical value such
that the mass of the Higgs mode is comparable to the mass of the
pseudo-Goldstone modes, the pseudo-Goldstone damping displays a novel scaling
behavior that follows $\Omega_\varphi/m_\varphi^2\propto
m_{\varphi}^{\Delta_\eta}$ with a correction $\Delta_\eta$ controlled by the
critical universalities. Moreover, we study how the correction depends on the
value of $N$ and show that $\Delta_\eta \rightarrow 0$ when fluctuations are
infinitely suppressed in the large $N$ limit. In this case, the proposed
relation works even in the critical region. Finally, we match our results to
the dissipative sector of the pion dynamics near the chiral phase transition.",2403.03503v2
1993-11-17,Early Reionization in Cosmology,"The cosmic microwave background (CMB) anisotropies have turned out to
represent one of the most stringent 'bottle necks' for scenarios of large scale
structure formation. As a possibility to relax this constraint, it has been
proposed that early reionization can damp CMB fluctuations on small scales due
to photon diffusion in the ionized plasma. As an example, I investigate the
recently proposed scenario with cold dark matter (CDM) and texture seeds.
There, an analysis of CMB anisotropies shows that early reionization is a
crucial ingredient for this scenario. Without damping, the small scale
anisotropies would dominate and exceed observed limits. In this paper I present
analytical and numerical results for the amount of damping due to early
reionization for CMB perturbations induced by a collapsing texture.
Furthermore, the spectral distortion of the CMB due to Compton scattering of
the hotter plasma electrons is calculated. Next I discuss the physical
processes which lead to a system of coupled ordinary differential equations for
the degree of ionization, the electron temperature and the evolution of the
ionizing radiation.",9311039v1
1994-08-18,The Damping and Excitation of Galactic Warps by Dynamical Friction,"We investigate the dynamical interaction of galactic warps with the
surrounding dark matter halo, using analytic perturbation theory. A precessing
warp induces a density wake in the collisionless dark matter, which acts back
on the original warp, transferring energy and angular momentum between the warp
and halo (dynamical friction). In most cases dynamical friction damps the warp,
but in unusual circumstances (such as a halo that rotates in the same direction
as the precession of the warp, or a warp in the equatorial plane of an
axisymmetric prolate halo) friction can excite a warp. The damping/excitation
time is usually short compared to the Hubble time for realistic systems. Thus
most warps cannot be primordial; they must be maintained by some ongoing
excitation mechanism.",9408068v1
1995-09-14,Another Look at Gaussian Isocurvature Hot Dark Matter Models For Large- Scale Structure,"We examine Gaussian isocurvature hot dark matter (massive neutrino) models
for large-scale structure in which the initial density perturbations are
produced in the baryons with a power--law spectrum $P_B(k) = Ak^{n_B}$. We
calculate the linearly-evolved power spectrum and cosmic microwave
fluctuations. We find that models with only isocurvature perturbations are
inconsistent with observations of damped Ly$\alpha$ systems and COBE
constraints on the power index. However, models which contain a mixture of
adiabatic and isocurvature perturbations can be made consistent with COBE,
galaxy surveys and damped Ly$\alpha$ systems.Isocurvature hot dark matter
models also produce a bias between baryons and neutrinos even in the linear
regime. We find that this ``natural bias'' can increase the baryon fraction in
small scale objects like damped Ly$\alpha$ systems, but it has no effect on
cluster scales.",9509075v1
1995-10-16,Star Formation and Chemical Evolution in Damped Lya Clouds,"Using the redshift evolution of the neutral hydrogen density, as inferred
from observations of damped Ly$\alpha$ clouds, we calculate the evolution of
star formation rates and elemental abundances in the universe. For most
observables our calculations are in rough agreement with previous results based
on the instantaneous re-cycling approximation (IRA). However, for the key
metallicity tracer Zn, we find a better match to the observed abundance at high
redshift than that given by the constant-yield IRA model. We investigate
whether the redshift evolution of deuterium, depressions in the diffuse
extragalactic gamma-ray background, and measurement of the MeV neutrino
background may help determine if observational bias due to dust obscuration is
important. We also indicate how the importance of dust on the calculations can
be significantly reduced if correlations of the HI column density with
metallicity are present. The possibilities for measuring $q_o$ with
observations of elemental abundances in damped Ly$\alpha$ systems are
discussed.",9510078v1
1995-12-12,A radio Search for high redshift HI absorption,"Ground based optical observations have yielded considerable information on
the statistics of damped-lyman alpha systems. In particular these systems are
known to be the dominant repository of the observed neutral gas at high
redshift. However, particularly at high redshift, there is the possibility that
optical observations could be biased due to the exclusion of damped-lyman alpha
systems that contain moderate to significant amounts of dust. Independent
observational constraints on the neutral hydrogen content at high redshifts and
the amount of dust in high redshift systems can be obtained from a radio search
against the bright lobes of distant radio galaxies (which is less affected by
the presence of dust in foreground damped-lyman alpha systems). We describe
here a pilot radio survey along the line of sight to a small sample of high
redshift radio galaxies, and also present some preliminary results. The survey
uses a novel observing mode at the WSRT which enables one to make sensitive
searches of a large redshift interval in a modest amount of telescope time.",9512069v1
1996-01-26,The chemical evolution of galaxies at high redshift,"Observations of absorption lines in the spectra of distant QSOs offer a new
approach for tracking the evolution of normal galaxies from early epochs to the
present day. The damped Ly alpha systems are particularly suitable for
measuring the properties of what are likely to be the progenitors of
present-day luminous galaxies. We have recently concluded a long-term survey of
30 damped absorbers (including eight from the literature) aimed at measuring
the metallicity and dust content of the universe from redshift z = 3.39 to
0.69. The major conclusions are that the epoch of chemical enrichment in
galaxies may have begun at z = 2.5-3--corresponding to a look-back time of 14
Gyr--and that at z = 2 the typical metallicity was 1/15 of solar. There is
clear evidence for the presence of interstellar dust at z = 2, although several
high-redshift galaxies, particularly the most metal-poor, appear to be
essentially dust-free. We discuss the nature of the damped Ly alpha galaxies in
the light of these and other new results.",9601153v1
1996-07-23,A damped Ly-alpha candidate at z~0.1 toward Q 0439-433,"We report on the detection of a z_gal=0.101 galaxy projected on the sky at
4.2 arcsec (or 5.2 h^{-1} kpc for q_o=0.5) from the quasar Q 0439-433
(z_em=0.594). The HST spectrum of the quasar shows strong MgII, FeII, SiII,
AlII and CIV absorption lines at the same redshift as the galaxy. The
equivalent width ratios of the low ionization lines indicate that this system
is probably damped with a neutral hydrogen column density of
N_HI~10^{20}cm^{-2}. The CIV doublet presents a complex structure, and in
particular a satellite with a velocity v=1100km/s relative to the galaxy.
Additional HST and redshifted 21cm observations of this QSO-galaxy pair would
offer an ideal opportunity to study the morphology of a damped absorber and the
kinematics of the halo of a low-redshift galaxy.",9607111v2
1997-08-11,Dynamos with different formulations of a dynamic alpha-effect,"We investigate the behaviour of $\alpha\Omega$ dynamos with a dynamic
$\alpha$, whose evolution is governed by the imbalance between a driving and a
damping term. We focus on truncated versions of such dynamo models which are
often studied in connection with solar and stellar variability. Given the
approximate nature of such models, it is important to study how robust they are
with respect to reasonable changes in the formulation of the driving and
damping terms. For each case, we also study the effects of changes of the
dynamo number and its sign, the truncation order and initial conditions. Our
results show that changes in the formulation of the driving term have important
consequences for the dynamical behaviour of such systems, with the detailed
nature of these effects depending crucially on the form of the driving term
assumed, the value and the sign of the dynamo number and the initial
conditions. On the other hand, the change in the damping term considered here
seems to produce little qualitative effect.",9708093v1
1997-11-20,ORT observations of the damped Lyman alpha system towards PKS 0201+113,"We report a deep radio search with the Ooty Radio Telescope (ORT) for the
redshifted 21 cm absorption line from the damped Lyman alpha system seen at
redshift 3.388 against the quasar PKS 0201+113. This is currently the most
distant system for which a detection of 21 cm absorption has been claimed. The
present observations have a sensitivity comparable to the earlier ones and
detect no statistically significant absorption. We use the non-detection to
place an upper limit of ~ 0.011 on the optical depth of the damped Lyman alpha
absorber. This corresponds to a lower limit of ~ 5600 K to the spin temperature
of the system. This is considerably higher than the previous upper limit of ~
1380 K.",9711234v1
1998-01-28,Dynamical Tide in Solar-Type Binaries,"Circularization of late-type main-sequence binaries is usually attributed to
turbulent convection, while that of early-type binaries is explained by
resonant excitation of g modes. We show that the latter mechanism operates in
solar-type stars also and is at least as effective as convection, despite
inefficient damping of g modes in the radiative core. The maximum period at
which this mechanism can circularize a binary composed of solar-type stars in
10 Gyr is as low as 3 days, if the modes are damped by radiative diffusion only
and g-mode resonances are fixed; or as high as 6 days, if one allows for
evolution of the resonances and for nonlinear damping near inner turning
points. Even the larger theoretical period falls short of the observed
transition period by a factor two.",9801289v1
1998-02-06,Acoustic oscillations and viscosity,"Using a simple thermo-hydrodynamic model that respects relativistic
causality, we revisit the analysis of qualitative features of acoustic
oscillations in the photon-baryon fluid. The growing photon mean free path
introduces transient effects that can be modelled by the causal generalization
of relativistic Navier-Stokes-Fourier theory. Causal thermodynamics provides a
more satisfactory hydrodynamic approximation to kinetic theory than the
quasi-stationary (and non-causal) approximations arising from standard
thermodynamics or from expanding the photon distribution to first order in the
Thomson scattering time. The causal approach introduces small corrections to
the dispersion relation obtained in quasi-stationary treatments. A dissipative
contribution to the speed of sound slightly increases the frequency of the
oscillations. The diffusion damping scale is slightly increased by the causal
corrections. Thus quasi-stationary approximations tend to over-estimate the
spacing and under-estimate the damping of acoustic peaks. In our simple model,
the fractional corrections at decoupling are $\gtrsim 10^{-3}$.",9802074v2
2000-02-29,Metallicity Evolution in the Early Universe,"Observations of the damped Lya systems provide direct measurements on the
chemical enrichment history of neutral gas in the early universe. In this
Letter, we present new measurements for four damped Lya systems at high
redshift. Combining these data with [Fe/H] values culled from the literature,
we investigate the metallicity evolution of the universe from z~1.5-4.5.
Contrary to our expectations and the predictions of essentially every chemical
evolution model, the N(HI)-weighted mean [Fe/H] metallicity exhibits minimal
evolution over this epoch. For the individual systems, we report tentative
evidence for an evolution in the unweighted [Fe/H] mean and the scatter in
[Fe/H] with the higher redshift systems showing lower scatter and lower typical
[Fe/H] values. We also note that no damped Lya system has [Fe/H] < -2.7 dex.
Finally, we discuss the potential impact of small number statistics and dust on
our conclusions and consider the implications of these results on chemical
evolution in the early universe.",0002513v3
2000-06-02,Surveys for z > 3 Damped Lyman-alpha Absorption Systems,"We have completed spectroscopic observations using LRIS on the Keck 1
telescope of 30 very high redshift quasars, 11 selected for the presence of
damped Ly-alpha absorption systems and 19 with redshifts z > 3.5 not previously
surveyed for absorption systems. We have surveyed an additional 10 QSOs with
the Lick 120'' and the Anglo-Australian Telescope. We have combined these with
previous data resulting in a statistical sample of 646 QSOs and 85 damped
Ly-alpha absorbers with column densities N(HI) >= 2 x 10^20 atoms/cm^2 covering
the redshift range 0.008 <= z <= 4.694. To make the data in our statistical
sample more readily available for comparison with scenarios from various
cosmological models, we provide tables that includes all 646 QSOs from our new
survey and previously published surveys. They list the minimum and maximum
redshift defining the redshift path along each line of sight, the QSO emission
redshift, and when an absorber is detected, the absorption redshift and
measured HI column density. [see the paper for the complete abstract]",0006044v1
2000-06-21,Constraints on the physical properties of the damped Ly-alpha system of Q0000-2619 at z = 3.054,"We present the detection of CII and CII* absorption in the z = 3.0543 damped
Ly-alpha system toward Q0000-2619. The derived population ratio implies a fine
structure excitation temperature between 19.6 and 21.6 K. The upper value sets
a strict upper limit on the CMB temperature at this redshift, which is
consistent with the predicted value of 11.05 K from standard cosmology. Under
the assumptions of an ionization degree ranging from 0 to 10%, a gas kinetic
temperature between 100 and 10000 K and a UV field with a Milky Way spectrum,
the density of the absorber is constrained to be between 0.7 and 40 cm^-3 and
the H-ionizing flux between 1 and 80 times the intensity of the Galactic UV
field. If the damped Ly-alpha system is assumed to be homogeneous, the
implication is that its size in the direction of the line of sight must be
between 1 and 100 pc.",0006308v1
2001-04-10,Damping scales of neutralino cold dark matter,"The lightest supersymmetric particle, most likely the neutralino, might
account for a large fraction of dark matter in the Universe. We show that the
primordial spectrum of density fluctuations in neutralino cold dark matter
(CDM) has a sharp cut-off due to two damping mechanisms: collisional damping
during the kinetic decoupling of the neutralinos at about 30 MeV (for typical
neutralino and sfermion masses) and free streaming after last scattering of
neutralinos. The last scattering temperature is lower than the kinetic
decoupling temperature by one order of magnitude. The cut-off in the primordial
spectrum defines a minimal mass for CDM objects in hierarchical structure
formation. For typical neutralino and sfermion masses the first gravitationally
bound neutralino clouds have to have masses above 10^(-7) solar masses.",0104173v2
2002-05-15,Building the bridge between Damped Ly-alpha Absorbers and Lyman Break galaxies,"In 2000, we started the program ``Building the Bridge between Damped Ly-alpha
Absorbers and Lyman-Break Galaxies: Ly-alpha Selection of Galaxies'' at the
European Southern Observatory's Very Large Telescope. This project is an
attempt to use Ly-alpha selection of high-z galaxies to bridge the gap between
absorption- and emission-selected galaxies by creating a large database of z=3
galaxies belonging to the abundant population of faint (R>25.5) galaxies probed
by the Damped Ly-alpha Absorbers (DLAs). Here we present the first results of
our program, namely the results from a deep Ly-alpha study of the field of the
z=2.85 DLA towards Q2138-4427.",0205234v2
2002-05-23,Constraining the strength of Dark Matter Interactions from Structure Formation,"We discuss the damping of primordial dark matter fluctuations, taking into
account explicitly the interactions of dark matter - whatever their intensity -
both with itself and with other particle species. Relying on a general
classification of dark matter particle candidates, our analysis provides, from
structure formation, a new set of constraints on the dark matter particle mass
and interaction rates (in particular with photons and neutrinos).
  This determines up to which cross sections the dark matter interactions may
effectively be disregarded, and when they start playing an essential role,
either through collisional damping or through an enhancement of the
free-streaming scale. It leads us to extend the notions of Cold, Warm and Hot
Dark Matter scenarios when dark matter interactions are no longer taken to be
negligible. It also suggests the possibility of new scenarios of Collisional
Warm Dark Matter, with moderate damping induced by dark matter interactions.",0205406v1
2002-06-06,A catalogue of damped Lyman alpha absorption systems and radio flux densities of the background quasars,"We present a catalogue of the 322 damped Lyman alpha absorbers taken from the
literature. All damped Lyman alpha absorbers are included, with no selection on
redshift or quasar magnitude. Of these, 123 are candidates and await
confirmation using high resolution spectroscopy. For all 322 objects we
catalogue the radio properties of the background quasars, where known. Around
60 quasars have radio flux densities above 0.1 Jy and approximately half of
these have optical magnitudes brighter than V = 18. This compilation should
prove useful in several areas of extragalactic/cosmological research.",0206091v1
2002-11-14,Formation of small-scale structure in SUSY CDM,"The lightest supersymmetric particle, most likely the lightest neutralino, is
one of the most prominent particle candidates for cold dark matter (CDM). We
show that the primordial spectrum of density fluctuations in neutralino CDM has
a sharp cut-off, induced by two different damping mechanisms. During the
kinetic decoupling of neutralinos, non-equilibrium processes constitute
viscosity effects, which damp or even absorb density perturbations in CDM.
After the last scattering of neutralinos, free streaming induces neutralino
flows from overdense to underdense regions of space. Both damping mechanisms
together define a minimal mass scale for perturbations in neutralino CDM,
before the inhomogeneities enter the nonlinear epoch of structure formation. We
find that the very first gravitationally bound neutralino clouds ought to have
masses above 10^{-6} solar masses, which is six orders of magnitude above the
mass of possible axion miniclusters.",0211325v1
2002-12-09,Galaxies at z=3 around Damped Ly-alpha Clouds,"We are exploring the connection between damped Ly-alpha absorbers (DLAs) and
Lyman break galaxies (LBGs) using deep -- (5sigma)=26 m_{AB}-- broad band
imaging (UBVI) of four wide fields (0.25 sq. deg. each) obtained at the Kitt
Peak 4-m telescope with MOSAIC. Each field contains a damped system at z=3.
  We want to address the nature of DLAs at high-redshifts: (1) Are they
embedded in much larger systems of galaxies? (2) How does the spatial
distribution of LBGs in 3D (space and redshift) correlate with the absorber?
Contrary to most previous DLA studies, we are not looking for the absorber, and
we do not rely on control fields because each of our fields is 40 Mpc
(co-moving) on a side. We present preliminary results in two of our fields. In
one case, we see an indication of an overdensity of galaxies on a scale of 5
Mpc. We discuss the possible implications and sources of contamination of our
results.",0212206v1
2003-04-16,Building Blocks in Hierarchical Clustering Scenarios and their Connection with Damped Ly$α$ Systems,"We carried out a comprehensive analysis of the chemical properties of the
interstellar medium (ISM) and the stellar population (SP) of current normal
galaxies and their progenitors in a hierarchical clustering scenario. We
compared the results with observations of Damped Lyman-$\alpha$ systems (DLAs)
under the hypothesis that, at least, part of the observed DLAs could originate
in the building blocks of today normal galaxies. We used a hydrodynamical
cosmological code which includes star formation and chemical enrichment.
Galaxy-like objects are identified at $z=0$ and then followed back in time.
Random line-of-sights (LOS) are drawn through these structures in order to
mimic Damped Lyman $\alpha$ systems. We then analysed the chemical properties
of the ISM and SP along the LOS. We found that the progenitors of current
galaxies in the field with mean $L <0.5 L^* $ and virial circular velocity of
$100-250 {\rm km/sec}$ could be the associated DLA galaxies. For these systems
we detected a trend for $<L/L^*>$ to increase with redshift.(Abridged)",0304303v2
2003-05-16,The ESI/KeckII Damped Lya Abundance Database,"This paper presents chemical abundance measurements for 37 damped Lya systems
at z>2.5 observed with the Echellette Spectrograph and Imager on the KeckII
telescope. We measure the HI column densities of these damped systems through
Voigt profile fits to their Lya profiles and we implement the apparent optical
depth method to determine ionic column densities. Figures and tables of all
relevant data are presented. A full analysis of the chemical enrichment history
described by these observations will be presented in a future paper. This
dataset is also valuable for efficiently planning future echelle observations
and for rough abundance pattern analyses. We aim to make this entire data set
public within three years of this publication.",0305312v1
2003-10-28,Chemical Abundances in the Damped Lya Systems,"I introduce and review the data and analysis techniques used to measure
abundances in the damped Lya systems, quasar absorption-line systems associated
with galaxies in the early Universe. The observations and issues associated
with their abundance analysis are very similar to those of the Milky Way's
interstellar medium. We measure gas-phase abundances and are therefore subject
to the effects of differential depletion. I review the impact of dust depletion
and then present a summary of current results on the age-metallicity relation
derived from damped Lya systems and new results impacting theories of
nucleosynthesis in the early Universe.",0310814v1
2004-08-10,Cosmic Ray Scattering and Streaming in Compressible Magnetohydrodynamic Turbulence,"Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call
for revisions in the picture of cosmic ray transport. In this paper we use
recently obtained scaling laws for MHD modes to obtain the scattering frequency
for cosmic rays. Using quasilinear theory we calculate gyroresonance with MHD
modes (Alfv\'{e}nic, slow and fast) and transit-time damping (TTD) by fast
modes. We provide calculations of cosmic ray scattering for various phases of
interstellar medium with realistic interstellar turbulence driving that is
consistent with the velocity dispersions observed in diffuse gas. We account
for the turbulence cutoff arising from both collisional and collisionless
damping. We obtain analytical expressions for diffusion coefficients that enter
Fokker-Planck equation describing cosmic ray evolution. We obtain the
scattering rate and show that fast modes provide the dominant contribution to
cosmic ray scattering for the typical interstellar conditions in spite of the
fact that fast modes are subjected to damping. We determine how the efficiency
of the scattering depends on the characteristics of ionized media, e.g. plasma
$\beta$. We calculate the range of energies for which the streaming instability
is suppressed by the ambient MHD turbulence.",0408172v1
2004-12-14,Radiative Effects on Particle Acceleration in Electromagnetic Dominated Outflows,"Plasma outflows from gamma-ray bursts (GRB), pulsar winds, relativistic jets,
and ultra-intense laser targets radiate high energy photons. However, radiation
damping is ignored in conventional PIC simulations. In this letter, we study
the radiation damping effect on particle acceleration via Poynting fluxes in
two-and-half-dimensional particle-in-cell (PIC) plasma simulation of
electron-positron plasmas. Radiation damping force is self-consistently
calculated for each particle and reduces the net acceleration force. The
emitted radiation is peaked within a few degrees from the direction of Poynting
flux and strongly linear-polarized.",0412310v3
2005-09-16,Damped Lyman alpha Systems,"Observations of damped Lyman alpha systems offer a unique window on the
neutral-gas reservoirs that gave rise to galaxies at high redshifts. This
review focuses on critical properties such as the H I and metal content of the
gas and on independent evidence for star formation. Together, these provide an
emerging picture of gravitationally bound objects in which accretion of gas
from the IGM replenishes gas consumed by star formation. Other properties such
as dust content, molecular content, ionized-gas content, gas kinematics, and
galaxy identifications are also reviewed. These properties point to a
multiphase ISM in which radiative and hydrodynamic feedback processes are
present. Numerical simulations and other types of models used to describe
damped Lyman alpha systems within the context of galaxy formation are also
discussed.",0509481v2
2005-11-11,Oscillation mode lifetimes in ksi Hydrae: Will strong mode damping limit asteroseismology of red giant stars?,"We introduce a new method to measure frequency separations and mode lifetimes
of stochastically excited and damped oscillations, so-called solar-like
oscillations. Our method shows that velocity data of the red giant star ksi Hya
(Frandsen et al. 2002) support a large frequency separation between modes of
roughly 7 microHz. We also conclude that the data are consistent with a mode
lifetime of 2 days, which is so short relative to its pulsation period that
none of the observed frequencies are unambiguous. Hence, we argue that the
maximum asteroseismic output that can be obtained from these data is an average
large frequency separation, the oscillation amplitude and the average mode
lifetime. However, the significant discrepancy between the theoretical
calculations of the mode lifetime (Houdek & Gough 2002) and our result based on
the observations of ksi Hya, implies that red giant stars can help us better
understand the damping and driving mechanisms of solar-like p-modes by
convection.",0511344v1
1996-12-14,Nonlinear Landau damping in collisionless plasma and inviscid fluid,"The evolution of an initial perturbation in Vlasov plasma is studied in the
intrinsically nonlinear long-time limit dominated by the effects of particle
trapping. After the possible transient linear exponential Landau damping, the
evolution enters into a universal regime with an algebraically damped electric
field, $E\propto1/t$. The trick used for the Vlasov equation is also applied to
the two-dimensional (2D) Euler equation. It is shown that the stream function
perturbation to a stable shear flow decays as $t^{-5/2}$ in the long-time
limit. These results imply a strong non-ergodicity of the fluid element motion,
which invalidates Gibbs-ensemble-based statistical theories of Vlasov and 2D
fluid turbulence.",9612021v1
1998-03-05,On how a joint interaction of two innocent partners (smooth advection & linear damping) produces a strong intermittency,"Forced advection of passive scalar by a smooth $d$-dimensional incompressible
velocity in the presence of a linear damping is studied. Acting separately
advection and dumping do not lead to an essential intermittency of the steady
scalar statistics, while being mixed together produce a very strong
non-Gaussianity in the convective range: $q$-th (positive) moment of the
absolute value of scalar difference, $<|\theta (t;{\bf r})-\theta (t;0)|^{q}> $
is proportional to $r^{\xi_{q}}$, $\xi _{q}=\sqrt{d^{2}/4+\alpha dq/[
(d-1)D]}-d/2$, where $\alpha /D$ measures the rate of the damping in the units
of the stretching rate. Probability density function (PDF) of the scalar
difference is also found.",9803007v1
1999-02-05,Nonlinear Dynamics of A Damped Magnetic Oscillator,"We consider a damped magnetic oscillator, consisting of a permanent magnet in
a periodically oscillating magnetic field. A detailed investigation of the
dynamics of this dissipative magnetic system is made by varying the field
amplitude $A$. As $A$ is increased, the damped magnetic oscillator, albeit
simple looking, exhibits rich dynamical behaviors such as symmetry-breaking
pitchfork bifurcations, period-doubling transitions to chaos,
symmetry-restoring attractor-merging crises, and saddle-node bifurcations
giving rise to new periodic attractors. Besides these familiar behaviors, a
cascade of ``resurrections'' (i.e., an infinite sequence of alternating
restabilizations and destabilizations) of the stationary points also occurs. It
is found that the stationary points restabilize (destabilize) through
alternating subcritical (supercritical) period-doubling and pitchfork
bifurcations. We also discuss the critical behaviors in the period-doubling
cascades.",9902005v1
1996-09-03,Mode damping in a commensurate monolayer solid,"The normal modes of a commensurate monolayer solid may be damped by mixing
with elastic waves of the substrate. This was shown by B. Hall et al., Phys.
Rev. B 32, 4932 (1985), for perpendicular adsorbate vibrations in the presence
of an isotropic elastic medium. That work is generalized with an elastic
continuum theory of the response of modes of either parallel or perpendicular
polarization for a spherical adsorbate on a hexagonal substrate. The results
are applied to the discussion of computer simulations and inelastic atomic
scattering experiments for adsorbates on graphite. The extreme anisotropy of
the elastic behavior of the graphite leads to quite different wave vector
dependence of the damping for modes polarized perpendicular and parallel to the
substrate. A phenomenological extension of the elasticity theory of the
graphite to include bond-bending energies improves the description of substrate
modes with strong anomalous dispersion and enables a semi-quantitative account
of observed avoided crossings of the adlayer perpendicular vibration mode and
the substrate Rayleigh mode.",9609032v1
1997-12-08,Collective oscillations in superconductors revisited,"In the recent paper Ohashi and Takada (OT) made statements that in the clean
limit considered by us (AV) in 1975, weakly damped collective oscillations in
superconductors do not exist due to the Landau damping and their spectrum
differs from that obtained in AV. In this Comment we would like to note that
these statements arise as a result of a misunderstanding of the term ""clean""
case. OT considered the limit of frequencies larger, than elastic scattering
rate, meanwhile AV obtained weakly damped mode in the case when temperature is
larger than scattering rate, the frequencies being smaller (!) than elastic
scattering rate. All these problems were discussed in our review article in
1979 which was, presumably, unknown to OT.",9712086v1
1999-01-11,Vortex motion in superconducting YBCO inferred from the damping of the oscillations of a levitating magnetic microsphere,"The damping of the oscillations of a small permanent magnet (spherical shape,
radius 0.1 mm) levitating between two parallel YBCO surfaces is measured as a
function of oscillation amplitude and temperature. The losses in the samples
(epitaxial thin films, bulk granular and bulk melt-textured) are analyzed in
terms of oscillating shielding currents flowing through trapped flux lines
whose motion gives rise to electric fields. We find dissipation to originate
from different mechanisms of flux dynamics. At small amplitudes there is a
linear regime described by a surface resistance varying from 10^-9 Ohm for bulk
samples down to 10^-13 Ohm for the thin films at low temperatures. With
increasing amplitude various nonlinear regimes are observed, firstly collective
pinning with diverging energy barriers, secondly in bulk samples above 85 K
hysteretic damping, and finally in thin films exponentially large losses which
can be described by pinning energies vanishing linearly at large currents.",9901085v1
1999-10-07,On the relative positions of the $2Δ$ peaks in Raman and tunneling spectra of d-wave superconductors,"We study $B_{1g}$ Raman intensity $R(\Omega)$ and the density of states
$N(\omega)$ in isotropic 2D d-wave superconductors. For an ideal gas,
$R(\Omega)$ and $N(\omega)$ have sharp peaks at $\Omega =2\Delta$ and $\omega
=\Delta$, respectively, where $\Delta$ is the maximum value of the gap.
  We study how the peak positions are affected by the fermionic damping due to
impurity scattering.
  We show that while the damping generally shifts the peak positions to larger
frequencies, the peak in $R(\Omega)$ still occurs at almost twice the peak
position in $N(\omega)$ and therefore cannot account for the experimentally
observed downturn shift of the peak frequency in $R(\Omega)$ in underdoped
cuprates compared to twice that in $N(\omega)$. We also discuss how the
fermionic damping affects the dynamical spin susceptibility.",9910090v1
1999-11-22,Two-fluid hydrodynamics of a Bose gas including damping from normal fluid transport coefficients,"We extend our recent work on the two-fluid hydrodynamics of the condensate
and non-condensate in a trapped Bose gas by including the dissipation
associated with viscosity and thermal conduction. For purposes of illustration,
we consider the hydrodynamic modes in the case of a uniform Bose gas. A finite
thermal conductivity and shear viscosity give rise to a damping of the first
and second sound modes in addition to that found previously due to the lack of
diffusive equilibrium between the condensate and non-condensate. The
relaxational mode associated with this equilibration process is strongly
coupled to thermal fluctuations and reduces to the usual thermal diffusion mode
above the Bose-Einstein transition. In contrast to the standard Landau
two-fluid hydrodynamics, we predict a damped mode centered at zero frequency,
in addition to the usual second sound doublet.",9911336v1
2000-03-31,Kinetic Theory of Collective Excitations and Damping in Bose-Einstein Condensed Gases,"We calculate the frequencies and damping rates of the low-lying collective
modes of a Bose-Einstein condensed gas at nonzero temperature. We use a complex
nonlinear Schr\""odinger equation to determine the dynamics of the condensate
atoms, and couple it to a Boltzmann equation for the noncondensate atoms. In
this manner we take into account both collisions between
noncondensate-noncondensate and condensate-noncondensate atoms. We solve the
linear response of these equations, using a time-dependent gaussian trial
function for the condensate wave function and a truncated power expansion for
the deviation function of the thermal cloud. As a result, our calculation turns
out to be characterized by two dimensionless parameters proportional to the
noncondensate-noncondensate and condensate-noncondensate mean collision times.
We find in general quite good agreement with experiment, both for the
frequencies and damping of the collective modes.",0003517v1
2000-09-01,The broad Brillouin doublets and central peak of KTaO_3,"The incipient ferroelectric KTaO3 presents low-T Brillouin spectra
anomalies,e.g. a broad central peak (CP), and some additional Brillouin
doublets (BD), whose origin is interpreted in terms of phonon-density
fluctuation processes. A parameterisation from new extensive high-resolution
neutron-scattering measurements is used to show that hydrodynamic second sound
from high damping (compared to BD frequency) TA phonons may exist in the
crystal. Furthermore, low damping thermal phonons may scatter light through
two-phonon difference processes and appear on the Brillouin spectra either as a
sharp or a broader BD, depending on the phonon damping and group velocity . The
comparison between computed anisotropies and experimental measurements favours
the second process.",0009012v1
2001-01-15,Temperature Dependence of Damping and Frequency Shifts of the Scissors Mode of a trapped Bose-Einstein Condensate,"We have studied the properties of the scissors mode of a trapped
Bose-Einstein condensate of $^{87}$Rb atoms at finite temperature. We measured
a significant shift in the frequency of the mode below the hydrodynamic limit
and a strong dependence of the damping rate as the temperature increased. We
compared our damping rate results to recent theoretical calculations for other
observed collective modes finding a fair agreement. From the frequency
measurements we deduce the moment of inertia of the gas and show that it is
quenched below the transition point, because of the superfluid nature of the
condensed gas.",0101213v2
2001-03-16,Gap Anisotropy and de Haas-van Alphen Effect in Type-II Superconductors,"We present a theoretical study on the de Haas-van Alphen (dHvA) oscillation
in the vortex state of type-II superconductors, with a special focus on the
connection between the gap anisotropy and the oscillation damping. Numerical
calculations for three different gap structures clearly indicate that the
average gap along extremal orbits is relevant for the magnitude of the extra
damping, thereby providing a support for experimental efforts to probe gap
anisotropy through the dHvA signal. We also derive an analytic formula for the
extra damping which gives a good fit to the numerical results.",0103336v3
2001-04-10,Quantum phase transitions and collective modes in d-wave superconductors,"Fluctuations near second-order quantum phase transitions in d-wave
superconductors can cause strong damping of fermionic excitations, as observed
in photoemission experiments. The damping of the gapless nodal quasiparticles
can arise naturally in the quantum-critical region of a transition with an
additional spin-singlet, zero momentum order parameter; we argue that the
transition to a d_x^2-y^2 + i d_xy pairing state is the most likely possibility
in this category. On the other hand, the gapped antinodal quasiparticles can be
strongly damped by the coupling to antiferromagnetic spin fluctuations arising
from the proximity to a Neel-ordered state. We review some aspects of the
low-energy field theories for both transitions and the corresponding
quantum-critical behavior. In addition, we discuss the spectral properties of
the collective modes associated with the proximity to a superconductor with
d_x^2-y^2 + i d_xy symmetry, and implications for experiments.",0104176v1
2002-04-11,Nonequilibrium relaxation in neutral BCS superconductors: Ginzburg-Landau approach with Landau damping in real time,"We present a field-theoretical method to obtain consistently the equations of
motion for small amplitude fluctuations of the order parameter directly in real
time for a homogeneous, neutral BCS superconductor. This method allows to study
the nonequilibrium relaxation of the order parameter as an initial value
problem. We obtain the Ward identities and the effective actions for small
phase the amplitude fluctuations to one-loop order. Focusing on the
long-wavelength, low-frequency limit near the critical point, we obtain the
time-dependent Ginzburg-Landau effective action to one-loop order, which is
nonlocal as a consequence of Landau damping. The nonequilibrium relaxation of
the phase and amplitude fluctuations is studied directly in real time. The
long-wavelength phase fluctuation (Bogoliubov-Anderson-Goldstone mode) is
overdamped by Landau damping and the relaxation time scale diverges at the
critical point, revealing critical slowing down.",0204239v2
2002-05-21,Linear spin waves in a trapped Bose gas,"An ultra-cold Bose gas of two-level atoms can be thought of as a spin-1/2
Bose gas. It supports spin-wave collective modes due to the exchange mean
field. Such collective spin oscillations have been observed in recent
experiments at JILA with ${}^{87}$Rb atoms confined in a harmonic trap. We
present a theory of the spin-wave collective modes based on the moment method
for trapped gases. In the collisionless and hydrodynamic limits, we derive
analytic expressions for the frequencies and damping rates of modes with dipole
and quadrupole symmetry. We find that the frequency for a given mode is given
by a temperature independent function of the peak density $n$, and falls off as
$1/n$. We also find that, to a very good approximation, excitations in the
radial and axial directions are decoupled. We compare our model to the
numerical integration of a one dimensional version of the kinetic equation and
find very good qualitative agreement. The damping rates, however, show the
largest deviation for intermediate densities, where one expects Landau damping
-- which is unaccounted for in our moment approach -- to play a significant
role.",0205450v1
2002-08-02,Landau damping of transverse quadrupole oscillations of an elongated Bose-Einstein condensate,"We study the interaction between low-lying transverse collective oscillations
and thermal excitations of an elongated Bose-Einstein condensate by means of
perturbation theory. We consider a cylindrically trapped condensate and
calculate the transverse elementary excitations at zero temperature by solving
the linearized Gross-Pitaevskii equations in two dimensions. We use them to
calculate the matrix elements between thermal excited states coupled with the
quasi-2D collective modes. The Landau damping of transverse collective modes is
investigated as a function of temperature. At low temperatures, the damping
rate due to the Landau decay mechanism is in agreement with the experimental
data for the decay of the transverse quadrupole mode, but it is too small to
explain the slow experimental decay of the transverse breathing mode. The
reason for this discrepancy is discussed.",0208047v1
2002-08-28,Transverse modes of a cigar-shaped Bose-Einstein condensate,"We discuss the collective modes in a harmonically trapped, highly-elongated
Bose condensed gas. The transverse breathing mode exhibits a number of
interesting features, such as the insensitivity of the condensate mode
frequency to the interaction strength, and the closeness of the frequency to
that of the non-condensed thermal cloud in the collisionless limit. Using
finite temperature simulations, we show that these features are responsible for
the very small damping rate observed experimentally. Our results for the
temperature dependence of the damping rate and frequency shift are in excellent
agreement with experiment. We also demonstrate that the unusually small damping
rate does not arise for the $m=2$ mode or for more isotropic trap potentials,
suggesting further possible experimental tests of our theory.",0208567v1
2002-10-31,Stationary quantum statistics of a non-Markovian atom laser,"We present a steady state analysis of a quantum-mechanical model of an atom
laser. A single-mode atomic trap coupled to a continuum of external modes is
driven by a saturable pumping mechanism. In the dilute flux regime, where
atom-atom interactions are negligible in the output, we have been able to solve
this model without making the Born-Markov approximation. The more exact
treatment has a different effective damping rate and occupation of the lasing
mode, as well as a shifted frequency and linewidth of the output. We examine
gravitational damping numerically, finding linewidths and frequency shifts for
a range of pumping rates. We treat mean field damping analytically, finding a
memory function for the Thomas-Fermi regime. The occupation and linewidth are
found to have a nonlinear scaling behavior which has implications for the
stability of atom lasers.",0210688v1
2003-03-23,Damping of micromechanical structures by paramagnetic relaxation,"We find that the damping of micromechanical cantilevers is sensitive to the
relaxation dynamics of paramagnetic ions contained within the levers. We
measure cantilevers containing paramagnetic Mn ions as a function of
temperature, magnetic field, and the vibrational mode of the lever and find
that the levers damping is strongly enhanced by the interplay between the
motion of the lever, the ions magnetic anisotropy, and the ratio of the ions
longitudinal relaxation rate to the resonance frequency of the cantilever. This
enhancement can improve the levers ability to probe the relaxation behavior of
paramagnetic or superparamagetic systems; it may also represent a previously
unrecognized source of intrinsic dissipation in micromechanical structures.",0303489v1
2003-03-27,Oscillatory wave fronts in chains of coupled nonlinear oscillators,"Wave front pinning and propagation in damped chains of coupled oscillators
are studied. There are two important thresholds for an applied constant stress
$F$: for $|F|<F_{cd}$ (dynamic Peierls stress), wave fronts fail to propagate,
for $F_{cd} < |F| < F_{cs}$ stable static and moving wave fronts coexist, and
for $|F| > F_{cs}$ (static Peierls stress) there are only stable moving wave
fronts. For piecewise linear models, extending an exact method of Atkinson and
Cabrera's to chains with damped dynamics corroborates this description. For
smooth nonlinearities, an approximate analytical description is found by means
of the active point theory. Generically for small or zero damping, stable wave
front profiles are non-monotone and become wavy (oscillatory) in one of their
tails.",0303576v1
2003-06-03,Local Relaxation and Collective Stochastic Dynamics,"Damping and thermal fluctuations have been introduced to collective normal
modes of a magnetic system in recent modeling of dynamic thermal magnetization
processes. The connection between this collective stochastic dynamics and
physical local relaxation processes is investigated here. A system of two
coupled magnetic grains embedded in two separate oscillating thermal baths is
analyzed with no \QTR{it}{a priori} assumptions except that of a Markovian
process. It is shown explicitly that by eliminating the oscillating thermal
bath variables, collective stochastic dynamics occurs in the normal modes of
the magnetic system. The grain interactions cause local relaxation to be felt
by the collective system and the dynamic damping to reflect the system
symmetry. This form of stochastic dynamics is in contrast to a common
phenomenological approach where a thermal field is added independently to the
dynamic equations of each discretized cell or interacting grain. The dependence
of this collective stochastic dynamics on the coupling strength of the magnetic
grains and the relative local damping is discussed.",0306047v1
2003-07-22,Classical dynamics of a nano-mechanical resonator coupled to a single-electron transistor,"We analyze the dynamics of a nano-mechanical resonator coupled to a
single-electron transistor (SET) in the regime where the resonator behaves
classically. A master equation is derived describing the dynamics of the
coupled system which is then used to obtain equations of motion for the average
charge state of the SET and the average position of the resonator. We show that
the action of the SET on the resonator is very similar to that of a thermal
bath, as it leads to a steady-state probability-distribution for the resonator
which can be described by mean values of the resonator position, a renormalized
frequency, an effective temperature and an intrinsic damping constant.
Including the effects of extrinsic damping and finite temperature, we find that
there remain experimentally accessible regimes where the intrinsic damping of
the resonator still dominates its behavior. We also obtain the average current
through the SET as a function of the coupling to the resonator.",0307528v1
2003-10-09,Direct measurement of molecular stiffness and damping in confined water layers,"We present {\em direct} and {\em linear} measurements of the normal stiffness
and damping of a confined, few molecule thick water layer. The measurements
were obtained by use of a small amplitude (0.36 $\textrm{\AA}$), off-resonance
Atomic Force Microscopy (AFM) technique. We measured stiffness and damping
oscillations revealing up to 7 layers separated by 2.56 $\pm$ 0.20
$\textrm{\AA}$. Relaxation times could also be calculated and were found to
indicate a significant slow-down of the dynamics of the system as the confining
separation was reduced. We found that the dynamics of the system is determined
not only by the interfacial pressure, but more significantly by solvation
effects which depend on the exact separation of tip and surface. Thus `
solidification\rq seems to not be merely a result of pressure and confinement,
but depends strongly on how commensurate the confining cavity is with the
molecule size. We were able to model the results by starting from the simple
assumption that the relaxation time depends linearly on the film stiffness.",0310219v1
2004-03-08,Mean-field magnetization relaxation in conducting ferromagnets,"Collective ferromagnetic motion in a conducting medium is damped by the
transfer of the magnetic moment and energy to the itinerant carriers. We
present a calculation of the corresponding magnetization relaxation as a
linear-response problem for the carrier dynamics in the effective exchange
field of the ferromagnet. In electron systems with little intrinsic spin-orbit
interaction, a uniform magnetization motion can be formally eliminated by going
into the rotating frame of reference for the spin dynamics. The ferromagnetic
damping in this case grows linearly with the spin-flip rate when the latter is
smaller than the exchange field and is inversely proportional to the spin-flip
rate in the opposite limit. These two regimes are analogous to the
""spin-pumping"" and the ""breathing Fermi-surface"" damping mechanisms,
respectively. In diluted ferromagnetic semiconductors, the hole-mediated
magnetization can be efficiently relaxed to the itinerant-carrier degrees of
freedom due to the strong spin-orbit interaction in the valence bands.",0403224v2
2004-04-05,Low-temperature specific heat of real crystals: Possibility of leading contribution of optical and short-wavelength acoustical vibrations,"We point out that the repeatedly reported glass-like properties of
crystalline materials are not necessarily associated with localized (or
quasilocalized) excitations. In real crystals, optical and short-wavelength
acoustical vibrations remain damped due to defects down to zero temperature. If
such a damping is frequency-independent, e.g. due to planar defects or charged
defects, these optical and short-wavelength acoustical vibrations yield a
linear-in-$T$ contribution to the low-temperature specific heat of the crystal
lattices. At low enough temperatures such a contribution will prevail over that
of the long-wavelength acoustical vibrations (Debye contribution). The
crossover between the linear and the Debye regime takes place at $T^* \propto
\sqrt N$, where $N$ is the concentration of the defects responsible for the
damping. Estimates show that this crossover could be observable.",0404063v4
2004-04-20,Decoherence processes during active manipulation of excitonic qubits in semiconductor quantum dots,"Using photoluminescence spectroscopy, we have investigated the nature of Rabi
oscillation damping during active manipulation of excitonic qubits in
self-assembled quantum dots. Rabi oscillations were recorded by varying the
pulse amplitude for fixed pulse durations between 4 ps and 10 ps. Up to 5
periods are visible, making it possible to quantify the excitation dependent
damping. We find that this damping is more pronounced for shorter pulse widths
and show that its origin is the non-resonant excitation of carriers in the
wetting layer, most likely involving bound-to-continuum and continuum-to-bound
transitions.",0404465v1
2004-07-29,From subdiffusion to superdiffusion of particles on solid surfaces,"We present a numerical and partially analytical study of classical particles
obeying a Langevin equation that describes diffusion on a surface modeled by a
two dimensional potential. The potential may be either periodic or random.
Depending on the potential and the damping, we observe superdiffusion,
large-step diffusion, diffusion, and subdiffusion. Superdiffusive behavior is
associated with low damping and is in most cases transient, albeit often long.
Subdiffusive behavior is associated with highly damped particles in random
potentials. In some cases subdiffusive behavior persists over our entire
simulation and may be characterized as metastable. In any case, we stress that
this rich variety of behaviors emerges naturally from an ordinary Langevin
equation for a system described by ordinary canonical Maxwell-Boltzmann
statistics.",0407781v1
2004-08-18,Theory of Magnetic Polaron,"The concept of magnetic polaron is analysed and developed to elucidate the
nature of itinerant charge carrier states in magnetic semiconductors and
similar complex magnetic materials. By contrasting the scattering and bound
states of carriers within the $s-d$ exchange model, the nature of bound states
at finite temperatures is clarified. The free magnetic polaron at certain
conditions is realized as a bound state of the carrier (electron or hole) with
the spin wave. Quite generally, a self-consistent theory of a magnetic polaron
is formulated within a nonperturbative many-body approach, the Irreducible
Green Functions (IGF) method which is used to describe the quasiparticle
many-body dynamics at finite temperatures. Within the above many-body approach
we elaborate a self-consistent picture of dynamic behavior of two interacting
subsystems, the localized spins and the itinerant charge carriers. In
particular, we show that the relevant generalized mean fields emerges naturally
within our formalism. At the same time, the correct separation of elastic
scattering corrections permits one to consider the damping effects (inelastic
scattering corrections) in the unified and coherent fashion. The damping of
magnetic polaron state, which is quite different from the damping of the
scattering states, finds a natural interpretation within the present
self-consistent scheme.",0408404v2
2004-09-27,Dephasing and delay time fluctuations in the chaotic scattering of a quantum particle weakly coupled to a complicated background,"Effect of a complicated many-body environment is analyzed on the chaotic
motion of a quantum particle in a mesoscopic ballistic structure. The dephasing
and absorption phenomena are treated on the same footing in the framework of a
schematic microscopic model. The single-particle doorway resonance states
excited in the structure via an external channel are damped not only because of
the escape onto such channels but also due to ulterior population of the
long-lived background states. The transmission through the structure is
presented as an incoherent sum of the flow formed by the interfering damped
doorway resonances and the retarded flow of the particles reemitted by the
environment. The resulting internal damping as well as the dephasing rate are
uniquely expressed in terms of the spreading width which controls the coupling
to the background. The formation of the long-lived fine-structure resonances
strongly enhances delay time fluctuations thus broadening the delay time
distribution.",0409690v1
2005-01-18,Damping effects and the metal-insulator transition in the two-dimensional electron gas,"The damping of single-particle degrees of freedom in strongly correlated
two-dimensional Fermi systems is analyzed. Suppression of the scattering
amplitude due to the damping effects is shown to play a key role in preserving
the validity of the Landau-Migdal quasiparticle picture in a region of a phase
transition, associated with the divergence of the quasiparticle effective mass.
The results of the analysis are applied to elucidate the behavior of the
conductivity $\sigma(T)$ of the two-dimensional dilute electron gas in the
density region where it undergoes a metal-insulator transition.",0501427v2
2005-04-17,Dynamics of thermoelastic thin plates: A comparison of four theories,"Four distinct theories describing the flexural motion of thermoelastic thin
plates are compared. The theories are due to Chadwick, Lagnese and Lions,
Simmonds, and Norris. Chadwick's theory requires a 3D spatial equation for the
temperature but is considered the most accurate as the others are derivable
from it by different approximations. Attention is given to the damping of
flexural waves. Analytical and quantitative comparisons indicate that the
Lagnese and Lions model with a 2D temperature equation captures the essential
features of the thermoelastic damping, but contains systematic inaccuracies.
These are attributable to the approximation for the first moment of the
temperature used in deriving the Lagnese and Lions equation. Simmonds' model
with an explicit formula for temperature in terms of plate deflection is the
simplest of all but is accurate only at low frequency, where the damping is
linearly proportional to the frequency. It is shown that the Norris model,
which is almost as simple as Simmond's, is as accurate as the more precise but
involved theory of Chadwick.",0504412v1
2005-04-29,Probing temperature and damping rates in Bose-Einstein condensates using ultraslow light experiments,"We propose a method to probe Landau and Beliaev processes in dilute trapped
atomic condensates with a multiple state structure using ultraslow light
experimental configurations. Under certain conditions, damping rates from these
collisional processes are directly proportional to the dephasing rates, making
it possible to determine damping rates through measurement of the dephasing. In
the ultraslow light systems we consider, Landau decay rates are enhanced at low
momenta, which allows one to distinguish between Landau-dominated and
Beliaev-dominated regimes at the same temperature. Furthermore, the enhancement
of Landau rates potentially provides a way to measure low temperatures ($T \ll
T_c$) in dilute condensates more accurately than current methods permit.",0504784v2
2005-05-23,Anharmonic vs. relaxational sound damping in glasses: I. Brillouin scattering from densified silica,"This series discusses the origin of sound damping and dispersion in glasses.
In particular, we address the relative importance of anharmonicity versus
thermally activated relaxation. In this first article, Brillouin-scattering
measurements of permanently densified silica glass are presented. It is found
that in this case the results are compatible with a model in which damping and
dispersion are only produced by the anharmonic coupling of the sound waves with
thermally excited modes. The thermal relaxation time and the unrelaxed velocity
are estimated.",0505558v3
2005-05-23,Anharmonic vs. relaxational sound damping in glasses: II. Vitreous silica,"The temperature dependence of the frequency dispersion in the sound velocity
and damping of vitreous silica is reanalyzed. Thermally activated relaxation
accounts for the sound attenuation observed above 10 K at sonic and ultrasonic
frequencies. Its extrapolation to the hypersonic regime reveals that the
anharmonic coupling to the thermal bath becomes important in
Brillouin-scattering measurements. At 35 GHz and room temperature, the damping
due to this anharmonicity is found to be nearly twice that produced by
thermally activated relaxation. The analysis also reveals a sizeable velocity
increase with temperature which is not related with sound dispersion. This
suggests that silica experiences a gradual structural change that already
starts well below room temperature.",0505560v2
2005-06-06,Heat Bath Approach to Landau Damping and Pomeranchuk Quantum Critical Points,"We study the problem of the damping of collective modes close to a
Pomeranchuk quantum critical point in a Fermi liquid. In analogy with problems
in dissipative open quantum systems, we derive the Landau damping of a Fermi
liquid by integrating out a macroscopic number of degrees of freedom from a
generating functional. Being a reformulation of the linearized Boltzmann
equation this approach reproduces well-known results from the theory of Fermi
liquids. We also study the Bethe-Salpeter equations within the Landau theory
and discuss the implications of these results on quantum phase transitions of
the Pomeranchuk type and its dynamical exponent, z. We apply our results to the
electronic nematic instability and find z=3 in the collisionless limit.",0506146v3
2005-07-01,Measurement of Dissipation of a Three-Level rf SQUID Qubit,"The dissipation-induced relaxation (T_1) time of a macroscopic quantum system
- a \{lambda}-type three-level rf SQUID flux qubit weakly coupled to control
and readout circuitry (CRC) - is investigated via time-domain measurement. The
measured interwell relaxation time of the qubit's first excited state,
T_1=3.45+/-0.06 \{mu}s, corresponds to an effective damping resistance of the
flux qubit R=1.6+/-0.1 M\{omega} which is much lower than the intrinsic
quasiparticle resistance of the Josephson tunnel junction. An analysis of the
system shows that although the CRC is very weakly coupled to the qubit it is
the primary source of damping. This type of damping can be significantly
reduced by the use of more sophisticated circuit design to allow coherent
manipulation of qubit states.",0507008v1
2005-09-19,Interaction effects on magnetooscillations in a two-dimensional electron gas,"Motivated by recent experiments, we study the interaction corrections to the
damping of magnetooscillations in a two-dimensional electron gas (2DEG). We
identify leading contributions to the interaction-induced damping which are
induced by corrections to the effective mass and quantum scattering time. The
damping factor is calculated for Coulomb and short-range interaction in the
whole range of temperatures, from the ballistic to the diffusive regime. It is
shown that the dominant effect is that of the renormalization of the effective
electron mass due to the interplay of the interaction and impurity scattering.
The results are relevant to the analysis of experiments on magnetooscillations
(in particular, for extracting the value of the effective mass) and are
expected to be useful for understanding the physics of a high-mobility 2DEG
near the apparent metal-insulator transition.",0509463v2
2005-12-20,Damping of zero sound in Luttinger liquids,"We calculate the damping gamma_q of collective density oscillations (zero
sound) in a one-dimensional Fermi gas with dimensionless forward scattering
interaction F and quadratic energy dispersion k^2 / 2 m at zero temperature.
For wave-vectors | q| /k_F small compared with F we find to leading order
gamma_q = v_F^{-1} m^{-2} Y (F) | q |^3, where v_F is the Fermi velocity, k_F
is the Fermi wave-vector, and Y (F) is proportional to F^3 for small F. We also
show that zero-sound damping leads to a finite maximum proportional to |k - k_F
|^{-2 + 2 eta} of the charge peak in the single-particle spectral function,
where eta is the anomalous dimension. Our prediction agrees with photoemission
data for the blue bronze K_{0.3}MoO_3.",0512494v4
2006-04-11,Damping and dispersion of oscillating modes of a multicomponent ionic mixture in a magnetic field,"The collective-mode spectrum of a multicomponent magnetized ionic mixture for
small wave number k is studied with the use of magnetohydrodynamics and formal
kinetic theory. Apart from the usual thermal and diffusive modes, the spectrum
contains a set of four oscillating modes. By evaluating the k^2 contributions
to the eigenfrequencies, the damping and the dispersion of these oscillating
modes are determined. The long-range nature of the Coulomb interactions is
shown to imply that Burnett terms with higher-order gradients in the linear
phenomenological laws have to be taken into account in order to obtain a full
description of all damping and dispersion effects.",0604272v1
2006-05-16,Collective mode damping and viscosity in a 1D unitary Fermi gas,"We calculate the damping of the Bogoliubov-Anderson mode in a one-dimensional
two-component attractive Fermi gas for arbitrary coupling strength within a
quantum hydrodynamic approach. Using the Bethe-Ansatz solution of the 1D
BCS-BEC crossover problem, we derive analytic results for the viscosity
covering the full range from a Luther-Emery liquid of weakly bound pairs to a
Lieb-Liniger gas of strongly bound bosonic dimers. At the unitarity point, the
system is a Tonks-Girardeau gas with a universal constant $\alpha_{\zeta}=0.38$
in the viscosity $\zeta=\alpha_{\zeta}\hbar n$ for T=0. For the trapped case,
we calculate the Q-factor of the breathing mode and show that the damping
provides a sensitive measure of temperature in 1D Fermi gases.",0605413v2
2006-07-06,Low energy theory of a single vortex and electronic quasiparticles in a d-wave superconductor,"We highlight the properties of a simple model (contained in our recent work)
of the quantum dynamics of a single point vortex interacting with the nodal
fermionic quasiparticles of a d-wave superconductor. We describe the
renormalization of the vortex motion by the quasiparticles: at T=0, the
quasiparticles renormalize the vortex mass and introduce only a weak sub-Ohmic
damping. Ohmic (or `Bardeen-Stephen' damping) appears at T>0, with the damping
co-efficient vanishing ~ T^2 with a universal prefactor. Conversely, quantum
fluctuations of the vortex renormalize the quasiparticle spectrum. A point
vortex oscillating in a harmonic pinning potential has no zero-bias peak in the
electronic local density of states (LDOS), but has small satellite features at
an energy determined by the pinning potential. These are proposed as the origin
of sub-gap LDOS peaks observed in scanning tunneling microscopic studies of the
LDOS near a vortex.",0607137v2
2005-08-23,Investigations of Process Damping Forces in Metal Cutting,"Using finite element software developed for metal cutting by Third Wave
Systems we investigate the forces involved in chatter, a self-sustained
oscillation of the cutting tool. The phenomena is decomposed into a vibrating
tool cutting a flat surface work piece, and motionless tool cutting a work
piece with a wavy surface. While cutting the wavy surface, the shearplane was
seen to oscillate in advance of the oscillation of the depth of cut, as were
the cutting, thrust, and shear plane forces. The vibrating tool was used to
investigate process damping through the interaction of the relief face of the
tool and the workpiece. Crushing forces are isolated and compared to the
contact length between the tool and workpiece. We found that the wavelength
dependence of the forces depended on the relative size of the wavelength to the
length of the relief face of the tool. The results indicate that the damping
force from crushing will be proportional to the cutting speed for short tools,
and inversely proportional for long tools.",0508102v1
1999-09-27,R-Modes in Superfluid Neutron Stars,"The analogs of r-modes in superfluid neutron stars are studied here. These
modes, which are governed primarily by the Coriolis force, are identical to
their ordinary-fluid counterparts at the lowest order in the small
angular-velocity expansion used here. The equations that determine the next
order terms are derived and solved numerically for fairly realistic superfluid
neutron-star models. The damping of these modes by superfluid ``mutual
friction'' (which vanishes at the lowest order in this expansion) is found to
have a characteristic time-scale of about 10^4 s for the m=2 r-mode in a
``typical'' superfluid neutron-star model. This time-scale is far too long to
allow mutual friction to suppress the recently discovered gravitational
radiation driven instability in the r-modes. However, the strength of the
mutual friction damping depends very sensitively on the details of the
neutron-star core superfluid. A small fraction of the presently acceptable
range of superfluid models have characteristic mutual friction damping times
that are short enough (i.e. shorter than about 5 s) to suppress the
gravitational radiation driven instability completely.",9909084v1
2001-02-08,Cyclotron damping and Faraday rotation of gravitational waves,"We study the propagation of gravitational waves in a collisionless plasma
with an external magnetic field parallel to the direction of propagation. Due
to resonant interaction with the plasma particles the gravitational wave
experiences cyclotron damping or growth, the latter case being possible if the
distribution function for any of the particle species deviates from
thermodynamical equilibrium. Furthermore, we examine how the damping and
dispersion depends on temperature and on the ratio between the cyclotron- and
gravitational wave frequency. The presence of the magnetic field leads to
different dispersion relations for different polarizations, which in turn imply
Faraday rotation of gravitational waves.",0102031v2
2007-02-07,Relativistic r-modes and shear viscosity,"We derive the relativistic equations for stellar perturbations, including in
a consistent way shear viscosity in the stress-energy tensor, and we
numerically integrate our equations in the case of large viscosity. We consider
the slow rotation approximation, and we neglect the coupling between polar and
axial perturbations. In our approach, the frequency and damping time of the
emitted gravitational radiation are directly obtained. We find that,
approaching the inviscid limit from the finite viscosity case, the continuous
spectrum is regularized. Constant density stars, polytropic stars, and stars
with realistic equations of state are considered. In the case of constant
density stars and polytropic stars, our results for the viscous damping times
agree, within a factor two, with the usual estimates obtained by using the
eigenfunctions of the inviscid limit. For realistic neutron stars, our
numerical results give viscous damping times with the same dependence on mass
and radius as previously estimated, but systematically larger of about 60%.",0702040v1
2000-08-18,Fabrication Process of Rounded Damped Detuned Structure,"Following the successful design and fabrication of Damped Detuned Structures
(DDS), the JLC/NLC linear collider project advanced to Rounded Damped Detuned
Structures (RDDS) with curved cross section of the cavity shape for increased
shunt impedance. Various advanced techniques for fabricating RDDS1 disks
comparing to those for DDS were established to satisfy the dimension accuracy
of +-1 micron over the entire surface made by ultra-precision turning. These
disks were assembled with almost the same stacking and bonding jigs and
processes as those of DDS3 assembly. In consequence, the assembly showed little
disk-to-disk misalignment within 1 micron before and after the process. Though,
it had 200 micron smooth bowing, which was subsequently corrected as DDS3, and
flares at both ends.",0008034v1
2000-08-18,Meeting Tight Frequency Requirement of Rounded Damped Detuned Structure,"Following successful design and fabrication of damped detuned structures, the
R&D for the accelerating structures of the NLC/JLC linear collider project
proceeded to studies of Rounded Damped Detuned Structure with curved cross
section of the cavity shape for increased shunt impedance. The important
features of the structure are the accurately tuned accelerating mode frequency
and the distribution of the first dipole modes smooth and close to the design
distribution. These requirements were met based on the high-accuracy diamond
turning with its capability to realize the periphery tolerance of two microns.
The lowest dipole mode frequencies scattered by 0.6 MHz RMS. The error in the
accelerating mode frequency averaged over a structure was 0.1 MHz by applying a
feed-forward method.",0008035v1
1992-03-16,Comment on ``Damping of energetic gluons and quarks in high-temperature QCD'',"Burgess and Marini have recently pointed out that the leading contribution to
the damping rate of energetic gluons and quarks in the QCD plasma, given by
$\gamma=c g^2\ln(1/g)T$, can be obtained by simple arguments obviating the need
of a fully resummed perturbation theory as developed by Braaten and Pisarski.
Their calculation confirmed previous results of Braaten and Pisarski, but
contradicted those proposed by Lebedev and Smilga. While agreeing with the
general considerations made by Burgess and Marini, I correct their actual
calculation of the damping rates, which is based on a wrong expression for the
static limit of the resummed gluon propagator. The effect of this, however,
turns out to be cancelled fortuitously by another mistake, so as to leave all
of their conclusions unchanged. I also verify the gauge independence of the
results, which in the corrected calculation arises in a less obvious manner.",9203211v1
1995-02-16,The Infrared Sensitivity of Screening and Damping in a Quark-Gluon Plasma,"All the next-to-leading order contributions to the quasi-particle dispersion
laws of a quark-gluon plasma which due to infrared singularities are sensitive
to the magnetic-mass scale are calculated using Braaten-Pisarski resummation.
These relative-order-$g\ln(g)$ corrections are shown here to generally
contribute to the dynamical screening of gluonic fields with frequencies below
the plasma frequency as well as to the damping of propagating gluonic and
fermionic quasi-particles. In the limit of vanishing wave-vector the infrared
singularities disappear, but in a way that raises the possibility for formally
higher orders of the Braaten-Pisarski scheme to equally contribute at
next-to-leading order when the wave-vector is of the order of or less than the
magnetic-mass scale. This is argued to be a problem in particular for the
fermionic damping rate.",9502324v1
1997-10-30,Damping rate for transverse gluons with finite soft momentum in hot QCD,"We calculate the damping rate for transverse gluons with {\nineti finite}
soft momentum to leading order in perturbative hot QCD. The internal momenta of
the one-loop contributing diagrams are soft. This means we have to use
effective vertices and propagators which incorporate the so-called hard thermal
loops. We expand the damping rate in powers of the incoming momentum and argue
that the series ought to converge within a finite radius of convergence. We
contrast such a behavior with the one obtained from a previous calculation that
produced a logarithmic behavior, a calculation based on letting the gluon
momentum come from the hard limit down towards the interior of the soft region.
This difference in behavior may point to interesting physics around some
`critical' region.",9710549v2
1998-07-21,An infrared singularity in the damping rate for longitudinal gluons in hot QCD,"We calculate $\gamma_l(0)$, the damping rate for longitudinal on-shell gluons
with zero momentum in hot QCD using the hard-thermal-loop (htl) scheme. We find
it to be divergent in the infrared, which means that in this scheme
$\gamma_l(0)$ is different from $\gamma_t(0)$, the corresponding damping rate
for transverse gluons which is known to be finite. This result suggests that
the htl scheme is infrared sensitive and thus may need to be improved upon in
this sector. We discuss this issue after we present our calculation.",9807439v2
1998-09-25,Damping rates in the MSSM and electroweak baryogenesis,"We present an analysis of the thermalization rate of Higgsinos and winos
based on the imaginary part of the two-point Green function in the {\it
unbroken} phase of the MSSM. We use improved propagators including resummation
of hard thermal loops and the thermalization rate is computed at the one-loop
level in the high temperature approximation. We find that the damping is
typically dominated by scattering with gauge bosons, resulting in a damping
rate of about $\gamma_{\Ht}\simeq 0.025T$, $\gamma_{\Wt}\simeq 0.065T$. The
contribution from scattering with scalars is relatively small. Implications for
baryogenesis are also discussed.",9809529v1
2006-10-27,The soft fermion dispersion relation at next-to-leading order in hot QED,"We study next-to-leading order contributions to the soft static fermion
dispersion relation in hot QED. We derive an expression for the complete
next-to-leading order contribution to the retarded fermion self-energy. The
real and imaginary parts of this expression give the next-to-leading order
contributions to the mass and damping rate of the fermionic quasi-particle.
Many of the terms that are expected to contribute according to the traditional
power counting argument are actually subleading. We explain why the power
counting method over estimates the contribution from these terms. For the
electron damping rate in QED we obtain: $\gamma_{QED} = \frac{e^2
T}{4\pi}(2.70)$. We check our method by calculating the next-to-leading order
contribution to the damping rate for the case of QCD with two flavours and
three coulours. Our result agrees with the result obtained previously in the
literature. The numerical evaluation of the nlo contribution to the mass is
left to a future publication.",0610372v1
2007-03-26,Preheating and Affleck-Dine leptogenesis after thermal inflation,"Previously, we proposed a model of low energy Affleck-Dine leptogenesis in
the context of thermal inflation. The lepton asymmetry is generated at the end
of thermal inflation, which occurs at a relatively low energy scale with the
Hubble parameter somewhere in the range $1 \keV \lesssim H \lesssim 1 \MeV$.
Thus Hubble damping will be ineffective in bringing the Affleck-Dine field into
the lepton conserving region near the origin, leaving the possibility that the
lepton number could be washed out. Previously, we suggested that preheating
could damp the amplitude of the Affleck-Dine field allowing conservation of the
lepton number. In this paper, we demonstrate numerically that preheating does
efficiently damp the amplitude of the Affleck-Dine field and that the lepton
number is conserved as the result. In addition to demonstrating a crucial
aspect of our model, it also opens the more general possibility of low energy
Affleck-Dine baryogenesis.",0703275v1
1996-03-14,Dissipation and Topologically Massive Gauge Theories in Pseudoeuclidean Plane,"In the pseudo-euclidean metrics Chern-Simons gauge theory in the infrared
region is found to be associated with dissipative dynamics. In the infrared
limit the Lagrangian of 2+1 dimensional pseudo-euclidean topologically massive
electrodynamics has indeed the same form of the Lagrangian of the damped
harmonic oscillator. On the hyperbolic plane a set of two damped harmonic
oscillators, each other time-reversed, is shown to be equivalent to a single
undamped harmonic oscillator. The equations for the damped oscillators are
proven to be the same as the ones for the Lorentz force acting on two particles
carrying opposite charge in a constant magnetic field and in the electric
harmonic potential. This provides an immediate link with Chern-Simons-like
dynamics of Bloch electrons in solids propagating along the lattice plane with
hyperbolic energy surface. The symplectic structure of the reduced theory is
finally discussed in the Dirac constrained canonical formalism.",9603092v1
2002-08-31,Neutrino damping rate at finite temperature and density,"A first principle derivation is given of the neutrino damping rate in
real-time thermal field theory. Starting from the discontinuity of the neutrino
self energy at the two loop level, the damping rate can be expressed as
integrals over space phase of amplitudes squared, weighted with statistical
factors that account for the possibility of particle absorption or emission
from the medium. Specific results for a background composed of neutrinos,
leptons, protons and neutrons are given. Additionally, for the real part of the
dispersion relation we discuss the relation between the results obtained from
the thermal field theory, and those obtained by the thermal average of the
forward scattering amplitude.",0209006v1
2004-10-20,Ergodicity for the weakly damped stochastic non-linear Schrödinger equations,"We study a damped stochastic non-linear Schr\""{o}dinger (NLS) equation driven
by an additive noise. It is white in time and smooth in space. Using a coupling
method, we establish convergence of the Markovian transition semi-group toward
a unique invariant probability measure. This kind of method was originally
developped to prove exponential mixing for strongly dissipative equations such
as the Navier-Stokes equations. We consider here a weakly dissipative equation,
the damped nonlinear Schr\""{o}dinger equation in the one dimensional cubic
case. We prove that the mixing property holds and that the rate of convergence
to equilibrium is at least polynomial of any power.",0410443v2
2006-07-30,Non-autonomous dynamics of wave equations with nonlinear damping and critical nonlinearity,"The authors consider non-autonomous dynamical behavior of wave-type
evolutionary equations with nonlinear damping and critical nonlinearity. These
type of waves equations are formulated as non-autonomous dynamical systems
(namely, cocycles). A sufficient and necessary condition for the existence of
pullback attractors is established for norm-to-weak continuous non-autonomous
dynamical systems, in terms of pullback asymptotic compactness or pullback
$\kappa-$contraction criteria. A technical method for verifying pullback
asymptotic compactness, via contractive functions, is devised. These results
are then applied to the wave-type evolutionary equations with nonlinear damping
and critical nonlinearity, to obtain the existence of pullback attractors. The
required pullback asymptotic compactness for the existence of pullback
attractors is fulfilled by some new a priori estimates for concrete wave type
equations arising from applications. Moreover, the pullback
$\kappa-$contraction criterion for the existence of pullback attractors is of
independent interest.",0607774v3
2000-09-28,"Quantization of Damped Harmonic Oscillator, Thermal Field Theories and q-Groups","We study the canonical quantization of the damped harmonic oscillator by
resorting to the realization of the q-deformation of the Weyl-Heisenberg
algebra (q-WH) in terms of finite difference operators. We relate the damped
oscillator hamiltonian to the q-WH algebra and to the squeezing generator of
coherent states theory. We also show that the q-WH algebra is the natural
candidate to study thermal field theory. The well known splitting, in the
infinite volume limit, of the space of physical states into unitarily
inequivalent representations of the canonical commutation relations is briefly
commented upon in relation with the von Neumann theorem in quantum mechanics
and with q-WH algebra.",0009036v1
2001-11-14,"Soliton-radiation coupling in the parametrically driven, damped nonlinear Schrödinger equation","We use the Riemann-Hilbert problem to study the interaction of the soliton
with radiation in the parametrically driven, damped nonlinear Schr\""odinger
equation. The analysis is reduced to the study of a finite-dimensional
dynamical system for the amplitude and phase of the soliton and the complex
amplitude of the long-wavelength radiation. In contrast to previously utilised
Inverse Scattering-based perturbation techniques, our approach is valid for
arbitrarily large driving strengths and damping coefficients. We show that,
contrary to suggestions made in literature, the complexity observed in the
soliton's dynamics cannot be accounted for just by its coupling to the
long-wavelength radiation.",0111034v1
2002-02-12,Landau Damping and Coherent Structures in Narrow-Banded 1+1 Deep Water Gravity Waves,"We study the nonlinear energy transfer around the peak of the spectrum of
surface gravity waves by taking into account nonhomogeneous effects. In the
narrow-banded approximation the kinetic equation resulting from a
nonhomogeneous wave field is a Vlasov-Poisson type equation which includes at
the same time the random version of the Benjamin-Feir instability and the
Landau damping phenomenon. We analytically derive the values of the Phillips'
constant $\alpha$ and the enhancement factor $\gamma$ for which the
narrow-banded approximation of the JONSWAP spectrum is unstable. By performing
numerical simulations of the nonlinear Schr\""{o}dinger equation we check the
validity of the prediction of the related kinetic equation. We find that the
effect of Landau damping is to suppress the formation of coherent structures.
The problem of predicting freak waves is briefly discussed.",0202026v1
2005-10-24,Stability of a nonlinear oscillator with random damping,"A noisy damping parameter in the equation of motion of a nonlinear oscillator
renders the fixed point of the system unstable when the amplitude of the noise
is sufficiently large. However, the stability diagram of the system can not be
predicted from the analysis of the moments of the linearized equation. In the
case of a white noise, an exact formula for the Lyapunov exponent of the system
is derived. We then calculate the critical damping for which the {\em
nonlinear} system becomes unstable. We also characterize the intermittent
structure of the bifurcated state above threshold and address the effect of
temporal correlations of the noise by considering an Ornstein-Uhlenbeck noise.",0510063v1
2006-10-20,Vibration of Generalized Double Well Oscillators,"We have applied the Melnikov criterion to examine a global homoclinic
bifurcation and transition to chaos in a case of a double well dynamical system
with a nonlinear fractional damping term and external excitation. The usual
double well Duffing potential having a negative square term and positive
quartic term has been generalized to a double well potential with a negative
square term and a positive one with an arbitrary real exponent $q > 2$. We have
also used a fractional damping term with an arbitrary power $p$ applied to
velocity which enables one to cover a wide range of realistic damping factors:
from dry friction $p \to 0$ to turbulent resistance phenomena $p=2$.
  Using perturbation methods we have found a critical forcing amplitude $\mu_c$
above which the system may behave chaotically. Our results show that the
vibrating system is less stable in transition to chaos for smaller $p$
satisfying an exponential scaling low. The critical amplitude $\mu_c$ as an
exponential function of $p$.
  The analytical results have been illustrated by numerical simulations using
standard nonlinear tools such as
  Poincare maps and the maximal Lyapunov exponent. As usual for chosen system
parameters we have identified a chaotic motion above the critical Melnikov
amplitude $\mu_c$.",0610052v1
1998-06-18,Relativity Damps OPEP in Nuclear Matter,"Using a relativistic Dirac-Brueckner analysis the OPEP contribution to the
ground state energy of nuclear matter is studied. In the study the pion is
derivative-coupled. We find that the role of the tensor force in the saturation
mechanism is substantially reduced compared to its dominant role in a usual
nonrelativistic treatment. We show that the damping of derivative-coupled OPEP
is actually due to the decrease of $M^*/M$ with increasing density. We point
out that if derivative-coupled OPEP is the preferred form of nuclear effective
lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking
the notion of $M^*$ it cannot replicate the damping. We suggest an examination
of the feasibility of using pseudoscalar coupled $\pi$N interaction before
reaching a final conclusion about nonrelativistic treatment of nuclear matter.",9806054v1
1999-07-05,Damping of IVGDR - Fermi-liquid or Fermi-gas ?,"Collisional relaxation rates of collective modes in nuclei are calculated
using the Levinson equation for the reduced density matrix with a memory
dependent collision term. Linearizing the collision integral two contribution
have to be distinguished, the one from the quasiparticle energy and the one
from occupation factors. The first one yields the known Landau formula of zero
sound damping and the second one leads to the Fermi gas model of Ref.1 with the
additional factor 3 in front of the frequencies. Adding both contribution we
obtain a final relaxation rate for the Fermi liquid model. Calculations of the
temperature dependence of the damping rates and of the shape evolution of IVGDR
are in good agreement with the experiment and show only minor differences
between both models.",9907012v1
2001-01-08,Collisional Damping of Giant Monopole and Quadrupole Resonances,"Collisional damping widths of giant monopole and quadrupole excitations for
$^{120}$Sn and $^{208}$Pb at zero and finite temperatures are calculated within
Thomas-Fermi approximation by employing the microscopic in-medium
cross-sections of Li and Machleidt and the phenomenological Skyrme and Gogny
forces, and are compared with each other. The results for the collisional
widths of giant monopole and quadrupole vibrations at zero temperature as a
function of the mass number show that the collisional damping of giant monopole
vibrations accounts for about 30-40% of the observed widths at zero
temperature, while for giant quadrupole vibrations it accounts for only 20-30%
of the observed widths of zero temperature.",0101016v1
1996-12-08,Towards a Simple Model of Compressible Alfvenic Turbulence,"A simple model collisionless, dissipative, compressible MHD (Alfvenic)
turbulence in a magnetized system is investigated. In contrast to more familiar
paradigms of turbulence, dissipation arises from Landau damping, enters via
nonlinearity, and is distributed over all scales. The theory predicts that two
different regimes or phases of turbulence are possible, depending on the ratio
of steepening to damping coefficient (m_1/m_2). For strong damping
(|m_1/m_2|<1), a regime of smooth, hydrodynamic turbulence is predicted. For
|m_1/m_2|>1, steady state turbulence does not exist in the hydrodynamic limit.
Rather, spikey, small scale structure is predicted.",9612005v2
1998-10-01,Mode-coupling and nonlinear Landau damping effects in auroral Farley-Buneman turbulence,"The fundamental problem of Farley-Buneman turbulence in the auroral
$E$-region has been discussed and debated extensively in the past two decades.
In the present paper we intend to clarify the different steps that the auroral
$E$-region plasma has to undergo before reaching a steady state. The
mode-coupling calculation, for Farley-Buneman turbulence, is developed in order
to place it in perspective and to estimate its magnitude relative to the
anomalous effects which arise through the nonlinear wave-particle interaction.
This nonlinear effect, known as nonlinear ``Landau damping'' is due to the
coupling of waves which produces other waves which in turn lose energy to the
bulk of the particles by Landau damping. This leads to a decay of the wave
energy and consequently a heating of the plasma. An equation governing the
evolution of the field spectrum is derived and a physical interpration for each
of its terms is provided.",9810062v1
2000-08-20,Fabrication and Tolerance Issues and their Influence on Multi-Bunch Bbu and Emittance Dilution in the Construction of X-Band RDDS Linacs for the NLC,"The main linacs of the Next Linear Collider (NLC) will contain several
thousand X-band RDDS (Rounded Damped Detuned Structures). The transverse
wakefield in the structures is reduced by detuning the modal frequencies such
that they destructively interfere and by four damping manifolds per structure
which provide weak damping. Errors in the fabrication of the individual cells
and in the alignment of the cells will reduce the cancellation of the modes.
Here, we calculate the tolerances on random errors in the synchronous
frequencies of the cells and the cell-to-cell alignment.",0008198v1
2003-09-17,A New Damping Mechanism in Non-linear Bubble Dynamics,"Non-linear equations of radial motion of a gas bubble in a compressible
viscous liquid have been modified considering effects of viscosity and
compressibility more complete than all previous works. A new set of equations
has been derived including new terms resulted from consideration of the
viscosity and compressibility not only at the bubble interface, but also in the
bulk of liquid. The new equations are two non-linear coupled equations, which
can not be merged into one equation unlike all previously derived equations.
Numerical calculations have been performed considering effects of heat and mass
transfer at the bubble interface. The results indicate that the new terms
exhibit an important damping role at the collapse, so that their consideration
dramatically weakens the bubble rebounds after the collapse. Dependence of this
new damping mechanism to amplitude and frequency of the deriving pressure has
been investigated.",0309080v1
2003-11-26,Eigenvector Expansion and Petermann Factor for Ohmically Damped Oscillators,"Correlation functions $C(t) \sim <\phi(t)\phi(0)>$ in ohmically damped
systems such as coupled harmonic oscillators or optical resonators can be
expressed as a single sum over modes $j$ (which are not power-orthogonal), with
each term multiplied by the Petermann factor (PF) $C_j$, leading to ""excess
noise"" when $|C_j| > 1$. It is shown that $|C_j| > 1$ is common rather than
exceptional, that $|C_j|$ can be large even for weak damping, and that the PF
appears in other processes as well: for example, a time-independent
perturbation $\sim\ep$ leads to a frequency shift $\sim \ep C_j$. The
coalescence of $J$ ($>1$) eigenvectors gives rise to a critical point, which
exhibits ""giant excess noise"" ($C_j \to \infty$). At critical points, the
divergent parts of $J$ contributions to $C(t)$ cancel, while time-independent
perturbations lead to non-analytic shifts $\sim \ep^{1/J}$.",0311127v2
2004-04-02,DAFNE injection system upgrade,"High luminosity in DAFNE needs very high electron and positron currents
stored. A full energy (510 MeV) injection system composed by a full energy
electron and positron linac and an accumulator-damping ring is presently used.
The electron and positron beams, alternatively accelerated by the linac, are
injected and stacked in the accumulator with high efficiency thanks to its
large acceptance and short damping time. The damped beams are extracted and
transferred to the main ring through a long transfer line that has been built
inside already existing buildings. The refill time of the collider is limited
by the transfer line set-up change between the two different beams modes. In
this paper a transfer line modification is proposed in order to reduce the
switch time. A possible injection scheme for the main rings is also described.",0404010v1
2004-05-05,Langmuir wave self-focusing versus decay instability,"Electron trapping in a finite amplitude Langmuir wave (LW) leads to a
frequency shift, \Delta\omega_{TP} < 0, and reduced Landau damping. These may
lead to modulational instability. Its growth rate and damping threshold, due to
escape of trapped electrons at rate \nu, are calculated for the first time in
the short wavelength regime. If the background plasma is in thermal
equilibrium, it is shown that this trapped particle modulational instability
(TPMI) is not possible when k \lambda_D > 0.46, while for 0.33 < k \lambda_D <
0.46, TPMI requires that the fluctuation wavevector have a component
perpendicular to k, the LW wavevector, with \lambda_D the electron Debye
length. Its nonlinear evolution leads to self-focusing. Comparison is made with
a re-evaluated LW ion acoustic decay instability (LDI): compared to classical
estimates, the new LDI threshold is lowered by primary LW \Delta\omega_{TP}
since frequency matching leads to wavenumber and hence damping reduction of the
daughter LW. For parameters estimates relevant to a recent stimulated Raman
scatter experiment (Kline et al., submitted to PRL), the LDI and TPMI
thresholds cross in the range 0.28 < k \lambda_D < 0.34, consistent with the
observed LDI regime change. However, if \nu exceeds a critical value, estimated
to be order 1% of the electron plasma frequency, then TPMI is not possible at
any wavenumber.",0405015v1
2005-06-16,Mesoscale Quantization and Self-Organized Stability,"In the world of technology, one of the most important forms of friction is
that of rolling friction. Yet it is one of the least studied of all the known
forms of energy dissipation. In the present experiments we investigate the
oscillatory free-decay of a rigid cube, whose side-length is less than the
diameter of the rigid cylinder on which it rests. The resulting free-decay is
one of harmonic motion with damping. The non-dissipative character of the
oscillation yields to a linear differential equation; however, the damping is
found to involve more than a deterministic nonlinearity. Dominated by rolling
friction, the damping is sensitive to the material properties of the contact
surfaces. For `clean' surfaces of glass on glass, the decay shows features of
mesoscale quantization and self-organized stability.",0506143v1
2006-10-31,Ultimate parameters of the photon collider at the ILC,"At linear colliders, the e+e- luminosity is limited by beam-collision
effects, which determine the required emittances of beams in damping rings
(DRs). While in gamma-gamma collisions at the photon collider, these effects
are absent, and so smaller emittances are desirable. In present damping rings
designs, nominal DR parameters correspond to those required for e+e-
collisions. In this note, I would like to stress once again that as soon as we
plan the photon-collider mode of ILC operation, the damping-ring emittances are
dictated by the photon-collider requirements--namely, they should be as small
as possible. This can be achieved by adding more wigglers to the DRs; the
incremental cost is easily justified by a considerable potential improvement of
the gamma-gamma luminosity. No expert analysis exists as of yet, but it seems
realistic to obtain a factor five increase of the gamma-gamma luminosity
compared to the ``nominal'' DR design.",0610285v1
2006-04-27,On the weak solutions of the McKendrick equation: Existence of demography cycles,"We develop the qualitative theory of the solutions of the McKendrick partial
differential equation of population dynamics. We calculate explicitly the weak
solutions of the McKendrick equation and of the Lotka renewal integral equation
with time and age dependent birth rate. Mortality modulus is considered age
dependent. We show the existence of demography cycles. For a population with
only one reproductive age class, independently of the stability of the weak
solutions and after a transient time, the temporal evolution of the number of
individuals of a population is always modulated by a time periodic function.
The periodicity of the cycles is equal to the age of the reproductive age
class, and a population retains the memory from the initial data through the
amplitude of oscillations. For a population with a continuous distribution of
reproductive age classes, the amplitude of oscillation is damped. The
periodicity of the damped cycles is associated with the age of the first
reproductive age class. Damping increases as the dispersion of the fertility
function around the age class with maximal fertility increases. In general, the
period of the demography cycles is associated with the time that a species
takes to reach the reproductive maturity.",0604035v2
1999-03-05,Exact Diagonalization of Two Quantum Models for the Damped Harmonic Oscillator,"The damped harmonic oscillator is a workhorse for the study of dissipation in
quantum mechanics. However, despite its simplicity, this system has given rise
to some approximations whose validity and relation to more refined descriptions
deserve a thorough investigation. In this work, we apply a method that allows
us to diagonalize exactly the dissipative Hamiltonians that are frequently
adopted in the literature. Using this method we derive the conditions of
validity of the rotating-wave approximation (RWA) and show how this approximate
description relates to more general ones. We also show that the existence of
dissipative coherent states is intimately related to the RWA. Finally, through
the evaluation of the dynamics of the damped oscillator, we notice an important
property of the dissipative model that has not been properly accounted for in
previous works; namely, the necessity of new constraints to the application of
the factorizable initial conditions.",9903022v2
1999-04-06,Nonclassical correlations in damped quantum solitons,"Using cumulant expansion in Gaussian approximation, the internal quantum
statistics of damped soliton-like pulses in Kerr media are studied numerically,
considering both narrow and finite bandwidth spectral pulse components. It is
shown that the sub-Poissonian statistics can be enhanced, under certain
circumstances, by absorption, which damps out some destructive interferences.
Further, it is shown that both the photon-number correlation and the
correlation of the photon-number variance between different pulse components
can be highly nonclassical even for an absorbing fiber. Optimum frequency
windows are determined in order to realize strong nonclassical behavior, which
offers novel possibilities of using solitons in optical fibers as a source of
nonclassically correlated light beams.",9904017v2
1999-04-19,Quantum theory of fluctuations in a cold damped accelerometer,"We present a quantum network approach to real high sensitivity measurements.
Thermal and quantum fluctuations due to active as well as passive elements are
taken into account. The method is applied to the analysis of the capacitive
accelerometer using the cold damping technique, developed for fundamental
physics in space by ONERA and the ultimate limits of this instrument are
discussed. It is confirmed in this quantum analysis that the cold damping
technique allows one to control efficiently the test mass motion without
degrading the noise level.",9904073v2
2000-07-04,Stochastic limit approximation for rapidly decaying systems,"The stochastic limit approximation method for ``rapid'' decay is presented,
where the damping rate \gamma is comparable to the system frequency \Omega,
i.e., \gamma \sim \Omega, whereas the usual stochastic limit approximation is
applied only to the weak damping situation \gamma << \Omega. The key formulas
for rapid decay are very similar to those for weak damping, but the dynamics is
quite different. From a microscopic Hamiltonian, the spin-boson model, a Bloch
equation containing two independent time scales is derived. This is a useful
method to extract the minimal dissipative dynamics at high temperature kT >>
\hbar\Omega and the master equations obtained are of the Lindblad form even for
the Caldeira-Leggett model. The validity of the method is confirmed by
comparing the master equation derived through this method with the exact one.",0007007v2
2000-08-01,Full mechanical characterization of a cold damped mirror,"We describe an experiment in which we have used a cold damping feedback
mechanism to reduce the thermal noise of a mirror around its mechanical
resonance frequency. The monitoring of the brownian motion of the mirror allows
to apply an additional viscous force without any thermal fluctuations
associated. This scheme has been experimentally implemented with the radiation
pressure of an intensity-modulated laser beam. Large noise reductions, up to 30
dB, have been obtained. We have also checked the mechanical response of the
cold damped mirror, and monitored its transient evolution between the cooled
regime and the room temperature equilibrium. A simple theoretical model allows
to fully explain the experimental results. A possible application to the active
cooling of the violin modes in a gravitational-wave interferometer is
discussed.",0008004v1
2003-11-05,Exact decoherence to pointer states in free open quantum systems is universal,"In this paper it is shown that exact decoherence to minimal uncertainty
Gaussian pointer states is generic for free quantum particles coupled to a heat
bath. More specifically, the paper is concerned with damped free particles
linearly coupled under product initial conditions to a heat bath at arbitrary
temperature, with arbitrary coupling strength and spectral densities covering
the Ohmic, subohmic, and supraohmic regime. Then it is true that there exists a
time t_c such that for times t>t_c the state can always be exactly represented
as a mixture (convex combination) of particular minimal uncertainty Gaussian
states, regardless of and independent from the initial state. This exact
`localisation' is hence not a feature specific to high temperatures and weak
damping limit, but is rather a generic property of damped free particles.",0311022v3
2004-07-30,Kraus representation of damped harmonic oscillator and its application,"By definition, the Kraus representation of a harmonic oscillator suffering
from the environment effect, modeled as the amplitude damping or the phase
damping, is directly given by a simple operator algebra solution. As examples
and applications, we first give a Kraus representation of a single qubit whose
computational basis states are defined as bosonic vacuum and single particle
number states. We further discuss the environment effect on qubits whose
computational basis states are defined as the bosonic odd and even coherent
states. The environment effects on entangled qubits defined by two different
kinds of computational basis are compared with the use of fidelity.",0407263v2
2005-01-31,"The non dissipative damping of the Rabi oscillations as a ""which-path"" information","Rabi oscillations may be viewed as an interference phenomenon due to a
coherent superposition of different quantum paths, like in the Young's two-slit
experiment. The inclusion of the atomic external variables causes a non
dissipative damping of the Rabi oscillations. More generally, the atomic
translational dynamics induces damping in the correlation functions which
describe non classical behaviors of the field and internal atomic variables,
leading to the separability of these two subsystems. We discuss on the
possibility of interpreting this intrinsic decoherence as a ""which-way""
information effect and we apply to this case a quantitative analysis of the
complementarity relation as introduced by Englert [Phys. Rev. Lett.
\textbf{77}, 2154 (1996)].",0501181v1
2006-01-12,Driven harmonic oscillator as a quantum simulator for open systems,"We show theoretically how a driven harmonic oscillator can be used as a
quantum simulator for non-Markovian damped harmonic oscillator. In the general
framework, the results demonstrate the possibility to use a closed system as a
simulator for open quantum systems. The quantum simulator is based on sets of
controlled drives of the closed harmonic oscillator with appropriately tailored
electric field pulses. The non-Markovian dynamics of the damped harmonic
oscillator is obtained by using the information about the spectral density of
the open system when averaging over the drives of the closed oscillator. We
consider single trapped ions as a specific physical implementation of the
simulator, and we show how the simulator approach reveals new physical insight
into the open system dynamics, e.g. the characteristic quantum mechanical
non-Markovian oscillatory behavior of the energy of the damped oscillator,
usually obtained by the non-Lindblad-type master equation, can have a simple
semiclassical interpretation.",0601081v2
2006-07-31,Nonadiabatic Transitions for a Decaying Two-Level-System: Geometrical and Dynamical Contributions,"We study the Landau-Zener Problem for a decaying two-level-system described
by a non-hermitean Hamiltonian, depending analytically on time. Use of a
super-adiabatic basis allows to calculate the non-adiabatic transition
probability P in the slow-sweep limit, without specifying the Hamiltonian
explicitly. It is found that P consists of a ``dynamical'' and a
``geometrical'' factors. The former is determined by the complex adiabatic
eigenvalues E_(t), only, whereas the latter solely requires the knowledge of
\alpha_(+-)(t), the ratio of the components of each of the adiabatic
eigenstates. Both factors can be split into a universal one, depending only on
the complex level crossing points, and a nonuniversal one, involving the full
time dependence of E_(+-)(t). This general result is applied to the
Akulin-Schleich model where the initial upper level is damped with damping
constant $\gamma$. For analytic power-law sweeps we find that Stueckelberg
oscillations of P exist for gamma smaller than a critical value gamma_c and
disappear for gamma > gamma_c. A physical interpretation of this behavior will
be presented by use of a damped harmonic oscillator.",0607221v1
2007-05-05,Damped Corrections to Inflationary Spectra from a Fluctuating Cutoff,"We reconsider trans-Planckian corrections to inflationary spectra by taking
into account a physical effect which has been overlooked and which could have
important consequences. We assume that the short length scale characterizing
the new physics is endowed with a finite width, the origin of which could be
found in quantum gravity. As a result, the leading corrections responsible for
superimposed osillations in the CMB temperature anisotropies are generically
damped by the blurring of the UV scale. To determine the observational
ramifications of this damping, we compare it to that which effectively occurs
when computing the angular power spectrum of temperature anisotropies. The
former gives an overall change of the oscillation amplitudes whereas the latter
depends on the angular scale. Therefore, in principle they could be
distinguished. In any case, the observation of superimposed oscillations would
place tight constraint on the variance of the UV cutoff.",0705.0747v1
2007-05-10,Magnetization oscillations induced by a spin-polarized current in a point-contact geometry: mode hopping and non-linear damping effects,"In this paper we study magnetization excitations induced in a thin extended
film by a spin-polarized dc-current injected through a point contact in the
current-perpendicular-to-plane (CPP) geometry. Using full-scale micromagnetic
simulations, we demonstrate that in addition to the oscillations of the
propagating wave type, there exist also two localized oscillation modes. The
first localized mode has a relatively homogeneous magnetization structure of
its kernel and corresponds to the so called 'bullet' predicted analytically by
Slavin and Tiberkevich (Phys. Rev. Lett., 95 (2005) 237201). Magnetization
pattern of the second localized mode kernel is highly inhomogeneous, leading to
a much smaller power of magnetoresistance oscillations caused by this mode. We
have also studied the influence of a non-linear damping for this system and
have found the following main qualitative effects: (i) the appearance of
frequency jumps within the existence region of the propagating wave mode and
(ii) the narrowing of the current region where the 'bullet' mode exists, until
this mode completely disappears for a sufficiently strong non-linear damping.",0705.1515v1
2007-05-27,Amplitude Damping for single-qubit System with single-qubit mixed-state Environment,"We study a generalized amplitude damping channel when environment is
initially in the single-qubit mixed state. Representing the affine
transformation of the generalized amplitude damping by a three-dimensional
volume, we plot explicitly the volume occupied by the channels simulatable by a
single-qubit mixed-state environment. As expected, this volume is embedded in
the total volume by the channels which is simulated by two-qubit enviroment.
The volume ratio is approximately 0.08 which is much smaller than 3/8, the
volume ratio for generalized depolarizing channels.",0705.3952v3
2007-06-01,The geometrical quantity in damped wave equations on a square,"The energy in a square membrane $\Omega$ subject to constant viscous damping
on a subset $\omega\subset \Omega$ decays exponentially in time as soon as
$\omega$ satisfies a geometrical condition known as the ""Bardos-Lebeau-Rauch""
condition. The rate $\tau(\omega)$ of this decay satisfies $\tau(\omega)= 2
\min(-\mu(\omega), g(\omega))$ (see Lebeau [Math. Phys. Stud. 19 (1996)
73-109]). Here $\mu(\omega)$ denotes the spectral abscissa of the damped wave
equation operator and $g(\omega)$ is a number called the geometrical quantity
of $\omega$ and defined as follows. A ray in $\Omega$ is the trajectory
generated by the free motion of a mass-point in $\Omega$ subject to elastic
reflections on the boundary. These reflections obey the law of geometrical
optics. The geometrical quantity $g(\omega)$ is then defined as the upper limit
(large time asymptotics) of the average trajectory length. We give here an
algorithm to compute explicitly $g(\omega)$ when $\omega$ is a finite union of
squares.",0706.0172v1
2007-06-08,Kinetic-Ion Simulations Addressing Whether Ion Trapping Inflates Stimulated Brillouin Backscattering Reflectivities,"An investigation of the possible inflation of stimulated Brillouin
backscattering (SBS) due to ion kinetic effects is presented using
electromagnetic particle simulations and integrations of three-wave
coupled-mode equations with linear and nonlinear models of the nonlinear ion
physics. Electrostatic simulations of linear ion Landau damping in an ion
acoustic wave, nonlinear reduction of damping due to ion trapping, and
nonlinear frequency shifts due to ion trapping establish a baseline for
modeling the electromagnetic SBS simulations. Systematic scans of the laser
intensity have been undertaken with both one-dimensional particle simulations
and coupled-mode-equations integrations, and two values of the electron-to-ion
temperature ratio (to vary the linear ion Landau damping) are considered. Three
of the four intensity scans have evidence of SBS inflation as determined by
observing more reflectivity in the particle simulations than in the
corresponding three-wave mode-coupling integrations with a linear ion-wave
model, and the particle simulations show evidence of ion trapping.",0706.1236v1
2007-06-29,Driving-dependent damping of Rabi oscillations in two-level semiconductor systems,"We propose a mechanism to explain the nature of the damping of Rabi
oscillations with increasing driving-pulse area in localized semiconductor
systems, and have suggested a general approach which describes a coherently
driven two-level system interacting with a dephasing reservoir. Present
calculations show that the non-Markovian character of the reservoir leads to
the dependence of the dephasing rate on the driving-field intensity, as
observed experimentally. Moreover, we have shown that the damping of Rabi
oscillations might occur as a result of different dephasing mechanisms for both
stationary and non-stationary effects due to coupling to the environment.
Present calculated results are found in quite good agreement with available
experimental measurements.",0706.4372v1
2007-08-06,Collisionsless amplifying of longitudinal electron waves in two-stream plasma,"To better understanding the principal features of collisionless
damping/growing plasma waves we have implemented a demonstrative calculation
for the simplest cases of electron waves in two-stream plasmas with the
delta-function type electron velocity distribution function of each of the
streams with velocities v(1) and v(2). The traditional dispersion equation is
reduced to an algebraic 4th order equation, for which numerical solutions are
presented for a variant of equal stream densities. In the case of uniform
half-infinite slab one finds two dominant type solutions: non-damping forward
waves and forward complex conjugated exponentially both damping and growing
waves. Beside it in this case there is no necessity of calculation any
logarithmically divergent indefinite integrals. The possibility of wave
amplifying might be useful in practical applications.",0708.0767v1
2007-08-09,The Highly Damped Quasinormal Modes of Extremal Reissner-Nordström and Reissner-Nordström-de Sitter Black Holes,"We analyze in detail the highly damped quasinormal modes of $D$-dimensional
extremal Reissner-Nordstr$\ddot{\rm{o}}$m and
Reissner-Nordstr$\ddot{\rm{o}}$m-de Sitter black holes. We only consider the
extremal case where the event horizon and the Cauchy inner horizon coincide. We
show that, even though the topology of the Stokes/anti-Stokes lines in the
extremal case is different than the non-extremal case, the highly damped
quasinormal mode frequencies of extremal black holes match exactly with the
extremal limit of the non-extremal black hole quasinormal mode frequencies.",0708.1333v2
2007-08-28,Resonantly damped surface and body MHD waves in a solar coronal slab with oblique propagation,"The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a
zero-$\beta$ configuration and for parallel propagation of waves does not allow
the existence of surface waves. When oblique propagation of perturbations is
considered both surface and body waves are able to propagate. When the
perpendicular wave number is larger than a certain value, the body kink mode
becomes a surface wave. In addition, a sausage surface mode is found below the
internal cut-off frequency. When non-uniformity in the equilibrium is included,
surface and body modes are damped due to resonant absorption. In this paper,
first, a normal-mode analysis is performed and the period, the damping rate,
and the spatial structure of eigenfunctions are obtained. Then, the
time-dependent problem is solved, and the conditions under which one or the
other type of mode is excited are investigated.",0708.3783v1
2007-09-11,Teleportation of qubit states through dissipative channels: Conditions for surpassing the no-cloning limit,"We investigate quantum teleportation through dissipative channels and
calculate teleportation fidelity as a function of damping rates. It is found
that the average fidelity of teleportation and the range of states to be
teleported depend on the type and rate of the damping in the channel. Using the
fully entangled fraction, we derive two bounds on the damping rates of the
channels: one is to beat the classical limit and the second is to guarantee the
non-existence of any other copy with better fidelity. Effect of the initially
distributed maximally entangled state on the process is presented; and the
concurrence and the fully entangled fraction of the shared states are
discussed. We intend to show that prior information on the dissipative channel
and the range of qubit states to be teleported is helpful for the evaluation of
the success of teleportation, where success is defined as surpassing the
fidelity limit imposed by the fidelity of 1-to-2 optimal cloning machine for
the specific range of qubits.",0709.1662v1
2007-10-03,Global stability of travelling fronts for a damped wave equation with bistable nonlinearity,"We consider the damped wave equation \alpha u_tt + u_t = u_xx - V'(u) on the
whole real line, where V is a bistable potential. This equation has travelling
front solutions of the form u(x,t) = h(x-st) which describe a moving interface
between two different steady states of the system, one of which being the
global minimum of V. We show that, if the initial data are sufficiently close
to the profile of a front for large |x|, the solution of the damped wave
equation converges uniformly on R to a travelling front as t goes to plus
infinity. The proof of this global stability result is inspired by a recent
work of E. Risler and relies on the fact that our system has a Lyapunov
function in any Galilean frame.",0710.0794v1
2007-12-19,Cosmic String Dynamics and Evolution in Warped Spacetime,"We study the dynamics and evolution of Nambu-Goto strings in a warped
spacetime, where the warp factor is a function of the internal coordinates
giving rise to a `throat' region. The microscopic equations of motion for
strings in this background include potential and friction terms, which attract
the strings towards the bottom of the warping throat. However, by considering
the resulting macroscopic equations for the velocities of strings in the
vicinity of the throat, we note the absence of enough classical damping to
guarantee that the strings actually reach the warped minimum and stabilise
there. Instead, our classical analysis supports a picture in which the strings
experience mere deflections and bounces around the tip, rather than strongly
damped oscillations. Indeed, 4D Hubble friction is inefficient in the internal
dimensions and there is no other classical mechanism known, which could provide
efficient damping. These results have potentially important implications for
the intercommuting probabilities of cosmic superstrings.",0712.3224v2
2007-12-20,The Critical Exponent of the Fractional Langevin Equation is $α_c\approx 0.402$,"We investigate the dynamical phase diagram of the fractional Langevin
equation and show that critical exponents mark dynamical transitions in the
behavior of the system. For a free and harmonically bound particle the critical
exponent $\alpha_c= 0.402\pm 0.002$ marks a transition to a non-monotonic
under-damped phase. The critical exponent $\alpha_{R}=0.441...$ marks a
transition to a resonance phase, when an external oscillating field drives the
system. Physically, we explain these behaviors using a cage effect, where the
medium induces an elastic type of friction. Phase diagrams describing the
under-damped, the over-damped and critical frequencies of the fractional
oscillator, recently used to model single protein experiments, show behaviors
vastly different from normal.",0712.3407v1
2008-01-24,Particle Acceleration by Fast Modes in Solar Flares,"We address the problem of particle acceleration in solar flares by fast modes
which may be excited during the reconnection and undergo cascade and are
subjected to damping. We extend the calculations beyond quasilinear
approximation and compare the acceleration and scattering by transit time
damping and gyroresonance interactions. We find that the acceleration is
dominated by the so called transit time damping mechanism. We estimate the
total energy transferred into particles, and show that our approach provides
sufficiently accurate results We compare this rate with energy loss rate.
Scattering by fast modes appears to be sufficient to prevent the protons from
escaping the system during the acceleration. Confinement of electrons, on the
other hand, requires the existence of plasma waves. Electrons can be
accelerated to GeV energies through the process described here for solar flare
conditions.",0801.3786v2
2008-02-07,Analysis of squeal noise and mode coupling instabilities including damping and gyroscopic effects,"This paper deals with an audible disturbance known as automotive clutch
squeal noise from the viewpoint of friction-induced mode coupling instability.
Firstly, an auto-coupling model is presented showing a non-conservative
circulatory effect originating from friction forces. Secondly, the stability of
an equilibrium is investigated by determining the eigenvalues of the system
linearized equations. The effects of the circulatory and gyroscopic actions are
examined analytically and numerically to determine their influence on the
stability region. Separate and combined effects are analysed with and without
structural damping and important information is obtained on the role of each
parameter and their interactions regarding overall stability. Not only is
structural damping shown to be of primary importance, as reported in many
previous works, this article also highlights a particular relationship with
gyroscopic effects. A method of optimizing both the stability range and its
robustness with respect to uncertainty on system parameters is discussed after
which practical design recommendations are given.",0802.0923v1
2008-02-12,Nonlinear Saturation of g-modes in Proto-Neutron Stars: Quieting the Acoustic Engine,"According to Burrows et al.'s acoustic mechanism for core-collapse supernova
explosions, the primary, l=1, g-mode in the core of the proto-neutron star is
excited to an energy of ~ 10^{50} ergs and damps by the emission of sound
waves. Here we calculate the damping of the primary mode by the parametric
instability, i.e., by nonlinear, 3-mode coupling between the low-order primary
mode and pairs of high-order g-modes. We show that the primary mode is strongly
coupled to highly resonant, neutrino damped pairs with n>10; such short
wavelength interactions cannot be resolved in the simulations. We find that the
parametric instability saturates the primary mode energy at ~10^{48} ergs, well
below the energy needed to drive an explosion. We therefore conclude that
acoustic power is unlikely to be energetically significant in core-collapse
supernova explosions.",0802.1522v3
2008-02-21,Gas Damping Coefficient Research for MEMS Comb Linear Vibration Gyroscope,"Silicon-MEMS gyroscope is an important part of MEMS (Micro Electrical
Mechanical System). There are some disturb ignored in traditional gyroscope
that must be evaluated newly because of its smaller size (reach the level of
micron). In these disturb, the air pressure largely influences the performance
of MEMS gyroscope. Different air pressure causes different gas damping
coefficient for the MEMS comb linear vibration gyroscope and different gas
damping coefficient influences the quality factor of the gyroscope directive.
The quality factor influences the dynamic working bandwidth of the MEMS comb
linear vibration gyroscope, so it is influences the output characteristic of
the MEMS comb linear vibration gyroscope. The paper shows the relationship
between the air pressure and the output amplified and phase of the detecting
axis through analyzing the air pressure influence on the MEMS comb linear
vibration gyroscope. It discusses the influence on the frequency distribute and
quality factor of the MEMS comb linear vibration gyroscope for different air
pressure.",0802.3048v1
2008-03-03,Damped harmonic oscillator interpretation of the soft-state power spectra of Cyg X-1,"We develop a model of an accretion disc in which the variability induced at a
given radius is governed by a damped harmonic oscillator at the corresponding
epicyclic frequency. That variability induces both linear and non-linear
responses in the locally emitted radiation. The total observed variability of a
source is the sum of these contributions over the disc radius weighted by the
energy dissipation rate at each radius. It is shown that this simple model,
which effectively has only three parameters including the normalization, can
explain the range of the power spectra observed from Cyg X-1 in the soft state.
Although a degeneracy between the black hole mass and the strength of the
damping does not allow a unique determination of the mass, we can still
constrain it to <16--20 solar masses. We also show that our model preserves the
observed linear rms-flux relationship even in the presence of the non-linear
flux response.",0803.0238v2
2008-03-05,The Secular Evolution of a Close Ring-Satellite System: The Excitation of Spiral Density Waves at a Nearby Gap Edge,"The Lagrange planetary equations are used to study to secular evolution of a
small, eccentric satellite that orbits within a narrow gap in a broad,
self-gravitating planetary ring. These equations show that the satellite's
secular perturbations of the ring will excite a very long-wavelength spiral
density wave that propagates away from the gap's outer edge. The amplitude of
these waves, as well as their dispersion relation, are derived here. That
dispersion relation reveals that a planetary ring can sustain two types of
density waves: long waves that, in Saturn's A ring, would have wavelengths of
order 100 km, and short waves that tend to be very nonlinear and are expected
to quickly damp. The excitation of these waves also transports angular momentum
from the ring to the satellite in a way that damps the satellite's eccentricity
e, which also tends to reduce the amplitude of subsequent waves. The rate of
eccentricity damping due to this wave action is then compared to the rates at
which the satellite's Lindblad and corotation resonances alter the satellite's
e. These results are then applied to the gap-embedded Saturnian satellites Pan
and Daphnis, and the long-term stability of their eccentricities is assessed.",0803.0576v1
2008-03-06,Hypersound damping in vitreous silica measured by picosecond acoustics,"The attenuation of longitudinal acoustic phonons up to frequencies nearing
250 GHz is measured in vitreous silica with a picosecond optical technique.
Taking advantage of interferences on the probe beam, difficulties encountered
in early pioneering experiments are alleviated. Sound damping at 250 GHz and
room temperature is consistent with relaxation dominated by anharmonic
interactions with the thermal bath, extending optical Brillouin scattering
data. Our result is at variance with claims of a recent deep-UV experiment
which reported a rapid damping increase beyond 100 GHz. A comprehensive picture
of the frequency dependence of sound attenuation in $v$-SiO$_2$ can be
proposed.",0803.0832v1
2008-03-07,Resonance distribution in open quantum chaotic systems,"In order to study the resonance spectra of chaotic cavities subject to some
damping (which can be due to absorption or partial reflection at the
boundaries), we use a model of damped quantum maps. In the high-frequency
limit, the distribution of (quantum) decay rates is shown to cluster near a
``typical'' value, which is larger than the classical decay rate of the
corresponding damped ray dynamics. The speed of this clustering may be quite
slow, which could explain why it has not been detected in previous numerical
data.",0803.1075v4
2008-04-03,Single flux quantum circuits with damping based on dissipative transmission lines,"We propose and demonstrate the functioning of a special Rapid Single Flux
Quantum (RSFQ) circuit with frequency-dependent damping. This damping is
achieved by shunting individual Josephson junctions by pieces of open-ended RC
transmission lines. Our circuit includes a toggle flip-flop cell, Josephson
transmission lines transferring single flux quantum pulses to and from this
cell, as well as DC/SFQ and SFQ/DC converters. Due to the desired
frequency-dispersion in the RC line shunts which ensures sufficiently low noise
at low frequencies, such circuits are well-suited for integrating with the
flux/phase Josephson qubit and enable its efficient control.",0804.0442v1
2008-05-14,"Reconciling results of LSND, MiniBooNE and other experiments with soft decoherence","We propose an explanation of the LSND signal via quantum-decoherence of the
mass states, which leads to damping of the interference terms in the
oscillation probabilities. The decoherence parameters as well as their energy
dependence are chosen in such a way that the damping affects only oscillations
with the large (atmospheric) $\Delta m^2$ and rapidly decreases with the
neutrino energy. This allows us to reconcile the positive LSND signal with
MiniBooNE and other null-result experiments. The standard explanations of
solar, atmospheric, KamLAND and MINOS data are not affected. No new particles,
and in particular, no sterile neutrinos are needed. The LSND signal is
controlled by the 1-3 mixing angle $\theta_{13}$ and, depending on the degree
of damping, yields $0.0014 < \sin^2\theta_{13} < 0.034$ at $3\sigma$. The
scenario can be tested at upcoming $\theta_{13}$ searches: while the comparison
of near and far detector measurements at reactors should lead to a null-result
a positive signal for $\theta_{13}$ is expected in long-baseline accelerator
experiments. The proposed decoherence may partially explain the results of
Gallium detector calibrations and it can strongly affect supernova neutrino
signals.",0805.2098v1
2008-06-02,Observations of Solar Doppler Shift Oscillations with the EUV Imaging Spectrometer on Hinode,"Damped Doppler shift oscillations have been observed in emission lines from
ions formed at flare temperatures with the Solar Ultraviolet Measurements of
Emitted Radiation spectrometer on the Solar and Heliospheric Observatory and
with the Bragg Crystal Spectrometer on Yohkoh. This Letter reports the
detection of low-amplitude damped oscillations in coronal emission lines formed
at much lower temperatures observed with the EUV Imaging Spectrometer on the
Hinode satellite. The oscillations have an amplitude of about 2 km/s, and a
period of around 35 min. The decay times show some evidence for a temperature
dependence with the lowest temperature of formation emission line (Fe XII
195.12 Angstroms) exhibiting a decay time of about 43 min, while the highest
temperature of formation emission line (Fe XV 284.16 Angstroms) shows no
evidence for decay over more than two periods of the oscillation. The data
appear to be consistent with slow magnetoacoustic standing waves, but may be
inconsistent with conductive damping.",0806.0265v1
2008-07-07,Using squeezed field to preserve two-atom entanglement against spontaneous emissions,"Tunable interaction between two atoms in a cavity is realized by interacting
the two atoms with an extra controllable single-mode squeezed field. Such a
controllable interaction can be further used to control entanglement between
the two atoms against amplitude damping decoherence caused by spontaneous
emissions. For the independent amplitude damping decoherence channel,
entanglement will be lost completely without controls, while it can be
partially preserved by the proposed strategy. For the collective amplitude
damping decoherence channel, our strategy can enhance the entanglement compared
with the uncontrolled case when the entanglement of the uncontrolled stationary
state is not too large.",0807.0965v2
2008-07-17,Connecting high-redshift galaxy populations through observations of local Damped Lyman Alpha dwarf galaxies,"I report on observations of the z=0.01 dwarf galaxy SBS1543+593 which is
projected onto the background QSO HS1543+5921. As a star-forming galaxy first
noted in emission, this dwarf is playing a pivotal role in our understanding of
high-redshift galaxy populations, because it also gives rise to a Damped Lyman
Alpha system. This enabled us to analyze, for the first time, the chemical
abundance of $\alpha$ elements in a Damped Lyman Alpha galaxy using both,
emission and absorption diagnostics. We find that the abundances agree with one
another within the observational uncertainties. I discuss the implications of
this result for the interpretation of high-redshift galaxy observations. A
catalog of dwarf-galaxy--QSO projections culled from the Sloan Digital Sky
Survey is provided to stimulate future work.",0807.2853v1
2008-07-23,"Damped driven coupled oscillators: entanglement, decoherence and the classical limit","The interaction of (two-level) Rydberg atoms with dissipative QED cavity
fields can be described classically or quantum mechanically, even for very low
temperatures and mean number of photons, provided the damping constant is large
enough. We investigate the quantum-classical border, the entanglement and
decoherence of an analytically solvable model, analog to the atom-cavity
system, in which the atom (field) is represented by a (driven and damped)
harmonic oscillator. The maximum value of entanglement is shown to depend on
the initial state and the dissipation-rate to coupling-constant ratio. While in
the original model the atomic entropy never grows appreciably (for large
dissipation rates), in our model it reaches a maximum before decreasing.
Although both models predict small values of entanglement and dissipation, for
fixed times of the order of the inverse of the coupling constant and large
dissipation rates, these quantities decrease faster, as a function of the ratio
of the dissipation rate to the coupling constant, in our model.",0807.3715v1
2008-07-26,A Monte Carlo Method for Modeling Thermal Damping: Beyond the Brownian-Motion Master Equation,"The ""standard"" Brownian motion master equation, used to describe thermal
damping, is not completely positive, and does not admit a Monte Carlo method,
important in numerical simulations. To eliminate both these problems one must
add a term that generates additional position diffusion. He we show that one
can obtain a completely positive simple quantum Brownian motion, efficiently
solvable, without any extra diffusion. This is achieved by using a stochastic
Schroedinger equation (SSE), closely analogous to Langevin's equation, that has
no equivalent Markovian master equation. Considering a specific example, we
show that this SSE is sensitive to nonlinearities in situations in which the
master equation is not, and may therefore be a better model of damping for
nonlinear systems.",0807.4211v3
2008-07-31,Finite-dimensional attractors for the quasi-linear strongly-damped wave equation,"We present a new method of investigating the so-called quasi-linear strongly
damped wave equations $$ \partial_t^2u-\gamma\partial_t\Delta_x u-\Delta_x
u+f(u)= \nabla_x\cdot \phi'(\nabla_x u)+g $$ in bounded 3D domains. This method
allows us to establish the existence and uniqueness of energy solutions in the
case where the growth exponent of the non-linearity $\phi$ is less than 6 and
$f$ may have arbitrary polynomial growth rate. Moreover, the existence of a
finite-dimensional global and exponential attractors for the solution semigroup
associated with that equation and their additional regularity are also
established. In a particular case $\phi\equiv0$ which corresponds to the
so-called semi-linear strongly damped wave equation, our result allows to
remove the long-standing growth restriction $|f(u)|\leq C(1+ |u|^5)$.",0807.5078v1
2008-08-01,Field-Driven Domain-Wall Dynamics in GaMnAs Films with Perpendicular Anisotropy,"We combine magneto-optical imaging and a magnetic field pulse technique to
study domain wall dynamics in a ferromagnetic (Ga,Mn)As layer with
perpendicular easy axis. Contrary to ultrathin metallic layers, the depinning
field is found to be smaller than the Walker field, thereby allowing for the
observation of the steady and precessional flow regimes. The domain wall width
and damping parameters are determined self-consistently. The damping, 30 times
larger than the one deduced from ferromagnetic resonance, is shown to
essentially originate from the non-conservation of the magnetization modulus.
An unpredicted damping resonance and a dissipation regime associated with the
existence of horizontal Bloch lines are also revealed.",0808.0119v1
2008-08-11,Effect of frequency and temperature on microwave-induced magnetoresistance oscillations in two-dimensional electron systems,"Experimental results on microwave-induced magnetoresistance oscillation in
two-dimensional electron systems show a similar behavior of these systems
regarding temperature and microwave frequency. It is found that these
oscillations tend to quench when frequency or temperature increase, approaching
magnetoresistance to the response of the dark system. In this work we show that
this experimental behavior can be addressed on the same theoretical basis.
Microwave radiation forces the electron orbits to move back and forth being
damped by interaction with the lattice. We show that this damping depends
dramatically on microwave frequency and also on temperature. An increase in
frequency or temperature gives rise to an increase in the lattice damping
producing eventually a quenching effect in the magnetoresistance oscillations.",0808.1489v1
2008-11-13,Higher order energy decay rates for damped wave equations with variable coefficients,"Under appropriate assumptions the energy of wave equations with damping and
variable coefficients $c(x)u_{tt}-\hbox{div}(b(x)\nabla u)+a(x)u_t =h(x)$ has
been shown to decay. Determining the rate of decay for the higher order
energies involving the $k$th order spatial and time derivatives has been an
open problem with the exception of some sparse results obtained for $k=1,2,3$.
We establish estimates that optimally relate the higher order energies with the
first order energy by carefully analyzing the effects of linear damping. The
results concern weighted (in time) and also pointwise (in time) energy decay
estimates. We also obtain $L^\infty$ estimates for the solution $u$. As an
application we compute explicit decay rates for all energies which involve the
dimension $n$ and the bounds for the coefficients $a(x)$ and $b(x)$ in the case
$c (x)=1$ and $h(x)=0.$",0811.2159v1
2009-01-12,Nonlinear Wigner solid transport over superfluid helium under AC conditions,"Nonlinear transport properties of the two-dimensional Wigner solid of surface
electrons on superfluid helium are studied for alternating current conditions.
For time-averaged quantities like Fourier coefficients, the field-velocity
characteristics are shown to be qualitatively different as compared to that
found in the DC theory. For a spatially uniform current we found a general
solution for the field-velocity relationship which appears to be strongly
dependent on the current frequency. If the current frequency is much lower than
the ripplon damping parameter, the Bragg-Cherenkov resonances which appear at
high enough drift velocities acquire a distinctive saw-tooth shape with long
right-side tails independent of small damping. For current frequencies which
are close or higher than the ripplon damping coefficient, the interference of
ripplons excited at different time intervals results in a new oscillatory (in
drift velocity) regime of Bragg-Cherenkov scattering.",0901.1508v1
2009-01-14,"Brownian motion with respect to time-changing Riemannian metrics, applications to Ricci flow","We generalize Brownian motion on a Riemannian manifold to the case of a
family of metrics which depends on time. Such questions are natural for
equations like the heat equation with respect to time dependent Laplacians
(inhomogeneous diffusions). In this paper we are in particular interested in
the Ricci flow which provides an intrinsic family of time dependent metrics. We
give a notion of parallel transport along this Brownian motion, and establish a
generalization of the Dohrn-Guerra or damped parallel transport, Bismut
integration by part formulas, and gradient estimate formulas. One of our main
results is a characterization of the Ricci flow in terms of the damped parallel
transport. At the end of the paper we give an intrinsic definition of the
damped parallel transport in terms of stochastic flows, and derive an intrinsic
martingale which may provide information about singularities of the flow.",0901.1999v2
2009-01-15,The sound damping constant for generalized theories of gravity,"The near-horizon metric for a black brane in Anti-de Sitter (AdS) space and
the metric near the AdS boundary both exhibit hydrodynamic behavior. We
demonstrate the equivalence of this pair of hydrodynamic systems for the sound
mode of a conformal theory. This is first established for Einstein's gravity,
but we then show how the sound damping constant will be modified, from its
Einstein form, for a generalized theory. The modified damping constant is
expressible as the ratio of a pair of gravitational couplings that are
indicative of the sound-channel class of gravitons. This ratio of couplings
differs from both that of the shear diffusion coefficient and the shear
viscosity to entropy ratio. Our analysis is mostly limited to conformal
theories but suggestions are made as to how this restriction might eventually
be lifted.",0901.2191v1
2009-01-26,Damping of sound waves in superfluid nucleon-hyperon matter of neutron stars,"We consider sound waves in superfluid nucleon-hyperon matter of massive
neutron-star cores. We calculate and analyze the speeds of sound modes and
their damping times due to the shear viscosity and non-equilibrium weak
processes of particle transformations. For that, we employ the dissipative
relativistic hydrodynamics of a superfluid nucleon-hyperon mixture, formulated
recently [M.E. Gusakov and E.M. Kantor, Phys. Rev. D78, 083006 (2008)]. We
demonstrate that the damping times of sound modes calculated using this
hydrodynamics and the ordinary (nonsuperfluid) one, can differ from each other
by several orders of magnitude.",0901.4108v1
2009-03-02,Attenuation and damping of electromagnetic fields: Influence of inertia and displacement current,"New results for attenuation and damping of electromagnetic fields in rigid
conducting media are derived under the conjugate influence of inertia due to
charge carriers and displacement current. Inertial effects are described by a
relaxation time for the current density in the realm of an extended Ohm's law.
The classical notions of poor and good conductors are rediscussed on the basis
of an effective electric conductivity, depending on both wave frequency and
relaxation time. It is found that the attenuation for good conductors at high
frequencies depends solely on the relaxation time. This means that the
penetration depth saturates to a minimum value at sufficiently high
frequencies. It is also shown that the actions of inertia and displacement
current on damping of magnetic fields are opposite to each other. That could
explain why the classical decay time of magnetic fields scales approximately as
the diffusion time. At very small length scales, the decay time could be given
either by the relaxation time or by a fraction of the diffusion time, depending
whether inertia or displacement current, respectively, would prevail on
magnetic diffusion.",0903.0210v1
2009-04-06,Scrutinizing single-qubit quantum channels: Theory and experiment with trapped ions,"We report experimental implementation of various types of qubit channels
using an individual trapped ion. We analyzed experimental data and we performed
tomographic reconstruction of quantum channels based on these data.
Specifically, we studied phase damping channels, where the damping acts either
in the xy-plane of the Bloch sphere or in an arbitrary plane that includes the
origin of the Bloch sphere. We also experimentally realized and consequently
analyzed quantum channels that in addition to phase damping affect also a
polarization rotation. We used three reconstruction schemes for estimation of
quantum channels from experimental data: (1) a linear inverse method, (2) a
maximum likelihood estimation, and (3) a constrained maximum likelihood
estimation. We took into account realistic experimental conditions where
imperfect test-state preparations and biased measurements are incorporated into
the estimation schemes. As a result we found that imperfections present in the
process of preparation of test states and as well as in measurements of the
considered ion trap system do not limit the control of the implementation of
the desired channel. Even imperfect preparation of test state and subsequent
measurements still provide sufficient resources for the complete
quantum-channel tomography.",0904.0923v1
2009-05-13,Time-dependent barrier passage of Two-dimensional non-Ohmic damping system,"The time-dependent barrier passage of an anomalous damping system is studied
via the generalized Langevin equation (GLE) with non-Ohmic memory damping
friction tensor and corresponding thermal colored noise tensor describing a
particle passing over the saddle point of a two-dimensional quadratic potential
energy surface. The time-dependent passing probability and transmission
coefficient are analytically obtained by using of the reactive flux method. The
long memory aspect of friction is revealed to originate a non-monotonic
$\delta$(power exponent of the friction) dependence of the passing probability,
the optimal incident angle of the particle and the steady anomalous
transmission coefficient. In the long time limit a bigger steady transmission
coefficient is obtained which means less barrier recrossing than the
one-dimensional case.",0905.2074v1
2009-06-04,Viscous cavity damping of a microlever in a simple fluid,"We consider the problem of oscillation damping in air of a thermally actuated
microlever as it is gradually approached towards an infinite wall in parallel
geometry. As the gap is decreased from 20 nm down to 400 nm, we observe the
increasing damping of the lever Brownian motion in the fluid laminar regime.
This manifests itself as a linear decrease with distance of the lever quality
factor accompanied by a dramatic softening of its resonance, and eventually
leads to the freezing of the CL oscillation. We are able to quantitatively
explain this behavior by analytically solving the Navier-Stokes equation with
perfect slip boundary conditions. Our findings may have implications for
microfluidics and micro- nano-electromechanical applications.",0906.0782v1
2009-06-19,Wakefield damping for the CLIC crab cavity,"A crab cavity is required in the CLIC to allow effective head-on collision of
bunches at the IP. A high operating frequency is preferred as the deflection
voltage required for a given rotation angle and the RF phase tolerance for a
crab cavity are inversely proportional to the operating frequency. The short
bunch spacing of the CLIC scheme and the high sensitivity of the crab cavity to
dipole kicks demand very high damping of the inter-bunch wakes, the major
contributor to the luminosity loss of colliding bunches. This paper
investigates the nature of the wakefields in the CLIC crab cavity and the
possibility of using various damping schemes to suppress them effectively.",0906.3593v1
2009-07-06,Non-Fermi liquid behavior due to U(1) gauge field in two dimensions,"We study the damping rate of massless Dirac fermions due to the U(1) gauge
field in (2+1)-dimensional quantum electrodynamics. In the absence of a Maxwell
term for the gauge field, the fermion damping rate
$\mathrm{Im}\Sigma(\omega,T)$ is found to diverge in both perturbative and
self-consistent results. In the presence of a Maxwell term, there is still
divergence in the perturbative results for $\mathrm{Im}\Sigma(\omega,T)$. Once
the Maxwell term is included into the self-consistent equations for fermion
self-energy and vacuum polarization functions, the fermion damping rate is free
of divergence and exhibits non-Fermi liquid behavior:
$\mathrm{Im}\Sigma(\omega,T) \propto \mathrm{max}(\sqrt{\omega},\sqrt{T})$.",0907.1022v3
2009-07-30,Gas damping force noise on a macroscopic test body in an infinite gas reservoir,"We present a simple analysis of the force noise associated with the
mechanical damping of the motion of a test body surrounded by a large volume of
rarefied gas. The calculation is performed considering the momentum imparted by
inelastic collisions against the sides of a cubic test mass, and for other
geometries for which the force noise could be an experimental limitation. In
addition to arriving at an accurated estimate, by two alternative methods, we
discuss the limits of the applicability of this analysis to realistic
experimental configurations in which a test body is surrounded by residual gas
inside an enclosure that is only slightly larger than the test body itself.",0907.5375v2
2009-08-19,Nonlinear viscoelastic wave propagation: an extension of Nearly Constant Attenuation (NCQ) models,"Hysteretic damping is often modeled by means of linear viscoelastic
approaches such as ""nearly constant Attenuation (NCQ)"" models. These models do
not take into account nonlinear effects either on the stiffness or on the
damping, which are well known features of soil dynamic behavior. The aim of
this paper is to propose a mechanical model involving nonlinear viscoelastic
behavior for isotropic materials. This model simultaneously takes into account
nonlinear elasticity and nonlinear damping. On the one hand, the shear modulus
is a function of the excitation level; on the other, the description of
viscosity is based on a generalized Maxwell body involving non-linearity. This
formulation is implemented into a 1D finite element approach for a dry soil.
The validation of the model shows its ability to retrieve low amplitude ground
motion response. For larger excitation levels, the analysis of seismic wave
propagation in a nonlinear soil layer over an elastic bedrock leads to results
which are physically satisfactory (lower amplitudes, larger time delays, higher
frequency content).",0908.2715v2
2009-08-26,Influence of an external magnetic field on forced turbulence in a swirling flow of liquid metal,"We report an experimental investigation on the influence of an external
magnetic field on forced 3D turbulence of liquid gallium in a closed vessel. We
observe an exponential damping of the turbulent velocity fluctuations as a
function of the interaction parameter N (ratio of Lorentz force over inertial
terms of the Navier-Stokes equation). The flow structures develop some
anisotropy but do not become bidimensional. From a dynamical viewpoint, the
damping first occurs homogeneously over the whole spectrum of frequencies. For
larger values of N, a very strong additional damping occurs at the highest
frequencies. However, the injected mechanical power remains independent of the
applied magnetic field. The simultaneous measurement of induced magnetic field
and electrical potential differences shows a very weak correlation between
magnetic field and velocity fluctuations. The observed reduction of the
fluctuations is in agreement with a previously proposed mechanism for the
saturation of turbulent dynamos and with the order of magnitude of the Von
Karman Sodium dynamo magnetic field.",0908.3821v1
2009-09-30,Electronic damping of molecular motion at metal surfaces,"A method for the calculation of the damping rate due to electron-hole pair
excitation for atomic and molecular motion at metal surfaces is presented. The
theoretical basis is provided by Time Dependent Density Functional Theory
(TDDFT) in the quasi-static limit and calculations are performed within a
standard plane-wave, pseudopotential framework. The artificial periodicity
introduced by using a super-cell geometry is removed to derive results for the
motion of an isolated atom or molecule, rather than for the coherent motion of
an ordered over-layer. The algorithm is implemented in parallel, distributed
across both ${\bf k}$ and ${\bf g}$ space, and in a form compatible with the
CASTEP code. Test results for the damping of the motion of hydrogen atoms above
the Cu(111) surface are presented.",0909.5495v1
2009-10-14,Constraint on the growth factor of the cosmic structure from the damping of the baryon acoustic oscillation signature,"We determine a constraint on the growth factor by measuring the damping of
the baryon acoustic oscillations in the matter power spectrum using the Sloan
Digital Sky Survey luminous red galaxy sample. The damping of the BAO is
detected at the one sigma level. We obtain \sigma_8D_1(z=0.3) =
0.42^{+0.34}_{-0.28} at the 1\sigma statistical level, where \sigma_8 is the
root mean square overdensity in a sphere of radius 8h^{-1}Mpc and D_1(z) is the
growth factor at redshift z. The above result assumes that other parameters are
fixed and the cosmology is taken to be a spatially flat cold dark matter
universe with the cosmological constant.",0910.2513v1
2009-10-27,On the Interpretation of Magnetic Helicity Signatures in the Dissipation Range of Solar Wind Turbulence,"Measurements of small-scale turbulent fluctuations in the solar wind find a
non-zero right-handed magnetic helicity. This has been interpreted as evidence
for ion cyclotron damping. However, theoretical and empirical evidence suggests
that the majority of the energy in solar wind turbulence resides in low
frequency anisotropic kinetic Alfven wave fluctuations that are not subject to
ion cyclotron damping. We demonstrate that a dissipation range comprised of
kinetic Alfven waves also produces a net right-handed fluctuating magnetic
helicity signature consistent with observations. Thus, the observed magnetic
helicity signature does not necessarily imply that ion cyclotron damping is
energetically important in the solar wind.",0910.5023v1
2009-12-08,Coupling Photosphere and Corona: Linear and Turbulent Regimes,"In a recent work Grappin et al. [1] have shown that low- frequency movements
can be transmitted from one footpoint to the other along a magnetic loop, thus
mimicking a friction effect of the corona on the photosphere, and invalidating
the line-tying approximation. We consider here successively the effect of high
frequencies and turbulent damping on the process. We use a very simple
atmospheric model which allows to study analytically the laminar case, and to
study the turbulent case both using simple phenomenological arguments and a
more sophisticated turbulence model [2]. We find that, except when turbulent
damping is such that all turbulence is damped during loop traversal, coupling
still occurs between distant footpoints, and moreover the coronal field induced
by photospheric movements saturates at finite values.",0912.1497v1
2009-12-16,The role of $r$-mode damping in the thermal evolution of neutron stars,"The thermal evolution of neutron stars (NSs) is investigated by coupling with
the evolution of $\textit{r}$-mode instability that is described by a second
order model.The heating effect due to shear viscous damping of the
$\textit{r}$-modes enables us to understand the high temperature of two young
pulsars (i.e., PSR B0531+21 and RX J0822-4300) in the framework of the simple
$npe$ NS model, without superfluidity or exotic particles.Moreover, the light
curves predicted by the model within an acceptable parameter regime may
probably cover all of the young and middle-aged pulsars in the $\lg
T_s^{\infty}-\lg t$ panel, and an artificially strong $p$ superfluidity invoked
in some early works is not needed here. Additionally, by considering the
radiative viscous damping of the $\textit{r}$-modes, a surprising extra cooling
effect is found, which can even exceed the heating effect sometimes although
plays an ignorable role in the thermal history.",0912.3052v1
2009-12-25,Noisy non-transitive quantum games,"We study the effect of quantum noise in 3 by 3 entangled quantum games. By
considering different noisy quantum channels we analyze that how a two-player,
three-strategy Rock-Scissor-Paper game is influenced by the quantum noise. We
consider the winning non-transitive strategies R, S and P such as R beats S, S
beats P, and P beats R. The game behaves as a noiseless game for maximum value
of the quantum noise parameter. It is seen that Alice's payoff is heavily
influenced by the depolarizing noise as compared to the amplitude damping
noise. Depolarizing channel causes a monotonic decrease in players payoffs as
we increase the amount of of quantum noise. In case of amplitude damping
channel, the Alice's payoff function reaches its minimum for alpha=0.5 and is
symmetrical. This means that larger values of quantum noise influence the game
weakly. On the other hand, phase damping channel does not influence the game's
payoff. Furthermore, the game's Nash equilibrium and non-transitive character
of the game are not affected under the influence of quantum noise.",0912.4961v1
2010-01-26,Damping in high-frequency metallic nanomechanical resonators,"We have studied damping in polycrystalline Al nanomechanical resonators by
measuring the temperature dependence of their resonance frequency and quality
factor over a temperature range of 0.1 - 4 K. Two regimes are clearly
distinguished with a crossover temperature of 1 K. Below 1 K we observe a
logarithmic temperature dependence of the frequency and linear dependence of
damping that cannot be explained by the existing standard models. We attribute
these phenomena to the effect of the two-level systems characterized by the
unexpectedly long (at least two orders of magnitude longer) relaxation times
and discuss possible microscopic models for such systems. We conclude that the
dynamics of the two-level systems is dominated by their interaction with
one-dimensional phonon modes of the resonators.",1001.4612v1
2010-04-28,Inviscid dynamical structures near Couette flow,"Consider inviscid fluids in a channel {-1<y<1}. For the Couette flow
v_0=(y,0), the vertical velocity of solutions to the linearized Euler equation
at v_0 decays in time. At the nonlinear level, such inviscid damping has not
been proved. First, we show that in any (vorticity) H^{s}(s<(3/2)) neighborhood
of Couette flow, there exist non-parallel steady flows with arbitrary minimal
horizontal period. This implies that nonlinear inviscid damping is not true in
any (vorticity) H^{s}(s<(3/2)) neighborhood of Couette flow and for any
horizontal period. Indeed, the long time behavior in such neighborhoods are
very rich, including nontrivial steady flows, stable and unstable manifolds of
nearby unstable shears. Second, in the (vorticity) H^{s}(s>(3/2)) neighborhood
of Couette, we show that there exist no non-parallel steadily travelling flows
v(x-ct,y), and no unstable shears. This suggests that the long time dynamics in
H^{s}(s>(3/2)) neighborhoods of Couette might be much simpler. Such contrasting
dynamics in H^{s} spaces with the critical power s=(3/2) is a truly nonlinear
phenomena, since the linear inviscid damping near Couette is true for any
initial vorticity in L^2.",1004.5149v1
2010-06-14,Parallel electric field amplification by phase-mixing of Alfven waves,"Previous numerical studies have identified ""phase mixing"" of low-frequency
Alfven waves as a mean of parallel electric field amplification and
acceleration of electrons in a collisionless plasma. Theoretical explanations
are given of how this produces an amplification of the parallel electric field,
and as a consequence, also leads to enhanced collisionless damping of the wave
by energy transfer to the electrons. Our results are based on the properties of
the Alfven waves in a warm plasma which are obtained from drift-kinetic theory,
in particular, the rate of their electron Landau damping. Phase mixing in a
collisionless low-$\beta$ plasma proceeds in a manner very similar to the
visco-resistive case, except for the fact that electron Landau damping is the
primary energy dissipation channel. The time and length scales involved are
evaluated. We also focus on the evolution of the parallel electric field and
calculate its maximum value in the course of its amplification.",1006.2729v1
2010-07-19,Anomalously large damping of long-wavelength quasiparticles caused by long-range interaction,"We demonstrate that long-range interaction in a system can lead to a very
strong interaction between long-wavelength quasiparticles and make them heavily
damped. In particular, we discuss magnon spectrum using 1/S expansion in 3D
Heisenberg ferromagnet (FM) with arbitrary small dipolar forces at T<<T_C. We
obtain that a fraction of long-wavelength magnons with energies e_k<T has
anomalously large damping G_k (ratio G_k/e_k reaches 0.3 for certain k). This
effect is observed both in quantum and classical FMs. Remarkably, this result
contradicts expectation of the quasiparticle concept according which a weakly
excited state of a many-body system can be represented as a collection of
weakly interacting elementary excitations. Particular materials are pointed out
which are suitable for corresponding experiments.",1007.3081v2
2010-07-29,The Quasinormal Mode Spectrum of a Kerr Black Hole in the Eikonal Limit,"It is well established that the response of a black hole to a generic
perturbation is characterized by a spectrum of damped resonances, called
quasinormal modes; and that, in the limit of large angular momentum ($l \gg
1$), the quasinormal mode frequency spectrum is related to the properties of
unstable null orbits. In this paper we develop an expansion method to explore
the link. We obtain new closed-form approximations for the lightly-damped part
of the spectrum in the large-$l$ regime. We confirm that, at leading order in
$l$, the resonance frequency is linked to the orbital frequency, and the
resonance damping to the Lyapunov exponent, of the relevant null orbit. We go
somewhat further than previous studies to establish (i) a spin-dependent
correction to the frequency at order $1 / l$ for equatorial ($m = \pm l$)
modes, and (ii) a new result for polar modes ($m = 0$). We validate the
approach by testing the closed-form approximations against frequencies obtained
numerically with Leaver's method.",1007.5097v1
2010-08-30,"Caldeira-Leggett Model, Landau Damping, and the Vlasov-Poisson System","The Caldeira-Leggett Hamiltonian (Eq. (1) below) describes the interaction of
a discrete harmonic oscillator with a continuous bath of harmonic oscillators.
This system is a standard model of dissipation in macroscopic low temperature
physics, and has applications to superconductors, quantum computing, and
macroscopic quantum tunneling. The similarities between the Caldeira-Leggett
model and the linearized Vlasov-Poisson equation are analyzed, and it is shown
that the damping in the Caldeira-Leggett model is analogous to that of Landau
damping in plasmas [1]. An invertible linear transformation [2, 3] is presented
that converts solutions of the Caldeira-Leggett model into solutions of the
linearized Vlasov-Poisson system.",1008.5190v1
2010-09-09,A number-conserving linear response study of low-velocity ion stopping in a collisional magnetized classical plasma,"The results of a theoretical investigation on the low-velocity stopping power
of the ions moving in a magnetized collisional plasma are presented. The
stopping power for an ion is calculated employing linear response theory using
the dielectric function approach. The collisions, which leads to a damping of
the excitations in the plasma, is taken into account through a
number-conserving relaxation time approximation in the linear response
function. In order to highlight the effects of collisions and magnetic field we
present a comparison of our analytical and numerical results obtained for a
nonzero damping or magnetic field with those for a vanishing damping or
magnetic field. It is shown that the collisions remove the anomalous friction
obtained previously [Nersisyan et al., Phys. Rev. E 61, 7022 (2000)] for the
collisionless magnetized plasmas at low ion velocities. One of major objectives
of this study is to compare and contrast our theoretical results with those
obtained through a novel diffusion formulation based on Dufty-Berkovsky
relation evaluated in magnetized one-component plasma models framed on target
ions and electrons.",1009.1700v1
2010-10-03,A High Phase Advance Damped and Detuned Structure for the Main Linacs of Clic,"The main accelerating structures for the CLIC are designed to operate at an
average accelerating gradient of 100 MV/m. The accelerating frequency has been
optimised to 11.994 GHz with a phase advance of 2{\pi}/3 of the main
accelerating mode. The moderately damped and detuned structure (DDS) design is
being studied as an alternative to the strongly damped WDS design. Both these
designs are based on the nominal accelerating phase advance. Here we explore
high phase advance (HPA) structures in which the group velocity of the rf
fields is reduced compared to that of standard (2{\pi}/3) structures. The
electrical breakdown strongly depends on the fundamental mode group velocity.
Hence it is expected that electrical breakdown is less likely to occur in the
HPA structures. We report on a study of both the fundamental and dipole modes
in a CLIC_DDS_HPA structure, designed to operate at 5{\pi}/6 phase advance per
cell. Higher order dipole modes in both the standard and HPA structures are
also studied.",1010.0438v1
2010-10-23,Environmental influences on Quantum Monty Hall problem,"We reformulate the quantum Monty Hall problem in the presence of decoherence.
The decoherence destroys the fairness of the game. A new Nash equilibrium for a
particular strategy profile in the presence of decoherence emerges. It is shown
that in the presence of decoherence under the action of amplitude damping
channel, Bob's winning probability is always higher than three-forth,
irrespective of Alice's strategy, if he does not switch to the other door and
always wins for a fully decohered case of the channel. Depolarizing channel
damps up Bob's winning probability and gets better off if he sticks to his
current selection. Phase damping channel leaves the winning probability
unaffected. Unlike the classical and the quantum forms of the game, Bob's
dominant strategy in the presence of decoherence is not switching.",1010.4875v2
2010-12-14,Controlling transfer of quantum correlations among bi-partitions of a composite quantum system by combining noisy environments,"The correlation dynamics is investigated for various bi-partitions of a
composite system consisting of two qubits, and two independent and
non-identical noisy environments. The two qubits have no direct interaction
with each other and locally interact with their environments. Classical and
quantum correlations including entanglement are initially prepared only between
the two qubits. We find that, contrary to the identical noisy environment case,
the entanglement and quantum correlation transfer directions can be controlled
by combining different noisy environments. The amplitude damping environment
determines whether there exists entanglement transfer among the bi-partitions
of a composite system. When one qubit is coupled to an amplitude damping
environment but another one to a bit-flip one, we find a very interesting
result that all the quantum and classical correlations, and even the
entanglement, originally existing between the qubits, can be completely
transferred without any loss to the qubit coupled to the bit-flip environment
and the amplitude-damping environment. We also notice that it is possible to
distinguish the quantum correlation from the classical correlation and
entanglement by combining different noisy environments.",1012.3033v1
2010-12-22,Viscous damping of r-modes: Small amplitude instability,"We study the viscous damping of r-modes of compact stars and analyze in
detail the regions where small amplitude modes are unstable to the emission of
gravitational radiation. We present general expressions for the viscous damping
times for arbitrary forms of interacting dense matter and derive general
semi-analytic results for the boundary of the instability region. These results
show that many aspects, like in particular the physically important minima of
the instability boundary, are surprisingly insensitive to detailed microscopic
properties of the considered form of matter. Our general expressions are
applied to the cases of hadronic stars, strange stars, and hybrid stars, and we
focus on equations of state that are compatible with the recent measurement of
a heavy compact star. We find that hybrid stars with a sufficiently small core
can ""masquerade"" as neutron stars and feature an instability region that is
indistinguishable from that of a neutron star, whereas neutron stars with a
core density high enough to allow direct Urca reactions feature a notch on the
right side of the instability region.",1012.4883v2
2010-12-27,Phenomenology of Current-Induced Dynamics in Antiferromagnets,"We derive a phenomenological theory of current-induced staggered
magnetization dynamics in antiferromagnets. The theory captures the reactive
and dissipative current-induced torques and the conventional effects of
magnetic fields and damping. A Walker ansatz describes the dc current-induced
domain-wall motion when there is no dissipation. If magnetic damping and
dissipative torques are included, the Walker ansatz remains robust when the
domain-wall moves slowly. As in ferromagnets, the domain-wall velocity is
proportional to the ratio between the dissipative-torque and the magnetization
damping. In addition, a current-driven antiferromagnetic domain-wall acquires a
net magnetic moment.",1012.5655v2
2011-02-02,"Harmonic Oscillator in Heat Bath: Exact simulation of time-lapse-recorded data, exact analytical benchmark statistics","The stochastic dynamics of the damped harmonic oscillator in a heat bath is
simulated with an algorithm that is exact for time steps of arbitrary size.
Exact analytical results are given for correlation functions and power spectra
in the form they acquire when computed from experimental time-lapse recordings.
Three applications are discussed: (i) Effects of finite sampling-rate and
-time, described exactly here, are similar for other stochastic dynamical
systems-e.g. motile micro-organisms and their time-lapse recorded trajectories.
(ii) The same statistics is satisfied by any experimental system to the extent
it is interpreted as a damped harmonic oscillator at finite temperature-such as
an AFM cantilever. (iii) Three other models of fundamental interest are
limiting cases of the damped harmonic oscillator at finite temperature; it
consequently bridges their differences and describes effects of finite sampling
rate and sampling time for these models as well. Finally, we give a brief
discussion of nondimensionalization.",1102.0524v1
2011-02-04,A symmetry trip from Caldirola to Bateman damped systems,"For the Caldirola-Kanai system, describing a quantum damped harmonic
oscillator, a couple of constant-of-motion operators generating the Heisenberg
algebra can be found. The inclusion of the standard time evolution symmetry in
this algebra for damped systems, in a unitary manner, requires a non-trivial
extension of this basic algebra and hence the physical system itself.
Surprisingly, this extension leads directly to the so-called Bateman's dual
system, which now includes a new particle acting as an energy reservoir. The
group of symmetries of the dual system is presented, as well as a quantization
that implies, in particular, a first-order Schr\""odinger equation. The usual
second-order equation and the inclusion of the original Caldirola-Kanai model
in Bateman's system are also discussed.",1102.0990v1
2011-03-03,Determination of the pairing state in iron-based superconductors through neutron scattering,"We calculate the spin susceptibility in the s_{+-} and s_{++} superconducting
states of the iron pnictides using the effective five orbital model and
considering the quasiparticle damping. For the experimentally evaluated
magnitude of the quasiparticle damping and the superconducting gap, the results
at the wave vector ~ (pi,0) show that the s_{+-} state is more consistent with
the neutron scattering experiments, while for larger quasiparticle damping and
the superconducting gap, the s_{++} state can be more consistent. To
distinguish between two cases that reproduce the experiments at the wave vector
~ (pi,0), we propose to investigate experimentally the wave vector ~ (pi,pi).",1103.0586v2
2011-03-03,Transmission of classical and quantum information through a quantum memory channel with damping,"We consider the transfer of classical and quantum information through a
memory amplitude damping channel. Such a quantum channel is modeled as a damped
harmonic oscillator, the interaction between the information carriers - a train
of qubits - and the oscillator being of the Jaynes-Cummings kind. We prove that
this memory channel is forgetful, so that quantum coding theorems hold for its
capacities. We analyze entropic quantities relative to two uses of this
channel. We show that memory effects improve the channel aptitude to transmit
both classical and quantum information, and we investigate the mechanism by
which memory acts in changing the channel transmission properties.",1103.0747v2
2011-03-08,Steady states of the parametric rotator and pendulum,"We discuss several steady-state rotation and oscillation modes of the planar
parametric rotator and pendulum with damping. We consider a general elliptic
trajectory of the suspension point for both rotator and pendulum, for the
latter at an arbitrary angle with gravity, with linear and circular
trajectories as particular cases. We treat the damped, non-linear equation of
motion of the parametric rotator and pendulum perturbatively for small
parametric excitation and damping, although our perturbative approach can be
extended to other regimes as well. Our treatment involves only ordinary
second-order differential equations with constant coefficients, and provides
numerically accurate perturbative solutions in terms of elementary functions.
Some of the steady-state rotation and oscillation modes studied here have not
been discussed in the previous literature. Other well-known ones, such as
parametric resonance and the inverted pendulum, are extended to elliptic
parametric excitation tilted with respect to gravity. The results presented
here should be accessible to advanced undergraduates, and of interest to
graduate students and specialists in the field of non-linear mechanics.",1103.1413v1
2011-03-18,Time-periodic solitons in a damped-driven nonlinear Schrödinger equation,"Time-periodic solitons of the parametrically driven damped nonlinear
Schr\""odinger equation are obtained as solutions of the boundary-value problem
on a two-dimensional spatiotemporal domain. We follow the transformation of the
periodic solitons as the strength of the driver is varied. The resulting
bifurcation diagrams provide a natural explanation for the overall form and
details of the attractor chart compiled previously via direct numerical
simulations. In particular, the diagrams confirm the occurrence of the
period-doubling transition to temporal chaos for small values of dissipation
and the absence of such transitions for larger dampings. This difference in the
soliton's response to the increasing driving strength can be traced to the
difference in the radiation frequencies in the two cases. Finally, we relate
the soliton's temporal chaos to the homoclinic bifurcation.",1103.3604v1
2011-03-28,Motion of position-dependent mass as a damping-antidamping process: Application to the Fermi gas and to the Morse potential,"The object of this paper is to investigate, classically and quantum
mechanically, the relation existing between the position-dependent effective
mass and damping-antidamping dynamics. The quantization of the equations of
motion is carried out using the geometric interpretation of the motion, and we
compare it with the one based on the ordering ambiguity scheme. Furthermore, we
apply the obtained results to a Fermi gas of damped-antidamped particles, and
we solve the Schr\""odinger equation for an exponentially increasing
(decreasing) mass in the presence of the Morse potential.",1103.5440v3
2011-04-30,Resonantly Damped Propagating Kink Waves in Longitudinally Stratified Solar Waveguides,"It has been shown that resonant absorption is a robust physical mechanism to
explain the observed damping of magnetohydrodynamic (MHD) kink waves in the
solar atmosphere due to naturally occurring plasma inhomogeneity in the
direction transverse to the direction of the magnetic field. Theoretical
studies of this damping mechanism were greatly inspired by the first
observations of post-flare standing kink modes in coronal loops using the
Transition Region And Coronal Explorer (TRACE). More recently, these studies
have been extended to explain the attenuation of propagating coronal kink waves
observed by the Coronal Multi-Channel Polarimeter (CoMP). In the present study,
for the first time we investigate the properties of propagating kink waves in
solar waveguides including the effects of both longitudinal and transverse
plasma inhomogeneity. Importantly, it is found that the wavelength is only
dependent on the longitudinal stratification and the amplitude is simply a
product of the two effects. In light of these results the advancement of solar
atmospheric magnetoseismology by exploiting high spatial/temporal resolution
observations of propagating kink waves in magnetic waveguides to determine the
length scales of the plasma inhomogeneity along and transverse to the direction
of the magnetic field is discussed.",1105.0067v1
2011-05-05,The effect of twisted magnetic field on the resonant absorption of MHD waves in coronal loops,"The standing quasi modes in a cylindrical incompressible flux tube with
magnetic twist that undergoes a radial density structuring is considered in
ideal magnetohydrodynamics (MHD). The radial structuring is assumed to be a
linearly varying density profile. Using the relevant connection formulae, the
dispersion relation for the MHD waves is derived and solved numerically to
obtain both the frequencies and damping rates of the fundamental and
first-overtone modes of both the kink (m=1) and fluting (m=2,3) waves. It was
found that a magnetic twist will increase the frequencies, damping rates and
the ratio of the oscillation frequency to the damping rate of these modes. The
period ratio P_1/P_2 of the fundamental and its first-overtone surface waves
for kink (m=1) and fluting (m=2,3) modes is lower than 2 (the value for an
untwisted loop) in the presence of twisted magnetic field. For the kink modes,
particularly, the magnetic twists B_{\phi}/B_z=0.0065 and 0.0255 can achieve
deviations from 2 of the same order of magnitude as in the observations.
Furthermore, for the fundamental kink body waves, the frequency bandwidth
increases with increasing the magnetic twist.",1105.1120v1
2011-05-05,Interpreting Graph Cuts as a Max-Product Algorithm,"The maximum a posteriori (MAP) configuration of binary variable models with
submodular graph-structured energy functions can be found efficiently and
exactly by graph cuts. Max-product belief propagation (MP) has been shown to be
suboptimal on this class of energy functions by a canonical counterexample
where MP converges to a suboptimal fixed point (Kulesza & Pereira, 2008).
  In this work, we show that under a particular scheduling and damping scheme,
MP is equivalent to graph cuts, and thus optimal. We explain the apparent
contradiction by showing that with proper scheduling and damping, MP always
converges to an optimal fixed point. Thus, the canonical counterexample only
shows the suboptimality of MP with a particular suboptimal choice of schedule
and damping. With proper choices, MP is optimal.",1105.1178v1
2011-05-14,Crossovers in the non-Markovian dynamics of two-qubit entanglements,"We study the entanglement dynamics of two non-interacting, spatially
separated qubits subject to local environment noises. Based on exactly solvable
models for non-Markovian amplitude damping and phase damping noises, we are
able to analyze the entanglement dynamics of the two qubits for different
coupling bandwidths and different detunings. We show that entanglement
oscillations can occur for both amplitude and phase damping noises. Moreover,
we demonstrate that changing the coupling bandwidth can lead to crossover
between dissipative and non-dissipative entanglement dynamics, while varying
the detuning controls the crossover between strong and weak coupling limits.
Our findings can help provide a synthesized picture for the entanglement
dynamics of two qubits subject to local environment noises.",1105.2859v2
2011-06-17,Controlling Excitations Inversion of a Cooper Pair Box Interacting with a Nanomechanical Resonator,"We investigate the action of time dependent detunings upon the excitation
inversion of a Cooper pair box interacting with a nanomechanical resonator. The
method employs the Jaynes-Cummings model with damping, assuming different decay
rates of the Cooper pair box and various fixed and t-dependent detunings. It is
shown that while the presence of damping plus constant detunings destroy the
collapse/revival effects, convenient choices of time dependent detunings allow
one to reconstruct such events in a perfect way. It is also shown that the mean
excitation of the nanomechanical resonator is more robust against damping of
the Cooper pair box for convenient values of t-dependent detunings.",1106.3379v1
2011-06-22,Tunable Magnonic Frequency and Damping in [Co/Pd]8 Multilayers with Variable Co Layer Thickness,"We report the experimental observation of collective picosecond magnetization
dynamics in [Co/Pd]8 multilayers with perpendicular magnetic anisotropy. The
precession frequency shows large and systematic variation from about 5 GHz to
about 90 GHz with the decrease in the Co layer thickness from 1.0 nm to 0.22 nm
due to the linear increase in the perpendicular magnetic anisotropy. The
damping coefficient 'alpha' is found to be inversely proportional to the Co
layer thickness and a linear relation between the perpendicular magnetic
anisotropy and 'alpha' is established. We discuss the possible reasons behind
the enhanced damping as the d-d hybridization at the interface and spin
pumping. These observations are significant for the applications of these
materials in spintronics and magnonic crystals.",1106.4491v1
2011-07-04,An HI column density threshold for cold gas formation in the Galaxy,"We report the discovery of a threshold in the HI column density of Galactic
gas clouds below which the formation of the cold phase of HI is inhibited. This
threshold is at $N_{HI} = 2 \times 10^{20}$ per cm$^{2}$; sightlines with lower
HI column densities have high spin temperatures (median $T_s \sim 1800$ K),
indicating low fractions of the cold neutral medium (CNM), while sightlines
with $N_{HI} \ge 2 \times 10^{20}$ per cm$^{2}$ have low spin temperatures
(median $T_s \sim 240$ K), implying high CNM fractions. The threshold for CNM
formation is likely to arise due to inefficient self-shielding against
ultraviolet photons at lower HI column densities. The threshold is similar to
the defining column density of a damped Lyman-$\alpha$ absorber; this indicates
a physical difference between damped and sub-damped Lyman-$\alpha$ systems,
with the latter class of absorbers containing predominantly warm gas.",1107.0744v2
2011-07-11,One-dimensional vertical dust strings in a glass box,"The oscillation spectrum of a one-dimensional vertical dust string formed
inside a glass box on top of the lower electrode in a GEC reference cell was
studied. A mechanism for creating a single vertical dust string is described.
It is shown that the oscillation amplitudes, resonance frequencies, damping
coefficients, and oscillation phases of the dust particles separate into two
distinct groups. One group exhibits low damping coefficients, increasing
amplitudes and decreasing resonance frequencies for dust particles closer to
the lower electrode. The other group shows high damping coefficients but
anomalous resonance frequencies and amplitudes. At low oscillation frequencies,
the two groups are also separated by a {\pi}-phase difference. One possible
cause for the difference in behavior between the two groups is discussed.",1107.2074v1
2011-07-24,Traveling kinks in cubic nonlinear Ginzburg-Landau equations,"Nonlinear cubic Euler-Lagrange equations of motion in the traveling variable
are usually derived from Ginzburg-Landau free energy functionals frequently
encountered in several fields of physics. Many authors considered in the past
damped versions of such equations with the damping term added by hand
simulating the friction due to the environment. It is known that even in this
damped case kink solutions can exist. By means of a factorization method, we
provide analytic formulas for several possible kink solutions of such equations
of motion in the undriven and constant field driven cases, including the
recently introduced Riccati parameter kinks which were not considered
previously in such a context. The latter parameter controls the delay of the
switching stage of the kinks",1107.4773v4
2011-08-22,On conditions for asymptotic stability of dissipative infinite-dimensional systems with intermittent damping,"We study the asymptotic stability of a dissipative evolution in a Hilbert
space subject to intermittent damping. We observe that, even if the
intermittence satisfies a persistent excitation condition, if the Hilbert space
is infinite-dimensional then the system needs not being asymptotically stable
(not even in the weak sense). Exponential stability is recovered under a
generalized observability inequality, allowing for time-domains that are not
intervals. Weak asymptotic stability is obtained under a similarly generalized
unique continuation principle. Finally, strong asymptotic stability is proved
for intermittences that do not necessarily satisfy some persistent excitation
condition, evaluating their total contribution to the decay of the trajectories
of the damped system. Our results are discussed using the example of the wave
equation, Schr\""odinger's equation and, for strong stability, also the special
case of finite-dimensional systems.",1108.4327v2
2011-08-26,Aligned Major Axes in a Planetary System without Tidal Evolution: The 61 Virginis example,"Tidal damping of one of the orbits in a planetary system can lead to aligned
major-axes (the so-called ""fixed-point"" condition), but currently aligned major
axes do not necessarily imply such a history. An example is the nominal orbital
solution for the 61 Virginis system where two orbits librate about alignment,
but evaluation of the eigenmodes of the secular theory shows it could not be
the result of tidal damping but rather of initial conditions. Nevertheless, the
amplitudes of the eigenmodes suggest that this system may have undergone some
degree of tidal damping.",1108.5369v1
2011-09-09,Optimal linear optical implementation of a single-qubit damping channel,"We experimentally demonstrate a single-qubit decohering quantum channel using
linear optics. We implement the channel, whose special cases include both the
amplitude-damping channel and the bit-flip channel, using a single, static
optical setup. Following a recent theoretical result [M. Piani et al., Phys.
Rev. A, 84, 032304 (2011)], we realize the channel in an optimal way,
maximizing the probability of success, i.e., the probability for the photonic
qubit to remain in its encoding. Using a two-photon entangled resource, we
characterize the channel using ancilla-assisted process tomography and find
average process fidelities of 0.9808 \pm 0.0002 and 0.9762 \pm 0.0002 for
amplitude-damping and the bit-flip case, respectively.",1109.2070v1
2011-11-20,Detection of picosecond magnetization dynamics of 50 nm magnetic dots down to the single dot regime,"We report an all-optical time-domain detection of picosecond magnetization
dynamics of arrays of 50 nm Ni80Fe20 (permalloy) dots down to the single
nanodot regime. In the single nanodot regime the dynamics reveals one dominant
resonant mode corresponding to the edge mode of the 50 nm dot with slightly
higher damping than that of the unpatterned thin film. With the increase in
areal density of the array both the precession frequency and damping increases
significantly due to the increase in magnetostatic interactions between the
nanodots and a mode splitting and sudden jump in apparent damping are observed
at an edge-to-edge separation of 50 nm.",1111.4625v1
2011-12-02,An energy-based computational method in the analysis of the transmission of energy in a chain of coupled oscillators,"In this paper we study the phenomenon of nonlinear supratransmission in a
semi-infinite discrete chain of coupled oscillators described by modified
sine-Gordon equations with constant external and internal damping, and subject
to harmonic external driving at the end. We develop a consistent and
conditionally stable finite-difference scheme in order to analyze the effect of
damping in the amount of energy injected in the chain of oscillators; numerical
bifurcation analyses to determine the dependence of the amplitude at which
supratransmission first occurs with respect to the frequency of the driving
oscillator are carried out in order to show the consequences of damping on
harmonic phonon quenching and the delay of appearance of critical amplitude.",1112.0581v1
2012-01-09,Universal response of optimal granular damping devices,"Granular damping devices constitute an emerging technology for the
attenuation of vibrations based on the dissipative nature of particle
collisions. We show that the performance of such devices is independent of the
material properties of the particles for working conditions where damping is
optimal. Even the suppression of a dissipation mode (collisional or frictional)
is unable to alter the response. We explain this phenomenon in terms of the
inelastic collapse of granular materials. These findings provide a crucial
standpoint for the design of such devices in order to achieve the desired low
maintenance feature that makes particle dampers particularly suitable to harsh
environments.",1201.1866v2
2012-01-09,Radiative energy loss reduction in an absorptive plasma,"The influence of the damping of radiation on the radiative energy loss
spectrum of a relativistic charge in an infinite, absorptive plasma is studied.
We find increasing reduction of the spectrum with increasing damping. Our
studies, which represent an Abelian approximation for the colour charge
dynamics in the quark-gluon plasma, may influence the analysis of jet quenching
phenomena observed in high-energy nuclear collisions. Here, we focus on a
formal discussion of the limiting behaviour with increasing radiation
frequency. In an absorptive (and polarizable) medium, this is determined by the
behaviour of the exponential damping factor entering the spectrum and the
formation time of radiation.",1201.1890v1
2012-01-10,Nonequilibrium Damping of Collective Motion of Homogeneous Cold Fermi Condensates with Feshbach Resonances,"Collisionless damping of a condensate of cold Fermi atoms, whose scattering
is controlled by a Feshbach resonance, is explored throughout the BCS and BEC
regimes when small perturbations on its phase and amplitude modes are turned on
to drive the system slightly out of equilibrium. Using a one-loop effective
action, we first recreate the known result that for a broad resonance the
amplitude of the condensate decays as $t^{-1/2}$ at late times in the BCS
regime whereas it decays as $t^{-3/2}$ in the BEC regime. We then examine the
case of an idealized narrow resonance, and find that this collective mode
decays as $t^{-3/2}$ throughout both the BCS and BEC regimes. Although this
seems to contradict earlier results that damping is identical for both broad
and narrow resonances, the breakdown of the narrow resonance limit restores
this universal behaviour. More measureably, the phase perturbation may give a
shift on the saturated value to which the collective amplitude mode decays,
which vanishes only in the deep BCS regime when the phase and amplitude modes
are decoupled.",1201.2019v1
2012-01-30,Modeling electricity spot prices using mean-reverting multifractal processes,"We discuss stochastic modeling of volatility persistence and
anti-correlations in electricity spot prices, and for this purpose we present
two mean-reverting versions of the multifractal random walk (MRW). In the first
model the anti-correlations are modeled in the same way as in an
Ornstein-Uhlenbeck process, i.e. via a drift (damping) term, and in the second
model the anti-correlations are included by letting the innovations in the MRW
model be fractional Gaussian noise with H < 1/2. For both models we present
approximate maximum likelihood methods, and we apply these methods to estimate
the parameters for the spot prices in the Nordic electricity market. The
maximum likelihood estimates show that electricity spot prices are
characterized by scaling exponents that are significantly different from the
corresponding exponents in stock markets, confirming the exceptional nature of
the electricity market. In order to compare the damped MRW model with the
fractional MRW model we use ensemble simulations and wavelet-based variograms,
and we observe that certain features of the spot prices are better described by
the damped MRW model. The characteristic correlation time is estimated to
approximately half a year.",1201.6137v1
2012-05-06,Fractional wave equation and damped waves,"In this paper, a fractional generalization of the wave equation that
describes propagation of damped waves is considered. In contrast to the
fractional diffusion-wave equation, the fractional wave equation contains
fractional derivatives of the same order $\alpha,\ 1\le \alpha \le 2$ both in
space and in time. We show that this feature is a decisive factor for
inheriting some crucial characteristics of the wave equation like a constant
propagation velocity of both the maximum of its fundamental solution and its
gravity and mass centers. Moreover, the first, the second, and the Smith
centrovelocities of the damped waves described by the fractional wave equation
are constant and depend just on the equation order $\alpha$. The fundamental
solution of the fractional wave equation is determined and shown to be a
spatial probability density function evolving in time that possesses finite
moments up to the order $\alpha$. To illustrate analytical findings, results of
numerical calculations and numerous plots are presented.",1205.1199v2
2012-05-14,Critical viscoelastic response in jammed solids,"We determine the linear viscoelastic response of jammed packings of athermal
repulsive viscous spheres, a model for emulsions, wet foams, and soft colloidal
suspensions. We numerically measure the complex shear modulus, a fundamental
characterization of the response, and demonstrate that low frequency response
displays dynamic critical scaling near unjamming. Viscoelastic shear response
is governed by the relaxational eigenmodes of a packing. We use scaling
arguments to explain the distribution of eigenrates, which develops a
divergence at unjamming. We then derive the critical exponents characterizing
response, including a vanishing shear modulus, diverging viscosity, and
critical shear thinning regime. Finally, we demonstrate that macroscopic
rheology is sensitive to details of the local viscous force law. By varying the
ratio of normal and tangential damping coefficients, we identify and explain a
qualitative difference between systems with strong and weak damping of sliding
motion. When sliding is weakly damped there is no diverging time scale, no
diverging viscosity, and no critical shear thinning regime.",1205.2960v1
2012-06-11,Testing the 130 GeV gamma-ray line with high energy resolution detectors,"Recently some hints of the existence of $\gamma$-ray line around 130 GeV are
reported according to the analysis of Fermi-LAT data. If confirmed it would be
the first direct evidence to show the existence of new physics beyond the
standard model. Here we suggest that using the forthcoming high energy
resolution $\gamma$-ray detectors, such as CALET and DAMPE, we may test whether
it is real line structure or just the background effect. For DAMPE like
detector with designed energy resolution $\sim1.5%$, a line significance will
reach $11\sigma$ for the same statistics as Fermi-LAT. For about 1.4 yr survey
observation, DAMPE may detect a $5\sigma$ signal of such a $\gamma$-ray line.",1206.2241v2
2012-06-14,Finite-temperature dynamics of matter-wave dark solitons in linear and periodic potentials: an example of an anti-damped Josephson junction,"We study matter-wave dark solitons in atomic Bose-Einstein condensates at
finite temperatures, under the effect of linear and periodic potentials. Our
model, namely a dissipative Gross-Pitaevskii equation, is treated analytically
by means of dark soliton perturbation theory, which results in a Newtonian
equation of motion for the dark soliton center. This reduced model, which
incorporates an effective washboard potential and an anti-damping term,
constitutes an example of an anti-damped Josephson junction. We present a
qualitative (local and global) analysis of the equation of motion. For
sufficiently small wavenumbers of the periodic potential and weak linear
potentials, the results are found to be in good agreement with pertinent ones
obtained via a Bogoliubov-de Gennes analysis and direct numerical simulations.",1206.2993v1
2012-06-15,Damping of giant dipole resonance in hot rotating nuclei,"The phonon damping model (PDM) is extended to include the effect of angular
momentum at finite temperature. The model is applied to the study of damping of
giant dipole resonance (GDR) in hot and noncollectively rotating spherical
nuclei. The numerical results obtained for Mo88 and Sn106 show that the GDR
width increases with both temperature T and angular momentum M. At T > 4 MeV
and M<= 60 hbar the increase in the GDR width slows down for Sn106, whereas at
M<= 80 hbar the GDR widths in both nuclei nearly saturate. By adopting the
nuclear shear viscosity extracted from fission data at T= 0, it is shown that
the maximal value of the angular momentum for Mo88 and Sn106 should be around
46 and 55 hbar, respectively, so that the universal conjecture for the lower
bound of the specific shear viscosity for all fluids is not violated up to T= 5
MeV.",1206.3361v1
2012-06-18,Sampled-data design for robust control of a single qubit,"This paper presents a sampled-data approach for the robust control of a
single qubit (quantum bit). The required robustness is defined using a sliding
mode domain and the control law is designed offline and then utilized online
with a single qubit having bounded uncertainties. Two classes of uncertainties
are considered involving the system Hamiltonian and the coupling strength of
the system-environment interaction. Four cases are analyzed in detail including
without decoherence, with amplitude damping decoherence, phase damping
decoherence and depolarizing decoherence. Sampling periods are specifically
designed for these cases to guarantee the required robustness. Two sufficient
conditions are presented for guiding the design of unitary control for the
cases without decoherence and with amplitude damping decoherence. The proposed
approach has potential applications in quantum error-correction and in
constructing robust quantum gates.",1206.3897v2
2012-06-25,Trap anharmonicity and sloshing mode of a Fermi gas,"For a gas trapped in a harmonic potential, the sloshing (or Kohn) mode is
undamped and its frequency coincides with the trap frequency, independently of
the statistics, interaction and temperature of the gas. However, experimental
trap potentials have usually Gaussian shape and anharmonicity effects appear as
the temperature and, in the case of Fermions, the filling of the trap are
increased. We study the sloshing mode of a degenerate Fermi gas in an
anharmonic trap within the Boltzmann equation, including in-medium effects in
both the transport and collision terms. The calculated frequency shifts and
damping rates of the sloshing mode due to the trap anharmonicity are in
satisfactory agreement with the available experimental data. We also discuss
higher-order dipole, octupole, and bending modes and show that the damping of
the sloshing mode is caused by its coupling to these modes.",1206.5688v2
2012-09-06,Radiative energy loss in the absorptive QGP: taming the long formation lengths in coherent emission,"In an absorptive plasma, damping of radiation mechanisms can influence the
bremsstrahlung formation in case of large radiation formation lengths. We study
qualitatively the influence of this effect on the gluon bremsstrahlung spectrum
off heavy quarks in the quark-gluon plasma. Independent of the heavy-quark
mass, the spectrum is found to be strongly suppressed in an intermediate gluon
energy region which grows with increasing gluon damping rate and increasing
energy of the heavy quark. Thus, just as polarization effects in the plasma
render the bremsstrahlung spectra independent of the quark mass in the soft
gluon regime, damping effects tend to have a similar impact for larger gluon
energies.",1209.1149v1
2012-09-17,Power spectra in the eikonal approximation with adiabatic and non-adiabatic modes,"We use the so-called eikonal approximation, recently introduced in the
context of cosmological perturbation theory, to compute power spectra for
multi-component fluids. We demonstrate that, at any given order in standard
perturbation theory, multipoint power spectra do not depend on the large-scale
adiabatic modes. Moreover, we employ perturbation theories to decipher how
nonadiabatic modes, such as a relative velocity between two different
components, damp the small-scale matter power spectrum, a mechanism recently
described in the literature. In particular, we do an explicit calculation at
1-loop order of this effect. While the 1-loop result eventually breaks down, we
show how the damping effect can be fully captured by the help of the eikonal
approximation. A relative velocity not only induces mode damping but also
creates large-scale anisotropic modulations of the matter power spectrum
amplitude. We illustrate this for the Local Group environment.",1209.3662v2
2012-09-26,Linear response theory for hydrodynamic and kinetic equations with long-range interactions,"We apply the linear response theory to systems with long-range interactions
described by hydrodynamic equations such as the Euler, Smoluchowski, and damped
Euler equations. We analytically determine the response of the system submitted
to a pulse and to a step function. We compare these results with those obtained
for collisionless systems described by the Vlasov equation. We show that, in
the linear regime, the evolution of a collisionless system (Vlasov) with the
waterbag distribution is the same as the evolution of a collision-dominated gas
without dissipation (Euler). In this analogy, the maximum velocity of the
waterbag distribution plays the role of the velocity of sound in the
corresponding barotropic gas. When submitted to a step function, these systems
exhibit permanent oscillations. Other distributions exhibit Landau damping and
relax towards a steady state. We illustrate this behaviour with the Cauchy
distribution which can be studied analytically. We apply our results to the HMF
model and obtain a generalized Curie-Weiss law for the magnetic susceptibility.
Finally, we compare the linear response theory to the initial value problem for
the linearized Vlasov equation and report a case of algebraic damping of the
initial perturbation.",1209.5987v1
2012-09-15,Phase mixing of propagating Alfven waves in a stratified atmosphere: Solar spicules,"Alfvenic waves are thought to play an important role in coronal heating and
solar wind acceleration. Recent observations by Hinode/SOT showed that the
spicules mostly exhibit upward propagating high frequency waves. Here we
investigate the dissipation of such waves due to phase mixing in stratified
environment of solar spicules. Since they are highly dynamic structures with
speeds at about significant fractions of the Alfven phase speed, we take into
account the effects of steady flows. Our numerical simulations show that in the
presence of stratification due to gravity, damping takes place in space than in
time. The exponential damping low, exp(-At^3), is valid under spicule
conditions, however the calculated damping time is much longer than the
reported spicule lifetimes from observations.",1210.0485v1
2012-10-03,Effect of temperature and velocity on superlubricity,"We study the effects of temperature and sliding velocity on superlubricity in
numerical simulations of the Frenkel-Kontorova model. We show that resonant
excitations of the phonons in an incommensurate sliding body lead to an
effective friction and to thermal equilibrium with energy distributed over the
internal degrees of freedom. For finite temperature, the effective friction can
be described well by a viscous damping force, with a damping coefficient that
emerges naturally from the microscopic dynamics. This damping coefficient is a
non-monotonic function of the sliding velocity which peaks around resonant
velocities and increases with temperature. At low velocities, it remains finite
and nonzero, indicating the preservation of superlubricity in the zero-velocity
limit. Finally, we propose experimental systems in which our results could be
verified.",1210.1124v1
2012-10-04,Basic microscopic plasma physics unified and simplified by N-body classical mechanics,"Debye shielding, collisional transport, Landau damping of Langmuir waves, and
spontaneous emission of these waves are introduced, in typical plasma physics
textbooks, in different chapters. This paper provides a compact unified
introduction to these phenomena without appealing to fluid or kinetic models,
but by using Newton's second law for a system of $N$ electrons in a periodic
box with a neutralizing ionic background. A rigorous equation is derived for
the electrostatic potential. Its linearization and a first smoothing reveal
this potential to be the sum of the shielded Coulomb potentials of the
individual particles. Smoothing this sum yields the classical Vlasovian
expression including initial conditions in Landau contour calculations of
Langmuir wave growth or damping. The theory is extended to accommodate a
correct description of trapping or chaos due to Langmuir waves. In the linear
regime, the amplitude of such a wave is found to be ruled by Landau growth or
damping and by spontaneous emission. Using the shielded potential, the
collisional diffusion coefficient is computed for the first time by a
convergent expression including the correct calculation of deflections for all
impact parameters. Shielding and collisional transport are found to be two
related aspects of the repulsive deflections of electrons.",1210.1546v2
2012-10-11,Measurement of the damping of nuclear shell effect in the doubly magic $^{208}$Pb region,"The damping of the nuclear shell effect with excitation energy has been
measured through an analysis of the neutron spectra following the triton
transfer in the $^7$Li induced reaction on $^{205}$Tl. The measured neutron
spectra demonstrate the expected large shell correction energy for the nuclei
in the vicinity of doubly magic $^{208}$Pb and a small value for $^{184}$W. A
quantitative extraction of the allowed values of the damping parameter
$\gamma$, along with those for the asymptotic nuclear level density parameter
$\tilde{a}$, has been made for the first time.",1210.3213v2
2012-10-16,Optimal control of laser plasma instabilities using Spike Trains of Uneven Duration and Delay (STUD pulses) for ICF and IFE,"An adaptive method of controlling parametric instabilities in laser produced
plasmas is proposed. It involves fast temporal modulation of a laser pulse on
the fastest instability's amplification time scale, adapting to changing and
unknown plasma conditions. These pulses are comprised of on and off sequences
having at least one or two orders of magnitude contrast between them. Such
laser illumination profiles are called STUD pulses for Spike Trains of Uneven
Duration and Delay. The STUD pulse program includes scrambling the speckle
patterns spatially in between the laser spikes. The off times allow damping of
driven waves. The scrambling of the hot spots allows tens of damping times to
elapse before hot spot locations experience recurring high intensity spikes.
Damping in the meantime will have healed the scars of past growth. Another
unique feature of STUD pulses on crossing beams is that their temporal profiles
can be interlaced or staggered, and their interactions thus controlled with an
on-off switch and a dimmer.",1210.4462v1
2012-10-28,Mass Dependence of Instabilities of an Oscillator with Multiplicative and Additive Noise,"We study the instabilities of a harmonic oscillator subject to additive and
dichotomous multiplicative noise, focussing on the dependance of the
instability threshold on the mass. For multiplicative noise in the damping, the
instability threshold is crossed as the mass is decreased, as long as the
smaller damping is in fact negative. For multiplicative noise in the stiffness,
the situation is more complicated and in fact the transition is reentrant for
intermediate noise strength and damping. For multiplicative noise in the mass,
the results depend on the implementation of the noise. One can take the
velocity or the momentum to be conserved as the mass is changed. In these cases
increasing the mass destabilizes the system. Alternatively, if the change in
mass is caused by the accretion/loss of particles to the Brownian particle,
these processes are asymmetric with momentum conserved upon accretion and
velocity upon loss. In this case, there is no instability, as opposed to the
other two implementations. We also study the distribution of the energy,
finding a power-law cutoff at a value which increases with time.",1210.7433v1
2012-10-30,Extending the Concept of Analog Butterworth Filter for Fractional Order Systems,"This paper proposes the design of Fractional Order (FO) Butterworth filter in
complex w-plane (w=sq; q being any real number) considering the presence of
under-damped, hyper-damped, ultra-damped poles. This is the first attempt to
design such fractional Butterworth filters in complex w-plane instead of
complex s-plane, as conventionally done for integer order filters. Firstly, the
concept of fractional derivatives and w-plane stability of linear fractional
order systems are discussed. Detailed mathematical formulation for the design
of fractional Butterworth-like filter (FBWF) in w-plane is then presented.
Simulation examples are given along with a practical example to design the FO
Butterworth filter with given specifications in frequency domain to show the
practicability of the proposed formulation.",1210.8194v3
2012-11-24,Effects of Quantum Error Correction on Entanglement Sudden Death,"We investigate the effects of error correction on non-local quantum coherence
as a function of time, extending the study by Sainz and Bj\""ork. We consider
error correction of amplitude damping, pure phase damping and combinations of
amplitude and phase damping as they affect both fidelity and quantum
entanglement. Initial two-qubit entanglement is encoded in arbitrary real
superpositions of both \Phi-type and \Psi-type Bell states. Our main focus is
on the possibility of delay or prevention of ESD (early stage decoherence, or
entanglement sudden death). We obtain the onset times for ESD as a function of
the state-superposition mixing angle. Error correction affects entanglement and
fidelity differently, and we exhibit initial entangled states for which error
correction increases fidelity but decreases entanglement, and vice versa.",1211.5654v2
2012-12-04,Polarization dependence of phonon influences in exciton-biexciton quantum dot systems,"We report on a strong dependence of the phonon-induced damping of Rabi
dynamics in an optically driven exciton-biexciton quantum dot system on the
polarization of the exciting pulse. While for a fixed pulse intensity the
damping is maximal for linearly polarized excitation, it decreases with
increasing ellipticity of the polarization. This finding is most remarkable
considering that the carrier-phonon coupling is spin-independent. In addition
to simulations based on a numerically exact real-time path integral approach,
we present an analysis within a weak coupling theory that allows for analytical
expressions for the pertinent damping rates. We demonstrate that an efficient
coupling to the biexciton state is of central importance for the reported
polarization dependencies. Further, we discuss influences of various system
parameters and show that for finite biexciton binding energies Rabi scenarios
differ qualitatively from the widely studied two-level dynamics.",1212.0642v1
2012-12-10,Heat-induced damping modification in YIG/Pt hetero-structures,"We experimentally demonstrate the manipulation of magnetization relaxation
utilizing a temperature difference across the thickness of an yttrium iron
garnet/platinum (YIG/Pt) hetero-structure: the damping is either increased or
decreased depending on the sign of the temperature gradient. This effect might
be explained by a thermally-induced spin torque on the magnetization
precession. The heat-induced variation of the damping is detected by microwave
techniques as well as by a DC voltage caused by spin pumping into the adjacent
Pt layer and the subsequent conversion into a charge current by the inverse
spin Hall effect.",1212.2073v1
2012-12-13,Surface plasmon polaritons in a semi-bounded degenerate plasma: role of spatial dispersion and collisions,"Surface plasmon polaritons (SPPs) in a semi-bounded degenerate plasma (e.g.,
a metal) are studied using the quasiclassical mean-field kinetic model, taking
into account the spatial dispersion of the plasma (due to quantum degeneracy of
electrons) and electron-ion (electron-lattice, for metals) collisions. SPP
dispersion and damping are obtained in both retarded ($\omega/k_z\sim c$) and
non-retarded ($\omega/k_z\ll c$) regions, as well as in between. It is shown
that the plasma spatial dispersion significantly affects the properties of
SPPs, especially at short wavelengths (less than the collisionless skin depth,
$\lambda\lesssim c/\omega_{pe}$). Namely, the collisionless (Landau) damping of
SPPs (due to spatial dispersion) is comparable to the purely collisional
(Ohmic) damping (due to electron-lattice collisions) in a wide range of SPP
wavelengths, e.g., from $\lambda\sim20$ nm to $\lambda\sim0.8$ nm for SPP in
gold at T=293 K, and from $\lambda\sim400$ nm to $\lambda\sim0.7$ nm for SPPs
in gold at T=100 K. The spatial dispersion is also shown to affect, in a
qualitative way, the dispersion of SPPs at short wavelengths $\lambda\lesssim
c/\omega_{pe}$.",1212.3040v1
2012-12-13,Branching of quasinormal modes for nearly extremal Kerr black holes,"We show that nearly extremal Kerr black holes have two distinct sets of
quasinormal modes, which we call zero-damping modes (ZDMs) and damped modes
(DMs). The ZDMs exist for all harmonic indices $l$ and $m \ge 0$, and their
frequencies cluster onto the real axis in the extremal limit. The DMs have
nonzero damping for all black hole spins; they exist for all counterrotating
modes ($m<0$) and for corotating modes with $0\leq \mu\lesssim \mu_c=0.74$ (in
the eikonal limit), where $\mu\equiv m/(l+1/2)$. When the two families coexist,
ZDMs and DMs merge to form a single set of quasinormal modes as the black hole
spin decreases. Using the effective potential for perturbations of the Kerr
spacetime, we give intuitive explanations for the absence of DMs in certain
areas of the spectrum and for the branching of the spectrum into ZDMs and DMs
at large spins.",1212.3271v1
2012-12-31,Effects of lateral device size and material properties on the ferromagnetic resonance response of spinwave eigen-modes in magnetic devices,"We analyze the effects of lateral device size and magnetic material
parameters on the ferromagnetic resonance (FMR) response. Results presented are
directly relevant to widely used FMR experimental techniques for extracting
magnetic parameters from thin films, the results of which are often assumed to
carry over to corresponding nanometer-sized patterned devices. We show that
there can be significant variation in the FMR response with device size, and
that the extent of the variation depends on the magnetic material properties.
This explains, for example, why different experiments along these lines have
yielded different size-dependent trends from damping measurements. Observed
trends with increasing size and different material parameters are explained
through the evolution of three distinct eigen-modes, demonstrating the
respective roles of demagnetization and exchange. It is also shown that there
is a crossover of dominant eigen-modes in the response signal, accompanied by
conjugating edge-type modes, leading to evident effects in measured linewidth
and damping. Among the sizes considered, in higher saturation magnetization, we
observe as much as a 40% increase in apparent damping, due solely to device
size variation.",1212.6835v1
2013-01-16,Gain-tunable optomechanical cooling in a laser cavity,"We study the optical cooling of the resonator mirror in a
cavity-optomechanical system that contains an optical gain medium. We find that
the optical damping rate is vanishingly small for an incoherently pumped laser
above threshold. In the presence of an external coherent drive however, the
optical damping rate can be enhanced substantially with respect to that of a
passive cavity. We show that the strength of the incoherent pump provides a
conduit to tune the damping rate and the minimum attainable phonon number with
the same radiation pressure force, and the latter can be lowered from that of a
passive cavity if the thermal contribution is nonnegligible. We also show that
the system can undergo a transition from the weak optomechanical coupling
regime to the strong optomechanical coupling regime as the incoherent pump
strength is varied.",1301.3762v2
2013-01-18,Adiabatic stability under semi-strong interactions: The weakly damped regime,"We rigorously derive multi-pulse interaction laws for the semi-strong
interactions in a family of singularly-perturbed and weakly-damped
reaction-diffusion systems in one space dimension. Most significantly, we show
the existence of a manifold of quasi-steady N-pulse solutions and identify a
""normal-hyperbolicity"" condition which balances the asymptotic weakness of the
linear damping against the algebraic evolution rate of the multi-pulses. Our
main result is the adiabatic stability of the manifolds subject to this normal
hyperbolicity condition. More specifically, the spectrum of the linearization
about a fixed N-pulse configuration contains essential spectrum that is
asymptotically close to the origin as well as semi-strong eigenvalues which
move at leading order as the pulse positions evolve. We characterize the
semi-strong eigenvalues in terms of the spectrum of an explicit N by N matrix,
and rigorously bound the error between the N-pulse manifold and the evolution
of the full system, in a polynomially weighted space, so long as the
semi-strong spectrum remains strictly in the left-half complex plane, and the
essential spectrum is not too close to the origin.",1301.4466v1
2013-01-24,Spin transport parameters in metallic multilayers determined by ferromagnetic resonance measurements of spin pumping,"We measured spin transport in nonferromagnetic (NM) metallic multilayers from
the contribution to damping due to spin pumping from a ferromagnetic Co90Fe10
thin film. The multilayer stack consisted of NM1/NM2/Co90Fe10(2 nm)/NM2/NM3
with varying NM materials and thicknesses. Using conventional theory for one
dimensional diffusive spin transport in metals, we show that the effective
damping due to spin pumping can be strongly affected by the spin transport
properties of each NM in the multilayer, which permits the use of damping
measurements to accurately determine the spin transport properties of the
various NM layers in the full five-layer stack. We find that due to its high
electrical resistivity, amorphous Ta is a poor spin conductor, in spite of a
short spin-diffusion length of 1.0 nm, and that Pt is an excellent spin
conductor by virtue of its low electrical resistivity and a spin diffusion
length of only 0.5 nm. Spin Hall effect measurements may have underestimated
the spin Hall angle in Pt by assuming a much longer spin diffusion length.",1301.5861v1
2013-02-11,Low-damping epsilon-near-zero slabs: nonlinear and nonlocal optical properties,"We investigate second harmonic generation, low-threshold multistability,
all-optical switching, and inherently nonlocal effects due to the free-electron
gas pressure in an epsilon-near-zero (ENZ) metamaterial slab made of
cylindrical, plasmonic nanoshells illuminated by TM-polarized light. Damping
compensation in the ENZ frequency region, achieved by using gain medium inside
the shells' dielectric cores, enhances the nonlinear properties. Reflection is
inhibited and the electric field component normal to the slab interface is
enhanced near the effective pseudo-Brewster angle, where the effective
\epsilon-near-zero condition triggers a non-resonant, impedance-matching
phenomenon. We show that the slab displays a strong effective, spatial
nonlocality associated with leaky modes that are mediated by the compensation
of damping. The presence of these leaky modes then induces further spectral and
angular conditions where the local fields are enhanced, thus opening new
windows of opportunity for the enhancement of nonlinear optical processes.",1302.2392v1
2013-02-14,A Matlab toolbox for fractional relaxation-oscillation equations,"Stress relaxation and oscillation damping of complex viscoelastic media often
manifest history- and path-dependent physical behaviors and cannot accurately
be described by the classical models. Recent research found that fractional
derivative models can characterize such complex relaxation and damping.
However, to our best knowledge, easy-to-use numerical software is not available
for fractional relaxation-oscillation (FRO) equations. This paper is to
introduce an open source free Matlab toolbox which we developed in recent years
for numerical solution of the FRO equations. This FRO toolbox uses the
predictor-corrector approach for the discretization of time fractional
derivative, and non-expert users can accurately solve fractional
relaxation-oscillation equations via a friendly graphical user interface.
Compared with experimental data, our numerical experiments show that the FRO
toolbox is highly efficient and accurate to simulate viscoelastic stress
relaxation and damped vibration. This free toolbox will help promote the
research and practical use of fractional relaxation-oscillation equations.",1302.3384v1
2013-03-11,The Analysis of Long-Term Frequency and Damping Wandering in Buildings Using the Random Decrement Technique,"The characterization and monitoring of buildings is an issue that has
attracted the interest of many sectors over the last two decades. With the
increasing use of permanent, continuous and real-time networks, ambient
vibrations can provide a simple tool for the identification of dynamic building
parameters. This study is focused on the long-term variation of frequency and
damping in several buildings, using the Random Decrement Technique (RDT). RDT
provides a fast, robust and accurate long-term analysis and improves the
reliability of frequency and damping measurements for structural health
monitoring. This reveals particularly useful information in finding out
precisely how far changes in modal parameters can be related to changes in
physical properties. This paper highlights the reversible changes of the
structure's dynamic parameters, correlated with external forces, such as
temperature and exposure to the sun. Contrasting behaviors are observed,
including correlation and anti-correlation with temperature variations.",1303.2642v1
2013-03-21,Optimizing atomic resolution of force microscopy in ambient conditions,"Ambient operation poses a challenge to AFM because in contrast to operation
in vacuum or liquid environments, the cantilever dynamics change dramatically
from oscillating in air to oscillating in a hydration layer when probing the
sample. We demonstrate atomic resolution by imaging of the KBr(001) surface in
ambient conditions by frequency-modulation atomic force microscopy with a
cantilever based on a quartz tuning fork (qPlus sensor) and analyze both long-
and short-range contributions to the damping. The thickness of the hydration
layer increases with relative humidity, thus varying humidity enables us to
study the in uence of the hydration layer thickness on cantilever damping.
Starting with measurements of damping versus amplitude, we analyzed the signal
and the noise characteristics at the atomic scale. We then determined the
optimal amplitude which enabled us to acquire high-quality atomically resolved
images.",1303.5204v2
2013-04-10,Current Sheets and Collisionless Damping in Kinetic Plasma Turbulence,"We present the first study of the formation and dissipation of current sheets
at electron scales in a wave-driven, weakly collisional, 3D kinetic turbulence
simulation. We investigate the relative importance of dissipation associated
with collisionless damping via resonant wave-particle interactions versus
dissipation in small-scale current sheets in weakly collisional plasma
turbulence. Current sheets form self-consistently from the wave-driven
turbulence, and their filling fraction is well correlated to the electron
heating rate. However, the weakly collisional nature of the simulation
necessarily implies that the current sheets are not significantly dissipated
via Ohmic dissipation. Rather, collisionless damping via the Landau resonance
with the electrons is sufficient to account for the measured heating as a
function of scale in the simulation, without the need for significant Ohmic
dissipation. This finding suggests the possibility that the dissipation of the
current sheets is governed by resonant wave-particle interactions and that the
locations of current sheets correspond spatially to regions of enhanced
heating.",1304.2958v2
2013-04-22,Constant residual electrostatic electron plasma mode in Vlasov-Ampere system,"In a collisionless Vlasov-Poisson (V-P) electron plasma system, two types of
modes for electric field perturbation exist: the exponentially Landau damped
electron plasma waves and the initial-value sensitive ballistic modes. Here,
the V-P system is modified slightly to a Vlasov-Ampere (V-A) system. A new
constant residual mode is revealed. Mathematically, this mode comes from the
Laplace transform of an initial electric field perturbation, and physically
represents that an initial perturbation (e.g., external electric field
perturbation) would not be damped away. Thus, this residual mode is more
difficult to be damped than the ballistic mode. [Physics of Plasmas 20, 112108
(2013); doi: 10.1063/1.4831761]",1304.5883v2
2013-04-23,Existence and non-existence of breather solutions in damped and driven nonlinear lattices,"We investigate the existence of spatially localised solutions, in the form of
discrete breathers, in general damped and driven nonlinear lattice systems of
coupled oscillators. Conditions for the exponential decay of the difference
between the maximal and minimal amplitudes of the oscillators are provided
which proves that initial non-uniform spatial patterns representing breathers
attain exponentially fast a spatially uniform state preventing the formation
and/or preservation of any breather solution at all. Strikingly our results are
generic in the sense that they hold for arbitrary dimension of the system, any
attractive interaction, coupling strength and on-site potential and general
driving fields. Furthermore, our rigorous quantitative results establish
conditions under which discrete breathers in general damped and driven
nonlinear lattices can exist at all and open the way for further research on
the emergent dynamical scenarios, in particular features of pattern formation,
localisation and synchronisation, in coupled cell networks.",1304.6370v3
2013-06-21,Inviscid damping and the asymptotic stability of planar shear flows in the 2D Euler equations,"We prove asymptotic stability of shear flows close to the planar Couette flow
in the 2D inviscid Euler equations on $\Torus \times \Real$. That is, given an
initial perturbation of the Couette flow small in a suitable regularity class,
specifically Gevrey space of class smaller than 2, the velocity converges
strongly in L^2 to a shear flow which is also close to the Couette flow. The
vorticity is asymptotically driven to small scales by a linear evolution and
weakly converges as $t \rightarrow \pm\infty$. The strong convergence of the
velocity field is sometimes referred to as inviscid damping, due to the
relationship with Landau damping in the Vlasov equations. This convergence was
formally derived at the linear level by Kelvin in 1887 and it occurs at an
algebraic rate first computed by Orr in 1907; our work appears to be the first
rigorous confirmation of this behavior on the nonlinear level.",1306.5028v3
2013-07-12,Spin injection from topological insulator tunnel-coupled to metallic leads,"We study theoretically helical edge states of 2D and 3D topological
insulators (TI) tunnel-coupled to metal leads and show that their transport
properties are strongly affected by contacts as the latter play a role of a
heat bath and induce damping and relaxation of electrons in the helical states
of TI. A simple structure that produces a pure spin current in the external
circuit is proposed. The current and spin current delivered to the external
circuit depend on relation between characteristic lengths: damping length due
to tunneling, contact length and, in case of 3D TI, mean free path and spin
relaxation length caused by momentum scattering. If the damping length due to
tunneling is the smallest one, then the electric and spin currents are
proportional to the conductance quantum in 2D TI, and to the conductance
quantum multiplied by the ratio of the contact width to the Fermi wavelength in
3D TI.",1307.3333v1
2013-07-19,Damping and non-linearity of a levitating magnet in rotation above a superconductor,"We study the dissipation of moving magnets in levitation above a
superconductor. The rotation motion is analyzed using optical tracking
techniques. It displays a remarkable regularity together with long damping time
up to several hours. The magnetic contribution to the damping is investigated
in detail by comparing 14 distinct magnetic configurations, and points towards
amplitude-dependent dissipation mechanisms. The non-linear dynamics of the
mechanical rotation motion is also revealed and described with an effective
Duffing model. The obtained picture of the coupling of levitating magnets to
their environment sheds light on their potential as ultra-low dissipation
mechanical oscillators for high precision physics.",1307.5155v1
2013-07-19,Perfect squeezing by damping modulation in circuit quantum electrodynamics,"Dissipation-driven quantum state engineering uses the environment to steer
the state of quantum systems and preserve quantum coherence in the steady
state. We show that modulating the damping rate of a microwave resonator
generates a vacuum squeezed state of arbitrary squeezing strength, thereby
constituting a mechanism allowing perfect squeezing. Given the recent
experimental realizations in circuit QED of a microwave resonator with a
tunable damping rate [Yin et al., Phys. Rev. Lett. 110, 107001 (2013)],
superconducting circuits are an ideal playground to implement this technique.
By dispersively coupling a qubit to the microwave resonator, it is possible to
obtain qubit-state dependent squeezing.",1307.5311v2
2013-07-27,"Charge-carrier-induced frequency renormalization, damping and heating of vibrational modes in nanoscale junctions","In nanoscale junctions the interaction between charge carriers and the local
vibrations results in renormalization, damping and heating of the vibrational
modes. We here formulate a nonequilibrium Green's functions based theory to
describe such effects. Studying a generic junction model with an off-resonant
electronic level, we find a strong bias dependence of the frequency
renormalization and vibrational damping accompanied by pronounced nonlinear
vibrational heating in junctions with intermediate values of the coupling to
the leads. Combining our theory with ab-initio calculations we furthermore show
that the bias dependence of the Raman shifts and linewidths observed
experimentally in an OPV3 junction [D. Ward et al., Nature Nano. 6, 33 (2011)]
may be explained by a combination of dynamic carrier screening and molecular
charging.",1307.7288v3
2013-07-30,Phase retrapping in a pointlike $\varphi$ Josephson junction: the Butterfly effect,"We consider a $\varphi$ Josephson junction, which has a bistable zero-voltage
state with the stationary phases $\psi=\pm\varphi$. In the non-zero voltage
state the phase ""moves"" viscously along a tilted periodic double-well
potential. When the tilting is reduced quasistatically, the phase is retrapped
in one of the potential wells. We study the viscous phase dynamics to determine
in which well ($-\varphi$ or $+\varphi$) the phase is retrapped for a given
damping, when the junction returns from the finite-voltage state back to
zero-voltage state. In the limit of low damping the $\varphi$ Josephson
junction exhibits a butterfly effect --- extreme sensitivity of the destination
well on damping. This leads to an impossibility to predict the destination
well.",1307.8042v1
2013-08-10,CESR Test Accelerator,"The Cornell Electron Storage Ring (CESR) was reconfigured in 2008 as a test
accelerator to investigate the physics of ultra-low emittance damping rings.
During the approximately 40 days/year available for dedicated operation as a
test accelerator, specialized instrumentation is used to measure growth and
mitigation of the electron cloud, emittance growth due to electron cloud,
intra-beam scattering, and ions, and single and multi-bunch instabilities
generated by collective effects. The flexibility of the CESR guide field optics
and the integration of accelerator modeling codes with the control system have
made possible an extraordinary range of experiments. Findings at CesrTA with
respect to electron cloud effects, emittance tuning techniques, and beam
instrumentation for measuring electron cloud, beam sizes, and beam positions
are the basis for much of the design of the ILC damping rings as documented in
the ILC-Technical Design Report. The program has allowed the Cornell group to
cultivate the kind of talent and expertise that will be absolutely essential to
the final engineering design, and commissioning of the damping rings for a
linear collider.",1308.2325v1
2013-09-09,Characterization of the International Linear Collider damping ring optics,"A method is presented for characterizing the emittance dilution and dynamic
aperture for an arbitrary closed lattice that includes guide field magnet
errors, multipole errors and misalignments. This method, developed and tested
at the Cornell Electron Storage Ring Test Accelerator (CesrTA), has been
applied to the damping ring lattice for the International Linear Collider
(ILC). The effectiveness of beam based emittance tuning is limited by beam
position monitor (BPM) measurement errors, number of corrector magnets and
their placement, and correction algorithm. The specifications for damping ring
magnet alignment, multipole errors, number of BPMs, and precision in BPM
measurements are shown to be consistent with the required emittances and
dynamic aperture. The methodology is then used to determine the minimum number
of position monitors that is required to achieve the emittance targets, and how
that minimum depends on the location of the BPMs. Similarly, the maximum
tolerable multipole errors are evaluated. Finally, the robustness of each BPM
configuration with respect to random failures is explored.",1309.2248v3
2013-09-19,Van der Waals Coefficients for the Alkali-metal Atoms in the Material Mediums,"The damping coefficients for the alkali atoms are determined very accurately
by taking into account the optical properties of the atoms and three distinct
types of trapping materials such as Au (metal), Si (semi-conductor) and
vitreous SiO2 (dielectric). Dynamic dipole polarizabilities are calculated
precisely for the alkali atoms that reproduce the damping coefficients in the
perfect conducting medium within 0.2% accuracy. Upon the consideration of the
available optical data of the above wall materials, the damping coefficients
are found to be substantially different than those of the ideal conductor. We
also evaluated dispersion coefficients for the alkali dimers and compared them
with the previously reported values. These coefficients are fitted into a
ready-to-use functional form to aid the experimentalists the interaction
potentials only with the knowledge of distances.",1309.4897v1
2013-10-13,What the Timing of Millisecond Pulsars Can Teach us about Their Interior,"The cores of compact stars reach the highest densities in nature and
therefore could consist of novel phases of matter. We demonstrate via a
detailed analysis of pulsar evolution that precise pulsar timing data can
constrain the star's composition, through unstable global oscillations
(r-modes) whose damping is determined by microscopic properties of the
interior. If not efficiently damped, these modes emit gravitational waves that
quickly spin down a millisecond pulsar. As a first application of this general
method, we find that ungapped interacting quark matter is consistent with both
the observed radio and x-ray data, whereas for ordinary nuclear matter some
additional enhanced damping mechanism is required.",1310.3524v2
2013-11-28,Conservative effects in spin-transfer-driven magnetization dynamics,"It is shown that under appropriate conditions spin-transfer-driven
magnetization dynamics in a single-domain nanomagnet is conservative in nature
and admits a specific integral of motion, which is reduced to the usual
magnetic energy when the spin current goes to zero. The existence of this
conservation law is connected to the symmetry properties of the dynamics under
simultaneous inversion of magnetisation and time. When one applies an external
magnetic field parallel to the spin polarization, the dynamics is transformed
from conservative into dissipative. More precisely, it is demonstrated that
there exists a state function such that the field induces a monotone relaxation
of this function toward its minima or maxima, depending on the field
orientation. These results hold in the absence of intrinsic damping effects.
When intrinsic damping is included in the description, a competition arises
between field-induced and damping-induced relaxations, which leads to the
appearance of limit cycles, that is, of magnetization self-oscillations.",1311.7344v1
2013-12-05,The initial condition problems of damped quantum harmonic oscillator,"We investigate the exact dynamics of the damped quantum harmonic oscillator
under the (un)correlated initial conditions. The master equation is generalized
to the cases of the arbitrary factorized state and/or Gaussian state. We show
that the variances of the factorized Gaussian state do not sensitively depend
on the initial oscillator-bath correlation, which however can remarkably affect
the mean values even at high temperature. We also illustrate that the
correlations among the factorized states still give rise to the initial dips
during the purity evolutions, which can be smoothed out by increasing the
amount of correlation to some extent. We finally study the effects of repeated
measurements on the time evolution of the damped oscillator analytically, which
are compared with the weak coupling results to indicate that they give rather
different transient behaviors even for an intermediate coupling.",1312.1454v1
2013-12-13,Optical variability of quasars: a damped random walk,"A damped random walk is a stochastic process, defined by an exponential
covariance matrix that behaves as a random walk for short time scales and
asymptotically achieves a finite variability amplitude at long time scales.
Over the last few years, it has been demonstrated, mostly but not exclusively
using SDSS data, that a damped random walk model provides a satisfactory
statistical description of observed quasar variability in the optical
wavelength range, for rest-frame timescales from 5 days to 2000 days. The
best-fit characteristic timescale and asymptotic variability amplitude scale
with the luminosity, black hole mass, and rest wavelength, and appear
independent of redshift. In addition to providing insights into the physics of
quasar variability, the best-fit model parameters can be used to efficiently
separate quasars from stars in imaging surveys with adequate long-term
multi-epoch data, such as expected from LSST.",1312.3966v1
2013-12-25,Non-linear damping of visco-resistive Alfven waves in solar spicules,"Interaction of Alfven waves with plasma inhomogeneities generates phase
mixing which can lead to dissipate Alfven waves and to heat the solar plasma.
Here we study the dissipation of Alfven waves by phase mixing due to viscosity
and resistivity variations with height. We also consider nonlinear
magnetohydrodynamic (MHD) equations in our theoretical model. Non-linear terms
of MHD equations include perturbed velocity, magnetic field, and density. To
investigate the damping of Alfven waves in a stratified atmosphere of solar
spicules, we solve the non-linear MHD equations in the x-z plane. Our
simulations show that the damping is enhanced due to viscosity and resistivity
gradients. Moreover, energy variations is influenced due to nonlinear terms in
MHD equations.",1312.7866v1
2013-12-31,A novel variability-based method for quasar selection: evidence for a rest frame ~54 day characteristic timescale,"We compare quasar selection techniques based on their optical variability
using data from the Catalina Real-time Transient Survey (CRTS). We introduce a
new technique based on Slepian wavelet variance (SWV) that shows comparable or
better performance to structure functions and damped random walk models but
with fewer assumptions. Combining these methods with WISE mid-IR colors
produces a highly efficient quasar selection technique which we have validated
spectroscopically. The SWV technique also identifies characteristic timescales
in a time series and we find a characteristic rest frame timescale of ~54 days,
confirmed in the light curves of ~18000 quasars from CRTS, SDSS and MACHO data,
and anticorrelated with absolute magnitude. This indicates a transition between
a damped random walk and $P(f) \propto f^{-1/3}$ behaviours and is the first
strong indication that a damped random walk model may be too simplistic to
describe optical quasar variability.",1401.1785v1
2014-02-09,Manipulation of tripartite-to-bipartite entanglement localization under quantum noises and its application to entanglement distribution,"This paper is to investigate the effects of quantum noises on entanglement
localization by taking an example of reducing a three-qubit
Greenberger-Horne-Zeilinger (GHZ) state to a two-qubit entangled state. We
consider, respectively, two types of quantum decoherence, i.e.,
amplitude-damping and depolarizing decoherence, and explore the best von
Neumann measurements on one of three qubits of the triple GHZ state for making
the amount of entanglement of the collapsed bipartite state be as large as
possible. The results indicate that different noises have different impacts on
entanglement localization, and that the optimal strategy for reducing a
three-qubit GHZ state to a two-qubit one via local measurements and classical
communications in the amplitude-damping case is different from that in the
noise-free case. We also show that the idea of entanglement localization could
be utilized to improve the quality of bipartite entanglement distributing
through amplitude-damping channels. These findings might shed a new light on
entanglement manipulations and transformations.",1402.1914v2
2014-02-25,Thermodynamic anomalies in the presence of dissipation: from the free particle to the harmonic oscillator,"A free particle coupled to a heat bath can exhibit a number of thermodynamic
anomalies like a negative specific heat or reentrant classicality. These
low-temperature phenomena are expected to be modified at very low temperatures
where finite-size effects associated with the discreteness of the energy
spectrum become relevant. In this paper, we explore in which form the
thermodynamic anomalies of the free damped particle appear for a damped
harmonic oscillator. Since the discreteness of the oscillator's energy spectrum
is fully accounted for, the results are valid for arbitrary temperatures. As
expected, they are in agreement with the third law of thermodynamics and
indicate how the thermodynamic anomalies of the free damped particle can be
reconciled with the third law. Particular attention is paid to the transition
from the harmonic oscillator to the free particle when the limit of the
oscillator frequency to zero is taken.",1402.6221v1
2014-02-26,Magneto-elastic modes and lifetime of magnons in thin yttrium-iron garnet films,"We calculate the effects of the spin-lattice coupling on the magnon spectrum
of thin ferromagnetic films consisting of the magnetic insulator yttrium-iron
garnet. The magnon-phonon hybridisation generates a characteristic minimum in
the spin dynamic structure factor which quantitatively agrees with recent
Brillouin light scattering experiments. We also show that at room temperature
the phonon contribution to the magnon damping exhibits a rather complicated
momentum dependence: In the exchange regime the magnon damping is dominated by
Cherenkov type scattering processes, while in the long-wavelength dipolar
regime these processes are subdominant and the magnon damping is two orders of
magnitude smaller. We supplement our calculations by actual measurements of the
magnon relaxation in the dipolar regime. Our theory provides a simple
explanation of a recent experiment probing the different temperatures of the
magnon and phonon gases in yttrium-iron garnet.",1402.6575v2
2014-02-28,A new way to evaluate x-ray Brillouin scattering data,"Making use of the classical second moment sum rule, it is possible to convert
a series of constant-Q x-ray Brillouin scattering scans (Q momentum transfer)
into a series of constant frequency scans over the measured $Q$ range. The
method is applied to literature results for the phonon dispersion in liquid
vitreous silica and in glassy polybutadiene. It turns out that the constant
frequency scans are again well fitted by the damped harmonic oscillator
function, but now in terms of a Q-independent phonon damping depending
exclusively on the frequency. At low frequency, the sound velocity and the
damping of both evaluations agree, but at higher frequencies one gets
significant differences. The results in silica suggest a new interpretation of
x-ray Brillouin data in terms of a strong mixing of longitudinal and transverse
phonons toward higher frequencies. The results in polybutadiene enlighten the
crossover from Brillouin to Umklapp scattering.",1402.7237v1
2014-03-10,Quantum Fisher Information of W States in Decoherence Channels,"We study the quantum Fisher information (QFI) of W states analytically with
respect to SU(2) rotations in the basic decoherence channels i.e. depolarizing
(DPC), amplitude damping (ADC) and phase damping (PDC), and present the
interesting behavior of QFI of W states, especially when compared to that of
GHZ states [Ma et al., Phys. Rev. A, 84, 022302 (2011)]. We find that when
initially pure W states are under decoherence, i) DPC: as decoherence starts
and increases, QFI smoothly decays; ii) ADC: just as decoherence starts, QFI
exhibits a sudden drop to the shot noise level and as decoherence increases,
QFI continues to decrease to zero and then increases back to the shot noise
level; iii) PDC: just as decoherence starts, a sudden death of QFI occurs and
QFI remains zero for any rate of decoherence, therefore W states in phase
damping channel do not provide phase sensitivity. We also find that, on the
contrary to GHZ states, pure or decohered W states are not sensitive with
respect to rotations in z direction and the sensitivities with respect to
rotations in x and y directions are equal to each other, implying no sudden
change points of QFI due to competition between directions.",1403.2376v1
2014-03-14,Silk damping at a redshift of a billion: a new limit on small-scale adiabatic perturbations,"We study the dissipation of small-scale adiabatic perturbations at early
times when the Universe is hotter than T ~ 0.5 keV. When the wavelength falls
below the damping scale 1/kD, the acoustic modes diffuse and thermalize,
causing entropy production. Before neutrino decoupling, kD is primarily set by
the neutrino shear viscosity, and we study the effect of acoustic damping on
the relic neutrino number, primordial nucleosynthesis, dark-matter freeze-out,
and baryogenesis. This sets a new limit on the amplitude of primordial
fluctuations of DeltaR^2 < 0.007 at 10^4/Mpc< k < 10^5/Mpc and a model
dependent limit of DeltaR^2 < 0.3 at k < 10^{20-25}/Mpc.",1403.3697v1
2014-06-02,CMB $μ$ distortion from primordial gravitational waves,"We propose a new mechanism of generating the $\mu$ distortion in cosmic
microwave background (CMB) originated from primordial gravitational waves. Such
$\mu$ distortion is generated by the damping of the temperature anisotropies
through the Thomson scattering, even on scales larger than that of Silk
damping. This mechanism is in sharp contrast with that from the primordial
curvature (scalar) perturbations, in which the temperature anisotropies mainly
decay by Silk damping effects. We estimate the size of the $\mu$ distortion
from the new mechanism, which can be used to constrain the amplitude of
primordial gravitational waves on smaller scales independently from the CMB
anisotropies, giving more wide-range constraint on their spectral index by
combining the amplitude from the CMB anisotropies.",1406.0451v2
2014-06-04,Self-organized escape processes of linear chains in nonlinear potentials,"An enhancement of localized nonlinear modes in coupled systems gives rise to
a novel type of escape process. We study a spatially one dimensional set-up
consisting of a linearly coupled oscillator chain of $N$ mass-points situated
in a metastable nonlinear potential. The Hamilton-dynamics exhibits breather
solutions as a result of modulational instability of the phonon states. These
breathers localize energy by freezing other parts of the chain. Eventually this
localised part of the chain grows in amplitude until it overcomes the critical
elongation characterized by the transition state. Doing so, the breathers
ignite an escape by pulling the remaining chain over the barrier. Even if the
formation of singular breathers is insufficient for an escape, coalescence of
moving breathers can result in the required concentration of energy. Compared
to a chain system with linear damping and thermal fluctuations the breathers
help the chain to overcome the barriers faster in the case of low damping. With
larger damping, the decreasing life time of the breathers effectively inhibits
the escape process.",1406.0938v1
2014-06-08,Dissipation-driven squeezed and sub-Poissonian mechanical states in quadratic optomechanical systems,"In this work we study an optomechanical system in which there is a purely
quadratic optomechanical coupling between the optical and mechanical modes. The
optical mode is pumped by three coherent fields and the mechanical mode is
parametrically driven. We show that if the frequencies and amplitudes of both
optical and mechanical drivings are properly chosen, the optomechanical
interaction gives rise to an effective interaction, which, in the presence of
optical damping and in the absence of mechanical damping, has the squeezed
vacuum state and the squeezed one phonon state as dark states of the dynamics.
These states are well known for presenting quadrature squeezing and
sub-Poissonian statistics. However, even in the presence of mechanical damping
it is possible to find steady states with large degrees of quadrature squeezing
or strong sub-Poissonian statistics. Furthermore, we find a counter-intuitive
behavior in which a nonzero temperature of the mechanical environment allows
the observation of mechanical states with more pronounced sub-Poissonian
statistics.",1406.1987v3
2014-06-13,Frequency-dependent damping in propagating slow magneto-acoustic waves,"Propagating slow magneto-acoustic waves are often observed in polar plumes
and active region fan loops. The observed periodicities of these waves range
from a few minutes to few tens of minutes and their amplitudes were found to
decay rapidly as they travel along the supporting structure. Previously,
thermal conduction, compressive viscosity, radiation, density stratification,
and area divergence, were identified to be some of the causes for change in the
slow wave amplitude. Our recent studies indicate that the observed damping in
these waves is frequency dependent. We used imaging data from SDO/AIA, to study
this dependence in detail and for the first time from observations we attempted
to deduce a quantitative relation between damping length and frequency of these
oscillations. We developed a new analysis method to obtain this relation. The
observed frequency dependence does not seem to agree with the current linear
wave theory and it was found that the waves observed in the polar regions show
a different dependence from those observed in the on-disk loop structures
despite the similarity in their properties.",1406.3565v1
2014-06-24,On finite density effects on cosmic reheating and moduli decay and implications for Dark Matter production,"We study the damping of an oscillating scalar field in a
Friedmann-Robertson-Walker spacetime by perturbative processes, taking into
account the finite density effects that interactions with the plasma of decay
products have on the damping rate. The scalar field may be identified with the
inflaton, in which case this process leads to the reheating of the universe
after inflation. It can also resemble a modulus that dominates the energy
density of the universe at later times. We find that the finite density
corrections to the damping rate can have a drastic effect on the thermal
history and considerably increase both, the maximal temperature in the early
universe and the reheating temperature at the onset of the radiation dominated
era. As a result abundance of some Dark Matter candidates may be considerably
larger than previously estimated. We give improved analytic estimates for the
maximal and the reheating temperatures and confirm them numerically in a simple
model.",1406.6243v2
2014-08-13,Probing dense matter in compact star cores with radio pulsar data,"Astrophysical observations of compact stars provide, in addition to collider
experiments, the other big source of information on matter under extreme
conditions. The largest and most precise data set about neutron stars is the
timing data of radio pulsars. We show how this unique data can be used to learn
about the ultra-dense matter in the compact star interior. The method relies on
astro-seismology based on special global oscillation modes (r-modes) that emit
gravitational waves. They would prevent pulsars from spinning with their
observed high frequencies, unless the damping of these modes, determined by the
microscopic properties of matter, can prevent this. We show that for each form
of matter there is a distinct region in a frequency/spindown-rate diagram where
r-modes can be present. We find that stars containing ungapped quark matter are
consistent with both the observed radio and x-ray data, whereas, even when
taking into account the considerable uncertainties, neutron star models with
standard viscous damping are inconsistent with both data sets and additional
damping mechanisms would be required.",1408.3152v1
2014-08-25,Spin-Scattering Rates in Metallic Thin Films Measured by Ferromagnetic Resonance Damping Enhanced by Spin-Pumping,"We determined the spin-transport properties of Pd and Pt thin films by
measuring the increase in ferromagnetic resonance damping due to spin-pumping
in ferromagnetic (FM)-nonferromagnetic metal (NM) multilayers with varying NM
thicknesses. The increase in damping with NM thickness depends strongly on both
the spin- and charge-transport properties of the NM, as modeled by diffusion
equations that include both momentum- and spin-scattering parameters. We use
the analytical solution to the spin-diffusion equations to obtain
spin-diffusion lengths for Pt and Pd. By measuring the dependence of
conductivity on NM thickness, we correlate the charge- and spin-transport
parameters, and validate the applicability of various models for
momentum-scattering and spin-scattering rates in these systems: constant,
inverse-proportional (Dyakanov-Perel), and linear-proportional (Elliot-Yafet).
We confirm previous reports that the spin-scattering time can be shorter than
the momentum scattering time in Pt, and the Dyakanov-Perel-like model is the
best fit to the data.",1408.5921v2
2014-08-27,Quasi-particle Lifetime in a Mixture of Bose and Fermi Superfluids,"In this letter, to reveal the effect of quasi-particle interactions in a
Bose-Fermi superfluid mixture, we consider the lifetime of quasi-particle of
Bose superfluid due to its interaction with quasi-particles in Fermi
superfluid. We find that this damping rate, i.e. inverse of the lifetime, has
quite different threshold behavior at the BCS and the BEC side of the Fermi
superfluid. The damping rate is a constant nearby the threshold momentum in the
BCS side, while it increases rapidly in the BEC side. This is because in the
BCS side the decay processe is restricted by constant density-of-state of
fermion quasi-particle nearby Fermi surface, while such a restriction does not
exist in the BEC side where the damping process is dominated by bosonic
quasi-particles of Fermi superfluid. Our results are related to collective mode
experiment in recently realized Bose-Fermi superfluid mixture.",1408.6419v1
2014-09-04,A numerical study of the pull-in instability in some free boundary models for MEMS,"In this work we numerically compute the bifurcation curve of stationary
solutions for the free boundary problem for MEMS in one space dimension. It has
a single turning point, as in the case of the small aspect ratio limit. We also
find a threshold for the existence of global-in-time solutions of the evolution
equation given by either a heat or a damped wave equation. This threshold is
what we term the dynamical pull-in value: it separates the stable operation
regime from the touchdown regime. The numerical calculations show that the
dynamical threshold values for the heat equation coincide with the static
values. For the damped wave equation the dynamical threshold values are smaller
than the static values. This result is in agreement with the observations
reported for a mass-spring system studied in the engineering literature. In the
case of the damped wave equation, we also show that the aspect ratio of the
device is more important than the inertia in the determination of the pull-in
value.",1409.1291v2
2014-09-15,"Direct path from microscopic mechanics to Debye shielding, Landau damping, and wave-particle interaction","The derivation of Debye shielding and Landau damping from the $N$-body
description of plasmas is performed directly by using Newton's second law for
the $N$-body system. This is done in a few steps with elementary calculations
using standard tools of calculus, and no probabilistic setting. Unexpectedly,
Debye shielding is encountered together with Landau damping. This approach is
shown to be justified in the one-dimensional case when the number of particles
in a Debye sphere becomes large. The theory is extended to accommodate a
correct description of trapping and chaos due to Langmuir waves. Shielding and
collisional transport are found to be two related aspects of the repulsive
deflections of electrons, in such a way that each particle is shielded by all
other ones while keeping in uninterrupted motion.",1409.4323v1
2014-09-19,Damping of metallized bilayer nanomechanical resonators at room temperature,"We investigate the influence of gold thin-films subsequently deposited on a
set of initially bare, doubly clamped, high-stress silicon nitride string
resonators at room temperature. Analytical expressions for resonance frequency,
quality factor and damping for both in- and out-of-plane flexural modes of the
bilayer system are derived, which allows for the determination of effective
elastic parameters of the composite structure from our experimental data. We
find the inverse quality factor to scale linearly with the gold film thickness,
indicating that the overall damping is governed by losses in the metal.
Correspondingly, the mechanical linewidth increases by more than one order of
magnitude compared to the bare silicon nitride string resonator. Furthermore,
we extract mechanical quality factors of the gold film for both flexural modes
and show that they can be enhanced by complete deposition of the metal in a
single step, suggesting that surface and interface losses play a vital role in
metal thin-films.",1409.5670v1
2014-10-09,Non-Fermi-liquid behavior and anomalous suppression of Landau damping in layered metals close to ferromagnetism,"We analyse the low-energy physics of nearly ferromagnetic metals in two
spatial dimensions using the functional renormalization group technique. We
find a new low-energy fixed point, at which the fermionic (electron-like)
excitations are non-Fermi-liquid ($z_f = 13/10$) and the magnetic fluctuations
exhibit an anomalous Landau damping whose rate vanishes as $\Gamma_{\bf q} \sim
\vert {\bf q} \vert^{3/5}$ in the low-$\vert {\bf q} \vert$ limit. We discuss
this renormalization of the Landau-damping exponent, which is the major novel
prediction of our work, and highlight the possible link between that
renormalization and neutron-scattering data on UGe$_2$ and related compounds.
Implications of our analysis for YFe$_2$Al$_{10}$ are also discussed.",1410.2539v3
2014-10-09,Special mean motion resonance pairs: Mimas-Tethys and Titan-Hyperion,"Five pairs of large solar system satellites occupy first order mean-motion
resonances (MMRs). Among these, the pairs of Mimas-Tethys and Titan-Hyperion
are special. They are located much deeper in resonance than the others and
their critical arguments librate with much greater amplitudes. These
characteristics are traced to the insignificant damping, over $\Gyr$
timescales, of Mimas's orbital inclination and Hyperion's orbital eccentricity.
Absent that, these resonances would not survive. Instead their librations would
be overstable and escape from resonance would occur on the relevant damping
time. Unlike the aforementioned MMRs, those involving Enceladus-Dione,
Io-Europa, and Europa-Ganymede are limited by eccentricity damping. They must
either remain at the shallow depths they currently occupy, or, if they venture
deeper, retreat after a limited time. The latter seems almost certain for
Enceladus-Dione and quite likely for the others, We examine the MMRs involving
Mimas-Tethys and Titan-Hyperion under the assumption that they formed as a
result of convergent migration. Capture probabilities are $\sim 6\%$ for the
former and $100\%$ for the latter. The possibility of collisional excitation of
their large librations is investigated but largely discounted.",1410.2648v1
2014-11-13,Stability and bifurcation for the Kuramoto model,"We study the mean-field limit of the Kuramoto model of globally coupled
oscillators. By studying the evolution in Fourier space and understanding the
domain of dependence, we show a global stability result. Moreover, we can
identify function norms to show damping of the order parameter for velocity
distributions and perturbations in $\mathcal{W}^{n,1}$ for $n > 1$. Finally,
for sufficiently regular velocity distributions we can identify exponential
decay in the stable case and otherwise identify finitely many eigenmodes. For
these eigenmodes we can show a center-unstable manifold reduction, which gives
a rigorous tool to obtain the bifurcation behaviour. The damping is similar to
Landau damping for the Vlasov equation.",1411.3752v3
2014-11-26,A singular finite element technique for calculating continuum damping of Alfvén eigenmodes,"Damping due to continuum resonances can be calculated using dissipation-less
ideal magnetohydrodynamics (MHD) provided that the poles due to these
resonances are properly treated. We describe a singular finite element
technique for calculating the continuum damping of Alfv\'{e}n waves. A
Frobenius expansion is used to determine appropriate finite element basis
functions on an inner region surrounding a pole due to the continuum resonance.
The location of the pole due to the continuum resonance and mode frequency are
calculated iteratively using a Galerkin method. This method is used to find the
complex frequency and mode structure of a toroidicity-induced Alfv\'{e}n
eigenmode (TAE) in a large aspect ratio circular tokamak and are shown to agree
closely with a complex contour technique.",1411.7111v1
2014-11-26,Energy decay for a locally undamped wave equation,"We study the decay rate for the energy of solutions of a damped wave equation
in a situation where the Geometric Control Condition is violated. We assume
that the set of undamped trajectories is a flat torus of positive codimension
and that the metric is locally flat around this set. We further assume that the
damping function enjoys locally a prescribed homogeneity near the undamped set
in traversal directions. We prove a sharp decay estimate at a polynomial rate
that depends on the homogeneity of the damping function. Our method relies on a
refined microlocal analysis linked to a second microlocalization procedure to
cut the phase space into tiny regions respecting the uncertainty principle but
way too small to enter a standard semi-classical analysis localization. Using a
multiplier method, we obtain the energy estimates in each region and we then
patch the microlocal estimates together.",1411.7271v1
2014-12-05,Entanglement Dynamics of Quantum Oscillators Nonlinearly Coupled to Thermal Environments,"We study the asymptotic entanglement of two quantum harmonic oscillators
nonlinearly coupled to an environment. Coupling to independent baths and a
common bath are investigated. Numerical results obtained using the
Wangsness-Bloch-Redfield method are supplemented by analytical results in the
rotating wave approximation. The asymptotic negativity as function of
temperature, initial squeezing and coupling strength, is compared to results
for systems with linear system-reservoir coupling. We find that due to the
parity conserving nature of the coupling, the asymptotic entanglement is
considerably more robust than for the linearly damped cases. In contrast to
linearly damped systems, the asymptotic behavior of entanglement is similar for
the two bath configurations in the nonlinearly damped case. This is due to the
two-phonon system-bath exchange causing a supression of information exchange
between the oscillators via the bath in the common bath configuration at low
temperatures.",1412.1999v1
2014-12-08,The dispersion modification of electrostatic geodesic acoustic mode by electron geodesic drift current,"The past studies treated the perturbed distribution of circulating electrons
as adiabatic one when studying the dispersion relation of electrostatic
geodesic acoustic mode(GAM). In this paper, the flow of electron geodesic
current (FEGC) is added to modify this adiabatic distribution. Based on the
drift kinetic theory, it is found that FEGC obviously increases the magnitude
of the standard GAM's frequency and reduces its damping rate. The increase of
frequency results from the contribution of FEGC to the radial flow. The reason
for the reduction of damping rate is that when the effect of FEGC counts, the
new resonant velocity becomes much larger than ions thermal velocity with
equilibrium distribution obeying Maxwellian distribution, compared with
unmodified Landau resonant velocity. Especially, FEGC changes the characters of
the frequency and damping rate of low-frequency GAM as functions of safety
factor $q$ .",1412.2481v1
2014-12-10,Alfvenic Turbulence Beyond the Ambipolar Diffusion Scale,"We investigate the nature of the Alfv\'enic turbulence cascade in two fluid
MHD simulations in order to determine if turbulence is damped once the ion and
neutral species become decoupled at a critical scale called the ambipolar
diffusion scale (L$_{AD}$). Using mode decomposition to separate the three
classical MHD modes, we study the second order structure functions of the
Alfv\'en mode velocity field of both neutrals and ions in the reference frame
of the local magnetic field. On scales greater than L$_{AD}$ we confirm that
two fluid turbulence strongly resembles single fluid MHD turbulence. Our
simulations show that the behavior of two fluid turbulence becomes more complex
on scales less than L$_{AD}$. We find that Alfvenic turbulence can exist past
L$_{AD}$ when the turbulence is globally super-Alfv\'enic, with the ions and
neutrals forming separate cascades once decoupling has taken place. When
turbulence is globally sub-Alfvenic and hence strongly anisotropic with a large
separation between the parallel and perpendicular decoupling scales, turbulence
is damped at L$_{AD}$. We also find that the power spectrum of the kinetic
energy in the damped regime is consistent with a $k^{-4}$ scaling (in agreement
with the predictions of Lazarian, Vishniac & Cho 2004).",1412.3452v1
2015-01-19,"Linear wave action decay entailed by Landau damping in inhomogeneous, nonstationary and anisotropic plasma","This paper addresses the linear propagation of an electron wave in a
collisionless, inhomogeneous, nonstationary and anisotropic plasma. The plasma
is characterized by its distribution function, $f_H$, at zero order in the wave
amplitude. This distribution function, from which are derived all the
hydrodynamical quantities, may be chosen arbitrarily, provided that it solves
Vlasov equation. Then, from the linearized version of the electrons equation of
motion, and from Gauss law, is derived an envelope equation for the wave
amplitude, assumed to evolve over time and space scales much larger than the
oscillation periods of the wave. The envelope equation may be cast into an
equation for the the wave action, derived from Whitham's variational principle,
that demonstrates the action decay due to Landau damping. Moreover, the Landau
damping rate is derived at first order in the variations of the wave number and
frequency. As briefly discussed, this paper generalizes numerous previous works
on the subject, provides a theoretical basis for heuristic arguments regarding
the action decay, and also addresses the propagation of an externally driven
wave.",1501.04485v1
2015-01-23,"Response solutions for quasi-periodically forced, dissipative wave equations","We consider several models of nonlinear wave equations subject to very strong
damping and quasi-periodic external forcing. This is a singular perturbation,
since the damping is not the highest order term. We study the existence of
response solutions (i.e., quasi-periodic solutions with the same frequency as
the forcing). Under very general non-resonance conditions on the frequency, we
show the existence of asymptotic expansions of the response solution; moreover,
we prove that the response solution indeed exists and depends analytically on
$\varepsilon$ (where $\varepsilon$ is the inverse of the coefficient
multiplying the damping) for $\varepsilon$ in a complex domain, which in some
cases includes disks tangent to the imaginary axis at the origin. In other
models, we prove analyticity in cones of aperture $\pi/2$ and we conjecture it
is optimal. These results have consequences for the asymptotic expansions of
the response solutions considered in the literature. The proof of our results
relies on reformulating the problem as a fixed point problem, constructing an
approximate solution and studying the properties of iterations that converge to
the solutions of the fixed point problem.",1501.05979v1
2015-01-30,A large-scale magnetic shield with 10^6 damping at mHz frequencies,"We present a magnetically shielded environment with a damping factor larger
than one million at the mHz frequency regime and an extremely low field and
gradient over an extended volume. This extraordinary shielding performance
represents an improvement of the state of the art in damping the difficult
regime of very low-frequency distortions by more than an order of magnitude.
This technology enables a new generation of high precision measurements in
fundamental physics and metrology, including searches for new physics far
beyond the reach of accelerator-based experiments. We discuss the technical
realization of the shield with its improvements in design.",1501.07861v4
2015-02-01,A Study on the Impact of Wind Generation on the Stability of Electromechanical Oscillations,"Wind is becoming an increasingly significant source of energy in modern power
generation. Amongst existing technologies, Variable Speed Wind Turbines (VSWT)
equipped with Double Fed Induction Generators (DFIG) is widely deployed.
Consequently, power systems are now experiencing newer power flow patterns and
operating conditions. This paper investigates the impact of a DFIG based Wind
Farm (WF) on the stability of electromechanical oscillations. This is achieved
by performing modal analysis to evaluate the stability of a two-area power
network when subjected to different wind penetration levels and different
geographical installed locations. The approach via eigenvalues analysis
involves the design of voltage and Supplementary Damping Controllers (SDCs)
that contribute to network damping. The effect of Power System Stabilizer (PSS)
is also examined for several network conditions. Simulations demonstrate a
damping improvement up to 933% when the control systems are activated and the
system operates with 25% wind integration.",1502.00215v1
2015-02-16,"Biomimetic Staggered Composites with Highly Enhanced Energy Dissipation: Design, Modeling, and Test","We investigate the damping enhancement in a class of biomimetic staggered
composites via a combination of design, modeling, and experiment. In total,
three kinds of staggered composites are designed by mimicking the structure of
bone and nacre. These composite designs are realized by 3D printing a rigid
plastic and a viscous elastomer simultaneously. Greatly-enhanced energy
dissipation in the designed composites is observed from both the experimental
results and theoretical prediction. The designed polymer composites have loss
modulus up to ~500 MPa, higher than most of the existing polymers. In addition,
their specific loss modulus (up to 0.43 $Km^2/s^2$) is among the highest of
damping materials. The damping enhancement is attributed to the large shear
deformation of the viscous soft matrix and the large strengthening effect from
the rigid inclusion phase.",1502.04568v1
2015-02-24,High Quality Yttrium Iron Garnet Grown by Room Temperature Pulsed Laser Deposition and Subsequent Annealing,"We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG)
by annealing in oxygen atmosphere. Our findings show that well below the
melting temperature the material transforms into a fully epitaxial layer with
exceptional quality, both structural and magnetic.\\ In ferromagnetic resonance
(FMR) ultra low damping and extremely narrow linewidth can be observed. For a
56 nm thick layer a damping constant of
$\alpha$=(6.63$\pm$1.50)$\cdot$10$^{-5}$ is found and the linewidth at 9.6 GHz
is as small as 1.30$\pm$0.05 Oe which are the lowest values for PLD grown thin
films reported so far. Even for a 20 nm thick layer a damping constant of
$\alpha$=(7.51$\pm$1.40)$\cdot$10$^{-5}$ is found which is the lowest value for
ultrathin films published so far. The FMR linewidth in this case is
3.49$\pm$0.10 Oe at 9.6 GHz. Our results not only present a method of
depositing thin film YIG of unprecedented quality but also open up new options
for the fabrication of thin film complex oxides or even other crystalline
materials.",1502.06724v2
2015-03-02,DAMPE silicon tracker on-board data compression algorithm,"The Dark Matter Particle Explorer (DAMPE) is an upcoming scientific satellite
mission for high energy gamma-ray, electron and cosmic rays detection. The
silicon tracker (STK) is a sub detector of the DAMPE payload with an excellent
position resolution (readout pitch of 242um), which measures the incident
direction of particles, as well as charge. The STK consists 12 layers of
Silicon Micro-strip Detector (SMD), equivalent to a total silicon area of
6.5m$^2$. The total readout channels of the STK are 73728, which leads to a
huge amount of raw data to be dealt. In this paper, we focus on the on-board
data compression algorithm and procedure in the STK, which was initially
verified by cosmic-ray measurements.",1503.00415v1
2015-03-08,MHD Seismology of a loop-like filament tube by observed kink waves,"We report and analyze the observational evidence of global kink oscillations
in a solar filament as observed in H alpha by National Solar Observatory
(NSO)/Global Oscillation Network Group (GONG) instrument. An M1.1-class flare
in active region 11692 on 2013 March 15 induced a global kink mode in the
filament lying in the south-west of AR11692.We find periods of about 61 - 67
minutes and damping times of 92 - 117 minutes at three vertical slice positions
chosen in and around the filament apex. We find that the waves are damped. From
the observed global kink mode period and damping time scale using the theory of
resonant absorption we perform prominence seismology. We estimate a lower
cut-off value for the inhomogeneity length-scale to be around 0.34 - 0.44 times
the radius of the filament cross-section.",1503.02281v1
2015-03-13,Comparison of spin-orbit torques and spin pumping across NiFe/Pt and NiFe/Cu/Pt interfaces,"We experimentally investigate spin-orbit torques and spin pumping in NiFe/Pt
bilayers with direct and interrupted interfaces. The damping-like and
field-like torques are simultaneously measured with spin-torque ferromagnetic
resonance tuned by a dc bias current, whereas spin pumping is measured
electrically through the inverse spin Hall effect using a microwave cavity.
Insertion of an atomically thin Cu dusting layer at the interface reduces the
damping-like torque, field-like torque, and spin pumping by nearly the same
factor of ~1.4. This finding confirms that the observed spin-orbit torques
predominantly arise from diffusive transport of spin current generated by the
spin Hall effect. We also find that spin-current scattering at the NiFe/Pt
interface contributes to additional enhancement in magnetization damping that
is distinct from spin pumping.",1503.04104v3
2015-03-24,Global weak solutions to compressible quantum Navier-Stokes equations with damping,"The global-in-time existence of weak solutions to the barotropic compressible
quantum Navier-Stokes equations with damping is proved for large data in three
dimensional space. The model consists of the compressible Navier-Stokes
equations with degenerate viscosity, and a nonlinear third-order differential
operator, with the quantum Bohm potential, and the damping terms. The global
weak solutions to such system is shown by using the Faedo-Galerkin method and
the compactness argument. This system is also a very important approximated
system to the compressible Navier-Stokes equations. It will help us to prove
the existence of global weak solutions to the compressible Navier-Stokes
equations with degenerate viscosity in three dimensional space.",1503.06894v4
2015-03-30,Suppression of Spin Pumping Between Ni$_{80}$Fe$_{20}$ and Cu by a Graphene Interlayer,"We compare ferromagnetic resonance measurements of Permalloy
Ni$_{80}$Fe$_{20}$ (Py) films sputtered onto Cu(111) films with and without a
graphene (Gr) interlayer grown by chemical vapor deposition before Py
deposition. A two-angle sputtering method ensured that neither Gr nor Py was
degraded by the sample preparation process. We find the expected damping
enhancement from spin pumping for the Py/Cu case and no detectable enhancement
for the Py/Gr/Cu case. Since damping is sensitive to effects other than spin
pumping, we used magnetometry to verify that differences in Py magnetostatic
properties are not responsible for the difference in damping. We attribute the
suppression of spin pumping in Py/Gr/Cu to the large contact resistance of the
Gr/Cu interface.",1503.08777v1
2015-04-02,Protecting the $\sqrt{SWAP}$ operation from general and residual errors by continuous dynamical decoupling,"We study the occurrence of errors in a continuously decoupled two-qubit state
during a $\sqrt{SWAP}$ quantum operation under decoherence. We consider a
realization of this quantum gate based on the Heisenberg exchange interaction,
which alone suffices for achieving universal quantum computation. Furthermore,
we introduce a continuous-dynamical-decoupling scheme that commutes with the
Heisenberg Hamiltonian to protect it from the amplitude damping and dephasing
errors caused by the system-environment interaction. We consider two
error-protection settings. One protects the qubits from both amplitude damping
and dephasing errors. The other features the amplitude damping as a residual
error and protects the qubits from dephasing errors only. In both settings, we
investigate the interaction of qubits with common and independent environments
separately. We study how errors affect the entanglement and fidelity for
different environmental spectral densities.",1504.00592v1
2015-04-07,Damped Oscillating Dark Energy: Ideal Fluid and Scalar-Tensor description,"In this paper, we study damped oscillating form of dark energy for explaining
dynamics of universe. First of all, we consider universe is filled with an
ideal fluid which has damped oscillating dark energy in terms of this case we
calculate several physical quantities such as Hubble parameter, acceleration
parameter, energy density, pressure and others for dark energy, dark
energy-matter coupling and non-coupling cases. Secondly, we consider as
universe is filled with scalar field instead of an ideal fluid we obtain these
physical quantities in terms of scalar potential and kinetic term for the same
cases in scalar-tensor formalism. Finally, we show that ideal fluid description
and scalar-tensor description of dark energy give mathematically equivalent
results for this EoS parameter, even if they haven't same physical meaning.",1504.01509v2
2015-04-09,"Periodic-coefficient damping estimates, and stability of large-amplitude roll waves in inclined thin film flow","A technical obstruction preventing the conclusion of nonlinear stability of
large-Froude number roll waves of the St. Venant equations for inclined thin
film flow is the ""slope condition"" of Johnson-Noble-Zumbrun, used to obtain
pointwise symmetrizability of the linearized equations and thereby
high-frequency resolvent bounds and a crucial H s nonlinear damping estimate.
Numerically, this condition is seen to hold for Froude numbers 2 \textless{} F
3.5, but to fail for 3.5 F. As hydraulic engineering applications typically
involve Froude number 3 F 5, this issue is indeed relevant to practical
considerations. Here, we show that the pointwise slope condition can be
replaced by an averaged version which holds always, thereby completing the
nonlinear theory in the large-F case. The analysis has potentially larger
interest as an extension to the periodic case of a type of weighted
""Kawashima-type"" damping estimate introduced in the asymptotically-constant
coefficient case for the study of stability of large-amplitude viscous shock
waves.",1504.02292v1
2015-04-17,Temperature-dependent Plasmons and Their Damping Rates for Graphene with a Finite Energy Bandgap,"We obtained numerical and closed-form analytic expressions for
finite-temperature plasmon dispersion relations for intrinsic graphene in the
presence of a finite energy gap in the energy spectrum. The calculations were
carried out using the random-phase approximation. The analytic results have
been derived in the high temperature regime and long-wavelength limit. We have
found that the plasmon damping rate decreases in the presence of a band gap.
Our method of calculation could also be applied to silicene and other buckled
honeycomb lattice structures. The finite-temperature plasmon dispersion
relations are presented when a single graphene layer is Coulomb coupled to a
semi infinite conductor. Both cases of gapless and gapped monolayer graphene
have been investigated when a thick substrate is in their proximity. Both the
plasmon excitation frequency and damping rate are linear functions of the
in-plane wave vector in the long wavelength limit when a monolayer interacts
with a conducting substrate which is not the case for free-standing pristine or
gapped graphene.",1504.04552v1
2015-05-08,Existence and general stabilization of the Timoshenko system with a thermo-viscoelastic damping and a delay term in the internal feedback,"In this paper, we consider a Timoshenko system with a thermo-viscoelastic
damping and a delay term in the internal feedback together with initial datum
and boundary conditions of Dirichlet type, where g is a positive non-increasing
relaxation function and {\mu}1, {\mu}2 are positive constants. Under an
hypothesis between the weight of the delay term in the feedback and the the
weight of the friction damping term, using the Faedo-Galerkin approximations
together with some energy estimates, we prove the global existence of the
solutions. Then, by introducing appropriate Lyapunov functionals, under the
imposed constrain on the weights of the two feedbacks and the coefficients, we
establish the general energy decay result from which the exponential and
polynomial types of decay are only special cases.",1505.01899v1
2015-05-09,"Existence, general decay and blow-up of solutions for a viscoelastic Kirchhoff equation with Balakrishnan-Taylor damping and dynamic boundary conditions","Our aim in this article is to study a nonlinear viscoelastic Kirchhoff
equation with strong damping, Balakrishnan-Taylor damping, nonlinear source and
dynamical boundary condition. Firstly, we prove the local existence of
solutions by using the Faedo-Galerkin approximation method combined with a
contraction mapping theorem. We then prove that if the initial data enter into
the stable set, the solution globally exists, and if the initial data enter
into the unstable set, the solution blows up in a finite time. Moreover, we
obtain a general decay result of the energy, from which the usual exponential
and polynomial decay rates are only special cases.",1505.02220v3
2015-06-03,Migration of two massive planets into (and out of) first order mean motion resonances,"We consider the dynamical evolution of two planets orbiting in the vicinity
of a first order mean motion reso- nance while simultaneously undergoing
eccentricity damping and convergent migration. Following Goldreich &
Schlichting (2014), we include a coupling between the dissipative semimajor
axis evolution and the damping of the eccentricities. In agreement with past
studies, we find that this coupling can lead to overstability of the resonance
and that for a certain range of parameters capture into resonance is only
temporary. Using a more general model, we show that whether overstable motion
can occur depends in a characteristic way on the mass ratio between the two
planets as well as their relative eccentricity damping timescales. Moreover, we
show that even when escape from resonance does occur, the timescale for escape
is long enough such at any given time a pair of planets is more likely to be
found in a resonance rather than migrating between them. Thus, we argue that
overstability of resonances cannot singlehandedly reconcile convergent
migration with the observed lack of Kepler planet pairs found near resonances.
However, it is possible that overstable motion in combination with other
effects such as large scale orbital instability could produce the observed
period ratio distribution.",1506.01382v1
2015-06-12,"Linear inviscid damping for monotone shear flows in a finite periodic channel, boundary effects, blow-up and critical Sobolev regularity","In a previous article, \cite{Zill3}, we have established linear inviscid
damping for a large class of monotone shear flows in a finite periodic channel
and have further shown that boundary effects asymptotically lead to the
formation of singularities of derivatives of the solution. As the main results
of this article, we provide a detailed description of the singularity formation
and establish stability in all sub-critical fractional Sobolev spaces and
blow-up in all super-critical spaces. Furthermore, we discuss the implications
of the blow-up to the problem of nonlinear inviscid damping in a finite
periodic channel, where high regularity would be essential to control nonlinear
effects.",1506.04010v1
2015-06-12,Nonlinear damped partial differential equations and their uniform discretizations,"We establish sharp energy decay rates for a large class of nonlinearly
first-order damped systems, and we design discretization schemes that inherit
of the same energy decay rates, uniformly with respect to the space and/or time
discretization parameters, by adding appropriate numerical viscosity terms. Our
main arguments use the optimal-weight convexity method and uniform
observability inequalities with respect to the discretization parameters. We
establish our results, first in the continuous setting, then for space
semi-discrete models, and then for time semi-discrete models. The full
discretization is inferred from the previous results. Our results cover, for
instance, the Schr\""odinger equation with nonlinear damping, the nonlinear wave
equation, the nonlinear plate equation, as well as certain classes of equations
with nonlocal terms.",1506.04163v2
2015-06-17,Landau Damping of Electrostatic Waves in Arbitrarily Degenerate Quantum Plasmas,"We carry out a systematic study of the dispersion relation for linear
electrostatic waves in an arbitrarily degenerate quantum electron plasma. We
solve for the complex frequency spectrum for arbitrary values of wavenumber $k$
and level of degeneracy $\mu$. Our finding is that for large $k$ and high $\mu$
the real part of the frequency $\omega_{r}$ grows linearly with $k$ and scales
with $\mu$ only because of the scaling of the Fermi energy. In this regime the
relative Landau damping rate $\gamma/\omega_{r}$ becomes independent of $k$ and
varies inversly with $\mu$. Thus, damping is weak but finite at moderate levels
of degeneracy for short wavelengths.",1506.05494v2
2015-06-25,Simultaneous Interconnection and Damping Assignment Passivity-based Control of Mechanical Systems Using Generalized Forces,"To extend the realm of application of the well known controller design
technique of interconnection and damping assignment passivity-based control
(IDA-PBC) of mechanical systems two modifications to the standard method are
presented in this article. First, similarly to [1], it is proposed to avoid the
splitting of the control action into energy-shaping and damping injection
terms, but instead to carry them out simultaneously. Second, motivated by [2],
we propose to consider the inclusion of generalised forces, going beyond the
gyroscopic ones used in standard IDA-PBC. It is shown that several new
controllers for mechanical systems designed invoking other (less systematic
procedures) that do not satisfy the conditions of standard IDA-PBC, actually
belong to this new class of SIDA-PBC.",1506.07679v1
2015-07-20,Bifurcation of the quasinormal spectrum and Zero Damped Modes for rotating dilatonic black holes,"It has been recently found that for the near extremal Kerr black holes
appearing of Zero Damped Modes (accompanied by qusinormal mode branching)
signifies about inapplicability of the regime of small perturbations and the
onset of turbulence. Here we show that this phenomena is not limited by Kerr or
Kerr-Newman solutions only, but also takes place for rotating dilatonic black
holes for which we have found Zero Damped Modes both numerically and
analytically. We have also shown that, contrary to recent claims, there is no
instability of a charged massive scalar field in the background of the rotating
dilatonic black hole under physically adequate boundary conditions. Analytic
expression for dominant quasinormal frequencies is deduced in the regime of
large coupling qQ, where q and Q are the field and black hole charges
respectively.",1507.05649v1
2015-07-24,Effect of Landau damping on alternative ion-acoustic solitary waves in a magnetized plasma consisting of warm adiabatic ions and non-thermal electrons,"Bandyopadhyay and Das [Phys. Plasmas, 9, 465-473, 2002] have derived a
nonlinear macroscopic evolution equation for ion acoustic wave in a magnetized
plasma consisting of warm adiabatic ions and non-thermal electrons including
the effect of Landau damping. In that paper they have also derived the
corresponding nonlinear evolution equation when coefficient of the nonlinear
term of the above mentioned macroscopic evolution equation vanishes, the
nonlinear behaviour of the ion acoustic wave is described by a modified
macroscopic evolution equation. But they have not considered the case when the
coefficient is very near to zero. This is the case we consider in this paper
and we derive the corresponding evolution equation including the effect of
Landau damping. Finally, a solitary wave solution of this macroscopic evolution
is obtained, whose amplitude is found to decay slowly with time.",1507.06733v1
2015-08-05,Quantum discord protection from amplitude damping decoherence,"Entanglement is known to be an essential resource for many quantum
information processes. However, it is now known that some quantum features may
be acheived with quantum discord, a generalized measure of quantum correlation.
In this paper, we study how quantum discord, or more specifically, the measures
of entropic discord and geometric discord are affected by the influence of
amplitude damping decoherence. We also show that a protocol deploying weak
measurement and quantum measurement reversal can effectively protect quantum
discord from amplitude damping decoherence, enabling to distribute quantum
correlation between two remote parties in a noisy environment.",1508.00972v1
2015-09-03,Stability analysis of degenerately-damped oscillations,"Presented here is a study of well-posedness and asymptotic stability of a
""degenerately damped"" PDE modeling a vibrating elastic string. The coefficient
of the damping may vanish at small amplitudes thus weakening the effect of the
dissipation. It is shown that the resulting dynamical system has strictly
monotonically decreasing energy and uniformly decaying lower-order norms,
however, is not uniformly stable on the associated finite-energy space. These
theoretical findings were motivated by numerical simulations of this model
using a finite element scheme and successive approximations. A description of
the numerical approach and sample plots of energy decay are supplied. In
addition, for certain initial data the solution can be determined in closed
form up to a dissipative nonlinear ordinary differential equation. Such
solutions can be used to assess the accuracy of the numerical examples.",1509.00917v1
2015-09-27,On the well-posedness and asymptotic behavior of the generalized KdV-Burgers equation,"In this paper we are concerned with the well-posedness and the exponential
stabilization of the generalized Korteweg-de Vries Burgers equation, posed on
the whole real line, under the effect of a damping term. Both problems are
investigated when the exponent p in the nonlinear term ranges over the interval
$[1,5)$. We first prove the global well-posedness in $H^s(R)$, for $0 \leq s
\leq 3$ and $1 \leq p < 2$, and in $H^3(R)$, when $p \geq 2$. For $2 \leq p <
5$, we prove the existence of global solutions in the $L^2$-setting. Then, by
using multiplier techniques combined with interpolation theory, the exponential
stabilization is obtained for a indefinite damping term and $1 \leq p < 2$.
Under the effect of a localized damping term the result is obtained when $2
\leq p < 5$. Combining multiplier techniques and compactness arguments it is
shown that the problem of exponential decay is reduced to prove the unique
continuation property of weak solutions",1509.08148v1
2015-10-11,Error estimates of finite element method for semi-linear stochastic strongly damped wave equation,"In this paper, we consider a semi-linear stochastic strongly damped wave
equation driven by additive Gaussian noise. Following a semigroup framework, we
establish existence, uniqueness and space-time regularity of a mild solution to
such equation. Unlike the usual stochastic wave equation without damping, the
underlying problem with space-time white noise (Q = I) allows for a mild
solution with a positive order of regularity in multiple spatial dimensions.
Further, we analyze a spatio-temporal discretization of the problem, performed
by a standard finite element method in space and a well-known linear implicit
Euler scheme in time. The analysis of the approximation error forces us to
significantly enrich existing error estimates of semidiscrete and fully
discrete finite element methods for the corresponding linear deterministic
equation. The main results show optimal convergence rates in the sense that the
orders of convergence in space and in time coincide with the orders of the
spatial and temporal regularity of the mild solution, respectively. Numerical
examples are finally included to confirm our theoretical findings.",1510.03028v1
2015-11-10,A study of energy correction for the electron beam data in the BGO ECAL of the DAMPE,"The DArk Matter Particle Explorer (DAMPE) is an orbital experiment aiming at
searching for dark matter indirectly by measuring the spectra of photons,
electrons and positrons originating from deep space. The BGO electromagnetic
calorimeter is one of the key sub-detectors of the DAMPE, which is designed for
high energy measurement with a large dynamic range from 5 GeV to 10 TeV. In
this paper, some methods for energy correction are discussed and tried, in
order to reconstruct the primary energy of the incident electrons. Different
methods are chosen for the appropriate energy ranges. The results of Geant4
simulation and beam test data (at CERN) are presented.",1511.02998v1
2015-11-10,Quantum Fisher and Skew information for Unruh accelerated Dirac qubit,"We develop a Bloch vector representation of Unruh channel for a Dirac field
mode. This is used to provide a unified, analytical treatment of quantum Fisher
and Skew information for a qubit subjected to the Unruh channel, both in its
pure form as well as in the presence of experimentally relevant external noise
channels. The time evolution of Fisher and Skew information is studied along
with the impact of external environment parameters such as temperature and
squeezing. The external noises are modelled by both purely dephasing phase
damping as well as the squeezed generalized amplitude damping channels. An
interesting interplay between the external reservoir temperature and squeezing
on the Fisher and Skew information is observed, in particular, for the action
of the squeezed generalized amplitude damping channel. It is seen that for some
regimes, squeezing can enhance the quantum information against the
deteriorating influence of the ambient environment. Similar features are also
observed for the analogous study of Skew information, highlighting the similar
origin of the Fisher and Skew information.",1511.03029v1
2015-11-23,Detection of high frequency oscillations and damping from multi-slit spectroscopic observations of the corona,"During the total solar eclipse of 11 July 2010, multi-slit spectroscopic
observations of the solar corona were performed from Easter Island, Chile. To
search for high-frequency waves, observations were taken at a high cadence in
the green line at 5303 A due to [Fe xiv] and the red line at 6374 A due to [Fe
x]. The data are analyzed to study the periodic variations in the intensity,
Doppler velocity and line width using wavelet analysis. The data with high
spectral and temporal resolution enabled us to study the rapid dynamical
changes within coronal structures. We find that at certain locations each
parameter shows significant oscillation with periods ranging from 6 - 25 s. For
the first time, we could detect damping of high-frequency oscillations with
periods of the order of 10 s. If the observed damped oscillations are due to
magnetohydrodynamic (MHD) waves then they can contribute significantly in the
heating of the corona. From a statistical study we try to characterize the
nature of the observed oscillations while looking at the distribution of power
in different line parameters.",1511.07160v1
2015-11-26,Uniform exponential stability of Galerkin approximations for damped wave systems,"We consider the numerical approximation of linear damped wave systems by
Galerkin approximations in space and appropriate time-stepping schemes. Based
on a dissipation estimate for a modified energy, we prove exponential decay of
the physical energy on the continuous level provided that the damping is
effective everywhere in the domain. The methods of proof allow us to analyze
also a class of Galerkin approximations based on a mixed variational
formulation of the problem. Uniform exponential stability can be guaranteed for
these approximations under a general compatibility condition on the
discretization spaces. As a particular example, we discuss the discretization
by mixed finite element methods for which we obtain convergence and uniform
error estimates under minimal regularity assumptions. We also prove
unconditional and uniform exponential stability for the time discretization by
certain one-step methods. The validity of the theoretical results as well as
the necessity of some of the conditions required for our analysis are
demonstrated in numerical tests.",1511.08341v1
2015-12-01,Epitaxial patterning of nanometer-thick Y3Fe5O12 films with low magnetic damping,"Magnetic insulators such as yttrium iron garnet, Y3Fe5O12, with extremely low
magnetic damping have opened the door for low power spin-orbitronics due to
their low energy dissipation and efficient spin current generation and
transmission. We demonstrate reliable and efficient epitaxial growth and
nanopatterning of Y3Fe5O12 thin-film based nanostructures on insulating
Gd3Ga5O12 substrates. In particular, our fabrication process is compatible with
conventional sputtering and liftoff, and does not require aggressive ion
milling which may be detrimental to the oxide thin films. Structural and
magnetic properties indicate good qualities, in particular low magnetic damping
of both films and patterned structures. The dynamic magnetic properties of the
nanostructures are systematically investigated as a function of the lateral
dimension. By comparing to ferromagnetic nanowire structures, a distinct edge
mode in addition to the main mode is identified by both experiments and
simulations, which also exhbits cross-over with the main mode upon varying the
width of the wires. The non-linear evolution of dynamic modes over
nanostructural dimensions highlights the important role of size confinement to
their material properties in magnetic devices where Y3Fe5O12 nanostructures
serve as the key functional component.",1512.00286v1
2015-12-03,Probing Bogoliubov quasiparticles in superfluid $^3$He with a 'vibrating-wire like' MEMS device,"We have measured the interaction between superfluid $^3$He-B and a
micro-machined goalpost-shaped device at temperatures below $0.2\,T_c$. The
measured damping follows well the theory developed for vibrating wires, in
which the Andreev reflection of quasiparticles in the flow field around the
moving structure leads to a nonlinear frictional force. At low velocities the
damping force is proportional to velocity while it tends to saturate for larger
excitations. Above a velocity of 2.6$\,$mms$^{-1}$ the damping abruptly
increases, which is interpreted in terms of Cooper-pair breaking.
Interestingly, this critical velocity is significantly lower than reported with
other mechanical probes immersed in superfluid $^3$He. Furthermore, we report
on a nonlinear resonance shape for large motion amplitudes that we interpret as
an inertial effect due to quasiparticle friction, but other mechanisms could
possibly be invoked as well.",1512.01033v1
2016-01-03,Event-triggered Communication in Wide-area Damping Control: A Limited Output Feedback Based Approach,"A conceptual design methodology is proposed for event-triggered based power
system wide area damping controller. The event-triggering mechanism is adopted
to reduce the communication burden between origin of the remote signal and the
wide area damping controller (WADC) location. The remote signal is transmitted
to the WADC only when an event-triggering condition based on a predefined
system output, is satisfied. The triggering condition is derived from a
stability criterion, and is monitored continuously by a separate
event-monitoring unit located at the origin of the remote signal. The stability
of the resulting closed loop system is guaranteed via the input-to-state
stability (ISS) technique. The proposed event triggered WADC (ET-WADC) is
implemented on two typical test power systems - two area four machine and IEEE
39 bus 10 machine. The validation of proposed mechanism is carried out through
non-linear simulation studies on MATLAB/Simulink platform. The numerical
results show the efficacy of the controller in managing the communication
channel usage without compromising the stated system stability objectives.",1601.00255v1
2016-01-05,Lie transformation method on quantum state evolution of a general time-dependent driven and damped parametric oscillator,"A variety of dynamics in nature and society can be approximately treated as a
driven and damped parametric oscillator. An intensive investigation of this
time-dependent model from an algebraic point of view provides a consistent
method to resolve the classical dynamics and the quantum evolution in order to
understand the time-dependent phenomena that occur not only in the macroscopic
classical scale for the synchronized behaviors but also in the microscopic
quantum scale for a coherent state evolution. By using a Floquet
U-transformation on a general time-dependent quadratic Hamiltonian, we exactly
solve the dynamic behaviors of a driven and damped parametric oscillator to
obtain the optimal solutions by means of invariant parameters of $K$s to
combine with Lewis-Riesenfeld invariant method. This approach can discriminate
the external dynamics from the internal evolution of a wave packet by producing
independent parametric equations that dramatically facilitate the parametric
control on the quantum state evolution in a dissipative system. In order to
show the advantages of this method, several time-dependent models proposed in
the quantum control field are analyzed in details.",1601.00727v3
2016-02-19,Distinctive response of many-body localized systems to strong electric field,"We study systems which are close to or within the many-body localized (MBL)
regime and are driven by strong electric field. In the ergodic regime, the
disorder extends applicability of the equilibrium linear--response theory to
stronger drivings, whereas the response of the MBL systems is very distinctive,
revealing currents with damped oscillations. The oscillation frequency is
independent of driving and the damping is not due to heating but rather due to
dephasing. The details of damping depend on the system's history reflecting
nonergodicity of the MBL phase, while the frequency of the oscillations remains
a robust hallmark of localization. We show that the distinctive characteristic
of the driven MBL phase is also a logarithmic increase of the energy and the
polarization with time.",1602.06055v1
2016-02-24,Pressure of a gas of underdamped active dumbbells,"The pressure exerted on a wall by a gas at equilibrium does not depend on the
shape of the confining potential defining the wall. In contrast, it has been
shown recently [A.P. Solon et al., Nat. Phys. 11, 673 (2015)] that a gas of
overdamped active particles exerts on a wall a force that depends on the
confining potential, resulting in a net force on an asymmetric wall between two
chambers at equal densities. Here, considering a model of underdamped
self-propelled dumbbells in two dimensions, we study how the behavior of the
pressure depends on the damping coefficient of the dumbbells, thus exploring
inertial effects. We find in particular that the force exerted on a moving wall
between two chambers at equal density continuously vanishes at low damping
coefficient, and exhibits a complex dependence on the damping coefficient at
low density, when collisions are scarce. We further show that this behavior of
the pressure can to a significant extent be understood in terms of the
trajectories of individual particles close to and in contact with the wall.",1602.07420v1
2016-03-07,Optimal Load and Stiffness for Displacement-Constrained Vibration Energy Harvesters,"The power electronic interface to a vibration energy harvester not only
provides ac-dc conversion, but can also set the electrical damping to maximize
output power under displacement-constrained operation. This is commonly
exploited for linear two-port harvesters by synchronous switching to realize a
Coulomb-damped resonant generator, but has not been fully explored when the
harvester is asynchronously switched to emulate a resistive load. In order to
understand the potential of such an approach, the optimal values of load
resistance and other control parameters need to be known. In this paper we
determine analytically the optimal load and stiffness of a harmonically driven
two-port harvester with displacement constraints. For weak-coupling devices, we
do not find any benefit of load and stiffness adjustment beyond maintaining a
saturated power level. For strong coupling we find that the power can be
optimized to agree with the velocity damped generator beyond the first critical
force for displacement-constrained operation. This can be sustained up to a
second critical force, determined by a resonator figure-of-merit, at which the
power ultimately levels out.",1603.01909v1
2016-03-22,Generation and protection of steady-state quantum correlations due to quantum channels with memory,"We have proposed a scheme of the generation and preservation of two-qubit
steady state quantum correlations through quantum channels where successive
uses of the channels are correlated. Different types of noisy channels with
memory, such as amplitude damping, phase-damping, and depolarizing channels
have been taken into account. Some analytical or numerical results are
presented. The effect of channels with memory on dynamics of quantum
correlations has been discussed in detail. The results show that, steady state
entanglement between two independent qubits without entanglement subject to
amplitude damping channel with memory can be generated. Besides, we compare the
dynamics of entanglement with that of quantum discord when a two-qubit system
is prepared in an entangled state. We show that entanglement dynamics suddenly
disappears, while quantum discord displays only in the asymptotic limit.
Two-qubit quantum correlations can be preserved at a long time in the limit of
$\mu\rightarrow1$.",1603.06676v2
2016-03-31,Recovery of time-dependent damping coefficients and potentials appearing in wave equations from partial data,"We consider the inverse problem of determining a time-dependent damping
coefficient $a$ and a time-dependent potential $q$, appearing in the wave
equation $\partial_t^2u-\Delta_x u+a(t,x)\partial_tu+q(t,x)u=0$ in
$Q=(0,T)\times\Omega$, with $T>0$ and $\Omega$ a $ \mathcal C^2$ bounded domain
of $\mathbb R^n$, $n\geq2$, from partial observations of the solutions on
$\partial Q$. More precisely, we look for observations on $\partial Q$ that
allow to determine uniquely a large class of time-dependent damping
coefficients $a$ and time-dependent potentials $q$ without involving an
important set of data. We prove global unique determination of $a\in
W^{1,p}(Q)$, with $p>n+1$, and $q\in L^\infty(Q)$ from partial observations on
$\partial Q$.",1603.09600v2
2016-04-22,Feedback-induced Bistability of an Optically Levitated Nanoparticle: A Fokker-Planck Treatment,"Optically levitated nanoparticles have recently emerged as versatile
platforms for investigating macroscopic quantum mechanics and enabling
ultrasensitive metrology. In this article we theoretically consider two damping
regimes of an optically levitated nanoparticle cooled by cavityless parametric
feedback. Our treatment is based on a generalized Fokker-Planck equation
derived from the quantum master equation presented recently and shown to agree
very well with experiment [1]. For low damping, we find that the resulting
Wigner function yields the single-peaked oscillator position distribution and
recovers the appropriate energy distribution derived earlier using a classical
theory and verified experimentally [2]. For high damping, in contrast, we
predict a double-peaked position distribution, which we trace to an underlying
bistability induced by feedback. Unlike in cavity-based optomechanics,
stochastic processes play a major role in determining the bistable behavior. To
support our conclusions, we present analytical expressions as well as numerical
simulations using the truncated Wigner function approach. Our work opens up the
prospect of developing bistability-based devices, characterization of
phase-space dynamics, and investigation of the quantum-classical transition
using levitated nanoparticles.",1604.06767v2
2016-05-06,Multidimensional Thermoelasticity for Nonsimple Materials -- Well-Posedness and Long-Time Behavior,"An initial-boundary value problem for the multidimensional type III
thermoelaticity for a nonsimple material with a center of symmetry is
considered. In the linear case, the well-posedness with and without
Kelvin-Voigt and/or frictional damping in the elastic part as well as the lack
of exponential stability in the elastically undamped case is proved. Further, a
frictional damping for the elastic component is shown to lead to the
exponential stability. A Cattaneo-type hyperbolic relaxation for the thermal
part is introduced and the well-posedness and uniform stability under a
nonlinear frictional damping are obtained using a compactness-uniqueness-type
argument. Additionally, a connection between the exponential stability and
exact observability for unitary $C_{0}$-groups is established.",1605.02049v1
2016-05-16,The Cauchy problem for the nonlinear damped wave equation with slowly decaying data,"We study the Cauchy problem for the nonlinear damped wave equation and
establish the large data local well-posedness and small data global
well-posedness with slowly decaying initial data. We also prove that the
asymptotic profile of the global solution is given by a solution of the
corresponding parabolic problem, which shows that the solution of the damped
wave equation has the diffusion phenomena. Moreover, we show blow-up of
solution and give the estimate of the lifespan for a subcritical nonlinearity.
In particular, we determine the critical exponent for any space dimension.",1605.04616v2
2016-05-20,High-frequency behavior of FeN thin films fabricated by reactive sputtering,"We investigated high-frequency behavior of FeN thin films prepared by
reactive sputtering through ferromagnetic resonance (FMR) and its relationship
with the static magnetic properties. The FMR was observed in the frequency
range from 2 to 18 GHz in the FeN films fabricated at proper nitrogen flow rate
(NFR). In those FeN thin films, a decrease of the saturation magnetization and
the corresponding decrease of the FMR frequency were observed as NFR was
increased during the deposition. The external field dependences of the FMR
frequencies were well fit to the Kittel formula and the Land\'e g-factors
determined from the fit were found to be very close to the free electron value.
The high-field damping parameters were almost insensitive to the growth
condition of NFR. However, the low-field damping parameters exhibited high
sensitivity to NFR very similar to the dependence of the hard-axis coercivity
on NFR, suggesting that extrinsic material properties such as impurities and
defect structures could be important in deciding the low-field damping
behavior.",1605.06179v1
2016-05-26,Thickness and temperature dependence of the magnetodynamic damping of pulsed laser deposited $\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ on (111)-oriented SrTi$\text{O}_3$,"We have investigated the magnetodynamic properties of
$\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ (LSMO) films of thickness 10, 15
and 30 nm grown on (111)-oriented SrTi$\text{O}_3$ (STO) substrates by pulsed
laser deposition. Ferromagnetic resonance (FMR) experiments were performed in
the temperature range 100--300 K, and the magnetodynamic damping parameter
$\alpha$ was extracted as a function of both film thickness and temperature. We
found that the damping is lowest for the intermediate film thickness of 15 nm
with $\alpha \approx 2 \cdot 10^{-3}$, where $\alpha$ is relatively constant as
a function of temperature well below the Curie temperature of the respective
films.",1605.08195v2
2016-06-08,Effect of quantum noise on deterministic joint remote state preparation of a qubit state via a GHZ channel,"Quantum secure communication brings a new direction for information security.
As an important component of quantum secure communication, deterministic joint
remote state preparation (DJRSP) could securely transmit a quantum state with
100\% success probability. In this paper, we study how the efficiency of DJRSP
is affected when qubits involved in the protocol are subjected to noise or
decoherence. Taking a GHZ based DJRSP scheme as an example, we study all types
of noise usually encountered in real-world implementations of quantum
communication protocols, i.e., the bit-flip, phase-flip (phase-damping),
depolarizing, and amplitude-damping noise. Our study shows that the fidelity of
the output state depends on the phase factor, the amplitude factor and the
noise parameter in the bit-flip noise, while the fidelity only depends on the
amplitude factor and the noise parameter in the other three types of noise. And
the receiver will get different output states depending on the first preparer's
measurement result in the amplitude-damping noise. Our results will be helpful
for improving quantum secure communication in real implementation.",1606.02484v2
2016-06-28,Radiation Damping by Thomson Scattering,"Synchrotron radiation of relativistic electrons in storage rings naturally
leads to the process of damping of betatron oscillations. Damping time and
transverse beam emittance can be reduced by wigglers or undulators while the
beam parameters are still well defined by the common radiation integrals, based
on the properties of synchrotron radiation. However, the quantum excitation of
betatron oscillations in principle can be considerably reduced if an electron
radiation occurs due to the Thomson scattering in the periodic electromagnetic
field. After a brief introduction we compare radiation properties for different
cases and suggest the modification of the radiation integrals.",1606.08602v5
2016-06-29,"Kinodynamic Motion Planning: A Novel Type Of Nonlinear, Passive Damping Forces And Advantages","This article extends the capabilities of the harmonic potential field
approach to planning to cover both the kinematic and dynamic aspects of a robot
motion. The suggested approach converts the gradient guidance field from a
harmonic potential to a control signal by augmenting it with a novel type of
damping forces called nonlinear, anisotropic, damping forces. The combination
of the two provides a signal that can both guide a robot and effectively manage
its dynamics. The kinodynamic planning signal inherits the guidance
capabilities of the harmonic gradient field. It can also be easily configured
to efficiently suppress the inertia-induced transients in the robot trajectory
without compromising the speed of operation. The approach works with
dissipative systems as well as systems acted on by external forces without
needing the full knowledge of the system dynamics. Theoretical developments and
simulation results are provided in this article.",1606.09270v1
2016-07-20,"Envelope equation for the linear and nonlinear propagation of an electron plasma wave, including the effects of Landau damping, trapping, plasma inhomogeneity, and the change in the state of wave","This paper addresses the linear and nonlinear three-dimensional propagation
of an electron wave in a collisionless plasma that may be inhomogeneous,
nonstationary, anisotropic and even weakly magnetized. The wave amplitude,
together with any hydrodynamic quantity characterizing the plasma (density,
temperature,...) are supposed to vary very little within one wavelength or one
wave period. Hence, the geometrical optics limit is assumed, and the wave
propagation is described by a first order differential equation. This equation
explicitly accounts for three-dimensional effects, plasma inhomogeneity, Landau
damping, and the collisionless dissipation and electron acceleration due to
trapping. It is derived by mixing results obtained from a direct resolution of
the Vlasov-Poisson system and from a variational formalism involving a nonlocal
Lagrangian density. In a one-dimensional situation, abrupt transitions are
predicted in the coefficients of the wave equation. They occur when the state
of the electron plasma wave changes, from a linear wave to a wave with trapped
electrons. In a three dimensional geometry, the transitions are smoother,
especially as regards the nonlinear Landau damping rate, for which a very
simple effective and accurate analytic expression is provided.",1607.05844v2
2016-09-02,Particle dynamics and Stochastic Resonance in Periodic potentials,"We have studied the dynamics of a particle in a periodically driven
underdamped periodic potential. Recent studies have reported the occurrence of
Stochastic Resonance (SR) in such systems in the high frequency regime, using
input energy per period of external drive as a quantifier. The particle
trajectories in these systems can be in two dynamical states characterised by
their definite energy and phase relation with the external drive. SR is due to
the noise assisted transition of the particles between these two states. We
study the role of damping on the occurrence of SR. We show that a driven
underdamped periodic system exhibits SR only if the damping is below a
particular limit. To explain this we study the syatem in the deterministic
regime. The existence of the two dynamical states in the deterministic regime
is dependent on the amount of damping and the amplitude od external drive. We
also study the input energy distributions and phase difference of the response
amplitude with the external drive as afunction of the friction parameter.",1609.00678v1
2016-09-26,An efficient quantum algorithm for spectral estimation,"We develop an efficient quantum implementation of an important signal
processing algorithm for line spectral estimation: the matrix pencil method,
which determines the frequencies and damping factors of signals consisting of
finite sums of exponentially damped sinusoids. Our algorithm provides a quantum
speedup in a natural regime where the sampling rate is much higher than the
number of sinusoid components. Along the way, we develop techniques that are
expected to be useful for other quantum algorithms as well - consecutive phase
estimations to efficiently make products of asymmetric low rank matrices
classically accessible and an alternative method to efficiently exponentiate
non-Hermitian matrices. Our algorithm features an efficient quantum-classical
division of labor: The time-critical steps are implemented in quantum
superposition, while an interjacent step, requiring only exponentially few
parameters, can operate classically. We show that frequencies and damping
factors can be obtained in time logarithmic in the number of sampling points,
exponentially faster than known classical algorithms.",1609.08170v1
2016-10-01,On the regularization of impact without collision: the Painlevé paradox and compliance,"We consider the problem of a rigid body, subject to a unilateral constraint,
in the presence of Coulomb friction. We regularize the problem by assuming
compliance (with both stiffness and damping) at the point of contact, for a
general class of normal reaction forces. Using a rigorous mathematical
approach, we recover impact without collision (IWC) in both the inconsistent
and indeterminate Painlev\'e paradoxes, in the latter case giving an exact
formula for conditions that separate IWC and lift-off. We solve the problem for
arbitrary values of the compliance damping and give explicit asymptotic
expressions in the limiting cases of small and large damping, all for a large
class of rigid bodies.",1610.00143v2
2016-11-25,Bulk viscous corrections to screening and damping in QCD at high temperatures,"Non-equilibrium corrections to the distribution functions of quarks and
gluons in a hot and dense QCD medium modify the ""hard thermal loops"" (HTL). The
HTLs determine the retarded, advanced, and symmetric (time-ordered) propagators
for gluons with soft momenta as well as the Debye screening and Landau damping
mass scales. We compute such corrections to a thermal as well as to a
non-thermal fixed point.The screening and damping mass scales are sensitive to
the bulk pressure and hence to (pseudo-) critical dynamical scaling of the bulk
viscosity in the vicinity of a second-order critical point. This could be
reflected in the properties of quarkonium bound states in the deconfined phase
and in the dynamics of soft gluon fields.",1611.08379v2
2016-12-07,Investigation of Stimulated Brillouin Scattering in Laser-Plasma Interactions,"In this paper, we present our numerical simulation results on the Stimulated
Brillouin Scattering (SBS) with injection of an ordinary mode (O-mode)
electromagnetic wave (our pump wave) with frequencies 70 GHz and 110 GHz.
Solving the Fourier transformed Vlasov equation in the velocity space, creates
a profile for distribution function. Time evolution of the distribution
function is investigated as well. Considering an average density for plasma
fusion (n_{0} ~ 10^{19} m^{-3}), we gain a profile for density. Then
two-dimensional instability rate for SBS is obtained. So, the fluctuation of
distribution function affects density and again density affects instability
rate. Increasing the incident light wave frequency causes the instability
growth rate to decrease. Time evolution shows a clear damping for instability
rate since the pump wave's energy is absorbed in plasma (plasma heating).
Furthermore, changing Landau damping for ion acoustic waves (IAW) by changing
ion-to-electron temperature ratio is presented as well, because this damping is
more dominant in high temperatures.",1612.02214v1
2016-12-08,Damped spin-wave excitations in the itinerant antiferromagnet $γ$-Fe$_{0.7}$Mn$_{0.3}$,"The collective spin-wave excitations in the antiferromagnetic state of
$\gamma$-Fe$_{0.7}$Mn$_{0.3}$ were investigated using the inelastic neutron
scattering technique. The spin excitations remain isotropic up to the high
excitation energy, ${\hbar\omega}= 78$ meV. The excitations gradually become
broad and damped above 40 meV. The damping parameter ${\gamma}$ reaches 110(16)
meV at ${\hbar\omega} = 78$ meV, which is much larger than that for other
metallic compounds, e.g., CaFe$_2$As$_2$ (24 meV),
La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ ($52-72$ meV), and Mn$_{90}$Cu$_{10}$ (88
meV). In addition, the spin-wave dispersion shows a deviation from the relation
$({\hbar\omega})^2 = c^2q^2 + {\Delta}^2$ above 40 meV. The group velocity
above this energy increases to 470(40) meV{\AA}, which is higher than that at
the low energies, $c = 226(5)$ meV{\AA}. These results could suggest that the
spin-wave excitations merge with the continuum of the individual particle-hole
excitations at 40 meV.",1612.02515v2
2016-12-09,How strong a logistic damping can prevent blow-up for the minimal Keller-Segel chemotaxis system?,"In this paper, we study the minimal Keller-Segel model with a logistic source
and obtain quantitative and qualitative descriptions of the competition between
logistic damping and other ingredient, especially, chemotactic aggregation to
guarantee boundedness and convergence. More specifically, we establish how
precisely strong a logistic source can prevent blow-up, and then we obtain an
explicit relationship between logistic damping and other ingredient,
especially, chemotactic aggregation so that convergences are ensured and their
respective convergence rates are explicitly calculated out. Known results in
the literature are completed and refined.
  Furthermore, our findings provide clues on how to produce blowup solutions
for KS chemotaxis models with logistic sources.",1612.03024v2
2016-12-28,Quantum coherence of two-qubit over quantum channels with memory,"Using the axiomatic definition of the coherence measure, such as the $l_{1}$
norm and the relative entropy, we study the phenomena of two-qubit system
quantum coherence through quantum channels where successive uses of the
channels are memory. Different types of noisy channels with memory, such as
amplitude damping, phase-damping, and depolarizing channels effect on quantum
coherence have been discussed in detail. The results show that, quantum
channels with memory can efficiently protect coherence from noisy channels.
Particularly, as channels with perfect memory, quantum coherence is unaffected
by the phase damping as well as depolarizing channels. Besides, we also
investigate the cohering and decohering power of quantum channels with memory.",1612.08791v1
2017-01-04,Hamiltonian of mean force and a damped harmonic oscillator in an anisotropic medium,"The quantum dynamics of a damped harmonic oscillator is investigated in the
presence of an anisotropic heat bath. The medium is modeled by a continuum of
three dimensional harmonic oscillators and anisotropic coupling is treated by
introducing tensor coupling functions. Starting from a classical Lagrangian,
the total system is quantized in the framework of the canonical quantization.
Following Fano technique, Hamiltonian of the system is diagonalized in terms of
creation and annihilation operators that are linear combinations of the basic
dynamical variables. Using the diagonalized Hamiltonian, the mean force
internal energy, free energy and entropy of the damped oscillator are
calculated.",1701.00964v2
2017-01-30,Quantization of energy and weakly turbulent profiles of the solutions to some damped second order evolution equations,"We consider a second order equation with a linear ""elastic"" part and a
nonlinear damping term depending on a power of the norm of the velocity. We
investigate the asymptotic behavior of solutions, after rescaling them suitably
in order to take into account the decay rate and bound their energy away from
zero.We find a rather unexpected dichotomy phenomenon. Solutions with finitely
many Fouriercomponents are asymptotic to solutions of the linearized
equationwithout damping, and exhibit some sort of equipartition of theenergy
among the components. Solutions with infinitely manyFourier components tend to
zero weakly but not strongly. We showalso that the limit of the energy of
solutions depends only on thenumber of their Fourier components.The proof of
our results is inspired by the analysis of asimplified model which we devise
through an averaging procedure,and whose solutions exhibit the same asymptotic
properties as thesolutions to the original equation.",1701.08604v1
2017-02-15,Topological Properties of a Coupled Spin-Photon System Induced by Damping,"We experimentally examine the topological nature of a strongly coupled
spin-photon system induced by damping. The presence of both spin and photonic
losses results in a non-Hermitian system with a variety of exotic phenomena
dictated by the topological structure of the eigenvalue spectra and the
presence of an exceptional point (EP), where the coupled spin-photon
eigenvectors coalesce. By controlling both the spin resonance frequency and the
spin-photon coupling strength we observe a resonance crossing for
cooperativities above one, suggesting that the boundary between weak and strong
coupling should be based on the EP location rather than the cooperativity.
Furthermore we observe dynamic mode switching when encircling the EP and
identify the potential to engineer the topological structure of coupled
spin-photon systems with additional modes. Our work therefore further
highlights the role of damping within the strong coupling regime, and
demonstrates the potential and great flexibility of spin-photon systems for
studies of non-Hermitian physics.",1702.04797v2
2017-02-22,Modified quantum-speed-limit bounds for open quantum dynamics in quantum channels,"The minimal evolution time between two distinguishable states is of
fundamental interest in quantum physics. Very recently Mirkin et al. argue that
some most common quantum-speed-limit (QSL) bounds which depend on the actual
evolution time do not cleave to the essence of the QSL theory as they grow
indefinitely but the final state is reached at a finite time in a damped
Jaynes-Cummings (JC) model. In this paper, we thoroughly study this puzzling
phenomenon. We find the inconsistent estimates will happen if and only if the
limit of resolution of a calculation program is achieved, through which we
propose that the nature of the inconsistency is not a violation to the essence
of the QSL theory but an illusion caused by the finite precision in numerical
simulations. We also present a generic method to overcome the inconsistent
estimates and confirm its effectiveness in both amplitude-damping and
phase-damping channels. Additionally, we show special cases which may restrict
the QSL bound defined by ""quantumness"".",1702.06748v3
2017-03-07,Lower Bound and optimality for a nonlinearly damped Timoshenko system with thermoelasticity,"In this paper, we consider a vibrating nonlinear Timoshenko system with
thermoelasticity with second sound. We first investigate the strong stability
of this system, then we devote our efforts to obtain the strong lower energy
estimates using Alabau--Boussouira's energy comparison principle introduced in
\cite{2} (see also \cite{alabau}). One of the main advantages of these results
is that they allows us to prove the optimality of the asymptotic results (as
$t\rightarrow \infty$) obtained in \cite{ali}. We also extend to our model the
nice results achieved in \cite{alabau} for the case of nonlinearly damped
Timoshenko system with thermoelasticity. The optimality of our results is also
investigated through some explicit examples of the nonlinear damping term. The
proof of our results relies on the approach in \cite{AB1, AB2}.",1703.02599v4
2017-03-08,A Parameterized Energy Correction Method for Electromagnetic Showers in BGO-ECAL of DAMPE,"DAMPE is a space-based mission designed as a high energy particle detector
measuring cosmic-rays and $\gamma-$rays which was successfully launched on
Dec.17, 2015. The BGO electromagnetic calorimeter is one of the key
sub-detectors of DAMPE for energy measurement of electromagnetic showers
produced by $e^{\pm}/{\gamma}$. Due to energy loss in dead material and energy
leakage outside the calorimeter, the deposited energy in BGO underestimates the
primary energy of incident $e^{\pm}/{\gamma}$. In this paper, based on detailed
MC simulations, a parameterized energy correction method using the lateral and
longitudinal information of electromagnetic showers has been studied and
verified with data of electron beam test at CERN. The measurements of energy
linearity and resolution are significantly improved by applying this correction
method for electromagnetic showers.",1703.02821v2
2017-03-08,A GAMP Based Low Complexity Sparse Bayesian Learning Algorithm,"In this paper, we present an algorithm for the sparse signal recovery problem
that incorporates damped Gaussian generalized approximate message passing
(GGAMP) into Expectation-Maximization (EM)-based sparse Bayesian learning
(SBL). In particular, GGAMP is used to implement the E-step in SBL in place of
matrix inversion, leveraging the fact that GGAMP is guaranteed to converge with
appropriate damping. The resulting GGAMP-SBL algorithm is much more robust to
arbitrary measurement matrix $\boldsymbol{A}$ than the standard damped GAMP
algorithm while being much lower complexity than the standard SBL algorithm. We
then extend the approach from the single measurement vector (SMV) case to the
temporally correlated multiple measurement vector (MMV) case, leading to the
GGAMP-TSBL algorithm. We verify the robustness and computational advantages of
the proposed algorithms through numerical experiments.",1703.03044v2
2017-03-28,Singularity formation for the 1D compressible Euler equation with variable damping coefficient,"In this paper, we consider some blow-up problems for the 1D Euler equation
with time and space dependent damping. We investigate sufficient conditions on
initial data and the rate of spatial or time-like decay of the coefficient of
damping for the occurrence of the finite time blow-up. In particular, our
sufficient conditions ensure that the derivative blow-up occurs in finite time
with the solution itself and the pressure bounded. Our method is based on
simple estimates with Riemann invariants. Furthermore, we give sharp lower and
upper estimates of the lifespan of solutions, when initial data are small
perturbations of constant states.",1703.09821v3
2017-04-07,Underdamped stochastic harmonic oscillator,"We investigate stationary states of the linear damped stochastic oscillator
driven by L\'evy noises. In the long time limit kinetic and potential energies
of the oscillator do not fulfill the equipartition theorem and their
distributions follow the power-law asymptotics. At the same time, partition of
the mechanical energy is controlled by the damping coefficient. We show that in
the limit of vanishing damping a stochastic analogue of the equipartition
theorem can be proposed, namely the statistical properties of potential and
kinetic energies attain distributions characterized by the same width. Finally,
we demonstrate that the ratio of instantaneous kinetic and potential energies
which signifies departure from the mechanical energy equipartition, follows
universal power-law asymptotics.",1704.02119v2
2017-04-13,Quantum behaviour of open pumped and damped Bose-Hubbard trimers,"We propose and analyse analogs of optical cavities for atoms using three-well
inline Bose-Hubbard models with pumping and losses. With one well pumped and
one damped, we find that both the mean-field dynamics and the quantum
statistics show a qualitative dependence on the choice of damped well. The
systems we analyse remain far from equilibrium, although most do enter a
steady-state regime. We find quadrature squeezing, bipartite and tripartite
inseparability and entanglement, and states exhibiting the EPR paradox,
depending on the parameter regimes. We also discover situations where the
mean-field solutions of our models are noticeably different from the quantum
solutions for the mean fields. Due to recent experimental advances, it should
be possible to demonstrate the effects we predict and investigate in this
article.",1704.04021v1
2017-05-10,Negative mobility of a Brownian particle: strong damping regime,"We study impact of inertia on directed transport of a Brownian particle under
non-equilibrium conditions: the particle moves in a one-dimensional periodic
and symmetric potential, is driven by both an unbiased time-periodic force and
a constant force, and is coupled to a thermostat of temperature T. Within
selected parameter regimes this system exhibits negative mobility, which means
that the particle moves in the direction opposite to the direction of the
constant force. It is known that in such a setup the inertial term is essential
for the emergence of negative mobility and it cannot be detected in the
limiting case of overdamped dynamics. We analyse inertial effects and show that
negative mobility can be observed even in the strong damping regime. We
determine the optimal dimensionless mass for the presence of negative mobility
and reveal three mechanisms standing behind this anomaly: deterministic
chaotic, thermal noise induced and deterministic non-chaotic. The last origin
has never been reported. It may provide guidance to the possibility of
observation of negative mobility for strongly damped dynamics which is of
fundamental importance from the point of view of biological systems, all of
which in situ operate in fluctuating environments.",1705.03661v1
2017-05-27,Power System Supplementary Damping Controllers in the Presence of Saturation,"This paper presents the analysis and a method to design supplementary damping
controllers (SDCs) for synchronous generators considering the effects of
saturation limits. Usually such saturations of control signals are imposed in
order to enforce practical limitations such as component ratings. However, to
guarantee the stability in the presence of saturation limits, the state
trajectories must remain inside the domain of attraction (DA). In this paper,
the domain of attraction of a single-machine infinite-bus (SMIB) power system
with saturation nonlinearity is estimated and compared with the exact
description of the null controllable region. Then, state-feedback controllers
are designed to enlarge the DA. Our analysis shows that nonlinear effects of
saturation should be considered to guarantee stability and satisfactory
performance. Simulation results on a detailed nonlinear model of a synchronous
generator indicate that the DA enlarges with the proposed controller. The
results also indicate that Critical Clearing Time (CCT) and damping of the
system with saturation can be improved by the proposed method.",1705.09849v1
2017-05-26,Absence of Landau damping in driven three-component Bose-Einstein condensate in optical lattices,"We explore the quantum many-body physics of a three-component Bose-Einstein
condensate (BEC) in an optical lattices driven by laser fields in $V$ and
$\Lambda$ configurations. We obtain exact analytical expressions for the energy
spectrum and amplitudes of elementary excitations, and discover symmetries
among them. We demonstrate that the applied laser fields induce a gap in the
otherwise gapless Bogoliubov spectrum. We find that Landau damping of the
collective modes above the energy of the gap is carried by laser-induced roton
modes and is considerably suppressed compared to the phonon-mediated damping
endemic to undriven scalar BECs.",1705.10199v2
2017-05-31,Low-energy modes of spin-imbalanced Fermi gases in BCS phase,"The low-energy modes of a spin-imbalanced superfluid Fermi gas in the
Bardeen-Cooper-Schrieffer (BCS) side are studied. The gas is assumed to be
sufficiently dilute so that the pairing of atoms can be considered effective
only in s-wave between fermions of different internal state. The order
parameter at equilibrium is determined by the mean-field approximation, while
the properties of the collective modes are calculated within a Gaussian
approximation for the fluctuations of the order parameter. In particular we
investigate the effects of asymmetry between the populations of the two
different components and of temperature on the frequency and damping of
collective modes. It is found that the temperature does not much affect the
frequency and the damping of the modes, whereas an increase of the imbalance
shifts the frequency toward lower values and enhances the damping sensitively.
Besides the Bogoliubov-Anderson phonons, we observe modes at zero frequency for
finite values of the wave-number. These modes indicate that an instability
develops driving the system toward two separate phases, normal and superfluid.",1705.11162v1
2017-06-01,Global Stabilization of the Navier-Stokes-Voight and the damped nonlinear wave equations by finite number of feedback controllers,"In this paper we introduce a finite-parameters feedback control algorithm for
stabilizing solutions of the Navier-Stokes-Voigt equations, the strongly damped
nonlinear wave equations and the nonlinear wave equation with nonlinear damping
term, the Benjamin-Bona-Mahony-Burgers equation and the KdV-Burgers equation.
This algorithm capitalizes on the fact that such infinite-dimensional
dissipative dynamical systems posses finite-dimensional long-time behavior
which is represented by, for instance, the finitely many determining parameters
of their long-time dynamics, such as determining Fourier modes, determining
volume elements, determining nodes , etc..The algorithm utilizes these finite
parameters in the form of feedback control to stabilize the relevant solutions.
For the sake of clarity, and in order to fix ideas, we focus in this work on
the case of low Fourier modes feedback controller, however, our results and
tools are equally valid for using other feedback controllers employing other
spatial coarse mesh interpolants.",1706.00162v1
2017-06-08,Realistic clocks for a Universe without time,"There are a number of problematic features within the current treatment of
time in physical theories, including the ""timelessness"" of the Universe as
encapsulated by the Wheeler-DeWitt equation. This paper considers one
particular investigation into resolving this issue; a conditional probability
interpretation that was first proposed by Page and Wooters. Those authors
addressed the apparent timelessness by subdividing a faux Universe into two
entangled parts, ""the clock"" and ""the remainder of the Universe"", and then
synchronizing the effective dynamics of the two subsystems by way of
conditional probabilities. The current treatment focuses on the possibility of
using a (somewhat) realistic clock system; namely, a coherent-state description
of a damped harmonic oscillator. This clock proves to be consistent with the
conditional probability interpretation; in particular, a standard evolution
operator is identified with the position of the clock playing the role of time
for the rest of the Universe. Restrictions on the damping factor are determined
and, perhaps contrary to expectations, the optimal choice of clock is not
necessarily one of minimal damping.",1706.02531v1
2017-06-26,High $β$ Effects on Cosmic Ray Streaming in Galaxy Clusters,"Diffuse, extended radio emission in galaxy clusters, commonly referred to as
radio halos, indicate the presence of high energy cosmic ray (CR) electrons and
cluster-wide magnetic fields. We can predict from theory the expected surface
brightness of a radio halo, given magnetic field and CR density profiles.
Previous studies have shown that the nature of CR transport can radically
effect the expected radio halo emission from clusters (Wiener et al. 2013).
Reasonable levels of magnetohydrodynamic (MHD) wave damping can lead to
significant CR streaming speeds. But a careful treatment of MHD waves in a high
$\beta$ plasma, as expected in cluster environments, reveals damping rates may
be enhanced by a factor of $\beta^{1/2}$. This leads to faster CR streaming and
lower surface brightnesses than without this effect. In this work we re-examine
the simplified, 1D Coma cluster simulations (with radial magnetic fields) of
Wiener et al. (2013) and discuss observable consequences of this high $\beta$
damping. Future work is required to study this effect in more realistic
simulations.",1706.08525v2
2017-07-02,Metastability of Kolmogorov flows and inviscid damping of shear flows,"First, we consider Kolmogorov flow (a shear flow with a sinusoidal velocity
profile) for 2D Navier-Stokes equation on a torus. Such flows, also called bar
states, have been numerically observed as one type of metastable states in the
study of 2D turbulence. For both rectangular and square tori, we prove that the
non-shear part of perturbations near Kolmogorov flow decays in a time scale
much shorter than the viscous time scale. The results are obtained for both the
linearized NS equations with any initial vorticity in L^2, and the nonlinear NS
equation with initial L^2 norm of vorticity of the size of viscosity. In the
proof, we use the Hamiltonian structure of the linearized Euler equation and
RAGE theorem to control the low frequency part of the perturbation. Second, we
consider two classes of shear flows for which a sharp stability criterion is
known. We show the inviscid damping in a time average sense for non-shear
perturbations with initial vorticity in L^2. For the unstable case, the
inviscid damping is proved on the center space. Our proof again uses the
Hamiltonian structure of the linearized Euler equation and an instability index
theory recently developed by Lin and Zeng for Hamiltonian PDEs.",1707.00278v1
2017-08-30,Convergence to diffusion waves for solutions of Euler equations with time-depending damping on quadrant,"This paper is concerned with the asymptotic behavior of the solution to the
Euler equations with time-depending damping on quadrant $(x,t)\in
\mathbb{R}^+\times\mathbb{R}^+$, \begin{equation}\notag \partial_t v
  -
  \partial_x u=0, \qquad \partial_t u
  +
  \partial_x p(v)
  =\displaystyle
  -\frac{\alpha}{(1+t)^\lambda} u, \end{equation} with null-Dirichlet boundary
condition or null-Neumann boundary condition on $u$. We show that the
corresponding initial-boundary value problem admits a unique global smooth
solution which tends time-asymptotically to the nonlinear diffusion wave.
Compared with the previous work about Euler equations with constant coefficient
damping, studied by Nishihara and Yang (1999, J. Differential Equations, 156,
439-458), and Jiang and Zhu (2009, Discrete Contin. Dyn. Syst., 23, 887-918),
we obtain a general result when the initial perturbation belongs to the same
space. In addition, our main novelty lies in the facts that the cut-off points
of the convergence rates are different from our previous result about the
Cauchy problem. Our proof is based on the classical energy method and the
analyses of the nonlinear diffusion wave.",1708.09127v1
2017-09-06,Linear gyrokinetic investigation of the geodesic acoustic modes in realistic tokamak configurations,"Geodesic acoustic modes (GAMs) are studied by means of the gyrokinetic global
particle-in-cell code ORB5. Linear electromagnetic simulations in the low
electron beta limit have been performed, in order to separate acoustic and
Alfv\'enic time scales and obtain more accurate measurements. The dependence of
the frequency and damping rate on several parameters such as the safety factor,
the GAM radial wavenumber and the plasma elongation is studied. All simulations
have been performed with kinetic electrons with realistic electron/ion mass
ratio. Interpolating formulae for the GAM frequency and damping rate, based on
the results of the gyrokinetic simulations, have been derived. Using these
expressions, the influence of the temperature gradient on the damping rate is
also investigated. Finally, the results are applied to the study of a real
discharge of the ASDEX Upgrade tokamak.",1709.01818v1
2017-09-17,Further insights into the damping-induced self-recovery phenomenon,"In a series of papers, D. E. Chang, et al., proved and experimentally
demonstrated a phenomenon they termed ""damping-induced self-recovery"". However,
these papers left a few questions concerning the observed phenomenon unanswered
- in particular, the effect of the intervening lubricant-fluid and its
viscosity on the recovery, the abrupt change in behaviour with the introduction
of damping, a description of the energy dynamics, and the curious occurrence of
overshoots and oscillations and its dependence on the control law. In this
paper we attempt to answer these questions through theory. In particular, we
derive an expression for the infinite-dimensional fluid-stool-wheel system,
that approximates its dynamics to that of the better understood
finite-dimensional case.",1709.05596v5
2017-09-19,An Improved Primal-Dual Interior Point Solver for Model Predictive Control,"We propose a primal-dual interior-point (PDIP) method for solving quadratic
programming problems with linear inequality constraints that typically arise
form MPC applications. We show that the solver converges (locally)
quadratically to a suboptimal solution of the MPC problem. PDIP solvers rely on
two phases: the damped and the pure Newton phases. Compared to state-of-the-art
PDIP methods, our solver replaces the initial damped Newton phase (usually used
to compute a medium-accuracy solution) with a dual solver based on Nesterov's
fast gradient scheme (DFG) that converges with a sublinear convergence rate of
order O(1/k^2) to a medium-accuracy solution. The switching strategy to the
pure Newton phase, compared to the state of the art, is computed in the dual
space to exploit the dual information provided by the DFG in the first phase.
Removing the damped Newton phase has the additional advantage that our solver
saves the computational effort required by backtracking line search. The
effectiveness of the proposed solver is demonstrated on a 2-dimensional
discrete-time unstable system and on an aerospace application.",1709.06362v1
2017-09-22,Nonlinear stage of Benjamin-Feir instability in forced/damped deep water waves,"We study a three-wave truncation of a recently proposed damped/forced
high-order nonlinear Schr\""odinger equation for deep-water gravity waves under
the effect of wind and viscosity. The evolution of the norm (wave-action) and
spectral mean of the full model are well captured by the reduced dynamics.
Three regimes are found for the wind-viscosity balance: we classify them
according to the attractor in the phase-plane of the truncated system and to
the shift of the spectral mean. A downshift can coexist with both net forcing
and damping, i.e., attraction to period-1 or period-2 solutions. Upshift is
associated with stronger winds, i.e., to a net forcing where the attractor is
always a period-1 solution. The applicability of our classification to
experiments in long wave-tanks is verified.",1709.07850v2
2017-09-27,On long-time asymptotics for viscous hydrodynamic models of collective behavior with damping and nonlocal interactions,"Hydrodynamic systems arising in swarming modelling include nonlocal forces in
the form of attractive-repulsive potentials as well as pressure terms modelling
strong local repulsion. We focus on the case where there is a balance between
nonlocal attraction and local pressure in presence of confinement in the whole
space. Under suitable assumptions on the potentials and the pressure functions,
we show the global existence of weak solutions for the hydrodynamic model with
viscosity and linear damping. By introducing linear damping in the system, we
ensure the existence and uniqueness of stationary solutions with compactly
supported density, fixed mass and center of mass. The associated velocity field
is zero in the support of the density. Moreover, we show that global weak
solutions converge for large times to the set of these stationary solutions in
a suitable sense. In particular cases, we can identify the limiting density
uniquely as the global minimizer of the free energy with the right mass and
center of mass.",1709.09290v2
2017-09-28,Landau Damping with Electron Lenses in Space-Charge Dominated Beams,"Progress on the Intensity Frontier of high energy physics critically depends
on record high intensity charged particles accelerators. Beams in such machines
become operationally limited by coherent beam instabilities, particularly
enhanced in the regime of strong space charge (SC). Usual methods to control
the instabilities, such as octupole magnets, beam feedback dampers and
employment of chromatic effects, become less effective and insufficient. In [1]
it was proposed to employ electron lenses for introduction of sufficient spread
in particle oscillation frequencies needed for beam stabilization and in [2] it
was shown that electron lenses are uniquely effective for Landau damping of
transverse beam instabilities in high energy particle accelerators and their
employment does not compromise incoherent (single particle) stability, dynamic
aperture and the beam lifetime. Here we consider an important issue of
effectiveness of the Landau damping with electron lenses in space-charge
dominated beams and demonstrate that the desired stability can be assured with
proper choice of the electron beam parameters and current distributions.",1709.10020v1
2017-10-13,Hydrodynamic-to-ballistic crossover in Dirac fluid,"We develop an exactly solvable classical kinetic model of transport in Dirac
materials accounting for strong electron-electron (e-e) and electron-hole (e-h)
collisions. We use this model to track the evolution of graphene conductivity
and properties of its collective excitations across the
hydrodynamic-to-ballistic crossover. We find the relaxation rate of electric
current by e-e collisions that is possible due to the lack of Galilean
invariance, and introduce a universal numerical measure of this non-invariance
in arbitrary dimension. We find the two branches of collective excitations in
the Dirac fluid: plasmons and electron-hole sound. The sound waves have small
viscous damping at the neutrality point both in the hydrodynamic and ballistic
regimes, but acquire large damping due to e-h friction even at slight doping.
On the contrary, plasmons acquire strong frictional damping at the neutrality
point and become well-defined in doped samples.",1710.05054v3
2017-10-13,The second hyperpolarizability of systems described by the space-fractional Schrodinger equation,"The static second hyperpolarizability is derived from the space-fractional
Schr\""{o}dinger equation in the particle-centric view. The Thomas-Reiche-Kuhn
sum rule matrix elements and the three-level ansatz determines the maximum
second hyperpolarizability for a space-fractional quantum system. The total
oscillator strength is shown to decrease as the space-fractional parameter
$\alpha$ decreases, which reduces the optical response of a quantum system in
the presence of an external field. This damped response is caused by the
wavefunction dependent position and momentum commutation relation. Although the
maximum response is damped, we show that the one-dimensional quantum harmonic
oscillator is no longer a linear system for $\alpha \neq 1$, where the second
hyperpolarizability becomes negative before ultimately damping to zero at the
lower fractional limit of $\alpha \rightarrow 1/2$.",1710.05099v2
2017-11-01,Tunable magnetization relaxation of Fe_{2}Cr_{1-x}Co_{x}Si half-metallic Heusler alloys by band structure engineering,"We report a systematic investigation on the magnetization relaxation
properties of iron-based half-metallic Heusler alloy
Fe$_{2}$Cr$_{1-x}$Co_${x}$Si (FCCS) thin films using broadband angular-resolved
ferromagnetic resonance. Band structure engineering through Co doping (x)
demonstrated by first-principles calculations is shown to tune the intrinsic
magnetic damping over an order of magnitude, namely 0.01-0.0008. Notably, the
intrinsic damping constants for samples with high Co concentration are among
the lowest reported for Heusler alloys and even comparable to magnetic
insulator yttrium iron garnet. Furthermore, a significant reduction of both
isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys
was found in the FCCS films with x=0.5-0.75, which is of particular importance
for applications. These results demonstrate a practical recipe to tailor
functional magnetization for Heusler alloy-based spintronics at room
temperature",1711.00406v1
2017-11-08,Bulk viscous corrections to screening and damping in the deconfined phase at high temperature,"Non-equilibrium corrections in a hot QCD medium modify the ""hard thermal
loops"" (HTL) which determine the resummed propagators for gluons with soft
momenta as well as the Debye screening and Landau damping mass scales. We focus
on bulk viscous corrections to a thermal fixed point. The screening and damping
mass scales are sensitive to the bulk pressure and perhaps to (pseudo-)
critical dynamical scaling of the bulk viscosity in the vicinity of a
second-order critical point. This would affect the properties of quarkonium
bound states in the deconfined phase.",1711.03072v1
2017-11-29,A model explaining neutrino masses and the DAMPE cosmic ray electron excess,"We propose a flavored $U(1)_{e\mu}$ neutrino mass and dark matter~(DM) model
to explain the recent DArk Matter Particle Explorer (DAMPE) data, which feature
an excess on the cosmic ray electron plus positron flux around 1.4 TeV. Only
the first two lepton generations of the Standard Model are charged under the
new $U(1)_{e\mu}$ gauge symmetry. A vector-like fermion $\psi$, which is our DM
candidate, annihilates into $e^{\pm}$ and $\mu^{\pm}$ via the new gauge boson
$Z'$ exchange and accounts for the DAMPE excess. We have found that the data
favors a $\psi$ mass around 1.5~TeV and a $Z'$ mass around 2.6~TeV, which can
potentially be probed by the next generation lepton colliders and DM direct
detection experiments.",1711.10995v2
2017-11-29,Electrophilic dark matter with dark photon: from DAMPE to direct detection,"The electron-positron excess reported by the DAMPE collaboration recently may
be explained by an electrophilic dark matter (DM). A standard model singlet
fermion may play the role of such a DM when it is stablized by some symmetries,
such as a dark $U(1)_X^{}$ gauge symmetry, and dominantly annihilates into the
electron-positron pairs through the exchange of a scalar mediator. The model,
with appropriate Yukawa couplings, can well interpret the DAMPE excess. Naively
one expects that in this type of models the DM-nucleon cross section should be
small since there is no tree-level DM-quark interactions. We however find that
at one-loop level, a testable DM-nucleon cross section can be induced for
providing ways to test the electrophilic model. We also find that a $U(1)$
kinetic mixing can generate a sizable DM-nucleon cross section although the
$U(1)_X^{}$ dark photon only has a negligible contribution to the DM
annihilation. Depending on the signs of the mixing parameter, the dark photon
can enhance/reduce the one-loop induced DM-nucleon cross section.",1711.11000v2
2017-11-30,Leptophilic dark matter in gauged $U(1)_{L_e-L_μ}$ model in light of DAMPE cosmic ray $e^+ + e^-$ excess,"Motivated by the very recent cosmic-ray electron+positron excess observed by
DAMPE collaboration, we investigate a Dirac fermion dark matter (DM) in the
gauged $L_e - L_\mu$ model. DM interacts with the electron and muon via the
$U(1)_{e-\mu}$ gauge boson $Z^{'}$. The model can explain the DAMPE data well.
Although a non-zero DM-nucleon cross section is only generated at one loop
level and there is a partial cancellation between $Z^{'}ee$ and $Z^{'}\mu\mu$
couplings, we find that a large portion of $Z^{'}$ mass is ruled out from
direct DM detection limit leaving the allowed $Z^{'}$ mass to be close to two
times of the DM mass. Implications for $pp \to Z^{'} \to 2\ell$ and $pp \to
2\ell + Z^{'}$ , and muon $g-2$ anomaly are also studied.",1711.11563v3
2017-12-03,Explaining the DAMPE $e^+ e^-$ excess using the Higgs triplet model with a vector dark matter,"We explain the $e^+ e^-$ excess observed by the DAMPE Collaboration using a
dark matter model based upon the Higgs triplet model and an additional hidden
$SU(2)_X$ gauge symmetry. Two of the $SU(2)_X$ gauge bosons are stable due to a
residual discrete symmetry and serve as the dark matter candidate. We search
the parameter space for regions that can explain the observed relic abundance,
and compute the flux of $e^+ e^-$ coming from a nearby dark matter subhalo.
With the inclusion of background cosmic rays, we show that the model can render
a good fit to the entire energy spectrum covering the AMS-02, Fermi-LAT and
DAMPE data.",1712.00793v2
2017-12-06,Explain DAMPE Results by Dark Matter With Hierarchical Lepton-Specific Yukawa Interactions,"We propose to interpret the DAMPE electron excess at 1.5 TeV through scalar
or Dirac fermion dark matter (DM) annihilation with doubly charged scalar
mediators that have lepton-specific Yukawa couplings. Hierarchy of such
lepton-specific Yukawa couplings is generated through the Froggatt-Nielsen
mechanism, so that the dark matter annihilation products can be dominantly
electrons. Stringent constraints from LEP2 on intermediate vector boson
production can be evaded in our scenarios. In the case of scalar DM, we discuss
one scenario with DM annihilating directly to leptons and the other scenario
with DM annihilating to scalar mediators followed by their decays. We also
discuss the Breit-Wigner resonant enhancement and the Sommerfeld enhancement in
case that the s-wave annihilation process is small or helicity suppressed. With
both types of enhancement, constraints on the parameters can be relaxed and new
ways for model building will be open in explaining the DAMPE results.",1712.02381v3
2017-12-08,Kinetic damping in the spectra of the spherical impedance probe,"The impedance probe is a measurement device to measure plasma parameter like
electron density. It consists of one electrode connected to a network analyzer
via a coaxial cable and is immersed into a plasma. A bias potential superposed
with an alternating potential is applied to the electrode and the response of
the plasma is measured. Its dynamical interaction with the plasma in
electrostatic, kinetic description can be modeled in an abstract notation based
on functional analytic methods. These methods provide the opportunity to derive
a general solution, which is given as the response function of the probe-plasma
system. It is defined by the matrix elements of the resolvent of an appropriate
dynamical operator. Based on the general solution a residual damping for
vanishing pressure can be predicted and can only be explained by kinetic
effects. Within this manuscript an explicit response function of the spherical
impedance probe is derived. Therefore, the resolvent is determined by its
algebraic representation based on an expansion in orthogonal basis functions.
This allows to compute an approximated response function and its corresponding
spectra. These spectra show additional damping due to kinetic effects and are
in good agreement with former kinetically determined spectra.",1712.03126v1
2017-12-14,DAMPE squib? Significance of the 1.4 TeV DAMPE excess,"We present a Bayesian and frequentist analysis of the DAMPE charged cosmic
ray spectrum. The spectrum, by eye, contained a spectral break at about 1 TeV
and a monochromatic excess at about 1.4 TeV. The break was supported by a Bayes
factor of about $10^{10}$ and we argue that the statistical significance was
resounding. We investigated whether we should attribute the excess to dark
matter annihilation into electrons in a nearby subhalo. We found a local
significance of about $3.6\sigma$ and a global significance of about
$2.3\sigma$, including a two-dimensional look-elsewhere effect by simulating
1000 pseudo-experiments. The Bayes factor was sensitive to our choices of
priors, but favoured the excess by about 2 for our choices. Thus, whilst
intriguing, the evidence for a signal is not currently compelling.",1712.05089v1
2017-12-15,Radiative Seesaw Model and DAMPE Excess from Leptophilic Gauge Symmetry,"In the light of the $e^{+}+e^{-}$ excess observed by DAMPE experiment, we
propose an anomaly-free radiative seesaw model with an alternative leptophilic
$U(1)_X$ gauge symmetry. In the model, only right-handed leptons are charged
under $U(1)_X$ symmetry. The tiny Dirac neutrino masses are generated at
one-loop level and charged leptons acquire masses though the type-I seesaw-like
mechanism with heavy intermediate fermions. In order to cancel the anomaly,
irrational $U(1)_{X}$ charge numbers are assigned to some new particles. After
the spontaneous breaking of $U(1)_{X}$ symmetry, the dark $Z_{2}$ symmetry
could appear as a residual symmetry such that the stability of inert particles
with irrational charge numbers are guaranteed, naturally leading to stable DM
candidates. We show that the Dirac fermion DM contained in the model can
explain the DAMPE excess. Meanwhile, experimental constraints from DM relic
density, direct detection, LEP and anomalous magnetic moments are satisfied.",1712.05722v2
2017-12-19,Damping of Josephson oscillations in strongly correlated one-dimensional atomic gases,"We study Josephson oscillations of two strongly correlated one-dimensional
bosonic clouds separated by a localized barrier. Using a quantum-Langevin
approach and the exact Tonks-Girardeau solution in the impenetrable-boson
limit, we determine the dynamical evolution of the particle-number imbalance,
displaying an effective damping of the Josephson oscillations which depends on
barrier height, interaction strength and temperature. We show that the damping
originates from the quantum and thermal fluctuations intrinsically present in
the strongly correlated gas. Thanks to the density-phase duality of the model,
the same results apply to particle-current oscillations in a one-dimensional
ring where a weak barrier couples different angular momentum states.",1712.06949v2
2017-12-21,The gluon condensation effects in the DAMPE cosmic ray spectrum of electrons and positrons,"Gluons dominate the proton behavior at high energy collisions, they can be
condensed at ultra high energy. The collisions of the accelerated high energy
protons with interplanetary matter in cosmic rays will produce a huge number of
secondary particles at the gluon condensate energy region, which break the
primary power-law of cosmic rays. The above predictions seem to be consistent
with the recent DAMPE data concerning the electron plus positron spectra. We
find that the smoothly broken power-law at $\sim 0.9 TeV$ and $3\sim 4 TeV$ in
the DAMPE data can be understood as the gluon condensation effects in proton.",1712.07868v2
2017-12-22,Low-momentum dynamic structure factor of a strongly interacting Fermi gas at finite temperature: The Goldstone phonon and its Landau damping,"We develop a microscopic theory of dynamic structure factor to describe the
Bogoliubov-Anderson-Goldstone phonon mode and its damping rate in a strongly
interacting Fermi gas at finite temperature. It is based on a density
functional approach - the so-called superfluid local density approximation. The
accuracy of the theory is quantitatively examined by comparing the theoretical
predictions with the recent experimental measurements for the local dynamic
structure factor of a nearly homogeneous unitary Fermi gas at low transferred
momentum {[}S. Hoinka \textit{et al.}, Nat. Phys. \textbf{13}, 943 (2017){]},
without any free parameters. We calculate the dynamic structure factor as
functions of temperature and transferred momentum, and determine the
temperature evolution of the phonon damping rate, by considering the dominant
decay process of the phonon mode via scatterings off fermionic quasiparticles.
These predictions can be confronted with future Bragg scattering experiments on
a unitary Fermi gas near the superfluid transition.",1712.08318v1
2017-12-22,A brief summary of nonlinear echoes and Landau damping,"In this expository note we review some recent results on Landau damping in
the nonlinear Vlasov equations, focusing specifically on the recent
construction of nonlinear echo solutions by the author [arXiv:1605.06841] and
the associated background. These solutions show that a straightforward
extension of Mouhot and Villani's theorem on Landau damping to Sobolev spaces
on $\mathbb T^n_x \times \mathbb R^n_v $ is impossible and hence emphasize the
subtle dependence on regularity of phase mixing problems. This expository note
is specifically aimed at mathematicians who study the analysis of PDEs, but not
necessarily those who work specifically on kinetic theory. However, for the
sake of brevity, this review is certainly not comprehensive.",1712.08498v1
2017-12-28,Coherence evolution in two-qubit system going through amplitude damping channel,"In this paper, we analyze the evolution of quantum coherence in a two-qubit
system going through the amplitude damping channel. After they have gone
through this channel many times, we analyze the systems with respect to the
coherence of their output states. When only one subsystem goes through the
channel, frozen coherence occurs if and only if this subsystem is incoherent
and an auxiliary condition is satisfied for the other subsystem. When two
subsystems go through this quantum channel, quantum coherence can be frozen if
and only if the two subsystems are both incoherent. We also investigate the
evolution of coherence for maximally incoherent-coherent states and derive an
equation for the output states after one or two subsystems have gone through
the amplitude damping channel.",1712.09769v1
2018-01-09,Balanced Truncation Model Reduction of a Nonlinear Cable-Mass PDE System with Interior Damping,"We consider model order reduction of a nonlinear cable-mass system modeled by
a 1D wave equation with interior damping and dynamic boundary conditions. The
system is driven by a time dependent forcing input to a linear mass-spring
system at one boundary. The goal of the model reduction is to produce a low
order model that produces an accurate approximation to the displacement and
velocity of the mass in the nonlinear mass-spring system at the opposite
boundary. We first prove that the linearized and nonlinear unforced systems are
well-posed and exponentially stable under certain conditions on the damping
parameters, and then consider a balanced truncation method to generate the
reduced order model (ROM) of the nonlinear input-output system. Little is known
about model reduction of nonlinear input-output systems, and so we present
detailed numerical experiments concerning the performance of the nonlinear ROM.
We find that the ROM is accurate for many different combinations of model
parameters.",1801.02792v1
2018-01-18,Analytic solutions to various dissipation models of the simple and driven quantum harmonic oscillator,"We obtain analytic solutions to various models of dissipation of the quantum
harmonic oscillator, employing a simple method in the Wigner function Fourier
transform description of the system; and study as an exemplification, the
driven open quantum harmonic oscillator. The environmental models we use are
based on optical master equations for the zero and finite temperature bath and
whose open dynamics are described by a Lindblad master equation, and also we
use the Caldeira-Leggett model for the high temperature limit, in the the under
damped an the over damped case. Under the Wigner Fourier transform or chord
function as it has been called, it becomes particularly simple to solve the
dynamics of the open oscillator in the sense that the dynamics of the system
are reduced to the application of an evolution matrix related to the damped
motion of the oscillator.",1801.05943v1
2018-01-23,The effect of liquid on the vibrational intensity of a wineglass at steady state resonance,"As a liquid is inserted into a wineglass, the natural frequency of the
wineglass decreases. This phenomenon, known as pitch lowering, is well
explained in past papers. However, previous literature have not yet mentioned
that pitch lowering also reduces the resonance intensity of a wineglass. Thus,
this present paper aims to extend the body of research on this topic by
describing the relationship between pitch lowering and its effect on resonation
intensity. To do so, we identify the vibrating wineglass wall as a damped
harmonic oscillator, derive a theoretical model, and find that the resonance
intensity of the wineglass is proportional to the square of its natural
frequency, under the assumption that damping stays constant. However, our
experiments showed the coefficient of damping to increase with respect to the
amount of liquid, which caused the data to deviate from its theoretical
predictions. We conclude by discussing the accuracy and limitation of our
proposed model.",1801.07514v5
2018-02-12,Chance-constrained optimal location of damping control actuators under wind power variability,"This paper proposes a new probabilistic energy-based method to determine the
optimal installation location of electronically-interfaced resources (EIRs)
considering dynamic reinforcement under wind variability in systems with high
penetration of wind power. The oscillation energy and total action are used to
compare the dynamic performance for different EIR locations. A linear
approximation of the total action critically reduces the computational time
from hours to minutes. Simulating an IEEE-39 bus system with 30% of power
generation sourced from wind, a chance-constrained optimization is carried out
to decide the location of an energy storage system (ESS) adding damping to the
system oscillations. The results show that the proposed method, selecting the
bus location that guarantees the best dynamic performance with highest
probability, is superior to both traditional dominant mode analysis and
arbitrary benchmarks for damping ratios.",1802.04354v1
2018-02-21,On the vibron-polaron damping in quasi 1D macromolecular chains,"The properties of the intramolecular vibrational excitation (vibron) in a
quasi 1D macromolecular structure are studied. It is supposed that due to the
vibron interaction with optical phonon modes, a vibron might form partially
dressed small polaron states. The properties of these states are investigated
in dependence on the basic system parameters and temperature of a thermal bath.
We also investigate the process of damping of the polaron amplitude as a
function of temperature and vibron-phonon coupling strength. Two different
regimes of the polaron damping are found and discussed.",1802.07424v1
2018-02-27,Impact of damping on superconducting gap oscillations induced by intense Terahertz pulses,"We investigate the interplay between gap oscillations and damping in the
dynamics of superconductors taken out of equilibrium by strong optical pulses
with sub-gap Terahertz frequencies. A semi-phenomenological formalism is
developed to include the damping within the electronic subsystem that arises
from effects beyond BCS, such as interactions between Bogoliubov quasiparticles
and decay of the Higgs mode. Such processes are conveniently expressed as
$T_{1}$ and $T_{2}$ times in the standard pseudospin language for
superconductors. Comparing with data on NbN that we report here, we argue that
the superconducting dynamics in the picosecond time scale, after the pump is
turned off, is governed by the $T_{2}$ process.",1802.09711v2
2018-02-28,Analysis of imperfections in the coherent optical excitation of single atoms to Rydberg states,"We study experimentally various physical limitations and technical
imperfections that lead to damping and finite contrast of optically-driven Rabi
oscillations between ground and Rydberg states of a single atom. Finite
contrast is due to preparation and detection errors and we show how to model
and measure them accurately. Part of these errors originates from the finite
lifetime of Rydberg states and we observe its $n^3$-scaling with the principal
quantum number $n$. To explain the damping of Rabi oscillations, we use simple
numerical models, taking into account independently measured experimental
imperfections, and show that the observed damping actually results from the
accumulation of several small effects, each at the level of a few percents. We
discuss prospects for improving the coherence of ground-Rydberg Rabi
oscillations in view of applications in quantum simulation and quantum
information processing with arrays of single Rydberg atoms.",1802.10424v1
2018-03-07,Connecting dissipation and noncommutativity: A Bateman system case study,"Quantum effects on a pair of Bateman oscillators embedded in an ambient
noncommutative space (Moyal plane) is analyzed using both path integral and
canonical quantization schemes within the framework of Hilbert-Schmidt operator
formulation. We adopt a method which is distinct from the one which employs 't
Hooft's scheme of quantization, carried out earlier in the literature where the
ambient space was taken to be commutative. Our quantization shows that we end
up finally again with a Bateman system except that the damping factor undergoes
renormalization. The corresponding expression shows that the renormalized
damping factor can be non-zero even if ""bare"" one is zero to begin with.
Conversely, the noncommuatative parameter $\theta$, taken to be a free one now,
can be fine-tuned to get a vanishing renormalized damping factor. This
indicates a duality between dissipative commutative theory and non-dissipative
noncommutative theory.",1803.03334v1
2018-03-18,A machine learning method to separate cosmic ray electrons from protons from 10 to 100 GeV using DAMPE data,"DArk Matter Particle Explorer (DAMPE) is a general purpose high energy cosmic
ray and gamma ray observatory, aiming to detect high energy electrons and
gammas in the energy range 5 GeV to 10 TeV and hundreds of TeV for nuclei. This
paper provides a method using machine learning to identify electrons and
separate them from gammas,protons,helium and heavy nuclei with the DAMPE data
from 2016 January 1 to 2017 June 30, in energy range from 10 to 100 GeV.",1803.06628v2
2018-03-20,Estimating Participation Factors and Mode Shapes for Electromechanical Oscillations in Ambient Conditions,"In this paper, a new technique is applied to conduct mode identification
using ambient measurement data. The proposed hybrid measurement- and
model-based method can accurately estimate the system state matrix in ambient
conditions, the eigenvalues and eigenvectors of which readily provide all the
modal knowledge including frequencies, damping ratios, mode shapes, and more
importantly, participation factors. Numerical simulations show that the
proposed technique is able to provide accurate estimation of modal knowledge
for all modes. In addition, the discrepancy between the participation factor
and the mode shape is shown through a numerical example, demonstrating that
using the mode shape may not effectively pinpoint the best location for damping
control. Therefore, the proposed technique capable of estimating participation
factors may greatly facilitate designing damping controls.",1803.07264v1
2018-03-21,Globally Stable Output Feedback Synchronization of Teleoperation with Time-Varying Delays,"This paper presents a globally stable teleoperation control strategy for
systems with time-varying delays that eliminates the need for velocity
measurements through novel augmented Immersion and Invariance velocity
observers. The new observers simplify a recent constructive Immersion and
Invariance velocity observer to achieve globally convergent velocity estimation
with only $n+2$ states, where $n$ is the number of degrees of freedom of the
master and slave robots. They introduce dynamic scaling factors to accelerate
the speed of convergence of the velocity estimates and, thus, to limit the
energy generated by the velocity estimation errors and to guarantee sufficient
estimate-based damping injection to dissipate the energy generated by the
time-varying delays. The paper shows that Proportional plus damping control
with the simplified and augmented Immersion and Invariance-based velocity
observers can synchronize the free master and slave motions in the presence of
time-varying delays without using velocity measurements. Numerical results
illustrate the estimation performance of the new observers and the stability of
a simulated two degrees-of-freedom nonlinear teleoperation system with
time-varying delays under the proposed output feedback Proportional plus
damping control.",1803.08159v1
2018-03-29,Stochastic conformal multi-symplectic method for damped stochastic nonlinear Schrodinger equation,"In this paper, we propose a stochastic conformal multi-symplectic method for
a class of damped stochastic Hamiltonian partial differential equations in
order to inherit the intrinsic properties, and apply the numerical method to
solve a kind of damped stochastic nonlinear Schrodinger equation with
multiplicative noise. It is shown that the stochastic conformal
multi-symplectic method preserves the discrete stochastic conformal
multi-symplectic conservation law, the discrete charge exponential dissipation
law almost surely, and we also deduce the recurrence relation of the discrete
global energy. Numerical experiments are preformed to verify the good
performance of the proposed stochastic conformal multi-symplectic method,
compared with a Crank-Nicolson type method. Finally, we present the mean square
convergence result of the proposed numerical method in temporal direction
numerically.",1803.10885v1
2018-04-01,Bounded Connectivity-Preserving Coordination of Networked Euler-Lagrange Systems,"This paper derives sufficient conditions for bounded distributed
connectivity-preserving coordination of Euler-Lagrange systems with only
position measurements and with system uncertainties, respectively. The paper
proposes two strategies that suitably scale conventional gradient-based
controls to account for the actuation bounds and to reserve sufficient
actuation for damping injection. For output feedback control of networked
systems with only position measurements, the paper incorporates a first-order
filter to estimate velocities and to inject damping for stability. For networks
of uncertain systems, the paper augments conventional linear filter-based
adaptive compensation with damping injection to maintain the local connectivity
of the network. Analyses based on monotonically decreasing Lyapunov-like
functions and Barbalat's lemma lead to sufficient conditions for bounded local
connectivity-preserving coordination of Euler-Lagrange networks under the two
strategies. The sufficient conditions clarify the interrelationships among the
bounded actuations, initial system velocities and initial inter-system
distances. Simulation results validate these conditions.",1804.00333v1
2018-04-09,Damping and clustering into crowded environment of catalytic chemical oscillators,"A system formed by a crowded environment of catalytic obstacles and complex
oscillatory chemical reactions is inquired. The obstacles are static spheres of
equal radius, which are placed in a random way. The chemical reactions are
carried out in a fluid following a multiparticle collision scheme where the
mass, energy and local momentum are conserved. Firstly, it is explored how the
presence of catalytic obstacles changes the oscillatory dynamics from a limit
cycle to a fix point reached after a damping. The damping is characterized by
the decay constant, which grows linearly with volume fraction for low values of
the mesoscale collision time and the catalytic reaction constant. Additionally,
it is shown that, although the distribution of obstacles is random, there are
regions in the system where the catalytic chemical reactions are favored. This
entails that in average the radius of gyrations of catalytic chemical reaction
does not match with the radius of gyration of obstacles, that is, clusters of
reactions emerge on the catalytic obstacles, even when the diffusion is
significant.",1804.03174v1
2018-04-11,A global existence result for a semilinear wave equation with scale-invariant damping and mass in even space dimension,"In the present article a semilinear wave equation with scale-invariant
damping and mass is considered. The global (in time) existence of radial
symmetric solutions in even spatial dimension $n$ is proved using weighted
$L^\infty-L^\infty$ estimates, under the assumption that the multiplicative
constants, which appear in the coefficients of damping and of mass terms,
fulfill an interplay condition which yields somehow a ""wave-like"" model. In
particular, combining this existence result with a recently proved blow-up
result, a suitable shift of Strauss exponent is proved to be the critical
exponent for the considered model. Moreover, the still open part of a
conjecture done by D'Abbicco - Lucente - Reissig is proved to be true in the
massless case.",1804.03978v1
2018-04-17,Modelling linewidths of Kepler red giants in NGC 6819,"We present a comparison between theoretical, frequency-dependent, damping
rates and linewidths of radial-mode oscillations in red-giant stars located in
the open cluster NGC 6819. The calculations adopt a time-dependent non-local
convection model, with the turbulent pressure profile being calibrated to
results of 3D hydrodynamical simulations of stellar atmospheres. The linewidths
are obtained from extensive peakbagging of Kepler lightcurves. These
observational results are of unprecedented quality owing to the long continuous
observations by Kepler. The uniqueness of the Kepler mission also means that,
for asteroseismic properties, this is the best data that will be available for
a long time to come. We therefore take great care in modelling nine RGB stars
in NGC 6819 using information from 3D simulations to obtain realistic
temperature stratifications and calibrated turbulent pressure profiles. Our
modelled damping rates reproduce well the Kepler observations, including the
characteristic depression in the linewidths around the frequency of maximum
oscillation power. Furthermore, we thoroughly test the sensitivity of the
calculated damping rates to changes in the parameters of the nonlocal
convection model.",1804.06255v1
2018-04-24,$\text{Co}_{25}\text{Fe}_{75}$ Thin Films with Ultralow Total Damping,"We measure the dynamic properties of $\text{Co}_{25}\text{Fe}_{75}$ thin
films grown by dc magnetron sputtering. Using ferromagnetic resonance
spectroscopy, we demonstrate an ultralow total damping parameter in the
out-of-plane configuration of < 0.0013, whereas for the in-plane configuration
we find a minimum total damping of < 0.0020. In both cases, we observe low
inhomogeneous linewidth broadening in macroscopic films. We observe a minimum
full-width half-maximum linewidth of 1 mT at 10 GHz resonance frequency for a
12 nm thick film. We characterize the morphology and structure of these films
as a function of seed layer combinations and find large variation of the
qualitative behavior of the in-plane linewidth vs. resonance frequency.
Finally, we use wavevector-dependent Brillouin light scattering spectroscopy to
characterize the spin-wave dispersion at wave vectors up to 23 $\mu
\text{m}^{-1}$.",1804.08786v1
2018-05-15,Simple Nonlinear Models with Rigorous Extreme Events and Heavy Tails,"Extreme events and the heavy tail distributions driven by them are ubiquitous
in various scientific, engineering and financial research. They are typically
associated with stochastic instability caused by hidden unresolved processes.
Previous studies have shown that such instability can be modeled by a
stochastic damping in conditional Gaussian models. However, these results are
mostly obtained through numerical experiments, while a rigorous understanding
of the underlying mechanism is sorely lacking. This paper contributes to this
issue by establishing a theoretical framework, in which the tail density of
conditional Gaussian models can be rigorously determined. In rough words, we
show that if the stochastic damping takes negative values, the tail is
polynomial; if the stochastic damping is nonnegative but takes value zero, the
tail is between exponential and Gaussian. The proof is established by
constructing a novel, product-type Lyapunov function, where a Feynman-Kac
formula is applied. The same framework also leads to a non-asymptotic large
deviation bound for long-time averaging processes.",1805.05615v3
2018-06-18,Theoretical interpretations of DAMPE first results: a critical review,"The DAMPE experiment recently published its first results on the lepton ($e^+
+ e^-$) cosmic-ray (CRs) flux. These results are of importance since they
account for the first direct detection of the lepton break around the energy of
1 TeV and confirm the discoveries of ground-based Cherenkov detectors.
Meanwhile they reveal a new high-energy feature in the spectrum which triggered
a lot of excitement on the theory side, when interpreted as the typical
signature of leptophilic dark-matter annihilation. In this proceeding I mainly
focus on the theoretical understanding of the lepton break. Then I quickly
review the status of the more speculative line-like DAMPE excess, whose
astrophysical (pulsar) or exotic (dark matter) explanation is strongly
constrained by multi-messenger astronomy.",1806.06534v1
2018-06-22,Optimal Design of Virtual Inertia and Damping Coefficients for Virtual Synchronous Machines,"Increased penetration of inverter-connected renewable energy sources (RES) in
the power system has resulted in a decrease in available rotational inertia
which serves as an immediate response to frequency deviation due to
disturbances. The concept of virtual inertia has been proposed to combat this
decrease by enabling the inverters to produce active power in response to a
frequency deviation like a synchronous generator. In this paper, we present an
algorithm to optimally design the inertia and damping coefficient required for
an inverter-based virtual synchronous machine (VSM) to participate efficiently
in the inertia response portion of primary frequency control. We design the
objective function to explicitly trade-off between competing objectives such as
the damping rate the the frequency nadir. Specifically, we formulate the design
problem as a constrained and regularized H2 norm minimization problem, and
develop an efficient gradient algorithm for this non-convex problem. This
proposed algorithm is applied to a test case to demonstrate its performance
against existing methods.",1806.08488v1
2018-07-17,Bipartite and Tripartite Entanglement for Three Damped Driven Qubits,"We investigate bipartite and tripartite entanglement in an open quantum
system, specifically three qubits, all of which are damped, and one of which is
driven. We adapt a systematic approach in calculating the entanglement of
various bipartite splits usinga generalized concurrence as an indicator of
entanglement. Our calculations are based on a direct detection scheme that is a
particular unravelling of the density matrix. This system has a collective
dipole-dipole energy shift that couples the atoms and the dissipation is via
partially collective spontaneous emission described by the Lehmberg-Agarwal
master equation.Our results are unravelling dependent, but apply to
applications of entanglement based on direct detection. We also calculate the
three-way tangle or residual entanglement for this system. We present
calculations for a variety of driving and damping rates, and examine what decay
rate is adequate for the system to be reduced to two qubits with a readout
port. We also consider a specific model of three atoms located at particular
positions in free space.",1807.06178v1
2018-07-17,Boundary-to-Displacement Asymptotic Gains for Wave Systems With Kelvin-Voigt Damping,"We provide estimates for the asymptotic gains of the displacement of a
vibrating string with endpoint forcing, modeled by the wave equation with
Kelvin-Voigt and viscous damping and a boundary disturbance. Two asymptotic
gains are studied: the gain in the L2 spatial norm and the gain in the spatial
sup norm. It is shown that the asymptotic gain property holds in the L2 norm of
the displacement without any assumption for the damping coefficients. The
derivation of the upper bounds for the asymptotic gains is performed by either
employing an eigenfunction expansion methodology or by means of a small-gain
argument, whereas a novel frequency analysis methodology is employed for the
derivation of the lower bounds for the asymptotic gains. The graphical
illustration of the upper and lower bounds for the gains shows that that the
asymptotic gain in the L2 norm is estimated much more accurately than the
asymptotic gain in the sup norm.",1807.06549v1
2018-07-24,Stabilization of an unstable wave equation using an infinite dimensional dynamic controller,"This paper deals with the stabilization of an anti-stable string equation
with Dirichlet actuation where the instability appears because of the
uncontrolled boundary condition. Then, infinitely many unstable poles are
generated and an infinite dimensional control law is therefore proposed to
exponentially stabilize the system. The idea behind the choice of the
controller is to extend the domain of the PDE so that the anti-damping term is
compensated by a damping at the other boundary condition. Additionally, notice
that the system can then be exponentially stabilized with a chosen decay-rate
and is robust to uncertainties on the wave speed and the anti-damped
coefficient of the wave equation, with the only use of a point-wise boundary
measurement. The efficiency of this new control strategy is then compared to
the backstepping approach.",1807.08999v2
2018-07-24,Interplay between intermittency and dissipation in collisionless plasma turbulence,"We study the damping of collisionless Alfv\'enic turbulence by two
mechanisms: stochastic heating (whose efficiency depends on the local
turbulence amplitude $\delta z_\lambda$) and linear Landau damping (whose
efficiency is independent of $\delta z_\lambda$), describing in detail how they
affect and are affected by intermittency. The overall efficiency of linear
Landau damping is not affected by intermittency in critically balanced
turbulence, while stochastic heating is much more efficient in the presence of
intermittent turbulence. Moreover, stochastic heating leads to a drop in the
scale-dependent kurtosis over a narrow range of scales around the ion
gyroscale.",1807.09301v2
2018-07-31,Input-to-State Stability of a Clamped-Free Damped String in the Presence of Distributed and Boundary Disturbances,"This note establishes the Exponential Input-to-State Stability (EISS)
property for a clamped-free damped string with respect to distributed and
boundary disturbances. While efficient methods for establishing ISS properties
for distributed parameter systems with respect to distributed disturbances have
been developed during the last decades, establishing ISS properties with
respect to boundary disturbances remains challenging. One of the well-known
methods for well-posedness analysis of systems with boundary inputs is the use
of a lifting operator for transferring the boundary disturbance to a
distributed one. However, the resulting distributed disturbance involves time
derivatives of the boundary perturbation. Thus, the subsequent ISS estimate
depends on its amplitude, and may not be expressed in the strict form of ISS
properties. To solve this problem, we show for a clamped-free damped string
equation that the projection of the original system trajectories in an adequate
Riesz basis can be used to establish the desired EISS property.",1807.11696v2
2018-07-31,Spin absorption at ferromagnetic-metal/platinum-oxide interface,"We investigate the absorption of a spin current at a
ferromagnetic-metal/Pt-oxide interface by measuring current-induced
ferromagnetic resonance. The spin absorption was characterized by the magnetic
damping of the heterostructure. We show that the magnetic damping of a
Ni$_{81}$Fe$_{19}$ film is clearly enhanced by attaching Pt-oxide on the
Ni$_{81}$Fe$_{19}$ film. The damping enhancement is disappeared by inserting an
ultrathin Cu layer between the Ni$_{81}$Fe$_{19}$ and Pt-oxide layers. These
results demonstrate an essential role of the direct contact between the
Ni$_{81}$Fe$_{19}$ and Pt-oxide to induce sizable interface spin-orbit
coupling. Furthermore, the spin-absorption parameter of the
Ni$_{81}$Fe$_{19}$/Pt-oxide interface is comparable to that of intensively
studied heterostructures with strong spin-orbit coupling, such as an oxide
interface, topological insulators, metallic junctions with Rashba spin-orbit
coupling. This result illustrates strong spin-orbit coupling at the
ferromagnetic-metal/Pt-oxide interface, providing an important piece of
information for quantitative understanding the spin absorption and spin-charge
conversion at the ferromagnetic-metal/metallic-oxide interface.",1807.11806v1
2018-08-16,Stability analysis of dissipative systems subject to nonlinear damping via Lyapunov techniques,"In this article, we provide a general strategy based on Lyapunov functionals
to analyse global asymptotic stability of linear infinite-dimensional systems
subject to nonlinear dampings under the assumption that the origin of the
system is globally asymp-totically stable with a linear damping. To do so, we
first characterize, in terms of Lyapunov functionals, several types of
asymptotic stability for linear infinite-dimensional systems, namely the
exponential and the polynomial stability. Then, we derive a Lyapunov functional
for the nonlinear system, which is the sum of a Lyapunov functional coming from
the linear system and another term with compensates the nonlinearity. Our
results are then applied to the linearized Korteweg-de Vries equation and some
wave equations.",1808.05370v1
2018-08-30,The influence of the coefficients of a system of coupled wave equations with fractional damping on its stabilization,"In this work, we consider a system of two wave equations coupled by
velocities in one-dimensional space, with one boundary fractional damping.
First, we show that the system is strongly asymptotically stable if and only if
the coupling parameter b of the two equations is outside a discrete set of
exceptional real values. Next, we show that our system is not uniformly stable.
Hence, we look for a polynomial decay rate for smooth initial data. Using
frequency domain approach combining with multiplier method, we prove that the
energy decay rate is greatly influenced by the nature of the coupling parameter
b, the arithmetic property of the ratio of the wave propagation speeds a, the
order of the fractional damping. Indeed, under the equal speed propagation
condition, we establish an optimal polynomial energy decay rate. Furthermore,
when the wave propagate with different speeds, under some arithmetic conditions
on the ratio of the wave propagation speeds, we prove that the energy of our
system decays polynomially to zero.",1808.10285v4
2018-09-05,On the forced Euler and Navier-Stokes equations: Linear damping and modified scattering,"We study the asymptotic behavior of the forced linear Euler and nonlinear
Navier-Stokes equations close to Couette flow in a periodic channel. As our
main result we show that for smooth time-periodic forcing linear inviscid
damping persists, i.e. the velocity field (weakly) asymptotically converges.
However, stability and scattering to the transport problem fail in $H^{s},
s>-1$. We further show that this behavior is consistent with the nonlinear
Euler equations and that a similar result also holds for the nonlinear
Navier-Stokes equations. Hence, these results provide an indication that
nonlinear inviscid damping may still hold in Sobolev regularity in the above
sense despite the Gevrey regularity instability results of [Deng-Masmoudi
2018].",1809.01729v1
2018-09-12,Theory of bifurcation amplifiers utilizing the nonlinear dynamical response of an optically damped mechanical oscillator,"We consider a standard optomechanical system where a mechanical oscillator is
coupled to a cavity mode through the radiation pressure interaction. The
oscillator is coherently driven at its resonance frequency, whereas the cavity
mode is driven below its resonance, providing optical damping of the mechanical
oscillations. We study the nonlinear coherent response of the mechanical
oscillator in this setup. For large mechanical amplitudes, we find that the
system can display dynamical multistability if the optomechanical cooperativity
exceeds a critical value. This analysis relates standard optomechanical damping
to the dynamical attractors known from the theory of optomechanical
self-sustained oscillations. We also investigate the effect of thermal and
quantum noise and estimate the noise-induced switching rate between the stable
states of the system. We then consider applications of this system and
primarily focus on how it can be used as bifurcation amplifiers for the
detection of small mechanical or optical signals. Finally, we show that in a
related but more complicated setup featuring resonant optomechanical
interactions, the same effects can be realized with a relaxed requirement on
the size of the mechanical oscillations.",1809.04592v2
2018-09-13,Second order asymptotical regularization methods for inverse problems in partial differential equations,"We develop Second Order Asymptotical Regularization (SOAR) methods for
solving inverse source problems in elliptic partial differential equations with
both Dirichlet and Neumann boundary data. We show the convergence results of
SOAR with the fixed damping parameter, as well as with a dynamic damping
parameter, which is a continuous analog of Nesterov's acceleration method.
Moreover, by using Morozov's discrepancy principle together with a newly
developed total energy discrepancy principle, we prove that the approximate
solution of SOAR weakly converges to an exact source function as the
measurement noise goes to zero. A damped symplectic scheme, combined with the
finite element method, is developed for the numerical implementation of SOAR,
which yields a novel iterative regularization scheme for solving inverse source
problems. Several numerical examples are given to show the accuracy and the
acceleration effect of SOAR. A comparison with the state-of-the-art methods is
also provided.",1809.04971v2
2018-09-24,Oscillation Damping Control of Pendulum-like Manipulation Platform using Moving Masses,"This paper presents an approach to damp out the oscillatory motion of the
pendulum-like hanging platform on which a robotic manipulator is mounted. To
this end, moving masses were installed on top of the platform. In this paper,
asymptotic stability of the platform (which implies oscillation damping) is
achieved by designing reference acceleration of the moving masses properly. A
main feature of this work is that we can achieve asymptotic stability of not
only the platform, but also the moving masses, which may be challenging due to
the under-actuation nature. The proposed scheme is validated by the simulation
studies.",1809.08819v1
2018-07-16,A unified N-SECE strategy for highly coupled piezoelectric energy scavengers,"This paper proposes a novel vibration energy harvesting strategy based on an
extension of the Synchronous Electric Charge Extraction (SECE) approach,
enabling both the maximization of the harvested power and a consequent
bandwidth enlargement in the case of highly coupled/lightly damped
piezoelectric energy harvesters. The proposed strategy relies on the tuning of
the frequency of the energy extraction events, which is either N times greater
than the vibration frequency (Multiple SECE case, N > 1) or 1/N times smaller
(Regenerative SECE, N < 1). We first prove analytically than increasing or
decreasing N both lead to a damping reduction. While N has no impact on the
system's resonance frequency in the Regenerative case (N < 1), we show that
this resonant frequency becomes a function of N in the Multiple SECE case (N >
1). Experimental results on a highly coupled/lowly damped piezoelectric
harvester (k^2= 0.44, Q_m = 20) demonstrates the potential of this strategy,
leading to 257% harvested power improvement compared to SECE (N = 1). and the
possibility to tune the resonant frequency on a range as large as 35% of the
short-circuit resonant frequency of the harvester.",1809.09685v1
2018-10-09,The lifespan of solutions of semilinear wave equations with the scale-invariant damping in one space dimension,"The critical constant of time-decaying damping in the scale-invariant case is
recently conjectured. It also has been expected that the lifespan estimate is
the same as for the associated semilinear heat equations if the constant is in
the \heat-like"" domain. In this paper, we point out that this is not true if
the total integral of the sum of initial position and speed vanishes. In such a
case, we have a new type of the lifespan estimates which is closely related to
the non-damped case in shifted space dimensions.",1810.03780v2
2018-10-24,Justification of the Lugiato-Lefever model from a damped driven $φ^4$ equation,"The Lugiato-Lefever equation is a damped and driven version of the well-known
nonlinear Schr\""odinger equation. It is a mathematical model describing complex
phenomena in dissipative and nonlinear optical cavities. Within the last two
decades, the equation has gained a wide attention as it becomes the basic model
describing optical frequency combs. Recent works derive the Lugiato-Lefever
equation from a class of damped driven $\phi^4$ equations closed to resonance.
In this paper, we provide a justification of the envelope approximation. From
the analysis point of view, the result is novel and non-trivial as the drive
yields a perturbation term that is not square integrable. The main approach
proposed in this work is to decompose the solutions into a combination of the
background and the integrable component. This paper is the first part of a
two-manuscript series.",1810.10630v1
2018-11-06,Decay properties and asymptotic profiles for elastic waves with Kelvin-Voigt damping in 2D,"In this paper we consider elastic waves with Kelvin-Voigt damping in 2D. For
the linear problem, applying pointwise estimates of the partial Fourier
transform of solutions in the Fourier space and asymptotic expansions of
eigenvalues and their eigenprojections, we obtain sharp energy decay estimates
with additional $L^m$ regularity and $L^p-L^q$ estimates on the conjugate line.
Furthermore, we derive asymptotic profiles of solutions under different
assumptions of initial data. For the semilinear problem, we use the derived
$L^2-L^2$ estimates with additional $L^m$ regularity to prove global (in time)
existence of small data solutions to the weakly coupled system. Finally, to
deal with elastic waves with Kelvin-Voigt damping in 3D, we apply the Helmholtz
decomposition.",1811.02223v3
2018-12-06,Damping and Anti-Damping Phenomena in Metallic Antiferromagnets: An ab-initio Study,"We report on a first principles study of anti-ferromagnetic resonance (AFMR)
phenomena in metallic systems [MnX (X=Ir,Pt,Pd,Rh) and FeRh] under an external
electric field. We demonstrate that the AFMR linewidth can be separated into a
relativistic component originating from the angular momentum transfer between
the collinear AFM subsystem and the crystal through the spin orbit coupling
(SOC), and an exchange component that originates from the spin exchange between
the two sublattices. The calculations reveal that the latter component becomes
significant in the low temperature regime. Furthermore, we present results for
the current-induced intersublattice torque which can be separated into the
Field-Like (FL) and Damping-Like (DL) components, affecting the intersublattice
exchange coupling and AFMR linewidth, respectively.",1812.02844v2
2018-12-12,Extreme wave events for a nonlinear Schrödinger equation with linear damping and Gaussian driving,"We perform a numerical study of the initial-boundary value problem, with
vanishing boundary conditions, of a driven nonlinear Schr\""odinger equation
(NLS) with linear damping and a Gaussian driver. We identify Peregrine-like
rogue waveforms, excited by two different types of vanishing initial data
decaying at an algebraic or exponential rate. The observed extreme events
emerge on top of a decaying support. Depending on the spatial/temporal scales
of the driver, the transient dynamics -- prior to the eventual decay of the
solutions -- may resemble the one in the semiclassical limit of the integrable
NLS, or may, e.g., lead to large-amplitude breather-like patterns. The effects
of the damping strength and driving amplitude, in suppressing or enhancing
respectively the relevant features, as well as of the phase of the driver in
the construction of a diverse array of spatiotemporal patterns, are numerically
analyzed.",1812.05439v3
2018-12-13,Stability of elastic transmission systems with a local Kelvin-Voigt damping,"In this paper, we consider the longitudinal and transversal vibrations of the
transmission Euler-Bernoulli beam with Kelvin-Voigt damping distributed locally
on any subinterval of the region occupied by the beam and only in one side of
the transmission point. We prove that the semigroup associated with the
equation for the transversal motion of the beam is exponentially stable,
although the semigroup associated with the equation for the longitudinal motion
of the beam is polynomially stable. Due to the locally distributed and
unbounded nature of the damping, we use a frequency domain method and combine a
contradiction argument with the multiplier technique to carry out a special
analysis for the resolvent.",1812.05923v1
2018-12-13,Energy decay estimates of elastic transmission wave/beam systems with a local Kelvin-Voigt damping,"We consider a beam and a wave equations coupled on an elastic beam through
transmission conditions. The damping which is locally distributed acts through
one of the two equations only; its effect is transmitted to the other equation
through the coupling. First we consider the case where the dissipation acts
through the beam equation. Using a recent result of Borichev and Tomilov on
polynomial decay characterization of bounded semigroups we provide a precise
decay estimates showing that the energy of this coupled system decays
polynomially as the time variable goes to infinity. Second, we discuss the case
where the damping acts through the wave equation. Proceeding as in the first
case, we prove that this system is also polynomially stable and we provide
precise polynomial decay estimates for its energy. Finally, we show the lack of
uniform exponential decay of solutions for both models.",1812.05924v1
2018-12-20,Sound attenuation in stable glasses,"Understanding the difference between universal low-temperature properties of
amorphous and crystalline solids requires an explanation of the stronger
damping of long-wavelength phonons in amorphous solids. A longstanding sound
attenuation scenario, resulting from a combination of experiments, theories,
and simulations, leads to a quartic scaling of sound attenuation with the
wavevector, which is commonly attributed to Rayleigh scattering of the sound.
Modern computer simulations offer conflicting conclusions regarding the
validity of this picture. We simulate glasses with an unprecedentedly broad
range of stabilities to perform the first microscopic analysis of sound damping
in model glass formers across a range of experimentally relevant preparation
protocols. We present a convincing evidence that quartic scaling is recovered
for small wavevectors irrespective of the glass's stability. With increasing
stability, the wavevector where the quartic scaling begins increases by
approximately a factor of three and the sound attenuation decreases by over an
order of magnitude. Our results uncover an intimate connection between glass
stability and sound damping.",1812.08736v2
2018-12-21,"Reply to the Comment on ""Negative Landau damping in bilayer graphene""","Here we address the concerns of Svintsov and Ryzhii [arXiv:1812.03764] on our
article on negative Landau damping in graphene [Phys. Rev. Lett. 119, 133901
(2017)]. We prove that due to the differences between the kinetic and canonical
momenta, the conductivity of drift-current biased graphene is ruled by a
Galilean transformation when the electron-electron interactions predominate and
force the electron gas to move with constant velocity, similar to a moving
medium. Furthermore, it is shown that the nonlocal effects in graphene neither
preclude a negative Landau damping nor the emergence of instabilities in
graphene platforms.",1812.09103v3
2018-12-27,Nonexistence of global solutions for a weakly coupled system of semilinear damped wave equations of derivative type in the scattering case,"In this paper we consider the blow-up for solutions to a weakly coupled
system of semilinear damped wave equations of derivative type in the scattering
case. After introducing suitable functionals proposed by Lai-Takamura for the
corresponding single semilinear equation, we employ Kato's lemma to derive the
blow-up result in the subcritical case. On the other hand, in the critical case
an iteration procedure based on the slicing method is employed. Let us point
out that we find as critical curve in the p-q plane for the pair of exponents
(p, q) in the nonlinear terms the same one as for the weakly coupled system of
semilinear not-damped wave equations with the same kind of nonlinearities.",1812.10653v1
2018-12-30,"Smooth, Time-invariant Regulation of Nonholonomic Systems via Energy Pumping-and-Damping","In this paper we propose an energy pumping-and-damping technique to regulate
nonholonomic systems described by kinematic models. The controller design
follows the widely popular interconnection and damping assignment
passivity-based methodology, with the free matrices partially structured. Two
asymptotic regulation objectives are considered: drive to zero the state or
drive the systems total energy to a desired constant value. In both cases, the
control laws are smooth, time-invariant, state-feedbacks. For the nonholonomic
integrator we give an almost global solution for both problems, with the
objectives ensured for all system initial conditions starting outside a set
that has zero Lebesgue measure and is nowhere dense. For the general case of
higher-order nonholonomic systems in chained form, a local stability result is
given. Simulation results comparing the performance of the proposed controller
with other existing designs are also provided.",1812.11538v2
2019-01-05,Simulations of wobble damping in viscoelastic rotators,"Using a damped mass-spring model, we simulate wobble of spinning homogeneous
viscoelastic ellipsoids undergoing non-principal axis rotation. Energy damping
rates are measured for oblate and prolate bodies with different spin rates,
spin states, viscoelastic relaxation timescales, axis ratios, and strengths.
Analytical models using a quality factor by Breiter et al. (2012) and for the
Maxwell rheology by Frouard & Efroimsky (2018) match our numerical measurements
of the energy dissipation rate after we modify their predictions for the
numerically simulated Kelvin-Voigt rheology. Simulations of nearly spherical
but wobbling bodies with hard and soft cores show that the energy dissipation
rate is more sensitive to the material properties in the core than near the
surface. The sensitivity to viscoelastic model implies that inferred statistics
of tumbling lifetimes in asteroids might be interpreted in terms of differences
in their material properties.",1901.01439v3
2019-01-16,"Laboratory investigations of the bending rheology of floating saline ice, and physical mechanisms of wave damping, in the HSVA ice tank","An experiment on the propagation of flexural-gravity waves was performed in
the HSVA ice tank. Physical characteristics of the water-ice system were
measured in different locations in the tank during the tests, with a number of
sensors deployed in the water, on the ice and in the air. Water velocity was
measured with an acoustic doppler velocimeter (ADV) and an acoustic doppler
current profiler (ADCP); wave amplitudes were measured with ultrasonic sensors
and the optical system Qualisys; in-plane deformations of the ice and the
temperature of the ice and water were measured by fiber optic sensors, and
acoustic emissions were recorded with compressional crystal sensors. All
together 61 tests were performed, with ice thicknesses of 3 cm and 5 cm. The
experimental setup and selected results of the tests are discussed in this
paper. We show that cyclic motion of the ice along the tank, imitating ice
drift, causes an increase in wave damping. We also show that the formation of
non-through cracks in the ice, caused by the action of waves, increases wave
damping.",1901.05333v1
2019-01-24,Generalized framework for testing gravity with gravitational-wave propagation. III. Future prospect,"The properties of gravitational-wave (GW) propagation are modified in
alternative theories of gravity and are crucial observables to test gravity at
cosmological distance. The propagation speed has already been measured from
GW170817 so precisely and pinned down to the speed of light, while other
properties of GW propagation have not constrained tightly yet. In this paper,
we investigate the measurement precisions of the amplitude damping rate
(equivalently, the time variation of the gravitational coupling for GWs) and
graviton mass in the generalized framework of GW propagation with the future
detectors such as Voyager, Cosmic Explorer, and Einstein Telescope. As a
result, we show that the future GW observation can reach 1% error for the
amplitude damping. We also study the time variation of the gravitational
couplings in Horndeski theory by performing Monte Carlo-based numerical
simulations. From the simulation results, we find that the current accelerating
Universe prefers the models with less damping of GWs and that the equivalence
principle can be tested at the level of 1% by the future GW observation.",1901.08249v2
2019-01-31,Perturbed Markov Chains and Information Networks,"The paper is devoted to studies of perturbed Markov chains commonly used for
description of information networks. In such models, the matrix of transition
probabilities for the corresponding Markov chain is usually regularised by
adding a special damping matrix multiplied by a small damping (perturbation)
parameter $\varepsilon$. We give effective upper bounds for the rate of
approximation for stationary distributions of unperturbed Markov chains by
stationary distributions of perturbed Markov chains with regularised matrices
of transition probabilities, asymptotic expansions for approximating stationary
distributions with respect to damping parameter, as well as explicit upper
bounds for the rate of convergence in ergodic theorems for $n$-step transition
probabilities in triangular array mode, where perturbation parameter
$\varepsilon \to 0$ and $n \to \infty$, simultaneously. The results of
numerical experiments are also presented",1901.11483v3
2019-02-14,Dynamic Interconnection and Damping Injection for Input-to-State Stable Bilateral Teleoperation,"In bilateral teleoperation, the human who operates the master and the
environment which interacts with the slave are part of the force feedback loop.
Yet, both have time-varying and unpredictable dynamics and are challenging to
model. A conventional strategy for sidestepping the demand for their models in
the stability analysis is to assume passive user and environment, and to
control the master-communications-slave system to be passive as well. This
paper circumvents the need to model the user and environment in a novel way: it
regards their forces as external excitations for a semi-autonomous force
feedback loop, which it outfits with a dynamic interconnection and damping
injection controller that renders bilateral teleoperation with time-varying
delays exponentially input-to-state stable. The controller uses the position
and velocity measurements of the local robot and the delayed position
transmitted from the other robot to robustly synchronize the master and slave
under the user and environment perturbations. Lyapunov-Krasovskii stability
analysis shows that the proposed strategy (i) can confine the position error
between the master and slave to an invariant set, and (ii) can drive it
exponentially to a globally attractive set. Thus, the dynamic interconnection
and damping injection approach has practical relevance for telemanipulation
tasks with given precision requirements.",1902.05500v1
2019-02-15,Evidence for Electron Landau Damping in Space Plasma Turbulence,"How turbulent energy is dissipated in weakly collisional space and
astrophysical plasmas is a major open question. Here, we present the
application of a field-particle correlation technique to directly measure the
transfer of energy between the turbulent electromagnetic field and electrons in
the Earth's magnetosheath, the region of solar wind downstream of the Earth's
bow shock. The measurement of the secular energy transfer from the parallel
electric field as a function of electron velocity shows a signature consistent
with Landau damping. This signature is coherent over time, close to the
predicted resonant velocity, similar to that seen in kinetic Alfv\'en
turbulence simulations, and disappears under phase randomisation. This suggests
that electron Landau damping could play a significant role in turbulent plasma
heating, and that the technique is a valuable tool for determining the particle
energisation processes operating in space and astrophysical plasmas.",1902.05785v1
2019-02-22,Thermal induced monochromatic microwave generation in magnon-polariton,"We propose thermal induced generation of monochromatic microwave radiation in
magnon-polariton. Mechanism of thermal to microwave energy transformation is
based on intrinsic energy loss compensation of coupled magnon and microwave
cavity oscillators by thermal induced ""negative damping"". A singularity at an
exceptional point is achieved when at the critical value of ""negative damping""
the damping of the system is fully compensated. At the exceptional point, the
input energy is equally distributed between the magnon and photon subsystems of
the magnon-polariton. The efficiency of transformation of thermal energy into
useful microwave radiation is estimated to be as large as 17 percent due to
magnon-photon coupling mediated direct conversation of spin current into
microwave photons.",1902.08383v1
2019-03-04,Nonlinear inviscid damping for zero mean perturbation of the 2D Euler Couette flow,"In this note we revisit the proof of Bedrossian and Masmoudi
[arXiv:1306.5028] about the inviscid damping of planar shear flows in the 2D
Euler equations under the assumption of zero mean perturbation. We prove that a
small perturbation to the 2D Euler Couette flow in $\mathbb{T}\times
\mathbb{R}$ strongly converge to zero, under the additional assumption that the
average in $x$ is always zero. In general the mean is not a conserved quantity
for the nonlinear dynamics, for this reason this is a particular case.
Nevertheless our assumption allow the presence of echoes in the problem, which
we control by an approximation of the weight built in [arXiv:1306.5028]. The
aim of this note is to present the mathematical techniques used in
[arXiv:1306.5028] and can be useful as a first approach to the nonlinear
inviscid damping.",1903.01543v1
2019-03-10,Orbital stabilization of nonlinear systems via Mexican sombrero energy shaping and pumping-and-damping injection,"In this paper we show that a slight modification to the widely popular
interconnection and damping assignment passivity-based control
method---originally proposed for stabilization of equilibria of nonlinear
systems---allows us to provide a solution to the more challenging orbital
stabilization problem. Two different, though related, ways how this procedure
can be applied are proposed. First, the assignment of an energy function that
has a minimum in a closed curve, i.e., with the shape of a Mexican sombrero.
Second, the use of a damping matrix that changes ""sign"" according to the
position of the state trajectory relative to the desired orbit, that is,
pumping or dissipating energy. The proposed methodologies are illustrated with
the example of the induction motor and prove that it yields the industry
standard field oriented control.",1903.04070v3
2019-03-11,Impact of thermal effects on the evolution of eccentricity and inclination of low-mass planets,"Using linear perturbation theory, we evaluate the time-dependent force
exerted on an eccentric and inclined low-mass planet embedded in a gaseous
protoplanetary disc with finite thermal diffusivity $\chi$. We assume the
eccentricity and inclination to be small compared to the size of the thermal
lobes $\lambda\sim(\chi/\Omega)^{1/2}$, itself generally much smaller than the
scalelength of pressure $H$. When the planet is non-luminous, we find that its
eccentricity and inclination are vigorously damped by the disc, over a
timescale shorter by a factor $H/\lambda$ than the damping timescale in
adiabatic discs. On the contrary, when the luminosity-to-mass ratio of the
planet exceeds a threshold that depends on the disc's properties, its
eccentricity and inclination undergo an exponential growth. In the limit of a
large luminosity, the growth rate of the eccentricity is 2.5~times larger than
that of the inclination, in agreement with previous numerical work. Depending
on their luminosity, planetary embryos therefore exhibit much more diverse
behaviours than the mild damping of eccentricity and inclination considered
hitherto.",1903.04470v2
2019-03-14,The Strichartz estimates for the damped wave equation and the behavior of solutions for the energy critical nonlinear equation,"For the linear damped wave equation (DW), the $L^p$-$L^q$ type estimates have
been well studied. Recently, Watanabe showed the Strichartz estimates for DW
when $d=2,3$. In the present paper, we give Strichartz estimates for DW in
higher dimensions. Moreover, by applying the estimates, we give the local
well-posedness of the energy critical nonlinear damped wave equation (NLDW)
$\partial_t^2 u - \Delta u +\partial_t u = |u|^{\frac{4}{d-2}}u$, $(t,x) \in
[0,T) \times \mathbb{R}^d$, where $3 \leq d \leq 5$. Especially, we show the
small data global existence for NLDW. In addition, we investigate the behavior
of the solutions to NLDW. Namely, we give a decay result for solutions with
finite Strichartz norm and a blow-up result for solutions with negative Nehari
functional.",1903.05887v1
2019-04-17,Decays for Kelvin-Voigt damped wave equations I : the black box perturbative method,"We show in this article how perturbative approaches~from our work with Hitrik
(see also the work by Anantharaman-Macia) and the {\em black box} strategy
from~ our work with Zworski allow to obtain decay rates for Kelvin-Voigt damped
wave equations from quite standard resolvent estimates : Carleman estimates or
geometric control estimates for Helmoltz equationCarleman or other resolvent
estimates for the Helmoltz equation. Though in this context of Kelvin Voigt
damping, such approach is unlikely to allow for the optimal results when
additional geometric assumptions are considered (see \cite{BuCh, Bu19}), it
turns out that using this method, we can obtain the usual logarithmic decay
which is optimal in general cases. We also present some applications of this
approach giving decay rates in some particular geometries (tori).",1904.08318v2
2019-04-17,Non-Hermitian skin effect and chiral damping in open quantum systems,"One of the unique features of non-Hermitian Hamiltonians is the non-Hermitian
skin effect, namely that the eigenstates are exponentially localized at the
boundary of the system. For open quantum systems, a short-time evolution can
often be well described by the effective non-Hermitian Hamiltonians, while
long-time dynamics calls for the Lindblad master equations, in which the
Liouvillian superoperators generate time evolution. In this Letter, we find
that Liouvillian superoperators can exhibit the non-Hermitian skin effect, and
uncover its unexpected physical consequences. It is shown that the
non-Hermitian skin effect dramatically shapes the long-time dynamics, such that
the damping in a class of open quantum systems is algebraic under periodic
boundary condition but exponential under open boundary condition. Moreover, the
non-Hermitian skin effect and non-Bloch bands cause a chiral damping with a
sharp wavefront. These phenomena are beyond the effective non-Hermitian
Hamiltonians; instead, they belong to the non-Hermitian physics of full-fledged
open quantum dynamics.",1904.08432v2
2019-04-19,Plasmon-Emitter Interactions at the Nanoscale,"Plasmon-emitter interactions are of paramount importance in modern
nanoplasmonics and are generally maximal at short emitter-surface separations.
However, when the separation falls below 10-20 nm, the classical theory
progressively deteriorates due to its neglect of quantum mechanical effects
such as nonlocality, electronic spill-out, and Landau damping. Here, we show
how this neglect can be remedied by presenting a unified theoretical treatment
of mesoscopic electrodynamics grounded on the framework of Feibelman
$d$-parameters. Crucially, our technique naturally incorporates nonclassical
resonance shifts and surface-enabled Landau damping - a nonlocal damping effect
- which have a dramatic impact on the amplitude and spectral distribution of
plasmon-emitter interactions. We consider a broad array of plasmon-emitter
interactions ranging from dipolar and multipolar spontaneous emission
enhancement, to plasmon-assisted energy transfer and enhancement of two-photon
transitions. The formalism presented here gives a complete account of both
plasmons and plasmon-emitter interactions at the nanoscale, constituting a
simple yet rigorous and general platform to incorporate nonclassical effects in
plasmon-empowered nanophotonic phenomena.",1904.09279v1
2019-04-23,Ultrafast depinning of domain wall in notched antiferromagnetic nanostructures,"The pinning and depinning of antiferromagnetic (AFM) domain wall is certainly
the core issue of AFM spintronics. In this work, we study theoretically the
N\'eel-type domain wall pinning and depinning at a notch in an
antiferromagnetic (AFM) nano-ribbon. The depinning field depending on the notch
dimension and intrinsic physical parameters are deduced and also numerically
calculated. Contrary to conventional conception, it is revealed that the
depinning field is remarkably dependent of the damping constant and the
time-dependent oscillation of the domain wall position in the weakly damping
regime benefits to the wall depinning, resulting in a gradual increase of the
depinning field up to a saturation value with increasing damping constant. A
one-dimensional model accounting of the internal dynamics of domain wall is
used to explain perfectly the simulated results. It is demonstrated that the
depinning mechanism of an AFM domain wall differs from ferromagnetic domain
wall by exhibiting a depinning speed typically three orders of magnitude faster
than the latter, suggesting the ultrafast dynamics of an AFM system.",1904.10197v2
2019-05-08,Discrete Energy behavior of a damped Timoshenko system,"In this article, we consider a one-dimensional Timoshenko system subject to
different types of dissipation (linear and nonlinear dampings). Based on a
combination between the finite element and the finite difference methods, we
design a discretization scheme for the different Timoshenko systems under
consideration. We first come up with a numerical scheme to the free-undamped
Timoshenko system. Then, we adapt this numerical scheme to the corresponding
linear and nonlinear damped systems. Interestingly, this scheme reaches to
reproduce the most important properties of the discrete energy. Namely, we show
for the discrete energy the positivity, the energy conservation property and
the different decay rate profiles. We numerically reproduce the known
analytical results established on the decay rate of the energy associated with
each type of dissipation.",1905.03050v1
2019-05-08,Attractors for semilinear wave equations with localized damping and external forces,"This paper is concerned with long-time dynamics of semilinear wave equations
defined on bounded domains of $\mathbb{R}^3$ with cubic nonlinear terms and
locally distributed damping. The existence of regular finite-dimensional global
attractors established by Chueshov, Lasiecka and Toundykov (2008) reflects a
good deal of the current state of the art on this matter. Our contribution is
threefold. First, we prove uniform boundedness of attractors with respect to a
forcing parameter. Then, we study the continuity of attractors with respect to
the parameter in a residual dense set. Finally, we show the existence of
generalized exponential attractors. These aspects were not previously
considered for wave equations with localized damping.",1905.03285v1
2019-05-16,Global attractors and their upper semicontinuity for a structural damped wave equation with supercritical nonlinearity on $\mathbb{R}^{N}$,"The paper investigates the existence of global attractors and their upper
semicontinuity for a structural damped wave equation on $\mathbb{R}^{N}:
u_{tt}-\Delta u+(-\Delta)^\alpha u_{t}+u_{t}+u+g(u)=f(x)$, where $\alpha\in
(1/2, 1)$ is called a dissipative index. We propose a new method based on the
harmonic analysis technique and the commutator estimate to exploit the
dissipative effect of the structural damping $(-\Delta)^\alpha u_{t}$ and to
overcome the essential difficulty: ""both the unbounded domain $\mathbb{R}^N$
and the supercritical nonlinearity cause that the Sobolev embedding loses its
compactness""; Meanwhile we show that there exists a supercritical index
$p_\alpha\equiv\frac{N+4\alpha}{N-4\alpha}$ depending on $\alpha$ such that
when the growth exponent $p$ of the nonlinearity $g(u)$ is up to the
supercritical range: $1\leqslant p<p_\alpha$: (i) the IVP of the equation is
well-posed and its solution is of additionally global smoothness when $t>0$;
(ii) the related solution semigroup possesses a global attractor
$\mathcal{A}_\alpha$ in natural energy space for each $\alpha\in (1/2, 1)$;
(iii) the family of global attractors $\{\mathcal{A}_\alpha\}_{\alpha\in (1/2,
1) }$ is upper semicontinuous at each point $\alpha_0\in (1/2, 1)$.",1905.06778v1
2019-05-20,Quantum parameter-estimation of frequency and damping of a harmonic-oscillator,"We determine the quantum Cram\'er-Rao bound for the precision with which the
oscillator frequency and damping constant of a damped quantum harmonic
oscillator in an arbitrary Gaussian state can be estimated. This goes beyond
standard quantum parameter estimation of a single mode Gaussian state for which
typically a mode of fixed frequency is assumed. We present a scheme through
which the frequency estimation can nevertheless be based on the known results
for single-mode quantum parameter estimation with Gaussian states. Based on
these results, we investigate the optimal measurement time. For measuring the
oscillator frequency, our results unify previously known partial results and
constitute an explicit solution for a general single-mode Gaussian state.
Furthermore, we show that with existing carbon nanotube resonators (see J.
Chaste et al.~Nature Nanotechnology 7, 301 (2012)) it should be possible to
achieve a mass sensitivity of the order of an electron mass $\text{Hz}^{-1/2}$.",1905.08288v1
2019-05-24,Damped oscillations of the probability of random events followed by absolute refractory period: exact analytical results,"There are numerous examples of natural and artificial processes that
represent stochastic sequences of events followed by an absolute refractory
period during which the occurrence of a subsequent event is impossible. In the
simplest case of a generalized Bernoulli scheme for uniform random events
followed by the absolute refractory period, the event probability as a function
of time can exhibit damped transient oscillations. Using stochastically-spiking
point neuron as a model example, we present an exact and compact analytical
description for the oscillations without invoking the standard renewal theory.
The resulting formulas stand out for their relative simplicity, allowing one to
analytically obtain the amplitude damping of the 2nd and 3rd peaks of the event
probability.",1905.10172v3
2019-06-10,Global existence of weak solutions to the compressible quantum Navier-Stokes equations with degenerate viscosity,"We study the compressible quantum Navier-Stokes (QNS) equations with
degenerate viscosity in the three dimensional periodic domains. On the one
hand, we consider QNS with additional damping terms. Motivated by the recent
works [Li-Xin, arXiv:1504.06826] and [Antonelli-Spirito, Arch. Ration. Mech.
Anal., 203(2012), 499--527], we construct a suitable approximate system which
has smooth solutions satisfying the energy inequality and the BD entropy
estimate. Using this system, we obtain the global existence of weak solutions
to the compressible QNS equations with damping terms for large initial data.
Moreover, we obtain some new a priori estimates, which can avoid using the
assumption that the gradient of the velocity is a well-defined function, which
is indeed used directly in [Vasseur-Yu, SIAM J. Math. Anal., 48 (2016),
1489--1511; Invent. Math., 206 (2016), 935--974]. On the other hand, in the
absence of damping terms, we also prove the global existence of weak solutions
to the compressible QNS equations without the lower bound assumption on the
dispersive coefficient, which improves the previous result due to
[Antonelli-Spirito, Arch. Ration. Mech. Anal., 203(2012), 499--527].",1906.03971v1
2019-06-11,Study of semi-linear $σ$-evolution equations with frictional and visco-elastic damping,"In this article, we study semi-linear $\sigma$-evolution equations with
double damping including frictional and visco-elastic damping for any
$\sigma\ge 1$. We are interested in investigating not only higher order
asymptotic expansions of solutions but also diffusion phenomenon in the
$L^p-L^q$ framework, with $1\le p\le q\le \infty$, to the corresponding linear
equations. By assuming additional $L^{m}$ regularity on the initial data, with
$m\in [1,2)$, we prove the global (in time) existence of small data energy
solutions and indicate the large time behavior of the global obtained solutions
as well to semi-linear equations. Moreover, we also determine the so-called
critical exponent when $\sigma$ is integers.",1906.04471v1
2019-07-08,Damping of density oscillations in neutrino-transparent nuclear matter,"We calculate the bulk-viscous dissipation time for adiabatic density
oscillations in nuclear matter at densities of 1-7 times nuclear saturation
density and at temperatures ranging from 1 MeV, where corrections to previous
low-temperature calculations become important, up to 10 MeV, where the
assumption of neutrino transparency is no longer valid. Under these conditions,
which are expected to occur in neutron star mergers, damping of density
oscillations arises from beta equilibration via weak interactions. We find that
for 1 kHz oscillations the shortest dissipation times are in the 5 to 20 ms
range, depending on the equation of state, which means that bulk viscous
damping could affect the dynamics of a neutron star merger. For higher
frequencies the dissipation time can be even shorter.",1907.03795v2
2019-07-12,Decoherence of collective motion in warm nuclei,"Collective states in cold nuclei are represented by a wave function that
assigns coherent phases to the participating nucleons. The degree of coherence
decreases with excitation energy above the yrast line because of coupling to
the increasingly dense background of quasiparticle excitations. The
consequences of decoherence are discussed, starting with the well studied case
of rotational damping. In addition to superdeformed bands, a highly excited
oblate band is presented as a new example of screening from rotational damping.
Suppression of pair correlation leads to incoherent thermal M1 radiation, which
appears as an exponential spike (LEMAR) at zero energy in the $\gamma$ strength
function of spherical nuclei. In deformed nuclei a Scissors Resonance appears
and LEMAR changes to damped magnetic rotation, which is interpreted as partial
restoration of coherence.",1907.05569v1
2019-07-24,First-order optimization algorithms via inertial systems with Hessian driven damping,"In a Hilbert space setting, for convex optimization, we analyze the
convergence rate of a class of first-order algorithms involving inertial
features. They can be interpreted as discrete time versions of inertial
dynamics involving both viscous and Hessian-driven dampings. The geometrical
damping driven by the Hessian intervenes in the dynamics in the form $\nabla^2
f (x(t)) \dot{x} (t)$. By treating this term as the time derivative of $ \nabla
f (x (t)) $, this gives, in discretized form, first-order algorithms in time
and space. In addition to the convergence properties attached to Nesterov-type
accelerated gradient methods, the algorithms thus obtained are new and show a
rapid convergence towards zero of the gradients. On the basis of a
regularization technique using the Moreau envelope, we extend these methods to
non-smooth convex functions with extended real values. The introduction of time
scale factors makes it possible to further accelerate these algorithms. We also
report numerical results on structured problems to support our theoretical
findings.",1907.10536v2
2019-07-26,L^p-asymptotic stability analysis of a 1D wave equation with a nonlinear damping,"This paper is concerned with the asymptotic stability analysis of a one
dimensional wave equation with Dirichlet boundary conditions subject to a
nonlinear distributed damping with an L p functional framework, p $\in$ [2,
$\infty$]. Some well-posedness results are provided together with exponential
decay to zero of trajectories, with an estimation of the decay rate. The
well-posedness results are proved by considering an appropriate functional of
the energy in the desired functional spaces introduced by Haraux in [11].
Asymptotic behavior analysis is based on an attractivity result on a trajectory
of an infinite-dimensional linear time-varying system with a special structure,
which relies on the introduction of a suitable Lyapunov functional. Note that
some of the results of this paper apply for a large class of nonmonotone
dampings.",1907.11712v1
2019-08-13,"A Gevrey class semigroup, exponential decay and Lack of analyticity for a system formed by a Kirchhoff-Love plate equation and the equation of a membrane-like electric network with indirect fractional damping","The emphasis in this paper is on the Coupled System of a Kirchhoff-Love Plate
Equation with the Equation of a Membrane-like Electrical Network, where the
coupling is of higher order given by the Laplacian of the displacement velocity
$\gamma\Delta u_t$ and the Laplacian of the electric potential field
$\gamma\Delta v_t $, here only one of the equations is conservative and the
other has dissipative properties. The dissipative mechanism is given by an
intermediate damping $(-\Delta)^\theta v_t$ between the electrical damping
potential for $\theta=0$ and the Laplacian of the electric potential for
$\theta=1$. We show that $S(t)=e^{\mathbb{B}t}$ is not analytic for
$\theta\in[0, 1)$ and analytic for $\theta=1$, however $S(t)=e^{\mathbb{B}t}$
decays exponentially for $0\leq \theta\leq 1$ and $S(t)$ is of Gevrey class $s>
\frac{2+\theta}{\theta}$ when the parameter $\theta$ lies in the interval
$(0,1)$.",1908.04826v3
2019-08-20,Partial Optomechanical Refrigeration via Multimode Cold-Damping Feedback,"We provide a fully analytical treatment for the partial refrigeration of the
thermal motion of a quantum mechanical resonator under the action of feedback.
As opposed to standard cavity optomechanics where the aim is to isolate and
cool a single mechanical mode, the aim here is to extract the thermal energy
from many vibrational modes within a large frequency bandwidth. We consider a
standard cold-damping technique where homodyne read-out of the cavity output
field is fed into a feedback loop that provides a cooling action directly
applied on the mechanical resonator. Analytical and numerical results predict
that low final occupancies are achievable independently of the number of modes
addressed by the feedback as long as the cooling rate is smaller than the
intermode frequency separation. For resonators exhibiting a few nearly
degenerate pairs of modes cooling is less efficient and a weak dependence on
the number of modes is obtained. These scalings hint towards the design of
frequency resolved mechanical resonators where efficient refrigeration is
possible via simultaneous cold-damping feedback.",1908.07348v2
2019-08-19,Time Delay in the Swing Equation: A Variety of Bifurcations,"The present paper addresses the swing equation with additional delayed
damping as an example for pendulum-like systems. In this context, it is proved
that recurring sub- and supercritical Hopf bifurcations occur if time delay is
increased. To this end, a general formula for the first Lyapunov coefficient in
second order systems with additional delayed damping and delay-free
nonlinearity is given. In so far the paper extends results about stability
switching of equilibria in linear time delay systems from Cooke and Grossman.
In addition to the analytical results, periodic solutions are numerically dealt
with. The numerical results demonstrate how a variety of qualitative behaviors
is generated in the simple swing equation by only introducing time delay in a
damping term.",1908.07996v3
2019-08-26,Description and classification of 2-solitary waves for nonlinear damped Klein-Gordon equations,"We describe completely 2-solitary waves related to the ground state of the
nonlinear damped Klein-Gordon equation \begin{equation*}
\partial_{tt}u+2\alpha\partial_{t}u-\Delta u+u-|u|^{p-1}u=0 \end{equation*} on
$\bf R^N$, for $1\leq N\leq 5$ and energy subcritical exponents $p>2$. The
description is twofold.
  First, we prove that 2-solitary waves with same sign do not exist. Second, we
construct and classify the full family of 2-solitary waves in the case of
opposite signs. Close to the sum of two remote solitary waves, it turns out
that only the components of the initial data in the unstable direction of each
ground state are relevant in the large time asymptotic behavior of the
solution. In particular, we show that $2$-solitary waves have a universal
behavior: the distance between the solitary waves is asymptotic to $\log t$ as
$t\to \infty$. This behavior is due to damping of the initial data combined
with strong interactions between the solitary waves.",1908.09527v1
2019-08-30,"Magnetization reversal, damping properties and magnetic anisotropy of L10-ordered FeNi thin films","L10 ordered magnetic alloys such as FePt, FePd, CoPt and FeNi are well known
for their large magnetocrystalline anisotropy. Among these, L10-FeNi alloy is
economically viable material for magnetic recording media because it does not
contain rare earth and noble elements. In this work, L10-FeNi films with three
different strengths of anisotropy were fabricated by varying the deposition
process in molecular beam epitaxy system. We have investigated the
magnetization reversal along with domain imaging via magneto optic Kerr effect
based microscope. It is found that in all three samples, the magnetization
reversal is happening via domain wall motion. Further ferromagnetic resonance
(FMR) spectroscopy was performed to evaluate the damping constant and magnetic
anisotropy. It was observed that the FeNi sample with moderate strength of
anisotropy exhibits low value of damping constant ~ 4.9X10^-3. In addition to
this, it was found that the films possess a mixture of cubic and uniaxial
anisotropies.",1908.11761v1
2019-09-24,DAMPE Excess from Leptophilic Vector Dark Matter: Model Independent Approach,"We study all extensions of the Standard Model (SM) with a vector dark matter
(VDM) candidate which can explain the peak structure observed by recent DAMPE
experiment in electron-positron cosmic ray spectrum. In this regard, we
consider all leptophilic renormalizable VDM-SM interactions through scalar,
spinor, and vector mediators. We show that only two out of six possible models
could produce DAMPE signal by annihilation of VDM with the mass about 1.5 TeV
in a nearby subhalo whilst simultaneously satisfying constraints from DM relic
density, direct/indirect detection, and the collider bounds. These two models
are the ones with scalar/pseudoscalar mediator $ \phi $ with $ M_{\phi} \in
[1500,3000] $ GeV.",1909.10729v2
2019-09-24,Evaluating the Impacts of Transmission Expansion on Sub-Synchronous Resonance Risk,"While transmission expansions are planned to have positive impact on
reliability of power grids, they could increase the risk and severity of some
of the detrimental incidents in power grid mainly by virtue of changing system
configuration, consequently electrical distance. This paper aims to evaluate
and quantify the impact of transmission expansion projects on Sub-Synchronous
Resonance (SSR) risk through a two-step approach utilizing outage count index
and Sub-synchronous damping index. A graph-theory based SSR screening tool is
introduced to quantify the outage count associated with all grid contingencies
which results in radial connection between renewable generation resources and
nearby series compensated lines. Moreover, a frequency-scan based damping
analysis is performed to assess the impact of transmission expansion on the
system damping in sub-synchronous frequency range. The proposed approach has
been utilized to evaluate the impact of recently-built transmission expansion
project on SSR risk in a portion of Electric Reliability Council of Texas
(ERCOT) grid.",1909.11024v1
2019-10-02,Data-Driven Identification of Rayleigh-Damped Second-Order Systems,"In this paper, we present a data-driven approach to identify second-order
systems, having internal Rayleigh damping. This means that the damping matrix
is given as a linear combination of the mass and stiffness matrices. These
systems typically appear when performing various engineering studies, e.g.,
vibrational and structural analysis. In an experimental setup, the frequency
response of a system can be measured via various approaches, for instance, by
measuring the vibrations using an accelerometer. As a consequence, given
frequency samples, the identification of the underlying system relies on
rational approximation. To that aim, we propose an identification of the
corresponding second-order system, extending the Loewner framework for this
class of systems. The efficiency of the proposed method is demonstrated by
means of various numerical benchmarks.",1910.00838v1
2019-10-06,Deterministic and random attractors for a wave equation with sign changing damping,"The paper gives a detailed study of long-time dynamics generated by weakly
damped wave equations in bounded 3D domains where the damping exponent depends
explicitly on time and may change sign. It is shown that in the case when the
non-linearity is superlinear, the considered equation remains dissipative if
the weighted mean value of the dissipation rate remains positive and that the
conditions of this type are not sufficient in the linear case. Two principally
different cases are considered. In the case when this mean is uniform (which
corresponds to deterministic dissipation rates), it is shown that the
considered system possesses smooth uniform attractors as well as non-autonomous
exponential attractors. In the case where the mean is not uniform (which
corresponds to the random dissipation rate, for instance, when this dissipation
rate is generated by the Bernoulli process), the tempered random attractor is
constructed. In contrast to the usual situation, this random attractor is
expected to have infinite Hausdorff and fractal dimension. The simplified model
example which demonstrates infinite-dimensionality of the random attractor is
also presented.",1910.02430v1
2019-10-23,On the exponential stability of a stratified flow to the 2D IDEAL MHD equations with damping,"We study the stability of a type of stratified flows of the two dimensional
inviscid incompressible MHD equations with velocity damping. The exponential
stability for the perturbation near certain stratified flow is investigated in
a strip-type area R*[0,1]. Although the magnetic filed potential is governed by
a transport equation, by using the algebraic structure of the incompressible
condition, it turns out that the linearized MHD equations around the given
stratified flow retain a non-local damping mechanism. After carefully analyzing
the non-linear structure and introducing some suitable weighted energy norms,
we get the exponential stability by combining the exponential decay in time in
the lower order energy with that in the high order energy.",1910.10598v1
2019-10-24,Wigner instability analysis of the damped Hirota equation,"We address the modulation instability of the Hirota equation in the presence
of stochastic spatial incoherence and linear time-dependent
amplification/attenuation processes via the Wigner function approach. We show
that the modulation instability remains baseband type, though the damping
mechanisms substantially reduce the unstable spectrum independent of the
higher-order contributions (e.g. the higher-order nonlinear interaction and the
third-order dispersion). Additionally, we find out that the unstable structure
due to the Kerr interaction exhibits a significant resilience to the
third-order-dispersion stabilizing effects in comparison with the higher-order
nonlinearity, as well as a moderate Lorentzian spectrum damping may assist the
rising of instability. Finally, we also discuss the relevance of our results in
the context of current experiments exploring extreme wave events driven by the
modulation instability (e.g. the generation of the so-called rogue waves).",1910.11045v2
2019-11-01,The spherical multipole resonance probe: kinetic damping in its spectrum,"The multipole resonance probe is one of the recently developed measurement
devices to measure plasma parameter like electron density and temperature based
on the concept of active plasma resonance spectroscopy. The dynamical
interaction between the probe and the plasma in electrostatic, kinetic
description can be modeled in an abstract notation based on functional analytic
methods. These methods provide the opportunity to derive a general solution,
which is given as the response function of the probe-plasma system. It is
defined by the matrix elements of the resolvent of an appropriate dynamical
operator. Based on the general solution a residual damping for vanishing
pressure can be predicted and can only be explained by kinetic effects. Within
this manuscript an explicit response function of the multipole resonance probe
is derived. Therefore, the resolvent is determined by its algebraic
representation based on an expansion in orthogonal basis functions. This allows
to compute an approximated response function and its corresponding spectra,
which show additional damping due to kinetic effects.",1911.00514v1
2019-11-04,Current-driven skyrmion motion in granular films,"Current-driven skyrmion motion in random granular films is investigated with
interesting findings. For a given current, there exists a critical disorder
strength below which its transverse motion could either be boosted below a
critical damping or be hindered above the critical damping, resulting in
current and disorder dependences of skyrmion Hall angle. The boosting comes
mainly from the random force that is opposite to the driving force (current).
The critical damping depends on the current density and disorder strength.
However, the longitudinal motion of a skyrmion is always hindered by the
disorder. Above the critical disorder strength, skyrmions are pinned. The
disorder-induced random force on a skyrmion can be classified as static and
kinetic ones, similar to the friction force in the Newtonian mechanics. In the
pinning phase, the static (pinning) random force is transverse to the current
density. The kinetic random force is opposite to the skyrmion velocity when
skyrmions are in motion. Furthermore, we provide strong evidences that the
Thiele equation can perfectly describe skyrmion dynamics in granular films.
These findings provide insight to skyrmion motion and should be important for
skyrmiontronics.",1911.01245v1
2019-11-05,"Reduction of damped, driven Klein-Gordon equations into a discrete nonlinear Schrödinger equation: justification and numerical comparisons","We consider a discrete nonlinear Klein-Gordon equations with damping and
external drive. Using a small amplitude ansatz, one usually approximates the
equation using a damped, driven discrete nonlinear Schr\""odinger equation.
Here, we show for the first time the justification of this approximation by
finding the error bound using energy estimate. Additionally, we prove the local
and global existence of the Schr\""odinger equation. Numerical simulations are
performed that describe the analytical results. Comparisons between discrete
breathers of the Klein-Gordon equation and discrete solitons of the discrete
nonlinear Schr\""odinger equation are presented.",1911.01631v1
2019-11-14,Stability of coupled solitary wave in biomembranes and nerves,"In this work, we consider the electromechanical density pulse as a coupled
solitary waves represented by a longitudinal compression wave and an
out-of-plane transversal wave (i.e., perpendicular to the membrane surface). We
analyzed using, the variational approach, the characteristics of the coupled
solitary waves in the presence of damping within the framework of coupled
nonlinear Burger-Korteweg-de Vries-Benjamin-Bona-Mahony (BKdV-BBM) equation. It
is shown that, the inertia parameter increases the stability of coupled
solitary waves while the damping parameter decreases it. Moreover, the presence
of damping term induces a discontinuity of stable regions in the inertia-speed
parameter space, appearing in he form of an island of points. Bell shape and
solitary-shock like wave profiles were obtained by varying the propagation
speed and their linear stability spectrum computed. It is shown that bell shape
solitary wave exhibit bound state eigenvalue spectrum, therefore stable. On the
other hand, the solitary-shock like wave profiles exhibit unbound state
eigenvalue spectrum and are therefore generally unstable.",1911.05993v1
2019-11-19,On the theory of the nonlinear Landau damping,"An exact solution of the collisionless time-dependent Vlasov equation is
found for the first time. By means of this solution the behavior of the
Langmuir waves in the nonlinear stage is considered. The analysis is restricted
by the consideration of the first nonlinear approximation keeping the second
power of the electric strength. It is shown that in general the waves with
finite amplitudes are not subject to damping. Only in the linear approximation,
when the wave amplitude is very small, are the waves experiencing damping. It
is shown that with the definite resonance conditions imposed, the waves become
unstable.",1911.08294v2
2019-11-16,Justification of the discrete nonlinear Schrödinger equation from a parametrically driven damped nonlinear Klein-Gordon equation and numerical comparisons,"We consider a damped, parametrically driven discrete nonlinear Klein-Gordon
equation, that models coupled pendula and micromechanical arrays, among others.
To study the equation, one usually uses a small-amplitude wave ansatz, that
reduces the equation into a discrete nonlinear Schr\""odinger equation with
damping and parametric drive. Here, we justify the approximation by looking for
the error bound with the method of energy estimates. Furthermore, we prove the
local and global existence of {solutions to the discrete nonlinear}
Schr\""odinger equation. To illustrate the main results, we consider numerical
simulations showing the dynamics of errors made by the discrete nonlinear
equation. We consider two types of initial conditions, with one of them being a
discrete soliton of the nonlinear Schr\""odinger equation, that is expectedly
approximate discrete breathers of the nonlinear Klein-Gordon equation.",1911.08514v1
2019-11-26,On the Complexity of Minimum-Cost Networked Estimation of Self-Damped Dynamical Systems,"In this paper, we consider the optimal design of networked estimators to
minimize the communication/measurement cost under the networked observability
constraint. This problem is known as the minimum-cost networked estimation
problem, which is generally claimed to be NP-hard. The main contribution of
this work is to provide a polynomial-order solution for this problem under the
constraint that the underlying dynamical system is self-damped. Using
structural analysis, we subdivide the main problem into two NP-hard subproblems
known as (i) optimal sensor selection, and (ii) minimum-cost communication
network. For self-damped dynamical systems, we provide a polynomial-order
solution for subproblem (i). Further, we show that the subproblem (ii) is of
polynomial-order complexity if the links in the communication network are
bidirectional. We provide an illustrative example to explain the methodologies.",1911.11381v1
2019-12-30,A Link Between Relativistic Rest Energy and Fractionary Momentum Operators of Order 1/2,"The solution of a causal fractionary wave equation in an infinite potential
well was obtained. First, the so-called ""free particle"" case was solved, giving
as normalizable solutions a superposition of damped oscillations similar to a
wave packet. From this results, the infinite potential well case was then
solved. The damping coefficient of the equation obtained was matched with the
exponent appearing in the Yucawa potential or ""screened"" Coulomb potential.
When this matching was forced, the particle aquires an offset energy of E =
mc^2/2 which then can be increased by each energy level. The expontential
damping of the wave solutions in the box was found to be closely related with
the radius of the proton when the particle has a mass equal to the mass of the
proton. Lastly the fractionary wave equation was expressed in spherical
coordinates and remains to be solved through analytical or numerical methods.",1912.12770v4
2020-01-06,A continuous contact force model for impact analysis in multibody dynamics,"A new continuous contact force model for contacting problems with regular or
irregular contacting surfaces and energy dissipations in multibody systems is
presented and discussed in this work. The model is developed according to Hertz
law and a hysteresis damping force is introduced for modeling the energy
dissipation during the contact process. As it is almost impossible to obtain an
analytical solution based on the system dynamic equation, an approximate
dynamic equation for the collision system is proposed, achieving a good
approximation of the system dynamic equation. An approximate function between
deformation velocity and deformation is founded on the approximate dynamic
equation, then it is utilized to calculate the energy loss due to the damping
force. The model is established through modifying the original formula of the
hysteresis damping parameter derived by combining the energy balance and the
law of conservation of linear momentum. Numerical results of five different
continuous contact models reveal the capability of our new model as well as the
effect of the geometry of the contacting surfaces on the dynamic system
response.",2001.01344v1
2020-01-06,Boresight Alignment of DArk Matter Particle Explorer,"The DArk Matter Particle Explorer (DAMPE) can measure $\gamma$-rays in the
energy range from a few GeV to about 10 TeV. The direction of each $\gamma$-ray
is reconstructed with respect to the reference system of the DAMPE payload. In
this paper, we adopt a maximum likelihood method and use the $\gamma$-ray data
centered around several bright point-like sources to measure and correct the
angular deviation from the real celestial coordinate system, the so called
``boresight alignment'' of the DAMPE payload. As a check, we also estimate the
boresight alignment for some sets of simulation data with artificial
orientation and obtain consistent results. The time-dependent boresight
alignment analysis does not show evidence for significant variation of the
parameters.",2001.01804v1
2020-01-09,Nonlinear inviscid damping near monotonic shear flows,"We prove nonlinear asymptotic stability of a large class of monotonic shear
flows among solutions of the 2D Euler equations in the channel
$\mathbb{T}\times[0,1]$. More precisely, we consider shear flows $(b(y),0)$
given by a function $b$ which is Gevrey smooth, strictly increasing, and linear
outside a compact subset of the interval $(0,1)$ (to avoid boundary
contributions which are incompatible with inviscid damping). We also assume
that the associated linearized operator satisfies a suitable spectral
condition, which is needed to prove linear inviscid damping.
  Under these assumptions, we show that if $u$ is a solution which is a small
and Gevrey smooth perturbation of such a shear flow $(b(y),0)$ at time $t=0$,
then the velocity field $u$ converges strongly to a nearby shear flow as the
time goes to infinity. This is the first nonlinear asymptotic stability result
for Euler equations around general steady solutions for which the linearized
flow cannot be explicitly solved.",2001.03087v1
2020-02-03,Semi-active $\mathcal{H}_{\infty}$ damping optimization by adaptive interpolation,"In this work we consider the problem of semi-active damping optimization of
mechanical systems with fixed damper positions. Our goal is to compute a
damping that is locally optimal with respect to the $\mathcal{H}_\infty$-norm
of the transfer function from the exogenous inputs to the performance outputs.
We make use of a new greedy method for computing the $\mathcal{H}_\infty$-norm
of a transfer function based on rational interpolation. In this paper, this
approach is adapted to parameter-dependent transfer functions. The
interpolation leads to parametric reduced-order models that can be optimized
more efficiently. At the optimizers we then take new interpolation points to
refine the reduced-order model and to obtain updated optimizers. In our
numerical examples we show that this approach normally converges fast and thus
can highly accelerate the optimization procedure. Another contribution of this
work are heuristics for choosing initial interpolation points.",2002.00617v1
2020-03-25,A Novel Wide-Area Control Strategy for Damping of Critical Frequency Oscillations via Modulation of Active Power Injections,"This paper proposes a novel wide-area control strategy for modulating the
active power injections to damp the critical frequency oscillations in power
systems, this includes the inter-area oscillations and the transient frequency
swing. The proposed method pursues an efficient utilization of the limited
power reserve of existing distributed energy resources (DERs) to mitigate these
oscillations. This is accomplished by decoupling the damping control actions at
different sites using the oscillation signals of the concerned mode as the
power commands. A theoretical basis for this decoupled modulating control is
provided. Technically, the desired sole modal oscillation signals are filtered
out by linearly combining the system-wide frequencies, which is determined by
the linear quadratic regulator based sparsity-promoting (LQRSP) technique. With
the proposed strategy, the modulation of each active power injection can be
effectively engineered considering the response limit and steady-state output
capability of the supporting device. The method is validated based on a
two-area test system and is further demonstrated based on the New England
39-bus test system.",2003.11397v1
2020-03-25,Sharp ultimate velocity bounds for the general solution of some linear second order evolution equation with damping and bounded forcing,"We consider a class of linear second order differential equations with
damping and external force. We investigate the link between a uniform bound on
the forcing term and the corresponding ultimate bound on the velocity of
solutions, and we study the dependence of that bound on the damping and on the
""elastic force"".
  We prove three results. First of all, in a rather general setting we show
that different notions of bound are actually equivalent. Then we compute the
optimal constants in the scalar case. Finally, we extend the results of the
scalar case to abstract dissipative wave-type equations in Hilbert spaces. In
that setting we obtain rather sharp estimates that are quite different from the
scalar case, in both finite and infinite dimensional frameworks.
  The abstract theory applies, in particular, to dissipative wave, plate and
beam equations.",2003.11579v1
2020-03-28,Energy correction based on fluorescence attenuation of DAMPE,"The major scientific goals of DArk Matter Particle Explorer (DAMPE) are to
study cosmic-ray electrons (including positrons) and gamma rays from 5 GeV to
10 TeV and nuclei from Z = 1 to 26 up to 100 TeV. The deposited energy measured
by the Bismuth Germanate Oxide (BGO) calorimeter of DAMPE is affected by
fluorescence attenuation in BGO crystals that are 600 mm long. In this work, an
in-orbit attenuation calibration method is reported, and energy correction of
the sensitive detector unit of the BGO calorimeter is also presented.",2003.12717v1
2020-04-02,A finite element model for seismic response analysis of free-standing rocking columns with vertical dampers,"This paper investigates finite-element modeling of a vertically damped
free-standing rocking column. The paper first derives the nonlinear equation of
motion for the coupled system and then compares the analytical solution with
finite-element model. Finite-element model is being produced using open source
framework named OpenSees. The rocking surface is modeled using zero-length
fiber cross-section element and the dampers are modeled with two node link
elements. In order to simulate energy dissipation during the rocking motion
Hilber-Hughes-Taylor numerical dissipative time step integration is being
adopted. The paper also compares two types of hysteretic and viscous damping
devices and it shows that the viscous damping behavior is favorable when it is
used along with a rocking block. The results of analytical model of a rigid
block with viscous dampers in MATLAB is then compared with OpenSees model and
the paper concludes that the finite-element model compares satisfactory with
the analytical model.",2004.01060v1
2020-04-02,Simulating the effect of weak measurements by a phase damping channel and determining different measures of bipartite correlations in nuclear magnetic resonance,"Quantum discord is a measure based on local projective measurements which
captures quantum correlations that may not be fully captured by entanglement. A
change in the measurement process, achieved by replacing rank-one projectors
with a weak positive operator-valued measure (POVM), allows one to define weak
variants of quantum discord. In this work, we experimentally simulate the
effect of a weak POVM on a nuclear magnetic resonance quantum information
processor. The two-qubit system under investigation is part of a three-qubit
system, where one of the qubits is used as an ancillary to implement the phase
damping channel. The strength of the weak POVM is controlled by varying the
strength of the phase damping channel. We experimentally observed two weak
variants of quantum discord namely, super quantum discord and weak quantum
discord, in two-qubit Werner and Bell-diagonal states. The resultant dynamics
of the states is investigated as a function of the measurement strength.",2004.01237v2
2020-04-24,A rigorous derivation and energetics of a wave equation with fractional damping,"We consider a linear system that consists of a linear wave equation on a
horizontal hypersurface and a parabolic equation in the half space below. The
model describes longitudinal elastic waves in organic monolayers at the
water-air interface, which is an experimental setup that is relevant for
understanding wave propagation in biological membranes. We study the scaling
regime where the relevant horizontal length scale is much larger than the
vertical length scale and provide a rigorous limit leading to a
fractionally-damped wave equation for the membrane. We provide the associated
existence results via linear semigroup theory and show convergence of the
solutions in the scaling limit. Moreover, based on the energy-dissipation
structure for the full model, we derive a natural energy and a natural
dissipation function for the fractionally-damped wave equation with a time
derivative of order 3/2",2004.11830v1
2020-04-25,Pulse-assisted magnetization switching in magnetic nanowires at picosecond and nanosecond timescales with low energy,"Detailed understanding of spin dynamics in magnetic nanomaterials is
necessary for developing ultrafast, low-energy and high-density spintronic
logic and memory. Here, we develop micromagnetic models and analytical
solutions to elucidate the effect of increasing damping and uniaxial anisotropy
on magnetic field pulse-assisted switching time, energy and field requirements
of nanowires with perpendicular magnetic anisotropy and yttrium iron
garnet-like spin transport properties. A nanowire is initially magnetized using
an external magnetic field pulse (write) and self-relaxation. Next, magnetic
moments exhibit deterministic switching upon receiving 2.5 ns-long external
magnetic pulses in both vertical polarities. Favorable damping
({\alpha}~0.1-0.5) and anisotropy energies (10^4-10^5 J m^-3) allow for as low
as picosecond magnetization switching times. Magnetization reversal with fields
below coercivity was observed using spin precession instabilities. A
competition or a nanomagnetic trilemma arises among the switching rate, energy
cost and external field required. Developing magnetic nanowires with optimized
damping and effective anisotropy could reduce the switching energy barrier down
to 3163kBT at room temperature. Thus, pulse-assisted picosecond and low energy
switching in nanomagnets could enable ultrafast nanomagnetic logic and cellular
automata.",2004.12243v1
2020-05-01,Stability of Forced-Damped Response in Mechanical Systems from a Melnikov Analysis,"Frequency responses of multi-degree-of-freedom mechanical systems with weak
forcing and damping can be studied as perturbations from their conservative
limit. Specifically, recent results show how bifurcations near resonances can
be predicted analytically from conservative families of periodic orbits
(nonlinear normal modes). However, the stability of forced-damped motions is
generally determined a posteriori via numerical simulations. In this paper, we
present analytic results on the stability of periodic orbits that perturb from
conservative nonlinear normal modes. In contrast with prior approaches to the
same problem, our method can tackle strongly nonlinear oscillations, high-order
resonances and arbitrary types of non-conservative forces affecting the system,
as we show with specific examples.",2005.00444v2
2020-05-04,Remarks on asymptotic order for the linear wave equation with the scale-invariant damping and mass with $L^r$-data,"In the present paper, we consider the linear wave equation with the
scale-invariant damping and mass. It is known that the global behavior of the
solution depends on the size of the coefficients in front of the damping and
mass at initial time $t=0$. Indeed, the solution satisfies the similar decay
estimate to that of the corresponding heat equation if it is large and to that
of the modified wave equation if it is small. In our previous paper, we obtain
the scattering result and its asymptotic order for the data in the energy space
$H^1\times L^2$ when the coefficients are in the wave regime. In fact, the
threshold of the coefficients relies on the spatial decay of the initial data.
Namely, it varies depending on $r$ when the initial data is in $L^r$ ($1\leq r
< 2$). In the present paper, we will show the scattering result and the
asymptotic order in the wave regime for $L^r$-data, which is wider than the
wave regime for the data in the energy space. Moreover, we give an improvement
of the asymptotic order obtained in our previous paper for the data in the
energy space.",2005.01335v2
2020-05-13,Periodically Forced Nonlinear Oscillators With Hysteretic Damping,"We perform a detailed study of the dynamics of a nonlinear, one-dimensional
oscillator driven by a periodic force under hysteretic damping, whose linear
version was originally proposed and analyzed by Bishop in [1]. We first add a
small quadratic stiffness term in the constitutive equation and construct the
periodic solution of the problem by a systematic perturbation method,
neglecting transient terms as $t\rightarrow \infty$. We then repeat the
analysis replacing the quadratic by a cubic term, which does not allow the
solutions to escape to infinity. In both cases, we examine the dependence of
the amplitude of the periodic solution on the different parameters of the model
and discuss the differences with the linear model. We point out certain
undesirable features of the solutions, which have also been alluded to in the
literature for the linear Bishop's model, but persist in the nonlinear case as
well. Finally, we discuss an alternative hysteretic damping oscillator model
first proposed by Reid [2], which appears to be free from these difficulties
and exhibits remarkably rich dynamical properties when extended in the
nonlinear regime.",2005.06187v1
2020-05-13,Magnetic circular dichroism spectra from resonant and damped coupled cluster response theory,"A computational expression for the Faraday A term of magnetic circular
dichroism (MCD) is derived within coupled cluster response theory and
alternative computational expressions for the B term are discussed. Moreover,
an approach to compute the (temperature-independent) MCD ellipticity in the
context of coupled cluster damped response is presented, and its equivalence
with the stick-spectrum approach in the limit of infinite lifetimes is
demonstrated. The damped response approach has advantages for molecular systems
or spectral ranges with a high density of states. Illustrative results are
reported at the coupled cluster singles and doubles level and compared to
time-dependent density functional theory results.",2005.06190v1
2020-05-21,Convective Excitation and Damping of Solar-like Oscillations,"The last decade has seen a rapid development in asteroseismology thanks to
the CoRoT and Kepler missions. With more detailed asteroseismic observations
available, it is becoming possible to infer exactly how oscillations are driven
and dissipated in solar-type stars. We have carried out three-dimensional (3D)
stellar atmosphere simulations together with one-dimensional (1D) stellar
structural models of key benchmark turn-off and subgiant stars to study this
problem from a theoretical perspective. Mode excitation and damping rates are
extracted from 3D and 1D stellar models based on analytical expressions. Mode
velocity amplitudes are determined by the balance between stochastic excitation
and linear damping, which then allows the estimation of the frequency of
maximum oscillation power, $\nu_{\max}$, for the first time based on ab initio
and parameter-free modelling. We have made detailed comparisons between our
numerical results and observational data and achieved very encouraging
agreement for all of our target stars. This opens the exciting prospect of
using such realistic 3D hydrodynamical stellar models to predict solar-like
oscillations across the HR-diagram, thereby enabling accurate estimates of
stellar properties such as mass, radius and age.",2005.10519v1
2020-05-21,Non-Markovian memory in a measurement-based quantum computer,"We study the exact open system dynamics of single qubit gates during a
measurement-based quantum computation considering non-Markovian environments.
We obtain analytical solutions for the average gate fidelities and analyze it
for amplitude damping and dephasing channels. We show that the average fidelity
is identical for the X-gate and Z-gate and that neither fast application of the
projective measurements necessarily implies high gate fidelity, nor slow
application necessarily implies low gate fidelity. Indeed, for highly
non-Markovian environments, it is of utmost importance to know the best time to
perform the measurements, since a huge variation in the gate fidelity may occur
given this scenario. Furthermore, we show that while for the amplitude damping
the knowledge of the dissipative map is sufficient to determine the best
measurement times, i.e. the best times in which measures are taken, the same is
not necessarily true for the phase damping. To the later, the time of the set
of measures becomes crucial since a phase error in one qubit can fix the phase
error that takes place in another.",2005.10883v1
2020-05-22,Improving Dynamic Performance of Low-Inertia Systems through Eigensensitivity Optimization,"An increasing penetration of renewable generation has led to reduced levels
of rotational inertia and damping in the system. The consequences are higher
vulnerability to disturbances and deterioration of the dynamic response of the
system. To overcome these challenges, novel converter control schemes that
provide virtual inertia and damping have been introduced, which raises the
question of optimal distribution of such devices throughout the network. This
paper presents a framework for performance-based allocation of virtual inertia
and damping to the converter-interfaced generators in a low-inertia system.
This is achieved through an iterative, eigensensitivity-based optimization
algorithm that determines the optimal controller gains. Two conceptually
different problem formulations are presented and validated on a 3-area, 12-bus
test system.",2005.11032v1
2020-05-24,Theory of Solutions for An Inextensible Cantilever,"Recent equations of motion for the large deflections of a cantilevered
elastic beam are analyzed. In the traditional theory of beam (and plate) large
deflections, nonlinear restoring forces are due to the effect of stretching on
bending; for an inextensible cantilever, the enforcement of arc-length
preservation leads to quasilinear stiffness effects and inertial effects that
are both nonlinear and nonlocal. For this model, smooth solutions are
constructed via a spectral Galerkin approach. Additional compactness is needed
to pass to the limit, and this is obtained through a complex procession of
higher energy estimates. Uniqueness is obtained through a non-trivial
decomposition of the nonlinearity. The confounding effects of nonlinear inertia
are overcome via the addition of structural (Kelvin-Voigt) damping to the
equations of motion. Local well-posedness of smooth solutions is shown first in
the absence of nonlinear inertial effects, and then shown with these inertial
effects present, taking into account structural damping. With damping in force,
global-in-time, strong well-posedness result is obtained by achieving
exponential decay for small data.",2005.11836v2
2020-05-25,Nonlinear losses in magnon transport due to four-magnon scattering,"We report on the impact of nonlinear four-magnon scattering on magnon
transport in microstructured Co25Fe75 waveguides with low magnetic damping. We
determine the magnon propagation length with microfocused Brillouin light
scattering over a broad range of excitation powers and detect a decrease of the
attenuation length at high powers. This is consistent with the onset of
nonlinear four-magnon scattering. Hence, it is critical to stay in the linear
regime, when deriving damping parameters from the magnon propagation length.
Otherwise, the intrinsic nonlinearity of magnetization dynamics may lead to a
misinterpretation of magnon propagation lengths and, thus, to incorrect values
of the magnetic damping of the system.",2005.12113v2
2020-06-02,Rigid body dynamics of diamagnetically levitating graphite resonators,"Diamagnetic levitation is a promising technique for realizing resonant
sensors and energy harvesters, since it offers thermal and mechanical isolation
from the environment at zero power. To advance the application of
diamagnetically levitating resonators, it is important to characterize their
dynamics in the presence of both magnetic and gravitational fields. Here we
experimentally actuate and measure rigid body modes of a diamagnetically
levitating graphite plate. We numerically calculate the magnetic field and
determine the influence of magnetic force on the resonance frequencies of the
levitating plate. By analyzing damping mechanisms, we conclude that eddy
current damping dominates dissipation in mm-sized plates. We use finite element
simulations to model eddy current damping and find close agreement with
experimental results. We also study the size-dependent Q-factors (Qs) of
diamagnetically levitating plates and show that Qs above 100 million are
theoretically attainable by reducing the size of the diamagnetic resonator down
to microscale, making these systems of interest for next generation low-noise
resonant sensors and oscillators.",2006.01733v3
2020-06-11,Signatures of Spatial Curvature on Growth of Structures,"We write down Boltzmann equation for massive particles in a spatially curved
FRW universe and solve the approximate line-of-sight solution for evolution of
matter density, including the effects of spatial curvature to the first order
of approximation. It is shown that memory of early time gravitational potential
is affected by presence of spatial curvature. Then we revisit Boltzmann
equation for photons in the general FRW background. Using it, we show that how
the frequency of oscillations and damping factor (known as Silk damping)
changed in presence of spatial curvature. At last, using this modified damping
factor in hydrodynamic regime of cosmological perturbations, we find our
analytic solution which shows the effects of spatial curvature on growing mode
of matter density.",2006.06347v2
2020-06-29,"HFQPOs and discoseismic mode excitation in eccentric, relativistic discs. II. Magnetohydrodynamic simulations","Trapped inertial oscillations (r-modes) provide a promising explanation for
high-frequency quasi-periodic oscillations (HFQPOs) observed in the emission
from black hole X-ray binary systems. An eccentricity (or warp) can excite
r-modes to large amplitudes, but concurrently the oscillations are likely
damped by magnetohydrodynamic (MHD) turbulence driven by the magnetorotational
instability (MRI). We force eccentricity in global, unstratified, zero-net flux
MHD simulations of relativistic accretion discs, and find that a sufficiently
strong disc distortion generates trapped inertial waves despite this damping.
In our simulations, eccentricities above ~ 0.03 in the inner disc excite
trapped waves. In addition to the competition between r-mode damping and
driving, we observe that larger amplitude eccentric structures modify and in
some cases suppress MRI turbulence. Given the variety of distortions (warps as
well as eccentricities) capable of amplifying r-modes, the robustness of
trapped inertial wave excitation in the face of MRI turbulence in our
simulations provides support for a discoseismic explanation for HFQPOs.",2006.16266v2
2020-07-01,"An integrable family of torqued, damped, rigid rotors","Expositions of the Euler equations for the rotation of a rigid body often
invoke the idea of a specially damped system whose energy dissipates while its
angular momentum magnitude is conserved in the body frame. An attempt to
explicitly construct such a damping function leads to a more general, but still
integrable, system of cubic equations whose trajectories are confined to nested
sets of quadric surfaces in angular momentum space. For some choices of
parameters, the lines of fixed points along both the largest and smallest
moment of inertia axes can be simultaneously attracting. Limiting cases are
those that conserve either the energy or the magnitude of the angular momentum.
Parallels with rod mechanics, micromagnetics, and particles with effective mass
are briefly discussed.",2007.00707v1
2020-07-10,Approximate Time-Optimal Trajectories for Damped Double Integrator in 2D Obstacle Environments under Bounded Inputs,"This article provides extensions to existing path-velocity decomposition
based time optimal trajectory planning algorithm \cite{kant1986toward} to
scenarios in which agents move in 2D obstacle environment under double
integrator dynamics with drag term (damped double integrator). Particularly, we
extend the idea of a tangent graph \cite{liu1992path} to $\calC^1$-Tangent
graph to find continuously differentiable ($\calC^1$) shortest path between any
two points. $\calC^1$-Tangent graph has a continuously differentiable
($\calC^1$) path between any two nodes. We also provide analytical expressions
for a near time-optimal velocity profile for an agent moving on these shortest
paths under the damped double integrator with bounded acceleration.",2007.05155v2
2020-08-11,Ab initio results for the plasmon dispersion and damping of the warm dense electron gas,"Warm dense matter (WDM) is an exotic state on the border between condensed
matter and dense plasmas. Important occurrences of WDM include dense
astrophysical objects, matter in the core of our Earth, as well as matter
produced in strong compression experiments. As of late, x-ray Thomson
scattering has become an advanced tool to diagnose WDM. The interpretation of
the data requires model input for the dynamic structure factor $S(q,\omega)$
and the plasmon dispersion $\omega(q)$. Recently the first \textit{ab initio}
results for $S(q,\omega)$ of the homogeneous warm dense electron gas were
obtained from path integral Monte Carlo simulations, [Dornheim \textit{et al.},
Phys. Rev. Lett. \textbf{121}, 255001 (2018)]. Here, we analyse the effects of
correlations and finite temperature on the dynamic dielectric function and the
plasmon dispersion. Our results for the plasmon dispersion and damping differ
significantly from the random phase approximation and from earlier models of
the correlated electron gas. Moreover, we show when commonly used weak damping
approximations break down and how the method of complex zeros of the dielectric
function can solve this problem for WDM conditions.",2008.04605v1
2020-08-18,Singularity formation for compressible Euler equations with time-dependent damping,"In this paper, we consider the compressible Euler equations with
time-dependent damping \frac{\a}{(1+t)^\lambda}u in one space dimension. By
constructing 'decoupled' Riccati type equations for smooth solutions, we
provide some sufficient conditions under which the classical solutions must
break down in finite time. As a byproduct, we show that the derivatives blow
up, somewhat like the formation of shock wave, if the derivatives of initial
data are appropriately large at a point even when the damping coefficient goes
to infinity with a algebraic growth rate. We study the case \lambda\neq1 and
\lambda=1 respectively, moreover, our results have no restrictions on the size
of solutions and the positivity/monotonicity of the initial Riemann invariants.
In addition, for 1<\gamma<3 we provide time-dependent lower bounds on density
for arbitrary classical solutions, without any additional assumptions on the
initial data.",2008.07756v1
2020-08-18,"Survey of 360$^{\circ}$ domain walls in magnetic heterostructures: topology, chirality and current-driven dynamics","Chirality and current-driven dynamics of topologically nontrivial
360$^{\circ}$ domain walls (360DWs) in magnetic heterostructures (MHs) are
systematically investigated. For MHs with normal substrates, the static 360DWs
are N\'{e}el-type with no chirality. While for those with heavy-metal
substrates, the interfacial Dzyaloshinskii-Moriya interaction (iDMI) therein
makes 360DWs prefer specific chirality. Under in-plane driving charge currents,
as the direct result of ""full-circle"" topology a certain 360DW does not undergo
the ""Walker breakdown""-type process like a well-studied 180$^{\circ}$ domain
wall as the current density increases. Alternatively, it keeps a fixed
propagating mode (either steady-flow or precessional-flow, depending on the
effective damping constant of the MH) until it collapses or changes to other
types of solition when the current density becomes too high. Similarly, the
field-like spin-orbit torque (SOT) has no effects on the dynamics of 360DWs,
while the anti-damping SOT has. For both modes, modifications to the mobility
of 360DWs by iDMI and anti-damping SOT are provided.",2008.08196v1
2020-08-20,Combining $T_1$ and $T_2$ estimation with randomized benchmarking and bounding the diamond distance,"The characterization of errors in a quantum system is a fundamental step for
two important goals. First, learning about specific sources of error is
essential for optimizing experimental design and error correction methods.
Second, verifying that the error is below some threshold value is required to
meet the criteria of threshold theorems. We consider the case where errors are
dominated by the generalized damping channel (encompassing the common intrinsic
processes of amplitude damping and dephasing) but may also contain additional
unknown error sources. We demonstrate the robustness of standard $T_1$ and
$T_2$ estimation methods and provide expressions for the expected error in
these estimates under the additional error sources. We then derive expressions
that allow a comparison of the actual and expected results of fine-grained
randomized benchmarking experiments based on the damping parameters. Given the
results of this comparison, we provide bounds that allow robust estimation of
the thresholds for fault-tolerance.",2008.09197v1
2020-08-25,The atomic damping basis and the collective decay of interacting two-level atoms,"We find analytical solutions to the evolution of interacting two-level atoms
when the master equation is symmetric under the permutation of atomic labels.
The master equation includes atomic independent dissipation. The method to
obtain the solutions is: First, we use the system symmetries to describe the
evolution in an operator space whose dimension grows polynomially with the
number of atoms. Second, we expand the solutions in a basis composed of
eigenvectors of the dissipative part of the master equation that models the
independent dissipation of the atoms. This atomic damping basis is an atomic
analog to the damping basis used for bosonic fields. The solutions show that
the system decays as a sum of sub- and super-radiant exponential terms.",2008.11056v1
2020-09-11,Accuracy of relativistic Cowling approximation in protoneutron star asteroseismology,"The relativistic Cowling approximation, where the metric perturbations are
neglected during the fluid oscillations, is often adopted for considering the
gravitational waves from the protoneutron stars (PNSs) provided via
core-collapse supernova explosions. In this study, we evaluate how the Cowling
approximation works well by comparing the frequencies with the Cowling
approximation to those without the approximation. Then, we find that the
behavior of the frequencies with the approximation is qualitatively the same
way as that without the approximation, where the frequencies with the
approximation can totally be determined within $\sim 20\%$ accuracy. In
particular, the fundamental mode with the Cowling approximation is
overestimated. In addition, we also discuss the damping time of various
eigenmodes in gravitational waves from the PNSs, where the damping time for the
PNSs before the avoided crossing between the $f$- and $g_1$-modes, is quite
different from that for cold neutron stars, but it is more or less similar to
that for cold neutron stars in the later phase. The damping time is long enough
compared to the typical time interval of short-Fourier transformation that
often used in the analysis, and that ideally guarantees the validity of the
transformation.",2009.05206v1
2020-09-17,Resonant absorption: transformation of compressive motions into vortical motions,"This paper investigates the changes in spatial properties when
magnetohydrodynamic (MHD) waves undergo resonant damping in the Alfv\'en
continuum. The analysis is carried out for a 1D cylindrical pressure-less
plasma with a straight magnetic field. The effect of the damping on the spatial
wave variables is determined by using complex frequencies that arise as a
result of the resonant damping. Compression and vorticity are used to
characterise the spatial evolution of the MHD wave. The most striking result is
the huge spatial variation in the vorticity component parallel to the magnetic
field. Parallel vorticity vanishes in the uniform part of the equilibrium.
However, when the MHD wave moves into the non-uniform part, parallel vorticity
explodes to values that are orders of magnitude higher than those attained by
the transverse components in planes normal to the straight magnetic field. In
the non-uniform part of the equilibrium plasma, the MHD wave is controlled by
parallel vorticity and resembles an Alfv\'en wave, with the unfamiliar property
that it has pressure variations even in the linear regime.",2009.08152v1
2020-09-19,Random vibrations of stress-driven nonlocal beams with external damping,"Stochastic flexural vibrations of small-scale Bernoulli-Euler beams with
external damping are investigated by stress-driven nonlocal mechanics. Damping
effects are simulated considering viscous interactions between beam and
surrounding environment. Loadings are modeled by accounting for their random
nature. Such a dynamic problem is characterized by a stochastic partial
differential equation in space and time governing time-evolution of the
relevant displacement field. Differential eigenanalyses are performed to
evaluate modal time coordinates and mode shapes, providing a complete
stochastic description of response solutions. Closed-form expressions of power
spectral density, correlation function, stationary and non-stationary variances
of displacement fields are analytically detected. Size-dependent dynamic
behaviour is assessed in terms of stiffness, variance and power spectral
density of displacements. The outcomes can be useful for design and
optimization of structural components of modern small-scale devices, such as
Micro- and Nano-Electro-Mechanical-Systems (MEMS and NEMS).",2009.09184v1
2020-09-20,Correction Method for the Readout Saturation of the DAMPE Calorimeter,"The DArk Matter Particle Explorer (DAMPE) is a space-borne high energy
cosmic-ray and $\gamma$-ray detector which operates smoothly since the launch
on December 17, 2015. The bismuth germanium oxide (BGO) calorimeter is one of
the key sub-detectors of DAMPE used for energy measurement and electron proton
identification. For events with total energy deposit higher than decades of
TeV, the readouts of PMTs coupled on the BGO crystals would become saturated,
which results in an underestimation of the energy measurement. Based on
detailed simulations, we develop a correction method for the saturation effect
according to the shower development topologies and energies measured by
neighbouring BGO crystals. The verification with simulated and on-orbit events
shows that this method can well reconstruct the energy deposit in the saturated
BGO crystal.",2009.09438v1
2020-09-21,Complete complementarity relations in system-environment decoherent dynamics,"We investigate the system-environment information flow from the point of view
ofcomplete complementarity relations. We consider some commonly used noisy
quantum channels:Amplitude damping, phase damping, bit flip, bit-phase flip,
phase flip, depolarizing, and correlatedamplitude damping. By starting with an
entangled bipartite pure quantum state, with the linearentropy being the
quantifier of entanglement, we study how entanglement is redistributed and
turnedinto general correlations between the degrees of freedom of the whole
system. For instance, it ispossible to express the entanglement entropy in
terms of the multipartite quantum coherence or interms of the correlated
quantum coherence of the different partitions of the system. In addition,we
notice that for the depolarizing and bit-phase flip channels the wave and
particle aspects candecrease or increase together. Besides, by considering the
environment as part of a pure quantumsystem, the linear entropy is shown to be
not just a measure of mixedness of a particular subsystem,but a correlation
measure of the subsystem with rest of the world.",2009.09769v3
2020-09-15,Delay-induced resonance suppresses damping-induced unpredictability,"Combined effects of the damping and forcing in the underdamped time-delayed
Duffing oscillator are considered in this paper. We analyze the generation of a
certain damping-induced unpredictability, due to the gradual suppression of
interwell oscillations. We find the minimal amount of the forcing amplitude and
the right forcing frequency to revert the effect of the dissipation, so that
the interwell oscillations can be restored, for different time delay values.
This is achieved by using the delay-induced resonance, in which the time delay
replaces one of the two periodic forcings present in the vibrational resonance.
A discussion in terms of the time delay of the critical values of the forcing
for which the delay-induced resonance can tame the dissipation effect is
finally carried out.",2009.11760v1
2020-10-06,A dissiptive logarithmic type evolution equation: asymptotic profile and optimal estimates,"We introduce a new model of the logarithmic type of wave-like equation with a
nonlocal logarithmic damping mechanism, which is rather weakly effective as
compared with frequently studied fractional damping cases. We consider the
Cauchy problem for this new model in the whole space, and study the asymptotic
profile and optimal decay and/or blowup rates of solutions as time goes to
infinity in L^{2}-sense. The operator L considered in this paper was used to
dissipate the solutions of the wave equation in the paper studied by
Charao-Ikehata in 2020, and in the low frequency parameters the principal part
of the equation and the damping term is rather weakly effective than those of
well-studied power type operators.",2010.02485v1
2020-10-12,Line-drag damping of Alfvén waves in radiatively driven winds of magnetic massive stars,"Line-driven stellar winds from massive (OB) stars are subject to a strong
line-deshadowing instability. Recently, spectropolarimetric surveys have
collected ample evidence that a subset of Galactic massive stars hosts strong
surface magnetic fields. We investigate here the propagation and stability of
magneto-radiative waves in such a magnetised, line-driven wind. Our analytic,
linear stability analysis includes line-scattering from the stellar radiation,
and accounts for both radial and non-radial perturbations. We establish a
bridging law for arbitrary perturbation wavelength after which we analyse
separately the long- and short-wavelength limits. While long-wavelength
radiative and magnetic waves are found to be completely decoupled, a key result
is that short-wavelength, radially propagating Alfv\'en waves couple to the
scattered radiation field and are strongly damped due to the line-drag effect.
This damping of magnetic waves in a scattering-line-driven flow could have
important effects on regulating the non-linear wind dynamics, and so might also
have strong influence on observational diagnostics of the wind structure and
clumping of magnetic line-driven winds.",2010.05650v1
2020-10-20,Long Time Behavior of a Quasilinear Hyperbolic System Modelling Elastic Membranes,"The paper studies the long time behavior of a system that describes the
motion of a piece of elastic membrane driven by surface tension and inner air
pressure. The system is a degenerate quasilinear hyperbolic one that involves
the mean curvature, and also includes a damping term that models the
dissipative nature of genuine physical systems. With the presence of damping, a
small perturbation of the sphere converges exponentially in time to the sphere,
and without the damping the evolution that is $\varepsilon$-close to the sphere
has life span longer than $\varepsilon^{-1/6}$. Both results are proved using a
new Nash-Moser-H\""{o}rmander type theorem proved by Baldi and Haus.",2010.10663v6
2020-10-09,Rapid parameter determination of discrete damped sinusoidal oscillations,"We present different computational approaches for the rapid extraction of the
signal parameters of discretely sampled damped sinusoidal signals. We compare
time- and frequency-domain-based computational approaches in terms of their
accuracy and precision and computational time required in estimating the
frequencies of such signals, and observe a general trade-off between precision
and speed. Our motivation is precise and rapid analysis of damped sinusoidal
signals as these become relevant in view of the recent experimental
developments in cavity-enhanced polarimetry and ellipsometry, where the
relevant time scales and frequencies are typically within the $\sim1-10\,\mu$s
and $\sim1-100$MHz ranges, respectively. In such experimental efforts,
single-shot analysis with high accuracy and precision becomes important when
developing experiments that study dynamical effects and/or when developing
portable instrumentations. Our results suggest that online, running-fashion,
microsecond-resolved analysis of polarimetric/ellipsometric measurements with
fractional uncertainties at the $10^{-6}$ levels, is possible, and using a
proof-of-principle experimental demonstration we show that using a
frequency-based analysis approach we can monitor and analyze signals at kHz
rates and accurately detect signal changes at microsecond time-scales.",2010.11690v1
2020-10-22,Effective shear and bulk viscosities for anisotropic flow,"We evaluate the viscous damping of anisotropic flow in heavy-ion collisions
for arbitrary temperature-dependent shear and bulk viscosities. We show that
the damping is solely determined by effective shear and bulk viscosities, which
are weighted averages over the temperature. We determine the relevant weights
for nucleus-nucleus collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV and 200 GeV,
corresponding to the maximum LHC and RHIC energies, by running ideal and
viscous hydrodynamic simulations. The effective shear viscosity is driven by
temperatures below $210$ MeV at RHIC, and below $280$ MeV at the LHC, with the
largest contributions coming from the lowest temperatures, just above
freeze-out. The effective bulk viscosity is driven by somewhat higher
temperatures, corresponding to earlier stages of the collision. We show that at
a fixed collision energy, the effective viscosity is independent of centrality
and system size, to the same extent as the mean transverse momentum of outgoing
hadrons. The variation of viscous damping is determined by Reynolds number
scaling.",2010.11919v2
2020-10-23,Is PSR J0855$-$4644 responsible for the 1.4 TeV electron spectral bump hinted by DAMPE?,"DAMPE observation on the cosmic ray electron spectrum hints a narrow excess
at $\sim$ 1.4 TeV. Although the excess can be ascribed to dark matter
particles, pulsars and pulsar wind nebulae are believed to be a more natural
astrophysical origin: electrons injected from nearby pulsars at their early
ages can form a bump-like feature in the spectrum due to radiative energy
losses. In this paper, with a survey of nearby pulsars, we find 4 pulsars that
may have notable contributions to $\sim$ 1.4 TeV cosmic ray electrons. Among
them, PSR J0855$-$4644 has a spin down luminosity more than 50 times higher
than others and presumably dominates the electron fluxes from them. X-ray
observations on the inner compact part (which may represent a tunnel for the
transport of electrons from the pulsar) of PWN G267.0$-$01.0 are then used to
constrain the spectral index of high energy electrons injected by the pulsar.
We show that high-energy electrons released by PSR J0855$-$4644 could indeed
reproduce the 1.4 TeV spectral feature hinted by the DAMPE with reasonable
parameters.",2010.12170v1
2020-11-02,Effect of retardation on the frequency and linewidth of plasma resonances in a two-dimensional disk of electron gas,"We theoretically analyze dominant plasma modes in a two-dimensional disk of
electron gas by calculating the absorption of an incident electromagnetic wave.
The problem is solved in a self-consistent approximation, taking into account
electromagnetic retardation effects. We use the Drude model to describe the
conductivity of the system. The absorption spectrum exhibits a series of peaks
corresponding to the excitation of plasma waves. The position and linewidth of
the peaks designating, respectively, the frequency and damping rate of the
plasma modes. We estimate the influence of retardation effects on the frequency
and linewidth of the fundamental (dipole) and axisymmetric (quadrupole) plasma
modes both numerically and analytically. We find the net damping rate of the
modes to be dependent on not only the sum of the radiative and collisional
decays but also their intermixture, even for small retardation. We show that
the net damping rate can be noticeably less than that determined by collisions
alone.",2011.00877v1
2020-11-05,Low-Complexity Models for Acoustic Scene Classification Based on Receptive Field Regularization and Frequency Damping,"Deep Neural Networks are known to be very demanding in terms of computing and
memory requirements. Due to the ever increasing use of embedded systems and
mobile devices with a limited resource budget, designing low-complexity models
without sacrificing too much of their predictive performance gained great
importance. In this work, we investigate and compare several well-known methods
to reduce the number of parameters in neural networks. We further put these
into the context of a recent study on the effect of the Receptive Field (RF) on
a model's performance, and empirically show that we can achieve high-performing
low-complexity models by applying specific restrictions on the RFs, in
combination with parameter reduction methods. Additionally, we propose a
filter-damping technique for regularizing the RF of models, without altering
their architecture and changing their parameter counts. We will show that
incorporating this technique improves the performance in various low-complexity
settings such as pruning and decomposed convolution. Using our proposed filter
damping, we achieved the 1st rank at the DCASE-2020 Challenge in the task of
Low-Complexity Acoustic Scene Classification.",2011.02955v1
2020-11-14,Learning a Reduced Basis of Dynamical Systems using an Autoencoder,"Machine learning models have emerged as powerful tools in physics and
engineering. Although flexible, a fundamental challenge remains on how to
connect new machine learning models with known physics. In this work, we
present an autoencoder with latent space penalization, which discovers finite
dimensional manifolds underlying the partial differential equations of physics.
We test this method on the Kuramoto-Sivashinsky (K-S), Korteweg-de Vries (KdV),
and damped KdV equations. We show that the resulting optimal latent space of
the K-S equation is consistent with the dimension of the inertial manifold. The
results for the KdV equation imply that there is no reduced latent space, which
is consistent with the truly infinite dimensional dynamics of the KdV equation.
In the case of the damped KdV equation, we find that the number of active
dimensions decreases with increasing damping coefficient. We then uncover a
nonlinear basis representing the manifold of the latent space for the K-S
equation.",2011.07346v1
2020-11-23,Sharp lifespan estimates for the weakly coupled system of semilinear damped wave equations in the critical case,"The open question, which seems to be also the final part, in terms of
studying the Cauchy problem for the weakly coupled system of damped wave
equations or reaction-diffusion equations, is so far known as the sharp
lifespan estimates in the critical case. In this paper, we mainly investigate
lifespan estimates for solutions to the weakly coupled system of semilinear
damped wave equations in the critical case. By using a suitable test function
method associated with nonlinear differential inequalities, we catch upper
bound estimates for the lifespan. Moreover, we establish polynomial-logarithmic
type time-weighted Sobolev spaces to obtain lower bound estimates for the
lifespan in low spatial dimensions. Then, together with the derived lifespan
estimates, new and sharp results on estimates for the lifespan in the critical
case are claimed. Finally, we give an application of our results to the
semilinear reaction-diffusion system in the critical case.",2011.11366v2
2020-12-10,Stochastic Damped L-BFGS with Controlled Norm of the Hessian Approximation,"We propose a new stochastic variance-reduced damped L-BFGS algorithm, where
we leverage estimates of bounds on the largest and smallest eigenvalues of the
Hessian approximation to balance its quality and conditioning. Our algorithm,
VARCHEN, draws from previous work that proposed a novel stochastic damped
L-BFGS algorithm called SdLBFGS. We establish almost sure convergence to a
stationary point and a complexity bound. We empirically demonstrate that
VARCHEN is more robust than SdLBFGS-VR and SVRG on a modified DavidNet problem
-- a highly nonconvex and ill-conditioned problem that arises in the context of
deep learning, and their performance is comparable on a logistic regression
problem and a nonconvex support-vector machine problem.",2012.05783v1
2020-12-29,Twist-induced Near-field Thermal Switch Using Nonreciprocal Surface Magnon-Polaritons,"We explore that two ferromagnetic insulator slabs host a strong twist-induced
near-field radiative heat transfer in the presence of twisted magnetic fields.
Using the formalism of fluctuational electrodynamics, we find the existence of
large twist-induced thermal switch ratio in large damping condition and
nonmonotonic twist manipulation for heat transfer in small damping condition,
associated with the different twist-induced effects of nonreciprocal elliptic
surface magnon-polaritons, hyperbolic surface magnon-polaritons, and
twist-non-resonant surface magnon-polaritons. Moreover, the near-field
radiative heat transfer can be significantly enhanced by the twist-non-resonant
surface magnon-polaritons in the ultra-small damping condition. Such
twist-induced effect is applicable for other kinds of anisotropic slabs with
timereversal symmetry breaking. Our findings provide a way to twisted and
magnetic control in nanoscale thermal management and improve it with
twistronics concepts.",2012.14733v1
2021-01-04,The damped harmonic oscillator at the classical limit of the Snyder-de Sitter space,"Valtancoli in his paper entitled [P. Valtancoli, Canonical transformations,
and minimal length J. Math. Phys. 56, 122107 (2015)] has shown how the
deformation of the canonical transformations can be made compatible with the
deformed Poisson brackets. Based on this work and through an appropriate
canonical transformation, we solve the problem of one dimensional (1D) damped
harmonic oscillator at the classical limit of the Snyder-de Sitter (SdS) space.
We show that the equations of the motion can be described by trigonometric
functions with frequency and period depending on the deformed and the damped
parameters. We eventually discuss the influences of these parameters on the
motion of the system.",2101.01223v2
2021-01-11,Damped (linear) response theory within the resolution-of-identity coupled cluster singles and approximate doubles (RI-CC2) method,"An implementation of a complex solver for the solution of the response
equations required to compute the complex response functions of damped response
theory is presented for the resolution-of-identity (RI) coupled-cluster singles
and approximate doubles CC2 method. The implementation uses a partitioned
formulation that avoids the storage of double excitation amplitudes to make it
applicable to large molecules. The solver is the keystone element for the
development of the damped coupled-cluster response formalism for linear and
nonlinear effects in resonant frequency regions at the RI-CC2 level of theory.
Illustrative results are reported for the one-photon absorption cross section
of C60, the electronic circular dichroism of $n$-helicenes ($n$ = 5, 6, 7), and
the $C_6$ dispersion coefficients of a set of selected organic molecules and
fullerenes.",2101.03756v1
2021-01-26,Generalized Damped Newton Algorithms in Nonsmooth Optimization via Second-Order Subdifferentials,"The paper proposes and develops new globally convergent algorithms of the
generalized damped Newton type for solving important classes of nonsmooth
optimization problems. These algorithms are based on the theory and
calculations of second-order subdifferentials of nonsmooth functions with
employing the machinery of second-order variational analysis and generalized
differentiation. First we develop a globally superlinearly convergent damped
Newton-type algorithm for the class of continuously differentiable functions
with Lipschitzian gradients, which are nonsmooth of second order. Then we
design such a globally convergent algorithm to solve a structured class of
nonsmooth quadratic composite problems with extended-real-valued cost
functions, which typically arise in machine learning and statistics. Finally,
we present the results of numerical experiments and compare the performance of
our main algorithm applied to an important class of Lasso problems with those
achieved by other first-order and second-order optimization algorithms.",2101.10555v3
2021-01-26,Damped and Driven Breathers and Metastability,"In this article we prove the existence of a new family of periodic solutions
for discrete, nonlinear Schrodinger equations subject to spatially localized
driving and damping. They provide an alternate description of the metastable
behavior in such lattice systems which agrees with previous predictions for the
evolution of metastable states while providing more accurate approximations to
these states. We analyze the stability of these breathers, finding a very small
positive eigenvalue whose eigenvector lies almost tangent to the surface of the
cylinder formed by the family of breathers. This causes solutions to slide
along the cylinder without leaving its neighborhood for very long times.",2101.10999v2
2021-02-05,A simple artificial damping method for total Lagrangian smoothed particle hydrodynamics,"In this paper, we present a simple artificial damping method to enhance the
robustness of total Lagrangian smoothed particle hydrodynamics (TL-SPH).
Specifically, an artificial damping stress based on the Kelvin-Voigt type
damper with a scaling factor imitating a von Neumann-Richtmyer type artificial
viscosity is introduced in the constitutive equation to alleviate the spurious
oscillation in the vicinity of the sharp spatial gradients. After validating
the robustness and accuracy of the present method with a set of benchmark tests
with very challenging cases, we demonstrate its potentials in the field of
bio-mechanics by simulating the deformation of complex stent structures.",2102.04898v1
2021-02-18,Probing black hole microstructure with the kinetic turnover of phase transition,"By treating black hole as the macroscopic stable state on the free energy
landscape, we propose that the stochastic dynamics of the black hole phase
transition can be effectively described by the Langevin equation or
equivalently by the Fokker-Planck equation in phase space. We demonstrate the
turnover of the kinetics for the charged anti-de Sitter black hole phase
transition, which shows that the mean first passage time is linear with the
friction in the high damping regime and inversely proportional to the friction
in the low damping regime. The fluctuations in the kinetics are shown to be
large/small in the high/low damping regime and the switching behavior from the
small fluctuations to the large fluctuations takes place at the kinetic
turnover point. Because the friction is a reflection of the microscopic degrees
of freedom acting on the order parameter of the black hole, the turnover and
the corresponding fluctuations of the phase transition kinetics can be used to
probe the black hole microstructure.",2102.09439v1
2021-02-25,Energy Decay of some boundary coupled systems involving wave$\backslash$ Euler-Bernoulli beam with one locally singular fractional Kelvin-Voigt damping,"In this paper, we investigate the energy decay of hyperbolic systems of
wave-wave, wave-Euler- Bernoulli beam and beam-beam types. The two equations
are coupled through boundary connection with only one localized non-smooth
fractional Kelvin-Voigt damping. First, we reformulate each system into an
augmented model and using a general criteria of Arendt-Batty, we prove that our
models are strongly stable. Next, by using frequency domain approach, combined
with multiplier technique and some interpolation inequalities, we establish
different types of polynomial energy decay rate which depends on the order of
the fractional derivative and the type of the damped equation in the system.",2102.12732v2
2021-03-01,Fluid-plate interaction under periodic forcing,"The motion of a thin elastic plate interacting with a viscous fluid is
investigated. A periodic force acting on the plate is considered, which in a
setting without damping could lead to a resonant response. The interaction with
the viscous fluid provides a damping mechanism due to the energy dissipation in
the fluid. Moreover, an internal damping mechanism in the plate is introduced.
In this setting, we show that the periodic forcing leads to a time-periodic
(non-resonant) solution. We employ the Navier-Stokes and the Kirchhoff-Love
plate equation in a periodic cell structure to model the motion of the viscous
fluid and the elastic plate, respectively. Maximal Lp regularity for the
linearized system is established in a framework of time-periodic function
spaces. Existence of a solution to the fully nonlinear system is subsequently
shown with a fixed-point argument.",2103.00795v1
2021-03-25,Nonlinear inviscid damping and shear-buoyancy instability in the two-dimensional Boussinesq equations,"We investigate the long-time properties of the two-dimensional inviscid
Boussinesq equations near a stably stratified Couette flow, for an initial
Gevrey perturbation of size $\varepsilon$. Under the classical Miles-Howard
stability condition on the Richardson number, we prove that the system
experiences a shear-buoyancy instability: the density variation and velocity
undergo an $O(t^{-1/2})$ inviscid damping while the vorticity and density
gradient grow as $O(t^{1/2})$. The result holds at least until the natural,
nonlinear timescale $t \approx \varepsilon^{-2}$. Notice that the density
behaves very differently from a passive scalar, as can be seen from the
inviscid damping and slower gradient growth. The proof relies on several
ingredients: (A) a suitable symmetrization that makes the linear terms amenable
to energy methods and takes into account the classical Miles-Howard spectral
stability condition; (B) a variation of the Fourier time-dependent energy
method introduced for the inviscid, homogeneous Couette flow problem developed
on a toy model adapted to the Boussinesq equations, i.e. tracking the potential
nonlinear echo chains in the symmetrized variables despite the vorticity
growth.",2103.13713v1
2021-03-31,Research of Damped Newton Stochastic Gradient Descent Method for Neural Network Training,"First-order methods like stochastic gradient descent(SGD) are recently the
popular optimization method to train deep neural networks (DNNs), but
second-order methods are scarcely used because of the overpriced computing cost
in getting the high-order information. In this paper, we propose the Damped
Newton Stochastic Gradient Descent(DN-SGD) method and Stochastic Gradient
Descent Damped Newton(SGD-DN) method to train DNNs for regression problems with
Mean Square Error(MSE) and classification problems with Cross-Entropy
Loss(CEL), which is inspired by a proved fact that the hessian matrix of last
layer of DNNs is always semi-definite. Different from other second-order
methods to estimate the hessian matrix of all parameters, our methods just
accurately compute a small part of the parameters, which greatly reduces the
computational cost and makes convergence of the learning process much faster
and more accurate than SGD. Several numerical experiments on real datesets are
performed to verify the effectiveness of our methods for regression and
classification problems.",2103.16764v1
2021-04-08,Landau Damping in the Transverse Modulational Dynamics of Co-Propagating Light and Matter Beams,"The optomechanical coupling and transverse stability of a co-propagating
monochromatic electromagnetic wave and mono-energetic beam of two-level atoms
is investigated in the collisionless regime. The coupled dynamics are studied
through a Landau stability analysis of the coupled gas- kinetic and paraxial
wave equations, including the effect of the electronic nonlinearity. The
resulting dispersion relation captures the interaction of kinetic and
saturation effects and shows that for blue detuning the combined nonlinear
interaction is unstable below a critical wavenumber which reduces to the result
of Bespalov and Talanov in the limit of a negligible kinetic nonlinearity. For
red detuning we find that under a saturation parameter threshold exists whereby
the system stabilizes unconditionally. With negligible saturation, an
optomechanical form of Landau damping stabilizes all wavenumbers above a
critical wavenumber determined by the combined strength of the kinetic and
refractive optomechanical feedback. The damping is mediated primarily by atoms
traveling along the primary diagonals of the Talbot carpet.",2104.04100v1
2021-04-15,Simulating cosmological supercooling with a cold atom system II,"We perform an analysis of the supercooled state in an analogue of an early
universe phase transition based on a one dimensional, two-component Bose gas
with time-dependent interactions. We demonstrate that the system behaves in the
same way as a thermal, relativistic Bose gas undergoing a first order phase
transition. We propose a way to prepare the state of the system in the
metastable phase as an analogue to supercooling in the early universe. While we
show that parametric resonances in the system can be suppressed by thermal
damping, we find that the theoretically estimated thermal damping in our model
is too weak to suppress the resonances for realistic experimental parameters.
However, we propose that experiments to investigate the effective damping rate
in experiments would be worthwhile.",2104.07428v1
2021-04-29,Nano-patterning of surfaces by ion sputtering: Numerical study of the anisotropic damped Kuramoto-Sivashinsky equation,"Nonlinear models for pattern evolution by ion beam sputtering on a material
surface present an ongoing opportunity for new numerical simulations. A
numerical analysis of the evolution of preexisting patterns is proposed to
investigate surface dynamics, based on a 2D anisotropic damped
Kuramoto-Sivashinsky equation, with periodic boundary conditions. A
finite-difference semi-implicit time splitting scheme is employed on the
discretization of the governing equation. Simulations were conducted with
realistic coefficients related to physical parameters (anisotropies, beam
orientation, diffusion). The stability of the numerical scheme is analyzed with
time step and grid spacing tests for the pattern evolution, and the Method of
Manufactured Solutions has been used to verify the proposed scheme. Ripples and
hexagonal patterns were obtained from a monomodal initial condition for certain
values of the damping coefficient, while spatiotemporal chaos appeared for
lower values. The anisotropy effects on pattern formation were studied, varying
the angle of incidence of the ion beam with respect to the irradiated surface.
Analytical discussions are based on linear and weakly nonlinear analysis.",2104.14104v1
2021-05-04,Linear response theory and damped modes of stellar clusters,"Because all stars contribute to its gravitational potential, stellar clusters
amplify perturbations collectively. In the limit of small fluctuations, this is
described through linear response theory, via the so-called response matrix.
While the evaluation of this matrix is somewhat straightforward for unstable
modes (i.e. with a positive growth rate), it requires a careful analytic
continuation for damped modes (i.e. with a negative growth rate). We present a
generic method to perform such a calculation in spherically symmetric stellar
clusters. When applied to an isotropic isochrone cluster, we recover the
presence of a low-frequency weakly damped $\ell = 1$ mode. We finally use a set
of direct $N$-body simulations to test explicitly this prediction through the
statistics of the correlated random walk undergone by a cluster's density
centre.",2105.01371v1
2021-05-10,Passivity-based control of mechanical systems with linear damping identification,"We propose a control approach for a class of nonlinear mechanical systems to
stabilize the system under study while ensuring that the oscillations of the
transient response are reduced. The approach is twofold: (i) we apply our
technique for linear viscous damping identification of the system to improve
the accuracy of the selected control technique, and (ii) we implement a
passivity-based controller to stabilize and reduce the oscillations by
selecting the control parameters properly in accordance with the identified
damping. Moreover, we provide an analysis for a particular passivity-based
control approach that has been shown successfully for reducing such
oscillations. Also, we validate the methodology by implementing it
experimentally in a planar manipulator.",2105.04324v4
2021-05-26,Decay dynamics of Localised Surface Plasmons: damping of coherences and populations of the oscillatory plasmon modes,"Properties of plasmonic materials are associated with surface plasmons - the
electromagnetic excitations coupled to coherent electron charge density
oscillations on a metal/dielectric interface. Although decay of such
oscillations cannot be avoided, there are prospects for controlling plasmon
damping dynamics. In spherical metal nanoparticles (MNPs) the basic properties
of Localized Surface Plasmons (LSPs) can be controlled with their radius. The
present paper handles the link between the size-dependent description of LSP
properties derived from the dispersion relation based on Maxwell's equations
and the quantum picture in which MNPs are treated as ""quasi-particles"". Such
picture, based on the reduced density-matrix of quantum open systems ruled by
the master equation in the Lindblad form, enables to distinguish between
damping processes of populations and coherences of multipolar plasmon
oscillatory states and to establish the intrinsic relations between the rates
of these processes, independently of the size of MNP. The impact of the
radiative and the nonradiative energy dissipation channels is discussed.",2105.12463v1
2021-06-05,The electron acoustic waves in plasmas with two kappa-distributed electrons at the same temperatures and immobile ions,"The linear electron acoustic waves propagating in plasmas with two
kappa-distributed electrons and stationary ions are investigated. The
temperatures of the two electrons are assumed to be the same, but the kappa
indices are not. It shows that if one kappa index is small enough and the other
one is large enough, a weak damping regime of the electron acoustic waves
exists. The dispersions and damping rates are numerically studied. The
parameter spaces for the weakly damped electron acoustic waves are analyzed.
Moreover, the electron acoustic waves in the present model are compared with
those in other models, especially the plasmas with two-temperature electrons.
At last, we perform Vlasov-Poisson simulations to verify the theory.",2106.02910v2
2021-06-18,Global existence and asymptotic behavior for semilinear damped wave equations on measure spaces,"This paper is concerned with the semilinear damped wave equation on a measure
space with a self-adjoint operator, instead of the standard Laplace operator.
Under a certain decay estimate on the corresponding heat semigroup, we
establish the linear estimates which generalize the so-called Matsumura
estimates, and prove the small data global existence of solutions to the damped
wave equation based on the linear estimates. Our approach is based on a direct
spectral analysis analogous to the Fourier analysis. The self-adjoint operators
treated in this paper include some important examples such as the Laplace
operators on Euclidean spaces, the Dirichlet Laplacian on an arbitrary open
set, the Robin Laplacian on an exterior domain, the Schr\""odinger operator, the
elliptic operator, the Laplacian on Sierpinski gasket, and the fractional
Laplacian.",2106.10322v3
2021-06-21,On the small time asymptotics of stochastic Ladyzhenskaya-Smagorinsky equations with damping perturbed by multiplicative noise,"The Ladyzhenskaya-Smagorinsky equations model turbulence phenomena, and are
given by $$\frac{\partial \boldsymbol{u}}{\partial t}-\mu
\mathrm{div}\left(\left(1+|\nabla\boldsymbol{u}|^2\right)^{\frac{p-2}{2}}\nabla\boldsymbol{u}\right)+(\boldsymbol{u}\cdot\nabla)\boldsymbol{u}+\nabla
p=\boldsymbol{f}, \ \nabla\cdot\boldsymbol{u}=0,$$ for $p\geq 2,$ in a bounded
domain $\mathcal{O}\subset\mathbb{R}^d$ ($2\leq d\leq 4$). In this work, we
consider the stochastic Ladyzhenskaya-Smagorinsky equations with the damping
$\alpha\boldsymbol{u}+\beta|\boldsymbol{u}|^{r-2}\boldsymbol{u},$ for $r\geq 2$
($\alpha,\beta\geq 0$), subjected to multiplicative Gaussian noise. We show the
local monotoincity ($p\geq \frac{d}{2}+1,\ r\geq 2$) as well as global
monotonicity ($p\geq 2,\ r\geq 4$) properties of the linear and nonlinear
operators, which along with an application of stochastic version of
Minty-Browder technique imply the existence of a unique pathwise strong
solution. Then, we discuss the small time asymptotics by studying the effect of
small, highly nonlinear, unbounded drifts (small time large deviation
principle) for the stochastic Ladyzhenskaya-Smagorinsky equations with damping.",2106.10861v1
2021-06-23,Improved convergence rates and trajectory convergence for primal-dual dynamical systems with vanishing damping,"In this work, we approach the minimization of a continuously differentiable
convex function under linear equality constraints by a second-order dynamical
system with asymptotically vanishing damping term. The system is formulated in
terms of the augmented Lagrangian associated to the minimization problem. We
show fast convergence of the primal-dual gap, the feasibility measure, and the
objective function value along the generated trajectories. In case the
objective function has Lipschitz continuous gradient, we show that the
primal-dual trajectory asymptotically weakly converges to a primal-dual optimal
solution of the underlying minimization problem. To the best of our knowledge,
this is the first result which guarantees the convergence of the trajectory
generated by a primal-dual dynamical system with asymptotic vanishing damping.
Moreover, we will rediscover in case of the unconstrained minimization of a
convex differentiable function with Lipschitz continuous gradient all
convergence statements obtained in the literature for Nesterov's accelerated
gradient method.",2106.12294v1
2021-06-24,Landau damping of electron-acoustic waves due to multi-plasmon resonances,"The linear and nonlinear theories of electron-acoustic waves (EAWs) are
studied in a partially degenerate quantum plasma with two-temperature electrons
and stationary ions. The initial equilibrium of electrons is assumed to be
given by the Fermi-Dirac distribution at finite temperature. By employing the
multi-scale asymptotic expansion technique to the one-dimensional Wigner-Moyal
and Poisson equations, it is shown that the effects of multi-plasmon resonances
lead to a modified complex Korteweg-de Vries (KdV) equation with a new nonlocal
nonlinearity. Besides giving rise to a nonlocal nonlinear term, the
wave-particle resonance also modifies the local nonlinear coupling coefficient
of the KdV equation. The latter is shown to conserve the number of particles,
however, the wave energy decays with time. A careful analysis shows that the
two-plasmon resonance is the dominant mechanism for nonlinear Landau damping of
EAWs. An approximate soliton solution of the KdV equation is also obtained, and
it is shown that the nonlinear Landau damping causes the wave amplitude to
decay slowly with time compared to the classical theory.",2106.12754v2
2021-07-01,On behavior of solutions to a Petrovsky equation with damping and variable-exponent source,"This paper deals with the following Petrovsky equation with damping and
nonlinear source \[u_{tt}+\Delta^2 u-M(\|\nabla u\|_2^2)\Delta u-\Delta
u_t+|u_t|^{m(x)-2}u_t=|u|^{p(x)-2}u\] under initial-boundary value conditions,
where $M(s)=a+ bs^\gamma$ is a positive $C^1$ function with parameters
$a>0,~b>0,~\gamma\geq 1$, and $m(x),~p(x)$ are given measurable functions. The
upper bound of the blow-up time is derived for low initial energy using the
differential inequality technique. For $m(x)\equiv2$, in particular, the upper
bound of the blow-up time is obtained by the combination of Levine's concavity
method and some differential inequalities under high initial energy. In
addition, by making full use of the strong damping, the lower bound of the
blow-up time is discussed. Moreover, the global existence of solutions and an
energy decay estimate are presented by establishing some energy estimates and
by exploiting a key integral inequality.",2107.00273v2
2021-07-21,A combined volume penalization / selective frequency damping approach for immersed boundary methods applied to high-order schemes,"There has been an increasing interest in developing efficient immersed
boundary method (IBM) based on Cartesian grids, recently in the context of
high-order methods. IBM based on volume penalization is a robust and easy to
implement method to avoid body-fitted meshes and has been recently adapted to
high order discretisations (Kou et al., 2021). This work proposes an
improvement over the classic penalty formulation for flux reconstruction high
order solvers. We include a selective frequency damping (SFD) approach
(Aakervik et al., 2006) acting only inside solid body defined through the
immersed boundary masking, to damp spurious oscillations. An encapsulated
formulation for the SFD method is implemented, which can be used as a wrapper
around an existing time-stepping code. The numerical properties have been
studied through eigensolution analysis based on the advection equation. These
studies not only show the advantages of using the SFD method as an alternative
of the traditional volume penalization, but also show the favorable properties
of combining both approaches. This new approach is then applied to the
Navier-Stokes equation to simulate steady flow past an airfoil and unsteady
flow past a circular cylinder. The advantages of the SFD method in providing
improved accuracy are reported.",2107.10177v1
2021-07-25,Dispatch of Virtual Inertia and Damping: Numerical Method with SDP and ADMM,"Power grids are evolving toward 100% renewable energy interfaced by
inverters. Virtual inertia and damping provided by inverters are essential to
synchronism and frequency stability of future power grids. This paper
numerically addresses the problem of dispatch of virtual inertia and damping
(DID) among inverters in the transmission network. The DID problem is first
formulated as a nonlinear program (NLP) by the Radua collocation method which
is flexible to handle various types of disturbances and bounds constraints.
Since the NLP of DID is highly non-convex, semi-definite programming (SDP)
relaxation for the NLP is further derived to tackle the non-convexity, followed
by its sparsity being exploited hierarchically based on chordality of graphs to
seek enhancement of computational efficiency. Considering high dimension and
inexactness of the SDP relaxation, a feasibility-embedded distributed approach
is finally proposed under the framework of alternating direction method of
multipliers (ADMM), which achieves parallel computing and solution feasibility
regarding the original NLP. Numerical simulations carried out for five test
power systems demonstrate the proposed method and necessity of DID.",2107.11764v1
2021-07-29,Microscopic analysis of sound attenuation in low-temperature amorphous solids reveals quantitative importance of non-affine effects,"Sound attenuation in low temperature amorphous solids originates from their
disordered structure. However, its detailed mechanism is still being debated.
Here we analyze sound attenuation starting directly from the microscopic
equations of motion. We derive an exact expression for the zero-temperature
sound damping coefficient. We verify that the sound damping coefficients
calculated from our expression agree very well with results from independent
simulations of sound attenuation. The small wavevector analysis of our
expression shows that sound attenuation is primarily determined by the
non-affine displacements' contribution to the sound wave propagation
coefficient coming from the frequency shell of the sound wave. Our expression
involves only quantities that pertain to solids' static configurations. It can
be used to evaluate the low temperature sound damping coefficients without
directly simulating sound attenuation.",2107.14254v2
2021-08-09,Damping perturbation based time integration asymptotic method for structural dynamics,"The light damping hypothesis is usually assumed in structural dynamics since
dissipative forces are in general weak with respect to inertial and elastic
forces. In this paper a novel numerical method of time integration based on the
artificial perturbation of damping is proposed. The asymptotic expansion of the
transient response results in an infinite series which can be summed, leading
to a well-defined explicit iterative step-by-step scheme. Conditions for
convergence are rigorously analyzed, enabling the determination of the
methodology boundaries in form of maximum time step. The numerical properties
of the iterative scheme, i.e. stability, accuracy and computational effort are
also studied in detail. The approach is validated with two numerical examples,
showing a high accuracy and computational efficiency relative to other methods.",2108.03813v1
2021-08-12,The damping and diffusion of atoms moving in the background electromagnetic environment,"The interaction between an atom and the quantized electromagnetic field
depends on the position of the atom. Then the atom experiences a force which is
the minus gradient of this interaction. Through the Heisenberg equations of
motion and the Born-Markov approximation, the mean and correlation of the force
are obtained, showing that the center-of-mass motion of the atom is damped and
diffused. This approach can be easily generalized to multi-level atoms, where
the damping force and diffusion coefficients are just the weighted average of
the contributions from all pairs of energy levels that have nonvanishing dipole
elements. It is shown that these results are invariant under Galilean
transformation, and in principle can be used to determine the velocity of the
lab relative to the background radiation.",2108.05590v3
2021-09-22,Antibunching via cooling by heating,"We investigate statistics of the photon (phonon) field undergoing linear and
nonlinear damping processes. An effective two-photon (phonon) nonlinear
""cooling by heating"" process is realized from linear damping by spectral
filtering of the heat baths present in the system. This cooling process driven
by incoherent quantum thermal noise can create quantum states of the photon
field. In fact, for high temperatures of the spectrally filtered heat baths,
sub-Poissonian statistics with strong antibunching in the photon (phonon) field
are reported. This notion of the emergence and control of quantumness by
incoherent thermal quantum noise is applied to a quantum system comprising of a
two-level system and a harmonic oscillator or analogous optomechanical setting.
Our analysis may provide a promising direction for the preparation and
protection of quantum features via nonlinear damping that can be controlled
with incoherent thermal quantum noise.",2109.10516v2
2021-10-13,Tutorial on stochastic systems,"In this tutorial, three examples of stochastic systems are considered: A
strongly-damped oscillator, a weakly-damped oscillator and an undamped
oscillator (integrator) driven by noise. The evolution of these systems is
characterized by the temporal correlation functions and spectral densities of
their displacements, which are determined and discussed. Damped oscillators
reach steady stochastic states. Their correlations are decreasing functions of
the difference between the sample times and their spectra have peaks near their
resonance frequencies. An undamped oscillator never reaches a steady state. Its
energy increases with time and its spectrum is sharply peaked at low
frequencies. The required mathematical methods and physical concepts are
explained on a just-in-time basis, and some theoretical pitfalls are mentioned.
The insights one gains from studies of oscillators can be applied to a wide
variety of physical systems, such as atom and semiconductor lasers, which will
be discussed in a subsequent tutorial.",2110.06966v1
2021-10-18,Structured vector fitting framework for mechanical systems,"In this paper, we develop a structure-preserving formulation of the
data-driven vector fitting algorithm for the case of modally damped mechanical
systems. Using the structured pole-residue form of the transfer function of
modally damped second-order systems, we propose two possible structured
extensions of the barycentric formula of system transfer functions. Integrating
these new forms within the classical vector fitting algorithm leads to the
formulation of two new algorithms that allow the computation of modally damped
mechanical systems from data in a least squares fashion. Thus, the learned
model is guaranteed to have the desired structure. We test the proposed
algorithms on two benchmark models.",2110.09220v1
2021-10-27,Integrability and solvability of polynomial Liénard differential systems,"We provide the necessary and sufficient conditions of Liouvillian
integrability for Li\'{e}nard differential systems describing nonlinear
oscillators with a polynomial damping and a polynomial restoring force. We
prove that Li\'{e}nard differential systems are not Darboux integrable
excluding subfamilies with certain restrictions on the degrees of the
polynomials arising in the systems. We demonstrate that if the degree of a
polynomial responsible for the restoring force is greater than the degree of a
polynomial producing the damping, then a generic Li\'{e}nard differential
system is not Liouvillian integrable with the exception of linear Li\'{e}nard
systems. However, for any fixed degrees of the polynomials describing the
damping and the restoring force we present subfamilies possessing Liouvillian
first integrals. As a by-product of our results, we find a number of novel
Liouvillian integrable subfamilies. In addition, we study the existence of
non-autonomous Darboux first integrals and non-autonomous Jacobi last
multipliers with a time-dependent exponential factor.",2110.14306v2
2021-10-28,Global Solution to the Vacuum Free Boundary Problem with Physical Singularity of Compressible Euler Equations with Damping and Gravity,"The global existence of smooth solutions to the vacuum free boundary problem
with physical singularity of compressible Euler equations with damping and
gravity is proved in space dimensions $n=1, 2, 3$, for the initial data being
small perturbations of the stationary solution. Moreover, the exponential decay
of the velocity is obtained for $n=1, 2, 3$. The exponentially fast convergence
of the density and vacuum boundary to those of the stationary solution is shown
for $n=1$, and it is proved for $n=2, 3$ that they stay close to those of the
stationary solution if they do so initially. The proof is based on the weighted
estimates of both hyperbolic and parabolic types with weights capturing the
singular behavior of higher-order normal derivatives near vacuum states,
exploring the balance between the physical singularity which pushes the vacuum
boundary outwards and the effect of gravity which pulls it inwards, and the
dissipation of the frictional damping. The results obtained in this paper are
the first ones on the global existence of solutions to the vacuum free boundary
problems of inviscid compressible fluids with the non-expanding background
solutions. Exponentially fast convergence when the vacuum state is involved
discovered in this paper is a new feature of the problem studied.",2110.14909v1
2021-10-29,Spinons and damped phonons in spin-1/2 quantum-liquid Ba$_{4}$Ir${}_3$O${}_{10}$ observed by Raman scattering,"In spin-1/2 Mott insulators, non-magnetic quantum liquid phases are often
argued to arise when the system shows no magnetic ordering, but identifying
positive signatures of these phases or related spinon quasiparticles can be
elusive. Here we use Raman scattering to provide three signatures for spinons
in a possible spin-orbit quantum liquid material Ba${}_4$Ir${}_3$O${}_{10}$:
(1) A broad hump, which we show can arise from Luttinger Liquid spinons in
Raman with parallel photon polarizations normal to 1D chains; (2) Strong phonon
damping from phonon-spin coupling via the spin-orbit interaction; and (3) the
absence of (1) and (2) in the magnetically ordered phase that is produced when
2% of Ba is substituted by Sr
((Ba${}_{0.98}$Sr${}_{0.02}$)${}_4$Ir${}_3$O${}_{10}$). The phonon damping via
itinerant spinons seen in this quantum-liquid insulator suggests a new
mechanism for enhancing thermoelectricity in strongly correlated conductors,
through a neutral quantum liquid that need not affect electronic transport.",2110.15916v1
2021-11-03,Pointwise space-time estimates of two-phase fluid model in dimension three,"In this paper, we investigate the pointwise space-time behavior of two-phase
fluid model derived by Choi \cite{Choi} [SIAM J. Math. Anal., 48(2016), pp.
3090-3122], which is the compressible damped Euler equations coupled with
compressible Naiver-Stokes equations. Based on Green's function method together
with frequency analysis and nonlinear coupling of different wave patterns, it
shows that both of two densities and momentums obey the generalized Huygens'
principle as the compressible Navier-Stokes equations \cite{LW}, however, it is
different from the compressible damped Euler equations \cite{Wang2}. The main
contributions include seeking suitable combinations to avoid the singularity
from the Hodge decomposition in the low frequency part of the Green's function,
overcoming the difficulty of the non-conservation arising from the damped
mechanism of the system, and developing the detailed description of the
singularities in the high frequency part of the Green's function. Finally, as a
byproduct, we extend $L^2$-estimate in \cite{Wugc} [SIAM J. Math. Anal.,
52(2020), pp. 5748-5774] to $L^p$-estimate with $p>1$.",2111.01987v1
2021-11-09,Turbulent cascades for a family of damped Szegö equations,"In this paper, we study the transfer of energy from low to high frequencies
for a family of damped Szeg\""o equations. The cubic Szeg\""o equation has been
introduced as a toy model for a totally non-dispersive degenerate Hamiltonian
equation. It is a completely integrable system which develops growth of high
Sobolev norms, detecting transfer of energy and hence cascades phenomena.
  Here, we consider a two-parameter family of variants of the cubic Szeg\""o
equation and prove that adding a damping term unexpectedly promotes the
existence of turbulent cascades. Furthermore, we give a panorama of the
dynamics for such equations on a six-dimensional submanifold.",2111.05247v1
2021-11-18,Sharp Stability of a String with Local Degenerate Kelvin-Voigt Damping,"This paper is on the asymptotic behavior of the elastic string equation with
localized degenerate Kelvin--Voigt damping $$
u_{tt}(x,t)-[u_{x}(x,t)+b(x)u_{x,t}(x,t)]_{x}=0,\; x\in(-1,1),\; t>0,$$ where
$b(x)=0$ on $x\in (-1,0]$, and $b(x)=x^\alpha>0$ on $x\in (0,1)$ for
$\alpha\in(0,1)$. It is known that the optimal decay rate of solution is
$t^{-2}$ in the limit case $\alpha=0$, and exponential decay rate for
$\alpha\ge 1$. When $\alpha\in (0,1)$, the damping coefficient $b(x)$ is
continuous, but its derivative has a singularity at the interface $x=0$. In
this case, the best known decay rate is $t^{-\frac{3-\alpha}{2(1-\alpha)}}$.
Although this rate is consistent with the exponential one at $\alpha=1$, it
failed to match the optimal one at $\alpha=0$.
  In this paper, we obtain a sharper polynomial decay rate
$t^{-\frac{2-\alpha}{1-\alpha}}$. More significantly, it is consistent with the
optimal polynomial decay rate at $\alpha=0$ and the exponential decay rate at
$\alpha = 1$.This is a big step toward the goal of obtaining eventually the
optimal decay rate.",2111.09500v1
2021-11-22,Global well-posedness for a generalized Keller-Segel system with degenerate dissipation and mixing,"We study the mixing effect for a generalized Keller-Segel system with
degenerate dissipation and advection by a weakly mixing. Here the attractive
operator has weak singularity, namely, the negative derivative appears in the
nonlinear term by singular integral. Without advection, the solution of
equation blows up in finite time. We show that the global well-posedness of
solution with large advection. Since dissipation term degenerate into the
damping, the enhanced dissipation effect of mixing no longer occurs, we prove
that the mixing effect can weak the influence of nonlinear term. In this case,
the mixing effect is similar with inviscid damping of shear flow. Combining to
the mixing effect and damping effect of degenerate dissipation, the global
$L^\infty$ estimate of solution is established.",2111.11083v1
2021-11-26,Damping of Pseudo-Goldstone Fields,"Approximate symmetries abound in Nature. If these symmetries are also
spontaneously broken, the would-be Goldstone modes acquire a small mass, or
inverse correlation length, and are referred to as pseudo-Goldstones. At
nonzero temperature, the effects of dissipation can be captured by
hydrodynamics at sufficiently long scales compared to the local equilibrium.
Here we show that in the limit of weak explicit breaking, locality of
hydrodynamics implies that the damping of pseudo-Goldstones is completely
determined by their mass and diffusive transport coefficients. We present many
applications: superfluids, QCD in the chiral limit, Wigner crystal and density
wave phases in the presence of an external magnetic field or not, nematic
phases and (anti-)ferromagnets. For electronic density wave phases,
pseudo-Goldstone damping generates a contribution to the resistivity
independent of the strength of disorder, which can have a linear temperature
dependence provided the associated diffusivity saturates a bound. This is
reminiscent of the phenomenology of strange metal high $T_c$ superconductors,
where charge density waves are observed across the phase diagram.",2111.13459v2
2021-11-26,Transition from order to chaos in reduced quantum dynamics,"We study a damped kicked top dynamics of a large number of qubits ($N
\rightarrow \infty$) and focus on an evolution of a reduced single-qubit
subsystem. Each subsystem is subjected to the amplitude damping channel
controlled by the damping constant $r\in [0,1]$, which plays the role of the
single control parameter. In the parameter range for which the classical
dynamics is chaotic, while varying $r$ we find the universal period-doubling
behavior characteristic to one-dimensional maps: period-two dynamics starts at
$r_1 \approx 0.3181$, while the next bifurcation occurs at $ r_2 \approx
0.5387$. In parallel with period-four oscillations observed for $r \leq r_3
\approx 0.5672$, we identify a secondary bifurcation diagram around $r\approx
0.544$, responsible for a small-scale chaotic dynamics inside the attractor.
The doubling of the principal bifurcation tree continues until $r \leq
r_{\infty} \sim 0.578$, which marks the onset of the full scale chaos
interrupted by the windows of the oscillatory dynamics corresponding to the
Sharkovsky order.",2111.13477v1
2021-12-06,"Damped physical oscillators, temperature and chemical clocks","The metaphor of a clock in physics describes near-equilibrium reversible
phenomena such as an oscillating spring. It is surprising that for chemical and
biological clocks the focus has been exclusively on the far-from-equilibrium
dissipative processes. We show here that one can represent chemical
oscillations (the Lotka-Volterra system and the Brusselator) by equations
analogous to Onsager's phenomenological equations when the condition of the
reciprocal relations, i.e. the symmetry in the coupling of thermodynamic forces
to fluxes is relaxed and antisymmetric contributions are permitted. We compare
these oscillations to damped oscillators in physics (e.g., springs, coupled
springs and electrical circuits) which are represented by similar equations.
Onsager's equations and harmonic Hamiltonian systems are shown to be limiting
cases of a more general formalism.
  The central element of un-damped physical oscillations is the conservation of
entropy which unavoidably results in reversible temperature oscillations. Such
temperature oscillations exist in springs and electrical LC-circuits, but have
among others also been found in the oscillating Belousov-Zhabotinsky reaction,
in oscillations of yeast cells, and during the nervous impulse. This suggests
that such oscillations contain reversible entropy-conserving elements, and that
physical and chemical clocks may be more similar than expected.",2112.03083v1
2021-12-10,Existence of Zero-damped Quasinormal Frequencies for Nearly Extremal Black Holes,"It has been observed that many spacetimes which feature a near-extremal
horizon exhibit the phenomenon of zero-damped modes. This is characterised by
the existence of a sequence of quasinormal frequencies which all converge to
some purely imaginary number $i\alpha$ in the extremal limit and cluster in a
neighbourhood of the line $\Im s=\alpha$. In this paper, we establish that this
property is present for the conformal Klein-Gordon equation on a
Reissner-Nordstr\""om-de Sitter background. This follows from a similar result
that we prove for a class of spherically symmetric black hole spacetimes with a
cosmological horizon. We also show that the phenomenon of zero-damped modes is
stable to perturbations that arise through adding a potential.",2112.05669v3
2021-12-22,Quantifying Spin-Orbit Torques in Antiferromagnet/Heavy Metal Heterostructures,"The effect of spin currents on the magnetic order of insulating
antiferromagnets (AFMs) is of fundamental interest and can enable new
applications. Toward this goal, characterizing the spin-orbit torques (SOT)
associated with AFM/heavy metal (HM) interfaces is important. Here we report
the full angular dependence of the harmonic Hall voltages in a predominantly
easy-plane AFM, epitaxial c-axis oriented $\alpha$-Fe$_2$O$_3$ films, with an
interface to Pt. By modeling the harmonic Hall signals together with the
$\alpha$-Fe$_2$O$_3$ magnetic parameters, we determine the amplitudes of
field-like and damping-like SOT. Out-of-plane field scans are shown to be
essential to determining the damping-like component of the torques. In contrast
to ferromagnetic/heavy metal heterostructures, our results demonstrate that the
field-like torques are significantly larger than the damping-like torques,
which we correlate with the presence of a large imaginary component of the
interface spin-mixing conductance. Our work demonstrates a direct way of
characterizing SOT in AFM/HM heterostructures.",2112.12238v1
2022-01-04,Focusing of nonlinear eccentric waves in astrophysical discs. II. Excitation and damping of tightly-wound waves,"In this paper I develop a nonlinear theory of tightly-wound (highly twisted)
eccentric waves in astrophysical discs, based on the averaged Lagrangian method
of Whitham. Viscous dissipation is included in the theory by use of a
pseudo-Lagrangian. This work is an extension of the theory developed by Lee \&
Goodman to 3D discs, with the addition of viscosity. I confirm that linear
tightly-wound eccentric waves are overstable and are excited by the presence of
a shear viscosity and show this persists for weakly nonlinear waves. I find the
waves are damped by shear viscosity when the wave become sufficiently
nonlinear, a result previously found in particulate discs. Additionally I
compare the results of this model to recent simulations of eccentric waves
propagating in the inner regions of black hole discs and show that an ingoing
eccentric wave can be strongly damped near the marginally stable orbit,
resulting in a nearly circular disc with a strong azimuthal variation in the
disc density.",2201.01156v1
2022-01-12,Local Well-Posedness of the Gravity-Capillary Water Waves System in the Presence of Geometry and Damping,"We consider the gravity-capillary water waves problem in a domain $\Omega_t
\subset \mathbb{T} \times \mathbb{R}$ with substantial geometric features.
Namely, we consider a variable bottom, smooth obstacles in the flow and a
constant background current. We utilize a vortex sheet model introduced by
Ambrose, et. al. in arXiv:2108.01786. We show that the water waves problem is
locally-in-time well-posed in this geometric setting and study the lifespan of
solutions. We then add a damping term and derive evolution equations that
account for the damper. Ultimately, we show that the same well-posedness and
lifespan results apply to the damped system. We primarily utilize energy
methods.",2201.04713v2
2022-02-04,"Finite-temperature plasmons, damping and collective behavior for $α-\mathcal{T}_3$ model","We have conducted a thorough theoretical and numerical investigation of the
electronic susceptibility, polarizability, plasmons, their damping rates, as
well as the static screening in pseudospin-1 Dirac cone materials with a flat
band, or for a general $\alpha - \mathcal{T}_3$ model, at finite temperatures.
This includes calculating the polarization function, plasmon dispersions and
their damping rates at arbitrary temperatures and obtaining analytical
approximations the long wavelength limit, low and high temperatures. We
demonstrate that the integral transformation of the polarization function
cannot be used directly for a dice lattice revealing some fundamental
properties and important applicability limits of the flat band dispersions
model. At $k_B T \ll E_F$, the largest temperature-induced change of the
polarization function and plasmons comes from the mismatch between the chemical
potential and the Fermi energy. We have also obtained a series of closed-form
semi-analytical expressions for the static limit of the polarization function
of an arbitrary $\alpha - \mathcal{T}_3$ material at any temperature with exact
analytical formulas for the high, low and zero temperature limits which is of
tremendous importance for all types of transport and screening calculations for
the flat band Dirac materials.",2202.01945v1
2022-02-04,Enhancing the Formation of Wigner Negativity in a Kerr Oscillator via Quadrature Squeezing,"Motivated by quantum experiments with nanomechanical systems, the evolution
of a Kerr oscillator with focus on creation of states with a negative Wigner
function is investigated. Using the phase space formalism, results are
presented that demonstrate an asymptotic behavior in the large squeezing regime
for the negativity of a squeezed vacuum state under unitary evolution. The
analysis and model are extended to squeezed vacuum states of open systems,
adding the decoherence effects of damping and dephasing. To increase
experimental relevance, the regime of strong damping is considered. These
effects are investigated, yielding similar asymptotic results for the behavior
of these effects in the large squeezing regime. Combining these results, it is
shown that a weak nonlinearity as compared to damping may be improved by
increasing the squeezing of the initial state. It is also shown that this may
be done without exacerbating the effects of dephasing.",2202.02285v1
2022-02-11,"Spin stiffness, spectral weight, and Landau damping of magnons in metallic spiral magnets","We analyze the properties of magnons in metallic electron systems with spiral
magnetic order. Our analysis is based on the random phase approximation for the
susceptibilities of tight binding electrons with a local Hubbard interaction in
two or three dimensions. We identify three magnon branches from poles in the
susceptibilities, one associated with in-plane, the other two associated with
out-of-plane fluctuations of the spiral order parameter. We derive general
expressions for the spin stiffnesses and the spectral weights of the magnon
modes, from which also the magnon velocities can be obtained. Moreover, we
determine the size of the decay rates of the magnons due to Landau damping.
While the decay rate of the in-plane mode is of the order of its excitation
energy, the decay rate of the out-of-plane mode is smaller so that these modes
are asymptotically stable excitations even in the presence of Landau damping.",2202.05660v1
2022-02-16,On the strong convergence of the trajectories of a Tikhonov regularized second order dynamical system with asymptotically vanishing damping,"This paper deals with a second order dynamical system with vanishing damping
that contains a Tikhonov regularization term, in connection to the minimization
problem of a convex Fr\'echet differentiable function $g$.
  We show that for appropriate Tikhonov regularization parameters the value of
the objective function in a generated trajectory converges fast to the global
minimum of the objective function and a trajectory generated by the dynamical
system converges weakly to a minimizer of the objective function. We also
obtain the fast convergence of the velocities towards zero and some integral
estimates. Nevertheless, our main goal is to extend and improve some recent
results obtained in \cite{ABCR} and \cite{AL-nemkoz} concerning the strong
convergence of the generated trajectories to an element of minimal norm from
the $\argmin$ set of the objective function $g$. Our analysis also reveals that
the damping coefficient and the Tikhonov regularization coefficient are
strongly correlated.",2202.08980v1
2022-04-01,Effect of interfacial spin mixing conductance on gyromagnetic ratio of Gd substituted Y$_{3}$Fe$_{5}$O$_{12}$,"Due to its low intrinsic damping, Y$_3$Fe$_5$O$_{12}$ and its substituted
variations are often used for ferromagnetic layer at spin pumping experiment.
Spin pumping is an interfacial spin current generation in the interface of
ferromagnet and non-magnetic metal, governed by spin mixing conductance
parameter $G^{\uparrow\downarrow}$. $G^{\uparrow\downarrow}$ has been shown to
enhance the damping of the ferromagnetic layer. The theory suggested that the
effect of $G^{\uparrow\downarrow}$ on gyromagnetic ratio only come from its
negligible imaginary part. In this article, we show that the different damping
of ferrimagnetic lattices induced by $G^{\uparrow\downarrow}$ can affect the
gyromagnetic ratio of Gd-substituted Y$_3$Fe$_5$O$_{12}$.",2204.00310v1
2022-04-04,A Vanka-based parameter-robust multigrid relaxation for the Stokes-Darcy Brinkman problems,"We propose a block-structured multigrid relaxation scheme for solving the
Stokes-Darcy Brinkman equations discretized by the marker and cell scheme. An
element-based additive Vanka smoother is used to solve the corresponding
shifted Laplacian operator. Using local Fourier analysis, we present the
stencil for the additive Vanka smoother and derive an optimal smoothing factor
for Vanka-based Braess-Sarazin relaxation for the Stokes-Darcy Brinkman
equations. Although the optimal damping parameter is dependent on meshsize and
physical parameter, it is very close to one. Numerical results of two-grid and
V(1,1)-cycle are presented, which show high efficiency of the proposed
relaxation scheme and its robustness to physical parameters and the meshsize.
Using a damping parameter equal to one gives almost the same results as these
for the optimal damping parameter at a lower computational overhead.",2204.01237v1
2022-04-19,Blow-up and lifespan estimate for wave equations with critical damping term of space-dependent type related to Glassey conjecture,"The main purpose of the present paper is to study the blow-up problem of the
wave equation with space-dependent damping in the \textit{scale-invariant case}
and time derivative nonlinearity with small initial data. Under appropriate
initial data which are compactly supported, by using a test function method and
taking into account the effect of the damping term
($\frac{\mu}{\sqrt{1+|x|^2}}u_t$), we provide that in higher dimensions the
blow-up region is given by $p \in (1, p_G(N+\mu)]$ where $p_G(N)$ is the
Glassey exponent. Furthermore, we shall establish a blow-up region, independent
of $\mu$ given by $p\in (1, 1+\frac{2}{N}),$ for appropriate initial data in
the energy space with noncompact support.",2204.09156v1
2022-04-28,Strong coupling of quantum emitters and the exciton polariton in MoS$_2$ nanodisks,"As a quasiparticle formed by light and excitons in semiconductors, the
exciton-polariton (EP) as a quantum bus is promising for the development of
quantum interconnect devices at room temperature. However, the significant
damping of EPs in the material generally causes a loss of quantum information.
We propose a mechanism to overcome the destructive effect of a damping EP on
its mediated correlation dynamics of quantum emitters (QEs). Via an
investigation of the near-field coupling between two QEs and the EP in a
monolayer MoS$_{2}$ nanodisk, we find that, with the complete dissipation of
the QEs efficiently avoided, a persistent quantum correlation between the QEs
can be generated and stabilized even to their steady state. This is due to the
fact that, with upon decreasing the QE-MoS$_2$ distance, the QEs become so
hybridized with the EP that one or two bound states are formed between them.
Our result supplies a useful way to avoid the destructive impact of EP damping,
and it refreshes our understanding of the light-matter interaction in absorbing
medium.",2204.13383v2
2022-05-09,Scalable all-optical cold damping of levitated nanoparticles,"The field of levitodynamics has made significant progress towards controlling
and studying the motion of a levitated nanoparticle. Motional control relies on
either autonomous feedback via a cavity or measurement-based feedback via
external forces. Recent demonstrations of measurement-based ground-state
cooling of a single nanoparticle employ linear velocity feedback, also called
cold damping, and require the use of electrostatic forces on charged particles
via external electrodes. Here we introduce a novel all-optical cold damping
scheme based on spatial modulation of the trap position that is scalable to
multiple particles. The scheme relies on using programmable optical tweezers to
provide full independent control over trap frequency and position of each
tweezer. We show that the technique cools the center-of-mass motion of
particles down to $17\,$mK at a pressure of $2 \times 10^{-6}\,$mbar and
demonstrate its scalability by simultaneously cooling the motion of two
particles. Our work paves the way towards studying quantum interactions between
particles, achieving 3D quantum control of particle motion without cavity-based
cooling, electrodes or charged particles, and probing multipartite entanglement
in levitated optomechanical systems.",2205.04455v1
2022-06-08,Thermal ion kinetic effects and Landau damping in fishbone modes,"The kinetic-MHD hybrid simulation approach for macroscopic instabilities in
plasmas can be extended to include the kinetic effects of both thermal ions and
energetic ions. The new coupling scheme includes synchronization of density and
parallel velocity between thermal ions and MHD, in addition to pressure
coupling, to ensure the quasineutrality condition and avoid numerical errors.
The new approach has been implemented in the kinetic-MHD code M3D-C1-K, and was
used to study the thermal ion kinetic effects and Landau damping in fishbone
modes in both DIII-D and NSTX. It is found that the thermal ion kinetic effects
can cause an increase of the frequencies of the non-resonant $n=1$ fishbone
modes driven by energetic particles for $q_\mathrm{min}>1$, and Landau damping
can provide additional stabilization effects. A nonlinear simulation for $n=1$
fishbone mode in NSTX is also performed, and the perturbation on magnetic flux
surfaces and the transport of energetic particles are calculated.",2206.03648v1
2022-07-12,Resonant Multilevel Amplitude Damping Channels,"We introduce a new set of quantum channels: resonant multilevel amplitude
damping (ReMAD) channels. Among other instances, they can describe energy
dissipation effects in multilevel atomic systems induced by the interaction
with a zero-temperature bosonic environment. At variance with the already known
class of multilevel amplitude damping (MAD) channels, this new class of maps
allows the presence of an environment unable to discriminate transitions with
identical energy gaps. After characterizing the algebra of their composition
rules, by analyzing the qutrit case, we show that this new set of channels can
exhibit degradability and antidegradability in vast regions of the allowed
parameter space. There we compute their quantum capacity and private classical
capacity. We show that these capacities can be computed exactly also in regions
of the parameter space where the channels aren't degradable nor antidegradable.",2207.05646v2
2022-07-14,Estimates for the nonlinear viscoelastic damped wave equation on compact Lie groups,"Let $G$ be a compact Lie group. In this article, we investigate the Cauchy
problem for a nonlinear wave equation with the viscoelastic damping on $G$.
More preciously, we investigate some $L^2$-estimates for the solution to the
homogeneous nonlinear viscoelastic damped wave equation on $G$ utilizing the
group Fourier transform on $G$. We also prove that there is no improvement of
any decay rate for the norm $\|u(t,\cdot)\|_{L^2(G)}$ by further assuming the
$L^1(G)$-regularity of initial data. Finally, using the noncommutative Fourier
analysis on compact Lie groups, we prove a local in time existence result in
the energy space $\mathcal{C}^1([0,T],H^1_{\mathcal L}(G)).$",2207.06645v3
2022-08-04,Normal and Quasinormal Modes of Holographic Multiquark Star,"The quadrupole normal-mode oscillation frequency $f_{n}$ of multiquark star
are computed for $n=1-5$. At the transition from low to high density multiquark
in the core region, the first 2 modes jump to larger values, a distinctive
signature of the presence of the high-density core. When the star oscillation
couples with spacetime, gravitational waves~(GW) will be generated and the star
will undergo damped oscillation. The quasinormal modes~(QNMs) of the
oscillation are computed using two methods, direct scan and WKB, for QNMs with
small and large imaginary parts respectively. The small imaginary QNMs have
frequencies $1.5-2.6$ kHz and damping times $0.19-1.7$ secs for multiquark star
with mass $M=0.6-2.1 M_{\odot}$~(solar mass). The WKB QNMs with large imaginary
parts have frequencies $5.98-9.81$ kHz and damping times $0.13-0.46$ ms for
$M\simeq 0.3-2.1 M_{\odot}$. They are found to be the fluid $f-$modes and
spacetime curvature $w-$modes respectively.",2208.02761v2
2022-08-10,Erasure qubits: Overcoming the $T_1$ limit in superconducting circuits,"The amplitude damping time, $T_1$, has long stood as the major factor
limiting quantum fidelity in superconducting circuits, prompting concerted
efforts in the material science and design of qubits aimed at increasing $T_1$.
In contrast, the dephasing time, $T_{\phi}$, can usually be extended above
$T_1$ (via, e.g., dynamical decoupling), to the point where it does not limit
fidelity. In this article we propose a scheme for overcoming the conventional
$T_1$ limit on fidelity by designing qubits in a way that amplitude damping
errors can be detected and converted into erasure errors. Compared to standard
qubit implementations our scheme improves the performance of fault-tolerant
protocols, as numerically demonstrated by the circuit-noise simulations of the
surface code. We describe two simple qubit implementations with superconducting
circuits and discuss procedures for detecting amplitude damping errors,
performing entangling gates, and extending $T_\phi$. Our results suggest that
engineering efforts should focus on improving $T_\phi$ and the quality of
quantum coherent control, as they effectively become the limiting factor on the
performance of fault-tolerant protocols.",2208.05461v1
2022-08-12,Critical exponent for nonlinear wave equations with damping and potential terms,"The aim of this paper is to determine the critical exponent for the nonlinear
wave equations with damping and potential terms of the scale invariant order,
by assuming that these terms satisfy a special relation. We underline that our
critical exponent is different from the one for related equations such as the
nonlinear wave equation without lower order terms, only with a damping term,
and only with a potential term. Moreover, we study the effect of the decaying
order of initial data at spatial infinity. In fact, we prove that not only the
lower order terms but also the order of the initial data affects the critical
exponent, as well as the sharp upper and lower bounds of the maximal existence
time of the solution.",2208.06106v3
2022-08-17,Conservation laws and variational structure of damped nonlinear wave equations,"All low-order conservation laws are found for a general class of nonlinear
wave equations in one dimension with linear damping which is allowed to be
time-dependent. Such equations arise in numerous physical applications and have
attracted much attention in analysis. The conservation laws describe
generalized momentum and boost momentum, conformal momentum, generalized
energy, dilational energy, and light-cone energies. Both the conformal momentum
and dilational energy have no counterparts for nonlinear undamped wave
equations in one dimension. All of the conservation laws are obtainable through
Noether's theorem, which is applicable because the damping term can be
transformed into a time-dependent self-interaction term by a change of
dependent variable. For several of the conservation laws, the corresponding
variational symmetries have a novel form which is different than any of the
well known variation symmetries admitted by nonlinear undamped wave equations
in one dimension.",2208.08026v2
2022-08-27,Impact of the free-streaming neutrinos to the second order induced gravitational waves,"The damping effect of the free-streaming neutrinos on the second order
gravitational waves is investigated in detail. We solve the Boltzmann equation
and give the anisotropic stress induced by neutrinos to second order. The first
order tensor and its coupling with scalar perturbations induced gravitational
waves are considered. We give the analytic equations of the damping kernel
functions and finally obtain the energy density spectrum. The results show that
the free-streaming neutrinos suppress the density spectrum significantly for
low frequency gravitational waves and enlarge the logarithmic slope $n$ in the
infrared region ($k \ll k_*$) of the spectrum. For the spectrum of $k_*\sim
10^{-7}$Hz, the damping effect in the range of $k<k_*$ is significant. The
combined effect of the first and second order could reduce the amplitude by
$30\%$ and make $n$ jump from $1.54$ to $1.63$ at $k\sim 10^{-9}$Hz, which may
be probed by the pulsar timing arrays (PTA) in the future.",2208.12948v1
2022-08-28,The small mass limit for long time statistics of a stochastic nonlinear damped wave equation,"We study the long time statistics of a class of semi--linear damped wave
equations with polynomial nonlinearities and perturbed by additive Gaussian
noise in dimensions 2 and 3. We find that if sufficiently many directions in
the phase space are stochastically forced, the system is exponentially
attractive toward its unique invariant measure with a convergent rate that is
uniform with respect to the mass. Then, in the small mass limit, we prove the
convergence of the first marginal of the invariant measures in a suitable
Wasserstein distance toward the unique invariant measure of a stochastic
reaction--diffusion equation. This together with uniform geometric ergodcity
implies the validity of the small mass limit for the solutions on the infinite
time horizon $[0,\infty)$, thereby extending previously known results
established for the damped wave equations under Lipschitz nonlinearities.",2208.13287v2
2022-08-30,Results on high energy galactic cosmic rays from the DAMPE space mission,"DAMPE (Dark Matter Particle Explorer) is a satellite-born experiment launched
in 2015 in a sun-synchronous orbit at 500 km altitude, and it has been taking
data in stable conditions ever since. Its main goals include the spectral
measurements up to very high energies, cosmic electrons/positrons and gamma
rays up to tens of TeV, and protons and nuclei up to hundreds of TeV. The
detector's main features include the 32 radiation lengths deep calorimeter and
large geometric acceptance, making DAMPE one of the most powerful space
instruments in operation, covering with high statistics and small systematics
the high energy frontier up to several hundreds TeV. The results of spectral
measurements of different species are shown and discussed.",2208.14300v2
2022-09-05,Generation and routing of nanoscale droplet solitons without compensation of magnetic damping,"Magnetic droplet soliton is a localized dynamic spin state which can serve as
a nanoscale information carrier and nonlinear oscillator. The present opinion
is that the formation of droplet solitons requires the compensation of magnetic
damping by a torque created by a spin-polarized electric current or pure spin
current. Here we demonstrate theoretically that nanoscale droplet solitons can
be generated and routed in ferromagnetic nanostructures with voltage-controlled
magnetic anisotropy in the presence of uncompensated magnetic damping.
Performing micromagnetic simulations for the MgO/Fe/MgO trilayer with almost
perpendicular-to-plane magnetization, we reveal the formation of the droplet
soliton under a nanoscale gate electrode subjected to a sub-nanosecond voltage
pulse. The soliton lives up to 50 ns at room temperature and can propagate over
micrometer distances in a ferromagnetic waveguide due to nonzero gradient of
the demagnetizing field. Furthermore, we show that an electrical routing of the
soliton to different outputs of a spintronic device can be realized with the
aid of an additional semiconducting nanostripe electrode creating controllable
gradient of the perpendicular magnetic anisotropy.",2209.01893v1
2022-09-06,Emergence of damped-localized excitations of the Mott state due to disorder,"A key aspect of ultracold bosonic quantum gases in deep optical lattice
potential wells is the realization of the strongly interacting Mott insulating
phase. Many characteristics of this phase are well understood, however little
is known about the effects of a random external potential on its gapped
quasiparticle and quasihole low-energy excitations. In the present study we
investigate the effect of disorder upon the excitations of the Mott insulating
state at zero temperature described by the Bose-Hubbard model. Using a
field-theoretical approach we obtain a resummed expression for the disorder
ensemble average of the spectral function. Its analysis shows that disorder
leads to an increase of the effective mass of both quasiparticle and quasihole
excitations. Furthermore, it yields the emergence of damped states, which
exponentially decay during propagation in space and dominate the whole band
when disorder becomes comparable to interactions. We argue that such
damped-localized states correspond to single-particle excitations of the
Bose-glass phase.",2209.02435v2
2022-09-21,Asymptotic profile of L^2-norm of solutions for wave equations with critical log-damping,"We consider wave equations with a special type of log-fractional damping. We
study the Cauchy problem for this model in the whole space, and we obtain an
asymptotic profile and optimal estimates of solutions as time goes to infinity
in L^2-sense. A maximal discovery of this note is that under the effective
damping, in case of n = 1 L^2-norm of the solution blows up in infinite time,
and in case of n = 2 L^2-norm of the solution never decays and never blows up
in infinite time. The latter phenomenon seems to be a rare case.",2209.10154v2
2022-09-25,Origin of Immediate Damping of Coherent Oscillations in Photoinduced Charge Density Wave Transition,"In stark contrast to the conventional charge density wave (CDW) materials,
the one-dimensional CDW on the In/Si(111) surface exhibits immediate damping of
the CDW oscillation during the photoinduced phase transition. Here, by
successfully reproducing the experimentally observed photoinduced CDW
transition on the In/Si(111) surface by performing real-time time-dependent
density functional theory (rt-TDDFT) simulations, we demonstrate that
photoexcitation promotes valence electrons from Si substrate to empty surface
bands composed primarily of the covalent p-p bonding states of the long In-In
bonds, generating interatomic forces to shorten the long bonds and in turn
drives coherently the structural transition. We illustrate that after the
structural transition, the component of these surface bands occurs a switch
among different covalent In bonds, causing a rotation of the interatomic forces
by about {\pi}/6 and thus quickly damping the oscillations in feature CDW
modes. These findings provide a deeper understanding of photoinduced phase
transitions.",2209.12135v1
2022-10-11,QKD in the NISQ era: enhancing secure key rates via quantum error correction,"Error mitigation is one of the key challenges in realising the full potential
of quantum cryptographic protocols. Consequently, there is a lot of interest in
adapting techniques from quantum error correction (QEC) to improve the
robustness of quantum cryptographic protocols. In this work, we benchmark the
performance of different QKD protocols on noisy quantum devices, with and
without error correction. We obtain the secure key rates of BB84, B92 and BBM92
QKD protocols over a quantum channel that is subject to amplitude-damping
noise. We demonstrate, theoretically and via implementations on the IBM quantum
processors, that B92 is the optimal protocol under amplitude-damping and
generalized amplitude-damping noise. We then show that the security of the
noisy BBM92 protocol crucially depends on the type and the mode of distribution
of an entangled pair. Finally, we implement an error-corrected BB84 protocol
using dual-rail encoding on a noisy quantum processor, and show that the
dual-rail BB84 implementation outperforms the conventional BB84 in the presence
of noise. Our secure key rate calculation also takes into account the effects
of CNOT imperfections on the error rates of the protocols.",2210.05297v1
2022-10-17,"Engineering imaginary stark ladder in a dissipative lattice: passive $\mathcal{PT}$ symmetry, K symmetry and localized damping","We study an imaginary stark ladder model and propose a realization of the
model in a dissipative chain with linearly increasing site-dependent
dissipation strength. Due to the existence of a $K$-symmetry and passive
$\mathcal{PT}$ symmetry, the model exhibits quite different feature from its
Hermitian counterpart. With the increase of dissipation strength, the system
first undergoes a passive $\mathcal{PT}$-symmetry breaking transition, with the
shifted eigenvalues changing from real to complex, and then a $K$-symmetry
restoring transition, characterized by the emergence of pure imaginary spectrum
with equal spacing. Accordingly, the eigenstates change from
$\mathcal{PT}$-unbroken extended states to the $\mathcal{PT}$-broken states,
and finally to stark localized states. In the framework of the quantum open
system governed by Lindblad equation with linearly increasing site-dependent
dissipation, we unveil that the dynamical evolution of single particle
correlation function is governed by the Hamiltonian of the imaginary stark
ladder model. By studying the dynamical evolution of the density distribution
under various initial states, we demonstrate that the damping dynamics displays
distinct behaviors in different regions. A localized damping is observed in the
strong dissipation limit.",2210.08725v3
2022-10-18,A quasi-local inhomogeneous dielectric tensor for arbitrary distribution functions,"Treatments of plasma waves usually assume homogeneity, but the parallel
gradients ubiquitous in plasmas can modify wave propagation and absorption. We
derive a quasilocal inhomogeneous correction to the plasma dielectric for
arbitrary distributions by expanding the phase correlation integral and develop
a novel integration technique that allows our correction to be applied in many
situations and has greater accuracy than other inhomogeneous dielectric
formulas found in the literature. We apply this dielectric tensor to the
lower-hybrid current drive problem and demonstrate that inhomogeneous wave
damping does not affect the lower-hybrid wave's linear damping condition, and
in the non-Maxwellian problem damping and propagation should remain unchanged
except in the case of waves with very large phase velocities.",2210.10214v1
2022-11-04,On the collisional damping of plasma velocity space instabilities,"For plasma velocity space instabilities driven by particle distributions
significantly deviated from a Maxwellian, weak collisions can damp the
instabilities by an amount that is significantly beyond the collisional rate
itself. This is attributed to the dual role of collisions that tend to relax
the plasma distribution toward a Maxwellian and to suppress the linearly
perturbed distribution function. The former effect can dominate in cases where
the unstable non-Maxwellian distribution is driven by collisionless transport
on a time scale much shorter than that of collisions, and the growth rate of
the ideal instability has a sensitive dependence on the distribution function.
The whistler instability driven by electrostatically trapped electrons is used
as an example to elucidate such a strong collisional damping effect of plasma
velocity space instabilities, which is confirmed by first-principles kinetic
simulations.",2211.02723v3
2022-11-12,Exponential Stability and exact controllability of a system of coupled wave equations by second order terms (via Laplacian) with only one non-smooth local damping,"The purpose of this work is to investigate the exponential stability of a
second order coupled wave equations by laplacian with one locally internal
viscous damping. Firstly, using a unique continuation theorem combined with a
Carleman estimate, we prove that our system is strongly stable without any
geometric condition. Secondly, using a combination of the multiplier techniques
and the frequency domain approach, we show that our system is exponentially
stable under \textbf{(PMGC)} condition on the damping region without any
restriction on wave propagation speed (i.e whether the two wave equations
propagate at the same speed or not)",2211.06706v2
2022-11-10,Generalized Bagley-Torvik Equation and Fractional Oscillators,"In this paper the Bagley-Torvik Equation is considered with the order of the
damping term allowed to range between one and two. The solution is found to be
representable as a convolution of trigonometric and exponential functions with
the driving force. The properties of the effective decay rate and the
oscillation frequency with respect to the order of the fractional damping are
also studied. It is found that the effective decay rate and oscillation
frequency have a complex dependency on the order of the derivative of the
damping term and exhibit properties one might expect of a thermodynamic
Equation of state: critical point, phase change, and lambda transition.",2211.07575v1
2022-11-21,Lifespan estimates for the compressible Euler equations with damping via Orlicz spaces techniques,"In this paper we are interested in the upper bound of the lifespan estimate
for the compressible Euler system with time dependent damping and small initial
perturbations. We employ some techniques from the blow-up study of nonlinear
wave equations. The novelty consists in the introduction of tools from the
Orlicz spaces theory to handle the nonlinear term emerging from the pressure $p
\equiv p(\rho)$, which admits different asymptotic behavior for large and small
values of $\rho-1$, being $\rho$ the density. Hence we can establish, in high
dimensions $n\in\{2,3\}$, unified upper bounds of the lifespan estimate
depending only on the dimension $n$ and on the damping strength, and
independent of the adiabatic index $\gamma>1$. We conjecture our results to be
optimal. The method employed here not only improves the known upper bounds of
the lifespan for $n\in\{2,3\}$, but has potential application in the study of
related problems.",2211.11377v1
2022-11-24,A brief introduction to the mathematics of Landau damping,"In these short, rather informal, expository notes I review the current state
of the field regarding the mathematics of Landau damping, based on lectures
given at the CIRM Research School on Kinetic Theory, November 14--18, 2022.
These notes are mainly on Vlasov-Poisson in $(x,v) \in \mathbb T^d \times
\mathbb R^d$ however a brief discussion of the important case of $(x,v) \in
\mathbb R^d \times \mathbb R^d$ is included at the end. The focus will be
nonlinear and these notes include a proof of Landau damping on $(x,v) \in
\mathbb T^d \times \mathbb R^d$ in the Vlasov--Poisson equations meant for
graduate students, post-docs, and others to learn the basic ideas of the
methods involved. The focus is also on the mathematical side, and so most
references are from the mathematical literature with only a small number of the
many important physics references included. A few open problems are included at
the end.
  These notes are not currently meant for publication so they may not be
perfectly proof-read and the reference list might not be complete. If there is
an error or you have some references which you think should be included, feel
free to send me an email and I will correct it when I get a chance.",2211.13707v1
2022-12-04,Vibration suppression of a state-of-the-art wafer gripper,"In this paper the implementation of piezoelectrics to a state-of-the-art
wafer gripper is investigated. The objective is to propose and validate a
solution method, which includes a mechanical design and control system, to
achieve at least 5% damping for two eigenmodes of a wafer gripper. This
objective serves as a 'proof of concept' to show the possibilities of
implementing a state-of-the-art damping method to an industrial application,
which in turn can be used to dampen different thin structures. The coupling
relation between the piezoelectrics and their host structure were used to
design the placement of the piezoelectric patches, together with modal analysis
data of the a state-of-the-art wafer gripper. This data had been measured
through an experimental setup. Active damping has been succesfully implemented
onto the wafer gripper where positive position feedback (PPF) is used as a
control algorithm to dampen two eigenmodes.",2212.01854v1
2022-12-20,Algebra of L-banded Matrices,"Convergence is a crucial issue in iterative algorithms. Damping is commonly
employed to ensure the convergence of iterative algorithms. The conventional
ways of damping are scalar-wise, and either heuristic or empirical. Recently,
an analytically optimized vector damping was proposed for memory
message-passing (iterative) algorithms. As a result, it yields a special class
of covariance matrices called L-banded matrices. In this paper, we show these
matrices have broad algebraic properties arising from their L-banded structure.
In particular, compact analytic expressions for the LDL decomposition, the
Cholesky decomposition, the determinant after a column substitution, minors,
and cofactors are derived. Furthermore, necessary and sufficient conditions for
an L-banded matrix to be definite, a recurrence to obtain the characteristic
polynomial, and some other properties are given. In addition, we give new
derivations of the determinant and the inverse. (It's crucial to emphasize that
some works have independently studied matrices with this special structure,
named as L-matrices. Specifically, L-banded matrices are regarded as L-matrices
with real and finite entries.)",2212.12431v3
2023-01-23,Non-Markovianity in the time evolution of open quantum systems assessed by means of quantum state distance,"We provide a quantitative evaluation of non-Markovianity (NM) for an XX chain
of interacting qubits with one end coupled to a reservoir. The NM of several
non-Markovian spectral densities is assessed in terms of various quantum state
distance (QSD) measures. Our approach is based on the construction of the
density matrix of the open chain, without the necessity of a master equation.
For the quantification of NM we calculate the dynamics of the QSD measures
between the Markovian-damped and various types of non-Markovian-damped cases.
Since in the literature several QSD measures, appear in forms that imply trace
preserving density matrices, we introduced appropriate modifications so as to
render them applicable to the case of decaying traces. The results produce
remarkable consistency between the various QSD measures. They also reveal a
subtle and potentially useful interplay between qubit-qubit interaction and
non-Markovian damping. Our calculations have also uncovered a surprisingly
dramatic slowing-down of dissipation by the squared Lorentzian reservoir.",2301.09323v2
2023-01-26,Optimisation of Power Grid Stability Under Uncertainty,"The increased integration of intermittent and decentralised forms of power
production has eroded the stability margins of power grids and made it more
challenging to ensure reliable and secure power transmission. Reliable grid
operation requires system-scale stability in response to perturbations in
supply or load; previous studies have shown that this can be achieved by tuning
the effective damping parameters of the generators in the grid. In this paper,
we present and analyse the problem of tuning damping parameters when there is
some uncertainty in the underlying system. We show that sophisticated methods
that assume no uncertainty can yield results that are less robust than those
produced by simpler methods. We define a quantile-based metric of stability
that ensures that power grids remain stable even as worst-case scenarios are
approached, and we develop optimisation methods for tuning damping parameters
to achieve this stability. By comparing optimisation methods that rely on
different assumptions, we suggest efficient heuristics for finding parameters
that achieve highly stable and robust grids.",2301.11215v1
2023-02-11,Uniform stabilization for the semi-linear wave equation with nonlinear Kelvin-Voigt damping,"This paper is concerned with the decay estimate of solutions to the
semilinear wave equation subject to two localized dampings in a bounded domain.
The first one is of the nonlinear Kelvin-Voigt type and is distributed around a
neighborhood of the boundary according to the Geometric Control Condition.
While the second one is a frictional damping and we consider it hurting the
geometric condition of control. We show uniform decay rate results of the
corresponding energy for all initial data taken in bounded sets of finite
energy phase-space. The proof is based on obtaining an observability inequality
which combines unique continuation properties and the tools of the Microlocal
Analysis Theory.",2302.05667v1
2023-02-20,Exponentially stable breather solutions in nonautonomous dissipative nonlinear Schrödinger lattices,"We consider damped and forced discrete nonlinear Schr\""odinger equations on
the lattice $\mathbb{Z}$. First we establish the existence of periodic and
quasiperiodic breather solutions for periodic and quasiperiodic driving,
respectively. Notably, quasiperiodic breathers cannot exist in the system
without damping and driving. Afterwards the existence of a global uniform
attractor for the dissipative dynamics of the system is shown. For strong
dissipation we prove that the global uniform attractor has finite fractal
dimension and consists of a single trajectory that is confined to a finite
dimensional subspace of the infinite dimensional phase space, attracting any
bounded set in phase space exponentially fast. Conclusively, for strong damping
and periodic (quasiperiodic) forcing the single periodic (quasiperiodic)
breather solution possesses a finite number of modes and is exponentially
stable.",2302.09869v2
2023-02-11,"Quasinormal modes, Hawking radiation and absorption of the massless scalar field for Bardeen black hole surrounded by perfect fluid dark matter","Bardeen black hole surrounded by perfect fluid dark matter for a massless
scalar field. Our result shows that the oscillation frequency of quasinormal
modes is enhanced as magnetic charge $g$ or the dark matter parameter $\alpha$
increases. For damping rate of quasinormal modes, the influence of them is
different. Specifically, the increase of dark matter parameter $\alpha$ makes
the damping rate increasing at first and then decreasing. While the damping
rate is continuously decreasing with the increase of the magnetic charge $g$.
Moreover, we find that the increase of the dark matter parameter $\alpha$
enhances the power emission spectrum whereas magnetic charge $g$ suppresses it.
This means that the lifespan of black holes increases for smaller value of
$\alpha$ and larger value of $g$ when other parameters are fixed. Finally, the
absorption cross section of the considered black hole is calculated with the
help of the partial wave approach. Our result suggests that the absorption
cross section decreases with the dark matter $\alpha$ or the magnetic charge
$g$ increasing.",2302.10758v1
2023-02-24,A Numerical Approach for Modeling the Shunt Damping of Thin Panels with Arrays of Separately Piezoelectric Patches,"Two-dimensional thin plates are widely used in many aerospace and automotive
applications. Among many methods for the attenuation of vibration of these
mechanical structures, piezoelectric shunt damping is a promising way. It
enables a compact vibration damping method without adding significant mass and
volumetric occupancy. Analyzing the dynamics of these electromechanical systems
requires precise modeling tools that properly consider the coupling between the
piezoelectric elements and the host structure. This paper presents a
methodology for separately shunted piezoelectric patches for achieving higher
performance on vibration attenuation. The Rayleigh-Ritz method is used for
performing the modal analysis and obtaining the frequency response functions of
the electro-mechanical system. The effectiveness of the method is investigated
for a broader range of frequencies, and it was shown that separately shunted
piezoelectric patches are more effective.",2302.12525v1
2023-02-27,"Enhancing quantum synchronization through homodyne measurement, noise and squeezing","Quantum synchronization has been a central topic in quantum nonlinear
dynamics. Despite rapid development in this field, very few have studied how to
efficiently boost synchronization. Homodyne measurement emerges as one of the
successful candidates for this task, but preferably in the semi-classical
regime. In our work, we focus on the phase synchronization of a harmonic-driven
quantum Stuart-Landau oscillator, and show that the enhancement induced by
homodyne measurement persists into the quantum regime. Interestingly, optimal
two-photon damping rates exist when the oscillator and driving are at resonance
and with a small single-photon damping rate. We also report noise-induced
enhancement in quantum synchronization when the single-photon damping rate is
sufficiently large. Apart from these results, we discover that adding a
squeezing Hamiltonian can further boost synchronization, especially in the
semi-classical regime. Furthermore, the addition of squeezing causes the
optimal two-photon pumping rates to shift and converge.",2302.13465v2
2023-03-06,Larmor precession in strongly correlated itinerant electron systems,"Many-electron systems undergo a collective Larmor precession in the presence
of a magnetic field. In a paramagnetic metal, the resulting spin wave provides
insight into the correlation effects generated by the electron-electron
interaction. Here, we use dynamical mean-field theory to investigate the
collective Larmor precession in the strongly correlated regime, where dynamical
correlation effects such as quasiparticle lifetimes and non-quasiparticle
states are essential. We study the spin excitation spectrum, which includes a
dispersive Larmor mode as well as electron-hole excitations that lead to Stoner
damping. We also extract the momentum-resolved damping of slow spin waves. The
accurate theoretical description of these phenomena relies on the Ward
identity, which guarantees a precise cancellation of self-energy and vertex
corrections at long wavelengths. Our findings pave the way towards a better
understanding of spin wave damping in correlated materials.",2303.03468v2
2023-03-19,Asymptotic-preserving finite element analysis of Westervelt-type wave equations,"Motivated by numerical modeling of ultrasound waves, we investigate robust
conforming finite element discretizations of quasilinear and possibly nonlocal
equations of Westervelt type. These wave equations involve either a strong
dissipation or damping of fractional-derivative type and we unify them into one
class by introducing a memory kernel that satisfies non-restrictive regularity
and positivity assumptions. As the involved damping parameter is relatively
small and can become negligible in certain (inviscid) media, it is important to
develop methods that remain stable as the said parameter vanishes. To this end,
the contributions of this work are twofold. First, we determine sufficient
conditions under which conforming finite element discretizations of (non)local
Westervelt equations can be made robust with respect to the dissipation
parameter. Secondly, we establish the rate of convergence of the semi-discrete
solutions in the singular vanishing dissipation limit. The analysis hinges upon
devising appropriate energy functionals for the semi-discrete solutions that
remain uniformly bounded with respect to the damping parameter.",2303.10743v1
2023-03-31,Measurement of the cosmic p+He energy spectrum from 46 GeV to 316 TeV with the DAMPE space mission,"Recent observations of the light component of the cosmic-ray spectrum have
revealed unexpected features that motivate further and more precise
measurements up to the highest energies. The Dark Matter Particle Explorer
(DAMPE) is a satellite-based cosmic-ray experiment that is operational since
December 2015, continuously collecting data on high-energy cosmic particles
with very good statistics, energy resolution, and particle identification
capabilities. In this work, the latest measurements of the energy spectrum of
proton+helium in the energy range from 46 GeV to 316 TeV are presented. Among
the most distinctive features of the spectrum, a spectral hardening at
$\sim$600 GeV has been observed, along with a softening at $\sim$29 TeV
measured with a 6.6$\sigma$ significance. Moreover, by measuring the energy
spectrum up to 316 TeV, a strong link is established between space- and
ground-based experiments, also suggesting the presence of a second hardening at
$\sim$150 TeV.",2304.00137v4
2023-04-18,Edge-selective extremal damping from topological heritage of dissipative Chern insulators,"One of the most important practical hallmarks of topological matter is the
presence of topologically protected, exponentially localised edge states at
interfaces of regions characterised by unequal topological invariants. Here, we
show that even when driven far from their equilibrium ground state, Chern
insulators can inherit topological edge features from their parent Hamiltonian.
In particular, we show that the asymptotic long-time approach of the
non-equilibrium steady state, governed by a Lindblad Master equation, can
exhibit edge-selective extremal damping. This phenomenon derives from edge
states of non-Hermitian extensions of the parent Chern insulator Hamiltonian.
The combination of (non-Hermitian) topology and dissipation hence allows to
design topologically robust, spatially localised damping patterns.",2304.09040v3
2023-04-25,Weakly damped bosons and precursor gap in the vicinity of an antiferromagnetic metallic transition,"We study the electronic spectral function of a metal in the vicinity of an
antiferromagnetic (AFM) quantum critical point, focusing on a situation where
the bare bandwidth of the spin fluctuations is significantly smaller than the
Fermi energy. In this limit, we identify a range of energies where the
fermionic quasiparticles near the ""hot spots'' on the Fermi surface are
strongly scattered by the quantum critical fluctuations, whereas the damping of
the AFM fluctuations by the electrons is negligible. Within a one-loop
approximation, there is a parameter range where the $T=0$ spectral function at
the hot spots has a ""precursor gap'' feature, with a local maximum at a finite
frequency. However, the ratio of the bare spin wave velocity to the Fermi
velocity required to obtain a precursor gap is probably too small to explain
experiments in the electron-doped cuprate superconductors (He et al., Proc.
Natl. Acad. Sci 116, 3449 (2019)). At lower frequencies, the Landau damping of
the AFM fluctuations becomes important, and the electronic spectral function
has the familiar ${\omega}^{-1/2}$ singularity. Our one-loop perturbative
results are supported by a numerical Monte Carlo simulation of electrons
coupled to an undamped, nearly-critical AFM mode.",2304.12697v1
2023-05-04,Vibrational resonance in a damped and two-frequency driven system of particle on a rotating parabola,"In the present work, we examine the role of nonlinearity in vibrational
resonance (VR) of a forced and damped form of a velocity-dependent potential
system. Many studies have focused on studying the vibrational resonance in
different potentials, like bistable potential, asymmetrically deformed
potential, and rough potential. In this connection, velocity-dependent
potential systems are very important from a physical point of view (Ex:
pion-pion interaction, cyclotrons and other electromagnetic devices influenced
by the Lorentz force, magnetrons, mass spectrometers). They also appear in
several mechanical contexts. In this paper, we consider a nonlinear dynamical
system with velocity-dependent potential along with additional damping and
driven forces, namely a particle moving on a rotating-parabola system, and
study the effect of two-frequency forcing with a wide difference in the
frequencies. We report that the system exhibits vibrational resonance in a
certain range of nonlinear strength. Using the method of separation of motions
(MSM), an analytical equation for the slow oscillations of the system is
obtained in terms of the parameters of the fast signal. The analytical
computations and the numerical studies concur well.",2305.02674v1
2023-05-06,Stochastic wave equation with Hölder noise coefficient: well-posedness and small mass limit,"We construct unique martingale solutions to the damped stochastic wave
equation $$ \mu \frac{\partial^2u}{\partial t^2}(t,x)=\Delta
u(t,x)-\frac{\partial u}{\partial
t}(t,x)+b(t,x,u(t,x))+\sigma(t,x,u(t,x))\frac{dW_t}{dt},$$
  where $\Delta$ is the Laplacian on $[0,1]$ with Dirichlet boundary condition,
$W$ is space-time white noise, $\sigma$ is $\frac{3}{4}+\epsilon$ -H\""older
continuous in $u$ and uniformly non-degenerate, and $b$ has linear growth. The
same construction holds for the stochastic wave equation without damping term.
More generally, the construction holds for SPDEs defined on separable Hilbert
spaces with a densely defined operator $A$, and the assumed H\""older regularity
on the noise coefficient depends on the eigenvalues of $A$ in a quantitative
way. We further show the validity of the Smoluchowski-Kramers approximation:
assume $b$ is H\""older continuous in $u$, then as $\mu$ tends to $0$ the
solution to the damped stochastic wave equation converges in distribution, on
the space of continuous paths, to the solution of the corresponding stochastic
heat equation. The latter result is new even in the case of additive noise.",2305.04068v2
2023-05-08,Information capacity analysis of fully correlated multi-level amplitude damping channels,"The primary objective of quantum Shannon theory is to evaluate the capacity
of quantum channels. In spite of the existence of rigorous coding theorems that
quantify the transmission of information through quantum channels,
superadditivity effects limit our understanding of the channel capacities. In
this paper, we mainly focus on a family of channels known as multi-level
amplitude damping channels. We investigate some of the information capacities
of the simplest member of multi-level Amplitude Damping Channel, a qutrit
channel, in the presence of correlations between successive applications of the
channel. We find the upper bounds of the single-shot classical capacities and
calculate the quantum capacities associated with a specific class of maps after
investigating the degradability property of the channels. Additionally, the
quantum and classical capacities of the channels have been computed in
entanglement-assisted scenarios.",2305.04481v2
2023-05-09,Lifespan estimates for semilinear damped wave equation in a two-dimensional exterior domain,"Lifespan estimates for semilinear damped wave equations of the form
$\partial_t^2u-\Delta u+\partial_tu=|u|^p$ in a two dimensional exterior domain
endowed with the Dirichlet boundary condition are dealt with. For the critical
case of the semilinear heat equation $\partial_tv-\Delta v=v^2$ with the
Dirichlet boundary condition and the initial condition $v(0)=\varepsilon f$,
the corresponding lifespan can be estimated from below and above by
$\exp(\exp(C\varepsilon^{-1}))$ with different constants $C$. This paper
clarifies that the same estimates hold even for the critical semilinear damped
wave equation in the exterior of the unit ball under the restriction of radial
symmetry. To achieve this result, a new technique to control $L^1$-type norm
and a new Gagliardo--Nirenberg type estimate with logarithmic weight are
introduced.",2305.05124v1
2023-05-19,Cold damping of levitated optically coupled nanoparticles,"Methods for controlling the motion of single particles, optically levitated
in vacuum, have developed rapidly in recent years. The technique of cold
damping makes use of feedback-controlled, electrostatic forces to increase
dissipation without introducing additional thermal fluctuations. This process
has been instrumental in the ground-state cooling of individual electrically
charged nanoparticles. Here we show that the same method can be applied to a
pair of nanoparticles, coupled by optical binding forces. These optical binding
forces are about three orders of magnitude stronger than typical Coulombic
inter-particle force and result in a coupled motion of both nanoparticles
characterized by a pair of normal modes. We demonstrate cold damping of these
normal modes, either independently or simultaneously, to sub-Kelvin
temperatures at pressures of 5x10^{-3} mbar. Experimental observations are
captured by a theoretical model which we use to survey the parameter space more
widely and to quantify the limits imposed by measurement noise and time delays.
Our work paves the way for the study of quantum interactions between meso-scale
particles and the exploration of multiparticle entanglement in levitated
optomechanical systems.",2305.11809v1
2023-05-25,Damping of three-dimensional waves on coating films dragged by moving substrates,"Paints and coatings often feature interfacial defects due to disturbances
during the deposition process which, if they persist until solidification,
worsen the product quality. In this article, we investigate the stability of a
thin liquid film dragged by a vertical substrate moving against gravity, a flow
configuration found in a variety of coating processes. The receptivity of the
liquid film to three-dimensional disturbances is discussed with Direct
Numerical Simulations (DNS), an in-house non-linear Integral Boundary Layer
(IBL) film model, and Linear Stability Analysis (LSA). The thin film model,
successfully validated with the DNS computations, implements a pseudo-spectral
approach for the capillary terms that allows for investigating non-periodic
surface tension dominated flows. The combination of these numerical tools
allows for describing the mechanisms of capillary and non-linear damping, and
identifying the instability threshold of the coating processes. The results
show that transverse modulations can be beneficial for the damping of
two-dimensional waves within the range of operational conditions considered in
this study, typical of air-knife and slot-die coating.",2305.16139v3
2023-06-12,Realizable Eddy Damped Markovian Anisotropic Closure for Turbulence and Rossby Wave Interactions,"A realizable Eddy Damped Markovian Anisotropic Closure (EDMAC) is presented
for the interaction of two dimensional turbulence and transient waves such as
Rossby waves. The structure of the EDMAC ensures that it is as computationally
efficient as the Eddy Damped Quasi Normal Markovian (EDQNM) closure but unlike
the EDQNM is guaranteed to be realizable in the presence of transient waves.
Jack Herring's important contributions to laying the foundations of statistical
dynamical closure theories of fluid turbulence are briefly reviewed. The topics
covered include equilibrium statistical mechanics, Eulerian and Lagrangian
statistical dynamical closure theories, and the statistical dynamics of the
interaction of turbulence with topography. The impact of Herring's work is
described and placed in the context of related developments. Some of the
further works that have built on Herring's foundations are discussed. The
relationships between theoretical approaches employed in statistical classical
and quantum field theories, and their overlap, are outlined. The seminal
advances made by the pioneers in strong interaction fluid turbulence are put
into perspective by comparing related developments in strong interaction
quantum filed theory.",2306.06921v1
2023-06-18,Partial data inverse problem for hyperbolic equation with time-dependent damping coefficient and potential,"We study an inverse problem of determining a time-dependent damping
coefficient and potential appearing in the wave equation in a compact
Riemannian manifold of dimension three or higher. More specifically, we are
concerned with the case of conformally transversally anisotropic manifolds, or
in other words, compact Riemannian manifolds with boundary conformally embedded
in a product of the Euclidean line and a transversal manifold. With an
additional assumption of the attenuated geodesic ray transform being injective
on the transversal manifold, we prove that the knowledge of a certain partial
Cauchy data set determines time-dependent damping coefficient and potential
uniquely.",2306.10442v2
2023-06-26,"Blow-up result for a weakly coupled system of wave equations with a scale-invariant damping, mass term and time derivative nonlinearity","We study in this article the blow-up of solutions to a coupled semilinear
wave equations which are characterized by linear damping terms in the
\textit{scale-invariant regime}, time-derivative nonlinearities, mass terms and
Tricomi terms. The latter are specifically of great interest from both physical
and mathematical points of view since they allow the speeds of propagation to
be time-dependent ones. However, we assume in this work that both waves are
propagating with the same speeds. Employing this fact together with other
hypotheses on the aforementioned parameters (mass and damping coefficients), we
obtain a new blow-up region for the system under consideration, and we show a
lifespan estimate of the maximal existence time.",2306.14768v1
2023-06-26,Revisiting the damped quantum harmonic oscillator,"We reanalyse the quantum damped harmonic oscillator, introducing three less
than common features. These are (i) the use of a continuum model of the
reservoir rather than an ensemble of discrete oscillators, (ii) an exact
diagonalisation of the Hamiltonian by adapting a technique pioneered by Fano,
and (iii) the use of the thermofield technique for describing a finite
temperature reservoir. We recover in this way a number of well-known and some,
perhaps, less familiar results. An example of the latter is an ab initio proof
that the oscillator relaxes to the mean-force Gibbs state. We find that special
care is necessary when comparing the damped oscillator with its undamped
counterpart as the former has two distinct natural frequencies, one associated
with short time evolution and the other with longer times.",2306.15013v1
2023-06-27,SPDER: Semiperiodic Damping-Enabled Object Representation,"We present a neural network architecture designed to naturally learn a
positional embedding and overcome the spectral bias towards lower frequencies
faced by conventional implicit neural representation networks. Our proposed
architecture, SPDER, is a simple MLP that uses an activation function composed
of a sinusoidal multiplied by a sublinear function, called the damping
function. The sinusoidal enables the network to automatically learn the
positional embedding of an input coordinate while the damping passes on the
actual coordinate value by preventing it from being projected down to within a
finite range of values. Our results indicate that SPDERs speed up training by
10x and converge to losses 1,500-50,000x lower than that of the
state-of-the-art for image representation. SPDER is also state-of-the-art in
audio representation. The superior representation capability allows SPDER to
also excel on multiple downstream tasks such as image super-resolution and
video frame interpolation. We provide intuition as to why SPDER significantly
improves fitting compared to that of other INR methods while requiring no
hyperparameter tuning or preprocessing.",2306.15242v1
2023-07-03,Fast Convergence of Inertial Multiobjective Gradient-like Systems with Asymptotic Vanishing Damping,"We present a new gradient-like dynamical system related to unconstrained
convex smooth multiobjective optimization which involves inertial effects and
asymptotic vanishing damping. To the best of our knowledge, this system is the
first inertial gradient-like system for multiobjective optimization problems
including asymptotic vanishing damping, expanding the ideas laid out in [H.
Attouch and G. Garrigos, Multiobjective optimization: an inertial approach to
Pareto optima, preprint, arXiv:1506.02823, 201]. We prove existence of
solutions to this system in finite dimensions and further prove that its
bounded solutions converge weakly to weakly Pareto optimal points. In addition,
we obtain a convergence rate of order $O(t^{-2})$ for the function values
measured with a merit function. This approach presents a good basis for the
development of fast gradient methods for multiobjective optimization.",2307.00975v3
2023-07-05,Strong convergence rates for a full discretization of stochastic wave equation with nonlinear damping,"The paper establishes the strong convergence rates of a spatio-temporal full
discretization of the stochastic wave equation with nonlinear damping in
dimension one and two. We discretize the SPDE by applying a spectral Galerkin
method in space and a modified implicit exponential Euler scheme in time. The
presence of the super-linearly growing damping in the underlying model brings
challenges into the error analysis. To address these difficulties, we first
achieve upper mean-square error bounds, and then obtain mean-square convergence
rates of the considered numerical solution. This is done without requiring the
moment bounds of the full approximations. The main result shows that, in
dimension one, the scheme admits a convergence rate of order $\tfrac12$ in
space and order $1$ in time. In dimension two, the error analysis is more
subtle and can be done at the expense of an order reduction due to an
infinitesimal factor. Numerical experiments are performed and confirm our
theoretical findings.",2307.01975v1
2023-07-12,Decoherence effects on lepton number violation from heavy neutrino-antineutrino oscillations,"We study decoherence effects and phase corrections in heavy
neutrino-antineutrino oscillations (NNOs), based on quantum field theory with
external wave packets. Decoherence damps the oscillation pattern, making it
harder to resolve experimentally. Additionally, it enhances lepton number
violation (LNV) for processes in symmetry-protected low-scale seesaw models by
reducing the destructive interference between mass eigenstates. We discuss a
novel time-independent shift in the phase and derive formulae for calculating
decoherence effects and the phase shift in the relevant regimes, which are the
no dispersion regime and transverse dispersion regime. We find that the phase
shift can be neglected in the parameter region under consideration since it is
small apart from parameter regions with large damping. In the oscillation
formulae, decoherence can be included by an effective damping parameter. We
discuss this parameter and present averaged results, which apply to simulations
of NNOs in the dilepton-dijet channel at the HL-LHC. We show that including
decoherence effects can dramatically change the theoretical prediction for the
ratio of LNV over LNC events.",2307.06208v1
2023-07-23,Visco-elastic damped wave models with time-dependent coefficient,"In this paper, we study the following Cauchy problem for linear visco-elastic
damped wave models with a general time-dependent coefficient $g=g(t)$:
\begin{equation} \label{EqAbstract} \tag{$\star$} \begin{cases} u_{tt}- \Delta
u + g(t)(-\Delta)u_t=0, &(t,x) \in (0,\infty) \times \mathbb{R}^n, \\ u(0,x)=
u_0(x),\quad u_t(0,x)= u_1(x), &x \in \mathbb{R}^n. \end{cases} \end{equation}
We are interested to study the influence of the damping term $g(t)(-\Delta)u_t$
on qualitative properties of solutions to \eqref{EqAbstract} as decay estimates
for energies of higher order and the parabolic effect. The main tools are
related to WKB-analysis. We apply elliptic as well as hyperbolic WKB-analysis
in different parts of the extended phase space.",2307.12340v1
2023-07-24,Phonon damping in a 2D superfluid: insufficiency of Fermi's golden rule at low temperature,"It is generally accepted that the phonon gas of a superfluid always enters a
weak coupling regime at sufficiently low temperatures, whatever the strength of
the interactions between the underlying particles (constitutive of the
superfluid). Thus, in this limit, we should always be able to calculate the
damping rate of thermal phonons by applying Fermi's golden rule to the $H\_3$
Hamiltonian of cubic phonon-phonon coupling taken from quantum hydrodynamics,
at least in the case of a convex acoustic branch and in the collisionless
regime (where the eigenfrequency of the considered phonons remains much greater
than the gas thermalization rate). Using the many-body Green's function method,
we predict that, unexpectedly, this is not true in two dimensions, contrary to
the three-dimensional case. We confirm this prediction with classical
phonon-field simulations and a non-perturbative theory in $H\_3$, where the
fourth order is regularized by hand, giving a complex energy to the virtual
phonons of the four-phonon collisional processes. For a weakly interacting
fluid and a phonon mode in the long-wavelength limit, we predict a damping rate
about three times lower than that of the golden rule.",2307.12705v1
2023-08-01,Regularity for the Timoshenko system with fractional damping,"We study, the Regularity of the Timoshenko system with two fractional
dampings $(-\Delta)^\tau u_t$ and $(-\Delta)^\sigma \psi_t$; both of the
parameters $(\tau, \sigma)$ vary in the interval $[0,1]$. We note that
($\tau=0$ or $\sigma=0$) and ($\tau=1$ or $\sigma=1$) the dampings are called
frictional and viscous, respectively. Our main contribution is to show that the
corresponding semigroup $S(t)=e^{\mathcal{B}t}$, is analytic for
$(\tau,\sigma)\in R_A:=[1/2,1]\times[ 1/2,1]$ and determine the Gevrey's class
$\nu>\dfrac{1}{\phi}$, where $\phi=\left\{\begin{array}{ccc}
\dfrac{2\sigma}{\sigma+1} &{\rm for} & \sigma\leq \tau,\\\\
\dfrac{2\tau}{\tau+1} &{\rm for} & \tau\leq \sigma. \end{array}\right.$ \quad
and \quad $(\tau,\sigma)\in R_{CG}:= (0,1)^2$.",2308.00573v2
2023-08-16,Large time asymptotics for partially dissipative hyperbolic systems without Fourier analysis: application to the nonlinearly damped p-system,"A new framework to obtain time-decay estimates for partially dissipative
hyperbolic systems set on the real line is developed. Under the classical
Shizuta-Kawashima (SK) stability condition, equivalent to the Kalman rank
condition in control theory, the solutions of these systems decay exponentially
in time for high frequencies and polynomially for low ones. This allows to
derive a sharp description of the space-time decay of solutions for large time.
However, such analysis relies heavily on the use of the Fourier transform that
we avoid here, developing the ""physical space version"" of the hyperbolic
hypocoercivity approach introduced by Beauchard and Zuazua, to prove new
asymptotic results in the linear and nonlinear settings. The new physical space
version of the hyperbolic hypocoercivity approach allows to recover the natural
heat-like time-decay of solutions under sharp rank conditions, without
employing Fourier analysis or $L^1$ assumptions on the initial data. Taking
advantage of this Fourier-free framework, we establish new enhanced time-decay
estimates for initial data belonging to weighted Sobolev spaces. These results
are then applied to the nonlinear compressible Euler equations with linear
damping. We also prove the logarithmic stability of the nonlinearly damped
$p$-system.",2308.08280v1
2023-09-06,Effective Description of the Quantum Damped Harmonic Oscillator: Revisiting the Bateman Dual System,"In this work, we present a quantization scheme for the damped harmonic
oscillator (QDHO) using a framework known as momentous quantum mechanics. Our
method relies on a semiclassical dynamical system derived from an extended
classical Hamiltonian, where the phase-space variables are given by expectation
values of observables and quantum dispersions. The significance of our study
lies in its potential to serve as a foundational basis for the effective
description of open quantum systems (OQS), and the description of dissipation
in quantum mechanics. By employing the Bateman's dual model as the initial
classical framework, and undergoing quantization, we demonstrate that our
description aligns exceptionally well with the well-established Lindblad master
equation. Furthermore, our approach exhibits robustness and broad applicability
in the context of OQS, rendering it a versatile and powerful tool for studying
various phenomena. We intend to contribute to the advancement of quantum
physics by providing an effective means of quantizing the damped harmonic
oscillator and shedding light on the behavior of open quantum systems.",2309.02689v1
2023-09-09,Secondary cosmic-ray nuclei in the model of Galactic halo with nonlinear Landau damping,"We employ our recent model of the cosmic-ray (CR) halo by Chernyshov et al.
(2022) to compute the Galactic spectra of stable and unstable secondary nuclei.
In this model, confinement of the Galactic CRs is entirely determined by the
self-generated Alfvenic turbulence whose spectrum is controlled by nonlinear
Landau damping. We analyze the physical parameters affecting propagation
characteristics of CRs, and estimate the best set of free parameters providing
accurate description of available observational data. We also show that
agreement with observations at lower energies may be further improved by taking
into account the effect of ion-neutral damping which operates near the Galactic
disk.",2309.04772v1
2023-09-20,On the damping of tidally driven oscillations,"Expansions in the oscillation modes of tidally perturbed bodies provide a
useful framework for representing tidally induced flows. However, recent work
has demonstrated that such expansions produce inaccurate predictions for
secular orbital evolution when mode damping rates are computed independently.
We explore the coupling of collectively driven modes by frictional and viscous
dissipation, in tidally perturbed bodies that are both non-rotating and rigidly
rotating. This exploration leads us to propose an alternative approach to
treating the damping of tidally driven oscillations that accounts for
dissipative mode coupling, but which does not require any information beyond
the eigenfunctions and eigenfrequencies of adiabatic modes.",2309.11502v1
2023-09-25,Linearly implicit exponential integrators for damped Hamiltonian PDEs,"Structure-preserving linearly implicit exponential integrators are
constructed for Hamiltonian partial differential equations with linear constant
damping. Linearly implicit integrators are derived by polarizing the polynomial
terms of the Hamiltonian function and portioning out the nonlinearly of
consecutive time steps. They require only a solution of one linear system at
each time step. Therefore they are computationally more advantageous than
implicit integrators. We also construct an exponential version of the
well-known one-step Kahan's method by polarizing the quadratic vector field.
These integrators are applied to one-dimensional damped Burger's,
Korteweg-de-Vries, and nonlinear Schr{\""o}dinger equations. Preservation of the
dissipation rate of linear and quadratic conformal invariants and the
Hamiltonian is illustrated by numerical experiments.",2309.14184v2
2023-10-12,Plasmon dispersion and Landau damping in the nonlinear quantum regime,"We study the dispersion properties of electron plasma waves, or plasmons,
which can be excited in quantum plasmas in the nonlinear regime. In order to
describe nonlinear electron response to finite amplitude plasmons, we apply the
Volkov approach to non-relativistic electrons. For that purpose, we use the
Schr\""odinger equation and describe the electron population of a quantum plasma
as a mixture of quantum states. Within the kinetic framework that we are able
to derive from the Volkov solutions, we discuss the role of the wave amplitude
on the nonlinear plasma response. Finally, we focus on the quantum properties
of nonlinear Landau damping and study the contributions of multi-plasmon
absorption and emission processes.",2310.08544v1
2023-10-29,Asymptotic profiles for the Cauchy problem of damped beam equation with two variable coefficients and derivative nonlinearity,"In this article we investigate the asymptotic profile of solutions for the
Cauchy problem of the nonlinear damped beam equation with two variable
coefficients: \[ \partial_t^2 u + b(t) \partial_t u - a(t) \partial_x^2 u +
\partial_x^4 u
  = \partial_x \left( N(\partial_x u) \right). \] In the authors' previous
article [17], the asymptotic profile of solutions for linearized problem ($N
\equiv 0$) was classified depending on the assumptions for the coefficients
$a(t)$ and $b(t)$ and proved the asymptotic behavior in effective damping
cases. We here give the conditions of the coefficients and the nonlinear term
in order that the solution behaves as the solution for the heat equation: $b(t)
\partial_t u - a(t) \partial_x^2 u=0$ asymptotically as $t \to \infty$.",2310.18878v1
2023-11-09,Landau Damping in an Electron Gas,"Material science methods aim at developing efficient computational schemes
for describing complex many-body effects and how they are revealed in
experimentally measurable properties. Bethe-Salpeter equation in the
self-consistent Hartree-Fock basis is often used for this purpose, and in this
paper we employ the real-frequency diagrammatic Monte Carlo framework for
solving the ladder-type Bethe-Salpeter equation for the 3-point vertex function
(and, ultimately, for the system's polarization) to study the effect of
electron-hole Coulomb scattering on Landau damping in the homogeneous electron
gas. We establish how this damping mechanism depends on the Coulomb parameter
$r_s$ and changes with temperature between the correlated liquid and thermal
gas regimes. In a broader context of dielectric response in metals, we also
present the full polarization and the typical dependence of the
exchange-correlation kernel on frequency at finite momentum and temperature
within the same computational framework.",2311.05611v2
2023-11-11,On asymptotic properties of solutions to $σ$-evolution equations with general double damping,"In this paper, we would like to consider the Cauchy problem for semi-linear
$\sigma$-evolution equations with double structural damping for any $\sigma\ge
1$. The main purpose of the present work is to not only study the asymptotic
profiles of solutions to the corresponding linear equations but also describe
large-time behaviors of globally obtained solutions to the semi-linear
equations. We want to emphasize that the new contribution is to find out the
sharp interplay of ``parabolic like models"" corresponding to $\sigma_1 \in
[0,\sigma/2)$ and ``$\sigma$-evolution like models"" corresponding to $\sigma_2
\in (\sigma/2,\sigma]$, which together appear in an equation. In this
connection, we understand clearly how each damping term influences the
asymptotic properties of solutions.",2311.06660v1
2023-11-14,Enhanced classical radiation damping of electronic cyclotron motion in the vicinity of the Van Hove singularity in a waveguide,"We study the damping process of electron cyclotron motion and the resulting
emission in a waveguide using the classical Friedrichs model without relying on
perturbation analysis such as Fermi's golden rule. A classical Van Hove
singularity appears at the lower bound (or cut-off frequency) of the dispersion
associated with each of the electromagnetic field modes in the waveguide. In
the vicinity of the Van Hove singularity, we found that not only is the decay
process associated with the resonance pole enhanced (amplification factor ~
$10^4$) but the branch-point effect is also comparably enhanced. As a result,
the timescale on which most of the decay occurs is dramatically shortened.
Further, this suggests that the non-Markovian branch point effect should be
experimentally observable in the vicinity of the Van Hove singularity. Our
treatment yields a physically-acceptable solution without the problematic
runaway solution that is well known to appear in the traditional treatment of
classical radiation damping based on the Abraham-Lorentz equation.",2311.08121v3
2023-11-18,The temperature dependent Boltzmann equation beyond local equilibrium assumption,"In this manuscript, we present a temperature dependent Boltzmann equation for
the particles transport through a environmental reservoir, where the
temperature refers to the equilibrium temperature of reservoir, a new damping
force and a inverse damping relaxation time are derived based on the classical
Boltzmann equation, which have obvious influence on the external force and the
relaxation time of transport particles. For comparison, we also define a
non-equilibrium temperature for the transport particle by its distribution
function out of equilibrium, which is different from the equilibrium
temperature of reservoir. There exist heat transfer between the transport
particle and the reservoir, because the whole transport particles are in
non-equilibrium state. Finally, we illustrate them by an example of
one-dimensional transport procedure, the damping force and the non-equilibrium
temperature defined by us are shown numerically.",2311.11028v1
2023-12-13,"Integrating Superregenerative Principles in a Compact, Power-Efficient NMR/NQR Spectrometer: A Novel Approach with Pulsed Excitation","We present a new approach to Nuclear Quadrupole Resonance (NQR)/Nuclear
Magnetic Resonance (NMR) spectroscopy, the Damp-Enhanced Superregenerative
Nuclear Spin Analyser (DESSA). This system integrates Superregenerative
principles with pulsed sample excitation and detection, offering significant
advancements over traditional Super-Regenerative Receivers (SRRs). Our approach
overcomes certain limitations associated with traditional Super-Regenerative
Receivers (SRRs) by integrating direct digital processing of the oscillator
response delay time (T$_d$) and an electronic damp unit to regulate the
excitation pulse decay time (T$_e$). The essence is combining pulsed excitation
with a reception inspired by, but distinct from, conventional SRRs. The damp
unit allows a rapid termination of the oscillation pulse and the initiation of
detection within microseconds, and direct digital processing avoids the need
for a second lower frequency which is used for quenching in a traditional SRRs,
thereby avoiding the formation of sidebands. We demonstrate the effectiveness
of DESSA on a \ch{NaClO3} sample containing the isotope Chlorine-35 where it
accurately detects the NQR signal with sub-kHz resolution.",2312.08491v1
2023-12-26,"Dynamical polarization function, plasmons, their damping and collective effects in semi-Dirac bands","We have calculated the dynamical polarization, plasmons and damping rates in
semi-Dirac bands (SDB's) with zero band gap and half-linear, half-parabolic
low-energy spectrum. The obtained plasmon dispersions are strongly anisotropic
and demonstrate some crucial features of both two-dimensional electron gas and
graphene. Such gapless energy dispersions lead to a localized area of undamped
and low-damped plasmons in a limited range of the frequencies and wave vectors.
The calculated plasmon branches demonstrate an increase of their energies for a
finite tilting of the band structure and a fixed Fermi level which could be
used as a signature of a specific tilted spectrum in a semi-Dirac band.",2312.16117v1
2024-01-09,Coherent errors in stabilizer codes caused by quasistatic phase damping,"Quantum error correction is a key challenge for the development of practical
quantum computers, a direction in which significant experimental progress has
been made in recent years. In solid-state qubits, one of the leading
information loss mechanisms is dephasing, usually modelled by phase flip
errors. Here, we introduce quasistatic phase damping, a more subtle error model
which describes the effect of Larmor frequency fluctuations due to 1/f noise.
We show how this model is different from a simple phase flip error model, in
terms of multi-cycle error correction. Considering the surface code, we provide
numerical evidence for an error threshold, in the presence of quasistatic phase
damping and readout errors. We discuss the implications of our results for spin
qubits and superconducting qubits.",2401.04530v2
2024-01-19,Composite learning backstepping control with guaranteed exponential stability and robustness,"Adaptive backstepping control provides a feasible solution to achieve
asymptotic tracking for mismatched uncertain nonlinear systems. However,
input-to-state stability depends on high-gain feedback generated by nonlinear
damping terms, and closed-loop exponential stability with parameter convergence
involves a stringent condition named persistent excitation (PE). This paper
proposes a composite learning backstepping control (CLBC) strategy based on
modular backstepping and high-order tuners to compensate for the transient
process of parameter estimation and achieve closed-loop exponential stability
without the nonlinear damping terms and the PE condition. A novel composite
learning mechanism that maximizes the staged exciting strength is designed for
parameter estimation, such that parameter convergence can be achieved under a
condition of interval excitation (IE) or even partial IE that is strictly
weaker than PE. An extra prediction error is employed in the adaptive law to
ensure the transient performance without nonlinear damping terms. The
exponential stability of the closed-loop system is proved rigorously under the
partial IE or IE condition. Simulations have demonstrated the effectiveness and
superiority of the proposed method in both parameter estimation and control
compared to state-of-the-art methods.",2401.10785v1
2024-01-23,Model-Free $δ$-Policy Iteration Based on Damped Newton Method for Nonlinear Continuous-Time H$\infty$ Tracking Control,"This paper presents a {\delta}-PI algorithm which is based on damped Newton
method for the H{\infty} tracking control problem of unknown continuous-time
nonlinear system. A discounted performance function and an augmented system are
used to get the tracking Hamilton-Jacobi-Isaac (HJI) equation. Tracking HJI
equation is a nonlinear partial differential equation, traditional
reinforcement learning methods for solving the tracking HJI equation are mostly
based on the Newton method, which usually only satisfies local convergence and
needs a good initial guess. Based upon the damped Newton iteration operator
equation, a generalized tracking Bellman equation is derived firstly. The
{\delta}-PI algorithm can seek the optimal solution of the tracking HJI
equation by iteratively solving the generalized tracking Bellman equation.
On-policy learning and off-policy learning {\delta}-PI reinforcement learning
methods are provided, respectively. Off-policy version {\delta}-PI algorithm is
a model-free algorithm which can be performed without making use of a priori
knowledge of the system dynamics. NN-based implementation scheme for the
off-policy {\delta}-PI algorithms is shown. The suitability of the model-free
{\delta}-PI algorithm is illustrated with a nonlinear system simulation.",2401.12882v1
2024-01-30,The nonlinear dynamic behavior of a Rubber-Layer Roller Bearing (RLRB) for vibration isolation,"In this paper, we study the dynamic behavior of a Rubber-Layer Roller Bearing
(RLRB) interposed between a spring-mass elemental superstructure and a
vibrating base. Thanks to the viscoelastic rolling contact between the rigid
rollers and the rubber layers, the RLRB is able to provide a nonlinear damping
behavior. The effect of the RLRB geometric and material parameters is
investigated under periodic base excitation, showing that both periodic and
aperiodic responses can be achieved. Specifically, since the viscoelastic
damping is non-monotonic (bell shaped), there exist systemdynamic conditions
involving the decreasing portion of the damping curve in which a strongly
nonlinear behavior is experienced. In the second part of the paper, we
investigate the effectiveness of the nonlinear device in terms of seismic
isolation. Focusing on the mean shock of the Central Italy 2016 earthquake, we
opportunely tune the material and geometrical RLRB parameters, showing that a
significant reduction of both the peak and root-mean-square value of the
inertial force acting on the superstructure is achieved, compared to the best
performance of a linear base isolation system.",2401.16880v1
2024-01-30,Poynting-Robertson damping of laser beam driven lightsails,"Lightsails using Earth-based lasers for propulsion require passive
stabilization to stay within the beam. This can be achieved through the sail's
scattering properties, creating optical restoring forces and torques. Undamped
restoring forces produce uncontrolled oscillations, which could jeopardize the
mission, but it is not obvious how to achieve damping in the vacuum of space.
Using a simple two-dimensional model we show that the Doppler effect and
relativistic aberration of the propelling laser beam create damping terms in
the optical forces and torques. The effect is similar to the Poynting-Robertson
effect causing loss of orbital momentum of dust particles around stars, but can
be enhanced by design of the sail's geometry.",2401.16924v1
2024-02-29,The Equation of Motion for Taut-Line Buzzers,"Equations of motion are developed for the oscillatory rotation of a disk
suspended between twisted strings kept under tension by a hanging mass, to
which additional forces may be applied. In the absence of forcing, damped
harmonic oscillations are observed to decay with an exponential time envelope
for two different string types. This is consistent with damping caused by
string viscosity, rather than air turbulence, and may be quantified in terms of
a quality factor. To test the proposed equation of motion and model for viscous
damping within the string, we measure both the natural oscillation frequency
and the quality factor for widely varied values of string length, string
radius, disk moment of inertia, and hanging mass. The data are found to scale
in good accord with predictions. A variation where rotational kinetic energy is
converted back and forth to spring potential energy is also discussed.",2402.19285v1
2024-03-08,A design methodology for nonlinear oscillator chains enabling energy localization tuning and soliton stability enhancement with optimal damping,"In this paper, the vibration energy localization in coupled nonlinear
oscillators is investigated, based on the creation of standing solitons. The
main objective is to establish a design methodology for mechanical lattices
using the Nonlinear Schr\""odinger Equation (NLSE) as a guide strategy, even in
the presence of damping. A three-dimensional diagram is used to illustrate
stable parameter regions for damped stationary solitons. Moreover, an analysis
of the influence of the number of oscillators in the system, and a numerical
investigation regarding the stability of solitonic behavior is done. Through
numerical analyses, it is observed that the developed algorithm not only has
the capability to locate the highest amplitudes in the chain of oscillators,
but also to control the intensity at which these amplitudes are located
according to design requirements. The outcomes of the proposed methodology
elucidate the impact that the coupling stiffness has on the stabilization of
the NLSE, as well as the influence of the number of oscillators on the
continuity hypothesis. The developed algorithm holds potential for practical
applications in mechanical engineering since the NLSE is used as a design line
rather than as a consequence of the phenomenon description.",2403.05176v1
2024-03-08,Damping Obliquities of Hot Jupiter Hosts by Resonance Locking,"When orbiting hotter stars, hot Jupiters are often highly inclined relative
to their host star equator planes. By contrast, hot Jupiters orbiting cooler
stars are more aligned. Prior attempts to explain this correlation between
stellar obliquity and effective temperature have proven problematic. We show
how resonance locking -- the coupling of the planet's orbit to a stellar
gravity mode (g mode) -- can solve this mystery. Cooler stars with their
radiative cores are more likely to be found with g-mode frequencies increased
substantially by core hydrogen burning. Strong frequency evolution in resonance
lock drives strong tidal evolution; locking to an axisymmetric g mode damps
semi-major axes, eccentricities, and as we show for the first time,
obliquities. Around cooler stars, hot Jupiters evolve into spin-orbit alignment
and avoid engulfment. Hotter stars lack radiative cores, and therefore preserve
congenital spin-orbit misalignments. We focus on resonance locks with
axisymmetric modes, supplementing our technical results with simple physical
interpretations, and show that non-axisymmetric modes also damp obliquity.",2403.05616v1
2024-03-10,Linear-in-temperature resistivity and Planckian dissipation arise in a stochastic quantization model of Cooper pairs,"We suppose that a Cooper pair (CP) will experience a damping force exerted by
the condensed matter. A Langevin equation of a CP in two dimensional condensed
matter is established. Following a method similar to Nelson's stochastic
mechanics, generalized Schr\""{o}dinger equation of a CP in condensed matter is
derived. If the CPs move with a constant velocity, then the corresponding
direct current (DC) electrical conductivity can be calculated. Therefore, a
Drude like formula of resistivity of CPs is derived. We suppose that the
damping coefficient of CPs in two dimensional cuprate superconductors is a
linear function of temperature. Then the resistivity and scattering rate of CPs
turn out to be also linear-in-temperature. The origin of linear-in-temperature
resistivity and Planckian dissipation in cuprate superconductors may be the
linear temperature dependence of the damping coefficient of CPs.",2403.09710v1
1995-10-04,Microlensing By a Prolate All-Macho Halo,"It is widely believed that dark matter halos are flattened, that is closer to
oblate than prolate. The evidence cited is based largely on observations of
galaxies which do not look anything like our own and on numerical simulations
which use ad hoc initial conditions. Given what we believe to be a ``reasonable
doubt'' concerning the shape of dark Galactic halo we calculate the optical
depth and event rate for microlensing of stars in the LMC assuming a wide range
of models that include both prolate and oblate halos. We find, in agreement
with previous analysis, that the optical depth for a spherical (E0) halo and
for an oblate (E6) halo are roughly the same, essentially because two competing
effects cancel approximately. However the optical depth for an E6 prolate halo
is reduced by ~35%. This means that an all-Macho prolate halo with reasonable
parameters for the Galaxy is consistent with the published microlensing event
rate.",9510023v1
1997-04-25,Constraints on the density perturbation spectrum from primordial black holes,"We re-examine the constraints on the density perturbation spectrum, including
its spectral index $n$, from the production of primordial black holes. The
standard cosmology, where the Universe is radiation dominated from the end of
inflation up until the recent past, was studied by Carr, Gilbert and Lidsey; we
correct two errors in their derivation and find a significantly stronger
constraint than they did, $n \lesssim 1.25$ rather than their 1.5. We then
consider an alternative cosmology in which a second period of inflation, known
as thermal inflation and designed to solve additional relic over-density
problems, occurs at a lower energy scale than the main inflationary period. In
that case, the constraint weakens to $n \lesssim 1.3$, and thermal inflation
also leads to a `missing mass' range, $10^{18} g \lesssim M \lesssim 10^{26}
g$, in which primordial black holes cannot form. Finally, we discuss the effect
of allowing for the expected non-gaussianity in the density perturbations
predicted by Bullock and Primack, which can weaken the constraints further by
up to 0.05.",9704251v1
1998-02-26,Inversion of polarimetric data from eclipsing binaries,"We describe a method for determining the limb polarization and limb darkening
of stars in eclipsing binary systems, by inverting photometric and polarimetric
light curves.
  Because of the ill-conditioning of the problem, we use the Backus-Gilbert
method to control the resolution and stability of the recovered solution, and
to make quantitative estimates of the maximum accuracy possible. Using this
method we confirm that the limb polarization can indeed be recovered, and
demonstrate this with simulated data, thus determining the level of
observational accuracy required to achieve a given accuracy of reconstruction.
This allows us to set out an optimal observational strategy, and to critcally
assess the claimed detection of limb polarization in the Algol system.
  The use of polarization in stars has been proposed as a diagnostic tool in
microlensing surveys by Simmons et al. (1995), and we discuss the extension of
this work to the case of microlensing of extended sources.",9802334v1
1998-09-04,Cluster-Cluster Strong Lensing: Expectations and Detection Methods,"We calculate the all-sky number of galaxy clusters that are expected to be
gravitationally lensed by foreground massive clusters. We describe the redshift
and number distributions of clusters using a Press-Schechter analysis, and
model the foreground lensing clusters as singular isothermal spheres. If
Omega_m=0.3 and Omega_Lambda=0.7, we expect ~ 30 cluster-cluster strong lensing
events that involve foreground X-ray luminous clusters with total mass greater
than 7.5 x 10^14 h^-1 M_sun, or X-ray luminosity L_x (2-10 keV) 8 x 10^44 h^-2
ergs s^-1, and background clusters with total mass greater than 10^14 h^-1
M_sun. The number expected in an open universe with Omega_m = 0.3 is less than
\~ 4. Because of uncertainty in sigma_8, the root-mean-square density
fluctuations in spheres of radius 8 h^-1 Mpc, the exact number of such lensing
events is uncertain by a factor of about 5. We examine methods to detect
cluster-cluster lensing events based on optical, X-ray, and Sunyaev-Zel'dovich
effect observations.",9809062v3
2000-04-14,Source Reconstruction as an Inverse Problem,"Inverse Problem techniques offer powerful tools which deal naturally with
marginal data and asymmetric or strongly smoothing kernels, in cases where
parameter-fitting methods may be used only with some caution. Although they are
typically subject to some bias, they can invert data without requiring one to
assume a particular model for the source. The Backus-Gilbert method in
particular concentrates on the tradeoff between resolution and stability, and
allows one to select an optimal compromise between them. We use these tools to
analyse the problem of reconstructing features of the source star in a
microlensing event, show that it should be possible to obtain useful
information about the star with reasonably obtainable data, and note that the
quality of the reconstruction is more sensitive to the number of data points
than to the quality of individual ones.",0004200v1
2000-04-18,"Galaxy Cluster Baryon Fractions, Cluster Surveys and Cosmology","The properties of nearby galaxy clusters limit the range of cosmological
parameters consistent with our universe. We describe the limits which arise
from studies of the intracluster medium (ICM) mass fraction fICM and
consideration of the possible sources of systematic error:
Omega_M<0.44h_{50}^{-1/2} at 95% confidence. We emphasize that independent of
Type Ia supernovae (SNe Ia) observations, this cluster study, taken together
with published cosmic microwave background (CMB) anisotropy studies, indicates
a non-zero quintessence or dark energy component Omega_Q>0.
  We then discuss future galaxy cluster surveys which will probe the abundance
of galaxy clusters to intermediate and high redshift. We investigate the
sensitivity of these surveys to the cosmological density parameter Omega_M and
the equation of state parameter w of any quintessence component. In particular,
we show that cluster survey constraints from a proposed large solid angle X-ray
survey are comparable in precision and complementary in nature to constraints
expected from future CMB anisotropy and SNe Ia studies.",0004244v1
2000-05-11,Measurement of [OIII] Emission in Lyman Break Galaxies,"Measurements of [OIII] emission in Lyman Break galaxies (LBGs) at z>3 are
presented. Four galaxies were observed with narrow-band filters using the
Near-IR Camera on the Keck I 10-m telescope. A fifth galaxy was observed
spectroscopically during the commissioning of NIRSPEC, the new infrared
spectrometer on Keck II. The emission-line spectrum is used to place limits on
the metallicity. Comparing these new measurements with others available from
the literature, we find that strong oxygen emission in LBGs may suggest
sub-solar metallicity for these objects. The [OIII]5007 line is also used to
estimate the star formation rate (SFR) of the LBGs. The inferred SFRs are
higher than those estimated from the UV continuum, and may be evidence for dust
extinction.",0005254v1
2001-03-02,Clusters in the Precision Cosmology Era,"Over the coming decade, the observational samples available for studies of
cluster abundance evolution will increase from tens to hundreds, or possibly to
thousands, of clusters. Here we assess the power of future surveys to determine
cosmological parameters. We quantify the statistical differences among
cosmologies, including the effects of the cosmic equation of state parameter w,
in mock cluster catalogs simulating a 12 sq. deg Sunyaev-Zeldovich Effect
survey and a deep 10^4 sq. deg X-ray survey. The constraints from clusters are
complementary to those from studies of high-redshift Supernovae (SNe), CMB
anisotropies, or counts of high-redshift galaxies. Our results indicate that a
statistical uncertainty of a few percent on both Omega_m and w can be reached
when cluster surveys are used in combination with any of these other datasets.",0103049v1
2002-07-05,New Tests of the Cluster Entropy Floor Hypothesis,"Recent efforts to account for the observed X-ray luminosity - temperature
relation of galaxy clusters has led to suggestions that the ICM has an apparent
``entropy floor'' at or above the level of 300 keV cm^2. Here, we propose new
tests based on the thermal Sunyaev-Zeldovich effect and on the cluster gas mass
- temperature trend (from X-ray data) to probe the level of excess entropy in
the ICM. We show that these new tests lend further support to the case for a
high entropy floor in massive clusters.",0207147v1
2003-06-18,Kinematic Masses of Super Star Clusters in M82 from High-Resolution Near-Infrared Spectroscopy,"Using high-resolution (R~22,000) near-infrared (1.51 -- 1.75 microns) spectra
from Keck Observatory, we measure the kinematic masses of two super star
clusters in M82. Cross-correlation of the spectra with template spectra of cool
evolved stars gives stellar velocity dispersions of sigma_r=15.9 +/- 0.8 km/s
for MGG-9 and sigma_r=11.4 +/- 0.8 km/s for MGG-11. The cluster spectra are
dominated by the light of red supergiants, and correlate most closely with
template supergiants of spectral types M0 and M4.5. We fit King models to the
observed profiles of the clusters in archival HST/NICMOS images to measure the
half-light radii. Applying the virial theorem, we determine masses of 1.5 +/-
0.3 x 10^6 M_sun for MGG-9 and 3.5 +/- 0.7 x 10^5 M_sun for MGG-11. Population
synthesis modelling suggests that MGG-9 is consistent with a standard initial
mass function, whereas MGG-11 appears to be deficient in low-mass stars
relative to a standard IMF. There is, however, evidence of mass segregation in
the clusters, in which case the virial mass estimates would represent lower
limits.",0306373v1
2003-09-10,The CMB Quadrupole in a Polarized Light,"The low quadrupole of the cosmic microwave background (CMB), measured by COBE
and confirmed by WMAP, has generated much discussion recently. We point out
that the well-known correlation between temperature and polarization
anisotropies of the CMB further constrains the low multipole anisotropy data.
This correlation originates from the fact that the low-multipole polarization
signal is sourced by the CMB quadrupole as seen by free electrons during the
relatively recent cosmic history. Consequently, the large-angle temperature
anisotropy data make restrictive predictions for the large-angle polarization
anisotropy, which depend primarily on the optical depth for electron scattering
after cosmological recombination, tau. We show that if current cosmological
models for the generation of large angle anisotropy are correct and the
COBE/WMAP data are not significantly contaminated by non-CMB signals, then the
observed C_te amplitude on the largest scales is discrepant at the 99.8% level
with the observed C_tt for the concordance LCDM model with tau=0.10. Using
tau=0.17, the preferred WMAP model-independent value, the discrepancy is at the
level of 98.5%.",0309281v2
2003-10-11,Statistics of Giant Arcs in Galaxy Clusters,"We study the expected properties and statistics of giant arcs produced by
galaxy clusters in a LambdaCDM universe and investigate how the characteristics
of CDM clusters determine the properties of the arcs they generate. Due to the
triaxiality and substructure of CDM halos, the giant arc cross section for
individual clusters varies by more than an order of magnitude as a function of
viewing angle. In addition, the shallow density cusps and triaxiality of CDM
clusters cause systematic alignments of giant arcs which should be testable
with larger samples from forthcoming lensing surveys. We compute the predicted
statistics of giant arcs for the LambdaCDM model and compare to results from
previous surveys. The predicted arc statistics are in excellent agreement with
the numbers of giant arcs observed around low redshift (0.2 < z < 0.6) clusters
from the EMSS sample, however there are hints of a possible excess of arcs
observed around high redshift z > 0.6 clusters. This excess, if real, appears
to be due to the presence of highly massive or concentrated clusters at high
redshifts.",0310306v1
2004-01-23,Gravitational Lensing of the Microwave Background by Galaxy Clusters,"Galaxy clusters will distort the pattern of temperature anisotropies in the
microwave background via gravitational lensing. We create lensed microwave
background maps using clusters drawn from numerical cosmological simulations. A
distinctive dipole-like temperature fluctuation pattern is formed aligned with
the underlying microwave temperature gradient. For a massive cluster, the
characteristic angular size of the temperature distortion is a few arcminutes
and the characteristic amplitude a few micro-Kelvin. We demonstrate a simple
technique for estimating the lensing deflection induced by the cluster;
microwave background lensing measurements have the potential to determine the
mass distribution for some clusters with good accuracy on angular scales up to
a few arcminutes. Future high-resolution and high-sensitivity microwave
background maps will have the capability to detect lensing by clusters; we
discuss various systematic limitations on probing cluster masses using this
technique.",0401519v2
2004-04-15,Is the slope of the intrinsic Baldwin effect constant?,"We investigate the relationship between emission-line strength and continuum
luminosity in the best-studied nearby Seyfert 1 galaxy NGC5548. Our analysis of
13 years of ground-based optical monitoring data reveals significant
year-to-year variations in the observed H-beta emission-line response in this
source. More specifically, we confirm the result of Gilbert and Peterson (2003)
of a non-linear relationship between the continuum and H-beta emission-line
fluxes. Furthermore, we show that the slope of this relation is not constant,
but rather decreases as the continuum flux increases. Both effects are
consistent with photoionisation model predictions of a luminosity-dependent
response in this line.",0404296v1
2005-08-04,"Gravitino, Axino, Kaluza-Klein Graviton Warm and Mixed Dark Matter and Reionisation","Stable particle dark matter may well originate during the decay of long-lived
relic particles, as recently extensively examined in the cases of the axino,
gravitino, and higher-dimensional Kaluza-Klein (KK) graviton. It is shown that
in much of the viable parameter space such dark matter emerges naturally
warm/hot or mixed. In particular, decay produced gravitinos (KK-gravitons) may
only be considered cold for the mass of the decaying particle in the several
TeV range, unless the decaying particle and the dark matter particle are almost
degenerate. Such dark matter candidates are thus subject to a host of
cosmological constraints on warm and mixed dark matter, such as limits from a
proper reionisation of the Universe, the Lyman-alpha forest, and the abundance
of clusters of galaxies.. It is shown that constraints from an early
reionsation epoch, such as indicated by recent observations, may potentially
limit such warm/hot components to contribute only a very small fraction to the
dark matter.",0508141v2
1999-08-10,Magnetic relaxation in a classical spin chain as model for nanowires,"With decreasing particle size, different mechanisms dominate the thermally
activated magnetization reversal in ferromagnetic particles. We investigate
some of these mechanisms for the case of elongated, single-domain nanoparticles
which we describe by a classical Heisenberg spin chain driven by an external
magnetic field. For sufficiently small system size the magnetic moments rotate
coherently. With increasing size a crossover to a reversal due to
soliton-antisoliton nucleation sets in. For even larger systems many of these
soliton-antisoliton pairs nucleate at the same time. These effects give rise to
a complex size dependence of the energy barriers and characteristic time scales
of the relaxation. We study these quantities using Monte Carlo simulations as
well as a direct integration of the Landau-Lifshitz-Gilbert equation of motion
with Langevin dynamics and we compare our results with asymptotic solutions for
the escape rate following from the Fokker-Planck equation. Also, we investigate
the crossover from coherent rotation to soliton-antisoliton nucleation and
multi-droplet nucleation, especially its dependence on the system size, the
external field and the anisotropy of the system.",9908150v1
2000-07-17,Fine-grid Simulations of Thermally Activated Switching in Nanoscale Magets,"Numerical integration of the Landau-Lifshitz-Gilbert equation with thermal
fluctuations is used to study the dynamic response of single-domain nanomagnets
to rapid changes in the applied magnetic field. The simulation can resolve
magnetization patterns within nanomagnets and uses the Fast Multipole method to
calculate dipole-dipole interactions efficiently. The thermal fluctuations play
an essential part in the reversal process whenever the applied field is less
than the zero-temperature coercive field. In this situation pillar-shaped
nanomagnets are found to reverse through a local curling mode that involves the
formation and propagation of a domain wall. Tapering the ends of the pillars to
reduce pole-avoidance effects changes the energies involved but not the
fundamental process. The statistical distribution of switching times is well
described by the independent nucleation and subsequent growth of regions of
reversed magnetization at both ends of the pillar.",0007279v1
2001-01-31,Langevin Simulation of Thermally Activated Magnetization Reversal in Nanoscale Pillars,"Numerical solutions of the Landau-Lifshitz-Gilbert micromagnetic model
incorporating thermal fluctuations and dipole-dipole interactions (calculated
by the Fast Multipole Method) are presented for systems composed of nanoscale
iron pillars of dimension 9 nm x 9 nm x 150 nm. Hysteresis loops generated
under sinusoidally varying fields are obtained, while the coercive field is
estimated to be 1979 $\pm$ 14 Oe using linear field sweeps at T=0 K. Thermal
effects are essential to the relaxation of magnetization trapped in a
metastable orientation, such as happens after a rapid reversal of an external
magnetic field less than the coercive value. The distribution of switching
times is compared to a simple analytic theory that describes reversal with
nucleation at the ends of the nanomagnets. Results are also presented for
arrays of nanomagnets oriented perpendicular to a flat substrate. Even at a
separation of 300 nm, where the field from neighboring pillars is only $\sim$ 1
Oe, the interactions have a significant effect on the switching of the magnets.",0101477v2
2001-05-04,On a common circle: natural scenes and Gestalt rules,"To understand how the human visual system analyzes images, it is essential to
know the structure of the visual environment. In particular, natural images
display consistent statistical properties that distinguish them from random
luminance distributions. We have studied the geometric regularities of oriented
elements (edges or line segments) present in an ensemble of visual scenes,
asking how much information the presence of a segment in a particular location
of the visual scene carries about the presence of a second segment at different
relative positions and orientations. We observed strong long-range correlations
in the distribution of oriented segments that extend over the whole visual
field. We further show that a very simple geometric rule, cocircularity,
predicts the arrangement of segments in natural scenes, and that different
geometrical arrangements show relevant differences in their scaling properties.
Our results show similarities to geometric features of previous physiological
and psychophysical studies. We discuss the implications of these findings for
theories of early vision.",0105097v1
2002-10-11,Fluctuations and Dissipation of Coherent Magnetization,"A quantum mechanical model is used to derive a generalized Landau-Lifshitz
equation for a magnetic moment, including fluctuations and dissipation. The
model reproduces the Gilbert-Brown form of the equation in the classical limit.
The magnetic moment is linearly coupled to a reservoir of bosonic degrees of
freedom. Use of generalized coherent states makes the semiclassical limit more
transparent within a path-integral formulation. A general
fluctuation-dissipation theorem is derived. The magnitude of the magnetic
moment also fluctuates beyond the Gaussian approximation. We discuss how the
approximate stochastic description of the thermal field follows from our
result. As an example, we go beyond the linear-response method and show how the
thermal fluctuations become anisotropy-dependent even in the uniaxial case.",0210273v2
2002-11-18,Field dependence of magnetization reversal by spin transfer,"We analyse the effect of the applied field (Happl) on the current-driven
magnetization reversal in pillar-shaped Co/Cu/Co trilayers, where we observe
two different types of transition between the parallel (P) and antiparallel
(AP) magnetic configurations of the Co layers. If Happl is weaker than a rather
small threshold value, the transitions between P and AP are irreversible and
relatively sharp. For Happl exceding the threshold value, the same transitions
are progressive and reversible. We show that the criteria for the stability of
the P and AP states and the experimentally observed behavior can be precisely
accounted for by introducing the current-induced torque of the spin transfer
models in a Landau-Lifschitz-Gilbert equation. This approach also provides a
good description for the field dependence of the critical currents.",0211371v1
2003-10-18,NMR Investigation of the Organic Conductor lambda-(BETS)2FeCl4,"The two-dimensional organic conductor lambda-(BETS)2FeCl4 has an unusual
phase diagram as a function of temperature and magnetic field that includes a
paramagnetic metal (PM) phase, an antiferromagnetic insulating (AFI) phase, and
a field-induced superconducting phase [S. Uji, H. Kobayashi, L. Balicas, and
James S. Brooks, Adv. Mater. 14, 243 (2002), and cited references]. Here, we
report a preliminary investigation of the PM and AFI phases at 9.0 T over the
temperature range 2.0-180 K that uses proton NMR measurements of the spectrum,
the spin-lattice relaxation rate (1/T1), and the spin echo decay rate (1/T2).
The sample is asmall single crystal whose mass is approximately 3 micrograms
(approximately 2E16 protons). Its small size creates several challenges that
include detecting small signals and excluding parasitic proton signals that are
not from the sample [H. N. Bachman and I. F. Silvera, J. Mag. Res. 162, 417
(2003)]. These strategies and other techniques used to obtain viable signals
are described.",0310433v1
2004-04-22,Non-collinear magnetic structures: a possible cause for current induced switching,"Current induced switching in Co/Cu/Co trilayers is described in terms of
ab-initio determined magnetic twisting energies and corresponding sheet
resistances. In viewing the twisting energy as an energy flux the
characteristic time thereof is evaluated by means of the
Landau-Lifshitz-Gilbert equation using ab-initio parameters. The obtained
switching times are in very good agreement with available experimental data. In
terms of the calculated currents, scalar quantities since a classical Ohm's law
is applied, critical currents needed to switch magnetic configurations from
parallel to antiparallel and vice versa can unambiguously be defined. It is
found that the magnetoresistance viewed as a function of the current is
essentially determined by the twisting energy as a function of the relative
angle between the orientations of the magnetization in the magnetic slabs,
which in turn can also explain in particular cases the fact that after having
switched off the current the system remains in the switched magnetic
configuration. For all ab-initio type calculations the fully relativistic
Screened Korringa-Kohn-Rostoker method and the corresponding Kubo-Greenwood
equation in the context of density functional theory are applied.",0404534v1
2004-06-21,Basic considerations for magnetization dynamics in the combined presence of spin-transfer torques and thermal fluctuations,"This article reviews basic theoretical features of Gilbert magnetization
dynamics of a single domain magnetic film in the presence of Slonczewski
spin-transfer torques, with and without thermal fluctuations taken into
account. Rather than showing results of detailed numerical calculations, the
discussion here is restricted to basic analytical results and conclusions which
can mostly be derived from simply the form of the equations of motion, as well
as elementary considerations based on classical stability analysis and the
fluctuation-dissipation theorem. The presents work describes how interesting
features of spin-transfer may be viewed as arising from non-equilibrium
thermodynamics that are a direct consequence of the nonreciprocal nature of
spin-transfer torques. The present article discusses fairly general results for
spin-torque induced instability without thermal fluctuations, as well as the
case of thermally activated magnetization reversal in uniaxial devices in the
combined presence of external fields, thermal fluctuations, and spin-transfer
torques. The results will be discussed and briefly compared and contrasted with
that of prior work.",0406486v1
2004-06-24,Thermal Effects on the Magnetic Field Dependence of Spin Transfer Induced Magnetization Reversal,"We have developed a self-aligned, high-yield process to fabricate CPP
(current perpendicular to the plane) magnetic sensors of sub 100 nm dimensions.
A pinned synthetic antiferromagnet (SAF) is used as the reference layer which
minimizes dipole coupling to the free layer and field induced rotation of the
reference layer. We find that the critical currents for spin transfer induced
magnetization reversal of the free layer vary dramatically with relatively
small changes the in-plane magnetic field, in contrast to theoretical
predictions based on stability analysis of the Gilbert equations of
magnetization dynamics including Slonczewski-type spin-torque terms. The
discrepancy is believed due to thermal fluctuations over the time scale of the
measurements. Once thermal fluctuations are taken into account, we find good
quantitative agreement between our experimental results and numerical
simulations.",0406574v1
2004-07-23,Micromagnetic understanding of current-driven domain wall motion in patterned nanowires,"In order to explain recent experiments reporting a motion of magnetic domain
walls (DW) in nanowires carrying a current, we propose a modification of the
spin transfer torque term in the Landau-Lifchitz-Gilbert equation. We show that
it explains, with reasonable parameters, the measured DW velocities as well as
the variation of DW propagation field under current. We also introduce
coercivity by considering rough wires. This leads to a finite DW propagation
field and finite threshold current for DW propagation, hence we conclude that
threshold currents are extrinsic. Some possible models that support this new
term are discussed.",0407628v2
2004-08-07,Hysteresis multicycles in nanomagnet arrays,"We predict two new physical effects in arrays of single-domain nanomagnets by
performing simulations using a realistic model Hamiltonian and physical
parameters. First, we find hysteretic multicycles for such nanomagnets. The
simulation uses continuous spin dynamics through the Landau-Lifshitz-Gilbert
(LLG) equation. In some regions of parameter space, the probability of finding
a multicycle is as high as ~0.6. We find that systems with larger and more
anisotropic nanomagnets tend to display more multicycles. This result
demonstrates the importance of disorder and frustration for multicycle
behavior. We also show that there is a fundamental difference between the more
realistic vector LLG equation and scalar models of hysteresis, such as Ising
models. In the latter case, spin and external field inversion symmetry is
obeyed but in the former it is destroyed by the dynamics, with important
experimental implications.",0408158v1
2004-12-03,High frequency magnetic permeability of nanocomposite film,"The high frequency magnetic permeability of nanocomposite film consisting of
the single-domain spherical ferromagnetic particles in the dielectric matrix is
studied. The permeability is assumed to be determined by rotation of the
ferromagnetic inclusion magnetic moments around equilibrium direction in AC
magnetic field. The composite is modeled by a cubic array of ferromagnetic
particles. The magnetic permeability tensor is calculated by solving the
Landau-Lifshits-Gilbert equation accounting for the dipole interaction of
magnetic particles. The permeability tensor components are found as functions
of the frequency, temperature, ferromagnetic inclusions density and magnetic
anisotropy. The obtained results show that nanocomposite films could have
rather high value of magnetic permeability in the microwave range.",0412073v1
2005-01-07,Dielectric resonances of ordered passive arrays,"The electrical and optical properties of ordered passive arrays, constituted
of inductive and capacitive components, are usually deduced from Kirchhoff's
rules. Under the assumption of periodic boundary conditions, comparable results
may be obtained via an approach employing transfer matrices. In particular,
resonances in the dielectric spectrum are demonstrated to occur if all
eigenvalues of the transfer matrix of the entire array are unity. The latter
condition, which is shown to be equivalent to the habitual definition of a
resonance in impedance for an array between electrodes, allows for a convenient
and accurate determination of the resonance frequencies, and may thus be used
as a tool for the design of materials with a specific dielectric response. For
the opposite case of linear arrays in a large network, where periodic boundary
condition do not apply, several asymptotic properties are derived. Throughout
the article, the derived analytic results are compared to numerical models,
based on either Exact Numerical Renormalisation or the spectral method.",0501137v1
2005-07-27,"""Stochastic Modeling of Coercivity "" - A Measure of Non-equilibrium State","A typical coercivity versus particle size curve for magnetic nanoparticles
has been explained by using the Gilbert equation followed by the corresponding
Fokker Plank equation. Kramer's treatment has been employed to explain the
increase in coercivity in the single domain region. The single to multi-domain
transformation has been assumed to explain the decrease in coercive field
beyond a certain particle size. The justification for using Langevin theory of
paramagnetism (including anisotropy energy) to fit the M vs H curve is
discussed. The super-symmetric Hamiltonian approach is used to find out the
relaxation time for the spins (making an angle greater than $90^0$ with applied
field) at domain wall. The main advantage of our technique is that we can
easily take into account the time of measurement as we usually do in realistic
measurement.",0507640v1
2005-09-13,Synchronization of spin-transfer oscillators driven by stimulated microwave currents,"We have simulated the non-linear dynamics of networks of spin-transfer
oscillators. The oscillators are magnetically uncoupled but electrically
connected in series. We use a modified Landau-Lifschitz- Gilbert equation to
describe the motion of each oscillator in the presence of the oscillations of
all the others. We show that the oscillators of the network can be synchronized
not only in frequency but also in phase. The coupling is due to the microwave
components of the current induced in each oscillator by the oscillations in all
the other oscillators. Our results show how the emitted microwave power of
spin-transfer oscillators can be considerably enhanced by current-induced
synchronization in an electrically connected network. We also discuss the
possible application of our synchronization mechanism to the interpretation of
the surprisingly narrow microwave spectrum in some isolated spin-transfer
oscillators.",0509326v2
2005-11-04,Synchronized Magnetization Oscillations in F/N/F Nanopillars,"Current-induced magnetization dynamics in a trilayer structure composed of
two ferromagnetic free layers and a nonmagnetic spacer is examined. Both free
layers are treated as a monodomain magnetic body with an uniform agnetization.
The dynamics of the two magnetizations is modeled by modified
Landau-Lifshitz-Gilbert equations with spin-transfer torque terms. By solving
the equations simultaneously, we discuss their various solutions in detail. We
show that there exists the synchronous motion of two magnetizations among the
various solutions; the magnetizations are resonantly coupled via spin-transfer
torques and perform precessional motions with the same period. The condition to
excite the synchronous motion depends on the difference between the intrinsic
frequencies of the two ferromagnetic free layers as well as the magnitude of
current.",0511095v1
2006-01-27,Dynamics of thin-film spin-flip transistors with perpendicular source-drain magnetizations,"A ""spin-flip transistor"" is a lateral spin valve consisting of ferromagnetic
source drain contacts to a thin-film normal-metal island with an electrically
floating ferromagnetic base contact on top. We analyze the
\emph{dc}-current-driven magnetization dynamics of spin-flip transistors in
which the source-drain contacts are magnetized perpendicularly to the device
plane by magnetoelectronic circuit theory and the macrospin
Landau-Lifshitz-Gilbert equation. Spin flip scattering and spin pumping effects
are taken into account. We find a steady-state rotation of the base
magnetization at GHz frequencies that is tuneable by the source-drain bias. We
discuss the advantages of the lateral structure for high-frequency generation
and actuation of nanomechanical systems over recently proposed nanopillar
structures.",0601630v1
2007-03-17,Large-amplitude coherent spin waves exited by spin-polarized current in nanoscale spin valves,"We present spectral measurements of spin-wave excitations driven by direct
spinpolarized current in the free layer of nanoscale
Ir20Mn80/Ni80Fe20/Cu/Ni80Fe20 spin valves. The measurements reveal that
large-amplitude coherent spin wave modes are excited over a wide range of bias
current. The frequency of these excitations exhibits a series of jumps as a
function of current due to transitions between different localized nonlinear
spin wave modes of the Ni80Fe20 nanomagnet. We find that micromagnetic
simulations employing the Landau-Lifshitz-Gilbert equation of motion augmented
by the Slonczewski spin torque term (LLGS) accurately describe the frequency of
the current-driven excitations including the mode transition behavior. However
LLGS simulations give qualitatively incorrect predictions for the amplitude of
excited spin waves as a function of current.",0703458v2
2001-12-11,A Data Mining Framework for Optimal Product Selection in Retail Supermarket Data: The Generalized PROFSET Model,"In recent years, data mining researchers have developed efficient association
rule algorithms for retail market basket analysis. Still, retailers often
complain about how to adopt association rules to optimize concrete retail
marketing-mix decisions. It is in this context that, in a previous paper, the
authors have introduced a product selection model called PROFSET. This model
selects the most interesting products from a product assortment based on their
cross-selling potential given some retailer defined constraints. However this
model suffered from an important deficiency: it could not deal effectively with
supermarket data, and no provisions were taken to include retail category
management principles. Therefore, in this paper, the authors present an
important generalization of the existing model in order to make it suitable for
supermarket data as well, and to enable retailers to add category restrictions
to the model. Experiments on real world data obtained from a Belgian
supermarket chain produce very promising results and demonstrate the
effectiveness of the generalized PROFSET model.",0112013v1
2005-02-22,The QuarkNet/Grid Collaborative Learning e-Lab,"We describe a case study that uses grid computing techniques to support the
collaborative learning of high school students investigating cosmic rays.
Students gather and upload science data to our e-Lab portal. They explore those
data using techniques from the GriPhyN collaboration. These techniques include
virtual data transformations, workflows, metadata cataloging and indexing, data
product provenance and persistence, as well as job planners. Students use web
browsers and a custom interface that extends the GriPhyN Chiron portal to
perform all of these tasks. They share results in the form of online posters
and ask each other questions in this asynchronous environment. Students can
discover and extend the research of other students, modeling the processes of
modern large-scale scientific collaborations. Also, the e-Lab portal provides
tools for teachers to guide student work throughout an investigation.
http://quarknet.uchicago.edu/elab/cosmic",0502089v1
2006-10-11,Properties of codes in rank metric,"We study properties of rank metric and codes in rank metric over finite
fields. We show that in rank metric perfect codes do not exist. We derive an
existence bound that is the equivalent of the Gilbert--Varshamov bound in
Hamming metric. We study the asymptotic behavior of the minimum rank distance
of codes satisfying GV. We derive the probability distribution of minimum rank
distance for random and random $\F{q}$-linear codes. We give an asymptotic
equivalent of their average minimum rank distance and show that random
$\F{q}$-linear codes are on GV bound for rank metric.
  We show that the covering density of optimum codes whose codewords can be
seen as square matrices is lower bounded by a function depending only on the
error-correcting capability of the codes. We show that there are quasi-perfect
codes in rank metric over fields of characteristic 2.",0610057v1
1995-12-28,MSSM radiative contributions to the WW$γ$ and WWZ form factors,"We evaluate one-loop contributions to the C and P conserving $WW\gamma, WWZ$
form factors in the Minimal Supersymmetric Standard Model (MSSM), and in a more
constrained Supergravity Grand Unified Theory (SUGRA-GUT). A systematic search
of maximal effects in the available parameter space, shows that at LEP2 energy
MSSM contributions can hardly reach the border of the most optimistic accuracy
expected on those couplings, even for particles close to their production
thresholds. At NLC energies, the effects are more comfortably of the order of
the expected sensitivity, and may therefore provide useful information on MSSM
parameter values which will not be available from direct particle production.
We also discuss briefly some variance with other studies.",9512437v2
1998-07-10,Inverting the Supersymmetric Standard Model Spectrum: from Physical to Lagrangian Ino Parameters,"We examine the possibility of recovering the supersymmetric (and soft
supersymmetry breaking) Lagrangian parameters as direct {\em analytical}
expressions of appropriate physical masses, for the unconstrained (but CP and
R-parity conserving) minimal supersymmetric standard model. We concentrate
mainly on the algebraically non-trivial ""inversion"" for the ino parameters, and
obtain, for given values of $\tan\beta$, simple analytical expressions for the
$\mu$, $M_1$ and $M_2$ parameters in terms of three arbitrary input physical
masses, namely either two chargino and one neutralino masses, or alternatively
one chargino and two neutralino masses. We illustrate and discuss in detail the
possible occurrence of ambiguities in this reconstruction. The dependence of
the resulting ino Lagrangian parameters upon physical masses is illustrated,
and some simple generic behaviour uncovered in this way. We finally briefly
sketch generalizing such an inversion to the full set of MSSM Lagrangian
parameters.",9807336v2
1999-07-01,A convergent scheme for one-loop evolutions of the Yukawa couplings in the MSSM,"Integrated forms of the one-loop evolution equations are given for the Yukawa
couplings in the MSSM, valid for any value of $\tan \beta$, generalizable to
virtually any number of Yukawa fermions, and including all gauge couplings.
These forms turn out to have nice mathematical convergence properties which we
prove, and we determine the ensuing convergence criteria. Furthermore, they
allow to write down general sufficient and necessary conditions to avoid
singularities in the evolution of the Yukawa couplings over physically relevant
energy ranges. We also comment briefly on the possible use of these features
for physics issues and give a short numerical illustration.",9907204v1
1999-07-14,Phases in the gaugino sector: direct reconstruction of the basic parameters and impact on the neutralino pair production,"We consider recovering analytically the (generally complex) parameters $\mu$,
$M_1$ and $M_2$ of the gaugino and Higgsino Lagrangian, from appropriate
physical input in the chargino and neutralino sectors. For given $\tan\beta$,
we obtain very simple analytic solutions for $M_2$, $| \mu|$, $Arg[\mu]$ in the
chargino sector and a twofold $| M_1 |$, $Arg[M_1]$ analytic solution in the
neutralino sector, assuming two chargino, two neutralino masses, and one of the
chargino mixing angles as physical input. The twofold ambiguity in the
neutralino parameters reconstruction may be essentially resolved by measuring
the $e^+e^- \to \chi^0_1 \chi^0_2$ production cross-section at future linear
collider energies, which we study explicitly with the phase dependences. Some
salient features and specific properties of this complex case gaugino ""spectrum
inversion"" are illustrated and compared with the similar inversion in the real
case. In particular, our algorithms exhibit in a direct and transparent way the
non-trivial theoretical correlation among the chargino and neutralino
parameters, and the resulting allowed domains when only a subset of the
required physical input masses and production cross-sections is known.",9907360v1
1999-12-08,Analytical Study of Non-Universality of the Soft Terms in the MSSM,"We obtain general analytical forms for the solutions of the one-loop
renormalization group equations in the top/bottom/$\tau$ sector of the MSSM.
These solutions are valid for any value of $\tan \beta$ as well as any
non-universal initial conditions for the soft SUSY breaking parameters and
non-unification of the Yukawa couplings. We establish analytically a generic
screening effect of non-universality, in the vicinity of the infrared quasi
fixed point, which allows to determine sector-wise a hierarchy of sensitivity
to initial conditions. We give also various numerical illustrations of this
effect away from the quasi fixed point and assess the sensitivity of the Higgs
and sfermion spectra to the non-universality of the various soft breaking
sectors. As a by-product, a typical anomaly-mediated non-universality of the
gaugino sector would have marginal influence on the scalar spectrum.",9912271v1
2001-01-22,General one-loop renormalization group evolutions and electroweak symmetry breaking in the (M+1)SSM,"We study analytically the general features of electroweak symmetry breaking
in the context of the Minimal Supersymmetric Standard Model extended by one
Higgs singlet. The exact analytical forms of the renormalization group
evolutions of the Yukawa couplings and of the soft supersymmetry breaking
parameters are derived to one-loop order. They allow on one hand controllable
approximations in closed analytical form, and on the other a precise study of
the behaviour of infrared quasi fixed point regimes which we carry out. Some of
these regimes are shown to be phenomenologically inconsistent, leading to too
small an effective $\mu$-parameter. The remaining ones serve as a suitable
benchmark to understand analytically some salient aspects, often noticed
numerically in the literature, in relation to the electroweak symmetry breaking
in this model. The study does not need any specific assumption on $\tan \beta$
or on boundary conditions for the soft supersymmetry breaking parameters, thus
allowing a general insight into the sensitivity of the low energy physics to
high energy assumptions.",0101237v1
2001-12-28,Infrared Quasi Fixed Point Structure in Extended Yukawa Sectors and Application to R-parity Violation,"We investigate one-loop renormalization group evolutions of extended sectors
of Yukawa type couplings. It is shown that Landau Poles which usually provide
necessary low energy upper bounds that saturate quickly with increasing initial
value conditions, lead in some cases to the opposite behaviour: some of the low
energy couplings decrease and become vanishingly small for increasingly large
initial conditions. We write down the general criteria for this to happen in
typical situations, highlighting a concept of {\sl repulsive} quasi-fixed
points, and illustrate the case both within a two-Yukawa toy model as well as
in the minimal supersymmetric standard model with R-parity violation. In the
latter case we consider the theoretical upper bounds on the various couplings,
identifying regimes where $\lambda_{kl3}, \lambda'_{kkk}, \lambda''_{3kl}$ are
dynamically suppressed due to the Landau Pole. We stress the importance of
considering a large number of couplings simultaneously. This leads altogether
to a phenomenologically interesting seesaw effect in the magnitudes of the
various R-parity violating couplings, complementing and in some cases improving
the existing limits.",0112353v1
2005-04-04,Natural gravitino dark matter in SO(10) gauge mediated supersymmetry breaking,"It is shown that gravitinos with mass m_{3/2} ~ 0.1-1 MeV may provide
suitable cold dark matter candidates in scenarios of gauge mediated
supersymmetry breaking (GMSB) under SO(10) grand unification coupled to
supergravity, which accommodate a messenger sector of mass scale M_X ~ 10^6
GeV. This is due to the combined effects of renormalizable loop-suppressed
operators and generic non-renormalizable ones governing the dilution of a
pre-existing equilibrium gravitino abundance via messenger decay. The above
range of gravitino and messenger masses can be accommodated in indirect GMSB
scenarios. The gravitino abundance does not depend on the post-inflationary
reheat temperature and it is shown that leptogenesis can generate successfully
the baryon asymmetry.",0504021v2
2005-06-14,Gravitino dark matter in gauge mediated supersymmetry breaking,"This paper investigates the parameter space of theories with gauge mediated
supersymmetry breaking leading to gravitino (cold) dark matter with mass
m_{3/2}= 1keV - 10MeV. We pay particular attention to the cosmological role of
messenger fields. Cosmology requires that these messengers decay to the visible
sector if the lightest messenger mass M_X > 30TeV. We then examine the various
possible messenger number violating interactions allowed by the symmetries of
the theory and by phenomenology. Late messenger decay generally results in
entropy production hence in the dilution of pre-existing gravitinos. We find
that in SU(5) grand unification only specific messenger-matter couplings allow
to produce the required amount of gravitino dark matter particles. Gravitino
dark matter with the correct abundance is however expected in larger gauge
groups such as SO(10) for generic non-renormalizable messenger-matter
interactions and for arbritrarily high post-inflationary reheating
temperatures.",0506129v2
1991-08-22,On the Perturbations of String-Theoretic Black Holes,"The perturbations of string-theoretic black holes are analyzed by
generalizing the method of Chandrasekhar. Attention is focussed on the case of
the recently considered charged string-theoretic black hole solutions as a
representative example. It is shown that string-intrinsic effects greatly alter
the perturbed motions of the string-theoretic black holes as compared to the
perturbed motions of black hole solutions of the field equations of general
relativity, the consequences of which bear on the questions of the scattering
behavior and the stability of string-theoretic black holes. The explicit forms
of the axial potential barriers surrounding the string-theoretic black hole are
derived. It is demonstrated that one of these, for sufficiently negative values
of the asymptotic value of the dilaton field, will inevitably become negative
in turn, in marked contrast to the potentials surrounding the static black
holes of general relativity. Such potentials may in principle be used in some
cases to obtain approximate constraints on the value of the string coupling
constant. The application of the perturbation analysis to the case of
two-dimensional string-theoretic black holes is discussed.",9108012v1
1992-10-31,All Or Nothing: On the Small Fluctuations of Two-Dimensional String-Theoretic Black Holes,"A comprehensive analysis of small fluctuations about two-dimensional
string-theoretic and string-inspired black holes is presented. It is shown with
specific examples that two-dimensional black holes behave in a radically
different way from all known black holes in four dimensions. For both the
$SL(2,R)/U(1)$ black hole and the two-dimensional black hole coupled to a
massive dilaton with constant field strength, it is shown that there are a {\it
continuous infinity} of solutions to the linearized equations of motion, which
are such that it is impossible to ascertain the classical linear response. It
is further shown that the two-dimensional black hole coupled to a massive,
linear dilaton admits {\it no small fluctuations at all}. We discuss possible
implications of our results for the Callan-Giddings-Harvey-Strominger black
hole.",9210165v3
1993-04-01,Wavelet transforms versus Fourier transforms,"This note is a very basic introduction to wavelets. It starts with an
orthogonal basis of piecewise constant functions, constructed by dilation and
translation. The ``wavelet transform'' maps each $f(x)$ to its coefficients
with respect to this basis. The mathematics is simple and the transform is fast
(faster than the Fast Fourier Transform, which we briefly explain), but
approximation by piecewise constants is poor. To improve this first wavelet, we
are led to dilation equations and their unusual solutions. Higher-order
wavelets are constructed, and it is surprisingly quick to compute with them ---
always indirectly and recursively. We comment informally on the contest between
these transforms in signal processing, especially for video and image
compression (including high-definition television). So far the Fourier
Transform --- or its 8 by 8 windowed version, the Discrete Cosine Transform ---
is often chosen. But wavelets are already competitive, and they are ahead for
fingerprints. We present a sample of this developing theory.",9304214v1
1998-04-24,Enumeration of m-ary cacti,"The purpose of this paper is to enumerate various classes of cyclically
colored m-gonal plane cacti, called m-ary cacti. This combinatorial problem is
motivated by the topological classification of complex polynomials having at
most m critical values, studied by Zvonkin and others. We obtain explicit
formulae for both labelled and unlabelled m-ary cacti, according to i) the
number of polygons, ii) the vertex-color distribution, iii) the vertex-degree
distribution of each color. We also enumerate m-ary cacti according to the
order of their automorphism group. Using a generalization of Otter's formula,
we express the species of m-ary cacti in terms of rooted and of pointed cacti.
A variant of the m-dimensional Lagrange inversion is then used to enumerate
these structures. The method of Liskovets for the enumeration of unrooted
planar maps can also be adapted to m-ary cacti.",9804119v2
2002-08-21,Toric codes over finite fields,"In this note, a class of error-correcting codes is associated to a toric
variety associated to a fan defined over a finite field $\fff_q$, analogous to
the class of Goppa codes associated to a curve. For such a ``toric code''
satisfying certain additional conditions, we present an efficient decoding
algorithm for the dual of a Goppa code. Many examples are given. For small $q$,
many of these codes have parameters beating the Gilbert-Varshamov bound. In
fact, using toric codes, we construct a $(n,k,d)=(49,11,28)$ code over
$\fff_8$, which is better than any other known code listed in Brouwer's on-line
tables for that $n$ and $k$.",0208155v2
2002-12-05,Automorphisms of hyperbolic groups and graphs of groups,"Using the canonical JSJ splitting, we describe the outer automorphism group
$\Out(G)$ of a one-ended word hyperbolic group $G$. In particular, we discuss
to what extent $\Out(G)$ is virtually a direct product of mapping class groups
and a free abelian group, and we determine for which groups $\Out(G)$ is
infinite. We also show that there are only finitely many conjugacy classes of
torsion elements in $\Out(G)$, for $G$ any torsion-free hyperbolic group.
  More generally, let $\Gamma $ be a finite graph of groups decomposition of an
arbitrary group $G$ such that edge groups $G_e$ are rigid (i.e\. $\Out(G_e)$ is
finite). We describe the group of automorphisms of $G$ preserving $\Gamma $, by
comparing it to direct products of suitably defined mapping class groups of
vertex groups.",0212088v1
2004-06-08,"The structure and labelled enumeration of K_{3,3}-subdivision-free projective-planar graphs","We consider the class F of 2-connected non-planar K_{3,3}-subdivision-free
graphs that are embeddable in the projective plane. We show that these graphs
admit a unique decomposition as a graph K_5 (the core) where the edges are
replaced by two-pole networks constructed from 2-connected planar graphs. A
method to enumerate these graphs in the labelled case is described. Moreover,
we enumerate the homeomorphically irreducible graphs in F and homeomorphically
irreducible 2-connected planar graphs. Particular use is made of two-pole
directed series-parallel networks. We also show that the number m of edges of
graphs in F with n vertices satisfies the bound m <=3n-6, for n >= 6.",0406140v5
2004-09-16,Translation equivalence in free groups,"Motivated by the work of Leininger on hyperbolic equivalence of homotopy
classes of closed curves on surfaces, we investigate a similar phenomenon for
free groups. Namely, we study the situation when two elements $g,h$ in a free
group $F$ have the property that for every free isometric action of $F$ on an
$\mathbb{R}$-tree $X$ the translation lengths of $g$ and $h$ on $X$ are equal.
We give a combinatorial characterization of this phenomenon, called translation
equivalence, in terms of Whitehead graphs and exhibit two difference sources of
it. The first source of translation equivalence comes from representation
theory and $SL_2$ trace identities. The second source comes from geometric
properties of groups acting on real trees and a certain power redistribution
trick. We also analyze to what extent these are applicable to the tree actions
of surface groups that occur in the Thurston compactification of the
Teichmuller space.",0409284v2
2004-11-16,"Characterization and enumeration of toroidal K_{3,3}-subdivision-free graphs","We describe the structure of 2-connected non-planar toroidal graphs with no
K_{3,3}-subdivisions, using an appropriate substitution of planar networks into
the edges of certain graphs called toroidal cores. The structural result is
based on a refinement of the algorithmic results for graphs containing a fixed
K_5-subdivision in [A. Gagarin and W. Kocay, ""Embedding graphs containing
K_5-subdivisions'', Ars Combin. 64 (2002), 33-49]. It allows to recognize these
graphs in linear-time and makes possible to enumerate labelled 2-connected
toroidal graphs containing no K_{3,3}-subdivisions and having minimum vertex
degree two or three by using an approach similar to [A. Gagarin, G. Labelle,
and P. Leroux, ""Counting labelled projective-planar graphs without a
K_{3,3}-subdivision"", submitted, arXiv:math.CO/0406140, (2004)].",0411356v1
2005-01-19,The outer space of a free product,"We associate a contractible ``outer space'' to any free product of groups
G=G_1*...*G_q. It equals Culler-Vogtmann space when G is free,
McCullough-Miller space when no G_i is Z. Our proof of contractibility (given
when G is not free) is based on Skora's idea of deforming morphisms between
trees.
  Using the action of Out(G) on this space, we show that Out(G) has finite
virtual cohomological dimension, or is VFL (it has a finite index subgroup with
a finite classifying space), if the groups G_i and Out(G_i) have similar
properties. We deduce that Out(G) is VFL if G is a torsion-free hyperbolic
group, or a limit group (finitely generated fully residually free group).",0501288v3
2005-07-28,"Free-group automorphisms, train tracks and the beaded decomposition","We study the automorphisms \phi of a finitely generated free group F.
Building on the train-track technology of Bestvina, Feighn and Handel, we
provide a topological representative f:G\to G of a power of \phi that behaves
very much like the realization on the rose of a positive automorphism. This
resemblance is encapsulated in the Beaded Decomposition Theorem which describes
the structure of paths in G obtained by repeatedly passing to f-images of an
edge and taking subpaths. This decomposition is the key to adapting our proof
of the quadratic isoperimetric inequality for $F\rtimes_\phi\mathbb Z$, with
\phi positive, to the general case. To illustrate the wider utility of our
topological normal form, we provide a short proof that for every w in F, the
function $n\mapsto |\phi^n(w)|$ grows either polynomially or exponentially.",0507589v2
2007-02-02,Line-of-sight percolation,"Given $\omega\ge 1$, let $Z^2_{(\omega)}$ be the graph with vertex set $Z^2$
in which two vertices are joined if they agree in one coordinate and differ by
at most $\omega$ in the other. (Thus $Z^2_{(1)}$ is precisely $Z^2$.) Let
$p_c(\omega)$ be the critical probability for site percolation in
$Z^2_{(\omega)}$. Extending recent results of Frieze, Kleinberg, Ravi and
Debany, we show that $\lim_{\omega\to\infty} \omega\pc(\omega)=\log(3/2)$. We
also prove analogues of this result on the $n$-by-$n$ grid and in higher
dimensions, the latter involving interesting connections to Gilbert's continuum
percolation model. To prove our results, we explore the component of the origin
in a certain non-standard way, and show that this exploration is well
approximated by a certain branching random walk.",0702061v2
2000-03-06,"Entropy Production, Fractals, and Relaxation to Equilibrium","The theory of entropy production in nonequilibrium, Hamiltonian systems,
previously described for steady states using partitions of phase space, is here
extended to time dependent systems relaxing to equilibrium. We illustrate the
main ideas by using a simple multibaker model, with some nonequilibrium initial
state, and we study its progress toward equilibrium. The central results are
(i) the entropy production is governed by an underlying, exponentially decaying
fractal structure in phase space, (ii) the rate of entropy production is
largely independent of the scale of resolution used in the partitions, and
(iii) the rate of entropy production is in agreement with the predictions of
nonequilibrium thermodynamics.",0003012v2
2002-03-21,Entropy production of diffusion in spatially periodic deterministic systems,"This paper presents an {\it ab initio} derivation of the expression given by
irreversible thermodynamics for the rate of entropy production for different
classes of diffusive processes. The first class are Lorentz gases, where
non-interacting particles move on a spatially periodic lattice, and collide
elastically with fixed scatterers. The second class are periodic systems where
$N$ particles interact with each other, and one of them is a tracer particle
which diffuses among the cells of the lattice. We assume that, in either case,
the dynamics of the system is deterministic and hyperbolic, with positive
Lyapunov exponents. This work extends methods originally developed for a
chaotic two-dimensional model of diffusion, the multi-baker map, to higher
dimensional, continuous time dynamical systems appropriate for systems with one
or more moving particles. Here we express the rate of entropy production in
terms of hydrodynamic measures that are determined by the fractal properties of
microscopic hydrodynamic modes that describe the slowest decay of the system to
an equilibrium state.",0203046v1
2001-11-09,Spatial diffusion in a periodic optical lattice: revisiting the Sisyphus effect,"We numerically study the spatial diffusion of an atomic cloud experiencing
Sisyphus cooling in a three-dimensional lin$\bot$lin optical lattice in a broad
range of lattice parameters. In particular, we investigate the dependence on
the size of the lattice sites which changes with the angle between the laser
beams. We show that the steady-state temperature is largely independent of the
lattice angle, but that the spatial diffusion changes significantly. It is
shown that the numerical results fulfil the Einstein relations of Brownian
motion in the jumping regime as well as in the oscillating regime. We finally
derive an effective Brownian motion model from first principles which gives
good agreement with the simulations.",0111070v2
2006-07-24,Use of specific Green's functions for solving direct problems involving a heterogeneous rigid frame porous medium slab solicited by acoustic waves,"A domain integral method employing a specific Green's function (i.e.,
incorporating some features of the global problem of wave propagation in an
inhomogeneous medium) is developed for solving direct and inverse scattering
problems relative to slab-like macroscopically inhomogeneous porous obstacles.
It is shown how to numerically solve such problems, involving both
spatially-varying density and compressibility, by means of an iterative scheme
initialized with a Born approximation. A numerical solution is obtained for a
canonical problem involving a two-layer slab.",0607212v1
2005-12-12,"Cloning, expression and purification of the general stress protein Yhbo from Escherichia coli","We cloned, expressed and purified the Escherichia coli yhbO gene product,
which is homolog to the Bacillus subtilis general stress protein 18 (the yfkM
gene product), the Pyrococcus furiosus intracellular protease PfpI, and the
human Parkinson disease protein DJ-1. The gene coding for YhbO was generated by
amplifying the yhbO gene from E. coli by polymerase chain reaction. It was
inserted in the expression plasmid pET-21a, under the transcriptional control
of the bacteriophage T7 promoter and lac operator. A BL21(DE3) E. coli strain
transformed with the YhbO-expression vector pET-21a-yhbO, accumulates large
amounts of a soluble protein of 20 kDa in SDS-PAGE that matches the expected
YhbO molecular weight. YhbO was purified to homogeneity by HPLC DEAE ion
exchange chromatography and hydroxylapatite chromatography and its identity was
confirmed by N-terminal sequencing and mass spectrometry analysis. The native
protein exists in monomeric, trimeric and hexameric forms.",0512028v1
2003-01-24,Rayleigh Scattering and Atomic Dynamics in Dissipative Optical Lattices,"We investigate Rayleigh scattering in dissipative optical lattices. In
particular, following recent proposals (S. Guibal {\it et al}, Phys. Rev. Lett.
{\bf 78}, 4709 (1997); C. Jurczak {\it et al}, Phys. Rev. Lett. {\bf 77}, 1727
(1996)), we study whether the Rayleigh resonance originates from the
diffraction on a density grating, and is therefore a probe of transport of
atoms in optical lattices. It turns out that this is not the case: the Rayleigh
line is instead a measure of the cooling rate, while spatial diffusion
contributes to the scattering spectrum with a much broader resonance.",0301139v1
2005-12-19,More on the Asymmetric Infinite Square Well: Energy Eigenstates with Zero Curvature,"We extend the standard treatment of the asymmetric infinite square well to
include solutions that have zero curvature over part of the well. This type of
solution, both within the specific context of the asymmetric infinite square
well and within the broader context of bound states of arbitrary
piecewise-constant potential energy functions, is not often discussed as part
of quantum mechanics texts at any level. We begin by outlining the general
mathematical condition in one-dimensional time-independent quantum mechanics
for a bound-state wave function to have zero curvature over an extended region
of space and still be a valid wave function. We then briefly review the
standard asymmetric infinite square well solutions, focusing on zero-curvature
solutions as represented by energy eigenstates in position and momentum space.",0512156v1
2006-05-09,Communicating over adversarial quantum channels using quantum list codes,"We study quantum communication in the presence of adversarial noise. In this
setting, communicating with perfect fidelity requires using a quantum code of
bounded minimum distance, for which the best known rates are given by the
quantum Gilbert-Varshamov (QGV) bound. By asking only for arbitrarily high
fidelity and allowing the sender and reciever to use a secret key with length
logarithmic in the number of qubits sent, we achieve a dramatic improvement
over the QGV rates. In fact, we find protocols that achieve arbitrarily high
fidelity at noise levels for which perfect fidelity is impossible. To achieve
such communication rates, we introduce fully quantum list codes, which may be
of independent interest.",0605086v2
2007-05-16,Quantization Bounds on Grassmann Manifolds of Arbitrary Dimensions and MIMO Communications with Feedback,"This paper considers the quantization problem on the Grassmann manifold with
dimension n and p. The unique contribution is the derivation of a closed-form
formula for the volume of a metric ball in the Grassmann manifold when the
radius is sufficiently small. This volume formula holds for Grassmann manifolds
with arbitrary dimension n and p, while previous results are only valid for
either p=1 or a fixed p with asymptotically large n. Based on the volume
formula, the Gilbert-Varshamov and Hamming bounds for sphere packings are
obtained. Assuming a uniformly distributed source and a distortion metric based
on the squared chordal distance, tight lower and upper bounds are established
for the distortion rate tradeoff. Simulation results match the derived results.
As an application of the derived quantization bounds, the information rate of a
Multiple-Input Multiple-Output (MIMO) system with finite-rate channel-state
feedback is accurately quantified for arbitrary finite number of antennas,
while previous results are only valid for either Multiple-Input Single-Output
(MISO) systems or those with asymptotically large number of transmit antennas
but fixed number of receive antennas.",0705.2272v1
2007-05-24,Local spin dynamic arising from the non-perturbative SU(2) gauge field of the spin orbit effect,"We use the non-perturbative gauge field approach to study the effects of spin
orbit coupling on the dynamic of magnetic moment. We present a general equation
of motion (EOM) which unifies i) the spin orbit coupling effect derived from
the SU(2) spin gauge field, and ii) the moment chirality effect previously
derived from the topological U(1)xU(1) rotation gauge under the adiabatic
condition. We present a modified Landau-Liftshitz-Gilbert equation and discuss
the implication of the modified EOM in various technological applications, such
as current-induced switching and trajectory of magnetic moments in spin-valve
multilayers, magnetic memory and diluted magnetic semiconductor.",0705.3502v1
2007-06-07,$^{77}$Se NMR measurements of the $π-d$ exchange field in the organic conductor $λ-$(BETS)$_{2}$FeCl$_{4}$,"$^{77}$Se-NMR spectrum and frequency shift measurements in the paramagnetic
metal (PM) and antiferromagnetic insulating (AFI) phases are reported for a
small single crystal of the organic conductor $\lambda-$(BETS)$_{2}$FeCl$_{4}$
as a function of temperature ($T$) and field alignment for an applied magnetic
field $B_{0}$ = 9 T. The results show that in the low $T$ limit, where the
localized Fe$^{3+}$ spins ($S_{d}$ = 5/2) are almost fully polarized, the
conduction electrons (Se $\pi$-electrons, spin $s_{\pi}$ = 1/2) in the BETS
molecules experience an exchange field ($\bf{B}$$_{\pi d}$) from the Fe$^{3+}$
spins with a value of $-$ 32.7 $\pm$ 1.5 T at 5 K and 9 T aligned opposite to
$\bf{B}$$_{0}$. This large negative value of $\bf{B}$$_{\pi d}$ is consistent
with that predicted by the resistivity measurements and supports the
Jaccarino-Peter internal field-compensation mechanism being responsible for the
origin of field-induced superconductivity.",0706.0933v1
2007-11-05,Feedback Capacity of the Compound Channel,"In this work we find the capacity of a compound finite-state channel with
time-invariant deterministic feedback. The model we consider involves the use
of fixed length block codes. Our achievability result includes a proof of the
existence of a universal decoder for the family of finite-state channels with
feedback. As a consequence of our capacity result, we show that feedback does
not increase the capacity of the compound Gilbert-Elliot channel. Additionally,
we show that for a stationary and uniformly ergodic Markovian channel, if the
compound channel capacity is zero without feedback then it is zero with
feedback. Finally, we use our result on the finite-state channel to show that
the feedback capacity of the memoryless compound channel is given by
$\inf_{\theta} \max_{Q_X} I(X;Y|\theta)$.",0711.0705v1
2007-11-12,Mutual phase-locking in high frequency microwave nanooscillators as function of field angle,"We perform a qualitative analysis of phase locking in a double point-contact
spinvalve system by solving the Landau-Lifshitz-Gilbert-Slonzewski equation
using a hybrid-finite-element method. We show that the phase-locking behaviour
depends on the applied field angle. Starting from a low field angle, the
locking-current difference between the current through contact A and B
increases with increasing angle up to a maximum of 14 mA at 30 degree and it
decreases thereafter until it reaches a minimum of 1 mA at 75 degree. The
tunability of the phase-lock frequency with current decreases linearly with
increasing out of plane angle from 45 to 21 MHz/mA.",0711.1770v2
2007-11-14,Emergent singular solutions of non-local density-magnetization equations in one dimension,"We investigate the emergence of singular solutions in a non-local model for a
magnetic system. We study a modified Gilbert-type equation for the
magnetization vector and find that the evolution depends strongly on the length
scales of the non-local effects. We pass to a coupled density-magnetization
model and perform a linear stability analysis, noting the effect of the length
scales of non-locality on the system's stability properties. We carry out
numerical simulations of the coupled system and find that singular solutions
emerge from smooth initial data. The singular solutions represent a collection
of interacting particles (clumpons). By restricting ourselves to the
two-clumpon case, we are reduced to a two-dimensional dynamical system that is
readily analyzed, and thus we classify the different clumpon interactions
possible.",0711.2177v1
2007-11-27,Nonequilibrium interacting electrons in a ferromagnet,"Dynamics of the magnetization in ferromagnets is examined in the presence of
transport electrons allowing the latter to interact. It is found that the
existence of inhomogeneities such as domain wall (DW) structures, leads to
changes that affect the dynamical structure of the equations of motion for the
magnetization. Only in the limit of uniform magnetizations or sufficiently wide
DW's, the equations of motion maintain the form they have in the noninteracting
case. In this limit, results like the spin torques, the Gilbert parameter, and
the DW velocities become renormalized. However the length scale that defines
such a limit depends on the strength of the interaction. It is shown that if
large ferromagnetic fluctuations exist in the metallic band then the range for
which conformity with the noninteracting case holds extends to the limit of
arbitrarily narrow DW's.",0711.4170v2
2007-12-01,On Precision - Redundancy Relation in the Design of Source Coding Algorithms,"We study the effects of finite-precision representation of source's
probabilities on the efficiency of classic source coding algorithms, such as
Shannon, Gilbert-Moore, or arithmetic codes. In particular, we establish the
following simple connection between the redundancy $R$ and the number of bits
$W$ necessary for representation of source's probabilities in computer's memory
($R$ is assumed to be small): \begin{equation*} W \lesssim \eta \log_2
\frac{m}{R}, \end{equation*} where $m$ is the cardinality of the source's
alphabet, and $\eta \leqslant 1$ is an implementation-specific constant. In
case of binary alphabets ($m=2$) we show that there exist codes for which $\eta
= 1/2$, and in $m$-ary case ($m > 2$) we show that there exist codes for which
$\eta = m/(m+1)$. In general case, however (which includes designs relying on
progressive updates of frequency counters), we show that $\eta = 1$. Usefulness
of these results for practical designs of source coding algorithms is also
discussed.",0712.0057v1
2007-12-03,Kinetic models of heterogeneous dissipation,"We suggest kinetic models of dissipation for an ensemble of interacting
oriented particles, for example, moving magnetized particles. This is achieved
by introducing a double bracket dissipation in kinetic equations using an
oriented Poisson bracket, and employing the moment method to derive continuum
equations for magnetization and density evolution. We show how our continuum
equations generalize the Debye-Hueckel equations for attracting round
particles, and Landau-Lifshitz-Gilbert equations for spin waves in magnetized
media. We also show formation of singular solutions that are clumps of aligned
particles (orientons) starting from random initial conditions. Finally, we
extend our theory to the dissipative motion of self-interacting curves.",0712.0397v1
2007-12-13,Euler equation of the optimal trajectory for the fastest magnetization reversal of nano-magnetic structures,"Based on the modified Landau-Lifshitz-Gilbert equation for an arbitrary
Stoner particle under an external magnetic field and a spin-polarized electric
current, differential equations for the optimal reversal trajectory, along
which the magnetization reversal is the fastest one among all possible reversal
routes, are obtained. We show that this is a Euler-Lagrange problem with
constrains. The Euler equation of the optimal trajectory is useful in designing
a magnetic field pulse and/or a polarized electric current pulse in
magnetization reversal for two reasons. 1) It is straightforward to obtain the
solution of the Euler equation, at least numerically, for a given magnetic
nano-structure characterized by its magnetic anisotropy energy. 2) After
obtaining the optimal reversal trajectory for a given magnetic nano-structure,
finding a proper field/current pulse is an algebraic problem instead of the
original nonlinear differential equation.",0712.2101v1
2007-12-18,Effect of Edge Roughness on Electronic Transport in Graphene Nanoribbon Channel Metal Oxide Semiconductor Field-Effect Transistors,"Results of quantum mechanical simulations of the influence of edge disorder
on transport in graphene nanoribbon metal oxide semiconductor field-effect
transistors (MOSFETs) are reported. The addition of edge disorder significantly
reduces ON-state currents and increases OFF-state currents, and introduces wide
variability across devices. These effects decrease as ribbon widths increase
and as edges become smoother. However the bandgap decreases with increasing
width, thereby increasing the band-to-band tunneling mediated subthreshold
leakage current even with perfect nanoribbons. These results suggest that
without atomically precise edge control during fabrication, MOSFET performance
gains through use of graphene will be difficult to achieve.",0712.3068v1
2007-12-22,Explicit Non-Adaptive Combinatorial Group Testing Schemes,"Group testing is a long studied problem in combinatorics: A small set of $r$
ill people should be identified out of the whole ($n$ people) by using only
queries (tests) of the form ""Does set X contain an ill human?"". In this paper
we provide an explicit construction of a testing scheme which is better
(smaller) than any known explicit construction. This scheme has $\bigT{\min[r^2
\ln n,n]}$ tests which is as many as the best non-explicit schemes have. In our
construction we use a fact that may have a value by its own right: Linear
error-correction codes with parameters $[m,k,\delta m]_q$ meeting the
Gilbert-Varshamov bound may be constructed quite efficiently, in $\bigT{q^km}$
time.",0712.3876v5
2007-12-31,"Risk management for analytical methods: conciliating objectives of methods, validation phase and routine decision rules","In the industries that involved either chemistry or biology, such as
pharmaceutical industries, chemical industries or food industry, the analytical
methods are the necessary eyes and hear of all the material produced or used.
If the quality of an analytical method is doubtful, then the whole set of
decision that will be based on those measures is questionable. For those
reasons, being able to assess the quality of an analytical method is far more
than a statistical challenge; it's a matter of ethic and good business
practices. Many regulatory documents have been releases, primarily ICH and FDA
documents in the pharmaceutical industry (FDA, 1995, 1997, 2001) to address
that issue.",0801.0207v1
2008-01-06,An Efficient Method for Quantum Transport Calculations in Nanostructures using Full Band Structure,"Scaling of semiconductor devices has reached a stage where it has become
absolutely imperative to consider the quantum mechanical aspects of transport
in these ultra small devices. In these simulations, often one excludes a
rigorous band structure treatment, since it poses a huge computational
challenge. We have proposed here an efficient method for calculating full
three-dimensionally coupled quantum transport in nanowire transistors including
full band structure. We have shown the power of the method by simulating hole
transport in p-type Ge nanowire transistors. The hole band structure obtained
from our nearest neighbor sp3s* tight binding Hamiltonian agrees well
qualitatively with more complex and accurate calculations that take third
nearest neighbors into account. The calculated I-V results show how shifting of
the energy bands due to confinement can be accurately captured only in a full
band full quantum simulation.",0801.0880v1
2008-01-07,Magnetization reversal driven by spin-injection : a mesoscopic spin-transfer effect,"A mesoscopic description of spin-transfer effect is proposed, based on the
spin-injection mechanism occurring at the junction with a ferromagnet. The
effect of spin-injection is to modify locally, in the ferromagnetic
configuration space, the density of magnetic moments. The corresponding
gradient leads to a current-dependent diffusion process of the magnetization.
In order to describe this effect, the dynamics of the magnetization of a
ferromagnetic single domain is reconsidered in the framework of the
thermokinetic theory of mesoscopic systems. Assuming an Onsager
cross-coefficient that couples the currents, it is shown that spin-dependent
electric transport leads to a correction of the Landau-Lifshitz-Gilbert
equation of the ferromagnetic order parameter with supplementary diffusion
terms. The consequence of spin-injection in terms of activation process of the
ferromagnet is deduced, and the expressions of the effective energy barrier and
of the critical current are derived. Magnetic fluctuations are calculated: the
correction to the fluctuations is similar to that predicted for the activation.
These predictions are consistent with the measurements of spin-transfer
obtained in the activation regime and for ferromagnetic resonance under
spin-injection.",0801.1019v1
2008-01-25,New Lower Bounds on Sizes of Permutation Arrays,"A permutation array(or code) of length $n$ and distance $d$, denoted by
$(n,d)$ PA, is a set of permutations $C$ from some fixed set of $n$ elements
such that the Hamming distance between distinct members
$\mathbf{x},\mathbf{y}\in C$ is at least $d$. Let $P(n,d)$ denote the maximum
size of an $(n,d)$ PA. This correspondence focuses on the lower bound on
$P(n,d)$. First we give three improvements over the Gilbert-Varshamov lower
bounds on $P(n,d)$ by applying the graph theorem framework presented by Jiang
and Vardy. Next we show another two new improved bounds by considering the
covered balls intersections. Finally some new lower bounds for certain values
of $n$ and $d$ are given.",0801.3986v1
2008-01-30,Femtosecond Control of the Magnetization in Ferromagnetic Semiconductors,"We develop a theory of collective spin dynamics triggered by ultrafast
optical excitation of ferromagnetic semiconductors. Using the density matrix
equations of motion in the mean field approximation and including magnetic
anisotropy and hole spin dephasing effects, we predict the development of a
light--induced magnetization tilt during ultra--short time intervals comparable
to the pulse duration. This femtosecond dynamics in the coherent temporal
regime is governed by the interband nonlinear optical polarizations and is
followed by a second temporal regime governed by the magnetic anisotropy of the
Fermi sea. We interpret our numerical results by deriving a
Landau--Gilbert--like equation for the collective spin, which demonstrates an
ultrafast correction to the magnetic anisotropy effective field due to second
order coherent nonlinear optical processes. Using the Lindblad semigroup
method, we also derive a contribution to the interband polarization dephasing
determined by the Mn spin and the hole spin dephasing. Our predicted
magnetization tilt and subsequent nonlinear dynamics due to the magnetic
anisotropy can be controlled by varying the optical pulse intensity, duration,
and helicity and can be observed with pump--probe magneto--optical
spectroscopy.",0801.4641v1
2008-02-01,Vortex Ferroelectric Domains,"We show experimental switching data on microscale capacitors of
lead-zirconate-titanate (PZT), which reveal time-resolved domain behavior
during switching on a 100-ns scale. For small circular capacitors, an
unswitched domain remains in the center while complete switching is observed in
square capacitors. The observed effect is attributed to the formation of vortex
domain during polarization switching in circular capacitors. This dynamical
behavior is modeled using the Landau-Liftshitz-Gilbert equations and found to
be in detailed agreement with experiment. This simulation implies rotational
motion of polarization in the xy-plane, a Heisenberg-like result supported by
the recent model of Naumov and Fu [Phys. Rev. Lett. 98, 077603 (2007)],
although not directly measurable by the present quasi-static measurements.",0802.0186v1
2008-02-11,Structure and Optimality of Myopic Policy in Opportunistic Access with Noisy Observations,"A restless multi-armed bandit problem that arises in multichannel
opportunistic communications is considered, where channels are modeled as
independent and identical Gilbert-Elliot channels and channel state
observations are subject to errors. A simple structure of the myopic policy is
established under a certain condition on the false alarm probability of the
channel state detector. It is shown that the myopic policy has a semi-universal
structure that reduces channel selection to a simple round-robin procedure and
obviates the need to know the underlying Markov transition probabilities. The
optimality of the myopic policy is proved for the case of two channels and
conjectured for the general case based on numerical examples.",0802.1379v2
2008-02-12,"Domain walls in (Ga,Mn)As diluted magnetic semiconductor","We report experimental and theoretical studies of magnetic domain walls in an
in-plane magnetized (Ga,Mn)As dilute moment ferromagnetic semiconductor. Our
high-resolution electron holography technique provides direct images of domain
wall magnetization profiles. The experiments are interpreted based on
microscopic calculations of the micromagnetic parameters and
Landau-Lifshitz-Gilbert simulations. We find that the competition of uniaxial
and biaxial magnetocrystalline anisotropies in the film is directly reflected
in orientation dependent wall widths, ranging from approximately 40 nm to 120
nm. The domain walls are of the N\'eel type and evolve from near-$90^{\circ}$
walls at low-temperatures to large angle [1$\bar{1}$0]-oriented walls and small
angle [110]-oriented walls at higher temperatures.",0802.1574v1
2008-02-21,Solving functional reliability issue for an optical electrostatic switch,"In this paper, we report the advantage of using AC actuating signal for
driving MEMS actuators instead of DC voltages. The study is based upon micro
mirror devices used in digital mode for optical switching operation. When the
pull-in effect is used, charge injection occurs when the micro mirror is
maintained in the deflected position. To avoid this effect, a geometrical
solution is to realize grounded landing electrodes which are electro-statically
separated from the control electrodes. Another solution is the use of AC signal
which eliminates charge injection particularly if a bipolar signal is used.
Long term experiments have demonstrated the reliability of such a signal
command to avoid injection of electric charges.",0802.3075v1
2008-02-21,First principles calculation of spin-interactions and magnetic ground states of Cr trimers on Au(111),"We present calculations of the magnetic ground states of Cr trimers in
different geometries on top of a Au(111) surface. By using a least square fit
method based on a fully relativistic embedded-cluster Green's function method
first we determined the parameters of a classical vector-spin model consisting
of second and fourth order interactions. The newly developed method requires no
symmetry constraints, therefore, it is throughout applicable for small
nanoparticles of arbitrary geometry. The magnetic ground states were then found
by solving the Landau-Lifshitz-Gilbert equations. In all considered cases the
configurational energy of the Cr trimers is dominated by large
antiferromagnetic nearest neighbor interactions, whilst biquadratic
spin-interactions have the second largest contributions to the energy. We find
that an equilateral Cr trimer exhibits a frustrated 120$^\circ$ N\'eel type of
ground state with a small out-of-plane component of the magnetization and we
show that the Dzyaloshinsky-Moriya interactions determine the chirality of the
magnetic ground state. In cases of a linear chain and an isosceles trimer
collinear antiferromagnetic ground states are obtained with a magnetization
lying parallel to the surface.",0802.3113v1
2008-04-07,"Energy equilibriation processes of electrons, magnons and phonons on the femtosecond timescale","By means of time-resolved Kerr spectroscopy experiments we relate the energy
dissipation processes on the femtosecond (electron-spin relaxation time
$\tau_{el-sp}$) and nanosecond timescale (Gilbert relaxation $\tau_{\alpha}$)
and compare the results to the first microscopic model, which was proposed by
Koopmans. For both energy dissipation processes, Elliot-Yafet scattering is
proposed as the dominant contributor. We controllably manipulate the energy
dissipation processes by transition metal doping (Pd) and rare earth doping
(Dy) of a Permalloy film and find that while a change of $\tau_{\alpha}$ of
more than a factor two is observed, \tau_{el-sp}$ remains constant, contrary to
the predictions of the model. We explain the discrepancies by relaxation
channels not considered in the original microscopic model and identify thereby
the applicability of the model and possible necessary extensions to the model.",0804.0985v1
2008-04-07,Woven Graph Codes: Asymptotic Performances and Examples,"Constructions of woven graph codes based on constituent block and
convolutional codes are studied. It is shown that within the random ensemble of
such codes based on $s$-partite, $s$-uniform hypergraphs, where $s$ depends
only on the code rate, there exist codes satisfying the Varshamov-Gilbert (VG)
and the Costello lower bound on the minimum distance and the free distance,
respectively. A connection between regular bipartite graphs and tailbiting
codes is shown. Some examples of woven graph codes are presented. Among them an
example of a rate $R_{\rm wg}=1/3$ woven graph code with $d_{\rm free}=32$
based on Heawood's bipartite graph and containing $n=7$ constituent rate
$R^{c}=2/3$ convolutional codes with overall constraint lengths $\nu^{c}=5$ is
given. An encoding procedure for woven graph codes with complexity proportional
to the number of constituent codes and their overall constraint length
$\nu^{c}$ is presented.",0804.0996v2
2008-05-26,Photometric Follow-up Observations of the Transiting Neptune-Mass Planet GJ 436b,"This paper presents multi-band photometric follow-up observations of the
Neptune-mass transiting planet GJ 436b, consisting of 5 new ground-based
transit light curves obtained in May 2007. Together with one already published
light curve we have at hand a total of 6 light curves, spanning 29 days. The
analysis of the data yields an orbital period P = 2.64386+-0.00003 days,
mid-transit time T_c [HJD] =2454235.8355+-0.0001, planet mass M_p = 23.1+-0.9
M_{\earth} = 0.073+-0.003 M_{Jup}, planet radius R_p = 4.2+-0.2 R_{\earth} =
0.37+-0.01 R_{Jup} and stellar radius R_s = 0.45+-0.02 R_{\sun}. Our typical
precision for the mid transit timing for each transit is about 30 seconds. We
searched the data for a possible signature of a second planet in the system
through transit timing variations (TTV) and variation of the impact parameter.
The analysis could not rule out a small, of the order of a minute, TTV and a
long-term modulation of the impact parameter, of the order of +0.2 year^{-1}.",0805.3915v2
2008-06-04,"Broadband electrical detection of spin excitations in (Ga,Mn)As using a photovoltage technique","We report on microwave photovoltage and simultaneous magnetotransport
measurements in a (Ga,Mn)As film oriented normal to the magnetic field. We
detect the ferromagnetic resonance over a broad frequency range of 2 GHz to
18.5 GHz and determine the spectroscopic g-factor and separate the Gilbert from
the inhomogeneous contribution to magnetization relaxation. Temperature
dependent measurements below the saturation magnetization indicate that the
photovoltage signal can serve as a sensitive tool to study the crystal
anisotropy. We demonstrate that the combination of spin dynamics with charge
transport is a promising tool to study microstructured ferromagnetic
semiconductor samples.",0806.0785v1
2008-07-10,Mechanical and Electronic Properties of Ferromagnetic GaMnAs Using Ultrafast Coherent Acoustic Phonons,"Ultrafast two-color pump-probe measurements, involving coherent acoustic
phonon (CAP) waves, have provided information simultaneously on the mechanical
properties and on the electronic structure of ferromagnetic GaMnAs. The elastic
constant C11 of Ga1-xMnxAs (0.03<x<0.07) are observed to be systematically
smaller than those of GaAs. Both C11 and Vs of GaMnAs are found to increase
with temperature (78 K<T<295 K), again in contrast to the opposite behavior in
GaAs. In addition, the fundamental bandgap (at E0 critical point) of Ga1-xMnxAs
is found to shift slightly to higher energies with Mn concentration.",0807.1740v2
2008-08-05,A Proof of George Andrews' and Dave Robbins' q-TSPP Conjecture (modulo a finite amount of routine calculations),"In the historic conference Combinatoire Enumerative[LL] wonderfully organized
by Gilbert Labelle and Pierre Leroux there were many stimulating lectures,
including a very interesting one by Pierre Leroux himself, who talked about his
joint work with Xavier Viennot[LV], on solving differential equations
combinatorially! During the problem session of that very same colloque, chaired
by Pierre Leroux, Richard Stanley raised some intriguing problems about the
enumeration of plane partitions, that he later expanded into a fascinating
article[Sta1]. Most of these problems concerned the enumeration of symmetry
classes of plane partitions, that were discussed in more detail in another
article of Stanley[Sta2]. All of the conjectures in the latter article have
since been proved (see Dave Bressoud's modern classic[B]), except one, that, so
far, resisted the efforts of the greatest minds in enumerative combinatorics.
It concerns the proof of an explicit formula for the q-enumeration of totally
symmetric plane partitions, conjectured independently by George Andrews and
Dave Robbins([Sta2],[Sta1](conj. 7), [B](conj. 13)). In this tribute to Pierre
Leroux, we describe how to prove that last stronghold.",0808.0571v2
2008-08-09,On some deterministic dictionaries supporting sparsity,"We describe a new construction of an incoherent dictionary, referred to as
the oscillator dictionary, which is based on considerations in the
representation theory of finite groups. The oscillator dictionary consists of
order of p^5 unit vectors in a Hilbert space of dimension p, where p is an odd
prime, whose pairwise inner products have magnitude of at most 4/sqrt(p). An
explicit algorithm to construct a large portion of the oscillator dictionary is
presented.",0808.1368v2
2008-08-13,"Spin Filter, Spin Amplifier and Other Spintronic Applications in Graphene Nanodisks","Graphene nanodisk is a graphene derivative with a closed edge. The trigonal
zigzag nanodisk with size $N$ has $N$-fold degenerated zero-energy states. A
nanodisk can be interpletted as a quantum dot with an internal degree of
freedom. The grand state of nanodisk has been argued to be a quasi-ferromagnet,
which is a ferromagnetic-like states with a finite but very long life time. We
investigate the spin-filter effects in the system made of nanodisks and leads
based on the master equation. The finite-size effect on spin filter is
intriguing due to a reaction from the polarization of incoming current to a
quasi-ferromagnet. Analyzing the relaxation process with the use of the
Landau-Lifshitz-Gilbert equation, we explore the response to four types of
incoming currents, namely, unpolarized current, perfectly polarized current,
partially polarized current and pulse polarized current. We propose some
applications for spintronics, such as spin memory, spin amplifier, spin valve,
spin-field-effect transistor and spin diode.",0808.1779v1
2008-08-26,Codes on hypergraphs,"Codes on hypergraphs are an extension of the well-studied family of codes on
bipartite graphs. Bilu and Hoory (2004) constructed an explicit family of codes
on regular t-partite hypergraphs whose minimum distance improves earlier
estimates of the distance of bipartite-graph codes. They also suggested a
decoding algorithm for such codes and estimated its error-correcting
capability.
  In this paper we study two aspects of hypergraph codes. First, we compute the
weight enumerators of several ensembles of such codes, establishing conditions
under which they attain the Gilbert-Varshamov bound and deriving estimates of
their distance. In particular, we show that this bound is attained by codes
constructed on a fixed bipartite graph with a large spectral gap.
  We also suggest a new decoding algorithm of hypergraph codes that corrects a
constant fraction of errors, improving upon the algorithm of Bilu and Hoory.",0808.3453v2
2008-09-26,Ultra-fast spin dynamics: the effect of colored noise,"Recent experimental results have pushed the limits of magnetization dynamics
to pico- and femtosecond timescales. This ultra-fast spin dynamics occurs in
extreme conditions of strong and rapidly varying fields and high temperatures.
This situation requires new description of magnetization dynamics, even on a
phenomenological level of the atomistic Landau-Lifshitz-Gilbert equation,
taking into account that the correlation time for electron system could be of
the order of the inverse characteristic spin frequency. For this case we
introduce the thermodynamically correct phenomenological approach for spin
dynamics based on the Landau-Lifshitz-Miyasaki-Seki equation. The influence of
the noise correlation time on longitudinal and transverse magnetization
relaxation is investigated. We also demonstrate the effect of the noise
correlation time on demagnetisation rate of different materials during
laser-induced dynamics.",0809.4595v1
2008-10-08,Magnetic particle hyperthermia: Neel relaxation in magnetic nanoparticles under circularly polarized field,"The mechanism of magnetization reversal in single-domain ferromagnetic
particles is of interest in many applications, in most of which losses must be
minimized. In cancer therapy by hyperthermia the opposite requirement prevails:
the specific loss power should be maximized. Of the mechanisms of dissipation,
here we study the effect of Neel relaxation on magnetic nanoparticles unable to
move or rotate and compare the losses in linearly and circularly polarized
field. We present exact analytical solutions of the Landau-Lifshitz equation as
derived from the Gilbert equation and use the calculated time-dependent
magnetizations to find the energy loss per cycle. In frequencies lower than the
Larmor frequency linear polarization is found to be the better source of heat
power, at high frequencies (beyond the Larmor frequency) circular polarization
is preferable.",0810.1455v2
2008-10-10,SOSEMANUK: a fast software-oriented stream cipher,"Sosemanuk is a new synchronous software-oriented stream cipher, corresponding
to Profile 1 of the ECRYPT call for stream cipher primitives. Its key length is
variable between 128 and 256 bits. It ac- commodates a 128-bit initial value.
Any key length is claimed to achieve 128-bit security. The Sosemanuk cipher
uses both some basic design principles from the stream cipher SNOW 2.0 and some
transformations derived from the block cipher SERPENT. Sosemanuk aims at
improv- ing SNOW 2.0 both from the security and from the efficiency points of
view. Most notably, it uses a faster IV-setup procedure. It also requires a
reduced amount of static data, yielding better performance on several
architectures.",0810.1858v1
2008-11-14,Trees of cylinders and canonical splittings,"Let T be a tree with an action of a finitely generated group G. Given a
suitable equivalence relation on the set of edge stabilizers of T (such as
commensurability, co-elementarity in a relatively hyperbolic group, or
commutation in a commutative transitive group), we define a tree of cylinders
T_c. This tree only depends on the deformation space of T; in particular, it is
invariant under automorphisms of G if T is a JSJ splitting. We thus obtain
Out(G)-invariant cyclic or abelian JSJ splittings. Furthermore, T_c has very
strong compatibility properties (two trees are compatible if they have a common
refinement).",0811.2383v2
2008-11-21,Numerical Study of Current-Induced Domain-Wall Dynamics: Crossover from Spin Transfer to Momentum Transfer,"We study current-induced dynamics of a magnetic domain wall by solving a
time-dependent Schr\""{o}dinger equation combined with Landau-Lifshitz-Gilbert
equation in a one-dimensional electron system coupled to localized spins. Two
types of domain-wall motions are observed depending on the hard-axis
anisotropy, $K_{\perp}$, of the localized spin system. For small values of
$K_{\perp}$, the magnetic domain wall shows a streaming motion driven by spin
transfer. In contrast, for large values of $K_{\perp}$, a stick-slip motion
driven by momentum transfer is obtained. We clarify the origin of these
characters of domain-wall motions in terms of the dynamics of one-particle
energy levels and distribution functions.",0811.3545v2
2008-12-02,Application of Conformal Mapping to the determination of Magnetic Moment Distributions in typical Antidot Film Nanostructures,"There has been an increasing technological interest on magnetic thin films
containing antidot arrays of hexagonal or square symmetry. Part of this
interest is related to the possibility of domain formation and pinning at the
antidots boundaries. In this paper, we develop a method for the calculation of
the magnetic moment distribution for such arrays which concentrates on the
immediate vicinity of each antidot. For each antidot distribution (square or
hexagonal) a suitable system of coordinates is defined to exploit the shape of
the unit-cells of the overall nanostructure. The Landau-Lifshitz-Gilbert-Brown
equations that govern the distribution of moments are rewritten in terms of
these coordinates. The equilibrium moments orientation is calculated for each
position in a Cartesian grid defined for these new coordinate systems, and then
a conformal transformation is applied to insert the moment vectors into the
actual unit-cell. The resulting vector maps display quite clearly regions of
different moment orientation around the antidots, which can be associated with
nanoscale domains. These results are similar to the ones obtained by other
authors[1-4] using the NIST oommf method.",0812.0566v1
2009-01-09,A Better Way to Deal the Cards,"This paper considers the effect of riffle shuffling on decks of cards,
allowing for some cards to be indistinguishable from other cards. The dual
problem of dealing a game with hands, such as bridge or poker, is also
considered. The Gilbert-Shannon-Reeds model of card shuffling is used, along
with variation distance for measuring how close to uniform a deck has become.
  The surprising results are that for a deck with only two types of cards (such
as red and black), the shuffler can greatly improve the randomness of the deck
by insuring that the top and bottom cards are the same before shuffling. And in
the case of dealing cards for a game with ""hands"", such as bridge or poker, the
normal method of dealing cyclically around the table is very far from optimal.
In the case of a well-shuffled bridge deck, changing to another dealing method
is as good as doing 3.7 extra shuffles. How the deck is cut in poker affects
its randomness as well.",0901.1324v4
2009-03-12,Accuracy thresholds of topological color codes on the hexagonal and square-octagonal lattices,"Accuracy thresholds of quantum error correcting codes, which exploit
topological properties of systems, defined on two different arrangements of
qubits are predicted. We study the topological color codes on the hexagonal
lattice and on the square-octagonal lattice by the use of mapping into the spin
glass systems. The analysis for the corresponding spin glass systems consists
of the duality, and the gauge symmetry, which has succeeded in deriving
locations of special points, which are deeply related with the accuracy
thresholds of topological error correcting codes. We predict that the accuracy
thresholds for the topological color codes would be $1-p_c = 0.1096-8 $ for the
hexagonal lattice and $1-p_c = 0.1092-3$ for the square-octagonal lattice,
where $1-p$ denotes the error probability on each qubit. Hence both of them are
expected to be slightly lower than the probability $1-p_c = 0.110028$ for the
quantum Gilbert-Varshamov bound with a zero encoding rate.",0903.2102v5
2009-03-12,Designing Optimal Flow Networks,"We investigate the problem of designing a minimum cost flow network
interconnecting n sources and a single sink, each with known locations and
flows. The network may contain other unprescribed nodes, known as Steiner
points. For concave increasing cost functions, a minimum cost network of this
sort has a tree topology, and hence can be called a Minimum Gilbert
Arborescence (MGA). We characterise the local topological structure of Steiner
points in MGAs for linear cost functions. This problem has applications to the
design of drains, gas pipelines and underground mine access.",0903.2124v1
2009-04-13,Refined Coding Bounds and Code Constructions for Coherent Network Error Correction,"Coherent network error correction is the error-control problem in network
coding with the knowledge of the network codes at the source and sink nodes.
With respect to a given set of local encoding kernels defining a linear network
code, we obtain refined versions of the Hamming bound, the Singleton bound and
the Gilbert-Varshamov bound for coherent network error correction. Similar to
its classical counterpart, this refined Singleton bound is tight for linear
network codes. The tightness of this refined bound is shown by two construction
algorithms of linear network codes achieving this bound. These two algorithms
illustrate different design methods: one makes use of existing network coding
algorithms for error-free transmission and the other makes use of classical
error-correcting codes. The implication of the tightness of the refined
Singleton bound is that the sink nodes with higher maximum flow values can have
higher error correction capabilities.",0904.1897v2
2009-04-27,Effect of resistance feedback on spin torque-induced switching of nanomagnets,"In large magnetoresistance devices spin torque-induced changes in resistance
can produce GHz current and voltage oscillations which can affect magnetization
reversal. In addition, capacitive shunting in large resistance devices can
further reduce the current, adversely affecting spin torque switching. Here, we
simultaneously solve the Landau-Lifshitz-Gilbert equation with spin torque and
the transmission line telegrapher's equations to study the effects of
resistance feedback and capacitance on magnetization reversal of both spin
valves and magnetic tunnel junctions. While for spin valves parallel (P) to
anti-parallel (AP) switching is adversely affected by the resistance feedback
due to saturation of the spin torque, in low resistance magnetic tunnel
junctions P-AP switching is enhanced. We study the effect of resistance
feedback on the switching time of MTJ's, and show that magnetization switching
is only affected by capacitive shunting in the pF range.",0904.4159v2
2009-04-30,A microscopic model for current-induced switching of magnetization for half-metallic leads,"We study the behaviour of the magnetization in a half-metallic
ferromagnet/nonmagnetic insulator/ferromagnetic metal/paramagnetic metal
(FM1/NI/FM2/PM) tunnel junction. It is calculated self-consistently within the
nonequilibrium Keldysh formalism. The magnetic regions are treated as band
ferromagnets and are described by the single-band Hubbard model. We developed a
nonequilibrium spectral density approach to solve the Hubbard model
approximately in the switching magnet. By applying a voltage to the junction it
is possible to switch between antiparallel (AP) and parallel (P) alignment of
the magnetizations of the two ferromagnets. The transition from AP to P occurs
for positive voltages while the inverse transition from P to AP can be induced
by negative voltages only. This behaviour is in agreement with the Slonczewski
model of current-induced switching and appears self-consistently within the
model, i.e. without using half-classical methods like the
Landau-Lifshitz-Gilbert equation.",0904.4821v1
2009-05-26,Scattering Theory of Charge-Current Induced Magnetization Dynamics,"In ferromagnets, charge currents can excite magnons via the spin-orbit
coupling. We develop a novel and general scattering theory of charge current
induced macrospin magnetization torques in normal metal$|$ferromagnet$|$normal
metal layers. We apply the formalism to a dirty GaAs$|$(Ga,Mn)As$|$GaAs system.
By computing the charge current induced magnetization torques and solving the
Landau-Lifshitz-Gilbert equation, we find magnetization switching for current
densities as low as $ 5\times 10^{6}$~A/cm$^2$. Our results are in agreement
with a recent experimental observation of charge-current induced magnetization
switching in (Ga,Mn)As.",0905.4170v2
2009-05-28,Riffle shuffles of a deck with repeated cards,"We study the Gilbert-Shannon-Reeds model for riffle shuffles and ask
  'How many times must a deck of cards be shuffled for the deck to be in close
to random order?'. In 1992, Bayer and Diaconis gave a solution which gives
exact and asymptotic results for all decks of practical interest, e.g. a deck
of 52 cards. But what if one only cares about the colors of the cards or
disregards the suits focusing solely on the ranks? More generally, how does the
rate of convergence of a Markov chain change if we are interested in only
certain features? Our exploration of this problem takes us through random walks
on groups and their cosets, discovering along the way exact formulas leading to
interesting combinatorics, an 'amazing matrix', and new analytic methods which
produce a completely general asymptotic solution that is remarkable accurate.",0905.4698v1
2009-07-20,Correcting Limited-Magnitude Errors in the Rank-Modulation Scheme,"We study error-correcting codes for permutations under the infinity norm,
motivated by a novel storage scheme for flash memories call rank modulation. In
this scheme, a set of $n$ flash cells are combined to create a single virtual
multi-level cell. Information is stored in the permutation induced by the cell
charge levels. Spike errors, which are characterized by a limited-magnitude
change in cell charge levels, correspond to a low-distance change under the
infinity norm.
  We define codes protecting against spike errors, called limited-magnitude
rank-modulation codes (LMRM codes), and present several constructions for these
codes, some resulting in optimal codes. These codes admit simple recursive, and
sometimes direct, encoding and decoding procedures.
  We also provide lower and upper bounds on the maximal size of LMRM codes both
in the general case, and in the case where the codes form a subgroup of the
symmetric group. In the asymptotic analysis, the codes we construct out-perform
the Gilbert-Varshamov-like bound estimate.",0907.3387v2
2009-07-22,Searching for variable stars in Galactic Open Clusters,"A long-term project, aiming at systematic search for variable stars in
Galactic Open Clusters, was started at the Geneva Observatory in 2002. We have
been observing regularly a sample of twenty-seven Galactic Open Clusters in the
U, B, V Geneva filters. The goal is to identify and to study their variable
stars, as well as the connection between the variable stars in a cluster and
the cluster properties. We present the status of this work in progress, and
show preliminary results for one of these clusters, IC 4651.",0907.3834v1
2009-07-23,Variability morphologies in the color-magnitude diagram. Searching for secular variability,"This work is part of an effort to detect secular variable objects in large
scale surveys by analysing their path in color-magnitude diagrams. To this aim,
we first present the variability morphologies in the V/V-I diagram of several
types of variable stars. They comprise both periodic and non periodic variable
stars from the Large Magellanic Cloud, such as classical Cepheids, long period
variables or Be and R Coronae Borealis stars, as well as two of the detected
secular variable stars in the Galaxy, FG Sge and V4334 Sgr. The study of the
different variability morphologies allows the identification of regions in the
color-magnitude diagram where those secular variable stars could be detected.
We also estimate the number of such secular variable stars expected in the
Large Magellanic Cloud.",0907.4090v1
2009-08-03,Regret Bounds for Opportunistic Channel Access,"We consider the task of opportunistic channel access in a primary system
composed of independent Gilbert-Elliot channels where the secondary (or
opportunistic) user does not dispose of a priori information regarding the
statistical characteristics of the system. It is shown that this problem may be
cast into the framework of model-based learning in a specific class of
Partially Observed Markov Decision Processes (POMDPs) for which we introduce an
algorithm aimed at striking an optimal tradeoff between the exploration (or
estimation) and exploitation requirements. We provide finite horizon regret
bounds for this algorithm as well as a numerical evaluation of its performance
in the single channel model as well as in the case of stochastically identical
channels.",0908.0319v1
2009-08-14,Non-Gaussian Scatter in Cluster Scaling Relations,"We investigate the impact of non-Gaussian scatter in the cluster
mass-observable scaling relation on the mass and redshift distribution of
clusters detected by wide area surveys. We parameterize non-Gaussian scatter by
incorporating the third and forth moments (skewness and kurtosis) into the
distribution P(Mobs|M). We demonstrate that for low scatter mass proxies the
higher order moments do not significantly affect the observed cluster mass and
redshift distributions. However, for high scatter mass indicators it is
necessary for the survey limiting mass threshold to be less than 10^14 h^-1
Msol to prevent the skewness from having a significant impact on the observed
number counts, particularly at high redshift. We also show that an unknown
level of non-Gaussianity in the scatter is equivalent to an additional
uncertainty on the variance in P(Mobs|M) and thus may limit the constraints
that can be placed on the dark energy equation of state parameter w.
Furthermore, positive skewness flattens the mass function at the high mass end,
and so one must also account for skewness in P(Mobs|M) when using the shape of
the mass function to constrain cluster scaling-relations.",0908.1978v1
2009-08-17,A local moment approach to the degenerate Anderson impurity model,"The local moment approach is extended to the orbitally-degenerate [SU(2N)]
Anderson impurity model (AIM). Single-particle dynamics are obtained over the
full range of energy scales, focussing here on particle-hole symmetry in the
strongly correlated regime where the onsite Coulomb interaction leads to
many-body Kondo physics with entangled spin and orbital degrees of freedom. The
approach captures many-body broadening of the Hubbard satellites, recovers the
correct exponential vanishing of the Kondo scale for all N, and its universal
scaling spectra are found to be in very good agreement with numerical
renormalization group (NRG) results. In particular the high-frequency
logarithmic decays of the scaling spectra, obtained here in closed form for
arbitrary N, coincide essentially perfectly with available numerics from the
NRG. A particular case of an anisotropic Coulomb interaction, in which the
model represents a system of N `capacitively-coupled' SU(2) AIMs, is also
discussed. Here the model is generally characterised by two low-energy scales,
the crossover between which is seen directly in its dynamics.",0908.2245v1
2009-10-20,Bifurcation and chaos in spin-valve pillars in a periodic applied magnetic field,"We study the bifurcation and chaos scenario of the macro-magnetization vector
in a homogeneous nanoscale-ferromagnetic thin film of the type used in
spin-valve pillars. The underlying dynamics is described by a generalized
Landau-Lifshitz-Gilbert (LLG) equation. The LLG equation has an especially
appealing form under a complex stereographic projection, wherein the
qualitative equivalence of an applied field and a spin-current induced torque
is transparent. Recently chaotic behavior of such a spin vector has been
identified by Zhang and Li using a spin polarized current passing through the
pillar of constant polarization direction and periodically varying magnitude,
owing to the spin-transfer torque effect. In this paper we show that the same
dynamical behavior can be achieved using a periodically varying applied
magnetic field, in the presence of a constant DC magnetic field and constant
spin current, which is technically much more feasible, and demonstrate
numerically the chaotic dynamics in the system for an infinitely thin film.
Further, it is noted that in the presence of a nonzero crystal anisotropy field
chaotic dynamics occurs at much lower magnitudes of the spin-current and DC
applied field.",0910.3776v1
2009-12-08,Evidence of superconductivity on the border of quasi-2D ferromagnetism in Ca2RuO4 at high pressure,"The layered perovskite Ca2RuO4 is a spin-one Mott insulator at ambient
pressure and exhibits metallic ferromagnetism at least up to ~ 80 kbar with a
maximum Curie temperature of 28 K. Above ~ 90 kbar and up to 140 kbar, the
highest pressure reached, the resistivity and ac susceptibility show pronounced
downturns below ~ 0.4 K in applied magnetic fields of up to ~10 mT. This
indicates that our specimens of Ca2RuO4 are weakly superconducting on the
border of a quasi-2D ferromagnetic state.",0912.1513v1
2010-02-24,"JSJ decompositions: definitions, existence, uniqueness. II. Compatibility and acylindricity","This paper and its companion arXiv:0911.3173 have been replaced by
arXiv:1602.05139.
  We define the compatibility JSJ tree of a group G over a class of subgroups.
It exists whenever G is finitely presented and leads to a canonical tree (not a
deformation space) which is invariant under automorphisms. Under acylindricity
hypotheses, we prove that the (usual) JSJ deformation space and the
compatibility JSJ tree exist, and we describe their flexible subgroups. We
apply these results to finitely generated CSA groups, \Gamma-limit groups
(allowing torsion), and relatively hyperbolic groups.",1002.4564v3
2010-03-05,Magnetoresistance in nanostructures: the role of nonuniform current,"We developed a method to calculate the magnetoresistance of magnetic
nanostructures. We discretize a magnetic disk in small cells and numerically
solve the Landau-Lifshitz-Gilbert (LLG) equation in order to obtain its
magnetization profile. We consider a anisotropic magnetoresistance (AMR) that
depends on the local magnetization as the main source of the magnetoresistance.
We then use it as an input to calculate the resistance and current distribution
numerically, using a relaxation method. We show how magnetoresistance
measurements can be useful to obtain information on the magnetic structure.
Additionally, we obtain non-homogeneous current distributions for different
magnetic configurations in static and dynamical regimes.",1003.1323v2
2010-03-21,Current-induced domain wall motion with adiabatic spin torque only in cylindrical nanowires,"We investigate current-driven domain wall (DW) propagation in magnetic
nanowires in the framework of the modified Landau-Lifshitz-Gilbert equation
with both adiabatic and nonadiabatic spin torque (NAST) terms. Contrary to the
common opinion that NAST is indispensable for DW motion[1,2], we point out that
adiabatic spin torque (AST) only is enough for current-driven DW motion in a
cylindrical (uniaxial) nanowire. Apart from a discussion of the rigid DW motion
from the energy and angular momentum viewpoint, we also propose an experimental
scheme to measure the spin current polarization by combining both field and
current driven DW motion in a flat (biaxial) wire.",1003.3976v1
2010-04-01,Multipliers of locally compact quantum groups via Hilbert C$^*$-modules,"A result of Gilbert shows that every completely bounded multiplier $f$ of the
Fourier algebra $A(G)$ arises from a pair of bounded continuous maps
$\alpha,\beta:G \rightarrow K$, where $K$ is a Hilbert space, and $f(s^{-1}t) =
(\beta(t)|\alpha(s))$ for all $s,t\in G$. We recast this in terms of
adjointable operators acting between certain Hilbert C$^*$-modules, and show
that an analogous construction works for completely bounded left multipliers of
a locally compact quantum group. We find various ways to deal with right
multipliers: one of these involves looking at the opposite quantum group, and
this leads to a proof that the (unbounded) antipode acts on the space of
completely bounded multipliers, in a way which interacts naturally with our
representation result. The dual of the universal quantum group (in the sense of
Kustermans) can be identified with a subalgebra of the completely bounded
multipliers, and we show how this fits into our framework. Finally, this
motivates a certain way to deal with two-sided multipliers.",1004.0215v3
2010-04-22,Optimal time-dependent polarized current pattern for fast domain wall propagation in nanowires: Exact solutions for biaxial and uniaxial anisotropies,"One of the important issues in nanomagnetism is to lower the current needed
for a technologically useful domain wall (DW) propagation speed. Based on the
modified Landau-Lifshitz-Gilbert (LLG) equation with both Slonczewski
spin-transfer torque and the field-like torque, we derive the optimal spin
current pattern for fast DW propagation along nanowires. Under such conditions,
the DW velocity in biaxial wires can be enhanced as much as ten times compared
to the velocities achieved in experiments so far. Moreover, the fast variation
of spin polarization can help DW depinning. Possible experimental realizations
are discussed.",1004.3840v1
2010-05-03,Criticality of an isotropic-to-smectic transition induced by anisotropic quenched disorder,"We report combined optical birefringence and neutron scattering measurements
on the liquid crystal 12CB nanoconfined in mesoporous silicon layers. This
liquid crystal exhibits strong nematic-smectic coupling responsible for a
discontinuous isotropic-to-smectic phase transition in the bulk state. Confined
in porous silicon, 12CB is subjected to strong anisotropic quenched disorder: a
short-ranged smectic state evolves out of a paranematic phase. This
transformation appears continuous, losing its bulk first order character. This
contrasts with previously reported observations on liquid crystals under
isotropic quenched disorder. In the low temperature phase, both orientational
and translational order parameters obey the same power-law.",1005.0240v1
2010-05-21,A Study on Potential of Integrating Multimodal Interaction into Musical Conducting Education,"With the rapid development of computer technology, computer music has begun
to appear in the laboratory. Many potential utility of computer music is
gradually increasing. The purpose of this paper is attempted to analyze the
possibility of integrating multimodal interaction such as vision-based hand
gesture and speech interaction into musical conducting education. To achieve
this purpose, this paper is focus on discuss some related research and the
traditional musical conducting education. To do so, six musical conductors had
been interviewed to share their musical conducting learning/ teaching
experience. These interviews had been analyzed in this paper to show the
syllabus and the focus of musical conducting education for beginners.",1005.4014v1
2010-05-28,Dissipative structures in a nonlinear dynamo,"This paper considers magnetic field generation by a fluid flow in a system
referred to as the Archontis dynamo: a steady nonlinear magnetohydrodynamic
(MHD) state is driven by a prescribed body force. The field and flow become
almost equal and dissipation is concentrated in cigar-like structures centred
on straight-line separatrices. Numerical scaling laws for energy and
dissipation are given that extend previous calculations to smaller
diffusivities. The symmetries of the dynamo are set out, together with their
implications for the structure of field and flow along the separatrices. The
scaling of the cigar-like dissipative regions, as the square root of the
diffusivities, is explained by approximations near the separatrices. Rigorous
results on the existence and smoothness of solutions to the steady, forced MHD
equations are given.",1005.5259v2
2010-06-11,Spherical single-roll dynamos at large magnetic Reynolds numbers,"This paper concerns kinematic helical dynamos in a spherical fluid body
surrounded by an insulator. In particular, we examine their behaviour in the
regime of large magnetic Reynolds number $\Rm$, for which dynamo action is
usually concentrated upon a simple resonant stream-surface. The dynamo
eigensolutions are computed numerically for two representative single-roll
flows using a compact spherical harmonic decomposition and fourth-order
finite-differences in radius. These solutions are then compared with the growth
rates and eigenfunctions of the Gilbert and Ponty (2000) large $\Rm$ asymptotic
theory. We find good agreement between the growth rates when $\Rm>10^4$, and
between the eigenfunctions when $\Rm>10^5$.",1006.2308v2
2010-06-11,On the Queueing Behavior of Random Codes over a Gilbert-Elliot Erasure Channel,"This paper considers the queueing performance of a system that transmits
coded data over a time-varying erasure channel. In our model, the queue length
and channel state together form a Markov chain that depends on the system
parameters. This gives a framework that allows a rigorous analysis of the queue
as a function of the code rate. Most prior work in this area either ignores
block-length (e.g., fluid models) or assumes error-free communication using
finite codes. This work enables one to determine when such assumptions provide
good, or bad, approximations of true behavior. Moreover, it offers a new
approach to optimize parameters and evaluate performance. This can be valuable
for delay-sensitive systems that employ short block lengths.",1006.2403v1
2010-06-16,Storing Small Photonic Cluster States in a Dephasing Environment,"We consider the effects of decoherence on the entanglement of photonic
cluster states. Large photonic cluster states can be built by fusing together
smaller photonic cluster states via probabilistic fusion operations. For this
construction process it is necessary to store these smaller cluster states in
some way so as to have them available for attempted fusion operations. While in
storage the photonic cluster states may undergo dephasing. The effects of
dephasing on small, primitive cluster states is explored here with the aim of
determining how to locally rotate the qubits of the cluster state so as to lose
the least amount of entanglement due to the dephasing process.",1006.3192v1
2010-08-05,Subsystem codes with spatially local generators,"We study subsystem codes whose gauge group has local generators in the 2D
geometry. It is shown that there exists a family of such codes defined on
lattices of size LxL with the number of logical qubits k and the minimum
distance d both proportional to L. The gauge group of these codes involves only
two-qubit generators of type XX and ZZ coupling nearest neighbor qubits (and
some auxiliary one-qubit generators). Our proof is not constructive as it
relies on a certain version of the Gilbert-Varshamov bound for classical codes.
Along the way we introduce and study properties of generalized Bacon-Shor codes
which might be of independent interest. Secondly, we prove that any 2D
subsystem [n,k,d] code with spatially local generators obeys upper bounds
kd=O(n) and d^2=O(n). The analogous upper bound proved recently for 2D
stabilizer codes is kd^2=O(n). Our results thus demonstrate that subsystem
codes can be more powerful than stabilizer codes under the spatial locality
constraint.",1008.1029v1
2010-08-14,Escape of resources in distributed clustering processes,"In a distributed clustering algorithm introduced by Coffman, Courtois,
Gilbert and Piret \cite{coffman91}, each vertex of $\mathbb{Z}^d$ receives an
initial amount of a resource, and, at each iteration, transfers all of its
resource to the neighboring vertex which currently holds the maximum amount of
resource. In \cite{hlrnss} it was shown that, if the distribution of the
initial quantities of resource is invariant under lattice translations, then
the flow of resource at each vertex eventually stops almost surely, thus
solving a problem posed in \cite{berg91}. In this article we prove the
existence of translation-invariant initial distributions for which resources
nevertheless escape to infinity, in the sense that the the final amount of
resource at a given vertex is strictly smaller in expectation than the initial
amount. This answers a question posed in \cite{hlrnss}.",1008.2426v1
2010-08-25,The self-avoiding walk in a strip,"We review the existence of the infinite length self-avoiding walk in the half
plane and its relationship to bridges. We prove that this probability measure
is also given by the limit as $\beta \rightarrow \beta_c-$ of the probability
measure on all finite length walks $\omega$ with the probability of $\omega$
proportional to $\beta_c^{|\omega|}$ where $|\omega|$ is the number of steps in
$\omega$. The self-avoiding walk in a strip $\{z : 0<\Im(z)<y\}$ is defined by
considering all self-avoiding walks $\omega$ in the strip which start at the
origin and end somewhere on the top boundary with probability proportional to
$\beta_c^{|\omega|}$ We prove that this probability measure may be obtained by
conditioning the SAW in the half plane to have a bridge at height $y$. This
observation is the basis for simulations to test conjectures on the
distribution of the endpoint of the SAW in a strip and the relationship between
the distribution of this strip SAW and SLE$_{8/3}$.",1008.4321v2
2010-08-29,Chirality control via double vortices in asymmetric Co dots,"Reproducible control of the magnetic vortex state in nanomagnets is of
critical importance. We report on chirality control by manipulating the size
and/or thickness of asymmetric Co dots. Below a critical diameter and/or
thickness, chirality control is achieved by the nucleation of single vortex.
Interestingly, above these critical dimensions chirality control is realized by
the nucleation and subsequent coalescence of two vortices, resulting in a
single vortex with the opposite chirality as found in smaller dots.
Micromagnetic simulations and magnetic force microscopy highlight the role of
edge-bound halfvortices in facilitating the coalescence process.",1008.4963v2
2010-09-18,Composite excitation of Josephson phase and spin waves in Josephson junctions with ferromagnetic insulator,"Coupling of Josephson-phase and spin-waves is theoretically studied in a
superconductor/ferromagnetic insulator/superconductor (S/FI/S) junction.
Electromagnetic (EM) field inside the junction and the Josephson current
coupled with spin-waves in FI are calculated by combining Maxwell and
Landau-Lifshitz-Gilbert equations. In the S/FI/S junction, it is found that the
current-voltage (I-V) characteristic shows two resonant peaks. Voltages at the
resonant peaks are obtained as a function of the normal modes of EM field,
which indicates a composite excitation of the EM field and spin-waves in the
S/FI/S junction. We also examine another type of junction, in which a
nonmagnetic insulator (I) is located at one of interfaces between S and FI. In
such a S/I/FI/S junction, three resonant peaks appear in the I-V curve, since
the Josephson-phase couples to the EM field in the I layer.",1009.3551v3
2010-09-21,On the Flow-Level Delay of a Spatial Multiplexing MIMO Wireless Channel,"The MIMO wireless channel offers a rich ground for quality of service
analysis. In this work, we present a stochastic network calculus analysis of a
MIMO system, operating in spatial multiplexing mode, using moment generating
functions (MGF). We quantify the spatial multiplexing gain, achieved through
multiple antennas, for flow level quality of service (QoS) performance.
Specifically we use Gilbert-Elliot model to describe individual spatial paths
between the antenna pairs and model the whole channel by an N-State Markov
Chain, where N depends upon the degrees of freedom available in the MIMO
system. We derive probabilistic delay bounds for the system and show the impact
of increasing the number of antennas on the delay bounds under various
conditions, such as channel burstiness, signal strength and fading speed.
Further we present results for multi-hop scenarios under statistical
independence.",1009.4091v1
2010-09-22,Optimal control of magnetization dynamics in ferromagnetic heterostructures by spin--polarized currents,"We study the switching-process of the magnetization in a
ferromagnetic-normal-metal multilayer system by a spin polarized electrical
current via the spin transfer torque. We use a spin drift-diffusion equation
(SDDE) and the Landau-Lifshitz-Gilbert equation (LLGE) to capture the coupled
dynamics of the spin density and the magnetization dynamic of the
heterostructure. Deriving a fully analytic solution of the stationary SDDE we
obtain an accurate, robust, and fast self-consistent model for the
spin-distribution and spin transfer torque inside general ferromagnetic/normal
metal heterostructures. Using optimal control theory we explore the switching
and back-switching process of the analyzer magnetization in a seven-layer
system. Starting from a Gaussian, we identify a unified current pulse profile
which accomplishes both processes within a specified switching time.",1009.4296v2
2010-09-29,Acoustically driven ferromagnetic resonance,"Surface acoustic waves (SAW) in the GHz frequency range are exploited for the
all-elastic excitation and detection of ferromagnetic resonance (FMR) in a
ferromagnetic/ferroelectric (nickel/lithium niobate) hybrid device. We measure
the SAW magneto-transmission at room temperature as a function of frequency,
external magnetic field magnitude, and orientation. Our data are well described
by a modified Landau-Lifshitz-Gilbert approach, in which a virtual,
strain-induced tickle field drives the magnetization precession. This causes a
distinct magnetic field orientation dependence of elastically driven FMR that
we observe in both model and experiment.",1009.5798v2
2010-10-05,Effects of Strong Gravitational Lensing on Millimeter-Wave Galaxy Number Counts,"We study the effects of strong lensing on the observed number counts of mm
sources using a ray tracing simulation and two number count models of unlensed
sources. We employ a quantitative treatment of maximum attainable magnification
factor depending on the physical size of the sources, also accounting for
effects of lens halo ellipticity. We calculate predicted number counts and
redshift distributions of mm galaxies including the effects of strong lensing
and compare with the recent source count measurements of the South Pole
Telescope (SPT). The predictions have large uncertainties, especially the
details of the mass distribution in lens galaxies and the finite extent of
sources, but the SPT observations are in good agreement with predictions. The
sources detected by SPT are predicted to largely consist of strongly lensed
galaxies at z>2. The typical magnifications of these sources strongly depends
on both the assumed unlensed source counts and the flux of the observed
sources.",1010.0998v2
2010-10-15,The Significance of Non-ergodicity Property of Statistical Mechanics Systems for Understanding Resting State of a Living Cell,"A better grasp of the physical foundations of life is necessary before we can
understand the processes occurring inside a living cell. In his physical theory
of the cell, American physiologist Gilbert Ling introduced an important notion
of the resting state of the cell. He describes this state as an independent
stable thermodynamic state of a living substance in which it has stored all the
energy it needs to perform all kinds of biological work. This state is
characterised by lower entropy of the system than in an active state. However,
Ling's approach is primarily qualitative in terms of thermodynamics and it
needs to be characterised more specifically. To this end, we propose a new
thermodynamic approach to studying Ling's model of the living cell (Ling's
cell), the center piece of which is the non-ergodicity property which has
recently been proved for a wide range of systems in statistical mechanics [7].
These approach allowed us to develop general thermodynamic approaches to
explaining some of the well-known physiological phenomena, which can be used
for further physical analysis of these phenomena using specific physical
models.",1010.3226v1
2010-11-29,Superoperator Analysis of Entanglement in a Four-Qubit Cluster State,"In this paper we utilize superoperator formalism to explore the entanglement
evolution of four-qubit cluster states in a number of decohering environments.
A four-qubit cluster state is a resource for the performance of an arbitrary
single logical qubit rotation via measurement based cluster state quantum
computation. We are specifically interested in the relationship between
entanglement evolution and the fidelity with which the arbitrary single logical
qubit rotation can be implemented in the presence of decoherence as this will
have important experimental ramifications. We also note the exhibition of
entanglement sudden death (ESD) and ask how severely its onset affects the
utilization of the cluster state as a means of implementing an arbitrary single
logical qubit rotation.",1011.6336v2
2011-02-14,Computing the Ball Size of Frequency Permutations under Chebyshev Distance,"Let $S_n^\lambda$ be the set of all permutations over the multiset
$\{\overbrace{1,...,1}^{\lambda},...,\overbrace{m,...,m}^\lambda\}$ where
$n=m\lambda$. A frequency permutation array (FPA) of minimum distance $d$ is a
subset of $S_n^\lambda$ in which every two elements have distance at least $d$.
FPAs have many applications related to error correcting codes. In coding
theory, the Gilbert-Varshamov bound and the sphere-packing bound are derived
from the size of balls of certain radii. We propose two efficient algorithms
that compute the ball size of frequency permutations under Chebyshev distance.
Both methods extend previous known results. The first one runs in $O({2d\lambda
\choose d\lambda}^{2.376}\log n)$ time and $O({2d\lambda \choose
d\lambda}^{2})$ space. The second one runs in $O({2d\lambda \choose
d\lambda}{d\lambda+\lambda\choose \lambda}\frac{n}{\lambda})$ time and
$O({2d\lambda \choose d\lambda})$ space. For small constants $\lambda$ and $d$,
both are efficient in time and use constant storage space.",1102.2799v2
2011-02-25,Modeling Extragalactic Foregrounds and Secondaries for Unbiased Estimation of Cosmological Parameters From Primary CMB Anisotropy,"Using the latest physical modeling and constrained by the most recent data,
we develop a phenomenological parameterized model of the contributions to
intensity and polarization maps at millimeter wavelengths from external
galaxies and Sunyaev-Zeldovich effects. We find such modeling to be necessary
for estimation of cosmological parameters from Planck data. For example,
ignoring the clustering of the infrared background would result in a bias in
n_s of 7 sigma. We show that the simultaneous marginalization over a full
foreground model can eliminate such biases, while increasing the statistical
uncertainty in cosmological parameters by less than 20%. The small increases in
uncertainty can be significantly reduced with the inclusion of
higher-resolution ground-based data.
  The multi-frequency analysis we employ involves modeling 46 total power
spectra and marginalization over 17 foreground parameters. We show that we can
also reduce the data to a best estimate of the CMB power spectra, and just two
principal components (with constrained amplitudes) describing residual
foreground contamination.",1102.5195v1
2011-03-02,Switching dynamics of a magnetostrictive single-domain nanomagnet subjected to stress,"The temporal evolution of the magnetization vector of a single-domain
magnetostrictive nanomagnet, subjected to in-plane stress, is studied by
solving the Landau-Lifshitz-Gilbert equation. The stress is ramped up linearly
in time and the switching delay, which is the time it takes for the
magnetization to flip, is computed as a function of the ramp rate. For high
levels of stress, the delay exhibits a non-monotonic dependence on the ramp
rate, indicating that there is an {\it optimum} ramp rate to achieve the
shortest delay. For constant ramp rate, the delay initially decreases with
increasing stress but then saturates showing that the trade-off between the
delay and the stress (or the energy dissipated in switching) becomes less and
less favorable with increasing stress. All of these features are due to a
complex interplay between the in-plane and out-of-plane dynamics of the
magnetization vector induced by stress.",1103.0352v1
2011-03-21,Delay Constrained Throughput Analysis of a Correlated MIMO Wireless Channel,"The maximum traffic arrival rate at the network for a given delay guarantee
(delay constrained throughput) has been well studied for wired channels.
However, few results are available for wireless channels, especially when
multiple antennas are employed at the transmitter and receiver. In this work,
we analyze the network delay constrained throughput of a multiple input
multiple output (MIMO) wireless channel with time-varying spatial correlation.
The MIMO channel is modeled via its virtual representation, where the
individual spatial paths between the antenna pairs are Gilbert-Elliot channels.
The whole system is then described by a K-State Markov chain, where K depends
upon the degree of freedom (DOF) of the channel. We prove that the DOF based
modeling is indeed accurate. Furthermore, we study the impact of the delay
requirements at the network layer, violation probability and the number of
antennas on the throughput under different fading speeds and signal strength.",1103.4016v1
2011-03-29,Current induced rotational torques in the skyrmion lattice phase of chiral magnets,"In chiral magnets without inversion symmetry, the magnetic structure can form
a lattice of magnetic whirl lines, a two-dimensional skyrmion lattice,
stabilized by spin-orbit interactions in a small range of temperatures and
magnetic fields. The twist of the magnetization within this phase gives rise to
an efficient coupling of macroscopic magnetic domains to spin currents. We
analyze the resulting spin-transfer effects, and, in particular, focus on the
current induced rotation of the magnetic texture by an angle. Such a rotation
can arise from macroscopic temperature gradients in the system as has recently
been shown experimentally and theoretically. Here we investigate an alternative
mechanism, where small distortions of the skyrmion lattice and the transfer of
angular momentum to the underlying atomic lattice play the key role. We employ
the Landau-Lifshitz-Gilbert equation and adapt the Thiele method to derive an
effective equation of motion for the rotational degree of freedom. We discuss
the dependence of the rotation angle on the orientation of the applied magnetic
field and the distance to the phase transition.",1103.5548v2
2011-04-07,Finite-size effects on the magnetoelectric response of field-driven ferroelectric/ferromagnetic chains,"We study theoretically the coupled multiferroic dynamics of one-dimensional
ferroelectric/ferromagnet chains driven by harmonic magnetic and electric
fields as a function of the chain length. A linear magnetoelectric coupling is
dominated by the spin-polarized screening charge at the interface. We performed
Monte-Carlo simulations and calculations based on the coupled
Landau-Lifshitz-Gilbert and Landau-Khalatnikov equations showing that the net
magnetization and the total polarization of thin heterostructures, i.e. with up
to ten ferroelectric and ferromagnetic sites counted from the interface, can be
completely reversed by external electric and magnetic fields, respectively.
However, for larger system solely a certain magnetoelectrical control can be
achieved.",1104.1269v3
2011-04-12,The Effect of Disorder in Superfluid Double Layer Graphene,"We investigate the superfluid properties of disordered double layer graphene
systems using the non-equilibrium Green's function (NEGF) formalism. The
complexity of such a structure makes it imperative to study the effects of
lattice vacancies which will inevitably arise during fabrication. We present
and compare room temperature performance characteristics for both ideal and
disordered bilayer graphene systems in an effort to illustrate the behavior of
a Bose-Einstein Condensate in the presence of lattice defects under
non-equilibrium conditions. We find that lattice vacancies spread throughout
the top layer past the coherence length have a reduced effect compared to the
ideal case. However, vacancies concentrated near the metal contacts within the
coherence length significantly alter the interlayer superfluid transport
properties.",1104.2343v1
2011-05-12,"Incremental Cycle Detection, Topological Ordering, and Strong Component Maintenance","We present two on-line algorithms for maintaining a topological order of a
directed $n$-vertex acyclic graph as arcs are added, and detecting a cycle when
one is created. Our first algorithm handles $m$ arc additions in $O(m^{3/2})$
time. For sparse graphs ($m/n = O(1)$), this bound improves the best previous
bound by a logarithmic factor, and is tight to within a constant factor among
algorithms satisfying a natural {\em locality} property. Our second algorithm
handles an arbitrary sequence of arc additions in $O(n^{5/2})$ time. For
sufficiently dense graphs, this bound improves the best previous bound by a
polynomial factor. Our bound may be far from tight: we show that the algorithm
can take $\Omega(n^2 2^{\sqrt{2\lg n}})$ time by relating its performance to a
generalization of the $k$-levels problem of combinatorial geometry. A
completely different algorithm running in $\Theta(n^2 \log n)$ time was given
recently by Bender, Fineman, and Gilbert. We extend both of our algorithms to
the maintenance of strong components, without affecting the asymptotic time
bounds.",1105.2397v1
2011-05-30,Orthogonal Matching Pursuit: A Brownian Motion Analysis,"A well-known analysis of Tropp and Gilbert shows that orthogonal matching
pursuit (OMP) can recover a k-sparse n-dimensional real vector from 4 k log(n)
noise-free linear measurements obtained through a random Gaussian measurement
matrix with a probability that approaches one as n approaches infinity. This
work strengthens this result by showing that a lower number of measurements, 2
k log(n - k), is in fact sufficient for asymptotic recovery. More generally,
when the sparsity level satisfies kmin <= k <= kmax but is unknown, 2 kmax
log(n - kmin) measurements is sufficient. Furthermore, this number of
measurements is also sufficient for detection of the sparsity pattern (support)
of the vector with measurement errors provided the signal-to-noise ratio (SNR)
scales to infinity. The scaling 2 k log(n - k) exactly matches the number of
measurements required by the more complex lasso method for signal recovery with
a similar SNR scaling.",1105.5853v1
2011-06-07,Magneto-optical Kerr Effect Studies of Square Artificial Spin Ice,"We report a magneto-optical Kerr effect study of the collective magnetic
response of artificial square spin ice, a lithographically-defined array of
single-domain ferromagnetic islands. We find that the anisotropic inter-island
interactions lead to a non-monotonic angular dependence of the array coercive
field. Comparisons with micromagnetic simulations indicate that the two
perpendicular sublattices exhibit distinct responses to island edge roughness,
which clearly influence the magnetization reversal process. Furthermore, such
comparisons demonstrate that disorder associated with roughness in the island
edges plays a hitherto unrecognized but essential role in the collective
behavior of these systems.",1106.1394v2
2011-06-15,Dissipative hydrodynamic equation of a ferromagnetic Bose-Einstein condensate: Analogy to magnetization dynamics in conducting ferromagnets,"The hydrodynamic equation of a spinor Bose-Einstein condensate (BEC) gives a
simple description of spin dynamics in the condensate. We introduce the
hydrodynamic equation of a ferromagnetic BEC with dissipation originating from
the energy dissipation of the condensate. The dissipative hydrodynamic equation
has the same form as an extended Landau-Lifshitz-Gilbert (LLG) equation, which
describes the magnetization dynamics of ferromagnets interacting with
spin-polarized currents. Employing the dissipative hydrodynamic equation, we
demonstrate the magnetic domain pattern dynamics of a ferromagnetic BEC in the
presence and absence of a current of particles, and discuss the effects of the
current on domain pattern formation. We also discuss the characteristic lengths
of domain patterns that have domain walls with and without finite
magnetization.",1106.2876v4
2011-07-02,Energy dissipation and switching delay in spin-transfer torque switching of nanomagnets with low-saturation magnetization in the presence of thermal fluctuations,"A common ploy to reduce the switching current and energy dissipation in
spin-transfer-torque driven magnetization switching of shape-anisotropic
single-domain nanomagnets is to employ magnets with low saturation
magnetization $M_s$ and high shape-anisotropy. The high shape-anisotropy
compensates for low $M_s$ to keep the static switching error rate constant.
However, this ploy increases the switching delay, its variance in the presence
of thermal noise, and the dynamic switching error rate. Using the stochastic
Landau-Lifshitz-Gilbert equation with a random torque emulating thermal noise,
we show that pumping some excess spin-polarized current into the nanomagnet
during switching will keep the mean switching delay and its variance constant
as we reduce $M_s$, while still reducing the energy dissipation significantly.",1107.0387v2
2011-08-01,Noise Sensitivity in Continuum Percolation,"We prove that the Poisson Boolean model, also known as the Gilbert disc
model, is noise sensitive at criticality. This is the first such result for a
Continuum Percolation model, and the first for which the critical probability
p_c \ne 1/2. Our proof uses a version of the Benjamini-Kalai-Schramm Theorem
for biased product measures. A quantitative version of this result was recently
proved by Keller and Kindler. We give a simple deduction of the
non-quantitative result from the unbiased version. We also develop a quite
general method of approximating Continuum Percolation models by discrete models
with p_c bounded away from zero; this method is based on an extremal result on
non-uniform hypergraphs.",1108.0310v2
2011-08-23,Vortex Lines in Topological Insulator-Superconductor Heterostructures,"3D topological insulator/s-wave superconductor heterostructures have been
predicted as candidate systems for the observation of Majorana fermions in the
presence of superconducting vortices. In these systems, Majorana fermions are
expected to form at the interface between the topological insulator and the
superconductor while the bulk plays no role. Yet the bulk of a 3D topological
insulator penetrated by a magnetic flux is not inert and can gap the surface
vortex modes destroying their Majorana nature. In this work, we demonstrate the
circumstances under which only the surface physics is important and when the
bulk physics plays an important role in the location and energy of the Majorana
modes.",1108.4711v1
2011-08-28,Low-complexity quantum codes designed via codeword-stabilized framework,"We consider design of the quantum stabilizer codes via a two-step,
low-complexity approach based on the framework of codeword-stabilized (CWS)
codes. In this framework, each quantum CWS code can be specified by a graph and
a binary code. For codes that can be obtained from a given graph, we give
several upper bounds on the distance of a generic (additive or non-additive)
CWS code, and the lower Gilbert-Varshamov bound for the existence of additive
CWS codes. We also consider additive cyclic CWS codes and show that these codes
correspond to a previously unexplored class of single-generator cyclic
stabilizer codes. We present several families of simple stabilizer codes with
relatively good parameters.",1108.5490v1
2011-09-16,Parallel Sparse Matrix-Matrix Multiplication and Indexing: Implementation and Experiments,"Generalized sparse matrix-matrix multiplication (or SpGEMM) is a key
primitive for many high performance graph algorithms as well as for some linear
solvers, such as algebraic multigrid. Here we show that SpGEMM also yields
efficient algorithms for general sparse-matrix indexing in distributed memory,
provided that the underlying SpGEMM implementation is sufficiently flexible and
scalable. We demonstrate that our parallel SpGEMM methods, which use
two-dimensional block data distributions with serial hypersparse kernels, are
indeed highly flexible, scalable, and memory-efficient in the general case.
This algorithm is the first to yield increasing speedup on an unbounded number
of processors; our experiments show scaling up to thousands of processors in a
variety of test scenarios.",1109.3739v2
2011-10-06,A new class of codes for Boolean masking of cryptographic computations,"We introduce a new class of rate one-half binary codes: {\bf complementary
information set codes.} A binary linear code of length $2n$ and dimension $n$
is called a complementary information set code (CIS code for short) if it has
two disjoint information sets. This class of codes contains self-dual codes as
a subclass. It is connected to graph correlation immune Boolean functions of
use in the security of hardware implementations of cryptographic primitives.
Such codes permit to improve the cost of masking cryptographic algorithms
against side channel attacks. In this paper we investigate this new class of
codes: we give optimal or best known CIS codes of length $<132.$ We derive
general constructions based on cyclic codes and on double circulant codes. We
derive a Varshamov-Gilbert bound for long CIS codes, and show that they can all
be classified in small lengths $\le 12$ by the building up construction. Some
nonlinear permutations are constructed by using $\Z_4$-codes, based on the
notion of dual distance of an unrestricted code.",1110.1193v2
2011-10-31,Calculation of coercivity of magnetic nanostructures at finite temperatures,"We report a finite temperature micromagnetic method (FTM) that allows for the
calculation of the coercive field of arbitrary shaped magnetic nanostructures
at time scales of nanoseconds to years. Instead of directly solving the
Landau-Lifshitz-Gilbert equation, the coercive field is obtained without any
free parameter by solving a non linear equation, which arises from the
transition state theory. The method is applicable to magnetic structures where
coercivity is determined by one thermally activated reversal or nucleation
process. The method shows excellent agreement with experimentally obtained
coercive fields of magnetic nanostructures and provides a deeper understanding
of the mechanism of coercivity.",1110.6789v1
2011-11-10,Magnetic friction: From Stokes to Coulomb behavior,"We demonstrate that in a ferromagnetic substrate, which is continuously
driven out of equilibrium by a field moving with constant velocity $v$, at
least two types of friction may occur when $v$ goes to zero: The substrate may
feel a friction force proportional to $v$ (Stokes friction), if the field
changes on a time scale which is longer than the intrinsic relaxation time. On
the other hand, the friction force may become independent of $v$ in the
opposite case (Coulomb friction). These observations are analogous to e.g.
solid friction. The effect is demonstrated in both, the Ising (one spin
dimension) and the Heisenberg model (three spin dimensions), irrespective which
kind of dynamics (Metropolis spin-flip dynamics or Landau-Lifshitz-Gilbert
precessional dynamics) is used. For both models the limiting case of Coulomb
friction can be treated analytically. Furthermore we present an empiric
expression reflecting the correct Stokes behavior and therefore yielding the
correct cross-over velocity and dissipation.",1111.2494v1
2011-11-15,Revisiting No-Scale Supergravity Inspired Scenarios,"We consider no-scale supergravity inspired scenarios, emphasizing the
possible dynamical determination of the soft supersymmetry-breaking parameters
as triggered by the radiative corrections that lift an essentially flat
tree-level potential in the hidden sector. We (re)emphasize the important role
played by the scale-dependent vacuum energy contribution to the effective
potential for the occurrence of consistent no-scale minima. The most relevant
input parameters are introduced as $B_0$ (the soft breaking mixing Higgs
parameter) and $\eta_0$ (the cosmological constant value at high energy)
instead of $\mhalf$ and $\tan \beta$, the latter being determined through a
(generalized) potential minimization at electroweak scales. We examine the
theoretical and phenomenological viability of such a mechanism when confronted
with up-to-date calculations of the low energy sparticle spectrum and with
present constraints from the LHC and other observables. The tight dark matter
relic density constraint for a neutralino LSP scenario can be considerably
relaxed for a gravitino LSP scenario possible in this framework.",1111.3455v1
2011-11-24,Spin-Wave Modes and Their Intense Excitation Effects in Skyrmion Crystals,"We theoretically study spin-wave modes and their intense excitations
activated by microwave magnetic fields in the skyrmion-crystal phase of
insulating magnets by numerically analyzing a two-dimensional spin model using
the Landau-Lifshitz-Gilbert equation. Two peaks of spin-wave resonances with
frequencies of ~1 GHz are found for in-plane a.c. magnetic field where
distribution of the out-of-plane spin components circulates around each
skyrmion core. Directions of the circulations are opposite between these two
modes, and hence the spectra exhibit salient dependence on the circular
polarization of irradiating microwave. A breathing-type mode is also found for
out-of-plane a.c. magnetic field. By intensively exciting these collective
modes, melting of the skyrmion crystal accompanied by a red shift of the
resonant frequency is achieved within nano seconds.",1111.5667v1
2011-11-26,Energy dissipation and switching delay in stress-induced switching of multiferroic devices in the presence of thermal fluctuations,"Switching the magnetization of a shape-anisotropic 2-phase multiferroic
nanomagnet with voltage-generated stress is known to dissipate very little
energy ($<$ 1 aJ for a switching time of $\sim$0.5 ns) at 0 K temperature.
Here, we show by solving the stochastic Landau-Lifshitz-Gilbert equation that
switching can be carried out with $\sim$100% probability in less than 1 ns
while dissipating less than 2 aJ at {\it room temperature}. This makes
nanomagnetic logic and memory systems, predicated on stress-induced magnetic
reversal, one of the most energy-efficient computing hardware extant. We also
study the dependence of energy dissipation, switching delay, and the critical
stress needed to switch, on the rate at which stress is ramped up or down.",1111.6129v1
2011-11-30,Multi-Weyl Topological Semimetals Stabilized by Point Group Symmetry,"We perform a complete classification of two-band $\bk\cdot\mathbf{p}$
theories at band crossing points in 3D semimetals with $n$-fold rotation
symmetry and broken time-reversal symmetry. Using this classification, we show
the existence of new 3D topological semimetals characterized by
$C_{4,6}$-protected double-Weyl nodes with quadratic in-plane (along $k_{x,y}$)
dispersion or $C_6$-protected triple-Weyl nodes with cubic in-plane dispersion.
We apply this theory to the 3D ferromagnet HgCr$_2$Se$_4$ and confirm it is a
double-Weyl metal protected by $C_4$ symmetry. Furthermore, if the direction of
the ferromagnetism is shifted away from the [001]- to the [111]-axis, the
double-Weyl node splits into four single Weyl nodes, as dictated by the point
group $S_6$ of that phase. Finally, we discuss experimentally relevant effects
including splitting of multi-Weyl nodes by applying $C_n$ breaking strain and
the surface Fermi arcs in these new semimetals.",1111.7309v2
2011-12-01,Gate controlled Spin-Density Wave and Chiral FFLO Superconducting phases in interacting Quantum Spin Hall edge states,"We explore the phases exhibited by an interacting quantum spin Hall edge
state in the presence of finite chemical potential (applied gate voltage) and
spin imbalance (applied magnetic field). We find that the helical nature of the
edge state gives rise to orders that are expected to be absent in non-chiral
one-dimensional electronic systems. For repulsive interactions, the ordered
state has an oscillatory spin texture whose ordering wavevector is controlled
by the chemical potential. We analyze the manner in which a magnetic impurity
provides signatures of such oscillations. We find that finite spin imbalance
favors a finite current carrying groundstate that is not condensed in the
absence of interactions and is superconducting for attractive interactions.
This state is characterized by FFLO-type oscillations where the Cooper pairs
obtain a finite center of mass momentum.",1112.0289v1
2011-12-04,A New Approach to Incremental Cycle Detection and Related Problems,"We consider the problem of detecting a cycle in a directed graph that grows
by arc insertions, and the related problems of maintaining a topological order
and the strong components of such a graph. For these problems, we give two
algorithms, one suited to sparse graphs, and the other to dense graphs. The
former takes the minimum of O(m^{3/2}) and O(mn^{2/3}) time to insert m arcs
into an n-vertex graph; the latter takes O(n^2 log(n)) time. Our sparse
algorithm is considerably simpler than a previous O(m^{3/2})-time algorithm; it
is also faster on graphs of sufficient density. The time bound of our dense
algorithm beats the previously best time bound of O(n^{5/2}) for dense graphs.
Our algorithms rely for their efficiency on topologically ordered vertex
numberings; bounds on the size of the numbers give bound on running times.",1112.0784v1
2011-12-05,Vortex core magnetization dynamics induced by thermal excitation,"We investigate the effect of temperature on the dynamic properties of
magnetic vortices in small disks. Our calculations use a stochastic version of
the Landau-Lifshitz-Gilbert (LLG) equation, valid for finite temperatures well
below the Curie critical temperature. We show that a finite temperature induces
a vortex precession around the center of the disk, even in the absence of other
excitation sources. We discuss the origin and implications of the appearance of
this new dynamics. We also show that a temperature gradient plays a role
similar to that of a small constant magnetic field.",1112.0911v2
2011-12-08,A 2-20 GHz Analog Lag-Correlator for Radio Interferometry,"We present the design and testing of a 2-20 GHz continuum band analog lag
correlator with 16 frequency channels for astronomical interferometry. The
correlator has been designed for future use with a prototype single-baseline
interferometer operating at 185-275 GHz. The design uses a broadband Wilkinson
divider tree with integral thin-film resistors implemented on an alumina
substrate, and custom-made broadband InGaP/GaAs Gilbert Cell multipliers. The
prototype correlator has been fully bench-tested, together with the necessary
readout electronics for acquisition of the output signals. The results of these
measurements show that the response of the correlator is well behaved over the
band. An investigation of the noise behaviour also shows that the
signal-to-noise of the system is not limited by the correlator performance.",1112.1982v1
2011-12-12,An analysis of constraints on relativistic species from primordial nucleosynthesis and the cosmic microwave background,"We present constraints on the number of relativistic species from a joint
analysis of cosmic microwave background (CMB) fluctuations and light element
abundances (helium and deuterium) compared to big bang nucleosynthesis (BBN)
predictions. Our BBN calculations include updates of nuclear rates in light of
recent experimental and theoretical information, with the most significant
change occuring for the d(p,gamma)^3He cross section. We calculate a likelihood
function for BBN theory and observations that accounts for both observational
errors and nuclear rate uncertainties and can be easily embedded in
cosmological parameter fitting. We then demonstrate that CMB and BBN are in
good agreement, suggesting that the number of relativistic species did not
change between the time of BBN and the time of recombination. The level of
agreement between BBN and CMB, as well as the agreement with the standard model
of particle physics, depends somewhat on systematic differences among
determinations of the primordial helium abundance. We demonstrate that
interesting constraints can be derived combining only CMB and D/H observations
with BBN theory, suggesting that an improved D/H constraint would be an
extremely valuable probe of cosmology.",1112.2683v1
2011-12-22,Higgs boson decay into 2 photons in the type~II Seesaw Model,"We study the two photon decay channel of the Standard Model-like component of
the CP-even Higgs bosons present in the type II Seesaw Model. The corresponding
cross-section is found to be significantly enhanced in parts of the parameter
space, due to the (doubly-)charged Higgs bosons' $(H^{\pm \pm})H^\pm$ virtual
contributions, while all the other Higgs decay channels remain Standard
Model(SM)-like. In other parts of the parameter space $H^{\pm \pm}$ (and
$H^{\pm}$) interfere destructively, reducing the two photon branching ratio
tremendously below the SM prediction. Such properties allow to account for any
excess such as the one reported by ATLAS/CMS at $\approx 125$ GeV if confirmed
by future data; if not, for the fact that a SM-like Higgs exclusion in the
diphoton channel around 114-115 GeV as reported by ATLAS, does not contradict a
SM-like Higgs at LEP(!), and at any rate, for the fact that ATLAS/CMS exclusion
limits put stringent lower bounds on the $H^{\pm \pm}$ mass, particularly in
the parameter space regions where the direct limits from same-sign leptonic
decays of $H^{\pm \pm}$ do not apply.",1112.5453v1
2012-01-18,Cavity approach to sphere packing in Hamming space,"In this paper we study the hard sphere packing problem in the Hamming space
by the cavity method. We show that both the replica symmetric and the replica
symmetry breaking approximations give maximum rates of packing that are
asymptotically the same as the lower bound of Gilbert and Varshamov.
Consistently with known numerical results, the replica symmetric equations also
suggest a crystalline solution, where for even diameters the spheres are more
likely to be found in one of the subspaces (even or odd) of the Hamming space.
These crystalline packings can be generated by a recursive algorithm which
finds maximum packings in an ultra-metric space. Finally, we design a message
passing algorithm based on the cavity equations to find dense packings of hard
spheres. Known maximum packings are reproduced efficiently in non trivial
ranges of dimensions and number of spheres.",1201.3863v2
2012-01-19,"Impact of microstructure, temperature and strain ratio on energy-based low- cycle fatigue life prediction models for TiAl alloys","In this paper, two fatigue lifetime prediction models are tested on TiAl
intermetallic using results from uniaxial low-cycle fatigue tests. Both
assessments are based on dissipated energy but one of them considers a
hydrostatic pressure correction. This work allows to confirm, on this kind of
material, the linear nature, already noticed on silicon molybdenum cast iron,
TiNi shape memory alloy and 304L stainless steel, of dissipated energy,
corrected or not with hydrostatic pressure, according to the number of cycles
to failure. This study also highlights that, firstly, the dissipated energy
model is here more adequate to estimate low-cycle fatigue life and that,
secondly, intrinsic parameters like microstructure as well as extrinsic
parameters like temperature or strain ratio have an impact on prediction
results.",1201.4084v1
2012-01-23,Influence of the magnetoelectric coupling on the electric field induced magnetization reversal in a composite non-strained multiferroic chain,"We study theoretically the multiferroic dynamics in a composite
one-dimensional system consisting of BaTiO3 multiferroically coupled to an iron
chain. The method treats the magnetization and the polarization as
thermodynamic quantities describable via a combination of the Landau-Lifshits-
Gilbert and the Ginzburg-Landau dynamics coupled via an additional term in the
total free energy density. This term stems from the multiferroic interaction at
the interface. For a wide range of strengths of this coupling we predict the
possibility of obtaining a well-developed hysteresis in the ferromagnetic part
of the system induced by an external electric field. The dependence of the
reversal modes on the electric field frequency is also investigated and we
predict a considerable stability of the magnetization reversal for frequencies
in the range of 0.5 - 12 [GHz].",1201.4740v1
2012-01-27,Domain-wall complexes in ferromagnetic stripes,"Interaction of domain walls (DWs) in ferromagnetic stripes is studied with
relevance to the formation of stable complexes of many domains. Two DW system
is described with the Landau-Lifshitz-Gilbert equation including regimes of
narrow and wide stripes which correspond the presence of transverse and vortex
DWs. The DWs of both kinds are characterized with their chiralities (the
direction of the magnetization rotation in the stripe plane) and polarities
(the magnetization orientation in the center of a vortex and/or halfvortices),
hence, their interactions are analyzed with dependence on these properties. In
particular, pairs of the DWs of opposite or like both chiralities and
polarities are investigated as well as pairs of opposite (like) chiralities and
of like (opposite) polarities. Conditions of the creation of stationary
magnetic bubbles built of two interacting DWs are formulated with relevance to
the situations of presence and absence of the external magnetic field.",1201.5760v3
2012-01-31,Interlayer Transport in Disordered Semiconductor Electron Bilayers,"We study the effects of disorder on the interlayer transport properties of
disordered semiconductor bilayers outside of the quantum Hall regime by
performing self-consistent quantum transport calculations. We find that the
addition of material disorder to the system affects interlayer interactions
leading to significant deviations in the interlayer transfer characteristics.
In particular, we find that disorder decreases and broadens the tunneling peak,
effectively reducing the interacting system to the non-interacting system, when
the mean-free path for the electrons becomes shorter than the system length.
Our results suggest that the experimental observation of exchange-enhanced
interlayer transport in semiconductor bilayers requires materials with
mean-free paths larger than the spatial extent of the system.",1202.0053v1
2012-02-01,Imaging topologically protected transport with quantum degenerate gases,"Ultracold and quantum degenerate gases held near conductive surfaces can
serve as sensitive, high resolution, and wide-area probes of electronic current
flow. Previous work has imaged transport around grain boundaries in a gold wire
by using ultracold and Bose-Einstein condensed atoms held microns from the
surface with an atom chip trap. We show that atom chip microscopy may be
applied to useful purpose in the context of materials exhibiting topologically
protected surface transport. Current flow through lithographically tailored
surface defects in topological insulators (TI)---both idealized and with the
band-structure and conductivity typical of Bi$_{2}$Se$_{3}$---is numerically
calculated. We propose that imaging current flow patterns enables the
differentiation of an ideal TI from one with a finite bulk--to--surface
conductivity ratio, and specifically, that the determination of this ratio may
be possible by imaging transport around trenches etched into the TI's surface.",1202.0060v2
2012-02-02,Large deviations and transitions between equilibria for stochastic Landau-Lifshitz-Gilbert equation,"We study a stochastic Landau-Lifshitz equation on a bounded interval and with
finite dimensional noise. We first show that there exists a pathwise unique
solution to this equation and that this solution enjoys the maximal regularity
property. Next, we prove the large deviations principle for small noise
asymptotic of solutions using the weak convergence method. An essential
ingredient of the proof is compactness, or weak to strong continuity, of the
solution map for a deterministic Landau-Lifschitz equation, when considered as
a transformation of external fields. We then apply this large deviations
principle to show that small noise can cause magnetisation reversal. We also
show the importance of the shape anisotropy parameter for reducing the
disturbance of the solution caused by small noise. The problem is motivated by
applications of ferromagnetic nanowires to the fabrication of magnetic
memories.
  This is an updated version of the previous version of this paper.",1202.0370v2
2012-02-06,Atomic level micromagnetic model of recording media switching at elevated temperatures,"An atomic level micromagnetic model of granular recording media is developed
and applied to examine external field-induced grain switching at elevated
temperatures which captures non-uniform reversal modes. The results are
compared with traditional methods which employ the Landau-Lifshitz-Gilbert
equations based on uniformly magnetized grains with assigned intrinsic
temperature profiles for $M(T)$ and $K(T)$. Using nominal parameters
corresponding to high-anisotropy FePt-type media envisioned for Energy Assisted
Magnetic Recording, our results demonstrate that atomic-level reversal slightly
reduces the field required to switch grains at elevated temperatures, but
results in larger fluctuations, when compared to a uniformly magnetized grain
model.",1202.1131v1
2012-02-10,A model of magnetic order in hexagonal HoMnO3,"Symmetry arguments are used to develop a spin Hamiltonian for the description
of the complex magnetic ordering in HoMnO$_3$. Using a novel application of the
Landau Lifshitz Gilbert dynamic torque equations to this model of the
frustrated Mn ions on an $AB$ stacked triangular antiferromagnetic, it is shown
that the four principal spin configurations observed in this compound are
stabilized. Ho-Mn coupling is found to be a consequence of an unusual trigonal
anisotropy term which is responsible for simultaneous Mn spin reorientation and
onset of Ho magnetic order. Based on these microscopic considerations, a
mean-field Landau-type free energy is derived which reproduces the succession
of observed temperature driven magnetic phase transitions at zero field,
including re-entrant behavior. In addition, our analysis suggests that the
basal-plane magnetic order should be slightly incommensurate with the lattice.",1202.2321v1
2012-02-13,Switching Distributions for Perpendicular Spin-Torque Devices within the Macrospin Approximation,"We model ""soft"" error rates for writing (WSER) and for reading (RSER) for
perpendicular spin-torque memory devices by solving the Fokker-Planck equation
for the probability distribution of the angle that the free layer magnetization
makes with the normal to the plane of the film. We obtain: (1) an exact, closed
form, analytical expression for the zero-temperature switching time as a
function of initial angle; (2) an approximate analytical expression for the
exponential decay of the WSER as a function of the time the current is applied;
(3) comparison of the approximate analytical expression for the WSER to
numerical solutions of the Fokker-Planck equation; (4) an approximate
analytical expression for the linear increase in RSER with current applied for
reading; (5) comparison of the approximate analytical formula for the RSER to
the numerical solution of the Fokker-Planck equation; and (6) confirmation of
the accuracy of the Fokker-Planck solutions by comparison with results of
direct simulation using the single-macrospin Landau-Lifshitz-Gilbert (LLG)
equations with a random fluctuating field in the short-time regime for which
the latter is practical.",1202.2621v1
2012-02-13,Error- and Loss-Tolerances of Surface Codes with General Lattice Structures,"We propose a family of surface codes with general lattice structures, where
the error-tolerances against bit and phase errors can be controlled
asymmetrically by changing the underlying lattice geometries. The surface codes
on various lattices are found to be efficient in the sense that their threshold
values universally approach the quantum Gilbert-Varshamov bound. We find that
the error-tolerance of surface codes depends on the connectivity of underlying
lattices; the error chains on a lattice of lower connectivity are easier to
correct. On the other hand, the loss-tolerance of surface codes exhibits an
opposite behavior; the logical information on a lattice of higher connectivity
has more robustness against qubit loss. As a result, we come upon a fundamental
trade-off between error- and loss-tolerances in the family of the surface codes
with different lattice geometries.",1202.2743v1
2012-02-28,A method for exploratory repeated-measures analysis applied to a breast-cancer screening study,"When a model may be fitted separately to each individual statistical unit,
inspection of the point estimates may help the statistician to understand
between-individual variability and to identify possible relationships. However,
some information will be lost in such an approach because estimation
uncertainty is disregarded. We present a comparative method for exploratory
repeated-measures analysis to complement the point estimates that was motivated
by and is demonstrated by analysis of data from the CADET II breast-cancer
screening study. The approach helped to flag up some unusual reader behavior,
to assess differences in performance, and to identify potential random-effects
models for further analysis.",1202.6133v1
2012-03-15,"Size bias and differential lensing of strongly lensed, dusty galaxies identified in wide-field surveys","We address two selection effects that operate on samples of gravitationally
lensed dusty galaxies identified in millimeter- and submillimeter-wavelength
surveys. First, we point out the existence of a ""size bias"" in such samples:
due to finite source effects, sources with higher observed fluxes are
increasingly biased towards more compact objects. Second, we examine the effect
of differential lensing in individual lens systems by modeling each source as a
compact core embedded in an extended diffuse halo. Considering the ratio of
magnifications in these two components, we find that at high overall
magnifications the compact component is amplified by a much larger factor than
the diffuse component, but at intermediate magnifications (~10) the probability
of a larger magnification for the extended region is higher. Lens models
determined from multi-frequency resolved imaging data are crucial to correct
for this effect.",1203.3267v2
2012-03-28,Decoherence and mode-hopping in a magnetic tunnel junction-based spin-torque oscillator,"We discuss the coherence of magnetic oscillations in a magnetic tunnel
junction-based spin-torque oscillator as a function of external field angle.
Time-frequency analysis shows mode-hopping between distinct oscillator modes,
which arises from linear and nonlinear couplings in the Landau-Lifshitz-Gilbert
equation, analogous to mode-hopping observed in semiconductor ring lasers.
These couplings and therefore mode-hopping are minimized near the current
threshold for antiparallel (AP) alignment of free layer with reference layer
magnetization. Away from the AP alignment, mode-hopping limits oscillator
coherence.",1203.6300v1
2012-04-28,Topological Excitonic Superfluids in Three Dimensions,"We study the equilibrium and non-equilibrium properties of topological
dipolar intersurface exciton condensates within time-reversal invariant
topological insulators in three spatial dimensions without a magnetic field. We
elucidate that, in order to correctly identify the proper pairing symmetry
within the condensate order parameter, the full three-dimensional Hamiltonian
must be considered. As a corollary, we demonstrate that only particles with
similar chirality play a significant role in condensate formation. Furthermore,
we find that the intersurface exciton condensation is not suppressed by the
interconnection of surfaces in three-dimensional topological insulators as the
intersurface polarizability vanishes in the condensed phase. This eliminates
the surface current flow leaving only intersurface current flow through the
bulk. We conclude by illustrating how the excitonic superfluidity may be
identified through an examination of the terminal currents above and below the
condensate critical current.",1204.6351v2
2012-05-29,Thermally-Assisted Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets,"We simulate the stochastic Landau-Lifshitz-Gilbert (LLG) dynamics of a
uniaxial nanomagnet out to sub-millisecond timescales using a graphical
processing unit based micromagnetic code and determine the effect of
geometrical tilts between the spin-current and uniaxial anisotropy axes on the
thermally assisted reversal dynamics. The asymptotic behavior of the switching
time ($I\rightarrow 0$, $<\tau>\propto\exp(-\xi(1-I)^2)$) is approached
gradually, indicating a broad crossover regime between ballistic and thermally
assisted spin transfer reversal. Interestingly, the mean switching time is
shown to be nearly independent of the angle between the spin current and
magnet's uniaxial axes. These results have important implications for modeling
the energetics of thermally assisted magnetization reversal of spin transfer
magnetic random access memory bit cells.",1205.6509v1
2012-06-06,Fractional Spin Josephson Effect and Electrically Controlled Magnetization in Quantum Spin Hall Edges,"We explore a spin Josephson effect in a system of two ferromagnets coupled by
a tunnel junction formed of 2D time-reversal invariant topological insulators.
In analogy with the more commonly studied instance of the Josephson effect for
charge in superconductors, we investigate properties of the phase-coherent {\it
spin} current resulting from the misalignment of the in-plane magnetization
angles of the two ferromagnets. We show that the topological insulating barrier
offers the exciting prospect of hosting a {\it fractional} spin Josephson
effect mediated by bound states at the ferromagnet-topological insulator
interface. We provide multiple perspectives to understand the $4\pi$ periodic
nature of this effect. We discuss several measurable consequences, such as, the
generation of a transverse voltage signal which allows for purely electrical
measurements, an inverse of this effect where an applied voltage gives rise to
a transverse spin-current, and a fractional AC spin-Josephson effect.",1206.1295v2
2012-06-07,Magnetic particle hyperthermia: Power losses under circularly polarized field in anisotropic nanoparticles,"The deterministic Landau-Lifshitz-Gilbert equation has been used to
investigate the nonlinear dynamics of magnetization and the specific loss power
in magnetic nanoparticles with uniaxial anisotropy driven by a rotating
magnetic field, generalizing the results obtained for the isotropic case found
in [P. F. de Chatel, I. Nandori, J. Hakl, S. Meszaros and K. Vad, J. Phys.:
Condens. Matter 21, 124202 (2009)]. As opposed to many applications of
magnetization reversal in single-domain ferromagnetic particles where losses
must be minimized, in this paper, we study the mechanisms of dissipation used
in cancer therapy by hyperthermia which requires the enhancement of energy
losses. We show that for circularly polarized field, the loss energy per cycle
is decreased by the anisotropy compared to the isotropic case when only
dynamical effects are taken into account. Thus, in this case, in the low
frequency limit, a better heating efficiency can be achieved for isotropic
nanoparticles. The possible role of thermal fluctuations is also discussed.
Results obtained are compared to experimental data.",1206.1544v2
2012-06-27,Searching for Fast Optical Transients using VERITAS Cherenkov Telescopes,"Astronomical transients are intrinsically interesting things to study. Fast
optical transients (microsecond timescale) are a largely unexplored field of
optical astronomy mainly due to the fact that large optical telescopes are
oversubscribed. Furthermore, most optical observations use instruments with
integration times on the order of seconds and are thus unable to resolve fast
transients. Current-generation atmospheric Cherenkov gamma-ray telescopes,
however, have huge collecting areas (e.g., VERITAS, which consists of four 12-m
telescopes), larger than any existing optical telescopes, and time is typically
available for such studies without interfering with gamma-ray observations. The
following outlines the benefits of using a Cherenkov telescope to detect
optical transients and the implementation of the VERITAS Transient Detector
(TRenDy), a dedicated multi-channel photometer based on field-programmable gate
arrays. Data are presented demonstrating the ability of TRenDy to detect
transient events such as a star passing through its field of view and the
optical light curve of a pulsar.",1206.6535v1
2012-07-05,Perpendicular Magnetization and Generic Realization of the Ising Model in Artificial Spin Ice,"We have studied frustrated kagome arrays and unfrustrated honeycomb arrays of
magnetostatically-interacting single-domain ferromagnetic islands with
magnetization normal to the plane. The measured pairwise spin correlations of
both lattices can be reproduced by models based solely on nearest-neighbor
correlations. The kagome array has qualitatively different magnetostatics but
identical lattice topology to previously-studied 'artificial spin ice' systems
composed of in-plane moments. The two systems show striking similarities in the
development of moment pair correlations, demonstrating a universality in
artificial spin ice behavior independent of specific realization in a
particular material system.",1207.1456v1
2012-07-13,Magnetic vortices induced by a moving tip,"A two-dimensional easy-plane ferromagnetic substrate, interacting with a
dipolar tip which is magnetised perpendicular with respect to the easy plane is
studied numerically by solving the Landau-Lifshitz Gilbert equation. Due to the
symmetry of the dipolar field of the tip, in addition to the collinear
structure a magnetic vortex structure becomes stable. It is robust against
excitations caused by the motion of the tip. We show that for high excitations
the system may perform a transition between the two states. The influence of
domain walls, which may also induce this transition, is examined.",1207.3225v2
2012-07-24,Bulk Topological Invariants in Noninteracting Point Group Symmetric Insulators,"We survey various quantized bulk physical observables in two- and
three-dimensional topological band insulators invariant under translational
symmetry and crystallographic point group symmetries (PGS). In two-dimensional
insulators, we show that: (i) the Chern number of a $C_n$-invariant insulator
can be determined, up to a multiple of $n$, by evaluating the eigenvalues of
symmetry operators at high-symmetry points in the Brillouin zone; (ii) the
Chern number of a $C_n$-invariant insulator is also determined, up to a
multiple of $n$, by the $C_n$ eigenvalue of the Slater determinant of a
noninteracting many-body system and (iii) the Chern number vanishes in
insulators with dihedral point groups $D_n$, and the quantized electric
polarization is a topological invariant for these insulators. In
three-dimensional insulators, we show that: (i) only insulators with point
groups $C_n$, $C_{nh}$ and $S_n$ PGS can have nonzero 3D quantum Hall
coefficient and (ii) only insulators with improper rotation symmetries can have
quantized magnetoelectric polarization $P_3$ in the term
$P_3\mathbf{E}\cdot\mathbf{B}$, the axion term in the electrodynamics of the
insulator (medium).",1207.5767v2
2012-07-30,'MOHAWK' : a 4000-fiber positioner for DESpec,"We present a concept for a 4000-fibre positioner for DESpec, based on the
Echidna 'tilting spine' technology. The DESpec focal plane is 450mm across and
curved, and the required pitch is ~6.75mm. The size, number of fibers and
curvature are all comparable with various concept studies for similar
instruments already undertaken at the AAO, but present new challenges in
combination. A simple, low-cost, and highly modular design is presented,
consisting of identical modules populated by identical spines. No show-stopping
issues in accommodating either the curvature or the smaller pitch have been
identified, and the actuators consist largely of off-the-shelf components. The
actuators have been prototyped at AAO, and allow reconfiguration times of ~15s
to reach position errors 7 microns or less. Straightforward designs for
metrology, acquisition, and guiding are also proposed. The throughput losses of
the entire positioner system are estimated to be ~15%, of which 6.3% is
attributable to the tilting-spine technology.",1207.7011v2
2012-07-31,Throughput of Rateless Codes over Broadcast Erasure Channels,"In this paper, we characterize the throughput of a broadcast network with n
receivers using rateless codes with block size K. We assume that the underlying
channel is a Markov modulated erasure channel that is i.i.d. across users, but
can be correlated in time. We characterize the system throughput asymptotically
in n. Specifically, we explicitly show how the throughput behaves for different
values of the coding block size K as a function of n, as n approaches infinity.
For finite values of K and n, under the more restrictive assumption of
Gilbert-Elliott channels, we are able to provide a lower bound on the maximum
achievable throughput. Using simulations we show the tightness of the bound
with respect to system parameters n and K, and find that its performance is
significantly better than the previously known lower bounds.",1207.7298v1
2012-08-01,Streaming Codes for Channels with Burst and Isolated Erasures,"We study low-delay error correction codes for streaming recovery over a class
of packet-erasure channels that introduce both burst-erasures and isolated
erasures. We propose a simple, yet effective class of codes whose parameters
can be tuned to obtain a tradeoff between the capability to correct burst and
isolated erasures. Our construction generalizes previously proposed low-delay
codes which are effective only against burst erasures. We establish an
information theoretic upper bound on the capability of any code to
simultaneously correct burst and isolated erasures and show that our proposed
constructions meet the upper bound in some special cases. We discuss the
operational significance of column-distance and column-span metrics and
establish that the rate 1/2 codes discovered by Martinian and Sundberg [IT
Trans.\, 2004] through a computer search indeed attain the optimal
column-distance and column-span tradeoff. Numerical simulations over a
Gilbert-Elliott channel model and a Fritchman model show significant
performance gains over previously proposed low-delay codes and random linear
codes for certain range of channel parameters.",1208.0072v1
2012-08-23,Inconsistencies in the description of pairing effects in nuclear level densities,"Pairing correlations have a strong influence on nuclear level densities.
Empirical descriptions and theoretical models have been developed to take these
effects into account. The present article discusses cases, where descriptions
of nuclear level densities are inconsistent or in conflict with the present
understanding of nuclear properties. Phenomenological approaches consider a
back-shift parameter. However, the absolute magnitude of the back-shift, which
actually corresponds to the pairing condensation energy, is generally not
compatible with the observation that stable pairing correlations are present in
essentially all nuclei. It is also shown that in the BCS model pairing
condensation energies and critical pairing energies are inconsistent for light
nuclei. A modification to the composite Gilbert-Cameron level-density
description is proposed, and the use of more realistic pairing theories is
suggested.",1208.4709v1
2012-09-26,Symmetry Protected Josephson Supercurrents in Three-Dimensional Topological Insulators,"Coupling the surface state of a topological insulator (TI) to an s-wave
superconductor is predicted to produce the long-sought Majorana quasiparticle
excitations. However, superconductivity has not been measured in surface states
when the bulk charge carriers are fully depleted, i.e., in the true topological
regime that is relevant for investigating Majorana modes. Here, we report
measurements of DC Josephson effects in TI-superconductor junctions as the
chemical potential is moved from the bulk bands into the band gap, or through
the true topological regime characterized by the presence of only surface
currents. We examine the relative behavior of the system at different
bulk/surface ratios, determining the effects of strong bulk/surface mixing,
disorder, and magnetic field. We compare our results to 3D quantum transport
simulations to conclude that the supercurrent is largely carried by surface
states, due to the inherent topology of the bands, and that it is robust
against disorder.",1209.5830v2
2012-10-09,A microscopic model for ultrafast remagnetization dynamics,"In this letter, we provide a microscopic model for the ultrafast
remagnetization of atomic moments already quenched above Stoner-Curie
temperature by a strong laser fluence. Combining first principles density
functional theory, atomistic spin dynamics utilizing the
Landau-Lifshitz-Gilbert equation and a three temperature model, we show the
temporal evolution of atomic moments as well as the macroscopic magnetization
of bcc Fe and hcp Co covering a broad time scale, ranging from femtoseconds to
picoseconds. Our simulations show a variety of complex temporal behavior of the
magnetic properties resulting from an interplay between electron, spin and
lattice subsystems, which causes an intricate time evolution of the atomic
moment, where longitudinal and transversal fluctuations result in a macro spin
moment that evolves non-monotonically.",1210.2616v1
2012-10-31,Theory and Simulation of the diffusion of kinks on dislocations in bcc metals,"Isolated kinks on thermally fluctuating (1/2)<111> screw, <100> edge and
(1/2)<111> edge dislocations in bcc iron are simulated under zero stress
conditions using molecular dynamics (MD). Kinks are seen to perform stochastic
motion in a potential landscape that depends on the dislocation character and
geometry, and their motion provides fresh insight into the coupling of
dislocations to a heat bath. The kink formation energy, migration barrier and
friction parameter are deduced from the simulations. A discrete
Frenkel-Kontorova-Langevin (FKL) model is able to reproduce the coarse grained
data from MD at a fraction of the computational cost, without assuming an a
priori temperature dependence beyond the fluctuation-dissipation theorem.
Analytic results reveal that discreteness effects play an essential r\^ole in
thermally activated dislocation glide, revealing the existence of a crucial
intermediate length scale between molecular and dislocation dynamics. The model
is used to investigate dislocation motion under the vanishingly small stress
levels found in the evolution of dislocation microstructures in irradiated
materials.",1210.8327v2
2012-11-01,Dynamically-generated pure spin current in single-layer graphene,"The conductance mismatch problem limits the spin-injection efficiency
significantly, and spin-injection into graphene has been usually requiring
high-quality tunnel barriers to circumvent the conductance mismatch. We
introduce a novel approach, which enables generation of a pure spin current
into single-layer graphene (SLG) free from electrical conductance mismatch by
using dynamical spin injection. Experimental demonstration of
spin-pumping-induced spin current generation and spin transport in SLG at room
temperature was successfully achieved and the spin coherence was estimated to
be 1.36 {\mu}m by using a conventional theoretical model based on
Landau-Lifshitz-Gilbert equation. The spin coherence is proportional to the
quality of SLG, which indicates that spin relaxation in SLG is governed by the
Elliot-Yafet mechanism as was reported.",1211.0124v1
2012-12-04,Phenomenological theory of the giant magnetoimpedance of composite wires,"Composite wires with a three-layered structure are known to show a
particularly large magnetoimpedance effect. The wires consist of a highly
conductive core, an insulating layer and an outer ferromagnetic shell. In order
to understand the origin of the effect a theory based on a coupling of the
Maxwell equations to the Landau-Lifschitz-Gilbert equation is suggested. The
theory is phenomenological in the sense that it does not account for a domain
structure. However, theoretical results nicely reproduce those obtained in
various measurements. Furthermore, an upper limit of the magnetoimpedance ratio
for a given combination of materials can be determined.",1212.0710v3
2012-12-12,Giant magnetoimpedance of composite wires with an insulation layer,"Composite wires with a three-layered structure exhibit a large giant
magneto-impedance (GMI) effect, which can be used in sensitive magnetic field
sensors. To further investigate the origin of the GMI effect, composite wires
consisting of a highly conductive copper core, a silicon dioxide layer and an
outer Permalloy shell were prepared by radio frequency (RF) magnetron
sputtering. The GMI ratio was measured at various driving current frequencies
and with different insulating layer thicknesses. A theoretical model by
coupling the Maxwell equations to the Landau-Lifschitz-Gilbert equation was
developed to investigate the composite wire impedance and its dependence on
external magnetic field, current frequency and insulating layer thickness.
Experimental results corroborate the theoretical model.",1212.2745v2
2012-12-13,Theory of quasiparticle interference in mirror symmetric 2D systems and its application to surface states of topological crystalline insulators,"We study symmetry protected features in the quasiparticle interference (QPI)
pattern of 2D systems with mirror symmetries and time-reversal symmetry, around
a single static point impurity. We show that, in the Fourier transformed local
density of states (FT-LDOS), $\rho(\bq,\omega)$, while the position of high
intensity peaks generically depends on the geometric features of the iso-energy
contour at energy $\omega$, the \emph{absence} of certain peaks is guaranteed
by the opposite mirror eigenvalues of the two Bloch states that are (i) on the
mirror symmetric lines in the Brillouin zone (BZ) and (ii) separated by
scattering vector $\bq$. We apply the general result to the QPI on the $ <{001}
>$-surface of topological crystalline insulator Pb$_{1-x}$Sn$_x$Te and predict
all vanishing peaks in $\rho(\bq,\omega)$. The model-independent analysis is
supported by numerical calculations using an effective four-band model derived
from symmetry analysis.",1212.3285v2
2013-01-25,Chiral magnetism and helimagnons in a pyrochlore antiferromagnet,"Recent neutron scattering measurements on the spinel CdCr2O4 revealed a rare
example of helical magnetic order in geometrically frustrated pyrochlore
antiferromagnet. The spin spiral characterized by an incommensurate wavevector
Q = 2pi (0, delta, 1) with delta ~0.09 is accompanied by a tetragonal
distortion. Here we conduct a systematic study on the magnetic ground state
resulting from the interplay between the Dzyaloshinskii-Moriya interaction and
further neighbor exchange couplings, two of the most important mechanisms for
stabilizing incommensurate spin orders. We compute the low-energy spin-wave
spectrum based on a microscopic spin Hamiltonian and find a dispersion relation
characteristic of the helimagnons. By numerically integrating the
Landau-Lifshitz-Gilbert equation with realistic model parameters, an overall
agreement between experiment and the numerical spectrum, lending further
support to the view that a softened optical phonon triggers the magnetic
transition and endows the lattice a chirality.",1301.5958v1
2013-01-31,Switching of Dipole Coupled Multiferroic Nanomagnets in the Presence of Thermal Noise: Reliability of Nanomagnetic Logic,"The stress-induced switching behavior of a multiferroic nanomagnet, dipole
coupled to a hard nanomagnet, is numerically studied by solving the stochastic
Landau-Lifshitz-Gilbert (LLG) equation for a single domain macro-spin state.
Different factors were found to affect the switching probability in the
presence of thermal noise at room temperature: (i) dipole coupling strength,
(ii) stress levels, and (iii) stress withdrawal rates (ramp rates). We report
that the thermal broadening of the magnetization distribution causes large
switching error rates. This could render nanomagnetic logic schemes that rely
on dipole coupling to perform Boolean logic operations impractical whether they
are clocked by stress or field or other means.",1301.7490v2
2013-02-01,Vortex mechanics in planar nano-magnets,"A collective-variable approach for the study of non-linear dynamics of
magnetic textures in planar nano-magnets is proposed. The variables are just
arbitrary parameters (complex or real) in the specified analytical function of
a complex variable, describing the texture in motion. Starting with such a
function, a formal procedure is outlined, allowing a (non-linear) system of
differential equations of motion to be obtained for the variables. The
resulting equations are equivalent to Landau-Lifshitz-Gilbert dynamics as far
as the definition of collective variables allows it. Apart from the
collective-variable specification, the procedure does not involve any
additional assumptions (such as translational invariance or steady-state
motion). As an example, the equations of weakly non-linear motion of a magnetic
vortex are derived and solved analytically. A simple formula for the dependence
of the vortex precession frequency on its amplitude is derived. The results are
verified against special cases from the literature and agree quantitatively
with experiments and simulations.",1302.0222v3
2013-02-03,Correcting Camera Shake by Incremental Sparse Approximation,"The problem of deblurring an image when the blur kernel is unknown remains
challenging after decades of work. Recently there has been rapid progress on
correcting irregular blur patterns caused by camera shake, but there is still
much room for improvement. We propose a new blind deconvolution method using
incremental sparse edge approximation to recover images blurred by camera
shake. We estimate the blur kernel first from only the strongest edges in the
image, then gradually refine this estimate by allowing for weaker and weaker
edges. Our method competes with the benchmark deblurring performance of the
state-of-the-art while being significantly faster and easier to generalize.",1302.0439v2
2013-03-01,Entropy Distance,"Motivated by the approach of random linear codes, a new distance in the
vector space over a finite field is defined as the logarithm of the ""surface
area"" of a Hamming ball with radius being the corresponding Hamming distance.
It is named entropy distance because of its close relation with entropy
function. It is shown that entropy distance is a metric for a non-binary field
and a pseudometric for the binary field. The entropy distance of a linear code
is defined to be the smallest entropy distance between distinct codewords of
the code. Analogues of the Gilbert bound, the Hamming bound, and the Singleton
bound are derived for the largest size of a linear code given the length and
entropy distance of the code. Furthermore, as an important property related to
lossless joint source-channel coding, the entropy distance of a linear encoder
is defined. Very tight upper and lower bounds are obtained for the largest
entropy distance of a linear encoder with given dimensions of input and output
vector spaces.",1303.0070v2
2013-03-20,On the Behavior of RObust Header Compression U-mode in Channels with Memory,"The existing studies of RObust Header Compression (ROHC) have provided some
understanding for memoryless channel, but the behavior of ROHC for correlated
wireless channels is not well investigated in spite of its practical
importance. In this paper, the dependence of ROHC against its design parameters
for the Gilbert Elliot channel is studied by means of three analytical models.
A first more elaborated approach accurately predicts the behavior of the
protocol for the single RTP flow profile, while a simpler, analytically
tractable model yields clear and insightful mathematical relationships that
explain the qualitative trends of ROHC. The results are validated against a
real world implementation of this protocol. Moreover, a third model studies
also the less conventional yet practically relevant setting of multiple RTP
flows.",1303.4970v1
2013-03-21,Tuning magnetic anisotropy in (001) oriented L10 (Fe1-xCux)55Pt45 films,"We have achieved (001) oriented L10 (Fe1-xCux)55Pt45 thin films, with
magnetic anisotropy up to 3.6x10^7 erg/cm^3, using atomic-scale multilayer
sputtering and post annealing at 400 {\deg}C for 10 seconds. By fixing the Pt
concentration, structure and magnetic properties are systematically tuned by
the Cu addition. Increasing Cu content results in an increase in the tetragonal
distortion of the L10 phase, significant changes to the film microstructure,
and lowering of the saturation magnetization and anisotropy. The relatively
convenient synthesis conditions, along with the tunable magnetic properties,
make such materials highly desirable for future magnetic recording
technologies.",1303.5208v1
2013-03-28,Spin Torque on Magnetic Textures Coupled to the Surface of a Three-Dimensional Topological Insulator,"We investigate theoretically the spin torque and magnetization dynamic in a
thin ferromagnetic (FM) layer with spatially varying magnetization. The FM
layer is deposited on the surface of a topological insulator (TI). In the limit
of the adiabatic relaxation of electron spin along the magnetization, the
interaction between the exchange interaction and the Rashba-like surface
texture of a TI yields a topological gauge field. Under the gauge field and an
applied current, spin torque is induced according to the direction of the
current. We derived the corresponding effective anisotropy field and hence the
modified Landau-Lifshitz-Gilbert equation, which describes the spin torque and
the magnetization dynamic. In addition, we study the effective field for
exemplary magnetic textures, such as domain wall, skyrmion, and vortex
configurations. The estimated strength of the effective field is comparable to
the switching fields of typical FM materials, and hence can significantly
influence the dynamics of the FM layer.",1303.7031v1
2013-04-03,Synchronization of an array of spin torque nano oscillators in periodic applied external magnetic field,"Considering an array of spin torque transfer nano oscillators (STNOs), we
have investigated the synchronization property of the system under the action
of a common periodically driven applied external magnetic field by numerically
analyzing the underlying system of Landau-Lifshitz-Gilbert-Slonczewski (LLGS)
equations for the macro-spin variables. We find the novel result that the
applied external magnetic field can act as a medium to induce synchronization
of periodic oscillations, both in-phase and anti-phase, even without coupling
through spin current, thereby leading to the exciting possibility of
enhancement of microwave power in a straightforward way.",1304.0875v1
2013-04-06,Towards a living earth simulator,"The Living Earth Simulator (LES) is one of the core components of the
FuturICT architecture. It will work as a federation of methods, tools,
techniques and facilities supporting all of the FuturICT simulation-related
activities to allow and encourage interactive exploration and understanding of
societal issues. Society-relevant problems will be targeted by leaning on
approaches based on complex systems theories and data science in tight
interaction with the other components of FuturICT. The LES will evaluate and
provide answers to real-world questions by taking into account multiple
scenarios. It will build on present approaches such as agent-based simulation
and modeling, multiscale modelling, statistical inference, and data mining,
moving beyond disciplinary borders to achieve a new perspective on complex
social systems.",1304.1903v1
2013-05-13,Backhopping effect in magnetic tunnel junctions: comparison between theory and experiment,"We report on the magnetic switching and backhopping effects due to
spin-transfer-torque in magnetic tunnel junctions. Experimental data on the
current-induced switching in junctions with MgO tunnel barrier reveal a random
back-and-forth switching between the magnetization states, which appears when
the current direction favors the parallel magnetic configuration. The effect
depends on the barrier thickness $t_b$, and is not observed in tunnel junctions
with very thin MgO tunnel barriers, $t_b$ $<$ 0.95 nm. Switching dependence on
the bias voltage and barrier thickness is explained in terms of the macrospin
model, with the magnetization dynamics described by the modified
Landau-Lifshitz-Gilbert equation. Numerical simulations indicate that the
competition between in-plane and out-of-plane torque components can result at
high bias voltages in a non-deterministic switching behavior, in agreement with
experimental observations. When the barrier thickness is reduced, the overall
coupling between the magnetic layers across the barrier becomes ferromagnetic,
which suppresses the backhopping effect.",1305.2711v1
2013-05-15,Robust Streaming Erasure Codes based on Deterministic Channel Approximations,"We study near optimal error correction codes for real-time communication. In
our setup the encoder must operate on an incoming source stream in a sequential
manner, and the decoder must reconstruct each source packet within a fixed
playback deadline of $T$ packets. The underlying channel is a packet erasure
channel that can introduce both burst and isolated losses.
  We first consider a class of channels that in any window of length ${T+1}$
introduce either a single erasure burst of a given maximum length $B,$ or a
certain maximum number $N$ of isolated erasures. We demonstrate that for a
fixed rate and delay, there exists a tradeoff between the achievable values of
$B$ and $N,$ and propose a family of codes that is near optimal with respect to
this tradeoff. We also consider another class of channels that introduce both a
burst {\em and} an isolated loss in each window of interest and develop the
associated streaming codes.
  All our constructions are based on a layered design and provide significant
improvements over baseline codes in simulations over the Gilbert-Elliott
channel.",1305.3596v1
2013-05-16,Size-dependent magnetization switching characteristics and spin wave modes of FePt nanostructures,"We present a comprehensive investigation of the size-dependent switching
characteristics and spin wave modes of FePt nanoelements. Curved nanomagnets
(""caps"") are compared to flat disks of identical diameter and volume over a
size range of 100 to 300nm. Quasi-static magnetization reversal analysis using
first-order reversal curves (FORC) shows that spherical caps have lower vortex
nucleation and annihilation fields than the flat disks. As the element diameter
decreases, the reversal mechanism in the caps crosses over sooner to coherent
rotation than in the disks. The magnetization dynamics are studied using
optically induced small angle precession and reveal a strong size dependence
that differs for the two shapes. Flat disks exhibit well-known center and edge
modes at all sizes, but as the diameter of the caps increases from 100 to 300
nm, additional oscillation modes appear in agreement with dynamic micromagnetic
simulations. In addition, we show that the three-dimensional curvature of the
cap causes a much greater sensitivity to the applied field angle which provides
an additional way for controlling the ultrafast response of nanomagnetic
elements.",1305.3686v1
2013-05-28,Reallocation Problems in Scheduling,"In traditional on-line problems, such as scheduling, requests arrive over
time, demanding available resources. As each request arrives, some resources
may have to be irrevocably committed to servicing that request. In many
situations, however, it may be possible or even necessary to reallocate
previously allocated resources in order to satisfy a new request. This
reallocation has a cost. This paper shows how to service the requests while
minimizing the reallocation cost. We focus on the classic problem of scheduling
jobs on a multiprocessor system. Each unit-size job has a time window in which
it can be executed. Jobs are dynamically added and removed from the system. We
provide an algorithm that maintains a valid schedule, as long as a sufficiently
feasible schedule exists. The algorithm reschedules only a total number of
O(min{log^* n, log^* Delta}) jobs for each job that is inserted or deleted from
the system, where n is the number of active jobs and Delta is the size of the
largest window.",1305.6555v1
2013-06-04,Generalized splines on arbitrary graphs,"Let G be a graph whose edges are labeled by ideals of a commutative ring. We
introduce a generalized spline, which is a vertex-labeling of G by elements of
the ring so that the difference between the labels of any two adjacent vertices
lies in the corresponding edge ideal. Generalized splines arise naturally in
combinatorics (em algebraic splines of Billera and others) and in algebraic
topology (certain equivariant cohomology rings, described by
Goresky-Kottwitz-MacPherson and others). The central question of this
manuscript asks when an arbitrary edge-labeled graph has nontrivial generalized
splines. The answer is `always', and we prove the stronger result that
generalized splines contain a free submodule whose rank is the number of
vertices in G. We describe all generalized splines when G is a tree, and give
several ways to describe the ring of generalized splines as an intersection of
generalized splines for simpler subgraphs of G. We also present a new tool
which we call the GKM matrix, an analogue of the incidence matrix of a graph,
and end with open questions.",1306.0801v2
2013-06-04,Large Chern Number Quantum Anomalous Hall Effect In Thin-film Topological Crystalline Insulators,"Quantum anomalous Hall (QAH) insulators are two-dimensional (2D) insulating
states exhibiting properties similar to those of quantum Hall states but
without external magnetic field. They have quantized Hall conductance
$\sigma^H=Ce^2/h$, where integer $C$ is called the Chern number, and represents
the number of gapless edge modes. Recent experiments demonstrated that chromium
doped thin-film (Bi,Sb)$_2$Te$_3$ is a QAH insulator with Chern number
$C=\pm1$. Here we theoretically predict that thin-film topological crystalline
insulators (TCI) can host various QAH phases, when doped by ferromagnetically
ordered dopants. Any Chern number between $\pm4$ can, in principle, be reached
as a result of the interplay between (a) the induced Zeeman field, depending on
the magnetic doping concentration, (b) the structural distortion, either
intrinsic or induced by a piezoelectric material through proximity effect and
(c) the thickness of the thin film. The tunable Chern numbers found in TCI
possess significant potential for ultra-low power information processing
applications.",1306.0888v2
2013-06-07,Free energy generalization of the Peierls potential in iron,"In body-centered cubic (bcc) crystals, ${1}{2}111$ screw dislocations exhibit
high intrinsic lattice friction as a consequence of their non-planar core
structure, which results in a periodic energy landscape known as the Peierls
potential, $U_P$. The main features determining plastic flow, including its
stress and temperature dependences, can be derived directly from this
potential, hence its importance. In this Letter, we use thermodynamic
integration to provide a full thermodynamic extension of $U_P$ for bcc Fe. We
compute the Peierls free energy path as a function of stress and temperature
and show that the critical stress vanishes at 700K, supplying the qualitative
elements that explain plastic behavior in the athermal limit.",1306.1633v4
2013-06-14,On a decoupled linear FEM integrator for Eddy-current-LLG,"We propose a numerical integrator for the coupled system of the eddy-current
equation with the nonlinear Landau-Lifshitz-Gilbert equation. The considered
effective field contains a general field contribution, and we particularly
cover exchange, anisotropy, applied field, and magnetic field (stemming from
the eddy-current equation). Even though the considered problem is nonlinear,
our scheme requires only the solution of two linear systems per time-step.
Moreover, our algorithm decouples both equations so that in each time-step, one
linear system is solved for the magnetization, and afterwards one linear system
is solved for the magnetic field. Unconditional convergence -- at least of a
subsequence -- towards a weak solution is proved, and our analysis even
provides existence of such weak solutions. Numerical experiments with a
micromagnetic benchmark problem underline the performance of the proposed
algorithm.",1306.3319v1
2013-06-20,"Lower Bounds for the Area of Black Holes in Terms of Mass, Charge, and Angular Momentum","The most general formulation of Penrose's inequality yields a lower bound for
ADM mass in terms of the area, charge, and angular momentum of black holes.
This inequality is in turn equivalent to an upper and lower bound for the area
in terms of the remaining quantities. In this note, we establish the lower
bound for a single black hole in the setting of axisymmetric maximal initial
data sets for the Einstein-Maxwell equations, when the non-electromagnetic
matter fields are not charged and satisfy the dominant energy condition. It is
shown that the inequality is saturated if and only if the initial data arise
from the extreme Kerr-Newman spacetime. Further refinements are given when
either charge or angular momentum vanish. Lastly, we discuss the validity of
the lower bound in the presence of multiple black holes.",1306.4739v2
2013-06-28,Coherent Nonlinear Quantum Model for Composite Fermions,"Originally proposed by Read [1] and Jain [2], the so-called
""composite-fermion"" is a phenomenological attachment of two infinitely thin
local flux quanta seen as nonlocal vortices to two-dimensional (2D) electrons
embedded in a strong orthogonal magnetic field. In this letter, it is described
as a highly-nonlinear and coherent mean-field quantum process of the soliton
type by use of a 2D stationary Schroedinger-Poisson differential model with
only two Coulomb-interacting electrons. At filling factor $\nu={1}{3}$ of the
lowest Landau level, it agrees with both the exact two-electron antisymmetric
Schroedinger wave function and Laughlin's Jastrow-type guess for the fractional
quantum Hall effect, hence providing this later with a tentative physical
justification based on first principles.",1306.6869v1
2013-06-29,First-principles calculations of current-induced spin-transfer torques in magnetic domain walls,"Current-induced spin-transfer torques (STTs) have been studied in Fe, Co and
Ni domain walls (DWs) by the method based on the first-principles noncollinear
calculations of scattering wave functions expanded in the tight-binding
linearized muffin-tin orbital (TB-LMTO) basis. The results show that the
out-of-plane component of nonadiabatic STT in Fe DW has localized form, which
is in contrast to the typical nonlocal oscillating nonadiabatic torques
obtained in Co and Ni DWs. Meanwhile, the degree of nonadiabaticity in STT is
also much greater for Fe DW. Further, our results demonstrate that compared to
the well-known first-order nonadiabatic STT, the torque in the third-order
spatial derivative of local spin can better describe the distribution of
localized nonadiabatic STT in Fe DW. The dynamics of local spin driven by this
third-order torques in Fe DW have been investigated by the
Landau-Lifshitz-Gilbert (LLG) equation. The calculated results show that with
the same amplitude of STTs the DW velocity induced by this third-order term is
about half of the wall speed for the case of the first-order nonadiabatic STT.",1307.0062v1
2013-07-02,Reversal mode instability and magnetoresistance in perpendicular (Co/Pd)/Cu/(Co/Ni) pseudo-spin-valves,"We have observed distinct temperature-dependent magnetization reversal modes
in a perpendicular (Co/Pd)4/Co/Cu/(Co/Ni)4/Co pseudo-spin-valve, which are
correlated with spin-transport properties. At 300 K, magnetization reversal
occurs by vertically correlated domains. Below 200 K the hysteresis loop
becomes bifurcated due to laterally correlated reversal of the individual
stacks. The magnetic configuration change also leads to higher spin disorders
and a significant increase in the giant magnetoresistance effect. First order
reversal curve measurements reveal that the coupled state can be re-established
through field cycling, and allow direct determination of the interlayer
coupling strength as a function of temperature.",1307.0853v1
2013-07-08,Modal Analysis with Compressive Measurements,"Structural Health Monitoring (SHM) systems are critical for monitoring aging
infrastructure (such as buildings or bridges) in a cost-effective manner. Such
systems typically involve collections of battery-operated wireless sensors that
sample vibration data over time. After the data is transmitted to a central
node, modal analysis can be used to detect damage in the structure. In this
paper, we propose and study three frameworks for Compressive Sensing (CS) in
SHM systems; these methods are intended to minimize power consumption by
allowing the data to be sampled and/or transmitted more efficiently. At the
central node, all of these frameworks involve a very simple technique for
estimating the structure's mode shapes without requiring a traditional CS
reconstruction of the vibration signals; all that is needed is to compute a
simple Singular Value Decomposition. We provide theoretical justification
(including measurement bounds) for each of these techniques based on the
equations of motion describing a simplified Multiple-Degree-Of-Freedom (MDOF)
system, and we support our proposed techniques using simulations based on
synthetic and real data.",1307.1960v1
2013-07-15,On the Instabilities of the Walker Propagating Domain Wall Solution,"A powerful mathematical method for front instability analysis that was
recently developed in the field of nonlinear dynamics is applied to the 1+1
(spatial and time) dimensional Landau-Lifshitz-Gilbert (LLG) equation. From the
essential spectrum of the LLG equation, it is shown that the famous Walker
rigid body propagating domain wall (DW) is not stable against the spin wave
emission. In the low field region only stern spin waves are emitted while both
stern and bow waves are generated under high fields. By using the properties of
the absolute spectrum of the LLG equation, it is concluded that in a high
enough field, but below the Walker breakdown field, the Walker solution could
be convective/absolute unstable if the transverse magnetic anisotropy is larger
than a critical value, corresponding to a significant modification of the DW
profile and DW propagating speed. Since the Walker solution of 1+1 dimensional
LLG equation can be realized in experiments, our results could be also used to
test the mathematical method in a controlled manner.",1307.3825v3
2013-07-30,Accurate Decoding of Pooled Sequenced Data Using Compressed Sensing,"In order to overcome the limitations imposed by DNA barcoding when
multiplexing a large number of samples in the current generation of
high-throughput sequencing instruments, we have recently proposed a new
protocol that leverages advances in combinatorial pooling design (group
testing) doi:10.1371/journal.pcbi.1003010. We have also demonstrated how this
new protocol would enable de novo selective sequencing and assembly of large,
highly-repetitive genomes. Here we address the problem of decoding pooled
sequenced data obtained from such a protocol. Our algorithm employs a
synergistic combination of ideas from compressed sensing and the decoding of
error-correcting codes. Experimental results on synthetic data for the rice
genome and real data for the barley genome show that our novel decoding
algorithm enables significantly higher quality assemblies than the previous
approach.",1307.7810v1
2013-08-09,Relativistic and thermal effects on the magnon spectrum of a ferromagnetic monolayer,"A spin model including magnetic anisotropy terms and Dzyaloshinsky-Moriya
interactions is studied for the case of a ferromagnetic monolayer with C2v
symmetry like Fe/W(110). Using the quasiclassical stochastic
Landau-Lifshitz-Gilbert equations, the magnon spectrum of the system is derived
using linear response theory. The Dzyaloshinsky-Moriya interaction leads to
asymmetry in the spectrum, while the anisotropy terms induce a gap. It is shown
that in the presence of lattice defects, both the Dzyaloshinsky-Moriya
interactions and the two-site anisotropy lead to a softening of the magnon
energies. Two methods are developed to investigate the magnon spectrum at
finite temperatures. The theoretical results are compared to atomistic spin
dynamics simulations and a good agreement is found between them.",1308.2082v2
2013-08-11,New class of topological superconductors protected by magnetic group symmetries,"We study a new type of three-dimensional topological superconductors that
exhibit Majorana zero modes (MZM) protected by a magnetic group symmetry, a
combined antiunitary symmetry composed of a mirror reflection and
time-reversal. This new symmetry enhances the noninteracting topological
classification of a superconducting vortex from $Z_2$ to $Z$, indicating that
multiple MZMs can coexist at the end of one magnetic vortex of unit flux.
Specially, we show that a vortex binding two MZMs can be realized on the
$(001)$-surface of a topological crystalline insulator SnTe with proximity
induced BCS Cooper pairing, or in bulk superconductor In$_x$Sn$_{1-x}$Te.",1308.2424v3
2013-08-26,A Radio-Frequency-over-Fiber link for large-array radio astronomy applications,"A prototype 425-850 MHz Radio-Frequency-over-Fiber (RFoF) link for the
Canadian Hydrogen Intensity Mapping Experiment (CHIME) is presented. The design
is based on a directly modulated Fabry-Perot (FP) laser, operating at ambient
temperature, and a single-mode fiber. The dynamic performance, gain stability,
and phase stability of the RFoF link are characterized. Tests on a two-element
interferometer built at the Dominion Radio Astrophysical Observatory for CHIME
prototyping demonstrate that RFoF can be successfully used as a cost-effective
solution for analog signal transport on the CHIME telescope and other
large-array radio astronomy applications",1308.5481v2
2013-08-30,Energy dissipation of moved magnetic vortices,"A two-dimensional easy-plane ferromagnetic substrate, interacting with a
dipolar tip which is magnetised perpendicular with respect to the easy plane is
studied numerically by solving the Landau-Lifshitz Gilbert equation. The
dipolar tip stabilises a vortex structure which is dragged through the system
and dissipates energy. An analytical expression for the friction force in the
v$\rightarrow$0-limit based on the Thiele equation is presented. The
limitations of this result which predicts a diverging friction force in the
thermodynamic limit, are demonstrated by a study of the size dependence of the
friction force. While for small system sizes the dissipation depends
logarithmically on the system size, it saturates at a specific velocity
dependent value. This size can be regarded as an effective vortex size and it
is shown how this effective vortex size agrees with the infinite extension of a
vortex in the thermodynamic limit. A magnetic friction number is defined which
represents a general criterion for the validity of the Thiele equation and
quantifies the degree of nonlinearity in the response of a driven spin
configuration.",1308.6714v1
2013-10-16,Domain wall motion in magnetic nanowires: An asymptotic approach,"We develop a systematic asymptotic description for domain wall motion in
one-dimensional magnetic nanowires under the influence of small applied
magnetic fields and currents and small material anisotropy. The magnetization
dynamics, as governed by the Landau--Lifshitz--Gilbert equation, is
investigated via a perturbation expansion. We compute leading-order behaviour,
propagation velocities, and first-order corrections of both travelling waves
and oscillatory solutions, and find bifurcations between these two types of
solutions. This treatment provides a sound mathematical foundation for numerous
results in the literature obtained through more ad hoc arguments.",1310.4442v1
2013-10-23,Exchange-dominated Standing Spin Wave Excitations under microwave irradiation in Ni80Fe20 Thin Films,"We investigated the microwave-assisted DC voltages of ferromagnetic
resonances and exchangedominated standing spin wave excitations in two
different in-plane magnetized permalloy thin films via homodyne detection. The
line shapes of ferromagnetic resonance spectra and the dispersion curves of
ferromagnetic resonance and standing spin wave are in agreement of previous
studies, while further investigations of DC voltage spectra for these two
excitations reveal that 1. unlike ferromagnetic resonance signals, the
anti-symmetrical line shapes of standing spin wave excitations are not depend
on the electromagnetic relative phase of assisted microwave, and 2. linewidths
of their DC voltage spectra are distinct. The complicated spin dynamics of
standing spin wave is consequently discussed by applying
Landau-Lifshitz-Gilbert equation in term of exchange interaction.",1310.6108v1
2013-10-25,Mode coupling in spin torque oscillators,"A number of recent experimental works have shown that the dynamics of a
single spin torque oscillator can exhibit complex behavior that stems from
interactions between two or more modes of the oscillator. Examples are observed
mode-hopping or mode coexistence. There has been some intial work indicating
how the theory for a single-mode (macro-spin) spin torque oscillator should be
generalized to include several modes and the interactions between them. In the
present work, we derive such a theory starting with the Landau-Lifshitz-Gilbert
equation for magnetization dynamics. We compare our results with the
single-mode theory, and show how it is a natural extension of that theory to
include mode interactions.",1310.6791v2
2013-10-31,A Labeling Approach to Incremental Cycle Detection,"In the \emph{incremental cycle detection} problem arcs are added to a
directed acyclic graph and the algorithm has to report if the new arc closes a
cycle. One seeks to minimize the total time to process the entire sequence of
arc insertions, or until a cycle appears.
  In a recent breakthrough, Bender, Fineman, Gilbert and Tarjan
\cite{BeFiGiTa11} presented two different algorithms, with time complexity
$O(n^2 \log n)$ and $O(m \cdot \min \{m^{1/2}, n^{2/3} \})$, respectively.
  In this paper we introduce a new technique for incremental cycle detection
that allows us to obtain both bounds (up to a logarithmic factor). Furthermore,
our approach seems more amiable for distributed implementation.",1310.8381v1
2013-11-01,Superfluid Spin Transport through Easy-Plane Ferromagnetic Insulators,"Superfluid spin transport $-$ dissipationless transport of spin $-$ is
theoretically studied in a ferromagnetic insulator with easy-plane anisotropy.
We consider an open geometry where spin current is injected into the
ferromagnet from one side by a metallic reservoir with a nonequilibrium spin
accumulation, and ejected into another metallic reservoir located downstream.
Spin transport through the device is studied using a combination of
magnetoelectric circuit theory, Landau-Lifshitz-Gilbert phenomenology, and
microscopic linear-response theory. We discuss how spin superfluidity can be
probed using a magnetically-mediated electron-drag experiment.",1311.0288v4
2013-11-12,Vertex finiteness for splittings of relatively hyperbolic groups,"Consider a group G and a family $\mathcal{A}$ of subgroups of G. We say that
vertex finiteness holds for splittings of G over $\mathcal{A}$ if, up to
isomorphism, there are only finitely many possibilities for vertex stabilizers
of minimal G-trees with edge stabilizers in $\mathcal{A}$.
  We show vertex finiteness when G is a toral relatively hyperbolic group and
$\mathcal{A}$ is the family of abelian subgroups.
  We also show vertex finiteness when G is hyperbolic relative to virtually
polycyclic subgroups and $\mathcal{A}$ is the family of virtually cyclic
subgroups; if moreover G is one-ended, there are only finitely many minimal
G-trees with virtually cyclic edge stabilizers, up to automorphisms of G.",1311.2835v2
2013-11-13,Fokker-Planck approach to the theory of magnon-driven spin Seebeck effect,"Following the theoretical approach by Xiao et al [Phys. Rev. B 81, 214418
(2010)] to the spin Seebeck effect, we calculate the mean value of the total
spin current flowing through a normalmetal/ ferromagnet interface. The spin
current emitted from the ferromagnet to the normal metal is evaluated in the
framework of the Fokker-Planck approach for the stochastic
Landau-Lifshitz-Gilbert equation. We show that the total spin current depends
not only on the temperature difference between the electron and the magnon
baths, but also on the external magnetic field and magnetic anisotropy. Apart
from this, the spin current is shown to saturate with increasing magnon
temperature, and the saturation temperature increases with increasing magnetic
field and/or magnetic anisotropy.",1311.3117v1
2013-11-20,Recent integral cross section validation measurements at the ASP facility,"This work presents new integral data measured at the ASP 14 MeV neutron
irradiation facility at Aldermaston in the UK, which has recently become
available for fusion-related work through the CCFE materials programme.
Measurements of reaction products from activation experiments using elemental
foils were carried out using gamma spectrometry in a high efficiency,
high-purity germanium (HPGe) detector and associated digital signal processing
hardware. Following irradiation and rapid extraction to the measurement cell,
gamma emissions were acquired with both energy and time bins. Integral cross
section and half-life data have been derived from these measurements. Selected
integral cross section values are presented from the measurement campaigns.",1311.5074v1
2013-11-25,Application of the Moment-SOS Approach to Global Optimization of the OPF Problem,"Finding a global solution to the optimal power flow (OPF) problem is
difficult due to its nonconvexity. A convex relaxation in the form of
semidefinite programming (SDP) has attracted much attention lately as it yields
a global solution in several practical cases. However, it does not in all
cases, and such cases have been documented in recent publications. This paper
presents another SDP method known as the moment-sos (sum of squares) approach,
which generates a sequence that converges towards a global solution to the OPF
problem at the cost of higher runtime. Our finding is that in the small
examples where the previously studied SDP method fails, this approach finds the
global solution. The higher cost in runtime is due to an increase in the matrix
size of the SDP problem, which can vary from one instance to another. Numerical
experiment shows that the size is very often a quadratic function of the number
of buses in the network, whereas it is a linear function of the number of buses
in the case of the previously studied SDP method.",1311.6370v2
2013-12-06,Lazy Cops and Robbers played on Graphs,"We consider a variant of the game of Cops and Robbers, called Lazy Cops and
Robbers, where at most one cop can move in any round. We investigate the
analogue of the cop number for this game, which we call the lazy cop number.
Lazy Cops and Robbers was recently introduced by Offner and Ojakian, who
provided asymptotic upper and lower bounds on the lazy cop number of the
hypercube. By investigating expansion properties, we provide asymptotically
almost sure bounds on the lazy cop number of binomial random graphs
$\mathcal{G}(n,p)$ for a wide range of $p=p(n)$. By coupling the probabilistic
method with a potential function argument, we also improve on the existing
lower bounds for the lazy cop number of hypercubes. Finally, we provide an
upper bound for the lazy cop number of graphs with genus $g$ by using the
Gilbert-Hutchinson-Tarjan separator theorem.",1312.1750v1
2014-01-03,Spin-Transfer-Torque Driven Magneto-Logic Gates Using Nano Spin-Valve Pillars,"We propose model magneto-logic NOR and NAND gates using a spin valve pillar,
wherein the logical operation is induced by spin-polarized currents which also
form the logical inputs. The operation is facilitated by the simultaneous
presence of a constant controlling magnetic field. The same spin-valve assembly
can also be used as a magnetic memory unit. We identify regions in the
parameter space of the system where the logical operations can be effectively
performed. The proposed gates retain the non-volatility of a magnetic random
access memory,(MRAM). We verify the functioning of the gate by numerically
simulating its dynamics, governed by the appropriate Landau-Lifshitz-Gilbert
equation with the spin-transfer torque term. The flipping time for the logical
states is estimated to be within nano seconds.",1401.0723v1
2014-01-17,Diffuse Scattering on Graphs,"We formulate and analyze difference equations on graphs analogous to
time-independent diffusion equations arising in the study of diffuse scattering
in continuous media. Moreover, we show how to construct solutions in the
presence of weak scatterers from the solution to the homogeneous (background
problem) using Born series, providing necessary conditions for convergence and
demonstrating the process through numerous examples. In addition, we outline a
method for finding Green's functions for Cayley graphs for both abelian and
non-abelian groups. Finally, we conclude with a discussion of the effects of
sparsity on our method and results, outlining the simplifications that can be
made provided that the scatterers are weak and well-separated.",1401.4428v2
2014-01-25,"Linear Boolean classification, coding and ""the critical problem""","The problem of constructing a minimal rank matrix over GF(2) whose kernel
does not intersect a given set S is considered. In the case where S is a
Hamming ball centered at 0, this is equivalent to finding linear codes of
largest dimension. For a general set, this is an instance of ""the critical
problem"" posed by Crapo and Rota in 1970. This work focuses on the case where S
is an annulus. As opposed to balls, it is shown that an optimal kernel is
composed not only of dense but also of sparse vectors, and the optimal mixture
is identified in various cases. These findings corroborate a proposed
conjecture that for annulus of inner and outer radius nq and np respectively,
the optimal relative rank is given by (1-q)H(p/(1-q)), an extension of the
Gilbert-Varshamov bound H(p) conjectured for Hamming balls of radius np.",1401.6528v3
2014-01-30,Langevin spin dynamics based on ab initio calculations: numerical schemes and applications,"A method is proposed to study the finite-temperature behaviour of small
magnetic clusters based on solving the stochastic Landau-Lifshitz-Gilbert
equations, where the effective magnetic field is calculated directly during the
solution of the dynamical equations from first principles instead of relying on
an effective spin Hamiltonian. Different numerical solvers are discussed in the
case of a one-dimensional Heisenberg chain with nearest-neighbour interactions.
We performed detailed investigations for a monatomic chain of ten Co atoms on
top of Au(001) surface. We found a spiral-like ground state of the spins due to
Dzyaloshinsky-Moriya interactions, while the finite-temperature magnetic
behaviour of the system was well described by a nearest-neighbour Heisenberg
model including easy-axis anisotropy.",1401.7885v2
2014-02-25,Flux $1/f^α$ noise in 2D Heisenberg spin glasses: effects of weak anisotropic interactions,"We study the dynamics of a two-dimensional ensemble of randomly distributed
classical Heisenberg spins with isotropic RKKY and weaker anisotropic
dipole-dipole couplings. Such ensembles may give rise to the flux noise
observed in SQUIDs with a $1/f^{\alpha}$ power spectrum ($\alpha \lesssim 1$).
We solve numerically the Landau-Lifshiftz-Gilbert equations of motion in the
dissipationless limit. We find that Ising type fluctuators, which arise from
spin clustering close to a spin-glass critical behavior with $T_c =0$, give
rise to $1/f^{\alpha}$ noise. Even weak anisotropic interactions lead to a
crossover from the Heisenberg-type criticality to the much stronger Ising-type
criticality. The temperature dependent exponent $\alpha(T) \lesssim 1$ grows
and approaches unity when the temperature is lowered. This mechanism acts in
parallel to the spin diffusion mechanism. Whereas the latter is sensitive to
the device geometry, the spin-clustering mechanism is largely geometry
independent.",1402.6229v2
2014-02-25,Spinless Topological Insulators without Time-Reversal Symmetry,"We explore the 32 crystallographic point groups and identify topological
phases of matter with robust surface modes. For n =3,4 and 6 of the C_{nv}
groups, we find the first-known 3D topological insulators without spin-orbit
coupling, and with surface modes that are protected only by point groups, i.e.,
not needing time-reversal symmetry. To describe these C_{nv} systems, we
introduce the notions of (a) a halved mirror chirality: an integer invariant
which characterizes half-mirror-planes in the 3D Brillouin zone, and (b) a bent
Chern number: the traditional TKNN invariant generalized to bent 2D manifolds.
We find that a Weyl semimetallic phase intermediates two gapped phases with
distinct halved chiralities.",1402.6323v1
2014-04-08,Resonant Spin Wave Excitation by Terahertz Magnetic Near-field Enhanced with Split Ring Resonator,"Excitation of antiferromagnetic spin waves in HoFeO$_{3}$ crystal combined
with a split ring resonator (SRR) is studied using terahertz (THz)
electromagnetic pulses. The magnetic field in the vicinity of the SRR induced
by the incident THz electric field component excites and the Faraday rotation
of the polarization of a near-infrared probe pulse directly measures
oscillations that correspond to the antiferromagnetic spin resonance mode. The
good agreement of the temperature-dependent magnetization dynamics with the
calculation using the two-lattice Landau-Lifshitz-Gilbert equation confirms
that the spin wave is resonantly excited by the THz magnetic near-field
enhanced at the LC resonance frequency of the SRR, which is 20 times stronger
than the incident magnetic field.",1404.2179v1
2014-04-09,Spin switches for compact implementation of neuron and synapse,"Nanomagnets driven by spin currents provide a natural implementation for a
neuron and a synapse: currents allow convenient summation of multiple inputs,
while the magnet provides the threshold function. The objective of this paper
is to explore the possibility of a hardware neural network (HNN) implementation
using a spin switch (SS) as its basic building block. SS is a recently proposed
device based on established technology with a transistor-like gain and
input-output isolation. This allows neural networks to be constructed with
purely passive interconnections without intervening clocks or amplifiers. The
weights for the neural network are conveniently adjusted through analog
voltages that can be stored in a non-volatile manner in an underlying CMOS
layer using a floating gate low dropout voltage regulator. The operation of a
multi-layer SS neural network designed for character recognition is
demonstrated using a standard simulation model based on coupled
Landau-Lifshitz-Gilbert (LLG) equations, one for each magnet in the network.",1404.2654v2
2014-06-30,Coercivity reduction in a two-dimensional array of nanoparticles,"We report on theoretical investigation of the magnetization reversal in
two-dimensional arrays of ferromagnetic nano-particles with parameters of
cobalt. The system was optimized for achieving the lowest coercivity in an
array of particles located in the nodes of triangular, hexagonal and square
grids. Based on the numerical solution of the non-stochastic
Landau-Lifshitz-Gilbert equation we show that each particle distribution type
is characterized with a proper optimal distance, allowing to lower the
coercivity values for approximately 30% compared with the reference value
obtained for a single nano-particle. It was shown that the reduction of
coercivity occurs even if the particle position in the array is not very
precise. In particular, the triangular particle arrangement maintained the same
optimal distance between the particles under up to 20% random displacements of
their position within the array.",1406.7786v1
2014-07-17,Spatial ordering of nano-dislocation loops in ion-irradiated materials,"Defect microstructures formed in ion-irradiated metals, for example iron or
tungsten, often exhibit patterns of spatially ordered nano-scale dislocation
loops. We show that such ordered dislocation loop structures may form
spontaneously as a result of Brownian motion of loops, biased by the
angular-dependent elastic interaction between the loops. Patterns of spatially
ordered loops form once the local density of loops produced by ion irradiation
exceeds a critical threshold value.",1407.4683v1
2014-07-22,"Lattice swelling and modulus change in a helium-implanted tungsten alloy: X-ray micro-diffraction, surface acoustic wave measurements, and multiscale modelling","Using X-ray micro-diffraction and surface acoustic wave spectroscopy, we
measure lattice swelling and elastic modulus changes in a W-1%Re alloy after
implantation with 3110 appm of helium. A fraction of a percent observed lattice
expansion gives rise to an order of magnitude larger reduction in the surface
acoustic wave velocity. A multiscale elasticity, molecular dynamics, and
density functional theory model is applied to the interpretation of
observations. The measured lattice swelling is consistent with the relaxation
volume of self-interstitial and helium-filled vacancy defects that dominate the
helium-implanted material microstructure. Molecular dynamics simulations
confirm the elasticity model for swelling. Elastic properties of the implanted
surface layer also change due to defects. The reduction of surface acoustic
wave velocity predicted by density functional theory calculations agrees
remarkably well with experimental observations.",1407.6051v1
2014-07-26,Principles and Parameters: a coding theory perspective,"We propose an approach to Longobardi's parametric comparison method (PCM) via
the theory of error-correcting codes. One associates to a collection of
languages to be analyzed with the PCM a binary (or ternary) code with one code
words for each language in the family and each word consisting of the binary
values of the syntactic parameters of the language, with the ternary case
allowing for an additional parameter state that takes into account phenomena of
entailment of parameters. The code parameters of the resulting code can be
compared with some classical bounds in coding theory: the asymptotic bound, the
Gilbert-Varshamov bound, etc. The position of the code parameters with respect
to some of these bounds provides quantitative information on the variability of
syntactic parameters within and across historical-linguistic families. While
computations carried out for languages belonging to the same family yield codes
below the GV curve, comparisons across different historical families can give
examples of isolated codes lying above the asymptotic bound.",1407.7169v1
2014-07-28,Eddy current effects in the magnetization dynamics of ferromagnetic metal nanoparticles,"We develop an analytical model for describing the magnetization dynamics in
ferromagnetic metal nanoparticles, which is based on the coupled system of the
Landau-Lifshitz-Gilbert (LLG) and Maxwell equations. By solving Maxwell's
equations in the quasi-static approximation and finding the magnetic field of
eddy currents, we derive the closed LLG equation for the magnetization that
fully accounts for the effects of conductivity. We analyze the difference
between the LLG equations in metallic and dielectric nanoparticles and show
that these effects can strongly influence the magnetization dynamics. As an
example illustrating the importance of eddy currents, the phenomenon of
precessional switching of magnetization is considered.",1407.7466v1
2014-08-02,Standards for Graph Algorithm Primitives,"It is our view that the state of the art in constructing a large collection
of graph algorithms in terms of linear algebraic operations is mature enough to
support the emergence of a standard set of primitive building blocks. This
paper is a position paper defining the problem and announcing our intention to
launch an open effort to define this standard.",1408.0393v1
2014-08-02,McCool groups of toral relatively hyperbolic groups,"The outer automorphism group Out(G) of a group G acts on the set of conjugacy
classes of elements of G. McCool proved that the stabilizer $Mc(c_1,...,c_n)$
of a finite set of conjugacy classes is finitely presented when G is free. More
generally, we consider the group $Mc(H_1,...,H_n)$ of outer automorphisms
$\Phi$ of G acting trivially on a family of subgroups $H_i$, in the sense that
$\Phi$ has representatives $\alpha_i$ with $\alpha_i$ equal to the identity on
$H_i$.
  When G is a toral relatively hyperbolic group, we show that these two
definitions lead to the same subgroups of Out(G), which we call ""McCool groups""
of G. We prove that such McCool groups are of type VF (some finite index
subgroup has a finite classifying space). Being of type VF also holds for the
group of automorphisms of G preserving a splitting of G over abelian groups.
  We show that McCool groups satisfy a uniform chain condition: there is a
bound, depending only on G, for the length of a strictly decreasing sequence of
McCool groups of G. Similarly, fixed subgroups of automorphisms of G satisfy a
uniform chain condition.",1408.0418v1
2014-08-06,The first SPIE software Hack Day,"We report here on the software Hack Day organised at the 2014 SPIE conference
on Astronomical Telescopes and Instrumentation in Montreal. The first ever Hack
Day to take place at an SPIE event, the aim of the day was to bring together
developers to collaborate on innovative solutions to problems of their choice.
Such events have proliferated in the technology community, providing
opportunities to showcase, share and learn skills. In academic environments,
these events are often also instrumental in building community beyond the
limits of national borders, institutions and projects. We show examples of
projects the participants worked on, and provide some lessons learned for
future events.",1408.1278v1
2014-08-07,A broadband silicon quarter-wave retarder for far-infrared spectroscopic circular dichroism,"The high brightness, broad spectral coverage and pulsed characteristics of
infrared synchrotron radiation enable time-resolved spectroscopy under
throughput-limited optical systems, as can occur with the high-field magnet
cryostat systems used to study electron dynamics and cyclotron resonance by
far-infrared techniques. A natural extension for magnetospectroscopy is to
sense circular dichroism, i.e. the difference in a material's optical response
for left and right circularly polarized light. A key component for
spectroscopic circular dichroism is an achromatic 1/4 wave retarder functioning
over the spectral range of interest. We report here the development of an
in-line retarder using total internal reflection in high-resistivity silicon.
We demonstrate its performance by distinguishing electronic excitations of
different handednesses for GaAs in a magnetic field. This 1/4 wave retarder is
expected to be useful for far-infrared spectroscopy of circular dichroism in
many materials.",1408.1650v1
2014-08-12,Probing the A1 to L10 Transformation in FeCuPt Using the First Order Reversal Curve Method,"The A1- L10 phase transformation has been investigated in (001) FeCuPt thin
films prepared by atomic-scale multilayer sputtering and rapid thermal
annealing (RTA). Traditional x-ray diffraction is not always applicable in
generating a true order parameter, due to non-ideal crystallinity of the A1
phase. Using the first-order reversal curve (FORC) method, the A1 and L10
phases are deconvoluted into two distinct features in the FORC distribution,
whose relative intensities change with the RTA temperature. The L10 ordering
takes place via a nucleation-and-growth mode. A magnetization-based phase
fraction is extracted, providing a quantitative measure of the L10 phase
homogeneity.",1408.2860v1
2014-09-09,Magnetization pumping and dynamics in a Dzyaloshinskii-Moriya magnet,"We formulate a phenomenological description of thin ferromagnetic layers with
inversion asymmetry where the single-domain magnetic dynamics experiences
magnon current-induced torques and leads to magnon-motive forces. We first
construct a phenomenological theory based on irreversible thermodynamics,
taking into account the symmetries of the system. Furthermore, we confirm that
these effects originate from Dzyaloshinskii-Moriya interactions from the
analysis based on the stochastic Landau-Lifshitz-Gilbert equation. Our
phenomenological results generalize to a general form of Dzyaloshinskii-Moriya
interactions and to other systems, such as pyrochlore crystals and chiral
magnets. Possible applications include spin current generation, magnetization
reversal and magnonic cooling.",1409.2846v3
2014-09-17,Communities and Hierarchical Structures in Dynamic Social Networks: Analysis and Visualization,"Detection of community structures in social networks has attracted lots of
attention in the domain of sociology and behavioral sciences. Social networks
also exhibit dynamic nature as these networks change continuously with the
passage of time. Social networks might also present a hierarchical structure
led by individuals that play important roles in a society such as Managers and
Decision Makers. Detection and Visualization of these networks changing over
time is a challenging problem where communities change as a function of events
taking place in the society and the role people play in it.
  In this paper we address these issues by presenting a system to analyze
dynamic social networks. The proposed system is based on dynamic graph
discretization and graph clustering. The system allows detection of major
structural changes taking place in social communities over time and reveals
hierarchies by identifying influential people in a social networks. We use two
different data sets for the empirical evaluation and observe that our system
helps to discover interesting facts about the social and hierarchical
structures present in these social networks.",1409.5040v1
2014-09-30,Free upper boundary value problems for the semi-geostrophic equations,"The semi-geostrophic system is widely used in the modelling of large-scale
atmospheric flows. In this paper, we prove existence of solutions of the
incompressible semi-geostrophic equations in a fully three-dimensional domain
with a free upper boundary condition.
  We show that, using methods similar to those introduced in the pioneering
work of Benamou and Brenier, who analysed the same system but with a rigid
boundary condition, we can prove the existence of solutions for the
incompressible free boundary problem. The proof is based on optimal transport
results as well as the analysis of Hamiltonian ODEs in spaces of probability
measures given by Ambrosio and Gangbo. We also show how these techniques can be
modified to yield the same result also for the compressible version of the
system.",1409.8560v3
2014-10-21,Voltage Induced Dynamical Quantum Phase Transitions in Exciton Condensates,"We explore non-analytic quantum phase dynamics of dipolar exciton condensates
formed in a system of 1D quantum layers subjected to voltage quenches. We map
the exciton condensate physics on to the pseudospin ferromagnet model showing
an additional oscillatory metastable and paramagnetic phase beyond the
well-known ferromagnetic phase by utilizing a time-dependent, non-perturbative
theoretical model. We explain the coherent phase of the exciton condensate in
quantum Hall bilayers, observed for currents equal to and slightly larger than
the critical current, as a stable time-dependent phase characterized by
persistent charged meron flow in each of the individual layers with a
characteristic AC Josephson frequency. As the magnitude of the voltage quench
is further increased, we find that the time-dependent current oscillations
associated with the charged meron flow decay, resulting in a transient
pseudospin paramagnet phase characterized by partially coherent charge transfer
between layers, before the state relaxes to incoherent charge transfer between
the layers.",1410.5564v1
2014-10-22,Landau-Lifshitz-Bloch equation for exchange coupled grains,"Heat assisted recording is a promising technique to further increase the
storage density in hard disks. Multilayer recording grains with graded Curie
temperature is discussed to further assist the write process. Describing the
correct magnetization dynamics of these grains, from room temperature to far
above the Curie point, during a write process is required for the calculation
of bit error rates. We present a coarse grained approach based on the
Landau-Lifshitz-Bloch (LLB) equation to model exchange coupled grains with low
computational effort. The required temperature dependent material properties
such as the zero-field equilibrium magnetization as well as the parallel and
normal susceptibilities are obtained by atomistic Landau-Lifshitz-Gilbert (LLG)
simulations. Each grain is described with one magnetization vector. In order to
mimic the atomistic exchange interaction between the grains a special treatment
of the exchange field in the coarse grained approach is presented.",1410.6066v2
2014-10-22,A three-dimensional spin-diffusion model for micromagnetics,"We implement a finite-element scheme that solves the Landau-Lifshitz-Gilbert
equation coupled to a diffusion equation accounting for spin-polarized
currents. The latter solves for the spin accumulation not only in magnetic
materials but also in nonmagnetic conductors. The presented method incorporates
the model by Slonczewski for the description of spin torque in magnetic
multilayers as well as the model of Zhang and Li for the description of current
driven domain-wall motion. Furthermore it is able to do both resolve the time
evolution of the spin accumulation or treat it in an adiabatic fashion by the
choice of sufficiently large time steps.",1410.6067v2
2014-11-13,Random geometric graphs with general connection functions,"In the original (1961) Gilbert model of random geometric graphs, nodes are
placed according to a Poisson point process, and links formed between those
within a fixed range. Motivated by wireless ad-hoc networks ""soft"" or
""probabilistic"" connection models have recently been introduced, involving a
""connection function"" H(r) that gives the probability that two nodes at
distance r are linked (directly connect). In many applications (not only
wireless networks), it is desirable that the graph is connected, that is every
node is linked to every other node in a multihop fashion. Here, the connection
probability of a dense network in a convex domain in two or three dimensions is
expressed in terms of contributions from boundary components, for a very
general class of connection functions. It turns out that only a few quantities
such as moments of the connection function appear. Good agreement is found with
special cases from previous studies and with numerical simulations.",1411.3617v3
2014-11-24,Enhancement of Spin-transfer torque switching via resonant tunneling,"We propose the use of resonant tunneling as a route to enhance the
spin-transfer torque switching characteristics of magnetic tunnel junctions.
The proposed device structure is a resonant tunneling magnetic tunnel junction
based on a MgO-semiconductor heterostructure sandwiched between a fixed magnet
and a free magnet. Using the non-equilibrium Green's function formalism coupled
self consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation, we
demonstrate enhanced tunnel magneto-resistance characteristics as well as lower
switching voltages in comparison with traditional trilayer devices. Two device
designs based on MgO based heterostructures are presented, where the physics of
resonant tunneling leads to an enhanced spin transfer torque thereby reducing
the critical switching voltage by up to 44%. It is envisioned that the
proof-of-concept presented here may lead to practical device designs via
rigorous materials and interface studies.",1411.6454v1
2014-12-22,Langevin dynamics for vector variables driven by multiplicative white noise: a functional formalism,"We discuss general multi-dimensional stochastic processes driven by a system
of Langevin equations with multiplicative white noise. In particular, we
address the problem of how time reversal diffusion processes are affected by
the variety of conventions available to deal with stochastic integrals. We
present a functional formalism to built up the generating functional of
correlation functions without any type of discretization of the Langevin
equations at any intermediate step. The generating functional is characterized
by a functional integration over two sets of commuting variables as well as
Grassmann variables. In this representation, time reversal transformation
became a linear transformation in the extended variables, simplifying in this
way the complexity introduced by the mixture of prescriptions and the
associated calculus rules. The stochastic calculus is codified in our formalism
in the structure of the Grassmann algebra. We study some examples such as
higher order derivatives Langevin equations and the functional representation
of the micromagnetic stochastic Landau-Lifshitz-Gilbert equation.",1412.7015v2
2014-12-30,"Mapping tori of free group automorphisms, and the Bieri-Neumann-Strebel invariant of graphs of groups","Let $G$ be the mapping torus of a polynomially growing automorphism of a
finitely generated free group. We determine which epimorphisms from $G$ to
$\mathbb{Z}$ have finitely generated kernel, and we compute the rank of the
kernel. We thus describe all possible ways of expressing $G$ as the mapping
torus of a free group automorphism. This is similar to the case for 3--manifold
groups, and different from the case of mapping tori of exponentially growing
free group automorphisms. The proof uses a hierarchical decomposition of $G$
and requires determining the Bieri-Neumann-Strebel invariant of the fundamental
group of certain graphs of groups.",1412.8582v1
2015-01-12,Magnetic correlations beyond the Heisenberg model in an Fe monolayer on Rh(001),"Motivated by a recent experimental observation of a complex magnetic
structure [Takada et al. 2013 J. Magn. Magn. Mater. 329 95] we present a
theoretical study of the magnetic structure of an Fe monolayer deposited on
Rh(001). We use a classical spin Hamiltonian with parameters obtained from ab
initio calculations and go beyond the usual anisotropic Heisenberg model by
including isotropic biquadratic interactions. Zero-temperature
Landau--Lifshitz--Gilbert spin dynamics simulations lead to a complex collinear
spin configuration that, however, contradicts experimental finding. We thus
conclude that higher order multi-spin interactions are likely needed to account
for the magnetic ordering of the system.",1501.02657v1
2015-01-22,Relativistic dynamical spin excitations of magnetic adatoms,"We present a first-principles theory of dynamical spin excitations in the
presence of spin-orbit coupling. The broken global spin rotational invariance
leads to a new sum rule. We explore the competition between the magnetic
anisotropy energy and the external magnetic field, as well as the role of
electron-hole excitations, through calculations for 3$d$-metal adatoms on the
Cu(111) surface. The spin excitation resonance energy and lifetime display
non-trivial behavior, establishing the strong impact of relativistic effects.
We legitimate the use of the Landau-Lifshitz-Gilbert equation down to the
atomic limit, but with parameters that differ from a stationary theory.",1501.05509v1
2015-01-23,Tuning Range-Separated Density Functional Theory for Photocatalytic Water Splitting Systems,"We discuss the system-specific optimization of long-range separated density
functional theory (DFT) for the prediction of electronic properties relevant
for a photocatalytic cycle based on an Ir(III) photosensitizer (IrPS). Special
attention is paid to the charge-transfer properties, which are of key
importance for the photoexcitation dynamics, but and cannot be correctly
described by means of conventional DFT. The optimization of the
range-separation parameter using the $\Delta$SCF method is discussed for IrPS
including its derivatives and complexes with electron donors and acceptors used
in photocatalytic hydrogen production. Particular attention is paid to the
problems arising for a description of medium effects by means of a polarizable
continuum model.",1501.05863v2
2015-01-26,Dynamics of magnon fluid in Dzyaloshinskii-Moriya magnet and its manifestation in magnon-Skyrmion scattering,"We construct Holstein-Primakoff Hamiltonian for magnons in arbitrary slowly
varying spin background, for a microscopic spin Hamiltonian consisting of
ferromagnetic spin exchange,Dzyaloshinskii-Moriya exchange, and the Zeeman
term. The Gross-Pitaevskii-type equation for magnon dynamics contains several
background gauge fields pertaining to local spin chirality, inhomogeneous
potential, and anomalous scattering that violates the boson number
conservation. Non-trivial corrections to previous formulas derived in the
literature are given. Subsequent mapping to hydrodynamic fields yields the
continuity equation and the Euler equation of the magnon fluid dynamics. Magnon
wave scattering off a localized Skyrmion is examined numerically based on our
Gross-Pitaevskii formulation. Dependence of the effective flux experienced by
the impinging magnon on the Skyrmion radius is pointed out, and compared with
analysis of the same problem using the Landau-Lifshitz-Gilbert equation.",1501.06467v1
2015-02-05,Improved efficiency of heat generation in nonlinear dynamics of magnetic nanoparticles,"The deterministic Landau-Lifshitz-Gilbert equation has been used to
investigate the nonlinear dynamics of magnetization and the specific loss power
in magnetic nanoparticles with uniaxial anisotropy driven by a rotating
magnetic field. We propose a new type of applied field, which is
""simultaneously rotating and alternating"", i.e. the direction of the rotating
external field changes periodically. We show that a more efficient heat
generation by magnetic nanoparticles is possible with this new type of applied
field and we suggest its possible experimental realization in cancer therapy
which requires the enhancement of loss energies.",1502.01619v2
2015-03-10,Microwave-induced dynamic switching of magnetic skyrmion cores in nanodots,"The nonlinear dynamic behavior of a magnetic skyrmion in circular nanodots
was studied numerically by solving the Landau-Lifshitz-Gilbert equation with a
classical spin model. We show that a skyrmion core reversal can be achieved
within nanoseconds using a perpendicular oscillating magnetic field. Two
symmetric switching processes that correspond to excitations of the breathing
mode and the mixed mode (combination of the breathing mode and a radial
spin-wave mode) are identified. For excitation of the breathing mode, the
skyrmion core switches through nucleation of a new core from a transient
uniform state. In the mixed mode, the skyrmion core reverses with the help of
spins excited both at the edge and core regions. Unlike the magnetic vortex
core reversal, the excitation of radial spin waves does not dominate the
skyrmion core reversal process.",1503.02869v1
2015-03-23,Local dynamics of topological magnetic defects in the itinerant helimagnet FeGe,"Chiral magnetic interactions induce complex spin textures including helical
and conical spin waves, as well as particle-like objects such as magnetic
skyrmions and merons. These spin textures are the basis for innovative device
paradigms and give rise to exotic topological phenomena, thus being of interest
for both applied and fundamental sciences. Present key questions address the
dynamics of the spin system and emergent topological defects. Here we analyze
the micromagnetic dynamics in the helimagnetic phase of FeGe. By combining
magnetic force microscopy, single-spin magnetometry, and
Landau-Lifschitz-Gilbert simulations we show that the nanoscale dynamics are
governed by the depinning and subsequent motion of magnetic edge dislocations.
The motion of these topologically stable objects triggers perturbations that
can propagate over mesoscopic length scales. The observation of stochastic
instabilities in the micromagnetic structure provides new insight to the
spatio-temporal dynamics of itinerant helimagnets and topological defects, and
discloses novel challenges regarding their technological usage.",1503.06622v2
2015-04-01,Minimum-cost matching in a random graph with random costs,"Let $G_{n,p}$ be the standard Erd\H{o}s-R\'enyi-Gilbert random graph and let
$G_{n,n,p}$ be the random bipartite graph on $n+n$ vertices, where each $e\in
[n]^2$ appears as an edge independently with probability $p$. For a graph
$G=(V,E)$, suppose that each edge $e\in E$ is given an independent uniform
exponential rate one cost. Let $C(G)$ denote the random variable equal to the
length of the minimum cost perfect matching, assuming that $G$ contains at
least one. We show that w.h.p. if $d=np\gg(\log n)^2$ then w.h.p. ${\bf
E}[C(G_{n,n,p})] =(1+o(1))\frac{\p^2}{6p}$. This generalises the well-known
result for the case $G=K_{n,n}$. We also show that w.h.p. ${\bf E}[C(G_{n,p})]
=(1+o(1))\frac{\p^2}{12p}$ along with concentration results for both types of
random graph.",1504.00312v5
2015-04-04,"Graphs, Matrices, and the GraphBLAS: Seven Good Reasons","The analysis of graphs has become increasingly important to a wide range of
applications. Graph analysis presents a number of unique challenges in the
areas of (1) software complexity, (2) data complexity, (3) security, (4)
mathematical complexity, (5) theoretical analysis, (6) serial performance, and
(7) parallel performance. Implementing graph algorithms using matrix-based
approaches provides a number of promising solutions to these challenges. The
GraphBLAS standard (istc-bigdata.org/GraphBlas) is being developed to bring the
potential of matrix based graph algorithms to the broadest possible audience.
The GraphBLAS mathematically defines a core set of matrix-based graph
operations that can be used to implement a wide class of graph algorithms in a
wide range of programming environments. This paper provides an introduction to
the GraphBLAS and describes how the GraphBLAS can be used to address many of
the challenges associated with analysis of graphs.",1504.01039v2
2015-04-08,A Global Star Forming Episode in M31 2-4 Gyr Ago,"We have identified a major global enhancement of star formation in the inner
M31 disk that occurred between 2-4 Gyr ago, producing $\sim$60% of the stellar
mass formed in the past 5 Gyr. The presence of this episode in the inner disk
was discovered by modeling the optical resolved star color-magnitude diagrams
of low extinction regions in the main disk of M31 (3$<$R$<$20 kpc) as part of
the Panchromatic Hubble Andromeda Treasury. This measurement confirms and
extends recent measurements of a widespread star formation enhancement of
similar age in the outer disk, suggesting that this burst was both massive and
global. Following the galaxy-wide burst, the star formation rate of M31 has
significantly declined. We briefly discuss possible causes for these features
of the M31 evolutionary history, including interactions with M32, M33 and/or a
merger.",1504.02120v1
2015-04-13,Ultra-low-energy non-volatile straintronic computing using single multiferroic composites,"The primary impediment to continued downscaling of traditional charge-based
electronic devices in accordance with Moore's law is the excessive energy
dissipation that takes place in the device during switching of bits. One very
promising solution is to utilize multiferroic heterostructures, comprised of a
single-domain magnetostrictive nanomagnet strain-coupled to a piezoelectric
layer, in which the magnetization can be switched between its two stable states
while dissipating minuscule amount of energy. However, no efficient and viable
means of computing is proposed so far. Here we show that such single
multiferroic composites can act as universal logic gates for computing
purposes, which we demonstrate by solving the stochastic
Landau-Lifshitz-Gilbert (LLG) equation of magnetization dynamics in the
presence of room-temperature thermal fluctuations. The proposed concept can
overwhelmingly simplify the design of large-scale circuits and portend a highly
dense yet an ultra-low-energy computing paradigm for our future information
processing systems.",1504.03907v1
2015-04-20,"Electric field-induced magnetization switching in interface-coupled multiferroic heterostructures: A highly-dense, non-volatile, and ultra-low-energy computing paradigm","Electric-field induced magnetization switching in multiferroic
magnetoelectric devices is promising for beyond Moore's law computing. We show
here that interface-coupled multiferroic heterostructures, i.e., a
ferroelectric layer coupled with a ferromagnetic layer, are particularly
suitable for highly-dense, non-volatile, and ultra-low-energy computing. By
solving stochastic Landau-Lifshitz-Gilbert equation of magnetization dynamics
in the presence of room-temperature thermal fluctuations, we demonstrate that
error-resilient switching of magnetization is possible in sub-nanosecond delay
while expending a minuscule amount of energy of $\sim$1 attojoule. Such devices
can be operated by drawing energy from the environment without the need for an
external battery.",1504.05572v1
2015-04-23,Quantum Magnets and Matrix Lorenz Systems,"The Landau--Lifshitz--Gilbert equations for the evolution of the
magnetization, in presence of an external torque, can be cast in the form of
the Lorenz equations and, thus, can describe chaotic fluctuations. To study
quantum effects, we describe the magnetization by matrices, that take values in
a Lie algebra. The finite dimensionality of the representation encodes the
quantum fluctuations, while the non-linear nature of the equations can describe
chaotic fluctuations. We identify a criterion, for the appearance of such
non-linear terms. This depends on whether an invariant, symmetric tensor of the
algebra can vanish or not. This proposal is studied in detail for the
fundamental representation of
$\mathfrak{u}(2)=\mathfrak{u}(1)\times\mathfrak{su}(2)$. We find a knotted
structure for the attractor, a bimodal distribution for the largest Lyapunov
exponent and that the dynamics takes place within the Cartan subalgebra, that
does not contain only the identity matrix, thereby can describe the quantum
fluctuations.",1504.06161v1
2015-04-26,Speed of field driven domain walls in nanowires with large transverse magnetic anisotropy,"Recent analytical and numerical work on field driven domain wall propagation
in nanowires has shown that for large transverse anisotropy and sufficiently
large applied fields the Walker profile becomes unstable before the breakdown
field, giving way to a slower stationary domain wall. We perform an asymptotic
expansion of the Landau Lifshitz Gilbert equation for large transverse magnetic
anisotropy and show that the asymptotic dynamics reproduces this behavior. At
low applied field the speed increases linearly with the field and the profile
is the classic Landau profile. Beyond a critical value of the applied field the
domain wall slows down. The appearance of a slower domain wall profile in the
asymptotic dynamics is due to a transition from a pushed to a pulled front of a
reaction diffusion equation.",1504.06865v1
2015-04-27,New Reversal Mode in Exchange Coupled Antiferromagnetic/Ferromagnetic Disks: Distorted Viscous Vortex,"Magnetic vortices have generated intense interest in recent years due to
their unique reversal mechanisms, fascinating topological properties, and
exciting potential applications. Additionally, the exchange coupling of
magnetic vortices to antiferromagnets has also been shown to lead to a range of
novel phenomena and functionalities. Here we report a new magnetization
reversal mode of magnetic vortices in exchange coupled Ir20Mn80/Fe20Ni80
microdots: distorted viscous vortex reversal. Contrary to the previously known
or proposed reversal modes, the vortex is distorted close to the interface and
viscously dragged due to the uncompensated spins of a thin antiferromagnet,
which leads to unexpected asymmetries in the annihilation and nucleation
fields. These results provide a deeper understanding of the physics of exchange
coupled vortices and may also have important implications for applications
involving exchange coupled nanostructures.",1504.07121v1
2015-05-03,Driving magnetic skyrmions with microwave fields,"We show theoretically by numerically solving the Landau-Lifshitz-Gilbert
equation with a classical spin model on a two-dimensional system that both
magnetic skyrmions and skyrmion lattices can be moved with microwave magnetic
fields. The mechanism is enabled by breaking the axial symmetry of the
skyrmion, for example through application of a static in-plane external field.
The net velocity of the skyrmion depends on the frequency and amplitude of the
microwave fields as well as the strength of the in-plane field. The maximum
velocity is found where the frequency of the microwave coincides with the
resonance frequency of the breathing mode of the skyrmions.",1505.00445v2
2015-05-04,Landau-Lifshitz theory of the thermomagnonic torque,"We derive the thermomagnonic torque associated with smooth magnetic textures
subjected to a temperature gradient, in the framework of the stochastic
Landau-Lifshitz-Gilbert equation. Our approach captures on equal footing two
distinct contributions: (1) A local entropic torque that is caused by a
temperature dependence of the effective exchange field, the existence of which
had been previously suggested based on numerics and (2) the well-known
spin-transfer torque induced by thermally-induced magnon flow. The dissipative
components of two torques have the same structure, following a common
phenomenology, but opposite signs, with the twice larger entropic torque
leading to a domain-wall motion toward the hotter region. We compare the
efficiency of the torque-driven domain-wall motion with the recently proposed
Brownian thermophoresis.",1505.00818v1
2015-05-05,Three-dimensional Character of the Magnetization Dynamics in Magnetic Vortex Structures - Hybridization of Flexure Gyromodes with Spin Waves,"Three-dimensional linear spin-wave eigenmodes of a Permalloy disk having
finite thickness are studied by micromagnetic simulations based on the
Landau-Lifshitz-Gilbert equation. The eigenmodes found in the simulations are
interpreted as linear superpositions (hybridizations) of 'approximate'
three-dimensional eigenmodes, which are the fundamental gyromode $G_0$, the
spin-wave modes and the higher-order gyromodes $G_N$ (flexure modes), the
thickness dependence of which is represented by perpendicular standing spin
waves. This hybridization leads to new and surprising dependencies of the mode
frequencies on the disk thickness. The three-dimensional character of the
eigenmodes is essential to explain the recent experimental results on
vortex-core reversal observed in relatively thick Permalloy disks.",1505.01148v2
2015-05-14,A Subset Selection Algorithm for Wireless Sensor Networks,"One of the main challenges facing wireless sensor networks (WSNs) is the
limited power resources available at small sensor nodes. It is therefore
desired to reduce the power consumption of sensors while keeping the distortion
between the source information and its estimate at the fusion centre (FC) below
a specific threshold. In this paper, given the channel state information at the
FC, we propose a subset selection algorithm of sensor nodes to reduce the
average transmission power of the WSN. We assume the channels between the
source and the sensors to be correlated fading channels, modeled by the
Gilbert-Elliott model. We show that when these channels are known at the FC, a
subset of sensors can be selected by the FC such that the received observations
from this subset is sufficient to estimate the source information at the FC
while maintaining the distortion between source information and its estimate
below a specific threshold. Through analyses, we find the probability
distribution of the size of this subset and provide results to evaluate the
power efficiency of our proposed algorithm.",1505.03640v1
2015-05-20,Effect of Transverse Magnetic Field on Dynamics of Current Driven Domain Wall Motion in the Presence of Spin-Hall Effect,"Theoretically, we study the dynamics of a current induced domain wall in the
bi-layer structure consists of a ferromagnetic layer and a non-magnetic metal
layer with strong spin-orbit coupling in the presence of spin-Hall effect. The
analytical expressions for the velocity and width of the domain wall interms of
excitation angle are obtained by solving the Landau-Lifshitz-Gilbert equation
with adiabatic, nonadiabatic and spin Hall effect-spin transfer torques using
Schryers and Walker's method. Numerical results show that the occurance of
polarity switching in the domain wall is observed only above the threshold
current density. The presence of transverse magnetic field along with spin Hall
effect-spin transfer torque enchances the value of the threshold current
density, and the corresponding saturated velocity at the threshold current
density is also increased.",1505.05249v1
2015-05-25,New Explicit Binary Constant Weight Codes from Reed-Solomon Codes,"Binary constant weight codes have important applications and have been
studied for many years. Optimal or near-optimal binary constant weight codes of
small lengths have been determined. In this paper we propose a new construction
of explicit binary constant weight codes from $q$-ary Reed-Solomon codes. Some
of our binary constant weight codes are optimal or new. In particular new
binary constant weight codes $A(64, 10, 8) \geq 4108$ and $A(64, 12, 8) \geq
522$ are constructed. We also give explicitly constructed binary constant
weight codes which improve Gilbert and Graham-Sloane lower bounds in some range
of parameters. An extension to algebraic geometric codes is also presented.",1505.06524v4
2015-06-01,Closing the hierarchy for non-Markovian magnetization dynamics,"We propose a stochastic approach for the description of the time evolution of
the magnetization of nanomagnets, that interpolates between the
Landau--Lifshitz--Gilbert and the Landau--Lifshitz--Bloch approximations, by
varying the strength of the noise. In addition, we take into account the
autocorrelation time of the noise and explore the consequences, when it is
finite, on the scale of the response of the magnetization, i.e. when it may be
described as colored, rather than white, noise and non-Markovian features
become relevant. We close the hierarchy for the moments of the magnetization,
by introducing a suitable truncation scheme, whose validity is tested by direct
numerical solution of the moment equations and compared to the average deduced
from a numerical solution of the corresponding stochastic Langevin equation. In
this way we establish a general framework, that allows both coarse-graining
simulations and faster calculations beyond the truncation approximation used
here.",1506.00544v1
2015-06-02,Spin Superfluidity in the $ν=0$ Quantum Hall State of Graphene,"A proposal to detect the purported canted antiferromagnet order for the
$\nu=0$ quantum Hall state of graphene based on a two-terminal spin transport
setup is theoretically discussed. In the presence of a magnetic field normal to
the graphene plane, a dynamic and inhomogeneous texture of the N\'eel vector
lying within the plane should mediate (nearly dissipationless) superfluid
transport of spin angular momentum polarized along the $z$ axis, which could
serve as a strong support for the canted antiferromagnet scenario. Spin
injection and detection can be achieved by coupling two spin-polarized edge
channels of the $|\nu|=2$ quantum Hall state on two opposite ends of the
$\nu=0$ region. A simple kinetic theory and Onsager reciprocity are invoked to
model the spin injection and detection processes, and the transport of spin
through the antiferromagnet is accounted for using the Landau-Lifshitz-Gilbert
phenomenology.",1506.01061v1
2015-06-05,Multi-reference approach to the calculation of photoelectron spectra including spin-orbit coupling,"X-ray photoelectron spectra provide a wealth of information on the electronic
structure. The extraction of molecular details requires adequate theoretical
methods, which in case of transition metal complexes has to account for effects
due to the multi-configurational and spin-mixed nature of the many-electron
wave function. Here, the Restricted Active Space Self-Consistent Field method
including spin-orbit coupling is used to cope with this challenge and to
calculate valence and core photoelectron spectra. The intensities are estimated
within the frameworks of the Dyson orbital formalism and the sudden
approximation. Thereby, we utilize an efficient computational algorithm that is
based on a biorthonormal basis transformation. The approach is applied to the
valence photoionization of the gas phase water molecule and to the core
ionization spectrum of the $\text{[Fe(H}_2\text{O)}_6\text{]}^{2+}$ complex.
The results show good agreement with the experimental data obtained in this
work, whereas the sudden approximation demonstrates distinct deviations from
experiments.",1506.01826v1
2015-06-10,Parafermionic phases with symmetry-breaking and topological order,"Parafermions are the simplest generalizations of Majorana fermions that
realize topological order. We propose a less restrictive notion of topological
order in 1D open chains, which generalizes the seminal work by Fendley [J.
Stat. Mech., P11020 (2012)]. The first essential property is that the
groundstates are mutually indistinguishable by local, symmetric probes, and the
second is a generalized notion of zero edge modes which cyclically permute the
groundstates. These two properties are shown to be topologically robust, and
applicable to a wider family of topologically-ordered Hamiltonians than has
been previously considered. An an application of these edge modes, we formulate
a new notion of twisted boundary conditions on a closed chain, which guarantees
that the closed-chain groundstate is topological, i.e., it originates from the
topological manifold of degenerate states on the open chain. Finally, we
generalize these ideas to describe symmetry-breaking phases with a
parafermionic order parameter. These exotic phases are condensates of
parafermion multiplets, which generalizes Cooper pairing in superconductors.
The stability of these condensates are investigated on both open and closed
chains.",1506.03455v1
2015-06-17,Magnetic field control of the spin Seebeck effect,"The origin of the suppression of the longitudinal spin Seebeck effect by
applied magnetic fields is studied. We perform numerical simulations of the
stochastic Landau-Lifshitz-Gilbert equation of motion for an atomistic spin
model and calculate the magnon accumulation in linear temperature gradients for
different strengths of applied magnetic fields and different length scales of
the temperature gradient. We observe a decrease of the magnon accumulation with
increasing magnetic field and we reveal that the origin of this effect is a
field dependent change of the frequency distribution of the propagating
magnons. With increasing field the magnonic spin currents are reduced due to a
suppression of parts of the frequency spectrum. By comparison with measurements
of the magnetic field dependent longitudinal spin Seebeck effect in YIG thin
films with various thicknesses, we find that our model describes the
experimental data very well, demonstrating the importance of this effect for
experimental systems.",1506.05290v1
2015-06-18,The pion quasiparticle in the low-temperature phase of QCD,"We investigate the properties of the pion quasiparticle in the
low-temperature phase of two-flavor QCD on the lattice with support from chiral
effective theory. We find that the pion quasiparticle mass is significantly
reduced compared to its value in the vacuum, by contrast with the static
screening mass, which increases with temperature. By a simple argument, near
the chiral limit the two masses are expected to determine the quasiparticle
dispersion relation. Analyzing two-point functions of the axial charge density
at non-vanishing spatial momentum, we find that the predicted dispersion
relation and the residue of the pion pole are simultaneously consistent with
the lattice data at low momentum. The test, based on fits to the correlation
functions, is confirmed by a second analysis using the Backus-Gilbert method.",1506.05732v1
2015-06-23,Bounds on the Parameters of Locally Recoverable Codes,"A locally recoverable code (LRC code) is a code over a finite alphabet such
that every symbol in the encoding is a function of a small number of other
symbols that form a recovering set. In this paper we derive new finite-length
and asymptotic bounds on the parameters of LRC codes. For LRC codes with a
single recovering set for every coordinate, we derive an asymptotic
Gilbert-Varshamov type bound for LRC codes and find the maximum attainable
relative distance of asymptotically good LRC codes. Similar results are
established for LRC codes with two disjoint recovering sets for every
coordinate. For the case of multiple recovering sets we derive a lower bound on
the parameters using expander graph arguments. Finally, we also derive
finite-length upper bounds on the rate and distance of LRC codes with multiple
recovering sets.",1506.07196v2
2015-06-24,From Random Matrix Theory to Coding Theory: Volume of a Metric Ball in Unitary Group,"Volume estimates of metric balls in manifolds find diverse applications in
information and coding theory. In this paper, some new results for the volume
of a metric ball in unitary group are derived via various tools from random
matrix theory. The first result is an integral representation of the exact
volume, which involves a Toeplitz determinant of Bessel functions. The
connection to matrix-variate hypergeometric functions and Szeg\H{o}'s strong
limit theorem lead independently from the finite size formula to an asymptotic
one. The convergence of the limiting formula is exceptionally fast due to an
underlying mock-Gaussian behavior. The proposed volume estimate enables simple
but accurate analytical evaluation of coding-theoretic bounds of unitary codes.
In particular, the Gilbert-Varshamov lower bound and the Hamming upper bound on
cardinality as well as the resulting bounds on code rate and minimum distance
are derived. Moreover, bounds on the scaling law of code rate are found.
Lastly, a closed-form bound on diversity sum relevant to unitary space-time
codes is obtained, which was only computed numerically in literature.",1506.07259v1
2015-06-18,Ultra-low-energy computing paradigm using giant spin Hall devices,"Spin Hall effect converts charge current to spin current, which can exert
spin-torque to switch the magnetization of a nanomagnet. Recently, it is shown
that the ratio of spin current to charge current using spin Hall effect can be
made more than unity by using the areal geometry judiciously, unlike the case
of conventional spin-transfer-torque switching of nanomagnets. This can enable
energy-efficient means to write a bit of information in nanomagnets. Here, we
study the energy dissipation in such spin Hall devices. By solving stochastic
Landau-Lifshitz-Gilbert equation of magnetization dynamics in the presence of
room temperature thermal fluctuations, we show a methodology to simultaneously
reduce switching delay, its variance and energy dissipation, while lateral
dimensions of the spin Hall devices are scaled down.",1506.07863v1
2015-06-18,Separating read and write units in multiferroic devices,"Strain-mediated multiferroic composites, i.e., piezoelectric-magnetostrictive
heterostructures, hold profound promise for energy-efficient computing in
beyond Moore's law era. While reading a bit of information stored in the
magnetostrictive nanomagnets using a magnetic tunnel junction (MTJ), a material
selection issue crops up since magnetostrictive materials in general cannot be
utilized as the free layer of the MTJ. This is an important issue since we need
to achieve a high magnetoresistance for technological applications. We show
here that magnetically coupling the magnetostrictive nanomagnet and the free
layer e.g., utilizing the magnetic dipole coupling between them can circumvent
this issue. By solving stochastic Landau-Lifshitz-Gilbert equation of
magnetization dynamics in the presence of room-temperature thermal
fluctuations, we show that such design can eventually lead to a superior
energy-delay product.",1506.07865v1
2015-06-26,Estimating the Parameters of the Waxman Random Graph,"The Waxman random graph is a generalisation of the simple Erd\H{o}s-R\'enyi
or Gilbert random graph. It is useful for modelling physical networks where the
increased cost of longer links means they are less likely to be built, and thus
less numerous than shorter links. The model has been in continuous use for over
two decades with many attempts to select parameters which match real networks.
In most the parameters have been arbitrarily selected, but there are a few
cases where they have been calculated using a formal estimator. However, the
performance of the estimator was not evaluated in any of these cases. This
paper presents both the first evaluation of formal estimators for the
parameters of these graphs, and a new Maximum Likelihood Estimator with $O(n)$
computational time complexity that requires only link lengths as input.",1506.07974v2
2015-07-07,Rayleigh-Jeans condensation of pumped magnons in thin film ferromagnets,"We show that the formation of a magnon condensate in thin ferromagnetic films
can be explained within the framework of a classical stochastic non-Markovian
Landau-Lifshitz-Gilbert equation where the properties of the random magnetic
field and the dissipation are determined by the underlying phonon dynamics. We
have numerically solved this equation for a tangentially magnetized
yttrium-iron garnet film in the presence of a parallel parametric pumping
field. We obtain a complete description of all stages of the nonequilibrium
time evolution of the magnon gas which is in excellent agreement with
experiments. Our calculation proves that the experimentally observed
condensation of magnons in yttrium-iron garnet at room temperature is a purely
classical phenomenon which should be called Rayleigh-Jeans rather than
Bose-Einstein condensation.",1507.01717v2
2015-07-07,Dynamic Reallocation Problems in Scheduling,"In this paper we look at the problem of scheduling tasks on a
single-processor system, where each task requires unit time and must be
scheduled within a certain time window, and each task can be added to or
removed from the system at any time. On each operation, the system is allowed
to reschedule any tasks, but the goal is to minimize the number of rescheduled
tasks. Our main result is an allocator that maintains a valid schedule for all
tasks in the system if their time windows have constant size and reschedules
O(1/{\epsilon}*log(1/{\epsilon})) tasks on each insertion as {\epsilon}->0,
where {\epsilon} is a certain measure of the schedule flexibility of the
system. We also show that it is optimal for any allocator that works on
arbitrary instances. We also briefly mention a few variants of the problem,
such as if the tasks have time windows of difference sizes, for which we have
an allocator that we conjecture reschedules only 1 task on each insertion if
the schedule flexibility remains above a certain threshold.",1507.01981v2
2015-08-03,Stable oscillation in spin torque oscillator excited by a small in-plane magnetic field,"Theoretical conditions to excite self-oscillation in a spin torque oscillator
consisting of a perpendicularly magnetized free layer and an in-plane
magnetized pinned layer are investigated by analytically solving the
Landau-Lifshitz-Gilbert equation. The analytical relation between the current
and oscillation frequency is derived. It is found that a large amplitude
oscillation can be excited by applying a small field pointing to the direction
anti-parallel to the magnetization of the pinned layer. The validity of the
analytical results is confirmed by comparing with numerical simulation, showing
good agreement especially in a low current region.",1508.00601v1
2015-08-07,Spin Dynamics in Driven Composite Multiferroics,"A spin dynamics approach has been used to study the behavior of the magnetic
spins and the electric pseudo-spins in a 1-D composite multiferroic chain with
a linear magneto-electric coupling at the interface. The response is
investigated with either external magnetic or electric fields driving the
system. The spin dynamics is based on the Landau-Lifshitz-Gilbert equation. A
Gaussian white noise is later added into the dynamic process to include the
thermal effects. The interface requires a closer inspection of the
magneto-electric effects. Thus, we construct a 2-D ladder model to describe the
behavior of the magnetic spins and the electric pseudo-spins with different
magneto-electric couplings.",1508.01584v2
2015-08-11,Analysis of a coupled spin drift-diffusion Maxwell-Landau-Lifshitz system,"The existence of global weak solutions to a coupled spin drift-diffusion and
Maxwell-Landau-Lifshitz system is proved. The equations are considered in a
two-dimensional magnetic layer structure and are supplemented with
Dirichlet-Neumann boundary conditions. The spin drift-diffusion model for the
charge density and spin density vector is the diffusion limit of a spinorial
Boltzmann equation for a vanishing spin polarization constant. The
Maxwell-Landau-Lifshitz system consists of the time-dependent Maxwell equations
for the electric and magnetic fields and of the Landau-Lifshitz-Gilbert
equation for the local magnetization, involving the interaction between
magnetization and spin density vector. The existence proof is based on a
regularization procedure, $L^2$-type estimates, and Moser-type iterations which
yield the boundedness of the charge and spin densities. Furthermore, the free
energy is shown to be nonincreasing in time if the magnetization-spin
interaction constant in the Landau-Lifshitz equation is sufficiently small.",1508.02660v1
2015-08-12,Bounds for codes on pentagon and other cycles,"The capacity of a graph is defined as the rate of exponential grow of
independent sets in the strong powers of the graph. In strong power, an edge
connects two sequences if at each position letters are equal or adjacent. We
consider a variation of the problem where edges in the power graphs are removed
among sequences which differ in more than a fraction $\delta$ of coordinates.
For odd cycles, we derive an upper bound on the corresponding rate which
combines Lov\'asz' bound on the capacity with Delsarte's linear programming
bounds on the minimum distance of codes in Hamming spaces. For the pentagon,
this shows that for $\delta \ge {1-{1\over\sqrt{5}}}$ the Lov\'asz rate is the
best possible, while we prove by a Gilbert-Varshamov-type bound that a higher
rate is achievable for $\delta < {2\over 5}$.
  Communication interpretation of this question is the problem of sending
quinary symbols subject to $\pm 1\mod 5$ disturbance. The maximal communication
rate subject to the zero undetected-error equals capacity of a pentagon. The
question addressed here is how much this rate can be increased if only a
fraction $\delta$ of symbols is allowed to be disturbed",1508.03020v1
2015-08-14,Smoothed Analysis of Dynamic Networks,"We generalize the technique of smoothed analysis to distributed algorithms in
dynamic network models. Whereas standard smoothed analysis studies the impact
of small random perturbations of input values on algorithm performance metrics,
dynamic graph smoothed analysis studies the impact of random perturbations of
the underlying changing network graph topologies. Similar to the original
application of smoothed analysis, our goal is to study whether known strong
lower bounds in dynamic network models are robust or fragile: do they withstand
small (random) perturbations, or do such deviations push the graphs far enough
from a precise pathological instance to enable much better performance? Fragile
lower bounds are likely not relevant for real-world deployment, while robust
lower bounds represent a true difficulty caused by dynamic behavior. We apply
this technique to three standard dynamic network problems with known strong
worst-case lower bounds: random walks, flooding, and aggregation. We prove that
these bounds provide a spectrum of robustness when subjected to
smoothing---some are extremely fragile (random walks), some are moderately
fragile / robust (flooding), and some are extremely robust (aggregation).",1508.03579v1
2015-08-16,The Computational Power of Beeps,"In this paper, we study the quantity of computational resources (state
machine states and/or probabilistic transition precision) needed to solve
specific problems in a single hop network where nodes communicate using only
beeps. We begin by focusing on randomized leader election. We prove a lower
bound on the states required to solve this problem with a given error bound,
probability precision, and (when relevant) network size lower bound. We then
show the bound tight with a matching upper bound. Noting that our optimal upper
bound is slow, we describe two faster algorithms that trade some state
optimality to gain efficiency. We then turn our attention to more general
classes of problems by proving that once you have enough states to solve leader
election with a given error bound, you have (within constant factors) enough
states to simulate correctly, with this same error bound, a logspace TM with a
constant number of unary input tapes: allowing you to solve a large and
expressive set of problems. These results identify a key simplicity threshold
beyond which useful distributed computation is possible in the beeping model.",1508.03859v1
2015-09-02,Topological dynamics and current-induced motion in a skyrmion lattice,"We study the Thiele equation for current-induced motion in a skyrmion lattice
through two soluble models of the pinning potential. Comprised by a Magnus
term, a dissipative term and a pinning force, Thiele's equation resembles
Newton's law but in virtue of the topological character of the first two, it
differs significantly from Newtonian mechanics and because the Magnus force is
dominant, unlike its mechanical counterpart, the Coriolis force, skyrmion
trajectories do not necessarily have mechanical counterparts. This is important
if we are to understand skykrmion dynamics and tap into its potential for
data-storage technology. We identify a pinning threshold velocity for the
one-dimensional potential and for a two-dimensional potential we find a pinning
point and the skyrmion trajectories toward the point are spirals whose
frequency (compare Kepler's second law) and amplitude decay depends only on the
Gilbert constant and potential at the pinning point.",1509.00591v1
2015-09-02,Thermally-Activated Phase Slips in Superfluid Spin Transport in Magnetic Wires,"We theoretically study thermally-activated phase slips in superfluid spin
transport in easy-plane magnetic wires within the stochastic
Landau-Lifshitz-Gilbert phenomenology, which runs parallel to the
Langer-Ambegaokar-McCumber-Halperin theory for thermal resistances in
superconducting wires. To that end, we start by obtaining the exact solutions
for free-energy minima and saddle points. We provide an analytical expression
for the phase-slip rate in the zero spin-current limit, which involves detailed
analysis of spin fluctuations at extrema of the free energy. An experimental
setup of a magnetoeletric circuit is proposed, in which thermal phase slips can
be inferred by measuring nonlocal magnetoresistance.",1509.00904v1
2015-09-11,Comparison between a quantum kinetic theory of spin transfer dynamics in Mn doped bulk semiconductors and its Markov limit for non-zero Mn magnetization,"We investigate the transfer between carrier and Mn spins due to the
s-d-exchange interaction in a Mn doped bulk semiconductor within a microscopic
quantum kinetic theory. We demonstrate that the spin transfer dynamics is
qualitatively different for components of the carrier spin parallel and
perpendicular to the Mn magnetization. From our quantum kinetic equations we
have worked out the corresponding Markov limit which is equivalent to rate
equations based on Fermi's golden rule. The resulting equations resemble the
widely used Landau-Lifshitz-Gilbert-equations, but also describe genuine spin
transfer due to quantum corrections. Although it is known that the Markovian
rate description works well for bulk systems when the initial Mn magnetization
is zero, we find large qualitative deviations from the full quantum kinetic
theory for finite initial Mn magnetizations. These deviations mainly reflect
corrections of higher than leading order in the interaction which are not
accounted for in golden rule-type rates.",1509.03479v1
2015-09-14,Spectral characteristics of time resolved magnonic spin Seebeck effect,"Spin Seebeck effect (SSE) holds promise for new spintronic devices with
low-energy consumption. The underlying physics, essential for a further
progress, is yet to be fully clarified. This study of the time resolved
longitudinal SSE in the magnetic insulator yttrium iron garnet (YIG) concludes
that a substantial contribution to the spin current stems from small
wave-vector subthermal exchange magnons. Our finding is in line with the recent
experiment by S. R. Boona and J. P. Heremans, Phys. Rev. B 90, 064421 (2014).
Technically, the spin-current dynamics is treated based on the
Landau-Lifshitz-Gilbert (LLG) equation also including magnons back-action on
thermal bath, while the formation of the time dependent thermal gradient is
described self-consistently via the heat equation coupled to the magnetization
dynamics",1509.04018v1
2015-09-21,The pion quasiparticle in the low-temperature phase of QCD,"We investigate the properties of the pion quasiparticle in the
low-temperature phase of two-flavor QCD on the lattice with support from chiral
effective theory. We find that the pion quasiparticle mass is significantly
reduced compared to its value in the vacuum, in contrast to the static
screening mass, which increases with temperature. By a simple argument, the two
masses are expected to determine the quasiparticle dispersion relation near the
chiral limit. Analyzing two-point functions of the axial charge density at
non-vanishing spatial momentum, we find that the predicted dispersion relation
and the residue of the pion pole are simultaneously consistent with the lattice
data at low momentum. The test, based on fits to the correlation functions, is
confirmed by a second analysis using the Backus-Gilbert method.",1509.06241v1
2015-10-29,On Differentially Private Online Collaborative Recommendation Systems,"In collaborative recommendation systems, privacy may be compromised, as
users' opinions are used to generate recommendations for others. In this paper,
we consider an online collaborative recommendation system, and we measure
users' privacy in terms of the standard differential privacy. We give the first
quantitative analysis of the trade-offs between recommendation quality and
users' privacy in such a system by showing a lower bound on the best achievable
privacy for any non-trivial algorithm, and proposing a near-optimal algorithm.
From our results, we find that there is actually little trade-off between
recommendation quality and privacy for any non-trivial algorithm. Our results
also identify the key parameters that determine the best achievable privacy.",1510.08546v1
2015-11-05,Non-Markovian magnetization dynamics for uniaxial nanomagnets,"A stochastic approach for the description of the time evolution of the
magnetization of nanomagnets is proposed, that interpolates between the
Landau-Lifshitz-Gilbert and the Landau-Lifshitz-Bloch approximations, by
varying the strength of the noise. Its finite autocorrelation time, i.e. when
it may be described as colored, rather than white, is, also, taken into account
and the consequences, on the scale of the response of the magnetization are
investigated. It is shown that the hierarchy for the moments of the
magnetization can be closed, by introducing a suitable truncation scheme, whose
validity is tested by direct numerical solution of the moment equations and
compared to the averages obtained from a numerical solution of the
corresponding colored stochastic Langevin equation. This comparison is
performed on magnetic systems subject to both an external uniform magnetic
field and an internal one-site uniaxial anisotropy.",1511.01693v1
2015-11-06,Colored-noise magnetization dynamics: from weakly to strongly correlated noise,"Statistical averaging theorems allow us to derive a set of equations for the
averaged magnetization dynamics in the presence of colored (non-Markovian)
noise. The non-Markovian character of the noise is described by a finite
auto-correlation time, tau, that can be identified with the finite response
time of the thermal bath to the system of interest. Hitherto, this model was
only tested for the case of weakly correlated noise (when tau is equivalent or
smaller than the integration timestep). In order to probe its validity for a
broader range of auto-correlation times, a non-Markovian integration model,
based on the stochastic Landau-Lifshitz-Gilbert equation is presented.
Comparisons between the two models are discussed, and these provide evidence
that both formalisms remain equivalent, even for strongly correlated noise
(i.e. tau much larger than the integration timestep).",1511.02008v1
2015-12-17,A self-consistent spin-diffusion model for micromagnetics,"We propose a three-dimensional micromagnetic model that dynamically solves
the Landau-Lifshitz-Gilbert equation coupled to the full spin-diffusion
equation. In contrast to previous methods, we solve for the magnetization
dynamics and the electric potential in a self-consistent fashion. This
treatment allows for an accurate description of magnetization dependent
resistance changes. Moreover, the presented algorithm describes both spin
accumulation due to smooth magnetization transitions and due to material
interfaces as in multilayer structures. The model and its finite-element
implementation are validated by current driven motion of a magnetic vortex
structure. In a second experiment, the resistivity of a magnetic multilayer
structure in dependence of the tilting angle of the magnetization in the
different layers is investigated. Both examples show good agreement with
reference simulations and experiments respectively.",1512.05519v4
2015-12-17,Statics and field-driven dynamics of transverse domain walls in biaxial nanowires under uniform transverse magnetic fields,"In this work, we report analytical results on transverse domain wall (TDW)
statics and field-driven dynamics in quasi one-dimensional biaxial nanowires
under arbitrary uniform transverse magnetic fields (TMFs) based on the
Landau-Lifshitz-Gilbert equation. Without axial driving fields, the static TDW
should be symmetric about its center meanwhile twisted in its azimuthal angle
distribution. By decoupling of polar and azimuthal degrees of freedom, an
approximate solution is provided which reproduces these features to a great
extent. When an axial driving field is applied, the dynamical behavior of a TDW
is viewed as the response of its static profile to external excitations. By
means of the asymptotic expansion method, the TDW velocity in traveling-wave
mode is obtained, which provides the extent and boundary of the
""velocity-enhancement"" effect of TMFs to TDWs in biaxial nanowires. Finally
numerical simulations are performed and strongly support our analytics.",1512.05627v2
2015-12-24,Eroding dipoles and vorticity growth for Euler flows in $ \scriptstyle{\mathbb{R}}^3$ I. Axisymmetric flow without swirl,"A review of analyses based upon anti-parallel vortex structures suggests that
structurally stable vortex structures with eroding circulation may offer a path
to the study of rapid vorticity growth in solutions of Euler's equations in $
\scriptstyle{\mathbb{R}}^3$. We examine here the possible formation of such a
structure in axisymmetric flow without swirl, leading to maximal growth of
vorticity as $t^{4/3}$. Our study suggests that the optimizing flow giving the
$t^{4/3}$ growth mimics an exact solution of Euler's equations representing an
eroding toroidal vortex dipole which locally conserves kinetic energy. The
dipole cross-section is a perturbation of the classical Sadovskii dipole having
piecewise constant vorticity, which breaks the symmetry of closed streamlines.
The structure of this perturbed Sadovskii dipole is analyzed asymptotically at
large times, and its predicted properties are verified numerically.",1512.07898v1
2016-01-11,Reliable spin-transfer torque driven precessional magnetization reversal with an adiabatically decaying pulse,"We show that a slowly decaying current pulse can lead to nearly deterministic
precessional switching in the presence of noise. We consider a biaxial
macrospin, with an easy axis in the plane and a hard axis out-of-the plane,
typical of thin film nanomagnets patterned into asymmetric shapes. Out-of-plane
precessional magnetization orbits are excited with a current pulse with a
component of spin polarization normal to the film plane. By numerically
integrating the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation we show
that thermal noise leads to strong dephasing of the magnetization orbits.
However, an adiabatically decreasing pulse amplitude overwhelmingly leads to
magnetization reversal, with a final state that {\em only} depends on the pulse
polarity, not on the pulse amplitude. We develop an analytic model to explain
this phenomena and to determine the pulse decay time necessary for adiabatic
magnetization relaxation and thus precessional magnetization switching.",1601.02336v1
2016-01-19,Minimal Radius of Magnetic Skyrmions: Statics and Dynamics,"In a broad range of applied magnetic fields and material parameters isolated
magnetic skyrmions condense into skyrmion lattices. While the geometry of
isolated skyrmions and their lattice counterparts strongly depend on field and
Dzyaloshinski-Moriya interaction, this issue has not been adequately addressed
in previous studies. Meanwhile, this information is extremely important for
applications, because the skyrmion size and the interskyrmion distance have to
be tuned for skyrmion based memory and logic devices. In this investigation we
elucidate the size and density-dependent phase diagram showing traditional
phases in field vs. material parameters space by means of Monte-Carlo
simulations on a discrete lattice. The obtained diagram permits us to establish
that, in contrast to the continuum limit, skyrmions on a discrete lattice
cannot be smaller than some critical size and have a very specific shape. These
minimal skyrmions correspond to the micromagnetic configuration at the energy
barrier between the ferromagnetic and the skyrmionic states. Furthermore, we
use atomistic Landau-Lifshitz-Gilbert simulations to study dynamics of the
skyrmion annihilation. It is shown that this procees consists of two stages:
the continuous skyrmion contraction and its discontinuous annihilation. The
detailed analysis of this dynamical process is given.",1601.04898v1
2016-01-20,Limited-Magnitude Error-Correcting Gray Codes for Rank Modulation,"We construct Gray codes over permutations for the rank-modulation scheme,
which are also capable of correcting errors under the infinity-metric. These
errors model limited-magnitude or spike errors, for which only
single-error-detecting Gray codes are currently known. Surprisingly, the
error-correcting codes we construct achieve a better asymptotic rate than that
of presently known constructions not having the Gray property, and exceed the
Gilbert-Varshamov bound. Additionally, we present efficient ranking and
unranking procedures, as well as a decoding procedure that runs in linear time.
Finally, we also apply our methods to solve an outstanding issue with
error-detecting rank-modulation Gray codes (snake-in-the-box codes) under a
different metric, the Kendall $\tau$-metric, in the group of permutations over
an even number of elements $S_{2n}$, where we provide asymptotically optimal
codes.",1601.05218v3
2016-01-20,Many-body effects on graphene conductivity: Quantum Monte Carlo calculations,"Optical conductivity of graphene is studied using Quantum Monte Carlo
calculations. We start from Euclidean current-current correlator and extract
$\sigma (\omega)$ from Green-Kubo relations using Backus-Gilbert method.
Calculations were performed both for long-range interactions and taking into
account only contact term. In both cases we vary interaction strength and study
its influence on optical conductivity. We compare our results with previous
theoretical calculations choosing $\omega \approx \kappa$ thus working in the
region of the plateau in $\sigma(\omega)$ which corresponds to optical
conductivity of Dirac quasiparticles. No dependence of optical conductivity on
interaction strength is observed unless we approach antiferromagnetic phase
transition in case of artificially enhanced contact term. Our results strongly
support previous theoretical studies claimed very weak regularization of
graphene conductivity.",1601.05315v2
2016-02-01,Efficient thermal energy harvesting using nanoscale magnetoelectric heterostructures,"Thermomechanical cycles with a ferroelectric working substance convert heat
to electrical energy. As shown here, magnetoelectrically coupled
ferroelectric/ferromangtic composites (also called multiferroics) add new
functionalities and allow for an efficient thermal energy harvesting at room
temperature by exploiting the pyroelectric effect. By virtue of the
magnetoelectric coupling, external electric and magnetic fields can steer the
operation of these heat engines. Our theoretical predictions are based on a
combination of Landau-Khalatnikov-Tani approach (with a
Ginzburg-Landau-Devonshire potential) to simulate the ferroelectric dynamics
coupled to the magnetic dynamics. The latter is treated via the
electric-polarization-dependent Landau-Lifshitz-Gilbert equation. Performing an
adapted Olsen cycle we show that a multiferroic working substance is
potentially much more superior to sole ferroelectrics, as far as thermal energy
harvesting using pyroelectric effect is concerned. Our proposal holds promise
not only for low-energy consuming devices but also for cooling technology.",1602.00433v1
2016-02-04,A double oracle approach for minmax regret optimization problems with interval data,"In this paper, we provide a generic anytime lower bounding procedure for
minmax regret optimization problems. We show that the lower bound obtained is
always at least as accurate as the lower bound recently proposed by Chassein
and Goerigk (2015). This lower bound can be viewed as the optimal value of a
linear programming relaxation of a mixed integer programming formulation of
minmax regret optimization, but the contribution of the paper is to compute
this lower bound via a double oracle algorithm (McMahan et al., 2003) that we
specify. The double oracle algorithm is designed by relying on a game theoretic
view of robust optimization, similar to the one developed by Mastin et al.
(2015), and it can be efficiently implemented for any minmax regret
optimization problem whose standard version is ""easy"". We describe how to
efficiently embed this lower bound in a branch and bound procedure. Finally, we
apply our approach to the robust shortest path problem. Our numerical results
show a significant gain in the computation times compared to previous
approaches in the literature.",1602.01764v3
2016-02-10,Temperature dependence of the threshold magnetic field for nucleation and domain wall propagation in an inhomogeneous structure with grain boundary,"In order to study the dependence of the coercive force of sintered magnets on
temperature, nucleation and domain wall propagation at the grain boundary are
studied as rate-determining processes of the magnetization reversal phenomena
in magnets consisting of bulk hard magnetic grains contacting via grain
boundaries of a soft magnetic material. These systems have been studied
analytically for a continuum model at zero temperature (A. Sakuma, et al. J.
Mag. Mag. Mat. {\bf 84} 52 (1990)). In the present study, the temperature
dependence is studied by making use of the stochastic Landau-Lifshitz-Gilbert
equation at finite temperatures. In particular, the threshold fields for
nucleation and domain wall propagation are obtained as functions of ratios of
magnetic interactions and anisotropies of the soft and hard magnets for various
temperatures. It was found that the threshold field for domain wall propagation
is robust against thermal fluctuations, while that for nucleation is fragile.
The microscopic mechanisms of the observed temperature dependence are
discussed.",1602.03285v2
2016-02-26,The magnetic monopole and the separation between fast and slow magnetic degrees of freedom,"The Landau-Lifshitz-Gilbert (LLG) equation that describes the dynamics of a
macroscopic magnetic moment finds its limit of validity at very short times.
The reason for this limit is well understood in terms of separation of the
characteristic time scales between slow degrees of freedom (the magnetization)
and fast degrees of freedom. The fast degrees of freedom are introduced as the
variation of the angular momentum responsible for the inertia. In order to
study the effect of the fast degrees of freedom on the precession, we calculate
the geometric phase of the magnetization (i.e. the Hannay angle) and the
corresponding magnetic monopole. In the case of the pure precession (the slow
manifold), a simple expression of the magnetic monopole is given as a function
of the slowness parameter, i.e. as a function of the ratio of the slow over the
fast characteristic times.",1602.08470v1
2016-03-01,Instability analysis of spin torque oscillator with an in-plane magnetized free layer and a perpendicularly magnetized pinned layer,"We study the theoretical conditions to excite a stable self-oscillation in a
spin torque oscillator with an in-plane magnetized free layer and a
perpendicularly magnetized pinned layer in the presence of magnetic field
pointing in an arbitrary direction. The linearized Landau-Lifshitz-Gilbert
(LLG) equation is found to be inapplicable to evaluate the threshold between
the stable and self-oscillation states because the critical current density
estimated from the linearized equation is considerably larger than that found
in the numerical simulation. We derive a theoretical formula of the threshold
current density by focusing on the energy gain of the magnetization from the
spin torque during a time shorter than a precession period. A good agreement
between the derived formula and the numerical simulation is obtained. The
condition to stabilize the out-of-plane self-oscillation above the threshold is
also discussed.",1603.00155v2
2016-03-02,Electric-Field-Induced Spin Resonance in Antiferromagnetic Insulators: Inverse Process of the Dynamical Chiral Magnetic Effect,"We propose a realization of the electric-field-induced antiferromagnetic
resonance. We consider three-dimensional antiferromagnetic insulators with
spin-orbit coupling characterized by the existence of a topological term called
the $\theta$ term. By solving the Landau-Lifshitz-Gilbert equation in the
presence of the $\theta$ term, we show that, in contrast to conventional
methods using ac magnetic fields, the antiferromagnetic resonance state is
realized by ac electric fields along with static magnetic fields. This
mechanism can be understood as the inverse process of the dynamical chiral
magnetic effect, an alternating current generation by magnetic fields. In other
words, we propose a way to electrically induce the dynamical axion field in
condensed matter. We discuss a possible experiment to observe our proposal,
which utilizes the spin pumping from the antiferromagnetic insulator into a
heavy metal contact.",1603.00614v3
2016-03-25,Microscopic theory of spin-orbit torques and skyrmion dynamics,"We formulate a general microscopic approach to spin-orbit torques in thin
ferromagnet/heavy-metal bilayers in linear response to electric current or
electric field. The microscopic theory we develop avoids the notion of spin
currents and spin-Hall effect. Instead, the torques are directly related to a
local spin polarization of conduction electrons, which is computed from
generalized Kubo-St\v{r}eda formulas. A symmetry analysis provides a one-to-one
correspondence between polarization susceptibility tensor components and
different torque terms in the Landau-Lifshitz-Gilbert equation for
magnetization dynamics. The spin-orbit torques arising from Rashba or
Dresselhaus type of spin-orbit interaction are shown to have different
symmetries. We analyze these spin-orbit torques microscopically for a generic
electron model in the presence of an arbitrary smooth magnetic texture. For a
model with spin-independent disorder we find a major cancelation of the
torques. In this case the only remaining torque corresponds to the
magnetization-independent Edelstein effect. Furthermore, our results are
applied to analyze the dynamics of a Skyrmion under the action of electric
current.",1603.07994v2
2016-04-01,Modular Anomalies in (2+1) and (3+1)-D Edge Theories,"The classification of topological phases of matter in the presence of
interactions is an area of intense interest. One possible means of
classification is via studying the partition function under modular transforms,
as the presence of an anomalous phase arising in the edge theory of a
D-dimensional system under modular transformation, or modular anomaly, signals
the presence of a (D+1)-D non-trivial bulk. In this work, we discuss the
modular transformations of conformal field theories along a (2+1)-D and a
(3+1)-D edge. Using both analytical and numerical methods, we show that chiral
complex free fermions in (2+1)-D and (3+1)-D are modular invariant. However, we
show in (3+1)-D that when the edge theory is coupled to a background U(1) gauge
field this results in the presence of a modular anomaly that is the
manifestation of a quantum Hall effect in a (4+1)-D bulk. Using the modular
anomaly, we find that the edge theory of (4+1)-D insulator with spacetime
inversion symmetry(P*T) and fermion number parity symmetry for each spin
becomes modular invariant when 8 copies of the edges exist.",1604.00407v1
2016-04-12,Voltage-driven magnetization switching and spin pumping in Weyl semimetals,"We demonstrate electrical magnetization switching and spin pumping in
magnetically doped Weyl semimetals. The Weyl semimetal is a new class of
topological semimetals, known to have nontrivial coupling between the charge
and the magnetization due to the chiral anomaly. By solving the
Landau-Lifshitz-Gilbert equation for a multilayer structure of a Weyl
semimetal, an insulator and a metal whilst taking the charge-magnetization
coupling into account, magnetization dynamics is analyzed. It is shown that the
magnetization dynamics can be driven by the electric voltage. Consequently,
switching of the magnetization with a pulsed electric voltage can be achieved,
as well as precession motion with an applied oscillating electric voltage. The
effect requires only a short voltage pulse and may therefore be more
energetically efficient for us in spintronics devices compared to conventional
spin transfer torque switching.",1604.03326v1
2016-04-29,Current induced magnetization dynamics and magnetization switching in superconducting ferromagnetic hybrid (F$|$S$|$F) structures,"We investigate the current induced magnetization dynamics and magnetization
switching in an unconventional p-wave superconductor sandwiched between two
misaligned ferromagnetic layers by numerically solving Landau-Lifshitz-Gilbert
equation modified with current induced Slonczewski's spin torque term. A
modified form of Ginzburg-Landau free energy functional has been used for this
purpose. We demonstrated the possibility of current induced magnetization
switching in the spin-triplet ferromagnetic superconducting hybrid structures
with strong easy axis anisotropy and the condition for magnetization reversal.
The switching time for such arrangement is calculated and is found to be highly
dependent on the magnetic configuration along with the biasing current. This
study would be useful in designing practical superconducting-spintronic
devices.",1604.08704v3
2016-05-04,Asymptotic behaviors of Landau-Lifshitz flows from $\Bbb R^2$ to Kähler manifolds,"In this paper, we study the asymptotic behaviors of finite energy solutions
to the Landau-Lifshitz flows from $\Bbb R^2$ into K\""ahler manifolds. First, we
prove that the solution with initial data below the critical energy converges
to a constant map in the energy space as $t\to \infty$ for the compact
Riemannian surface targets. In particular, when the target is a two dimensional
sphere, we prove that the solution to the Landau-Lifshitz-Gilbert equation with
initial data having an energy below $4\pi$ converges to some constant map in
the energy space. Second, for general compact K\""ahler manifolds and initial
data of an arbitrary finite energy, we obtain a bubbling theorem analogous to
the Struwe's results on the heat flows.",1605.01245v2
2016-05-04,Phase transition and uniqueness of levelset percolation,"The main purpose of this paper is to introduce and establish basic results of
a natural extension of the classical Boolean percolation model (also known as
the Gilbert disc model). We replace the balls of that model by a positive
non-increasing attenuation function $l:(0,\infty) \to (0,\infty)$ to create the
random field $\Psi(y)=\sum_{x\in \eta}l(|x-y|),$ where $\eta$ is a homogeneous
Poisson process in ${\mathbb R}^d.$ The field $\Psi$ is then a random potential
field with infinite range dependencies whenever the support of the function $l$
is unbounded.
  In particular, we study the level sets $\Psi_{\geq h}(y)$ containing the
points $y\in {\mathbb R}^d$ such that $\Psi(y)\geq h.$ In the case where $l$
has unbounded support, we give, for any $d\geq 2,$ exact conditions on $l$ for
$\Psi_{\geq h}(y)$ to have a percolative phase transition as a function of $h.$
  We also prove that when $l$ is continuous then so is $\Psi$ almost surely.
Moreover, in this case and for $d=2,$ we prove uniqueness of the infinite
component of $\Psi_{\geq h}$ when such exists, and we also show that the
so-called percolation function is continuous below the critical value $h_c$.",1605.01275v1
2016-06-21,A stochastic model of supercoiling-dependent transcription,"We propose a stochastic model for gene transcription coupled to DNA
supercoiling, where we incorporate the experimental observation that
polymerases create supercoiling as they unwind the DNA helix, and that these
enzymes bind more favourably to regions where the genome is unwound. Within
this model, we show that when the transcriptionally induced flux of
supercoiling increases, there is a sharp crossover from a regime where
torsional stresses relax quickly and gene transcription is random, to one where
gene expression is highly correlated and tightly regulated by supercoiling. In
the latter regime, the model displays transcriptional bursts, waves of
supercoiling, and up-regulation of divergent or bidirectional genes. It also
predicts that topological enzymes which relax twist and writhe should provide a
pathway to down-regulate transcription. This article has been published in
Physical Review Letters, May 2016.",1606.06555v3
2016-06-22,Induced magnetization and power loss for a periodically driven system of ferromagnetic nanoparticles with randomly oriented easy axes,"We study the effect of an elliptically polarized magnetic field on a system
of non-interacting, single-domain ferromagnetic nanoparticles characterized by
a uniform distribution of easy axis directions. Our main goal is to determine
the average magnetization of this system and the power loss in it. In order to
calculate these quantities analytically, we develop a general perturbation
theory for the Landau-Lifshitz-Gilbert (LLG) equation and find its steady-state
solution for small magnetic field amplitudes. On this basis, we derive the
second-order expressions for the average magnetization and power loss,
investigate their dependence on the magnetic field frequency, and analyze the
role of subharmonic resonances resulting from the nonlinear nature of the LLG
equation. For arbitrary amplitudes, the frequency dependence of these
quantities is obtained from the numerical solution of this equation. The impact
of transitions between different regimes of regular and chaotic dynamics of
magnetization, which can be induced in nanoparticles by changing the magnetic
field frequency, is examined in detail.",1606.07131v1
2016-07-20,Performance of Topological Insulator Interconnects,"The poor performance of copper interconnects at the nanometer scale calls for
new material solutions for continued scaling of integrated circuits. We propose
the use of three dimensional time-reversal-invariant topological insulators
(TIs), which host backscattering-protected surface states, for this purpose.
Using semiclassical methods, we demonstrate that nanoscale TI interconnects
have a resistance 1-3 orders of magnitude lower than copper interconnects and
graphene nanoribbons at the nanometer scale. We use the nonequilibrium Green
function (NEGF) formalism to measure the change in conductance of nanoscale TI
and metal interconnects caused by the presence of impurity disorder. We show
that metal interconnects suffer a resistance increase, relative to the clean
limit, in excess of 500% due to disorder while the TI's surface states increase
less than 35% in the same regime.",1607.06131v2
2016-07-21,Rate-distance tradeoff for codes above graph capacity,"The capacity of a graph is defined as the rate of exponential growth of
independent sets in the strong powers of the graph. In the strong power an edge
connects two sequences if at each position their letters are equal or adjacent.
We consider a variation of the problem where edges in the power graphs are
removed between sequences which differ in more than a fraction $\delta$ of
coordinates. The proposed generalization can be interpreted as the problem of
determining the highest rate of zero undetected-error communication over a link
with adversarial noise, where only a fraction $\delta$ of symbols can be
perturbed and only some substitutions are allowed.
  We derive lower bounds on achievable rates by combining graph homomorphisms
with a graph-theoretic generalization of the Gilbert-Varshamov bound. We then
give an upper bound, based on Delsarte's linear programming approach, which
combines Lov\'asz' theta function with the construction used by McEliece et al.
for bounding the minimum distance of codes in Hamming spaces.",1607.06384v1
2016-07-25,A geometric approach to optimal nonequilibrium control: Minimizing dissipation in nanomagnetic spin systems,"Optimal control of nanomagnets has become an urgent problem for the field of
spintronics as technological tools approach thermodynamically determined limits
of efficiency. In complex, fluctuating systems, like nanomagnetic bits, finding
optimal protocols is challenging, requiring detailed information about the
dynamical fluctuations of the controlled system. We provide a new, physically
transparent derivation of a metric tensor for which the length of a protocol is
proportional to its dissipation. This perspective simplifies nonequilibrium
optimization problems by recasting them in a geometric language. We then
describe a numerical method, an instance of geometric minimum action methods,
that enables computation of geodesics even when the number of control
parameters is large. We apply these methods to two models of nanomagnetic bits:
a simple Landau-Lifshitz-Gilbert description of a single magnetic spin
controlled by two orthogonal magnetic fields and a two dimensional Ising model
in which the field is spatially controlled. These calculations reveal
nontrivial protocols for bit erasure and reversal, providing important,
experimentally testable predictions for ultra-low power computing.",1607.07425v1
2016-08-02,"Affordable echelle spectroscopy of the eccentric HAT-P-2, WASP-14 and XO-3 planetary systems with a sub-meter-class telescope","A new off-shelf low-cost echelle spectrograph was installed recently on the
0.6m telescope at the Star\'a Lesn\'a Observatory (Slovakia). In this paper we
describe in details the radial velocity (RV) analysis of the first three
transiting planetary systems, HAT-P-2, WASP-14 and XO-3, observed with this
instrument. Furthermore, we compare our data with the RV data achieved with
echelle spectrographs of other sub-meter-, meter- and two-meter-class
telescopes in terms of their precision. Finally, we investigate the
applicability of our RV data for modeling orbital parameters.",1608.00745v1
2016-08-06,"High current, high efficiency graded band gap perovskite solar cells","Organic-inorganic halide perovskite materials have emerged as attractive
alternatives to conventional solar cell building blocks. Their high light
absorption coefficients and long diffusion lengths suggest high power
conversion efficiencies (PCE),1-5 and indeed perovskite-based single band gap
and tandem solar cell designs have yielded impressive performances.1-16 One
approach to further enhance solar spectrum utilization is the graded band gap,
but this has not been previously achieved for perovskites. In this study, we
demonstrate graded band gap perovskite solar cells with steady-state conversion
efficiencies averaging 18.4%, with a best of 21.7%, all without reflective
coatings. An analysis of the experimental data yields high fill factors of ~75%
and high short circuit current densities up to 42.1 mA/cm2. These cells, which
are based on a novel architecture of two perovskite layers (MASnI3 and
MAPbI3-xBrx), incorporating GaN, monolayer hexagonal boron nitride, and
graphene aerogel, display the highest efficiency ever reported for perovskite
solar cells.",1608.02150v1
2016-08-09,Existence of weak solutions to an evolutionary model for magnetoelasticity,"We prove existence of weak solutions to an evolutionary model derived for
magnetoelastic materials. The model is phrased in Eulerian coordinates and
consists in particular of (i) a Navier-Stokes equation that involves magnetic
and elastic terms in the stress tensor obtained by a variational approach, of
(ii) a regularized transport equation for the deformation gradient and of (iii)
the Landau-Lifshitz-Gilbert equation for the dynamics of the magnetization. The
proof is built on a Galerkin method and a fixed-point argument. It is based on
ideas from F.-H. Lin and the third author for systems modeling the flow of
liquid crystals as well as on methods by G. Carbou and P. Fabrie for solutions
of the Landau-Lifshitz equation.",1608.02992v1
2016-08-16,Magnetic Yoking and Tunable Interactions in FePt-Based Hard/Soft Bilayers,"Assessing and controlling magnetic interactions in magnetic nanostructures
are critical to nanomagnetic and spintronic explorations, such as magnetic
recording media, permanent magnets, magnetic memory and logic devices, etc.
Here we demonstrate an extremely sensitive magnetic yoking effect and tunable
interactions in FePt based hard/soft bilayers mediated by the soft layer. Below
the exchange length, a thin soft layer strongly exchange couples to the
perpendicular moments of the hard layer; above the exchange length, just a few
nanometers thicker, the soft layer moments turn in-plane and act to yoke the
dipolar fields from the adjacent hard layer perpendicular domains. The
evolution from exchange to dipolar-dominated interactions is experimentally
captured by first-order reversal curves, the delta-M method, and polarized
neutron reflectometry, and confirmed by micromagnetic simulations. These
findings demonstrate an effective yoking approach to design and control
magnetic interactions in wide varieties of magnetic nanostructures and devices.",1608.04630v1
2016-08-17,Current-induced instability of domain walls in cylindrical nanowires,"We study the current-driven domain wall (DW) motion in cylindrical nanowires
using micromagnetic simulations by implementing the Landau-Lifshitz-Gilbert
equation with nonlocal spin-transfer torque in a finite difference
micromagnetic package. We find that in the presence of DW Gaussian wave packets
(spin waves) will be generated when the charge current is applied to the system
suddenly. And this effect is excluded when using the local spin-transfer
torque. The existence of spin waves emission indicates that transverse domain
walls can not move arbitrarily fast in cylindrical nanowires although they are
free from the Walker limit. We establish an upper-velocity limit for the DW
motion by analyzing the stability of Gaussian wave packets using the local
spin-transfer torque. Micromagnetic simulations show that the stable region
obtained by using nonlocal spin-transfer torque is smaller than that by using
its local counterpart. This limitation is essential for multiple domain walls
since the instability of Gaussian wave packets will break the structure of
multiple domain walls.",1608.04876v2
2016-08-22,Disorder Induced Phase Transitions of Type-II Weyl Semimetal,"Weyl semimetals are a newly discovered class of materials that host
relativistic massless Weyl fermions as their low-energy bulk excitations. Among
this new class of materials, there exist two general types of semimetals that
are of particular interest: type-I Weyl semimetals, that have broken inversion
or time-reversal symmetry symmetry, and type-II Weyl semimetals, that
additionally breaks Lorentz invariance. In this work, we use Born approximation
to analytically demonstrate that the type-I Weyl semimetals may undergo a
quantum phase transition to type-II Weyl semimetals in the presence of the
finite charge and magnetic disorder when non-zero tilt exist. The phase
transition occurs when the disorder renormalizes the topological mass, thereby
reducing the Fermi velocity near the Weyl cone below the tilt of the cone. We
also confirm the presence of the disorder induced phase transition in Weyl
semimetals using exact diagonalization of a three-dimensional tight-binding
model to calculate the resultant phase diagram of the type-I Weyl semimetal.",1608.06311v1
2016-08-25,Convergence of a mass-lumped finite element method for the Landau-Lifshitz equation,"The dynamics of the magnetic distribution in a ferromagnetic material is
governed by the Landau-Lifshitz equation, which is a nonlinear geometric
dispersive equation with a nonconvex constraint that requires the magnetization
to remain of unit length throughout the domain. In this article, we present a
mass-lumped finite element method for the Landau-Lifshitz equation. This method
preserves the nonconvex constraint at each node of the finite element mesh, and
is energy nonincreasing. We show that the numerical solution of our method for
the Landau-Lifshitz equation converges to a weak solution of the
Landau-Lifshitz-Gilbert equation using a simple proof technique that cancels
out the product of weakly convergent sequences. Numerical tests for both
explicit and implicit versions of the method on a unit square with periodic
boundary conditions are provided for structured and unstructured meshes.",1608.07312v3
2016-08-30,LiRa: A New Likelihood-Based Similarity Score for Collaborative Filtering,"Recommender system data presents unique challenges to the data mining,
machine learning, and algorithms communities. The high missing data rate, in
combination with the large scale and high dimensionality that is typical of
recommender systems data, requires new tools and methods for efficient data
analysis. Here, we address the challenge of evaluating similarity between two
users in a recommender system, where for each user only a small set of ratings
is available. We present a new similarity score, that we call LiRa, based on a
statistical model of user similarity, for large-scale, discrete valued data
with many missing values. We show that this score, based on a ratio of
likelihoods, is more effective at identifying similar users than traditional
similarity scores in user-based collaborative filtering, such as the Pearson
correlation coefficient. We argue that our approach has significant potential
to improve both accuracy and scalability in collaborative filtering.",1608.08646v2
2016-09-09,An Empirical Study of Cycle Toggling Based Laplacian Solvers,"We study the performance of linear solvers for graph Laplacians based on the
combinatorial cycle adjustment methodology proposed by
[Kelner-Orecchia-Sidford-Zhu STOC-13]. The approach finds a dual flow solution
to this linear system through a sequence of flow adjustments along cycles. We
study both data structure oriented and recursive methods for handling these
adjustments.
  The primary difficulty faced by this approach, updating and querying long
cycles, motivated us to study an important special case: instances where all
cycles are formed by fundamental cycles on a length $n$ path. Our methods
demonstrate significant speedups over previous implementations, and are
competitive with standard numerical routines.",1609.02957v1
2016-09-21,Harmonic space analysis of pulsar timing array redshift maps,"In this paper, we propose a new framework for treating the angular
information in the pulsar timing array response to a gravitational wave
background based on standard cosmic microwave background techniques. We
calculate the angular power spectrum of the all-sky gravitational redshift
pattern induced at the earth for both a single bright source of gravitational
radiation and a statistically isotropic, unpolarized Gaussian random
gravitational wave background. The angular power spectrum is the harmonic
transform of the Hellings & Downs curve. We use the power spectrum to examine
the expected variance in the Hellings & Downs curve in both cases. Finally, we
discuss the extent to which pulsar timing arrays are sensitive to the angular
power spectrum and find that the power spectrum sensitivity is dominated by the
quadrupole anisotropy of the gravitational redshift map.",1609.06758v2
2016-09-22,Ultrafast generation of skyrmionic defects with vortex beams: printing laser profiles on magnets,"Controlling electric and magnetic properties of matter by laser beams is
actively explored in the broad region of condensed matter physics, including
spintronics and magneto-optics. Here we theoretically propose an application of
optical and electron vortex beams carrying intrinsic orbital angular momentum
to chiral ferro- and antiferro- magnets. We analyze the time evolution of spins
in chiral magnets under irradiation of vortex beams, by using the stochastic
Landau-Lifshitz-Gilbert equation. We show that beam-driven nonuniform
temperature lead to a class of ring-shaped magnetic defects, what we call
skyrmion multiplex, as well as conventional skyrmions. We discuss the proper
beam parameters and the optimal way of applying the beams for the creation of
these topological defects. Our findings provide an ultrafast scheme of
generating topological magnetic defects in a way applicable to both metallic
and insulating chiral (anti-) ferromagnets.",1609.06816v3
2016-10-02,Syntactic Structures and Code Parameters,"We assign binary and ternary error-correcting codes to the data of syntactic
structures of world languages and we study the distribution of code points in
the space of code parameters. We show that, while most codes populate the lower
region approximating a superposition of Thomae functions, there is a
substantial presence of codes above the Gilbert-Varshamov bound and even above
the asymptotic bound and the Plotkin bound. We investigate the dynamics induced
on the space of code parameters by spin glass models of language change, and
show that, in the presence of entailment relations between syntactic parameters
the dynamics can sometimes improve the code. For large sets of languages and
syntactic data, one can gain information on the spin glass dynamics from the
induced dynamics in the space of code parameters.",1610.00311v1
2016-10-03,Linear dynamics of classical spin as Möbius transformation,"Although the overwhelming majority of natural processes occurs far from the
equilibrium, general theoretical approaches to non-equilibrium phase
transitions remain scarce. Recent breakthroughs introducing description of open
dissipative systems in terms of non-Hermitian quantum mechanics allowed to
identify a class of non-equilibrium phase transitions associated with the loss
of combined parity (reflection) and time-reversal symmetries. Here we report
that time evolution of a single classical spin (e.g. monodomain ferromagnet)
governed by the Landau-Lifshitz-Gilbert-Slonczewski equation in absence of
higher-order anisotropy terms is described by a M\""{o}bius transformation in
complex stereographic coordinates. We identify the \textit{parity-time}
symmetry-breaking phase transition occurring in spin-transfer torque-driven
linear spin systems as a transition between hyperbolic and loxodromic classes
of M\""{o}bius transformations, with the critical point of the transition
corresponding to the parabolic transformation. This establishes the
understanding of non-equilibrium phase transitions as topological transitions
in configuration space.",1610.00762v1
2016-10-11,Self-Consistent Field Theory studies of the thermodynamics and quantum spin dynamics of magnetic Skyrmions,"A self-consistent field theory is introduced and used to investigate the
thermodynamics and spin dynamics of an $S = 1$ quantum spin system with a
magnetic Skyrmion. The temperature dependence of the Skyrmion profile as well
as the phase diagram are calculated. It is shown that the Skyrmion carries a
phase transition to the ferromagnetic phase of first order with increasing
temperature, while the magnetization of the surrounding ferromagnet undergoes a
phase transition of second order when changing to the paramagnetic phase.
Furthermore, the electric field driven annihilation process of the Skyrmion is
described quantum mechanical by solving the time dependent Schr\""odinger
equation. The results are compared with the trajectories of the semi-classical
description of the spin expectation values using a differential equation
similar to the classical Landau-Lifshitz-Gilbert equation.",1610.03191v2
2016-10-12,Variational approximation of functionals defined on 1-dimensional connected sets: the planar case,"In this paper we consider variational problems involving 1-dimensional
connected sets in the Euclidean plane, such as the classical Steiner tree
problem and the irrigation (Gilbert-Steiner) problem. We relate them to optimal
partition problems and provide a variational approximation through
Modica-Mortola type energies proving a $\Gamma$-convergence result. We also
introduce a suitable convex relaxation and develop the corresponding numerical
implementations. The proposed methods are quite general and the results we
obtain can be extended to $n$-dimensional Euclidean space or to more general
manifold ambients, as shown in the companion paper [11].",1610.03839v5
2016-10-24,"Field-free, spin-current control of magnetization in non-collinear chiral antiferromagnets","Non-collinear chiral antiferromagnets like Mn3Sn and Mn3Ge are known to show
gigantic anomalous Hall response depending on the orientation of their inverse
chiral magnetic order of Mn atoms in Kagome layers. Here we study the stability
of such magnetic order in the absence of external magnetic fields on the basis
of stochastic Landau-Lifshitz-Gilbert equation for a simplified two-dimensional
model of these materials. We find that even without external magnetic fields,
the ordered state is, once formed, highly stable against thermal fluctuations.
Moreover, we show that if Mn spins are well confined inside each Kagome layers,
by injecting spin-current using spin-filtering effect of ferromagnetic metals,
we can control the in-plane magnetic structure in a field free way.",1610.07615v2
2016-11-04,Struwe-like solutions for the Stochastic Harmonic Map Flow,"We give a new result on the well-posedness of the two-dimensional Stochastic
Harmonic Map flow, whose study is motivated by the Landau-Lifshitz-Gilbert
model for thermal fluctuations in micromagnetics. We construct strong solutions
that belong locally to the spaces $C([s,t);H^1)\cap L^2([s,t);H^2)$, $0\leq
s<t\leq T$. It that sense, these maps are a counterpart of the so-called
""Struwe solutions"" of the deterministic model. We also give a natural criterion
of uniqueness that extends A.\ Freire's Theorem to the stochastic case. Both
results are obtained under the condition that the noise term has a trace-class
covariance in space.",1611.01565v2
2016-11-07,Compactness results for static and dynamic chiral skyrmions near the conformal limit,"We examine lower order perturbations of the harmonic map prob- lem from
$\mathbb{R}^2$ to $\mathbb{S}^2$ including chiral interaction in form of a
helicity term that prefers modulation, and a potential term that enables decay
to a uniform background state. Energy functionals of this type arise in the
context of magnetic systems without inversion symmetry. In the almost conformal
regime, where these perturbations are weighted with a small parameter, we
examine the existence of relative minimizers in a non-trivial homotopy class,
so-called chiral skyrmions, strong compactness of almost minimizers, and their
asymptotic limit. Finally we examine dynamic stability and compactness of
almost minimizers in the context of the Landau-Lifshitz-Gilbert equation
including spin-transfer torques arising from the interaction with an external
current.",1611.01984v1
2016-11-08,A variational method for spectral functions,"The Generalized Eigenvalue Problem (GEVP) has been used extensively in the
past in order to reliably extract energy levels from time-dependent Euclidean
correlators calculated in Lattice QCD. We propose a formulation of the GEVP in
frequency space. Our approach consists of applying the model-independent
Backus-Gilbert method to a set of Euclidean two-point functions with common
quantum numbers. A GEVP analysis in frequency space is then applied to a matrix
of estimators that allows us, among other things, to obtain particular linear
combinations of the initial set of operators that optimally overlap to
different local regions in frequency. We apply this method to lattice data from
NRQCD. This approach can be interesting both for vacuum physics as well as for
finite-temperature problems.",1611.02499v1
2016-11-14,Hidden fluctuations close to a quantum bicritical point,"In this paper we describe physical properties arising in the vicinity of two
coupled quantum phase transitions. We consider a phenomenological model based
on two scalar order parameter fields locally coupled biquadratically and having
a common quantum critical point as a function of a quantum tuning parameter
such as pressure or magnetic field. A self-consistent treatment suggests that
the uniform static susceptibilities of the two order parameter fields may have
the same qualitative form at low temperature even where the forms differ
sharply in the absence of the biquadratic coupling. The possible limitations of
the self-consistent analysis leading to this prediction are considered.",1611.04621v2
2016-11-22,New bounds of permutation codes under Hamming metric and Kendall's $τ$-metric,"Permutation codes are widely studied objects due to their numerous
applications in various areas, such as power line communications, block
ciphers, and the rank modulation scheme for flash memories. Several kinds of
metrics are considered for permutation codes according to their specific
applications. This paper concerns some improvements on the bounds of
permutation codes under Hamming metric and Kendall's $\tau$-metric
respectively, using mainly a graph coloring approach. Specifically, under
Hamming metric, we improve the Gilbert-Varshamov bound asymptotically by a
factor $n$, when the minimum Hamming distance $d$ is fixed and the code length
$n$ goes to infinity. Under Kendall's $\tau$-metric, we narrow the gap between
the known lower bounds and upper bounds. Besides, we also obtain some sporadic
results under Kendall's $\tau$-metric for small parameters.",1611.07188v1
2016-12-01,Encoding orbital angular momentum of light in magnets,"Breaking the diffraction limit and focusing laser beams to subwavelength
scale are becoming possible with the help of recent developments in plasmonics.
Such subwavelength focusing bridges different length scales of laser beams and
matter. Here we consider optical vortex, or laser beam carrying orbital angular
momentum (OAM) and discuss potential subwavelength magnetic phenomena induced
by such laser. On the basis of numerical calculations using
Landau-Lifshitz-Gilbert equation, we propose two OAM-dependent phenomena
induced by optical vortices, generation of radially anisotropic spin waves and
generation of topological defects in chiral magnets. The former could lead to
the transient topological Hall effect through the laser-induced scalar spin
chirality, and the latter reduces the timescale of generating skyrmionic
defects by several orders compared to other known means.",1612.00176v2
2016-12-26,Credibility and Dynamics of Collective Attention,"Today, social media provide the means by which billions of people experience
news and events happening around the world. However, the absence of traditional
journalistic gatekeeping allows information to flow unencumbered through these
platforms, often raising questions of veracity and credibility of the reported
information. Here we ask: How do the dynamics of collective attention directed
toward an event reported on social media vary with its perceived credibility?
By examining the first large-scale, systematically tracked credibility database
of public Twitter messages (47M messages corresponding to 1,138 real-world
events over a span of three months), we established a relationship between the
temporal dynamics of events reported on social media and their associated level
of credibility judgments. Representing collective attention by the aggregate
temporal signatures of an event reportage, we found that the amount of
continued attention focused on an event provides information about its
associated levels of perceived credibility. Events exhibiting sustained,
intermittent bursts of attention were found to be associated with lower levels
of perceived credibility. In other words, as more people showed interest during
moments of transient collective attention, the associated uncertainty
surrounding these events also increased.",1612.08440v1
2017-01-07,Modulation calorimetry in diamond anvil cells I: heat flow models,"Numerical simulations of heat transport in diamond anvil cells reveal a
possibility for absolute measurements of specific heat via high-frequency
modulation calorimetry. Such experiments could reveal and help characterize
temperature-driven phase transitions at high-pressure, such as melting, the
glass transition, magnetic and electric orderings, or superconducting
transitions. Specifically, we show that calorimetric information of a sample
cannot be directly extracted from measurements at frequencies slower than the
timescale of conduction to the diamond anvils (10s to 100s of kHz) since the
experiment is far from adiabatic. At higher frequencies, laser-heating
experiments allow relative calorimetric measurements, where changes in specific
heat of the sample are discriminated from changes in other material properties
by scanning the heating frequency from $\sim 1$ MHz to 1 GHz. But laser-heating
generates large temperature gradients in metal samples, preventing absolute
heat capacities to be inferred. High-frequency Joule heating, on the other
hand, allows accurate, absolute specific heat measurements if it can be
performed at high-enough frequency: assuming a thin layer of KBr insulation,
the specific heat of a 5 $\mu$m-thick metal sample heated at 100 kHz, 1 MHz, or
10 MHz frequency would be measured with 30%, 8% or 2% accuracy, respectively.",1701.01872v1
2017-01-08,Topological crystalline superconductors with linearly and projectively represented $C_{n}$ symmetry,"We study superconductors with $n$-fold rotational invariance both in the
presence and in the absence of spin-orbit interactions. More specifically, we
classify the non-interacting Hamiltonians by defining a series of $Z$-numbers
for the Bogoliubov-de Gennes (BdG) symmetry classes of the Altland-Zimbauer
classification of random matrices in $1$D, $2$D, and $3$D in the presence of
discrete rotational invariance. Our analysis emphasizes the important role
played by the angular momentum of the Cooper pairs in the system: for pairings
of nonzero angular momentum, the rotation symmetry may be represented
projectively, and a projective representation of rotation symmetry may have
anomalous properties, including the anti-commutation with the time-reversal
symmetry. In 1D and 3D, we show how an $n$-fold axis enhances the topological
classification and give additional topological numbers; in 2D, we establish a
relation between the Chern number (in class D and CI) and the eigenvalues of
rotation symmetry at high-symmetry points. For each nontrivial class in 3D, we
write down a minimal effective theory for the surface Majorana states.",1701.01944v1
2017-01-09,Temperature dependence of shear viscosity of $SU(3)$--gluodynamics within lattice simulation,"In this paper we study the shear viscosity temperature dependence of
$SU(3)$--gluodynamics within lattice simulation. To do so, we measure the
correlation functions of energy-momentum tensor in the range of temperatures
$T/T_c\in [0.9, 1.5]$. To extract the values of shear viscosity we used two
approaches. The first one is to fit the lattice data with some physically
motivated ansatz for the spectral function with unknown parameters and then
determine shear viscosity. The second approach is to apply the Backus-Gilbert
method which allows to extract shear viscosity from the lattice data
nonparametrically. The results obtained within both approaches agree with each
other. Our results allow us to conclude that within the temperature range
$T/T_c \in [0.9, 1.5]$ SU(3)--gluodynamics reveals the properties of a strongly
interacting system, which cannot be described perturbatively, and has the ratio
$\eta/s$ close to the value ${1}/{4\pi}$ in $N = 4$ Supersymmetric Yang-Mills
theory.",1701.02266v2
2017-01-25,Statistical Decoding,"The security of code-based cryptography relies primarily on the hardness of
generic decoding with linear codes. The best generic decoding algorithms are
all improvements of an old algorithm due to Prange: they are known under the
name of information set decoding techniques (ISD). A while ago a generic
decoding algorithm which does not belong to this family was proposed:
statistical decoding. It is a randomized algorithm that requires the
computation of a large set of parity-check equations of moderate weight. We
solve here several open problems related to this decoding algorithm.
  We give in particular the asymptotic complexity of this algorithm, give a
rather efficient way of computing the parity-check equations needed for it
inspired by ISD techniques and give a lower bound on its complexity showing
that when it comes to decoding on the Gilbert-Varshamov bound it can never be
better than Prange's algorithm.",1701.07416v2
2017-02-03,Enhanced Spin Conductance of a Thin-Film Insulating Antiferromagnet,"We investigate spin transport by thermally excited spin waves in an
antiferromagnetic insulator. Starting from a stochastic Landau-Lifshitz-Gilbert
phenomenology, we obtain the out-of-equilibrium spin-wave properties. In linear
response to spin biasing and a temperature gradient, we compute the spin
transport through a normal metal$|$antiferromagnet$|$normal metal
heterostructure. We show that the spin conductance diverges as one approaches
the spin-flop transition; this enhancement of the conductance should be readily
observable by sweeping the magnetic field across the spin-flop transition. The
results from such experiments may, on the one hand, enhance our understanding
of spin transport near a phase transition, and on the other be useful for
applications that require a large degree of tunability of spin currents. In
contrast, the spin Seebeck coefficient does not diverge at the spin-flop
transition. Furthermore, the spin Seebeck coefficient is finite even at zero
magnetic field, provided that the normal metal contacts break the symmetry
between the antiferromagnetic sublattices.",1702.00975v2
2017-02-07,Giant-spin nonlinear response theory of magnetic nanoparticle hyperthermia: a field dependence study,"Understanding high-field amplitude electromagnetic heat loss phenomena is of
great importance, in particular in the biomedical field, since the
heat-delivery treatment plans might rely on analytical models that are only
valid at low field amplitudes. Here, we develop a nonlinear response model
valid for single- domain nanoparticles of larger particle sizes and higher
field amplitudes in comparison to linear response theory. A nonlinear
magnetization expression and a generalized heat loss power equation are
obtained and compared with the exact solution of the stochastic
Landau-Lifshitz-Gilbert equation assuming the giant-spin hypothesis. The model
is valid within the hyperthermia therapeutic window and predicts a shift of
optimum particle size and distinct heat loss field amplitude exponents.
Experimental hyperthermia data with distinct ferrite-based nanoparticles, as
well as third harmonic magnetization data supports the nonlinear model, which
also has implications for magnetic particle imaging and magnetic thermometry.",1702.02022v1
2017-02-17,Spin-orbit torque in MgO/CoFeB/Ta/CoFeB/MgO symmetric structure with interlayer antiferromagnetic coupling,"Spin current generated by spin Hall effect in the heavy metal would diffuse
up and down to adjacent ferromagnetic layers and exert torque on their
magnetization, called spin-orbit torque. Antiferromagnetically coupled
trilayers, namely the so-called synthetic antiferromagnets (SAF), are usually
employed to serve as the pinned layer of spintronic devices based on spin
valves and magnetic tunnel junctions to reduce the stray field and/or increase
the pinning field. Here we investigate the spin-orbit torque in
MgO/CoFeB/Ta/CoFeB/MgO perpendicularly magnetized multilayer with interlayer
antiferromagnetic coupling. It is found that the magnetization of two CoFeB
layers can be switched between two antiparallel states simultaneously. This
observation is replicated by the theoretical calculations by solving
Stoner-Wohlfarth model and Landau-Lifshitz-Gilbert equation. Our findings
combine spin-orbit torque and interlayer coupling, which might advance the
magnetic memories with low stray field and low power consumption.",1702.05331v1
2017-02-19,Multiscale simulations of topological transformations in magnetic Skyrmions,"Magnetic Skyrmions belong to the most interesting spin structures for the
development of future information technology as they have been predicted to be
topologically protected. To quantify their stability, we use an innovative
multiscale approach to simulating spin dynamics based on the
Landau-Lifshitz-Gilbert equation. The multiscale approach overcomes the
micromagnetic limitations that have hindered realistic studies using
conventional techniques. We first demonstrate how the stability of a Skyrmion
is influenced by the refinement of the computational mesh and reveal that
conventionally employed traditional micromagnetic simulations are inadequate
for this task. Furthermore, we determine the stability quantitatively using our
multiscale approach. As a key operation for devices, the process of
annihilating a Skyrmion by exciting it with a spin polarized current pulse is
analyzed, showing that Skyrmions can be reliably deleted by designing the pulse
shape.",1702.05767v1
2017-02-21,Spin texture motion in antiferromagnetic and ferromagnetic nanowires,"We propose a Hamiltonian dynamics formalism for the current and magnetic
field driven dynamics of ferromagnetic and antiferromagnetic domain walls in
one dimensional systems. To demonstrate the power of this formalism, we derive
Hamilton equations of motion via Poisson brackets based on the
Landau-Lifshitz-Gilbert phenomenology, and add dissipative dynamics via the
evolution of the energy. We use this approach to study current induced domain
wall motion and compute the drift velocity. For the antiferromagnetic case, we
show that a nonzero magnetic moment is induced in the domain wall, which
indicates that an additional application of a magnetic field would influence
the antiferromagnetic domain-wall dynamics. We consider both cases of the
magnetic field being parallel and transverse to the N{\'e}el field. Based on
this formalism, we predict an orientation switch mechanism for
antiferromagnetic domain walls which can be tested with the recently discovered
N{\'e}el spin orbit torques.",1702.06274v1
2017-02-23,Fulde-Ferrell States in Inverse Proximity Coupled Magnetically-Doped Topological Heterostructures,"We study the superconducting properties of the thin film BCS superconductor
proximity coupled to a magnetically doped topological insulator(TI). Using the
mean field theory, we show that Fulde-Ferrell(FF) pairing can be induced in the
conventional superconductor by having inverse proximity effect(IPE). This
occurs when the IPE of the TI to the superconductor is large enough that the
normal band of the superconductor possesses a proximity induced spin-orbit
coupling and magnetization. We find that the energetics of the different
pairings are dependent on the coupling strength between the TI and the BCS
superconductor and the thickness of the superconductor film. As the thickness
of the superconductor film is increased, we find a crossover from the FF
pairing to the BCS pairing phase. This is a consequence of the increased number
of the superconducting bands, which favor the BCS pairing, implying that the FF
phase can only be observed in the thin-film limit. In addition, we also propose
transport experiments that show distinct signatures of the FF phase.",1702.07383v1
2017-02-27,Quantum critical scaling and fluctuations in Kondo lattice materials,"We propose a new phenomenological framework for three classes of Kondo
lattice materials that incorporates the interplay between the fluctuations
associated with the antiferromagnetic quantum critical point and those produced
by the hybridization quantum critical point that marks the end of local moment
behavior. We show that these fluctuations give rise to two distinct regions of
quantum critical scaling: hybridization fluctuations are responsible for the
logarithmic scaling in the density of states of the heavy electron Kondo liquid
that emerges below the coherence temperature T*; while the unconventional power
law scaling in the resistivity that emerges at lower temperatures below T_QC
may reflect the combined effects of hybridization and antiferromagnetic quantum
critical fluctuations. Our framework is supported by experimental measurements
on CeCoIn5, CeRhIn5 and other heavy electron materials.",1702.08132v2
2017-03-09,On linear complementary-dual multinegacirculant codes,"Linear codes with complementary-duals (LCD) are linear codes that intersect
with their dual trivially. Multinegacirculant codes of index $2$ that are LCD
are characterized algebraically and some good codes are found in this family.
Exact enumeration is performed for indices 2 and 3, and for all indices $t$ for
a special case of the co-index by using their concatenated structure.
Asymptotic existence results are derived for the special class of such codes
that are one-generator and have co-index a power of two by means of Dickson
polynomials. This shows that there are infinite families of LCD
multinegacirculant codes with relative distance satisfying a modified
Varshamov-Gilbert bound.",1703.03115v1
2017-03-16,Electronic transport in a two-dimensional superlattice engineered via self-assembled nanostructures,"Nanoscience offers a unique opportunity to design modern materials from the
bottom up, via low-cost, solution processed assembly of nanoscale building
blocks. These systems promise electronic band structure engineering using not
only the nanoscale structural modulation, but also the mesoscale spatial
patterning, although experimental realization of the latter has been
challenging. Here we design and fabricate a new type of artificial solid by
stacking graphene on a self-assembled, nearly periodic array of nanospheres,
and experimentally observe superlattice miniband effects. We find conductance
dips at commensurate fillings of charge carriers per superlattice unit cell,
which are key features of minibands that are induced by the quasi-periodic
deformation of the graphene lattice. These dips become stronger when the
lattice strain is larger. Using a tight-binding model, we simulate the effect
of lattice deformation as a parameter affecting the inter-atomic hopping
integral, and confirm the superlattice transport behavior. This 2D
material-nanoparticle heterostructure enables facile band structure engineering
via self-assembly, promising for large area electronics and optoelectronics
applications.",1703.05689v3
2017-03-27,Dipolar ferromagnetism in three-dimensional superlattices of nanoparticles,"A series of atomistic finite temperature simulations on a model of an FCC
lattice of maghemite nanoparticles using the stochastic Landau-Lifshitz-Gilbert
(sLLG) equation are presented. The model exhibits a ferromagnetic transition
that is in good agreement with theoretical expectations. The simulations also
reveal an orientational disorder in the orientational order parameter for $T <
0.5 T_c$ due to pinning of the surface domain walls of the nanoparticles by
surface vacancies. The extent of the competition between surface pinning and
dipolar interactions provides support for the conjecture that recent
measurements on systems of FCC superlattices of iron-oxide nanoparticles
provide evidence for dipolar ferromagnetism is discussed.",1703.09290v1
2017-03-06,Ultralow Energy Analog Straintronics Using Multiferroic Composites,"Electric field-induced magnetization switching in multiferroics holds
profound promise for ultra-low-energy computing in beyond Moore's law era.
Bistable nanomagnets in the multiferroics are usually deemed to be suitable for
storing a binary bit of information and switching between the two stable states
allows us to process digital information. However, it requires to process
continuous analog signals too for seamless integration of nanomagnetic devices
in our future information processing systems. Here, we show that it is possible
to harness the analog nature in the magnetostrictive nanomagnets, contrary to
writing a digital bit of information. By solving stochastic
Landau-Lifshitz-Gilbert equation of magnetization dynamics at room-temperature,
we demonstrate such possibility and show that there exists a transistor-like
high-gain region in the input-output characteristics of the magnetostrictive
nanomagnets in strain-mediated multiferroic composites. This can be the basis
of ultra-low-energy analog and mixed signal precessing in our future
information processing systems and it eliminates the requirement of using
charge-based transistors.",1704.02337v1
2017-04-12,The gradient condition and the contribution of the dynamical part of Green-Kubo formula to the diffusion coefficient,"In the diffusive hydrodynamic limit for a symmetric interacting particle
system (such as the exclusion process, the zero range process, the stochastic
Ginzburg-Landau model, the energy exchange model), a possibly non-linear
diffusion equation is derived as the hydrodynamic equation. The bulk diffusion
coefficient of the limiting equation is given by Green-Kubo formula and it can
be characterized by a variational formula. In the case the system satisfies the
gradient condition, the variational problem is explicitly solved and the
diffusion coefficient is given from the Green-Kubo formula through a static
average only. In other words, the contribution of the dynamical part of
Green-Kubo formula is 0. In this paper, we consider the converse, namely if the
contribution of the dynamical part of Green-Kubo formula is 0, does it imply
the system satisfies the gradient condition or not. We show that if the
equilibrium measure {\mu} is product and {L^2} space of its single site
marginal is separable, then the converse also holds. As an application of the
result, we consider a class of stochastic models for energy transport studied
by Gaspard and Gilbert in [1, 2], where the exact problem is discussed for this
specific model.",1704.03745v2
2017-04-12,The Origin of Sequential Chromospheric Brightenings,"Sequential chromospheric brightenings (SCBs) are often observed in the
immediate vicinity of erupting flares and are associated with coronal mass
ejections. Since their initial discovery in 2005, there have been several
subsequent investigations of SCBs. These studies have used differing detection
and analysis techniques, making it difficult to compare results between
studies. This work employs the automated detection algorithm of Kirk et al.
(Solar Phys. 283, 97, 2013) to extract the physical characteristics of SCBs in
11 flares of varying size and intensity. We demonstrate that the magnetic
substructure within the SCB appears to have a significantly smaller area than
the corresponding H-alpha emission. We conclude that SCBs originate in the
lower corona around 0.1 R_sun above the photosphere, propagate away from the
flare center at speeds of 35 - 85 km/s, and have peak photosphere magnetic
intensities of 148 +/- 2.9 G. In light of these measurements, we infer SCBs to
be distinctive chromospheric signatures of erupting coronal mass ejections.",1704.03828v1
2017-04-12,Relationships Between Sequential Chromospheric Brightening and the Corona,"The chromosphere is a complex region that acts as an intermediary between the
magnetic flux emergence in the photosphere and the magnetic features seen in
the corona. Large eruptions in the chromosphere of flares and filaments are
often accompanied by ejections of coronal mass off the sun. Several studies
have observed fast-moving progressive trains of compact bright points (called
Sequential Chromospheric Brightenings or SCBs) streaming away from
chromospheric flares that also produce a coronal mass ejection (CME). In this
work, we review studies of SCBs and search for commonalties between them. We
place these findings into a larger context with contemporary chromospheric and
coronal observations. SCBs are fleeting indicators of the solar atmospheric
environment as it existed before their associated eruption. Since they appear
at the very outset of a flare eruption, SCBs are good early indication of a CME
measured in the chromosphere.",1704.03835v1
2017-05-16,Constructive mathematics,"This text is reproduced with the kind permission of Fran\c{c}ois Ap\'ery.
  It was originally edited by Fran\c{c}ois Gu\'enard and Gilbert Leli\`evre for
the book ""Penser les math\'ematiques"".
  It is the modified and abridged version of a text that appeared previously as
S\'eminaire de philosophie et math\'ematiques de l'\'Ecole normale sup\'erieure
(s\'eance du 26 avril 1976), Paris, IREM Paris-Nord, 1980, 15 pp.,
http://www.numdam.org/item?id=SPHM_1976___1_A1_0, as well as in Langage et
pens\'ee math\'ematiques: actes du colloque international (Luxembourg, 9-11
juin 1976), Luxembourg, Centre universitaire de Luxembourg, 1976, pp. 391--410.
  In its introduction, Ap\'ery writes: ""In default of convincing, this text can
set the record straight: we show that the constructive conception does not
mutilate, on the contrary, it enriches classical mathematics.""",1705.05581v2
2017-05-17,Magnetic-Visual Sensor Fusion based Medical SLAM for Endoscopic Capsule Robot,"A reliable, real-time simultaneous localization and mapping (SLAM) method is
crucial for the navigation of actively controlled capsule endoscopy robots.
These robots are an emerging, minimally invasive diagnostic and therapeutic
technology for use in the gastrointestinal (GI) tract. In this study, we
propose a dense, non-rigidly deformable, and real-time map fusion approach for
actively controlled endoscopic capsule robot applications. The method combines
magnetic and vision based localization, and makes use of frame-to-model fusion
and model-to-model loop closure. The performance of the method is demonstrated
using an ex-vivo porcine stomach model. Across four trajectories of varying
speed and complexity, and across three cameras, the root mean square
localization errors range from 0.42 to 1.92 cm, and the root mean square
surface reconstruction errors range from 1.23 to 2.39 cm.",1705.06196v2
2017-05-21,First-Order Reversal Curves of the Magnetostructural Phase Transition in FeTe,"We apply the first-order reversal curve (FORC) method, borrowed from studies
of ferromagnetic materials, to the magneto-structural phase transition of FeTe.
FORC measurements reveal two features in the hysteretic phase transition, even
in samples where traditional temperature measurements display only a single
transition. For Fe1.13Te, the influence of magnetic field suggests that the
main feature is primarily structural while a smaller, slightly
higher-temperature transition is magnetic in origin. By contrast Fe1.03Te has a
single transition which shows a uniform response to magnetic field, indicating
a stronger coupling of the magnetic and structural phase transitions. We also
introduce uniaxial stress, which spreads the distribution width without
changing the underlying energy barrier of the transformation. The work shows
how FORC can help disentangle the roles of the magnetic and structural phase
transitions in FeTe.",1705.07380v1
2017-05-24,Towards Understanding the Invertibility of Convolutional Neural Networks,"Several recent works have empirically observed that Convolutional Neural Nets
(CNNs) are (approximately) invertible. To understand this approximate
invertibility phenomenon and how to leverage it more effectively, we focus on a
theoretical explanation and develop a mathematical model of sparse signal
recovery that is consistent with CNNs with random weights. We give an exact
connection to a particular model of model-based compressive sensing (and its
recovery algorithms) and random-weight CNNs. We show empirically that several
learned networks are consistent with our mathematical analysis and then
demonstrate that with such a simple theoretical framework, we can obtain
reasonable re- construction results on real images. We also discuss gaps
between our model assumptions and the CNN trained for classification in
practical scenarios.",1705.08664v1
2017-03-06,Ultra-low-energy Electric field-induced Magnetization Switching in Multiferroic Heterostructures,"Electric field-induced magnetization switching in multiferroics is intriguing
for both fundamental studies and potential technological applications. Here, we
review the recent developments on electric field-induced magnetization
switching in multiferroic heterostructures. Particularly, we study the dynamics
of magnetization switching between the two stable states in a shape-anisotropic
single-domain nanomagnet using stochastic Landau-Lifshitz-Gilbert (LLG)
equation in the presence of thermal fluctuations. For magnetostrictive
nanomagnets in strain-coupled multiferroic composites, such study of
magnetization dynamics, contrary to steady-state scenario, revealed intriguing
new phenomena on binary switching mechanism. While the traditional method of
binary switching requires to tilt the potential profile to the desired state of
switching, we show that no such tilting is necessary to switch successfully
since the magnetization's excursion out of magnet's plane can generate a
built-in asymmetry during switching. We also study the switching dynamics in
multiferroic heterostructures having magnetoelectric coupling at the interface
and magnetic exchange coupling that can facilitate to maintain the direction of
switching with the polarity of the applied electric field. We calculate the
performance metrics like switching delay and energy dissipation during
switching while simulating LLG dynamics. The performance metrics turn out to be
very encouraging for potential technological applications.",1706.03039v1
2017-06-11,Local List Recovery of High-rate Tensor Codes and Applications,"In this work, we give the first construction of high-rate locally
list-recoverable codes. List-recovery has been an extremely useful building
block in coding theory, and our motivation is to use these codes as such a
building block. In particular, our construction gives the first
capacity-achieving locally list-decodable codes (over constant-sized alphabet);
the first capacity achieving globally list-decodable codes with nearly linear
time list decoding algorithm (once more, over constant-sized alphabet); and a
randomized construction of binary codes on the Gilbert-Varshamov bound that can
be uniquely decoded in near-linear-time, with higher rate than was previously
known.
  Our techniques are actually quite simple, and are inspired by an approach of
Gopalan, Guruswami, and Raghavendra (Siam Journal on Computing, 2011) for
list-decoding tensor codes. We show that tensor powers of (globally)
list-recoverable codes are ""approximately"" locally list-recoverable, and that
the ""approximately"" modifier may be removed by pre-encoding the message with a
suitable locally decodable code. Instantiating this with known constructions of
high-rate globally list-recoverable codes and high-rate locally decodable codes
finishes the construction.",1706.03383v1
2017-05-31,Local Differential Privacy for Physical Sensor Data and Sparse Recovery,"In this work we explore the utility of locally differentially private thermal
sensor data. We design a locally differentially private recovery algorithm for
the 1-dimensional, discrete heat source location problem and analyse its
performance in terms of the Earth Mover Distance error. Our work indicates that
it is possible to produce locally private sensor measurements that both keep
the exact locations of the heat sources private and permit recovery of the
""general geographic vicinity"" of the sources. We also discuss the relationship
between the property of an inverse problem being ill-conditioned and the amount
of noise needed to maintain privacy.",1706.05916v4
2017-06-22,High-performance nanoscale topological energy transduction,"The realization of high-performance, small-footprint, on-chip inductors
remains a challenge in radio-frequency and power microelectronics, where they
perform vital energy transduction in filters and power converters. Modern
planar inductors consist of metallic spirals that consume significant chip
area, resulting in low inductance densities. We present a novel method for
magnetic energy transduction that utilizes ferromagnetic islands (FIs) on the
surface of a 3D time-reversal-invariant topological insulator (TI) to produce
paradigmatically different inductors. Depending on the chemical potential, the
FIs induce either an anomalous or quantum anomalous Hall effect in the
topological surface states. These Hall effects direct current around the FIs,
concentrating magnetic flux and producing a highly inductive device. Using a
novel self-consistent simulation that couples AC non-equilibrium Green
functions to fully electrodynamic solutions of Maxwell's equations, we
demonstrate excellent inductance densities up to terahertz frequencies, thus
harnessing the unique properties of topological materials for practical device
applications.",1706.07381v1
2017-06-28,Extension and Applications of a Variational Approach with Deformed Derivatives,"We have recently presented an extension of the standard variational calculus
to include the presence of deformed derivatives in the Lagrangian of a system
of particles and in the Lagrangian density of field-theoretic models. Classical
Euler-Lagrange equations and the Hamiltonian formalism have been re-assessed in
this approach. Whenever applied to a number of physical systems, the resulting
dynamical equations come out to be the correct ones found in the literature,
specially with mass-dependent and with non-linear equations for classical and
quantum-mechanical systems. In the present contribution, we extend the
variational approach with the intervalar form of deformed derivatives to study
higher-order dissipative systems, with application to concrete situations, such
as an accelerated point charge - this is the problem of the
Abraham-Lorentz-Dirac force - to stochastic dynamics like the Langevin, the
advection-convection-reaction and Fokker-Planck equations, Korteweg-de Vries
equation, Landau-Lifshits-Gilbert equation and the Caldirola-Kanai Hamiltonian.
By considering these different applications, we show that the formulation
investigated in this paper may be a simple and promising path for dealing with
dissipative, non-linear and stochastic systems through the variational
approach.",1706.09504v1
2017-07-06,Relaxation time and critical slowing down of a spin-torque oscillator,"The relaxation phenomena of spin-torque oscillators consisting of
nanostructured ferromagnets are interesting research targets in magnetism. A
theoretical study on the relaxation time of a spin-torque oscillator from one
self-oscillation state to another is investigated. By solving the
Landau-Lifshitz-Gilbert equation both analytically and numerically, it is shown
that the oscillator relaxes to the self-oscillation state exponentially within
a few nanoseconds, except when magnetization is close to a critical point. The
relaxation rate, which is an inverse of relaxation time, is proportional to the
current. On the other hand, a critical slowing down appears near the critical
point, where relaxation is inversely proportional to time, and the relaxation
time becomes on the order of hundreds of nanoseconds. These conclusions are
primarily obtained for a spin-torque oscillator consisting of a perpendicularly
magnetized free layer and an in-plane magnetized pinned layer, and are further
developed for application to arbitrary types of spin-torque oscillators.",1707.01960v1
2017-07-07,Pandeia: A Multi-mission Exposure Time Calculator for JWST and WFIRST,"Pandeia is the exposure time calculator (ETC) system developed for the James
Webb Space Telescope (JWST) that will be used for creating JWST proposals. It
includes a simulation-hybrid Python engine that calculates the two-dimensional
pixel-by-pixel signal and noise properties of the JWST instruments. This allows
for appropriate handling of realistic point spread functions, MULTIACCUM
detector readouts, correlated detector readnoise, and multiple photometric and
spectral extraction strategies. Pandeia includes support for all the JWST
observing modes, including imaging, slitted/slitless spectroscopy, integral
field spectroscopy, and coronagraphy. Its highly modular, data-driven design
makes it easily adaptable to other observatories. An implementation for use
with WFIRST is also available.",1707.02202v2
2017-07-10,Convex optimization over classes of multiparticle entanglement,"A well-known strategy to characterize multiparticle entanglement utilizes the
notion of stochastic local operations and classical communication (SLOCC), but
characterizing the resulting entanglement classes is difficult. Given a
multiparticle quantum state, we first show that Gilbert's algorithm can be
adapted to prove separability or membership in a certain entanglement class. We
then present two algorithms for convex optimization over SLOCC classes. The
first algorithm uses a simple gradient approach, while the other one employs
the accelerated projected-gradient method. For demonstration, the algorithms
are applied to the likelihood-ratio test using experimental data on bound
entanglement of a noisy four-photon Smolin state [Phys. Rev. Lett. 105, 130501
(2010)].",1707.02958v3
2017-07-13,Collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model,"In this article, we discuss the non-trivial collective charge excitations
(plasmons) of the extended square-lattice Hubbard model. Using a fully
non-perturbative approach, we employ the hybrid Monte Carlo algorithm to
simulate the system at half-filling. A modified Backus-Gilbert method is
introduced to obtain the spectral functions via numerical analytic
continuation. We directly compute the single-particle density of states which
demonstrates the formation of Hubbard bands in the strongly-correlated phase.
The momentum-resolved charge susceptibility is also computed on the basis of
the Euclidean charge density-density correlator. In agreement with previous
EDMFT studies, we find that at large strength of the electron-electron
interaction, the plasmon dispersion develops two branches.",1707.04212v2
2017-07-25,Partially Ionized Plasmas in Astrophysics,"Partially ionized plasmas are found across the Universe in many different
astrophysical environments. They constitute an essential ingredient of the
solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary
disks, among other environments, and display a richness of physical effects
which are not present in fully ionized plasmas. This review provides an
overview of the physics of partially ionized plasmas, including recent advances
in different astrophysical areas in which partial ionization plays a
fundamental role. We outline outstanding observational and theoretical
questions and discuss possible directions for future progress.",1707.07975v2
2017-07-14,Spatially variant PSF modeling in confocal macroscopy,"Point spread function (PSF) plays an essential role in image reconstruction.
In the context of confocal microscopy, optical performance degrades towards the
edge of the field of view as astigmatism, coma and vignetting. Thus, one should
expect the related artifacts to be even stronger in macroscopy, where the field
of view is much larger. The field aberrations in macroscopy fluorescence
imaging system was observed to be symmetrical and to increase with the distance
from the center of the field of view. In this paper we propose an experiment
and an optimization method for assessing the center of the field of view. The
obtained results constitute a step towards reducing the number of parameters in
macroscopy PSF model.",1707.09858v1
2017-08-09,Bubble Magnetometry of Nanoparticle Heterogeneity and Interaction,"Bubbles have a rich history as transducers in particle-physics experiments.
In a solid-state analogue, we use bubble domains in nanomagnetic films to
measure magnetic nanoparticles. This technique can determine the magnetic
orientation of a single nanoparticle in a fraction of a second, and generate a
full hysteresis loop in a few seconds, which is much faster than any other
reported technique. We achieve this unprecedented speed by tuning the
nanomagnetic properties of the films, including the Dzyaloshinskii-Moriya
interaction, in the first application of topological protection from the
skyrmion state to a nanoparticle sensor. We demonstrate the technique on
iron/nickel nanorods and iron oxide nanoparticles, which delineate a wide range
of properties and applications. Bubble magnetometry enables the first
measurement with high throughput for statistical analysis of the magnetic
hysteresis of dispersed nanoparticles, and the first direct measurement of a
transition from superparamagnetic behavior as single nanoparticles to
collective behavior in nanoscale agglomerates. These results demonstrate a
breakthrough capability for measuring the heterogeneity and interaction of
magnetic nanoparticles.",1708.02706v2
2017-08-18,Antiferromagnetic nano-oscillator in external magnetic fields,"We describe the dynamics of an antiferromagnetic nano-oscillator in an
external magnetic field of any given time distribution. The oscillator is
powered by a spin current originating from spin-orbit effects in a neighboring
heavy metal layer, and is capable of emitting a THz signal in the presence of
an additional easy-plane anisotropy. We derive an analytical formula describing
the interaction between such a system and an external field, which can affect
the output signal character. Interactions with magnetic pulses of different
shapes, with a sinusoidal magnetic field and with a sequence of rapidly
changing magnetic fields are discussed. We also perform numerical simulations
based on the Landau-Lifshitz-Gilbert equation with spin-transfer torque effects
to verify the obtained results and find a very good quantitative agreement
between analytical and numerical predictions.",1708.05590v2
2017-09-07,A sharp bound for winning within a proportion of the maximum of a sequence,"This note considers a variation of the full-information secretary problem
where the random variables to be observed are independent and identically
distributed. Consider $X_1,\dots,X_n$ to be an independent sequence of random
variables, let $M_n:=\max\{X_1,\dots,X_n\}$, and the objective is to select the
maximum of the sequence. What is the maximum probability of ""stopping at the
maximum""? That is, what is the stopping time $\tau$ adapted to $X_1,...,X_n$
that maximizes $P(X_{\tau}=M_n)$? This problem was examined by Gilbert and
Mosteller \cite{GilMost} when in addition the common distribution is
continuous. The optimal win probability in this case is denoted by
$v_{n,max}^*$. What if it is desired to ""stop within a proportion of the
maximum""? That is, for $0<\alpha<1$, what is the stopping rule $\tau$ that
maximizes $P(X_{\tau} \geq \alpha M_n)$? In this note both problems are treated
as games, it is proven that for any continuous random variable $X$, if $\tau^*$
is the optimal stopping rule then $P(X_{\tau^*} \geq \alpha M_n)\geq
v_{n,max}^*$, and this lower bound is sharp. Some examples and another
interesting result are presented.",1709.02416v1
2017-09-18,"Endo-VMFuseNet: Deep Visual-Magnetic Sensor Fusion Approach for Uncalibrated, Unsynchronized and Asymmetric Endoscopic Capsule Robot Localization Data","In the last decade, researchers and medical device companies have made major
advances towards transforming passive capsule endoscopes into active medical
robots. One of the major challenges is to endow capsule robots with accurate
perception of the environment inside the human body, which will provide
necessary information and enable improved medical procedures. We extend the
success of deep learning approaches from various research fields to the problem
of uncalibrated, asynchronous, and asymmetric sensor fusion for endoscopic
capsule robots. The results performed on real pig stomach datasets show that
our method achieves sub-millimeter precision for both translational and
rotational movements and contains various advantages over traditional sensor
fusion techniques.",1709.06041v2
2017-09-22,On self-dual negacirculant codes of index two and four,"In this paper, we study a special kind of factorization of $x^n+1$ over
$\mathbb{F}_q, $ with $q$ a prime power $\equiv 3~({\rm mod}~4)$ when $n=2p,$
with $p\equiv 3~({\rm mod}~4)$ and $p$ is a prime. Given such a $q$ infinitely
many such $p$'s exist that admit $q$ as a primitive root by the Artin
conjecture in arithmetic progressions. This number theory conjecture is known
to hold under GRH. We study the double (resp. four)-negacirculant codes over
finite fields $\mathbb{F}_q, $ of co-index such $n$'s, including the exact
enumeration of the self-dual subclass, and a modified Varshamov-Gilbert bound
on the relative distance of the codes it contains.",1709.07546v2
2017-03-06,Ultra-Low-Energy Straintronics Using Multiferroic Composites,"The primary impediment to continued improvement of charge-based electronics
is the excessive energy dissipation incurred in switching a bit of information.
With suitable choice of materials, devices made of multiferroic composites,
i.e., strain-coupled piezoelectric-magnetostrictive heterostructures, dissipate
miniscule amount of energy of ~1 attojoule at room-temperature, while switching
in sub-nanosecond delay. Apart from devising memory bits, such devices can be
also utilized for building logic, so that they can be deemed suitable for
computing purposes as well. Here, we first review the current state of the art
for building nanoelectronics using multiferroic composites. On a recent
development, it is shown that these multiferroic straintronic devices can be
also utilized for analog signal processing, with suitable choice of materials.
By solving stochastic Landau-Lifshitz-Gilbert equation of magnetization
dynamics at room-temperature, it is shown that we can achieve a voltage gain,
i.e., these straintronic devices can act as voltage amplifiers.",1710.00612v1
2017-10-12,Modeling the aging kinetics of zirconia ceramics,"Yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) with different
microstructures were elaborated. The isothermal tetragonal to monoclinic
transformation was investigated at 134 {\deg}C in steam by X-ray diffraction,
Atomic Force Microscopy (AFM) and optical interferometry. The aging kinetics
were analyzed in terms of nucleation and growth, using the Mehl-Avrami-Johnson
(MAJ) formalism. Numerical simulation of the aging of zirconia surfaces was
also conducted, and the results were used to better fit the aging kinetics. The
simulation shows that the exponent of the MAJ laws is controlled not only by
the nucleation and growth mechanisms, but also - and mainly - by their
respective kinetic parameters. Measurements of nucleation and growth rates at
the surface, at the beginning of aging, and the use of numerical simulation
allow the accurate prediction of aging kinetics.",1710.04454v1
2017-10-13,Microstructural investigation of the aging behavior of $(3Y-TZP)-Al_2O_3$ composites,"The low temperature autoclave aging behavior of zirconia toughened alumina
composites processed by a classical powder mixing processing route was analyzed
using atomic force microscopy (AFM), scanning electron microscopy and X-Ray
diffraction. The transformation was evaluated in terms of nucleation and
growth, assessed by XRD. The time-temperature equivalency of the transformation
was used to measure an apparent activation energy of the nucleation stage of
the transformation of 78kJ/mol. The microstructural features influencing the
transformation were identified, and the influence of the alumina matrix on the
transformation was investigated. Transformation progression grain by grain was
observed by AFM. Transformation does not only occur in zirconia agglomerates
but also in isolated zirconia grains. The matrix could partially inhibit the
transformation. This behavior could be rationalized considering the
constraining effect of the alumina matrix, shape strain accommodation arguments
and microstructural homogeneity effects.",1710.04923v1
2017-10-16,Tunable Low Density Palladium Nanowire Foams,"Nanostructured palladium foams offer exciting potential for applications in
diverse fields such as catalyst, fuel cell, and particularly hydrogen storage
technologies. We have fabricated palladium nanowire foams using a cross-linking
and freeze-drying technique. These foams have a tunable density down to 0.1% of
the bulk, and a surface area to volume ratio of up to 1,540,000:1. They exhibit
highly attractive characteristics for hydrogen storage, in terms of loading
capacity, rate of absorption and heat of absorption. The hydrogen
absorption/desorption process is hysteretic in nature, accompanied by
substantial lattice expansion/contraction as the foam converts between Pd and
PdHx.",1710.05906v1
2017-10-19,An estimate for the thermal photon rate from lattice QCD,"We estimate the production rate of photons by the quark-gluon plasma in
lattice QCD. We propose a new correlation function which provides better
control over the systematic uncertainty in estimating the photon production
rate at photon momenta in the range {\pi}T/2 to 2{\pi}T. The relevant Euclidean
vector current correlation functions are computed with $N_{\mathrm f}$ = 2
Wilson clover fermions in the chirally-symmetric phase. In order to estimate
the photon rate, an ill-posed problem for the vector-channel spectral function
must be regularized. We use both a direct model for the spectral function and a
model-independent estimate from the Backus-Gilbert method to give an estimate
for the photon rate.",1710.07050v1
2017-10-26,Spin dynamics in MgO based magnetic tunnel junctions with dynamical exchange coupling,"We study the spin dynamics in Fe|MgO|Fe tunnel junction with the dynamical
exchange coupling by coupled Landau-Lifshitz-Gilbert equations. The effects of
spin pumping on the spin dynamics are investigated in detail. It is observed
that the spin pumping can stabilize a quasi-antiparallel state rather than a
quasi-parallel one. More interestingly, our work suggests that the spin pumping
torque can efficiently modulate the magnetization, similar to the
thermal-bias-driven and electricbias-driven spin torques.",1710.09666v2
2017-10-27,Bulk and edge spin transport in topological magnon insulators,"We investigate the spin transport properties of a topological magnon
insulator, a magnetic insulator characterized by topologically nontrivial bulk
magnon bands and protected magnon edge modes located in the bulk band gaps.
Employing the Landau-Lifshitz-Gilbert phenomenology, we calculate the spin
current driven through a normal metal$|$topological magnon insulator$|$normal
metal heterostructure by a spin accumulation imbalance between the metals, with
and without random lattice defects. We show that bulk and edge transport are
characterized by different length scales. This results in a characteristic
system size where the magnon transport crosses over from being bulk-dominated
for small systems to edge-dominated for larger systems. These findings are
generic and relevant for topological transport in systems of nonconserved
bosons.",1710.09998v2
2017-10-30,Spin-transfer Antiferromagnetic Resonance,"Currents can induce spin excitations in antiferromagnets, even when they are
insulating. We investigate how spin transfer can cause antiferromagnetic
resonance in bilayers and trilayers that consist of one antiferromagnetic
insulator and one or two metals. An ac voltage applied to the metal generates a
spin Hall current that drives the magnetic moments in the antiferromagnet. We
consider excitation of the macrospin mode and of transverse standing-spin-wave
modes. By solving the Landau-Lifshitz-Gilbert equation in the antiferromagnetic
insulator and the spin-diffusion equation in the normal metal, we derive
analytical expressions for the spin-Hall-magnetoresistance and spin-pumping
inverse-spin-Hall dc voltages. In bilayers, the two contributions compensate
each other and cannot easily be distinguished. We present numerical results for
a MnF$_2|$Pt bilayer. Trilayers facilitate separation of the
spin-Hall-magnetoresistance and spin-pumping voltages, thereby revealing more
information about the spin excitations. We also compute the decay of the pumped
spin current through the antiferromagnetic layer as a function of frequency and
the thickness of the antiferromagnetic layer.",1710.10909v1
2017-10-31,Compact Multi-Class Boosted Trees,"Gradient boosted decision trees are a popular machine learning technique, in
part because of their ability to give good accuracy with small models. We
describe two extensions to the standard tree boosting algorithm designed to
increase this advantage. The first improvement extends the boosting formalism
from scalar-valued trees to vector-valued trees. This allows individual trees
to be used as multiclass classifiers, rather than requiring one tree per class,
and drastically reduces the model size required for multiclass problems. We
also show that some other popular vector-valued gradient boosted trees
modifications fit into this formulation and can be easily obtained in our
implementation. The second extension, layer-by-layer boosting, takes smaller
steps in function space, which is empirically shown to lead to a faster
convergence and to a more compact ensemble. We have added both improvements to
the open-source TensorFlow Boosted trees (TFBT) package, and we demonstrate
their efficacy on a variety of multiclass datasets. We expect these extensions
will be of particular interest to boosted tree applications that require small
models, such as embedded devices, applications requiring fast inference, or
applications desiring more interpretable models.",1710.11547v1
2017-11-14,Stationary Vacuum Black Holes in 5 Dimensions,"We study the problem of asymptotically flat bi-axially symmetric stationary
solutions of the vacuum Einstein equations in $5$-dimensional spacetime. In
this setting, the cross section of any connected component of the event horizon
is a prime $3$-manifold of positive Yamabe type, namely the $3$-sphere $S^3$,
the ring $S^1\times S^2$, or the lens space $L(p,q)$. The Einstein vacuum
equations reduce to an axially symmetric harmonic map with prescribed
singularities from $\mathbb{R}^3$ into the symmetric space
$SL(3,\mathbb{R})/SO(3)$. In this paper, we solve the problem for all possible
topologies, and in particular the first candidates for smooth vacuum
non-degenerate black lenses are produced. In addition, a generalization of this
result is given in which the spacetime is allowed to have orbifold
singularities. We also formulate conditions for the absence of conical
singularities which guarantee a physically relevant solution.",1711.05229v2
2017-11-27,Voltage induced switching of an antiferromagnetically ordered topological Dirac semimetal,"An antiferromagnetic semimetal has been recently identified as a new member
of topological semimetals that may host three-dimensional symmetry-protected
Dirac fermions. A reorientation of the N\'{e}el vector may break the underlying
symmetry and open a gap in the quasi-particle spectrum, inducing the
(semi)metal-insulator transition. Here, we predict that such transition may be
controlled by manipulating the chemical potential location of the material. We
perform both analytical and numerical analysis on the thermodynamic potential
of the model Hamiltonian and find that the gapped spectrum is preferred when
the chemical potential is located at the Dirac point. As the chemical potential
deviates from the Dirac point, the system shows a possible transition from the
gapped to the gapless phase and switches the corresponding N\'{e}el vector
configuration. We perform density functional theory calculations to verify our
analysis using a realistic material and discuss a two terminal transport
measurement as a possible route to identify the voltage induced switching of
the N\'{e}el vector.",1711.09926v2
2017-12-11,Convergent tangent plane integrators for the simulation of chiral magnetic skyrmion dynamics,"We consider the numerical approximation of the Landau-Lifshitz-Gilbert
equation, which describes the dynamics of the magnetization in ferromagnetic
materials. In addition to the classical micromagnetic contributions, the energy
comprises the Dzyaloshinskii-Moriya interaction, which is the most important
ingredient for the enucleation and the stabilization of chiral magnetic
skyrmions. We propose and analyze three tangent plane integrators, for which we
prove (unconditional) convergence of the finite element solutions towards a
weak solution of the problem. The analysis is constructive and also establishes
existence of weak solutions. Numerical experiments demonstrate the
applicability of the methods for the simulation of practically relevant problem
sizes.",1712.03795v3
2017-12-31,Proper dissipative torques in antiferromagnetic dynamics,"There is little doubt that the magnetization dynamics of ferromagnetic
systems is governed by the Landau-Lifshitz-Gilbert equation or its
generalization with various spin torques. In contrast, there are several sets
of dynamic equations for two-sublattice antiferromagnets (AFMs) in literature
that have different forms of dissipative torques and no proper dynamic
equations for multi-sublattice AFMs and ferrimagnets in general. Here we
introduce the general Rayleigh dissipation functional into the Lagrange
equation and derive the proper form of the dissipative torques in the
phenomenological equations for the AFMs with multiple sublattices. A new type
of dissipative torque arising from inter-sublattice drag effect is discovered
that has important influences on magnon lifetime and domain wall motion. In
particular, our theory unifies different dynamic equations of AFMs in
literature.",1801.00217v1
2018-01-12,Optimal Streaming Codes for Channels with Burst and Arbitrary Erasures,"This paper considers transmitting a sequence of messages (a streaming source)
over a packet erasure channel. In each time slot, the source constructs a
packet based on the current and the previous messages and transmits the packet,
which may be erased when the packet travels from the source to the destination.
Every source message must be recovered perfectly at the destination subject to
a fixed decoding delay. We assume that the channel loss model introduces either
one burst erasure or multiple arbitrary erasures in any fixed-sized sliding
window. Under this channel loss assumption, we fully characterize the maximum
achievable rate by constructing streaming codes that achieve the optimal rate.
In addition, our construction of optimal streaming codes implies the full
characterization of the maximum achievable rate for convolutional codes with
any given column distance, column span and decoding delay. Numerical results
demonstrate that the optimal streaming codes outperform existing streaming
codes of comparable complexity over some instances of the Gilbert-Elliott
channel and the Fritchman channel.",1801.04241v2
2018-01-16,Detecting Electron Density Fluctuations from Cosmic Microwave Background Polarization using a Bispectrum Approach,"Recent progress in high sensitivity Cosmic Microwave Background (CMB)
polarization experiments opens up a window on large scale structure (LSS), as
CMB polarization fluctuations on small angular scales can arise from a
combination of LSS and ionization fluctuations in the late universe.
Gravitational lensing effects can be extracted from CMB datasets with quadratic
estimators but reconstructions of electron density fluctuations (EDFs) with
quadratic estimators are found to be significantly biased by the much larger
lensing effects in the secondary CMB fluctuations. In this paper we establish a
bispectrum formalism using tracers of LSS to extract the subdominant EDFs from
CMB polarization data. We find that this bispectrum can effectively reconstruct
angular band-powers of cross correlation between EDFs and LSS tracers. Next
generation CMB polarization experiments in conjunction with galaxy surveys and
cosmic infrared background experiments can detect signatures of EDFs with high
significance.",1801.05396v1
2018-01-18,Magpy: A C++ accelerated Python package for simulating magnetic nanoparticle stochastic dynamics,"Magpy is a C++ accelerated Python package for modelling and simulating the
magnetic dynamics of nano-sized particles. Nanoparticles are modelled as a
system of three-dimensional macrospins and simulated with a set of coupled
stochastic differential equations (the Landau-Lifshitz-Gilbert equation), which
are solved numerically using explicit or implicit methods. The results of the
simulations may be used to compute equilibrium states, the dynamic response to
external magnetic fields, and heat dissipation. Magpy is built on a C++
library, which is optimised for serial execution, and exposed through a Python
interface utilising an embarrassingly parallel strategy. Magpy is free,
open-source, and available on github under the 3-Clause BSD License.",1801.06073v2
2018-01-22,On the List Decodability of Self-orthogonal Rank Metric Codes,"V. Guruswami and N. Resch prove that the list decodability of
$\mathbb{F}_q$-linear rank metric codes is as good as that of random rank
metric codes in~\cite{venkat2017}. Due to the potential applications of
self-orthogonal rank metric codes, we focus on list decoding of them. In this
paper, we prove that with high probability, an $\F_q$-linear self-orthogonal
rank metric code over $\mathbb{F}_q^{n\times m}$ of rate
$R=(1-\tau)(1-\frac{n}{m}\tau)-\epsilon$ is shown to be list decodable up to
fractional radius $\tau\in(0,1)$ and small $\epsilon\in(0,1)$ with list size
depending on $\tau$ and $q$ at most $O_{\tau, q}(\frac{1}{\epsilon})$. In
addition, we show that an $\mathbb{F}_{q^m}$-linear self-orthogonal rank metric
code of rate up to the Gilbert-Varshamov bound is $(\tau n, \exp(O_{\tau,
q}(\frac{1}{\epsilon})))$-list decodable.",1801.07033v1
2018-01-25,Smoothing Algorithms for Computing the Projection onto a Minkowski Sum of Convex Sets,"In this paper, the problem of computing the projection, and therefore the
minimum distance, from a point onto a Minkowski sum of general convex sets is
studied. Our approach is based on the minimum norm duality theorem originally
stated by Nirenberg and the Nesterov smoothing techniques. It is shown that
projection points onto a Minkowski sum of sets can be represented as the sum of
points on constituent sets so that, at these points, all of the sets share the
same normal vector which is the negative of the dual solution. The proposed
NESMINO algorithm improves the theoretical bound on number of iterations from
$O(\frac{1}{\epsilon})$ by Gilbert [SIAM J. Contr., vol. 4, pp. 61--80, 1966]
to $O\left(\frac{1}{\sqrt{\epsilon}}\ln(\frac{1}{\epsilon})\right)$, where
$\epsilon$ is the desired accuracy for the objective function. Moreover, the
algorithm also provides points on each component sets such that their sum is
equal to the projection point.",1801.08285v1
2018-01-25,Finite momentum Cooper pairing in 3D topological insulator Josephson junctions,"Unconventional superconductivity arising from the interplay between strong
spin-orbit coupling and magnetism is an intensive area of research. One form of
unconventional superconductivity arises when Cooper pairs subjected to a
magnetic exchange coupling acquire a finite momentum. Here, we report on a
signature of finite momentum Cooper pairing in the 3D topological insulator
Bi2Se3. We apply in-plane and out-of-plane magnetic fields to proximity-coupled
Bi2Se3 and find that the in-plane field creates a spatially oscillating
superconducting order parameter in the junction as evidenced by the emergence
of an anomalous Fraunhofer pattern. We describe how the anomalous Fraunhofer
patterns evolve for different device parameters, and we use this to understand
the microscopic origin of the oscillating order parameter. The agreement
between the experimental data and simulations shows that the finite momentum
pairing originates from the coexistence of the Zeeman effect and Aharonov-Bohm
flux.",1801.08504v1
2018-01-31,Numerical analytic continuation of Euclidean data,"In this work we present a direct comparison of three different numerical
analytic continuation methods: the Maximum Entropy Method, the Backus-Gilbert
method and the Schlessinger point or Resonances Via Pad\'{e} method. First, we
perform a benchmark test based on a model spectral function and study the
regime of applicability of these methods depending on the number of input
points and their statistical error. We then apply these methods to more
realistic examples, namely to numerical data on Euclidean propagators obtained
from a Functional Renormalization Group calculation, to data from a lattice
Quantum Chromodynamics simulation and to data obtained from a tight-binding
model for graphene in order to extract the electrical conductivity.",1801.10348v2
2018-02-03,Stochastic dynamics of planar magnetic moments in a three-dimensional environment,"We study the stochastic dynamics of a two-dimensional magnetic moment
embedded in a three-dimensional environment, described by means of the
stochastic Landau-Lifshitz-Gilbert (sLLG) equation. We define a covariant
generalization of this equation, valid in the ""generalized Stratonovich
discretization prescription"". We present a path integral formulation that
allows to compute any $n-$point correlation function, independently of the
stochastic calculus used. Using this formalism, we show the equivalence between
the cartesian formulation with vectorial noise, with the polar formulation with
just one scalar fluctuation term. In particular, we show that, for isotropic
fluctuations, the system is represented by an {\em additive stochastic
process}, despite of the multiplicative terms appearing in the original
formulation of the sLLG equation, but, for anisotropic fluctuations the noise
turns out to be truly multiplicative.",1802.01027v2
2018-02-07,Asymptotically Locally Euclidean/Kaluza-Klein Stationary Vacuum Black Holes in 5 Dimensions,"We produce new examples, both explicit and analytical, of bi-axisymmetric
stationary vacuum black holes in 5 dimensions. A novel feature of these
solutions is that they are asymptotically locally Euclidean in which spatial
cross-sections at infinity have lens space $L(p,q)$ topology, or asymptotically
Kaluza-Klein so that spatial cross-sections at infinity are topologically
$S^1\times S^2$. These are nondegenerate black holes of cohomogeneity 2, with
any number of horizon components, where the horizon cross-section topology is
any one of the three admissible types: $S^3$, $S^1\times S^2$, or $L(p,q)$.
Uniqueness of these solutions is also established. Our method is to solve the
relevant harmonic map problem with prescribed singularities, having target
symmetric space $SL(3,\mathbb{R})/SO(3)$. In addition, we analyze the
possibility of conical singularities and find a large family for which
geometric regularity is guaranteed.",1802.02457v2
2018-02-16,A Reallocation Algorithm for Online Split Packing of Circles,"The Split Packing algorithm \cite{splitpacking_ws, splitpackingsoda,
splitpacking} is an offline algorithm that packs a set of circles into
triangles and squares up to critical density. In this paper, we develop an
online alternative to Split Packing to handle an online sequence of insertions
and deletions, where the algorithm is allowed to reallocate circles into new
positions at a cost proportional to their areas. The algorithm can be used to
pack circles into squares and right angled triangles. If only insertions are
considered, our algorithm is also able to pack to critical density, with an
amortised reallocation cost of $O(c\log \frac{1}{c})$ for squares, and
$O(c(1+s^2)\log_{1+s^2}\frac{1}{c})$ for right angled triangles, where $s$ is
the ratio of the lengths of the second shortest side to the shortest side of
the triangle, when inserting a circle of area $c$. When insertions and
deletions are considered, we achieve a packing density of $(1-\epsilon)$ of the
critical density, where $\epsilon>0$ can be made arbitrarily small, with an
amortised reallocation cost of $O(c(1+s^2)\log_{1+s^2}\frac{1}{c} +
c\frac{1}{\epsilon})$.",1802.05873v3
2018-02-22,Super-Resolution 1H Magnetic Resonance Spectroscopic Imaging utilizing Deep Learning,"Magnetic resonance spectroscopic imaging (SI) is a unique imaging technique
that provides biochemical information from in vivo tissues. The 1H spectra
acquired from several spatial regions are quantified to yield metabolite
concentrations reflective of tissue metabolism. However, since these
metabolites are found in tissues at very low concentrations, SI is often
acquired with limited spatial resolution. In this work we test the hypothesis
that deep learning is able to upscale low resolution SI, together with the
T1-weighted (T1w) image, to reconstruct high resolution SI. We report a novel
densely connected Unet (D-Unet) architecture capable of producing
super-resolution spectroscopic images. The inputs for the D-UNet are the T1w
image and the low resolution SI image while the output is the high resolution
SI. The results of the D-UNet are compared both qualitatively and
quantitatively to simulated and in vivo high resolution SI. It is found that
this deep learning approach can produce high quality spectroscopic images and
reconstruct entire 1H spectra from low resolution acquisitions, which can
greatly advance the current SI workflow.",1802.07909v3
2018-02-26,Devil's Staircases in SFS Josephson Junctions,"We study the effect of coupling between the superconducting current and
magnetization in the superconductor/ferromagnet/superconductor Josephson
junction under an applied circularly polarized magnetic field. Manifestation of
ferromagnetic resonance in the frequency dependence of the amplitude of the
magnetization and the average critical current density is demonstrated
numerically. The IV-characteristics show subharmonic steps that form devil's
staircases, following a continued fraction algorithm. The origin of the found
steps is related to the effect of the magnetization dynamics on the phase
difference in the Josephson junction. The dynamics of our system is described
by a generalized RCSJ model coupled to the Landau-Lifshitz-Gilbert equation. In
the suplement we justify analytically the appearance of the fractional steps in
IV-characteristics of the superconductor/ferromagnet/superconductor Josephson
junction.",1802.09212v2
2018-02-26,Controlled creation and stability of kπ-skyrmions on a discrete lattice,"We determine sizes and activation energies of k{\pi}-skyrmions on a discrete
lattice using the Landau- Lifshitz-Gilbert equation and the geodesic nudged
elastic band method. The employed atomic material parameters are based on the
skyrmionic material system Pd/Fe/Ir(111). We find that the critical magnetic
fields for collapse of the 2{\pi}-skyrmion and 3{\pi}-skyrmion are very close
to each other and considerably lower than the critical field of the
1{\pi}-skyrmion. The activation energy protecting the structures does not
strictly decrease with increasing k as it can be larger for the 3{\pi}-skyrmion
than for the 2{\pi}-skyrmion depending on the applied magnetic field.
Furthermore, we propose a method of switching the skyrmion order k by a
reversion of the magnetic field direction in samples of finite size.",1802.09257v1
2018-03-14,Subnanosecond magnetization reversal of magnetic nanoparticle driven by chirp microwave field pulse,"We investigate the magnetization reversal of single-domain magnetic
nanoparticle driven by linear down-chirp microwave magnetic field pulse.
Numerical simulations based on the Landau-Lifshitz-Gilbert equation reveal that
solely down-chirp pulse is capable of inducing subnanosecond magnetization
reversal. With a certain range of initial frequency and chirp rate, the
required field amplitude is much smaller than that of constant-frequency
microwave field. The fast reversal is because the down-chirp microwave field
acts as an energy source and sink for the magnetic particle before and after
crossing over the energy barrier, respectively. Applying a spin-polarized
current additively to the system further reduces the microwave field amplitude.
Our findings provide a new way to realize low-cost and fast magnetization
reversal.",1803.05261v1
2018-03-14,Dynamics of distorted skyrmions in strained chiral magnets,"In this work, we study the microscopic dynamics of distorted skyrmions in
strained chiral magnets [K. Shibata et al., Nat. Nanotech. 10, 589 (2015)]
under gradient magnetic field or electric current by Landau-Lifshitz-Gilbert
simulations of the anisotropic spin model. It is observed that the dynamical
responses are also anisotropic, and the velocities of the distorted skyrmions
are periodically dependent on the directions of the external stimuli.
Furthermore, in addition to the uniform motion, our work also demonstrates
anti-phase harmonic vibrations of the two skyrmions in nanostripes, and the
frequencies are mainly determined by the exchange anisotropy. The simulated
results are well explained by Thiele theory, which may provide useful
information in understanding the dynamics of the distorted skyrmions in
strained chiral magnets.",1803.05298v1
2018-03-19,Dynamics and Stability of Meshed Multiterminal HVDC Networks,"This paper investigates the existence of an equilibrium point in
multiterminal HVDC (MT-HVDC) grids, assesses its uniqueness and defines
conditions to ensure its stability. An offshore MT-HVDC system including two
wind farms is selected as application test case. At first, a generalized
dynamic model of the network is proposed, using hypergraph theory. Such model
captures the frequency dependence of transmission lines and cables, it is
non-linear due to the constant power behavior of the converter terminals using
droop regulation, and presents a suitable degree of simplifications of the MMC
converters, under given conditions, to allow system level studies over
potentially large networks. Based on this model, the existence and uniqueness
of the equilibrium point is demonstrated by returning the analysis to a
load-flow problem and using the Banach fixed point theorem. Additionally, the
stability of the equilibrium is analyzed by obtaining a Lyapunov function by
the Krasovskii's theorem. Computational results obtained for the selected 4
terminals MT-HVDC grid corroborate the requirement for the existence and
stability of the equilibrium point.",1803.06892v2
2018-03-16,Motion of vortices in ferromagnetic spin-1 BEC,"The paper investigates dynamics of nonsingular vortices in a ferromagnetic
spin-1 BEC, where spin and mass superfluidity coexist in the presence of
uniaxial anisotropy (linear and quadratic Zeeman effect). The analysis is based
on hydrodynamics following from the Gross-Pitaevskii theory. Cores of
nonsingular vortices are skyrmions with charge, which is tuned by uniaxial
anisotropy and can have any fractal value between 0 and 1. There are
circulations of mass and spin currents around these vortices. The results are
compared with the equation of vortex motion derived earlier in the
Landau-Lifshitz-Gilbert theory for magnetic vortices in easy-plane
ferromagnetic insulators. In the both cases the transverse gyrotropic force
(analog of the Magnus force in superfluid and classical hydrodynamics) is
proportional to the charge of skyrmions in vortex cores.",1803.06939v1
2018-03-22,Mapping ideals of quantum group multipliers,"We study the dual relationship between quantum group convolution maps
$L^1(\mathbb{G})\rightarrow L^{\infty}(\mathbb{G})$ and completely bounded
multipliers of $\widehat{\mathbb{G}}$. For a large class of locally compact
quantum groups $\mathbb{G}$ we completely isomorphically identify the mapping
ideal of row Hilbert space factorizable convolution maps with
$M_{cb}(L^1(\widehat{\mathbb{G}}))$, yielding a quantum Gilbert representation
for completely bounded multipliers. We also identify the mapping ideals of
completely integral and completely nuclear convolution maps, the latter case
coinciding with $\ell^1(\widehat{b\mathbb{G}})$, where $b\mathbb{G}$ is the
quantum Bohr compactification of $\mathbb{G}$. For quantum groups whose dual
has bounded degree, we show that the completely compact convolution maps
coincide with $C(b\mathbb{G})$. Our techniques comprise a mixture of operator
space theory and abstract harmonic analysis, including Fubini tensor products,
the non-commutative Grothendieck inequality, quantum Eberlein
compactifications, and a suitable notion of quasi-SIN quantum group, which we
introduce and exhibit examples from the bicrossed product construction. Our
main results are new even in the setting of group von Neumann algebras $VN(G)$
for quasi-SIN locally compact groups $G$.",1803.08342v2
2018-03-28,Low-temperature ageing of zirconia-toughened alumina ceramics and its implication in biomedical implants,"Changes in crystalline phases resulting from low-temperature ageing of
different yttria doped and non-doped zirconia-toughened alumina composites and
nanocomposites were investigated under controlled humidity and temperature
conditions in autoclave. A classical powder mixing processing route and a new
modified colloidal processing route were used to process the composites.
Different compositions ranging from 2.5 wt.% zirconia in a matrix of alumina to
pure zirconia (3Y-TZP) were studied. It was observed that Al2O3+yttria
stabilised ZrO2 composites exhibited significant ageing. However, ageing was
much slower than traditionally observed for Y-TZP ceramics, due to the presence
of the alumina matrix. Ageing was clearly limited for zirconia content beyond
25 wt.%. On the other side of the spectrum, Al2O3+2.5 wt.% ZrO2 initially
presented a monoclinic fraction but did not show any ageing degradation. These
composites seem to represent the best choice between slow crack growth and
ageing resistance.",1803.10465v1
2018-03-28,Accelerated Aging in 3 mol%-Yttria-Stabilized Tetragonal Zirconia Ceramics Sintered in Reducing Conditions,"The aging behavior of 3-mol%-yttria-stabilized tetragonal zirconia (3Y-TZP)
ceramics sintered in air and in reducing conditions was investigated at
140{\deg}C in water vapor. It was observed by X-ray diffraction (XRD) that
3Y-TZP samples sintered in reducing conditions exhibited significantly higher
tetragonal-to-monoclinic transformation than samples with similar density and
average grain size values but obtained by sintering in air. This fact is
explained by the increase of the oxygen vacancy concentration and by the
presence at the grain boundary region of a new aggregate phase formed because
of the exolution of Fe2+ ions observed by X-ray photoelectron spectroscopy.",1803.10580v1
2018-03-30,Atomic force microscopy study of the surface degradation mechanisms of zirconia based ceramics,"Atomic force microscopy (AFM) can be used to characterise several aspects of
the surface degradation and reinforcement mechanisms of zirconia based
ceramics, such as crack propagation, martensitic relief formation, grains
pull-out and transformation toughening. AFM can also be used to quantify
precisely the transformation and provide reliable parameters for long term
degradation prediction. In particular, the tetragonal to monoclinic (t-m) phase
transformation of zirconia has been the object of extensive investigations of
the last twenty years, and is now recognised as being of martensitic nature.
New strong evidences supporting the martensitic nature of the transformation
are reported here. These observations, considering their scale and precision,
are a new step toward the understanding of the t-m phase transformation of
zirconia and related degradation mechanisms.",1804.00002v1
2018-04-05,Stochastic ferrimagnetic Landau-Lifshitz-Bloch equation for finite magnetic structures,"Precise modeling of the magnetization dynamics of nanoparticles with finite
size effects at fast varying temperatures is a computationally challenging
task. Based on the Landau-Lifshitz-Bloch (LLB) equation we derive a coarse
grained model for disordered ferrimagnets, which is both fast and accurate.
First, we incorporate stochastic fluctuations to the existing ferrimagnetic LLB
equation. Further, we derive a thermodynamic expression for the temperature
dependent susceptibilities, which is essential to model finite size effects.
Together with the zero field equilibrium magnetization the susceptibilities are
used in the stochastic ferrimagnetic LLB to simulate a $5\times10$ nm$^2$
ferrimagnetic GdFeCo particle with 70 % FeCo and 30 % Gd under various external
applied fields and heat pulses. The obtained trajectories agree well with those
of an atomistic model, which solves the stochastic Landau-Lifshitz-Gilbert
equation for each atom. Additionally, we derive an expression for the
intergrain exchange field which couple the ferromagnetic sublattices of a
ferrimagnet. A comparison of the magnetization dynamics obtained from this
simpler model with those of the ferrimagnetic LLB equation shows a perfect
agreement.",1804.01724v1
2018-04-06,Temperature dependence of bulk viscosity within lattice simulation of $SU(3)$--gluodynamics,"In this paper the temperature dependence of the $SU(3)$--gluodynamics bulk
viscosity is studied within lattice simulations. To carry out this study we
measure the correlation function of the trace of the energy-momentum tensor for
a set of temperatures within the range $T/T_c \in (0.9, 1.5)$. To extract the
bulk viscosity from the correlation function we apply the Backus-Gilbert method
and the Tikhonov regularization method. We show that the ratio $\zeta/s$ is
small in the region $T/T_c \geqslant 1.1-1.2$ and in the vicinity of the
transition $T/T_c \leqslant 1.1-1.2$ it quickly rises. Our results are in
agreement with previous lattice studies and in a reasonable agreement with
other phenomenological approaches. Obtained values of the bulk viscosity are
significantly larger than perturbative results, what confirms that QGP is a
strongly correlated system.",1804.02382v2
2018-04-16,Anisotropy of exchange stiffness based on atomic-scale magnetic properties in rare-earth permanent magnet Nd$_2$Fe$_{14}$B,"We examine the anisotropic properties of the exchange stiffness constant,
$\mathcal{A}$, for rare-earth permanent magnet, Nd$_2$Fe$_{14}$B, by connecting
analyses with two different scales of length, i.e., Monte Carlo (MC) method
with an atomistic spin model and Landau-Lifshitz-Gilbert (LLG) equation with a
continuous magnetic model. The atomistic MC simulations are performed on the
spin model of Nd$_2$Fe$_{14}$B constructed from ab-initio calculations, and the
LLG micromagnetics simulations are performed with the parameters obtained by
the MC simulations. We clarify that the amplitude and the thermal property of
$\mathcal{A}$ depend on the orientation in the crystal, which are attributed to
the layered structure of Nd atoms and weak exchange couplings between Nd and Fe
atoms. We also confirm that the anisotropy of $\mathcal{A}$ significantly
affects the threshold field for the magnetization reversal (coercivity) given
by the depinning process.",1804.05824v2
2018-03-29,Percolative Mechanism of Aging in Zirconia-Containing Ceramics for Medical Applications,"Recently, several episodes of fracture of zirconia ceramic femoral heads of
total hip prostheses have alarmed the medical and scientific community
regarding aging problems in zirconia prostheses. Such fractures cause immediate
local tissue reactions, which require urgent medical intervention to prevent
further complications. As a result, it has been promoted that yttria-stabilized
zirconia (Y-TZP) hip prostheses be substituted by alumina and alumina/Y-TZP
ceramics. In the present investigation, we have found an upper limit of Y-TZP
concentration in alumina/Y-TZP composites (16 vol.%) to avoid future aging
problems. This limit coincides with the percolation threshold measured by
infrared (IR) reflectance in a series of alumina/Y-TZP composites.",1804.08696v1
2018-03-30,Reliability assessment in advanced nanocomposite materials for orthopaedic applications,"Alumina-zirconia nano-composites were recently developed as alternative
bearing materials for orthopedics. Previous, preliminary reports show that such
alumina-zirconia nanocomposites exhibit high crack resistance and low wear
rate. In this paper, additional information is given in terms of wear, crack
resistance and ageing behaviour: femoral heads are inspected after 7 million
cycles of wear testing on a hip simulator, crack resistance is measured and
compared to other ceramics used today in orthopedics, slow crack growth is
reported under static and cyclic fatigue, and aging resistance is assessed. We
also report on the load to failure of femoral heads prototypes during
compression tests. This overall reliability assessment ensures a potential
future development for these kinds of new nanocomposites in the orthopedic
field.",1804.08702v1
2018-04-26,Shape of a skyrmion,"We propose a method of determining the shape of a two-dimensional magnetic
skyrmion, which can be parameterized as the position dependence of the
orientation of the local magnetic moment, by using the expansion in terms of
the eigenfunctions of the Schr\""{o}dinger equation of a harmonic oscillator. A
variational calculation is done, up to the next-to-next-to-leading order. This
result is verified by a lattice simulation based on Landau-Lifshitz-Gilbert
equation. Our method is also applied to the dissipative matrix in the Thiele
equation as well as two interacting skyrmions in a bilayer system.",1804.10162v3
2018-04-30,Modular Compact Modeling of Magnetic Tunnel Junction Devices,"This paper describes a robust, modular, and physics- based circuit framework
to model conventional and emerging Magnetic Tunnel Junction (MTJ) devices.
Magnetization dynamics are described by the stochastic Landau-Lifshitz-Gilbert
(sLLG) equation whose results are rigorously benchmarked with a Fokker-Planck
Equation (FPE) description of magnet dynamics. We then show how sLLG is coupled
to transport equations of MTJ-based devices in a unified circuit platform. Step
by step, we illustrate how the physics-based MTJ model can be extended to
include different spintronics phenomena, including spin-transfer-torque (STT),
voltage-control of magnetic anisotropy (VCMA) and spin-orbit torque (SOT)
phenomena by experimentally benchmarked examples. To demonstrate how our
approach can be used in the exploration of novel MTJ-based devices, we also
present a recently proposed MEMS resonator- driven spin-torque nano oscillator
(STNO) that can reduce the phase noise of STNOs. We briefly elaborate on the
use of our framework beyond conventional devices.",1805.00066v2
2018-05-22,Loss of Hall Conductivity Quantization in a Non-Hermitian Quantum Anomalous Hall Insulator,"Recent work has extended topological band theory to open, non-Hermitian
Hamiltonians, yet little is understood about how non-Hermiticity alters the
topological quantization of associated observables. We address this problem by
studying the quantum anomalous Hall effect (QAHE) generated in the Dirac
surface states of a 3D time-reversal-invariant topological insulator (TI) that
is proximity-coupled to a metallic ferromagnet. By constructing a contact
self-energy for the ferromagnet, we show that in addition to generating a mass
gap in the surface spectrum, the ferromagnet can introduce a non-Hermitian
broadening term, which can obscure the mass gap in the spectral function. We
calculate the Hall conductivity for the effective non-Hermitian Hamiltonian
describing the heterostructure and show that it is no longer quantized despite
being classified as a Chern insulator based on non-Hermitian topological band
theory. Our results indicate that the QAHE will be challenging to
experimentally observe in ferromagnet-TI heterostructures due to the finite
lifetime of quasi-particles at the interface.",1805.08892v2
2018-05-31,Spin-orbit torque induced dipole skyrmion motion at room temperature,"We demonstrate deterministic control of dipole-field-stabilized skyrmions by
means of spin-orbit torques arising from heavy transition-metal seed layers.
Experiments are performed on amorphous Fe/Gd multilayers that are patterned
into wires and exhibit stripe domains and dipole skyrmions at room temperature.
We show that while the domain walls and skyrmions are achiral on average due to
lack of Dzyaloshinskii-Moriya interactions, the N\'eel-like closure domain
walls at each surface are chiral and can couple to spin-orbit torques. The
current-induced domain evolutions are reported for different magnetic phases,
including disordered stripe domains, coexisting stripes and dipole skyrmions
and a closed packed dipole skyrmion lattice. The magnetic textures exhibit
motion under current excitations with a current density ~10^8 A/m2. By
comparing the motion resulting from magnetic spin textures in Fe/Gd films with
different heavy transition-metal interfaces, we confirm spin currents can be
used to manipulate achiral dipole skyrmions via spin-orbit torques.",1805.12517v1
2018-06-11,Geometric Lagrangian averaged Euler-Boussinesq and primitive equations,"In this article we derive the equations for a rotating stratified fluid
governed by inviscid Euler-Boussinesq and primitive equations that account for
the effects of the perturbations upon the mean. Our method is based on the
concept of geometric generalized Lagrangian mean recently introduced by Gilbert
and Vanneste, combined with generalized Taylor and horizontal isotropy of
fluctuations as turbulent closure hypotheses. The models we obtain arise as
Euler-Poincar\'{e} equations and inherit from their parent systems conservation
laws for energy and potential vorticity. They are structurally and
geometrically similar to Euler-Boussinesq-$\alpha$ and primitive
equations-$\alpha$ models, however feature a different regularizing second
order operator.",1806.05053v2
2018-06-14,Topological quantization of the flow of magnetic skyrmions driven by a ratchet-like potential under thermal fluctuations,"We consider a magnetic skyrmion adiabatically driven by a spin-polarized
electrical current periodic in both space and time and asymmetric in space, and
also subject to a random magnetic field representing the thermal fluctuations.
We show that when the random magnetic field is low enough, while the time
variation of the driving current is slow enough, the skyrmion flow is an
integer multiply of the ratio between the space and time periods, the integer
being a topological invariant called Chern number. This result is also
demonstrated by numerically solving the stochastic Landau-Lifshitz-Gilbert
(sLLG) and Langevin equations. Our work suggests a novel method of manipulating
skyrmions with topological stability.",1806.05354v1
2018-06-17,Skyrmion Formation Induced by Antiferromagnetic-enhanced Interfacial Dzyaloshinskii Moriya Interaction,"Ne\'el skyrmions originate from interfacial Dzyaloshinskii Moriya interaction
(DMI). Recent studies have explored using ferromagnet to host Ne\'el skyrmions
for device applications. However, challenges remain to reduce the size of
skyrmion to near 10 nm. Amorphous rare-earth-transitional-metal ferrimagnets
are attractive alternative materials to obtain ultrasmall skyrmions at room
temperature. Their intrinsic perpendicular magnetic anisotropy and tunable
magnetization provides a favorable environment for skyrmion stability. In this
work, we employ atomistic stochastic Landau-Liftshitz-Gilbert (LLG) algorithm
to investigate skyrmions in GdFe within the interfacial DMI model. Despite the
rapid decay of DMI away from the interface, small skyrmions of near 10 nm are
found in thick ~ 5 nm amorphous GdFe film at 300K. We have also considered
three scenarios for the sign of DMI between Gd-Fe pair. It is revealed that
antiferromagnetic coupling in the ferrimagnet plays an important role in
enhancing the effect of interfacial DMI and to stabilize skyrmion. These
results show that ferrimagnets and antiferromagnets with intrinsic
antiferromagnetic couplings are appealing materials to host small skyrmions at
room temperature, which is crucial to improve density and energy efficiency in
skyrmion based devices.",1806.06334v1
2018-06-17,Property Testing for Differential Privacy,"We consider the problem of property testing for differential privacy: with
black-box access to a purportedly private algorithm, can we verify its privacy
guarantees? In particular, we show that any privacy guarantee that can be
efficiently verified is also efficiently breakable in the sense that there
exist two databases between which we can efficiently distinguish. We give lower
bounds on the query complexity of verifying pure differential privacy,
approximate differential privacy, random pure differential privacy, and random
approximate differential privacy. We also give algorithmic upper bounds. The
lower bounds obtained in the work are infeasible for the scale of parameters
that are typically considered reasonable in the differential privacy
literature, even when we suppose that the verifier has access to an (untrusted)
description of the algorithm. A central message of this work is that verifying
privacy requires compromise by either the verifier or the algorithm owner.
Either the verifier has to be satisfied with a weak privacy guarantee, or the
algorithm owner has to compromise on side information or access to the
algorithm.",1806.06427v2
2018-06-25,Coupled Wire Models of Interacting Dirac Nodal Superconductors,"Topological nodal superconductors possess gapless low energy excitations that
are characterized by point or line nodal Fermi surfaces. In this work, using a
coupled wire construction, we study topological nodal superconductors that have
protected Dirac nodal points. In this construction, the low-energy electronic
degrees of freedom are confined in a three dimensional array of wires, which
emerge as pairing vortices of a microscopic superconducting system. The vortex
array harbors an antiferromagnetic time-reversal and a mirror glide symmetry
that protect the massless Dirac fermion in the single-body non-interacting
limit. Within this model, we demonstrate exact-solvable many-body interactions
that preserve the underlying symmetries and introduce a finite excitation
energy gap. These gapping interactions support fractionalization and
generically lead to non-trivial topological order. We also construct a special
case of $N=16$ Dirac fermions where corresponding the gapping interaction leads
to a trivial $E_8$ topological order that is closely related to the
cancellation of the large gravitational anomaly.",1806.09599v1
2018-07-02,A Broader View on Bias in Automated Decision-Making: Reflecting on Epistemology and Dynamics,"Machine learning (ML) is increasingly deployed in real world contexts,
supplying actionable insights and forming the basis of automated
decision-making systems. While issues resulting from biases pre-existing in
training data have been at the center of the fairness debate, these systems are
also affected by technical and emergent biases, which often arise as
context-specific artifacts of implementation. This position paper interprets
technical bias as an epistemological problem and emergent bias as a dynamical
feedback phenomenon. In order to stimulate debate on how to change machine
learning practice to effectively address these issues, we explore this broader
view on bias, stress the need to reflect on epistemology, and point to
value-sensitive design methodologies to revisit the design and implementation
process of automated decision-making systems.",1807.00553v2
2018-07-06,Spin-torque-induced magnetization dynamics in ferrimagnets based on Landau-Lifshitz-Bloch Equation,"A theoretical model based on the Landau-Lifshitz-Bloch equation is developed
to study the spin-torque effect in ferrimagnets. Experimental findings, such as
the temperature dependence, the peak in spin torque, and the angular-momentum
compensation, can be well captured. In contrast to the ferromagnet system, the
switching trajectory in ferrimagnets is found to be precession free. The two
sublattices are not always collinear, which produces large exchange field
affecting the magnetization dynamics. The study of material composition shows
the existence of an oscillation region at intermediate current density, induced
by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert
model, our developed model based on the Landau-Lifshitz-Bloch equation enables
the systematic study of spin-torque effect and the evaluation of
ferrimagnet-based devices.",1807.02445v1
2018-07-10,Plumbing Constructions and the Domain of Outer Communication for 5-Dimensional Stationary Black Holes,"The topology of the domain of outer communication for 5-dimensional
stationary bi-axisymmetric black holes is classified in terms of disc bundles
over the 2-sphere and plumbing constructions. In particular we find an
algorithmic bijective correspondence between the plumbing of disc bundles and
the rod structure formalism for such spacetimes. Furthermore, we describe a
canonical fill-in for the black hole region and cap for the asymptotic region.
The resulting compactified domain of outer communication is then shown to be
homeomorphic to $S^4$, a connected sum of $S^2\times S^2$'s, or a connected sum
of complex projective planes $\mathbb{CP}^2$. Combined with recent existence
results, it is shown that all such topological types are realized by vacuum
solutions. In addition, our methods treat all possible types of asymptotic
ends, including spacetimes which are asymptotically flat, asymptotically
Kaluza-Klein, or asymptotically locally Euclidean.",1807.03452v1
2018-07-13,Deep Learning in the Wild,"Deep learning with neural networks is applied by an increasing number of
people outside of classic research environments, due to the vast success of the
methodology on a wide range of machine perception tasks. While this interest is
fueled by beautiful success stories, practical work in deep learning on novel
tasks without existing baselines remains challenging. This paper explores the
specific challenges arising in the realm of real world tasks, based on case
studies from research \& development in conjunction with industry, and extracts
lessons learned from them. It thus fills a gap between the publication of
latest algorithmic and methodical developments, and the usually omitted
nitty-gritty of how to make them work. Specifically, we give insight into deep
learning projects on face matching, print media monitoring, industrial quality
control, music scanning, strategy game playing, and automated machine learning,
thereby providing best practices for deep learning in practice.",1807.04950v1
2018-07-16,Digital frequency multiplexing with sub-Kelvin SQUIDs,"Digital frequency multiplexing (dfMux) is a readout architecture for
transition edge sensor-based detector arrays and is used on telescopes
including SPT-3G, POLARBEAR-2, and LiteBIRD. Here, we present recent progress
and plans for development of a sub-Kelvin SQUID architecture for digital
frequency multiplexed bolometers. This scheme moves the SQUID from the 4 K
stage to the 250 mK stage, adjacent to the bolometers. Operating the SQUID on
the detector stage may offer lower noise and greater scalability. Electrical
performance will be improved as a result of decreased wiring length and reduced
parasitics, allowing for higher multiplexing factors and lower bolometer
R_normal . These performance improvements will enable ultra-large focal planes
for future instruments such as CMB-S4.",1807.05995v1
2018-07-20,Sphinx: a massively multiplexed fiber positioner for MSE,"In this paper we present the Australian Astronomical Observatory's concept
design for Sphinx - a fiber positioned with 4332 spines on a 7.77mm pitch for
CFHT's Mauna Kea Spectroscopic Explorer (MSE) Telescope. Based on the Echidna
technology used with FMOS (on Subaru) and 4MOST (on VISTA), the next evolution
of the tilting spine design delivers improved performance and superior
allocation efficiency. Several prototypes have been constructed that
demonstrate the suitability of the new design for MSE. Results of prototype
testing are presented, along with an analysis of the impact of tilting spines
on the overall survey efficiency. The Sphinx fiber positioned utilizes a novel
metrology system for spine position feedback. The metrology design and the
careful considerations required to achieve reliable, high accuracy measurements
of all fibres in a realistic telescope environment are also presented.",1807.09181v1
2018-07-30,Graphs admitting only constant splines,"We study {\em generalized graph splines,} introduced by Gilbert, Viel, and
the last author. For a large class of rings, we characterize the graphs that
only admit constant splines. To do this, we prove that if a graph has a
particular type of cutset (e.g., a bridge), then the space of splines naturally
decomposes as a certain direct sum of submodules. As an application, we use
these results to describe splines on a triangulation studied by Zhou and Lai,
but over a different ring than they used.",1807.11515v2
2018-08-05,Searching for patchy reionization from cosmic microwave background with hybrid quadratic estimators,"We propose a hybrid quadratic estimator to measure cross correlations between
gravitational lensing of the cosmic microwave background (CMB) and differential
screening effects arising from fluctuations in the electron column density,
such as could arise from patchy reionization. The hybrid quadratic estimators
are validated by simulated data sets with both Planck and CMB-Stage 4 (CMB-S4)
instrumental properties and found to be able to recover the cross-power spectra
with almost no biases. We apply this technique to Planck 2015 temperature data
and obtain cross-power spectra between gravitational lensing and differential
screening effects. Planck data alone cannot detect the
patchy-reionization-induced cross-power spectrum but future experiment like
CMB-S4 will be able to robustly measure the expected signal and deliver new
insights on reionization.",1808.01592v1
2018-08-08,"Revisiting Gilbert Strang's ""A Chaotic Search for $i$""","In the paper ""A Chaotic Search for $i$""~(\cite{strang1991chaotic}), Strang
completely explained the behaviour of Newton's method when using real initial
guesses on $f(x) = x^{2}+1$, which has only a pair of complex roots $\pm i$. He
explored an exact symbolic formula for the iteration, namely $x_{n}=\cot{
\left( 2^{n} \theta_{0} \right) }$, which is valid in exact arithmetic. In this
paper, we extend this to to $k^{th}$ order Householder methods, which include
Halley's method, and to the secant method. Two formulae, $x_{n}=\cot{ \left(
\theta_{n-1}+\theta_{n-2} \right) }$ with
$\theta_{n-1}=\mathrm{arccot}{\left(x_{n-1}\right)}$ and
$\theta_{n-2}=\mathrm{arccot}{\left(x_{n-2}\right)}$, and $x_{n}=\cot{ \left(
(k+1)^{n} \theta_{0} \right) }$ with $\theta_{0} = \mathrm{arccot}(x_{0})$, are
provided. The asymptotic behaviour and periodic character are illustrated by
experimental computation. We show that other methods (Schr\""{o}der iterations
of the first kind) are generally not so simple. We also explain an old method
that can be used to allow Maple's \textsl{Fractals[Newton]} package to
visualize general one-step iterations by disguising them as Newton iterations.",1808.03229v1
2018-08-11,Micromagnetic modeling of Terahertz oscillations in an antiferromagnetic material driven by spin-Hall effect,"The realization of THz sources is a fundamental aspect for a wide range of
applications. Over different approaches, compact THz oscillators can be
realized taking advantage of dynamics in antiferromagnetic (AFMs) thin films
driven by spin-Hall effect. Here we perform a systematic study of these THz
oscillators within a full micromagnetic solver based on the numerical solution
of two coupled Landau-Lifshitz-Gilbert-Slonczewski equations, for the case of
ultra-thin films, i.e. when the N\'eel temperature of an AFM is substantially
reduced. We have found two different dynamical modes depending on the strength
of the Dzyaloshinskii-Moriya interaction (DMI). At low DMI, a large amplitude
precession is excited where both the magnetizations of the sublattices are in a
uniform state and rotate in the same direction. At large enough DMI, the ground
state of the AFM becomes non-uniform and the antiferromagnetic dynamics is
characterized by ultrafast domain wall motion.",1808.03773v1
2018-08-30,Iterative solution and preconditioning for the tangent plane scheme in computational micromagnetics,"The tangent plane scheme is a time-marching scheme for the numerical solution
of the nonlinear parabolic Landau-Lifshitz-Gilbert equation (LLG), which
describes the time evolution of ferromagnetic configurations. Exploiting the
geometric structure of LLG, the tangent plane scheme requires only the solution
of one linear variational form per time-step, which is posed in the discrete
tangent space determined by the nodal values of the current magnetization. We
develop an effective solution strategy for the arising constrained linear
systems, which is based on appropriate Householder reflections. We derive
possible preconditioners, which are (essentially) independent of the time-step,
and prove that the preconditioned GMRES algorithm leads to linear convergence.
Numerical experiments underpin the theoretical findings.",1808.10281v1
2018-09-12,Iterative Delegations in Liquid Democracy with Restricted Preferences,"In this paper, we study liquid democracy, a collective decision making
paradigm which lies between direct and representative democracy. One main
feature of liquid democracy is that voters can delegate their votes in a
transitive manner so that: A delegates to B and B delegates to C leads to A
delegates to C. Unfortunately, this process may not converge as there may not
even exist a stable state (also called equilibrium). In this paper, we
investigate the stability of the delegation process in liquid democracy when
voters have restricted types of preference on the agent representing them
(e.g., single-peaked preferences). We show that various natural structures of
preferences guarantee the existence of an equilibrium and we obtain both
tractability and hardness results for the problem of computing several
equilibria with some desirable properties.",1809.04362v2
2018-09-25,Phase change materials for nano-polaritonics: a case study of hBN/VO2 heterostructures,"Polaritonic excitation and control in van der Waals (vdW) materials exhibit
superior merits than conventional materials and thus hold new promise for
exploring light matter interactions. In this work, we created vdW
heterostructures combining hexagonal boron nitride (hBN) and a representative
phase change material - vanadium dioxide (VO2). Using infrared
nano-spectroscopy and nano-imaging, we demonstrated the dynamic tunability of
hyperbolic phonon polaritons in hBN/VO2 heterostructures by temperature control
in a precise and reversible fashion. The dynamic tuning of the polaritons stems
from the change of local dielectric properties of the VO2 sublayer through
insulator to metal transition by the temperature control. The high
susceptibility of polaritons to electronic phase transitions opens
possibilities for applications of vdW materials in combination with correlated
phase change materials.",1809.09652v1
2018-10-08,Causal isotonic regression,"In observational studies, potential confounders may distort the causal
relationship between an exposure and an outcome. However, under some
conditions, a causal dose-response curve can be recovered using the
G-computation formula. Most classical methods for estimating such curves when
the exposure is continuous rely on restrictive parametric assumptions, which
carry significant risk of model misspecification. Nonparametric estimation in
this context is challenging because in a nonparametric model these curves
cannot be estimated at regular rates. Many available nonparametric estimators
are sensitive to the selection of certain tuning parameters, and performing
valid inference with such estimators can be difficult. In this work, we propose
a nonparametric estimator of a causal dose-response curve known to be monotone.
We show that our proposed estimation procedure generalizes the classical
least-squares isotonic regression estimator of a monotone regression function.
Specifically, it does not involve tuning parameters, and is invariant to
strictly monotone transformations of the exposure variable. We describe
theoretical properties of our proposed estimator, including its irregular limit
distribution and the potential for doubly-robust inference. Furthermore, we
illustrate its performance via numerical studies, and use it to assess the
relationship between BMI and immune response in HIV vaccine trials.",1810.03269v2
2018-10-10,On the Approximation Properties of Random ReLU Features,"We study the approximation properties of random ReLU features through their
reproducing kernel Hilbert space (RKHS). We first prove a universality theorem
for the RKHS induced by random features whose feature maps are of the form of
nodes in neural networks. The universality result implies that the random ReLU
features method is a universally consistent learning algorithm. We prove that
despite the universality of the RKHS induced by the random ReLU features,
composition of functions in it generates substantially more complicated
functions that are harder to approximate than those functions simply in the
RKHS. We also prove that such composite functions can be efficiently
approximated by multi-layer ReLU networks with bounded weights. This depth
separation result shows that the random ReLU features models suffer from the
same weakness as that of shallow models. We show in experiments that the
performance of random ReLU features is comparable to that of random Fourier
features and, in general, has a lower computational cost. We also demonstrate
that when the target function is the composite function as described in the
depth separation theorem, 3-layer neural networks indeed outperform both random
ReLU features and 2-layer neural networks.",1810.04374v3
2018-10-15,ABACUS: Unsupervised Multivariate Change Detection via Bayesian Source Separation,"Change detection involves segmenting sequential data such that observations
in the same segment share some desired properties. Multivariate change
detection continues to be a challenging problem due to the variety of ways
change points can be correlated across channels and the potentially poor
signal-to-noise ratio on individual channels. In this paper, we are interested
in locating additive outliers (AO) and level shifts (LS) in the unsupervised
setting. We propose ABACUS, Automatic BAyesian Changepoints Under Sparsity, a
Bayesian source separation technique to recover latent signals while also
detecting changes in model parameters. Multi-level sparsity achieves both
dimension reduction and modeling of signal changes. We show ABACUS has
competitive or superior performance in simulation studies against
state-of-the-art change detection methods and established latent variable
models. We also illustrate ABACUS on two real application, modeling genomic
profiles and analyzing household electricity consumption.",1810.06167v1
2018-10-24,Photoinduced topological spin texture in a metallic ferromagnet,"Photoinduced nonequilibrium spin structure is examined in the double-exchange
model, in which itinerant electrons couple with localized spins through the
ferromagnetic Hund coupling. In particular, we focus on the transient spin
structure from the initial ferromagnetic metallic state to the steady
antiferromagnetic ordered state reported in [Phys. Rev. Lett. 119, 207202
(2017)]. By solving the Schr\""odinger equation combined with the
Landau-Lifshitz-Gilbert equation, we find finite winding number and chirality,
which implies emergence of topological chiral spin textures. These observations
are reproduced by a calculation where spin dynamics after sudden quench of the
chemical potential are examined in larger clusters. A possible mechanism of the
topological spin texture in the transient dynamics is discussed.",1810.10244v1
2018-11-01,Time Quantified Monte Carlo Method for Long-range Interacting Systems,"We propose a method for simulating the stochastic dynamics of classical spin
systems with long-range interactions. The method incorporates the stochastic
cutoff (SCO) method, which is originally specialized for simulating equilibrium
state, into time quantified Monte Carlo (TQMC) method. We analytically prove
that the present method gives the same real-time dynamics with the stochastic
Landau-Lifshitz-Gilbert (s-LLG) equation, i.e., both method derives the same
Fokker-Planck coefficients. We demonstrate magnetization reversal processes and
confirm that the result is in good agreement with the result obtained by s-LLG.
Using our method enables us to analyze complicated lattice systems consisting
of many spins in a unit cell. Technical improvement of TQMC is also proposed.",1811.00237v2
2018-11-01,Spatial Functional Linear Model and its Estimation Method,"The classical functional linear regression model (FLM) and its extensions,
which are based on the assumption that all individuals are mutually
independent, have been well studied and are used by many researchers. This
independence assumption is sometimes violated in practice, especially when data
with a network structure are collected in scientific disciplines including
marketing, sociology and spatial economics. However, relatively few studies
have examined the applications of FLM to data with network structures. We
propose a novel spatial functional linear model (SFLM), that incorporates a
spatial autoregressive parameter and a spatial weight matrix into FLM to
accommodate spatial dependencies among individuals. The proposed model is
relatively flexible as it takes advantage of FLM in handling high-dimensional
covariates and spatial autoregressive (SAR) model in capturing network
dependencies. We develop an estimation method based on functional principal
component analysis (FPCA) and maximum likelihood estimation. Simulation studies
show that our method performs as well as the FPCA-based method used with FLM
when no network structure is present, and outperforms the latter when network
structure is present. A real weather data is also employed to demonstrate the
utility of the SFLM.",1811.00314v1
2018-11-12,New Theoretical Bounds and Constructions of Permutation Codes under Block Permutation Metric,"Permutation codes under different metrics have been extensively studied due
to their potentials in various applications. Generalized Cayley metric is
introduced to correct generalized transposition errors, including previously
studied metrics such as Kendall's $\tau$-metric, Ulam metric and Cayley metric
as special cases. Since the generalized Cayley distance between two
permutations is not easily computable, Yang et al. introduced a related metric
of the same order, named the block permutation metric. Given positive integers
$n$ and $d$, let $\mathcal{C}_{B}(n,d)$ denote the maximum size of a
permutation code in $S_n$ with minimum block permutation distance $d$. In this
paper, we focus on the theoretical bounds of $\mathcal{C}_{B}(n,d)$ and the
constructions of permutation codes under block permutation metric. Using a
graph theoretic approach, we improve the Gilbert-Varshamov type bound by a
factor of $\Omega(\log{n})$, when $d$ is fixed and $n$ goes into infinity. We
also propose a new encoding scheme based on binary constant weight codes.
Moreover, an upper bound beating the sphere-packing type bound is given when
$d$ is relatively close to $n$.",1811.04600v1
2018-11-13,Classical Access Structures of Ramp Secret Sharing Based on Quantum Stabilizer Codes,"In this paper we consider to use the quantum stabilizer codes as secret
sharing schemes for classical secrets. We give necessary and sufficient
conditions for qualified and forbidden sets in terms of quantum stabilizers.
Then we give a Gilbert-Varshamove-type sufficient condition for existence of
secret sharing schemes with given parameters, and by using that sufficient
condition, we show that roughly 19% of participants can be made forbidden
independently of the size of classical secret, in particular when an $n$-bit
classical secret is shared among $n$ participants having 1-qubit share each. We
also consider how much information is obtained by an intermediate set and
express that amount of information in terms of quantum stabilizers. All the
results are stated in terms of linear spaces over finite fields associated with
the quantum stabilizers.",1811.05217v7
2018-11-13,Enhanced domain wall velocity near a ferromagnetic instability,"Assuming a Fermi liquid behavior for $s$-conduction electrons, we rewrite the
extended Landau-Lifshitz-Gilbert (LLG) equation renormalized by interactions
through the Landau parameters $F^{a}_{l}$ ($l=0,1,2 \cdots$) in an explicit
form to describe the dynamic of a domain wall (DW) due to spin transfer torque
phenomenon. The interaction between spins of the \textit{s}-conduction
electrons explains qualitatively the DW velocity experimental observations in
$\mathrm{Ni_{81}}\mathrm{Fe_{19}}$ (Permalloy) recalculated by us without
defects or impurity hypothesis. Close to Stoner ferromagnetic instability point
where $F^{a}_{0} \approx -0.99$, the DW velocity becomes high
($v^{*}_{DW}\approx 600$ $ms^{-1}$) and critical spin current density becomes
reduced ($j^{*}_{c}\approx1\times10^{12}$ $Am^{-2}$) when compared to that
calculated by nonadiabatic approach. At the critical point, the DW velocity
diverges while critical spin current density at the same point goes to zero.
Our theory also provides a prediction to looking for materials in which is
possible applies a smallest critical spin current density and observes higher
DW velocity.",1811.05380v4
2018-12-07,Coding over Sets for DNA Storage,"In this paper we study error-correcting codes for the storage of data in
synthetic deoxyribonucleic acid (DNA). We investigate a storage model where a
data set is represented by an unordered set of $M$ sequences, each of length
$L$. Errors within that model are a loss of whole sequences and point errors
inside the sequences, such as insertions, deletions and substitutions. We
derive Gilbert-Varshamov lower bounds and sphere packing upper bounds on
achievable cardinalities of error-correcting codes within this storage model.
We further propose explicit code constructions than can correct errors in such
a storage system that can be encoded and decoded efficiently. Comparing the
sizes of these codes to the upper bounds, we show that many of the
constructions are close to optimal.",1812.02936v3
2018-12-14,Computational micromagnetics with Commics,"We present our open-source Python module Commics for the study of the
magnetization dynamics in ferromagnetic materials via micromagnetic
simulations. It implements state-of-the-art unconditionally convergent finite
element methods for the numerical integration of the Landau-Lifshitz-Gilbert
equation. The implementation is based on the multiphysics finite element
software Netgen/NGSolve. The simulation scripts are written in Python, which
leads to very readable code and direct access to extensive post-processing.
Together with documentation and example scripts, the code is freely available
on GitLab.",1812.05931v1
2019-01-10,Multi-Parameter Regression Survival Modelling: An Alternative to Proportional Hazards,"It is standard practice for covariates to enter a parametric model through a
single distributional parameter of interest, for example, the scale parameter
in many standard survival models. Indeed, the well-known proportional hazards
model is of this kind. In this paper we discuss a more general approach whereby
covariates enter the model through more than one distributional parameter
simultaneously (e.g., scale and shape parameters). We refer to this practice as
""multi-parameter regression"" (MPR) modelling and explore its use in a survival
analysis context. We find that multi-parameter regression leads to more
flexible models which can offer greater insight into the underlying data
generating process. To illustrate the concept, we consider the two-parameter
Weibull model which leads to time-dependent hazard ratios, thus relaxing the
typical proportional hazards assumption and motivating a new test of
proportionality. A novel variable selection strategy is introduced for such
multi-parameter regression models. It accounts for the correlation arising
between the estimated regression coefficients in two or more linear predictors
-- a feature which has not been considered by other authors in similar
settings. The methods discussed have been implemented in the mpr package in R.",1901.03277v1
2019-02-01,A Penrose-Type Inequality with Angular Momentum and Charge for Axisymmetric Initial Data,"A lower bound for the ADM mass is established in terms of angular momentum,
charge, and horizon area in the context of maximal, axisymmetric initial data
for the Einstein-Maxwell equations which satisfy the weak energy condition. If,
on the horizon, the given data agree to a certain extent with the associated
model Kerr-Newman data, then the inequality reduces to the conjectured Penrose
inequality with angular momentum and charge. In addition, a rigidity statement
is also proven whereby equality is achieved if and only if the data set arises
from the canonical slice of a Kerr-Newman spacetime.",1902.00501v3
2019-02-08,Field-tuned spin excitation spectrum of $kπ$-skyrmion,"We study spin-wave excitation modes of $k\pi$ skyrmion in a magnetic nanodot
under an external magnetic field along $z$-direction using micromagnetic
simulations based on Landau-Lifshitz-Gilbert equation. We find that a
transition of $k\pi$ skyrmion to other skyrmion-like structures appears under
some critical external field, the corresponding spin-wave spectra are simulated
for each state in the process of applying magnetic field. For skyrmion, the
frequencies of excitation modes increases and then decreases with the low
frequency modes splitting at a critical magnetic field. In addition to the well
known two in-plane rotational modes and a out-of-plane breathing mode of
skyrmion, a higher number of excitation modes are found with increasing $k$
($k=2, 3$). The excitation modes vary as a function of magnetic field, and the
excitation frequencies for different modes exhibit a rapid or slight change
depending on the field induced change of magnetization profile. Our study
indicates the rich spin-wave excitations for $k\pi$ skyrmion and opens a
possibility in theoretical or experimental investigation of magnonics
application.",1902.02901v2
2019-02-08,Simulation of the Magnetization Dynamics of a Single Domain BiFeO$_3$ Thin Film,"The switching dynamics of a single-domain BiFeO$_3$ thin films is
investigated through combining the dynamics of polarization and Neel vector.
The evolution of the ferroelectric polarization is described by the
Landau-Khalatnikov (LK) equation, and the Landau-Lifshitz-Gilbert (LLG)
equations for spins in two sublattices to model the time evolution of the
antiferromagnetic order (Neel vector) in a G-type antiferromagnet. This work
theoretically demonstrates that due to the rotation of the magnetic hard axis
following the polarization reversal, the Neel vector can be switched by 180
degrees, while the weak magnetization can remain unchanged. The simulation
results are consistent with the ab initio calculation, where the Neel vector
rotates during polarization rotation, and also match our calculation of the
dynamics of order parameter using Landau-Ginzburg theory. We also find that the
switching time of the Neel vector is determined by the speed polarization
switching and is predicted to be as short as 30 ps.",1902.03330v1
2019-02-13,Dynamics of ferromagnetic domain walls under extreme fields,"We report the existence of a new regime for domain wall motion in uniaxial
and near-uniaxial ferromagnetic nanowires, characterised by applied magnetic
fields sufficiently strong that one of the domains becomes unstable. There
appears a new stable solution of the Landau-Lifshitz-Gilbert equation,
describing a nonplanar domain wall moving with constant velocity and precessing
with constant frequency. Even in the presence of thermal noise, the new
solution can propagate for distances on the order of 500 times the field-free
domain wall width before fluctuations in the unstable domain become
appreciable.",1902.04968v3
2019-02-28,Topological $d$-wave Superconductivity and Nodal Line-Arc Intersections in Weyl Semimetals,"Superconducting Weyl semimetals present a novel and promising system to
harbor new forms of unconventional topological superconductivity. Within the
context of time-reversal symmetric Weyl semimetals with $d$-wave
superconductivity, we demonstrate that the number of Majorana cones equates to
the number of intersections between the $d$-wave nodal lines and the Fermi
arcs. We illustrate the importance of nodal line-arc intersections by
demonstrating the existence of locally stable surface Majorana cones that the
winding number does not predict. The discrepancy between Majorana cones and the
winding number necessitates an augmentation of the winding number formulation
to account for each intersection. In addition, we show that imposing additional
mirror symmetries globally protect the nodal line-arc intersections and the
corresponding Majorana cones.",1903.00024v2
2019-03-07,Stronger L2/L2 Compressed Sensing; Without Iterating,"We consider the extensively studied problem of $\ell_2/\ell_2$ compressed
sensing. The main contribution of our work is an improvement over [Gilbert, Li,
Porat and Strauss, STOC 2010] with faster decoding time and significantly
smaller column sparsity, answering two open questions of the aforementioned
work.
  Previous work on sublinear-time compressed sensing employed an iterative
procedure, recovering the heavy coordinates in phases. We completely depart
from that framework, and give the first sublinear-time $\ell_2/\ell_2$ scheme
which achieves the optimal number of measurements without iterating; this new
approach is the key step to our progress. Towards that, we satisfy the
$\ell_2/\ell_2$ guarantee by exploiting the heaviness of coordinates in a way
that was not exploited in previous work. Via our techniques we obtain improved
results for various sparse recovery tasks, and indicate possible further
applications to problems in the field, to which the aforementioned iterative
procedure creates significant obstructions.",1903.02742v1
2019-03-17,A Brief history of mangnetism,"In this article an overview of the historical development of the key ideas in
the field of magnetism is presented. The presentation is semi-technical in
nature.Starting by noting down important contribution of Greeks, William
Gilbert, Coulomb, Poisson, Oersted, Ampere, Faraday, Maxwell, and Pierre Curie,
we review early 20th century investigations by Paul Langevin and Pierre Weiss.
The Langevin theory of paramagnetism and the Weiss theory of ferromagnetism
were partly successful and real understanding of magnetism came with the advent
of quantum mechanics. Van Vleck was the pioneer in applying quantum mechanics
to the problem of magnetism and we discuss his main contributions: (1) his
detailed quantum statistical mechanical study of magnetism of real gases; (2)
his pointing out the importance of the crystal fields or ligand fields in the
magnetic behavior of iron group salts (the ligand field theory); and (3) his
many contributions to the elucidation of exchange interactions in d electron
metals. Next, the pioneering contributions (but lesser known) of Dorfman are
discussed. Then, in chronological order, the key contributions of Pauli,
Heisenberg, and Landau are presented. Finally, we discuss a modern topic of
quantum spin liquids.",1903.07031v1
2019-03-19,Separability Properties of Nilpotent $\mathbb{Q}[x]$-Powered Groups,"In this paper we study conjugacy and subgroup separability properties in the
class of nilpotent $\mathbb{Q}[x]$-powered groups. Many of the techniques used
to study these properties in the context of ordinary nilpotent groups carry
over naturally to this more general class. Among other results, we offer a
generalization of a theorem due to G. Baumslag. The generalized version states
that if $G$ is a finitely $\mathbb{Q}[x]$-generated
$\mathbb{Q}[x]$-torsion-free nilpotent $\mathbb{Q}[x]$-powered group and $H$ is
a $\mathbb{Q}[x]$-isolated subgroup of $G,$ then for any prime $\pi \in
\mathbb{Q}[x]$, $\bigcap_{i = 1}^{\infty} G^{{\pi}^{i}}H = H.$",1903.08220v1
2019-03-24,"Synchronized, periodic, and chaotic dynamics in spin torque oscillator with two free layers","A phase diagram of the magnetization dynamics is studied by numerically
solving the Landau-Lifshitz-Gilbert (LLG) equation in a spin torque oscillator
consisting of asymmetric two free layers that are magnetized in in-plane
direction. We calculated the dynamics for a wide range of current density for
both low and high field cases, and found many dynamical phases such as
synchronization, auto-oscillation with different frequencies, and chaotic
dynamics. The observation of the synchronization indicates the presence of a
dynamical phase which has not been found experimentally by using the
conventional electrical detection method. The auto-oscillations with different
frequencies lead to an oscillation of magnetoresistance with a high frequency,
which can be measured experimentally. The chaotic and/or periodic behavior of
magnetoresistance in a high current region, on the other hand, leads to a
discontinuous change of the peak frequency in Fourier spectrum.",1903.09938v2
2019-04-07,Hybrid Approaches to Detect Comments Violating Macro Norms on Reddit,"In this dataset paper, we present a three-stage process to collect Reddit
comments that are removed comments by moderators of several subreddits, for
violating subreddit rules and guidelines. Other than the fact that these
comments were flagged by moderators for violating community norms, we do not
have any other information regarding the nature of the violations. Through this
procedure, we collect over 2M comments removed by moderators of 100 different
Reddit communities, and publicly release the data. Working with this dataset of
removed comments, we identify 8 macro norms---norms that are widely enforced on
most parts of Reddit. We extract these macro norms by employing a hybrid
approach---classification, topic modeling, and open-coding---on comments
identified to be norm violations within at least 85 out of the 100 study
subreddits. Finally, we label over 40K Reddit comments removed by moderators
according to the specific type of macro norm being violated, and make this
dataset publicly available. By breaking down a collection of removed comments
into more granular types of macro norm violation, our dataset can be used to
train more nuanced machine learning classifiers for online moderation.",1904.03596v2
2019-04-11,Triangular array of iron-oxide nanoparticles: A simulation study of intra- and inter-particle magnetism,"A study of spherical maghemite nanoparticles on a two dimensional triangular
array was carried out using a stochastic Landau-Lifshitz-Gilbert (sLLG)
approach. The simulation method was first validated with a triangular array of
simple dipoles, where results show the expected phase transition to a
ferromagnetic state at a finite temperature. The ground state exhibited a
continuous degeneracy that was lifted by an order-from-disorder mechanism at
infinitesimal temperatures with the appearance of a six-fold planar anisotropy.
The nanoparticle array consisted of 7.5 nm diameter maghemite spheres with
bulk-like superexchange interactions between Fe-ions in the core, and weaker
exchange between surface Fe-ions and a radial anisotropy. The triangular
nanoparticle array ordered at the same reduced temperature as the simple dipole
array, but exhibited different behaviour at low temperatures due to the surface
anisotropy. We find that the vacancies on the octahedral sites in the
nanoparticles combine with the surface anisotropy to produce an effective
random temperature-dependent anisotropy for each particle. This leads to a
reduction in the net magnetization of the nanoparticle array at zero
temperature compared to the simple dipole array.",1904.05515v1
2019-04-15,Mathematical analysis of weak and strong solutions to an evolutionary model for magnetoviscoelasticity,"The paper is concerned with the analysis of an evolutionary model for
magnetoviscoelastic materials in two dimensions. The model consists of a
Navier-Stokes system featuring a dependence of the stress tensor on elastic and
magnetic terms, a regularized system for the evolution of the deformation
gradient and the Landau-Lifshitz-Gilbert system for the dynamics of the
magnetization.
  First, we show that our model possesses global in time weak solutions, thus
extending work by Bene\v{s}ov\'a et al. 2018. Compared to that work, we include
the stray field energy and relax the assumptions on the elastic energy density.
Second, we prove the local in time existence of strong solutions. Both
existence results are based on the Galerkin method. Finally, we show a
weak-strong uniqueness property.",1904.07179v1
2019-04-25,Message Randomization and Strong Security in Quantum Stabilizer-Based Secret Sharing for Classical Secrets,"We improve the flexibility in designing access structures of quantum
stabilizer-based secret sharing schemes for classical secrets, by introducing
message randomization in their encoding procedures. We generalize the
Gilbert-Varshamov bound for deterministic encoding to randomized encoding of
classical secrets. We also provide an explicit example of a ramp secret sharing
scheme with which multiple symbols in its classical secret are revealed to an
intermediate set, and justify the necessity of incorporating strong security
criterion of conventional secret sharing. Finally, we propose an explicit
construction of strongly secure ramp secret sharing scheme by quantum
stabilizers, which can support twice as large classical secrets as the
McEliece-Sarwate strongly secure ramp secret sharing scheme of the same share
size and the access structure.",1904.11114v3
2019-05-02,Benchmark Instances and Branch-and-Cut Algorithm for the Hashiwokakero Puzzle,"Hashiwokakero, or simply Hashi, is a Japanese single-player puzzle played on
a rectangular grid with no standard size. Some cells of the grid contain a
circle, called island, with a number inside it ranging from one to eight. The
remaining positions of the grid are empty. The player must connect all of the
islands by drawing a series of horizontal or vertical bridges between them,
respecting a series of rules: the number of bridges incident to an island
equals the number indicated in the circle, at most two bridges are incident to
any side of an island, bridges cannot cross each other or pass through islands,
and each island must eventually be reachable from any other island. In this
paper, we present some complexity results and relationships between Hashi and
well-known graph theory problems. We give a formulation of the problem by means
of an integer linear mathematical programming model, and apply a branch-and-cut
algorithm to solve the model in which connectivity constraints are dynamically
generated. We also develop a puzzle generator. Our experiments on 1440 Hashi
puzzles show that the algorithm can consistently solve hard puzzles with up to
400 islands.",1905.00973v1
2019-05-06,An excess of non-Gaussian fluctuations in the cosmic infrared background consistent with gravitational lensing,"The cosmic infrared background (CIB) is gravitationally lensed. A
quadratic-estimator technique that is inherited from lensing analyses of the
cosmic microwave background (CMB) can be applied to detect the CIB lensing
effects. However, the CIB fluctuations are intrinsically strongly non-Gaussian,
making CIB lensing reconstruction highly biased. We perform numerical
simulations to estimate the intrinsic non-Gaussianity and establish a
cross-correlation approach to precisely extract the CIB lensing signal from raw
data. We apply this technique to CIB data from the Planck satellite and
cross-correlate the resulting lensing estimate with the CIB data, galaxy number
counts and the CMB lensing potential. We detect an excess that is consistent
with a lensing contribution at $>4\sigma$.",1905.02084v1
2019-05-14,Multi-reference quantum chemistry protocol for simulating autoionization spectra: Test of ionization continuum models for the neon atom,"In this contribution we present a protocol to evaluate partial and total
Auger decay rates combining the restricted active space self-consistent field
electronic structure method for the bound part of the spectrum and numerically
obtained continuum orbitals in the single-channel scattering theory framework.
On top of that, the two-step picture is employed to evaluate the partial rates.
The performance of the method is exemplified for the prototypical Auger decay
of the neon $1s^{-1}3p$ resonance. Different approximations to obtain the
continuum orbitals, the partial rate matrix elements, and the electronic
structure of the bound part are tested against theoretical and experimental
reference data. It is demonstrated that the partial and total rates are most
sensitive to the accuracy of the continuum orbitals. For instance, it is
necessary to account for the direct Coulomb potential of the ion for the
determination of the continuum wave functions. The Auger energies can be
reproduced quite well already with a rather small active space. Finally,
perspectives of the application of the proposed protocol to molecular systems
are discussed.",1905.05785v2
2019-06-16,A concise guide to existing and emerging vehicle routing problem variants,"Vehicle routing problems have been the focus of extensive research over the
past sixty years, driven by their economic importance and their theoretical
interest. The diversity of applications has motivated the study of a myriad of
problem variants with different attributes. In this article, we provide a
concise overview of existing and emerging problem variants. Models are
typically refined along three lines: considering more relevant objectives and
performance metrics, integrating vehicle routing evaluations with other
tactical decisions, and capturing fine-grained yet essential aspects of modern
supply chains. We organize the main problem attributes within this structured
framework. We discuss recent research directions and pinpoint current
shortcomings, recent successes, and emerging challenges.",1906.06750v2
2019-07-01,Formation process of skyrmion lattice domain boundaries: The role of grain boundaries,"We report on the formation process of skyrmion lattice (SkL) domain
boundaries in FeGe using Lorentz transmission electron microscopy and
small-angle electron diffraction. We observed that grain boundaries and edges
play an important role in the formation of SkL domain boundaries; The SkL
domain boundary is stabilized at the intersection of two grains. A
micromagnetic simulation using the Landau-Lifshitz-Gilbert equation revealed
that the SkL domains separated by a boundary represent the lowest energy
configuration. Conversely, in a wide area, SkL domain boundaries were not
formed and SkL domains with different orientations rotated to form a single SkL
domain.",1907.00774v1
2019-07-02,Quantum Data-Syndrome Codes,"Performing active quantum error correction to protect fragile quantum states
highly depends on the correctness of error information--error syndromes. To
obtain reliable error syndromes using imperfect physical circuits, we propose
the idea of quantum data-syndrome (DS) codes that are capable of correcting
both data qubits and syndrome bits errors. We study fundamental properties of
quantum DS codes, including split weight enumerators, generalized MacWilliams
identities, and linear programming bounds. In particular, we derive Singleton
and Hamming-type upper bounds on degenerate quantum DS codes. Then we study
random DS codes and show that random DS codes with a relatively small
additional syndrome measurements achieve the Gilbert-Varshamov bound of
stabilizer codes. Constructions of quantum DS codes are also discussed. A
family of quantum DS codes is based on classical linear block codes, called
syndrome measurement codes, so that syndrome bits are encoded in additional
redundant stabilizer measurements. Another family of quantum DS codes is
CSS-type quantum DS codes based on classical cyclic codes, and this includes
the Steane code and the quantum Golay code.",1907.01393v1
2019-07-02,Prediction of topological Hall effect in a driven magnetic domain wall,"We investigate the possible emergence of topological Hall effect (THE) in a
driven magnetic DW. Numerical simulation based on the
Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation shows that the emergent
magnetic flux appears when the DW is in a non-equilibrium state. The magnitude
of magnetic flux is modulated by Dzyaloshinskii-Moriya interaction (DMI) or
in-plane longitudinal magnetic field, providing an experimental test of the
predicted THE. These results indicate that the THE can be observed even in a
topologically trivial magnetic DW, and therefore open up new possibility to
electrically detect the dynamical spin structure.",1907.01648v2
2019-07-04,Resonant Acoustic Wave Assisted Spin-Transfer-Torque Switching of Nanomagnets,"We report the possibility of achieving an order of magnitude reduction in the
energy dissipation needed to write bits in perpendicular magnetic tunnel
junctions (p-MTJs) by simulating the magnetization dynamics under a combination
of resonant surface acoustic waves (r-SAW) and spin-transfer-torque (STT). The
magnetization dynamics were simulated using the Landau-Lifshitz-Gilbert
equation under macrospin assumption with the inclusion of thermal noise. The
resonant magnetization dynamics in the magnetostrictive nanomagnet build over
few 10s of cycles of SAW application that drives the magnetization to precess
in a cone with a deflection of ~45 degrees from the perpendicular direction.
This reduces the STT current density required to switch the magnetization
direction without increasing the STT application time or degrading the
switching probability in the presence of room temperature thermal noise. This
could lead to a pathway to achieve energy efficient switching of spin transfer
torque random access memory (STTRAM) whose lateral dimensions can be scaled
aggressively despite using materials with low magnetostriction by employing
resonant excitation.",1907.02255v1
2019-07-04,Second-order semi-implicit projection methods for micromagnetics simulations,"Micromagnetics simulations require accurate approximation of the
magnetization dynamics described by the Landau-Lifshitz-Gilbert equation, which
is nonlinear, nonlocal, and has a non-convex constraint, posing interesting
challenges in developing numerical methods. In this paper, we propose two
second-order semi-implicit projection methods based on the second-order
backward differentiation formula and the second-order interpolation formula
using the information at previous two temporal steps. Unconditional unique
solvability of both methods is proved, with their second-order accuracy
verified through numerical examples in both 1D and 3D. The efficiency of both
methods is compared to that of another two popular methods. In addition, we
test the robustness of both methods for the first benchmark problem with a
ferromagnetic thin film material from National Institute of Standards and
Technology.",1907.02358v1
2019-07-11,"Astro2020 Activity, Project of State of the Profession Consideration (APC) White Paper: All-Sky Near Infrared Space Astrometry. State of the Profession Considerations: Development of Scanning NIR Detectors for Astronomy","Gaia is a revolutionary space mission developed by ESA and is delivering 5
parameter astrometry, photometry and radial velocities over the whole sky with
astrometric accuracies down to a few tens of micro-arcseconds. A weakness of
Gaia is that it only operates at optical wavelengths. However, much of the
Galactic centre and the spiral arm regions, important for certain studies, are
obscured by interstellar extinction and this makes it difficult for Gaia to
deeply probe. This problem can be overcome by switching to the Near Infra-Red
(NIR) but this is not possible with silicon CCDs. Additionally, to scan the
entire sky and make global absolute parallax measurements the spacecraft must
have a constant rotation and this requires the detectors operate in Time
Delayed Integration (TDI) mode or similar.",1907.05191v1
2019-07-21,Performance of a low-parasitic frequency-domain multiplexing readout,"Frequency-domain multiplexing is a readout technique for transition edge
sensor bolometer arrays used on modern CMB experiments, including the SPT-3G
receiver. Here, we present design details and performance measurements for a
low-parasitic frequency-domain multiplexing readout. Reducing the parasitic
impedance of the connections between cryogenic components provides a path to
improving both the crosstalk and noise performance of the readout. Reduced
crosstalk will in turn allow higher multiplexing factors. We have demonstrated
a factor of two improvement in parasitic resistance compared to SPT-3G
hardware. Reduced parasitics also permits operation of lower-resistance
bolometers, which enables better optimization of R$_{\rm{bolo}}$ for improved
readout noise performance. The prototype system exhibits noise performance
comparable to SPT-3G readout hardware when operating SPT-3G detectors.",1907.09035v1
2019-08-09,MakeSense: An IoT Testbed for Social Research of Indoor Activities,"There has been increasing interest in deploying IoT devices to study human
behaviour in locations such as homes and offices. Such devices can be deployed
in a laboratory or `in the wild' in natural environments. The latter allows one
to collect behavioural data that is not contaminated by the artificiality of a
laboratory experiment. Using IoT devices in ordinary environments also brings
the benefits of reduced cost, as compared with lab experiments, and less
disturbance to the participants' daily routines which in turn helps with
recruiting them into the research. However, in this case, it is essential to
have an IoT infrastructure that can be easily and swiftly installed and from
which real-time data can be securely and straightforwardly collected. In this
paper, we present MakeSense, an IoT testbed that enables real-world
experimentation for large scale social research on indoor activities through
real-time monitoring and/or situation-aware applications. The testbed features
quick setup, flexibility in deployment, the integration of a range of IoT
devices, resilience, and scalability. We also present two case studies to
demonstrate the use of the testbed, one in homes and one in offices.",1908.03380v1
2019-08-13,On Steane-Enlargement of Quantum Codes from Cartesian Product Point Sets,"In this work, we study quantum error-correcting codes obtained by using
Steane-enlargement. We apply this technique to certain codes defined from
Cartesian products previously considered by Galindo et al. in [4]. We give
bounds on the dimension increase obtained via enlargement, and additionally
give an algorithm to compute the true increase. A number of examples of codes
are provided, and their parameters are compared to relevant codes in the
literature, which shows that the parameters of the enlarged codes are
advantageous. Furthermore, comparison with the Gilbert-Varshamov bound for
stabilizer quantum codes shows that several of the enlarged codes match or
exceed the parameters promised by the bound.",1908.04560v1
2019-08-17,Band-pass Magnetic Tunnel Junction based Magnetoresistive Random Access Memory,"We propose spin transfer torque--magnetoresistive random access memory
(STT-MRAM) based on magneto-resistance and spin transfer torque physics of
band-pass spin filtering. Utilizing the electronic analogs of optical phenomena
such as anti-reflection coating and resonance for spintronic devices, we
present the design of an STT-MRAM device with improved features when compared
with a traditional trilayer device. The device consists of a superlattice
heterostructure terminated with the anti-reflective regions sandwiched between
the fixed and free ferromagnetic layers. Employing the Green's function spin
transport formalism coupled self-consistently with the stochastic
Landau-Lifshitz-Gilbert-Slonczewski equation, we present the design of an
STT-MRAM based on the band-pass filtering having an ultra-high TMR (3.5*10e4)
and large spin current. We demonstrate that the STT-MRAM design having
band-pass spin filtering are nearly 1100% more energy efficient than
traditional trilayer magnetic tunnel junction (MTJ) based STT-MRAM. We also
present detailed probabilistic switching and energy analysis for a trilayer MTJ
and band-pass filtering based STT-MRAM. Our predictions serve as a template to
consider the heterostructures for next-generation spintronic device
applications.",1908.06279v1
2019-09-09,Narrow autoresonant magnetization structures in finite length ferromagnetic nanoparticles,"The autoresonant approach to excitation and control of large amplitude
uniformly precessing magnetization structures in finite length easy axis
ferromagnetic nanoparticles is suggested and analyzed within the
Landau-Lifshitz-Gilbert model. These structures are excited by using a
spatially uniform, oscillating, chirped frequency magnetic field, while the
localization is imposed via boundary conditions. The excitation requires the
amplitude of the driving oscillations to exceed a threshold. The dissipation
effect on the threshold is also discussed. The autoresonant driving effectively
compensates the effect of dissipation, but lowers the maximum amplitude of the
excited structures. Fully nonlinear localized autoresonant solutions are
illustrated in simulations and described via an analog of a quasi-particle in
an effective potential. The precession frequency of these solutions is
continuously locked to that of the drive, while the spatial magnetization
profile approaches the soliton limit when the length of the nanoparticle and
the amplitude of the excited solution increase.",1909.03671v1
2019-09-09,Reliability and Error Burst Length Analysis of Wireless Multi-Connectivity,"Multi-connectivity offers diversity in terms of multiple interfaces through
which the data can be sent, thereby improving simultaneously the overall
reliability and latency. This makes interface diversity a natural candidate for
supporting Ultra-Reliable Low Latency Communications (URLLC). This work
investigates how the packet error statistics from different interfaces impacts
the overall reliability-latency characteristics. We use the simple
Gilbert-Elliott model for burst errors and estimate its parameters based on
experimental measurement traces from LTE and {Wi-Fi} packet transmissions
collected over several days. The results show that using interface diversity
configurations that include at least one {Wi-Fi} interface leads to, somewhat
surprisingly, since Wi-Fi is generally less reliable than LTE, superior results
in terms of packet success and error burst duration. Another interesting
finding is that {Wi-Fi}-based interface diversity configurations outperform
even ultra-reliable single links.",1909.03875v1
2019-09-13,Hidden spin-orbital order in the Kitaev hyperhoneycomb $β$-Li$_2$IrO$_3$,"We report the existence of a phase transition at high temperature in the 3D
Kitaev candidate material, $\beta$-Li$_2$IrO$_3$. We show that the transition
is bulk, intrinsic and orders a tiny magnetic moment with a spatially
anisotropic saturation moment. We show that even though this transition is
global, it does not freeze the local Ir moments, which order at much lower
temperatures into an incommensurate state. Rather, the ordered moment has an
orbital origin that is coupled to spin correlations, likely of a Kitaev origin.
The separate ordering of spin-correlated orbital moments and of local Ir
moments reveals a novel way in which magnetic frustration in Kitaev systems can
lead to coexisting magnetic states.",1909.06355v1
2019-10-08,Gravitational Lensing of the Cosmic Neutrino Background,"We study gravitational lensing of the cosmic neutrino background. This signal
is undetectable for the foreseeable future, but there is a rich trove of
information available. At least some of the neutrinos from the early universe
will be non-relativistic today, with a closer surface of last scattering
(compared to the cosmic microwave background) and with larger angles of
deflection. Lensing of massive neutrinos is strongly chromatic: both the
amplitude of lensing and the cosmic time at which the potential is traversed
depend on neutrino momentum, in principle giving access to our entire causal
volume, not restricted to the light cone. As a concrete example, we focus on
the case where the cosmic neutrino background would be strongly lensed when
passing through halos of galaxy clusters and galaxies. We calculate the
Einstein radius for cosmic neutrinos and investigate the impact of neutrino
mass.",1910.03550v3
2019-10-17,A multi-scale approach for magnetisation dynamics: Unraveling exotic magnetic states of matter,"Crystallographic lattice defects strongly influence dynamical properties of
magnetic materials at both microscopic and macroscopic length scales. A
multi-scale approach to magnetisation dynamics, which is presented in this
paper, accurately captures such effects. The method is illustrated using
examples of systems with localized, non-trivial topological properties, e.g. in
the form of skyrmions and chiral domain walls that interact with lattice
dislocations. Technical aspects of the methodology involve multi-scale
magnetisation dynamics that connects atomistic and continuum descriptions. The
technique is capable of solving the Landau-Lifshitz-Gilbert equations
efficiently in two regions of a magnetic material --- the mesoscopic and the
atomistic regions, which are coupled in a seamless way. It is demonstrated that
this methodology allows simulating realistically-sized magnetic skyrmions
interacting with material defects and novel physical effects, uncovered using
this theoretical methodology, are described.",1910.07807v1
2019-10-21,Generation of exchange magnons in thin ferromagnetic films by ultrashort acoustic pulses,"We investigate generation of exchange magnons by ultrashort, picosecond
acoustic pulses propagating through ferromagnetic thin films. Using the
Landau-Lifshitz-Gilbert equations we derive the dispersion relation for
exchange magnons for an external magnetic field tilted with respect to the film
normal. Decomposing the solution in a series of standing spin wave modes, we
derive a system of ordinary differential equations and driven harmonic
oscillator equations describing the dynamics of individual magnon mode. The
external magnetoelastic driving force is given by the time-dependent spatial
Fourier components of acoustic strain pulses inside the layer. Dependencies of
the magnon excitation efficiencies on the duration of the acoustic pulses and
the external magnetic field highlight the role of acoustic bandwidth and
phonon-magnon phase matching. Our simulations for ferromagnetic nickel evidence
the possibility of ultrafast magneto-acoustic excitation of exchange magnons
within the bandwidth of acoustic pulses in thin samples under conditions
readily obtained in femtosecond pump-probe experiments.",1910.09481v1
2019-11-05,Numerical methods for antiferromagnetics,"Compared with ferromagnetic counterparts, antiferromagnetic materials are
considered as the future of spintronic applications since these materials are
robust against the magnetic perturbation, produce no stray field, and display
ultrafast dynamics. There are (at least) two sets of magnetic moments in
antiferromagnets (with magnetization of the same magnitude but antiparallel
directions) and ferrimagnets (with magnetization of the different magnitude).
The coupled dynamics for the bipartite collinear antiferromagnets is modeled by
a coupled system of Landau-Lifshitz-Gilbert equations with an additional term
originated from the antiferromagnetic exchange, which leads to femtosecond
magnetization dynamics. In this paper, we develop three Gauss-Seidel projection
methods for micromagnetics simulation in antiferromagnets and ferrimagnets.
They are first-order accurate in time and second-order in space, and only solve
linear systems of equations with constant coefficients at each step.
Femtosecond dynamics, N\'{e}el wall structure, and phase transition in presence
of an external magnetic field for antiferromagnets are provided with the
femtosecond stepsize.",1911.01717v1
2019-11-08,A filamentary cascade model of the inertial range,"This paper develops a simple model of the inertial range of turbulent flow,
based on a cascade of vortical filaments. A binary branching structure is
proposed, involving the splitting of filaments at each step into pairs of
daughter filaments with differing properties, in effect two distinct
simultaneous cascades. Neither of these cascades has the Richardson-Kolmogorov
exponent of 1/3. This bimodal structure is also different from bifractal models
as vorticity volume is conserved. If cascades are assumed to be initiated
continuously and throughout space we obtain a model of the inertial range of
stationary turbulence. We impose the constraint associated with Kolmogorov's
four-fifths law and then adjust the splitting to achieve good agreement with
the observed structure exponents $\zeta_p$. The presence of two elements to the
cascade is responsible for the nonlinear dependence of $\zeta_p$ upon $p$.
  A single cascade provides a model for the initial-value problem of the
Navier--Stokes equations in the limit of vanishing viscosity. To simulate this
limit we let the cascade continue indefinitely, energy removal occurring in the
limit. We are thus able to compute the decay of energy in the model.",1911.03537v2
2019-11-14,Beyond Pairwise Comparisons in Social Choice: A Setwise Kemeny Aggregation Problem,"In this paper, we advocate the use of setwise contests for aggregating a set
of input rankings into an output ranking. We propose a generalization of the
Kemeny rule where one minimizes the number of k-wise disagreements instead of
pairwise disagreements (one counts 1 disagreement each time the top choice in a
subset of alternatives of cardinality at most k differs between an input
ranking and the output ranking). After an algorithmic study of this k-wise
Kemeny aggregation problem, we introduce a k-wise counterpart of the majority
graph. This graph reveals useful to divide the aggregation problem into several
sub-problems, which enables to speed up the exact computation of a consensus
ranking. By introducing a k-wise counterpart of the Spearman distance, we also
provide a 2-approximation algorithm for the k-wise Kemeny aggregation problem.
We conclude with numerical tests.",1911.06226v2
2019-11-15,A geometric look at momentum flux and stress in fluid mechanics,"We develop a geometric formulation of fluid dynamics, valid on arbitrary
Riemannian manifolds, that regards the momentum-flux and stress tensors as
1-form valued 2-forms, and their divergence as a covariant exterior derivative.
We review the necessary tools of differential geometry and obtain the
corresponding coordinate-free form of the equations of motion for a variety of
inviscid fluid models -- compressible and incompressible Euler equations,
Lagrangian-averaged Euler-$\alpha$ equations, magnetohydrodynamics and
shallow-water models -- using a variational derivation which automatically
yields a symmetric momentum flux. We also consider dissipative effects and
discuss the geometric form of the Navier--Stokes equations for viscous fluids
and of the Oldroyd-B model for visco-elastic fluids.",1911.06613v2
2019-11-18,Theoretical condition for switching the magnetization in a perpendicularly magnetized ferromagnet via the spin Hall effect,"A theoretical formula is derived for the threshold current to switch a
perpendicular magnetization in a ferromagnet by the spin Hall effect. The
numerical simulation of the Landau-Lifshitz-Gilbert equation indicates that
magnetization switching is achieved when the steady-state solution of the
magnetization in the presence of the current is outside an energetically
unstable region. Based on the numerical result, an analytical theory deriving
the threshold current is developed by focusing on the first-order perturbation
to the unstable state. The analytical formula clarifies that the magnitude of
the magnetic field applied to the current direction should be larger than 15\%
of the perpendicular magnetic anisotropy field, and the current is less than
the derived threshold value.",1911.07961v1
2019-12-11,Constructions of quasi-twisted quantum codes,"In this work, our main objective is to construct quantum codes from
quasi-twisted (QT) codes. At first, a necessary and sufficient condition for
Hermitian self-orthogonality of QT codes is introduced by virtue of the Chinese
Remainder Theorem (CRT). Then we utilize these self-orthogonal QT codes to
provide quantum codes via the famous Hermitian Construction. Moreover, we
present a new construction method of q-ary quantum codes, which can be viewed
as an effective generalization of the Hermitian Construction. General QT codes
that are not self-orthogonal are also employed to construct quantum codes. As
the computational results, some binary, ternary and quaternary quantum codes
are constructed and their parameters are determined, which all exceed the
Quantum Gilbert-Varshamov (GV) Bound. In the binary case, a small number of
quantum codes are derived with strictly improved parameters compared with the
current records. In the ternary and quaternary cases, our codes fill some gaps
or have better performances than the current results.",1912.05142v2
2019-12-12,The strange metal Hall effect connects quantum criticality and superconductivity in an iron-based superconductor,"Many unconventional superconductors exhibit a common set of anomalous charge
transport properties that characterize them as `strange metals', which provides
hope that there is single theory that describes them. However,
model-independent connections between the strange metal and superconductivity
have remained elusive. In this letter, we show that the Hall effect of the
unconventional superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$ contains an
anomalous contribution arising from the correlations within the strange metal.
This term has a distinctive dependence on magnetic field, which allows us to
track its behavior across the doping-temperature phase diagram, even under the
superconducting dome. These measurements demonstrate that the strange metal
Hall component emanates from a quantum critical point and, in the zero
temperature limit, decays in proportion to the superconducting critical
temperature. This creates a clear and novel connection between quantum
criticality and superconductivity, and suggests that similar connections exist
in other strange metal superconductors.",1912.06130v1
2019-12-17,SINR percolation for Cox point processes with random powers,"Signal-to-interference plus noise ratio (SINR) percolation is an
infinite-range dependent variant of continuum percolation modeling connections
in a telecommunication network. Unlike in earlier works, in the present paper
the transmitted signal powers of the devices of the network are assumed random,
i.i.d. and possibly unbounded. Additionally, we assume that the devices form a
stationary Cox point process, i.e., a Poisson point process with stationary
random intensity measure, in two or higher dimensions. We present the following
main results. First, under suitable moment conditions on the signal powers and
the intensity measure, there is percolation in the SINR graph given that the
device density is high and interferences are sufficiently reduced, but not
vanishing. Second, if the interference cancellation factor $\gamma$ and the
SINR threshold $\tau$ satisfy $\gamma \geq 1/(2\tau)$, then there is no
percolation for any intensity parameter. Third, in the case of a Poisson point
process with constant powers, for any intensity parameter that is supercritical
for the underlying Gilbert graph, the SINR graph also percolates with some
small but positive interference cancellation factor.",1912.07895v2
2019-12-18,Magnetic hysteresis behavior of granular manganite La$_{0.67}$Ca$_{0.33}$MnO$_3$ nanotubes,"A silicon micromechanical torsional oscillator is used to measure the
hysteresis loops of two manganite La_0.67Ca_0.33MnO_3 nanotubes at different
temperatures, applying an external field along its main axes. These structures
are composed of nanograins with a ferromagnetic core surrounded by a dead
layer. Micromagnetic calculations based on the stochastic
Landau-Lifshitz-Gilbert equation, are performed to validate a simple model that
allows for quantitatively describing the ferromagnetic behavior of the system.
Further simulations are used to analyze the experimental data more in depth and
to calculate the coercive field, the saturation and remanent magnetizations,
and the effective magnetic volume for single nanotubes, over a wide temperature
range.",1912.08844v2
2019-12-30,Distribution of the minimal distance of random linear codes,"In this paper, we study the distribution of the minimal distance (in the
Hamming metric) of a random linear code of dimension $k$ in $\mathbb{F}_q^n$.
We provide quantitative estimates showing that the distribution function of the
minimal distance is close ({\it{}superpolynomially} in $n$)to the cumulative
distribution function of the minimum of $(q^k-1)/(q-1)$ independent binomial
random variables with parameters $\frac{1}{q}$ and $n$. The latter, in turn,
converges to a Gumbel distribution at integer points when $\frac{k}{n}$
converges to a fixed number in $(0,1)$. Our result confirms in a strong sense
that apart from identification of the weights of proportional codewords, the
probabilistic dependencies introduced by the linear structure of the random
code, produce a negligible effect on the minimal code weight. As a corollary of
the main result, we obtain an improvement of the Gilbert--Varshamov bound for
$2<q<49$.",1912.12833v2
2020-01-12,Magnetic Skyrmions in FePt Square-Based Nanoparticles Around Room-Temperature,"Magnetic skyrmions formed at temperatures around room temperature in
square-based parallelepiped magnetic FePt nanoparticles with perpendicular
magnetocrystalline anisotropy (MCA) were studied during the magnetization
reversal using micromagnetic simulations. Finite Differences (FD) method were
used for the solution of the Landau-Lifshitz-Gilbert equation. Magnetic
configurations exhibiting N\'eel skyrmionic formations were detected. The
magnetic skyrmions can be created in different systems generated by the
variation of external field, side length and width of the squared-based
parallelepiped magnetic nanoparticles. Micromagnetic configurations revealed a
variety of states which include skyrmionic textures with one distinct skyrmion
formed and being stable for a range of external fields around room-temperature.
The size of the formed N\'eel skyrmion is calculated as a function of the
external field, temperature, MCA and nanoparticle's geometrical characteristic
lengths which can be adjusted to produce N\'eel type skyrmions on demand having
diameters down to 12 nm. The micromagnetic simulations revealed that stable
skyrmions at the temperature range 270 - 330 K can be created for FePt magnetic
nanoparticle systems lacking of chiral interactions such as
Dzyaloshinskii-Moriya.",2001.03902v3
2020-01-20,Investigation of Patient-sharing Networks Using a Bayesian Network Model Selection Approach for Congruence Class Models,"A Bayesian approach to conduct network model selection is presented for a
general class of network models referred to as the congruence class models
(CCMs). CCMs form a broad class that includes as special cases several common
network models, such as the Erd\H{o}s-R\'{e}nyi-Gilbert model, stochastic block
model and many exponential random graph models. Due to the range of models able
to be specified as a CCM, investigators are better able to select a model
consistent with generative mechanisms associated with the observed network
compared to current approaches. In addition, the approach allows for
incorporation of prior information. We utilize the proposed Bayesian network
model selection approach for CCMs to investigate several mechanisms that may be
responsible for the structure of patient-sharing networks, which are associated
with the cost and quality of medical care. We found evidence in support of
heterogeneity in sociality but not selective mixing by provider type nor
degree.",2001.06974v1
2020-02-11,Fidimag -- a finite difference atomistic and micromagnetic simulation package,"Fidimag is an open-source scientific code for the study of magnetic materials
at the nano- or micro-scale using either atomistic or finite difference
micromagnetic simulations, which are based on solving the
Landau-Lifshitz-Gilbert equation. In addition, it implements simple procedures
for calculating energy barriers in the magnetisation through variants of the
nudged elastic band method. This computer software has been developed with the
aim of creating a simple code structure that can be readily installed, tested,
and extended. An agile development approach was adopted, with a strong emphasis
on automated builds and tests, and reproducibility of results. The main code
and interface to specify simulations are written in Python, which allows simple
and readable simulation and analysis configuration scripts. Computationally
costly calculations are written in C and exposed to the Python interface as
Cython extensions. Docker containers are shipped for a convenient setup
experience. The code is freely available on GitHub and includes documentation
and examples in the form of Jupyter notebooks.",2002.04318v1
2020-01-13,Malware propagation in urban D2D networks,"We introduce and analyze models for the propagation of malware in pure D2D
networks given via stationary Cox-Gilbert graphs. Here, the devices form a
Poisson point process with random intensity measure $\lambda\Lambda$, where
$\Lambda$ is stationary and given, for example, by the edge-length measure of a
realization of a Poisson-Voronoi tessellation that represents an urban street
system. We assume that, at initial time, a typical device at the center of the
network carries a malware and starts to infect neighboring devices after random
waiting times. Here we focus on Markovian models, where the waiting times are
exponential random variables, and non-Markovian models, where the waiting times
feature strictly positive minimal and finite maximal waiting times. We present
numerical results for the speed of propagation depending on the system
parameters. In a second step, we introduce and analyze a counter measure for
the malware propagation given by special devices called white knights, which
have the ability, once attacked, to eliminate the malware from infected devices
and turn them into white knights. Based on simulations, we isolate parameter
regimes in which the malware survives or is eliminated, both in the Markovian
and non-Markovian setting.",2002.06248v1
2020-02-17,How fast can you update your MST? (Dynamic algorithms for cluster computing),"Imagine a large graph that is being processed by a cluster of computers,
e.g., described by the $k$-machine model or the Massively Parallel Computation
Model. The graph, however, is not static; instead it is receiving a constant
stream of updates. How fast can the cluster process the stream of updates? The
fundamental question we want to ask in this paper is whether we can update the
graph fast enough to keep up with the stream. We focus specifically on the
problem of maintaining a minimum spanning tree (MST), and we give an algorithm
for the $k$-machine model that can process $O(k)$ graph updates per $O(1)$
rounds with high probability. (And these results carry over to the Massively
Parallel Computation (MPC) model.) We also show a lower bound, i.e., it is
impossible to process $k^{1+\epsilon}$ updates in $O(1)$ rounds. Thus we
provide a nearly tight answer to the question of how fast a cluster can respond
to a stream of graph modifications while maintaining an MST.",2002.06762v1
2020-02-22,Bose-Einstein Condensation of Nonequilibrium Magnons in Confined Systems,"We study the formation of a room temperature magnon Bose-Einstein condensate
(BEC) in nanoscopic systems and demonstrate that its lifetime is influenced by
the spatial confinement. We predict how dipolar interactions and nonlinear
magnon scattering assist in the generation of a metastable magnon BEC in
energy-quantized nanoscopic devices. We verify our prediction by a full
numerical simulation of the Landau-Lifshitz-Gilbert equation and demonstrate
the generation of magnon BEC in confined insulating magnets of yttrium iron
garnet. We directly map out the nonlinear magnon scattering processes behind
this phase transition to show how fast quantized thermalization channels allow
the BEC formation in confined structures. Based on our results, we discuss a
new mechanism to manipulate the BEC lifetime in nanoscaled systems. Our study
greatly extends the freedom to study the dynamics of magnon BEC in realistic
systems and to design integrated circuits for BEC-based applications at room
temperature.",2002.09777v2
2020-02-25,Bias-field-free spin Hall nano-oscillators with an out-of-plane precession mode,"Spin Hall nano-oscillators (SHNOs) are promising candidates for new microwave
oscillators with high durability due to a small driving current. However,
conventional SHNOs with an in-plane precession (IPP) mode require a bias field
for stable oscillations which is not favored in certain applications such as
neuromorphic computing. Here, we propose and theoretically analyze a
bias-field-free SHNO with an in-plane hard axis and an out-of-plane precession
(OPP) mode by solving the Landau-Lifshitz-Gilbert (LLG) equation analytically
and numerically. We derive formulas for driving currents and precession
frequency, and show that they are in good agreement with numerical simulation
results. We show that our proposed SHNOs can be driven by much smaller bias
current than conventional spin torque nano-oscillators.",2002.10753v1
2020-03-06,Spin-accumulation induced magnetic texture in a metal-insulator bilayer,"We consider the influence of a spin accumulation in a normal metal on the
magnetic statics and dynamics in an adjacent magnetic insulator. In particular,
we focus on arbitary angles between the spin accumulation and the easy-axis of
the magnetic insulator. Based on Landau-Lifshitz-Gilbert phenomenology
supplemented with magnetoelectronic circuit theory, we find that the magnetic
texture twists into a stable configuration that turns out to be described by a
virtual, or image, domain wall configuration, i.e., a domain wall outside the
ferromagnet. We show that even when the spin accumulation is perpendicular to
the anisotropy axis, the magnetic texture develops a component parallel to the
spin accumulation for sufficiently large spin bias. The emergence of this
parallel component gives rise to threshold behavior in the spin Hall
magnetoresistance and nonlocal magnon transport. This threshold can be used to
design novel spintronic and magnonic devices that can be operated without
external magnetic fields.",2003.03226v1
2020-04-05,Domain wall diode based on functionally graded Dzyaloshinskii-Moriya interaction,"We present a general approach for studying the dynamics of domain walls in
biaxial ferromagnetic stripes with functionally graded Dzyaloshinskii-Moriya
interaction (DMI). By engineering the spatial profile of the DMI parameter we
propose the concept of a diode, which implements filtering of domain walls of
certain topological charge and helicity. We base our study on phenomenological
Landau-Lifshitz-Gilbert equations with additional Zhang-Li spin-transfer terms
using a collective variable approach. In the effective equations of motion the
gradients of DMI play the role of a driving force which competes with current
driving. All analytical predictions are confirmed by numerical simulations.",2004.02175v1
2020-05-03,Philosophy-Guided Mathematical Formalism for Complex Systems Modelling,"We recently presented the so-called allagmatic method, which includes a
system metamodel providing a framework for describing, modelling, simulating,
and interpreting complex systems. Its development and programming was guided by
philosophy, especially by Gilbert Simondon's philosophy of individuation,
Alfred North Whitehead's philosophy of organism, and concepts from cybernetics.
Here, a mathematical formalism is presented to better describe and define the
system metamodel of the allagmatic method, thereby further generalising it and
extending its reach to a more formal treatment and allowing more theoretical
studies. By using the formalism, an example for such a further study is
provided with mathematical definitions and proofs for model creation and
equivalence of cellular automata and artificial neural networks.",2005.01192v5
2020-05-07,"A closer look at the non-Hopfianness of $BS(2,3)$","The Baumslag-Solitar group $BS(2,3)$, is a so-called non-Hopfian group,
meaning that it has an epimorphism $\phi$ onto itself, that is not injective.
In particular this is equivalent to saying that $BS(2,3)$ has a non-trivial
quotient that is isomorphic to itself. As a consequence the Cayley graph of
$BS(2,3)$ has a quotient that is isomorphic to itself up to change of
generators. We describe this quotient on the graph-level and take a closer look
at the most common epimorphism $\phi$. We show its kernel is a free group of
infinite rank with an explicit set of generators. Finally we show how $\phi$
appears as a morphism on fundamental groups induced by some continuous map.
This point of view was communicated to the author by Gilbert Levitt.",2005.03396v2
2020-05-08,Project and Forget: Solving Large-Scale Metric Constrained Problems,"Given a set of dissimilarity measurements amongst data points, determining
what metric representation is most ""consistent"" with the input measurements or
the metric that best captures the relevant geometric features of the data is a
key step in many machine learning algorithms. Existing methods are restricted
to specific kinds of metrics or small problem sizes because of the large number
of metric constraints in such problems. In this paper, we provide an active set
algorithm, Project and Forget, that uses Bregman projections, to solve metric
constrained problems with many (possibly exponentially) inequality constraints.
We provide a theoretical analysis of \textsc{Project and Forget} and prove that
our algorithm converges to the global optimal solution and that the $L_2$
distance of the current iterate to the optimal solution decays asymptotically
at an exponential rate. We demonstrate that using our method we can solve large
problem instances of three types of metric constrained problems: general weight
correlation clustering, metric nearness, and metric learning; in each case,
out-performing the state of the art methods with respect to CPU times and
problem sizes.",2005.03853v2
2020-05-27,The Kirillov model in families,"Let $F$ be a non-archimedean local field, let $k$ be an algebraically closed
field of characteristic $\ell$ different from the residual characteristic of
$F$, and let $A$ be a commutative Noetherian $W(k)$-algebra, where $W(k)$
denotes the Witt vectors. Using the Rankin-Selberg functional equations and
extending recent results of the second author, we show that if $V$ is an
$A[\text{GL}_n(F)]$-module of Whittaker type, then the mirabolic restriction
map on its Whittaker space is injective. This gives a new quick proof of the
existence of Kirillov models for representations of Whittaker type, including
complex representations, which generalizes to the $\ell$-modular and families
setting, in contrast with the previous proofs. In the special case where
$A=k=\overline{\mathbb{F}_{\ell}}$ and $V$ is irreducible generic, our result
in particular answers a question of Vign\'eras from 1989.",2005.13484v3
2020-05-29,An Explicit Formula for the Zero-Error Feedback Capacity of a Class of Finite-State Additive Noise Channels,"It is known that for a discrete channel with correlated additive noise, the
ordinary capacity with or without feedback both equal $ \log q-\mathcal{H} (Z)
$, where $ \mathcal{H}(Z) $ is the entropy rate of the noise process $ Z $ and
$ q $ is the alphabet size. In this paper, a class of finite-state additive
noise channels is introduced. It is shown that the zero-error feedback capacity
of such channels is either zero or $C_{0f} =\log q -h (Z) $, where $ h (Z) $ is
the {\em topological entropy} of the noise process. A topological condition is
given when the zero-error capacity is zero, with or without feedback. Moreover,
the zero-error capacity without feedback is lower-bounded by $ \log q-2 h (Z)
$. We explicitly compute the zero-error feedback capacity for several examples,
including channels with isolated errors and a Gilbert-Elliot channel.",2006.00892v1
2020-06-01,BBN constraints on dark radiation isocurvature,"The existence of dark radiation that is completely decoupled from the
standard model in the early Universe leaves open the possibility of an
associated dark radiation isocurvature mode. We show that the presence of dark
radiation isocurvature leads to spatial variation in the primordial abundances
of helium and deuterium due to spatial variation in $N_{\rm eff}$ during Big
Bang nucleosynthesis. We use the result to constrain the existence of such an
isocurvature mode on scales down to $\sim 1$ Mpc scales. By measuring the
excess variance in the primordial helium to hydrogen and deuterium to hydrogen
ratio in different galaxies, we constrain the variance in average isocurvature
in a galaxy to be less than $0.13/\Delta \bar{N}_{\rm eff}$ at 95\% confidence.
Here $\Delta \bar{N}_{\rm eff}$ is the spatially averaged increase in $N_{\rm
eff}$ due to the additional dark radiation component.",2006.01165v2
2020-06-12,Enhanced Stability of Antiferromagnetic Skyrmion during Its Motion by Anisotropic Dzyaloshinskii Moriya Interaction,"Searching for new methods to enhance the stability of antiferromagnetic (AFM)
skyrmion during its motion is an important issue for AFM spintronic devices.
Herein, the spin polarized current-induced dynamics of a distorted AFM skyrmion
is numerically studied, based on the Landau Lifshitz Gilbert simulations of the
model with an anisotropic Dzyaloshinskii Moriya (DM) interaction. It is
demonstrated that the DM interaction anisotropy induces the skyrmion
deformation, which suppresses the distortion during the motion and enhances the
stability of the skyrmion. Moreover, the effect of the DM interaction
anisotropy on the skyrmion velocity is investigated in detail, and the
simulated results are further explained by Thiele theory. This work unveils a
promising strategy to enhance the stability and the maximum velocity of AFM
skyrmion, benefiting future spintronic applications.",2006.06938v1
2020-07-02,Spectral Methods for Ranking with Scarce Data,"Given a number of pairwise preferences of items, a common task is to rank all
the items. Examples include pairwise movie ratings, New Yorker cartoon caption
contests, and many other consumer preferences tasks. What these settings have
in common is two-fold: a scarcity of data (it may be costly to get comparisons
for all the pairs of items) and additional feature information about the items
(e.g., movie genre, director, and cast). In this paper we modify a popular and
well studied method, RankCentrality for rank aggregation to account for few
comparisons and that incorporates additional feature information. This method
returns meaningful rankings even under scarce comparisons. Using diffusion
based methods, we incorporate feature information that outperforms
state-of-the-art methods in practice. We also provide improved sample
complexity for RankCentrality in a variety of sampling schemes.",2007.01346v1
2020-07-23,High Precision Real Time Collision Detection,"Collision detection and collision avoidance are essential components in these
systems for safe human-robot interactions. Robotics systems that can work
""out-of-the-box"" without excessive amount of installation and calibration from
the experts is highly ideal. For this, we propose a generic, high precision,
collision detect system that only requires the unified robot description format
(URDF) and is capable of running in real time. We extended the
Gilbert-Johnson-Keerthi (GJK) algorithm by utilizing a geometrical approach to
determine the distance between each rigid body in the environment and check for
collisions. The proposed system's performance is shown by checking the
self-collision of the KUKA LBR iiwa 7 R800 and the Mecademic Meca500. The
performance is compared to the Flexible Collision Library (FCL).",2007.12045v2
2020-08-10,Coherent spin qubit transport in silicon,"A fault-tolerant quantum processor may be configured using stationary qubits
interacting only with their nearest neighbours, but at the cost of significant
overheads in physical qubits per logical qubit. Such overheads could be reduced
by coherently transporting qubits across the chip, allowing connectivity beyond
immediate neighbours. Here we demonstrate high-fidelity coherent transport of
an electron spin qubit between quantum dots in isotopically-enriched silicon.
We observe qubit precession in the inter-site tunnelling regime and assess the
impact of qubit transport using Ramsey interferometry and quantum state
tomography techniques. We report a polarization transfer fidelity of 99.97% and
an average coherent transfer fidelity of 99.4%. Our results provide key
elements for high-fidelity, on-chip quantum information distribution, as long
envisaged, reinforcing the scaling prospects of silicon-based spin qubits.",2008.04020v2
2020-08-20,Linear hash-functions and their applications to error detection and correction,"We describe and explore so-called linear hash functions and show how they can
be used to build error detection and correction codes. The method can be
applied for different types of errors (for example, burst errors). When the
method is applied to a model where number of distorted letters is limited, the
obtained estimate of its performance is slightly better than the known
Varshamov-Gilbert bound. We also describe random code whose performance is
close to the same boundary, but its construction is much simpler. In some cases
the obtained methods are simpler and more flexible than the known ones. In
particular, the complexity of the obtained error detection code and the
well-known CRC code is close, but the proposed code, unlike CRC, can detect
with certainty errors whose number does not exceed a predetermined limit.",2008.08955v1
2020-08-27,Electrical conductivity of the quark-gluon plasma: perspective from lattice QCD,"A discussion on the electrical conductivity of the quark-gluon plasma as
determined by lattice QCD is given. After a reminder of basic definitions and
expectations, various methods for spectral reconstruction are reviewed,
including the use of Ans\""atze and sum rules, the Maximum Entropy and
Backus-Gilbert methods, and Tikhonov regularisation. A comprehensive overview
of lattice QCD results obtained so far is given, including a comparison of the
different lattice formulations. A noticeable consistency for the conductivities
obtained is seen, in spite of the differences in the lattice setups and
spectral reconstruction methods. It is found that in the case of quenched QCD
little temperature dependence of $\sigma/T$ is seen in the temperature range
investigated, while for QCD with dynamical quarks a reduction of $\sigma/T$ in
the vicinity of the thermal crossover is observed, compared to its value in the
QGP. Several open questions are posed at the end.",2008.12326v1
2020-09-02,Heterobilayer moiré magnets: moiré skyrmions and the commensurate-incommensurate transition,"We study untwisted heterobilayers of ferromagnetic and antiferromagnetic van
der Waals materials, with in particular a Dzyaloshinskii-Moriya interaction in
the ferromagnetic layer. A continuum low energy field theory is utilized to
study such systems. We develop a phase diagram as a function of the strength of
inter-layer exchange and Dzyaloshinskii-Moriya interactions, combining
perturbative and strong coupling analyses with numerical simulations using
Landau-Lifshitz-Gilbert equations. Various moir\'e-periodic commensurate phases
are found, and the commensurate-incommensurate transition is discussed. Among
the commensurate phases, we observe an interesting skyrmion lattice phase
wherein each moir\'e unit cell hosts one skyrmion.",2009.00860v3
2020-09-04,5-Dimensional Space-Periodic Solutions of the Static Vacuum Einstein Equations,"An affirmative answer is given to a conjecture of Myers concerning the
existence of 5-dimensional regular static vacuum solutions that balance an
infinite number of black holes, which have Kasner asymptotics. A variety of
examples are constructed, having different combinations of ring $S^1\times S^2$
and sphere $S^3$ cross-sectional horizon topologies. Furthermore, we show the
existence of 5-dimensional vacuum solitons with Kasner asymptotics. These are
regular static space-periodic vacuum spacetimes devoid of black holes.
Consequently, we also obtain new examples of complete Riemannian manifolds of
nonnegative Ricci curvature in dimension 4, and zero Ricci curvature in
dimension 5, having arbitrarily large as well as infinite second Betti number.",2009.01999v2
2020-09-24,Quarantined! Examining the Effects of a Community-Wide Moderation Intervention on Reddit,"Should social media platforms override a community's self-policing when it
repeatedly break rules? What actions can they consider? In light of this
debate, platforms have begun experimenting with softer alternatives to outright
bans. We examine one such intervention called quarantining, that impedes direct
access to and promotion of controversial communities. Specifically, we present
two case studies of what happened when Reddit quarantined the influential
communities r/TheRedPill (TRP) and r/The_Donald (TD). Using over 85M Reddit
posts, we apply causal inference methods to examine the quarantine's effects on
TRP and TD. We find that the quarantine made it more difficult to recruit new
members: new user influx to TRP and TD decreased by 79.5% and 58%,
respectively. Despite quarantining, existing users' misogyny and racism levels
remained unaffected. We conclude by reflecting on the effectiveness of this
design friction in limiting the influence of toxic communities and discuss
broader implications for content moderation.",2009.11483v3
2020-10-24,Hunting for Dark Matter Subhalos in Strong Gravitational Lensing with Neural Networks,"Dark matter substructures are interesting since they can reveal the
properties of dark matter. Collisionless N-body simulations of cold dark matter
show more substructures compared with the population of dwarf galaxy satellites
observed in our local group. Therefore, understanding the population and
property of subhalos at cosmological scale would be an interesting test for
cold dark matter. In recent years, it has become possible to detect individual
dark matter subhalos near images of strongly lensed extended background
galaxies. In this work, we discuss the possibility of using deep neural
networks to detect dark matter subhalos, and showing some preliminary results
with simulated data. We found that neural networks not only show promising
results on detecting multiple dark matter subhalos, but also learn to reject
the subhalos on the lensing arc of a smooth lens where there is no subhalo.",2010.12960v2
2020-10-28,Skyrmions Near Defects,"We study the impact of an exchange-reducing defect on a skyrmion for a thin
film of finite thickness. Attraction of the skyrmion to a defect is
demonstrated in a lattice model by computing the micromagnetic energy
accounting for the exchange, Dzyaloshinskii-Moriya interaction, magnetic
anisotropy, and dipole-dipole coupling. The spiraling dynamics of the skyrmion
towards the defect is illustrated by solving numerically the full
Landau-Lifshitz-Gilbert equations on a lattice and, independently, the Thiele
equation, with the two methods in agreement with each other. We find that the
skyrmion deforms when approaching the defect. Deformation is small in the
parameter space far from the phase boundary that determines stability of
skyrmions. It increases dramatically near the phase boundary, leading to the
transformation of the skyrmion by the defect into a snake-like magnetic domain.",2010.14683v2
2020-10-29,Micromagnetics of thin films in the presence of Dzyaloshinskii-Moriya interaction,"In this paper, we study the thin-film limit of the micromagnetic energy
functional in the presence of bulk Dzyaloshinskii-Moriya interaction (DMI). Our
analysis includes both a stationary $\Gamma$-convergence result for the
micromagnetic energy, as well as the identification of the asymptotic behavior
of the associated Landau-Lifshitz-Gilbert equation. In particular, we prove
that, in the limiting model, part of the DMI term behaves like the projection
of the magnetic moment onto the normal to the film, contributing this way to an
increase in the shape anisotropy arising from the magnetostatic self-energy.
Finally, we discuss a convergent finite element approach for the approximation
of the time-dependent case and use it to numerically compare the original
three-dimensional model with the two-dimensional thin-film limit.",2010.15541v1
2020-11-11,Role of impurity clusters for the current-driven motion of magnetic Skyrmions,"We study how impurities influence the current-induced dynamics of magnetic
Skyrmions moving in a racetrack geometry. For this, we solve numerically the
generalized Landau-Lifshitz-Gilbert equation extended by the current-induced
spin transfer torque. In particular, we investigate two classes of impurities,
non-conducting and magnetic impurities. The former are magnetically rigid
objects and yield to an inhomogeneous current density over the racetrack which
we determine separately by solving the fundamental electrostatic equations. In
contrast, magnetic impurities leave the applied current density homogeneous
throughout the stripe. Depending on parameters, we observe four different
scenarios of Skyrmion motions in the presence of disorder, the Skyrmion decay,
the pinning, the creation of additional Skyrmions, and ordinary Skyrmion
passage. We calculate and discuss phase diagrams in dependence of the impurity
concentration and radii of the impurities.",2011.06027v1
2020-11-12,Communication Efficient Coresets for Maximum Matching,"In this paper we revisit the problem of constructing randomized composable
coresets for bipartite matching. In this problem the input graph is randomly
partitioned across $k$ players, each of which sends a single message to a
coordinator, who then must output a good approximation to the maximum matching
in the input graph. Assadi and Khanna gave the first such coreset, achieving a
$1/9$-approximation by having every player send a maximum matching, i.e. at
most $n/2$ words per player. The approximation factor was improved to $1/3$ by
Bernstein et al.
  In this paper, we show that the matching skeleton construction of Goel,
Kapralov and Khanna, which is a carefully chosen (fractional) matching, is a
randomized composable coreset that achieves a $1/2-o(1)$ approximation using at
most $n-1$ words of communication per player. We also show an upper bound of
$2/3+o(1)$ on the approximation ratio achieved by this coreset.",2011.06481v1
2020-11-17,Thermally assisted magnetization reversal of a magnetic nanoparticle driven by a down-chirp microwave field pulse,"It has been shown that a single-domain magnetic nanoparticle can be
effectively switched by a linear down-chirp microwave field pulse (DCMWP) in
zero temperature limit. However, finite temperature is ubiquitous in practice.
Here, we study the effect of finite temperature on the DCMWP-induced
magnetization reversal based on the stochastic Landau-Lifshitz-Gilbert
equation. It is found that any one of the three controlling parameters of a
DCMWP, i.e. the amplitude, chirp rate, or initial frequency, decreases with
increasing temperature while the other two are fixed. The maximal temperature
at which the reversal can happen increases with enlarging the system size.
These phenomena are related to the facts that the energy barrier induced by
anisotropy increases with the system volume, and the effective magnetization
decreases with temperature. We also provide a set of optimal parameters for
practical realization of our proposal. These findings may provide a way to
realize low-cost and fast magnetization reversal with a wide operating
temperature.",2011.08610v2
2020-11-17,Sum-frequency excitation of coherent magnons,"Coherent excitation of magnons is conventionally achieved through Raman
scattering processes, in which the difference-frequency components of the
driving field are resonant with the magnon energy. Here, we describe mechanisms
by which the sum-frequency components of the driving field can be used to
coherently excite magnons through two-particle absorption processes. We use the
Landau-Lifshitz-Gilbert formalism to compare the spin-precession amplitudes
that different types of impulsive stimulated and ionic Raman scattering
processes and their sum-frequency counterparts induce in an antiferromagnetic
model system. We show that sum-frequency mechanisms enabled by linearly
polarized driving fields yield excitation efficiencies comparable or larger
than established Raman techniques, while elliptical polarizations produce only
weak and circularly polarizations no sum-frequency components at all. The
mechanisms presented here complete the map for dynamical spin control by the
means of Raman-type processes.",2011.08730v1
2020-11-26,3D Nanomagnetism in Low Density Interconnected Nanowire Networks,"Free-standing, interconnected metallic nanowire networks with density as low
as 40 mg/cm^{3} have been achieved over cm-scale areas, using electrodeposition
into polycarbonate membranes that have been ion-tracked at multiple angles.
Networks of interconnected magnetic nanowires further provide an exciting
platform to explore 3-dimensional nanomagnetism, where their structure,
topology and frustration may be used as additional degrees of freedom to tailor
the materials properties. New magnetization reversal mechanisms in cobalt
networks are captured by the first-order reversal curve method, which
demonstrate the evolution from strong demagnetizing dipolar interactions to
intersections-mediated domain wall pinning and propagation, and eventually to
shape-anisotropy dominated magnetization reversal. These findings open up new
possibilities for 3-dimensional integrated magnetic devices for memory, complex
computation, and neuromorphics.",2011.13468v2
2020-12-02,Quantum Annealed Criticality: A Scaling Description,"Experimentally there exist many materials with first-order phase transitions
at finite temperature that display quantum criticality. Classically, a
strain-energy density coupling is known to drive first-order transitions in
compressible systems, and here we generalize this Larkin-Pikin mechanism to the
quantum case. We show that if the T=0 system lies above its upper critical
dimension, the line of first-order transitions ends in a ""quantum annealed
critical point"" where zero-point fluctuations restore the underlying
criticality of the order parameter. The generalized Larkin-Pikin phase diagram
is presented and experimental consequences are discussed.",2012.01601v1
2020-12-04,Rethinking movie genre classification with fine-grained semantic clustering,"Movie genre classification is an active research area in machine learning.
However, due to the limited labels available, there can be large semantic
variations between movies within a single genre definition. We expand these
'coarse' genre labels by identifying 'fine-grained' semantic information within
the multi-modal content of movies. By leveraging pre-trained 'expert' networks,
we learn the influence of different combinations of modes for multi-label genre
classification. Using a contrastive loss, we continue to fine-tune this
'coarse' genre classification network to identify high-level intertextual
similarities between the movies across all genre labels. This leads to a more
'fine-grained' and detailed clustering, based on semantic similarities while
still retaining some genre information. Our approach is demonstrated on a newly
introduced multi-modal 37,866,450 frame, 8,800 movie trailer dataset,
MMX-Trailer-20, which includes pre-computed audio, location, motion, and image
embeddings.",2012.02639v3
2020-12-04,Nutation in antiferromagnetic resonance,"The effect of inertial spin dynamics is compared between ferromagnetic,
antiferromagnetic and ferrimagnetic systems. The linear response to an
oscillating external magnetic field is calculated within the framework of the
inertial Landau--Lifshitz--Gilbert equation using analytical theory and
computer simulations. Precession and nutation resonance peaks are identified,
and it is demonstrated that the precession frequencies are reduced by the spin
inertia, while the lifetime of the excitations is enhanced. The interplay
between precession and nutation is found to be the most prominent in
antiferromagnets, where the timescale of the exchange-driven sublattice
dynamics is comparable to inertial relaxation times. Consequently,
antiferromagnetic resonance techniques should be better suited for the search
for intrinsical inertial spin dynamics on ultrafast timescales than
ferromagnetic resonance.",2012.02790v3
2020-12-14,Thermally induced spin torque and domain wall motion in superconductor/antiferromagnetic insulator bilayers,"We theoretically investigate domain wall motion in an antiferromagnetic
insulator layer caused by thermally generated spin currents in an adjacent
spin-split superconductor layer. An uncompensated antiferromagnet interface
enables the two crucial ingredients underlying the mechanism - spin splitting
in the superconductor and absorption of spin currents by the antiferromagnet.
Treating the superconductor using the quasiclassical theory and the
antiferromagnet via Landau-Lifshitz-Gilbert description, we find domain wall
propagation along the thermal gradient with relatively large velocities $\sim
100$ m/s. Our proposal exploits the giant thermal response of spin-split
superconductors in achieving large spin torques towards driving domain wall and
other spin textures in antiferromagnets.",2012.07405v1
2020-11-04,A note on the intuitionistic logic of false belief,"In this paper we analyse logic of false belief in intuitionistic setting.
This logic, studied in its classical version by Steinsvold, Fan, Gilbert and
Venturi, describes the following situation: a formula F is not satisfied in a
given world, but we still believe in it (or we think that it should be
accepted). Another interpretations are also possible: e.g. that we do not
accept F but it is imposed on us by a kind of council or advisory board. From
the mathematical point of view, the idea is expressed by an adequate form of
modal operator W which is interpreted in relational frames with neighborhoods.
We discuss monotonicity of forcing, soundness, completeness and several other
issues. We present also some simple systems in which confirmation of previously
accepted formula is modelled.",2012.08309v1
2021-01-05,Efficient domain wall motion in asymmetric magnetic tunnel junctions with vertical current flow,"In this paper, we study the domain wall motion induced by vertical current
flow in asymmetric magnetic tunnel junctions. The domain wall motion in the
free layer is mainly dictated by the current-induced field-like torque acting
on it. We show that as we increase the MTJ asymmetry, by considering dissimilar
ferromagnetic contacts, a linear-in-voltage field-like torque behavior is
accompanied by an enhancement in the domain wall displacement efficiency and a
higher degree of bidirectional propagation. Our analysis is based on a
combination of a quantum transport model and magnetization dynamics as
described by the Landau-Lifshitz-Gilbert equation, along with comparison to the
intrinsic characteristics of a benchmark in-plane current injection domain wall
device.",2101.01581v1
2021-01-12,Modeling of Thermal Magnetic Fluctuations in Nanoparticle Enhanced Magnetic Resonance Detection,"We present a systematic numerical modeling investigation of magnetization
dynamics and thermal magnetic moment fluctuations of single magnetic domain
nanoparticles in a configuration applicable to enhancing inductive magnetic
resonance detection signal to noise ratio (SNR). Previous proposals for
oriented anisotropic single magnetic domain nanoparticle amplification of
magnetic flux in MRI coil focused only on the coil pick-up voltage signal
enhancement. Here we extend the analysis to the numerical evaluation of the SNR
by modeling the inherent thermal magnetic noise introduced into the detection
coil by the insertion of such anisotropic nanoparticle-filled coil core. We
utilize the Landau-Lifshitz-Gilbert equation under the Stoner-Wohlfarth single
magnetic domain (macrospin) assumption to simulate the magnetization dynamics
in such nanoparticles due to AC drive field as well as thermal noise. These
simulations are used to evaluate the nanoparticle configurations and shape
effects on enhancing SNR. Finally, we explore the effect of narrow band
filtering of the broadband magnetic moment thermal fluctuation noise on the
SNR. Our results provide the impetus for relatively simple modifications to
existing MRI systems for achieving enhanced detection SNR in scanners with
modest polarizing magnetic fields.",2101.04649v1
2021-01-20,Spin-current mediated exchange coupling in MgO-based magnetic tunnel junctions,"Heterostructures composed of ferromagnetic layers that are mutually
interacting through a nonmagnetic spacer are at the core of magnetic sensor and
memory devices. In the present study, layer-resolved ferromagnetic resonance
was used to investigate the coupling between the magnetic layers of a
Co/MgO/Permalloy magnetic tunnel junction. Two magnetic resonance peaks were
observed for both magnetic layers, as probed at the Co and Ni L3 x-ray
absorption edges, showing a strong interlayer interaction through the
insulating MgO barrier. A theoretical model based on the
Landau-Lifshitz-Gilbert-Slonczewski equation was developed, including exchange
coupling and spin pumping between the magnetic layers. Fits to the experimental
data were carried out, both with and without a spin pumping term, and the
goodness of the fit was compared using a likelihood ratio test. This rigorous
statistical approach provides an unambiguous proof of the existence of
interlayer coupling mediated by spin pumping.",2101.08157v1
2021-01-27,Numerical simulation of the viral entry into a cell driven by receptor diffusion,"The present study focuses on the receptor driven endocytosis typical of viral
entry into a cell. A locally increased density of receptors at the time of
contact between the cell and the virus is necessary in this case. The virus is
considered as a substrate with fixed receptors on its surface, whereas the
receptors of the host cell are free to move over its membrane, allowing a local
change in their concentration. In the contact zone the membrane inflects and
forms an envelope around the virus. The created vesicle imports its cargo into
the cell. This paper assumes the diffusion equation accompanied by boundary
conditions requiring the conservation of binders to describe the process.
Moreover, it introduces a condition defining the energy balance at the front of
the adhesion zone. The latter yields the upper limit for the size of virus
which can be engulfed by the cell membrane. The described moving boundary
problem in terms of the binder density and the velocity of the adhesion front
is well posed and numerically solved by using the finite difference method. The
illustrative examples have been chosen to show the influence of the process
parameters on the initiation and the duration of the process.",2101.11515v1
2021-02-04,AI Development for the Public Interest: From Abstraction Traps to Sociotechnical Risks,"Despite interest in communicating ethical problems and social contexts within
the undergraduate curriculum to advance Public Interest Technology (PIT) goals,
interventions at the graduate level remain largely unexplored. This may be due
to the conflicting ways through which distinct Artificial Intelligence (AI)
research tracks conceive of their interface with social contexts. In this paper
we track the historical emergence of sociotechnical inquiry in three distinct
subfields of AI research: AI Safety, Fair Machine Learning (Fair ML) and
Human-in-the-Loop (HIL) Autonomy. We show that for each subfield, perceptions
of PIT stem from the particular dangers faced by past integration of technical
systems within a normative social order. We further interrogate how these
histories dictate the response of each subfield to conceptual traps, as defined
in the Science and Technology Studies literature. Finally, through a
comparative analysis of these currently siloed fields, we present a roadmap for
a unified approach to sociotechnical graduate pedagogy in AI.",2102.04255v1
2021-02-15,An In-Depth Investigation of the Performance Characteristics of Hyperledger Fabric,"Private permissioned blockchains are deployed in ever greater numbers to
facilitate cross-organizational processes in various industries, particularly
in supply chain management. One popular example of this trend is Hyperledger
Fabric. Compared to public permissionless blockchains, it promises improved
performance and provides certain features that address key requirements of
enterprises. However, also permissioned blockchains are still not as scalable
as centralized systems, and due to the scarcity of theoretical results and
empirical data, their real-world performance cannot be predicted with the
necessary precision. We intend to address this issue by conducting an in-depth
performance analysis of Hyperledger Fabric. The paper presents a detailed
compilation of various performance characteristics using an enhanced version of
the Distributed Ledger Performance Scan (DLPS). Researchers and practitioners
alike can use the various performance properties identified and discussed as
guidelines to better configure and implement their Hyperledger Fabric network.
Likewise, they are encouraged to use the DLPS framework to conduct their
measurements.",2102.07731v2
2021-02-18,On isodual double Toeplitz codes,"Double Toeplitz (shortly DT) codes are introduced here as a generalization of
double circulant codes. We show that such a code is isodual, hence formally
self-dual. Self-dual DT codes are characterized as double circulant or double
negacirculant. Likewise, even DT binary codes are characterized as double
circulants. Numerical examples obtained by exhaustive search show that the
codes constructed have best-known minimum distance, up to one unit, amongst
formally self-dual codes, and sometimes improve on the known values. Over
$\F_4$ an explicit construction of DT codes, based on quadratic residues in a
prime field, performs equally well. We show that DT codes are asymptotically
good over $\F_q$. Specifically, we construct DT codes arbitrarily close to the
asymptotic varshamov-Gilbert bound for codes of rate one half.",2102.09233v1
2021-02-20,Design of Ciphers based on the Geometric Structure of the Möbius Plane,"Till now geometric structures don't play a major role in cryptography.
Gilbert, MacWilliams and Sloane introduced in 1974 an authentication scheme in
the projective plane and showed its perfectness in the sense of the definition
of Shannon. In this paper we will show that this authentication scheme also
fulfills the requirement of completeness according to Kam and Davida and we
will extend the application of geometric structures in cryptography by
introducing an encryption scheme in the M\""obius plane. We will further examine
its properties, showing that it also fulfills the requirement of completeness
and Shannon's requirement of perfectness in first approximation. The results of
this paper can be used to define similar encryption schemes in the circle
geometries of Laguerre and Minkowski.",2102.10321v2
2021-03-02,Struwe-like solutions for an evolutionary model of magnetoviscoelastic fluids,"In this work we investigate the existence and uniqueness of Struwe-like
solutions for a system of partial differential equations modeling the dynamics
of magnetoviscoelastic fluids. The considered system couples a Navier-Stokes
type equation with a dissipative equation for the deformation tensor and a
Landau-Lifshitz-Gilbert type equation for the magnetization field. The main
purpose is to establish a well-posedness theory in a two-dimensional periodic
domain under standard assumption of critical regularity for the (possibly
large) initial data. We prove that the considered weak solutions are everywhere
smooth, except for a discrete set of time values. The proof of the uniqueness
is based on suitable energy estimates for the solutions within a functional
framework which is less regular than the one of the Struwe energy level. These
estimates rely on several techniques of harmonic analysis and paradifferential
calculus.",2103.01647v1
2021-03-07,Design of Ciphers based on the Geometric Structure of the Laguerre and Minkowski Planes,"Till now geometric structures don't play a major role in cryptography.
Gilbert, MacWilliams and Sloane introduced an authentication scheme in the
projective plane and showed its perfectness in the sense of Shannon. In
arXiv:2102.10321 we introduced an encryption scheme in the M\""obius plane and
showed that it fulfills Shannon's requirement of perfectness in first
approximation and also the requirement of completeness according to Kam and
Davida. In this paper we will apply a similar approach to define encryption
schemes in the geometries of the Laguerre plande and the Minkowski plane. We
will show that the encryption scheme in the Laguerre geometry meets Shannon's
requirement of perfectness sharp and that the encryption scheme in the
Minkowski geometry meets this requirement in first approximation. The Laguerre
cipher also fulfills the requirement of completeness according to Kam and
Davida.",2103.04428v1
2021-03-09,An atomic perspective on the serpentine-chlorite solid-state transformation,"Serpentine minerals are important components of metamorphic rocks and
promising geo-materials for nanotechnology. Lizardite, the most abundant
serpentine mineral, can be transformed into chlorite during metamorphism. This
intriguing phase transformation should affect the deformation behavior during
aseismic creep and slow slip at the base of the subduction zone, but has not
been understood structurally and chemically at the atomic scale. Here we
visualized cations and oxygen atoms using the state-of-the-art low-dose
scanning transmission electron microscopy and found that restructuring mainly
involves the synergistic migration of tetrahedral cations and oxygen anions,
coupled with the migration of octahedral trivalent cations into the
brucite-like interlayer. Further, we show that different serpentine polytypes
result in distinct regular interstratifications of serpentine and chlorite. Our
results clarify the long-standing puzzle of how solid-state layer silicate
transformations occur and lead to long-period ordered structures.",2103.05210v1
2021-03-13,On Bounds for Ring-Based Coding Theory,"Coding Theory where the alphabet is identified with the elements of a ring or
a module has become an important research topic over the last 30 years. Such
codes over rings had important applications and many interesting mathematical
problems are related to this line of research.
  It has been well established, that with the generalization of the algebraic
structure to rings there is a need to also generalize the underlying metric
beyond the usual Hamming weight used in traditional coding theory over finite
fields.
  This paper introduces a new weight, called the overweight, which can be seen
as a generalization of the Lee weight on the integers modulo $4$. For this new
weight we provide a number of well-known bounds, like a Plotkin bound, a
sphere-packing bound, and a Gilbert-Varshamov bound. A further highlight is the
proof of a Johnson bound for the homogeneous weight on a general finite
Frobenius ring.",2103.07749v2
2021-03-17,ALADIN: All Layer Adaptive Instance Normalization for Fine-grained Style Similarity,"We present ALADIN (All Layer AdaIN); a novel architecture for searching
images based on the similarity of their artistic style. Representation learning
is critical to visual search, where distance in the learned search embedding
reflects image similarity. Learning an embedding that discriminates
fine-grained variations in style is hard, due to the difficulty of defining and
labelling style. ALADIN takes a weakly supervised approach to learning a
representation for fine-grained style similarity of digital artworks,
leveraging BAM-FG, a novel large-scale dataset of user generated content
groupings gathered from the web. ALADIN sets a new state of the art accuracy
for style-based visual search over both coarse labelled style data (BAM) and
BAM-FG; a new 2.62 million image dataset of 310,000 fine-grained style
groupings also contributed by this work.",2103.09776v1
2021-03-23,A Massively Parallel Time-Domain Coupled Electrodynamics-Micromagnetics Solver,"We present a new, high-performance coupled electrodynamics-micromagnetics
solver for full physical modeling of signals in microelectronic circuitry. The
overall strategy couples a finite-difference time-domain (FDTD) approach for
Maxwell's equations to a magnetization model described by the
Landau-Lifshitz-Gilbert (LLG) equation. The algorithm is implemented in the
Exascale Computing Project software framework, AMReX, which provides effective
scalability on manycore and GPU-based supercomputing architectures.
Furthermore, the code leverages ongoing developments of the Exascale
Application Code, WarpX, primarily developed for plasma wakefield accelerator
modeling. Our novel temporal coupling scheme provides second-order accuracy in
space and time by combining the integration steps for the magnetic field and
magnetization into an iterative sub-step that includes a trapezoidal
discretization for the magnetization. The performance of the algorithm is
demonstrated by the excellent scaling results on NERSC multicore and GPU
systems, with a significant (59x) speedup on the GPU using a node-by-node
comparison. We demonstrate the utility of our code by performing simulations of
an electromagnetic waveguide and a magnetically tunable filter.",2103.12819v1
2021-04-06,Geometry and Symmetry in Skyrmion Dynamics,"The uniform motion of chiral magnetic skyrmions induced by a spin-transfer
torque displays an intricate dependence on the skyrmions' topological charge
and shape. We reveal surprising patterns in this dependence through simulations
of the Landau-Lifshitz-Gilbert equation with Zhang-Li torque and explain them
through a geometric analysis of Thiele's equation. In particular, we show that
the velocity distribution of topologically non-trivial skyrmions depends on
their symmetry: it is a single circle for skyrmions of high symmetry and a
family of circles for low-symmetry configurations. We also show that the
velocity of the topologically trivial skyrmions, previously believed to be the
fastest objects, can be surpassed, for instance, by antiskyrmions. The
generality of our approach suggests the validity of our results for exchange
frustrated magnets, bubble materials, and others.",2104.02342v1
2021-04-06,Diffusion of a magnetic skyrmion in 2-dimensional space,"Two-dimensional magnetic skyrmions are particle-like magnetic domains in
magnetic thin films. The kinetic property of the magnetic skyrmions at finite
temperature is well described by the Thiele equation, including a stochastic
field and a finite mass. In this paper, the validity of the constant-mass
approximation is examined by comparing the Fourier spectrum of Brownian motions
described by the Thiele equation and the Landau-Lifshitz-Gilbert equation.
Then, the 4-dimensional Fokker-Planck equation is derived from the Thiele
equation with a mass-term. Consequently, an expression of the diffusion flow
and diffusion constant in a tensor form is derived, extending Chandrasekhar's
method for Thiele dynamics.",2104.02345v2
2021-04-08,Computation and Bribery of Voting Power in Delegative Simple Games,"Following Zhang and Grossi~(AAAI 2021), we study in more depth a variant of
weighted voting games in which agents' weights are induced by a transitive
support structure. This class of simple games is notably well suited to study
the relative importance of agents in the liquid democracy framework. We first
propose a pseudo-polynomial time algorithm to compute the Banzhaf and
Shapley-Shubik indices for this class of game. Then, we study a bribery
problem, in which one tries to maximize/minimize the voting power/weight of a
given agent by changing the support structure under a budget constraint. We
show that these problems are computationally hard and provide several
parameterized complexity results.",2104.03692v2
2021-05-10,Role of higher-order effects in spin-misalignment small-angle neutron scattering of high-pressure torsion nickel,"Magnetic-field-dependent unpolarized small-angle neutron scattering (SANS)
experiments demonstrate that high-pressure torsion (HPT) straining induces spin
misalignments in pure Ni, which persist in magnetic fields up to 4 T. The
spin-misalignment scattering patterns are elongated perpendicular to the
applied magnetic field due to an unusual predominant longitudinal
$sin^2(\theta)$-type angular anisotropy. Such a contribution cannot be
explained by the conventional second order (in spin misalignment amplitude)
micromagnetic SANS theory in the approach-to-saturation regime, nor can its
magnitude relative to the other features of the cross sections by the third
order micromagnetic SANS theory. This indicates that the high-density of
crystal defects induced via HPT straining in Ni makes such higher-order effects
in the micromagnetic SANS cross sections observable.",2105.04167v1
2021-04-26,Axes for Sociotechnical Inquiry in AI Research,"The development of artificial intelligence (AI) technologies has far exceeded
the investigation of their relationship with society. Sociotechnical inquiry is
needed to mitigate the harms of new technologies whose potential impacts remain
poorly understood. To date, subfields of AI research develop primarily
individual views on their relationship with sociotechnics, while tools for
external investigation, comparison, and cross-pollination are lacking. In this
paper, we propose four directions for inquiry into new and evolving areas of
technological development: value--what progress and direction does a field
promote, optimization--how the defined system within a problem formulation
relates to broader dynamics, consensus--how agreement is achieved and who is
included in building it, and failure--what methods are pursued when the problem
specification is found wanting. The paper provides a lexicon for sociotechnical
inquiry and illustrates it through the example of consumer drone technology.",2105.06551v1
2021-05-21,$\mathbb{F}_q$-zeros of sparse trivariate polynomials and toric 3-fold codes,"For a given lattice polytope $P$ in $\mathbb{R}^3$, consider the space
$\mathcal{L}_P$ of trivariate polynomials over a finite field $\mathbb{F}_q$,
whose Newton polytopes are contained in $P$. We give an upper bound for the
maximum number of $\mathbb{F}_q$-zeros of polynomials in $\mathcal{L}_P$ in
terms of the Minkowski length of $P$ and $q$, the size of the field.
Consequently, this produces lower bounds for the minimum distance of toric
codes defined by evaluating elements of $\mathcal{L}_P$ at the points of the
algebraic torus $(\mathbb{F}_q^*)^3$. Our approach is based on understanding
factorizations of polynomials in $\mathcal{L}_P$ with the largest possible
number of non-unit factors. The related combinatorial result that we obtain is
a description of Minkowski sums of lattice polytopes contained in $P$ with the
largest possible number of non-trivial summands.",2105.10071v2
2021-05-24,Spatio-temporal dynamics of voltage-induced resistance transition in the double-exchange model,"We present multi-scale dynamical simulations of voltage-induced
insulator-to-metal transition in the double exchange model, a canonical example
of itinerant magnet and correlated electron systems. By combining
nonequilibrium Green's function method with large-scale Landau-Lifshitz-Gilbert
dynamics, we show that the transition from an antiferromagnetic insulator to
the low-resistance state is initiated by the nucleation of a thin ferromagnetic
conducting layer at the anode. The metal-insulator interface separating the two
phases is then driven toward the opposite electrode by the voltage stress,
giving rise to a growing metallic region. We further show that the initial
transformation kinetics is well described by the Kolmogorov-Avrami-Ishibashi
model with an effective spatial-dimension that depends on the applied voltage.
Implications of our findings for the resistive switching in colossal
magnetoresistant materials are also discussed.",2105.11076v2
2021-05-26,"High-speed programmable photonic circuits in a cryogenically compatible, visible-NIR 200 mm CMOS architecture","Recent advances in photonic integrated circuits (PICs) have enabled a new
generation of ""programmable many-mode interferometers"" (PMMIs) realized by
cascaded Mach Zehnder Interferometers (MZIs) capable of universal
linear-optical transformations on N input-output optical modes. PMMIs serve
critical functions in photonic quantum information processing, quantum-enhanced
sensor networks, machine learning and other applications. However, PMMI
implementations reported to date rely on thermo-optic phase shifters, which
limit applications due to slow response times and high power consumption. Here,
we introduce a large-scale PMMI platform, based on a 200 mm CMOS process, that
uses aluminum nitride (AlN) piezo-optomechanical actuators coupled to silicon
nitride (SiN) waveguides, enabling low-loss propagation with phase modulation
at greater than 100 MHz in the visible to near-infrared wavelengths. Moreover,
the vanishingly low holding-power consumption of the piezo-actuators enables
these PICs to operate at cryogenic temperatures, paving the way for a fully
integrated device architecture for a range of quantum applications.",2105.12531v1
2021-05-27,On the Complexity of Load Balancing in Dynamic Networks,"In the load balancing problem, each node in a network is assigned a load, and
the goal is to equally distribute the loads among the nodes, by preforming
local load exchanges. While load balancing was extensively studied in static
networks, only recently a load balancing algorithm for dynamic networks with a
bounded convergence time was presented. In this paper, we further study the
time complexity of load balancing in the context of dynamic networks.
  First, we show that randomness is not necessary, and present a deterministic
algorithm which slightly improves the running time of the previous algorithm,
at the price of not being matching-based. Then, we consider integral loads,
i.e., loads that cannot be split indefinitely, and prove that no matching-based
algorithm can have a bounded convergence time for this case.
  To circumvent both this impossibility result, and a known one for the
non-integral case, we apply the method of smoothed analysis, where random
perturbations are made over the worst-case choices of network topologies. We
show both impossibility results do not hold under this kind of analysis,
suggesting that load-balancing in real world systems might be faster than the
lower bounds suggest.",2105.13194v1
2021-06-09,A Compact Model for Scalable MTJ Simulation,"This paper presents a physics-based modeling framework for the analysis and
transient simulation of circuits containing Spin-Transfer Torque (STT) Magnetic
Tunnel Junction (MTJ) devices. The framework provides the tools to analyze the
stochastic behavior of MTJs and to generate Verilog-A compact models for their
simulation in large VLSI designs, addressing the need for an industry-ready
model accounting for real-world reliability and scalability requirements.
Device dynamics are described by the Landau-Lifshitz-Gilbert-Slonczewsky
(s-LLGS ) stochastic magnetization considering Voltage-Controlled Magnetic
Anisotropy (VCMA) and the non-negligible statistical effects caused by thermal
noise. Model behavior is validated against the OOMMF magnetic simulator and its
performance is characterized on a 1-Mb 28 nm Magnetoresistive-RAM (MRAM) memory
product.",2106.04976v1
2021-06-14,Can Explainable AI Explain Unfairness? A Framework for Evaluating Explainable AI,"Many ML models are opaque to humans, producing decisions too complex for
humans to easily understand. In response, explainable artificial intelligence
(XAI) tools that analyze the inner workings of a model have been created.
Despite these tools' strength in translating model behavior, critiques have
raised concerns about the impact of XAI tools as a tool for `fairwashing` by
misleading users into trusting biased or incorrect models. In this paper, we
created a framework for evaluating explainable AI tools with respect to their
capabilities for detecting and addressing issues of bias and fairness as well
as their capacity to communicate these results to their users clearly. We found
that despite their capabilities in simplifying and explaining model behavior,
many prominent XAI tools lack features that could be critical in detecting
bias. Developers can use our framework to suggest modifications needed in their
toolkits to reduce issues likes fairwashing.",2106.07483v1
2021-06-17,Density of Free Modules over Finite Chain Rings,"In this paper we focus on modules over a finite chain ring $\mathcal{R}$ of
size $q^s$. We compute the density of free modules of $\mathcal{R}^n$, where we
separately treat the asymptotics in $n,q$ and $s$. In particular, we focus on
two cases: one where we fix the length of the module and one where we fix the
rank of the module. In both cases, the density results can be bounded by the
Andrews-Gordon identities. We also study the asymptotic behaviour of modules
generated by random matrices over $\mathcal{R}$. Since linear codes over
$\mathcal{R}$ are submodules of $\mathcal{R}^n$ we get direct implications for
coding theory. For example, we show that random codes achieve the
Gilbert-Varshamov bound with high probability.",2106.09403v2
2021-06-28,Combinatorial BLAS 2.0: Scaling combinatorial algorithms on distributed-memory systems,"Combinatorial algorithms such as those that arise in graph analysis, modeling
of discrete systems, bioinformatics, and chemistry, are often hard to
parallelize. The Combinatorial BLAS library implements key computational
primitives for rapid development of combinatorial algorithms in
distributed-memory systems. During the decade since its first introduction, the
Combinatorial BLAS library has evolved and expanded significantly.
  This paper details many of the key technical features of Combinatorial BLAS
version 2.0, such as communication avoidance, hierarchical parallelism via
in-node multithreading, accelerator support via GPU kernels, generalized
semiring support, implementations of key data structures and functions, and
scalable distributed I/O operations for human-readable files. Our paper also
presents several rules of thumb for choosing the right data structures and
functions in Combinatorial BLAS 2.0, under various common application
scenarios.",2106.14402v1
2021-07-01,From Epidemic to Pandemic Modelling,"We present a methodology for systematically extending epidemic models to
multilevel and multiscale spatio-temporal pandemic ones. Our approach builds on
the use of coloured stochastic and continuous Petri nets facilitating the sound
component-based extension of basic SIR models to include population
stratification and also spatio-geographic information and travel connections,
represented as graphs, resulting in robust stratified pandemic metapopulation
models. This method is inherently easy to use, producing scalable and reusable
models with a high degree of clarity and accessibility which can be read either
in a deterministic or stochastic paradigm. Our method is supported by a
publicly available platform PetriNuts; it enables the visual construction and
editing of models; deterministic, stochastic and hybrid simulation as well as
structural and behavioural analysis. All the models are available as
supplementary material, ensuring reproducibility.",2107.00835v1
2021-07-12,Primitive Rateless Codes,"In this paper, we propose primitive rateless (PR) codes. A PR code is
characterized by the message length and a primitive polynomial over
$\mathbf{GF}(2)$, which can generate a potentially limitless number of coded
symbols. We show that codewords of a PR code truncated at any arbitrary length
can be represented as subsequences of a maximum-length sequence ($m$-sequence).
We characterize the Hamming weight distribution of PR codes and their duals and
show that for a properly chosen primitive polynomial, the Hamming weight
distribution of the PR code can be well approximated by the truncated binomial
distribution. We further find a lower bound on the minimum Hamming weight of PR
codes and show that there always exists a PR code that can meet this bound for
any desired codeword length. We provide a list of primitive polynomials for
message lengths up to $40$ and show that the respective PR codes closely meet
the Gilbert-Varshamov bound at various rates. Simulation results show that PR
codes can achieve similar block error rates as their BCH counterparts at
various signal-to-noise ratios (SNRs) and code rates. PR codes are
rate-compatible and can generate as many coded symbols as required; thus,
demonstrating a truly rateless performance.",2107.05774v1
2021-07-16,Linear Programming Bounds for Almost-Balanced Binary Codes,"We revisit the linear programming bounds for the size vs. distance trade-off
for binary codes, focusing on the bounds for the almost-balanced case, when all
pairwise distances are between $d$ and $n-d$, where $d$ is the code distance
and $n$ is the block length. We give an optimal solution to Delsarte's LP for
the almost-balanced case with large distance $d \geq (n - \sqrt{n})/2 + 1$,
which shows that the optimal value of the LP coincides with the Grey-Rankin
bound for self-complementary codes.
  We also show that a limitation of the asymptotic LP bound shown by
Samorodnitsky, namely that it is at least the average of the first MRRW upper
bound and Gilbert-Varshamov bound, continues to hold for the almost-balanced
case.",2107.07672v1
2021-07-17,Magnetization switching in the inertial regime,"We have numerically solved the Landau-Lifshitz-Gilbert (LLG) equation in its
standard and inertial forms to study the magnetization switching dynamics in a
$3d$ thin film ferromagnet. The dynamics is triggered by ultrashort magnetic
field pulses of varying width and amplitude in the picosecond and Tesla range.
We have compared the solutions of the two equations in terms of switching
characteristic, speed and energy analysis. Both equations return qualitatively
similar switching dynamics, characterized by regions of slower precessional
behavior and faster ballistic motion. In case of inertial dynamics, ballistic
switching is found in a 25 % wider region in the parameter space given by the
magnetic field amplitude and width. The energy analysis of the dynamics is
qualitatively different for the standard and inertial LLG equations. In the
latter case, an extra energy channel, interpreted as the kinetic energy of the
system, is available. Such extra channel is responsible for a resonant energy
absorption at THz frequencies, consistent with the occurence of spin nutation.",2107.08234v1
2021-10-06,Controlled-Phase Gate by Dynamic Coupling of Photons to a Two-Level Emitter,"We propose an architecture for achieving high-fidelity deterministic quantum
logic gates on dual-rail encoded photonic qubits by letting photons interact
with a two-level emitter (TLE) inside an optical cavity. The photon wave
packets that define the qubit are preserved after the interaction due to a
quantum control process that actively loads and unloads the photons from the
cavity and dynamically alters their effective coupling to the TLE. The controls
rely on nonlinear wave mixing between cavity modes enhanced by strong
externally modulated electromagnetic fields or on AC Stark shifts of the TLE
transition energy. We numerically investigate the effect of imperfections in
terms of loss and dephasing of the TLE as well as control field miscalibration.
Our results suggest that III-V quantum dots in GaAs membranes is a promising
platform for photonic quantum information processing.",2110.02960v2
2021-10-12,Magnetization dynamics in the density matrix formalism,"Magnetization dynamics described by the Landau-Lifshitz-Gilbert-Slonczewski
(LLGS) equation can be formulated to have the form of the well-known
two-level-system (TLS) equations. Recently, we showed that a DC spin-transfer
torque (STT) term in the LLGS equation can be mapped to a modulation of the
carrier relaxation rates in the analogous TLS equations. Here, we extend the
analogy to the TLS dynamics by including the AC magnetic field, AC
demagnetization field, and AC STT excitation that we show constitute the
interaction term in the analogous TLS picture. Interestingly, we find that the
carrier injection rate in the TLS equations that is responsible for transitions
between the excited and ground states of the system naturally translates to an
intense short magnetic pulse that reverses the magnetization state.
Furthermore, we also show that the two helicities of circularly polarized
magnetic pulses correspond to the two carrier injection rates in the analogous
TLS picture. In the context of the highly debated all-optical helicity
dependent switching experiment, it offers a new explanation of the
magnetization reversal from first principles.",2110.06138v3
2021-10-12,Period Ratio Sculpting Near Second-Order Mean-Motion Resonances,"Second-order mean-motion resonances lead to an interesting phenomenon in the
sculpting of the period ratio distribution due to their shape and width in
period-ratio/eccentricity space. As the osculating periods librate in
resonance, the time-averaged period ratio approaches the exact
commensurability. The width of second-order resonances increases with
increasing eccentricity, and thus more eccentric systems have a stronger peak
at commensurability when averaged over sufficient time. The libration period is
short enough that this time-averaging behavior is expected to appear on the
timescale of the Kepler mission. Using N-body integrations of simulated planet
pairs near the 5:3 and 3:1 mean-motion resonances, we investigate the
eccentricity distribution consistent with the planet pairs observed by Kepler.
This analysis, an approach independent from previous studies, shows no
statistically significant peak at the 3:1 resonance and a small peak at the 5:3
resonance, placing an upper limit on the Rayleigh scale parameter, $\sigma$, of
the eccentricity of the observed Kepler planets at $\sigma=0.245$ (3:1) and
$\sigma=0.095$ (5:3) at 95% confidence, consistent with previous results from
other methods.",2110.06317v1
2021-10-15,Macroscopic elastic stress and strain produced by irradiation,"Using the notion of eigenstrain produced by the defects formed in a material
exposed to high energy neutron irradiation, we develop a method for computing
macroscopic elastic stress and strain arising in components of a fusion power
plant during operation. In a microstructurally isotropic material, the primary
cause of macroscopic elastic stress and strain fields is the spatial variation
of neutron exposure. We show that under traction-free boundary conditions, the
volume-average elastic stress always vanishes, signifying the formation of a
spatially heterogeneous stress state, combining compressive and tensile elastic
deformations at different locations in the same component, and resulting solely
from the spatial variation of radiation exposure. Several case studies
pertinent to the design of a fusion power plant are analysed analytically and
numerically, showing that a spatially varying distribution of defects produces
significant elastic stresses in ion-irradiated thin films, pressurised
cylindrical tubes and breeding blanket modules.",2110.07955v1
2021-10-21,Physics-Based Models for Magneto-Electric Spin-Orbit Logic Circuits,"Spintronic devices are a promising beyond-CMOS device option thanks to their
energy efficiency and compatibility with CMOS. To accurately capture their
multi-physics dynamics, a rigorous treatment of both spin and charge and their
inter-conversion is required. Here we present physics-based device models based
on 4x4 matrices for the spin-orbit coupling part of the magneto-electric
spin-orbit (MESO) device. Also, a more rigorous physics model of ferroelectric
and magnetoelectric switching of ferromagnets, based on Landau-Lifshitz-Gilbert
(LLG) and Landau-Khalatnikov (LK) equations, is presented. With the combined
model implemented in a SPICE circuit simulator environment, simulation results
were obtained which show feasibility of MESO implementation and functional
operation of buffers, oscillators, and majority gates.",2110.10890v1
2021-10-29,Thermal melting of discrete time crystals: a dynamical phase transition induced by thermal fluctuations,"The stability of a discrete time crystal against thermal fluctuations has
been studied numerically by solving a stochastic Landau-Lifshitz-Gilbert
equation of a periodically-driven classical system composed of interacting
spins, each of which couples to a thermal bath. It is shown that in the
thermodynamic limit, even though the long-range temporary crystalline order is
stable at low temperature, it is melting above a critical temperature, at which
the system experiences a non-equilibrium phase transition. The critical
behaviors of the continuous phase transition have been systematically
investigated, and it is shown that despite the genuine non-equilibrium feature
of such a periodically driven system, its critical properties fall into the 3D
Ising universality class with a dynamical exponent ($z=2$) identical to that in
the critical dynamics of kinetic Ising model without driving.",2110.15506v3
2021-10-29,Magnetism and Magnetotransport in the Kagome Antiferromagnet $\text{Mn}_3\text{Ge}$,"We perform classical Monte Carlo and stochastic Landau-Lifshitz-Gilbert
simulations to study temperature dependent magnetism of Kagome antiferromagnet
(AFM) Weyl metal $\text{Mn}_3\text{Ge}$ and find that a long range chiral order
sets in at a transition temperature well below the N{\'e}el temperature
($T_N$). Based on the crystalline symmetries, imposed by the chiral magnetic
order, we argue for the presence of multiple iso-energetic Weyl nodes (nodes
that are at same energy and with congruent Fermi surface around them) near
chemical potential. Using the semi-classical Boltzmann equations, we show that
the combined contribution to the net longitudinal magnetoconductance (LMC) and
the planar Hall conductance (PHC) from tilted Weyl nodes can lead to
signatures, qualitatively distinct from that of a single pair of Weyl nodes. In
particular, we show that magnetic orders with different chiralities can give
rise to different periods in LMC and PHC as a function of the in-plane magnetic
field direction. This is ultimately related to differences in the
symmetry-imposed constraints on the Weyl nodes.",2110.15864v2
2021-11-10,Experimental Search for Neutron to Mirror Neutron Oscillations as an Explanation of the Neutron Lifetime Anomaly,"An unexplained $>4\,\sigma$ discrepancy persists between ""beam"" and ""bottle""
measurements of the neutron lifetime. A new model proposed that conversions of
neutrons $n$ into mirror neutrons $n'$, part of a dark mirror sector, can
increase the apparent neutron lifetime by $1\%$ via a small mass splitting
$\Delta{m}$ between $n$ and $n'$ inside the 4.6 T magnetic field of the
National Institute of Standards and Technology Beam Lifetime experiment. A
search for neutron conversions in a 6.6 T magnetic field was performed at the
Spallation Neutron Source which excludes this explanation for the neutron
lifetime discrepancy.",2111.05543v2
2021-11-12,Whirling interlayer fields as a source of stable topological order in moiré CrI3,"The moir\'e engineering of two-dimensional magnets opens unprecedented
opportunities to design novel magnetic states with promises for spintronic
device applications. The possibility of stabilizing skyrmions in these
materials without chiral spin-orbit couplings or dipolar interactions is yet to
be explored. Here, we investigate the formation and control of ground state
topological spin textures (TSTs) in moir\'e CrI3 using stochastic
Landau-Lifshitz-Gilbert simulations. We unveil the emergence of interlayer
vortex and antivortex Heisenberg exchange fields, stabilizing spontaneous and
field-assisted ground state TSTs with various topologies. The developed study
accounts for the full bilayer spin dynamics, thermal fluctuations, and
intrinsic spin-orbit couplings. By examining the effect of the Kitaev
interaction and the next nearest-neighbor Dzyaloshinskii-Moriya interaction, we
propose the latter as the unique spin-orbit coupling mechanism compatible with
experiments on monolayer and twisted CrI3. Our findings contribute to the
current knowledge about moir\'e skyrmionics and uncover the nature of
spin-orbit coupling in CrI3.",2111.06936v2
2021-11-21,Explicit complex-valued solutions of the 2D eikonal equation,"We present a method to obtain explicit solutions of the complex eikonal
equation in the plane. This equation arises in the approximation of Helmholtz
equation by the WKBJ or EWT methods. We obtain the complex-valued solutions
(called eikonals) as parameterizations in a complex variable. We consider both
the cases of constant and non-constant index of refraction. In both cases, the
relevant parameterizations depend on some holomorphic function. In the case of
non-constant index of refraction, the parametrization also depends on some
extra exponential complex-valued function and on a quasi-conformal
homeomorphism. This is due to the use of the theory of pseudo-analytic
functions and the related similarity principle. The parameterizations give
information about the formation of caustics and the light and shadow regions
for the relevant eikonals.",2111.10852v1
2021-12-08,A comparison of spectral reconstruction methods applied to non-zero temperature NRQCD meson correlation functions,"We present results from the fastsum collaboration's programme to determine
the spectrum of the bottomonium system as a function of temperature. Three
different methods of extracting spectral information are discussed: a Maximum
Likelihood approach using a Gaussian spectral function for the ground state,
the Backus Gilbert method, and the Kernel Ridge Regression machine learning
procedure. We employ the fastsum anisotropic lattices with 2+1 dynamical quark
flavours, with temperatures ranging from 47 to 375 MeV.",2112.04201v1
2021-12-23,Nutation spin waves in ferromagnets,"Magnetization dynamics and spin waves in ferromagnets are investigated using
the inertial Landau-Lifshitz-Gilbert equation. Taking inertial magnetization
dynamics into account, dispersion relations describing the propagation of
nutation spin waves in an arbitrary direction relative to the applied magnetic
field are derived via Maxwell's equations. It is found that the inertia of
magnetization causes the hybridization of electromagnetic waves and nutation
spin waves in ferromagnets, hybrid nutation spin waves emerge, and the redshift
of frequencies of precession spin waves is initiated, which transforms to
precession-nutation spin waves. These effects depend sharply on the direction
of wave propagation relative to the applied magnetic field. Moreover, the waves
propagating parallel to the applied field are circularly polarized, while the
waves propagating perpendicular to that field are elliptically polarized. The
characteristics of these spin nutation waves are also analyzed.",2112.12503v3
2021-12-30,Spin Torque Oscillations Triggered by In-plane Field,"We study the dynamics of a spin torque nano oscillator that consists of
parallelly magnetized free and pinned layers by numerically solving the
associated Landau-Lifshitz-Gilbert-Slonczewski equation in the presence of a
field-like torque. We observe that an in-plane magnetic field which is applied
for a short interval of time ($<$1ns) triggers the magnetization to exhibit
self-oscillations from low energy initial magnetization state. Also, we confirm
that the frequency of oscillations can be tuned over the range $\sim$25 GHz to
$\sim$72 GHz by current, even in the absence of field-like torque. We find the
frequency enhancement up to 10 GHz by the presence of field-like torque. We
determine the Q-factor for different frequencies and show that it increases
with frequency. Our analysis with thermal noise confirms that the system is
stable against thermal noise and the dynamics is not altered appreciably by it.",2112.15004v1
2022-01-11,Ultrahigh quality infrared polaritonic resonators based on bottom-up-synthesized van der Waals nanoribbons,"van der Waals nanomaterials supporting phonon polariton quasiparticles
possess unprecedented light confinement capabilities, making them ideal systems
for molecular sensing, thermal emission, and subwavelength imaging
applications, but they require defect-free crystallinity and nanostructured
form factors to fully showcase these capabilities. We introduce
bottom-up-synthesized {\alpha}-MoO3 structures as nanoscale phonon polaritonic
systems that feature tailorable morphologies and crystal qualities consistent
with bulk single crystals. {\alpha}-MoO3 nanoribbons serve as low-loss
hyperbolic Fabry-P\'erot nanoresonators, and we experimentally map hyperbolic
resonances over four Reststrahlen bands spanning the far- and mid-infrared
spectral range, including resonance modes beyond the tenth order. The measured
quality factors are the highest from phonon polaritonic van der Waals
structures to date. We anticipate that bottom-up-synthesized polaritonic van
der Waals nanostructures will serve as an enabling high-performance and
low-loss platform for infrared optical and optoelectronic applications.",2201.03748v1
2022-01-12,The angular dependence of magnetization dynamics induced by a GHz range strain pulse,"The dynamics of magnetization is important in spintronics, where the coupling
between phonon and magnon attracts much attention. In this work, we study the
angular dependence of the coupling between longitudinal-wave phonon and magnon.
We investigated the magnetization dynamics using the time-resolved
magneto-optical Kerr effect, which allows measuring spin-wave resonances and
the magnetic echo signal. The frequency, mode number, and amplitude of the
spin-wave resonance change with the out-of-plane angle of the external magnetic
field. The amplitude of the magnetic echo signal caused by the strain pulse
also changes with the angle. We calculate these angular dependences based on
the Landau-Lifshitz-Gilbert equation and find that the angles of the external
field and magnetic moment are important factors for the phonon-magnon coupling
when phonon propagates in the thickness direction under the out-of-plane
magnetic field.",2201.04396v1
2022-01-17,A Theory of Second-Order Wireless Network Optimization and Its Application on AoI,"This paper introduces a new theoretical framework for optimizing second-order
behaviors of wireless networks. Unlike existing techniques for network utility
maximization, which only considers first-order statistics, this framework
models every random process by its mean and temporal variance. The inclusion of
temporal variance makes this framework well-suited for modeling stateful fading
wireless channels and emerging network performance metrics such as
age-of-information (AoI). Using this framework, we sharply characterize the
second-order capacity region of wireless access networks. We also propose a
simple scheduling policy and prove that it can achieve every interior point in
the second-order capacity region. To demonstrate the utility of this framework,
we apply it for an important open problem: the optimization of AoI over
Gilbert-Elliott channels. We show that this framework provides a very accurate
characterization of AoI. Moreover, it leads to a tractable scheduling policy
that outperforms other existing work.",2201.06486v1
2022-01-18,Self-Modifying Code in Open-Ended Evolutionary Systems,"Having a model and being able to implement open-ended evolutionary systems is
important for advancing our understanding of open-endedness. Complex systems
science and newest generation high-level programming languages provide
intriguing possibilities to do so. First, some recent advances in modelling and
implementing open-ended evolutionary systems are reviewed. Then, the so-called
allagmatic method is introduced that describes, models, implements, and allows
interpretation of complex systems. After highlighting some current modelling
and implementation challenges, model building blocks of open-ended evolutionary
systems are identified, a system metamodel of open-ended evolution is
formalised in the allagmatic method, an implementation self-modifying code
prototype with a high-level programming language is provided, and guidance from
the allagmatic method to create code blocks is described. The proposed
prototype allows modifying code at runtime in a controlled way within a system
metamodel. Since the allagmatic method has been built based on metaphysical
concepts borrowed from Gilbert Simondon and Alfred N. Whitehead, the proposed
prototype provides a promising starting point to interpret novelty generated at
runtime with the help of a metaphysical framework.",2201.06858v2
2022-01-28,Piezo-optomechanical cantilever modulators for VLSI visible photonics,"Visible-wavelength very large-scale integration (VLSI) photonic circuits have
potential to play important roles in quantum information and sensing
technologies. The realization of scalable, high-speed, and low-loss photonic
mesh circuits depends on reliable and well-engineered visible photonic
components. Here we report a low-voltage optical phase shifter based on
piezo-actuated mechanical cantilevers, fabricated on a CMOS compatible, 200 mm
wafer-based visible photonics platform. We show linear phase and amplitude
modulation with 6 V$_{\pi}$-cm in differential operation, -1.5 dB to -2 dB
insertion loss, and up to 40 dB contrast in the 700 nm - 780 nm range. By
adjusting selected cantilever parameters, we demonstrate a low-displacement and
a high-displacement device, both exhibiting a nearly flat frequency response
from DC to a peak mechanical resonance at 23 MHz and 6.8 MHz respectively,
which through resonant enhancement of Q~40, further decreases the operating
voltage down to 0.15 V$_{\pi}$-cm.",2201.12447v1
2022-01-30,"Spintronics-compatible approach to solving maximum satisfiability problems with probabilistic computing, invertible logic and parallel tempering","The search of hardware-compatible strategies for solving NP-hard
combinatorial optimization problems (COPs) is an important challenge of today s
computing research because of their wide range of applications in real world
optimization problems. Here, we introduce an unconventional scalable approach
to face maximum satisfiability problems (Max-SAT) which combines probabilistic
computing with p-bits, parallel tempering, and the concept of invertible logic
gates. We theoretically show the spintronic implementation of this approach
based on a coupled set of Landau-Lifshitz-Gilbert equations, showing a
potential path for energy efficient and very fast (p-bits exhibiting ns time
scale switching) architecture for the solution of COPs. The algorithm is
benchmarked with hard Max-SAT instances from the 2016 Max-SAT competition
(e.g., HG-4SAT-V150-C1350-1.cnf which can be described with 2851 p-bits),
including weighted Max-SAT and Max-Cut problems.",2201.12858v1
2022-02-01,Numerical Model Of Harmonic Hall Voltage Detection For Spintronic Devices,"We present a numerical macrospin model for harmonic voltage detection in
multilayer spintronic devices. The core of the computational backend is based
on the Landau-Lifshitz-Gilbert-Slonczewski equation, which combines high
performance with satisfactory, for large-scale applications, agreement with the
experimental results. We compare the simulations with the experimental findings
in Ta/CoFeB bilayer system for angular- and magnetic field-dependent resistance
measurements, electrically detected magnetisation dynamics, and harmonic Hall
voltage detection. Using simulated scans of the selected system parameters such
as the polar angle $\theta$, magnetisation saturation
($\mu_\textrm{0}M_\textrm{s}$) or uniaxial magnetic anisotropy ($K_\textrm{u}$)
we show the resultant changes in the harmonic Hall voltage, demonstrating the
dominating influence of the $\mu_\textrm{0}M_\textrm{s}$ on the first and
second harmonics. In the spin-diode ferromagnetic resonance (SD-FMR) technique
resonance method the ($\mu_\textrm{0}M_\textrm{s}$, $K_\textrm{u}$) parameter
space may be optimised numerically to obtain a set of viable curves that fit
the experimental data.",2202.00364v1
2022-02-03,Magnetic domain wall dynamics under external electric field in bilayer CrI$_3$,"Motivated by manipulating the magnetic order of bilayer CrI$_3$, we carry out
microscopic calculations to find the magnetic order and various magnetic
domains of the system in the presence of an electric field. Making use of
density functional simulations, a spin model Hamiltonian is introduced
consisting of isotropic exchange couplings, Dzyaloshinskii-Moriya (DM)
interaction, and on-site magnetic anisotropy. The spin dynamics of two
well-known states of bilayer CrI$_3$, low temperature (LT) and high temperature
(HT) phases, are obtained by solving the Landau-Lifshitz-Gilbert equation. We
show that the magnetic texture is stacking-dependent in bilayer CrI$_3$ and
stable magnetic domains can appear in the HT stack which are tunable by
external electric and magnetic fields. Therefore, we suggest that the HT phase
represents a promising candidate for data storage in the modern generation of
spintronic devices working on magnetic domain engineering.",2202.01394v2
2022-02-07,Spin-transfer-assisted parametric pumping of magnons in yttrium iron garnet,"The combination of parametric pumping and spin-transfer torque is a powerful
approach that enables high-level control over magnetic excitations in thin-film
ferromagnets. The excitation parameters, such as pumping power and external
field strength, affect the instabilities of individual magnon modes. We
theoretically explore how the simultaneous effects of parametric pumping and
spin transfer torque influence these magnetic instabilities in a thin-film
ferromagnet. Within the Landau-Lifshitz-Gilbert framework, we perform
micromagnetic simulations of magnon excitations in yttrium iron garnet by
pumping, spin transfer torque, and a combination of the two. We find that
consistent with experimental results, the magnitude and direction of the
spin-transfer torque tune the parametric instability thresholds.",2202.03247v2
2022-02-13,Critical-layer instability of shallow water magnetohydrodynamic shear flows,"In this paper, the instability of shallow water shear flow with a sheared
parallel magnetic field is studied. Waves propagating in such magnetic shear
flows encounter critical levels where the phase velocity relative to the basic
flow $c-U(y)$ matches the Alfv\'en wave velocities $\pm B(y)/\sqrt{\mu\rho}$,
based on the local magnetic field $B(y)$, the magnetic permeability $\mu$ and
the mass density of the fluid $\rho$. It is shown that when the two critical
levels are close to each other, the critical layer can generate an instability.
The instability problem is solved, combining asymptotic solutions at large
wavenumbers and numerical solutions, and the mechanism of instability explained
using the conservation of momentum. For the shallow water MHD system, the paper
gives the general form of the local differential equation governing such
coalescing critical layers for any generic field and flow profiles, and
determines precisely how the magnetic field modifies the purely hydrodynamic
stability criterion based on the potential vorticity gradient in the critical
layer. The curvature of the magnetic field profile, or equivalently the
electric current gradient, $J' = - B''/\mu$ in the critical layer is found to
play a complementary role in the instability.",2202.06272v1
2022-02-21,On Grid Codes,"Versions of the Hamming and Gilbert-Varshamov bounds for codes in
$\prod_{i=1}^{n}[0,m_{i}-1]$ with respect to the Manhattan distance are
presented. Given an abelian group $G$ isomorphic to $C_{m_{1}}\times \cdots
\times C_{m_{n}}$, the Hamming, Manhattan, and Lee distances are defined in
$G$; a formula for the minimum Hamming distance of codes that are cyclic
subgroups of $G$ is provided, and some lower bounds for the minimum Manhattan
distance of these codes are determined in terms of their minimum Hamming and
Lee distances. Examples illustrating the main results and an application of
these are provided.",2202.10005v4
2022-02-23,Convergence of Oja's online principal component flow,"Online principal component analysis (PCA) has been an efficient tool in
practice to reduce dimension. However, convergence properties of the
corresponding ODE are still unknown, including global convergence, stable
manifolds, and convergence rate. In this paper, we focus on the stochastic
gradient ascent (SGA) method proposed by Oja. By regarding the corresponding
ODE as a Landau-Lifshitz-Gilbert (LLG) equation on the Stiefel manifold, we
proved global convergence of the ODE. Moreover, we developed a new technique to
determine stable manifolds. This technique analyzes the rank of the initial
datum. Using this technique, we derived the explicit expression of the stable
manifolds. As a consequence, exponential convergence to stable equilibrium
points was also proved. The success of this new technique should be attributed
to the semi-decoupling property of the SGA method: iteration of previous
components does not depend on that of later ones. As far as we know, our result
is the first complete one on the convergence of an online PCA flow, providing
global convergence, explicit characterization of stable manifolds, and closed
formula of exponential convergence depending on the spectrum gap.",2202.11308v1
2022-02-28,Curb Your Self-Modifying Code,"Self-modifying code has many intriguing applications in a broad range of
fields including software security, artificial general intelligence, and
open-ended evolution. Having control over self-modifying code, however, is
still an open challenge since it is a balancing act between providing as much
freedom as possible so as not to limit possible solutions, while at the same
time imposing restriction to avoid security issues and invalid code or
solutions. In the present study, I provide a prototype implementation of how
one might curb self-modifying code by introducing control mechanisms for code
modifications within specific regions and for specific transitions between code
and data. I show that this is possible to achieve with the so-called allagmatic
method - a framework to formalise, model, implement, and interpret complex
systems inspired by Gilbert Simondon's philosophy of individuation and Alfred
North Whitehead's philosophy of organism. Thereby, the allagmatic method serves
as guidance for self-modification based on concepts defined in a metaphysical
framework. I conclude that the allagmatic method seems to be a suitable
framework for control mechanisms in self-modifying code and that there are
intriguing analogies between the presented control mechanisms and gene
regulation.",2202.13830v2
2022-03-03,A general adaptive framework for multivariate point null testing,"As a common step in refining their scientific inquiry, investigators are
often interested in performing some screening of a collection of given
statistical hypotheses. For example, they may wish to determine whether any one
of several patient characteristics are associated with a health outcome of
interest. Existing generic methods for testing a multivariate hypothesis --
such as multiplicity corrections applied to individual hypothesis tests -- can
easily be applied across a variety of problems but can suffer from low power in
some settings. Tailor-made procedures can attain higher power by building
around problem-specific information but typically cannot be easily adapted to
novel settings. In this work, we propose a general framework for testing a
multivariate point null hypothesis in which the test statistic is adaptively
selected to provide increased power. We present theoretical large-sample
guarantees for our test under both fixed and local alternatives. In simulation
studies, we show that tests created using our framework can perform as well as
tailor-made methods when the latter are available, and we illustrate how our
procedure can be used to create tests in two settings in which tailor-made
methods are not currently available.",2203.01897v1
2022-03-09,KPE: Keypoint Pose Encoding for Transformer-based Image Generation,"Transformers have recently been shown to generate high quality images from
text input. However, the existing method of pose conditioning using skeleton
image tokens is computationally inefficient and generate low quality images.
Therefore we propose a new method; Keypoint Pose Encoding (KPE); KPE is 10
times more memory efficient and over 73% faster at generating high quality
images from text input conditioned on the pose. The pose constraint improves
the image quality and reduces errors on body extremities such as arms and legs.
The additional benefits include invariance to changes in the target image
domain and image resolution, making it easily scalable to higher resolution
images. We demonstrate the versatility of KPE by generating photorealistic
multiperson images derived from the DeepFashion dataset. We also introduce a
evaluation method People Count Error (PCE) that is effective in detecting error
in generated human images.",2203.04907v2
2022-03-09,Finiteness for Hecke algebras of $p$-adic groups,"Let $G$ be a reductive group over a non-archimedean local field $F$ of
residue characteristic $p$. We prove that the Hecke algebras of $G(F)$ with
coefficients in a ${\mathbb Z}_{\ell}$-algebra $R$ for $\ell$ not equal to $p$
are finitely generated modules over their centers, and that these centers are
finitely generated $R$-algebras. Following Bernstein's original strategy, we
then deduce that ""second adjointness"" holds for smooth representations of
$G(F)$ with coefficients in any ring $R$ in which $p$ is invertible. These
results had been conjectured for a long time. The crucial new tool that unlocks
the problem is the Fargues-Scholze morphism between a certain ""excursion
algebra"" defined on the Langlands parameters side and the Bernstein center of
$G(F)$. Using this bridge, our main results are representation theoretic
counterparts of the finiteness of certain morphisms between coarse moduli
spaces of local Langlands parameters that we also prove here, which may be of
independent interest",2203.04929v2
2022-03-10,StyleBabel: Artistic Style Tagging and Captioning,"We present StyleBabel, a unique open access dataset of natural language
captions and free-form tags describing the artistic style of over 135K digital
artworks, collected via a novel participatory method from experts studying at
specialist art and design schools. StyleBabel was collected via an iterative
method, inspired by `Grounded Theory': a qualitative approach that enables
annotation while co-evolving a shared language for fine-grained artistic style
attribute description. We demonstrate several downstream tasks for StyleBabel,
adapting the recent ALADIN architecture for fine-grained style similarity, to
train cross-modal embeddings for: 1) free-form tag generation; 2) natural
language description of artistic style; 3) fine-grained text search of style.
To do so, we extend ALADIN with recent advances in Visual Transformer (ViT) and
cross-modal representation learning, achieving a state of the art accuracy in
fine-grained style retrieval.",2203.05321v2
2022-03-12,The mass-lumped midpoint scheme for computational micromagnetics: Newton linearization and application to magnetic skyrmion dynamics,"We discuss a mass-lumped midpoint scheme for the numerical approximation of
the Landau-Lifshitz-Gilbert equation, which models the dynamics of the
magnetization in ferromagnetic materials. In addition to the classical
micromagnetic field contributions, our setting covers the non-standard
Dzyaloshinskii-Moriya interaction, which is the essential ingredient for the
enucleation and stabilization of magnetic skyrmions. Our analysis also includes
the inexact solution of the arising nonlinear systems, for which we discuss
both a constraint preserving fixed-point solver from the literature and a novel
approach based on the Newton method. We numerically compare the two
linearization techniques and show that the Newton solver leads to a
considerably lower number of nonlinear iterations. Moreover, in a numerical
study on magnetic skyrmions, we demonstrate that, for magnetization dynamics
that are very sensitive to energy perturbations, the midpoint scheme, due to
its conservation properties, is superior to the dissipative tangent plane
schemes from the literature.",2203.06445v1
2022-03-16,The Geometry and Topology of Stationary Multi-Axisymmetric Vacuum Black Holes in Higher Dimensions,"Extending recent work in 5 dimensions, we prove the existence and uniqueness
of solutions to the reduced Einstein equations for vacuum black holes in
$(n+3)$-dimensional spacetimes admitting the isometry group $\mathbb{R}\times
U(1)^{n}$, with Kaluza-Klein asymptotics for $n\geq3$. This is equivalent to
establishing existence and uniqueness for singular harmonic maps $\varphi:
\mathbb{R}^3\setminus\Gamma\rightarrow SL(n+1,\mathbb{R})/SO(n+1)$ with
prescribed blow-up along $\Gamma$, a subset of the $z$-axis in $\mathbb{R}^3$.
We also analyze the topology of the domain of outer communication for these
spacetimes, by developing an appropriate generalization of the plumbing
construction used in the lower dimensional case. Furthermore, we provide a
counterexample to a conjecture of Hollands-Ishibashi concerning the topological
classification of the domain of outer communication. A refined version of the
conjecture is then presented and established in spacetime dimensions less than
8.",2203.08325v1
2022-03-18,Smectite phase separation is driven by emergent interfacial dynamics,"Smectite clay minerals have an outsize impact on the response of clay-rich
media to common stimuli, such as water imbibition and ion exchange, motivating
extensive effort to understand microscopic behaviors resulting from these
processes such as swelling and exfoliation. Nonetheless, there is no general
consensus about the microscopic forces that govern smectite properties, which
are model systems for understanding colloidal and interfacial phenomena more
generally. We find that the complex free energy surface arising from the
interplay of at least four intermolecular forces and their nonlinear couplings
that control local particle-particle interactions leads to dynamic, unstable
equilibria between distinct phases. Mechanical disequilibrium arising from
osmotic gradients between curved or interacting interfaces drive the dynamic
exchange of layers and ions between dense and dilute phases via avalanche
transitions that are sustained by thermal fluctuations. We suggest that the
surprising interfacial dynamics displayed by smectite minerals, arising from
the vastly different mobilities of water, ions and mineral, makes them
fundamentally distinct from non-clay minerals because their structures are
easily perturbed away from simultaneous chemical and mechanical equilibrium.",2203.10129v1
2022-03-27,Low power In Memory Computation with Reciprocal Ferromagnet/Topological Insulator Heterostructures,"The surface state of a 3D topological insulator (3DTI) is a spin-momentum
locked conductive state, whose large spin hall angle can be used for the
energy-efficient spin orbit torque based switching of an overlying ferromagnet
(FM). Conversely, the gated switching of the magnetization of a separate FM in
or out of the TI surface plane, can turn on and off the TI surface current. The
gate tunability of the TI Dirac cone gap helps reduce its sub-threshold swing.
By exploiting this reciprocal behaviour, we can use two FM/3DTI
heterostructures to design a 1-Transistor 1-magnetic tunnel junction random
access memory unit (1T1MTJ RAM) for an ultra low power Processing-in-Memory
(PiM) architecture. Our calculation involves combining the Fokker-Planck
equation with the Non-equilibrium Green Function (NEGF) based flow of
conduction electrons and Landau-Lifshitz-Gilbert (LLG) based dynamics of
magnetization. Our combined approach allows us to connect device performance
metrics with underlying material parameters, which can guide proposed
experimental and fabrication efforts.",2203.14389v3
2022-03-17,Symmetry effects on the static and dynamic properties of coupled magnetic oscillators,"The effect of symmetry on the resonance spectra of antiferromagnetically
coupled oscillators has attracted new interest with the discovery of
symmetry-breaking induced anti-crossings. Here, we experimentally characterise
the resonance spectrum of a synthetic antiferromagnet Pt/CoFeB/Ru/CoFeB/Pt,
where we are able to independently tune the effective magnetisation of the two
coupled magnets. To model our results we apply the mathematical methods of
group theory to the solutions of the Landau Lifshitz Gilbert equation. This
general approach, usually applied to quantum mechanical systems, allows us to
identify the main features of the resonance spectrum in terms of symmetry
breaking and to make a direct comparison with crystal antiferromagnets.",2204.01490v1
2022-04-17,Gravitational Solitons and Complete Ricci Flat Riemannian Manifolds of Infinite Topological Type,"We present several new space-periodic solutions of the static vacuum Einstein
equations in higher dimensions, both with and without black holes, having
Kasner asymptotics. These latter solutions are referred to as gravitational
solitons. Further partially compactified solutions are also obtained by taking
appropriate quotients, and the topologies are computed explicitly in terms of
connected sums of products of spheres. In addition, it is shown that there is a
correspondence, via Wick rotation, between the spacelike slices of the solitons
and black hole solutions in one dimension less. As a corollary, the solitons
give rise to complete Ricci flat Riemannian manifolds of infinite topological
type and generic holonomy, in dimensions 4 and higher.",2204.08048v2
2022-04-26,Cosmology from the kinetic polarized Sunyaev Zel'dovich effect,"The cosmic microwave background (CMB) photons that scatter off free electrons
in the large-scale structure induce a linear polarization pattern proportional
to the remote CMB temperature quadrupole observed in the electrons' rest frame.
The associated blackbody polarization anisotropies are known as the polarized
Sunyaev Zel'dovich (pSZ) effect. Relativistic corrections to the remote
quadrupole field give rise to a non-blackbody polarization anisotropy
proportional to the square of the transverse peculiar velocity field; this is
the kinetic polarized Sunyaev Zel'dovich (kpSZ) effect. In this paper, we
forecast the ability of future CMB and galaxy surveys to detect the kpSZ
effect, finding that a statistically significant detection is within the reach
of planned experiments. We further introduce a quadratic estimator for the
square of the peculiar velocity field based on a galaxy survey and CMB
polarization. Finally, we outline how the kpSZ effect is a probe of cosmic
birefringence and primordial non-Gaussianity, forecasting the reach of future
experiments.",2204.12503v2
2022-04-27,Advantages of maintaining a multi-task project-specific bot: an experience report,"Bots are becoming a popular method for automating basic everyday tasks in
many software projects. This is true in particular because of the availability
of many off-the-shelf task-specific bots that teams can quickly adopt (which
are sometimes completed with additional task-specific custom bots). Based on
our experience in the Coq project, where we have developed and maintained a
multi-task project-specific bot, we argue that this alternative approach to
project automation should receive more attention because it strikes a good
balance between productivity and adaptibility. In this article, we describe the
kind of automation that our bot implements, what advantages we have gained by
maintaining a project-specific bot, and the technology and architecture choices
that have made it possible. We draw conclusions that should generalize to other
medium-sized software teams willing to invest in project automation without
disrupting their workflows.",2204.12758v1
2022-04-29,Self-consistent solution of magnetic and friction energy losses of a magnetic nanoparticle,"We present a simple simulation model for analysing magnetic and frictional
losses of magnetic nano-particles in viscous fluids subject to alternating
magnetic fields. Assuming a particle size below the single-domain limit, we use
a macrospin approach and solve the Landau-Lifshitz-Gilbert equation coupled to
the mechanical torque equation. Despite its simplicity the presented model
exhibits surprisingly rich physics and enables a detailed analysis of the
different loss processes depending on field parameters and initial arrangement
of the particle and the field. Depending on those parameters regions of
different steady states emerge: a region with dominating N\'eel relaxation and
high magnetic losses and another region region with high frictional losses at
low fields or low frequencies. The energy increases continuously even across
regime boundaries up to frequencies above the Brownian relaxation limit. At
those higher frequencies the steady state can also depend on the initial
orientation of the particle in the external field. The general behavior and
special cases and their specific absorption rates are compared and discussed.",2204.14106v3
2022-05-04,Separations in Proof Complexity and TFNP,"It is well-known that Resolution proofs can be efficiently simulated by
Sherali-Adams (SA) proofs. We show, however, that any such simulation needs to
exploit huge coefficients: Resolution cannot be efficiently simulated by SA
when the coefficients are written in unary. We also show that Reversible
Resolution (a variant of MaxSAT Resolution) cannot be efficiently simulated by
Nullstellensatz (NS).
  These results have consequences for total NP search problems. First, we
characterise the classes PPADS, PPAD, SOPL by unary-SA, unary-NS, and
Reversible Resolution, respectively. Second, we show that, relative to an
oracle, PLS $\not\subseteq$ PPP, SOPL $\not\subseteq$ PPA, and EOPL
$\not\subseteq$ UEOPL. In particular, together with prior work, this gives a
complete picture of the black-box relationships between all classical TFNP
classes introduced in the 1990s.",2205.02168v2
2022-05-10,Programming Data Structures for Large-Scale Desktop Simulations of Complex Systems,"The investigation of complex systems requires running large-scale simulations
over many temporal iterations. It is therefore important to provide efficient
implementations. The present study borrows philosophical concepts from Gilbert
Simondon to identify data structures and algorithms that have the biggest
impact on running time and memory usage. These are the entity $e$-tuple
$\mathcal{E}$ and the intertwined update function $\phi$. Focusing on
implementing data structures in C#, $\mathcal{E}$ is implemented as a list of
objects according to current software engineering practice and as an array of
pointers according to theoretical considerations. Cellular automaton
simulations with $10^9$ entities over one iteration reveal that the object-list
with dynamic typing and multi-state readiness has a drastic effect on running
time and memory usage, especially dynamic typing as it has a big impact on the
evolution time. Pointer-arrays are possible to implement in C# and are more
running time and memory efficient as compared to the object-list
implementation, however, they are cumbersome to implement. In conclusion,
avoiding dynamic typing in object-list based implementations or using
pointer-arrays gives evolution times that are acceptable in practice, even on
desktop computers.",2205.04837v2
2022-05-10,Sensible AI: Re-imagining Interpretability and Explainability using Sensemaking Theory,"Understanding how ML models work is a prerequisite for responsibly designing,
deploying, and using ML-based systems. With interpretability approaches, ML can
now offer explanations for its outputs to aid human understanding. Though these
approaches rely on guidelines for how humans explain things to each other, they
ultimately solve for improving the artifact -- an explanation. In this paper,
we propose an alternate framework for interpretability grounded in Weick's
sensemaking theory, which focuses on who the explanation is intended for.
Recent work has advocated for the importance of understanding stakeholders'
needs -- we build on this by providing concrete properties (e.g., identity,
social context, environmental cues, etc.) that shape human understanding. We
use an application of sensemaking in organizations as a template for discussing
design guidelines for Sensible AI, AI that factors in the nuances of human
cognition when trying to explain itself.",2205.05057v1
2022-05-14,SaiNet: Stereo aware inpainting behind objects with generative networks,"In this work, we present an end-to-end network for stereo-consistent image
inpainting with the objective of inpainting large missing regions behind
objects. The proposed model consists of an edge-guided UNet-like network using
Partial Convolutions. We enforce multi-view stereo consistency by introducing a
disparity loss. More importantly, we develop a training scheme where the model
is learned from realistic stereo masks representing object occlusions, instead
of the more common random masks. The technique is trained in a supervised way.
Our evaluation shows competitive results compared to previous state-of-the-art
techniques.",2205.07014v1
2022-05-15,Sociotechnical Specification for the Broader Impacts of Autonomous Vehicles,"Autonomous Vehicles (AVs) will have a transformative impact on society.
Beyond the local safety and efficiency of individual vehicles, these effects
will also change how people interact with the entire transportation system.
This will generate a diverse range of large and foreseeable effects on social
outcomes, as well as how those outcomes are distributed. However, the ability
to control both the individual behavior of AVs and the overall flow of traffic
also provides new affordances that permit AVs to control these effects. This
comprises a problem of sociotechnical specification: the need to distinguish
which essential features of the transportation system are in or out of scope
for AV development. We present this problem space in terms of technical,
sociotechnical, and social problems, and illustrate examples of each for the
transport system components of social mobility, public infrastructure, and
environmental impacts. The resulting research methodology sketches a path for
developers to incorporate and evaluate more transportation system features
within AV system components over time.",2205.07395v1
2022-05-19,Collision Detection Accelerated: An Optimization Perspective,"Collision detection between two convex shapes is an essential feature of any
physics engine or robot motion planner. It has often been tackled as a
computational geometry problem, with the Gilbert, Johnson and Keerthi (GJK)
algorithm being the most common approach today. In this work we leverage the
fact that collision detection is fundamentally a convex optimization problem.
In particular, we establish that the GJK algorithm is a specific sub-case of
the well-established Frank-Wolfe (FW) algorithm in convex optimization. We
introduce a new collision detection algorithm by adapting recent works linking
Nesterov acceleration and Frank-Wolfe methods. We benchmark the proposed
accelerated collision detection method on two datasets composed of strictly
convex and non-strictly convex shapes. Our results show that our approach
significantly reduces the number of iterations to solve collision detection
problems compared to the state-of-the-art GJK algorithm, leading to up to two
times faster computation times.",2205.09663v2
2022-05-31,"Solutions of the matrix equation $p(X)=A$, with polynomial function $p(λ)$ over field extensions of $\mathbb{Q}$","Let $\mathbb{H}$ be a field with
$\mathbb{Q}\subset\mathbb{H}\subset\mathbb{C}$, and let $p(\lambda)$ be a
polynomial in $\mathbb{H}[\lambda]$, and let $A\in\mathbb{H}^{n\times n}$ be
nonderogatory. In this paper we consider the problem of finding a solution
$X\in\mathbb{H}^{n\times n}$ to $p(X)=A$. A necessary condition for this to be
possible is already known from a paper by M.P. Drazin. Under an additional
condition we provide an explicit construction of such solutions. The
similarities and differences with the derogatory case will be discussed as
well.
  One of the tools needed in the paper is a new canonical form, which may be of
independent interest. It combines elements of the rational canonical form with
elements of the Jordan canonical form.",2205.15682v1
2022-06-02,A Fast Randomized Algorithm for Computing an Approximate Null Space,"Randomized algorithms in numerical linear algebra can be fast, scalable and
robust. This paper examines the effect of sketching on the right singular
vectors corresponding to the smallest singular values of a tall-skinny matrix.
We analyze a fast algorithm by Gilbert, Park and Wakin for finding the trailing
right singular vectors using randomization by examining the quality of the
solution using multiplicative perturbation theory. For an $m\times n$ ($m\geq
n$) matrix, the algorithm runs with complexity $O(mn\log n +n^3)$ which is
faster than the standard $O(mn^2)$ methods. In applications, numerical
experiments show great speedups including a $30\times$ speedup for the AAA
algorithm and $10\times$ speedup for the total least squares problem.",2206.00975v3
2022-06-10,Differentiable Rendering of Neural SDFs through Reparameterization,"We present a method to automatically compute correct gradients with respect
to geometric scene parameters in neural SDF renderers. Recent physically-based
differentiable rendering techniques for meshes have used edge-sampling to
handle discontinuities, particularly at object silhouettes, but SDFs do not
have a simple parametric form amenable to sampling. Instead, our approach
builds on area-sampling techniques and develops a continuous warping function
for SDFs to account for these discontinuities. Our method leverages the
distance to surface encoded in an SDF and uses quadrature on sphere tracer
points to compute this warping function. We further show that this can be done
by subsampling the points to make the method tractable for neural SDFs. Our
differentiable renderer can be used to optimize neural shapes from multi-view
images and produces comparable 3D reconstructions to recent SDF-based inverse
rendering methods, without the need for 2D segmentation masks to guide the
geometry optimization and no volumetric approximations to the geometry.",2206.05344v1
2022-06-15,Cautious Learning of Multiattribute Preferences,"This paper is dedicated to a cautious learning methodology for predicting
preferences between alternatives characterized by binary attributes (formally,
each alternative is seen as a subset of attributes). By ""cautious"", we mean
that the model learned to represent the multi-attribute preferences is general
enough to be compatible with any strict weak order on the alternatives, and
that we allow ourselves not to predict some preferences if the data collected
are not compatible with a reliable prediction. A predicted preference will be
considered reliable if all the simplest models (following Occam's razor
principle) explaining the training data agree on it. Predictions are based on
an ordinal dominance relation between alternatives [Fishburn and LaValle,
1996]. The dominance relation relies on an uncertainty set encompassing the
possible values of the parameters of the multi-attribute utility function.
Numerical tests are provided to evaluate the richness and the reliability of
the predictions made.",2206.07341v1
2022-06-23,Probabilistic load forecasting for the low voltage network: forecast fusion and daily peaks,"Short-term forecasts of energy consumption are invaluable for the operation
of energy systems, including low voltage electricity networks. However, network
loads are challenging to predict when highly desegregated to small numbers of
customers, which may be dominated by individual behaviours rather than the
smooth profiles associated with aggregate consumption. Furthermore,
distribution networks are challenged almost entirely by peak loads, and tasks
such as scheduling storage and/or demand flexibility maybe be driven by
predicted peak demand, a feature that is often poorly characterised by
general-purpose forecasting methods. Here we propose an approach to predict the
timing and level of daily peak demand, and a data fusion procedure for
combining conventional and peak forecasts to produce a general-purpose
probabilistic forecast with improved performance during peaks. The proposed
approach is demonstrated using real smart meter data and a hypothetical low
voltage network hierarchy comprising feeders, secondary and primary
substations. Fusing state-of-the-art probabilistic load forecasts with peak
forecasts is found to improve performance overall, particularly at smart-meter
and feeder levels and during peak hours, where improvement in terms of CRPS
exceeds 10%.",2206.11745v2
2022-06-26,Impact of Channel Memory on the Data Freshness,"In this letter, we investigate the impact of channel memory on the average
age of information (AoI) for networks with various packet arrival models under
first-come-first-served (FCFS) and preemptive last-generated-first-served
(pLGFS) policies over Gilbert-Elliott (GE) erasure channel. For networks with
Bernoulli arrival model, we first derive the average AoI under the pLGFS
queuing policy, and then characterize the AoI gap between the FCFS and pLGFS
policies. For networks with Bernoulli arrival and generate-at-will arrival
models, the AoI performances under the FCFS and pLGFS policies are derived
explicitly. For networks with periodic arrival model, we derive the closed-form
expression for the average AoI under pLGFS over a general GE channel and
propose a numerical algorithm for calculating that under FCFS efficiently. It
is revealed that for pLGFS policy, the average AoI increases monotonically with
channel memory $\eta$ at $\frac{\eta}{1-\eta}$ over the symmetric GE channel.
For FCFS, the average AoI increases even faster due to the queuing delay, with
an additional term related to the packet arrival rate.",2206.12797v3
2022-07-06,Light-weight spatio-temporal graphs for segmentation and ejection fraction prediction in cardiac ultrasound,"Accurate and consistent predictions of echocardiography parameters are
important for cardiovascular diagnosis and treatment. In particular,
segmentations of the left ventricle can be used to derive ventricular volume,
ejection fraction (EF) and other relevant measurements. In this paper we
propose a new automated method called EchoGraphs for predicting ejection
fraction and segmenting the left ventricle by detecting anatomical keypoints.
Models for direct coordinate regression based on Graph Convolutional Networks
(GCNs) are used to detect the keypoints. GCNs can learn to represent the
cardiac shape based on local appearance of each keypoint, as well as global
spatial and temporal structures of all keypoints combined. We evaluate our
EchoGraphs model on the EchoNet benchmark dataset. Compared to semantic
segmentation, GCNs show accurate segmentation and improvements in robustness
and inference runtime. EF is computed simultaneously to segmentations and our
method also obtains state-of-the-art ejection fraction estimation. Source code
is available online: https://github.com/guybenyosef/EchoGraphs.",2207.02549v1
2022-07-15,Probing helium reionization with kinetic Sunyaev Zel'dovich tomography,"Reionization of helium is expected to occur at redshifts $z\sim3$ and have
important consequences for quasar populations, galaxy formation, and the
morphology of the intergalactic medium, but there is little known empirically
about the process. Here we show that kinetic Sunyaev-Zeldovich (kSZ)
tomography, based on the combination of CMB measurements and galaxy surveys,
can be used to infer the primordial helium abundance as well as the time and
duration of helium reionization. We find a high-significance detection at
${\sim10\sigma}$ can be expected from Vera Rubin Observatory and CMB-S4 in the
near future. A more robust characterization of helium reionization will require
next-generation experiments like MegaMapper (a proposed successor to DESI) and
CMB-HD.",2207.07660v1
2022-07-18,Optimal and tight Bell inequalities for state-independent contextuality sets,"Two fundamental quantum resources, nonlocality and contextuality, can be
connected through Bell inequalities that are violated by state-independent
contextuality (SI-C) sets. These Bell inequalities allow for applications that
require simultaneous nonlocality and contextuality. However, for existing Bell
inequalities, the nonlocality produced by SI-C sets is very sensitive to noise.
This precludes experimental implementation. Here we identify the Bell
inequalities for which the nonlocality produced by SI-C sets is optimal, i.e.,
maximally robust to either noise or detection inefficiency, for the simplest
SI-C [S. Yu and C. H. Oh, Phys. Rev. Lett. 108, 030402 (2012)] and
Kochen-Specker sets [A. Cabello et al., Phys. Lett. A 212, 183 (1996)] and show
that, in both cases, nonlocality is sufficiently resistant for experiments. Our
work enables experiments that combine nonlocality and contextuality and
therefore paves the way for applications that take advantage of their synergy.",2207.08850v3
2022-07-25,Minimax Rates for High-dimensional Double Sparse Structure over $\ell_u(\ell_q)$-balls,"In this paper, we focus on the high-dimensional double sparse structure,
where the parameter of interest simultaneously encourages group-wise sparsity
and element-wise sparsity in each group. By combining the Gilbert-Varshamov
bound and its variants, we develop a novel lower bound technique for the metric
entropy of the parameter space, specifically tailored for the double sparse
structure over $\ell_u(\ell_q)$-balls with $u,q \in [0,1]$. We prove lower
bounds on the estimation error using an information-theoretic approach,
leveraging our proposed lower bound technique and Fano's inequality. To
complement the lower bounds, we establish matching upper bounds through a
direct analysis of constrained least-squares estimators and utilize results
from empirical processes. A significant finding of our study is the discovery
of a phase transition phenomenon in the minimax rates for $u,q \in (0, 1]$.
Furthermore, we extend the theoretical results to the double sparse regression
model and determine its minimax rate for estimation error. To tackle double
sparse linear regression, we develop the DSIHT (Double Sparse Iterative Hard
Thresholding) algorithm, demonstrating its optimality in the minimax sense.
Finally, we demonstrate the superiority of our method through numerical
experiments.",2207.11888v2
2022-08-02,Two-Stream Transformer Architecture for Long Video Understanding,"Pure vision transformer architectures are highly effective for short video
classification and action recognition tasks. However, due to the quadratic
complexity of self attention and lack of inductive bias, transformers are
resource intensive and suffer from data inefficiencies. Long form video
understanding tasks amplify data and memory efficiency problems in transformers
making current approaches unfeasible to implement on data or memory restricted
domains. This paper introduces an efficient Spatio-Temporal Attention Network
(STAN) which uses a two-stream transformer architecture to model dependencies
between static image features and temporal contextual features. Our proposed
approach can classify videos up to two minutes in length on a single GPU, is
data efficient, and achieves SOTA performance on several long video
understanding tasks.",2208.01753v1
2022-08-03,Mass and generalized Thiele equation of the magnetic skyrmion,"An analytical expression is obtained for the mass of an isolated magnetic
skyrmion and its linearized equation of motion. The magnetic skyrmion is viewed
as a topologically protected spin-wave soliton in the magnetic ultrathin films
stabilized by the interfacial-Dzyaloshinskii-Moriya interaction. The equations
of motion are derived from the Landau-Lifshitz-Gilbert equation for both the
skyrmion charge and magnetization centers. They are generalized Thiele
equations, including the gyro-term, dissipation term, external force,
acceleration term with the tensorial mass, and time derivatives of the external
forces. The equation of motion of the center of the skyrmion charge essentially
shows the massless nature of the skyrmion. In contrast, the equation of motion
for the magnetization center results in a finite mass that is in the same order
as the Doring mass density for the linear domain wall. Furthermore, the time
derivative of the external force predominantly contributes to the immediate
response of the skyrmion motion, i.e., the mass-less property remains even
after the skyrmion acquires its kinetic mass.
  A micromagnetic simulation based on the LLG equation was performed for
various magnetic parameters. Obtained trajectories at 0 K are compared with the
theoretical predictions.",2208.01835v2
2022-08-07,Transition state theory characterizes thin film macrospin dynamics driven by an oscillatory magnetic field: Inertial effects,"Understanding the magnetization switching process in ferromagnetic thin films
is essential for many technological applications. We investigate the effects of
periodic driving via magnetic fields on a macrospin system under explicit
consideration of inertial dynamics. This is usually achieved by extending the
Landau-Lifshitz-Gilbert equation with a term including the second time
derivative of the magnetization. The dynamics of the magnetization switching
can then be characterized by its switching rate. We apply methods from
transition state theory for driven systems to resolve the rate of magnetization
switching in this general case. In doing so, we find that magnetization
exhibits resonance-like behavior under certain driving conditions, and it can
be affected strongly by the system's relaxation rate.",2208.03613v1
2022-08-09,HyperNST: Hyper-Networks for Neural Style Transfer,"We present HyperNST; a neural style transfer (NST) technique for the artistic
stylization of images, based on Hyper-networks and the StyleGAN2 architecture.
Our contribution is a novel method for inducing style transfer parameterized by
a metric space, pre-trained for style-based visual search (SBVS). We show for
the first time that such space may be used to drive NST, enabling the
application and interpolation of styles from an SBVS system. The technical
contribution is a hyper-network that predicts weight updates to a StyleGAN2
pre-trained over a diverse gamut of artistic content (portraits), tailoring the
style parameterization on a per-region basis using a semantic map of the facial
regions. We show HyperNST to exceed state of the art in content preservation
for our stylized content while retaining good style transfer performance.",2208.04807v1
2022-08-19,Byzantine Consensus is Θ(n^2): The Dolev-Reischuk Bound is Tight even in Partial Synchrony! [Extended Version],"The Dolev-Reischuk bound says that any deterministic Byzantine consensus
protocol has (at least) quadratic communication complexity in the worst case.
While it has been shown that the bound is tight in synchronous environments, it
is still unknown whether a consensus protocol with quadratic communication
complexity can be obtained in partial synchrony. Until now, the most efficient
known solutions for Byzantine consensus in partially synchronous settings had
cubic communication complexity (e.g., HotStuff, binary DBFT).
  This paper closes the existing gap by introducing SQuad, a partially
synchronous Byzantine consensus protocol with quadratic worst-case
communication complexity. In addition, SQuad is optimally-resilient and
achieves linear worst-case latency complexity. The key technical contribution
underlying SQuad lies in the way we solve view synchronization, the problem of
bringing all correct processes to the same view with a correct leader for
sufficiently long. Concretely, we present RareSync, a view synchronization
protocol with quadratic communication complexity and linear latency complexity,
which we utilize in order to obtain SQuad.",2208.09262v2
2022-08-26,Randomised Composition and Small-Bias Minimax,"We prove two results about randomised query complexity $\mathrm{R}(f)$.
First, we introduce a ""linearised"" complexity measure $\mathrm{LR}$ and show
that it satisfies an inner-optimal composition theorem: $\mathrm{R}(f\circ g)
\geq \Omega(\mathrm{R}(f) \mathrm{LR}(g))$ for all partial $f$ and $g$, and
moreover, $\mathrm{LR}$ is the largest possible measure with this property. In
particular, $\mathrm{LR}$ can be polynomially larger than previous measures
that satisfy an inner composition theorem, such as the max-conflict complexity
of Gavinsky, Lee, Santha, and Sanyal (ICALP 2019).
  Our second result addresses a question of Yao (FOCS 1977). He asked if
$\epsilon$-error expected query complexity $\bar{\mathrm{R}}_{\epsilon}(f)$
admits a distributional characterisation relative to some hard input
distribution. Vereshchagin (TCS 1998) answered this question affirmatively in
the bounded-error case. We show that an analogous theorem fails in the
small-bias case $\epsilon=1/2-o(1)$.",2208.12896v1
2022-09-04,Lévy flights as an emergent phenomenon in a spatially extended system,"Anomalous diffusion and L\'evy flights, which are characterized by the
occurrence of random discrete jumps of all scales, have been observed in a
plethora of natural and engineered systems, ranging from the motion of
molecules to climate signals. Mathematicians have recently unveiled mechanisms
to generate anomalous diffusion, both stochastically and deterministically.
However, there exists to the best of our knowledge no explicit example of a
spatially extended system which exhibits anomalous diffusion without being
explicitly driven by L\'evy noise. We show here that the
Landau-Lifshitz-Gilbert equation, a stochastic partial differential equation
(SPDE), despite only driven by Gaussian white noise, exhibits superdiffusive
behaviour. The anomalous diffusion is an entirely emergent behaviour and
manifests itself in jumps in the location of its travelling front solution.
Using a collective coordinate approach we reduce the SPDE to a set of
stochastic differential equations (SDEs) driven by Gaussian white noise. This
allows us to identify the mechanism giving rise to the anomalous diffusion as
random widening events of the front interface.",2209.01520v3
2022-08-29,Probably Something: A Multi-Layer Taxonomy of Non-Fungible Tokens,"Purpose: This paper aims to establish a fundamental and comprehensive
understanding of Non-Fungible Tokens (NFTs) by identifying and structuring
common characteristics within a taxonomy. NFTs are hyped and increasingly
marketed as essential building blocks of the Metaverse. However, the dynamic
evolution of the NFT space has posed challenges for those seeking to develop a
deep and comprehensive understanding of NFTs, their features, and capabilities.
  Design/methodology/approach: Utilizing common guidelines for the creation of
taxonomies, we developed (over three iterations), a multi-layer taxonomy based
on workshops and interviews with 11 academic and 15 industry experts. Through
an evaluation of 25 NFTs, we demonstrate the usefulness of our taxonomy.
  Findings: The taxonomy has four layers, 14 dimensions and 42 characteristics,
which describe NFTs in terms of reference object, token properties, token
distribution, and realizable value.
  Originality: Our framework is the first to systematically cover the emerging
NFT phenomenon. It is concise yet extendible and presents many avenues for
future research in a plethora of disciplines. The characteristics identified in
our taxonomy are useful for NFT and Metaverse related research in Finance,
Marketing, Law, and Information Systems. Additionally, the taxonomy can serve
as an information source for policymakers as they consider NFT regulation.",2209.05456v1
2022-09-19,Introducing the step Monte Carlo method for simulating dynamic properties,"In this work, we introduce a simple modification of the Monte Carlo
algorithm, which we call step Monte Carlo (sMC). The sMC approach allows to
simulate processes far from equilibrium and obtain information about the
dynamic properties of the system under investigation. In the approach proposed
here the probability of accepting the final (trial) state depends on the
activation energy, not on the relative energy between the final and initial
state. This barrier height is probed on an ongoing basis, by generating
intermediate states along the path connecting the initial and trial positions.
Importantly, to calculate the activation energy, our model only requires
knowledge of the Hamiltonian without having to introduce additional input
parameters such as transition rates etc. The details of sMC are explained for
the case of a simple spin model. The comparison of its results with the ones
obtained within the frame of stochastic Landau-Lifshitz-Gilbert indicates the
correctness of sMC. In our opinion, the proposed here method can be applied to
simulate other processes, for example dynamics of classical atoms and complex
fluids, diffusion, nucleation, surface adsorption and crystal growth processes.",2209.08961v3
2022-09-23,Logarithmically larger deletion codes of all distances,"The deletion distance between two binary words $u,v \in \{0,1\}^n$ is the
smallest $k$ such that $u$ and $v$ share a common subsequence of length $n-k$.
A set $C$ of binary words of length $n$ is called a $k$-deletion code if every
pair of distinct words in $C$ has deletion distance greater than $k$. In 1965,
Levenshtein initiated the study of deletion codes by showing that, for $k\ge 1$
fixed and $n$ going to infinity, a $k$-deletion code $C\subseteq \{0,1\}^n$ of
maximum size satisfies $\Omega_k(2^n/n^{2k}) \leq |C| \leq O_k( 2^n/n^k)$. We
make the first asymptotic improvement to these bounds by showing that there
exist $k$-deletion codes with size at least $\Omega_k(2^n \log n/n^{2k})$. Our
proof is inspired by Jiang and Vardy's improvement to the classical
Gilbert--Varshamov bounds. We also establish several related results on the
number of longest common subsequences and shortest common supersequences of a
pair of words with given length and deletion distance.",2209.11882v2
2022-10-19,Generalised form of the magnetic anisotropy field in micromagnetic and atomistic spin models,"We present a general approach to the derivation of the effective anisotropy
field which determines the dynamical behaviour of magnetic spins according to
the Landau-Lifshitz-Gilbert equation. The approach is based on the gradient in
spherical polar coordinates with the final results being expressed in Cartesian
coordinates as usually applied in atomistic and micromagnetic model
calculations. The approach is generally valid for all orders of anisotropies
including higher order combinations of azimuthal and rotational anisotropies
often found in functional magnetic materials such as permanent magnets and an
emerging class of antiferromagnetic materials with applications in spintronics.
Anisotropies are represented in terms of spherical harmonics which have the
important property of rational temperature scaling. Effective field vectors are
given for anisotropies up to sixth order, presenting a unified framework for
implementing higher order magnetic anisotropies in numerical simulations.",2210.10916v4
2022-10-27,Formal Semantics for the Halide Language,"We present the first formalization and metatheory of language soundness for a
user-schedulable language, the widely used array processing language Halide.
User-schedulable languages strike a balance between abstraction and control in
high-performance computing by separating the specification of what a program
should compute from a schedule for how to compute it. In the process, they make
a novel language soundness claim: the result of a program should always be the
same, regardless of how it is scheduled. This soundness guarantee is tricky to
provide in the presence of schedules that introduce redundant recomputation and
computation on uninitialized data, rather than simply reordering statements. In
addition, Halide ensures memory safety through a compile-time bounds inference
engine that determines safe sizes for every buffer and loop in the generated
code, presenting a novel challenge: formalizing and analyzing a language
specification that depends on the results of unreliable program synthesis
algorithms. Our formalization has revealed flaws and led to improvements in the
practical Halide system, and we believe it provides a foundation for the design
of new languages and tools that apply programmer-controlled scheduling to other
domains.",2210.15740v1
2022-11-08,SLATE: A Sequence Labeling Approach for Task Extraction from Free-form Inked Content,"We present SLATE, a sequence labeling approach for extracting tasks from
free-form content such as digitally handwritten (or ""inked"") notes on a virtual
whiteboard. Our approach allows us to create a single, low-latency model to
simultaneously perform sentence segmentation and classification of these
sentences into task/non-task sentences. SLATE greatly outperforms a baseline
two-model (sentence segmentation followed by classification model) approach,
achieving a task F1 score of 84.4%, a sentence segmentation (boundary
similarity) score of 88.4% and three times lower latency compared to the
baseline. Furthermore, we provide insights into tackling challenges of
performing NLP on the inking domain. We release both our code and dataset for
this novel task.",2211.04454v2
2022-11-10,Unifying the communicable disease spreading paradigm with Gompertzian growth,"A number of studies have shown that cumulative mortality followed a Gompertz
curve in the initial Covid pandemic period, March-April 2020. We show that the
Gompertz curve is incompatible with expected initial logistic growth curves as
predicted by traditional Susceptible-Infected-Recovered (SIR) models, and
propose a new theory which better explains the nature of the mortality
characteristics based on a global biosphere disturbance. Second, we show that
for the Gompertz curve to emerge, the disturbance has to act on everyone
simultaneously, rejecting the possibility of a disease propagation stage.
Third, we connect logistic growth with Gompertzian growth by augmenting the
logistic growth equation with higher order interaction terms, and show that the
SIR model family is compatible with Gompertzian growth only when all nodes in
the transmission network communicate with infinite speed and interaction.
Crucially, this augmentation must be accompanied by a causality-reversal where
the source of growth is not the pool of infected but the pool of susceptible
people. We thus find a novel bridge between logistic and Gompertzian growth,
separate from the existing Richards model (also called $\theta$-logistic
growth).",2211.05653v2
2022-11-12,Helio2024 Science White Paper: ngGONG -- Future Ground-based Facilities for Research in Heliophysics and Space Weather Operational Forecast,"Long-term synoptic observations of the Sun are critical for advancing our
understanding of Sun as an astrophysical object, understanding the solar
irradiance and its role in solar-terrestrial climate, for developing predictive
capabilities of solar eruptive phenomena and their impact on our home planet,
and heliosphere in general, and as a data provider for the operational space
weather forecast. We advocate for the development of a ground-based network of
instruments provisionally called ngGONG to maintain critical observing
capabilities for synoptic research in solar physics and for the operational
space weather forecast.",2211.06712v1
2022-11-14,SVS: Adversarial refinement for sparse novel view synthesis,"This paper proposes Sparse View Synthesis. This is a view synthesis problem
where the number of reference views is limited, and the baseline between target
and reference view is significant. Under these conditions, current radiance
field methods fail catastrophically due to inescapable artifacts such 3D
floating blobs, blurring and structural duplication, whenever the number of
reference views is limited, or the target view diverges significantly from the
reference views.
  Advances in network architecture and loss regularisation are unable to
satisfactorily remove these artifacts. The occlusions within the scene ensure
that the true contents of these regions is simply not available to the model.
In this work, we instead focus on hallucinating plausible scene contents within
such regions. To this end we unify radiance field models with adversarial
learning and perceptual losses. The resulting system provides up to 60%
improvement in perceptual accuracy compared to current state-of-the-art
radiance field models on this problem.",2211.07301v1
2022-11-15,Viscosity of pure-glue QCD from the lattice,"We calculate shear viscosity and bulk viscosity in SU(3) gauge theory on the
lattice at $1.5 \,T_c$. The viscosities are extracted via a Kubo formula from
the reconstructed spectral function which we determine from the Euclidean-time
dependence of the corresponding channel of the energy-momentum tensor
correlators. We obtain unprecedented precision for the correlators by applying
gradient flow and blocking methods. The correlators are extrapolated to the
continuum and then to zero flow time. To extract the viscosities we fit
theoretically inspired models to the lattice data and crosscheck the fit
results using the Backus Gilbert method. The final estimates for shear and bulk
viscosity are $\eta/s = 0.15-0.48$ and $\zeta/s = 0.017-0.059$.",2211.08230v2
2022-11-15,Nonlinear chiral photocurrent in parity-violating magnetic Weyl semimetals,"The strong correlation between the non-trivial band topology and the magnetic
texture makes magnetic Weyl semimetals excellent candidates for the
manipulation and detection of magnetization dynamics. The parity violation
together with the Pauli blocking cause only one Weyl node to contribute to the
photocurrent response, which in turn affects the magnetic texture due to the
spin transfer torque. Utilizing the Landau-Lifshitz-Gilbert equation and the
spin-transfer torque in non-centrosymmetric Weyl magnets, we show that the
chiral photocurrent rotates the magnetization from the easy c axis to the a or
b axis, which leads to an exotic current next to the photocurrent response. The
chiral photocurrent is calculated in the context of quantum kinetic theory and
it has a strong resonance on the order of mA/W near the Weyl nodes, the
magnitude of which is controlled by the momentum relaxation time. Remarkably,
we study the influence of magnetic texture dynamics on the topological
nonlinear photocurrent response, including shift and injection currents along
with the new chiral photocurrent, and show that both the magnitude and the
in-plane orientation of the chiral photocurrent are strongly correlated with
the direction of the magnetic moments.",2211.08521v1
2022-11-17,3D Interconnected Magnetic Nanowire Networks as Potential Integrated Multistate Memristors,"Interconnected magnetic nanowire (NW) networks offer a promising platform for
3-dimensional (3D) information storage and integrated neuromorphic computing.
Here we report discrete propagation of magnetic states in interconnected Co
nanowire networks driven by magnetic field and current, manifested in distinct
magnetoresistance (MR) features. In these networks, when only a few
interconnected NWs were measured, multiple MR kinks and local minima were
observed, including a significant minimum at a positive field during the
descending field sweep. Micromagnetic simulations showed that this unusual
feature was due to domain wall (DW) pinning at the NW intersections, which was
confirmed by off-axis electron holography imaging. In a complex network with
many intersections, sequential switching of nanowire sections separated by
interconnects was observed, along with stochastic characteristics. The
pinning/depinning of the DWs can be further controlled by the driving current
density. These results illustrate the promise of such interconnected networks
as integrated multistate memristors.",2211.09687v2
2022-11-22,Enabling On-Demand Cyber-Physical Control Applications with UAV Access Points,"Achieving cyber-physical control over a wireless channel requires satisfying
both the timeliness of a single packet and preserving the latency reliability
across several consecutive packets. To satisfy those requirements as an
ubiquitous service requires big infrastructural developments, or flexible
on-demand equipment such as UAVs. To avoid the upfront cost in terms of finance
and energy, this paper analyzes the capability of UAV access points (UAVAPs) to
satisfy the requirements for cyber-physical traffic. To investigate this, we
perform a Gilbert-Eliott burst-error analysis that is analytically derived as a
combination of two separate latency measurement campaigns and provide an
upper-bound analysis of the UAVAP system. The analysis is centered around a
UAVAP that uses its LTE connection to reach the backhaul, while providing
service to ground nodes (GNs) with a Wi-Fi access point (AP). Thus, we combine
both measurement campaigns to analyze the plausibility of the described setup
in casual, crowded or mixed network settings.",2211.12249v1
2022-11-30,SuSpect3: A C++ Code for the Supersymmetric and Higgs Particle Spectrum of the MSSM,"We present the program SuSpect3 that calculates the masses and couplings of
the Higgs and supersymmetric particles predicted by the Minimal Supersymmetric
Standard Model (MSSM). The model is implemented in both its non-constrained
version, the MSSM, and its constrained versions, such as the minimal
supergravity and the gauge or anomaly mediated supersymmetry breaking models,
in which the soft supersymmetry-breaking parameters obey certain universal
boundary conditions at the high energy scale. The low energy parameters are
then obtained using renormalization group equations and electroweak symmetry
breaking, and all the dominant radiative corrections have been consistently
implemented. SuSpect3 is a major rewrite, in C++ object oriented programming,
of the FORTRAN code SuSpect. It includes all the features of the earlier code
in an improved and updated manner, and involves new options such as compressed
SUSY scenarios, an MSSM-inflation model and the possibility of using the
observed Higgs mass as an input. The main features and the use of the program
are explained.",2211.16956v2
2022-12-06,Ground-based Synoptic Studies of the Sun,"Ground-based synoptic solar observations provide critical contextual data
used to model the large-scale state of the heliosphere. The next decade will
see a combination of ground-based telescopes and space missions that will study
our Sun's atmosphere microscopic processes with unprecedented detail. This
white paper describes contextual observations from a ground-based network
needed to fully exploit this new knowledge of the underlying physics that leads
to the magnetic linkages between the heliosphere and the Sun. This combination
of a better understanding of small-scale processes and the appropriate global
context will enable a physics-based approach to Space Weather comparable to
Terrestrial Weather forecasting.",2212.03247v2
2022-12-14,Non-uniform Superlattice Magnetic Tunnel Junctions,"We propose a new class of non-uniform superlattice magnetic tunnel junctions
(Nu-SLTJs) with the Linear, Gaussian, Lorentzian, and P\""oschl-teller width and
height based profiles manifesting a sizable enhancement in the TMR($\approx
10^4-10^6\%$) with a significant suppression in the switching bias($\approx$9
folds) owing to the physics of broad-band spin filtering. By exploring the
negative differential resistance region in the current-voltage characteristics
of the various Nu-SLTJs, we predict the Nu-SLTJs offer the fastest spin
transfer torque switching in the order of a few hundred picoseconds. We
self-consistently employ the atomistic non-equilibrium Green's function
formalism coupled with the Landau-Lifshitz-Gilbert-Slonczewski equation to
evaluate the device performance of the various Nu-SLTJs. We also present the
design of minimal three-barrier Nu-SLTJs having significant TMR($\approx
10^4\%$) and large spin current for ease of device fabrication. We hope that
the class of Nu-SLTJs proposed in this work may lay the bedrock to embark on
the exhilarating voyage of exploring various non-uniform superlattices for the
next generation of spintronic devices.",2212.07202v2
2022-12-20,A combinatorial proof of a tantalizing symmetry on Catalan objects,"We investigate a tantalizing symmetry on Catalan objects. In terms of Dyck
paths, this symmetry is interpreted in the following way: if $w_{n,k,m}$ is the
number of Dyck paths of semilength $n$ with $k$ occurrences of $UD$ and $m$
occurrences of $UUD$, then $w_{2k+1,k,m}=w_{2k+1,k,k+1-m}$. We give two proofs
of this symmetry: an algebraic proof using generating functions, and a
combinatorial proof which makes heavy use of the cycle lemma and an alternate
interpretation of the numbers $w_{n,k,m}$ using plane trees. In particular, our
combinatorial proof expresses the numbers $w_{2k+1,k,m}$ in terms of Narayana
numbers, and we generalize this to a relationship between the numbers
$w_{n,k,m}$ and a family of generalized Narayana numbers due to Callan. Some
further generalizations and applications of our combinatorial proofs are
explored. Finally, we investigate properties of the polynomials $W_{n,k}(t)=
\sum_{m=0}^k w_{n,k,m} t^m$, including real-rootedness, $\gamma$-positivity,
and a symmetric decomposition.",2212.10586v1
2022-12-30,Asymptotic Analysis of Harmonic Maps With Prescribed Singularities,"Motivated by stationary vacuum solutions of the Einstein field equations, we
study singular harmonic maps from domains of 3-dimensional Euclidean space to
the hyperbolic plane having bounded hyperbolic distance to Kerr harmonic maps.
In the degenerate case, we prove that every such harmonic map admits a unique
tangent harmonic map at the extreme black hole horizon. The possible tangent
maps are classified and shown to be shifted 'extreme Kerr' geodesics in the
hyperbolic plane that depend on two parameters, one determined by angular
momentum and another by conical singularities. In addition, rates of
convergence to the tangent map are established. Similarly, expansions in the
asymptotically flat end are presented. These results, together with those of
Li-Tian and Weinstein, provide a complete regularity theory for harmonic maps
from $\mathbb R^3\setminus z\text{-axis}$ to $\mathbb H^2$ with prescribed
singularities. Lastly, the analysis is utilized to prove existence of the so
called near horizon limit, and to compute the associated near horizon
geometries of extreme black holes.",2212.14826v1
2023-01-06,Measuring a Priori Voting Power -- Taking Delegations Seriously,"We introduce new power indices to measure the a priori voting power of voters
in liquid democracy elections where an underlying network restricts
delegations. We argue that our power indices are natural extensions of the
standard Penrose-Banzhaf index in simple voting games. We show that computing
the criticality of a voter is #P-hard even when voting weights are
polynomially-bounded in the size of the instance. However, for specific
settings, such as when the underlying network is a bipartite or complete graph,
recursive formulas can compute these indices for weighted voting games in
pseudo-polynomial time. We highlight their theoretical properties and provide
numerical results to illustrate how restricting the possible delegations can
alter voters' voting power.",2301.02462v4
2023-01-10,The spectral reconstruction of inclusive rates,"A recently re-discovered variant of the Backus-Gilbert algorithm for spectral
reconstruction enables the controlled determination of smeared spectral
densities from lattice field theory correlation functions. A particular
advantage of this approach is the \emph{a priori} specification of the kernel
with which the underlying spectral density is smeared, allowing for variation
of its peak position, smearing width, and functional form. If the unsmeared
spectral density is sufficiently smooth in the neighborhood of a particular
energy, it can be obtained from an extrapolation to zero smearing-kernel width
at fixed peak position. A natural application for this approach is scattering
processes summed over all hadronic final states. As a proof-of-principle test,
an inclusive rate is computed in the two-dimensional O(3) sigma model from a
two-point correlation function of conserved currents. The results at finite and
zero smearing radius are in good agreement with the known analytic form up to
energies at which 40-particle states contribute, and are sensitive to the
4-particle contribution to the inclusive rate. The straight-forward adaptation
to compute the $R$-ratio in lattice QCD from two-point functions of the
electromagnetic current is briefly discussed.",2301.04072v1
2023-01-12,Redundancy of Codes with Graph Constraints,"In this paper, we study the redundancy of linear codes with graph
constraints. First we consider linear parity check codes based on bipartite
graphs with diversity and with generalized graph constraints. We describe
sufficient conditions on the constraint probabilities and use the probabilistic
method to obtain linear codes that achieve the Gilbert-Varshamov redundancy
bound in addition to satisfying the constraints and the diversity index. In the
second part we consider a generalization of graph capacity which we call as the
fractional graph capacity and use the probabilistic method to determine bounds
on the fractional capacity for arbitrary graphs. Specifically, we establish an
upper bound in terms of the full graph capacity and a lower bound in terms of
the average and maximum vertex degree of the graph.",2301.04808v1
2023-01-12,Magnetic-field-free nonreciprocal transport in graphene multi-terminal Josephson junctions,"Nonreciprocal superconducting devices have attracted growing interest in
recent years as they potentially enable directional charge transport for
applications in superconducting quantum circuits. Specifically, the
superconducting diode effect has been explored in two-terminal devices that
exhibit superconducting transport in one current direction while showing
dissipative transport in the opposite direction. Here, we exploit
multi-terminal Josephson junctions (MTJJs) to engineer magnetic-field-free
nonreciprocity in multi-port networks. We show that when treated as a two-port
electrical network, a three-terminal Josephson junction (JJ) with an asymmetric
graphene region exhibits reconfigurable two-port nonreciprocity. We observe
nonreciprocal (reciprocal) transport between superconducting terminals with
broken (preserved) spatial mirror symmetry. We explain our observations by
considering a circuit-network of JJs with different critical currents.",2301.05081v3
2023-01-24,Recent Results from the FASTSUM Collaboration,"The FASTSUM Collaboration has developed a comprehensive research programme in
thermal QCD using 2+1 flavour, anisotropic ensembles. In this talk, we
summarise some of our recent results including thermal hadron spectrum
calculations using our ``Generation 2L'' ensembles which have pion masses of
239(1) MeV. These include open charm mesons and charm baryons. We also
summarise our work using the Backus Gilbert approach to determining the
spectral function of the NRQCD bottomonium system. Finally, we review our
determination of the interquark potential in the same system, but using our
``Generation 2'' ensembles which have heavier pion masses of 384(4) MeV.",2301.10282v1
2023-01-27,Women's Perspectives on Harm and Justice after Online Harassment,"Social media platforms aspire to create online experiences where users can
participate safely and equitably. However, women around the world experience
widespread online harassment, including insults, stalking, aggression, threats,
and non-consensual sharing of sexual photos. This article describes women's
perceptions of harm associated with online harassment and preferred platform
responses to that harm. We conducted a survey in 14 geographic regions around
the world (N = 3,993), focusing on regions whose perspectives have been
insufficiently elevated in social media governance decisions (e.g. Mongolia,
Cameroon). {Results show} that, on average, women perceive greater harm
associated with online harassment than men, especially for non-consensual image
sharing. Women also prefer most platform responses compared to men, especially
removing content and banning users; however, women are less favorable towards
payment as a response. Addressing global gender-based violence online requires
understanding how women experience online harms and how they wish for it to be
addressed. This is especially important given that the people who build and
govern technology are not typically those who are most likely to experience
online harms.",2301.11733v1
2023-02-02,Thermal and atomic effects on coupled-channels heavy-ion fusion,"Stellar nuclear fusion reactions take place in a hot, dense plasma within
stars. To account for the effect of these environments, the theory of open
quantum systems is used to conduct pioneering studies of thermal and atomic
effects on fusion probability at a broad range of temperatures and densities.
Since low-lying excited states are more likely to be populated at stellar
temperatures and increase nuclear plasma interaction rates, a 188Os nucleus was
used as a target that interacts with an inert 16O projectile. Key results
showed thermal effects yield an average increase in fusion probability of 15.5%
and 36.9% for our test nuclei at temperatures of 0.1 and 0.5 MeV respectively,
compared to calculations at zero temperature. Thermal effects could be tested
in a laboratory using targets prepared in excited states as envisaged in
facilities exploiting laser-nucleus interactions.",2302.01272v2
2023-02-02,Topological data analysis reveals differences between simulated galaxies and dark matter haloes,"We use topological summaries based on Betti curves to characterize the
large-scale spatial distribution of simulated dark matter haloes and galaxies.
Using the IllustrisTNG and CAMELS-SAM simulations, we show that the topology of
the galaxy distribution is significantly different from the topology of the
dark matter halo distribution. Further, there are significant differences
between the distributions of star-forming and quiescent galaxies. These
topological differences are broadly consistent across all simulations, while at
the same time there are noticeable differences when comparing between different
models. Finally, using the CAMELS-SAM simulations, we show that the topology of
the quiescent galaxies in particular depends strongly on the amount of
supernova feedback. These results suggest that topological summary statistics
could be used to help better understand the processes of galaxy formation and
evolution.",2302.01363v2
2023-02-06,Landau theory for ferro-paramagnetic phase transition in finitely-strained viscoelastic magnets,"The thermodynamic model of visco-elastic deformable magnetic materials at
finite strains is formulated in a fully Eulerian way in rates. The Landau
theory applies for ferro-to-para-magnetic phase transition, the gradient theory
(leading exchange energy) for magnetization with general mechanically dependent
coefficient, hysteresis in magnetization evolution by Landau-Lifshitz-Gilbert
equation involving objective corotational time derivative of magnetization, and
demagnetizing field are considered in the model. The Kelvin-Voigt viscoelastic
rheology with a higher-order viscosity (exploiting the concept of multipolar
materials) is used, allowing for physically relevant frame-indifferent stored
energies and for local invertibility of deformation. The model complies with
energy conservation and Clausius-Duhem entropy inequality. Existence and a
certain regularity of weak solutions is proved by a Faedo-Galerkin
semi-discretization and a suitable regularization.",2302.02850v1
2023-02-13,Zero-frequency chiral magnonic edge states protected by non-equilibrium topology,"Topological bosonic excitations must, in contrast to their fermionic
counterparts, appear at finite energies. This is a key challenge for magnons,
as it prevents straightforward excitation and detection of
topologically-protected magnonic edge states and their use in magnonic devices.
In this work, we show that in a non-equilibrium state, in which the
magnetization is pointing against the external magnetic field, the
topologically-protected chiral edge states in a magnon Chern insulator can be
lowered to zero frequency, making them directly accessible by existing
experimental techniques. We discuss the spin-orbit torque required to stabilize
this non-equilibrium state, and show explicitly using numerical
Landau-Lifshitz-Gilbert simulations that the edge states can be excited with a
microwave field. Finally, we consider a propagating spin wave spectroscopy
experiment, and demonstrate that the edge states can be directly detected.",2302.06597v3
2023-02-15,Reliable optimization of arbitrary functions over quantum measurements,"As the connection between classical and quantum worlds, quantum measurements
play a unique role in the era of quantum information processing. Given an
arbitrary function of quantum measurements, how to obtain its optimal value is
often considered as a basic yet important problem in various applications.
Typical examples include but not limited to optimizing the likelihood functions
in quantum measurement tomography, searching the Bell parameters in Bell-test
experiments, and calculating the capacities of quantum channels. In this work,
we propose reliable algorithms for optimizing arbitrary functions over the
space of quantum measurements by combining the so-called Gilbert's algorithm
for convex optimization with certain gradient algorithms. With extensive
applications, we demonstrate the efficacy of our algorithms with both convex
and nonconvex functions.",2302.07534v1
2023-02-18,Distributed Optimization for Reactive Power Sharing and Stability of Inverter-Based Resources Under Voltage Limits,"Reactive power sharing and containment of voltages within limits for
inverter-based resources (IBRs) are two important, yet coupled objectives in ac
networks. In this article, we propose a distributed control technique to
simultaneously achieve these objectives. Our controller consists of two
components: a purely local nonlinear integral controller which adjusts the IBR
voltage setpoint, and a distributed primal-dual optimizer that coordinates
reactive power sharing between the IBRs. The controller prioritizes the voltage
containment objective over reactive power sharing at all points in time;
excluding the IBRs with saturated voltages, it provides reactive power sharing
among all the IBRs. Considering the voltage saturation and the coupling between
voltage and angle dynamics, a formal closed-loop stability analysis based on
singular perturbation theory is provided, yielding practical tuning guidance
for the overall control system. To validate the effectiveness of the proposed
controller for different case studies, we apply it to a low-voltage microgrid
and a microgrid adapted from the CIGRE medium-voltage network benchmark, both
simulated in the MATLAB/Simulink environment.",2302.09241v2
2023-02-21,Micromagnetic study of inertial spin waves in ferromagnetic nanodots,"Here we report the possibility to excite ultra-short spin waves in
ferromagnetic thin-films by using time-harmonic electromagnetic fields with
terahertz frequency. Such ultra-fast excitation requires to include inertial
effects in the description of magnetization dynamics. In this respect, we
consider the inertial Landau-Lifshitz-Gilbert (iLLG) equation and develop
analytical theory for exchange-dominated inertial spin waves. The theory
predicts a finite limit for inertial spin wave propagation velocity, as well as
spin wave spatial decay and lifetime as function of material parameters. Then,
guided by the theory, we perform numerical micromagnetic simulations that
demonstrate the excitation of ultra-short inertial spin waves (20 nm long)
propagating at finite speed in a confined magnetic nanodot. The results are in
agreement with the theory and provide the order of magnitude of quantities
observable in realistic ultra-fast dynamics experiments.",2302.10759v2
2023-03-04,Dynamic Modeling and Validation of Soft Robotic Snake Locomotion,"Soft robotic snakes made of compliant materials can continuously deform their
bodies and, therefore, mimic the biological snakes' flexible and agile
locomotion gaits better than their rigid-bodied counterparts. Without wheel
support, to date, soft robotic snakes are limited to emulating planar
locomotion gaits, which are derived via kinematic modeling and tested on
robotic prototypes. Given that the snake locomotion results from the reaction
forces due to the distributed contact between their skin and the ground, it is
essential to investigate the locomotion gaits through efficient dynamic models
capable of accommodating distributed contact forces. We present a complete
spatial dynamic model that utilizes a floating-base kinematic model with
distributed contact dynamics for a pneumatically powered soft robotic snake. We
numerically evaluate the feasibility of the planar and spatial rolling gaits
utilizing the proposed model and experimentally validate the corresponding
locomotion gait trajectories on a soft robotic snake prototype. We
qualitatively and quantitatively compare the numerical and experimental results
which confirm the validity of the proposed dynamic model.",2303.02291v1
2023-03-20,Semiparametric inference for relative heterogeneous vaccine efficacy between strains in observational case-only studies,"The aim of this manuscript is to explore semiparametric methods for inferring
subgroup-specific relative vaccine efficacy in a partially vaccinated
population against multiple strains of a virus. We consider methods for
observational case-only studies with informative missingness in viral strain
type due to vaccination status, pre-vaccination variables, and also
post-vaccination factors such as viral load. We establish general causal
conditions under which the relative conditional vaccine efficacy between
strains can be identified nonparametrically from the observed data-generating
distribution. Assuming that the relative strain-specific conditional vaccine
efficacy has a known parametric form, we propose semiparametric asymptotically
linear estimators of the parameters based on targeted (debiased) machine
learning estimators for partially linear logistic regression models. Finally,
we apply our methods to estimate the relative strain-specific conditional
vaccine efficacy in the ENSEMBLE COVID-19 vaccine trial.",2303.11462v1
2023-03-16,Factoring the Matrix of Domination: A Critical Review and Reimagination of Intersectionality in AI Fairness,"Intersectionality is a critical framework that, through inquiry and praxis,
allows us to examine how social inequalities persist through domains of
structure and discipline. Given AI fairness' raison d'etre of ""fairness"", we
argue that adopting intersectionality as an analytical framework is pivotal to
effectively operationalizing fairness. Through a critical review of how
intersectionality is discussed in 30 papers from the AI fairness literature, we
deductively and inductively: 1) map how intersectionality tenets operate within
the AI fairness paradigm and 2) uncover gaps between the conceptualization and
operationalization of intersectionality. We find that researchers
overwhelmingly reduce intersectionality to optimizing for fairness metrics over
demographic subgroups. They also fail to discuss their social context and when
mentioning power, they mostly situate it only within the AI pipeline. We: 3)
outline and assess the implications of these gaps for critical inquiry and
praxis, and 4) provide actionable recommendations for AI fairness researchers
to engage with intersectionality in their work by grounding it in AI
epistemology.",2303.17555v2
2023-04-04,Direct in situ determination of the surface area and structure of deposited metallic lithium within lithium metal batteries using ultra small and small angle neutron scattering,"Despite being the major cause of battery safety issues and detrimental
performance, a comprehensive growth mechanism for metallic lithium deposited at
electrode surfaces in lithium metal batteries remains elusive. While lithium
surface morphology is often derived indirectly, here, detailed information is
directly obtained using in situ small and ultra-small angle neutron scattering,
in bulk and non-destructively. Features of 1-10 um and 100-300 nm are
identified; the latter contribute to most of the surface area and their size
inversely correlates to applied current density. Surface area per unit volume
increases continuously during charging from 1-4 h at 2 mA/cm2 but more slowly
during discharge. Comparatively higher values are reached after just 1 h at 20
mA/cm2 which remain constant in subsequent cycles. Such quantitative insight
into the processes of metallic lithium growth within batteries may enable the
development of safer high performance lithium metal batteries.",2304.01557v1
2023-04-10,EKILA: Synthetic Media Provenance and Attribution for Generative Art,"We present EKILA; a decentralized framework that enables creatives to receive
recognition and reward for their contributions to generative AI (GenAI). EKILA
proposes a robust visual attribution technique and combines this with an
emerging content provenance standard (C2PA) to address the problem of synthetic
image provenance -- determining the generative model and training data
responsible for an AI-generated image. Furthermore, EKILA extends the
non-fungible token (NFT) ecosystem to introduce a tokenized representation for
rights, enabling a triangular relationship between the asset's Ownership,
Rights, and Attribution (ORA). Leveraging the ORA relationship enables creators
to express agency over training consent and, through our attribution model, to
receive apportioned credit, including royalty payments for the use of their
assets in GenAI.",2304.04639v1
2023-04-11,NeAT: Neural Artistic Tracing for Beautiful Style Transfer,"Style transfer is the task of reproducing the semantic contents of a source
image in the artistic style of a second target image. In this paper, we present
NeAT, a new state-of-the art feed-forward style transfer method. We
re-formulate feed-forward style transfer as image editing, rather than image
generation, resulting in a model which improves over the state-of-the-art in
both preserving the source content and matching the target style. An important
component of our model's success is identifying and fixing ""style halos"", a
commonly occurring artefact across many style transfer techniques. In addition
to training and testing on standard datasets, we introduce the BBST-4M dataset,
a new, large scale, high resolution dataset of 4M images. As a component of
curating this data, we present a novel model able to classify if an image is
stylistic. We use BBST-4M to improve and measure the generalization of NeAT
across a huge variety of styles. Not only does NeAT offer state-of-the-art
quality and generalization, it is designed and trained for fast inference at
high resolution.",2304.05139v1
2023-04-12,ALADIN-NST: Self-supervised disentangled representation learning of artistic style through Neural Style Transfer,"Representation learning aims to discover individual salient features of a
domain in a compact and descriptive form that strongly identifies the unique
characteristics of a given sample respective to its domain. Existing works in
visual style representation literature have tried to disentangle style from
content during training explicitly. A complete separation between these has yet
to be fully achieved. Our paper aims to learn a representation of visual
artistic style more strongly disentangled from the semantic content depicted in
an image. We use Neural Style Transfer (NST) to measure and drive the learning
signal and achieve state-of-the-art representation learning on explicitly
disentangled metrics. We show that strongly addressing the disentanglement of
style and content leads to large gains in style-specific metrics, encoding far
less semantic information and achieving state-of-the-art accuracy in downstream
multimodal applications.",2304.05755v2
2023-04-18,"UPGPT: Universal Diffusion Model for Person Image Generation, Editing and Pose Transfer","Text-to-image models (T2I) such as StableDiffusion have been used to generate
high quality images of people. However, due to the random nature of the
generation process, the person has a different appearance e.g. pose, face, and
clothing, despite using the same text prompt. The appearance inconsistency
makes T2I unsuitable for pose transfer. We address this by proposing a
multimodal diffusion model that accepts text, pose, and visual prompting. Our
model is the first unified method to perform all person image tasks -
generation, pose transfer, and mask-less edit. We also pioneer using small
dimensional 3D body model parameters directly to demonstrate new capability -
simultaneous pose and camera view interpolation while maintaining the person's
appearance.",2304.08870v2
2023-05-02,The Pseudoinverse of $A=CR$ is $A^+=R^+C^+$ (?),"This paper gives three formulas for the pseudoinverse of a matrix product $A
= CR$. The first is sometimes correct, the second is always correct, and the
third is almost never correct. But that third randomized pseudoinverse $A^+_r$
may be very useful when $A$ is a very large matrix.
  1. $A^+ = R^+C^+$ when $A = CR$ and $C$ has independent columns and $R$ has
independent rows.
  2. $A^+ = (C^+CR)^+(CRR^+)^+$ is always correct.
  3. $A^+_r = (P^TCR)^+P^TCRQ(CRQ)^+ = A^+$ only when $\mathrm{rank}(P^TA) =
\mathrm{rank}(AQ) = \mathrm{rank}(A)$ with $A = CR$.",2305.01716v3
2023-05-10,Symmetry and nonlinearity of spin wave resonance excited by focused surface acoustic waves,"The use of a complex ferromagnetic system to manipulate GHz surface acoustic
waves is a rich current topic under investigation, but the high-power nonlinear
regime is under-explored. We introduce focused surface acoustic waves, which
provide a way to access this regime with modest equipment. Symmetry of the
magneto-acoustic interaction can be tuned by interdigitated transducer design
which can introduce additional strain components. Here, we compare the impact
of focused acoustic waves versus standard unidirectional acoustic waves in
significantly enhancing the magnon-phonon coupling behavior. Analytical
simulation results based on modified Landau-Lifshitz-Gilbert theory show good
agreement with experimental findings. We also report nonlinear input power
dependence of the transmission through the device. This experimental
observation is supported by the micromagnetic simulation using mumax3 to model
the nonlinear dependence. These results pave the way for extending the
understanding and design of acoustic wave devices for exploration of
acoustically driven spin wave resonance physics.",2305.06259v1
2023-05-16,Phase locking in voltage-controlled parametric oscillator,"A recent experimental demonstration of a parametric magnetization oscillation
excited by applying a microwave voltage to a ferromagnetic metal will be
applicable not only to a new magnetization switching method but also to
bio-inspired computing. It should be, however, noted that a phase of the
parametric magnetization oscillation is not uniquely locked, related to the
fact that a frequency of the microwave voltage is twice the value of the
magnetization oscillation. There are two possible phases in the parametric
oscillation state, and which of the two is realized depends on the initial
condition of the magnetization. Here, we examine two approaches to lock the
phase uniquely. One is to suppress the distribution of the initial state by
enhancing the perpendicular magnetic anisotropy before applying microwave
voltage, and the other is to use a sweeping frequency. Through numerical
simulation of the Landau-Lifshitz-Gilbert equation and quantification of locked
rate, we find that the sweeping frequency is more effective to lock the phase
of the parametric magnetization oscillation.",2305.09143v1
2023-05-16,Non-periodic input-driven magnetization dynamics in voltage-controlled parametric oscillator,"Input-driven dynamical systems have attracted attention because their
dynamics can be used as resources for brain-inspired computing. The recent
achievement of human-voice recognition by spintronic oscillator also utilizes
an input-driven magnetization dynamics. Here, we investigate an excitation of
input-driven chaos in magnetization dynamics by voltage controlled magnetic
anisotropy effect. The study focuses on the parametric magnetization
oscillation induced by a microwave voltage and investigates the effect of
random-pulse input on the oscillation behavior. Solving the
Landau-Lifshitz-Gilbert equation, temporal dynamics of the magnetization and
its statistical character are evaluated. In a weak perturbation limit, the
temporal dynamics of the magnetization are mainly determined by the input
signal, which is classified as input-driven synchronization. In a large
perturbation limit, on the other hand, chaotic dynamics are observed, where the
dynamical response is sensitive to the initial state. The existence of chaos is
also identified by the evaluation of the Lyapunov exponent.",2305.09151v1
2023-05-23,Approaches to inclusive semileptonic $B_{(s)}$-meson decays from Lattice QCD,"We address the nonperturbative calculation of the inclusive decay rate of
semileptonic $B_{(s)}$-meson decays from lattice QCD. Precise Standard-Model
predictions are key ingredients in searches for new physics, and this type of
computation may eventually provide new insight into the long-standing tension
between the inclusive and exclusive determinations of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix elements $|V_{cb}|$ and $|V_{ub}|$. We
present results from a pilot lattice computation for $B_s \rightarrow X_c\, l
\nu_l$, where the initial $b$ quark described by the relativistic-heavy-quark
(RHQ) formalism on the lattice and the other valence quarks discretised with
domain-wall fermions are simulated approximately at their physical quark
masses. We compare two different methods for computing the decay rate from
lattice data of Euclidean $n$-point functions, namely Chebyshev and
Backus-Gilbert approaches. We further study how much the ground-state meson
dominates the inclusive decay rate and indicate our strategy towards a
computation with a more comprehensive systematic error budget.",2305.14092v2
2023-05-25,Crystallization dynamics of magnetic skyrmions in a frustrated itinerant magnet,"We investigate the phase ordering kinetics of skyrmion lattice (SkL) in a
metallic magnet. The SkL can be viewed as a superposition of magnetic stripes
whose periods are determined by the quasi-nesting wave vectors of the
underlying Fermi surface. An effective magnetic Hamiltonian that describes the
electron-mediated spin-spin interaction is obtained for a two-dimensional s-d
model with the Rashba spin-orbit coupling. Large-scale Landau-Lifshitz-Gilbert
dynamics simulations based on the effective spin Hamiltonian reveal a two-stage
phase ordering of the SkL phase after a thermal quench. The initial fast
crystallization of skyrmions is followed by a slow relaxation dominated by the
annihilation dynamics of dislocations, which are topological defects of the
constituent magnetic stripe orders. The late-stage phase ordering also exhibits
a dynamical scaling symmetry. We further show that the annihilation of
dislocations follows a power-law time dependence with a logarithmic correction
that depends on magnetic fields. Implications of our results for SkL phases in
magnetic materials are also discussed.",2305.16182v1
2023-05-31,Magnetization dynamics in a three-dimensional interconnected nanowire array,"Three-dimensional magnetic nanostructures have recently emerged as artificial
magnetic material types with unique properties bearing potential for
applications, including magnonic devices. Interconnected magnetic nanowires are
a sub-category within this class of materials that is attracting particular
interest. We investigate the high-frequency magnetization dynamics in a cubic
array of cylindrical magnetic nanowires through micromagnetic simulations based
on a frequency-domain formulation of the linearized Landau-Lifshitz-Gilbert
equation. The small-angle high-frequency magnetization dynamics excited by an
external oscillatory field displays clear resonances at distinct frequencies.
These resonances are identified as oscillations connected to specific geometric
features and micromagnetic configurations. The geometry- and
configuration-dependence of the nanowire array's absorption spectrum
demonstrates the potential of such magnetic systems for tuneable and
reprogrammable magnonic applications.",2306.00174v1
2023-06-12,Continuum Limit of Spin Dynamics on Hexagonal Lattice,"Compared to their three-dimensional counterparts, two-dimensional materials
exhibit intriguing electronic and magnetic properties. Notable examples include
twisted graphene's superconducting states and chromium trichloride's meron spin
textures. Understanding nontrivial topological spin textures is crucial for
magnetization dynamics and spintronic technologies. In this study, we analyze
the full model of discrete spin dynamics on a two-dimensional hexagonal lattice
used in experiments with chromium trichloride. We prove its convergence to the
continuum Landau-Lifshitz-Gilbert equation in the weak sense, despite
difficulties arising from the absence of central symmetry when constructing
difference quotient and interpolation operators on hexagonal lattices. To
overcome these challenges, we introduce multi-step difference quotient and
interpolation operators that possess an isometric property as a generalization
of Ladysenskaya's interpolation operator. This result not only establishes a
precise connection between parameters in atomistic models and those in
continuum models but also provides necessary tools for analyzing weak
convergence in other nonlinear problems on hexagonal lattices at microscopic
and macroscopic scales seamlessly.",2306.06958v1
2023-06-23,Molecular Insights into Chemical Reactions at Aqueous Aerosol Interfaces,"Atmospheric aerosols facilitate reactions between ambient gases and dissolved
species. Here, we review our efforts to interrogate the uptake of these gases
and the mechanisms of their reactions both theoretically and experimentally. We
highlight the fascinating behavior of $\mathrm{N}_2\mathrm{O}_5$ in solutions
ranging from pure water to complex mixtures, chosen because its
aerosol-mediated reactions significantly impact global ozone, hydroxyl, and
methane concentrations. As a hydrophobic, weakly soluble, and highly reactive
species, $\mathrm{N}_2\mathrm{O}_5$ is a sensitive probe of the chemical and
physical properties of aerosol interfaces. We employ contemporary theory to
disentangle the fate of $\mathrm{N}_2\mathrm{O}_5$ as it approaches pure and
salty water, starting with adsorption and ending with hydrolysis to HNO$_3$,
chlorination to $\mathrm{ClNO}_2$, or evaporation. Flow reactor and gas-liquid
scattering experiments probe even greater complexity as added ions, organic
molecules, and surfactants alter interfacial composition and reaction rates.
Together, we reveal a new perspective on multiphase chemistry in the
atmosphere.",2306.13811v1
2023-07-09,DIFF-NST: Diffusion Interleaving For deFormable Neural Style Transfer,"Neural Style Transfer (NST) is the field of study applying neural techniques
to modify the artistic appearance of a content image to match the style of a
reference style image. Traditionally, NST methods have focused on texture-based
image edits, affecting mostly low level information and keeping most image
structures the same. However, style-based deformation of the content is
desirable for some styles, especially in cases where the style is abstract or
the primary concept of the style is in its deformed rendition of some content.
With the recent introduction of diffusion models, such as Stable Diffusion, we
can access far more powerful image generation techniques, enabling new
possibilities. In our work, we propose using this new class of models to
perform style transfer while enabling deformable style transfer, an elusive
capability in previous models. We show how leveraging the priors of these
models can expose new artistic controls at inference time, and we document our
findings in exploring this new direction for the field of style transfer.",2307.04157v2
2023-07-11,Charge conservation in spin torque oscillators leads to a self-induced torque,"Spin torque oscillators are conventionally described by the
Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. However, at the onset of
oscillations, the predictions of the conventional LLGS equation differ
qualitatively from experimental results and thus appear to be incomplete. In
this work we show that taking charge conservation into account leads to a
previously-overlooked self-induced torque, which modifies the LLGS equation. We
show that the self-induced torque originates from the pumping current that a
precessing magnetization drives through a magnetic tunnel junction. To
illustrate the importance of the self-induced torque, we consider an in-plane
magnetized nanopillar, where it gives clear qualitative corrections to the
conventional LLGS description.",2307.05105v3
2023-07-13,Magnon-magnon coupling in synthetic ferrimagnets,"Magnetic multilayers with interlayer exchange coupling have been widely
studied for both static and dynamic regimes. Their dynamical responses depend
on the exchange coupling strength and magnetic properties of individual layers.
Magnetic resonance spectra in such systems are conveniently discussed in terms
of coupling of acoustic and optical modes. At a certain value of applied
magnetic field, the two modes come close to being degenerate and the spectral
gap indicates the strength of mode hybridisation. In this work, we
theoretically and experimentally study the mode hybridisation of
interlayer-exchange-coupled moments with dissimilar magnetisation and thickness
of two ferromagnetic layers. In agreement with symmetry analysis for
eigenmodes, our low-symmetry multilayers exhibit sizable spectral gaps for all
experimental conditions. The spectra agree well with the predictions from the
Landau-Lifshitz-Gilbert equation at the macrospin limit whose parameters are
independently fixed by static measurements.",2307.06888v2
2023-07-14,Mod $\ell$ gamma factors and a converse theorem for finite general linear groups,"For $q$ a power of a prime $p$, we study gamma factors of representations of
$GL_n(\mathbb{F}_q)$ over an algebraically closed field $k$ of positive
characteristic $\ell \neq p$. We show that the reduction mod $\ell$ of the
gamma factor defined in characteristic zero fails to satisfy the analogue of
the local converse theorem of Piatetski-Shapiro. To remedy this, we construct
gamma factors valued in arbitrary $\mathbb{Z}[1/p, \zeta_p]$-algebras $A$,
where $\zeta_p$ is a primitive $p$-th root of unity, for Whittaker-type
representations $\rho$ and $\pi$ of $GL_n(\mathbb{F}_q)$ and
$GL_m(\mathbb{F}_q)$ over $A$. We let $P(\pi)$ be the projective envelope of
$\pi$ and let $R(\pi)$ be its endomorphism ring and define new gamma factors
$\widetilde\gamma(\rho \times \pi) = \gamma((\rho\otimes_kR(\pi)) \times
P(\pi))$, which take values in the local Artinian $k$-algebra $R(\pi)$. We
prove a converse theorem for cuspidal representations using the new gamma
factors. When $n=2$ and $m=1$ we construct a different ``new'' gamma factor
$\gamma^{\ell}(\rho,\pi)$, which takes values in $k$ and satisfies a converse
theorem.",2307.07593v1
2023-07-20,Pathwise central limit theorem and moderate deviations via rough paths for SPDEs with multiplicative noise,"We put forward a general framework for the study of a pathwise central limit
theorem (CLT) and a moderate deviation principle (MDP) for stochastic partial
differential equations perturbed with a small multiplicative linear noise by
means of the theory of rough paths. The CLT can be interpreted as the
convergence to a pathwise derivative of the It\^o-Lyons map. The result follows
by applying a pathwise Malliavin-like calculus for rough paths and from
compactness methods. The convergence in the CLT is quantified by an optimal
speed of convergence. From the exponential equivalence principle and the
knowledge of the speed of convergence, we can derive easily a MDP. In
particular, we do not apply the weak convergence approach usually employed in
this framework. We derive a pathwise CLT and a MDP for the stochastic
Landau-Lifschitz-Gilbert equation in one dimension, for the heat equation and
for a stochastic reaction-diffusion equation. As a further application, we
derive a pathwise convergence to the CLT limit and a corresponding MDP for
equations driven by linear It\^o noise.",2307.10965v1
2023-07-26,Learning sources of variability from high-dimensional observational studies,"Causal inference studies whether the presence of a variable influences an
observed outcome. As measured by quantities such as the ""average treatment
effect,"" this paradigm is employed across numerous biological fields, from
vaccine and drug development to policy interventions. Unfortunately, the
majority of these methods are often limited to univariate outcomes. Our work
generalizes causal estimands to outcomes with any number of dimensions or any
measurable space, and formulates traditional causal estimands for nominal
variables as causal discrepancy tests. We propose a simple technique for
adjusting universally consistent conditional independence tests and prove that
these tests are universally consistent causal discrepancy tests. Numerical
experiments illustrate that our method, Causal CDcorr, leads to improvements in
both finite sample validity and power when compared to existing strategies. Our
methods are all open source and available at github.com/ebridge2/cdcorr.",2307.13868v2
2023-07-26,An Asynchronous and Low-Power True Random Number Generator using STT-MTJ,"The emerging Spin Transfer Torque Magnetic Tunnel Junction (STT-MTJ)
technology exhibits interesting stochastic behavior combined with small area
and low operation energy. It is, therefore, a promising technology for security
applications, specifically the generation of random numbers. In this paper,
STT-MTJ is used to construct an asynchronous true random number generator
(TRNG) with low power and a high entropy rate. The asynchronous design enables
decoupling of the random number generation from the system clock, allowing it
to be embedded in low-power devices. The proposed TRNG is evaluated by a
numerical simulation, using the Landau-Lifshitz-Gilbert (LLG) equation as the
model of the STT-MTJ devices. Design considerations, attack analysis, and
process variation are discussed and evaluated. We show that our design is
robust to process variation, achieving an entropy generating rate between
99.7Mbps and 127.8Mbps with 6-7.7 pJ per bit for 90% of the instances.",2307.14476v1
2023-07-31,Evidence of Pseudogravitational Distortions of the Fermi Surface Geometry in the Antiferromagnetic Metal FeRh,"The confluence between high-energy physics and condensed matter has produced
groundbreaking results via unexpected connections between the two traditionally
disparate areas. In this work, we elucidate additional connectivity between
high-energy and condensed matter physics by examining the interplay between
spin-orbit interactions and local symmetry-breaking magnetic order in the
magnetotransport of thin-film magnetic semimetal FeRh. We show that the change
in sign of the normalized longitudinal magnetoresistance observed as a function
of increasing in-plane magnetic field results from changes in the Fermi surface
morphology. We demonstrate that the geometric distortions in the Fermi surface
morphology are more clearly understood via the presence of pseudogravitational
fields in the low-energy theory. The pseudogravitational connection provides
additional insights into the origins of a ubiquitous phenomenon observed in
many common magnetic materials and points to an alternative methodology for
understanding phenomena in locally-ordered materials with strong spin-orbit
interactions.",2308.00192v1
2023-08-02,MammoDG: Generalisable Deep Learning Breaks the Limits of Cross-Domain Multi-Center Breast Cancer Screening,"Breast cancer is a major cause of cancer death among women, emphasising the
importance of early detection for improved treatment outcomes and quality of
life. Mammography, the primary diagnostic imaging test, poses challenges due to
the high variability and patterns in mammograms. Double reading of mammograms
is recommended in many screening programs to improve diagnostic accuracy but
increases radiologists' workload. Researchers explore Machine Learning models
to support expert decision-making. Stand-alone models have shown comparable or
superior performance to radiologists, but some studies note decreased
sensitivity with multiple datasets, indicating the need for high generalisation
and robustness models. This work devises MammoDG, a novel deep-learning
framework for generalisable and reliable analysis of cross-domain multi-center
mammography data. MammoDG leverages multi-view mammograms and a novel
contrastive mechanism to enhance generalisation capabilities. Extensive
validation demonstrates MammoDG's superiority, highlighting the critical
importance of domain generalisation for trustworthy mammography analysis in
imaging protocol variations.",2308.01057v1
2023-08-02,Sphaleron rate of $N_f=2+1$ QCD,"We compute the sphaleron rate of $N_f=2+1$ QCD at the physical point for a
range of temperatures $200$ MeV $\lesssim T \lesssim 600$ MeV. We adopt a
strategy recently applied in the quenched case, based on the extraction of the
rate via a modified version of the Backus-Gilbert method from
finite-lattice-spacing and finite-smoothing-radius Euclidean topological charge
density correlators. The physical sphaleron rate is finally computed by
performing a continuum limit at fixed physical smoothing radius, followed by a
zero-smoothing extrapolation. Dynamical fermions were discretized using the
staggered formulation, which is known to yield large lattice artifacts for the
topological susceptibility. However, we find them to be rather mild for the
sphaleron rate.",2308.01287v3
2023-07-07,AI and the EU Digital Markets Act: Addressing the Risks of Bigness in Generative AI,"As AI technology advances rapidly, concerns over the risks of bigness in
digital markets are also growing. The EU's Digital Markets Act (DMA) aims to
address these risks. Still, the current framework may not adequately cover
generative AI systems that could become gateways for AI-based services. This
paper argues for integrating certain AI software as core platform services and
classifying certain developers as gatekeepers under the DMA. We also propose an
assessment of gatekeeper obligations to ensure they cover generative AI
services. As the EU considers generative AI-specific rules and possible DMA
amendments, this paper provides insights towards diversity and openness in
generative AI services.",2308.02033v1
2023-08-04,"Federated Learning: Organizational Opportunities, Challenges, and Adoption Strategies","Restrictive rules for data sharing in many industries have led to the
development of federated learning. Federated learning is a machine-learning
technique that allows distributed clients to train models collaboratively
without the need to share their respective training data with others. In this
paper, we first explore the technical foundations of federated learning and its
organizational opportunities. Second, we present a conceptual framework for the
adoption of federated learning, mapping four types of organizations by their
artificial intelligence capabilities and limits to data sharing. We then
discuss why exemplary organizations in different contexts - including public
authorities, financial service providers, manufacturing companies, as well as
research and development consortia - might consider different approaches to
federated learning. To conclude, we argue that federated learning presents
organizational challenges with ample interdisciplinary opportunities for
information systems researchers.",2308.02219v2
2023-08-04,Algorithm for evaluating distance-based entanglement measures,"Quantifying entanglement in quantum systems is an important yet challenging
task due to its NP-hard nature. In this work, we propose an efficient algorithm
for evaluating distance-based entanglement measures. Our approach builds on
Gilbert's algorithm for convex optimization, providing a reliable upper bound
on the entanglement of a given arbitrary state. We demonstrate the
effectiveness of our algorithm by applying it to various examples, such as
calculating the squared Bures metric of entanglement as well as the relative
entropy of entanglement for GHZ states, $W$ states, Horodecki states, and
chessboard states. These results demonstrate that our algorithm is a versatile
and accurate tool that can quickly provide reliable upper bounds for
entanglement measures.",2308.02326v1
2023-08-07,Robust Ordinal Regression for Subsets Comparisons with Interactions,"This paper is dedicated to a robust ordinal method for learning the
preferences of a decision maker between subsets. The decision model, derived
from Fishburn and LaValle (1996) and whose parameters we learn, is general
enough to be compatible with any strict weak order on subsets, thanks to the
consideration of possible interactions between elements. Moreover, we accept
not to predict some preferences if the available preference data are not
compatible with a reliable prediction. A predicted preference is considered
reliable if all the simplest models (Occam's razor) explaining the preference
data agree on it. Following the robust ordinal regression methodology, our
predictions are based on an uncertainty set encompassing the possible values of
the model parameters. We define a robust ordinal dominance relation between
subsets and we design a procedure to determine whether this dominance relation
holds. Numerical tests are provided on synthetic and real-world data to
evaluate the richness and reliability of the preference predictions made.",2308.03376v1
2023-08-07,Strong Byzantine Agreement with Adaptive Word Complexity,"The strong Byzantine agreement (SBA) problem is defined among n processes,
out of which t < n can be faulty and behave arbitrarily. SBA allows correct
(non-faulty) processes to agree on a common value. Moreover, if all correct
processes have proposed the same value, only that value can be agreed upon. It
has been known for a long time that any solution to the SBA problem incurs
quadratic worst-case word complexity; additionally, the bound was known to be
tight. However, no existing protocol achieves adaptive word complexity, where
the number of exchanged words depends on the actual number of faults, and not
on the upper bound. Therefore, it is still unknown whether SBA with adaptive
word complexity exists. This paper answers the question in the affirmative.
Namely, we introduce STRONG, a synchronous protocol that solves SBA among n =
(2 + Omega(1))t + 1 processes and achieves adaptive word complexity. We show
that the fundamental challenge of adaptive SBA lies in efficiently solving
certification, the problem of obtaining a constant-sized, locally-verifiable
proof that a value can safely be decided.",2308.03524v1
2023-08-24,Methods for transverse and longitudinal spin-photon coupling in silicon quantum dots with intrinsic spin-orbit effect,"In a full-scale quantum computer with a fault-tolerant architecture, having
scalable, long-range interaction between qubits is expected to be a highly
valuable resource. One promising method of achieving this is through the
light-matter interaction between spins in semiconductors and photons in
superconducting cavities. This paper examines the theory of both transverse and
longitudinal spin-photon coupling and their applications in the silicon
metal-oxide-semiconductor (SiMOS) platform. We propose a method of coupling
which uses the intrinsic spin-orbit interaction arising from orbital
degeneracies in SiMOS qubits. Using theoretical analysis and experimental data,
we show that the strong coupling regime is achievable in the transverse scheme.
We also evaluate the feasibility of a longitudinal coupling driven by an AC
modulation on the qubit. These coupling methods eschew the requirement for an
external micromagnet, enhancing prospects for scalability and integration into
a large-scale quantum computer.",2308.12626v1
2023-08-24,Object level footprint uncertainty quantification in infrastructure based sensing,"We examine the problem of estimating footprint uncertainty of objects imaged
using the infrastructure based camera sensing. A closed form relationship is
established between the ground coordinates and the sources of the camera
errors. Using the error propagation equation, the covariance of a given ground
coordinate can be measured as a function of the camera errors. The uncertainty
of the footprint of the bounding box can then be given as the function of all
the extreme points of the object footprint. In order to calculate the
uncertainty of a ground point, the typical error sizes of the error sources are
required. We present a method of estimating the typical error sizes from an
experiment using a static, high-precision LiDAR as the ground truth. Finally,
we present a simulated case study of uncertainty quantification from
infrastructure based camera in CARLA to provide a sense of how the uncertainty
changes across a left turn maneuver.",2308.12846v1
2023-08-28,Data fusion using weakly aligned sources,"We introduce a new data fusion method that utilizes multiple data sources to
estimate a smooth, finite-dimensional parameter. Most existing methods only
make use of fully aligned data sources that share common conditional
distributions of one or more variables of interest. However, in many settings,
the scarcity of fully aligned sources can make existing methods require unduly
large sample sizes to be useful. Our approach enables the incorporation of
weakly aligned data sources that are not perfectly aligned, provided their
degree of misalignment can be characterized by a prespecified density ratio
model. We describe gains in efficiency and provide a general means to construct
estimators achieving these gains. We illustrate our results by fusing data from
two harmonized HIV monoclonal antibody prevention efficacy trials to study how
a neutralizing antibody biomarker associates with HIV genotype.",2308.14836v1
2023-08-31,Bi-level iterative regularization for inverse problems in nonlinear PDEs,"We investigate the ill-posed inverse problem of recovering unknown spatially
dependent parameters in nonlinear evolution PDEs. We propose a bi-level
Landweber scheme, where the upper-level parameter reconstruction embeds a
lower-level state approximation. This can be seen as combining the classical
reduced setting and the newer all-at-once setting, allowing us to,
respectively, utilize well-posedness of the parameter-to-state map, and to
bypass having to solve nonlinear PDEs exactly. Using this, we derive stopping
rules for lower- and upper-level iterations and convergence of the bi-level
method. We discuss application to parameter identification for the
Landau-Lifshitz-Gilbert equation in magnetic particle imaging.",2308.16617v2
2023-09-03,On Galois self-orthogonal algebraic geometry codes,"Galois self-orthogonal (SO) codes are generalizations of Euclidean and
Hermitian SO codes. Algebraic geometry (AG) codes are the first known class of
linear codes exceeding the Gilbert-Varshamov bound. Both of them have attracted
much attention for their rich algebraic structures and wide applications in
these years. In this paper, we consider them together and study Galois SO AG
codes. A criterion for an AG code being Galois SO is presented. Based on this
criterion, we construct several new classes of maximum distance separable (MDS)
Galois SO AG codes from projective lines and several new classes of Galois SO
AG codes from projective elliptic curves, hyper-elliptic curves and hermitian
curves. In addition, we give an embedding method that allows us to obtain more
MDS Galois SO codes from known MDS Galois SO AG codes.",2309.01051v2
2023-09-17,Unleashing Quantum Simulation Advantages: Hamiltonian Subspace Encoding for Resource Efficient Quantum Simulations,"Number-conserved subspace encoding for fermionic Hamiltonians, which
exponentially reduces qubit cost, is necessary for quantum advantages in
variational quantum eigensolver (VQE). However, optimizing the trade-off
between qubit compression and increased measurement cost poses a challenge. By
employing the Gilbert-Varshamov bound on linear code, we optimize qubit scaling
$\mathcal{O}(N\log_2M)$ and measurement cost $\mathcal{O}(M^4)$ for $M$ modes
$N$ electrons chemistry problems. The compression is implemented with the
Randomized Linear Encoding (RLE) algorithm on VQE for $\text{H}_2$ and LiH in
the 6-31G* and STO-3G/6-31G* basis respectively. The resulting subspace circuit
expressivity and trainability are enhanced with less circuit depth and higher
noise tolerance.",2309.09370v1
2023-09-20,Dimensions of splines of degree two,"Splines are defined as piecewise polynomials on the faces of a polyhedral
complex that agree on the intersections of two faces. Splines are used in
approximation theory and numerical analysis, with applications in data
interpolation, to create smooth curves in computer graphics and to find
numerical solutions to partial differential equations. Gilbert, Tymoczko, and
Viel generalized the classical splines combinatorially and algebraically: a
generalized spline is a vertex labeling of a graph $G$ by elements of the ring
so that the difference between the labels of any two adjacent vertices lies in
the ideal generated by the corresponding edge label. We study the generalized
splines on the planar graphs whose edges are labeled by two-variable
polynomials of the form $(ax+by+c)^2$ and whose vertices are labeled by
polynomials of degree at most two. In this paper we address the upper-bound
conjecture for the dimension of degree-2 splines of smoothness 1 when the edge
labels are generic. The dimension is expressed in terms of the rank of the
extended cycle basis matrix. We also provide a combinatorial algorithm on
graphs to compute the rank.",2309.11650v1
2023-09-25,DECORAIT -- DECentralized Opt-in/out Registry for AI Training,"We present DECORAIT; a decentralized registry through which content creators
may assert their right to opt in or out of AI training as well as receive
reward for their contributions. Generative AI (GenAI) enables images to be
synthesized using AI models trained on vast amounts of data scraped from public
sources. Model and content creators who may wish to share their work openly
without sanctioning its use for training are thus presented with a data
governance challenge. Further, establishing the provenance of GenAI training
data is important to creatives to ensure fair recognition and reward for their
such use. We report a prototype of DECORAIT, which explores hierarchical
clustering and a combination of on/off-chain storage to create a scalable
decentralized registry to trace the provenance of GenAI training data in order
to determine training consent and reward creatives who contribute that data.
DECORAIT combines distributed ledger technology (DLT) with visual
fingerprinting, leveraging the emerging C2PA (Coalition for Content Provenance
and Authenticity) standard to create a secure, open registry through which
creatives may express consent and data ownership for GenAI.",2309.14400v1
2023-10-05,Multi-Resolution Audio-Visual Feature Fusion for Temporal Action Localization,"Temporal Action Localization (TAL) aims to identify actions' start, end, and
class labels in untrimmed videos. While recent advancements using transformer
networks and Feature Pyramid Networks (FPN) have enhanced visual feature
recognition in TAL tasks, less progress has been made in the integration of
audio features into such frameworks. This paper introduces the Multi-Resolution
Audio-Visual Feature Fusion (MRAV-FF), an innovative method to merge
audio-visual data across different temporal resolutions. Central to our
approach is a hierarchical gated cross-attention mechanism, which discerningly
weighs the importance of audio information at diverse temporal scales. Such a
technique not only refines the precision of regression boundaries but also
bolsters classification confidence. Importantly, MRAV-FF is versatile, making
it compatible with existing FPN TAL architectures and offering a significant
enhancement in performance when audio data is available.",2310.03456v1
2023-10-20,The History and Risks of Reinforcement Learning and Human Feedback,"Reinforcement learning from human feedback (RLHF) has emerged as a powerful
technique to make large language models (LLMs) easier to use and more
effective. A core piece of the RLHF process is the training and utilization of
a model of human preferences that acts as a reward function for optimization.
This approach, which operates at the intersection of many stakeholders and
academic disciplines, remains poorly understood. RLHF reward models are often
cited as being central to achieving performance, yet very few descriptors of
capabilities, evaluations, training methods, or open-source models exist. Given
this lack of information, further study and transparency is needed for learned
RLHF reward models. In this paper, we illustrate the complex history of
optimizing preferences, and articulate lines of inquiry to understand the
sociotechnical context of reward models. In particular, we highlight the
ontological differences between costs, rewards, and preferences at stake in
RLHF's foundations, related methodological tensions, and possible research
directions to improve general understanding of how reward models function.",2310.13595v2
2023-11-24,The quenched glueball spectrum from smeared spectral densities,"The standard approach to compute the glueball spectrum on the lattice relies
on the evaluation of effective masses from two-point correlation functions of
operators with the quantum numbers of the desired state. In this work, we
propose an alternative procedure, based on the numerical computation of smeared
spectral densities. Even though the extraction of the latter from lattice
correlators is a notoriously ill-posed inverse problem, we show that a recently
developed numerical method, based on the Backus-Gilbert regularization,
provides a robust way to evaluate a smeared version of the spectral densities.
Fitting the latter to a combination of Gaussians, we extract the masses of the
lightest glueball and of its first excitation in the spectrum of the theory.
While the preliminary results presented in this contribution are restricted to
simulations at finite lattice spacing and finite volume, and for the purely
gluonic sector of QCD, they represent the first step in a systematic
investigation of glueballs using spectral-reconstruction methods.",2311.14806v1
2023-11-28,Data-efficient operator learning for solving high Mach number fluid flow problems,"We consider the problem of using SciML to predict solutions of high Mach
fluid flows over irregular geometries. In this setting, data is limited, and so
it is desirable for models to perform well in the low-data setting. We show
that Neural Basis Functions (NBF), which learns a basis of behavior modes from
the data and then uses this basis to make predictions, is more effective than a
basis-unaware baseline model. In addition, we identify continuing challenges in
the space of predicting solutions for this type of problem.",2311.16860v2
2023-11-30,ZeST-NeRF: Using temporal aggregation for Zero-Shot Temporal NeRFs,"In the field of media production, video editing techniques play a pivotal
role. Recent approaches have had great success at performing novel view image
synthesis of static scenes. But adding temporal information adds an extra layer
of complexity. Previous models have focused on implicitly representing static
and dynamic scenes using NeRF. These models achieve impressive results but are
costly at training and inference time. They overfit an MLP to describe the
scene implicitly as a function of position. This paper proposes ZeST-NeRF, a
new approach that can produce temporal NeRFs for new scenes without retraining.
We can accurately reconstruct novel views using multi-view synthesis techniques
and scene flow-field estimation, trained only with unrelated scenes. We
demonstrate how existing state-of-the-art approaches from a range of fields
cannot adequately solve this new task and demonstrate the efficacy of our
solution. The resulting network improves quantitatively by 15% and produces
significantly better visual results.",2311.18491v1
2023-12-05,ViscoNet: Bridging and Harmonizing Visual and Textual Conditioning for ControlNet,"This paper introduces ViscoNet, a novel method that enhances text-to-image
human generation models with visual prompting. Unlike existing methods that
rely on lengthy text descriptions to control the image structure, ViscoNet
allows users to specify the visual appearance of the target object with a
reference image. ViscoNet disentangles the object's appearance from the image
background and injects it into a pre-trained latent diffusion model (LDM) model
via a ControlNet branch. This way, ViscoNet mitigates the style mode collapse
problem and enables precise and flexible visual control. We demonstrate the
effectiveness of ViscoNet on human image generation, where it can manipulate
visual attributes and artistic styles with text and image prompts. We also show
that ViscoNet can learn visual conditioning from small and specific object
domains while preserving the generative power of the LDM backbone.",2312.03154v1
2023-12-08,Convergent finite element methods for antiferromagnetic and ferrimagnetic materials,"We consider the numerical approximation of a continuum model of
antiferromagnetic and ferrimagnetic materials. The state of the material is
described in terms of two unit-length vector fields, which can be interpreted
as the magnetizations averaging the spins of two sublattices. For the static
setting, which requires the solution of a constrained energy minimization
problem, we introduce a discretization based on first-order finite elements and
prove its $\Gamma$-convergence. Then, we propose and analyze two iterative
algorithms for the computation of low-energy stationary points. The algorithms
are obtained from (semi-)implicit time discretizations of gradient flows of the
energy. Finally, we extend the algorithms to the dynamic setting, which
consists of a nonlinear system of two Landau-Lifshitz-Gilbert equations solved
by the two fields, and we prove unconditional stability and convergence of the
finite element approximations toward a weak solution of the problem. Numerical
experiments assess the performance of the algorithms and demonstrate their
applicability for the simulation of physical processes involving
antiferromagnetic and ferrimagnetic materials.",2312.04939v1
2023-12-18,Modelling the 3D spatiotemporal organisation of chromatin replication,"We propose a polymer model for the dynamics of chromatin replication in three
dimensional space. Our simulations indicate that both immobile and tracking
replisomes may self-assemble during the process, reconciling previous
apparently discordant experimental evidence in favour of either scenario. Which
of the two morphologies appears in our model depends on the balance between
non-specific and origin-targeting interactions between chromatin and firing
factors -- polymerases and other components of the replisome. Non-specific
interactions are also necessary to yield clustering of factors and replication
forks, creating structures akin to the replication foci observed in mammalian
cells in vivo. We suggest that cluster formation provides an underappreciated
but robust pathway to avoid stalled or faulty forks, which would otherwise
diminish the efficiency of the replication process. Additionally, our
simulations allow us to predict different modes of cluster growth during
S-phase, which could be tested experimentally, and they show that the three
dimensional chromatin context is important to understand replication patterns
in fission yeast.",2312.11275v1
2024-01-09,Revealing dark exciton signatures in polariton spectra of 2D materials,"Dark excitons in transition metal dichalcogenides (TMD) have been so far
neglected in the context of polariton physics due to their lack of oscillator
strength. However, in tungsten-based TMDs, dark excitons are known to be the
energetically lowest states and could thus provide important scattering
partners for polaritons. In this joint theory-experiment work, we investigate
the impact of the full exciton energy landscape on polariton absorption and
reflectance. By changing the cavity detuning, we vary the polariton energy
relative to the unaffected dark excitons in such a way that we open or close
specific phonon-driven scattering channels. We demonstrate both in theory and
experiment that this controlled switching of scattering channels manifests in
characteristic sharp changes in optical spectra of polaritons. These spectral
features can be exploited to extract the position of dark excitons. Our work
suggests new possibilities for exploiting polaritons for fingerprinting
nanomaterials via their unique exciton landscape.",2401.04588v1
2024-01-10,Electrical Non-Hermitian Control of Topological Magnon Spin Transport,"Magnonic topological phases realize chiral edge spin waves that are protected
against backscattering, potentially enabling highly efficient spin transport.
Here we show that the spin transport through these magnonic chiral edge states
can be electrically manipulated by non-Hermitian control. We consider the
paradigmatic magnon Haldane model and show that it is transformed into an
effective non-Hermitian magnon Chern insulator by including a
sublattice-dependent spin-orbit torque. In linear spin-wave theory, this
electrically induced torque causes a lasing of the chiral edge magnons along
certain edge directions, leading to an enhancement of the spin-wave amplitude.
This prediction is confirmed by numerical simulations based on the
Landau-Lifshitz-Gilbert equation. For a spin-wave transport setup, in which
magnons are excited by a microwave field and detected with a normal metal
conductor, we find that the magnon amplification is remarkably robust against
disorder, establishing non-Hermitian control as a promising avenue for
topological magnonics.",2401.04967v2
2024-01-24,The Dynamics of (Not) Unfollowing Misinformation Spreaders,"Many studies explore how people 'come into' misinformation exposure. But much
less is known about how people 'come out of' misinformation exposure. Do people
organically sever ties to misinformation spreaders? And what predicts doing so?
Over six months, we tracked the frequency and predictors of ~900K followers
unfollowing ~5K health misinformation spreaders on Twitter. We found that
misinformation ties are persistent. Monthly unfollowing rates are just 0.52%.
In other words, 99.5% of misinformation ties persist each month. Users are also
31% more likely to unfollow non-misinformation spreaders than they are to
unfollow misinformation spreaders. Although generally infrequent, the factors
most associated with unfollowing misinformation spreaders are (1) redundancy
and (2) ideology. First, users initially following many spreaders, or who
follow spreaders that tweet often, are most likely to unfollow later. Second,
liberals are more likely to unfollow than conservatives. Overall, we observe a
strong persistence of misinformation ties. The fact that users rarely unfollow
misinformation spreaders suggests a need for external nudges and the importance
of preventing exposure from arising in the first place.",2401.13480v2
2024-01-29,FPGA Technology Mapping Using Sketch-Guided Program Synthesis,"FPGA technology mapping is the process of implementing a hardware design
expressed in high-level HDL (hardware design language) code using the
low-level, architecture-specific primitives of the target FPGA. As FPGAs become
increasingly heterogeneous, achieving high performance requires hardware
synthesis tools that better support mapping to complex, highly configurable
primitives like digital signal processors (DSPs). Current tools support DSP
mapping via handwritten special-case mapping rules, which are laborious to
write, error-prone, and often overlook mapping opportunities. We introduce
Lakeroad, a principled approach to technology mapping via sketch-guided program
synthesis. Lakeroad leverages two techniques -- architecture-independent sketch
templates and semantics extraction from HDL -- to provide extensible technology
mapping with stronger correctness guarantees and higher coverage of mapping
opportunities than state-of-the-art tools. Across representative
microbenchmarks, Lakeroad produces 2--3.5$\times$ the number of optimal
mappings compared to proprietary state-of-the-art tools and 6--44$\times$ the
number of optimal mappings compared to popular open-source tools, while also
providing correctness guarantees not given by any other tool.",2401.16526v1
2024-02-05,Cybersickness Detection through Head Movement Patterns: A Promising Approach,"Despite the widespread adoption of Virtual Reality (VR) technology,
cybersickness remains a barrier for some users. This research investigates head
movement patterns as a novel physiological marker for cybersickness detection.
Unlike traditional markers, head movements provide a continuous, non-invasive
measure that can be easily captured through the sensors embedded in all
commercial VR headsets. We used a publicly available dataset from a VR
experiment involving 75 participants and analyzed head movements across six
axes. An extensive feature extraction process was then performed on the head
movement dataset and its derivatives, including velocity, acceleration, and
jerk. Three categories of features were extracted, encompassing statistical,
temporal, and spectral features. Subsequently, we employed the Recursive
Feature Elimination method to select the most important and effective features.
In a series of experiments, we trained a variety of machine learning
algorithms. The results demonstrate a 76% accuracy and 83% precision in
predicting cybersickness in the subjects based on the head movements. This
study contribution to the cybersickness literature lies in offering a
preliminary analysis of a new source of data and providing insight into the
relationship of head movements and cybersickness.",2402.02725v2
2024-02-05,Bifurcation to complex dynamics in largely modulated voltage-controlled parametric oscillator,"An experimental demonstration of a parametric oscillation of a magnetization
in a ferromagnet was performed recently by applying a microwave voltage,
indicating the potential to be applied in a switching method in non-volatile
memories. In the previous works, the modulation of a perpendicular magnetic
anisotropy field produced by the microwave voltage was small compared with an
external magnetic field pointing in an in-plane direction. A recent trend is,
however, opposite, where an efficiency of the voltage controlled magnetic
anisotropy (VCMA) effect is increased significantly by material research and
thus, the modulated magnetic anisotropy field can be larger than the external
magnetic field. Here, we solved the Landau-Lifshitz-Gilbert equation
numerically and investigated the magnetization dynamics driven under a wide
range of the microwave VCMA effect. We evaluated bifurcation diagrams, which
summarize local maxima of the magnetization dynamics. For low modulation
amplitudes, the local maximum is a single point because the dynamics is the
periodic parametric oscillation. The bifurcation diagrams show distributions of
the local maxima when the microwave magnetic anisotropy field becomes larger
than the external magnetic field. The appearance of this broadened distribution
indicates complex dynamics such as chaotic and transient-chaotic behaviors,
which were confirmed from an analysis of temporal dynamics.",2402.02742v1
2024-02-12,Gravitational Lensing of Galaxy Clustering,"We investigate lensing reconstruction using the clustered galaxy distribution
as a source field, using both the traditional cosmic microwave background
quadratic estimator and a shear-only estimator. We calculate the expected
signal-to-noise ratio of the cross power spectrum of such reconstructions with
cosmic shear measurements for an LSST-like galaxy survey. Modeling the galaxy
field as a Gaussian random field, we find that there is substantial clustering
signal in the source field at angular scales substantially smaller than those
typically used by CMB reconstructions. The expected signal-to-noise for
cross-correlations in LSST from cosmic shear is $\sim$60 in the presence of
shape noise, while cross correlating with a sample-variance limited mass map
would have signal-to-noise in the hundreds. This type of cross-correlation
could be used as a way to identify systematic errors in lensing studies and is
just one example of many possible higher order correlations in galaxy surveys
that may contain substantial cosmological information.",2402.07988v1
2024-03-05,Spintronic Implementation of UNet for Image Segmentation,"Image segmentation plays a crucial role in computer vision applications like
self-driving cars, satellite imagery analysis, and medical diagnosis.
Implementing these complex deep neural networks on conventional hardware is
highly inefficient. In this work, we propose hardware implementation of UNet
for segmentation tasks, using spintronic devices. Our approach involves
designing hardware for convolution, deconvolution, ReLU, and max pooling layers
of the UNet architecture. We demonstrate the synaptic behavior of the domain
wall MTJ, and design convolution and deconvolution layers using the domain
wall-based crossbar array. We utilize the orthogonal current injected MTJ with
its continuous resistance change and showcase the ReLU and max pooling
functions. We employ a hybrid simulation setup by coupling micromagnetic
simulation, non-equilibrium Green's function,
Landau-Lifshitz-Gilbert-Slonczewski equations, and circuit simulation with
Python programming to incorporate the diverse physics of spin-transport,
magnetization dynamics, and CMOS elements in our proposed designs. We evaluate
our UNet design on the CamVid dataset and achieve segmentation accuracies that
are comparable to software implementation. During training, our design consumes
43.59pJ of energy for synaptic weight updates.",2403.02863v1
2024-03-06,A Survey on Adversarial Contention Resolution,"Contention resolution addresses the challenge of coordinating access by
multiple processes to a shared resource such as memory, disk storage, or a
communication channel. Originally spurred by challenges in database systems and
bus networks, contention resolution has endured as an important abstraction for
resource sharing, despite decades of technological change. Here, we survey the
literature on resolving worst-case contention, where the number of processes
and the time at which each process may start seeking access to the resource is
dictated by an adversary. We highlight the evolution of contention resolution,
where new concerns -- such as security, quality of service, and energy
efficiency -- are motivated by modern systems. These efforts have yielded
insights into the limits of randomized and deterministic approaches, as well as
the impact of different model assumptions such as global clock synchronization,
knowledge of the number of processors, feedback from access attempts, and
attacks on the availability of the shared resource.",2403.03876v1
2024-03-01,Sketching the Heat Kernel: Using Gaussian Processes to Embed Data,"This paper introduces a novel, non-deterministic method for embedding data in
low-dimensional Euclidean space based on computing realizations of a Gaussian
process depending on the geometry of the data. This type of embedding first
appeared in (Adler et al, 2018) as a theoretical model for a generic manifold
in high dimensions.
  In particular, we take the covariance function of the Gaussian process to be
the heat kernel, and computing the embedding amounts to sketching a matrix
representing the heat kernel. The Karhunen-Lo\`eve expansion reveals that the
straight-line distances in the embedding approximate the diffusion distance in
a probabilistic sense, avoiding the need for sharp cutoffs and maintaining some
of the smaller-scale structure.
  Our method demonstrates further advantage in its robustness to outliers. We
justify the approach with both theory and experiments.",2403.07929v1
2024-03-27,PLOT-TAL -- Prompt Learning with Optimal Transport for Few-Shot Temporal Action Localization,"This paper introduces a novel approach to temporal action localization (TAL)
in few-shot learning. Our work addresses the inherent limitations of
conventional single-prompt learning methods that often lead to overfitting due
to the inability to generalize across varying contexts in real-world videos.
Recognizing the diversity of camera views, backgrounds, and objects in videos,
we propose a multi-prompt learning framework enhanced with optimal transport.
This design allows the model to learn a set of diverse prompts for each action,
capturing general characteristics more effectively and distributing the
representation to mitigate the risk of overfitting. Furthermore, by employing
optimal transport theory, we efficiently align these prompts with action
features, optimizing for a comprehensive representation that adapts to the
multifaceted nature of video data. Our experiments demonstrate significant
improvements in action localization accuracy and robustness in few-shot
settings on the standard challenging datasets of THUMOS-14 and EpicKitchens100,
highlighting the efficacy of our multi-prompt optimal transport approach in
overcoming the challenges of conventional few-shot TAL methods.",2403.18915v1
2024-04-02,Exploring Spin Polarization of Heavy Quarks in Magnetic Fields and Hot Medium,"Relativistic heavy-ion collisions give rise to the formation of both
deconfined QCD matter and a strong magnetic field. The spin of heavy quarks is
influenced by interactions with the external magnetic field as well as by
random scatterings with thermal light partons. The presence of QCD matter
comprising charged quarks can extend the lifetime and strength of the magnetic
field, thereby enhancing the degree of heavy quark polarization. However, the
random scatterings with QCD matter tend to diminish heavy quark polarization.
In this study, we utilize the Landau-Lifshitz-Gilbert (LLG) equation to
investigate both these contributions. Taking into account the realistic
evolutions of medium temperatures and the in-medium magnetic fields at the
Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC), we
observe that heavy quark polarization is limited by the short lifetime of the
magnetic field and the high temperatures of the medium. Furthermore, we explore
the mass dependence of quark polarization, revealing that the polarization
degree of strange quarks is much larger than that of charm quarks.",2404.02032v1
1996-05-06,A Keck HIRES Investigation of the Metal Abundances and Kinematics of Three Damped Lya Systems Toward Q2206-199,"We present high resolution, high SNR spectra of the QSO Q2206-199 obtained
with HIRES on the 10m W.M. Keck Telescope. Our analysis focuses on the two
previously identified damped \lya systems found at $z=1.920$ and $z=2.076$. For
each system, we measure accurate abundances. The $z=1.920$ system exhibits the
highest metallicity we have measured for a damped \lya system. We report the
first confident ($>5 \sigma$) detection of Ti in a QSO absorption line system.
By contrast the $z=2.076$ system is the most metal poor we have analyzed,
showing absorption features for only the strongest transitions. We find no
positive evidence for the presence of dust in either system. The two damped
systems exhibit significantly different kinematic characteristics, yet we
contend the two systems are consistent with one physical description: that of a
thick, rotating disk.
  We investigate a very strong Mg II system at $z=0.752$ which is very likely
yet a third damped \lya system. The very weak Mn II and Ti II transitions have
been positively measured and imply $\log \N{HI} > 19.0$. We analyze the
abundance ratios [Mn/Fe] and [Ti/Fe] and their values are inconsistent with
dust depletion, yet consistent with the abundance pattern detected for halo
stars in the Galaxy (see Lu et al. 1996a).
  Finally, we identify a C IV system at $z=2.014$ that shows a very narrow
feature in Si IV and C IV absorption. The corresponding $b$ values (5.5 \kms
and 8.9 \kms for Si IV and C IV) for this component suggest a temperature of
$4.7 \sci{4} \rm K$. Because collisional ionization can explain the observed
abundances only for $T > 8 \sci{4} \rm K$, we contend these ions must have
formed through a different physical process (e.g. photoionization).",9605021v2
1996-09-09,The Population of Damped Lyman-alpha and Lyman Limit Systems in the Cold Dark Matter Model,"Lyman limit and damped Lyman-alpha absorption systems probe the distribution
of collapsed, cold gas at high redshift. Numerical simulations that incorporate
gravity and gas dynamics can predict the abundance of such absorbers in
cosmological models. We develop a semi-analytical method to correct the
numerical predictions for the contribution of unresolved low mass halos, and we
apply this method to the Katz et al. (1996) simulation of the standard cold
dark matter model ($\Omega=1$, $h=0.5$, $\Omega_b=0.05$, $\sigma_8=0.7$). Using
this simulation and higher resolution simulations of individual low mass
systems, we determine the relation between a halo's circular velocity $v_c$ and
its cross section for producing Lyman limit or damped absorption. We combine
this relation with the Press-Schechter formula for the abundance of halos to
compute the number of absorbers per unit redshift. The resolution correction
increases the predicted abundances by about a factor of two at z=2, 3, and 4,
bringing the predicted number of damped absorbers into quite good agreement
with observations. Roughly half of the systems reside in halos with circular
velocities $v_c>100\kms$ and half in halos with $35\kms<v_c<100\kms$. Halos
with $v_c>150\kms$ typically harbor two or more systems capable of producing
damped absorption. Even with the resolution correction, the predicted abundance
of Lyman limit systems is a factor of three below observational estimates,
signifying either a failure of standard CDM or a failure of these simulations
to resolve the systems responsible for most Lyman limit absorption. By
comparing simulations with and without star formation, we find that depletion
of the gas supply by star formation affects absorption line statistics at
$z>=2$ only for column densities exceeding $N_{HI}=10^{22} cm^{-2}$.",9609072v1
1998-05-22,Protogalactic Disk Models of Damped Lya Kinematics,"We present new observational results on the kinematics of the damped lya
systems. Our full sample is now comprised of 31 low-ion profiles and exhibits
similar characteristics to the sample from Paper I. The primary exception is
that the new distribution of velocity widths includes values out to a maximum
of nearly 300 km/s, approx 100 km/s greater than the previous maximum. These
high velocity width systems will significantly leverage models introduced to
explain the damped lya systems. Comparing the characteristics from low-redshift
and high-redshift sub-samples, we find no evidence for significant evolution in
the kinematic properties of protogalaxies from z = 2.0 - 3.3.
  The new observations give greater statistical significance to the main
conclusions of our first paper. In particular, those models inconsistent with
the damped lya observations in Paper I are ruled out at even higher levels of
confidence. At the same time, the observations are consistent with a population
of rapidly rotating, thick disks (the TRD model) at high redshift.
  Buoyed by the success of the TRD model, we investigate it more closely by
considering more realistic disk properties. Our goal is to demonstrate the
statistical power of the damped lya observations by investigating the
robustness of the TRD model. In particular, we study the effects of warping,
realistic rotation curves, and photoionization on the kinematics of disks in
the TRD model. The principal results are: (1) disk warping has only minimal
effect on the kinematic results, primarily influencing the effective disk
thickness, (2) the TRD model is robust to more realistic rotation curves; (3)
the effects of photoionization require thicker disks to give consistent
velocity width distributions. [abridged]",9805293v1
2000-05-05,UVES observations of QSO 0000-2620: oxygen and zinc abundances in the Damped Ly-alpha galaxy at z_abs=3.3901,"Observations of the QSO 0000-2620 with UVES spectrograph at the 8.2m ESO
KUEYEN telescope are used for abundance analysis of the damped Ly-alpha system
at z_{abs}=3.3901. Several Oxygen lines are identified in the Ly_alpha forest
and a measure for the oxygen abundance is obtained at [O/H]=-1.85 +/- 0.1 by
means of the unsaturated OI 925 A and OI 950 A lines. This represents the most
accurate O measurement in a damped Ly_alpha galaxy so far. We have also
detected ZnII 2026 A and CrII 2056, 2062 A redshifted at about 8900 A and found
abundances [Zn/H] = -2.07 +/- 0.1 and [Cr/H]=-1.99 +/- 0.1. Furthermore,
previous measurements of Fe, Si, Ni and N have been refined yielding
[Fe/H]=-2.04 +/- 0.1, [Si/H]=-1.90 +/- 0.1, [Ni/H]=-2.27 +/- 0.1, and
[N/H]=-2.68 +/- 0.1. The abundance of the non-refractory element zinc is the
lowest among the damped Ly-alpha systems showing that the associated
intervening galaxy is indeed in the early stages of its chemical evolution. The
fact that the Zn abundance is identical to that of the refractory elements Fe
and Cr suggests that dust grains have not formed yet. In this Damped Ly-alpha
system the observed [O,S,Si/Zn,Fe,Cr] ratios, in whatever combination are
taken, are close to solar (i.e 0.1-0.2 dex) and do not show the
[alpha-element/Fe] enhancement observed in Milky Way stars of comparable
metallicity. The observed behavior supports a galaxy evolution model
characterized by either episodic or low star formation rate rather than a
Milky-Way-type evolutionary model.",0005098v1
2002-02-06,The UCSD HIRES/KeckI Damped Lya Abundance Database III. An Empirical Study of Photoionization in the Damped Lya System Toward GB1759+7539,"We investigate the ionization state of the damped Lya system at z=2.62 toward
GB1759+7539 through an analysis of ionic ratios sensitive to photoionization:
ArI/SII, FeIII/FeII, NII/NI, AlIII/AlII. Approximately half of the metals arise
in a mostly neutral velocity component with HI/H > 0.9, based on FeIII/FeII <
0.013. In contrast, the remaining half exhibits FeIII/FeII~0.3 indicative of a
partially ionized medium with HI/H~0.5. These conclusions are supported by the
observed NII/NI, AlIII/AlII, and ArI/SII ratios.
  We assess ionization corrections for the observed column densities through
photoionization models derived from the CLOUDY software package. In the neutral
gas, the ionization corrections are negligible except for ArI. However for the
partially ionized gas, element abundance ratios differ from the ionic ratios by
0.1-0.3 dex for (SiII, SII, NiII, AlII)/FeII ratios and more for (NI,
ArI)/FeII. Independent of the shape of the photoionizing spectrum and
assumptions on the number of ionization phases, these ionization corrections
have minimal impact (<0.1dex) on the total metallicity inferred for this damped
Lya system. Measurements on the relative elemental abundances of the partially
ionized gas, however, have a greater than ~0.15 dex uncertainty which hides the
effects of nucleosynthesis and dust depletion.
  We caution the reader that this damped system is unusual for a number of
reasons (e.g. a very low ArI/SII ratio) and we believe its ionization
properties are special but not unique. Nevertheless, it clearly shows the value
of examining photoionization diagnostics like FeIII/FeII in a larger sample of
systems.",0202140v1
2009-09-26,Damped and sub-damped Lyman-? absorbers in z > 4 QSOs,"We present the results of a survey for damped (DLA, log N(H I) > 20.3) and
sub-damped Lyman-? systems (19.5 < log N(H I) < 20.3) at z > 2.55 along the
lines-of-sight to 77 quasars with emission redshifts in the range 4 < zem <
6.3. Intermediate resolution (R ? 4300) spectra have been obtained with the
Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total
of 100 systems with log N(H I) > 19.5 are detected of which 40 systems are
damped Lyman-? systems for an absorption length of ?X = 378. About half of the
lines of sight of this homogeneous survey have never been investigated for
DLAs. We study the evolution with redshift of the cosmological density of the
neutral gas and find, consis- tently with previous studies at similar
resolution, that ?DLA,H I decreases at z > 3.5. The overall cosmological
evolution of ?HI shows a peak around this redshift. The H I column density
distribution for log N(H I) ? 20.3 is ?tted, consistently with previous
surveys, with a single power-law of index ? ? -1.8$\pm$0.25. This power-law
overpredicts data at the high-end and a second, much steeper, power-law (or a
gamma function) is needed. There is a flattening of the function at lower H I
column densities with an index of ? ? ?1.4 for the column density range log N(H
I) = 19.5?21. The fraction of H I mass in sub-DLAs is of the order of 30%. The
H column density distribution does not evolve strongly from z ? 2.5 to z ? 4.5.",0909.4839v2
2009-10-28,Nonlinear envelope equation and nonlinear Landau damping rate for a driven electron plasma wave,"In this paper, we provide a theoretical description, and calculate, the
nonlinear frequency shift, group velocity and collionless damping rate, $\nu$,
of a driven electron plasma wave (EPW). All these quantities, whose physical
content will be discussed, are identified as terms of an envelope equation
allowing one to predict how efficiently an EPW may be externally driven. This
envelope equation is derived directly from Gauss law and from the investigation
of the nonlinear electron motion, provided that the time and space rates of
variation of the EPW amplitude, $E_p$, are small compared to the plasma
frequency or the inverse of the Debye length. $\nu$ arises within the EPW
envelope equation as more complicated an operator than a plain damping rate,
and may only be viewed as such because $(\nu E_p)/E_p$ remains nearly constant
before abruptly dropping to zero. We provide a practical analytic formula for
$\nu$ and show, without resorting to complex contour deformation, that in the
limit $E_p \to 0$, $\nu$ is nothing but the Landau damping rate. We then term
$\nu$ the ""nonlinear Landau damping rate"" of the driven plasma wave. As for the
nonlinear frequency shift of the EPW, it is also derived theoretically and
found to assume values significantly different from previously published ones,
assuming that the wave is freely propagating. Moreover, we find no limitation
in $k \lambda_D$, $k$ being the plasma wavenumber and $\lambda_D$ the Debye
length, for a solution to the dispertion relation to exist, and want to stress
here the importance of specifying how an EPW is generated to discuss its
properties. Our theoretical predictions are in excellent agreement with results
inferred from Vlasov simulations of stimulated Raman scattering (SRS), and an
application of our theory to the study of SRS is presented.",0910.5289v1
2011-05-19,"Tidal dissipation compared to seismic dissipation: in small bodies, in earths, and in superearths","While the seismic quality factor and phase lag are defined solely by the bulk
properties of the mantle, their tidal counterparts are determined both by the
bulk properties and self-gravitation of a body as a whole. For a qualitative
estimate, we model the body with a homogeneous sphere and express the tidal
phase lag through the lag in a sample of material. Although simplistic, our
model is sufficient to understand that the lags are not identical. The
difference emerges because self-gravitation pulls the tidal bulge down. At low
frequencies, this reduces strain and makes tidal damping less efficient in
larger bodies. At high frequencies, competition between self-gravitation and
rheology becomes more complex, though for sufficiently large superearths the
same rule works: the larger the body, the weaker tidal damping in it. Being
negligible for small terrestrial planets and moons, the difference between the
seismic and tidal lagging (and likewise between the seismic and tidal damping)
becomes very considerable for superearths. In those, it is much lower than what
one might expect from using a seismic quality factor. The tidal damping rate
deviates from the seismic damping rate especially in the zero-frequency limit,
and this difference takes place for bodies of any size. So the equal in
magnitude but opposite in sign tidal torques, exerted on one another by the
primary and the secondary, go smoothly through zero as the secondary crosses
the synchronous orbit. We describe the mantle rheology with the Andrade model,
allowing it to lean towards the Maxwell model at the lowest frequencies. To
implement this additional flexibility, we reformulate the Andrade model by
endowing it with a free parameter which is the ratio of the anelastic timescale
to the viscoelastic Maxwell time of the mantle. Some uncertainty in this
parameter's frequency-dependence does not influence our principal conclusions.",1105.3936v12
2014-10-07,The Effect of Nonlinear Landau Damping on Ultrarelativistic Beam Plasma Instabilities,"Very-high energy gamma-rays from extragalactic sources pair-produce off of
the extragalactic background light, yielding an electron-positron pair beam.
This pair beam is unstable to various plasma instabilities, especially the
""oblique"" instability, which can be the dominant cooling mechanism for the
beam. However, recently, it has been claimed that nonlinear Landau damping
renders it physically irrelevant by reducing the effective damping rate to a
low level. Here, we show with numerical calculations that the effective damping
rate is $8\times 10^{-4}$ of the growth rate of the linear instability, which
is sufficient for the ""oblique"" instability to be the dominant cooling
mechanism of these pair beams. In particular, we show that previous estimates
of this rate ignored the exponential cutoff in the scattering amplitude at
large wavenumber and assumed that the damping of scattered waves entirely
depends on collisions, ignoring collisionless processes. We find that the total
wave energy eventually grows to approximate equipartition with the beam by
increasingly depositing energy into long wavelength modes. As we have not
included the effect of nonlinear wave-wave interactions on these long
wavelength modes, this scenario represents the ""worst-case"" scenario for the
oblique instability. As it continues to drain energy from the beam at a faster
rate than other processes, we conclude that the ""oblique"" instability is
sufficiently strong to make it the physically dominant cooling mechanism for
high-energy pair beams in the intergalactic medium.",1410.3797v2
2014-10-17,Hunting down systematics in baryon acoustic oscillations after cosmic high noon,"Future dark energy experiments will require better and more accurate
theoretical predictions for the baryonic acoustic oscillations (BAO) signature
in the spectrum of cosmological perturbations. Here, we use large N-body
simulations of the \LambdaCDM Planck cosmology to study any possible systematic
shifts and damping in BAO due to the impact of nonlinear gravitational growth
of structure, scale dependent and non-local bias, and redshift-space
distortions. The effect of cosmic variance is largely reduced by dividing the
tracer power spectrum by that from a BAO-free simulation starting with the same
phases. This permits us to study with unprecedented accuracy (better than 0.02%
for dark matter and 0.07% for low-bias halos) small shifts of the pristine BAO
wavenumbers towards larger k, and non-linear damping of BAO wiggles in the
power spectrum of dark matter and halo populations in the redshift range z=0-1.
For dark matter, we provide an accurate parametrization of the evolution of
\alpha as a function of the linear growth factor D(z). For halo samples, with
bias ranging from 1.2 to 2.8, we measure a typical BAO shift of ~0.25%,
observed in real-space, which does not show an appreciable evolution with
redshift within the uncertainties. Moreover, we report a constant shift as a
function of halo bias. We find a different evolution of the damping of the
acoustic feature in all halo samples as compared to dark matter with haloes
suffering less damping, and also find some weak dependence on bias. A larger
BAO shift and damping is measured in redshift-space which can be well explained
by linear theory due to redshift-space distortions. A clear modulation in phase
with the acoustic scale is observed in the scale-dependent halo bias due to the
presence of the baryonic acoustic oscillations.",1410.4684v2
2017-01-24,Influence of interlayer coupling on the spin torque driven excitations in a spin torque oscillator,"The influence of dynamic interlayer interactions on the spin torque driven
and damped excitations are illustrated for a three layer macrospin model system
that corresponds to a standard spin-torque oscillator. The free layer and a
synthetic antiferromagnetic (SyF) pinned layer of the spin-torque oscillator
are in-plane magnetized. In order to understand experimental results, numerical
simulations have been performed considering three types of interlayer
interactions: exchange interaction between the two magnetic layers of the SyF,
mutual spin torque between the top layer of the SyF and the free layer and
dipolar interaction between all three magnetic layers. It will be shown that
the dynamic dipolar coupling plays a predominant role. First, it leads to a
hybridization of the free layer and the SyF linear modes and through this gives
rise to a strong field dependence of the critical current. In particular, there
is a field range of enhanced damping in which much higher current is required
to drive the modes into steady state. This results in a gap in the excitation
spectrum. Second, the dynamic dipolar interaction is also responsible for the
non-linear interaction between the current driven steady state mode and the
damped modes of the system. Here one can distinguish: (i) a resonant
interaction that leads to a kink in the frequency-field and frequency-current
dispersions accompanied by a small hysteresis and a reduction of the linewidth
of the steady state mode and (ii) a non-resonant interaction that leads to a
strong frequency redshift of the damped mode. The results underline the strong
impact of interlayer coupling on the excitation spectra of spin-torque
oscillators and illustrate in a simple three mode model system how in the
non-linear regime the steady state and damped modes influence each other.",1701.06787v1
2017-04-07,Global Alfven Eigenmodes in the H-1 heliac,"Recent upgrades in H-1 power supplies have enabled the operation of the H-1
experiment at higher heating powers than previously attainable. A heating power
scan in mixed hydrogen/helium plasmas reveals a change in mode activity with
increasing heating power. At low power (<50 kW) modes with beta-induced Alfven
eigenmode (BAE) frequency scaling are observed. At higher power modes
consistent with an analysis of nonconventional Global Alfven Eigenmodes (GAEs)
are observed, the subject of this work. We have computed the mode continuum,
and identified GAE structures using the ideal MHD solver CKA and the
gyrokinetic code EUTERPE. An analytic model for ICRH-heated minority ions is
used to estimate the fast ion temperature from the hydrogen species. Linear
growth rate scans using a local flux surface stability calculation, LGRO, are
performed. These studies demonstrate growth from circulating particles whose
speed is significantly less than the Alfven speed, and are resonant with the
mode through harmonics of the Fourier decomposition of the strongly-shaped
heliac magnetic field. They reveal drive is possible with a small, hot
energetic tail of the hydrogen species. Local linear growth rate scans are also
complemented with global calculations from CKA and EUTERPE. These qualitatively
confirm the findings from the LGRO study, and show that the inclusion of finite
Larmor radius effects can reduce the growth rate by a factor of three, but do
not affect marginal stability. Finally, a study of damping of the global mode
with the thermal plasma is conducted, computing continuum, and the damping
arising from parallel electric fields. We find that continuum damping is of
order 0.1% for the configuration studied. The inclusion of resistivity lifts
the damping to 19%. Such large damping is consistent with experimental
observations that in absence of drive the mode decays rapidly (~0.1 ms).",1704.02089v1
2017-11-30,Scalar dark matter interpretation of the DAMPE data with U(1) gauge interactions,"Recently, DAMPE experiment released the new measurement of the total cosmic
$e^+e^-$ flux between 25 GeV and 4.6 TeV which indicates a spectral softening
at around 0.9 TeV and a tentative peak at around 1.4 TeV. We utilize the scalar
dark matter (DM) annihilation scenario to explain the DAMPE peak by extending
$G_{SM}\equiv SU(3)_C \times SU(2)_L \times U(1)_Y$ with additional $U(1)$
gauge symmetries while keeping anomaly free to generate $\chi \chi \to Z^\prime
Z^\prime \to \ell\bar{\ell}\ell^\prime\overline{\ell^\prime}$, where $\chi,
Z^\prime, \ell^{(^\prime)}$ denote the scalar DM, the new gauge boson and
$\ell^{(^\prime)}=e,\mu,\tau$, respectively, with $m_\chi \sim m_{Z^\prime}
\sim 2 \times 1.5$ (TeV). We first illustrate that the minimal framework
$G_{SM} \times U(1)_{Y^\prime}$ with the above mass choices can explain the
DAMPE excess but has been excluded by LHC constraints from the $Z^\prime$
searches. Then we study a non-minimal framework $G_{SM} \times U(1)_{Y^\prime}
\times U(1)_{Y^{\prime \prime}}$ in which $U(1)_{Y^{\prime \prime}}$ mixes with
$U(1)_{Y^\prime}$. We show that such a framework can interpret the DAMPE data
while passing other constraints including the DM relic abundance, DM direct
detection and collider bounds. We also investigate the predicted $e^+e^-$
spectrum in this framework and find that the mass splitting $\Delta m = m_\chi
- m_{Z'}$ should be less than about 17 GeV to produce the peak-like structure.",1711.11452v2
2017-12-14,Scalar dark matter explanation of the DAMPE data in the minimal Left-Right symmetric model,"Left-Right symmetric model (LRSM) has been an attractive extension of the
Standard Model (SM) which can address the origin of parity violation in the SM
electroweak (EW) interactions, generate tiny neutrino masses, accommodate dark
matter (DM) candidates and provide a natural framework for baryogenesis through
leptogenesis. In this work we utilize the minimal LRSM to study the recently
reported DAMPE results of cosmic $e^+e^-$ spectrum which exhibits a tentative
peak around 1.4 TeV, while satisfying the current neutrino data. We propose to
explain the DAMPE peak with a complex scalar DM $\chi$ in two scenarios: 1)
$\chi\chi^* \to H_1^{++}H_1^{--} \to \ell_i^+\ell_i^+\ell_j^-\ell_j^-$; 2)
$\chi\chi^* \to H_{k}^{++}H_{k}^{--} \to \ell_i^+\ell_i^+\ell_j^-\ell_j^-$
accompanied by $\chi\chi^* \to H_1^+ H_1^- \to \ell_i^+ \nu_{\ell_i} \ell_j^-
\nu_{\ell_j}$ with $\ell_{i,j}=e,\mu,\tau$ and $k=1,2$. We fit the theoretical
prediction on $e^+e^-$ spectrum to relevant experimental data to determine the
scalar mass spectrum favored by the DAMPE excess. We also consider various
constraints from theoretical principles, collider experiments as well as DM
relic density and direct search experiments. We find that there are ample
parameter space which can interpret the DAMPE data while passing the
constraints. Our explanations, on the other hand, usually imply the existence
of other new physics at the energy scale ranging from $10^7 {\rm GeV}$ to
$10^{11} {\rm GeV}$. Collider tests of our explanations are also discussed.",1712.05351v3
2018-02-20,The chemical connection between damped Lyman-α systems and Local Group dwarf galaxies,"Abundances of the volatile elements S and Zn have now been measured in around
80 individual stars in the Sculptor dwarf spheroidal galaxy, covering the
metallicity range $-2.4\leq\text{[Fe/H]}\leq-0.9$. These two elements are of
particular interest as they are not depleted onto dust in gas, and their ratio,
[S/Zn], has thus commonly been used as a proxy for [$\alpha$/Fe] in Damped
Lyman-$\alpha$ systems. The S abundances in Sculptor are similar to other
$\alpha$-elements in this galaxy, consistent with S being mainly created in
core-collapse supernovae, but also having some contribution from supernovae
Type Ia. However, our results show that Zn and Fe do not trace all the same
nucleosynthetic production channels. In particular, (contrary to Fe) Zn is not
significantly produced by supernovae Type Ia. Thus, [S/Zn] cannot be reliably
used as a proxy for [$\alpha$/Fe]. We propose [O/S] as a function of [S/H] as a
possible alternative. At higher metallicities, the values of [S/Zn] measured in
Damped Lyman-$\alpha$ systems are inconsistent with those in local dwarf
galaxies, and are more compatible with the Milky Way disk. Low-metallicity
Damped Lyman-$\alpha$ systems are, however, consistent with the most metal-poor
stars in Local Group dwarf spheroidal galaxies. Assuming that the dust
depletions of S and Zn are negligible, our comparison indicates that the star
formation histories of Damped Lyman-$\alpha$ systems are on average different
from both the Milky Way and the Sculptor dwarf spheroidal galaxy.",1802.07325v5
2019-01-12,GW170817 implications on the frequency and damping time of f-mode oscillations of neutron stars,"Within a minimum model for neutron stars consisting of nucleons, electrons
and muons at $\beta$-equilibrium using about a dozen Equation of States (EOSs)
from microscopic nuclear many-body theories and 40,000 EOSs randomly generated
using an explicitly isospin-dependent parametric EOS model for high-density
neutron-rich nucleonic matter within its currently known uncertainty range, we
study correlations among the f-mode frequency, its damping time and the tidal
deformability as well as the compactness of neutron stars. Except for quark
stars, both the f-mode frequency and damping time of canonical neutron stars
are found to scale with the tidal deformability independent of the EOSs used.
Applying the constraint on the tidal deformability of canonical neutron stars
$\Lambda_{1.4}=190^{+390}_{-120}$ extracted by the LIGO+VIRGO Collaborations
from their improved analyses of the GW170817 event, the f-mode frequency and
its damping time of canonical neutron stars are limited to 1.67 kHz - 2.18 kHz
and 0.155 s - 0.255 s, respectively, providing a useful guidance for the
ongoing search for gravitational waves from the f-mode oscillations of isolated
neutron stars. Moreover, assuming either or both the f-mode frequency and its
damping time will be measured precisely in future observations with advanced
gravitational wave detectors, we discuss how information about the mass and/or
radius as well as the still rather elusive nuclear symmetry energies at
supra-saturation densities may be extracted.",1901.03779v2
2019-01-27,"An introductory guide to fluid models with anisotropic temperatures Part 2 -- Kinetic theory, Padé approximants and Landau fluid closures","In Part 2 of our guide to collisionless fluid models, we concentrate on
Landau fluid closures. These closures were pioneered by Hammett and Perkins and
allow for the rigorous incorporation of collisionless Landau damping into a
fluid framework. It is Landau damping that sharply separates traditional fluid
models and collisionless kinetic theory, and is the main reason why the usual
fluid models do not converge to the kinetic description, even in the
long-wavelength low-frequency limit. We start with a brief introduction to
kinetic theory, where we discuss in detail the plasma dispersion function
$Z(\zeta)$, and the associated plasma response function $R(\zeta)=1+\zeta
Z(\zeta)=-Z'(\zeta)/2$. We then consider a 1D (electrostatic) geometry and make
a significant effort to map all possible Landau fluid closures that can be
constructed at the 4th-order moment level. These closures for parallel moments
have general validity from the largest astrophysical scales down to the Debye
length, and we verify their validity by considering examples of the (proton and
electron) Landau damping of the ion-acoustic mode, and the electron Landau
damping of the Langmuir mode. We proceed by considering 1D closures at
higher-order moments than the 4th-order, and as was concluded in Part 1, this
is not possible without Landau fluid closures. We show that it is possible to
reproduce linear Landau damping in the fluid framework to any desired
precision, thus showing the convergence of the fluid and collisionless kinetic
descriptions. We then consider a 3D (electromagnetic) geometry in the
gyrotropic (long-wavelength low-frequency) limit and map all closures that are
available at the 4th-order moment level. In the Appendix A, we provide
comprehensive tables with Pad\'e approximants of $R(\zeta)$ up to the 8th-pole
order, with many given in an analytic form.",1901.09360v2
2019-01-28,Revisit of non-linear Landau damping for electrostatic instability driven by blazar-induced pair beams,"We revisit the effect of non-linear Landau (NL) damping on the electrostatic
instability of blazar-induced pair beams, using a realistic pair-beam
distribution. We employ a simplified 2D model in ${\bf k}$-space to study the
evolution of the electric-field spectrum and to calculate the relaxation time
of the beam. We demonstrate that the 2D model is an adequate representation of
the 3D physics. We find that non-linear Landau damping, once it operates
efficiently, transports essentially the entire wave energy to small wavenumbers
where wave driving is weak or absent. The relaxation time also strongly depends
on the IGM temperature, $T_\mathrm{IGM}$, and for $T_\mathrm{IGM}\ll10$ eV, and
in the absence of any other damping mechanism, the relaxation time of the pair
beam is longer than the inverse Compton (IC) scattering time. The weak
late-time beam energy losses arise from the accumulation of wave energy at
small $k$, that non-linearly drains the wave energy at the resonant
$\mathbf{k}$ of the pair-beam instability. Any other dissipation process
operating at small $k$ would reduce that wave-energy drain and hence lead to
stronger pair-beam energy losses. As an example, collisions reduce the
relaxation time by an order of magnitude, although their rate is very small.
Other non-linear processes, such as the modulation instability, could provide
additional damping of the non-resonant waves and dramatically reduce the
relaxation time of the pair beam. An accurate description of the spectral
evolution of the electrostatic waves is crucial for calculating the relaxation
time of the pair beam.",1901.09640v3
2019-11-22,"Role of Element-Specific Damping on the Ultrafast, Helicity-Independent All-Optical Switching Dynamics in Amorphous (Gd,Tb)Co Thin Films","Ultrafast control of the magnetization in ps timescales by fs laser pulses
offers an attractive avenue for applications such as fast magnetic devices for
logic and memory. However, ultrafast helicity-independent all-optical switching
(HI-AOS) of the magnetization has thus far only been observed in Gd-based,
ferrimagnetic amorphous (\textit{a}-) rare earth-transition metal
(\textit{a}-RE-TM) systems, and a comprehensive understanding of the reversal
mechanism remains elusive. Here, we report HI-AOS in ferrimagnetic
\textit{a}-Gd$_{22-x}$Tb$_x$Co$_{78}$ thin films, from x = 0 to x = 18, and
elucidate the role of Gd in HI-AOS in \textit{a}-RE-TM alloys and multilayers.
Increasing Tb content results in increasing perpendicular magnetic anisotropy
and coercivity, without modifying magnetization density, and slower
remagnetization rates and higher critical fluences for switching but still
shows picosecond HI-AOS. Simulations of the atomistic spin dynamics based on
the two-temperature model reproduce these results qualitatively and predict
that the lower damping on the RE sublattice arising from the small spin-orbit
coupling of Gd (with $L = 0$) is instrumental for the faster dynamics and lower
critical fluences of the Gd-rich alloys. Annealing
\textit{a}-Gd$_{10}$Tb$_{12}$Co$_{78}$ leads to slower dynamics which we argue
is due to an increase in damping. These simulations strongly indicate that
acounting for element-specific damping is crucial in understanding HI-AOS
phenomena. The results suggest that engineering the element specific damping of
materials can open up new classes of materials that exhibit low-energy,
ultrafast HI-AOS.",1911.09803v3
2020-06-08,Hysteretic depinning of a particle in a periodic potential: Phase diagram and criticality,"We consider a massive particle driven with a constant force in a periodic
potential and subjected to a dissipative friction. As a function of the drive
and damping, the phase diagram of this paradigmatic model is well known to
present a pinned, a sliding, and a bistable regime separated by three distinct
bifurcation lines. In physical terms, the average velocity $v$ of the particle
is nonzero only if either (i) the driving force is large enough to remove any
stable point, forcing the particle to slide, or (ii) there are local minima but
the damping is small enough, below a critical damping, for the inertia to allow
the particle to cross barriers and follow a limit cycle; this regime is
bistable and whether $v > 0$ or $v = 0$ depends on the initial state. In this
paper, we focus on the asymptotes of the critical line separating the bistable
and the pinned regimes. First, we study its behavior near the ""triple point""
where the pinned, the bistable, and the sliding dynamical regimes meet. Just
below the critical damping we uncover a critical regime, where the line
approaches the triple point following a power-law behavior. We show that its
exponent is controlled by the normal form of the tilted potential close to its
critical force. Second, in the opposite regime of very low damping, we revisit
existing results by providing a simple method to determine analytically the
exact behavior of the line in the case of a generic potential. The analytical
estimates, accurately confirmed numerically, are obtained by exploiting exact
soliton solutions describing the orbit in a modified tilted potential which can
be mapped to the original tilted washboard potential. Our methods and results
are particularly useful for an accurate description of underdamped nonuniform
oscillators driven near their triple point.",2006.04912v2
2020-09-14,Large field-like torque in amorphous Ru2Sn3 originated from the intrinsic spin Hall effect,"We investigated temperature dependent current driven spin-orbit torques in
magnetron sputtered Ru2Sn3 (4 and 10 nm) /Co20Fe60B20 (5 nm) layered structures
with in-plane magnetic anisotropy. The room temperature damping-like and
field-like spin torque efficiencies of the amorphous Ru2Sn3 films were measured
to be 0.14 +- 0.008 (0.07 +- 0.012) and -0.03 +- 0.006 (-0.20 +- 0.009), for
the 4 (10 nm) films respectively, by utilizing the second harmonic Hall
technique. The large field-like torque in the relatively thicker Ru2Sn3 (10 nm)
thin film is unique compared to the traditional spin Hall materials interfaced
with thick magnetic layers with in-plane magnetic anisotropy which typically
have dominant damping-like and negligible field-like torques. Additionally, the
observed room temperature field-like torque efficiency in Ru2Sn3 (10 nm)/CoFeB
(5 nm) is up to three times larger than the damping-like torque (-0.20 +- 0.009
and 0.07 +- 0.012, respectively) and thirty times larger at 50 K (-0.29 +-
0.014 and 0.009 +- 0.017, respectively). The temperature dependence of the
field-like torques show dominant contributions from the intrinsic spin Hall
effect while the damping-like torques show dominate contributions from the
extrinsic spin Hall effects, skew scattering and side jump. Through macro-spin
calculations, we found that including field-like torques on the order or larger
than the damping-like torque can reduce the switching critical current and
decrease magnetization procession for a perpendicular ferromagnetic layer.",2009.06711v2
2021-01-12,Phase Retrieval using Expectation Consistent Signal Recovery Algorithm based on Hypernetwork,"Phase retrieval (PR) is an important component in modern computational
imaging systems. Many algorithms have been developed over the past
half-century. Recent advances in deep learning have introduced new
possibilities for a robust and fast PR. An emerging technique called deep
unfolding provides a systematic connection between conventional model-based
iterative algorithms and modern data-based deep learning. Unfolded algorithms,
which are powered by data learning, have shown remarkable performance and
convergence speed improvement over original algorithms. Despite their
potential, most existing unfolded algorithms are strictly confined to a fixed
number of iterations when layer-dependent parameters are used. In this study,
we develop a novel framework for deep unfolding to overcome existing
limitations. Our development is based on an unfolded generalized expectation
consistent signal recovery (GEC-SR) algorithm, wherein damping factors are left
for data-driven learning. In particular, we introduce a hypernetwork to
generate the damping factors for GEC-SR. Instead of learning a set of optimal
damping factors directly, the hypernetwork learns how to generate the optimal
damping factors according to the clinical settings, thereby ensuring its
adaptivity to different scenarios. To enable the hypernetwork to adapt to
varying layer numbers, we use a recurrent architecture to develop a dynamic
hypernetwork that generates a damping factor that can vary online across
layers. We also exploit a self-attention mechanism to enhance the robustness of
the hypernetwork. Extensive experiments show that the proposed algorithm
outperforms existing ones in terms of convergence speed and accuracy and still
works well under very harsh settings, even under which many classical PR
algorithms are unstable.",2101.04348v2
2021-06-18,Sloshing dynamics of liquid tank with built-in buoys for wave energy harvesting,"This paper proposes a novel design of liquid tank with built-in buoys for
wave energy harvesting, named the 'sloshing wave energy converter (S-WEC)'.
When the tank is oscillated by external loads (such as ocean waves), internal
liquid sloshing is activated, and the mechanical energy of sloshing waves can
be absorbed by the power take-off (PTO) system attached to these buoys. A
fully-nonlinear numerical model is established based on the boundary element
method for a systematic investigation on dynamic properties of the proposed
S-WEC. A motion decoupling algorithm based on auxiliary functions is developed
to solve the nonlinear interaction of sloshing waves and floating buoys in the
tank. An artificial damping model is introduced to reflect viscous effects of
the sloshing liquid. Physical experiments are carried out on a scaled S-WEC
model to validate the mathematical and numerical methodologies. Natural
frequencies of the S-WEC system are first investigated through spectrum
analyses on motion histories of the buoy and sloshing liquid. The viscous
damping strength is identified through comparisons with experimental
measurements. Effects of the PTO damping on power generation characteristics of
S-WEC is further explored. An optimal PTO damping can be found for each
excitation frequency, leading to the maximisation of both the power generation
and conversion efficiency of the buoy. To determine a constant PTO damping for
engineering design, a practical approach based on diagram analyses is proposed.
Effects of the buoy's geometry on power generation characteristics of the S-WEC
are also investigated. In engineering practice, the present design of S-WEC can
be a promising technical solution of ocean wave energy harvesting, based on its
comprehensive advantages on survivability enhancement, metal corrosion or
fouling organism inhibition, power generation stability and efficiency, and so
on.",2106.10005v1
2024-03-22,Investigating the Relationship between Simulation Parameters and Flow Variables in Simulating Atmospheric Gravity Waves in Wind Energy Applications,"Wind farms, particularly offshore clusters, are becoming larger than ever
before. Besides influencing wind farms and local meteorology downstream, large
wind farms can trigger atmospheric gravity waves in the inversion layer and the
free atmosphere aloft. Wind farm-induced gravity waves can cause adverse
pressure gradients upstream of the wind farm, that contribute to the global
blockage effect, and favorable pressure gradients above and downstream of the
wind farm that enhance wake recovery.
  Numerical modeling is a powerful means of studying wind farm-induced
atmospheric gravity waves, but it comes with the challenge of handling spurious
reflections of these waves from domain boundaries. Approaches like radiation
boundary conditions and forcing zones are used to avoid the reflections.
However, the simulation setup heavily relies on ad-hoc processes. For instance,
the widely used Rayleigh damping method requires ad-hoc tuning to acquire a
setup only applicable to a particular case. To surmount this hurdle, we conduct
a systematic LES study for flow over a 2D hill and through wind farm canopies
that explores the dependence of domain size and damping layer setup on
parameters driving linearly stratified atmospheric flows.
  Mainly the internal waves in the free atmosphere reflect from the boundaries,
therefore by simulation linearly stratified conditions we focus on internal
waves only. The Froude number drives most of the internal wave properties, such
as wavelengths, amplitude, and direction. Therefore, the domain sizing and
Rayleigh damping layer setup mainly depends on the Froude number. We
anticipated the effective wavelengths to be the correct length scale to size
the domain and damping layer thickness. Also, the damping coefficient is scaled
with Brunt-V\""ais\""al\""a frequency.",2403.18863v1
1994-10-06,Damped Lyman Alpha Systems vs. Cold + Hot Dark Matter,"Damped Ly$\alpha$ systems provide possibly the most significant evidence for
early structure formation, and thus a stringent constraint on the Cold + Hot
Dark Matter (CHDM) cosmology. Using the numbers of halos in N-body simulations
to normalize Press-Schechter (PS) estimates of the number densities of
protogalaxies as a function of redshift, we find that CHDM with
$\Omega_c/\Omega_\nu/\Omega_b = 0.6/0.3/0.1$ is compatible with the damped
Ly$\alpha$ data only at $z<2.5$, but that it is probably incompatible with data
at $z>3$. The predictions of CHDM are quite sensitive to the neutrino fraction.
We find that $\Omega_c/\Omega_\nu/\Omega_b = 0.725/0.20/0.075$ is compatible
with the $z>3$ data. With one massive neutrino species, this corresponds to
lowering the neutrino mass from 7.0 to 4.7 eV, for $H_0=50\kmsMpc$ and
$T=2.726$ K. By analysing our numerical simulations with different resolutions
and box sizes as well as those of Ma \& Bertchinger (1994), we show that for
the CHDM models with $\Omega_\nu$=0.2--0.3 the PS approximation should be used
with Gaussian filter with $\delta_c=1.3-1.4$ if one tries to recover the total
mass of a collapsed halo and to include nonlinear effects, due to waves both
longer and shorter than those within the simulation box.",9410022v1
1995-12-05,Small Scale Structure and High Redshift HI,"Cosmological simulations with gas dynamics suggest that the Lyman-alpha
forest is produced mainly by ""small scale structure"" --- filaments and sheets
that are the high redshift analog of today's galaxy superclusters. There is no
sharp distinction between Lyman-alpha clouds and ""Gunn-Peterson"" absorption
produced by the fluctuating IGM -- the Lyman-alpha forest {\it is} the
Gunn-Peterson effect. Lyman limit and damped Lyman-alpha absorption arises in
the radiatively cooled gas of forming galaxies. At $z~2-3$, most of the gas is
in the photoionized, diffuse medium associated with the Lyman-alpha forest, but
most of the {\it neutral} gas is in damped Lyman-alpha systems. We discuss
generic evolution of cosmic gas in a hierarchical scenario of structure
formation, with particular attention to the prospects for detecting 21cm
emission from high redshift HI. A scaling argument based on the present-day
cluster mass function suggests that objects with $M_{HI} >~ 5e11 h^{-1} \msun$
should be extremely rare at $z~3$, so detections with existing instruments will
be difficult. An instrument like the proposed Square Kilometer Array could
detect individual damped Lyman-alpha systems at high redshift, making it
possible to map structure in the high redshift universe in much the same way
that today's galaxy redshift surveys map the local large scale structure.",9512016v1
1996-04-03,APM z>4 QSO Survey: Spectra and Intervening Absorption Systems,"The APM multicolor survey for bright z > 4 objects, covering 2500 deg^2 of
sky to m(R)~19, resulted in the discovery of thirty-one quasars with z > 4.
High signal-to-noise optical spectrophotometry at 5A resolution has been
obtained for the twenty-eight quasars easily accessible from the northern
hemisphere. These spectra have been surveyed to create new samples of high
redshift Lyman-limit systems, damped Lyman-alpha absorbers, and metal
absorption systems (e.g. CIV and MgII). In this paper we present the spectra,
together with line lists of the detected absorption systems. The QSOs display a
wide variety of emission and absorption line characteristics, with 5 exhibiting
broad absorption lines and one with extremely strong emission lines
(BR2248-1242). Eleven candidate damped Ly-alpha absorption systems have been
identified covering the redshift range 2.8<z<4.4 (8 with z>3.5). An analysis of
the measured redshifts of the high ionization emission lines with the low
ionization lines shows them to be blueshifted by 430+/-60 km/s. In a previous
paper (Storrie-Lombardi et. al. 1994) we discussed the redshift evolution of
the Lyman limit systems catalogued here. In subsequent papers we will discuss
the properties of the Ly-alpha forest absorbers and the redshift and column
density evolution of the damped Ly-alpha absorbers.",9604021v1
1996-04-10,A Keck HIRES Investigation of the Metal Abundances and Kinematics of the z=2.46 Damped Lya System Toward Q0201+365,"We present high resolution ($\approx 8$ \kms) spectra of the QSO Q0201+365
obtained with HIRES, the echelle spectrograph on the 10m W.M. Keck Telescope.
Although we identify over $80\%$ of the absorption features and analyze several
of the more complex metal-line systems, we focus our analysis on the damped
\Lya system at $z=2.462$. Ionization simulations suggest the hydrogen in this
system is significantly neutral and all of the observed metals are
predominantly singly ionized. We measure accurate abundances for Fe, Cr, Si, Ni
and place a lower limit on the abundance of Zn: [Fe/H] = $-0.830 \pm 0.051$,
[Cr/H] = $-0.902 \pm 0.064$, [Si/H] = $-0.376 \pm 0.052$, [Ni/H] = $-1.002 \pm
0.054$ and [Zn/H] $> -0.562 \pm 0.064$. We give evidence suggesting the actual
Zn abundance is [Zn/H] $\approx -0.262$, implying the highest metallicity
observed at a redshift $z \geq 2$. The relative abundances of these elements
remains constant over essentially the entire system ($\approx 150$ \kms in
velocity space), suggesting it is well mixed. Furthermore, we use the lack of
abundance variations to infer properties of the dust responsible for element
depletion. Finally, we discuss the kinematic characteristics of this damped
\Lya system, comparing and contrasting it with other systems. The low-ion line
profiles span $\approx 200$ \kms in velocity space and have an asymmetric shape
with the strongest feature on the red edge. These kinematic characteristics are
consistent with a rotating disk model.",9604042v1
1996-06-13,Damping of Cosmic Magnetic Fields,"We examine the evolution of magnetic fields in an expanding fluid composed of
matter and radiation with particular interest in the evolution of cosmic
magnetic fields. We derive the propagation velocities and damping rates for
relativistic and non-relativistic fast and slow magnetosonic, and Alfv\'en
waves in the presence of viscous and heat conducting processes. The analysis
covers all MHD modes in the radiation diffusion and the free-streaming regimes.
When our results are applied to the evolution of magnetic fields in the early
universe, we find that cosmic magnetic fields are damped from prior to the
epoch of neutrino decoupling up to recombination. Our findings have multifold
implications for cosmology. The dissipation of magnetic field energy into heat
during the epoch of neutrino decoupling ensures that most magnetic field
configurations generated in the very early universe satisfy big bang
nucleosynthesis constraints. Further dissipation before recombination
constrains models in which primordial magnetic fields give rise to galactic
magnetic fields or density perturbations. Finally, the survival of Alfv\'en and
slow magnetosonic modes on scales well below the Silk mass may be of
significance for the formation of structure on small scales (abridged).",9606080v2
1997-01-09,Molecular Hydrogen Absorption in the z= 1.97 Damped Lyman alpha Absorption system toward QSO 0013-004,"We present a new ultra-violet spectrum of the QSO 0013-004 with 0.9 \AA
resolution obtained with the MMT Blue spectrograph. The \upsilon = 0 - 0, 1 -
0, 2 - 0 and 3 - 0 Lyman bands of H_2 associated with the z = 1.9731 damped Ly
alpah absorption line system have been detected. The H_2 column density is
N(H_2) = 6.9 (\pm 1.6)\times 10^{19} cm^{-2}, and the Doppler parameter b =
15\pm 2 km/s. The populations of different rotational levels are measured and
used to derive the excitation temperatures. The estimated kinetic temperature
T_K\sim 70 K, and the total particle number density n(H) \sim 300 cm^{-3}. The
UV photoabsorption rate $\beta_0 \sim 6.7\times 10^{-9}$ s^{-1}, about a factor
of few times greater than that in a typical diffuse Milky Way interstellar
cloud. The total hydrogen column density is $N(H) = 6.4(\pm 0.5)\times 10^{20}
cm^{-2}$. The fractional H_2 abundance f = 2N(H_2)/(2N(H_2) + N(H I)) \sim 0.22
\pm 0.05 is the highest among all observed damped Ly\al absorbers. The high
fractional H_2 abundance is consistent with the inferred presence of dust and
strong C I absorption in this absorber.",9701041v1
1997-02-06,Abundance Patterns of Heavy Elements in Damped Lyman-Alpha Galaxies,"We present a quantitative analysis of the abundances of heavy elements in
damped Ly-alpha galaxies in the sample of Lu et al. (1996). In particular, we
compare the observed gas-phase abundances with those expected when the
intrinsic (i.e., nucleosynthetic) pattern is the same as that in either the Sun
or in Galactic halo stars and when the depletion pattern is the same as that in
the warm Galactic interstellar medium, but with various values of the
dust-to-metals ratio. We find that the observations are equally consistent with
the solar and halo-star intrinsic patterns and that they favor some depletion,
the typical dust-to-metals ratio being 40%-90% of that in the Milky Way today.
However, neither intrinsic pattern matches the observations perfectly. For the
solar pattern, the discrepancy is mainly with [Mn/Fe], while for the halo-star
pattern, the discrepancy is with [Zn/Fe], [Ni/Fe], and possibly [Al/Fe]. Our
analysis does not support the claim by Lu et al. that the damped Ly-alpha
galaxies have halo-star abundance patterns and no dust depletion.",9702066v2
1997-07-15,"Linear Response, Dynamical Friction and the Fluctuation-Dissipation Theorem in Stellar Dynamics","We apply linear response theory to a general, inhomogeneous, stationary
stellar system, with particular emphasis on dissipative processes analogous to
Landau damping. Assuming only that the response is causal, we show that the
irreversible work done by an external perturber is described by the
anti-Hermitian part of a linear response operator, and damping of collective
modes is described by the anti-Hermitian part of a related polarization
operator. We derive an exact formal expression for the response operator, which
is the classical analog of a well-known result in quantum statistical physics.
When the self-gravity of the response can be ignored, and the ensemble-averaged
gravitational potential is integrable, the expressions for the mode energy,
damping rate, and polarization operator reduce to well-known formulae derived
from perturbation theory in action-angle variables. In this approximation,
dissipation occurs only via resonant interaction with stellar orbits or
collective modes. For stellar systems in thermal equilibrium, the
anti-Hermitian part of the response operator is directly related to the
correlation function of the fluctuations. Thus dissipative properties of the
system are completely determined by the spectrum of density fluctuations---the
fluctuation-dissipation theorem. In particular, we express the coefficient of
dynamical friction for an orbiting test particle in terms of the fluctuation
spectrum; this reduces to the known Chandrasekhar formula in the restrictive
case of an infinite homogeneous system with a Maxwellian velocity distribution.",9707161v1
1997-08-04,"Violent Relaxation, Phase Mixing, and Gravitational Landau Damping","This paper proposes a geometric interpretation of flows generated by the
collisionless Boltzmann equation (CBE), focusing on the coarse-grained approach
towards equilibrium. The CBE is a noncanonical Hamiltonian system with the
distribution function f the fundamental dynamical variable, the mean field
energy H[f] playing the role of the Hamiltonian and the natural arena of
physics being the infinite-dimensional phase space of distribution functions.
Every time-independent equilibrium f_0 is an energy extremal with respect to
all perturbations that preserve the constraints associated with Liouville's
Theorem, local energy minima corresponding to linearly stable equilibria. If an
initial f(t=0) is sufficiently close to some linearly stable lower energy f_0,
its evolution involves linear phase space oscillations about f_0 which, in many
cases, would be expected to exhibit linear Landau damping. If f(t=0) is far
from any stable extremal, the flow will be more complicated but, in general,
one would anticipate that the evolution involves nonlinear oscillations about
some lower energy f_0. In this picture, the coarse-grained approach towards
equilibrium usually termed violent relaxation is interpreted as nonlinear
Landau damping. The evolution of a generic initial f(t=0) involves a coherent
initial excitation, not necessarily small, being converted into incoherent
motion associated with nonlinear oscillations about some equilibrium f_0 which,
in general, will exhibit destructive interference.",9708026v1
1998-11-23,The Physical Nature of the Lyman Limit Systems,"We analyze Keck HIRES observations of a Lyman limit system at z=2.652 toward
Q2231-00. These observations afford the most comprehensive study of the
physical properties of a LL system to date. By comparing the ionic column
densities for Fe^+, Fe^{++}, Si^+, and Si^{3+} against calculations derived
from the CLOUDY software package, we have strictly constrained the ionization
state of this system. This has enabled us to calculate accurate abundances of a
Lyman limit system for the first time at z > 2, e.g., [Fe/H] = -0.5 \pm 0.1. We
also derive a total hydrogen column density, log N(H) = 20.73 \pm 0.2, which is
comparable to values observed for the damped lya systems.
  The system is special for exhibiting CII* 1335 absorption, allowing an
estimate of the electron density, n_e = 6.5 \pm 1.3 x 10^{-2} cm^{-3}. Coupling
this measurement with our knowledge of the ionization state, we derive the
following physical properties: (1) hydrogen volume density, n_H = 5.9 \pm 1.2 x
10^{-2} cm^{-3}, (2) path length, l = 3 \pm 1.6 kpc, and (3) ionizing
intensity, log J_{912} = -20.22 \pm 0.21. We point out that a number of the
physical properties (e.g. [Fe/H], N(H), n_H) resemble those observed for the
damped lya systems, which suggests this system may be the photoionized analog
of a damped system. The techniques introduced in this Letter should be
applicable to a number of Lyman limit systems and therefore enable a survey of
their chemical abundances and other physical properties.",9811357v1
1998-12-03,Gravity-Modes in ZZ Ceti Stars III. Eigenvalues and Eigenfuctions,"We report on numerical calculations of nonadiabatic eigenvalues and
eigenfunctions for g-modes in ZZ Ceti variables. The spectrum of overstable
$l=1$ modes delineates the instability strip. Its blue edge occurs where
$\omega \tau_c \approx 1$ for the $n=1$ mode. Here $\omega$ is radian frequency
and $\tau_c$ is about four times the thermal timescale at the bottom of the
surface convection zone. As a ZZ Ceti cools, its convection zone deepens,
longer period modes become overstable, but the critical value of $\omega\tau_c$
separating overstable and damped modes rises. The latter is a consequence of
enhanced radiative damping for modes which propagate immediately below the
convection zone. The critical value of $\omega\tau_c$ is of observational
significance because modes with the smallest value of $\omega\tau_c$ are most
observable photometrically. Maximum periods for overstable modes predicted for
our cooler model envelopes are about a factor two longer than the observational
upper limit of $1,200\s$. We assess a number of plausible resolutions for this
discrepancy among which convective overshoot and nonlinear saturation look
promising. The nonadiabatic eigenfunctions enable us to predict relative
amplitudes and phases of photospheric variations of flux and velocity,
quantities made accessible by recent observations. We also present asymptotic
formula for damping rates of high order modes, a result of consequence for
future investigations of nonlinear saturation of the amplidues of overstable
modes.",9812085v1
1999-01-19,"Collisionless Dissipative Nonlinear Alfven Waves: Nonlinear Steepening, Compressible Turbulence, and Particle Trapping","The magnetic energy of nonlinear Alfven waves in compressible plasmas may be
ponderomotively coupled only to ion-acoustic quasi-modes which modulate the
wave phase velocity and cause wave-front steepening. In the collisionless
plasma with $\beta\not=0$, the dynamics of nonlinear Alfven wave is also
affected by the resonant particle-wave interactions. Upon relatively rapid
evolution (compared to the particle bounce time), the quasi-stationary wave
structures, identical to the so called (Alfvenic) Rotational Discontinuities,
form, the emergence and dynamics of which has not been previously understood.
Collisionless (Landau) dissipation of nonlinear Alfven waves is also a
plausible and natural mechanism of the solar wind heating. Considering a
strong, compressible, Alfvenic turbulence as an ensemble of randomly
interacting Alfvenic discontinuities and nonlinear waves, it is shown that
there exist two distinct phases of turbulence. What phase realizes depends on
whether this collisionless damping is strong enough to provide adequate energy
sink at all scales and, thus, to support a steady-state cascade of the wave
energy. In long-time asymptotics, however, the particle distribution function
is affected by the wave magnetic fields. In this regime of nonlinear Landau
damping, resonant particles are trapped in the quasi-stationary Alfvenic
discontinuities, giving rise to a formation of a plateau on the distribution
function and quenching collisionless damping. Using the virial theorem for
trapped particles, it is analytically demonstrated that their effect on the
nonlinear dynamics of such discontinuities is non-trivial and forces a
significant departure of the theory from the conventional paradigm.",9901257v1
2000-06-06,A Model of Metallicity Evolution in the Early Universe,"We apply the phenomenological model used to explain the abundances of Fe and
r-process elements in very metal-poor stars in the Galaxy to [Fe/H] of damped
Ly alpha systems. It is assumed that the first stars formed after the Big Bang
were very massive and promptly enriched the interstellar medium to [Fe/H] ~ -3,
at which metallicity formation of normal stars took over. Subsequent Fe
enrichment was provided by Type II supernovae. The range of [Fe/H] at a given
redshift z for damped Ly alpha systems is explained by the time t* after the
Big Bang at which normal star formation started in an individual protogalactic
system. The average t* is approx 80% the age of the universe for damped Ly
alpha systems at z approx 1.5 to 4.5, indicating a long delay between the Big
Bang and the turn-on of protogalaxies. It is inferred that a substantial
fraction of the total baryonic matter may not have been aggregated into
protogalaxies where normal star formation had occurred down to z ~ 1.5. The
data near z = 2.2 suggest that the rate of turn-on of protogalaxies was
initially very low and slowly reached a maximum at ~ 3 Gyr after the Big Bang.
This may be important in understanding the rate of formation of quasars.",0006082v2
2000-09-27,Lensing properties of 7 damped Lyman-alpha absorbing galaxy-QSO pairs,"Le Brun et al. (1997) presented the first identifications of the galaxies
giving rise to 7 intermediate redshift damped Ly-alpha (DLA) absorption
systems. Here, we study the gravitational lensing properties of these
foreground galaxies based on their observed optical appearance and on the
absence of any secondary lensed quasar image. We consider the possibility that
any secondary image be hidden due to extinction by dust, but find it unlikely.
We derive upper limits on the amplification factor affecting the luminosity of
the background quasars; in each case, this factor is found to be less than 0.3
mag. We also obtain upper limits on the total mass of the damped Ly-alpha
galaxies, within radii equal to the quasar impact parameters. Mass-to-light
ratios are found to be consistent with existing estimates based on X-ray
emission or on motion of dwarf satellites. Although we show that lensing is not
important in this sample, we note that existing DLA surveys used to determine
the cosmological density of gas at z<1 are based on samples of quasars brighter
than the ones considered here and for which the amplification bias is likely to
be stronger.",0009433v1
2000-11-14,Sharp HI edges at high z: the gas distribution from Damped Lyman-alpha to Lyman-limit absorption systems,"We derive the distribution of neutral and ionized gas in high redshift clouds
which are optically thick to hydrogen ionizing radiation, using published data
on Lyman-limit and Damped Lyman-alpha absorption systems in the redshift range
1.75 < z < 3.25. We assume that the distribution of the hydrogen total (HI+HII)
column density in the absorbers follows a power law K N_H^{-alpha}, whereas the
observed HI column density distribution deviates from a pure power law as a
result of ionization from a background radiation field. Comparison of the
models and observations give Maximum Likelihood solutions for the exponent
alpha and for X, the value of log(N_H/N_HI) when the Lyman-limit optical depth
is unity: alpha=2.7^{+1.0}_{-0.7} and X=2.75\pm0.35. X is much lower than what
would be obtained for a gaseous distribution in equilibrium under its own
gravity but the ratio of dark matter to gas density is not well constrained
being log(eta_0)=1.1\pm 0.8. An extrapolation of our derived power law
distribution towards systems of lower column density, the Lyman-alpha forest,
favours models with log(eta_0) < 1.1 and alpha=2.7-3.3. With alpha appreciably
larger than 2, Lyman-limit systems contain more gas than Damped Lyman-alpha
systems and Lyman-alpha forest clouds even more. Estimates of the cosmological
gas and dark matter density due to absorbers of different column density around
z=2.5 are also given.",0011268v1
2000-11-29,Implications of 21cm observations for damped Ly-$α$ systems,"We present Giant Metrewave Radio Telescope HI 21cm absorption observations,
of candidate and confirmed damped Lyman-$\alpha$ systems (DLAS). The derived
spin temperatures (T_s) are in all cases $\sim 1000$ K or higher. We have also
collated from the literature a list of DLAS for which 21cm observations exist,
and discuss their implications for the nature of the absorbers.
  A cross-comparison of the 21cm profiles with low ionization metal profiles
shows that the 21cm absorption coincides in velocity with the deepest metal
line feature. This is consistent with models in which the deep metal line
features arise from discrete clouds but not with models where the deepest
features are the result of velocity crowding.
  We also find that the typical derived spin temperatures of DLAS are
considerably higher than those in the Galaxy or nearby spirals. The only
exceptions are DLAS which are known to be associated with the disks of spirals;
these do, in fact, show low spin temperatures. In a multi-phase medium,the
derived T_s is a weighted average of the temperatures of the individual phases.
High derived T_s values are hence to be expected from small, low metallicity
objects, since these objects should have a lower fraction of the cold phase in
their ISM as compared to large galaxies. The high T_s in DLAS is hence
consistent with their observed low metallicities as well as with recent
observations that DLAS are also associated with dwarf/LSB galaxies. Finally, we
suggest that the following trend may be identified: at low redshift, damped
absorption arises from a range of systems, including spiral galaxy disks,
while, at high redshift, absorption occurs predominantly in smaller systems.
(Abridged)",0011540v1
2001-01-18,A Comprehensive Statistical Analysis of the Gas Distribution in Lyman-limit and Damped Lyman-alpha Absorption Systems,"In this paper we show how to use data on Lyman-limit and Damped Lyman-alpha
absorption systems to derive the hydrogen ionization fractions and the
distribution of the face-on total gas column density. We consider axially
symmetric, randomly oriented absorbers, ionized by an external background
radiation field in order to relate the face-on total gas distribution to that
of the neutral hydrogen observed along the line of sight. We devise a
statistical procedure based on the Maximum Likelihood criterion, that is able
to treat simultaneously data coming from different surveys and statistically
recovers the ""true"" column densities in the presence of large uncertainties:
this is especially important for Lyman-limit systems which leave an
unmeasurable residual flux at wavelengths shorter than the Lyman break. We make
use of simulated data to look for possible observational biases and extensively
test our procedure. For a large statistical sample of real data in the redshift
range [1.75,3.25] (collected from all published surveys) our Maximum Likelihood
procedure gives a power-law slope for the total hydrogen distribution of -2.7.
All together Lyman-limit systems therefore contain more gas than Damped
Lyman-alpha systems. Analysis of data at other redshifts shows that more
observations are needed to reach a compelling evidence for a cosmological
evolution of the slope of the gas distribution.",0101335v1
2001-04-29,The First Detection of Co in a Damped Lyman Alpha System,"The study of elemental abundances in Damped Lyman Alpha systems (DLAs) at
high redshift represents one of our best opportunities to probe galaxy
formation and chemical evolution at early times. By coupling measurements made
in high z DLAs with our knowledge of abundances determined locally and with
nucleosynthetic models, we can start to piece together the star formation
histories of these galaxies. Here, we discuss the clues to galactic chemical
evolution that may be gleaned from studying the abundance of Co in DLAs. We
present high resolution echelle spectra of two QSOs, Q2206-199 and Q1223+17,
both already known to exhibit intervening damped systems. These observations
have resulted in the first ever detection of Co at high redshift, associated
with the z= 1.92 DLA in the sightline towards Q2206-199. We find that the
abundance of Co is approximately 1/4 solar and that there is a clear
overabundance relative to iron, [Co/Fe] = +0.31 +/- 0.05. From the abundance of
Zn, we determine that this is a relatively metal-rich DLA, with a metallicity
approximately 1/3 solar. Therefore, this first detection of Co is similar to
the marked overabundance relative to Fe seen in Galactic bulge and thick disk
stars.",0104466v1
2001-06-22,Self-Absorption of Ionizing Radiation and Extended Lyman Alpha Emission in High- Redshift QSOs,"We calculate the neutral hydrogen column density of self-absorption in QSOs
predicted in a model where the QSOs are located in the same halos that contain
the gas in damped Lya absorption systems. The model is parameterized by the
probability P_0 that any halo has an active QSO. We assume that the QSOs ionize
the gas, but do not expel or heat it. The derived HI column densities produce
negligible Lyman limit absorption, even in the lowest luminosity QSOs, with an
optical depth of only ~ 10% for luminosity L=0.01 L_*, when P_0=10^{-2}. We
also compute the HeII Lyman limit self-absorption, which is slightly higher but
still negligible. The self-absorption can be higher if the gas is highly
clumped; only in this case the overall emissivity from QSOs could be
significantly reduced due to absorption by the known damped Lya systems, to
affect the predicted intensity of the ionizing background or the epoch of HeII
reionization. The presence of the gas associated with damped absorption systems
around QSOs could also be detected from the narrow Lya emission line, which
should have and angular extent of 0.1 to 1'' in typical high-redshift QSOs.",0106424v2
2001-06-22,Compressible MHD Turbulence in Interstellar Plasmas,"Radio-wave scintillation observations reveal a nearly Kolmogorov spectrum of
density fluctuations in the ionized interstellar medium. Although this density
spectrum is suggestive of turbulence, no theory relevant to its interpretation
exists. We calculate the density spectrum in turbulent magnetized plasmas by
extending the theory of incompressible MHD turbulence given by Goldreich &
Sridhar to include the effects of compressibility and particle transport. Our
most important results are as follows. (1) Density fluctuations are due to the
slow mode and the entropy mode. Both modes are passively mixed by the cascade
of shear Alfven waves. Since the shear Alfven waves have a Kolmogorov spectrum,
so do the density fluctuations. (2) Observed density fluctuation amplitudes
imply either that the magnetic and gas pressures are comparable, or that the
outer scale of the turbulence is very small. (3) A high degree of ionization is
required for the cascade to survive damping by neutrals and thereby to extend
to small lengthscales. Regions that are insufficiently ionized produce density
fluctuations only on lengthscales larger than the neutral damping scale. These
regions may account for the excess of power that is found on large scales. (4)
Both the entropy mode and the slow mode are damped on lengthscales below that
at which protons can diffuse across an eddy during the eddy's turnover time.
Consequently, eddies whose extents along the magnetic field are smaller than
the proton collisional mean free path do not contribute to the density
spectrum. However, in MHD turbulence eddies are highly elongated along the
magnetic field. From an observational perspective, the relevant lengthscale is
that transverse to the magnetic field. Thus the cut-off lengthscale for density
fluctuations is significantly smaller than the proton mean free path.",0106425v1
2001-11-20,Collisional Cascades in Planetesimal Disks I. Stellar Flybys,"We use a new multiannulus planetesimal accretion code to investigate the
evolution of a planetesimal disk following a moderately close encounter with a
passing star. The calculations include fragmentation, gas and
Poynting-Robertson drag, and velocity evolution from dynamical friction and
viscous stirring. We assume that the stellar encounter increases planetesimal
velocities to the shattering velocity, initiating a collisional cascade in the
disk. During the early stages of our calculations, erosive collisions damp
particle velocities and produce substantial amounts of dust. For a wide range
of initial conditions and input parameters, the time evolution of the dust
luminosity follows a simple relation, L_d/L_{\star} = L_0 / [alpha +
(t/t_d)^{beta}]. The maximum dust luminosity L_0 and the damping time t_d
depend on the disk mass, with L_0 proportional to M_d and t_d proportional to
M_d^{-1}. For disks with dust masses of 1% to 100% of the `minimum mass solar
nebula' (1--100 earth masses at 30--150 AU), our calculations yield t_d approx
1--10 Myr, alpha approx 1--2, beta = 1, and dust luminosities similar to the
range observed in known `debris disk' systems, L_0 approx 10^{-3} to 10^{-5}.
Less massive disks produce smaller dust luminosities and damp on longer
timescales. Because encounters with field stars are rare, these results imply
that moderately close stellar flybys cannot explain collisional cascades in
debris disk systems with stellar ages of 100 Myr or longer.",0111384v1
2002-02-11,The Contribution of HI-rich Galaxies to the Damped Lyman-alpha Absorber Population at z=0,"We present a study of the expected properties of the low redshift damped
Lyman-alpha absorber population determined from a sample of HI-selected
galaxies in the local universe. Because of a tight correlation between the HI
mass and HI cross-section, which we demonstrate spans all galaxy types, we can
use our HI-selected sample to predict the properties of the absorption line
systems. We use measurements of the number density and HI cross-section of
galaxies to show that the total HI cross-section at column densities sufficient
to produce damped Lyman-alpha absorption is consistent with no evolution of the
absorber population. We also find that the dN/dz distribution is dominated by
galaxies with HI masses near 10^9 Msolar. However, because of the large
dispersion in the correlation between HI mass and stellar luminosity, we find
that the distribution of dN/dz as a function of L_J is fairly flat.
Additionally, we examine the line widths of the HI-selected galaxies and show
that there may be evolution in the kinematics of HI-rich galaxies, but it is
not necessary for the higher redshift population to contain a greater
proportion of high mass galaxies than we find locally.",0202216v2
2002-03-18,Monte Carlo Simulation of Lyman Alpha Scattering and Application to Damped Lyman Alpha Systems,"A Monte Carlo code to solve the transfer of Lyman alpha (Lya) photons is
developed, which can predict the Lya image and two-dimensional Lya spectra of a
hydrogen cloud with any given geometry, Lya emissivity, neutral hydrogen
density distribution, and bulk velocity field. We apply the code to several
simple cases of a uniform cloud to show how the Lya image and emitted line
spectrum are affected by the column density, internal velocity gradients, and
emissivity distribution. We then apply the code to two models for damped Lya
absorption systems: a spherical, static, isothermal cloud, and a flattened,
axially symmetric, rotating cloud. If the emission is due to fluorescence of
the external background radiation, the Lya image should have a core
corresponding to the region where hydrogen is self-shielded. The emission line
profile has the characteristic double peak with a deep central trough. We show
how rotation of the cloud causes the two peaks to shift in wavelength as the
slit is perpendicular to the rotation axis, and how the relative amplitude of
the two peaks is changed. In reality, damped Lya systems are likely to have a
clumpy gas distribution with turbulent velocity fields, which should smooth the
line emission profile, but should still leave the rotation signature of the
wavelength shift across the system.",0203287v2
2002-04-09,The Non-Damped Nature of Twelve Low-Redshift Damped Lyman Alpha Candidate Systems,"Hubble Space Telescope (HST) UV spectroscopy of 12 candidate low-redshift
damped Lyman alpha (DLA) systems in 11 QSOs (z=0.103 in Q0054+144, z=0.969 and
z=0.987 in Q0302-223, z=0.478 in Q0454-220, z=1.476 in Q1047+550, z=1.070 in
Q1206+459, z=1.228 in Q1247+267, z=0.399 in Q1318+290B, z=0.519 in Q1329+412,
z=0.276 in Q1451-375, z=0.204 in Q2112+059, z=0.263 in Q2251+113) are
presented; the observations demonstrate that they are not DLAs with
$N(HI)\ge2\times10^{20}$ atoms cm$^{-2}$. In all cases except two the systems
either do not exist or are well below the DLA threshold column density; the
exceptions are a z=0.474 system in Q0454-220 which has $N(HI)=3\times10^{19}$
atoms cm$^{-2}$ and a z=1.223 system in Q1247+267 which has
$N(HI)=8\times10^{19}$ atoms cm$^{-2}$. Despite the availability of data in the
HST archives demonstrating that these are not suitable targets, many have
unfortunately been approved for observation with Chandra, Gemini, and/or HST
with the intent of doing followup work on low-redshift DLAs. Furthermore, these
results indicate that the low-redshift DLA statistics derived from IUE spectra
and presented by Lanzetta, Wolfe, & Turnshek (1995) and Wolfe et al. (1995) are
invalid.",0204155v1
2002-05-17,High matter density peaks from UVES observations of QSO pairs: correlation properties and chemical abundances,"We study the transverse clustering properties of high matter density peaks as
traced by high column density absorption systems (either Lyman limit systems
characterized by N(HI)> 2 x 10^{17} cm^{-2} or CIV systems with W_{r}> 0.5 A)
at redshifts between 2 and 3 with UVES spectra of two QSO pairs (UM680/UM681 at
56 arcsec angular separation and Q2344+1228/Q2343+1232 at 5 arcmin angular
separation) and a QSO triplet (Q2139-4433/Q2139-4434/Q2138-4427 at 1, 7 and 8
arcmin angular separation). We find 3 damped Ly-alpha systems (N(HI)> 2 x
10^{20} cm^{-2}): 2 coinciding with strong metal systems in the nearby line of
sight and 1 matching the emission redshift of the paired QSO; plus 7 Lyman
limit systems: 4 forming two matching couples and 3 without a corresponding
metal system within ~3000 km/s in the coupled line of sight. In summary, we
detect five out of ten matching systems within 1000 km/s, indicating a highly
significant overdensity of strong absorption systems over separation lengths
from ~1 to 8 h^{-1} Mpc. The observed coincidences could arise in gas due to
starburst-driven superwinds associated with a quasar or a galaxy, or gas
belonging to large scale structures like filaments or sheets. We also determine
chemical abundance ratios for three damped Ly-alpha systems. In particular, for
the damped system at z ~ 2.53788 in the spectrum of Q2344+1228, new estimates
of the ratios O/Fe, C/Fe are obtained: [C/Fe]<0.06, [O/Fe]<0.2. They indicate
that O and C are not over-solar in this system.",0205299v1
2002-08-28,Complex rotation with internal dissipation. Applications to cosmic-dust alignment and to wobbling comets and asteroids,"Neutron stars, asteroids, comets, cosmic-dust granules, spacecraft, as well
as whatever other freely spinning body dissipate energy when they rotate about
any axis different from principal. We discuss the internal-dissipation-caused
relaxation of a freely precessing rotator towards its minimal-energy mode (mode
that corresponds to the spin about the maximal-inertia axis). While the body
nutates at some rate, the internal stresses and strains within the body
oscillate at frequencies both higher and lower than this rate. The internal
dissipation takes place mostly the second and higher harmonics. We discuss the
application of our findings to asteroids. Regarding the comets, estimates show
that the currently available angular resolution of spacecraft-based instruments
makes it possible to observe wobble damping within year- or maybe even
month-long spans of time. We also discuss cosmic-dust astrophysics; in
particular, the role played by precession damping in the dust alignment. We
show that this damping provides coupling of the grain's rotational and
vibrational degrees of freedom; this entails occasional flipping of dust grains
due to thermal fluctuations. During such a flip, grain preserves its angular
momentum, but the direction of torques arising from H2 formation reverses. As a
result, flipping grain will not rotate fast in spite of the action of
uncompensated H2 formation torques. The grains get ``thermally trapped,'' and
their alignment is marginal.",0208489v1
2003-06-16,Damping of Tensor Modes in Cosmology,"An analytic formula is given for the traceless transverse part of the
anisotropic stress tensor due to free streaming neutrinos, and used to derive
an integro-differential equation for the propagation of cosmological
gravitational waves. The solution shows that anisotropic stress reduces the
squared amplitude by 35.6 % for wavelengths that enter the horizon during the
radiation-dominated phase, independent of any cosmological parameters. This
decreases the tensor temperature and polarization correlation functions for
these wavelengths by the same amount. The effect is less for wavelengths that
enter the horizon at later times. At the longest wavelengths the decrease in
the tensor correlation functions due to neutrino free streaming ranges from
10.7% for $\Omega_Mh^2=0.1$ to 9.0% for $\Omega_Mh^2=0.15$. An Appendix gives a
general proof that tensor as well as scalar modes satisfy a conservation law
for perturbations outside the horizon, even when the anisotropic stress tensor
is not negligible.",0306304v2
2003-12-30,Nonlinear Pulsations in Differentially Rotating Neutron Stars: Mass-Shedding-Induced Damping and Splitting of the Fundamental Mode,"We study small-amplitude, nonlinear pulsations of uniformly and
differentially rotating neutron stars employing a two-dimensional evolution
code for general-relativistic hydrodynamics. Using Fourier transforms at
several points inside the star, both the eigenfrequencies and two-dimensional
eigenfunctions of pulsations are extracted. The centrifugal forces and the
degree of differential rotation have significant effects on the
mode-eigenfunction. We find that near the mass-shedding limit, the pulsations
are damped due to shocks forming at the surface of the star. This new damping
mechanism may set a small saturation amplitude for modes that are unstable to
the emission of gravitational waves. After correcting for the assumption of the
Cowling approximation (used in our numerical code), we construct empirical
relations that predict the range of gravitational-wave frequencies from
quasi-periodic post-bounce oscillations in the core collapse of massive stars.
We also find that the fundamental quasi-radial mode is split, at least in the
Cowling approximation and mainly in differentially rotating stars, into two
different sequences.",0312648v2
2004-01-16,Simulating stochastically excited oscillations. The mode lifetime of xi Hya,"The discovery of solar-like oscillations in the giant star xy Hya (G7III) was
reported by Frandsen et al. (2002). Their frequency analysis was very limited
due to alias problems in the data set (caused by single-site observations). The
extent to which the aliasing affected their analysis was unclear due to the
unknown damping time of the stellar oscillation modes. In this paper we
describe a simulator created to generate time series of stochastically excited
oscillations, which takes as input an arbitrary window function and includes
both white and non-white noise. We also outline a new method to compare a large
number of simulated time series with an observed time series to determine the
damping time, amplitude, and limited information on the degree of the
stochastically excited modes. For xi Hya we find the most likely amplitude to
be ~ 2 m/s, in good agreement with theory (Houdek & Gough, 2002), and the most
likely damping time to be ~ 2 days, which is much shorter than the theoretical
value of 15-20 days calculated by Houdek & Gough (2002).",0401331v1
2004-10-13,On the Importance of Local Sources of Radiation in Cosmological Absorption Systems,"An upper limit to the importance of local sources of radiation compared to
the cosmic background in cosmological absorption systems is derived, as a
simple consequence of the conservation of surface brightness. The limit depends
only on the rate of incidence of the absorbers and the mean free path of the
radiation. It is found that, on average, the ionizing radiation intensity from
local sources in Lyman limit systems at z>2 must be less than half of the
intensity of the cosmic background. In absorbers with column densities much
lower than Lyman limit systems, the local source contribution must be
negligible. The limit on the ratio of local source to background intensities is
then applied to the class of damped Lya absorption systems with detectable
excited CII lines. A cooling rate of the gas in these systems has been measured
by Wolfe et al., who assumed that the balancing heating source is photoelectric
heating on dust by light at ~ 1500 A . The intensity from local star formation
at this wavelength in this class of damped Lya systems is found to be at most ~
3 times the background intensity. If the heating source is indeed photoelectric
heating of dust, the background created by sources associated with damped Lya
systems can then be estimated from the average cooling rates measured in the
absorbers. Current results yield a background intensity higher than previous
estimates based on observed galaxy and quasar luminosity functions, although
with a large uncertainty. The possibility of other sources of heating, such as
shock-heating in a turbulent medium, should be explored.",0410315v1
2005-04-04,Relativistic r-modes and Shear viscosity: regularizing the continuous spectrum,"Within a fully relativistic framework, we derive and solve numerically the
perturbation equations of relativistic stars, including the stresses produced
by a non-vanishing shear viscosity in the stress-energy tensor. With this
approach, the real and imaginary parts of the frequency of the modes are
consistently obtained. We find that, approaching the inviscid limit from the
finite viscosity case, the continuous spectrum is regularized and we can
calculate the quasi-normal modes for stellar models that do not admit solutions
at first order in perturbation theory when the coupling between the polar and
axial perturbations is neglected. The viscous damping time is found to agree
within factor 2 with the usual estimate obtained by using the eigenfunctions of
the inviscid limit and some approximation for the energy dissipation integrals.
We find that the frequencies and viscous damping times for relativistic
$r-$modes lie between the Newtonian and Cowling results. We compare the results
obtained with homogeneous, polytropic and realistic equations of state and find
that the frequencies depend only on the rotation rate and on the compactness
parameter (M/R), being almost independent of the equation of state. Our
numerical results for realistic neutron stars give viscous damping times with
the same dependence on mass and radius as previously estimated, but
systematically larger of about 60%.",0504062v1
2005-04-29,Evidence for a magnitude-dependent bias in the Hamburg/ESO Survey for Damped Lyman-alpha Systems,"We present preliminary results from the Hamburg/ESO survey for Damped
Ly-alpha (hereafter, DLA) Systems. This survey is characterized by (i) the good
knowledge of the biases affecting the parent QSO survey, (ii) the brightness
and (iii) the relatively wide magnitude distribution of the background QSOs.
Therefore, it is well-suited to study possible magnitude-dependent biases in
DLA surveys, such as the one expected from dust obscuration. We have
systematically searched for damped Lyman-alpha line candidates in 5 A
resolution spectra of the 188 QSOs that constitute our statistical sample.
These candidates have later been reobserved with UVES at the ESO--Very Large
Telescope (VLT) for confirmation and accurate N(HI) measurements. In the
redshift range covered by the survey, 19 DLA systems have been discovered. Over
the whole survey, we find that the number density, n(z), and cosmological
density of gas, Omega_gas, have comparable values to the ones obtained by
CORALS (Ellison et al. 2001). However, the number densities of DLA systems n(z)
in two sub-samples of equal absorption distance path defined by the magnitude
of the background QSOs differ by a factor of about 5. We estimate that the
probability that n(z) is equal in the two sub-samples is < 0.003. A similar,
only slightly less significant difference is found for Omega_gas.",0504657v1
2005-07-06,The free precession and libration of Mercury,"An analysis based on the direct torque equations including tidal dissipation
and a viscous core-mantle coupling is used to determine the damping time scales
of O(10^5) years for free precession of the spin about the Cassini state and
free libration in longitude for Mercury. The core-mantle coupling dominates the
damping over the tides by one to two orders of magnitude for the plausible
parameters chosen. The short damping times compared with the age of the solar
system means we must find recent or on-going excitation mechanisms if such free
motions are found by the current radar experiments or the future measurement by
the MESSENGER and BepiColombo spacecraft that will orbit Mercury. We also show
that the average precession rate is increased by about 30% over that obtained
from the traditional precession constant because of a spin-orbit resonance
induced contribution by the C_{22} term in the expansion of the gravitational
field. The C_{22} contribution also causes the path of the spin during the
precession to be slightly elliptical with a variation in the precession rate
that is a maximum when the obliquity is a minimum. An observable free
precession will compromise the determination of obliquity of the Cassini state
and hence of C/MR^2 for Mercury, but a detected free libration will not
compromise the determination of the forced libration amplitude and thus the
verification of a liquid core",0507117v1
2005-10-12,Ly-alpha Radiative Transfer in Cosmological Simulations and Application to a z~8 Emitter,"We develop a Ly-alpha radiative transfer (RT) Monte Carlo code for
cosmological simulations.High resolution,along with appropriately treated
cooling can result in simulated environments with very high optical
depths.Thus,solving the Ly-alpha RT problem in cosmological simulations can
take an unrealistically long time.For this reason,we develop methods to speed
up the Ly-alpha RT.With these accelerating methods,along with the
parallelization of the code,we make the problem of Ly-alpha RT in the complex
environments of cosmological simulations tractable.We test the RT code against
simple Ly-alpha emitter models,and then we apply it to the brightest Ly-alpha
emitter of a gasdynamics+N-body Adaptive Refinement Tree (ART) simulation at
z~8.We find that recombination rather than cooling radiation Ly-alpha photons
is the dominant contribution to the intrinsic Ly-alpha luminosity of the
emitter,which is ~4.8x10e43 ergs/s.The size of the emitter is pretty
small,making it unresolved for currently available instruments.Its spectrum
before adding the Ly-alpha Gunn-Peterson absorption (GP) resembles that of
static media,despite some net inward radial peculiar motion.This is because for
such high optical depths as those in ART simulations,velocities of order some
hundreds km/s are not important.We add the GP in two ways.First we assume no
damping wing,corresponding to the situation where the emitter lies within the
HII region of a very bright quasar,and second we allow for the damping
wing.Including the damping wing leads to a maximum line brightness suppression
by roughly a factor of ~62.The line fluxes,even though quite faint for current
ground-based telescopes,should be within reach for JWST.",0510347v2
2005-12-05,Kinematics and star formation activity in the z=2.03954 damped Lyman-alpha system towards PKS 0458-020,"We present UVES observations of the log N(HI)= 21.7 damped Lyman-alpha system
at z=2.03954 towards the quasar PKS 0458-020. HI Lyman-alpha emission is
detected in the center of the damped Lyman-alpha absorption trough.
Metallicities are derived for MgII, SiII, PII, CrII, MnII, FeII and ZnII and
are found to be -1.21\pm0.12, -1.28\pm0.20, -1.54\pm0.11, -1.66\pm0.10,
-2.05\pm0.11, -1.87\pm0.11, -1.22\pm0.10, respectively, relative to solar. The
depletion factor is therefore of the order of [Zn/Fe]=0.65. We observe metal
absorption lines to be blueshifted compared to the Lyman-alpha emission up to a
maximum of 100 and 200 km/s for low and high-ionization species respectively.
This can be interpreted either as the consequence of rotation in a large
(~7kpc) disk or as the imprint of a galactic wind. The star formation rate
(SFR) derived from the Lyman-alpha emission, 1.6 solar masses/yr, is compared
with that estimated from the observed CII* absorption. No molecular hydrogen is
detected in our data, yielding a molecular fraction f<-6.52. This absence of H2
can be explained as the consequence of a high ambient UV flux which is one
order of magnitude larger than the radiation field in the ISM of our Galaxy and
originates in the observed emitting region.",0512118v1
2006-02-14,On the magnetic structure and wind parameter profiles of Alfven wave driven winds in late-type supergiant stars,"Cool stars at giant and supergiant evolutionary phases present low velocity
and high density winds, responsible for the observed high mass-loss rates.
Although presenting high luminosities, radiation pressure on dust particles is
not sufficient to explain the wind acceleration process. Among the possible
solutions to this still unsolved problem, Alfven waves are, probably, the most
interesting for their high efficiency in transfering energy and momentum to the
wind. Typically, models of Alfven wave driven winds result in high velocity
winds if they are not highly damped. In this work we determine
self-consistently the magnetic field geometry and solve the momentum, energy
and mass conservation equations, to demonstrate that even a low damped Alfven
wave flux is able to reproduce the low velocity wind. We show that the magnetic
fluxtubes expand with a super-radial factor S>30 near the stellar surface,
larger than that used in previous semi-empirical models. The rapid expansion
results in a strong spatial dilution of the wave flux. We obtained the wind
parameter profiles for a typical supergiant star of 16 M_sun. The wind is
accelerated in a narrow region, coincident with the region of high divergence
of the magnetic field lines, up to 100 km/s. For the temperature, we obtained a
slight decrease near the surface for low damped waves, because the wave heating
mechanism is less effective than the radiative losses. The peak temperature
occurs at 1.5 r_0 reaching 6000 K. Propagating outwards, the wind cools down
mainly due to adiabatic expansion.",0602305v1
2006-03-17,Electron impact excitation of Helium-like ions up to n=4 levels including radiation damping,"Helium-like ions provide the most important X-ray spectral diagnostics in
high temperature fusion and astrophysical plasmas. We previously presented
computed collision strengths for O~VII including relativistic fine structure,
levels up to the $n=4$ complex and radiation damping of autoionizing
resonances. We have extended this work to other He-like ions (N, Ne, Mg, Al,
Si, S, Ca). The calculations are carried out using the Breit-Pauli R-matrix
(BPRM) method with a 31-level eigenfunction expansion. Collision strengths for
the principal lines important in X-ray plasma diagnostics, w, x, y and z,
corresponding to the 4 transitions to the ground level 1s^2(^1S_0) <-
1s2p(^1P^o_1), 1s2p(^3P^o_2), 1s2p(^3P^o_1), 1s2s(^3S_1), are explicitly shown.
We find the effect of radiation damping to be significant for the forbidden
transitions in heavier He-like ions, which should affect the diagnostic line
ratios. We extrapolated the collision strengths to their values at infinite
energy using the Burgess-Tully extrapolation technique. This is required to
calculate the Maxwellian average collision strengths at high temperature. We
show that the coupling between dipole allowed and inter-combination transitions
affects increasingly the effective collision strengths for the n ^1S_0 - n'
^3P_1 transition as the charge of the ion increases. This clearly affects the
treatment of the extrapolation toward the infinite energy point of the
collision strength. This work is carried out as part of the Iron Project-RmaX
Network.",0603482v1
2006-07-25,Metal-rich Damped/sub-Damped Lyman-alpha Quasar Absorbers at z<1,"Damped Lyman-alpha absorbers (DLAs), seen in absorption against a background
quasar, provide the most detailed probes available of element abundances in the
Universe over > 90 % of its age. DLAs can be used to observationally measure
the global mean metallicity in the Universe and its evolution with time.
Paradoxically, these observations are more difficult at lower redshifts, where
the absorber rest-frame UV spectra are cut-off due to the atmospheric
absorption. We present here high-resolution VLT/UVES observations of several
elements contained in three DLAs and one sub-DLA with 0.6<z_abs<0.9. We detect
Mg I, Mg II, Fe II, Zn II, Cr II, Mn II, Ti II and Ca II. Our observations more
than double the high-resolution sample of [Zn/H] at z<1. We also report the
discovery of three metal-rich systems, whereas most previous measurements show
low N(HI)-weighted mean metallicity projecting to about 1/6th solar level at
z=0. We derive [Zn/H]=-0.11+/-0.04 at z_abs=0.725, [Zn/H]=-0.54+/-0.20 at
z_abs=0.740 and [Zn/H]=-0.49+/-0.22 at z_abs=0.652, plus one additional upper
limit ([Zn/H]<-0.36 at z_abs=0.842). These measurements confirm the existence
of quasar absorbers with relatively high metallicities based on abundance
estimates free from the effect of dust depletion. Possible implications of
these results for the metallicity of neutral gas phase in the past ~ 8 Gyr are
presented and compared with models.",0607561v1
1994-09-29,Avalanches in the Weakly Driven Frenkel-Kontorova Model,"A damped chain of particles with harmonic nearest-neighbor interactions in a
spatially periodic, piecewise harmonic potential (Frenkel-Kontorova model) is
studied numerically. One end of the chain is pulled slowly which acts as a weak
driving mechanism. The numerical study was performed in the limit of infinitely
weak driving. The model exhibits avalanches starting at the pulled end of the
chain. The dynamics of the avalanches and their size and strength distributions
are studied in detail. The behavior depends on the value of the damping
constant. For moderate values a erratic sequence of avalanches of all sizes
occurs. The avalanche distributions are power-laws which is a key feature of
self-organized criticality (SOC). It will be shown that the system selects a
state where perturbations are just able to propagate through the whole system.
For strong damping a regular behavior occurs where a sequence of states
reappears periodically but shifted by an integer multiple of the period of the
external potential. There is a broad transition regime between regular and
irregular behavior, which is characterized by multistability between regular
and irregular behavior. The avalanches are build up by sound waves and shock
waves. Shock waves can turn their direction of propagation, or they can split
into two pulses propagating in opposite directions leading to transient
spatio-temporal chaos. PACS numbers: 05.70.Ln,05.50.+q,46.10.+z",9409006v1
1998-06-21,Collective intersubband transitions in quantum wells: a comparative density-functional study,"We use time-dependent (current) density functional theory to study collective
transitions between the two lowest subbands in GaAs/AlGaAs quantum wells. We
focus on two systems where experimental results are available: a wide single
and a narrow asymmetric double well. The aim is to calculate frequency and
linewidth of collective electronic modes damped via electron-electron
interaction only. Since Landau damping is not effective here, the dominant
damping mechanism involves dynamical exchange-correlation effects such as
multipair production. To capture these effects, one has to go beyond the widely
used adiabatic local density approximation (ALDA) and include retardation. We
perform a comparative study of two approaches which fall in this category: the
dynamical extension of the ALDA by Gross and Kohn, and a more recent method
which treats exchange and correlation beyond the ALDA as viscoelastic stresses
in the electron liquid. We find that the former method is more robust: it
performs similarly for strongly different degrees of collectivity of the
electronic motion. Results for quantum wells compare reasonably to experiment,
with a tendency towards overdamping. By contrast, the viscoelastic approach is
superior for systems where the electron dynamics is predominantly collective,
but breaks down if the local velocity field is too rapidly varying, as in the
case of a single-electron-like behavior such as tunneling through a potential
barrier.",9806252v1
1998-11-27,Renormalization group analysis of the quantum non-linear sigma model with a damping term,"We investigate the behavior of the zero-temperature quantum non-linear sigma
model in d dimensions in the presence of a damping term of the form f(w)~
|w|^alpha, with 1 \le alpha <2. We find two fixed points: a spin-wave fixed
point FP1 showing a dynamic scaling exponent z=1 and a dissipative fixed point
FP2 with z>1. In the framework of the \epsilon-expansion it is seen that there
is a range of values alpha_*(d) \le alpha \le 2 where the point FP1 is stable
with respect to FP2, so that the system realizes a z=1 quantum critical
behavior even in the presence of a dissipative term. However, reasonable
arguments suggest that in d=2 this range is very narrow. In the broken symmetry
phase we discuss a phenomenological scaling approach, treating damping as a
perturbation of the ordered ground state. The relation of these results with
the pseudogap effect observed in underdoped layered cuprates is discussed.",9811392v2
1999-12-14,Spinwave damping in the two-dimensional ferromagnetic XY model,"The effect of damping of spinwaves in a two-dimensional classical
ferromagnetic XY model is considered. The damping rate $\Gamma_{q}$ is
calculated using the leading diagrams due to the quartic-order deviations from
the harmonic spin Hamiltonian. The resulting four-dimensional integrals are
evaluated by extending the techniques developed by Gilat and others for
spectral density types of integrals. $\Gamma_{q}$ is included into the memory
function formalism due to Reiter and Solander, and Menezes, to determine the
dynamic structure function $S(q,\omega)$. For the infinite sized system, the
memory function approach is found to give non-divergent spinwave peaks, and a
smooth nonzero background intensity (``plateau'' or distributed intensity) for
the whole range of frequencies below the spinwave peak. The background
amplitude relative to the spinwave peak rises with temperature, and eventually
becomes higher than the spinwave peak, where it appears as a central peak. For
finite-sized systems, there are multiple sequences of weak peaks on both sides
of the spinwave peaks whose number and positions depend on the system size and
wavevector in integer units of $2\pi/L$. These dynamical finite size effects
are explained in the memory function analysis as due to either spinwave
difference processes below the spinwave peak or sum processes above the
spinwave peak. These features are also found in classical Monte Carlo --
Spin-Dynamics simulations.",9912241v1
2002-01-25,Time-dependent current density functional theory for the linear response of weakly disordered systems,"This paper develops a quantitatively accurate first-principles description
for the frequency and the linewidth of collective electronic excitations in
inhomogeneous weakly disordered systems. A finite linewidth in general has
intrinsic and extrinsic sources. At low temperatures and outside the region
where electron-phonon interaction occurs, the only intrinsic damping mechanism
is provided by electron-electron interaction. This kind of intrinsic damping
can be described within time-dependent density-functional theory (TDFT), but
one needs to go beyond the adiabatic approximation and include retardation
effects. It was shown previously that a density-functional response theory that
is local in space but nonlocal in time has to be constructed in terms of the
currents, rather than the density. This theory will be reviewed in the first
part of this paper. For quantitatively accurate linewidths, extrinsic
dissipation mechanisms, such as impurities or disorder, have to be included. In
the second part of this paper, we discuss how extrinsic dissipation can be
described within the memory function formalism. We first review this formalism
for homogeneous systems, and then present a synthesis of TDFT with the memory
function formalism for inhomogeneous systems, to account simultaneously for
intrinsic and extrinsic damping of collective excitations. As example, we
calculate frequencies and linewidths of intersubband plasmons in a 40 nm wide
GaAs/AlGaAs quantum well.",0201483v1
2003-06-10,Oscillations of Bose-Einstein condensates with vortex lattices. II. Finite temperatures,"We derive the finite temperature oscillation modes of a harmonically confined
Bose-Einstein condensed gas undergoing rigid body rotation supported by a
vortex lattice in the condensate. The hydrodynamic modes separate into two
classes corresponding to in-phase (center-of-mass) and counter-phase (relative)
oscillations of the thermal cloud and the condensate. The in- and counter-phase
oscillations are independent of each other in the case where the thermal cloud
is inviscid for all modes studied, except the radial pulsations which couple
them because the pressure perturbations of the condensate and the thermal cloud
are governed by different adiabatic indices. If the thermal cloud is viscous,
the two classes of oscillations are coupled, i.e. each type of motion involves
simultaneously mass and entropy currents. The counter-phase oscillations are
damped by the mutual friction between the condensate and the thermal cloud
mediated by the vortex lattice. The damping is large for the values of the
drag-to-lift ratio of the order of unity and becomes increasingly ineffective
in either limit of small or large friction. An experimental measurement of a
subset of these oscillation modes and their damping rates can provide
information on the values of the phenomenological mutual friction coefficients,
and hence the quasiparticle-vortex scattering processes in dilute atomic Bose
gases.",0306245v2
2004-05-14,Thermoelastic relaxation in elastic structures with applications to thin plates,"A new result enables direct calculation of thermoelastic damping in vibrating
elastic solids. The mechanism for energy loss is thermal diffusion caused by
inhomogeneous deformation, flexure in thin plates. The general result is
combined with the Kirchhoff assumption to obtain a new equation for the
flexural vibration of thin plates incorporating thermoelastic loss as a damping
term. The thermal relaxation loss is inhomogeneous and depends upon the local
state of vibrating flexure, specifically, the principal curvatures at a given
point on the plate. Thermal loss is zero at points where the principal
curvatures are equal and opposite, that is, saddle shaped or pure anticlastic
deformation. Conversely, loss is maximum at points where the curvatures are
equal, that is, synclastic or spherical flexure. The influence of modal
urvature on the thermoelastic damping is described through a modal
pparticipation factor. The effect of transverse thermal diffusion on plane wave
propagation is also examined. It is shown that transverse diffusion effects are
always small provided the plate thickness is far greater than the thermal
phonon mean free path, a requirement for the validity of the classical theory
of heat transport. These results generalize Zener's theory of thermoelastic
loss in beams and are useful in predicting mode widths in MEMS and NEMS
oscillators.",0405323v2
2005-04-21,Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals,"The femtosecond optical pump-probe technique was used to study dynamics of
photoexcited electrons and coherent optical phonons in transition metals Zn and
Cd as a function of temperature and excitation level. The optical response in
time domain is well fitted by linear combination of a damped harmonic
oscillation because of excitation of coherent $E_{2g}$ phonon and a
subpicosecond transient response due to electron-phonon thermalization. The
electron-phonon thermalization time monotonically increases with temperature,
consistent with the thermomodulation scenario, where at high temperatures the
system can be well explained by the two-temperature model, while below
$\approx$ 50 K the nonthermal electron model needs to be applied. As the
lattice temperature increases, the damping of the coherent $E_{2g}$ phonon
increases, while the amplitudes of both fast electronic response and the
coherent $E_{2g}$ phonon decrease. The temperature dependence of the damping of
the $E_{2g}$ phonon indicates that population decay of the coherent optical
phonon due to anharmonic phonon-phonon coupling dominates the decay process. We
present a model that accounts for the observed temperature dependence of the
amplitude assuming the photoinduced absorption mechanism, where the signal
amplitude is proportional to the photoinduced change in the quasiparticle
density. The result that the amplitude of the $E_{2g}$ phonon follows the
temperature dependence of the amplitude of the fast electronic transient
indicates that under the resonant condition both electronic and phononic
responses are proportional to the change in the dielectric function.",0504540v1
2005-10-10,Quantum master equation descriptions of a nanomechanical resonator coupled to a single-electron transistor,"We analyse the quantum dynamics of a nanomechanical resonator coupled to a
normal-state single-electron transistor (SET). Starting from a microscopic
description of the system, we derive a master equation for the SET island
charge and resonator which is valid in the limit of weak electro-mechanical
coupling. Using this master equation we show that, apart from brief transients,
the resonator always behaves like a damped harmonic oscillator with a shifted
frequency and relaxes into a thermal-like steady state. Although the behaviour
remains qualitatively the same, we find that the magnitude of the resonator
damping rate and frequency shift depend very sensitively on the relative
magnitudes of the resonator period and the electron tunnelling time. Maximum
damping occurs when the electrical and mechanical time-scales are the same, but
the frequency shift is greatest when the resonator moves much more slowly than
the island charge. We then derive reduced master equations which describe just
the resonator dynamics. By making slightly different approximations, we obtain
two different reduced master equations for the resonator. Apart from minor
differences, the two reduced master equations give rise to a consistent picture
of the resonator dynamics which matches that obtained from the master equation
including the SET island charge.",0510236v1
2005-10-16,Magnetic vortex dynamics in a 2D easy plane ferromagnet,"In this thesis, we consider the dynamics of vortices in the easy plane
insulating ferromagnet in two dimensions. In addition to the quasiparticle
excitations, here spin waves or magnons, this magnetic system admits a family
of vortex solutions carrying two topological invariants, the winding number or
vorticity, and the polarization. A vortex is approximately described as a
particle moving about the system, endowed with an effective mass and acted upon
by a variety of forces. Classically, the vortex has an inter-vortex potential
energy giving a Coulomb-like force (attractive or repulsive depending on the
relative vortex vorticity), and a gyrotropic force, behaving as a self-induced
Lorentz force, whose direction depends on both topological indices. Expanding
semiclassically about a many-vortex solution, the vortices are quantized by
considering the scattered magnon states, giving a zero point energy correction
and a many-vortex mass tensor. The vortices cannot be described as independent
particles--that is, there are off-diagonal mass terms, such as 1/2 Mij vi vj,
that are non-negligible. This thesis examines the full vortex dynamics in
further detail by evaluating the Feynman-Vernon influence functional, which
describes the evolution of the vortex density matrix after the magnon modes
have been traced out. In addition to the set of forces already known, we find
new damping forces acting both longitudinally and transversely to the vortex
motion. The vortex motion within a collective cannot be entirely separated:
there are damping forces acting on one vortex due to the motion of another. The
effective damping forces have memory effects: they depend not only on the
current motion of the vortex collection but also on the motion history.",0510414v1
2006-05-19,Enhancement of noncontact friction between closely spaced bodies by two-dimensional systems,". We consider the effect of an external bias voltage and the spatial
variation of the surface potential, on the damping of cantilever vibrations.
The electrostatic friction is due to energy losses in the sample created by the
electromagnetic field from the oscillating charges induced on the surface of
the tip by the bias voltage and spatial variation of the surface potential. A
similar effect arises when the tip is oscillating in the electrostatic field
created by charged defects in a dielectric substrate. The electrostatic
friction is compared with the van der Waals friction originating from the
fluctuating electromagnetic field due to quantum and thermal fluctuation of the
current density inside the bodies. We show that the electrostatic and van der
Waals friction can be greatly enhanced if on the surfaces of the sample and the
tip there are two-dimension (2D) systems, e.g. a 2D-electron system or
incommensurate layers of adsorbed ions exhibiting acoustic vibrations. We show
that the damping of the cantilever vibrations due to the electrostatic friction
may be of similar magnitude as the damping observed in recent experiments of
Stipe \textit{et al} [B.C.Stipe, H.J.Mamin, T.D.Stowe, T.W.Kenny, and D.Rugar,
Phys.Rev. Lett.% \textbf{87}, 0982001]. We also show that at short separation
the van der Waals friction may be large enough to be measured experimentally.",0605480v1
2006-09-12,Slowing down Josephson vortex lattice in Bi_2Sr_2CaCu_2O_{8+d} with pancake vortices,"We study theoretically and experimentally influence of pancake vortices on
motion of the Josephson vortex lattice in layered high-temperature
superconductors. Mobility of the Josephson vortices in layered superconductors
is strongly suppressed by small amount of pancake-vortex stacks. Moving
Josephson vortex lattice forces oscillating zigzag deformation of the
pancake-vortex stacks contributing to damping. The salient feature of this
contribution is its nonmonotonic dependence on the lattice velocity and the
corresponding voltage. Maximum pancake effect is realized when the Josephson
frequency matches the relaxation frequency of the stacks. The pancake-vortex
damping is strongly suppressed by thermal fluctuations of the pancake vortices.
This theoretical picture was qualitatively confirmed by experiments on two
mesas prepared out of Bi_2Sr_2CaCu_2O_{8+d} whiskers. We found that the
Josephson-vortex flux-flow voltage is very sensitive to small c-axis magnetic
field. The pancake-vortex contribution to the current indeed nonmonotonically
depends on voltage and decreases with increasing temperature and in-plane
magnetic field. We also found that irradiation with heavy ions has no
noticeable direct influence on motion of the Josephson vortices but
dramatically reduces the pancake-vortex contribution to the damping of the
Josephson vortex lattice at low temperatures.",0609262v2
2003-08-24,Numerical analysis of quasinormal modes in nearly extremal Schwarzschild-de Sitter spacetimes,"We calculate high-order quasinormal modes with large imaginary frequencies
for electromagnetic and gravitational perturbations in nearly extremal
Schwarzschild-de Sitter spacetimes. Our results show that for low-order
quasinormal modes, the analytical approximation formula in the extremal limit
derived by Cardoso and Lemos is a quite good approximation for the quasinormal
frequencies as long as the model parameter $r_1\kappa_1$ is small enough, where
$r_1$ and $\kappa_1$ are the black hole horizon radius and the surface gravity,
respectively. For high-order quasinormal modes, to which corresponds
quasinormal frequencies with large imaginary parts, on the other hand, this
formula becomes inaccurate even for small values of $r_1\kappa_1$. We also find
that the real parts of the quasinormal frequencies have oscillating behaviors
in the limit of highly damped modes, which are similar to those observed in the
case of a Reissner-Nordstr{\"" o}m black hole. The amplitude of oscillating
${\rm Re(\omega)}$ as a function of ${\rm Im}(\omega)$ approaches a non-zero
constant value for gravitational perturbations and zero for electromagnetic
perturbations in the limit of highly damped modes, where $\omega$ denotes the
quasinormal frequency. This means that for gravitational perturbations, the
real part of quasinormal modes of the nearly extremal Schwarzschild-de Sitter
spacetime appears not to approach any constant value in the limit of highly
damped modes. On the other hand, for electromagnetic perturbations, the real
part of frequency seems to go to zero in the limit.",0308077v4
2006-02-01,Radiation Damping in Einstein-Aether Theory,"This work concerns the loss of energy of a material system due to
gravitational radiation in Einstein-aether theory-an alternative theory of
gravity in which the metric couples to a dynamical, timelike, unit-norm vector
field. Derived to lowest post-Newtonian order are waveforms for the metric and
vector fields far from a nearly Newtonian system and the rate of energy
radiated by the system. The expressions depend on the quadrupole moment of the
source, as in standard general relativity, but also contain monopolar and
dipolar terms. There exists a one-parameter family of Einstein-aether theories
for which only the quadrupolar contribution is present, and for which the
expression for the damping rate is identical to that of general relativity to
the order worked to here. This family cannot yet be declared observationally
viable, since effects due to the strong internal fields of bodies in the actual
systems used to test the damping rate are not included.",0602004v5
1998-02-20,Real-time Relaxation and Kinetics in Hot Scalar QED: Landau Damping,"The real time evolution of field condensates with soft length scales
k^{-1}>(eT)^{-1} is solved in hot scalar electrodynamics, with a view towards
understanding relaxational phenomena in the QGP and the electroweak plasma. We
find that transverse gauge invariant non-equilibrium expectation values of
fields relax via {\em power laws} to asymptotic amplitudes that are determined
by the quasiparticle poles. The long time relaxational dynamics and relevant
time scales are determined by the behaviour of the retarded self-energy not at
the small frequencies, but at the Landau damping thresholds. This explains the
presence of power laws and not of exponential decay. Furthermore, we derive the
influence functional, the Langevin equation and the fluctuation-dissipation
theorem for the soft modes, identifying the correlation functions that emerge
in the classical limit. We show that a Markovian approximation fails to
describe the dynamics {\em both} at short and long times. We also introduce a
novel kinetic approach that goes beyond the standard Boltzmann equation and
incorporates off-shell processes and find that the distribution function for
soft quasiparticles relaxes with a power law through Landau damping. We also
find an unusual dressing dynamics of bare particles and anomalous (logarithmic)
relaxation of hard quasiparticles.",9802370v2
2003-03-04,Asymptotic quasinormal modes of Reissner-Nordström and Kerr black holes,"According to a recent proposal, the so-called Barbero-Immirzi parameter of
Loop Quantum Gravity can be fixed, using Bohr's correspondence principle, from
a knowledge of highly-damped black hole oscillation frequencies. Such
frequencies are rather difficult to compute, even for Schwarzschild black
holes. However, it is now quite likely that they may provide a fundamental link
between classical general relativity and quantum theories of gravity. Here we
carry out the first numerical computation of very highly damped quasinormal
modes (QNM's) for charged and rotating black holes. In the Reissner-Nordstr\""om
case QNM frequencies and damping times show an oscillatory behaviour as a
function of charge. The oscillations become faster as the mode order increases.
At fixed mode order, QNM's describe spirals in the complex plane as the charge
is increased, tending towards a well defined limit as the hole becomes
extremal. Kerr QNM's have a similar oscillatory behaviour when the angular
index $m=0$. For $l=m=2$ the real part of Kerr QNM frequencies tends to
$2\Omega$, $\Omega$ being the angular velocity of the black hole horizon, while
the asymptotic spacing of the imaginary parts is given by $2\pi T_H$.",0303029v3
2005-01-28,Summation of divergent series and Borel summability for strongly dissipative equations with periodic or quasi-periodic forcing terms,"We consider a class of second order ordinary differential equations
describing one-dimensional systems with a quasi-periodic analytic forcing term
and in the presence of damping. As a physical application one can think of a
resistor-inductor-varactor circuit with a periodic (or quasi-periodic) forcing
function, even if the range of applicability of the theory is much wider. In
the limit of large damping we look for quasi-periodic solutions which have the
same frequency vector of the forcing term, and we study their analyticity
properties in the inverse of the damping coefficient. We find that already the
case of periodic forcing terms is non-trivial, as the solution is not analytic
in a neighbourhood of the origin: it turns out to be Borel-summable. In the
case of quasi-periodic forcing terms we need Renormalization Group techniques
in order to control the small divisors arising in the perturbation series. We
show the existence of a summation criterion of the series in this case also,
but, however, this can not be interpreted as Borel summability.",0501500v1
1997-11-17,Fusion and Binary-Decay Mechanisms in the $^{35}$Cl+$^{24}$Mg System at E/A $\approx$ 8 MeV/Nucleon,"Compound-nucleus fusion and binary-reaction mechanisms have been investigated
for the $^{35}$Cl+$^{24}$Mg system at an incident beam energy of E$_{Lab}$= 282
MeV. Charge distributions, inclusive energy spectra, and angular distributions
have been obtained for the evaporation residues and the binary fragments.
Angle-integrated cross sections have been determined for evaporation residues
from both the complete and incomplete fusion mechanisms. Energy spectra for
binary fragment channels near to the entrance-channel mass partition are
characterized by an inelastic contribution that is in addition to a fully
energy damped component. The fully damped component which is observed in all
the binary mass channels can be associated with decay times that are comparable
to, or longer than the rotation period. The observed mass-dependent cross
sections for the fully damped component are well reproduced by the fission
transition-state model, suggesting a fusion followed by fission origin. The
present data cannot, however, rule out the possibility that a long-lived
orbiting mechanism accounts for part or all of this yield.",9711005v1
1996-12-31,Fluid Models for Kinetic Effects on Coherent Nonlinear Alfven Waves. II. Numerical Solutions,"The influence of various kinetic effects (e.g. Landau damping, diffusive and
collisional dissipation, and finite Larmor radius terms) on the nonlinear
evolution of finite amplitude Alfvenic wave trains in a finite-beta environment
is systematically investigated using a novel, kinetic nonlinear Schrodinger
(KNLS) equation. The dynamics of Alfven waves is sensitive to the sense of
polarization as well as the angle of propagation with respect to the ambient
magnetic field. Numerical solution for the case with Landau damping reveals the
formation of dissipative structures, which are quasi-stationary, S-polarized
directional (and rotational) discontinuities which self-organize from parallel
propagating, linearly polarized waves. Parallel propagating circularly
polarized packets evolve to a few circularly polarized Alfven harmonics on
large scales. Stationary arc-polarized rotational discontinuities form from
obliquely propagating waves. Collisional dissipation, even if weak, introduces
enhanced wave damping when beta is very close to unity. Cyclotron motion
effects on resonant particle interactions introduce cyclotron resonance into
the nonlinear Alfven wave dynamics.",9612018v1
2000-09-06,"Design, fabrication and measurement of the first rounded damped detuned accelerator structure (RDDS1)","As a joint effort in the JLC/NLC research program, we have developed a new
type of damped detuned accelerator structure with optimized round-shaped
cavities (RDDS). This paper discusses some important R&D aspects of the first
structure in this series (RDDS1). The design aspects covered are the cell
design with sub-MHz precision, HOM detuning, coupling and damping technique and
wakefield simulation. The fabrication issues covered are ultra-precision cell
machining with micron accuracy, assembly and diffusion bonding technologies to
satisfactorily meet bookshelf, straightness and cell rotational alignment
requirements. The measurements described are the RF properties of single
cavities and complete accelerator section, as well as wakefields from the ASSET
tests at SLAC. Finally, future improvements are also discussed.",0009025v1
2001-07-19,Dipole Wakefield Suppression In High Phase Advance Detuned Linear Accelerators For The JLC/NLC Designed To Minimise Electrical Breakdown And Cumulative BBU,"Recent experiments at SLAC [1,2] and CERN [3] have revealed evidence of
significant deformation in the form of ""pitting"" of the cells of the 1.8m
series of structures DDS/RDDS (Damped Detuned Structure/Rounded Damped Detuned
Structure). This pitting occurs in the high group velocity (vg /c = 0.012) end
of the accelerating structure and little evidence of breakdown has been found
in the lower group velocity end of the structure. Additional, albeit
preliminary experimental evidence, suggests that shorter and lower group
velocity structures have reduced breakdown events with increasing accelerating
field strengths. Two designs are presented here, firstly a 90cm structure
consisting of 83 cells with an initial vg/c = 0.0506 (known as H90VG5) and
secondly, an even shorter structure of length 60cm consisting of 55 cells with
an initial vg /c = 0.03 (known as H60VG3). The feasibility of using these
structures to accelerate a charged beam over 10km is investigated. The
particular issue focussed upon is suppression of the dipole wakefields via
detuning of the cell frequencies and by locally damping individual cells in
order to avoid BBU (Beam Break Up). Results are presented on beam-induced
dipole wakefields and on the beam dynamics encountered on tracking the progress
of the beam through several thousand accelerating structures.
  [1] C. Adolphsen, ROAA003, this conf. [2] R.H. Miller et al, FPAH062, this
conf. [3] L. Groening et al, MPPH039, this conf",0107049v1
2000-12-10,Chaotic atomic population oscillations between two coupled Bose-Einstein condensates with time-dependent asymmetric trap potential,"We have investigated the chaotic atomic population oscillations between two
coupled Bose-Einstein condensates (BEC) with time-dependent asymmetric trap
potential. In the perturbative regime, the population oscillations can be
described by the Duffing equation, and the chaotic oscillations near the
separatrix solution are analyzed. The sufficient-necessary conditions for
stable oscillations depend on the physical parameters and initial conditions
sensitively. The first-order necessary condition indicates that the Melnikov
function is equal to zero, so the stable oscillations are Melnikov chaotic. For
the ordinary parameters and initial conditions, the chaotic dynamics is
simulated with numerical calculation. If the damping is absent, with the
increasing of the trap asymmetry, the regular oscillations become chaotic
gradually, the corresponding stroboscopic Poincare sections (SPS) vary from a
single island to more islands, and then the chaotic sea. For the completely
chaotic oscillations, the long-term localization disappears and the short-term
localization can be changed from one of the BECs to the other through the route
of Rabi oscillation. When there exists damping, the stationary chaos
disappears, the transient chaos is a common phenomenon before regular stable
frequency locked oscillations. And proper damping can keep localization
long-lived.",0012043v1
2003-01-23,Revivals and entanglement from initially entangled mixed states of a damped Jaynes-Cummings model,"An exact density matrix of a phase-damped Jaynes - Cummings model (JCM) with
entangled Bell-like initial states formed from a model two-state atom and sets
of adjacent photon number states of a single mode radiation field is presented.
The entanglement of the initial states and the subsequent time evolution is
assured by finding a positive lower bound on the concurrence of local 2x2
projections of the full 2xinfinity JCM density matrix. It is found that the
time evolution of the lower bound of the concurrence systematically captures
the corresponding collapse and revival features in atomic inversion, relative
entropies of atomic and radiation, mutual entropy, and quantum deficit. The
atom and radiation subsystems exhibit alternating sets of collapses and
revivals in a complementary fashion due to the initially mixed states of the
atom and radiation employed here. This is in contrast with the result obtained
when the initial state of the dissipationless system is a factored pure state
of atom and radiation, where the atomic and radiation entropies are necessarily
the same. The magnitudes of the entanglement lower bound and the atomic and
radiation revivals become larger as both magnitude and phase of the Bell-like
initial state contribution increases. The time evolution of the entropy
difference of the total system and that of the radiation subsystem exhibits
negative regions called ""supercorrelated"" states which do not appear in the
atomic subsystem. Entangled initial states are found to enhance this
supercorrelated feature. Finally, the effect of phase damping is to randomize
both the subsystems for asymptotically long times .",0301126v1
2003-03-18,A Method for Modeling Decoherence on a Quantum Information Processor,"We develop and implement a method for modeling decoherence processes on an
N-dimensional quantum system that requires only an $N^2$-dimensional quantum
environment and random classical fields. This model offers the advantage that
it may be implemented on small quantum information processors in order to
explore the intermediate regime between semiclassical and fully quantum models.
We consider in particular $\sigma_z\sigma_z$ system-environment couplings which
induce coherence (phase) damping, though the model is directly extendable to
other coupling Hamiltonians. Effective, irreversible phase-damping of the
system is obtained by applying an additional stochastic Hamiltonian on the
environment alone, periodically redressing it and thereby irreversibliy
randomizing the system phase information that has leaked into the environment
as a result of the coupling. This model is exactly solvable in the case of
phase-damping, and we use this solution to describe the model's behavior in
some limiting cases. In the limit of small stochastic phase kicks the system's
coherence decays exponentially at a rate which increases linearly with the kick
frequency. In the case of strong kicks we observe an effective decoupling of
the system from the environment. We present a detailed implementation of the
method on an nuclear magnetic resonance quantum information processor.",0303115v1
2005-11-25,The electrodynamic 2-body problem and the origin of quantum mechanics,"We numerically solve the functional differential equations (FDE's) of
2-particle electrodynamics, using the full electrodynamic force obtained from
the retarded Lienard-Wiechert potentials and the Lorentz force law. In
contrast, the usual formulation uses only the Coulomb force (scalar potential),
reducing the electrodynamic 2-body problem to a system of ordinary differential
equations (ODE's). The ODE formulation is mathematically suspect since FDE's
and ODE's are known to be incompatible; however, the Coulomb approximation to
the full electrodynamic force has been believed to be adequate for physics. We
can now test this long-standing belief by comparing the FDE solution with the
ODE solution, in the historically interesting case of the classical hydrogen
atom. The solutions differ.
  A key qualitative difference is that the full force involves a `delay'
torque. Our existing code is inadequate to calculate the detailed interaction
of the delay torque with radiative damping. However, a symbolic calculation
provides conditions under which the delay torque approximately balances (3rd
order) radiative damping. Thus, further investigations are required, and it was
prematurely concluded that radiative damping makes the classical hydrogen atom
unstable. Solutions of FDE's naturally exhibit an_infinite_ spectrum of
_discrete_ frequencies. The conclusion is that (a) the Coulomb force is_not_ a
valid approximation to the full electrodynamic force, so that (b) the n-body
interaction needs to be reformulated in various current contexts such as
molecular dynamics.",0511235v1
2007-05-11,Ground-state cooling of a micromechanical oscillator: generalized framework for cold damping and cavity-assisted cooling schemes,"We provide a general framework to describe cooling of a micromechanical
oscillator to its quantum ground state by means of radiation-pressure coupling
with a driven optical cavity. We apply it to two experimentally realized
schemes, back-action cooling via a detuned cavity and cold-damping
quantum-feedback cooling, and we determine the ultimate quantum limits of both
schemes for the full parameter range of a stable cavity. While both allow to
reach the oscillator's quantum ground state, we find that back-action cooling
is more efficient in the good cavity limit, i.e. when the cavity bandwidth is
smaller than the mechanical frequency, while cold damping is more suitable for
the bad cavity limit. The results of previous treatments are recovered as
limiting cases of specific parameter regimes.",0705.1728v6
2007-11-08,Solving non-linear equations of longitudinal and transverse electron waves in collisionless Maxwellian plasma,"We have considered an expansion of solutions of the non-linear equations for
both longitudinal and transverse waves in collisionless Maxwellian plasma in
series of non-damping overtones of the field E(x,t) and electron velocity
distribution function f=f(0) +f(1) where f(0) is background Maxwellian electron
distribution function and f(1) is perturbation. The electrical field and
perturbation f(1) are presented as a series of non-damping harmonics with
increasing frequencies of the order n and the same propagation speed. It is
shown presence of recurrent relations for arising overtones. Convergence of the
series is provided by a power law parameter series convergence. There are
proposed also successive procedures of cutting off the distribution function
f(1) to the condition of positivity f near the singularity points where kinetic
equation becomes inapplicable. In this case, at poles absence the solution
reduces to non-damping Vlasov waves (oscillations). In the case of transverse
waves, dispersion equation has two roots, corresponding to the branches of fast
electromagnetic and slow electron waves. There is noted a possibility of
experimental testing appearing exotic results with detecting frequencies and
amplitudes of n-order overtones.",0711.1321v8
2008-02-14,Influence of an inner disc on the orbital evolution of massive planets migrating in resonance,"The formation of resonant pairs of planets in exoplanetary systems involves
planetary migration in the protoplanetary disc. After a resonant capture, the
subsequent migration in this configuration leads to a large increase of
planetary eccentricities if no damping mechanism is applied. This has led to
the conclusion that the migration of resonant planetary systems cannot occur
over large radial distances and has to be terminated sufficiently rapidly
through disc dissipation.
  In this study, we investigate whether the presence of an inner disc might
supply an eccentricity damping of the inner planet, and if this effect could
explain the observed eccentricities in some systems. To investigate the
influence of an inner disc, we first compute hydrodynamic simulations of giant
planets orbiting with a given eccentricity around an inner gas disc, and
measure the effect of the latter on the planetary orbital parameters. We then
perform detailed long term calculations of the GJ 876 system. We also run
N-body simulations with artificial forces on the planets mimicking the effects
of the inner and outer discs.
  We find that the influence of the inner disc can not be neglected, and that
it might be responsible for the observed eccentricities. In particular, we
reproduce quite well the orbital parameters of a few systems engaged in 2:1
mean motion resonances: GJ 876, HD 73526, HD 82943 and HD 128311. Finally, we
derive analytically the effect that the inner disc should have on the inner
planet to reach a specific orbital configuration with a given damping effect of
the outer disc on the outer planet.",0802.2014v1
2008-04-10,Embedded Oscillating Starless Cores,"In a previous paper we demonstrated that non-radial hydrodynamic oscillations
of a thermally-supported (Bonnor-Ebert) sphere embedded in a low-density,
high-temperature medium persist for many periods. The predicted column density
variations and molecular spectral line profiles are similar to those observed
in the Bok globule B68 suggesting that the motions in some starless cores may
be oscillating perturbations on a thermally supported equilibrium structure.
Such oscillations can produce molecular line maps which mimic rotation,
collapse or expansion, and thus could make determining the dynamical state from
such observations alone difficult.
  However, while B68 is embedded in a very hot, low-density medium, many
starless cores are not, having interior/exterior density contrasts closer to
unity. In this paper we investigate the oscillation damping rate as a function
of the exterior density. For concreteness we use the same interior model
employed in Broderick et al. (2007), with varying models for the exterior gas.
We also develop a simple analytical formalism, based upon the linear
perturbation analysis of the oscillations, which predicts the contribution to
the damping rates due to the excitation of sound waves in the external medium.
We find that the damping rate of oscillations on globules in dense molecular
environments is always many periods, corresponding to hundreds of thousands of
years, and persisting over the inferred lifetimes of the globules.",0804.1790v1
2008-05-07,Design of parametrically forced patterns and quasipatterns,"The Faraday wave experiment is a classic example of a system driven by
parametric forcing, and it produces a wide range of complex patterns, including
superlattice patterns and quasipatterns. Nonlinear three-wave interactions
between driven and weakly damped modes play a key role in determining which
patterns are favoured. We use this idea to design single and multi-frequency
forcing functions that produce examples of superlattice patterns and
quasipatterns in a new model PDE with parametric forcing. We make quantitative
comparisons between the predicted patterns and the solutions of the PDE.
Unexpectedly, the agreement is good only for parameter values very close to
onset. The reason that the range of validity is limited is that the theory
requires strong damping of all modes apart from the driven pattern-forming
modes. This is in conflict with the requirement for weak damping if three-wave
coupling is to influence pattern selection effectively. We distinguish the two
different ways that three-wave interactions can be used to stabilise
quasipatterns, and present examples of 12-, 14- and 20-fold approximate
quasipatterns. We identify which computational domains provide the most
accurate approximations to 12-fold quasipatterns, and systematically
investigate the Fourier spectra of the most accurate approximations.",0805.0878v1
2008-06-19,Itinerant spin excitations near the hidden order transition in URu2Si2,"By means of neutron scattering we show that the high-temperature precursor to
the hidden order state of the heavy fermion superconductor URu$_{2}$Si$_{2}$
exhibits heavily damped incommensurate paramagnons whose strong energy
dispersion is very similar to that of the long-lived longitudinal f-spin
excitations that appear below T$_{0}$. Since the underlying local f-exchange is
preserved we expect only the f-d interactions to change across the phase
transition and to cause the paramagnetic damping. The damping exhibits
single-ion behavior independent of wave vector and vanishes below the hidden
order transition. We suggest that this arises from a transition from valence
fluctuations to a hybridized f-d state below T$_{0}$. Here we present evidence
that the itinerant excitations, like those in chromium, are due to Fermi
surface nesting of hole and electron pockets so that the hidden order phase
likely originates from a Fermi-surface instability. We identify wave vectors
that span nested regions of a band calculation and that match the neutron spin
crossover from incommensurate to commensurate on approach to the hidden order
phase.",0806.3137v2
2008-11-21,Specific heat anomalies of open quantum systems,"The evaluation of the specific heat of an open, damped quantum system is a
subtle issue. One possible route is based on the thermodynamic partition
function which is the ratio of the partition functions of system plus bath and
of the bath alone. For the free damped particle it has been shown, however,
that the ensuing specific heat may become negative for appropriately chosen
environments. Being an open system this quantity then naturally must be
interpreted as the change of the specific heat obtained as the difference
between the specific heat of the heat bath coupled to the system degrees of
freedom and the specific heat of the bath alone. While this difference may
become negative, the involved specific heats themselves are always positive;
thus, the known thermodynamic stability criteria are perfectly guaranteed. For
a damped quantum harmonic oscillator, instead of negative values, under
appropriate conditions one can observe a dip in the difference of specific
heats as a function of temperature. Stylized minimal models containing a single
oscillator heat bath are employed to elucidate the occurrence of the anomalous
temperature dependence of the corresponding specific heat values. Moreover, we
comment on the consequences for the interpretation of the density of states
based on the thermal partitionfunction.",0811.3509v2
2008-11-26,Three-dimensional simulations of multiple protoplanets embedded in a protostellar disc,"Protoplanet eccentricities of e >~ H/r can slow or reverse migration, but
previous 2D studies have shown that gravitational scattering cannot maintain
significant planet eccentricities against disc-induced damping. We simulate the
evolution of low-mass protoplanetary swarms in three dimensions. The aim is to
examine both protoplanet survival rates and the dynamical structure of the
resulting planetary systems, and to compare them with 2D simulations. We
present results from a 3D hydrodynamic simulation of eight protoplanets
embedded in a protoplanetary disc. We also present a suite of simulations
performed using an N-body code, modified to include prescriptions for planetary
migration and for eccentricity and inclination damping. These prescriptions
were obtained by fitting analytic formulae to hydrodynamic simulations of
planets embedded in discs with initially eccentric and/or inclined orbits. As
was found in two dimensions, differential migration produces groups of
protoplanets in stable, multiple mean-motion resonances that migrate in
lockstep, preventing prolonged periods of gravitational scattering. In almost
all simulations, this leads to large-scale migration of the protoplanet swarm
into the central star in the absence of a viable stopping mechanism. The
evolution involves mutual collisions, occasional instances of large-scale
scattering, and the frequent formation of the long-lived, co-orbital planet
systems that arise in > 30% of all runs. Disc-induced damping overwhelms
eccentricity and inclination growth due to planet-planet interactions.
Co-orbital planets are a natural outcome of dynamical relaxation in a strongly
dissipative environment, and if observed in nature would imply that such a
period of evolution commonly arises during planetary formation.",0811.4322v1
2008-12-15,Swift-UVOT captures the earliest ultraviolet spectrum of a Gamma Ray Burst,"We present the earliest ever ultraviolet spectrum of a gamma-ray burst (GRB)
as observed with the Swift-UVOT. The GRB 081203A spectrum was observed for 50
seconds with the UV grism starting 251 seconds after the Swift-BAT trigger when
the GRB was of u ~13.4 mag and still rising to its peak optical brightness. The
UV grism spectrum shows a damped Ly-alpha line, Ly-beta, and the Lyman
continuum break at a redshift z = 2.05 +/- 0.01. A model fit to the Lyman
absorption implies log N(HI) = 22.0 +/- 0.2 cm-2, which is typical for GRB host
galaxies with damped Ly-alpha absorbers. This observation of GRB 081203A
demonstrates that for GRBs brighter than v ~14 mag and with 0.5 < z < 3.5 the
UVOT will be able to provide redshifts, and probe for damped Ly-alpha absorbers
within 4-6 minutes from the time of the Swift-BAT trigger.",0812.2943v2
2008-12-16,On the oscillations of dissipative superfluid neutron stars,"We investigate the oscillations of slowly rotating superfluid stars, taking
into account the vortex mediated mutual friction force that is expected to be
the main damping mechanism in mature neutron star cores. Working to linear
order in the rotation of the star, we consider both the fundamental f-modes and
the inertial r-modes. In the case of the (polar) f-modes, we work out an
analytic approximation of the mode which allows us to write down a closed
expression for the mutual friction damping timescale. The analytic result is in
good agreement with previous numerical results obtained using an energy
integral argument. We extend previous work by considering the full range of
permissible values for the vortex drag, e.g. the friction between each
individual vortex and the electron fluid. This leads to the first ever results
for the f-mode in the strong drag regime. Our estimates provide useful insight
into the dependence on, and relevance of, various equation of state parameters.
In the case of the (axial) r-modes, we confirm the existence of two classes of
modes. However, we demonstrate that only one of these sets remains purely axial
in more realistic neutron star models. Our analysis lays the foundation for
companion studies of the mutual friction damping of the r-modes at second order
in the slow-rotation approximation, the first time evolutions for superfluid
neutron star perturbations and also the first detailed attempt at studying the
dynamics of superfluid neutron stars with both a relative rotation between the
components and mutual friction.",0812.3023v1
2009-03-27,Cascade and Damping of Alfvén-Cyclotron Fluctuations: Application to Solar Wind Turbulence,"It is well-recognized that the presence of magnetic fields will lead to
anisotropic energy cascade and dissipation of astrophysical turbulence. With
the diffusion approximation and linear dissipation rates, we study the cascade
and damping of Alfv\'en-cyclotron fluctuations in solar plasmas numerically.
For an isotropic case the steady-state turbulence spectra are nearly isotropic
in the inertial range and can be fitted by a single power-law function with a
spectral index of -3/2, similar to the Iroshnikov-Kraichnan phenomenology.
Beyond the MHD regime the kinetic effects make the spectrum softer at higher
wavenumbers. In the dissipation range the turbulence spectrum cuts off at the
wavenumber, where the damping rate becomes comparable to the cascade rate, and
the cutoff wavenumber changes with the wave propagation direction. The angle
averaged turbulence spectrum of the isotropic model resembles a broken
power-law. Taking into account the Doppler effects, the model naturally
reproduces the broken power-law turbulence spectra observed in the solar wind
and predicts that a higher break frequency always comes along with a softer
dissipation range spectrum that may be caused by the increase of the turbulence
intensity, the reciprocal of the plasma \beta, and/or the angle between the
solar wind velocity and the mean magnetic field. These predictions can be
tested by detailed comparisons with more accurate observations.",0903.4904v1
2009-04-17,Plasmons and polaritons in a semi-infinite plasma and a plasma slab,"Plasmon and polariton modes are derived for an ideal semi-infinite
(half-space) plasma and an ideal plasma slab by using a general, unifying
procedure, based on equations of motion, Maxwell's equations and suitable
boundary conditions. Known results are re-obtained in much a more direct manner
and new ones are derived. The approach consists of representing the charge
disturbances by a displacement field in the positions of the moving particles
(electrons). The dielectric response and the electron energy loss are computed.
The surface contribution to the energy loss exhibits an oscillatory behaviour
in the transient regime near the surfaces. The propagation of an
electromagnetic wave in these plasmas is treated by using the retarded
electromagnetic potentials. The resulting integral equations are solved and the
reflected and refracted waves are computed, as well as the reflection
coefficient. For the slab we compute also the transmitted wave and the
transmission coefficient. Generalized Fresnel's relations are thereby obtained
for any incidence angle and polarization. Bulk and surface plasmon-polariton
modes are identified. As it is well known, the field inside the plasma is
either damped (evanescent) or propagating (transparency regime), and the
reflection coefficient for a semi-infinite plasma exhibits an abrupt
enhancement on passing from the propagating regime to the damped one (total
reflection). Similarly, apart from characteristic oscillations, the reflection
and transmission coefficients for a plasma slab exhibit an appreciable
enhancement in the damped regime.",0904.2662v1
2009-04-29,Synthetic electric fields and phonon damping in carbon nanotubes and graphene,"Smoothly varying lattice strain in graphene affects the Dirac carriers
through a synthetic gauge field. When the lattice strain is time dependent, as
in connection with phononic excitations, the gauge field becomes time dependent
and the synthetic vector potential is also associated with an electric field.
We show that this synthetic electric field has observable consequences. Joule
heating associated with the currents driven by the synthetic electric field
dominates the intrinsic damping, caused by the electron-phonon interaction, of
many acoustic phonon modes of graphene and metallic carbon nanotubes when
including the effects of disorder and Coulomb interactions. Several important
consequences follow from the observation that by time-reversal symmetry, the
synthetic electric field associated with the vector potential has opposite
signs for the two valleys. First, this implies that the synthetic electric
field drives charge-neutral valley currents and is therefore unaffected by
screening. This frequently makes the effects of the synthetic vector potential
more relevant than a competing effect of the scalar deformation potential which
has a much larger bare coupling constant. Second, valley currents decay by
electron-electron scattering (valley Coulomb drag) which causes interesting
temperature dependence of the damping rates. While our theory pertains first
and foremost to metallic systems such as doped graphene and metallic carbon
nanotubes, the underlying mechanisms should also be relevant for semiconducting
carbon nanotubes when they are doped.",0904.4660v1
2009-09-30,Dynamic polarization of graphene by moving external charges: random phase approximation,"We evaluate the stopping and image forces on a charged particle moving
parallel to a doped sheet of graphene by using the dielectric response
formalism for graphene's $\pi$-electron bands in the random phase approximation
(RPA). The forces are presented as functions of the particle speed and the
particle distance for a broad range of charge-carrier densities in graphene. A
detailed comparison with the results from a kinetic equation model reveal the
importance of inter-band single-particle excitations in the RPA model for high
particle speeds. We also consider the effects of a finite gap between graphene
and a supporting substrate, as well as the effects of a finite damping rate
that is included through the use of Mermin's procedure. The damping rate is
estimated from a tentative comparison of the Mermin loss function with a HREELS
experiment. In the limit of low particle speeds, several analytical results are
obtained for the friction coefficient that show an intricate relationship
between the charge-carrier density, the damping rate, and the particle
distance, which may be relevant to surface processes and electrochemistry
involving graphene.",0909.5598v3
2010-02-05,Implementation of an Innovative Bio Inspired GA and PSO Algorithm for Controller design considering Steam GT Dynamics,"The Application of Bio Inspired Algorithms to complicated Power System
Stability Problems has recently attracted the researchers in the field of
Artificial Intelligence. Low frequency oscillations after a disturbance in a
Power system, if not sufficiently damped, can drive the system unstable. This
paper provides a systematic procedure to damp the low frequency oscillations
based on Bio Inspired Genetic (GA) and Particle Swarm Optimization (PSO)
algorithms. The proposed controller design is based on formulating a System
Damping ratio enhancement based Optimization criterion to compute the optimal
controller parameters for better stability. The Novel and contrasting feature
of this work is the mathematical modeling and simulation of the Synchronous
generator model including the Steam Governor Turbine (GT) dynamics. To show the
robustness of the proposed controller, Non linear Time domain simulations have
been carried out under various system operating conditions. Also, a detailed
Comparative study has been done to show the superiority of the Bio inspired
algorithm based controllers over the Conventional Lead lag controller.",1002.1184v1
2010-03-12,Improving the model of emission from spinning dust: effects of grain wobbling and transient spin-up,"Observations continue to support the interpretation of the anomalous
microwave foreground as electric dipole radiation from spinning dust grains as
proposed by Draine and Lazarian (1998ab). In this paper we present a refinement
of the original model by improving the treatment of a number of physical
effects. First, we consider a disk-like grain rotating with angular velocity at
an arbitrary angle with respect to the grain symmetry axis and derive the
rotational damping and excitation coefficients arising from infrared emission,
plasma-grain interactions and electric dipole emission. The angular velocity
distribution and the electric dipole emission spectrum for grains is calculated
using the Langevin equation, for cases both with and without fast internal
relaxation. Our results show that, the peak emissivity of spinning dust,
compared to earlier studies, increases by a factor of ~2 for the Warm Neutral
Medium (WNM), the Warm Ionized Medium (WIM), the Cold Neutral Medium (CNM) and
the Photodissociation Region (PDR), and by a factor ~4 for Reflection Nebulae
(RN). The frequency at the emission peak also increases by factors ~1.4 to ~2
for these media. The increased emission and peak frequency result from the
non-sphericity of grain shape and from the anisotropy in damping and excitation
along directions parallel and perpendicular to the grain symmetry axis. Second,
we provide a detailed numerical study including transient spin-up of grains by
single-ion collisions. The impulses broaden the emission spectrum and increase
the peak emissivity for the CNM, WNM and WIM. In addition, we present an
improved treatment of rotational excitation and damping by infrared emission.",1003.2638v2
2010-03-15,Small BGK waves and nonlinear Landau damping,"Consider 1D Vlasov-poisson system with a fixed ion background and periodic
condition on the space variable. First, we show that for general homogeneous
equilibria, within any small neighborhood in the Sobolev space W^{s,p}
(p>1,s<1+(1/p)) of the steady distribution function, there exist nontrivial
travelling wave solutions (BGK waves) with arbitrary minimal period and
traveling speed. This implies that nonlinear Landau damping is not true in
W^{s,p}(s<1+(1/p)) space for any homogeneous equilibria and any spatial period.
Indeed, in W^{s,p} (s<1+(1/p)) neighborhood of any homogeneous state, the long
time dynamics is very rich, including travelling BGK waves, unstable
homogeneous states and their possible invariant manifolds. Second, it is shown
that for homogeneous equilibria satisfying Penrose's linear stability
condition, there exist no nontrivial travelling BGK waves and unstable
homogeneous states in some W^{s,p} (p>1,s>1+(1/p)) neighborhood. Furthermore,
when p=2,we prove that there exist no nontrivial invariant structures in the
H^{s} (s>(3/2)) neighborhood of stable homogeneous states. These results
suggest the long time dynamics in the W^{s,p} (s>1+(1/p)) and particularly, in
the H^{s} (s>(3/2)) neighborhoods of a stable homogeneous state might be
relatively simple. We also demonstrate that linear damping holds for initial
perturbations in very rough spaces, for linearly stable homogeneous state. This
suggests that the contrasting dynamics in W^{s,p} spaces with the critical
power s=1+(1/p) is a trully nonlinear phenomena which can not be traced back to
the linear level.",1003.3005v1
2010-04-06,Electronic screening and damping in magnetars,"We calculate the screening of the ion-ion potential due to electrons in the
presence of a large background magnetic field, at densities of relevance to
neutron star crusts. Using the standard approach to incorporate electron
screening through the one-loop polarization function, we show that the magnetic
field produces important corrections both at short and long distances. In
extreme fields, realized in highly magnetized neutron stars called magnetars,
electrons occupy only the lowest Landau levels in the relatively low density
region of the crust. Here our results show that the screening length for
Coulomb interactions between ions can be smaller than the inter-ion spacing.
More interestingly, we find that the screening is anisotropic and the screened
potential between two static charges exhibits long range Friedel oscillations
parallel to the magnetic field. This long-range oscillatory behavior is likely
to affect the lattice structure of ions, and can possibly create rod-like
structures in the magnetar crusts. We also calculate the imaginary part of the
electron polarization function which determines the spectrum of electron-hole
excitations and plays a role in damping lattice phonon excitations. We
demonstrate that even for modest magnetic fields this damping is highly
anisotropic and will likely lead to anisotropic phonon heat transport in the
outer neutron star crust.",1004.0926v1
2010-06-25,Decoherence window and electron-nuclear cross-relaxation in the molecular magnet V 15,"Rabi oscillations in the V_15 Single Molecule Magnet (SMM) embedded in the
surfactant DODA have been studied at different microwave powers. An intense
damping peak is observed when the Rabi frequency Omega_R falls in the vicinity
of the Larmor frequency of protons w_N, while the damping time t_R of
oscillations reaches values 10 times shorter than the phase coherence time t_2
measured at the same temperature. The experiments are interpreted by the N-spin
model showing that t_R is directly associated with the decoherence via
electronic/nuclear spin cross-relaxation in the rotating reference frame. It is
shown that this decoherence is accompanied with energy dissipation in the range
of the Rabi frequencies w_N - sigma_e < Omega_R < w_N, where sigma_e is the
mean super-hyperfine field (in frequency units) induced by protons at SMMs.
Weaker damping without dissipation takes place outside this dissipation window.
Simple local field estimations suggest that this rapid cross-relaxation in
resonant microwave field observed for the first time in SMMV_15 should take
place in other SMMs like Fe_8 and Mn_12 containing protons, too.",1006.4960v3
2010-08-12,Dynamical damping terms for symmetry-seeking shift conditions,"Suitable gauge conditions are fundamental for stable and accurate
numerical-relativity simulations of inspiralling compact binaries. A number of
well-studied conditions have been developed over the last decade for both the
lapse and the shift and these have been successfully used both in vacuum and
non-vacuum spacetimes when simulating binaries with comparable masses. At the
same time, recent evidence has emerged that the standard ""Gamma-driver"" shift
condition requires a careful and non-trivial tuning of its parameters to ensure
long-term stable evolutions of unequal-mass binaries. We present a novel gauge
condition in which the damping constant is promoted to be a dynamical variable
and the solution of an evolution equation. We show that this choice removes the
need for special tuning and provides a shift damping term which is free of
instabilities in our simulations and dynamically adapts to the individual
positions and masses of the binary black-hole system. Our gauge condition also
reduces the variations in the coordinate size of the apparent horizon of the
larger black hole and could therefore be useful when simulating binaries with
very small mass ratios.",1008.2212v2
2010-08-31,A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - II. Dynamical Properties of the Galaxies towards Q0302-223 and Q1009-0026,"Details of processes through which galaxies convert their gas into stars need
to be studied in order to obtain a complete picture of galaxy formation. One
way to tackle these phenomena is to relate the HI gas and the stars in
galaxies. Here, we present dynamical properties of Damped and sub-Damped
Lyman-alpha Systems identified in H-alpha emission with VLT/SINFONI at near
infra-red wavelengths. While the DLA towards Q0302-223 is found to be
dispersion-dominated, the sub-DLA towards Q1009-0026 shows clear signatures of
rotation. We use a proxy to circular velocity to estimate the mass of the halo
in which the sub-DLA resides and find M_halo=10^12.6 M_sun. We also derive
dynamical masses of these objects, and find M_dyn=10^10.3 M_sun and 10^10.9
M_sun. For one of the two systems (towards Q0302-223), we are able to derive a
stellar mass of M_*=10^9.5 M_sun from Spectral Energy Distribution fit. The gas
fraction in this object is 1/3rd, comparable to similar objects at these
redshifts. Our work illustrates that detailed studies of quasar absorbers can
offer entirely new insights into our knowledge of the interaction between stars
and the interstellar gas in galaxies.",1009.0027v1
2010-11-10,"Standing Slow-Mode Waves in Hot Coronal Loops: Observations, Modeling, and Coronal Seismology","Strongly damped Doppler shift oscillations are observed frequently associated
with flarelike events in hot coronal loops. In this paper, a review of the
observed properties and the theoretical modeling is presented. Statistical
measurements of physical parameters (period, decay time, and amplitude) have
been obtained based on a large number of events observed by SOHO/SUMER and
Yohkoh/BCS. Several pieces of evidence are found to support their
interpretation in terms of the fundamental standing longitudinal slow mode. The
high excitation rate of these oscillations in small- or micro-flares suggest
that the slow mode waves are a natural response of the coronal plasma to
impulsive heating in closed magnetic structure. The strong damping and the
rapid excitation of the observed waves are two major aspects of the waves that
are poorly understood, and are the main subject of theoretical modeling. The
slow waves are found mainly damped by thermal conduction and viscosity in hot
coronal loops. The mode coupling seems to play an important role in rapid
excitation of the standing slow mode. Several seismology applications such as
determination of the magnetic field, temperature, and density in coronal loops
are demonstrated. Further, some open issues are discussed.",1011.2483v1
2010-11-29,Long-time dynamics of Kirchhoff wave models with strong nonlinear damping,"We study well-posedness and long-time dynamics of a class of quasilinear wave
equations with a strong damping. We accept the Kirchhoff hypotheses and assume
that the stiffness and damping coefficients are $C^1$ functions of the
$L_2$-norm of the gradient of the displacement. We first prove the existence
and uniqueness of weak solutions and study their properties for a rather wide
class of nonlinearities which covers the case of possible degeneration (or even
negativity) of the stiffness coefficient and the case of a supercritical source
term. Our main results deal with global attractors. In the case of strictly
positive stiffness factors we prove that in the natural energy space endowed
with a partially strong topology there exists a global attractor whose fractal
dimension is finite. In the non-supercritical case the partially strong
topology becomes strong and a finite dimensional attractor exists in the strong
topology of the energy space. Moreover, in this case we also establish the
existence of a fractal exponential attractor and give conditions that guarantee
the existence of a finite number of determining functionals. Our arguments
involve a recently developed method based on ""compensated"" compactness and
quasi-stability estimates.",1011.6271v3
2010-12-01,Dissipative processes in superfluid neutron stars,"We present some results about a novel damping mechanism of r-mode
oscillations in neutron stars due to processes that change the number of
protons, neutrons and electrons. Deviations from equilibrium of the number
densities of the various species lead to the appearance in the Euler equations
of the system of a dissipative mechanism, the so-called rocket effect. The
evolution of the r-mode oscillations of a rotating neutron star are influenced
by the rocket effect and we present estimates of the corresponding damping
timescales. In the description of the system we employ a two-fluid model, with
one fluid consisting of all the charged components locked together by the
electromagnetic interaction, while the second fluid consists of superfluid
neutrons. Both components can oscillate however the rocket effect can only
efficiently damp the countermoving r-mode oscillations, with the two fluids
oscillating out of phase. In our analysis we include the mutual friction
dissipative process between the neutron superfluid and the charged component.
We neglect the interaction between the two r-mode oscillations as well as
effects related with the crust of the star. Moreover, we use a simplified model
of neutron star assuming a uniform mass distribution.",1012.0345v1
2010-12-08,Nonequilibrium dynamics of the Holstein polaron driven by external electric field,"This work represents a fundamental study of a Holstein polaron in one
dimension driven away from the ground state by a constant electric field.
Taking fully into account quantum effects we follow the time-evolution of the
system from its ground state as the constant electric field is switched on at t
= 0, until it reaches a steady state. At weak electron phonon coupling (EP) the
system experiences damped Bloch oscillations (BO) characteristic for
noninteracting electron band. An analytic expression of the steady state
current is proposed in terms of weak EP coupling and large electric field. For
moderate values of EP coupling the oscillations are almost critically damped
and the system reaches the steady state after a short time. In the strong
coupling limit weakly damped BO, consistent with nearly adiabatic evolution
within the polaron band, persist up to extremely large electric fields. A
traveling polaron under the influence of the electric field leaves behind a
trail of phonon excitations absorbing the excess energy gained from the
electric field. The shape of the traveling polaron is investigated in details.",1012.1716v3
2011-01-19,Numerical simulation of fundamental trapped sausage modes,"Context: We integrate the 2D MHD ideal equations of a straight slab to
simulate observational results associated with fundamental sausage trapped
modes. Aims: Starting from a non-equilibrium state with a dense chromospheric
layer, we analyse the evolution of the internal plasma dynamics of magnetic
loops, subject to line-tying boundary conditions, and with the coronal
parameters described in Asai et al. (2001) and Melnikov et al. (2002) to
investigate the onset and damping of sausage modes. Methods: To integrate the
equations we used a high resolution shock-capturing (HRSC) method specially
designed to deal appropriately with flow discontinuities. Results: Due to
non-linearities and inhomogeneities, pure modes are difficult to sustain and
always occur coupled among them so as to satisfy, e.g., the line-tying
constraint. We found that, in one case, the resonant coupling of the sausage
fundamental mode with a slow one results in a non-dissipative damping of the
former. Conclusions: In scenarios of thick and dense loops, where the
analytical theory predicts the existence of fundamental trapped sausage modes,
the coupling of fast and slow quasi-periodic modes -with a node at the center
of the longitudinal speed- occur contributing to the damping of the fast mode.
If a discontinuity in the total pressure between the loop and the corona is
assumed, a fundamental fast sausage transitory leaky regime is spontaneously
produced and an external compressional Alfv\'en wave takes away the magnetic
energy.",1101.3782v1
2011-03-25,Dissipation and Vertical Energy Transport in Radiation-Dominated Accretion Disks,"Standard models of radiation supported accretion disks generally assume that
diffusive radiation flux is solely responsible for vertical heat transport.
This requires that heat must be generated at a critical rate per unit volume if
the disk is to be in hydrostatic and thermal equilibrium. This raises the
question of how heat is generated and how energy is transported in MHD
turbulence. By analysis of a number of radiation/MHD stratified shearing-box
simulations, we show that the divergence of the diffusive radiation flux is
indeed capped at the critical rate, but deep inside the disk, substantial
vertical energy flux is also carried by advection of radiation. Work done by
radiation pressure is a significant part of the energy budget, and much of this
work is dissipated later through damping by radiative diffusion. We show how
this damping can be measured in the simulations, and identify its physical
origins. Radiative damping accounts for as much as tens of percent of the total
dissipation, and is the only realistic physical mechanism for dissipation of
turbulence that can actually be resolved in numerical simulations of accretion
disks. Buoyancy associated with dynamo-driven, highly magnetized,
nearly-isobaric nonlinear slow magnetosonic fluctuations is responsible for the
radiation advection flux, and also explains the persistent periodic magnetic
upwelling seen at all values of the radiation to gas pressure ratio. The
intimate connection between radiation advection and magnetic buoyancy is the
first example we know of in astrophysics in which a dynamo has direct impact on
the global energetics of a system.",1103.5052v1
2011-06-09,Planet-disk interaction in highly inclined systems,"We study the interaction of a proto-planetary disk and a planet on a highly
inclined orbit in the linear regime. The evolution of the planet is dominated
by dynamical friction for planet masses above several Earth-masses. Smaller
planets are dominated by aerodynamic drag, especially for very high
inclinations and retrograde orbits.
  The time-scales associated with migration and inclination damping are
calculated. For certain values of the inclination, the inclination damping
time-scale is longer than the migration time-scale and the disk lifetime. This
result shows that highly inclined planets can not (re-)align with the
proto-planetary disk.
  We discuss the dependence of numerical simulations on the gravitational
softening parameter. We find only a logarithmic dependence, making global three
dimensional simulations of this process computationally feasible.
  A large fraction of Hot Jupiters is on highly inclined orbits with respect to
the rotation axis of the star. On the other hand small-mass planetary systems
discovered by the Kepler mission have low mutual inclinations. This shows that
there are two distinct formation mechanisms at work. The process that creates
inclined Hot Jupiters does not operate on small mass planets because the
damping timescales are so long that these systems would still be inclined
today.",1106.1869v2
2011-08-16,Brownian force noise from molecular collisions and the sensitivity of advanced gravitational wave observatories,"We present an analysis of Brownian force noise from residual gas damping of
reference test masses as a fundamental sensitivity limit in small force
experiments. The resulting acceleration noise increases significantly when the
distance of the test mass to the surrounding experimental apparatus is smaller
than the dimension of the test mass itself. For the Advanced LIGO
interferometric gravitational wave observatory, where the relevant test mass is
a suspended 340 mm diameter cylindrical end mirror, the force noise power is
increased by roughly a factor 40 by the presence of a similarly shaped reaction
mass at a nominal separation of 5 mm. The force noise, of order 20 fN\rthz\ for
$2 \times 10^{-6}$ Pa of residual H$_2$ gas, rivals quantum optical
fluctuations as the dominant noise source between 10 and 30 Hz. We present here
a numerical and analytical analysis for the gas damping force noise for
Advanced LIGO, backed up by experimental evidence from several recent
measurements. Finally, we discuss the impact of residual gas damping on the
gravitational wave sensitivity and possible mitigation strategies.",1108.3254v2
2011-09-23,Accretion of Rocky Planets by Hot Jupiters,"The observed population of Hot Jupiters displays a stunning variety of
physical properties, including a wide range of densities and core sizes for a
given planetary mass. Motivated by the observational sample, this paper studies
the accretion of rocky planets by Hot Jupiters, after the Jovian planets have
finished their principal migration epoch and become parked in $\sim4$-day
orbits. In this scenario, rocky planets form later and then migrate inward due
to torques from the remaining circumstellar disk, which also damps the orbital
eccentricity. This mechanism thus represents one possible channel for
increasing the core masses and metallicities of Hot Jupiters. This paper
determines probabilities for the possible end states for the rocky planet:
collisions with the Jovian planets, accretion onto the star, ejection from the
system, and long-term survival of both planets. These probabilities depend on
the mass of the Jovian planet and its starting orbital eccentricity, as well as
the eccentricity damping rate for the rocky planet. Since these systems are
highly chaotic, a large ensemble ($N\sim10^3$) of simulations with effectively
equivalent starting conditions is required. Planetary collisions are common
when the eccentricity damping rate is sufficiently low, but are rare otherwise.
For systems that experience planetary collisions, this work determines the
distributions of impact velocities -- both speeds and impact parameters -- for
the collisions. These velocity distributions help determine the consequences of
the impacts, e.g., where energy and heavy elements are deposited within the
giant planets.",1109.5104v1
2011-09-27,Dispersion and damping of zone-boundary magnons in the noncentrosymmetric superconductor CePt3Si,"Inelastic neutron scattering (INS) is employed to study damped spin-wave
excitations in the noncentrosymmetric heavy-fermion superconductor CePt3Si
along the antiferromagnetic Brillouin-zone boundary in the low-temperature
magnetically ordered state. Measurements along the (1/2 1/2 L) and (H H 1/2-H)
reciprocal-space directions reveal deviations in the spin-wave dispersion from
the previously reported model. Broad asymmetric shape of the peaks in energy
signifies strong spin-wave damping by interactions with the particle-hole
continuum. Their energy width exhibits no evident anomalies as a function of
momentum along the (1/2 1/2 L) direction, which could be attributed to
Fermi-surface nesting effects, implying the absence of pronounced commensurate
nesting vectors at the magnetic zone boundary. In agreement with a previous
study, we find no signatures of the superconducting transition in the magnetic
excitation spectrum, such as a magnetic resonant mode or a superconducting spin
gap, either at the magnetic ordering wavevector (0 0 1/2) or at the zone
boundary. However, the low superconducting transition temperature in this
material still leaves the possibility of such features being weak and therefore
hidden below the incoherent background at energies ~0.1 meV, precluding their
detection by INS.",1109.5784v1
2011-11-06,The various manifestations of collisionless dissipation in wave propagation,"The propagation of an electrostatic wave packet inside a collisionless and
initially Maxwellian plasma is always dissipative because of the irreversible
acceleration of the electrons by the wave. Then, in the linear regime, the wave
packet is Landau damped, so that in the reference frame moving at the group
velocity, the wave amplitude decays exponentially with time. In the nonlinear
regime, once phase mixing has occurred and when the electron motion is nearly
adiabatic, the damping rate is strongly reduced compared to the Landau one, so
that the wave amplitude remains nearly constant along the characteristics. Yet,
we show here that the electrons are still globally accelerated by the wave
packet, and, in one dimension, this leads to a non local amplitude dependence
of the group velocity. As a result, a freely propagating wave packet would
shrink, and, therefore, so would its total energy. In more than one dimension,
not only does the magnitude of the group velocity nonlinearly vary, but also
its direction. In the weakly nonlinear regime, when the collisionless damping
rate is still significant compared to its linear value, this leads to an
effective defocussing effect which we quantify, and which we compare to the
self-focussing induced by wave front bowing.",1111.1391v2
2011-11-15,Spin waves in nanosized magnetic films,"We have studied spin excitations in nanosized magnetic films in the
Heisenberg model with magnetic dipole and exchange interactions by the spin
operator diagram technique. Dispersion relations of spin waves in thin magnetic
films (in two-dimensional magnetic monolayers and in two-layer magnetic films)
and the spin-wave resonance spectrum in N-layer structures are found. For thick
magnetic films generalized Landau-Lifshitz equations are derived from first
principles. Landau-Lifshitz equations have the integral (pseudodifferential)
form, but not differential one. Spin excitations are determined by simultaneous
solution of the Landau-Lifshitz equations and the equation for the
magnetostatic potential. For normal magnetized ferromagnetic films the spin
wave damping has been calculated in the one-loop approximation for a diagram
expansion of the Green functions at low temperature. In thick magnetic films
the magnetic dipole interaction makes a major contribution to the relaxation of
long-wavelength spin waves. Thin films have a region of low relaxation of
long-wavelength spin waves. In thin magnetic films four-spin-wave processes
take place and the exchange interaction makes a major contribution to the
damping. It is found that the damping of spin waves propagating in magnetic
monolayer is proportional to the quadratic dependence on the temperature and is
very low for spin waves with small wavevectors. Spin-wave devices on the base
of nanosized magnetic films are proposed -- tunable narrow-band spin-wave
filters with high quality at the microwave frequency range and field-effect
transistor (FET) structures contained nanosized magnetic films under the gate
electrode. Spin-wave resonances in nanosized magnetic films can be used to
construct FET structures operating in Gigahertz and Terahertz frequency bands.",1111.3532v1
2011-12-16,Nonlinear viscous damping and gravitational wave detectability of the f-mode instability in neutron stars,"We study the damping of the gravitational radiation-driven f-mode instability
in rotating neutron stars by nonlinear bulk viscosity in the so-called
supra-thermal regime. In this regime the dissipative action of bulk viscosity
is known to be enhanced as a result of nonlinear contributions with respect to
the oscillation amplitude. Our analysis of the f-mode instability is based on a
time-domain code that evolves linear perturbations of rapidly rotating
polytropic neutron star models. The extracted mode frequency and eigenfunctions
are subsequently used in standard energy integrals for the gravitational wave
growth and viscous damping. We find that nonlinear bulk viscosity has a
moderate impact on the size of the f-mode instability window, becoming an
important factor and saturating the mode's growth at a relatively large
oscillation amplitude. We show similarly that nonlinear bulk viscosity leads to
a rather high saturation amplitude even for the r-mode instability. In
addition, we show that the action of bulk viscosity can be significantly
mitigated by the presence of superfluidity in neutron star matter. Apart from
revising the f-mode's instability window we provide results on the mode's
gravitational wave detectability. Considering an f-mode-unstable neutron star
located in the Virgo cluster and assuming a mode amplitude at the level allowed
by bulk viscosity, we find that the emitted gravitational wave signal could be
detectable by advanced ground-based detectors such as Advanced LIGO/Virgo and
the Einstein Telescope.",1112.3931v2
2012-01-23,PageRank and rank-reversal dependence on the damping factor,"PageRank (PR) is an algorithm originally developed by Google to evaluate the
importance of web pages. Considering how deeply rooted Google's PR algorithm is
to gathering relevant information or to the success of modern businesses, the
question of rank-stability and choice of the damping factor (a parameter in the
algorithm) is clearly important. We investigate PR as a function of the damping
factor d on a network obtained from a domain of the World Wide Web, finding
that rank-reversal happens frequently over a broad range of PR (and of d). We
use three different correlation measures, Pearson, Spearman, and Kendall, to
study rank-reversal as d changes, and show that the correlation of PR vectors
drops rapidly as d changes from its frequently cited value, $d_0=0.85$.
Rank-reversal is also observed by measuring the Spearman and Kendall rank
correlation, which evaluate relative ranks rather than absolute PR.
Rank-reversal happens not only in directed networks containing rank-sinks but
also in a single strongly connected component, which by definition does not
contain any sinks. We relate rank-reversals to rank-pockets and bottlenecks in
the directed network structure. For the network studied, the relative rank is
more stable by our measures around $d=0.65$ than at $d=d_0$.",1201.4787v1
2012-02-28,Planetesimal Dynamics in Inclined Binary Systems: The Role of Gas-Disk Gravity,"We investigate the effects of gas-disk gravity on the planetesimal dynamics
in inclined binary systems, where the circumprimary disk plane is tilted by a
significant angle ($i_B$) with respect to the binary disk plane. Our focus is
on the Lidov-Kozai mechanism and the evolution of planetesimal eccentricity and
inclination. Using both analytical and numerical methods, we find that, on one
hand, the disk gravity generally narrows down the Kozai-on region, i.e., the
Lidov-Kozai effect can be suppressed in certain parts of (or even the whole of)
the disk, depending on various parameters. In the Kozai-off region,
planetesimals would move on orbits close to the mid-plane of gas-disk, with the
relative angle ($i^{'}$) following a small amplitude periodical oscillation. On
the other hand, when we include the effects of disk gravity, we find that the
Lidov-Kozai effect can operate even at arbitrarily low inclinations ($i_B$),
although lower $i_B$ leads to a smaller Kozai-on region. Furthermore, in the
Kozai-on region, most planetesimals' eccentricities can be excited to extremely
high values ($\sim 1$), and such extreme high eccentricities usually accompany
orbital flipping, i.e., planetesimal orbit flips back and forth between
anterograde and retrograde. Once a planetesimal reaches very high orbital
eccentricity, gas drag damping will shrink the planetesimal orbit, forming a
""hot planetesimal"" on a near circular orbit very close to the primary star.
Such a mechanism, if replacing the planetesimals and gas drag damping with
Jupiters and tidal damping respectively, may lead to frequent production of
hot-Jupiters.",1202.6102v1
2012-04-20,The Stability of Massive Main Sequence Stars as a Function of Metallicity,"We investigate the pulsational stability of massive (M >~ 120 Msun) main
sequence stars of a range of metallicities, including primordial, Population
III stars. We include a formulation of convective damping motivated by
numerical simulations of the interaction between convection and periodic shear
flows. We find that convective viscosity is likely strong enough to stabilize
radial pulsations whenever nuclear-burning (the epsilon-mechanism) is the
dominant source of driving. This suggests that massive main sequence stars with
Z <~ 2 x 10^-3 are pulsationally stable and are unlikely to experience
pulsation-driven mass loss on the main sequence. These conclusions are,
however, sensitive to the form of the convective viscosity and highlight the
need for further high-resolution simulations of the convection-oscillation
interaction. For more metal-rich stars (Z >~ 2 x 10^-3), the dominant
pulsational driving arises due to the kappa-mechanism arising from the
iron-bump in opacity and is strong enough to overcome convective damping. Our
results highlight that even for oscillations with periods a few orders of
magnitude shorter than the outer convective turnover time, the ""frozen-in""
approximation for the convection-oscillation interaction is inappropriate, and
convective damping should be taken into account when assessing mode stability.",1204.4741v1
2012-05-14,Dynamics of multipartite quantum correlations under decoherence,"Quantum discord is an optimal resource for the quantification of classical
and non-classical correlations as compared to other related measures. Geometric
measure of quantum discord is another measure of quantum correlations.
Recently, the geometric quantum discord for multipartite states has been
introduced by Jianwei Xu [arxiv:quant/ph.1205.0330]. Motivated from the recent
study [Ann. Phys. 327 (2012) 851] for the bipartite systems, I have
investigated global quantum discord (QD) and geometric quantum discord (GQD)
under the influence of external environments for different multipartite states.
Werner-GHZ type three-qubit and six-qubit states are considered in inertial and
non-inertial settings. The dynamics of QD and GQD is investigated under
amplitude damping, phase damping, depolarizing and flipping channels. It is
seen that the quantum discord vanishes for p>0.75 in case of three-qubit GHZ
states and for p>0.5 for six qubit GHZ states. This implies that multipartite
states are more fragile to decoherence for higher values of N. Surprisingly, a
rapid sudden death of discord occurs in case of phase flip channel. However,
for bit flip channel, no sudden death happens for the six-qubit states. On the
other hand, depolarizing channel heavily influences the QD and GQD as compared
to the amplitude damping channel. It means that the depolarizing channel has
the most destructive influence on the discords for multipartite states. From
the perspective of accelerated observers, it is seen that effect of environment
on QD and GQD is much stronger than that of the acceleration of non-inertial
frames. The degradation of QD and GQD happens due to Unruh effect. Furthermore,
QD exhibits more robustness than GQD when the multipartite systems are exposed
to environment.",1205.3133v1
2012-06-04,In search of random uncorrelated particle motion (RUM) in a simple random flow field,"DNS studies of dispersed particle motion in isotropic homogeneous turbulence
[1] have revealed the existence of a component of random uncorrelated motion
(RUM)dependent on the particle inertia {\tau}p(normalised particle response
time or Stoke number). This paper reports the presence of RUM in a simple
linear random smoothly varying flow field of counter rotating vortices where
the two-particle velocity correlation was measured as a function of spatial
separation. Values of the correlation less than one for zero separation
indicated the presence of RUM. In terms of Stokes number, the motion of the
particles in one direction corresponds to either a heavily damped ({\tau}p <
0.25) or lightly damped ({\tau}p > 0.25)harmonic oscillator. In the lightly
damped case the particles overshoot the stagnation lines of the flow and are
projected from one vortex to another (the so-called sling-shot effect). It is
shown that RUM occurs only when {\tau}p > 0.25, increasing monotonically with
increasing Stokes number. Calculations of the particle pair separation
distribution function show that equilibrium of the particle concentration field
is never reached, the concentration at zero separation increasing monotonically
with time. This is consistent with the calculated negative values of the
average Liapounov exponent (finite compressibility) of the particle velocity
field.",1206.0572v1
2012-06-11,Solitons in a parametrically driven damped discrete nonlinear Schrödinger equation,"We consider a parametrically driven damped discrete nonlinear Schr\""odinger
(PDDNLS) equation. Analytical and numerical calculations are performed to
determine the existence and stability of fundamental discrete bright solitons.
We show that there are two types of onsite discrete soliton, namely onsite type
I and II. We also show that there are four types of intersite discrete soliton,
called intersite type I, II, III, and IV, where the last two types are
essentially the same, due to symmetry. Onsite and intersite type I solitons,
which can be unstable in the case of no dissipation, are found to be stabilized
by the damping, whereas the other types are always unstable. Our further
analysis demonstrates that saddle-node and pitchfork (symmetry-breaking)
bifurcations can occur. More interestingly, the onsite type I, intersite type
I, and intersite type III-IV admit Hopf bifurcations from which emerge periodic
solitons (limit cycles). The continuation of the limit cycles as well as the
stability of the periodic solitons are computed through the numerical
continuation software Matcont. We observe subcritical Hopf bifurcations along
the existence curve of the onsite type I and intersite type III-IV. Along the
existence curve of the intersite type I we observe both supercritical and
subcritical Hopf bifurcations.",1206.2405v1
2012-07-13,Axion as a cold dark matter candidate: low-mass case,"Axion as a coherently oscillating scalar field is known to behave as a cold
dark matter in all cosmologically relevant scales. For conventional axion mass
with 10^{-5} eV, the axion reveals a characteristic damping behavior in the
evolution of density perturbations on scales smaller than the solar system
size. The damping scale is inversely proportional to the square-root of the
axion mass. We show that the axion mass smaller than 10^{-24} eV induces a
significant damping in the baryonic density power spectrum in cosmologically
relevant scales, thus deviating from the cold dark matter in the scale smaller
than the axion Jeans scale. With such a small mass, however, our basic
assumption about the coherently oscillating scalar field is broken in the early
universe. This problem is shared by other dark matter models based on the
Bose-Einstein condensate and the ultra-light scalar field. We introduce a
simple model to avoid this problem by introducing evolving axion mass in the
early universe, and present observational effects of present-day low-mass axion
on the baryon density power spectrum, the cosmic microwave background radiation
(CMB) temperature power spectrum, and the growth rate of baryon density
perturbation. In our low-mass axion model we have a characteristic small-scale
cutoff in the baryon density power spectrum below the axion Jeans scale. The
small-scale deviations from the cold dark matter model in both matter and CMB
power spectra clearly differ from the ones expected in the cold dark matter
model mixed with the massive neutrinos as a hot dark matter component.",1207.3124v1
2012-09-04,Solving Vlasov Equations Using NRxx Method,"In this paper, we propose a moment method to numerically solve the Vlasov
equations using the framework of the NRxx method developed in [6, 8, 7] for the
Boltzmann equation. Due to the same convection term of the Boltzmann equation
and the Vlasov equation, it is very convenient to use the moment expansion in
the NRxx method to approximate the distribution function in the Vlasov
equations. The moment closure recently presented in [5] is applied to achieve
the globally hyperbolicity so that the local well-posedness of the moment
system is attained. This makes our simulations using high order moment
expansion accessible in the case of the distribution far away from the
equilibrium which appears very often in the solution of the Vlasov equations.
With the moment expansion of the distribution function, the acceleration in the
velocity space results in an ordinary differential system of the macroscopic
velocity, thus is easy to be handled. The numerical method we developed can
keep both the mass and the momentum conserved. We carry out the simulations of
both the Vlasov-Poisson equations and the Vlasov-Poisson-BGK equations to study
the linear Landau damping. The numerical convergence is exhibited in terms of
the moment number and the spatial grid size, respectively. The variation of
discretized energy as well as the dependence of the recurrence time on moment
order is investigated. The linear Landau damping is well captured for different
wave numbers and collision frequencies. We find that the Landau damping rate
linearly and monotonically converges in the spatial grid size. The results are
in perfect agreement with the theoretic data in the collisionless case.",1209.0527v1
2012-10-09,A close-pair analysis of damp mergers at intermediate redshifts,"We have studied the kinematics of ~2800 candidate close pair galaxies at
0.1<z<1.2 identified from the Canada-France-Hawaii Telescope Legacy Survey
fields. Spectra of these systems were obtained using spectrometers on the 6.5m
Magellan and 5m Hale telescopes. These data allow us to constrain the rate of
dry mergers at intermediate redshifts and to test the `hot halo' model for
quenching of star formation. Using virial radii estimated from the correlation
between dynamical and stellar masses published by Leauthaud et al. (2011), we
find that around 1/5 of our candidate pairs are likely to share a common dark
matter halo (our metric for close physical association). These pairs are
divided into red-red, blue-red and blue-blue systems using the rest-frame
colors classification method introduced in Chou et al. (2011). Galaxies
classified as red in our sample have very low star-formation rates, but they
need not be totally quiescent, and hence we refer to them as `damp', rather
than `dry', systems. After correcting for known selection effects, the fraction
of blue-blue pairs is significantly greater than that of red-red and blue-red
pairs. Red-red pairs are almost entirely absent from our sample, suggesting
that damp mergers are rare at z~0.5. Our data supports models with a short
merging timescale (<0.5 Gyr) in which star-formation is enhanced in the early
phase of mergers, but quenched in the late phase. Hot halo models may explain
this behaviour, but only if virial shocks that heat gas are inefficient until
major mergers are nearly complete.",1210.2692v1
2012-10-24,Dual Trigger of Transverse Oscillations in a Prominence by EUV Fast and Slow Coronal Waves: SDO/AIA and STEREO/EUVI Observations,"We analyze flare-associated transverse oscillations in a quiescent solar
prominence on 8-9 September, 2010. Both the flaring active region and the
prominence were located near the West limb, with a favorable configuration and
viewing angle. The fulldisk extreme ultraviolet (EUV) images of the Sun
obtained with high spatial and temporal resolution by the Atmospheric Imaging
Assembly (AIA) aboard the Solar Dynamics Observatory, show flare-associated
lateral oscillations of the prominence sheet. The STEREO-A spacecraft, 81.5
degrees ahead of the Sun-Earth line, provides on-disk view of the
flare-associated coronal disturbances. We derive the temporal profile of the
lateral displacement of the prominence sheet by using the image
cross-correlation technique. The displacement curve was de-trended and the
residual oscillatory pattern was derived. We fit these oscillations with a
damped cosine function with a variable period and find that the period is
increasing. The initial oscillation period (P0) is 28.2 minutes and the damping
time (t_D) of 44 minutes. We confirm the presence of fast and slow EUV wave
components. Using STEREO-A observations we derive a propagation speed of 250
km/s for the slow EUV wave by applying time-slice technique to the running
difference images. We propose that the prominence oscillations are excited by
the fast EUV wave while the increase in oscillation period of the prominence is
an apparent effect, related to a phase change due to the slow EUV wave acting
as a secondary trigger. We discuss implications of the dual trigger effect for
coronal prominence seismology and scaling law studies of damping mechanisms.",1210.6690v1
2012-10-25,Molecular dissipation in the nonlinear eddy viscosity in the Navier-Stokes equations: modelling of accretion discs,"Physical damping, regarding the nonlinear Navier-Stokes viscous flow
dynamics, refers to a tensorial turbulent dissipation term, attributed to
adjacent moving macroscopic flow components. Mutual dissipation among these
parts of fluid is described by a braking term in the momentum equation together
with a heating term in the energy equation, both responsible of the damping of
the momentum variation and of the viscous conversion of mechanical energy into
heat. A macroscopic mixing scale length is currently the only characteristic
length needed in the nonlinear modelling of viscous fluid dynamics describing
the nonlinear eddy viscosity through the kinematic viscosity coefficient in the
viscous stress tensor, without any reference to the chemical composition and to
the atomic dimensions. Therefore, in this paper, we write a new formulation for
the kinematic viscosity coefficient to the turbulent viscous physical
dissipation in the Navier-Stokes equations, where molecular parameters are also
included. Results of 2D tests are shown, where comparisons among flow
structures are made on 2D shockless radial viscous transport and on 2D damping
of collisional chaotic turbulence. An application to the 3D accretion disc
modelling in low mass cataclysmic variables is also discussed. Consequences of
the kinematic viscosity coefficient reformulation in a more strictly physical
terms on the thermal conductivity coefficient for dilute gases are also
discussed. The physical nature of the discussion here reported excludes any
dependence by the pure mathematical aspect of the numerical modelling.",1210.6848v3
2012-11-07,Gaussification through decoherence,"We investigate the loss of nonclassicality and non-Gaussianity of a
single-mode state of the radiation field in contact with a thermal reservoir.
The damped density matrix for a Fock-diagonal input is written using the Weyl
expansion of the density operator. Analysis of the evolution of the
quasiprobability densities reveals the existence of two successive
characteristic times of the reservoir which are sufficient to assure the
positivity of the Wigner function and, respectively, of the $P$ representation.
We examine the time evolution of non-Gaussianity using three recently
introduced distance-type measures. They are based on the Hilbert-Schmidt
metric, the relative entropy, and the Bures metric. Specifically, for an
$M$-photon-added thermal state, we obtain a compact analytic formula of the
time-dependent density matrix that is used to evaluate and compare the three
non-Gaussianity measures. We find a good consistency of these measures on the
sets of damped states. The explicit damped quasiprobability densities are shown
to support our general findings regarding the loss of negativities of Wigner
and $P$ functions during decoherence. Finally, we point out that Gaussification
of the attenuated field mode is accompanied by a nonmonotonic evolution of the
von Neumann entropy of its state conditioned by the initial value of the mean
photon number.",1211.1701v3
2012-11-14,New algorithm for footstep localization using seismic sensors in an indoor environment,"In this study, we consider the use of seismic sensors for footstep
localization in indoor environments. A popular strategy of localization is to
use the measured differences in arrival times of source signals at multiple
pairs of receivers. In the literature, most algorithms that are based on time
differences of arrival (TDOA) assume that the propagation velocity is a
constant as a function of the source position, which is valid for air
propagation or even for narrow band signals. However a bounded medium such as a
concrete slab (encountered in indoor environement) is usually dispersive and
damped. In this study, we demonstrate that under such conditions, the concrete
slab can be assimilated to a thin plate; considering a Kelvin-Voigt damping
model, we introduce the notion of {\em perceived propagation velocity}, which
decreases when the source-sensor distance increases. This peculiar behaviour
precludes any possibility to rely on existing localization methods in indoor
environment. Therefore, a new localization algorithm that is adapted to a
damped and dispersive medium is proposed, using only on the sign of the
measured TDOA (SO-TDOA). A simulation and some experimental results are
included, to define the performance of this SO-TDOA algorithm.",1211.3233v2
2013-02-05,Complex fragment emission in low energy light-ion reactions,"Inclusive energy spectra of the complex fragments (3 $\leq$ Z $\leq$ 5)
emitted in the reactions $^{12}$C (77 MeV)+ $^{28}$Si, $^{11}$B (64 MeV)+
$^{28}$Si and $^{12}$C (73 MeV)+ $^{27}$Al (all having the same excitation
energy of $ \sim$ 67 MeV), have been measured in the angular range of
10$^\circ$ $\lesssim \theta_{lab} \lesssim$ 60$^\circ$. The fully energy damped
(fusion-fission) and the partially energy damped (deep inelastic) components of
the fragment energy spectra have been extracted. It has been found that the
yields of the fully energy damped fragments for all the above reactions are in
conformity with the respective statistical model predictions. The time scales
of various deep inelastic fragment emissions have been extracted from the
angular distribution data. The angular momentum dissipation in deep inelastic
collisions has been estimated from the data and it has been found to be close
to the corresponding sticking limit value.",1302.1002v1
2013-02-11,Propagation of Alfvénic Waves From Corona to Chromosphere and Consequences for Solar Flares,"How do magnetohydrodynamic waves travel from the fully ionized corona, into
and through the underlying partially ionized chromosphere, and what are the
consequences for solar flares? To address these questions, we have developed a
2-fluid model (of plasma and neutrals) and used it to perform 1D simulations of
Alfv\'en waves in a solar atmosphere with realistic density and temperature
structure. Studies of a range of solar features (faculae, plage, penumbra and
umbra) show that energy transmission from corona to chromosphere can exceed 20%
of incident energy for wave periods of one second or less. Damping of waves in
the chromosphere depends strongly on wave frequency: waves with periods 10
seconds or longer pass through the chromosphere with relatively little damping,
however, for periods of 1 second or less, a substantial fraction (37%-100%) of
wave energy entering the chromosphere is damped by ion-neutral friction in the
mid and upper chromosphere, with electron resistivity playing some role in the
lower chromosphere and in umbras. We therefore conclude that Alfv\'enic waves
with periods of a few seconds or less are capable of heating the chromosphere
during solar flares, and speculate that they could also contribute to electron
acceleration or exciting sunquakes.",1302.2458v1
2013-02-25,Non-classical Correlations in the Quantum Search Algorithm,"Entanglement lies at the heart of quantum mechanics and has no classical
analogue. It is central to the speed up achieved by quantum algorithms over
their classical counterparts. The Grover's search algorithm is one such
algorithm which enables us to achieve a quadratic speed up over any known
classical algorithm that searches for an element in an unstructured database.
Here, we analyse and quantify the effects of entanglement in the generalized
version of this algorithm for two qubits. By 'generalized', it is meant that
the use of any arbitrary single qubit unitary gate is permitted to create
superposed states. Our analysis has been firstly on a noise free environment
and secondly in the presence of noise. In the absence of noise, we establish a
relation between the concurrence and the amplitude of the final state thereby
showing the explicit effects of entanglement on the same. Moreover, the effects
of noisy channels, namely amplitude and phase damping channels are studied. We
investigate the amount of quantum correlation in the states obtained after the
phase inversion stage of the algorithm followed by interaction of those states
with the noisy environment. The quantum correlations are quantified by
geometric discord. It has been revealed that the states generated after the
effect of amplitude damping on the phase inverted states of the quantum search
algorithm possess non-zero quantum correlation even when entanglement is
absent. However, this is absent in the phase damping scenario.",1302.6005v1
2013-03-01,Generation of Electrostatic Waves via Parametric Instability and Heating of Solar Corona,"In the upper layers of the solar atmosphere the temperature increases
sharply. We studied possibility of the transfer of neutrals motion energy into
the electrostatic waves.Electrostatic waves could damp in the upper layers of
the solar atmosphere and their energy could be transformed into the thermal
energy of the solar atmosphere plasma. When studying the plasma dynamics in the
low altitudes of the solar atmosphere, we investigated hydrodynamics of the
plasma which consists of thee components-electrons, ions and neutrals. In order
to study evolution of disturbances of high amplitudes the parametric resonance
technique is used. The dispersion relation for the electrostatic waves excited
due tot he motion of neutrals is derived. The frequencies of electromagnetic
waves which could be excited due to existence of the acoustic wave are found.
The increment of excited electrostatic waves are determined. The motion of the
neutrals in the lower solar atmosphere, where ionization rate is low, could
excite electrostatic waves. In the upper solar atmosphere the ionization rate
increases and motion of the neutrals could not support electrostatic waves and
these waves could damp due to the collision of the charged particles. The
energy of the damping waves could be transformed into the thermal energy of the
plasma in the upper atmosphere.",1303.0151v1
2013-03-19,Cosmic Ray Streaming in Clusters of Galaxies,"The observed bimodality in radio luminosity in galaxy clusters is puzzling.
We investigate the possibility that cosmic-ray (CR) streaming in the
intra-cluster medium can 'switch off' hadronically induced radio and gamma-ray
emission. For self-confined CRs, this depends on the source of MHD wave
damping: if only non-linear Landau damping operates, then CRs stream on the
slow Alfvenic timescale, but if turbulent wave damping operates, super-Alfvenic
streaming is possible. As turbulence increases, it promotes outward streaming
more than it enables inward turbulent advection. Curiously, the CR flux is
independent of $\nabla f$ (as long as it is non-zero) and depends only on
plasma parameters; this enables radio halos with flat inferred CR profiles to
turn off. We perform 1D time-dependent calculations of a radio mini-halo
(Perseus) and giant radio halo (Coma) and find that both diminish in radio
luminosity by an order of magnitude in several hundred Myr, given plausible
estimates for the magnetic field in the outskirts of the cluster. Due to the
energy dependence of CR streaming, spectral curvature develops, and radio halos
turn off more slowly at low frequencies -- properties consistent with
observations. Similarly, CR streaming rapidly turns off gamma-ray emission at
the high-energies probed by Cherenkov telescopes, but not at the low energies
probed by Fermi. CR mediated wave-heating of the ICM is unaffected, as it is
dominated by ~GeV CRs which stream Alfvenically.",1303.4746v1
2013-05-13,New features of ion acoustic waves in inhomogeneous and permeating plasmas,"It is generally accepted that the ion acoustic (IA) wave in plasmas
containing ions and electrons with the same temperature is of minor importance
due to strong damping of the wave by hot resonant ions. In this work it will be
shown that the IA wave is susceptible to excitation even in plasmas with hot
ions when both an electromagnetic transverse wave and a background density
gradient are present in the plasma, and in addition the wave is in fact
unstable (i.e., growing) in the case of permeating homogeneous plasmas. The
multi-component fluid theory is used to describe the IA wave susceptibility for
excitation in inhomogeneous plasmas and its coupling with electromagnetic
waves. The growing IA wave in permeating homogeneous plasmas is described by
the kinetic theory. In plasmas with density and temperature gradients the IA
wave is effectively coupled with the electromagnetic waves. In comparison to
ordinary IA wave in homogeneous plasma, the Landau damping of the present wave
is much smaller, and to demonstrate this effect a simple but accurate fluid
model is presented for the Landau damping. In the case of permeating plasmas, a
kinetic mechanism for the current-less IA wave instability is presented, with a
very low threshold for excitation as compared with ordinary
electron-current-driven kinetic instability. Such growing IA waves can
effectively heat plasma in the upper solar atmosphere by a stochastic heating
mechanism presented in the work. The results of this work suggest that the IA
wave role in the heating of the solar atmosphere (chromosphere and corona)
should be reexamined.",1305.2739v1
2013-05-15,Beam energy dependence of the viscous damping of anisotropic flow,"The flow harmonics $v_{2,3}$ for charged hadrons, are studied for a broad
range of centrality selections and beam collision energies in Au+Au
($\sqrt{s_{NN}}= 7.7 - 200$ GeV) and Pb+Pb ($\sqrt{s_{NN}}= 2.76$ TeV)
collisions. They validate the characteristic signature expected for the system
size dependence of viscous damping at each collision energy studied. The
extracted viscous coefficients, that encode the magnitude of the ratio of shear
viscosity to entropy density $\eta/s$, are observed to decrease to an apparent
minimum as the collision energy is increased from $\sqrt{s_{NN}}= 7.7$ to
approximately 62.4 GeV; thereafter, they show a slow increase with
$\sqrt{s_{NN}}$ up to 2.76 TeV. This pattern of viscous damping provides the
first experimental constraint for $\eta/s$ in the temperature-baryon chemical
potential ($T, \mu_B$) plane, and could be an initial indication for decay
trajectories which lie close to the critical end point in the phase diagram for
nuclear matter.",1305.3341v3
2013-07-19,Exact 3D solution for static and damped harmonic response of simply supported general laminates,"The state-space method is adapted to obtain three dimensional exact solutions
for the static and damped dynamic behaviors of simply supported general
laminates. The state-space method is written in a general form that permits to
handle both cross-ply and antisymmetric angle-ply laminates. This general form
also permits to obtain exact solutions for general laminates, albeit with some
constraints. For the general case and for the static behavior, either an
additive term is added to the load to simulate simply supported boundary
conditions, or the plate bends in a particular way. For the dynamic behavior,
the general case leads to pairs of natural frequencies for each order, with
associated mode shapes. Finite element simulations have been performed to
validate most of the results presented in this study. As the boundary
conditions needed for the general case are not so straightforward, a specific
discussion has been added. It is shown that these boundary conditions also work
for the two aforementioned laminate classes. The damped harmonic response of a
non symmetrical isotropic sandwich is studied for different frequencies around
the fundamental frequency. The static and undamped dynamic behaviors of the
[-15/15], [0/30/0] and [-10/0/40] laminates are studied for various
length-to-thickness ratios.",1307.5285v2
2013-07-25,Lyman-alpha Heating of Inhomogeneous High-redshift Intergalactic Medium,"The intergalactic medium (IGM) prior to the epoch of reionization consists
mostly of neutral hydrogen gas. Ly-alpha photons produced by early stars
resonantly scatter off hydrogen atoms, causing energy exchange between the
radiation field and the gas. This interaction results in moderate heating of
the gas due to the recoil of the atoms upon scattering, which is of great
interest for future studies of the pre-reionization IGM in the HI 21 cm line.
We investigate the effect of this Ly-alpha heating in the IGM with linear
density, temperature, and velocity perturbations. Perturbations smaller than
the diffusion length of photons could be damped due to heat conduction by
Ly-alpha photons. The scale at which damping occurs and the strength of this
effect depend on various properties of the gas, the flux of Ly-alpha photons
and the way in which photon frequencies are redistributed upon scattering. To
find the relevant length scale and the extent to which Ly-alpha heating affects
perturbations, we calculate the gas heating rates by numerically solving
linearized Boltzmann equations in which scattering is treated by the
Fokker-Planck approximation. We find that (1) perturbations add a small
correction to the gas heating rate, and (2) the damping of temperature
perturbations occurs at scales with comoving wavenumber k>10^4 Mpc^{-1}, which
are much smaller than the Jeans scale and thus unlikely to substantially affect
the observed 21 cm signal.",1307.6859v2
2013-09-13,Analytical and experimental stability investigation of a hardware-in-the-loop satellite docking simulator,"The European Proximity Operation Simulator (EPOS) of the DLR-German Aerospace
Center is a robotics-based simulator that aims at validating and verifying a
satellite docking phase. The generic concept features a robotics tracking
system working in closed loop with a force/torque feedback signal. Inherent
delays in the tracking system combined with typical high stiffness at contact
challenge the stability of the closed-loop system. The proposed concept of
operations is hybrid: the feedback signal is a superposition of a measured
value and of a virtual value that can be tuned in order to guarantee a desired
behavior. This paper is concerned with an analytical study of the system's
closed-loop stability, and with an experimental validation of the hybrid
concept of operations in one dimension (1D). The robotics simulator is modeled
as a second-order loop-delay system and closed-form expressions for the
critical delay and associated frequency are derived as a function of the
satellites' mass and the contact dynamics stiffness and damping parameters. A
numerical illustration sheds light on the impact of the parameters on the
stability regions. A first-order Pade approximation provides additional means
of stability investigation. Experiments were performed and tests results are
described for varying values of the mass and the damping coefficients. The
empirical determination of instability is based on the coefficient of
restitution and on the observed energy. There is a very good agreement between
the critical damping values predicted by the analysis and observed during the
tests...",1309.3512v1
2013-11-12,Investigation into electron cloud effects in the International Linear Collider positron damping ring,"We report modeling results for electron cloud buildup and instability in the
International Linear Collider positron damping ring. Updated optics, wiggler
magnets, and vacuum chamber designs have recently been developed for the 5 GeV,
3.2-km racetrack layout. An analysis of the synchrotron radiation profile
around the ring has been performed, including the effects of diffuse and
specular photon scattering on the interior surfaces of the vacuum chamber. The
results provide input to the cloud buildup simulations for the various magnetic
field regions of the ring. The modeled cloud densities thus obtained are used
in the instability threshold calculations. We conclude that the mitigation
techniques employed in this model will suffice to allow operation of the
damping ring at the design operational specifications.",1311.2890v4
2013-12-18,The behavior of transverse waves in nonuniform solar flux tubes. II. Implications for coronal loop seismology,"Seismology of coronal loops using observations of damped transverse
oscillations in combination with results from theoretical models is a tool to
indirectly infer physical parameters in the solar atmospheric plasma. Existing
seismology schemes based on approximations to the period and damping time of
kink oscillations are often used beyond their theoretical range of
applicability. These approximations assume that the variation of density across
the loop is confined to a nonuniform layer much thinner than the radius of the
loop, but the results of the inversion problem often do not satisfy this
preliminary hypothesis. Here, we determine the accuracy of the analytic
approximations to the period and damping time, and its impact on seismology
estimates, when largely nonuniform loops are considered. We find that the
accuracy of the approximations when used beyond their range of applicability is
strongly affected by the form of the density profile across the loop, that is
observationally unknown and so must be arbitrarily imposed as part of the
theoretical model. The error associated with the analytic approximations can be
larger than 50% even for relatively thin nonuniform layers. This error directly
affects the accuracy of approximate seismology estimates compared to actual
numerical inversions. In addition, assuming different density profiles can
produce noncoincident intervals of the seismic variables in inversions of the
same event. The ignorance about the true shape of density variation across the
loop is an important source of error that may dispute the reliability of
parameters seismically inferred assuming an ad hoc density profile.",1312.5079v1
2014-01-02,Quasi-Normal Modes for Subtracted Rotating and Magnetised Geometries,"We obtain explicit separable solutions of the wave equation of massless
minimally coupled scalar fields in the subtracted geometry of four-dimensional
rotating and Melvin (magnetised) four-charge black holes of the STU model, a
consistent truncation of maximally supersymmetric supergravity with four types
of electromagnetic fields. These backgrounds possess a hidden SL(2,R) x SL(2,R)
x SO(3) symmetry and faithfully model the near horizon geometry of these black
holes, but locate them in a confining asymptotically conical box. For each
subtracted geometry we obtain two branches of quasi-normal modes, given in
terms of hypergeometric functions and spherical harmonics. One branch is
over-damped and the other under-damped and they exhibit rotational splitting.
No black hole bomb is possible because the Killing field which co-rotates with
the horizon is everywhere timelike outside the black hole. A five-dimensional
lift of these geometries is given locally by the product of a BTZ black hole
with a two-sphere. This allows an explicit analysis of the minimally coupled
massive five-dimensional scalar field. Again, there are two branches, both
damped, however now their oscillatory parts are shifted by the quantised wave
number $k$ along the fifth circle direction.",1401.0544v3
2014-03-12,Enhancing robustness of multiparty quantum correlations using weak measurement,"Multipartite quantum correlations are important resources for the development
of quantum information and computation protocols. However, the resourcefulness
of multipartite quantum correlations in practical settings is limited by its
fragility under decoherence due to environmental interactions. Though there
exist protocols to protect bipartite entanglement under decoherence, the
implementation of such protocols for multipartite quantum correlations has not
been sufficiently explored. Here, we study the effect of local amplitude
damping channel on the generalized Greenberger-Horne-Zeilinger state, and use a
protocol of optimal reversal quantum weak measurement to protect the
multipartite quantum correlations. We observe that the weak measurement
reversal protocol enhances the robustness of multipartite quantum correlations.
Further it increases the critical damping value that corresponds to
entanglement sudden death. To emphasize the efficacy of the technique in
protection of multipartite quantum correlation, we investigate two proximately
related quantum communication tasks, namely, quantum teleportation in a one
sender, many receivers setting and multiparty quantum information splitting,
through a local amplitude damping channel. We observe an increase in the
average fidelity of both the quantum communication tasks under the weak
measurement reversal protocol. The method may prove beneficial, for combating
external interactions, in other quantum information tasks using multipartite
resources.",1403.2939v1
2014-04-11,Functional Regression for Quasar Spectra,"The Lyman-alpha forest is a portion of the observed light spectrum of distant
galactic nuclei which allows us to probe remote regions of the Universe that
are otherwise inaccessible. The observed Lyman-alpha forest of a quasar light
spectrum can be modeled as a noisy realization of a smooth curve that is
affected by a `damping effect' which occurs whenever the light emitted by the
quasar travels through regions of the Universe with higher matter
concentration. To decode the information conveyed by the Lyman-alpha forest
about the matter distribution, we must be able to separate the smooth
`continuum' from the noise and the contribution of the damping effect in the
quasar light spectra. To predict the continuum in the Lyman-alpha forest, we
use a nonparametric functional regression model in which both the response and
the predictor variable (the smooth part of the damping-free portion of the
spectrum) are function-valued random variables. We demonstrate that the
proposed method accurately predicts the unobservable continuum in the
Lyman-alpha forest both on simulated spectra and real spectra. Also, we
introduce distribution-free prediction bands for the nonparametric functional
regression model that have finite sample guarantees. These prediction bands,
together with bootstrap-based confidence bands for the projection of the mean
continuum on a fixed number of principal components, allow us to assess the
degree of uncertainty in the model predictions.",1404.3168v1
2014-06-04,Constraints on the gas masses of low-z damped Lyman-$α$ systems,"We report a deep search for redshifted HI 21 cm emission from three damped
and sub-damped Lyman-$\alpha$ absorbers (DLAs) at $z \approx 0.1$ with the
Green Bank Telescope (GBT). No evidence for a redshifted HI 21 cm emission
signal was obtained in the GBT spectra of two absorbers, with the data on the
third rendered unusable by terrestrial interference. The non-detections of HI
21 cm emission yield strong constraints on the HI masses of the associated
galaxies, M$_{\rm HI} < 2.3 \times 10^9 \times (\Delta V/100)^{1/2}$ M$_\odot$
for the sub-DLA at $z = 0.0830$ towards J1553+3548, and M$_{\rm HI} < 2.7
\times 10^9 \times (\Delta V/100)^{1/2}$ M$_\odot$ for the DLA at $z = 0.0963$
towards J1619+3342, where $\Delta V$ is the HI 21 cm line width, in km
s$^{-1}$. This continues the trend of low HI masses found in all low-$z$ DLAs
and sub-DLAs that have been searched for redshifted HI 21 cm emission.
Low-redshift absorbers with relatively low HI column densities, $\lesssim few
\times 10^{20}$ cm$^{-2}$, thus do not typically arise in massive gas-rich
galaxies.",1406.0991v2
2014-06-09,Evolution of eccentricity and orbital inclination of migrating planets in 2:1 mean motion resonance,"We determine, analytically and numerically, the conditions needed for a
system of two migrating planets trapped in a 2:1 mean motion resonance to enter
an inclination-type resonance. We provide an expression for the asymptotic
equilibrium value that the eccentricity $e_{\rm i}$ of the inner planet reaches
under the combined effects of migration and eccentricity damping. We also show
that, for a ratio $q$ of inner to outer masses below unity, $e_{\rm i}$ has to
pass through a value $e_{\rm i,res}$ of order 0.3 for the system to enter an
inclination-type resonance. Numerically, we confirm that such a resonance may
also be excited at another, larger, value $e_{\rm i, res} \simeq 0.6$, as found
by previous authors. A necessary condition for onset of an inclination-type
resonance is that the asymptotic equilibrium value of $e_{\rm i}$ is larger
than $e_{\rm i,res}$. We find that, for $q \le 1$, the system cannot enter an
inclination-type resonance if the ratio of eccentricity to semimajor axis
damping timescales $t_e/t_a$ is smaller than 0.2. This result still holds if
only the eccentricity of the outer planet is damped and $q \lesssim 1$. As the
disc/planet interaction is characterized by $t_e/t_a \sim 10^{-2}$, we conclude
that excitation of inclination through the type of resonance described here is
very unlikely to happen in a system of two planets migrating in a disc.",1406.2189v1
2014-06-13,Magnetic-Field Amplification in the Thin X-ray Rims of SN1006,"Several young supernova remnants (SNRs), including SN1006, emit synchrotron
X-rays in narrow filaments, hereafter thin rims, along their periphery. The
widths of these rims imply 50 to 100 $\mu$G fields in the region immediately
behind the shock, far larger than expected for the interstellar medium
compressed by unmodified shocks, assuming electron radiative losses limit rim
widths. However, magnetic-field damping could also produce thin rims. Here we
review the literature on rim width calculations, summarizing the case for
magnetic-field amplification. We extend these calculations to include an
arbitrary power-law dependence of the diffusion coefficient on energy, $D
\propto E^{\mu}$. Loss-limited rim widths should shrink with increasing photon
energy, while magnetic-damping models predict widths almost independent of
photon energy. We use these results to analyze Chandra observations of SN 1006,
in particular the southwest limb. We parameterize the full widths at half
maximum (FWHM) in terms of energy as FWHM $\propto E^{m_E}_{\gamma}$. Filament
widths in SN1006 decrease with energy; $m_E \sim -0.3$ to $-0.8$, implying
magnetic field amplification by factors of 10 to 50, above the factor of 4
expected in strong unmodified shocks. For SN 1006, the rapid shrinkage rules
out magnetic damping models. It also favors short mean free paths (small
diffusion coefficients) and strong dependence of $D$ on energy ($\mu \ge 1$).",1406.3630v2
2014-07-15,C$ν$B damping of primordial gravitational waves and the fine-tuning of the C$γ$B temperature anisotropy,"Damping of primordial gravitational waves due to the anisotropic stress
contribution owing to the cosmological neutrino background (C$\nu$B) is
investigated in the context of a radiation-to-matter dominated Universe.
Besides its inherent effects on the gravitational wave propagation, the
inclusion of the C$\nu$B anisotropic stress into the dynamical equations also
affects the tensor mode contribution to the anisotropy of the cosmological
microwave background (C$\gamma$B) temperature. Given that the fluctuations of
the C$\nu$B temperature in the (ultra)relativistic regime are driven by a
multipole expansion, the mutual effects on the gravitational waves and on the
C$\gamma$B are obtained through a unified prescription for a
radiation-to-matter dominated scenario. The results are confronted with some
preliminary results for the radiation dominated scenario. Both scenarios are
supported by a simplified analytical framework, in terms of a scale independent
dynamical variable, $k \eta$, that relates cosmological scales, $k$, and the
conformal time, $\eta$. The background relativistic (hot dark) matter
essentially works as an effective dispersive medium for the gravitational waves
such that the damping effect is intensified for the Universe evolving to the
matter dominated era. Changes on the temperature variance owing to the
inclusion of neutrino collision terms into the dynamical equations result into
spectral features that ratify that the multipole expansion coefficients
$C_{l}^{T}$'s die out for $l \sim 100$.",1407.4058v1
2014-08-08,Stable Magnetic Droplet Solitons in Spin Transfer Nanocontacts,"Magnetic thin films with perpendicular magnetic anisotropy (PMA) have
localized excitations that correspond to reversed dynamically precessing
magnetic moments, known as magnetic droplet solitons. Fundamentally, these
excitations are associated with an attractive interaction between elementary
spin-excitations (i.e., magnons) and were predicted to occur in PMA materials
in the absence of damping [1,2]. While damping, present in all magnetic
materials, suppresses these excitations, it is now possible to compensate
damping by spin transfer torques through electrical current flow in nanometer
scale contacts to ferromagnetic thin films [3,4]. A theory predicts the
appearance of magnetic droplet solitons at a threshold current in nanocontacts
[5] and, recently, experimental signatures of droplet nucleation have been
reported [6]. However, thus far, they have been observed to be nearly
reversible excitations, with only partially reversed magnetization and to be
subject to instabilities that cause them to drift away from the nanocontacts
(i.e., drift instabilities) [6]. Here we show that magnetic droplet solitons
can be stabilized in a spin transfer nanocontact. Further, they exhibit a
strong hysteretic response to fields and currents and a nearly fully reversed
magnetization in the contact. These observations, in addition to their
fundamental interest, open up new applications for magnetic droplet solitons as
multi-state high frequency current and field tunable oscillators.",1408.1902v1
2014-08-19,Probing Electron Interactions in a Two-Dimensional System by Quantum Magneto-Oscillations,"We have experimentally studied the renormalized effective mass m* and Dingle
temperature T_D in two spin subbands with essentially different electron
populations. Firstly, we found that the product (m*T_D) that determines damping
of quantum oscillations, to the first approximation, is the same in the
majority and minority subbands even at the spin polarization degree as high as
66\%. This result confirms the theoretical predictions that the interaction
takes place at high energies ~ E_F rather than within a narrow strip of
energies E_F\pm k_BT. Secondly, to the next approximation, we revealed a
difference in the damping factor of the two spin subbands, which causes
skewness of the oscillation lineshape. In the absence of the in-plane magnetic
field, the damping factor (m*T_D) is systematically smaller in the
spin-majority subband. The difference, quantified with the skew factor \gamma =
(T_{D\downarrow}-T_{D\uparrow})/2T_{D0} can be as large as 20%. The skew factor
tends to decrease as B_\parallel or temperature grow, or perpendicular field
decreases; for low electron densities and high in-plane fields the skew factor
even changes sign. Finally, we compared the temperature and magnetic field
dependencies of the magneto-oscillations amplitude with predictions of the
interaction correction theory, and found, besides some qualitative
similarities, several quantitative and qualitative differences. To explain
qualitatively our results, we suggested an empirical model that assumes the
existence of easily magnetized triplet scatterers on the Si/SiO_2 interface.",1408.4393v1
2014-08-20,Josephson junction ratchet: effects of finite capacitances,"We study transport in an asymmetric SQUID which is composed of a loop with
three capacitively and resistively shunted Josephson junctions: two in series
in one arm and the remaining one in the other arm. The loop is threaded by an
external magnetic flux and the system is subjected to both a time-periodic and
a constant current. We formulate the deterministic and, as well, the stochastic
dynamics of the SQUID in terms of the Stewart-McCumber model and derive an
equation for the phase difference across one arm, in which an effective
periodic potential is of the ratchet type, i.e. its reflection symmetry is
broken. In doing so, we extend and generalize earlier study by Zapata et al.
[Phys. Rev. Lett. 77, 2292 (1996)] and analyze directed transport in wide
parameter regimes: covering the over-damped to moderate damping regime up to
its fully under-damped regime. As a result we detect the intriguing features of
a negative (differential) conductance, repeated voltage reversals, noise
induced voltage reversals and solely thermal noise-induced ratchet currents. We
identify a set of parameters for which the ratchet effect is most pronounced
and show how the direction of transport can be controlled by tailoring the
external magnetic flux.",1408.4607v1
2014-09-30,Collective modes in two- and three-dimensional electron systems with Rashba spin-orbit coupling,"In addition to charge plasmons, a 2D electron system with Rashba-type
spin-orbit coupling (SOC) also supports three collective modes in the spin
sector: the chiral-spin modes. We study the dispersions of the charge and spin
modes and their coupling to each other within a generalized Random Phase
Approximation for arbitrarily strong SOC, and both in 2D and 3D systems. In
both 2D and 3D, we find that the charge plasmons are coupled to only one of the
three chiral-spin modes. This coupling is shown to affect the dispersions of
the modes at finite but not at zero wavenumbers. In 3D, the chiral-spin modes
are strongly damped by particle-hole excitations and disappear for weak
electron-electron interaction. Landau damping of the chiral-spin modes in 3D is
directly related to the fact that, in contrast to 2D, there is no gap for
particle-hole excitations between spin-split subbands. The gapless continuum is
also responsible for Landau damping of the charge plasmon in 3D - a
qualitatively new feature of the SOC system. We also discuss the optical
conductivity of clean 2D and 3D systems and show that SOC introduces spectral
weight at finite frequency in a such way that the sum rule is satisfied. The
in-plane tranverse chiral-spin mode shows up as dispersing peak in the optical
conductivity at finite number which can can be measured in the presence of
diffraction grating. We also discuss possible experimental manifestations of
chiral-spin modes in semiconductor quantum wells such InGaAs/AlGaAs and 3D
giant Rashba materials of the BiTeI family.",1409.8666v1
2014-11-15,Spin-transfer-torque through antiferromagnetic IrMn,"Spin-transfer-torque, a transfer of angular momentum between the electron
spin and the local magnetic moments, is a promising and key mechanism to
control ferromagnetic materials in modern spintronic devices . However, much
less attention has been paid to the same effect in antiferromagnets. For the
sake of investigating how the spin current interacts with the magnetic moments
in antiferromagnets, we perform spin-torque ferromagnetic resonance
measurements on Co20Fe60B20 4nm/Ir25Mn75 tIrMn nm/Pt 4 nm multilayers under a
spin Hall effect of Pt. The effective magnetic damping in Co20Fe60B20 is
modified by the spin current injected from the Pt layer via the IrMn layer. The
results indicate that the spin current interacts with IrMn magnetic moments and
exerts the anti-damping torque on the magnetic moments of Co20Fe60B20 through
the IrMn. It is also found that the reduction of the exchange bias in the
IrMn/Pt interface degrades the anti-damping torque exerted on the Co20Fe60B20
layer, suggesting the transmission of the spin torque becomes less efficient as
the interface exchange coupling degrades. Our work infers that the magnetic
moments in IrMn can be manipulated by spin torque similarly to the one in a
ferromagnetic layer.",1411.4100v4
2014-11-28,On damped second-order gradient systems,"Using small deformations of the total energy, as introduced in [31], we
establish that damped second order gradient systems
$$u^{\prime\prime}(t)+\gamma u^\prime(t)+\nabla G(u(t))=0,$$may be viewed as
quasi-gradient systems. In order to study the asymptotic behavior of these
systems, we prove that any (nontrivial) desingularizing function appearing in
KL inequality satisfies $\varphi(s)\ge c\sqrt s$ whenever the original function
is definable and $C^2.$ Variants to this result are given. These facts are used
in turn to prove that a desingularizing function of the potential $G$ also
desingularizes the total energy and its deformed versions. Our approach brings
forward several results interesting for their own sake: we provide an
asymptotic alternative for quasi-gradient systems, either a trajectory
converges, or its norm tends to infinity. The convergence rates are also
analyzed by an original method based on a one-dimensional worst-case gradient
system.We conclude by establishing the convergence of solutions of damped
second order systems in various cases including the definable case. The
real-analytic case is recovered and some results concerning convex functions
are also derived.",1411.8005v5
2014-12-08,Variable frequency characterization of interaction at nanoscale in linear dynamic AFM: an FFM primer,"Using electrostatic coupling between an AFM tip and a metallic surface as a
test interaction, we here present the measurement of the force between the tip
and the surface, together with the measurement of the interaction stiffness and
the associated dissipation. These three quantities constitute a full
characterization of the interaction at nanoscale. They are measured
independently, simultaneously and quantitatively at the same place. This is
made possible thanks to a force feedback method that ensures the DC immobility
of the tip and to the simultaneous application of a sub-nanometer oscillation
to the tip. In this established linear regime, stiffness and damping are
directly obtained from amplitude and phase change measurements. The needed
information for this linear transformation is solely the lever properties in
the experimental context. Knowledge of k, its stiffness, its damping
coefficient and Q0, its first resonance frequency is shown to be sufficient in
the frequency range we are here exploring. Finally, we demonstrate that this
method is not restricted to the lever resonance frequency. To the contrary,
this interaction characterization whose resolution is limited by the Brownian
motion, can be used at any frequencies with essentially the same performances.
We believe that simultaneous and independent measurements of force, stiffness
and damping, out of lever resonance, at nanoscale, and within the context of
linear response define a new AFM paradigm that we call Force Feedback
Microscopy (FFM). This article details the use of FFM using a well known and
easy to implement electrostatic interaction between a regular AFM tip and a
metallic surface in air.",1412.2640v1
2015-01-12,Standing Slow MHD Waves in Radiatively Cooling Coronal Loops,"The standing slow magneto-acoustic oscillations in cooling coronal loops are
investigated. There are two damping mechanisms which are considered to generate
the standing acoustic modes in coronal magnetic loops namely thermal conduction
and radiation. The background temperature is assumed to change temporally due
to optically thin radiation. In particular, the background plasma is assumed to
be radiatively cooling. The effects of cooling on longitudinal slow MHD modes
is analytically evaluated by choosing a simple form of radiative function that
ensures the temperature evolution of the background plasma due to radiation
coincides with the observed cooling profile of coronal loops. The assumption of
low-beta plasma leads to neglect the magnetic field perturbation and eventually
reduces the MHD equations to a 1D system modelling longitudinal MHD
oscillations in a cooling coronal loop. The cooling is assumed to occur on a
characteristic time scale much larger than the oscillation period that
subsequently enables using the WKB theory to study the properties of standing
wave. The governing equation describing the time-dependent amplitude of waves
is obtained and solved analytically. The analytically derived solutions are
numerically evaluated to give further insight into the evolution of the
standing acoustic waves. We find that the plasma cooling gives rise to a
decrease in the amplitude of oscillations. In spite of the reduction in damping
rate caused by rising the cooling, the damping scenario of slow standing MHD
waves strongly increases in hot coronal loops.",1501.02689v1
2015-01-12,Beta decay of 252Cf on the way to scission from the exit point,"Upon increasing significantly the nuclear elongation, the beta-decay energy
grows. This paper investigates within a simple yet partly microscopic approach,
the transition rate of the beta decay of the 252Cf nucleus on the way to
scission from the exit point for a spontaneous fission process. A rather crude
classical approximation is made for the corresponding damped collective motion
assumed to be one dimensional. Given these assumptions, we only aim in this
paper at providing the order of magnitudes of such a phenomenon. At each
deformation the energy available for beta decay, is determined from such a
dynamical treatment. Then, for a given elongation, transition rates for the
allowed (Fermi) beta decay are calculated from pair correlated wave functions
obtained within a macroscopic-microscopic approach and then integrated over the
time corresponding to the whole descent from exit to scission. The results are
presented as a function of the damping factor (inverse of the characteristic
damping time) in use in our classical dynamical approach. For instance, in the
case of a descent time from the exit to the scission points of about $10^{-
20}$ second, one finds a total rate of beta decay corresponding roughly to 20
events per year and per milligram of 252Cf. The inclusion of pairing
correlations does not affect much these results.",1501.02701v1
2015-01-13,Fundamental oscillation modes of neutron stars: validity of universal relations,"We study the $f$-mode frequencies and damping times of nonrotating neutron
stars (NS) in general relativity (GR) by solving the linearized perturbation
equations, with the aim to establish ""universal"" relations that depend only
weakly on the equations of state (EOS). Using a more comprehensive set of EOSs,
we re-examine some proposed linearizations that describe the $f$-mode
parameters in terms of mass and radius of the neutron star (NS), and we test a
more recent proposal for expressing the $f$-mode parameters as quadratic
functions of the effective compactness. Our extensive results for each equation
of state considered allow us to study the accuracy of each proposal. In
particular, we find that the damping time deviates quite considerably from the
proposed linearization. We introduce a new universal relation for the product
of the $f$-mode frequency and damping time as a function of the (ordinary)
compactness, which proved to be more accurate. The relations using the
effective compactness on the other hand also fit our data accurately. Our
results show that the maximum oscillation frequency depends strongly on the
EOS, such that the measurement of a high oscillation frequency would rule out
several EOSs. Lastly, we compare the exact mode frequencies to those obtained
in the Cowling approximation, and also to results obtained with a nonlinear
evolution code, validating the implementations of the different approaches.",1501.02970v2
2015-02-13,Magnetohydrodynamic kink waves in nonuniform solar flux tubes: phase mixing and energy cascade to small scales,"Magnetohydrodynamic (MHD) kink waves are ubiquitously observed in the solar
atmosphere. The propagation and damping of these waves may play relevant roles
for the transport and dissipation of energy in the solar atmospheric medium.
However, in the atmospheric plasma dissipation of transverse MHD wave energy by
viscosity or resistivity needs very small spatial scales to be efficient. Here,
we theoretically investigate the generation of small scales in nonuniform solar
magnetic flux tubes due to phase mixing of MHD kink waves. We go beyond the
usual approach based on the existence of a global quasi-mode that is damped in
time due to resonant absorption. Instead, we use a modal expansion to express
the MHD kink wave as a superposition of Alfv\'en continuum modes that are phase
mixed as time evolves. The comparison of the two techniques evidences that the
modal analysis is more physically transparent and describes both the damping of
global kink motions and the building up of small scales due to phase mixing. In
addition, we discuss that the processes of resonant absorption and phase mixing
are intimately linked. They represent two aspects of the same underlying
physical mechanism: the energy cascade from large scales to small scales due to
naturally occurring plasma and/or magnetic field inhomogeneities. This process
may provide the necessary scenario for efficient dissipation of transverse MHD
wave energy in the solar atmospheric plasma.",1502.03949v1
2015-03-25,Wave Propagation at Oblique Shocks: How Did Tycho Get Its Stripes?,"We describe a new model for the ""stripes"" of synchrotron radiation seen in
the remnant of Tycho's supernova. In our picture, cosmic rays streaming ahead
of the forward shock generate parallel (with respect to the local magnetic
field direction) circularly polarized Alfven waves that are almost free of
dissipation, and due to being circularly polarized exhibit no spatial variation
of magnetic field strength. Following interaction with the SNR shock with
nonzero obliquity, these parallel waves become obliquely propagating, due the
the wave refraction (different in principle for the different plane wave
components), and dissipation sets in. The magnetosonic polarization decays
faster, due to transit time damping, leaving only the Alfven mode. This
surviving mode now exhibits a spatial variation of the magnetic field, leading
to local maxima and minima in the synchrotron emission, i.e. the stripes. We
attribute the initial wave generation to the Bell instability, which in
contrast to the resonant generation of upstream Alfven waves, gives rise to a
preferred wavelength, and hence the single wave period at which the stripes are
seen. Based on estimates for damping rates due to turbulent cascade and transit
time damping, we estimate the dependence of the visibility of the stripes on
the shock obliquity, and determine a maximum cosmic ray energy in Tycho's SNR
in the range $6\times 10^{14} - 1\times 10^{15}$ eV.",1503.07497v1
2015-03-30,Superradiance and instability of small rotating charged AdS black holes in all dimensions,"Rotating small AdS black holes exhibit the superradiant instability to
low-frequency scalar perturbations, which is amenable to a complete analytic
description in four dimensions. In this paper, we extend this description to
all higher dimensions, focusing on slowly rotating charged AdS black holes with
a single angular momentum. We divide the spacetime of these black holes into
the near-horizon and far regions and find solutions to the scalar wave equation
in each of these regions. Next, we perform the matching of these solutions in
the overlap between the regions, by employing the idea that the orbital quantum
number $ \ell $ can be thought of as an approximate integer. Thus, we obtain
the complete low-frequency solution that allows us to calculate the complex
frequency spectrum of quasinormal modes, whose imaginary part is determined by
a small damping parameter. Finally, we find a remarkably instructive expression
for the damping parameter, which appears to be a complex quantity in general.
We show that the real part of the damping parameter can be used to give a {\it
universal} analytic description of the superradiant instability for slowly
rotating charged AdS black holes in all spacetime dimensions.",1503.08607v2
2015-04-12,Evolution of Kinetic and Magnetic Energy in Intra Cluster Media,"Intra Cluster Media (ICMs) located at galaxy clusters is in the state of hot,
tenuous, magnetized, and highly ionized X-ray emitting plasmas. This overall
collisionless, viscous, and conductive magnetohydrodynamic (MHD) turbulence in
ICM is simulated using hyper and physical magnetic diffusivity. The results
show that fluctuating random plasma motion amplifies the magnetic field, which
cascades toward the diffusivity scale passing through the viscous scale. The
kinetic eddies in the subviscous scale are driven and constrained by the
magnetic tension which finally gets balanced with the highly damping effect of
the kinetic eddies. However, the saturated kinetic energy spectrum is deeper
than that of the incompressible or compressible hydrodynamics fluid. To explain
this unusual field profile we set up two simultaneous differential equations
for the kinetic and magnetic energy spectrum using an Eddy Damped Quasi Normal
Markovianized (EDQNM) approximation. The analytic solution tells us that the
magnetic energy in addition to the viscous damping effect constrains the plasma
motion leading to the power spectra: kinetic energy spectrum $E_V^k\sim k^{-3}$
and corresponding representative magnetic energy spectrum $E_M^k\sim k^{-1/2}$.
Also the comparison of simulation results with different resolutions and
magnetic diffusivities implies the role of small scale magnetic energy in
dynamo.",1504.02940v3
2015-04-17,Effective Action for Cosmological Scalar Fields at Finite Temperature,"Scalar fields appear in many theories beyond the Standard Model of particle
physics. In the early universe, they are exposed to extreme conditions,
including high temperature and rapid cosmic expansion. Understanding their
behavior in this environment is crucial to understand the implications for
cosmology. We calculate the finite temperature effective action for the field
expectation value in two particularly important cases, for damped oscillations
near the ground state and for scalar fields with a flat potential. We find that
the behavior in both cases can in good approximation be described by a complex
valued effective potential that yields Markovian equations of motion. Near the
potential minimum, we recover the solution to the well-known Langevin equation.
For large field values we find a very different behavior, and our result for
the damping coefficient differs from the expressions frequently used in the
literature. We illustrate our results in a simple scalar model, for which we
give analytic approximations for the effective potential and damping
coefficient. We also provide various expressions for loop integrals at finite
temperature that are useful for future calculations in other models.",1504.04444v2
2015-05-19,The elusive HI-> H2 transition in high-z damped Lyman-alpha systems,"We study the H2 molecular content in high redshift damped Lyman-alpha systems
(DLAs) as a function of the HI column density. We find a significant increase
of the H2 molecular content around log N(HI) (cm^-2)~21.5-22, a regime unprobed
until now in intervening DLAs, beyond which the majority of systems have log
N(H2) > 17. This is in contrast with lines of sight towards nearby stars, where
such H2 column densities are always detected as soon as log N(HI)>20.7. This
can qualitatively be explained by the lower average metallicity and possibly
higher surrounding UV radiation in DLAs. However, unlike in the Milky Way, the
overall molecular fractions remain modest, showing that even at a large N(HI)
only a small fraction of overall HI is actually associated with the
self-shielded H2 gas. Damped Lyman-alpha systems with very high-N(HI) probably
arise along quasar lines of sight passing closer to the centre of the host
galaxy where the gas pressure is higher. We show that the colour changes
induced on the background quasar by continuum (dust) and line absorption (HI
Lyman and H2 Lyman & Werner bands) in DLAs with log N(HI)~22 and metallicity
~1/10 solar is significant, but not responsible for the long-discussed lack of
such systems in optically selected samples. Instead, these systems are likely
to be found towards intrinsically fainter quasars that dominate the quasar
luminosity function. Colour biasing should in turn be severe at higher
metallicities.",1505.04997v1
2015-06-11,Dynamics near the subcritical transition of the 3D Couette flow I: Below threshold case,"We study small disturbances to the periodic, plane Couette flow in the 3D
incompressible Navier-Stokes equations at high Reynolds number $\textbf{Re}$.
We prove that for sufficiently regular initial data of size $\epsilon \leq
c_0\textbf{Re}^{-1}$ for some universal $c_0 > 0$, the solution is global,
remains within $O(c_0)$ of the Couette flow in $L^2$, and returns to the
Couette flow as $t \rightarrow \infty$. For times $t \gtrsim
\textbf{Re}^{1/3}$, the streamwise dependence is damped by a mixing-enhanced
dissipation effect and the solution is rapidly attracted to the class of ""2.5
dimensional"" streamwise-independent solutions referred to as streaks. Our
analysis contains perturbations that experience a transient growth of kinetic
energy from $O(\textbf{Re}^{-1})$ to $O(c_0)$ due to the algebraic linear
instability known as the lift-up effect. Furthermore, solutions can exhibit a
direct cascade of energy to small scales. The behavior is very different from
the 2D Couette flow, in which stability is independent of $\textbf{Re}$,
enstrophy experiences a direct cascade, and inviscid damping is dominant
(resulting in a kind of inverse energy cascade). In 3D, inviscid damping will
play a role on one component of the velocity, but the primary stability
mechanism is the mixing-enhanced dissipation. Central to the proof is a
detailed analysis of the interplay between the stabilizing effects of the
mixing and enhanced dissipation and the destabilizing effects of the lift-up
effect, vortex stretching, and weakly nonlinear instabilities connected to the
non-normal nature of the linearization.",1506.03720v1
2015-06-12,Casimir Friction Between Polarizable Particle and Half-Space with Radiation Damping and Image Damping at Zero Temperature,"Casimir friction between a polarizable particle and a semi-infinite space is
a delicate physical phenomenon, as it concerns the interaction between a
microscopic quantum particle and a semi-infinite reservoir. Not unexpectedly,
results obtained in the past about the friction force obtained via different
routes are sometimes, at least apparently, wildly different from each other.
  Recently, we considered the Casimir friction force for two dielectric
semi-infinite plates moving parallel to each other [J. S. H{\o}ye and I.
Brevik, Eur. Phys. J. D {\bf 68}, 61 (2014)], and managed to get essential
agreement with results obtained by Pendry (1997), Volokitin and Persson (2007),
and Barton (2011). Our method was based upon use of the Kubo formalism. In the
present paper we focus on the interaction between a polarizable particle and a
dielectric half-space again, and calculate the friction force using the same
basic method as before. The new ingredient in the present analysis is that we
take into account radiative damping, and derive the modifications thereof. Some
comparisons are also made with works from others. Essential agreement with the
results of Intravaia, Behunin, and Dalvit can also be achieved using the
modification of the atomic polarizability by the metallic plate.",1506.03937v2
2015-07-08,Periods and damping rates of fast sausage oscillations in multi-shelled coronal loops,"Standing sausage modes are important in interpreting quasi-periodic
pulsations in the lightcurves of solar flares. Their periods and damping times
play an important role in seismologically diagnosing key parameters like the
magnetic field strength in regions where flare energy is released. Usually such
applications are based on theoretical results neglecting unresolved fine
structures in magnetized loops. However, the existence of fine structuring is
suggested on both theoretical and observational grounds. Adopting the framework
of cold magnetohydrodynamics (MHD), we model coronal loops as magnetized
cylinders with a transverse equilibrium density profile comprising a monolithic
part and a modulation due to fine structuring in the form of concentric shells.
The equation governing the transverse velocity perturbation is solved with an
initial-value-problem approach, and the effects of fine structuring on the
periods $P$ and damping times $\tau$ of global, leaky, standing sausage modes
are examined. A parameter study shows that fine structuring, be it periodically
or randomly distributed, brings changes of only a few percent to $P$ and $\tau$
when there are more than about ten shells. The monolithic part, its steepness
in particular, plays a far more important role in determining $P$ and $\tau$.
We conclude that when measured values of $P$ and $\tau$ of sausage modes are
used for seismological purposes, it is justified to use theoretical results
where the effects due to fine structuring are neglected.",1507.02169v1
2015-06-23,Resonant absorption of kink magnetohydrodynamic waves by a magnetic twist in coronal loops,"There is ample evidence of twisted magnetic structures in the solar corona.
This motivates us to consider the magnetic twist as the cause of Alfven
frequency continuum in the coronal loops, which can support the resonant
absorption as a rapid damping mechanism for the observed coronal kink
magnetohydrodynamic (MHD) oscillations. We model a coronal loop with a straight
cylindrical magnetic flux tube which has constant but different densities in
the interior and exterior regions. The magnetic field is assumed to be constant
and aligned with the cylinder axis everywhere except a thin layer near the
boundary of the flux tube which has an additional small magnetic field twist.
Then, we investigate a number of possible instabilities that may arise in our
model. In the thin tube thin boundary approximation, we derive the dispersion
relation and solve it analytically to obtain the frequencies and damping rates
of the fundamental (l=1) and first/second overtone (l=2,3) kink (m=1) MHD
modes. We conclude that the resonant absorption by the magnetic twist can
justify the rapid damping of kink MHD waves observed in coronal loops.
Furthermore, the magnetic twist in the inhomogeneous layer can cause deviations
from P1/P2=2 and P1/P3=3 which are comparable with the observations.",1507.02653v4
2015-07-23,Asteroseismology of rapidly rotating neutron stars - an alternative approach,"In the present paper we examine gravitational wave asteroseismology relations
for f-modes of rapidly rotating neutron stars. An approach different to the
previous studies is employed - first, the moment of inertia is used instead of
the stellar radius, and second, the normalization of the oscillation
frequencies and damping times is different. It was shown that in the
non-rotating case this can lead to a much stronger equation of state
independence and our goal is to generalize the static relations to the rapidly
rotating case and values of the spherical mode number $l\ge2$. We employ
realistic equations of state that cover a very large range of stiffness in
order to check better the universality of the relations. At the end we explore
the inverse problem, i.e. obtain the neutron star parameters from the observed
gravitational frequencies and damping times. It turns out that with this new
set of relations we can solve the inverse problem with a very good accuracy
using three frequencies that was not possible in the previous studies where one
needs also the damping times. The asteroseismology relations are also
particularly good for the massive rapidly rotating models that are subject to
secular instabilities.",1507.06606v1
2015-07-31,Eccentricity Evolution Through Accretion of Protoplanets,"Most of super-Earths detected by the radial velocity (RV) method have
significantly smaller eccentricities than the eccentricities corresponding to
velocity dispersion equal to their surface escape velocity (""escape
eccentricities""). If orbital instability followed by giant impacts among
protoplanets that have migrated from outer region is considered, it is usually
considered that eccentricities of the merged bodies become comparable to those
of orbital crossing bodies, which are excited up to their escape eccentricities
by close scattering. However, the eccentricity evolution in the {\it in situ}
accretion model has not been studied in detail. Here, we investigate the
eccentricity evolution through {\it N}-body simulations. We have found that the
merged planets tend to have much smaller eccentricities than the escape
eccentricities due to very efficient collision damping. If the protoplanet
orbits are initially well separated and their eccentricities are securely
increased, an inner protoplanet collides at its apocenter with an outer
protoplanet at its pericenter. The eccentricity of the merged body is the
smallest for such configuration. Orbital inclinations are also damped by this
mechanism and planets tend to share a same orbital plane, which is consistent
with {\it Kepler} data. Such efficient collision damping is not found when we
start calculations from densely packed orbits of the protoplanets. If the
protoplanets are initially in the mean-motion resonances, which corresponds to
well separated orbits, the {\it in situ} accretion model well reproduces the
features of eccentricities and inclinations of multiple super-Earths/Earth
systems discovered by RV and {\it Kepler} surveys.",1507.08809v1
2015-08-25,Effects of inertia on the steady-shear rheology of disordered solids,"We study the finite-shear-rate rheology of disordered solids by means of
molecular dynamics simulations in two dimensions. By systematically varying the
damping magnitude $\zeta$ in the low-temperature limit, we identify two well
defined flow regimes, separated by a thin (temperature-dependent) crossover
region. In the overdamped regime, the athermal rheology is governed by the
competition between elastic forces and viscous forces, whose ratio gives the
Weissenberg number $Wi= \zeta \dot\gamma$ (up to elastic parameters); the
macroscopic stress $\Sigma$ follows the frequently encountered Herschel-Bulkley
law $\Sigma= \Sigma\_0 + k \sqrt{Wi}$, with yield stress
$\Sigma\_0\textgreater{}0$. In the underdamped (inertial) regime, dramatic
changes in the rheology are observed for low damping: the flow curve becomes
non-monotonic. This change is not caused by longer-lived correlations in the
particle dynamics at lower damping; instead, for weak dissipation, the sample
heats up considerably due to, and in proportion to, the driving. By suitably
thermostatting more or less underdamped systems, we show that their rheology
only depends on their kinetic temperature and the shear rate, rescaled with
Einstein's vibration frequency.",1508.06067v3
2015-09-01,Persistence of a Non-Equilibrium State: Observation of a Boltzmannian Special Case,"Well before the atomistic nature of matter was experimentally established,
Ludwig Boltzmann's audacious effort to explain the macroscopic world of human
experience in terms of the workings of an unseen microscopic world met with
vigorous opposition. A contentious point was the problem of irreversibility:
the microscopic equations of motion are reversible, yet friction and viscosity
cause things always to slow down and warm up, never to speed up and cool down.
What was worse, Boltzmann himself discovered that his transport equation
predicts special cases in which gases never come to thermal equilibrium, a
particular example being that the monopole ""breathe"" mode of gas will never
damp if it is confined in 3D to a perfectly isotropic harmonic potential. Such
absences of damping were not observed in nature. Nondamping of a monopole mode
in lower dimensional systems has only very recently been observed, using cold
atoms. Kinoshita et al. and Chevy et al. have experimentally observed
suppressed relaxation in highly elongated geometries. The difficulty in
generating sufficiently spherical harmonic confinement for ultracold atoms,
however, has meant that Boltzmann's fully 3D, isotropic case has never been
observed. With the development of a new magnetic trap capable of producing
near-spherical harmonic confinement for ultracold atoms, we have been able to
make the first observation of this historically significant oddity. We observe
a monopole mode for which the collisional contribution to damping vanishes, a
long-delayed vindication for Boltzmann's microscopic theory.",1509.00366v1
2015-09-07,Spectral inequality and resolvent estimate for the bi-Laplace operator,"On a compact Riemannian manifold with boundary, we prove a spectral
inequality for the bi-Laplace operator in the case of so-called ""clamped""
boundary conditions , that is, homogeneous Dirichlet and Neumann conditions
simultaneously. We also prove a resolvent estimate for the generator of the
damped plate semigroup associated with these boundary conditions. The spectral
inequality allows one to observe finite sums of eigenfunctions for this
fourth-order elliptic operator, from an arbitrary open subset of the manifold.
Moreover, the constant that appears in the inequality grows as exp(C$\mu$ 1/4)
where $\mu$ is the largest eigenvalue associated with the eigenfunctions
appearing in the sum. This type of inequality is known for the Laplace
operator. As an application, we obtain a null-controllability result for a
higher-order parabolic equation. The resolvent estimate provides the spectral
behavior of the plate semigroup generator on the imaginary axis. This type of
estimate is known in the case of the damped wave semigroup. As an application ,
we deduce a stabilization result for the damped plate equation, with a log-type
decay. The proofs of both the spectral inequality and the resolvent estimate
are based on the derivation of different types of Carleman estimates for an
elliptic operator related to the bi-Laplace operator: in the interior and at
some boundaries. One of these estimates exhibits a loss of one full derivative.
Its proof requires the introduction of an appropriate semi-classical calculus
and a delicate microlocal argument.",1509.02098v5
2015-09-14,Nonlinear Energetic Particle Transport in the Presence of Multiple Alfvenic Waves in ITER,"This work presents the results of a multi mode ITER study on Toroidal Alfven
Eigenmodes, using the nonlinear hybrid HAGIS-LIGKA model. It is found that main
conclusions from earlier studies of ASDEX Upgrade discharges can be transferred
to the ITER scenario: global, nonlinear effects are crucial for the evolution
of the multi mode scenario. This work focuses on the ITER 15 MA baseline
scenario with with a safety factor at the magnetic axis of $q_0 =$ 0.986. The
least damped eigenmodes of the system are identified with the gyrokinetic,
non-perturbative LIGKA solver, concerning mode structure, frequency and
damping. Taking into account all weakly damped modes that can be identified
linearly, nonlinear simulations with HAGIS reveal strong multi mode behavior:
while in some parameter range, quasi-linear estimates turn out to be reasonable
approximations for the nonlinearly relaxed energetic particle profile, under
certain conditions low-n TAE branches can be excited. As a consequence, not
only grow amplitudes of all modes to (up to orders of magnitude) higher values
compared to the single mode cases but also, strong redistribution is triggered
in the outer radial area between $\rho_\mathrm{pol} =$ 0.6 and 0.85, far above
quasi-linear estimates.",1509.04010v1
2015-09-30,Dynamic Quantum Tomography Model for Phase-Damping Channels,"In this article we propose a dynamic quantum tomography model for open
quantum systems with evolution given by phase-damping channels. Mathematically,
these channels correspond to completely positive trace-preserving maps defined
by the Hadamard product of the initial density matrix with a time-dependent
matrix which carries the knowledge about the evolution. Physically, there is a
strong motivation for considering this kind of evolution because such channels
appear naturally in the theory of open quantum systems. The main idea behind a
dynamic approach to quantum tomography claims that by performing the same kind
of measurement at some time instants one can obtain new data for state
reconstruction. Thus, this approach leads to a decrease in the number of
distinct observables which are required for quantum tomography; however, the
exact benefit for employing the dynamic approach depends strictly on how the
quantum system evolves in time. Algebraic analysis of phase-damping channels
allows one to determine optimal criteria for quantum tomography of systems in
question. General theorems and observations presented in the paper are
accompanied by a specific example, which shows step by step how the theory
works. The results introduced in this article can potentially be applied in
experiments where there is a tendency a look at quantum tomography from the
point of view of economy of measurements, because each distinct kind of
measurement requires, in general, preparing a separate setup.",1509.09318v3
2015-10-24,Propagation of GeV neutrinos through Earth,"We have studied the Earth matter effect on the oscillation of upward going
GeV neutrinos by taking into account the three active neutrino flavors. For
neutrino energy in the range 3 to 12 GeV we observed three distinct resonant
peaks for the oscillation process $\nu_e\leftrightarrow \nu_{\mu,\tau}$ in
three \textit{distinct} densities. However, according to the most realistic
density profile of the Earth, the second peak at neutrino energy 6.18 GeV
corresponding to the density $6.6\,g/cm^3$ does not exist. So the resonance at
this energy can not be of MSW-type. For the calculation of observed flux of
these GeV neutrinos on Earth, we considered two different flux ratios at the
source, the standard scenario with the flux ratio $1:2:0$ and the muon damped
scenario with $0:1:0$. It is observed that at the detector while the standard
scenario gives the observed flux ratio $1:1:1$, the muon damped scenario has a
different ratio. For muon damped case with $E_{\nu} < 20$ GeV, we always get
observed neutrino fluxes as $\Phi_{\nu_e} < \Phi_{\nu_\mu}\simeq
\Phi_{\nu_\tau}$ and for $E_{\nu} > 20$ GeV, we get the average
$\Phi_{\nu_e}\sim 0$ and $\Phi_{\nu_\mu}\simeq \Phi_{\nu_\tau}\simeq 0.45$. The
upcoming PINGU will be able to shed more light on the nature of the resonance
in these GeV neutrinos and hopefully will also be able to discriminate among
different processes of neutrino production at the source in GeV energy range.",1510.07103v2
2015-11-18,Surface waves propagation on a turbulent flow forced electromagnetically,"We study the propagation of monochromatic surface waves on a turbulent flow.
The flow is generated in a layer of liquid metal by an electromagnetic forcing.
This forcing creates a quasi two-dimensional (2D) turbulence with strong
vertical vorticity. The turbulent flow contains much more energy than the
surface waves. In order to focus on the surface wave, the deformations induced
by the turbulent flow are removed. This is done by performing a coherent phase
averaging. For wavelengths smaller than the forcing lengthscale, we observe a
significant increase of the wavelength of the propagating wave that has not
been reported before. We suggest that it can be explained by the random
deflection of the wave induced by the velocity gradient of the turbulent flow.
Under this assumption, the wavelength shift is an estimate of the fluctuations
of deflection angle. The local measurements of the wave frequency far from the
wavemaker do not reveal such systematic behavior, although a small shift is
measured. Finally we quantify the damping enhancement induced by the turbulent
flow. We review various theoretical scaling laws proposed previously. Most of
them propose a damping that increases as the square of Froude number. In
contrast, our experimental results show a turbulent damping increasing linearly
with the Froude number. We interpret this linear behaviour as a balance between
the time spent by a wave to cross a turbulent structure with the turbulent
mixing time. The larger is the ratio of these 2 times, the more energy is
extracted from the progressive wave. Finally, mechanisms of energy exchange and
open issues are discussed and further studies are proposed.",1511.05900v1
2015-12-15,Correlations between compositions and orbits established by the giant impact era of planet formation,"The giant impact phase of terrestrial planet formation establishes
connections between super-Earths' orbital properties (semimajor axis spacings,
eccentricities, mutual inclinations) and interior compositions (the presence or
absence of gaseous envelopes). Using N-body simulations and analytic arguments,
we show that spacings derive not only from eccentricities, but also from
inclinations. Flatter systems attain tighter spacings, a consequence of an
eccentricity equilibrium between gravitational scatterings, which increase
eccentricities, and mergers, which damp them. Dynamical friction by residual
disk gas plays a critical role in regulating mergers and in damping
inclinations and eccentricities. Systems with moderate gas damping and high
solid surface density spawn gas-enveloped super-Earths with tight spacings,
small eccentricities, and small inclinations. Systems in which super-Earths
coagulate without as much ambient gas, in disks with low solid surface density,
produce rocky planets with wider spacings, larger eccentricities, and larger
mutual inclinations. A combination of both populations can reproduce the
observed distributions of spacings, period ratios, transiting planet
multiplicities, and transit duration ratios exhibited by Kepler super-Earths.
The two populations, both formed in situ, also help to explain observed trends
of eccentricity vs. planet size, and bulk density vs. method of mass
measurement (radial velocities vs. transit timing variations). Simplifications
made in this study --- including the limited timespan of the simulations, and
the approximate treatments of gas dynamical friction and gas depletion history
--- should be improved upon in future work to enable a detailed quantitative
comparison to the observations.",1512.04951v2
2015-12-18,Seismic waves damping with arrays of inertial resonators,"We investigate the elastic stop band properties of a theoretical cubic array
of iron spheres connected to a bulk of concrete via iron or rubber ligaments.
Each sphere can move freely within a surrounding air cavity, but ligaments
couple it to the bulk and further facilitate bending and rotational motions.
Associated low frequency local resonances are well predicted by an asymptotic
formula. We find complete stop bands (for all wave-polarizations) in the
frequency range $[16,21]$ Hertz (resp. $[6,11]$ Hertz) for $7.4$-meter (resp.
$0.74$-meter) diameter iron spheres with a $10$-meter (resp. $1$-meter)
center-to-center spacing, when they are connected to concrete via steel (resp.
rubber) ligaments. The scattering problem shows that only bending modes are
responsible for damping and that rotational modes are totally overwritten by
bending modes. Regarding seismic applications, we further consider soil as a
bulk medium, in which case the relative bandwidth of the low frequency stop
band can be enlarged through ligaments of different sizes that allow for well
separated bending and rotational modes. We finally achieve some damping of
elastodynamic waves from $8$ to $49$ Hertz (relative stop band of $143$
percent) for iron spheres $0.74$-meter in diameter that are connected to soil
with six rubber ligaments of optimized shapes. These results represent a
preliminary step in the design of seismic shields placed around, or underneath,
the foundations of large civil infrastructures.",1512.06078v2
2016-01-08,Kinetic Simulation of Slow Magnetosonic Waves and Quasi-periodic Upflows in the Solar Corona,"Quasi-periodic disturbances of emission-line parameters are frequently
observed in the corona. These disturbances propagate upward along the magnetic
field with speeds $\sim100~\rm{km~s}^{-1}$. This phenomenon has been
interpreted as evidence of the propagation of slow magnetosonic waves or argued
to be signature of the intermittent outflows superposed on the background
plasmas. Here we aim to present a new ""wave + flow"" model to interpret these
observations. In our scenario, the oscillatory motion is a slow mode wave, and
the flow is associated with a beam created by the wave-particle interaction
owing to Landau resonance. With the help of a Vlasov model, we simulate the
propagation of the slow mode wave and the generation of the beam flow. We find
that weak periodic beam flows can be generated owing to Landau resonance in the
solar corona, and the phase with strongest blueward asymmetry is ahead of that
with strongest blueshift by about 1/4 period. We also find that the slow wave
damps to the level of 1/e after the transit time of two wave periods, owing to
Landau damping and Coulomb collisions in our simulation. This damping time
scale is similar to that resulting from thermal-conduction in the
magnetohydrodynamics regime. The beam flow is weakened/attenuated with
increasing wave period and decreasing wave amplitude since Coulomb collision
becomes more and more dominant over the wave action. We suggest that this ""wave
+ flow"" kinetic model provides an alternative explanation for the observed
quasi-periodic propagating perturbations in various parameters in the solar
corona.",1601.01823v1
2016-01-25,Comprehensive evaluation of the linear stability of Alfvén eigenmodes driven by alpha particles in an ITER baseline scenario,"The linear stability of Alfv\'en eigenmodes in the presence of fusion-born
alpha particles is thoroughly assessed for two variants of an ITER baseline
scenario, which differ significantly in their core and pedestal temperatures. A
systematic approach is used that considers all possible eigenmodes for a given
magnetic equilibrium and determines their growth rates due to alpha-particle
drive and Landau damping on fuel ions, helium ashes and electrons. This
extensive stability study is efficiently conducted through the use of a
specialized workflow that profits from the performance of the hybrid MHD
drift-kinetic code $\mbox{CASTOR-K}$ (Borba D. and Kerner W. 1999 J. Comput.
Phys. ${\bf 153}$ 101; Nabais F. ${\it et\,al}$ 2015 Plasma Sci. Technol. ${\bf
17}$ 89), which can rapidly evaluate the linear growth rate of an eigenmode. It
is found that the fastest growing instabilities in the aforementioned ITER
scenario are core-localized, low-shear toroidal Alfv\'en eigenmodes. The
largest growth-rates occur in the scenario variant with higher core
temperatures, which has the highest alpha-particle density and density
gradient, for eigenmodes with toroidal mode numbers $n\approx30$. Although
these eigenmodes suffer significant radiative damping, which is also evaluated,
their growth rates remain larger than those of the most unstable eigenmodes
found in the variant of the ITER baseline scenario with lower core
temperatures, which have $n\approx15$ and are not affected by radiative
damping.",1601.06621v1
2016-01-27,Flash ionisation signature in coherent cyclotron emission from Brown Dwarfs,"Brown dwarfs form mineral clouds in their atmospheres, where charged
particles can produce large-scale discharges in form of lightning resulting in
a substantial sudden increase of local ionisation. Brown dwarfs are observed to
emit cyclotron radio emission. We show that signatures of strong transient
atmospheric ionisation events (flash ionisation) can be imprinted on a
pre-existing radiation. Detection of such flash ionisation events will open
investigations into the ionisation state and atmospheric dynamics. Such
ionisation events can also result from explosion shock waves, bursts or
eruptions. We present an analytical model that describes the modulation of a
pre-existing electromagnetic radiation by a time-dependent (flash) conductivity
that is characteristic for flash ionisation events like lightning. Our
conductivity model reproduces the conductivity function derived from
observations of Terrestrial Gamma Ray Flashes, and is applicable to
astrophysical objects with strong temporal variations in the local ionization,
as in planetary atmospheres and protoplanetary disks. We show that the field
responds with a characteristic flash-shaped pulse to a conductivity flash of
intermediate intensity. More powerful ionisation events result in smaller
variations of the initial radiation, or in its damping. We show that the
characteristic damping of the response field for high-power initial radiation
carries information about the ionisation flash magnitude and duration. The
duration of the pulse amplification or the damping is consistently shorter for
larger conductivity variations and can be used to evaluate the intensity of the
flash ionisation. Our work suggests that cyclotron emission could be probe
signals for electrification processes inside BD atmosphere.",1601.07474v1
2016-02-02,Sudden-quench dynamics of Bardeen-Cooper-Schrieffer states in deep optical lattices,"We determine the exact dynamics of an initial Bardeen-Cooper-Schrieffer (BCS)
state of ultra-cold atoms in a deep hexagonal optical lattice. The dynamical
evolution is triggered by a quench of the lattice potential, such that the
interaction strength $U_f$ is much larger than the hopping amplitude $J_f$. The
quench initiates collective oscillations with frequency $|U_f|/(2\pi)$ in the
momentum occupation numbers and imprints an oscillating phase with the same
frequency on the BCS order parameter $\Delta$. The oscillation frequency of
$\Delta$ is not reproduced by treating the time evolution in mean-field theory.
In our theory, the momentum noise (i.e. density-density) correlation functions
oscillate at frequency $|U_f|/2\pi$ as well as at its second harmonic. For a
very deep lattice, with zero tunneling energy, the oscillations of momentum
occupation numbers are undamped. Non-zero tunneling after the quench leads to
dephasing of the different momentum modes and a subsequent damping of the
oscillations. The damping occurs even for a finite-temperature initial BCS
state, but not for a non-interacting Fermi gas. Furthermore, damping is
stronger for larger order parameter and may therefore be used as a signature of
the BCS state. Finally, our theory shows that the noise correlation functions
in a honeycomb lattice will develop strong anti-correlations near the Dirac
point.",1602.00979v2
2016-03-09,Conclusive Identification of Quantum Channels via Monogamy of Quantum Correlations,"We investigate the action of local and global noise on monogamy of quantum
correlations, when monogamy scores are considered as observables, and
three-qubit systems are subjected to global noise and various local noisy
channels, namely, amplitude-damping, phase-damping, and depolarizing channels.
We show that the dynamics of monogamy scores corresponding to negativity and
quantum discord, in the case of generalized W states, as inputs to the noisy
channels, can exhibit non-monotonic dynamics with respect to increasing noise
parameter, which is in contrast to the monotonic decay of monogamy scores when
generalized Greenberger-Horne-Zeilinger states are exposed to noise. We
quantify the persistence of monogamy against noise via a characteristic value
of the noise parameter, and show that depolarizing noise destroys monogamy of
quantum correlation faster compared to other noisy channels. We demonstrate
that the negativity monogamy score is more robust than the quantum discord
monogamy score, when the noise is of the phase-damping type. We also
investigate the variation of monogamy with increasing noise for arbitrary
three-qubit pure states as inputs. Finally, depending on these results, we
propose a two-step protocol, which can conclusively identify the type of noise
applied to the quantum system, by using generalized Greenberger-Horne-Zeilinger
and generalized W states as resource states. We discuss a possible
generalization of the results to higher number of parties.",1603.02801v3
2016-05-05,Electromagnetic fields in the exterior of an oscillating relativistic star -- II. Electromagnetic damping,"An important issue in the asteroseismology of compact and magnetized stars is
the determination of the dissipation mechanism which is most efficient in
damping the oscillations when these are produced. In a linear regime and for
low-multipolarity modes these mechanisms are confined to either
gravitational-wave or electromagnetic losses. We here consider the latter and
compute the energy losses in the form of Poynting fluxes, Joule heating and
Ohmic dissipation in a relativistic oscillating spherical star with a dipolar
magnetic field in vacuum. While this approach is not particularly realistic for
rapidly rotating stars, it has the advantage that it is fully analytic and that
it provides expressions for the electric and magnetic fields produced by the
most common modes of oscillation both in the vicinity of the star and far away
from it. In this way we revisit and extend to a relativistic context the
classical estimates of McDermott et al. Overall, we find that
general-relativistic corrections lead to electromagnetic damping time-scales
that are at least one order of magnitude smaller than in Newtonian gravity.
Furthermore, with the only exception of $g$ (gravity) modes, we find that $f$
(fundamental), $p$ (pressure), $i$ (interface) and $s$ (shear) modes are
suppressed more efficiently by gravitational losses than by electromagnetic
ones.",1605.01709v1
2016-06-14,Landau damping to partially locked states in the Kuramoto model,"In the Kuramoto model of globally coupled oscillators, partially locked
states (PLS) are stationary solutions that incorporate the emergence of partial
synchrony when the interaction strength increases. While PLS have long been
considered, existing results on their stability are limited to neutral
stability of the linearized dynamics in strong topology, or to specific
invariant subspaces (obtained via the so-called Ott-Antonsen (OA) ansatz) with
specific frequency distributions for the oscillators. In the mean field limit,
the Kuramoto model shows various ingredients of the Landau damping mechanism in
the Vlasov equation. This analogy has been a source of inspiration for
stability proofs of regular Kuramoto equilibria. Besides, the major
mathematical issue with PLS asymptotic stability is that these states consist
of heterogeneous and singular measures. Here, we establish an explicit
criterion for their spectral stability and we prove their local asymptotic
stability in weak topology, for a large class of analytic frequency marginals.
The proof strongly relies on a suitable functional space that contains (Fourier
transforms of) singular measures, and for which the linearized dynamics is well
under control. For illustration, the stability criterion is evaluated in some
standard examples. We show in particular that no loss of generality results in
assuming the OA ansatz. To our best knowledge, our result provides the first
proof of Landau damping to heterogeneous and irregular equilibria, in absence
of dissipation.",1606.04470v1
2016-06-29,On the global existence and blowup of smooth solutions to the multi-dimensional compressible Euler equations with time-depending damping,"In this paper, we are concerned with the global existence and blowup of
smooth solutions to the multi-dimensional compressible Euler equations with
time-depending damping \begin{equation*}
  \partial_t\rho+\operatorname{div}(\rho u)=0, \quad
  \partial_t(\rho u)+\operatorname{div}\left(\rho u\otimes
u+p\,I_d\right)=-\alpha(t)\rho u, \quad
  \rho(0,x)=\bar \rho+\varepsilon\rho_0(x),\quad u(0,x)=\varepsilon u_0(x),
\end{equation*} where $x=(x_1, \cdots, x_d)\in\Bbb R^d$ $(d=2,3)$, the
frictional coefficient is $\alpha(t)=\frac{\mu}{(1+t)^\lambda}$ with
$\lambda\ge0$ and $\mu>0$, $\bar\rho>0$ is a constant, $\rho_0,u_0 \in
C_0^\infty(\Bbb R^d)$, $(\rho_0,u_0)\not\equiv 0$, $\rho(0,x)>0$, and
$\varepsilon>0$ is sufficiently small. One can totally divide the range of
$\lambda\ge0$ and $\mu>0$ into the following four cases:
  Case 1: $0\le\lambda<1$, $\mu>0$ for $d=2,3$;
  Case 2: $\lambda=1$, $\mu>3-d$ for $d=2,3$;
  Case 3: $\lambda=1$, $\mu\le 3-d$ for $d=2$;
  Case 4: $\lambda>1$, $\mu>0$ for $d=2,3$.
  \noindent We show that there exists a global $C^{\infty}-$smooth solution
$(\rho, u)$ in Case 1, and Case 2 with $\operatorname{curl} u_0\equiv 0$, while
in Case 3 and Case 4, in general, the solution $(\rho, u)$ blows up in finite
time. Therefore, $\lambda=1$ and $\mu=3-d$ appear to be the critical power and
critical value, respectively, for the global existence of small amplitude
smooth solution $(\rho, u)$ in $d-$dimensional compressible Euler equations
with time-depending damping.",1606.08935v1
2016-07-20,Electromagnon in the Z-type hexaferrite $({\rm Ba}_{x}{\rm Sr}_{1-x})_3\rm Co_2Fe_{24}O_{41}$,"We studied experimentally the high-temperature magnetoelectric $({\rm
Ba}_{x}{\rm Sr}_{1-x})_3\rm Co_2Fe_{24}O_{41}$ prepared as ceramics (x = 0,
0.2) and a single crystal (x = 0.5) using inelastic neutron scattering, THz
time-domain, Raman and far-infrared spectroscopies. The spectra, measured with
varying temperature and magnetic field, reveal rich information about the
collective spin and lattice excitations. In the ceramics, we observed an
infrared-active magnon which is absent in $E^{\omega}\perp z$ polarized THz
spectra of the crystal, and we assume that it is an electromagnon active in
$E^{\omega} \| z$ polarized spectra. On heating from 7 to 250 K, the frequency
of this electromagnon drops from 36 to 25 cm$^{-1}$ and its damping gradually
increases, so it becomes overdamped at room temperature. Applying external
magnetic field has a similar effect on the damping and frequency of the
electromagnon, and the mode is no more observable in the THz spectra above 2 T,
as the transverse-conical magnetic structure transforms into a collinear one.
Raman spectra reveal another spin excitation with a slightly different
frequency and much higher damping. Upon applying magnetic field higher than 3
T, in the low-frequency part of the THz spectra, a narrow excitation appears
whose frequency linearly increases with magnetic field. We interpret this
feature as the ferromagnetic resonance.",1607.05878v1
2016-07-28,Damping of the Milky Way bar by manifold-driven spirals,"We describe a new phenomenon of `bar damping' that may have played an
important role in shaping the Milky Way bar and bulge as well as its spiral
structure. We use a collisionless N-body simulation of a Milky Way-like galaxy
initially composed of a dark matter halo and an exponential disk with Toomre
parameter slightly above unity. In this configuration, dominated by the disk in
the center, a bar forms relatively quickly, after 1 Gyr of evolution. This is
immediately followed by the formation of two manifold-driven spiral arms and
the outflow of stars that modifies the potential in the vicinity of the bar,
apparently shifting the position of the L_1/L_2 Lagrange points. This
modification leads to the shortening of the bar and the creation of a next
generation of manifold-driven spiral arms at a smaller radius. The process
repeats itself a few times over the next 0.5 Gyr resulting in further
substantial weakening and shortening of the bar. The time when the damping
comes to an end coincides with the first buckling episode in the bar which
rebuilds the orbital structure so that no more new spiral arms are formed. The
morphology of the bar and the spiral structure at this time show remarkable
similarity to the present properties of the Milky Way. Later on, the bar starts
to grow rather steadily again, weakened only by subsequent buckling episodes
occurring at more distant parts of the disk.",1607.08339v2
2016-11-29,Dissipative self-gravitating Bose-Einstein condensates with arbitrary nonlinearity as a model of dark matter halos,"We develop a general formalism applying to Newtonian self-gravitating
Bose-Einstein condensates. This formalism may find application in the context
of dark matter halos. We introduce a generalized Gross-Pitaevskii equation
including a source of dissipation (damping) and an arbitrary nonlinearity.
Using the Madelung transformation, we derive the hydrodynamic representation of
this generalized Gross-Pitaevskii equation and obtain a damped quantum Euler
equation involving a friction force proportional and opposite to the velocity
and a pressure force associated with an equation of state determined by the
nonlinearity present in the generalized Gross-Pitaevskii equation. In the
strong friction limit, we obtain a quantum Smoluchowski equation. These
equations satisfy an $H$-theorem for a free energy functional constructed with
a generalized entropy. We specifically consider the Boltzmann and Tsallis
entropies associated with isothermal and polytropic equations of state. We also
consider the entropy associated with the logotropic equation of state. We
derive the virial theorem corresponding to the generalized Gross-Pitaevskii
equation, damped quantum Euler equation, and quantum Smoluchowski equation.
Using a Gaussian ansatz, we obtain a simple equation governing the dynamical
evolution of the size of the condensate. We highlight a specific model of dark
matter halos corresponding to a generalized Gross-Pitaevskii equation with a
logarithmic nonlinearity and a cubic nonlinearity. It leads to dark matter
halos with an equation of state $P=\rho k_B T_{\rm eff}/m+2\pi
a_s\hbar^2\rho^{2}/m^3$ presenting a condensed core (BEC/soliton) and an
isothermal halo with an effective temperature $T_{\rm eff}$. We propose that
this model provides an effective coarse-grained parametrization of dark matter
halos experiencing gravitational cooling.",1611.09610v1
2016-12-06,Breakdown of Fermi liquid theory in topological multi-Weyl semimetals,"Fermi liquid theory works very well in most normal metals, but is found
violated in many strongly correlated electron systems, such as cuprate and
heavy-fermion superconductors. A widely accepted criterion is that, the Fermi
liquid theory is valid when the interaction-induced fermion damping rate
approaches zero more rapidly than the energy. Otherwise, it is invalid. Here,
we demonstrate that this criterion breaks down in topological double-and
triple-Weyl semimetals. Renormalization group analysis reveals that, although
the damping rate of double- and triple-Weyl fermions induced by the Coulomb
interaction approaches zero more rapidly than the energy, the quasiparticle
residue vanishes and the Fermi liquid theory is invalid. This behavior
indicates a weaker-than-marginal violation of the Fermi liquid theory. Such an
unconventional non-Fermi liquid state originates from the special dispersion of
double- and triple-Weyl fermions, and is qualitatively different from all the
other Fermi-liquid and non-Fermi-liquid states. The predicted properties of the
fermion damping rate and the spectral function can be probed by the
angle-resolved photoemission spectroscopy. The density of states, specific
heat, and conductivities are also calculated and analyzed after incorporating
the corrections induced by the Coulomb interaction.",1612.01729v2
2016-12-08,Quantifying acoustic damping using flame chemiluminescence,"Thermoacoustic instabilities in gas turbines and aeroengine combustors falls
within the category of complex systems. They can be described
phenomenologically using nonlinear stochastic differential equations, which
constitute the grounds for output-only model-based system identification. It
has been shown recently that one can extract the governing parameters of the
instabilities, namely the linear growth rate and the nonlinear component of the
thermoacoustic feedback, using dynamic pressure time series only. This is
highly relevant for practical systems, which cannot be actively controlled due
to a lack of cost-effective actuators. The thermoacoustic stability is given by
the linear growth rate, which results from the combination of the acoustic
damping and the coherent feedback from the flame. In this paper, it is shown
that it is possible to quantify the acoustic damping of the system, and thus to
separate its contribution to the linear growth rate from the one of the flame.
This is achieved by post-processing in a simple way simultaneously acquired
chemiluminescence and acoustic pressure data. It provides an additional
approach to further unravel from observed time series the key mechanisms
governing the system dynamics. This straightforward method is illustrated here
using experimental data from a combustion chamber operated at several linearly
stable and unstable operating conditions.",1612.02609v1
2016-12-29,A quasi-mode theory of chiral phonons,"The coherence properties of mechanical resonators are often limited by
multiple unavoidable forms of loss -- including phonon-phonon and phonon-defect
scattering -- which result in the scattering of sound into other resonant modes
and into the phonon bath. Dynamic suppression of this scattering loss can lift
constraints on device structure and can improve tolerance to defects in the
material, even after fabrication. Inspired by recent experiments, here we
introduce a model of phonon losses resulting from disorder in a whispering
gallery mode resonator with acousto-optical coupling between optical and
mechanical modes. We show that a typical elastic scattering mechanism of high
quality factor (Q) mechanical modes flips the direction of phonon propagation
via high-angle scattering, leading to damping into modes with the opposite
parity. When the optical mode overlaps co-propagating high-Q and bulk
mechanical modes, the addition of laser cooling via sideband-resolved damping
of the mechanical mode of a chosen parity also damps and modifies the response
of the bulk modes of the same parity. This, in turn, simultaneously improves
the quality factor and reduces the thermal load of the counter-propagating
high-Q modes, leading to the dynamical creation of a cold phononic shield. We
compare our theoretical results to the recent experiments of Kim et al., and
find quantitative agreement with our theory.",1612.09240v1
2017-01-03,A Model for Dissipation of Solar Wind Magnetic Turbulence by Kinetic Alfvén Waves at Electron Scales: Comparison with Observations,"In hydrodynamic turbulence, it is well established that the length of the
dissipation scale depends on the energy cascade rate, i.e., the larger the
energy input rate per unit mass, the more the turbulent fluctuations need to be
driven to increasingly smaller scales to dissipate the larger energy flux.
Observations of magnetic spectral energy densities indicate that this intuitive
picture is not valid in solar wind turbulence. Dissipation seems to set in at
the same length scale for different solar wind conditions independently of the
energy flux. To investigate this difference in more detail, we present an
analytic dissipation model for solar wind turbulence at electron scales, which
we compare with observed spectral densities. Our model combines the energy
transport from large to small scales and collisionless damping, which removes
energy from the magnetic fluctuations in the kinetic regime. We assume
wave-particle interactions of kinetic Alfv\'{e}n waves (KAW) to be the main
damping process. Wave frequencies and damping rates of KAW are obtained from
the hot plasma dispersion relation. Our model assumes a critically balanced
turbulence, where larger energy cascade rates excite larger parallel
wavenumbers for a certain perpendicular wavenumber. If the dissipation is
additionally wave driven such that the dissipation rate is proportional to the
parallel wavenumber - as with KAW - then an increase of the energy cascade rate
is counter-balanced by an increased dissipation rate for the same perpendicular
wavenumber leading to a dissipation length independent of the energy cascade
rate.",1701.00680v1
2017-02-07,Constraining color flavor locked strange stars in the gravitational wave era,"We perform a detailed analysis of the fundamental mode of non-radial
pulsations of color flavor locked strange stars. Solving the general
relativistic equations for non-radial pulsations for an equation of state
derived within the MIT bag model, we calculate the frequency and the
gravitational damping time of the fundamental mode for all the parametrizations
of the equation of state that lead to self-bound matter.
  Our results show that color flavor locked strange stars can emit
gravitational radiation in the optimal range for present gravitational wave
detectors and that it is possible to constrain the equation of state's
parameters if the fundamental oscillation mode is observed and the stellar mass
is determined.
  We also show that the $f$-mode frequency can be fitted as a function of the
square root of the average stellar density $\sqrt{M/R^3}$ by a single linear
relation that fits quite accurately the results for all parametrizations of the
equation of state. All results for the damping time can also be fitted as a
function of the compactness $M/R$ by a single empirical relation. Therefore, if
a given compact object is identified as a color flavor locked strange star
these two relations could be used to determine the mass and the radius from the
knowledge of the frequency and the damping time of gravitational waves from the
$f$ mode.",1702.02081v1
2017-02-16,"Designing the Optimal Bit: Balancing Energetic Cost, Speed and Reliability","We consider the technologically relevant costs of operating a reliable bit
that can be erased rapidly. We find that both erasing and reliability times are
non-monotonic in the underlying friction, leading to a trade-off between
erasing speed and bit reliability. Fast erasure is possible at the expense of
low reliability at moderate friction, and high reliability comes at the expense
of slow erasure in the underdamped and overdamped limits. Within a given class
of bit parameters and control strategies, we define ""optimal"" designs of bits
that meet the desired reliability and erasing time requirements with the lowest
operational work cost. We find that optimal designs always saturate the bound
on the erasing time requirement, but can exceed the required reliability time
if critically damped. The non-trivial geometry of the reliability and erasing
time-scales allows us to exclude large regions of parameter space as
sub-optimal. We find that optimal designs are either critically damped or close
to critical damping under the erasing procedure.",1702.04950v2
2017-02-16,Effects of Landau damping on ion-acoustic solitary waves in a semiclassical plasma,"We study the nonlinear propagation of ion-acoustic waves (IAWs) in an
unmagnetized collisionless plasma with the effects of electron and ion Landau
damping in the weak quantum (semiclassical) regime, i.e., when the typical
ion-acoustic (IA) length scale is larger than the thermal de Broglie
wavelength. Starting from a set of classical and semiclassical Vlasov equations
for ions and electrons, coupled to the Poisson equation, we derive a modified
(by the particle dispersion) Korteweg-de Vries (KdV) equation which governs the
evolution of IAWs with the effects of wave-particle resonance. It is found that
in contrast to the classical results, the nonlinear IAW speed $(\lambda)$ and
the linear Landau damping rate $(\gamma)$ are no longer constants, but can vary
with the wave number $(k)$ due to the quantum particle dispersion. The effects
of the quantum parameter $H$ (the ratio of the plasmon energy to the thermal
energy) and the electron to ion temperature ratio $(T)$ on the profiles of
$\lambda$, $\gamma$ and the solitary wave amplitude are also studied. It is
shown that the decay rate of the wave amplitude is reduced by the effects of
$H$.",1702.05035v2
2017-03-07,Higgs Modes in the Pair Density Wave Superconducting State,"The pair density wave (PDW) superconducting state has been proposed to
explain the layer- decoupling effect observed in the compound
La$_{2-x}$Ba$_x$CuO$_4$ at $x=1/8$ (Phys. Rev. Lett. 99, 127003). In this state
the superconducting order parameter is spatially modulated, in contrast with
the usual superconducting (SC) state where the order parameter is uniform. In
this work, we study the properties of the amplitude (Higgs) modes in a
unidirectional PDW state. To this end we consider a phenomenological model of
PDW type states coupled to a Fermi surface of fermionic quasiparticles. In
contrast to conventional superconductors that have a single Higgs mode,
unidirectional PDW superconductors have two Higgs modes. While in the PDW state
the Fermi surface largely remains gapless, we find that the damping of the PDW
Higgs modes into fermionic quasiparticles requires exceeding an energy
threshold. We show that this suppression of damping in the PDW state is due to
kinematics. As a result, only one of the two Higgs modes is significantly
damped. In addition, motivated by the experimental phase diagram, we discuss
the mixing of Higgs modes in the coexistence regime of the PDW and uniform SC
states. These results should be observable directly in a Raman spectroscopy, in
momentum resolved electron energy loss spectroscopy, and in resonant inelastic
X-ray scattering, thus providing evidence of the PDW states.",1703.02541v2
2017-04-29,Low-frequency wide band-gap elastic/acoustic meta-materials using the K-damping concept,"The terms ""acoustic/elastic meta-materials"" describe a class of periodic
structures with unit cells exhibiting local resonance. This localized resonant
structure has been shown to result in negative effective stiffness and/or mass
at frequency ranges close to these local resonances. As a result, these
structures present unusual wave propagation properties at wavelengths well
below the regime corresponding to band-gap generation based on spatial
periodicity, (i.e. ""Bragg scattering""). Therefore, acoustic/elastic
meta-materials can lead to applications, especially suitable in the
low-frequency range. However, low frequency range applications of such
meta-materials require very heavy internal moving masses, as well as additional
constraints at the amplitudes of the internally oscillating locally resonating
structures, which may prohibit their practical implementation. In order to
resolve this disadvantage, the K-Damping concept will be analyzed. According to
this concept, the acoustic/elastic meta-materials are designed to include
negative stiffness elements instead or in addition to the internally resonating
added masses. This concept removes the need for the heavy locally added heavy
masses, while it simultaneously exploits the negative stiffness damping
phenomenon. Application of both Bloch's theory and the classical modal analysis
at the one-dimensional mass-in-mass lattice is analyzed and corresponding
dispersion relations are derived. The results indicate significant advantages
over the conventional mass-in-a mass lattice, such as broader band-gaps and
increased damping ratio and reveal significant potential in the proposed
solution. Preliminary feasibility analysis for seismic meta-structures and low
frequency acoustic isolation-damping confirm the strong potential and
applicability of this concept.",1705.00226v2
2017-05-07,Precision cosmology with redshift-space bispectrum: a perturbation theory based model at one-loop order,"The large-scale matter distribution in the late-time Universe exhibits
gravity-induced non-Gaussianity, and the bispectrum, three-point cumulant is
expected to contain significant cosmological information. In particular, the
measurement of the bispectrum helps to tighten the constraints on dark energy
and modified gravity through the redshift-space distortions (RSD). In this
paper, extending the work by Taruya, Nishimichi & Saito (2010, Phys.Rev.D 82,
063522), we present a perturbation theory (PT) based model of redshift-space
matter bispectrum that can keep the non-perturbative damping effect under
control. Characterizing this non-perturbative damping by a univariate function
with single free parameter, the PT model of the redshift-space bispectrum is
tested against a large set of cosmological $N$-body simulations, finding that
the predicted monopole and quadrupole moments are in a good agreement with
simulations at the scales of baryon acoustic oscillations (well beyond the
range of agreement of standard PT). The validity of the univariate ansatz of
the damping effect is also examined, and with the PT calculation at
next-to-leading order, the fitted values of the free parameter is shown to
consistently match those obtained from the PT model of power spectrum by
Taruya, Nishimichi & Saito (2010).",1705.02574v1
2017-05-13,Large-amplitude longitudinal oscillations in a solar filament,"In this paper, we report our multiwavelength observations of the
large-amplitude longitudinal oscillations of a filament on 2015 May 3. Located
next to active region 12335, the sigmoidal filament was observed by the
ground-based H$\alpha$ telescopes from GONG and by AIA aboard SDO. The filament
oscillations were most probably triggered by the magnetic reconnection in the
filament channel. The directions of oscillations have angles of
4$^\circ$-36$^\circ$ with respect to the filament axis. The whole filament did
not oscillate in phase as a rigid body. Meanwhile, the periods (3100$-$4400 s)
of oscillations have a spatial dependence. The values of $R$ are estimated to
be 69.4$-$133.9 Mm, and the minimum transverse magnetic field of the dips is
estimated to be 15 G. The amplitudes of S5-S8 grew with time, while the
amplitudes of S9-S14 damped with time. The amplitudes of oscillations range
from a few to ten Mm, and the maximal velocity can reach 30 km s$^{-1}$.
Interestingly, the filament experienced mass drainage southwards at a speed of
$\sim$27 km s$^{-1}$. The oscillations continued after the mass drainage and
lasted for more than 11 hr. After the mass drainage, the phases of oscillations
did not change a lot. The periods of S5-S8 decreased, while the periods of
S9-S14 increased. The amplitudes of S5$-$S8 damped with time, while the
amplitudes of S9-S14 grew. Most of the damping (growing) ratios are between -9
and 14. We propose a schematic cartoon to explain the complex behaviors of
oscillations by introducing thread-thread interaction.",1705.04820v1
2017-05-14,Inter-Area Oscillation Damping With Non-Synchronized Wide-Area Power System Stabilizer,"One of the major issues in an interconnected power system is the low damping
of inter-area oscillations which significantly reduces the power transfer
capability. Advances in Wide-Area Measurement System (WAMS) makes it possible
to use the information from geographical distant location to improve power
system dynamics and performances. A speed deviation based Wide-Area Power
System Stabilizer (WAPSS) is known to be effective in damping inter-area modes.
However, the involvement of wide-area signals gives rise to the problem of
time-delay, which may degrade the system performance. In general, time-stamped
synchronized signals from Phasor Data Concentrator (PDC) are used for WAPSS, in
which delays are introduced in both local and remote signals. One can opt for a
feedback of remote signal only from PDC and uses the local signal as it is
available, without time synchronization. This paper utilizes configurations of
time-matched synchronized and nonsychronized feedback and provides the
guidelines to design the controller. The controllers are synthesized using
$H_\infty$ control with regional pole placement for ensuring adequate dynamic
performance. To show the effectiveness of the proposed approach, two power
system models have been used for the simulations. It is shown that the
controllers designed based on the nonsynchronized signals are more robust to
time time delay variations than the controllers using synchronized signal.",1705.04953v2
2017-05-19,Analytical Prediction of Reflection Coefficients for Wave Absorbing Layers in Flow Simulations of Regular Free-Surface Waves,"Undesired wave reflections, which occur at domain boundaries in flow
simulations with free-surface waves, can be minimized by applying source terms
in the vicinity of the boundary to damp the waves. Examples of such approaches
are absorbing layers, damping zones, forcing zones, relaxation zones and sponge
layers. A problem with these approaches is that the effectivity of the wave
damping depends on the parameters in the source term functions, which are
case-dependent and must be adjusted to the wave. The present paper presents a
theory which analytically predicts the reflection coefficients and which can be
used to optimally select the source term parameters before running the
simulation. The theory is given in a general form so that it is applicable to
many existing implementations. It is validated against results from
finite-volume-based flow simulations of regular free-surface waves and found to
be of satisfactory accuracy for practical purposes.",1705.06940v2
2017-06-16,Challenges testing the no-hair theorem with gravitational waves,"General relativity's no-hair theorem states that isolated astrophysical black
holes are described by only two numbers: mass and spin. As a consequence, there
are strict relationships between the frequency and damping time of the
different modes of a perturbed Kerr black hole. Testing the no-hair theorem has
been a longstanding goal of gravitational-wave astronomy. The recent detection
of gravitational waves from black hole mergers would seem to make such tests
imminent. We investigate how constraints on black hole ringdown parameters
scale with the loudness of the ringdown signal---subject to the constraint that
the post-merger remnant must be allowed to settle into a perturbative,
Kerr-like state. In particular, we require that---for a given detector---the
gravitational waveform predicted by numerical relativity is indistinguishable
from an exponentially damped sine after time $t^\text{cut}$. By requiring the
post-merger remnant to settle into such a perturbative state, we find that
confidence intervals for ringdown parameters do not necessarily shrink with
louder signals. In at least some cases, more sensitive measurements probe later
times without necessarily providing tighter constraints on ringdown frequencies
and damping times. Preliminary investigations are unable to explain this result
in terms of a numerical relativity artifact.",1706.05152v2
2017-06-26,Simulating the effect of high column density absorbers on the one-dimensional Lyman-alpha forest flux power spectrum,"We measure the effect of high column density absorbing systems of neutral
hydrogen (HI) on the one-dimensional (1D) Lyman-alpha forest flux power
spectrum using cosmological hydrodynamical simulations from the Illustris
project. High column density absorbers (which we define to be those with HI
column densities $N(\mathrm{HI}) > 1.6 \times
10^{17}\,\mathrm{atoms}\,\mathrm{cm}^{-2}$) cause broadened absorption lines
with characteristic damping wings. These damping wings bias the 1D Lyman-alpha
forest flux power spectrum by causing absorption in quasar spectra away from
the location of the absorber itself. We investigate the effect of high column
density absorbers on the Lyman-alpha forest using hydrodynamical simulations
for the first time. We provide templates as a function of column density and
redshift, allowing the flexibility to accurately model residual contamination,
i.e., if an analysis selectively clips out the largest damping wings. This
flexibility will improve cosmological parameter estimation, e.g., allowing more
accurate measurement of the shape of the power spectrum, with implications for
cosmological models containing massive neutrinos or a running of the spectral
index. We provide fitting functions to reproduce these results so that they can
be incorporated straightforwardly into a data analysis pipeline.",1706.08532v2
2017-07-19,Engineering elliptical spin-excitations by complex anisotropy fields in Fe adatoms and dimers on Cu(111),"We investigate the dynamics of Fe adatoms and dimers deposited on the Cu(111)
metallic surface in the presence of spin-orbit coupling, within time-dependent
density functional theory. The \textit{ab initio} results provide
material-dependent parameters that can be used in semiclassical approaches,
which are used for insightful interpretations of the excitation modes. By
manipulating the surroundings of the magnetic elements, we show that elliptical
precessional motion may be induced through the modification of the magnetic
anisotropy energy. We also demonstrate how different kinds of spin precession
are realized, considering the symmetry of the magnetic anisotropy energy, the
ferro- or antiferromagnetic nature of the exchange coupling between the
impurities, and the strength of the magnetic damping. In particular, the normal
modes of a dimer depend on the initial magnetic configuration, changing
drastically by going from a ferromagnetic metastable state to the
antiferromagnetic ground state. By taking into account the effect of the
damping into their resonant frequencies, we reveal that an important
contribution arises for strongly biaxial systems and specially for the
antiferromagnetic dimers with large exchange couplings. Counter intuitively,
our results indicate that the magnetic damping influences the quantum
fluctuations by decreasing the zero-point energy of the system.",1707.06087v2
2017-08-16,Effects of group velocity and multi-plasmon resonances on the modulation of Langmuir waves in a degenerate plasma,"We study the nonlinear wave modulation of Langmuir waves (LWs) in a fully
degenerate plasma. Using the Wigner-Moyal equation coupled to the Poisson
equation and the multiple scale expansion technique, a modified nonlocal
nonlinear Schr{\""{o}}dinger (NLS) equation is derived which governs the
evolution of LW envelopes in degenerate plasmas. The nonlocal nonlinearity in
the NLS equation appears due to the group velocity and multi-plasmon
resonances, i.e., resonances induced by the simultaneous particle absorption of
multiple wave quanta. We focus on the regime where the resonant velocity of
electrons is larger than the Fermi velocity and thereby the linear Landau
damping is forbidden. As a result, the nonlinear wave-particle resonances due
to the group velocity and multi-plasmon processes are the dominant mechanisms
for wave-particle interaction. It is found that in contrast to classical or
semiclassical plasmas, the group velocity resonance does not necessarily give
rise the wave damping in the strong quantum regime where $ \hbar k\sim mv_{F}$
with $\hbar$ denoting the reduced Planck's constant, $m$ the electron mass and
$v_F$ the Fermi velocity, however, the three-plasmon process plays a dominant
role in the nonlinear Landau damping of wave envelopes. In this regime, the
decay rate of the wave amplitude is also found to be higher compared to that in
the modest quantum regime where the multi-plasmon effects are forbidden.",1708.04965v3
2017-10-02,The gas and stellar mass of low-redshift damped Lyman-$α$ absorbers,"We report Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet
and Arecibo Telescope H{\sc i} 21cm spectroscopic studies of six damped and
sub-damped Lyman-$\alpha$ absorbers (DLAs and sub-DLAs, respectively) at $z
\lesssim 0.1$, that have yielded estimates of their H{\sc i} column density,
metallicity and atomic gas mass. This significantly increases the number of
DLAs with gas mass estimates, allowing the first comparison between the gas
masses of DLAs and local galaxies. Including three absorbers from the
literature, we obtain H{\sc i} masses $\approx (0.24 - 5.2) \times 10^9 \: {\rm
M}_\odot$, lower than the knee of the local H{\sc i} mass function. This
implies that massive galaxies do not dominate the absorption cross-section for
low-$z$ DLAs. We use Sloan Digital Sky Survey photometry and spectroscopy to
identify the likely hosts of four absorbers, obtaining low stellar masses,
$\approx 10^7-10^{8.7} M_\odot$, in all cases, consistent with the hosts being
dwarf galaxies. We obtain high H{\sc i} 21\,cm or CO emission line widths,
$\Delta V_{20} \approx 100-290$~km~s$^{-1}$, and high gas fractions, $f_{\rm
HI} \approx 5-100$, suggesting that the absorber hosts are gas-rich galaxies
with low star formation efficiencies. However, the H{\sc i} 21\,cm velocity
spreads ($\gtrsim 100$~km~s$^{-1}$) appear systematically larger than the
velocity spreads in typical dwarf galaxies.",1710.00710v1
2017-10-25,Two-Level System Damping in a Quasi-One-Dimensional Optomechanical Resonator,"Nanomechanical resonators have demonstrated great potential for use as
versatile tools in a number of emerging quantum technologies. For such
applications, the performance of these systems is restricted by the decoherence
of their fragile quantum states, necessitating a thorough understanding of
their dissipative coupling to the surrounding environment. In bulk amorphous
solids, these dissipation channels are dominated at low temperatures by
parasitic coupling to intrinsic two-level system (TLS) defects, however, there
remains a disconnect between theory and experiment on how this damping
manifests in dimensionally-reduced nanomechanical resonators. Here, we present
an optomechanically-mediated thermal ringdown technique, which we use to
perform simultaneous measurements of the dissipation in four mechanical modes
of a cryogenically-cooled silicon nanoresonator, with resonant frequencies
ranging from 3 - 19 MHz. Analyzing the device's mechanical damping rate at
fridge temperatures between 10 mK - 10 K, we demonstrate quantitative agreement
with the standard tunneling model for TLS ensembles confined to one dimension.
From these fits, we extract the defect density of states ($P_0 \sim$ 1 - 4
$\times$ 10$^{44}$ J$^{-1}$ m$^{-3}$) and deformation potentials ($\gamma \sim$
1 - 2 eV), showing that each mechanical mode couples on average to less than a
single thermally-active defect at 10 mK.",1710.09439v3
2017-11-10,"Vortex axisymmetrization, inviscid damping, and vorticity depletion in the linearized 2D Euler equations","Coherent vortices are often observed to persist for long times in turbulent
2D flows even at very high Reynolds numbers and are observed in experiments and
computer simulations to potentially be asymptotically stable in a weak sense
for the 2D Euler equations. We consider the incompressible 2D Euler equations
linearized around a radially symmetric, strictly monotone decreasing vorticity
distribution. For sufficiently regular data, we prove the inviscid damping of
the $\theta$-dependent radial and angular velocity fields with the optimal
rates $\|u^r(t)\| \lesssim \langle t \rangle^{-1}$ and $\|u^\theta(t)\|
\lesssim \langle t \rangle^{-2}$ in the appropriate radially weighted $L^2$
spaces. We moreover prove that the vorticity weakly converges back to radial
symmetry as $t \rightarrow \infty$, a phenomenon known as vortex
axisymmetrization in the physics literature, and characterize the dynamics in
higher Sobolev spaces. Furthermore, we prove that the $\theta$-dependent
angular Fourier modes in the vorticity are ejected from the origin as $t \to
\infty$, resulting in faster inviscid damping rates than those possible with
passive scalar evolution. This non-local effect is called vorticity depletion.
Our work appears to be the first to find vorticity depletion relevant for the
dynamics of vortices.",1711.03668v1
2017-11-15,Anomalous spin-orbit torque switching due to field-like torque-assisted domain wall reflection,"Spin-orbit torques (SOT) allow the electrical control of magnetic states.
Current-induced SOT switching of the perpendicular magnetization is of
particular technological importance. The SOT consists of damping-like and
field-like torques so that the efficient SOT switching requires to understand
combined effects of the two torque-components. Previous quasi-static
measurements have reported an increased switching probability with the width of
current pulses, as predicted with considering the damping-like torque only.
Here we report a decreased switching probability at longer pulse-widths, based
on time-resolved measurements. Micromagnetic analysis reveals that this
anomalous SOT switching results from domain wall reflections at sample edges.
The domain wall reflection is found to strongly depend on the field-like torque
and its relative sign to the damping-like torque. Our result demonstrates a key
role of the field-like torque in the deterministic SOT switching and notifies
the importance of sign correlation of the two torque-components, which may shed
light on the SOT switching mechanism.",1711.05367v1
2017-11-24,Influence of surfactants on the electrohydrodynamic stretching of water drops in oil,"In this paper we present experimental and numerical studies of the
electrohydrodynamic stretching of a sub-millimetre-sized salt water drop,
immersed in oil with added non-ionic surfactant, and subjected to a suddenly
applied electric field of magnitude approaching 1 kV/mm. By varying the drop
size, electric field strength and surfactant concentration we cover the whole
range of electric capillary numbers ($Ca_E$) from 0 up to the limit of drop
disintegration. The results are compared with the analytical result by Taylor
(1964) which predicts the asymptotic deformation as a function of $Ca_E$. We
find that the addition of surfactant damps the transient oscillations and that
the drops may be stretched slightly beyond the stability limit found by Taylor.
We proceed to study the damping of the oscillations, and show that increasing
the surfactant concentration has a dual effect of first increasing the damping
at low concentrations, and then increasing the asymptotic deformation at higher
concentrations. We explain this by comparing the Marangoni forces and the
interfacial tension as the drops deform. Finally, we have observed in the
experiments a significant hysteresis effect when drops in oil with large
concentration of surfactant are subjected to repeated deformations with
increasing electric field strengths. This effect is not attributable to the
flow nor the interfacial surfactant transport.",1711.08969v2
2017-11-30,Model-independent analysis of the DAMPE excess,"The Dark Matter Particle Explorer (DAMPE) recently released measurements of
the electron spectrum with a hint of a narrow peak at about 1.4 TeV. We
investigate dark matter (DM) models that could produce such a signal by
annihilation in a nearby subhalo whilst simultaneously satisfying constraints
from DM searches. In our model-independent approach, we consider all
renormalizable interactions via a spin 0 or 1 mediator between spin 0 or 1/2 DM
particles and the Standard Model leptons. We find that of the 20 combinations,
10 are ruled out by velocity or helicity suppression of the annihilation cross
section to fermions. The remaining 10 models, though, evade constraints from
the relic density, collider and direct detection searches, and include models
of spin 0 and 1/2 DM coupling to a spin 0 or 1 mediator. We delineate the
regions of mediator mass and couplings that could explain the DAMPE excess. In
all cases the mediator is required to be heaver than about 2 TeV by LEP limits.",1711.11376v3
2017-12-07,Flavor Structure of the Cosmic-Ray Electron/Positron Excesses at DAMPE,"The Dark Matter Particle Explorer (DAMPE) satellite detector announced its
first result for measuring the cosmic-ray electron/positron (CRE) energy
spectrum up to 4.6TeV, including a tentative peak-like event excess at
(1.3-1.5)TeV. In this work, we uncover a significant hidden excess in the DAMPE
CRE spectrum over the energy range (0.6-1.1)TeV, which has a non-peak-like
structure. We propose a new mechanism to explain this excess by a set of 1.5TeV
$\mu^\pm$ events with subsequent decays into $e^\pm$ plus neutrinos. For
explaining this new excess together with the peak excess around 1.4TeV, we
demonstrate that the {\it flavor structure} of the original lepton final-state
produced by dark matter (DM) annihilations (or other mechanism) should have a
composition ratio $N_e : (N_\mu +\frac{1}{6}N_\tau) = 1 : y$, with $y \simeq
2.6-10.8$. For lepton portal DM models, this puts important constraint on the
lepton-DM-mediator couplings $\lambda_e : (\lambda_\mu^4 +
\frac{1}{6}\lambda_\tau^4)^{\frac{1}{4}} = 1 : y^{\frac{1}{4}}$ with a narrow
range $y^{\frac{1}{4}} \simeq 1.3-1.8$.",1712.02744v3
2017-12-22,Low-momentum dynamic structure factor of a strongly interacting Fermi gas at finite temperature: A two-fluid hydrodynamic description,"We provide a description of the dynamic structure factor of a homogeneous
unitary Fermi gas at low momentum and low frequency, based on the dissipative
two-fluid hydrodynamic theory. The viscous relaxation time is estimated and is
used to determine the regime where the hydrodynamic theory is applicable and to
understand the nature of sound waves in the density response near the
superfluid phase transition. By collecting the best knowledge on the shear
viscosity and thermal conductivity known so far, we calculate the various
diffusion coefficients and obtain the damping width of the (first and second)
sounds. We find that the damping width of the first sound is greatly enhanced
across the superfluid transition and very close to the transition the second
sound might be resolved in the density response for the transferred momentum up
to the half of Fermi momentum. Our work is motivated by the recent measurement
of the local dynamic structure factor at low momentum at Swinburne University
of Technology and the on-going experiment on sound attenuation of a homogeneous
unitary Fermi gas at Massachusetts Institute of Technology. We discuss how the
measurement of the velocity and damping width of the sound modes in
low-momentum dynamic structure factor may lead to an improved determination of
the universal superfluid density, shear viscosity and thermal conductivity of a
unitary Fermi gas.",1712.08320v1
2018-01-15,Amplitude- and gas pressure-dependent nonlinear damping of high-Q oscillatory MEMS micro mirrors,"Silicon-based micro-electromechanical systems (MEMS) can be fabricated using
bulk and surface micromachining technology. A micro mirror designed as an
oscillatory MEMS constitutes a prominent example. Typically, in order to
minimize energy consumption, the micro mirror is designed to have high quality
factors. In addition, a phase-locked loop guarantees resonant actuation despite
the occurrence of frequency shifts. In these cases, the oscillation amplitude
of the micro mirror is expected to scale linearly with the actuation input
power. Here, however, we report on an experimental observation which clearly
shows an amplitude depletion that is not in accordance with any linear
behaviour. As a consequence, the actuation forces needed to reach the desired
oscillation amplitude are by multiples higher than expected. We are able to
explain the experimental observations accurately by introducing a single
degree-of-freedom model including an amplitude-dependent nonlinear damping
term. Remarkably, we find that the nonlinear damping shows a clear gas pressure
dependency. We investigate the concepts and compare our findings on two
different micro mirror design layouts.",1801.04758v2
2018-01-30,Model Based Active Slosh Damping Experiment,"This paper presents a model based experimental investigation to demonstrate
the usefulness of an active damping strategy to manage fluid sloshing motion in
spacecraft tanks. The active damping strategy is designed to reduce the
degrading impact on maneuvering and pointing performance via a force feedback
strategy. Many problems have been encountered until now, such as instability of
the closed loop system, excessive consumption in the attitude propellant or
problems for engine re-ignition in upper stages. Mostly, they have been
addressed in a passive way via the design of baffles and membranes, which on
their own have mass and constructive impacts. Active management of propellant
motion in launchers and satellites has the potential to increase performance on
various levels. This paper demonstrates active slosh management using force
feedback for the compensation of the slosh resonances. Force sensors between
tank and the carrying structure provide information of the fluid motion via the
reaction force. The control system is designed to generate an appropriate
acceleration profile that leads to desired attenuation profiles in amplitude,
frequency and time. Two robust control design methods, one based on $\mu$
design and the other on parametric structured design based on non-smooth
optimization of the worst-case $H_{\infty}$ norm, are applied. The controller
is first tested with a computational fluid dynamics simulation in the loop.
Finally a water tank mounted on a Hexapod with up to $1100$ liter is used to
evaluate the control performance. The paper illustrates that is possible to
actively influence sloshing via closed loop.",1801.10017v1
2018-03-22,Propagative and diffusive regimes of acoustic damping in bulk amorphous material,"In amorphous solids, a non-negligible part of thermal conductivity results
from phonon scattering on the structural disorder. The conversion of acoustic
energy into thermal energy is often measured by the Dynamical Structure Factor
(DSF) thanks to inelastic neutron or X-Ray scattering. The DSF is used to
quantify the dispersion relation of phonons, together with their damping.
However, the connection of the dynamical structure factor with dynamical
attenuation of wave packets in glasses is still a matter of debate. We focus
here on the analysis of wave packets propagation in numerical models of
amorphous silicon. We show that the DHO fits (Damped Harmonic Oscillator model)
of the dynamical structure factors give a good estimate of the wave packets
mean-free path, only below the Ioffe-Regel limit. Above the Ioffe-Regel limit
and below the mobility edge, a pure diffusive regime without a definite mean
free path is observed. The high-frequency mobility edge is characteristic of a
transition to localized vibrations. Below the Ioffe-Regel criterion, a mixed
regime is evidenced at intermediate frequencies, with a coexistence of
propagative and diffusive wave fronts. The transition between these different
regimes is analyzed in details and reveals a complex dynamics for energy
transportation, thus raising the question of the correct modeling of thermal
transport in amorphous materials.",1803.08594v1
2018-04-11,Axial quasi-normal modes of neutron stars in $R^2$ gravity,"In the present paper the axial quasi-normal modes of neutron stars in $f(R)$
gravity are examined using a large set of equations of state. The numerical
calculations are made using two different approaches -- performing time
evolution of the perturbation equations and solving the time-independent
representation of the equations as a boundary value problem. According to the
results the mode frequencies and the damping times decrease with the increase
of the free parameter of the theory in comparison to the pure general
relativistic case. While the frequencies deviate significantly from Einstein's
theory for all realistic neutron star masses (say above $1M_\odot$), the
damping times reach non-negligible differences only for the more massive
models. We have constructed as well universal (equation of state independent)
gravitational wave asteroseismology relations involving the frequencies and the
damping times. It turns out that the equation of state independence is
preserved using the same normalization as in pure general relativity and the
qualitative differences of the phenomenological relations with respect to
Einstein's theory of gravity can be large for large values of the free
parameter in $f(R)$ gravity.",1804.04060v1
2018-05-10,Dust modification of the plasma conductivity in the mesosphere,"Relative transverse drift (with respect to the ambient magnetic field)
between the weakly magnetized electrons and the unmagnetized ions at the lower
altitude (80 km) and between the weakly magnetized ions and unmagnetized dust
at the higher altitude (90 km) gives rise to the finite Hall conductivity in
the Earth's mesosphere. If, on the other hand, the number of free electrons is
sparse in the mesosphere and most of the negative charge resides on the weakly
magnetized, fine, nanometre sized dust powder and positive charge on the more
massive, micron sized, unmagnetized dust, the sign of the Hall conductivity due
to their relative transverse drift will be opposite to the previous case. Thus
the sign of the Hall effect not only depends on the direction of the local
magnetic field but also on the nature of the charge carrier in the partially
ionized dusty medium.
  As the Hall and the Ohm diffusion are comparable below 80 km, the low
frequency long wavelength waves will be damped at this altitude with the
damping rate typically of the order of few minutes. Therefore, the ultra--low
frequency magnetohydrodynamic waves can not originate below 80 km in the
mesosphere. However, above 80 km since Hall effect dominates Ohm diffusion the
mesosphere can host the ultra--low frequency waves which can propagate across
the ionosphere with little or, no damping.",1805.03799v1
2018-05-19,Migration of Planets Into and Out of Mean Motion Resonances in Protoplanetary Discs: Overstability of Capture and Nonlinear Eccentricity Damping,"A number of multiplanet systems are observed to contain planets very close to
mean motion resonances, although there is no significant pileup of precise
resonance pairs. We present theoretical and numerical studies on the outcome of
capture into first-order mean motion resonances (MMRs) using a parametrized
planet migration model that takes into account nonlinear eccentricity damping
due to planet-disk interaction. This parametrization is based on numerical
hydrodynamical simulations and is more realistic than the simple linear
parametrization widely used in previous analytic studies. We find that
nonlinear eccentricity damping can significantly influence the stability and
outcome of resonance capture. In particular, the equilibrium eccentricity of
the planet captured into MMRs become larger, and the captured MMR state tends
to be more stable compared to the prediction based on the simple migration
model. In addition, when the migration is sufficiently fast or/and the planet
mass ratio is sufficiently small, we observe a novel phenomenon of eccentricity
overshoot, where the planet's eccentricity becomes very large before settling
down to the lower equilibrium value. This can lead to the ejection of the
smaller planet if its eccentricity approaches unity during the overshoot. This
may help explain the lack of low-mass planet companion of hot Jupiters when
compared to warm Jupiters.",1805.07501v1
2018-06-04,Density Waves and the Viscous Overstability in Saturn's Rings,"This paper addresses resonantly forced spiral density waves in a dense
planetary ring which is close to the threshold for viscous overstability. We
solve numerically the hydrodynamical equations for a dense, axisymmetric thin
disk in the vicinity of an inner Lindblad resonance with a perturbing
satellite. The spiral shape of a density wave is taken into account through a
suitable approximation of the advective terms arising from the fluid orbital
motion. This paper is a first attempt to model the co-existence of resonantly
forced density waves and short-scale axisymmetric overstable wavetrains in
Saturn's rings by conducting large-scale hydrodynamical integrations. These
integrations reveal that the two wave types undergo complex interactions, not
taken into account in existing models for the damping of density waves. In
particular it is found that, depending on the relative magnitude of both wave
types, the presence of viscous overstability can lead to a damping of an
unstable density wave and vice versa. The damping of viscous overstability by a
density wave is investigated further by employing a simplified model of an
axisymmetric ring perturbed by a nearby Lindblad resonance. A linear
hydrodynamic stability analysis as well as local N-body simulations of this
model system are performed and support the results of our large-scale
hydrodynamical integrations.",1806.01211v3
2018-07-02,Thermoplasmonic behavior of semiconductor nanoparticles: A comparison with metals,"A number of applications in nanoplasmonics utilize noble metals, gold (Au)
and silver (Ag), as the materials of choice. However, these materials suffer
from problems of poor thermal and chemical stability accompanied by significant
dissipative losses under high-temperature conditions. In this regard,
semiconductor nanoparticles have attracted attention with their promising
characteristics of highly tunable plasmonic resonances, low ohmic losses and
greater thermochemical stability. Here, we investigate the size-dependent
thermoplasmonic properties of semiconducting silicon and gallium arsenide
nanoparticles to compare them with metallic Au nanoparticles using Mie theory.
To this end, we employ experimentally estimated models of dielectric
permittivity in our computations. Among the various permittivity models for Au,
we further compare the Drude-Lorentz (DL) and the Drude and critical points
(DCP) models. Results show a redshift in the scattering and absorption
resonances for the DL model while the DCP model presents a blueshift. The
dissipative damping in the semiconductor nanoparticles is strongest for the
sharp electric octupole resonances followed by the quadrupole and dipole modes.
However, a reverse order with strongest values for the broad dipole resonance
is observed for the Au nanoparticles. A massive Drude broadening contributes
strongly to the damping of resonances in Au nanoparticles at elevated
temperatures. In contrast, the semiconductor nanoparticles do not exhibit any
significant deterioration in their scattering and absorption resonances at high
temperatures. In combination with low dissipative damping, this makes the
semiconductor nanoparticles better suited for high-temperature applications in
nanoplasmonics wherein the noble metals suffer from excessive heating.",1807.00881v1
2018-07-26,Aspherical deformations of the Choptuik spacetime,"We perform dynamical and nonlinear numerical simulations to study critical
phenomena in the gravitational collapse of massless scalar fields in the
absence of spherical symmetry. We evolve axisymmetric sets of initial data and
examine the effects of deviation from spherical symmetry. For small deviations
we find values for the critical exponent and echoing period of the discretely
self-similar critical solution that agree well with established values;
moreover we find that such small deformations behave like damped oscillations
whose damping coefficient and oscillation frequencies are consistent with those
predicted in the linear perturbation calculations of Martin-Garcia and
Gundlach. However, we also find that the critical exponent and echoing period
appear to decrease with increasing departure from sphericity, and that, for
sufficiently large departures from spherical symmetry, the deviations become
unstable and grow, confirming earlier results by Choptuik et.al.. We find some
evidence that these growing modes lead to a bifurcation, similar to those
reported by Choptuik et.al., with two centers of collapse forming on the
symmetry axis above and below the origin. These findings suggest that nonlinear
perturbations of the critical solution lead to changes in the effective values
of the critical exponent, echoing period and damping coefficient, and may even
change the sign of the latter, so that perturbations that are stable in the
linear regime can become unstable in the nonlinear regime.",1807.10342v2
2018-08-03,Witnessing galaxy assembly at the edge of the reionization epoch,"We report the discovery of Serenity-18, a galaxy at z=5.939 for which we
could measure the content of molecular gas, M(H_2)~ 5 x10^9 M_sun, traced by
the CO(6-5) emission, together with the metal-poor ([Fe/H]=-3.08 +- 0.12,
[Si/H]=-2.86 +- 0.14) gas clump/filament which is possibly feeding its growth.
The galaxy has an estimated star formation rate of ~100 M_sun yr^{-1}, implying
that it is a typical main sequence galaxy at these redshifts. The metal-poor
gas is detected through a damped Lyman-alpha absorber (DLA) observed at a
spatial separation of 40 kpc and at the same redshift of Serenity-18, along the
line of sight to the quasar SDSS J2310+1855 (z_em = 6.0025). The chemical
abundances measured for the damped Lyman-alpha system are in very good
agreement with those measured for other DLAs discovered at similar redshifts,
indicating an enrichment due to massive PopII stars. The galaxy/Damped system
we discovered is a direct observational evidence of the assembly of a galaxy at
the edge of the reionization epoch.",1808.01146v2
2018-08-13,Fluidization of collisionless plasma turbulence,"In a collisionless, magnetized plasma, particles may stream freely along
magnetic-field lines, leading to phase ""mixing"" of their distribution function
and consequently to smoothing out of any ""compressive"" fluctuations (of
density, pressure, etc.,). This rapid mixing underlies Landau damping of these
fluctuations in a quiescent plasma-one of the most fundamental physical
phenomena that make plasma different from a conventional fluid. Nevertheless,
broad power-law spectra of compressive fluctuations are observed in turbulent
astrophysical plasmas (most vividly, in the solar wind) under conditions
conducive to strong Landau damping. Elsewhere in nature, such spectra are
normally associated with fluid turbulence, where energy cannot be dissipated in
the inertial scale range and is therefore cascaded from large scales to small.
By direct numerical simulations and theoretical arguments, it is shown here
that turbulence of compressive fluctuations in collisionless plasmas strongly
resembles one in a collisional fluid and does have broad power-law spectra.
This ""fluidization"" of collisionless plasmas occurs because phase mixing is
strongly suppressed on average by ""stochastic echoes"", arising due to nonlinear
advection of the particle distribution by turbulent motions. Besides resolving
the long-standing puzzle of observed compressive fluctuations in the solar
wind, our results suggest a conceptual shift for understanding kinetic plasma
turbulence generally: rather than being a system where Landau damping plays the
role of dissipation, a collisionless plasma is effectively dissipationless
except at very small scales. The universality of ""fluid"" turbulence physics is
thus reaffirmed even for a kinetic, collisionless system.",1808.04284v1
2018-08-15,Neural Material: Learning Elastic Constitutive Material and Damping Models from Sparse Data,"The accuracy and fidelity of deformation simulations are highly dependent
upon the underlying constitutive material model. Commonly used linear or
nonlinear constitutive material models only cover a tiny part of possible
material behavior. In this work we propose a unified framework for modeling
deformable material. The key idea is to use a neural network to correct a
nominal model of the elastic and damping properties of the object. The neural
network encapsulates a complex function that is hard to explicitly model. It
injects force corrections that help the forward simulation to more accurately
predict the true behavior of a given soft object, which includes non-linear
elastic forces and damping. Attempting to satisfy the requirement from real
material interference and animation design scenarios, we learn material models
from examples of dynamic behavior of a deformable object's surface. The
challenge is that such data is sparse as it is consistently given only on part
of the surface. Sparse reduced space-time optimization is employed to gradually
generate increasingly accurate training data, which further refines and
enhances the neural network. We evaluate our choice of network architecture and
show evidence that the modest amount of training data we use is suitable for
the problem tackled. Our method is demonstrated with a set of synthetic
examples.",1808.04931v1
2018-09-06,Forming Gliese 876 Through Smooth Disk Migration,"We run a suite of dissipative N-body simulations to determine which regions
of phase space for smooth disk migration are consistent with the GJ876 system,
an M-dwarf hosting three planets orbiting in a chaotic 4:2:1 Laplace resonance.
We adopt adaptive mesh refinement (AMR) methods which are commonly used in
hydrodynamical simulations to efficiently explore the parameter space defined
by the semi-major axis and eccentricity damping timescales. We find that there
is a large region of phase space which produces systems in the chaotic Laplace
resonance and a smaller region consistent with the observed eccentricities and
libration amplitudes for the resonant angles. Under the assumptions of Type I
migration for the outer planet, we translate these damping timescales into
constraints on the protoplanetary disk surface density and thickness. When we
strongly (weakly) damp the eccentricities of the inner two Laplace planets,
these timescales correspond to disk surface densities around ten thousand (a
few hundred) grams per square centimeter and disk aspect ratios between 1-10%.
Additionally, smooth migration produces systems with a range of chaotic
timescales, from decades and centuries to upwards of thousands of years. In
agreement with previous studies, the less chaotic regions of phase space
coincide with the system being in a low energy double apsidal corotation
resonance. Our detailed modeling of multi-planetary systems coupled with our
AMR exploration method enhances our ability to map out the parameter space of
planet formation models, and is well suited to study other resonant chain
systems such as Trappist-1, Kepler-60, and others.",1809.02200v2
2018-09-15,New closures for more precise modeling of Landau damping in the fluid framework,"Incorporation of kinetic effects such as Landau damping into a fluid
framework was pioneered by Hammett and Perkins PRL 1990, by obtaining closures
of the fluid hierarchy, where the gyrotropic heat flux fluctuations or the
deviation of the 4th-order gyrotropic fluid moment, are expressed through
lower-order fluid moments. To obtain a closure of a fluid model expanded around
a bi-Maxwellian distribution function, the usual plasma dispersion function
$Z(\zeta)$ that appears in kinetic theory or the associated plasma response
function $R(\zeta)=1 + \zeta Z(\zeta)$, have to be approximated with a suitable
Pad\'e approximant in such a way, that the closure is valid for all $\zeta$
values. Such closures are rare, and the original closures of Hammett and
Perkins are often employed. Here we present a complete mapping of all plausible
Landau fluid closures that can be constructed at the level of 4th-order moments
in the gyrotropic limit and we identify the most precise closures. Furthermore,
by considering 1D closures at higher-order moments, we show that it is possible
to reproduce linear Landau damping in the fluid framework to any desired
precision, thus showing convergence of the fluid and collisionless kinetic
descriptions.",1809.05718v1
2018-10-04,Sub-photospheric turbulence as a heating mechanism in gamma-ray bursts,"We examine the possible role of turbulence in feeding the emission of
gamma-ray bursts (GRBs). Turbulence may develop in a GRB jet as the result of
hydrodynamic or current-driven instabilities. The jet carries dense radiation
and the turbulence cascade can be damped by Compton drag, passing kinetic fluid
energy to photons through scattering. We identify two regimes of turbulence
dissipation: (1) ""Viscous"" - the turbulence cascade is Compton damped on a
scale $\ell_{\rm damp}$ greater than the photon mean free path $\ell_\star$.
Then turbulence energy is passed to photons via bulk Comptonization by smooth
shear flows on scale $\ell_\star<\ell_{\rm damp}$. (2) ""Collisionless"" - the
cascade avoids Compton damping and extends to microscopic plasma scales much
smaller than $\ell_\star$. The collisionless dissipation energizes plasma
particles, which radiate the received energy; how the dissipated power is
partitioned between particles needs further investigation with kinetic
simulations. We show that the dissipation regime switches from viscous to
collisionless during the jet expansion, at a critical value of the jet optical
depth which depends on the amplitude of turbulence. Turbulent GRB jets are
expected to emit nonthermal photospheric radiation. Our analysis also suggests
revisions of turbulent Comptonization in black hole accretion disks discussed
in previous works.",1810.02228v1
2018-10-15,Zombie Vortex Instability. III. Persistence with Nonuniform Stratification and Radiative Damping,"The Zombie Vortex Instability (ZVI) occurs in the dead zones of
protoplanetary disks (PPDs) where perturbations excite baroclinic critical
layers, generating ""zombie"" vortices and turbulence. In this work, we
investigate ZVI with nonuniform vertical stratification; while ZVI is triggered
in the stratified regions away from the midplane, the subsequent turbulence
propagates into and fills the midplane. ZVI turbulence alters the background
Keplerian shear flow, creating a steady-state zonal flow. Intermittency is
observed, where the flow cycles through near-laminar phases of zonal flow
punctuated by chaotic bursts of new vortices. ZVI persists in the presence of
radiative damping, as long as the thermal relaxation timescale is more than a
few orbital periods. We refute the premature claim by Lesur & Latter (2016)
that radiative damping inhibits ZVI for disk radii r>0.3 au. Their conclusions
were based on unrealistically short cooling times using opacities with
virtually no grain growth. We explore different grain growth and vertical
settling scenarios, and find that the gas and dust in off-midplane regions are
not necessarily in local thermodynamic equilibrium (LTE) with each other. In
such cases, thermal relaxation timescales can be orders of magnitude longer
than the optically thin cooling times assuming LTE because of the finite time
for energy to be exchanged between gas and dust grains via collisions. With
minimal amounts of grain growth and dust settling, the off-midplane regions of
disks are susceptible to ZVI and much of the planet-forming regions can be
filled with zombie vortices and turbulence.",1810.06588v1
2018-09-21,High performance passive vibration isolation system for optical tables using six-degree-of-freedom viscous damping combined with steel springs,"Mechanical vibrations in buildings are ubiquitous. Such vibrations limit the
performance of sensitive instruments used, for example, for high-precision
manufacturing, nanofabrication, metrology, medical systems, or microscopy. For
improved precision, instruments and optical tables need to be isolated from
mechanical vibrations. However, common active or passive vibration isolation
systems often perform poorly when low-frequency vibration isolation is required
or are expensive. Furthermore, a simple solution such as suspension from common
bungee cords may require high ceilings. Here we developed a vibration isolation
system that uses steel springs to suspend an optical table from a common-height
ceiling. The system was designed for a fundamental resonance frequency of 0.5
Hz. Resonances and vibrations were efficiently damped in all translational and
rotational degrees of freedom of the optical table by spheres, which were
mounted underneath the table and immersed in a highly viscous silicone oil. Our
low-cost, passive system outperformed several state-of-the-art passive and
active systems in particular in the frequency range between 1-10 Hz. We
attribute this performance to a minimal coupling between the degrees of freedom
and the truly three dimensional viscous damping combined with a nonlinear
hydrodynamic finite-size effect. Furthermore, the system can be adapted to
different loads, resonance frequencies, and dimensions. In the long term, the
excellent performance of the system will allow high-precision measurements for
many different instruments.",1810.06641v4
2018-10-17,Resonance-broadened transit time damping of particles in MHD turbulence,"As a fundamental astrophysical process, the scattering of particles by
turbulent magnetic fields has its physical foundation laid by the
magnetohydrodynamic (MHD) turbulence theory. In the framework of the modern
theory of MHD turbulence, we derive a generalized broadened resonance function
by taking into account both the magnetic fluctuations and nonlinear
decorrelation of turbulent magnetic fields arising in MHD turbulence, and we
specify the energy range of particles for the dominance of different broadening
mechanisms. The broadened resonance allows for scattering of particles beyond
the energy threshold of the linear resonance. By analytically determining the
pitch-angle diffusion coefficients for transit time damping (TTD) with slow and
fast modes, we demonstrate that the turbulence anisotropy of slow modes
suppresses their scattering efficiency. Furthermore, we quantify the dependence
of the relative importance between slow and fast modes in TTD scattering on (i)
particle energy, (ii) plasma $\beta$ (the ratio of gas pressure to magnetic
pressure), and (iii) damping of MHD turbulence, and we also provide the
parameter space for the dominance of slow modes. To exemplify its applications,
we find that among typical partially ionized interstellar phases, in the warm
neutral medium slow and fast modes have comparable efficiencies in TTD
scattering of cosmic rays. For low-energy particles, e.g., sub-Alfv\'{e}nic
charged grains, we show that slow modes always dominate TTD scattering.",1810.07726v1
2018-10-23,Calibration of the DAMPE Plastic Scintillator Detector and its on-orbit performance,"DArk Matter Particle Explorer (DAMPE) is a space-borne apparatus for
detecting the high-energy cosmic-rays like electrons, $\gamma$-rays, protons
and heavy-ions. Plastic Scintillator Detector (PSD) is the top-most
sub-detector of the DAMPE. The PSD is designed to measure the charge of
incident high-energy particles and it also serves as a veto detector for
discriminating $\gamma$-rays from charged particles. In this paper, PSD
on-orbit calibration procedure is described, which includes five steps of
pedestal, dynode correlation, response to minimum-ionizing particles (MIPs),
light attenuation function and energy reconstruction. A method for
reconstructing the charge of incident high energy cosmic-ray particles is
introduced. The detection efficiency of each PSD strip is verified to be above
99.5%, the total efficiency of the PSD for charged particles is above 99.99%.",1810.09901v1
2018-10-25,Charge Measurement of Cosmic Ray Nuclei with the Plastic Scintillator Detector of DAMPE,"One of the main purposes of the DArk Matter Particle Explorer (DAMPE) is to
measure the cosmic ray nuclei up to several tens of TeV or beyond, whose origin
and propagation remains a hot topic in astrophysics. The Plastic Scintillator
Detector (PSD) on top of DAMPE is designed to measure the charges of cosmic ray
nuclei from H to Fe and serves as a veto detector for discriminating gamma-rays
from charged particles. We propose in this paper a charge reconstruction
procedure to optimize the PSD performance in charge measurement. Essentials of
our approach, including track finding, alignment of PSD, light attenuation
correction, quenching and equalization correction are described detailedly in
this paper after a brief description of the structure and operational principle
of the PSD. Our results show that the PSD works very well and almost all the
elements in cosmic rays from H to Fe are clearly identified in the charge
spectrum.",1810.10784v1
2018-11-14,Anderson-Bogoliubov and Carlson-Goldman modes in counterflow superconductors: Case study of a double monolayer graphene,"The impact of electron-hole pairing on the spectrum of plasma excitations in
double layer systems is investigated. The theory is developed with reference to
a double monolayer graphene. Taking into account the coupling of scalar
potential oscillations with oscillations of the order parameter $\Delta$, we
show that the spectrum of antisymmetric (acoustic) plasma excitations contains
two modes: a weakly damped mode below the gap $2\Delta$ and a strongly damped
mode above the gap. The lower mode can be interpreted as an analog of the
Carlson-Goldman mode. This mode has an acoustic dispersion relation at small
wave vectors and it saturates at the level $2\Delta$ at large wave vectors. Its
velocity is larger than the velocity of the Anderson-Bogoliubov mode
$v_{AB}=v_F$/$\sqrt{2}$, and it can be smaller than the Fermi velocity $v_F$.
The damping rate of this mode strongly increases under increase of temperature.
Out-of-phase oscillations of two order parameters in two spin subsystems are
also considered. This part of the spectrum contains two more modes. One of them
is interpreted as an analog of the Anderson-Bogoliubov (phase) mode and the
other, as an analog of the Schmid (amplitude) mode. With minor modifications
the theory can be extended to describe collective modes in a double bilayer
graphene as well.",1811.05899v3
2018-12-07,Magnetic Braking and Damping of Differential Rotation in Massive Stars,"Fragmentation of highly differentially rotating massive stars that undergo
collapse has been suggested as a possible channel for binary black hole
formation. Such a scenario could explain the formation of the new population of
massive black holes detected by the LIGO/VIRGO gravitational wave laser
interferometers. We probe that scenario by performing general relativistic
magnetohydrodynamic simulations of differentially rotating massive stars
supported by thermal radiation pressure plus a gas pressure perturbation. The
stars are initially threaded by a dynamically weak, poloidal magnetic field
confined to the stellar interior. We find that magnetic braking and turbulent
viscous damping via magnetic winding and the magnetorotational instability in
the bulk of the star redistribute angular momentum, damp differential rotation
and induce the formation of a massive and nearly uniformly rotating inner core
surrounded by a Keplerian envelope. The core + disk configuration evolves on a
secular timescale and remains in quasi-stationary equilibrium until the
termination of our simulations. Our results suggest that the high degree of
differential rotation required for $m=2$ seed density perturbations to trigger
gas fragmentation and binary black hole formation is likely to be suppressed
during the normal lifetime of the star prior to evolving to the point of
dynamical instability to collapse. Other cataclysmic events, such as stellar
mergers leading to collapse, may therefore be necessary to reestablish
sufficient differential rotation and density perturbations to drive
nonaxisymmetric modes leading to binary black hole formation.",1812.03176v3
2018-12-18,Inferring physical parameters in solar prominence threads,"High resolution observations have permitted to resolve the solar
prominences/filaments as sets of threads/fibrils. However, the values of the
physical parameters of these threads and their structuring remain poorly
constrained. We use prominence seismology techniques to analyse transverse
oscillations in threads through the comparison between magnetohydrodynamic
(MHD) models and observations. We apply Bayesian methods to obtain two
different types of information. We first infer the marginal posterior
distribution of physical parameters, such as the magnetic field strength or the
length of the thread, when a totally filled tube, a partially filled tube, and
three damping models (resonant absorption in the Alfv\'en continuum, resonant
absorption in the slow continuum, and Cowling's diffusion) are considered as
certain. Then, we compare the relative plausibility between alternative MHD
models by computing the Bayes factors. Well constrained probability density
distributions can be obtained for the magnetic field strength, the length of
the thread, the density contrast, and parameters associated to damping models.
When comparing the damping models of resonant absorption in the Alfv\'en
continuum, resonant absorption in the slow continuum and Cowling's diffusion
due to partial ionisation of prominence plasma, the resonant absorption in the
Alfv\'en continuum is the most plausible mechanism in explaining the existing
observations. Relations between periods of fundamental and first overtone kink
modes with values around 1 are better explained by expressions of the period
ratio in the long thread approximation, while the rest of the values are more
probable in the short thread limit for the period ratio. Our results show that
Bayesian analysis offers valuable methods for performing parameter inference
and model comparison in the context of prominence seismology.",1812.07262v1
2019-01-07,Abnormal anti-crossing effect in photon-magnon coupling,"We report the experimental demonstration of an abnormal, opposite
anti-crossing effect in a photon-magnon-coupled system that consists of an
Yttrium Iron Garnet film and an inverted pattern of split-ring resonator
structure (noted as ISRR) in a planar geometry. It is found that the normal
shape of anti-crossing dispersion typically observed in photon-magnon coupling
is changed to its opposite anti-crossing shape just by changing the
position/orientation of the ISRR's split gap with respect to the microstrip
line axis along which ac microwave currents are applied. Characteristic
features of the opposite anti-crossing dispersion and its linewidth evolution
are analyzed with the help of analytical derivations based on electromagnetic
interactions. The observed opposite anti-crossing dispersion is ascribed to the
compensation of both intrinsic damping and coupling-induced damping in the
magnon modes. This compensation is achievable by controlling the relative
strength and phase of oscillating magnetic fields generated from the ISRR's
split gap and the microstrip feeding line. The position/orientation of an
ISRR's split gap provides a robust means of controlling the dispersion shape of
anti-crossing and its damping in a photon-magnon coupling, thereby offering
more opportunity for advanced designs of microwave devices.",1901.01729v2
2019-01-24,A compact actively damped vibration isolation platform for optical experiments in ultra-high vacuum,"We present a tabletop six-axis vibration isolation system, compatible with
Ultra-High Vacuum (UHV), which is actively damped and provides 25 dB of
isolation at 10 Hz and 65 dB at 100 Hz. While this isolation platform has been
primarily designed to support optics in the Laser Interferometer
Gravitational-Wave Observatory (LIGO) detectors, it is suitable for a variety
of applications. The system has been engineered to facilitate the construction
and assembly process, while minimizing cost. The platform provides passive
isolation for six degrees of freedom using a combination of vertical springs
and horizontal pendula. It is instrumented with voice-coil actuators and
optical shadow sensors to damp the resonances. All materials are compatible
with stringent vacuum requirements. Thanks to its architecture, the system's
footprint can be adapted to meet spatial requirements, while maximizing the
dimensions of the optical table. Three units are currently operating for LIGO.
We present the design of the system, controls principle, and experimental
results.",1901.09666v2
2019-01-28,Strong damping-like spin-orbit torque and tunable Dzyaloshinskii-Moriya interaction generated by low-resistivity Pd$_{1-x}$Pt$_x$ alloys,"Despite their great promise for providing a pathway for very efficient and
fast manipulation of magnetization at the nanoscale, spin-orbit torque (SOT)
operations are currently energy inefficient due to a low damping-like SOT
efficiency per unit current bias, and/or the very high resistivity of the spin
Hall materials. Here, we report an advantageous spin Hall material, Pd1-xPtx,
which combines a low resistivity with a giant spin Hall effect as evidenced
through the use of three independent SOT ferromagnetic detectors. The optimal
Pd0.25Pt0.75 alloy has a giant internal spin Hall ratio of >0.47 (damping-like
SOT efficiency of ~ 0.26 for all three ferromagnets) and a low resistivity of
~57.5 {\mu}{\Omega} cm at 4 nm thickness. Moreover, we find the
Dzyaloshinskii-Moriya interaction (DMI), the key ingredient for the
manipulation of chiral spin arrangements (e.g. magnetic skyrmions and chiral
domain walls), is considerably strong at the Pd1-xPtx/Fe0.6Co0.2B0.2 interface
when compared to that at Ta/Fe0.6Co0.2B0.2 or W/Fe0.6Co0.2B0.2 interfaces and
can be tuned by a factor of 5 through control of the interfacial spin-orbital
coupling via the heavy metal composition. This work establishes a very
effective spin current generator that combines a notably high energy efficiency
with a very strong and tunable DMI for advanced chiral spintronics and spin
torque applications.",1901.09954v1
2019-02-13,Two-mediator dark matter models and cosmic electron excess,"The cosmic electron energy spectrum recently observed by the DAMPE experiment
exhibits two interesting features, including a break around 0.9 TeV and a sharp
resonance near 1.4 TeV. In this analysis, we propose a dark matter explanation
to both exotic features seen by DAMPE. In our model, dark matter annihilates in
the galaxy via two different channels that lead to both a narrow resonance
spectrum near 1.4 TeV and electron excess events over an extended energy range
thus generating the break structure around TeV. The two annihilation channels
are mediated by two gauge bosons that interact both with dark matter and with
the standard model fermions. Dark matter annihilations through the s-channel
process mediated by the heavier boson produce monoenergetic electron-positron
pairs leading to the resonance excess. The lighter boson has a mass smaller
than the dark matter such that they can be on-shell produced in dark matter
annihilations in the galaxy; the lighter bosons in the final state subsequently
decay to generate the extended excess events due to the smeared electron energy
spectrum in this process. We further analyze constraints from various
experiments, including HESS, Fermi, AMS, and LHC, to the parameter space of the
model where both excess events can be accounted for. In order to interpret the
two new features in the DAMPE data, dark matter annihilation cross sections in
the current galaxy are typically much larger than the canonical thermal cross
section needed for the correct dark matter relic abundance. This discrepancy,
however, is remedied by the nonperturbative Sommerfeld enhancement because of
the existence of a lighter mediator in the model.",1902.04916v1
2019-02-18,Coherent control of magnon radiative damping with local photon states,"The collective excitation of ordered spins, known as spin waves or magnons,
can in principle radiate by emitting travelling photons to an open system when
decaying to the ground state. However, in contrast to the electric dipoles,
magnetic dipoles contributed by magnons are more isolated from electromagnetic
environment with negligible radiation in the vacuum, limiting their application
in coherent communication by photons. Recently, strong interaction between
cavity standing-wave photons and magnons has been reported, indicating the
possible manipulation of magnon radiation via tailoring photon states. Here,
with loading an yttrium iron garnet sphere in a one-dimensional circular
waveguide cavity in the presence of both travelling and standing photon modes,
we demonstrate an efficient photon emissions from magnon and a significant
magnon radiative damping with radiation rate found to be proportional to the
local density of states (LDOS) of photon. By modulating the LDOS including its
magnitude and/or polarization, we can flexibly tune the photon emission and
magnon radiative damping on demand. Our findings provide a general way in
manipulating photon emission from magnon radiation for harnessing energy and
angular momentum generation, transfer and storage modulated by magnon in the
cavity and waveguide electrodynamics.",1902.06795v2
2019-03-04,Quantum speed limit time for the damped Jaynes-Cummings and Ohmic-like dephasing models in Schwarzschild spacetime,"Quantum theory sets the bound on the minimal evolution time between initial
and final states of the quantum system. This minimal evolution time can be used
to specify the maximal speed of the evolution in open and closed quantum
systems. Quantum speed limit is one of the interesting issue in the theory of
open quantum systems. One may investigate the influence of the relativistic
effect on the quantum speed limit time. When several observers are placed in
different inertial or non-inertial frames, or in Schwarzschild space-time, the
relativistic effect should be taken into account. In this work, the quantum
speed limit time in Schwarzschild space-time will be studied for two various
model consist of damped Jaynes-Cummings and Ohmic-like dephasing. First, it
will be observed that how quantum coherence is affected by Hawking radiation.
According to the dependence of quantum speed limit time on quantum coherence
and the dependence of quantum coherence on relative distance of quantum system
to event horizon $R_{0}$, it will be represented that the quantum speed limit
time in Schwarzschild space-time is decreased by increasing $R_{0}$ for damped
Jaynes-Cummings model and conversely, It is increased by increasing $R_{0}$ for
Ohmic-like dephasing model .",1903.01230v2
2019-03-07,Non-linear diffusion of cosmic rays escaping from supernova remnants - II. Hot ionized media,"We study the problem of the escape and transport of Cosmic-Rays (CR) from a
source embedded in a fully ionised, hot phase of the interstellar medium (HIM).
In particular, we model the CR escape and their propagation in the source
vicinity taking into account excitation of Alfv\'enic turbulence by CR
streaming and mechanisms damping the self-excited turbulence itself. Our
estimates of escape radii and times result in large values (100 pc,
$2\times10^5$ yr) for particle energies $\lesssim20$ GeV and smaller values for
particles with increasing energies (35 pc and 14 kyr at 1 TeV). These escape
times and radii, when used as initial conditions for the CR propagation outside
the source, result in relevant suppression of the diffusion coefficient (by a
factor 5-10) on time-scales comparable with their (energy dependent) escape
time-scale. The damping mechanisms are fast enough that even on shorter time
scales the Alfv\'enic turbulence is efficiently damped, and the ratio between
random and ordered component of the magnetic field is $\delta B/B_0\ll 1$,
justifying the use of quasi-linear theory. In spite of the suppressed diffusion
coefficient, and then the increased residence time in the vicinity (<200 pc) of
their source, the grammage accumulated by CRs after their escape is found to be
negligible (at all energies) as compared to the one accumulated while diffusing
in the whole Galaxy, due to the low density of the HIM.",1903.03193v1
2019-03-25,Stabilised Asynchronous Fast Adaptive Composite Multigrid using Additive Damping,"Multigrid solvers face multiple challenges on parallel computers. Two
fundamental ones read as follows: Multiplicative solvers issue coarse grid
solves which exhibit low concurrency and many multigrid implementations suffer
from an expensive coarse grid identification phase plus adaptive mesh
refinement overhead. We propose a new additive multigrid variant for
spacetrees, i.e. meshes as they are constructed from octrees and quadtrees: It
is an additive scheme, i.e. all multigrid resolution levels are updated
concurrently. This ensures a high concurrency level, while the transfer
operators between the mesh levels can still be constructed algebraically. The
novel flavour of the additive scheme is an augmentation of the solver with an
additive, auxiliary damping parameter per grid level per vertex that is in turn
constructed through the next coarser level---an idea which utilises smoothed
aggregation principles or the motivation behind AFACx: Per level, we solve an
additional equation whose purpose is to damp too aggressive solution updates
per vertex which would otherwise, in combination with all the other levels,
yield an overcorrection and, eventually, oscillations. This additional equation
is constructed additively as well, i.e. is once more solved concurrently to all
other equations. This yields improved stability, closer to what is seen with
multiplicative schemes, while pipelining techniques help us to write down the
additive solver with single-touch semantics for dynamically adaptive meshes.",1903.10367v3
2019-04-04,The DAMPE excess and gamma-ray constraints,"The direct measurements of the cosmic electron-positron spectrum around 1 TeV
made by DAMPE have induced many theoretical speculations about possible
excesses in the data above the standard astrophysical predictions that might
have the dark matter (DM) origin. These attempts mainly fall into two
categories: i) DM annihilation (or decay) in the Galactic halo producing the
broad spectrum excess; ii) DM annihilation in the nearby compact subhalo
producing the sharp peak at 1.4 TeV. We investigate the gamma-ray emission
accompanying $e^+e^-$ production in DM annihilation, as well as various
theoretical means to suppress the prompt radiation, such as specific
interaction vertices or multi-cascade modes, and conclude that these attempts
are in tension with various gamma-ray observations. We show that the DM
explanations of the broad spectrum excess tend to contradict the diffuse
isotropic gamma-ray background (IGRB), measured by Fermi-LAT, while the nearby
subhalo scenario is constrained by nonobservation in the surveys, performed by
Fermi-LAT, MAGIC and HESS. We also briefly review other types of gamma-ray
constraints, which seem to rule out the DM interpretations of the DAMPE broad
spectrum excess as well.",1904.02456v2
2019-04-10,Stochastic nonlinear wave dynamics on compact surfaces,"We study the Cauchy problem for the nonlinear wave equations (NLW) with
random data and/or stochastic forcing on a two-dimensional compact Riemannian
manifold without boundary. (i) We first study the defocusing stochastic damped
NLW driven by additive space-time white-noise, and with initial data
distributed according to the Gibbs measure. By introducing a suitable
space-dependent renormalization, we prove local well-posedness of the
renormalized equation. Bourgain's invariant measure argument then allows us to
establish almost sure global well-posedness and invariance of the Gibbs measure
for the renormalized stochastic damped NLW. (ii) Similarly, we study the random
data defocusing NLW (without stochastic forcing), and establish the same
results as in the previous setting. (iii) Lastly, we study the stochastic NLW
without damping. By introducing a space-time dependent renormalization, we
prove its local well-posedness with deterministic initial data in all
subcritical spaces.
  These results extend the corresponding recent results on the two-dimensional
torus obtained by (i) Gubinelli-Koch-Oh-Tolomeo (2018), (ii) Oh-Thomann (2017),
and (iii) Gubinelli-Koch-Oh (2018), to a general class of compact manifolds.
The main ingredient is the Green's function estimate for the Laplace-Beltrami
operator in this setting to study regularity properties of stochastic terms
appearing in each of the problems.",1904.05277v3
2019-04-30,Damping rates and frequency corrections of Kepler LEGACY stars,"Linear damping rates and modal frequency corrections of radial oscillation
modes in selected LEGACY main-sequence stars are estimated by means of a
nonadiabatic stability analysis. The selected stellar sample covers stars
observed by Kepler with a large range of surface temperatures and surface
gravities. A nonlocal, time-dependent convection model is perturbed to assess
stability against pulsation modes. The mixing-length parameter is calibrated to
the surface-convection-zone depth of a stellar model obtained from fitting
adiabatic frequencies to the LEGACY observations, and two of the nonlocal
convection parameters are calibrated to the corresponding LEGACY linewidth
measurements. The remaining nonlocal convection parameters in the 1D
calculations are calibrated so as to reproduce profiles of turbulent pressure
and of the anisotropy of the turbulent velocity field of corresponding 3D
hydrodynamical simulations. The atmospheric structure in the 1D stability
analysis adopts a temperature-optical-depth relation derived from 3D
hydrodynamical simulations. Despite the small number of parameters to adjust,
we find good agreement with detailed shapes of both turbulent pressure profiles
and anisotropy profiles with depth, and with damping rates as a function of
frequency. Furthermore, we find the absolute modal frequency corrections,
relative to a standard adiabatic pulsation calculation, to increase with
surface temperature and surface gravity.",1904.13170v1
2019-05-09,An excess of excesses examined via dark matter radio emissions from galaxies,"Cosmic-ray and gamma-ray observations have yielded several notable excesses
that often lend themselves to explanation by various dark matter
annihilation/decay models. In particular, the AMS-02 anti-proton and positron
excesses have continued to grow more robust with the collection of more data.
This is supplemented by gamma-ray excesses in the Galactic Centre and a
high-energy break in spectrum of electron/positron cosmic rays seen by DAMPE.
In this work we carefully model the magnetic field environments of M31 and M33
and use this to estimate expected synchrotron emissions from electrons produced
via dark matter annihilation. By comparing this to available radio data we
review simplifying assumptions used previously for dark matter hunting in these
environments and produce novel constraints that are capable of fully ruling out
dark matter models proposed to accommodate all the aforementioned excesses
barring that of DAMPE. However, we do show that significant constraints can be
placed upon the DAMPE parameter space with M31 data. In addition to this we
project SKA non-observation constraints for the Reticulum II and Triangulum II
dwarf galaxies and find these have potential to rule out cosmic-ray and
gamma-ray excess-producing models of dark matter, even when the most
conservative assumptions are employed.",1905.05599v5
2019-05-17,Statics and Dynamics of Polymeric Droplets on Chemically Homogeneous and Heterogeneous Substrates,"We present a molecular dynamics study of the motion of cylindrical polymer
droplets on striped surfaces. We first consider the equilibrium properties of
droplets on different surfaces, we show that for small stripes the
Cassie-Baxter equation gives a good approximation of the equilibrium contact
angle. As the stripe width becomes non-negligible compared to the dimension of
the droplets, the droplet has to deform significantly to minimize its free
energy, this results in a smaller value of the contact angle than the continuum
model predicts. We then evaluate the slip length, and thus the damping
coefficient as a function of the stripe width. For very small stripes, the
heterogeneous surface behaves as an effective surface, with the same damping as
an homogeneous surface with the same contact angle. However, as the stripe
width increases, damping at the surface increases until reaching a plateau.
Afterwards, we study the dynamics of droplets under a bulk force. We show that
if the stripes are large enough the droplets are pinned until a critical
acceleration. The critical acceleration increases linearly with stripe width.
For large enough accelerations, the average velocity increases linearly with
the acceleration, we show that it can then be predicted by a model depending
only the size of droplet, viscosity and slip length. We show that the velocity
of the droplet varies sinusoidally as a function of its position on the
substrate. On the other hand, for accelerations just above the depinning
acceleration we observe a characteristic stick-slip motion, with successive
pinnings and depinnings.",1905.07214v1
2019-05-20,"Exploring the damping of Alfvén waves along a long off-limb coronal loop, up to 1.4 R$_\odot$","The Alfv\'en wave energy flux in the corona can be explored using the
electron density and velocity amplitude of the waves. The velocity amplitude of
Alfv\'en waves can be obtained from the non-thermal velocity of the spectral
line profiles. Previous calculations of the Alfv\'en wave energy flux with
height in active regions and polar coronal holes have provided evidence for the
damping of Alfv\'en waves with height. We present off-limb Hinode EUV imaging
spectrometer (EIS) observations of a long coronal loop up to 1.4~R$_\odot$. We
have obtained the electron density along the loop and found the loop to be
almost in hydrostatic equilibrium. We obtained the temperature using the
EM-loci method and found the loop to be isothermal across, as well as along,
the loop with a temperature of about 1.37 MK. We significantly improve the
estimate of non-thermal velocities over previous studies by using the estimated
ion (equal to electron) temperature. Estimates of electron densities are
improved using the significant updates of the CHIANTI v.8 atomic data. More
accurate measurements of propagating Alfv\'en wave energy along the coronal
loop and its damping are presented up to distances of 1.4 R$_\odot$, further
than have been previously explored. The Alfv\'en wave energy flux obtained
could contribute to a significant part of the coronal losses due to radiation
along the loop.",1905.08194v2
2019-06-14,Influence of External Magnetic Field on Dust$-$Acoustic Waves in a Capacitive RF Discharge,"This paper reports experiments on self$-$excited dust acoustic waves (DAWs)
and its propagation characteristics in a magnetized rf discharge plasma. The
DAWs are spontaneously excited in dusty plasma after adding more particles in
the confining potential well and found to propagate in the direction of
streaming ions. The spontaneous excitation of such low-frequency modes is
possible due to the instabilities associated with streaming ions through the
dust grain medium. The background E-field and neutral pressure determine the
stability of excited DAWs. The characteristics of DAWs strongly depend on the
strength of external magnetic field. The magnetic field of strength B $<$ 0.05
T only modifies the characteristics of propagating waves in dusty plasma at
moderate power and pressure, P = 3.5 W and p = 27 Pa respectively. It is found
that DAWs start to be damped with increasing the magnetic field beyond B $>$
0.05 T and get completely damped at higher magnetic field B $\sim$ 0.13 T.
After lowering the power and pressure to 3 W and 23 Pa respectively, the
excited DAWs in the absence of B are slightly unstable. In this case, the
magnetic field only stabilizes and modifies the propagation characteristics of
DAWs while the strength of B is increased up to 0.1 T or even higher. The
modification of the sheath electric field where particles are confined in the
presence of the external magnetic field is the main cause of the modification
and damping of the DAWs in a magnetized rf discharge plasma.",1906.06255v2
2019-06-18,A Dynamic Robotic Actuator with Variable Physical Stiffness and Damping,"This study is part of research aiming at increasing the range of dynamic
tasks for teleoperated field robotics in order to allow operators to use the
full range of human motions without being limited by the dynamics of the
robotic manipulator. A new variable impedance actuator (VIA) was designed,
capable of reproducing motions through teleoperation from precise positioning
tasks to highly dynamic tasks. The design requirements based on previous human
user studies were a stiffness changing time of 50 ms, a peak output velocity of
20 rad/s and variable damping allowing to suppress undesired oscillations. This
is a unique combination of features that was not met by other VIAs. The new
design has three motors in parallel configuration: two responsible for changing
the VIA's neutral position and effective stiffness through a sliding pivot
point lever mechanism, and the third acting as variable damper. A prototype was
built and its performance measured with an effective stiffness changing time of
50 to 120 ms for small to large stiffness steps, nominal output velocity of 16
rad/s and a variable damper with a damping torque from 0 to 3 Nm. Its effective
stiffness range is 0.2 to 313 Nm/rad. This concludes that the new actuator is
particularly suitable for highly dynamic tasks. At the same time, the new
actuator is also very versatile, making it especially interesting for
teleoperation and human-robot collaboration.",1906.07669v2
2019-06-27,Frequency Fluctuations in Tunable and Nonlinear Microwave Cavities,"We present a model for how frequency fluctuations comparable to the total
cavity linewidth may arise in tunable and nonlinear microwave cavities, and how
these fluctuations affect the measurement of scattering matrix elements.
Applying this model to the specific case of a two-sided cavity, we obtain
closed-form expressions for the average scattering matrix elements in several
important cases. A key signature of our model is the subtle deformation of the
trajectories swept out by scattering matrix elements in the complex plane.
Despite this signature, the fluctuating and non-fluctuating models are
qualitatively similar enough to be mistaken for one another. In the case of
tunable cavities we show that if one fails to account for these fluctuations
then one will find damping rates that appear to depend on the tuning parameter,
which is a common observation in such systems. In the case of a Kerr cavity, we
show that there exists a fundamental lower bound to the scale of these
frequency fluctuations in the steady state, imposed by quantum mechanical
uncertainty, which can appreciably affect the apparent damping rates of the
cavity as the strength of the nonlinearity approaches the single-photon level.
By using the model we present as a fitting function for experimental data,
however, one can extract both the true damping rates of the cavity and the
effective scale of these frequency fluctuations over the scattering
measurement's bandwidth. Lastly, we compare this new method for observing
frequency fluctuations to other methods, one of which we extend beyond the
regime of small fluctuations.",1906.11989v3
2019-08-08,Anisotropic damping of the spin fluctuations in doped La2-xSrxCuO4 studied by resonant inelastic x-ray scattering,"We report high-resolution resonant inelastic x-ray scattering (RIXS)
measurements of the collective spin fluctuations in three compositions of the
superconducting cuprate system La2-xSrxCuO4. We have mapped out the excitations
throughout much of the 2-D (h,k) Brillouin zone. The spin fluctuations in
La2-xSrxCuO4 are found to be fairly well-described by a damped harmonic
oscillator model, thus our data allows us to determine the full wavevector
dependence of the damping parameter. This parameter increases with doping and
is largest along the (h, h) line, where it is peaked near (0.2,0.2). We have
used a new procedure to determine the absolute wavevector-dependent
susceptibility for the doped compositions La2-xSrxCuO4 (x=0.12,0.16) by
normalising our data to La2CuO4 measurements made with inelastic neutron
scattering (INS). We find that the evolution with doping of the intensity of
high-energy excitations measured by RIXS and INS is consistent. For the doped
compositions, the wavevector-dependent susceptibility is much larger at
(1/4,1/4) than at (1/2,0). It increases rapidly along the (h,h) line towards
the antiferromagnetic wavevector of the parent compound (1/2,1/2). Thus, the
strongest magnetic excitations, and those predicted to favour superconductive
pairing, occur towards the (1/2,1/2) position as observed by INS.",1908.03086v2
2019-08-14,Two-fluid simulations of waves in the solar chromosphere II. Propagation and damping of fast magneto-acoustic waves and shocks,"Waves and shocks traveling through the solar chromospheric plasma are
influenced by its partial ionization and weak collisional coupling, and may
become susceptible to multi-fluid effects, similar to interstellar shock waves.
In this study, we consider fast magneto-acoustic shock wave formation and
propagation in a stratified medium, that is permeated by a horizontal magnetic
field, with properties similar to that of the solar chromosphere. The evolution
of plasma and neutrals is modeled using a two-fluid code that evolves a set of
coupled equations for two separate fluids. We observed that waves in neutrals
and plasma, initially coupled at the upper photosphere, become uncoupled at
higher heights in the chromosphere. This decoupling can be a consequence of
either the characteristic spatial scale at the shock front, that becomes
similar to the collisional scale, or the change in the relation between the
wave frequency, ion cyclotron frequency, and the collisional frequency with
height. The decoupling height is a sensitive function of the wave frequency,
wave amplitude, and the magnetic field strength. We observed that decoupling
causes damping of waves and an increase in the background temperature due to
the frictional heating. The comparison between analytical and numerical results
allows us to separate the role of the nonlinear effects from the linear ones on
the decoupling and damping of waves.",1908.05262v1
2019-09-16,Inviscid damping and enhanced dissipation of the boundary layer for 2D Navier-Stokes linearized around Couette flow in a channel,"We study the 2D Navier-Stokes equations linearized around the Couette flow
$(y,0)^t$ in the periodic channel $\mathbb T \times [-1,1]$ with no-slip
boundary conditions in the vanishing viscosity $\nu \to 0$ limit. We split the
vorticity evolution into the free evolution (without a boundary) and a boundary
corrector that is exponentially localized to at most an $O(\nu^{1/3})$ boundary
layer. If the initial vorticity perturbation is supported away from the
boundary, we show inviscid damping of both the velocity and the vorticity
associated to the boundary layer. For example, our $L^2_t L^1_y$ estimate of
the boundary layer vorticity is independent of $\nu$, provided the initial data
is $H^1$. For $L^2$ data, the loss is only logarithmic in $\nu$. Note both such
estimates are false for the vorticity in the interior. To the authors'
knowledge, this inviscid decay of the boundary layer vorticity seems to be a
new observation not previously isolated in the literature. Both velocity and
vorticity satisfy the expected $O(\exp(-\delta\nu^{1/3}\alpha^{2/3}t))$
enhanced dissipation in addition to the inviscid damping. Similar, but slightly
weaker, results are obtained also for $H^1$ data that is against the boundary
initially. For $L^2$ data against the boundary, we at least obtain the boundary
layer localization and enhanced dissipation.",1909.07230v1
2019-10-19,Anomalies in the switching dynamics of C-type antiferromagnets and antiferromagnetic nanowires,"Antiferromagnets (AFMs) are widely believed to be superior than ferromagnets
in spintronics because of their high stability due to the vanishingly small
stray field. It is thus expected that the order parameter of AFM should always
align along the easy-axis of the crystalline anisotropy. In contrast to this
conventional wisdom, we find that the AFM order parameter switches away from
the easy-axis below a critical anisotropy strength when an AFM is properly
tailored into a nano-structure. The switching time first decreases and then
increases with the damping. Above the critical anisotropy, the AFM order
parameter is stable and precesses under a microwave excitation. However, the
absorption peak is not at resonance frequency even for magnetic damping as low
as 0.01. To resolve these anomalies, we first ascertain the hidden role of
dipolar interaction that reconstructs the energy landscape of the nano-system
and propose a model of damped non-linear pendulum to explain the switching
behavior. In this framework, the second anomaly appears when an AFM is close to
the boundary between underdamped and overdamped phases, where the observed
absorption lineshape has small quality factor and thus is not reliable any
longer. Our results should be significant to extract the magnetic parameters
through resonance techniques.",1910.08668v1
2019-11-01,Importance of Giant Impact Ejecta for Orbits of Planets Formed during the Giant Impact Era,"Terrestrial planets are believed to be formed via giant impacts of Mars-sized
protoplanets. Planets formed via giant impacts have highly eccentric orbits. A
swarm of planetesimals around the planets may lead to eccentricity damping for
the planets via the equipartition of random energies (dynamical friction).
However, dynamical friction increases eccentricities of planetesimals,
resulting in high velocity collisions between planetesimals. The collisional
cascade grinds planetesimals to dust until dust grains are blown out due to
radiation pressure. Therefore, the total mass of planetesimals decreases due to
collisional fragmentation, which weakens dynamical friction. We investigate the
orbital evolution of protoplanets in a planetesimal disk, taking into account
collisional fragmentation of planetesimals. For 100 km-sized or smaller
planetesimals, dynamical friction is insignificant for eccentricity damping of
planets because of collisional fragmentation. On the other hand, giant impacts
eject collisional fragments. Although the total mass of giant impact ejecta is
0.1-0.3 Earth masses, the largest impact ejecta are ~ 1,000 km in size. We also
investigate the orbital evolution of single planets with initial eccentricities
0.1 in a swarm of such giant impact ejecta. Although the total mass of giant
impact ejecta decreases by a factor of 3 in 30 Myrs, eccentricities of planets
are damped down to the Earth level (~0.01) due to interaction with giant impact
ejecta. Therefore, giant impact ejecta play an important role for determination
of terrestrial planet orbits.",1911.00278v3
2019-11-06,Damping in Ru/Co-based multilayer films with large Dzyaloshinskii-Moriya interaction,"Recent development of the magnetic material engineering led to achievement of
the systems with a high interfacial Dzyaloshinskii-Moriya interaction (DMI). As
a result, the formation of non-collinear magnetic soliton states or
nonreciprocal spin wave dynamics is achievable. Typically used materials are
based on bi-layers Heavy Metal/Ferromagnet, e.g., Pt/Co. These layers are
characterized not only by a strong DMI, but also by the spin pumping effect and
the resulting relatively large damping. Here, we show that the considerable
interfacial DMI can be also present in bi-layers based on Ru/Co, characterized
with low spin pumping effect and low damping. It is therefore a good candidate
for the dynamical studies and implementations of chiral DMI. It is demonstrated
by theoretical calculations that the value of DMI can be strongly affected and
controlled by the strain of the lattice. We show a systematic experimental and
theoretical comparison of magnetic material parameters between Pt/Co and Ru/Co
bi-layers as a deserving candidate for spintronic and spin-orbitronic
applications.",1911.02467v1
2019-11-14,Studies of the beam-ion instability and its mitigation with feedback system,"The beam-ion interaction is a potential limitation of beam performance in
electron accelerators, especially where the beam emittance is of a great
concern in future ultra-low emittance light source. ""Conventionally"", the beam
instability due to beam-ion interaction is attributed to two types of effects:
ion trapping effect and fast ion effect, which emphasize the beam-ion dynamics
in different time scales. Whereas, in accelerators, the beam suffers from a
mixture of ion trapping effect and fast ion effect, leading to a more
complicated process and requiring a self-consistent treatment. To evaluate the
beam characteristics, as emittance growth under the influence from beam-ion
effect, a new numerical simulation code based on the ""quasi-strong-strong""
model has been developed, including modules of ionization, beam-ion
interaction, synchrotron radiation damping, quantum excitation, bunch-by-bunch
feedback, etc. In the study, we do not regularly distinguish the ion trapping
effect and the fast ion effect, but treat beam-ion interaction more generally
and consistently. The lattice of High Energy Photon Source, a diffraction limit
ring under construction in Beijing, is used as an example to show the beam-ion
effect. It is found that in this low emittance ring, the beam-ion instability
is not a dominant mechanism in operation mode with a high beam current, but
seriously occurs in a lower beam current region. When the beam-ion instability
were significantly driven and can not be damped by the synchrotron radiation
damping, the simulations show the bunch-by-bunch feedback system based on the
Finite Impulse Response filter technique can be adopted to mitigate it
effectively.",1911.05958v1
2019-12-05,Steering magnonic dynamics and permeability at exceptional points in a parity-time symmetric waveguide,"Tuning the low-energy magnetic dynamics is a key element in designing novel
magnetic metamaterials, spintronic devices and magnonic logic circuits. This
study uncovers a new, highly effective way of controlling the magnetic
permeability via shaping the magnonic properties in coupled magnetic waveguides
separated by current carrying spacer with strong spin-orbit coupling. The
spin-orbit torques exerted on the waveguides leads to an externally tunable
enhancement of magnetic damping in one waveguide and a decreased damping in the
other, constituting so a magnetic parity-time (PT) symmetric system with
emergent magnetic properties at the verge of the exceptional point where
magnetic gains/losses are balanced. In addition to controlling the magnetic
permeability, phenomena inherent to PT-symmetric systems are identified,
including the control on magnon power oscillations, nonreciprocal magnon
propagation, magnon trapping and enhancement as well as the increased
sensitivity to magnetic perturbation and abrupt spin reversal. These
predictions are demonstrated analytically and confirmed by full numerical
simulations under experimentally feasible conditions. The position of the
exceptional points and the strength of the spontaneous PT symmetry breaking can
be tuned by external electric and/or magnetic fields. The roles of the
intrinsic magnetic damping, and the possibility of an electric control via
Dzyaloshinskii-Moriya interaction are exposed and utilized for mode dispersion
shaping and magnon amplification and trapping. The results point to a new route
to designing optomagnonic waveguides, traps, sensors, and circuits.",1912.02500v1
2020-01-13,Modelling Stochastic Signatures in Classical Pulsators,"We consider the impact of stochastic perturbations on otherwise coherent
oscillations of classical pulsators. The resulting dynamics are modelled by a
driven damped harmonic oscillator subject to either an external or an internal
forcing and white noise velocity fluctuations. We characterize the phase and
relative amplitude variations using analytical and numerical tools. When the
forcing is internal the phase variation displays a random walk behaviour and a
red noise power spectrum with a ragged erratic appearance. We determine the
dependence of the root mean square phase and relative amplitude variations
($\sigma_{\Delta \varphi}$ and $\sigma_{\Delta A/A}$, respectively) on the
amplitude of the stochastic perturbations, the damping constant $\eta$, and the
total observation time $t_{\rm obs}$ for this case, under the assumption that
the relative amplitude variations remain small, showing that $\sigma_{\Delta
\varphi}$ increases with $t_{\rm obs}^{1/2}$ becoming much larger than
$\sigma_{\Delta A/A}$ for $t_{\rm obs} \gg \eta^{-1}$. In the case of an
external forcing the phase and relative amplitude variations remain of the same
order, independent of the observing time. In the case of an internal forcing,
we find that $\sigma_{\Delta \varphi}$ does not depend on $\eta$. Hence, the
damping time cannot be inferred from fitting the power of the signal, as done
for solar-like pulsators, but the amplitude of the stochastic perturbations may
be constrained from the observations. Our results imply that, given sufficient
time, the variation of the phase associated to the stochastic perturbations in
internally driven classical pulsators will become sufficiently large to be
probed observationally.",2001.04558v1
2020-01-23,Skyrmion Dynamics and Topological Sorting on Periodic Obstacle Arrays,"We examine skyrmions under a dc drive interacting with a square array of
obstacles for varied obstacle size and damping. When the drive is applied in a
fixed direction, we find that the skyrmions are initially guided in the drive
direction but also move transverse to the drive due to the Magnus force. The
skyrmion Hall angle, which indicates the difference between the skyrmion
direction of motion and the drive direction, increases with drive in a series
of quantized steps as a result of the locking of the skyrmion motion to
specific symmetry directions of the obstacle array. On these steps, the
skyrmions collide with an integer number of obstacles to create a periodic
motion. The transitions between the different locking steps are associated with
jumps or dips in the velocity-force curves. In some regimes, the skyrmion Hall
angle is actually higher than the intrinsic skyrmion Hall angle that would
appear in the absence of obstacles. In the limit of zero damping, the skyrmion
Hall angle is 90$^\circ$, and we find that it decreases as the damping
increases. For multiple interacting skyrmion species in the collective regime,
we find jammed behavior at low drives where the different skyrmion species are
strongly coupled and move in the same direction. As the drive increases, the
species decouple and each can lock to a different symmetry direction of the
obstacle lattice, making it possible to perform topological sorting in analogy
to the particle sorting methods used to fractionate different species of
colloidal particles moving over two-dimensional obstacle arrays.",2001.08835v1
2020-03-03,Linear stability analysis for 2D shear flows near Couette in the isentropic Compressible Euler equations,"In this paper, we investigate linear stability properties of the 2D
isentropic compressible Euler equations linearized around a shear flow given by
a monotone profile, close to the Couette flow, with constant density, in the
domain $\mathbb{T}\times \mathbb{R}$. We begin by directly investigating the
Couette shear flow, where we characterize the linear growth of the compressible
part of the fluid while proving time decay for the incompressible part
(inviscid damping with slower rates). Then we extend the analysis to monotone
shear flows near Couette, where we are able to give an upper bound, superlinear
in time, for the compressible part of the fluid. The incompressible part enjoys
an inviscid damping property, analogous to the Couette case. In the pure
Couette case, we exploit the presence of an additional conservation law (which
connects the vorticity and the density on the moving frame) in order to reduce
the number of degrees of freedom of the system. The result then follows by
using weighted energy estimates. In the general case, unfortunately, this
conservation law no longer holds. Therefore we define a suitable weighted
energy functional for the whole system, which can be used to estimate the
irrotational component of the velocity but does not provide sharp bounds on the
solenoidal component. However, even in the absence of the aforementioned
additional conservation law, we are still able to show the existence of a
functional relation which allows us to recover somehow the vorticity from the
density, on the moving frame. By combining the weighted energy estimates with
the functional relation we also recover the inviscid damping for the solenoidal
component of the velocity.",2003.01694v1
2020-03-06,Lattice dynamics and polarization-dependent phonon damping in $α$-phase FeSi$_{2}$ nanoislands,"We determined the lattice dynamics of metastable, surface-stabilized
$\alpha$-phase FeSi$_2$ nanoislands epitaxially grown on the Si(111) surface
with average heights and widths ranging from 1.5 to 20 nm and 18 to 72 nm,
respectively. The crystallographic orientation, surface morphology and local
crystal structure of the nanoislands were investigated by reflection
high-energy electron diffraction, atomic force microscopy and X-ray absorption
spectroscopy. The Fe-partial phonon density of states (PDOS), obtained by
nuclear inelastic scattering, exhibits a pronounced damping and broadening of
the spectral features with decreasing average island height. First-principles
calculations of the polarization-projected Si- and Fe-partial phonon
dispersions and PDOS enable the disentanglement of the contribution of the
$xy$- and $z$-polarized phonons to the experimental PDOS. Modeling of the
experimental data with the theoretical results unveils an enhanced damping of
the $z$-polarized phonons for islands with average sizes below 10 nm. This
phenomenon is attributed to the fact that the low-energy $z$-polarized phonons
couple to the low-energy surface/interface vibrational modes. The thermodynamic
and elastic properties obtained from the experimental data show a pronounced
size-dependent behavior.",2003.02969v1
2020-03-20,The resonant drag instability of dust streaming in turbulent protoplanetary disc,"Damping of the previously discovered resonant drag instability (RDI) of dust
streaming in protoplanetary disc is studied using the local approach to
dynamics of gas-dust perturbations in the limit of the small dust fraction.
Turbulence in a disc is represented by the effective viscosity and diffusivity
in equations of motion for gas and dust, respectively. In the standard case of
the Schmidt number (ratio of the effective viscosity to diffusivity) Sc = 1,
the reduced description of RDI in terms of the inertial wave (IW) and the
streaming dust wave (SDW) falling in resonance with each other reveals that
damping solution differs from the inviscid solution simply by adding the
characteristic damping frequency to its growth rate. RDI is fully suppressed at
the threshold viscosity, which is estimated analytically, first, for radial
drift, next, for vertical settling of dust, and at last, in the case of
settling combined with radial drift of the dust. In the last case, RDI survives
up to the highest threshold viscosity, with a greater excess for smaller
solids. Once Sc \neq 1, a new instability specific for dissipative
perturbations on the dust settling background emerges. This instability of the
quasi-resonant nature is referred to as settling viscous instability (SVI). The
mode akin to SDW (IW) becomes growing in a region of long waves provided that
Sc > 1 (Sc < 1). SVI leads to an additional increase of the threshold
viscosity.",2003.09212v1
2020-05-22,"Quasinormal modes, shadow and greybody factors of 5D electrically charged Bardeen black holes","We study quasinormal modes (QNMs) in 5D electrically charged Bardeen black
holes spacetime by considering the scalar and electromagnetic field
perturbations. The black holes spacetime is an exact solution of Einstein
gravity coupled to nonlinear electrodynamics in five dimensions, which has
nonsingular behavior. To calculate QNMs, we use the WKB approximation method up
to sixth order. Due to the presence of electric charge $q_e > 0$, both the
scalar and electromagnetic field perturbations decay more slowly when compared
to the Schwarzschild-Tangherlini black holes. We discover that the scalar field
perturbations oscillate more rapidly when compared to the electromagnetic field
perturbations. In terms of damping, the scalar field perturbations damp more
quickly. Graphically we show that the transmission (reflection) coefficients
decrease (increase) with an increase in the magnitude of the electric charge
$q_e$. The emission of gravitational waves allows spacetime to undergo damped
oscillations due to the nonzero value of the imaginary part, which is always
negative. The imaginary part of the QNMs frequencies is continuously decreasing
with an increase in the magnitude of the electric charge $q_e$ for a given mode
($l,n$). A connection between the QNMs frequencies and the black hole shadow,
as well as the geometric cross-section in the eikonal limit, is also described.",2005.11080v2
2020-05-27,Role of diffusive surface scattering in nonlocal plasmonics,"The recent generalised nonlocal optical response (GNOR) theory for plasmonics
is analysed, and its main input parameter, namely the complex hydrodynamic
convection-diffusion constant, is quantified in terms of enhanced Landau
damping due to diffusive surface scattering of electrons at the surface of the
metal. GNOR has been successful in describing plasmon damping effects, in
addition to the frequency shifts originating from induced-charge screening,
through a phenomenological electron diffusion term implemented into the
traditional hydrodynamic Drude model of nonlocal plasmonics. Nevertheless, its
microscopic derivation and justification is still missing. Here we discuss how
the inclusion of a diffusion-like term in standard hydrodynamics can serve as
an efficient vehicle to describe Landau damping without resorting to
computationally demanding quantum-mechanical calculations, and establish a
direct link between this term and the Feibelman $d$ parameter for the centroid
of charge. Our approach provides a recipe to connect the phenomenological
fundamental GNOR parameter to a frequency-dependent microscopic
surface-response function. We therefore tackle one of the principal limitations
of the model, and further elucidate its range of validity and limitations, thus
facilitating its proper application in the framework of nonclassical
plasmonics.",2005.13218v2
2020-07-15,On the Extension of Linear Damping to Quantum Mechanics through Fractionary Momentum Operators Pt. I,"The use of fractional momentum operators and fractionary kinetic energy used
to model linear damping in dissipative systems such as resistive circuits and a
spring-mass ensambles was extended to a quantum mechanical formalism. Three
important associated 1 dimensional problems were solved: the free particle
case, the infinite potential well, and the harmonic potential. The wave
equations generated reproduced the same type of 2-order ODE observed in
classical dissipative systems, and produced quantized energy levels. In the
infinite potential well, a zero-point energy emerges, which can be fitted to
the rest energy of the particle described by special relativity, given by
relationship $E_r=mc^2$. In the harmonic potential, new fractional creation and
destruction operators were introduced to solve the problem in the energy basis.
The energy eigenvalues found are different to the ones reported by earlier
approaches to the quantum damped oscillator problem reported by other authors.
In this case, a direct relationship between the relativistic rest energy of the
particle and the expected value of the fractionary kinetic energy in the base
state was obtained. We conclude that there exists a relationship between
fractional kinetic energy and special relativity energies, that remains unclear
and needs further exploration, but also conclude that the current form of
transforming fractionary momentum operators to the position basis will yield
non-observable imaginary momentum quantities, and thus a correction to the way
of transforming them needs to be explored further.",2007.07434v3
2020-07-18,Results from the Alfvén Eigenmode Active Diagnostic during the 2019-2020 JET deuterium campaign,"This paper presents results of extensive analysis of mode excitation observed
during the operation of the Alfv\'{e}n Eigenmode Active Diagnostic (AEAD) in
the JET tokamak during the 2019-2020 deuterium campaign. Six of eight
toroidally spaced antennas, each with independent power and phasing, were
successful in actively exciting stable MHD modes in 479 plasmas. In total, 4768
magnetic resonances were detected with up to fourteen fast magnetic probes. In
this work, we present the calculations of resonant frequencies $f_0$, damping
rates $\gamma < 0$, and toroidal mode numbers $n$, spanning the parameter range
$f_0 \approx$ 30 - 250 kHz, $-\gamma \approx$ 0 - 13 kHz, and $\vert n \vert
\leq 30$. In general, good agreement is seen between the resonant and the
calculated toroidal Alfv\'{e}n Eigenmode frequencies, and between the toroidal
mode numbers applied by the AEAD and estimated of the excited resonances. We
note several trends in the database: the probability of resonance detection
decreases with plasma current and external heating power; the normalized
damping rate increases with edge safety factor but decreases with external
heating. These results provide key information to prepare future experimental
campaigns and to better understand the physics of excitation and damping of
Alfv\'{e}n Eigenmodes in the presence of alpha particles during the upcoming DT
campaign, thereby extrapolating with confidence to future tokamaks.",2007.09412v1
2020-08-18,A Quasi-Linear Diffusion Model for Resonant Wave-Particle Instability in Homogeneous Plasma,"In this paper, we develop a model to describe the generalized wave-particle
instability in a quasi-neutral plasma. We analyze the quasi-linear diffusion
equation for particles by expressing an arbitrary unstable and resonant wave
mode as a Gaussian wave packet, allowing for an arbitrary direction of
propagation with respect to the background magnetic field. We show that the
localized energy density of the Gaussian wave packet determines the
velocity-space range in which the dominant wave-particle instability and
counter-acting damping contributions are effective. Moreover, we derive a
relation describing the diffusive trajectories of resonant particles in
velocity space under the action of such an interplay between the wave-particle
instability and damping. For the numerical computation of our theoretical
model, we develop a mathematical approach based on the Crank-Nicolson scheme to
solve the full quasi-linear diffusion equation. Our numerical analysis solves
the time evolution of the velocity distribution function under the action of a
dominant wave-particle instability and counteracting damping and shows a good
agreement with our theoretical description. As an application, we use our model
to study the oblique fast-magnetosonic/whistler instability, which is proposed
as a scattering mechanism for strahl electrons in the solar wind. In addition,
we numerically solve the full Fokker-Planck equation to compute the time
evolution of the electron-strahl distribution function under the action of
Coulomb collisions with core electrons and protons after the collisionless
action of the oblique fast-magnetosonic/whistler instability.",2008.08169v2
2020-09-10,Spin waves in alloys at finite temperatures: application for FeCo magnonic crystal,"We study theoretically the influence of the temperature and disorder on the
spin wave spectrum of the magnonic crystal Fe$_{1-c}$Co$_{c}$. Our formalism is
based on the analysis of a Heisenberg Hamiltonian by means of the wave vector
and frequency dependent transverse magnetic susceptibility. The exchange
integrals entering the model are obtained from the \emph{ab initio} magnetic
force theorem. The coherent potential approximation is employed to treat the
disorder and random phase approximation in order to account for the softening
of the magnon spectrum at finite temperatures. The alloy turns out to exhibit
many advantageous properties for spintronic applications. Apart from high Curie
temperature, its magnonic bandgap remains stable at elevated temperatures and
is largely unaffected by the disorder. We pay particular attention to the
attenuation of magnons introduced by the alloying. The damping turns out to be
a non-monotonic function of the impurity concentration due to the non-trivial
evolution of the value of exchange integrals with the Co concentration. The
disorder induced damping of magnons is estimated to be much smaller than their
Landau damping.",2009.04712v6
2020-09-14,On the response of a star cluster to a tidal perturbation,"We study the response of star clusters to individual tidal perturbations
using controlled $N$-body simulations. We consider perturbations by a moving
point mass and by a disc, and vary the duration of the perturbation as well as
the cluster density profile. For fast perturbations (i.e. `shocks'), the
cluster gains energy in agreement with theoretical predictions in the impulsive
limit. For slow disc perturbations, the energy gain is lower, and this has
previously been attributed to adiabatic damping. However, the energy gain due
to slow perturbations by a point-mass is similar to, or larger than that due to
fast shocks, which is not expected because adiabatic damping should be almost
independent of the nature of the tides. We show that the geometric distortion
of the cluster during slow perturbations is of comparable importance for the
energy gain as adiabatic damping, and that the combined effect can
qualitatively explain the results. The half-mass radius of the bound stars
after a shock increases up to $\sim$7\% for low-concentration clusters, and
decreases $\sim$3\% for the most concentrated ones. The fractional mass loss is
a non-linear function of the energy gain, and depends on the nature of the
tides and most strongly on the cluster density profile, making semi-analytic
model predictions for cluster lifetimes extremely sensitive to the adopted
density profile.",2009.06643v2
2020-09-18,African Easterly Waves in an Idealized General Circulation Model: Instability and Wavepacket Diagnostics,"We examine the group dynamic of African easterly waves (AEW) generated in a
realistic, spatially non-homogeneous African easterly jet (AEJ) using an
idealized general circulation model. Our objective is to investigate whether
the limited zonal extent of the AEJ is an impediment to AEW development. We
construct a series of basic states using global reanalysis fields and
initialize waves via transient heating over West Africa. The dominant response
is a localized wavepacket that disperses upstream and downstream. The inclusion
of a crude representation of boundary layer damping stabilizes the waves in
most cases. In some basic states, however, exponential growth occurs even in
the presence of damping. This shows that AEWs can occasionally emerge
spontaneously. The key result is that the wavepacket in almost all cases
remains within the AEJ instead of being swept away. Drawing from other studies,
this also suggests that even the damped waves can grow if coupled with
additional sources of energy such as moist convection and dust radiative
feedback. The wavepacket in the localized AEJ appears to satisfy a condition
for absolute instability, a form of spatial hydrodynamic instability. However,
this needs to be verified more rigorously. Our results also suggest that the
intermittent nature of AEWs is mediated, not by transitions between convective
and absolute instability, but likely by external sources such as propagating
equatorial wave modes",2009.08604v1
2020-09-25,Polaronic Contributions to Friction in a Manganite Thin Film,"Despite the huge importance of friction in regulating movement in all natural
and technological processes, the mechanisms underlying dissipation at a sliding
contact are still a matter of debate. Attempts to explain the dependence of
measured frictional losses at nanoscale contacts on the electronic degrees of
freedom of the surrounding materials have so far been controversial. Here, it
is proposed that friction can be explained by considering damping of stick-slip
pulses in a sliding contact. Based on friction force microscopy studies of
La$_{(1-x)}$Sr$_x$MnO$_3$ films at the ferromagnetic-metallic to
paramagnetic-polaronic conductor phase transition, it is confirmed that the
sliding contact generates thermally-activated slip pulses in the nanoscale
contact, and argued that these are damped by direct coupling into phonon bath.
Electron-phonon coupling leads to the formation of Jahn-Teller polarons and a
clear increase in friction in the high temperature phase. There is no evidence
for direct electronic drag on the atomic force microscope tip nor any
indication of contributions from electrostatic forces. This intuitive scenario,
that friction is governed by the damping of surface vibrational excitations,
provides a basis for reconciling controversies in literature studies as well as
suggesting possible tactics for controlling friction.",2009.12137v1
2020-09-25,Direct computation of nonlinear mapping via normal form for reduced-order models of finite element nonlinear structures,"The direct computation of the third-order normal form for a geometrically
nonlinear structure discretised with the finite element (FE) method, is
detailed. The procedure allows to define a nonlinear mapping in order to derive
accurate reduced-order models (ROM) relying on invariant manifold theory. The
proposed reduction strategy is direct and simulation free, in the sense that it
allows to pass from physical coordinates (FE nodes) to normal coordinates,
describing the dynamics in an invariant-based span of the phase space. The
number of master modes for the ROM is not a priori limited since a complete
change of coordinate is proposed. The underlying theory ensures the quality of
the predictions thanks to the invariance property of the reduced subspace,
together with their curvatures in phase space that accounts for the nonresonant
nonlinear couplings. The method is applied to a beam discretised with 3D
elements and shows its ability in recovering internal resonance at high energy.
Then a fan blade model is investigated and the correct prediction given by the
ROMs are assessed and discussed. A method is proposed to approximate an
aggregate value for the damping, that takes into account the damping
coefficients of all the slave modes, and also using the Rayleigh damping model
as input. Frequency-response curves for the beam and the blades are then
exhibited, showing the accuracy of the proposed method.",2009.12145v1
2020-10-08,Modeling of the ECCD injection effect on the Heliotron J and LHD plasma stability,"The aim of the study is to analyze the stability of the Energetic Particle
Modes (EPM) and Alfven Eigenmodes (AE) in Helitron J and LHD plasma if the
electron cyclotron current drive (ECCD) is applied. The analysis is performed
using the code FAR3d that solves the reduced MHD equations describing the
linear evolution of the poloidal flux and the toroidal component of the
vorticity in a full 3D system, coupled with equations of density and parallel
velocity moments for the energetic particle (EP) species, including the effect
of the acoustic modes. The Landau damping and resonant destabilization effects
are added via the closure relation. The simulation results show that the n=1
EPM and n=2 Global AE (GAE) in Heliotron J plasma can be stabilized if the
magnetic shear is enhanced at the plasma periphery by an increase (co-ECCD
injection) or decrease (ctr-ECCD injection) of the rotational transform at the
magnetic axis iota0. In the ctr-ECCD simulations, the EPM/AE growth rate
decreases only below a given iota0, similar to the ECCD intensity threshold
observed in the experiments. In addition, ctr-ECCD simulations show an
enhancement of the continuum damping. The simulations of the LHD discharges
with ctr-ECCD injection indicate the stabilization of the n=1 EPM, n=2 Toroidal
AE (TAE) and n=3 TAE, caused by an enhancement of the continuum damping in the
inner plasma leading to a higher EP beta threshold with respect to the co- and
no-ECCD simulations.",2010.03892v1
2020-10-08,A blow-up result for the wave equation with localized initial data: the scale-invariant damping and mass term with combined nonlinearities,"We are interested in this article in studying the damped wave equation with
localized initial data, in the \textit{scale-invariant case} with mass term and
two combined nonlinearities. More precisely, we consider the following
equation: $$ (E) {1cm} u_{tt}-\Delta
u+\frac{\mu}{1+t}u_t+\frac{\nu^2}{(1+t)^2}u=|u_t|^p+|u|^q, \quad \mbox{in}\
\mathbb{R}^N\times[0,\infty), $$ with small initial data. Under some
assumptions on the mass and damping coefficients, $\nu$ and $\mu>0$,
respectively, we show that blow-up region and the lifespan bound of the
solution of $(E)$ remain the same as the ones obtained in \cite{Our2} in the
case of a mass-free wave equation, it i.e. $(E)$ with $\nu=0$.
  Furthermore, using in part the computations done for $(E)$, we enhance the
result in \cite{Palmieri} on the Glassey conjecture for the solution of $(E)$
with omitting the nonlinear term $|u|^q$. Indeed, the blow-up region is
extended from $p \in (1, p_G(N+\sigma)]$, where $\sigma$ is given by (1.12)
below, to $p \in (1, p_G(N+\mu)]$ yielding, hence, a better estimate of the
lifespan when $(\mu-1)^2-4\nu^2<1$. Otherwise, the two results coincide.
Finally, we may conclude that the mass term {\it has no influence} on the
dynamics of $(E)$ (resp. $(E)$ without the nonlinear term $|u|^q$), and the
conjecture we made in \cite{Our2} on the threshold between the blow-up and the
global existence regions obtained holds true here.",2010.05455v1
2020-10-14,Kink Oscillations in Solar Coronal Loops with Elliptical Cross-Sections. I. the linear regime,"The cross sections of solar coronal loops are suggested to be rarely
circular. We examine linear kink oscillations in straight, density-enhanced,
magnetic cylinders with elliptical cross-sections by solving the
three-dimensional magnetohydrodynamic equations from an initial-value-problem
perspective. Motivated by relevant eigen-mode analyses, we distinguish between
two independent polarizations, one along the major axis (the M-modes) and the
other along the minor one (the m-modes). We find that, as happens for coronal
loops with circular cross-sections, the apparent damping of the transverse
displacement of the loop axis is accompanied by the accumulation of transverse
Alfv\'enic motions and the consequent development of small-scales therein,
suggesting the robustness of the concepts of resonant absorption and
phase-mixing. In addition, two stages can in general be told apart in the
temporal evolution of the loop displacement; a Gaussian time dependence
precedes an exponential one. For the two examined density ratios between loops
and their surroundings, the periods of the M-modes (m-modes) tend to increase
(decrease) with the major-to-minor-half-axis ratio, and the damping times in
the exponential stage for the M-modes tend to exceed their m-mode counterparts.
This is true for the two transverse profiles we examine. However, the relative
magnitudes of the damping times in the exponential stage for different
polarizations depend on the specification of the transverse profile and/or the
density contrast. The applications of our numerical findings are discussed in
the context of coronal seismology.",2010.06991v1
2020-11-04,The impact of astrophysical dust grains on the confinement of cosmic rays,"We argue that charged dust grains could significantly impact the confinement
and transport of galactic cosmic rays. For sub-GeV to ~1000GeV cosmic rays,
small-scale parallel Alfv\'en waves, which isotropize cosmic rays through
gyro-resonant interactions, are also gyro-resonant with charged grains. If the
dust is nearly stationary, as in the bulk of the interstellar medium, Alfv\'en
waves are damped by dust. This will reduce the amplitude of Alfv\'en waves
produced by the cosmic rays through the streaming instability, thus enhancing
cosmic-ray transport. In well-ionized regions, the dust damping rate is larger
by a factor of ~10 than other mechanisms that damp parallel Alfv\'en waves at
the scales relevant for ~GeV cosmic rays, suggesting that dust could play a key
role in regulating cosmic-ray transport. In astrophysical situations in which
the dust moves through the gas with super-Alfv\'enic velocities, Alfv\'en waves
are rendered unstable, which could directly scatter cosmic rays. This
interaction has the potential to create a strong feedback mechanism where dust,
driven through the gas by radiation pressure, then strongly enhances the
confinement of cosmic rays, increasing their capacity to drive outflows. This
mechanism may act in the circumgalactic medium around star-forming galaxies and
active galactic nuclei.",2011.02497v2
2020-11-17,A Phase Resonance Approach for Modal Testing of Structures with Nonlinear Dissipation,"The concept of nonlinear modes is useful for the dynamical characterization
of nonlinear mechanical systems. While efficient and broadly applicable methods
are now available for the computation of nonlinear modes, nonlinear modal
testing is still in its infancy. The purpose of this work is to overcome its
present limitation to conservative nonlinearities. Our approach relies on the
recently extended periodic motion concept, according to which nonlinear modes
of damped systems are defined as family of periodic motions induced by an
appropriate artificial excitation that compensates the natural dissipation. The
particularly simple experimental implementation with only a single-point,
single-frequency, phase resonant forcing is analyzed in detail. The method
permits the experimental extraction of natural frequencies, modal damping
ratios and deflection shapes (including harmonics), for each mode of interest,
as function of the vibration level. The accuracy, robustness and current
limitations of the method are first demonstrated numerically. The method is
then verified experimentally for a friction-damped system. Moreover, a
self-contained measure for estimating the quality of the extracted modal
properties is investigated. The primary advantages over alternative vibration
testing methods are noise robustness, broad applicability and short measurement
duration. The central limitation of the identified modal quantities is that
they only characterize the system in the regime near isolated resonances.",2011.08500v1
2020-12-08,"Meta Learning-based MIMO Detectors: Design, Simulation, and Experimental Test","Deep neural networks (NNs) have exhibited considerable potential for
efficiently balancing the performance and complexity of multiple-input and
multiple-output (MIMO) detectors. We propose a receiver framework that enables
efficient online training by leveraging the following simple observation:
although NN parameters should adapt to channels, not all of them are
channel-sensitive. In particular, we use a deep unfolded NN structure that
represents iterative algorithms in signal detection and channel decoding
modules as multi layer deep feed forward networks. An expectation propagation
(EP) module, called EPNet, is established for signal detection by unfolding the
EP algorithm and rendering the damping factors trainable. An unfolded turbo
decoding module, called TurboNet, is used for channel decoding. This component
decodes the turbo code, where trainable NN units are integrated into the
traditional max-log-maximum a posteriori decoding procedure. We demonstrate
that TurboNet is robust for channels and requires only one off-line training.
Therefore, only a few damping factors in EPNet must be re-optimized online. An
online training mechanism based on meta learning is then developed. Here, the
optimizer, which is implemented by long short-term memory NNs, is trained to
update damping factors efficiently by using a small training set such that they
can quickly adapt to new environments. Simulation results indicate that the
proposed receiver significantly outperforms traditional receivers and that the
online learning mechanism can quickly adapt to new environments. Furthermore,
an over-the-air platform is presented to demonstrate the significant robustness
of the proposed receiver in practical deployment.",2012.04379v1
2020-12-31,Adaptive Surgical Robotic Training Using Real-Time Stylistic Behavior Feedback Through Haptic Cues,"Surgical skill directly affects surgical procedure outcomes; thus, effective
training is needed to ensure satisfactory results. Many objective assessment
metrics have been developed and some are widely used in surgical training
simulators. These objective metrics provide the trainee with descriptive
feedback about their performance however, often lack feedback on how to proceed
to improve performance. The most effective training method is one that is
intuitive, easy to understand, personalized to the user and provided in a
timely manner. We propose a framework to enable user-adaptive training using
near-real-time detection of performance, based on intuitive styles of surgical
movements (e.g., fluidity, smoothness, crispness, etc.), and propose a haptic
feedback framework to assist with correcting styles of movement. We evaluate
the ability of three types of force feedback (spring, damping, and spring plus
damping feedback), computed based on prior user positions, to improve different
stylistic behaviors of the user during kinematically constrained reaching
movement tasks. The results indicate that four out of the six styles studied
here were statistically significantly improved (p<0.05) using spring guidance
force feedback and a significant reduction in task time was also found using
spring feedback. The path straightness and targeting error in the task were
other task performance metrics studied which were improved significantly using
the spring-damping feedback. This study presents a groundwork for adaptive
training in robotic surgery based on near-real-time human-centric models of
surgical behavior.",2101.00097v3
2021-01-08,Damped dust-ion-acoustic solitons in collisional magnetized nonthermal plasmas,"A multi-species magnetized collisional nonthermal plasma system containing
inertial ion species, non-inertial electron species following nonthermal
$\kappa-$ distribution, and immobile dust particles, is considered to examine
the characteristics of the dissipative dust-ion-acoustic (DIA) soliton modes,
\textbf{theoretically and parametrically}. The electrostatic solitary modes are
found to be associated with the low frequency dissipative dust-ion-acoustic
solitary waves (DIASWs). The ion-neutral collision is taken into account, and
the influence of ion-neutral collisional effects on the dynamics of dissipative
DIASWs is investigated. It is reported that most of the plasma mediums in space
and laboratory are far from thermal equilibrium, and the particles in such
plasma systems are well fitted via the $\kappa-$nonthermal distribution than
via the thermal Maxwellian distribution. The reductive perturbation approach is
adopted to derive the damped KdV (dKdV) equation, and the solitary wave
solution of the dKdV equation is derived via the tangent hyperbolic method to
analyze the basic features (amplitude, width, speed, time evolution, etc.) of
dissipative DIASWs. The propagation nature and also the basic features of
dissipative DIASWs are seen to influence significantly due to the variation of
the plasma configuration parameters and also due to the variation of the
supethermality index $\kappa$ in the considered plasma system. The implication
of the results of this study could be useful for better understanding the
electrostatic localized disturbances, in the ion length and time scale, in
space and experimental dusty plasmas, where the presence of excess energetic
electrons and ion-neutral collisional damping are accountable.",2101.03183v2
2020-12-28,Global complexity effects due to local damping in a nonlinear system in 1:3 internal resonance,"It is well-known that nonlinearity may lead to localization effects and
coupling of internally resonant modes. However, research focused primarily on
conservative systems commonly assumes that the near-resonant forced response
closely follows the autonomous dynamics. Our results for even a simple system
of two coupled oscillators with a cubic spring clearly contradict this common
belief. We demonstrate analytically and numerically global effects of a weak
local damping source in a harmonically forced nonlinear system under condition
of 1:3 internal resonance: The global motion becomes asynchronous, i.e., mode
complexity is introduced with a non-trivial phase difference between the modal
oscillations. In particular, we show that a maximum mode complexity with a
phase difference of $90^\circ$ is attained in a multi-harmonic sense. This
corresponds to a transition from generalized standing to traveling waves in the
system's modal space. We further demonstrate that the localization is crucially
affected by the system's damping. Finally, we propose an extension of the
definition of mode complexity and mode localization to nonlinear quasi-periodic
motions, and illustrate their application to a quasi-periodic regime in the
forced response.",2101.03233v1
2021-01-27,"New estimations of the added mass and damping of two cylinders vibrating in a viscous fluid, from theoretical and numerical approaches","This paper deals with the small oscillations of two circular cylinders
immersed in a viscous stagnant fluid. A new theoretical approach based on an
Helmholtz expansion and a bipolar coordinate system is presented to estimate
the fluid forces acting on the two bodies. We show that these forces are linear
combinations of the {\textcolor{black}{cylinder accelerations}} and velocities,
through viscous fluid added coefficients. {\textcolor{black}{To assess the
validity of this theory, we consider the case of two equal size cylinders, one
of them being stationary while the other one is forced sinusoidally}}. The
self-added mass and damping coefficients are shown to decrease with both the
Stokes number and the separation distance. The cross-added mass and damping
coefficients tend to increase with the Stokes number and the separation
distance. Compared to the inviscid results, the effect of viscosity is to add a
correction term which scales as $Sk^{-1/2}$. When the separation distance is
sufficiently large, the two cylinders behave as if they were independent and
the Stokes predictions for an isolated cylinder are recovered. Compared to
previous works, the present theory offers a simple and flexible alternative for
an easy determination of the fluid forces and related added coefficients. To
our knowledge, this is also the first time that a numerical approach based on a
penalization method is presented in the context of fluid-structure interactions
for relatively small Stokes numbers, and successfully compared to theoretical
predictions.",2101.11346v1
2021-01-28,Vortex-induced Vibrations of a Confined Circular Cylinder for Efficient Flow Power Extraction,"A simple method to increase the flow power extraction efficiency of a
circular cylinder, undergoing vortex-induced vibration (VIV), by confining it
between two parallel plates is proposed. A two-dimensional numerical study was
performed on VIV of a circular cylinder inside a parallel plate channel of
height H at Reynolds number 150 to quantify the improvement. The cylinder is
elastically mounted with a spring such that it is only free to vibrate in the
direction transverse to the channel flow and has a fixed mass ratio (m*) of 10.
The energy extraction process is modelled as a damper, with spatially constant
damping ration ((), attached to the cylinder. The simulations are performed by
varying the reduced velocity for a set of fixed mass-damping ({\alpha} = m*()
values ranging between 0 to 1. The blockage ratio (b = D/H) is varied from 0.25
to 0.5 by changing the channel height. The quasi-periodic initial branch found
for the unconfined cylinder shrinks with the increasing blockage. The extracted
power is found to increase rapidly with the blockage. For maximum blockage (b =
0.2), the maximum flow power extracted by the cylinder is an order of magnitude
larger as compared to what it would extract in an open domain with free stream
velocity equal to the channel mean velocity. The optimal mass-damping
({\alpha}c ) for extracting maximum power is found to lie between 0.2 to 0.3.
An expression is derived to predict the maximum extracted power from the
undamped response of a confined/unconfined cylinder. With the assumption
{\alpha}c = 0.25, the derived expression can predict the maximum power
extraction within +-20% of the actual values obtained from present and previous
numerical and experimental studies.",2101.11803v1
2021-03-08,"A Self-Consistent, Time-Dependent Treatment of Dynamical Friction: New Insights regarding Core Stalling and Dynamical Buoyancy","Dynamical friction is typically regarded a secular process, in which the
subject ('perturber') evolves very slowly (secular approximation), and has been
introduced to the host over a long time (adiabatic approximation). These
assumptions imply that dynamical friction arises from the LBK torque with
non-zero contribution only from pure resonance orbits. However, dynamical
friction is only of astrophysical interest if its timescale is shorter than the
age of the Universe. In this paper we therefore relax the adiabatic and secular
approximations. We first derive a generalized LBK torque, which reduces to the
LBK torque in the adiabatic limit, and show that it gives rise to transient
oscillations due to non-resonant orbits that slowly damp out, giving way to the
LBK torque. This is analogous to how a forced, damped oscillator undergoes
transients before settling to a steady state, except that here the damping is
due to phase mixing rather than dissipation. Next, we present a self-consistent
treatment, that properly accounts for time-dependence of the perturber
potential and circular frequency (memory effect), which we use to examine
orbital decay in a cored galaxy. We find that the memory effect results in a
phase of accelerated, super-Chandrasekhar friction before the perturber stalls
at a critical radius, $R_{\mathrm{crit}}$, in the core (core-stalling). Inside
of $R_{\mathrm{crit}}$ the torque flips sign, giving rise to dynamical
buoyancy, which counteracts friction and causes the perturber to stall. This
phenomenology is consistent with $N$-body simulations, but has thus far eluded
proper explanation.",2103.05004v1
2021-03-26,First-order strong-field QED processes including the damping of particles states,"Volkov states are exact solutions of the Dirac equation in the presence of an
arbitrary plane wave. Volkov states, as well as free photon states, are not
stable in the presence of the background plane-wave field but ""decay"" as
electrons/positrons can emit photons and photons can transform into
electron-positron pairs. By using the solutions of the corresponding
Schwinger-Dyson equations within the locally-constant field approximation, we
compute the probabilities of nonlinear single Compton scattering and nonlinear
Breit-Wheeler pair production by including the effects of the decay of
electron, positron, and photon states. As a result, we find that the
probabilities of these processes can be expressed as the integral over the
light-cone time of the known probabilities valid for stable states per unit of
light-cone time times a light-cone time-dependent exponential damping function
for each interacting particle. The exponential function for an incoming
(outgoing) either electron/positron or photon at each light-cone time
corresponds to the total probability that either the electron/positron emits a
photon via nonlinear Compton scattering or the photon transforms into an
electron-positron pair via nonlinear Breit-Wheeler pair production until that
light-cone time (from that light-cone time on). It is interesting that the
exponential damping terms depend not only on the particles momentum but also on
their spin (for electrons/positrons) and polarization (for photons). This
additional dependence on the discrete quantum numbers prevents the application
of the electron/positron spin and photon polarization sum-rules, which
significantly simplify the computations in the perturbative regime.",2103.14637v1
2021-04-10,Non-Markovian open quantum system approach to the early universe: I. Damping of gravitational waves by matter,"By revising the application of the open quantum system approach to the early
universe and extending it to the conditions beyond the Markovian approximation,
we obtain a new non-Markovian quantum Boltzmann equation. Throughout the paper,
we also develop an extension of the quantum Boltzmann equation to describe the
processes that are irreversible at the macroscopic level. This new kinetic
equation is, in principle, applicable to a wide variety of processes in the
early universe. For instance, using this equation one can accurately study the
microscopic influence of a cosmic environment on a system of cosmic background
photons or stochastic gravitational waves. In this paper, we apply the
non-Markovian quantum Boltzmann equation to study the damping of gravitational
waves propagating in a medium consisting of decoupled ultra-relativistic
neutrinos. For such a system, we study the time evolution of the intensity and
the polarization of the gravitational waves. It is shown that, in contrast to
intensity and linear polarization which are damped, the circular polarization
(V-mode) of the gravitational wave (if present) is amplified by propagating
through such a medium.",2104.04836v2
2021-04-19,Giant spin-orbit torque efficiency in all-epitaxial heterostructures,"A large anti-damping spin-obit torque (SOT) efficiency in magnetic
heterostructures is a prerequisite to realize energy efficient spin torque
based magnetic memories and logic devices. The efficiency can be characterized
in terms of the spin-orbit fields generated by anti-damping torques when an
electric current is passed through the non-magnetic layer. We report a giant
spin-orbit field of 48.96 (27.50) mT at an applied current density of 1 MAcm-2
in beta-W interfaced Co60Fe40 (Ni81Fe19)/TiN epitaxial structures due to an
anti-damping like torque, which results in a magnetization auto-oscillation
current density as low as 1.68(3.27) MAcm-2. The spin-orbit field value
increases with decrease of beta-W layer thickness, which affirms that epitaxial
surface states are responsible for the extraordinary large efficiency. SOT
induced energy efficient in-plane magnetization switching in large 20x100 um2
structures has been demonstrated by Kerr microscopy and the findings are
supported by results from micromagnetic simulations. The observed giant SOT
efficiencies in the studied all-epitaxial heterostructures are comparable to
values reported for topological insulators. These results confirm that by
utilizing epitaxial material combinations an extraordinary large SOT efficiency
can be achieved using semiconducting industry compatible 5d heavy metals, which
provides immediate solutions for the realization of energy efficient spin-logic
devices.",2104.09168v1
2021-06-10,Constraining extra dimensions using observations of black hole quasi-normal modes,"The presence of extra dimensions generically modify the spacetime geometry of
a rotating black hole, by adding an additional hair, besides the mass $M$ and
the angular momentum $J$, known as the `tidal charge' parameter, $\beta$. In a
braneworld scenario with one extra spatial dimension, the extra dimension is
expected to manifest itself through -- (a) negative values of $\beta$, and (b)
modified gravitational perturbations. This in turn would affect the
quasi-normal modes of rotating black holes. We numerically solve the perturbed
gravitational field equations using the continued fractions method and
determine the quasi-normal mode spectra for the braneworld black hole. We find
that increasingly negative values of $\beta$ correspond to a diminishing
imaginary part of the quasi-normal mode, or equivalently, an increasing damping
time. Using the publicly available data of the properties of the remnant black
hole in the gravitational wave signal GW150914, we check for consistency
between the predicted values (for a given $\beta$) of the frequency and damping
time of the least-damped $\ell=2,m=2$ quasi-normal mode and measurements of
these quantities using other independent techniques. We find that it is highly
unlikely for the tidal charge, $\beta \lesssim -0.05$, providing a conservative
limit on the tidal charge parameter. Implications and future directions are
discussed.",2106.05558v2
2021-06-24,A Polarizable Water Potential Derived from a Model Electron Density,"A new empirical potential for efficient, large scale molecular dynamics
simulation of water is presented. The HIPPO (Hydrogen-like Intermolecular
Polarizable POtential) force field is based upon the model electron density of
a hydrogen-like atom. This framework is used to derive and parameterize
individual terms describing charge penetration damped permanent electrostatics,
damped polarization, charge transfer, anisotropic Pauli repulsion, and damped
dispersion interactions. Initial parameter values were fit to Symmetry Adapted
Perturbation Theory (SAPT) energy components for ten water dimer
configurations, as well as the radial and angular dependence of the canonical
dimer. The SAPT-based parameters were then systematically refined to extend the
treatment to water bulk phases. The final HIPPO water model provides a balanced
representation of a wide variety of properties of gas phase clusters, liquid
water and ice polymorphs, across a range of temperatures and pressures. This
water potential yields a rationalization of water structure, dynamics and
thermodynamics explicitly correlated with an ab initio energy decomposition,
while providing a level of accuracy comparable or superior to previous
polarizable atomic multipole force fields. The HIPPO water model serves as a
cornerstone around which similarly detailed physics-based models can be
developed for additional molecular species.",2106.13116v3
2021-07-19,Long term behavior of 2D and 3D non-autonomous random convective Brinkman-Forchheimer equations driven by colored noise,"The long time behavior of Wong-Zakai approximations of 2D as well as 3D
non-autonomous stochastic convective Brinkman-Forchheimer (CBF) equations with
non-linear diffusion terms on bounded and unbounded ($\mathbb{R}^d$ for
$d=2,3$) domains is discussed in this work. To establish the existence of
random pullback attractors, the concept of asymptotic compactness (AC) is used.
In bounded domains, AC is proved via compact Sobolev embeddings. In unbounded
domains, due to the lack of compact embeddings, the ideas of energy equations
and uniform tail estimates are exploited to prove AC. In the literature, CBF
equations are also known as \emph{Navier-Stokes equations (NSE) with damping},
and it is interesting to see that the modification in NSE by linear and
nonlinear damping provides better results than that available for NSE. The
presence of linear damping term helps to establish the results in the whole
domain $\mathbb{R}^d$. The nonlinear damping term supports to obtain better
results in 3D and also for a large class of nonlinear diffusion terms.
Moreover, we prove the existence of a unique random pullback attractor for
stochastic CBF equations with additive white noise. Finally, for additive as
well as multiplicative noise case, we establish the convergence of solutions
and upper semicontinuity of random pullback attractors for Wong-Zakai
approximations of stochastic CBF equations towards the random pullback
attractors for stochastic CBF equations when correlation time of colored noise
converges to zero.",2107.08890v1
2021-07-28,Queue-Channel Capacities with Generalized Amplitude Damping,"The generalized amplitude damping channel (GADC) is considered an important
model for quantum communications, especially over optical networks. We make two
salient contributions in this paper apropos of this channel. First, we consider
a symmetric GAD channel characterized by the parameter $n=1/2,$ and derive its
exact classical capacity, by constructing a specific induced classical channel.
We show that the Holevo quantity for the GAD channel equals the Shannon
capacity of the induced binary symmetric channel, establishing at once the
capacity result and that the GAD channel capacity can be achieved without the
use of entanglement at the encoder or joint measurements at the decoder.
Second, motivated by the inevitable buffering of qubits in quantum networks, we
consider a generalized amplitude damping \emph{queue-channel} -- that is, a
setting where qubits suffer a waiting time dependent GAD noise as they wait in
a buffer to be transmitted. This GAD queue channel is characterized by
non-i.i.d. noise due to correlated waiting times of consecutive qubits. We
exploit a conditional independence property in conjunction with additivity of
the channel model, to obtain a capacity expression for the GAD queue channel in
terms of the stationary waiting time in the queue. Our results provide useful
insights towards designing practical quantum communication networks, and
highlight the need to explicitly model the impact of buffering.",2107.13486v1
2021-07-31,Damped inertial dynamics with vanishing Tikhonov regularization: strong asymptotic convergence towards the minimum norm solution,"In a Hilbert space, we provide a fast dynamic approach to the hierarchical
minimization problem which consists in finding the minimum norm solution of a
convex minimization problem. For this, we study the convergence properties of
the trajectories generated by a damped inertial dynamic with Tikhonov
regularization. When the time goes to infinity, the Tikhonov regularization
parameter is supposed to tend towards zero, not too fast, which is a key
property to make the trajectories strongly converge towards the minimizer of
$f$ of minimum norm. According to the structure of the heavy ball method for
strongly convex functions, the viscous damping coefficient is proportional to
the square root of the Tikhonov regularization parameter. Therefore, it also
converges to zero, which will ensure rapid convergence of values. Precisely,
under a proper tuning of these parameters, based on Lyapunov's analysis, we
show that the trajectories strongly converge towards the minimizer of minimum
norm, and we provide the convergence rate of the values. We show a trade off
between the property of fast convergence of values, and the property of strong
convergence towards the minimum norm solution. This study improves several
previous works where this type of results was obtained under restrictive
hypotheses.",2108.00203v1
2021-08-11,Numerical investigation of the formation and stability of homogeneous pairs of soft particles in inertial microfluidics,"We investigate the formation and stability of a pair of identical soft
capsules in channel flow under mild inertia. We employ a combination of the
lattice Boltzmann, finite element and immersed boundary methods to simulate the
elastic particles in flow. Validation tests show excellent agreement with
numerical results obtained by other research groups. Our results reveal new
trajectory types that have not been observed for pairs of rigid particles.
While particle softness increases the likelihood of a stable pair forming, the
pair stability is determined by the lateral position of the particles. A key
finding is that stabilisation of the axial distance occurs after lateral
migration of the particles. During the later phase of pair formation, particles
undergo damped oscillations that are independent of initial conditions. These
damped oscillations are driven by a strong hydrodynamic coupling of the
particle dynamics, particle inertia and viscous dissipation. While the
frequency and damping coefficient of the oscillations depend on particle
softness, the pair formation time is largely determined by the initial particle
positions: the time to form a stable pair grows exponentially with the initial
axial distance. Our results demonstrate that particle softness has a strong
impact on the behaviour of particle pairs. The findings could have significant
ramifications for microfluidic applications where a constant and reliable axial
distance between particles is required, such as flow cytometry.",2108.05277v1
2021-08-13,Nonlinear modal testing of damped structures: Velocity feedback vs. phase resonance,"In recent years, a new method for experimental nonlinear modal analysis has
been developed, which is based on the extended periodic motion concept. The
method is well suited to experimentally obtain amplitude-dependent modal
properties (modal frequency, damping ratio and deflection shape) for strongly
nonlinear systems. To isolate a nonlinear mode, the negative viscous damping
term of the extended periodic motion concept is approximated by ensuring phase
resonance between excitation and response. In this work, an alternative
approach to isolate a nonlinear mode is developed and analyzed: velocity
feedback. The accuracy of the extracted modal properties and robustness of
velocity feedback is first assessed by means of simulated experiments. The two
approaches phase resonance and velocity feedback are then compared in terms of
accuracy and experimental implementation effort. To this end, both approaches
are applied to an experimental specimen, which is a cantilevered beam
influenced by a strong dry friction nonlinearity. In this work, the discussion
is limited to single-point excitation. It is shown that a robust implementation
of velocity feedback requires the measurement of several response signals,
distributed over the structure. An advantage of velocity feedback is that no
controller is needed. The accuracy of the modal properties can, however, suffer
from imperfections of the excitation mechanism such as a phase lag due to
exciter-structure interactions or gyroscopic forces due to single-point
excitation.",2108.06189v1
2021-09-21,Double diffusion structure of logarithmically damped wave equations with a small parameter,"We consider a wave equation with a nonlocal logarithmic damping depending on
a small parameter $\theta \in (0,1/2)$. This research is a counter part of that
was initiated by Charao-D'Abbicco-Ikehata considered in [5] for the large
parameter case $\theta \in (1/2,1)$. We study the Cauchy problem for this model
in the whole space for the small parameter case, and we obtain an asymptotic
profile and optimal estimates in time of solutions as time goes to infinity in
$L^2$-sense. An important discovery in this research is that in the one
dimensional case, we can present a threshold $\theta^{*} = 1/4$ of the
parameter $\theta$ such that the solution of the Cauchy problem decays with
some optimal rate for $\theta \in (0,\theta^{*})$, while the $L^2$-norm of the
corresponding solution blows up in infinite time for $\theta \in
[\theta^{*},1/2)$. The former (i.e., $\theta \in (0,\theta^{*})$ case)
indicates an usual diffusion phenomenon, while the latter (i.e., $\theta \in
[\theta^{*},1/2)$ case) implies, so to speak, a singular diffusion phenomenon.
Such a singular diffusion in the one dimensional case is a quite novel
phenomenon discovered through our new model produced by logarithmic damping
with a small parameter $\theta$.",2109.09944v2
2021-09-21,Non-intrusive Balancing Transformation of Highly Stiff Systems with Lightly-damped Impulse Response,"Balanced truncation (BT) is a model reduction method that utilizes a
coordinate transformation to retain eigen-directions that are highly observable
and reachable. To address realizability and scalability of BT applied to highly
stiff and lightly-damped systems, a non-intrusive data-driven method is
developed for balancing discrete-time systems via the eigensystem realization
algorithm (ERA). The advantage of ERA for balancing transformation makes
full-state outputs tractable. Further, ERA enables balancing despite stiffness,
by eliminating computation of balancing modes and adjoint simulations. As a
demonstrative example, we create balanced ROMs for a one-dimensional reactive
flow with pressure forcing, where the stiffness introduced by the chemical
source term is extreme (condition number $10^{13}$), preventing analytical
implementation of BT. We investigate the performance of ROMs in prediction of
dynamics with unseen forcing inputs and demonstrate stability and accuracy of
balanced ROMs in truly predictive scenarios whereas without ERA, POD-Galerkin
and Least-squares Petrov-Galerkin projections fail to represent the true
dynamics. We show that after the initial transients under unit impulse forcing,
the system undergoes lightly-damped oscillations, which magnifies the influence
of sampling properties on predictive performance of the balanced ROMs. We
propose an output domain decomposition approach and couple it with tangential
interpolation to resolve sharp gradients at reduced computational costs.",2109.10408v2
2021-10-08,Site characterization at Treasure Island and Delaney Park downhole arrays by heterogeneous data assimilation,"This article extends a recently proposed heterogeneous data assimilation
technique for site characterization to estimate compression and shear wave
velocity (Vp and Vs, respectively) and damping at Treasure Island and Delaney
Park downhole arrays. The adopted method is based on the joint inversion of
earthquake acceleration time series and experimental surface wave dispersion
data, and including physical constraints to improve the inverse problem's
well-posedness. We first use synthetic data at these two sites to refine the
proposed approach and then apply the refined algorithm to real data sets
available at the Treasure Island and Delaney Park downhole arrays. The joint
inversion results show that the estimated Vs and Vp profiles are in very good
agreement with measured profiles at these two sites. Our synthetic and real
data experiment results suggest that Vp estimation from inversion at downhole
arrays can be improved by integrating the water table depth information or the
higher modes of the Rayleigh wave dispersion data. Depending on the site
complexity, water table information can also help reduce uncertainties
associated with damping estimation. In the last part of this article, we
compare the performance of the inverted profiles to other methods used to
incorporate spatial variability and wave scattering effects in 1D ground
response analysis (GRA). The comparisons show that the joint inversion-based Vs
and Vp profiles and damping ratios estimated in this article can effectively
integrate the effects of spatial variability and wave scattering into 1D GRAs,
especially at the Delaney Park downhole array, which is classified as a poorly
modeled site using traditional 1D GRA.",2110.03849v1
2021-11-01,On the stochastic nature of Galactic cosmic-ray sources,"The precision measurements of the spectra of cosmic ray nuclei and leptons in
recent years have revealed the existence of multiple features, such as the
spectral break at $\sim 300$ GV rigidity seen by PAMELA and AMS-02 and more
recently confirmed by DAMPE and CALET, the softening in the spectra of H and He
nuclei at $\sim 10$ TV reported by DAMPE, confirming previous hints by NUCLEON
and CREAM, a tiny change of slope at $\sim 40$ GeV in the electron spectrum,
revealed by AMS-02, and the large spectral break at $\sim$ TeV reported by
indirect (HESS, MAGIC and VERITAS) and direct (DAMPE, CALET) measurements of
the total (electrons+positrons) lepton spectrum. In all these cases, the
possibility has been suggested that these features might reflect the occasional
presence of a local cosmic ray source, inducing a noticeable reshaping of the
average expected spectra. All these proposals have to face the question of how
likely it is for such a source to exist, a question that we address here in a
quantitative way. We study the statistical properties of random distribution of
sources in space and time, and the effect of the spiral structure of our Galaxy
for both the spectra of light nuclei (p and He) and leptons (electrons and
positrons) in different energy regions.",2111.01171v2
2021-11-09,The In Situ Signature of Cyclotron Resonant Heating,"The dissipation of magnetized turbulence is an important paradigm for
describing heating and energy transfer in astrophysical environments such as
the solar corona and wind; however, the specific collisionless processes behind
dissipation and heating remain relatively unconstrained by measurements. Remote
sensing observations have suggested the presence of strong temperature
anisotropy in the solar corona consistent with cyclotron resonant heating. In
the solar wind, in situ magnetic field measurements reveal the presence of
cyclotron waves, while measured ion velocity distribution functions have hinted
at the active presence of cyclotron resonance. Here, we present Parker Solar
Probe observations that connect the presence of ion-cyclotron waves directly to
signatures of resonant damping in observed proton-velocity distributions. We
show that the observed cyclotron wave population coincides with both flattening
in the phase space distribution predicted by resonant quasilinear diffusion and
steepening in the turbulent spectra at the ion-cyclotron resonant scale. In
measured velocity distribution functions where cyclotron resonant flattening is
weaker, the distributions are nearly uniformly subject to ion-cyclotron wave
damping rather than emission, indicating that the distributions can damp the
observed wave population. These results are consistent with active cyclotron
heating in the solar wind.",2111.05400v2
2021-11-10,Quantum amplitude damping for solving homogeneous linear differential equations: A noninterferometric algorithm,"In contexts where relevant problems can easily attain configuration spaces of
enormous sizes, solving Linear Differential Equations (LDEs) can become a hard
achievement for classical computers; on the other hand, the rise of quantum
hardware can conceptually enable such high-dimensional problems to be solved
with a foreseeable number of qubits, whilst also yielding quantum advantage in
terms of time complexity. Nevertheless, in order to bridge towards experimental
realizations with several qubits and harvest such potential in a short-term
basis, one must dispose of efficient quantum algorithms that are compatible
with near-term projections of state-of-the-art hardware, in terms of both
techniques and limitations. As the conception of such algorithms is no trivial
task, insights on new heuristics are welcomed. This work proposes a novel
approach by using the Quantum Amplitude Damping operation as a resource, in
order to construct an efficient quantum algorithm for solving homogeneous LDEs.
As the intended implementation involves performing Amplitude Damping
exclusively via a simple equivalent quantum circuit, our algorithm shall be
given by a gate-level quantum circuit (predominantly composed of elementary
2-qubit gates) and is particularly nonrestrictive in terms of connectivity
within and between some of its main quantum registers. We show that such an
open quantum system-inspired circuitry allows for constructing the real
exponential terms in the solution in a non-interferometric way; we also provide
a guideline for guaranteeing a lower bound on the probability of success for
each realization, by exploring the decay properties of the underlying quantum
operation.",2111.05646v2
2021-11-13,Attenuation of surface modes in granular media,"In this work, an unconsolidated granular medium, made of silica microbeads,
is experimentally tested in a laboratory setting. The objective is to
investigate the attenuation mechanisms of vertically polarized seismic waves
traveling at the surface of unconsolidated substrates that are characterized by
power-law rigidity profiles. Both geometric spreading and material damping due
to skeletal dissipation are considered. An electromagnetic shaker is employed
to excite the granular medium between 300 and 550 Hz, generating linear modes
that are localized near the surface. A densely sampled section is recorded at
the surface using a laser vibrometer. The explicit solution of the geometric
attenuation law of Rayleigh-like waves in layered media is employed to
calculate the geometric spreading function of the vertically polarized surface
modes within the granular material. In accordance with recent studies, the
dynamics of these small-amplitude multi-modal linear waves can be analysed by
considering the granular medium as perfectly continuous and elastic. By
performing a non-linear regression analysis on particle displacements,
extracted from experimental velocity data, we determine the frequency-dependent
attenuation coefficients, which account for the material damping.
  The findings of this work show that laboratory-scale physical models can be
used to study the geometric spreading of vertically polarized seismic waves
induced by the soil inhomogeneity and characterize the material damping of the
medium.",2111.07199v1
2021-11-15,The Interplay of Regularizing Factors in the Model of Upper Hybrid Oscillations of Cold Plasma,"A one-dimensional nonlinear model of the so-called upper hybrid oscillations
in a magnetoactive plasma is investigated taking into account electron-ion
collisions. It is known that both the presence of an external magnetic field of
strength $ B_0 $ and a sufficiently large collisional factor $ \nu $ help
suppress the formation of a finite-dimensional singularity in a solution
(breaking of oscillations). Nevertheless, the suppression mechanism is
different: an external magnetic field increases the oscillation frequency, and
collisions tend to stabilize the medium and suppress oscillations. In terms of
the initial data and the coefficients $ B_0 $ and $ \nu $, we establish a
criterion for maintaining the global smoothness of the solution. Namely, for
fixed $ B_0 $ and $ \nu \ge 0 $ one can precisely divide the initial data into
two classes: one leads to stabilization to the equilibrium and the other leads
to the destruction of the solution in a finite time. Next, we examine the
nature of the stabilization. We show that for small $ B_0 $ an increase in the
intensity factor first leads to a change in the oscillatory behavior of the
solution to monotonic damping, which is then again replaced by oscillatory
damping. At large values of $ B_0 $, the solution is characterized by
oscillatory damping regardless of the value of the intensity factor $ \nu $.",2111.07826v3
2021-11-20,Excitation and Damping of Slow Magnetosonic Waves in Flaring Hot Coronal Loops: Effects of Compressive Viscosity,"Slow magnetosonic waves associated with flares were observed in coronal loops
by SOHO/SUMER, SDO/AIA in various EUV bandpasses, and other instruments. The
excitation and damping of slow magnetosonic waves provides information on the
magnetic, temperature, and density structure of the loops. Recently, it was
found using 1.5D models that the thermal conduction is suppressed and
compressive viscosity is enhanced in hot (T>6 MK) flaring coronal loops. We
model the excitation and dissipation of slow magnetosonic waves in hot coronal
loops with realistic magnetic geometry, enhanced density, and temperature
(compared to background corona) guided by EUV observations using 3D MHD
visco-resistive model. The effects of compressive viscosity tensor component
along the magnetic field are included with classical and enhanced viscosity
coefficient values for the first time in 3D MHD coronal loop model. The waves
are excited by a velocity pulse at the footpoint of the loop at coronal lower
boundary. The modeling results demonstrate the excitation of the slow
magnetosonic waves and nonlinear coupling to other wave modes, such as the kink
and fast magnetosonic. We find significant leakage of the waves from the hot
coronal loops with small effect of viscous dissipation in cooler (6MK) loops,
and more significant effects of viscous dissipation in hotter (10.5MK) coronal
loops. Our results demonstrate that nonlinear 3D MHD models are required to
fully account for various wave couplings, damping, standing wave formation, and
viscous dissipation in hot flaring coronal loops. Our viscous 3D MHD code
provides a new tool for improved coronal seismology.",2111.10696v1
2021-11-27,Rate of Entropy Production in Stochastic Mechanical Systems,"Entropy production in stochastic mechanical systems is examined here with
strict bounds on its rate. Stochastic mechanical systems include pure
diffusions in Euclidean space or on Lie groups, as well as systems evolving on
phase space for which the fluctuation-dissipation theorem applies, i.e.,
return-to-equilibrium processes. Two separate ways for ensembles of such
mechanical systems forced by noise to reach equilibrium are examined here.
First, a restorative potential and damping can be applied, leading to a
classical return-to-equilibrium process wherein energy taken out by damping can
balance the energy going in from the noise. Second, the process evolves on a
compact configuration space (such as random walks on spheres, torsion angles in
chain molecules, and rotational Brownian motion) lead to long-time solutions
that are constant over the configuration space, regardless of whether or not
damping and random forcing balance. This is a kind of potential-free
equilibrium distribution resulting from topological constraints. Inertial and
noninertial (kinematic) systems are considered. These systems can consist of
unconstrained particles or more complex systems with constraints, such as
rigid-bodies or linkages. These more complicated systems evolve on Lie groups
and model phenomena such as rotational Brownian motion and nonholonomic robotic
systems. In all cases, it is shown that the rate of entropy production is
closely related to the appropriate concept of Fisher information matrix of the
probability density defined by the Fokker-Planck equation. Classical results
from information theory are then repurposed to provide computable bounds on the
rate of entropy production in stochastic mechanical systems.",2111.13930v1
2021-12-22,Strong Stabilization of a 3D Potential Flow via a Weakly Damped von Karman Plate,"The elimination of aeroelastic instability (resulting in sustained
oscillations of bridges, buildings, airfoils) is a central engineering and
design issue. Mathematically, this translates to strong asymptotic
stabilization of a 3D flow by a 2D elastic structure. The stabilization
(convergence to the stationary set) of a aerodynamic wave-plate model is
established here. A 3D potential flow on the half-space has a spatially-bounded
von Karman plate embedded in the boundary. The physical model, then, is a
Neumann wave equation with low regularity of coupling conditions. Motivated on
empirical observations, we examine if intrinsic panel damping can stabilize the
subsonic flow-plate system to a stationary point. Several partial results have
been established through partial regularization of the model. Without doing so,
classical approaches attempting to treat the given wave boundary data have
fallen short, owing to the failure of the Lopatinski condition (in the sense of
Kreiss, Sakamoto) and the associated regularity defect of the hyperbolic
Neumann mapping. Here, we operate on the panel model as in the engineering
literature with no regularization or modifications; we completely resolve the
question of stability by demonstrating that weak plate damping strongly
stabilizes system trajectories. This is accomplished by microlocalizing the
wave data (given by the plate) and observing an ""anisotropic"" a microlocal
compensation by the plate dynamics precisely where the regularity of the 3D
wave is compromsed (in the characteristic sector). Several additional stability
results for both wave and plate subsystems are established to ""push"" strong
stability of the plate onto the flow.",2112.12208v1
2021-12-28,Kinetic investigation of the planar Multipole Resonance Probe under arbitrary pressure,"Active plasma resonance spectroscopy (APRS) refers to a class of plasma
diagnostic methods that use the ability of plasma to resonate at or near the
electron plasma frequency for diagnostic purposes. The planar multipole
resonance probe (pMRP) is an optimized realization of APRS. It has a
non-invasive structure and allows simultaneous measurement of the electron
density, electron temperature, and electron-neutral collision frequency.
Previous work has investigated the pMRP through the Drude model and
collision-less kinetic model. The Drude model misses important kinetic effects
such as collision-less kinetic damping. The collision-less kinetic model is
able to capture pure kinetic effects. However, it is only applicable to
low-pressure plasma. To further study the behavior of the pMRP, we develop a
collisional kinetic model in this paper, which applies to arbitrary pressure.
In this model, the kinetic equation is coupled to the Poisson equation under
the electrostatic approximation. The real part of the general admittance is
calculated to describe the spectral response of the probe-plasma system. Both
collision-less kinetic damping and collisional damping appear in the spectrum.
This model provides a possibility to calculate the electron density, electron
temperature, and electron-neutral collision frequency from the measurements.",2112.14190v2
2021-12-28,Metadamping in inertially amplified metamaterials: Trade-off between spatial attenuation and temporal attenuation,"Metadamping is the phenomenon of either enhanced or diminished intrinsic
dissipation in a material stemming from the material's internal structural
dynamics. It has been previously shown that a locally resonant elastic
metamaterial may be designed to exhibit higher or lower dissipation compared to
a statically equivalent phononic crystal with the same amount of prescribed
damping. Here we reveal that even further dissipation, or alternatively further
reduction of loss, may be reached in an inertially amplified metamaterial that
is also statically equivalent and has the same amount of prescribed damping.
This is demonstrated by a passive configuration whereby an attenuation peak is
generated by the motion of a mass supported by an inclined lever arm. We
further show that by coupling this inertially amplified attenuation peak with
that of a local resonance attenuation peak, a trade-off between the intensity
of spatial attenuation versus temporal attenuation is realized for a range of
the inclination angles. Design for performance along this trade-off is
therefore possible by adjustment of the lever angle. These findings open the
way for highly expanding the Ashby space for stiffness-damping capacity or
stiffness-spatial attenuation capacity through design of the internal structure
of materials.",2112.14322v1
2022-01-10,Tidal erasure of stellar obliquities constrains the timing of hot Jupiter formation,"Stars with hot Jupiters sometimes have high obliquities, which are possible
relics of hot Jupiter formation. Based on the characteristics of systems with
and without high obliquities, it is suspected that obliquities are tidally
damped when the star has a thick convective envelope, as is the case for
main-sequence stars cooler than ~6100K, and the orbit is within ~8 stellar
radii. A promising theory for tidal obliquity damping is the dissipation of
inertial waves within the star's convective envelope. Here, we consider the
implications of this theory for the timing of hot Jupiter formation.
Specifically, hot stars that currently lack a convective envelope possess one
during their pre-main sequence. We find that hot Jupiters orbiting within a
critical distance of ~0.02au from a misaligned main-sequence star lacking a
thick convective envelope must have acquired their tight orbits after a few
tens of millions of years in order to have retained their obliquities
throughout the pre-main-sequence. There are 4 known systems for which this
argument applies--XO-3b, Corot-3b, WASP-14b, and WASP-121b--subject to
uncertainties surrounding inertial wave dissipation. Moreover, we conclude that
a recently-identified overabundance of near-polar hot Jupiters is unlikely
sculpted by tides, instead reflecting their primordial configuration. Finally,
hot Jupiters arriving around cool stars after a few 100s of millions of years
likely find the host star rotating too slowly for efficient obliquity damping.
We predict that the critical effective temperature separating aligned and
misaligned stars should vary with metallicity, from 6300K to 6000K as [Fe/H]
varies from -0.3 to +0.3.",2201.03653v1
2022-01-22,Examining AGN UV/optical Variability Beyond the Simple Damped Random Walk,"We present damped harmonic oscillator (DHO) light-curve modeling for a sample
of 12,714 spectroscopically confirmed quasars in the Sloan Digital Sky Survey
Stripe 82 region. DHO is a second-order continuous-time autoregressive
moving-average (CARMA) process, which can be fully described using four
independent parameters: a natural oscillation frequency ($\omega_{0}$), a
damping ratio ($\xi$), a characteristic perturbation timescale
($\tau_{\mathrm{perturb}}$), and an amplitude for the perturbing white noise
($\sigma_{\mathrm{\epsilon}}$). The asymptotic variability amplitude of a DHO
process is quantified by $\sigma_{\mathrm{DHO}}$ -- a function of $\omega_{0}$,
$\xi$, $\tau_{\mathrm{perturb}}$, and $\sigma_{\mathrm{\epsilon}}$. We find
that both $\tau_{\mathrm{perturb}}$ and $\sigma_{\mathrm{\epsilon}}$ follow
different dependencies with rest-frame wavelength ($\lambda_{\mathrm{RF}}$) on
either side of 2500 \AA, whereas $\sigma_{\mathrm{DHO}}$ follows a single
power-law relation with $\lambda_{\mathrm{RF}}$. After correcting for
wavelength dependence, $\sigma_{\mathrm{DHO}}$ exhibits anti-correlations with
both the Eddington ratio and the black hole mass, while
$\tau_{\mathrm{perturb}}$ -- with a typical value of days in the rest-frame --
shows an anti-correlation with the bolometric luminosity. Modeling AGN
variability as a DHO offers more insight into the workings of accretion disks
close to the supermassive black holes (SMBHs) at the center of AGN. The newly
discovered short-term variability (characterized by $\tau_{\mathrm{perturb}}$
and $\sigma_{\mathrm{\epsilon}}$) and its correlation with bolometric
luminosity pave the way for new algorithms that will derive fundamental
properties (e.g., Eddington ratio) of AGN using photometric data alone.",2201.08943v2
2022-04-20,Ferrimagnet GdFeCo characterization for spin-orbitronics: large field-like and damping-like torques,"Spintronics is showing promising results in the search for new materials and
effects to reduce energy consumption in information technology. Among these
materials, ferrimagnets are of special interest, since they can produce large
spin currents that trigger the magnetization dynamics of adjacent layers or
even their own magnetization. Here, we present a study of the generation of
spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice
magnetization is dominant at room temperature. Magnetic properties such as the
saturation magnetization are deduced from magnetometry measurements while
damping constant is estimated from spin-torque ferromagnetic resonance
(ST-FMR). We show that the overall damping-like (DL) and field-like (FL)
effective fields as well as the associated spin Hall angles can be reliably
obtained by performing the dependence of ST-FMR by an added dc current. The sum
of the spin Hall angles for both the spin Hall effect (SHE) and the spin
anomalous Hall effect (SAHE) symmetries are: $\theta_{DL}^{SAHE} +
\theta_{DL}^{SHE}=-0.15 \pm 0.05$ and $\theta_{FL}^{SAHE} +
\theta_{FL}^{SHE}=0.026 \pm 0.005$. From the symmetry of ST-FMR signals we find
that $\theta_{DL}^{SHE}$ is positive and dominated by the negative
$\theta_{DL}^{SAHE}$. The present study paves the way for tuning the different
symmetries in spin conversion in highly efficient ferrimagnetic systems.",2204.09776v1
2022-04-21,Characterizing the $γ$-Ray Variability of Active Galactic Nuclei with Stochastic Process Method,"The $\gamma$-ray astronomy in time domain has been by now progressed further
as the variabilities of Active Galactic Nuclei (AGNs) on different timescales
have been reported a lot. We study the $\gamma$-ray variabilities of 23 jetted
AGNs through applying a stochastic process method to the ~12.7 yr long-term
light curve (LC) obtained by Fermi-Large Area Telescope (Fermi-LAT). In this
method, the stochastically driven damped simple harmonic oscillator (SHO) and
the damped random walk (DRW) models are used to model the long-term LCs. Our
results show that the long-term variabilities of 23 AGNs can be characterized
well by both SHO and DRW models. However, the SHO model is restricted in the
over-damped mode and the parameters are poorly constrained. The SHO power
spectral densities (PSDs) are same as the typical DRW PSD. In the plot of the
rest-frame timescale that corresponds to the broken frequency in the PSD versus
black hole mass, the intrinsic $\gamma$-ray characteristic timescales of 23
AGNs occupy almost the same space with the optical variability timescales
obtained from the accretion disk emission. This suggests a connection between
the jet and the accretion disk. Same as the optical variability of AGN
accretion disk, the $\gamma$-ray timescale is also consistent with the thermal
timescale caused by the thermal instability in the standard accretion disk of
AGN.",2204.09987v1
2022-04-29,A fast point charge interacting with the screened Vlasov-Poisson system,"We consider the long-time behavior of a fast, charged particle interacting
with an initially spatially homogeneous background plasma. The background is
modeled by the screened Vlasov-Poisson equations, whereas the interaction
potential of the point charge is assumed to be smooth. We rigorously prove the
validity of the \emph{stopping power theory} in physics, which predicts a
decrease of the velocity $V(t)$ of the point charge given by $\dot{V} \sim
-|V|^{-3} V$, a formula that goes back to Bohr (1915). Our result holds for all
initial velocities larger than a threshold value that is larger than the
velocity of all background particles and remains valid until (i) the particle
slows down to the threshold velocity, or (ii) the time is exponentially long
compared to the velocity of the point charge. The long-time behavior of this
coupled system is related to the question of Landau damping which has remained
open in this setting so far. Contrary to other results in nonlinear Landau
damping, the long-time behavior of the system is driven by the non-trivial
electric field of the plasma, and the damping only occurs in regions that the
point charge has already passed.",2205.00035v2
2022-05-06,"Discovery of a coherent, wave-like velocity pattern for the Radcliffe Wave","Recently studies discovered that part of the Gould Belt belongs to a 2.7
kpc-long {coherent, thin} wave consisting of a chain of clouds, where a damped
undulation pattern has been identified from the spatial arrangement of the
clouds. We use the proper motions of Young Stellar Objects (YSOs) anchored
inside the clouds to study the kinematic structure of the Radcliffe Wave in
terms of $v_z$, and identify a damped, wave-like pattern from the $v_z$ space,
which we call ""velocity undulation"". We propose a new formalism based on the
Ensemble Empirical Mode Decomposition (EEMD) to determine the amplitude,
period, and phase of the undulation pattern, and find that the spatial and the
velocity undulation share an almost identical spatial frequency of about 1.5
kpc, and both are damped when measured from one side to the other. Measured for
the first cycle, they exhibit a phase difference of around $2\pi/3$. The
structure is oscillating around the midplane of the Milky Way disk with an
amplitude of $\sim\,130\,\pm\,20\,\rm pc$. The vertical extent of the Radcliffe
Wave exceeds the thickness of the molecular disk, suggesting that the
undulation of the undulation signature might originate from a perturbation,
e.g. the passage of a dwarf galaxy.",2205.03218v1
2022-05-17,Resolving the HI in Damped Lyman-α systems that power star-formation,"Reservoirs of dense atomic gas (primarily hydrogen), contain approximately 90
percent of the neutral gas at a redshift of 3, and contribute to 2-3 percent of
the total baryons in the Universe. These damped Lyman-${\alpha}$ systems (so
called because they absorb Lyman-${\alpha}$ photons from within and from
background sources) have been studied for decades, but only through absorption
lines present in the spectra of background quasars and gamma-ray bursts. Such
pencil beams do not constrain the physical extent of the systems. Here, we
report integral-field spectroscopy of a bright, gravitationally lensed galaxy
at a redshift of 2.7 with two foreground damped Lyman-${\alpha}$ systems. These
systems are $>$ 238 $kpc^2$ in extent, with column densities of neutral
hydrogen varying by more than an order of magnitude on $<$ 3 kpc-scales. The
mean column densities are $10^{20.46}$ - $10^{20.84} cm^{-2}$ and the total
masses are $> 5.5 \times 10^{8}$ - $1.4 \times 10^{9} M_{\odot}$, showing that
they contain the necessary fuel for the next generation of star formation,
consistent with relatively massive, low-luminosity primeval galaxies at
redshifts $>$ 2.",2205.08554v1
2022-05-21,Accuracy of one-dimensional approximation in neutron star quasi-normal modes,"Since the eigenfrequency of gravitational waves from cold neutron stars
becomes a complex number, where the real and imaginary parts respectively
correspond to an oscillation frequency and damping rate, one has to somehow
solve the eigenvalue problem concerning the eigenvalue in two-dimensional
parameter space. To avoid this bother, one sometimes adopts an approximation,
where the eigenvalue is in one-dimensional parameter space. In this study,
first, we show the accuracy of the zero-damping approximation, which is one of
the one-dimensional approximations, for the fundamental and 1st pressure modes.
But, this approximation is not applicable to the spacetime mode, because the
damping rate of the spacetime mode is generally comparable to the oscillation
frequency. Nevertheless, we find the empirical relation for the ratio of the
imaginary part to the real part of the eigenfrequency, which is expressed as a
function of the steller compactness almost independently of the adopted
equations of state for neutron star matter. Adopting this empirical relation,
one can express the eigenfrequency in terms of just the real part, i.e., the
problem to solve becomes an eigenvalue problem with a one-dimensional
eigenvalue. Then, we find that the frequencies are estimated with good accuracy
even with such approximations even for the 1st spacetime mode.",2205.10523v1
2022-06-02,Proximity of exoplanets to first-order mean-motion resonances,"Planetary formation theories and, more specifically, migration models predict
that planets can be captured in mean-motion resonances (MMRs) during the disc
phase. The distribution of period ratios between adjacent planets shows an
accumulation in the vicinity of the resonance, which is not centred on the
nominal resonance but instead presents an offset slightly exterior to it. Here
we extend on previous works by thoroughly exploring the effect of different
disc and planet parameters on the resonance offset during the disc migration
phase. The dynamical study is carried out for several first-order MMRs and for
both low-mass Earth-like planets undergoing type-I migration and giant planets
evolving under type-II migration. We find that the offset varies with time
during the migration of the two-planet system along the apsidal corotation
resonance family. The departure from the nominal resonance increases for higher
planetary masses and stronger eccentricity damping. In the Earth to super-Earth
regime, we find offset values in agreement with the observations when using a
sophisticated modelling for the planet-disc interactions, where the damping
timescale depends on the eccentricity. This dependence causes a feedback which
induces an increase of the resonance offsets. Regarding giant planets, the
offsets of detected planet pairs are well reproduced with a classical
$K$-factor prescription for the planet-disc interactions when the eccentricity
damping rate remains low to moderate. In both regimes, eccentricities are in
agreement with the observations too. As a result, planet-disc interactions
provide a generic channel to generate the offsets found in the observations.",2206.00943v1
2022-06-03,Dynamical Instability in Multi-Orbiter Systems with Gas Friction,"Closely-packed multi-planet systems are known to experience dynamical
instability if the spacings between the planets are too small. Such instability
can be tempered by the frictional forces acting on the planets from gaseous
discs. A similar situation applies to stellar-mass black holes embedded in AGN
discs around supermassive black holes. In this paper, we use $N$-body
integrations to evaluate how the frictional damping of orbital eccentricity
affects the growth of dynamical instability for a wide range of planetary
spacing and planet-to-star mass ratios. We find that the stability of a system
depends on the damping timescale $\tau$ relative to the zero-friction
instability growth timescale $t_{\rm inst}$. In a two-planet system, the
frictional damping can stabilise the dynamical evolution if $t_{\rm
inst}\gtrsim\tau$. With three planets, $t_{\rm inst} \gtrsim 10\tau - 100\tau$
is needed for stabilisation. When the separations between the planetary orbits
are sufficiently small, $t_{\rm inst}$ can be less than the synodic period
between the planets, which makes frictional stabilisation unlikely to occur. As
the orbital spacing increases, the instability timescale tends to grow
exponentially on average, but it can vary by a few orders of magnitude
depending on the initial orbital phases of the planets. In general, the stable
region (at large orbital spacings) and unstable region (at small orbital
spacings) are separated by a transition zone, in which the (in)stability of the
system is not guaranteed. We also devise a linear map to analyse the dynamical
instability of the ""planet + test-mass"" system, and we find qualitatively
similar results to the $N$-body simulations.",2206.01755v1
2022-08-15,Nonperturbative approach to interfacial spin-orbit torques induced by Rashba effect,"Current-induced spin-orbit torque (SOT) in normal metal/ferromagnet (NM/FM)
bilayers bears great promise for technological applications, but the
microscopic origin of purely interfacial SOTs in ultra-thin systems is not yet
fully understood. Here, we show that a linear response theory with a
nonperturbative treatment of spin-dependent interactions and impurity
scattering potential predicts damping-like SOTs that are strictly absent in
perturbative approaches. The technique is applied to a two-dimensional
Rashba-coupled ferromagnet (the paradigmatic model of a NM/FM interface), where
higher-order scattering processes encoding skew scattering from nonmagnetic
impurities allow for current-induced spin polarization with nonzero components
along all spatial directions. This is in stark contrast to previous results of
perturbative methods (neglecting skew scattering), which predict a coplanar
spin-polarization locked perpendicular to the charge current as a result of
conventional Rashba-Edelstein effect. Furthermore, the angular dependence of
ensuing SOTs and their dependence upon the scattering potential strength is
analysed numerically. Simple analytic expressions for the
spin-density--charge-current response function, and related SOT efficiencies,
are obtained in the weak scattering limit. We find that the extrinsic
damping-like torques driven by impurity scattering reaches efficiencies of up
to 7% of the field-like (Rashba-Edelstein) torque. Our microscopic theory shows
that bulk phenomena, such as the spin Hall effect, are not a necessity in the
generation of the damping-like SOTs of the type observed in experiments on
ultra-thin systems.",2208.07296v1
2022-08-22,Plasma heating and nanoflare caused by slow-mode wave in a coronal loop,"We present a detailed analysis of a reflecting intensity perturbation in a
large coronal loop that appeared as sloshing oscillation and lasted for at
least one and a half periods. The perturbation is initiated by a microflare at
one footpoint of the loop, propagates along the loop and is eventually
reflected at the remote footpoint where significant brightenings are observed
in all the AIA extreme-ultraviolet (EUV) channels. This unique observation
provides us with the opportunity to better understand not only the thermal
properties and damping mechanisms of the sloshing oscillation, but also the
energy transfer at the remote footpoint. Based on differential emission
measures (DEM) analysis and the technique of coronal seismology, we find that
1) the calculated local sound speed is consistent with the observed propagation
speed of the perturbation during the oscillation, which is suggestive of a slow
magnetoacoustic wave; 2) thermal conduction is the major damping mechanism of
the wave but additional damping mechanism such as anomalous enhancement of
compressive viscosity or wave leakage is also required to account for the rapid
decay of the observed waves; 3) the wave produced a nanoflare at the remote
footpoint, with a peak thermal energy of $\thicksim10^{24}-10^{25}$ erg. This
work provides a consistent picture of the magnetoacoustic wave propagation and
reflection in a coronal loop, and reports the first solid evidence of a
wave-induced nanoflare. The results reveal new clues for further simulation
studies and may help solving the coronal heating problem.",2208.10029v1
2022-09-07,AlH lines in the blue spectrum of Proxima Centauri,"The recently-computed ExoMol line lists for isotopologues of AlH are used to
analyse the blue spectrum (4000-4500 {\AA}) of Proxima Cen (M5.5 V). Comparison
of the observed and computed spectra enables the identification of a large
number of 27AlH lines of the A1{\Pi} - X1{\Sigma}+ band system: the spectral
range covering 1-0, 0-0 and 1-1 bands is dominated by clearly resolved AlH
lines. We reveal the diffuse nature of transitions close to the dissociation
limit which appears in the form of increasingly wider(up to 5 {\AA}) and
shallower (up to the continuum confusion limit) AlH line profiles. The
predicted wavelengths of AlH diffuse lines are systematically displaced. The
effect broadening by pre-dissociation states on the line profiles is included
by increasing the radiative damping rate by up to 5 orders of magnitude. We
determine empirical values of damping rates for a number of the clean 0-0
Q-branch transitions by comparing the observed and synthetic stellar spectra.
We find excellent agreement between our damping rates and lifetimes available
in the literature. A comparison of 27Al1H ExoMol and REALH spectra shows that
the observed spectrum is better described by the ExoMol line list. A search for
26Al1H lines in the Proxima Cen spectrum does not reveal any notable features;
giving an upper limit of 27Al1H/26Al1H {>} 100.",2209.03037v2
2022-09-19,Semi-implicit Integration and Data-Driven Model Order Reduction in Structural Dynamics with Hysteresis,"Structural damping is known to be approximately rate-independent in many
cases. Popular models for rate-independent dissipation are hysteresis models;
and a highly popular hysteresis model is the Bouc-Wen model. If such hysteretic
dissipation is incorporated in a refined finite element model, then the
mathematical model includes the usual structural dynamics equations along with
nonlinear nonsmooth ordinary differential equations for a large number of
internal hysteretic states at Gauss points, to be used within the virtual work
calculation for dissipation. For such systems, numerical integration becomes
difficult due to both the distributed non-analytic nonlinearity of hysteresis
as well as the very high natural frequencies in the finite element model. Here
we offer two contributions. First, we present a simple semi-implicit
integration approach where the structural part is handled implicitly based on
the work of Pich\'e, and where the hysteretic part is handled explicitly. A
cantilever beam example is solved in detail using high mesh refinement.
Convergence is good for lower damping and a smoother hysteresis loop. For a
less smooth hysteresis loop and/or higher damping, convergence is observed to
be roughly linear on average. Encouragingly, the time step needed for stability
is much larger than the time period of the highest natural frequency of the
structural model. Subsequently, data from several simulations conducted using
the above semi-implicit method are used to construct reduced order models of
the system, where the structural dynamics is projected onto a small number of
modes and the number of hysteretic states is reduced significantly as well.
Convergence studies of error against the number of retained hysteretic states
show very good results.",2209.08765v2
2022-09-21,Performance enhancement of a spin-wave-based reservoir computing system utilizing different physical conditions,"The authors have numerically studied how to enhance reservoir computing
performance by thoroughly extracting their spin-wave device potential for
higher-dimensional information generation. The reservoir device has a 1-input
exciter and 120-output detectors on the top of a continuous magnetic garnet
film for spin-wave transmission. For various nonlinear and fading-memory
dynamic phenomena distributing in the film space, small in-plane magnetic
fields were used to prepare stripe domain structures and various damping
constants at the film sides and bottom were explored. The ferromagnetic
resonant frequency and relaxation time of spin precession clearly characterized
the change in spin dynamics with the magnetic field and damping constant. The
common input signal for reservoir computing was a 1 GHz cosine wave with random
6-valued amplitude modulation. A basic 120-dimensional reservoir output vector
was obtained from time-series signals at the 120 output detectors under each of
the three magnetic field conditions. Then, 240- and 360-dimensional reservoir
output vectors were also constructed by concatenating two and three basic ones,
respectively. In nonlinear autoregressive moving average (NARMA) prediction
tasks, the computational performance was enhanced as the dimension of the
reservoir output vector becomes higher and a significantly low prediction error
was achieved for the 10th-order NARMA using the 360-dimensional vector and
optimum damping constant. The results are clear evidence that the collection of
diverse output signals efficiently increases the dimensionality effective for
reservoir computing, i.e., reservoir-state richness. This paper demonstrates
that performance enhancement through various configuration settings is a
practical approach for on-chip reservoir computing devices with small numbers
of real output nodes.",2209.10123v1
2022-10-02,Reduction in turbulence-induced non-linear dynamic vibration using tuned liquid damper (TLD),"In the present research work, an attempt is made to develop a coupled
non-linear turbulence-structure-damper model in a finite volume-finite
difference (FV-FD) framework. Tuned liquid damper (TLD) is used as the
additional damping system along with inherent structural damping. Real-time
simulation of flow-excited bridge box girder or chimney section and the
vibration reduction using TLD can be performed using the developed model. The
turbulent flow field around a structure is modeled using an OpenFOAM transient
PISO solver, and the time-varying drag force is calculated. This force perturbs
the structure, causing the sloshing phenomena of the attached TLD, modeled
using shallow depth approximation, damping the flow-induced vibration of the
structure. The structural motion with and without the attached TLD is modeled
involving the FD-based Newmark-Beta method using in-house MATLAB codes. The TLD
is tuned with the vortex-shedding frequency of the low-Reynolds number flows,
and it is found to be reducing the structural excitation significantly. On the
other hand, the high-Reynolds number turbulent flow exhibits a broadband
excitation, for which by tuning the TLD with few frequencies obtained through
investigations, a good reduction in vibration is observed.",2210.00428v3
2022-10-17,Interpretations of the cosmic ray secondary-to-primary ratios measured by DAMPE,"Precise measurements of the boron-to-carbon and boron-to-oxygen ratios by
DAMPE show clear hardenings around $100$ GeV/n, which provide important
implications on the production, propagation, and interaction of Galactic cosmic
rays. In this work we investigate a number of models proposed in literature in
light of the DAMPE findings. These models can roughly be classified into two
classes, driven by propagation effects or by source ones. Among these models
discussed, we find that the re-acceleration of cosmic rays, during their
propagation, by random magnetohydrodynamic waves may not reproduce sufficient
hardenings of B/C and B/O, and an additional spectral break of the diffusion
coefficient is required. The other models can properly explain the hardenings
of the ratios. However, depending on simplifications assumed, the models differ
in their quality in reproducing the data in a wide energy range. The models
with significant re-acceleration effect will under-predict low-energy
antiprotons but over-predict low-energy positrons, and the models with
secondary production at sources over-predict high-energy antiprotons. For all
models high-energy positron excess exists.",2210.09205v3
2022-10-19,Energy Dissipation in Synchronous Binary Asteroids,"Synchronous binary asteroids can experience libration about their
tidally-locked equilibrium, which will result in energy dissipation. This is an
important topic to the Asteroid Impact and Deflection Assessment, where
excitation caused by the DART kinetic impact in the Didymos binary asteroid
system may be reduced through dissipation before Hera arrives to survey the
effects of the impact. We develop a numeric model for energy dissipation in
binary asteroids to explore how different system configurations affect the rate
of energy dissipation. We find tumbling within the synchronous state eliminates
a systematic trend in libration damping on short timescales (several years),
but not over long times (hundreds of years) depending on the material
conditions. Furthermore, damping of libration, eccentricity, and fluctuations
in the semimajor axis are primarily dependent on the stiffness of the
secondary, whereas the semimajor axis secular expansion rate is dictated by the
stiffness of the primary, as expected. Systems experiencing stable planar
libration in the secondary can see a noticeable reduction in libration
amplitude after only a few years depending on the stiffness of the secondary,
and thus dissipation should be considered during Hera's survey of Didymos. For
a very dissipative secondary undergoing stable libration, Hera may be able to
calculate the rate of libration damping in Dimorphos and therefore constrain
its tidal parameters.",2210.10877v1
2022-11-14,Heavily Damped Precessional Switching with Very Low Write-error Rate in Elliptical-cylinder Magnetic Tunnel Junction,"Voltage-induced dynamic switching in magnetic tunnel junctions (MTJs) is a
writing technique for voltage-controlled magnetoresistive random access memory
(VCMRAM), which is expected to be an ultimate non-volatile memory with
ultra-low power consumption. In conventional dynamic switching, the width of
sub-nanosecond write voltage pulses must be precisely controlled to achieve a
sufficiently low write-error rate (WER). This very narrow tolerance of pulse
width is the biggest technical difficulty in developing VCMRAM. Heavily damped
precessional switching is a writing scheme for VCMRAM with a substantially high
tolerance of pulse width although the minimum WER has been much higher than
that of conventional dynamic switching with an optimum pulse width. In this
study, we theoretically investigate the effect of MTJ shape and the direction
of the applied magnetic field on the WER of heavily damped precessional
switching. The results show that the WER in elliptical-cylinder MTJ can be
several orders of magnitude smaller than that in usual circular-cylinder MTJ
when the external magnetic field is applied parallel to the minor axis of the
ellipse. The reduction in WER is due to the fact that the demagnetization field
narrows the component of the magnetization distribution perpendicular to the
plane direction immediately before the voltage is applied.",2211.07148v1
2022-11-19,Regularity to Timoshenko's System with Thermoelasticity of Type III with Fractional Damping,"The article, presents the study of the regularity of two thermoelastic beam
systems defined by the Timoshenko beam model coupled with the heat conduction
of Green-Naghdiy theory of type III, both mathematical models are
differentiated by their coupling terms that arise as a consequence of the
constitutive laws initially considered. The systems presented in this work have
3 fractional dampings: $\mu_1(-\Delta)^\tau \phi_t$, $\mu_2(-\Delta)^\sigma
\psi_t$ and $K(-\Delta)^\xi \theta_t$, where $\phi,\psi$ and $\theta$ are
transverse displacement, rotation angle and empirical temperature of the bean
respectively and the parameters $(\tau,\sigma,\xi)\in [0,1]^3$. It is noted
that for values 0 and 1 of the parameter $\tau$, the so-called frictional or
viscous damping will be faced, respectively. The main contribution of this
article is to show that the corresponding semigroup
$S_i(t)=e^{\mathcal{B}_it}$, with $i=1,2$, is of Gevrey class
$s>\frac{r+1}{2r}$ for $r=\min \{\tau,\sigma,\xi\}$ for all
  $(\tau,\sigma,\xi )\in R_{CG}:= (0, 1)^3$. It is also showed that
$S_1(t)=e^{\mathcal{B}_1t}$ is analytic in the region $R_{A_1}:=\{(\tau,\sigma,
\xi )\in [\frac{1}{2},1]^3\}$ and $S_2(t)=e^{\mathcal{B}_2t}$ is analytic in
the region $R_{A_2}:=\{(\tau,\sigma, \xi )\in [\frac{1}{2},1]^3/ \tau=\xi\}$.",2211.10816v2
2022-11-28,Exciting the TTV Phases of Resonant Sub-Neptunes,"There are excesses of sub-Neptunes just wide of period commensurabilities
like the 3:2 and 2:1, and corresponding deficits narrow of them. Any theory
that explains this period ratio structure must also explain the strong transit
timing variations (TTVs) observed near resonance. Besides an amplitude and a
period, a sinusoidal TTV has a phase. Often overlooked, TTV phases are
effectively integration constants, encoding information about initial
conditions or the environment. Many TTVs near resonance exhibit non-zero
phases. This observation is surprising because dissipative processes that
capture planets into resonance also damp TTV phases to zero. We show how both
the period ratio structure and the non-zero TTV phases can be reproduced if
pairs of sub-Neptunes capture into resonance in a gas disc while accompanied by
a third eccentric non-resonant body. Convergent migration and eccentricity
damping by the disc drives pairs to orbital period ratios wide of
commensurability; then, after the disc clears, secular forcing by the third
body phase-shifts the TTVs. The scenario predicts that resonant planets are
apsidally aligned and possess eccentricities up to an order of magnitude larger
than previously thought.",2211.15701v2
2022-12-04,An Unsupervised Machine Learning Method for Electron--Proton Discrimination of the DAMPE Experiment,"Galactic cosmic rays are mostly made up of energetic nuclei, with less than
$1\%$ of electrons (and positrons). Precise measurement of the electron and
positron component requires a very efficient method to reject the nuclei
background, mainly protons. In this work, we develop an unsupervised machine
learning method to identify electrons and positrons from cosmic ray protons for
the Dark Matter Particle Explorer (DAMPE) experiment. Compared with the
supervised learning method used in the DAMPE experiment, this unsupervised
method relies solely on real data except for the background estimation process.
As a result, it could effectively reduce the uncertainties from simulations.
For three energy ranges of electrons and positrons, 80--128 GeV, 350--700 GeV,
and 2--5 TeV, the residual background fractions in the electron sample are
found to be about (0.45 $\pm$ 0.02)$\%$, (0.52 $\pm$ 0.04)$\%$, and (10.55
$\pm$ 1.80)$\%$, and the background rejection power is about (6.21 $\pm$ 0.03)
$\times$ $10^4$, (9.03 $\pm$ 0.05) $\times$ $10^4$, and (3.06 $\pm$ 0.32)
$\times$ $10^4$, respectively. This method gives a higher background rejection
power in all energy ranges than the traditional morphological parameterization
method and reaches comparable background rejection performance compared with
supervised machine learning~methods.",2212.01843v1
2022-12-05,Stability of Cnoidal Waves for the Damped Nonlinear Schrödinger Equation,"We consider the cubic nonlinear Schr\""odinger (NLS) equation with a linear
damping on the one dimensional torus and we investigate the stability of some
solitary wave profiles within the dissipative dynamics. The undamped cubic NLS
equation is well known to admit a family of periodic waves given by Jacobi
elliptic functions of cnoidal type. We show that the family of cnoidal waves is
orbitally stable. More precisely, by considering a sufficiently small
perturbation of a given cnoidal wave at initial time, the evolution will always
remain close (up to symmetries of the equation) to the cnoidal wave whose mass
is modulated according to the dissipative dynamics. This result extends the
concept of orbital stability to this non-Hamiltonian evolution. Since cnoidal
waves are not exact solutions to the damped NLS, the perturbation is forced
away from the family of solitary wave profiles. In order to control this
secular growth of the error, we find a first order approximation of the
solitary wave that takes into account the dissipative term. Then we use a
suitable, exponentially decreasing Lyapunov functional that controls the
$H^1$-norm of the perturbation around the approximated solitons.",2212.02195v2
2022-12-08,Strong photon-magnon coupling using a lithographically defined organic ferrimagnet,"We demonstrate a hybrid quantum system composed of superconducting resonator
photons and magnons hosted by the organic-based ferrimagnet vanadium
tetracyanoethylene (V[TCNE]$_x$). Our work is motivated by the challenge of
scalably integrating an arbitrarily-shaped, low-damping magnetic system with
planar superconducting circuits, thus enabling a host of quantum magnonic
circuit designs that were previously inaccessible. For example, by leveraging
the inherent properties of magnons, one can enable nonreciprocal
magnon-mediated quantum devices that use magnon propagation rather than
electrical current. We take advantage of the properties of V[TCNE]$_x$, which
has ultra-low intrinsic damping, can be grown at low processing temperatures on
arbitrary substrates, and can be patterned via electron beam lithography. We
demonstrate the scalable, lithographically integrated fabrication of hybrid
quantum magnonic devices consisting of a thin-film superconducting resonator
coupled to a low-damping, thin-film V[TCNE]$_x$ microstructure. Our devices
operate in the strong coupling regime, with a cooperativity as high as 1181(44)
at T$\sim$0.4 K, suitable for scalable quantum circuit integration. This work
paves the way for the exploration of high-cooperativity hybrid magnonic quantum
devices in which magnonic circuits can be designed and fabricated as easily as
electrical wires.",2212.04423v1
2022-12-28,Scattering of the UHECR at small pitch angle by damped plasma waves,"In spite a lot of theoretical and experimental effort that has been achieved
in ultra-high energy cosmic ray (UHECR) scattering research in last few
decades, some questions remain unanswered, or partially answered. Two of them,
that will be in the focus of this paper are: possible source of UHECRs and the
acceleration mechanism of cosmic rays beyond PeV energies. Small pitch-angle
scattering of UHECRs and possible confinement has been investigated using
quasilinear theory in order to analytically calculate pitch-angle Fokker-Planck
coefficient. CR particles resonantly interact with oblique low frequency damped
waves. We show that the resonance function is broadened due to damping effects
and this result is compared with the nonlinear broadening. Unlike the case of
purely parallel (or antiparallel) propagating waves in slab turbulence, the
presence of the compressive magnetic field component of oblique fast-mode waves
allows the cosmic ray particles to resonantly interact with these waves through
the n = 0 resonance, together with gyroresonance, which strongly influence the
Hillas limit. The derived results can be used to compute the parallel mean free
path for all forms of the turbulence spectrum; it has been applied on the
transport and propagation of CRs close to ultra-high energies in the Galaxy. An
accurate understanding of particle acceleration in astrophysical sources could
help to interpret eventual transition from Galactic to extragalactic origin of
cosmic rays, if any, and the shape of the UHECR spectrum at the highest
energies.",2212.13755v1
2023-01-23,Estimation of turbulent proton and electron heating rates via Landau damping constrained by Parker Solar Probe observations,"The heating of ions and electrons due to turbulent dissipation plays a
crucial role in the thermodynamics of the solar wind and other plasma
environments. Using magnetic field and thermal plasma observations from the
first two perihelia of the Parker Solar Probe (PSP), we model the relative
heating rates as a function of radial distance, magnetic spectra, and plasma
conditions, enabling us to better characterize the thermodynamics of the inner
heliosphere. We employ the Howes et al. 2008 steady-state cascade model, which
considers the behavior of turbulent, low-frequency, wavevector-anisotropic,
critically balanced Alfv\'enic fluctuations that dissipate via Landau damping
to determine proton-to-electron heating rates $Q_p/Q_e$. We distinguish
ion-cyclotron frequency circularly polarized waves from low-frequency
turbulence and constrain the cascade model using spectra constructed from the
latter. We find that the model accurately describes the observed energy
spectrum from over 39.4 percent of the intervals from Encounters 1 and 2,
indicating the possibility for Landau damping to heat the young solar wind. The
ability of the model to describe the observed turbulent spectra increases with
the ratio of thermal-to-magnetic pressure, $\beta_p$, indicating that the model
contains the necessary physics at higher $\beta_p$. We estimate high magnitudes
for the Kolmogorov constant which is inversely proportional to the non-linear
energy cascade rate. We verify the expected strong dependency of $Q_p/Q_e$ on
$\beta_p$ and the consistency of the critical balance assumption.",2301.09713v1
2023-02-02,Leveraging symmetry for an accurate spin-orbit torques characterization in ferrimagnetic insulators,"Spin-orbit torques (SOTs) have emerged as an efficient means to electrically
control the magnetization in ferromagnetic heterostructures. Lately, an
increasing attention has been devoted to SOTs in heavy metal (HM)/magnetic
insulator (MI) bilayers owing to their tunable magnetic properties and
insulating nature. Quantitative characterization of SOTs in HM/MI
heterostructures are, thus, vital for fundamental understanding of charge-spin
interrelations and designing novel devices. However, the accurate determination
of SOTs in MIs have been limited so far due to small electrical signal outputs
and dominant spurious thermoelectric effects caused by Joule heating. Here, we
report a simple methodology based on harmonic Hall voltage detection and
macrospin simulations to accurately quantify the damping-like and field-like
SOTs, and thermoelectric contributions separately in MI-based systems.
Experiments on the archetypical Bi-doped YIG/Pt heterostructure using the
developed method yield precise values for the field-like and damping-like SOTs,
reaching -0.14 and -0.15 mT per 1.7x$10^{ 11}$ A/$m^2$, respectively. We
further reveal that current-induced Joule heating changes the spin transparency
at the interface, reducing the spin Hall magnetoresistance and damping-like
SOT, simultaneously. These results and the devised method can be beneficial for
fundamental understanding of SOTs in MI-based heterostructures and designing
new devices where accurate knowledge of SOTs is necessary.",2302.01141v2
2022-12-31,Genuine three qubit Einstein-Podolsky-Rosen steering under decoherence: Revealing hidden genuine steerability via pre-processing,"The behaviour of genuine EPR steering of three qubit states under various
environmental noises is investigated. In particular, we consider the two
possible steering scenarios in the tripartite setting: (1 -> 2), where Alice
demonstrates genuine steering to Bob-Charlie, and (2 -> 1), where Alice-Bob
together demonstrates genuine steering to Charlie. In both these scenarios, we
analyze the genuine steerability of the generalized Greenberger-Horne-Zeilinger
(gGHZ) states or the W-class states under the action of noise modeled by
amplitude damping (AD), phase flip (PF), bit flip (BF), and phase damping (PD)
channels. In each case, we consider three different interactions with the noise
depending upon the number of parties undergoing decoherence. We observed that
the tendency to demonstrate genuine steering decreases as the number of parties
undergoing decoherence increases from one to three. We have observed several
instances where the genuine steerability of the state revives after collapsing
if one keeps on increasing the damping. However, the hidden genuine
steerability of a state cannot be revealed solely from the action of noise. So,
the parties having a characterized subsystem, perform local pre-processing
operations depending upon the steering scenario and the state shared with the
dual intent of revealing hidden genuine steerability or enhancing it.",2302.02987v1
2023-02-20,Optimal energy harvesting efficiency from vortex-induced vibration of a circular cylinder under flow,"This work applies a combined approach a reduced-order model (ROM) together
with experiments and direct numerical simulations to investigate the optimal
efficiency of fluid-flow energy harvesting from transverse vortex-induced
vibration (VIV) of a circular cylinder. High resolution efficiency maps were
predicted over wide ranges of flow reduced velocities and structural damping
ratios, and the maximum efficiency and optimal settings of damping ratio and
reduced velocity were then examined for different mass ratios and Reynolds
numbers. Efficiencies predicted by the ROM were also validated against either
experiments or direct simulations. The present work indicates that: (i) the
maximum efficiency is controlled by both the incoming reduced velocity and the
product of mass ratio and structural damping ratio, which is similar to the
maximum amplitude of VIV; (ii) the maximum efficiency at a relatively high
Reynolds number ($Re \approx 6 \times 10^3$) in subcritical regime is higher
than that of a low Reynolds number ($Re = 150$) in laminar regime; (iii) the
energy harvesting efficiency from VIV of a circular cylinder with a low mass
ratio is more robust than that with a high mass ratio. This finding suggests
that the VIV harvester performs better in water than in air.",2302.09975v1
2023-04-12,Liouvillian exceptional points in continuous variable system,"The Liouvillian exceptional points for a quantum Markovian master equation of
an oscillator in a generic environment are obtained. They occur at the points
when the modified frequency of the oscillator vanishes, whereby the eigenvalues
of the Liouvillian become real. In a generic system there are two parameters
that modify the oscillator's natural frequency. One of the parameters can be
the damping rate. The exceptional point then corresponds to critical damping of
the oscillator. This situation is illustrated by the Caldeira--Leggett (CL)
equation and the Markovian limit of the Hu--Paz--Zhang (HPZ) equation. The
other parameter changes the oscillator's effective mass whereby the exceptional
point is reached in the limit of extremely heavy oscillator. This situation is
illustrated by a modified form of the Kossakowski--Lindblad (KL) equation. The
eigenfunctions coalesce at the exceptional points and break into subspaces
labelled by a natural number $N$. In each of the $N$-subspace, there is a
$(N+1)$-fold degeneracy and the Liouvillian has a Jordan block structure of
order-$(N+1)$. We obtain the explicit form of the generalized eigenvectors for
a few Liouvillians. Because of the degeneracies, there is a freedom of choice
in the generalized eigenfunctions. This freedom manifests itself as an
invariance in the Jordan block structure under a similarity transformation
whose form is obtained. We compare the relaxation of the first excited state of
an oscillator in the underdamped region, critically damped region which
corresponds to the exceptional point, and overdamped region using the
generalized eigenvectors of the CL equation.",2304.05792v2
2023-04-13,Network-Reconfiguration-Aware Power Oscillation Damping Controller for Newly Commissioned Converter-Interfaced Power Plants,"In recent years, transmission system operators have started requesting
converter-interfaced generators (CIGs) to participate in grid services such as
power oscillation damping (POD). As power systems are prone to topology changes
because of connection and disconnection of generators and electrical lines, one
of the most important requirements in the POD controller design is to account
for these changes and to deal with them by using either adaptive or robust
approaches. The robust approach is usually preferred by system operators
because of the fixed structure of the controller. In this paper, a procedure to
design POD controllers for CIG-based power plants that takes into consideration
all possible network configurations is presented. This procedure is based on
frequency-response techniques, so it is suitable for the commissioning in newly
installed power plants, even in those cases when a detailed small-signal model
of the system is not available. This procedure can be used to damp critical
system modes by using active power, reactive power, or both power components
simultaneously. The proposed procedure is applied to the design of the POD
controller for a CIG-based power plant connected to the IEEE 39 Bus system.
Simulations performed in Matlab and SimPowerSystems are used to validate the
proposed design procedure.",2304.06555v1
2023-06-13,Particle-resolved study of the onset of turbulence,"The transition from laminar to turbulent flow is an immensely important topic
that is still being studied. Here we show that complex plasmas, i.e.,
microparticles immersed in a low temperature plasma, make it possible to study
the particle-resolved onset of turbulence under the influence of damping, a
feat not possible with conventional systems. We performed three-dimensional
(3D) molecular dynamics (MD) simulations of complex plasmas flowing past an
obstacle and observed 3D turbulence in the wake and fore-wake region of this
obstacle. We found that we could reliably trigger the onset of turbulence by
changing key parameters such as the flow speed and particle charge, which can
be controlled in experiments, and show that the transition to turbulence
follows the conventional pathway involving the intermittent emergence of
turbulent puffs. The power spectra for fully developed turbulence in our
simulations followed the -5/3 power law of Kolmogorovian turbulence in both
time and space. We demonstrate that turbulence in simulations with damping
occurs after the formation of shock fronts, such as bow shocks and Mach cones.
By reducing the strength of damping in the simulations, we could trigger a
transition to turbulence in an undamped system. This work opens the pathway to
detailed experimental and simulation studies of the onset of turbulence on the
level of the carriers of the turbulent interactions, i.e., the microparticles.",2306.07711v1
2023-07-10,Vibroacoustic simulations of acoustic damping materials using a fictitious domain approach,"The numerical investigation of acoustic damping materials, such as foams,
constitutes a valuable enhancement to experimental testing. Typically, such
materials are modeled in a homogenized way in order to reduce the computational
effort and to circumvent the need for a computational mesh that resolves the
complex micro-structure. However, to gain detailed insight into the acoustic
behavior, e.g., the transmittance of noise, such fully resolved models are
mandatory. The meshing process can still be avoided by using a ficticious
domain approach. We propose the finite cell method, which combines the
ficticious domain approach with high-order finite elements and resolves the
complex geometry using special quadrature rules. In order to take into account
the fluid-filled pores of a typical damping material, a coupled vibroacoustic
problem needs to be solved. To this end, we construct two separate finite cell
discretizations and prescribe coupling conditions at the interface in the usual
manner. The only difference to a classical boundary fitted approach to
vibroacoustics is that the fluid-solid interface is immersed into the
respective discretization and does not correspond to the element boundaries.
The proposed enhancement of the finite cell method for vibroacoustics is
verified based on a comparison with commercial software and used within an
exemplary application.",2307.04624v1
2023-07-12,A coupled rate-dependent/rate-independent system for adhesive contact in Kirchhoff-Love plates,"We perform a dimension reduction analysis for a coupled
rate-dependent/rate-independent adhesive-contact model in the setting of
visco-elastodynamic plates. We work with a weak solvability notion inspired by
the theory of (purely) rate-independent processes, and accordingly term the
related solutions `Semistable Energetic'. For Semistable Energetic solutions,
the momentum balance holds in a variational sense, whereas the flow rule for
the adhesion parameter is replaced by a semi-stability condition coupled with
an energy-dissipation inequality. Prior to addressing the dimension reduction
analysis, we show that Semistable Energetic solutions to the three-dimensional
damped adhesive contact model converge, as the viscosity term tends to zero, to
three-dimensional Semistable Energetic solutions for the undamped corresponding
system. We then perform a dimension reduction analysis, both in the case of a
vanishing viscosity tensor (leading, in the limit, to an undamped model), and
in the complementary setting in which the damping is assumed to go to infinity
as the thickness of the plate tends to zero. In both regimes, the presence of
adhesive contact yields a nontrivial coupling of the in-plane and out-of-plane
contributions. In the undamped scenario we obtain in the limit an
energy-dissipation inequality and a semistability condition. In the damped
case, instead, we achieve convergence to an enhanced notion of solution,
fulfilling an energy-dissipation balance.",2307.06327v1
2023-08-28,The Effects of Non-Equilibrium Velocity Distributions on Alfvén Ion-Cyclotron Waves in the Solar Wind,"In this work, we investigate how the complex structure found in solar wind
proton velocity distribution functions (VDFs), rather than the commonly assumed
two-component bi-Maxwellian structure, affects the onset and evolution of
parallel-propagating microinstabilities. We use the Arbitrary Linear Plasma
Solver (ALPS), a numerical dispersion solver, to find the real frequencies and
growth/damping rates of the Alfv\'en modes calculated for proton VDFs extracted
from Wind spacecraft observations of the solar wind. We compare this wave
behavior to that obtained by applying the same procedure to core-and-beam
bi-Maxwellian fits of the Wind proton VDFs. We find several significant
differences in the plasma waves obtained for the extracted data and
bi-Maxwellian fits, including a strong dependence of the growth/damping rate on
the shape of the VDF. By application of the quasilinear diffusion operator to
these VDFs, we pinpoint resonantly interacting regions in velocity space where
differences in VDF structure significantly affect the wave growth and damping
rates. This demonstration of the sensitive dependence of Alfv\'en mode behavior
on VDF structure may explain why the Alfv\'en ion-cyclotron instability
thresholds predicted by linear theory for bi-Maxwellian models of solar wind
proton background VDFs do not entirely constrain spacecraft observations of
solar wind proton VDFs, such as those made by the Wind spacecraft.",2308.14944v1
2023-08-31,Search for the gamma-ray spectral lines with the DAMPE and the Fermi-LAT observations,"Weakly interacting massive particles, as a major candidate of dark matter
(DM), may directly annihilate or decay into high-energy photons, producing
monochromatic spectral lines in the gamma-ray band. These spectral lines, if
detected, are smoking-gun signatures for the existence of new physics. Using
the 5 years of DAMPE and 13 years of Fermi-LAT data, we search for line-like
signals in the energy range of 3 GeV to 1 TeV from the Galactic halo. Different
regions of interest are considered to accommodate different DM density
profiles. We do not find any significant line structure, and the previously
reported line-like feature at $\sim$133 GeV is also not detected in our
analysis. Adopting a local DM density of $\rho_{\rm local}=0.4\,{\rm
GeV\,cm^{-3}}$, we derive 95% confidence level constraints on the
velocity-averaged cross-section of $\langle{\sigma v}\rangle_{\gamma\gamma}
\lesssim 4 \times 10^{-28}\,{\rm cm^{3}\,s^{-1}}$ and the decay lifetime of
$\tau_{\gamma\nu} \gtrsim 5 \times 10^{29}\,{\rm s}$ at 100 GeV, achieving the
strongest constraints to date for the line energies of 6-660 GeV. The
improvement stems from the longer Fermi-LAT data set used and the inclusion of
DAMPE data in the analysis. The simultaneous use of two independent data sets
could also reduce the systematic uncertainty of the search.",2308.16762v1
2023-09-06,Strong magnon-magnon coupling in an ultralow damping all-magnetic-insulator heterostructure,"Magnetic insulators such as yttrium iron garnets (YIGs) are of paramount
importance for spin-wave or magnonic devices as their ultralow damping enables
ultralow power dissipation that is free of Joule heating, exotic magnon quantum
state, and coherent coupling to other wave excitations. Magnetic insulator
heterostructures bestow superior structural and magnetic properties and house
immense design space thanks to the strong and engineerable exchange interaction
between individual layers. To fully unleash their potential, realizing low
damping and strong exchange coupling simultaneously is critical, which often
requires high quality interface. Here, we show that such a demand is realized
in an all-insulator thulium iron garnet (TmIG)/YIG bilayer system. The ultralow
dissipation rates in both YIG and TmIG, along with their significant spin-spin
interaction at the interface, enable strong and coherent magnon-magnon coupling
with a benchmarking cooperativity value larger than the conventional
ferromagnetic metal-based heterostructures. The coupling strength can be tuned
by varying the magnetic insulator layer thickness and magnon modes, which is
consistent with analytical calculations and micromagnetic simulations. Our
results demonstrate TmIG/YIG as a novel platform for investigating hybrid
magnonic phenomena and open opportunities in magnon devices comprising
all-insulator heterostructures.",2309.03116v1
2023-09-14,A new break near 10 TeV in the energy spectrum of protons according to data from space-based instruments: astrophysical interpretation,"Recent experimental data from space-based instruments of the DAMPE and CALET
collaborations have shown that the energy spectrum of protons has a new
feature, a break in the $\sim 10$ TeV region. In this energy range, the
spectrum index of the observed particles varies from $-2.6$ to $-2.9$.
  The purpose of this work is to establish the local sources's position and age
that determine this break, the index of the proton generation spectrum in them,
as well as the astrophysical interpretation of the results obtained in the
DAMPE and CALET experiments.
  Within the framework of the model of nonclassical diffusion of cosmic rays
developed by the authors, which has break due to the propagation of particles
in a sharply inhomogeneous (fractal type) galactic medium, it is shown that
break in this energy range is formed by tevatron located at a distance of $\sim
120$ pc from the Earth. These source, whose age is $\sim 5 \cdot 10^5$ years,
generate particles with a spectrum index $\sim 2.7$.
  The power-law behavior of the proton spectrum before and after the break,
soft spectrum of particles generation in the source, first obtained in the
DAMPE and CALET experiments, should be considered as an indication of the need
to revise the standard paradigm accepted today about the sources of cosmic
rays, mechanisms of particle acceleration in them and particles propagation in
the Galaxy.",2309.07420v1
2023-11-06,Phase mixing of propagating Alfv{é}n waves in a single-fluid partially ionized solar plasma,"Phase mixing of Alfven waves is one of the most promising mechanisms for
heating of the solar atmosphere. The damping of waves in this case requires
small transversal scales, relative to the magnetic field direction. Here this
requirement is achieved by considering a transversal inhomogeneity in the
equilibrium plasma density profile. Using a single fluid approximation of a
partially ionized chromospheric plasma we study the effectiveness of the
damping of phase mixed shear Alfven waves and investigate the effect of varying
the ionization degree on the dissipation of waves. Our results show that the
dissipation length of shear Alfven waves strongly depends on the ionization
degree of the plasma, but more importantly, in a partially ionized plasma, the
damping length of shear Alfven waves is several orders of magnitude shorter
than in the case of a fully ionized plasma, providing evidence that phase
mixing could be a large contributor to heating the solar chromosphere. The
effectiveness of phase mixing is investigated for various ionization degrees,
ranging from very weakly to very strongly ionized plasmas. Our results show
that phase mixed propagating Alfven waves in a partially ionized plasma with
ionization degrees in the range 0.518 to 0.657, corresponding to heights of
1916 to 2150 km above the solar surface, can provide sufficient heating to
balance chromospheric radiative losses in the quiet Sun.",2311.02989v1
2023-11-15,Damped Proximal Augmented Lagrangian Method for weakly-Convex Problems with Convex Constraints,"We give a damped proximal augmented Lagrangian method (DPALM) for solving
problems with a weakly-convex objective and convex linear/nonlinear
constraints. Instead of taking a full stepsize, DPALM adopts a damped dual
stepsize to ensure the boundedness of dual iterates. We show that DPALM can
produce a (near) $\vareps$-KKT point within $O(\vareps^{-2})$ outer iterations
if each DPALM subproblem is solved to a proper accuracy. In addition, we
establish overall iteration complexity of DPALM when the objective is either a
regularized smooth function or in a regularized compositional form. For the
former case, DPALM achieves the complexity of
$\widetilde{\mathcal{O}}\left(\varepsilon^{-2.5} \right)$ to produce an
$\varepsilon$-KKT point by applying an accelerated proximal gradient (APG)
method to each DPALM subproblem. For the latter case, the complexity of DPALM
is $\widetilde{\mathcal{O}}\left(\varepsilon^{-3} \right)$ to produce a near
$\varepsilon$-KKT point by using an APG to solve a Moreau-envelope smoothed
version of each subproblem. Our outer iteration complexity and the overall
complexity either generalize existing best ones from unconstrained or
linear-constrained problems to convex-constrained ones, or improve over the
best-known results on solving the same-structured problems. Furthermore,
numerical experiments on linearly/quadratically constrained non-convex
quadratic programs and linear-constrained robust nonlinear least squares are
conducted to demonstrate the empirical efficiency of the proposed DPALM over
several state-of-the art methods.",2311.09065v1
2023-12-07,Nonlinear aspects of stochastic particle acceleration,"In turbulent magnetized plasmas, charged particles can be accelerated to high
energies through their interactions with the turbulent motions. As they do so,
they draw energy from the turbulence, possibly up to the point where they start
modifying the turbulent cascade. Stochastic acceleration then enters a
nonlinear regime because turbulence damping back-reacts in turn on the
acceleration process. This article develops a phenomenological model to examine
this situation in detail and to explore its consequences for the particle and
turbulent energy spectra. We determine a criterion that specifies the threshold
of nonthermal particle energy density and the characteristic momentum beyond
which back-reaction becomes effective. Once the back-reaction sets in, the
turbulence cascade becomes damped below a length scale that keeps increasing in
time. The accelerated particle momentum distribution develops a near power-law
of the form ${\rm d}n/{\rm d}p\propto p^{-s}$ with $s\sim2$ beyond the momentum
at which back-reaction first sets in. At very high energies, where the
gyroradius of accelerated particles becomes comparable to the outer scale of
the turbulence, the energy spectrum can display an even harder spectrum with
$s\sim 1.3-1.5$ over a short segment. The low-energy part of the spectrum,
below the critical momentum, is expected to be hard ($s\sim 1$ or harder), and
shaped by any residual acceleration process in the damped region of the
turbulence cascade. This characteristic broken power-law shape with $s\sim 2$
at high energies may find phenomenological applications in various high-energy
astrophysical contexts.",2312.04443v2
2023-12-12,Circularization in the damped Kepler problem,"In this paper, we revisit the damped Kepler problem within a general family
of nonlinear damping forces with magnitude $\delta \vert u\vert^{\beta}\vert
\dot u\vert^{\alpha+1}$, depending on three parameters $\delta>0,\alpha\ge 0$
and $\beta\ge 0$, and address the general question of circularization whereby
orbits tend to become more circular as they approach the sun. Our approach is
based on dynamical systems theory, using blowup and desingularization as our
main technical tools. We find that $\gamma=\alpha+2\beta-3$ is an important
quantity, with the special case $\gamma=0$ separating circularization
($-3<\gamma<0$) where the eccentricity converges to zero, i.e. $e(t)\rightarrow
0$ as $u(t)\rightarrow 0$, from cases ($\gamma>0$) where $e(t)\rightarrow 1$ as
$u(t)\rightarrow 0$, both on open sets of initial conditions. We find that
circularization for $-3<\gamma<0$ occurs due to asymptotic stability of a
zero-Hopf equilibrium point (i.e., the eigenvalues are $\pm i \omega,0$) of a
three-dimensional reduced problem (which is analytic in the blowup
coordinates). The attraction is therefore not hyperbolic and in particular not
covered by standard dynamical systems theory. Instead we use recent results on
normal forms of the zero-Hopf to locally bring the system into a form where the
stability can be addressed directly. We believe that our approach can be used
to describe unbounded solutions.",2312.07249v1
2023-12-21,Annealing reduces Si$_3$N$_4$ microwave-frequency dielectric loss in superconducting resonators,"The dielectric loss of silicon nitride (Si$_3$N$_4$) limits the performance
of microwave-frequency devices that rely on this material for sensing, signal
processing, and quantum communication. Using superconducting resonant circuits,
we measure the cryogenic loss tangent of either as-deposited or
high-temperature annealed stoichiometric Si$_3$N$_4$ as a function of drive
strength and temperature. The internal loss behavior of the electrical
resonators is largely consistent with the standard tunneling model of two-level
systems (TLS), including damping caused by resonant energy exchange with TLS
and by the relaxation of non-resonant TLS. We further supplement the TLS model
with a self-heating effect to explain an increase in the loss observed in
as-deposited films at large drive powers. Critically, we demonstrate that
annealing remedies this anomalous power-induced loss, reduces the
relaxation-type damping by more than two orders of magnitude, and reduces the
resonant-type damping by a factor of three. Employing infrared absorption
spectroscopy, we find that annealing reduces the concentration of hydrogen in
the Si$_3$N$_4$, suggesting that hydrogen impurities cause substantial
dissipation.",2312.13504v1
2024-01-11,Instability windows of relativistic r-modes,"The detectability of the gravitational-wave signal from $r$-modes depends on
the interplay between the amplification of the mode by the CFS instability and
its damping due to dissipative mechanisms present in the stellar matter. The
instability window of $r$-modes describes the region of stellar parameters
(angular velocity, $\Omega$, and redshifted stellar temperature, $T^\infty$),
for which the mode is unstable. In this study, we reexamine this problem in
nonbarotropic neutron stars, taking into account the previously overlooked
nonanalytic behavior (in $\Omega$) of relativistic $r$-modes and enhanced
energy dissipation resulting from diffusion in superconducting stellar matter.
We demonstrate that at slow rotation rates, relativistic $r$-modes exhibit
weaker amplification by the CFS instability compared to Newtonian ones.
However, their dissipation through viscosity and diffusion is significantly
more efficient. In rapidly rotating neutron stars within the framework of
general relativity, the amplification of $r$-modes by the CFS mechanism and
their damping due to shear viscosity become comparable to those predicted by
Newtonian theory. In contrast, the relativistic damping of the mode by
diffusion and bulk viscosity remains significantly stronger than in the
nonrelativistic case. Consequently, account for diffusion and general
relativity leads to a substantial modification of the $r$-mode instability
window compared to the Newtonian prediction. This finding is important for the
interpretation of observations of rotating neutron stars, as well as for
overall understanding of $r$-mode physics.",2401.06200v1
2024-02-02,Controllable frequency tunability and parabolic-like threshold current behavior in spin Hall nano-oscillators,"We investigate the individual impacts of critical magnetodynamical
parameters-effective magnetization and magnetic damping-on the auto-oscillation
characteristics of nano-constriction-based Spin Hall Nano-Oscillators (SHNOs).
Our micromagnetic simulations unveil a distinctive non-monotonic relationship
between current and auto-oscillation frequency in out-of-plane magnetic fields.
The influence of effective magnetization on frequency tunability varies with
out-of-plane field strengths. At large out-of-plane fields, the frequency
tunability is predominantly governed by effective magnetization, achieving a
current tunability of 1 GHz/mA-four times larger than that observed at the
lowest effective magnetization. Conversely, at low out-of-plane fields,
although a remarkably high-frequency tunability of 4 GHz/mA is observed, the
effective magnetization alters the onset of the transition from a linear-like
mode to a spin-wave bullet mode. Magnetic damping primarily affects the
threshold current with negligible impact on auto-oscillation frequency
tunability. The threshold current scales linearly with increased magnetic
damping at a constant out-of-plane field but exhibits a parabolic behavior with
variations in out-of-plane fields. This behavior is attributed to the
qualitatively distinct evolution of the auto-oscillation mode across different
out-of-plane field values. Our study not only extends the versatility of SHNOs
for oscillator-based neuromorphic computing with controllable frequency
tunability but also unveils the intricate auto-oscillation dynamics in
out-of-plane fields.",2402.01570v1
2024-02-06,The fermion self-energy and damping rate in a hot magnetized plasma,"We derive a general expression for the fermion self-energy in a hot
magnetized plasma by using the Landau-level representation. In the one-loop
approximation, the Dirac structure of the self-energy is characterized by five
different functions that depend on the Landau-level index $n$ and the
longitudinal momentum $p_z$. We derive general expressions for all five
functions and obtain closed-form expressions for their imaginary parts. The
latter receive contributions from three types of on-shell processes, which are
interpreted in terms of Landau-level transitions, accompanied by a single
photon (gluon) emission or absorption. By making use of the imaginary parts of
the self-energy functions, we also derive the Landau-level dependent fermion
damping rates $\Gamma_{n}(p_z)$ and study them numerically in a wide range of
model parameters. We also demonstrate that the two-spin degeneracy of the
Landau levels is lifted by the one-loop self-energy corrections. While the spin
splitting of the damping rates is small, it may be important for some spin and
chiral effects. We argue that the general method and the numerical results for
the rates can have interesting applications in heavy-ion physics, astrophysics,
and cosmology, where strongly magnetized QED or QCD plasmas are ubiquitous.",2402.04307v2
2024-03-18,Radiative loss and ion-neutral collisional effects in astrophysical plasmas,"In this paper we study the role of radiative cooling in a two-fluid model
consisting of coupled neutrals and charged particles. We first analyze the
linearized two-fluid equations where we include radiative losses in the energy
equation for the charged particles. In a 1D geometry for parallel propagation
and in the limiting cases of weak and strong coupling, it can be shown
analytically that the instability conditions for the thermal mode and the sound
waves, the isobaric and isentropic criteria, respectively, remain unchanged
with respect to one-fluid radiative plasmas. For the parameters considered in
this paper, representative for the solar corona, the radiative cooling produces
growth of the thermal mode and damping of the sound waves. When neutrals are
included and are sufficiently coupled to the charges, the thermal mode growth
rate and the wave damping both reduce by the same factor, which depends on the
ionization fraction only. For a heating function which is constant in time, we
find that the growth of the thermal mode and the damping of the sound waves are
slightly larger. The numerical calculation of the eigenvalues of the general
system of equations in a 3D geometry confirm the analytic results. We then run
2D fully nonlinear simulations which give consistent results: a higher
ionization fraction or lower coupling will increase the growth rate. The
magnetic field contribution is negligible in the linear phase.
Ionization-recombination effects might play an important role because the
radiative cooling produces a large range of temperatures in the system. In the
numerical simulation, after the first condensation phase, when the minimum
temperature is reached, the fraction of neutrals increases four orders of
magnitude because of the recombination.",2403.11900v1
2024-04-02,A new gap in the critical exponent for semi-linear structurally damped evolution equations,"Our aim in this paper is to discuss the critical exponent in semi-linear
structurally damped wave and beam equations with additional dispersion term.
The special model we have in mind is $$
u_{tt}(t,x)+(-\Delta)^{\sigma}u(t,x)+(-\Delta)^{2\delta}u(t,x)+2(-\Delta)^{\delta}u_{t}(t,x)=\left|u(t,x)\right|
^{p} $$ where the initial displacement $u(0,x)=u_{0}(x)$, the initial velocity
$u_{t}(0,x)=u_{1}(x)$ and the parameters $ t\in [0,\infty)$, $x\in
\mathbb{R}^{n}$, $\sigma\geq 1$, $\delta\in(0,\frac{\sigma}{2})$, $p>1$. The
solution to the linear equation at low frequency region involves an interplay
of diffusion and oscillation phenomena represented by a real-complex Fourier
multiplier of the form $$m(t,\xi)=\frac{e^{-|\xi|^{2\delta}t\pm
i|\xi|^{\sigma}t}}{2i|\xi|^{\sigma}}, \ \ \xi\in \mathbb{R}^{n}, \ \
i=\sqrt{-1}.$$ The scaling argument shows that the diffusive part leads to
faster decay rates compared to the oscillatory one. This interplay creates a
new gap in the critical exponent between the blow up (in finite time) result
when $1<p<1+\frac{4\delta}{n-2\delta}$ (sub-critical case) and the global (in
time) existence result when $p>1+\frac{\sigma+2\delta}{n-\sigma}$
(super-critical case). We leave an open to show if this gap will be closed at
least in low or high space dimensions because, to the best of authors
knowledge, the necessary Fourier multiplier that leads to the sub-critical case
does not explicitly appear in $m(t,\xi)$.",2404.01544v1
1999-07-23,Autoregressive model of 1/f noise,"An analytically solvable model is proposed exhibiting 1/f spectrum in any
desirably wide range of frequency (but excluding the point f=0). The model
consists of pulses whose recurrence times obey an autoregressive process with
very small damping.",9907008v1
1996-08-22,Evolution of Neutral Gas at High Redshift -- Implications for the Epoch of Galaxy Formation,"Though observationally rare, damped Lya absorption systems dominate the mass
density of neutral gas in the Universe. Eleven high redshift damped Lya systems
covering 2.8<z<4.4 were discovered in 26 QSOs from the APM z>4 QSO Survey,
extending these absorption system surveys to the highest redshifts currently
possible. Combining our new data set with previous surveys we find that the
cosmological mass density in neutral gas, omega_g, does not rise as steeply
prior to z~2 as indicated by previous studies. There is evidence in the
observed omega_g for a flattening at z~2 and a possible turnover at z~3. When
combined with the decline at z>3.5 in number density per unit redshift of
damped systems with column densities log N(HI)>21 atoms cm^-2, these results
point to an epoch at z>3 prior to which the highest column density damped
systems are still forming. We find that over the redshift range 2<z<4 the total
mass in neutral gas is marginally comparable with the total visible mass in
stars in present day galaxies. However, if one considers the total mass visible
in stellar disks alone, ie excluding galactic bulges, the two values are
comparable. We are observing a mass of neutral gas comparable to the mass of
visible disk stars. Lanzetta, Wolfe & Turnshek (1995) found that omega_g(z~3.5)
was twice omega_g(z~2), implying a much larger amount of star formation must
have taken place between z=3.5 and z=2 than is indicated by metallicity
studies. This created a `cosmic G-dwarf problem'. The more gradual evolution of
omega_g we find alleviates this. These results have profound implications for
theories of galaxy formation.",9608147v1
1997-07-14,Damped Lyman-alpha Absorption Associated with an Early-Type Galaxy at Redshift z = 0.16377,"We report new HST and ground-based observations of a damped Lyman-alpha
absorption system toward the QSO 0850+4400. The redshift of the absorption
system is z = 0.163770 and the neutral hydrogen column density of the
absorption system is log N = 19.81 cm**-2. The absorption system is by far the
lowest redshift confirmed damped Lyman-alpha absorption system yet identified,
which provides an unprecedented opportunity to examine the nature, impact
geometry, and kinematics of the absorbing galaxy in great detail. The
observations indicate that the absorption system is remarkable in three
respects: First, the absorption system is characterized by weak metal
absorption lines and a low metal abundance, possibly less than 4% of the solar
metal abundance. This cannot be explained as a consequence of dust, because the
neutral hydrogen column density of the absorption system is far too low for
obscuration by dust to introduce any significant selection effects. Second, the
absorption system is associated with a moderate-luminosity early-type S0
galaxy, although the absorption may actually arise in one of several very faint
galaxies detected very close to the QSO line of sight. Third, the absorbing
material moves counter to the rotating galaxy disk, which rules out the
possibility that the absorption arises in a thin or thick co-rotating gaseous
disk. These results run contrary to the expectation that low-redshift damped
Lyman-alpha absorption systems generally arise in the gas- and metal-rich inner
parts of late-type spiral galaxies. We suggest instead that mounting evidence
indicates that low-redshift galaxies of a variety of morphological types may
contain significant quantities of low metal abundance gas at large
galactocentric distances.",9707157v1
1997-08-27,Reionization of the Intergalactic Medium and the Damping Wing of the Gunn-Peterson Trough,"Observations of high-redshift quasars show that the IGM must have been
reionized at some redshift $z>5$. If a source of radiation could be observed at
the rest-frame Lya wavelength, at a sufficiently high redshift where some of
the IGM in the line-of-sight was not yet reionized, the Gunn-Peterson trough
should be present. Longward of the Lya wavelength, a damping wing should be
observed caused by the neutral IGM whose absorption profile can be predicted.
Measuring the shape of this damping wing would provide irrefutable evidence of
the observation of the IGM before reionization, and a determination of the
density of the neutral IGM. This measurement might be hindered by the possible
presence of a dense absorption system associated with the source.
  Shortward of the \lya wavelength, absorption should be seen from the patchy
structure of the IGM in the process of reionization. We show that a complete
Gunn-Peterson trough is most likely to continue to be observed through the
epoch where the IGM is partially ionized. The damping wings of the neutral
patches should overlap if the proper pathlength through an ionized region is
less than 1 h^{-1} Mpc; even in larger ionized regions, the characteristic
background intensity should be low enough to yield a very high optical depth
due to the residual neutral fraction, although occasionally some flux may be
transmitted through large, underdense voids within an ionized region. The case
of the HeII reionization is also discussed, and we argue that helium was
already doubly ionized by z=3 throughout the IGM.
  The recently discovered afterglows of gamma-ray bursts might soon be observed
at very high redshifts. Their featureless continuum spectrum and high
luminosities make them ideal sources for studying absorption by the IGM.",9708253v1
1997-09-16,On the nature of z(abs) ~ z(em) damped absorbers in quasar spectra,"We present spectroscopic observations of the damped Ly-alpha absorber at
redshift z=1.9342 seen in the spectrum of the quasar Q0151+048A. The redshift
of the absorber is greater than the redshift of the quasar, so the system
resembles the z(abs) ~ z(em) damped absorber at z=2.81 towards the quasar
PKS0528-250. We have previously reported the detection of Ly-alpha emission
from the latter absorber, one of only two damped absorbers for which Ly-alpha
emission has unambiguously been detected. The resemblance between the
PKS0528-250 and Q0151+048A systems is made closer by the detection of a weak
emission feature in the trough of the Q0151+048A absorber. This leads us to
consider whether these z(abs) ~ z(em) DLA absorbers are different objects to
the intervening DLA absorbers. Two possibilities are examined and rejected.
Firstly the Q0151+048A and PKS0528-250 z(abs) ~ z(em) absorbers appear to be
unrelated to the intrinsic absorbers (i.e. gas close to the quasar nucleus,
ejected by the quasar), as intrinsic absorbers are of higher metallicity, have
higher ionisation parameter, and show complex absorption profiles. Secondly
these two DLA absorbers cannot be equated with the gaseous disks of the quasar
host galaxies, as the absorber redshifts differ significantly from the quasar
systemic redshifts. It is likely, then, that intrinsically the z(abs) ~ z(em)
DLA absorbers are the same as the intervening DLA absorbers, so that
peculiarities in some of the z(abs) ~ z(em) absorbers can be ascribed to their
different environment i.e. proximity to the quasar, or membership of the same
cluster as the quasar. We point out that the proximity effect may play some
role, by reducing the Ly-alpha forest line blanketing of any Ly-alpha emission
line from z(abs) ~ z(em) absorbers.",9709160v1
1998-01-15,A HST Spectroscopic study of QSOs with intermediate redshift damped Lyman-alpha systems,"We present HST spectra for a sample of six QSOs with intermediate redshift
(z_a < 1) damped Ly-alpha systems. These observations aim at measuring the HI
column density and detect metal lines in order to investigate the metal
enrichment of the gas, as well as the presence of neutral species, molecules
and dust. All systems selected on the basis of 21 cm absorption and/or strong
FeII lines relative to MgII ones turn out to have N(HI) larger than 10^20 cm-2.
It appears that although the scatter of metallicities is as large at z_a<1 as
at high redshift, an increasing proportion of systems with metallicities ~ 30%
solar are found when going at lower redshifts. Our results suggest that
available observations may be biased against dust-rich absorbers. Further, when
all available measurements of N(HI) and [Zn/H] are considered, a clear
deficiency of systems with large N(HI) and high metallicity is apparent. We
conclude that dust extinction causes a preferential selection of QSOs with
intervening gas relatively poor in metals, dust and molecules. As a
consequence, the high end of the HI column density distribution (and hence
Omega_g, the contribution of neutral gas to the cosmological mass density) is
probably more heavily underestimated than previously thought, especially at low
redshift. Such a bias could also explain the high incidence of non-spiral
morphologies in our sample. We stress that observation of a larger sample of
low z damped Ly-alpha systems as well as surveys of damped Ly-alpha systems in
fainter QSOs would give a more representative view of the true diversity of
absorber properties and should help to probe the denser phases of the
interstellar medium in distant galaxies.",9801146v1
1998-06-15,On the kinematics of damped Lyman-alpha systems,"We report on high spectral resolution observations of five damped Ly-alpha
absorbers. Line velocity profiles and heavy element abundances are discussed.
Nitrogen is found to have abundances less than silicon in the systems toward Q
0347-383, Q 0913+072, and Q 1213+093. The absorber toward Q 0913+072 is the
most metal-deficient damped system known, with [Fe/H] < -3.2. The simple
kinematical structure of the metal absorptions makes this system ideal to
discuss the [O/Si] and [N/O] ratios. We find [O/H] ~ -2.7 and -2.7 < [Si/H] <
-2.2. By combining these data with information gathered in the literature, we
study the kinematics of the low and high ionization phases in a sample of 26
damped Ly-alpha systems in the redshift range 1.17-4.38. We note a strong
correlation between the velocity broadenings of the SiII,1808 and FeII,1608
lines whatever the line optical depth, implying that the physical conditions
are quite homogeneous in the sample. Statistically this shows that large
variations of abundance ratios and thus large variations of depletion into dust
grains are unlikely. The velocity broadening of the absorption lines, Delta V,
is correlated with the asymmetry of the lines for Delta V < 150 km/s. The
broader the line the more asymmetric it is, as expected in case rotation
dominates the line broadening. However this correlation does not hold for
larger Delta V suggesting that evidence for rotational motions is restricted to
velocity broadenings Delta V < 150 km/s. The systems with Delta V > 200 km/s
are peculiar with kinematics consistent with random motions. They show
sub-systems as those expected if the objects are in the process of merging
(abridged).",9806202v1
1999-10-07,Si and Mn Abundances in Damped Lya Systems with Low Dust Content,"We have measured the abundances of Zn, Si, Mn, Cr, Fe, and Ni in three damped
Lyman alpha systems at redshifts z < 1 from high resolution echelle spectra of
QSOs recorded with the Keck I telescope. In all three cases the abundances of
Cr, Fe, and Ni relative to Zn indicate low levels of dust depletions. We
propose that when the proportion of refractory elements locked up in dust
grains is less than about 50 percent, it is plausible to assume an
approximately uniform level of depletion for all grain constituents and, by
applying a small dust correction, recover the intrisic abundances of Si and Mn.
We use this approach on a small sample of damped systems for which it is
appropriate, with the aim of comparing the metallicity dependence of the ratios
[Si/Fe] and [Mn/Fe] with analogous measurements in Milky Way stars. The main
conclusion is that the relative abundances of both elements in distant galaxies
are broadly in line with expectations based on Galactic data. Si displays a
mild enhancement at low metallicities, as expected for an alpha-capture
element, but there are also examples of near-solar [Si/Fe] at [Fe/H] < -1. The
underabundance of Mn at low metallicities is possibly even more pronounced than
that in metal-poor stars, and no absorption system has yet been found where
[Mn/Fe] is solar. The heterogeneous chemical properties of damped Lyman alpha
systems, evident even from this limited set of measurements, provide further
support for the conclusion from imaging studies that a varied population of
galaxies gives rise to this class of QSO absorbers.",9910131v1
1999-11-23,On the orbital evolution and growth of protoplanets embedded in a gaseous disc,"We present a new computation of the linear tidal interaction of a
protoplanetary core with a thin gaseous disc in which it is fully embedded. For
the first time a discussion of the orbital evolution of cores with eccentricity
(e) significantly larger than the gas-disc scale height to radius ratio (H/r)
is given. We find that the direction of orbital migration reverses for
e>1.1H/r. This occurs as a result of the orbital crossing of resonances in the
disc that do not overlap the orbit when the eccentricity is very small. Simple
expressions giving approximate fits to the eccentricity damping rate and the
orbital migration rate are presented. We go on to calculate the rate of
increase of the mean eccentricity for a system of protoplanetary cores due to
dynamical relaxation. By equating the eccentricity damping time-scale with the
dynamical relaxation time-scale we deduce that an equilibrium between
eccentricity damping and excitation through scattering is attained on a 10^3 to
10^4 yr time-scale, at 1au. The equilibrium thickness of the protoplanet
distribution is such that it is generally well confined within the gas disc. By
use of a three dimensional N-body code we simulate the evolution of a system of
protoplanetary cores, incorporating our eccentricity damping and migration
rates. Assuming that collisions lead to agglomeration, we find that the
vertical confinement of the protoplanet distribution permits cores to build up
from 0.1 to 1 earth mass in only ~10^4 yr, within 1au. The time-scale required
to achieve this is comparable to the migration time-scale. We deduce that it is
not possible to build up a massive enough core to form a gas giant planet
before orbital migration ultimately results in the preferential delivery of all
such bodies to the neighbourhood of the central star. [Abridged]",9911431v1
1999-12-14,Finding typical high redshift galaxies with the NOT,"We present results from an ongoing search for galaxy counterparts of a
subgroup of Quasar Absorption Line Systems called Damped Ly-alpha Absorbers
(DLAs). DLAs have several characteristics that make them prime candidates for
being the progenitors of typical present day galaxies.",9912278v1
2000-10-21,UVES observations of QSO 0000-2620: Argon and Phosphorus abundances in the dust-free damped Ly-alpha system at zabs = 3.3901,"The UV resonance transitions of neutral argon ArI 1066 A, and of singly
ionized phosphorus PII 963 A, originated in the damped Ly_alpha system (DLA) at
zabs = 3.3901 towards QSO 0000--2620 have been detected by means of the UVES
spectrograph at the 8.2m ESO KUEYEN telescope. So far, this is the first
measurement of ArI, and the second of PII, ever performed in damped galaxies
and in high redshift objects. This DLA is well known for having one of the
lowest metal abundances and dust content, and the lowest fractional abundance
of molecular hydrogen H_2. The measured Ar abundance is [Ar/H] = - 1.91 (+/-
0.09) which is equal to the abundances of the other alpha-chain elements (O, S
and Si). The similarity of the Ar abundance with the other alpha-chain elements
implies the absence of significant photoionization by either UV background or
stellar sources along the sightline throughout the damped Ly_alpha system. Both
log(Ar/O) and log(Ar/S) ratios are found close to those measured in the
extragalactic HII regions and in blue compact galaxies where O is more abundant
by at least one order of magnitude. This strengthens the universality of the
Ar/O and Ar/S ratios and lends support to the existence of a universal IMF. The
abundance of the non-refractory element phosphorus [P/H] = - 2.31 (+/- 0.10)
confirms the low amount of chemical evolution in the DLA. This is the
measurement of P in the most metal-poor material and shows a subsolar [P/Fe] =
--0.27 value. The measured ratios [P/Si] = - 0.40 (+/- 0.13) and [P/S] = - 0.33
(+/- 0.13) provide evidence for a mild odd-even effect. Finally, a stringent
upper limit to the population of the 3P_1 level in the ground state of OI is
derived, which provides a lower limit to the physical dimensions of the zabs =
3.3901 system of L > 7 pc.",0010434v1
2001-09-21,Coincidences of high density peaks in UVES spectra of QSO pairs,"We present preliminary results of an investigation of the clustering
properties of high matter density peaks between redshift ~2 and ~3, as traced
by Lyman limit and Damped Ly-alpha systems in spectra of close QSO pairs and
groups.",0109373v1
2002-01-31,Electron impact excitation of helium-like oxygen up to n = 4 levels including radiation damping,"The primary X-ray diagnostic lines in He-like ions are mainly excited by
electron impact from the ground level to the n = 2 levels, but at high
temperatures n > 2 levels are also excited. In order to describe the atomic
processes more completely collision strengths are computed for OVII including
for the first time all of the following: (i) relativistic fine structure, (ii)
levels up to the n = 4, and (iii) radiation damping of autoionizing resonances.
The calculations are carried out using the Breit-Pauli R-matrix (BPRM) method
with a 31-level eigenfunction expansion. Resonance structures in collision
strengths are delineated in detail up to the n = 4 thresholds. For highly
charged He-like ions radiation damping of autoionizing resonances is known to
be significant. We investigate this effect in detail and find that while
resonances are discernibly damped radiatively as the series limit n --> infty
is approached from below, the overall effect on effective cross sections and
rate coefficients is found to be very small. Collision strengths for the
principal lines important in X-ray plasma diagnostics, w,x,y and z,
corresponding to the 4 transitions to the ground level 1s^2 (^1S_0) <-- 1s2p
(^1P^o_1), 1s2p (^3P^o_2), 1s2p (^3P^o_1), 1s2s (^3S_1), are explicitly shown.
It is found that the effective collision strength of the forbidden z-line is up
to a factor of 4 higher at T < 10^6 K than previous values. This is likely to
be of considerable importance in the diagnostics of photoionized astrophysical
plasmas. Significant differences are also found with previous works for several
other transitions. This work is carried out as part of the Iron Project-RmaX
Network.",0201535v1
2002-12-07,Improved Bounds on Violation of the Strong Equivalence Principle,"I describe a unique, 20-year-long timing program for the binary pulsar
B0655+64, the stalwart control experiment for measurements of gravitational
radiation damping in relativistic neutron-star binaries. Observed limits on
evolution of the B0655+64 orbit provide new bounds on the existence of dipolar
gravitational radiation, and hence on violation of the Strong Equivalence
Principle.",0212180v1
2004-04-13,The Fine-structure Constant as a Probe of Chemical Evolution and AGB Nucleosynthesis in Damped Lyman-alpha Systems,"Evidence from a large sample of quasar absorption-line spectra in damped
Lyman-alpha systems has suggested a possible time variation of the fine
structure constant alpha. The most statistically significant portion of this
sample involves the comparison of Mg and Fe wavelength shifts using the
many-multiplet (MM) method. However, the sensitivity of this method to the
abundance of heavy isotopes, especially Mg, is enough to imitate an apparent
variation in alpha in the redshift range 0.5 < z < 1.8. We implement recent
yields of intermediate mass (IM) stars into a chemical evolution model and show
that the ensuing isotope distribution of Mg can account for the observed
variation in alpha provided the early IMF was particularly rich in intermediate
mass stars (or the heavy Mg isotope yields from AGB stars are even higher than
in present-day models). As such, these observations of quasar absorption
spectra can be used to probe the nucleosynthetic history of low-metallicity
damped Lyman-alpha systems in the redshift range 0.5 < z < 1.8. This analysis,
in conjunction with other abundance measurements of low-metallicity systems,
reinforces the mounting evidence that star formation at low metallicities may
have been strongly influenced by a population of IM stars. Such IM stars have a
significant influence on other abundances, particularly nitrogen. We constrain
our models with independent measurements of N, Si, and Fe in damped Lyman-alpha
systems as well as C/O in low-metallicity stars. In this way, we obtain
consistent model parameters for this chemical-evolution interpretation of the
MM method results.",0404257v2
2006-01-23,"Bulk viscosity of a gas of neutrinos and coupled scalar particles, in the era of recombination","Bulk viscosity may serve to damp sound waves in a system of neutrinos coupled
to very light scalar particles, in the era after normal neutrino decoupling but
before recombination. We calculate the bulk viscosity parameter in a minimal
scheme involving the coupling of the two systems. We add some remarks on the
bulk viscosity of a system of fully ionized hydrogen plus photons.",0601525v1
2006-09-28,Turbulent Comptonization in Relativistic Accretion Disks,"Turbulent Comptonization, a potentially important damping and radiation
mechanism in relativistic accretion flows, is discussed. Particular emphasis is
placed on the physical basis, relative importance, and thermodynamics of
turbulent Comptonization. The effects of metal-absorption opacity on the
spectral component resulting from turbulent Comptonization is considered as
well.",0609797v1
1994-05-16,Bifurcations of two coupled classical spin oscillators,"Two classical, damped and driven spin oscillators with an isotropic exchange
interaction are considered. They represent a nontrivial physical system whose
equations of motion are shown to allow for an analytic treatment of local
codimension 1 and 2 bifurcations. In addition, numerical results are presented
which exhibit a Feigenbaum route to chaos.",9405011v1
1998-04-02,The Decay Properties of the Finite Temperature Density Matrix in Metals,"Using ordinary Fourier analysis, the asymptotic decay behavior of the density
matrix F(r,r') is derived for the case of a metal at a finite electronic
temperature. An oscillatory behavior which is damped exponentially with
increasing distance between r and r' is found. The decay rate is not only
determined by the electronic temperature, but also by the Fermi energy. The
theoretical predictions are confirmed by numerical simulations.",9804013v1
1998-12-02,Dissipative properties of vibrated granular materials,"We investigate collective dissipative properties of vibrated granular
materials by means of molecular dynamics simulations. Rates of energy losses
indicate three different regimes or ""phases""in the amplitude-frequency plane of
the external forcing, namely, solid, convective, and gas-like regimes. The
behavior of effective damping decrement in the solid regime is glassy.
Practical applications are dicussed.",9812036v1
1999-01-14,Spin dynamics in the generalized ferromagnetic Kondo model for manganites,"Dynamical spin susceptibility is calculated for the generalized ferromagnetic
Kondo model which describes itinerant $e_{g}$ electrons interacting with
localized $t_{2g}$ electrons with antiferromagnetic coupling. The calculations
done in the mean field approximation show that the spin-wave spectrum of the
system in ferromagnetic state has two branches, acoustic and optic ones.
Self-energy corrections to the spectrum are considered and the acoustic
spin-wave damping is evaluated.",9901141v1
1999-10-01,Properties of excitations in systems with a spinor Bose-Einstein condensate,"General theory in case of homogenous Bose-Einstein condensed systems with
spinor condensate is presented for the correlation functions of density and
spin fluctuations and for the one-particle propagators as well. The random
phase approximation is investigated and the damping of the modes is given in
the intermediate temperature region. It is shown that the collective and the
one-particle excitation spectra do not coincide fully.",9910010v1
2001-07-16,Anomalous Levy decoherence,"We investigate the decoherence of a small quantum system weakly coupled to a
complex, chaotic environment when the dynamics is not Gaussian but Levy
anomalous. By studying the time dependence of the linear entropy and the
damping of the interference of two Gaussian wave packets in the Wigner
representation, we show that the decoherence time for a quantum Levy stable
process is always smaller than for Gaussian diffusion.",0107344v1
2001-09-05,Nuclear resonant scattering of Synchrotron radiation from nuclei in the Browninan motion,"The time evolution of the coherent forward scattering of Synchrotron
radiation for resonant nuclei in Brownian motion is studied . Apart from target
thickness, the appearance of dynamical beats also depends on $\alpha$ which is
the ratio of harmonic force constant to the damping force constant of a
harmonic oscillator undergoing Brownian motion.",0109074v2
2002-03-06,Effect of electron-phonon interaction on the shift and attenuation of optical phonons,"Using the Boltzmann equation for electrons in metals, we show that the
optical phonons soften and have a dispersion due to screening in agreement with
the results reported recently [M. Reizer, Phys. Rev. B {\bf 61}, 40 (2000)].
Additional phonon damping and frequency shift arise when the electron--phonon
interaction is properly included.",0203112v1
2002-04-09,Spatial resolution of spin waves in an ultra-cold gas,"We present the first spatially resolved images of spin waves in a gas. The
complete longitudinal and transverse spin field as a function of time and space
is reconstructed. Frequencies and damping rates for a standing-wave mode are
extracted and compared with theory.",0204182v1
2002-08-14,Three-wave mixing of Bogoliubov quasi-particles in a Bose condensate,"A dressed basis is used to calculate the dynamics of three-wave mixing
between Bogoliubov quasi-particles in a Bose condensate. Due to the observed
oscillations between different momenta modes, an energy splitting, analogous to
the optical Mollow triplet, appears in the Beliaev damping spectrum of the
excitations from the oscillating modes.",0208283v2
2002-11-08,"Reply on ``Fluctuation-dissipation considerations for phenomenological damping models for ferromagnetic thin films'' [N. Smith, J. Appl. Phys. \bf{92}, 3877 (2002)]","We show that the critique of our recent papers presented in the
abovementioned paper (NS) appeals to an incorrect mathematical analogy between
electrical circuits and linear magnetization dynamics, improperly uses
classical concepts of normal modes and basic equations, gives inconsistent
results and therefore comes to incorrect conclusions.",0211147v1
2003-02-04,Squeezing and temperature measurement in Bose-Einstein Condensates,"In this paper we discuss the presence of temperature-dependent squeezing in
the collective excitations of trapped Bose-Einstein condensates, based on a
recent theory of quasiparticle damping. A new scheme to measure temperature
below the critical temperature is also considered.",0302068v1
2003-03-12,Time-Dependent Dynamics of the Bose-Fermi Mixed Condensed System,"We study the monopole oscillation in the bose-fermi mixed condensed system by
performing the time-dependent Gross-Pitaevsky (GP) and Vlasov equations. We
find that the big damping exists for the fermion oscillation in the mixed
system even at zero temperature",0303216v1
2005-10-06,Thermal processes induced in carbon nanotubes by attosecond laser pulses,"In this paper the heat transport in carbon nanotubes is investigated. When
the dimension of the structure is of the order of the de Broglie wave length
the transport phenomena must be analyzed within quantum mechanics. In this
paper we developed the Dirac type thermal equation. The solution of the
equation the temperature fields for electrons can be damped or can oscillate
depending on the dynamics of the scattering.",0510141v1
2006-09-05,Lifetimes of electrons in the Shockley surface state band of Ag(111),"We present a theoretical many-body analysis of the electron-electron (e-e)
inelastic damping rate $\Gamma$ of electron-like excitations in the Shockley
surface state band of Ag(111). It takes into account ab-initio band structures
for both bulk and surface states. $\Gamma$ is found to increase more rapidly as
a function of surface state energy E than previously reported, thus leading to
an improved agreement with experimental data.",0609080v1
2006-09-28,Transition-Event Durations in One Dimensional Activated Processes,"Despite their importance in activated processes, transition-event durations
-- which are much shorter than first passage times -- have not received a
complete theoretical treatment. We therefore study the distribution of
durations of transition events over a barrier in a one-dimensional system
undergoing over-damped Langevin dynamics.",0609741v1
2007-01-08,Coefficient of restitution for viscoelastic disks,"The dissipative collision of two identical viscoelastic disks is studied. By
using a known law for the elastic part of the interaction force and the
viscoelastic damping model an analytical solution for the coefficient of
restitution shall be given. The coefficient of restitution depends
significantly on the impact velocity. It approaches one for small velocities
and decreases for increasing velocities.",0701142v1
2007-01-09,Enhanced Weiss oscillations in graphene,"The magneto-conductivity of a single graphene layer where the electrons are
described by the Dirac Hamiltonian weakly modulated by a periodic potential is
calculated. It is shown that Weiss oscillations periodic in the inverse
magnetic field appear, that are more pronounced and less damped with the
increment of temperature as compared with the same oscillations in a typical
two-dimensional electron system with a standard parabolic energy spectrum.",0701175v1
2007-03-15,A new electromagnetic mode in graphene,"A new, weakly damped, {\em transverse} electromagnetic mode is predicted in
graphene. The mode frequency $\omega$ lies in the window
$1.667<\hbar\omega/\mu<2$, where $\mu$ is the chemical potential, and can be
tuned from radiowaves to the infrared by changing the density of charge
carriers through a gate voltage.",0703406v1
1997-04-01,Controversies in the History of the Radiation Reaction problem in General Relativity,"This paper examines the historical controversy over whether gravitationally
bound systems, such as binary stars, experienced orbital damping due to the
emission of gravitational radiation, focusing especially on the period of the
1950s, but also discussing the work of Einstein and Rosen in the 1930s on
cylindrical gravitational waves and the later quadrupole formula controversy.",9704002v1
2000-11-14,Binary black holes coalescence: transition from adiabatic inspiral to plunge,"Using two recent techniques giving non-perturbative re-summed estimates of
the damping and of the conservative part of the dynamics of two-body systems,
we describe the transition between adiabatic inspiral and plunge in binary
non-spinning black holes moving along quasi-circular orbits.",0011052v1
2004-06-24,Hawking temperature from quasi-normal modes,"A perturbed black hole has characteristic frequencies (quasi-normal modes).
Here I apply a quantum measurement analysis of the quasi-normal mode frequency
in the limit of high damping. It turns out that a measurement of this mode
necessarily adds noise to it. For a Schwarzschild black hole, this corresponds
exactly to the Hawking temperature. The situation for other black holes is
briefly discussed.",0406097v1
2005-08-10,Quasinormal modes of Unruh's Acoustic Black Hole,"We have studied the sound perturbation of Unruh's acoustic geometry and we
present an exact expression for the quasinormal modes of this geometry. We are
obtain that the quasinormal frequencies are pure-imaginary, that give a purely
damped modes.",0508040v2
2005-08-12,Self-similar and charged spheres in the diffusion approximation,"We study spherical, charged and self--similar distributions of matter in the
diffusion approximation. We propose a simple, dynamic but physically meaningful
solution. For such a solution we obtain a model in which the distribution
becomes static and changes to dust. The collapse is halted with damped mass
oscillations about the absolute value of the total charge.",0508055v1
2006-12-01,Quasinormal modes of gravitational perturbation around a Schwarzschild black hole surrounded by quintessence,"In this paper, the quasinormal modes of gravitational perturbation around a
Schwarzschild black hole surrounded by quintessence were evaluated by using the
third-order WKB approximation. Due to the presence of quintessence, the
gravitational wave damps more slowly.",0612009v1
1992-09-14,Lyapunov Exponent of SU(3) Gauge Theory,"The classical SU(3) gauge theory is shown to be deterministic chaotic. Its
largest Lyapunov exponent is dertermined, from which a short time scale of
thermalization of a pure gluon system is estimated. The connection to gluon
damping rate is discussed.",9209018v1
1993-06-11,Coherence and Decoherence in Radiation off Colliding Heavy Ions,"We discuss the kinetics of a disoriented chiral condensate, treated as an
open quantum system. We suggest that the problem is analogous to that of a
damped harmonic oscillator. Master equations are used to establish a hierarchy
of relevant time scales. Some phenomenological consequences are briefly
outlined.",9306260v1
1995-01-06,Thermal Two Point Function of a Heavy Muon in hot QED plasma within Bloch Nordsieck Approximation,"The thermal propagator of a heavy muon propagating in a hot QED plasma is
examined within the Bloch-Nordsieck approximation, which is valid in the
infrared region. It is shown that the muon damping rate is finite, in contrast
to the lower-order calculation with hard thermal loop resummations taken into
account.",9501223v1
1997-08-29,Numerical study of plasmon properties in the SU(2)-Higgs model,"We discuss an explorative computation of real time autocorrelation functions,
in the classical approximation. The results for the `plasmon' frequencies and
damping rates appear compatible with the divergencies expected from
perturbation theory.",9708493v1
1999-07-31,Structure of the Quark Propagator at High Temperature,"In the high temperature, chirally invariant phase of QCD, the quark
propagator is shown to have two sets of poles with different dispersion
relations. A reflection property in momentum space relates all derivatives at
zero-momentum of the particle and hole energies, the particle and hole damping
rates, and the particle and hole residues. No use is made of perturbation
theory.",9908204v1
1999-11-12,Covariant Perturbation Theory of Non-Abelian Kinetic Theory,"A double perturbation idea is presented in framework of the quark-gluon
plasma kinetic theory. A solvable set of equations from the 'double
perturbation' is derived and the equations are showed to be gauge-independent.
The formalism of Landau damping rate for the plasmon at zero momentum is given
and discussed.",9911325v2
2000-10-25,Resummation and damping in the O(N) model,"In this talk I summarize the one loop and higher loop calculations of the
effective equations of motion of the O(N) symmetric scalar model in the linear
response approximation. At one loop one finds essential difference in long time
behavior for the fields below and above a dynamically generated length scale. A
partial resummation assuming quasi-particle propagation seems to cancel the
relevance of this scale.",0010290v1
2001-07-16,A generating functional for ultrasoft amplitudes in hot QCD,"The effective amplitudes for gluon momentum p<<gT in hot QCD exhibit damping
as a result of collisions. The whole set of n-point amplitudes is shown to be
generated from one functional K(x,y;A), in addition to the induced current
j(x;A).",0107168v2
2004-11-01,Brane inflation with dark reheating,"In brane world scenarios inflationary vacuum energy may escape into the
higher dimensional bulk leaving behind a dark radiation effect on the brane.
The paper analyses the damping of an inflaton by massless bulk scalar radiation
and the production of dark radiation in a Randall-Sundrum type of model.",0411021v1
2005-04-14,Monopolonium in confining phase,"This paper has been withdrawn by the author(s), due the following reasons. A
similar system for a different purpose has already been studied in
Phys.Rev.D60:083001,1999 (astro-ph/9904315). Moreover, our analysis was wrong
because we have missed the large frictional forces that will rapidly damp out
the energy in the oscillating monopolonium system.",0504108v2
2005-06-03,MINT - A Simple Model for Low Energy Hadronic Interactions,"The bulk of inelastic hadronic interactions is characterized by longitudinal
phase space and exponentially damped transverse momentum spectra. A simple
model with only a single adjustable parameter is presented, making it a very
convenient tool for systematic studies, which gives a surprisingly good
description of pA-collisions at 920 GeV beam energy.",0506028v1
1996-05-17,Non-Abelian Kubo Formula and the Multiple Time-Scale Method,"The non-Abelian Kubo formula is derived from the kinetic theory. That
expression is compared with the one obtained using the eikonal for a
Chern-Simons theory. The multiple time-scale method is used to solve the
non-Abelian Kubo formula, and the damping rate for longitudinal color waves is
computed.",9605120v1
1996-10-02,Self-consistent determination of hard modes in hot QCD,"We determine self-consistently the hard-quark and hard-gluon modes in hot
QCD. The damping-rate part in resummed hard-quark or hard-gluon propagators,
rather than the thermal-mass part, plays the dominant role.",9610010v1
2000-11-06,Note on Open String/D-brane System and Noncommutative Soliton,"This is a summary of a series of papers hep-th/9910263,0005283,0010066
written with B. Chen, T. Matsuo and K. Murakami on a p-p', (p<p^{\prime}) open
string with B_{ij} field, which has led us to the explicit identification of
the Dp-brane with the noncommutative projector soliton via the gaussian damping
factor. A lecture given at Summer Institute 2000, FujiYoshida, Yamanashi,
Japan, at August 7-14, 2000.",0011028v1
2002-10-11,A simple mechanical analog of the field theory of tachyon matter,"In this brief note we show that the zero dimensional version of the field
theory of tachyon matter proposed by Sen, provides an action integral
formulation for the motion of a particle in the presence of Newtonian gravity
and nonlinear damping (quadratic in velocity).",0210108v2
2003-07-01,Highly damped quasinormal modes of Kerr black holes,"Motivated by recent suggestions that highly damped black hole quasinormal
modes (QNM's) may provide a link between classical general relativity and
quantum gravity, we present an extensive computation of highly damped QNM's of
Kerr black holes. We do not limit our attention to gravitational modes, thus
filling some gaps in the existing literature. The frequency of gravitational
modes with l=m=2 tends to \omega_R=2 \Omega, \Omega being the angular velocity
of the black hole horizon. If Hod's conjecture is valid, this asymptotic
behaviour is related to reversible black hole transformations. Other highly
damped modes with m>0 that we computed do not show a similar behaviour. The
real part of modes with l=2 and m<0 seems to asymptotically approach a constant
value \omega_R\simeq -m\varpi, \varpi\simeq 0.12 being (almost) independent of
a. For any perturbing field, trajectories in the complex plane of QNM's with
m=0 show a spiralling behaviour, similar to the one observed for
Reissner-Nordstrom (RN) black holes. Finally, for any perturbing field, the
asymptotic separation in the imaginary part of consecutive modes with m>0 is
given by 2\pi T_H (T_H being the black hole temperature). We conjecture that
for all values of l and m>0 there is an infinity of modes tending to the
critical frequency for superradiance (\omega_R=m) in the extremal limit.
Finally, we study in some detail modes branching off the so--called
``algebraically special frequency'' of Schwarzschild black holes. For the first
time we find numerically that QNM multiplets emerge from the algebraically
special Schwarzschild modes, confirming a recent speculation.",0307013v2
2004-01-22,Noncommutative inflation and the large-scale damping in the CMB anisotropy,"We show that a certain class of short-distance cutoff can give rise to large
suppression on the CMB anisotropies at large angular scales.",0401153v2
2006-05-19,Energy Loss of Heavy Quarks from Asymptotically AdS Geometries,"We investigate some universal features of AdS/CFT models of heavy quark
energy loss. In addition, as a specific example, we examine quark damping in
the spinning D3-brane solution dual to N=4 SU(N_c) super Yang-Mills at finite
temperature and R-charge chemical potential.",0605191v2
2003-06-30,Damped oscillatory integrals and boundedness of maximal operators associated to mixed homogeneous hypersurfaces,"We study the boundedness problem for maximal operators in 3-dimensional
Euclidean space associated to hypersurfaces given as the graph of $c+f$, where
$f$ is a mixed homogeneous function which is smooth away from the origin and
$c$ is a constant. Our result generalizes a corresponding theorem on mixed
homogeneous polynomial functions by A. Iosevich and E. Sawyer.",0306429v1
2003-12-19,Energy Decay of Damped Systems,"We present a new and simple bound for the exponential decay of second order
systems using the spectral shift. This result is applied to finite matrices as
well as to partial differential equations of Mathematical Physics. The type of
the generated semigroup is shown to be bounded by the upper real part of the
numerical range of the underlying quadratic operator pencil.",0312376v1
2004-04-06,Bounds for contractive semigroups and second order systems,"We derive a uniform bound for the difference of two contractive semigroups,
if the difference of their generators is form-bounded by the Hermitian parts of
the generators themselves. We construct a semigroup dynamics for second order
systems with fairly general operator coefficients and apply our bound to the
perturbation of the damping term. The result is illustrated on a dissipative
wave equation. As a consequence the exponential decay of some second order
systems is proved.",0404120v1
2006-12-07,Fractional Hamiltonian analysis of higher order derivatives systems,"The fractional Hamiltonian analysis of 1+1 dimensional field theory is
investigated and the fractional Ostrogradski's formulation is obtained. The
fractional path integral of both simple harmonic oscillator with an
acceleration-squares part and a damped oscillator are analyzed. The classical
results are obtained when fractional derivatives are replaced with the integer
order derivatives.",0612024v1
2000-02-23,Two-frequency forced Faraday waves: Weakly damped modes and pattern selection,"Recent experiments (Kudrolli, Pier and Gollub, 1998) on two-frequency
parametrically excited surface waves exhibit an intriguing ""superlattice"" wave
pattern near a codimension-two bifurcation point where both subharmonic and
harmonic waves onset simultaneously, but with different spatial wavenumbers.
The superlattice pattern is synchronous with the forcing, spatially periodic on
a large hexagonal lattice, and exhibits small-scale triangular structure.
Similar patterns have been shown to exist as primary solution branches of a
generic 12-dimensional $D_6\dot{+}T^2$-equivariant bifurcation problem, and may
be stable if the nonlinear coefficients of the bifurcation problem satisfy
certain inequalities (Silber and Proctor, 1998). Here we use the spatial and
temporal symmetries of the problem to argue that weakly damped harmonic waves
may be critical to understanding the stabilization of this pattern in the
Faraday system. We illustrate this mechanism by considering the equations
developed by Zhang and Vinals (1997, J. Fluid Mech. 336) for small amplitude,
weakly damped surface waves on a semi-infinite fluid layer. We compute the
relevant nonlinear coefficients in the bifurcation equations describing the
onset of patterns for excitation frequency ratios of 2/3 and 6/7. For the 2/3
case, we show that there is a fundamental difference in the pattern selection
problems for subharmonic and harmonic instabilities near the codimension-two
point. Also, we find that the 6/7 case is significantly different from the 2/3
case due to the presence of additional weakly damped harmonic modes. These
additional harmonic modes can result in a stabilization of the superpatterns.",0002041v2
2000-05-18,Environment-induced dynamical chaos,"We examine the interplay of nonlinearity of a dynamical system and thermal
fluctuation of its environment in the ``physical limit'' of small damping and
slow diffusion in a semiclassical context and show that the trajectories of
c-number variables exhibit dynamical chaos due to the thermal fluctuations of
the bath.",0005037v1
2003-02-12,On Whitham theory for perturbed integrable equations,"Whitham theory of modulations is developed for periodic waves described by
nonlinear wave equations integrable by the inverse scattering transform method
associated with $2\times2$ matrix or second order scalar spectral problems. The
theory is illustrated by derivation of the Whitham equations for perturbed
Korteweg-de Vries equation and nonlinear Schr\""odinger equation with linear
damping.",0302027v1
2003-02-24,Reverse Integration for Computing Stationary Points of Unstable Stiff Systems,"Using existing, forward-in-time integration schemes, we demonstrate that it
is possible to compute unstable, saddle-type fixed points of stiff systems of
ODEs when the stable compenents are fast (i.e., rapidly damped) while the
unstable components are slow. The approach has implications for the reverse
(backward in time) integration of such stiff systems, and for the coarse
reverse integration of microscopic/stochastic simulations.",0302055v1
2003-09-02,Breather lattice and its stabilization for the modified Korteweg-de Vries equation,"We obtain an exact solution for the breather lattice solution of the modified
Korteweg-de Vries (MKdV) equation. Numerical simulation of the breather lattice
demonstrates its instability due to the breather-breather interaction. However,
such multi-breather structures can be stabilized through the concurrent
application of ac driving and viscous damping terms.",0309003v1
2003-12-19,Existence of travelling waves in discrete sine-Gordon rings,"We prove existence results for travelling waves in discrete, damped,
dc-driven sine-Gordon equations with periodic boundary conditions.",0312042v5
2006-12-05,Colliding Particles in Highly Turbulent Flows,"We discuss relative velocities and the collision rate of small particles
suspended in a highly turbulent fluid. In the limit where the viscous damping
is very weak, we estimate the relative velocities using the Kolmogorov cascade
principle.",0612008v2
1998-05-29,Magnetic Faraday-Instability,"In a magnetic fluid parametrically driven surface waves can be excited by an
external oscillating magnetic field. A static magnetic field changes the
restoring forces and damping coefficients of the various surface waves. This
property enables the excitation of both subharmonic and harmonic responses of
the standing waves.",9806001v1
1999-06-08,Electromagnetic modes in cold magnetized strongly coupled plasmas,"The spectrum of electromagnetic waves propagating in a strongly coupled
magnetized fully ionized hydrogen plasma is found. The ion motion and damping
being neglected, the influence of the Coulomb coupling on the electromagnetic
spectrum is analyzed.",9906016v1
2000-08-12,The effects of the rotation in plasma,"Electric and magnetic self-fields can exist in the rotating plasma. A
self-sustained rotation can be established in the plasma. The disturbed
distribution function of rotating plasma is derived from the Vlasov equation.
The propagation of waves in rotating plasma differs from that in the usual
plasma. New terms for Landau damping appear. The local rotational behaviour may
become prevailing.",0008039v1
2000-12-11,An improved empirical equation for bunch lengthening in electron storage rings,"In this paper we propose an improved empirical equation for the bunch
lengthening in electron storage rings. The comparisons are made between the
analytical and experimental results, and the agreements are quite well. This
improved equation can be equally applied to the case where a storage ring is
very resistive (such as the improved SLC damping rings) instead of inductive as
usual.",0012020v2
2001-07-25,Causal Classical Theory of Radiation Damping,"It is shown how initial conditions can be appropriately defined for the
integration of Lorentz-Dirac equations of motion. The integration is performed
\QTR{it}{forward} in time. The theory is applied to the case of the motion of
an electron in an intense laser pulse, relevant to nonlinear Compton
scattering.",0107062v1
2001-11-26,Methods of Laser Cooling of Electron Beams in Storage Rings,"Methods of enhanced laser cooling of particle beams in storage rings and
Robinson's damping criterion are discussed. The dynamics of amplitudes of
betatron oscillations and instantaneous orbits of electrons interacting with
laser beams being displaced in the radial direction is investigated.",0111184v2
2002-04-17,Soliton self-modulation of the turbulence amplitude and plasma rotation,"The space-uniform amplitude envelope of the Ion Temperature Gradient driven
turbulence is unstable to small perturbations and evolves to nonuniform,
soliton-like modulated profiles. The induced poloidal asymmetry of the
transport fluxes can generate spontaneous poloidal spin-up of the tokamak
plasma.",0204050v2
2002-05-06,Delayed Equation for Charged Rigid Nonrelativistic Ball,"Simple expression for self-force acting on radiating rigid charged ball is
derived (Sommerfeld ball). It is shown that appropriate delayed equation of
motion has solutions in general differ from that for Sommerfeld sphere - there
are no ""radiationless"" solutions, but there are oscillating without damping
solutions though self-force has nonzero value.",0205012v1
2003-12-10,Charge Fluctuation of Dust Grains and its Impact on Dusty Wave Propagation,"In this paper we consider the influence of dust charge fluctuations on
damping of the dust-ion-acoustic waves. Fluid approximation of longitudinal
electrostatic waves in unmagnetized plasmas is considered. We show that for a
weak acoustic wave the attenuation depends on a phenomenological charging
coefficient.",0312067v1
2004-09-03,Relativistic electron beam acceleration by Compton scattering of lower-hybrid waves,"It has been proved theoetically and numerically that the highly relativistic
electron beam can be accelerated efficiently via the Compton scattering induced
by nonlinear Landau and cyclotron damping of the lower-hybrid waves.",0409024v1
2005-07-26,On simulations of the classical harmonic oscillator equation by difference equations,"We show that any second order linear ordinary diffrential equation with
constant coefficients (including the damped and undumped harmonic oscillator
equation) admits an exact discretization, i.e., there exists a difference
equation whose solutions exactly coincide with solutions of the corresponding
differential equation evaluated at a discrete sequence of points (a lattice).
Such exact discretization is found for an arbitrary lattice spacing.",0507182v1
1998-02-16,Classical states via decoherence,"The initial states which minimize the predictability loss for a damped
harmonic oscillator are identified as quasi-free states with a symmetry
dictated by the environment's diffusion coefficients. For an isotropic
diffusion in phase space, coherent states (or mixtures of coherent states) are
selected as the most stable ones.",9802044v1
2000-01-08,Quantum computation with mesoscopic superposition states,"We present a strategy to engineer a simple cavity-QED two-bit universal
quantum gate using mesoscopic distinct quantum superposition states. The
dissipative effect on decoherence and amplitude damping of the quantum bits are
analyzed and the critical parameters are presented.",0001018v1
2001-10-03,Thermal and quantum noise in active systems,"We present a quantum network approach to the treatment of thermal and quantum
fluctuations in measurement devices. The measurement is described as a
scattering process of input fluctuations towards output ones. We present the
results obtained with this method for the treatment of a cold damped capacitive
accelerometer.",0110021v1
2001-11-24,Deformed versus undeformed cat states encoding qubit,"We study the possibility of exploiting superpositions of coherent states to
encode qubit. A comparison between the use of deformed and undeformed bosonic
algebra is made in connection with the amplitude damping errors.",0111128v1
2002-11-05,Unitary reduction of the Liouville equation relative to a two-level atom coupled to a bimodal lossy cavity,"The Liouville equation of a two-level atom coupled to a degenerate bimodal
lossy cavity is unitarily and exactly reduced to two uncoupled Liouville
equations. The first one describes a dissipative Jaynes-Cummings model and the
other one a damped harmonic oscillator. Advantages related to the reduction
method are discussed.",0211015v1
2003-11-10,Cavity Assisted Nondestructive Laser Cooling of Atomic Qubits,"We analyze two configurations for laser cooling of neutral atoms whose
internal states store qubits. The atoms are trapped in an optical lattice which
is placed inside a cavity. We show that the coupling of the atoms to the damped
cavity mode can provide a mechanism which leads to cooling of the motion
without destroying the quantum information.",0311054v2
2003-11-19,Noise enhancing the classical information capacity of a quantum channel,"We present a simple model of quantum communication where a noisy quantum
channel may benefit from the addition of further noise at the decoding stage.
We demonstrate enhancement of the classical information capacity of an
amplitude damping channel, with a predetermined detection threshold, by the
addition of noise in the decoding measurement.",0311126v1
2003-12-22,Observation of Exceptional Points in Electronic Circuits,"Two damped coupled oscillators have been used to demonstrate the occurrence
of exceptional points in a purely classical system. The implementation was
achieved with electronic circuits in the kHz-range. The experimental results
perfectly match the mathematical predictions at the exceptional point. A
discussion about the universal occurrence of exceptional points -- connecting
dissipation with spatial orientation -- concludes the paper.",0312182v1
2004-08-01,Remark on the additivity conjecture for the quantum depolarizing channel,"We consider bistochastic quantum channels generated by unitary
representations of the discret group. The proof of the additivity conjecture
for the quantum depolarizing channel $\Phi$ based on the decreasing property of
the relative entropy is given. We show that the additivity conjecture is true
for the channel $\Xi =\Psi \circ \Phi $, where $\Psi $ is the phase damping.",0408004v2
2005-03-26,Markovian feedback to control continuous variable entanglement,"We present a model to realize quantum feedback control of continuous variable
entanglement. It consists of two interacting bosonic modes subject to amplitude
damping and achieving entangled Gaussian steady state. The possibility to
greatly improve the degree of entanglement by means of Markovian (direct)
feedback is then shown.",0503206v2
2005-04-12,Generation of Werner states and preservation of entnglement in a noisy environment,"We study the influence of noisy environment on the evolution of two-atomic
system in the presence of collective damping. Generation of Werner states as
asymptotic states of evolution is described. We also show that for some initial
states the amount of entanglement is preserved during the evolution.",0504090v2
2005-04-25,Dissipative dynamics of nondegenerate two-photon Jaynes-Cummings model,"A nondegenerate two-photon Jaynes-Cummings model is investigated where the
leakage of photon through the cavity is taken into account. The effect of
cavity damping on the mean photon number, atomic populations, field statistics
and both field and atomic squeezing is considered on the basis of master
equation in dressed-state approximation for initial coherent fields and excited
atom.",0504184v1
2005-07-20,A minimal coupling method for dissipative quantum systems,"Quantum dynamics of a general dissipative system investigated by its coupling
to a Klein-Gordon type field as the environment by introducing a minimal
coupling method. As an example, the quantum dynamics of a damped three
dimensional harmonic oscillator investigated and some transition probabilities
indicating the way energy flows between the subsystems obtained. The quantum
dynamics of a dissipative two level system considered.",0507195v1
2007-02-09,Linear-optics manipulations of photon-loss codes,"We discuss codes for protecting logical qubits carried by optical fields from
the effects of amplitude damping, i.e. linear photon loss. We demonstrate that
the correctability condition for one-photon loss imposes limitations on the
range of manipulations than can be implemented with passive linear-optics
networks.",0702091v1
2007-08-27,Band-Gap Engineering of Phononic Crystals: A Computational Survey of Two-Dimensional Systems,"We present graphic results with high-levels of abstraction to desribe the
basic principles and rules of thumb for acoustic or phononic band-gap
engineering. We use these rules for developing an improved machien mount for
damping acoustic vibrations, a phononic lens and a frequency selective filter
in the acoustic regime.",0708.3669v1
2007-09-01,Comments on 'Controversy on a Dispersion Relation for MHD Waves' by Chandra and Kumthekar,"We comment on the work by Chandra and Kumthekar (2007, henceforth CK) which
is questionable. In the derivation of dispersion relation, CK neither invoke
the concept of vector space nor do they follow the basic criterion for the
elimination of perturbation terms under which the damped magnetoacoustic waves
are derived.",0709.0040v1
2007-09-17,Intrinsic dissipation in cantilevers,"We consider the effects of a velocity-independent friction force on
cantilever damping. It is shown that this dissipation mechanism causes
nonlinear effects in the cantilever vibrations. The size of the nonlinearity
increases with decreasing cantilever velocity. Our analysis makes it possible
to understand experiments [Stipe et al, PRL 87, 096801 (2001)] where an
amplitude dependence of the cantilever eigenfrequency and anomalous dissipation
was observed only at small amplitudes.",0709.2582v1
2007-09-21,Enhanced Optical Cooling of Particle Beams in Storage Rings,"A method of enhanced optical cooling (EOC) based on nonlinear selective
interaction between particles and theirs amplified undulator radiation wavelets
(URW) in storage rings is discussed. It leads to non-exponential fast damping.
The selectivity is arranged by a moving screen located on the image plane of
the optical system projecting URW there.",0709.3403v1
2007-10-26,Vacuum - induced stationary entanglement in radiatively coupled three - level atoms,"We consider a pair of three - level atoms interacting with a common vacuum
and analyze the process of entanglement production due to spontaneous emission.
We show that in the case of closely separated atoms, collective damping can
generate robust entanglement of the asymptotic states.",0710.5048v2
2007-11-15,$C^m$-theory of damped wave equations with stabilisation,"The aim of this note is to extend the energy decay estimates from [J. Wirth,
J. Differential Equations 222 (2006) 487--514] to a broader class of
time-dependent dissipation including very fast oscillations. This is achieved
using stabilisation conditions on the coefficient in the spirit of [F.
Hirosawa, Math. Ann. 339/4 (2007) 819--839].",0711.2403v1
2008-04-21,Resonant excitation amidst dephasing: An exact analytic solution,"An exact analytic solution is presented for coherent resonant excitation of a
two-state quantum system driven by a time-dependent pulsed external field with
a hyperbolic-secant shape in the presence of dephasing. Analytic results are
derived for the amplitude and the phase shift of the damped Rabi oscillations.",0804.3315v1
2008-05-06,Logarithmic decay of hyperbolic equations with arbitrary boundary damping,"In this paper, we study the logarithmic stability for the hyperbolic
equations by arbitrary boundary observation. Based on Carleman estimate, we
first prove an estimate of the resolvent operator of such equation. Then we
prove the logarithmic stability estimate for the hyperbolic equations without
any assumption on an observation subboundary.",0805.0625v1
2008-07-14,A z = 3 Lyman Alpha Blob Associated with a Damped Lyman Alpha System Proximate to its Background Quasar,"We report on the discovery of a bright Lyman alpha blob associated with the
z=3 quasar SDSSJ124020.91+145535.6 which is also coincident with strong damped
Lyman alpha absorption from a foreground galaxy (a so-called proximate damped
Lyman alpha system; PDLA). The one dimensional spectrum acquired by the Sloan
Digital Sky Survey (SDSS) shows a broad Lyman alpha emission line with a FWHM ~
500 km/s and a luminosity of L_{Lya} = 3.9e43 erg/s superposed on the trough of
the PDLA. Mechanisms for powering this large Lyman alpha luminosity are
discussed. We argue against emission from HII regions in the PDLA galaxy since
this requires an excessive star-formation rate ~ 500 Msun/yr and would
correspond to the largest Lyman alpha luminosity ever measured from a damped
Lyman alpha system or starburst galaxy. We use a Monte Carlo radiative transfer
simulation to investigate the possibility that the line emission is fluorescent
recombination radiation from the PDLA galaxy powered by the ionizing flux of
the quasar, but find that the predicted Lyman alpha flux is several orders of
magnitude lower than observed. We conclude that the Lyman alpha emission is not
associated with the PDLA galaxy at all, but instead is intrinsic to the
quasar's host and similar to the extended Lyman alpha 'fuzz' which is detected
around many AGN. PDLAs are natural coronagraphs that block their background
quasar at Lyman alpha, and we discuss how systems similar to
SDSSJ124020.91+145535.6 might be used to image the neutral hydrogen in the PDLA
galaxy in silhouette against the screen of extended Lyman alpha emission from
the background quasar.",0807.2271v1
2008-09-23,Analysis of complete positivity conditions for quantum qutrit channels,"We present an analysis of complete positivity (CP) constraints on qutrit
quantum channels that have a form of affine transformations of generalized
Bloch vector. For diagonal (damping) channels we derive conditions analogous to
the ones that in qubit case produce tetrahedron structure in the channel
parameter space.",0809.3882v3
2008-10-28,Excitation and damping of p-mode oscillations of alpha Cen B,"This paper presents an analysis of observational data on the p-mode spectrum
of the star alpha Cen B and a comparison with theoretical computations of the
stochastic excitation and damping of the modes. We find that at frequencies >
4500 micro-Hz, the model damping rates appear to be too weak to explain the
observed shape of the power spectral density of alpha Cen B. The conclusion
rests on the assumption that most of the disagreement is due to problems
modelling the damping rates, not the excitation rates, of the modes. This
assumption is supported by a parallel analysis of BiSON Sun-as-a-star data, for
which it is possible to use analysis of very long timeseries to place tight
constraints on the assumption. The BiSON analysis shows that there is a similar
high-frequency disagreement between theory and observation in the Sun.
  We demonstrate that by using suitable comparisons of theory and observation
it is possible to make inference on the dependence of the p-mode linewidths on
frequency, without directly measuring those linewidths, even though the alpha
Cen B dataset is only a few nights long. Use of independent measures from a
previous study of the alpha Cen B linewidths in two parts of its spectrum also
allows us to calibrate our linewidth estimates for the star. The resulting
calibrated linewidth curve looks similar to a frequency-scaled version of its
solar cousin, with the scaling factor equal to the ratio of the respective
acoustic cut-off frequencies of the two stars. The ratio of the frequencies at
which the onset of high-frequency problems is seen in both stars is also given
approximately by the same scaling factor.",0810.5022v1
2008-11-03,Equation of state for QCD matter in a quasiparticle model,"A phenomenological QCD quasiparticle model provides a means to map lattice
QCD results to regions relevant for a variety of heavy-ion collision
experiments at larger baryon density. We report on effects of collectives modes
and damping on the equation of state.",0811.0274v1
2009-01-14,On the use of continuous wavelet analysis for modal identification,"This paper reviews two different uses of the continuous wavelet transform for
modal identification purposes. The properties of the wavelet transform, mainly
energetic, allow to emphasize or filter the main information within measured
signals and thus facilitate the modal parameter identification especially when
mechanical systems exhibit modal coupling and/or relatively strong damping.",0901.2000v1
2009-01-20,Quasi-periodic motions in strongly dissipative forced systems,"We consider a class of ordinary differential equations describing
one-dimensional systems with a quasi-periodic forcing term and in the presence
of large damping. We discuss the conditions to be assumed on the mechanical
force and the forcing term for the existence of quasi-periodic solutions which
have the same frequency vector as the forcing.",0901.3009v1
2009-01-23,On the regularity of global attractors,"This note is focused on a novel technique in order to establish the
boundedness in more regular spaces for global attractors of dissipative
dynamical systems, without appealing to uniform-in-time estimates. As an
application of the abstract result, the semigroup generated by the strongly
damped wave equation $$u_{tt}-\Delta u_t-\Delta u+\phi(u)=f$$ with critical
nonlinearity is considered, whose attractor is shown to possess the optimal
regularity.",0901.3607v1
2009-05-07,On a Stochastic Wave Equation Driven by a Non-Gaussian Levy Process,"This paper investigates a damped stochastic wave equation driven by a
non-Gaussian Levy noise. The weak solution is proved to exist and be unique.
Moreover we show the existence of a unique invariant measure associated with
the transition semigroup under mild conditions.",0905.0992v1
2009-05-07,Metal-Enriched Plasma in Protogalactic Halos: A Survey of N V Absorption in High-z Damped & Sub-Damped Lyman-alpha Systems,"We continue our recent work to characterize the plasma content of
high-redshift damped and sub-damped Lyman-alpha systems (DLAs/sub-DLAs), which
represent multi-phase gaseous (proto)galactic disks and halos seen toward a
background source. We survey N V absorption in a sample of 91 DLAs and 18
sub-DLAs in the redshift range 1.67<z<4.28 with unblended coverage of the N V
doublet, using data from VLT/UVES, Keck/HIRES, and Keck/ESI. In DLAs, we find
eight secure N V detections, four marginal detections, and 79 non-detections.
The detection rate of N V in DLAs is therefore 13^{+5}_{-4}%. Two sub-DLA N V
detections are found among a sample of 18, at a similar detection rate of
11^{+15}_{-7}%. We show that the N V detection rate is a strong function of
metallicity, increasing by a factor of ~4 at [N/H]=[NI/HI]>-2.3. The N V and
CIV component b-value distributions in DLAs are statistically similar, but the
median b(N V) of 18 km/s is lower than the median b(O VI) of 25 km/s. Some ~20%
of the N V components have b<10 km/s and thus arise in warm photoionized plasma
at log (T/K)<4.92; local sources of ionizing radiation (as opposed to the
extragalactic background) are required to keep the cloud sizes physically
reasonable. The nature of the remaining ~80% of (broad) N V components is
unclear; models of radiatively-cooling collisionally-ionized plasma at
log(T/K)=5.2-5.4 are fairly successful in reproducing the observed integrated
high-ion column density ratios and the component line widths, but we cannot
rule out photoionization by local sources. Finally, we identify several unusual
DLAs with extremely low metallicity (<0.01 solar) but strong high-ion
absorption [log N(N V)>14 or log N(O VI)>14.2] that present challenges to
either galactic inflow or outflow models.",0905.1042v2
2009-05-12,Quantum measurement with chaotic apparatus,"We study a dissipative quantum mechanical model of the projective measurement
of a qubit. We demonstrate how a correspondence limit, damped quantum
oscillator can realise chaotic-like or periodic trajectories that emerge in
sympathy with the projection of the qubit state, providing a model of the
measurement process.",0905.1867v2
2009-06-12,Tailoring the carrier mobility of semiconducting nanowires by remote dielectrics,"The dielectric environment of thin semiconductor nanowires can affect the
charge transport properties inside the wire. In this work, it is shown that
Coulomb impurity scattering inside thin nanowires can be damped strongly by
coating the wire with a high-k dielectric. This will lead to an increase in the
mobility of free charges inside the wire.",0906.2371v1
2009-10-22,Modelling collisions in a relativistic plasma,"Generalising the work of Lenard and Bernstein, we introduce a new, fully
relativistic model to describe collisional plasmas. Like the Fokker-Planck
operator, this equation represents velocity diffusion and conserves particle
number. However, unlike the Fokker-Planck operator it is linear in the
distribution function, and so more amenable to a fluid treatment. By taking
moments, we derive a new fluid model, and demonstrate the damping effects of
collisions on Langmuir waves.",0910.4368v1
2009-11-24,Non-Markovian master equation for a damped driven two-state system,"We present a detailed microscopic derivation for a non-Markovian master
equation for a driven two-state system interacting with a general structured
reservoir. The master equation is derived using the time-convolutionless
projection operator technique in the limit of weak coupling between the
two-state quantum system and its environment. We briefly discuss the Markov
approximation, the secular approximation and their validity.",0911.4600v1
2009-12-07,Analyticity and Gevrey-class regularity for the second-grade fluid equations,"We address the global persistence of analyticity and Gevrey-class regularity
of solutions to the two and three-dimensional visco-elastic second-grade fluid
equations. We obtain an explicit novel lower bound on the radius of analyticity
of the solutions to the second-grade fluid equations that does not vanish as
$t\to \infty$. Applications to the damped Euler equations are given.",0912.1327v1
2010-02-15,Analysis on Path Spaces over Riemmannian Manifolds with Boundary,"By using Hsu's multiplicative functional for the Neumann heat equation, a
natural damped gradient operator is defined for the reflecting Brownian motion
on compact manifolds with boundary. This operator is linked to quasi-invariant
flows in terms of a integration by parts formula, which leads to the standard
log-Sobolev inequality for the associated Dirichlet form on the path space.",1002.2887v1
2010-03-07,Decay of Langmuir wave in dense plasmas and warm dense matter,"The decays of the Langmuir waves in dense plasmas are computed using the
dielectric function theory widely used in the solid state physics.
  Four cases are considered: a classical plasma, a Maxwellian plasma, a
degenerate quantum plasma, and a partially degenerate plasma. The result is
considerably different from the conventional Landau damping theory.",1003.1524v2
2010-05-20,Cavity spin optodynamics,"The dynamics of a large quantum spin coupled parametrically to an optical
resonator is treated in analogy with the motion of a cantilever in cavity
optomechanics. New spin optodynamic phenonmena are predicted, such as
cavity-spin bistability, optodynamic spin-precession frequency shifts, coherent
amplification and damping of spin, and the spin optodynamic squeezing of light.",1005.3853v2
2011-02-21,Noncommutative gauge theory and renormalisability,"We review two different noncommutative gauge models generalizing approaches
which lead to renormalizable scalar quantum field theories. One of them
implements the crucial IR damping of the gauge field propagator in the
so-called ``soft breaking'' part. We discuss one-loop renormalisability.",1102.4167v1
2011-04-10,Stabilization of the wave equation with external force,"We study the rate of decay of the energy functional of solutions of the wave
equation with localized damping and a external force. We prove that the decay
rates of the energy functional is determined from a forced differential
equation.",1104.1808v3
2011-05-01,"Set, Reset, and Retention Times for Ionic and Filamentary Mem-Resistors","A dynamic systems model has previously been proposed for mem-resistors based
on a driven damped harmonic oscillator differential equation describing
electron and ionic depletion widths in a thin semiconductor film. This paper
derives equations for set, reset, and retention times based on the previously
proposed model. Keywords- mem-resistor, RRAM, ReRAM",1105.0134v3
2011-07-30,Ion-kinetic D'Angelo mode,"An extension of hydrodynamic D'Angelo mode of inhomogeneous sheared plasma
flow along the magnetic field into the short-wavelength limit, where the
hydrodynamic treatment is not valid, has been considered. We find that D'Angelo
mode in this wavelength range is excited by inverse ion Landau damping and
becomes the shear flow driven ion-kinetic mode.",1108.0093v1
2011-11-14,Twist of fractional oscillations,"Using the method of the Laplace transform, we consider fractional
oscillations. They are obtained by the time-clock randomization of ordinary
harmonic vibrations. In contrast to sine and cosine, the functions describing
the fractional oscillations exhibit a finite number of damped oscillations with
an algebraic decay. Their fractional differential equation is derived.",1111.5298v1
2011-12-02,On the transmission of binary bits in discrete Josephson-junction arrays,"In this work, we use supratransmission and infratransmission in the
mathematical modeling of the propagation of digital signals in weakly damped,
discrete Josephson-junction arrays, using energy-based detection criteria. Our
results show an efficient and reliable transmission of binary information.",1112.0589v1
2012-01-12,Superconducting elliptical cavities,"We give a brief overview of the history, state of the art, and future for
elliptical superconducting cavities. Principles of the cell shape optimization,
criteria for multi-cell structures design, HOM damping schemes and other
features are discussed along with examples of superconducting structures for
various applications.",1201.2598v1
2012-02-19,Cluster-based Superconducting Tunneling Networks,"A 2D tunneling network consisting of nanoclusters placed on a surface is
studied. It is shown that such a network is capable of transferring large
supercurrent at high temperatures. For a realistic set of parameters the
damping is quite small, and the smallness is due to strong renormalization of
the capacitance of a cluster. The critical field also turns out to be lar",1202.4132v1
2012-02-25,Design of a Fractional Order Phase Shaper for Iso-damped Control of a PHWR under Step-back Condition,"Phase shaping using fractional order (FO) phase shapers has been proposed by
many contemporary researchers as a means of producing systems with iso-damped
closed loop response due to a stepped variation in input. Such systems, with
the closed loop damping remaining invariant to gain changes can be used to
produce dead-beat step response with only rise time varying with gain. This
technique is used to achieve an active step-back in a Pressurized Heavy Water
Reactor (PHWR) where it is desired to change the reactor power to a
pre-determined value within a short interval keeping the power undershoot as
low as possible. This paper puts forward an approach as an alternative for the
present day practice of a passive step-back mechanism where the control rods
are allowed to drop during a step-back action by gravity, with release of
electromagnetic clutches. The reactor under a step-back condition is identified
as a system using practical test data and a suitable Proportional plus Integral
plus Derivative (PID) controller is designed for it. Then the combined plant is
augmented with a phase shaper to achieve a dead-beat response in terms of power
drop. The fact that the identified static gain of the system depends on the
initial power level at which a step-back is initiated, makes this application
particularly suited for using a FO phase shaper. In this paper, a model of a
nuclear reactor is developed for a control rod drop scenario involving rapid
power reduction in a 500MWe Canadian Deuterium Uranium (CANDU) reactor using
AutoRegressive Exogenous (ARX) algorithm. The system identification and reduced
order modeling are developed from practical test data. For closed loop active
control of the identified reactor model, the fractional order phase shaper
along with a PID controller is shown to perform better than the present Reactor
Regulating System (RRS) due to its iso-damped nature.",1202.5657v1
2012-02-27,Simple absorbing boundary conditions for wave simulations with Smoothed Particle Hydrodynamics,"We study and implement a simple method, based on the Perfectly Matched Layer
approach, to treat non reflecting boundary conditions with the Smoothed
Particles Hydrodynamics numerical algorithm. The method is based on the concept
of physical damping. We illustrate how it works in the case of 1D and 2D time
dependent waves propagating in a finite domain.",1202.5893v1
2012-07-22,Singularity and existence to a wave system of nematic liquid crystals,"In this paper, we prove the global existence and singularity formation for a
wave system from modelling nematic liquid crystals in one space dimension. In
our model, although the viscous damping term is included, the solution with
smooth initial data still has gradient blowup in general, even when the initial
energy is arbitrarily small.",1207.5190v1
2012-07-26,Upsilon Suppression in PbPb Collisions at sqrt(s_NN) = 2.76 TeV,"We suggest that the combined effect of screening, gluon-induced dissociation,
collisional damping, and reduced feed-down explains most of the sequential
suppression of Y(nS) states that has been observed in PbPb relative to pp
collisions at sqrt(s_NN) = 2.76 TeV. The suppression is thus a clear, albeit
indirect, indication for the presence of a qgp.",1207.6227v1
2012-09-08,Local energy decay for the wave equation with nonlinear time dependent damping,"This paper addresses a wave equation on a exterior domain in R^{d}(d odd)
with nonlinear time dependent dissipation. Under a microlocal geometric
condition we prove that the decay rates of the local energy functional are
obtained by solving a nonlinear non-autonomous differential equation.",1209.1733v1
2012-09-08,Evidence for anisotropic polar nanoregions in relaxor PMN: A neutron study of the elastic constants and anomalous TA phonon damping,"We use neutron scattering to characterize the acoustic phonons in the relaxor
PMN and demonstrate the presence of an anisotropic damping mechanism directly
related to short-range, polar correlations. For a large range of temperatures
above Tc ~ 210, K, where dynamic polar correlations exist, acoustic phonons
propagating along [1\bar{1}0] and polarized along [110] (TA2 phonons) are
overdamped and softened across most of the Brillouin zone. By contrast,
acoustic phonons propagating along [100] and polarized along [001] (TA1
phonons) are overdamped and softened for only a limited range of wavevectors.
The anisotropy and temperature dependence of the acoustic phonon energy
linewidth are directly correlated with the elastic diffuse scattering,
indicating that polar nanoregions are the cause of the anomalous behavior. The
damping and softening vanish for q -> 0, i.e. for long-wavelength acoustic
phonons, which supports the notion that the anomalous damping is a result of
the coupling between the relaxational component of the diffuse scattering and
the harmonic TA phonons. Therefore, these effects are not due to large changes
in the elastic constants with temperature because the elastic constants
correspond to the long-wavelength limit. We compare the elastic constants we
measure to those from Brillouin scattering and to values reported for pure PT.
We show that while the values of C44 are quite similar, those for C11 and C12
are significantly less in PMN and result in a softening of (C11-C12) over PT.
There is also an increased elastic anisotropy (2C44/(C11-C12)) versus that in
PT. These results suggest an instability to TA2 acoustic fluctuations in
relaxors. We discuss our results in the context of the debate over the
""waterfall"" effect and show that they are inconsistent with TA-TO phonon
coupling or other models that invoke the presence of a second optic mode.",1209.1736v1
2012-12-28,Turbulence-Induced Instabilities in EP and QGP,"Polarization properties of turbulent stochastically inhomogeneous
ultrarelativistic QED plasma are studied. It is shown that the sign of
nonlinear turbulent Landau damping corresponds to an instability of the
spacelike modes and, for sufficiently large turbulent fields, to an actual
instability of a system.",1212.6555v1
2013-02-26,Spin Mixing in Spinor Fermi Gases,"We study a spinor fermionic system under the effect of spin-exchange
interaction. We focus on the interplay between the spin-exchange interaction
and the effective quadratic Zeeman shift. We examine the static and the dynamic
properties of both two- and many-body system. We find that the spin-exchange
interaction induces coherent Rabi oscillation in the two-body system, but the
oscillation is quickly damped when the system is extended to the many-body
case.",1302.6549v1
2013-03-12,Damped jump-telegraph processes,"We study a one-dimensional Markov modulated random walk with jumps. It is
assumed that amplitudes of jumps as well as a chosen velocity regime are random
and depend on a time spent by the process at a previous state of the underlying
Markov process.
  Equations for the distribution and equations for its moments are derived. We
characterise the martingale distributions in terms of observable proportions
between jump and velocity regimes.",1303.2796v1
2013-03-14,Drag and Diffusion coefficients in extreme scenarios of temperature and chemical potential,"A comparative study of high and zero temperature plasma for the case of
damping rate, drag and diffusion coefficients have been presented. In each of
these quantities, it is revealed how the magnetic interaction dominates over
the electric one at zero temperature unlike what happens at high temperature.",1303.3353v1
2013-05-19,On Collective Properties of Turbulent QED Plasma,"Polarization properties of turbulent stochastically inhomogeneous
ultrarelativistic QED plasma are studied. It is shown that the sign of
nonlinear turbulent Landau damping corresponds to an instability of the
spacelike modes and, for sufficiently large turbulent fields, to an actual
instability of a system. Modification of plasmon dispersion relations due to
turbulent effects are studied.",1305.4414v1
2013-06-17,Uniformly polynomially stable approximations for a class of second order evolution equations,"In this paper we study time semi-discrete approximations of a class of
polynomially stable infinite dimensional systems modeling the damped
vibrations. We prove that adding a suitable numerical viscosity term in the
numerical scheme, one obtains approximations that are uniformly polynomially
stable with respect to the discretization parameter.",1306.3807v1
2013-08-21,Overstable Librations can account for the Paucity of Mean Motion Resonances among Exoplanet Pairs,"We assess the multi-planet systems discovered by the Kepler satellite in
terms of current ideas about orbital migration and eccentricity damping due to
planet-disk interactions. Our primary focus is on mean motion resonances. Only
a few percent of planet pairs are in close proximity to a resonance. However,
predicted migration rates (parameterized by $\tau_n=n/{|\dot n|}$) imply that
during convergent migration most planets would have been captured into first
order resonances. Eccentricity damping (parameterized by $\tau_e=e/{|\dot e|}$)
offers a plausible resolution. Estimates suggest $\tau_e/\tau_n\sim (h/a)^2\sim
10^{-2}$, where $h/a$ is the ratio of disk thickness to radius. Together,
eccentricity damping and orbital migration give rise to an equilibrium
eccentricity, $e_{eq}\sim(\tau_e/\tau_n)^{1/2}$. Capture is permanent provided
$e_{eq}\lesssim \mu^{1/3}$, where $\mu$ denotes the planet to star mass ratio.
But for $e_{eq}\gtrsim \mu^{1/3}$, capture is only temporary because librations
around equilibrium are overstable and lead to passage through resonance on
timescale $\tau_e$. Most Kepler planet pairs have $e_{eq}>\mu^{1/3}$. Since
$\tau_n>> \tau_e$ is the timescale for migration between neighboring
resonances, only a modest percentage of pairs end up trapped in resonances
after the disk disappears. Planet pairs close to a mean motion resonance
typically exhibit period ratios 1-2% larger than those for exact resonance. The
direction of this shift undoubtedly reflects the same asymmetry that requires
convergent migration for resonance capture. Permanent resonance capture at
these separations from exact resonance would demand $\mu
(\tau_n/\tau_e)^{1/2}\gtrsim 0.01$, a value that estimates of $\mu$ from
transit data and $(\tau_e/\tau_n)^{1/2}$ from theory are insufficient to match.
Plausible alternatives involve eccentricity damping during or after disk
dispersal. (Abridged)",1308.4688v2
2013-08-30,Nested Head-Tail Vlasov Solver,"Nested Head-Tail (NHT) is a Mathematica-based Vlasov solver for transverse
oscillations in multi-bunch beams. It takes into account azimuthal, radial,
coupled-bunch and beam-beam degrees of freedom, single- and inter-bunch dipole
wakes, an arbitrary damper, beam-beam effects and Landau damping.",1309.0044v3
2013-09-24,Attractors for damped quintic wave equations in bounded domains,"The dissipative wave equation with a critical quintic nonlinearity in smooth
bounded three dimensional domain is considered. Based on the recent extension
of the Strichartz estimates to the case of bounded domains, the existence of a
compact global attractor for the solution semigroup of this equation is
established. Moreover, the smoothness of the obtained attractor is also shown.",1309.6272v1
2013-09-30,Harmonic oscillator: an analysis via Fourier series,"The Fourier series method is used to solve the homogeneous equation governing
the motion of the harmonic oscillator. It is shown that the general solution to
the problem can be found in a surprisingly simple way for the case of the
simple harmonic oscillator. It is also shown that the damped harmonic
oscillator is susceptible to the analysis.",1309.7918v1
2013-10-01,"Observations and predictions at CesrTA, and outlook for ILC","In this paper, we will describe some of the recent experimental measurements
[1, 2, 3] performed at CESRTA [4], and the supporting simulations, which probe
the interaction of the electron cloud with the stored beam. These experiments
have been done over a wide range of beam energies, emittances, bunch currents,
and fill patterns, to gather sufficient information to be able to fully
characterize the beam-electron-cloud interaction and validate the simulation
programs. The range of beam conditions is chosen to be as close as possible to
those of the ILC damping ring, so that the validated simulation programs can be
used to predict the performance of these rings with regard to electroncloud-
related phenomena. Using the new simulation code Synrad3D to simulate the
synchrotron radiation environment, a vacuum chamber design has been developed
for the ILC damping ring which achieves the required level of photoelectron
suppression. To determine the expected electron cloud density in the ring, EC
buildup simulations have been done based on the simulated radiation environment
and on the expected performance of the ILC damping ring chamber mitigation
prescriptions. The expected density has been compared with analytical estimates
of the instability threshold, to verify that the ILC damping ring vacuum
chamber design is adequate to suppress the electron cloud single-bunch
head-tail instability.",1310.0261v1
2013-10-21,A Critical History of Renormalization,"The history of renormalization is reviewed with a critical eye, starting with
Lorentz's theory of radiation damping, through perturbative QED with Dyson,
Gell-Mann & Low, and others, to Wilson's formulation and Polchinski's
functional equation, and applications to ""triviality"", and dark energy in
cosmology.",1310.5533v1
2013-10-27,Fundamental limitations of half-metallicicity in spintronic materials,"Zero-point spin fluctuations are shown to strongly influence the ground state
of ferromagnetic metals and to impose limitations for the fully spin polarized
state assumed in half-metallic ferromagnets, which may influence their
applications in spintronics. This phenomenon leads to the low-frequency Stoner
excitations and cause strong damping and softening of magnons in
magnetoresistive manganites observed experimentally.",1310.7174v1
2013-12-13,Probing Intergalactic Neutral Hydrogen by the Lyman Alpha Red Damping Wing of Gamma-Ray Burst 130606A Afterglow Spectrum at z = 5.913,"The unprecedentedly bright optical afterglow of GRB 130606A located by Swift
at a redshift close to the reionization era (z = 5.913) provides a new
opportunity to probe the ionization status of intergalactic medium (IGM). Here
we present an analysis of the red Ly alpha damping wing of the afterglow
spectrum taken by Subaru/FOCAS during 10.4-13.2 hr after the burst. We find
that the minimal model including only the baseline power-law and HI absorption
in the host galaxy does not give a good fit, leaving residuals showing concave
curvature in 8400-8900 A with an amplitude of about 0.6% of the flux. Such a
curvature in the short wavelength range cannot be explained either by
extinction at the host with standard extinction curves, intrinsic curvature of
afterglow spectra, or by the known systematic uncertainties in the observed
spectrum. The red damping wing by intervening HI gas outside the host can
reduce the residual by about 3 sigma statistical significance. We find that a
damped Ly alpha system is not favored as the origin of this intervening HI
absorption, from the observed Ly beta and metal absorption features. Therefore
absorption by diffuse IGM remains as a plausible explanation. A fit by a simple
uniform IGM model requires HI neutral fraction of f_HI ~ 0.1-0.5 depending on
the distance to the GRB host, implying high f_HI IGM associated with the
observed dark Gunn-Peterson (GP) troughs. This gives a new evidence that the
reionization is not yet complete at z ~ 6.",1312.3934v3
2014-02-01,Effects of stellar flybys on planetary systems: 3D modeling of the circumstellar disks damping effects,"Stellar flybys in star clusters are suspected to affect the orbital
architecture of planetary systems causing eccentricity excitation and orbital
misalignment between the planet orbit and the equatorial plane of the star. We
explore whether the impulsive changes in the orbital elements of planets,
caused by an hyperbolic stellar flyby, can be fully damped by the circumstellar
disk surrounding the star. The time required to disperse stellar clusters is in
fact comparable to circumstellar disk's lifetime. We have modelled in 3D a
system made of a solar type star surrounded by a low density disk with a giant
planet embedded in it approached on a hyperbolic encounter trajectory by a
second star, of similar mass and with its own disk. We focus on extreme
configurations where a very deep stellar flyby perturbs a Jovian planet on an
external orbit. This allows to test in full the ability of the disk to erase
the effects of the stellar encounter. We find that the amount of mass lost by
the disk during the stellar flyby is less than in 2D models where a single disk
was considered due to the mass exchange between the two disks at the encounter.
The damping in eccentricity is slightly faster than in 2D models and it occurs
on timescales of the order of a few kyr. The only trace of the flyby left in
the planet system, after about 10^4 yr, is a small misalignment, lower than 9
degrees, between the star equatorial plane and the planet orbit. In a realistic
model based on 3D simulations of star--planet--disk interactions, we find that
stellar flybys cannot excite significant eccentricities and inclinations of
planets in stellar clusters. The circumstellar disks hosting the planets damp
on a short timescale all the step changes in the two orbital parameters
produced during any stellar encounter. All records of past encounters are
erased.",1402.0077v1
2014-02-21,Damping of electron Zitterbewegung in carbon nanotubes,"Zitterbewegung (ZB, trembling motion) of electrons in semiconductor carbon
nanotubes is described taking into account dephasing processes. The density
matrix formalism is used for the theory. Differences between decay of ZB
oscillations due to electron localization and that due to dephasing are
discussed.",1402.5393v1
2014-04-18,Exponential mixing for the white - forced damped nonlinear wave equation,"The paper is devoted to studying the stochastic nonlinear wave (NLW) equation
in a bounded domain D $\subset$ R3. We show that the Markov process associated
with the flow of solution has a unique stationary measure $\mu$, and the law of
any solution converges to $\mu$ with exponential rate in the dual-Lipschitz
norm",1404.4697v1
2014-04-22,A unique continuation result for the plate equation and an application,"In this paper, we prove the unique continuation property for the weak
solution of the plate equation with non-smooth coefficients. Then, we apply
this result to study the global attractor for the semilinear plate equation
with a localized damping.",1404.5586v3
2014-05-13,Magneto-seismological insights into the penumbral chromosphere and evidence for wave damping in spicules,"The observation of propagating magneto-hydrodynamic kink waves in magnetic
structures and measurement of their properties (amplitude, phase speed) can be
used to diagnose the plasma conditions in the neighbourhood of the magnetic
structure via magneto-seismology (MS). We aim to reveal properties of the
chromosphere/Transition Region above the sunspot penumbra using this technique.
Hinode observed a sunspot as it was crossing the limb, providing a unique side
on view of the sunspot atmosphere. The presence of large spicule-like jets is
evident in \ion{Ca}{II} H images. The jets are found to support transverse wave
motions that displace the central axis, which can be interpreted as a kink
wave. The properties of a wave event are measured and used to determine the
magnetic and density stratification along the structure. We also measure the
width of the spicule and the intensity profile along the structure. The
measured wave properties reveal an initial rapid increase in amplitude with
height above the solar surface, followed by a decrease in amplitude. The MS
inversion suggests this initial increase corresponds to large changes in
density and magnetic field strength. In addition, we provide the first
measurements of spicule width with height, which confirm that the spicule under
goes rapid expansion. The measured expansion shows good agreement with the
results from the MS. The observed variations in plasma parameters are suggested
to be partly due to the presence of a gravitational stratified, ambient
atmosphere. Combining width measurements with phase speed measurements implies
the observed decrease in wave amplitude at greater heights can be explained by
wave damping. Hence, we provide the first direct evidence of wave damping in
chromospheric spicules and the quality factor of the damping is found to be
significantly smaller than estimated coronal values.",1405.3203v1
2014-05-27,Interior feedback stabilization of wave equations with dynamic boundary delay,"In this paper we consider an interior stabilization problem for the wave
equation with dynamic boundary delay.We prove some stability results under the
choice of damping operator. The proof of the main result is based on a
frequency domain method and combines a contradiction argument with the
multiplier technique to carry out a special analysis for the resolvent.",1405.6865v2
2014-07-11,Remark on stabilization of second order evolution equations by unbounded dynamic feedbacks and applications,"In this paper we consider second order evolution equations with unbounded
dynamic feedbacks. Under a regularity assumption we show that observability
properties for the undamped problem imply decay estimates for the damped
problem. We consider both uniform and non uniform decay properties.",1407.3070v1
2014-09-11,Eliminating flutter for clamped von Karman plates immersed in subsonic flows,"We address the long-time behavior of a non-rotational von Karman plate in an
inviscid potential flow. The model arises in aeroelasticity and models the
interaction between a thin, nonlinear panel and a flow of gas in which it is
immersed [6, 21, 23]. Recent results in [16, 18] show that the plate component
of the dynamics (in the presence of a physical plate nonlinearity) converge to
a global compact attracting set of finite dimension; these results were
obtained in the absence of mechanical damping of any type. Here we show that,
by incorporating mechanical damping the full flow-plate system, full
trajectories---both plate and flow---converge strongly to (the set of)
stationary states. Weak convergence results require ""minimal"" interior damping,
and strong convergence of the dynamics are shown with sufficiently large
damping. We require the existence of a ""good"" energy balance equation, which is
only available when the flows are subsonic. Our proof is based on first showing
the convergence properties for regular solutions, which in turn requires
propagation of initial regularity on the infinite horizon. Then, we utilize the
exponential decay of the difference of two plate trajectories to show that full
flow-plate trajectories are uniform-in-time Hadamard continuous. This allows us
to pass convergence properties of smooth initial data to finite energy type
initial data. Physically, our results imply that flutter (a non-static end
behavior) does not occur in subsonic dynamics. While such results were known
for rotational (compact/regular) plate dynamics [14] (and references therein),
the result presented herein is the first such result obtained for
non-regularized---the most physically relevant---models.",1409.3308v5
2014-12-15,Optomechanical laser cooling with mechanical modulations,"We theoretically study the laser cooling of cavity optomechanics when the
mechanical resonance frequency and damping depend on time. In the regime of
weak optomechanical coupling we extend the theory of laser cooling using an
adiabatic approximation. We discuss the modifications of the cooling dynamics
and compare it with numerical simulations in a wide range of modulation
frequencies.",1412.4497v1
2015-03-08,An Analytical Formulation of Power System Oscillation Frequency,"This letter proposes an analytical approach to formulate the power system
oscillation frequency under a large disturbance. A fact is revealed that the
oscillation frequency is only the function of the oscillation amplitude when
the system's model and operating condition are fixed. Case studies also show
that this function is damping-insensitive and could be applied to an inter-area
model of a multi-machine power system.",1503.07554v1
2015-04-07,Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque,"Spin-orbit effects [1-4] have the potential of radically changing the field
of spintronics by allowing transfer of spin angular momentum to a whole new
class of materials. In a seminal letter to Nature [5], Kajiwara et al. showed
that by depositing Platinum (Pt, a normal metal) on top of a 1.3 $\mu$m thick
Yttrium Iron Garnet (YIG, a magnetic insulator), one could effectively transfer
spin angular momentum through the interface between these two different
materials. The outstanding feature was the detection of auto-oscillation of the
YIG when enough dc current was passed in the Pt. This finding has created a
great excitement in the community for two reasons: first, one could control
electronically the damping of insulators, which can offer improved properties
compared to metals, and here YIG has the lowest damping known in nature;
second, the damping compensation could be achieved on very large objects, a
particularly relevant point for the field of magnonics [6,7] whose aim is to
use spin-waves as carriers of information. However, the degree of coherence of
the observed auto-oscillations has not been addressed in ref. [5]. In this
work, we emphasize the key role of quasi-degenerate spin-wave modes, which
increase the threshold current. This requires to reduce both the thickness and
lateral size in order to reach full damping compensation [8] , and we show
clear evidence of coherent spin-orbit torque induced auto-oscillation in
micron-sized YIG discs of thickness 20 nm.",1504.01512v1
2015-05-01,Periodic solutions for nonlinear hyperbolic evolution systems,"We shall deal with the periodic problem for nonlinear perturbations of
abstract hyperbolic evolution equations generating an evolution system of
contractions. We prove an averaging principle for the translation along
trajectories operator associated to the nonlinear evolution system, expressed
in terms of the topological degree. The abstract results shall be applied to
the damped hyperbolic partial differential equation.",1505.00150v1
2015-05-28,"Moore-Gibson-Thompson equation with memory, part I: exponential decay of energy","We are interested in the Moore-Gibson-Thompson(MGT) equation with memory
\begin{equation}\nonumber \tau u_{ttt}+ \alpha u_{tt}+c^2\A u+b\A u_t
-\int_0^tg(t-s)\A w(s)ds=0. \end{equation} We first classify the memory into
three types. Then we study how a memory term creates damping mechanism and how
the memory causes energy decay.",1505.07523v1
2015-05-29,Fission barriers heights in A$\sim$ 200 mass region,"Statistical model analysis has been carried out for $p$ and $\alpha$ induced
fission reactions using a consistent description for fission barrier and level
density in A $\sim$ 200 mass region. A continuous damping of shell correction
with excitation energy have been considered. Extracted fission barriers agree
well with the recent microscopic-macroscopic model. The shell corrections at
the saddle point were found to be not significant.",1505.08026v1
2015-06-16,Revisit on How to Derive Asymptotic Profiles to Some Evolution Equations,"We consider the Cauchy problem in ${\bf R}^{n}$ for heat and damped wave
equations. We derive asymptotic profiles to those solutions with weighted
$L^{1,1}({\bf R}^{n})$ data by presenting a simple method.",1506.04858v1
2015-06-21,Predicting the Influence of Plate Geometry on the Eddy Current Pendulum,"We quantitatively analyze a familiar classroom demonstration, Van
Waltenhofen's eddy current pendulum, to predict the damping effect for a
variety of plate geometries from first principles. Results from conformal
mapping, finite element simulations and a simplified model suitable for
introductory classes are compared with experiments.",1506.06401v1
2015-07-19,"Alfvén wave phase-mixing in flows: Why over-dense, solar coronal, open magnetic field structures are cool?","The motivation for this study is to include the effect of plasma flow in
Alfv\'en wave (AW) damping via phase mixing and to explore the observational
implications. Our magnetohydrodynamic (MHD) simulations and analytical
calculations show that, when a background flow is present, mathematical
expressions for the AW damping via phase mixing are modified by the following
substitution: $C_A^\prime(x) \to C_A^\prime(x)+V_0^\prime(x)$, where $C_A$ and
$V_0$ are AW phase and the flow speeds, and the prime denotes a derivative in
the direction across the background magnetic field. In uniform magnetic fields
and over-dense plasma structures, where $C_A$ is smaller than in the
surrounding plasma, the flow, which is confined to the structure and going in
the same direction as the AW, reduces the effect of phase-mixing, because on
the edges of the structure $C_A^\prime$ and $V_0^\prime$ have opposite signs.
Thus, the wave damps by means of slower phase-mixing compared to the case
without the flow. This is the result of the co-directional flow that reduces
the wave front stretching in the transverse direction. We apply our findings to
addressing the question why over-dense solar coronal open magnetic field
structures (OMFS) are cooler than the background plasma. Observations show that
the over-dense OMFS (e.g. solar coronal polar plumes) are cooler than
surrounding plasma and that, in these structures, Doppler line-broadening is
consistent with bulk plasma motions, such as AW. If over-dense solar coronal
OMFS are heated by AW damping via phase-mixing, we show that, co-directional
with AW, plasma flow in them reduces the phase-mixing induced-heating, thus
providing an explanation of why they appear cooler than the background.",1507.05293v2
2015-09-28,Linear inviscid damping for a class of monotone shear flow in Sobolev spaces,"In this paper, we prove the decay estimates of the velocity and $H^1$
scattering for the 2D linearized Euler equations around a class of monotone
shear flow in a finite channel. Our result is consistent with the decay rate
predicted by Case in 1960.",1509.08228v1
2015-10-09,Energy Dissipation and Landau Damping in Two- and Three-Dimensional Plasma Turbulence,"Plasma turbulence is ubiquitous in space and astrophysical plasmas, playing
an important role in plasma energization, but the physical mechanisms leading
to dissipation of the turbulent energy remain to be definitively identified.
Kinetic simulations in two dimensions (2D) have been extensively used to study
the dissipation process. How the limitation to 2D affects energy dissipation
remains unclear. This work provides a model of comparison between two- and
three-dimensional (3D) plasma turbulence using gyrokinetic simulations; it also
explores the dynamics of distribution functions during the dissipation process.
It is found that both 2D and 3D nonlinear gyrokinetic simulations of a low-beta
plasma generate electron velocity-space structures with the same
characteristics as that of linear Landau damping of Alfv\'en waves in a 3D
linear simulation. The continual occurrence of the velocity-space structures
throughout the turbulence simulations suggests that the action of Landau
damping may be responsible for the turbulent energy transfer to electrons in
both 2D and 3D, and makes possible the subsequent irreversible heating of the
plasma through collisional smoothing of the velocity-space fluctuations.
Although, in the 2D case where variation along the equilibrium magnetic field
is absent, it may be expected that Landau damping is not possible, a common
trigonometric factor appears in the 2D resonant denominator, leaving the
resonance condition unchanged from the 3D case. The evolution of the 2D and 3D
cases is qualitatively similar. However, quantitatively the nonlinear energy
cascade and subsequent dissipation is significantly slower in the 2D case.",1510.02842v2
2015-10-10,Boundary layers and incompressible Navier-Stokes-Fourier limit of the Boltzmann Equation in Bounded Domain (I),"We establish the incompressible Navier-Stokes-Fourier limit for solutions to
the Boltzmann equation with a general cut-off collision kernel in a bounded
domain. Appropriately scaled families of DiPerna-Lions-(Mischler) renormalized
solutions with Maxwell reflection boundary conditions are shown to have
fluctuations that converge as the Knudsen number goes to zero. Every limit
point is a weak solution to the Navier-Stokes-Fourier system with different
types of boundary conditions depending on the ratio between the accommodation
coefficient and the Knudsen number. The main new result of the paper is that
this convergence is strong in the case of Dirichlet boundary condition. Indeed,
we prove that the acoustic waves are damped immediately, namely they are damped
in a boundary layer in time. This damping is due to the presence of viscous and
kinetic boundary layers in space. As a consequence, we also justify the first
correction to the infinitesimal Maxwellian that one obtains from the
Chapman-Enskog expansion with Navier-Stokes scaling.
  This extends the work of Golse and Saint-Raymond \cite{Go-Sai04, Go-Sai05}
and Levermore and Masmoudi \cite{LM} to the case of a bounded domain. The case
of a bounded domain was considered by Masmoudi and Saint-Raymond \cite{M-S} for
linear Stokes-Fourier limit and Saint-Raymond \cite{SRM} for Navier-Stokes
limit for hard potential kernels. Both \cite{M-S} and \cite{SRM} didn't study
the damping of the acoustic waves. This paper extends the result of \cite{M-S}
and \cite{SRM} to the nonlinear case and includes soft potential kernels. More
importantly, for the Dirichlet boundary condition, this work strengthens the
convergence so as to make the boundary layer visible. This answers an open
problem proposed by Ukai \cite{Ukai}.",1510.02977v1
2015-11-12,Global weak solutions to 3D compressible Navier-Stokes-Poisson equations with density-dependent viscosity,"Global-in-time weak solutions to the Compressible Navier-Stokes-Poisson
equations in a three-dimensional torus for large data are considered in this
paper. The system takes into account density-dependent viscosity and
non-monotone presseur. We prove the existence of global weak solutions to NSP
equations with damping term by using the Faedo-Galerkin method and the
compactness arguments on the condition that the adiabatic constant satisfies
$\gamma>\frac{4}{3}$.",1511.03841v1
2015-11-18,Temperature cooling in quantum dissipation channel and the correspondimg thermal vacuum state,"We examine temperature cooling of optical chaotic light in a quantum
dissipation channel with the damping parameter k.The way we do it is by
introducing its thermal vacuum state which can expose entangling effect between
the system and the reservoir. The temperature cooling formula is derived, which
depends on the parameter k, by adjusting k one can control temperature.",1511.05777v1
2015-12-03,Lieb-Thirring inequalities on the torus,"We consider the Lieb-Thirring inequalities on the d-dimensional torus with
arbitrary periods. In the space of functions with zero average with respect to
the shortest coordinate we prove the Lieb-Thirring inequalities for the
$\gamma$-moments of the negative eigenvalues with constants independent of
ratio of the periods. Applications to the attractors of the damped
Navier-Stokes system are given.",1512.01160v1
2016-01-30,Quantum Dynamics of Complex Hamiltonians,"Non hermitian Hamiltonians play an important role in the study of dissipative
quantum systems. We show that using states with time dependent normalization
can simplify the description of such systems especially in the context of the
classical limit. We apply this prescription to study the damped harmonic
oscillator system. This is then used to study the problem of radiation in leaky
cavity.",1602.00157v2
2016-02-17,Instability of a witness bunch in a plasma bubble,"The stability of a trailing witness bunch, accelerated by a plasma wake
accelerator (PWA) in a blow-out regime, is discussed. The instability growth
rate as well as the energy spread, required for BNS damping, are obtained. A
relationship between the PWA power efficiency and the BNS energy spread is
derived.",1602.05260v2
2016-02-25,Strong Ly alpha Emission in the Proximate Damped Ly alpha Absorption Trough toward the Quasar SDSS J095253.83+011422.0,"SDSS J095253.83+011422.0 (SDSS J0952+0114) was reported by Hall et al. (2004)
as an exotic quasar at $z_{\rm em}=3.020$. In contrast to prominent broad
metal--line emissions with FWHM~9000 km/s, only a narrow Ly \alpha emission
line is present with FWHM~1000 km/s. The absence of broad Ly alpha emission
line has been a mystery for more than a decade. In this paper, we demonstrate
that this is due to dark Proximate Damped Ly alpha Absorption (PDLA) at $z_{\rm
abs}=3.010$ by identifying associated Lyman absorption line series from the
damped Ly beta up to Ly9, as well as the Lyman limit absorption edge. The PDLA
cloud has a column density of $\log N_{\rm H\,I}({\rm cm}^{-2})=21.8\pm0.2$, a
metallicity of [Zn/H]$>-1.0$, and a spatial extent exceeding the Narrow
Emission Line Region (NELR) of the quasar. With a luminosity of $L_{{\rm
Ly}\alpha}\sim10^{45}$ erg s$^{-1}$, the residual Ly alpha emission superposed
on the PDLA trough is of two orders of magnitude stronger than previous
reports. This is best explained as re-radiated photons arising from the quasar
outflowing gas at a scale larger than the NELR. The PDLA here, acting like a
natural coronagraph, provides us with a good insight into the illuminated gas
in the vicinity of the quasar, which are usually hard to resolve due to their
small size and ""seeing fuzz"" of bright quasars. Notably, SDSS J0952+0114
analogs might be easily omitted in the spectroscopic surveys of DLAs and PDLAs,
as their damped Ly alpha troughs can be fully filled by additional strong Ly
alpha emissions. Our preliminary survey shows that such systems are not very
rare. They are potentially a unique sample for probing strong quasar feedback
phenomena in the early universe.",1602.07880v2
2016-03-27,Evolution of One-Dimensional Wind-Driven Sea Spectra,"We analyze modern operational models of wind wave prediction on the subject
for compliance dissipation. Our numerical simulations from the ""first
principle"" demonstrate that heuristic formulas for damping rate of free wind
sea due to ""white capping"" (or wave breaking) dramatically exaggerates the role
of this effect in these models.",1603.08229v1
2016-03-07,Faddeev-Jackiw Quantization of Non-Autonomous Singular Systems,"We extend the quantization \`a la Faddeev-Jackiw for non-autonomous singular
systems. This leads to a generalization of the Schr\""odinger equation for those
systems. The method is exemplified by the quantization of the damped harmonic
oscillator and the relativistic particle in an external electromagnetic field.",1603.08407v1
2016-05-06,Existence of invariant measures for the stochastic damped Schrödinger equation,"In this paper, we address the long time behaviour of solutions of the
stochastic Schrodinger equation in $\mathbb{R}^d$. We prove the existence of an
invariant measure and establish asymptotic compactness of solutions, implying
in particular the existence of an ergodic measure.",1605.02014v1
2016-05-25,"Dynamic analysis of simultaneous adaptation of force, impedance and trajectory","When carrying out tasks in contact with the environment, humans are found to
concurrently adapt force, impedance and trajectory. Here we develop a robotic
model of this mechanism in humans and analyse the underlying dynamics. We
derive a general adaptive controller for the interaction of a robot with an
environment solely characterised by its stiffness and damping, using Lyapunov
theory.",1605.07834v1
2016-06-24,Mixing for the Burgers equation driven by a localised two-dimensional stochastic forcing,"We consider the one-dimensional Burgers equation perturbed by a stochastic
forcing, which is assumed to be white in time and localised and low-dimensional
in space. We establish a mixing property for the Markov process associated with
the problem in question. The proof is based on a general criterion for mixing
and a recent result on global approximate controllability to trajectories for
damped conservation laws.",1606.07763v1
2016-07-01,Randomized block proximal damped Newton method for composite self-concordant minimization,"In this paper we consider the composite self-concordant (CSC) minimization
problem, which minimizes the sum of a self-concordant function $f$ and a
(possibly nonsmooth) proper closed convex function $g$. The CSC minimization is
the cornerstone of the path-following interior point methods for solving a
broad class of convex optimization problems. It has also found numerous
applications in machine learning. The proximal damped Newton (PDN) methods have
been well studied in the literature for solving this problem that enjoy a nice
iteration complexity. Given that at each iteration these methods typically
require evaluating or accessing the Hessian of $f$ and also need to solve a
proximal Newton subproblem, the cost per iteration can be prohibitively high
when applied to large-scale problems. Inspired by the recent success of block
coordinate descent methods, we propose a randomized block proximal damped
Newton (RBPDN) method for solving the CSC minimization. Compared to the PDN
methods, the computational cost per iteration of RBPDN is usually significantly
lower. The computational experiment on a class of regularized logistic
regression problems demonstrate that RBPDN is indeed promising in solving
large-scale CSC minimization problems. The convergence of RBPDN is also
analyzed in the paper. In particular, we show that RBPDN is globally convergent
when $g$ is Lipschitz continuous. It is also shown that RBPDN enjoys a local
linear convergence. Moreover, we show that for a class of $g$ including the
case where $g$ is Lipschitz differentiable, RBPDN enjoys a global linear
convergence. As a striking consequence, it shows that the classical damped
Newton methods [22,40] and the PDN [31] for such $g$ are globally linearly
convergent, which was previously unknown in the literature. Moreover, this
result can be used to sharpen the existing iteration complexity of these
methods.",1607.00101v1
2016-11-09,Witnessing quantum capacities of correlated channels,"We test a general method to detect lower bounds of the quantum channel
capacity for two-qubit correlated channels. We consider in particular
correlated dephasing, depolarising and amplitude damping channels. We show that
the method is easily implementable, it does not require a priori knowledge
about the channels, and it is very efficient, since it does not rely on full
quantum process tomography.",1611.02857v1
2017-03-20,Recovery of the starting times of delayed signals,"We present a new method to locate the starting points in time of an arbitrary
number of (damped) delayed signals. For a finite data sequence, the method
permits to first locate the starting point of the component with the longest
delay, and then --by iteration-- all the preceding ones. Numerical examples are
given and noise sensitivity is tested for weak noise.",1703.07001v1
2017-05-13,Eigenvalues of one-dimensional non-self-adjoint Dirac operators and applications,"We analyze eigenvalues emerging from thresholds of the essential spectrum of
one-dimensional Dirac operators perturbed by complex and non-symmetric
potentials. In the general non-self-adjoint setting we establish the existence
and asymptotics of weakly coupled eigenvalues and Lieb-Thirring inequalities.
As physical applications we investigate the damped wave equation and armchair
graphene nanoribbons.",1705.04833v1
2017-09-07,"The driven oscillator, with friction","This paper develops further the semi-classical theory of an harmonic
oscillator acted on by a Gaussian white noise force discussed in
(arXiv:1508.02379). Here I add to that theory the effects of Brownian damping
(friction). Albeit semi-classical, the theory can be used to model quantum
expectations and probabilities. I consider several examples.",1709.03391v1
2017-09-24,Exceptional points in two simple textbook examples,"We propose to introduce the concept of exceptional points in intermediate
courses on mathematics and classical mechanics by means of simple textbook
examples. The first one is an ordinary second-order differential equation with
constant coefficients. The second one is the well known damped harmonic
oscillator. They enable one to connect the occurrence of linearly dependent
exponential solutions with a defective matrix that cannot be diagonalized but
can be transformed into a Jordan canonical form.",1710.00067v1
2017-11-16,Correlations in the three-dimensional Lyman-alpha forest contaminated by high column density absorbers,"Correlations measured in three dimensions in the Lyman-alpha forest are
contaminated by the presence of the damping wings of high column density (HCD)
absorbing systems of neutral hydrogen (HI; having column densities
$N(\mathrm{HI}) > 1.6\times10^{17}\,\mathrm{atoms}\,\mathrm{cm}^{-2}$), which
extend significantly beyond the redshift-space location of the absorber. We
measure this effect as a function of the column density of the HCD absorbers
and redshift by measuring 3D flux power spectra in cosmological hydrodynamical
simulations from the Illustris project. Survey pipelines exclude regions
containing the largest damping wings. We find that, even after this procedure,
there is a scale-dependent correction to the 3D Lyman-alpha forest flux power
spectrum from residual contamination. We model this residual using a simple
physical model of the HCD absorbers as linearly biased tracers of the matter
density distribution, convolved with their Voigt profiles and integrated over
the column density distribution function. We recommend the use of this model
over existing models used in data analysis, which approximate the damping wings
as top-hats and so miss shape information in the extended wings. The simple
'linear Voigt model' is statistically consistent with our simulation results
for a mock residual contamination up to small scales ($|k| <
1\,h\,\mathrm{Mpc}^{-1}$). It does not account for the effect of the highest
column density absorbers on the smallest scales (e.g., $|k| >
0.4\,h\,\mathrm{Mpc}^{-1}$ for small damped Lyman-alpha absorbers; HCD
absorbers with $N(\mathrm{HI}) \sim
10^{21}\,\mathrm{atoms}\,\mathrm{cm}^{-2}$). However, these systems are in any
case preferentially removed from survey data. Our model is appropriate for an
accurate analysis of the baryon acoustic oscillations feature. It is
additionally essential for reconstructing the full shape of the 3D flux power
spectrum.",1711.06275v2
2017-12-05,Harnessing Electrical Power from Vortex-Induced Vibration of a Circular Cylinder,"The generation of electrical power from Vortex-Induced Vibration (VIV) of a
cylinder is investigated numerically. The cylinder is free to oscillate in the
direction transverse to the incoming flow. The cylinder is attached to a magnet
that can move along the axis of a coil made from conducting wire. The magnet
and the coil together constitute a basic electrical generator. When the
cylinder undergoes VIV, the motion of the magnet creates a voltage across the
coil, which is connected to a resistive load. By Lenz's law, induced current in
the coil applies a retarding force to the magnet. Effectively, the electrical
generator applies a damping force on the cylinder with a spatially varying
damping coefficient. For the initial investigation reported here, the Reynolds
number is restricted to Re < 200, so that the flow is laminar and
two-dimensional (2D). The incompressible 2D Navier-Stokes equations are solved
using an extensively validated spectral-element based solver. The effects of
the electromagnetic (EM) damping constant xi_m, coil dimensions (radius a,
length L), and mass ratio on the electrical power extracted are quantified. It
is found that there is an optimal value of xi_m (xi_opt) at which maximum
electrical power is generated. As the radius or length of the coil is
increased, the value of xi_opt is observed to increase. Although the maximum
average power remains the same, a larger coil radius or length results in a
more robust system in the sense that a relatively large amount of power can be
extracted when xi_m is far from xi_opt, unlike the constant damping ratio case.
The average power output is also a function of Reynolds number, primarily
through the increased maximum oscillation amplitude that occurs with increased
Reynolds number at least within the laminar range, although the general
qualitative findings seem likely to carry across to high Reynolds number VIV.",1712.01588v1
2017-12-08,An algorithm to resolve γ-rays from charged cosmic rays with DAMPE,"The DArk Matter Particle Explorer (DAMPE), also known as Wukong in China,
launched on December 17, 2015, is a new high energy cosmic ray and {\gamma}-ray
satellite-borne observatory in space. One of the main scientific goals of DAMPE
is to observe GeV-TeV high energy {\gamma}-rays with accurate energy, angular,
and time resolution, to indirectly search for dark matter particles and for the
study of high energy astrophysics. Due to the comparatively higher fluxes of
charged cosmic rays with respect to {\gamma}-rays, it is challenging to
identify {\gamma}-rays with sufficiently high efficiency minimizing the amount
of charged cosmic ray contamination. In this work we present a method to
identify {\gamma}-rays in DAMPE data based on Monte Carlo simulations, using
the powerful electromagnetic/hadronic shower discrimination provided by the
calorimeter and the veto detection of charged particles provided by the plastic
scintillation detector. Monte Carlo simulations show that after this selection
the number of electrons and protons that contaminate the selected {\gamma}-ray
events at $\sim10$ GeV amounts to less than 1% of the selected sample. Finally,
we use flight data to verify the effectiveness of the method by highlighting
known {\gamma}-ray sources in the sky and by reconstructing preliminary light
curves of the Geminga pulsar.",1712.02939v1
2017-12-27,A simple and natural interpretations of the DAMPE cosmic-ray electron/positron spectrum within two sigma deviations,"The DArk Matter Particle Explorer (DAMPE) experiment has recently announced
the first results for the measurement of total electron plus positron fluxes
between 25 GeV and 4.6 TeV. A spectral break at about 0.9 TeV and a tentative
peak excess around 1.4 TeV have been found. However, it is very difficult to
reproduce both the peak signal and the smooth background including spectral
break simultaneously. We point out that the numbers of events in the two energy
ranges (bins) close to the 1.4 TeV excess have $1\sigma$ deficits. With the
basic physics principles such as simplicity and naturalness, we consider the
$-2\sigma$, $+2\sigma$, and $-1\sigma$ deviations due to statistical
fluctuations for the 1229.3~GeV bin, 1411.4~GeV bin, and 1620.5~GeV bin.
Interestingly, we show that all the DAMPE data can be explained consistently
via both the continuous distributed pulsar and dark matter interpretations,
which have $\chi^{2} \simeq 17.2 $ and $\chi^{2} \simeq 13.9$ (for all the 38
points in DAMPE electron/positron spectrum with 3 of them revised),
respectively. These results are different from the previous analyses by
neglecting the 1.4 TeV excess. At the same time, we do a similar global fitting
on the newly released CALET lepton data, which could also be interpreted by
such configurations. Moreover, we present a $U(1)_D$ dark matter model with
Breit-Wigner mechanism, which can provide the proper dark matter annihilation
cross section and escape the CMB constraint. Furthermore, we suggest a few ways
to test our proposal.",1712.09586v6
2018-03-21,Well-posedness and stabilization of the Benjamin-Bona-Mahony equation on star-shaped networks,"We study the stabilization issue of the Benjamin-Bona-Mahony (BBM) equation
on a finite star-shaped network with a damping term acting on the central node.
In a first time, we prove the well-posedness of this system. Then thanks to the
frequency domain method, we get the asymptotic stabilization result.",1803.07914v1
2018-04-05,Finite time blow up for wave equations with strong damping in an exterior domain,"We consider the initial boundary value problem in exterior domain for
semilinear wave equations with power-type nonlinearity |u| p. We will establish
blow-up results when p is less than or equal to Strauss' exponent which is the
same one for the whole space case R n .",1804.01689v1
2018-04-13,Well-posedness and long time behavior of singular Langevin stochastic differential equations,"In this paper, we study damped Langevin stochastic differential equations
with singular velocity fields. We prove the strong well-posedness of such
equations. Moreover, by combining the technique of Lyapunov functions with
Krylov's estimate, we also establish the exponential ergodicity for the unique
strong solution.",1804.05086v2
2018-04-27,Contribution of phase-mixing of Alfvén waves to coronal heating in multi-harmonic loop oscillations,"Kink oscillations of a coronal loop are observed and studied in detail
because they provide a unique probe into the structure of coronal loops through
MHD seismology and a potential test of coronal heating through the phase-mixing
of Alfv\'en waves. In particular, recent observations show that standing
oscillations of loops often involve also higher harmonics, beside the
fundamental mode. The damping of these kink oscillations is explained by mode
coupling with Alfv\'en waves. We investigate the consequences for wave-based
coronal heating of higher harmonics and what coronal heating observational
signatures we may use to infer the presence of higher harmonic kink
oscillations. We perform a set of non-ideal MHD simulations where the damping
of the kink oscillation of a flux tube via mode coupling is modelled. Our MHD
simulation parameters are based on the seismological inversion of an
observation for which the first three harmonics are detected. We study the
phase-mixing of Alfv\'en waves that leads to the deposition of heat in the
system, and we apply the seismological inversion techniques to the MHD
simulation output. We find that the heating due to phase-mixing of the Alfv\'en
waves triggered by the damping of the kink oscillation is relatively small,
however we can illustrate i) how the heating location drifts due to the
subsequent damping of lower order harmonics. We also address the role of the
higher order harmonics and the width of the boundary shell in the energy
deposition. We conclude that the coronal heating due to phase-mixing seems not
to provide enough energy to maintain the thermal structure of the solar corona
even when multi-harmonics oscillations are included, and these oscillations
play an inhibiting role in the development of smaller scale structures.",1804.10562v1
2018-05-23,Effect of time varying transmission rates on coupled dynamics of epidemic and awareness over multiplex network,"In the present work, a non-linear stochastic model is presented to study the
effect of time variation of transmission rates on the co-evolution of epidemics
and its corresponding awareness over a two layered multiplex network. In this
model, the infection transmission rate of a given node in the epidemic layer
depends upon its awareness probability in the awareness layer. Similarly, the
infection information transmission rate of a node in the awareness layer
depends upon its infection probability in the epidemic layer. The spread of
disease resulting from physical contacts is described in terms of SIS
(Susceptible Infected Susceptible) process over the epidemic layer and the
spread of information about the disease outbreak is described in terms of UAU
(Unaware Aware Unaware) process over the virtual interaction mediated awareness
layer. The time variation of the transmission rates and the resulting
co-evolution of these mutually competing processes is studied in terms of a
network topology depend parameter({\alpha}). Using a second order linear theory
it has been shown that in the continuous time limit, the co-evolution of these
processes can be described in terms of damped and driven harmonic oscillator
equations. From the results of the Monte-Carlo simulation, it is shown that for
the suitable choice of parameter({\alpha}), the two process can either exhibit
sustained oscillatory or damped dynamics. The damped dynamics corresponds to
the endemic state. Further, for the case of endemic state it is shown that the
inclusion of awareness layer significantly lowers the disease transmission rate
and reduces the size of epidemic. The endemic state infection probability of a
given node corresponding to the damped dynamics is found to have dependence
upon both the transmission rates as well as on both absolute intra-layer and
relative inter-layer degree of the individual nodes.",1805.08947v2
2018-06-09,Recovery Analysis of Damped Spectrally Sparse Signals and Its Relation to MUSIC,"One of the classical approaches for estimating the frequencies and damping
factors in a spectrally sparse signal is the MUSIC algorithm, which exploits
the low-rank structure of an autocorrelation matrix. Low-rank matrices have
also received considerable attention recently in the context of optimization
algorithms with partial observations, and nuclear norm minimization (NNM) has
been widely used as a popular heuristic of rank minimization for low-rank
matrix recovery problems. On the other hand, it has been shown that NNM can be
viewed as a special case of atomic norm minimization (ANM), which has achieved
great success in solving line spectrum estimation problems. However, as far as
we know, the general ANM (not NNM) considered in many existing works can only
handle frequency estimation in undamped sinusoids. In this work, we aim to fill
this gap and deal with damped spectrally sparse signal recovery problems. In
particular, inspired by the dual analysis used in ANM, we offer a novel
optimization-based perspective on the classical MUSIC algorithm and propose an
algorithm for spectral estimation that involves searching for the peaks of the
dual polynomial corresponding to a certain NNM problem, and we show that this
algorithm is in fact equivalent to MUSIC itself. Building on this connection,
we also extend the classical MUSIC algorithm to the missing data case. We
provide exact recovery guarantees for our proposed algorithms and quantify how
the sample complexity depends on the true spectral parameters. In particular,
we provide a parameter-specific recovery bound for low-rank matrix recovery of
jointly sparse signals rather than use certain incoherence properties as in
existing literature. Simulation results also indicate that the proposed
algorithms significantly outperform some relevant existing methods (e.g., ANM)
in frequency estimation of damped exponentials.",1806.03511v5
2018-07-13,N-body simulations of structure formation in thermal inflation cosmologies,"Thermal inflation models (which feature two inflationary stages) can display
damped primordial curvature power spectra on small scales which generate damped
matter fluctuations. For a reasonable choice of parameters, thermal inflation
models naturally predict a suppression of the matter power spectrum on galactic
and sub-galactic scales, mimicking the effect of warm or interacting dark
matter. Matter power spectra in these models are also characterised by an
excess of power (w.r.t. the standard $\Lambda$CDM power spectrum) just below
the suppression scale. By running a suite of N-body simulations we investigate
the non-linear growth of structure in models of thermal inflation. We measure
the non-linear matter power spectrum and extract halo statistics, such as the
halo mass function, and compare these quantities with those predicted in the
standard $\Lambda$CDM model and in other models with damped matter
fluctuations. We find that the thermal inflation models considered here produce
measurable differences in the matter power spectrum from $\Lambda$CDM at
redshifts $z>5$, while the halo mass functions are appreciably different at all
redshifts. The halo mass function at $z=0$ for thermal inflation displays an
enhancement of around $\sim 20\%$ w.r.t. $\Lambda$CDM and a damping at lower
halo masses, with the position of the enhancement depending on the value of the
free parameter in the model. The enhancement in the halo mass function (w.r.t.
$\Lambda$CDM ) increases with redshift, reaching $\sim 40\%$ at $z=5$. We also
study the accuracy of the analytical Press-Schechter approach, using different
filters to smooth the density field, to predict halo statistics for thermal
inflation. We find that the predictions with the smooth-$k$ filter agree with
the simulation results over a wider range of halo masses than is the case with
other filters commonly used in the literature.",1807.04980v2
2018-07-16,Global existence for semilinear damped wave equations in relation with the Strauss conjecture,"We study the global existence of solutions to semilinear wave equations with
power-type nonlinearity and general lower order terms on $n$ dimensional
nontrapping asymptotically Euclidean manifolds, when $n=3, 4$. In addition, we
prove almost global existence with sharp lower bound of the lifespan for the
four dimensional critical problem.",1807.05908v1
2018-07-20,Effect of correlated noise channels on quantum speed limit,"We study the effect of correlated Markovian noise channels on the quantum
speed limit of an open system. This is done for correlated dephasing and
amplitude damping channels for a two qubit atomic model. Our model serves as a
platform for a detailed study of speed of quantum evolution in correlated open
systems.",1807.07782v2
2018-08-20,Local existence of Strong solutions for a fluid-structure interaction model,"We are interested in studying a system coupling the compressible
Navier-Stokes equations with an elastic structure located at the boundary of
the fluid domain. Initially the fluid domain is rectangular and the beam is
located on the upper side of the rectangle. The elastic structure is modeled by
an Euler-Bernoulli damped beam equation. We prove the local in time existence
of strong solutions for that coupled system.",1808.06716v1
2018-09-04,Creation of bipartite steering correlations by a fast damped auxiliary mode,"We consider a three-mode system and show how steering correlations can be
created between two modes of the system using the fast dissipation of the third
mode. These correlations result in a directional form of entanglement, called
quantum or EPR steering. We illustrate this on examples of the interactions
among damped radiation modes in an optomechanical three-mode system. By
assuming that one of the modes undergoes fast dissipation, we show that the
coupling of that mode to one or two other modes of the system may result in
one- or two-way quantum steering. Explicit analytical results are given for the
steering parameters. We find that two modes coupled by the parametric-type
interaction and damped with the same rates can be entangled but cannot exhibit
quantum steering. When, in addition, one of the modes is coupled to a fast
damped mode, steering correlations are created and the modes then exhibit
one-way steering. The creation of the steering correlations is interpreted in
the context of the variances of the quadrature components of the modes that the
steering correlations result from an asymmetry in the variances of the
quadrature components of the modes induced by the auxiliary mode. It is found
that the fluctuations act directionally that quantum steering may occur only
when the variance of the steering mode is larger that the variance of the
steered mode. The scheme is shown to be quite robust against the thermal
excitation of the modes if the fluctuations of the steering mode are larger
than the fluctuations of the steered mode.",1809.01176v1
2018-10-06,Global Well-Posedness and Global Attractor for Two-dimensional Zakharov-Kuznetsov Equation,"The initial value problem for two-dimensional Zakharov-Kuznetsov equation is
shown to be globally well-posed in $H^s({\mathbb{R}^2})$ for all
$\frac{5}{7}<s<1$ via using $I$-method in the context of atomic spaces. By
means of the increment of modified energy, the exsitence of global attractor
for weakly damped, forced Zakharov-Kuznetsov equation is also established in
$H^s({\mathbb{R}^2})$ for $\frac{10}{11}<s<1$.",1810.02984v1
2018-10-07,Uniform attractors for measure-driven quintic wave equation with periodic boundary conditions,"We give a detailed study of attractors for measure driven quintic damped wave
equations with periodic boundary conditions. This includes uniform
energy-to-Strichartz estimates, the existence of uniform attractors in a weak
or strong topology in the energy phase space, the possibility to present them
as a union of all complete trajectories, further regularity, etc.",1810.03149v1
2018-10-13,Exponential Decay in a Timoshenko-type System of Thermoelasticity of Type III with Frictional versus Viscoelatic Damping and Delay,"In this work, a Timoshenko system of type III of thermoelasticity with
frictional versus viscoelastic under Dirichlet-Dirichlet-Neumann boundary
conditions was considered. By exploiting energy method to produce a suitable
Lyapunov functional, we establish the global existence, exponential decay of
Type-III case.",1810.05820v1
2018-12-22,Damping of acoustic waves in straight ducts and turbulent flow conditions,"In this paper the propagation of acoustic plane waves in turbulent, fully
developed flow is studied by means of an experimental investigation carried out
in a straight, smooth-walled duct.The presence of a coherent perturbation, such
as an acoustic wave in a turbulent confined flow, generates the oscillation of
the wall shear stress. In this circumstance a shear wave is excited and
superimposed on the sound wave. The turbulent shear stress is modulated by the
shear wave and the wall shear stress is strongly affected by the turbulence.
From the experimental point of view, it results in a measured damping strictly
connected to the ratio between the thickness of the acoustic sublayer, which is
frequency dependent, and the thickness of the viscous sublayer of the turbulent
mean flow, the last one being dependent on the Mach number. By reducing the
turbulence, the viscous sublayer thickness increases and the wave propagation
is mainly dominated by convective effects. In the present work, the damping and
wall impedance have been extracted from the measured complex wavenumber, which
represents the most important parameter used to characterize the wave
propagation. An experimental approach, referred to as iterative plane wave
decomposition, has been used in order to obtain the results. The investigations
have been carried out at low Mach number turbulent flows, low Helmholtz numbers
and low shear wavenumbers. The aim is to overcome a certain lack of
experimental results found by the authors of the most recent models for the
plane wave propagation in turbulent flows, such as Knutsson et al. (The effect
of turbulence damping on acoustic wave propagation in tubes, Journal of Sound
and Vibration, Vol. 329, No. 22, 2010), and Weng et al. (The attenuation of
sound by turbulence in internal flows, The Journal of the Acoustical Society of
America 133(6), 2013).",1812.11063v1
2019-01-30,Transverse waves in coronal flux tubes with thick boundaries: The effect of longitudinal flows,"Observations show that transverse magnetohydrodynamic (MHD) waves and flows
are often simultaneously present in magnetic loops of the solar corona. The
waves are resonantly damped in the Alfv\'en continuum because of plasma and/or
magnetic field nonuniformity across the loop. The resonant damping is relevant
in the context of coronal heating, since it provides a mechanism to cascade
energy down to the dissipative scales. It has been theoretically shown that the
presence of flow affects the waves propagation and damping, but most of the
studies rely on the unjustified assumption that the transverse nonuniformity is
confined to a boundary layer much thinner than the radius of the loop. Here we
present a semi-analytic technique to explore the effect of flow on resonant MHD
waves in coronal flux tubes with thick nonuniform boundaries. We extend a
published method, which was originally developed for a static plasma, in order
to incorporate the effect of flow. We allowed the flow velocity to continuously
vary within the nonuniform boundary from the internal velocity to the external
velocity. The analytic part of the method is based on expressing the wave
perturbations in the thick nonuniform boundary of the loop as a Frobenius
series that contains a singular term accounting for the Alfv\'en resonance,
while the numerical part of the method consists of solving iteratively the
transcendental dispersion relation together with the equation for the Alfv\'en
resonance position. As an application of this method, we investigated the
impact of flow on the phase velocity and resonant damping length of MHD kink
waves. We consistently recover results in the thin boundary approximation
obtained in previous studies. We have extended those results to the case of
thick boundaries. We also explored the error associated with the use of the
thin boundary approximation beyond its regime of applicability.",1901.10785v1
2019-02-07,Violent relaxation in the Hamiltonian Mean Field model: I. Cold collapse and effective dissipation,"In $N$-body systems with long-range interactions mean-field effects dominate
over binary interactions (collisions), so that relaxation to thermal
equilibrium occurs on time scales that grow with $N$, diverging in the
$N\to\infty$ limit. However, a faster and non-collisional relaxation process,
referred to as violent relaxation, sets in when starting from generic initial
conditions: collective oscillations (referred to as virial oscillations)
develop and damp out on timescales not depending on the system's size. After
the damping of such oscillations the system is found in a quasi-stationary
state that survives virtually forever when the system is very large. During
violent relaxation the distribution function obeys the collisionless Boltzmann
(or Vlasov) equation, that, being invariant under time reversal, does not
""naturally"" describe a relaxation process. Indeed, the dynamics is moved to
smaller and smaller scales in phase space as time goes on, so that observables
that do not depend on small-scale details appear as relaxed after a short time.
We propose an approximation scheme to describe collisionless relaxation, based
on the introduction of moments of the distribution function, and apply it to
the Hamiltonian Mean Field (HMF) model. To the leading order, virial
oscillations are equivalent to the motion of a particle in a one-dimensional
potential. Inserting higher-order contributions in an effective way, inspired
by the Caldeira-Leggett model of quantum dissipation, we derive a dissipative
equation describing the damping of the oscillations, including a
renormalization of the effective potential and yielding predictions for
collective properties of the system after the damping in very good agreement
with numerical simulations. Here we restrict ourselves to ""cold"" initial
conditions; generic initial conditions will be considered in a forthcoming
paper.",1902.02436v2
2019-05-16,Boundary control of partial differential equations using frequency domain optimization techniques,"We present a frequency domain based $H_\infty$-control strategy to solve
boundary control problems for systems governed by parabolic or hyperbolic
partial differential equation, where controllers are constrained to be
physically implementable and of simple structure suited for practical
applications. The efficiency of our technique is demonstrated by controlling a
reaction-diffusion equation with input delay, and a wave equation with boundary
anti-damping.",1905.06786v1
2019-05-20,Sharp Bounds for Oscillatory Integral Operators with Homogeneous Polynomial Phases,"We obtain sharp $L^p$ bounds for oscillatory integral operators with generic
homogeneous polynomial phases in several variables. The phases considered in
this paper satisfy the rank one condition which is an important notion
introduced by Greenleaf, Pramanik and Tang. Under certain additional
assumptions, we can establish sharp damping estimates with critical exponents
to prove endpoint $L^p$ estimates.",1905.07980v1
2019-06-06,Well-posedness and exponential decay estimates for a Korteweg-de Vries-Burgers equation with time-delay,"We consider the KdV-Burgers equation and its linear version in presence of a
delay feedback. We prove well-posedness of the models and exponential decay
estimates under appropriate conditions on the damping coefficients. Our
arguments rely on a Lyapunov functional approach combined with a step by step
procedure and semigroup theory.",1906.02488v1
2019-06-19,Accurate Lindblad-Form Master Equation for Weakly Damped Quantum Systems Across All Regimes,"Realistic models of quantum systems must include dissipative interactions
with an environment. For weakly-damped systems the Lindblad-form Markovian
master equation is invaluable for this task due to its tractability and
efficiency. This equation only applies, however, when the frequencies of any
subset of the system's transitions are either equal (degenerate), or their
differences are much greater than the transitions' linewidths (far-detuned).
Outside of these two regimes the only available efficient description has been
the Bloch-Redfield (B-R) master equation, the efficacy of which has long been
controversial due to its failure to guarantee the positivity of the density
matrix. The ability to efficiently simulate weakly-damped systems across all
regimes is becoming increasingly important, especially in the area of quantum
technologies. Here we solve this long-standing problem. We discover that a
condition on the slope of the spectral density is sufficient to derive a
Lindblad form master equation that is accurate for all regimes. We further show
that this condition is necessary for weakly-damped systems to be described by
the B-R equation or indeed any Markovian master equation. We thus obtain a
replacement for the B-R equation over its entire domain of applicability that
is no less accurate, simpler in structure, completely positive, allows
simulation by efficient quantum trajectory methods, and unifies the previous
Lindblad master equations. We also show via exact simulations that the new
master equation can describe systems in which slowly-varying transition
frequencies cross each other during the evolution. System identification tools,
developed in systems engineering, play an important role in our analysis. We
expect these tools to prove useful in other areas of physics involving complex
systems.",1906.08279v2
2019-07-10,Heuristic construction of codeword stabilized codes,"The family of codeword stabilized codes encompasses the stabilizer codes as
well as many of the best known nonadditive codes. However, constructing optimal
$n$-qubit codeword stabilized codes is made difficult by two main factors. The
first of these is the exponential growth with $n$ of the number of graphs on
which a code can be based. The second is the NP-hardness of the maximum clique
search required to construct a code from a given graph. We address the second
of these issues through the use of a heuristic clique finding algorithm. This
approach has allowed us to find $((9,97\leq K\leq100,2))$ and $((11,387\leq
K\leq416,2))$ codes, which are larger than any previously known codes. To
address the exponential growth of the search space, we demonstrate that graphs
that give large codes typically yield clique graphs with a large number of
nodes. The number of such nodes can be determined relatively efficiently, and
we demonstrate that $n$-node graphs yielding large clique graphs can be found
using a genetic algorithm. This algorithm uses a novel spectral bisection based
crossover operation that we demonstrate to be superior to more standard
crossover operations. Using this genetic algorithm approach, we have found
$((13,18,4))$ and $((13,20,4))$ codes that are larger than any previously known
code. We also consider codes for the amplitude damping channel. We demonstrate
that for $n\leq9$, optimal codeword stabilized codes correcting a single
amplitude damping error can be found by considering standard form codes that
detect one of only three of the $3^{n}$ possible equivalent error sets. By
combining this error set selection with the genetic algorithm approach, we have
found $((11,68))$ and $((11,80))$ codes capable of correcting a single
amplitude damping error and $((11,4))$, $((12,4))$, $((13,8))$, and $((14,16))$
codes capable of correcting two amplitude damping",1907.04537v2
2019-07-10,Exponential stability for the nonlinear Schrödinger equation on a star-shaped network,"In this paper, we prove the exponential stability of the solution of the
nonlinear dissipative Schr\""odinger equation on a star-shaped network and where
the damping is localized on one branch and at the infinity.",1907.04950v1
2019-07-22,Role of charge equilibration in multinucleon transfer in damped collisions of heavy ions,"In this work, the charge equilibration process has been analyzed within the
Langevin-type dynamical approach. Its duration and energy dependence are
discussed. We have analyzed the isotopic distributions of final products
obtained in the isospin-asymmetric 58Ni,40Ca + 208Pb reactions. Comparison of
58Ni,64Ni + 208Pb systems have been done in order to analyze the final yields
of neutron-rich heavy nuclides.",1907.09352v1
2019-09-25,Neutrino decoherence in a fermion and scalar background,"We consider the decoherence effects in the propagation of neutrinos in a
background composed of a scalar particle and a fermion due to the non-forward
neutrino scattering processes. Using a simple model for the coupling of the
form $\bar f_R\nu_L\phi$ we calculate the contribution to the imaginary part of
the neutrino self-energy arising from the non-forward neutrino scattering
processes in such backgrounds, from which the damping terms are determined. In
the case we are considering, in which the initial neutrino state is depleted
but does not actually disappear (the initial neutrino transitions into a
neutrino of a different flavor but does not decay into a $f\phi$ pair, for
example), we associate the damping terms with decoherence effects. For this
purpose we give a precise prescription to identify the decoherence terms, as
used in the context of the master or Linblad equation, in terms of the damping
terms we have obtained from the calculation of the imaginary part of the
neutrino self-energy from the non-forward neutrino scattering processes. The
results can be directly useful in the context of Dark Matter-neutrino
interaction models in which the scalar and/or fermion constitute the
dark-matter, and can also serve to guide the generalizations to other models
and/or situations in which the decoherence effects in the propagation of
neutrinos originate from the non-forward scattering processes may be important.
As a guide to estimating such decoherence effects, the contributions to the
absorptive part of the self-energy and the corresponding damping terms are
computed explicitly in the context of the model we consider, for several
limiting cases of the momentum distribution functions of the background
particles.",1909.11271v2
2019-10-15,Adversarial Examples for Models of Code,"Neural models of code have shown impressive results when performing tasks
such as predicting method names and identifying certain kinds of bugs. We show
that these models are vulnerable to adversarial examples, and introduce a novel
approach for attacking trained models of code using adversarial examples. The
main idea of our approach is to force a given trained model to make an
incorrect prediction, as specified by the adversary, by introducing small
perturbations that do not change the program's semantics, thereby creating an
adversarial example. To find such perturbations, we present a new technique for
Discrete Adversarial Manipulation of Programs (DAMP). DAMP works by deriving
the desired prediction with respect to the model's inputs, while holding the
model weights constant, and following the gradients to slightly modify the
input code. We show that our DAMP attack is effective across three neural
architectures: code2vec, GGNN, and GNN-FiLM, in both Java and C#. Our
evaluations demonstrate that DAMP has up to 89% success rate in changing a
prediction to the adversary's choice (a targeted attack) and a success rate of
up to 94% in changing a given prediction to any incorrect prediction (a
non-targeted attack). To defend a model against such attacks, we empirically
examine a variety of possible defenses and discuss their trade-offs. We show
that some of these defenses can dramatically drop the success rate of the
attacker, with a minor penalty of 2% relative degradation in accuracy when they
are not performing under attack. Our code, data, and trained models are
available at https://github.com/tech-srl/adversarial-examples .",1910.07517v5
2019-11-21,Special Itô maps and an $L^2$ Hodge theory for one forms on path spaces,"We prove a Kodaira-Hodge decomposition on differential 1-forms on the space
of non-smooth paths over a Riemannian manifold, allowing us to define the
corresponding first cohomology group. This uses the It\^o map of a Brownian
system and damped stochastic parallel translation.",1911.09618v1
2019-12-03,The global classical solution to compressible Euler system with velocity alignment,"In this paper, the compressible Euler system with velocity alignment and
damping is considered, where the influence matrix of velocity alignment is not
positive definite. Sound speed is used to reformulate the system into symmetric
hyperbolic type. The global existence and uniqueness of smooth solution for
small initial data is provided.",1912.01374v1
2019-12-23,Signal Analysis using Born-Jordan-type Distribution,"In this note we exhibit recent advances in signal analysis via time-frequency
distributions. New members of the Cohen class, generalizing the Wigner
distribution, reveal to be effective in damping artefacts of some signals. We
will survey their main properties and drawbacks and present open problems
related to such phenomena.",1912.11387v1
2020-01-15,Weak pseudo-bosons,"We show how the notion of {\em pseudo-bosons}, originally introduced as
operators acting on some Hilbert space, can be extended to a distributional
settings. In doing so, we are able to construct a rather general framework to
deal with generalized eigenvectors of the multiplication and of the derivation
operators. Connections with the quantum damped harmonic oscillator are also
briefly considered.",2001.05219v1
2020-02-14,Testing Physical Models for Cosmic Ray Transport Coefficients on Galactic Scales: Self-Confinement and Extrinsic Turbulence at GeV Energies,"The microphysics of ~GeV cosmic ray (CR) transport on galactic scales remain
deeply uncertain, with almost all studies adopting simple prescriptions (e.g.
constant-diffusivity). We explore different physically-motivated, anisotropic,
dynamical CR transport scalings in high-resolution cosmological FIRE
simulations of dwarf and ~$L_{\ast}$ galaxies where scattering rates vary with
local plasma properties motivated by extrinsic turbulence (ET) or
self-confinement (SC) scenarios, with varying assumptions about e.g. turbulent
power spectra on un-resolved scales, Alfven-wave damping, etc. We
self-consistently predict observables including $\gamma$-rays ($L_{\gamma}$),
grammage, residence times, and CR energy densities to constrain the models. We
demonstrate many non-linear dynamical effects (not captured in simpler models)
tend to enhance confinement. For example, in multi-phase media, even allowing
arbitrary fast transport in neutral gas does not substantially reduce CR
residence times (or $L_{\gamma}$), as transport is rate-limited by the ionized
WIM and 'inner CGM' gaseous halo ($10^{4}-10^{6}$ K gas within 10-30 kpc), and
$L_{\gamma}$ can be dominated by trapping in small 'patches.' Most physical ET
models contribute negligible scattering of ~1-10 GeV CRs, but it is crucial to
account for anisotropy and damping (especially of fast modes) or else
scattering rates would violate observations. We show that the most
widely-assumed scalings for SC models produce excessive confinement by factors
>100 in the WIM and inner CGM, where turbulent and Landau damping dominate.
This suggests either a breakdown of quasi-linear theory used to derive the CR
transport parameters in SC, or that other novel damping mechanisms dominate in
intermediate-density ionized gas.",2002.06211v2
2020-02-18,Boundary feedback control of an anti-stable wave equation,"We discuss boundary control of a wave equation with a non-linear anti-damping
boundary condition. We design structured finite-dimensional $H_\infty$-output
feedback controllers which stabilize the infinite dimensional system
exponentially in closed loop. The method is applied to control torsional
vibrations in drilling systems with the goal to avoid slip-stick.",2002.07567v1
2020-03-23,Critical exponent for the wave equation with a time-dependent scale invariant damping and a cubic convolution,"In the present paper, we study the Cauchy problem for the wave equation with
a time-dependent scale invariant damping $\frac{2}{1+t}\partial_t v$ and a
cubic convolution $(|x|^{-\gamma}*v^2)v$ with $\gamma\in
\left(-\frac{1}{2},3\right)$ in three spatial dimension for initial data
$\left(v(x,0),\partial_tv(x,0)\right)\in C^2(\mathbb{R}^3)\times
C^1(\mathbb{R}^3)$ with a compact support, where $v=v(x,t)$ is an unknown
function to the problem on $\mathbb{R}^3\times[0,T)$. Here $T$ denotes a
maximal existence time of $v$.
  The first aim of the present paper is to prove unique global existence of the
solution to the problem and asymptotic behavior of the solution in the
supercritical case $\gamma\in (0,3)$, and show a lower estimate of the lifespan
in the critical or subcritical case $\gamma\in \left(-\frac{1}{2},0\right]$.
The essential part for their proofs is to derive a weaker estimate under the
weaker condition than the case without damping and to recover the weakness by
the effect of the dissipative term.
  The second aim of the present paper is to prove a small data blow-up and the
almost sharp upper estimate of the lifespan for positive data with a compact
support in the subcritical case $\gamma\in \left(-\frac{1}{2},0\right)$. The
essential part for the proof is to refine the argument for the proof of Theorem
6.1 in \cite{H20} to obtain the upper estimate of the lifespan.
  Our two results determine that a critical exponent $\gamma_c$ which divides
global existence and blow-up for small solutions is $0$, namely $\gamma_c=0$.
As the result, we can see that the critical exponent shift from $2$ to $0$ due
to the effect of the scale invariant damping term.",2003.10329v2
2020-06-29,General decay and blow-up of solutions for a nonlinear wave equation with memory and fractional boundary damping terms,"The paper studies the global existence and general decay of solutions using
Lyaponov functional for a nonlinear wave equation, taking into account the
fractional derivative boundary condition and memory term. In addition, we
establish the blow up of solutions with nonpositive initial energy.",2006.16325v1
2020-07-19,Entanglement-Coherence and Discord-Coherence analytical relations for X states,"In this work we derive analytical relations between Entanglement and
Coherence as well as between Discord and Coherence, for Bell-diagonal states
and for X states, evolving under the action of several noise channels: Bit
Flip, Phase Damping and Depolarizing. We demonstrate that for these families,
Coherence is the fundamental correlation, that is: Coherence is necessary for
the presence of Entanglement and Discord.",2007.09792v1
2020-08-08,Linear Stability of the 2D Irrotational Circulation Flow around An Elliptical Cylinder,"In this article we prove a linear inviscid damping result with optimal decay
rates of the 2D irrotational circulation flow around an elliptical cylinder. In
our result, all components of the asymptotic velocity field do not vanish and
the asymptotic flow lines are not ellipse any more.",2008.03451v1
2020-09-01,On the first $δ$ Sct--roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars,"Strong magnetic fields in chemically peculiar A-type (Ap) stars typically
suppress low-overtone pressure modes (p modes) but allow high-overtone p modes
to be driven. KIC 11296437 is the first star to show both. We obtained and
analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances
similar to other magnetic Ap stars, and we estimate a mean magnetic field
modulus of $2.8\pm0.5$ kG. The same spectrum rules out a double-lined
spectroscopic binary, and we use other techniques to rule out binarity over a
wide parameter space, so the two pulsation types originate in one $\delta$
Sct--roAp hybrid pulsator. We construct stellar models depleted in helium and
demonstrate that helium settling is second to magnetic damping in suppressing
low-overtone p modes in Ap stars. We compute the magnetic damping effect for
selected p and g modes, and find that modes with frequencies similar to the
fundamental mode are driven for polar field strengths $\lesssim4$ kG, while
other low-overtone p modes are driven for polar field strengths up to $\sim$1.5
kG. We find that the high-order g modes commonly observed in $\gamma$ Dor stars
are heavily damped by polar fields stronger than 1--4 kG, with the damping
being stronger for higher radial orders. We therefore explain the observation
that no magnetic Ap stars have been observed as $\gamma$ Dor stars. We use our
helium-depleted models to calculate the $\delta$ Sct instability strip for
metallic-lined A (Am) stars, and find that driving from a Rosseland mean
opacity bump at $\sim$$5\times10^4$ K caused by the discontinuous H-ionization
edge in bound-free opacity explains the observation of $\delta$ Sct pulsations
in Am stars.",2009.00730v1
2020-09-24,The eccentricity distribution of giant planets and their relation to super-Earths in the pebble accretion scenario,"Observations of the population of cold Jupiter planets ($r>$1 AU) show that
nearly all of these planets orbit their host star on eccentric orbits. For
planets up to a few Jupiter masses, eccentric orbits are thought to be the
outcome of planet-planet scattering events taking place after gas dispersal. We
simulate the growth of planets via pebble and gas accretion as well as the
migration of multiple planetary embryos in their gas disc. We then follow the
long-term dynamical evolution of our formed planetary system up to 100 Myr
after gas disc dispersal. We investigate the importance of the initial number
of protoplanetary embryos and different damping rates of eccentricity and
inclination during the gas phase for the final configuration of our planetary
systems. We constrain our model by comparing the final dynamical structure of
our simulated planetary systems to that of observed exoplanet systems. Our
results show that the initial number of planetary embryos has only a minor
impact on the final orbital eccentricity distribution of the giant planets, as
long as damping of eccentricity and inclination is efficient. If damping is
inefficient (slow), systems with a larger initial number of embryos harbor
larger average eccentricities. In addition, for slow damping rates, we observe
that scattering events already during the gas disc phase are common and that
the giant planets formed in these simulations match the observed giant planet
eccentricity distribution best. These simulations also show that massive giant
planets (above Jupiter mass) on eccentric orbits are less likely to host inner
super-Earths as these get lost during the scattering phase, while systems with
less massive giant planets on nearly circular orbits should harbor systems of
inner super-Earths. Finally, our simulations predict that giant planets are on
average not single, but live in multi-planet systems.",2009.11725v3
2020-10-12,Period Estimates for Autonomous Evolution Equations with Lipschitz Nonlinearities,"We derive an estimate for the minimal period of autonomous strongly damped
hyperbolic problems. Our result corresponds to the works by Yorke, Busenberg et
al. for ordinary differential equations as well as Robinson and Vidal-Lopez for
parabolic problems. A general approach is developed for treating both
hyperbolic and parabolic problems. An example of application to a class of beam
equations is provided.",2010.05829v1
2020-12-16,Observation of anti-damping spin-orbit torques generated by in-plane and out-of-plane spin polarizations in MnPd3,"High spin-orbit torques (SOTs) generated by topological materials and heavy
metals interfaced with a ferromagnetic layer show promise for next generation
magnetic memory and logic devices. SOTs generated from the in-plane spin
polarization along y-axis originated by the spin Hall and Edelstein effects can
switch magnetization collinear with the spin polarization in the absence of
external magnetic fields. However, an external magnetic field is required to
switch the magnetization along x and z-axes via SOT generated by y-spin
polarization. Here, we present that the above limitation can be circumvented by
unconventional SOT in magnetron-sputtered thin film MnPd3. In addition to the
conventional in-plane anti-damping-like torque due to the y-spin polarization,
out-of-plane and in-plane anti-damping-like torques originating from z-spin and
x-spin polarizations, respectively have been observed at room temperature. The
spin torque efficiency corresponding to the y-spin polarization from MnPd3 thin
films grown on thermally oxidized silicon substrate and post annealed at 400
Deg C is 0.34 - 0.44. Remarkably, we have demonstrated complete external
magnetic field-free switching of perpendicular Co layer via unconventional
out-of-plane anti-damping-like torque from z-spin polarization. Based on the
density functional theory calculations, we determine that the observed x- and
z- spin polarizations with the in-plane charge current are due to the low
symmetry of the (114) oriented MnPd3 thin films. Taken together, the new
material reported here provides a path to realize a practical spin channel in
ultrafast magnetic memory and logic devices.",2012.09315v1
2021-02-15,A transmission problem for waves under time-varying delay and nonlinear weight,"This manuscript focus on in the transmission problem for one dimensional
waves with nonlinear weights on the frictional damping and time-varying delay.
We prove global existence of solutions using Kato's variable norm technique and
we show the exponential stability by the energy method with the construction of
a suitable Lyapunov functional.",2102.07829v1
2021-05-16,Linear stability analysis of the Couette flow for the two dimensional non-isentropic compressible Euler equations,"This note is devoted to the linear stability of the Couette flow for the
non-isentropic compressible Euler equations in a domain $\mathbb{T}\times
\mathbb{R}$. Exploiting the several conservation laws originated from the
special structure of the linear system, we obtain a Lyapunov type instability
for the density, the temperature, the compressible part of the velocity field,
and also obtain an inviscid damping for the incompressible part of the velocity
field.",2105.07395v1
2021-05-21,Effects of ambipolar diffusion on waves in the solar chromosphere,"The chromosphere is a partially ionized layer of the solar atmosphere, the
transition between the photosphere where the gas motion is determined by the
gas pressure and the corona dominated by the magnetic field. We study the
effect of partial ionization for 2D wave propagation in a gravitationally
stratified, magnetized atmosphere with properties similar to the solar
chromosphere. We adopt an oblique uniform magnetic field in the plane of
propagation with strength suitable for a quiet sun region. The theoretical
model used is a single fluid magnetohydrodynamic approximation, where
ion-neutral interaction is modeled by the ambipolar diffusion term. Magnetic
energy can be converted into internal energy through the dissipation of the
electric current produced by the drift between ions and neutrals. We use
numerical simulations where we continuously drive fast waves at the bottom of
the atmosphere. The collisional coupling between ions and neutrals decreases
with the decrease of the density and the ambipolar effect becomes important.
Fast waves excited at the base of the atmosphere reach the equipartition layer
and reflect or transmit as slow waves. While the waves propagate through the
atmosphere and the density drops, the waves steepen into shocks. The main
effect of ambipolar diffusion is damping of the waves. We find that for the
parameters chosen in this work, the ambipolar diffusion affects the fast wave
before it is reflected, with damping being more pronounced for waves which are
launched in a direction perpendicular to the magnetic field. Slow waves are
less affected by ambipolar effects. The damping increases for shorter periods
and larger magnetic field strengths. Small scales produced by the nonlinear
effects and the superposition of different types of waves created at the
equipartition height are efficiently damped by ambipolar diffusion.",2105.10285v1
2021-05-26,Global Attractor for the Periodic Generalized Korteweg-de Vries Equation Through Smoothing,"We establish a smoothing result for the generalized KdV (gKdV) on the torus
with polynomial non-linearity, damping, and forcing that matches the smoothing
level for the gKdV at $H^1$. As a consequence, we establish the existence of a
global attractor for this equation as well as its compactness in
$H^s(\mathbb{T})$, $s\in (1,2).$",2105.13405v2
2021-06-01,On the Well-Posedness of Two Driven-Damped Gross Pitaevskii-Type Models for Exciton-Polariton Condensates,"We study the well-posedness of two systems modeling the non-equilibrium
dynamics of pumped decaying Bose-Einstein condensates. In particular, we
present the local theory for rough initial data using the Fourier restricted
norm method introduced by Bourgain. We extend the result globally for initial
data in $L^2$.",2106.00438v1
2021-06-11,Dynamics and Nonmonotonic Drag for Individually Driven Skyrmions,"We examine the motion of an individual skyrmion driven through an assembly of
other skyrmions by a constant or increasing force in the absence of quenched
disorder. The skyrmion behavior is determined by the ratio of the damping and
Magnus terms, as expressed in terms of the intrinsic skyrmion Hall angle. For a
fixed driving force in the damping dominated regime, the effective viscosity
decreases monotonically with increasing skyrmion density, similar to what is
observed in overdamped systems where it becomes difficult for the driven
particle to traverse the surrounding medium at high densities. In contrast, in
the Magnus dominated regime the velocity dependence on the density is
nonmonotonic, and there is a regime in which the skyrmion moves faster with
increasing density, as well as a pronounced speed-up effect in which a skyrmion
traveling through a dense medium moves more rapidly than it would at low
densities or in the single particle limit. At higher densities, the effective
damping increases and the velocity decreases. The velocity-force curves in the
Magnus-dominated regime show marked differences from those in the
damping-dominated regimes. Under an increasing drive we find that there is a
threshold force for skyrmion motion which increases with density. Additionally,
the skyrmion Hall angle is drive dependent, starting near zero at the threshold
for motion and increasing with increasing drive before reaching a saturation
value, similar to the behavior found for skyrmions driven over quenched
disorder. We map dynamic phase diagrams showing the threshold for motion,
nonlinear flow, speed-up, and saturation regimes. We also find that in some
cases, increasing the density can reduce the skyrmion Hall angle while
producing a velocity boost, which could be valuable for applications.",2106.06093v1
2021-06-23,On generalized damped Klein-Gordon equation with nonlinear memory,"In this paper we consider the Cauchy problem for linear dissipative
generalized Klein-Gordon equations with nonlinear memory in the right hand
side. Our goal is to study the effect of this nonlinearity on both the decay
estimates of global solutions as well as the admissible range of the exponent
p.",2106.12296v1
2021-07-21,"Convergence rates for the Heavy-Ball continuous dynamics for non-convex optimization, under Polyak-Łojasiewicz condition","We study convergence of the trajectories of the Heavy Ball dynamical system,
with constant damping coefficient, in the framework of convex and non-convex
smooth optimization. By using the Polyak-{\L}ojasiewicz condition, we derive
new linear convergence rates for the associated trajectory, in terms of
objective function values, without assuming uniqueness of the minimizer.",2107.10123v2
2021-08-29,A note on the energy transfer in coupled differential systems,"We study the energy transfer in the linear system $$ \begin{cases} \ddot
u+u+\dot u=b\dot v\\ \ddot v+v-\epsilon \dot v=-b\dot u \end{cases} $$ made by
two coupled differential equations, the first one dissipative and the second
one antidissipative. We see how the competition between the damping and the
antidamping mechanisms affect the whole system, depending on the coupling
parameter $b$.",2108.12776v1
2021-08-29,Well-posedness and stability for semilinear wave-type equations with time delay,"In this paper we analyze a semilinear abstract damped wave-type equation with
time delay. We assume that the delay feedback coefficient is variable in time
and belonging to $L^1_{loc}([0, +\infty)).$ Under suitable assumptions, we show
well-posedness and exponential stability for small initial data. Our strategy
combines careful energy estimates and continuity arguments. Some examples
illustrate the abstract results.",2108.12786v1
2021-08-30,Application of Rothe's method to a nonlinear wave equation on graphs,"We study a nonlinear wave equation on finite connected weighted graphs. Using
Rothe's and energy methods, we prove the existence and uniqueness of solution
under certain assumption. For linear wave equation on graphs, Lin and Xie
\cite{Lin-Xie} obtained the existence and uniqueness of solution. The main
novelty of this paper is that the wave equation we considered has the nonlinear
damping term $|u_t|^{p-1}\cdot u_t$ ($p>1$).",2108.12980v1
2021-09-08,Stabilisation of Waves on Product Manifolds by Boundary Strips,"We show that a transversely geometrically controlling boundary damping strip
is sufficient but not necessary for $t^{-1/2}$-decay of waves on product
manifolds. We give a general scheme to turn resolvent estimates for impedance
problems on cross-sections to wave decay on product manifolds.",2109.03928v1
2021-09-10,Smoothing effect and large time behavior of solutions to nonlinear elastic wave equations with viscoelastic term,"The Cauchy problem for a nonlinear elastic wave equations with viscoelastic
damping terms is considered on the 3 dimensional whole space. Decay and
smoothing properties of the solutions are investigated when the initial data
are sufficiently small; and asymptotic profiles as $t \to \infty$ are also
derived.",2109.04628v3
2021-10-04,Overdamped limit at stationarity for non-equilibrium Langevin diffusions,"In this note, we establish that the stationary distribution of a possibly
non-equilibrium Langevin diffusion converges, as the damping parameter goes to
infinity (or equivalently in the Smoluchowski-Kramers vanishing mass limit),
toward a tensor product of the stationary distribution of the corresponding
overdamped process and of a Gaussian distribution.",2110.01238v2
2021-10-22,p-Laplacian wave equations in non-cylindrical domains,"This paper is devoted to studying the stability of p-Laplacian wave equations
with strong damping in non-cylindrical domains. The method of proof based on
some estimates for time-varying coefficients rising from moving boundary and a
modified Kormonik inequality. Meanwhile, by selecting appropriate auxiliary
functions, finally we obtain the polynomial stability (p > 2) and exponential
stability (p = 2) for such systems in some unbounded development domains.",2110.11547v1
2021-11-17,Transverse kink oscillations of inhomogeneous prominence threads: numerical analysis and H$α$ forward modelling,"Prominence threads are very long and thin flux tubes which are partially
filled with cold plasma. Observations have shown that transverse oscillations
are frequent in these solar structures. The observations are usually
interpreted as the fundamental kink mode, while the detection of the first
harmonic remains elusive. Here, we aim to study how the density inhomogeneity
in the longitudinal and radial directions modify the periods and damping times
of kink oscillations, and how this effect would be reflected in observations.
We solve the ideal magnetohydrodynamics equations through two different
methods: a) performing 3D numerical simulations, and b) solving a 2D
generalised eigenvalue problem. We study the dependence of the periods, damping
times and amplitudes of transverse kink oscillations on the ratio between the
densities at the centre and at the ends of the tube, and on the average
density. We apply forward modelling on our 3D simulations to compute synthetic
H$\alpha$ profiles. We confirm that the ratio of the period of the fundamental
oscillation mode to the period of the first harmonic increases as the ratio of
the central density to the footpoint density is increased or as the averaged
density of the tube is decreased. We find that the damping times due to
resonant absorption decrease as the central to footpoint density ratio
increases. Contrary to the case of longitudinally homogeneous tubes, we find
that the damping time to period ratio also increases as the density ratio is
increased or the average density is reduced. We present snapshots and
time-distance diagrams of the emission in the H$\alpha$ line. The results
presented here have implications for the field of prominence seismology. While
the H$\alpha$ emission can be used to detect the fundamental mode, the first
harmonic is barely detectable in H$\alpha$. This may explain the lack of
detections of the first harmonic.",2111.09036v1
2021-11-26,A novel measurement of marginal Alfvén Eigenmode stability during high power auxiliary heating in JET,"The interaction of Alfv\'{e}n Eigenmodes (AEs) and energetic particles is one
of many important factors determining the success of future tokamaks. In JET,
eight in-vessel antennas were installed to actively probe stable AEs with
frequencies ranging 25-250 kHz and toroidal mode numbers $\vert n \vert < 20$.
During the 2019-2020 deuterium campaign, almost 7500 resonances and their
frequencies $f_0$, net damping rates $\gamma < 0$, and toroidal mode numbers
were measured in almost 800 plasma discharges. From a statistical analysis of
this database, continuum and radiative damping are inferred to increase with
edge safety factor, edge magnetic shear, and when including non-ideal effects.
Both stable AE observations and their associated damping rates are found to
decrease with $\vert n \vert$. Active antenna excitation is also found to be
ineffective in H-mode as opposed to L-mode; this is likely due to the increased
edge density gradient's effect on accessibility and ELM-related noise's impact
on mode identification. A novel measurement is reported of a marginally stable,
edge-localized Ellipticity-induced AE probed by the antennas during high-power
auxiliary heating (ICRH and NBI) up to 25 MW. NOVA-K kinetic-MHD simulations
show good agreement with experimental measurements of $f_0$, $\gamma$, and $n$,
indicating the dominance of continuum and electron Landau damping in this case.
Similar experimental and computational studies are planned for the recent
hydrogen and ongoing tritium campaigns, in preparation for the upcoming DT
campaign.",2111.13569v1
2021-12-08,IGM damping wing constraints on reionisation from covariance reconstruction of two $z\gtrsim7$ QSOs,"Bright, high redshift ($z>6$) QSOs are powerful probes of the ionisation
state of the intervening intergalactic medium (IGM). The detection of
Ly$\alpha$ damping wing absorption imprinted in the spectrum of high-z QSOs can
provide strong constraints on the epoch of reionisation (EoR). In this work, we
perform an independent Ly$\alpha$ damping wing analysis of two known $z>7$
QSOs; DESJ0252-0503 at $z=7.00$ (Wang et al.) and J1007+2115 at $z=7.51$ (Yang
et al.). For this, we utilise our existing Bayesian framework which
simultaneously accounts for uncertainties in: (i) the intrinsic Ly$\alpha$
emission profile (reconstructed from a covariance matrix of measured emission
lines; extended in this work to include NV) and (ii) the distribution of
ionised (H\,{\scriptsize II}) regions within the IGM using a $1.6^3$ Gpc$^3$
reionisation simulation. This approach is complementary to that used in the
aforementioned works as it focuses solely redward of Ly$\alpha$ ($1218 <
\lambda < 1230$\AA) making it more robust to modelling uncertainties while also
using a different methodology for (i) and (ii). We find, for a fiducial EoR
morphology, $\bar{x}_{\rm HI} = 0.64\substack{+0.19 \\ -0.23}$ (68 per cent) at
$z=7$ and $\bar{x}_{\rm HI} = 0.27\substack{+0.21 \\ -0.17}$ at $z=7.51$
consistent within $1\sigma$ to the previous works above, though both are
slightly lower in amplitude. Following the inclusion of NV into our
reconstruction pipeline, we perform a reanalysis of ULASJ1120+0641 at $z=7.09$
(Mortlock et al.) and ULASJ1342+0928 at $z=7.54$ (Ba\~nados et al.) finding
$\bar{x}_{\rm HI} = 0.44\substack{+0.23 \\ -0.24}$ at $z=7.09$ and
$\bar{x}_{\rm HI} = 0.31\substack{+0.18 \\ -0.19}$ at $z=7.54$. Finally, we
combine the QSO damping wing constraints for all four $z\gtrsim7$ QSOs to
obtain a single, unified constraint of $\bar{x}_{\rm HI} = 0.49\substack{+0.11
\\ -0.11}$ at $z=7.29$.",2112.04091v1
2022-01-24,A blow-up result for a Nakao-type weakly coupled system with nonlinearities of derivative-type,"In this paper, we consider a weakly coupled system of a wave and damped
Klein-Gordon equation with nonlinearities of derivative type. We prove a
blow-up result for the Cauchy problem associated with this system for
nonnegative and compactly supported data by means of an iteration argument.",2201.09462v1
2022-03-11,On the small noise limit in the Smoluchowski-Kramers approximation of nonlinear wave equations with variable friction,"We study the validity of a large deviation principle for a class of
stochastic nonlinear damped wave equations, of Klein-Gordon type, in the joint
small mass and small noise limit. The friction term is assumed to be state
dependent.",2203.05923v2
2022-03-28,Composite Anderson acceleration method with dynamic window-sizes and optimized damping,"In this paper, we propose and analyze a set of fully non-stationary Anderson
acceleration algorithms with dynamic window sizes and optimized damping.
Although Anderson acceleration (AA) has been used for decades to speed up
nonlinear solvers in many applications, most authors are simply using and
analyzing the stationary version of Anderson acceleration (sAA) with fixed
window size and a constant damping factor. The behavior and potential of the
non-stationary version of Anderson acceleration methods remain an open
question. Since most efficient linear solvers use composable algorithmic
components. Similar ideas can be used for AA to solve nonlinear systems. Thus
in the present work, to develop non-stationary Anderson acceleration
algorithms, we first propose two systematic ways to dynamically alternate the
window size $m$ by composition. One simple way to package sAA(m) with sAA(n) in
each iteration is applying sAA(m) and sAA(n) separately and then average their
results. It is an additive composite combination. The other more important way
is the multiplicative composite combination, which means we apply sAA(m) in the
outer loop and apply sAA(n) in the inner loop. By doing this, significant gains
can be achieved. Secondly, to make AA to be a fully non-stationary algorithm,
we need to combine these strategies with our recent work on the non-stationary
Anderson acceleration algorithm with optimized damping (AAoptD), which is
another important direction of producing non-stationary AA and nice performance
gains have been observed. Moreover, we also investigate the rate of convergence
of these non-stationary AA methods under suitable assumptions. Finally, our
numerical results show that some of these proposed non-stationary Anderson
acceleration algorithms converge faster than the stationary sAA method and they
may significantly reduce the storage and time to find the solution in many
cases.",2203.14627v1
2022-03-28,The higher order nonlinear Schrödinger equation with quadratic nonlinearity on the real axis,"The initial value problem is considered for a higher order nonlinear
Schr\""odinger equation with quadratic nonlinearity. Results on existence and
uniqueness of weak solutions are obtained. In the case of an effective at
infinity additional damping large-time decay of solutions without any smallness
assumptions is also established. The main difficulty of the study is the
non-smooth character of the nonlinearity.",2203.14830v1
2022-04-03,Strong Solution of Modified Anistropic 3D-Navier-Stokes Equations,"In this paper we study the anisotropic incompressible Navier-Stokes equations
with a logarithm damping $\alpha \log(e+|u|^2)|u|^2u$ in $H^{0.1}$, where we
used new methods, new tools and Fourier analysis.",2204.01717v2
2022-04-28,"Coupling between turbulence and solar-like oscillations: A combined Lagrangian PDF/SPH approach. II - Mode driving, damping and modal surface effect","The first paper of this series established a linear stochastic wave equation
for solar-like p-modes, correctly taking the effect of turbulence thereon into
account. In this second paper, we aim at deriving simultaneous expressions for
the excitation rate, damping rate, and modal surface effect associated with any
given p-mode, as an explicit function of the statistical properties of the
turbulent velocity field. We reduce the stochastic wave equation to complex
amplitude equations for the normal oscillating modes of the system. We then
derive the equivalent Fokker-Planck equation for the real amplitudes and phases
of all the oscillating modes of the system simultaneously. The effect of the
finite-memory time of the turbulent fluctuations (comparable to the period of
the modes) on the modes themselves is consistently and rigorously accounted
for, by means of the simplified amplitude equation formalism. This formalism
accounts for mutual linear mode coupling in full, and we then turn to the
special single-mode case. This allows us to derive evolution equations for the
mean energy and mean phase of each mode, from which the excitation rate, the
damping rate, and the modal surface effect naturally arise.
  We show that the expression for the excitation rate of the modes is identical
to previous results obtained through a different modelling approach, thus
supporting the validity of the formalism presented here. We also recover the
fact that the damping rate and modal surface effect correspond to the real and
imaginary part of the same single complex quantity. We explicitly separate the
different physical contributions to these observables, in particular the
turbulent pressure contribution and the joint effect of the
pressure-rate-of-strain correlation and the turbulent dissipation. We show that
the former dominates for high-frequency modes and the latter for low-frequency
modes.",2204.13367v1
2022-05-05,Blow-up solutions of damped Klein-Gordon equation on the Heisenberg group,"Inthisnote,weprovetheblow-upofsolutionsofthesemilineardamped Klein-Gordon
equation in a finite time for arbitrary positive initial energy on the
Heisenberg group. This work complements the paper [21] by the first author and
Tokmagambetov, where the global in time well-posedness was proved for the small
energy solutions.",2205.02705v1
2022-05-06,Quaternion-based attitude stabilization via discrete-time IDA-PBC,"In this paper, we propose a new sampled-data controller for stabilization of
the attitude dynamics at a desired constant configuration. The design is based
on discrete-time interconnection and damping assignment (IDA) passivity-based
control (PBC) and the recently proposed Hamiltonian representation of
discrete-time nonlinear dynamics. Approximate solutions are provided with
simulations illustrating performances.",2205.03086v1
2022-05-23,Extended random-phase-approximation study of fragmentation of giant quadrupole resonance in $^{16}$O,"The damping of isoscalar giant quadrupole resonance in $^{16}$O is studied
using extended random-phase-approximation approaches derived from the
time-dependent density-matrix theory. It is pointed out that the effects of
ground-state correlations bring strong fragmentation of quadrupole strength
even if the number of two particle--two hole configurations is strongly
limited.",2205.11654v2
2022-06-21,Nonlinear Compton scattering and nonlinear Breit-Wheeler pair production including the damping of particle states,"In the presence of an electromagnetic background plane-wave field, electron,
positron, and photon states are not stable, because electrons and positrons
emit photons and photons decay into electron-positron pairs. This decay of the
particle states leads to an exponential damping term in the probabilities of
single nonlinear Compton scattering and nonlinear Breit-Wheeler pair
production. In this paper we investigate analytically and numerically the
probabilities of nonlinear Compton scattering and nonlinear Breit-Wheeler pair
production including the particle states' decay. For this we first compute
spin- and polarization-resolved expressions of the probabilities, provide some
of their asymptotic behaviors and show that the results of the total
probabilities are independent of the spin and polarization bases. Then, we
present several plots of the total and differential probabilities for different
pulse lengths and for different spin and polarization quantum numbers. We
observe that it is crucial to take into account the damping of the states in
order for the probabilities to stay always below unity and we show that the
damping factors also scale with the intensity and pulse duration of the
background field. In the case of nonlinear Compton scattering we show
numerically that the total probability behaves like a Poissonian distribution
in the regime where the photon recoil is negligible. In all considered cases,
the kinematic conditions are such that the final particles momenta transverse
to the propagation direction of the plane wave are always much smaller than the
particles longitudinal momenta and the main spread of the momentum distribution
on the transverse plane is along the direction of the plane-wave electric
field.",2206.10345v2
2022-06-23,Nonlinear Landau damping for the 2d Vlasov-Poisson system with massless electrons around Penrose-stable equilibria,"In this paper, we prove the nonlinear asymptotic stability of the
Penrose-stable equilibria among solutions of the $2d$ Vlasov-Poisson system
with massless electrons.",2206.11744v2
2022-07-25,Inviscid limit for the compressible Navier-Stokes equations with density dependent viscosity,"We consider the compressible Navier-Stokes system describing the motion of a
barotropic fluid with density dependent viscosity confined in a
three-dimensional bounded domain $\Omega$. We show the convergence of the weak
solution to the compressible Navier-Stokes system to the strong solution to the
compressible Euler system when the viscosity and the damping coefficients tend
to zero.",2207.12222v1
2022-08-25,Polynomial energy decay rate of a 2D Piezoelectric beam with magnetic effect on a rectangular domain without geometric conditions,"In this paper, we investigate the stability of coupled equations modelling a
2D piezoelectric beam with magnetic effect with only one local viscous damping
on a rectangular domain without geometric conditions. We prove that the energy
of the system decays polynomially with the rate 1/t .",2208.12012v1
2022-10-12,Backward problem for the 1D ionic Vlasov-Poisson equation,"In this paper, we study the backward problem for the one-dimensional
Vlasov-Poisson system with massless electrons, and we show the Landau damping
by fixing the asymptotic behaviour of our solution.",2210.06123v2
2022-10-28,"Oblique Quasi-Kink Modes in Solar Coronal Slabs Embedded in an Asymmetric Magnetic Environment: Resonant Damping, Phase and Group Diagrams","There has been considerable interest in magnetoacoustic waves in static,
straight, field-aligned, one-dimensional equilibria where the exteriors of a
magnetic slab are different between the two sides. We focus on trapped,
transverse fundamental, oblique quasi-kink modes in pressureless setups where
the density varies continuously from a uniform interior (with density
$\rho_{\rm i}$) to a uniform exterior on either side (with density $\rho_{\rm
L}$ or $\rho_{\rm R}$), assuming $\rho_{\rm L}\le\rho_{\rm R}\le\rho_{\rm i}$.
The continuous structuring and oblique propagation make our study new relative
to pertinent studies, and lead to wave damping via the Alfv$\acute{\rm e}$n
resonance. We compute resonantly damped quasi-kink modes as resistive
eigenmodes, and isolate the effects of system asymmetry by varying $\rho_{\rm
i}/\rho_{\rm R}$ from the ``Fully Symmetric'' ($\rho_{\rm i}/\rho_{\rm
R}=\rho_{\rm i}/\rho_{\rm L}$) to the ``Fully Asymmetric'' limit ($\rho_{\rm
i}/\rho_{\rm R}=1$). We find that the damping rates possess a nonmonotonic
$\rho_{\rm i}/\rho_{\rm R}$-dependence as a result of the difference between
the two Alfv$\acute{\rm e}$n continua, and resonant absorption occurs only in
one continuum when $\rho_{\rm i}/\rho_{\rm R}$ is below some threshold. We also
find that the system asymmetry results in two qualitatively different regimes
for the phase and group diagrams. The phase and group trajectories lie
essentially on the same side (different sides) relative to the equilibrium
magnetic field when the configuration is not far from a ``Fully Asymmetric''
(``Fully Symmetric'') one. Our numerical results are understood by making
analytical progress in the thin-boundary limit, and discussed for imaging
observations of axial standing modes and impulsively excited wavetrains.",2210.16091v1
2022-11-02,Data-driven modeling of Landau damping by physics-informed neural networks,"Kinetic approaches are generally accurate in dealing with microscale plasma
physics problems but are computationally expensive for large-scale or
multiscale systems. One of the long-standing problems in plasma physics is the
integration of kinetic physics into fluid models, which is often achieved
through sophisticated analytical closure terms. In this paper, we successfully
construct a multi-moment fluid model with an implicit fluid closure included in
the neural network using machine learning. The multi-moment fluid model is
trained with a small fraction of sparsely sampled data from kinetic simulations
of Landau damping, using the physics-informed neural network (PINN) and the
gradient-enhanced physics-informed neural network (gPINN). The multi-moment
fluid model constructed using either PINN or gPINN reproduces the time
evolution of the electric field energy, including its damping rate, and the
plasma dynamics from the kinetic simulations. In addition, we introduce a
variant of the gPINN architecture, namely, gPINN$p$ to capture the Landau
damping process. Instead of including the gradients of all the equation
residuals, gPINN$p$ only adds the gradient of the pressure equation residual as
one additional constraint. Among the three approaches, the gPINN$p$-constructed
multi-moment fluid model offers the most accurate results. This work sheds
light on the accurate and efficient modeling of large-scale systems, which can
be extended to complex multiscale laboratory, space, and astrophysical plasma
physics problems.",2211.01021v3
2022-11-04,New Clues About Light Sterile Neutrinos: Preference for Models with Damping Effects in Global Fits,"This article reports global fits of short-baseline neutrino data to
oscillation models involving light sterile neutrinos. In the commonly-used 3+1
plane wave model, there is a well-known 4.9$\sigma$ tension between data sets
sensitive to appearance versus disappearance of neutrinos. We find that models
that damp the oscillation prediction for the reactor data sets, especially at
low energy, substantially improve the fits and reduce the tension. We consider
two such scenarios. The first scenario introduces the quantum mechanical
wavepacket effect that accounts for the source size in reactor experiments into
the 3+1 model. We find that inclusion of the wavepacket effect greatly improves
the overall fit compared to a 3$\nu$ model by $\Delta \chi^2/$DOF$=61.1/4$
($7.1\sigma$ improvement) with best-fit $\Delta m^2=1.4$ eV$^2$ and wavepacket
length of 67fm. The internal tension is reduced to 3.4$\sigma$. If reactor-data
only is fit, then the wavepacket preferred length is 91 fm ($>20$ fm at 99\%
CL). The second model introduces oscillations involving sterile flavor and
allows the decay of the heaviest, mostly sterile mass state, $\nu_4$. This
model introduces a damping term similar to the wavepacket effect, but across
all experiments. Compared to a three-neutrino fit, this has a $\Delta
\chi^2/$DOF$=60.6/4$ ($7\sigma$ improvement) with preferred $\Delta m^2=1.4$
eV$^2$ and decay $\Gamma = 0.35$ eV$^2$. The internal tension is reduced to
3.7$\sigma$.
  For many years, the reactor event rates have been observed to have structure
that deviates from prediction. Community discussion has focused on an excess
compared to prediction observed at 5 MeV; however, other deviations are
apparent. This structure has $L$ dependence that is well-fit by the damped
models. Before assuming this points to new physics, we urge closer examination
of systematic effects that could lead to this $L$ dependence.",2211.02610v5
2022-12-07,A recipe for orbital eccentricity damping in the type-I regime for low viscosity 2D-discs,"It is known that gap opening depends on the disc's viscosity; however,
eccentricity damping formulas have only been derived at high viscosities,
ignoring partial gap opening. We aim at obtaining a simple formula to model
$e$-damping of the type-I regime in low viscosity discs, where even small
planets may start opening partial. We perform high resolution 2D locally
isothermal hydrodynamical simulations of planets with varying masses on fixed
orbits in discs with varying aspect ratios and viscosities. We determine the
torque and power felt by the planet to derive migration and eccentricity
damping timescales. We first find a lower limit to the gap depths below which
vortices appear; this happens roughly at the transition between type-I and
type-II regimes. For the simulations that remain stable, we obtain a fit to the
observed gap depth in the limit of vanishing eccentricities that is similar to
the one currently used in the literature but is accurate down to
$\alpha=3.16\times 10^{-5}$. We record the $e$-damping efficiency as a function
of the observed gap depth and $e$: when the planet has opened a deep enough
gap, a linear trend is observed independently of $e$; at shallower gaps this
linear trend is preserved at low $e$, while it deviates to more efficient
damping when $e$ is comparable to the disc's scale height. Both trends can be
understood on theoretical grounds and are reproduced by a simple fitting
formula. Our combined fits yield a simple recipe to implement type-I
$e$-damping in $N$-body for partial gap opening planets that is consistent with
high-resolution 2D hydro-simulations. The typical error of the fit is of the
order of a few percent, and lower than the error of type-I torque formulas
widely used in the literature. This will allow a more self-consistent treatment
of planet-disc interactions of the type-I regime for population synthesis
models at low viscosities.",2212.03608v1
2022-12-10,Linear stabilization for a degenerate wave equation in non divergence form with drift,"We consider a degenerate wave equation in one dimension, with drift and in
presence of a leading operator which is not in divergence form. We impose a
homogeneous Dirichlet boundary condition where the degeneracy occurs and a
boundary damping at the other endpoint. We provide some conditions for the
uniform exponential decay of solutions for the associated Cauchy problem.",2212.05264v1
2022-12-31,"On the stability of shear flows in bounded channels, II: non-monotonic shear flows","We give a proof of linear inviscid damping and vorticity depletion for
non-monotonic shear flows with one critical point in a bounded periodic
channel. In particular, we obtain quantitative depletion rates for the
vorticity function without any symmetry assumptions.",2301.00288v2
2023-03-18,Spin waves in a superconductor,"Spin waves that can propagate in normal and superconducting metals are
investigated. Unlike normal metals, the velocity of spin waves becomes
temperature-dependent in a superconductor. The low frequency spin waves survive
within the narrow region below the superconducting transition temperature. At
low temperatures the high frequency waves alone can propagate with an
additional damping due to pair-breaking.",2303.10468v1
2023-04-07,Echo disappears: momentum term structure and cyclic information in turnover,"We extract cyclic information in turnover and find it can explain the
momentum echo. The reversal in recent month momentum is the key factor that
cancels out the recent month momentum and excluding it makes the echo regress
to a damped shape. Both rational and behavioral theories can explain the
reversal. This study is the first explanation of the momentum echo in U.S.
stock markets.",2304.03437v1
2023-04-26,Plasma echoes in graphene,"Plasma echo is a dramatic manifestation of plasma damping process
reversibility. In this paper we calculate temporal and spatial plasma echoes in
graphene in the acoustic plasmon regime when echoes dominate over plasmon
emission. We show an extremely strong spatial echo response and discuss how
electron collisions reduce the echo. We also discuss differences between
various electron dispersions, and differences between semiclassical and quantum
model of echoes.",2304.13440v1
2023-06-01,JWST Measurements of Neutral Hydrogen Fractions and Ionized Bubble Sizes at $z=7-12$ Obtained with Ly$α$ Damping Wing Absorptions in 26 Bright Continuum Galaxies,"We present volume-averaged neutral hydrogen fractions $x_{\rm \HI}$ and
ionized bubble radii $R_{\rm b}$ measured with Ly$\alpha$ damping wing
absorption of galaxies at the epoch of reionization. We combine JWST/NIRSpec
spectra taken by CEERS, GO-1433, DDT-2750, and JADES programs, and obtain a
sample containing 26 bright UV-continuum ($M_{\rm UV}<-18.5~{\rm mag}$)
galaxies at $7<z<12$. We construct 4 composite spectra binned by redshift, and
find the clear evolution of softening break towards high redshift at the
rest-frame $1216$ {\AA}, suggesting the increase of Ly$\alpha$ damping wing
absorption. We estimate Ly$\alpha$ damping wing absorption in the galaxy
spectra with realistic templates including Ly$\alpha$ emission and
circum-galactic medium absorptions. Assuming the standard inside-out
reionization picture having an ionized bubble with radius $R_b$ around a galaxy
embedded in the intergalactic medium with $x_{\rm \HI}$, we obtain $x_{\rm
\HI}$ ($R_{\rm b}$) values generally increasing (decreasing) from $x_{\rm
\HI}={0.54}^{+0.13}_{-0.54}$ to ${0.94}^{+0.06}_{-0.41}$ ($\log R_{\rm
b}={1.89}^{+0.49}_{-1.54}$ to ${-0.72}^{+1.57}_{-0.28}$ comoving Mpc) at
redshift $7.12^{+0.06}_{-0.08}$ to $10.28^{+1.12}_{-1.40}$. The redshift
evolution of $x_{\rm \HI}$ indicates a moderately late reionization history
consistent with the one previously suggested from the electron scattering of
cosmic microwave background and the evolution of UV luminosity function with an
escape fraction $f_{\rm esc}\sim 0.2$. Our ${R_{\rm b}}$ measurements suggest
that bubble sizes could be up to a few dex larger than the cosmic average
values estimated by analytic calculations for a given $x_{\rm \HI}$, while our
$R_{\rm b}$ measurements are roughly comparable with the values for merged
ionized bubbles around bright galaxies predicted by recent numerical
simulations.",2306.00487v2
2023-06-20,New results on controllability and stability for degenerate Euler-Bernoulli type equations,"In this paper we study the controllability and the stability for a degenerate
beam equation in divergence form via the energy method. The equation is clamped
at the left end and controlled by applying a shearing force or a damping at the
right end.",2306.11851v3
2023-07-18,"Nonlinear feedback, double bracket dissipation and port control of Lie-Poisson systems","Methods from controlled Lagrangians, double bracket dissipation and
interconnection and damping assignment -- passivity based control (IDA-PBC) are
used to construct nonlinear feedback controls which (asymptotically) stabilize
previously unstable equilibria of Lie-Poisson Hamiltonian systems. The results
are applied to find an asymptotically stabilizing control for the rotor driven
satellite, and a stabilizing control for Hall magnetohydrodynamic flow.",2307.09235v1
2023-08-01,Aerodynamics of the square-back Ahmed body under rainfall conditions,"We report an experimental investigation about the aerodynamics of a
simplified road vehicle, the so-called square-back Ahmed body, under rainfall
conditions. A particular emphasis is put on the evolution of the body base
pressure distribution with respect to the operating conditions. It is found
that rainfall significantly damps both mean base pressure drag and wake
dynamics in comparison to dry conditions.",2308.00276v1
2023-09-11,Study of damped oscillating structures from charged and neutral K-meson electromagnetic form factors data,"The damped oscillating structures (OS) were recently revealed in the proton
""effective"" form factor (FF) data. For the time being they can be neither
confirmed nor disproved by investigations of timelike data on the individual
proton electric and proton magnetic FFs because their precision and reliability
(especially of the proton electric FF data) has not achieved required level for
this aim. On the other hand, conjectures that the OS are direct manifestations
of the quark-gluon structure of the proton indicate that they must not be
specific only for the proton and neutron, but that they should be present also
for other hadrons. This opens a plausibility to find damped oscillatory
structures also from the EM FFs data of such hadrons, for which adequate EM FFs
data exist, by using the same procedure as for the proton. Consequently in this
paper damped oscillatory structures are investigated in the EM FFs data of the
charged and neutral $K$-mesons to be extracted from the corresponding
production cross sections, $\sigma^{bare}_{tot}(e^+e^-\to K^+ K^-)$ measured
from the threshold up to 64 GeV$^2$ and $\sigma^{bare}_{tot}(e^+e^-\to K_s
K_L)$ measured from the threshold up to 9.5 GeV$^2$ of the total c.m. energy
squared. The following results have been obtained. If the charged and neutral
K-meson EM FFs timelike data are described by the three parametric formula by
means of which OS have been revealed from the ""effective"" proton FF data then
OS appear. If physically well founded Unitary and Analytic model of the K-meson
EM structure is used for a description of the charged K-meson EM FFs data, no
OS are visible. However, in the case of the neutral K-meson EM FF data one
cannot make a definite decision. The overall results indicate that OS obtained
from the ""effective"" proton FF data are likely an artefact of the three
parametric formula which does not describe these data well.",2309.05354v1
2023-10-31,"Variational principle for a damped, quadratically interacting particle chain with nonconservative forcing","A method for designing variational principles for the dynamics of a possibly
dissipative and non-conservatively forced chain of particles is demonstrated.
Some qualitative features of the formulation are discussed.",2311.00106v2
2023-12-25,IMEX-RK methods for Landau-Lifshitz equation with arbitrary damping,"Magnetization dynamics in ferromagnetic materials is modeled by the
Landau-Lifshitz (LL) equation, a nonlinear system of partial differential
equations. Among the numerical approaches, semi-implicit schemes are widely
used in the micromagnetics simulation, due to a nice compromise between
accuracy and efficiency. At each time step, only a linear system needs to be
solved and a projection is then applied to preserve the length of
magnetization. However, this linear system contains variable coefficients and a
non-symmetric structure, and thus an efficient linear solver is highly desired.
If the damping parameter becomes large, it has been realized that efficient
solvers are only available to a linear system with constant, symmetric, and
positive definite (SPD) structure. In this work, based on the implicit-explicit
Runge-Kutta (IMEX-RK) time discretization, we introduce an artificial damping
term, which is treated implicitly. The remaining terms are treated explicitly.
This strategy leads to a semi-implicit scheme with the following properties:
(1) only a few linear system with constant and SPD structure needs to be solved
at each time step; (2) it works for the LL equation with arbitrary damping
parameter; (3) high-order accuracy can be obtained with high-order IMEX-RK time
discretization. Numerically, second-order and third-order IMEX-RK methods are
designed in both the 1-D and 3-D domains. A comparison with the backward
differentiation formula scheme is undertaken, in terms of accuracy and
efficiency. The robustness of both numerical methods is tested on the first
benchmark problem from National Institute of Standards and Technology. The
linearized stability estimate and optimal rate convergence analysis are
provided for an alternate IMEX-RK2 numerical scheme as well.",2312.15654v1
2024-01-30,Linear stability analysis of the Couette flow for the 2D Euler-Poisson system,"This paper is concerned with the linear stability analysis for the Couette
flow of the Euler-Poisson system for both ionic fluid and electronic fluid in
the domain $\bb{T}\times\bb{R}$. We establish the upper and lower bounds of the
linearized solutions of the Euler-Poisson system near Couette flow. In
particular, the inviscid damping for the solenoidal component of the velocity
is obtained.",2401.17102v1
2024-03-21,Non-resonant invariant foliations of quasi-periodically forced systems,"We show the existence and uniqueness of invariant foliations about invariant
tori in analytic discrete-time dynamical systems. The parametrisation method is
used prove the result. Our theory is a foundational block of data-driven model
order reduction, that can only be carried out using invariant foliations. The
theory is illustrated by two mechanical examples, where instantaneous
frequencies and damping ratios are calculated about the invariant tori.",2403.14771v1
2024-04-03,"Comment on ""Machine learning conservation laws from differential equations""","In lieu of abstract, first paragraph reads: Six months after the author
derived a constant of motion for a 1D damped harmonic oscillator [1], a similar
result appeared by Liu, Madhavan, and Tegmark [2, 3], without citing the
author. However, their derivation contained six serious errors, causing both
their method and result to be incorrect. In this Comment, those errors are
reviewed.",2404.02896v1
2007-03-01,Stellar Kinematics in the Complicated Inner Spheroid of M31: Discovery of Substructure Along the Southeastern Minor Axis and its Relationship to the Giant Southern Stream,"We present the discovery of a kinematically-cold stellar population along the
SE minor axis of the Andromeda galaxy (M31) that is likely the forward
continuation of M31's giant southern stream. This discovery was made in the
course of an on-going spectroscopic survey of red giant branch (RGB) stars in
M31 using the DEIMOS instrument on the Keck II 10-m telescope. Stellar
kinematics are investigated in eight fields located 9-30 kpc from M31's center
(in projection). A likelihood method based on photometric and spectroscopic
diagnostics is used to isolate confirmed M31 RGB stars from foreground Milky
Way dwarf stars: for the first time, this is done without using radial velocity
as a selection criterion, allowing an unbiased study of M31's stellar
kinematics. The radial velocity distribution of the 1013 M31 RGB stars shows
evidence for the presence of two components. The broad (hot) component has a
velocity dispersion of 129 km/s and presumably represents M31's virialized
spheroid. A significant fraction (19%) of the population is in a narrow (cold)
component centered near M31's systemic velocity with a velocity dispersion that
decreases with increasing radial distance, from 55.5 km/s at R_proj=12 kpc to
10.6 km/s at R_proj=18 kpc. The spatial and velocity distribution of the cold
component matches that of the ""Southeast shelf"" predicted by the Fardal et al.
(2007) orbital model of the progenitor of the giant southern stream. The
metallicity distribution of the cold component matches that of the giant
southern stream, but is about 0.2 dex more metal rich on average than that of
the hot spheroidal component. We discuss the implications of our discovery on
the interpretation of the intermediate-age spheroid population found in this
region in recent ultra-deep HST imaging studies.",0703029v3
2017-02-26,Limits on the ultra-bright Fast Radio Burst population from the CHIME Pathfinder,"We present results from a new incoherent-beam Fast Radio Burst (FRB) search
on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its
large instantaneous field of view (FoV) and relative thermal insensitivity
allow us to probe the ultra-bright tail of the FRB distribution, and to test a
recent claim that this distribution's slope, $\alpha\equiv-\frac{\partial \log
N}{\partial \log S}$, is quite small. A 256-input incoherent beamformer was
deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were
described by a single power-law with $\alpha=0.7$, we would expect an FRB
detection every few days, making this the fastest survey on sky at present. We
collected 1268 hours of data, amounting to one of the largest exposures of any
FRB survey, with over 2.4\,$\times$\,10$^5$\,deg$^2$\,hrs. Having seen no
bursts, we have constrained the rate of extremely bright events to
$<\!13$\,sky$^{-1}$\,day$^{-1}$ above $\sim$\,220$\sqrt{(\tau/\rm ms)}$ Jy\,ms
for $\tau$ between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also
allows us to rule out $\alpha\lesssim0.9$ with 95$\%$ confidence, after
marginalizing over uncertainties in the GBT rate at 700--900\,MHz, though we
show that for a cosmological population and a large dynamic range in flux
density, $\alpha$ is brightness-dependent. Since FRBs now extend to large
enough distances that non-Euclidean effects are significant, there is still
expected to be a dearth of faint events and relative excess of bright events.
Nevertheless we have constrained the allowed number of ultra-intense FRBs.
While this does not have significant implications for deeper, large-FoV surveys
like full CHIME and APERTIF, it does have important consequences for other
wide-field, small dish experiments.",1702.08040v2
2019-04-01,"Astro2020 Science White Paper: Construction of an L* Galaxy: the Transformative Power of Wide Fields for Revealing the Past, Present and Future of the Great Andromeda System","The Great Andromeda Galaxy (M31) is the nexus of the near-far galaxy
evolution connection and a principal data point for near-field cosmology. Due
to its proximity (780 kpc), M31 can be resolved into individual stars like the
Milky Way (MW). Unlike the MW, we have the advantage of a global view of M31,
enabling M31 to be observed with techniques that also apply to more distant
galaxies. Moreover, recent evidence suggests that M31 may have survived a major
merger within the last several Gyr, shaping the morphology of its stellar halo
and triggering a starburst, while leaving the stellar disk largely intact. The
MW and M31 thus provide complementary opportunities for in-depth studies of the
disks, halos, and satellites of L* galaxies.
  Our understanding of the M31 system will be transformed in the 2020s if they
include wide field facilities for both photometry (HST-like sensitivity and
resolution) and spectroscopy (10-m class telescope, >1 sq. deg. field, highly
multiplexed, R~ 3000 to 6000). We focus here on the power of these facilities
to constrain the past, present, and future merger history of M31, via
chemo-dynamical analyses and star formation histories of phase-mixed stars
accreted at early times, as well as stars in surviving tidal debris features,
M31's extended disk, and intact satellite galaxies that will eventually be
tidally incorporated into the halo. This will yield an unprecedented view of
the hierarchical formation of the M31 system and the subhalos that built it
into the L* galaxy we observe today.",1904.01074v1
2021-09-28,Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System,"We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic
is a young (22 Myr) early M dwarf known to host two transiting planets -
$P_{b}\sim8.46$ days, $R_{b}=4.38_{-0.18}^{+0.18}\ R_{\oplus}$,
$P_{c}\sim18.86$ days, $R_{c}=3.51_{-0.16}^{+0.16}\ R_{\oplus}$. With visible
RVs from CARMENES-VIS, CHIRON, HARPS, HIRES, {\sc
{\textsc{Minerva}}}-Australis, and TRES, as well as near-infrared (NIR) RVs
from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a
$5\sigma$ upper limit to the mass of AU Mic c of $M_{c}\leq20.13\ M_{\oplus}$
and present a refined mass of AU Mic b of $M_{b}=20.12_{-1.57}^{+1.72}\
M_{\oplus}$. Used in our analyses is a new RV modeling toolkit to exploit the
wavelength dependence of stellar activity present in our RVs via
wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible
and near-infrared RVs, we also compute the temporal evolution of RV-``color''
and introduce a regressional method to aid in isolating Keplerian from stellar
activity signals when modeling RVs in future works. Using a multi-wavelength
Gaussian process model, we demonstrate the ability to recover injected planets
at $5\sigma$ significance with semi-amplitudes down to $\approx$
10\,m\,s$^{-1}$ with a known ephemeris, more than an order of magnitude below
the stellar activity amplitude. However, we find that the accuracy of the
recovered semi-amplitudes is $\sim$50\% for such signals with our model.",2109.13996v1
2022-03-04,Scaling K2. V. Statistical Validation of 60 New Exoplanets From K2 Campaigns 2-18,"The NASA K2 mission, salvaged from the hardware failures of the Kepler
telescope, has continued Kepler's planet-hunting success. It has revealed
nearly 500 transiting planets around the ecliptic plane, many of which are the
subject of further study, and over 1000 additional candidates. Here we present
the results of an ongoing project to follow-up and statistically validate new
K2 planets, in particular to identify promising new targets for further
characterization. By analyzing the reconnaissance spectra, high-resolution
imaging, centroid variations, and statistical likelihood of the signals of 91
candidates, we validate 60 new planets in 46 systems. These include: a number
of planets amenable to transmission spectroscopy (K2-384 f, K2-387 b, K2-390 b,
K2-403 b, and K2-398 c), emission spectroscopy (K2-371 b, K2-370 b, and K2-399
b), and both (K2-405 b and K2-406 b); several systems with planets in or close
to mean motion resonances (K2-381, K2-398) including a compact, TRAPPIST-1-like
system of five small planets orbiting a mid-M dwarf (K2-384); an ultra-short
period sub-Saturn in the hot Saturn desert (K2-399 b); and a super-Earth
orbiting a moderately bright (V=11.93), metal-poor ([Fe/H]=-0.579+/-0.080) host
star (K2-408 b). In total we validate planets around 4 F stars, 26 G stars, 13
K stars, and 3 M dwarfs. In addition, we provide a list of 37 vetted planet
candidates that should be prioritized for future follow-up observation in order
to be confirmed or validated.",2203.02087v2
1994-06-27,Reverberation mapping of active galactic nuclei : The SOLA method for time-series inversion,"In this paper a new method is presented to find the transfer function of the
broad-line region in active galactic nuclei. The subtractive optimally
localized averages (SOLA) method is a modified version of the Backus-Gilbert
method and is presented as an alternative to the more often used
maximum-entropy method. The SOLA method has been developed for use in
helioseismology. It has been applied to the solar oscillation frequency
splitting data currently available to deduce the internal rotation rate of the
sun. The original SOLA method is reformulated in the present paper to cope with
the slightly different problem of inverting time series. We use simulations to
test the viability of the method and apply the SOLA method to the real data of
the Seyfert-1 galaxy NGC 5548. We investigate the effects of measurement errors
and how the resolution of the TF critically depends upon both the sampling rate
and the photometric accuracy of the data. A uuencoded compressed postscript
file of the paper which includes the figures is available by anonymous ftp at
ftp://solaris.astro.uu.se/pub/articles/atmos/frank/PijWan.uue",9406070v1
1997-06-20,Rejection of the Binary Broad-Line Region Interpretation of Double-Peaked Emission Lines in Three Active Galactic Nuclei,"It has been suggested that the peculiar double-peaked Balmer lines of certain
broad-line radio galaxies come from individual broad-line regions associated
with the black holes of a supermassive binary. We continue to search for
evidence of the radial velocity variations characteristic of a double-lined
spectroscopic binary that are required in such a model. After spectroscopic
monitoring of three suitable candidates (Arp 102B, 3C 390.3, and 3C 332)
spanning two decades, we find no such long-term systematic changes in radial
velocity. A trend noticed by Gaskell in one of the Balmer-line peaks of 3C
390.3 before 1988 did not continue after that year, invalidating his inferred
orbital period and mass. Instead, we find lower limits on the plausible orbital
periods that would require the assumed supermassive binaries in all three
objects to have total masses in excess of 10^10 solar masses. In the case of 3C
390.3 the total binary mass must exceed 10^11 solar masses to satisfy
additional observational constraints on the inclination angle. Such large
binary black hole masses are difficult to reconcile with other observations and
with theory. In addition, there are peculiar properties of the line profiles
and flux ratios in these objects that are not explained by ordinary broad-line
region cloud models. We therefore doubt that the double-peaked line profiles of
the three objects arise in a pair of broad-line regions. Rather, they are much
more likely to be intimately associated with a single black hole.",9706222v2
1999-08-13,Infrared Spectroscopy of the High Redshift Radio Galaxy MRC~2025-218 and a Neighboring Extremely Red Galaxy,"This paper presents infrared spectra taken with the newly commissioned
NIRSPEC spectrograph on the Keck Telescope of the High Redshift Radio Galaxy
MRC 2025-218 (z=2.630) and an extremely red galaxy (R-K > 6 mag) 9'' away.
These observations represent the deepest infrared spectra of a radio galaxy to
date and have allowed for the detection of Hbeta, OIII (4959/5007), OI (6300),
Halpha, NII (6548/6583) and SII (6716/6713). The Halpha emission is very broad
(FWHM~6000 km/s) and strongly supports AGN unification models linking radio
galaxies and quasars. The line ratios are most consistent with a partially
obscured nuclear region and very high excitation. The OIII (5007) line is
extended several arcseconds and shows high velocity clouds in the extended
emission. The nucleus also appears spectrally double and we argue that the
radio galaxy is undergoing a violent merger process. The red galaxy, by
comparison, is very featureless even though we have a good continuum detection
in the H and K bands. We suggest that this object is a foreground galaxy,
probably at a redshift less than 1.5.",9908153v1
2000-01-11,2 micron Spectroscopy within 0.3 arcseconds of SgrA*,"We present moderate (R~$\approx$~2,700) and high resolution
(R~$\approx$~22,000) 2.0$-$2.4 \micron\ spectroscopy of the central 0.1 square
arcseconds of the Galaxy obtained with NIRSPEC, the facility near-infrared
spectrometer for the Keck II telescope. The composite spectra do not have any
features attributable to the brightest stars in the central cluster, i.e.\
after background subtraction, W$_{\rm ^{12}CO(2-0)}$~$<$~2~\AA. This stringent
limit leads us to conclude that the majority, if not all, of the stars are
hotter than typical red giants. Coupled with previously reported photometry, we
conclude that the sources are likely OB main sequence stars. In addition, the
continuum slope in the composite spectrum is bluer than that of a red giant and
is similar to that of the nearby hot star, IRS16NW. It is unlikely that they
are late-type giants stripped of their outer envelopes because such sources
would be much fainter than those observed. Given their inferred youth
($\tau_{\rm age}$~$<$~20~\Myr), we suggest the possibility that the stars have
formed within 0.1 pc of the supermassive black hole. We find a newly-identified
broad-line component (V$_{\rm FWHM}$ $\approx$ 1,000 \kms) to the 2.2178
\micron\ [\ion{Fe}{3}] line located within a few arcseconds of Sgr~A$^*$. A
similar component is not seen in the Br-$\gamma$ emission.",0001171v1
2000-02-17,Discovery of an Obscured Broad Line Region in the High Redshift Radio Galaxy MRC 2025-218,"This paper presents infrared spectra taken with the newly commissioned
NIRSPEC spectrograph on the Keck II Telescope of the High Redshift Radio Galaxy
MRC 2025-218 (z=2.63) These observations represent the deepest infrared spectra
of a radio galaxy to date and have allowed for the detection of Hbeta, [OIII]
(4959/5007), [OI] (6300), Halpha, [NII] (6548/6583) and [SII] (6716/6713). The
Halpha emission is very broad (FWHM = 9300 km/s) and luminous (2.6x10^44
ergs/s) and it is very comparable to the line widths and strengths of radio
loud quasars at the same redshift. This strongly supports AGN unification
models linking radio galaxies and quasars, although we discuss some of the
outstanding differences. The [OIII] (5007) line is extremely strong and has
extended emission with large relative velocities to the nucleus. We also derive
that if the extended emission is due to star formation, each knot has a star
formation rate comparable to a Lyman Break Galaxy at the same redshift.",0002335v1
2000-02-26,Hot Stars and Cool Clouds: The Photodissociation Region M16,"We present high-resolution spectroscopy and images of a photodissociation
region (PDR) in M16 obtained during commissioning of NIRSPEC on the Keck II
telescope. PDRs play a significant role in regulating star formation, and M16
offers the opportunity to examine the physical processes of a PDR in detail. We
simultaneously observe both the molecular and ionized phases of the PDR and
resolve the spatial and kinematic differences between them. The most prominent
regions of the PDR are viewed edge-on. Fluorescent emission from nearby stars
is the primary excitation source, although collisions also preferentially
populate the lowest vibrational levels of H2. Variations in density-sensitive
emission line ratios demonstrate that the molecular cloud is clumpy, with an
average density n = 3x10^5 cm^(-3). We measure the kinetic temperature of the
molecular region directly and find T_H2 = 930 K. The observed density,
temperature, and UV flux imply a photoelectric heating efficiency of 4%. In the
ionized region, n_i=5x10^3 cm^(-3) and T_HII = 9500 K. In the brightest regions
of the PDR, the recombination line widths include a non-thermal component,
which we attribute to viewing geometry.",0002491v1
2000-02-28,The Rest-Frame Optical Spectrum of MS 1512-cB58,"Moderate resolution, near-IR spectroscopy of MS1512-cB58 is presented,
obtained during commissioning of the the Near IR Spectrometer (NIRSPEC) on the
Keck II telescope. The strong lensing of this z=2.72 galaxy by the foreground
cluster MS1512+36 makes it the best candidate for detailed study of the
rest-frame optical properties of Lyman Break Galaxies.
  A redshift of z=2.7290+/-0.0007 is inferred from the emission lines, in
contrast to the z=2.7233 calculated from UV observations of interstellar
absorption lines. Using the Balmer line ratios, we find an extinction of
E(B-V)=0.27. Using the line strengths, we infer an SFR=620+/-18 Msun/yr
(H_0=75, q_0=0.1, Lambda =0), a factor of 2 higher than that measured from
narrow-band imaging observations of the galaxy, but a factor of almost 4 lower
than the SFR inferred from the UV continuum luminosity. The width of the Balmer
lines yields a mass of M_vir=1.2x10^10 Msun. We find that the oxygen abundance
is 1/3 solar, in good agreement with other estimates of the metallicity.
However, we infer a high nitrogen abundance, which may argue for the presence
of an older stellar population.",0002508v1
2000-03-06,The Sunyaev-Zel'dovich Effect in Abell 370,"We present interferometric measurements of the Sunyaev-Zel'dovich (SZ) effect
towards the galaxy cluster Abell 370. These measurements, which directly probe
the pressure of the cluster's gas, show the gas distribution to be strongly
aspherical, as do the x-ray and gravitational lensing observations. We
calculate the cluster's gas mass fraction in two ways. We first compare the gas
mass derived from the SZ measurements to the lensing-derived gravitational mass
near the critical lensing radius. We also calculate the gas mass fraction from
the SZ data by deprojecting the three-dimensional gas density distribution and
deriving the total mass under the assumption that the gas is in hydrostatic
equilibrium (HSE). We test the assumptions in the HSE method by comparing the
total cluster mass implied by the two methods and find that they agree within
the errors of the measurement. We discuss the possible systematic errors in the
gas mass fraction measurement and the constraints it places on the matter
density parameter, OmegaM.",0003085v1
2000-12-04,Galaxy Cluster Gas Mass Fractions from Sunyaev-Zel'dovich Effect Measurements: Constraints on Omega_M,"Using sensitive centimeter-wave receivers mounted on the Owens Valley Radio
Observatory and Berkeley-Illinois-Maryland-Association millimeter arrays, we
have obtained interferometric measurements of the Sunyaev-Zel'dovich (SZ)
effect toward massive galaxy clusters. We use the SZ data to determine the
pressure distribution of the cluster gas and, in combination with published
X-ray temperatures, to infer the gas mass and total gravitational mass of 18
clusters. The gas mass fraction, f_g, is calculated for each cluster, and is
extrapolated to the fiducial radius r_{500} using the results of numerical
simulations. The mean f_g within r_{500} is 0.081+0.009 -0.011/(h_{100}
(statistical uncertainty at 68% confidence level, assuming OmegaM=0.3,
OmegaL=0.7). We discuss possible sources of systematic errors in the mean f_g
measurement. We derive an upper limit for OmegaM from this sample under the
assumption that the mass composition of clusters within r_{500} reflects the
universal mass composition: Omega_M h < Omega_B/f_g. The gas mass fractions
depend on cosmology through the angular diameter distance and the r_{500}
correction factors.
  For a flat universe (OmegaL = 1 - OmegaM) and h=0.7, we find the measured gas
mass fractions are consistent with Omegam less than 0.40, at 68% confidence.
Including estimates of the baryons contained in galaxies and the baryons which
failed to become bound during the cluster formation process, we find OmegaM
\~0.25.",0012067v1
2001-01-02,Science Prospects for SPI,"After the recent beautiful results on gamma-ray lines obtained with CGRO, the
INTEGRAL mission with the imaging-spectrometer SPI will set the next milestone,
combining improved sensitivity and angular resolution with a considerable
increase in spectral resolution. SPI is expected to provide significant new
information on galactic nucleosynthesis processes and star formation activity,
as traced by the distributions of annihilation radiation and radioactive
isotopes such as 26Al and 60Fe. The unprecedented spectral resolution will
allow the study of dynamic processes in stellar mass ejections and will provide
access to kinematic distance estimates for gamma-ray line sources. The study of
supernovae and their remnants will be prime objectives for SPI observations.
Nearby type Ia SN, within 15 Mpc or so, are in reach of the instrument and a
few such events are expected during the lifetime of INTEGRAL. Young galactic
supernova remnants, possibly hidden by interstellar dust, may be unveiled by
their characteristic gamma-ray line signature from the radioactive decay of
44Ti, as has been demonstrated by COMPTEL for Cas A and possibly RX
J0852.0-4622. Classical novae are also among the SPI targets, which may observe
the gamma-ray lines from radioactive 7Be and 22Na. Such observations can
constrain the physics of the nova explosions and will allow to evaluate their
role as nucleosynthesis sites. The interaction of cosmic rays with the dense
matter in molecular clouds may be another source of gamma-ray lines that is
potentially accessible to SPI. Finally after the SIGMA results on Nova Muscae
and 1E1740.7-2942, and a possible 2.223 MeV line detection by COMPTEL, the
search for lines from X novae is another way to participate in the
understanding of the physical conditions in these close binary systems.",0101018v1
2002-08-07,Massive Stars in the Arches Cluster,"We present and use new spectra and narrow-band images, along with previously
published broad-band images, of stars in the Arches cluster to extract
photometry, astrometry, equivalent width, and velocity information. The data
are interpreted with a wind/atmosphere code to determine stellar temperatures,
luminosities, mass-loss rates, and abundances. We have doubled the number of
known emission-line stars, and we have also made the first spectroscopic
identification of the main sequence for any population in the Galactic Center.
We conclude that the most massive stars are bona-fide Wolf-Rayet (WR) stars and
are some of the most massive stars known, having M_{initial} > 100 Msun, and
prodigious winds, Mdot > 10^{-5} Msun yr^{-1}, that are enriched with helium
and nitrogen; with these identifications, the Arches cluster contains about 5%
of all known WR stars in the Galaxy. We find an upper limit to the velocity
dispersion of 22 kms^{-1}, implying an upper limit to the cluster mass of
7(10^4) Msun within a radius of 0.23 pc; we also estimate the bulk heliocentric
velocity of the cluster to be v_{cluster,odot} approximately +95 kms^{-1}.",0208145v1
2003-01-31,Ultraviolet spectroscopy of narrow coronal mass ejections,"We present Ultraviolet Coronagraph Spectrometer (UVCS) observations of 5
narrow coronal mass ejections (CMEs) that were among 15 narrow CMEs originally
selected by Gilbert et al. (2001). Two events (1999 March 27, April 15) were
""structured"", i.e. in white light data they exhibited well defined interior
features, and three (1999 May 9, May 21, June 3) were ""unstructured"", i.e.
appeared featureless. In UVCS data the events were seen as 4-13 deg wide
enhancements of the strongest coronal lines HI Ly-alpha and OVI (1032,1037 A).
We derived electron densities for several of the events from the Large Angle
Spectrometric Coronagraph (LASCO) C2 white light observations. They are
comparable to or smaller than densities inferred for other CMEs. We modeled the
observable properties of examples of the structured (1999 April 15) and
unstructured (1999 May 9) narrow CMEs at different heights in the corona
between 1.5 and 2 R(Sun). The derived electron temperatures, densities and
outflow speeds are similar for those two types of ejections. They were compared
with properties of polar coronal jets and other CMEs. We discuss different
scenarios of narrow CME formation either as a jet formed by reconnection onto
open field lines or CME ejected by expansion of closed field structures.
Overall, we conclude that the existing observations do not definitively place
the narrow CMEs into the jet or the CME picture, but the acceleration of the
1999 April 15 event resembles acceleration seen in many CMEs, rather than
constant speeds or deceleration observed in jets.",0301649v1
2003-02-05,Cluster Sunyaev-Zeldovich Effect Scaling Relations,"X-ray observations of an ""entropy floor"" in nearby groups and clusters of
galaxies offer evidence that important non-gravitational processes, such as
radiative cooling and/or ""preheating"", have strongly influenced the evolution
of the intracluster medium (ICM). We examine how the presence of an entropy
floor modifies the thermal Sunyaev-Zeldovich (SZ) effect. A detailed analysis
of scaling relations between X-ray and SZ effect observables and also between
the two primary SZ effect observables is presented. We find that relationships
between the central Compton parameter and the temperature or mass of a cluster
are extremely sensitive to the presence of an entropy floor. The same is true
for correlations between the integrated Compton parameter and the X-ray
luminosity or the central Compton parameter. In fact, if the entropy floor is
as high as inferred in recent analyses of X-ray data, a comparison of these
correlations with both current and future SZ effect observations should show a
clear signature of this excess entropy. Moreover, because the SZ effect is
redshift-independent, the relations can potentially be used to track the
evolution of the cluster gas and possibly discriminate between the possible
sources of the excess entropy. To facilitate comparisons with observations, we
provide analytic fits to these scaling relations.",0302087v1
2003-03-20,"The SZ Effect Signature of Excess Entropy in Distant, Massive Clusters","Studies of cluster X-ray scaling relations have led to suggestions that
non-gravitational processes, e.g., radiative cooling and/or ""preheating"", have
significantly modified the entropy of the intracluster medium (ICM). For the
first time, we test this hypothesis through a comparison of predicted thermal
Sunyaev-Zeldovich (SZ) effect scaling relations with available data from the
literature. One of the relations that we explore, in principle, depends solely
on SZ effect observations, thus offering an X-ray independent probe of the ICM.
A detailed comparison of the theoretical relations with the largest compilation
of high redshift SZ effect data to date indicates that the presence of an
entropy floor is favored by the data. Furthermore, the inferred level of that
floor, 300 keV cm^2 or higher, is comparable to that found in studies of X-ray
scaling relations of nearby massive clusters. Thus, we find no evidence for
significant evolution of the entropy floor out to z = 0.7. We further
demonstrate that the high quality data to be obtained from the upcoming
Sunyaev-Zeldovich Array (SZA) and the (soon-to-be) upgraded Owens Valley Radio
Observatory (OVRO) array will open powerful new windows into the properties of
the ICM. Specifically, the new measurements will allow for accurate
measurements of the ICM entropy for even the most distant galaxy clusters.",0303451v2
2005-08-01,Transit Photometry of the Core-Dominated Planet HD 149026b,"We report g, V, and r photometric time series of HD 149026 spanning predicted
times of transit of the Saturn-mass planetary companion, which was recently
discovered by Sato and collaborators. We present a joint analysis of our
observations and the previously reported photometry and radial velocities of
the central star. We refine the estimate of the transit ephemeris to Tc [HJD] =
2453527.87455^{+0.00085}_{-0.00091} + N * 2.87598^{+0.00012}_{-0.00017}.
Assuming that the star has a radius of 1.45 +/- 0.10 R_Sun and a mass of 1.30
+/- 0.10 M_Sun, we estimate the planet radius to be 0.726 +/- 0.064 R_Jup,
which implies a mean density of 1.07^{+0.42}_{-0.30} g/cm^3. This density is
significantly greater than that predicted for models which include the effects
of stellar insolation and for which the planet has only a small core of solid
material. Thus we confirm that this planet likely contains a large core, and
that the ratio of core mass to total planet mass is more akin to that of Uranus
and Neptune than that of either Jupiter or Saturn.",0508051v1
2005-10-28,Photoionized HBeta Emission in NGC 5548: It Breathes!,"Emission-line regions in active galactic nuclei and other photoionized
nebulae should become larger in size when the ionizing luminosity increases.
This 'breathing' effect is observed for the Hbeta emission in NGC 5548 by using
Hbeta and optical continuum lightcurves from the 13-year 1989-2001 AGN Watch
monitoring campaign. To model the breathing, we use two methods to fit the
observed lightcurves in detail: (i) parameterized models and, (ii) the MEMECHO
reverberation mapping code. Our models assume that optical continuum variations
track the ionizing radiation, and that the Hbeta variations respond with time
delays due to light travel time. By fitting the data using a delay map that is
allowed to change with continuum flux, we find that the strength of the Hbeta
response decreases and the time delay increases with ionizing luminosity. The
parameterized breathing models allow the time delay and the Hbeta flux to
depend on the continuum flux so that, the time delay is proportional to the
continuum flux to the power beta, and the Hbeta flux is proportional to the
continuum flux to the power alpha. Our fits give 0.1 < beta < 0.46 and 0.57 <
alpha < 0.66. alpha is consistent with previous work by Gilbert and Peterson
(2003) and Goad, Korista and Knigge (2004). Although we find beta to be flatter
than previously determined by Peterson et al. (2002) using cross-correlation
methods, it is closer to the predicted values from recent theoretical work by
Korista and Goad (2004).",0510800v1
2006-07-25,The Transit Light Curve (TLC) Project. I. Four Consecutive Transits of the Exoplanet XO-1b,"We present RIz photometry of four consecutive transits of the newly
discovered exoplanet XO-1b. We improve upon the estimates of the transit
parameters, finding the planetary radius to be R_P = 1.184 +0.028/-0.018
R_Jupiter and the stellar radius to be R_S = 0.928 +0.018/-0.013 R_Sun,
assuming a stellar mass of M_S = 1.00 +/- 0.03 M_Sun. The uncertainties in the
planetary and stellar radii are dominated by the uncertainty in the stellar
mass. These uncertainties increase by a factor of 2-3 if a more conservative
uncertainty of 0.10 M_Sun is assumed for the stellar mass. Our estimate of the
planetary radius is smaller than that reported by McCullough et al. (2006) and
yields a mean density that is comparable to that of TrES-1 and HD 189733b. The
timings of the transits have an accuracy ranging from 0.2 to 2.5 minutes, and
are marginally consistent with a uniform period.",0607571v1
2006-09-12,TrES-2: The First Transiting Planet in the Kepler Field,"We announce the discovery of the second transiting hot Jupiter discovered by
the Trans-atlantic Exoplanet Survey. The planet, which we dub TrES-2, orbits
the nearby star GSC 03549-02811 every 2.47063 days. From high-resolution
spectra, we determine that the star has T_eff = 5960 +/- 100 K and log(g) = 4.4
+/- 0.2, implying a spectral type of G0V and a mass of 1.08 +0.11/-0.05 M_sun.
High-precision radial-velocity measurements confirm a sinusoidal variation with
the period and phase predicted by the photometry, and rule out the presence of
line-bisector variations that would indicate that the spectroscopic orbit is
spurious. We estimate a planetary mass of 1.28 +0.09/-0.04 M_Jup. We model B,
r, R, and I photometric timeseries of the 1.4%-deep transits and find a
planetary radius of 1.24 +0.09/-0.06 R_Jup. This planet lies within the field
of view of the NASA Kepler mission, ensuring that hundreds of upcoming transits
will be monitored with exquisite precision and permitting a host of
unprecedented investigations.",0609335v1
2006-10-19,Precise Radius Estimates for the Exoplanets WASP-1b and WASP-2b,"We present precise z-band photometric time series spanning times of transit
of the two exoplanets recently discovered by the SuperWASP collaboration. We
find planetary radii of 1.44 +/- 0.08 R_J and 1.04 +/- 0.06 R_J for WASP-1b and
WASP-2b, respectively. These error estimates include both random errors in the
photometry and also the uncertainty in the stellar masses. Our results are 5
times more precise than the values derived from the discovery data alone. Our
measurement of the radius of WASP-2b agrees with previously published models of
hot Jupiters that include both a 20-M_Earth core of solid material and the
effects of stellar insolation. In contrast, we find that the models cannot
account for the large size of WASP-1b, even if the planet has no core. Thus, we
add WASP-1b to the growing list of hot Jupiters that are larger than expected.
This suggests that ``inflated'' hot Jupiters are more common than previously
thought, and that any purported explanations involving highly unusual
circumstances are disfavored.",0610589v1
2007-02-16,The Extended Star Formation History of the Andromeda Spheroid at Twenty One Kiloparsecs on the Minor Axis,"Using the HST ACS, we have obtained deep optical images of a southeast
minor-axis field in the Andromeda Galaxy, 21 kpc from the nucleus. In both star
counts and metallicity, this field represents a transition zone between the
metal-rich, highly-disturbed inner spheroid that dominates within 15 kpc and
the metal-poor, diffuse population that dominates beyond 30 kpc. The
color-magnitude diagram reaches well below the oldest main-sequence turnoff in
the population, allowing a reconstruction of the star formation history in this
field. Compared to the spheroid population at 11 kpc, the population at 21 kpc
is ~1.3 Gyr older and ~0.2 dex more metal-poor, on average. However, like the
population at 11 kpc, the population at 21 kpc exhibits an extended star
formation history; one third of the stars are younger than 10 Gyr, although
only a few percent are younger than 8 Gyr. The relatively wide range of
metallicity and age is inconsistent with a single, rapid star-formation
episode, and instead suggests that the spheroid even at 21 kpc is dominated by
the debris of earlier merging events likely occurring more than 8 Gyr ago.",0702448v1
2007-02-23,Discovery of Andromeda XIV: A Dwarf Spheroidal Dynamical Rogue in the Local Group?,"In the course of our survey of the outer halo of the Andromeda Galaxy we have
discovered a remote, possible satellite of that system at a projected 162 kpc
(11.7 degrees) radius. The fairly elongated (0.31 +/- 0.09 ellipticity) dwarf
can be fit with a King profile of 1.07 kpc (d/784 kpc) limiting radius, where
the satellite distance, d, is estimated at ~630-850 kpc from the tip of the red
giant branch. The newfound galaxy, ``Andromeda XIV'' (``AndXIV''),
distinguishes itself from other Local Group galaxies by its extreme dynamics:
Keck/DEIMOS spectroscopy reveals it to have a large heliocentric radial
velocity (-481 km/s), or -206 km/s velocity relative to M31. Even at its
projected radius AndXIV already is at the M31 escape velocity based on the
latest M31 mass models. If AndXIV is bound to M31, then recent models with
reduced M31 virial masses need revision upward. If not bound to M31, then
AndXIV is just now falling into the Local Group for the first time and
represents a dwarf galaxy that formed and spent almost its entire life in
isolation.",0702635v2
1998-05-27,"Survival Analysis, Master Equation, Efficient Simulation of Path-Related Quantities, and Hidden State Concept of Transitions","This paper presents and derives the interrelations between survival analysis
and master equation. Survival analysis deals with modeling the transitions
between succeeding states of a system in terms of hazard rates. Questions
related with this are the timing and sequencing of the states of a time series.
The frequency and characteristics of time series can be investigated by
Monte-Carlo simulations. If one is interested in cross-sectional data connected
with the stochastic process under consideration, one needs to know the temporal
evolution of the distribution of states. This can be obtained by simulation of
the associated master equation. Some new formulas allow the determination of
path-related (i.e. longitudinal) quantities like the occurence probability, the
occurence time distribution, or the effective cumulative life-time distribution
of a certain sequencing of states (path). These can be efficiently evaluated
with a recently developed simulation tool (EPIS). The effective cumulative
life-time distribution facilitates the formulation of a hidden state concept of
behavioral changes which allows an interpretation of the respective
time-dependence of hazard rates. Hidden states represent states which are
either not phenomenological distinguishable from other states, not externally
measurable, or simply not detected.",9805361v1
1999-09-09,Micromagnetic simulations of thermally activated magnetization reversal of nanoscale magnets,"Numerical integration of a stochastic Landau-Lifshitz-Gilbert equation is
used to study dynamic processes in single-domain nanoscale magnets at nonzero
temperatures. Special attention is given to including thermal fluctuations as a
Langevin term, and the Fast Multipole Method is used to calculate dipole-dipole
interactions. It is feasible to simulate these dynamics on the nanosecond time
scale for spatial discretizations that involve on the order of 10000 nodes
using a desktop workstation. The nanoscale magnets considered here are single
pillars with large aspect ratio. Hysteresis-loop simulations are employed to
study the stable and metastable configurations of the magnetization. Each
pillar has magnetic end caps. In a time-dependent field the magnetization of
the pillars is observed to reverse via nucleation, propagation, and coalescence
of the end caps. In particular, the end caps propagate into the magnet and meet
near the middle. A relatively long-lived defect is formed when end caps with
opposite vorticity meet. Fluctuations are more important in the reversal of the
magnetization for fields weaker than the zero-temperature coercive field, where
the reversal is thermally activated. In this case, the process must be
described by its statistical properties, such as the distribution of switching
times, averaged over a large number of independent thermal histories.",9909136v2
2000-10-12,Thermal Magnetization Reversal in Arrays of Nanoparticles,"The results of large-scale simulations investigating the dynamics of
magnetization reversal in arrays of single-domain nanomagnets after a rapid
reversal of the applied field at nonzero temperature are presented. The
numerical micromagnetic approach uses the Landau-Lifshitz-Gilbert equation
including contributions from thermal fluctuations and long-range dipole-dipole
demagnetizing effects implemented using a fast-multipole expansion. The
individual model nanomagnets are 9 nm x 9 nm x 150 nm iron pillars similar to
those fabricated on a surface with STM-assisted chemical vapor deposition [S.
Wirth, et al., J. Appl. Phys {\bf 85}, 5249 (1999)]. Nanomagnets oriented
perpendicular to the surface and spaced 300 nm apart in linear arrays are
considered. The applied field is always oriented perpendicular to the surface.
When the magnitude of the applied field is less than the coercive value, about
2000 Oe for an individual nanomagnet, magnetization reversal in the nanomagnets
can only occur by thermally activated processes. Even though the interaction
from the dipole moment of neighboring magnets in this geometry is only about 1
Oe, less than 1% of the coercive field, it can have a large impact on the
switching dynamics. What determines the height of the free-energy barrier is
the difference between the coercive and applied fields, and 1 Oe can be a
significant fraction of that. The magnetic orientations of the neighbors are
seen to change the behavior of the nanomagnets in the array significantly.",0010184v2
2001-12-12,"High Magnetic Field NMR Studies of LiVGe$_2$O$_6$, a quasi 1-D Spin $S = 1$ System","We report $^{7}$Li pulsed NMR measurements in polycrystalline and single
crystal samples of the quasi one-dimensional S=1 antiferromagnet
LiVGe$_2$O$_6$, whose AF transition temperature is $T_{\text{N}}\simeq 24.5$ K.
The field ($B_0$) and temperature ($T$) ranges covered were 9-44.5 T and
1.7-300 K respectively. The measurements included NMR spectra, the spin-lattice
relaxation rate ($T_1^{-1}$), and the spin-phase relaxation rate ($T_2^{-1}$),
often as a function of the orientation of the field relative to the crystal
axes. The spectra indicate an AF magnetic structure consistent with that
obtained from neutron diffraction measurements, but with the moments aligned
parallel to the c-axis. The spectra also provide the $T$-dependence of the AF
order parameter and show that the transition is either second order or weakly
first order. Both the spectra and the $T_1^{-1}$ data show that $B_0$ has at
most a small effect on the alignment of the AF moment. There is no spin-flop
transition up to 44.5 T. These features indicate a very large magnetic
anisotropy energy in LiVGe$_2$O$_6$ with orbital degrees of freedom playing an
important role. Below 8 K, $T_1^{-1}$ varies substantially with the orientation
of $B_0$ in the plane perpendicular to the c-axis, suggesting a small energy
gap for magnetic fluctuations that is very anisotropic.",0112203v1
2003-10-07,Endogenous Versus Exogenous Shocks in Complex Networks: an Empirical Test Using Book Sale Ranking,"Are large biological extinctions such as the Cretaceous/Tertiary KT boundary
due to a meteorite, extreme volcanic activity or self-organized critical
extinction cascades? Are commercial successes due to a progressive reputation
cascade or the result of a well orchestrated advertisement? Determining the
chain of causality for extreme events in complex systems requires disentangling
interwoven exogenous and endogenous contributions with either no clear or too
many signatures. Here, we study the precursory and recovery signatures
accompanying shocks, that we test on a unique database of the Amazon sales
ranking of books. We find clear distinguishing signatures classifying two types
of sales peaks. Exogenous peaks occur abruptly and are followed by a power law
relaxation, while endogenous sale peaks occur after a progressively
accelerating power law growth followed by an approximately symmetrical power
law relaxation which is slower than for exogenous peaks. These results are
rationalized quantitatively by a simple model of epidemic propagation of
interactions with long memory within a network of acquaintances. The slow
relaxation of sales implies that the sales dynamics is dominated by cascades
rather than by the direct effects of news or advertisements, indicating that
the social network is close to critical.",0310135v2
2004-08-18,Irreversible spin-transfer and magnetization reversal under spin-injection,"In the context of spin electronics, the two spin-channel model assumes that
the spin carriers are composed of two distinct populations: the conduction
electrons of spin up, and the conduction electrons of spin down. In order to
distinguish the paramagnetic and ferromagnetic contributions in spin injection,
we describe the current injection with four channels : the two spin populations
of the conduction bands ($s$ or paramagnetic) and the two spin populations of
the more correlated electrons ($d$ or ferromagnetic). The redistribution of the
conduction electrons at the interface is described by relaxation mechanisms
between the channels. Providing that the $d$ majority-spin band is frozen,
$s-d$ relaxation essentially concerns the minority-spin channels. Accordingly,
even in the abscence of spin-flip scattering (i.e. without standard
spin-accumulation or giant magnetoresistance), the $s-d$ relaxation leads to a
$d$ spin accumulation effect. The coupled diffusion equations for the two
relaxation processes ($s-d$ and spin-flip) are derived. The link with the
ferromagnetic order parameter $\vec{M}$ is performed by assuming that only the
$d$ channel contributes to the Landau-Lifshitz-Gilbert equation. The effect of
magnetization reversal induced by spin injection is explained by these
relaxations under the assumption that the spins of the conduction electrons act
as environmental degrees of freedom on the magnetization.",0408410v1
2004-12-02,Dielectric resonances in disordered media,"Binary disordered systems are usually obtained by mixing two ingredients in
variable proportions: conductor and insulator, or conductor and
super-conductor. and are naturally modeled by regular bi-dimensional or
tri-dimensional lattices, on which sites or bonds are chosen randomly with
given probabilities. In this article, we calculate the impedance of the
composite by two independent methods: the so-called spectral method, which
diagonalises Kirchhoff's Laws via a Green function formalism, and the Exact
Numerical Renormalization method (ENR). These methods are applied to mixtures
of resistors and capacitors (R-C systems), simulating e.g. ionic
conductor-insulator systems, and to composites consituted of resistive
inductances and capacitors (LR-C systems), representing metal inclusions in a
dielectric bulk. The frequency dependent impedances of the latter composites
present very intricate structures in the vicinity of the percolation threshold.
We analyse the LR-C behavior of compounds formed by the inclusion of small
conducting clusters (``$n$-legged animals'') in a dielectric medium. We
investigate in particular their absorption spectra who present a pattern of
sharp lines at very specific frequencies of the incident electromagnetic field,
the goal being to identify the signature of each animal. This enables us to
make suggestions of how to build compounds with specific absorption or
transmission properties in a given frequency domain.",0412061v1
2005-01-12,Current induced magnetization switching in exchange biased spin-valves for CPP-GMR heads,"In contrast to earlier studies performed on simple Co/Cu/Co sandwiches, we
have investigated spin transfer effects in complex spin-valve pillars with a
diameter of 130nm developed for current-perpendicular to the plane (CPP)
magneto-resistive heads. The structure of the samples included an exchange
biased synthetic pinned layer and a free layer both laminated by insertion of
several ultrathin Cu layers. Despite the small thickness of the polarizing
layer, our results show that the free layer can be switched between the
parallel (P) and the antiparallel (AP) states by applying current densities of
the order of 10^7 A/cm^2. A strong asymmetry is observed between the two
critical currents IcAP-P and IcP-AP, as predicted by the model of Slonczewski
model. Thanks to the use of exchange biased structures, the stability phase
diagrams could be obtained in the four quadrants of the (H, I) plan. The
critical lines derived from the magnetoresistance curves measured with
different sense currents, and from the resistance versus current curves
measured for different applied fields, match each other very well. The main
features of the phase diagrams can be reproduced by investigating the stability
of the solutions of the Landau Lifshitz Gilbert equation including spin torque
term within a macrospin model. A spin-transfer saturation effect was observed
in the positive currents range. We attribute it to a de-depolarization effect
which appears as a consequence of the asymmetric heating of the pillars, whose
top and the bottom leads are made of different materials.",0501281v1
2005-12-20,Theory of Spin Torque in a nanomagnet,"We present a complete theory of the spin torque phenomena in a ultrasmall
nanomagnet coupled to non-collinear ferromagnetic electrodes through tunnelling
junctions. This model system can be described by a simple microscopic model
which captures many physical effects characteristic of spintronics: tunneling
magneto resistance, intrinsic and transport induced magnetic relaxation,
current induced magnetization reversal and spin accumulation. Treating on the
same footing the magnetic and transport degrees of freedom, we arrive at a
closed equation for the time evolution of the magnetization. This equation is
very close to the Landau-Lifshitz-Gilbert equation used in spin valves
structures. We discuss how the presence of the Coulomb blockade phenomena and
the discretization of the one-body spectrum gives some additional features to
the current induced spin torque. Depending on the regime, the dynamic induced
by the coupling to electrode can be viewed either as a spin torque or as a
relaxation process. In addition to the possibility of stabilizing uniform spin
precession states, we find that the system is highly hysteretic: up to three
different magnetic states can be simultaneously stable in one region of the
parameter space (magnetic field and bias voltage).We also discuss how the
magneto-resistance can be used to provide additional information on the
non-equilibrium peaks present in the nanomagnet spectroscopy experiments.",0512508v1
2005-09-19,Capacity-Achieving Codes with Bounded Graphical Complexity on Noisy Channels,"We introduce a new family of concatenated codes with an outer low-density
parity-check (LDPC) code and an inner low-density generator matrix (LDGM) code,
and prove that these codes can achieve capacity under any memoryless
binary-input output-symmetric (MBIOS) channel using maximum-likelihood (ML)
decoding with bounded graphical complexity, i.e., the number of edges per
information bit in their graphical representation is bounded. In particular, we
also show that these codes can achieve capacity on the binary erasure channel
(BEC) under belief propagation (BP) decoding with bounded decoding complexity
per information bit per iteration for all erasure probabilities in (0, 1). By
deriving and analyzing the average weight distribution (AWD) and the
corresponding asymptotic growth rate of these codes with a rate-1 inner LDGM
code, we also show that these codes achieve the Gilbert-Varshamov bound with
asymptotically high probability. This result can be attributed to the presence
of the inner rate-1 LDGM code, which is demonstrated to help eliminate high
weight codewords in the LDPC code while maintaining a vanishingly small amount
of low weight codewords.",0509062v3
2006-07-20,List decoding of noisy Reed-Muller-like codes,"First- and second-order Reed-Muller (RM(1) and RM(2), respectively) codes are
two fundamental error-correcting codes which arise in communication as well as
in probabilistically-checkable proofs and learning. In this paper, we take the
first steps toward extending the quick randomized decoding tools of RM(1) into
the realm of quadratic binary and, equivalently, Z_4 codes. Our main
algorithmic result is an extension of the RM(1) techniques from Goldreich-Levin
and Kushilevitz-Mansour algorithms to the Hankel code, a code between RM(1) and
RM(2). That is, given signal s of length N, we find a list that is a superset
of all Hankel codewords phi with dot product to s at least (1/sqrt(k)) times
the norm of s, in time polynomial in k and log(N). We also give a new and
simple formulation of a known Kerdock code as a subcode of the Hankel code. As
a corollary, we can list-decode Kerdock, too. Also, we get a quick algorithm
for finding a sparse Kerdock approximation. That is, for k small compared with
1/sqrt{N} and for epsilon > 0, we find, in time polynomial in (k
log(N)/epsilon), a k-Kerdock-term approximation s~ to s with Euclidean error at
most the factor (1+epsilon+O(k^2/sqrt{N})) times that of the best such
approximation.",0607098v2
1994-05-31,The Behavior of a Spherical Hole in an Infinite Uniform Universe,"In this paper, the behavior of a spherical hole in an otherwise infinite and
uniform universe is investigated. First, the Newtonian theory is developed. The
concept of negative gravity, an outward gravitational force acting away from
the center of the spherical hole, is presented, and the resulting expansion of
the hole is investigated. Then, the same result is derived using the techniques
of Einstein's theory of general relativity. The field equations are solved for
an infinite uniform universe and then for an infinite universe in which matter
is uniformly distributed except for a spherical hole. Negative pressure caused
by negative gravity is utilized. The physical significance of the cosmological
constant is explained, and a new physical concept, that of the gravitational
potential of a hole, is discussed. The relationship between the Newtonian
potential for a hole and the Schwarzschild solution of the field equations is
explored. Finally, the geodesic equations are considered. It is shown that
photons and particles are deflected away from the hole. An application of this
idea is pursued, in which a new cosmology based upon expanding holes in a
uniform universe is developed. The microwave background radiation and Hubble's
Law, among others, are explained. Finally, current astronomical data are used
to compute a remarkably accurate value of Hubble's constant, as well as
estimates of the average mass density of the universe and the cosmological
constant.",9405075v1
2002-11-21,SuSpect: a Fortran Code for the Supersymmetric and Higgs Particle Spectrum in the MSSM,"We present the Fortran code SuSpect version 2.3, which calculates the
Supersymmetric and Higgs particle spectrum in the Minimal Supersymmetric
Standard Model (MSSM). The calculation can be performed in constrained models
with universal boundary conditions at high scales such as the gravity (mSUGRA),
anomaly (AMSB) or gauge (GMSB) mediated breaking models, but also in the
non-universal MSSM case with R-parity and CP conservation. Care has been taken
to treat important features such as the renormalization group evolution of
parameters between low and high energy scales, the consistent implementation of
radiative electroweak symmetry breaking and the calculation of the physical
masses of the Higgs bosons and supersymmetric particles taking into account the
dominant radiative corrections. Some checks of important theoretical and
experimental features, such as the absence of non desired minima, large
fine-tuning in the electroweak symmetry breaking condition, as well as
agreement with precision measurements can be performed. The program is user
friendly, simple to use, self-contained and can easily be linked with other
codes; it is rather fast and flexible, thus allowing scans of the parameter
space with several possible options and choices for model assumptions and
approximations.",0211331v2
2004-11-04,Theoretical and Experimental Analysis of a Randomized Algorithm for Sparse Fourier Transform Analysis,"We analyze a sublinear RAlSFA (Randomized Algorithm for Sparse Fourier
Analysis) that finds a near-optimal B-term Sparse Representation R for a given
discrete signal S of length N, in time and space poly(B,log(N)), following the
approach given in \cite{GGIMS}. Its time cost poly(log(N)) should be compared
with the superlinear O(N log N) time requirement of the Fast Fourier Transform
(FFT). A straightforward implementation of the RAlSFA, as presented in the
theoretical paper \cite{GGIMS}, turns out to be very slow in practice. Our main
result is a greatly improved and practical RAlSFA. We introduce several new
ideas and techniques that speed up the algorithm. Both rigorous and heuristic
arguments for parameter choices are presented. Our RAlSFA constructs, with
probability at least 1-delta, a near-optimal B-term representation R in time
poly(B)log(N)log(1/delta)/ epsilon^{2} log(M) such that
||S-R||^{2}<=(1+epsilon)||S-R_{opt}||^{2}. Furthermore, this RAlSFA
implementation already beats the FFTW for not unreasonably large N. We extend
the algorithm to higher dimensional cases both theoretically and numerically.
The crossover point lies at N=70000 in one dimension, and at N=900 for data on
a N*N grid in two dimensions for small B signals where there is noise.",0411102v2
2006-12-04,Krull dimension and deviation in certain parafree groups,"Hanna Neumann asked whether it was possible for two non-isomorphic residually
nilpotent finitely generated (fg) groups, one of them free, to share the lower
central sequence. Gilbert Baumslag answered the question in the affirmative and
thus gave rise to parafree groups. A group G is termed parafree of rank n if it
is residually nilpotent and shares the lower central sequence with a free group
of rank n. The deviation of a finitely generated (fg) parafree group G is the
difference between the minimum possible number of generators of G and the rank
of G.
  Let G be a fg group, then Hom(G,SL(2, C)) inherits the structure of an
algebraic variety, denoted by R(G), and known as its ""representation variety"".
If G is an n generated parafree group, then the deviation of G is 0 iff
Dim(R(G))=3n. It is known that for n \ge 2 there exist infinitely many parafree
groups of rank n and deviation 1 with non-isomorphic representation varieties
of dimension 3n. In this paper it is shown that given integers n \ge 2, and k
\ge 1, there exist infinitely many parafree groups of rank n and deviation k
with non-isomorphic representation varieties of dimension different from 3n; in
particular, it is shown that there exist infinitely many parafree groups G of
rank n with Dim(R(G))> q, where q \ge 3n is an arbitrary integer.",0612102v2
2004-07-27,Domain wall dynamics driven by adiabatic spin transfer torques,"In a first approximation, known as the adiabatic process, the direction of
the spin polarization of currents is parallel to the local magnetization vector
in a domain wall. Thus the spatial variation of the direction of the spin
current inside the domain wall results in an adiabatical spin transfer torque
on the magnetization. We show that domain wall motion driven by this spin
torque has many unique features that do not exist in the conventional wall
motion driven by a magnetic field. By analytically and numerically solving the
Landau-Lifshitz-Gilbert equation along with the adiabatic spin torque in
magnetic nanowires, we find the domain wall has its maximum velocity at the
initial application of the current but the velocity decreases to zero as the
domain wall begins to deform during its motion. We have computed domain wall
displacement and domain wall deformation of nanowires, and concluded that the
spin torque based on the adiabatic propagation of the spin current in the
domain wall is unable to maintain wall movement. We also introduce a novel
concept of domain wall inductance to characterize the capacity of the
spin-torque induced magnetic energy stored in a domain wall. In the presence of
domain wall pinning centers, we construct a phase diagram for the domain wall
depinning by the combined action of the magnetic field and the spin current.",0407064v1
1997-02-07,Two-pion correlations in Au+Au collisions at 10.8 GeV/c per nucleon,"Two-particle correlation functions for positive and negative pions have been
measured in Au+Au collisions at 10.8~GeV/c per nucleon. The data were analyzed
using one- and three-dimensional correlation functions. From the results of the
three-dimensional fit the phase space density of pions was calculated. It is
consistent with local thermal equilibrium.",9702008v1
2007-01-30,Huddling behavior in emperor penguins : dynamics of huddling,"Although huddling was shown to be the key by which emperor penguins
(Aptenodytes forsteri) save energy and sustain their breeding fast during the
Antarctic winter, the intricacies of this social behavior have been poorly
studied. We recorded abiotic variables with data loggers glued to the feathers
of eight individually marked emperor penguins to investigate their
thermoregulatory behavior and to estimate their ""huddling time budget""
throughout the breeding season (pairing and incubation period). Contrary to the
classic view, huddling episodes were discontinuous and of short and variable
duration, lasting 1.6+/-1.7 (S.D.) h on average. Despite heterogeneous huddling
groups, birds had equal access to the warmth of the huddles. Throughout the
breeding season, males huddled for 38+/-18% (S.D.) of their time, which raised
the ambient temperature that birds were exposed to above 0 degrees C (at
average external temperatures of -17 degrees C). As a consequence of tight
huddles, ambient temperatures were above 20 degrees C during 13+/-12% (S.D.) of
their huddling time. Ambient temperatures increased up to 37.5 degrees C, close
to birds' body temperature. This complex social behavior therefore enables all
breeders to get a regular and equal access to an environment which allows them
to save energy and successfully incubate their eggs during the Antarctic
winter.",0701051v1
2003-10-14,The Minimum Distance Problem for Two-Way Entanglement Purification,"Entanglement purification takes a number of noisy EPR pairs and processes
them to produce a smaller number of more reliable pairs. If this is done with
only a forward classical side channel, the procedure is equivalent to using a
quantum error-correcting code (QECC). We instead investigate entanglement
purification protocols with two-way classical side channels (2-EPPs) for finite
block sizes. In particular, we consider the analog of the minimum distance
problem for QECCs, and show that 2-EPPs can exceed the quantum Hamming bound
and the quantum Singleton bound. We also show that 2-EPPs can achieve the rate
k/n = 1 - (t/n) \log_2 3 - h(t/n) - O(1/n) (asymptotically reaching the quantum
Hamming bound), where the EPP produces at least k good pairs out of n total
pairs with up to t arbitrary errors, and h(x) = -x \log_2 x - (1-x) \log_2
(1-x) is the usual binary entropy. In contrast, the best known lower bound on
the rate of QECCs is the quantum Gilbert-Varshamov bound k/n \geq 1 - (2t/n)
\log_2 3 - h(2t/n). Indeed, in some regimes, the known upper bound on the
asymptotic rate of good QECCs is strictly below our lower bound on the
achievable rate of 2-EPPs.",0310097v4
2005-06-02,Enhanced algorithms for Local Search,"Let G=(V,E) be a finite graph, and f:V->N be any function. The Local Search
problem consists in finding a local minimum of the function f on G, that is a
vertex v such that f(v) is not larger than the value of f on the neighbors of v
in G. In this note, we first prove a separation theorem slightly stronger than
the one of Gilbert, Hutchinson and Tarjan for graphs of constant genus. This
result allows us to enhance a previously known deterministic algorithm for
Local Search with query complexity O(\log n)\cdot d+O(\sqrt{g})\cdot\sqrt{n},
so that we obtain a deterministic query complexity of
d+O(\sqrt{g})\cdot\sqrt{n}, where n is the size of G, d is its maximum degree,
and $g$ is its genus. We also give a quantum version of our algorithm, whose
query complexity is of O(\sqrt{d})+O(\sqrt[4]{g})\cdot\sqrt[4]{n}\log\log n.
Our deterministic and quantum algorithms have query complexities respectively
smaller than the generic algorithms of Aldous and of Aaronson for large classes
of graphs, including graphs of bounded genus and planar graphs. Independently
from this work, Zhang has recently given a quantum algorithm which finds a
local minimum on the planar grid over \{1,...,\sqrt{n}\}^2 using
O(\sqrt[4]{n}(\log\log n)^2) queries. Our quantum algorithm can be viewed as a
strongly generalized, and slightly enhanced version of this algorithm.",0506019v1
2007-09-27,Predictions of the causal entropic principle for environmental conditions of the universe,"The causal entropic principle has been proposed as a superior alternative to
the anthropic principle for understanding the magnitude of the cosmological
constant. In this approach, the probability to create observers is assumed to
be proportional to the entropy production \Delta S in a maximal causally
connected region -- the causal diamond. We improve on the original treatment by
better quantifying the entropy production due to stars, using an analytic model
for the star formation history which accurately accounts for changes in
cosmological parameters. We calculate the dependence of \Delta S on the density
contrast Q=\delta\rho/\rho, and find that our universe is much closer to the
most probable value of Q than in the usual anthropic approach and that
probabilities are relatively weakly dependent on this amplitude. In addition,
we make first estimates of the dependence of \Delta S on the baryon fraction
and overall matter abundance. Finally, we also explore the possibility that
decays of dark matter, suggested by various observed gamma ray excesses, might
produce a comparable amount of entropy to stars.",0709.4443v2
2007-10-24,"The Impact of Halo Properties, Energy Feedback and Projection Effects on the Mass-SZ Flux Relation","We present a detailed analysis of the intrinsic scatter in the integrated SZ
effect - cluster mass (Y-M) relation, using semi-analytic and simulated cluster
samples. Specifically, we investigate the impact on the Y-M relation of energy
feedback, variations in the host halo concentration and substructure
populations, and projection effects due to unresolved clusters along the line
of sight (the SZ background). Furthermore, we investigate at what radius (or
overdensity) one should measure the integrated SZE and define cluster mass so
as to achieve the tightest possible scaling. We find that the measure of Y with
the least scatter is always obtained within a smaller radius than that at which
the mass is defined; e.g. for M_{200} (M_{500}) the scatter is least for
Y_{500} (Y_{1100}). The inclusion of energy feedback in the gas model
significantly increases the intrinsic scatter in the Y-M relation due to larger
variations in the gas mass fraction compared to models without feedback. We
also find that variations in halo concentration for clusters of a given mass
may partly explain why the integrated SZE provides a better mass proxy than the
central decrement. Substructure is found to account for approximately 20% of
the observed scatter in the Y-M relation. Above M_{200} = 2x10^{14} h^{-1}
msun, the SZ background does not significantly effect cluster mass
measurements; below this mass, variations in the background signal reduce the
optimal angular radius within which one should measure Y to achieve the
tightest scaling with M_{200}.",0710.4555v1
2007-10-31,Spin-Torque Driven Magnetization Dynamics: Micromagnetic Modelling,"In this paper we present an overview of recent progress made in the
understanding of the spin-torque induced magnetization dynamics in nanodevices
using mesoscopic micromagnetic simulations. We first specify how a spin-torque
term may be added to the usual Landau-Lifshitz-Gilbert equation of
magnetization motion and detail its physical meaning. After a brief description
of spin-torque driven dynamics in the macrospin approximation, we discuss the
validity of this approximation for various experimentally relevant geometries.
Next, we perform a detailed comparison between accurate experimental data
obtained from nanopillar devices and corresponding numerical modelling. We show
that, on the one hand, many qualitatively important features of the observed
magnetization dynamics (e.g., non-linear frequency shift and frequency jumps
with increasing current) can be satisfactory explained by sophisticated
micromagnetic models, but on the other hand, understanding of these experiments
is still far from being complete. We proceed with the numerical analysis of
point-contact experiments, where an even more complicated magnetization
dynamics is observed. Simulations reveal that such a rich behaviour is due to
the formation of several strongly non-linear oscillation modes. In the last
part of the paper we emphasize the importance of sample characterization and
conclude with some important remarks concerning the relation between
micromagnetic modelling and real experiments.",0710.5924v1
2007-11-19,The Kohn-Sham system in one-matrix functional theory,"A system of electrons in a local or nonlocal external potential can be
studied with 1-matrix functional theory (1MFT), which is similar to density
functional theory (DFT) but takes the one-particle reduced density matrix
(1-matrix) instead of the density as its basic variable. Within 1MFT, Gilbert
derived [PRB 12, 2111 (1975)] effective single-particle equations analogous to
the Kohn-Sham (KS) equations in DFT. The self-consistent solution of these
1MFT-KS equations reproduces not only the density of the original electron
system but also its 1-matrix. While in DFT it is usually possible to reproduce
the density using KS orbitals with integer (0 or 1) occupancy, in 1MFT
reproducing the 1-matrix requires in general fractional occupancies. The
variational principle implies that the KS eigenvalues of all fractionally
occupied orbitals must collapse at self-consistency to a single level, equal to
the chemical potential. We show that as a consequence of the degeneracy the
iteration of the KS equations is intrinsically divergent. Fortunately, the
level shifting method, commonly introduced in Hartree-Fock calculations, is
always able to force convergence. We introduce an alternative derivation of the
1MFT-KS equations that allows control of the eigenvalue collapse by
constraining the occupancies. As an explicit example, we apply the 1MFT-KS
scheme to calculate the ground state 1-matrix of an exactly solvable two-site
Hubbard model.",0711.2996v1
2007-12-01,"On Myopic Sensing for Multi-Channel Opportunistic Access: Structure, Optimality, and Performance","We consider a multi-channel opportunistic communication system where the
states of these channels evolve as independent and statistically identical
Markov chains (the Gilbert-Elliot channel model). A user chooses one channel to
sense and access in each slot and collects a reward determined by the state of
the chosen channel. The problem is to design a sensing policy for channel
selection to maximize the average reward, which can be formulated as a
multi-arm restless bandit process. In this paper, we study the structure,
optimality, and performance of the myopic sensing policy. We show that the
myopic sensing policy has a simple robust structure that reduces channel
selection to a round-robin procedure and obviates the need for knowing the
channel transition probabilities. The optimality of this simple policy is
established for the two-channel case and conjectured for the general case based
on numerical results. The performance of the myopic sensing policy is analyzed,
which, based on the optimality of myopic sensing, characterizes the maximum
throughput of a multi-channel opportunistic communication system and its
scaling behavior with respect to the number of channels. These results apply to
cognitive radio networks, opportunistic transmission in fading environments,
and resource-constrained jamming and anti-jamming.",0712.0035v3
2007-12-12,Two-connected graphs with prescribed three-connected components,"We adapt the classical 3-decomposition of any 2-connected graph to the case
of simple graphs (no loops or multiple edges). By analogy with the
block-cutpoint tree of a connected graph, we deduce from this decomposition a
bicolored tree tc(g) associated with any 2-connected graph g, whose white
vertices are the 3-components of g (3-connected components or polygons) and
whose black vertices are bonds linking together these 3-components, arising
from separating pairs of vertices of g. Two fundamental relationships on graphs
and networks follow from this construction. The first one is a dissymmetry
theorem which leads to the expression of the class B=B(F) of 2-connected
graphs, all of whose 3-connected components belong to a given class F of
3-connected graphs, in terms of various rootings of B. The second one is a
functional equation which characterizes the corresponding class R=R(F) of
two-pole networks all of whose 3-connected components are in F. All the
rootings of B are then expressed in terms of F and R. There follow
corresponding identities for all the associated series, in particular the edge
index series. Numerous enumerative consequences are discussed.",0712.1869v2
2008-03-13,Optimal spatial transportation networks where link-costs are sublinear in link-capacity,"Consider designing a transportation network on $n$ vertices in the plane,
with traffic demand uniform over all source-destination pairs. Suppose the cost
of a link of length $\ell$ and capacity $c$ scales as $\ell c^\beta$ for fixed
$0<\beta<1$. Under appropriate standardization, the cost of the minimum cost
Gilbert network grows essentially as $n^{\alpha(\beta)}$, where $\alpha(\beta)
= 1 - \frac{\beta}{2}$ on $0 < \beta \leq {1/2}$ and $\alpha(\beta) = {1/2} +
\frac{\beta}{2}$ on ${1/2} \leq \beta < 1$. This quantity is an upper bound in
the worst case (of vertex positions), and a lower bound under mild regularity
assumptions. Essentially the same bounds hold if we constrain the network to be
efficient in the sense that average route-length is only $1 + o(1)$ times
average straight line length. The transition at $\beta = {1/2}$ corresponds to
the dominant cost contribution changing from short links to long links. The
upper bounds arise in the following type of hierarchical networks, which are
therefore optimal in an order of magnitude sense. On the large scale, use a
sparse Poisson line process to provide long-range links. On the medium scale,
use hierachical routing on the square lattice. On the small scale, link
vertices directly to medium-grid points. We discuss one of many possible
variant models, in which links also have a designed maximum speed $s$ and the
cost becomes $\ell c^\beta s^\gamma$.",0803.2037v1
2008-03-24,Was the Andromeda Stream Produced by a Disk Galaxy?,"The halo region of M31 exhibits a startling level of stellar inhomogeneities,
the most prominent of which is the ""giant southern stream"". Our previous
analysis indicates that this stream, as well as several other observed
features, are products of the tidal disruption of a single satellite galaxy
with stellar mass ~10^9 solar masses less than 1 Gyr ago. Here we show that the
specific observed morphology of the stream and halo debris favors a cold,
rotating, disk-like progenitor over a dynamically hot, non-rotating one. These
observed characteristics include the asymmetric distribution of stars along the
stream cross-section and its metal-rich core/metal-poor sheath structure. We
find that a disk-like progenitor can also give rise to arc-like features on the
minor axis at certain orbital phases that resemble the recently discovered
minor-axis ""streams"", even reproducing the lower observed metallicity of these
streams. Though interpreted by the discoverers as new, independent tidal
streams, our analysis suggests that these minor-axis streams may alternatively
arise from the progenitor of the giant southern stream. Overall, our study
points the way to a more complete reconstruction of the stream progenitor and
its merger with M31, based on the emerging picture that most of the major
inhomogeneities observed in the M31 halo share a common origin with the giant
stream.",0803.3476v2
2008-04-23,Geometric dynamics of Vlasov kinetic theory and its moments,"The Vlasov equation of kinetic theory is introduced and the Hamiltonian
structure of its moments is presented. Then we focus on the geodesic evolution
of the Vlasov moments. As a first step, these moment equations generalize the
Camassa-Holm equation to its multi-component version. Subsequently, adding
electrostatic forces to the geodesic moment equations relates them to the
Benney equations and to the equations for beam dynamics in particle
accelerators. Next, we develop a kinetic theory for self assembly in
nano-particles. Darcy's law is introduced as a general principle for
aggregation dynamics in friction dominated systems (at different scales). Then,
a kinetic equation is introduced for the dissipative motion of isotropic
nano-particles. The zeroth-moment dynamics of this equation recovers the
classical Darcy's law at the macroscopic level. A kinetic-theory description
for oriented nano-particles is also presented. At the macroscopic level, the
zeroth moments of this kinetic equation recover the magnetization dynamics of
the Landau-Lifshitz-Gilbert equation. The moment equations exhibit the
spontaneous emergence of singular solutions (clumpons) that finally merge in
one singularity. This behaviour represents aggregation and alignment of
oriented nano-particles. Finally, the Smoluchowski description is derived from
the dissipative Vlasov equation for anisotropic interactions. Various levels of
approximate Smoluchowski descriptions are proposed as special cases of the
general treatment. As a result, the macroscopic momentum emerges as an
additional dynamical variable that in general cannot be neglected.",0804.3676v1
2008-05-05,On Expanded Cyclic Codes,"The paper has a threefold purpose. The first purpose is to present an
explicit description of expanded cyclic codes defined in $\GF(q^m)$. The
proposed explicit construction of expanded generator matrix and expanded parity
check matrix maintains the symbol-wise algebraic structure and thus keeps many
important original characteristics. The second purpose of this paper is to
identify a class of constant-weight cyclic codes. Specifically, we show that a
well-known class of $q$-ary BCH codes excluding the all-zero codeword are
constant-weight cyclic codes. Moreover, we show this class of codes achieve the
Plotkin bound. The last purpose of the paper is to characterize expanded cyclic
codes utilizing the proposed expanded generator matrix and parity check matrix.
We characterize the properties of component codewords of a codeword and
particularly identify the precise conditions under which a codeword can be
represented by a subbasis. Our developments reveal an alternative while more
general view on the subspace subcodes of Reed-Solomon codes. With the new
insights, we present an improved lower bound on the minimum distance of an
expanded cyclic code by exploiting the generalized concatenated structure. We
also show that the fixed-rate binary expanded Reed-Solomon codes are
asymptotically ""bad"", in the sense that the ratio of minimum distance over code
length diminishes with code length going to infinity. It overturns the
prevalent conjecture that they are ""good"" codes and deviates from the ensemble
of generalized Reed-Solomon codes which asymptotically achieves the
Gilbert-Varshamov bound.",0805.0615v2
2008-05-14,Path Diversity over Packet Switched Networks: Performance Analysis and Rate Allocation,"Path diversity works by setting up multiple parallel connections between the
end points using the topological path redundancy of the network. In this paper,
\textit{Forward Error Correction} (FEC) is applied across multiple independent
paths to enhance the end-to-end reliability. Network paths are modeled as
erasure Gilbert-Elliot channels. It is known that over any erasure channel,
\textit{Maximum Distance Separable} (MDS) codes achieve the minimum probability
of irrecoverable loss among all block codes of the same size. Based on the
adopted model for the error behavior, we prove that the probability of
irrecoverable loss for MDS codes decays exponentially for an asymptotically
large number of paths. Then, optimal rate allocation problem is solved for the
asymptotic case where the number of paths is large. Moreover, it is shown that
in such asymptotically optimal rate allocation, each path is assigned a
positive rate \textit{iff} its quality is above a certain threshold. The
quality of a path is defined as the percentage of the time it spends in the bad
state. Finally, using dynamic programming, a heuristic suboptimal algorithm
with polynomial runtime is proposed for rate allocation over a finite number of
paths. This algorithm converges to the asymptotically optimal rate allocation
when the number of paths is large. The simulation results show that the
proposed algorithm approximates the optimal rate allocation (found by
exhaustive search) very closely for practical number of paths, and provides
significant performance improvement compared to the alternative schemes of rate
allocation.",0805.2185v1
2008-06-25,HAT-P-9b: A Low Density Planet Transiting a Moderately Faint F star,"We report the discovery of a planet transiting a moderately faint (V=12.3
mag) late F star, with an orbital period of 3.92289 +/- 0.00004 days. From the
transit light curve and radial velocity measurements we determine that the
radius of the planet is R_p = 1.40 +/- 0.06 R_Jup and that the mass is M_p =
0.78 +/- 0.09 M_Jup. The density of the new planet, rho = 0.35 +/- 0.06 g
cm^{-3}, fits to the low-density tail of the currently known transiting
planets. We find that the center of transit is at T_c = 2454417.9077 +/- 0.0003
(HJD), and the total transit duration is 0.143 +/- 0.004 days. The host star
has M_s = 1.28 +/- 0.13 M_Sun and R_s = 1.32 +/- 0.07 R_Sun.",0806.4008v2
2008-07-07,Micropropagation of three genotypes of Indian mustard [{Brassica juncea} (L.) Czern.] using seedling-derived transverse thin cell layer (tTCL) explants,"Micropropagation of three genotypes of Indian mustard [\textit{Brassica
juncea} (L.) Czern.] using 7-days old seedling-derived transverse thin cell
layer (tTCL) explants was accomplished.
  The genotype, explant source and addition of silver nitrate to the medium
significantly influenced shoot bud induction. MS medium with 26.6 $\mu$M of
6-Benzylaminopurin (BAP) and 3.22 $\mu$M of 1-naphtaleneacetic acid (NAA) was
identical (in the case of cotyledon tTCLs whatever the organ) and superior for
the induction of buds (in the cases of petiole tTCL explants of genotypes 1 and
2 and hypocotyl tTCL explants of genotypes 1 and 3) than 53.3 $\mu$M of BAP and
3.22 $\mu$M of NAA. However, 53.3 $\mu$M of BAP was superior for the induction
of buds than 26.6 $\mu$M in the presence of the same concentration of NAA for
petiole tTCL explants of genotype 3 and hypocotyl tTCL explants of genotype 2.
  The addition of silver nitrate significantly enhanced the rate of shoot
induction in all genotypes. Cotyledon-derived tTCL explants exhibited the
highest shoot bud induction potential and was followed by petiole- and
hypocotyl-derived ones. Addition of 10 $\mu$M of silver nitrate to BAP and NAA
supplemented medium induced higher frequency shoot bud induction (up to 100 %)
with the highest means of 4.45 shoots per cotyledon-derived tTCL explants
obtained with the genotype 2. Shoot regenerated were rooted on MS basal medium
without PGRs which induced 99 % of roots per shoot. The plantlets established
in greenhouse conditions with 99 % survival, flowered normally and set seeds.",0807.1061v1
2008-07-18,"On Probability Distributions for Trees: Representations, Inference and Learning","We study probability distributions over free algebras of trees. Probability
distributions can be seen as particular (formal power) tree series [Berstel et
al 82, Esik et al 03], i.e. mappings from trees to a semiring K . A widely
studied class of tree series is the class of rational (or recognizable) tree
series which can be defined either in an algebraic way or by means of
multiplicity tree automata. We argue that the algebraic representation is very
convenient to model probability distributions over a free algebra of trees.
First, as in the string case, the algebraic representation allows to design
learning algorithms for the whole class of probability distributions defined by
rational tree series. Note that learning algorithms for rational tree series
correspond to learning algorithms for weighted tree automata where both the
structure and the weights are learned. Second, the algebraic representation can
be easily extended to deal with unranked trees (like XML trees where a symbol
may have an unbounded number of children). Both properties are particularly
relevant for applications: nondeterministic automata are required for the
inference problem to be relevant (recall that Hidden Markov Models are
equivalent to nondeterministic string automata); nowadays applications for Web
Information Extraction, Web Services and document processing consider unranked
trees.",0807.2983v1
2008-11-02,Stretch-Twist torus dynamo in compact Riemannian manifolds,"Earlier Arnold, Zeldovich, Ruzmaikin and Sokoloff [\textbf{JETP (1982)}] have
computed the eigenvalue of a uniform stretching torus transformation which
result on the first Riemann metric solution of the dynamo action problem.
Recently some other attempts to obtain Riemann metrics representing dynamo
action through conformal maps have been undertaken [{\textbf{Phys. Plasmas 14
(2007)}]. Earlier, Gilbert [\textbf{Proc. Roy. Soc. London A(2003)}] has
investigated a more realistic dynamo map solution than the one presented by
Arnold et al by producing a shearing of the Arnold's cat map, by eigenvalue
problem of a dynamo operator. In this paper, the eigenvalue of the Riemann
twisted torus dynamo flow metric is obtained as the ratio between the poloidal
and toroidal components of the flow. This result is obtained from the Euler
equation. In the twisted torus, the eigenvalue of the Riemann metric is
${m}_{\pm}=\frac{1\pm{\sqrt{5}}}{2}$, which is quite close to the value
obtained by Arnold. In the case the viscosity Reynolds number $Re\to{\infty}$,
the torus flow is unstable as one approaches the torus axis. In Arnold's dynamo
metric the eigenvalues are ${\chi}_{\pm}=\frac{3\pm{\sqrt{5}}}{2}$ which are
very close to the above value. Eigenvalues determine the growth rates of the
velocity ratio between poloidal and toroidal components of the flow. The curved
flow in torus follow previous work by Chen et al [\textbf{Phys Fluids (2006)}].
The ${\alpha}$-effect dynamo is shown to be a second-order effect in the torus
curvature and velocity flow. Loop dynamo flows and maps are also discussed.",0811.0142v1
2008-11-21,Geodesic dynamo chaotic flows and non-Anosov maps in twisted magnetic flux tubes,"Recently Tang and Boozer [{\textbf{Phys. Plasmas (2000)}}], have investigated
the anisotropies in magnetic field dynamo evolution, from local Lyapunov
exponents, giving rise to a metric tensor, in the Alfven twist in magnetic flux
tubes (MFTs). Thiffeault and Boozer [\textbf{Chaos}(2001)] have investigated
the how the vanishing of Riemann curvature constrained the Lyapunov exponential
stretching of chaotic flows. In this paper, Tang-Boozer-Thiffeault differential
geometric framework is used to investigate effects of twisted magnetic flux
tube filled with helical chaotic flows on the Riemann curvature tensor. When
Frenet torsion is positive, the Riemann curvature is unstable, while the
negative torsion induces an stability when time $t\to{\infty}$. This enhances
the dynamo action inside the MFTs. The Riemann metric, depends on the radial
random flows along the poloidal and toroidal directions. The Anosov flows has
been applied by Arnold, Zeldovich, Ruzmaikin and Sokoloff [\textbf{JETP
(1982)}] to build a uniformly stretched dynamo flow solution, based on Arnold's
Cat Map. It is easy to show that when the random radial flow vanishes, the
magnetic field vanishes, since the exponential Lyapunov stretches vanishes.
This is an example of the application of the Vishik's anti-fast dynamo theorem
in the magnetic flux tubes. Geodesic flows of both Arnold and twisted MFT
dynamos are investigated. It is shown that a constant random radial flow can be
obtained from the geodesic equation. Throughout the paper one assumes, the
reasonable plasma astrophysical hypothesis of the weak torsion. Pseudo-Anosov
dynamo flows and maps have also been addressed by Gilbert [\textbf{Proc Roy Soc
A London (1993)}",0811.3630v1
2008-12-03,Gravitino Dark Matter and the Cosmic Lithium Abundances,"Supersymmetric extensions of the standard model of particle physics assuming
the gravitino to be the lightest supersymmetric particle (LSP), and with the
next-to-LSP decaying to the gravitino during Big Bang nucleosynthesis, are
analyzed. Particular emphasis is laid on their potential to solve the ""Li7
problem"", an apparent factor 2-4 overproduction of Li7 in standard Big Bang
nucleosynthesis (BBN), their production of cosmologically important amounts of
Li6, as well as the resulting gravitino dark matter densities in these models.
The study includes several improvements compared to prior studies. Heavy
gravitinos in the constrained minimal supersymmetric standard model (CMMSM) are
reanalyzed, whereas light gravitinos in gauge-mediated supersymmetry breaking
scenarios (GMSB) are studied for the first time. It is confirmed that decays of
NLSP staus to heavy gravitinos, while producing all the dark matter, may at the
same time resolve the Li7 problem. For NLSP decay times ~ 1000 sec, such
scenarios also lead to cosmologically important Li6 (and possibly Be9)
abundances. However, as such scenarios require heavy > 1 TeV staus they are
likely not testable at the LHC. It is found that decays of NLSP staus to light
gravitinos may lead to significant Li6 (and Be9) abundances, whereas NLSP
neutralinos decaying into light gravitinos may solve the Li7 problem. Though
both scenarios are testable at the LHC they may not lead to the production of
the bulk of the dark matter. A section of the paper outlines particle
properties required to significantly reduce the Li7 abundance, and/or enhance
the Li6 (and possibly Be9) abundances, by the decay of an arbitrary relic
particle.",0812.0788v2
2009-01-26,A Bayesian framework for estimating vaccine efficacy per infectious contact,"In vaccine studies for infectious diseases such as human immunodeficiency
virus (HIV), the frequency and type of contacts between study participants and
infectious sources are among the most informative risk factors, but are often
not adequately adjusted for in standard analyses. Such adjustment can improve
the assessment of vaccine efficacy as well as the assessment of risk factors.
It can be attained by modeling transmission per contact with infectious
sources. However, information about contacts that rely on self-reporting by
study participants are subject to nontrivial measurement error in many studies.
We develop a Bayesian hierarchical model fitted using Markov chain Monte Carlo
(MCMC) sampling to estimate the vaccine efficacy controlled for exposure to
infection, while adjusting for measurement error in contact-related factors.
Our method is used to re-analyze two recent HIV vaccine studies, and the
results are compared with the published primary analyses that used standard
methods. The proposed method could also be used for other vaccines where
contact information is collected, such as human papilloma virus vaccines.",0901.4025v1
2009-01-28,Theoretical characterization of a model of aragonite crystal orientation in red abalone nacre,"Nacre, commonly known as mother-of-pearl, is a remarkable biomineral that in
red abalone consists of layers of 400-nm thick aragonite crystalline tablets
confined by organic matrix sheets, with the $(001)$ crystal axes of the
aragonite tablets oriented to within $\pm$ 12 degrees from the normal to the
layer planes. Recent experiments demonstrate that this orientational order
develops over a distance of tens of layers from the prismatic boundary at which
nacre formation begins.
  Our previous simulations of a model in which the order develops because of
differential tablet growth rates (oriented tablets growing faster than
misoriented ones) yield patterns of tablets that agree qualitatively and
quantitatively with the experimental measurements. This paper presents an
analytical treatment of this model, focusing on how the dynamical development
and eventual degree of order depend on model parameters. Dynamical equations
for the probability distributions governing tablet orientations are introduced
whose form can be determined from symmetry considerations and for which
substantial analytic progress can be made. Numerical simulations are performed
to relate the parameters used in the analytic theory to those in the
microscopic growth model. The analytic theory demonstrates that the dynamical
mechanism is able to achieve a much higher degree of order than naive estimates
would indicate.",0901.4482v1
2009-02-07,Partially-erupting prominences: a comparison between observations and model-predicted observables,"AIM: To investigate several partially-erupting prominences to study their
relationship with other CME-associated phenomena and to compare these
observations with observables predicted by a model of partially-expelled flux
ropes (Gibson & Fan, 2006a, b).
  METHODS: We have studied 6 selected events with partially-erupting
prominences using multi wavelength observations recorded by the
Extreme-ultraviolet Imaging Telescope (EIT), Transition Region and Coronal
Explorer (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar
Observatory (BBSO) and soft X-ray telescope (SXT). The observational features
associated with partially-erupting prominences were then compared with the
predicted observables from the model.
  RESULTS: The partially-expelled-flux-rope (PEFR) model of Gibson & Fan
(2006a, b) can explain the partial eruption of these prominences, and in
addition predicts a variety of other CME-related observables that provide
evidence for internal reconnection during eruption. We find that all of the
partially-erupting prominences studied in this paper exhibit indirect evidence
for internal reconnection. Moreover, all cases showed evidence of at least one
observable unique to the PEFR model, e.g., dimmings external to the source
region, and/or a soft X-ray cusp overlying a reformed sigmoid.
  CONCLUSIONS: The PEFR model provides a plausible mechanism to explain the
observed evolution of partially-erupting-prominence-associated CMEs in our
study.",0902.1228v1
2009-03-03,Proportional hazards models with continuous marks,"For time-to-event data with finitely many competing risks, the proportional
hazards model has been a popular tool for relating the cause-specific outcomes
to covariates [Prentice et al. Biometrics 34 (1978) 541--554]. This article
studies an extension of this approach to allow a continuum of competing risks,
in which the cause of failure is replaced by a continuous mark only observed at
the failure time. We develop inference for the proportional hazards model in
which the regression parameters depend nonparametrically on the mark and the
baseline hazard depends nonparametrically on both time and mark. This work is
motivated by the need to assess HIV vaccine efficacy, while taking into account
the genetic divergence of infecting HIV viruses in trial participants from the
HIV strain that is contained in the vaccine, and adjusting for covariate
effects. Mark-specific vaccine efficacy is expressed in terms of one of the
regression functions in the mark-specific proportional hazards model. The new
approach is evaluated in simulations and applied to the first HIV vaccine
efficacy trial.",0903.0487v1
2009-03-06,Five More Massive Binaries in the Cygnus OB2 Association,"We present the orbital solutions for four OB spectroscopic binaries, MT145,
GSC 03161-00815, 2MASS J20294666+4105083, and Schulte 73, and the partial
orbital solution to the B spectroscopic binary, MT372, as part of an ongoing
study to determine the distribution of orbital parameters for massive binaries
in the Cygnus OB2 Association. MT145 is a new, single-lined, moderately
eccentric (e=0.291+/-0.009) spectroscopic binary with period of 25.140+/-0.008
days. GSC 03161-00815 is a slightly eccentric (e=0.10+/-0.01), eclipsing,
interacting and double-lined spectroscopic binary with a period of
4.674+/-0.004 days. 2MASS J20294666+4105083 is a moderately eccentric
(e=0.273+/-0.002) double-lined spectroscopic binary with a period of
2.884+/-0.001 days. Schulte 73 is a slightly eccentric (e=0.169+/-0.009),
double-lined spectroscopic binary with a period of 17.28+/-0.03 days and the
first ""twin"" in our survey with a mass ratio of q=0.99+/-0.02. MT372 is a
single-lined, eclipsing system with a period of 2.228 days and low eccentricity
(e~0). Of the now 18 known OB binaries in Cyg OB2, 14 have periods and mass
ratios. Emerging evidence also shows that the distribution of log(P) is flat
and consistent with Oepik's Law.",0903.1265v1
2009-03-16,The Transit Light Curve Project. XII. Six Transits of the Exoplanet XO-2b,"We present photometry of six transits of the exoplanet XO-2b. By combining
the light-curve analysis with theoretical isochrones to determine the stellar
properties, we find the planetary radius to be 0.996 +0.031/-0.018 rjup and the
planetary mass to be 0.565 +/- 0.054 mjup. These results are consistent with
those reported previously, and are also consistent with theoretical models for
gas giant planets. The mid-transit times are accurate to within 1 min and are
consistent with a constant period. However, the period we derive differs by 2.5
sigma from the previously published period. More data are needed to tell
whether the period is actually variable (as it would be in the presence of an
additional body) or if the timing errors have been underestimated.",0903.2687v1
2009-03-19,Approximation of Bounds on Mixed Level Orthogonal Arrays,"Mixed level orthogonal arrays are basic structures in experimental design. We
develop three algorithms that compute Rao and Gilbert-Varshamov type bounds for
mixed level orthogonal arrays. The computational complexity of the terms
involved in these bounds can grow fast as the parameters of the arrays increase
and this justifies the construction of these algorithms. The first is a
recursive algorithm that computes the bounds exactly, the second is based on an
asymptotic analysis and the third is a simulation algorithm. They are all based
on the representation of the combinatorial expressions that appear in the
bounds as expectations involving a symmetric random walk. The Markov property
of the underlying random walk gives the recursive formula to compute the
expectations. A large deviation (LD) analysis of the expectations provide the
asymptotic algorithm. The asymptotically optimal importance sampling (IS) of
the same expectation provides the simulation algorithm. Both the LD analysis
and the construction of the IS algorithm uses a representation of these
problems as a sequence of stochastic optimal control problems converging to a
limit calculus of variations problem. The construction of the IS algorithm uses
a recently discovered method of using subsolutions to the Hamilton Jacobi
Bellman equation associated with the limit problem.",0903.3438v2
2009-04-16,Good Concatenated Code Ensembles for the Binary Erasure Channel,"In this work, we give good concatenated code ensembles for the binary erasure
channel (BEC). In particular, we consider repeat multiple-accumulate (RMA) code
ensembles formed by the serial concatenation of a repetition code with multiple
accumulators, and the hybrid concatenated code (HCC) ensembles recently
introduced by Koller et al. (5th Int. Symp. on Turbo Codes & Rel. Topics,
Lausanne, Switzerland) consisting of an outer multiple parallel concatenated
code serially concatenated with an inner accumulator. We introduce stopping
sets for iterative constituent code oriented decoding using maximum a
posteriori erasure correction in the constituent codes. We then analyze the
asymptotic stopping set distribution for RMA and HCC ensembles and show that
their stopping distance hmin, defined as the size of the smallest nonempty
stopping set, asymptotically grows linearly with the block length. Thus, these
code ensembles are good for the BEC. It is shown that for RMA code ensembles,
contrary to the asymptotic minimum distance dmin, whose growth rate coefficient
increases with the number of accumulate codes, the hmin growth rate coefficient
diminishes with the number of accumulators. We also consider random puncturing
of RMA code ensembles and show that for sufficiently high code rates, the
asymptotic hmin does not grow linearly with the block length, contrary to the
asymptotic dmin, whose growth rate coefficient approaches the Gilbert-Varshamov
bound as the rate increases. Finally, we give iterative decoding thresholds for
the different code ensembles to compare the convergence properties.",0904.2482v1
2009-10-10,Multi-channel Opportunistic Access: A Case of Restless Bandits with Multiple Plays,"This paper considers the following stochastic control problem that arises in
opportunistic spectrum access: a system consists of n channels (Gilbert-Elliot
channels)where the state (good or bad) of each channel evolves as independent
and identically distributed Markov processes. A user can select exactly k
channels to sense and access (based on the sensing result) in each time slot. A
reward is obtained whenever the user senses and accesses a good channel. The
objective is to design a channel selection policy that maximizes the expected
discounted total reward accrued over a finite or infinite horizon. In our
previous work we established the optimality of a greedy policy for the special
case of k = 1 (i.e., single channel access) under the condition that the
channel state transitions are positively correlated over time. In this paper we
show under the same condition the greedy policy is optimal for the general case
of k >= 1; the methodology introduced here is thus more general. This problem
may be viewed as a special case of the restless bandit problem, with multiple
plays. We discuss connections between the current problem and existing
literature on this class of problems.",0910.1954v1
2010-03-12,Anosov branches of dynamo spectra in one dimensional plasmas,"Recently Guenther et al the globally diagonalized ${\alpha}^{2}$ dynamo
operator spectrum [J Phys A 2007) in mean field media, and its Krein space
related perturbation theory [J Phys A 2006). Earlier, an example of fast
dynamos in stretch shear and fold Anosov maps have been given by Gilbert [PRSA
[1993)). In this paper, analytical solutions representing general turbulent
dynamo filaments are obtained in resistive plasmas. When turbulent diffusivity
is present and kinetic helicity vanishes, a fast dynamo mode is obtained, and
the Anosov eigenvalue obtained. The magnetic field lays down on a Frenet 2
plane along the filaments embedded in a 3D flow. Curvature effects on fast
dynamo are also investigate. In case of weak curvature filaments the one
dimensional manifolds in plasmas present a fast dynamo action. A parallel
result has been obtained by Chicone et al [Comm Math Phys), in the case fast
dynamo spectrum in two dimensional compact Riemannian manifolds of negative
constant curvature, called Anosov spaces. While problems of embedding may
appear in their case here no embedding problems appear since the one
dimensional curved plasmas are embedded in three dimensional Euclidean spaces.
In the examples considered here, equipartion between normal and binormal
components of the magnetic field components is considered. In the opposite
case, non Anosov oscillatory, purely imaginary, branches of the spectrum are
found in dynamo manifold. Negative constant curvature non-compact
$\textbf{H}^{2}$ manifold, has also been used in one-component electron 2D
plasma by Fantoni and Tellez (Stat. Phys, (2008))",1003.2482v1
2010-04-05,"A Prograde, Low-Inclination Orbit for the Very Hot Jupiter WASP-3b","We present new spectroscopic and photometric observations of the transiting
exoplanetary system WASP-3. Spectra obtained during two separate transits
exhibit the Rossiter-McLaughlin (RM) effect and allow us to estimate the
sky-projected angle between the planetary orbital axis and the stellar rotation
axis, lambda = 3.3^{+2.5}_{-4.4} degrees. This alignment between the axes
suggests that WASP-3b has a low orbital inclination relative to the equatorial
plane of its parent star. During our first night of spectroscopic measurements,
we observed an unexpected redshift briefly exceeding the expected sum of the
orbital and RM velocities by 140 m/s. This anomaly could represent the
occultation of material erupting from the stellar photosphere, although it is
more likely to be an artifact caused by moonlight scattered into the
spectrograph.",1004.0692v2
2010-06-09,"NLTT 41135: a field M-dwarf + brown dwarf eclipsing binary in a triple system, discovered by the MEarth observatory","We report the discovery of an eclipsing companion to NLTT 41135, a nearby M5
dwarf that was already known to have a wider, slightly more massive common
proper motion companion, NLTT 41136, at 2.4 arcsec separation. Analysis of
combined-light and radial velocity curves of the system indicates that NLTT
41135B is a 31-34 +/- 3 MJup brown dwarf (where the range depends on the
unknown metallicity of the host star) on a circular orbit. The visual M-dwarf
pair appears to be physically bound, so the system forms a hierarchical triple,
with masses approximately in the ratio 8:6:1. The eclipses are grazing,
preventing an unambiguous measurement of the secondary radius, but follow-up
observations of the secondary eclipse (e.g. with the James Webb Space
Telescope) could permit measurements of the surface brightness ratio between
the two objects, and thus place constraints on models of brown dwarfs.",1006.1793v1
2010-09-28,Connectivity in Sub-Poisson Networks,"We consider a class of point processes (pp), which we call {\em sub-Poisson};
these are pp that can be directionally-convexly ($dcx$) dominated by some
Poisson pp. The $dcx$ order has already been shown useful in comparing various
point process characteristics, including Ripley's and correlation functions as
well as shot-noise fields generated by pp, indicating in particular that
smaller in the $dcx$ order processes exhibit more regularity (less clustering,
less voids) in the repartition of their points. Using these results, in this
paper we study the impact of the $dcx$ ordering of pp on the properties of two
continuum percolation models, which have been proposed in the literature to
address macroscopic connectivity properties of large wireless networks. As the
first main result of this paper, we extend the classical result on the
existence of phase transition in the percolation of the Gilbert's graph (called
also the Boolean model), generated by a homogeneous Poisson pp, to the class of
homogeneous sub-Poisson pp. We also extend a recent result of the same nature
for the SINR graph, to sub-Poisson pp. Finally, as examples we show that the
so-called perturbed lattices are sub-Poisson. More generally, perturbed
lattices provide some spectrum of models that ranges from periodic grids,
usually considered in cellular network context, to Poisson ad-hoc networks, and
to various more clustered pp including some doubly stochastic Poisson ones.",1009.5696v1
2010-10-23,Closure method for spatially averaged dynamics of particle chains,"We study the closure problem for continuum balance equations that model
mesoscale dynamics of large ODE systems. The underlying microscale model
consists of classical Newton equations of particle dynamics. As a mesoscale
model we use the balance equations for spatial averages obtained earlier by a
number of authors: Murdoch and Bedeaux, Hardy, Noll and others. The momentum
balance equation contains a flux (stress), which is given by an exact function
of particle positions and velocities. We propose a method for approximating
this function by a sequence of operators applied to average density and
momentum. The resulting approximate mesoscopic models are systems in closed
form. The closed from property allows one to work directly with the mesoscale
equaitons without the need to calculate underlying particle trajectories, which
is useful for modeling and simulation of large particle systems. The proposed
closure method utilizes the theory of ill-posed problems, in particular
iterative regularization methods for solving first order linear integral
equations. The closed from approximations are obtained in two steps. First, we
use Landweber regularization to (approximately) reconstruct the interpolants of
relevant microscale quantitites from the average density and momentum. Second,
these reconstructions are substituted into the exact formulas for stress. The
developed general theory is then applied to non-linear oscillator chains. We
conduct a detailed study of the simplest zero-order approximation, and show
numerically that it works well as long as fluctuations of velocity are nearly
constant.",1010.4832v1
2010-10-26,Dualities and Identities for Entanglement-Assisted Quantum Codes,"The dual of an entanglement-assisted quantum error-correcting (EAQEC) code is
the code resulting from exchanging the original code's information qubits with
its ebits. To introduce this notion, we show how entanglement-assisted (EA)
repetition codes and accumulator codes are dual to each other, much like their
classical counterparts, and we give an explicit, general quantum shift-register
circuit that encodes both classes of codes.We later show that our constructions
are optimal, and this result completes our understanding of these dual classes
of codes. We also establish the Gilbert-Varshamov bound and the Plotkin bound
for EAQEC codes, and we use these to examine the existence of some EAQEC codes.
Finally, we provide upper bounds on the block error probability when
transmitting maximal-entanglement EAQEC codes over the depolarizing channel,
and we derive variations of the hashing bound for EAQEC codes, which is a lower
bound on the maximum rate at which reliable communication over Pauli channels
is possible with the use of pre-shared entanglement.",1010.5506v4
2010-11-12,"Magnetization Dynamics, Bennett Clocking and Associated Energy Dissipation in Multiferroic Logic","It has been recently shown that multiferroic logic - where logic bits are
encoded in the magnetization orientation of a nanoscale magnetostrictive layer
elastically coupled to a piezoelectric layer - can be Bennett clocked with
small electrostatic potentials of few tens of mV applied to the piezoelectric
layer. The potential generates stress in the magnetostrictive layer and rotates
its magnetization by a large angle to carry out Bennett clocking. This method
of clocking is far more energy-efficient than using spin transfer torque. In
order to assess if such a clocking scheme can be also reasonably fast, we have
studied the magnetization dynamics of a multiferroic logic array with nearest
neighbor dipole coupling using the Landau-Lifshitz-Gilbert (LLG) equation. We
find that switching delays of ~ 3 ns (clock rates of 0.33 GHz) can be achieved
with proper design provided we clock non-adiabatically and dissipate ~48,000 kT
(at room temperature) of energy per clock cycle per bit flip in the clocking
circuit. This dissipation far exceeds the energy barrier separating the two
logic states, which we assumed to be 32 kT to yield a bit error probability of
. Had we used spin transfer torque to switch with the same ~ 3 ns delay, the
energy dissipation would have been much larger (~ $6 \times 106$ kT). This
shows that spin transfer torque, widely used in magnetic random access memory,
is an inefficient way to switch a magnet, and multiferroic logic clocked with
voltage-induced stress is a superior nanomagnetic logic scheme.",1011.2914v2
2010-12-30,One-dimensional Gromov minimal filling,"The present paper opens a new branch in the theory of variational problems
with branching extremals, the investigation of one-dimensional minimal fillings
of finite pseudo-metric spaces. On the one hand, this problem is a
one-dimensional version of a generalization of Gromov's minimal fillings
problem to the case of stratified manifolds (the filling in our case is a
weighted graph). On the other hand, this problem is interesting in itself and
also can be considered as a generalization of another classical problem,
namely, the Steiner problem on the construction of a shortest network joining a
given set of terminals. Besides the statement of the problem, we discuss
several properties of the minimal fillings, describe minimal fillings of
additive spaces, and state several conjectures. We also include some
announcements concerning the very recent results obtained in our group,
including a formula calculating the weight of the minimal filling for an
arbitrary finite pseudo-metric space and the concept of pseudo-additive space
which generalizes the classical concept of additive space. We hope that the
theory of one-dimensional minimal fillings refreshes the interest in the
Steiner problem and gives an opportunity to solve several long standing
problems, such as the calculation of the Steiner ratio, in particular the
verification of the Gilbert--Pollack conjecture on the Steiner ratio of the
Euclidean plane.",1101.0106v2
2011-02-02,Kepler Input Catalog: Photometric Calibration and Stellar Classification,"We describe the photometric calibration and stellar classification methods
used to produce the Kepler Input Catalog (KIC). The KIC is a catalog containing
photometric and physical data for sources in the Kepler Mission field of view;
it is used by the mission to select optimal targets. We derived atmospheric
extinction corrections from hourly observations of secondary standard fields
within the Kepler field of view. Repeatability of absolute photometry for stars
brighter than magnitude 15 is typically 2%. We estimated stellar parameters
Teff, log(g), log (Z), E_{B-V} using Bayesian posterior probability
maximization to match observed colors to Castelli stellar atmosphere models. We
applied Bayesian priors describing the distribution of solar-neighborhood stars
in the color-magnitude diagram (CMD), in log (Z)$, and in height above the
galactic plane. Comparisons with samples of stars classified by other means
indicate that in most regions of the CMD, our classifications are reliable
within about +/- 200 K and +/- 0.4 dex in log (g). It is difficult to assess
the reliability of our log(Z) estimates, but there is reason to suspect that it
is poor, particularly at extreme Teff. Of great importance for the Kepler
Mission, for Teff <= 5400 K, the distinction between main-sequence stars and
giants has proved to be reliable with better than 98% confidence. The KIC is
available through the MAST data archive.",1102.0342v2
2011-05-10,Interstellar Solid Hydrogen,"We consider the possibility that solid molecular hydrogen is present in
interstellar space. If so cosmic-rays and energetic photons cause ionisation in
the solid leading to the formation of H6+. This ion is not produced by
gas-phase reactions and its radiative transitions therefore provide a signature
of solid H2 in the astrophysical context. The vibrational transitions of H6+
are yet to be observed in the laboratory, but we have characterised them in a
quantum-theoretical treatment of the molecule; our calculations include
anharmonic corrections, which are large. Here we report on those calculations
and compare our results with astronomical data. In addition to the H6+
isotopomer, we focus on the deuterated species (HD)3+ which is expected to
dominate at low ionisation rates as a result of isotopic condensation
reactions. We can reliably predict the frequencies of the fundamental bands for
five modes of vibration. For (HD)3+ all of these are found to lie close to some
of the strongest of the pervasive mid-infrared astronomical emission bands,
making it difficult to exclude hydrogen precipitates on observational grounds.
By the same token these results suggest that (HD)3+ could be the carrier of the
observed bands. We consider this possibility within the broader picture of ISM
photo-processes and we conclude that solid hydrogen may indeed be abundant in
astrophysical environments.",1105.1861v1
2011-05-12,The History of Star Formation in Galaxy Disks in the Local Volume as Measured by the ACS Nearby Galaxy Survey Treasury,"We present a measurement of the age distribution of stars residing in spiral
disks and dwarf galaxies. We derive a complete star formation history of the
~140 Mpc^3 covered by the volume-limited sample of galaxies in the Advanced
Camera for Surveys (ACS) Nearby Galaxy Survey Treasury (ANGST). The total star
formation rate density history is dominated by the large spirals in the volume,
although the sample consists mainly of dwarf galaxies. Our measurement shows a
factor of ~3 drop at z~2, in approximate agreement with results from other
measurement techniques. While our results show that the overall star formation
rate density has decreased since z~1, the measured rates during this epoch are
higher than those obtained from other measurement techniques. This enhanced
recent star formation rate appears to be largely due to an increase in the
fraction of star formation contained in low-mass disks at recent times.
Finally, our results indicate that despite the differences at recent times, the
epoch of formation of ~50% of the stellar mass in dwarf galaxies was similar to
that of ~50% of the stellar mass in large spiral galaxies (z>~2), despite the
observed galaxy-to-galaxy diversity among the dwarfs.",1105.2571v1
2011-06-30,Revisiting No-Scale Supergravity Inspired Scenarios: Updated Theoretical and Phenomenological Constraints,"We consider no-scale inspired supergravity scenarios, where the gravitino
mass and related soft supersymmetry-breaking parameters are determined
dynamically by radiative corrections to an essentially flat tree-level
potential in the supersymmetry breaking hidden sector. We examine the
theoretical and phenomenological viability of such a mechanism, when including
up-to-date calculations of the low energy sparticle spectrum and taking into
account the latest LHC results and other experimental constraints. We
(re)emphasize the role of the scale-dependent vacuum energy contribution to the
effective potential, in obtaining realistic no-scale electroweak minima,
examining carefully the impact of boundary conditions and of variants of the
minimization procedure. We also discuss and implement the B_0 (soft breaking
Higgs mixing parameter) input boundary condition at high scale, therefore
fixing tan beta(B_0) at low scales. For general high scale boundary conditions
with non-vanishing B_0, m_0..., our analysis provides theoretical correlations
among the supersymmetric, soft and vacuum energy parameters and related
phenomenological consequences at the LHC. For instance, a zero vacuum energy at
the GUT scale would lead to a decoupled supersymmetric spectrum, together with
a light standard model-like Higgs boson at the electroweak scale. Given the
experimental exclusion limits, a substantial class of the boundary conditions,
and in particular the strict no-scale with m_0=A_0=B_0=0, are only compatible
with a stau being the lightest MSSM particle. Then an enlarged allowed
parameter space emerges when assuming a gravitino LSP to account for the
observed dark matter relic density.",1106.6325v2
2012-02-21,Making Evildoers Pay: Resource-Competitive Broadcast in Sensor Networks,"Consider a time-slotted, single-hop, wireless sensor network (WSN) consisting
of n correct devices and and t=f*n Byzantine devices where f>=0 is any
constant; that is, the Byzantine devices may outnumber the correct ones. There
exists a trusted sender Alice who wishes to deliver a message m over a single
channel to the correct devices. There also exists a malicious user Carol who
controls the t Byzantine devices and uses them to disrupt the communication
channel. For a constant k>=2, the correct and Byzantine devices each possess a
meager energy budget of O(n^{1/k}), Alice and Carol each possess a limited
budget of \tilde{O}(n^{1/k}), and sending or listening in a slot incurs unit
cost. This general setup captures the inherent challenges of guaranteeing
communication despite scarce resources and attacks on the network. Given this
Alice versus Carol scenario, we ask: Is communication of m feasible and, if so,
at what cost?
  We develop a protocol which, for an arbitrarily small constant \epsilon>0,
ensures that at least (1-\epsilon)n correct devices receive m with high
probability. Furthermore, if Carol's devices expend T energy jamming the
channel, then Alice and the correct devices each spend only
\tilde{O}(T^{1/(k+1)}). In other words, delaying the transmission of m forces a
jammer to rapidly deplete its energy supply and, consequently, cease attacks on
the network.",1202.4576v4
2012-03-28,Bispectrum of the Sunyaev-Zel'dovich Effect,"We perform a detailed study of the bispectrum of the Sunyaev-Zel'dovich
effect. Using an analytical model for the pressure profiles of the intracluster
medium, we demonstrate the SZ bispectrum to be a sensitive probe of the
amplitude of the matter power spectrum parameter sigma_8. We find that the
bispectrum amplitude scales as B_SZ ~ sigma_8^{11-12}, compared to that of the
power spectrum, which scales as A_tSZ ~ sigma_8^{7-9}. We show that the SZ
bispectrum is principally sourced by massive clusters at redshifts around
z~0.4, which have been well-studied observationally. This is in contrast to the
SZ power spectrum, which receives a significant contribution from less-well
understood low-mass and high-redshift groups and clusters. Therefore, the
amplitude of the bispectrum at l~3000 is less sensitive to astrophysical
uncertainties than the SZ power spectrum. We show that current high resolution
CMB experiments should be able to detect the SZ bispectrum amplitude with high
significance, in part due to the low contamination from extra-galactic
foregrounds. A combination of the SZ bispectrum and the power spectrum can
sharpen the measurements of thermal and kinetic SZ components and help
distinguish cosmological and astrophysical information from high-resolution CMB
maps.",1203.6368v3
2012-05-01,A quasi-analytical model for energy-delay-reliability tradeoff studies during write operations in perpendicular STT-RAM cell,"One of the biggest challenges the current STT-RAM industry faces is
maintaining a high thermal stability while trying to switch within a given
voltage pulse and energy cost. In this paper, we present a physics based
analytical model that uses a modified Simmons' tunneling expression to capture
the spin dependent tunneling in a magnetic tunnel junction(MTJ). Coupled with
an analytical derivation of the critical switching current based on the
Landau-Lifshitz-Gilbert equation, and the write error rate derived from a
solution to the Fokker-Planck equation, this model provides us a quick estimate
of the energydelay- reliability tradeoffs in perpendicular STTRAMs due to
thermal fluctuations. In other words, the model provides a simple way to
calculate the energy consumed during a write operation that ensures a certain
error rate and delay time, while being numerically far less intensive than a
full-fledged stochastic calculation. We calculate the worst case energy
consumption during anti-parallel (AP) to parallel (P) and P to AP switchings
and quantify how increasing the anisotropy field HK and lowering the saturation
magnetization MS, can significantly reduce the energy consumption. A case study
on how manufacturing variations of the MTJ cell can affect the energy
consumption and delay is also reported.",1205.0183v1
2012-05-16,Transients in porous media: asymptotic time-domain Green functions and limits of current frequency-domain models,"Time domain responses of porous media have been studied by some authors, but
generally the possible descriptions have been given in the frequency domain.
The aim of this paper, limited to materials with rigid skeleton considered as
equivalent fluids, is to compare the descriptions by Johnson-Allard ($JA$%) as
well as by Pride-Lafarge ($PL$) with i) some analytical, approximate formulas,
based upon asymptotic high frequency expansion ; ii) the exact formula by
Zwikker and Kosten for the case of cylindrical pores. The paper starts with a
short summary of the statement of the different general full frequency models
($JA$ and $PL).$ The Green function in the time domain is shown to exhibit
interesting properties of materials. In particular the maximum response depends
on one dimensionless parameter only, which is denoted $\xi $ and is the ratio
of the travelled distance to the product of the \textquotedblleft
frozen\textquotedblright\ sound speed and a characteristic viscous relaxation
time. The distance $\xi $ is related to a time domain Stokes number. The
numerical computation of the Green function is done by FFT, with some
precautions, because of the importance of the higher frequencies on the
response shape. The $PL$ description is shown to be the best full frequency
general model, but some discrepancies with the exact model appear at short
times or short distances. When the distance $\xi $ increases from zero, the
asymptotic expansion shows that the maximum of the Green function decreases
first as $1/\xi ^{2}$, then exponentially.",1205.3775v2
2012-05-20,Externally-driven transformations of vortex textures in flat submicrometer magnets,"Two effects of oscillatory transformations of vortex textures in flat
nanomagnets due to the application of an external field or a spin-polarized
electric current are analytically described with relevance to soft-magnetic
structures of submicrometer sizes (whose thickness is significantly bigger than
the magnetostatic exchange length). These are changes of a domain wall (DW)
structure in a long magnetic stripe (oscillations between a transverse DW, a
vortex DW, and an antivortex DW) and periodic vortex-core reversals in a
circular magnetic dot which are accompanied by oscillatory displacements of the
vortex from the dot center. In nanostructures of smaller thicknesses
(comparable to the exchange length), where nonlocal magnetostatic effects are
very strong because of fast spatial variation of the magnetization, similar
phenomena have been widely studied previously. Here, the dynamics is
investigated within a local approach including magnetostatic field via boundary
conditions on solutions to the Landau-Lifshitz-Gilbert equation only. Both the
DWs in stripes and vortex states of the dot are treated as fragments of a
cross-tie DW. Despite similarity of the cyclic transformations of the ordering
to the dynamics of more strongly confined nanomagnets, details of motion
(trajectories) of the vortices and antivortices (Bloch lines) of the textures
under study are different, which is related to prohibition of rapid jumps of
the polarization of Bloch lines. In addition to the magnetization rotation
about the direction of magnetic field or current polarization, the evolution of
textures is shown to relate to oscillatory changes of the direction of a
cross-tie DW with respect to any arbitrary axis in the magnet plane accompanied
by oscillations of the DW width.",1205.5008v1
2012-06-11,Multi-Gigabit Wireless data transfer at 60 GHz,"In this paper we describe the status of the first prototype of the 60 GHz
wireless Multi-gigabit data transfer topology currently under development at
University of Heidelberg using IBM 130 nm SiGe HBT BiCMOS technology. The 60
GHz band is very suitable for high data rate and short distance applications as
for example needed in the HEP experments. The wireless transceiver consist of a
transmitter and a receiver. The transmitter includes an On-Off Keying (OOK)
modulator, an Local Oscillator (LO), a Power Amplifier (PA) and a BandPass
Filter (BPF). The receiver part is composed of a BandPass- Filter (BPF), a Low
Noise Amplifier (LNA), a double balanced down-convert Gilbert mixer, a Local
Oscillator (LO), then a BPF to remove the mixer introduced noise, an
Intermediate Amplifier (IF), an On-Off Keying demodulator and a limiting
amplifier. The first prototype would be able to handle a data-rate of about 3.5
Gbps over a link distance of 1 m. The first simulations of the LNA show that a
Noise Figure (NF) of 5 dB, a power gain of 21 dB at 60 GHz with a 3 dB
bandwidth of more than 20 GHz with a power consumption 11 mW are achieved.
Simulations of the PA show an output referred compression point P1dB of 19.7 dB
at 60 GHz.",1206.2287v1
2012-06-14,On the Interpretation of the Foundations of Quantum Mechanics,"This study discusses the quantum behavior of a particle, which is controlled
by fluctuations in the physical space-time (ST) variables, rather than provides
a novel interpretation of quantum theory. The fluctuations, i.e.,
inhomogeneities in a homogeneous phase ST, are prescribed by their probability.
They determine the reciprocal space and correlate with the correlation entropy
different from zero. Alongside with the minimum entropy, action, and the
presence of the Winn-Ehrenfest adiabatic invariant (AI), the fluctuations
require the Gilbert information (probabilistic) space linking the physical and
the reciprocal ST. Physical quantities in the information space are represented
by linear Hermitian operators, which is due to the entropy production in the
presence of an AI. Evolution of a quantum system is described by the wave
functions having the meaning of information concerning all virtually possible
states of a quantum particle. The wave functions are the solutions to the
Schrodinger equation and represent a navigation 'roadmap' for the particle to
follow. A quantum system is in fact a classical Hamiltonian system in the space
of coefficients of the wave function decomposition with respect to the operator
eigenfunctions. It is the linearity and the Hermitian nature of the operators
which determine the trajectory and the superposition principle in case of the
wave behavior of fluctuations. The uncertainty principle, reflects correlation
of the fluctuations and, hence, their nonlocality. This study discusses the
wave function phase, the Berry phase and its relationship to quantization,
discriminability of states and macroscopic quantum effects caused by
localization of the particle, followed by a possible entropy change during its
transition into a new thermodynamic state.",1206.2998v1
2012-08-08,RMR-Efficient Randomized Abortable Mutual Exclusion,"Recent research on mutual exclusion for shared-memory systems has focused on
""local spin"" algorithms. Performance is measured using the ""remote memory
references"" (RMRs) metric. As common in recent literature, we consider a
standard asynchronous shared memory model with N processes, which allows atomic
read, write and compare-and-swap (short: CAS) operations.
  In such a model, the asymptotically tight upper and lower bound on the number
of RMRs per passage through the Critical Section is Theta(log N) for the
optimal deterministic algorithms (see Yang and Anderson,1995, and Attiya,
Hendler and Woelfel, 2008). Recently, several randomized algorithms have been
devised that break the Omega(log N) barrier and need only o(log N) RMRs per
passage in expectation (see Hendler and Woelfel, 2010, Hendler and Woelfel,
2011, and Bender and Gilbert, 2011). In this paper we present the first
randomized ""abortable"" mutual exclusion algorithm that achieves a
sub-logarithmic expected RMR complexity. More precisely, against a weak
adversary (which can make scheduling decisions based on the entire past
history, but not the latest coin-flips of each process) every process needs an
expected number of O(log N/ log log N) RMRs to enter end exit the critical
section. If a process receives an abort-signal, it can abort an attempt to
enter the critical section within a finite number of its own steps and by
incurring O(log N/ log log N) RMRs.",1208.1723v1
2012-08-16,QIRAL: A High Level Language for Lattice QCD Code Generation,"Quantum chromodynamics (QCD) is the theory of subnuclear physics, aiming at
mod- eling the strong nuclear force, which is responsible for the interactions
of nuclear particles. Lattice QCD (LQCD) is the corresponding discrete
formulation, widely used for simula- tions. The computational demand for the
LQCD is tremendous. It has played a role in the history of supercomputers, and
has also helped defining their future. Designing efficient LQCD codes that
scale well on large (probably hybrid) supercomputers requires to express many
levels of parallelism, and then to explore different algorithmic solutions.
While al- gorithmic exploration is the key for efficient parallel codes, the
process is hampered by the necessary coding effort. We present in this paper a
domain-specific language, QIRAL, for a high level expression of parallel
algorithms in LQCD. Parallelism is expressed through the mathematical struc-
ture of the sparse matrices defining the problem. We show that from these
expressions and from algorithmic and preconditioning formulations, a parallel
code can be automatically generated. This separates algorithms and mathematical
formulations for LQCD (that be- long to the field of physics) from the
effective orchestration of parallelism, mainly related to compilation and
optimization for parallel architectures.",1208.4035v1
2012-08-22,Entanglement Spectrum Classification of $C_n$-invariant Noninteracting Topological Insulators in Two Dimensions,"We study the single particle entanglement spectrum in 2D topological
insulators which possess $n$-fold rotation symmetry. By defining a series of
special choices of subsystems on which the entanglement is calculated, or real
space cuts, we find that the number of protected in-gap states for each type of
these real space cuts is a quantum number indexing (if any) non-trivial
topology in these insulators. We explicitly show the number of protected in-gap
states is determined by a $Z^n$-index, $(z_1,...,z_n)$, where $z_m$ is the
number of occupied states that transform according to $m$-th one-dimensional
representation of the $C_n$ point group. We find that the entanglement spectrum
contains in-gap states pinned in an interval of entanglement eigenvalues
$[1/n,1-1/n]$. We determine the number of such in-gap states for an exhaustive
variety of cuts, in terms of the $Z_m$ quantum numbers. Furthermore, we show
that in a homogeneous system, the $Z^n$ index can be determined through an
evaluation of the eigenvalues of point group symmetry operators at all
high-symmetry points in the Brillouin zone. When disordered $n$-fold
rotationally symmetric systems are considered, we find that the number of
protected in-gap states is identical to that in the clean limit as long as the
disorder preserves the underlying point group symmetry and does not close the
bulk insulating gap.",1208.4603v1
2012-09-25,Multiscale modeling in micromagnetics: existence of solutions and numerical integration,"Various applications ranging from spintronic devices, giant magnetoresistance
sensors, and magnetic storage devices, include magnetic parts on very different
length scales. Since the consideration of the Landau-Lifshitz-Gilbert equation
(LLG) constrains the maximum element size to the exchange length within the
media, it is numerically not attractive to simulate macroscopic parts with this
approach. On the other hand, the magnetostatic Maxwell equations do not
constrain the element size, but cannot describe the short-range exchange
interaction accurately. A combination of both methods allows to describe
magnetic domains within the micromagnetic regime by use of LLG and also
considers the macroscopic parts by a non-linear material law using the Maxwell
equations. In our work, we prove that under certain assumptions on the
non-linear material law, this multiscale version of LLG admits weak solutions.
Our proof is constructive in the sense that we provide a linear-implicit
numerical integrator for the multiscale model such that the numerically
computable finite element solutions admit weak $H^1$-convergence (at least for
a subsequence) towards a weak solution.",1209.5548v2
2012-10-05,"Rapid Size-Controlled Synthesis of Dextran-Coated, 64Cu-Doped Iron Oxide Nanoparticles","Research into developing dual modality probes enabled for magnetic resonance
imaging (MRI) and positron emission tomography (PET) has been on the rise
recently due to the potential to combine the high resolution of MRI and the
high sensitivity of PET. Current synthesis techniques for developing multimodal
probes is largely hindered in part by prolonged reaction times during
radioisotope incorporation - leading to a weakening of the radioactivity. Along
with a time-efficient synthesis, the resulting products must fit within a
critical size range (between 20-100nm) to increase blood retention time. In
this work, we describe a novel, rapid, microwave-based synthesis technique to
grow dextran-coated iron oxide nanoparticles doped with copper (DIO/Cu).
Traditional methods for coprecipitation of dextran-coated iron oxide
nanoparticles require refluxing for 2 hours and result in approximately 50 nm
diameter particles. We demonstrate that microwave synthesis can produce 50 nm
nanoparticles with 5 minutes of heating. We discuss the various parameters used
in the microwave synthesis protocol to vary the size distribution of DIO/Cu,
and demonstrate the successful incorporation of 64Cu into these particles with
the aim of future use for dual-mode MR/PET imaging.",1210.1823v1
2012-10-05,Rapid Microwave-Assisted Synthesis of Dextran-Coated Iron Oxide Nanoparticles for Magnetic Resonance Imaging,"Currently, magnetic iron oxide nanoparticles are the only nano-sized magnetic
resonance imaging (MRI) contrast agents approved for clinical use, yet
commercial manufacturing of these agents has been limited or discontinued.
Though there is still widespread demand for these particles both for clinical
use and research, they are difficult to obtain commercially, and complicated
syntheses make in-house preparation infeasible for most biological research
labs or clinics. To make commercial production viable and increase
accessibility of these products, it is crucial to develop simple, rapid, and
reproducible preparations of biocompatible iron oxide nanoparticles. Here, we
report a rapid, straightforward microwave-assisted synthesis of
superparamagnetic dextran-coated iron oxide nanoparticles. The nanoparticles
were produced in two hydrodynamic sizes with differing core morphologies by
varying the synthetic method as either a two-step or single step process. A
striking benefit of these methods is the ability to obtain swift and consistent
results without the necessity for air, pH, or temperature sensitive techniques;
therefore, reaction times and complex manufacturing processes are greatly
reduced as compared to conventional synthetic methods. This is a great benefit
for cost-effective translation to commercial production. The nanoparticles are
found to be superparamagnetic and exhibit properties consistent for use in MRI.
In addition, the dextran coating imparts the water-solubility and
biocompatibility necessary for in vivo utilization.",1210.1827v1
2012-10-16,Dark Matter Substructure Detection Using Spatially Resolved Spectroscopy of Lensed Dusty Galaxies,"We investigate how strong lensing of dusty, star-forming galaxies by
foreground galaxies can be used as a probe of dark matter halo substructure. We
find that spatially resolved spectroscopy of lensed sources allows dramatic
improvements to measurements of lens parameters. In particular we find that
modeling of the full, three-dimensional (angular position and radial velocity)
data can significantly facilitate substructure detection, increasing the
sensitivity of observables to lower mass subhalos. We carry out simulations of
lensed dusty sources observed by early ALMA (Cycle 1) and use a Fisher matrix
analysis to study the parameter degeneracies and mass detection limits of this
method. We find that, even with conservative assumptions, it is possible to
detect galactic dark matter subhalos of ~ 10^8 M_{\odot} with high significance
in most lensed DSFGs. Specifically, we find that in typical DSFG lenses, there
is a ~ 55 % probability of detecting a substructure with M>10^8 M_{\odot} with
more than 5 sigma detection significance in each lens, if the abundance of
substructure is consistent with previous lensing results. The full ALMA array,
with its significantly enhanced sensitivity and resolution, should improve
these estimates considerably. Given the sample of ~100 lenses provided by
surveys like the South Pole Telescope, our understanding of dark matter
substructure in typical galaxy halos is poised to improve dramatically over the
next few years.",1210.4562v1
2012-10-22,Shared Information -- New Insights and Problems in Decomposing Information in Complex Systems,"How can the information that a set ${X_{1},...,X_{n}}$ of random variables
contains about another random variable $S$ be decomposed? To what extent do
different subgroups provide the same, i.e. shared or redundant, information,
carry unique information or interact for the emergence of synergistic
information?
  Recently Williams and Beer proposed such a decomposition based on natural
properties for shared information. While these properties fix the structure of
the decomposition, they do not uniquely specify the values of the different
terms. Therefore, we investigate additional properties such as strong symmetry
and left monotonicity. We find that strong symmetry is incompatible with the
properties proposed by Williams and Beer. Although left monotonicity is a very
natural property for an information measure it is not fulfilled by any of the
proposed measures.
  We also study a geometric framework for information decompositions and ask
whether it is possible to represent shared information by a family of posterior
distributions.
  Finally, we draw connections to the notions of shared knowledge and common
knowledge in game theory. While many people believe that independent variables
cannot share information, we show that in game theory independent agents can
have shared knowledge, but not common knowledge. We conclude that intuition and
heuristic arguments do not suffice when arguing about information.",1210.5902v1
2012-10-23,Lensing Noise in mm-wave Galaxy Cluster Surveys,"We study the effects of gravitational lensing by galaxy clusters of the
background of dusty star-forming galaxies (DSFGs) and the Cosmic Microwave
Background (CMB), and examine the implications for Sunyaev-Zel'dovich-based
(SZ) galaxy cluster surveys. At the locations of galaxy clusters, gravitational
lensing modifies the probability distribution of the background flux of the
DSFGs as well as the CMB. We find that, in the case of a single-frequency 150
GHz survey, lensing of DSFGs leads to both a slight increase (~10%) in detected
cluster number counts (due to a ~ 50% increase in the variance of the DSFG
background, and hence an increased Eddington bias), as well as to a rare
(occurring in ~2% of clusters) ""filling-in"" of SZ cluster signals by bright
strongly lensed background sources. Lensing of the CMB leads to a ~55%
reduction in CMB power at the location of massive galaxy clusters in a
spatially-matched single-frequency filter, leading to a net decrease in
detected cluster number counts. We find that the increase in DSFG power and
decrease in CMB power due to lensing at cluster locations largely cancel, such
that the net effect on cluster number counts for current SZ surveys is
sub-dominant to Poisson errors.",1210.6354v1
2012-10-29,Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets with Thermal Noise,"We consider the general Landau-Lifshitz-Gilbert (LLG) dynamical theory
underlying the magnetization switching rates of a thin film uniaxial magnet
subject to spin-torque effects and thermal fluctuations (thermal noise). After
discussing the various dynamical regimes governing the switching phenomena, we
present analytical results for the mean switching time behavior. Our approach,
based on explicitly solving the first passage time problem, allows for a
straightforward analysis of the thermally assisted, low spin-torque, switching
asymptotics of thin film magnets. To verify our theory, we have developed an
efficient GPU-based micromagnetic code to simulate the stochastic LLG dynamics
out to millisecond timescales. We explore the effects of geometrical tilts
between the spin-current and uniaxial anisotropy axes on the thermally assisted
dynamics. We find that even in the absence of axial symmetry, the switching
times can be functionally described in a form virtually identical to the
collinear case. We further verify that asymptotic behavior is reached fairly
slowly, thus quantifying the role of thermal noise in the crossover regime
linking deterministic to thermally assisted magnetization reversal.",1210.7675v3
2012-12-06,Splittings and automorphisms of relatively hyperbolic groups,"We study automorphisms of a relatively hyperbolic group G. When G is
one-ended, we describe Out(G) using a preferred JSJ tree over subgroups that
are virtually cyclic or parabolic. In particular, when G is toral relatively
hyperbolic, Out(G) is virtually built out of mapping class groups and subgroups
of GL_n(Z) fixing certain basis elements. When more general parabolic groups
are allowed, these subgroups of GL_n(Z) have to be replaced by McCool groups:
automorphisms of parabolic groups acting trivially (i.e. by conjugation) on
certain subgroups. Given a malnormal quasiconvex subgroup P of a hyperbolic
group G, we view G as hyperbolic relative to P and we apply the previous
analysis to describe the group Out(P to G) of automorphisms of P that extend to
G: it is virtually a McCool group. If Out(P to G) is infinite, then P is a
vertex group in a splitting of G. If P is torsion-free, then Out(P to G) is of
type VF, in particular finitely presented. We also determine when Out(G) is
infinite, for G relatively hyperbolic. The interesting case is when G is
infinitely-ended and has torsion. When G is hyperbolic, we show that Out(G) is
infinite if and only if G splits over a maximal virtually cyclic subgroup with
infinite center. In general we show that infiniteness of Out(G) comes from the
existence of a splitting with infinitely many twists, or having a vertex group
that is maximal parabolic with infinitely many automorphisms acting trivially
on incident edge groups.",1212.1434v3
2013-01-23,"Localization, metabelian groups, and the isomorphism problem","If G and H are finitely generated, residually nilpotent metabelian groups, H
is termed para-G if there is a homomorphism of G into H which induces an
isomorphism between the corresponding terms of their lower central quotient
groups. We prove that this is an equivalence relation. It is a much coarser
relation than isomorphism, our ultimate concern. It turns out that many of the
groups in a given equivalence class share various properties including finite
presentability. There are examples, such as the lamplighter group, where an
equivalence class consists of a single isomorphism class and others where this
is not the case. We give several examples where we solve the Isomorphism
Problem. We prove also that the sequence of torsion-free ranks of the lower
central quotients of a finitely generated metabelian group is computable. In a
future paper we plan on proving that there is an algorithm to compute the
numerator and denominator of the rational Poincar\'e series of a finitely
generated metabelian group and will carry out this computation in a number of
examples, which may shed a tiny bit of light on the Isomorphism Problem. Our
proofs use localization, class field theory and some constructive commutative
algebra.",1301.5533v2
2013-01-26,Crystal nucleation and near-epitaxial growth in nacre,"Nacre is a layered, iridescent lining found inside many mollusk shells, with
a unique brick-and-mortar periodic structure at the sub-micron scale, and
remarkable resistance to fracture. Despite extensive studies, it remains
unclear how nacre forms. Here we present 20-nm, 2{\deg}-resolution
Polarization-dependent Imaging Contrast (PIC) images of shells from 15 mollusk
shell species, mapping nacre tablets and their orientation patterns, showing
where new crystal orientations appear and how they propagate across organic
sheets as nacre grows. In all shells we found stacks of co-oriented aragonite
(CaCO3) tablets arranged into vertical columns or staggered diagonally. Only
near the nacre-prismatic boundary are disordered crystals nucleated, as
spherulitic aragonite. Overgrowing nacre tablet crystals are most frequently
co-oriented with the underlying spherulitic aragonite or with another tablet,
connected by mineral bridges. Therefore aragonite crystal growth in nacre is
epitaxial or near-epitaxial, with abrupt or gradual changes in orientation,
with c-axes within 20{\deg}. Based on these data, we propose that there is one
mineral bridge per tablet, and that ""bridge-tilting"" is a possible mechanism to
introduce small, gradual or abrupt changes in the orientation of crystals
within a stack of tablets as nacre grows.",1301.6273v2
2013-02-03,A generalization of variable elimination for separable inverse problems beyond least squares,"In linear inverse problems, we have data derived from a noisy linear
transformation of some unknown parameters, and we wish to estimate these
unknowns from the data. Separable inverse problems are a powerful
generalization in which the transformation itself depends on additional unknown
parameters and we wish to determine both sets of parameters simultaneously.
When separable problems are solved by optimization, convergence can often be
accelerated by elimination of the linear variables, a strategy which appears
most prominently in the variable projection methods due to Golub, Pereyra, and
Kaufman. Existing variable elimination methods require an explicit formula for
the optimal value of the linear variables, so they cannot be used in problems
with Poisson likelihoods, bound constraints, or other important departures from
least squares.
  To address this limitation, we propose a generalization of variable
elimination in which standard optimization methods are modified to behave as
though a variable has been eliminated. We verify that this approach is a proper
generalization by using it to re-derive several existing variable elimination
techniques. We then extend the approach to bound-constrained and Poissonian
problems, showing in the process that many of the best features of variable
elimination methods can be duplicated in our framework. Tests on difficult
exponential sum fitting and blind deconvolution problems indicate that the
proposed approach can have significant speed and robustness advantages over
standard methods.",1302.0441v2
2013-04-05,City versus wetland: Predicting urban growth in the Vecht area with a cellular automaton model,"There are many studies dealing with the protection or restoration of wetlands
and the sustainable economic growth of cities as separate subjects. This study
investigates the conflict between the two in an area where city growth is
threatening a protected wetland area. We develop a stochastic cellular
automaton model for urban growth and apply it to the Vecht area surrounding the
city of Hilversum in the Netherlands, using topographic maps covering the past
150 years. We investigate the dependence of the urban growth pattern on the
values associated with the protected wetland and other types of landscape
surrounding the city. The conflict between city growth and wetland protection
is projected to occur before 2035, assuming full protection of the wetland. Our
results also show that a milder protection policy, allowing some of the wetland
to be sacrificed, could be beneficial for maintaining other valuable
landscapes. This insight would be difficult to achieve by other analytical
means. We conclude that even slight changes in usage priorities of landscapes
can significantly affect the landscape distribution in near future. Our results
also point to the importance of a protection policy to take the value of
surrounding landscapes and the dynamic nature of urban areas into account.",1304.1609v1
2013-04-22,Topological Insulators with Commensurate Antiferromagnetism,"We study the topological features of non-interacting insulators subject to an
antiferromangetic (AFM) Zeeman field, or AFM insulators, the period of which is
commensurate with the lattice period. These insulators can be classified by the
presence/absence of an emergent anti-unitary symmetry: the combined operation
of time-reversal and a lattice translation by vector $\mathbf{D}$. For AFM
insulators that preserve this combined symmetry, regardless of any details in
lattice structure or magnetic structure, we show that (i) there is a new type
of Kramers' degeneracy protected by the combined symmetry; (ii) a new $Z_2$
index may be defined for 3D AFM insulators, but not for those in lower
dimensions and (iii) in 3D AFM insulators with a non-trivial $Z_2$ index, there
are odd number of gapless surface modes if and only if the surface termination
also preserves the combined symmetry, but the dispersion of surface states
becomes highly anisotropic if the AFM propagation vector becomes small compared
with the reciprocal lattice vectors. We numerically demonstrate the theory by
calculating the spectral weight of the surface states of a 3D TI in the
presence of AFM fields with different propagation vectors, which may be
observed by ARPES in Bi$_2$Se$_3$ or Bi$_2$Te$_3$ with induced
antiferromagnetism.",1304.6081v3
2013-05-17,Spectral gap for stochastic energy exchange model with nonuniformly positive rate function,"We give a lower bound on the spectral gap for a class of stochastic energy
exchange models. In 2011, Grigo et al. introduced the model and showed that,
for a class of stochastic energy exchange models with a uniformly positive rate
function, the spectral gap of an $N$-component system is bounded from below by
a function of order $N^{-2}$. In this paper, we consider the case where the
rate function is not uniformly positive. For this case, the spectral gap
depends not only on $N$ but also on the averaged energy $\mathcal{E}$, which is
the conserved quantity under the dynamics. Under some assumption, we obtain a
lower bound of the spectral gap which is of order $C(\mathcal{E})N^{-2}$ where
$C(\mathcal{E})$ is a positive constant depending on $\mathcal {E}$. As a
corollary of the result, a lower bound of the spectral gap for the mesoscopic
energy exchange process of billiard lattice studied by Gaspard and Gilbert [J.
Stat. Mech. Theory Exp. 2008 (2008) p11021, J. Stat. Mech. Theory Exp. 2009
(2009) p08020] and the stick process studied by Feng et al. [Stochastic
Process. Appl. 66 (1997) 147-182] are obtained.",1305.4066v3
2013-08-18,Layered Constructions for Low-Delay Streaming Codes,"We propose a new class of error correction codes for low-delay streaming
communication. We consider an online setup where a source packet arrives at the
encoder every $M$ channel uses, and needs to be decoded with a maximum delay of
$T$ packets. We consider a sliding-window erasure channel --- $\cC(N,B,W)$ ---
which introduces either up to $N$ erasures in arbitrary positions, or $B$
erasures in a single burst, in any window of length $W$. When $M=1$, the case
where source-arrival and channel-transmission rates are equal, we propose a
class of codes --- MiDAS codes --- that achieve a near optimal rate. Our
construction is based on a {\em layered} approach. We first construct an
optimal code for the $\cC(N=1,B,W)$ channel, and then concatenate an additional
layer of parity-check symbols to deal with $N>1$. When $M > 1$, the case where
source-arrival and channel-transmission rates are unequal, we characterize the
capacity when $N=1$ and $W \ge M(T+1),$ and for $N>1$, we propose a
construction based on a layered approach. Numerical simulations over
Gilbert-Elliott and Fritchman channel models indicate significant gains in the
residual loss probability over baseline schemes. We also discuss the connection
between the error correction properties of the MiDAS codes and their underlying
column distance and column span.",1308.3827v1
2013-08-31,Delay Minimization for Instantly Decodable Network Coding in Persistent Channels with Feedback Intermittence,"In this paper, we consider the problem of minimizing the multicast decoding
delay of generalized instantly decodable network coding (G-IDNC) over
persistent forward and feedback erasure channels with feedback intermittence.
In such an environment, the sender does not always receive acknowledgement from
the receivers after each transmission. Moreover, both the forward and feedback
channels are subject to persistent erasures, which can be modelled by a two
state (good and bad states) Markov chain known as Gilbert-Elliott channel
(GEC). Due to such feedback imperfections, the sender is unable to determine
subsequent instantly decodable packets combination for all receivers. Given
this harsh channel and feedback model, we first derive expressions for the
probability distributions of decoding delay increments and then employ these
expressions in formulating the minimum decoding problem in such environment as
a maximum weight clique problem in the G-IDNC graph. We also show that the
problem formulations in simpler channel and feedback models are special cases
of our generalized formulation. Since this problem is NP-hard, we design a
greedy algorithm to solve it and compare it to blind approaches proposed in
literature. Through extensive simulations, our adaptive algorithm is shown to
outperform the blind approaches in all situations and to achieve significant
improvement in the decoding delay, especially when the channel is highly
persistent",1309.0145v2
2013-09-06,Energy release from impacting prominence material following the 2011 June 7 eruption,"Solar filaments exhibit a range of eruptive-like dynamic activity, ranging
from the full or partial eruption of the filament mass and surrounding magnetic
structure as a coronal mass ejection (CME), to a fully confined or 'failed'
eruption. On 2011 June 7, a dramatic partial eruption of a filament was
observed by multiple instruments on SDO and STEREO. One of the interesting
aspects of this event is the response of the solar atmosphere as non-escaping
material falls inward under the influence of gravity. The impact sites show
clear evidence of brightening in the observed EUV wavelengths due to energy
release. Two plausible physical mechanisms explaining the brightening are
considered: heating of the plasma due to the kinetic energy of impacting
material compressing the plasma, or reconnection between the magnetic field of
low-lying loops and the field carried by the impacting material. By analyzing
the emission of the brightenings in several SDO/AIA wavelengths, and comparing
the kinetic energy of the impacting material (7.6 x 10^26 - 5.8 x 10^27 ergs)
to the radiative energy (1.9 x 10^25 - 2.5 x 10^26 ergs) we find the dominant
mechanism of energy release involved in the observed brightening is plasma
compression.",1309.1769v1
2013-09-26,Constraints on a second planet in the WASP-3 system,"There have been previous hints that the transiting planet WASP-3 b is
accompanied by a second planet in a nearby orbit, based on small deviations
from strict periodicity of the observed transits. Here we present 17 precise
radial velocity measurements and 32 transit light curves that were acquired
between 2009 and 2011. These data were used to refine the parameters of the
host star and transiting planet. This has resulted in reduced uncertainties for
the radii and masses of the star and planet. The radial-velocity data and the
transit times show no evidence for an additional planet in the system.
Therefore, we have determined the upper limit on the mass of any hypothetical
second planet, as a function of its orbital period.",1309.6733v1
2013-09-28,Synthetic Multiferroic Interconnects for Magnetic Logic Circuits,"In this work, we consider the possibility of using synthetic multiferroics
comprising piezoelectric and magnetostrictive materials as an interconnect for
nano magnetic logic circuits. The proposed interconnect resembles a parallel
plate capacitor filled with a piezoelectric, where one of the plates is made of
a magnetoelastic material. The operation of the interconnect is based on the
effect of stress-mediated anisotropy modulation, where an electric field
applied across the piezoelectric material produces stress, which, in turn,
affects the anisotropy field in the magnetostrictive material. We present the
results of numerical modeling illustrating signal propagation through the
interconnect. The model combines electric and magnetic parts, where the
electric part describes the distribution of an electric field through the
piezoelectric and the magnetic part describes the change of magnetization in
the magnetoelastic layer. The model is based on the Landau-Lifshitz-Gilbert
equation with the electric field dependent anisotropy term included. The
utilization of the electro-magnetic coupling makes it possible to amplify
magnetic signal during its propagation via energy conversion from the electric
to magnetic domains. Potentially, synthetic multiferroic interconnects can be
implemented in a variety of spin-based devices ensuring reliable and low-energy
consuming data transmission. According to the estimates, the group velocity of
magnetic signals may be up to 100 km/s with energy dissipation less than aJ per
bit per 100nm. The fundamental limits and practical shortcoming of the proposed
approach are also discussed.",1309.7399v1
2013-10-01,Ionized Plasma and Neutral Gas Coupling in the Sun's Chromosphere and Earth's Ionosphere/Thermosphere,"We review our understanding of ionized plasma and neutral gas coupling in the
weakly ionized, stratified, electromagnetically-permeated regions of the Sun's
chromosphere and Earth's ionosphere/thermosphere. Using representative models
for each environment we derive fundamental descriptions of the coupling of the
constituent parts to each other and to the electric and magnetic fields, and we
examine the variation in magnetization of the ionized component. Using these
descriptions we compare related phenomena in the two environments, and discuss
electric currents, energy transfer and dissipation. We present a coupled
theoretical and numerical study of plasma instabilities in the two environments
that serves as an example of how the chromospheric and ionospheric communities
can further collaborate. We also suggest future collaborative studies that will
help improve our understanding of these two different atmospheres which share
many similarities, but have large disparities in key quantities.",1310.0405v4
2013-11-13,Excitation of radial collective modes in a quantum dot: Beyond linear response,"We compare the response of five different models of two interacting electrons
in a quantum dot to an external short lived radial excitation that is strong
enough to excite the system well beyond the linear response regime. The models
considered describe the Coulomb interaction between the electrons in different
ways ranging from mean-field approaches to configuration interaction (CI)
models, where the two-electron Hamiltonian is diagonalized in a large truncated
Fock space. The radially symmetric excitation is selected in order to severely
put to test the different approaches to describe the interaction and
correlations of an electron system in a nonequilibrium state. As can be
expected for the case of only two electrons none of the mean-field models can
in full details reproduce the results obtained by the CI model. Nonetheless,
some linear and nonlinear characteristics are reproduced reasonably well. All
the models show activation of an increasing number of collective modes as the
strength of the excitation is increased. By varying slightly the confinement
potential of the dot we observe how sensitive the properties of the excitation
spectrum are to the Coulomb interaction and its correlation effects. In order
to approach closer the question of nonlinearity we solve one of the mean-field
models directly in a nonlinear fashion without resorting to iterations.",1311.3252v2
2013-11-20,"Neutron-induced dpa, transmutations, gas production, and helium embrittlement of fusion materials","In a fusion reactor materials will be subjected to significant fluxes of
high-energy neutrons. As well as causing radiation damage, the neutrons also
initiate nuclear reactions leading to changes in the chemical composition of
materials (transmutation). Many of these reactions produce gases, particularly
helium, which cause additional swelling and embrittlement of materials. This
paper investigates, using a combination of neutron-transport and inventory
calculations, the variation in displacements per atom (dpa) and helium
production levels as a function of position within the high flux regions of a
recent conceptual model for the ""next-step"" fusion device DEMO. Subsequently,
the gas production rates are used to provide revised estimates, based on new
density-functional-theory results, for the critical component lifetimes
associated with the helium-induced grain-boundary embrittlement of materials.
The revised estimates give more optimistic projections for the lifetimes of
materials in a fusion power plant compared to a previous study, while at the
same time indicating that helium embrittlement remains one of the most
significant factors controlling the structural integrity of fusion power plant
components.",1311.5079v1
2013-12-19,The availability of research data declines rapidly with article age,"Policies ensuring that research data are available on public archives are
increasingly being implemented at the government [1], funding agency [2-4], and
journal [5,6] level. These policies are predicated on the idea that authors are
poor stewards of their data, particularly over the long term [7], and indeed
many studies have found that authors are often unable or unwilling to share
their data [8-11]. However, there are no systematic estimates of how the
availability of research data changes with time since publication. We therefore
requested datasets from a relatively homogenous set of 516 articles published
between 2 and 22 years ago, and found that availability of the data was
strongly affected by article age. For papers where the authors gave the status
of their data, the odds of a dataset being extant fell by 17% per year. In
addition, the odds that we could find a working email address for the first,
last or corresponding author fell by 7% per year. Our results reinforce the
notion that, in the long term, research data cannot be reliably preserved by
individual researchers, and further demonstrate the urgent need for policies
mandating data sharing via public archives.",1312.5670v1
2014-01-13,On List-decodability of Random Rank Metric Codes,"In the present paper, we consider list decoding for both random rank metric
codes and random linear rank metric codes. Firstly, we show that, for arbitrary
$0<R<1$ and $\epsilon>0$ ($\epsilon$ and $R$ are independent), if
$0<\frac{n}{m}\leq \epsilon$, then with high probability a random rank metric
code in $F_{q}^{m\times n}$ of rate $R$ can be list-decoded up to a fraction
$(1-R-\epsilon)$ of rank errors with constant list size $L$ satisfying $L\leq
O(1/\epsilon)$. Moreover, if $\frac{n}{m}\geq\Theta_R(\epsilon)$, any rank
metric code in $F_{q}^{m\times n}$ with rate $R$ and decoding radius
$\rho=1-R-\epsilon$ can not be list decoded in ${\rm poly}(n)$ time. Secondly,
we show that if $\frac{n}{m}$ tends to a constant $b\leq 1$, then every
$F_q$-linear rank metric code in $F_{q}^{m\times n}$ with rate $R$ and list
decoding radius $\rho$ satisfies the Gilbert-Varsharmov bound, i.e., $R\leq
(1-\rho)(1-b\rho)$. Furthermore, for arbitrary $\epsilon>0$ and any $0<\rho<1$,
with high probability a random $F_q$-linear rank metric codes with rate
$R=(1-\rho)(1-b\rho)-\epsilon$ can be list decoded up to a fraction $\rho$ of
rank errors with constant list size $L$ satisfying $L\leq O(\exp(1/\epsilon))$.",1401.2693v2
2014-01-30,Quantitative Decoding of Interactions in Tunable Nanomagnet Arrays Using First Order Reversal Curves,"To develop a full understanding of interactions in nanomagnet arrays is a
persistent challenge, critically impacting their technological acceptance. This
paper reports the experimental, numerical and analytical investigation of
interactions in arrays of Co nanoellipses using the first-order reversal curve
(FORC) technique. A mean-field analysis has revealed the physical mechanisms
giving rise to all of the observed features: a shift of the non-interacting
FORC-ridge at the low-H$_c$ end off the local coercivity H$_c$ axis; a stretch
of the FORC-ridge at the high-H$_c$ end without shifting it off the H$_c$ axis;
and a formation of a tilted edge connected to the ridge at the low-H$_c$ end.
Changing from flat to Gaussian coercivity distribution produces a negative
feature, bends the ridge, and broadens the edge. Finally, nearest neighbor
interactions segment the FORC-ridge. These results demonstrate that the FORC
approach provides a comprehensive framework to qualitatively and quantitatively
decode interactions in nanomagnet arrays.",1401.7749v1
2014-02-07,For-all Sparse Recovery in Near-Optimal Time,"An approximate sparse recovery system in $\ell_1$ norm consists of parameters
$k$, $\epsilon$, $N$, an $m$-by-$N$ measurement $\Phi$, and a recovery
algorithm, $\mathcal{R}$. Given a vector, $\mathbf{x}$, the system approximates
$x$ by $\widehat{\mathbf{x}} = \mathcal{R}(\Phi\mathbf{x})$, which must satisfy
$\|\widehat{\mathbf{x}}-\mathbf{x}\|_1 \leq
(1+\epsilon)\|\mathbf{x}-\mathbf{x}_k\|_1$. We consider the 'for all' model, in
which a single matrix $\Phi$, possibly 'constructed' non-explicitly using the
probabilistic method, is used for all signals $\mathbf{x}$. The best existing
sublinear algorithm by Porat and Strauss (SODA'12) uses $O(\epsilon^{-3}
k\log(N/k))$ measurements and runs in time $O(k^{1-\alpha}N^\alpha)$ for any
constant $\alpha > 0$.
  In this paper, we improve the number of measurements to $O(\epsilon^{-2} k
\log(N/k))$, matching the best existing upper bound (attained by super-linear
algorithms), and the runtime to $O(k^{1+\beta}\textrm{poly}(\log
N,1/\epsilon))$, with a modest restriction that $\epsilon \leq (\log k/\log
N)^{\gamma}$, for any constants $\beta,\gamma > 0$. When $k\leq \log^c N$ for
some $c>0$, the runtime is reduced to $O(k\textrm{poly}(N,1/\epsilon))$. With
no restrictions on $\epsilon$, we have an approximation recovery system with $m
= O(k/\epsilon \log(N/k)((\log N/\log k)^\gamma + 1/\epsilon))$ measurements.",1402.1726v2
2014-03-11,Measuring the power spectrum of dark matter substructure using strong gravitational lensing,"In recent years, it has become possible to detect individual dark matter
subhalos near images of strongly lensed extended background galaxies.
Typically, only the most massive subhalos in the strong lensing region may be
detected this way. In this work, we show that strong lenses may also be used to
constrain the much more numerous population of lower mass subhalos that are too
small to be detected individually. In particular, we show that the power
spectrum of projected density fluctuations in galaxy halos can be measured
using strong gravitational lensing. We develop the mathematical framework of
power spectrum estimation, and test our method on mock observations. We use our
results to determine the types of observations required to measure the
substructure power spectrum with high significance. We predict that deep
observations ($\sim10$ hours on a single target) with current facilities can
measure this power spectrum at the $3\sigma$ level, with no apparent degeneracy
with unknown clumpiness in the background source structure or fluctuations from
detector noise. Upcoming ALMA measurements of strong lenses are capable of
placing strong constraints on the abundance of dark matter subhalos and the
underlying particle nature of dark matter.",1403.2720v3
2014-03-14,Cosmological Spectral Deconvolution,"One of the main goals of modern observational cosmology is to map the large
scale structure of the Universe. A potentially powerful approach for doing this
would be to exploit three-dimensional spectral maps, i.e. the specific
intensity of extragalactic light as a function of wavelength and direction on
the sky, to measure spatial variations in the total extragalactic light
emission and use these as a tracer of the clustering of matter. A main
challenge is that the observed intensity as a function of wavelength is a
convolution of the source luminosity density with the rest-frame spectral
energy distribution. In this paper, we introduce the method of spectral
deconvolution as a way to invert this convolution and extract the clustering
information. We show how one can use observations of the mean and angular
fluctuations of extragalactic light as a function of wavelength, assuming
statistical isotropy, to reconstruct jointly the rest-frame spectral energy
distribution of the sources and the source spatial density fluctuations. This
method is more general than the well known line mapping technique as it does
not rely on spectral lines in the emitted spectra. After introducing the
general formalism, we discuss its implementation and limitations. This formal
paper sets the stage for future more practical studies.",1403.3727v1
2014-03-27,On the Performance of Short Block Codes over Finite-State Channels in the Rare-Transition Regime,"As the mobile application landscape expands, wireless networks are tasked
with supporting different connection profiles, including real-time traffic and
delay-sensitive communications. Among many ensuing engineering challenges is
the need to better understand the fundamental limits of forward error
correction in non-asymptotic regimes. This article characterizes the
performance of random block codes over finite-state channels and evaluates
their queueing performance under maximum-likelihood decoding. In particular,
classical results from information theory are revisited in the context of
channels with rare transitions, and bounds on the probabilities of decoding
failure are derived for random codes. This creates an analysis framework where
channel dependencies within and across codewords are preserved. Such results
are subsequently integrated into a queueing problem formulation. For instance,
it is shown that, for random coding on the Gilbert-Elliott channel, the
performance analysis based on upper bounds on error probability provides very
good estimates of system performance and optimum code parameters. Overall, this
study offers new insights about the impact of channel correlation on the
performance of delay-aware, point-to-point communication links. It also
provides novel guidelines on how to select code rates and block lengths for
real-time traffic over wireless communication infrastructures.",1403.7232v1
2014-04-08,Cost-oblivious storage reallocation,"Databases need to allocate and free blocks of storage on disk. Freed blocks
introduce holes where no data is stored. Allocation systems attempt to reuse
such deallocated regions in order to minimize the footprint on disk. If
previously allocated blocks cannot be moved, the problem is called the memory
allocation problem, which is known to have a logarithmic overhead in the
footprint.
  This paper defines the storage reallocation problem, where previously
allocated blocks can be moved, or reallocated, but at some cost. The algorithms
presented here are cost oblivious, in that they work for a broad and reasonable
class of cost functions, even when they do not know what the cost function is.
  The objective is to minimize the storage footprint, that is, the largest
memory address containing an allocated object, while simultaneously minimizing
the reallocation costs. This paper gives asymptotically optimal algorithms for
storage reallocation, in which the storage footprint is at most (1+epsilon)
times optimal, and the reallocation cost is at most (1/epsilon) times the
original allocation cost, which is also optimal. The algorithms are cost
oblivious as long as the allocation/reallocation cost function is subadditive.",1404.2019v3
2014-04-14,Magneto-photonic phenomena at terahertz frequencies,"Magneto-terahertz phenomena are the main focus of the thesis. This work
started as supporting research for the science of an X-ray laser (SwissFEL).
X-ray lasers have recently drawn great attention as an unprecedented tool for
scientific research on the ultrafast scale..... To answer this fundamental
question, we performed original numerical simulations using a coupled Landau-
Lifshitz-Gilbert Maxwell model. ... Those requirements were the motivations for
the experiments performed in the second part of the thesis. To shape the
terahertz pulses, .... Regarding the field intensities, we followed two
approaches. The first deals with field enhancement in nanoslits arrays. We
designed a subwavelength structure characterized by simultaneous high field
enhancement and high transmission at terahertz frequencies to suit nonlinear
sources. The second approach depended on up-scaling the generation from
laser-induced plasma by increasing the pump wavelengths. Numerical calculations
have also brought to our attention the importance of linear magnetoterahertz
effects. In particular, the simulations showed that the ultrafast dynamics
could lead to significant rotation of the polarization plane of the triggering
terahertz pulse. Motivated by this finding, we focused in the last part of the
thesis on the linear effects. We performed three original studies coming out
with first demonstrations of broadband non-reciprocal terahertz phase
retarders, terahertz magnetic modulators, and the non-reciprocal terahertz
isolators. In the first two experiments, we extended the unique properties of
the magnetic liquids (Ferrofluids) to the terahertz regime. In the latter
experiment, we used a permanent magnet (Ferrite) to experimentally show
complete isolation (unidirectional transmission) of the terahertz waves.",1404.3764v1
2014-05-13,The Star Formation Histories of Local Group Dwarf Galaxies II. Searching For Signatures of Reionization,"We search for signatures of reionization in the star formation histories
(SFHs) of 38 Local Group dwarf galaxies (10$^4$ $<$ M$_{\star}$ $<$ 10$^9$
M$_{\odot}$). The SFHs are derived from color-magnitude diagrams using archival
Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five
quenched galaxies (And V, And VI, And XIII, Leo IV, Hercules) are consistent
with forming the bulk of their stars before reionization, when full
uncertainties are considered. Observations of 13 of the predicted `true
fossils' identified by Bovill & Ricotti show that only two (Hercules and Leo
IV) indicate star formation quenched by reionization. However, both are within
the virial radius of the Milky Way and evidence of tidal disturbance
complicates this interpretation. We argue that the late-time gas capture
scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil
candidate Leo T is observationally indistinguishable from simple gas retention.
Given the ambiguity between environmental effects and reionization, the best
reionization fossil candidates are quenched low mass field galaxies (e.g., KKR
25).",1405.3281v1
2014-05-26,Constraints for the Progenitor Masses of 17 Historic Core-Collapse Supernovae,"Using resolved stellar photometry measured from archival HST imaging, we
generate color-magnitude diagrams of the stars within 50 pc of the locations of
historic core-collapse supernovae that took place in galaxies within 8 Mpc. We
fit these color-magnitude distributions with stellar evolution models to
determine the best-fit age distribution of the young population. We then
translate these age distributions into probability distributions for the
progenitor mass of each SNe. The measurements are anchored by the main-sequence
stars surrounding the event, making them less sensitive to assumptions about
binarity, post-main-sequence evolution, or circumstellar dust. We demonstrate
that, in cases where the literature contains masses that have been measured
from direct imaging, our measurements are consistent with (but less precise
than) these measurements. Using this technique, we constrain the progenitor
masses of 17 historic SNe, 11 of which have no previous estimates from direct
imaging. Our measurements still allow the possibility that all SNe progenitor
masses are <20 M_sun. However, the large uncertainties for the highest-mass
progenitors also allow the possibility of no upper-mass cutoff.",1405.6626v1
2014-06-09,"Calibrating CHIME, A New Radio Interferometer to Probe Dark Energy","The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit
interferometer currently being built at the Dominion Radio Astrophysical
Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral
hydrogen in the frequency range 400 -- 800\,MHz over half of the sky, producing
a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 --
2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that
will yield constraints on the BAO power spectrum and provide a test-bed for our
calibration scheme. I will discuss the CHIME calibration requirements and
describe instrumentation we are developing to meet these requirements.",1406.2267v1
2014-07-10,Beating the Heat! Automated Characterization of Piezoelectric Tubes for Starbugs,"The Australian Astronomical Observatory has extensively prototyped a new
robotic positioner to allow simultaneous positioning of optical fibers at the
focal plane called 'Starbugs'. The Starbug devices each consist of two
concentric piezoelectric tubes that 'walk' the optical fiber over the focal
plane to accuracy of several microns. Ongoing research has led to the
development of several Starbug prototypes, but lack of performance data has
hampered further progress in the design of the Starbug positioners and the
support equipment required to power and control them. Furthermore, Starbugs
have been selected for the TAIPAN instrument, a prototype for MANIFEST on the
GMT. A need now arises to measure and characterize 100's of piezoelectric tubes
before full scale production of Starbugs for TAIPAN. The manual measurements of
these piezoelectric tubes are a time consuming process taking several hours.
Therefore, a versatile automated system is needed to measure and characterize
these tubes in the laboratory before production of Starbugs. We have solved
this problem with the design of an automated LabVIEW application that
significantly reduces test times to several minutes. We present the various
design aspects of the automation system and provide analyses of example
piezoelectric tubes for Starbugs.",1407.2681v1
2014-07-16,TriAnd and its Siblings: Satellites of Satellites in the Milky Way Halo,"We explore the Triangulum-Andromeda (TriAnd) overdensity in the SPLASH
(Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo) and SEGUE
(the Sloan Extension for Galactic Understanding and Exploration) spectroscopic
surveys. Milky Way main sequence turn-off stars in the SPLASH survey reveal
that the TriAnd overdensity and the recently discovered PAndAS stream (Martin
et al. 2014) share a common heliocentric distance (D ~ 20 kpc), position on the
sky, and line-of-sight velocity (V_GSR ~ 50 km/s). Similarly, A-type, giant,
and main sequence turn-off stars selected from the SEGUE survey in the vicinity
of the Segue 2 satellite show that TriAnd is prevalent in these fields, with a
velocity and distance similar to Segue 2. The coincidence of the PAndAS stream
and Segue 2 satellite in positional and velocity space to TriAnd suggests that
these substructures are all associated, and may be a fossil record of
group-infall onto the Milky Way halo. In this scenario, the Segue 2 satellite
and PAndAS stream are ""satellites of satellites"", and the large, metal-rich
TriAnd overdensity is the remains of the group central.",1407.4458v2
2014-07-17,The Green's Function for the Hückel (Tight Binding) Model,"Applications of the H\""uckel (tight binding) model are ubiquitous in quantum
chemistry and solid state physics. The matrix representation of this model is
isomorphic to an unoriented vertex adjacency matrix of a bipartite graph, which
is also the Laplacian matrix plus twice the identity. In this paper, we
analytically calculate the determinant and, when it exists, the inverse of this
matrix in connection with the Green's function, $\mathbf{G}$, of the $N\times
N$ H\""uckel matrix. A corollary is a closed form expression for a Harmonic sum
(Eq. 12). We then extend the results to $d-$dimensional lattices, whose linear
size is $N$. The existence of the inverse becomes a question of number theory.
We prove a new theorem in number theory pertaining to vanishing sums of cosines
and use it to prove that the inverse exists if and only if $N+1$ and $d$ are
odd and $d$ is smaller than the smallest divisor of $N+1$. We corroborate our
results by demonstrating the entry patterns of the Green's function and discuss
applications related to transport and conductivity.",1407.4780v4
2014-07-29,Formation of magnetic skyrmions with tunable properties in PdFe bilayer deposited on Ir(111),"We perform an extensive study of the spin-configurations in a PdFe bilayer on
Ir(111) in terms of ab initio and spin-model calculations. We use the
spin-cluster expansion technique to obtain spin model parameters, and solve the
Landau-Lifshitz-Gilbert equations at zero temperature. In particular, we focus
on effects of layer relaxations and the evolution of the magnetic ground state
in external magnetic field. In the absence of magnetic field, we find a
spin-spiral ground state, while applying external magnetic field skyrmions are
generated in the system. Based on energy calculations of frozen spin
configurations with varying magnetic field we obtain excellent agreement for
the phase boundaries with available experiments. We find that the wave length
of spin-spirals and the diameter of skyrmions decrease with increasing inward
Fe layer relaxation which is correlated with the increasing ratio of the
nearest-neighbor Dzyaloshinskii-Moriya interaction and the isotropic exchange
coupling, $D/J$. Our results also indicate that the applied field needed to
stabilize the skyrmion lattice increases when the diameter of individual
skyrmions decreases. Based on our observations, we suggest that the formation
of the skyrmion lattice can be tuned by small structural modification of the
thin film.",1407.7718v2
2014-08-14,"Developing Structural, High-heat flux and Plasma Facing Materials for a near-term DEMO Fusion Power Plant: the EU Assessment","The findings of the EU 'Materials Assessment Group' (MAG), within the 2012 EU
Fusion Roadmap exercise, are discussed. MAG analysed the technological
readiness of structural, plasma facing and high heat flux materials for a DEMO
concept to be constructed in the early 2030s, proposing a coherent strategy for
R&D up to a DEMO construction decision. Technical consequences for the
materials required and the development, testing and modelling programmes, are
analysed using: a systems engineering approach, considering reactor operational
cycles, efficient maintenance and inspection requirements, and interaction with
functional materials/coolants; and a project-based risk analysis, with R&D to
mitigate risks from material shortcomings including development of specific
risk mitigation materials.",1408.3546v1
2014-08-26,"Weedy adaptation in Setaria spp.: IX. Effects of salinity, temperature, light and seed dormancy on Setaria faberi seed germination","Life in salty habitats is a function of tolerance to those chemicals at all
critical phases of a plant's life history. The ability to withstand salt as an
established plant may require different mechanisms and plant traits than those
needed to germinate in salty soils. Seeds establishing themselves in high salt
content may respond differently depending on the light conditions and seed
germinability at the time of salty water imbibition. S. faberi seed (and S.
viridis and S. pumila) plants were discovered thriving along the seacoasts of
Southern Japan. These plants possess the ability to after-ripen, germinate,
emerge and establish themselves, grow and reproduce in the salty soils and
salt-laden atmospheres present in these windy habitats. The objectives of this
paper are to determine the effect of salt (NaCl) in water imbibed by S. faberi
seed during after-ripening and germination, as well temperature and light.
Observations made also provide insights on the possible relationship between
salt and drought tolerance. Seed germination of all phenotypes inhibited by two
percent or more of NaCl. The effects of lesser amounts of NaCl on each of the
three phenotypes was highly dependent on the specific temperature and light
conditions. The three test phenotypes provided a good range to detect responses
to salinity, allowing the observation of both stimulatory and inhibitory
responses.",1408.6187v1
2014-09-02,Accessing Different Spin-Disordered States using First Order Reversal Curves,"Combined first order reversal curve (FORC) analyses of the magnetization
(M-FORC) and magnetoresistance (MR-FORC) have been employed to provide a
comprehensive study of the M-MR correlation in two canonical systems: a
NiFe/Cu/FePt pseudo spin-valve (PSV) and a [Co/Cu]8 multilayer. In the PSV, due
to the large difference in switching fields and minimal interactions between
the NiFe and FePt layers, the M and MR show a simple one-to-one relationship
during reversal. In the [Co/Cu]8 multilayer, the correlation between the
magnetization reversal and MR evolution is more complex. This is primarily due
to the similar switching fields of, and interactions between, the constituent
Co layers. The FORC protocol accesses states with much higher spin disorders
and larger MR than those found along the conventional major loop field-cycle.
Unlike the M-FORC measurements, which only probe changes in the macroscopic
magnetization, the MR-FORCs are more sensitive to the microscopic domain
configurations, as those are most important in determining the resultant MR
effect size. This approach is generally applicable to spintronic systems to
realize the maximum spin-disorder and the largest MR.",1409.0825v1
2014-10-20,Momentum space imaging of Cooper pairing in a half-Dirac-gas topological superconductor (a helical 2D topological superconductor),"Superconductivity in Dirac electrons has recently been proposed as a new
platform between novel concepts in high-energy and condensed matter physics. It
has been proposed that supersymmetry and exotic quasiparticles, both of which
remain elusive in particle physics, may be realized as emergent particles in
superconducting Dirac electron systems. Using artificially fabricated
topological insulator-superconductor heterostructures, we present direct
spectroscopic evidence for the existence of Cooper pairing in a half Dirac gas
2D topological superconductor. Our studies reveal that superconductivity in a
helical Dirac gas is distinctly different from that of in an ordinary
two-dimensional superconductor while considering the spin degrees of freedom of
electrons. We further show that the pairing of Dirac electrons can be
suppressed by time-reversal symmetry breaking impurities removing the
distinction. Our demonstration and momentum-space imaging of Cooper pairing in
a half Dirac gas and its magnetic behavior taken together serve as a critically
important 2D topological superconductor platform for future testing of novel
fundamental physics predictions such as emergent supersymmetry and quantum
criticality in topological systems.",1410.5405v1
2014-12-23,Dynamical symmetries of Markov processes with multiplicative white noise,"We analyse various properties of stochastic Markov processes with
multiplicative white noise. We take a single-variable problem as a simple
example, and we later extend the analysis to the Landau-Lifshitz-Gilbert
equation for the stochastic dynamics of a magnetic moment. In particular, we
focus on the non-equilibrium transfer of angular momentum to the magnetization
from a spin-polarised current of electrons, a technique which is widely used in
the context of spintronics to manipulate magnetic moments. We unveil two hidden
dynamical symmetries of the generating functionals of these Markovian
multiplicative white-noise processes. One symmetry only holds in equilibrium
and we use it to prove generic relations such as the fluctuation-dissipation
theorems. Out of equilibrium, we take profit of the symmetry-breaking terms to
prove fluctuation theorems. The other symmetry yields strong dynamical
relations between correlation and response functions which can notably simplify
the numerical analysis of these problems. Our construction allows us to clarify
some misconceptions on multiplicative white-noise stochastic processes that can
be found in the literature. In particular, we show that a first-order
differential equation with multiplicative white noise can be transformed into
an additive-noise equation, but that the latter keeps a non-trivial memory of
the discretisation prescription used to define the former.",1412.7564v2
2015-01-09,Random Triangle Theory with Geometry and Applications,"What is the probability that a random triangle is acute? We explore this old
question from a modern viewpoint, taking into account linear algebra, shape
theory, numerical analysis, random matrix theory, the Hopf fibration, and much
much more. One of the best distributions of random triangles takes all six
vertex coordinates as independent standard Gaussians. Six can be reduced to
four by translation of the center to $(0,0)$ or reformulation as a 2x2 matrix
problem.
  In this note, we develop shape theory in its historical context for a wide
audience. We hope to encourage other to look again (and differently) at
triangles.
  We provide a new constructive proof, using the geometry of parallelians, of a
central result of shape theory: Triangle shapes naturally fall on a hemisphere.
We give several proofs of the key random result: that triangles are uniformly
distributed when the normal distribution is transferred to the hemisphere. A
new proof connects to the distribution of random condition numbers.
Generalizing to higher dimensions, we obtain the ""square root ellipticity
statistic"" of random matrix theory.
  Another proof connects the Hopf map to the SVD of 2 by 2 matrices. A new
theorem describes three similar triangles hidden in the hemisphere. Many
triangle properties are reformulated as matrix theorems, providing insight to
both. This paper argues for a shift of viewpoint to the modern approaches of
random matrix theory. As one example, we propose that the smallest singular
value is an effective test for uniformity. New software is developed and
applications are proposed.",1501.03053v1
2015-02-03,The use of covariates and random effects in evaluating predictive biomarkers under a potential outcome framework,"Predictive or treatment selection biomarkers are usually evaluated in a
subgroup or regression analysis with focus on the treatment-by-marker
interaction. Under a potential outcome framework (Huang, Gilbert and Janes
[Biometrics 68 (2012) 687-696]), a predictive biomarker is considered a
predictor for a desirable treatment benefit (defined by comparing potential
outcomes for different treatments) and evaluated using familiar concepts in
prediction and classification. However, the desired treatment benefit is
unobservable because each patient can receive only one treatment in a typical
study. Huang et al. overcome this problem by assuming monotonicity of potential
outcomes, with one treatment dominating the other in all patients. Motivated by
an HIV example that appears to violate the monotonicity assumption, we propose
a different approach based on covariates and random effects for evaluating
predictive biomarkers under the potential outcome framework. Under the proposed
approach, the parameters of interest can be identified by assuming conditional
independence of potential outcomes given observed covariates, and a sensitivity
analysis can be performed by incorporating an unobserved random effect that
accounts for any residual dependence. Application of this approach to the
motivating example shows that baseline viral load and CD4 cell count are both
useful as predictive biomarkers for choosing antiretroviral drugs for
treatment-naive patients.",1502.00757v1
2015-02-03,The Blackhole-Dark Matter Halo Connection,"We explore the connection between the central supermassive blackholes (SMBH)
in galaxies and the dark matter halo through the relation between the masses of
the SMBHs and the maximum circular velocities of the host galaxies, as well as
the relationship between stellar velocity dispersion of the spheroidal
component and the circular velocity. Our assumption here is that the circular
velocity is a proxy for the mass of the dark matter halo. We rely on a
heterogeneous sample containing galaxies of all types. The only requirement is
that the galaxy has a direct measurement of the mass of its SMBH and a direct
measurement of its circular velocity and its velocity dispersion. Previous
studies have analyzed the connection between the SMBH and dark matter halo
through the relationship between the circular velocity and the bulge velocity
dispersion, with the assumption that the bulge velocity dispersion stands in
for the mass of the SMBH, via the well{}-established SMBH mass{}-bulge velocity
dispersion relation. Using intermediate relations may be misleading when one is
studying them to decipher the active ingredients of galaxy formation and
evolution. We believe that our approach will provide a more direct probe of the
SMBH and the dark matter halo connection. We find that the correlation between
the mass of supermassive blackholes and the circular velocities of the host
galaxies is extremely weak, leading us to state the dark matter halo may not
play a major role in regulating the blackhole growth in the present Universe.",1502.00775v1
2015-03-01,Computing in continuous space with self-assembling polygonal tiles,"In this paper we investigate the computational power of the polygonal tile
assembly model (polygonal TAM) at temperature 1, i.e. in non-cooperative
systems. The polygonal TAM is an extension of Winfree's abstract tile assembly
model (aTAM) which not only allows for square tiles (as in the aTAM) but also
allows for tile shapes that are polygons. Although a number of self-assembly
results have shown computational universality at temperature 1, these are the
first results to do so by fundamentally relying on tile placements in
continuous, rather than discrete, space. With the square tiles of the aTAM, it
is conjectured that the class of temperature 1 systems is not computationally
universal. Here we show that the class of systems whose tiles are composed of a
regular polygon P with n > 6 sides is computationally universal. On the other
hand, we show that the class of systems whose tiles consist of a regular
polygon P with n <= 6 cannot compute using any known techniques. In addition,
we show a number of classes of systems whose tiles consist of a non-regular
polygon with n >= 3 sides are computationally universal.",1503.00327v2
2015-03-05,Nonparametric Bounds and Sensitivity Analysis of Treatment Effects,"This paper considers conducting inference about the effect of a treatment (or
exposure) on an outcome of interest. In the ideal setting where treatment is
assigned randomly, under certain assumptions the treatment effect is
identifiable from the observable data and inference is straightforward.
However, in other settings such as observational studies or randomized trials
with noncompliance, the treatment effect is no longer identifiable without
relying on untestable assumptions. Nonetheless, the observable data often do
provide some information about the effect of treatment, that is, the parameter
of interest is partially identifiable. Two approaches are often employed in
this setting: (i) bounds are derived for the treatment effect under minimal
assumptions, or (ii) additional untestable assumptions are invoked that render
the treatment effect identifiable and then sensitivity analysis is conducted to
assess how inference about the treatment effect changes as the untestable
assumptions are varied. Approaches (i) and (ii) are considered in various
settings, including assessing principal strata effects, direct and indirect
effects and effects of time-varying exposures. Methods for drawing formal
inference about partially identified parameters are also discussed.",1503.01598v1
2015-03-16,Dynamics of Current and Field Driven Domain Wall Motion under the Influence of Transverse Magnetic Field,"The dynamics of transverse Neel domain wall in a ferromagnetic nanostrip in
the presence of driving field, current and transverse magnetic field is
investigated by the Landau-Lifshitz-Gilbert(LLG) equation with the adiabatic
and non-adiabatic spin-transfer torques both analytically and numerically. The
analytical expressions for the velocity, width, excitation angle and
displacement for the domain wall are obtained by using small angle
approximation along with Walkers trial function. The results show that the
initial velocity of the domain wall can be controlled by the adiabatic
spin-transfer torque and the saturated velocity can be controlled by the
non-adiabatic spin-transfer torque and driving field. The large increase in the
saturated velocity of the domain wall driven by current and field due to the
transverse magnetic field is identified through the presence of driving field.
There is no impact in the saturated velocity of the domain wall driven by
current from the transverse magnetic field. For the domain wall driven by the
current in the presence of the transverse magnetic field, the saturated
velocity remains constant. The transverse magnetic field along with current and
driving field is more advantageous that the transverse magnetic field along
with current for increasing the saturated velocity of the domain wall. The
numerical results showed that the saturated velocity is increased by the
transverse magnetic field with the irrespective of the directions of the
driving field and current further it is higher and lower when the directions of
driving field and current are antiparallel and parallel respectively. The
obtained analytical solutions are closely coincided with the computed numerical
results.",1503.04560v2
2015-03-17,Single Hit Energy-resolved Laue Diffraction,"In-situ white light Laue diffraction has been successfully used to
interrogate the structure of single crystal materials undergoing rapid
(nanosecond) dynamic compression up to megabar pressures. However, information
on strain state accessible via this technique is limited, reducing its
applicability for a range of applications. We present an extension to the
existing Laue diffraction platform in which we record the photon energy of a
subset of diffraction peaks. This allows for a measurement of the longitudinal
and transverse strains in-situ during compression. Consequently, we demonstrate
measurement of volumetric compression of the unit cell, in addition to the
limited aspect ratio information accessible in conventional white light Laue.
We present preliminary results for silicon, where only an elastic strain is
observed. VISAR measurements show the presence of a two wave structure and
measurements show that material downstream of the second wave does not
contribute to the observed diffraction peaks, supporting the idea that this
material may be highly disordered, or has undergone large scale rotation.",1503.05131v2
2015-03-24,No variations in transit times for Qatar-1 b,"The transiting hot Jupiter planet Qatar-1 b was presented to exhibit
variations in transit times that could be of perturbative nature. A hot Jupiter
with a planetary companion on a nearby orbit would constitute an unprecedented
planetary configuration, important for theories of formation and evolution of
planetary systems. We performed a photometric follow-up campaign to confirm or
refute transit timing variations. We extend the baseline of transit
observations by acquiring 18 new transit light curves acquired with 0.6-2.0 m
telescopes. These photometric time series, together with data available in the
literature, were analyzed in a homogenous way to derive reliable transit
parameters and their uncertainties. We show that the dataset of transit times
is consistent with a linear ephemeris leaving no hint for any periodic
variations with a range of 1 min. We find no compelling evidence for the
existence of a close-in planetary companion to Qatar-1 b. This finding is in
line with a paradigm that hot Jupiters are not components of compact
multi-planetary systems. Based on dynamical simulations, we place tighter
constraints on a mass of any fictitious nearby planet in the system.
Furthermore, new transit light curves allowed us to redetermine system
parameters with the precision better than that reported in previous studies.
Our values generally agree with previous determinations.",1503.07191v1
2015-03-25,Rigorous numerical study of strong microwave photon-magnon coupling in all-dielectric magnetic multilayers,"We demonstrate theoretically a strong local enhancement of the intensity of
the in-plane microwave magnetic field in multilayered structures made from a
magneto-insulating yttrium iron garnet (YIG) layer sandwiched between two
non-magnetic layers with a high dielectric constant matching that of YIG. The
enhancement is predicted for the excitation regime when the microwave magnetic
field is induced inside the multilayer by the transducer of a stripline
Broadband Ferromagnetic Resonance (BFMR) setup. By means of a rigorous
numerical solution of the Landau-Lifshitz-Gilbert equation consistently with
the Maxwell's equations, we investigate the magnetisation dynamics in the
multilayer. We reveal a strong photon-magnon coupling, which manifests itself
as anti-crossing of the ferromagnetic resonance (FMR) magnon mode supported by
the YIG layer and the electromagnetic resonance mode supported by the whole
multilayered structure. The frequency of the magnon mode depends on the
external static magnetic field, which in our case is applied tangentially to
the multilayer in the direction perpendicular to the microwave magnetic field
induced by the stripline of the BFMR setup. The frequency of the
electromagnetic mode is independent of the static magnetic field. Consequently,
the predicted photon-magnon coupling is sensitive to the applied magnetic field
and thus can be used in magnetically tuneable metamaterials based on
simultaneously negative permittivity and permeability achievable thanks to the
YIG layer. We also suggest that the predicted photon-magnon coupling may find
applications in microwave quantum information systems.",1503.07282v1
2015-04-22,Thermally Driven Ratchet Motion of Skyrmion Microcrystal and Topological Magnon Hall Effect,"Spontaneously emergent chirality is an issue of fundamental importance across
the natural sciences. It has been argued that a unidirectional (chiral)
rotation of a mechanical ratchet is forbidden in thermal equilibrium, but
becomes possible in systems out of equilibrium. Here we report our finding that
a topologically nontrivial spin texture known as a skyrmion - a particle-like
object in which spins point in all directions to wrap a sphere - constitutes
such a ratchet. By means of Lorentz transmission electron microscopy we show
that micron-sized crystals of skyrmions in thin films of Cu2OSeO3 and MnSi
display a unidirectional rotation motion. Our numerical simulations based on a
stochastic Landau-Lifshitz-Gilbert equation suggest that this rotation is
driven solely by thermal fluctuations in the presence of a temperature
gradient, whereas in thermal equilibrium it is forbidden by the Bohr-van
Leeuwen theorem. We show that the rotational flow of magnons driven by the
effective magnetic field of skyrmions gives rise to the skyrmion rotation,
therefore suggesting that magnons can be used to control the motion of these
spin textures.",1504.05860v1
2015-05-05,Evaluating the Potential of a Dual Randomized Kaczmarz Solver for Laplacian Linear Systems,"A new method for solving Laplacian linear systems proposed by Kelner et al.
involves the random sampling and update of fundamental cycles in a graph.
Kelner et al. proved asymptotic bounds on the complexity of this method but did
not report experimental results. We seek to both evaluate the performance of
this approach and to explore improvements to it in practice. We compare the
performance of this method to other Laplacian solvers on a variety of real
world graphs. We consider different ways to improve the performance of this
method by exploring different ways of choosing the set of cycles and the
sequence of updates, with the goal of providing more flexibility and potential
parallelism. We propose a parallel model of the Kelner et al. method, for
evaluating potential parallelism in terms of the span of edges updated at each
iteration. We provide experimental results comparing the potential parallelism
of the fundamental cycle basis and our extended cycle set. Our preliminary
experiments show that choosing a non-fundamental set of cycles can save
significant work compared to a fundamental cycle basis.",1505.00875v3
2015-06-18,Area-Delay-Energy Tradeoffs of Strain-Mediated Multiferroic Devices,"Multiferroic devices hold profound promise for ultra-low energy computing in
beyond Moore's law era. The magnetization of a magnetostrictive
shape-anisotropic single-domain nanomagnet strain-coupled with a piezoelectric
layer in a multiferroic composite structure can be switched between its two
stable states (separated by an energy barrier) with a tiny amount of voltage
via converse magnetoelectric effect. With appropriate choice of materials, the
magnetization can be switched with a few tens of millivolts of voltages in
sub-nanosecond switching delay while spending a miniscule amount of energy of
~1 attojoule at room-temperature. Here, we analyze the area-delay-energy
trade-offs of these multiferroic devices by solving stochastic
Landau-Lifshitz-Gilbert equation in the presence of room-temperature thermal
fluctuations. We particularly put attention on scaling down the lateral area of
the magnetostrictive nanomagnet that can increase the device density on a chip.
We show that the vertical thickness of the nanomagnet can be increased while
scaling down the lateral area and keeping the assumption of single-domain limit
valid. This has important consequence since it helps to some extent preventing
the deterioration of the induced stress-anisotropy energy in the
magnetostrictive nanomagnet, which is proportional to the nanomagnet's volume.
The results show that if we scale down the lateral area, the switching delay
increases while energy dissipation decreases. Avenues available to decrease the
switching delay while still reducing the energy dissipation are discussed.",1506.07859v1
2015-07-30,Confirmation of the Planetary Microlensing Signal and Star and Planet Mass Determinations for Event OGLE-2005-BLG-169,"We present Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3)
observations of the source and lens stars for planetary microlensing event
OGLE-2005-BLG-169, which confirm the relative proper motion prediction due to
the planetary light curve signal observed for this event. This (and the
companion Keck result) provide the first confirmation of a planetary
microlensing signal, for which the deviation was only 2%. The follow-up
observations determine the flux of the planetary host star in multiple
passbands and remove light curve model ambiguity caused by sparse sampling of
part of the light curve. This leads to a precise determination of the
properties of the OGLE-2005-BLG-169Lb planetary system. Combining the
constraints from the microlensing light curve with the photometry and
astrometry of the HST/WFC3 data, we find star and planet masses of M_* = 0.69+-
0.02 M_solar and m_p = 14.1 +- 0.9 M_earth. The planetary microlens system is
located toward the Galactic bulge at a distance of D_L = 4.1 +- 0.4 kpc, and
the projected star-planet separation is a_perp = 3.5 +- 0.3 AU, corresponding
to a semi-major axis of a = 4.0 (+2.2 -0.6) AU.",1507.08661v1
2015-08-19,Variations in solar wind fractionation as seen by ACE/SWICS over a solar cycle and the implications for Genesis Mission results,"We use ACE/SWICS elemental composition data to compare the variations in
solar wind fractionation as measured by SWICS during the last solar maximum
(1999-2001), the solar minimum (2006-2009) and the period in which the Genesis
spacecraft was collecting solar wind (late 2001 - early 2004). We differentiate
our analysis in terms of solar wind regimes (i.e. originating from interstream
or coronal hole flows, or coronal mass ejecta). Abundances are normalized to
the low-FIP ion magnesium to uncover correlations that are not apparent when
normalizing to high-FIP ions. We find that relative to magnesium, the other
low-FIP elements are measurably fractionated, but the degree of fractionation
does not vary significantly over the solar cycle. For the high-FIP ions,
variation in fractionation over the solar cycle is significant: greatest for
Ne/Mg and C/Mg, less so for O/Mg, and the least for He/Mg. When abundance
ratios are examined as a function of solar wind speed, we find a strong
correlation, with the remarkable observation that the degree of fractionation
follows a mass-dependent trend. We discuss the implications for correcting the
Genesis sample return results to photospheric abundances.",1508.04566v1
2015-08-28,Cosmic variance in the nanohertz gravitational wave background,"We use large N-body simulations and empirical scaling relations between dark
matter halos, galaxies, and supermassive black holes to estimate the formation
rates of supermassive black hole binaries and the resulting low-frequency
stochastic gravitational wave background (GWB). We find this GWB to be
relatively insensitive ($\lesssim10\%$) to cosmological parameters, with only
slight variation between WMAP5 and Planck cosmologies. We find that uncertainty
in the astrophysical scaling relations changes the amplitude of the GWB by a
factor of $\sim 2$. Current observational limits are already constraining this
predicted range of models. We investigate the Poisson variance in the amplitude
of the GWB for randomly-generated populations of supermassive black holes,
finding a scatter of order unity per frequency bin below 10 nHz, and increasing
to a factor of $\sim 10$ near 100 nHz. This variance is a result of the rarity
of the most massive binaries, which dominate the signal, and acts as a
fundamental uncertainty on the amplitude of the underlying power law spectrum.
This Poisson uncertainty dominates at $\gtrsim 20$ nHz, while at lower
frequencies the dominant uncertainty is related to our poor understanding of
the astrophysical scaling relations, although very low frequencies may be
dominated by uncertainties related to the final parsec problem and the
processes which drive binaries to the gravitational wave dominated regime.
Cosmological effects are negligible at all frequencies.",1508.07336v2
2015-09-01,Magnon-driven longitudinal spin Seebeck effect in F|N and N|F|N structures: role of asymmetric in-plane magnetic anisotropy,"The influence of an asymmetric in-plane magnetic anisotropy on the thermally
activated spin current is studied theoretically for two different systems; (i)
the system consisting of a ferromagnetic insulator in a direct contact with a
nonmagnetic metal, and the sandwich structure consisting of a ferromagnetic
insulating part sandwiched between two nonmagnetic metals. It is shown that
when the difference between the temperatures of the two nonmagnetic metals in a
structure is not large, the spin pumping currents from the magnetic part to the
nonmagnetic ones are equal in amplitude and have opposite directions, so only
the spin torque current contributes to the total spin current. The spin current
flows then from the nonmagnetic metal with the higher temperature to the
nonmagnetic metal having a lower temperature. Its amplitude varies linearly
with the difference in temperatures. In addition, we have found that if the
magnetic anisotropy is in the layer plane, then the spin current increases with
the magnon temperature, while in the case of an out-of-plane magnetic
anisotropy the spin current decreases when the magnon temperature enhances.
Enlarging the difference between the temperatures of the nonmagnetic metals,
the linear response becomes important, as confirmed by analytical expressions
inferred from the Fokker-Planck approach and by the results obtained upon a
full numerical integration of the stochastic Landau-Lifshitz-Gilbert equation.",1509.00376v1
2015-09-08,Stellar Dynamics around a Massive Black Hole II: Resonant Relaxation,"We present a first-principles theory of Resonant Relaxation (RR) of a low
mass stellar system orbiting a more massive black hole (MBH). We first extend
the kinetic theory of Gilbert (1968) to include the Keplerian field of a black
hole of mass $M_\bullet$. Specializing to a Keplerian stellar system of mass $M
\ll M_\bullet$, we use the orbit-averaging method of Sridhar & Touma (2015;
Paper I) to derive a kinetic equation for RR. This describes the collisional
evolution of a system of $N \gg 1$ Gaussian Rings in a reduced 5-dim space,
under the combined actions of self-gravity, 1 PN and 1.5 PN relativistic
effects of the MBH and an arbitrary external potential. In general geometries
RR is driven by both apsidal and nodal resonances, so the distinction between
scalar-RR and vector-RR disappears. The system passes through a sequence of
quasi-steady secular collisionless equilibria, driven by irreversible 2-Ring
correlations that accrue through gravitational interactions, both direct and
collective. This correlation function is related to a `wake function', which is
the linear response of the system to the perturbation of a chosen Ring. The
wake function is easier to appreciate, and satisfies a simpler equation, than
the correlation function. We discuss general implications for the interplay of
secular dynamics and non-equilibrium statistical mechanics in the evolution of
Keplerian stellar systems toward secular thermodynamic equilibria, and set the
stage for applications to the RR of axisymmetric discs in Paper III.",1509.02401v2
2015-10-11,End-to-End Error-Correcting Codes on Networks with Worst-Case Symbol Errors,"The problem of coding for networks experiencing worst-case symbol errors is
considered. We argue that this is a reasonable model for highly dynamic
wireless network transmissions. We demonstrate that in this setup prior network
error-correcting schemes can be arbitrarily far from achieving the optimal
network throughput. A new transform metric for errors under the considered
model is proposed. Using this metric, we replicate many of the classical
results from coding theory. Specifically, we prove new Hamming-type,
Plotkin-type, and Elias-Bassalygo-type upper bounds on the network capacity. A
commensurate lower bound is shown based on Gilbert-Varshamov-type codes for
error-correction. The GV codes used to attain the lower bound can be
non-coherent, that is, they do not require prior knowledge of the network
topology. We also propose a computationally-efficient concatenation scheme. The
rate achieved by our concatenated codes is characterized by a Zyablov-type
lower bound. We provide a generalized minimum-distance decoding algorithm which
decodes up to half the minimum distance of the concatenated codes. The
end-to-end nature of our design enables our codes to be overlaid on the
classical distributed random linear network codes [1]. Furthermore, the
potentially intensive computation at internal nodes for the link-by-link
error-correction is un-necessary based on our design.",1510.03060v1
2015-10-12,Analysis of laser shock experiments on precompressed samples using a quartz reference and application to warm dense hydrogen and helium,"Megabar (1 Mbar = 100 GPa) laser shocks on precompressed samples allow
reaching unprecedented high densities and moderately high 10000-100000K
temperatures. We describe here a complete analysis framework for the
velocimetry (VISAR) and pyrometry (SOP) data produced in these experiments.
Since the precompression increases the initial density of both the sample of
interest and the quartz reference for pressure-density, reflectivity and
temperature measurements, we describe analytical corrections based on available
experimental data on warm dense silica and density-functional-theory based
molecular dynamics computer simulations. Using our improved analysis framework
we report a re-analysis of previously published data on warm dense hydrogen and
helium, compare the newly inferred pressure, density and temperature data with
most advanced equation of state models and provide updated reflectivity values.",1510.03301v1
2015-11-09,Simulations of the Pairwise Kinematic Sunyaev-Zel'dovich Signal,"The pairwise kinematic Sunyaev-Zel'dovich (kSZ) signal from galaxy clusters
is a probe of their line-of-sight momenta, and thus a potentially valuable
source of cosmological information. In addition to the momenta, the amplitude
of the measured signal depends on the properties of the intra-cluster gas and
observational limitations such as errors in determining cluster centers and
redshifts. In this work we simulate the pairwise kSZ signal of clusters at z<1,
using the output from a cosmological N-body simulation and including the
properties of the intra-cluster gas via a model that can be varied in
post-processing. We find that modifications to the gas profile due to star
formation and feedback reduce the pairwise kSZ amplitude of clusters by ~50%,
relative to the naive 'gas traces mass' assumption. We demonstrate that
mis-centering can reduce the overall amplitude of the pairwise kSZ signal by up
to 10%, while redshift errors can lead to an almost complete suppression of the
signal at small separations. We confirm that a high-significance detection is
expected from the combination of data from current-generation, high-resolution
CMB experiments, such as the South Pole Telescope, and cluster samples from
optical photometric surveys, such as the Dark Energy Survey. Furthermore, we
forecast that future experiments such as Advanced ACTPol in conjunction with
data from the Dark Energy Spectroscopic Instrument will yield detection
significances of at least 20{\sigma}, and up to 57{\sigma} in an optimistic
scenario. Our simulated maps are publicly available at:
http://www.hep.anl.gov/cosmology/ksz.html",1511.02843v2
2015-11-11,Magnetization switching by current and microwaves,"We propose a theoretical model of magnetization switching in a ferromagnetic
multilayer by both electric current and microwaves. The electric current gives
a spin transfer torque on the magnetization, while the microwaves induce a
precession of the magnetization around the initial state. Based on numerical
simulation of the Landau-Lifshitz-Gilbert (LLG) equation, it is found that the
switching current is significantly reduced compared with the switching caused
solely by the spin transfer torque when the microwave frequency is in a certain
range. We develop a theory of switching from the LLG equation averaged over a
constant energy curve. It was found that the switching current should be
classified into four regions, depending on the values of the microwave
frequency. Based on the analysis, we derive an analytical formula of the
optimized frequency minimizing the switching current, which is smaller than the
ferromagnetic resonance frequency. We also derive an analytical formula of the
minimized switching current. Both the optimized frequency and the minimized
switching current decrease with increasing the amplitude of the microwave
field. The results will be useful to achieve high thermal stability and low
switching current in spin torque systems simultaneously.",1511.03366v2
2015-11-13,"Time-domain numerical modeling of brass instruments including nonlinear wave propagation, viscothermal losses, and lips vibration","A time-domain numerical modeling of brass instruments is proposed. On one
hand, outgoing and incoming waves in the resonator are described by the
Menguy-Gilbert model, which incorporates three key issues: nonlinear wave
propagation, viscothermal losses, and a variable section. The non-linear
propagation is simulated by a TVD scheme well-suited to non-smooth waves. The
fractional derivatives induced by the viscothermal losses are replaced by a set
of local-in-time memory variables. A splitting strategy is followed to couple
optimally these dedicated methods. On the other hand, the exciter is described
by a one-mass model for the lips. The Newmark method is used to integrate the
nonlinear ordinary differential equation so-obtained. At each time step, a
coupling is performed between the pressure in the tube and the displacement of
the lips. Finally, an extensive set of validation tests is successfully
completed. In particular, self-sustained oscillations of the lips are simulated
by taking into account the nonlinear wave propagation in the tube. Simulations
clearly indicate that the nonlinear wave propagation has a major influence on
the timbre of the sound, as expected. Moreover, simulations also highlight an
influence on playing frequencies, time envelopes and on the playability of the
low frequencies in the case of a variable lips tension.",1511.04247v1
2015-11-24,Planetary Candidates from the First Year of the K2 Mission,"The Kepler Space Telescope is currently searching for planets transiting
stars along the ecliptic plane as part of its extended K2 mission. We processed
the publicly released data from the first year of K2 observations (Campaigns 0,
1, 2, and 3) and searched for periodic eclipse signals consistent with
planetary transits. Out of 59,174 targets we searched, we detect 234 planetary
candidates around 208 stars. These candidates range in size from gas giants to
smaller than the Earth, and range in orbital periods from hours to over a
month. We conducted initial reconnaissance spectroscopy of 68 of the brighter
candidate host stars, and present high resolution optical spectra for these
stars. We make all of our data products, including light curves, spectra, and
vetting diagnostics available to users online.",1511.07820v2
2015-11-25,A Search for Water in the Atmosphere of HAT-P-26b Using LDSS-3C,"The characterization of a physically-diverse set of transiting exoplanets is
an important and necessary step towards establishing the physical properties
linked to the production of obscuring clouds or hazes. It is those planets with
identifiable spectroscopic features that can most effectively enhance our
understanding of atmospheric chemistry and metallicity. The newly-commissioned
LDSS-3C instrument on Magellan provides enhanced sensitivity and suppressed
fringing in the red optical, thus advancing the search for the spectroscopic
signature of water in exoplanetary atmospheres from the ground. Using data
acquired by LDSS-3C and the Spitzer Space Telescope, we search for evidence of
water vapor in the transmission spectrum of the Neptune-mass planet HAT-P-26b.
Our measured spectrum is best explained by the presence of water vapor, a lack
of potassium, and either a high-metallicity, cloud-free atmosphere or a
solar-metallicity atmosphere with a cloud deck at ~10 mbar. The emergence of
multi-scale-height spectral features in our data suggests that future
observations at higher precision could break this degeneracy and reveal the
planet's atmospheric chemical abundances. We also update HAT-P-26b's transit
ephemeris, t_0 = 2455304.65218(25) BJD_TDB, and orbital period, p =
4.2345023(7) days.",1511.08226v2
2015-12-22,Induced voltage in an open wire,"A puzzle arising from Faraday's law is considered and solved concerning the
question which voltage is induced in an open wire with a time-varying
homogeneous magnetic field. In contrast to closed wires where the voltage is
determined by the time variance of magnetic field and enclosed area, in an open
wire we have to integrate the electric field along the wire. It is found that
the longitudinal electric field contributes with 1/3 and the transverse field
with 2/3 to the induced voltage. In order to find the electric fields the
sources of the magnetic fields are necessary to know. The representation of a
homogeneous and time-varying magnetic field implies unavoidably a certain
symmetry point or symmetry line which depend on the geometry of the source. As
a consequence the induced voltage of an open wire is found to be the area
covered with respect to this symmetry line or point perpendicular to the
magnetic field. This in turn allows to find the symmetry points of a magnetic
field source by measuring the voltage of an open wire placed with different
angles in the magnetic field. We present exactly solvable models for a symmetry
point and for a symmetry line, respectively. The results are applicable to open
circuit problems like corrosion and for astrophysical applications.",1512.07133v3
2015-12-22,Charge transport and vector meson dissociation across the thermal phase transition in lattice QCD with two light quark flavors,"We compute and analyze correlation functions in the isovector vector channel
at vanishing spatial momentum across the deconfinement phase transition in
lattice QCD. The simulations are carried out at temperatures $T/T_c=0.156, 0.8,
1.0, 1.25$ and $1.67$ with $T_c\simeq203$MeV for two flavors of Wilson-Clover
fermions with a zero-temperature pion mass of $\simeq270$MeV. Exploiting exact
sum rules and applying a phenomenologically motivated ansatz allows us to
determine the spectral function $\rho(\omega,T)$ via a fit to the lattice
correlation function data. From these results we estimate the electrical
conductivity across the deconfinement phase transition via a Kubo formula and
find evidence for the dissociation of the $\rho$ meson by resolving its
spectral weight at the available temperatures. We also apply the Backus-Gilbert
method as a model-independent approach to this problem. At any given frequency,
it yields a local weighted average of the true spectral function. We use this
method to compare kinetic theory predictions and previously published
phenomenological spectral functions to our lattice study.",1512.07249v1
2016-01-18,Search for transiting exoplanets and variable stars in the open cluster NGC 7243,"We report results of the first five observing campaigns for the open stellar
cluster NGC 7243 in the frame of project Young Exoplanet Transit Initiative
(YETI). The project focuses on the monitoring of young and nearby stellar
clusters, with the aim to detect young transiting exoplanets, and to study
other variability phenomena on time-scales from minutes to years. After five
observing campaigns and additional observations during 2013 and 2014, a clear
and repeating transit-like signal was detected in the light curve of
J221550.6+495611. Furthermore, we detected and analysed 37 new eclipsing binary
stars in the studied region. The best fit parameters and light curves of all
systems are given. Finally, we detected and analysed 26 new, presumably
pulsating variable stars in the studied region. The follow-up investigation of
these objects, including spectroscopic measurements of the exoplanet candidate,
is currently planned.",1601.04562v1
2016-01-21,Basker: A Threaded Sparse LU Factorization Utilizing Hierarchical Parallelism and Data Layouts,"Scalable sparse LU factorization is critical for efficient numerical
simulation of circuits and electrical power grids. In this work, we present a
new scalable sparse direct solver called Basker. Basker introduces a new
algorithm to parallelize the Gilbert-Peierls algorithm for sparse LU
factorization. As architectures evolve, there exists a need for algorithms that
are hierarchical in nature to match the hierarchy in thread teams, individual
threads, and vector level parallelism. Basker is designed to map well to this
hierarchy in architectures. There is also a need for data layouts to match
multiple levels of hierarchy in memory. Basker uses a two-dimensional
hierarchical structure of sparse matrices that maps to the hierarchy in the
memory architectures and to the hierarchy in parallelism. We present
performance evaluations of Basker on the Intel SandyBridge and Xeon Phi
platforms using circuit and power grid matrices taken from the University of
Florida sparse matrix collection and from Xyce circuit simulations. Basker
achieves a geometric mean speedup of 5.91x on CPU (16 cores) and 7.4x on Xeon
Phi (32 cores) relative to KLU. Basker outperforms Intel MKL Pardiso (PMKL) by
as much as 53x on CPU (16 cores) and 13.3x on Xeon Phi (32 cores) for low
fill-in circuit matrices. Furthermore, Basker provides 5.4x speedup on a
challenging matrix sequence taken from an actual Xyce simulation.",1601.05725v1
2016-02-16,JSJ decompositions of groups,"This is an account of the theory of JSJ decompositions of finitely generated
groups, as developed in the last twenty years or so.
  We give a simple general definition of JSJ decompositions (or rather of their
Bass-Serre trees), as maximal universally elliptic trees. In general, there is
no preferred JSJ decomposition, and the right object to consider is the whole
set of JSJ decompositions, which forms a contractible space: the JSJ
deformation space (analogous to Outer Space).
  We prove that JSJ decompositions exist for any finitely presented group,
without any assumption on edge groups. When edge groups are slender, we
describe flexible vertices of JSJ decompositions as quadratically hanging
extensions of 2-orbifold groups.
  Similar results hold in the presence of acylindricity, in particular for
splittings of torsion-free CSA groups over abelian groups, and splittings of
relatively hyperbolic groups over virtually cyclic or parabolic subgroups.
Using trees of cylinders, we obtain canonical JSJ trees (which are invariant
under automorphisms).
  We introduce a variant in which the property of being universally elliptic is
replaced by the more restrictive and rigid property of being universally
compatible. This yields a canonical compatibility JSJ tree, not just a
deformation space. We show that it exists for any finitely presented group.
  We give many examples, and we work throughout with relative decompositions
(restricting to trees where certain subgroups are elliptic).",1602.05139v2
2016-03-28,Write error rate of spin-transfer-torque random access memory including micromagnetic effects using rare event enhancement,"Spin-transfer-torque random access memory (STT-RAM) is a promising candidate
for the next-generation of random-access-memory due to improved scalability,
read-write speeds and endurance. However, the write pulse duration must be long
enough to ensure a low write error rate (WER), the probability that a bit will
remain unswitched after the write pulse is turned off, in the presence of
stochastic thermal effects. WERs on the scale of 10$^{-9}$ or lower are
desired. Within a macrospin approximation, WERs can be calculated analytically
using the Fokker-Planck method to this point and beyond. However, dynamic
micromagnetic effects within the bit can affect and lead to faster switching.
Such micromagnetic effects can be addressed via numerical solution of the
stochastic Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. However,
determining WERs approaching 10$^{-9}$ would require well over 10$^{9}$ such
independent simulations, which is infeasible. In this work, we explore
calculation of WER using ""rare event enhancement"" (REE), an approach that has
been used for Monte Carlo simulation of other systems where rare events
nevertheless remain important. Using a prototype REE approach tailored to the
STT-RAM switching physics, we demonstrate reliable calculation of a WER to
10$^{-9}$ with sets of only approximately 10$^{3}$ ongoing stochastic LLGS
simulations, and the apparent ability to go further.",1603.08512v2
2016-04-04,Probing unconventional superconductivity in inversion symmetric doped Weyl semimetal,"Unconventional superconductivity has been predicted to arise in the
topologically non-trivial Fermi surface of doped inversion symmetric Weyl
semimetals (WSM). In particular, Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and
nodal BCS states are theoretically predicted to be possible superconductor
pairing states in inversion symmetric doped WSM. In an effort to resolve
preferred pairing state, we theoretically study two separate four terminal
quantum transport methods that each exhibit a unique electrical signature in
the presence of FFLO and nodal BCS states in doped WSMs. We first introduce a
Josephson junction that consists of a doped WSM and an s-wave superconductor in
which we show that the application of a transverse uniform current in s-wave
superconductor effectively cancels the momentum carried by FFLO states in doped
WSM. From our numerical analysis, we find a peak in Josephson current amplitude
at finite uniform current in s-wave superconductor that serves as an indicator
of FFLO states in doped WSMs. Furthermore, we show using a four terminal
measurement configuration that the nodal points may be shifted by an
application of transverse uniform current in doped WSM. We analyze the
topological phase transitions induced by nodal pair annihilation in
non-equilibrium by constructing the phase diagram and we find a characteristic
decrease in the density of states that serves as a signature of the quantum
critical point in the topological phase transition, thereby identifying nodal
BCS states in doped WSM.",1604.01040v1
2016-04-22,Opt: A Domain Specific Language for Non-linear Least Squares Optimization in Graphics and Imaging,"Many graphics and vision problems can be expressed as non-linear least
squares optimizations of objective functions over visual data, such as images
and meshes. The mathematical descriptions of these functions are extremely
concise, but their implementation in real code is tedious, especially when
optimized for real-time performance on modern GPUs in interactive applications.
In this work, we propose a new language, Opt (available under
http://optlang.org), for writing these objective functions over image- or
graph-structured unknowns concisely and at a high level. Our compiler
automatically transforms these specifications into state-of-the-art GPU solvers
based on Gauss-Newton or Levenberg-Marquardt methods. Opt can generate
different variations of the solver, so users can easily explore tradeoffs in
numerical precision, matrix-free methods, and solver approaches. In our
results, we implement a variety of real-world graphics and vision applications.
Their energy functions are expressible in tens of lines of code, and produce
highly-optimized GPU solver implementations. These solver have performance
competitive with the best published hand-tuned, application-specific GPU
solvers, and orders of magnitude beyond a general-purpose auto-generated
solver.",1604.06525v3
2016-05-06,Spin orbit alignment for KELT-7b and HAT-P-56b via Doppler tomography with TRES,"We present Doppler tomographic analyses for the spectroscopic transits of
KELT-7b and HAT-P-56b, two hot-Jupiters orbiting rapidly rotating F-dwarf host
stars. These include analyses of archival TRES observations for KELT-7b, and a
new TRES transit observation of HAT-P-56b. We report spin-orbit aligned
geometries for KELT-7b (2.7 +/- 0.6 deg) and HAT-P-56b (8 +/- 2 deg). The host
stars KELT-7 and HAT-P-56 are among some of the most rapidly rotating
planet-hosting stars known. We examine the tidal re-alignment model for the
evolution of the spin-orbit angle in the context of the spin rates of these
stars. We find no evidence that the rotation rates of KELT-7 and HAT-P-56 have
been modified by star-planet tidal interactions, suggesting that the spin-orbit
angle of systems around these hot stars may represent their primordial
configuration. In fact, KELT-7 and HAT-P-56 are two of three systems in
super-synchronous, spin-orbit aligned states, where the rotation periods of the
host stars are faster than the orbital periods of the planets.",1605.01991v1
2016-06-18,Mathematical Foundations of the GraphBLAS,"The GraphBLAS standard (GraphBlas.org) is being developed to bring the
potential of matrix based graph algorithms to the broadest possible audience.
Mathematically the Graph- BLAS defines a core set of matrix-based graph
operations that can be used to implement a wide class of graph algorithms in a
wide range of programming environments. This paper provides an introduction to
the mathematics of the GraphBLAS. Graphs represent connections between vertices
with edges. Matrices can represent a wide range of graphs using adjacency
matrices or incidence matrices. Adjacency matrices are often easier to analyze
while incidence matrices are often better for representing data. Fortunately,
the two are easily connected by matrix mul- tiplication. A key feature of
matrix mathematics is that a very small number of matrix operations can be used
to manipulate a very wide range of graphs. This composability of small number
of operations is the foundation of the GraphBLAS. A standard such as the
GraphBLAS can only be effective if it has low performance overhead. Performance
measurements of prototype GraphBLAS implementations indicate that the overhead
is low.",1606.05790v2
2016-07-15,Influence of grain size and exchange interaction on the LLB modeling procedure,"Reliably predicting bit-error rates in realistic heat-assisted magnetic
recording simulations is a challenging task. Integrating the
Landau-Lifshitz-Bloch (LLB) equation can reduce the computational effort to
determine the magnetization dynamics in the vicinity of the Curie temperature.
If one aims that these dynamics coincide with trajectories calculated from the
atomistic Landau-Lifshitz-Gilbert equation, one has to carefully model required
temperature dependent material functions such as the zero-field equilibrium
magnetization as well as the parallel and normal susceptibilities. We present
an extensive study on how these functions depend on grain size and exchange
interactions. We show that, if the size or the exchange constant of a reference
grain is modified, the material functions can be scaled, according to the
changed Curie temperature, yielding negligible errors. This is shown to be
valid for volume changes of up to $\pm 40$ % and variations of the exchange
constant of up to $\pm10$ %. Besides the temperature dependent material curves,
computed switching probabilities also agree well with probabilities separately
determined for each system. Our study suggest that there is no need to
recalculate the required LLB input functions for each particle. Within the
presented limits it is sufficient to scale them to the Curie temperature of the
altered system.",1607.04480v1
2016-08-23,Thermal stability and irreversibility of skyrmion-lattice phases in Cu$_2$OSeO$_3$,"Small angle neutron scattering measurements have been performed to study the
thermodynamic stability of skyrmion-lattice phases in Cu$_2$OSeO$_3$. We found
that the two distinct skyrmion-lattice phases [SkX(1) and SkX(2) phases] can be
stabilized through different thermal histories; by cooling from the
paramagnetic phase under finite magnetic field, the SkX(2) phase is selected.
On the other hand, the 30$^{\circ}$-rotated SkX(1) phase becomes dominant by
heating the sample from the ordered conical phase under finite field. This
difference in stabilization is surprisingly similar to the irreversibility
observed in spin glasses. The zero-field cooling results in the co-existence of
the two phases. It is further found that once one of the skyrmion-lattice
phases is formed, it is hardly destabilized. This indicates unusual thermal
stability of the two skyrmion-lattice phases originating from an unexpectedly
large energy barrier between them.",1608.06359v2
2016-08-24,Carbon Stars in the Satellites and Halo of M31,"We spectroscopically identify a sample of carbon stars in the satellites and
halo of M31 using moderate-resolution optical spectroscopy from the
Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey. We
present the photometric properties of our sample of 41 stars, including their
brightness with respect to the tip of the red giant branch (TRGB) and their
distributions in various color-color spaces. This analysis reveals a bluer
population of carbon stars fainter than the TRGB and a redder population of
carbon stars brighter than the TRGB. We then apply principal component analysis
to determine the sample's eigenspectra and eigencoefficients. Correlating the
eigencoefficients with various observable properties reveals the spectral
features that trace effective temperature and metallicity. Putting the
spectroscopic and photometric information together, we find the carbon stars in
the satellites and halo of M31 to be minimally impacted by dust and internal
dynamics. We also find that while there is evidence to suggest that the
sub-TRGB stars are extrinsic in origin, it is also possible that they are are
particularly faint members of the asymptotic giant branch.",1608.06714v1
2016-09-12,"Discovery and Precise Characterization by the MEarth Project of LP 661-13, an Eclipsing Binary Consisting of Two Fully Convective Low-mass Stars","We report the detection of stellar eclipses in the LP 661-13 system. We
present the discovery and characterization of this system, including high
resolution spectroscopic radial velocities and a photometric solution spanning
two observing seasons. LP 661-13 is a low mass binary system with an orbital
period of $4.7043512^{+0.0000013}_{-0.0000010}$ days at a distance of $24.9 \pm
1.3$ parsecs. LP 661-13A is a $0.30795 \pm 0.00084$ $M_\odot$ star while LP
661-13B is a $0.19400 \pm 0.00034$ $M_\odot$ star. The radius of each component
is $0.3226 \pm 0.0033$ $R_\odot$ and $0.2174 \pm 0.0023$ $R_\odot$,
respectively. We detect out of eclipse modulations at a period slightly shorter
than the orbital period, implying that at least one of the components is not
rotating synchronously. We find that each component is slightly inflated
compared to stellar models, and that this cannot be reconciled through age or
metallicity effects. As a nearby eclipsing binary system where both components
are near or below the full-convection limit, LP 661-13 will be a valuable test
of models for the structure of cool dwarf stars.",1609.03591v1
2016-09-14,"Topological superconductivity in an ultrathin, magnetically-doped topological insulator proximity coupled to a conventional superconductor","As a promising candidate system to realize topological superconductivity, the
system of a 3D topological insulator (TI) grown on top of the s-wave
superconductor has been extensively studied. To access the topological
superconductivity experimentally, the 3D TI sample must be thin enough to allow
for Cooper pair tunneling to the exposed surface of TI. The use of magnetically
ordered dopants to break time-reversal symmetry may allow the surface of a TI
to host Majorana fermion, which are believed to be a signature of topological
superconductivity. In this work, we study a magnetically-doped thin film
TI-superconductor hybrid systems. Considering the proximity induced order
parameter in thin film of TI, we analyze the gap closing points of the
Hamiltonian and draw the phase diagram as a function of relevant parameters:
the hybridization gap, Zeeman energy, and chemical potential of the TI system.
Our findings provide a useful guide in choosing relevant parameters to
facilitate the observation of topological superconductivity in thin film
TI-superconductor hybrid systems. In addition, we further perform numerical
analysis on a TI proximity coupled to a s-wave superconductor and find that,
due to the spin-momentum locked nature of the surface states in TI, the induced
s-wave order parameter of the surface states persists even at large magnitude
of the Zeeman energy.",1609.04129v2
2016-09-16,Convex separation from convex optimization for large-scale problems,"We present a scheme, based on Gilbert's algorithm for quadratic minimization
[SIAM J. Contrl., vol. 4, pp. 61-80, 1966], to prove separation between a point
and an arbitrary convex set $S\subset\mathbb{R}^{n}$ via calls to an oracle
able to perform linear optimizations over $S$. Compared to other methods, our
scheme has almost negligible memory requirements and the number of calls to the
optimization oracle does not depend on the dimensionality $n$ of the underlying
space. We study the speed of convergence of the scheme under different promises
on the shape of the set $S$ and/or the location of the point, validating the
accuracy of our theoretical bounds with numerical examples. Finally, we present
some applications of the scheme in quantum information theory. There we find
that our algorithm out-performs existing linear programming methods for certain
large scale problems, allowing us to certify nonlocality in bipartite scenarios
with upto $42$ measurement settings. We apply the algorithm to upper bound the
visibility of two-qubit Werner states, hence improving known lower bounds on
Grothendieck's constant $K_G(3)$. Similarly, we compute new upper bounds on the
visibility of GHZ states and on the steerability limit of Werner states for a
fixed number of measurement settings.",1609.05011v2
2016-09-18,Narrowly distributed crystal orientation in biomineral vaterite,"Biominerals formed by animals provide skeletal support, and many other
functions. They were previously shown to grow by aggregation of amorphous
nanoparticles, but never to grow ion-by-ion from solution, which is a common
growth mechanism for abiotic crystals. We analyze vaterite CaCO3 multi
crystalline spicules from the solitary tunicate Herdmania momus, with
Polarization dependent Imaging Contrast PIC mapping, scanning and aberration
corrected transmission electron microscopies. The first fully quantitative PIC
mapping data, presented here, measured 0{\deg} 30{\deg} angle spreads between
immediately adjacent crystals. Such narrowly distributed crystal orientations
demonstrate that crystallinity does not propagate from one crystal to another
0{\deg} angle spreads, nor that new crystals with random orientation 90{\deg}
nucleate. There are no organic layers at the interface between crystals, hence
a new, unknown growth mechanism must be invoked, with crystal nucleation
constrained within 30{\deg}. Two observations are consistent with crystal
growth from solution: vaterite microcrystals express crystal faces, and are
smooth at the nanoscale after cryo fracture. The observation of 30{\deg} angle
spreads, lack of interfacial organic layers, and smooth fracture figures
broadens the range of known biomineralization mechanisms and may inspire novel
synthetic crystal growth strategies. Spherulitic growth from solution is one
possible mechanism consistent with all these observations.",1609.05449v1
2016-09-29,Multiscale Model Approach for Magnetization Dynamics Simulations,"Simulations of magnetization dynamics in a multiscale environment enable
rapid evaluation of the Landau-Lifshitz-Gilbert equation in a mesoscopic sample
with nanoscopic accuracy in areas where such accuracy is required. We have
developed a multiscale magnetization dynamics simulation approach that can be
applied to large systems with spin structures that vary locally on small length
scales. To implement this, the conventional micromagnetic simulation framework
has been expanded to include a multiscale solving routine. The software
selectively simulates different regions of a ferromagnetic sample according to
the spin structures located within in order to employ a suitable discretization
and use either a micromagnetic or an atomistic model. To demonstrate the
validity of the multiscale approach, we simulate the spin wave transmission
across the regions simulated with the two different models and different
discretizations. We find that the interface between the regions is fully
transparent for spin waves with frequency lower than a certain threshold set by
the coarse scale micromagnetic model with no noticeable attenuation due to the
interface between the models. As a comparison to exact analytical theory, we
show that in a system with Dzyaloshinskii-Moriya interaction leading to spin
spiral, the simulated multiscale result is in good quantitative agreement with
the analytical calculation.",1609.09295v1
2016-12-21,Geometric generalised Lagrangian mean theories,"Many fluctuation-driven phenomena in fluids can be analysed effectively using
the generalised Lagrangian mean (GLM) theory of Andrews & McIntyre (1978). This
theory relies on particle-following averaging to incorporate the constraints
imposed by the material conservations. It relies implicitly on an Euclidean
structure; as a result, it does not have a geometrically intrinsic
interpretation and suffers from undesirable features, including the divergence
of the Lagrangian-mean velocity for incompressible fluids. Motivated by this,
we develop a geometric generalisation of GLM that we formulate intrinsically.
The theory applies to arbitrary Riemannian manifolds; it also establishes a
clear distinction between results that stem directly from geometric consistency
and those that depend on particular choices. We show that the Lagrangian mean
momentum -- the average of the pull-back of the momentum one-form -- obeys a
simple equation which guarantees the conservation of Kelvin's circulation,
irrespective of the mean-flow definition. We discuss four possible definitions
of the mean flow: a direct extension of standard GLM, a definition based on
optimal transportation, a definition based on a geodesic distance in the group
of volume-preserving diffeomorphisms, and the glm definition proposed by Soward
& Roberts (2010). Assuming small-amplitude perturbations, we carry out
order-by-order calculations to obtain explicit expressions for the mean flow
and pseudomomentum at leading order. We also show how the wave-action
conservation of GLM extends to the geometric setting. To make the paper
self-contained, we introduce the tools of differential geometry and main ideas
of geometric fluid dynamics on which we rely. We mostly focus on the Euler
equations for incompressible inviscid fluids but sketch out extensions to the
rotating-stratified Boussinesq, compressible Euler and magnetohydrodynamic
equations.",1612.07111v3
2017-01-13,A Multi-Planet System Transiting the $V$ = 9 Rapidly Rotating F-Star HD 106315,"We report the discovery of a multi-planet system orbiting HD 106315, a
rapidly rotating mid F-type star, using data from the K2 mission. HD 106315
hosts a $2.51\pm0.12\,R_\oplus$ sub-Neptune in a 9.5 day orbit, and a
$4.31_{-0.27}^{+0.24}\,R_\oplus$ super-Neptune in a 21 day orbit. The projected
rotational velocity of HD 106315 (12.9 km s$^{-1}$) likely precludes precise
measurements of the planets' masses, but could enable a measurement of the
sky-projected spin-orbit obliquity for the outer planet via Doppler tomography.
The eccentricities of both planets were constrained to be consistent with 0,
following a global modeling of the system that includes a Gaia distance and
dynamical arguments. The HD 106315 system is one of few multi-planet systems
hosting a Neptune-sized planet for which orbital obliquity measurements are
possible, making it an excellent test-case for formation mechanisms of
warm-Neptunian systems. The brightness of the host star also makes HD 106315 c
a candidate for future transmission spectroscopic follow-up studies.",1701.03807v2
2017-01-17,"The Landau-Lifshitz equation, the NLS, and the magnetic rogue wave as a by-product of two colliding regular ""positons""","In this article we present a new method for construction of exact solutions
of the Landau-Lifshitz-Gilbert equation (LLG) for ferromagnetic nanowires. The
method is based on the established relationship between the LLG and the
nonlinear Schr\""odinger equation (NLS), and is aimed at resolving an old
problem: how to produce multiple-rogue wave solutions of NLS using just the
Darboux-type transformations. The solutions of this type - known as P-breathers
- have been proven to exist by Dubard and Matveev, but their technique heavily
relied on using the solutions of yet another nonlinear equation,
Kadomtsev-Petviashvili I equation (KP-I), and its relationship with NLS. We
have shown that in fact one doesn't have to use KP-I but can instead reach the
same results just with NLS solutions, but only if they are dressed via the
binary Darboux transformation. In particular, our approach allows to construct
all the Dubard-Matveev P-breathers. Furthermore, the new method can lead to
some completely new, previously unknown solutions. One particular solution that
we have constructed describes two positon-like waves, colliding with each other
and in the process producing a new, short-lived rogue wave. We called this
unusual solution (rogue wave begotten after the impact of two solitons) the
""impacton"".",1701.04903v3
2017-01-24,Partial Bridging of Vaccine Efficacy to New Populations,"Suppose one has data from one or more completed vaccine efficacy trials and
wishes to estimate the efficacy in a new setting. Often logistical or ethical
considerations make running another efficacy trial impossible. Fortunately, if
there is a biomarker that is the primary modifier of efficacy, then the
biomarker-conditional efficacy may be identical in the completed trials and the
new setting, or at least informative enough to meaningfully bound this
quantity. Given a sample of this biomarker from the new population, we might
hope we can bridge the results of the completed trials to estimate the vaccine
efficacy in this new population. Unfortunately, even knowing the true
conditional efficacy in the new population fails to identify the marginal
efficacy due to the unknown conditional unvaccinated risk. We define a curve
that partially identifies (lower bounds) the marginal efficacy in the new
population as a function of the population's marginal unvaccinated risk, under
the assumption that one can identify bounds on the conditional unvaccinated
risk in the new population. Interpreting the curve only requires identifying
plausible regions of the marginal unvaccinated risk in the new population. We
present a nonparametric estimator of this curve and develop valid lower
confidence bounds that concentrate at a parametric rate. We use vaccine
terminology throughout, but the results apply to general binary interventions
and bounded outcomes.",1701.06739v1
2017-02-07,Resonant spin transfer torque nano-oscillators,"Spin transfer torque nano-oscillators are potential candidates for replacing
the traditional inductor based voltage controlled oscillators in modern
communication devices. Typical oscillator designs are based on trilayer
magnetic tunnel junctions which are disadvantaged by low power outputs and poor
conversion efficiencies. In this letter, we theoretically propose to use
resonant spin filtering in pentalayer magnetic tunnel junctions as a possible
route to alleviate these issues and present device designs geared toward a high
microwave output power and an efficient conversion of the d.c. input power. We
attribute these robust qualities to the resulting non-trivial spin current
profiles and the ultra high tunnel magnetoresistance, both arising from
resonant spin filtering. The device designs are based on the nonequilibrium
Green's function spin transport formalism self-consistently coupled with the
stochastic Landau-Lifshitz-Gilbert-Slonczewski's equation and the Poisson's
equation. We demonstrate that the proposed structures facilitate oscillator
designs featuring a large enhancement in microwave power of around $775\%$ and
an efficiency enhancement of over $1300\%$ in comparison with typical trilayer
designs. We also rationalize the optimum operating regions via an analysis of
the dynamic and static device resistances. This work sets stage for pentalyer
spin transfer torque nano-oscillator device designs that extenuate most of the
issues faced by the typical trilayer designs.",1702.01869v1
2017-03-17,Communication Primitives in Cognitive Radio Networks,"Cognitive radio networks are a new type of multi-channel wireless network in
which different nodes can have access to different sets of channels. By
providing multiple channels, they improve the efficiency and reliability of
wireless communication. However, the heterogeneous nature of cognitive radio
networks also brings new challenges to the design and analysis of distributed
algorithms.
  In this paper, we focus on two fundamental problems in cognitive radio
networks: neighbor discovery, and global broadcast. We consider a network
containing $n$ nodes, each of which has access to $c$ channels. We assume the
network has diameter $D$, and each pair of neighbors have at least $k\geq 1$,
and at most $k_{max}\leq c$, shared channels. We also assume each node has at
most $\Delta$ neighbors. For the neighbor discovery problem, we design a
randomized algorithm CSeek which has time complexity
$\tilde{O}((c^2/k)+(k_{max}/k)\cdot\Delta)$. CSeek is flexible and robust,
which allows us to use it as a generic ""filter"" to find ""well-connected""
neighbors with an even shorter running time. We then move on to the global
broadcast problem, and propose CGCast, a randomized algorithm which takes
$\tilde{O}((c^2/k)+(k_{max}/k)\cdot\Delta+D\cdot\Delta)$ time. CGCast uses
CSeek to achieve communication among neighbors, and uses edge coloring to
establish an efficient schedule for fast message dissemination.
  Towards the end of the paper, we give lower bounds for solving the two
problems. These lower bounds demonstrate that in many situations, CSeek and
CGCast are near optimal.",1703.06130v1
2017-03-22,Magnetization induced dynamics of a Josephson junction coupled to a nanomagnet,"We study the superconducting current of a Josephson junction (JJ) coupled to
an external nanomagnet driven by a time dependent magnetic field both without
and in the presence of an external AC drive. We provide an analytic, albeit
perturbative, solution for the Landau-Lifshitz (LL) equations governing the
coupled JJ-nanomagnet system in the presence of a magnetic field with arbitrary
time-dependence oriented along the easy axis of the nanomagnet's magnetization
and in the limit of weak dimensionless coupling $\epsilon_0$ between the JJ and
the nanomagnet. We show the existence of Shapiro-like steps in the I-V
characteristics of the JJ subjected to a voltage bias for a constant or
periodically varying magnetic field and explore the effect of rotation of the
magnetic field and the presence of an external AC drive on these steps. We
support our analytic results with exact numerical solution of the LL equations.
We also extend our results to dissipative nanomagnets by providing a
perturbative solution to the Landau-Lifshitz-Gilbert (LLG) equations for weak
dissipation. We study the fate of magnetization-induced Shapiro steps in the
presence of dissipation both from our analytical results and via numerical
solution of the coupled LLG equations. We discuss experiments which can test
our theory.",1703.07717v3
2017-04-19,Integrating optimization with thermodynamics and plant physiology for crop ideotype design,"A computational framework integrating optimization algorithms, parallel
computing and plant physiology was developed to explore crop ideotype design.
The backbone of the framework is a plant physiology model that accurately
tracks water use (i.e. a plant hydraulic model) coupled with mass transport
(CO2 exchange and transport), energy conversion (leaf temperature due to
radiation, convection and mass transfer) and photosynthetic biochemistry of an
adult maize plant. For a given trait configuration, soil parameters and hourly
weather data, the model computes water use and photosynthetic output over the
life of an adult maize plant. We coupled this validated model with a parallel,
meta-heuristic optimization algorithm, specifically a genetic algorithm (GA),
to identify trait sets (ideotypes) that resulted in desired water use behavior
of the adult maize plant. We detail features of the model as well as the
implementation details of the coupling with the optimization framework and
deployment on high performance computing platforms. We illustrate a
representative result of this framework by identifying maize ideotypes with
optimized photosynthetic yields using weather and soil conditions corresponding
to Davis, CA. Finally, we show how the framework can be used to identify broad
ideotype trends that can inform breeding efforts. The developed presented tool
has the potential to inform the development of future climate-resilient crops.",1704.05885v1
2017-04-28,From deep inelastic scattering to heavy-flavor semi-leptonic decays: Total rates into multi-hadron final states from lattice QCD,"We present a new technique for extracting decay and transition rates into
final states with any number of hadrons. The approach is only sensitive to
total rates, in which all out-states with a given set of QCD quantum numbers
are included. For processes involving photons or leptons, differential rates
with respect to the non-hadronic kinematics may also be extracted. Our method
involves constructing a finite-volume Euclidean four-point function, whose
corresponding spectral function measures the decay and transition rates in the
infinite-volume limit. This requires solving the inverse problem of extracting
the spectral function from the correlator and also necessitates a smoothing
procedure so that a well-defined infinite-volume limit exists. Both of these
steps are accomplished by the Backus-Gilbert method and, as we show with a
numerical example, reasonable precision can be expected in cases with multiple
open decay channels. Potential applications include nucleon structure functions
and the onset of the deep inelastic scattering regime, as well as semi-leptonic
$D$ and $B$ decay rates.",1704.08993v2
2017-05-01,Measuring galaxy cluster masses with CMB lensing using a Maximum Likelihood estimator: Statistical and systematic error budgets for future experiments,"We develop a Maximum Likelihood estimator (MLE) to measure the masses of
galaxy clusters through the impact of gravitational lensing on the temperature
and polarization anisotropies of the cosmic microwave background (CMB). We show
that, at low noise levels in temperature, this optimal estimator outperforms
the standard quadratic estimator by a factor of two. For polarization, we show
that the Stokes Q/U maps can be used instead of the traditional E- and B-mode
maps without losing information. We test and quantify the bias in the recovered
lensing mass for a comprehensive list of potential systematic errors. Using
realistic simulations, we examine the cluster mass uncertainties from
CMB-cluster lensing as a function of an experiment's beam size and noise level.
We predict the cluster mass uncertainties will be 3 - 6% for SPT-3G, AdvACT,
and Simons Array experiments with 10,000 clusters and less than 1% for the
CMB-S4 experiment with a sample containing 100,000 clusters. The mass
constraints from CMB polarization are very sensitive to the experimental beam
size and map noise level: for a factor of three reduction in either the beam
size or noise level, the lensing signal-to-noise improves by roughly a factor
of two.",1705.00411v2
2017-05-03,Current driven second harmonic domain wall resonance in ferromagnetic metal/ nonmagnetic metal bilayer: a field-free method for spin Hall angle measurements,"We study the ac current-driven domain wall motion in bilayer ferromagnetic
metal (FM)/nonmagnetic metal (NM) nanowire. The solution of the modified
Landau-Lifshitz-Gilbert equation including all the spin transfer torques is
used to describe motion of the domain wall in presence of the spin Hall effect.
We show that the domain wall center has second harmonic frequency response in
addition to the known first harmonic excitation. In contrast to the
experimentally observed second harmonic response in harmonic Hall measurements
of spin-orbit torque in magnetic thin films, this second harmonic response
directly originates from spin-orbit torque driven domain wall dynamics. Based
on the spin current generated by domain wall dynamics, the longitudinal spin
motive force generated voltage across the length of the nanowire is determined.
The second harmonic response introduces additionally a new practical field-free
and all-electrical method to probe the effective spin Hall angle for FM/NM
bilayer structures that could be applied in experiments. Our results also
demonstrate the capability of utilizing FM/NM bilayer structure in domain wall
based spin torque signal generators and resonators.",1705.01355v5
2017-05-20,SVM via Saddle Point Optimization: New Bounds and Distributed Algorithms,"We study two important SVM variants: hard-margin SVM (for linearly separable
cases) and $\nu$-SVM (for linearly non-separable cases). We propose new
algorithms from the perspective of saddle point optimization. Our algorithms
achieve $(1-\epsilon)$-approximations with running time $\tilde{O}(nd+n\sqrt{d
/ \epsilon})$ for both variants, where $n$ is the number of points and $d$ is
the dimensionality. To the best of our knowledge, the current best algorithm
for $\nu$-SVM is based on quadratic programming approach which requires
$\Omega(n^2 d)$ time in worst case~\cite{joachims1998making,platt199912}. In
the paper, we provide the first nearly linear time algorithm for $\nu$-SVM. The
current best algorithm for hard margin SVM achieved by Gilbert
algorithm~\cite{gartner2009coresets} requires $O(nd / \epsilon )$ time. Our
algorithm improves the running time by a factor of $\sqrt{d}/\sqrt{\epsilon}$.
Moreover, our algorithms can be implemented in the distributed settings
naturally. We prove that our algorithms require $\tilde{O}(k(d
+\sqrt{d/\epsilon}))$ communication cost, where $k$ is the number of clients,
which almost matches the theoretical lower bound. Numerical experiments support
our theory and show that our algorithms converge faster on high dimensional,
large and dense data sets, as compared to previous methods.",1705.07252v4
2017-06-15,On the Maximum Size of Block Codes Subject to a Distance Criterion,"We establish a general formula for the maximum size of finite length block
codes with minimum pairwise distance no less than $d$. The achievability
argument involves an iterative construction of a set of radius-$d$ balls, each
centered at a codeword. We demonstrate that the number of such balls that cover
the entire code alphabet cannot exceed this maximum size. Our approach can be
applied to codes $i)$ with elements over arbitrary code alphabets, and $ii)$
under a broad class of distance measures, thereby ensuring the generality of
our formula. Our formula indicates that the maximum code size can be fully
characterized by the cumulative distribution function of the distance measure
evaluated at two independent and identically distributed random codewords. When
the two random codewords assume a uniform distribution over the entire code
alphabet, our formula recovers and obtains a natural generalization of the
Gilbert-Varshamov (GV) lower bound. We also establish a general formula for the
zero-error capacity of any sequence of channels. Finally, we extend our study
to the asymptotic setting, where we establish first- and second-order bounds on
the asymptotic code rate subject to a normalized minimum distance constraint.",1706.04709v2
2017-06-19,Capability of Detecting Ultra-Violet Counterparts of Gravitational Waves with GLUV,"With the discovery of gravitational waves (GW), attention has turned towards
detecting counterparts to these sources. In discussions on counterpart
signatures and multi-messenger follow-up strategies to GW detections,
ultra-violet (UV) signatures have largely been neglected, due to UV facilities
being limited to SWIFT, which lacks high-cadence UV survey capabilities. In
this paper, we examine the UV signatures from merger models for the major GW
sources, highlighting the need for further modelling, while presenting
requirements and a design for an effective UV survey telescope. Using $u'$-band
models as an analogue, we find that a UV survey telescope requires a limiting
magnitude of m$_{u'}\rm (AB)\approx 24$ to fully complement the aLIGO range and
sky localisation. We show that a network of small, balloon-based UV telescopes
with a primary mirror diameter of 30~cm could be capable of covering the aLIGO
detection distance from $\sim$60--100\% for BNS events and $\sim$40\% for BHNS
events. The sensitivity of UV emission to initial conditions suggests that a UV
survey telescope would provide a unique dataset, that can act as an effective
diagnostic to discriminate between models.",1706.06106v2
2017-07-27,LCD codes over ${\mathbb F}_q $ are as good as linear codes for q at least four,"The hull $H(C)$ of a linear code $C$ is defined by $H(C)=C \cap C^\perp$. A
linear code with a complementary dual (LCD) is a linear code with $H(C)=\{0\}$.
The dimension of the hull of a code is an invariant under permutation
equivalence. For binary and ternary codes the dimension of the hull is also
invariant under monomial equivalence and we show that this invariant is
determined by the extended weight enumerator of the code.\\ The hull of a code
is not invariant under monomial equivalence if $q\geq 4$. We show that every
${\mathbb F}_q $-linear code is monomial equivalent with an LCD code in case $q
\geq 4$. The proof uses techniques from Gr\""obner basis theory. We conclude
that if there exists an ${\mathbb F}_q $-linear code with parameters
$[n,k,d]_q$ and $q \geq 4$, then there exists also a LCD code with the same
parameters. Hence this holds for optimal and MDS codes. In particular there
exist LCD codes that are above the Gilbert-Varshamov bound if $q$ is a square
and $q\geq 49$ by the existence of such codes that are algebraic geometric.\\
Similar results are obtained with respect to Hermitian LCD codes.",1707.08856v1
2017-08-04,Energy release in the solar atmosphere from a stream of infalling prominence debris,"Recent high-resolution and high-cadence EUV imaging has revealed a new
phenomenon, impacting prominence debris, where prominence material from failed
or partial eruptions can impact the lower atmosphere, releasing energy. We
report a clear example of energy release and EUV brightening due to infalling
prominence debris that occurred on 2011 September 7-8. The initial eruption of
material was associated with an X1.8-class flare from AR11283, occurring at
22:30 UT on 2011 September 7. Subsequently, a semi-continuous stream of this
material returned to the solar surface with a velocity v > 150 km/s, impacting
a region remote from the original active region between 00:20 - 00:40 UT on
2011 September 8. Using SDO/AIA, the differential emission measure of the
plasma was estimated throughout this brightening event. We found that the
radiated energy of the impacted plasma was L_rad ~10^27 ergs, while the thermal
energy peaked at ~10^28 ergs. From this we were able to determine the mass
content of the debris to be in the range 2x10^14 < m < 2x10^15 g. Given typical
promimence masses, the likely debris mass is towards the lower end of this
range. This clear example of a prominence debris event shows that significant
energy release takes place during these events, and that such impacts may be
used as a novel diagnostic tool for investigating prominence material
properties.",1708.01555v2
2017-08-16,Magneto Acoustic Spin Hall Oscillators,"This paper introduces a novel oscillator that combines the tunability of spin
Hall-driven nano oscillators with the high quality factor (Q) of high overtone
bulk acoustic wave resonators (HBAR), integrating both reference and tunable
oscillators on the same chip with CMOS. In such magneto acoustic spin Hall
(MASH) oscillators, voltage oscillations across the magnetic tunnel junction
(MTJ) that arise from a spin-orbit torque (SOT) are shaped by the transmission
response of the HBAR that acts as a multiple peak-bandpass filter and a delay
element due to its large time constant, providing delayed feedback. The
filtered voltage oscillations can be fed back to the MTJ via a) strain, b)
current, or c) magnetic field. We develop a SPICE-based circuit model by
combining experimentally benchmarked models including the stochastic
Landau-Lifshitz-Gilbert (sLLG) equation for magnetization dynamics and the
Butterworth Van Dyke (BVD) circuit for the HBAR. Using the self-consistent
model, we project up to $\sim$ 50X enhancement in the oscillator linewidth with
Q reaching up to 52825 at 3 GHz, while preserving the tunability by locking the
STNO to the nearest high Q peak of the HBAR. We expect that our results will
inspire MEMS-based solutions to spintronic devices by combining attractive
features of both fields for a variety of applications.",1708.04735v2
2017-09-01,An order optimal policy for exploiting idle spectrum in cognitive radio networks,"In this paper a spectrum sensing policy employing recency-based exploration
is proposed for cognitive radio networks. We formulate the problem of finding a
spectrum sensing policy for multi-band dynamic spectrum access as a stochastic
restless multi-armed bandit problem with stationary unknown reward
distributions. In cognitive radio networks the multi-armed bandit problem
arises when deciding where in the radio spectrum to look for idle frequencies
that could be efficiently exploited for data transmission. We consider two
models for the dynamics of the frequency bands: 1) the independent model where
the state of the band evolves randomly independently from the past and 2) the
Gilbert-Elliot model, where the states evolve according to a 2-state Markov
chain. It is shown that in these conditions the proposed sensing policy attains
asymptotically logarithmic weak regret. The policy proposed in this paper is an
index policy, in which the index of a frequency band is comprised of a sample
mean term and a recency-based exploration bonus term. The sample mean promotes
spectrum exploitation whereas the exploration bonus encourages for further
exploration for idle bands providing high data rates. The proposed recency
based approach readily allows constructing the exploration bonus such that it
will grow the time interval between consecutive sensing time instants of a
suboptimal band exponentially, which then leads to logarithmically increasing
weak regret. Simulation results confirming logarithmic weak regret are
presented and it is found that the proposed policy provides often improved
performance at low complexity over other state-of-the-art policies in the
literature.",1709.00237v1
2017-09-08,EndoSensorFusion: Particle Filtering-Based Multi-sensory Data Fusion with Switching State-Space Model for Endoscopic Capsule Robots,"A reliable, real time multi-sensor fusion functionality is crucial for
localization of actively controlled capsule endoscopy robots, which are an
emerging, minimally invasive diagnostic and therapeutic technology for the
gastrointestinal (GI) tract. In this study, we propose a novel multi-sensor
fusion approach based on a particle filter that incorporates an online
estimation of sensor reliability and a non-linear kinematic model learned by a
recurrent neural network. Our method sequentially estimates the true robot pose
from noisy pose observations delivered by multiple sensors. We experimentally
test the method using 5 degree-of-freedom (5-DoF) absolute pose measurement by
a magnetic localization system and a 6-DoF relative pose measurement by visual
odometry. In addition, the proposed method is capable of detecting and handling
sensor failures by ignoring corrupted data, providing the robustness expected
of a medical device. Detailed analyses and evaluations are presented using
ex-vivo experiments on a porcine stomach model prove that our system achieves
high translational and rotational accuracies for different types of endoscopic
capsule robot trajectories.",1709.03401v3
2017-09-12,Distributed Scheduling in Time Dependent Environments: Algorithms and Analysis,"Consider the problem of a multiple access channel in a time dependent
environment with a large number of users. In such a system, mostly due to
practical constraints (e.g., decoding complexity), not all users can be
scheduled together, and usually only one user may transmit at any given time.
Assuming a distributed, opportunistic scheduling algorithm, we analyse the
system's properties, such as delay, QoS and capacity scaling laws.
Specifically, we start with analyzing the performance while \emph{assuming the
users are not necessarily fully backlogged}, focusing on the queueing problem
and, especially, on the \emph{strong dependence between the queues}. We first
extend a known queueing model by Ephremides and Zhu, to give new results on the
convergence of the probability of collision to its average value (as the number
of users grows), and hence for the ensuing system performance metrics, such as
throughput and delay. This model, however, is limited in the number of users
one can analyze. We thus suggest a new model, which is much simpler yet can
accurately describes the system behaviour when the number of users is large.
  We then proceed to the analysis of this system under the assumption of time
dependent channels. Specifically, we assume each user experiences a different
channel state sequence, expressing different channel fluctuations
(specifically, the Gilbert-Elliott model). The system performance under this
setting is analysed, along with the channel capacity scaling laws.",1709.04361v1
2017-09-16,A differential memristive synapse circuit for on-line learning in neuromorphic computing systems,"Spike-based learning with memristive devices in neuromorphic computing
architectures typically uses learning circuits that require overlapping pulses
from pre- and post-synaptic nodes. This imposes severe constraints on the
length of the pulses transmitted in the network, and on the network's
throughput. Furthermore, most of these circuits do not decouple the currents
flowing through memristive devices from the one stimulating the target neuron.
This can be a problem when using devices with high conductance values, because
of the resulting large currents. In this paper we propose a novel circuit that
decouples the current produced by the memristive device from the one used to
stimulate the post-synaptic neuron, by using a novel differential scheme based
on the Gilbert normalizer circuit. We show how this circuit is useful for
reducing the effect of variability in the memristive devices, and how it is
ideally suited for spike-based learning mechanisms that do not require
overlapping pre- and post-synaptic pulses. We demonstrate the features of the
proposed synapse circuit with SPICE simulations, and validate its learning
properties with high-level behavioral network simulations which use a
stochastic gradient descent learning rule in two classification tasks.",1709.05484v1
2017-09-21,Impacts of Surface Depletion on the Plasmonic Properties of Doped Semiconductor Nanocrystals,"Degenerately doped semiconductor nanocrystals (NCs) exhibit a localized
surface plasmon resonance (LSPR) in the infrared range of the electromagnetic
spectrum. Unlike metals, semiconductor NCs offer tunable LSPR characteristics
enabled by doping, or via electrochemical or photochemical charging. Tuning
plasmonic properties through carrier density modulation suggests potential
applications in smart optoelectronics, catalysis, and sensing. Here, we
elucidate fundamental aspects of LSPR modulation through dynamic carrier
density tuning in Sn-doped Indium Oxide NCs. Monodisperse Sn-doped Indium Oxide
NCs with various doping level and sizes were synthesized and assembled in
uniform films. NC films were then charged in an in situ electrochemical cell
and the LSPR modulation spectra were monitored. Based on spectral shifts and
intensity modulation of the LSPR, combined with optical modeling, it was found
that often-neglected semiconductor properties, specifically band structure
modification due to doping and surface states, strongly affect LSPR modulation.
Fermi level pinning by surface defect states creates a surface depletion layer
that alters the LSPR properties; it determines the extent of LSPR frequency
modulation, diminishes the expected near field enhancement, and strongly
reduces sensitivity of the LSPR to the surroundings.",1709.07136v2
2017-10-05,Transport theory for femtosecond laser-induced spin-transfer torques,"Ultrafast demagnetization of magnetic layers pumped by a femtosecond laser
pulse is accompanied by a nonthermal spin-polarized current of hot electrons.
These spin currents are studied here theoretically in a spin valve with
noncollinear magnetizations. To this end, we introduce an extended model of
superdiffusive spin transport that enables to treat noncollinear magnetic
configurations, and apply it to the perpendicular spin valve geometry. We show
how spin-transfer torques arise due to this mechanism and calculate their
action on the magnetization present, as well as how the latter depends on the
thicknesses of the layers and other transport parameters. We demonstrate that
there exists a certain optimum thickness of the out-of-plane magnetized
spin-current polarizer such that the torque acting on the second magnetic layer
is maximal. Moreover, we study the magnetization dynamics excited by the
superdiffusive spin-transfer torque due to the flow of hot electrons employing
the Landau-Lifshitz-Gilbert equation. Thereby we show that a femtosecond laser
pulse applied to one magnetic layer can excite small-angle precessions of the
magnetization in the second magnetic layer. We compare our calculations with
recent experimental results.",1710.02083v2
2017-10-12,A critical comparison of methods for the determination of the ageing sensitivity in biomedical grade yttria stabilized zirconia,"Since the recent failure events of two particular series of zirconia femoral
heads for total hip replacement prosthesis, a large decrease in the use of
zirconia ceramics for orthopaedic implants has been observed. In spite of the
biomedical success of this material during the last ten years, this was
required for safety reasons, until the cause of the failures is known. It has
been shown that these failures were related to the low temperature hydrothermal
degradation (also known as ageing). Thus it is crucial to better understand the
ageing behaviour, in order to be able to assess its importance and then control
it if required. In this paper, various techniques relevant to assess the
hydrothermal degradation sensitivity of biomedical grade yttria stabilized
zirconia are discussed and compared. The expected outputs of conventional
methods, i.e. X-Ray diffraction and scanning electron microscopy are examined.
More recent methods like optical interferometry and atomic force microscopy are
presented, with their respective benefits and drawbacks. An up to date
comparison of these different techniques is provided, and their use for
ensuring the long term reliability of a particular batch of zirconia in terms
of ageing degradation is demonstrated.",1710.04449v1
2017-10-26,Evaluation of Treatment Effect Modification by Biomarkers Measured Pre- and Post-randomization in the Presence of Non-monotone Missingness,"In vaccine studies, investigators are often interested in studying effect
modifiers of clinical treatment efficacy by biomarker-based principal strata,
which is useful for selecting biomarker study endpoints for evaluating
treatments in new trials, exploring biological mechanisms of clinical treatment
efficacy, and studying mediators of clinical treatment efficacy. However, in
trials where participants may enter the study with prior exposure therefore
with variable baseline biomarker values, clinical treatment efficacy may depend
jointly on a biomarker measured at baseline and measured at a fixed time after
vaccination. Therefore, it is of interest to conduct a bivariate effect
modification analysis by biomarker-based principal strata and baseline
biomarker values. Previous methods allow this assessment if participants who
have the biomarker measured at the the fixed time point post randomization
would also have the biomarker measured at baseline. However, additional
complications in study design could happen in practice. For example, in the
Dengue correlates study, baseline biomarker values were only available from a
fraction of participants who have biomarkers measured post-randomization. How
to conduct the bivariate effect modification analysis in these studies remains
an open research question. In this article, we propose an estimated likelihood
method to utilize the sub-sampled baseline biomarker in the effect modification
analysis and illustrate our method with datasets from two dengue phase 3
vaccine efficacy trials.",1710.09923v1
2017-10-29,"If it ain't broke, don't fix it: Sparse metric repair","Many modern data-intensive computational problems either require, or benefit
from distance or similarity data that adhere to a metric. The algorithms run
faster or have better performance guarantees. Unfortunately, in real
applications, the data are messy and values are noisy. The distances between
the data points are far from satisfying a metric. Indeed, there are a number of
different algorithms for finding the closest set of distances to the given ones
that also satisfy a metric (sometimes with the extra condition of being
Euclidean). These algorithms can have unintended consequences, they can change
a large number of the original data points, and alter many other features of
the data.
  The goal of sparse metric repair is to make as few changes as possible to the
original data set or underlying distances so as to ensure the resulting
distances satisfy the properties of a metric. In other words, we seek to
minimize the sparsity (or the $\ell_0$ ""norm"") of the changes we make to the
distances subject to the new distances satisfying a metric. We give three
different combinatorial algorithms to repair a metric sparsely. In one setting
the algorithm is guaranteed to return the sparsest solution and in the other
settings, the algorithms repair the metric. Without prior information, the
algorithms run in time proportional to the cube of the number of input data
points and, with prior information we can reduce the running time considerably.",1710.10655v1
2017-12-06,Monitoring the orientation of rare-earth-doped nanorods for flow shear tomography,"Rare-earth phosphors exhibit unique luminescence polarization features
originating from the anisotropic symmetry of the emitter ion's chemical
environment. However, to take advantage of this peculiar property, it is
necessary to control and measure the ensemble orientation of the host particles
with a high degree of precision. Here, we show a methodology to obtain the
photoluminescence polarization of Eu-doped LaPO4 nano rods assembled in an
electrically modulated liquid-crystalline phase. We measure Eu3+ emission
spectra for the three main optimal configurations ({\sigma}, {\pi} and
{\alpha}, depending on the direction of observation and the polarization axes)
and use them as a reference for the nano rod orientation analysis. Based on the
fact that flowing nano rods tend to orient along the shear strain profile, we
use this orientation analysis to measure the local shear rate in a flowing
liquid. The potential of this approach is then demonstrated through tomographic
imaging of the shear rate distribution in a microfluidic system.",1712.02191v1
2017-12-08,Shrewd Selection Speeds Surfing: Use Smart EXP3!,"In this paper, we explore the use of multi-armed bandit online learning
techniques to solve distributed resource selection problems. As an example, we
focus on the problem of network selection. Mobile devices often have several
wireless networks at their disposal. While choosing the right network is vital
for good performance, a decentralized solution remains a challenge. The
impressive theoretical properties of multi-armed bandit algorithms, like EXP3,
suggest that it should work well for this type of problem. Yet, its real-word
performance lags far behind. The main reasons are the hidden cost of switching
networks and its slow rate of convergence. We propose Smart EXP3, a novel
bandit-style algorithm that (a) retains the good theoretical properties of
EXP3, (b) bounds the number of switches, and (c) yields significantly better
performance in practice. We evaluate Smart EXP3 using simulations, controlled
experiments, and real-world experiments. Results show that it stabilizes at the
optimal state, achieves fairness among devices and gracefully deals with
transient behaviors. In real world experiments, it can achieve 18% faster
download over alternate strategies. We conclude that multi-armed bandit
algorithms can play an important role in distributed resource selection
problems, when practical concerns, such as switching costs and convergence
time, are addressed.",1712.03038v3
2017-12-08,Qatar Exoplanet Survey: Qatar-6b -- a grazing transiting hot Jupiter,"We report the discovery of Qatar-6b, a new transiting planet identified by
the Qatar Exoplanet Survey (QES). The planet orbits a relatively bright
(V=11.44), early-K main-sequence star at an orbital period of P~3.506 days. An
SED fit to available multi-band photometry, ranging from the near-UV to the
mid-IR, yields a distance of d = 101 +/- 6 pc to the system. From a global fit
to follow-up photometric and spectroscopic observations, we calculate the mass
and radius of the planet to be Mp = 0.67 +/- 0.07 Mjup and Rp = 1.06 +/- 0.07
Rjup, respectively. We use multi-color photometric light curves to show that
the transit is grazing, making Qatar-6b one of the few exoplanets known in a
grazing transit configuration. It adds to the short list of targets that offer
the best opportunity to look for additional bodies in the host planetary system
through variations in the transit impact factor and duration.",1712.03216v1
2018-01-25,"Generating survival times using Cox proportional hazards models with cyclic time-varying covariates, with application to a multiple-dose monoclonal antibody clinical trial","In two harmonized efficacy studies to prevent HIV infection through multiple
infusions of the monoclonal antibody VRC01, a key objective is to evaluate
whether the serum concentration of VRC01, which changes cyclically over time
along with the infusion schedule, is associated with the rate of HIV infection.
Simulation studies are needed in the development of such survival models. In
this paper, we consider simulating event time data with a continuous
time-varying covariate whose values vary with time through multiple drug
administration cycles, and whose effect on survival changes differently before
and after a threshold within each cycle. The latter accommodates settings with
a zero-protection biomarker threshold above which the drug provides a varying
level of protection depending on the biomarker level, but below which the drug
provides no protection. We propose two simulation approaches: one based on
simulating survival data under a single-dose regimen first before data are
aggregated over multiple doses, and another based on simulating survival data
directly under a multiple-dose regimen. We generate time-to-event data
following a Cox proportional hazards model based on inverting the cumulative
hazard function and a log link function for relating the hazard function to the
covariates. The method's validity is assessed in two sets of simulation
experiments. The results indicate that the proposed procedures perform well in
producing data that conform to their cyclic nature and assumptions of the Cox
proportional hazards model.",1801.08248v1
2018-01-29,Band-pass superlattice magnetic tunnel junctions,"Significant scientific and technological progress in the field of spintronics
is based on trilayer magnetic tunnel junction devices which principally rely on
the physics of single barrier tunneling. While technologically relevant devices
have been prototyped, the physics of single barrier tunneling poses ultimate
limitations on the performance of magnetic tunnel junction devices. Here, we
propose a fresh route toward high performance magnetic tunnel junctions by
making electronic analogs of optical phenomena such as anti-reflections and
Fabry-P\`erot resonances. The devices we propose feature anti-reflection
enabled superlattice heterostructures sandwiched between the fixed and the free
ferromagnets of the magnetic tunnel junction structure. Our predictions are
based on the non-equilibrium Green's function spin transport formalism coupled
self-consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation. Owing
to the physics of bandpass spin filtering in the bandpass superlattice magnetic
tunnel junction device, we demonstrate an ultra-high boost in the tunnel
magneto-resistance (TMR$\approx5\times10^4\%$) and nearly 92% suppression of
spin transfer torque switching bias in comparison to a traditional trilayer
magnetic tunnel junction device. We rationalize improvised spin transfer torque
switching via analysis of the Slonczewski spin current transmission spectra.
The proof of concepts presented here can lead to next-generation spintronics
device design harvesting the rich physics of superlattice heterostructures and
exploiting spintronic analogs of optical phenomena.",1801.09409v2
2018-01-29,Theory of AC quantum transport with fully electrodynamic coupling,"With the continued scaling of microelectronic devices along with the growing
demand of high-speed wireless telecommunications technologies, there is
increasing need for high-frequency device modeling techniques that accurately
capture the quantum mechanical nature of charge transport in nanoscale devices
along with the dynamic fields that are generated. In an effort to fill this
gap, we develop a simulation methodology that self-consistently couples AC
non-equilibrium Green functions (NEGF) with the full solution of Maxwell's
equations in the frequency domain. We apply this technique to simulate
radiation from a quantum-confined, quarter-wave, monopole antenna where the
length $L$ is equal to one quarter of the wavelength, $\lambda_0$. Classically,
such an antenna would have a narrower, more directed radiation pattern compared
to one with $L \ll \lambda_0$, but we find that a quantum quarter-wave antenna
has no directivity gain compared to the classical solution. We observe that the
quantized wave function within the antenna significantly alter the charge and
current density distribution along the length of the wire, which in turn
modifies the far-field radiation pattern from the antenna. These results show
that high-frequency radiation from quantum systems can be markedly different
from classical expectations. Our method, therefore, will enable accurate
modeling of the next generation of high-speed nanoscale electronic devices.",1801.09611v1
2018-02-17,Design and Implementation of the Andromeda Proof Assistant,"Andromeda is an LCF-style proof assistant where the user builds derivable
judgments by writing code in a meta-level programming language AML. The only
trusted component of Andromeda is a minimalist nucleus (an implementation of
the inference rules of an object-level type theory), which controls
construction and decomposition of type-theoretic judgments.
  Since the nucleus does not perform complex tasks like equality checking
beyond syntactic equality, this responsibility is delegated to the user, who
implements one or more equality checking procedures in the meta-language. The
AML interpreter requests witnesses of equality from user code using the
mechanism of algebraic operations and handlers. Dynamic checks in the nucleus
guarantee that no invalid object-level derivations can be constructed. %even if
the AML code (or interpreter) is untrusted.
  To demonstrate the flexibility of this system structure, we implemented a
nucleus consisting of dependent type theory with equality reflection. Equality
reflection provides a very high level of expressiveness, as it allows the user
to add new judgmental equalities, but it also destroys desirable meta-theoretic
properties of type theory (such as decidability and strong normalization).
  The power of effects and handlers in AML is demonstrated by a standard
library that provides default algorithms for equality checking, computation of
normal forms, and implicit argument filling. Users can extend these new
algorithms by providing local ""hints"" or by completely replacing these
algorithms for particular developments. We demonstrate the resulting system by
showing how to axiomatize and compute with natural numbers, by axiomatizing the
untyped $\lambda$-calculus, and by implementing a simple automated system for
managing a universe of types.",1802.06217v1
2018-03-02,Broadband spectroscopy of thermodynamic magnetization fluctuations through a ferromagnetic spin-reorientation transition,"We use scanning optical magnetometry to study the broadband frequency spectra
of spontaneous magnetization fluctuations, or ""magnetization noise"", in an
archetypal ferromagnetic film that can be smoothly tuned through a spin
reorientation transition (SRT). The SRT is achieved by laterally varying the
magnetic anisotropy across an ultrathin Pt/Co/Pt trilayer, from the
perpendicular to in-plane direction, via graded Ar$^+$ irradiation. In regions
exhibiting perpendicular anisotropy, the power spectrum of the magnetization
noise, $S(\nu)$, exhibits a remarkably robust $\nu^{-3/2}$ power law over
frequencies $\nu$ from 1~kHz to 1~MHz. As the SRT region is traversed, however,
$S(\nu)$ spectra develop a steadily-increasing critical frequency, $\nu_0$,
below which the noise power is spectrally flat, indicating an evolving
low-frequency cutoff for magnetization fluctuations. The magnetization noise
depends strongly on applied in- and out-of-plane magnetic fields, revealing
local anisotropies and also a field-induced emergence of fluctuations in
otherwise stable ferromagnetic films. Finally, we demonstrate that higher-order
correlators can be computed from the noise. These results highlight broadband
spectroscopy of thermodynamic fluctuations as a powerful tool to characterize
the interplay between thermal and magnetic energy scales, and as a means of
characterizing phase transitions in ferromagnets.",1803.00962v1
2018-03-06,On Simple Back-Off in Unreliable Radio Networks,"In this paper, we study local and global broadcast in the dual graph model,
which describes communication in a radio network with both reliable and
unreliable links. Existing work proved that efficient solutions to these
problems are impossible in the dual graph model under standard assumptions. In
real networks, however, simple back-off strategies tend to perform well for
solving these basic communication tasks. We address this apparent paradox by
introducing a new set of constraints to the dual graph model that better
generalize the slow/fast fading behavior common in real networks. We prove that
in the context of these new constraints, simple back-off strategies now provide
efficient solutions to local and global broadcast in the dual graph model. We
also precisely characterize how this efficiency degrades as the new constraints
are reduced down to non-existent, and prove new lower bounds that establish
this degradation as near optimal for a large class of natural algorithms. We
conclude with a preliminary investigation of the performance of these
strategies when we include additional generality to the model. These results
provide theoretical foundations for the practical observation that simple
back-off algorithms tend to work well even amid the complicated link dynamics
of real radio networks.",1803.02216v3
2018-04-12,Connectivity in Random Annulus Graphs and the Geometric Block Model,"We provide new connectivity results for {\em vertex-random graphs} or {\em
random annulus graphs} which are significant generalizations of random
geometric graphs. Random geometric graphs (RGG) are one of the most basic
models of random graphs for spatial networks proposed by Gilbert in 1961,
shortly after the introduction of the Erd\H{o}s-R\'{en}yi random graphs. They
resemble social networks in many ways (e.g. by spontaneously creating cluster
of nodes with high modularity). The connectivity properties of RGG have been
studied since its introduction, and analyzing them has been significantly
harder than their Erd\H{o}s-R\'{en}yi counterparts due to correlated edge
formation.
  Our next contribution is in using the connectivity of random annulus graphs
to provide necessary and sufficient conditions for efficient recovery of
communities for {\em the geometric block model} (GBM). The GBM is a
probabilistic model for community detection defined over an RGG in a similar
spirit as the popular {\em stochastic block model}, which is defined over an
Erd\H{o}s-R\'{en}yi random graph. The geometric block model inherits the
transitivity properties of RGGs and thus models communities better than a
stochastic block model. However, analyzing them requires fresh perspectives as
all prior tools fail due to correlation in edge formation. We provide a simple
and efficient algorithm that can recover communities in GBM exactly with high
probability in the regime of connectivity.",1804.05013v3
2018-04-19,Equilibrium magnetization of a quasispherical cluster of single-domain particles,"Equilibrium magnetization curve of a rigid finite-size spherical cluster of
single-domain particles is investigated both numerically and analytically. The
spatial distribution of particles within the cluster is random. Dipole-dipole
interactions between particles are taken into account. The particles are
monodisperse. It is shown, using the stochastic Landau-Lifshitz-Gilbert
equation that the magnetization of such clusters is generally lower than
predicted by the classical Langevin model. In a broad range of dipolar coupling
parameters and particle volume fractions, the cluster magnetization in the weak
field limit can be successfully described by the modified mean-field theory,
which was originally proposed for the description of concentrated ferrofluids.
In moderate and strong fields, the theory overestimates the cluster
magnetization. However, predictions of the theory can be improved by adjusting
the corresponding mean-field parameter. If magnetic anisotropy of particles is
additionally taken into account and if the distribution of the particles' easy
axes is random and uniform, then the cluster equilibrium response is even
weaker. The decrease of the magnetization with increasing anisotropy constant
is more pronounced at large applied fields. The phenomenological generalization
of the modified mean-field theory, that correctly describes this effect for
small coupling parameters, is proposed.",1804.07196v2
2018-05-28,Starbug fibre positioning robots: performance and reliability enhancements,"Starbugs are miniature piezoelectric walking robots that can be operated in
parallel to position many payloads like optical fibers across a telescopes
focal plane. They consist of two concentric piezoelectric ceramic tubes that
walk with micron step size. In addition to individual optical fibers, Starbugs
have moved a payload of 0.75kg at several millimeters per second. The
Australian Astronomical Observatory previously developed prototype devices and
tested them in the laboratory. Now we are optimizing the Starbug design for
production and deployment in the TAIPAN instrument, which will be capable of
configuring 300 optical fibers over a six degree field-of-view on the UK
Schmidt Telescope within a few minutes. The TAIPAN instrument will demonstrate
the technology and capability for MANIFEST (Many Instrument Fiber-System)
proposed for the Giant Magellan Telescope. Design is addressing: connector
density and voltage limitations, mechanical reliability and construction
repeatability, field plate residues and scratching, metrology stability, and
facilitation of improved motion in all aspects of the design for later
evaluation. Here we present the new design features of the AAO TAIPAN Starbug.",1805.10761v1
2018-06-14,Resolving interfacial charge transfer in titanate superlattices using resonant X-ray reflectometry,"Charge transfer in oxide heterostructures can be tuned to promote emergent
interfacial states, and accordingly, has been the subject of intense study in
recent years. However, accessing the physics at these interfaces, which are
often buried deep below the sample surface, remains difficult. Addressing this
challenge requires techniques capable of measuring the local electronic
structure with high-resolution depth dependence. Here, we have used
linearly-polarized resonant X-ray reflectometry (RXR) as a means to visualize
charge transfer in oxide superlattices with atomic layer precision. From our
RXR measurements, we extract valence depth profiles of SmTiO$_3$
(SmTO)/SrTiO$_3$ (STO) heterostructures with STO quantum wells varying in
thickness from 5 SrO planes down to a single, atomically thin SrO plane. At the
polar-nonpolar SmTO/STO interface, an electrostatic discontinuity leads to
approximately half an electron per areal unit cell transferred from the
interfacial SmO layer into the neighboring STO quantum well. We observe this
charge transfer as a suppression of the t$_{2g}$ absorption peaks that
minimizes contrast with the neighboring SmTO layers at those energies and leads
to a pronounced absence of superlattice peaks in the reflectivity data. Our
results demonstrate the sensitivity of RXR to electronic reconstruction at the
atomic scale, and establish RXR as a powerful means of characterizing charge
transfer at buried oxide interfaces.",1806.05733v1
2018-06-18,Formation Timescales for High-Mass X-ray Binaries in M33,"We have identified 55 candidate high-mass X-ray binaries (HMXBs) in M33 using
available archival {\it HST} and {\it Chandra} imaging to find blue stars
associated with X-ray positions. We use the {\it HST} photometric data to model
the color-magnitude diagrams in the vicinity of each candidate HMXB to measure
a resolved recent star formation history (SFH), and thus a formation timescale,
or age for the source. Taken together, the SFHs for all candidate HMXBs in M33
yield an age distribution that suggests preferred formation timescales for
HMXBs in M33 of $<$ 5 Myr and $\sim$ 40 Myr after the initial star formation
episode. The population at 40 Myr is seen in other Local Group galaxies, and
can be attributed to a peak in formation efficiency of HMXBs with neutron stars
as compact objects and B star secondary companions. This timescale is preferred
as neutron stars should form in abundance from $\sim$ 8 M$_{\odot}$
core-collapse progenitors on these timescales, and B stars are shown
observationally to be most actively losing mass around this time. The young
population at $<$ 5 Myr has not be observed in other Local Group HMXB
population studies, but may be attributed to a population of very massive
progenitors forming black holes very early on. We discuss these results in the
context of massive binary evolution, and the implications for compact object
binaries and gravitational wave sources.",1806.06863v1
2018-06-24,Nanoscopic time crystal obtained by nonergodic spin dynamics,"We study the far-from-equilibrium properties of quenched magnetic nanoscopic
classical spin systems. In particular, we focus on the interplay between
lattice vibrations and magnetic frustrations induced by surface effects typical
of an antiferromagnet. We use a combination of Monte Carlo simulations and
explore the dynamical behaviours by solving the stochastic
Landau-Lifshitz-Gilbert equation at finite temperature. The Monte Carlo
approach treats both the ionic degrees of freedom and spin variables on the
same footing, via an extended Lennard-Jones Hamiltonian with a spin-lattice
coupling. The zero temperature phase diagram of the finite size nanoscopic
systems with respect to the range of the Heisenberg interaction and the
Lennard-Jones coupling constant shows two main structures with non-trivial
magnetisation triggered by antiferromagnetism: a simple cubic and a
body-centred cubic. At non zero temperature, the competition between spins and
the ionic vibrations considerably affects the magnetization of the system.
Exploring the dynamics reveals a non-trivial structural induced behaviour in
the spin relaxation with a concomitant memory of the initially applied
ferromagnetic quench. We report the observation of a non-trivial dynamical
scenario, obtained after a ferromagnetic magnetic quench at low temperature.
Furthermore, we observe long-lived non-thermal states which could open new
avenues for nano-technology.",1806.09130v4
2018-06-29,The warm Neptunes around HD 106315 have low stellar obliquities,"We present the obliquity of the warm Neptune HD 106315c measured via a series
of spectroscopic transit observations. HD 106315c is a 4.4 REarth warm Neptune
orbiting a moderately rotating late F-star with a period of 21.05 days. HD
106315 also hosts a 2.5 REarth super-Earth on a 9.55 day orbit. Our Doppler
tomographic analyses of four transits observed by the Magellan/MIKE, HARPS, and
TRES facilities find HD 106315c to be in a low stellar obliquity orbit,
consistent with being well aligned with the spin axis of the host star at
lambda = -10 +3.6/-3.8 deg. We suggest, via dynamical N-body simulations, that
the two planets in the system must be co-planar, and thus are both well aligned
with the host star. HD 106315 is only the fourth warm Neptune system with
obliquities measured. All warm Neptune systems have been found in well aligned
geometries, consistent with the interpretation that these systems are formed
in-situ in the inner protoplanetary disk, and also consistent with the majority
of Kepler multi-planet systems that are in low obliquity orbits. With a transit
depth of 1.02 mmag, HD 106315c is among the smallest planets to have been
detected in transit spectroscopy, and we discuss its detection in the context
of TESS and the next generations of spectrographs.",1807.00024v1
2018-07-13,"BFORE: A CMB Balloon Payload to Measure Reionization, Neutrino Mass, and Cosmic Inflation","BFORE is a high-altitude ultra-long-duration balloon mission to map the
cosmic microwave background (CMB). During a 28-day mid-latitude flight launched
from Wanaka, New Zealand, the instrument will map half the sky to improve
measurements of the optical depth to reionization tau. This will break
parameter degeneracies needed to detect neutrino mass. BFORE will also hunt for
the gravitational wave B-mode signal, and map Galactic dust foregrounds. The
mission will be the first near-space use of TES/mSQUID multichroic detectors
(150/217 GHz and 280/353 GHz bands) with low-power readout electronics.",1807.05215v1
2018-07-19,Magnetization nutation induced by surface effects in nanomagnets,"We investigate the magnetization dynamics of ferromagnetic nanoparticles in
the atomistic approach taking account of surface anisotropy and the spin
misalignment it causes. We demonstrate that such inhomogeneous spin
configurations induce nutation in the dynamics of the particle's magnetization.
More precisely, in addition to the ordinary precessional motion with frequency
$f_{p}\sim10\,{\rm GHz}$, we find that the dynamics of the net magnetic moment
exhibits two more resonance peaks with frequencies $f_{c}$ and $f_{n}$ which
are higher than the frequency $f_{p} : f_{c}=4\times f_{p}\sim40\,{\rm GHz}$ is
related with the oscillations of the particle's magnetic moment between the
minima of the effective potential induced by weak surface anisotropy. On the
other hand, the much higher frequency $f_{n}\sim1\,{\rm THz}$ is attributed to
the magnetization fluctuations at the atomic level driven by exchange
interaction. We have compared our results on nutation induced by surface
effects with those rendered by the macroscopic approach based on the
Landau-Lifshitz-Gilbert equation augmented by an inertial term (proportional to
the second-order time derivative of the macroscopic moment) with a
phenomenological coefficient. The good agreement between the two models have
allowed us to estimate the latter coefficient in terms of the atomistic
parameters such as the surface anisotropy constant. We have thus proposed a new
origin for the magnetization nutations as being induced by surface effects and
have interpreted the corresponding resonance peaks and their frequencies.",1807.07392v1
2018-07-19,Unsupervised Metric Learning in Presence of Missing Data,"For many machine learning tasks, the input data lie on a low-dimensional
manifold embedded in a high dimensional space and, because of this
high-dimensional structure, most algorithms are inefficient. The typical
solution is to reduce the dimension of the input data using standard dimension
reduction algorithms such as ISOMAP, LAPLACIAN EIGENMAPS or LLES. This
approach, however, does not always work in practice as these algorithms require
that we have somewhat ideal data. Unfortunately, most data sets either have
missing entries or unacceptably noisy values. That is, real data are far from
ideal and we cannot use these algorithms directly. In this paper, we focus on
the case when we have missing data. Some techniques, such as matrix completion,
can be used to fill in missing data but these methods do not capture the
non-linear structure of the manifold. Here, we present a new algorithm
MR-MISSING that extends these previous algorithms and can be used to compute
low dimensional representation on data sets with missing entries. We
demonstrate the effectiveness of our algorithm by running three different
experiments. We visually verify the effectiveness of our algorithm on synthetic
manifolds, we numerically compare our projections against those computed by
first filling in data using nlPCA and mDRUR on the MNIST data set, and we also
show that we can do classification on MNIST with missing data. We also provide
a theoretical guarantee for MR-MISSING under some simplifying assumptions.",1807.07610v3
2018-08-09,Four new eclipsing mid M-dwarf systems from the New Luyten Two Tenths catalog,"Using data from the MEarth-North and MEarth-South transit surveys, we present
the detection of eclipses in four mid M-dwarf systems: LP 107-25, LP 261-75, LP
796-24, and LP 991-15. Combining the MEarth photometry with spectroscopic
follow-up observations, we show that LP 107-25 and LP 796-24 are short-period
(1.388 and 0.523 day, respectively) eclipsing binaries in triple-lined systems
with substantial third light contamination from distant companions. LP 261-75
is a short-period (1.882 day) single-lined system consisting of a mid M-dwarf
eclipsed by a probable brown dwarf secondary, with another distant visual brown
dwarf companion. LP 991-15 is a long-period (29.3 day) double-lined eclipsing
binary on an eccentric orbit with a geometry which produces only primary
eclipses. A spectroscopic orbit is given for LP 991-15, and initial orbits for
LP 107-25 and LP 261-75.",1808.03243v1
2018-08-14,"Addressing Johnson graphs, complete multipartite graphs, odd cycles and other graphs","Graham and Pollak showed that the vertices of any graph $G$ can be addressed
with $N$-tuples of three symbols, such that the distance between any two
vertices may be easily determined from their addresses. An addressing is
optimal if its length $N$ is minimum possible.
  In this paper, we determine an addressing of length $k(n-k)$ for the Johnson
graphs $J(n,k)$ and we show that our addressing is optimal when $k=1$ or when
$k=2, n=4,5,6$, but not when $n=6$ and $k=3$. We study the addressing problem
as well as a variation of it in which the alphabet used has more than three
symbols, for other graphs such as complete multipartite graphs and odd cycles.
We also present computations describing the distribution of the minimum length
of addressings for connected graphs with up to $10$ vertices. Motivated by
these computations we settle a problem of Graham, showing that most graphs on
$n$ vertices have an addressing of length at most $n-(2-o(1))\log_2 n$.",1808.04757v2
2018-09-26,On Bioelectric Algorithms: A Novel Application of Theoretical Computer Science to Core Problems in Developmental Biology,"Cellular bioelectricity describes the biological phenomenon in which cells in
living tissue generate and maintain patterns of voltage gradients induced by
differing concentrations of charged ions. A growing body of research suggests
that bioelectric patterns represent an ancient system that plays a key role in
guiding many important developmental processes including tissue regeneration,
tumor suppression, and embryogenesis. Understanding the relationship between
high-level bioelectric patterns and low-level biochemical processes might also
enable powerful new forms of synthetic biology. A key open question in this
area is understanding how a collection of cells, interacting with each other
and the extracellular environment only through simple ligand bindings and ion
fluxes, can compute non-trivial patterns and perform non-trivial information
processing tasks. The standard approach to this question is to model a given
bioelectrical network as a system of differential equations and then explore
its behavior using simulation techniques. In this paper, we propose applying a
computational approach. In more detail, we present the cellular bioelectric
model (CBM), a new computational model that captures the primary capabilities
and constraints of bioelectric interactions between cells and their
environment. We use this model to investigate several important topics in
cellular bioelectricity, including symmetry breaking and information
processing. Among other results, we describe and analyze a basic bioelectric
strategy the efficiently stabilizes arbitrary cell networks into maximal
independent sets (a structure known to play a role in the nervous system
development of flys), and prove cells in our model are Turing complete in their
ability to process information encoded in their initial voltage potential.",1809.10046v1
2018-10-02,Floquet engineering of classical systems,"We develop the Floquet-Magnus expansion for a classical equation of motion
under a periodic drive that is applicable to both isolated and open systems.
For classical systems, known approaches based on the Floquet theorem fail due
to the nonlinearity and the stochasticity of their equations of motion (EOMs)
in contrast to quantum ones. Here, employing their master equation, we
successfully extend the Floquet methodology to classical EOMs to obtain their
Floquet-Magnus expansions, thereby overcoming this difficulty. Our method has a
wide range of application from classical to quantum as long as they are
described by differential equations including the Langevin equation, the
Gross-Pitaevskii equation, and the time-dependent Ginzburg-Landau equation. By
analytically evaluating the higher-order terms of the Floquet-Magnus expansion,
we find that it is, at least asymptotically, convergent and well approximates
the relaxation to their prethermal or non-equilibrium steady states. To support
these analytical findings, we numerically analyze two examples: (i) the Kapitza
pendulum with friction and (ii) laser-driven magnets described by the
stochastic Landau-Lifshitz-Gilbert equation. In both cases, the effective EOMs
obtained from their Floquet-Magnus expansions correctly reproduce their exact
time evolution for a long time up to their non-equilibrium steady states. In
the example of driven magnets, we demonstrate the controlled generations of a
macroscopic magnetization and a spin chirality by laser and discuss possible
applications to spintronics.",1810.01103v2
2018-10-02,Geodesic motion on the groups of diffeomorphisms with $H^1$ metric as geometric generalised Lagrangian mean theory,"Generalized Lagrangian mean theories are used to analyze the interactions
between mean flows and fluctuations, where the decomposition is based on a
Lagrangian description of the flow. A systematic geometric framework was
recently developed by Gilbert and Vanneste (J. Fluid Mech., 2018) who cast the
decomposition in terms of intrinsic operations on the group of volume
preserving diffeomorphism or on the full diffeomorphism group. In this setting,
the mean of an ensemble of maps can be defined as the Riemannian center of mass
on either of these groups. We apply this decomposition in the context of
Lagrangian averaging where equations of motion for the mean flow arise via a
variational principle from a mean Lagrangian, obtained from the kinetic energy
Lagrangian of ideal fluid flow via a small amplitude expansion for the
fluctuations.
  We show that the Euler-$\alpha$ equations arise as Lagrangian averaged Euler
equations when using the $L^2$-geodesic mean on the volume preserving
diffeomorphism group of a manifold without boundaries, imposing a `Taylor
hypothesis', which states that first order fluctuations are transported as a
vector field by the mean flow, and assuming that fluctuations are statistically
isotropic. Similarly, the EPDiff equations arise as the Lagrangian averaged
Burgers' equations using the same argument on the full diffeomorphism group.
These results generalize an earlier observation by Oliver (Proc. R. Soc. A,
2017) to manifolds in geometrically fully intrinsic terms.",1810.01377v1
2018-10-07,Training Convolutional Neural Networks and Compressed Sensing End-to-End for Microscopy Cell Detection,"Automated cell detection and localization from microscopy images are
significant tasks in biomedical research and clinical practice. In this paper,
we design a new cell detection and localization algorithm that combines deep
convolutional neural network (CNN) and compressed sensing (CS) or sparse coding
(SC) for end-to-end training. We also derive, for the first time, a
backpropagation rule, which is applicable to train any algorithm that
implements a sparse code recovery layer. The key observation behind our
algorithm is that cell detection task is a point object detection task in
computer vision, where the cell centers (i.e., point objects) occupy only a
tiny fraction of the total number of pixels in an image. Thus, we can apply
compressed sensing (or, equivalently sparse coding) to compactly represent a
variable number of cells in a projected space. Then, CNN regresses this
compressed vector from the input microscopy image. Thanks to the SC/CS recovery
algorithm (L1 optimization) that can recover sparse cell locations from the
output of CNN. We train this entire processing pipeline end-to-end and
demonstrate that end-to-end training provides accuracy improvements over a
training paradigm that treats CNN and CS-recovery layers separately. Our
algorithm design also takes into account a form of ensemble average of trained
models naturally to further boost accuracy of cell detection. We have validated
our algorithm on benchmark datasets and achieved excellent performances.",1810.03075v1
2018-11-16,Asymmetric Drift in the Andromeda Galaxy (M31) as a Function of Stellar Age,"We analyze the kinematics of Andromeda's disk as a function of stellar age by
using photometry from the Panchromatic Hubble Andromeda Treasury (PHAT) survey
and spectroscopy from the Spectroscopic and Photometric Landscape of
Andromeda's Stellar Halo (SPLASH) survey. We use HI 21-cm and CO ($\rm J=1
\rightarrow 0$) data to examine the difference between the deprojected rotation
velocity of the gas and that of the stars. We divide the stars into four
stellar age bins, from shortest lived to longest lived: massive main sequence
stars (0.03 Gyr), more luminous intermediate mass asymptotic giant branch (AGB)
stars (0.4 Gyr), less luminous intermediate mass AGB stars (2 Gyr), and low
mass red giant branch stars (4 Gyr). There is a clear correlation between the
offset of the stellar and the gas rotation velocity, or the asymmetric drift:
the longer lived populations lag farther behind the gas than short lived
populations. We also examine possible causes of the substructure in the
rotation curves and find that the most significant cause of scatter in the
rotation curves comes from the tilted ring model being an imperfect way to
account for the multiple warps in Andromeda's disk.",1811.07037v2
2018-11-21,"Exploring interfacial exchange coupling and sublattice effect in heavy metal/ferrimagnetic insulator heterostructures using Hall measurements, x-ray magnetic circular dichroism, and neutron reflectometry","We use temperature-dependent Hall measurements to identify contributions of
spin Hall, magnetic proximity, and sublattice effects to the anomalous Hall
signal in heavy metal/ferrimagnetic insulator heterostructures with
perpendicular magnetic anisotropy. This approach enables detection of both the
magnetic proximity effect onset temperature and the magnetization compensation
temperature and provides essential information regarding the interfacial
exchange coupling. Onset of a magnetic proximity effect yields a local extremum
in the temperature-dependent anomalous Hall signal, which occurs at higher
temperature as magnetic insulator thickness increases. This magnetic proximity
effect onset occurs at much higher temperature in Pt than W. The magnetization
compensation point is identified by a sharp anomalous Hall sign change and
divergent coercive field. We directly probe the magnetic proximity effect using
x-ray magnetic circular dichroism and polarized neutron reflectometry, which
reveal an antiferromagnetic coupling between W and the magnetic insulator.
Finally, we summarize the exchange-coupling configurations and the anomalous
Hall-effect sign of the magnetized heavy metal in various heavy metal/magnetic
insulator heterostructures.",1811.08574v2
2018-12-13,Qatar Exoplanet Survey: Qatar-7b -- A Very Hot Jupiter Orbiting a Metal Rich F-Star,"We present the discovery of Qatar-7b --- a very hot and inflated giant gas
planet orbiting close its parent star. The host star is a relatively massive
main sequence F-star with mass and radius Mstar = 1.41 +/- 0.03 Msun and Rstar
= 1.56 +/- 0.02 Rsun, respectively, at a distance d = 726 +/- 26 pc, and an
estimated age ~1 Gyr. With its orbital period of P = 2.032 days the planet is
located less than 5 stellar radii from its host star and is heated to a high
temperature Teq ~ 2100 K. From a global solution to the available photometric
and radial velocity observations, we calculate the mass and radius of the
planet to be Mpl = 1.88 +/- 0.25 Mjup and Rpl = 1.70 +/- 0.03 Rjup,
respectively. The planet radius and equilibrium temperature put Qatar-7b in the
top 6% of the hottest and largest known exoplanets. With its large radius and
high temperature Qatar-7b is a valuable addition to the short list of targets
that offer the best opportunity for studying their atmospheres through
transmission spectroscopy.",1812.05601v1
2019-01-02,Leader Election in Well-Connected Graphs,"In this paper, we look at the problem of randomized leader election in
synchronous distributed networks with a special focus on the message
complexity. We provide an algorithm that solves the implicit version of leader
election (where non-leader nodes need not be aware of the identity of the
leader) in any general network with $O(\sqrt{n} \log^{7/2} n \cdot t_{mix})$
messages and in $O(t_{mix}\log^2 n)$ time, where $n$ is the number of nodes and
$t_{mix}$ refers to the mixing time of a random walk in the network graph $G$.
For several classes of well-connected networks (that have a large conductance
or alternatively small mixing times e.g. expanders, hypercubes, etc), the above
result implies extremely efficient (sublinear running time and messages) leader
election algorithms. Correspondingly, we show that any substantial improvement
is not possible over our algorithm, by presenting an almost matching lower
bound for randomized leader election. We show that
$\Omega(\sqrt{n}/\phi^{3/4})$ messages are needed for any leader election
algorithm that succeeds with probability at least $1-o(1)$, where $\phi$ refers
to the conductance of a graph. To the best of our knowledge, this is the first
work that shows a dependence between the time and message complexity to solve
leader election and the connectivity of the graph $G$, which is often
characterized by the graph's conductance $\phi$. Apart from the $\Omega(m)$
bound in [Kutten et al., J.ACM 2015] (where $m$ denotes the number of edges of
the graph), this work also provides one of the first non-trivial lower bounds
for leader election in general networks.",1901.00342v1
2019-01-23,Cooperation Speeds Surfing: Use Co-Bandit!,"In this paper, we explore the benefit of cooperation in adversarial bandit
settings. As a motivating example, we consider the problem of wireless network
selection. Mobile devices are often required to choose the right network to
associate with for optimal performance, which is non-trivial. The excellent
theoretical properties of EXP3, a leading multi-armed bandit algorithm, suggest
that it should work well for this type of problem. Yet, it performs poorly in
practice. A major limitation is its slow rate of stabilization. Bandit-style
algorithms perform better when global knowledge is available, i.e., when
devices receive feedback about all networks after each selection. But,
unfortunately, communicating full information to all devices is expensive.
Therefore, we address the question of how much information is adequate to
achieve better performance. We propose Co-Bandit, a novel cooperative bandit
approach, that allows devices to occasionally share their observations and
forward feedback received from neighbors; hence, feedback may be received with
a delay. Devices perform network selection based on their own observation and
feedback from neighbors. As such, they speed up each other's rate of learning.
We prove that Co-Bandit is regret-minimizing and retains the convergence
property of multiplicative weight update algorithms with full information.
Through simulation, we show that a very small amount of information, even with
a delay, is adequate to nudge each other to select the right network and yield
significantly faster stabilization at the optimal state (about 630x faster than
EXP3).",1901.07768v1
2019-01-31,Still out there: Modeling and Identifying Russian Troll Accounts on Twitter,"There is evidence that Russia's Internet Research Agency attempted to
interfere with the 2016 U.S. election by running fake accounts on Twitter -
often referred to as ""Russian trolls"". In this work, we: 1) develop machine
learning models that predict whether a Twitter account is a Russian troll
within a set of 170K control accounts; and, 2) demonstrate that it is possible
to use this model to find active accounts on Twitter still likely acting on
behalf of the Russian state. Using both behavioral and linguistic features, we
show that it is possible to distinguish between a troll and a non-troll with a
precision of 78.5% and an AUC of 98.9%, under cross-validation. Applying the
model to out-of-sample accounts still active today, we find that up to 2.6% of
top journalists' mentions are occupied by Russian trolls. These findings imply
that the Russian trolls are very likely still active today. Additional analysis
shows that they are not merely software-controlled bots, and manage their
online identities in various complex ways. Finally, we argue that if it is
possible to discover these accounts using externally - accessible data, then
the platforms - with access to a variety of private internal signals - should
succeed at similar or better rates.",1901.11162v1
2019-02-11,Efficient Randomized Test-And-Set Implementations,"We study randomized test-and-set (TAS) implementations from registers in the
asynchronous shared memory model with n processes. We introduce the problem of
group election, a natural variant of leader election, and propose a framework
for the implementation of TAS objects from group election objects. We then
present two group election algorithms, each yielding an efficient TAS
implementation. The first implementation has expected max-step complexity
$O(\log^\ast k)$ in the location-oblivious adversary model, and the second has
expected max-step complexity $O(\log\log k)$ against any read/write-oblivious
adversary, where $k\leq n$ is the contention. These algorithms improve the
previous upper bound by Alistarh and Aspnes [2] of $O(\log\log n)$ expected
max-step complexity in the oblivious adversary model. We also propose a
modification to a TAS algorithm by Alistarh, Attiya, Gilbert, Giurgiu, and
Guerraoui [5] for the strong adaptive adversary, which improves its space
complexity from super-linear to linear, while maintaining its $O(\log n)$
expected max-step complexity. We then describe how this algorithm can be
combined with any randomized TAS algorithm that has expected max-step
complexity $T(n)$ in a weaker adversary model, so that the resulting algorithm
has $O(\log n)$ expected max-step complexity against any strong adaptive
adversary and $O(T(n))$ in the weaker adversary model. Finally, we prove that
for any randomized 2-process TAS algorithm, there exists a schedule determined
by an oblivious adversary such that with probability at least $(1/4)^t$ one of
the processes needs at least t steps to finish its TAS operation. This
complements a lower bound by Attiya and Censor-Hillel [7] on a similar problem
for $n\geq 3$ processes.",1902.04002v1
2019-03-11,Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloys,"Shell ferromagnetism is a new functional property of certain Heusler alloys
which has been recently observed in
$\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$. We report the results of a
comparative study of the magnetic microstructure of bulk
$\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloys using
magnetometry, synchrotron x-ray diffraction, and magnetic small-angle neutron
scattering (SANS). By combining unpolarized and spin-polarized SANS (POLARIS)
we demonstrate that a number of important conclusions regarding the mesoscopic
spin structure can be made. In particular, the analysis of the magnetic neutron
data suggests that nanoprecipitates with an effective ferromagnetic component
form in an antiferromagnetic matrix on field annealing at $700 \, \mathrm{K}$.
These particles represent sources of perturbation, which seem to give rise to
magnetically disordered regions in the vicinity of the particle-matrix
interface. Analysis of the spin-flip SANS cross section via the computation of
the correlation function yields a value of $\sim 55 \, \mathrm{nm}$ for the
particle size and $\sim 20 \, \mathrm{nm}$ for the size of the spin-canted
region.",1903.04183v1
2019-03-14,"Low Field-size, Rate-Optimal Streaming Codes for Channels With Burst and Random Erasures","In this paper, we design erasure-correcting codes for channels with burst and
random erasures, when a strict decoding delay constraint is in place. We
consider the sliding-window-based packet erasure model proposed by Badr et al.,
where any time-window of width $w$ contains either up to $a$ random erasures or
an erasure burst of length at most $b$. One needs to recover any erased packet,
where erasures are as per the channel model, with a strict decoding delay
deadline of $\tau$ time slots. Presently existing rate-optimal constructions in
the literature require, in general, a field-size which grows exponential in
$\tau$, for a constant $\frac{a}{\tau}$. In this work, we present a new
rate-optimal code construction covering all channel and delay parameters, which
requires an $O(\tau^2)$ field-size. As a special case, when $(b-a)=1$, we have
a field-size linear in $\tau$. We also present three other constructions having
linear field-size, under certain constraints on channel and decoding delay
parameters. As a corollary, we obtain low field-size, rate-optimal
convolutional codes for any given column distance and column span. Simulations
indicate that the newly proposed streaming code constructions offer lower
packet-loss probabilities compared to existing schemes, for selected instances
of Gilbert-Elliott and Fritchman channels.",1903.06210v1
2019-03-21,Emergent topology and symmetry-breaking order in correlated quench dynamics,"Quenching a quantum system involves three basic ingredients: the initial
phase, the post-quench target phase, and the non-equilibrium dynamics which
carries the information of the former two. Here we propose a dynamical theory
to characterize both the topology and symmetry-breaking order in correlated
quantum system, through quenching the Haldane-Hubbard model from an initial
magnetic phase to topologically nontrivial regime. The equation of motion for
the complex pseudospin dynamics is obtained with the flow equation method, with
the pseudospin evolution shown to obey a microscopic
Landau-Lifshitz-Gilbert-Bloch equation. We find that the correlated quench
dynamics exhibit robust universal behaviors on the so-called band-inversion
surfaces (BISs), from which the nontrivial topology and magnetic order can be
extracted. In particular, the topology of the post-quench regime can be
characterized by an emergent dynamical topological pattern of quench dynamics
on BISs, which is robust against dephasing and heating induced by interactions;
the pre-quench symmetry-breaking orders is read out from a universal scaling
behavior of the quench dynamics emerging on the BIS, which is valid beyond the
mean-field regime. This work opens a way to characterize both the topology and
symmetry-breaking orders by correlated quench dynamics.",1903.09144v3
2019-03-22,Advanced Non-Destructive in Situ Characterization of Metals with the French Collaborating Research Group D2AM/BM02 Beamline at the European Synchrotron Radiation Facility,"The ability to non-destructively measure the structural properties of
devices, either in situ or operando, are now possible using an intense X-ray
synchrotron source combined with specialized equipment. This tool attracted
researchers, in particular metallurgists, to attempt more complex and ambitious
experiments aimed at answering unresolved questions in formation mechanisms,
phase transitions, and magnetism complex alloys for industrial applications. In
this paper, we introduce the diffraction diffusion anomale multi-longueur
d'onde (D2AM) beamline, a French collaborating research group (CRG) beamline at
the European Synchrotron Radiation Facility (ESRF), partially dedicated to in
situ X-ray scattering experiments. The design of the beamline combined with the
available equipment (two-dimensional fast photon counting detectors,
sophisticated high precision kappa diffractometer, a variety of sample
environments, continuous scanning for X-ray imaging, and specific software for
data analysis) has made the D2AM beamline a highly efficient tool for advanced,
in situ synchrotron characterization in materials science, e.g., single crystal
or polycrystalline materials, powders, liquids, thin films, or epitaxial
nanostructures. This paper gathers the main elements and equipment available at
the beamline and shows its potential and flexibility in performing a wide
variety of temporally, spatially, and energetically resolved X-ray synchrotron
scattering measurements in situ.",1903.09390v1
2019-03-31,Relaxation to equilibrium in models of classical spins with long-range interactions,"For a model long-range interacting system of classical Heisenberg spins, we
study how fluctuations, such as those arising from having a finite system size
or through interaction with the environment, affect the dynamical process of
relaxation to Boltzmann-Gibbs equilibrium. Under deterministic spin
precessional dynamics, we unveil the full range of quasistationary behavior
observed during relaxation to equilibrium, whereby the system is trapped in
nonequilibrium states for times that diverge with the system size. The
corresponding stochastic dynamics, modeling interaction with the environment
and constructed in the spirit of the stochastic Landau-Lifshitz-Gilbert
equation, however shows a fast relaxation to equilibrium on a size-independent
timescale and no signature of quasistationarity, provided the noise is strong
enough. Similar fast relaxation is also seen in Glauber Monte Carlo dynamics of
the model, thus establishing the ubiquity of what has been reported earlier in
particle dynamics (hence distinct from the spin dynamics considered here) of
long-range interacting systems, that quasistationarity observed in
deterministic dynamics is washed away by fluctuations induced through contact
with the environment.",1904.00432v2
2019-04-27,Blue-Light-Emitting Color Centers in High-Quality Hexagonal Boron Nitride,"Light emitters in wide band gap semiconductors are of great fundamental
interest and have potential as optically addressable qubits. Here we describe
the discovery of a new color center in high-quality hexagonal boron nitride
(h-BN) with a sharp emission line at 435 nm. The emitters are activated and
deactivated by electron beam irradiation and have spectral and temporal
characteristics consistent with atomic color centers weakly coupled to lattice
vibrations. The emitters are conspicuously absent from commercially available
h-BN and are only present in ultra-high-quality h-BN grown using a
high-pressure, high-temperature Ba-B-N flux/solvent, suggesting that these
emitters originate from impurities or related defects specific to this unique
synthetic route. Our results imply that the light emission is activated and
deactivated by electron beam manipulation of the charge state of an
impurity-defect complex.",1904.12107v6
2019-04-30,Realization of Ordered Magnetic Skyrmions in Thin Films at Ambient Conditions,"Magnetic skyrmions present interesting physics due to their topological
nature and hold significant promise for future information technologies. A key
barrier to realizing skyrmion devices has been stabilizing these spin
structures under ambient conditions. In this manuscript, we exploit the tunable
magnetic properties of amorphous Fe/Gd mulitlayers to realize skyrmion lattices
which are stable over a large temperature and magnetic field parameter space,
including room temperature and zero magnetic field. These hybrid skyrmions have
both Bloch-type and N\'eel-type character and are stabilized by dipolar
interactions rather than Dzyaloshinskii-Moriya interactions, which are
typically considered required for the generation of skyrmions. Small angle
neutron scattering (SANS) was used in combination with soft X-ray microscopy to
provide a unique, multi-scale probe of the local and long-range order of these
structures. These results identify a pathway to engineer controllable skyrmion
phases in thin film geometries which are stable at ambient conditions.",1904.13274v1
2019-05-16,Ultralow-loss domain wall motion driven by magnetocrystalline anisotropy gradient in antiferromagnetic nanowire,"Searching for new methods controlling antiferromagnetic (AFM) domain wall is
one of the most important issues for AFM spintronic device operation. In this
work, we study theoretically the domain wall motion of an AFM nanowire, driven
by the axial anisotropy gradient generated by external electric field, allowing
the electro control of AFM domain wall motion in the merit of ultra-low energy
loss. The domain wall velocity depending on the anisotropy gradient magnitude
and intrinsic material properties is simulated based on the
Landau-Lifshitz-Gilbert equation and also deduced using the energy dissipation
theorem. It is found that the domain wall moves at a nearly constant velocity
for small gradient, and accelerates for large gradient due to the enlarged
domain wall width. The domain wall mobility is independent of lattice dimension
and types of domain wall, while it is enhanced by the Dzyaloshinskii-Moriya
interaction. In addition, the physical mechanism for much faster AFM wall
dynamics than ferromagnetic wall dynamics is qualitatively explained. This work
unveils a promising strategy for controlling the AFM domain walls, benefiting
to future AFM spintronic applications.",1905.06695v2
2019-05-22,Constraining level densities using spectral data,"Several models of level densities exist and they often make simplified
assumptions regarding the overall behavior of the total level densities (LD)
and the intrinsic spin and parity distributions of the excited states.
Normally, such LD models are constrained only by the measured $D_0$, i.e. the
density of levels at the neutron separation energy of the compound nucleus
(target plus neutron), and the sometimes subjective extrapolation of discrete
levels. In this work we use microscopic Hartree-Fock-Bogoliubov (HFB) level
densities, which intrinsically provide more realistic spin and parity
distributions, and associate variations predicted by the HFB model with the
observed double-differential cross sections at low outgoing neutron energy,
region that is dominated by the LD input. With this approach we are able to
perform fits of the LD based on actual experimental data, constraining the
model and ensuring its consistency. This approach can be particularly useful in
extrapolating the LD to nuclei for which high-excited discrete levels and/or
values of $D_0$ are unknown. It also predicts inelastic gamma
(n,n$^{\prime}\gamma$) cross sections that in some cases can differ
significantly from more standard LD models such as Gilbert-Cameron.",1905.09194v1
2019-05-23,The Kepler Smear Campaign: Light curves for 102 Very Bright Stars,"We present the first data release of the Kepler Smear Campaign, using
collateral 'smear' data obtained in the Kepler four-year mission to reconstruct
light curves of 102 stars too bright to have been otherwise targeted. We
describe the pipeline developed to extract and calibrate these light curves,
and show that we attain photometric precision comparable to stars analyzed by
the standard pipeline in the nominal Kepler mission. In this paper, aside from
publishing the light curves of these stars, we focus on 66 red giants for which
we detect solar-like oscillations, characterizing 33 of these in detail with
spectroscopic chemical abundances and asteroseismic masses as benchmark stars.
We also classify the whole sample, finding nearly all to be variable, with
classical pulsations and binary effects. All source code, light curves, TRES
spectra, and asteroseismic and stellar parameters are publicly available as a
Kepler legacy sample.",1905.09831v1
2019-06-06,A Hot Saturn Near (but unassociated with) the Open Cluster NGC 1817,"We report on the discovery of a hot Saturn-sized planet (9.916 +/- 0.985
R_earth) around a late F star, EPIC 246865365, observed in Campaign 13 of the
K2 mission. We began studying this planet candidate because prior to the
release of Gaia DR2, the host star was thought to have been a member (> 90%
membership probability) of the approximately 1 Gyr open cluster NGC 1817 based
on its kinematics and photometric distance. We identify the host star (among
three stars within the K2 photometric aperture) using seeing-limited photometry
and rule out false positive scenarios using adaptive optics imaging and radial
velocity observations. We statistically validate EPIC 246865365b by calculating
a false positive probability rate of 0.01%. However, we also show using new
kinematic measurements provided by Gaia DR2 and our measured radial velocity of
the system that EPIC 246865365 is unassociated with the cluster NGC 1817.
Therefore, the long-running search for a giant transiting planet in an open
cluster remains fruitless. Finally, we note that our use of seeing-limited
photometry is a good demonstration of similar techniques that are already being
used to follow up TESS planet candidates, especially in crowded regions.",1906.02395v1
2019-06-12,Towards the nucleon hadronic tensor from lattice QCD,"We present the first calculation of the hadronic tensor on the lattice for
the nucleon. The hadronic tensor can be used to extract the structure functions
in deep inelastic scatterings and also provide information for the
neutrino-nucleon scattering which is crucial to the neutrino-nucleus scattering
experiments at low energies. The most challenging part in the calculation is to
solve an inverse problem. We have implemented and tested three algorithms using
mock data, showing that the Bayesian Reconstruction method has the best
resolution in extracting peak structures while the Backus-Gilbert and Maximum
Entropy methods are somewhat more stable for the flat spectral function.
Numerical results are presented for both the elastic case (clover fermions on
domain wall configuration with $m_\pi\sim$ 370 MeV and $a\sim$ 0.06 fm) and a
case (anisotropic clover lattice with $m_\pi\sim$ 380 MeV and $a_t\sim$ 0.035
fm) with large momentum transfer. For the former case, the reconstructed
Minkowski hadronic tensor gives precisely the vector charge which proves the
feasibility of the approach. While for the latter case, the nucleon resonances
and possibly shallow inelastic scattering contributions around $\nu=1$ GeV are
clearly observed but no information is obtained for higher excited states with
$\nu>2$ GeV. A check of the effective masses of $\rho$ meson with different
lattice setups indicates that, in order to reach higher energy transfers, using
lattices with smaller lattice spacings is essential.",1906.05312v1
2019-06-17,Non-equilibrium Green's Function and First Principle Approach to Modeling of Multiferroic Tunnel Junctions,"Recently, multiferroic tunnel junctions (MFTJs) have gained significant
spotlight in the literature due to its high tunneling electro-resistance
together with its non-volatility. In order to analyze such devices and to have
insightful understanding of its characteristics, there is a need for developing
a multi-physics modeling and simulation framework. The simulation framework
discussed in this paper is motivated by the scarcity of such multi-physics
studies in the literature. In this study, a theoretical analysis of MFTJs is
demonstrated using self-consistent analysis of spin-based non-equilibrium
Green's function (NEGF) method to estimate the tunneling current,
Landau-Khalatnikov (LK) equation to model the ferroelectric polarization
dynamics, together with landau-Lifshitz-Gilbert's (LLG) equations to capture
the magnetization dynamics. The spin-based NEGF method is equipped with a
magnetization dependent Hamiltonian that eases the modeling of the tunneling
electro-resistance (TER), tunneling magneto-resistance (TMR), and the
magnetoelectric effect (ME) in MFTJs. Moreover, we apply the first principle
calculations to estimate the screening lengths of the MFTJ electrodes that are
necessary for estimation of tunneling current. The simulation results of the
proposed framework are in good agreement with the experimental results.
Finally, a comprehensive analysis of TER and TMR of MFTJs and their dependence
on various device parameters is illustrated.",1906.06986v1
2019-06-27,Indications for Dzyaloshinskii-Moriya Interaction at the Pd/Fe Interface Studied by \textit{In Situ} Polarized Neutron Reflectometry,"Using \textit{in situ} polarized neutron reflectometry, the depth resolved
evolution of the magnetism and structure in a Pd/Fe/Pd trilayer thin-film is
measured during growth. The initial film structure of Pd/Fe shows a small
proximity induced magnetism in the underlayer and a magnetization in the Fe
layer of $\approx1.6$\,$\mu_{\text{B}}$ per Fe atom, less than the expected
bulk value of $2.2$\,$\mu_{\text{B}}$. Deposition of the Pd capping layer
initially follows an island-like growth mode with subsequent coalescence. With
increasing Pd deposition the Fe moment and the proximity-induced magnetism in
the Pd capping layer decrease. After final deposition of the Pd capping layer,
the magnetic profile is structurally and magnetically symmetric across the Fe
layer, with magnetism induced in Pd up to 0.92 \,nm from the interface.
Throughout the Pd deposition the Pd/Fe/Pd trilayer structure is becoming
increasingly symmetric, a fact which points to a Dzyaloshinskii-Moriya
interaction as a likely cause of the observed magnetic behavior.",1906.11532v1
2019-07-01,Robust Formation of Ultrasmall Room-Temperature Neél Skyrmions in Amorphous Ferrimagnets from Atomistic Simulations,"Ne\'el skyrmions originate from interfacial Dzyaloshinskii Moriya interaction
(DMI). Recent studies have explored using thin-film ferromagnets and
ferrimagnets to host Ne\'el skyrmions for spintronic applications. However, it
is unclear if ultrasmall (10 nm or less) skyrmions can ever be stabilized at
room temperature for practical use in high density parallel racetrack memories.
While thicker films can improve stability, DMI decays rapidly away from the
interface. As such, spins far away from the interface would experience
near-zero DMI, raising question on whether or not unrealistically large DMI is
needed to stabilize skyrmions, and whether skyrmions will also collapse away
from the interface. To address these questions, we have employed atomistic
stochastic Landau-Lifshitz-Gilbert simulations to investigate skyrmions in
amorphous ferrimagnetic GdCo. It is revealed that a significant reduction in
DMI below that of Pt is sufficient to stabilize ultrasmall skyrmions even in
films as thick as 15 nm. Moreover, skyrmions are found to retain a uniform
columnar shape across the film thickness despite the decaying DMI. Our results
show that increasing thickness and reducing DMI in GdCo can further reduce the
size of skyrmions at room temperature, which is crucial to improve the density
and energy efficiency in skyrmion based devices.",1907.00647v1
2019-07-03,Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors,"In the superconducting regime of FeTe$_{(1-x)}$Se$_x$, there exist two types
of vortices which are distinct by the presence or absence of zero energy states
in their core. To understand their origin, we examine the interplay of Zeeman
coupling and superconducting pairings in three-dimensional metals with band
inversion. Weak Zeeman fields are found to suppress the intra-orbital
spin-singlet pairing, known to localize the states at the ends of the vortices
on the surface. On the other hand, an orbital-triplet pairing is shown to be
stable against Zeeman interactions, but leads to delocalized zero-energy
Majorana modes which extend through the vortex. In contrast, the finite-energy
vortex modes remain localized at the vortex ends even when the pairing is of
orbital-triplet form. Phenomenologically, this manifests as an observed
disappearance of zero-bias peaks within the cores of topological vortices upon
increase of the applied magnetic field. The presence of magnetic impurities in
FeTe$_{(1-x)}$Se$_x$, which are attracted to the vortices, would lead to such
Zeeman-induced delocalization of Majorana modes in a fraction of vortices that
capture a large enough number of magnetic impurities. Our results provide an
explanation to the dichotomy between topological and non-topological vortices
recently observed in FeTe$_{(1-x)}$Se$_x$.",1907.02077v2
2019-07-10,Increasing Gender Diversity and Inclusion in Scientific Committees and Related Activities at STScI,"We present a new initiative by the Women in Astronomy Forum at Space
Telescope Science Institute (STScI) to increase gender diversity and inclusion
in STScI's scientific committees and the activities they generate. This
initiative offers new and uniform guidelines on binary gender representation
goals for each committee and recommendations on how to achieve them in a
homogeneous way, as well as metrics and tools to track progress towards defined
goals. While the new guidelines presented in the paper focus on binary gender
representation, they can be adapted and implemented to support all minority
groups. By creating diverse committees and making them aware of, and trained on
implicit bias, we expect to create a diverse outcome in the activities they
generate, which, in turn, will advance science further and faster.",1907.04880v1
2019-07-19,Sparse Recovery for Orthogonal Polynomial Transforms,"In this paper we consider the following sparse recovery problem. We have
query access to a vector $\vx \in \R^N$ such that $\vhx = \vF \vx$ is
$k$-sparse (or nearly $k$-sparse) for some orthogonal transform $\vF$. The goal
is to output an approximation (in an $\ell_2$ sense) to $\vhx$ in sublinear
time. This problem has been well-studied in the special case that $\vF$ is the
Discrete Fourier Transform (DFT), and a long line of work has resulted in
sparse Fast Fourier Transforms that run in time $O(k \cdot \mathrm{polylog}
N)$. However, for transforms $\vF$ other than the DFT (or closely related
transforms like the Discrete Cosine Transform), the question is much less
settled.
  In this paper we give sublinear-time algorithms---running in time $\poly(k
\log(N))$---for solving the sparse recovery problem for orthogonal transforms
$\vF$ that arise from orthogonal polynomials. More precisely, our algorithm
works for any $\vF$ that is an orthogonal polynomial transform derived from
Jacobi polynomials. The Jacobi polynomials are a large class of classical
orthogonal polynomials (and include Chebyshev and Legendre polynomials as
special cases), and show up extensively in applications like numerical analysis
and signal processing. One caveat of our work is that we require an assumption
on the sparsity structure of the sparse vector, although we note that vectors
with random support have this property with high probability.
  Our approach is to give a very general reduction from the $k$-sparse sparse
recovery problem to the $1$-sparse sparse recovery problem that holds for any
flat orthogonal polynomial transform; then we solve this one-sparse recovery
problem for transforms derived from Jacobi polynomials.",1907.08362v1
2019-08-28,Interplay of spin and mass superfluidity in antiferromagnetic spin-1 BEC and bicirculation vortices,"The paper investigates the coexistence and interplay of spin and mass
superfluidity in the antiferromagnetic spin-1 BEC. The hydrodynamical theory
describes the spin degree of freedom by the equations similar to the
Landau--Lifshitz--Gilbert theory for bipartite antiferromagnetic insulator. The
variables in the spin space are two subspins with absolute value $\hbar/2$,
which play the role of two sublattice spins in the antiferromagnetic
insulators. As well as in bipartite antiferromagnetic insulators, in the
antiferromagnetic spin-1 BEC there are two spin-wave modes, one is a gapless
Goldstone mode, another is gapped. The Landau criterion shows that in limit of
small total spin (two subspins are nearly antiparallel) instability of
supercurrents starts from the gapped mode. In the opposite limit of large total
spin (two subspins are nearly parallel) the gapless modes become unstable
earlier than the gapped one. Mass and spin supercurrents decay via phase slips,
when vortices cross streamlines of supercurrent. The vortices participating in
phase slips are nonsingular bicirculation vortices. They are characterized by
two topological charges, which are winding numbers describing circulations of
two angles around the vortex axis. The winding numbers can be half-integer. A
particular example of a half-integer vortex is a half-quantum vortex with the
superfluid velocity circulation $h/2m$. But the superfluid velocity circulation
is not a topological charge, and in general the quantum of this circulation can
be continuously tuned from 0 to $h/2m$.",1908.10633v2
2019-09-23,"The NASA Probe space mission concept, Cosmic Evolution Through UV Surveys (CETUS)","The mission concept, Cosmic Origins Through UV Surveys (CETUS) is an all-UV
space mission concept that was selected and funded by NASA for study in 2017.
The main capabilities of CETUS that even Hubble doesn't have are: (1)
wide-field (17.4'x17.4') imaging and spectroscopy of astronomical sources with
<0.5'' resolution; (2) spectral sensitivity to UV radiation at wavelengths as
short as 1000 {\AA}; (3) near-UV multi-object slit spectroscopy; and (4)
rapid-response UV spectroscopy and deep imaging of transients like GW 170817;
and (5) 23 times higher sensitivity to extended sources.
  The main purposes of this CETUS Final Report are to describe the CETUS
scientific program and to demonstrate the maturity of its instrumentation,
which forms the basis of its estimated cost. While there are similarities of
this Final Report to that submitted to NASA in March 2019 by the Goddard Space
Flight Center, there are important differences including the following. *
Science. The science case has been refreshed, deepened, and expanded as a
result of ideas and recommendations expressed in the Astro2020 science white
papers. * Instrumentation. Detailed investigations including a high-level error
budget for focus with implications for thermal management, target acquisition
in the MOS micro-shutter array, contamination control have been carried out. *
Mission Design. The spacecraft and mission operations concepts as developed by
NGIS Gilbert (formerly Orbital ATK) rather than the output of Goddard's Mission
Design Lab have been adopted.. * Technology. Technology maturation plans have
been updated.",1909.10437v1
2019-09-25,"Towards an improved understanding of molecular evolution: the relative roles of selection, drift, and everything in between","A major goal of molecular evolutionary biology is to identify loci or regions
of the genome under selection versus those evolving in a neutral manner.
Correct identification allows accurate inference of the evolutionary process
and thus comprehension of historical and contemporary processes driving
phenotypic change and adaptation. A fundamental difficulty lies in
distinguishing sites targeted by selection from both sites linked to these
targets and sites fully independent of selection. These three categories of
sites necessitate attention in light of the debate over the relative importance
of selection versus neutrality and the neutral theory. Modern genomic insights
have proved that complex processes such as linkage, demography, and biased gene
conversion complicate our understanding of the role of neutral versus selective
processes in evolution. In this perspective, we first highlight the importance
of the genomic and (a)biotic context of new mutations to identify the targets
of natural selection. We then present mechanisms that may constrain the
evolution of genomes and bias the inference of selection. We discuss these
mechanisms within the two critical levels that they occur: the population level
and the molecular level. We highlight that they should be taken into account to
correctly distinguish sites across the genome subject to selective or
non-selective forces and stress that a major current field-wide goal is to
quantify the absolute importance of these mechanisms.",1909.11490v4
2019-10-08,Correlated fluctuations in spin orbit torque-coupled perpendicular nanomagnets,"Low barrier nanomagnets have attracted a lot of research interest for their
use as sources of high quality true random number generation. More recently,
low barrier nanomagnets with tunable output have been shown to be a natural
hardware platform for unconventional computing paradigms such as probabilistic
spin logic. Efficient generation and tunability of high quality random bits is
critical for these novel applications. However, current spintronic random
number generators are based on superparamagnetic tunnel junctions (SMTJs) with
tunability obtained through spin transfer torque (STT), which unavoidably leads
to challenges in designing concatenated networks using these two terminal
devices. The more recent development of utilizing spin orbit torque (SOT)
allows for a three terminal device design, but can only tune in-plane
magnetization freely, which is not very energy efficient due to the needs of
overcoming a large demagnetization field. In this work, we experimentally
demonstrate for the first time, a stochastic device with perpendicular magnetic
anisotropy (PMA) that is completely tunable by SOT without the aid of any
external magnetic field. Our measurements lead us to hypothesize that a tilted
anisotropy might be responsible for the observed tunability. We carry out
stochastic Landau-Lifshitz-Gilbert (sLLG) simulations to confirm our
experimental observation. Finally, we build an electrically coupled network of
two such stochastic nanomagnet based devices and demonstrate that finite
correlation or anti-correlation can be established between their output
fluctuations by a weak interconnection, despite having a large difference in
their natural fluctuation time scale. Simulations based on a newly developed
dynamical model for autonomous circuits composed of low barrier nanomagnets
show close agreement with the experimental results.",1910.03184v1
2019-10-09,"Prophets, Secretaries, and Maximizing the Probability of Choosing the Best","Suppose a customer is faced with a sequence of fluctuating prices, such as
for airfare or a product sold by a large online retailer. Given distributional
information about what price they might face each day, how should they choose
when to purchase in order to maximize the likelihood of getting the best price
in retrospect? This is related to the classical secretary problem, but with
values drawn from known distributions. In their pioneering work, Gilbert and
Mosteller [\textit{J. Amer. Statist. Assoc. 1966}] showed that when the values
are drawn i.i.d., there is a thresholding algorithm that selects the best value
with probability approximately $0.5801$. However, the more general problem with
non-identical distributions has remained unsolved.
  In this paper we provide an algorithm for the case of non-identical
distributions that selects the maximum element with probability $1/e$, and we
show that this is tight. We further show that if the observations arrive in a
random order, this barrier of $1/e$ can be broken using a static threshold
algorithm, and we show that our success probability is the best possible for
any single-threshold algorithm under random observation order. Moreover, we
prove that one can achieve a strictly better success probability using more
general multi-threshold algorithms, unlike the non-random-order case. Along the
way, we show that the best achievable success probability for the random-order
case matches that of the i.i.d.\ case, which is approximately $0.5801$, under a
""no-superstars"" condition that no single distribution is very likely ex ante to
generate the maximum value. We also extend our results to the problem of
selecting one of the $k$ best values.",1910.03798v1
2019-10-24,Order and Information in the Patterns of Spinning Magnetic Micro-disks at the Air-water Interface,"The application of the Shannon entropy to study the relationship between
information and structures has yielded insights into molecular and material
systems. However, the difficulty in directly observing and manipulating atoms
and molecules hampers the ability of these systems to serve as model systems
for further exploring the links between information and structures. Here, we
use, as a model experimental system, hundreds of spinning magnetic micro-disks
self-organizing at the air-water interface to generate various spatiotemporal
patterns with varying degrees of orders. Using the neighbor distance as the
information-bearing variable, we demonstrate the links among information,
structure, and interactions. Most importantly, we establish a direct link
between information and structure without using explicit knowledge of
interactions. Finally, we show that the Shannon entropy by neighbor distances
is a powerful observable in characterizing structural changes. Our findings are
relevant for analyzing natural self-organizing systems and for designing
collective robots.",1910.11226v3
2019-11-15,A geometric look at MHD and the Braginsky dynamo,"This paper considers magnetohydrodynamics (MHD) and some of its applications
from the perspective of differential geometry, considering the dynamics of an
ideal fluid flow and magnetic field on a general three-dimensional manifold,
equipped with a metric and an induced volume form. The benefit of this level of
abstraction is that it clarifies basic aspects of fluid dynamics such as how
certain quantities are transported, how they transform under the action of
mappings (for example the flow map between Lagrangian labels and Eulerian
positions), how conservation laws arise, and the origin of certain
approximations that preserve the mathematical structure of classical mechanics.
First, the governing equations for ideal MHD are derived in a general setting
by means of an action principle, and making use of Lie derivatives. The way in
which these equations transform under a pull back, by the map taking the
position of a fluid parcel to a background location, is detailed. This is then
used to parameterise Alfv\'en waves using concepts of pseudomomentum and
pseudofield, in parallel with the development of Generalised Lagrangian Mean
theory in hydrodynamics. Finally non-ideal MHD is considered with a sketch of
the development of the Braginsky $\alpha\omega$-dynamo in a general setting.
Expressions for the $\alpha$-tensor are obtained, including a novel geometric
formulation in terms of connection coefficients, and related to formulae found
elsewhere in the literature.",1911.06592v2
2019-11-17,Interfacial-Redox-Induced Tuning of Superconductivity in YBa$_{2}$Cu$_{3}$O$_{7-δ}$,"Solid state ionic approaches for modifying ion distributions in getter/oxide
heterostructures offer exciting potentials to control material properties. Here
we report a simple, scalable approach allowing for total control of the
superconducting transition in optimally doped YBa$_{2}$Cu$_{3}$O$_{7-{\delta}}$
(YBCO) films via a chemically-driven ionic migration mechanism. Using a thin Gd
capping layer of up to 20 nm deposited onto 100 nm thick epitaxial YBCO films,
oxygen is found to leach from deep within the YBCO. Progressive reduction of
the superconducting transition is observed, with complete suppression possible
for a sufficiently thick Gd layer. These effects arise from the combined impact
of redox-driven electron doping and modification of the YBCO microstructure due
to oxygen migration and depletion. This work demonstrates an effective ionic
control of superconductivity in oxides, an interface induced effect that goes
well into the quasi-bulk regime, opening up possibilities for electric field
manipulation.",1911.07275v1
2019-12-10,Integration of Neural Network-Based Symbolic Regression in Deep Learning for Scientific Discovery,"Symbolic regression is a powerful technique that can discover analytical
equations that describe data, which can lead to explainable models and
generalizability outside of the training data set. In contrast, neural networks
have achieved amazing levels of accuracy on image recognition and natural
language processing tasks, but are often seen as black-box models that are
difficult to interpret and typically extrapolate poorly. Here we use a neural
network-based architecture for symbolic regression called the Equation Learner
(EQL) network and integrate it with other deep learning architectures such that
the whole system can be trained end-to-end through backpropagation. To
demonstrate the power of such systems, we study their performance on several
substantially different tasks. First, we show that the neural network can
perform symbolic regression and learn the form of several functions. Next, we
present an MNIST arithmetic task where a separate part of the neural network
extracts the digits. Finally, we demonstrate prediction of dynamical systems
where an unknown parameter is extracted through an encoder. We find that the
EQL-based architecture can extrapolate quite well outside of the training data
set compared to a standard neural network-based architecture, paving the way
for deep learning to be applied in scientific exploration and discovery.",1912.04825v2
2019-12-17,New search for mirror neutron regeneration,"The possibility of relatively fast neutron oscillations into a mirror neutron
state is not excluded experimentally when a mirror magnetic field is
considered. Direct searches for the disappearance of neutrons into mirror
neutrons in a controlled magnetic field have previously been performed using
ultracold neutrons, with some anomalous results reported. We describe a
technique using cold neutrons to perform a disappearance and regeneration
search, which would allow us to unambiguously identify a possible oscillation
signal. An experiment using the existing General Purpose-Small Angle Neutron
Scattering instrument at the High Flux Isotope Reactor at Oak Ridge National
Laboratory will have the sensitivity to fully explore the parameter space of
prior ultracold neutron searches and confirm or refute previous claims of
observation. This instrument can also conclusively test the validity of
recently suggested oscillation-based explanations for the neutron lifetime
anomaly.",1912.08264v1
2020-01-06,Highly efficient spin orbit torque in Pt/Co/Ir multilayers with antiferromagnetic interlayer exchange coupling,"We have studied the spin orbit torque (SOT) in Pt/Co/Ir multilayers with 3
repeats of the unit structure. As the system exhibits oscillatory interlayer
exchange coupling (IEC) with varying Ir layer thickness, we compare the SOT of
films when the Co layers are coupled ferromagnetically and
antiferromagnetically. SOT is evaluated using current induced shift of the
anomalous Hall resistance hysteresis loops. A relatively thick Pt layer,
serving as a seed layer to the multilayer, is used to generate spin current via
the spin Hall effect. In the absence of antiferromagnetic coupling, the SOT is
constant against the applied current density and the corresponding spin torque
efficiency (i.e. the effective spin Hall angle) is $\sim$0.09, in agreement
with previous reports. In contrast, for films with antiferromagnetic coupling,
the SOT increases with the applied current density and eventually saturates.
The SOT at saturation is a factor of $\sim$15 larger than that without the
antiferromagnetic coupling. The spin torque efficiency is $\sim$5 times larger
if we assume the net total magnetization is reduced by a factor of 3 due to the
antiferromagnetic coupling. Model calculations based on the Landau Lifshitz
Gilbert equation show that the presence of antiferromagnetic coupling can
increase the SOT but the degree of enhancement is limited, in this case, to a
factor of 1.2-1.4. We thus consider there are other sources of SOT, possibly at
the interfaces, which may account for the highly efficient SOT in the
uncompensated synthetic anti-ferromagnet (SAF) multilayers.",2001.01454v1
2019-11-24,Cybernetical Concepts for Cellular Automaton and Artificial Neural Network Modelling and Implementation,"As a discipline cybernetics has a long and rich history. In its first
generation it not only had a worldwide span, in the area of computer modelling,
for example, its proponents such as John von Neumann, Stanislaw Ulam, Warren
McCulloch and Walter Pitts, also came up with models and methods such as
cellular automata and artificial neural networks, which are still the
foundation of most modern modelling approaches. At the same time, cybernetics
also got the attention of philosophers, such as the Frenchman Gilbert Simondon,
who made use of cybernetical concepts in order to establish a metaphysics and a
natural philosophy of individuation, giving cybernetics thereby a philosophical
interpretation, which he baptised allagmatic. In this paper, we emphasise this
allagmatic theory by showing how Simondon's philosophical concepts can be used
to formulate a generic computer model or metamodel for complex systems
modelling and its implementation in program code, according to generic
programming. We also present how the developed allagmatic metamodel is capable
of building simple cellular automata and artificial neural networks.",2001.02037v3
2020-02-12,Competition between magnetic order and charge localization in Na$_2$IrO$_3$ thin crystal devices,"Spin orbit assisted Mott insulators such as sodium iridate (Na$_2$IrO$_3$)
have been an important subject of study in the recent years. In these
materials, the interplay of electronic correlations, spin-orbit coupling,
crystal field effects and a honeycomb arrangement of ions bring exciting ground
states, predicted in the frame of the Kitaev model. The insulating character of
Na$_2$IrO$_3$ has hampered its integration to an electronic device, desirable
for applications, such as the manipulation of quasiparticles interesting for
topological quantum computing. Here we show through electronic transport
measurements supported by Angle Resolved Photoemission Spectroscopy (ARPES)
experiments, that electronic transport in Na$_2$IrO$_3$ is ruled by variable
range hopping and it is strongly dependent on the magnetic ordering transition
known for bulk Na$_2$IrO$_3$, as well as on external electric fields.
Electronic transport measurements allow us to deduce a value for the
localization length and the density of states in our Na$_2$IrO$_3$ thin
crystals devices, offering an alternative approach to study insulating layered
materials.",2002.04785v1
2020-02-13,Electron Beam-Induced Nanopores in Bernal-Stacked Hexagonal Boron Nitride,"Controlling the size and shape of nanopores in two-dimensional materials is a
key challenge in applications such as DNA sequencing, sieving, and quantum
emission in artificial atoms. We here investigate experimentally and
theoretically triangular vacancies in (unconventional) Bernal-stacked AB-h-BN
formed using a high-energy electron beam. Due to the geometric configuration of
AB-h-BN, triangular pores in different layers are aligned, and their sizes are
controlled by the duration of the electron irradiation. Interlayer covalent
bonding at the vacancy edge is not favored, as opposed to what occurs in the
more common AA'-stacked BN. A variety of monolayer, concentric and bilayer
pores in bilayer AB-h-BN are observed in high-resolution transmission electron
microscopy and characterized using ab initio simulations. Bilayer pores in
AB-h-BN are commonly formed, and grow without breaking the bilayer character.
Nanopores in AB-h-BN exhibit a wide range of electronic properties, ranging
from half-metallic to non-magnetic and magnetic semiconducting. Therefore,
because of the controllability of the pore size, the electronic structure is
also highly controllable in these systems, and can potentially be tuned for
particular applications.",2002.05795v3
2020-02-26,Effect of chemical substitution on the skyrmion phase in Cu$_2$OSeO$_3$,"Magnetic skyrmions have been the focus of intense research due to their
unique qualities which result from their topological protections. Previous work
on Cu$_2$OSeO$_3$, the only known insulating multiferroic skyrmion material,
has shown that chemical substitution alters the skyrmion phase. We chemically
substitute Zn, Ag, and S into powdered Cu$_2$OSeO$_3$ to study the effect on
the magnetic phase diagram. In both the Ag and the S substitutions, we find
that the skyrmion phase is stabilized over a larger temperature range, as
determined via magnetometry and small-angle neutron scattering (SANS).
Meanwhile, while previous magnetometry characterization suggests two high
temperature skyrmion phases in the Zn-substituted sample, SANS reveals the high
temperature phase to be skyrmionic while we are unable to distinguish the other
from helical order. Overall, chemical substitution weakens helical and skyrmion
order as inferred from neutron scattering of the $|$q$| \approx$ 0.01
$\r{A}^{-1}$ magnetic peak.",2002.11827v1
2020-03-10,Smart City IoT Services Creation through Large Scale Collaboration,"Smart cities solutions are often monolithically implemented, from sensors
data handling through to the provided services. The same challenges are
regularly faced by different developers, for every new solution in a new city.
Expertise and know-how can be re-used and the effort shared. In this article we
present the methodologies to minimize the efforts of implementing new smart
city solutions and maximizing the sharing of components. The final target is to
have a live technical community of smart city application developers. The
results of this activity comes from the implementation of 35 city services in
27 cities between Europe and South Korea. To share efforts, we encourage
developers to devise applications using a modular approach. Single-function
components that are re-usable by other city services are packaged and published
as standalone components, named Atomic Services. We identify 15 atomic services
addressing smart city challenges in data analytics, data evaluation, data
integration, data validation, and visualization. 38 instances of the atomic
services are already operational in several smart city services. We detail in
this article, as atomic service examples, some data predictor components.
Furthermore, we describe real-world atomic services usage in the scenarios of
Santander and three Danish cities. The resulting atomic services also generate
a side market for smart city solutions, allowing expertise and know-how to be
re-used by different stakeholders.",2003.04843v1
2020-03-23,Low Power Unsupervised Anomaly Detection by Non-Parametric Modeling of Sensor Statistics,"This work presents AEGIS, a novel mixed-signal framework for real-time
anomaly detection by examining sensor stream statistics. AEGIS utilizes Kernel
Density Estimation (KDE)-based non-parametric density estimation to generate a
real-time statistical model of the sensor data stream. The likelihood estimate
of the sensor data point can be obtained based on the generated statistical
model to detect outliers. We present CMOS Gilbert Gaussian cell-based design to
realize Gaussian kernels for KDE. For outlier detection, the decision boundary
is defined in terms of kernel standard deviation ($\sigma_{Kernel}$) and
likelihood threshold ($P_{Thres}$). We adopt a sliding window to update the
detection model in real-time. We use time-series dataset provided from Yahoo to
benchmark the performance of AEGIS. A f1-score higher than 0.87 is achieved by
optimizing parameters such as length of the sliding window and decision
thresholds which are programmable in AEGIS. Discussed architecture is designed
using 45nm technology node and our approach on average consumes $\sim$75 $\mu$W
power at a sampling rate of 2 MHz while using ten recent inlier samples for
density estimation. \textcolor{red}{Full-version of this research has been
published at IEEE TVLSI}",2003.10088v1
2020-03-30,"Efficient nonparametric inference on the effects of stochastic interventions under two-phase sampling, with applications to vaccine efficacy trials","The advent and subsequent widespread availability of preventive vaccines has
altered the course of public health over the past century. Despite this
success, effective vaccines to prevent many high-burden diseases, including
HIV, have been slow to develop. Vaccine development can be aided by the
identification of immune response markers that serve as effective surrogates
for clinically significant infection or disease endpoints. However, measuring
immune response marker activity is often costly, which has motivated the usage
of two-phase sampling for immune response evaluation in clinical trials of
preventive vaccines. In such trials, the measurement of immunological markers
is performed on a subset of trial participants, where enrollment in this second
phase is potentially contingent on the observed study outcome and other
participant-level information. We propose nonparametric methodology for
efficiently estimating a counterfactual parameter that quantifies the impact of
a given immune response marker on the subsequent probability of infection.
Along the way, we fill in theoretical gaps pertaining to the asymptotic
behavior of nonparametric efficient estimators in the context of two-phase
sampling, including a multiple robustness property enjoyed by our estimators.
Techniques for constructing confidence intervals and hypothesis tests are
presented, and an open source software implementation of the methodology, the
txshift R package, is introduced. We illustrate the proposed techniques using
data from a recent preventive HIV vaccine efficacy trial.",2003.13771v2
2020-04-05,Effects of the Affordable Care Act Dependent Coverage Mandate on Health Insurance Coverage for Individuals in Same-Sex Couples,"A large body of research documents that the 2010 dependent coverage mandate
of the Affordable Care Act was responsible for significantly increasing health
insurance coverage among young adults. No prior research has examined whether
sexual minority young adults also benefitted from the dependent coverage
mandate, despite previous studies showing lower health insurance coverage among
sexual minorities and the fact that their higher likelihood of strained
relationships with their parents might predict a lower ability to use parental
coverage. Our estimates from the American Community Surveys using
difference-in-differences and event study models show that men in same-sex
couples age 21-25 were significantly more likely to have any health insurance
after 2010 compared to the associated change for slightly older 27 to
31-year-old men in same-sex couples. This increase is concentrated among
employer-sponsored insurance, and it is robust to permutations of time periods
and age groups. Effects for women in same-sex couples and men in different-sex
couples are smaller than the associated effects for men in same-sex couples.
These findings confirm the broad effects of expanded dependent coverage and
suggest that eliminating the federal dependent mandate could reduce health
insurance coverage among young adult sexual minorities in same-sex couples.",2004.02296v1
2020-04-07,A general framework for inference on algorithm-agnostic variable importance,"In many applications, it is of interest to assess the relative contribution
of features (or subsets of features) toward the goal of predicting a response
-- in other words, to gauge the variable importance of features. Most recent
work on variable importance assessment has focused on describing the importance
of features within the confines of a given prediction algorithm. However, such
assessment does not necessarily characterize the prediction potential of
features, and may provide a misleading reflection of the intrinsic value of
these features. To address this limitation, we propose a general framework for
nonparametric inference on interpretable algorithm-agnostic variable
importance. We define variable importance as a population-level contrast
between the oracle predictiveness of all available features versus all features
except those under consideration. We propose a nonparametric efficient
estimation procedure that allows the construction of valid confidence
intervals, even when machine learning techniques are used. We also outline a
valid strategy for testing the null importance hypothesis. Through simulations,
we show that our proposal has good operating characteristics, and we illustrate
its use with data from a study of an antibody against HIV-1 infection.",2004.03683v2
2020-04-15,Magic DIAMOND: Multi-Fascicle Diffusion Compartment Imaging with Tensor Distribution Modeling and Tensor-Valued Diffusion Encoding,"Diffusion tensor imaging provides increased sensitivity to microstructural
tissue changes compared to conventional anatomical imaging but also presents
limited specificity. To tackle this problem, the DIAMOND model subdivides the
voxel content into diffusion compartments and draws from diffusion-weighted
data to estimate compartmental non-central matrix-variate Gamma distribution of
diffusion tensors, thereby resolving crossing fascicles while accounting for
their respective heterogeneity. Alternatively, tensor-valued diffusion encoding
defines new acquisition schemes tagging specific features of the intra-voxel
diffusion tensor distribution directly from the outcome of the measurement.
However, the impact of such schemes on estimating brain microstructural
features has only been studied in a handful of parametric single-fascicle
models. In this work, we derive a general Laplace transform for the non-central
matrix-variate Gamma distribution, which enables the extension of DIAMOND to
tensor-valued encoded data. We then evaluate this ""Magic DIAMOND"" model in
silico and in vivo on various combinations of tensor-valued encoded data.
Assessing uncertainty on parameter estimation via stratified bootstrap, we
investigate both voxel-based and fixel-based metrics by carrying out multi-peak
tractography. We show that our estimated metrics can be mapped along tracks
robustly across regions of fiber crossing, which opens new perspectives for
tractometry and microstructure mapping along specific white-matter tracts.",2004.07340v2
2020-04-16,Measuring Human and Economic Activity from Satellite Imagery to Support City-Scale Decision-Making during COVID-19 Pandemic,"The COVID-19 outbreak forced governments worldwide to impose lockdowns and
quarantines to prevent virus transmission. As a consequence, there are
disruptions in human and economic activities all over the globe. The recovery
process is also expected to be rough. Economic activities impact social
behaviors, which leave signatures in satellite images that can be automatically
detected and classified. Satellite imagery can support the decision-making of
analysts and policymakers by providing a different kind of visibility into the
unfolding economic changes. In this work, we use a deep learning approach that
combines strategic location sampling and an ensemble of lightweight
convolutional neural networks (CNNs) to recognize specific elements in
satellite images that could be used to compute economic indicators based on it,
automatically. This CNN ensemble framework ranked third place in the US
Department of Defense xView challenge, the most advanced benchmark for object
detection in satellite images. We show the potential of our framework for
temporal analysis using the US IARPA Function Map of the World (fMoW) dataset.
We also show results on real examples of different sites before and after the
COVID-19 outbreak to illustrate different measurable indicators. Our code and
annotated high-resolution aerial scenes before and after the outbreak are
available on GitHub (https://github.com/maups/covid19-satellite-analysis).",2004.07438v4
2020-04-16,Subjectifying Objectivity: Delineating Tastes in Theoretical Quantum Gravity Research,"Research in Theoretical Quantum Gravity has continued expansively even as it
has become detached from classic arbiters of research such as direct empirical
falsification. This makes it an interesting test case for social-scientific
theories of what motivates and mediates contemporary scientific research and
the nature of scientific objectivity. For our empirical investigation, we
conducted 50 semi-structured interviews with researchers in the rival camps of
String Theory and Loop Quantum Gravity, coded a subset for reoccurring themes,
and subjected the resulting data to statistical analysis. Theoretically, we
mobilize aspects of Daston and Galison's depiction of the scientific self and
its relation to epistemic virtues, Pierre Bourdieu's field-centered account of
social space, and Kantian notions of aesthetics in order to delineate the
subjective tastes and the related process of collective consensus-making in
contemporary quantum gravity research. We make two key contributions. First,
our analysis sheds light on the inner workings of the field by connecting its
internal epistemic struggles with relevant social-scientific theories. For
example, we are able to suggest an explanation for how one approach, String
Theory, has become so dominant. Second, our application of theories of social
reproduction to the substance of scientific inquiry merits some substantive
generalizations to Daston and Galison's framework. Most significantly, we
propose as an addendum to their progression the notion of objectivity through
intersubjectivity: objectivity obtained not through the suppression of the self
but by its (regulated) pluralistic expression and performance.",2004.07450v2
2020-04-22,Excitation of high-frequency magnon modes in magnetoelastic films by short strain pulses,"Development of energy efficient techniques for generation of spin waves
(magnons) is important for implementation of low-dissipation spin-wave-based
logic circuits and memory elements. A promising approach to achieve this goal
is based on the injection of short strain pulses into ferromagnetic films with
a strong magnetoelastic coupling between spins and strains. Here we report
micromagnetoelastic simulations of the magnetization and strain dynamics
excited in Fe$_{81}$Ga$_{19}$ films by picosecond and nanosecond acoustic
pulses created in a GaAs substrate by a transducer subjected to an optical or
electrical impulse. The simulations performed via the numerical solution of the
coupled Landau-Lifshitz-Gilbert and elastodynamic equations show that the
injected strain pulse induces an inhomogeneous magnetization precession in the
ferromagnetic film. The precession lasts up to 1 ns and can be treated as a
superposition of magnon modes having the form of standing spin waves. For
Fe$_{81}$Ga$_{19}$ films with nanoscale thickness, up to seven (six) distinct
modes have been revealed under free-surface (pinning) magnetic boundary
conditions. Remarkably, magnon modes with frequencies over 1 THz can be excited
by acoustic pulses with an appropriate shape and duration in the films
subjected to a moderate external magnetic field. This finding shows that short
strain pulses represent a promising tool for the generation of THz spin waves
necessary for the implementation of high-speed magnonic devices.",2004.10838v1
2020-04-23,Correlation-driven eightfold magnetic anisotropy in a two-dimensional oxide monolayer,"Engineering magnetic anisotropy in two-dimensional systems has enormous
scientific and technological implications. The uniaxial anisotropy universally
exhibited by two-dimensional magnets has only two stable spin directions,
demanding 180 degrees spin switching between states. We demonstrate a novel
eightfold anisotropy in magnetic SrRuO3 monolayers by inducing a spin
reorientation in (SrRuO3)1/(SrTiO3)N superlattices, in which the magnetic easy
axis of Ru spins is transformed from uniaxial <001> direction (N = 1 and 2) to
eightfold <111> directions (N = 3, 4 and 5). This eightfold anisotropy enables
71 and 109 degrees spin switching in SrRuO3 monolayers, analogous to 71 and 109
degrees polarization switching in ferroelectric BiFeO3. First-principle
calculations reveal that increasing the SrTiO3 layer thickness induces an
emergent correlation-driven orbital ordering, tuning spin-orbit interactions
and reorienting the SrRuO3 monolayer easy axis. Our work demonstrates that
correlation effects can be exploited to substantially change spin-orbit
interactions, stabilizing unprecedented properties in two-dimensional magnets
and opening rich opportunities for low-power, multi-state device applications.",2004.10939v1
2020-04-27,"Dynamic Predictions of Postoperative Complications from Explainable, Uncertainty-Aware, and Multi-Task Deep Neural Networks","Accurate prediction of postoperative complications can inform shared
decisions regarding prognosis, preoperative risk-reduction, and postoperative
resource use. We hypothesized that multi-task deep learning models would
outperform random forest models in predicting postoperative complications, and
that integrating high-resolution intraoperative physiological time series would
result in more granular and personalized health representations that would
improve prognostication compared to preoperative predictions. In a longitudinal
cohort study of 56,242 patients undergoing 67,481 inpatient surgical procedures
at a university medical center, we compared deep learning models with random
forests for predicting nine common postoperative complications using
preoperative, intraoperative, and perioperative patient data. Our study
indicated several significant results across experimental settings that suggest
the utility of deep learning for capturing more precise representations of
patient health for augmented surgical decision support. Multi-task learning
improved efficiency by reducing computational resources without compromising
predictive performance. Integrated gradients interpretability mechanisms
identified potentially modifiable risk factors for each complication. Monte
Carlo dropout methods provided a quantitative measure of prediction uncertainty
that has the potential to enhance clinical trust. Multi-task learning,
interpretability mechanisms, and uncertainty metrics demonstrated potential to
facilitate effective clinical implementation.",2004.12551v2
2020-05-08,Tree! I am no Tree! I am a Low Dimensional Hyperbolic Embedding,"Given data, finding a faithful low-dimensional hyperbolic embedding of the
data is a key method by which we can extract hierarchical information or learn
representative geometric features of the data. In this paper, we explore a new
method for learning hyperbolic representations by taking a metric-first
approach. Rather than determining the low-dimensional hyperbolic embedding
directly, we learn a tree structure on the data. This tree structure can then
be used directly to extract hierarchical information, embedded into a
hyperbolic manifold using Sarkar's construction \cite{sarkar}, or used as a
tree approximation of the original metric. To this end, we present a novel fast
algorithm \textsc{TreeRep} such that, given a $\delta$-hyperbolic metric (for
any $\delta \geq 0$), the algorithm learns a tree structure that approximates
the original metric. In the case when $\delta = 0$, we show analytically that
\textsc{TreeRep} exactly recovers the original tree structure. We show
empirically that \textsc{TreeRep} is not only many orders of magnitude faster
than previously known algorithms, but also produces metrics with lower average
distortion and higher mean average precision than most previous algorithms for
learning hyperbolic embeddings, extracting hierarchical information, and
approximating metrics via tree metrics.",2005.03847v4
2020-07-08,On the production of He$^+$ of solar origin in the solar wind,"Solar wind measurements in the heliosphere are predominantly comprised of
protons, alphas, and minor elements in a highly ionized state. The majority of
low charge states, such as He$^{+}$, measured in situ are often attributed to
pick up ions of non-solar origin. However, through inspection of the velocity
distribution functions of near Earth measurements, we find a small but
significant population of He$^+$ ions in the normal solar wind whose properties
indicate that it originated from the Sun and has evolved as part of the normal
solar wind. Current ionization models, largely governed by electron impact and
radiative ionization and recombination processes, underestimate this population
by several orders of magnitude. Therefore, to reconcile the singly ionized He
observed, we investigate recombination of solar He$^{2+}$ through charge
exchange with neutrals from circumsolar dust as a possible formation mechanism
of solar He$^{+}$. We present an empirical profile of neutrals necessary for
charge exchange to become an effective vehicle to recombine He$^{2+}$ to
He$^{+}$ such that it meets observational He$^{+}$ values. We find the
formation of He$^{+}$ is not only sensitive to the density of neutrals but also
to the inner boundary of the neutral distribution encountered along the solar
wind path. However, further observational constraints are necessary to confirm
that the interaction between solar $\alpha$ particles and dust neutrals is the
primary source of the He$^{+}$ observations.",2007.04402v2
2020-07-28,Towers and the first-order theory of hyperbolic groups,"This paper is devoted to the first-order theory of torsion-free hyperbolic
groups. One of its purposes is to review some results and to provide precise
and correct statements and definitions, as well as some proofs and new results.
  A key concept is that of a tower (Sela) or NTQ system
(Kharlampovich-Myasnikov). We discuss them thoroughly.
  We state and prove a new general theorem which unifies several results in the
literature: elementarily equivalent torsion-free hyperbolic groups have
isomorphic cores (Sela); if $H$ is elementarily embedded in a torsion-free
hyperbolic group $G$, then $G$ is a tower over $H$ relative to $H$ (Perin);
free groups (Perin-Sklinos, Ould-Houcine), and more generally free products of
prototypes and free groups, are homogeneous.
  The converse to Sela and Perin's results just mentioned is true. This follows
from the solution to Tarski's problem on elementary equivalence of free groups,
due independently to Sela and Kharlampovich-Myasnikov, which we treat as a
black box throughout the paper.
  We present many examples and counterexamples, and we prove some new
model-theoretic results. We characterize prime models among torsion-free
hyperbolic groups, and minimal models among elementarily free groups. Using
Fra\""iss\'e's method, we associate to every torsion-free hyperbolic group $H$ a
unique homogeneous countable group $\mathcal{M}$ in which any hyperbolic group
$H'$ elementarily equivalent to $H$ has an elementary embedding.
  In an appendix we give a complete proof of the fact, due to Sela, that towers
over a torsion-free hyperbolic group $H$ are $H$-limit groups.",2007.14148v1
2020-08-13,Prediction of magnetization dynamics in a reduced dimensional feature space setting utilizing a low-rank kernel method,"We establish a machine learning model for the prediction of the magnetization
dynamics as function of the external field described by the
Landau-Lifschitz-Gilbert equation, the partial differential equation of motion
in micromagnetism. The model allows for fast and accurate determination of the
response to an external field which is illustrated by a thin-film standard
problem. The data-driven method internally reduces the dimensionality of the
problem by means of nonlinear model reduction for unsupervised learning. This
not only makes accurate prediction of the time steps possible, but also
decisively reduces complexity in the learning process where magnetization
states from simulated micromagnetic dynamics associated with different external
fields are used as input data. We use a truncated representation of kernel
principal components to describe the states between time predictions. The
method is capable of handling large training sample sets owing to a low-rank
approximation of the kernel matrix and an associated low-rank extension of
kernel principal component analysis and kernel ridge regression. The approach
entirely shifts computations into a reduced dimensional setting breaking down
the problem dimension from the thousands to the tens.",2008.05986v3
2020-07-20,Artificial Intelligence is stupid and causal reasoning won't fix it,"Artificial Neural Networks have reached Grandmaster and even super-human
performance across a variety of games: from those involving perfect-information
(such as Go) to those involving imperfect-information (such as Starcraft). Such
technological developments from AI-labs have ushered concomitant applications
across the world of business - where an AI brand tag is fast becoming
ubiquitous. A corollary of such widespread commercial deployment is that when
AI gets things wrong - an autonomous vehicle crashes; a chatbot exhibits racist
behaviour; automated credit scoring processes discriminate on gender etc. -
there are often significant financial, legal and brand consequences and the
incident becomes major news. As Judea Pearl sees it, the underlying reason for
such mistakes is that, 'all the impressive achievements of deep learning amount
to just curve fitting'. The key, Judea Pearl suggests, is to replace reasoning
by association with causal-reasoning - the ability to infer causes from
observed phenomena. It is a point that was echoed by Gary Marcus and Ernest
Davis in a recent piece for the New York Times: 'we need to stop building
computer systems that merely get better and better at detecting statistical
patterns in data sets - often using an approach known as Deep Learning - and
start building computer systems that from the moment of their assembly innately
grasp three basic concepts: time, space and causality'. In this paper,
foregrounding what in 1949 Gilbert Ryle termed a category mistake, I will offer
an alternative explanation for AI errors: it is not so much that AI machinery
cannot grasp causality, but that AI machinery - qua computation - cannot
understand anything at all.",2008.07371v1
2020-08-19,Dynamical decoupling in interacting systems: applications to signal-enhanced hyperpolarized readout,"Methods that preserve coherence broadly impact all quantum information
processing and metrology applications. Dynamical decoupling methods accomplish
this by protecting qubits in noisy environments but are typically constrained
to the limit where the qubits themselves are non-interacting. Here we consider
the alternate regime wherein the inter-qubit couplings are of the same order as
dephasing interactions with the environment. We propose and demonstrate a
multi-pulse protocol that protects transverse spin states by suitably
Hamiltonian engineering the inter-spin coupling while simultaneously
suppressing dephasing noise on the qubits. We benchmark the method on 13C
nuclear spin qubits in diamond, dipolar coupled to each other and embedded in a
noisy electronic spin bath, and hyperpolarized via optically pumped NV centers.
We observe effective state lifetimes of 13C nuclei $T_2^{\prime}\approx$2.5s at
room temperature, an extension of over 4700-fold over the conventional
$T_2^{\ast}$ free induction decay. The spins are continuously interrogated
during the applied quantum control, resulting in 13C NMR line narrowing and an
$>$500-fold boost in SNR due to the lifetime extension. Together with
hyperpolarization spin interrogation is accelerated by $>10^{11}$ over
conventional 7T NMR. This work suggests strategies for the dynamical decoupling
of coupled qubit systems with applications in a variety of experimental
platforms.",2008.08323v1
2020-08-30,Microwave and spin transfer torque driven coherent control in ferromagnets,"Coherent control is a method used to manipulate the state of matter using
oscillatory electromagnetic radiation which relies on the non-adiabatic
interaction. It is commonly applied in quantum processing applications. This
technique is interesting in the context of ferromagnetic materials because of
the ability to combine it with spintronics for the purpose of fundamental spin
transport research, low-power information processing, and potentially future
quantum bit (Qubit) applications. In this work we address the theoretical
grounds of coherent manipulation in practical ferromagnetic systems. We study
electromagnetic radiation driven interaction that is enhanced in the presence
of spin polarized currents and map the conditions that allow coherent
manipulation for which Rabi oscillations take place. The role of the magnetic
anisotropy field is shown to act as an additional oscillatory driving field. We
discuss the Gilbert losses in the context of effective coherence decay rates
and show that it is possible to control these rates by application of a static
spin current. The case of coherent manipulation using oscillatory spin currents
that is free of radiation is discussed as well. Our work paves the way towards
spin current amplification as well as radiation-free coherent control schemes
that may potentially lead to novel Qubits that are robust and scalable.",2008.13139v3
2020-08-31,Philosophy-Guided Modelling and Implementation of Adaptation and Control in Complex Systems,"Control was from its very beginning an important concept in cybernetics.
Later on, with the works of W. Ross Ashby, for example, biological concepts
such as adaptation were interpreted in the light of cybernetic systems theory.
Adaptation is the process by which a system is capable of regulating or
controlling itself in order to adapt to changes of its inner and outer
environment maintaining a homeostatic state. In earlier works we have developed
a system metamodel that on the one hand refers to cybernetic concepts such as
structure, operation, and system, and on the other to the philosophy of
individuation of Gilbert Simondon. The result is the so-called allagmatic
method that is capable of creating concrete models of systems such as
artificial neural networks and cellular automata starting from abstract
building blocks. In this paper, we add to our already existing method the
cybernetic concepts of control and especially adaptation. In regard to the
system metamodel, we rely again on philosophical theories, this time the
philosophy of organism of Alfred N. Whitehead. We show how these new
meta-theoretical concepts are described formally and how they are implemented
in program code. We also show what role they play in simple experiments. We
conclude that philosophical abstract concepts help to better understand the
process of creating computer models and their control and adaptation. In the
outlook we discuss how the allagmatic method needs to be extended in order to
cover the field of complex systems and Norbert Wiener's ideas on control.",2009.00110v4
2020-09-02,X-ray linear dichroic ptychography,"Biominerals such as seashells, corals skeletons, bone, and enamel are
optically anisotropic crystalline materials with unique nano- and micro-scale
organization that translates into exceptional macroscopic mechanical
properties, providing inspiration for engineering new and superior biomimetic
structures. Here we use particles of Seriatopora aculeata coral skeleton as a
model and demonstrate, for the first time, x-ray linear dichroic ptychography.
We map the aragonite (CaCO3) crystal c-axis orientations in coral skeleton with
35 nm spatial resolution. Linear dichroic phase imaging at the O K-edge energy
shows strong polarization-dependent contrast and reveals the presence of both
narrow (< 35{\deg}) and wide (> 35{\deg}) c-axis angular spread in
sub-micrometer coral particles. These x-ray ptychography results were
corroborated using 4D scanning transmission electron nano-diffraction on the
same particles. Evidence of co-oriented but disconnected corallite sub-domains
indicates jagged crystal boundaries consistent with formation by amorphous
nanoparticle attachment. Looking forward, we anticipate that x-ray linear
dichroic ptychography can be applied to study nano-crystallites, interfaces,
nucleation and mineral growth of optically anisotropic materials with sub-ten
nanometers spatial resolution in three dimensions.",2009.01093v1
2020-09-18,The effect of the surface magnetic anisotropy of the neodymium atoms on the coercivity in the neodymium permanent magnet,"The Nd permanent magnet (Nd$_{2}$Fe$_{14}$B) is an indispensable material
used in modern energy conversion devices. The realization of high coercivity at
finite temperatures is a burning issue. One of the important ingredients for
controlling the coercive force is the surface property of magnetic grains. It
has been reported by first-principles studies that the Nd atoms in the first
(001) surface layer facing the vacuum have in-plane anisotropy perpendicular to
the $c$ axis, which may decrease the coercivity. Focusing on the surface
anisotropy effect on the coercivity, we examine the coercivity at zero and
finite temperatures by using an atomistic model reflecting the lattice
structure of the Nd magnet with a stochastic Landau-Lifshitz-Gilbert equation
method. We study general three cases, in which the Nd atoms in surface layers
have (1) no anisotropy, (2) in-plane anisotropy, and (3) reinforced anisotropy
for two types of surfaces, (001) and (100) surfaces. We find that in contrast
to the zero-temperature case, due to the thermal fluctuation effect, the
modification of only the first surface layer has little effect on the
coercivity at finite temperatures. However, the modification of a few layers
results in significant effects. We discuss the details of the dependence of the
coercivity on temperature, type of surface, and modified layer depth, and also
the features of domain growth in magnetization reversal.",2009.08572v1
2020-09-18,Information- and Coding-Theoretic Analysis of the RLWE Channel,"Several cryptosystems based on the \emph{Ring Learning with Errors} (RLWE)
problem have been proposed within the NIST post-quantum cryptography
standardization process, e.g., NewHope. Furthermore, there are systems like
Kyber which are based on the closely related MLWE assumption. Both previously
mentioned schemes result in a non-zero decryption failure rate (DFR). The
combination of encryption and decryption for these kinds of algorithms can be
interpreted as data transmission over a noisy channel. To the best of our
knowledge this paper is the first work that analyzes the capacity of this
channel. We show how to modify the encryption schemes such that the input
alphabets of the corresponding channels are increased. In particular, we
present lower bounds on their capacities which show that the transmission rate
can be significantly increased compared to standard proposals in the
literature. Furthermore, under the common assumption of stochastically
independent coefficient failures, we give lower bounds on achievable rates
based on both the Gilbert-Varshamov bound and concrete code constructions using
BCH codes. By means of our constructions, we can either increase the total
bitrate (by a factor of $1.84$ for Kyber and by factor of $7$ for NewHope)
while guaranteeing the same DFR or for the same bitrate, we can significantly
reduce the DFR for all schemes considered in this work (e.g., for NewHope from
$2^{-216}$ to $2^{-12769}$).",2009.08681v3
2020-09-28,Precise control of $J_\mathrm{eff}=1/2$ magnetic properties in Sr$_2$IrO$_4$ epitaxial thin films by variation of strain and thin film thickness,"We report on a comprehensive investigation of the effects of strain and film
thickness on the structural and magnetic properties of epitaxial thin films of
the prototypal $J_\mathrm{eff}=1/2$ compound Sr$_2$IrO$_4$ by advanced X-ray
scattering. We find that the Sr$_2$IrO$_4$ thin films can be grown fully
strained up to a thickness of 108 nm. By using X-ray resonant scattering, we
show that the out-of-plane magnetic correlation length is strongly dependent on
the thin film thickness, but independent of the strain state of the thin films.
This can be used as a finely tuned dial to adjust the out-of-plane magnetic
correlation length and transform the magnetic anisotropy from two-dimensional
(2D) to three-dimensional (3D) behavior by incrementing film thickness. These
results provide a clearer picture for the systematic control of the magnetic
degrees of freedom in epitaxial thin films of Sr$_2$IrO$_4$ and bring to light
the potential for a rich playground to explore the physics of $5d$-transition
metal compounds.",2009.13185v1
2020-10-03,"WinterLab: Developing a low-cost, portable experiment platform to encourage engagement in the electronics lab","Encouraging student engagement is a key aim in any educational setting, and
allowing students the freedom to pursue their own methods of solving problems
through independent experimentation has been shown to markedly improve this. In
many contexts, however, allowing students this flexibility in their learning is
hampered by constraints of the material itself, such as in the electronics
laboratory, where expensive and bulky equipment confines the learning
environment to the laboratory room. Finding ourselves in the position of
teaching one such laboratory course at the undergraduate level, we sought to
encourage students to learn through independent investigation and the pursuit
of personal projects, by providing a more flexible and inquiry-based learning
environment and allowing them to take their measurement equipment -- and their
learning -- beyond the laboratory itself. We present this project as a case of
design both for and by students, with the lead designer undertaking the project
after attending the course in question, and pursuing its development as a
foundational step in their graduate career. We discuss the challenges and
opportunities we encountered over the course of the design and development
process, and the eventual key output of the project: a portable, low-cost,
integrated electronics experimentation platform called the Winterlab board.",2010.01426v2
2020-10-16,Hyperspectral interference tomography of nacre,"Structural characterization of biologically formed materials is essential for
understanding biological phenomena and their environment, and generating new
bio-inspired engineering concepts. For example, nacre -- formed by mollusks in
the ocean -- encodes local environmental conditions throughout its formation
and has exceptional strength due to its nanoscale brick-and-mortar structure.
This layered structure, comprising transparent aragonite tablets bonded with an
ultra-thin organic polymer, also results in stunning interference colors.
Existing methods of structural characterization of nacre rely on some form of
cross-sectional analysis, such as scanning electron microscopy or
polarization-dependent imaging contrast (PIC) mapping. However, these
techniques are destructive and too time- and resource-intensive to analyze
large sample areas. Here we present an all-optical, rapid, and non-destructive
imaging technique -- hyperspectral interference tomography (HIT) -- to
spatially map the structural parameters of nacre and other disordered layered
materials. We combined hyperspectral imaging with optical-interference modeling
to infer the mean tablet thickness and disordering of nacre layers across
entire mollusk shells at various stages of development, observing a previously
unknown relationship between the growth of the mollusk and tablet thickness.
Our rapid, inexpensive, and nondestructive method can be readily applied to
in-field studies.",2010.08170v1
2020-11-03,Recent results for the Landau-Lifshitz equation,"We give a survey on some recent results concerning the Landau-Lifshitz
equation, a fundamental nonlinear PDE with a strong geometric content,
describing the dynamics of the magnetization in ferromagnetic materials. We
revisit the Cauchy problem for the anisotropic Landau-Lifshitz equation,
without dissipation, for smooth solutions, and also in the energy space in
dimension one. We also examine two approximations of the Landau-Lifshitz
equation given by of the Sine-Gordon equation and cubic Schr\""odinger
equations, arising in certain singular limits of strong easy-plane and
easy-axis anisotropy, respectively.
  Concerning localized solutions, we review the orbital and asymptotic
stability problems for a sum of solitons in dimension one, exploiting the
variational nature of the solitons in the hydrodynamical framework.
  Finally, we survey results concerning the existence, uniqueness and stability
of self-similar solutions (expanders and shrinkers) for the isotropic
Landau-Lifshitz equation with Gilbert term. Since expanders are associated with
a singular initial condition with a jump discontinuity, we also review their
well-posedness in spaces linked to the BMO space.",2011.01692v3
2020-11-10,The Virtual Goniometer: A new method for measuring angles on 3D models of fragmentary bone and lithics,"The contact goniometer is a commonly used tool in lithic and
zooarchaeological analysis, despite suffering from a number of shortcomings due
to the physical interaction between the measuring implement, the object being
measured, and the individual taking the measurements. However, lacking a simple
and efficient alternative, researchers in a variety of fields continue to use
the contact goniometer to this day. In this paper, we present a new goniometric
method that we call the virtual goniometer, which takes angle measurements
virtually on a 3D model of an object. The virtual goniometer allows for rapid
data collection, and for the measurement of many angles that cannot be
physically accessed by a manual goniometer. We compare the intra-observer
variability of the manual and virtual goniometers, and find that the virtual
goniometer is far more consistent and reliable. Furthermore, the virtual
goniometer allows for precise replication of angle measurements, even among
multiple users, which is important for reproducibility of goniometric-based
research. The virtual goniometer is available as a plug-in in the open source
mesh processing packages Meshlab and Blender, making it easily accessible to
researchers exploring the potential for goniometry to improve archaeological
methods and address anthropological questions.",2011.04898v2
2020-11-17,Competing energy scales in topological superconducting heterostructures,"Artificially engineered topological superconductivity has emerged as a viable
route to create Majorana modes, exotic quasiparticles which have raised great
expectations for storing and manipulating information in topological quantum
computational schemes. The essential ingredients for their realization are spin
non-degenerate metallic states proximitized to an s-wave superconductor. In
this context, proximity-induced superconductivity in materials with a sizable
spin-orbit coupling has been heavily investigated in recent years. Although
there is convincing evidence that superconductivity may indeed be induced, it
has been difficult to elucidate its topological nature. In this work, we
systematically engineer an artificial topological superconductor by
progressively introducing superconductivity (Nb) into metals with strong
spin-orbital coupling (Pt) and 3D topological surface states (Bi2Te3). Through
a longitudinal study of the character of superconducting vortices within s-wave
superconducting Nb and proximity-coupled Nb/Pt and Nb/Bi2Te3, we detect the
emergence of a zero-bias peak that is directly linked to the presence of
topological surface states. Supported by a detailed theoretical model, our
results are rationalized in terms of competing energy trends which are found to
impose an upper limit to the size of the minigap separating Majorana and
trivial modes, its size being ultimately linked to fundamental materials
properties.",2011.08812v1
2020-12-01,Phase-field modeling of biomineralization in mollusks and corals: Microstructure vs. formation mechanism,"While biological crystallization processes have been studied on the
microscale extensively, models addressing the mesoscale aspects of such
phenomena are rare. In this work, we investigate whether the phase-field theory
developed in materials science for describing complex polycrystalline
structures on the mesoscale can be meaningfully adapted to model
crystallization in biological systems. We demonstrate the abilities of the
phase-field technique by modeling a range of microstructures observed in
mollusk shells and coral skeletons, including granular, prismatic,
sheet/columnar nacre, and sprinkled spherulitic structures. We also compare two
possible micromechanisms of calcification: the classical route via ion-by-ion
addition from a fluid state and a non-classical route, crystallization of an
amorphous precursor deposited at the solidification front. We show that with
appropriate choice of the model parameters microstructures similar to those
found in biomineralized systems can be obtained along both routes, though the
timescale of the non-classical route appears to be more realistic. The
resemblance of the simulated and natural biominerals suggests that, underneath
the immense biological complexity observed in living organisms, the underlying
design principles for biological structures may be understood with simple math,
and simulated by phase-field theory.",2012.00666v1
2020-12-02,Symmetry of the Magnetoelastic Interaction of Rayleigh and Shear Horizontal Magnetoacoustic Waves in Nickel Thin Films on LiTaO$_3$,"We study the interaction of Rayleigh and shear horizontal surface acoustic
waves (SAWs) with spin waves in thin Ni films on a piezoelectric LiTaO$_3$
substrate, which supports both SAW modes simultaneously. Because Rayleigh and
shear horizontal modes induce different strain components in the Ni thin films,
the symmetries of the magnetoelastic driving fields, of the magnetoelastic
response, and of the transmission nonreciprocity differ for both SAW modes. Our
experimental findings are well explained by a theoretical model based on a
modified Landau--Lifshitz--Gilbert approach. We show that the symmetries of the
magnetoelastic response driven by Rayleigh- and shear horizontal SAWs
complement each other, which makes it possible to excite spin waves for any
relative orientation of magnetization and SAW propagation direction and,
moreover, can be utilized to characterize surface strain components of unknown
acoustic wave modes.",2012.01055v2
2020-12-03,Localization of Malaria Parasites and White Blood Cells in Thick Blood Smears,"Effectively determining malaria parasitemia is a critical aspect in assisting
clinicians to accurately determine the severity of the disease and provide
quality treatment. Microscopy applied to thick smear blood smears is the de
facto method for malaria parasitemia determination. However, manual
quantification of parasitemia is time consuming, laborious and requires
considerable trained expertise which is particularly inadequate in highly
endemic and low resourced areas. This study presents an end-to-end approach for
localisation and count of malaria parasites and white blood cells (WBCs) which
aid in the effective determination of parasitemia; the quantitative content of
parasites in the blood. On a dataset of slices of images of thick blood smears,
we build models to analyse the obtained digital images. To improve model
performance due to the limited size of the dataset, data augmentation was
applied. Our preliminary results show that our deep learning approach reliably
detects and returns a count of malaria parasites and WBCs with a high precision
and recall. We also evaluate our system against human experts and results
indicate a strong correlation between our deep learning model counts and the
manual expert counts (p=0.998 for parasites, p=0.987 for WBCs). This approach
could potentially be applied to support malaria parasitemia determination
especially in settings that lack sufficient Microscopists.",2012.01994v1
2020-12-05,Age-Optimal Low-Power Status Update over Time-Correlated Fading Channel,"In this paper, we consider transmission scheduling in a status update system,
where updates are generated periodically and transmitted over a Gilbert-Elliott
fading channel. The goal is to minimize the long-run average age of information
(AoI) at the destination under an average energy constraint. We consider two
practical cases to obtain channel state information (CSI): (i) \emph{without
channel sensing} and (ii) \emph{with delayed channel sensing}. For case (i),
the channel state is revealed when an ACK/NACK is received at the transmitter
following a transmission, but when no transmission occurs, the channel state is
not revealed. Thus, we have to design schemes that balance tradeoffs across
energy, AoI, channel exploration, and channel exploitation. The problem is
formulated as a constrained partially observable Markov decision process
problem (POMDP). To reduce algorithm complexity, we show that the optimal
policy is a randomized mixture of no more than two stationary deterministic
policies each of which is of a threshold-type in the belief on the channel. For
case (ii), (delayed) CSI is available at the transmitter via channel sensing.
In this case, the tradeoff is only between the AoI and energy consumption and
the problem is formulated as a constrained MDP. The optimal policy is shown to
have a similar structure as in case (i) but with an AoI associated threshold.
Finally, the performance of the proposed structure-aware algorithms is
evaluated numerically and compared with a Greedy policy.",2012.02958v2
2020-11-30,Procode: the Swiss Multilingual Solution for Automatic Coding and Recoding of Occupations and Economic Activities,"Objective. Epidemiological studies require data that are in alignment with
the classifications established for occupations or economic activities. The
classifications usually include hundreds of codes and titles. Manual coding of
raw data may result in misclassification and be time consuming. The goal was to
develop and test a web-tool, named Procode, for coding of free-texts against
classifications and recoding between different classifications. Methods. Three
text classifiers, i.e. Complement Naive Bayes (CNB), Support Vector Machine
(SVM) and Random Forest Classifier (RFC), were investigated using a k-fold
cross-validation. 30 000 free-texts with manually assigned classification codes
of French classification of occupations (PCS) and French classification of
activities (NAF) were available. For recoding, Procode integrated a workflow
that converts codes of one classification to another according to existing
crosswalks. Since this is a straightforward operation, only the recoding time
was measured. Results. Among the three investigated text classifiers, CNB
resulted in the best performance, where the classifier predicted accurately
57-81% and 63-83% classification codes for PCS and NAF, respectively. SVM lead
to somewhat lower results (by 1-2%), while RFC coded accurately up to 30% of
the data. The coding operation required one minute per 10 000 records, while
the recoding was faster, i.e. 5-10 seconds. Conclusion. The algorithm
integrated in Procode showed satisfactory performance, since the tool had to
assign the right code by choosing between 500-700 different choices. Based on
the results, the authors decided to implement CNB in Procode. In future, if
another classifier shows a superior performance, an update will include the
required modifications.",2012.07521v1
2020-12-16,Dynamic clay microstructures emerge via ion complexation waves,"Clays control carbon, water and nutrient transport in the lithosphere,
promote cloud formation5 and lubricate fault slip through interactions among
hydrated mineral interfaces. Clay mineral properties are difficult to model
because their structures are disordered, curved and dynamic. Consequently,
interactions at the clay mineral-aqueous interface have been approximated using
electric double layer models based on single crystals of mica and atomistic
simulations. We discover that waves of complexation dipoles at dynamically
curving interfaces create an emergent long-range force that drives exfoliation
and restacking over time- and length-scales that are not captured in existing
models. Curvature delocalizes electrostatic interactions in ways that
fundamentally differ from planar surfaces, altering the ratio of ions bound to
the convex and concave sides of a layer. Multiple-scattering reconstruction of
low-dose energy-filtered cryo electron tomography enabled direct imaging of ion
complexes and electrolyte distributions at hydrated and curved mineral
interfaces with {\aa}ngstrom resolution over micron length scales. Layers
exfoliate and restack abruptly and repeatedly over timescales that depend
strongly on the counterion identity, demonstrating that the strong coupling
between elastic, electrostatic and hydration forces in clays promote collective
reorganization previously thought to be a feature only of active matter.",2012.09295v1
2020-12-17,Age-optimal Scheduling over Hybrid Channels,"We consider the problem of minimizing the age of information when a source
can transmit status updates over two heterogeneous channels. Our work is
motivated by recent developments in 5G mmWave technology, where transmissions
may occur over an unreliable but fast (e.g., mmWave) channel or a slow reliable
(e.g., sub-6GHz) channel. The unreliable channel is modeled as a
time-correlated Gilbert-Elliot channel at a high rate when the channel is in
the 'ON' state. The reliable channel provides a deterministic but lower data
rate. The scheduling strategy determines the channel to be used for
transmission in each time slot, aiming to minimize the time-average age of
information (AoI). The optimal scheduling problem is formulated as a Markov
Decision Process (MDP), which is challenging to solve because super-modularity
does not hold in a part of the state space. We address this challenge and show
that a multi-dimensional threshold-type scheduling policy is optimal for
minimizing the age. By exploiting the structure of the MDP and analyzing the
discrete-time Markov chains (DTMCs) of the threshold-type policy, we devise a
low-complexity bisection algorithm to compute the optimal thresholds. We
compare different scheduling policies using numerical simulations.",2012.09403v6
2020-12-21,Variations on the Maiani-Testa approach and the inverse problem,"We discuss a method to construct hadronic scattering and decay amplitudes
from Euclidean correlators, by combining the approach of a regulated inverse
Laplace transform with the work of Maiani and Testa. Revisiting the original
result, we observe that the key observation, i.e. that only threshold
scattering information can be extracted at large separations, can be understood
by interpreting the correlator as a spectral function, $\rho(\omega)$,
convoluted with the Euclidean kernel, $e^{- \omega t}$, which is sharply peaked
at threshold. We therefore consider a modification in which a smooth step
function, equal to one above a target energy, is inserted in the spectral
decomposition. This can be achieved either through Backus-Gilbert-like methods
or more directly using the variational approach. The result is a shifted
resolution function, such that the large $t$ limit projects onto scattering or
decay amplitudes above threshold. The utility of this method is highlighted
through large $t$ expansions of both three- and four-point functions that
include leading terms proportional to the real and imaginary parts (separately)
of the target observable. This work also presents new results relevant for the
un-modified correlator at threshold, including expressions for extracting the
$N \pi$ scattering length from four-point functions and a new strategy to
organize the large $t$ expansion that exhibits better convergence than the
expansion in powers of $1/t$.",2012.11488v1
2021-01-13,"PID passivity-based droop control of power converters: Large-signal stability, robustness and performance","We present a full review of PID passivity-based controllers (PBC) applied to
power electronic converters, discussing limitations, unprecedented merits and
potential improvements in terms of large-signal stability, robustness and
performance. We provide four main contributions. The nominal case is first
considered and it is shown, under the assumption of perfect knowledge of the
system parameters, that the PID-PBC is able to guarantee global exponential
stability of a desired operating point for any positive gains. Second, we
analyze robustness of the controller to parameters uncertainty for a specific
class of power converters, by establishing precise stability margins. Third, we
propose a modification of the controller by introducing a leakage, in order to
overcome some of the intrinsic performance and robustness limitations.
Interestingly, such controller can be interpreted at steady-state as a droop
between the input and the passive output, similar to traditional primary
controllers. Fourth, we robustify the design against saturation of the control
input via an appropriate monotone transformation of the controller. The
obtained results are thoroughly discussed and validated by simulations on two
relevant power applications: a dc/dc boost converter and an HVDC grid-connected
voltage source converter.",2101.05047v2
2021-02-15,Recent Developments in Blockchain Technology and their Impact on Energy Consumption,"The enormous power consumption of Bitcoin has led to undifferentiated
discussions in science and practice about the sustainability of blockchain and
distributed ledger technology in general. However, blockchain technology is far
from homogeneous - not only with regard to its applications, which now go far
beyond cryptocurrencies and have reached businesses and the public sector, but
also with regard to its technical characteristics and, in particular, its power
consumption. This paper summarizes the status quo of the power consumption of
various implementations of blockchain technology, with special emphasis on the
recent 'Bitcoin Halving' and so-called 'zk-rollups'. We argue that although
Bitcoin and other proof-of-work blockchains do indeed consume a lot of power,
alternative blockchain solutions with significantly lower power consumption are
already available today, and new promising concepts are being tested that could
further reduce in particular the power consumption of large blockchain networks
in the near future. From this we conclude that although the criticism of
Bitcoin's power consumption is legitimate, it should not be used to derive an
energy problem of blockchain technology in general. In many cases in which
processes can be digitised or improved with the help of more energy-efficient
blockchain variants, one can even expect net energy savings.",2102.07886v1
2021-03-11,Toward the Next Generation of News Recommender Systems,"This paper proposes a vision and research agenda for the next generation of
news recommender systems (RS), called the table d'hote approach. A table d'hote
(translates as host's table) meal is a sequence of courses that create a
balanced and enjoyable dining experience for a guest. Likewise, we believe news
RS should strive to create a similar experience for the users by satisfying the
news-diet needs of a user. While extant news RS considers criteria such as
diversity and serendipity, and RS bundles have been studied for other contexts
such as tourism, table d'hote goes further by ensuring the recommended articles
satisfy a diverse set of user needs in the right proportions and in a specific
order. In table d'hote, available articles need to be stratified based on the
different ways that news can create value for the reader, building from
theories and empirical research in journalism and user engagement. Using
theories and empirical research from communication on the uses and
gratifications (U&G) consumers derive from media, we define two main strata in
a table d'hote news RS, each with its own substrata: 1) surveillance, which
consists of information the user needs to know, and 2) serendipity, which are
the articles offering unexpected surprises. The diversity of the articles
according to the defined strata and the order of the articles within the list
of recommendations are also two important aspects of the table d'hote in order
to give the users the most effective reading experience. We propose our vision,
link it to the existing concepts in the RS literature, and identify challenges
for future research.",2103.06909v1
2021-03-16,Machine learning methods for the prediction of micromagnetic magnetization dynamics,"Machine learning (ML) entered the field of computational micromagnetics only
recently. The main objective of these new approaches is the automatization of
solutions of parameter-dependent problems in micromagnetism such as fast
response curve estimation modeled by the Landau-Lifschitz-Gilbert (LLG)
equation. Data-driven models for the solution of time- and parameter-dependent
partial differential equations require high dimensional training
data-structures. ML in this case is by no means a straight-forward trivial
task, it needs algorithmic and mathematical innovation. Our work introduces
theoretical and computational conceptions of certain kernel and neural network
based dimensionality reduction approaches for efficient prediction of solutions
via the notion of low-dimensional feature space integration. We introduce
efficient treatment of kernel ridge regression and kernel principal component
analysis via low-rank approximation. A second line follows neural network (NN)
autoencoders as nonlinear data-dependent dimensional reduction for the training
data with focus on accurate latent space variable description suitable for a
feature space integration scheme. We verify and compare numerically by means of
a NIST standard problem. The low-rank kernel method approach is fast and
surprisingly accurate, while the NN scheme can even exceed this level of
accuracy at the expense of significantly higher costs.",2103.09079v2
2021-03-18,Bounding the detection efficiency threshold in Bell tests using multiple copies of the maximally entangled two-qubit state carried by a single pair of particles,"In this paper, we investigate the critical efficiency of detectors to observe
Bell nonlocality using multiple copies of the maximally entangled two-qubit
state carried by a single pair of particles, such as hyperentangled states, and
the product of Pauli measurements. It is known that in a
Clauser-Horne-Shimony-Holt (CHSH) Bell test the symmetric detection efficiency
of $82.84\%$ can be tolerated for the two-qubit maximally entangled state. We
beat this enigmatic threshold by entangling two particles with multiple degrees
of freedom. The obtained upper bounds of the symmetric detection efficiency
thresholds are $80.86\%$, $73.99\%$ and $69.29\%$ for two, three and four
copies of the two-qubit maximally entangled state, respectively. The number of
measurements and outcomes in the respective cases are 4, 8 and 16. To find the
improved thresholds, we use large-scale convex optimization tools, which allows
us to significantly go beyond state-of-the-art results. The proof is exact up
to three copies, while for four copies it is due to reliable numerical
computations. Specifically, we used linear programming to obtain the two-copy
threshold and the corresponding Bell inequality, and convex optimization based
on Gilbert's algorithm for three and four copies of the two-qubit state. We
show analytically that the symmetric detection efficiency threshold decays
exponentially with the number of copies of the two-qubit state. Our techniques
can also be applied to more general Bell nonlocality scenarios with more than
two parties.",2103.10413v2
2021-04-05,When Can Liquid Democracy Unveil the Truth?,"In this paper, we investigate the so-called ODP-problem that has been
formulated by Caragiannis and Micha [10]. Here, we are in a setting with two
election alternatives out of which one is assumed to be correct. In ODP, the
goal is to organise the delegations in the social network in order to maximize
the probability that the correct alternative, referred to as ground truth, is
elected. While the problem is known to be computationally hard, we strengthen
existing hardness results by providing a novel strong approximation hardness
result: For any positive constant $C$, we prove that, unless $P=NP$, there is
no polynomial-time algorithm for ODP that achieves an approximation guarantee
of $\alpha \ge (\ln n)^{-C}$, where $n$ is the number of voters. The reduction
designed for this result uses poorly connected social networks in which some
voters suffer from misinformation. Interestingly, under some hypothesis on
either the accuracies of voters or the connectivity of the network, we obtain a
polynomial-time $1/2$-approximation algorithm. This observation proves formally
that the connectivity of the social network is a key feature for the efficiency
of the liquid democracy paradigm. Lastly, we run extensive simulations and
observe that simple algorithms (working either in a centralized or
decentralized way) outperform direct democracy on a large class of instances.
Overall, our contributions yield new insights on the question in which
situations liquid democracy can be beneficial.",2104.01828v1
2021-04-05,Floquet prethermalization with lifetime exceeding 90s in a bulk hyperpolarized solid,"We report the observation of long-lived Floquet prethermal states in a bulk
solid composed of dipolar-coupled $^{13}$C nuclei in diamond at room
temperature. For precessing nuclear spins prepared in an initial transverse
state, we demonstrate pulsed spin-lock Floquet control that prevents their
decay over multiple-minute long periods. We observe Floquet prethermal
lifetimes $T_2'\approx$90.9s, extended >60,000-fold over the nuclear free
induction decay times. The spins themselves are continuously interrogated for
$\sim$10min, corresponding to the application of $\approx$5.8M control pulses.
The $^{13}$C nuclei are optically hyperpolarized by lattice Nitrogen Vacancy
(NV) centers; the combination of hyperpolarization and continuous spin readout
yields significant signal-to-noise in the measurements. This allows probing the
Floquet thermalization dynamics with unprecedented clarity. We identify four
characteristic regimes of the thermalization process, discerning short-time
transient processes leading to the prethermal plateau, and long-time system
heating towards infinite temperature. This work points to new opportunities
possible via Floquet control in networks of dilute, randomly distributed,
low-sensitivity nuclei. In particular, the combination of minutes-long
prethermal lifetimes and continuous spin interrogation opens avenues for
quantum sensors constructed from hyperpolarized Floquet prethermal nuclei.",2104.01988v2
2021-04-14,Generalized Simple Streaming Codes from MDS Codes,"Streaming codes represent a packet-level FEC scheme for achieving reliable,
low-latency communication. In the literature on streaming codes, the
commonly-assumed Gilbert-Elliott channel model, is replaced by a more
tractable, delay-constrained, sliding-window (DCSW) channel model that can
introduce either random or burst erasures. The known streaming codes that are
rate optimal over the DCSW channel model are constructed by diagonally
embedding a scalar block code across successive packets. These code
constructions have field size that is quadratic in the delay parameter $\tau$
and have a somewhat complex structure with an involved decoding procedure. This
led to the introduction of simple streaming (SS) codes in which diagonal
embedding is replaced by staggered-diagonal embedding (SDE). The SDE approach
reduces the impact of a burst of erasures and makes it possible to construct
near-rate-optimal streaming codes using Maximum Distance Separable (MDS) code
having linear field size. The present paper takes this development one step
further, by retaining the staggered-diagonal feature, but permitting the
placement of more than one code symbol from a given scalar codeword within each
packet. These generalized, simple streaming codes allow us to improve upon the
rate of SS codes, while retaining the simplicity of working with MDS codes. We
characterize the maximum code rate of streaming codes under a constraint on the
number of contiguous packets over which symbols of the underlying scalar code
are dispersed. Such a constraint leads to simplified code construction and
reduced-complexity decoding.",2104.07005v1
2021-04-22,COVID-19 and Big Data: Multi-faceted Analysis for Spatio-temporal Understanding of the Pandemic with Social Media Conversations,"COVID-19 has been devastating the world since the end of 2019 and has
continued to play a significant role in major national and worldwide events,
and consequently, the news. In its wake, it has left no life unaffected. Having
earned the world's attention, social media platforms have served as a vehicle
for the global conversation about COVID-19. In particular, many people have
used these sites in order to express their feelings, experiences, and
observations about the pandemic. We provide a multi-faceted analysis of
critical properties exhibited by these conversations on social media regarding
the novel coronavirus pandemic. We present a framework for analysis, mining,
and tracking the critical content and characteristics of social media
conversations around the pandemic. Focusing on Twitter and Reddit, we have
gathered a large-scale dataset on COVID-19 social media conversations. Our
analyses cover tracking potential reports on virus acquisition, symptoms,
conversation topics, and language complexity measures through time and by
region across the United States. We also present a BERT-based model for
recognizing instances of hateful tweets in COVID-19 conversations, which
achieves a lower error-rate than the state-of-the-art performance. Our results
provide empirical validation for the effectiveness of our proposed framework
and further demonstrate that social media data can be efficiently leveraged to
provide public health experts with inexpensive but thorough insight over the
course of an outbreak.",2104.10807v1
2021-05-05,exoplanet: Gradient-based probabilistic inference for exoplanet data & other astronomical time series,"""exoplanet"" is a toolkit for probabilistic modeling of astronomical time
series data, with a focus on observations of exoplanets, using PyMC3 (Salvatier
et al., 2016). PyMC3 is a flexible and high-performance model-building language
and inference engine that scales well to problems with a large number of
parameters. ""exoplanet"" extends PyMC3's modeling language to support many of
the custom functions and probability distributions required when fitting
exoplanet datasets or other astronomical time series. While it has been used
for other applications, such as the study of stellar variability, the primary
purpose of ""exoplanet"" is the characterization of exoplanets or multiple star
systems using time-series photometry, astrometry, and/or radial velocity. In
particular, the typical use case would be to use one or more of these datasets
to place constraints on the physical and orbital parameters of the system, such
as planet mass or orbital period, while simultaneously taking into account the
effects of stellar variability.",2105.01994v2
2021-05-05,Elemental Abundances in M31: Gradients in the Giant Stellar Stream,"We analyze existing measurements of [Fe/H] and [$\alpha$/Fe] for individual
red giant branch (RGB) stars in the Giant Stellar Stream (GSS) of M31 to
determine whether spatial abundance gradients are present. These measurements
were obtained from low- ($R \sim 3000$) and moderate- ($R \sim 6000$)
resolution Keck/DEIMOS spectroscopy using spectral synthesis techniques as part
of the Elemental Abundances in M31 survey. From a sample of 62 RGB stars
spanning the GSS at 17, 22, and 33 projected kpc, we measure a [Fe/H] gradient
of $-$0.018 $\pm$ 0.003 dex kpc$^{-1}$ and negligible [$\alpha$/Fe] gradient
with M31-centric radius. We investigate GSS abundance patterns in the outer
halo using additional [Fe/H] and [$\alpha$/Fe] measurements for 6 RGB stars
located along the stream at 45 and 58 projected kpc. These abundances provide
tentative evidence that the trends in [Fe/H] and [$\alpha$/Fe] beyond 40 kpc in
the GSS are consistent with those within 33 kpc. We also compare the GSS
abundances to 65 RGB stars located along the possibly related Southeast (SE)
shelf substructure at 12 and 18 projected kpc. The abundances of the GSS and SE
shelf are consistent, supporting a common origin hypothesis, although this
interpretation may be complicated by the presence of [Fe/H] gradients in the
GSS. We discuss the abundance patterns in the context of photometric studies
from the literature and explore implications for the properties of the GSS
progenitor, suggesting that the high $\langle$[$\alpha$/Fe]$\rangle$ of the GSS
(+0.40 $\pm$ 0.05 dex) favors a major merger scenario for its formation.",2105.02339v1
2021-05-17,A Unified Adaptive Recoding Framework for Batched Network Coding,"Batched network coding is a variation of random linear network coding which
has low computational and storage costs. In order to adapt to random
fluctuations in the number of erasures in individual batches, it is not optimal
to recode and transmit the same number of packets for all batches. Different
distributed optimization models, which are called adaptive recoding schemes,
were formulated for this purpose. The key component of these optimization
problems is the expected value of the rank distribution of a batch at the next
network node, which is also known as the expected rank. In this paper, we put
forth a unified adaptive recoding framework with an arbitrary recoding field
size. We show that the expected rank functions are concave when the packet loss
pattern is a stationary stochastic process, which covers but not limited to
independent packet loss and Gilbert-Elliott packet loss model. Under this
concavity assumption, we show that there always exists a solution which not
only can minimize the randomness on the number of recoded packets but also can
tolerate rank distribution errors due to inaccurate measurements or limited
precision of the machine. We provide an algorithm to obtain such an optimal
optimal solution, and propose tuning schemes that can turn any feasible
solution into a desired optimal solution.",2105.07614v2
2021-05-18,Magnetic flux structuring of the quiet Sun internetwork. Center-to-limb analysis of solar-cycle variations,"It is now well established that the quiet Sun contains in total more magnetic
flux than active regions and represents an important reservoir of magnetic
energy. But the nature and evolution of these fields remain largely unknown.
  We investigate the solar-cycle and center-to-limb variations of magnetic-flux
structures at small scales in internetwork regions of the quiet Sun.
  We used Hinode SOT/SP data from the irradiance program between 2008 and 2016.
Maps of the magnetic-flux density are derived from the center-of gravity method
applied to the FeI 630.15 nm and FeI 630.25 nm lines. To correct the maps from
the instrumental smearing, we applied a deconvolution method based on a
principal component analysis of the line profiles and on a Richardson-Lucy
deconvolution of their coefficients. We then performed a spectral analysis of
the spatial fluctuations of the magnetic-flux density in 10'' x 10''
internetwork regions spanning a wide range of latitudes.
  At low and mid latitudes the power spectra do not vary significantly with the
solar cycle. However at solar maximum for one scan in the activity belt showing
an enhanced network, a marginal increase in the power of the magnetic
fluctuations is observed at granular and larger scales in the internetwork. At
high latitudes, we observe variations at granular and larger scales where the
power decreases at solar maximum. At all the latitudes the power of the
magnetic fluctuations at scales smaller than 0.5''remain constant throughout
the solar cycle.
  Our results favor a small-scale dynamo that operates in the internetwork, but
they show that the global dynamo also contributes to the internetwork fields.",2105.08657v1
2021-05-21,Hybrid Machine Learning for Scanning Near-field Optical Spectroscopy,"The underlying physics behind an experimental observation often lacks a
simple analytical description. This is especially the case for scanning probe
microscopy techniques, where the interaction between the probe and the sample
is nontrivial. Realistic modeling to include the details of the probe is always
exponentially more difficult than its ""spherical cow"" counterparts. On the
other hand, a well-trained artificial neural network based on real data can
grasp the hidden correlation between the signal and sample properties. In this
work, we show that, via a combination of model calculation and experimental
data acquisition, a physics-infused hybrid neural network can predict the
tip-sample interaction in the widely used scattering-type scanning near-field
optical microscope. This hybrid network provides a long-sought solution for
accurate extraction of material properties from tip-specific raw data. The
methodology can be extended to other scanning probe microscopy techniques as
well as other data-oriented physical problems in general.",2105.10551v1
2021-05-26,Contention Resolution with Predictions,"In this paper, we consider contention resolution algorithms that are
augmented with predictions about the network. We begin by studying the natural
setup in which the algorithm is provided a distribution defined over the
possible network sizes that predicts the likelihood of each size occurring. The
goal is to leverage the predictive power of this distribution to improve on
worst-case time complexity bounds. Using a novel connection between contention
resolution and information theory, we prove lower bounds on the expected time
complexity with respect to the Shannon entropy of the corresponding network
size random variable, for both the collision detection and no collision
detection assumptions. We then analyze upper bounds for these settings,
assuming now that the distribution provided as input might differ from the
actual distribution generating network sizes. We express their performance with
respect to both entropy and the statistical divergence between the two
distributions -- allowing us to quantify the cost of poor predictions. Finally,
we turn our attention to the related perfect advice setting, parameterized with
a length $b\geq 0$, in which all active processes in a given execution are
provided the best possible $b$ bits of information about their network. We
provide tight bounds on the speed-up possible with respect to $b$ for
deterministic and randomized algorithms, with and without collision detection.
These bounds provide a fundamental limit on the maximum power that can be
provided by any predictive model with a bounded output size.",2105.12706v1
2021-05-27,Balancing Static Vacuum Black Holes with Signed Masses in 4 and 5 Dimensions,"We construct a new set of asymptotically flat, static vacuum solutions to the
Einstein equations in dimensions 4 and 5, which may be interpreted as a
superposition of positive and negative mass black holes. The resulting
spacetimes are axisymmetric in 4-dimensions and bi-axisymmetric in
5-dimensions, and are regular away from the negative mass singularities, for
instance conical singularities are absent along the axes. In 5-dimensions, the
topologies of signed mass black holes used in the construction may be either
spheres $S^3$ or rings $S^1 \times S^2$; in particular, the negative mass
static black ring solution is introduced. A primary observation that
facilitates the superposition is the fact that, in Weyl-Papapetrou coordinates,
negative mass singularities arise as overlapping singular support for a
particular type of Green's function. Furthermore, a careful analysis of conical
singularities along axes is performed, and formulas are obtained for their
propagation across horizons, negative mass singularities, and corners. The
methods are robust, and may be used to construct a multitude of further
examples. Lastly, we show that balancing does not occur between any two signed
mass black holes of the type studied here in 4 dimensions, while in 5
dimensions two-body balancing is possible.",2105.13260v2
2021-06-11,Inference for treatment-specific survival curves using machine learning,"In the absence of data from a randomized trial, researchers often aim to use
observational data to draw causal inference about the effect of a treatment on
a time-to-event outcome. In this context, interest often focuses on the
treatment-specific survival curves; that is, the survival curves were the
entire population under study to be assigned to receive the treatment or not.
Under certain causal conditions, including that all confounders of the
treatment-outcome relationship are observed, the treatment-specific survival
can be identified with a covariate-adjusted survival function. Several
estimators of this function have been proposed, including estimators based on
outcome regression, inverse probability weighting, and doubly robust
estimators. In this article, we propose a new cross-fitted doubly-robust
estimator that incorporates data-adaptive (e.g. machine learning) estimators of
the conditional survival functions. We establish conditions on the nuisance
estimators under which our estimator is consistent and asymptotically linear,
both pointwise and uniformly in time. We also propose a novel ensemble learner
for combining multiple candidate estimators of the conditional survival
estimators. Notably, our methods and results accommodate events occurring in
discrete or continuous time (or both). We investigate the practical performance
of our methods using numerical studies and an application to the effect of a
surgical treatment to prevent metastases of parotid carcinoma on mortality.",2106.06602v1
2021-06-10,Hard Choices in Artificial Intelligence,"As AI systems are integrated into high stakes social domains, researchers now
examine how to design and operate them in a safe and ethical manner. However,
the criteria for identifying and diagnosing safety risks in complex social
contexts remain unclear and contested. In this paper, we examine the vagueness
in debates about the safety and ethical behavior of AI systems. We show how
this vagueness cannot be resolved through mathematical formalism alone, instead
requiring deliberation about the politics of development as well as the context
of deployment. Drawing from a new sociotechnical lexicon, we redefine vagueness
in terms of distinct design challenges at key stages in AI system development.
The resulting framework of Hard Choices in Artificial Intelligence (HCAI)
empowers developers by 1) identifying points of overlap between design
decisions and major sociotechnical challenges; 2) motivating the creation of
stakeholder feedback channels so that safety issues can be exhaustively
addressed. As such, HCAI contributes to a timely debate about the status of AI
development in democratic societies, arguing that deliberation should be the
goal of AI Safety, not just the procedure by which it is ensured.",2106.11022v1
2021-06-30,A long-period substellar object exhibiting a single transit in Kepler,"We report the detection of a single transit-like signal in the Kepler data of
the slightly evolved F star KIC4918810. The transit duration is ~45 hours, and
while the orbital period ($P\sim10$ years) is not well constrained, it is one
of the longest among companions known to transit. We calculate the size of the
transiting object to be $R_P = 0.910$ $R_J$. Objects of this size vary by
orders of magnitude in their densities, encompassing masses between that of
Saturn ($0.3$ $M_J$) and stars above the hydrogen-burning limit (~80 $M_J$).
Radial-velocity observations reveal that the companion is unlikely to be a
star. The mass posterior is bimodal, indicating a mass of either ~0.24 $M_J$ or
~26 $M_J$. Continued spectroscopic monitoring should either constrain the mass
to be planetary or detect the orbital motion, the latter of which would yield a
benchmark long-period brown dwarf with a measured mass, radius, and age.",2107.00027v1
2021-07-02,Scaling of Turbulent Viscosity and Resistivity: Extracting a Scale-dependent Turbulent Magnetic Prandtl Number,"Turbulent viscosity $\nu_t$ and resistivity $\eta_t$ are perhaps the simplest
models for turbulent transport of angular momentum and magnetic fields,
respectively. The associated turbulent magnetic Prandtl number $Pr_t\equiv
\nu_t/\eta_t$ has been well recognized to determine the final magnetic
configuration of accretion disks. Here, we present an approach to determining
these ''effective transport'' coefficients acting at different length-scales
using coarse-graining and recent results on decoupled kinetic and magnetic
energy cascades [Bian & Aluie 2019]. By analyzing the kinetic and magnetic
energy cascades from a suite of high-resolution simulations, we show that our
definitions of $\nu_t$, $\eta_t$, and $Pr_t$ have power-law scalings in the
''decoupled range.'' We observe that $Pr_t\approx1 \text{~to~}2$ at the
smallest inertial-inductive scales, increasing to $\approx 5$ at the largest
scales. However, based on physical considerations, our analysis suggests that
$Pr_t$ has to become scale-independent and of order unity in the decoupled
range at sufficiently high Reynolds numbers (or grid-resolution), and that the
power-law scaling exponents of velocity and magnetic spectra become equal. In
addition to implications to astrophysical systems, the scale-dependent
turbulent transport coefficients offer a guide for large eddy simulation
modeling.",2107.00861v1
2021-07-24,Dual-Attention Enhanced BDense-UNet for Liver Lesion Segmentation,"In this work, we propose a new segmentation network by integrating DenseUNet
and bidirectional LSTM together with attention mechanism, termed as
DA-BDense-UNet. DenseUNet allows learning enough diverse features and enhancing
the representative power of networks by regulating the information flow.
Bidirectional LSTM is responsible to explore the relationships between the
encoded features and the up-sampled features in the encoding and decoding
paths. Meanwhile, we introduce attention gates (AG) into DenseUNet to diminish
responses of unrelated background regions and magnify responses of salient
regions progressively. Besides, the attention in bidirectional LSTM takes into
account the contribution differences of the encoded features and the up-sampled
features in segmentation improvement, which can in turn adjust proper weights
for these two kinds of features. We conduct experiments on liver CT image data
sets collected from multiple hospitals by comparing them with state-of-the-art
segmentation models. Experimental results indicate that our proposed method
DA-BDense-UNet has achieved comparative performance in terms of dice
coefficient, which demonstrates its effectiveness.",2107.11645v1
2021-08-03,Comparative study of magnetic properties of Mn$^{3+}$ magnetic clusters in GaN using classical and quantum mechanical approach,"Currently, simulations of many-body quantum systems are known to be
computationally too demanding to be solved on classical computers. The main
problem is that the computation time and memory necessary for performing the
calculations usually grow exponentially with the number of particles $N$. An
efficient approach to simulate many-body quantum systems is the use of
classical approximation. However, it is known that at least at low
temperatures, the allowed spin fluctuations in this approach are overestimated
what results in enhanced thermal fluctuations. It is therefore timely and
important to assess the validity of the classical approximation. To this end,
in this work, we compare the results of numerical calculations of small
Mn$^{3+}$ magnetic clusters in GaN, where the Mn spins are treated classically
with those where they are treated quantum-mechanically (crystal field model).
In the first case, we solve the Landau-Lifshitz-Gilbert (LLG) equation that
describes the precessional dynamics of spins represented by classical vectors.
On the other hand, in the crystal field model, the state of Mn$^{3+}$ ion
($d^4$ configuration with $S=2$, $L=2$) is characterized by the set of orbital
and spin quantum numbers $|m_s,m_L>$. Particular attention is paid to use
numerical parameters that ensure the same single ion magnetic anisotropy in
both classical and quantum approximation. Finally, a detailed comparative study
of magnetization $\mathbf{M}(\mathbf{H}, T)$ as a function of the magnetic
field $\mathbf{H}$, temperature $T$, number of ions in a given cluster $N$ and
the strength of super-exchange interaction $J$, obtained from both approaches
will be presented.",2108.01474v1
2021-08-06,Performance trade-offs in cyber-physical control applications with multi-connectivity,"Modern communication devices are often equipped with multiple wireless
communication interfaces with diverse characteristics. This enables exploiting
a form of multi-connectivity known as interface diversity to provide path
diversity with multiple communication interfaces. Interface diversity helps to
combat the problems suffered by single-interface systems due to error bursts in
the link, which are a consequence of temporal correlation in the wireless
channel. The length of an error burst is an essential performance indicator for
cyber-physical control applications with periodic traffic, as these define the
period in which the control link is unavailable. However, the available
interfaces must be correctly orchestrated to achieve an adequate trade-off
between latency, reliability, and energy consumption. This work investigates
how the packet error statistics from different interfaces impacts the overall
latency-reliability characteristics and explores mechanisms to derive adequate
interface diversity policies. For this, we model the optimization problem as a
partially observable Markov Decision Process (POMDP), where the state of each
interface is determined by a Gilbert-Elliott model whose parameters are
estimated based on experimental measurement traces from LTE and Wi-Fi. Our
results show that the POMDP approach provides an all-round adaptable solution,
whose performance is only 0.1% below the absolute upper bound, dictated by the
optimal policy under the impractical assumption of full observability.",2108.03035v1
2021-08-16,$Q$-ary non-overlapping codes: a generating function approach,"Non-overlapping codes are a set of codewords in $\bigcup_{n \ge 2}
\mathbb{Z}_q^n$, where $\mathbb{Z}_q = \{0,1,\dots,q-1\}$, such that, the
prefix of each codeword is not a suffix of any codeword in the set, including
itself; and for variable-length codes, a codeword does not contain any other
codeword as a subword. In this paper, we investigate a generic method to
generalize binary codes to $q$-ary for $q > 2$, and analyze this generalization
on the two constructions given by Levenshtein (also by Gilbert; Chee, Kiah,
Purkayastha, and Wang) and Bilotta, respectively. The generalization on the
former construction gives large non-expandable fixed-length non-overlapping
codes whose size can be explicitly determined; the generalization on the later
construction is the first attempt to generate $q$-ary variable-length
non-overlapping codes. More importantly, this generic method allows us to
utilize the generating function approach to analyze the cardinality of the
underlying $q$-ary non-overlapping codes. The generating function approach not
only enables us to derive new results, e.g., recurrence relations on their
cardinalities, new combinatorial interpretations for the constructions, and the
limit superior of their cardinalities for some special cases, but also greatly
simplifies the arguments for these results. Furthermore, we give an exact
formula for the number of fixed-length words that do not contain the codewords
in a variable-length non-overlapping code as subwords. This thereby solves an
open problem by Bilotta and induces a recursive upper bound on the maximum size
of variable-length non-overlapping codes.",2108.06934v1
2021-08-17,Searching For or Reviewing Evidence Improves Crowdworkers' Misinformation Judgments and Reduces Partisan Bias,"Can crowd workers be trusted to judge whether news-like articles circulating
on the Internet are misleading, or does partisanship and inexperience get in
the way? And can the task be structured in a way that reduces partisanship? We
assembled pools of both liberal and conservative crowd raters and tested three
ways of asking them to make judgments about 374 articles. In a no research
condition, they were just asked to view the article and then render a judgment.
In an individual research condition, they were also asked to search for
corroborating evidence and provide a link to the best evidence they found. In a
collective research condition, they were not asked to search, but instead to
review links collected from workers in the individual research condition. Both
research conditions reduced partisan disagreement in judgments. The individual
research condition was most effective at producing alignment with journalists'
assessments. In this condition, the judgments of a panel of sixteen or more
crowd workers were better than that of a panel of three expert journalists, as
measured by alignment with a held out journalist's ratings.",2108.07898v3
2021-08-23,The Multiverse: Logical Modularity for Proof Assistants,"Proof assistants play a dual role as programming languages and logical
systems. As programming languages, proof assistants offer standard modularity
mechanisms such as first-class functions, type polymorphism and modules. As
logical systems, however, modularity is lacking, and understandably so:
incompatible reasoning principles -- such as univalence and uniqueness of
identity proofs -- can indirectly lead to logical inconsistency when used in a
given development, even when they appear to be confined to different modules.
The lack of logical modularity in proof assistants also hinders the adoption of
richer programming constructs, such as effects. We propose the multiverse, a
general type-theoretic approach to endow proof assistants with logical
modularity. The multiverse consists of multiple universe hierarchies that
statically describe the reasoning principles and effects available to define a
term at a given type. We identify sufficient conditions for this structuring to
modularly ensure that incompatible principles do not interfere, and to locally
restrict the power of dependent elimination when necessary. This extensible
approach generalizes the ad-hoc treatment of the sort of propositions in the
Coq proof assistant. We illustrate the power of the multiverse by describing
the inclusion of Coq-style propositions, the strict propositions of Gilbert et
al., the exceptional type theory of P\'edrot and Tabareau, and general
axiomatic extensions of the logic.",2108.10259v1
2021-08-27,Distributed Control and Optimization of DC Microgrids: A Port-Hamiltonian Approach,"This article proposes a distributed secondary control scheme that drives a dc
microgrid to an equilibrium point where the generators share optimal currents,
and their voltages have a weighted average of nominal value. The scheme does
not rely on the electric system topology nor its specifications; it guarantees
plug-and-play design and functionality of the generators. First, the
incremental model of the microgrid system with constant impedance, current, and
power devices is shown to admit a port-Hamiltonian (pH) representation, and its
passive output is determined. The economic dispatch problem is then solved by
the Lagrange multipliers method; the Karush-Kuhn-Tucker conditions and weighted
average formation of voltages are then formulated as the control objectives. We
propose a control scheme that is based on the Control by Interconnection design
philosophy, where the consensus-based controller is viewed as a virtual pH
system to be interconnected with the physical one. We prove the regional
asymptotic stability of the closed-loop system using Lyapunov and LaSalle
theorems. Equilibrium analysis is also conducted based on the concepts of graph
theory and economic dispatch. Finally, the effectiveness of the presented
scheme for different case studies is validated with a test microgrid system,
simulated in both MATLAB/Simulink and OPAL-RT environments.",2108.12341v1
2021-10-23,Bootstrap percolation in random geometric graphs,"Following Bradonji\'c and Saniee, we study a model of bootstrap percolation
on the Gilbert random geometric graph on the $2$-dimensional torus. In this
model, the expected number of vertices of the graph is $n$, and the expected
degree of a vertex is $a\log n$ for some fixed $a>1$. Each vertex is added with
probability $p$ to a set $A_0$ of initially infected vertices. Vertices
subsequently become infected if they have at least $ \theta a \log n $ infected
neighbours. Here $p, \theta \in [0,1]$ are taken to be fixed constants.
  We show that if $\theta < (1+p)/2$, then a sufficiently large local outbreak
leads with high probability to the infection spreading globally, with all but
$o(n)$ vertices eventually becoming infected. On the other hand, for $ \theta >
(1+p)/2$, even if one adversarially infects every vertex inside a ball of
radius $O(\sqrt{\log n} )$, with high probability the infection will spread to
only $o(n)$ vertices beyond those that were initially infected.
  In addition we give some bounds on the $(a, p, \theta)$ regions ensuring the
emergence of large local outbreaks or the existence of islands of vertices that
never become infected. We also give a complete picture of the (surprisingly
complex) behaviour of the analogous $1$-dimensional bootstrap percolation model
on the circle. Finally we raise a number of problems, and in particular make a
conjecture on an `almost no percolation or almost full percolation' dichotomy
which may be of independent interest.",2110.12166v1
2021-11-02,Orbital Dynamics and the Evolution of Planetary Habitability in the AU Mic System,"The diversity of planetary systems that have been discovered are revealing
the plethora of possible architectures, providing insights into planet
formation and evolution. They also increase our understanding of system
parameters that may affect planetary habitability, and how such conditions are
influenced by initial conditions. The AU~Mic system is unique among known
planetary systems in that it is a nearby, young, multi-planet transiting
system. Such a young and well characterized system provides an opportunity to
study orbital dynamical and habitability studies for planets in the very early
stages of their evolution. Here, we calculate the evolution of the Habitable
Zone of the system through time, including the pre-main sequence phase that the
system currently resides in. We discuss the planetary atmospheric processes
occurring for an Earth-mass planet during this transitionary period, and
provide calculations of the climate state convergence age for both volatile
rich and poor initial conditions. We present results of an orbital dynamical
analysis of the AU~Mic system that demonstrate the rapid eccentricity evolution
of the known planets, and show that terrestrial planets within the Habitable
Zone of the system can retain long-term stability. Finally, we discuss
follow-up observation prospects, detectability of possible Habitable Zone
planets, and how the AU Mic system may be used as a template for studies of
planetary habitability evolution.",2111.01816v1
2021-11-17,Privacy-preserving Federated Learning for Residential Short Term Load Forecasting,"With high levels of intermittent power generation and dynamic demand
patterns, accurate forecasts for residential loads have become essential. Smart
meters can play an important role when making these forecasts as they provide
detailed load data. However, using smart meter data for load forecasting is
challenging due to data privacy requirements. This paper investigates how these
requirements can be addressed through a combination of federated learning and
privacy preserving techniques such as differential privacy and secure
aggregation. For our analysis, we employ a large set of residential load data
and simulate how different federated learning models and privacy preserving
techniques affect performance and privacy. Our simulations reveal that
combining federated learning and privacy preserving techniques can secure both
high forecasting accuracy and near-complete privacy. Specifically, we find that
such combinations enable a high level of information sharing while ensuring
privacy of both the processed load data and forecasting models. Moreover, we
identify and discuss challenges of applying federated learning, differential
privacy and secure aggregation for residential short-term load forecasting.",2111.09248v4
2021-11-30,The AiiDA-Spirit plugin for automated spin-dynamics simulations and multi-scale modelling based on first-principles calculations,"Landau-Lifshitz-Gilbert (LLG) spin-dynamics calculations based on the
extended Heisenberg Hamiltonian is an important tool in computational materials
science involving magnetic materials. LLG simulations allow to bridge the gap
from expensive quantum mechanical calculations with small unit cells to large
supercells where the collective behavior of millions of spins can be studied.
In this work we present the AiiDA-Spirit plugin that connects the spin-dynamics
code Spirit to the AiiDA framework. AiiDA provides a Python interface that
facilitates performing high-throughput calculations while automatically
augmenting the calculations with metadata describing the data provenance
between calculations in a directed acyclic graph. The AiiDA-Spirit interface
thus provides an easy way for high-throughput spin-dynamics calculations. The
interface to the AiiDA infrastructure furthermore has the advantage that input
parameters for the extended Heisenberg model can be extracted from
high-throughput first-principles calculations including a proper treatment of
the data provenance that ensures reproducibility of the calculation results in
accordance to the FAIR principles. We describe the layout of the AiiDA-Spirit
plugin and demonstrate its capabilities using selected examples for LLG
spin-dynamics and Monte Carlo calculations. Furthermore, the integration with
first-principles calculations through AiiDA is demonstrated at the example of
$\gamma$-Fe, where the complex spin-spiral ground state is investigated.",2111.15229v1
2021-12-10,A Framework for Fairness: A Systematic Review of Existing Fair AI Solutions,"In a world of daily emerging scientific inquisition and discovery, the
prolific launch of machine learning across industries comes to little surprise
for those familiar with the potential of ML. Neither so should the congruent
expansion of ethics-focused research that emerged as a response to issues of
bias and unfairness that stemmed from those very same applications. Fairness
research, which focuses on techniques to combat algorithmic bias, is now more
supported than ever before. A large portion of fairness research has gone to
producing tools that machine learning practitioners can use to audit for bias
while designing their algorithms. Nonetheless, there is a lack of application
of these fairness solutions in practice. This systematic review provides an
in-depth summary of the algorithmic bias issues that have been defined and the
fairness solution space that has been proposed. Moreover, this review provides
an in-depth breakdown of the caveats to the solution space that have arisen
since their release and a taxonomy of needs that have been proposed by machine
learning practitioners, fairness researchers, and institutional stakeholders.
These needs have been organized and addressed to the parties most influential
to their implementation, which includes fairness researchers, organizations
that produce ML algorithms, and the machine learning practitioners themselves.
These findings can be used in the future to bridge the gap between
practitioners and fairness experts and inform the creation of usable fair ML
toolkits.",2112.05700v1
2021-12-12,Effect of Topological Non-hexagonal Rings and Stone Wale Defects on the Vibrational Response of Single and Multi-Layer Ion Irradiated Graphene,"Present study explores the observation of topological non-hexagonal rings
(NHR) and Stone Wale (SW) defects by Raman experiments in both single (SLG) and
multi-layer graphene (MLG) after they are irradiated with 100- 300 eV Ar ions.
Although predicted by theoretical studies, here it is experimentally shown for
the first time that graphene SW/NHR defects have a signature in Raman. Broad
bandwidth of the pertinent Raman features suggests the presence of more than
one SW/NHR defect mode, in agreement with the DFT studies. Variations in the
SW/NHR related Raman mode intensities demonstrate the annihilation of these
topological defects at higher energies. Behavior of Raman allowed G and 2D
excitations, as well as the disorder-activated D, D' and G* lines, has also
been investigated in SLG and MLG. These indicate an evolution of defects in
graphene with ion irradiation, as well as presence of a transition state beyond
which the Raman modes are dominated by a rise in sp3 content. Correlation of
these aspects with the SW/NHR Raman provide significant insight into ion
induced evolution of graphene. The direct observation of SW/NHR defects by
Raman spectroscopy could be important in promoting exploration of rich
topological aspects of Graphene in various fields.",2112.06294v1
2021-12-16,Minimal blowing pressure allowing periodic oscillations in a model of bass brass instruments,"In this study, an acoustic resonator -- a bass brass instrument -- with
multiple resonances coupled to an exciter -- the player's lips -- with one
resonance is modelled by a multidimensional dynamical system, and studied using
a continuation and bifurcation software. Bifurcation diagrams are explored with
respect to the blowing pressure, in particular with focus on the minimal
blowing pressure allowing stable periodic oscillations and the associated
frequency.The behaviour of the instrument is first studied close to a (non
oscillating) equilibrium using linear stability analysis. This allows to
determine the conditions at which an equilibrium destabilises and as such where
oscillating regimes can emerge (corresponding to a sound production). This
approach is useful to characterise the ease of playing of a brass instrument,
which is assumed here to be related -- as a first approximation -- to the
linear threshold pressure. In particular, the lower the threshold pressure, the
lower the physical effort the player has to make to play a note [Campbell et
al., 2021].Cases are highlighted where periodic solutions in the bifurcation
diagrams are reached for blowing pressures below the value given by the linear
stability analysis. Thus, bifurcation diagrams allow a more in-depth analysis.
Particular attention is devoted to the first playing regime of bass brass
instruments (the pedal note and the ghost note of a tuba in particular), whose
behaviour qualitatively differs from a trombone to a euphonium for instance.",2112.08751v2
2021-12-20,"Refined modelling of the radio SZ signal: kinematic terms, relativistic temperature corrections and anisotropies in the radio background","A significant cosmological radio background will inevitably lead to a radio
Sunyaev-Zeldovich (SZ) effect. In the simplest limit, the combined signal from
the scattered radio and cosmic microwave background exhibits a null at around
$\nu \simeq 735$ MHz. Here, we show that kinematic and relativistic temperature
corrections to this radio SZ signal are easily calculable. We treat both the
cluster and observer motion, and the scattering of anisotropies in the radio
background, highlighting how the spectrum of the radio SZ effect is affected in
each case. Although relativistic temperature corrections only enter at the
level of a few percent, our expressions allow high-precision modelling of these
terms. By measuring the SZ signal around the radio null, one is in principle
able to place constraints on the properties of a cosmological radio background.
A combination with standard SZ measurements from large cluster samples could
provide a promising avenue towards breaking degeneracies between different
contributions. Stacking analyses can reduce the effect of kinematic corrections
and dipolar anisotropies in the radio background, thereby providing a way to
constrain the redshift dependence of the average radio background. Our
qualitative discussion is meant to give an analytic understanding of the
various effects and also motivate further studies with the aim to obtain
quantitative forecasts of their observability. At this stage, a detection of
the corrections seems rather futuristic, but the advent of large SZ and X-ray
cluster samples could drastically improve our ability to disentangle various
effects.",2112.10666v2
2021-12-22,Conductive and convective heat transfer in inductive heating of subsea buried pipelines,"Inductive heating with high-voltage cables reduces the risk of hydrate
formation by raising the temperature of the production fluid in pipelines.
Heating the pipeline results in losing a certain fraction of the heat to the
surrounding soil through conduction or convection-dominated flow through the
soil. However, the amount of heat lost in conduction versus convection and the
transition from conduction to convection-dominated heat loss remains unknown.
Soil permeability, temperature gradient between cable and mudline, and burial
depth influence the mode of heat transfer and the amount of heat lost. We study
the dominant mode of heat transfer in pipelines with inductive heating using 2D
Finite Difference analysis under different soil and environmental conditions.
Low permeability soils primarily exhibit conductive heat transfer, thus losing
minimum heat to the surrounding soil. In contrast, convective flow drives a
significant fraction of the heat away from the pipeline and towards the ground
surface for highly permeable soils, barely heating the fluid in the pipe. We
identify a critical Rayleigh-Darcy number of 1 as the controlling value
separating conduction and convection-dominated heat transfer. An increase in
burial depth deteriorates the heating efficiency in convection-dominated high
permeability soils, while it remains unaffected in conduction-dominated low
permeability soils.",2112.11826v1
2021-12-28,"Phonon, Electron, and Magnon Excitations in Antiferromagnetic L1$_{0}$-type MnPt","Antiferromagnetic L1$_{0}$-type MnPt is a material with relatively simple
crystal and magnetic structure, recently attracting interest due to its high
N{\'{e}}el temperature and wide usage as a pinning layer in magnetic devices.
While it is experimentally well characterized, the theoretical understanding is
much less developed, in part due to the challenging accuracy requirements
dictated by the small underlying energy scales that govern magnetic ordering in
antiferromagnetic metals. In this work, we use density functional theory, the
Korringa-Kohn-Rostoker formalism, and a Heisenberg model to establish a
comprehensive theoretical description of antiferromagnetic L1$_{0}$-type MnPt,
along with accuracy limits, by thoroughly comparing to available literature
data. Our simulations show that the contribution of the magnetic dipole
interaction to the magnetocrystalline anisotropy energy of $K_{1}$=1.07$\times
10^{6}$\,J/m$^3$ is comparable in magnitude to the spin-orbit contribution.
Using our result for the magnetic susceptibility of $5.25\times10^{-4}$, a
lowest magnon frequency of about 2.02\,THz is predicted, confirming THz spin
dynamics in this material. From our data for electron, phonon, and magnon
dispersion we compute the individual contributions to the total heat capacity
and show that the dominant term at or above 2\,K arises from phonons. From the
Landau-Lifshitz-Gilbert equation, we compute a N\'{e}el temperature of
990--1070 K. Finally, we quantify the magnitude of the magneto-optical Kerr
effect generated by applying an external magnetic field. Our results provide
insight into the underlying physics, which is critical for a deep understanding
of fundamental limits of the time scale of spin dynamics, stability of the
magnetic ordering, and the possibility of magneto-optical detection of
collective spin motion.",2112.13954v1
2022-01-22,"Estimation and Hypothesis Testing of Strain-Specific Vaccine Efficacy with Missing Strain Types, with Applications to a COVID-19 Vaccine Trial","Statistical methods are developed for analysis of clinical and virus genetics
data from phase 3 randomized, placebo-controlled trials of vaccines against
novel coronavirus COVID-19. Vaccine efficacy (VE) of a vaccine to prevent
COVID-19 caused by one of finitely many genetic strains of SARS-CoV-2 may vary
by strain. The problem of assessing differential VE by viral genetics can be
formulated under a competing risks model where the endpoint is virologically
confirmed COVID-19 and the cause-of-failure is the infecting SARS-CoV-2
genotype. Strain-specific VE is defined as one minus the cause-specific hazard
ratio (vaccine/placebo). For the COVID-19 VE trials, the time to COVID-19 is
right-censored, and a substantial percentage of failure cases are missing the
infecting virus genotype. We develop estimation and hypothesis testing
procedures for strain-specific VE when the failure time is subject to right
censoring and the cause-of-failure is subject to missingness, focusing on $J
\ge 2$ discrete categorical unordered or ordered virus genotypes. The
stratified Cox proportional hazards model is used to relate the cause-specific
outcomes to explanatory variables. The inverse probability weighted
complete-case (IPW) estimator and the augmented inverse probability weighted
complete-case (AIPW) estimator are investigated. Hypothesis tests are developed
to assess whether the vaccine provides at least a specified level of efficacy
against some viral genotypes and whether VE varies across genotypes, adjusting
for covariates. The finite-sample properties of the proposed tests are studied
through simulations and are shown to have good performances. In preparation for
the real data analyses, the developed methods are applied to a pseudo dataset
mimicking the Moderna COVE trial.",2201.08946v1
2022-01-30,OverChain: Building a robust overlay with a blockchain,"Blockchains use peer-to-peer networks for disseminating information among
peers, but these networks currently do not have any provable guarantees for
desirable properties such as Byzantine fault tolerance, good connectivity and
small diameter. This is not just a theoretical problem, as recent works have
exploited unsafe peer connection policies and weak network synchronization to
mount partitioning attacks on Bitcoin. Cryptocurrency blockchains are safety
critical systems, so we need principled algorithms to maintain their networks.
  Our key insight is that we can leverage the blockchain itself to share
information among the peers, and thus simplify the network maintenance process.
Given that the peers have restricted computational resources, and at most a
constant fraction of them are Byzantine, we provide communication-efficient
protocols to maintain a hypercubic network for blockchains, where peers can
join and leave over time. Interestingly, we discover that our design can
\emph{recover} from substantial adversarial failures. Moreover, these
properties hold despite significant churn.
  A key contribution is a secure mechanism for joining the network that uses
the blockchain to help new peers to contact existing peers. Furthermore, by
examining how peers join the network, i.e., the ""bootstrapping service,"" we
give a lower bound showing that (within log factors) our network tolerates the
maximum churn rate possible. In fact, we can give a lower bound on churn for
any fully distributed service that requires connectivity.",2201.12809v1
2022-02-04,Three-axis torque investigation of interfacial exchange coupling in a NiFe/CoO bilayer micromagnetic disk,"Micrometer diameter bilayers of NiFe (permalloy, Py) and cobalt oxide (CoO)
deposited on nanomechanical resonators were used to investigate exchange bias
effects. The mechanical compliances of two resonator axes were enhanced by
severing one torsion arm, resulting in a unique three-axis resonator that
responds resonantly to torques generated by a three-axis RF field. Our
technique permits simultaneous measurement of three orthogonal torque
components. Measurements of the anisotropies associated with interfacial
exchange coupling effects have been made. At cryogenic temperatures,
observations of shifted linear hysteresis loops confirmed the presence of
exchange bias from the Py/CoO interface. An in-plane rotating DC bias field was
used to probe in-plane anisotropies through the out-of-plane torque. Training
effects in the rotational hysteresis data were observed and showed that
features due to interfacial coupling did not diminish irrespective of
substantial training of the unidirectional anisotropy. The data from the
rotational hysteresis loops were fit with parameters from a macrospin solution
to the Landau-Lifshitz-Gilbert equation. Each parameter of the exchange bias
model accounts for specific features of the rotational loop.",2202.02386v1
2022-02-11,"Choices, Risks, and Reward Reports: Charting Public Policy for Reinforcement Learning Systems","In the long term, reinforcement learning (RL) is considered by many AI
theorists to be the most promising path to artificial general intelligence.
This places RL practitioners in a position to design systems that have never
existed before and lack prior documentation in law and policy. Public agencies
could intervene on complex dynamics that were previously too opaque to
deliberate about, and long-held policy ambitions would finally be made
tractable. In this whitepaper we illustrate this potential and how it might be
technically enacted in the domains of energy infrastructure, social media
recommender systems, and transportation. Alongside these unprecedented
interventions come new forms of risk that exacerbate the harms already
generated by standard machine learning tools. We correspondingly present a new
typology of risks arising from RL design choices, falling under four
categories: scoping the horizon, defining rewards, pruning information, and
training multiple agents. Rather than allowing RL systems to unilaterally
reshape human domains, policymakers need new mechanisms for the rule of reason,
foreseeability, and interoperability that match the risks these systems pose.
We argue that criteria for these choices may be drawn from emerging subfields
within antitrust, tort, and administrative law. It will then be possible for
courts, federal and state agencies, and non-governmental organizations to play
more active roles in RL specification and evaluation. Building on the ""model
cards"" and ""datasheets"" frameworks proposed by Mitchell et al. and Gebru et
al., we argue the need for Reward Reports for AI systems. Reward Reports are
living documents for proposed RL deployments that demarcate design choices.",2202.05716v1
2022-02-22,Entropy-driven order in an array of nanomagnets,"Long-range ordering is typically associated with a decrease in entropy. Yet,
it can also be driven by increasing entropy in certain special cases. We
demonstrate that artificial spin ice arrays of single-domain nanomagnets can be
designed to produce entropy-driven order. We focus on the tetris artificial
spin ice structure, a highly frustrated array geometry with a zero-point Pauli
entropy, which is formed by selectively creating regular vacancies on the
canonical square ice lattice. We probe thermally active tetris artificial spin
ice both experimentally and through simulations, measuring the magnetic moments
of the individual nanomagnets. We find two-dimensional magnetic ordering in one
subset of these moments, which we demonstrate to be induced by disorder (i.e.,
increased entropy) in another subset of the moments. In contrast with other
entropy-driven systems, the discrete degrees of freedom in tetris artificial
spin ice are binary and are both designable and directly observable at the
microscale, and the entropy of the system is precisely calculable in
simulations. This example, in which the system's interactions and ground state
entropy are well-defined, expands the experimental landscape for the study of
entropy-driven ordering.",2202.11010v1
2022-03-30,Kinematics and Metallicity of Red Giant Branch Stars in the Northeast Shelf of M31,"We obtained Keck/DEIMOS spectra of 556 individual red giant branch stars in 4
spectroscopic fields spanning $13-31$ projected kpc along the Northeast (NE)
shelf of M31. We present the first detection of a complete wedge pattern in the
space of projected M31-centric radial distance versus line-of-sight velocity
for this feature, which includes the returning stream component of the shelf.
This wedge pattern agrees with expectations of a tidal shell formed in a radial
merger and provides strong evidence in favor of predictions of Giant Stellar
Stream (GSS) formation models in which the NE shelf originates from the second
orbital wrap of the tidal debris. The observed concentric wedge patterns of the
NE, West (W), and Southeast (SE) shelves corroborate this interpretation
independently of the models. We do not detect a kinematical signature in the NE
shelf region corresponding to an intact progenitor core, favoring GSS formation
models in which the progenitor is completely disrupted. The shelf's photometric
metallicity distribution implies that it is dominated by tidal material, as
opposed to the phase-mixed stellar halo or the disk. The metallicity
distribution ([Fe/H]$_{\rm phot}$ = $-0.42$ $\pm$ $0.01$) also matches the GSS,
and consequently the W and SE shelves, further supporting a direct physical
association between the tidal features.",2203.16675v1
2022-04-06,Stability and Safety through Event-Triggered Intermittent Control with Application to Spacecraft Orbit Stabilization,"In systems where the ability to actuate is a scarce resource, e.g.,
spacecrafts, it is desirable to only apply a given controller in an
intermittent manner--with periods where the controller is on and periods where
it is off. Motivated by the event-triggered control paradigm, where
state-dependent triggers are utilized in a sample-and-hold context, we
generalize this concept to include state triggers where the controller is off
thereby creating a framework for intermittent control. Our approach utilizes
certificates--either Lyapunov or barrier functions--to design intermittent
trigger laws that guarantee stability or safety; the controller is turned on
for the period for which is beneficial with regard to the certificate, and
turned off until a performance threshold is reached. The main result of this
paper is that the intermittent controller scheme guarantees (set) stability
when Lyapunov functions are utilized, and safety (forward set invariance) in
the setting of barrier functions. As a result, our trigger designs can leverage
the intermittent nature of the actuator, and at the same time, achieve the task
of stabilization or safety. We further demonstrate the application and benefits
of intermittent control in the context of the spacecraft orbit stabilization
problem.",2204.03110v1
2022-04-19,Higher-order modulations in the skyrmion-lattice phase of Cu$_2$OSeO$_3$,"Using small angle neutron scattering, we have investigated higher-order peaks
in the skyrmion-lattice phase of Cu$_2$OSeO$_3$, in which two different
skyrmion lattices, SkX1 and SkX2, are known to form. For each skyrmion-lattice
phase, we observed two sets of symmetrically inequivalent peaks at the
higher-order-reflection positions with the indices $(110)$ and $(200)$. Under
the condition where the SkX1 and SkX2 coexist, we confirmed the absence of the
scattering at $\mathbf{Q}$ positions combining reflections from the two phases,
indicating a significantly weak double-scattering component. Detailed analysis
of the peak profile, as well as the temperature and magnetic-field dependence
of the peak intensity, also supports the intrinsic higher-order modulation
rather than the parasitic double scattering. The two higher-order modulations
show contrasting magnetic-field dependence; the former $(110)$ increases as the
field is increased, whereas the latter $(200)$ decreases. This indicates that,
in Cu$_2$OSeO$_3$, skyrmions are weakly distorted, and the distortion is
field-dependent in a way that the dominant higher-order modulation switches
from $(110)$ to $(200)$ under field. Monte Carlo simulations under sweeping
external magnetic field qualitatively reproduce the observed magnetic-field
dependence, and suggests that the higher-order modulations correspond to the
superlattices of weak swirlings appearing in the middle of the original
triangular-latticed skyrmions.",2204.08614v1
2022-04-19,Emu: A Case Study for TDI-like Imaging for Infrared Observation from Space,"A wide-field zenith-looking telescope operating in a mode similar to
Time-Delay-Integration (TDI) or drift scan imaging can perform an infrared sky
survey without active pointing control but it requires a high-speed, low-noise
infrared detector. Operating from a hosted payload platform on the
International Space Station (ISS), the Emu space telescope employs the
paradigm-changing properties of the Leonardo SAPHIRA electron avalanche
photodiode array to provide powerful new observations of cool stars at the
critical water absorption wavelength (1.4 $\mu$m) largely inaccessible to
ground-based telescopes due to the Earth's own atmosphere. Cool stars,
especially those of spectral-type M, are important probes across contemporary
astrophysics, from the formation history of the Galaxy to the formation of
rocky exoplanets. Main sequence M-dwarf stars are the most abundant stars in
the Galaxy and evolved M-giant stars are some of the most distant stars that
can be individually observed. The Emu sky survey will deliver critical stellar
properties of these cool stars by inferring oxygen abundances via measurement
of the water absorption band strength at 1.4 $\mu$m. Here we present the
TDI-like imaging capability of Emu mission, its science objectives, instrument
details and simulation results.",2204.08713v2
2022-05-05,Photon emissivity of the quark-gluon plasma: a lattice QCD analysis of the transverse channel,"We present results for the thermal photon emissivity of the quark-gluon
plasma derived from spatially transverse vector correlators computed in lattice
QCD at a temperature of 250 MeV. The analysis of the spectral functions,
performed at fixed spatial momentum, is based on continuum-extrapolated
correlators obtained with two flavours of dynamical Wilson fermions. We compare
the next-to-leading order perturbative QCD correlators, as well as the ${\cal
N}=4$ supersymmetric Yang-Mills correlators at infinite coupling, to the
correlators from lattice QCD and find them to lie within $\sim10\%$ of each
other. We then refine the comparison, performing it at the level of filtered
spectral functions obtained model-independently via the Backus-Gilbert method.
Motivated by these studies, for frequencies $\omega\lesssim2.5\,$GeV we use fit
ans\""atze to the spectral functions that perform well when applied to mock data
generated from the NLO QCD or from the strongly-coupled SYM spectral functions,
while the high-frequency part, $\omega\gtrsim 2.5\,$GeV, is matched to NLO QCD.
We compare our results for the photon emissivity to our previous analysis of a
different vector channel at the same temperature. We obtain the most stringent
constraint at photon momenta around $k\simeq0.8\,$GeV, for which we find a
differential photon emission rate per unit volume of $d\Gamma_\gamma/d^3k =
(\alpha_{\rm em}/(\exp(k/T)-1))\times (2.2 \pm 0.8 ) \times 10^{-3}\,{\rm
GeV}$.",2205.02821v1
2022-05-17,"Highlighting relations between Wave-particle duality, Uncertainty principle, Phase space and Microstates","Wave-particle duality is often considered as the modern answer to the problem
of the nature of light after more than 2000 years of questioning. It is also
the answer given by quantum physics concerning the nature of matter particles
and any other radiations. The main objective of this work is to analyze the
relations that are existing between this concept of wave-particle duality, the
uncertainty principle and the concepts of phase space and microstates
considered in statistical mechanics. It is mainly highlighted that while the
concepts of phase space and microstates were already introduced in classical
physics before the discovery of the wave-particle duality, a correct
understanding of them cannot be achieved without the use of the concept of
quantum phase space and phase space representation of quantum mechanics which
are directly related to the uncertainty principle. The possibility of using
these concepts of quantum phase space and phase space representations of
quantum mechanics to help in a deeper description of the wave-particle duality
and in the study of some current issues related to foundational problems of
quantum mechanics like quantum decoherence and the measurement problem is also
discussed.",2205.08538v4
2022-05-26,New Explicit Good Linear Sum-Rank-Metric Codes,"Sum-rank-metric codes have wide applications in universal error correction,
multishot network coding, space-time coding and the construction of partial-MDS
codes for repair in distributed storage. Fundamental properties of
sum-rank-metric codes have been studied and some explicit or probabilistic
constructions of good sum-rank-metric codes have been proposed. In this paper
we give three simple constructions of explicit linear sum-rank-metric codes. In
finite length regime, numerous larger linear sum-rank-metric codes with the
same minimum sum-rank distances as the previous constructed codes can be
derived from our constructions. For example several better linear
sum-rank-metric codes over ${\bf F}_q$ with small block sizes and the matrix
size $2 \times 2$ are constructed for $q=2, 3, 4$ by applying our construction
to the presently known best linear codes. Asymptotically our constructed
sum-rank-metric codes are close to the Gilbert-Varshamov-like bound on
sum-rank-metric codes for some parameters. Finally we construct a linear MSRD
code over an arbitrary finite field ${\bf F}_q$ with various square matrix
sizes $n_1, n_2, \ldots, n_t$ satisfying $n_i \geq n_{i+1}^2+\cdots+n_t^2$ ,
$i=1, 2, \ldots, t-1$, for any given minimum sum-rank distance. There is no
restriction on the block lengths $t$ and parameters $N=n_1+\cdots+n_t$ of these
linear MSRD codes from the sizes of the fields ${\bf F}_q$. \end{abstract}",2205.13087v8
2022-06-17,Multi-scale Super-resolution Magnetic Resonance Spectroscopic Imaging with Adjustable Sharpness,"Magnetic Resonance Spectroscopic Imaging (MRSI) is a valuable tool for
studying metabolic activities in the human body, but the current applications
are limited to low spatial resolutions. The existing deep learning-based MRSI
super-resolution methods require training a separate network for each upscaling
factor, which is time-consuming and memory inefficient. We tackle this
multi-scale super-resolution problem using a Filter Scaling strategy that
modulates the convolution filters based on the upscaling factor, such that a
single network can be used for various upscaling factors. Observing that each
metabolite has distinct spatial characteristics, we also modulate the network
based on the specific metabolite. Furthermore, our network is conditioned on
the weight of adversarial loss so that the perceptual sharpness of the
super-resolved metabolic maps can be adjusted within a single network. We
incorporate these network conditionings using a novel Multi-Conditional Module.
The experiments were carried out on a 1H-MRSI dataset from 15 high-grade glioma
patients. Results indicate that the proposed network achieves the best
performance among several multi-scale super-resolution methods and can provide
super-resolved metabolic maps with adjustable sharpness.",2206.08984v1
2022-06-20,How to Assess Trustworthy AI in Practice,"This report is a methodological reflection on
Z-Inspection$^{\small{\circledR}}$. Z-Inspection$^{\small{\circledR}}$ is a
holistic process used to evaluate the trustworthiness of AI-based technologies
at different stages of the AI lifecycle. It focuses, in particular, on the
identification and discussion of ethical issues and tensions through the
elaboration of socio-technical scenarios. It uses the general European Union's
High-Level Expert Group's (EU HLEG) guidelines for trustworthy AI. This report
illustrates for both AI researchers and AI practitioners how the EU HLEG
guidelines for trustworthy AI can be applied in practice. We share the lessons
learned from conducting a series of independent assessments to evaluate the
trustworthiness of AI systems in healthcare. We also share key recommendations
and practical suggestions on how to ensure a rigorous trustworthy AI assessment
throughout the life-cycle of an AI system.",2206.09887v2
2022-06-23,LRPC codes with multiple syndromes: near ideal-size KEMs without ideals,"We introduce a new rank-based key encapsulation mechanism (KEM) with public
key and ciphertext sizes around 3.5 Kbytes each, for 128 bits of security,
without using ideal structures. Such structures allow to compress objects, but
give reductions to specific problems whose security is potentially weaker than
for unstructured problems. To the best of our knowledge, our scheme improves in
size all the existing unstructured post-quantum lattice or code-based
algorithms such as FrodoKEM or Classic McEliece. Our technique, whose
efficiency relies on properties of rank metric, is to build upon existing Low
Rank Parity Check (LRPC) code-based KEMs and to send multiple syndromes in one
ciphertext, allowing to reduce the parameters and still obtain an acceptable
decoding failure rate. Our system relies on the hardness of the Rank Support
Learning problem, a well-known variant of the Rank Syndrome Decoding problem.
The gain on parameters is enough to significantly close the gap between ideal
and non-ideal constructions. It enables to choose an error weight close to the
rank Gilbert-Varshamov bound, which is a relatively harder zone for algebraic
attacks. We also give a version of our KEM that keeps an ideal structure and
permits to roughly divide the bandwidth by two compared to previous versions of
LRPC KEMs submitted to the NIST with a Decoding Failure Rate (DFR) of
$2^{-128}$.",2206.11961v1
2022-07-08,Rate-Optimal Streaming Codes Over the Three-Node Decode-And-Forward Relay Network,"In this paper, we study the three-node Decode-and-Forward (D&F) relay network
subject to random and burst packet erasures. The source wishes to transmit an
infinite stream of packets to the destination via the relay. The three-node D&F
relay network is constrained by a decoding delay of T packets, i.e., the packet
transmitted by the source at time i must be decoded by the destination by time
i+T. For the individual channels from source to relay and relay to destination,
we assume a delay-constrained sliding-window (DCSW) based packet-erasure model
that can be viewed as a tractable approximation to the commonly-accepted
Gilbert-Elliot channel model. Under the model, any time-window of width w
contains either up to a random erasure or else erasure burst of length at most
b (>= a). Thus the source-relay and relay-destination channels are modeled as
(a_1, b_1, w_1, T_1) and (a_2, b_2, w_2, T_2) DCSW channels. We first derive an
upper bound on the capacity of the three-node D&F relay network. We then show
that the upper bound is tight for the parameter regime: max{b_1,
b_2}|(T-b_1-b_2-max{a_1, a_2}+1), a1=a2 OR b1=b2 by constructing streaming
codes achieving the bound. The code construction requires field size linear in
T, and has decoding complexity equivalent to that of decoding an MDS code.",2207.04025v2
2022-07-12,"Diversity of ghost notes in tubas, euphoniums and saxhorns","The ghost note is a natural note which can be played exclusively on bass
brass instruments with a predominantly-expanding bore profile such as tubas,
euphoniums or saxhorns. It stands between the pedal note-the lowest natural
note playable, or first regime-and the instrument's second regime. However, if
the interval between the pedal note and the second regime remains close to an
octave regardless of the instrument, the interval between the pedal note and
the ghost note vary from a minor third to a perfect fourth. References about
this note are very scarce, and it is not commonly known among tuba players.This
study shows that an elementary brass model describing the player coupled to the
instrument is capable of bringing both the ghost and the pedal note to light.
Here, we adopt a dynamical systems point of view and perform a bifurcation
analysis using a software of numerical continuation. The numerical results
provided in terms of frequency intervals between pedal note and ghost note are
compared with frequency intervals experimentally inferred from recordings of
seven different types of tuba, each of them being played by two professional
tuba players.",2207.05395v3
2022-07-20,Flow-based Visual Quality Enhancer for Super-resolution Magnetic Resonance Spectroscopic Imaging,"Magnetic Resonance Spectroscopic Imaging (MRSI) is an essential tool for
quantifying metabolites in the body, but the low spatial resolution limits its
clinical applications. Deep learning-based super-resolution methods provided
promising results for improving the spatial resolution of MRSI, but the
super-resolved images are often blurry compared to the experimentally-acquired
high-resolution images. Attempts have been made with the generative adversarial
networks to improve the image visual quality. In this work, we consider another
type of generative model, the flow-based model, of which the training is more
stable and interpretable compared to the adversarial networks. Specifically, we
propose a flow-based enhancer network to improve the visual quality of
super-resolution MRSI. Different from previous flow-based models, our enhancer
network incorporates anatomical information from additional image modalities
(MRI) and uses a learnable base distribution. In addition, we impose a guide
loss and a data-consistency loss to encourage the network to generate images
with high visual quality while maintaining high fidelity. Experiments on a
1H-MRSI dataset acquired from 25 high-grade glioma patients indicate that our
enhancer network outperforms the adversarial networks and the baseline
flow-based methods. Our method also allows visual quality adjustment and
uncertainty estimation.",2207.10181v1
2022-07-24,Contention Resolution for Coded Radio Networks,"Randomized backoff protocols, such as exponential backoff, are a powerful
tool for managing access to a shared resource, often a wireless communication
channel (e.g., [1]). For a wireless device to transmit successfully, it uses a
backoff protocol to ensure exclusive access to the channel. Modern radios,
however, do not need exclusive access to the channel to communicate; in
particular, they have the ability to receive useful information even when more
than one device transmits at the same time. These capabilities have now been
exploited for many years by systems that rely on interference cancellation,
physical layer network coding and analog network coding to improve efficiency.
For example, Zigzag decoding [56] demonstrated how a base station can decode
messages sent by multiple devices simultaneously.
  In this paper, we address the following question: Can we design a backoff
protocol that is better than exponential backoff when exclusive channel access
is not required. We define the Coded Radio Network Model, which generalizes
traditional radio network models (e.g., [30]). We then introduce the Decodable
Backoff Algorithm, a randomized backoff protocol that achieves an optimal
throughput of $1-o(1)$. (Throughput $1$ is optimal, as simultaneous reception
does not increase the channel capacity.) The algorithm breaks the constant
throughput lower bound for traditional radio networks [47-49], showing the
power of these new hardware capabilities.",2207.11824v1
2022-07-25,Control of dephasing in spin qubits during coherent transport in silicon,"One of the key pathways towards scalability of spin-based quantum computing
systems lies in achieving long-range interactions between electrons and
increasing their inter-connectivity. Coherent spin transport is one of the most
promising strategies to achieve this architectural advantage. Experimental
results have previously demonstrated high fidelity transportation of spin
qubits between two quantum dots in silicon and identified possible sources of
error. In this theoretical study, we investigate these errors and analyze the
impact of tunnel coupling, magnetic field and spin-orbit effects on the spin
transfer process. The interplay between these effects gives rise to double dot
configurations that include regimes of enhanced decoherence that should be
avoided for quantum information processing. These conclusions permit us to
extrapolate previous experimental conclusions and rationalize the future design
of large scale quantum processors.",2207.11865v2
2022-07-29,Orthogonal Spin Current Injected Magnetic Tunnel Junction for Convolutional Neural Networks,"We propose that a spin Hall effect driven magnetic tunnel junction device can
be engineered to provide a continuous change in the resistance across it when
injected with orthogonal spin currents. Using this concept, we develop a hybrid
device-circuit simulation platform to design a network that realizes multiple
functionalities of a convolutional neural network. At the atomistic level, we
use the Keldysh non-equilibrium Green's function technique that is coupled
self-consistently with the stochastic Landau-Lifshitz-Gilbert-Slonczewski
equations, which in turn is coupled with the HSPICE circuit simulator. We
demonstrate the simultaneous functionality of the proposed network to evaluate
the rectified linear unit and max-pooling functionalities. We present a
detailed power and error analysis of the designed network against the thermal
stability factor of the free ferromagnets. Our results show that there exists a
non-trivial power-error trade-off in the proposed network, which enables an
energy-efficient network design based on unstable free ferromagnets with
reliable outputs. The static power for the proposed ReLU circuit is $0.56\mu W$
and whereas the energy cost of a nine-input rectified linear unit-max-pooling
network with an unstable free ferromagnet($\Delta=15$) is $3.4pJ$ in the
worst-case scenario. We also rationalize the magnetization stability of the
proposed device by analyzing the vanishing torque gradient points.",2207.14603v3
2022-08-09,Good locally repairable codes via propagation rules,"In classical coding theory, it is common to construct new codes via
propagation rules. There are various propagation rules to construct classical
block codes. However, propagation rules have not been extensively explored for
constructions of locally repairable codes. In this paper, we introduce a few
propagation rules to construct good locally repairable codes. To our surprise,
these simple propagation rules produce a few interesting results. Firstly, by
concatenating a locally repairable code as an inner code with a classical block
code as an outer code, we obtain quite a few dimension-optimal binary locally
repairable codes. Secondly, from this concatenation, we explicitly build a
family of locally repairable codes that exceeds the Zyablov-type bound.
Thirdly, by a lengthening propagation rule that adds some rows and columns from
a parity-check matrix of a given linear code, we are able to produce a family
of dimension-optimal binary locally repairable codes from the extended Hamming
codes, and to convert a classical maximum distance separable (MDS) code into a
Singleton-optimal locally repairable code. Furthermore, via the lengthening
propagation rule, we greatly simplify the construction of a family of locally
repairable codes in \cite[Theorem 5]{MX20} that breaks the asymptotic
Gilbert-Varshamov bound. In addition, we make use of three other propagation
rules to produce more dimension-optimal binary locally repairable codes.
Finally, one of phenomena that we observe in this paper is that some trivial
propagation rules in classical block codes do not hold anymore for locally
repairable codes.",2208.04484v1
2022-08-10,Forward volume magnetoacoustic spin wave excitation with micron-scale spatial resolution,"The interaction between surface acoustic waves (SAWs) and spin waves (SWs) in
a piezoelectric-magnetic thin film heterostructure yields potential for the
realization of novel microwave devices and applications in magnonics. In the
present work, we characterize magnetoacoustic waves in three adjacent magnetic
micro-stripes made from CoFe+Ga, CoFe, and CoFe+Pt with a single pair of
tapered interdigital transducers (TIDTs). The magnetic micro-stripes were
deposited by focused electron beam-induced deposition (FEBID) and focused ion
beam-induced deposition (FIBID) direct-writing techniques. The transmission
characteristics of the TIDTs are leveraged to selectively address the
individual micro-stripes. Here, the external magnetic field is continuously
rotated out of the plane of the magnetic thin film and the forward volume SW
geometry is probed with the external magnetic field along the film normal. Our
experimental findings are well explained by an extended phenomenological model
based on a modified Landau-Lifshitz-Gilbert approach that considers SWs with
nonzero wave vectors. Magnetoelastic excitation of forward volume SWs is
possible because of the vertical shear strain $\varepsilon_{xz}$ of the
Rayleigh-type SAW.",2208.05205v1
2022-08-29,Programmable photonic integrated meshes for modular generation of optical entanglement links,"Large-scale generation of quantum entanglement between individually
controllable qubits is at the core of quantum computing, communications, and
sensing. Modular architectures of remotely-connected quantum technologies have
been proposed for a variety of physical qubits, with demonstrations reported in
atomic and all-photonic systems. However, an open challenge in these
architectures lies in constructing high-speed and high-fidelity reconfigurable
photonic networks for optically-heralded entanglement among target qubits. Here
we introduce a programmable photonic integrated circuit (PIC), realized in a
piezo-actuated silicon nitride (SiN)-in-oxide CMOS-compatible process, that
implements an N x N Mach-Zehnder mesh (MZM) capable of high-speed execution of
linear optical transformations. The visible-spectrum photonic integrated mesh
is programmed to generate optical connectivity on up to N = 8 inputs for a
range of optically-heralded entanglement protocols. In particular, we
experimentally demonstrated optical connections between 16 independent pairwise
mode couplings through the MZM, with optical transformation fidelities
averaging 0.991 +/- 0.0063. The PIC's reconfigurable optical connectivity
suffices for the production of 8-qubit resource states as building blocks of
larger topological cluster states for quantum computing. Our programmable PIC
platform enables the fast and scalable optical switching technology necessary
for network-based quantum information processors.",2208.13911v1
2022-09-15,Almost Ramanujan Expanders from Arbitrary Expanders via Operator Amplification,"We give an efficient algorithm that transforms any bounded degree expander
graph into another that achieves almost optimal (namely, near-quadratic, $d
\leq 1/\lambda^{2+o(1)}$) trade-off between (any desired) spectral expansion
$\lambda$ and degree $d$. Furthermore, the algorithm is local: every vertex can
compute its new neighbors as a subset of its original neighborhood of radius
$O(\log(1/\lambda))$. The optimal quadratic trade-off is known as the Ramanujan
bound, so our construction gives almost Ramanujan expanders from arbitrary
expanders.
  The locality of the transformation preserves structural properties of the
original graph, and thus has many consequences. Applied to Cayley graphs, our
transformation shows that any expanding finite group has almost Ramanujan
expanding generators. Similarly, one can obtain almost optimal explicit
constructions of quantum expanders, dimension expanders, monotone expanders,
etc., from existing (suboptimal) constructions of such objects. Another
consequence is a ""derandomized"" random walk on the original (suboptimal)
expander with almost optimal convergence rate. Our transformation also applies
when the degree is not bounded or the expansion is not constant.
  We obtain our results by a generalization of Ta-Shma's technique in his
breakthrough paper [STOC 2017], used to obtain explicit almost optimal binary
codes. Specifically, our spectral amplification extends Ta-Shma's analysis of
bias amplification from scalars to matrices of arbitrary dimension in a very
natural way. Curiously, while Ta-Shma's explicit bias amplification
derandomizes a well-known probabilistic argument (underlying the
Gilbert--Varshamov bound), there seems to be no known probabilistic (or other
existential) way of achieving our explicit (""high-dimensional"") spectral
amplification.",2209.07024v1
2022-09-15,An analytical study of the MHD clamshell instability on a sphere,"This paper studies the instability of two-dimensional magnetohydrodynamic
(MHD) systems on a sphere using analytical methods. The underlying flow
consists of a zonal differential rotation and a toroidal magnetic field is
present. Semicircle rules that prescribe the possible domain of the wave
velocity in the complex plane for general flow and field profiles are derived.
The paper then sets out an analytical study of the `clamshell instability',
which features field lines on the two hemispheres tilting in opposite
directions (Cally 2001, Sol. Phys. vol. 199, pp. 231--249). An asymptotic
solution for the instability problem is derived for the limit of weak shear of
the zonal flow, via the method of matched asymptotic expansions. It is shown
that when the zonal flow is solid body rotation, there exists a neutral mode
that tilts the magnetic field lines, referred to as the `tilting mode'. A weak
shear of the zonal flow excites the critical layer of the tilting mode, which
reverses the tilting direction to form the clamshell pattern and induces the
instability. The asymptotic solution provides insights into properties of the
instability for a range of flow and field profiles. A remarkable feature is
that the magnetic field affects the instability only through its local
behaviour in the critical layer.",2209.07349v1
2022-09-15,$\tilde{O}(n+\mathrm{poly}(k))$-time Algorithm for Bounded Tree Edit Distance,"Computing the edit distance of two strings is one of the most basic problems
in computer science and combinatorial optimization. Tree edit distance is a
natural generalization of edit distance in which the task is to compute a
measure of dissimilarity between two (unweighted) rooted trees with node
labels. Perhaps the most notable recent application of tree edit distance is in
NoSQL big databases, such as MongoDB, where each row of the database is a JSON
document represented as a labeled rooted tree, and finding dissimilarity
between two rows is a basic operation. Until recently, the fastest algorithm
for tree edit distance ran in cubic time (Demaine, Mozes, Rossman, Weimann;
TALG'10); however, Mao (FOCS'21) broke the cubic barrier for the tree edit
distance problem using fast matrix multiplication.
  Given a parameter $k$ as an upper bound on the distance, an $O(n+k^2)$-time
algorithm for edit distance has been known since the 1980s due to the works of
Myers (Algorithmica'86) and Landau and Vishkin (JCSS'88). The existence of an
$\tilde{O}(n+\mathrm{poly}(k))$-time algorithm for tree edit distance has been
posed as an open question, e.g., by Akmal and Jin (ICALP'21), who gave a
state-of-the-art $\tilde{O}(nk^2)$-time algorithm. In this paper, we answer
this question positively.",2209.07524v1
2022-09-23,Multiplexed control of spin quantum memories in a photonic circuit,"A central goal in many quantum information processing applications is a
network of quantum memories that can be entangled with each other while being
individually controlled and measured with high fidelity. This goal has
motivated the development of programmable photonic integrated circuits (PICs)
with integrated spin quantum memories using diamond color center spin-photon
interfaces. However, this approach introduces a challenge in the microwave
control of individual spins within closely packed registers. Here, we present a
quantum-memory-integrated photonics platform capable of (i) the integration of
multiple diamond color center spins into a cryogenically compatible, high-speed
programmable PIC platform; (ii) selective manipulation of individual spin
qubits addressed via tunable magnetic field gradients; and (iii) simultaneous
control of multiple qubits using numerically optimized microwave pulse shaping.
The combination of localized optical control, enabled by the PIC platform,
together with selective spin manipulation opens the path to scalable quantum
networks on intra-chip and inter-chip platforms.",2209.11853v2
2022-09-26,A detailed star formation history for the extremely diffuse Andromeda XIX dwarf galaxy,"We present deep imaging of the ultra-diffuse Andromeda XIX dwarf galaxy from
the Advance Camera for Surveys on the Hubble Space Telescope which resolves its
stellar populations to below the oldest main sequence turn-off. We derive a
full star formation history for the galaxy using MATCH, and find no evidence of
star formation in the past 8 Gyr. We calculate a quenching time of
$\tau_{90}=9.7\pm0.2$~Gyr, suggesting Andromeda~XIX ceased forming stars very
early on. This early quenching, combined with its extremely large half-light
radius, low density dark matter halo and lower than expected metallicity make
it a unique galaxy within the Local Group and raises questions about how it
formed. The early quenching time allows us to rule out feedback from bursty
star formation as a means to explain its diffuse stellar population and low
density dark matter halo. We find that the extended stellar population, low
density halo and star formation could be explained by either tidal interactions
(such as tidal shocking) or by late dry mergers, with the latter also
explaining its low metallicity. Proper motions and detailed abundances would
allow us to distinguish between these two scenarios.",2209.12912v1
2022-10-06,Scalable photonic integrated circuits for programmable control of atomic systems,"Advances in laser technology have driven discoveries in atomic, molecular,
and optical (AMO) physics and emerging applications, from quantum computers
with cold atoms or ions, to quantum networks with solid-state color centers.
This progress is motivating the development of a new generation of
""programmable optical control"" systems, characterized by criteria (C1) visible
(VIS) and near-infrared (IR) wavelength operation, (C2) large channel counts
extensible beyond 1000s of individually addressable atoms, (C3) high intensity
modulation extinction and (C4) repeatability compatible with low gate errors,
and (C5) fast switching times. Here, we address these challenges by introducing
an atom control architecture based on VIS-IR photonic integrated circuit (PIC)
technology. Based on a complementary metal-oxide-semiconductor (CMOS)
fabrication process, this Atom-control PIC (APIC) technology meets the system
requirements (C1)-(C5). As a proof of concept, we demonstrate a 16-channel
silicon nitride based APIC with (5.8$\pm$0.4) ns response times and -30 dB
extinction ratio at a wavelength of 780 nm. This work demonstrates the
suitability of PIC technology for quantum control, opening a path towards
scalable quantum information processing based on optically-programmable atomic
systems.",2210.03100v2
2022-10-10,Andreev processes in mesoscopic multi-terminal graphene Josephson junctions,"There is growing interest in using multi-terminal Josephson junctions (MTJJs)
as a platform to artificially emulate topological phases and to investigate
complex superconducting mechanisms such as quartet and multiplet Cooper
pairings. Current experimental signatures in MTJJs have led to conflicting
interpretations of the salient features. In this work, we report a
collaborative experimental and theoretical investigation of graphene-based
four-terminal Josephson junctions. We observe resonant features in the
differential resistance maps that resemble those ascribed to multiplet Cooper
pairings. To understand these features, we model our junctions using a circuit
network of coupled two-terminal resistively and capacitively shunted junctions
(RCSJs). Under appropriate bias current, the model predicts that a current
flowing between two diagonal terminals in a four-terminal geometry may be
represented as a sinusoidal function of a weighted sum of the superconducting
phases. We show that starting from a semi-classical model with diffusive
current-phase relations, the MTJJ effectively emulates a general form of the
expected current-phase relation for multiplet Cooper pairings. Our study
therefore suggests that differential resistance measurements alone are
insufficient to conclusively distinguish resonant Andreev reflection processes
from semi-classical circuit-network effects.",2210.04408v3
2022-10-10,Infrared Remote Sensing Using Low Noise Avalanche Photodiode Detector,"For a remote sensing optical payload to achieve a Ground Sampling Distance of
~ 10-30 m, a critical problem is platform-induced motion blur. While forward
motion compensation can reduce this transit speed, it comes at the expense of a
more challenging satellite attitude control system and induces a variable
observation/illumination angle. This relative motion can be frozen out by
simply reading the sensor system at a frame rate that matches the ground
resolution element's pixel crossing time. To achieve high resolution using this
Time-Delay Integration (TDI)-like approach requires high speed and hence near
""zero"" readout noise detector arrays to avoid swamping the observed signal.
This requires associated control electronics for fast frame readout and direct
interface with smart- Artificial Intelligence (AI) onboard processing. With
this technique, the platform freezes out its movement concerning the ground,
reducing the demands placed on the attitude control systems, which can
otherwise be difficult to implement on a small satellite platform. Here we
report the Australian National University's OzFuel mission which applies this
technical solution to deliver high ground resolution via high frame rate
imaging. OzFuel is built around the Leonardo SAPHIRA Mercury Cadmium Telluride
linear mode electron avalanche photodiode (LMeAPD) detector and the in-house
developed Rosella electronics control system. The mission will deliver an
integrated sensor system in a suite of Short-Wave Infrared (SWIR) passbands
dedicated to monitoring the flammability of Eucalypt trees. The OzFuel mission
concept focuses on the application of SWIR remote sensing data to deliver a
strategic evaluation of fuel loads and moisture content in the bushfire-prone
Australian environment.",2210.04770v1
2022-10-17,On construction of quantum codes with dual-containing quasi-cyclic codes,"One of the main objectives of quantum error-correction theory is to construct
quantum codes with optimal parameters and properties. In this paper, we propose
a class of 2-generator quasi-cyclic codes and study their applications in the
construction of quantum codes over small fields. Firstly, some sufficient
conditions for these 2-generator quasi-cyclic codes to be dual-containing
concerning Hermitian inner product are determined. Then, we utilize these
Hermitian dual-containing quasi-cyclic codes to produce quantum codes via the
famous Hermitian construction. Moreover, we present a lower bound on the
minimum distance of these quasi-cyclic codes, which is helpful to construct
quantum codes with larger lengths and dimensions. As the computational results,
many new quantum codes that exceed the quantum Gilbert-Varshamov bound are
constructed over $F_q$, where $q$ is $2,3,4,5$. In particular, 16 binary
quantum codes raise the lower bound on the minimum distance in Grassl's table
\cite{Grassl:codetables}. In nonbinary cases, many quantum codes are new or
have better parameters than those in the literature.",2210.08716v1
2022-10-18,Intense γ-photon and high-energy electron production by neutron irradiation: effects of nuclear excitations on reactor materials,"The effects of neutron irradiation on materials are often interpreted in
terms of atomic recoils, initiated by neutron impacts and producing crystal
lattice defects. In addition, there is a remarkable two-step process, strongly
pronounced in the medium-weight and heavy elements. This process involves the
generation of energetic {\gamma} photons in nonelastic collisions of neutrons
with atomic nuclei, achieved via capture and inelastic reactions. Subsequently,
high-energy electrons are excited through the scattering of {\gamma} photons by
the atomic electrons. We derive and validate equations enabling a fast and
robust evaluation of photon and electron fluxes produced by the neutrons in the
bulk of materials. The two-step n-{\gamma}-e scattering creates a
nonequilibrium dynamically fluctuating steady-state population of high-energy
electrons, with the spectra of photon and electron energies extending well into
the mega-electron-volt range. This stimulates vacancy diffusion through
electron-triggered atomic recoils, primarily involving vacancy-impurity
dissociation, even if thermal activation is ineffective. Tungsten converts the
energy of fusion or fission neutrons into a flux of {\gamma} radiation at the
conversion efficiency approaching 99%, with implications for structural
materials, superconductors, and insulators, as well as phenomena like
corrosion, and helium and hydrogen isotope retention.",2210.09667v2
2022-11-06,A framework for leveraging machine learning tools to estimate personalized survival curves,"The conditional survival function of a time-to-event outcome subject to
censoring and truncation is a common target of estimation in survival analysis.
This parameter may be of scientific interest and also often appears as a
nuisance in nonparametric and semiparametric problems. In addition to classical
parametric and semiparametric methods (e.g., based on the Cox proportional
hazards model), flexible machine learning approaches have been developed to
estimate the conditional survival function. However, many of these methods are
either implicitly or explicitly targeted toward risk stratification rather than
overall survival function estimation. Others apply only to discrete-time
settings or require inverse probability of censoring weights, which can be as
difficult to estimate as the outcome survival function itself. Here, we employ
a decomposition of the conditional survival function in terms of observable
regression models in which censoring and truncation play no role. This allows
application of an array of flexible regression and classification methods
rather than only approaches that explicitly handle the complexities inherent to
survival data. We outline estimation procedures based on this decomposition,
empirically assess their performance, and demonstrate their use on data from an
HIV vaccine trial.",2211.03031v4
2022-11-14,High-resolution single-shot spiral diffusion-weighted imaging at 7T using expanded encoding with compressed sensing,"Purpose: The expanded encoding model incorporates spatially- and time-varying
field perturbations for correction during reconstruction. So far, these
reconstructions have used the conjugate gradient method with early stopping
used as implicit regularization. However, this approach is likely suboptimal
for low-SNR cases like diffusion or high-resolution MRI. Here, we investigate
the extent that l1-wavelet regularization, or equivalently compressed sensing
(CS), combined with expanded encoding improves trade-offs between spatial
resolution, readout time and SNR for single-shot spiral diffusion-weighted
imaging at 7T. The reconstructions were performed using our open-source
GPU-enabled reconstruction toolbox, MatMRI, that allows inclusion of the
different components of the expanded encoding model, with or without CS.
Methods: In vivo accelerated single-shot spirals were acquired with five
acceleration factors (2-6) and three in-plane spatial resolutions (1.5, 1.3,
and 1.1 mm). From the in vivo reconstructions, we estimated diffusion tensors
and computed fractional anisotropy maps. Then, simulations were used to
quantitatively investigate and validate the impact of CS-based regularization
on image quality when compared to a known ground truth. Results: In vivo
reconstructions revealed improved image quality with retainment of small
features when CS was used. Simulations showed that the joint use of the
expanded encoding model and CS improves accuracy of image reconstructions
(reduced mean-squared error) over the range of acceleration factors
investigated. Conclusion: The expanded encoding model and CS regularization are
complementary tools for single-shot spiral diffusion MRI, which enables both
higher spatial resolutions and higher acceleration factors.",2211.07532v1
2022-11-17,On universal butterfly and antisymmetric magnetoresistances,"Butterfly magnetoresistance (BMR) and antisymmetric magnetoresistance (ASMR)
are about a butterfly-cross curve and a curve with one peak and one valley when
a magnetic field is swept up and down along a fixed direction. Other than the
parallelogram-shaped magnetoresistance-curve (MR-curve) often observed in
magnetic memory devices, BMR and ASMR are two ubiquitous types of MR-curves
observed in diversified magnetic systems, including van der Waals materials,
strongly correlated systems, and traditional magnets. Here, we reveal the
general principles and the picture behind the BMR and the ASMR that do not
depend on the detailed mechanisms of magnetoresistance: 1) The systems exhibit
hysteresis loops, common for most magnetic materials with coercivities. 2) The
magnetoresistance of the magnetic structures in a large positive magnetic field
and in a large negative magnetic field is approximately the same. With the
generalized Ohm's law in magnetic materials, these principles explain why most
BMR appears in the longitudinal resistance measurements and is very rare in the
Hall resistance measurements. Simple toy models, in which the
Landau-Lifshitz-Gilbert equation governs magnetization, are used to demonstrate
the principles and explain the appearance and disappearance of BMR in various
experiments. Our finding provides a simple picture to understand
magnetoresistance-related experiments.",2211.09369v1
2022-12-22,Photon production rate from Transverse-Longitudinal ($T-L$) mesonic correlator on the lattice,"Thermal photons from the QGP provide important information about the
interaction among plasma constituents. The photon production rate from a
thermally equilibrated system is proportional to the transverse spectral
function $\rho_T(\omega=|\vec k|, \vec k)$. One can also calculate the photon
production rate from the difference between $\rho_T(\omega,\vec k)$
(transverse) and $\rho_L(\omega,\vec k)$ (longitudinal) projections, as
$\rho_L$ vanishes on the photon point. Because the UV part of $\rho_T-\rho_L$
is suppressed, the corresponding Euclidean correlator receives most of its
contribution from the IR part. We calculate the $T\!-\!L$ correlator on
$N_f=2+1$ flavour HISQ configurations with $m_l=m_s/5$ at temperature of about
$1.15\,T_{pc}$ (220 MeV). We have used two ans\""{a}tze for the spectral
function: 1) A polynomial connected to the UV region consistent with OPE
expansion and 2) a hydro-inspired spectral function. We have also applied the
Backus-Gilbert method to estimate the spectral function. All these different
approaches are combined to estimate the photon production rate.",2212.11509v2
2023-01-12,Incremental Dead State Detection in Logarithmic Time,"Identifying live and dead states in an abstract transition system is a
recurring problem in formal verification; for example, it arises in our recent
work on efficiently deciding regex constraints in SMT. However,
state-of-the-art graph algorithms for maintaining reachability information
incrementally (that is, as states are visited and before the entire state space
is explored) assume that new edges can be added from any state at any time,
whereas in many applications, outgoing edges are added from each state as it is
explored. To formalize the latter situation, we propose guided incremental
digraphs (GIDs), incremental graphs which support labeling closed states
(states which will not receive further outgoing edges). Our main result is that
dead state detection in GIDs is solvable in $O(\log m)$ amortized time per edge
for $m$ edges, improving upon $O(\sqrt{m})$ per edge due to Bender, Fineman,
Gilbert, and Tarjan (BFGT) for general incremental directed graphs.
  We introduce two algorithms for GIDs: one establishing the logarithmic time
bound, and a second algorithm to explore a lazy heuristics-based approach. To
enable an apples-to-apples experimental comparison, we implemented both
algorithms, two simpler baselines, and the state-of-the-art BFGT baseline using
a common directed graph interface in Rust. Our evaluation shows $110$-$530$x
speedups over BFGT for the largest input graphs over a range of graph classes,
random graphs, and graphs arising from regex benchmarks.",2301.05308v2
2023-01-23,Correction of high-order phase variation effects in dynamic field monitoring,"Purpose: Field monitoring measures field perturbations, which can be
accounted for during image reconstructions. In certain field monitoring
environments, significant phase deviations can arise far from isocenter due to
the finite extent of the gradient and/or main magnet. This can degrade the
accuracy of field dynamics when field probes are placed near or outside the
diameter spherical volume of the gradient coils and/or main magnet, leading to
corrupted image quality. The objective of this work was to develop a correction
algorithm that reduces errors from highly nonlinear phase variations at distant
field probes in field dynamic fits. Methods: The algorithm is split into three
components. Component one fits phase coefficients one spatial order at a time,
while the second implements a weighted least squares solution based on probe
distance. After initial fitting, component three calculates phase residuals and
removes the phase for distant probes before re-fitting. Two healthy volunteers
were scanned on a head-only 7T MRI using diffusion-weighted single-shot spiral
and EPI sequences and field monitoring was performed. Images were reconstructed
with and without phase coefficient correction and compared qualitatively.
Results: The algorithm was able to correct corrupted field dynamics, resulting
in image quality improvements. Significant artefact reduction was observed when
correcting higher order fits, especially for diffusion weighted images.
Stepwise fitting provided the most correction benefit, which was marginally
improved when adding weighted least squares and phase residual corrections.
Conclusion: The proposed algorithm can mitigate effects of phase errors in
field monitoring, providing improved reliability of field dynamic
characterization.",2301.09726v1
2023-02-07,Computational capability for physical reservoir computing using a spin-torque oscillator with two free layers,"A numerical analysis on the computational capability of physical reservoir
computing utilizing a spin-torque oscillator with two free layers is reported.
Conventional spintronics devices usually consist of two ferromagnets, where the
direction of magnetization in one layer, called the free layer, can move while
that of the other, the reference layer, is fixed. Recently, however, devices
with two free layers, where the reference layer is replaced by another free
layer, have been developed for various practical applications. Adding another
free layer drastically changes the dynamical response of the device through the
couplings via the spin-transfer effect and the dipole magnetic field. A
numerical simulation of the Landau-Lifshitz-Gilbert equation and a statistical
analyses of the Lyapunov exponent and the synchronization index reveal the
appearance of an amplitude-modulated oscillation and chaos in the oscillators
with two free layers. Such complex dynamics qualitatively change the
computational capability of physical reservoir computing because the
computational resource is dynamics of the physical system. An evaluation of the
short-term memory capacity clarifies that oscillators with two free layers have
a larger capacity than those of conventional oscillators. An enhancement in
capacity near the edge of echo state property, i.e., the boundary between zero
and finite synchronization index, is also found.",2302.03769v1
2023-02-13,Ultra-bright single photon source based on an atomically thin material,"Solid-state single photon sources are central building blocks in quantum
communication networks and on-chip quantum information processing. Atomically
thin crystals were established as possible candidates to emit non-classical
states of light, however, the performance of monolayer-based single photon
sources has so far been lacking behind state-of-the-art devices based on volume
crystals. Here, we implement a single photon source based on an atomically thin
sheet of WSe2 coupled to a spectrally tunable optical cavity. It is
characterized by a high single photon purity with a $g^{(2)}(0)$ value as low
as $4.7 \pm 0.7 \%$ and a record-high first lens brightness of linearly
polarized photons as large as $65 \pm 4 \%$. Interestingly, the high
performance of our devices allows us to observe genuine quantum interference
phenomena in a Hong-Ou-Mandel experiment. Our results demonstrate that open
cavities and two-dimensional materials constitute an excellent platform for
ultra-bright quantum light sources: the unique properties of such
two-dimensional materials and the versatility of open cavities open an
inspiring avenue for novel quantum optoelectronic devices.",2302.06340v1
2023-02-21,A Prompt Pattern Catalog to Enhance Prompt Engineering with ChatGPT,"Prompt engineering is an increasingly important skill set needed to converse
effectively with large language models (LLMs), such as ChatGPT. Prompts are
instructions given to an LLM to enforce rules, automate processes, and ensure
specific qualities (and quantities) of generated output. Prompts are also a
form of programming that can customize the outputs and interactions with an
LLM. This paper describes a catalog of prompt engineering techniques presented
in pattern form that have been applied to solve common problems when conversing
with LLMs. Prompt patterns are a knowledge transfer method analogous to
software patterns since they provide reusable solutions to common problems
faced in a particular context, i.e., output generation and interaction when
working with LLMs. This paper provides the following contributions to research
on prompt engineering that apply LLMs to automate software development tasks.
First, it provides a framework for documenting patterns for structuring prompts
to solve a range of problems so that they can be adapted to different domains.
Second, it presents a catalog of patterns that have been applied successfully
to improve the outputs of LLM conversations. Third, it explains how prompts can
be built from multiple patterns and illustrates prompt patterns that benefit
from combination with other prompt patterns.",2302.11382v1
2023-03-11,Power efficient ReLU design for neuromorphic computing using spin Hall effect,"We demonstrate a magnetic tunnel junction injected with spin Hall current to
exhibit linear rotation of magnetization of the free-ferromagnet using only the
spin current. Using the linear resistance change of the MTJ, we devise a
circuit for the rectified linear activation (ReLU) function of the artificial
neuron. We explore the role of different spin Hall effect (SHE) heavy metal
layers on the power consumption of the ReLU circuit. We benchmark the power
consumption of the ReLU circuit with different SHE layers by defining a new
parameter called the spin Hall power factor. It combines the spin Hall angle,
resistivity, and thickness of the heavy metal layer, which translates to the
power consumption of the different SHE layers during spin-orbit
switching/rotation of the free FM. We employ a hybrid spintronics-CMOS
simulation framework that couples Keldysh non-equilibrium Green's function
formalism with Landau-Lifshitz-Gilbert-Slonzewski equations and the HSPICE
circuit simulator to account for diverse physics of spin-transport and the CMOS
elements in our proposed ReLU design. We also demonstrate the robustness of the
proposed ReLU circuit against thermal noise and non-trivial power-error
trade-off that enables the use of an unstable free-ferromagnet for
energy-efficient design. Using the proposed circuit, we evaluate the
performance of the convolutional neural network for MNIST datasets and
demonstrate comparable classification accuracies to the ideal ReLU with an
energy consumption of 75 $pJ$ per sample.",2303.06463v1
2023-03-28,Optimal Scheduling Policies for Remote Estimation of Autoregressive Markov Processes over Time-Correlated Fading Channel,"We consider the problem of transmission scheduling for the remote estimation
of a discrete-time autoregressive Markov process that is driven by white
Gaussian noise. A sensor observes this process, and then decides to either
encode the current state of this process into a data packet and attempts to
transmit it to the estimator over an unreliable wireless channel modeled as a
Gilbert-Elliott channel, or does not send any update. Each transmission attempt
consumes $\lambda$ units of transmission power, and the remote estimator is
assumed to be linear. The channel state is revealed only via the feedback
(ACK\slash NACK) of a transmission, and hence the channel state is not revealed
if no transmission occurs. The goal of the scheduler is to minimize the
expected value of an infinite-horizon cumulative discounted cost, in which the
instantaneous cost is composed of the following two quantities: (i)~squared
estimation error, (ii) transmission power. We show that this problem can
equivalently be posed as a partially observable Markov decision process
(POMDP), in which the scheduler maintains a belief about the current state of
the channel, and makes decisions on the basis of the current value of the
estimation error, and the belief state.~We then show that the optimal policy is
of threshold-type, i.e. for each value of the estimation error $e$, there is a
threshold $b\ust(e)$ such that when the error is equal to $e$, then it is
optimal to transmit only when the current belief state is greater than
$b\ust(e)$.",2303.16285v1
2023-04-14,Study on Soft Robotic Pinniped Locomotion,"Legged locomotion is a highly promising but under-researched subfield within
the field of soft robotics. The compliant limbs of soft-limbed robots offer
numerous benefits, including the ability to regulate impacts, tolerate falls,
and navigate through tight spaces. These robots have the potential to be used
for various applications, such as search and rescue, inspection, surveillance,
and more. The state-of-the-art still faces many challenges, including limited
degrees of freedom, a lack of diversity in gait trajectories, insufficient limb
dexterity, and limited payload capabilities. To address these challenges, we
develop a modular soft-limbed robot that can mimic the locomotion of pinnipeds.
By using a modular design approach, we aim to create a robot that has improved
degrees of freedom, gait trajectory diversity, limb dexterity, and payload
capabilities. We derive a complete floating-base kinematic model of the
proposed robot and use it to generate and experimentally validate a variety of
locomotion gaits. Results show that the proposed robot is capable of
replicating these gaits effectively. We compare the locomotion trajectories
under different gait parameters against our modeling results to demonstrate the
validity of our proposed gait models.",2304.06945v1
2023-04-19,Local object crop collision network for efficient simulation of non-convex objects in GPU-based simulators,"Our goal is to develop an efficient contact detection algorithm for
large-scale GPU-based simulation of non-convex objects. Current GPU-based
simulators such as IsaacGym and Brax must trade-off speed with fidelity,
generality, or both when simulating non-convex objects. Their main issue lies
in contact detection (CD): existing CD algorithms, such as
Gilbert-Johnson-Keerthi (GJK), must trade off their computational speed with
accuracy which becomes expensive as the number of collisions among non-convex
objects increases. We propose a data-driven approach for CD, whose accuracy
depends only on the quality and quantity of offline dataset rather than online
computation time. Unlike GJK, our method inherently has a uniform computational
flow, which facilitates efficient GPU usage based on advanced compilers such as
XLA (Accelerated Linear Algebra). Further, we offer a data-efficient solution
by learning the patterns of colliding local crop object shapes, rather than
global object shapes which are harder to learn. We demonstrate our approach
improves the efficiency of existing CD methods by a factor of 5-10 for
non-convex objects with comparable accuracy. Using the previous work on contact
resolution for a neural-network-based contact detector, we integrate our CD
algorithm into the open-source GPU-based simulator, Brax, and show that we can
improve the efficiency over IsaacGym and generality over standard Brax. We
highly recommend the videos of our simulator included in the supplementary
materials.",2304.09439v2
2023-04-25,Semantic Compression With Large Language Models,"The rise of large language models (LLMs) is revolutionizing information
retrieval, question answering, summarization, and code generation tasks.
However, in addition to confidently presenting factually inaccurate information
at times (known as ""hallucinations""), LLMs are also inherently limited by the
number of input and output tokens that can be processed at once, making them
potentially less effective on tasks that require processing a large set or
continuous stream of information. A common approach to reducing the size of
data is through lossless or lossy compression. Yet, in some cases it may not be
strictly necessary to perfectly recover every detail from the original data, as
long as a requisite level of semantic precision or intent is conveyed.
  This paper presents three contributions to research on LLMs. First, we
present the results from experiments exploring the viability of approximate
compression using LLMs, focusing specifically on GPT-3.5 and GPT-4 via ChatGPT
interfaces. Second, we investigate and quantify the capability of LLMs to
compress text and code, as well as to recall and manipulate compressed
representations of prompts. Third, we present two novel metrics -- Exact
Reconstructive Effectiveness (ERE) and Semantic Reconstruction Effectiveness
(SRE) -- that quantify the level of preserved intent between text compressed
and decompressed by the LLMs we studied. Our initial results indicate that
GPT-4 can effectively compress and reconstruct text while preserving the
semantic essence of the original text, providing a path to leverage
$\sim$5$\times$ more tokens than present limits allow.",2304.12512v1
2023-04-28,Optimal majority rules and quantitative Condorcet properties of setwise Kemeny voting schemes,"The important Kemeny problem, which consists of computing median consensus
rankings of an election with respect to the Kemeny voting rule, admits
important applications in biology and computational social choice and was
generalized recently via an interesting setwise approach by Gilbert et. al. Our
first results establish optimal quantitative extensions of the Unanimity
property and the well-known $3/4$-majority rule of Betzler et al. for the
classical Kemeny median problem. Moreover, by elaborating an exhaustive list of
quantified axiomatic properties (such as the Condorcet and Smith criteria, the
$5/6$-majority rule, etc.) of the $3$-wise Kemeny rule where not only pairwise
comparisons but also the discordance between the winners of subsets of three
candidates are also taken into account, we come to the conclusion that the
$3$-wise Kemeny voting scheme induced by the $3$-wise Kendall-tau distance
presents interesting advantages in comparison with the classical Kemeny rule.
For example, it satisfies several improved manipulation-proof properties. Since
the $3$-wise Kemeny problem is NP-hard, our results also provide some of the
first useful space reduction techniques by determining the relative orders of
pairs of alternatives. Our works suggest similar interesting properties of
higher setwise Kemeny voting schemes which justify and compensate for the more
expensive computational cost than the classical Kemeny scheme.",2304.14980v1
2023-05-25,Packaging code for reproducible research in the public sector,"The effective and ethical use of data to inform decision-making offers huge
value to the public sector, especially when delivered by transparent,
reproducible, and robust data processing workflows. One way that governments
are unlocking this value is through making their data publicly available,
allowing more people and organisations to derive insights. However, open data
is not enough in many cases: publicly available datasets need to be accessible
in an analysis-ready form from popular data science tools, such as R and
Python, for them to realise their full potential.
  This paper explores ways to maximise the impact of open data with reference
to a case study of packaging code to facilitate reproducible analysis. We
present the jtstats project, which consists of R and Python packages for
importing, processing, and visualising large and complex datasets representing
journey times, for many modes and purposes at multiple geographic levels,
released by the UK Department of Transport. jtstats shows how domain specific
packages can enable reproducible research within the public sector and beyond,
saving duplicated effort and reducing the risks of errors from repeated
analyses. We hope that the jtstats project inspires others, particularly those
in the public sector, to add value to their data sets by making them more
accessible.",2305.16205v1
2023-05-25,COMPLETE: A flagship mission for complete understanding of 3D coronal magnetic energy release,"COMPLETE is a flagship mission concept combining broadband spectroscopic
imaging and comprehensive magnetography from multiple viewpoints around the Sun
to enable tomographic reconstruction of 3D coronal magnetic fields and
associated dynamic plasma properties, which provide direct diagnostics of
energy release. COMPLETE re-imagines the paradigm for solar remote-sensing
observations through purposefully co-optimized detectors distributed on
multiple spacecraft that operate as a single observatory, linked by a
comprehensive data/model assimilation strategy to unify individual observations
into a single physical framework. We describe COMPLETE's science goals,
instruments, and mission implementation. With targeted investment by NASA,
COMPLETE is feasible for launch in 2032 to observe around the maximum of Solar
Cycle 26.",2305.16533v1
2023-05-25,Magnetic Energy Powers the Corona: How We Can Understand its 3D Storage & Release,"The coronal magnetic field is the prime driver behind many as-yet unsolved
mysteries: solar eruptions, coronal heating, and the solar wind, to name a few.
It is, however, still poorly observed and understood. We highlight key
questions related to magnetic energy storage, release, and transport in the
solar corona, and their relationship to these important problems. We advocate
for new and multi-point co-optimized measurements, sensitive to magnetic field
and other plasma parameters, spanning from optical to $\gamma$-ray wavelengths,
to bring closure to these long-standing and fundamental questions. We discuss
how our approach can fully describe the 3D magnetic field, embedded plasma,
particle energization, and their joint evolution to achieve these objectives.",2305.17146v1
2023-05-27,Optimization's Neglected Normative Commitments,"Optimization is offered as an objective approach to resolving complex,
real-world decisions involving uncertainty and conflicting interests. It drives
business strategies as well as public policies and, increasingly, lies at the
heart of sophisticated machine learning systems. A paradigm used to approach
potentially high-stakes decisions, optimization relies on abstracting the real
world to a set of decision(s), objective(s) and constraint(s). Drawing from the
modeling process and a range of actual cases, this paper describes the
normative choices and assumptions that are necessarily part of using
optimization. It then identifies six emergent problems that may be neglected:
1) Misspecified values can yield optimizations that omit certain imperatives
altogether or incorporate them incorrectly as a constraint or as part of the
objective, 2) Problematic decision boundaries can lead to faulty modularity
assumptions and feedback loops, 3) Failing to account for multiple agents'
divergent goals and decisions can lead to policies that serve only certain
narrow interests, 4) Mislabeling and mismeasurement can introduce bias and
imprecision, 5) Faulty use of relaxation and approximation methods,
unaccompanied by formal characterizations and guarantees, can severely impede
applicability, and 6) Treating optimization as a justification for action,
without specifying the necessary contextual information, can lead to ethically
dubious or faulty decisions. Suggestions are given to further understand and
curb the harms that can arise when optimization is used wrongfully.",2305.17465v2
2023-05-30,Hardness of Approximation in PSPACE and Separation Results for Pebble Games,"We consider the pebble game on DAGs with bounded fan-in introduced in
[Paterson and Hewitt '70] and the reversible version of this game in [Bennett
'89], and study the question of how hard it is to decide exactly or
approximately the number of pebbles needed for a given DAG in these games. We
prove that the problem of eciding whether $s$~pebbles suffice to reversibly
pebble a DAG $G$ is PSPACE-complete, as was previously shown for the standard
pebble game in [Gilbert, Lengauer and Tarjan '80]. Via two different graph
product constructions we then strengthen these results to establish that both
standard and reversible pebbling space are PSPACE-hard to approximate to within
any additive constant. To the best of our knowledge, these are the first
hardness of approximation results for pebble games in an unrestricted setting
(even for polynomial time). Also, since [Chan '13] proved that reversible
pebbling is equivalent to the games in [Dymond and Tompa '85] and [Raz and
McKenzie '99], our results apply to the Dymond--Tompa and Raz--McKenzie games
as well, and from the same paper it follows that resolution depth is
PSPACE-hard to determine up to any additive constant. We also obtain a
multiplicative logarithmic separation between reversible and standard pebbling
space. This improves on the additive logarithmic separation previously known
and could plausibly be tight, although we are not able to prove this. We leave
as an interesting open problem whether our additive hardness of approximation
result could be strengthened to a multiplicative bound if the computational
resources are decreased from polynomial space to the more common setting of
polynomial time.",2305.19104v1
2023-06-01,Every Bit Counts in Consensus,"Consensus enables n processes to agree on a common valid L-bit value, despite
t < n/3 processes being faulty and acting arbitrarily. A long line of work has
been dedicated to improving the worst-case communication complexity of
consensus in partial synchrony. This has recently culminated in the worst-case
word complexity of O(n^2). However, the worst-case bit complexity of the best
solution is still O(n^2 L + n^2 kappa) (where kappa is the security parameter),
far from the \Omega(n L + n^2) lower bound. The gap is significant given the
practical use of consensus primitives, where values typically consist of
batches of large size (L > n).
  This paper shows how to narrow the aforementioned gap while achieving optimal
linear latency. Namely, we present a new algorithm, DARE (Disperse, Agree,
REtrieve), that improves upon the O(n^2 L) term via a novel dispersal
primitive. DARE achieves O(n^{1.5} L + n^{2.5} kappa) bit complexity, an
effective sqrt{n}-factor improvement over the state-of-the-art (when L > n
kappa). Moreover, we show that employing heavier cryptographic primitives,
namely STARK proofs, allows us to devise DARE-Stark, a version of DARE which
achieves the near-optimal bit complexity of O(n L + n^2 poly(kappa)). Both DARE
and DARE-Stark achieve optimal O(n) latency.",2306.00431v2
2023-06-12,Accountability Infrastructure: How to implement limits on platform optimization to protect population health,"Attention capitalism has generated design processes and product development
decisions that prioritize platform growth over all other considerations. To the
extent limits have been placed on these incentives, interventions have
primarily taken the form of content moderation. While moderation is important
for what we call ""acute harms,"" societal-scale harms -- such as negative
effects on mental health and social trust -- require new forms of institutional
transparency and scientific investigation, which we group under the term
accountability infrastructure.
  This is not a new problem. In fact, there are many conceptual lessons and
implementation approaches for accountability infrastructure within the history
of public health. After reviewing these insights, we reinterpret the societal
harms generated by technology platforms through reference to public health. To
that end, we present a novel mechanism design framework and practical
measurement methods for that framework. The proposed approach is iterative and
built into the product design process, and is applicable for both
internally-motivated (i.e. self regulation by companies) and
externally-motivated (i.e. government regulation) interventions for a range of
societal problems, including mental health.
  We aim to help shape a research agenda of principles for the design of
mechanisms around problem areas on which there is broad consensus and a firm
base of support. We offer constructive examples and discussion of potential
implementation methods related to these topics, as well as several new data
illustrations for potential effects of exposure to online content.",2306.07443v1
2023-06-16,Microlayer in nucleate boiling seen as Landau-Levich film with dewetting and evaporation,"Both experimental and theoretical studies on the microscale and fast physical
phenomena occurring during the growth of vapor bubbles in nucleate pool boiling
are reported. The focus is on the liquid film of micrometric thickness
(``microlayer'') that can form between the heater and the liquid-vapor
interface of a bubble on the millisecond time scale. The microlayer strongly
affects the macroscale heat transfer and is thus important to be understood. It
is shown that the microlayer can be seen as the Landau-Levich film deposited by
the bubble foot edge during its receding when the bubble grows. The microlayer
profile measured with white-light interferometry, the temperature distribution
over the heater, and the bubble shape were observed with synchronized
high-speed cameras. The microlayer consists of two regions: a ridge near the
contact line followed by a longer and flatter part. The ridge could not be
measured because of the intrinsic limitation of interferometry, which is
analyzed. The simulations show that the ridge grows over time due to collection
of liquid at contact line receding, the theoretical dynamics of which agrees
with the experiment. The flatter part of the microlayer is bumped and its
physical origin is explained.",2306.09838v1
2023-06-20,High frequency oscillations in spin-torque nano oscillator due to bilinear coupling,"Exchange coupling in an interfacial context is crucial for spin-torque nano
oscillator (STNO) that consists of a non-magnetic spacer which is alloyed with
a ferromagnetic material. Currently, investigations on the dynamics of the free
layer magnetization and frequency enhancement in the STNO with bilinear
coupling are still being actively pursued. In the present work, we investigate
the dynamics of the STNO in the presence of bilinear coupling but in the
absence of an external magnetic field by analyzing the associated
Landau-Lifshitz-Gilbert-Sloncewski(LLGS) equation, and consequently the impact
of the bilinear coupling on the dynamics of the magnetization of the free layer
is studied. It is observed that the frequency of the oscillations in the
magnetization component along the direction of the pinned layer polarization
can be enhanced above 300 GHz by positive bilinear coupling and up to around 30
GHz by negative bilinear coupling. We further reveal a transition from in-plane
to out-of-plane precession both for positive and negative bi-linear couplings.
We also analyze the switching of the magnetization for different values of
current and bilinear coupling. Our detailed investigations of STNO with
bilinear coupling aim at the possibilities of high-frequency devices by
considering the applied current and bilinear coupling in the absence of a
magnetic field.",2306.11415v1
2023-06-20,Convolutional neural networks for large-scale dynamical modeling of itinerant magnets,"Complex spin textures in itinerant electron magnets hold promises for
next-generation memory and information technology. The long-ranged and often
frustrated electron-mediated spin interactions in these materials give rise to
intriguing localized spin structures such as skyrmions. Yet, simulations of
magnetization dynamics for such itinerant magnets are computationally difficult
due to the need for repeated solutions to the electronic structure problems. We
present a convolutional neural network (CNN) model to accurately and
efficiently predict the electron-induced magnetic torques acting on local
spins. Importantly, as the convolutional operations with a fixed kernel
(receptive field) size naturally take advantage of the locality principle for
many-electron systems, CNN offers a scalable machine learning approach to spin
dynamics. We apply our approach to enable large-scale dynamical simulations of
skyrmion phases in itinerant spin systems. By incorporating the CNN model into
Landau-Lifshitz-Gilbert dynamics, our simulations successfully reproduce the
relaxation process of the skyrmion phase and stabilize a skyrmion lattice in
larger systems. The CNN model also allows us to compute the effective receptive
fields, thus providing a systematic and unbiased method for determining the
locality of the original electron models.",2306.11833v1
2023-06-29,Relaxed Local Correctability from Local Testing,"We construct the first asymptotically good relaxed locally correctable codes
with polylogarithmic query complexity, bringing the upper bound polynomially
close to the lower bound of Gur and Lachish (SICOMP 2021). Our result follows
from showing that a high-rate locally testable code can boost the block length
of a smaller relaxed locally correctable code, while preserving the correcting
radius and incurring only a modest additive cost in rate and query complexity.
We use the locally testable code's tester to check if the amount of corruption
in the input is low; if so, we can ""zoom-in"" to a suitable substring of the
input and recurse on the smaller code's local corrector. Hence, iterating this
operation with a suitable family of locally testable codes due to Dinur, Evra,
Livne, Lubotzky, and Mozes (STOC 2022) yields asymptotically good codes with
relaxed local correctability, arbitrarily large block length, and
polylogarithmic query complexity.
  Our codes asymptotically inherit the rate and distance of any locally
testable code used in the final invocation of the operation. Therefore, our
framework also yields nonexplicit relaxed locally correctable codes with
polylogarithmic query complexity that have rate and distance approaching the
Gilbert-Varshamov bound.",2306.17035v2
2023-07-13,"Words are not Wind -- How Joint Commitment and Reputation Solve Social Dilemmas, without Repeated Interactions or Enforcement by Third Parties","Joint commitment was argued to ""make our social world"" (Gilbert, 2014) and to
separate us from other primates. 'Joint' entails that neither of us promises
anything, unless the other promises as well. When we need to coordinate for the
best mutual outcome, any commitment is beneficial. However, when we are tempted
to free-ride (i.e. in social dilemmas), commitment serves no obvious purpose.
We show that a reputation system, which judges action in social dilemmas only
after joint commitment, can prevent free-riding. Keeping commitments builds
trust. We can selectively enter joint commitments with trustworthy individuals
to ensure their cooperation (since they will now be judged). We simply do not
commit to cooperate with those we do not trust, and hence can freely defect
without losing the trust of others. This principle might be the reason for
pointedly public joint commitments, such as marriage. It is especially relevant
to our evolutionary past, in which no mechanisms existed to enforce commitments
reliably and impartially (e.g. via a powerful and accountable government). Much
research from anthropology, philosophy and psychology made the assumption that
past collaborations were mutually beneficial and had little possibilities to
free-ride, for which there is little support. Our evolutionary game theory
approach proves that this assumption is not necessary, because free-riding
could have been dealt with joint commitments and reputation.",2307.06898v1
2023-07-18,Multi-Stage Cable Routing through Hierarchical Imitation Learning,"We study the problem of learning to perform multi-stage robotic manipulation
tasks, with applications to cable routing, where the robot must route a cable
through a series of clips. This setting presents challenges representative of
complex multi-stage robotic manipulation scenarios: handling deformable
objects, closing the loop on visual perception, and handling extended behaviors
consisting of multiple steps that must be executed successfully to complete the
entire task. In such settings, learning individual primitives for each stage
that succeed with a high enough rate to perform a complete temporally extended
task is impractical: if each stage must be completed successfully and has a
non-negligible probability of failure, the likelihood of successful completion
of the entire task becomes negligible. Therefore, successful controllers for
such multi-stage tasks must be able to recover from failure and compensate for
imperfections in low-level controllers by smartly choosing which controllers to
trigger at any given time, retrying, or taking corrective action as needed. To
this end, we describe an imitation learning system that uses vision-based
policies trained from demonstrations at both the lower (motor control) and the
upper (sequencing) level, present a system for instantiating this method to
learn the cable routing task, and perform evaluations showing great performance
in generalizing to very challenging clip placement variations. Supplementary
videos, datasets, and code can be found at
https://sites.google.com/view/cablerouting.",2307.08927v5
2023-07-20,Fallout from U.S. atmospheric nuclear tests in New Mexico and Nevada (1945-1962),"One hundred and one atmospheric nuclear weapon tests were conducted between
1945 and 1962 in the United States, resulting in widespread dispersion of
radioactive fallout, and leading to environmental contamination and population
exposures. Accurate assessment of the extent of fallout from nuclear weapon
tests has been challenging in the United States and elsewhere, due to limited
monitoring and data accessibility. Here we address this deficit by combining
U.S. government data, high-resolution reanalyzed historical weather fields, and
atmospheric transport modeling to reconstruct radionuclide deposition across
the contiguous United States, with 10-kilometer spatial and one-hour temporal
resolution for five days following detonation, from all 94 atmospheric tests
detonated in New Mexico and Nevada with fission yields sufficient to generate
mushroom clouds. Our analysis also includes deposition estimates for 10 days
following the detonation of Trinity, the first ever nuclear weapon test, on
July 16, 1945. We identify locations where radionuclide deposition
significantly exceeded levels in areas covered by the U.S. Radiation Exposure
Compensation Act (RECA). These findings include deposition in all 48 contiguous
U.S. states. They provide an opportunity for re-evaluating the public health
and environmental implications from atmospheric nuclear testing. Finally, our
findings also speak to debates about marking the beginning of the Anthropocene
with nuclear weapons fallout. Our deposition estimates indicate that direct
fallout from Trinity, a plutonium device, reached Crawford Lake in Canada, the
proposed ""golden spike"" site marking the beginning of the Anthropocene epoch,
starting on July 20, 1945.",2307.11040v1
2023-07-23,Characterizing non-Markovian Quantum Process by Fast Bayesian Tomography,"To push gate performance to levels beyond the thresholds for quantum error
correction, it is important to characterize the error sources occurring on
quantum gates. However, the characterization of non-Markovian error poses a
challenge to current quantum process tomography techniques. Fast Bayesian
Tomography (FBT) is a self-consistent gate set tomography protocol that can be
bootstrapped from earlier characterization knowledge and be updated in
real-time with arbitrary gate sequences. Here we demonstrate how FBT allows for
the characterization of key non-Markovian error processes. We introduce two
experimental protocols for FBT to diagnose the non-Markovian behavior of
two-qubit systems on silicon quantum dots. To increase the efficiency and
scalability of the experiment-analysis loop, we develop an online FBT software
stack. To reduce experiment cost and analysis time, we also introduce a native
readout method and warm boot strategy. Our results demonstrate that FBT is a
useful tool for probing non-Markovian errors that can be detrimental to the
ultimate realization of fault-tolerant operation on quantum computing.",2307.12452v2
2023-07-27,Open Problems and Fundamental Limitations of Reinforcement Learning from Human Feedback,"Reinforcement learning from human feedback (RLHF) is a technique for training
AI systems to align with human goals. RLHF has emerged as the central method
used to finetune state-of-the-art large language models (LLMs). Despite this
popularity, there has been relatively little public work systematizing its
flaws. In this paper, we (1) survey open problems and fundamental limitations
of RLHF and related methods; (2) overview techniques to understand, improve,
and complement RLHF in practice; and (3) propose auditing and disclosure
standards to improve societal oversight of RLHF systems. Our work emphasizes
the limitations of RLHF and highlights the importance of a multi-faceted
approach to the development of safer AI systems.",2307.15217v2
2023-08-03,"Predicting Ki67, ER, PR, and HER2 Statuses from H&E-stained Breast Cancer Images","Despite the advances in machine learning and digital pathology, it is not yet
clear if machine learning methods can accurately predict molecular information
merely from histomorphology. In a quest to answer this question, we built a
large-scale dataset (185538 images) with reliable measurements for Ki67, ER,
PR, and HER2 statuses. The dataset is composed of mirrored images of H\&E and
corresponding images of immunohistochemistry (IHC) assays (Ki67, ER, PR, and
HER2. These images are mirrored through registration. To increase reliability,
individual pairs were inspected and discarded if artifacts were present (tissue
folding, bubbles, etc). Measurements for Ki67, ER and PR were determined by
calculating H-Score from image analysis. HER2 measurement is based on binary
classification: 0 and 1+ (IHC scores representing a negative subset) vs 3+ (IHC
score positive subset). Cases with IHC equivocal score (2+) were excluded. We
show that a standard ViT-based pipeline can achieve prediction performances
around 90% in terms of Area Under the Curve (AUC) when trained with a proper
labeling protocol. Finally, we shed light on the ability of the trained
classifiers to localize relevant regions, which encourages future work to
improve the localizations. Our proposed dataset is publicly available:
https://ihc4bc.github.io/",2308.01982v1
2023-08-06,Unravelling metallic contaminants in complex polyimide heterostructures using deep ultraviolet spectroscopic ellipsometry,"Metallic contaminants in complex heterostructures are important topics due to
their significant roles in determining physical properties as well as device
performance. Heterostructures of polyimide via on Al pad and Cu redistribution
layer (RDL) on polyimide have shown exotic properties and are important for
advanced semiconductor packaging systems. One main problem is significant
leakage current variations, which affect the performance of the devices, yet
the origin is far from understood. Furthermore, metal contaminations would
occur at the buried interfaces and it is particularly challenging to probe
them. Until now, the electronic and optical properties of complex polyimide
heterostructures and the roles of metallic contaminants, especially in the deep
ultraviolet (DUV) have not been studied extensively. Herewith, using
spectroscopic ellipsometry (SE) in a broad DUV range supported with
finite-difference time-domain (FDTD) calculations, we determine optical
properties of contaminants with various concentrations and reveal their
influence on device performance of under-bump vias and redistribution layer
(RDL) architectures. The complex dielectric function shows varying
contamination levels and different metals responsible for chip performance.
Metallic contaminants are found embedded within 50 nm in the polyimide and
different metals are distinguishable with varying concentrations, in agreement
with contact measurements in highly complex structures. Our result shows the
potency of spectroscopic ellipsometry in the DUV and paves the way for
non-destructive, advanced quality control and metrology applications in
integrated advanced electronics packaging systems.",2308.03015v1
2023-08-14,Nanoelectromechanical control of spin-photon interfaces in a hybrid quantum system on chip,"Atom-like defects or color centers (CC's) in nanostructured diamond are a
leading platform for optically linked quantum technologies, with recent
advances including memory-enhanced quantum communication, multi-node quantum
networks, and spin-mediated generation of photonic cluster states. Scaling to
practically useful applications motivates architectures meeting the following
criteria: C1 individual optical addressing of spin qubits; C2 frequency tuning
of CC spin-dependent optical transitions; C3 coherent spin control in CC ground
states; C4 active photon routing; C5 scalable manufacturability; and C6 low
on-chip power dissipation for cryogenic operations. However, no architecture
meeting C1-C6 has thus far been demonstrated. Here, we introduce a hybrid
quantum system-on-chip (HQ-SoC) architecture that simultaneously achieves
C1-C6. Key to this advance is the realization of piezoelectric strain control
of diamond waveguide-coupled tin vacancy centers to meet C2 and C3, with
ultra-low power dissipation necessary for C6. The DC response of our device
allows emitter transition tuning by over 20 GHz, while the large frequency
range (exceeding 2 GHz) enables low-power AC control. We show acoustic
manipulation of integrated tin vacancy spins and estimate single-phonon
coupling rates over 1 kHz in the resolved sideband regime. Combined with
high-speed optical routing with negligible static hold power, this HQ-SoC
platform opens the path to scalable single-qubit control with optically
mediated entangling gates.",2308.07161v1
2023-08-23,MOFO: MOtion FOcused Self-Supervision for Video Understanding,"Self-supervised learning (SSL) techniques have recently produced outstanding
results in learning visual representations from unlabeled videos. Despite the
importance of motion in supervised learning techniques for action recognition,
SSL methods often do not explicitly consider motion information in videos. To
address this issue, we propose MOFO (MOtion FOcused), a novel SSL method for
focusing representation learning on the motion area of a video, for action
recognition. MOFO automatically detects motion areas in videos and uses these
to guide the self-supervision task. We use a masked autoencoder which randomly
masks out a high proportion of the input sequence; we force a specified
percentage of the inside of the motion area to be masked and the remainder from
outside. We further incorporate motion information into the finetuning step to
emphasise motion in the downstream task. We demonstrate that our motion-focused
innovations can significantly boost the performance of the currently leading
SSL method (VideoMAE) for action recognition. Our method improves the recent
self-supervised Vision Transformer (ViT), VideoMAE, by achieving +2.6%, +2.1%,
+1.3% accuracy on Epic-Kitchens verb, noun and action classification,
respectively, and +4.7% accuracy on Something-Something V2 action
classification. Our proposed approach significantly improves the performance of
the current SSL method for action recognition, indicating the importance of
explicitly encoding motion in SSL.",2308.12447v2
2023-08-25,Thermal effect on microwave pulse driven magnetization switching of Stoner particle,"Recently it has been demonstrated that the cosine chirp microwave pulse
(CCMP) is capable of achieving fast and energy-efficient magnetization-reversal
of a nanoparticle with zero-Temperature. However, we investigate the finite
temperature, $T$ effect on the CCMP-driven magnetization reversal using the
framework of the stochastic Landau Lifshitz Gilbert equation. At finite
Temperature, we obtain the CCMP-driven fast and energy-efficient reversal and
hence estimate the maximal temperature, $T_{max}$ at which the magnetization
reversal is valid. $T_{max}$ increases with increasing the nanoparticle
cross-sectional area/shape anisotropy up to a certain value, and afterward
$T_{max}$ decreases with the further increment of nanoparticle cross-sectional
area/shape anisotropy. This is because of demagnetization/shape anisotropy
field opposes the magnetocrystalline anisotropy, i.e., reduces the energy
barrier which separates the two stable states. For smaller cross-sectional
area/shape anisotropy, the controlling parameters of CCMP show decreasing trend
with temperature. We also find that with the increment easy-plane
shape-anisotropy, the required initial frequency of CCMP significantly reduces.
For the larger volume of nanoparticles, the parameters of CCMP remains constant
for a wide range of temperature which are desired for the device application.
Therefore, The above findings might be useful to realize the CCMP-driven fast
and energy-efficient magnetization reversal in realistic conditions.",2308.13124v1
2023-09-04,Impact of electrostatic crosstalk on spin qubits in dense CMOS quantum dot arrays,"Quantum processors based on integrated nanoscale silicon spin qubits are a
promising platform for highly scalable quantum computation. Current CMOS spin
qubit processors consist of dense gate arrays to define the quantum dots,
making them susceptible to crosstalk from capacitive coupling between a dot and
its neighbouring gates. Small but sizeable spin-orbit interactions can transfer
this electrostatic crosstalk to the spin g-factors, creating a dependence of
the Larmor frequency on the electric field created by gate electrodes
positioned even tens of nanometers apart. By studying the Stark shift from tens
of spin qubits measured in nine different CMOS devices, we developed a
theoretical frawework that explains how electric fields couple to the spin of
the electrons in increasingly complex arrays, including those electric
fluctuations that limit qubit dephasing times $T_2^*$. The results will aid in
the design of robust strategies to scale CMOS quantum technology.",2309.01849v1
2023-09-05,Connectivity and interference in device-to-device networks in Poisson-Voronoi cities,"To study the overall connectivity in device-to-device networks in cities, we
incorporate a signal-to-interference-plus-noise connectivity model into a
Poisson-Voronoi tessellation model representing the streets of a city. Relays
are located at crossroads (or street intersections), whereas (user) devices are
scattered along streets. Between any two adjacent relays, we assume data can be
transmitted either directly between the relays or through users, given they
share a common street. Our simulation results reveal that the network
connectivity is ensured when the density of users (on the streets) exceeds a
certain critical value. But then the network connectivity disappears when the
user density exceeds a second critical value. The intuition is that for longer
streets, where direct relay-to-relay communication is not possible, users are
needed to transmit data between relays, but with too many users the
interference becomes too strong, eventually reducing the overall network
connectivity. This observation on the user density evokes previous results
based on another wireless network model, where transmitter-receivers were
scattered across the plane. This effect disappears when interference is removed
from the model, giving a variation of the classic Gilbert model and recalling
the lesson that neglecting interference in such network models can give overly
optimistic results. For physically reasonable model parameters, we show that
crowded streets (with more than six users on a typical street) lead to a sudden
drop in connectivity. We also give numerical results outlining a relationship
between the user density and the strength of any interference reduction
techniques.",2309.02137v2
2023-09-16,On non-expandable cross-bifix-free codes,"A cross-bifix-free code of length $n$ over $\mathbb{Z}_q$ is defined as a
non-empty subset of $\mathbb{Z}_q^n$ satisfying that the prefix set of each
codeword is disjoint from the suffix set of every codeword. Cross-bifix-free
codes have found important applications in digital communication systems. One
of the main research problems on cross-bifix-free codes is to construct
cross-bifix-free codes as large as possible in size. Recently, Wang and Wang
introduced a family of cross-bifix-free codes $S_{I,J}^{(k)}(n)$, which is a
generalization of the classical cross-bifix-free codes studied early by
Lvenshtein, Gilbert and Chee {\it et al.}. It is known that $S_{I,J}^{(k)}(n)$
is nearly optimal in size and $S_{I,J}^{(k)}(n)$ is non-expandable if $k=n-1$
or $1\leq k<n/2$. In this paper, we first show that $S_{I,J}^{(k)}(n)$ is
non-expandable if and only if $k=n-1$ or $1\leq k<n/2$, thereby improving the
results in [Chee {\it et al.}, IEEE-TIT, 2013] and [Wang and Wang, IEEE-TIT,
2022]. We then construct a new family of cross-bifix-free codes
$U^{(t)}_{I,J}(n)$ to expand $S_{I,J}^{(k)}(n)$ such that the resulting larger
code $S_{I,J}^{(k)}(n)\bigcup U^{(t)}_{I,J}(n)$ is a non-expandable
cross-bifix-free code whenever $S_{I,J}^{(k)}(n)$ is expandable. Finally, we
present an explicit formula for the size of $S_{I,J}^{(k)}(n)\bigcup
U^{(t)}_{I,J}(n)$.",2309.08915v1
2023-09-21,Real-time feedback protocols for optimizing fault-tolerant two-qubit gate fidelities in a silicon spin system,"Recently, several groups have demonstrated two-qubit gate fidelities in
semiconductor spin qubit systems above 99%. Achieving this regime of
fault-tolerant compatible high fidelities is nontrivial and requires exquisite
stability and precise control over the different qubit parameters over an
extended period of time. This can be done by efficiently calibrating qubit
control parameters against different sources of micro- and macroscopic noise.
Here, we present several single- and two-qubit parameter feedback protocols,
optimised for and implemented in state-of-the-art fast FPGA hardware.
Furthermore, we use wavelet-based analysis on the collected feedback data to
gain insight into the different sources of noise in the system. Scalable
feedback is an outstanding challenge and the presented implementation and
analysis gives insight into the benefits and drawbacks of qubit parameter
feedback, as feedback related overhead increases. This work demonstrates a
pathway towards robust qubit parameter feedback and systematic noise analysis,
crucial for mitigation strategies towards systematic high-fidelity qubit
operation compatible with quantum error correction protocols.",2309.12541v1
2023-09-21,Spatio-temporal correlations of noise in MOS spin qubits,"In quantum computing, characterising the full noise profile of qubits can aid
the efforts towards increasing coherence times and fidelities by creating error
mitigating techniques specific to the type of noise in the system, or by
completely removing the sources of noise. Spin qubits in MOS quantum dots are
exposed to noise originated from the complex glassy behaviour of two-level
fluctuators, leading to non-trivial correlations between qubit properties both
in space and time. With recent engineering progress, large amounts of data are
being collected in typical spin qubit device experiments, and it is beneficiary
to explore data analysis options inspired from fields of research that are
experienced in managing large data sets, examples include astrophysics, finance
and climate science. Here, we propose and demonstrate wavelet-based analysis
techniques to decompose signals into both frequency and time components to gain
a deeper insight into the sources of noise in our systems. We apply the
analysis to a long feedback experiment performed on a state-of-the-art
two-qubit system in a pair of SiMOS quantum dots. The observed correlations
serve to identify common microscopic causes of noise, as well as to elucidate
pathways for multi-qubit operation with a more scalable feedback system.",2309.12542v2
2023-09-29,Glioma subtype classification from histopathological images using in-domain and out-of-domain transfer learning: An experimental study,"We provide in this paper a comprehensive comparison of various transfer
learning strategies and deep learning architectures for computer-aided
classification of adult-type diffuse gliomas. We evaluate the generalizability
of out-of-domain ImageNet representations for a target domain of
histopathological images, and study the impact of in-domain adaptation using
self-supervised and multi-task learning approaches for pretraining the models
using the medium-to-large scale datasets of histopathological images. A
semi-supervised learning approach is furthermore proposed, where the fine-tuned
models are utilized to predict the labels of unannotated regions of the whole
slide images (WSI). The models are subsequently retrained using the
ground-truth labels and weak labels determined in the previous step, providing
superior performance in comparison to standard in-domain transfer learning with
balanced accuracy of 96.91% and F1-score 97.07%, and minimizing the
pathologist's efforts for annotation. Finally, we provide a visualization tool
working at WSI level which generates heatmaps that highlight tumor areas; thus,
providing insights to pathologists concerning the most informative parts of the
WSI.",2309.17223v1
2023-10-13,Midpoint geometric integrators for inertial magnetization dynamics,"We consider the numerical solution of the inertial version of
Landau-Lifshitz-Gilbert equation (iLLG), which describes high-frequency
nutation on top of magnetization precession due to angular momentum relaxation.
The iLLG equation defines a higher-order nonlinear dynamical system with very
different nature compared to the classical LLG equation, requiring twice as
many degrees of freedom for space-time discretization. It exhibits essential
conservation properties, namely magnetization amplitude preservation,
magnetization projection conservation, and a balance equation for generalized
free energy, leading to a Lyapunov structure (i.e. the free energy is a
decreasing function of time) when the external magnetic field is constant in
time. We propose two second-order numerical schemes for integrating the iLLG
dynamics over time, both based on implicit midpoint rule. The first scheme
unconditionally preserves all the conservation properties, making it the
preferred choice for simulating inertial magnetization dynamics. However, it
implies doubling the number of unknowns, necessitating significant changes in
numerical micromagnetic codes and increasing computational costs especially for
spatially inhomogeneous dynamics simulations. To address this issue, we present
a second time-stepping method that retains the same computational cost as the
implicit midpoint rule for classical LLG dynamics while unconditionally
preserving magnetization amplitude and projection. Special quasi-Newton
techniques are developed for solving the nonlinear system of equations required
at each time step due to the implicit nature of both time-steppings. The
numerical schemes are validated on analytical solution for macrospin terahertz
frequency response and the effectiveness of the second scheme is demonstrated
with full micromagnetic simulation of inertial spin waves propagation in a
magnetic thin-film.",2310.09043v1
2023-10-28,Einstein-de Haas torque as a discrete spectroscopic probe allows nanomechanical measurement of a magnetic resonance,"The Einstein-de Haas (EdH) effect is a fundamental, mechanical consequence of
any temporal change of magnetism in an object. EdH torque results from
conserving the object's total angular momentum: the angular momenta of all the
specimen's magnetic moments, together with its mechanical angular momentum.
Although the EdH effect is usually small and difficult to observe, it increases
in magnitude with detection frequency. We explore the frequency-dependence of
EdH torque for a thin film permalloy microstructure by employing a ladder of
flexural beam modes (with five distinct resonance frequencies spanning from 3
to 208 MHz) within a nanocavity optomechanical torque sensor via magnetic
hysteresis curves measured at mechanical resonances. At low DC fields the
gyrotropic resonance of a magnetic vortex spin texture overlaps the 208 MHz
mechanical mode. The massive EdH mechanical torques arising from this
co-resonance yield a fingerprint of vortex core pinning and depinning in the
sample. The experimental results are discussed in relation to mechanical
torques predicted from both macrospin (at high DC magnetic field) and
finite-difference solutions to the Landau-Lifshitz-Gilbert (LLG) equation. A
global fit of the LLG solutions to the frequency-dependent data reveals a
statistically significant discrepancy between the experimentally observed and
simulated torque phase behaviours at spin texture transitions that can be
reduced through the addition of a time constant to the conversion between
magnetic cross-product torque and mechanical torque, constrained by experiment
to be in the range of 0.5 - 4 ns.",2310.18546v2
2023-10-31,Ensemble models outperform single model uncertainties and predictions for operator-learning of hypersonic flows,"High-fidelity computational simulations and physical experiments of
hypersonic flows are resource intensive. Training scientific machine learning
(SciML) models on limited high-fidelity data offers one approach to rapidly
predict behaviors for situations that have not been seen before. However,
high-fidelity data is itself in limited quantity to validate all outputs of the
SciML model in unexplored input space. As such, an uncertainty-aware SciML
model is desired. The SciML model's output uncertainties could then be used to
assess the reliability and confidence of the model's predictions. In this
study, we extend a DeepONet using three different uncertainty quantification
mechanisms: mean-variance estimation, evidential uncertainty, and ensembling.
The uncertainty aware DeepONet models are trained and evaluated on the
hypersonic flow around a blunt cone object with data generated via
computational fluid dynamics over a wide range of Mach numbers and altitudes.
We find that ensembling outperforms the other two uncertainty models in terms
of minimizing error and calibrating uncertainty in both interpolative and
extrapolative regimes.",2311.00060v2
2023-11-11,Double-Free-Layer Stochastic Magnetic Tunnel Junctions with Synthetic Antiferromagnets,"Stochastic magnetic tunnel junctions (sMTJ) using low-barrier nanomagnets
have shown promise as fast, energy-efficient, and scalable building blocks for
probabilistic computing. Despite recent experimental and theoretical progress,
sMTJs exhibiting the ideal characteristics necessary for probabilistic bits
(p-bit) are still lacking. Ideally, the sMTJs should have (a) voltage bias
independence preventing read disturbance (b) uniform randomness in the
magnetization angle between the free layers, and (c) fast fluctuations without
requiring external magnetic fields while being robust to magnetic field
perturbations. Here, we propose a new design satisfying all of these
requirements, using double-free-layer sMTJs with synthetic antiferromagnets
(SAF). We evaluate the proposed sMTJ design with experimentally benchmarked
spin-circuit models accounting for transport physics, coupled with the
stochastic Landau-Lifshitz-Gilbert equation for magnetization dynamics. We find
that the use of low-barrier SAF layers reduces dipolar coupling, achieving
uncorrelated fluctuations at zero-magnetic field surviving up to diameters
exceeding ($D\approx 100$ nm) if the nanomagnets can be made thin enough
($\approx 1$-$2$ nm). The double-free-layer structure retains bias-independence
and the circular nature of the nanomagnets provides near-uniform randomness
with fast fluctuations. Combining our full sMTJ model with advanced transistor
models, we estimate the energy to generate a random bit as $\approx$ 3.6 fJ,
with fluctuation rates of $\approx$ 3.3 GHz per p-bit. Our results will guide
the experimental development of superior stochastic magnetic tunnel junctions
for large-scale and energy-efficient probabilistic computation for problems
relevant to machine learning and artificial intelligence.",2311.06642v2
2023-11-14,Toxicity Detection is NOT all you Need: Measuring the Gaps to Supporting Volunteer Content Moderators,"Extensive efforts in automated approaches for content moderation have been
focused on developing models to identify toxic, offensive, and hateful content
with the aim of lightening the load for moderators. Yet, it remains uncertain
whether improvements on those tasks have truly addressed moderators' needs in
accomplishing their work. In this paper, we surface gaps between past research
efforts that have aimed to provide automation for aspects of content moderation
and the needs of volunteer content moderators, regarding identifying violations
of various moderation rules. To do so, we conduct a model review on Hugging
Face to reveal the availability of models to cover various moderation rules and
guidelines from three exemplar forums. We further put state-of-the-art LLMs to
the test, evaluating how well these models perform in flagging violations of
platform rules from one particular forum. Finally, we conduct a user survey
study with volunteer moderators to gain insight into their perspectives on
useful moderation models. Overall, we observe a non-trivial gap, as missing
developed models and LLMs exhibit moderate to low performance on a significant
portion of the rules. Moderators' reports provide guides for future work on
developing moderation assistant models.",2311.07879v2
2023-11-14,All Byzantine Agreement Problems are Expensive,"Byzantine agreement, arguably the most fundamental problem in distributed
computing, operates among n processes, out of which t < n can exhibit arbitrary
failures. The problem states that all correct (non-faulty) processes must
eventually decide (termination) the same value (agreement) from a set of
admissible values defined by the proposals of the processes (validity).
Depending on the exact version of the validity property, Byzantine agreement
comes in different forms, from Byzantine broadcast to strong and weak
consensus, to modern variants of the problem introduced in today's blockchain
systems. Regardless of the specific flavor of the agreement problem, its
communication cost is a fundamental metric whose improvement has been the focus
of decades of research. The Dolev-Reischuk bound, one of the most celebrated
results in distributed computing, proved 40 years ago that, at least for
Byzantine broadcast, no deterministic solution can do better than Omega(t^2)
exchanged messages in the worst case. Since then, it remained unknown whether
the quadratic lower bound extends to seemingly weaker variants of Byzantine
agreement. This paper answers the question in the affirmative, closing this
long-standing open problem. Namely, we prove that any non-trivial agreement
problem requires Omega(t^2) messages to be exchanged in the worst case. To
prove the general lower bound, we determine the weakest Byzantine agreement
problem and show, via a novel indistinguishability argument, that it incurs
Omega(t^2) exchanged messages.",2311.08060v2
2023-11-21,Nonparametric variable importance for time-to-event outcomes with application to prediction of HIV infection,"In survival analysis, complex machine learning algorithms have been
increasingly used for predictive modeling. Given a collection of features
available for inclusion in a predictive model, it may be of interest to
quantify the relative importance of a subset of features for the prediction
task at hand. In particular, in HIV vaccine trials, participant baseline
characteristics are used to predict the probability of infection over the
intended follow-up period, and investigators may wish to understand how much
certain types of predictors, such as behavioral factors, contribute toward
overall predictiveness. Time-to-event outcomes such as time to infection are
often subject to right censoring, and existing methods for assessing variable
importance are typically not intended to be used in this setting. We describe a
broad class of algorithm-agnostic variable importance measures for prediction
in the context of survival data. We propose a nonparametric efficient
estimation procedure that incorporates flexible learning of nuisance
parameters, yields asymptotically valid inference, and enjoys
double-robustness. We assess the performance of our proposed procedure via
numerical simulations and analyze data from the HVTN 702 study to inform
enrollment strategies for future HIV vaccine trials.",2311.12726v2
2023-11-29,Atmospheric Escape From Three Terrestrial Planets in the L 98-59 System,"A critically important process affecting the climate evolution and potential
habitability of an exoplanet is atmospheric escape, in which high-energy
radiation from a star drives the escape of hydrogen atoms and other light
elements from a planet's atmosphere. L 98-59 is a benchmark system for studying
such atmospheric processes, with three transiting terrestrial-size planets
receiving Venus-like instellations (4-25 S$_\oplus$) from their M3 host star.
We use the VPLanet model to simulate the evolution of the L 98-59 system and
the atmospheric escape of its inner three small planets, given different
assumed initial water quantities. We find that, regardless of their initial
water content, all three planets accumulate significant quantities of oxygen
due to efficient water photolysis and hydrogen loss. All three planets also
receive enough XUV flux to drive rapid water loss, which considerably affects
their developing climates and atmospheres. Even in scenarios of low initial
water content, our results suggest that the James Webb Space Telescope (JWST)
will be sensitive to observations of retained oxygen on the L 98-59 planets in
its future scheduled observations, with planets b and c being the most likely
targets to possess an extended atmosphere. Our results constrain the
atmospheric evolution of these small rocky planets, and they provide context
for current and future observations of the L 98-59 system to generalize our
understanding of multi-terrestrial planet systems.",2312.00062v1
2023-12-03,Heisenberg machines with programmable spin-circuits,"We show that we can harness two recent experimental developments to build a
compact hardware emulator for the classical Heisenberg model in statistical
physics. The first is the demonstration of spin-diffusion lengths in excess of
microns in graphene even at room temperature. The second is the demonstration
of low barrier magnets (LBMs) whose magnetization can fluctuate rapidly even at
sub-nanosecond rates. Using experimentally benchmarked circuit models, we show
that an array of LBMs driven by an external current source has a steady-state
distribution corresponding to a classical system with an energy function of the
form $E = -1/2\sum_{i,j} J_{ij} (\hat{m}_i \cdot \hat{m}_j$). This may seem
surprising for a non-equilibrium system but we show that it can be justified by
a Lyapunov function corresponding to a system of coupled
Landau-Lifshitz-Gilbert (LLG) equations. The Lyapunov function we construct
describes LBMs interacting through the spin currents they inject into the spin
neutral substrate. We suggest ways to tune the coupling coefficients $J_{ij}$
so that it can be used as a hardware solver for optimization problems involving
continuous variables represented by vector magnetizations, similar to the role
of the Ising model in solving optimization problems with binary variables.
Finally, we implement a Heisenberg AND gate based on a network of three coupled
stochastic LLG equations, illustrating the concept of probabilistic computing
with a programmable Heisenberg model.",2312.01477v1
2023-12-05,A complex-projected Rayleigh quotient iteration for targeting interior eigenvalues,"We introduce a new Projected Rayleigh Quotient Iteration aimed at improving
the convergence behaviour of classic Rayleigh Quotient iteration (RQI) by
incorporating approximate information about the target eigenvector at each
step. While classic RQI exhibits local cubic convergence for Hermitian
matrices, its global behaviour can be unpredictable, whereby it may converge to
an eigenvalue far away from the target, even when started with accurate initial
conditions. This problem is exacerbated when the eigenvalues are closely
spaced. The key idea of the new algorithm is at each step to add a
complex-valued projection to the original matrix (that depends on the current
eigenvector approximation), such that the unwanted eigenvalues are lifted into
the complex plane while the target stays close to the real line, thereby
increasing the spacing between the target eigenvalue and the rest of the
spectrum. Making better use of the eigenvector approximation leads to more
robust convergence behaviour and the new method converges reliably to the
correct target eigenpair for a significantly wider range of initial vectors
than does classic RQI. We prove that the method converges locally cubically and
we present several numerical examples demonstrating the improved global
convergence behaviour. In particular, we apply it to compute eigenvalues in a
band-gap spectrum of a Sturm-Liouville operator used to model photonic crystal
fibres, where the target and unwanted eigenvalues are closely spaced. The
examples show that the new method converges to the desired eigenpair even when
the eigenvalue spacing is very small, often succeeding when classic RQI fails.",2312.02847v2
2023-12-14,On statistical zonostrophic instability and the effect of magnetic fields,"Zonal flows are mean flows in the east-west direction, which are ubiquitous
on planets, and can be formed through 'zonostrophic instability': within
turbulence or random waves, a weak large-scale zonal flow can grow
exponentially to become prominent. In this paper, we study the statistical
behaviour of the zonostrophic instability and the effect of magnetic fields. We
use a stochastic white noise forcing to drive random waves, and study the
growth of a mean flow in this random system. The dispersion relation for the
growth rate of the expectation of the mean flow is derived, and properties of
the instability are discussed. In the limits of weak and strong magnetic
diffusivity, the dispersion relation reduces to manageable expressions, which
provide clear insights into the effect of the magnetic field and scaling laws
for the threshold of instability. The magnetic field mainly plays a stabilising
role and thus impedes the formation of the zonal flow, but under certain
conditions it can also have destabilising effects. Numerical simulation of the
stochastic flow is performed to confirm the theory. Results indicate that the
magnetic field can significantly increase the randomness of the zonal flow. It
is found that the zonal flow of an individual realisation may behave very
differently from the expectation. For weak magnetic diffusivity and moderate
magnetic field strengths, this leads to considerable variation of the outcome,
that is whether zonostrophic instability takes place or not in individual
realisations.",2312.08905v1
2023-12-19,Towards a theta correspondence in families for type II dual pairs,"Let $R$ be a commutative $\mathbb{Z}[1/p]$-algebra, let $m \leq n$ be
positive integers, and let $G_n=\text{GL}_n(F)$ and $G_m=\text{GL}_m(F)$ where
$F$ is a $p$-adic field. The Weil representation is the smooth $R[G_n\times
G_m]$-module $C_c^{\infty}(\text{Mat}_{n\times m}(F),R)$ with the action
induced by matrix multiplication. When $R=\mathbb{C}$ or is any algebraically
closed field of banal characteristic compared to $G_n$ and $G_m$, the local
theta correspondence holds by the work of Howe and M\'inguez. At the level of
supercuspidal support, we interpret the theta correspondence as a morphism of
varieties $\theta_R$, which we describe as an explicit closed immersion. For
arbitrary $R$, we construct a canonical ring homomorphism $\theta^\#_{R} :
\mathfrak{Z}_{R}(G_n)\to \mathfrak{Z}_{R}(G_m)$ that controls the action of the
center $\mathfrak{Z}_{R}(G_n)$ of the category of smooth $R[G_n]$-modules on
the Weil representation. We use the rank filtration of the Weil representation
to first obtain $\theta_{\mathbb{Z}[1/p]}^\#$, then obtain $\theta^\#_R$ for
arbitrary $R$ by proving $\mathfrak{Z}_R(G_n)$ is compatible with scalar
extension. In particular, the map $\text{Spec}(\mathfrak{Z}_R(G_m))\to
\text{Spec}(\mathfrak{Z}_R(G_n))$ induced by $\theta_R^\#$ recovers $\theta_R$
in the $R=\mathbb{C}$ case and in the banal case. We use gamma factors to prove
$\theta_R^\#$ is surjective for any $R$. Finally, we describe $\theta^\#_R$ in
terms of the moduli space of Langlands parameters and use this description to
give an alternative proof of surjectivity in the tamely ramified case.",2312.12031v1
2023-12-19,Microscopic theory of current-induced skyrmion transport and its application in disordered spin textures,"Magnetic skyrmions hold great promise for realizing compact and stable memory
devices that can be manipulated at very low energy costs via electronic current
densities. In this work, we extend a recently introduced method to describe
classical skyrmion textures coupled to dynamical itinerant electrons. In this
scheme, the electron dynamics is described via nonequilibrium Green's functions
(NEGF) within the generalized Kadanoff-Baym ansatz, and the classical spins are
treated via the Landau-Lifshitz-Gilbert equation. The framework is here
extended to open systems, by the introduction of a non-interacting
approximation to the collision integral of NEGF. This, in turn, allows us to
perform computations of the real-time response of skyrmions to electronic
currents in large quantum systems coupled to electronic reservoirs, which
exhibit a linear scaling in the number of time steps. We use this approach to
investigate how electronic spin currents and dilute spin disorder affects
skyrmion transport and the skyrmion Hall drift. Our results show that the
skyrmion dynamics is sensitive to the specific form of spin disorder, such that
different disorder configurations leads to qualitatively different skyrmion
trajectories for the same applied bias. This sensitivity arises from the local
spin dynamics around the magnetic impurities, a feature that is expected not to
be well captured by phenomenological or spin-only descriptions. At the same
time, our findings illustrate the potential of engineering microscopic impurity
patterns to steer skyrmion trajectories.",2312.12201v1
2024-01-09,Characterization of two fast-turnaround dry dilution refrigerators for scanning probe microscopy,"Low-temperature scanning probe microscopes (SPMs) are critical for the study
of quantum materials and quantum information science. Due to the rising costs
of helium, cryogen-free cryostats have become increasingly desirable. However,
they typically suffer from comparatively worse vibrations than cryogen-based
systems, necessitating the understanding and mitigation of vibrations for SPM
applications. Here we demonstrate the construction of two cryogen-free dilution
refrigerator SPMs with minimal modifications to the factory default and we
systematically characterize their vibrational performance. We measure the
absolute vibrations at the microscope stage with geophones, and use both
microwave impedance microscopy and a scanning single electron transistor to
independently measure tip-sample vibrations. Additionally, we implement
customized filtering and thermal anchoring schemes, and characterize the
cooling power at the scanning stage and the tip electron temperature. This work
serves as a reference to researchers interested in cryogen-free SPMs, as such
characterization is not standardized in the literature or available from
manufacturers.",2401.04373v1
2024-01-11,Micromagnetic simulations of the size dependence of the Curie temperature in ferromagnetic nanowires and nanolayers,"We solve the Landau-Lifshitz-Gilbert equation in the finite-temperature
regime, where thermal fluctuations are modeled by a random magnetic field whose
variance is proportional to the temperature. By rescaling the temperature
proportionally to the computational cell size $\Delta x$ ($T \to T\,\Delta
x/a_{\text{eff}}$, where $a_{\text{eff}}$ is the lattice constant) [M. B. Hahn,
J. Phys. Comm., 3:075009, 2019], we obtain Curie temperatures $T_{\text{C}}$
that are in line with the experimental values for cobalt, iron and nickel. For
finite-sized objects such as nanowires (1D) and nanolayers (2D), the Curie
temperature varies with the smallest size $d$ of the system. We show that the
difference between the computed finite-size $T_{\text{C}}$ and the bulk
$T_{\text{C}}$ follows a power-law of the type: $(\xi_0/d)^\lambda$, where
$\xi_0$ is the correlation length at zero temperature, and $\lambda$ is a
critical exponent. We obtain values of $\xi_0$ in the nanometer range, also in
accordance with other simulations and experiments. The computed critical
exponent is close to $\lambda=2$ for all considered materials and geometries.
This is the expected result for a mean-field approach, but slightly larger than
the values observed experimentally.",2401.05722v1
2024-01-24,"How AI Ideas Affect the Creativity, Diversity, and Evolution of Human Ideas: Evidence From a Large, Dynamic Experiment","Exposure to large language model output is rapidly increasing. How will
seeing AI-generated ideas affect human ideas? We conducted an experiment (800+
participants, 40+ countries) where participants viewed creative ideas that were
from ChatGPT or prior experimental participants and then brainstormed their own
idea. We varied the number of AI-generated examples (none, low, or high
exposure) and if the examples were labeled as 'AI' (disclosure). Our dynamic
experiment design -- ideas from prior participants in an experimental condition
are used as stimuli for future participants in the same experimental condition
-- mimics the interdependent process of cultural creation: creative ideas are
built upon prior ideas. Hence, we capture the compounding effects of having
LLMs 'in the culture loop'. We find that high AI exposure (but not low AI
exposure) did not affect the creativity of individual ideas but did increase
the average amount and rate of change of collective idea diversity. AI made
ideas different, not better. There were no main effects of disclosure. We also
found that self-reported creative people were less influenced by knowing an
idea was from AI, and that participants were more likely to knowingly adopt AI
ideas when the task was difficult. Our findings suggest that introducing AI
ideas into society may increase collective diversity but not individual
creativity.",2401.13481v1
2024-01-31,Multimaterial Inkjet Printing of Mechanochromic Materials,"Inkjet printing technology achieves the precise deposition of liquid-phase
materials via the digitally controlled formation of picoliter-sized droplets.
Beyond graphical printing, inkjet printing has been employed for the deposition
of separated drops on surfaces or the formation of continuous layers, which
allows to construct materials gradients or periodic features that provide
enhanced functionalities. Here, we explore the use of multinozzle,
drop-on-demand piezoelectric inkjet technology for the manufacturing of
mechanochromic materials, i.e., materials that change their color or
fluorescence in response to mechanical deformation. To accomplish this,
suitable polyurethane polymers of differing hardness grades were tested with a
range of organic solvents to formulate low-viscosity, inkjet-printable
solutions. Following their rheological characterization, two solutions
comprised of ""soft"" and ""hard"" polyurethanes were selected for in-depth study.
The solutions were imbibed with a mechanochromic additive to yield fluorescent
inks, which were either dropcast onto polymeric substrates or printed to form
checkerboard patterns of alternating hardness using a lab-built, multimaterial
inkjet platform. Fluorescence imaging and spectroscopy were used to identify
different hardness grades in the dropcast and printed materials, as well as to
monitor the responses of these gradient materials to mechanical deformation.
The insights gained in this study are expected to facilitate the development of
inkjet-printable, mechanochromic polymer materials for a wide range of
applications.",2401.17758v2
2024-01-11,Resonant inelastic x-ray scattering in warm-dense Fe compounds beyond the SASE FEL resolution limit,"Resonant inelastic x-ray scattering (RIXS) is a widely used spectroscopic
technique, providing access to the electronic structure and dynamics of atoms,
molecules, and solids. However, RIXS requires a narrow bandwidth x-ray probe to
achieve high spectral resolution. The challenges in delivering an energetic
monochromated beam from an x-ray free electron laser (XFEL) thus limit its use
in few-shot experiments, including for the study of high energy density
systems. Here we demonstrate that by correlating the measurements of the
self-amplified spontaneous emission (SASE) spectrum of an XFEL with the RIXS
signal, using a dynamic kernel deconvolution with a neural surrogate, we can
achieve electronic structure resolutions substantially higher than those
normally afforded by the bandwidth of the incoming x-ray beam. We further show
how this technique allows us to discriminate between the valence structures of
Fe and Fe$_2$O$_3$, and provides access to temperature measurements as well as
M-shell binding energies estimates in warm-dense Fe compounds.",2402.00039v1
2024-02-08,Trustful Coopetitive Infrastructures for the New Space Exploration Era,"In the new space economy, space agencies, large enterprises, and start-ups
aim to launch space multi-robot systems (MRS) for various in-situ resource
utilization (ISRU) purposes, such as mapping, soil evaluation, and utility
provisioning. However, these stakeholders' competing economic interests may
hinder effective collaboration on a centralized digital platform. To address
this issue, neutral and transparent infrastructures could facilitate
coordination and value exchange among heterogeneous space MRS. While related
work has expressed legitimate concerns about the technical challenges
associated with blockchain use in space, we argue that weighing its potential
economic benefits against its drawbacks is necessary. This paper presents a
novel architectural framework and a comprehensive set of requirements for
integrating blockchain technology in MRS, aiming to enhance coordination and
data integrity in space exploration missions. We explored distributed ledger
technology (DLT) to design a non-proprietary architecture for heterogeneous MRS
and validated the prototype in a simulated lunar environment. The analyses of
our implementation suggest global ISRU efficiency improvements for map
exploration, compared to a corresponding group of individually acting robots,
and that fostering a coopetitive environment may provide additional revenue
opportunities for stakeholders.",2402.06014v1
2024-02-08,Designing Trustful Cooperation Ecosystems is Key to the New Space Exploration Era,"In the emerging space economy, autonomous robotic missions with specialized
goals such as mapping and mining are gaining traction, with agencies and
enterprises increasingly investing resources. Multirobot systems (MRS) research
has provided many approaches to establish control and communication layers to
facilitate collaboration from a technical perspective, such as granting more
autonomy to heterogeneous robotic groups through auction-based interactions in
mesh networks. However, stakeholders' competing economic interests often
prevent them from cooperating within a proprietary ecosystem. Related work
suggests that distributed ledger technology (DLT) might serve as a mechanism
for enterprises to coordinate workflows and trade services to explore space
resources through a transparent, reliable, non-proprietary digital platform. We
challenge this perspective by pointing to the core technical weaknesses of
blockchains, in particular, increased energy consumption, low throughput, and
full transparency through redundancy. Our objective is to advance the
discussion in a direction where the benefits of DLT from an economic
perspective are weighted against the drawbacks from a technical perspective. We
finally present a possible DLT-driven heterogeneous MRS for map exploration to
study the opportunities for economic collaboration and competitiveness.",2402.06036v1
2024-02-19,Density estimation for elliptic PDE with random input by preintegration and quasi-Monte Carlo methods,"In this paper, we apply quasi-Monte Carlo (QMC) methods with an initial
preintegration step to estimate cumulative distribution functions and
probability density functions in uncertainty quantification (UQ). The
distribution and density functions correspond to a quantity of interest
involving the solution to an elliptic partial differential equation (PDE) with
a lognormally distributed coefficient and a normally distributed source term.
There is extensive previous work on using QMC to compute expected values in UQ,
which have proven very successful in tackling a range of different PDE
problems. However, the use of QMC for density estimation applied to UQ problems
will be explored here for the first time. Density estimation presents a more
difficult challenge compared to computing the expected value due to
discontinuities present in the integral formulations of both the distribution
and density. Our strategy is to use preintegration to eliminate the
discontinuity by integrating out a carefully selected random parameter, so that
QMC can be used to approximate the remaining integral. First, we establish
regularity results for the PDE quantity of interest that are required for
smoothing by preintegration to be effective. We then show that an $N$-point
lattice rule can be constructed for the integrands corresponding to the
distribution and density, such that after preintegration the QMC error is of
order $\mathcal{O}(N^{-1+\epsilon})$ for arbitrarily small $\epsilon>0$. This
is the same rate achieved for computing the expected value of the quantity of
interest. Numerical results are presented to reaffirm our theory.",2402.11807v1
2024-02-29,Magnon spectrum of altermagnets: Time-dependent matrix product states vs. linearized Holstein-Primakoff calculations unravelling spontaneous magnon decay,"The energy-momentum dispersion of magnons, viewed as noninteracting and
infinitely long-lived quasiparticles describing collective low-energy
excitations of magnetic materials, is often presented as sharp bands obtained
from the effective quantum spin Hamiltonian, after being simplified via
linearized Holstein-Primakoff (HP) transformations. However, magnons are prone
to many-body interactions with other quasiparticles which can lead to their
spontaneous decay. The magnon-magnon interactions could affect newly classified
altermagnets. On the other hand, sharp bands of noninteracting chiral magnons
in RuO2, as the canonical example of altermagnets, have been very recently
predicted. Here, we employ nonperturbative numerically (quasi)exact quantum
many-body calculations, via time-dependent matrix product states (TDMPS), to
obtain magnon spectral function of RuO2. These calculations produce a broadened
magnon dispersion, which overlaps with linearized HP theory sharp bands only at
edges/center of the Brillouin zone. Substantially deviating otherwise.
Artificially making exchange interaction within two sublattices of RuO2 closer
in value forces these two spectra to overlap, thereby explaining the origin of
the failure of linearized HP theory. Such features translate into the
difference between their respective density of states, which we also compute
and which could be tested by Raman scattering experiments. Finally, we employ
popular Landau-Lifshitz-Gilbert (LLG) equation-based classical atomistic spin
dynamics (ASD) simulations to obtain dynamical structure factor and extract
magnon spectrum from it at finite temperature. Despite including magnon-magnon
interactions via nonlinearity of LLG equation, ASD simulations cannot fully
match the TDMPS-computed magnon spectrum due to nonclassical effects harbored
by altermagnets.",2402.19433v1
2024-03-07,Controllable Skyrmion Islands in a Moiré Magnet,"Antiferromagnetic(AFM) skyrmions have been in the spotlight as ideal
topological magnetic bits. Although they are topologically protected, they do
not exhibit the skyrmion Hall effect unlike the ferromagnetic ones. Thus, AFM
skyrmions are considered to provide a better control of the skyrmion's motion
due to the absence of the skyrmion Magnus effect. In this work, we propose a
possible realization of controllable AFM skyrmions in a twisted Moir\'e magnet.
The tunability of Moir\'e materials is not only a good platform for the
provision of rich phases, but also for the stabilization of skyrmion phase. We
investigate the ground state of twisted bilayer AFM system by solving the
Landau-Lifshitz-Gilbert equation in a continuum model. We show that the AFM
skyrmions are stabilized even in the absence of the external/dipolar magnetic
field, as a consequence of the interplay of interlayer coupling,
Dzyaloshinskii-Moriya (DM) interaction and Ising anisotropy. More
interestingly, due to the magnetoelectric effect, the application of an
external electric field locally stabilizes the skyrmions in the twisted bilayer
AFM systems, even in the absence of DM interaction. It also allows the skyrmion
helicity to change continuously when both the DM interaction and an electric
field are present. We show the phase diagram with respect to the strength of
interlayer coupling, the DM interaction and an electric field. Our results
suggest the possibility of using AFM skyrmions as stable, controllable
topological magnetic bits.",2403.04208v1
2024-03-08,A Data Augmentation Pipeline to Generate Synthetic Labeled Datasets of 3D Echocardiography Images using a GAN,"Due to privacy issues and limited amount of publicly available labeled
datasets in the domain of medical imaging, we propose an image generation
pipeline to synthesize 3D echocardiographic images with corresponding ground
truth labels, to alleviate the need for data collection and for laborious and
error-prone human labeling of images for subsequent Deep Learning (DL) tasks.
The proposed method utilizes detailed anatomical segmentations of the heart as
ground truth label sources. This initial dataset is combined with a second
dataset made up of real 3D echocardiographic images to train a Generative
Adversarial Network (GAN) to synthesize realistic 3D cardiovascular Ultrasound
images paired with ground truth labels. To generate the synthetic 3D dataset,
the trained GAN uses high resolution anatomical models from Computed Tomography
(CT) as input. A qualitative analysis of the synthesized images showed that the
main structures of the heart are well delineated and closely follow the labels
obtained from the anatomical models. To assess the usability of these synthetic
images for DL tasks, segmentation algorithms were trained to delineate the left
ventricle, left atrium, and myocardium. A quantitative analysis of the 3D
segmentations given by the models trained with the synthetic images indicated
the potential use of this GAN approach to generate 3D synthetic data, use the
data to train DL models for different clinical tasks, and therefore tackle the
problem of scarcity of 3D labeled echocardiography datasets.",2403.05384v1
2024-03-10,Dynamical generation of skyrmion and bimeron crystals by a circularly polarized electric field in frustrated magnets,"A skyrmion crystal (SkX) has attracted much attention in condensed matter
physics, since topologically nontrivial structures induce fascinating physical
phenomena. The SkXs have been experimentally observed in a variety of
materials, where the Zeeman coupling to the static magnetic field plays an
important role in the formation of the SkXs. In this study, we theoretically
propose another route to generate the SkXs by using a circularly polarized
electric field. We investigate a non-equilibrium steady state in a classical
frustrated Heisenberg magnet under the circularly polarized electric field,
where the electric field is coupled to the electric polarization via the
spin-current mechanism. By numerically solving the Landau-Lifshitz-Gilbert
equation at zero temperature, we show that the electric field radiation
generates a SkX with a high topological number in the high-frequency regime,
where the sign of the skyrmion number is fixed to be negative (positive) under
the left (right) circularly polarized field. The intense electric field melts
these SkXs and generates isolated skyrmions. We clarify that the microscopic
origin is effective electric-field-induced three-spin interactions by adopting
the high-frequency expansion in the Floquet formalism. Furthermore, we find
that the electric field radiation generates another type of SkXs, a bimeron
crystal, in the low-frequency regime. Our results provide a way to generate the
SkXs and control the topology by the circularly polarized electric field.",2403.06118v1
2024-03-12,Flexible Non-intrusive Dynamic Instrumentation for WebAssembly,"A key strength of managed runtimes over hardware is the ability to gain
detailed insight into the dynamic execution of programs with instrumentation.
Analyses such as code coverage, execution frequency, tracing, and debugging,
are all made easier in a virtual setting. As a portable, low-level bytecode,
WebAssembly offers inexpensive in-process sandboxing with high performance. Yet
to date, Wasm engines have not offered much insight into executing programs,
supporting at best bytecode-level stepping and basic source maps, but no
instrumentation capabilities. In this paper, we show the first non-intrusive
dynamic instrumentation system for WebAssembly in the open-source Wizard
Research Engine. Our innovative design offers a flexible, complete hierarchy of
instrumentation primitives that support building high-level, complex analyses
in terms of low-level, programmable probes. In contrast to emulation or machine
code instrumentation, injecting probes at the bytecode level increases
expressiveness and vastly simplifies the implementation by reusing the engine's
JIT compiler, interpreter, and deoptimization mechanism rather than building
new ones. Wizard supports both dynamic instrumentation insertion and removal
while providing consistency guarantees, which is key to composing multiple
analyses without interference. We detail a fully-featured implementation in a
high-performance multi-tier Wasm engine, show novel optimizations specifically
designed to minimize instrumentation overhead, and evaluate performance
characteristics under load from various analyses. This design is well-suited
for production engine adoption as probes can be implemented to have no impact
on production performance when not in use.",2403.07973v1
2024-03-13,Highly confined epsilon-near-zero- and surface-phonon polaritons in SrTiO3 membranes,"Recent theoretical studies have suggested that transition metal perovskite
oxide membranes can enable surface phonon polaritons in the infrared range with
low loss and much stronger subwavelength confinement than bulk crystals. Such
modes, however, have not been experimentally observed so far. Here, using a
combination of far-field Fourier-transform infrared (FTIR) spectroscopy and
near-field synchrotron infrared nanospectroscopy (SINS) imaging, we study the
phonon-polaritons in a 100 nm thick freestanding crystalline membrane of SrTiO3
transferred on metallic and dielectric substrates. We observe a
symmetric-antisymmetric mode splitting giving rise to epsilon-near-zero and
Berreman modes as well as highly confined (by a factor of 10) propagating
phonon polaritons, both of which result from the deep-subwavelength thickness
of the membranes. Theoretical modeling based on the analytical finite-dipole
model and numerical finite-difference methods fully corroborate the
experimental results. Our work reveals the potential of oxide membranes as a
promising platform for infrared photonics and polaritonics.",2403.08500v1
2024-03-18,Lattice QCD estimates of thermal photon production from the QGP,"Thermal photons produced in heavy-ion collision experiments are an important
observable for understanding quark-gluon plasma (QGP). The thermal photon rate
from the QGP at a given temperature can be calculated from the spectral
function of the vector current correlator. Extraction of the spectral function
from the lattice correlator is known to be an ill-conditioned problem, as there
is no unique solution for a spectral function for a given lattice correlator
with statistical errors. The vector current correlator, on the other hand,
receives a large ultraviolet contribution from the vacuum, which makes the
extraction of the thermal photon rate difficult from this channel. We therefore
consider the difference between the transverse and longitudinal part of the
spectral function, only capturing the thermal contribution to the current
correlator, simplifying the reconstruction significantly. The lattice
correlator is calculated for light quarks in quenched QCD at $T=470~$MeV ($\sim
1.5\, T_c$), as well as in 2+1 flavor QCD at $T=220~$MeV ($\sim 1.2 \, T_{pc}$)
with $m_{\pi}=320$ MeV. In order to quantify the non-perturbative effects, the
lattice correlator is compared with the corresponding
$\text{NLO}+\text{LPM}^{\text{LO}}$ estimate of correlator. The reconstruction
of the spectral function is performed in several different frameworks, ranging
from physics-informed models of the spectral function to more general models in
the Backus-Gilbert method and Gaussian Process regression. We find that the
resulting photon rates agree within errors.",2403.11647v1
2024-03-20,Optimal Risk-Sensitive Scheduling Policies for Remote Estimation of Autoregressive Markov Processes,"We design scheduling policies that minimize a risk-sensitive cost criterion
for a remote estimation setup. Since risk-sensitive cost objective takes into
account not just the mean value of the cost, but also higher order moments of
its probability distribution, the resulting policy is robust to changes in the
underlying system's parameters. The setup consists of a sensor that observes a
discrete-time autoregressive Markov process, and at each time $t$ decides
whether or not to transmit its observations to a remote estimator using an
unreliable wireless communication channel after encoding these observations
into data packets. We model the communication channel as a Gilbert-Elliott
channel \cite{10384144}. Sensor probes the channel \cite{laourine2010betting}
and hence knows the channel state at each time $t$ before making scheduling
decision. The scheduler has to minimize the expected value of the exponential
of the finite horizon cumulative cost that is sum of the following two
quantities (i) the cumulative transmission power consumed, (ii) the cumulative
squared estimator error. We pose this dynamic optimization problem as a Markov
decision process (MDP), in which the system state at time $t$ is composed of
(i) the instantaneous error $\Delta(t):= x(t)-a\hat{x}(t-1)$, where
$x(t),\hat{x}(t-1)$ are the system state and the estimate at time $t,t-1$
respectively, and (ii) the channel state $c(t)$. We show that there exists an
optimal policy that has a threshold structure, i.e., at each time $t$, for each
possible channel state $c$, there is a threshold $\D\ust(c)$ such that if the
current channel state is $c$, then it transmits only when the error $\D(t)$
exceeds $\D\ust(c)$.",2403.13898v1
2024-03-27,"The Correlations of Scene Complexity, Workload, Presence, and Cybersickness in a Task-Based VR Game","This investigation examined the relationships among scene complexity,
workload, presence, and cybersickness in virtual reality (VR) environments.
Numerous factors can influence the overall VR experience, and existing research
on this matter is not yet conclusive, warranting further investigation. In this
between-subjects experimental setup, 44 participants engaged in the Pendulum
Chair game, with half exposed to a simple scene with lower optic flow and lower
familiarity, and the remaining half to a complex scene characterized by higher
optic flow and greater familiarity. The study measured the dependent variables
workload, presence, and cybersickness and analyzed their correlations.
Equivalence testing was also used to compare the simple and complex
environments. Results revealed that despite the visible differences between the
environments, within the 10% boundaries of the maximum possible value for
workload and presence, and 13.6% of the maximum SSQ value, a statistically
significant equivalence was observed between the simple and complex scenes.
Additionally, a moderate, negative correlation emerged between workload and SSQ
scores. The findings suggest two key points: (1) the nature of the task can
mitigate the impact of scene complexity factors such as optic flow and
familiarity, and (2) the correlation between workload and cybersickness may
vary, showing either a positive or negative relationship.",2403.19019v1
2024-03-28,Long-range Phase Coherence and Tunable Second Order $φ_0$-Josephson Effect in a Dirac Semimetal $1T-PtTe_2$,"Superconducting diode effects have recently attracted much attention for
their potential applications in superconducting logic circuits. Several
mechanisms such as magneto-chiral effects, finite momentum Cooper pairing,
asymmetric edge currents have been proposed to give rise to a supercurrent
diode effect in different materials. In this work, we establish the presence of
a large intrinsic Josephson diode effect in a type-II Dirac semimetal
$1T-PtTe_2$ facilitated by its helical spin-momentum locking and distinguish it
from other extrinsic effects. The magnitude of the Josephson diode effect is
shown to be directly correlated to the large second-harmonic component of the
supercurrent that is induced by the significant contribution of the topological
spin-momentum locked states that promote coherent Andreev processes in the
junction. We denote such junctions, where the relative phase between the two
harmonics corresponding to charge transfers of $2e$ and $4e$ can be tuned by a
magnetic field, as second order ${\phi}_0$-junctions. The direct correspondence
between the second harmonic supercurrent component and the diode effect in
$1T-PtTe_2$ junctions makes topological semimetals with high transparency an
ideal platform to study and implement the Josephson diode effect, while also
enabling further research on higher order supercurrent transport in Josephson
junctions.",2403.19445v1
1994-02-17,Power Spectrum Constraints from Spectral Distortions in the Cosmic Microwave Background,"%The content of this replacement paper is identical to the original. %We have
attempted to fix the postscript so that it will print out on %a larger number
of printers. Using recent experimental limits on $\mu$ distortions from COBE
FIRAS, and the large lever-arm spanning the damping of sub-Jeans scale
fluctuations to the scale of the COBE DMR fluctuations, we set a constraint on
the slope of the primordial power spectrum $n$. It is possible to analytically
calculate the contribution over the full range of scales and redshifts,
correctly taking into account fluctuation growth and damping as well as
thermalization processes. We find that the 95\% upper limit is weakly dependent
on cosmological parameters, e.g. $n<1.54 (h=0.5)$ and $n<1.56 (h=1.0)$ for
$\Omega_0=1$ with marginally weaker constraints for $\Omega_0<1$ in a flat
$\Omega_0 +\Omega_\Lambda=1$ universe.",9402045v2
1995-06-01,The epoch of structure formation in blue mixed dark matter models,"Recent data on the high--redshift abundance of damped Ly$\alpha$ systems are
compared with theoretical predictions for `blue' (i.e. $n>1$) Mixed Dark Matter
models. The results show that decreasing the hot component fraction
$\Omega_\nu$ and/or increasing the primordial spectral index $n$ implies an
earlier epoch of cosmic structure formation. However, we also show that varying
$\Omega_\nu$ and $n$ in these directions makes the models barely consistent
with the observed abundance of galaxy clusters. Therefore, requiring at the
same time observational constraints on damped Ly$\alpha$ systems and cluster
abundance to be satisfied represents a challenge for the Mixed Dark Matter
class of models.",9506003v2
1996-04-16,Cosmic Emissivity and Background Intensity from Damped Lyman-Alpha Galaxies,"We present a new method to compute the cosmic emissivity $\E_\nu$ and
background intensity $J_\nu$. Our method is based entirely on data from quasar
absorption-line studies, namely, the comoving density of HI and the mean
metallicity and dust-to-gas ratio in damped Ly$\alpha$ galaxies. These
observations, when combined with models of cosmic chemical evolution, are
sufficient to determine the comoving rate of star formation as a function of
redshift. From this, we compute $\E_\nu $ and $J_\nu$ using stellar population
synthesis models. Our method includes a self-consistent treatment of the
absorption and reradiation of starlight by dust. In all of our calculations,
the near-UV emissivity declines rapidly between $z\approx1$ and $z=0$, in
agreement with estimates from the Canada-France Redshift Survey. The background
intensity is consistent with a wide variety of observational limits and with a
tentative detection at far-IR wavelengths.",9604091v1
1996-05-24,Identification of a Galaxy Responsible for a High-Redshift Damped Ly-alpha Absorption System,"Galaxies believed to be responsible for damped Ly-alpha absorption (DLA)
systems in the spectra of high-redshift quasars represent a viable population
of progenitors of normal disk galaxies. They appear to contain a substantial
fraction of the baryons known to exist in normal galaxies today. Here we report
on the detection of an object, designated DLA 2233+131, responsible for a
previously known DLA system at z(abs)=3.150 in the spectrum of a quasar
2233+131 [z(QSO)=3.295]. This is the first unambiguous detection of a DLA
galaxy, in both emission line and stellar continuum. Its properties correspond
closely to what may be expected from a young disk galaxy in the early stages of
formation, with no sign of an active nucleus. This gives a strong support to
the idea that DLA systems represent a population of young galaxies at high
redshifts.",9605154v1
1996-10-18,The absorbers towards Q0836+113,"We have performed RIJHK_S imaging of the field around the z=2.67 quasar
Q0836+113, which presents several metal line and a damped Ly\alpha absorption
systems in its spectrum. The images reveal the existence of a red K_S=18.9
object \approx 11 arcsec from the quasar. On the basis of the empirical
relationships between absorption radius and luminosity we conclude that this
object may be the CIV absorber at z=1.82. This could be the first detection of
a high redshift galaxy causing high-ionisation absorption. After carefully
subtracting the QSO, we do not detect, up to a 3\sigma limiting magnitude for
extended objects of K_S=20.8, the damped Ly\alpha absorber apparently detected
as a Ly\alpha emitter at z=2.47. It is also suggested, that object ``SW'' from
Wolfe et al. (1992) could be the galaxy responsible for the claimed MgII
absorption at z=0.37.",9610141v1
1996-12-13,The 67 Hz Feature in the Black Hole Candidate GRS 1915+105 as a Possible ``Diskoseismic'' Mode,"The Rossi X-ray Timing Explorer (RXTE) has made feasible for the first time
the search for high-frequency (~ 100 Hz) periodic features in black hole
candidate (BHC) systems. Such a feature, with a 67 Hz frequency, recently has
been discovered in the BHC GRS 1915+105 (Morgan, Remillard, & Greiner). This
feature is weak (rms variability ~0.3%-1.6%), stable in frequency (to within ~2
Hz) despite appreciable luminosity fluctuations, and narrow (quality factor Q ~
20). Several of these properties are what one expects for a ``diskoseismic''
g-mode in an accretion disk about a 10.6 M_sun (nonrotating) - 36.3 M_sun
(maximally rotating) black hole (if we are observing the fundamental mode
frequency). We explore this possibility by considering the expected luminosity
modulation, as well as possible excitation and growth mechanisms---including
turbulent excitation, damping, and ``negative'' radiation damping. We conclude
that a diskoseismic interpretation of the observations is viable.",9612142v2
1997-01-15,Gravitational Lensing of Quasars by Spiral Galaxies,"Gravitational lensing by a spiral galaxy occurs when the line-of-sight to a
background quasar passes within a few kpc from the center of the galactic disk.
Since galactic disks are rich in neutral hydrogen, the quasar spectrum will
likely be marked by a damped Lyman-alpha absorption trough at the lens
redshift. Therefore, the efficiency of searches for gravitational lensing with
sub-arcsecond splitting can be enhanced by 1-2 orders of magnitude by focusing
on a subset of all bright quasars which show low-redshift (z<1) strong
Lyman-alpha absorption (N>10^{21} cm^{-2}}). The double-image signature of
lensing could, in principle, be identified spectroscopically and without the
need for high-resolution imaging. The absorption spectrum of a spiral lens
would show a generic double-step profile due to the superposition of the two
absorption troughs of the different images. Finally, we note that searches for
microlensing signatures of quasars with damped Lyman-alpha absorption could
calibrate the fraction of MACHOs in galactic halos at high redshift.",9701100v1
1997-02-27,Interacting Hot Dark Matter,"We discuss the viability of a light particle ($\sim 30$ eV neutrino) with
strong self-interactions as a dark matter candidate. The interaction prevents
the neutrinos from free-streaming during the radiation dominated regime so
galaxy sized density perturbations can survive. Smaller scale perturbations are
damped due to neutrino diffusion. We calculate the power spectrum in the
imperfect fluid approximation, and show that it is damped at the length scale
one would estimate due to neutrino diffusion. The strength of the
neutrino--neutrino coupling is only weakly constrained by observations, and
could be chosen by fitting the power spectrum to the observed amplitude of
matter density perturbations. The main shortcoming of our model is that
interacting neutrinos can not provide the dark matter in dwarf galaxies.",9702236v1
1997-05-20,Detection of the First Star Clusters With NGST,"We calculate the observable signatures of the first generation of stars at
high redshift (5<z<100). To determine the cosmic star-formation history, we use
an extension of the Press-Schechter formalism for Cold Dark Matter (CDM)
cosmologies that incorporates gas pressure. We calibrate the fraction of gas
converted into stars to be 6% so as to reproduce the 1% solar C/H ratio
observed in the intergalactic medium (IGM) at z=3. With this star-formation
efficiency, we find that NGST would be able to image more than 10^4 star
clusters from high redshifts (z>10) within its 4'x4' field of view. If stars
occupy a region comparable to the virial radius of the cluster, then 1% of
these clusters could be resolved. We calculate the expected number-flux
relation and angular size distribution for these early star clusters. We also
describe the reionization of the IGM due to the first generation of stars, and
the consequent damping of the CMB anisotropies on small angular scales. This
damping could be detected below 10 degree angular scales by MAP and PLANCK.",9705144v1
1997-09-04,Cosmic-Ray Momentum Diffusion In Magnetosonic Versus Alfvenic Turbulent Field,"Energetic particle transport in a finite amplitude magnetosonic and Alfvenic
turbulence is considered using Monte Carlo particle simulations, which involve
an integration of particle equation of motion. We show that in a low-Betha
plasma cosmic ray can be the most important damping process for magnetosonic
waves. Assuming such conditions we derive the momentum diffusion coefficient
for relativistic particles in the presence of anisotropic finite-amplitude
turbulent wave field, for flat and Kolmogorov-type turbulence spectra. We
confirm the possibility of larger values of a momentum diffusion coefficient
occuring due to transit-time damping resonance interaction in the presence of
isotropic fast-mode waves in comparison to the Alfven waves of the same
amplitude.",9709039v2
1997-09-12,Baryonic Features in the Matter Transfer Function,"We provide scaling relations and fitting formulae for adiabatic cold dark
matter cosmologies that account for all baryon effects in the matter transfer
function to better than 10% in the large-scale structure regime. They are based
upon a physically well-motivated separation of the effects of acoustic
oscillations, Compton drag, velocity overshoot, baryon infall, adiabatic
damping, Silk damping, and cold-dark-matter growth suppression. We also find a
simpler, more accurate, and better motivated form for the zero baryon transfer
function than previous works. These descriptions are employed to quantify the
amplitude and location of baryonic features in linear theory. While baryonic
oscillations are prominent if the baryon fraction exceeds $\Omega_0 h^2 + 0.2$,
the main effect in more conventional cosmologies is a sharp suppression in the
transfer function below the sound horizon. We provide a simple but accurate
description of this effect and stress that it is not well approximated by a
change in the shape parameter $\Gamma$.",9709112v1
1997-09-23,Nonlinear spherical Alfven waves,"We present an one-dimensional numerical study of Alfven waves propagating
along a radial magnetic field. Neglecting losses, any spherical Alfven wave, no
matter how small its initial amplitude is, becomes nonlinear at sufficiently
large radii. From previous simulations of Alfven waves in plane parallel
atmospheres we did expect the waves to steepen and produce current sheets in
the nonlinear regime, which was confirmed by our new calculations. On the other
hand we did find that even the least nonlinear waves were damped out almost
completely before 10 solar radii. A damping of that kind is required by models
of Alfven wave-driven winds from old low-mass stars as these winds are mainly
accelerated within a few stellar radii.",9709222v1
1997-12-10,Effects of Disks on Gravitational Lensing by Spiral Galaxies,"Gravitational lensing of a quasar by a spiral galaxy should often be
accompanied by damped Lyman-alpha absorption and dust extinction due to the
intervening gaseous disk. In nearly edge-on configurations, the surface mass
density of the gas and stars in the disk could by itself split the quasar image
and contribute significantly to the overall lensing cross section. We calculate
the lensing probability of a disk+halo mass model for spiral galaxies,
including cosmic evolution of the lens parameters. A considerable fraction of
the lens systems contains two images with sub-arcsecond separation, straddling
a nearly edge-on disk. Because of that, extinction by dust together with
observational selection effects (involving a minimum separation and a maximum
flux ratio for the lensed images), suppress the detection efficiency of spiral
lenses in optical wavebands by at least an order of magnitude. The missing
lenses could be recovered in radio surveys. In modifying the statistics of
damped Lyman-alpha absorbers, the effect of extinction dominates over the
magnification bias due to lensing.",9712138v1
1998-03-20,HI 21cm absoprtion in two low redshift damped Ly-alpha systems,"We report the discovery of two low redshift HI 21cm absorbers, one at z =
0.2212 towards the z_{em} = 0.630 quasar OI 363 (B0738+313), and the other at z
= 0.3127 towards PKS B1127-145 (z_{em} = 1.187). Both were found during a
survey of MgII selected systems at redshifts 0.2 < z < 1 using the new UHF-high
system at the Westerbork Synthesis Radio Telescope (WSRT). New HST/FOS
observations also identify both systems as damped Ly-alpha (DLa) absorbers. By
comparing the column density from the DLa line with that from the HI 21cm line,
we calculate the spin temperature, and find that T_s is approximately 1000 K
for both of these low redshift absorbers. We briefly discuss some implications
of this result.",9803243v1
1998-05-08,Infrared emission-line galaxies associated with damped Lyman-alpha and strong metal absorber redshifts,"Eighteen candidates for emission line galaxies were discovered in a
narrow-band infrared survey that targeted the redshifts of damped Lyman-alpha
or metal lines in the spectra of quasars. The presence of emission lines is
inferred from the photometric magnitudes in narrow and broad band interference
filters, corresponding to H-alpha at redshifts of 0.89 (6 objects) and 2.4 (10
objects), and [OII] at a redshift of 2.3 (2 objects). Most of the candidates
are small resolved objects, compatible with galaxies at the redshifts of the
absorbers. Because a similar survey targeted at the redshifts of quasars
themselves uncovered only one emission-line galaxy in a larger volume, the
results imply substantial clustering of young galaxies or formation within
filaments or sheets whose locations are indicated by the redshifts of strong
absorption along the lines of sight to more distant quasars.",9805103v1
1998-05-12,Resonant Thickening of Disks by Small Satellite Galaxies,"We study the vertical heating and thickening of galaxy disks due to accretion
of small satellites. Our simulations are restricted to axial symmetry, which
largely eliminates numerical evolution of the target galaxy but requires the
trajectory of the satellite to be along the symmetry axis of the target. We
find that direct heating of disk stars by the satellite is not important
because the satellite's gravitational perturbation has little power at
frequencies resonant with the vertical stellar orbits. The satellite does
little damage to the disk until its decaying orbit resonantly excites
large-scale disk bending waves. Bending waves can damp through dynamical
friction from the halo or internal wave-particle resonances; we find that
wave-particle resonances dominate the damping. The principal vertical heating
mechanism is therefore dissipation of bending waves at resonances with stellar
orbits in the disk. Energy can thus be deposited some distance from the point
of impact of the satellite. The net heating from a tightly bound satellite can
be substantial, but satellites that are tidally disrupted before they are able
to excite bending waves do not thicken the disk.",9805145v1
1998-09-14,Collisionless Relaxation of Stellar Systems,"The objective of the work summarised here has been to exploit and extend
ideas from plasma physics and accelerator dynamics to formulate a unified
description of collisionless relaxation that views violent relaxation, Landau
damping, and phase mixing as (manifestations of) a single phenomenon. This
approach embraces the fact that the collisionless Boltzmann equation (CBE), the
basic object of the theory, is an infinite-dimensional Hamiltonian system, with
the distribution function f playing the role of the fundamental dynamical
variable, and that, interpreted appropriately, an evolution described by the
{\it CBE} is no different fundamentally from an evolution described by any
other Hamiltonian system. Equilibrium solutions correspond to extremal points
of the Hamiltonian subject to the constraints associated with Liouville's
Theorem. Stable equilibria correspond to energy minima. The evolution of a
system out of equilibrium involves (in general nonlinear) phase space
oscillations which may -- or may not -- interfere destructively so as to damp
away.",9809178v1
1998-09-30,Discovery of a z=0.808 damped Lyman-alpha system candidate in a UV selected quasar spectrum,"We present the observation of a new intermediate redshift damped Lyman-alpha
absorption system candidate, discovered in the course of a spectroscopic
follow-up for identifying the sources detected in a 150 A wide bandpass
UV-imaging survey at 2000 A. The system displays very strong MgII and FeII
lines and a high FeII/MgII ratio, which, following photoionization models,
indicates a very high neutral hydrogen column density. Such kind of systems
being very rare at redshifts <1.7, but of prime importance for understanding
the evolution of star formation in galaxies, the newly discovered candidate
deserves further investigations in a near future",9809402v1
1998-10-02,Gravity-modes in ZZ Ceti Stars. II. Effects of Turbulent Dissipation,"We investigate dynamical interactions between turbulent convection and g-mode
pulsations in ZZ Ceti variables (DAVs). Since our understanding of turbulence
is rudimentary, we are compelled to settle for order of magnitude results. A
key feature of these interactions is that convective response times are much
shorter than pulsation periods. Thus the dynamical interactions enforce near
uniform horizontal velocity inside the convection zone. They also give rise to
a narrow shear layer in the region of convective overshoot at the top of the
radiative interior. Turbulent damping inside the convection zone is negligible
for all modes, but that in the region of convective overshoot may be
significant for a few long period modes near the red edge of the instability
strip. These conclusions are in accord with those reached earlier by Brickhill.
Our major new result concerns nonlinear damping arising from the
Kelvin-Helmholtz instability of the aforementioned shear layer. Amplitudes of
overstable modes saturate where dissipation due to this instability balances
excitation by convective driving. This mechanism of amplitude saturation is
most effective for long period modes, and it may play an important role in
defining the red edge of the instability strip.",9810038v1
1999-02-11,Element Abundances at High Redshifts,"I review measurements of element abundances in different components of the
high redshift universe, including the Lyman alpha forest, damped Lyman alpha
systems, and Lyman break galaxies. Although progress is being made in all three
areas, recent work has also produced some surprises and shown that established
ideas about the nature of the damped Lyman alpha systems in particular may be
too simplistic. Overall, our knowledge of metal abundances at high z is still
very sketchy. Most significantly, there seems to be an order of magnitude
shortfall in the comoving density of metals which have been measured up to now
compared with those produced by the star formation activity seen in Lyman break
galaxies. At least some of the missing metals are likely to be in hot gas in
galactic halos and proto-clusters.",9902173v1
1999-03-09,Numerical simulation of prominence oscillations,"We present numerical simulations, obtained with the Versatile Advection Code,
of the oscillations of an inverse polarity prominence. The internal prominence
equilibrium, the surrounding corona and the inert photosphere are well
represented. Gravity and thermodynamics are not taken into account, but it is
argued that these are not crucial. The oscillations can be understood in terms
of a solid body moving through a plasma. The mass of this solid body is
determined by the magnetic field topology, not by the prominence mass proper.
The model also allows us to study the effect of the ambient coronal plasma on
the motion of the prominence body. Horizontal oscillations are damped through
the emission of slow waves while vertical oscillations are damped through the
emission of fast waves.",9903128v1
1999-03-26,Nature and evolution of Damped Lyman alpha systems,"The main properties of Damped Lyman alpha (DLA) systems are briefly reviewed
with the aim of studying the nature and evolution of the galaxies associated
with this class of QSO absorbers. Candidate DLA galaxies identified at z </= 1
in the fields of background QSOs show a variety of morphological types without
a predominance of spirals. Most properties inferred from spectroscopic studies
at z >/= 1.65 differ from those expected for spiral galaxies. The observational
results instead suggest that a significant fraction of DLA systems originate in
low-mass and/or LSB galaxies. Evolution effects are generally not detected in
DLA systems. This fact suggests that the differences between the properties of
present-day spirals and those of high-z DLA systems may not be ascribed to
evolution. Several selection effects can bias the observed population of DLA
absorbers. Analysis of these effects indicates that the fraction of spiral
galaxies tends to be underestimated relative to the fraction of low-mass or LSB
galaxies.",9903406v1
1999-11-03,Tensor Microwave Anisotropies from a Stochastic Magnetic Field,"We derive an expression for the angular power spectrum of cosmic microwave
background anisotropies due to gravity waves generated by a stochastic magnetic
field and compare the result with current observations; we take into account
the non-linear nature of the stress energy tensor of the magnetic field.
  For almost scale invariant spectra, the amplitude of the magnetic field at
galactic scales is constrained to be of order 10^{-9} Gauss. If we assume that
the magnetic field is damped below the Alfven damping scale, we find that its
amplitude at
  0.1 h^{-1}Mpc, B_\lambda, is constrained to be B_\lambda<7.9 x10^{-6} e^{3n}
Gauss, for n<-3/2, and B_\lambda<9.5x10^{-8} e^{0.37n} Gauss, for n>-3/2, where
n is the spectral index of the magnetic field and H_0=100h km s^{-1}Mpc^{-1} is
the Hubble constant today.",9911040v1
1999-11-09,Viscous Boundary Layer Damping of R-Modes in Neutron Stars,"Recent work has raised the exciting possibility that r-modes (Rossby waves)
in rotating neutron star cores might be strong gravitational wave sources. We
estimate the effect of a solid crust on their viscous damping rate and show
that the dissipation rate in the viscous boundary layer between the oscillating
fluid and the nearly static crust is >10^5 times higher than that from the
shear throughout the interior. This increases the minimum frequency for the
onset of the gravitational r-mode instability to at least 500 Hz when the core
temperature is less than 10^10 K. It eliminates the conflict of the r-mode
instability with the accretion-driven spin-up scenario for millisecond radio
pulsars and makes it unlikely that the r-mode instability is active in
accreting neutron stars. For newborn neutron stars, the formation of a solid
crust shortly after birth affects their gravitational wave spin-down and hence
detectability by ground-based interferometric gravitational wave detectors.",9911155v1
1999-11-30,The formation and evolution of supermassive black holes and their host galaxies,"We discuss constraints on the assembly history of supermassive black holes
from the observed remnant black holes in nearby galaxies and from the emission
caused by accretion onto these black holes. We also summarize the results of a
specific model for the evolution of galaxies and their central black holes
which traces their hierachical build-up in CDM-like cosmogonies. The model
assumes (i) that black holes, ellipticals and starburts form during major
mergers of galaxies (ii) that the gas fraction in galaxies decreases with
decreasing redshift (iii) that the optical bright phase of a QSO lasts for
about 10^7 years. The model succesfully reproduces the evolution of cold gas as
traced by damped damped Lyman alpha systems, the evolution of optically bright
QSOs, the remnant black hole mass distribution and the host galaxy luminosities
of QSOs.",9911514v1
1999-12-06,The Metallicity evolution of Damped Lyman-alpha systems,"We have collected data for 69 Damped Lyman-alpha (DLA) systems, to
investigate the chemical evolution of galaxies in the redshift interval 0.0 < z
< 4.4. In doing that, we have adopted the most general approach used so far to
correct for dust depletion. The best solution, obtained through chi^2
minimization, gives as output parameters the global DLA metallicity and the
dust-to-metals ratio. Clear evolution of the metallicity vs. redshift is found
(99.99% significance level), with average values going from ~1/30 solar at
z~4.1 to ~3/5 solar at z~0.5. We also find that the majority of DLAs (~60%)
shows dust depletion patterns which most closely resemble that of the warm halo
clouds in the Milky Way, and have dust-to-metals ratios very close to warm halo
clouds.",9912112v2
1999-12-22,Alfvenic Heating of Protostellar Accretion Disks,"We investigate the effects of heating generated by damping of Alfven waves on
protostellar accretion disks. Two mechanisms of damping are investigated,
nonlinear and turbulent, which were previously studied in stellar winds
(Jatenco-Pereira & Opher 1989a, b). For the nominal values studied, f=delta
v/v_{A}=0.002 and F=varpi/Omega_{i}=0.1, where delta v, v_{A} and varpi are the
amplitude, velocity and average frequency of the Alfven wave, respectively, and
Omega_{i} is the ion cyclotron frequency, we find that viscous heating is more
important than Alfven heating for small radii. When the radius is greater than
0.5 AU, Alfvenic heating is more important than viscous heating. Thus, even for
the relatively small value of f=0.002, Alfvenic heating can be an important
source of energy for ionizing protostellar disks, enabling angular momentum
transport to occur by the Balbus-Hawley instability.",9912478v1
2000-01-18,Metallicity in damped Lyman-alpha systems: evolution or bias?,"Assuming that damped Lyman-alpha(DLA) systems are galactic discs, we
calculate the corresponding evolution of metal abundances. We use detailed
multi-zone models of galactic chemical evolution (reproducing successfully the
observed properties of disc galaxies) and appropriate statistics (including
geometrical propability factors) to calculate the average metallicity as a
function of redshift. The results are compatible with available observations,
provided that observational biases are taken into account, as suggested by
Boisse et al. (1998). In particular, high column density and high metallicity
systems are not detected because the light of backround quasars is severely
extinguished, while low column density and low metallicity systems are not
detectable through their absorption lines by current surveys. We show that
these observational constraints lead to a ``no-evolution'' picture for the DLA
metallicity, which does not allow to draw strong conclusions about the nature
of those systems or about their role in ``cosmic chemical evolution''.",0001313v1
2000-02-24,Optical Counterparts to Damped Lyman Alpha Systems,"Previously we have shown (Maller et al, 1998) that the kinematics of Damped
Lyman Alpha Systems (DLAS) as measured by Prochaska and Wolfe (1998) can be
reproduced in a multiple disk model (MDM) if the gaseous disks are of
sufficient radial extent. Here we discuss this model's predictions for the
relationship between DLAS and Lyman break galaxies (LBGs), which we here take
to be objects at z~3 brighter than R=25.5. We expect that future observations
of the correlations between DLAS and LBGs will provide a new data set able to
discriminate between different theoretical models of the DLAS. Djorgovski
(1997) has already detected a few optical counterparts and more studies are
underway.",0002452v1
2000-02-24,"Damped Ly-alpha Systems in Semi-Analytic Models: Sensitivity to dynamics, disk properties, and cosmology","Previously we have shown that it is possible to account for the kinematic
properties of damped Lyman alpha systems (DLAS) in the context of semi-analytic
models. In these models, hierarchical structure formation is approximated by
constructing a merger tree for each dark matter halo. A natural consequence is
that every virialized halo may contain not only a central galaxy, but also a
number of satellite galaxies as determined by its merging history. Thus the
kinematics of the DLAS arise from the combined effects of the internal rotation
of gas disks and the motions between gas disks within a common halo. Here we
investigate the sensitivity of this model to some of the assumptions made
previously, including the modeling of satellite dynamics, the scale height of
the gas, and the cosmology.",0002454v1
2000-07-31,UVES observations of QSO 0000-2620: Molecular hydrogen abundance in the damped Ly-alpha system at z_abs = 3.3901,"We have discovered molecular hydrogen in a fourth quasar damped Ly-alpha
system (hereafter DLA). The UVES spectrograph on the 8.2m ESO Kueyen telescope
has allowed the detection of H2 in gas with low metallicity, Z/Z_solar ~=
10^{-2}, and high neutral hydrogen column density, N(HI) ~= 2.6*10^{21}
cm^{-2}, at redshift z_abs = 3.3901 toward QSO 0000-2620. The measured H2
fractional abundance of f(H2) ~= 4*10^{-8} is lower than a typical value for
Galactic interstellar clouds of high N(HI) column density by a factor of
(2-3)*10^6. Since H2 molecules are formed efficiently on dust grains, it
implies that the dust condensation in this DLA is negligible, and hence the
abundances derived from metal absorption lines are the actual ones. The
obtained f(H2) value leads to an estimate of the dust number density of < n_d
>_DLA ~= 10^{-3}*< n_d >_ISM, which is consistent with the dust-to-gas ratio k
<= 1.6 10^{-3} derived independently from the [Cr/Zn] and [Fe/Zn] ratios.",0007472v1
2000-08-11,The Evolution and Space Density of Damped Lyman-alpha Galaxies,"The results of a new spectroscopic survey of 66 $z \simgt 4$ quasars for
Damped Lyman-alpha absorption systems are presented. The search led to the
discovery of 30 new DLA candidates which are analysed in order to compute the
comoving mass density of neutral gas in a non-zero lambda Universe. The
possible sources of uncertainty are discussed and the implications of our
results for the theories of galaxy formation and evolution are emphasized. A
subsequent paper will present details of the calculations summarised here and a
more extensive explanation of the consequences of our observations for the
understanding of the nature of DLAs.",0008172v1
2000-09-06,Damped Lyman-Alpha Galaxies,"Some results from an imaging program to identify low-redshift (0.09<z<1.63)
damped Lyman-alpha (DLA) galaxies are presented. The standard paradigm that was
widely accepted a decade ago, that DLA galaxies are the progenitors of luminous
disk galaxies, is now being seriously challenged. The indisputable conclusion
from imaging studies at low redshift is that the morphological types of DLA
galaxies are mixed and that they span a range in luminosities and surface
brightnesses.",0009096v2
2000-09-07,On ionisation effects and abundance ratios in damped Lyman-alpha systems,"The similarity between observed velocity structures of Al III and singly
ionised species in damped Lyman-alpha systems (DLAs) suggests the presence of
ionised gas in the regions where most metal absorption lines are formed.
  To explore the possible implications of ionisation effects we construct a
simplified two-region model for DLAs consisting of an ionisation bounded region
with an internal radiation field and a neutral region with a lower metal
content. Within this framework we find that ionisation effects are important.
If taken into account, the element abundance ratios in DLAs are quite
consistent with those observed in Milky Way stars and in metal-poor H II
regions in blue compact dwarf galaxies. In particular we cannot exclude the
same primary N origin in both DLAs and metal-poor galaxies. From our models no
dust depletion of heavy elements needs to be invoked; little depletion is
however not excluded.",0009107v1
2000-10-20,An Imaging and Spectroscopic Study of the z=3.38639 Damped Lyman Alpha System in Q0201+1120: Clues to Star Formation Rate at High Redshift,"We present the results of a series of imaging and spectroscopic observations
aimed at identifying and studying the galaxy responsible for the z = 3.38639
damped lya system in the z = 3.61 QSO Q0201+1120. We find that the DLA is part
of a concentration of matter which includes at least four galaxies (probably
many more) over linear comoving dimensions, greater than 5h^-1Mpc. The absorber
may be a 0.7 L* galaxy at an impact parameter of 15 h^-1 kpc, but follow-up
spectroscopy is still required for positive identification. The gas is
turbulent, with many absorption components distributed over approximately 270
km/s and a large spin temperature, T_s greater than 4000K. The metallicity is
relatively high for this redshift, Z(DLA) approximately 1/20 Z(solar). From
consideration of the relative ratios of elements which have different
nucleosynthetic timescales, it would appear that the last major episode of star
formation in this DLA occurred at z greater than 4.3, more than approximately
  500 Myr prior to the time when we observe it.",0010427v1
2000-10-31,Non-Linear Evolution of the r-Modes in Neutron Stars,"The evolution of a neutron-star r-mode driven unstable by gravitational
radiation (GR) is studied here using numerical solutions of the full non-linear
fluid equations. The amplitude of the mode grows to order unity before strong
shocks develop which quickly damp the mode. In this simulation the star loses
about 40% of its initial angular momentum and 50% of its rotational kinetic
energy before the mode is damped. The non-linear evolution causes the fluid to
develop strong differential rotation which is concentrated near the surface and
especially near the poles of the star.",0010653v2
2000-11-07,Damped Lyman-alpha absorption from a nearby Low Surface Brightness galaxy,"Ground-based & HST images of the nearby galaxy SBS 1543+593 (z=0.009) show it
to be a Low Surface Brightness (LSB) galaxy with a central surface brightness
of mu_B(0)=23.2 mag/arcsec-2 and scale length 0.9 h-1 kpc, values typical for
the local LSB galaxy population. The galaxy lies directly in front of the QSO
HS 1543+5921 (z=0.807); an HST STIS spectrum of the quasar reveals a damped
Lyman-alpha (DLA) line at the redshift of the interloper with an HI column
density of log N(HI) = 20.35, as well as several low-ionization metal lines
with strengths similar to those found in the Milky Way interstellar medium. Our
data show that LSB galaxies are certainly able to produce the DLA lines seen at
higher redshift, and fuels the speculation that LSB galaxies are a major
contributor to that population of absorbers.",0011134v1
2000-11-25,Molecular hydrogen abundance in the dust-free damped Ly-alpha galaxy at z = 3.4,"New results from the search for H2 absorption in the damped Ly-alpha galaxy
at redshift z = 3.4 toward QSO 0000-2620 (z_em = 4.1) are reported. The
high-resolution (lambda/Delta lambda = 48,000) spectra of Q0000-2620 were
obtained using the Ultraviolet - Visual Echelle Spectrograph (UVES) on the 8.2m
ESO Kueyen telescope. The ortho-H2 column density is found to be N(J=1) = (5.55
+/- 1.35) 10^{13} cm^{-2} (2sigma C.L.). The combination of N(J=1) with the
limits available for other low rotational levels restricts the excitation
temperature T_ex in the range (290-540) K. This gives the total H2 column
density of N(H2) = (8.75 +/- 1.25) 10^{13} cm^{-2} and the corresponding
fraction of hydrogen atoms bound in molecules of f(H2) = (6.8 +/- 2.0) 10^{-8}.",0011470v1
2000-11-25,The Metallicity Evolution of Damped Lyman-alpha Systems,"According to Pei, Fall & Hauser (1999), the global metallicity evolution of
the Universe can be represented by the ratio of the total metal content to the
total gas content measured in Damped Lyman-alpha (DLA) systems (the ``column
density weighted metallicity'' `a la Pettini). To minimize dust obscuration
effects, a DLA sample with negligible dust content is considered, namely, 50
DLAs with log N(HI) < 20.8. The global metallicity found shows clear evidence
of redshift evolution that goes from \sim1/30 solar at z\sim4.1 to solar at z
\sim 0.4. More generally, DLAs with measured heavy elements probe the ISM of
high redshift galaxies. The whole sample collected from the literature contains
75 DLAs. The metallicity is calculated adopting for the dust correction the
most general method used so far, based on models of the ISM dust depletions in
the Galaxy. The intrinsic metallicity evolution of DLA galaxies is dlog
Z(DLA)/dz \propto -0.33 +/- 0.06.",0011473v1
2000-12-04,ATCA search for 21 cm emission from a candidate damped Ly-$α$ absorber at z = 0.101,"We report a deep search for 21 cm emission/absorption from the $z \sim 0.101$
candidate damped Lyman-$\alpha$ system towards PKS 0439-433, using the
Australia Telescope Compact Array (ATCA). The spectrum shows a weak absorption
feature --- at the $3.3 \sigma$ level --- which yields a lower limit of 730 K
on the spin temperature of the system. No HI emission was detected: the
$3\sigma$ upper limit on the HI mass of the absorber is $2.25 \times 10^9
M_{\odot}$, for a velocity spread of $\sim 70$ km s$^{-1}$. The low HI mass and
the high spin temperature seem to rule out the possibility that the absorber is
a large gas-rich spiral galaxy.",0012079v1
2000-12-05,Lost and Found: The Damped Lyman Alpha Absorbers in the QSO OI 363,"The galaxy giving rise to the damped Ly$\alpha$ absorbing system in the QSO
OI 363 with z=0.221 has been found. A galaxy which is probably associated with
the second DLA in this same QSO at z=0.0912 has also been found. Neither galaxy
is very luminous, and neither galaxy shows signs of extensive current star
formation, a massive disk or lots of gas. The impact parameters for each of the
two galaxies with respect to the QSO are reasonable. If most DLA absorbers
arise in such low luminosity galaxies, it will be difficult to pick out the
correct galaxy giving rise to DLA systems at high redshift within the large
projected areal density on the sky of faint galaxies around distant QSOs.",0012109v1
2001-01-05,Constraints from the damping tail,"The detection of anisotropy in the cosmic microwave background on arcminute
scales by the Cosmic Background Imager (CBI) provides us with our first
measurement of the damping tail and closes one chapter in the CMB story. We now
have experimental verification for all of the features in the temperature
anisotropy spectrum predicted theoretically two decades ago. The CBI result
allows us to constrain both parameterized models based on the inflationary cold
dark matter (CDM) paradigm and to examine model independent constraints on the
matter content, the distance to last scattering and the thickness of the last
scattering surface. By providing a lower limit on the duration of recombination
it implies a lower limit on the polarization of the sub-degree scale anisotropy
which is close to current experimental upper limits.",0101086v2
2001-01-10,Magnetized gravitational waves,"We investigate the influence of cosmic magnetic fields on gravitational wave
perturbations, and find exact solutions on large scales. We show that a
large-scale magnetic field can generate large-scale non-decaying gravitational
waves. In the general case where gravitational waves are generated by other
mechanisms, a large-scale magnetic field introduces a new decaying tensor mode
and modifies the non-decaying mode. The direct effect of the magnetic field is
to damp the gravitational waves, while an indirect magneto-curvature effect can
either damp or boost the waves. A magnetic field also leads to a breaking of
statistical isotropy, and the magnetic imprint on the tensor spectrum in
principle provides a means of detecting a primordial field.",0101151v3
2001-01-15,Damping time and stability of density fermion perturbations in the expanding universe,"The classic problem of the growth of density perturbations in an expanding
Newtonian universe is revisited following the work of Bisnovatyi-Kogan and
Zel'dovich. We propose a more general analytical approach: a system of free
particles satisfying semi-degenerate Fermi-Dirac statistics on the background
of an exact expanding solution is examined in the linear approximation. This
differs from the corresponding work of Bisnovatyi-Kogan and Zel'dovich where
classical particles fulfilling Maxwell-Boltzmann statistics were considered.
The solutions of the Boltzmann equation are obtained by the method of
characteristics. An expression for the damping time of a decaying solution is
discussed and a zone in which free streaming is hampered is found,
corresponding to wavelengths less than the Jeans one. In the evolution of the
system, due to the decrease of the Jeans length, those perturbations may lead
to gravitational collapse. At variance with current opinions, we deduce that
perturbations with lambda >=lambda_(J Max)/1.48 are able to generate structures
and the lower limit for substructures mass is M = M_(J max)/(1.48)^3 ~ M_(J
max)/3, where M_(J max) is the maximum value of the Jeans mass.",0101222v1
2001-02-09,A new deuterium abundance measurement from a damped Ly-alpha system at z_abs = 3.025,"We present the first D/H measurement in a damped Ly-alpha system at z_abs =
3.025 towards QSO 0347-3819 obtained from the UVES-VLT spectra. The DLA
absorber has a metallicity of [Zn/H] = -1.25 and a relatively simple velocity
structure, with two dominating components detected in several metal lines. The
hydrogen Lyman series can be followed down to Ly12 thanks to the high UV-Blue
efficiency of UVES. The best fit of the Lyman series lines, and in particular
of Ly5, Ly8, Ly10 and Ly12, relatively free of local contamination, is obtained
when the DI absorption is included in the two main components. The measured
deuterium column density yields D/H = (2.24+/-0.67) 10^{-5} close to other low
D/H values from Lyman limit systems. The corresponding values for the baryon to
photon ratio and the baryon density derived from D/H are eta = 6 10^{-10} and
Omega_b h^2 = 0.023 respectively.",0102162v1
2001-03-19,Fluctuations in the Cosmic Microwave Background I: Form Factors and their Calculation in Synchronous Gauge,"It is shown that the fluctuation in the temperature of the cosmic microwave
background in any direction may be evaluated as an integral involving scalar
and dipole form factors, which incorporate all relevant information about
acoustic oscillations before the time of last scattering. A companion paper
gives asymptotic expressions for the multipole coefficient $C_\ell$ in terms of
these form factors. Explicit expressions are given here for the form factors in
a simplified hydrodynamic model for the evolution of perturbations.",0103279v2
2001-04-24,21-cm H I emission from the Damped Lyman-alpha absorber SBS 1543+593,"We detect 21-cm emission from the Low Surface Brightness (LSB) galaxy SBS
1543+593, which gives rise to a Damped Lyman-alpha (DLA) absorption line in the
spectrum of the background QSO HS 1543+5921 (z=0.807). We obtain an accurate
measure of the velocity of the H I gas in the LSB galaxy, v=2868 km/s, and
derive a mass of 1.3e9 solar masses. We compare this value with limits obtained
towards two other z~0.1 DLA systems, and show that SBS 1543+593 would not have
been detected. Hence LSB galaxies similar to SBS 1543+593 can be responsible
for DLA systems at even modest redshifts without being detectable from their
21-cm emission.",0104396v1
2001-05-23,Mapping the Dark Matter through the CMB Damping Tail,"The lensing of CMB photons by intervening large-scale structure leaves a
characteristic imprint on its arcminute-scale anisotropy that can be used to
map the dark matter distribution in projection on degree scales or ~100 Mpc/h
comoving. We introduce a new algorithm for mass reconstruction which optimally
utilizes information from the weak lensing of CMB anisotropies in the damping
tail. It can ultimately map individual degree scale mass structures with high
signal-to-noise. To achieve this limit an experiment must produce a high
signal-to-noise, foreground-free CMB map of arcminute scale resolution,
specifically with a FWHM beam of < 5' and a noise level of < 15 (10^-6-arcmin)
or 41 (uK-arcmin).",0105424v2
2001-06-30,Chandra Detection of X-ray Absorption Associated with a Damped Lyman Alpha System,"We have observed three quasars, PKS 1127-145, Q 1331+171 and Q0054+144, with
the ACIS-S aboard the Chandra X-ray Observatory, in order to measure soft X-ray
absorption associated with intervening 21-cm and damped Ly$\alpha$ absorbers.
For PKS 1127-145, we detect absorption which, if associated with an intervening
z_{abs}=0.312 absorber, implies a metallicity of 23% solar. If the absorption
is not at z_{abs}=0.312, then the metallicity is still constrained to be less
than 23% solar. The advantage of the X-ray measurement is that the derived
metallicity is insensitive to ionization, inclusion of an atom in a molecule,
or depletion onto grains. The X-ray absorption is mostly due to oxygen, and is
consistent with the oxygen abundance of 30% solar derived from optical nebular
emission lines in a foreground galaxy at the redshift of the absorber.
  For Q1331+171 and Q 0054+144, only upper limits were obtained, although the
exposure times were intentionally short, since for these two objects we were
interested primarily in measuring flux levels to plan for future observations.
The imaging results are presented in a companion paper.",0107003v1
2001-08-08,The Evolution of Neutral Gas in the Universe as Traced by Damped Lyman Alpha Systems,"We discuss our recent results on the statistical properties of damped Lyman
alpha systems (DLAs) at low redshift (z<1.65) (Rao & Turnshek 2000). Contrary
to expectations, we found that the cosmological neutral gas mass density as
traced by DLAs, $\Omega_{DLA}$, does not evolve from redshifts $z \approx 4$ to
$z \approx 0.5$ and that extrapolation to z=0 results in a value that is a
factor of ~6.5 times higher than what is derived from galaxies at the current
epoch using HI 21 cm emission measurements. We review the current status of HI
measurements at low redshift and at the current epoch, and discuss possible
causes of this discrepancy.",0108141v1
2001-08-08,Properties of Low-Redshift Damped Lyman Alpha Galaxies,"Images of five QSO fields containing six damped Lyman alpha (DLA) systems at
redshifts 0.09<z<0.53 are presented. Identifications for the DLA galaxies
giving rise to the DLA systems are made. The observed and modeled
characteristics of the DLA galaxies are discussed. The DLA galaxies have impact
parameters ranging from < 4 kpc to \approx 34 kpc and luminosities in the range
\approx 0.03L* to \approx 1.3L*. Their morphologies include amorphous low
surface brightness systems, a probable dwarf spiral, and luminous spirals.",0108146v1
2001-08-29,The impact of dust and ionization effects on abundance measurements of Damped Ly alpha systems,"Studies of elemental abundances are a fundamental tool for unveiling the
nature of the high-redshift (proto-)galaxies associated to Damped Ly alpha
systems (DLAs). The present contribution analyses the impact of dust and
ionization effects on abundance measurements in DLAs. The behaviour of the
alpha/Fe abundance ratio corrected for such effects is used to derive
information on the chemical history and nature of DLA galaxies. The alpha/Fe
data indicate that DLAs at z~2.5 do not represent a homogeneous class of
objects. On average, DLAs show non-enhanced alpha/Fe ratios at low metallicity,
suggesting an origin in galaxies with low or intermittent star formation rates.",0108466v2
2001-08-30,Reconciling Damped Ly-alpha Statistics and 21cm Studies at z=0,"Blind 21cm surveys in the local universe have shown that the local HI mass
density, Omega_HI, is dominated by luminous, high surface brightness, spiral
galaxies. On the other hand, surveys for host galaxies of damped Ly-alpha
systems have not always been successful in finding bright spiral galaxies. From
an analysis of 21cm aperture synthesis maps of nearby galaxies we show that
this apparent contradiction can be resolved by realizing that the HI mass
density is dominated by L* galaxies, but the HI cross section near the DLA
threshold is more evenly distributed over galaxies with a large range in
luminosity, gas mass, and surface brightness. The distributions of column
densities and impact parameters of optically identified and non-identified DLA
host galaxies in the literature and the HI maps are qualitatively in agreement.
Due to poor number statistics of low redshift DLA systems, there is no firm
indication that the redshift number count of low redshift DLA systems is
inconsistent with that calculated from the nearby galaxy population.",0108498v1
2001-09-03,GRB 000301C: a possible short/intermediate duration burst connected to a DLA system,"We discuss two main aspects of the GRB 000301C afterglow (Fynbo et al. 2000,
Jensen et al. 2000); its short duration and its possible connection with a
Damped Ly-alpha Absorber (DLA). GRB 000301C falls in the short class of bursts,
though it is consistent with belonging to the proposed intermediate class or
the extreme short end of the distribution of long-duration GRBs. Based on two
VLT spectra we estimate the HI column density to be Log(N(HI))=21.2+/-0.5. This
is the first direct indication of a connection between GRB host galaxies and
Damped Ly-alpha Absorbers.",0109020v1
2001-10-16,The UCSD HIRES/KeckI Damped Lya Abundance Database: I. The Data,"We present new chemical abundance measurements of 16 damped Lya systems at
z>1.5 and update our previous abundance analyses. The entire database presented
here was derived from HIRES observations on the Keck I telescope, reduced with
the same software package, and analysed with identical techniques. Altogether,
we present a large, homogeneous database of chemical abundance measurements for
protogalaxies in the early universe, ideal for studying a number of important
aspects of galaxy formation. In addition, we have established an online
directory for this database and will continuously update the results.",0110350v1
2001-10-16,A simple analytical model for the abundance of damped Ly-α absorbers,"A simple analytical model for estimating the fraction (\Omega_{gas}) of
matter in gaseous form within the collapsed dark matter (DM) haloes is
presented. The model is developed using (i) the Press-Schechter formalism to
estimate the fraction of baryons in DM haloes, and (ii) the observational
estimates of the star formation rate at different redshifts. The prediction for
\Omega_{gas} from the model is in broad agreement with the observed abundance
of the damped Ly-\alpha systems. Furthermore, it can be used for estimating the
circular velocities of the collapsed haloes at different redshifts, which could
be compared with future observations.",0110359v2
2001-10-16,Unusual Metal Abundances in a Pair of Damped Lyman Alpha Systems at z~2,"We present high resolution spectroscopic observations of two neighbouring
damped Lya systems (DLAs) along the same line of sight towards B2314-409. Due
to their separation (v ~ 2000 km/s) and the high spectral resolution of the
data, it is possible to fit not only the weak metal transitions, but also the
separate HI absorption profiles. This has permitted, for the first time, a
detailed study of metal abundances in two neighbouring galaxy-scale absorbers.
The two DLAs have z_abs = 1.8573 and 1.8745 and have column densities log N(HI)
= 20.9+/-0.1 and 20.1+/-0.2 respectively. We have determined abundances for a
range of chemical elements, and find that BOTH absorbers towards B2314-409 have
low alpha/Fe-peak abundances compared with other known DLAs. This indicates
that not only has the recent star formation history of these absorbers been
relatively passive, but that the group environment, or some other external
factor, may have influenced this.",0110391v2
2001-12-18,NICMOS Snapshot Survey of Damped Lyman Alpha Quasars,"We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W
filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the
Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5
sigma detection limits of ~H=22 in the majority of our images. We compare our
observations to the observed Lyman-break population of high-redshift galaxies,
as well as Bruzual & Charlot evolutionary models of present-day galaxies
redshifted to the distances of the absorption systems. We predict H magnitudes
for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy
(LBG) at their redshift. Comparing these predictions to our sensitivity, we
find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most
of our observations. We find only one new possible candidate, that near
LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most
DLA systems are not drawn from a normal LBG luminosity function nor a local
galaxy luminosity function placed at these high redshifts.",0112416v1
2002-02-19,Saturation of the R-mode Instability,"Rossby waves (r-modes) in rapidly rotating neutron stars are unstable because
of the emission of gravitational radiation. We study saturation of this
instability by nonlinear transfer of energy to stellar ""inertial"" oscillation
modes. We present detailed calculations of stellar inertial modes in the WKB
limit, their linear damping by bulk and shear viscosity, and the nonlinear
coupling forces among these modes. The saturation amplitude is derived in the
extreme limits of strong or weak driving by radiation reaction, as compared to
the damping rate of low order inertial modes. We find the saturation energy is
{\it extremely small}, at least four orders of magnitude smaller than that
found by previous investigators. We discuss the consequences of this result for
spin evolution of young neutron stars, and neutron stars being spun up by
accretion in Low Mass X-ray Binaries.We also discuss the detection of these
gravitational waves by LIGO.",0202345v2
2002-04-05,HI 21cm imaging of a nearby Damped Lyman-alpha system,"We present Giant Metrewave Radio Telescope (GMRT) HI 21cm emission images of
the z=0.009 damped Lyman-alpha (DLA) absorber towards the QSO HS 1543+5921. The
DLA has been earlier identified as a low surface brightness galaxy SBS 1543+593
at an impact parameter of ~ 400 pc to the QSO line of sight. The extremely low
redshift of the absorber allows us to make spatially resolved images of the
21cm emission; besides the HI mass, this also enables us to determine the
velocity field of the galaxy and, hence, to estimate its dynamical mass.
  We obtain a total HI mass of ~ 1.4x10^9 Msun, considerably smaller than the
value of M*(HI) determined from blind 21cm emission surveys. This continues the
trend of low HI mass in all low redshift DLAs for which HI emission
observations have been attempted. We also find that the QSO lies behind a
region of low local HI column density in the foreground galaxy. This is
interesting in view of suggestions that DLA samples are biased against high HI
column density systems. The dynamical mass of the galaxy is found to be Mdyn ~
5x10^9 Msun.",0204094v1
2002-07-15,On the Structure of the Iron K-Edge,"It is shown that the commonly held view of a sharp Fe K edge must be modified
if the decay pathways of the series of resonances converging to the K
thresholds are adequately taken into account. These resonances display damped
Lorentzian profiles of nearly constant widths that are smeared to impose
continuity across the threshold. By modeling the effects of K damping on
opacities, it is found that the broadening of the K edge grows with the
ionization level of the plasma and that the appearance at high ionization of a
localized absorption feature at 7.2 keV is identified as the K-beta unresolved
transition array.",0207324v2
2002-08-26,"Damped Lyman alpha systems and disk galaxies: number density, column density distribution and gas density","We present a comparison between the observed properties of damped Lyman alpha
systems (DLAs) and the predictions of simple models for the evolution of
present day disk galaxies, including both low and high surface brightness
galaxies. We focus in particular on the number density, column density
distribution and gas density of DLAs, which have now been measured in
relatively large samples of absorbers. From the comparison we estimate the
contribution of present day disk galaxies to the population of DLAs, and how it
varies with redshift. Based on the differences between the models and the
observations, we also speculate on the nature of the fraction of DLAs which
apparently do not arise in disk galaxies.",0208457v1
2002-09-10,A search for molecules in damped Lyman-alpha absorbers occulting millimetre-loud quasars,"We have used the SEST 15-metre and Onsala 20-metre telescopes to perform deep
(r.m.s. >~ 30 mJy) integrations of various molecular rotational transitions
towards damped Lyman-alpha absorption systems (DLAs) known to occult
millimetre-loud quasars. We have observed 6 new systems and improved the
existing limits for 11 transitions. These limits may be approaching the
sensitivities required to detect new systems and we present a small number of
candidate systems which we believe warrant further observation.",0209175v1
2002-11-13,Strong Absorption-line Systems at Low Redshift: MgII and Damped Lyman Alpha,"We detail a powerful indirect method for the study of damped Lyman alpha
systems (DLAs) at low redshift. We increase the probability of finding a
low-redshift DLA to nearly 50% by targeting QSOs that are known to have strong
low-redshift MgII and FeII absorption lines in their spectra. We are using
Sloan Digital Sky Survey QSO spectra complemented by a survey we are conducting
at the MMT to study the metal-line systems. The Hubble Space Telescope is being
used to confirm low-redshift DLAs. In addition, we are imaging low-redshift DLA
galaxies with several ground-based telescopes to directly study their
environments.",0211295v1
2002-11-22,On the Origin of Nitrogen in Damped Ly-alpha Systems,"Recent measurements of nitrogen and alpha elements in over 20 damped Ly-alpha
systems (DLA) are compared with similar measurements for numerous emission line
objects and stars. It is found that the DLA distribution in the N/alpha-alpha/H
plane is bimodal, where most sample DLAs fall along the N/alpha plateau defined
at low Z by dwarf irregulars, while a small group possesses N/alpha values
roughly 0.7 dex less than those on the plateau at similar alpha/H values. We
demonstrate with chemical evolution models that a top-heavy or truncated IMF
can account for the low N in this second group.",0211512v1
2002-12-16,Fragmentation and Collapse of Turbulent Molecular Clouds,"We performed simulations of self-gravitating hydrodynamic turbulence to model
the formation of filaments, clumps and cores in molecular clouds. We find that
when the mass on the initial computational grid is comparable to the Jeans
mass, turbulent pressure is able to prevent gravitational collapse. When the
turbulence has damped away sufficiently, gravitational collapse can occur, and
the resulting structure closely resembles the pre-singularity collapse of an
isothermal sphere of Penston (1969). If several Jeans masses are initially
placed on the grid, turbulence may not be sufficient to prevent collapse before
turbulence can be significantly damped. In this case, the cores have density
structures which are considerably shallower than expected for an isothermal
gas, and resemble the solutions for a logatropic equation of state.",0212359v1
2003-02-20,One-Armed Spiral Instability in Differentially Rotating Stars,"We investigate the dynamical instability of the one-armed spiral m=1 mode in
differentially rotating stars by means of 3+1 hydrodynamical simulations in
Newtonian gravitation. We find that both a soft equation of state and a high
degree of differential rotation in the equilibrium star are necessary to excite
a dynamical m=1 mode as the dominant instability at small values of the ratio
of rotational kinetic to potential energy, T/|W|. We find that this spiral mode
propagates outward from its point of origin near the maximum density at the
center to the surface over several central orbital periods. An unstable m=1
mode triggers a secondary m=2 bar mode of smaller amplitude, and the bar mode
can excite gravitational waves. As the spiral mode propagates to the surface it
weakens, simultaneously damping the emitted gravitational wave signal. This
behavior is in contrast to waves triggered by a dynamical m=2 bar instability,
which persist for many rotation periods and decay only after a
radiation-reaction damping timescale.",0302436v2
2003-03-21,Molecular Hydrogen in Damped Ly-alpha Systems: Spatial Distribution,"To interpret H_2 quasar absorption line observations in Damped Ly-alpha
clouds (DLAs), we model the H_2 spatial distribution within a DLA. Based on
numerical simulations of disk structures with parameters similar to those
derived for such absorbers, we calculate the H_2 distribution as a function of
ultraviolet background (UVB) intensity and dust-to-gas ratio. For typical
values of these two quantities we find that the area in which the H_2 fraction
exceeds 10^{-6} (typical observational detection limit) only covers $\la 10$%
of the disk surface, i.e. H_2 has a very inhomogeneous, clumpy distribution
even at these low abundance levels. This explains the relative paucity of H_2
detections in DLAs. We also show the dependence of the covering fraction of H_2
on dust-to-gas ratio and UVB intensity and we comment on the physics governing
the H_2 chemical network at high redshift.",0303495v1
2003-05-01,Scalar perturbation spectra from warm inflation,"We present a numerical integration of the cosmological scalar perturbation
equations in warm inflation. The initial conditions are provided by a
discussion of the thermal fluctuations of an inflaton field and thermal
radiation using a combination of thermal field theory and thermodynamics. The
perturbation equations include the effects of a damping coefficient $\Gamma$
and a thermodynamic potential $V$. We give an analytic expression for the
spectral index of scalar fluctuations in terms of a new slow-roll parameter
constructed from $\Gamma$. A series of toy models, inspired by spontaneous
symmetry breaking and a known form of the damping coefficient, lead to a
spectrum with $n_s>1$ on large scales and $n_s<1$ on small scales.",0305015v3
2003-05-02,The Critical Rotation of Strange Stars and Rapidly Rotating Pulsars,"We utilize the bulk viscosity of interacting strange quark matter to
reevaluate the damping time scale. The presence of medium effect of bulk
viscosity leads to a stronger damping of r-modes, which can be over an order of
magnitude for realistic parameters. We find that the r-mode instability window
is narrowed due to the medium effect, and hence when a pulsar reaches the
instability window it will only slow down by gravitational wave emission to a
period of 1.78msec instead of 2.5msec given by early estimate. As a theoretical
upper rotation limit of pulsars, the period of 1.78msec is very close to the
two most rapidly spinning pulsars known, with periods of about 1.6msec.",0305034v1
2003-06-02,Chemical Evolution of Damped Lyman Alpha Systems,"By means of detailed chemical evolution models for galaxies of different
morphological types (i.e. spirals, irregular/starburst galaxies and
ellipticals) we study the nature of Damped Lyman-Alpha systems. Our concern is
to infer which systems represent likely candidates for the DLA population and
which do not. By focusing on individual systems, we can derive some constraints
on both the nature of the associated galaxy and its age. Our results indicate
that, owing to their high metallicities and [alpha/Fe] ratios, big spheroids
represent unlikely DLA candidates whereas spirals (observed at different
galactocentric distances) and irregulars are ideal sites where DLA absorptions
can occur.",0306037v1
2003-07-01,Clustering of galaxies at z=3 around the probable Damped Ly-alpha absorber towards QSO APM 08279+5255,"[Abridged] We present results on the clustering og Lyman break galaxies
(LBGs) around a probable damped Ly-alpha absorption (DLA) line cloud at
z_DLA=2.974 from deep UBVI images of the field containing the quasar APM
08279+5255 (z=3.91). The large area covered by our images, 0.31 deg^2 or 40x40
Mpc co-moving at z=3, and their depth (27.6 mag arcsec^{-2}), allow us to
identify 450 LBG candidates brighter than I(AB)=24.80 at 2.75<z<3.25. LBG
candidates were selected using photometric redshift techniques that include
priors within a redshift slice of width Wz=0.15 centered at z_DLA.
  Within that redshift slice, we find an enhancement of galaxies near the DLA
using both the surface density and an estimator of the 3-D spatial
over-density. The surface overdensity (3\times) is significant at the >95%
significance level on scales 2.5<r<5 Mpc co-moving and imply that some DLA
could reside in high density regions.",0307033v1
2003-08-11,Imaging and spectroscopy of galaxies associated with two z~0.7 damped Lyman-alpha absorption systems,"We have identified galaxies near two quasars which are at the redshift of
damped Lyman-alpha (DLA) systems in the UV spectra of the quasars. Both
galaxies are actively forming stars. One galaxy has a luminosity close to the
break in the local galaxy luminosity function, L*, the other is significantly
fainter than L* and appears to be interacting with a nearby companion. Despite
the strong selection effects favoring spectroscopic identification of the most
luminous DLA galaxies, many of the spectroscopically-identified DLA galaxies in
the literature are sub-L*, suggesting that the majority of the DLA population
is probably sub-L*, in contrast to MgII absorbers at similar redshifts whose
mean luminosity is close to L*.",0308193v1
2003-09-03,The Thermal Stability of Mass-Loaded Flows,"We present a linear stability analysis of a flow undergoing
conductively-driven mass-loading from embedded clouds. We find that
mass-loading damps isobaric and isentropic perturbations, and in this regard is
similar to the effect of thermal conduction, but is much more pronounced where
many embedded clumps exist. The stabilizing influence of mass-loading is
wavelength independent against isobaric (condensing) perturbations, but
wavelength dependent against isentropic (wave-like) perturbations. We derive
equations for the degree of mass-loading needed to stabilize such
perturbations. We have also made 1D numerical simulations of a mass-loaded
radiative shock and demonstrated the damping of the overstability when
mass-loading is rapid enough.",0309086v1
2003-09-22,Hierarchical Structure Formation and Chemical Evolution of Damped Ly alpha Systems,"We present a model for chemical evolution of damped Ly alpha systems
considering production of metals by SNe II and infall associated with
hierarchical structure formation. The growth of metallicity in these systems is
a reflection of the competition between astration and infall. The apparent late
turn-on of these systems is due to the late cut-off of infall. The wide range
in [Fe/H] at a given redshift is explained by the range of the times for onset
of star formation and the range of the times for infall cessation in different
systems. The observed lower bound of [Fe/H] = -3 follows from the very rapid
initial rise of [Fe/H] subsequent to onset of star formation. To reach [Fe/H] =
-3 from a metal-free initial state requires only about 30 Myr so that the
probability of observing lower [Fe/H] values is very small.",0309600v1
2003-09-29,A common trend in the chemical evolution of Local Group dwarf spheroidals and Damped Ly-alpha systems,"We compare chemical abundances of Local Group dwarf spheroidals, obtained
from recent UVES/VLT observations, and of high redshift Damped Lyman alpha
systems (DLAs), corrected for dust effects. We focus, in particular, on the
abundance ratio between alpha-capture elements and iron, alpha/Fe, a well known
indicator of chemical evolution. Comparison of the data in the plane alpha/Fe
versus Fe/H shows a remarkable similarity between the dwarf spheroidals and the
DLAs, suggestive of a common trend in their chemical evolution. At any given
metallicity these two distinct types of astronomical targets show alpha/Fe
ratios systematically lower than those of Milky Way stars. In terms of chemical
evolution models, this suggests that, on average, dSph galaxies and DLA systems
are characterized by lower, or more episodic, star formation rates than the
Milky Way.",0309765v1
2003-10-15,H_2-bearing damped Lyman-alpha systems as tracers of cosmological chemical evolution,"The chemical abundances in damped Lyman-alpha systems (DLAs) show more than 2
orders of magnitude variation at a given epoch, possibly because DLAs arise in
a wide variety of host galaxies. This could significantly bias estimates of
chemical evolution. We explore the possibility that DLAs in which H_2
absorption is detected may trace cosmological chemical evolution more reliably
since they may comprise a narrower set of physical conditions. The 9 known H_2
absorption systems support this hypothesis: metallicity exhibits a faster, more
well-defined evolution with redshift than in the general DLA population. The
dust-depletion factor and, particularly, H_2 molecular fraction also show rapid
increases with decreasing redshift. We comment on possible observational
selection effects which may bias this evolution. Larger samples of H_2-bearing
DLAs are clearly required and may constrain evolution of the UV background and
DLA galaxy host type with redshift.",0310409v2
2004-01-21,Constraints on Early Nucleosynthesis from the Abundance Pattern of a Damped Ly-alpha System at z = 2.626,"We have investigated chemical evolution in the young universe by analysing
the detailed chemical enrichment pattern of a metal-rich galaxy at high
redshift. The recent detection of over 20 elements in the gas-phase of a damped
Lyman-alpha absorber (DLA) at z = 2.626 represents an exciting new avenue for
exploring early nucleosynthesis. Given a strict upper age of ~2.5 Gyr and a
gas-phase metallicity about one third solar, we have shown the DLA abundance
pattern to be consistent with the predictions of a chemical evolution model in
which the interstellar enrichment is dominated by massive stars with a small
contribution from Type Ia supernovae. Discrepancies between the empirical data
and the models are used to highlight outstanding issues in nucleosynthesis
theory, including a tendency for Type II supernovae models to overestimate the
magnitude of the ""odd-even"" effect at subsolar metallicities. Our results
suggest a possible need for supplemental sources of magnesium and zinc, beyond
that provided by massive stars.",0401413v1
2004-03-23,The clustering of galaxies around three damped Ly-alpha absorbers at Redshift Three,"[Abridged] We present out results on the cross-correlation of Lyman break
galaxies (LBGs) around three damped \Ly absorbers (DLAs) at redshift three from
deep multi-band MOSAIC images obtained at the KPNO 4m. The large area of the
MOSAIC images, 0.31 $\deg^2$ allows us to probe the clustering of LBGs on
scales up to 20 Mpc co-moving to test whether DLA halos are more or less
massive than LBG halos. . We present our survey that covers a total of 1
deg$^2$ and contains $\sim$3,000 LBGs with photometric redshifts between 2.8
and 3.5.
  Within a redshift slice of width $W_z=0.15$, we find that the DLA-LBG
cross-correlation is $1.6\pm 1.3$ times the LBG-LBG autocorrelation. This
corresponds to a correlation length of $r_o=5\pm4.5h^{-1}$ (co-moving). The
cross-correlation is most significant on scales 5-10 Mpc, and is significantly
greater than zero at the $>95$% level from Monte Carlo simulations.",0403544v2
2004-03-31,Cold Neutral Gas in a z=4.2 Damped Lyman-alpha System: The Fuel for Star Formation,"We discuss interstellar temperature determinations using the excitation
equilibrium of the ^2P levels of Si II and C II. We show how observations of
the ^2P_3/2 fine structure levels of Si II and C II (which have significantly
different excitation energies, corresponding to ~413 and 92 K, respectively)
can be used to limit gas kinetic temperatures. We apply this method to the
z=4.224 damped Lyman-alpha system toward the quasar PSS1443+27. The lack of
significant absorption out of the SiII ^2P_3/2 level and the presence of very
strong C II ^2P_3/2 provides an upper limit to the temperature of the C
II*-bearing gas in this system. Assuming a solar Si/C ratio, the observations
imply a 2-sigma limit T<954 K for this absorber; a super-solar Si/C ratio gives
stricter limits, T<524 K. The observations suggest the presence of a cold
neutral medium; such cold gas may serve as the fuel for star formation in this
young galaxy.",0404005v2
2004-04-27,Molecular fraction limits in damped Lyman-alpha absorption systems,"We have used the Green Bank Telescope (GBT) and Berkeley-Illinois-Maryland
Association (BIMA) array to search for redshifted millimetre absorption in a
sample of damped Lyman-alpha absorption systems (DLAs). This brings the number
of published systems searched from 18 to 30. In 17 cases we reach $3\sigma$
limits of $\tau\leq0.1$, which is a significant improvement over the previous
searches and more than sufficient to detect the 4 known redshifted millimetre
absorbers ($\tau\gapp1$). While the CO rotational (millimetre) column density
limits obtained are weaker than the electronic (optical) limits, they may
provide useful limits below the atmospheric cut-off for the Lyman and Werner
\MOLH-bands in the UV ($z_{\rm abs}\lapp1.8$). Using a model for the DLA
metallicity evolution combined with assumed HCO$^+$/\MOLH ~and CO/\MOLH
\~conversion ratios, we use the molecular column density limits to calculate
plausible \MOLH ~molecular fraction limits. Finally, we use these results to
discuss the feasibility of detecting rotational CO transitions in DLAs with the
next generation of large radio telescopes.",0404516v1
2004-08-07,Metals and Dust in Intermediate-redshift Damped Ly-alpha Galaxies,"We report spectroscopic observations with the Multiple Mirror Telescope for
11 damped Lyman-alpha absorbers (DLAs) or strong DLA candidates at 0.1 < z <
1.5, including several absorbers discovered in the Sloan Digital Sky Survey. In
particular, we have measured absorption lines of Zn II, Cr II, Ni II, Fe II, Mn
II, Ti II, Ca II, and Si II. These measurements have doubled the sample of Zn
and Cr measurements at z < 1. The average relative abundance patterns in these
objects are very similar to those found for high-redshift DLAs reported in the
literature. Our observations suggest that the dust content, as determined by
[Cr/Zn], does not show much change with redshift. We also examine the sample
for correlation of [Cr/Zn] with estimates of the quasar reddening. Our data
suggest that the global mean metallicity of DLAs, as measured by the gas phase
abundance of Zn, at best shows a weak evolution with redshift over the range
0.4 < z <3.9.",0408139v1
2004-09-22,On Detecting the X-ray Silhouette of a Damped Lyman alpha System,"We explore the possibility of resolving an image of a damped Lyman alpha
(DLA) system in absorption against an extended, diffuse background X-ray
source. Typical columns of neutral hydrogen in DLAs are high enough to block
out up to ~30% of the soft X-ray flux at an observed photon energy of 0.5 keV,
and we find that ~ 1% of the area of extended X-ray sources at z > 1 have their
0.5 keV flux reduced by at least 20%. We discuss the observability of such
absorption and find that < 2 arcsecond resolution, and > 300 photons per
angular resolution element are required in the 0.3-8 keV band for its
detection, and in order to distinguish it from intrinsic surface brightness
fluctuations. For the surface brightness of the currently known high-redshift
extended X-ray sources, this requires an integration time of a few Msec on
Chandra. The detection will be within the reach of a routine observation with a
next generation X-ray telescope such as XEUS or Generation X.",0409516v2
2004-10-11,Is the solar corona nonmodally self-heated?,"Recently it was pointed out that nonmodally (transiently and/or
adiabatically) pre-amplified waves in shear flows, undergoing subsequent
viscous damping, can ultimately heat the ambient flow. The key ingredient of
this process is the ability of waves to grow, by extracting energy from the
spatially inhomogeneous mean flow. In this paper we examine this mechanism in
the context of the solar coronal plasma flows. ""Self-heating"" (SH) processes
are examined when both viscous damping and magnetic resistivity are at work. We
show that if the plasma viscosity is in the favorable range of values the
asymptotic SH rate in these flows can be quite substantial.",0410279v1
2004-10-23,Extended Neutral Gas Around z ~ 0.5 Galaxies: Properties of Damped Lya Absorbing Galaxies,"I review current results from searching for galaxies giving rise to damped
Lya absorbers (DLAs) at z<1. Using 14 confirmed DLA galaxies, I further show
that intermediate-redshift galaxies possess large HI envelope out to 24-30
h^{-1} kpc radius. The photometric and spectral properties of these galaxies
confirm that DLA galaxies are drawn from the typical field population, and not
from a separate population of low surface brightness or dwarf galaxies.
Comparisons of the ISM abundances of the DLA galaxies and the metallicities of
the absorbers at large galactic radii suggest that some DLAs originate in the
relatively unevolved outskirts of galactic disks.",0410558v1
2004-11-25,Survey for Galaxies Associated with z~3 Damped Lyman alpha Systems I: Spectroscopic Calibration of u'BVRI Photometric Selection,"We present a survey for z~3 Lyman break galaxies (LBGs) associated with
damped Lyman alpha systems (DLAs) with the primary purpose of determining the
DLA-LBG cross-correlation. This paper describes the acquisition and analysis of
imaging and spectroscopic data of 9 quasar fields having 11 known z~3 DLAs
covering an area of 465 arcmin^2. Using deep u'BVRI images, 796 LBG candidates
to an apparent R_AB magnitude of 25.5 were photometrically selected from 17,343
sources detected in the field. Spectroscopic observations of 529 LBG candidates
using Keck LRIS yielded 339 redshifts. We have conservatively identified 211
z>2 objects with <z>=3.02+/-0.32. We discuss our method of z~3 LBG
identification and present a model of the u'BVRI photometric selection
function. We use the 339 spectra to evaluate our u'BVRI z~3 Lyman break
photometric selection technique.",0411681v1
2005-01-06,Observations of Solar Flare Doppler Shift Oscillations with the Bragg Crystal Spectrometer on Yohkoh,"Oscillations in solar coronal loops appear to be a common phenomenon.
Transverse and longitudinal oscillations have been observed with both the
Transition Region and Coronal Explorer and Extreme Ultraviolet Imaging
Telescope imaging experiments. Damped Doppler shift oscillations have been
observed in emission lines from ions formed at flare temperatures with the
Solar Ultraviolet Measurements of Emitted Radiation Spectrometer. These
observations provide valuable diagnostic information on coronal conditions and
may help refine our understanding of coronal heating mechanisms. I have
initiated a study of the time dependence of Doppler shifts measured during
flares with the Bragg Crystal Spectrometer (BCS) on Yohkoh. This Letter reports
the detection of oscillatory behavior in Doppler shifts measured as a function
of time in the emission lines of S XV and Ca XIX. For some flares, both lines
exhibit damped Doppler shift oscillations with amplitudes of a few km/s and
periods and decay times of a few minutes. The observations appear to be
consistent with transverse oscillations. Because the BCS observed continuously
for almost an entire solar cycle, it provides numerous flare data sets, which
should permit an excellent characterization of the average properties of the
oscillations.",0501093v1
2005-03-09,Abundances in Damped Ly-alpha Galaxies,"Damped Ly_alpha galaxies provide a sample of young galaxies where chemical
abundances can be derived throughout the whole universe with an accuracy
comparable to that for the local universe. Despite a large spread in redshift,
HI column density and metallicity, DLA galaxies show a remarkable uniformity in
the elemental ratios rather suggestive of similar chemical evolution if not of
an unique population. These galaxies are characterized by a moderate, if any,
enhancement of alpha-elements over Fe-peak elemental abundance with [S/Zn]
about 0 and [O/Zn] about 0.2, rather similarly to the dwarfs galaxies in the
Local Group. Nitrogen shows a peculiar behaviour with a bimodal distribution
and possibly two plateaux. In particular, the plateau at low N abundances
([N/H] < -3), is not observed in other atrophysical sites and might be evidence
for primary N production by massive stars.",0503214v1
2005-03-10,Pulsar: repeatable Lagrangian singularity,"In general, the interior of radially symmetric self-gravitating sphere is
considered in terms of hydrostatic equilibrium (HSE). This approach implies the
possibility of the static being of a body. Such a static state is assumed to be
the result of asymptotic damping of the process of formation. It is shown here
that the damping of this process is impossible: if a sphere vibrates radially,
then compressional wave is singular at the centre; dynamical singularity has no
intermediate stages of the fading; the HSE-state is unachievable.
Self-gravitating sphere perpetually vibrates in essentially singular way, it
contains dynamical central region -- pulsatile Lagrangian cavity. Theoretical
properties of this cavity indicate that this is a pulsar. A pulsar is common
structural feature for every self-gravitating structure.",0503231v2
2005-03-14,Quasi-Periodic Oscillations in Relativistic Tori,"Motivated by recent interesting work on p-mode oscillations in axisymmetric
hydrodynamic black-hole tori by Rezzolla, Zanotti, and collaborators, I explore
the robustness of these oscillations by means of two and three-dimensional
relativistic hydrodynamic and MHD simulations. The primary purpose of this
investigation is to determine how the amplitudes of these oscillations are
affected by the presence of known instabilities of black-hole tori, including
the Papaloizou-Pringle instability (PPI) and the magneto-rotational instability
(MRI). Both instabilities drive accretion at rates above those considered in
Rezzolla's work. The increased accretion can allow wave energy to leak out of
the torus into the hole. Furthermore, with the MRI, the presence of turbulence,
which is absent in the hydrodynamic simulations, can lead to turbulent damping
(or excitation) of modes. The current numerical results are preliminary, but
suggest that the PPI and MRI both significantly damp acoustic oscillations in
tori.",0503305v1
2005-03-17,The first observed stellar X-ray flare oscillation: Constraints on the flare loop length and the magnetic field,"We present the first X-ray observation of an oscillation during a stellar
flare. The flare occurred on the active M-type dwarf AT Mic and was observed
with XMM-Newton. The soft X-ray light curve (0.2-12 keV) is investigated with
wavelet analysis. The flare's extended, flat peak shows clear evidence for a
damped oscillation with a period of around 750 s, an exponential damping time
of around 2000 s, and an initial, relative peak-to-peak amplitude of around
15%. We suggest that the oscillation is a standing magneto-acoustic wave tied
to the flare loop, and find that the most likely interpretation is a
longitudinal, slow-mode wave, with a resulting loop length of (2.5 +- 0.2) e10
cm. The local magnetic field strength is found to be (105 +- 50) G. These
values are consistent with (oscillation-independent) flare cooling time models
and pressure balance scaling laws. Such a flare oscillation provides an
excellent opportunity to obtain coronal properties like the size of a flare
loop or the local magnetic field strength for the otherwise
spatially-unresolved star.",0503384v1
2005-04-25,Emission-line spectroscopy of Damped Lyman Alpha Systems: The case of SBS 1543+593/HS 1543+5921,"We report HST/STIS spectroscopy and Gemini/GMOS-N imaging of the Damped Lyman
Alpha (DLA) system toward HS 1543+5921 caused by the host star-forming galaxy
(SFG) SBS 1543+593. The Gemini image shows new morphological details of this
well resolved DLA galaxy. In combination with previous optical spectra, the new
UV spectra enable us to compare for the first time, ionized and neutral
gas-phase alpha-element abundances derived from emission- and absorption-line
spectroscopy, in a bona fide DLA galaxy. The abundances we determine using
emission-line diagnostics agree with those from absorption-line diagnostics. We
present our results on a metallicity versus redshift diagram that combines
local HII regions and SFGs with high-redshift DLAs, and discuss implications
for the chemical evolution of galaxies.",0504556v1
2005-04-27,Self-consistent radiative effect on relativistic electromagnetic particle acceleration,"We study the radiation damping effect on the relativistic acceleration of
electron-positron plasmas with two-and-half-dimensional particle-in-cell (PIC)
simulation. Particles are accelerated by Poynting flux via the diamagnetic
relativistic pulse accelerator (DRPA), and decelerated by the self-consistently
solved radiation damping force. With $\Omega_{ce}/\omega_{pe}\geq 10$, the
Lorentz factor of the highest energy particles reaches gamma>100, and the
acceleration still continues. The emitted radiation is peaked within few
degrees from the direction of Poynting flux and strongly linearly polarized,
which may be detectable in gamma-ray burst(GRB) observations. We also show that
the DRPA is insensitive to the initial supporting currents.",0504612v2
2005-07-13,UHE neutrino damping in a thermal gas of relic neutrinos,"We present a calculation of the damping of an ultra-energetic (UHE) cosmic
neutrino travelling through the thermal gas of relic neutrinos, using the
formalism of finite-temperature field theory. From the self-energy diagram due
to Z exchange, we obtain the annihilation cross section for an UHE neutrino
interacting with an antineutrino from the background. This method allows us to
derive the full expressions for the UHE neutrino transmission probability,
taking into account the momentum of relic neutrinos. We compare our results
with the approximations in use in the literature. We discuss the effect of
thermal motion on the shape of the absorption dips for different UHE neutrino
fluxes as well as in the context of relic neutrino clustering. We find that for
ratios of the neutrino mass to the relic background temperature $10^2$ or
smaller, the thermal broadening of the absorption lines could significantly
affect the determination of the neutrino mass and of the characteristics of the
population of UHE sources.",0507333v2
2005-07-25,Post-inflation increase of the cosmological tensor-to-scalar perturbation ratio,"We investigate the possibility that the amplitude of scalar density
perturbations may be damped after inflation. This would imply that CMB
anisotropies do not uniquely fix the amplitude of the perturbations generated
during inflation and that the present tensor-to-scalar ratio might be larger
than produced in inflation, increasing the prospects of detection of primordial
gravitational radiation. It turns out, however, that the damping of density
perturbations is hard to achieve.",0507573v3
2005-09-08,Possible Detection of Lyman-alpha Fluorescence from a Damped Lyman Alpha system at Redshift z=2.8,"We have detected Lyman-alpha emission from a damped Lyman-alpha system (DLA)
that lies near the bright quasar HS1549+1919. The DLA has the same redshift as
HS1549+1919 and was discovered in the spectrum of a faint QSO that lies 49""
away (380 proper kpc). The emission line's luminosity, double-peaked profile,
and small spatial separation from the DLA suggest that it may be fluorescent
Lyman-alpha emission from gas that is absorbing the nearby QSO's radiation. If
this is the case, our observations show that the DLA has a size of at least
1.5"" and that the QSO's luminosity one million years ago was similar to its
luminosity today. A survey for similar systems within 1' of bright QSOs would
put interesting limits on the mean quasar lifetime.",0509229v1
2005-11-17,Measurement of the Spatial Cross-Correlation Function of Damped Lyman Alpha Systems and Lyman Break Galaxies,"We present the first spectroscopic measurement of the spatial
cross-correlation function between damped Lyman alpha systems (DLAs) and Lyman
break galaxies (LBGs). We obtained deep u'BVRI images of nine QSO fields with
11 known z ~ 3 DLAs and spectroscopically confirmed 211 R < 25.5
photometrically selected z > 2 LBGs. We find strong evidence for an overdensity
of LBGs near DLAs versus random, the results of which are similar to that of
LBGs near other LBGs. A maximum likelihood cross-correlation analysis found the
best fit correlation length value of r_0 = 2.9^(+1.4)_(-1.5) h^(-1)Mpc using a
fixed value of gamma = 1.6. The implications of the DLA-LBG clustering
amplitude on the average dark matter halo mass of DLAs are discussed.",0511509v1
2006-01-29,Relative abundance pattern along the profile of high redshift Damped Lyman-alpha systems,"We investigated abundance ratios along the profiles of six high-redshift
Damped Lyman-alpha systems, three of them associated with H2 absorption, and
derived optical depths in each velocity pixel. The variations of the pixel
abundance ratios were found to be remarkably small and usually smaller than a
factor of two within a profile. This result holds even when considering
independent sub-clumps in the same system. The depletion factor is
significantly enhanced only in those components where H2 is detected. There is
a strong correlation between [Fe/S] and [Si/S] abundances ratios, showing that
the abundance ratio patterns are definitely related to the presence of dust.
The depletion pattern is usually close to the one seen in the warm halo gas of
our Galaxy.",0601664v1
2006-02-14,VLT/UVES constraints on the carbon isotope ratio 12C/13C at z=1.15 toward the quasar HE 0515-4414,"We analyzed the CI lines associated with the damped Ly-alpha system observed
at zabs = 1.15 in the spectrum of HE 0515-4414 to derive the 12C/13C ratio. The
spectrum was obtained by means of the UV-Visual Echelle Spectrograph (UVES) at
the ESO Very Large Telescope (VLT). The obtained lower limit 12C/13C > 80
(2sigma C.L.) shows for the first time that the abundance of 13C in the
extragalactic intervening clouds is very low. This rules out a significant
contribution from intermediate-mass stars to the chemical evolution of matter
sampled by this line of sight. The estimated low amount of 13C is in agreement
with low abundances of nitrogen observed in damped Ly-alpha systems - the
element produced in the same nuclear cycles and from about the same stars as
13C.",0602303v1
2006-06-08,The detectability of HI 21-cm absorption in damped Lyman-alpha systems,"In this paper we investigate the possible reasons why HI 21-cm absorption in
damped Lyman-alpha systems (DLAs) has only been detected at low redshift... We
suggest that the lack of 21-cm absorption detections at high redshift arises
from the fact that these DLAs are at similar angular diameter distances to the
background quasars (i.e. the distance ratios are always close to unity): Above
z~1.6 the covering factor becomes largely independent of the DLA--QSO distance,
making the high redshift absorbers much less effective at covering the
background continuum emission. At low redshift, small distance ratios are
strongly favoured by the 21-cm detections, whereas large ratios are favoured by
the non-detections. This mix of distance ratios gives the observed mix of
detections and non-detections at z<1.6.In addition to the predominance of large
distance ratios and non-detections at high redshift, this strongly suggests
that the observed distribution of 21-cm absorption in DLAs is dominated by
geometric effects.",0606180v1
2006-07-15,Damping and excitation variations of the solar acoustic modes using LOWL observations,"We have used observations made with the helioseismic instrument LOWL
collected over $\sim$ 6 years to carry out an independent study of the
variations of the p-mode damping and excitation rates with solar activity. We
observe significant variations in the mode height, mode width and mode velocity
power over a wide range of angular degree values. Their sensitivities to solar
activity show clear evidence of frequency dependence, the modes in the
frequency range from 2700 and 3300 $\mu$Hz showing the largest variations and
exhibiting a maximum change centered around 3100 $\mu$Hz. As for the mode
energy supply rate, it is consistent, at the level of precision of the
observations, with a zero change along the solar cycle and over the range of
studied frequencies. Moreover, the variations with solar activity of each of
these parameters are observed to be more or less $\ell$-independent over the
range of studied angular degrees. Our results provide the first in-depth
confirmation of the findings obtained from GONG measurements for intermediate
angular degrees.",0607346v1
2006-09-01,A line profile analysis of the pulsating red giant star epsilon Ophiuchi (G9.5III),"So far, solar-like oscillations have been studied using radial velocity
and/or light curve variations, which reveal frequencies of the oscillation
modes. Line-profile variations, however, are also a valuable diagnostic to
characterise radial and non-radial oscillations, including frequencies,
amplitudes, the spherical mode wavenumbers (l,m) and the stellar inclination
angle. Here we present a line profile analysis of epsilon Ophiuchi, which is a
pulsating red giant. The main differences compared to previous line profile
analyses done for heat-driven oscillations are the small amplitudes and the
predicted short damping and re-excitation times in red giants.
  Two line diagnostics have been tested to see whether these are sensitive to
the small line profile variations present in red giants. In addition, line
profiles have been simulated with short damping and re-excitation times and are
compared with the observations. This comparison reveals that non-radial modes
are detected in the observed line profile variations of epsilon Ophiuchi. This
is rather surprising, as theoretical predictions favours the occurrence of
radial modes.",0609043v1
2006-10-11,Determining the neutron star equation of state using the narrow-band gravitational wave detector Schenberg,"We briefly review the properties of quasi-normal modes of neutron stars and
black holes. We analyse the consequences of a possible detection of such modes
via the gravitational waves associated with them, especially addressing our
study to the Brazilian spherical antenna, on which a possible detection would
occur at 3.0-3.4 kHz. A question related to any putative gravitational wave
detection concerns the source that produces it. We argue that, since the
characteristic damping times for the gravitational waves of neutron stars and
black holes are different, a detection can distinguish between them, and also
distinguish the neutron stars oscillating modes. Moreover, since the source can
be identified by its characteristic damping time, we are able to extract
information about the neutron star or black hole. This information would lead,
for example, to a strong constraint in the nuclear matter equation of state,
namely the compression modulus should be K=220 MeV.",0610335v1
2006-12-14,Three dimensional numerical simulations of acoustic wave field in the upper convection zone of the Sun,"Results of numerical 3D simulations of propagation of acoustic waves inside
the Sun are presented. A linear 3D code which utilizes realistic OPAL equation
of state was developed by authors. Modified convectively stable standard solar
model with smoothly joined chromosphere was used as a background model. High
order dispersion relation preserving numerical scheme was used to calculate
spatial derivatives. The top non-reflecting boundary condition established in
the chromosphere absorbs waves with frequencies greater than the acoustic
cut-off frequency which pass to the chromosphere, simulating a realistic
situation. The acoustic power spectra obtained from the wave field generated by
sources randomly distributed below the photosphere are in good agreement with
observations. The influence of the height of the top boundary on results of
simulation was studied. It was shown that the energy leakage through the
acoustic potential barrier damps all modes uniformly and does not change the
shape of the acoustic spectrum. So the height of the top boundary can be used
for controlling a damping rate without distortion of the acoustic spectrum. The
developed simulations provide an important tool for testing local
helioseismology.",0612364v1
2006-12-15,Damp Mergers: Recent Gaseous Mergers without Significant Globular Cluster Formation?,"Here we test the idea that new globular clusters (GCs) are formed in the same
gaseous (""wet"") mergers or interactions that give rise to the young stellar
populations seen in the central regions of many early-type galaxies. We compare
mean GC colors with the age of the central galaxy starburst. The red GC
subpopulation reveals remarkably constant mean colors independent of galaxy
age. A scenario in which the red GC subpopulation is a combination of old and
new GCs (formed in the same event as the central galaxy starburst) can not be
ruled out; although this would require an age-metallicity relation for the
newly formed GCs that is steeper than the Galactic relation. However, the data
are also well described by a scenario in which most red GCs are old, and few,
if any, are formed in recent gaseous mergers. This is consistent with the old
ages inferred from some spectroscopic studies of GCs in external systems. The
event that induced the central galaxy starburst may have therefore involved
insufficient gas mass for significant GC formation. We term such gas-poor
events ""damp"" mergers.",0612415v1
2006-12-21,Accretion of Terrestrial Planets from Oligarchs in a Turbulent Disk,"We have investigated the final accretion stage of terrestrial planets from
Mars-mass protoplanets that formed through oligarchic growth in a disk
comparable to the minimum mass solar nebula (MMSN), through N-body simulation
including random torques exerted by disk turbulence due to
Magneto-Rotational-Instability. For the torques, we used the semi-analytical
formula developed by Laughlin et al.(2004). The damping of orbital
eccentricities (in all runs) and type-I migration (in some runs) due to the
tidal interactions with disk gas are also included. We found that the orbital
eccentricities pumped up by the turbulent torques and associated random walks
in semimajor axes tend to delay isolation of planets, resulting in more
coagulation of planets than in the case without turbulence. The eccentricities
are still damped after planets become isolated. As a result, the number of
final planets decreases with increase in strength of the turbulence, while
Earth-mass planets with small eccentricities are still formed. In the case of
relatively strong turbulence, the number of final planets are 4-5 at 0.5-2AU,
which is consistent with Solar system, for relatively wide range of disk
surface density (~10^{-4}-10^{-2} times MMSN).",0612619v1
2007-01-18,Models of the Collisional Damping Scenario for Ice Giant Planets and Kuiper Belt Formatio,"Chiang et al. 2006, hereafter C06 have recently proposed that the observed
structure of the Kuiper belt could be the result of a dynamical instability of
a system of ~5 primordial ice giant planets in the outer Solar System.
According to this scenario, before the instability occurred, these giants were
growing in a highly collisionally damped environment according to the arguments
in Goldreich et al. (2004a,b, hereafter G04). Here we test this hypothesis with
a series of numerical simulations using a new code designed to incorporate the
dynamical effects of collisions. We find that we cannot reproduce the observed
Solar System. In particular, G04 and C06 argue that during the instability, all
but two of the ice giants would be ejected from the Solar System by Jupiter and
Saturn, leaving Uranus and Neptune behind. We find that ejections are actually
rare and that instead the systems spread outward. This always leads to a
configuration with too many planets that are too far from the Sun. Thus, we
conclude that both G04's scheme for the formation of Uranus and Neptune and
C06's Kuiper belt formation scenario are not viable in their current forms.",0701544v1
2007-02-05,Ion Charge States in the Fast Solar Wind: New Data Analysis and Theoretical Refinements,"We present a further investigation into the increased ionization observed in
element charge states in the fast solar wind compared to its coronal hole
source regions. Once ions begin to be perpendicularly heated by ion cyclotron
waves and execute large gyro-orbits, density gradients in the flow can excite
lower hybrid waves that then damp by heating electrons in the parallel
direction. We give further analysis of charge state data from polar coronal
holes at solar minimum and maximum, and also from equatorial coronal holes. We
also consider further the damping of lower hybrid waves by ions and the effect
of non-Maxwellian electron distribution functions on the degree of increased
ionization, both of which appear to be negligible for the solar wind case
considered here. We also suggest that the density gradients required to heat
electrons sufficiently to further ionize the solar wind can plausibly result
from the turbulent cascade of MHD waves.",0702131v1
1995-10-11,Multiple Transitions to Chaos in a Damped Parametrically Forced Pendulum,"We study bifurcations associated with stability of the lowest stationary
point (SP) of a damped parametrically forced pendulum by varying $\omega_0$
(the natural frequency of the pendulum) and $A$ (the amplitude of the external
driving force). As $A$ is increased, the SP will restabilize after its
instability, destabilize again, and so {\it ad infinitum} for any given
$\omega_0$. Its destabilizations (restabilizations) occur via alternating
supercritical (subcritical) period-doubling bifurcations (PDB's) and pitchfork
bifurcations, except the first destabilization at which a supercritical or
subcritical bifurcation takes place depending on the value of $\omega_0$. For
each case of the supercritical destabilizations, an infinite sequence of PDB's
follows and leads to chaos. Consequently, an infinite series of period-doubling
transitions to chaos appears with increasing $A$. The critical behaviors at the
transition points are also discussed.",9510003v1
1996-03-04,Period Doublings in Coupled Parametrically Forced Damped Pendulums,"We study period doublings in $N$ $(N=2,3,4, \dots)$ coupled parametrically
forced damped pendulums by varying $A$ (the amplitude of the external driving
force) and $c$ (the strength of coupling). With increasing $A$, the stationary
point undergoes multiple period-doubling transitions to chaos. We first
investigate the two-coupled case with $N=2$. For each period-doubling
transition to chaos, the critical set consists of an infinity of critical line
segments and the zero-coupling critical point lying on the line $A=A^*_i$ in
the $A-c$ plane, where $A^*_i$ is the $i$th transition point for the uncoupled
case. We find three kinds of critical behaviors, depending on the position on
the critical set. They are the same as those for the coupled one-dimensional
maps. Finally, the results of the $N=2$ case are extended to many-coupled cases
with $N \geq 3$, in which the critical behaviors depend on the range of
coupling.",9603002v1
1996-12-05,Fractal Basins of Attraction Associated with a Damped Newton's Method,"An intriguing and unexpected result for students learning numerical analysis
is that Newton's method, applied to the simple polynomial z^3 - 1 = 0 in the
complex plane, leads to intricately interwoven basins of attraction of the
roots. As an example of an interesting open question that may help to stimulate
student interest in numerical analysis, we investigate the question of whether
a damping method, which is designed to increase the likelihood of convergence
for Newton's method, modifies the fractal structure of the basin boundaries.
The overlap of the frontiers of numerical analysis and nonlinear dynamics
provides many other problems that can help to make numerical analysis courses
interesting.",9612010v1
1999-01-28,Intrinsically localized chaos in discrete nonlinear extended systems,"The phenomenon of intrinsic localization in discrete nonlinear extended
systems, i.e. the (generic) existence of discrete breathers, is shown to be not
restricted to periodic solutions but it also extends to more complex (chaotic)
dynamical behaviour. We illustrate this with two different forced and damped
systems exhibiting this type of solutions: In an anisotropic Josephson junction
ladder, we obtain intrinsically localized chaotic solutions by following
periodic rotobreather solutions through a cascade of period-doubling
bifurcations. In an array of forced and damped van der Pol oscillators, they
are obtained by numerical continuation (path-following) methods from the
uncoupled limit, where its existence is trivially ascertained, following the
ideas of the anticontinuum limit.",9901030v1
1995-03-27,Dynamics of a Strongly Damped Two-Level System: Beyond the DBGA,"Dynamics of a dissipative two-level system is studied using quantum
relaxation theory. This calculation for the first time goes beyond the commonly
used dilute bounce gas approximation (DBGA), even for strong damping. The new
results obtained here deviate from the DBGA results at low temperatures,
however, the DBGA form is recovered at high temperatures. The results in the
parameter regime $ 1/2<\alpha <1$, where the model has connection with the
Kondo Hamiltonian, are of particular significance. In this regime, the spin
shows a cross-over to a slower exponential relaxation at intermediate times,
which is roughly half the relaxation rate at short times, as also observed in
Quantum Monte-Carlo simulation of the model. The asymptotic behavior of the
spin in the Kondo regime is in agreement with the exact conformal field theory
results for the Kondo model. A connection of the dissipative dynamics of the
two-level system with the quantum Zeno effect is also presented.",9503133v1
1995-05-23,The phase-dependent linear conductance of a superconducting quantum point contact,"The exact expression for the phase-dependent linear conductance of a weakly
damped superconducting quantum point contact is obtained. The calculation is
performed by summing up the complete perturbative series in the coupling
between the electrodes. The failure of any finite order perturbative expansion
in the limit of small voltage and small quasi-particle damping is analyzed in
detail. In the low transmission regime this nonperturbative calculation yields
a result which is at variance with standard tunnel theory. Our result predicts
the correct sign of the quasi-particle pair interference term and exhibits an
unusual phase-dependence at low temperatures in qualitative agreement with the
available experimental data.",9505102v1
1996-02-27,Quasiparticle properties of a coupled quantum wire electron-phonon system,"We study leading-order many-body effects of longitudinal optical (LO) phonons
on electronic properties of one-dimensional quantum wire systems. We calculate
the quasiparticle properties of a weakly polar one dimensional electron gas in
the presence of both electron-phonon and electron-electron interactions. The
leading-order dynamical screening approximation (GW approximation) is used to
obtain the electron self-energy, the quasiparticle spectral function, and the
quasiparticle damping rate in our calculation by treating electrons and phonons
on an equal footing. Our theory includes effects (within the random phase
approximation) of Fermi statistics, Landau damping, plasmon-phonon mode
coupling, phonon renormalization, dynamical screening, and impurity scattering.
In general, electron-electron and electron-phonon many-body renormalization
effects are found to be nonmultiplicative and nonadditive in our theoretical
results for quasiparticle properties.",9602143v1
1996-02-29,Dynamical response of a one dimensional quantum wire electron system,"We provide a self-contained theoretical analysis of the dynamical response of
a one dimensional electron system, as confined in a semiconductor quantum wire,
within the random phase approximation. We carry out a detailed comparison with
the corresponding two and three dimensional situations, and discuss the
peculiarities arising in the one dimensional linear response from the
non-existence of low energy single-particle excitations and from the linear
nature of the long wavelength plasmon mode. We provide a critical discussion of
the analytic properties of the complex dielectric function in the complex
frequency plane. We investigate the zeros of the complex dielectric function,
and calculate the plasmon dispersion, damping, and plasmon spectral weight in
one dimension. We consider finite temperature and impurity scattering effects
on one dimensional plasmon dispersion and damping.",9602157v1
1996-08-24,New Universality Class at the Superconductor--Insulator Transition,"We study dynamic properties of thin films near the superconductor - insulator
transition. We formulate the problem in a phase representation. The key new
feature of our model is the assumption of a {\it local} ohmic dissipative
mechanism. Coarse graining leads to a Ginzburg-Landau description, with
non-ohmic dynamics for the order parameter. For strong enough damping a new
universality class is observed. It is characterized by a {\it non-universal}
d.c. conductivity, and a damping dependent dynamical critical exponent. The
formulation also provides a description of the magnetic field-tuned transition.
Several microscopic mechanisms are proposed as the origin of the dissipation.",9608115v1
1996-10-07,Supersymmetric Fokker-Planck strict isospectrality,"I report a study of the nonstationary one-dimensional Fokker-Planck solutions
by means of the strictly isospectral method of supesymmetric quantum mechanics.
The main conclusion is that this technique can lead to a space-dependent
(modulational) damping of the spatial part of the nonstationary Fokker-Planck
solutions, which I call strictly isospectral damping. At the same time, using
an additive decomposition of the nonstationary solutions suggested by the
strictly isospectral procedure and by an argument of Englefield [J. Stat. Phys.
52, 369 (1988)], they can be normalized and thus turned into physical
solutions, i.e., Fokker-Planck probability densities. There might be
applications to many physical processes during their transient period",9610049v2
1997-04-03,Quasiparticle Many-Body Dynamics of Highly Correlated Electronic Systems,"The self-consistent theory of the correlation effects in Highly Correlated
Systems(HCS) is presented. The novel Irreducible Green's Functions(IGF) method
is discused in detail for the Hubbard model and random Hubbard model. The
interpolative solution for the quasiparticle spectrum, which is valid for both
the atomic and band limit is obtained. The (IGF) method permits to calculate
the quasiparticle spectra of many-particle systems with the complicated spectra
and strong interaction in a very natural and compact way. The inelastic
scattering corrections leads to the damping of the quasiparticles and are the
main topic of the present consideration. The calculation of the damping has
been done in a self-consistent way for both limits. For the random Hubbard
model the weak coupling case has been considered and the self-energy operator
has been calculated using the combination of the IGF method and Coherent
Potential Approximation (CPA). The other applications of the method to s-f
model, Anderson model, Heisenberg antiferromagnet, electron-phonon interaction
models are discussed briefly.",9704028v1
1997-12-17,Detecting flux creep in superconducting YBCO thin films via damping of the oscillations of a levitating permanent magnet,"The damping of the oscillations of a small permanent magnet (spherical shape,
radius 0.1 mm) levitating between two parallel epitaxial YBCO films is measured
as a function of oscillation amplitude and temperature. At small amplitudes the
dissipation is found to be orders of magnitude lower than in bulk YBCO,
Q-factors exceeding one million at low temperatures. With increasing amplitude
the dissipation becomes exponentially large, exceeding the bulk values at large
drives. We describe our results by calculating the ac shielding currents
flowing through trapped flux whose motion gives rise to electric fields. We
find dissipation to originate from different mechanisms of flux dynamics.",9712199v1
1998-02-06,Spin polaron damping in the spin-fermion model for cuprate superconductors,"A self-consistent, spin rotational invariant Green's function procedure has
been developed to calculate the spectral function of carrier excitations in the
spin-fermion model for the CuO2 plane. We start from the mean field description
of a spin polaron in the Mori-Zwanzig projection method. In order to determine
the spin polaron lifetime in the self-consistent Born approximation, the
self-energy is expressed by an irreducible Green's function. Both, spin polaron
and bare hole spectral functions are calculated. The numerical results show a
well pronounced quasiparticle peak near the bottom of the dispersion at
(pi/2,pi/2), the absence of the quasiparticle at the Gamma-point, a rather
large damping away from the minimum and an asymmetry of the spectral function
with respect to the antiferromagnetic Brillouin zone. These findings are in
qualitative agreement with photoemission data for undoped cuprates. The direct
oxygen-oxygen hopping is responsible for a more isotropic minimum at
(pi/2,pi/2).",9802074v1
1998-02-24,Resonant steps and spatiotemporal dynamics in the damped dc-driven Frenkel-Kontorova chain,"Kink dynamics of the damped Frenkel-Kontorova (discrete sine-Gordon) chain
driven by a constant external force are investigated. Resonant steplike
transitions of the average velocity occur due to the competitions between the
moving kinks and their radiated phasonlike modes. A mean-field consideration is
introduced to give a precise prediction of the resonant steps. Slip-stick
motion and spatiotemporal dynamics on those resonant steps are discussed. Our
results can be applied to studies of the fluxon dynamics of 1D
Josephson-junction arrays and ladders, dislocations, tribology and other
fields.",9802251v1
1998-05-09,The resonance peak in cuprate superconductors,"We pursue the consequences of a theory in which the resonance peak observed
in inelastic neutron scattering (INS) experiments on underdoped and optimally
doped YBa$_2$Cu$_3$O$_{6+x}$ compounds arises from a spin-wave excitation. We
find that it is heavily damped, and thus almost not observable, in the normal
state, but becomes visible in the superconducting state due to the drastic
decrease in spin damping. We show that a spin-fermion model correctly describes
the temperature dependence of the peak position for YBa$_2$Cu$_3$O$_7$, as well
as the doping dependence of the peak position and of the integrated intensity.
We explain why no resonance peak has been observed in La$_{2-x}$Sr$_x$CuO$_4$,
and make several predictions concerning resonance peaks in other cuprate
superconductors.",9805107v1
1998-05-22,On the driven Frenkel-Kontorova model: I. Uniform sliding states and dynamical domains of different particle densities,"The dynamical behavior of a harmonic chain in a spatially periodic potential
(Frenkel-Kontorova model, discrete sine-Gordon equation) under the influence of
an external force and a velocity proportional damping is investigated. We do
this at zero temperature for long chains in a regime where inertia and damping
as well as the nearest-neighbor interaction and the potential are of the same
order. There are two types of regular sliding states: Uniform sliding states,
which are periodic solutions where all particles perform the same motion
shifted in time, and nonuniform sliding states, which are quasi-periodic
solutions where the system forms patterns of domains of different uniform
sliding states. We discuss the properties of this kind of pattern formation and
derive equations of motion for the slowly varying average particle density and
velocity. To observe these dynamical domains we suggest experiments with a
discrete ring of at least fifty Josephson junctions.",9805287v1
1999-01-29,Acoustic radiation controls friction: Evidence from a spring-block experiment,"Brittle failures of materials and earthquakes generate acoustic/seismic waves
which lead to radiation damping feedbacks that should be introduced in the
dynamical equations of crack motion. We present direct experimental evidence of
the importance of this feedback on the acoustic noise spectrum of
well-controlled spring-block sliding experiments performed on a variety of
smooth surfaces. The full noise spectrum is quantitatively explained by a
simple noisy harmonic oscillator equation with a radiation damping force
proportional to the derivative of the acceleration, added to a standard viscous
term.",9901350v2
1999-03-02,d_{x^2-y^2}-Wave Pairing Fluctuations and Pseudo Spin Gap in Two-Dimensional Electron Systems,"Pseudogap phenomena of high-T_c cuprates are examined. In terms of AFM
(antiferromagnetic) and dSC (d_{x^2-y^2}-wave superconducting) auxiliary fields
introduced to integrate out the fermions, the effective action for 2D electron
systems with AFM and dSC fluctuations is considered. By the self-consistent
renormalization (SCR), the NMR relaxation rate T_1^{-1}, the spin correlation
length \xi_\sigma and the pairing correlation length \xi_d are calculated. From
this calculation, a mechanism of the pseudogap formation emerges as the region
of dominant d-wave short-range order (SRO) over AFM-SRO. When damping for the
AFM fluctuation strongly depends on the dSC correlation length through the
formation of precursor singlets around (\pi,0) and (0,\pi) points in the
momentum space, the pseudogap appears in a region of the normal state
characterized by decreasing 1/T_1T and increasing AFM correlation length with
decrease in temperature. This reproduces a characteristic feature of the
pseudogap phenomena in many underdoped cuprates. When the damping becomes
insensitive to the dSC correlation length, the pseudogap region shrinks as in
the overdoped cuprates.",9903030v2
1999-03-11,Thermally activated escape rates of uniaxial spin systems with transverse field,"Classical escape rates of uniaxial spin systems are characterized by a
prefactor differing from and much smaller than that of the particle problem,
since the maximum of the spin energy is attained everywhere on the line of
constant latitude: theta=const, 0 =< phi =< 2*pi. If a transverse field is
applied, a saddle point of the energy is formed, and high, moderate, and low
damping regimes (similar to those for particles) appear. Here we present the
first analytical and numerical study of crossovers between the uniaxial and
other regimes for spin systems. It is shown that there is one HD-Uniaxial
crossover, whereas at low damping the uniaxial and LD regimes are separated by
two crossovers.",9903192v2
1999-04-19,Numerical analysis of the dissipative two-state system with the density-matrix Hilbert-space-reduction algorithm,"Ground state of the dissipative two-state system is investigated by means of
the Lanczos diagonalization method. We adopted the Hilbert-space-reduction
scheme proposed by Zhang, Jeckelmann and White so as to reduce the overwhelming
reservoir Hilbert space to being tractable in computers. Both the
implementation of the algorithm and the precision applied for the present
system are reported in detail. We evaluate the dynamical susceptibility
(resolvent) with the continued-fraction-expansion formula. Through analysing
the resolvent over a frequency range, whose range is often called `interesting'
frequency, we obtain the damping rate and the oscillation frequency. Our
results agree with those of a recent quantum Monte-Carlo study, which concludes
that the critical dissipation from oscillatory to over-damped behavior
decreases as the tunneling amplitude is strengthened.",9904260v1
1999-05-02,Finite Temperature Time-Dependent Effective Theory For The Goldstone Field In A BCS-Type Superfluid,"We extend to finite temperature the time-dependent effective theory for the
Goldstone field (the phase of the pair field) $ \theta $ which is appropriate
for a superfluid containing one species of fermions with s-wave interactions,
described by the BCS Lagrangian. We show that, when Landau damping is
neglected, the effective theory can be written as a local time-dependent
non-linear Schr\""{o}dinger Lagrangian (TDNLSL) which preserves the Galilean
invariance of the zero temperature effective theory and is identified with the
superfluid component. We then calculate the relevant Landau terms which are
non-local and which destroy the Galilean invariance. We show that the retarded
$\theta$-propagator (in momentum space) can be well represented by two poles in
the lower-half frequency plane, describing damping with a predicted
temperature, frequency and momentum dependence. It is argued that the real
parts of the Landau terms can be approximately interpreted as contributing to
the normal fluid component.",9905008v2
1999-06-29,Simulation of I-V Hysteresis Branches in An Intrinsic Stack of Josephson Junctions in High $T_c$ Superconductors,"I-V characteristics of the high T$_c$ superconductor
Bi$_2$Sr$_2$Ca$_1$C$_2$O$_8$ shows a strong hysteresis, producing many
branches. The origin of hysteresis jumps is studied by use of the model of
multi-layered Josephson junctions proposed by one of the authors (T. K.). The
charging effect at superconducting layers produces a coupling between the next
nearest neighbor phase-differences, which determines the structure of
hysteresis branches. It will be shown that a solution of phase motions is
understood as a combination of rotating and oscillating phase-differences, and
that, at points of hysteresis jumps, there occurs a change in the number of
rotating phase-differences. Effects of dissipation are analyzed. The
dissipation in insulating layers works to damp the phase motion itself, while
the dissipation in superconducting layers works to damp relative motions of
phase-differences. Their effects to hysteresis jumps are discussed.",9906422v1
1999-07-05,The interplay between flattening and damping of single particle spectra in strongly correlated Fermi systems,"The self-consistent theory of the fermion condensation, a specific phase
transition which results in a rearrangement of the single particle degrees of
freedom in strongly correlated Fermi systems is developed. Beyond the phase
transition point, the single particle spectra are shown to be flat. The
interplay between the flattening and the damping of the single particle spectra
at $T\to 0$ is investigated. The width $\gamma(\epsilon)$ of the single
particle states is found to grow up linearly with $\epsilon$ over a wide range
of energy as in a marginal Fermi liquid. Our results gain insight into the
success of the phenomenological theory of the normal states of high-temperature
superconductors by Varma et al.",9907061v1
1999-10-19,Zener transitions between dissipative Bloch bands. II: Current Response at Finite Temperature,"We extend, to include the effects of finite temperature, our earlier study of
the interband dynamics of electrons with Markoffian dephasing under the
influence of uniform static electric fields. We use a simple two-band
tight-binding model and study the electric current response as a function of
field strength and the model parameters. In addition to the Esaki-Tsu peak,
near where the Bloch frequency equals the damping rate, we find current peaks
near the Zener resonances, at equally spaced values of the inverse electric
field. These become more prominenent and numerous with increasing bandwidth (in
units of the temperature, with other parameters fixed). As expected, they
broaden with increasing damping (dephasing).",9910290v1
1999-11-02,Shifts and widths of collective excitations in trapped Bose gases by the dielectric formalism,"We present predictions for the temperature dependent shifts and damping
rates. They are obtained by applying the dielectric formalism to a simple model
of a trapped Bose gas. Within the framework of the model we use lowest order
perturbation theory to determine the first order correction to the results of
Hartree-Fock-Bogoliubov-Popov theory for the complex collective excitation
frequencies, and present numerical results for the temperature dependence of
the damping rates and the frequency shifts. Good agreement with the
experimental values measured at JILA are found for the m=2 mode, while we find
disagreements in the shifts for m=0. The latter point to the necessity of a
non-perturbative treatment for an explanation of the temperature-dependence of
the m=0 shifts.",9911018v1
2000-06-13,Characteristic features of anharmonic effects in the lattice dynamics of fcc metals,"The dispersion in the entire Brillouin zone and the temperature dependence
(right up to the melting temperature) of the anharmonic frequency shift and
phonon damping in a number of fcc metals is investigated on the basis of
microscopic calculations. It is found that the anharmonic effects depend
sharply on the wave vector in the directions $\Gamma$-X, X-W, and $\Gamma$-L
and, in contrast to bcc metals, the magnitude of the effects is not due to the
softness of the initial phonon spectrum. It is shown that the relative
frequency shifts and the phonon damping near melting do not exceed 10-20%. The
relative role of various anharmonic processes is examined, and the relation
between the results obtained and existing experimental data is discussed.",0006205v1
2000-06-20,Collisional damping of the collective oscillations of a trapped Fermi gas,"We consider a Fermi gas confined by a harmonic trapping potential and we
highlight the role of the Fermi-Dirac statistics by studying frequency and
damping of collective oscillations of quadrupole type in the framework of the
quantum Boltzmann equation, in which statistical corrections are taken into
account in the collisional integral. We are able to describe the crossover from
the collisionless regime to the hydrodynamic one by introducing a
temperature-dependent relaxation time $\tau_Q$. We show that, in the degenerate
regime, the relaxation rate $1/\tau_Q$ exhibits a temperature dependence
different from the collision rate $\gamma$. We finally compare the collisional
properties of the Fermi gas with the ones of the Bose gas for temperatures
above the Bose-Einstein condensation.",0006305v2
2000-06-21,Resonances in the dynamics of $φ^4$ kinks perturbed by ac forces,"We study the dynamics of $\phi^4$ kinks perturbed by an ac force, both with
and without damping. We address this issue by using a collective coordinate
theory, which allows us to reduce the problem to the dynamics of the kink
center and width. We carry out a careful analysis of the corresponding ordinary
differential equations, of Mathieu type in the undamped case, finding and
characterizing the resonant frequencies and the regions of existence of
resonant solutions. We verify the accuracy of our predictions by numerical
simulation of the full partial differential equation, showing that the
collective coordinate prediction is very accurate. Numerical simulations for
the damped case establish that the strongest resonance is the one at half the
frequency of the internal mode of the kink. In the conclusion we discuss on the
possible relevance of our results for other systems, especially the sine-Gordon
equation. We also obtain additional results regarding the equivalence between
different collective coordinate methods applied to this problem.",0006313v1
2000-07-11,Quantum phase transitions in d-wave superconductors,"Motivated by the strong, low temperature damping of nodal quasiparticles
observed in some cuprate superconductors, we study quantum phase transitions in
d_{x^2-y^2} superconductors with a spin-singlet, zero momentum, fermion
bilinear order parameter. We present a complete, group-theoretic classification
of such transitions into 7 distinct cases (including cases with nematic order)
and analyze fluctuations by the renormalization group. We find that only 2, the
transitions to d_{x^2-y^2}+is and d_{x^2-y^2} + i d_{xy} pairing, possess
stable fixed points with universal damping of nodal quasiparticles; the latter
leaves the gapped quasiparticles along (1,0), (0,1) essentially undamped.",0007170v3
2000-07-12,Frequencies and Damping rates of a 2D Deformed Trapped Bose gas above the Critical Temperature,"We derive the equation of motion for the velocity fluctuations of a 2D
deformed trapped Bose gas above the critical temperature in the hydrodynamical
regime. From this equation, we calculate the eigenfrequencies for a few
low-lying excitation modes. Using the method of averages, we derive a
dispersion relation in a deformed trap that interpolates between the
collisionless and hydrodynamic regimes. We make use of this dispersion relation
to calculate the frequencies and the damping rates for monopole and quadrupole
mode in both the regimes. We also discuss the time evolution of the wave packet
width of a Bose gas in a time dependent as well as time independent trap.",0007210v2
2000-09-01,The Broad Brillouin Doublet and CP of Ktao_3 : Second Sound vs. Two-Phonon Difference Scattering,"Low-T Brillouin spectra of the incipient ferroelectric KTaO3 exhibit a broad
central peak (CP), and additional Brillouin doublets (BD), that can both be
related to phonon-density fluctuations. On the basis of new high-resolution
neutron data obtained of low-lying phonon branches, we analysed the
phonon-kinetics mechanisms that are possibly the origin of these unusual
features. Firstly, transverse acoustic (TA) phonons whose normal damping is
faster than the BD frequency can produce hydrodynamic second sound. Secondly,
two-phonon difference scattering from low damping thermal transverse phonons
contribute to the spectra with either a sharp or a broader doublet, depending
on the phonon group velocity and anisotropy of dispersion surfaces. The
position of the observed sharp doublet is consistent with both mechanisms, but
a comparison of the computed and experimental anisotropies favours the second
process.",0009011v1
2000-09-21,Landau-Khalatnikov two-fluid hydrodynamics of a trapped Bose gas,"Starting from the quantum kinetic equation for the non-condensate atoms and
the generalized Gross-Pitaevskii equation for the condensate, we derive the
two-fluid hydrodynamic equations of a trapped Bose gas at finite temperatures.
We follow the standard Chapman-Enskog procedure, starting from a solution of
the kinetic equation corresponding to the complete local equilibrium between
the condensate and the non-condensate components. Our hydrodynamic equations
are shown to reduce to a form identical to the well-known Landau-Khalatnikov
two-fluid equations, with hydrodynamic damping due to the deviation from local
equilibrium. The deviation from local equilibrium within the thermal cloud
gives rise to dissipation associated with shear viscosity and thermal
conduction. In addition, we show that effects due to the deviation from the
diffusive local equilibrium between the condensate and the non-condensate
(recently considered by Zaremba, Nikuni and Griffin) can be described by four
frequency-dependent second viscosity transport coefficients. We also derive
explicit formulas for all the transport coefficients. These results are used to
introduce two new characteristic relaxation times associated with hydrodynamic
damping. These relaxation times give the rate at which local equilibrium is
reached and hence determine whether one is in the two-fluid hydrodynamic
region.",0009333v1
2000-12-29,Finite Temperature Time-Dependent Effective Theory for the Phase Field in two-dimensional d-wave Neutral Superconductor,"We derive finite temperature time-dependent effective actions for the phase
of the pairing field, which are appropriate for a 2D electron system with both
non-retarded d- and s-wave attraction. As for s-wave pairing the d-wave
effective action contains terms with Landau damping, but their structure
appears to be different from the s-wave case due to the fact that the Landau
damping is determined by the quasiparticle group velocity v_{g}, which for
d-wave pairing does not have the same direction as the non-interacting Fermi
velocity v_{F}. We show that for d-wave pairing the Landau term has a linear
low temperature dependence and in contrast to the s-wave case are important for
all finite temperatures. A possible experimental observation of the phase
excitations is discussed.",0012511v4
2001-01-23,Ginzburg-Landau theory for the time-dependent phase field in a two-dimensional d-wave superconductor,"We derive a finite temperature time-dependent effective theory for the phase
$\theta$ of the pairing field, which is appropriate for a 2D conducting
electron system with non-retarded d-wave attraction. As for s-wave pairing the
effective action contains terms with Landau damping, but their structure
appears to be different from the s-wave case due to the fact that the Landau
damping is determined by the quasiparticle group velocity $v_g$, which for the
d-wave pairing does not have the same direction as the non-interacting Fermi
velocity $v_F$. We show that for the d-wave pairing the Landau terms have a
linear low temperature dependence and in contrast to the s-wave case are
important for all finite temperatures.",0101353v1
2001-06-05,Damping and frequency shift in the oscillations of two colliding Bose-Einstein condensates,"We have investigated the center-of-mass oscillations of a Rb87 Bose-Einstein
condensate in an elongated magneto-static trap. We start from a trapped
condensate and we transfer part of the atoms to another trapped level, by
applying a radio-frequency pulse. The new condensate is produced far from its
equilibrium position in the magnetic potential, and periodically collides with
the parent condensate. We discuss how both the damping and the frequency shift
of the oscillations are affected by the mutual interaction between the two
condensates, in a wide range of trapping frequencies. The experimental data are
compared with the prediction of a mean-field model.",0106072v1
2001-07-12,Ferromagnetism in the Hubbard model,"We investigate the possibility and stability of bandferromagnetism in the
single-band Hubbard model. This model poses a highly non-trivial many-body
problem the general solution of which has not been found up to now.
Approximations are still unavoidable. Starting from a simple two-pole ansatz
for the spectral density our approach is systematically improved by focusing on
the influence of quasiparticle damping and the correct weak-and strong coupling
behaviour. The compatibility of the different aproximative steps with decisive
moment sum rules is analysed and the importance of a spin-dependent band shift
mediated by higher correlation functions is worked out. Results are presented
in terms of temperature- and band occupation-dependent quasiparticle densities
of states and band structures as well as spontaneous magnetisations,
susceptibilities and Curie temperatures for varying electron densities and
coupling strengths. Comparison is made to numerically essentially exact Quantum
Monte Carlo calculations recently done by other authors using dynamical mean
field theory for infinite-dimensional lattices. The main conclusion will be
that the Hubbard model provides a qualitatively correct description of
bandferromagnetism if quasiparticle damping and selfconsistent spin-dependent
bandshifts are properly taken into account.",0107255v1
2001-09-10,Finite temperature theory of the scissors mode in a Bose gas using the moment method,"We use a generalized Gross-Pitaevskii equation for the condensate and a
semi-classical kinetic equation for the noncondensate atoms to discuss the
scissors mode in a trapped Bose-condensed gas at finite temperatures. Both
equations include the effect of $C_{12}$ collisions between the condensate and
noncondensate atoms. We solve the coupled moment equations describing
oscillations of the quadrupole moments of the condensate and noncondensate
components to find the collective mode frequencies and collisional damping
rates as a function of temperature. Our calculations extend those of
Gu\'ery-Odelin and Stringari at T=0 and in the normal phase. They complement
the numerical results of Jackson and Zaremba, although Landau damping is left
out of our approach. Our results are also used to calculate the quadrupole
response function, which is related to the moment of inertia. It is shown
explicitly that the moment of inertia of a trapped Bose gas at finite
temperatures involves a sum of an irrotational component from the condensate
and a rotational component from the thermal cloud atoms.",0109149v1
2002-01-24,Dynamic light scattering from colloidal fractal monolayers,"We address experimentally the problem of how the structure of a surface
monolayer determines the visco-elasticity of the interface. Optical microscopy
and surface quasi--elastic light scattering have been used to characterize
aggregation of CaCO$_3$ particles at the air--water interface. The structures
formed by cluster-cluster aggregation are two dimensional fractals which grow
to eventually form a percolating network. This process is measured through
image analysis. On the same system we measure the dynamics of interfacial
thermal fluctuations (surface ripplons), and we discuss how the relaxation
process is affected by the growing clusters. We show that the structures start
damping the ripplons strongly when the two length scales are comparable. No
macroscopic surface pressure is measured and this is in contrast to lipid,
surfactant or polymer monolayers at concentrations corresponding to surface
coverage. This observation and the difficulty in fitting the ripplon spectrum
with traditional models suggest that a different physical mechanism might be
responsible for the observed damping of ripplons in this system.",0201438v1
2002-08-08,Excitation and damping of collective modes of a Bose-Einstein condensate in a one-dimensional lattice,"The mode structure of a Bose-Einstein condensate non-adiabatically loaded
into a one-dimensional optical lattice is studied by analyzing the visibility
of the interference pattern as well as the radial profile of the condensate
after a time-of-flight. A simple model is proposed that predicts the short-time
decrease of the visibility as a function of the condensate parameters. In the
radial direction, heavily damped oscillations are observed, as well as an
increase in the condensate temperature. These findings are interpreted as a
re-thermalization due to dissipation of the initial condensate excitations into
high-lying modes.",0208162v1
2002-08-12,Spectral Properties of the Generalized Spin-Fermion Models,"In order to account for competition and interplay of localized and itinerant
magnetic behaviour in correlated many body systems with complex spectra the
various types of spin-fermion models have been considered in the context of the
Irreducible Green's Functions (IGF) approach. Examples are generalized d-f
model and Kondo-Heisenberg model. The calculations of the quasiparticle
excitation spectra with damping for these models has been performed in the
framework of the equation- of-motion method for two-time temperature Green's
Functions within a non-perturbative approach. A unified scheme for the
construction of Generalized Mean Fields (elastic scattering corrections) and
self-energy (inelastic scattering) in terms of the Dyson equation has been
generalized in order to include the presence of the two interacting subsystems
of localized spins and itinerant electrons. A general procedure is given to
obtain the quasiparticle damping in a self-consistent way. This approach gives
the complete and compact description of quasiparticles and show the flexibility
and richness of the generalized spin-fermion model concept.",0208227v1
2002-08-13,Itinerant Antiferromagnetism of Correlated Lattice Fermions,"The problem of finding of the ferromagnetic and antiferromagnetic ""symmetry
broken"" solutions of the correlated lattice fermion models beyond the
mean-field approximation has been investigated. The calculation of the
quasiparticle excitation spectra with damping for the single- and multi-orbital
Hubbard model has been performed in the framework of the equation- of-motion
method for two-time temperature Green's Functions within a non-perturbative
approach. A unified scheme for the construction of Generalized Mean Fields
(elastic scattering corrections) and self-energy (inelastic scattering) in
terms of the Dyson equation has been generalized in order to include the
presence of the ""source fields"". The damping of quasiparticles, which reflects
the interaction of the single-particle and collective degrees of freedom has
been calculated. The ""symmetry broken"" dynamical solutions of the Hubbard
model, which correspond to various types of itinerant antiferromagnetism has
been discussed. This approach complements previous studies and clarifies the
nature of the concepts of itinerant antiferromagnetism and ""spin-aligning
field"" of correlated lattice fermions.",0208242v1
2003-01-21,Zero temperature damping of Bose-Einstein condensate oscillations by vortex-antivortex pair creation,"We investigate vortex-antivortex pair creation in a supersonically expanding
and contracting quasi-2D Bose-Einstein condensate at zero temperature. For
sufficiently large amplitude condensate oscillations, pair production provides
the leading dissipation mechanism. The condensate oscillations decay in a
nonexponential fashion, and the dissipation rate depends strongly on the
oscillation amplitude. These features allow to distinguish the decay due to
pair creation from other possible damping mechanisms. Experimental observation
of the predicted oscillation behavior of the superfluid gas provides a direct
confirmation of the hydrodynamical analogy of quantum electrodynamics and
quantum vortex dynamics in two spatial dimensions.",0301397v3
2003-02-10,Damped orbital excitations in the titanates,"A possible mechanism for the removal of the orbital degeneracy in RTiO3
(where R=La, Y, ...) is considered. The calculation is based on the
Kugel-Khomskii Hamiltonian for electrons residing in the t2g orbitals of the Ti
ions, and uses a self-consistent pe rturbation expansion in the interaction
between the orbital and the spin degrees of freedom. The latter are assumed to
be ordered in a Neel state, brought about by delicate interactions that are not
included in the Kugel-Khomskii Hamiltonian. Within our model calculations, each
of the t2g bands is found to acquire a finite, temperature-dependent
dispersion, that lifts the orbital degeneracy. The orbital excitations are
found to be heavily damped over a rather wide band. Consequently, they do not
participate as a separate branch of excitations in the low-temperature
thermodynamics.e",0302182v1
2003-03-20,Energies and damping rates of elementary excitations in spin-1 Bose-Einstein condensed gases,"Finite temperature Green's function technique is used to calculate the
energies and damping rates of elementary excitations of the homogeneous,
dilute, spin-1 Bose gases below the Bose-Einstein condensation temperature both
in the density and spin channels. For this purpose the self-consistent
dynamical Hartree-Fock model is formulated, which takes into account the direct
and exchange processes on equal footing by summing up certain classes of
Feynman diagrams. The model is shown to fulfil the Goldstone theorem and to
exhibit the hybridization of one-particle and collective excitations correctly.
The results are applied to the gases of ^{23}Na and ^{87}Rb atoms.",0303424v3
2003-04-17,Non-Fermi liquid behavior from two-dimensional antiferromagnetic fluctuations: a renormalization-group and large-N analysis,"We analyze the Hertz-Moriya-Millis theory of an antiferromagnetic quantum
critical point, in the marginal case of two dimensions (d=2,z=2). Up to
next-to-leading order in the number of components (N) of the field, we find
that logarithmic corrections do not lead to an enhancement of the Landau
damping. This is in agreement with a renormalization-group analysis, for
arbitrary N. Hence, the logarithmic effects are unable to account for the
behavior reportedly observed in inelastic neutron scattering experiments on
CeCu_{6-x}Au_x. We also examine the extended dynamical mean-field treatment
(local approximation) of this theory, and find that only subdominant
corrections to the Landau damping are obtained within this approximation, in
contrast to recent claims.",0304415v1
2003-05-21,The path-coalescence transition and its applications,"We analyse the motion of a system of particles subjected a random force
fluctuating in both space and time, and experiencing viscous damping. When the
damping exceeds a certain threshold, the system undergoes a phase transition:
the particle trajectories coalesce. We analyse this transition by mapping it to
a Kramers problem which we solve exactly. In the limit of weak random force we
characterise the dynamics by computing the rate at which caustics are crossed,
and the statistics of the particle density in the coalescing phase. Last but
not least we describe possible realisations of the effect, ranging from
trajectories of raindrops on glass surfaces to animal migration patterns.",0305491v2
2003-05-21,Magnetoresistive response of a high mobility 2DES under electromagnetic wave excitation,"Oscillations of the resistance observed under electromagnetic wave excitation
in the high mobility GaAs/AlGaAs 2DES are examined as a function of the
radiation frequency and the power, utilizing an empirical lineshape based on
exponentially damped sinusoids. The fit-analysis indicates the resistance
oscillation frequency, F, increases with the radiation frequency, n, at the
rate dF/dn = 2.37 mTesla/GHz; the damping parameter, a, is approximately
independent of n at constant power; and the amplitude, A, of the oscillations
grows slowly with the incident power, at a constant temperature and frequency.
The lineshape appears to provide a good description of the data.",0305507v2
2003-06-16,Infrared Spectroscopy of Quantum Crossbars,"Infrared (IR) spectroscopy can be used as an important and effective tool for
probing periodic networks of quantum wires or nanotubes (quantum crossbars,
QCB) at finite frequencies far from the Luttinger liquid fixed point. Plasmon
excitations in QCB may be involved in resonance diffraction of incident
electromagnetic waves and in optical absorption in the IR part of the spectrum.
Direct absorption of external electric field in QCB strongly depends on the
direction of the wave vector ${\bf q}.$ This results in two types of $1D\to 2D$
dimensional crossover with varying angle of an incident wave or its frequency.
In the case of QCB interacting with semiconductor substrate, capacitive contact
between them does not destroy the Luttinger liquid character of the long wave
QCB excitations. However, the dielectric losses on a substrate surface are
significantly changed due to appearance of additional Landau damping. The
latter is initiated by diffraction processes on QCB superlattice and manifests
itself as strong but narrow absorption peaks lying below the damping region of
an isolated substrate.Submi",0306409v1
2003-06-19,Superradiant light scattering from a moving Bose-Einstein condensate,"We investigate the interaction of a moving BEC with a far detuned laser beam.
Superradiant Rayleigh scattering arises from the spontaneous formation of a
matter-wave grating due to the interference of two wavepackets with different
momenta. The system is described by the CARL-BEC model which is a
generalization of the Gross-Pitaevskii model to include the self-consistent
evolution of the scattered field. The experiment gives evidence of a damping of
the matter-wave grating which depends on the initial velocity of the
condensate. We describe this damping in terms of a phase-diffusion decoherence
process, in good agreement with the experimental results.",0306500v2
2003-07-25,Finite temperature excitations of a trapped Bose-Fermi mixture,"We present a detailed study of the low-lying collective excitations of a
spherically trapped Bose-Fermi mixture at finite temperature in the
collisionless regime. The excitation frequencies of the condensate are
calculated self-consistently using the static Hartree-Fock-Bogoliubov theory
within the Popov approximation. The frequency shifts and damping rates due to
the coupled dynamics of the condensate, noncondensate, and degenerate Fermi gas
are also taken into account by means of the random phase approximation and
linear response theory. In our treatment, the dipole excitation remains close
to the bare trapping frequency for all temperatures considered, and thus is
consistent with the generalized Kohn theorem. We discuss in some detail the
behavior of monopole and quadrupole excitations as a function of the Bose-Fermi
coupling. At nonzero temperatures we find that, as the mixture moves towards
spatial separation with increasing Bose-Fermi coupling, the damping rate of the
monopole (quadrupole) excitation increases (decreases). This provides us a
useful signature to identify the phase transition of spatial separation.",0307638v1
2003-09-18,Memory-function approach to the normal-state optical properties of the Bechgaard salt (TMTSF)_2PF_6,"The gauge invariant, two-component optical conductivity model, with a
correlation gap structure related to the umklapp scattering processes, is
applied to the quasi-one-dimensional electronic systems and compared to the
recent measurements on the Bechgaard salt (TMTSF)_2PF_6. The optical response
of both the insulating and metallic state is found for the half-filled
conduction band, depending on the ratio between the correlation energy scale 2
\Delta^0_2 and the transfer integral in the direction perpendicular to the
conducting chains, t_{{\rm b}'}. The estimated value 2 \Delta^0_2/t_{{\rm b}'}
agrees reasonably well with the previous experimental and theoretical
conclusions. Parallel to the chains the thermally activated conduction
electrons in the insulating state are found to exhibit an universal behaviour,
accounting for the observed single-particle optical conductivity of the ordered
ground state of charge-density-wave systems. The band parameters and the
related damping energies suitable to the normal metallic state of (TMTSF)_2PF_6
are estimated from the measured spectra. Not only the spectral weights but also
the damping energies clearly indicate an opening of the correlation gap in the
charge excitation spectrum",0309419v1
2003-10-03,Effects of electrostatic fields and Casimir force on cantilever vibrations,"The effect of an external bias voltage and fluctuating electromagnetic fields
on both the fundamental frequency and damping of cantilever vibrations is
considered. An external voltage induces surface charges causing
cantilever-sample electrostatic attraction. A similar effect arises from
charged defects in dielectrics that cause spatial fluctuations of electrostatic
fields. The cantilever motion results in charge displacements giving rise to
Joule losses and damping. It is shown that the dissipation increases with
decreasing conductivity and thickness of the substrate, a result that is
potentially useful for sample diagnostics. Fluctuating electromagnetic fields
between the two surfaces also induce attractive (Casimir) forces. It is shown
that the shift in the cantilever fundamental frequency due to the Casimir force
is close to the shift observed in recent experiments of Stipe et al. Both the
electrostatic and Casimir forces have a strong effect on the cantilever
eigenfrequencies, and both effects depend on the geometry of the cantilever
tip. We consider cylindrical, spherical, and ellipsoidal tips moving parallel
to a flat sample surface. The dependence of the cantilever effective mass and
vibrational frequencies on the geometry of the tip is studied both numerically
and analytically.",0310081v1
2003-10-07,Precessional switching of thin nanomagnets: analytical study,"We study analytically the precessional switching of the magnetization of a
thin macrospin. We analyze its response when subjected to an external field
along its in-plane hard axis. We derive the exact trajectories of the
magnetization. The switching versus non switching behavior is delimited by a
bifurcation trajectory, for applied fields equal to half of the effective
anisotropy field. A magnetization going through this bifurcation trajectory
passes exactly along the hard axis and exhibits a vanishing characteristic
frequency at that unstable point, which makes the trajectory noise sensitive.
Attempting to approach the related minimal cost in applied field makes the
magnetization final state unpredictable. We add finite damping in the model as
a perturbative, energy dissipation factor. For a large applied field, the
system switches several times back and forth. Several trajectories can be gone
through before the system has dissipated enough energy to converge to one
attracting equilibrium state. For some moderate fields, the system switches
only once by a relaxation dominated precessional switching. We show that the
associated switching field increases linearly with the damping parameter. The
slope scales with the square root of the effective anisotropy. Our simple
concluding expressions are useful to assess the potential application of
precessional switching in magnetic random access memories.",0310147v1
2003-11-27,Temperature dependent Bogoliubov approximation in the classical fields approach to weakly interacting Bose gas,"A classical fields approximation to the finite temperature microcanonical
thermodynamics of weakly interacting Bose gas is applied to the idealized case
of atoms confined in a box with periodic boundary conditions. We analyze in
some detail the microcanonical temperature in the model. We also analyze the
spectral properties of classical amplitudes of the plane waves -- the
eigenmodes of the time averaged one--particle density matrix. Looking at the
zero momentum component -- the order parameter of the condensate, we obtain the
nonperturbative results for the chemical potential. Analogous analysis of the
other modes yields nonperturbative temperature dependent Bogoliubov frequencies
and their damping rates. Damping rates are linear functions of momenta in the
phonon range and show more complex behavior for the particle sector. Where
available, we make comparison with the analytic estimates of these quantities.",0311622v1
2003-12-29,Plasmon attenuation and optical conductivity of a two-dimensional electron gas,"In a ballistic two-dimensional electron gas, the Landau damping does not lead
to plasmon attenuation in a broad interval of wave vectors q << k_F. Similarly,
it does not contribute to the optical conductivity \sigma (\omega, q) in a wide
domain of its arguments, E_F > \omega > qv_F, where E_F, k_F and v_F are,
respectively, the Fermi energy, wavevector and velocity of the electrons. We
identify processes that result in the plasmon attenuation in the absence of
Landau damping. These processes are: the excitation of two electron-hole pairs,
phonon-assisted excitation of one pair, and a direct plasmon-phonon conversion.
We evaluate the corresponding contributions to the plasmon linewidth and to the
optical conductivity.",0312684v3
2004-03-05,Mode-coupling theory and molecular dynamics simulation for heat conduction in a chain with transverse motions,"We study heat conduction in a one-dimensional chain of particles with
longitudinal as well as transverse motions. The particles are connected by
two-dimensional harmonic springs together with bending angle interactions. The
problem is analyzed by mode-coupling theory and compared with molecular
dynamics. We find very good, quantitative agreement for the damping of modes
between a full mode-coupling theory and molecular dynamics result, and a
simplified mode-coupling theory gives qualitative description of the damping.
The theories predict generically that thermal conductance diverges as N^{1/3}
as the size N increases for systems terminated with heat baths at the ends. The
N^{2/5} dependence is also observed in molecular dynamics which we attribute to
crossover effect.",0403162v1
2004-03-21,Evidence for Superfluidity in a Resonantly Interacting Fermi Gas,"We observe collective oscillations of a trapped, degenerate Fermi gas of
$^6$Li atoms at a magnetic field just above a Feshbach resonance, where the
two-body physics does not support a bound state. The gas exhibits a radial
breathing mode at a frequency of 2837(05) Hz, in excellent agreement with the
frequency of $\nu_H\equiv\sqrt{10\nu_x\nu_y/3}=2830(20)$ Hz predicted for a
{\em hydrodynamic} Fermi gas with unitarity limited interactions. The measured
damping times and frequencies are inconsistent with predictions for both the
collisionless mean field regime and for collisional hydrodynamics. These
observations provide the first evidence for superfluid hydrodynamics in a
resonantly interacting Fermi gas.",0403540v2
2004-03-22,Parametric Driving of Dark Solitons in Atomic Bose-Einstein Condensates,"A dark soliton oscillating in an elongated harmonically-confined atomic
Bose-Einstein condensate continuously exchanges energy with the sound field.
Periodic optical `paddles' are employed to controllably enhance the sound
density and transfer energy to the soliton, analogous to parametric driving. In
the absence of damping, the amplitude of the soliton oscillations can be
dramatically reduced, whereas with damping, a driven soliton equilibrates as a
stable dark soliton with lower energy, thereby extending the soliton lifetime
up to the lifetime of the condensate.",0403566v2
2004-04-09,Network-Induced Oscillatory Behavior in Material Flow Networks,"Network theory is rapidly changing our understanding of complex systems, but
the relevance of topological features for the dynamic behavior of metabolic
networks, food webs, production systems, information networks, or cascade
failures of power grids remains to be explored. Based on a simple model of
supply networks, we offer an interpretation of instabilities and oscillations
observed in biological, ecological, economic, and engineering systems. We find
that most supply networks display damped oscillations, even when their units -
and linear chains of these units - behave in a non-oscillatory way. Moreover,
networks of damped oscillators tend to produce growing oscillations. This
surprising behavior offers, for example, a new interpretation of business
cycles and of oscillating or pulsating processes. The network structure of
material flows itself turns out to be a source of instability, and cyclical
variations are an inherent feature of decentralized adjustments.",0404226v1
2004-04-28,Dynamics of the Electro-Reflective Response of TaS3,"We have observed a large (~1%) change in infrared reflectance of the
charge-density-wave (CDW) conductor, orthorhombic TaS3, when its CDW is
depinned. The change is concentrated near one current contact. Assuming that
the change in reflectance is proportional to the degree of CDW polarization, we
have studied the dynamics of CDW repolarization through position dependent
measurements of the variation of the electro-reflectance with the frequency of
square wave voltages applied to the sample, and have found that the response
could be characterized as a damped harmonic oscillator with a distribution of
relaxation (i.e. damping) times. The average relaxation time, which increases
away from the contacts, varies with applied voltage as t0 ~ 1/V^p with p ~ 3/2,
but the distribution of times broadens as the voltage approaches the depinning
threshold. Very low resonant frequencies (~ 1 kHz) indicate a surprisingly
large amount of inertia, which is observable in the time dependence of the
change in reflectance as a polarity dependent delay of ~ 100 microsec.",0404690v1
2004-05-06,Damping of the de Haas-van Alphen oscillations in the superconducting state of MgB_2,"The de Haas-van Alphen (dHvA) signal arising from orbits on the $\pi$ Fermi
surface sheet of the two-gap superconductor MgB$_2$ has been observed in the
vortex state below $H_{c2}$. An extra attenuation of the dHvA signal, beyond
those effects described in the conventional Lifshitz-Kosevich expression, is
seen due to the opening of the superconducting gap. Our data show that the
$\pi$ band gap is still present up to $H_{c2}$. The data are compared to
current theories of dHvA oscillations in the superconducting state which allow
us to extract estimates for the evolution of the $\pi$ band gap with magnetic
field. Contrary to results for other materials, we find that the most recent
theories dramatically underestimate the damping in MgB$_2$.",0405120v1
2004-05-26,Magnetic droplets in a metal close to a ferromagnetic quantum critical point,"Using analytical and path integral Monte Carlo methods, we study the
susceptibility $\chi_{dc}(T)$ of a spin-S impurity with XY rotational symmetry
embedded in a metal. Close to a ferromagnetic quantum critical point, the
impurity polarizes conduction electrons in its vicinity and forms a large
magnetic droplet with moment M>>S. At not too low temperatures, the strongly
damping paramagnon modes of the conduction electrons suppress large quantum
fluctuations (or spin flips) of this droplet. We show that the susceptibility
follows the law $\chi_{dc}(T)=(M^{2}/T)[1-(\pi g)^{-1}\ln(gE_{0}/T)]$, where
the parameter g>>1 describes the strong damping by conduction electrons, and
E_0 is the bandwidth of paramagnon modes. At exponentially low temperatures T
<< T_{*} ~ E_{0}\exp(-\pi g/2) we show that spin flips cannot be ignored. In
this regime we find that $\chi_{dc}(T) \approx \chi_{dc}(0)
[1-(2/3)(T/T_{*})^2]$, where $\chi_{dc}(0)\sim M^{2}/T_{*}$ is finite and
exponentially large in g. We also discuss these effects in the context of the
multi-channel Kondo impurity model.",0405618v2
2004-06-29,Pairing gaps in atomic gases at the BCS-BEC crossover,"Strong evidence for pairing and superfluidity has recently been found in
atomic Fermi gases at the BCS-BEC crossover both in collective modes and RF
excitation energies. It is argued that the scale for the effective pairing gaps
measured in RF experiments is set by the lowest quasiparticle in-gap excitation
energies. These are calculated at the BCS-BEC crossover from semiclassical
solutions to the Bogoliubov-deGennes equations. The strong damping of the
radial breathing mode observed in the BCS limit occur when the lowest
quasiparticle excitation energies coincide with the radial frequency, which
indicates that a coupling between them take place.",0406714v3
2004-08-26,Decoherence of Rabi oscillations in a single quantum dot,"We develop a realistic model of Rabi oscillations in a quantum-dot
photodiode. Based in a multi-exciton density matrix formulation we show that
for short pulses the two-level models fails and higher levels should be taken
into account. This affects some of the experimental conclusions, such as the
inferred efficiency of the state rotation (population inversion) and the
deduced value of the dipole interaction. We also show that the damping observed
cannot be explained using \emph{constant} rates with fixed pulse duration. We
demonstrate that the damping observed is in fact induced by an off-resonant
excitation to or from the continuum of wetting layer states. Our model
describes the nonlinear decoherence behavior observed in recent experiments.",0408570v2
2004-08-28,Breakdown of Hydrodynamics in the Radial Breathing Mode of a Strongly-Interacting Fermi Gas,"We measure the magnetic field dependence of the frequency and damping time
for the radial breathing mode of an optically trapped, Fermi gas of $^6$Li
atoms near a Feshbach resonance. The measurements address the apparent
discrepancy between the results of Kinast et al., [Phys. Rev. Lett. {\bf 92},
150402 (2004)] and those of Bartenstein et al., [Phys. Rev. Lett. {\bf 92},
203201 (2004)]. Over the range of magnetic field from 770 G to 910 G, the
measurements confirm the results of Kinast et al. Close to resonance, the
measured frequencies are in excellent agreement with predictions for a unitary
hydrodynamic gas. At a field of 925 G, the measured frequency begins to
decrease below predictions. For fields near 1080 G, we observe a breakdown of
hydrodynamic behavior, which is manifested by a sharp increase in frequency and
damping rate. The observed breakdown is in qualitative agreement with the sharp
transition observed by Bartenstein et al., at 910 G.",0408634v2
2004-10-01,Magnetic Properties of Cuprate Perovskites,"The magnetic susceptibility of underdoped yttrium and lanthanum cuprates is
interpreted based on the self-consistent solution of the t-J model of a Cu-O
plane. The calculations reproduce correctly the frequency dependencies of the
susceptibility in YBa2Cu3O_{7-y} and La_{2-x}Sr_xCuO4 attributing their
dissimilarity to the difference in the damping of spin excitations. In
YBa2Cu3O_{7-y} these excitations are well defined at the antiferromagnetic wave
vector Q=(\pi,\pi) even in the normal state which manifests itself in a
pronounced maximum -- the resonance peak -- in the susceptibility. In
La_{2-x}Sr_xCuO4 the spin excitations are overdamped which leads to a broad
low-frequency feature in the susceptibility. The low-frequency
incommensurability in the magnetic response is attributed to a dip in the
magnon damping at Q. The calculated concentration and temperature dependencies
of the incommensurability parameter conform with experimental observations.
Generally the incommensurate magnetic response is not accompanied with an
inhomogeneity of the carrier density.",0410009v1
2004-11-12,Microwave induced resistance oscillations on a high-mobility 2DEG: absorption/reflection and temperature damping experiments,"In this work we address experimentally a number of unresolved issues related
to microwave induced resistance oscillations (MIRO) and the zero-resistance
states observed recently on very high-mobility 2D electron gases in GaAs/AlGaAs
heterostructures. In particular, we examine electrodynamic effects via
reflection/absorption experiments and study the exact waveform of MIRO and
their damping due to temperature. It is shown that electrodynamic effects due
to metallic-like reflection and plasmons are important producing a wide
cyclotron resonance line and a number of oscillations which do not coincide
with the MIRO. To describe the MIRO waveform a simple model was employed
involving radiation-induced scattering with displacement. A very good
correlation was found between the temperature dependencies of the quantum
lifetime from MIRO and the transport scattering time from the electron
mobility. The results are compared with measurements of Shubnikov-de Haas
oscillations down to 30 mK on the same sample.",0411338v1
2004-11-17,Path integral derivation of Bloch-Redfield equations for a qubit weakly coupled to a heat bath: Application to nonadiabatic transitions,"Quantum information processing has greatly increased interest in the
phenomenon of environmentally-induced decoherence. The spin boson model is
widely used to study the interaction between a spin-modelling a quantum
particle moving in a double well potential-and its environment-modelled by a
heat bath of harmonic oscillators. This paper extends a previous analysis of
the static spin boson study to the driven spin boson case, with the derivation
of an exact integro-differential equation for the time evolution of the
propagator of the reduced spin density matrix. This is the first main result.
By specializing to weak damping we then obtain the next result, a set of
Bloch-Redfield equations for the equilibrium fixed spin initial condition.
Finally we show that these equations can be used to solve the classic
dissipative Landau-Zener problem and illustrate these solutions for the weak
damping case. The effect of dissipation is seen to be minimised as the speed of
passage is increased, implying that qubits need to be switched as fast as
possible.",0411443v1
2004-11-24,Josephson tunnel junctions with nonlinear damping for RSFQ-qubit circuit applications,"We demonstrate that shunting of Superconductor-Insulator-Superconductor
Josephson junctions by Superconductor-Insulator-Normal metal (S-I-N) structures
having pronounced non-linear I-V characteristics can remarkably modify the
Josephson dynamics. In the regime of Josephson generation the phase behaves as
an overdamped coordinate, while in the superconducting state the damping and
current noise are strikingly small, that is vitally important for application
of such junctions for readout and control of Josephson qubits. Superconducting
Nb/AlO${_x}$/Nb junction shunted by Nb/AlO${_x}$/AuPd junction of S-I-N type
was fabricated and, in agreement with our model, exhibited non-hysteretic I-V
characteristics at temperatures down to at least 1.4 K.",0411607v1
2004-12-01,"Reply to Millis et al. on ""A Tale of Two Theories: Quantum Griffiths Effects in Metallic Systems""","In a recent paper (cond-mat/0411197) we showed the equivalence of two
seemingly contradictory theories on Griffiths-McCoy singularities (GMS) in
metallic antiferromagnets close to a quantum critical point (QCP). In a recent
comment, Millis {\it et al.} (cond-mat/0411738) argue that in heavy-fermion
materials the electronic damping is large leading to the freezing of locally
magnetically ordered droplets at high temperatures. In this reply we show that
this erroneous conclusion is based on a treatment of the problem of disorder
close to a QCP which is not self-consistent. We argue that a self-consistent
treatment of the ordered droplets must lead to weak damping and to a large
region of GMS behavior, in agreement with the our ealier results.",0412020v2
2005-01-04,On continuum modeling of sputter erosion under normal incidence: interplay between nonlocality and nonlinearity,"Under specific experimental circumstances, sputter erosion on semiconductor
materials exhibits highly ordered hexagonal dot-like nanostructures. In a
recent attempt to theoretically understand this pattern forming process, Facsko
et al. [Phys. Rev. B 69, 153412 (2004)] suggested a nonlocal, damped
Kuramoto-Sivashinsky equation as a potential candidate for an adequate
continuum model of this self-organizing process. In this study we theoretically
investigate this proposal by (i) formally deriving such a nonlocal equation as
minimal model from balance considerations, (ii) showing that it can be exactly
mapped to a local, damped Kuramoto-Sivashinsky equation, and (iii) inspecting
the consequences of the resulting non-stationary erosion dynamics.",0501049v2
2005-01-18,Incommensurate spin dynamics in underdoped cuprate perovskites,"The incommensurate magnetic response observed in normal-state cuprate
perovskites is interpreted based on the projection operator formalism and the
t-J model of Cu-O planes. In agreement with experiment the calculated
dispersion of maxima in the susceptibility has the shape of two parabolas with
upward and downward branches which converge at the antiferromagnetic wave
vector. The maxima are located at the momenta $({1/2},{1/2}\pm\delta)$,
$({1/2}\pm\delta,{1/2})$ and at $({1/2}\pm\delta,{1/2}\pm\delta)$,
$({1/2}\pm\delta,{1/2}\mp\delta)$ in the lower and upper parabolas,
respectively. The upper parabola reflects the dispersion of magnetic
excitations of the localized Cu spins, while the lower parabola arises due to a
dip in the spin-excitation damping at the antiferromagnetic wave vector. For
moderate doping this dip stems from the weakness of the interaction between the
spin excitations and holes near the hot spots. The frequency dependence of the
susceptibility is shown to depend strongly on the hole bandwidth and damping
and varies from the shape observed in YBa$_2$Cu$_3$O$_{7-y}$ to that inherent
in La$_{2-x}$Sr$_x$CuO$_4$.",0501418v1
2005-02-21,Velocity dependence of atomic-scale friction: a comparative study of the one- and two-dimensional Tomlinson model,"We present a comparative analysis of the velocity dependence of atomic-scale
friction for the Tomlinson model, at zero and finite temperatures, in 1D and
2D, and for different values of the damping. Combining analytical arguments
with numerical simulations, we show that an appreciable velocity dependence of
the kinetic friction force $F_{fric}$, for small scanning velocities $v_s$
(from 1 nm/s to 2 $\mu$m/s), is inherent in the Tomlinson model. In the absence
of thermal fluctuations in the stick-slip regime, it has the form of a
power-law, $F_{fric}-F_0\propto v_s^{\beta}$ with $\beta=2/3$, irrespective of
dimensionality and value of the damping. Since thermal fluctuations enhance the
velocity dependence of friction, we provide guidelines to establish when
thermal effects are important and to which extent the surface corrugation
affects the velocity dependence.",0502496v1
2005-03-12,Collective Oscillations of Strongly Correlated One-Dimensional Bosons on a Lattice,"We study the dipole oscillations of strongly correlated 1D bosons, in the
hard-core limit, on a lattice, by an exact numerical approach. We show that far
from the regime where a Mott insulator appears in the system, damping is always
present and increases for larger initial displacements of the trap, causing
dramatic changes in the momentum distribution, $n_k$. When a Mott insulator
sets in the middle of the trap, the center of mass barely moves after an
initial displacement, and $n_k$ remains very similar to the one in the ground
state. We also study changes introduced by the damping in the natural orbital
occupations, and the revival of the center of mass oscillations after long
times.",0503302v2
2005-04-28,Coherence properties of bulk matter,"We prove a theorem, using the density functional approach and relying on a
classical result by Lieb and Simon on Thomas-Fermi model, showing that in the
thermodynamic limit bulk matter is at most semiclassical and coherence
preserving. The connection between quantum fluid dynamics and density
functional theory in the formulation due to Kohn and Sham play a significant
role leading to a Vlasov-Poisson system of equations for the Wigner function.
Coherence stability is achieved by noting that small oscillations in bulk
matter are damped by Landau damping. In some conditions the initial Wigner
function could generate an opposite effect and coherence stability can be lost
involving higher order quantum effects for a macroscopic body.",0504768v3
2005-05-19,Harmonic Content of Strain-induced Potential Modulation in Unidirectional Lateral Superlattices,"Detailed analysis of the commensurability oscillation (CO) has been performed
on unidirectional lateral superlattices with periods ranging from a=92 to 184
nm. Fourier analysis reveals the second (and the third) harmonics along with
the fundamental oscillation for a>=138 nm (184 nm) at low-enough temperature,
evincing the presence of corresponding harmonics in the profile of the
potential modulation. The harmonics manifest themselves in CO with demagnified
amplitude due to the low-pass filtering action of the thermal damping factor;
with a suitable consideration of the damping effect, the harmonics of the
modulation potential are found to have the amplitudes V_2 and V_3 up to roughly
30% of that of the fundamental component V_1, despite the small ratio of the
period a to the depth d = 99 nm of the two-dimensional electron gas (2DEG) from
the surface. The dependence of V_n on a indicates that the fundamental
component originates at the surface, while the higher harmonics arise from the
effect of the strain that penetrates down into subsurface. The manipulation of
high harmonics thus provides a useful technique to introduce small length-scale
modulation into high-mobility 2DEGs located deep inside the wafer.",0505479v1
2005-06-14,Lifetime of the first and second collective excitations in metallic nanoparticles,"We determine the lifetime of the surface plasmon in metallic nanoparticles
under various conditions, concentrating on the Landau damping, which is the
dominant mechanism for intermediate-size particles. Besides the main
contribution to the lifetime, which smoothly increases with the size of the
particle, our semiclassical evaluation yields an additional oscillating
component. For the case of noble metal particles embedded in a dielectric
medium, it is crucial to consider the details of the electronic confinement; we
show that in this case the lifetime is determined by the shape of the
self-consistent potential near the surface. Strong enough perturbations may
lead to the second collective excitation of the electronic system. We study its
lifetime, which is limited by two decay channels: Landau damping and
ionization. We determine the size dependence of both contributions and show
that the second collective excitation remains as a well defined resonance.",0506320v2
2005-07-27,Dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor,"We present an analysis of the dynamics of a nanomechanical resonator coupled
to a superconducting single electron transistor (SSET) in the vicinity of the
Josephson quasiparticle (JQP) and double Josephson quasiparticle (DJQP)
resonances. For weak coupling and wide separation of dynamical timescales, we
find that for either superconducting resonance the dynamics of the resonator is
given by a Fokker-Planck equation, i.e., the SSET behaves effectively as an
equilibrium heat bath, characterised by an effective temperature, which also
damps the resonator and renormalizes its frequency. Depending on the gate and
drain-source voltage bias points with respect to the superconducting resonance,
the SSET can also give rise to an instability in the mechanical resonator
marked by negative damping and temperature within the appropriate Fokker-Planck
equation. Furthermore, sufficiently close to a resonance, we find that the
Fokker-Planck description breaks down. We also point out that there is a close
analogy between coupling a nanomechanical resonator to a SSET in the vicinity
of the JQP resonance and Doppler cooling of atoms by means of lasers.",0507645v1
2005-08-01,Unexpected Effect of Internal Degrees of Freedom on Transverse Phonons in Supercooled Liquids,"We show experimentally that in a supercooled liquid composed of molecules
with internal degrees of freedom the internal modes contribute to the frequency
dependent shear viscosity and damping of transverse phonons, which results in
an additional broadening of the transverse Brillouin lines. Earlier, only the
effect of internal modes on the frequency dependent bulk viscosity and damping
of longitudinal phonons was observed and explained theoretically in the limit
of weak coupling of internal degrees of freedom to translational motion. A new
theory is needed to describe this new effect. We also demonstrate, that the
contributions of structural relaxation and internal processes to the width of
the Brillouin lines can be separated by measurements under high pressure.",0508046v1
2005-08-05,Damping of vortex waves in a superfluid,"The damping of vortex cyclotron modes is investigated within a generalized
quantum theory of vortex waves. Similarly to the case of Kelvin modes, the
friction coefficient turns out to be essentially unchanged under such
oscillations, but it is shown to be affected by appreciable memory corrections.
On the other hand, the nonequilibrium energetics of the vortex, which is
investigated within the framework of linear response theory, shows that its
memory corrections are negligible. The vortex response is found to be of the
Debye type, with a relaxation frequency whose dependence on temperature and
impurity concentration reflects the complexity of the heat bath and its
interaction with the vortex.",0508167v1
2005-08-08,Collective excitations of low density fermion-boson quantum-liquid mixtures,"We investigate the collective excitations of a low temperature dilute gas
mixture that consists of a Bose-Einstein condensate and a Fermi-gas that is a
normal (i.e. non-superfluid) Fermi-liquid. We find that the BEC-mediated
fermion-fermion interactions, as a consequence of retardation, can become
repulsive and support a zero-sound mode that is essentially undamped. In
addition, we find a damped zero-sound mode that can be described as a BEC-sound
mode modified by fermion mediated boson-boson interactions, and we derive its
decay-rate caused by Landau damping. We study the mode structure of these
excitations and find avoided crossing behavior as well as a termination point.
The collective mode dynamics also reveals that phase separation sets in when
the fermion-mediated boson-boson interaction destroys the stability of the
homogeneous BEC. We estimate the time and length scales of the onset of the
phase separation, and we discuss the feasibility of experimentally probing
these consequences of mediated interactions.",0508207v1
2005-09-02,Inhomogeneous soliton ratchets under two ac forces,"We extend our previous work on soliton ratchet devices [L. Morales-Molina et
al., Eur. Phys. J. B 37, 79 (2004)] to consider the joint effect of two ac
forces including non-harmonic drivings, as proposed for particle ratchets by
Savele'v et al. [Europhys. Lett. 67}, 179 (2004); Phys. Rev. E {\bf 70} 066109
(2004)]. Current reversals due to the interplay between the phases, frequencies
and amplitudes of the harmonics are obtained. An analysis of the effect of the
damping coefficient on the dynamics is presented. We show that solitons give
rise to non-trivial differences in the phenomenology reported for particle
systems that arise from their extended character. A comparison with soliton
ratchets in homogeneous systems with biharmonic forces is also presented. This
ratchet device may be an ideal candidate for Josephson junction ratchets with
intrinsic large damping.",0509051v1
2005-10-26,Multiple electron-hole scattering effect on quasiparticle properties in a homogeneous electron gas,"We present a detailed study of a contribution of the T matrix accounting for
multiple scattering between an electron and a hole to the quasiparticle
self-energy. This contribution is considered as an additional term to the GW
self-energy. The study is based on a variational solution of the T-matrix
integral equation within a local approximation. A key quantity of such a
solution, the local electron-hole interaction, is obtained at the small
four-momentum transfer limit. Performed by making use of this limit form,
extensive calculations of quasiparticle properties in the homogeneous electron
gas over a broad range of electron densities are reported. We carry out an
analysis of how the T-matrix contribution affects the quasiparticle damping
rate, the quasiparticle energy, the renormalization constant, and the effective
mass enhancement. We find that in comparison with the GW approximation the
inclusion of the T matrix leads to an essential increase of the damping rate, a
slight reduction of the GW band narrowing, a decrease of the renormalization
constant at the Fermi wave vector, and some ""weighting"" of quasiparticles at
the Fermi surface.",0510684v2
2005-10-27,Acoustic damping in Li$_2$O-2B$_2$O$_3$ glass observed by inelastic x-ray and optical Brillouin scattering,"The dynamic structure factor of lithium-diborate glass has been measured at
several values of the momentum transfer $Q$ using high resolution inelastic
x-ray scattering. Much attention has been devoted to the low $Q$-range, below
the observed Ioffe-Regel crossover \qco{}$\simeq$ 2.1 nm$^{-1}$. We find that
below \qco{}, the linewidth of longitudinal acoustic waves increases with a
high power of either $Q$, or of the frequency $\Omega$, up to the crossover
frequency \OMco{} $\simeq$ 9 meV that nearly coincides with the center of the
boson peak. This new finding strongly supports the view that resonance and
hybridization of acoustic waves with a distribution of rather local low
frequency modes forming the boson peak is responsible for the end of acoustic
branches in strong glasses. Further, we present high resolution Brillouin
light-scattering data obtained at much lower frequencies on the same sample.
These clearly rule out a simple $\Omega^2$-dependence of the acoustic damping
over the entire frequency range.",0510714v1
2005-12-07,Acoustic attenuation probe for fermion superfluidity in ultracold atom gases,"Dilute gas Bose-Einstein condensates (BEC's), currently used to cool
fermionic atoms in atom traps, can also probe the superfluidity of these
fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured
in the middle of the trap as a function of the phonon momentum, yields an
unambiguous signature of BCS-like superfluidity, provides a measurement of the
superfluid gap parameter and gives an estimate of the size of the Cooper-pairs
in the BEC-BCS crossover regime. We also predict kinks in the momentum
dependence of the damping rate which can reveal detailed information about the
fermion quasi-particle dispersion relation.",0512134v4
2006-01-11,"Apparent phonon side band modes in pi-conjugated systems: polymers, oligomers and crystals","The emission spectra of many pi-conjugated polymers and oligomers contain
side-band replicas with apparent frequencies that do not match the Raman active
mode frequencies. Using a time dependent model we show that in such many mode
systems, the increased damping of the time dependent transition dipole moment
correlation function results in an effective elimination of the vibrational
modes from the emission spectrum; subsequently causing the appearance of a
regularly spaced progression at a new apparent frequency. We use this damping
dependent vibrational reshaping to quantitatively account for the vibronic
structure in the emission spectra of pi-conjugated systems in the form of
films, dilute solutions and single crystals. In particular, we show that by
using the experimentally measured Raman spectrum we can account in detail for
the apparent progression frequencies and their relative intensities in the
emission spectrum.",0601218v1
2006-03-01,Renormalization of the electron-spin-fluctuation interaction in the t-t'-U Hubbard model,"We study the renormalization of the electron-spin-fluctuation (el-sp) vertex
in a two-dimensional Hubbard model with nearest-neighbor (t) and
next-nearest-neighbor (t') hopping by a Quantum-Monte-Carlo calculation. Our
results show that for t'=0, the renormalized el-sp vertex decreases quite
generally with decreasing temperature at all spin-fluctuation momentum
transfers. The suppression of the el-sp vertex results in a substantial
reduction of the effective pairing interaction mediated by antiferromagnetic
spin fluctuations in both the intermediate- and strong-correlation regimes. The
inclusion of a finite t'/t<0, increases the Landau damping rate of spin
fluctuations, especially in the overdoped region. The increased damping rate
leads to smaller vertex corrections, in agreement with earlier diagrammatic
calculations. Still, the vertex correction reduces the spin-fermion vertex, as
at t'=0.",0603014v3
2006-07-18,Equilibrium and non-equilibrium dynamics of the sub-ohmic spin-boson model,"Employing the non-perturbative numerical renormalization group method, we
study the dynamics of the spin-boson model, which describes a two-level system
coupled to a bosonic bath with spectral density J(omega) propto omega^s. We
show that, in contrast to the case of ohmic damping, the delocalized phase of
the sub-ohmic model cannot be characterized by a single energy scale only, due
to the presence of a non-trivial quantum phase transition. In the strongly
sub-ohmic regime, s<<1, weakly damped coherent oscillations on short time
scales are possible even in the localized phase - this is of crucial relevance,
e.g., for qubits subject to electromagnetic noise.",0607443v2
2006-09-29,Quantum master equation for electron transport through quantum dots and single molecules,"A quantum master equation (QME) is derived for the many-body density matrix
of an open current-carrying system weakly coupled to two metal leads. The
dynamics and the steady-state properties of the system for arbitrary bias are
studied using projection operator techniques, which keep track of number of
electrons in the system. We show that coherences between system states with
different number of electrons, n, (Fock space coherences) do not contribute to
the transport to second order in system-lead coupling.
  However, coherences between states with the same n may effect transport
properties when the damping rate is of the order or faster then the system Bohr
frequencies.
  For large bias, when all the system many-body states lie between the chemical
potentials of the two leads, we recover previous results. In the rotating wave
approximation (when the damping is slow compared to the Bohr frequencies of the
system), the dynamics of populations and the coherences in the system
eigenbasis are decoupled. The QME then reduces to a birth and death master
equation for populations.",0610004v1
2006-10-25,Pulse and hold strategy for switching current measurements,"We investigate by theory and experiment, the Josephson junction switching
current detector in an environment with frequency dependent damping. Analysis
of the circuit's phase space show that a favorable topology for switching can
be obtained with overdamped dynamics at high frequencies. A pulse-and-hold
method is described, where a fast switch pulse brings the circuit close to an
unstable point in the phase space when biased at the hold level. Experiments
are performed on Cooper pair transistors and Quantronium circuits, which are
overdamped at high frequencies with an on-chip RC shunt. For 20 us switch
pulses the switching process is well described by thermal equilibrium escape,
based on a generalization of Kramers formula to the case of frequency dependent
damping. A capacitor bias method is used to create very rapid, 25 ns switch
pulses, where it is observed that the switching process is not governed by
thermal equilibrium noise.",0610704v2
2006-10-29,Experimental Studies of Low-field Landau Quantization in Two-dimensional Electron Systems in GaAs/AlGaAs Heterostructures,"By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional
electron systems, we study the low-field Landau quantization when the thermal
damping is reduced with decreasing the temperature. Magneto-oscillations
following Shubnikov-de Haas (SdH) formula are observed even when their
amplitudes are so large that the deviation to such a formula is expected. Our
experimental results show the importance of the positive magneto-resistance to
the extension of SdH formula under the damping induced by the disorder.",0610805v1
2006-11-18,Distributions of switching times of single-domain particles using a time quantified Monte Carlo method,"Using a time quantified Monte Carlo scheme we performed simulations of the
switching time distribution of single mono-domain particles in the
Stoner-Wohlfarth approximation. We considered uniaxial anisotropy and different
conditions for the external applied field. The results obtained show the
switching time distribution can be well described by two relaxation times,
either when the applied field is parallel to the easy axis or for an oblique
external field and a larger damping constant. We found that in the low barrier
limit these relaxation times are in very good agreement with analytical results
obtained from solutions of the Fokker-Planck equation related to this problem.
When the damping is small and the applied field is oblique the shape of the
distribution curves shows several peaks and resonance effects.",0611494v2
2007-01-12,Electron spin quantum beats in positively charged quantum dots: nuclear field effects,"We have studied the electron spin coherence in an ensemble of positively
charged InAs/GaAs quantum dots. In a transverse magnetic field, we show that
two main contributions must be taken into account to explain the damping of the
circular polarization oscillations. The first one is due to the nuclear field
fluctuations from dot to dot experienced by the electron spin. The second one
is due to the dispersion of the transverse electron Lande g-factor, due to the
inherent inhomogeneity of the system, and leads to a field dependent
contribution to the damping. We have developed a model taking into account both
contributions, which is in good agreement with the experimental data. This
enables us to extract the pure contribution to dephasing due to the nuclei.",0701284v2
2007-02-05,Verification of stable operation of rapid single flux quantum devices with selective dissipation,"It has been suggested that Rapid Single Flux Quantum (RSFQ) devices could be
used as the classical interface of superconducting qubit systems. One problem
is that the interface acts as a dissipative environment for a qubit. Recently
ways to modify the RSFQ damping to reduce the dissipation have been introduced.
One of the solutions is to damp the Josephson junctions by a
frequency-dependent linear circuit instead of the plain resistor. The approach
has previously been experimentally tested with a simple SFQ comparator. In this
paper we perform experiments with a full RSFQ circuit, and thus conclude that
in terms of stable operation the approach is applicable for scalable RSFQ
circuits. Realisation and optimisation issues are also discussed.",0702104v1
2007-02-21,RPAE versus RPA for the Tomonaga model with quadratic energy dispersion,"Recently the damping of the collective charge (and spin) modes of interacting
fermions in one spatial dimension was studied. It results from the nonlinear
correction to the energy dispersion in the vicinity of the Fermi points. To
investigate the damping one has to replace the random phase approximation (RPA)
bare bubble by a sum of more complicated diagrams. It is shown here that a
better starting point than the bare RPA is to use the (conserving) linearized
time dependent Hartree-Fock equations, i.e. to perform a random phase
approximation (with) exchange
  (RPAE) calculation. It is shown that the RPAE equation can be solved
analytically for the special form of the two-body interaction often used in the
Luttinger liquid framework. While (bare) RPA and RPAE agree for the case of a
strictly linear disperson there are qualitative differences for the case of the
usual nonrelativistic quadratic dispersion.",0702488v2
2007-03-01,Spin dynamics across the superfluid-insulator transition of spinful bosons,"Bosons with non-zero spin exhibit a rich variety of superfluid and insulating
phases. Most phases support coherent spin oscillations, which have been the
focus of numerous recent experiments. These spin oscillations are Rabi
oscillations between discrete levels deep in the insulator, while deep in the
superfluid they can be oscillations in the orientation of a spinful condensate.
We describe the evolution of spin oscillations across the superfluid-insulator
quantum phase transition. For transitions with an order parameter carrying
spin, the damping of such oscillations is determined by the scaling dimension
of the composite spin operator. For transitions with a spinless order parameter
and gapped spin excitations, we demonstrate that the damping is determined by
an associated quantum impurity problem of a localized spin excitation
interacting with the bulk critical modes. We present a renormalization group
analysis of the quantum impurity problem, and discuss the relationship of our
results to experiments on ultracold atoms in optical lattices.",0703011v2
2007-03-21,Edge magnetoplasmons in a partially screened two-dimensional electron gas on a helium surface,"We report a study of edge magnetoplasmons in a partially-screened system of
electrons on a helium surface. We compare experimental results with theories of
the frequency, damping, and penetration-depth dependence on magnetic field,
temperature-dependent damping, and the dependence of the frequency on
screening. We show explicitly the dependence of frequency on the edge density
profile. The frequency and screening are in qualitative agreement with the
theory of Fetter at small fields, and the frequencies agree with theory in the
limit of zero magnetic field. The frequency and linewidths in intermediate and
large fields exhibit the features of the qualitative predictions of Volkov and
Mikhailov, but differ numerically. Deviations from theory for a finite sample
occur at smaller fields. The dependence of frequency on the density profile is
stronger than predicted by these authors, and the penetration-depth variation
with field confirms their prediction for small fields.",0703558v1
1997-02-12,On the problem of semiinfinite beam oscillation with internal damping,"We study the Cauchy problem for the equation of the form $$ \ddot{u}(t) +
(\aa A + B)\dot{u}(t) + (A+G)u(t) = 0,\tag* $$ where $A$, $B$, and $G$ are \o s
in a Hilbert space $\Cal H$ with $A$ selfadjoint, $\sigma(A)=[0,\infty)$,
$B\ge0$ bounded, and $G$ symmetric and $A$-subordinate in a certain sense.
Spectral properties of the correspondent operator pencil
  $L(\lambda) := \lambda^2I + \lambda (\alpha A + B) + A + G$ are studied, and
existence and uniqueness of generalized and classical solutions of the Cauchy
problem are proved. Equations of the type (*) include, e.g., an abstract model
for the problem of semiinfinite beam oscillations with internal damping.",9702007v1
1994-04-14,"Decoherence, Correlation, and Unstable Quantum States in Semiclassical Cosmology","It is demonstrated that almost any S-matrix of quantum field theory in curved
spaces posses an infinite set of complex poles (or branch cuts). These poles
can be transformed into complex eigenvalues, the corresponding eigenvectors
being Gamow vectors. All this formalism, which is heuristic in ordinary Hilbert
space, becomes a rigorous one within the framework of a properly chosen rigged
Hilbert space. Then complex eigenvalues produce damping or growing factors. It
is known that the growth of entropy, decoherence, and the appearance of
correlations, occur in the universe evolution, but only under a restricted set
of initial conditions. It is proved that the damping factors allow to enlarge
this set up to almost any initial conditions.",9404028v1
1994-09-27,Effects of weak self-interactions in a relativistic plasma on cosmological perturbations,"The exact solutions for linear cosmological perturbations which have been
obtained for collisionless relativistic matter within thermal field theory are
extended to a self-interacting case. The two-loop contributions of scalar
$\lambda\phi^4$ theory to the thermal graviton self-energy are evaluated, which
give the $O(\lambda)$ corrections in the perturbation equations. The changes
are found to be perturbative on scales comparable to or larger than the Hubble
horizon, but the determination of the large-time damping behavior of subhorizon
perturbations requires a resummation of thermally induced masses.",9409055v2
1995-03-07,ON THE OSCILLATION SPECTRA OF ULTRA COMPACT STARS,"Quasinormal modes of ultra compact stars with uniform energy density have
been calculated. For less compact stars, there is only one very slowly damped
polar mode (corresponding to the Kelvin f-mode) for each spherical harmonic
index $l$. Further long-lived modes become possible for a sufficiently compact
star (roughly when $M/R \ge 1/3$). We compare the characteristic frequencies of
these resonant polar modes to the axial modes first found by Chandrasekhar and
Ferrari [{\em Proc. Roy. Soc. London A} {\bf 434} 449 (1991)]. We find that the
two spectra approach each other as the star is made more compact. The
oscillation frequencies of the corresponding polar and axial modes agree to
within a percent for stars more compact than $M/R = 0.42$. At the same time,
the damping times are slightly different. The results illustrate that there is
no real difference between the origin of these axial and polar modes: They are
essentially spacetime modes.",9503012v1
1998-02-13,Radiation Damping in FRW Space-times with Different Topologies,"We study the role played by the compactness and the degree of connectedness
in the time evolution of the energy of a radiating system in the
Friedmann-Robertson-Walker (FRW) space-times whose $t=const $ spacelike
sections are the Euclidean 3-manifold ${\cal R}^3$ and six topologically
non-equivalent flat orientable compact multiply connected Riemannian
3-manifolds. An exponential damping of the energy $E(t)$ is present in the
${\cal R}^3$ case, whereas for the six compact flat 3-spaces it is found
basically the same pattern for the evolution of the energy, namely relative
minima and maxima occurring at different times (depending on the degree of
connectedness) followed by a growth of $E(t)$. Likely reasons for this
divergent behavior of $E(t)$ in these compact flat 3-manifolds are discussed
and further developments are indicated. A misinterpretation of Wolf's results
regarding one of the six orientable compact flat 3-manifolds is also indicated
and rectified.",9802031v1
1998-05-06,Damping of Gravitational Waves and Density Perturbations in the Early Universe,"Since the discovery of the large angular scale anisotropies in the microwave
background radiation, the behaviour of cosmological perturbations (especially,
density perturbations and gravitational waves) has been of great interest. In
this study, after a detailed and rigorous treatment of the behaviour of
gravitational waves in viscous cosmic media, we conclude that the damping of
cosmological gravitational waves of long wavelengths is negligible for most
cases of physical interest. A preliminary analysis suggests that similar
results hold for density perturbations in the long wavelength limit. Therefore,
long wavelength cosmological perturbations have not been practically affected
by viscous processes,and are good probes of the very early Universe.",9805016v1
1998-11-11,Late-Time Evolution of Realistic Rotating Collapse and The No-Hair Theorem,"We study analytically the asymptotic late-time evolution of realistic
rotating collapse. This is done by considering the asymptotic late-time
solutions of Teukolsky's master equation, which governs the evolution of
gravitational, electromagnetic, neutrino and scalar perturbations fields on
Kerr spacetimes. In accordance with the no-hair conjecture for rotating
black-holes we show that the asymptotic solutions develop inverse power-law
tails at the asymptotic regions of timelike infinity, null infinity and along
the black-hole outer horizon (where the power-law behaviour is multiplied by an
oscillatory term caused by the dragging of reference frames). The damping
exponents characterizing the asymptotic solutions at timelike infinity and
along the black-hole outer horizon are independent of the spin parameter of the
fields. However, the damping exponents at future null infinity are spin
dependent. The late-time tails at all the three asymptotic regions are
spatially dependent on the spin parameter of the field. The rotational dragging
of reference frames, caused by the rotation of the black-hole (or star) leads
to an active coupling of different multipoles.",9811032v2
1999-09-22,Vorticity affects the stability of neutron stars,"The spin rate \Omega of neutron stars at a given temperature T is constrained
by the interplay between gravitational-radiation instabilities and viscous
damping. Navier-Stokes theory has been used to calculate the viscous damping
timescales and produce a stability curve for r-modes in the (\Omega,T) plane.
In Navier-Stokes theory, viscosity is independent of vorticity, but kinetic
theory predicts a coupling of vorticity to the shear viscosity. We calculate
this coupling and show that it can in principle significantly modify the
stability diagram at lower temperatures. As a result, colder stars can remain
stable at higher spin rates.",9909073v2
2000-02-02,Active controls in interferometric detectors of gravitational waves: inertial damping of the VIRGO superattenuator,"The operation of an interferometer for gravitational waves detection requires
sophisticated feedback controls in many parts of the apparatus. The aim of this
lecture is to introduce the types of problems to be faced in this line of
research. The attention is focused on the ""inertial damping"" of the test mass
suspension of the VIRGO interferometer (the superattenuator): it is a
multidimensional local control aimed to reduce the residual motion of the
suspended mirror associated to the normal modes of the suspension. Its
performance is very important for the locking of the interferometer.",0002006v2
2000-08-09,Gravitational Wave Damping of Neutron Star Wobble,"We calculate the effect of gravitational wave (gw) back-reaction on realistic
neutron stars (NS's) undergoing torque-free precession. By `realistic' we mean
that the NS is treated as a mostly-fluid body with an elastic crust, as opposed
to a rigid body. We find that gw's damp NS wobble on a timescale tau_{theta}
approx 2 x 10^5 yr [10^{-7}/(DId/I_0)]^2 (kHz/ nu_s)^4, where nu_s is the spin
frequency and DId is the piece of the NS's inertia tensor that ""follows"" the
crust's principal axis (as opposed to its spin axis). We give two different
derivations of this result: one based solely on energy and angular momentum
balance, and another obtained by adding the Burke-Thorne radiation reaction
force to the Newtonian equations of motion. This problem was treated long ago
by Bertotti and Anile (1973), but their claimed result is wrong. When we
convert from their notation to ours, we find that their tau_{theta} is too
short by a factor of order 10^5 for typical cases of interest, and even has the
wrong sign for DId negative. We show where their calculation went astray.",0008021v1
2000-11-30,Tests of strong-field gravity and gravitational radiation damping in binary-pulsar systems,"This talk reviews the constraints imposed by binary-pulsar data on gravity
theories, and notably on ""scalar-tensor"" theories which are the most natural
alternatives to general relativity. Because neutron stars have a strong
gravitational binding energy, binary-pulsar tests are qualitatively different
from solar-system experiments: They have the capability of probing models which
are indistinguishable from general relativity in weak gravitational field
conditions. Besides the two most precise binary-pulsar experiments, in the
systems B1913+16 and B1534+12, we also present the results of the various
""null"" tests of general relativity provided by several neutron star-white dwarf
binaries, notably those of gravitational radiation damping. [The main interest
of this very short paper is its figure, which also takes into account the
""strong equivalence principle"" tests.]",0011114v1
2001-07-17,Properties of r modes in rotating magnetic neutron stars. I. Kinematic Secular Effects and Magnetic Evolution Equations,"The instability of r-mode oscillations in rapidly rotating neutron stars has
attracted attention as a potential mechanism for producing high frequency,
almost periodic gravitational waves. The analyses carried so far have shown the
existence of these modes and have considered damping by shear and bulk
viscosity. However, the magnetohydrodynamic coupling of the modes with a
stellar magnetic field and its role in the damping of the instability has not
been fully investigated yet. Following our introductory paper (Rezzolla, Lamb
and Shapiro 2000), we here discuss in more detail the existence of secular
higher-order kinematical effects which will produce toroidal fluid drifts. We
also define the sets of equations that account for the time evolution of the
magnetic fields produced by these secular velocity fields and show that the
magnetic fields produced can reach equipartition in less than a year. The full
numerical calculations as well as the evaluation of the impact of strong
magnetic fields on the onset and evolution of the r-mode instability will be
presented in a companion paper.",0107061v1
2004-01-13,Highly Damped Quasinormal Modes of Kerr Black Holes: A Complete Numerical Investigation,"We compute for the first time very highly damped quasinormal modes of the
(rotating) Kerr black hole. Our numerical technique is based on a decoupling of
the radial and angular equations, performed using a large-frequency expansion
for the angular separation constant_{s}A_{l m}. This allows us to go much
further in overtone number than ever before. We find that the real part of the
quasinormal frequencies approaches a non-zero constant value which does not
depend on the spin s of the perturbing field and on the angular index l:
\omega_R=m\varpi(a). We numerically compute \varpi(a). Leading-order
corrections to the asymptotic frequency are likely to be of order 1/\omega_I.
The imaginary part grows without bound, the spacing between consecutive modes
being a monotonic function of a.",0401052v1
2006-12-07,Improved calculation of relic gravitational waves,"In this paper, we improve the calculation of the relic gravitational waves
(RGW) in two aspects: First, we investigate the transfer function after
considering the redshift-suppression effect, the accelerating expansion effect,
the damping effect of free-streaming relativistic particles, and the damping
effect of cosmic phase transition, and give a simple approximate analytic
expression, which clearly illustrates the dependent relations on the
cosmological parameters. Second, we develop a numerical method to calculate the
primordial power spectrum of RGW at a very wide frequency range, where the
observed constraints on $n_s$ (the scalar spectral index) and $P_S(k_0)$ (the
amplitude of primordial scalar spectrum) and the Hamilton-Jacobi equation are
used. This method is applied to two kinds of inflationary models, which all
satisfy the current constraints on $n_s$, $\alpha$ (the running of $n_s$) and
$r$ (the tensor-scalar ratio). We plot them in the $r-\Omega_g$ diagram, where
$\Omega_g$ is the strength of RGW, and study their detection by the CMB
experiments and laser interferometers.",0612041v3
2007-01-16,Influence of Lorentz violation on Dirac quasinormal modes in the Schwarzschild black hole spacetime,"Using the third-order WKB approximation and monodromy methods, we investigate
the influence of Lorentz violating coefficient $b$ (associated with a special
axial-vector $b_{\mu}$ field) on Dirac quasinormal modes in the Schwarzschild
black hole spacetime. At fundamental overtone, the real part decreases linearly
as the parameter $b$ increases. But the variation of the imaginary part with
$b$ becomes more complex. For the larger multiple moment $k$, the magnitude of
imaginary part increases with the increase of $b$, which means that presence of
Lorentz violation makes Dirac field damps more rapidly. At high overtones, it
is found that the real part of high-damped quasinormal frequency does not tend
to zero, which is quite a different from the symptotic Dirac quasinormal modes
without Lorentz violation.",0701089v1
2007-03-29,Constraint Damping in First-Order Evolution Systems for Numerical Relativity,"A new constraint suppressing formulation of the Einstein evolution equations
is presented, generalizing the five-parameter first-order system due to Kidder,
Scheel and Teukolsky (KST). The auxiliary fields, introduced to make the KST
system first-order, are given modified evolution equations designed to drive
constraint violations toward zero. The algebraic structure of the new system is
investigated, showing that the modifications preserve the hyperbolicity of the
fundamental and constraint evolution equations. The evolution of the
constraints for pertubations of flat spacetime is completely analyzed, and all
finite-wavelength constraint modes are shown to decay exponentially when
certain adjustable parameters satisfy appropriate inequalities. Numerical
simulations of a single Schwarzschild black hole are presented, demonstrating
the effectiveness of the new constraint-damping modifications.",0703145v1
1992-06-21,Gauge Dependence of the Resummed Thermal Gluon Self Energy,"The gauge dependence of the hot gluon self energy is examined in the context
of Pisarski's method for resumming hard thermal loops. Braaten and Pisarski
have used the Ward identities satisfied by the hard corrections to the n-point
functions to argue the gauge fixing independence of the leading order resummed
QCD plasma damping rate in covariant and strict Coulomb gauges. We extend their
analysis to include all linear gauges that preserve rotational invariance and
display explicitly the conditions required for gauge fixing independence. It is
shown that in covariant gauges the resummed damping constant is gauge fixing
independent only if an infrared regulator is explicitly maintained throughout
the calculation.",9206239v1
1993-05-07,Thermal quark production in pure glue and quark gluon plasmas,"We calculate production rates for massless $(u,d)$ and massive $(s,c,b)$
quarks in pure glue and quark gluon plasmas to leading order in the strong
coupling constant $g$. The leading contribution comes from gluon decay into
$q\bar q$ pairs, using a thermal gluon propagator with finite thermal mass and
damping rate. The rate behaves as $\alpha_S^2(\ln 1/\alpha_S)^2 T^4$ when $m,
\alpha_S \rightarrow 0$ and depends linearly on the transverse gluon damping
rate for all values of the quark mass $m$. The light quark ($u$, $d$, $s$)
chemical equilibration time is approximately 10-100 $T^{-1}$ for $g=$2-3, so
that quarks are likely to remain far from chemical equilibrium in
ultrarelativistic nuclear collisions.",9305227v1
1994-01-21,Transport Properties of Quark and Gluon Plasmas,"The kinetic properties of relativistic quark-gluon and electron-photon
plasmas are described in the weak coupling limit. The troublesome Rutherford
divergence at small scattering angles is screened by Debye screening for the
longitudinal or electric part of the interactions. The transverse or magnetic
part of the interactions is effectively screened by Landau damping of the
virtual photons and gluons transferred in the QED and QCD interactions
respectively. Including screening a number of transport coefficients for QCD
and QED plasmas can be calculated to leading order in the interaction strength,
including rates of momentum and thermal relaxation, electrical conductivity,
viscosities, flavor and spin diffusion of both high temperature and degenerate
plasmas. Damping of quarks and gluons as well as color diffusion in quark-gluon
plasmas is, however, shown not to be sufficiently screened and the rates
depends on an infrared cut-off of order the ``magnetic mass"", $m_{\rm mag}\sim
g^2 T$.",9401300v1
1994-04-20,Electroweak Baryogenesis and Standard Model CP Violation,"We analyze the mechanism of electroweak baryogenesis proposed by Farrar and
Shaposhnikov in which the phase of the CKM mixing matrix is the only source of
$CP$ violation. This mechanism is based on a phase separation of baryons via
the scattering of quasiparticles by the wall of an expanding bubble produced at
the electroweak phase transition. In agreement with the recent work of Gavela,
Hern\'andez, Orloff and P\`ene, we conclude that QCD damping effects reduce the
asymmetry produced to a negligible amount. We interpret the damping as quantum
decoherence. We compute the asymmetry analytically. Our analysis reflects the
observation that only a thin, outer layer of the bubble contributes to the
coherent scattering of the quasiparticles. The generality of our arguments
rules out any mechanism of electroweak baryogenesis that does not make use of a
new source of $CP$ violation.",9404302v1
1994-06-11,Standard Model CP-violation and Baryon asymmetry Part II: Finite Temperature,"We consider the scattering of quasi-particles off the boundary created during
a first order electroweak phase transition. Spatial coherence is lost due to
the quasi-quark damping rate, and we show that reflection on the boundary is
suppressed, even at tree-level. Simply on CP considerations, we argue against
electroweak baryogenesis in the Standard Model via the charge transport
mechanism. A CP asymmetry is produced in the reflection properties of quarks
and antiquarks hitting the phase boundary. An effect is present at order
$\alpha_W^2$ in rate and a regular GIM behaviour is found, which can be
expressed in terms of two unitarity triangles. A crucial role is played by the
damping rate of quasi-particles in a hot plasma, which is a relevant scale
together with $M_W$ and the temperature. The effect is many orders of magnitude
below what observation requires.",9406289v2
1995-01-03,High temperature QCD and QED with unstable excitations,"We consider the partition functions of QCD and QED at high temperature
assuming small coupling constants, and present arguments in favor of an
improved perturbative expansion in terms of unstable excitations. Our effective
propagators are derived from spectral functions with a constant width. These
spectral functions describe screening and damping of gluons (photons) as well
as ``Brownian'' motion of quarks (electrons). BRST-invariance allows us to
reduce the number of independent width parameters to three. These are
determined in a self-consistent way from the one-loop self energy and
polarization tensor in the infrared limit thus rendering this limit finite. All
spectral width parameters are found to be proportional to $g T$. We reproduce
the well known expression for the electric ``Debye''-screening mass. The
transverse (magnetic) gluons (photons) are found to interact only at nonzero
momentum or energy, at least to leading order. As a consequence their spectral
function acquires a width only away from the infrared limit. Finally, plasmon
modes are determined and found to be strongly damped.",9501203v1
1995-12-12,Bubble Collisions and Defect Formation in a Damping Environment,"Within the context of a first-order phase transition in the early Universe,
we study the collision process for vacuum bubbles expanding in a plasma. The
effects of the plasma are simulated by introducing a damping term in the
equations of motion for a $U(1)$ global field. We find that Lorentz-contracted
spherically symmetric domain walls adequately describe the overdamped motion of
the bubbles in the thin wall approximation, and study the process of collision
and phase equilibration both numerically and analytically. With an analytical
model for the phase propagation in 1+1 dimensions, we prove that the phase
waves generated in the bubble merging are reflected by the walls of the true
vacuum cavity, giving rise to a long-lived oscillating state that delays the
phase equilibration. The existence of such a state in the 3+1 dimensional model
is then confirmed by numerical simulations, and the consequences for the
formation of vortices in three-bubble collisions are considered.",9512290v1
1996-09-02,The quasiparticle structure of hot gauge theories,"The study of the ultrarelativistic plasmas in perturbation theory is plagued
with infrared divergences which are not eliminated by the screening
corrections. They affect, in particular, the computation of the lifetime of the
elementary excitations, thus casting doubt on the validity of the quasiparticle
picture. We show that, for Abelian plasmas at least, the infrared problem of
the damping rate can be solved by a non-perturbative treatment based on the
Bloch-Nordsieck approximation. The resulting expression of the fermion
propagator is free of divergences, and exhibits a {\it non-exponential} damping
at large times: $S_R(t)\sim \exp\{-\alpha T t \ln\omega_pt\}$, where
$\omega_p=gT/3$ is the plasma frequency and $\alpha=g^2/4\pi$.",9609225v1
1996-10-18,Finiteness of Hot Classical Scalar Field Theory and the Plasmon Damping Rate,"We investigate the renormalizability of the classical $\phi^4$ theory at
finite temperature. We calculate the time-dependent two point function to two
loop order and show that it can be rendered finite by the counterterms of the
classical static theory. As an application the classical plasmon damping rate
is found to be $\gamma = \lambda^2 T^2/1536 \pi m$. When we use the high
temperature expression for $m$ given by dimensional reduction, the rate is
found to agree with the quantum mechanical result.",9610415v2
1996-12-30,Defect Formation in First Order Phase Transitions with Damping,"Within the context of first order phase transitions in the early universe, we
study the influence of a coupling between the (global U(1)) scalar driving the
transition and the rest of the matter content of the theory. The effect of the
coupling on the scalar is simulated by introducing a damping term in its
equations of motion, as suggested by recent results in the electroweak phase
transition. After a preceeding paper, in which we studied the influence that
this coupling has in the dynamics of bubble collisions and topological defect
formation, we proceed in this paper to quantify the impact of this new effects
on the probability of defect creation per nucleating bubble.",9612487v1
1997-07-28,Plasmon properties in classical lattice gauge theory,"In order to investigate the features of the classical approximation at high
temperatures for real time correlation functions, the plasmon frequencies and
damping rates were recently computed numerically in the SU(2)+Higgs model and
in the pure SU(2) theory. We compare the lattice results with leading order
hard thermal loop resummed perturbation theory. In the broken phase of the
SU(2)+Higgs model, we show that the lattice results can be reproduced and that
the lattices used are too coarse to observe some important plasmon effects. In
the symmetric phase, the main qualitative features of the lattice results can
also be understood. In the pure SU(2) theory, on the other hand, there are
discrepancies which might point to larger Landau and plasmon damping effects
than indicated by perturbation theory.",9707489v2
1998-09-11,Dynamical renormalization group resummation of finite temperature infrared divergences,"We introduce the method of dynamical renormalization group to study
relaxation and damping out of equilibrium directly in real time and applied it
to the study of infrared divergences in scalar QED. This method allows a
consistent resummation of infrared effects associated with the exchange of
quasistatic transverse photons and leads to anomalous logarithmic relaxation of
the form $e^{-\alpha T t \ln[t/t_0]}$ which prevents a quasiparticle
interpretation of charged collective excitations at finite temperature. The
hard thermal loop resummation program is incorporated consistently into the
dynamical renormalization group yielding a picture of relaxation and damping
phenomena in a plasma in real time that trascends the conceptual limitations of
the quasiparticle picture and other type of resummation schemes. We derive a
simple criterion for establishing the validity of the quasiparticle picture to
lowest order.",9809346v2
1999-02-12,Beyond HTL: The Classical Kinetic Theory of Landau Damping for Selfinteracting Scalar Fields in the Broken Phase,"The effective theory of low frequency fluctuations of selfinteracting scalar
fields is constructed in the broken symmetry phase. The theory resulting from
integrating fluctuations with frequencies much above the spontanously generated
mass scale $(p_0>>M)$ is found to be local. Non-local dynamics, especially
Landau damping emerges under the effect of fluctuations in the $p_0 \sim M$
region. A kinetic theory of relativistic scalar gas particles interacting via
their locally variable mass with the low frequency scalar field is shown to be
equivalent to this effective field theory for scales below the characteristic
mass, that is beyond the accuracy of the Hard Thermal Loop (HTL) approximation.",9902331v1
2000-04-05,A consistent nonperturbative approach to thermal damping-rates,"We propose a nonperturbative scheme for the calculation of thermal
damping-rates using exact renormalization group (RG)-equations. Special
emphasis is put on the thermal RG where first results for the rate were given
in M. Pietroni, Phys. Rev. Lett. 81 (1998), 2424. We point out that in order to
obtain a complete result that also reproduces the known perturbative behaviour
one has to take into account effects that were neglected in the work cited
above. We propose a well-defined way of doing the calculations that reproduces
perturbation theory in lowest order but goes considerably beyond perturbative
results and should be applicable also at second order phase-transitions.",0004039v2
2000-06-09,Random values of the cosmological constant,"One way that an anthropic selection mechanism may be manifest in a physical
theory involves multiple domains in the universe with different values of the
physical parameters. If this mechanism is to be relevant for understanding the
small observed value of the cosmological constant, it may involve a mechanism
by which some contributions to the cosmological constant can be fixed at a
continuous range of values in the different domains. I study the properties of
four possible mechanisms, including the possibility of the Hubble damping of a
scalar field with an extremely flat potential. Another interesting possibility
involves fixed random values of non-dynamical form fields, and a cosmological
mechanism is suggested. This case raises the possibility of anthropic selection
of other parameters in addition. Further requirements needed for a consistent
cosmology are discussed.",0006088v2
2000-07-07,Finite pion width effects on the rho--meson,"We study the influence of the finite damping width of pions on the in-medium
properties of the rho-meson in an interacting meson gas model at finite
temperature. Using vector dominance also implications on the resulting dilepton
spectra from the decay of the rho-meson are presented. A set of coupled Dyson
equations with self energies up to the sunset diagram level is solved self
consistently. Following a Phi-derivable scheme the self energies are
dynamically determined by the self consistent propagators. Some problems
concerning the self consistent treatment of vector or gauge bosons on the
propagator level, in particular, if coupled to currents arising from particles
with a sizable damping width, are discussed.",0007070v3
2000-08-31,New Regime for Dense String Networks,"We uncover a new transient regime that reconciles the apparent inconsistency
of the Martins Shellard one scale damped string evolution model with the
initial conditions predicted by the Kibble mechanism for string formation in a
second order phase transition. This regime carries (in a short cosmic time
$\sim .1 t_c$) the dense string network created by the Kibble {\it{mechanism}}
to the (dilute) Kibble {\it{regime}} in which friction dominated strings remain
till times $t_* \sim (M_P/T_c)^2 t_c$. This is possible beacause the cosmic
time at the phase transition ($t_c$) is much larger than the damping time scale
$l_f\sim T_c^2/T^3$. Our result has drastic implications for various non-GUT
scale string mediated mechanisms.}",0008330v1
2001-01-25,The Fermion Boson Interaction Within the Linear Sigma Model at Finite Temperature,"We reinvestigate the interaction of massless fermions with massless bosons at
finite temperature. Specifically, we calculate the self-energy of massless
fermions due the interaction with massless bosons at high temperature, which is
the region where thermal effects are maximal. The calculations are concentrated
in the limit of vanishing fermion three momentum and after considering the
effective fermion and boson dressed masses, we obtain the damping rate of the
fermion up to order $g^3$. It is shown that in the limit $k_0 \ll T$ the
fermion acquire a thermal mass of order $gT$ and the leading term of the
fermion damping rate is of order $g^2T+g^3T$.",0101283v3
2001-11-02,Quark Number Susceptibility in Hard Thermal Loop Approximation,"We calculate the quark number susceptibility in the deconfined phase of QCD
using the hard thermal loop (HTL) approximation for the quark propagator. This
improved perturbation theory takes into account important medium effects such
as thermal quark masses and Landau damping in the quark-gluon plasma. We
explicitly show that the Landau damping part in the quark propagator for
spacelike quark momenta does not contribute to the quark number susceptibility
due to the quark number conservation. We find that the quark number
susceptibility only due to the collective quark modes deviates from that of
free one around the critical temperature but approaches free results at
infinite temperature limit. The results are in conformity with recent lattice
calculations.",0111022v4
2001-12-29,Damped $\sin(β-α)$ of Higgs couplings and the lightest Higgs production at $γγ$ colliders in MSSM,"In the decoupling limit, $M^2_{A^0} \gg M^2_Z$, the heavy CP-even, CP-odd and
charged Higgs boson masses are nearly degenerate, $\sin(\beta-\alpha)$
approaches 1, and the lightest CP-even Higgs boson almost displays the same
properties as the Standard Model Higgs boson. But the stop and sbottom sector
can change this pattern through radiative corrections. We find that there are
parameter regions at small, moderate and large $\tan\beta$ in MSSM under
experimental constraints of $(g-2)_{\mu}$ and $b\to s\gamma$, where
$\sin^2(\beta-\alpha)$ is damped (say below 0.8), which has a significant
effect on Higgs couplings $g_{h^0VV} (V=W^\pm,Z^0)$ and $g_{h^0\gamma\gamma}$.
We discuss its impact on the lightest CP-even Higgs production at
$\gamma\gamma$ colliders.",0112356v1
2004-05-31,Gauge dependence of the fermion quasiparticle poles in hot gauge theories,"The gauge dependence of the complex fermion quasiparticle poles corresponding
to soft collective excitations is studied in hot gauge theories at one-loop
order and next-to-leading order in the high-temperature expansion, with a view
towards going beyond the leading order hard thermal loops and resummations
thereof. We find that for collective excitations of momenta k ~ eT the
dispersion relations are gauge independent, but the corresponding damping rates
are gauge dependent. For k<<eT and in k \to 0 limit, both the dispersion
relations and the damping rates are found to be gauge dependent. The gauge
dependence of the position of the complex quasiparticle poles signals the need
for resummation. Possible cancellation of the leading gauge dependence at
two-loop order in the case of QED is briefly discussed.",0406002v2
2004-11-09,Numerical investigation of friction in inflaton equations of motion,"The equation of motion for the expectation value of a scalar quantum field
does not have the local form that is commonly assumed in studies of
inflationary cosmology. We have recently argued that the true, temporally
non-local equation of motion does not possess a time-derivative expansion and
that the conversion of inflaton energy into particles is not, in principle,
described by the friction term estimated from linear response theory. Here, we
use numerical methods to investigate whether this obstacle to deriving a local
equation of motion is purely formal, or of some quantitative importance. Using
a simple scalar-field model, we find that, although the non-equilibrium
evolution can exhibit significant damping, this damping is not well described
by the local equation of motion obtained from linear response theory. It is
possible that linear response theory does not apply to the situation we study
only because thermalization turns out to be slow, but we argue that that the
large discrepancies we observe indicate a failure of the local approximation at
a more fundamental level.",0411130v1
2006-03-03,Damping of supernova neutrino transitions in stochastic shock-wave density profiles,"Supernova neutrino flavor transitions during the shock wave propagation are
known to encode relevant information not only about the matter density profile
but also about unknown neutrino properties, such as the mass hierarchy (normal
or inverted) and the mixing angle theta_13. While previous studies have
focussed on ""deterministic"" density profiles, we investigate the effect of
possible stochastic matter density fluctuations in the wake of supernova shock
waves. In particular, we study the impact of small-scale fluctuations on the
electron (anti)neutrino survival probability, and on the observable spectra of
inverse-beta-decay events in future water-Cherenkov detectors. We find that
such fluctuations, even with relatively small amplitudes, can have significant
damping effects on the flavor transition pattern, and can partly erase the
shock-wave imprint on the observable time spectra, especially for
sin^2(theta_13) > O(10^-3).",0603033v2
2006-08-11,Constraining SuperWIMPy and Warm Subhalos with Future Submillilensing,"We propose to observe QSO-galaxy strong lens systems to give a new constraint
on the damping scale of the initial fluctuations. We find that the future
observation of submilliarc scale astrometric shifts of the multiple lensed
images of QSOs would find \sim 10^{(3-9)} M_{\odot} subhalos inside the
macrolens halo. The superweakly interacting massive particles (superWIMPs)
produced from a WIMP decay and the warm dark matter (WDM) particles that
predict a comoving damping scale larger than \sim 2 kpc can be constrained if
\sim 10^3 M_{\odot} subhalos are detected.",0608126v2
2006-11-15,Time-to-Space Conversion in Neutrino Oscillations,"We study the neutrino oscillation problem in the framework of the wave packet
formalism. The neutrino state is described by a packet located initially in a
region S (source) and detected in another region D at a distance R from S. We
examine how the oscillation probability as a function of variable R can be
derived from he oscillation probability as a function of time t, the latter
being found by using the Schrodinger equation. We justify the known
prescription ""t --> R/c"" without referring to a specific form of the neutrino
wave packet and only assuming the finiteness of its support. The effect of the
oscillation damping at large R is revealed. For an illustration, an explicit
expression for the damping factor is obtained using Gaussian packet.",0611202v1
1991-09-26,The Damping of Energetic Gluons and Quarks in High-Temperature QCD,"When a gluon or a quark is sent through the hot QCD plasma it can be absorbed
into the ambient heat bath and so can acquire an effective lifetime. At high
temperatures and for weak couplings the inverse lifetime, or damping rate, for
energetic quarks and transverse gluons, (those whose momenta satisfy $|\p| \gg
gT$) is given by $\gamma(\p) = c\; g^2 \log\left({1\over g}\right)\; T +
O(g^2T)$. We show that very simple arguments suffice both to fix the numerical
coefficient, $c$, in this expression and to show that the $O(g^2T)$
contribution is incalculable in perturbation theory without further
assumptions. For QCD with $N_c$ colours we find (expressed in terms of the
casimir invariants $C_a=N_c$ and $C_f=(N_c^2-1)/(2N_c)$): $c_g=+{C_a\over
4\pi}$ for gluons and $c_q=+{C_f\over 4\pi}$ for quarks. These numbers agree
with the more detailed calculations of Pisarski \etal\ but disagree with those
of Lebedev and Smilga. The simplicity of the calculation also permits a direct
verification of the gauge-invariance and physical sign of the result.",9109051v1
1998-09-11,Damping and reaction rates and wave function renormalization of fermions in hot gauge theories,"We examine the relation between the damping rate of a chiral fermion mode
propagating in a hot plasma and the rate at which the mode approaches
equilibrium. We show how these two quantities, obtained from the imaginary part
of the fermion self-energy, are equal when the reaction rate is defined using
the appropriate wave function of the mode in the medium. As an application, we
compute the production rate of hard axions by Compton-like scattering processes
in a hot QED plasma starting from both, the axion self-energy and the electron
self-energy. We show that the latter rate coincides with the former only when
this is computed using the corresponding medium spinor modes.",9809083v2
2003-12-28,A mechanism of the large-scale damping in the CMB anisotropy,"We present a mechanism through which a certain class of short-distance cutoff
affects the CMB anisotropies at large angular scales. Our analysis is performed
in two steps. The first is given in an intuitive way, using the property of the
inflationary universe that quantum fluctuations of an inflaton field become
classical after crossing the Hubble horizon. We give a condition for a cutoff
to yield a damping on large scales, and show that the holographic cutoff
introduced in the preceding paper (hep-th/0307029) does satisfy the condition.
The second analysis is carried out by setting an initial condition such that
each mode of inflaton starts as the vacuum fluctuation of the Hamiltonian when
being released from the constraint of cutoff. The first intuitive discussion is
then shown to be correct qualitatively.",0312298v7
2005-03-03,Scalar field perturbations of the Schwarzschild black hole in the Gödel Universe,"We investigate the scalar field perturbations of the 4+1-dimensional
Schwarzschild black hole immersed in a G\""{o}del Universe, described by the
Gimon-Hashimoto solution.This may model the influence of the possible rotation
of the Universe upon the radiative processes near a black hole. In the regime
when the scale parameter $j$ of the G\""{o}del background is small, the
oscillation frequency is linearly decreasing with $j$, while the damping time
is increasing. The quasinormal modes are damping, implying stability of the
Schwarzschild-G\""{o}del space-time against scalar field perturbations. The
approximate analytical formula for large multipole numbers is found.",0503029v2
2005-06-28,Liouville Decoherence in a Model of Flavour Oscillations in the presence of Dark Energy,"We study in some detail the master equation, and its solution in a simplified
case modelling flavour oscillations of a two-level system, stemming from the
Liouville-string approach to quantum space time foam. In this framework we
discuss the appearance of diffusion terms and decoherence due to the
interaction of low-energy string matter with space-time defects, such as
D-particles in the specific model of ``D-particle foam'', as well as dark
energy contributions. We pay particular attention to contrasting the decoherent
role of a cosmological constant in inducing exponential quantum damping in the
evolution of low-energy observables, such as the probability of flavour
oscillations, with the situation where the dark energy relaxes to zero for
asymptotically large times, in which case such a damping is absent. Our
findings may be of interest to (astrophysical) tests of quantum space-time foam
models in the not-so-distant future.",0506242v1
2005-08-25,The Dynamics of Small Instanton Phase Transitions,"The small instanton transition of a five-brane colliding with one end of the
S1/Z2 interval in heterotic M-theory is discussed, with emphasis on the
transition moduli, their potential function and the associated non-perturbative
superpotential. Using numerical methods, the equations of motion of these
moduli coupled to an expanding Friedmann-Robertson-Walker spacetime are solved
including non-perturbative interactions. It is shown that the five-brane
collides with the end of the interval at a small instanton. However, the moduli
then continue to evolve to an isolated minimum of the potential, where they are
trapped by gravitational damping. The torsion free sheaf at the small instanton
is ``smoothed out'' into a vector bundle at the isolated minimum, thus
dynamically completing the small instanton phase transition. Radiative damping
at the origin of moduli space is discussed and shown to be insufficient to trap
the moduli at the small instanton point.",0508190v2
2006-11-21,Renormalization group study of damping in nonequilibrium field theory,"In this paper we shall study whether dissipation in a $\lambda\phi^{4}$ may
be described, in the long wavelength, low frequency limit, with a simple Ohmic
term $\kappa\dot{\phi}$, as it is usually done, for example, in studies of
defect formation in nonequilibrium phase transitions. We shall obtain an
effective theory for the long wavelength modes through the coarse graining of
shorter wavelengths. We shall implement this coarse graining by iterating a
Wilsonian renormalization group transformation, where infinitesimal momentum
shells are coarse-grained one at a time, on the influence action describing the
dissipative dynamics of the long wavelength modes. To the best of our
knowledge, this is the first application of the nonequilibrium renormalization
group to the calculation of a damping coefficient in quantum field theory.",0611222v1
2006-02-16,Exit from a basin of attraction for stochastic weakly damped nonlinear Schrödinger equations,"We consider weakly damped nonlinear Schr\""odinger equations perturbed by a
noise of small amplitude. The small noise is either complex and of additive
type or real and of multiplicative type. It is white in time and colored in
space. Zero is an asymptotically stable equilibrium point of the deterministic
equations. We study the exit from a neighborhood of zero, invariant by the flow
of the deterministic equation, in $\xLtwo$ or in $\xHone$. Due to noise, large
fluctuations off zero occur. Thus, on a sufficiently large time scale, exit
from these domains of attraction occur. A formal characterization of the small
noise asymptotic of both the first exit times and the exit points is given.",0602350v1
2006-04-07,"Quasi-periodic attractors, Borel summability and the Bryuno condition for strongly dissipative systems","We consider a class of ordinary differential equations describing
one-dimensional analytic systems with a quasi-periodic forcing term and in the
presence of damping. In the limit of large damping, under some generic
non-degeneracy condition on the force, there are quasi-periodic solutions which
have the same frequency vector as the forcing term. We prove that such
solutions are Borel summable at the origin when the frequency vector is either
any one-dimensional number or a two-dimensional vector such that the ratio of
its components is an irrational number of constant type. In the first case the
proof given simplifies that provided in a previous work of ours. We also show
that in any dimension $d$, for the existence of a quasi-periodic solution with
the same frequency vector as the forcing term, the standard Diophantine
condition can be weakened into the Bryuno condition. In all cases, under a
suitable positivity condition, the quasi-periodic solution is proved to
describe a local attractor.",0604162v1
2006-06-30,Uniform attractors for non-autonomous wave equations with nonlinear damping,"We consider dynamical behavior of non-autonomous wave-type evolutionary
equations with nonlinear damping, critical nonlinearity, and time-dependent
external forcing which is translation bounded but not translation compact
(i.e., external forcing is not necessarily time-periodic, quasi-periodic or
almost periodic). A sufficient and necessary condition for the existence of
uniform attractors is established using the concept of uniform asymptotic
compactness. The required compactness for the existence of uniform attractors
is then fulfilled by some new a priori estimates for concrete wave type
equations arising from applications. The structure of uniform attractors is
obtained by constructing a skew product flow on the extended phase space for
the norm-to-weak continuous process.",0606776v1
2001-04-17,Scattering and radiation damping in gyroscopic Lorentz electrodynamic,"Relativistic massive Lorentz electrodynamics (LED) is studied in a
``gyroscopic setup'' where the electromagnetic fields and the particle spin are
the only dynamical degrees of freedom.
  A rigorous proof of the global existence and uniqueness of the dynamics is
given for essentially the whole range of field strengths reasonable for a
classical theory.
  For a class of rotation-reflection symmetric field data it is shown that the
dynamics also satisfies the world-line equations for a non-moving Lorentz
electron, thus furnishing rigorous solutions of the full system of nonlinear
equations of LED.
  The previously proven soliton dynamics of the Lorentz electron is further
illucidated by showing that rotation-reflection symmetric deviations from the
soliton state of the renormalized particle die out exponentially fast through
radiation damping if the electrostatic mass is smaller than the bare rest mass.",0104023v2
2002-06-18,Hamiltonian and Linear-Space Structure for Damped Oscillators: I. General Theory,"The phase space of $N$ damped linear oscillators is endowed with a bilinear
map under which the evolution operator is symmetric. This analog of
self-adjointness allows properties familiar from conservative systems to be
recovered, e.g., eigenvectors are ""orthogonal"" under the bilinear map and obey
sum rules, initial-value problems are readily solved and perturbation theory
applies to the_complex_ eigenvalues. These concepts are conveniently
represented in a biorthogonal basis.",0206026v2
2002-06-17,Hamiltonian and Linear-Space Structure for Damped Oscillators: II. Critical Points,"The eigenvector expansion developed in the preceding paper for a system of
damped linear oscillators is extended to critical points, where eigenvectors
merge and the time-evolution operator $H$ assumes a Jordan-block structure. The
representation of the bilinear map is obtained in this basis. Perturbations
$\epsilon\Delta H$ around an $M$-th order critical point generically lead to
eigenvalue shifts $\sim\epsilon^{1/M}$ dependent on only_one_ matrix element,
with the $M$ eigenvalues splitting in equiangular directions in the complex
plane. Small denominators near criticality are shown to cancel.",0206027v2
2002-06-22,Yank and Hooke's constant group theoretically,"We study the second central extension of the (1+1) Aristotle Lie.We find that
the first central extension admit four orbits on the dual of second central
extension of the (1+1) Aristotle Lie group.The generic orbit is characterised
by a Hooke's constant k and a yank y.If the physics of the orbit is studied
with respect the evolution in time,it represents an elementary system with
internal energy U in a posotion-momentum under the conjugation of a Hooke's
force and a damping one proportional to the velocity as in particle
mechanics.If the physics of the orbit is studied with respect the evolution in
space, it represents an elementary system with an internal momentum P under the
conjugation of a kind of Hooke's force and a damping one proportional to a
slowness, slowness usually used in time travel waves.",0206038v1
2004-02-24,Classical harmonic oscillator with Dirac-like parameters and possible applications,"We obtain a class of parametric oscillation modes that we call K-modes with
damping and absorption that are connected to the classical harmonic oscillator
modes through the ""supersymmetric"" one-dimensional matrix procedure similar to
relationships of the same type between Dirac and Schroedinger equations in
particle physics. When a single coupling parameter, denoted by K, is used, it
characterizes both the damping and the dissipative features of these modes.
Generalizations to several K parameters are also possible and lead to
analytical results. If the problem is passed to the physical optics (and/or
acoustics) context by switching from the oscillator equation to the
corresponding Helmholtz equation, one may hope to detect the K-modes as
waveguide modes of specially designed waveguides and/or cavities",0402065v2
2000-02-22,Front motion for phase transitions in systems with memory,"We consider the Allen-Cahn equations with memory (a partial
integro-differential convolution equation). The prototype kernels are
exponentially decreasing functions of time and they reduce the
integrodifferential equation to a hyperbolic one, the damped Klein-Gordon
equation. By means of a formal asymptotic analysis we show that to the leading
order and under suitable assumptions on the kernels, the integro-differential
equation behave like a hyperbolic partial differential equation obtained by
considering prototype kernels: the evolution of fronts is governed by the
extended, damped Born-Infeld equation. We also apply our method to a system of
partial integro-differential equations which generalize the classical phase
field equations with a non-conserved order parameter and describe the process
of phase transitions where memory effects are present.",0002039v1
2002-03-01,Excitation of travelling multibreathers in anharmonic chains,"We study the dynamics of the ""externally"" forced and damped Fermi-Pasta-Ulam
(FPU) 1D lattice. The forcing has the spatial symmetry of the Fourier mode with
wavenumber p and oscillates sinusoidally in time with the frequency omega. When
omega is in the phonon band, the p-mode becomes modulationally unstable above a
critical forcing, which we determine analytically in terms of the parameters of
the system. For omega above the phonon band, the instability of the p-mode
leads to the formation of a travelling multibreather, that, in the
low-amplitude limit could be described in terms of soliton solutions of a
suitable driven-damped nonlinear Schroedinger (NLS) equation. Similar
mechanisms of instability could show up in easy-axis magnetic structures, that
are governed by such NLS equations.",0203002v1
2003-01-15,Resonant triad dynamics in weakly damped Faraday waves with two-frequency forcing,"Many of the interesting patterns seen in recent multi-frequency Faraday
experiments can be understood on the basis of three-wave interactions (resonant
triads). In this paper we consider two-frequency forcing and focus on a
resonant triad that occurs near the bicritical point where two pattern-forming
modes with distinct wavenumbers emerge simultaneously. This triad has been
observed directly (in the form of rhomboids) and has also been implicated in
the formation of quasipatterns and superlattices. We show how the symmetries of
the undamped unforced problem (time translation, time reversal, and Hamiltonian
structure) can be used, when the damping is weak, to obtain general scaling
laws and additional qualitative properties of the normal form coefficients
governing the pattern selection process near onset; such features help to
explain why this particular triad is seen only for certain ""low"" forcing
ratios, and predict the existence of drifting solutions and heteroclinic
cycles. We confirm the anticipated parameter dependence of the coefficients and
investigate its dynamical consequences using coefficients derived numerically
from a quasipotential formulation of the Faraday problem due to Zhang and
Vinals.",0301015v1
2003-03-21,Global well-posedness and multi-tone solutions of a class of nonlinear nonlocal cochlear models in hearing,"We study a class of nonlinear nonlocal cochlear models of the transmission
line type, describing the motion of basilar membrane (BM) in the cochlea. They
are damped dispersive partial differential equations (PDEs) driven by time
dependent boundary forcing due to the input sounds. The global well-posedness
in time follows from energy estimates. Uniform bounds of solutions hold in case
of bounded nonlinear damping. When the input sounds are multi-frequency tones,
and the nonlinearity in the PDEs is cubic, we construct smooth quasi-periodic
solutions (multi-tone solutions) in the weakly nonlinear regime, where new
frequencies are generated due to nonlinear interaction. When the input is two
tones at frequencies $f_1$, $f_2$ ($f_1 < f_2$), and high enough intensities,
numerical results illustrate the formation of combination tones at $2 f_1 -f_2$
and $2f_2 -f_1$, in agreement with hearing experiments. We visualize the
frequency content of solutions through the FFT power spectral density of
displacement at selected spatial locations on BM.",0303048v1
2004-05-11,Analytical approach to soliton ratchets in asymmetric potentials,"We use soliton perturbation theory and collective coordinate ansatz to
investigate the mechanism of soliton ratchets in a driven and damped asymmetric
double sine-Gordon equation. We show that, at the second order of the
perturbation scheme, the soliton internal vibrations can couple {\it
effectively}, in presence of damping, to the motion of the center of mass,
giving rise to transport. An analytical expression for the mean velocity of the
soliton is derived. The results of our analysis confirm the internal mode
mechanism of soliton ratchets proposed in [Phys. Rev. E {\bf 65} 025602(R)
(2002)].",0405023v1
2005-02-16,Controlling soliton explosions,"We investigate the dynamics of solitons in generalized Klein-Gordon equations
in the presence of nonlinear damping and spatiotemporal perturbations. We will
present different mechanisms for soliton explosions. We show (both analytically
and numerically) that some space-dependent perturbations or nonlinear damping
can make the soliton internal mode unstable leading to soliton explosion. We
will show that, in some cases, while some conditions are satisfied, the soliton
explodes becoming a permanent, extremely complex, spatiotemporal dynamics. We
believe these mechanisms can explain some of the phenomena that recently have
been reported to occur in excitable media. We present a method for controlling
soliton explosions.",0502033v1
2005-07-22,Global existence in infinite lattices of nonlinear oscillators: The Discrete Klein-Gordon equation,"Pointing out the difference between the Discrete Nonlinear Schr\""odinger
equation with the classical power law nonlinearity-for which solutions exist
globally, independently of the sign and the degree of the nonlinearity, the
size of the initial data and the dimension of the lattice-we prove either
global existence or nonexistence in time, for the Discrete Klein-Gordon
equation with the same type of nonlinearity (but of ``blow-up'' sign), under
suitable conditions on the initial data, and some times on the dimension of the
lattice. The results, consider both the conservative and the linearly damped
lattice. Similarities and differences with the continuous counterparts, are
remarked. We also make a short comment, on the existence of excitation
thresholds, for forced solutions of damped and parametrically driven,
Klein-Gordon lattices.",0507044v5
1992-12-14,Poisson and Porter-Thomas Fluctuations in off-Yrast Rotational Transitions,"Fluctuations associated with stretched E2 transitions from high spin levels
in nuclei around $^{168}$Yb are investigated by a cranked shell model extended
to include residual two-body interactions. It is found that the gamma-ray
energies behave like random variables and the energy spectra show the Poisson
fluctuation, in the cranked mean field model without the residual interaction.
With two-body residual interaction included, discrete transition pattern with
unmixed rotational bands is still valid up to around 600 keV above yrast, in
good agreement with experiments. At higher excitation energy, a gradual onset
of rotational damping emerges. At 1.8 MeV above yrast, complete damping is
observed with GOE type fluctuations for both energy levels and transition
strengths(Porter-Thomas fluctuations).",9212006v1
1993-11-25,Microscopic analysis of two-body correlations in light nuclei,"Within a nonperturbative dynamical two-body approach - based on coupled
equations of motion for the one-body density matrix and the two-body
correlation function - we study the distribution of occupation numbers in a
correlated system close to the groundstate, the relaxation of single-particle
excitations and the damping of collective modes. For this purpose the nonlinear
equations of motion are solved numerically within a finite oscillator basis for
the first time adopting short-range repulsive and long-range attractive
two-body forces. We find in all cases that the formation of long- and
short-range correlations and their mixing is related to the long- and
short-range part of the nucleon-nucleon interaction which dominate the
resummation of loop or ladder diagrams, respectively. However, the proper
description of relaxation or damping phenomena is found to require both types
of diagrams as well as the mixed terms simultaneously.",9311031v1
1997-03-26,A self-consistent treatment of damped motion for stable and unstable collective modes,"We address the dynamics of damped collective modes in terms of first and
second moments. The modes are introduced in a self-consistent fashion with the
help of a suitable application of linear response theory. Quantum effects in
the fluctuations are governed by diffusion coefficients D_{\mu\nu}. The latter
are obtained through a fluctuation dissipation theorem generalized to allow for
a treatment of unstable modes. Numerical evaluations of the D_{\mu\nu} are
presented. We discuss briefly how this picture may be used to describe global
motion within a locally harmonic approximation. Relations to other methods are
discussed, like ""dissipative tunneling"", RPA at finite temperature and
generalizations of the ""Static Path Approximation"".",9703056v1
1997-04-24,A Simple Mode on a Highly Excited Background: Collective Strength and Damping in the Continuum,"Simple states, such as isobaric analog states or giant resonances, embedded
into continuum are typical for mesoscopic many-body quantum systems. Due to the
coupling to compound states in the same energy range, a simple mode acquires a
damping width (""internal"" dynamics). When studied experimentally with the aid
of various reactions, such states reveal enhanced cross sections in specific
channels at corresponding resonance energies (""external"" dynamics which include
direct decay of a simple mode and decays of intrinsic compound states through
their own channels). We consider the interplay between internal and external
dynamics using a general formalism of the effective nonhermitian hamiltonian
and looking at the situation both from ""inside"" (strength functions and
spreading widths) and from ""outside"" (S-matrix, cross sections and delay
times). The restoration of isospin purity and disappearance of the collective
strength of giant resonances at high excitation energy are discussed as
important particular manifestations of this complex interplay.",9704055v1
1998-02-27,New collective mode due to collisional coupling,"Starting from a nonmarkovian conserving relaxation time approximation for
collisions we derive coupled dispersion relations for asymmetric nuclear
matter. The isovector and isoscalar modes are coupled due to asymmetric nuclear
meanfield acting on neutrons and protons differently. A further coupling is
observed by collisional correlations. The latter one leads to the appearance of
a new soft mode besides isoscalar and isovector modes in the system. We suggest
that this mode might be observable in asymmetric systems. This soft mode
approaches the isovector mode for high temperatures. At the same time the
isovector mode remains finite and approaches a constant value at higher
temperatures showing a transition from zero sound like damping to first sound.
The damping of the new soft mode is first sound like at all temperatures.",9802083v1
1998-10-12,Response function beyond mean field of neutron-rich nuclei,"The damping of single-particle and collective motion in exotic isotopes is a
new topic and its study may shed light on basic problems of nuclear dynamics.
For instance, it is known that nuclear structure calculations are not able, as
a rule, to account completely for the empirical single-particle damping. In
this contribution, we present calculations of the single-particle self-energy
in the case of the neutron-rich light nucleus $^{28}$O, by taking proper care
of the continuum, and we show that there are important differences with the
case of nuclei along the valley of stability.",9810033v1
1999-04-14,Scaling Analysis of Fluctuating Strength Function,"We propose a new method to analyze fluctuations in the strength function
phenomena in highly excited nuclei. Extending the method of multifractal
analysis to the cases where the strength fluctuations do not obey power scaling
laws, we introduce a new measure of fluctuation, called the local scaling
dimension, which characterizes scaling behavior of the strength fluctuation as
a function of energy bin width subdividing the strength function. We discuss
properties of the new measure by applying it to a model system which simulates
the doorway damping mechanism of giant resonances. It is found that the local
scaling dimension characterizes well fluctuations and their energy scales of
fine structures in the strength function associated with the damped collective
motions.",9904037v1
1999-07-07,Pair creation: back-reactions and damping,"We solve the quantum Vlasov equation for fermions and bosons, incorporating
spontaneous pair creation in the presence of back-reactions and collisions.
Pair creation is initiated by an external impulse field and the source term is
non-Markovian. A simultaneous solution of Maxwell's equation in the presence of
feedback yields an internal current and electric field that exhibit plasma
oscillations with a period tau_pl. Allowing for collisions, these oscillations
are damped on a time-scale, tau_r, determined by the collision frequency.
Plasma oscillations cannot affect the early stages of the formation of a
quark-gluon plasma unless tau_r >> tau_pl and tau_pl approx. 1/Lambda_QCD
approx 1 fm/c.",9907027v1
2000-10-23,Barrier penetration and rotational damping of thermally excited superdeformed nuclei,"We construct a microscopic model of thermally excited superdeformed states
that describes both the barrier penetration mechanism, leading to the decay-out
transitions to normal deformed states, and the rotational damping causing
fragmentation of rotational E2 transitions. We describe the barrier penetration
by means of a tunneling path in the two-dimensional deformation energy surface,
which is calculated with the cranked Nilsson-Strutinsky model. The individual
excited superdeformed states and associated E2 transition strengths are
calculated by the shell model diagonalization of the many-particle many-hole
excitations interacting with the delta-type residual two-body force. The effect
of the decay-out on the excited superdeformed states are discussed in detail
for $^{152}$Dy, $^{143}$Eu and $^{192}$Hg.",0010074v1
1996-02-22,Stability of Travelling Waves for a Damped Hyperbolic Equation,"We consider a nonlinear damped hyperbolic equation in $\real^n$, $1 \le n \le
4$, depending on a positive parameter $\epsilon$. If we set $\epsilon=0$, this
equation reduces to the well-known Kolmogorov-Petrovski-Piskunov equation. We
remark that, after a change of variables, this hyperbolic equation has the same
family of one-dimensional travelling waves as the KPP equation. Using various
energy functionals, we show that, if $\epsilon >0$, these fronts are locally
stable under perturbations in appropriate weighted Sobolev spaces. Moreover,
the decay rate in time of the perturbed solutions towards the front of minimal
speed $c=2$ is shown to be polynomial. In the one-dimensional case, if
$\epsilon < 1/4$, we can apply a Maximum Principle for hyperbolic equations and
prove a global stability result. We also prove that the decay rate of the
perturbated solutions towards the fronts is polynomial, for all $c > 2$.",9602004v1
1998-09-18,Stability of Propagating Fronts in Damped Hyperbolic Equations,"We consider the damped hyperbolic equation in one space dimension $\epsilon
u_{tt} + u_t = u_{xx} + F(u)$, where $\epsilon$ is a positive, not necessarily
small parameter. We assume that $F(0)=F(1)=0$ and that $F$ is concave on the
interval $[0,1]$. Under these assumptions, our equation has a continuous family
of monotone propagating fronts (or travelling waves) indexed by the speed
parameter $c \ge c_*$. Using energy estimates, we first show that the
travelling waves are locally stable with respect to perturbations in a weighted
Sobolev space. Then, under additional assumptions on the non-linearity, we
obtain global stability results using a suitable version of the hyperbolic
Maximum Principle. Finally, in the critical case $c = c_*$, we use self-similar
variables to compute the exact asymptotic behavior of the perturbations as $t
\to +\infty$. In particular, setting $\epsilon = 0$, we recover several
stability results for the travelling waves of the corresponding parabolic
equation.",9809007v1
1999-05-28,Existence threshold for the ac-driven damped nonlinear Schrödinger solitons,"It has been known for some time that solitons of the externally driven,
damped nonlinear Schr\""odinger equation can only exist if the driver's
strength, $h$, exceeds approximately $(2/ \pi) \gamma$, where $\gamma$ is the
dissipation coefficient. Although this perturbative result was expected to be
correct only to the leading order in $\gamma$, recent studies have demonstrated
that the formula $h_{thr}= (2 /\pi) \gamma$ gives a remarkably accurate
description of the soliton's existence threshold prompting suggestions that it
is, in fact, exact. In this note we evaluate the next order in the expansion of
$h_{thr}(\gamma)$ showing that the actual reason for this phenomenon is simply
that the next-order coefficient is anomalously small: $h_{thr}=(2/ \pi) \gamma
+ 0.002 \gamma^3$. Our approach is based on a singular perturbation expansion
of the soliton near the turning point; it allows to evaluate $h_{thr}(\gamma)$
to all orders in $\gamma$ and can be easily reformulated for other perturbed
soliton equations.",9906001v1
1996-10-01,Exact time evolution and master equations for the damped harmonic oscillator,"Using the exact path integral solution for the damped harmonic oscillator it
is shown that in general there does not exist an exact dissipative Liouville
operator describing the dynamics of the oscillator for arbitrary initial bath
preparations. Exact non-stationary Liouville operators can be found only for
particular preparations. Three physically meaningful examples are examined. An
exact new master equation is derived for thermal initial conditions. Second,
the Liouville operator governing the time-evolution of equilibrium correlations
is obtained. Third, factorizing initial conditions are studied. Additionally,
one can show that there are approximate Liouville operators independent of the
initial preparation describing the long time dynamics under appropriate
conditions. The general form of these approximate master equations is derived
and the coefficients are determined for special cases of the bath spectral
density including the Ohmic, Drude and weak coupling cases. The connection with
earlier work is discussed.",9610001v1
1999-01-09,Cluster ionization via two-plasmon excitation,"We calculate the two-photon ionization of clusters for photon energies near
the surface plasmon resonance. The results are expressed in terms of the
ionization rate of a double plasmon excitation, which is calculated
perturbatively. For the conditions of the experiment by Schlipper et al., we
find an ionization rate of the order of 0.05-0.10 fs^(-1). This rate is used to
determine the ionization probability in an external field in terms of the
number of photons absorbed and the duration of the field. The probability also
depends on the damping rate of the surface plasmon. Agreement with experiment
can only be achieved if the plasmon damping is considerably smaller than its
observed width in the room-temperature single-photon absorption spectrum.",9901008v1
2000-08-01,Rectangular Waveguide HOM Couplers for a TESLA Superstructure,"Some modifications of a Rectangular Waveguide HOM couplers for TESLA
superstructure have been investigated. These RWG HOM couplers are to be
installed between the cavities of the superstructure and also at the both ends
of it. We investigated a RWG HOM coupler attached to the beam pipe through the
slots orientated along beam pipe axis (longitudinal slots), perpendicular to it
(azimutal slots) and at some angle to this axis. For dipole modes of both
polarizations damping two RWG in every design were used. This paper presents
the results obtained for scaled-up setup at 3 GHz at room temperature. The
advantages of HOM coupler with longitudinal slots for damping dipole modes and
compact HOM coupler with slots at some angle to the axis are shown. Arrangement
of HOM coupler in cryostat and heating due to HOM and FM losses are presented.
Calculations and design of the feeding RWG coupler for superstructure are also
presented.",0008001v1
2000-08-14,Design of a 3 GHz Accelerator Structure for the CLIC Test Facility (CTF 3) Drive Beam,"For the CLIC two-beam scheme, a high-current, long-pulse drive beam is
required for RF power generation. Taking advantage of the 3 GHz klystrons
available at the LEP injector once LEP stops, a 180 MeV electron accelerator is
being constructed for a nominal beam current of 3.5 A and 1.5 microsecond pulse
length. The high current requires highly effective suppression of dipolar
wakes. Two concepts are investigated for the accelerating structure design: the
""Tapered Damped Structure"" developed for the CLIC main beam, and the ""Slotted
Iris - Constant Aperture"" structure. Both use 4 SiC loads per cell for
effective higher-order mode damping. A full-size prototype of the TDS structure
has been built and tested successfully at full power. A first prototype of the
SICA structure is being built.",0008052v1
2000-08-17,Superconducting Superstructure for the TESLA Collider: New Results,"A new cavity-chain layout has been proposed for the main linac of the TESLA
linear collider. This superstructure-layout is based upon four 7-cell
superconducting standing-wave cavities, coupled by short beam pipes. The main
advantages of the superstructure are an increase in the active accelerating
length in TESLA and a saving in rf components, especially power couplers, as
compared to the present 9-cell cavities. The proposed scheme allows to handle
the field-flatness tuning and the HOM damping at sub-unit level, in contrast to
standard multi-cell cavities. The superstructure-layout is extensively studied
at DESY since 1999. Computations have been performed for the rf properties of
the cavity-chain, the bunch-to-bunch energy spread and multibunch dynamics. A
copper model of the superstructure has been built in order to compare with the
simulations and for testing the field-profile tuning and the HOM damping
scheme. A ""proof of principle"" niobium prototype of the superstructure is now
under construction and will be tested with beam at the TESLA Test Facility in
2001. In this paper we present latest results of these investigations.",0008104v1
2000-08-20,An Investigation of Optimised Frequency Distributions for Damping Wakefields in X-Band Linacs for the NLC,"In the NLC (Next Linear Collider) small misalignments in each of the
individual accelerator structures (or the accelerator cells) will give rise to
wakefields which kick the beam from its electrical axis. This wakefield can
cause BBU (Beam Break Up) or at the very least it will dilute the emittance of
the beam. Several Gaussian detuned structures have been designed and tested [1]
at SLAC and in this paper we explore new distributions with possibly better
damping properties. The progress of the beam through approximately 5,000
structures is monitored in phase space and results on this are presented.
  [1] J.W. Wang et al, TUA03, LINAC2000",0008202v2
2001-04-14,Parameters for a 30 GeV Undulator Test Facility in the FFTB/LCLS,"The parameters for a 30 GeV test beam are outlined for use with an undulator
in the FFTB tunnel where the LCLS will eventually be housed. It is proposed to
use the SLAC linac and damping rings in their present mode of operation for PEP
II injection, where 30 GeV beams are also delivered at 10 Hz to the FFTB. High
peak currents are obtained with the addition of a second bunch compressor in
the linac. In order to minimize the synchrotron radiation induced emittance
growth in the bunch compressor it is necessary to locate the new bunch
compressor at the low-energy end of the linac, just after the damping rings.
The bunch compressor is a duplicate of the LCLS chicane-style bunch compressor.
This test beam would provide an exciting possibility to test LCLS undulator
sections and provide a unique high-brightness source of incoherent X-rays and
begin developing the LCLS experimental station. The facility will also act as a
much needed accelerator test bed for the production, diagnostics and tuning of
very short bunches in preparation for the LCLS after the photo injector is
commissioned.",0104045v1
2001-10-05,Characterization of a Low Frequency Power Spectral Density f^(-gamma) in a Threshold Model,"his study investigates the modifications of the thermal spectrum, at low
frequency, induced by an external damping on a system in heat contact with
internal fluctuating impurities. Those impurities can move among locations and
their oscillations are associated with a loss function depending on the model.
The fluctuation properties of the system are provided by a potential function
shaped by wells, in such a way that jumps between the stationary positions are
allowed. The power spectral density associated with this dissipation mechanism
shows a f^(-gamma)tail. The interest of this problem is that many systems are
characterized by a typical f^(-\gamma) spectral tail at low frequency. The
model presented in this article is based on a threshold type behaviour and its
generality allows applications in several fields. The effects of an external
force, introduced to produce damping, are studied by using both analytical
techniques and numerical simulations. The results obtained with the present
model show that no reduction of the power spectral density is appreciable below
the main peak of the spectral density.",0110019v1
2002-05-13,Damping of electromagnetic waves in low-collision electron-ion plasmas,"Using previously developed method of two-dimensional Laplace transform we
obtain the characteristic equations k(\omega) for electromagnetic waves in
low-collision fully ionized plasma of a plane geometry. We apply here a new,
different from the one used in our previous paper, iteration procedure of
taking into account the Coulomb collisions. The waves are collisionally damping
in the same extent as electromagnetic waves. Despite the different from
previous paper form of the dispersion (poles) equation, the obtained decrements
for fast and slow wave modes coincide with results obtained in our earlier
paper, if one neglects the terms of higher orders in v^2/c^2, (v and c are
electron and light velocities). We point out how one can determine mutually
dependent boundary conditions allowing to eliminate simultaneously both the
backward and kinematical waves for transversal as well as for longitudinal
oscillations.",0205035v2
2002-06-01,Intrabeam scattering analysis of measurements at KEK's ATF damping ring,"We derive a simple relation for estimating the relative emittance growth in x
and y due to intrabeam scattering (IBS) in electron storage rings. We show that
IBS calculations for the ATF damping ring, when using the formalism of
Bjorken-Mtingwa, a modified formalism of Piwinski (where eta squared divided by
beta has been replaced by the dispersion invariant), or a simple high-energy
approximate formula all give results that agree well. Comparing theory,
including the effect of potential well bunch lengthening, with a complete set
of ATF steady-state beam size vs. current measurements we find reasonably good
agreement for energy spread and horizontal emittance. The measured vertical
emittance, however, is larger than theory in both offset (zero current
emittance) and slope (emittance change with current). The slope error indicates
measurement error and/or additional current-dependent physics at the ATF; the
offset error, that the assumed Coulomb log is correct to within a factor of
1.75.",0206003v1
2002-08-24,Wakefield Band Partitioning In Linac Structures,"In the NLC project multiple bunches of electrons and positrons will be
accelerated initially to a centre of mass of 500 GeV and later to 1 TeV or
more. In the process of accelerating 192 bunches within a pulse train,
wakefields are excited which kick the trailing bunches off axis and can cause
luminosity dilution and BBU (Beam Break Up). Several structures to damp the
wakefield have been designed and tested at SLAC and KEK and these have been
found to successfully damp the wakefield [1]. However, these 2pi/3 structures
suffered from electrical breakdown and this has prompted us to explore lower
group velocity structures operating at higher fundamental mode phase advances.
The wakefield partitioning amongst the bands has been found to change markedly
with increased phase advance. Here we report on general trends in the kick
factor and associated wakefield band partitioning in dipole bands as a function
of phase advance of the synchronous mode in linacs. These results are
applicable to both TW (travelling wave) and SW (standing wave) structures [1]
R.M. Jones et al, PAC99, also SLAC-PUB-8103",0208086v1
2003-01-30,Calculation of the Coherent Synchrotron Radiation Impedance from a Wiggler,"Most studies of Coherent Synchrotron Radiation (CSR) have only considered the
radiation from independent dipole magnets. However, in the damping rings of
future linear colliders, a large fraction of the radiation power will be
emitted in damping wigglers. In this paper, the longitudinal wakefield and
impedance due to CSR in a wiggler are derived in the limit of a large wiggler
parameter $K$. After an appropriate scaling, the results can be expressed in
terms of universal functions, which are independent of $K$. Analytical
asymptotic results are obtained for the wakefield in the limit of large and
small distances, and for the impedance in the limit of small and high
frequencies.",0301073v1
2003-10-02,Damping factors for the gap-tooth scheme,"An important class of problems exhibits macroscopically smooth behaviour in
space and time, while only a microscopic evolution law is known. For such
time-dependent multi-scale problems, the gap-tooth scheme has recently been
proposed. The scheme approximates the evolution of an unavailable (in closed
form) macroscopic equation in a macroscopic domain; it only uses appropriately
initialized simulations of the available microscopic model in a number of small
boxes. For some model problems, including numerical homogenization, the scheme
is essentially equivalent to a finite difference scheme, provided we repeatedly
impose appropriate algebraic constraints on the solution for each box. Here, we
demonstrate that it is possible to obtain a convergent scheme without
constraining the microscopic code, by introducing buffers that ""shield"" over
relatively short times the dynamics inside each box from boundary effects. We
explore and quantify the behavior of these schemes systematically through the
numerical computation of damping factors of the corresponding coarse
time-stepper, for which no closed formula is available.",0310014v1
2004-07-31,Propagation of optical excitations by dipolar interactions in metal nanoparticle chains,"Dispersion relations for dipolar modes propagating along a chain of metal
nanoparticles are calculated by solving the full Maxwell equations, including
radiation damping. The nanoparticles are treated as point dipoles, which means
the results are valid only for a/d <= 1/3, where a is the particle radius and d
the spacing. The discrete modes for a finite chain are first calculated, then
these are mapped onto the dispersion relations appropriate for the infinite
chain. Computed results are given for a chain of 50-nm diameter Ag spheres
spaced by 75 nm. We find large deviations from previous quasistatic results:
Transverse modes interact strongly with the light line. Longitudinal modes
develop a bandwidth more than twice as large, resulting in a group velocity
that is more than doubled. All modes for which k_mode <= w/c show strongly
enhanced decay due to radiation damping.",0408003v2
2004-08-22,Tacoma Bridge Failure-- a Physical Model,"The cause of the collapse of the Tacoma Narrows Bridge has been a topic of
much debate and confusion since the day it fell. Many mischaracterizations of
the observed phenomena have limited the widespread understanding of the
problem. Nevertheless, there has always been an abundance of evidence in favour
of a negative damping model. Negative damping, or positive feedback, is
responsible for many large amplitude oscillations observed in many
applications. In this paper, we will explain some well-known examples of
positive feedback. We will then present a feedback model, derived from
fundamental physics, capable of explaining a number of features observed in the
instabilities of many bridge decks. This model is supported by computational,
experimental and historical data.",0408101v1
2004-08-30,Short waves and cyclotron losses in the relativistic gyrokinetic theory,"Radiation damping of the motion of charged particles in relativistic,
optically thin plasmas is described within the framework of the covariant
gyrokinetic theory. It involves description of the collisionless
single-particle dynamics as well as the Vlasov and Maxwell equations both
written in the covariant formulation. The damping causes corrections to the
phase-space trajectory of the particle, as well as to the form of the kinetic
equation itself, due to the failure of conditions of the Liouville theorem.
Both effects result independent of the gyrophase, which is retained as an
ignorable variable. In addition, the applicability range of the covariant
gyrokinetic theory is extended to describe short-wavelength perturbations with
the background of zero parallel electric field. The presented theory is
suitable for description of magnetized, relativistic, collisionless plasmas in
the context of astrophysical or laboratory problems. Non-uniquenes of the
gyrokinetic representation and consequences thereof are discussed.",0408128v1
2004-11-02,Supersymmetric free-damped oscillators: Adaptive observer estimation of the Riccati parameter,"A supersymmetric class of free damped oscillators with three parameters has
been obtained in 1998 by Rosu and Reyes through the factorization of the Newton
equation. The supplementary parameter is the integration constant of the
general Riccati solution. The estimation of the latter parameter is performed
here by employing the recent adaptive observer scheme of Besancon et al., but
applied in a nonstandard form in which a time-varying quantity containing the
unknown Riccati parameter is estimated first. Results of computer simulations
are presented to illustrate the good feasibility of this approach for a case in
which the estimation is not easily accomplished by other means",0411019v2
2004-11-05,Wave-kinetic description of nonlinear photons,"The nonlinear interaction, due to quantum electrodynamical (QED) effects,
between photons is investigated using a wave-kinetic description. Starting from
a coherent wave description, we use the Wigner transform technique to obtain a
set of wave-kinetic equations, the so called Wigner-Moyal equations. These
equations are coupled to a background radiation fluid, whose dynamics is
determined by an acoustic wave equation. In the slowly varying acoustic limit,
we analyse the resulting system of kinetic equations, and show that they
describe instabilities, as well as Landau-like damping. The instabilities may
lead to break-up and focusing of ultra-high intensity multi-beam systems, which
in conjunction with the damping may result in stationary strong field
structures. The results could be of relevance for the next generation of
laser-plasma systems.",0411058v1
2004-12-17,Optimal Determination of the Equilibrium Displacement of a Damped Harmonic Oscillator in the Presence of Thermal Noise,"Using a matched filter technique, we derive the minimum variance, unbiased
estimator for the equilibrium displacement of a damped harmonic oscillator in
thermal equilibrium when interactions with the thermal bath are the leading
source of noise. We compare the variance in this optimal estimator with the
variance in other, commonly used estimators in the presence of pure thermal
noise and pure white noise. We also compare the variance in these estimators
for a mixture of white and thermal noise. This result has implications for
experimental design and the collection and analysis of data.",0412102v1
2006-01-13,Atomic collider into dual-isotope magneto-optical trap,"When two of three pairs of the Gaussian laser beams of a traditional MOT are
misaligned in the racetrack configuration the effective coordinate-dependent
vortex force do arise. Then an atom is accelerated by this vortex force until
its velocity not balanced by the damping force. This situation may produce a
stable ring of revolving atoms of a certain radius. Due to the different
frequency and laser beams intensity dependences of the vortex, damping and
trapping forces it is possible to equalize the radii of two orbiting groups of
atoms in two-species or dual-isotope magneto-optical trap and so to arrange a
continuing collider of cooled atoms with the prescribed relative velocity. A
collider setup for atoms of two different types rotating with different angular
velocities along the same ring-like trajectory into MOT of the conventional
six-beam geometry is proposed and designed on example of two rubidium isotopes
Rb85 and Rb87.",0601097v1
2006-12-07,On some peculiarities of electric field pulse propagation in electron Maxwellian plasma and its back response,"In the spirit of continued study of general plasma wave properties we
investigated the boundary problem with the simplest form of electric field
pulse at the edge x=0 of half-infinite uniform plasma slab with Maxwellian
electron distribution function. In the case of longitudinal electric field
pulse its traveling velocity is essentially other than in the case of harmonic
waves; there is also no back response. In the case of transverse field pulse
there takes place the bimodal propagation rate of the non-damping fast pulse
signal and non-damping weak slow sign reversed pulse signals; some very weak
response (echo) arises with a time delay in the near coordinate zone of
formation of the asymptotical regime.",0612064v4
2007-01-30,Charge Fluctuation of Dust Grain and Its Impact on Dusty-Acoustic Wave Damping,"We consider the influence of dust charge fluctuations on damping of the
dust-ion-acoustic waves. It is assumed that all grains have equal masses but
charges are not constant in time - they may fluctuate in time. The dust charges
are not really independent of the variations in the plasma potentials. All
modes will influence the charging mechanism, and feedback will lead to several
new interesting and unexpected phenomena. The charging of the grains depends on
local plasma characteristics. If the waves disturb these characteristic, then
charging of the grains is affected and the grain charge is modified, with a
resulting feedback on the wave mode. In the case considered here, when the
temperature of electrons is much greater than the temperature of the ions and
the temperature of electrons is not great enough for further ionization of the
ions, we show that attenuation of the acoustic wave depends only on one
phenomenological coefficient",0701336v1
1996-10-29,Bosonic Quantum Codes for Amplitude Damping,"Traditional quantum error correction involves the redundant encoding of k
quantum bits using n quantum bits to allow the detection and correction of any
t bit error. The smallest general t=1 code requires n=5 for k=1. However, the
dominant error process in a physical system is often well known, thus inviting
the question: given a specific error model, can more efficient codes be
devised? We demonstrate new codes which correct just amplitude damping errors
which allow, for example, a t=1, k=1 code using effectively n=4.6. Our scheme
is based on using bosonic states of photons in a finite number of optical
modes. We present necessary and sufficient conditions for the codes, and
describe construction algorithms, physical implementation, and performance
bounds.",9610043v1
1997-01-16,Cooperative loss and decoherence in quantum computation and commuication,"Cooperative effects in the loss (the amplitude damping) and decoherence (the
phase damping) of the qubits (two-state quantum systems) due to the inevitable
coupling to the same environment are investigated. It is found that the qubits
undergo the dissipation coherently in this case. In particular, for a special
kind of input states (called the coherence-preserving states), whose form
depends on the type of the coupling, loss and decoherence in quantum memory are
much reduced. Based on this phenomenon, a scheme by encoding the general input
states of the qubits into the corresponding coherence-preserving states is
proposed for reducing the cooperative loss and decoherence in quantum
computation or communication.",9701020v1
1997-03-22,Preserving coherence in quantum computation by pairing quantum bits,"A scheme is proposed for protecting quantum states from both independent
decoherence and cooperative decoherence. The scheme operates by pairing each
qubit (two-state quantum system) with an ancilla qubit and by encoding the
states of the qubits into the corresponding coherence-preserving states of the
qubit-pairs. In this scheme, the amplitude damping (loss of energy) is
prevented as well as the phase damping (dephasing) by a strategy called the
free-Hamiltonian-elimination We further extend the scheme to include quantum
gate operations and show that loss and decoherence during the gate operations
can also be prevented.",9703040v2
1997-06-10,Perturbative expansions for the fidelities and spatially correlated dissipation of quantum bits,"We construct generally applicable short-time perturbative expansions for some
fidelities, such as the input-output fidelity, the entanglement fidelity, and
the average fidelity. Successive terms of these expansions yield characteristic
times for the damping of the fidelities involving successive powers of the
Hamiltonian. The second-order results, which represent the damping rates of the
fidelities, are extensively discussed. As an interesting application of these
expansions, we use them to study the spatially-correlated dissipation of
quantum bits. Spatial correlations in the dissipation are described by a
correlation function. Explicit conditions are derived for independent
decoherence and for collective decoherence.",9706020v2
1998-05-27,Measurement Process In a Two-Barrier System,"The description of a measuring process, such as that which occurs when a
quantum point contact (QPC) detector is influenced by a nearby external
electron which can take up two possible positions, provides a interesting
application of the method of quantum damping. We find a number of new effects,
due to the complete treatment of phases afforded by the formalism, although our
results are generally similiar to those of other treatments, particularly to
those of Buks et al.
  These are effects depending on the phase shift in the detector, effects which
depend on the direction of the measuring current, and in addition to damping or
dissipative effects, an energy shift of the measured system. In particular, the
phase shift effect leads to the conclusion that there can be effects of
""observation"" even when the two barriers in question pass the same current.
  The nature of the current through the barriers and its statistics is
discussed, giving a description of correlations in the current due to
""measurement"" and of the origin of ""telegraphic"" signals.",9805081v2
1998-10-06,Cumulant expansion for studying damped quantum solitons,"The quantum statistics of damped optical solitons is studied using
cumulant-expansion techniques. The effect of absorption is described in terms
of ordinary Markovian relaxation theory, by coupling the optical field to a
continuum of reservoir modes. After introduction of local bosonic field
operators and spatial discretization pseudo-Fokker-Planck equations for
multidimensional s-parameterized phase-space functions are derived. These
partial differential equations are equivalent to an infinite set of ordinary
differential equations for the cumulants of the phase-space functions.
Introducing an appropriate truncation condition, the resulting finite set of
cumulant evolution equations can be solved numerically. Solutions are presented
in Gaussian approximation and the quantum noise is calculated, with special
emphasis on squeezing and the recently measured spectral photon-number
correlations [Spaelter et al., Phys. Rev. Lett. 81, 786 (1998)].",9810018v3
1999-02-10,Quantum noise in the position measurement of a cavity mirror undergoing Brownian motion,"We perform a quantum theoretical calculation of the noise power spectrum for
a phase measurement of the light output from a coherently driven optical cavity
with a freely moving rear mirror. We examine how the noise resulting from the
quantum back action appears among the various contributions from other noise
sources. We do not assume an ideal (homodyne) phase measurement, but rather
consider phase modulation detection, which we show has a different shot noise
level. We also take into account the effects of thermal damping of the mirror,
losses within the cavity, and classical laser noise. We relate our theoretical
results to experimental parameters, so as to make direct comparisons with
current experiments simple. We also show that in this situation, the standard
Brownian motion master equation is inadequate for describing the thermal
damping of the mirror, as it produces a spurious term in the steady-state phase
fluctuation spectrum. The corrected Brownian motion master equation [L. Diosi,
Europhys. Lett. {\bf 22}, 1 (1993)] rectifies this inadequacy.",9902040v1
1999-10-05,"Uncertainty, entropy and decoherence of the damped harmonic oscillator in the Lindblad theory of open quantum systems","In the framework of the Lindblad theory for open quantum systems, expressions
for the density operator, von Neumann entropy and effective temperature of the
damped harmonic oscillator are obtained. The entropy for a state characterized
by a Wigner distribution function which is Gaussian in form is found to depend
only on the variance of the distribution function. We give a series of
inequalities, relating uncertainty to von Neumann entropy and linear entropy.
We analyze the conditions for purity of states and show that for a special
choice of the diffusion coefficients, the correlated coherent states (squeezed
coherent states) are the only states which remain pure all the time during the
evolution of the considered system. These states are also the most stable under
evolution in the presence of the environment and play an important role in the
description of environment induced decoherence.",9910019v1
2000-06-07,Phenomenological approach to introduce damping effects on radiation field states,"In this work we propose an approach to deal with radiation field states which
incorporates damping effects at zero temperature. By using some well known
results on dissipation of a cavity field state, obtained by standard ab-initio
methods, it was possible to infer through a phenomenological way the explicit
form for the evolution of the state vector for the whole system: the
cavity-field plus reservoir. This proposal turns out to be of extreme
convenience to account for the influence of the reservoir over the cavity
field.
  To illustrate the universal applicability of our approach we consider the
attenuation effects on cavity-field states engineering. A proposal to maximize
the fidelity of the process is presented.",0006035v2
2001-09-28,Decoherence in trapped ions due to polarization of the residual background gas,"We investigate the mechanism of damping and heating of trapped ions
associated with the polarization of the residual background gas induced by the
oscillating ions themselves. Reasoning by analogy with the physics of surface
electrons in liquid helium, we demonstrate that the decay of Rabi oscillations
observed in experiments on 9Be+ can be attributed to the polarization phenomena
investigated here. The measured sensitivity of the damping of Rabi oscillations
with respect to the vibrational quantum number of a trapped ion is also
predicted in our polarization model.",0109156v1
2002-06-18,Five Lectures On Dissipative Master Equations,"1 First Lecture: Basics
  1.1 Physical Derivation of the Master Equation
  1.2 Some Simple Implications
  1.3 Steady State
  1.4 Action to the Left
  2 Second Lecture: Eigenvalues and Eigenvectors of L
  2.1 A Simple Case First
  2.2 The General Case
  3 Third Lecture: Completeness of the Damping Bases
  3.1 Phase Space Functions
  3.2 Completeness of the Eigenvectors of L
  3.3 Positivity Conservation
  3.4 Lindblad Form of Liouville Operators
  4 Fourth Lecture: Quantum-Optical Applications
  4.1 Periodically Driven Damped Oscillator
  4.2 Conditional and Unconditional Evolution
  4.3 Physical Signicance of Statistical Operators
  5 Fifth Lecture: Statistics of Detected Atoms
  5.1 Correlation Functions
  5.2 Waiting Time Statistics
  5.3 Counting Statistics",0206116v1
2002-10-02,Radiation damping and decoherence in quantum electrodynamics,"The processes of radiation damping and decoherence in Quantum Electrodynamics
are studied from an open system's point of view. Employing functional
techniques of field theory, the degrees of freedom of the radiation field are
eliminated to obtain the influence phase functional which describes the reduced
dynamics of the matter variables. The general theory is applied to the dynamics
of a single electron in the radiation field. From a study of the wave packet
dynamics a quantitative measure for the degree of decoherence, the decoherence
function, is deduced. The latter is shown to describe the emergence of
decoherence through the emission of bremsstrahlung caused by the relative
motion of interfering wave packets. It is argued that this mechanism is the
most fundamental process in Quantum Electrodynamics leading to the destruction
of coherence, since it dominates for short times and because it is at work even
in the electromagnetic field vacuum at zero temperature. It turns out that
decoherence trough bremsstrahlung is very small for single electrons but
extremely large for superpositions of many-particle states.",0210013v1
2003-01-08,"Dissipation, Emergent Quantization and Quantum Fluctuations","We review some aspects of the quantization of the damped harmonic oscillator.
We derive the exact action for a damped mechanical system in the frame of the
path integral formulation of the quantum Brownian motion problem developed by
Schwinger and by Feynman and Vernon. The doubling of the phase-space degrees of
freedom for dissipative systems and thermal field theories is discussed and the
doubled variables are related to quantum noise effects. The 't Hooft proposal,
according to which the loss of information due to dissipation in a classical
deterministic system manifests itself in the quantum features of the system, is
analyzed and the quantum spectrum of the harmonic oscillator is shown to be
originated from the dissipative character of the original classical
deterministic system.",0301031v1
2004-01-28,Bloch Equations and Completely Positive Maps,"The phenomenological dissipation of the Bloch equations is reexamined in the
context of completely positive maps. Such maps occur if the dissipation arises
from a reduction of a unitary evolution of a system coupled to a reservoir. In
such a case the reduced dynamics for the system alone will always yield
completely positive maps of the density operator. We show that, for Markovian
Bloch maps, the requirement of complete positivity imposes some Bloch
inequalities on the phenomenological damping constants. For non-Markovian Bloch
maps some kind of Bloch inequalities involving eigenvalues of the damping basis
can be established as well. As an illustration of these general properties we
use the depolarizing channel with white and colored stochastic noise.",0401177v1
2004-02-12,Non-Markovian Quantum Trajectories Versus Master Equations: Finite Temperature Heat Bath,"The interrelationship between the non-Markovian stochastic Schr\""odinger
equations and the corresponding non-Markovian master equations is investigated
in the finite temperature regimes. We show that the general finite temperature
non-Markovian trajectories can be used to derive the corresponding
non-Markovian master equations. A simple, yet important solvable example is the
well-known damped harmonic oscillator model in which a harmonic oscillator is
coupled to a finite temperature reservoir in the rotating wave approximation.
The exact convolutionless master equation for the damped harmonic oscillator is
obtained by averaging the quantum trajectories relying upon no assumption of
coupling strength or time scale. The master equation derived in this way
automatically preserves the positivity, Hermiticity and unity.",0402086v2
2005-04-27,Decoherence models and their effects on quantum maps and algorithms,"In this work we study several models of decoherence and how different quantum
maps and algorithms react when perturbed by them. Following closely Ref. [1],
generalizations of the three paradigmatic one single qubit quantum channels
(these are the depolarizing channel, the phase damping channel and the
amplitude damping channel) for the case of an arbitrarily-sized
finite-dimensional Hilbert space are presented, as well as other types of noise
in phase space. More specifically, Grover's search algorithm's response to
decoherence is analyzed; together with those of a family of quantum versions of
chaotic and regular classical maps (the baker's map and the cat maps). A
relationship between how sensitive to decoherence a quantum map is and the
degree of complexity in the dynamics of its associated classical counterpart is
observed; resulting in a clear tendency to react the more decoherently the more
complex the associated classical dynamics is.",0504211v1
2005-09-22,Semiclassical quantization of non-Hamiltonian dynamical systems without memory,"We propose a new method of quantization of a wide class of dynamical systems
that originates directly from the equations of motion. The method is based on
the correspondence between the classical and the quantum Poisson brackets,
postulated by Dirac. This correspondence applied to open (non-Hamiltonian)
systems allows one to point out the way of transition from the quantum
description based on the Lindblad equation to the dynamical description of
their classical analogs by the equations of motion and vice versa. As the
examples of using of the method we describe the procedure of the quantization
of three widely considered dynamical systems: 1) the harmonic oscillator with
friction, 2) the oscillator with a nonlinear damping that simulates the process
of the emergence of the limit cycle, and 3) the system of two periodic rotators
with a weak interaction that synchronizes their oscillations. We discuss a
possible application of the method for a description of quantum fluctuations in
Josephson junctions with a strong damping and for the quantization of open
magnetic systems with a dissipation and a pumping.",0509159v1
2005-11-15,Classical Phase Space Density for the Relativistic Hydrogen Atom,"Quantum mechanics is considered to arise from an underlying classical
structure (``hidden variable theory'', ``sub-quantum mechanics''), where
quantum fluctuations follow from a physical noise mechanism. The stability of
the hydrogen ground state can then arise from a balance between Lorentz damping
and energy absorption from the noise. Since the damping is weak, the ground
state phase space density should predominantly be a function of the conserved
quantities, energy and angular momentum.
  A candidate for this phase space density is constructed for ground state of
the relativistic hydrogen problem of a spinless particle. The first excited
states and their spherical harmonics are also considered in this framework. The
analytic expression of the ground state energy can be reproduced, provided
averages of certain products are replaced by products of averages. This
analysis puts forward that quantum mechanics may arise from an underlying
classical level as a slow variable theory, where each new quantum operator
relates to a new, well separated time interval.",0511144v1
2006-01-10,Quantum Brownian motion and the Third Law of thermodynamics,"The quantum thermodynamic behavior of small systems is investigated in
presence of finite quantum dissipation. We consider the archetype cases of a
damped harmonic oscillator and a free quantum Brownian particle. A main finding
is that quantum dissipation helps to ensure the validity of the Third Law. For
the quantum oscillator, finite damping replaces the zero-coupling result of an
exponential suppression of the specific heat at low temperatures by a power-law
behavior. Rather intriguing is the behavior of the free quantum Brownian
particle. In this case, quantum dissipation is able to restore the Third Law:
Instead of being constant down to zero temperature, the specific heat now
vanishes proportional to temperature with an amplitude that is inversely
proportional to the ohmic dissipation strength. A distinct subtlety of finite
quantum dissipation is the result that the various thermodynamic functions of
the sub-system do not only depend on the dissipation strength but depend as
well on the prescription employed in their definition.",0601056v1
2006-03-13,Decoherence induced by a phase-damping reservoir,"A phase damping reservoir composed by $N$-bosons coupled to a system of
interest through a cross-Kerr interaction is proposed and its effects on
quantum superpo sitions are investigated. By means of analytical calculations
we show that: i-) the reservoir induces a Gaussian decay of quantum coherences,
and ii-) the inher ent incommensurate character of the spectral distribution
yields irreversibility . A state-independent decoherence time and a master
equation are both derived an alytically. These results, which have been
extended for the thermodynamic limit, show that nondissipative decoherence can
be suitably contemplated within the EI D approach. Finally, it is shown that
the same mechanism yielding decoherence ar e also responsible for inducing
dynamical disentanglement.",0603109v2
2007-01-21,Casimir-Polder forces on excited atoms in the strong atom-field coupling regime,"Based on macroscopic quantum electrodynamics in linear media, we develop a
general theory of the resonant Casimir-Polder force on an excited two-level
atom in the presence of arbitrary linear bodies, with special emphasis on the
strong-coupling regime where reabsorption of an emitted photon can give rise to
(vacuum) Rabi oscillations. We first derive a simple time-independent
expression for the force by using a dressed-state approximation. For initially
single-quantum excited atom-field systems we then study the dynamics of the
force by starting from the Lorentz force and evaluating its average as a
function of time. For strong atom-field coupling, we find that the force may
undergo damped Rabi oscillations. The damping is due to the decay of both the
atomic excitation and the field excitation, and both amplitude and mean value
of the oscillations depend on the chosen initial state.",0701151v2
2007-02-07,Protecting an optical qubit against photon loss,"We consider quantum error-correction codes for multimode bosonic systems,
such as optical fields, that are affected by amplitude damping. Such a process
is a generalization of an erasure channel. We demonstrate that the most
accessible method of transforming optical systems with the help of passive
linear networks has limited usefulness in preparing and manipulating such
codes. These limitations stem directly from the recoverability condition for
one-photon loss. We introduce a three-photon code protecting against the first
order of amplitude damping, i.e. a single photon loss, and discuss its
preparation using linear optics with single-photon sources and conditional
detection. Quantum state and process tomography in the code subspace can be
implemented using passive linear optics and photon counting. An experimental
proof-of-principle demonstration of elements of the proposed quantum error
correction scheme for a one-photon erasure lies well within present
technological capabilites.",0702075v1
1995-02-03,Shock waves in the dissipative Toda lattice,"We consider the propagation of a shock wave (SW) in the damped Toda lattice.
The SW is a moving boundary between two semi-infinite lattice domains with
different densities. A steadily moving SW may exist if the damping in the
lattice is represented by an ``inner'' friction, which is a discrete analog of
the second viscosity in hydrodynamics. The problem can be considered
analytically in the continuum approximation, and the analysis produces an
explicit relation between the SW's velocity and the densities of the two
phases. Numerical simulations of the lattice equations of motion demonstrate
that a stable SW establishes if the initial velocity is directed towards the
less dense phase; in the opposite case, the wave gradually spreads out. The
numerically found equilibrium velocity of the SW turns out to be in a very good
agreement with the analytical formula even in a strongly discrete case. If the
initial velocity is essentially different from the one determined by the
densities (but has the correct sign), the velocity does not significantly
alter, but instead the SW adjusts itself to the given velocity by sending
another SW in the opposite direction.",9502001v1
2007-04-04,An integral field spectroscopic survey for high redshift damped Lyman-alpha galaxies,"We search for galaxy counterparts to damped Lyman-alpha absorbers (DLAs) at
z>2 towards nine quasars, which have 14 DLAs and 8 sub-DLAs in their spectra.
We use integral field spectroscopy to search for Ly-alpha emission line objects
at the redshifts of the absorption systems. Besides recovering two previously
confirmed objects, we find six statistically significant candidate Ly-alpha
emission line objects. The candidates are identified as having wavelengths
close to the DLA line where the background quasar emission is absorbed. In
comparison with the six currently known Ly-alpha emitting DLA galaxies the
candidates have similar line fluxes and line widths, while velocity offsets
between the emission lines and systemic DLA redshifts are larger. The impact
parameters are larger than 10 kpc, and lower column density systems are found
at larger impact parameters. Assuming that a single gas cloud extends from the
QSO line of sight to the location of the candidate emission line, we find that
the average candidate DLA galaxy is surrounded by neutral gas with an
exponential scale length of ~5 kpc.",0704.0654v1
2007-04-06,9.7 micrometer Silicate Absorption in a Damped Lyman-alpha Absorber at z=0.52,"We report a detection of the 9.7 micrometer silicate absorption feature in a
damped Lyman-alpha (DLA) system at z_{abs} = 0.524 toward AO0235+164, using the
Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The feature
shows a broad shallow profile over about 8-12 micrometers in the absorber rest
frame and appears to be > 15 sigma significant in equivalent width. The feature
is fit reasonably well by the silicate absorption profiles for laboratory
amorphous olivine or diffuse Galactic interstellar clouds. To our knowledge,
this is the first indication of 9.7 micrometer silicate absorption in a DLA. We
discuss potential implications of this finding for the nature of the dust in
quasar absorbers. Although the feature is relatively shallow (tau_{9.7} =
0.08-0.09), it is about 2 times deeper than expected from extrapolation of the
tau_{9.7} vs. E(B-V) relation known for diffuse Galactic interstellar clouds.
Further studies of the 9.7 micrometer silicate feature in quasar absorbers will
open a new window on the dust in distant galaxies.",0704.0826v2
2007-04-17,Boolean network model predicts cell cycle sequence of fission yeast,"A Boolean network model of the cell-cycle regulatory network of fission yeast
(Schizosaccharomyces Pombe) is constructed solely on the basis of the known
biochemical interaction topology. Simulating the model in the computer,
faithfully reproduces the known sequence of regulatory activity patterns along
the cell cycle of the living cell. Contrary to existing differential equation
models, no parameters enter the model except the structure of the regulatory
circuitry. The dynamical properties of the model indicate that the biological
dynamical sequence is robustly implemented in the regulatory network, with the
biological stationary state G1 corresponding to the dominant attractor in state
space, and with the biological regulatory sequence being a strongly attractive
trajectory. Comparing the fission yeast cell-cycle model to a similar model of
the corresponding network in S. cerevisiae, a remarkable difference in
circuitry, as well as dynamics is observed. While the latter operates in a
strongly damped mode, driven by external excitation, the S. pombe network
represents an auto-excited system with external damping.",0704.2200v1
2007-05-08,Optical dilution and feedback cooling of a gram-scale oscillator to 6.9 mK,"We report on use of a radiation pressure induced restoring force, the optical
spring effect, to optically dilute the mechanical damping of a 1 gram suspended
mirror, which is then cooled by active feedback (cold damping). Optical
dilution relaxes the limit on cooling imposed by mechanical losses, allowing
the oscillator mode to reach a minimum temperature of 6.9 mK, a factor of
~40000 below the environmental temperature. A further advantage of the optical
spring effect is that it can increase the number of oscillations before
decoherence by several orders of magnitude. In the present experiment we infer
an increase in the dynamical lifetime of the state by a factor of ~200.",0705.1018v2
2007-05-14,Electron-muon heat conduction in neutron star cores via the exchange of transverse plasmons,"We calculate the thermal conductivity of electrons and muons kappa_{e-mu}
produced owing to electromagnetic interactions of charged particles in neutron
star cores and show that these interactions are dominated by the exchange of
transverse plasmons (via the Landau damping of these plasmons in
nonsuperconducting matter and via a specific plasma screening in the presence
of proton superconductivity). For normal protons, the Landau damping strongly
reduces kappa_{e-mu} and makes it temperature independent. Proton
superconductivity suppresses the reduction and restores the Fermi-liquid
behavior kappa_{e-mu} ~ 1/T. Comparing with the thermal conductivity of
neutrons kappa_n, we obtain kappa_{e-mu}> kappa_n for T>2 GK in normal matter
and for any T in superconducting matter with proton critical temperatures
T_c>3e9 K. The results are described by simple analytic formulae.",0705.1963v1
2007-05-24,Measurement of Newtonian fluid slip using a torsional ultrasonic oscillator,"The composite torsional ultrasonic oscillator, a versatile experimental
system, can be used to investigate slip of Newtonian fluid at a smooth surface.
A rigorous analysis of slip-dependent damping for the oscillator is presented.
Initially, the phenomenon of finite surface slip and the slip length are
considered for a half-space of Newtonian fluid in contact with a smooth,
oscillating solid surface. Definitions are revisited and clarified in light of
inconsistencies in the literature. We point out that, in general oscillating
flows, Navier's slip length b is a complex number. An intuitive velocity
discontinuity parameter of unrestricted phase is used to describe the effect of
slip on measurement of viscous shear damping. The analysis is applied to the
composite oscillator and preliminary experimental work for a 40 kHz oscillator
is presented. The Non-Slip Boundary Condition (NSBC) has been verified for a
hydrophobic surface in water to within ~60 nm of |b|=0 nm. Experiments were
carried out at shear rate amplitudes between 230 and 6800 /s, corresponding to
linear displacement amplitudes between 3.2 and 96 nm.",0705.3498v3
2007-06-05,Waves and instabilities in dissipative rotating superfluid neutron stars,"We discuss wave propagation in rotating superfluid neutron star cores, taking
into account the vortex mediated mutual friction force. For models where the
two fluids co-rotate in the unperturbed state, our analysis clarifies the role
of chemical coupling and entrainment for sound and inertial waves. We also
investigate the mutual friction damping, providing results that demonstrate the
well-known fact that sound waves propagating along a vortex array are undamped.
We show that the same is not true for inertial waves, which are damped by the
mutual friction regardless of the propagation direction. We then include the
vortex tension, which arises due to local vortex curvature. Focussing on purely
transverse inertial waves, we derive the small correction that the tension
induces in the wave frequency. Finally, we allow for a relative linear flow in
the background (along the rotation axis). In this case we show how the mutual
friction coupling may induce a dynamical instability in the inertial waves. We
discuss the critical flow required for the instability to be present, its
physical interpretation and the possible relevance it may have for neutron star
physics.",0706.0672v1
2007-07-20,Dissipation-Scale Turbulence in the Solar Wind,"We present a cascade model for turbulence in weakly collisional plasmas that
follows the nonlinear cascade of energy from the large scales of driving in the
MHD regime to the small scales of the kinetic Alfven wave regime where the
turbulence is dissipated by kinetic processes. Steady-state solutions of the
model for the slow solar wind yield three conclusions: (1) beyond the observed
break in the magnetic energy spectrum, one expects an exponential cut-off; (2)
the widely held interpretation that this dissipation range obeys power-law
behavior is an artifact of instrumental sensitivity limitations; and, (3) over
the range of parameters relevant to the solar wind, the observed variation of
dissipation range spectral indices from -2 to -4 is naturally explained by the
varying effectiveness of Landau damping, from an undamped prediction of -7/3 to
a strongly damped index around -4.",0707.3149v1
2007-08-09,An algorithm for detecting oscillatory behavior in discretized data: the damped-oscillator oscillator detector,"We present a simple algorithm for detecting oscillatory behavior in discrete
data. The data is used as an input driving force acting on a set of simulated
damped oscillators. By monitoring the energy of the simulated oscillators, we
can detect oscillatory behavior in data. In application to in vivo deep brain
basal ganglia recordings, we found sharp peaks in the spectrum at 20 and 70 Hz.
The algorithm is also compared to the conventional fast Fourier transform and
circular statistics techniques using computer generated model data, and is
found to be comparable to or better than fast Fourier transform in test cases.
Circular statistics performed poorly in our tests.",0708.1341v1
2007-08-22,The dynamics of vortex generation in superfluid 3He-B,"A profound change occurs in the stability of quantized vortices in externally
applied flow of superfluid 3He-B at temperatures ~ 0.6 Tc, owing to the rapidly
decreasing damping in vortex motion with decreasing temperature. At low damping
an evolving vortex may become unstable and generate a new independent vortex
loop. This single-vortex instability is the generic precursor to turbulence. We
investigate the instability with non-invasive NMR measurements on a rotating
cylindrical sample in the intermediate temperature regime (0.3 - 0.6) Tc. From
comparisons with numerical calculations we interpret that the instability
occurs at the container wall, when the vortex end moves along the wall in
applied flow.",0708.3003v2
2007-08-26,Geodesic plasma flows instabilities of Riemann twisted solar loops,"Riemann and sectional curvatures of magnetic twisted flux tubes in Riemannian
manifold are computed to investigate the stability of the plasma astrophysical
tubes. The geodesic equations are used to show that in the case of thick
magnetic tubes, the curvature of planar (Frenet torsion-free) tubes have the
effect ct of damping the flow speed along the tube. Stability of geodesic flows
in the Riemannian twisted thin tubes (almost filaments), against constant
radial perturbations is investigated by using the method of negative sectional
curvature for unstable flows. No special form of the flow like Beltrami flows
is admitted, and the proof is general for the case of thin magnetic flux tubes.
In the magnetic equilibrium state, the twist of the tube is shown to display
also a damping effect on the toroidal velocity of the plasma flow. It is found
that for positive perturbations and angular speed of the flow, instability is
achieved, since the sectional Ricci curvature of the magnetic twisted tube
metric is negative. Solar flare production may appear from these geometrical
instabilities of the twisted solar loops.",0708.3473v1
2007-09-05,Phonon bottleneck in the low-excitation limit,"The phonon-bottleneck problem in the relaxation of two-level systems (spins)
via direct phonon processes is considered numerically in the weak-excitation
limit where the Schroedinger equation for the spin-phonon system simplifies.
The solution for the relaxing spin excitation p(t), emitted phonons n_k(t),
etc. is obtained in terms of the exact many-body eigenstates. In the absence of
phonon damping Gamma_{ph} and inhomogeneous broadening, p(t) approaches the
bottleneck plateau p_\infty > 0 with strongly damped oscillations, the
frequency being related to the spin-phonon splitting Delta at the avoided
crossing. For any Gamma_{ph} > 0 one has p(t) -> 0 but in the case of strong
bottleneck the spin relaxation rate is much smaller than Gamma_{ph} and p(t) is
nonexponential. Inhomogeneous broadening exceeding Delta partially alleviates
the bottleneck and removes oscillations of p(t). The line width of emitted
phonons, as well as Delta, increase with the strength of the bottleneck, i.e.,
with the concentration of spins.",0709.0556v1
2007-09-13,Distribution of PageRank Mass Among Principle Components of the Web,"We study the PageRank mass of principal components in a bow-tie Web Graph, as
a function of the damping factor c. Using a singular perturbation approach, we
show that the PageRank share of IN and SCC components remains high even for
very large values of the damping factor, in spite of the fact that it drops to
zero when c goes to one. However, a detailed study of the OUT component reveals
the presence ``dead-ends'' (small groups of pages linking only to each other)
that receive an unfairly high ranking when c is close to one. We argue that
this problem can be mitigated by choosing c as small as 1/2.",0709.2016v1
2007-10-02,Oscillating Starless Cores: The Nonlinear Regime,"In a previous paper, we modeled the oscillations of a thermally-supported
(Bonnor-Ebert) sphere as non-radial, linear perturbations following a standard
analysis developed for stellar pulsations. The predicted column density
variations and molecular spectral line profiles are similar to those observed
in the Bok globule B68 suggesting that the motions in some starless cores may
be oscillating perturbations on a thermally supported equilibrium structure.
However, the linear analysis is unable to address several questions, among them
the stability, and lifetime of the perturbations. In this paper we simulate the
oscillations using a three-dimensional numerical hydrodynamic code. We find
that the oscillations are damped predominantly by non-linear mode-coupling, and
the damping time scale is typically many oscillation periods, corresponding to
a few million years, and persisting over the inferred lifetime of gobules.",0710.0625v1
2007-10-08,Jet quenching parameter \hat q in the stochastic QCD vacuum with Landau damping,"We argue that the radiative energy loss of a parton traversing the
quark-gluon plasma is determined by Landau damping of soft modes in the plasma.
Using this idea, we calculate the jet quenching parameter of a gluon. The
calculation is done in SU(3) quenched QCD within the stochastic vacuum model.
At the LHC-relevant temperatures, the result depends on the gluon condensate,
the vacuum correlation length, and the gluon Debye mass. Numerically, when the
temperature varies from T=T_c to T=900 MeV, the jet quenching parameter rises
from \hat q=0 to approximately 1.8 GeV^2/fm. We compare our results with the
predictions of perturbative QCD and other calculations.",0710.1540v2
2007-11-07,Tuning the effective coupling of an AFM lever to a thermal bath,"Fabrication of Nano-Electro-Mechanical-Systems (NEMS) of high quality is
nowadays extremely efficient. These NEMS will be used as sensors and actuators
in integrated systems. Their use however raises questions about their interface
(actuation, detection, read out) with external detection and control systems.
Their operation implies many fundamental questions related to single particle
effects such as Coulomb blockade, light matter interactions such as radiation
pressure, thermal effects, Casimir forces and the coupling of nanosystems to
external world (thermal fluctuations, back action effect). Here we specifically
present how the damping of an oscillating cantilever can be tuned in two
radically different ways: i) through an electro-mechanical coupling in the
presence of a strong Johnson noise, ii) through an external feedback control of
thermal fluctuations which is the cold damping closely related to Maxwell's
demon. This shows how the interplay between MEMS or NEMS external control and
their coupling to a thermal bath can lead to a wealth of effects that are
nowadays extensively studied in different areas.",0711.1024v1
2007-12-11,Neutrino oscillations in a stochastic model for space-time foam,"We study decoherence models for flavour oscillations in four-dimensional
stochastically fluctuating space times and discuss briefly the sensitivity of
current neutrino experiments to such models. We pay emphasis on demonstrating
the model dependence of the associated decoherence-induced damping coefficients
in front of the oscillatory terms in the respective transition probabilities
between flavours. Within the context of specific models of foam, involving
point-like D-branes and leading to decoherence-induced damping which is
inversely proportional to the neutrino energies, we also argue that future
limits on the relevant decoherence parameters coming from TeV astrophysical
neutrinos, to be observed in ICE-CUBE, are not far from theoretically expected
values with Planck mass suppression. Ultra high energy neutrinos from Gamma Ray
Bursts at cosmological distances can also exhibit in principle sensitivity to
such effects.",0712.1779v1
2008-01-21,Collective cyclotron motion of the relativistic plasma in graphene,"We present a theory of the finite temperature thermo-electric response
functions of graphene, in the hydrodynamic regime induced by electron-electron
collisions. In moderate magnetic fields, the Dirac particles undergo a
collective cyclotron motion with a temperature-dependent relativistic cyclotron
frequency proportional to the net charge density of the Dirac plasma. In
contrast to the undamped cyclotron pole in Galilean-invariant systems (Kohn's
theorem), here there is a finite damping induced by collisions between the
counter-propagating particles and holes. This cyclotron motion shows up as a
damped pole in the frequency dependent conductivities, and should be readily
detectable in microwave measurements at room temperature. We also discuss the
large Nernst effect to be expected in graphene.",0801.2970v3
2008-01-25,Sound waves and solitons in hot and dense nuclear matter,"Assuming that nuclear matter can be treated as a perfect fluid, we study the
propagation of perturbations in the baryon density. The equation of state is
derived from a relativistic mean field model, which is a variant of the
non-linear Walecka model. The expansion of the Euler and continuity equations
of relativistic hydrodynamics around equilibrium configurations leads to
differential equations for the density fluctuations. We solve them numerically
for linear and spherical perturbations and follow the time evolution of the
initial pulses. For linear perturbations we find single soliton solutions and
solutions with one or more solitons followed by radiation. Depending on the
equation of state a strong damping may occur. Spherical perturbations are
strongly damped and almost do not propagate. We study these equations also for
matter at finite temperature. Finally we consider the limiting case of shock
wave formation.",0801.3938v1
2008-01-28,Qualitative Analysis of Forced Response of Blisks With Friction Ring Dampers,"A damping strategy for blisks (integrally bladed disks) of turbomachinery
involving a friction ring is investigated. These rings, located in grooves
underside the wheel of the blisks, are held in contact by centrifugal loads and
the energy is dissipated when relative motions between the ring and the disk
occur. A representative lumped parameter model of the system is introduced and
the steady-state nonlinear response is derived using a multi-harmonic balance
method combined with an AFT procedure where the friction force is calculated in
the time domain. Numerical simulations are presented for several damper
characteristics and several excitation configurations. From these results, the
performance of this damping strategy is discussed and some design guidelines
are given.",0801.4350v1
2008-01-29,Long Term Evolution of Magnetic Turbulence in Relativistic Collisionless Shocks,"We study the long term evolution of magnetic fields generated by an initially
unmagnetized collisionless relativistic $e^+e^-$ shock. Our 2D particle-in-cell
numerical simulations show that downstream of such a Weibel-mediated shock,
particle distributions are approximately isotropic, relativistic Maxwellians,
and the magnetic turbulence is highly intermittent spatially, nonpropagating,
and decaying. Using linear kinetic theory, we find a simple analytic form for
these damping rates. Our theory predicts that overall magnetic energy decays
like $(\omega_p t)^{-q}$ with $q \sim 1$, which compares favorably with
simulations, but predicts overly rapid damping of short wavelength modes.
Magnetic trapping of particles within the magnetic structures may be the origin
of this discrepancy. We conclude that initially unmagnetized relativistic
shocks in electron-positron plasmas are unable to form persistent downstream
magnetic fields. These results put interesting constraints on synchrotron
models for the prompt and afterglow emission from GRBs.",0801.4583v1
2008-02-20,Mechanical mode dependence of bolometric back-action in an AFM microlever,"Two back action (BA) processes generated by an optical cavity based detection
device can deeply transform the dynamical behavior of an AFM microlever: the
photothermal force or the radiation pressure. Whereas noise damping or
amplifying depends on optical cavity response for radiation pressure BA, we
present experimental results carried out under vacuum and at room temperature
on the photothermal BA process which appears to be more complex. We show for
the first time that it can simultaneously act on two vibration modes in
opposite direction: noise on one mode is amplified whereas it is damped on
another mode. Basic modeling of photothermal BA shows that dynamical effect on
mechanical mode is laser spot position dependent with respect to mode shape.
This analysis accounts for opposite behaviors of different modes as observed.",0802.2763v2
2008-02-21,Propagation of cosmic rays in the foam-like Universe,"The model of a classical spacetime foam is considered, which consists of
static wormholes embedded in Minkowski spacetime. We examine the propagation of
particles in such a medium and demonstrate that a single thin ray undergoes a
specific damping in the density of particles depending on the traversed path
and the distribution of wormholes. The missing particles are scattered around
the ray. Wormholes was shown to form DM halos around point-like sources.
Therefore, the correlation predicted between the damping and the amount of DM
can be used to verify the topological nature of Dark Matter.",0802.3109v2
2008-02-21,Damping by slow relaxing rare earth impurities in Ni80Fe20,"Doping NiFe by heavy rare earth atoms alters the magnetic relaxation
properties of this material drastically. We show that this effect can be well
explained by the slow relaxing impurity mechanism. This process is a
consequence of the anisotropy of the on site exchange interaction between the
4f magnetic moments and the conduction band. As expected from this model the
magnitude of the damping effect scales with the anisotropy of the exchange
interaction and increases by an order of magnitude at low temperatures. In
addition our measurements allow us to determine the relaxation time of the 4f
electrons as a function of temperature.",0802.3206v3
2008-03-11,Domain wall motion of magnetic nanowires under a static field,"The propagation of a head-to-head magnetic domain-wall (DW) or a tail-to-tail
DW in a magnetic nanowire under a static field along the wire axis is studied.
Relationship between the DW velocity and DW structure is obtained from the
energy consideration. The role of the energy dissipation in the field-driven DW
motion is clarified. Namely, a field can only drive a domain-wall propagating
along the field direction through the mediation of a damping. Without the
damping, DW cannot propagate along the wire. Contrary to the common wisdom, DW
velocity is, in general, proportional to the energy dissipation rate, and one
needs to find a way to enhance the energy dissipation in order to increase the
propagation speed. The theory provides also a nature explanation of the
wire-width dependence of the DW velocity and velocity oscillation beyond Walker
breakdown field.",0803.1531v1
2008-03-11,"Equation of state for strongly interacting matter: collective effects, Landau damping and predictions for LHC","The equation of state (EOS) is of utmost importance for the description of
the hydrodynamic phase of strongly interacting matter in relativistic heavy-ion
collisions. Lattice QCD can provide useful information on the EOS, mainly for
small net baryon densities. The QCD quasiparticle model provides a means to map
lattice QCD results into regions relevant for a variety of experiments. We
report here on effects of collectives modes and damping on the EOS. Some
predictions for forthcoming heavy-ion collisions at LHC/ALICE are presented and
perspectives for deriving an EOS for FAIR/CBM are discussed.",0803.1571v1
2008-04-04,"Spin-charge coupling in a band ferromagnet: magnon-energy reduction, anomalous softening, and damping","The effects of correlation-induced coupling between spin and charge
fluctuations on spin-wave excitations in a band ferromagnet are investigated by
including self-energy and vertex corrections within a systematic
inverse-degeneracy expansion scheme which explicitly preserves the Goldstone
mode. Arising from the scattering of a magnon into intermediate spin-excitation
states (including both magnon and Stoner excitations) accompanied with charge
fluctuations in the majority spin band, this spin-charge coupling results not
only in a substantial reduction of magnon energies but also in anomalous
softening and significant magnon damping for zone-boundary modes lying within
the Stoner gap. Our results are in good qualitative agreement with recent
spin-wave excitation measurements in colossal magneto-resistive manganites and
ferromagnetic ultrathin films of transition metals.",0804.0680v1
2008-05-07,Noise Analysis and Noise-based Optimization for Resonant MEMS Structures,"This paper presents a detailed noise analysis and a noise-based optimization
procedure for resonant MEMS structures. A design for high sensitivity of MEMS
structures needs to take into account the noise shaping induced by damping
phenomena at micro scale. The existing literature presents detailed models for
the damping at microscale, but usually neglects them in the noise analysis
process, assuming instead a white spectrum approximation for the
mechano-thermal noise. The present work extends the implications of the complex
gas-solid interaction into the field of noise analysis for mechanical sensors,
and provides a semi-automatic procedure for behavioral macromodel extraction
and sensor optimization with respect to signal-to-noise ratio.",0805.0927v1
2008-05-07,Scaling crossovers in activated escape of nonequilibrium systems: a resonantly driven oscillator,"The rate of metastable decay in nonequilibrium systems is expected to display
scaling behavior: i.e., the logarithm of the decay rate should scale as a power
of the distance to a bifurcation point where the metastable state disappears.
Recently such behavior was observed and some of the earlier predicted exponents
were found in experiments on several types of systems described by a model of a
modulated oscillator. Here we establish the range where different scaling
behavior is displayed and show how the crossover between different types of
scaling occurs. The analysis is done for a nonlinear oscillator with two
coexisting stable states of forced vibrations. Our numerical calculations,
based on the the instanton method allow the mapping of the entire parameter
range of bi-stability. We find the regions where the scaling exponents are 1 or
3/2, depending on the damping. The exponent 3/2 is found to extend much further
from the bifurcation then were it would be expected to hold as a result of an
over-damped soft mode. We also uncover a new scaling behavior with exponent of
$\approx$ 1.3 which extends, numerically, beyond the close vicinity of the
bifurcation point.",0805.0972v2
2008-05-07,"Quantum Noise, Effective Temperature, and Damping in a Superconducting Single-Electron Transistor","We have directly measured the quantum noise of a superconducting
single-electron transistor (S-SET) embedded in a microwave resonator consisting
of a superconducting LC tank circuit. Using an effective bath description, we
find that the S-SET provides damping of the resonator modes proportional to its
differential conductance and has an effective temperature that depends strongly
on the S-SET bias conditions. In the vicinity of a double Cooper pair
resonance, when both resonances are red detuned the S-SET effective temperature
can be well below both the ambient temperature and the energy scale of the bias
voltage. When blue detuned, the S-SET shows negative differential conductivity,",0805.1037v1
2008-05-08,Adaptive Affinity Propagation Clustering,"Affinity propagation clustering (AP) has two limitations: it is hard to know
what value of parameter 'preference' can yield an optimal clustering solution,
and oscillations cannot be eliminated automatically if occur. The adaptive AP
method is proposed to overcome these limitations, including adaptive scanning
of preferences to search space of the number of clusters for finding the
optimal clustering solution, adaptive adjustment of damping factors to
eliminate oscillations, and adaptive escaping from oscillations when the
damping adjustment technique fails. Experimental results on simulated and real
data sets show that the adaptive AP is effective and can outperform AP in
quality of clustering results.",0805.1096v1
2008-06-06,On the stability of shocks with particle pressure,"We perform a linear stability analysis for corrugations of a Newtonian shock,
with particle pressure included, for an arbitrary diffusion coefficient. We
study first the dispersion relation for homogeneous media, showing that,
besides the conventional pressure waves and entropy/vorticity disturbances, two
new perturbation modes exist, dominated by the particles' pressure and damped
by diffusion. We show that, due to particle diffusion into the upstream region,
the fluid will be perturbed also upstream: we treat these perturbation in the
short wavelength (WKBJ) regime. We then show how to construct a corrugational
mode for the shock itself, one, that is, where the shock executes free
oscillations (possibly damped or growing) and sheds perturbations away from
itself: this global mode requires the new modes. Then, using the perturbed
Rankine-Hugoniot conditions, we show that this leads to the determination of
the corrugational eigenfrequency. We solve numerically the equations for the
eigenfrequency in the WKBJ regime for the models of Amato and Blasi (2005),
showing that they are stable. We then discuss the differences between our
treatment and previous work.",0806.1113v1
2008-06-17,Damping of Fast Magnetohydrodynamic Oscillations in Quiescent Filament Threads,"High-resolution observations provide evidence about the existence of
small-amplitude transverse oscillations in solar filament fine structures.
These oscillations are believed to represent fast magnetohydrodynamic (MHD)
waves and the disturbances are seen to be damped in short timescales of the
order of 1 to 4 periods. In this Letter we propose that, due to the highly
inhomogeneous nature of the filament plasma at the fine structure spatial
scale, the phenomenon of resonant absorption is likely to operate in the
temporal attenuation of fast MHD oscillations. By considering transverse
inhomogeneity in a straight flux tube model we find that, for density
inhomogeneities typical of filament threads, the decay times are of a few
oscillatory periods only.",0806.2728v1
2008-06-27,Global attractor and asymptotic smoothing effects for the weakly damped cubic Schrödinger equation in $L^2(\T)$,"We prove that the weakly damped cubic Schr\""odinger flow in $L^2(\T)$
provides a dynamical system that possesses a global attractor. The proof relies
on a sharp study of the behavior of the associated flow-map with respect to the
weak $ L^2(\T) $-convergence inspired by a previous work of the author.
Combining the compactness in $ L^2(\T) $ of the attractor with the approach
developed by Goubet, we show that the attractor is actually a compact set of $
H^2(\T) $. This asymptotic smoothing effect is optimal in view of the
regularity of the steady states.",0806.4578v3
2008-06-30,Thermal depinning of fluxons in discrete Josephson rings,"We study the thermal depinning of single fluxons in rings made of Josephson
junctions. Due to thermal fluctuations a fluxon can be excited from its energy
minima and move through the array, causing a voltage across each junction. We
find that for the initial depinning, the fluxon behaves as a single particle
and follows a Kramers-type escape law. However, under some conditions this
single particle description breaks down. At low values of the discreteness
parameter and low values of the damping, the depinning rate is larger than the
single particle result would suggest. In addition, for some values of the
parameters the fluxon can undergo low-voltage diffusion before switching to the
high-voltage whirling mode. This type of diffusion is similar to phase
diffusion in a single junction, but occurs without frequency-dependent damping.
We study the switching to the whirling state as well.",0806.4828v1
2008-07-03,Dependence of the decoherence of polarization states in phase-damping channels on the frequency spectrum envelope of photons,"We consider the decoherence of photons suffering in phase-damping channels.
By exploring the evolutions of single-photon polarization states and two-photon
polarization-entangled states, we find that different frequency spectrum
envelopes of photons induce different decoherence processes. A white frequency
spectrum can lead the decoherence to an ideal Markovian process. Some color
frequency spectrums can induce asymptotical decoherence, while, some other
color frequency spectrums can make coherence vanish periodically with variable
revival amplitudes. These behaviors result from the non-Markovian effects on
the decoherence process, which may give rise to a revival of coherence after
complete decoherence.",0807.0536v3
2008-07-17,"Planetary Migration in Resonance, the question of the Eccentricities : Les Houches contribution","The formation of resonant planets pairs in exoplanetary systems involves
planetary migration inside the protoplanetary disc : an inwards migrating outer
planet captures in Mean Motion Resonance an inner planet. During the migration
of the resonant pair of planets, the eccentricities are expected to rise
excessively, if no damping mechanism is applied on the inner planet. We express
the required damping action to match the observations, and we show that the
inner disk can play this role. This result applies for instance to the system
GJ 876 : we reproduce the observed orbital elements through a fully
hydrodynamical simulation of the evolution of the resonant planets.",0807.2828v2
2008-07-18,Heavily Damped Motion of One-Dimensional Bose Gases in an Optical Lattice,"We study the dynamics of strongly correlated one-dimensional Bose gases in a
combined harmonic and optical lattice potential subjected to sudden
displacement of the confining potential. Using the time-evolving block
decimation method, we perform a first-principles quantum many-body simulation
of the experiment of Fertig {\it et al.} [Phys. Rev. Lett. {\bf 94}, 120403
(2005)] across different values of the lattice depth ranging from the
superfluid to the Mott insulator regimes. We find good quantitative agreement
with this experiment: the damping of the dipole oscillations is significant
even for shallow lattices, and the motion becomes overdamped with increasing
lattice depth as observed. We show that the transition to overdamping is
attributed to the decay of superfluid flow accelerated by quantum fluctuations,
which occurs well before the emergence of Mott insulator domains.",0807.2898v2
2008-07-21,Mutual friction in a cold color flavor locked superfluid and r-mode instabilities in compact stars,"Dissipative processes acting in rotating neutron stars are essential in
preventing the growth of the r-mode instability. We estimate the damping time
of r-modes of an hypothetical compact quark star made up by color flavor locked
quark matter at a temperature $T \lesssim 0.01$ MeV. The dissipation that we
consider is due to the the mutual friction force between the normal and the
superfluid component arising from the elastic scattering of phonons with
quantized vortices. This process is the dominant one for temperatures $T
\lesssim 0.01$ MeV where the mean free path of phonons due to their
self-interactions is larger than the radius of the star and they can be
described as an ideal bosonic gas. We find that r-modes oscillations are
efficiently damped by this mechanism for pulsars rotating at frequencies of the
order of 1 Hz at most. Our analysis rules out the possibility that cold pulsars
rotating at higher frequencies are entirely made up by color flavor locked
quark matter.",0807.3264v2
2008-07-23,Dynamical Backaction of Microwave Fields on a Nanomechanical Oscillator,"We measure the response and thermal motion of a high-Q nanomechanical
oscillator coupled to a superconducting microwave cavity in the
resolved-sideband regime where the oscillator's resonance frequency exceeds the
cavity's linewidth. The coupling between the microwave field and mechanical
motion is strong enough for radiation pressure to overwhelm the intrinsic
mechanical damping. This radiation-pressure damping cools the fundamental
mechanical mode by a factor of 5 below the thermal equilibrium temperature in a
dilution refrigerator to a phonon occupancy of 140 quanta.",0807.3585v3
2008-07-28,Shear Viscosity of the outer crust of Neutron stars: Ion Contribution,"The shear viscosity of the crust might have a damping effect on the amplitude
of r-modes of rotating neutron stars. This damping has implications for the
emission of gravitational waves. We calculate the contribution to the shear
viscosity coming from the ions using both semi-analytical methods, that
consider binary collisions, and Molecular Dynamics simulations. We compare
these results with the contribution coming from electrons. We study how the
shear viscosity depends on density for conditions of interest in neutron star
envelopes and outer crusts. In the low density limit, we find good agreement
between results of our molecular dynamics simulations and classical
semi-analytic calculations.",0807.4353v2
2008-07-28,Unusual decoherence in qubit measurements with a Bose-Einstein condensate,"We consider an electrostatic qubit located near a Bose-Einstein condensate
(BEC) of noninteracting bosons in a double-well potential, which is used for
qubit measurements. Tracing out the BEC variables we obtain a simple analytical
expression for the qubit's density-matrix. The qubit's evolution exhibits a
slow ($\propto1/\sqrt{t}$) damping of the qubit's coherence term, which however
turns to be a Gaussian one in the case of static qubit. This stays in contrast
to the exponential damping produced by most classical detectors. The
decoherence is, in general, incomplete and strongly depends on the initial
state of the qubit.",0807.4440v2
2008-08-03,Superradiant Instability of Five-Dimensional Rotating Charged AdS Black Holes,"We study the instability of small AdS black holes with two independent
rotation parameters in minimal five-dimensional gauged supergravity to massless
scalar perturbations. We analytically solve the Klein-Gordon equation for
low-frequency perturbations in two regions of the spacetime of these black
holes: namely, in the region close to the horizon and in the far-region. By
matching the solutions in an intermediate region, we calculate the frequency
spectrum of quasinormal modes. We show that in the regime of superradiance only
the modes of even orbital quantum number undergo negative damping, resulting in
exponential growth of the amplitude. That is, the black holes become unstable
to these modes. Meanwhile, the modes of odd orbital quantum number do not
undergo any damping, oscillating with frequency-shifts. This is in contrast
with the case of four-dimensional small Kerr-AdS black holes which exhibit the
instability to all modes of scalar perturbations in the regime of
superradiance.",0808.0280v3
2008-08-15,Collective excitations in two-dimensional antiferromagnet in strong magnetic field,"We discuss spin-$\frac12$ two-dimensional (2D) Heisenberg antiferromagnet
(AF) on a square lattice at T=0 in strong magnetic field H near its saturation
value $H_c$. A perturbation approach is proposed to obtain spectrum of magnons
with momenta not very close to AF vector in the leading order in small
parameter $(H_c-H)/H_c$. We find that magnons are well-defined quasi-particles
at $H>0.9H_c$ although the damping is quite large near the zone boundary. A
characteristic rotonlike local minimum in the spectrum is observed at ${\bf
k}=(\pi,0)$ accompanied by decrease of the damping near $(\pi,0)$. The
suggested approach can be used in discussion of short-wavelength excitations in
other 2D Bose gases of particles or quasi-particles.",0808.2127v3
2008-08-26,Nonlinear regularization techniques for seismic tomography,"The effects of several nonlinear regularization techniques are discussed in
the framework of 3D seismic tomography. Traditional, linear, $\ell_2$ penalties
are compared to so-called sparsity promoting $\ell_1$ and $\ell_0$ penalties,
and a total variation penalty. Which of these algorithms is judged optimal
depends on the specific requirements of the scientific experiment. If the
correct reproduction of model amplitudes is important, classical damping
towards a smooth model using an $\ell_2$ norm works almost as well as
minimizing the total variation but is much more efficient. If gradients (edges
of anomalies) should be resolved with a minimum of distortion, we prefer
$\ell_1$ damping of Daubechies-4 wavelet coefficients. It has the additional
advantage of yielding a noiseless reconstruction, contrary to simple $\ell_2$
minimization (`Tikhonov regularization') which should be avoided. In some of
our examples, the $\ell_0$ method produced notable artifacts. In addition we
show how nonlinear $\ell_1$ methods for finding sparse models can be
competitive in speed with the widely used $\ell_2$ methods, certainly under
noisy conditions, so that there is no need to shun $\ell_1$ penalizations.",0808.3472v3
2008-09-09,Process tomography of field damping and measurement of Fock state lifetimes by quantum non-demolition photon counting in a cavity,"The relaxation of a quantum field stored in a high-$Q$ superconducting cavity
is monitored by non-resonant Rydberg atoms. The field, subjected to repetitive
quantum non-demolition (QND) photon counting, undergoes jumps between photon
number states. We select ensembles of field realizations evolving from a given
Fock state and reconstruct the subsequent evolution of their photon number
distributions. We realize in this way a tomography of the photon number
relaxation process yielding all the jump rates between Fock states. The damping
rates of the $n$ photon states ($0\leq n \leq 7$) are found to increase
linearly with $n$. The results are in excellent agreement with theory including
a small thermal contribution.",0809.1511v1
2008-10-01,Excitation of trapped oscillations in discs around black holes,"High-frequency quasi-periodic oscillations detected in the light curves of
black hole candidates can, according to one model, be identified with
hydrodynamic oscillations of the accretion disc. We describe a non-linear
coupling mechanism, suggested by Kato, through which inertial waves trapped in
the inner regions of accretion discs around black holes are excited. Global
warping and/or eccentricity of the disc have a fundamental role in this
coupling: they combine with trapped modes, generating negative energy waves,
that are damped as they approach the inner edge of the disc or their corotation
resonance. As a result of this damping, inertial oscillations are amplified. We
calculate the resulting eigenfunctions and their growth rates.",0810.0116v1
2008-10-09,Atomistic spin dynamics of the CuMn spin glass alloy,"We demonstrate the use of Langevin spin dynamics for studying dynamical
properties of an archetypical spin glass system. Simulations are performed on
CuMn (20% Mn) where we study the relaxation that follows a sudden quench of the
system to the low temperature phase. The system is modeled by a Heisenberg
Hamiltonian where the Heisenberg interaction parameters are calculated by means
of first-principles density functional theory. Simulations are performed by
numerically solving the Langevin equations of motion for the atomic spins. It
is shown that dynamics is governed, to a large degree, by the damping parameter
in the equations of motion and the system size. For large damping and large
system sizes we observe the typical aging regime.",0810.1645v1
2008-10-20,On the Existence of Exponentially Decreasing Solutions of the Nonlinear Landau Damping Problem,"In this paper we prove the existence of a large class of periodic solutions
of the Vlasov-Poisson in one space dimension that decay exponentially as t goes
to infinity. The exponential decay is well known for the linearized version of
the Landau damping problem and it has been proved in [4] for a class of
solutions of the Vlasov-Poisson system that behaves asymptotically as free
streaming solutions and are sufficiently flat in the space of velocities. The
results in this paper enlarge the class of possible asymptotic limits,
replacing the fatness condition in [4] by a stability condition for the
linearized problem.",0810.3456v2
2008-10-22,Thermal (in)stability of type I collagen fibrils,"We measured Young's modulus at temperatures ranging from 20 to 100 ^{\circ}$C
for a collagen fibril taken from rat's tendon. The hydration change under
heating and the damping decrement were measured as well. At physiological
temperatures $25-45^{\circ}$C Young's modulus decreases, which can be
interpreted as instability of collagen. For temperatures between
$45-80^{\circ}$C Young's modulus first stabilizes and then increases with
decreasing the temperature. The hydrated water content and the damping
decrement have strong maxima in the interval $70-80^{\circ}$C indicating on
complex inter-molecular structural changes in the fibril. All these effects
disappear after heat-denaturating the sample at $120^\circ$C. Our main result
is a five-stage mechanism by which the instability of a single collagen at
physiological temperatures is compensated by the interaction between collagen
molecules within the fibril.",0810.4172v1
2008-11-03,Ion thermal effects in oscillating multi-ion plasma sheath theory,"The effects of ion temperature are discussed in a two-ion electron plasma and
for a model applicable to the oscillating sheath theory that has recently been
much in the focus of researchers. The differences between the fluid and kinetic
models have been pointed out, as well as the differences between the
approximative kinetic description (which involves the expansion of the plasma
dispersion function), and the exact kinetic description. It is shown that the
approximative kinetic description, first, can not describe the additional
acoustic mode which naturally exists in the plasma with an additional ion
population with a finite temperature, and, second, it yields an inaccurate
Landau damping of the bulk ion acoustic mode. The reasons for these two
failures are described. In addition to this, a fluid model is presented that is
capable of capturing both of these features that are missing in the
approximative kinetic description, i.e., two (fast and slow) ion acoustic
modes, and the corresponding Landau damping of both modes.",0811.0251v1
2008-12-01,Self-Diffusion in 2D Dusty Plasma Liquids: Numerical Simulation Results,"We perform Brownian dynamics simulations for studying the self-diffusion in
two-dimensional (2D) dusty plasma liquids, in terms of both mean-square
displacement and velocity autocorrelation function (VAF). Super-diffusion of
charged dust particles has been observed to be most significant at infinitely
small damping rate $\gamma$ for intermediate coupling strength, where the
long-time asymptotic behavior of VAF is found to be the product of $t^{-1}$ and
$\exp{(-\gamma t)}$. The former represents the prediction of early theories in
2D simple liquids and the latter the VAF of a free Brownian particle. This
leads to a smooth transition from super-diffusion to normal diffusion, and then
to sub-diffusion with an increase of the damping rate. These results well
explain the seemingly contradictory scattered in recent classical molecular
dynamics simulations and experiments of dusty plasmas.",0812.0338v3
2008-12-11,Reduced nonlinear description of Farley-Buneman instability,"In the study on nonlinear wave-wave processes in an ionosphere and a
magnetosphere usually the main attention is paid to investigation of plasma
turbulence at well developed stage, when the wide spectrum of plasma wave is
present. On the other side, it is well known that even if the number of
cooperating waves remains small due to a competition of processes of their
instability and attenuation, the turbulence appears in the result of their
stochastic behavior. The regimes of nonlinear dynamics of low frequency waves
excited due to Farley-Buneman instability in weakly ionized and inhomogeneous
ionospheric plasma in the presence of electric current perpendicular to ambient
magnetic field are considered. The problem is essentially three dimensional and
difficult for full numerical simulation, but the strong collisional damping of
waves allow to assume that in this case a perturbed state of plasma can be
described as finite set of interacting waves, some of which are unstable and
other strongly damping. The proposed nonlinear model allow to make full study
of nonlinear stabilization, conditions of stochasticity and to consider the
different regimes and properties of few mode plasma turbulence.",0812.2182v1
2008-12-16,Reconstructing Baryon Oscillations: A Lagrangian Theory Perspective,"Recently Eisenstein and collaborators introduced a method to `reconstruct'
the linear power spectrum from a non-linearly evolved galaxy distribution in
order to improve precision in measurements of baryon acoustic oscillations. We
reformulate this method within the Lagrangian picture of structure formation,
to better understand what such a method does, and what the resulting power
spectra are. We show that reconstruction does not reproduce the linear density
field, at second order. We however show that it does reduce the damping of the
oscillations due to non-linear structure formation, explaining the improvements
seen in simulations. Our results suggest that the reconstructed power spectrum
is potentially better modeled as the sum of three different power spectra, each
dominating over different wavelength ranges and with different non-linear
damping terms. Finally, we also show that reconstruction reduces the
mode-coupling term in the power spectrum, explaining why mis-calibrations of
the acoustic scale are reduced when one considers the reconstructed power
spectrum.",0812.2905v3
2009-01-28,Location- and observation time-dependent quantum-tunneling,"We investigate quantum tunneling in a translation invariant chain of
particles. The particles interact harmonically with their nearest neighbors,
except for one bond, which is anharmonic. It is described by a symmetric double
well potential. In the first step, we show how the anharmonic coordinate can be
separated from the normal modes. This yields a Lagrangian which has been used
to study quantum dissipation. Elimination of the normal modes leads to a
nonlocal action of Caldeira-Leggett type. If the anharmonic bond defect is in
the bulk, one arrives at Ohmic damping, i.e. there is a transition of a
delocalized bond state to a localized one if the elastic constant exceeds a
critical value $C_{crit}$. The latter depends on the masses of the bond defect.
Superohmic damping occurs if the bond defect is in the site $M$ at a finite
distance from one of the chain ends. If the observation time $T$ is smaller
than a characteristic time $\tau_M \sim M$, depending on the location M of the
defect, the behavior is similar to the bulk situation. However, for $T \gg
\tau_M$ tunneling is never suppressed.",0901.4518v1
2009-02-16,Plasmon excitations in homogeneous neutron star matter,"We study the possible collective plasma modes which can affect neutron-star
thermodynamics and different elementary processes in the baryonic density range
between nuclear saturation ($\rho_0$) and $3\rho_0$. In this region, the
expected constituents of neutron-star matter are mainly neutrons, protons,
electrons and muons ($npe\mu$ matter), under the constraint of beta
equilibrium. The elementary plasma excitations of the $pe\mu$ three-fluid
medium are studied in the RPA framework. We emphasize the relevance of the
Coulomb interaction among the three species, in particular the interplay of the
electron and muon screening in suppressing the possible proton plasma mode,
which is converted into a sound-like mode. The Coulomb interaction alone is
able to produce a variety of excitation branches and the full spectral function
shows a rich structure at different energy. The genuine plasmon mode is pushed
at high energy and it contains mainly an electron component with a substantial
muon component, which increases with density. The plasmon is undamped for not
too large momentum and is expected to be hardly affected by the nuclear
interaction. All the other branches, which fall below the plasmon, are damped
or over-damped.",0902.2552v2
2009-02-27,Monogamy Inequality and Residual Entanglement of Three Qubits under Decoherence,"Exploring an analytical expression for the convex roof of the pure state
squared concurrence for rank 2 mixed states the entanglement of a system of
three particles under decoherence is studied, using the monogamy inequality for
mixed states and the residual entanglement obtained from it. The monogamy
inequality is investigated both for the concurrence and the negativity in the
case of local independent phase damping channel acting on generalized GHZ
states of three particles and the local independent amplitude damping channel
acting on generalized W state of three particles. It is shown that the
bipartite entanglement between one qubit and the rest has a qualitative similar
behavior to the entanglement between individual qubits, and that the residual
entanglement in terms of the negativity cannot be a good entanglement measure
for mixed states, since it can increase under local decoherence.",0903.0019v2
2009-03-12,X-band crab cavities for the CLIC beam delivery system,"The CLIC machine incorporates a 20 mrad crossing angle at the IP to aid the
extraction of spent beams. In order to recover the luminosity lost through the
crossing angle a crab cavity is proposed to rotate the bunches prior to
collision. The crab cavity is chosen to have the same frequency as the main
linac (11.9942 GHz) as a compromise between size, phase stability requirements
and beam loading. It is proposed to use a HE11 mode travelling wave structure
as the CLIC crab cavity in order to minimise beam loading and mode separation.
The position of the crab cavity close to the final focus enhances the effect of
transverse wake-fields so effective wake-field damping is required. A damped
detuned structure is proposed to suppress and de-cohere the wake-field hence
reducing their effect. Design considerations for the CLIC crab cavity will be
discussed as well as the proposed high power testing of these structures at
SLAC.",0903.2116v1
2009-03-16,Regularity of invariant sets in semilinear damped wave equations,"Under fairly general assumptions, we prove that every compact invariant
subset $\mathcal I$ of the semiflow generated by the semilinear damped wave
equation \epsilon u_{tt}+u_t+\beta(x)u-\sum_{ij}(a_{ij}
(x)u_{x_j})_{x_i}&=f(x,u),&& (t,x)\in[0,+\infty[\times\Omega,
u&=0,&&(t,x)\in[0,+\infty[\times\partial\Omega in $H^1_0(\Omega)\times
L^2(\Omega)$ is in fact bounded in $D(\mathbf A)\times H^1_0(\Omega)$. Here
$\Omega$ is an arbitrary, possibly unbounded, domain in $\R^3$, $\mathbf A
u=\beta(x)u-\sum_{ij}(a_{ij}(x)u_{x_j})_{x_i}$ is a positive selfadjoint
elliptic operator and $f(x,u)$ is a nonlinearity of critical growth. The
nonlinearity $f(x,u)$ needs not to satisfy any dissipativeness assumption and
the invariant subset $\mathcal I$ needs not to be an an attractor.",0903.2782v1
2009-03-20,Hawking-Unruh radiation as irreversible consequence of radiative action in dynamics,"Hawking-Unruh thermal state of warm surrounding field encountered in
non-inertial frames is shown to be a real phenomenon, a marker of nonstationary
dynamic evolutions. In accelerated motion of a charged particle it is shown
that the recoiled damping effect of Larmor radiation relaxation leads to
distinctive thermal power, which is akin to that of Hawking-Unruh radiation
from warm surrounding field of the accelerated charge. The damping effect from
recoil-momentum of transverse electromagnetic field is worked out by
considering torque imparted to the inherently existing angular evolution of
spherically polarized vacuum field around the point-like charged particle in
acceleration. Hawking-Unruh effects is generally noted to be a universal marker
of decoherence in evolution in all scales of microscopic, macroscopic and
megascopic systems. Besides detailing the case of electrodynamics, the various
efficacies of H-U relaxation are considered in the nonstationary evolutions.",0903.3529v2
2009-03-25,The covering factor of high redshift damped Lyman-$α$ systems,"We have used the Very Long Baseline Array to image 18 quasars with foreground
damped Lyman-$\alpha$ systems (DLAs) at 327, 610 or 1420 MHz, to measure the
covering factor $f$ of each DLA at or near its redshifted HI 21cm line
frequency. Including six systems from the literature, we find that none of 24
DLAs at $0.09 < z < 3.45$ has an exceptionally low covering factor, with $f
\sim 0.45 - 1$ for the 14 DLAs at $z > 1.5$, $f \sim 0.41 - 1$ for the 10
systems at $z < 1$, and consistent covering factor distributions in the two
sub-samples. The observed paucity of detections of HI 21cm absorption in
high-$z$ DLAs thus cannot be explained by low covering factors and is instead
likely to arise due to a larger fraction of warm HI in these absorbers.",0903.4483v1
2009-04-15,Size dependent Acoustic Phonon Dynamics of CdTe0.68Se0.32 Nanoparticles in Borosilicate glass,"Low frequency acoustic vibration and phonon linewidth for CdTe0.68Se0.32
nanoparticle embedded in borosilicate glass are calculated using two different
approaches by considering the elastic continuum model and fixed boundary
condition. The presence of medium significantly affects the phonon peaks and
results into the broadening of the modes. The linewidth is found to depend
inversely on the size, similar to that reported experimentally. The damping
time and quality factor have also been calculated. The damping time that is of
the order of picoseconds decreases with the decrease in size. High value of
quality factor for l=2 normal mode suggests the less loss of energy for this
mode.",0904.2278v1
2009-04-19,Incorporating Human Body Mass in Standards of Helmet Impact Protection against Traumatic Brain Injury,"Impact induced traumatic brain injury (ITBI) describes brain injury from head
impact not necessarily accompanied by skull fracture. For sufficiently abrupt
head impact decelerations, ITBI results from brain tissue stress incurred as
the brain crashes into the inside of the skull wall, displacing the surrounding
cerebral spinal fluid (CSF). Proper helmet cushioning can damp the impact force
and reduce ITBI. But force is mass times acceleration and commonly used helmet
blunt impact standards are based only on acceleration thresholds. Here I show
how this implies that present standards overestimate the minimum acceleration
onset for ITBI by implicitly assuming that the brain is mechanically decoupled
from the body. I quantify how an arbitrary orientation of the body with respect
to impact direction increases the effective mass that should be used in
calculating the required damping force and injury threshold accelerations. I
suggest a practical method to incorporate the body mass and impact angle into
ITBI helmet standards and provide direction for further work.",0904.2856v1
2009-04-21,Type II migration of planets on eccentric orbits,"The observed extrasolar planets possess both large masses (with a median M
sin i of 1.65 MJ) and a wide range in orbital eccentricity (0 < e < 0.94). As
planets are thought to form in circumstellar disks, one important question in
planet formation is determining whether, and to what degree, a gaseous disk
affects an eccentric planet's orbit. Recent studies have probed the interaction
between a disk and a terrestrial planet on an eccentric orbit, and the
interaction between a disk and a gas giant on a nearly circular orbit, but
little is known about the interaction between a disk and an eccentric gas
giant. Such a scenario could arise due to scattering while the disk is still
present, or perhaps through planet formation via gravitational instability. We
fill this gap with simulations of eccentric, massive (gap-forming) planets in
disks using the hydrodynamical code FARGO. Although the long-term orbital
evolution of the planet depends on disk properties, including the boundary
conditions used, the disk always acts to damp eccentricity when the planet is
released into the disk. This eccentricity damping takes place on a timescale of
40 years, 15 times faster than the migration timescale.",0904.3336v1
2009-05-13,J-transform applied to the detection of Gravitational Waves: preliminary results,"We propose to apply to the detection of Gravitational Waves a new method
developed for the spectral analysis of noisy time-series of damped oscillators.
  From the Pad\'e Approximations of the time-series Z-transform, a Jacobi
Matrix (J-Matrix) is constructed. We show that the J-Matrix has bound states
with eigenvalues strictly inside the unit circle. Each bound state can be
identified with one precise damped oscillator. Beside these bound states, there
is an essential spectrum sitting on the unit circle which represents the noise.
In this picture, signal and noise are clearly separated and identified in the
complex plane. Furthermore, we show that the J-transform enjoys the exceptional
feature of lossless undersampling. We take advantage of the above properties of
the J-transform to develop a procedure for the search of Gravitational Wave
bursts in interferometric data series such as those of LIGO and VIRGO projects.
Successful application of our procedure to simulated data having a poor signal
to noise ratio, highlights the power of our method.",0905.2000v1
2009-05-25,Non-Markovian dynamics of a biased qubit coupled to a structured bath,"A new analytical approach, beyond rotating wave approximation, based on
unitary transformations and the non-Markovian master equation for the density
operator, is applied to treat the biased spin boson model with a Lorentzian
structured bath for arbitrary detunings at zero temperature. Compared to zero
bias, we find that the dynamics demonstrates two more damping oscillation
frequencies and one additional relaxation frequency for non-zero bias, where
one of the damping oscillation frequencies is a new effect. Analytical
expressions for the non-Markovian dynamics and the corresponding spectrum, the
localized-delocalized transition point, the coherent-incoherent transition
point, the analytical ground energy, the renormalized tunneling factor and the
susceptibility are determined. The sum rule and the Shiba relation are checked
in the coherent regime.",0905.3965v3
2009-05-28,A black box method for solving the complex exponentials approximation problem,"A common problem, arising in many different applied contexts, consists in
estimating the number of exponentially damped sinusoids whose weighted sum best
fits a finite set of noisy data and in estimating their parameters. Many
different methods exist to this purpose. The best of them are based on
approximate Maximum Likelihood estimators, assuming to know the number of
damped sinusoids, which can then be estimated by an order selection procedure.
As the problem can be severely ill posed, a stochastic perturbation method is
proposed which provides better results than Maximum Likelihood based methods
when the signal-to-noise ratio is low. The method depends on some
hyperparameters which turn out to be essentially independent of the
application. Therefore they can be fixed once and for all, giving rise to a
black box method.",0905.4602v2
2009-06-10,GALEX Discovery of a Damped Ly-alpha System at Redshift z = 1,"We report the first discovery of a QSO damped Ly-alpha (DLA) system by the
GALEX satellite. The system was initially identified as an MgII absorption-line
system (z_abs=1.028) in the spectrum of SDSS QSO J0203-0910 (z_em=1.58). The
presence of unusually strong absorption due to metal lines of ZnII, CrII, MnII,
and FeII clearly suggested that it might be a DLA system with N{HI} > 2 x 10^20
atoms cm^-2. Follow-up GALEX NUV grism spectroscopy confirms the system
exhibits a DLA absorption line, with a measured HI column density of N{HI} =
1.50+/-0.45 x 10^21 atoms cm^-2. By combining the GALEX N{HI} determination
with the SDSS spectrum measurements of unsaturated metal-line absorption due to
ZnII, which is generally not depleted onto grains, we find that the system's
neutral-gas-phase metal abundance is [Zn/H] = -0.69+/-0.22, or ~20% solar. By
way of comparison, although this system has one of the largest Zn^+ column
densities, its metal abundances are comparable to other DLAs at z~1.
Measurements of the abundances of Cr, Fe, and Mn help to further pin down the
evolutionary state of the absorber.",0906.2018v1
2009-06-11,Longitudinal Stability of Recycler Bunches; Part I: Thresholds for Loss of Landau Damping,"We examine the stability of intense flat bunches in barrier buckets used in
the Recycler. We consider some common stationary distributions and show that
they would be unstable against rigid dipole oscillations. We then discuss an
analytical model for the line density that best describes measured bunch
profiles. We include space charge in this model to predict the bunch intensity
at which Landau damping would be lost. The dependence of this threshold on the
bunch length is studied and related to the results of an experimental study
with shorter bunch lengths. The threshold for the microwave instability is
estimated. These studies will be followed by more detailed numerical studies.",0906.2188v1
2009-06-15,Regge poles of the Schwarzschild black hole: a WKB approach,"We provide simple and accurate analytical expressions for the Regge poles of
the Schwarzschild black hole. This is achieved by using third-order WKB
approximations to solve the radial wave equations for spins 0, 1 and 2. These
results permit us to obtain analytically the dispersion relation and the
damping of the ""surface waves"" lying on the photon sphere of the Schwarzschild
black hole and which generate the weakly damped quasinormal modes of its
spectrum. Our results could be helpful in order to simplify considerably the
description of wave scattering from the Schwarzschild black hole as well as the
analysis of the gravitational radiation created in many black hole processes.
Furthermore, the existence of dispersion relations for the photons propagating
close to the photon sphere could have also important consequences in the
context of gravitational lensing.",0906.2601v3
2009-06-30,Cooling a magnetic resonance force microscope via the dynamical back-action of nuclear spins,"We analyze the back-action influence of nuclear spins on the motion of the
cantilever of a magnetic force resonance microscope. We calculate the
contribution of nuclear spins to the damping and frequency shift of the
cantilever. We show that, at the Rabi frequency, the energy exchange between
the cantilever and the spin system cools or heats the cantilever depending on
the sign of the high-frequency detuning. We also show that the spin noise leads
to a significant damping of the cantilever motion.",0906.5420v2
2009-07-03,Magnetic interference patterns in long disordered Josephson junctions,"We study a diffusive superconductor - normal metal - superconductor (SNS)
junction in an external magnetic field. In the limit of a long junction, we
find that the form of the dependence of the Josephson current on the field and
on the length of the junction depends on the ratio between the junction width
and the length associated with the magnetic field. A certain critical ratio
between these two length scales separates two different regimes. In narrow
junctions, the critical current exhibits a pure decay as a function of the
junction length or of the magnetic field. In wide junctions, the critical
current exhibits damped oscillations as a function of the same parameters. This
damped oscillating behavior differs from the Fraunhofer pattern typical for
short or tunnel junctions. In wide and long junctions, superconducting pair
correlations and supercurrent are localized along the edges of the junction.",0907.0632v3
2009-07-12,Symmetries shape the current in ratchets induced by a bi-harmonic force,"Equations describing the evolution of particles, solitons, or localized
structures, driven by a zero-average, periodic, external force, and invariant
under time reversal and a half-period time shift, exhibit a ratchet current
when the driving force breaks these symmetries. The bi-harmonic force
$f(t)=\epsilon_1\cos(q \omega t+\phi_1)+\epsilon_2\cos(p\omega t+\phi_2)$ does
it for almost any choice of $\phi_{1}$ and $\phi_{2}$, provided $p$ and $q$ are
two co-prime integers such that $p+q$ is odd. It has been widely observed, in
experiments in Josephson-junctions, photonic crystals, etc., as well as in
simulations, that the ratchet current induced by this force has the shape
$v\propto\epsilon_1^p\epsilon_2^q\cos(p \phi_{1} - q \phi_{2} + \theta_0)$ for
small amplitudes, where $\theta_0$ depends on the damping ($\theta_0=\pi/2$ if
there is no damping, and $\theta_0=0$ for overdamped systems). We rigorously
prove that this precise shape can be obtained solely from the broken symmetries
of the system and is independent of the details of the equation describing the
system.",0907.2029v2
2009-07-21,AFM Dissipation Topography of Soliton Superstructures in Adsorbed Overlayers,"In the atomic force microscope, the nanoscale force topography of even
complex surface superstructures is extracted by the changing vibration
frequency of a scanning tip. An alternative dissipation topography with similar
or even better contrast has been demonstrated recently by mapping the
(x,y)-dependent tip damping but the detailed damping mechanism is still
unknown. Here we identify two different tip dissipation mechanisms: local
mechanical softness and hysteresis. Motivated by recent data, we describe both
of them in a onedimensional model of Moire' superstructures of incommensurate
overlayers. Local softness at ""soliton"" defects yields a dissipation contrast
that can be much larger than the corresponding density or corrugation contrast.
At realistically low vibration frequencies, however, a much stronger and more
effective dissipation is caused by the tip-induced nonlinear jumping of the
soliton, naturally developing bistability and hysteresis. Signatures of this
mechanism are proposed for experimental identification.",0907.3585v4
2009-07-24,Harmonic damped oscillators with feedback. A Langevin study,"We consider a system in direct contact with a thermal reservoir and which, if
left unperturbed, is well described by a memory-less equilibrium Langevin
equation of the second order in the time coordinate. In such conditions, the
strength of the noise fluctuations is set by the damping factor, in accordance
with the Fluctuation and Dissipation theorem. We study the system when it is
subject to a feedback mechanism, by modifying the Langevin equation
accordingly. Memory terms now arise in the time evolution, which we study in a
non-equilibrium steady state. Two types of feedback schemes are considered, one
focusing on time shifts and one on phase shifts, and for both cases we evaluate
the power spectrum of the system's fluctuations. Our analysis finds application
in feedback cooled oscillators, such as the Gravitational Wave detector AURIGA.",0907.4309v1
2009-08-19,Quantum Energy Teleportation with Electromagnetic Field: Discrete vs. Continuous Variables,"It is well known that usual quantum teleportation protocols cannot transport
energy. Recently, new protocols called quantum energy teleportation (QET) have
been proposed, which transport energy by local operations and classical
communication with the ground states of many-body quantum systems. In this
paper, we compare two different QET protocols for transporting energy with
electromagnetic field. In the first protocol, a 1/2 spin (a qubit) is coupled
with the quantum fluctuation in the vacuum state and measured in order to
obtain one-bit information about the fluctuation for the teleportation. In the
second protocol, a harmonic oscillator is coupled with the fluctuation and
measured in order to obtain continuous-variable information about the
fluctuation. In the spin protocol, the amount of teleported energy is
suppressed by an exponential damping factor when the amount of input energy
increases. This suppression factor becomes power damping in the case of the
harmonic oscillator protocol. Therefore, it is concluded that obtaining more
information about the quantum fluctuation leads to teleporting more energy.
This result suggests a profound relationship between energy and quantum
information.",0908.2674v2
2009-08-25,Designing materials for plasmonic systems,"We use electronic structure calculations based upon density functional theory
to search for ideal plasmonic materials among the alkali noble intermetallics.
Importantly, we use density functional perturbation theory to calculate the
electron-phonon interaction and from there use a first order solution to the
Boltzmann equation to estimate the phenomenological damping frequency in the
Drude dielectric function. We discuss the necessary electronic features of a
plasmonic material and investigate the optical properties of the alkali-noble
intermetallics in terms of some generic plasmonic system quality factors. We
conclude that at low negative permittivities, KAu with a damping frequency of
0.0224 eV and a high optical gap to bare plasma frequency ratio, outperforms
gold and to some extent silver as a plasmonic material. Unfortunately, a low
plasma frequency (1.54 eV) reduces its utility in modern plasmonics
applications. We also discuss, briefly, the effect of local fields on the
optical properties of these materials.",0908.3707v1
2009-09-15,Quantum critical points of Helical Fermi Liquids,"Following our previous work, we study the quantum phase transitions which
spontaneously develop ferromagnetic spin order in helical fermi liquids which
breaks continuous spin-space rotation symmetry, with application to the edge
states of 3d topological band insulators. With finite fermi surface, the
critical point has both z = 3 over-damped and z = 2 propagating quantum
critical modes, and the z = 3 mode will lead to non-fermi liquid behavior on
the entire fermi surface. In the ordered phase, the Goldstone mode is
over-damped unless it propagates along special directions, and quasiparticle is
ill defined on most parts of the fermi surface except for special points.
Generalizations of our results to other systems with spin-orbit couplings are
also discussed.",0909.2647v3
2009-09-25,Evidence for Landau's critical velocity in superfluid helium nanodroplets from wave packet dynamics of attached potassium dimers,"Femtosecond pump-probe spectroscopy has been used to study vibrational
dynamics of potassium dimers attached to superfluid helium nanodroplets.
Comparing the measured data with theoretical results based on dissipative
quantum dynamics we propose that the most important effect of the helium
environment is a general damping of the vibrational dynamics as a result of the
interaction between dimer and collective degrees of freedom of the helium
droplet. The calculations allow us to explain crucial experimental findings
that are unobserved in gas-phase measurements. Remarkably, best agreement with
experiment is found for a model where we neglect damping once a wave packet
moves below a critical velocity. In this way the results provide first direct
evidence for the Landau critical velocity in superfluid nanodroplets.",0909.4691v1
2009-10-23,Fragmentation of the photoabsorption strength in neutral and charged metal microclusters,"The line shape of the plasma resonance in both neutral and charged small
sodium clusters is calculated. The overall properties of the multipeak
structure observed in the photoabsorption cross section of spherical Na_8 and
Na_20 neutral clusters can be understood in terms of Landau damping. Quantal
configurations are shown to play an important role. In the case of charged
Na_9+ and Na_21^+ clusters a single peak is predicted that carries most of the
oscillator strength.",0910.4576v1
2009-10-28,Quantum Decoherence of Two Qubits,"It is commonly stated that decoherence in open quantum systems is due to
growing entanglement with an environment. In practice, however, surprisingly
often decoherence may equally well be described by random unitary dynamics
without invoking a quantum environment at all. For a single qubit, for
instance, pure decoherence (or phase damping) is always of random unitary type.
Here, we construct a simple example of true quantum decoherence of two qubits:
we present a feasible phase damping channel of which we show that it cannot be
understood in terms of random unitary dynamics. We give a very intuitive
geometrical measure for the positive distance of our channel to the convex set
of random unitary channels and find remarkable agreement with the so-called
Birkhoff defect based on the norm of complete boundedness.",0910.5364v1
2009-10-29,System-reservoir dynamics of quantum and classical correlations,"We address the system-reservoir dynamics of classical and quantum
correlations in the decoherence phenomenon, regarding a two qubit composite
system interacting with two independent environments. The most common noise
channels (amplitude damping, phase damping, bit flip, bit-phase flip, and phase
flip) was studied. By analytical and numerical analysis we found that, contrary
to what is usually stated in the literature, decoherence may occurs without
entanglement between the system and the environment. We also found that, in
some cases, the bipartite quantum correlation initially presented in the system
is completely evaporated, it is not transferred to the environments.",0910.5711v3
2009-11-04,Nonlinear damping in a micromechanical oscillator,"Nonlinear elastic effects play an important role in the dynamics of
microelectromechanical systems (MEMS). Duffing oscillator is widely used as an
archetypical model of mechanical resonators with nonlinear elastic behavior. In
contrast, nonlinear dissipation effects in micromechanical oscillators are
often overlooked. In this work, we consider a doubly clamped micromechanical
beam oscillator, which exhibits nonlinearity in both elastic and dissipative
properties. The dynamics of the oscillator is measured in frequency domain and
time domain and compared to theoretical predictions based on Duffing-like model
with nonlinear dissipation. We especially focus on the behavior of the system
near bifurcation points. The results show that nonlinear dissipation can have a
significant impact on the dynamics of micromechanical systems. To account for
the results, we have developed a continuous model of a nonlinear viscoelastic
string with Voigt-Kelvin dissipation relation, which shows a relation between
linear and nonlinear damping. However, the experimental results suggest that
this model alone cannot fully account for all the experimentally observed
nonlinear dissipation, and that additional nonlinear dissipative processes
exist in our devices.",0911.0833v2
2009-11-04,Solar-like oscillations in massive main-sequence stars. I. Asteroseismic signatures of the driving and damping regions,"Motivated by the recent detection of stochastically excited modes in the
massive star V1449 Aql (Belkacem et al., 2009b), already known to be a $\beta$
Cephei, we theoretically investigate the driving by turbulent convection. By
using a full non-adiabatic computation of the damping rates, together with a
computation of the energy injection rates, we provide an estimate of the
amplitudes of modes excited by both the convective region induced by the iron
opacity bump and the convective core. Despite uncertainties in the dynamical
properties of such convective regions, we demonstrate that both are able to
efficiently excite $p$ modes above the CoRoT observational threshold and the
solar amplitudes. In addition, we emphasise the potential asteroseismic
diagnostics provided by each convective region, which we hope will help to
identify the one responsible for solar-like oscillations, and to give
constraints on this convective zone. A forthcoming work will be dedicated to an
extended investigation of the likelihood of solar-like oscillations across the
Hertzsprung-Russell diagram.",0911.0908v1
2009-11-11,Ginzburg-Landau equation for dynamical four-wave mixing in gain nonlinear media with relaxation,"We consider the dynamical degenerate four-wave mixing (FWM) model in a cubic
nonlinear medium including both the time relaxation of the induced nonlinearity
and the nonlocal coupling. The initial ten-dimensional FWM system can be
rewritten as a three-variable intrinsic system (namely the intensity pattern,
the amplitude of the nonlinearity and the total net gain) which is very close
to the pumped Maxwell-Bloch system. In the case of a purely nonlocal response
the initial system reduces to a real damped sine-Gordon (SG) equation. We
obtain a new solution of this equation in the form of a sech function with a
time-dependent coefficient. By applying the reductive perturbation method to
this damped SG equation, we obtain exactly the cubic complex Ginzburg Landau
equation (CGL3), but with a time dependence in the loss/gain coefficient. The
CGL3 describes the properties of the spatially localized interference pattern
formed by the FWM.",0911.2129v1
2009-12-10,Bipartite quantum channels using multipartite cluster-type entangled coherent states,"We propose a particular encoding for bipartite entangled states derived from
multipartite cluster-type entangled coherent states (CTECSs). We investigate
the effects of amplitude damping on the entanglement content of this bipartite
state, as well as its usefulness as a quantum channel for teleportation. We
find interesting relationships among the amplitude of the coherent states
constituting the CTECSs, the number of subsystems forming the logical qubits
(redundancy), and the extent to which amplitude damping affects the
entanglement of the channel. For instance, in the sense of sudden death of
entanglement, given a fixed value of the initial coherent state amplitude, the
entanglement life span is shortened if redundancy is increased.",0912.1949v2
2009-12-18,Oscillatory transient regime in the forced dynamics of a spin torque nano-oscillator,"We demonstrate that the transient non-autonomous dynamics of a spin torque
nano-oscillator (STNO) under a radio-frequency (rf) driving signal is
qualitatively different from the dynamics described by the Adler model. If the
external rf current $I_{rf}$ is larger than a certain critical value $I_{cr}$
(determined by the STNO bias current and damping) strong oscillations of the
STNO power and phase develop in the transient regime. The frequency of these
oscillations increases with $I_{rf}$ as $\propto\sqrt{I_{rf} - I_{cr}}$ and can
reach several GHz, whereas the damping rate of the oscillations is almost
independent of $I_{rf}$. This oscillatory transient dynamics is caused by the
strong STNO nonlinearity and should be taken into account in most STNO rf
applications.",0912.3650v1
2009-12-19,Study of sdO models: mode trapping,"We present the first description of mode trapping for sdO models. Mode
trapping of gravity modes caused by the He/H chemical transition is found for a
particular model, providing a selection effect for high radial order trapped
modes. Low- and intermediate-radial order {\em p}-modes (mixed modes with a
majority of nodes in the P-mode region) are found to be trapped by the C-O/He
transition, but with no significant effects on the driving. This region seems
to have also a subtle effect on the trapping of low radial order {\em g}-modes
(mixed modes with a majority of nodes in the G-mode region), but again with no
effect on the driving. We found that for mode trapping to have an influence on
the driving of sdO modes (1) the mode should be trapped in a way that the
amplitude of the eigenfunctions is lower in a damping region and (2) in this
damping region significant energy interchange has to be produced.",0912.3911v1
2009-12-20,Optimal Design of Fuzzy Based Power System Stabilizer Self Tuned by Robust Search Algorithm,"In the interconnected power system network, instability problems are caused
mainly by the low frequency oscillations of 0.2 to 2.5 Hz. The supplementary
control signal in addition with AVR and high gain excitation systems are
provided by means of Power System Stabilizer (PSS). Conventional power system
stabilizers provide effective damping only on a particular operating point. But
fuzzy based PSS provides good damping for a wide range of operating points. The
bottlenecks faced in designing a fuzzy logic controller can be minimized by
using appropriate optimization techniques like Genetic Algorithm, Particle Swam
Optimization, Ant Colony Optimization etc.In this paper the membership
functions of FLC are optimized by the new breed optimization technique called
Genetic Algorithm. This design methodology is implemented on a Single Machine
Infinite Bus (SMIB) system. Simulation results on SMIB show the effectiveness
and robustness of the proposed PSS over a wide range of operating conditions
and system configurations.",0912.3960v2
2009-12-23,Decoherence and Entanglement Dynamics in Fluctuating Fields,"We study pure phase damping of two qubits due to fluctuating fields. As
frequently employed, decoherence is thus described in terms of random unitary
(RU) dynamics, i.e., a convex mixture of unitary transformations. Based on a
separation of the dynamics into an average Hamiltonian and a noise channel, we
are able to analytically determine the evolution of both entanglement and
purity. This enables us to characterize the dynamics in a concurrence-purity
(CP) diagram: we find that RU phase damping dynamics sets constraints on
accessible regions in the CP plane. We show that initial state and dynamics
contribute to final entanglement independently.",0912.4654v2
2010-01-02,Distinguishing quantum channels via magic squares game,"We study the effect of quantum memory in magic squares game when played in
quantum domain. We consider different noisy quantum channels and analyze their
influence on the magic squares quantum pseudo-telepathy game. We show that the
probability of success can be used to distinguish the quantum channels. It is
seen that the mean success probability decreases with increase of quantum
noise. Where as the mean success probability increases with increase of quantum
memory. It is also seen that the behaviour of amplitude damping and phase
damping channels is similar. On the other hand, the behaviour of depolarizing
channel is similar to the flipping channels. Therefore, the probability of
success of the game can be used to distinguish the quantum channels.",1001.0295v1
2010-01-06,Freezing of spin dynamics and omega/T scaling in underdoped cuprates,"The memory function approach to spin dynamics in doped antiferromagnetic
insulator combined with the assumption of temperature independent static spin
correlations and constant collective mode damping leads to omega/T scaling in a
broad range. The theory involving a non universal scaling parameter is used to
analyze recent inelastic neutron scattering results for underdoped cuprates.
Adopting modified damping function also the emerging central peak in low-doped
cuprates at low temperatures can be explained within the same framework.",1001.0837v1
2010-01-15,Calculating Green Functions from Finite Systems,"In calculating Green functions for interacting quantum systems numerically
one often has to resort to finite systems which introduces a finite size level
spacing. In order to describe the limit of system size going to infinity
correctly, one has to introduce an artificial broadening larger than the finite
size level discretization. In this work we compare various discretization
schemes for impurity problems, i.e. a small system coupled to leads. Starting
from a naive linear discretization we will then discuss the logarithmic
discretization of the Wilson NRG, compare it to damped boundary conditions and
arbitrary discretization in energy space. We then discuss the importance of
choosing the right single particle basis when calculating bulk spectral
functions. Finally we show the influence of damped boundary conditions on the
time evolution of wave packets leading to a NRG-tsunami.",1001.2750v1
2010-02-02,Inertial Oscillations of Pinned Dislocations,"Dislocation pinning plays a vital role in the plastic behaviour of a
crystalline solid. Here we report the first observation of the damped
oscillations of a mobile dislocation after it gets pinned at an obstacle in the
presence of a constant static shear load. These oscillations are found to be
inertial, instead of forced as obtained in the studies of internal friction of
solid. The rate of damping enables us to determine the effective mass of the
dislocation. Nevertheless, the observed relation between the oscillation
frequency and the link length is found to be anomalous, when compared with the
theoretical results in the framework of Koehler's vibrating string model. We
assign this anomaly to the improper boundary conditions employed in the
treatment. Finally, we propose that the inertial oscillations may offer a
plausible explanation of the electromagnetic emissions during material
deformation and seismic activities.",1002.0422v1
2010-02-03,Nonlinear stability of viscous roll waves,"Extending results of Oh--Zumbrun and Johnson--Zumbrun for parabolic
conservation laws, we show that spectral stability implies nonlinear stability
for spatially periodic viscous roll wave solutions of the one-dimensional St.
Venant equations for shallow water flow down an inclined ramp. The main new
issues to be overcome are incomplete parabolicity and the nonconservative form
of the equations, which leads to undifferentiated quadratic source terms that
cannot be handled using the estimates of the conservative case. The first is
resolved by treating the equations in the more favorable Lagrangian
coordinates, for which one can obtain large-amplitude nonlinear damping
estimates similar to those carried out by Mascia--Zumbrun in the related shock
wave case, assuming only symmetrizability of the hyperbolic part. The second is
resolved by the observation that, similarly as in the relaxation and detonation
cases, sources occurring in nonconservative components experience greater than
expected decay, comparable to that experienced by a differentiated source.",1002.0788v2
2010-02-05,Damped-driven KdV and effective equation for long-time behaviour of its solutions,"For the damped-driven KdV equation $$ \dot
u-\nu{u_{xx}}+u_{xxx}-6uu_x=\sqrt\nu \eta(t,x), x\in S^1, \int u dx\equiv
\int\eta dx\equiv0, $$ with $0<\nu\le1$ and smooth in $x$ white in $t$ random
force $\eta$, we study the limiting long-time behaviour of the KdV integrals of
motions $(I_1,I_2,...)$, evaluated along a solution $u^\nu(t,x)$, as $\nu\to0$.
We prove that %if $u=u^\nu(t,x)$ is a solution of the equation above, for
$0\le\tau:= \nu t \lesssim1$ the vector $
I^\nu(\tau)=(I_1(u^\nu(\tau,\cdot)),I_2(u^\nu(\tau,\cdot)),...), $ converges in
distribution to a limiting process $I^0(\tau)=(I^0_1,I^0_2,...)$. The $j$-th
component $I_j^0$ equals $\12(v_j(\tau)^2+v_{-j}(\tau)^2)$, where
$v(\tau)=(v_1(\tau), v_{-1}(\tau),v_2(\tau),...)$ is the vector of Fourier
coefficients of a solution of an {\it effective equation} for the
dam-ped-driven KdV. This new equation is a quasilinear stochastic heat equation
with a non-local nonlinearity, written in the Fourier coefficients. It is well
posed.",1002.1294v1
2010-02-09,Fate of non-Fermi liquid behavior in QED$_{3}$ at finite chemical potential,"The damping rate of two-dimensional massless Dirac fermions exhibit non-Fermi
liquid behavior, $\propto \epsilon^{1/2}$, due to gauge field at zero
temperature and zero chemical potential. We study the fate of this behavior at
finite chemical potential. We fist calculate explicitly the temporal and
spatial components of vacuum polarization functions. The analytical expressions
imply that the temporal component of gauge field develops a static screening
length at finite chemical potential while the transverse component remains
long-ranged owing to gauge invariance. We then calculate the fermion damping
rate and show that the temporal gauge field leads to normal Fermi liquid
behavior but the transverse gauge field leads to non-Fermi liquid behavior
$\propto \epsilon^{2/3}$ at zero temperature. This energy-dependence is more
regular than $\propto \epsilon^{1/2}$ and does not change as chemical potential
varies.",1002.1760v3
2010-02-18,Direct Evidence for Two-Fluid Effects in Molecular Clouds,"We present a combination of theoretical and simulation-based examinations of
the role of two-fluid ambipolar drift on molecular line widths. The dissipation
provided by ion-neutral interactions can produce a significant difference
between the widths of neutral molecules and the widths of ionic species,
comparable to the sound speed. We demonstrate that Alfven waves and certain
families of magnetosonic waves become strongly damped on scales comparable to
the ambipolar diffusion scale. Using the RIEMANN code, we simulate two-fluid
turbulence with ionization fractions ranging from 10^{-2} to 10^{-6}. We show
that the wave damping causes the power spectrum of the ion velocity to drop
below that of the neutral velocity when measured on a relative basis. Following
a set of motivational observations by Li & Houde (2008), we produce synthetic
line width-size relations that shows a difference between the ion and neutral
line widths, illustrating that two-fluid effects can have an observationally
detectable role in modifying the MHD turbulence in the clouds.",1002.3443v1
2010-03-08,Potential mechanical loss mechanisms in bulk materials for future gravitational wave detectors,"Low mechanical loss materials are needed to further decrease thermal noise in
upcoming gravitational wave detectors. We present an analysis of the
contribution of Akhieser and thermoelastic damping on the experimental results
of resonant mechanical loss measurements. The combination of both processes
allows the fit of the experimental data of quartz in the low temperature region
(10 K to 25 K). A fully anisotropic numerical calculation over a wide
temperature range (10 K to 300 K) reveals, that thermoelastic damping is not a
dominant noise source in bulk silicon samples. The anisotropic numerical
calculation is sucessfully applied to the estimate of thermoelastic noise of an
advanced LIGO sized silicon test mass.",1003.1613v1
2010-03-31,Non-Markovian master equation for a damped oscillator with time-varying parameters,"We derive an exact non-Markovian master equation that generalizes the
previous work [Hu, Paz and Zhang, Phys. Rev. D {\bf 45}, 2843 (1992)] to damped
harmonic oscillators with time-varying parameters. This is achieved by
exploiting the linearity of the system and operator solution in Heisenberg
picture. Our equation governs the non-Markovian quantum dynamics when the
system is modulated by external devices. As an application, we apply our
equation to parity kick decoupling problems. The time-dependent dissipative
coefficients in the master equation are shown to be modified drastically when
the system is driven by $\pi$ pulses. For coherence protection to be effective,
our numerical results indicate that kicking period should be shorter than
memory time of the bath. The effects of using soft pulses in an ohmic bath are
also discussed.",1003.5975v1
2010-04-08,Doppler cooling a microsphere,"Doppler cooling the center-of-mass motion of an optically levitated
microsphere via the velocity dependent scattering force from narrow whispering
gallery mode (WGM) resonances is described. Light that is red detuned from the
WGM resonance can be used to damp the center-of-mass motion in a process
analogous to the Doppler cooling of atoms. Leakage of photons out of the
microsphere when the incident field is near resonant with the narrow WGM
resonance acts to damp the motion of the sphere. The scattering force is not
limited by saturation, but can be controlled by the incident power. Cooling
times on the order of seconds are calculated for a 20 micron diameter silica
microsphere trapped within optical tweezers, with a Doppler temperature limit
in the microKelvin regime.",1004.1443v1
2010-05-17,Concerning the statistics of cosmic magnetism,"Magnetic fields appear to be a generic feature of the early universe and are
a natural source of secondary CMB non-Gaussianity. In recent years the
statistical nature of the stresses of a primordial magnetic field has been well
studied. In this paper we confirm and extend these studies at one- and
two-point level, and present analytical results for a wide range of power-law
spectra. We also consider two non-power law cases of interest: a blue spectrum
with an extended damping tail on small scales, which could be generated by the
non-linear mixing of density and vorticity; and a red spectrum with a damping
tail on large scales. We then briefly consider the CMB impacts that result from
such fields. While this paper focuses on the one- and two-point moments, the
techniques we employ are designed to ease the analysis of the full bispectra
induced by primordial magnetic fields.",1005.2982v1
2010-05-20,Line Solutions for the Euler and Euler-Poisson Equations with Multiple Gamma Law,"In this paper, we study the Euler and Euler-Poisson equations in $R^{N}$,
with multiple $\gamma$-law for pressure function: \begin{equation}
P(\rho)=e^{s}\sum_{j=1}^{m}\rho^{\gamma_{j}}, \end{equation} where all
$\gamma_{i+1}>\gamma_{i}\geq1$, is the constants. The analytical line solutions
are constructed for the systems. It is novel to discover the analytical
solutions to handle the systems with mixed pressure function. And our solutions
can be extended to the systems with the generalized multiple damping and
pressure function.",1005.3651v1
2010-06-12,Mechanical filtering in forced-oscillation of two coupled pendulums,"Forced oscillation of a system composed of two pendulums coupled by a spring
in the presence of damping is investigated. In the steady state and within the
small angle approximation we solve the system equations of motion and obtain
the amplitudes and phases of in terms of the frequency of the sinusoidal
driving force. The resonance frequencies are obtained and the amplitude ratio
is discussed in details. Contrary to a single oscillator, in this two-degree of
freedom system four resonant frequencies, which are close to mode frequencies,
appear. Within the pass-band interval the system is shown to exhibit a rich and
complicated behaviour. It is shown that damping crucially affects the system
properties. Under certain circumstances, the amplitude of the oscillator which
is directly connected to the driving force becomes smaller than the one far
from it. Particularly we show the existence of a driving frequency at which the
connected oscillator's amplitude goes zero.",1006.2475v1
2010-07-12,Ferromagnetic Excitations in La$_{0.82}$Sr$_{0.18}$CoO$_{3}$ Observed Using Neutron Inelastic Scattering,"Polarized neutron inelastic scattering has been used to measure spin
excitations in ferromagnetic La$_{0.82}$Sr$_{0.18}$CoO$_{3}$. The magnon
spectrum of these spin excitations is well defined at low energies but becomes
heavily damped at higher energies, and can be modeled using a quadratic
dispersion. We determined a spin wave stiffness constant of $D=94\pm
3$\,meV\,\AA$^{2}$. Assuming a nearest-neighbor Heisenberg model we find
reasonable agreement between the exchange determined from D and the bulk Curie
temperature. Several possible mechanisms to account for the observed spin-wave
damping are discussed.",1007.1919v1
2010-07-28,Minimization of phonon-tunneling dissipation in mechanical resonators,"Micro- and nanoscale mechanical resonators have recently emerged as
ubiquitous devices for use in advanced technological applications, for example
in mobile communications and inertial sensors, and as novel tools for
fundamental scientific endeavors. Their performance is in many cases limited by
the deleterious effects of mechanical damping. Here, we report a significant
advancement towards understanding and controlling support-induced losses in
generic mechanical resonators. We begin by introducing an efficient numerical
solver, based on the ""phonon-tunneling"" approach, capable of predicting the
design-limited damping of high-quality mechanical resonators. Further, through
careful device engineering, we isolate support-induced losses and perform the
first rigorous experimental test of the strong geometric dependence of this
loss mechanism. Our results are in excellent agreement with theory,
demonstrating the predictive power of our approach. In combination with recent
progress on complementary dissipation mechanisms, our phonon-tunneling solver
represents a major step towards accurate prediction of the mechanical quality
factor.",1007.4948v1
2010-08-05,Linear and Non-Linear Landau Resonance of Kinetic Alfvén Waves: Consequences for Electron Distribution and Wave Spectrum in the Solar Wind,"Kinetic Alfven wave turbulence in solar wind is considered and it is shown
that non-Maxwellian electron distribution function has a significant effect on
the dynamics of the solar wind plasmas. Linear Landau damping leads to the
formation of a plateau in the parallel electron distribution function which
diminishes the Landau damping rate significantly. Nonlinear scattering of waves
by plasma particles is generalized to short wavelengths and it is found that
for the solar wind parameters this scattering is the dominant process as
compared to three wave decay and coalescence in the wave vector range .
Incorporation of these effects lead to the steepening of the wave spectrum
between the inertial and the dissipation ranges with a spectral index between 2
and 3. This region can be labeled as the scattering range. Such steepening has
been observed in the solar wind plasmas.",1008.0993v1
2010-08-11,Theory for a dissipative droplet soliton excited by a spin torque nanocontact,"A novel type of solitary wave is predicted to form in spin torque oscillators
when the free layer has a sufficiently large perpendicular anisotropy. In this
structure, which is a dissipative version of the conservative droplet soliton
originally studied in 1977 by Ivanov and Kosevich, spin torque counteracts the
damping that would otherwise destroy the mode. Asymptotic methods are used to
derive conditions on perpendicular anisotropy strength and applied current
under which a dissipative droplet can be nucleated and sustained. Numerical
methods are used to confirm the stability of the droplet against various
perturbations that are likely in experiments, including tilting of the applied
field, non-zero spin torque asymmetry, and non-trivial Oersted fields. Under
certain conditions, the droplet experiences a drift instability in which it
propagates away from the nanocontact and is then destroyed by damping.",1008.1898v1
2010-08-18,Modulation stabilization of Bloch oscillations of two-component Bose-Einstein condensates in optical lattices,"We study the Bloch oscillations (BOs) of two-component Bose-Einstein
condensates (BECs) trapped in spin-dependent optical lattices. Based on the
derived equations of motion of the wave packet in the basis of localized wave
functions of the lattice sites, the damping effect induced by the
intercomponent and intracomponent interactions to the BOs is explored
analytically and numerically. We also show that such damping of the BOs can be
suppressed entirely if all the atom-atom interactions are modulated
synchronously and harmonically in time with suitable frequency via the Feshbach
resonance. When the intercomponent and the intracomponent interactions have
inverse signs, we find that the long-living BOs and even the revival of the BOs
can be achieved via only statically modulating the configuration of optical
lattices. The results provide a valuable guidance for achieving long-living BOs
in the two-component BEC system by the Feshbach resonances and manipulating the
configuration of the optical lattices.",1008.3004v1
2010-08-19,Josephson Coupling and Fiske Dynamics in Ferromagnetic Tunnel Junctions,"We report on the fabrication of Nb/AlO_x/Pd_{0.82}Ni_{0.18}/Nb
superconductor/insulator/ferromagnetic metal/superconductor (SIFS) Josephson
junctions with high critical current densities, large normal resistance times
area products, high quality factors, and very good spatial uniformity. For
these junctions a transition from 0- to \pi-coupling is observed for a
thickness d_F ~ 6 nm of the ferromagnetic Pd_{0.82}Ni_{0.18} interlayer. The
magnetic field dependence of the \pi-coupled junctions demonstrates good
spatial homogeneity of the tunneling barrier and ferromagnetic interlayer.
Magnetic characterization shows that the Pd_{0.82}Ni_{0.18} has an out-of-plane
anisotropy and large saturation magnetization, indicating negligible dead
layers at the interfaces. A careful analysis of Fiske modes provides
information on the junction quality factor and the relevant damping mechanisms
up to about 400 GHz. Whereas losses due to quasiparticle tunneling dominate at
low frequencies, the damping is dominated by the finite surface resistance of
the junction electrodes at high frequencies. High quality factors of up to 30
around 200 GHz have been achieved. Our analysis shows that the fabricated
junctions are promising for applications in superconducting quantum circuits or
quantum tunneling experiments.",1008.3341v1
2010-09-03,A Simple Numerical Absorbing Layer Method in Elastodynamics,"The numerical analysis of elastic wave propagation in unbounded media may be
difficult to handle due to spurious waves reflected at the model artificial
boundaries. Several sophisticated techniques such as nonreflecting boundary
conditions, infinite elements or absorbing layers (e.g. Perfectly Matched
Layers) lead to an important reduction of such spurious reflections. In this
Note, a simple and efficient absorbing layer method is proposed in the
framework of the Finite Element Method. This method considers Rayleigh/Caughey
damping in the absorbing layer and its principle is presented first. The
efficiency of the method is then shown through 1D Finite Element simulations
considering homogeneous and heterogeneous damping in the absorbing layer. 2D
models are considered afterwards to assess the efficiency of the absorbing
layer method for various wave types (surface waves, body waves) and incidences
(normal to grazing). The method is shown to be efficient for different types of
elastic waves and may thus be used for various elastodynamic problems in
unbounded domains.",1009.0592v1
2010-09-09,Modulation of waves due to charge-exchange collisions in magnetized partially ionized space plasma,"A nonlinear time dependent fluid simulation model is developed that describes
the evolution of magnetohydrodynamic waves in the presence of collisional and
charge exchange interactions of a partially ionized plasma. The partially
ionized plasma consists of electrons, ions and a significant number of neutral
atoms. In our model, the electrons and ions are described by a single fluid
compressible magnetohydrodynamic (MHD) model and are coupled self-consistently
to the neutral gas, described by the compressible hydrodynamic equations. Both
the plasma and neutral fluids are treated with different energy equations that
describe thermal energy exchange processes between them. Based on our
self-consistent model, we find that propagating Alfv\'enic and fast/slow modes
grow and damp alternately through a nonlinear modulation process. The
modulation appears to be robust and survives strong damping by the neutral
component.",1009.1859v1
2010-09-15,A discontinuous Galerkin method for the Vlasov-Poisson system,"A discontinuous Galerkin method for approximating the Vlasov-Poisson system
of equations describing the time evolution of a collisionless plasma is
proposed. The method is mass conservative and, in the case that piecewise
constant functions are used as a basis, the method preserves the positivity of
the electron distribution function and weakly enforces continuity of the
electric field through mesh interfaces and boundary conditions. The performance
of the method is investigated by computing several examples and error estimates
associated system's approximation are stated. In particular, computed results
are benchmarked against established theoretical results for linear advection
and the phenomenon of linear Landau damping for both the Maxwell and Lorentz
distributions. Moreover, two nonlinear problems are considered: nonlinear
Landau damping and a version of the two-stream instability are computed. For
the latter, fine scale details of the resulting long-time BGK-like state are
presented. Conservation laws are examined and various comparisons to theory are
made. The results obtained demonstrate that the discontinuous Galerkin method
is a viable option for integrating the Vlasov-Poisson system.",1009.3046v2
2010-10-03,Measurement of damping and temperature: Precision bounds in Gaussian dissipative channels,"We present a comprehensive analysis of the performance of different classes
of Gaussian states in the estimation of Gaussian phase-insensitive dissipative
channels. In particular, we investigate the optimal estimation of the damping
constant and reservoir temperature. We show that, for two-mode squeezed vacuum
probe states, the quantum-limited accuracy of both parameters can be achieved
simultaneously. Moreover, we show that for both parameters two-mode squeezed
vacuum states are more efficient than either coherent, thermal or single-mode
squeezed states. This suggests that at high energy regimes two-mode squeezed
vacuum states are optimal within the Gaussian setup. This optimality result
indicates a stronger form of compatibility for the estimation of the two
parameters. Indeed, not only the minimum variance can be achieved at fixed
probe states, but also the optimal state is common to both parameters.
Additionally, we explore numerically the performance of non-Gaussian states for
particular parameter values to find that maximally entangled states within
D-dimensional cutoff subspaces perform better than any randomly sampled states
with similar energy. However, we also find that states with very similar
performance and energy exist with much less entanglement than the maximally
entangled ones.",1010.0442v1
2010-10-12,Movers and shakers: Granular damping in microgravity,"The response of an oscillating granular damper to an initial perturbation is
studied using experiments performed in microgravity and granular dynamics
mulations. High-speed video and image processing techniques are used to extract
experimental data. An inelastic hard sphere model is developed to perform
simulations and the results are in excellent agreement with the experiments.
The granular damper behaves like a frictional damper and a linear decay of the
amplitude is bserved. This is true even for the simulation model, where
friction forces are absent. A simple expression is developed which predicts the
optimal damping conditions for a given amplitude and is independent of the
oscillation frequency and particle inelasticities.",1010.2343v1
2010-10-18,"K-shell photoionization of Na-like to Cl-like ions of Mg, Si, S, Ar, and Ca","We present $R$-matrix calculations of photoabsorption and photoionization
cross sections across the K-edge of Mg, Si, S, Ar, and Ca ions with more than
10 electrons. The calculations include the effects of radiative and Auger
damping by means of an optical potential. The wave functions are constructed
from single-electron orbital bases obtained using a Thomas--Fermi--Dirac
statistical model potential. Configuration interaction is considered among all
states up to $n=3$. The damping processes affect the resonances converging to
the K-thresholds causing them to display symmetric profiles of constant width
that smear the otherwise sharp edge at the photoionization threshold. These
data are important for modeling of features found in photoionized plasmas.",1010.3734v1
2010-10-19,A possible signature of cosmic neutrino decoupling in the nHz region of the spectrum of primordial gravitational waves,"In this paper we study the effect of cosmic neutrino decoupling on the
spectrum of cosmological gravitational waves (GWs). At temperatures T>>1 MeV,
neutrinos constitute a perfect fluid and do not hinder GW propagation, while
for T<<1 MeV they free-stream and have an effective viscosity that damps
cosmological GWs by a constant amount. In the intermediate regime,
corresponding to neutrino decoupling, the damping is frequency-dependent. GWs
entering the horizon during neutrino decoupling have a frequency f ~ 1 nHz,
corresponding to a frequency region that will be probed by Pulsar Timing Arrays
(PTAs). In particular, we show how neutrino decoupling induces a spectral
feature in the spectrum of cosmological GWs just below 1 nHz. We briefly
discuss the conditions for a detection of this feature and conclude that it is
unlikely to be observed by PTAs.",1010.3849v2
2010-10-20,"Modified Landau levels, damped harmonic oscillator and two-dimensional pseudo-bosons","In a series of recent papers one of us has analyzed in some details a class
of elementary excitations called {\em pseudo-bosons}. They arise from a special
deformation of the canonical commutation relation $[a,a^\dagger]=\1$, which is
replaced by $[a,b]=\1$, with $b$ not necessarily equal to $a^\dagger$. Here,
after a two-dimensional extension of the general framework, we apply the theory
to a generalized version of the two-dimensional Hamiltonian describing Landau
levels. Moreover, for this system, we discuss coherent states and we deduce a
resolution of the identity. We also consider a different class of examples
arising from a classical system, i.e. a damped harmonic oscillator.",1010.4221v1
2010-11-16,Forcibly driven coherent soft phonons in GeTe with intense THz-rate pump fields,"We propose an experimental technique to generate large amplitude coherent
phonons with irradiation of THz-rate pump pulses and to study the dynamics of
phase transition in GeTe ferroelectrics. When a single pump pulse irradiates
the sample at various pump power densities, the frequency of the soft phonon
decreases sub-linearly and saturates at higher pump powers. By contrast, when
THz-rate pump pulse sequence irradiates the sample at matched time intervals to
forcibly drive the oscillation, a large red-shift of the phonon frequency is
observed without saturation effects. After excitation with a four pump pulse
sequence, the coherent soft phonon becomes strongly damped leading to a near
critical damping condition. This condition indicates that the lattice is driven
to a precursor state of the phase transition.",1011.3624v2
2010-11-21,Regular and chaotic transport of discrete solitons in asymmetric potentials,"Ratchet dynamics of topological solitons of the forced and damped discrete
double sine-Gordon system are studied. Directed transport occurring both in
regular and in chaotic regions of the phase space and its dependence on
damping, amplitude and frequency of the driving, asymmetry parameter, coupling
constant, has been extensively investigated. We show that the passage from
ratchet phase-locked regime to chaotic ratchets occurs via a period doubling
route to chaos and that, quite surprisingly, pinned states can exist inside
phase-locking and chaotic transport regions for intermediate values of the
coupling constant. The possibility to control chaotic discrete soliton ratchets
by means of both small subharmonic signals and more general periodic drivings,
has also been investigated.",1011.4707v1
2010-11-26,Dependence of entanglement on initial states under amplitude damping channel in non-inertial frames,"Under amplitude damping channel, the dependence of the entanglement on the
initial states $|\Theta>_{1}$ and $|\Theta>_{2}$, which reduce to four
orthogonal Bell states if we take the parameter of states $\alpha=\pm
1/\sqrt{2}$ are investigated. We find that the entanglements for different
initial states will decay along different curves even with the same
acceleration and parameter of the states. We note that, in an inertial frame,
the sudden death of the entanglement for $|\Theta>_{1}$ will occur if
$\alpha>1/\sqrt{2}$, while it will not take place for $|\Theta>_{2}$ for any
$\alpha$. We also show that the possible range of the sudden death of the
entanglement for $|\Theta>_{1}$ is larger than that for $|\Theta>_{2}$. There
exist two groups of Bell state here we can't distinguish only by concurrence.",1011.5700v3
2010-12-21,Characterization of Decoherence from an Environmental Perspective,"For the case of phase damping (pure decoherence) we investigate the extent to
which environmental traits are imprinted on an open quantum system. The
dynamics is described using the quantum channel approach. We study what the
knowledge of the channel may reveal about the nature of its underlying dynamics
and, conversely, what the dynamics tells us about how to consistently model the
environment. We find that for a Markov phase-damping channel, that is, a
channel compatible with a time-continuous Markovian evolution, the environment
may adequately be represented by a mixture of only a few coherent states. For
arbitrary Hilbert space dimension $N\geq 4$ we refine the idea of {\it quantum
phase damping}, of which we show a means of identification. Symmetry
considerations are used to identify decoherence-free subspaces of the system.",1012.4685v1
2010-12-28,Quantum Leptogenesis I,"Thermal leptogenesis explains the observed matter-antimatter asymmetry of the
universe in terms of neutrino masses, consistent with neutrino oscillation
experiments. We present a full quantum mechanical calculation of the generated
lepton asymmetry based on Kadanoff-Baym equations. Origin of the asymmetry is
the departure from equilibrium of the statistical propagator of the heavy
Majorana neutrino, together with CP violating couplings. The lepton asymmetry
is calculated directly in terms of Green's functions without referring to
""number densities"". Compared to Boltzmann and quantum Boltzmann equations, the
crucial difference are memory effects, rapid oscillations much faster than the
heavy neutrino equilibration time. These oscillations strongly suppress the
generated lepton asymmetry, unless the standard model gauge interactions, which
cause thermal damping, are properly taken into account. We find that these
damping effects essentially compensate the enhancement due to quantum
statistical factors, so that finally the conventional Boltzmann equations again
provide rather accurate predictions for the lepton asymmetry.",1012.5821v3
2011-01-06,Chemical Enrichment in the Carbon-enhanced Damped Lyman $α$ System,"We show that the recently observed elemental abundance pattern of the
carbon-rich metal-poor Damped Lyman $\alpha$ (DLA) system is in excellent
agreement with the nucleosynthesis yields of faint core-collapse supernovae of
primordial stars. The observed abundance pattern is not consistent with the
nucleosynthesis yields of pair-instability supernovae. The DLA abundance
pattern is very similar to that of carbon-rich extremely metal-poor (EMP)
stars, and the contributions from low-mass stars and/or binary effects should
be very small in DLAs. This suggests that chemical enrichment by the first
stars in the first galaxies is driven by core-collapse supernovae from $\sim
20-50 M_\odot$ stars, and also supports the supernova scenario as the
enrichment source of EMP stars in the Milky Way Galaxy.",1101.1227v2
2011-02-08,Quantization of Damping Particle Based On New Variational Principles,"In this paper a new approach is proposed to quantize mechanical systems whose
equations of motion can not be put into Hamiltonian form. This approach is
based on a new type of variational principle, which is adopted to a describe a
relation: a damping particle may shares a common phase curve with a free
particle, whose Lagrangian in the new variational principle can be considered
as a Lagrangian density in phase space. According to Feynman's theory, the
least action principle is adopted to modify the Feynman's path integral
formula, where Lagrangian is replaced by Lagrangian density. In the case of
conservative systems, the modification reduces to standard Feynman's propagator
formula. As an example a particle with friction is analyzed in detail.",1102.1573v2
2011-02-15,Spin dynamics in the strong spin-orbit coupling regime,"We study the spin dynamics in a high-mobility two dimensional electron gas
(2DEG) with generic spin-orbit interactions (SOIs). We derive a set of spin
dynamic equations which capture the purely exponential to the damped
oscillatory spin evolution modes observed in different regimes of SOI strength.
Hence we provide a full treatment of the D'yakonov-Perel's mechanism by using
the microscopic linear response theory from the weak to the strong SOI limit.
We show that the damped oscillatory modes appear when the electron scattering
time is larger than half of the spin precession time due to the SOI, in
agreement with recent observations. We propose a new way to measure the
scattering time and the relative strength of Rashba and linear Dresselhaus SOIs
based on these modes and optical grating experiments. We discuss the physical
interpretation of each of these modes in the context of Rabi oscillation.",1102.3170v1
2011-03-03,Collective modes and the speed of sound in the Fulde-Ferrell-Larkin-Ovchinnikov state,"We consider the density response of a spin-imbalanced ultracold Fermi gas in
an optical lattice in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We
calculate the collective mode spectrum of the system in the generalised random
phase approximation and find that though the collective modes are damped even
at zero tempererature, the damping is weak enough to have well-defined
collective modes. We calculate the speed of sound in the gas and show that it
is anisotropic due to the anisotropy of the FFLO pairing, which implies an
experimental signature for the FFLO state.",1103.0696v2
2011-03-10,"Shocks in financial markets, price expectation, and damped harmonic oscillators","Using a modified damped harmonic oscillator model equivalent to a model of
market dynamics with price expectations, we analyze the reaction of financial
markets to shocks. In order to do this, we gather data from indices of a
variety of financial markets for the 1987 Black Monday, the Russian crisis of
1998, the crash after September 11th (2001), and the recent downturn of markets
due to the subprime mortgage crisis in the USA (2008). Analyzing those data we
were able to establish the amount by which each market felt the shocks, a
dampening factor which expresses the capacity of a market of absorving a shock,
and also a frequency related with volatility after the shock. The results gauge
the efficiency of different markets in recovering from such shocks, and measure
some level of dependence between them. We also show, using the correlation
matrices between the indices used, that financial markets are now much more
connected than they were two decades ago.",1103.1992v2
2011-03-22,Inductive determination of the optimum tunnel barrier thickness in magnetic tunnelling junction stacks for spin torque memory applications,"We use pulsed inductive microwave magnetometry to study the precessional
magnetization dynamics of the free layer in CoFeB/MgO/CoFeB based magnetic
tunnelling junction stacks with varying MgO barrier thickness. From the field
dependence of the precession frequency we are able to derive the uniaxial
anisotropy energy and the exchange coupling between the free and the pinned
layer. Furthermore the field dependence of the effective damping parameter is
derived. Below a certain threshold barrier thickness we observe an increased
effective damping for antiparallel orientation of free and pinned layer which
would inhibit reversible low current density spin torque magnetization
reversal. Such inductive measurements, in combination with wafer probe station
based magneto transport experiments, allow a fast determination of the optimum
tunnel barrier thickness range for spin torque memory applications in a
lithography free process.",1103.4248v1
2011-04-11,Algebraic damping in the one-dimensional Vlasov equation,"We investigate the asymptotic behavior of a perturbation around a spatially
non homogeneous stable stationary state of a one-dimensional Vlasov equation.
Under general hypotheses, after transient exponential Landau damping, a
perturbation evolving according to the linearized Vlasov equation decays
algebraically with the exponent -2 and a well defined frequency. The
theoretical results are successfully tested against numerical $N$-body
simulations, corresponding to the full Vlasov dynamics in the large $N$ limit,
in the case of the Hamiltonian mean-field model. For this purpose, we use a
weighted particles code, which allows us to reduce finite size fluctuations and
to observe the asymptotic decay in the $N$-body simulations.",1104.1890v2
2011-04-25,Exactly Solvable Nonhomogeneous Burgers Equations with Variable Coefficients,"We consider a nonhomogeneous Burgers equation with time variable
coefficients, and obtain an explicit solution of the general initial value
problem in terms of solution to a corresponding linear ODE. Special exact
solutions such as generalized shock and multi-shock solitary waves, triangular
wave, N-wave and rational type solutions are found and discussed. As exactly
solvable models, we study forced Burgers equations with constant damping and an
exponentially decaying diffusion coefficient. Different type of exact solutions
are obtained for the critical, over and under damping cases, and their behavior
is illustrated explicitly. In particular, the existence of inelastic type of
collisions is observed by constructing multi-shock solitary wave solutions, and
for the rational type solutions the motion of the pole singularities is
described.",1104.4717v1
2011-05-06,System-environment dynamics of X-type states in noninertial frames,"The system-environment dynamics of noninertial systems is investigated. It is
shown that for the amplitude damping channel: (i) the biggest difference
between the decoherence effect and the Unruh radiation on the dynamics of the
entanglement is the former only leads to entanglement transfer in the whole
system, but the latter damages all types of entanglement; (ii) the
system-environment entanglement increases and then declines, while the
environment-environment entanglement always increases as the decay parameter
$p$ increases; and (iii) the thermal fields generated by the Unruh effect can
promote the sudden death of entanglement between the subsystems while postpone
the sudden birth of entanglement between the environments. It is also found
that there is no system-environment and environment-environment entanglements
when the system coupled with the phase damping environment.",1105.1216v2
2011-05-10,Spontaneous magnon decays in planar ferromagnet,"We predict that spin-waves in an easy-plane ferromagnet have a finite
lifetime at zero temperature due to spontaneous decays. In zero field the
damping is determined by three-magnon decay processes, whereas decays in the
two-particle channel dominate in a transverse magnetic field. Explicit
calculations of the magnon damping are performed in the framework of the
spin-wave theory for the $XXZ$ square-lattice ferromagnet with an anisotropy
parameter $\lambda<1$. In zero magnetic field the decays occur for
$\lambda^*<\lambda<1$ with $\lambda^*\approx 1/7$. We also discuss possibility
of experimental observation of the predicted effect in a number of
ferromagnetic insulators.",1105.1893v1
2011-05-19,"Scaling of the higher-order flow harmonics: implications for initial-eccentricity models and the ""viscous horizon""","The scaling properties of the flow harmonics for charged hadrons $v_{n}$ and
their ratios $[ v_n/(v_2)^{n/2}]_{n\geq 3}$, are studied for a broad range of
transverse momenta ($p_T$) and centrality selections in Au+Au and Pb+Pb
collisions at $\sqrt{s_{NN}}=0.2 \text{and} 2.76$ TeV respectively. At
relatively low $p_T$, these scaling properties are found to be compatible with
the expected growth of viscous damping for sound propagation in the plasma
produced in these collisions. They also provide important constraints for
distinguishing between the two leading models of collision eccentricities, as
well as a route to constrain the relaxation time and make estimates for the
ratio of viscosity to entropy density $\eta/s$, and the ""viscous horizon"" or
length-scale which characterizes the highest harmonic which survives viscous
damping.",1105.3782v2
2011-05-26,Dynamics in the production of superheavy nuclei in low-energy heavy-ion collisions,"We present a review of the recent progress of theoretical models on the
description of the formation of superheavy nuclei in collisions of heavy
systems. Two sorts of reactions that are the fusion-evaporation mechanism and
the massive damped collisions to produce superheavy nuclei are discussed.
Problems and further improvements of the capture of colliding partners, the
formation of compound nucleus and the de-excitation process are pointed out.
Possible combinations in the synthesis of the gap of the cold fusion and
$^{48}$Ca induced reactions are proposed by the calculations based on the
dinuclear system model and also compared with other approaches. The synthesis
of neutron-rich heavy isotopes near sub-shell closure N=162 via transfer
reactions in the damped collisions of two actinides and the influence of shell
closure on the production of heavy isotopes are investigated. Prospective
possibility to reach superheavy nuclei near N=184 via neutron-rich radioactive
beams of high intensity in the future is discussed.",1105.5224v2
2011-06-01,Effect of detuning on the phonon induced dephasing of optically driven InGaAs/GaAs quantum dots,"Recently, longitudinal acoustic phonons have been identified as the main
source of the intensity damping observed in Rabi rotation measurements of the
ground-state exciton of a single InAs/GaAs quantum dot. Here we report
experiments of intensity damped Rabi rotations in the case of detuned laser
pulses, the results have implications for the coherent optical control of both
excitons and spins using detuned laser pulses.",1106.0142v1
2011-06-03,Shear viscous effects on the primordial power spectrum from warm inflation,"We compute the primordial curvature spectrum generated during warm inflation,
including shear viscous effects. The primordial spectrum is dominated by the
thermal fluctuations of the radiation bath, sourced by the dissipative term of
the inflaton field. The dissipative coefficient \Upsilon, computed from first
principles in the close-to-equilibrium approximation, depends in general on the
temperature T, and this dependence renders the system of the linear
fluctuations coupled. Whenever the dissipative coefficient is larger than the
Hubble expansion rate H, there is a growing mode in the fluctuations before
horizon crossing. However, dissipation intrinsically means departures from
equilibrium, and therefore the presence of a shear viscous pressure in the
radiation fluid. This in turn acts as an extra friction term for the radiation
fluctuations that tends to damp the growth of the perturbations. Independently
of the T functional dependence of the dissipation and the shear viscosity, we
find that when the shear viscous coefficient \zeta_s is larger than 3 \rho_r/H
at horizon crossing, \rho_r being the radiation energy density, the shear
damping effect wins and there is no growing mode in the spectrum.",1106.0701v1
2011-06-06,Weakly nonlinear stochastic CGL equations,"We consider the linear Schr\""odinger equation under periodic boundary
condition, driven by a random force and damped by a quasilinear damping: $$
\frac{d}{dt}u+i\big(-\Delta+V(x)\big) u=\nu \Big(\Delta u-\gr |u|^{2p}u-i\gi
|u|^{2q}u \Big) +\sqrt\nu\, \eta(t,x).\qquad (*) $$ The force $\eta$ is white
in time and smooth in $x$. We are concerned with the limiting, as $\nu\to0$,
behaviour of its solutions on long time-intervals $0\le t\le\nu^{-1}T$, and
with behaviour of these solutions under the double limit $t\to\infty$ and
$\nu\to0$. We show that these two limiting behaviours may be described in terms
of solutions for the {\it system of effective equations for $(*)$} which is a
well posed semilinear stochastic heat equation with a non-local nonlinearity
and a smooth additive noise, written in Fourier coefficients. The effective
equations do not depend on the Hamiltonian part of the perturbation
$-i\gi|u|^{2q}u$ (but depend on the dissipative part $-\gr|u|^{2p}u$). If $p$
is an integer, they may be written explicitly.",1106.1158v1
2011-06-09,Investigating viscous damping using a webcam,"We describe an experiment involving a mass oscillating in a viscous fluid and
analyze viscous damping of harmonic motion. The mechanical oscillator is
tracked using a simple webcam and an image processing algorithm records the
position of the geometrical center as a function of time. Interesting
information can be extracted from the displacement-time graphs, in particular
for the underdamped case. For example, we use these oscillations to determine
the viscosity of the fluid. Our mean value of 1.08 \pm 0.07 mPa s for distilled
water is in good agreement with the accepted value at 20\circC. This experiment
has been successfully employed in the freshman lab setting.",1106.1823v1
2011-06-11,Conformal and covariant formulation of the Z4 system with constraint-violation damping,"We present a new formulation of the Einstein equations based on a conformal
and traceless decomposition of the covariant form of the Z4 system. This
formulation combines the advantages of a conformal decomposition, such as the
one used in the BSSNOK formulation (i.e. well-tested hyperbolic gauges, no need
for excision, robustness to imperfect boundary conditions) with the advantages
of a constraint-damped formulation, such as the generalized harmonic one (i.e.
exponential decay of constraint violations when these are produced). We
validate the new set of equations through standard tests and by evolving binary
black hole systems. Overall, the new conformal formulation leads to a better
behavior of the constraint equations and a rapid suppression of the violations
when they occur. The changes necessary to implement the new conformal
formulation in standard BSSNOK codes are very small as are the additional
computational costs.",1106.2254v2
2011-06-14,"Oscillations of hot, young neutron stars: Gravitational wave frequencies and damping times","We study how the frequencies and damping times of oscillations of a newly
born, hot proto-neutron star depend on the physical quantities which
characterize the star quasi-stationary evolution which follows the bounce.
Stellar configurations are modeled using a microscopic equation of state
obtained within the Brueckner-Hartree-Fock, nuclear many-body approach,
extended to the finite-temperature regime. We discuss the mode frequency
behaviour as function of the lepton composition, and of the entropy gradients
which prevail in the interior of the star. We find that, in the very early
stages, gravitational wave emission efficiently competes with neutrino
processes in dissipating the star mechanical energy residual of the
gravitational collapse.",1106.2736v1
2011-06-22,Samll BGK waves and nonlinear Landau damping (higher dimensions),"Consider Vlasov-Poisson system with a fixed ion background and periodic
condition on the space variables, in any dimension d\geq2. First, we show that
for general homogeneous equilibrium and any periodic x-box, within any small
neighborhood in the Sobolev space W_{x,v}^{s,p} (p>1,s<1+(1/p)) of the steady
distribution function, there exist nontrivial travelling wave solutions (BGK
waves) with arbitrary traveling speed. This implies that nonlinear Landau
damping is not true in W^{s,p}(s<1+(1/p)) space for any homogeneous equilibria
and in any period box. The BGK waves constructed are one dimensional, that is,
depending only on one space variable. Higher dimensional BGK waves are shown to
not exist. Second, for homogeneous equilibria satisfying Penrose's linear
stability condition, we prove that there exist no nontrivial invariant
structures in the (1+|v|^{2})^{b}-weighted H_{x,v}^{s} (b>((d-1)/4), s>(3/2))
neighborhood. Since arbitrarilly small BGK waves can also be constructed near
any homogeneous equilibria in such weighted H_{x,v}^{s} (s<(3/2)) norm, this
shows that s=(3/2) is the critical regularity for the existence of nontrivial
invariant structures near stable homogeneous equilibria. These generalize our
previous results in the one dimensional case.",1106.4368v1
2011-07-13,q-damped Oscillator and degenerate roots of constant coefficients q-difference ODE,"The classical model of q-damped oscillator is introduced and solved in terms
of Jackson q-exponential function for three different cases, under-damped,
over-damped and the critical one. It is shown that in all three cases solution
is oscillating in time but is unbounded and non-periodic. By q-periodic
function modulation, the self-similar micro-structure of the solution for small
time intervals is derived. In the critical case with degenerate roots, the
second linearly independent solution is obtained as a limiting case of two
infinitesimally close roots. It appears as standard derivative of q-exponential
and is rewritten in terms of the q-logarithmic function. We extend our result
by constructing n linearly independent set of solutions to a generic constant
coefficient q-difference equation degree N with n degenerate roots.",1107.2518v1
2011-07-13,Increased Brownian force noise from molecular impacts in a constrained volume,"We report on residual gas damping of the motion of a macroscopic test mass
enclosed in a nearby housing in the molecular flow regime. The damping
coefficient, and thus the associated thermal force noise, is found to increase
significantly when the distance between test mass and surrounding walls is
smaller than the test mass itself. The effect has been investigated with two
torsion pendulums of different geometry and has been modelled in a numerical
simulation whose predictions are in good agreement with the measurements.
Relevant to a wide variety of small-force experiments, the residual-gas force
noise power for the test masses in the LISA gravitational wave observatory is
roughly a factor 15 larger than in an infinite gas volume, though still
compatible with the target acceleration noise of 3 fm s^-2 Hz^-1/2 at the
foreseen pressure below 10^-6 Pa.",1107.2520v1
2011-07-13,Dimension of attractors and invariant sets of damped wave equations in unbounded domains,"Under fairly general assumptions, we prove that every compact invariant set
$\mathcal I$ of the semiflow generated by the semilinear damped wave equation
u_{tt}+\alpha u_t+\beta(x)u-\Deltau = f(x,u), (t,x)\in[0,+\infty[\times\Omega,
u = 0, (t,x)\in[0,+\infty[\times\partial\Omega in $H^1_0(\Omega)\times
L^2(\Omega) has finite Hausdorff and fractal dimension. Here $\Omega$ is a
regular, possibly unbounded, domain in $\R^3$ and $f(x,u)$ is a nonlinearity of
critical growth. The nonlinearity $f(x,u)$ needs not to satisfy any
dissipativeness assumption and the invariant subset $\mathcal I$ needs not to
be an attractor. If $f(x,u)$ is dissipative and $\mathcal I$ is the global
attractor, we give an explicit bound on the Hausdorff and fractal dimension of
$\mathcal I$ in terms of the structure parameters of the equation.",1107.2589v1
2011-07-15,K-shell photoionization of Nickel ions using R-matrix,"We present R-matrix calculations of photoabsorption and photoionization cross
sections across the K edge of the Li-like to Ca-like ions stages of Ni.
Level-resolved, Breit-Pauli calculations were performed for the Li-like to
Na-like stages. Term-resolved calculations, which include the mass-velocity and
Darwin relativistic corrections, were performed for the Mg-like to Ca-like ion
stages. This data set is extended up to Fe-like Ni using the distorted wave
approximation as implemented by AUTOSTRUCTURE. The R-matrix calculations
include the effects of radiative and Auger dampings by means of an optical
potential. The damping processes affect the absorption resonances converging to
the K thresholds causing them to display symmetric profiles of constant width
that smear the otherwise sharp edge at the K-shell photoionization threshold.
These data are important for the modeling of features found in photoionized
plasmas.",1107.3146v1
2011-07-20,Bayesian Magnetohydrodynamic Seismology of Coronal Loops,"We perform a Bayesian parameter inference in the context of resonantly damped
transverse coronal loop oscillations. The forward problem is solved in terms of
parametric results for kink waves in one-dimensional flux tubes in the thin
tube and thin boundary approximations. For the inverse problem, we adopt a
Bayesian approach to infer the most probable values of the relevant parameters,
for given observed periods and damping times, and to extract their confidence
levels. The posterior probability distribution functions are obtained by means
of Markov Chain Monte Carlo simulations, incorporating observed uncertainties
in a consistent manner. We find well localized solutions in the posterior
probability distribution functions for two of the three parameters of interest,
namely the Alfven travel time and the transverse inhomogeneity length-scale.
The obtained estimates for the Alfven travel time are consistent with previous
inversion results, but the method enables us to additionally constrain the
transverse inhomogeneity length-scale and to estimate real error bars for each
parameter. When observational estimates for the density contrast are used, the
method enables us to fully constrain the three parameters of interest. These
results can serve to improve our current estimates of unknown physical
parameters in coronal loops and to test the assumed theoretical model.",1107.3943v1
2011-07-31,Evolution of cat states in a dissipative parametric amplifier: decoherence and entanglement,"The evolution of the Schr\""{o}dinger-cat states in a dissipative parametric
amplifier is examined. The main tool in the analysis is the normally ordered
characteristic function. Squeezing, photon-number distribution and reduced
factorial moments are discussed for the single- and compound-mode cases. Also
the single-mode Wigner function is demonstrated. In addition to the decoherence
resulting from the interaction with the environment (damped case) there are two
sources which can cause such decoherence in the system even if it is completely
isolated: these are the decay of the pump and the relative phases of the
initial cat states. Furthermore, for the damped case there are two regimes,
which are underdamped and overdamped. In the first (second) regime the signal
mode or the idler mode ""collapses"" to a statistical mixture (thermal field).",1108.0127v1
2011-07-31,"Second-Order, Dissipative Tâtonnement: Economic Interpretation and 2-Point Limit Cycles","This paper proposes an alternative to the classical price-adjustment
mechanism (called ""t\^{a}tonnement"" after Walras) that is second-order in time.
The proposed mechanism, an analogue to the damped harmonic oscillator, provides
a dynamic equilibration process that depends only on local information. We show
how such a process can result from simple behavioural rules. The discrete-time
form of the model can result in two-step limit cycles, but as the distance
covered by the cycle depends on the size of the damping, the proposed mechanism
can lead to both highly unstable and relatively stable behaviour, as observed
in real economies.",1108.0188v3
2011-08-02,PHENIX Measurements of Higher-order Flow Harmonics in Au+Au collisions at Root_s = 200 GeV,"Flow coefficients $v_n$ for $n$ = 2, 3, 4, characterizing the anisotropic
collective flow in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, are
presented. They indicate the expected growth of viscous damping for sound
propagation in the quark gluon plasma (QGP) produced in these collisions.
Hydrodynamical model comparisons which include the effects of initial state
geometry fluctuations, highlight the role of higher harmonics ($v_{n, n>2}$) as
a constraint for disentangling the effects of viscosity and initial conditions,
and suggest a small specific viscosity for the QGP. This viscosity is
compatible with that obtained via a newly proposed technique
\cite{Lacey:2011ug} which employs the relative magnitudes of $v_n$ to estimate
the viscosity, and the ""viscous horizon"" or length-scale which characterizes
the highest harmonic that survives viscous damping.",1108.0457v1
2011-08-10,Critical exponents of steady-state phase transitions in fermionic lattice models,"We discuss reservoir induced phase transitions of lattice fermions in the
non-equilibrium steady state (NESS) of an open system with local reservoirs.
These systems may become critical in the sense of a diverging correlation
length upon changing the reservoir coupling. We here show that the transition
to a critical state is associated with a vanishing gap in the damping spectrum.
It is shown that although in linear systems there can be a transition to a
critical state there is no reservoir-induced quantum phase transition between
distinct phases with non-vanishing damping gap. We derive the static and
dynamical critical exponents corresponding to the transition to a critical
state and show that their possible values, defining universality classes of
reservoir-induced phase transitions are determined by the coupling range of the
independent local reservoirs. If a reservoir couples to N neighboring lattice
sites, the critical exponent can assume all fractions from 1 to 1/(N - 1).",1108.2263v5
2011-09-09,Observation of Spontaneous Brillouin Cooling,"While radiation-pressure cooling is well known, the Brillouin scattering of
light from sound is considered an acousto-optical amplification-only process.
It was suggested that cooling could be possible in multi-resonance Brillouin
systems when phonons experience lower damping than light. However, this regime
was not accessible in traditional Brillouin systems since backscattering
enforces high acoustical frequencies associated with high mechanical damping.
Recently, forward Brillouin scattering in microcavities has allowed access to
low-frequency acoustical modes where mechanical dissipation is lower than
optical dissipation, in accordance with the requirements for cooling. Here we
experimentally demonstrate cooling via such a forward Brillouin process in a
microresonator. We show two regimes of operation for the Brillouin process:
acoustical amplification as is traditional, but also for the first time, a
Brillouin cooling regime. Cooling is mediated by an optical pump, and scattered
light, that beat and electrostrictively attenuate the Brownian motion of the
mechanical mode.",1109.2084v2
2011-09-14,Oscillations of simple networks,"To describe the flow of a miscible quantity on a network, we introduce the
graph wave equation where the standard continuous Laplacian is replaced by the
graph Laplacian. This is a natural description of an array of inductances and
capacities, of fluid flow in a network of ducts and of a system of masses and
springs. The structure of the graph influences strongly the dynamics which is
naturally described using the basis of the eigenvectors. In particular, we show
that if two outer nodes are connected to a common third node with the same
coupling, then this coupling is an eigenvalue of the Laplacian. Assuming the
graph is forced and damped at specific nodes, we derive the amplitude
equations. These are analyzed for two simple non trivial networks: a tree and a
graph with a cycle. Forcing the network at a resonant frequency reveals that
damping can be ineffective if applied to the wrong node, leading to a
disastrous resonance and destruction of the network. These results could be
useful for complex physical networks and engineering networks like power grids.",1109.3071v2
2011-09-21,High-order explicit local time-stepping methods for damped wave equations,"Locally refined meshes impose severe stability constraints on explicit
time-stepping methods for the numerical simulation of time dependent wave
phenomena. Local time-stepping methods overcome that bottleneck by using
smaller time-steps precisely where the smallest elements in the mesh are
located. Starting from classical Adams-Bashforth multi-step methods, local
time-stepping methods of arbitrarily high order of accuracy are derived for
damped wave equations. When combined with a finite element discretization in
space with an essentially diagonal mass matrix, the resulting time-marching
schemes are fully explicit and thus inherently parallel. Numerical experiments
with continuous and discontinuous Galerkin finite element discretizations
validate the theory and illustrate the usefulness of these local time-stepping
methods.",1109.4480v2
2011-09-21,Anisotropic critical magnetic fluctuations in the ferromagnetic superconductor UCoGe,"We report neutron scattering measurements of critical magnetic excitations in
the weakly ferromagnetic superconductor UCoGe. The strong non-Landau damping of
the excitations we observe, although unusual has been found in another related
ferromagnet, UGe2 at zero pressure. However, we also find there is a
significant anisotropy of the magnetic correlation length in UCoGe that
contrasts with an almost isotropic length for UGe2. The values of the magnetic
correlation length and damping are found to be compatible with
superconductivity on small Fermi surface pockets. The anisotropy may be
important to explain why UCoGe is a superconductor at zero pressure while UGe2
is not.",1109.4541v1
2011-09-30,"PT-symmetry, indefinite damping and dissipation-induced instabilities","With perfectly balanced gain and loss, dynamical systems with indefinite
damping can obey the exact PT-symmetry being marginally stable with a pure
imaginary spectrum. At an exceptional point where the symmetry is spontaneously
broken, the stability is lost via passing through a non-semisimple 1:1
resonance. In the parameter space of a general dissipative system, marginally
stable PT-symmetric ones occupy singularities on the boundary of the asymptotic
stability. To observe how the singular surface governs dissipation-induced
destabilization of the PT-symmetric system when gain and loss are not matched,
an extension of recent experiments with PT-symmetric LRC circuits is proposed.",1110.0018v2
2011-10-01,Electrical measurement of antivortex wall eigenfrequency,"The dynamics of a ferromagnetic antivortex wall has been experimentally
studied in a magnetic nanostructure. Two different techniques have been used to
independently measure the eigenfrequency of an antivortex wall such as the
resonance excitation by sinusoidal microwave and the damped resonance
excitation induced by short voltage pulses. Direct observation of antivortex
wall nucleation has been measured in the frequency domain for the first time.
Electrical measurements of the antivortex dynamics in frequency domain reveal
the existence of multi-eigenmodes as well as nonlinear behaviors for large
excitation amplitudes. The time resolved measurements of the antivortex wall
show that the frequency of the damped gyration is similar to that of frequency
domain and coexistence of spin wave excitations.",1110.0113v1
2011-10-06,Comparative Wakefield Analysis of a First Prototype of a DDS Structure for CLIC Main Linac,"A Damped Detuned Structure (DDS) for CLIC main linac has been proposed as an
alternative to the present baseline design which is based on heavy damping. A
first prototype, CLIC_DDS_A, for high power tests has been already designed and
is under construction. It is also foreseen to design a further prototype,
CLIC_DDS_B, to test both the wakefield suppression and high power performances.
Wakefield calculations for DDS are, in the early design stage, based on single
infinitely periodic cells. Though cell-to-cell interaction is taken into
account to calculate the wakefields, it is important to study full structure
properties using computational tools. In particular this is fundamental for
defining the input parameters for the HOM coupler that is crucial for the
performances of DDS. In the following a full analysis of wakefields and
impedances based on simulations conducted with finite difference based
electromagnetic computer code GdfidL will be presented.",1110.1207v1
2011-10-12,Nonlinear dynamic analysis of an optimal particle damper,"We study the dynamical behavior of a single degree of freedom mechanical
system with a particle damper. The particle (granular) damping was optimized
for the primary system operating condition by using an appropriate gap size for
a prismatic enclosure. The particles absorb the kinetic energy of the vibrating
structure and convert it into heat through the inelastic collisions and
friction. This results in a highly nonlinear mechanical system. Considering
linear signal analysis, state space reconstruction, Poincar\'e sections and the
determination of maximal Lyapunov exponents, the motion of the granular system
inside the enclosure is characterized for a wide frequency range. With the
excitation frequency as control parameter, either regular and chaotic motion of
the granular bed are found and their influence on the damping is analyzed.",1110.2800v1
2011-10-14,Effect of Compton Scattering on the Electron Beam Dynamics at the ATF Damping Ring,"Compton scattering provides one of the most promising scheme to obtain
polarized positrons for the next generation of $e^-$ -- $e^+$ colliders.
Moreover it is an attractive method to produce monochromatic high energy
polarized gammas for nuclear applications and X-rays for compact light sources.
In this framework a four-mirror Fabry-P\'erot cavity has been installed at the
Accelerator Test Facility (ATF - KEK, Tsukuba, Japan) and is used to produce an
intense flux of polarized gamma rays by Compton scattering
\cite{ipac-mightylaser}. For electrons at the ATF energy (1.28 GeV) Compton
scattering may result in a shorter lifetime due to the limited bucket
acceptance. We have implemented the effect of Compton scattering on a 2D
tracking code with a Monte-Carlo method. This code has been used to study the
longitudinal dynamics of the electron beam at the ATF damping ring, in
particular the evolution of the energy spread and the bunch length under
Compton scattering. The results obtained are presented and discussed. Possible
methods to observe the effect of Compton scattering on the ATF beam are
proposed.",1110.3241v1
2011-10-28,Stability of linear and non-linear lambda and tripod systems in the presence of amplitude damping,"We present the stability analysis of the dark states in the adiabatic passage
for the linear and non-linear lambda and tripod systems in the presence of
amplitude damping (losses). We perform an analytic evaluation of the real parts
of eigenvalues of the corresponding Jacobians, the non-zero eigenvalues of
which are found from the quadratic characteristic equations, as well as by the
corresponding numerical simulations. For non-linear systems, we evaluate the
Jacobians at the dark states. Similarly to the linear systems, here we also
find the non-zero eigenvalues from the characteristic quadratic equations. We
reveal a common property of all the considered systems showing that the
evolution of the real parts of eigenvalues can be split into three stages. In
each of them the evolution of the stimulated Raman adiabatic passage (STIRAP)
is characterized by different effective dimension. This results in a possible
adiabatic reduction of one or two degrees of freedom.",1110.6379v2
2011-11-07,Control of Material Damping in High-Q Membrane Microresonators,"We study the mechanical quality factors of bilayer aluminum/silicon-nitride
membranes. By coating ultrahigh-Q Si3N4 membranes with a more lossy metal, we
can precisely measure the effect of material loss on Q's of tensioned resonator
modes over a large range of frequencies. We develop a theoretical model that
interprets our results and predicts the damping can be reduced significantly by
patterning the metal film. Using such patterning, we fabricate Al-Si3N4
membranes with ultrahigh Q at room temperature. Our work elucidates the role of
material loss in the Q of membrane resonators and informs the design of hybrid
mechanical oscillators for optical-electrical-mechanical quantum interfaces.",1111.1703v2
2011-11-15,Thermodynamic anomaly of the free damped quantum particle: the bath perspective,"A possible definition of the specific heat of open quantum systems is based
on the reduced partition function of the system. For a free damped quantum
particle, it has been found that under certain conditions, this specific heat
can become negative at low temperatures. In contrast to the conventional
approaches focusing on the system degree of freedom, here we concentrate on the
changes induced in the environment when the system is coupled to it. Our
analysis is carried out for an Ohmic environment consisting of harmonic
oscillators and allows to identify the mechanism by which the specific heat
becomes negative. Furthermore, the formal condition for the occurrence of a
negative specific heat is given a physical interpretation in terms of the total
mass of bath oscillators and the system mass.",1111.3594v2
2011-12-02,On the propagation of binary signals in damped mechanical systems of oscillators,"In the present work, we explore efficient ways to transmit binary information
in discrete, semi-infinite chains of coupled oscillators using the process of
nonlinear supratransmission. A previous work showed that such transmission is
possible and, indeed, reliable under the idealistic condition when weak or no
damping is present. In this paper, we study a more realistic case and propose
the design of mechanical devices in order to avoid the loss of information,
consisting on the linear concatenation of several such mechanical systems. Our
results demonstrate that the loss of information can be minimized or avoided
using such physical structures.",1112.0585v1
2011-12-02,On the simulation of the energy transmission in the forbidden band-gap of a spatially discrete double sine-Gordon system,"In this work, we present a numerical method to consistently approximate
solutions of a spatially discrete, double sine-Gordon chain which considers the
presence of external damping. In addition to the finite-difference scheme
employed to approximate the solution of the difference-differential equations
of the model under investigation, our method provides positivity-preserving
schemes to approximate the local and the total energy of the system, in such
way that the discrete rate of change of the total energy with respect to time
provides a consistent approximation of the corresponding continuous rate of
change. Simulations are performed, first of all, to assess the validity of the
computational technique against known qualitative solutions of coupled
sine-Gordon and coupled double sine-Gordon chains. Secondly, the method is used
in the investigation of the phenomenon of nonlinear transmission of energy in
double sine-Gordon systems; the qualitative effects of the damping coefficient
on the occurrence of the nonlinear process of supratransmission are briefly
determined in this work, too.",1112.0595v1
2011-12-11,Spin-polarized current effect on antiferromagnet magnetization in a ferromagnet - antiferromagnet nanojunction: Theory and simulation,"Spin-polarized current effect is studied on the static and dynamic
magnetization of the antiferromagnet in a ferromagnet - antiferromagnet
nanojunction. The macrospin approximation is generalized to antiferromagnets.
Canted antiferromagnetic configuration and resulting magnetic moment are
induced by an external magnetic field. The resonance frequency and damping are
calculated, as well as the threshold current density corresponding to
instability appearance. A possibility is shown of generating low-damping
magnetization oscillations in terahertz range. The fluctuation effect is
discussed on the canted antiferromagnetic configuration. Numerical simulation
is carried out of the magnetization dynamics of the antiferromagnetic layer in
the nanojunction with spin-polarized current. Outside the instability range,
the simulation results coincide completely with analytical calculations using
linear approximation. In the instability range, undamped oscillations occur of
the longitudinal and transverse magnetization components.",1112.2362v1
2011-12-15,Analytic gas orbits in an arbitrary rotating galactic potential using the linear epicyclic approximation,"A code, Epic5, has been developed which computes, in the two-dimensional
case, the initially circular orbits of guiding centra in an arbitrary
axisymmetric potential with an arbitrary, weak perturbing potential in solid
body rotation. This perturbing potential is given by its Fourier expansion. The
analytic solution solves the linear epicyclic approximation of the equations of
motion. To simulate the motion of interstellar matter and to damp the Lindblad
resonances, we have in these equations introduced a friction which is
proportional to the deviation from circular velocity. The corotation resonance
is also damped by a special parameter. The program produces, in just a few
seconds, orbital and density maps, as well as line of sight velocity maps for a
chosen orientation of the galaxy.
  We test Epic5 by comparing its results with previous simulations and
observations from the literature, which gives satisfactory agreement. The aim
is that this program should be a useful complement to elaborate numerical
simulations. Particularly so are its abilities to quickly explore the parameter
space, to construct artificial galaxies, and to isolate various single agents
important for developing structure of interstellar matter in disc galaxies.",1112.3658v1
2011-12-21,A numerical method for computing radially symmetric solutions of a dissipative nonlinear modified Klein-Gordon equation,"In this paper we develop a finite-difference scheme to approximate radially
symmetric solutions of the initial-value problem with smooth initial conditions
in an open sphere around the origin, where the internal and external damping
coefficients are constant, and the nonlinear term follows a power law. We prove
that our scheme is consistent of second order when the nonlinearity is
identically equal to zero, and provide a necessary condition for it to be
stable order n. Part of our study will be devoted to compare the physical
effects of the damping coefficients.",1112.4921v1
2011-12-23,Temperature gradient assisted magnetodynamics in a ferromagnetic nanowire,"The dynamics of the low energy excitations in a ferromagnet is studied in
case a temperature gradient is coupled to the local magnetization. Due to the
different time scales of changing temperature and magnetization it is argued
that only the coupling between the spatially varying part of the temperature
field and the magnetization is relevant. Using variational principles the
evolution equation for the magnetic system is found which is strongly
influenced by the local temperature profile. The system offers damped spin wave
excitations where the strength of damping is determined by the magneto-thermal
coupling. Applying the model to nanowires it is demonstrated that the energy
spectrum is significantly affected by the boundary conditions as well as the
initial temperature distribution. In particular, the coupling between
temperature and magnetization is expected to be several orders stronger for the
open as for the isolated wire.",1112.5562v1
2012-01-04,A new candidate for probing Population III nucleosynthesis with carbon-enhanced damped Lyman-alpha systems,"We report the identification of a very metal-poor damped Lyman-alpha system
(DLA) at z_abs = 3.067295 that is modestly carbon-enhanced, with an iron
abundance of ~1/700 solar ([Fe/H] = -2.84) and [C,O/Fe] ~ +0.6. Such an
abundance pattern is likely to be the result of nucleosynthesis by massive
stars. On the basis of 17 metal absorption lines, we derive a 2 sigma upper
limit on the DLA's kinetic temperature of T_DLA <= 4700 K, which is broadly
consistent with the range of spin temperature estimates for DLAs at this
redshift and metallicity. While the best-fitting abundance pattern shows the
expected hallmarks of Population III nucleosynthesis, models of high-mass
Population II stars can match the abundance pattern almost as well. We discuss
current limitations in distinguishing between these two scenarios and the
marked improvement in identifying the remnants of Population III stars expected
from the forthcoming generation of 30-metre class telescopes.",1201.1004v2
2012-01-06,Magnetic field decay with Hall drift in neutron star crusts,"The dynamics of magnetic field decay with Hall drift is investigated.
Assuming that axisymmetric magnetic fields are located in a spherical crust
with uniform conductivity and electron number density, long-term evolution is
calculated up to Ohmic dissipation. The nonlinear coupling between poloidal and
toroidal components is explored in terms of their energies and helicity.
Nonlinear oscillation by the drift in strongly magnetized regimes is clear only
around the equipartition between two components. Significant energy is
transferred to the poloidal component when the toroidal component initially
dominates. However, the reverse is not true. Once the toroidal field is less
dominant, it quickly decouples due to a larger damping rate. The polar field at
the surface is highly distorted from the initial dipole during the Hall drift
timescale, but returns to the initial dipole in a longer dissipation timescale,
since it is the least damped one.",1201.1346v1
2012-01-06,"Reversible Dissipative Processes, Conformal Motions and Landau Damping","The existence of a dissipative flux vector is known to be compatible with
reversible processes, provided a timelike conformal Killing vector (CKV)
$\chi^\alpha=\frac{V^\alpha}{T}$ (where $V^\alpha$ and $T$ denote the
four-velocity and temperature respectively) is admitted by the space-time. Here
we show that if a constitutive transport equation, either within the context of
standard irreversible thermodynamics or the causal Israel--Stewart theory, is
adopted, then such a compatibility also requires vanishing dissipative fluxes.
Therefore, in this later case the vanishing of entropy production generated by
the existence of such CKV is not actually associated to an imperfect fluid, but
to a non-dissipative one. We discuss also about Landau damping.",1201.1390v1
2012-01-19,Wave Leakage and Resonant Absorption in a Loop Embedded in a Coronal Arcade,"We investigate the temporal evolution of impulsively generated perturbations
in a potential coronal arcade with an embedded loop. As the initial
configuration we consider a coronal loop, represented by a density enhancement,
which is unbounded in the ignorable direction of the arcade. The linearized
time-dependent magnetohydrodynamic equations have been numerically solved in
field-aligned coordinates and the time evolution of the initial perturbations
has been studied in the zero-beta approximation. For propagation constrained to
the plane of the arcade, the considered initial perturbations do not excite
trapped modes of the system. This weakness of the model is overcome by the
inclusion of wave propagation in the ignorable direction. The inclusion of
perpendicular propagation produces two main results. First, damping by wave
leakage is less efficient because the loop is able to act as a wave trap of
vertical oscillations. Second, the consideration of an inhomogeneous corona
enables the resonant damping of vertical oscillations and the energy transfer
from the interior of the loop to the external coronal medium.",1201.4042v1
2012-02-07,The Fine Structure Constant and the CMB Damping Scale,"The recent measurements of the Cosmic Microwave Background anisotropies at
arcminute angular scales performed by the ACT and SPT experiments are probing
the damping regime of CMB fluctuations. The analysis of these datasets
unexpectedly suggests that the effective number of relativistic degrees of
freedom is larger than the standard value of Neff = 3.04, and inconsistent with
it at more than two standard deviations. In this paper we study the role of a
mechanism that could affect the shape of the CMB angular fluctuations at those
scales, namely a change in the recombination process through variations in the
fine structure constant. We show that the new CMB data significantly improve
the previous constraints on variations of {\alpha}, with {\alpha}/{\alpha}0 =
0.984 \pm 0.005, i.e. hinting also to a more than two standard deviation from
the current, local, value {\alpha}0. A significant degeneracy is present
between {\alpha} and Neff, and when variations in the latter are allowed the
constraints on {\alpha} are relaxed and again consistent with the standard
value. Deviations of either parameter from their standard values would imply
the presence of new, currently unknown physics.",1202.1476v1
2012-02-08,Evidence of Wave Damping at Low Heights in a Polar Coronal Hole,"We have measured the widths of spectral lines from a polar coronal hole using
the Extreme Ultraviolet Imaging Spectrometer onboard Hinode. Polar coronal
holes are regions of open magnetic field and the source of the fast solar wind.
We find that the line widths decrease at relatively low heights. Previous
observations have attributed such decreases to systematic effects, but we find
that such effects are too small to explain our results. We conclude that the
line narrowing is real. The non-thermal line widths are believed to be
proportional to the amplitude of Alfven waves propagating along these open
field lines. Our results suggest that Alfven waves are damped at unexpectedly
low heights in a polar coronal hole. We derive an estimate on the upper limit
for the energy dissipated between 1.1 and 1.3 solar radii and find that it is
enough to account for up to 70% of that required to heat the polar coronal hole
and accelerate the solar wind.",1202.1743v2
2012-02-14,The kinetic temperature in a damped Lyman-alpha absorption system in Q2206-199 - an example of the warm neutral medium,"By comparing the widths of absorption lines from OI, SiII and FeII in the
redshift z=2.076 single-component damped Lyman alpha absorption system in the
spectrum of Q2206-199 we establish that these absorption lines arise in Warm
Neutral Medium gas at ~12000 +/- 3000K. This is consistent with thermal
equilibrium model estimates of ~ 8000K for the Warm Neutral Medium in galaxies,
but not with the presence of a significant cold component. It is also
consistent with, but not required by, the absence of CII* fine structure
absorption in this system. Some possible implications concerning abundance
estimates in narrow-line WNM absorbers are discussed.",1202.3012v1
2012-02-23,Eigenmodes of the damped wave equation and small hyperbolic subsets,"We study stationary solutions of the damped wave equation on a compact and
smooth Riemannian manifold without boundary. In the high frequency limit, we
prove that a sequence of $\beta$-damped stationary solutions cannot be
completely concentrated in small neighborhoods of a small fixed hyperbolic
subset made of $\beta$-damped trajectories of the geodesic flow. The article
also includes an appendix (by S. Nonnenmacher and the author) where we
establish the existence of an inverse logarithmic strip without eigenvalues
below the real axis, under a pressure condition on the set of undamped
trajectories.",1202.5123v3
2012-02-25,Fractional Order Phase Shaper Design with Routh's Criterion for Iso-damped Control System,"Phase curve of an open loop system is flat in nature if the derivative of
phase with respect to frequency is zero. With a flat phase curve, the
corresponding closed-loop system exhibits an iso-damped property i.e. maintains
constant overshoot with the change of gain and with other parametric
variations. In recent past application, fractional order (FO) phase shapers
have been proposed by contemporary researchers to achieve enhanced parametric
robustness. In this paper, a simple Routh tabulation based methodology is
proposed to design an appropriate FO phase shaper to achieve phase flattening
in a control loop, comprising a system, controlled by a classical PID
controller. The method is demonstrated using MATLAB simulation of a second
order DC motor plant and also a first order with time delay system.",1202.5667v1
2012-03-04,Dissipation effects in random transverse-field Ising chains,"We study the effects of Ohmic, super-Ohmic, and sub-Ohmic dissipation on the
zero-temperature quantum phase transition in the random transverse-field Ising
chain by means of an (asymptotically exact) analytical strong-disorder
renormalization-group approach. We find that Ohmic damping destabilizes the
infinite-randomness critical point and the associated quantum Griffiths
singularities of the dissipationless system. The quantum dynamics of large
magnetic clusters freezes completely which destroys the sharp phase transition
by smearing. The effects of sub-Ohmic dissipation are similar and also lead to
a smeared transition. In contrast, super-Ohmic damping is an irrelevant
perturbation; the critical behavior is thus identical to that of the
dissipationless system. We discuss the resulting phase diagrams, the behavior
of various observables, and the implications to higher dimensions and
experiments.",1203.0698v2
2012-03-22,Large Amplitude Longitudinal Oscillations in a Solar Filament,"We have developed the first self-consistent model for the observed
large-amplitude oscillations along filament axes that explains the restoring
force and damping mechanism. We have investigated the oscillations of multiple
threads formed in long, dipped flux tubes through the thermal nonequilibrium
process, and found that the oscillation properties predicted by our simulations
agree with the observed behavior. We then constructed a model for the
large-amplitude longitudinal oscillations that demonstrates that the restoring
force is the projected gravity in the tube where the threads oscillate.
Although the period is independent of the tube length and the constantly
growing mass, the motions are strongly damped by the steady accretion of mass
onto the threads by thermal nonequilibrium. The observations and our model
suggest that a nearby impulsive event drives the existing prominence threads
along their supporting tubes, away from the heating deposition site, without
destroying them. The subsequent oscillations occur because the displaced
threads reside in magnetic concavities with large radii of curvature. Our model
yields a powerful seismological method for constraining the coronal magnetic
field and radius of curvature of dips. Furthermore, these results indicate that
the magnetic structure is most consistent with the sheared-arcade model for
filament channels.",1203.5027v1
2012-03-26,Analysis of the Energy Decay of a Degenerated Thermoelasticity System,"In this paper, we study a system of thermoelasticity with a degenerated
second order operator in the Heat equation. We analyze the evolution of the
energy density of a family of solutions. We consider two cases: when the set of
points where the ellipticity of the Heat operator fails is included in a
hypersurface and when it is an open set. In the first case and under special
assumptions, we prove that the evolution of the energy density is the one of a
damped wave equation: propagation along the rays of geometric optic and damping
according to a microlocal process. In the second case, we show that the energy
density propagates along rays which are distortions of the rays of geometric
optic.",1203.5606v1
2012-03-26,Infinite Energy Solutions for Damped Navier-Stokes Equations in R2,"We study the so-called damped Navier-Stokes equations in the whole 2D space.
The global well-posedness, dissipativity and further regularity of weak
solutions of this problem in the uniformly-local spaces are verified based on
the further development of the weighted energy theory for the Navier-Stokes
type problems. Note that any divergent free vector field $u_0\in
L^\infty(\mathbb R^2)$ is allowed and no assumptions on the spatial decay of
solutions as $|x|\to\infty$ are posed. In addition, applying the developed
theory to the case of the classical Navier-Stokes problem in R2, we show that
the properly defined weak solution can grow at most polynomially (as a quintic
polynomial) as time goes to infinity.",1203.5733v2
2012-03-28,Quantum-correlating power of local quantum channels,"Quantum correlation can be created by local operations from a classically
correlated state. We define quantum-correlating power (QCP) of a local quantum
channel as the maximum amount of quantum correlation that can be created by the
channel. The quantum correlation that we discuss in this article is defined on
the left part of the bipartite state. We prove that for any local channel, the
optimal input state, which corresponds to the maximum quantum correlation in
the output state, must be a classical-classical state. Further, the
single-qubit channels with maximum QCP can be found in the class of rank-1
channels which take their optimal input states to rank-2 quantum-classical
states. The analytic expression for QCP of single-qubit amplitude damping
channel is obtained. Super-activation property of QCP, i.e., two zero-QCP
channels can consist a positive-QCP channel, is discussed for single-qubit
phase damping channels.",1203.6149v1
2012-04-12,On the sizes of z>2 Damped Lyman-alpha Absorbing Galaxies,"Recently, the number of detected galaxy counterparts of z > 2 Damped
Lyman-alpha Absorbers in QSO spectra has increased substantially so that we
today have a sample of 10 detections. M{\o}ller et al. in 2004 made the
prediction, based on a hint of a luminosity-metallicity relation for DLAs, that
HI size should increase with increasing metallicity. In this paper we
investigate the distribution of impact parameter and metallicity that would
result from the correlation between galaxy size and metallicity. We compare our
observations with simulated data sets given the relation of size and
metallicity. The observed sample presented here supports the metallicity-size
prediction: The present sample of DLA galaxies is consistent with the model
distribution. Our data also show a strong relation between impact parameter and
column density of HI. We furthermore compare the observations with several
numerical simulations and demonstrate that the observations support a scenario
where the relation between size and metallicity is driven by feedback
mechanisms controlling the star-formation efficiency and outflow of enriched
gas.",1204.2833v1
2012-04-16,"Quasi-normal modes, area spectra and multi-horizon spacetimes","We suggest an interpretation for the highly damped QNM frequencies of the
spherically symmetric multi-horizon spacetimes (Reissner-Nordstrom,
Schwarzschild-deSitter, Reissner-Nordstrom-deSitter) following Maggiore's
proposal about the link between the asymptotic QNM frequencies and the black
hole thermodynamics. We show that the behavior of the asymptotic frequencies is
easy to understand if one assumes that all of the horizons have the same
equispaced area spectra. The QNM analysis is then consistent with the choice of
the area spectra to be the one originally proposed for the black hole's horizon
by Bekenstein: A=8\pi n (in Planck units). The interpretation of the highly
damped QNM frequencies in the multi-horizon case is based on the similar
grounds as in the single horizon (Schwarzschild) case, but it has some new
features that are discussed in the paper.",1204.3566v2
2012-05-03,Explicit local time-stepping methods for time-dependent wave propagation,"Semi-discrete Galerkin formulations of transient wave equations, either with
conforming or discontinuous Galerkin finite element discretizations, typically
lead to large systems of ordinary differential equations. When explicit time
integration is used, the time-step is constrained by the smallest elements in
the mesh for numerical stability, possibly a high price to pay. To overcome
that overly restrictive stability constraint on the time-step, yet without
resorting to implicit methods, explicit local time-stepping schemes (LTS) are
presented here for transient wave equations either with or without damping. In
the undamped case, leap-frog based LTS methods lead to high-order explicit LTS
schemes, which conserve the energy. In the damped case, when energy is no
longer conserved, Adams-Bashforth based LTS methods also lead to explicit LTS
schemes of arbitrarily high accuracy. When combined with a finite element
discretization in space with an essentially diagonal mass matrix, the resulting
time-marching schemes are fully explicit and thus inherently parallel.
Numerical experiments with continuous and discontinuous Galerkin finite element
discretizations validate the theory and illustrate the usefulness of these
local time-stepping methods.",1205.0654v2
2012-05-15,Molecular vibrations-induced quantum beats in two-dimensional electronic spectroscopy,"Quantum beats in nonlinear spectroscopy of molecular aggregates are often
attributed to electronic phenomena of excitonic systems, while nuclear degrees
of freedom are commonly included into models as overdamped oscillations of bath
constituents responsible for dephasing. However, molecular systems are coupled
to various high-frequency molecular vibrations, which can cause the spectral
beats hardly distinguishable from those created by purely electronic
coherences. Models containing damped, undamped and overdamped vibrational modes
coupled to an electronic molecular transition are discussed in this paper in
context of linear absorption and two-dimensional electronic spectroscopy.
Analysis of different types of bath models demonstrates how do vibrations map
onto two-dimensional spectra and how the damping strength of the coherent
vibrational modes can be resolved from spectroscopic signals.",1205.3383v2
2012-05-16,Deuterium at high-redshift: Primordial abundance in the zabs = 2.621 damped Ly-alpha system towards CTQ247,"The detection of neutral deuterium in the low-metallicity damped
Lyman-{\alpha} system at zabs = 2.621 towards the quasar CTQ247 is reported.
Using a high signal-to-noise and high spectral resolution (R = 60000) spectrum
from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we
precisely measure the deuterium-to-oxygen ratio log N(DI)/N(OI) = 0.74+/-0.04,
as well as the overall oxygen abundance, log N(OI)/N(HI)=-5.29+/-0.10 (or
equivalently [O/H]=-1.99+/-0.10 with respect to the solar value). Assuming
uniform metallicity throughout the system, our measurement translates to (D/H)
= (2.8+0.8 -0.6)x10^-5. This ratio is consistent within errors (<0.4sigma) with
the primordial ratio, (D/H)p = (2.59+/-0.15)x10^-5, predicted by standard
Big-Bang Nucleosynthesis using the WMAP7 value of the cosmological density of
baryons (100 Omega_b h^2 = 2.249+/-0.056). The DI absorption lines are observed
to be broader than the OI absorption lines. From a consistent fit of the
profiles we derive the turbulent broadening to be 5.2 km/s and the temperature
of the gas to be T = 8800+/-1500 K, corresponding to a warm neutral medium.",1205.3777v1
2012-05-23,Global existence for a damped wave equation and convergence towards a solution of the Navier-Stokes problem,"In two and three space dimensions, and under suitable assumptions on the
initial data, we show global existence for a damped wave equation which
approaches, in some sense, the Navier-Stokes problem. The proofs are based on a
refined energy method. In this paper, we improve the results in two papers by
Y. Brenier, R. Natalini and M. Puel and by M. Paicu and G. Raugel. We relax the
regularity of the initial data of the former, even though we still use energy
methods as a principal tool. Regarding the second paper, the improvement
consists in the simplicity of the proofs since we do not use any Strichartz
estimate and in requiring less regularity for the convergence to the
Navier-Stokes problem. Indeed, the convergence result we obtain is near-optimal
regularity.",1205.5166v2
2012-05-24,Modelling the Propagation of a Weak Fast-Mode MHD Shock Wave near a 2D Magnetic Null Point Using Nonlinear Geometrical Acoustics,"We present the results of analytical modelling of fast-mode
magnetohydrodynamic wave propagation near a 2D magnetic null point. We consider
both a linear wave and a weak shock and analyse their behaviour in cold and
warm plasmas. We apply the nonlinear geometrical acoustics method based on the
Wentzel-Kramers-Brillouin approximation. We calculate the wave amplitude, using
the ray approximation and the laws of solitary shock wave damping. We find that
a complex caustic is formed around the null point. Plasma heating is
distributed in space and occurs at a caustic as well as near the null point due
to substantial nonlinear damping of the shock wave. The shock wave passes
through the null point even in a cold plasma. The complex shape of the wave
front can be explained by the caustic pattern.",1205.5327v1
2012-05-31,Quasinormal modes for the scattering on a naked Reissner-Nordstrom singularity,"What should be the quasinormal modes associated with a spacetime that
contains a naked singularity instead of a black hole? In the present work we
address this problem by studying the scattering of scalar fields on a curved
background described by a Reissner-Nordstr\""om spacetime with $|q| > m$. We
show that there is a qualitative difference between cases with $1 < q^2/m^2
\lesssim 9/8$ and cases with $q^2/m^2 \gtrsim 9/8$. We discuss the necessary
conditions for the well-posedness of the problem, and present results for the
low damped modes in the low $l$ and large $l$ limit. We also consider the
asymptotically highly damped quasinormal modes. We present strong evidence that
such modes are absent in the case of a naked Reissner-Nordstr\""om singularity,
corroborating recent conjectures relating them to classical and quantum
properties of horizons.",1206.0037v3
2012-06-06,Perturbation theory for very long-range potentials,"Systems with very long-range interactions (that decay at large distances like
$U(r)\sim r^{-l}$ with $l\le d$ where $d$ is the space dimensionality) are
difficult to study by conventional statistical mechanics perturbation methods.
Examples of these systems are gravitational and charged (non-electroneutral).
In this work we propose two alternative methodologies to avoid these
difficulties and capture some of the properties of the original potential. The
first one consists in expressing the original potential in terms of a finite
sum of hard-core Yukawa potentials. In the second one, the potential is
rewritten as a damped potential, using a damping function with a parameter that
controls the range of the interaction. These new potentials, which mimic the
original one, can now be treated by conventional statistical mechanics methods.",1206.2211v2
2012-06-10,"Comments on ""Plasma oscillations and nonextensive statistics""","The paper, authored by J. A. S. Lima et al, was published in Phys. Rev. E in
2000 has discussed the dispersion relation and Landau damping of Langmuir wave
in the context of the nonextensive statistics proposed by Tsallis. It has been
cited by many authors because the dispersion relation in Tsallis formalism
present a good fit to the experimental data when q<1, while the classical
result based on Maxwellian distribution only provides a crude description.
However, the results obtained in this paper are problematic. In this comments
on the paper we shall derive the correct analytic formulas both for the
dispersion relation and Landau damping in Tsallis formalism. We hope that this
comments will be useful in providing the correct results.",1206.2345v1
2012-06-25,"Ideal MHD Ballooning modes, shear flow and the stable continuum","There is a well established theory of Ballooning modes in a toroidal plasma.
The cornerstone of this is a local eigenvalue lambda on each magnetic surface -
which also depends on the ballooning phase angle k. In stationary plasmas
lambda(k) is required only near its maximum, but in rotating plasmas its
average over k is required. Unfortunately in many case lambda(k) does not exist
for some range of k, because the spectrum there contains only a stable
continuum. This limits the application of the theory, and raises the important
question of whether this ""stable interval"" gives rise to significant damping.
This question is re-examined using a new, simplified, model - which leads to
the conclusion that there is no appreciable damping at small shear flow. In
particular, therefore, a small shear flow should not affect Ballooning mode
stability boundaries.",1206.5855v2
2012-06-26,A Numerical Perspective on Hartree-Fock-Bogoliubov Theory,"The method of choice for describing attractive quantum systems is
Hartree-Fock-Bogoliubov (HFB) theory. This is a nonlinear model which allows
for the description of pairing effects, the main explanation for the
superconductivity of certain materials at very low temperature. This paper is
the first study of Hartree-Fock-Bogoliubov theory from the point of view of
numerical analysis. We start by discussing its proper discretization and then
analyze the convergence of the simple fixed point (Roothaan) algorithm.
Following works by Canc\`es, Le Bris and Levitt for electrons in atoms and
molecules, we show that this algorithm either converges to a solution of the
equation, or oscillates between two states, none of them being a solution to
the HFB equations. We also adapt the Optimal Damping Algorithm of Canc\`es and
Le Bris to the HFB setting and we analyze it. The last part of the paper is
devoted to numerical experiments. We consider a purely gravitational system and
numerically discover that pairing always occurs. We then examine a simplified
model for nucleons, with an effective interaction similar to what is often used
in nuclear physics. In both cases we discuss the importance of using a damping
algorithm.",1206.6081v1
2012-06-27,Dynamics of zonal flow-like structures in the edge of the TJ-II stellarator,"The dynamics of fluctuating electric field structures in the edge of the
TJ-II stellarator, that display zonal flow-like traits, is studied. These
structures have been shown to be global and affect particle transport
dynamically [J.A. Alonso et al., Nucl. Fus. 52 063010 (2012)]. In this article
we discuss possible drive (Reynolds stress) and damping (Neoclassical
viscosity, geodesic transfer) mechanisms for the associated ExB velocity. We
show that: (a) while the observed turbulence-driven forces can provide the
necessary perpendicular acceleration, a causal relation could not be firmly
established, possibly because of the locality of the Reynolds stress
measurements, (b) the calculated neoclassical viscosity and damping times are
comparable to the observed zonal flow relaxation times, and (c) although an
accompanying density modulation is observed to be associated to the zonal flow,
it is not consistent with the excitation of pressure side-bands, like those
present in geodesic acoustic oscillations, caused by the compression of the ExB
flow field.",1206.6191v1
2012-07-13,Decay of capillary wave turbulence,"We report on the observation of freely decaying capillary wave turbulence on
the surface of a fluid. The capillary wave turbulence spectrum decay is found
to be self-similar in time with the same power law exponent than the one found
in the stationary regime, in agreement with weak turbulence predictions. The
amplitude of all Fourier modes are found to decrease exponentially with time at
the same damping rate. The longest wavelengths involved in the system are shown
to be damped by viscous surface boundary layer. These long waves play the role
of an energy source during the decay that sustains nonlinear interactions to
keep capillary waves in a wave turbulent state.",1207.3228v1
2012-07-17,Holographic Superfluids and the Dynamics of Symmetry Breaking,"We explore the far from equilibrium response of a holographic superfluid
using the AdS/CFT correspondence. We establish the dynamical phase diagram
corresponding to quantum quenches of the order parameter source field. We find
three distinct regimes of behaviour that are related to the spectrum of black
hole quasi-normal modes. These correspond to damped oscillations of the order
parameter, and over-damped approaches to the superfluid and normal states. The
presence of three regimes, which includes an emergent dynamical temperature
scale, is argued to occur more generally in time-reversal invariant systems
that display continuous symmetry breaking.",1207.4194v2
2012-07-18,Attractiveness of periodic orbits in parametrically forced systemswith time-increasing friction,"We consider dissipative one-dimensional systems subject to a periodic force
and study numerically how a time-varying friction affects the dynamics. As a
model system, particularly suited for numerical analysis, we investigate the
driven cubic oscillator in the presence of friction. We find that, if the
damping coefficient increases in time up to a final constant value, then the
basins of attraction of the leading resonances are larger than they would have
been if the coefficient had been fixed at that value since the beginning. From
a quantitative point of view, the scenario depends both on the final value and
the growth rate of the damping coefficient. The relevance of the results for
the spin-orbit model are discussed in some detail.",1207.4319v1
2012-07-19,Acoustic damping and dispersion in vitreous germanium oxide,"New Brillouin scattering measurements of velocity and attenuation of sound in
the hypersonic regime are presented. The data are analyzed together with the
literature results at sonic and ultrasonic frequencies. As usual, thermally
activated relaxation of structural entities describes the attenuation at sonic
and ultrasonic frequencies. As already shown in vitreous silica, we conclude
that the damping by network viscosity, resulting from relaxation of thermal
phonons, must be taken into account to describe the attenuation at hypersonic
frequencies. In addition, the bare velocity obtained by subtracting to the
experimental data the effect of the two above mechanisms is constant for
temperatures below 250 K, but increases almost linearly above, up to the glass
transition temperature. This might indicate the presence of a progressive local
polyamorphic transition, as already suggested for vitreous silica.",1207.4582v1
2012-07-26,Generic Mechanism of Optimal Energy Transfer Efficiency: A Scaling Theory of the Mean First Passage Time in Exciton Systems,"An asymptotic scaling theory is presented using the conceptual basis of
trapping-free subspace (i.e., orthogonal subspace) to establish the generic
mechanism of optimal efficiency of excitation energy transfer (EET) in
light-harvesting systems. Analogous to Kramers' turnover in classical rate
theory, the enhanced efficiency in the weak damping limit and the suppressed
efficiency in the strong damping limit define two asymptotic scaling regimes,
which are interpolated to predict the functional form of optimal efficiency of
the trapping-free subspace. In the presence of static disorder, the scaling law
of transfer time with respect to dephasing rate changes from linear to square
root, suggesting a weaker dependence on the environment. Though formulated in
the context of EET, the analysis and conclusions apply in general to open
quantum processes, including electron transfer, fluorescence emission, and heat
conduction.",1207.6197v1
2012-07-27,Dissipative and Non-dissipative Single-Qubit Channels: Dynamics and Geometry,"Single-qubit channels are studied under two broad classes: amplitude damping
channels and generalized depolarizing channels. A canonical derivation of the
Kraus representation of the former, via the Choi isomorphism is presented for
the general case of a system's interaction with a squeezed thermal bath. This
isomorphism is also used to characterize the difference in the geometry and
rank of these channel classes. Under the isomorphism, the degree of decoherence
is quantified according to the mixedness or separability of the Choi matrix.
Whereas the latter channels form a 3-simplex, the former channels do not form a
convex set as seen from an ab initio perspective. Further, where the rank of
generalized depolarizing channels can be any positive integer upto 4, that of
amplitude damping ones is either 2 or 4. Various channel performance parameters
are used to bring out the different influences of temperature and squeezing in
dissipative channels. In particular, a noise range is identified where the
distinguishability of states improves inspite of increasing decoherence due to
environmental squeezing.",1207.6519v1
2012-07-27,"Phonon Effects on Population Inversion in Quantum Dots: Resonant, Detuned and Frequency-swept Excitations","The effect of acoustic phonons on different light-induced excitations of a
semiconductor quantum dot is investigated. Resonant excitation of the quantum
dot leads to Rabi oscillations, which are damped due to the phonon interaction.
When the excitation frequency is detuned, an occupation can only occur due to
phonon absorption or emission processes. For frequency-swept excitations a
population inversion is achieved through adiabatic rapid passage, but the
inversion is also damped by phonons. For all three scenarios the influence of
the phonons depends non-monotonically on the pulse area.",1207.6660v2
2012-08-08,Mechanism of collisionless sound damping in dilute Bose gas with condensate,"We develop a microscopic theory of sound damping due to Landau mechanism in
dilute gas with Bose condensate. It is based on the coupled evolution equations
of the parameters describing the system. These equations have been derived in
earlier works within a microscopic approach which employs the
Peletminskii-Yatsenko reduced description method for quantum many-particle
systems and Bogoliubov model for a weakly nonideal Bose gas with a separated
condensate. The dispersion equations for sound oscillations were obtained by
linearization of the mentioned evolution equations in the collisionless
approximation. They were analyzed both analytically and numerically. The
expressions for sound speed and decrement rate were obtained in high and low
temperature limiting cases. We have shown that at low temperature the
dependence of the obtained quantities on temperature significantly differs from
those obtained by other authors in the semi-phenomenological approaches.
Possible effects connected with non-analytic temperature dependence of
dispersion characteristics of the system were also indicated.",1208.1653v2
2012-08-17,Detection of domain wall eigenfrequency in infinity-shaped magnetic nanostructures,"The dynamics of a magnetic infinity-shaped nanostructure has been
experimentally studied by two different techniques such as the sinusoidal
resonance excitation and the damped short pulse excitation to measure the
eigenfrequency of domain walls. Direct observation of the magnetic domain wall
nucleation has been measured in the frequency domain. Electrical measurements
of the domain wall dynamics in the frequency domain reveal the existence of
multi-eigenmodes for large excitation amplitudes. The time-resolved
measurements show that the frequency of the damped gyration is similar to that
of the frequency domain and coexistence of spin wave excitations.",1208.3527v1
2012-08-21,Stress field and spin axis relaxation for inelastic triaxial ellipsoids,"A compact formula for the stress tensor inside a self-gravitating, triaxial
ellipsoid in an arbitrary rotation state is given. It contains no singularity
in the incompressible medium limit. The stress tensor and the quality factor
model are used to derive a solution for the energy dissipation resulting in the
damping (short axis mode) or excitation (long axis) of wobbling. In the limit
of an ellipsoid of revolution, we compare our solution with earlier ones and
show that, with appropriate corrections, the differences in damping times
estimates are much smaller than it has been claimed.
  This version implements corrections of misprints found in the MNRAS published
text.",1208.4283v2
2012-08-21,Brownian transport in corrugated channels with inertia,"The transport of suspended Brownian particles dc-driven along corrugated
narrow channels is numerically investigated in the regime of finite damping. We
show that inertial corrections cannot be neglected as long as the width of the
channel bottlenecks is smaller than an appropriate particle diffusion length,
which depends on the the channel corrugation and the drive intensity. Being
such a diffusion length inversely proportional to the damping constant,
transport through sufficiently narrow obstructions turns out to be always
sensitive to the viscosity of the suspension fluid. The inertia corrections to
the transport quantifiers, mobility and diffusivity, markedly differ for
smoothly and sharply corrugated channels.",1208.4401v2
2012-08-22,On unorthodox solutions of the Bloch equations,"A systematic, rigorous, and complete investigation of the Bloch equations in
time-harmonic driving classical field is performed. Our treatment is unique in
that it takes full advantage of the partial fraction decomposition over real
number field, which makes it possible to find and classify all analytic
solutions. Torrey's analytic solution in the form of exponentially damped
harmonic oscillations [Phys. Rev. {\bf 76}, 1059 (1949)] is found to dominate
the parameter space, which justifies its use at numerous occasions in magnetic
resonance and in quantum optics of atoms, molecules, and quantum dots. The
unorthodox solutions of the Bloch equations, which do not have the form of
exponentially damped harmonic oscillations, are confined to rather small
detunings $\delta^2\lesssim (\gamma-\gamma_t)^2/27$ and small field strengths
$\Omega^2\lesssim 8 (\gamma-\gamma_t)^2/27$, where $\gamma$ and $\gamma_t$
describe decay rates of the excited state (the total population relaxation
rate) and of the coherence, respectively. The unorthodox solutions being
readily accessible experimentally are characterized by rather featureless time
dependence.",1208.5736v1
2012-08-29,Optically mediated nonlinear quantum optomechanics,"We consider theoretically the optomechanical interaction of several
mechanical modes with a single quantized cavity field mode for linear and
quadratic coupling. We focus specifically on situations where the optical
dissipation is the dominant source of damping, in which case the optical field
can be adiabatically eliminated, resulting in effective multimode interactions
between the mechanical modes. In the case of linear coupling, the coherent
contribution to the interaction can be exploited e.g. in quantum state swapping
protocols, while the incoherent part leads to significant modifications of cold
damping or amplification from the single-mode situation. Quadratic coupling can
result in a wealth of possible effective interactions including the analogs of
second-harmonic generation and four-wave mixing in nonlinear optics, with
specific forms depending sensitively on the sign of the coupling. The
cavity-mediated mechanical interaction of two modes is investigated in two
limiting cases, the resolved sideband and the Doppler regime. As an
illustrative application of the formal analysis we discuss in some detail a
two-mode system where a Bose-Einstein condensate is optomechanically linearly
coupled to the moving end mirror of a Fabry-P\'erot cavity.",1208.5821v1
2012-08-31,Spectrums of Black Hole in de Sitter Spacetime with Highly Damped Quasinormal Modes: High Overtone Case,"Motivated by recent physical interpretation on quasinormal modes presented by
Maggiore, the adiabatic quantity method given by Kunstatter is used to
calculate the spectrums of a non-extremal Schwarzschild de Sitter black hole in
this paper, as well as electrically charged case. According to highly damped
Konoplya and Zhidenko's numerical observational results for high overtone
modes\cite{Konoplya}, we found that the asymptotic non-flat spacetime structure
leads two interesting facts as followings: (i) near inner event horizon, the
area and entropy spectrums, which are given by $A_{en} = 8 n_1 \pi \hbar$,
$S_{en} = 2\pi n_1\hbar$, are equally spaced accurately. (ii) However, near
outer cosmological horizon the spectrums, which are in the form of $A_{cn} = 16
n_2 \pi \hbar - \sqrt{\frac{48\pi}{\Lambda}A_{cn} - 3 A_{cn}^2}$, $S_{cn} = 4
\pi n_2 \hbar - \sqrt{\frac{3\pi}{\Lambda}A_{cn} - 3/16 A_{cn}^2}$, are not
markedly equidistant. Finally, we also discuss the electrically charged case
and find the black holes in de Sitter spacetime have similar quantization
behavior no matter with or without charge.",1208.6485v1
2012-09-10,Rapid ramps across the BEC-BCS crossover: a novel route to measuring the superfluid gap,"We investigate the response of superfluid Fermi gases to rapid changes of the
three-dimensional s-wave scattering length a by solving the time-dependent
Bogoliubov-de Gennes equations. In general the magnitude of the order parameter
|\Delta| performs oscillations, which are sometimes called the ""Higgs"" mode,
with the angular frequency 2 \Delta_{gap}/ \hbar, where \Delta_{gap} is the gap
in the spectrum of fermionic excitations. Firstly, we excite the oscillations
with a linear ramp of 1/a and study the evolution of |\Delta|. Secondly, we
continously drive the system with a sinusoidal modulation of 1/a. In the first
case, the oscillations in |\Delta| damp according to a power law. In the second
case, the continued driving causes revivals in the oscillations. In both cases,
the excitation of the oscillations causes a reduction in the time-averaged
value of |\Delta|. We propose two experimental protocols, based around the two
approaches, to measure the frequency and damping of the oscillations, and hence
\Delta_{gap}.",1209.2025v1
2012-09-12,Loss of Landau Damping for Bunch Oscillations,"Conditions for the existence, uniqueness and stability of self-consistent
bunch steady states are considered. For the existence and uniqueness problems,
simple algebraic criteria are derived for both the action and Hamiltonian
domain distributions. For the stability problem, van Kampen theory is used. The
onset of a discrete van Kampen mode means the emergence of a coherent mode
without any Landau damping; thus, even a tiny couple-bunch or multi-turn wake
is sufficient to drive the instability. The method presented here assumes an
arbitrary impedance, RF shape, and beam distribution function. Available areas
on the intensity-emittance plane are shown for resistive wall wake and single
harmonic, bunch shortening and bunch lengthening RF configurations. Thresholds
calculated for the Tevatron parameters and impedance model are in agreement
with the observations. These thresholds are found to be extremely sensitive to
the small-argument behaviour of the bunch distribution function. Accordingly, a
method to increase the LLD threshold is suggested. This article summarizes and
extends recent author's publications.",1209.2715v1
2012-09-17,Generalized fluctuation-dissipation relation and statistics for the equilibrium of a system with conformation dependent damping,"Liouville's theorem, based on the Hamiltonian flow (micro-canonical ensemble)
for a many particle system, indicates that the (stationary) equilibrium
probability distribution is a function of the Hamiltonian. A canonical ensemble
corresponds to a micro-canonical one at thermodynamic limit. On the contrary,
the dynamics of a single Brownian particle (BP) being explicitly
non-Hamiltonian with a force and damping term in it and at the other extreme to
thermodynamic limit admits the Maxwell-distribution (MD) for its velocity and
Boltmann-distribution (BD) for positions (when in a potential). This is due to
the fluctuation-dissipation relation (FDR), as was first introduced by
Einstein, which forces the Maxwell distribution to the Brownian particles. For
a structureless BP, that, this theory works is an experimentally verified fact
over a century now. Considering a structured Brownian particle we will show
that the BD and MD fails to ensure equilibrium. We will derive a generalized
FDR on the basis of the demand of zero current on inhomogeneous space. Our FDR
and resulting generalized equilibrium distributions recover the standard ones
at appropriate limits.",1209.3654v3
2012-09-20,High Resolution BPM Upgrade for the ATF Damping Ring at KEK,"A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility
(ATF) damping ring has been accomplished, carried out by a KEK/FNAL/SLAC
collaboration under the umbrella of the global ILC R&D effort. The upgrade
consists of a high resolution, high reproducibility read-out system, based on
analog and processing, and also implements a new automatic gain error
correction schema. The technical concept and realization as well as results of
beam studies are presented.",1209.4569v1
2012-09-23,Ion Landau Damping on Drift Tearing Modes,"Kinetic treatments of drift-tearing modes that match an inner resonant layer
solution to an external MHD region solution, characterised by
$\Delta^{\prime}$, fail to properly match the ideal MHD boundary condition on
the parallel electric field, $E_{\parallel}.$ In this paper we demonstrate how
consideration of ion sound and ion Landau damping effects achieves this and
place the theory on a firm footing. As a consequence, these effects contribute
quite significantly to the critical value of $\Delta^{\prime}$ for instability
of drift-tearing modes and play a key role in determining the minimum value for
this threshold.",1209.5054v3
2012-09-26,Damping of giant dipole resonance in highly excited nuclei,"The giant dipole resonance's (GDR) width and shape at finite temperature and
angular momentum are described within the phonon damping model (PDM), which
predicts an overall increase in the GDR's total width at low and moderate
temperature T, and its saturation at high T. At T< 1 MeV the GDR width remains
nearly constant because of thermal pairing. The PDM description is compared
with the experimental systematics obtained from heavy-ion fusion, inelastic
scattering of light particles on heavy targets, and alpha induced fusion
reactions, as well as with predictions by other theoretical approaches. The
results obtained within the PDM and GDR's experimental data are also employed
to predict the viscosity of hot medium and heavy nuclei.",1209.5820v2
2012-09-26,Inverse Energy Cascade in Forced 2D Quantum Turbulence,"We demonstrate an inverse energy cascade in a minimal model of forced 2D
quantum vortex turbulence. We simulate the Gross-Pitaevskii equation for a
moving superfluid subject to forcing by a stationary grid of obstacle
potentials, and damping by a stationary thermal cloud. The forcing injects
large amounts of vortex energy into the system at the scale of a few healing
lengths. A regime of forcing and damping is identified where vortex energy is
efficiently transported to large length scales via an inverse energy cascade
associated with the growth of clusters of same-circulation vortices, a
Kolmogorov scaling law in the kinetic energy spectrum over a substantial
inertial range, and spectral condensation of kinetic energy at the scale of the
system size. Our results provide clear evidence that the inverse energy cascade
phenomenon, previously observed in a diverse range of classical systems, can
also occur in quantum fluids.",1209.5824v2
2012-09-27,Comparison of non-Markovianity criteria in a qubit system under random external fields,"We give the map representing the evolution of a qubit under the action of
non-dissipative random external fields. From this map we construct the
corresponding master equation that in turn allows us to phenomenologically
introduce population damping of the qubit system. We then compare, in this
system, the time-regions when non-Markovianity is present on the basis of
different criteria both for the non-dissipative and dissipative case. We show
that the adopted criteria agree both in the non-dissipative case and in the
presence of population damping.",1209.6331v2
2012-10-01,Gravitational Coleman-Weinberg Potential and It's Finite Temperature Counterpart,"Coleman-Weinberg (CW) phenomena for the case of gravitons minimally coupled
to massless scalar field is studied. The one loop effect completely vanishes if
there is no self interaction term present in the matter sector. The one loop
effective potential is shown to develop an instability in the form of acquiring
an imaginary part, which can be traced to the tachyonic pole in the graviton
propagator. The finite temperature counterpart of this CW potential is computed
to study the behaviour of the potential in the high and low temperature regimes
with respect to the typical energy scale of the theory. Finite temperature
contribution to the imaginary part of gravitational CW potential exhibits a
damped oscillatory behaviour; all thermal effects are damped out as the
temperature vanishes, consistent with the zero-temperature result. Possibility
of symmetry restoration at high temperature is also depicted.",1210.0497v4
2012-10-09,Analytic approximate seismology of propagating MHD waves in the solar corona,"Observations show that propagating magnetohydrodynamic (MHD) waves are
ubiquitous in the solar atmosphere. The technique of MHD seismology uses the
wave observations combined with MHD wave theory to indirectly infer physical
parameters of the solar atmospheric plasma and magnetic field. Here we present
an analytical seismological inversion scheme for propagating MHD waves. This
scheme uses in a consistent manner the observational information on wavelengths
and damping lengths, along with observed values of periods or phase velocities,
and is based on approximate asymptotic expressions for the theoretical values
of wavelengths and damping lengths. The applicability of the inversion scheme
is discussed and an example is given.",1210.2689v1
2012-10-12,Threshold current for switching of a perpendicular magnetic layer induced by spin Hall effect,"We theoretically investigate the switching of a perpendicular magnetic layer
by in-plane charge current due to the spin Hall effect. We find that, in the
high damping regime, the threshold switching current is independent of the
damping constant, and is almost linearly proportional to both effective
perpendicular magnetic anisotropy field and external in-plane field applied
along the current direction. We obtain an analytic expression of the threshold
current, in excellent agreement with numerical results. This expression can be
used to determine the physical quantities associated with spin Hall effect, and
to design relevant magnetic devices based on the switching of perpendicular
magnetic layers.",1210.3442v2
2012-10-12,Reversal of magnetization of a single-domain magnetic particle by the ac field of time-dependent frequency,"We report numerical and analytical studies of the reversal of the magnetic
moment of a single-domain magnetic particle by a circularly polarized ac field
of time-dependent frequency. For the time-linear frequency sweep, the phase
diagrams are computed that illustrate the dependence of the reversal on the
frequency sweep rate v, the amplitude of the ac field h, the magnetic
anisotropy field d, and the damping parameter alpha. It is shown that the most
efficient magnetization reversal requires a non-linear time dependence of the
frequency, omega(t), for which an exact analytical formula is derived with
account of damping. The necessary condition of the reversal is h > alpha d.
Implementation of a small-scale magnetization reversal is proposed in which a
nanomagnet is electromagnetically coupled to two weak superconducting links
controlled by the voltage. Dynamics of such a system is analyzed with account
of the back effect of the magnet on the superconducting links.",1210.3530v1
2012-10-15,Symmetries of the quantum damped harmonic oscillator,"For the non-conservative Caldirola-Kanai system, describing a quantum damped
harmonic oscillator, a couple of constant-of-motion operators generating the
Heisenberg-Weyl algebra can be found. The inclusion of the standard time
evolution generator (which is not a symmetry) as a symmetry in this algebra, in
a unitary manner, requires a non-trivial extension of this basic algebra and
hence of the physical system itself. Surprisingly, this extension leads
directly to the so-called Bateman dual system, which now includes a new
particle acting as an energy reservoir. In addition, the Caldirola-Kanai
dissipative system can be retrieved by imposing constraints. The algebra of
symmetries of the dual system is presented, as well as a quantization that
implies, in particular, a first-order Schr\""odinger equation. As opposed to
other approaches, where it is claimed that the spectrum of the Bateman
Hamiltonian is complex and discrete, we obtain that it is real and continuous,
with infinite degeneracy in all regimes.",1210.4058v1
2012-10-18,SDO/AIA Observations of Large-Amplitude Longitudinal Oscillations in a Solar Filament,"We present the first \emph{Solar Dynamics Observatory}/Atmospheric Imaging
Assembly observations of the large-amplitude longitudinal (LAL) oscillations in
the south and north parts (SP and NP) of a solar filament on 2012 April 7. Both
oscillations are triggered by flare activities close to the filament. The
period varies with filamentary threads, ranging from 44 to 67 min. The
oscillations of different threads are out of phase, and their velocity
amplitudes vary from 30 to 60 km s$^{-1}$, with a maximum displacement of about
25 Mm. The oscillations of the SP repeat for about 4 cycles without any
significant damping and then a nearby C2.4 flare causes the transition from the
LAL oscillations of the filament to its later eruption. The filament eruption
is also associated with a coronal mass ejection and a B6.8 flare. However, the
oscillations of the NP damp with time and die out at last. Our observations
show that the activated part of the SP repeatedly shows a helical motion. This
indicates that the magnetic structure of the filament is possibly modified
during this process. We suggest that the restoring force is the coupling of the
magnetic tension and gravity.",1210.5110v1
2012-10-31,The Kerr medium as an {\sf SU(2)} system,"The Kerr medium in the presence of damping and associated with SU(1,1)
symmetry, is solved using the techniques of Thermo field Dynamics (TFD).These
TFD techniques, well studied earlier (Chaturvedi and Srinivasan, 1991), help us
to exactly solve the Kerr medium as a spin damped system associated with SU(2)
symmetry. Using TFD, the association with SU(2) is exploited to express the
dynamics of the system as a Schrodinger-like equation, whose solution is
obtained using the appropriate disentanglement theorem. These considerations
are extended to a system with multi-mode coupled nonlinear oscillators.""",1210.8240v1
2012-12-06,A simple and effective Verlet-type algorithm for simulating Langevin dynamics,"We present a revision to the well known Stormer-Verlet algorithm for
simulating second order differential equations. The revision addresses the
inclusion of linear friction with associated stochastic noise, and we
analytically demonstrate that the new algorithm correctly reproduces diffusive
behavior of a particle in a flat potential. For a harmonic oscillator, our
algorithm provides the exact Boltzmann distribution for any value of damping,
frequency, and time step for both underdamped and over damped behavior within
the usual the stability limit of the Verlet algorithm. Given the structure and
simplicity of the method we conclude this approach can trivially be adapted for
contemporary applications, including molecular dynamics with extensions such as
molecular constraints.",1212.1244v4
2012-12-10,Shear viscosity and the r-mode instability window in superfluid neutron stars,"We analyze how recent computations of the shear viscosity $\eta$ in the core
of superfluid neutron stars affect the r-mode instability window. We first
analyze the contribution of superfluid phonons to the viscosity, both in their
hydrodynamical and ballistic regime. We also consider the recent computation of
$\eta$ arising from the collisions of electrons with electrons and protons by
Shternin and Yakovlev, and discuss how the interactions among superfluid
phonons and electrons might contribute to the shear viscosity. For assessing
the r-mode instability window we compare the shear viscosity due to phonons in
the hydrodynamical regime with respect to the shear viscosity due to electron
collisions. Only at high temperatures the superfluid phonon contribution to
$\eta$ starts to dominate the process of r-mode damping. While our results for
the instability window are preliminary, as other dissipative processes should
be taken into account as well, they differ from previous evaluations of the
r-mode damping due to the shear viscosity in superfluid neutron stars.",1212.2075v2
2012-12-12,The operator sum-difference representation for quantum maps: application to the two-qubit amplitude damping channel,"On account of the Abel-Galois no-go theorem for the algebraic solution to
quintic and higher order polynomials, the eigenvalue problem and the associated
characteristic equation for a general noise dynamics in dimension $d$ via the
Choi-Jamiolkowski approach cannot be solved in general via radicals. We provide
a way around this impasse by decomposing the Choi matrix into simpler, not
necessarily positive, Hermitian operators that are diagonalizable via radicals,
which yield a set of `positive' and `negative' Kraus operators. The price to
pay is that the sufficient number of Kraus operators is $d^4$ instead of $d^2$,
sufficient in the Kraus representation. We consider various applications of the
formalism: the Kraus repesentation of the 2-qubit amplitude damping channel,
the noise resulting from a 2-qubit system interacting dissipatively with a
vacuum bath; defining the maximally dephasing and purely dephasing components
of the channel in the new representation, and studying their entanglement
breaking and broadcast properties.",1212.2780v1
2012-12-13,Efficiency improvement of the frequency-domain BEM for rapid transient elastodynamic analysis,"The frequency-domain fast boundary element method (BEM) combined with the
exponential window technique leads to an efficient yet simple method for
elastodynamic analysis. In this paper, the efficiency of this method is further
enhanced by three strategies. Firstly, we propose to use exponential window
with large damping parameter to improve the conditioning of the BEM matrices.
Secondly, the frequency domain windowing technique is introduced to alleviate
the severe Gibbs oscillations in time-domain responses caused by large damping
parameters. Thirdly, a solution extrapolation scheme is applied to obtain
better initial guesses for solving the sequential linear systems in the
frequency domain. Numerical results of three typical examples with the problem
size up to 0.7 million unknowns clearly show that the first and third
strategies can significantly reduce the computational time. The second strategy
can effectively eliminate the Gibbs oscillations and result in accurate
time-domain responses.",1212.3032v2
2012-12-16,Decay of the solution to the bipolar Euler-Poisson system with damping in $\mathbb{R}^3$,"We construct the global solution to the Cauchy's problem of the bipolar
Euler-Poisson equations with damping in $\mathbb{R}^3$ when $H^3$ norm of the
initial data is small. If further, the $\dot{H}^{-s}$ norm ($0\leq s<3/2)$ or
$\dot{B}_{2,\infty}^{-s}$ norm ($0<s\leq3/2$) of the initial data is bounded,
we give the optimal decay rates of the solution. As a byproduct, the decay
results of the $L^p-L^2$ ($1\leq p\leq2$) type hold without the smallness of
the $L^p$ norm of the initial data. In particular, we deduce that
$\|\nabla^k(\rho_1-\rho_2)\|_{L^2} \sim(1+t)^{-5/4-\frac{k}{2}}$ and
$\|\nabla^k(\rho_i-\bar{\rho},u_i,\nabla\phi)\|_{L^2}
\sim(1+t)^{-3/4-\frac{k}{2}}$. We improve the decay results in Li and Yang
\cite{Li3}(\emph{J.Differential Equations} 252(2012), 768-791), where they
showed the decay rates as $\|\nabla^k(\rho_i-\bar{\rho})\|_{L^2}
\sim(1+t)^{-3/4-\frac{k}{2}}$ and $\|\nabla^k(u_i,\nabla\phi)\|_{L^2}
\sim(1+t)^{-1/4-\frac{k}{2}}$, when the $H^3\cap L^1$ norm of the initial data
is small. Our analysis is motivated by the technique developed recently in Guo
and Wang \cite{Guo}(\emph{Comm. Partial Differential Equations} 37(2012),
2165-2208) with some modifications.",1212.3754v2
2012-12-24,Effects of kappa distribution function on Landau damping in electrostatic Vlasov simulation,"Effects of non-thermal high-energy electrons on Langmuir wave-particle
interaction are investigated by an initial value approach. A Vlasov-Poisson
simulation is employed which is based on the splitting scheme by Cheng and
Knorr [Cheng, C.Z. and G. Knorr, 1976: J. Comput. Phys. 22, 330-351.]. The
kappa distribution function is taken as an example of non-thermal electrons.
The modification is manifested as an increase in the Landau damping rate and a
decrease in the real frequency for a long wavelength limit. A part of the
analyses by the modified plasma dispersion function [Summers, D. and
R.M.Thorne, 1991: Phys. Fluids, B 3, 1835-1847.] is reproduced for $\kappa =
2,3$ and 6. The dispersion relation from the initial value simulation and the
plasma dispersion function compare favorably.",1212.5872v1
2012-12-26,Anomalous dynamic back-action in interferometers,"We analyze the dynamic optomechanical back-action in signal-recycled
Michelson and Michelson-Sagnac interferometers that are operated off dark port.
We show that in this case --- and in contrast to the well-studied canonical
form of dynamic back-action on dark port --- optical damping in a
Michelson-Sagnac interferometer acquires a non-zero value on cavity resonance,
and additional stability/instability regions on either side of the resonance,
revealing new regimes of cooling/heating of micromechanical oscillators. In a
free-mass Michelson interferometer for a certain region of parameters we
predict a stable single-carrier optical spring (positive spring and positive
damping), which can be utilized for the reduction of quantum noise in
future-generation gravitational-wave detectors.",1212.6242v2
2013-01-01,A scattering approach to some aspects of the Schwarzschild Black Hole,"In this paper, we consider a massless field, with spin j, in interaction with
a Schwarzschild black hole in four dimensions, focusing mainly our study on the
s-wave scattering. First, using a Fourier analysis, we show that one can have a
simple and natural description of the Physics near the event horizon without
using any conformal field approaches. Then, within the same ""scattering
picture"", we derive analytically the imaginary part of the highly damped
quasinormal complex frequencies and, as a natural consequence of our analysis,
we show that thermal effects and in particular Hawking radiation, can be
understood through the scattering of an ingoing s-wave by the non null barrier
of the Regge-Wheeler potential associated with the Schwarzschild black hole.
Finally, with the help of the well-known expression of the highly damped
quasinormal complex frequencies, we propose a heuristic extension of the
""tripled Pauli statistics"" suggested by Motl, some years ago.",1301.0108v1
2013-01-02,Memory models of adaptive behaviour,"Adaptive response to a varying environment is a common feature of biological
organisms. Reproducing such features in electronic systems and circuits is of
great importance for a variety of applications. Here, we consider memory models
inspired by an intriguing ability of slime molds to both memorize the period of
temperature and humidity variations, and anticipate the next variations to
come, when appropriately trained. Effective circuit models of such behavior are
designed using i) a set of LC-contours with memristive damping, and ii) a
single memcapacitive system-based adaptive contour with memristive damping. We
consider these two approaches in detail by comparing their results and
predictions. Finally, possible biological experiments that would discriminate
between the models are discussed. In this work, we also introduce an effective
description of certain memory circuit elements.",1301.0209v2
2013-01-03,Collective modes of a two-dimensional spin-1/2 Fermi gas in a harmonic trap,"We derive analytical expressions for the frequency and damping of the lowest
collective modes of a two-dimensional Fermi gas using kinetic theory. For
strong coupling, we furthermore show that pairing correlations overcompensate
the effects of Pauli blocking on the collision rate for a large range of
temperatures, resulting in a rate which is larger than that of a classical gas.
Our results agree well with experimental data, and they recover the observed
cross-over from collisionless to hydrodynamic behaviour with increasing
coupling for the quadruple mode. Finally, we show that a trap anisotropy within
the experimental bounds results in a damping of the breathing mode which is
comparable to what is observed, even for a scale invariant system.",1301.0358v2
2013-01-09,Synthesis of new neutron-rich heavy nuclei: An experimentalist's view,"I attempt to experimentally evaluate the prospects of synthesizing new
neutron- rich superheavy nuclei. I consider three possible synthetic paths to
neutron- rich superheavy nuclei: (a) the use of neutron-rich radioactive beams.
(b) the use of damped collisions and (c) the use of multi-nucleon transfer
reactions. I consider the prospects of synthesizing new n-rich isotopes of
Rf-Bh using light n-rich radioactive beams and targeted beams from ReA3, FRIB
and SPIRAL2. For the damped collision path, I present the results of a study of
a surrogate reaction, 160Gd + 186W. These data indicate the formation of Au
(trans-target) fragments and the depletion of yields of target-like fragments
by fission and fragment emission. The data are compared to predictions of
Zagrebaev and Greiner. For the multi-nucleon transfer reactions, the results of
a study of the 136Xe + 208Pb reaction are discussed. I consider the possibility
of multi-nucleon transfer reactions with radioactive beams.",1301.1759v1
2013-01-13,Entanglement dynamics of non-inertial observers in a correlated environment,"Effect of decoherence and correlated noise on the entanglement of X-type
state of the Dirac fields in the non-inertial frame is investigated. A two
qubit X-state is considered to be shared between the partners where Alice is in
inertial frame and Rob in an accelerated frame. The concurrence is used to
quantify the entanglement of the X-state system influenced by time correlated
amplitude damping, depolarizing and bit flip channels. It is seen that
amplitude damping and bit flip channels heavily influence the entanglement of
the system as compared to the depolarizing channel. It is found possible to
avoid entanglement sudden death (ESD) for all the channels under consideration
for {\mu}>0.75 for any type of initial state. No ESD behaviour is seen for
depolarizing channel in the presence of correlated noise for entire range of
decoherence parameter p and Rob's acceleration r. It is also seen that the
effect of environment is much stronger than that of acceleration of the
accelerated partner. Furthermore, it is investigated that correlated noise
compensates the loss of entanglement caused by the Unruh effect.",1301.2759v1
2013-01-13,Decoherence and multipartite entanglement of non-inertial observers,"Decoherence effect on multipartite entanglement in non-inertial frames is
investigated. GHZ state is considered to be shared between the partners with
one partner in inertial frame whereas the other two in accelerated frames.
One-tangle and {\pi}-tangles are used to quantify the entanglement of the
multipartite system influenced by phase damping and phase flip channels. It is
seen that for phase damping channel, entanglement sudden death (ESD) occurs for
p>0.5 in the infinite acceleration limit. On the other hand, in case of phase
flip channel, ESD behaviour happens around 50% decoherence. It is also seen
that entanglement sudden birth (ESB) does occur in case of phase flip channel.
Furthermore, it is seen that effect of environment on multipartite entanglement
is much stronger than that of the acceleration of non-inertial frames.",1301.2765v2
2013-01-18,Current induced torques and interfacial spin-orbit coupling: Semiclassical Modeling,"In bilayer nanowires consisting of a ferromagnetic layer and a non-magnetic
layer with strong spin-orbit coupling, currents create torques on the
magnetization beyond those found in simple ferromagnetic nanowires. The
resulting magnetic dynamics appear to require torques that can be separated
into two terms, damping-like and field-like. The damping-like torque is
typically derived from models describing the bulk spin Hall effect and the spin
transfer torque, and the field-like torque is typically derived from a Rashba
model describing interfacial spin-orbit coupling. We derive a model based on
the Boltzmann equation that unifies these approaches. We also consider an
approximation to the Boltzmann equation, the drift-diffusion model, that
qualitatively reproduces the behavior, but quantitatively fails to reproduce
the results. We show that the Boltzmann equation with physically reasonable
parameters can match the torques for any particular sample, but in some cases,
it fails to describe the experimentally observed thickness dependences.",1301.4513v1
2013-01-23,Characterization of magnetostatic surface spin waves in magnetic thin films: evaluation for microelectronic applications,"The authors have investigated the possibility of utilizing spin waves for
inter- and intra-chip communications, and as logic elements using both
simulations and experimental techniques. Through simulations it has been shown
that the decay lengths of magnetostatic spin waves are affected most by the
damping parameter, and least by the exchange stiffness constant. The damping
and dispersion properties of spin waves limit the attenuation length to several
tens of microns. Thus, we have ruled out the possibility of inter-chip
communications via spin waves. Experimental techniques for the extraction of
the dispersion relationship have also been demonstrated, along with
experimental demonstrations of spin wave interference for amplitude modulation.
The effectiveness of spin wave modulation through interference, along with the
capability of determining the spin wave dispersion relationships electrically
during manufacturing and testing phase of chip production may pave the way for
using spin waves in analog computing wherein the circuitry required for
performing similar functionality becomes prohibitive.",1301.5395v1
2013-01-25,Driven skyrmions and dynamical transitions in chiral magnets,"We study the dynamics of skyrmions in chiral magnets in the presence of a
spin polarized current. The motion of skyrmions in the ferromagnetic background
excites spin waves and contributes to additional damping. At a large current,
the spin wave spectrum becomes gapless and skyrmions are created dynamically
from the ferromagnetic state. At an even higher current, these skyrmions are
strongly deformed due to the damping and become unstable at a threshold
current, leading to a chiral liquid. We show how skyrmions can be created by
increasing the current in the magnetic spiral state. We then construct a
dynamic phase diagram for a chiral magnet with a current. The instability
transitions between different states can be observed as experimentally clear
signatures in the transport measurements, such as jumps and hysteresis.",1301.5963v2
2013-02-13,Entanglement of Tripartite States with Decoherence in Noninertial frames,"The one-tangle and {\pi}-tangle are used to quantify the entanglement of a
tripartite GHZ state in noninertial frames when the system interacts with a
noisy environment in the form of phase damping, phase flip and bit flip
channel. It is shown that the two-tangles behave as a closed system. The
one-tangle and {\pi}-tangle have different behaviors in the three channel. In
the case of phase damping channel, depending on the kind of coupling, the
sudden death of both one-tangle and {\pi}-tangle may or may not happen. Whereas
in the case of phase flip channel the sudden death cannot be avoided. The
effect of decoherence may be ignored in the limit of infinite acceleration when
the system interacts with a bit flip channel. Furthermore, a sudden rebirth of
the one-tangle and {\pi}-tangle occur in the case of phase flip channel that
may be delayed when collective coupling is switched on.",1302.3005v1
2013-02-17,Global existence and exponential growth for a viscoelastic wave equation with dynamic boundary conditions,"The goal of this work is to study a model of the wave equation with dynamic
boundary conditions and a viscoelastic term. First, applying the Faedo-Galerkin
method combined with the fixed point theorem, we show the existence and
uniqueness of a local in time solution. Second, we show that under some
restrictions on the initial data, the solution continues to exist globally in
time. On the other hand, if the interior source dominates the boundary damping,
then the solution is unbounded and grows as an exponential function. In
addition, in the absence of the strong damping, then the solution ceases to
exist and blows up in finite time.",1302.4036v1
2013-02-22,Mixing of blackbodies: Increasing our view of inflation to 17 e-folds with spectral distortions from Silk damping,"Silk damping in the early Universe, before and during recombination, erases
anisotropies in the cosmic microwave background (CMB) on small scales. This
power, which disappears from anisotropies, appears in the monopole as y-type,
i-type and \mu-type distortions. The observation of the CMB spectral
distortions will thus make available to us the information about the primordial
power spectrum on scales corresponding to the comoving wavenumbers $8< k < 10^4
Mpc^{-1}$ increasing our total view of inflation, when combined with CMB
anisotropies, to span 17 e-folds. These distortions can be understood simply as
mixing of blackbodies of different temperatures and the subsequent
comptonization of the resulting distortions.",1302.5633v1
2013-02-26,Tenfold reduction of Brownian noise in optical interferometry,"Thermally induced fluctuations impose a fundamental limit on precision
measurement. In optical interferometry, the current bounds of stability and
sensitivity are dictated by the excess mechanical damping of the
high-reflectivity coatings that comprise the cavity end mirrors. Over the
preceding decade, the mechanical loss of these amorphous multilayer reflectors
has at best been reduced by a factor of two. Here we demonstrate a new paradigm
in optical coating technology based on direct-bonded monocrystalline
multilayers, which exhibit both intrinsically low mechanical loss and high
optical quality. Employing these ""crystalline coatings"" as end mirrors in a
Fabry-P\'erot cavity, we obtain a finesse of 150,000. More importantly, at room
temperature, we observe a thermally-limited noise floor consistent with a
tenfold reduction in mechanical damping when compared with the best dielectric
multilayers. These results pave the way for the next generation of
ultra-sensitive interferometers, as well as for new levels of laser stability.",1302.6489v1
2013-03-01,Quantum error correction and detection: quantitative analysis of a coherent-state amplitude damping code,"We re-examine a non-Gaussian quantum error correction code designed to
protect optical coherent-state qubits against errors due to an amplitude
damping channel. We improve on a previous result [Phys. Rev. A 81, 062344
(2010)] by providing a tighter upper bound on the performance attained when
considering realistic assumptions which constrain the operation of the gates
employed in the scheme. The quantitative characterization is performed through
measures of fidelity and concurrence, the latter obtained by employing the code
as an entanglement distillation protocol. We find that, when running the code
in fully-deterministic error correction mode, direct transmission can only be
beaten for certain combinations of channel and input state parameters, whereas
in error detection mode, the usage of higher repetition encodings remains
beneficial throughout.",1303.0273v2
2013-03-04,Transverse oscillations in solar spicules induced by propagating Alfvenic pulses,"The excitation of Alfvenic waves in the solar spicules due to the localized
Alfvenic pulse is investigated. A set of incompressible MHD equations in two
dimensional $x-z$ plane with steady flows and sheared magnetic fields is
solved. Stratification due to gravity and transition region between
chromosphere and corona are taken into account. An initially localized Alfvenic
pulse launched below the transition region can penetrate from transition region
into the corona. We show that the period of transversal oscillations is in
agreement with those observed in spicules. Moreover, it is found that the
excited Alfvenic waves spread during propagation along the spicule length, and
suffer efficient damping of the oscillations amplitude. The damping time of
transverse oscillations elongated with decrease in k_b values.",1303.0833v1
2013-03-04,Tidal damping of the mutual inclination in hierachical systems,"Hierarchical two-planet systems, in which the inner body's semi-major axis is
between 0.1 and 0.5 AU, usually present high eccentricity values, at least for
one of the orbits. As a result of the formation process, one may expect that
planetary systems with high eccentricities also have high mutual inclinations.
However, here we show that tidal effects combined with gravitational
interactions damp the initial mutual inclination to modest values in timescales
that are shorter than the age of the system. This effect is not a direct
consequence of tides on the orbits, but it results from a secular forcing of
the inner planet's flattening. We then conclude that these hierarchical
planetary systems are unlikely to present very high mutual inclinations, at
least as long as the orbits remain outside the Lidov-Kozai libration areas. The
present study can also be extended to systems of binary stars and to
planet-satellite systems.",1303.0864v2
2013-03-05,Anomalous velocity distributions in active Brownian suspensions,"Large scale simulations and analytical theory have been combined to obtain
the non-equilibrium velocity distribution, $f(v)$, of randomly accelerated
particles in suspension. The simulations are based on an event-driven
algorithm, generalised to include friction. They reveal strongly anomalous but
largely universal distributions which are independent of volume fraction and
collision processes, which suggests a one-particle model should capture all the
essential features. We have formulated this one-particle model and solved it
analytically in the limit of strong damping, where we find that $f(v)$ decays
as $1/v$ for multiple decades, eventually crossing over to a Gaussian decay for
the largest velocities. Many particle simulations and numerical solution of the
one-particle model agree for all values of the damping.",1303.0996v3
2013-03-07,Quantum critical metals in $d=3+1$,"We study the problem of disorder-free metals near a continuous Ising nematic
quantum critical point in $d=3+1$ dimensions. We begin with perturbation theory
in the `Yukawa' coupling between the electrons and undamped bosons (nematic
order parameter fluctuations) and show that the perturbation expansion breaks
down below energy scales where the bosons get substantially Landau damped.
Above this scale however, we find a regime in which low-energy fermions obtain
an imaginary self-energy that varies linearly with frequency, realizing the
`marginal Fermi liquid' phenomenology\cite{Varma}. We discuss a large N theory
in which the marginal Fermi liquid behavior is enhanced while the role of
Landau damping is suppressed, and show that quasiparticles obtain a decay rate
parametrically larger than their energy.",1303.1587v2
2013-03-08,Ultra High Energy Electrons Powered by Pulsar Rotation,"A new mechanism of particle acceleration to ultra high energies, driven by
the rotational slow down of a pulsar (Crab pulsar, for example), is explored.
The rotation, through the time dependent centrifugal force, can very
efficiently excite unstable Langmuir waves in the e-p plasma of the star
magnetosphere via a parametric process. These waves, then, Landau damp on
electrons accelerating them in the process. The net transfer of energy is
optimal when the wave growth and the Landau damping times are comparable and
are both very short compared to the star rotation time. We show, by detailed
calculations, that these are precisely the conditions for the parameters of the
Crab pulsar. This highly efficient route for energy transfer allows the
electrons in the primary beam to be catapulted to multiple TeV ($\sim 100$ TeV)
and even PeV energy domain. It is expected that the proposed mechanism may,
partially, unravel the puzzle of the origin of ultra high energy cosmic ray
electrons.",1303.2093v1
2013-04-01,Fidelity of remote state preparation can be enhanced by local operation,"Remote state preparation (RSP) is a quantum information protocol which allows
preparing a quantum state at a distant location with the help of a preshared
nonclassical resource state and a classical channel. The efficiency of
successfully doing this task can be represented by the RSP-fidelity of the
resource state. In this paper, we study the influence on the RSP-fidelity by
applying certain local operations on the resource state. We prove that
RSP-fidelity does not increase for any unital local operation. However, for
nonunital local operation, such as local amplitude damping channel, we find
that some resource states can be enhanced to increase the RSP-fidelity. We give
the optimal parameter of symmetric local amplitude damping channel for
enhancing Bell-diagonal resource states. In addition, we show RSP-fidelity can
suddenly change or even vanish at instant under local decoherence.",1304.0283v1
2013-04-06,Coronal loop physical parameters from the analysis of multiple observed transverse oscillations,"The analysis of quickly damped transverse oscillations of solar coronal loops
using magneto-hydrodynamic seismology allow us to infer physical parameters
that are difficult to measure otherwise. Under the assumption that such damped
oscillations are due to the resonant conversion of global modes into Alfven
oscillations of the tube surface, we carry out a global seismological analysis
of a large set of coronal loops. A Bayesian hierarchical method is used to
obtain distributions for coronal loop physical parameters by means of a global
analysis of a large number of observations. The resulting distributions
summarise global information and constitute data-favoured information that can
be used for the inversion of individual events. The results strongly suggest
that internal Alfven travel times along the loop are larger than 100 s and
smaller than 540 s with 95% probability. Likewise, the density contrast between
the loop interior and the surrounding is larger than 2.3 and below 6.9 with 95%
probability.",1304.1921v1
2013-04-15,Vibrational Resonance in the Morse Oscillator,"We investigate the occurrence of vibrational resonance in both classical and
quantum mechanical Morse oscillators driven by a biharmonic force. The
biharmonic force consists of two forces of widely different frequencies \omega
and \Omega with \Omega>>\omega. In the damped and biharmonically driven
classical Morse oscillator applying a theoretical approach we obtain an
analytical expression for the response amplitude at the low-frequency \omega.
We identify the conditions on the parameters for the occurrence of the
resonance. The system shows only one resonance and moreover at resonance the
response amplitude is 1/(d\omega) where d is the coefficient of linear damping.
When the amplitude of the high-frequency force is varied after resonance the
response amplitude does not decay to zero but approaches a nonzero limiting
value. We have observed that vibrational resonance occurs when the sinusoidal
force is replaced by a square-wave force. We also report the occurrence of
resonance and anti-resonance of transition probability of quantum mechanical
Morse oscillator in the presence of the biharmonic external field.",1304.3988v1
2013-04-15,Energy dissipation in DC-field driven electron lattice coupled to fermion baths,"Electron transport in electric-field-driven tight-binding lattice coupled to
fermion baths is comprehensively studied. We reformulate the problem by using
the scattering state method within the Coulomb gauge. Calculations show that
the formulation justifies direct access to the steady-state bypassing the
time-transient calculations, which then makes the steady-state methods
developed for quantum dot theories applicable to lattice models. We show that
the effective temperature of the hot-electron induced by a DC electric field
behaves as $T_{\rm eff}=C\gamma(\Omega/\Gamma)$ with a numerical constant $C$,
tight-binding parameter $\gamma$, the Bloch oscillation frequency $\Omega$ and
the damping parameter $\Gamma$. In the small damping limit $\Gamma/\Omega\to
0$, the steady-state has a singular property with the electron becoming
extremely hot in an analogy to the short-circuit effect. This leads to the
conclusion that the dissipation mechanism cannot be considered as an implicit
process, as treated in equilibrium theories. Finally, using the energy flux
relation, we derive a steady-state current for interacting models where only
on-site Green's functions are necessary.",1304.4269v1
2013-04-17,An oscillating motion of a red blood cell and a neutrally buoyant particle in Poiseuille flow in a narrow channel,"Two motions of oscillation and vacillating breathing (swing) of a red blood
cell have been observed in bounded Poiseuille flows (Phys. Rev. E 85, 16307
(2012)). To understand such motions, we have studied the oscillating motion of
a neutrally buoyant rigid particle of the same shape in Poiseuille flow in a
narrow channel and obtained that the crucial point is to have the particle
interacting with Poiseuille flow with its mass center moving up and down in the
channel central region. Since the mass center of the cell migrates toward the
channel central region, its oscillating motion of the inclination angle is
similar to the aforementioned motion as long as the cell keeps the shape of
long body. But as the up-and-down oscillation of the cell mass center damps
out, the oscillating motion of the inclination angle also damps out and the
cell inclination angle approaches to a fixed angle.",1304.4971v1
2013-04-24,Finite amplitude inhomogeneous waves in Mooney-Rivlin viscoelastic solids,"New exact solutions are exhibited within the framework of finite
viscoelasticity. More precisely, the solutions correspond to finite-amplitude,
transverse, linearly-polarized, inhomogeneous motions superposed upon a finite
homogeneous static deformation. The viscoelastic body is composed of a
Mooney-Rivlin viscoelastic solid, whose constitutive equation consists in the
sum of an elastic part (Mooney-Rivlin hyperelastic model) and a viscous part
(Newtonian viscous fluid model). The analysis shows that the results are
similar to those obtained for the purely elastic case; inter alia, the normals
to the planes of constant phase and to the planes of constant amplitude must be
orthogonal and conjugate with respect to the B-ellipsoid, where B is the left
Cauchy-Green strain tensor associated with the initial large static
deformation. However, when the constitutive equation is specialized either to
the case of a neo-Hookean viscoelastic solid or to the case of a Newtonian
viscous fluid, a greater variety of solutions arises, with no counterpart in
the purely elastic case. These solutions include travelling inhomogeneous
finite-amplitude damped waves and standing damped waves.",1304.6748v1
2013-04-28,On the role of transition region on the Alfven wave phase mixing in solar spicules,"Alfvenic waves are thought to play an important role in coronal heating and
solar wind acceleration. Here we investigate the dissipation of standing Alfven
waves due to phase mixing at the presence of steady flow and sheared magnetic
field in the stratified atmosphere of solar spicules. The transition region
between chromosphere and corona has also been considered. The initial flow is
assumed to be directed along spicule axis, and the equilibrium magnetic field
is taken 2-dimensional and divergence-free. It is determined that in contrast
to propagating Alfven waves, standing Alfven waves dissipate in time rather
than in space. Density gradients and sheared magnetic fields can enhance
damping due to phase mixing. Damping times deduced from our numerical
calculations are in good agreement with spicule lifetimes. Since spicules are
short living and transient structures, such a fast dissipation mechanism is
needed to transport their energy to the corona.",1304.7764v1
2013-05-03,"Viscosity, wave damping and shock wave formation in cold hadronic matter","We study linear and nonlinear wave propagation in a dense and cold hadron gas
and also in a cold quark gluon plasma, taking viscosity into account and using
the Navier-Stokes equation. The equation of state of the hadronic phase is
derived from the nonlinear Walecka model in the mean field approximation. The
quark gluon plasma phase is described by the MIT equation of state. We show
that in a hadron gas viscosity strongly damps wave propagation and also hinders
shock wave formation. This marked difference between the two phases may have
phenomenological consequences and lead to new QGP signatures.",1305.0798v2
2013-05-07,Periodically Driven Holographic Superconductor,"As a first step towards our holographic investigation of the
far-from-equilibrium physics of periodically driven systems at strong coupling,
we explore the real time dynamics of holographic superconductor driven by a
monochromatically alternating electric field with various frequencies. As a
result, our holographic superconductor is driven to the final oscillating
state, where the condensate is suppressed and the oscillation frequency is
controlled by twice of the driving frequency. In particular, in the large
frequency limit, the three distinct channels towards the final steady state are
found, namely under damped to superconducting phase, over damped to
superconducting and normal phase, which can be captured essentially by the low
lying spectrum of quasi-normal modes in the time averaged approximation,
reminiscent of the effective field theory perspective.",1305.1600v2
2013-05-07,Micromagnetic modelling of anisotropic damping in ferromagnet,"We report a numerical implementation of the Landau-Lifshitz-Baryakhtar
theory, which dictates that the micromagnetic relaxation term obeys the
symmetry of the magnetic crystal, i. e. replacing the single intrinsic damping
constant with a tensor of corresponding symmetry. The effect of anisotropic
relaxation is studied in thin saturated ferromagnetic disk and ellipse with and
without uniaxial magneto-crystalline anisotropy. We investigate the angular
dependency of the linewidth of magnonic resonances with respect to the given
structure of the relaxation tensor. The simulations suggest that the anisotropy
of the magnonic linewidth is determined by only two factors: the projection of
the relaxation tensor onto the plane of precession and the ellipticity of the
later.",1305.1641v2
2013-05-08,"Existence, uniqueness and analyticity of space-periodic solutions to the regularised long-wave equation","We consider space-periodic evolutionary and travelling-wave solutions to the
regularised long-wave equation (RLWE) with damping and forcing. We establish
existence, uniqueness and smoothness of the evolutionary solutions for smooth
initial conditions, and global in time spatial analyticity of such solutions
for analytical initial conditions. The width of the analyticity strip decays at
most polynomially. We prove existence of travelling-wave solutions and
uniqueness of travelling waves of a sufficiently small norm. The importance of
damping is demonstrated by showing that the problem of finding travelling-wave
solutions to the undamped RLWE is not well-posed. Finally, we demonstrate the
asymptotic convergence of the power series expansion of travelling waves for a
weak forcing.",1305.1813v1
2013-05-08,The Persistence of Uphill Anomalous Transport in Inhomogeneous Media,"For systems out of equilibrium and subjected to a static bias force it can
often be expected that particle transport will usually follow the direction of
this bias. However, counter-examples exist where particles exhibit uphill
motion (known as absolute negative mobility - ANM), particularly in the case of
coupled particles. Examples in single particle deterministic systems are less
common. Recently, in one such example, uphill motion was shown to occur for an
inertial driven and damped particle in a spatially symmetric periodic
potential. The source of this anomalous transport was a combination of two
periodic driving signals which together are asymmetric under time reversal. In
this paper we investigate the phenomena of ANM for a deterministic particle
evolving in a periodic and symmetric potential subjected to an external
unbiased periodic driving and nonuniform space- dependent damping. It will be
shown that this system exhibits a complicated response behaviour as certain
control parameters are varied, most notably being, enhanced parameter regimes
exhibiting ANM as the static bias force is increased. Moreover, the solutions
exhibiting ANM are shown to be, at least over intermediate time periods,
superdiffusive, in contrast to the solutions that follow the bias where the
diffusion is normal.",1305.1841v2
2013-05-11,Dividing Line between Quantum and Classical Trajectories: Bohmian Time Constant,"This work proposes an answer to a challenge posed by Bell on the lack of
clarity in regards to the line between the quantum and classical regimes in a
measurement problem. To this end, a generalized logarithmic nonlinear
Schr\""odinger equation is proposed to describe the time evolution of a quantum
dissipative system under continuous measurement. Within the Bohmian mechanics
framework, a solution to this equation reveals a novel result: it displays a
time constant which should represent the dividing line between the quantum and
classical trajectories. It is shown that continuous measurements and damping
not only disturb the particle but compel the system to converge in time to a
Newtonian regime. While the width of the wave packet may reach a stationary
regime, its quantum trajectories converge exponentially in time to classical
trajectories. In particular, it is shown that damping tends to suppress further
quantum effects on a time scale shorter than the relaxation time of the system.
If the initial wave packet width is taken to be equal to 2.8 10^{-15} m (the
approximate size of an electron), the Bohmian time constant is found to have an
upper limit, i. e., ${\tau_{B\max}} = {10^{- 26}}s$.",1305.2517v2
2013-05-11,Giant dipole resonance in $^{88}$Mo from phonon damping model's strength functions averaged over temperature and angular momentum distributions,"The line shapes of giant dipole resonance (GDR) in the decay of the compound
nucleus $^{88}$Mo, which is formed after the fusion-evaporation reaction
$^{48}$Ti + $^{40}$Ca at various excitation energies $E^{*}$ from 58 to 308
MeV, are generated by averaging the GDR strength functions predicted within the
phonon damping model (PDM) using the empirical probabilities for temperature
and angular momentum. The average strength functions are compared with the PDM
strength functions calculated at the mean temperature and mean angular
momentum, which are obtained by averaging the values of temperature and angular
momentum using the same temperature and angular-momentum probability
distributions, respectively. It is seen that these two ways of generating the
GDR linear line shape yield very similar results. It is also shown that the GDR
width approaches a saturation at angular momentum $J\geq$ 50$\hbar$ at $T=$ 4
MeV and at $J\geq$ 70$\hbar$ at any $T$.",1305.2518v1
2013-05-20,Quench Dynamics in Bose condensates in the Presence of a Bath: Theory and Experiment,"In this paper we study the transient dynamics of a Bose superfluid subsequent
to an interaction quench. Essential for equilibration is a source of
dissipation which we include following the approach of Caldeira and Leggett.
Here we solve the equations of motion exactly by integrating out an
environmental bath. We thereby derive precisely the time dependent density
correlation functions with the appropriate analytic and asymptotic properties.
The resulting structure factor exhibits the expected damping and thereby
differs from that of strict Bogoliubov theory. These damped sound modes, which
reflect the physics beyond mean field approaches, are characterized and the
structure factors are found to compare favorably with experiment.",1305.4594v2
2013-05-21,Restoration of Quantum State in Dephasing Channel,"In this paper, we propose an explicit scheme to fully recover a
multiple-qubit state subject to a phase damping noise. We establish the
theoretical framework and the operational procedure to restore an unknown
initial quantum state for an N-qubit model interacting with either individual
baths or a common bath. We give an explicit construction of the random unitary
(RU) Kraus decomposition for an N-qubit model interacting with a common bath.
We also demonstrate how to use only one unitary reversal operation to restore
an arbitrary state with phase damping noise. In principle, the initial state
can always be recovered with a success probability of 1. Interestingly, we
found that non-RU decomposition can also be used to restore some particular
entangled states. This may open a new path to restore a quantum state beyond
the standard RU scheme.",1305.4627v2
2013-05-28,"Generalized Plasma Dispersion Function: One-Solve-All Treatment, Visualizations, and Application to Landau Damping","A unified, fast, and effective approach is developed for numerical
calculation of the well-known plasma dispersion function with extensions from
Maxwellian distribution to almost arbitrary distribution functions, such as the
$\delta$, flat top, triangular, $\kappa$ or Lorentzian, slowing down, and
incomplete Maxwellian distributions. The singularity and analytic continuation
problems are also solved generally. Given that the usual conclusion
$\gamma\propto\partial f_0/\partial v$ is only a rough approximation when
discussing the distribution function effects on Landau damping, this approach
provides a useful tool for rigorous calculations of the linear wave and
instability properties of plasma for general distribution functions. The
results are also verified via a linear initial value simulation approach.
Intuitive visualizations of the generalized plasma dispersion function are also
provided.",1305.6476v2
2013-06-20,Linear flutter analysis of functionally graded panels using cell based smoothed finite element method and discrete shear gap technique,"In this paper, a cell-based smoothed finite element method with discrete
shear gap technique for triangular ele- ments is employed to study the linear
flutter characteristics of functionally graded material (FGM) flat panels. The
influence of thermal environment, the presence of a centrally located circular
cutout and the aerodynamic damping on the supersonic flutter characteristics of
flat FGM panels is also investigated. The structural for- mulation is based on
the first-order shear deformation theory and the material properties are
assumed to be temperature dependent and graded only in the thickness direction
according to power law distribution in terms of the volume fraction of its
constituent materials. The aerodynamic force is evaluated by considering the
first order high mach number approximation to linear potential flow theory. The
formulation includes transverse shear deformation and in-plane and rotary
inertia effects. The influence of the plate thickness, aspect ratio, boundary
conditions, material gradient index, temperature dependent material properties,
damping, cutout size, skewness of the plate and boundary conditions on the
critical aerodynamic pressure is numerically studied.",1306.4978v1
2013-06-29,Resolving the effects of frequency dependent damping and quantum phase diffusion in YBa$_2$Cu$_3$O$_{7-x}$ Josephson junctions,"We report on the study of the phase dynamics of high critical temperature
superconductor Josephson junctions. We realized YBa$_2$Cu$_3$O$_{7-x}$ (YBCO)
grain boundary (GB) biepitaxial junctions in the submicron scale, using low
loss substrates, and analyzed their dissipation by comparing the transport
measurements with Monte Carlo simulations. The behavior of the junctions can be
fitted using a model based on two quality factors, which results in a frequency
dependent damping. Moreover, our devices can be designed to have Josephson
energy of the order of the Coulomb energy. In this unusual energy range, phase
delocalization strongly influences the device's dynamics, promoting the
transition to a quantum phase diffusion regime. We study the signatures of such
a transition by combining the outcomes of Monte Carlo simulations with the
analysis of the device's parameters, the critical current and the temperature
behavior of the low voltage resistance $R_0$.",1307.0106v1
2013-07-03,A new mechanism for saturating unstable r-modes in neutron stars,"We consider a new mechanism for damping the oscillations of a mature neutron
star. The new dissipation channel arises if superfluid vortices are forced to
cut through superconducting fluxtubes. This mechanism is interesting because
the oscillation modes need to exceed a critical amplitude in order for it to
operate. Once it acts the effect is very strong (and nonlinear) leading to
efficient damping. The upshot of this is that modes are unlikely to ever evolve
far beyond the critical amplitude. We consider the effect of this new
dissipation channel on the r-modes, that may be driven unstable by the emission
of gravitational waves. Our estimates show that the fluxtube cutting leads to a
saturation threshold for the instability that can be smaller than that of other
proposed mechanisms. This suggests that the idea may be of direct astrophysical
relevance.",1307.0985v1
2013-07-03,Exotic matter influence on the polar quasi-normal modes of neutron stars with equations of state satisfying the $2 M_{\odot}$ constraint,"In this paper we analyze the quasi-normal mode spectrum of realistic neutron
stars by studying the polar modes. In particular we study the spatial wI mode,
the f mode, and the fundamental p mode. The study has been done for 15
different equations of state containing exotic matter and satisfying the $2
M_{\odot}$ constraint. Since f and p modes couple to matter perturbations, the
influence of the presence of hyperons and quarks in the core of the neutron
stars is more significant than for the axial component. We present
phenomenological relations for the frequency and damping time with the
compactness of the neutron star. We also consider new phenomenological
relations between the frequency and damping time of the w mode and the f mode.
These new relations are independent of the equation of state, and could be used
to estimate the central pressure, mass or radius, and eventually constrain the
equation of state of neutron stars. To obtain these results we have developed a
new method based on the Exterior Complex Scaling technique with variable angle.",1307.1063v1
2013-07-10,Absence of damping of low energy excitations in a quasi-2D dipolar Bose gas,"We develop a theory of damping of low energy, collective excitations in a
quasi-2D, homogenous, dipolar Bose gas at zero temperature, via processes
whereby an excitation decays into two excitations with lower energy. We find
that owing to the nature of the low energy spectrum of a quasi-2D dipolar gas,
such processes cannot occur unless the momentum of the incoming quasi-particle
exceeds a critical value k_{crit}. We find that as the dipolar interaction
strength is increased, this critical value shifts to larger momenta. Our
predictions can be directly verified in current experiments on dipolar Bose
condensates using Bragg spectroscopy, and provide valuable insight into the
quantum many-body physics of dipolar gases.",1307.2910v2
2013-07-14,Asteroseismic effects in close binary stars,"Turbulent processes in the convective envelopes of the sun and stars have
been shown to be a source of internal acoustic excitations. In single stars,
acoustic waves having frequencies below a certain cutoff frequency propagate
nearly adiabatically and are effectively trapped below the photosphere where
they are internally reflected. This reflection essentially occurs where the
local wavelength becomes comparable to the pressure scale height. In close
binary stars, the sound speed is a constant on equipotentials, while the
pressure scale height, which depends on the local effective gravity, varies on
equipotentials and may be much greater near the inner Lagrangian point (L_1).
As a result, waves reaching the vicinity of L_1 may propagate unimpeded into
low density regions, where they tend to dissipate quickly due to non-linear and
radiative effects. We study the three dimensional propagation and enhanced
damping of such waves inside a set of close binary stellar models using a WKB
approximation of the acoustic field. We find that these waves can have much
higher damping rates in close binaries, compared to their non-binary
counterparts. We also find that the relative distribution of acoustic energy
density at the visible surface of close binaries develops a ring-like feature
at specific acoustic frequencies and binary separations.",1307.3709v1
2013-07-31,Dynamics of ions in the selectivity filter of the KcsA channel: Towards a coupled Brownian particle description,"The statistical and dynamical properties of ions in the selectivity filter of
the KcsA ion channel are considered on the basis of molecular dynamics (MD)
simulations of the KcsA protein embedded in a lipid membrane surrounded by an
ionic solution. A new approach to the derivation of a Brownian dynamics (BD)
model of ion permeation through the filter is discussed, based on unbiased MD
simulations. It is shown that depending on additional assumptions, ion's
dynamics can be described either by under-damped Langevin equation with
constant damping and white noise or by Langevin equation with a fractional
memory kernel. A comparison of the potential of the mean force derived from
unbiased MD simulations with the potential produced by the umbrella sampling
method demonstrates significant differences in these potentials. The origin of
these differences is an open question that requires further clarifications.",1307.8298v1
2013-07-31,Intrabeam Scattering Studies at CesrTA,"Intrabeam scattering (IBS) limits the emittance and single-bunch current that
can be achieved in electron or positron storage ring colliders, damping rings,
and light sources. Much theoretical work on IBS exists, and while the theories
have been validated in hadron and ion machines, the presence of strong damping
makes IBS in lepton machines a different phenomenon. We present the results of
measurements at CesrTA of IBS dominated beams, and compare the data with
theory. The beams we study have parameters typical of those specified for the
next generation of wiggler dominated storage rings: low emittance, small bunch
length, and few GeV energy. Our measurements are in good agreement with IBS
theory, provided a tail-cut procedure is applied.",1308.0035v2
2013-08-05,Radiative damping and emission signatures of strong superluminal waves in pulsar winds,"We analyse the damping by radiation reaction and by Compton drag of strong,
superluminal electromagnetic waves in the context of pulsar winds. The
associated radiation signature is found by estimating the efficiency and the
characteristic radiation frequencies. Applying these estimates to the gamma-ray
binary containing PSR B1259-63, we show that the GeV flare observed by
Fermi-LAT can be understood as inverse Compton emission by particles scattering
photons from the companion star, if the pulsar wind termination shock acquires
a precursor of superluminal waves roughly 30 days after periastron. This
constrains the mass-loading factor of the wind $\mu=L/\dot{N}mc^2$ (where $L$
is the luminosity and $\dot{N}$ the rate of loss of electrons and positrons) to
be roughly $6\times 10^4$.",1308.0950v2
2013-08-09,Scale breaking and fluid dynamics in a dilute two-dimensional Fermi gas,"We study two observables related to the anomalous breaking of scale
invariance in a dilute two dimensional Fermi gas, the frequency shift and
damping rate of the monopole mode in a harmonic confinement potential. For this
purpose we compute the speed of sound and the bulk viscosity of the two
dimensional gas in the high temperature limit. We show that the anomaly in the
speed of sound scales as $(2P-\rho c_s^2)/P\sim z/[\log(T/E_B)]^2$, and that
the bulk viscosity $\zeta$ scales as $\zeta/\eta \sim z^2/[\log(T/E_B)]^6$.
Here, $P$ is the pressure, $c_s^2$ is the speed of sound, $\eta$ is the shear
viscosity, $z$ is the fugacity, and $E_B$ is the two-body binding energy. We
show that our results are consistent with the experimental results of Vogt et
al. [Phys. Rev. Lett. 108, 070404 (2012)]. Vogt et al. reported a frequency
shift $\delta\omega/\omega$ of the order of a few percent, and a damping rate
smaller than the background rate $\Gamma/\omega_0\sim 5%$.",1308.2004v1
2013-08-14,Reentrant classicality of a damped system,"For a free particle, the coupling to its environment can be the relevant
mechanism to induce quantum behavior as the temperature is lowered. We study
general linear environments with a spectral density proportional to {\omega}^s
at low frequencies and consider in particular the specific heat of the free
damped particle. For super-Ohmic baths with s>=2, a reentrant classical
behavior is found. As the temperature is lowered, the specific heat decreases
from the classical value of k_B/2, thereby indicating the appearence of quantum
effects. However, the classical value of the specific heat is restored as the
temperature approaches zero. This surprising behavior is due to the suppressed
density of bath degrees of freedom at low frequencies. For s<2, the specific
heat at zero temperature increases linearly with s from -k_B/2 to k_B/2. An
Ohmic bath, s=1, is thus very special in the sense that it represents the only
case where the specific heat vanishes at zero temperature.",1308.3049v1
2013-08-20,Group classification and exact solutions of variable-coefficient generalized Burgers equations with linear damping,"Admissible point transformations between Burgers equations with linear
damping and time-dependent coefficients are described and used in order to
exhaustively classify Lie symmetries of these equations. Optimal systems of
one- and two-dimensional subalgebras of the Lie invariance algebras obtained
are constructed. The corresponding Lie reductions to ODEs and to algebraic
equations are carried out. Exact solutions to particular equations are found.
Some generalized Burgers equations are linearized to the heat equation by
composing equivalence transformations with the Hopf-Cole transformation.",1308.4265v2
2013-08-31,Recent developments in the determination of the amplitude and phase of quantum oscillations for the linear chain of coupled orbits,"De Haas-van Alphen oscillations are studied for Fermi surfaces (FS)
illustrating the model proposed by Pippard in the early sixties, namely the
linear chain of orbits coupled by magnetic breakdown. This FS topology is
relevant for many multiband quasi-two dimensional (q-2D) organic metals such as
$\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ and
$\theta$-(BEDT-TTF)$_4$CoBr$_4$(C$_6$H$_4$Cl$_2$) which are considered in
detail. Whereas the Lifshits-Kosevich model only involves a first order
development of field- and temperature-dependent damping factors, second order
terms may have significant contribution on the Fourier components amplitude for
such q-2D systems at high magnetic field and low temperature. The strength of
these second order terms depends on the relative value of the involved damping
factors, which are in turns strongly dependent on parameters such as the
magnetic breakdown field, effective masses and, most of all, effective
Land\'{e} factors. In addition, the influence of field-dependent Onsager phase
factors on the oscillation spectra is considered.",1309.0102v1
2013-09-04,Surface Waves in the paritally ionized solar plasma slab,"The properties of surface waves in the partially ionized, incompressible
magnetized plasma slab are investigated in the present work. The waves are
affected by the non ideal MHD effects which causes the finite drift of the
magnetic field in the medium. When the finite drift of the magnetic field is
ignored, the characteristics of the wave propagation in the partially ionized
plasma fluid is similar to the ideal MHD except now the propagation properties
depend on the fractional ionization of the medium. In the presence of Hall
diffusion, the propagation of the sausage and kink surface waves depends on the
level of fractional ionization of the medium. When both the Hall and Pedersen
diffusion are present in the medium, the waves undergoes damping. For typical
solar parameters, waves may damp over few minutes.",1309.0881v1
2013-09-04,Origin and reduction of wakefields in photonic crystal accelerator cavities,"Photonic crystal (PhC) defect cavities that support an accelerating mode tend
to trap unwanted higher-order modes (HOMs) corresponding to zero-group-velocity
PhC lattice modes at the top of the bandgap. The effect is explained quite
generally from photonic band and perturbation theoretical arguments. Transverse
wakefields resulting from this effect are observed in a hybrid dielectric PhC
accelerating cavity based on a triangular lattice of sapphire rods. These
wakefields are, on average, an order of magnitude higher than those in the
waveguide-damped Compact Linear Collider (CLIC) copper cavities. The avoidance
of translational symmetry (and, thus, the bandgap concept) can dramatically
improve HOM damping in PhC-based structures.",1309.0914v2
2013-09-14,Damping of the quadrupole mode in a two-dimensional Fermi gas,"In a recent experiment [E. Vogt et al., Phys. Rev. Lett. 108, 070404 (2012)],
quadrupole and breathing modes of a two-dimensional Fermi gas were studied. We
model these collective modes by solving the Boltzmann equation via the method
of phase-space moments up to fourth order, including in-medium effects on the
scattering cross section. In our analysis, we use a realistic Gaussian
potential deformed by the presence of gravity and magnetic field gradients. We
conclude that the origin of the experimentally observed damping of the
quadrupole mode, especially in the weakly interacting (or even non-interacting)
case, cannot be explained by these mechanisms.",1309.3651v2
2013-09-24,Spin-driven tidal pumping: Tidally driven changes in planetary spin coupled with secular interactions between planets,"In a multiplanet system, tides acting on the inner planet can significantly
affect the orbital evolution of the entire system. While tides usually damp
eccentricities, a novel mechanism identified by Correia et al. (2012) tends to
raise eccentricities as a result of the tides' effect on the inner planet's
rotation. Our analytical description of this spin-driven tidal (SDT) effect
shows that, while the inner planet's eccentricity undergoes pumping, the
process is more completely described by an exchange of strength between the two
eigenmodes of the dynamical system. Our analysis allows derivation of criteria
for two-planet coplanar systems where the SDT effect can reverse tidal damping,
and may preclude the effect's being significant for realistic systems. For the
specific case quantified by Correia et al., the effect is strong because of the
large adopted tidal time lag, which may not be appropriate for the assumed
Saturn-like inner planet. On the other hand, the effective Q for any given
planet in exotic circumstances is very uncertain, so the SDT effect could play
a role in planetary evolution.",1309.6279v1
2013-10-01,The extrema of an action principle for dissipative mechanical systems,"A least action principle for damping motion has been previously proposed with
a Hamiltonian and a Lagrangian containing the energy dissipated by friction.
Due to the space-time nonlocality of the Lagrangian, mathematical uncertainties
persist about the appropriate variational calculus and the nature (maxima,
minima and inflection) of the stationary action. The aim of this work is to
make numerical simulation of damped motion and to compare the actions of
different paths in order to get evidence of the existence and the nature of
stationary action. The model is a small particle subject to conservative and
friction forces. Two conservative forces and three friction forces are
considered. The comparison of the actions of the perturbed paths with that of
the Newtonian path reveals the existence of extrema of action which are minima
for zero or very weak friction and shift to maxima when the motion is
overdamped. In the intermediate case, the action of the Newtonian path is
neither least nor most, meaning that the extreme feature of the Newtonian path
is lost. In this situation, however, no reliable evidence of stationary action
can be found from the simulation result.",1310.0455v1
2013-10-02,Effectiveness of Depolarizing noise in causing sudden death of entanglement,"Continuing on the recent observation that sudden death of entanglement can
occur even when a single qubit of a two qubit state is exposed to noisy
environment, we examine the local effects of several noises on bipartite
qubit-qutrit and qutrit-qutrit systems. In order to rule out any initial
interactions with environment, we consider maximally entangled pure states of
qubit-qutrit and qutrit-qutrit systems for our analysis. We show that
depolarizing and generalized amplitude damping noise can cause sudden death of
entanglement in these states even when they act only on one part of the system.
We also show that sudden death of entanglement occurs much faster under the
action of depolarizing noise when compared to that due to generalized amplitude
damping. This result strengthens the observation that depolarizing noise is
more effective than other noise models in causing sudden death of entanglement.",1310.0715v1
2013-10-09,Improved Coincident and Coherent Detection Statistics for Searches for Gravitational Wave Ringdown Signals,"We study an improved method for detecting gravitational wave (GW) signals
from perturbed black holes by earth-based detectors in the quest for searching
for intermediate-mass black holes (IMBHs). Such signals, called ringdowns, are
damped sinusoids whose frequency and damping constant can be used to measure a
black hole's mass and spin. Utilizing the output from a matched filter analysis
pipeline, we present an improved statistic for the detection of a ringdown
signal that is found to be coincident in multiple detectors. The statistic
addresses the non-Gaussianity of the data without the use of an additional
signal-based waveform consistency test. We also develop coherent network
statistics to check for consistency of signal amplitudes and phases in the
different detectors with their different orientations and signal arrival times.
We find that the detection efficiency can be improved at least by a few tens of
percent by applying these multi-detector statistics primarily because of the
ineffectiveness of single-detector based discriminators of non-stationary
noise, such as the chi-square test, in the case of ringdown signals studied
here.",1310.2341v2
2013-10-11,New foundations and unification of basic plasma physics by means of classical mechanics,"The derivation of Debye shielding and Landau damping from the $N$-body
description of plasmas requires many pages of heavy kinetic calculations in
classical textbooks and is done in distinct, unrelated chapters. Using Newton's
second law for the $N$-body system, we perform this derivation in a few steps
with elementary calculations using standard tools of calculus, and no
probabilistic setting. Unexpectedly, Debye shielding is encountered on the way
to Landau damping. The theory is extended to accommodate a correct description
of trapping or chaos due to Langmuir waves, and to avoid the small amplitude
assumption for the electrostatic potential. Using the shielded potential,
collisional transport is computed for the first time by a convergent expression
including the correct calculation of deflections for all impact parameters.
Shielding and collisional transport are found to be two related aspects of the
repulsive deflections of electrons.",1310.3096v1
2013-10-18,Analytical considerations for linear and nonlinear optimization of the TME cells. Application to the CLIC pre-damping rings,"The theoretical minimum emittance cells are the optimal configurations for
achieving the absolute minimum emittance, if specific optics constraints are
satisfied at the middle of the cell's dipole. Linear lattice design options
based on an analytical approach for the theoretical minimum emittance cells are
presented in this paper. In particular the parametrization of the quadrupole
strengths and optics functions with respect to the emittance and drift lengths
is derived. A multi-parametric space can be then created with all the cell
parameters, from which one can chose any of them to be optimized. An
application of this approach are finally presented for the linear and
non-linear optimization of the CLIC Pre-damping rings.",1310.5024v1
2013-10-20,Electromagnetic waves in an axion-active relativistic plasma non-minimally coupled to gravity,"We consider cosmological applications of a new self-consistent system of
equations, accounting for a nonminimal coupling of the gravitational,
electromagnetic and pseudoscalar (axion) fields in a relativistic plasma. We
focus on dispersion relations for electromagnetic perturbations in an initially
isotropic ultrarelativistic plasma coupled to the gravitational and axion
fields in the framework of isotropic homogeneous cosmological model of the de
Sitter type. We classify the longitudinal and transversal electromagnetic modes
in an axionically active plasma and distinguish between waves (damping,
instable or running), and nonharmonic perturbations (damping or instable). We
show that for the special choice of the guiding model parameters the
transversal electromagnetic waves in the axionically active plasma,
nonminimally coupled to gravity, can propagate with the phase velocity less
than speed of light in vacuum, thus displaying a possibility for a new type of
resonant particle-wave interactions.",1310.5333v2
2013-10-25,Effect of resonance on the existence of periodic solutions for strongly damped wave equation,"We are interested in the differential equation $\ddot u(t) = -A u(t) - c A
\dot u(t) + \lambda u(t) + F(t,u(t))$, where $c > 0$ is a damping factor, $A$
is a sectorial operator and $F$ is a continuous map. We consider the situation
where the equation is at resonance at infinity, which means that $\lambda$ is
an eigenvalue of $A$ and $F$ is a bounded map. We introduce new geometrical
conditions for the nonlinearity $F$ and use topological degree methods to find
$T$-periodic solutions for this equation as fixed points of Poincar\'e
operator.",1310.6794v4
2013-10-25,"Voltage noise, switching rates, and multiple phase-slips in moderately damped Josephson junctions","We study the voltage noise properties including the switching rates and
statistics of phase-slips in moderately damped Josephson junctions using a
novel efficient numerical approach combining the matrix continued-fraction
method with the full counting statistics. By analyzing the noise results
obtained for the RCSJ model we identify different dominating components, namely
the thermal noise close to equilibrium (small current-bias regime), the shot
noise of (multiple) phase-slips in the intermediate range of biases and the
switching noise for yet higher bias currents. We extract thus far inaccessible
characteristic rates of phase-slips in the shot noise regime as well as the
escape and retrapping rates in the switching regime as functions of various
junction's parameters. The method can be extended and applied to other
experimentally relevant Josephson junction circuits.",1310.6871v1
2013-11-06,Analytical estimation of ATF beam halo distribution,"In order to study the background status in the ATF2 beam line and the
interaction point (IP), this paper developed an analytical method to give the
estimation of ATF beam halo distribution based on K. Hirata and K. Yokoya's
theory. The equilibrium particle distribution of beam tail in ATF damping ring,
when each electron is being affected by, in addition to the synchrotron
radiation damping effects, several stochastic processes, such as beam-gas
scattring, beam-gas bremsstrahlung and intra-beam scattering, was presented.
This method is common and can be applied on other electron rings.",1311.1267v3
2013-11-13,Quantum turbulence in superfluids with wall-clamped normal component,"In Fermi superfluids, like superfluid 3He, the viscous normal component can
be considered to be stationary with respect to the container. The normal
component interacts with the superfluid component via mutual friction which
damps the motion of quantized vortex lines and eventually couples the
superfluid component to the container. With decreasing temperature and mutual
friction the internal dynamics of the superfluid component becomes more
important compared to the damping and coupling effects from the normal
component. This causes profound changes in superfluid dynamics: the
temperature-dependent transition from laminar to turbulent vortex motion and
the decoupling from the reference frame of the container at even lower
temperatures.",1311.3112v1
2013-11-19,Protecting qutrit-qutrit entanglement by weak measurement and reversal,"Entangled states in high dimensional systems are of great interest due to the
extended possibilities they provide in quantum information processing.
Recently, Sun et al. [Phys. Rev. A 82, 052323 (2010)] and Kim et al. [Nat.
Phys. 8, 117 (2012)] pointed out that weak measurement and quantum weak
measurement reversal can actively combat decoherence. We generalize their
studies from qubits to qutrits under amplitude damping decoherence. We find
that the qutrit-qutrit entanglement can be partially retrieved for certain
initial states when only weak measurement reversals are performed. However, we
can completely defeat amplitude damping decoherence for any initial states by
the combination of prior weak measurements and post optimal weak measurement
reversals. The experimental feasibility of our schemes is also discussed.",1311.4692v2
2013-11-27,Encapsulated formulation of the Selective Frequency Damping method,"We present an alternative ""encapsulated"" formulation of the Selective
Frequency Damping method for finding unstable equilibria of dynamical systems,
which is particularly useful when analysing the stability of fluid flows. The
formulation makes use of splitting methods, which means that it can be wrapped
around an existing time-stepping code as a ""black box"". The method is first
applied to a scalar problem in order to analyse its stability and highlight the
roles of the control coefficient $\chi$ and the filter width $\Delta$ in the
convergence (or not) towards the steady-state. Then the steady-state of the
incompressible flow past a two-dimensional cylinder at $Re=100$, obtained with
a code which implements the spectral/hp element method, is presented.",1311.7000v1
2013-12-02,The spatial distribution of dark-matter-annihilation originated gamma-ray line signal,"The GeV$-$TeV $\gamma-$ray line signal is the smoking gun signature of the
dark matter annihilation or decay. The detection of such a signal is one of the
main targets of some space-based telescopes, including Fermi-LAT and the
upcoming CALET, DAMPE and Gamma-400. An important feature of the
dark-matter-annihilation originated $\gamma-$ray line photons is their
concentration at the center of the Galaxy. So far no reliable $\gamma-$ray line
has been detected by Fermi-LAT and the upper limits on the cross section of
annihilation into $\gamma-$rays have been reported. We use these upper limits
to estimate the ""maximal"" number of $\gamma-$ray line photons detectable for
Fermi-LAT, DAMPE and Gamma-400 and then investigate the spatial distribution of
these photons. We show that usually the center of the distribution region will
be offset from the Galactic centre (Sgr A$^{\star}$) due to the limited
statistics. Such a result is almost independent of the dark matter distribution
models and renders the reconstruction of the dark matter distribution with the
$\gamma-$ray line signal very challenging for the foreseeable space-based
detectors.",1312.0357v2
2013-12-03,Inflationary Steps in the Planck Data,"We extend and improve the modeling and analysis of large-amplitude, sharp
inflationary steps for second order corrections required by the precision of
the Planck CMB power spectrum and for arbitrary Dirac-Born-Infeld sound speed.
With two parameters, the amplitude and frequency of the resulting oscillations,
step models improve the fit by $\Delta \chi^2 = -11.4$. Evidence for
oscillations damping before the Planck beam scale is weak: damping only
improves the fit to $\Delta \chi^2 = -14.0$ for one extra parameter, if step
and cosmological parameters are jointly fit, in contrast to analyses which fix
the latter. Likewise, further including the sound speed as a parameter only
marginally improves the fit to $\Delta \chi^2 = -15.2$ but has interesting
implications for the lowest multipole temperature and polarization anisotropy.
Since chance features in the noise can mimic these oscillatory features, we
discuss tests from polarization power spectra, lensing reconstruction and
squeezed and equilateral bispectra that should soon verify or falsify their
primordial origin.",1312.0946v1
2013-12-16,Exploiting Intrinsic Triangular Geometry in Relativistic He3+Au Collisions to Disentangle Medium Properties,"Recent results in d+Au and p+Pb collisions at RHIC and the LHC provide
evidence for collective expansion and flow of the created medium. We propose a
control set of experiments to directly compare particle emission patterns from
p+Au, d+Au, and He3+Au or t+Au collisions at the same sqrt(sNN). Using Monte
Carlo Glauber we find that a He3 or triton projectile, with a realistic
wavefunction description, induces a significant intrinsic triangular shape to
the initial medium and that, even with viscous damping, this survives into a
significant third order flow moment v3. By comparing systems with one, two, and
three initial hot spots, one can disentangle the effects from the initial
spatial distribution of the deposited energy and viscous damping. These are key
tools to answering the question of how small a droplet of matter is necessary
to form a quark-gluon plasma described by nearly inviscid hydrodynamics.",1312.4565v2
2013-12-17,Reversal time of the magnetization of magnetic nanoparticles at very low damping,"The magnetization reversal time of ferromagnetic nanoparticles is
investigated in the very low damping regime. The energy-controlled diffusion
equation rooted in a generalization of the Kramers escape rate theory for point
Brownian particles in a potential to the magnetic relaxation of a macrospin,
yields the reversal time in closed integral form. The latter is calculated for
a nanomagnet with uniaxial anisotropy with a uniform field applied at an angle
to the easy axis and for a nanomagnet with biaxial anisotropy with the field
along the easy axis. The results completely agree with those yielded by
independent numerical and asymptotic methods.",1312.4904v3
2013-12-18,Quantum speed limit for arbitrary initial states,"We investigate the generic bound on the minimal evolution time of the open
dynamical quantum system. This quantum speed limit time is applicable to both
mixed and pure initial states. We then apply this result to the damped
Jaynes-Cummings model and the Ohimc-like dephasing model starting from a
general time-evolution state. The bound of this time-dependent state at any
point in time can be found. For the damped Jaynes-Cummings model, the
corresponding bound first decreases and then increases in the Markovian
dynamics. While in the non-Markovian regime, the speed limit time shows an
interesting periodic oscillatory behavior. For the case of Ohimc-like dephasing
model, this bound would be gradually trapped to a fixed value. In addition, the
roles of the relativistic effects on the speed limit time for the observer in
non-inertial frames are discussed.",1312.5071v1
2013-12-26,Equilibrium of a Brownian particle in an inhomogeneous medium: An alternative approach,"We look at the equilibrium of a Brownian particle in an inhomogeneous space
following the alternative approach proposed in ref.[1]. We consider a
coordinate dependent damping that makes the stochastic dynamics the one with
multiplicative noise. Here we show that the mapping to an additive noise gives
the equilibrium distribution of the generalized Langevin dynamics of a particle
with mass. The procedure does not need inclusion of any ad hoc current
cancelling term in the Langevin dynamics. The result shows a modified
Maxwell-Boltzmann distribution with a damping dependent amplitude.",1312.7075v3
2014-01-22,On Stability of Hyperbolic Thermoelastic Reissner-Mindlin-Timoshenko Plates,"In the present article, we consider a thermoelastic plate of
Reissner-Mindlin-Timoshenko type with the hyperbolic heat conduction arising
from Cattaneo's law. In the absense of any additional mechanical dissipations,
the system is often not even strongly stable unless restricted to the
rotationally symmetric case, etc. We present a well-posedness result for the
linear problem under general mixed boundary conditions for the elastic and
thermal parts. For the case of a clamped, thermally isolated plate, we show an
exponential energy decay rate under a full damping for all elastic variables.
Restricting the problem to the rotationally symmetric case, we further prove
that a single frictional damping merely for the bending compoment is sufficient
for exponential stability. To this end, we construct a Lyapunov functional
incorporating the Bogovski\u{i} operator for irrotational vector fields which
we discuss in the appendix.",1401.5669v1
2014-01-27,Edge states in 2D lattices with hopping anisotropy and Chebyshev polynomials,"Analytic technique based on Chebyshev polynomials is developed for studying
two-dimensional lattice ribbons with hopping anisotropy. In particular, the
tight-binding models on square and triangle lattice ribbons are investigated
with anisotropic nearest neighbouring hoppings. For special values of hopping
parameters the square lattice becomes topologically equivalent to a honeycomb
one either with zigzag or armchair edges. In those cases as well as for
triangle lattices we perform the exact analytic diagonalization of
tight-binding Hamiltonians in terms of Chebyshev polynomials. Deep inside the
edge state subband the wave functions exhibit exponential spatial damping which
turns into power-law damping at edge-bulk transition point. It is shown that
strong hopping anisotropy crashes down edge states, and the corresponding
critical conditions are found.",1401.6770v2
2014-01-27,Dynamical pattern formations in two dimensional fluid and Landau pole bifurcation,"A phenomenological theory is proposed to analyze the asymptotic dynamics of
perturbed inviscid Kolmogorov shear flows in two dimensions. The phase diagram
provided by the theory is in qualitative agreement with numerical observations,
which include three phases depending on the aspect ratio of the domain and the
size of the perturbation: a steady shear flow, a stationary dipole, and four
traveling vortices. The theory is based on a precise study of the inviscid
damping of the linearized equation and on an analysis of nonlinear effects. In
particular, we show that the dominant Landau pole controlling the inviscid
damping undergoes a bifurcation, which has important consequences on the
asymptotic fate of the perturbation.",1401.6865v1
2014-02-05,On Linear Landau Damping for Relativistic Plasmas via Gevrey Regularity,"We examine the phenomenon of Landau Damping in relativistic plasmas via a
study of the relativistic Vlasov-Poisson system (both on the torus and on
$\mathbb{R}^3$) linearized around a sufficiently nice, spatially uniform
kinetic equilibrium. We find that exponential decay of spatial Fourier modes is
impossible under modest symmetry assumptions. However, by assuming the
equilibrium and initial data are sufficiently regular functions of velocity for
a given wavevector (in particular that they exhibit a kind of Gevrey
regularity), we show that it is possible for the mode associated to this
wavevector to decay sub-exponentially if its magnitude exceeds a certain
critical size. We also give a heuristic argument why one should not expect such
rapid decay for modes with wavevectors below this threshold.",1402.0992v2
2014-02-06,Time dependent elastic response to a local shear transformation in amorphous solids,"The elastic response of a two-dimensional amorphous solid to induced local
shear transformations, which mimic the elementary plastic events occurring in
deformed glasses, is investigated via Molecular Dynamics simulations. We show
that for different spatial realizations of the transformation, despite relative
fluctuations of order one, the long time equilibrium response averages out to
the prediction of the Eshelby inclusion problem for a continuum elastic medium.
We characterize the effects of the underlying dynamics on the propagation of
the elastic signal. A crossover from a propagative transmission in the case of
weakly-damped dynamics to a diffusive transmission for strong damping is
evidenced. In the latter case, the full time dependent elastic response is in
agreement with the theoretical prediction, obtained by solving the diffusion
equation for the displacement field in an elastic medium.",1402.1474v1
2014-02-07,A temperature dependent formation time approach for Υsuppression at LHC,"We present here a model to describe the bottomonium suppression in Pb$+$Pb
collisions at Large Hadron Collider (LHC), at $\sqrt{s_{NN}}=2.76$ TeV by using
the quasi-particle model (QPM) equation of state (EOS) for the Quark-Gluon
Plasma (QGP) expanding under Bjorken's hydrodynamical expansion. The current
model includes the modification of the formation time based on the temperature
of QGP, color screening during bottomonium production, gluon induced
dissociation and collisional damping. The cold nuclear matter (CNM) effects and
decay of higher resonances of bottomonium have also been included in the
present work. The final suppression of the bottomonium states, at mid rapidity
is calculated as a function of centrality. The results compare closely with the
recent data at Large hadron Collider (LHC) in the mid rapidity region for
various centrality bins. {\nd \it Keywords } : Color screening, Gluonic
dissociation, Collisional damping, Survival probability, CNM effects\\ {\nd \it
PACS numbers } : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa",1402.1560v5
2014-02-12,A numerical comparison between degenerate parabolic and quasilinear hyperbolic models of cell movements under chemotaxis,"We consider two models which were both designed to describe the movement of
eukaryotic cells responding to chemical signals. Besides a common standard
parabolic equation for the diffusion of a chemoattractant, like chemokines or
growth factors, the two models differ for the equations describing the movement
of cells. The first model is based on a quasilinear hyperbolic system with
damping, the other one on a degenerate parabolic equation. The two models have
the same stationary solutions, which may contain some regions with vacuum. We
first explain in details how to discretize the quasilinear hyperbolic system
through an upwinding technique, which uses an adapted reconstruction, which is
able to deal with the transitions to vacuum. Then we concentrate on the
analysis of asymptotic preserving properties of the scheme towards a
discretization of the parabolic equation, obtained in the large time and large
damping limit, in order to present a numerical comparison between the
asymptotic behavior of these two models. Finally we perform an accurate
numerical comparison of the two models in the time asymptotic regime, which
shows that the respective solutions have a quite different behavior for large
times.",1402.2831v2
2014-02-13,Surface Activity and Oscillation Amplitudes of Red Giants in Eclipsing Binaries,"Among 19 red-giant stars belonging to eclipsing binary systems that have been
identified in Kepler data, 15 display solar-like oscillations. We study whether
the absence of mode detection in the remaining 4 is an observational bias or
possibly evidence of mode damping that originates from tidal interactions. A
careful analysis of the corresponding Kepler light curves shows that modes with
amplitudes that are usually observed in red giants would have been detected if
they were present. We observe that mode depletion is strongly associated with
short-period systems, in which stellar radii account for 16-24 % of the
semi-major axis, and where red-giant surface activity is detected. We suggest
that when the rotational and orbital periods synchronize in close binaries, the
red-giant component is spun up, so that a dynamo mechanism starts and generates
a magnetic field, leading to observable stellar activity. Pressure modes would
then be damped as acoustic waves dissipate in these fields.",1402.3027v1
2014-02-18,Cherenkov friction on a neutral particle moving parallel to a dielectric,"Based on a fully relativistic framework and the assumption of local
equilibrium, we describe a simple mechanism of quantum friction for a particle
moving parallel to a dielectric. The Cherenkov effect explains how the bare
ground state becomes globally unstable and how fluctuations of the
electromagnetic field and the particle's dipole are converted into pairs of
excitations. Modelling the particle as a silver nano-sphere, we investigate the
spectrum of the force and its velocity dependence. We find that the damping of
the plasmon resonance in the silver particle has a relatively strong impact
near the Cherenkov threshold velocity. We also present an expansion of the
friction force near the threshold velocity for both damped and undamped
particles.",1402.4518v1
2014-02-20,Feed-forward control for quantum state protection against decoherence,"We propose a novel scheme of feed-forward control and its reversal for
protecting quantum state against decoherence. Before the noise channel our
pre-weak measurement and feed-forward are just to change the protected state
into the state almost immune to the noise channel, and after the channel our
reversed operations and post-weak measurements are just to restore the
protected state. Unlike most previous state protection schemes, ours only
concerns the noise channel and does not care about the protected state. We show
that our scheme can effectively protect unknown states, nonorthogonal states
and entangled states against amplitude damping noise. Our scheme has dramatic
merits of protecting quantum states against heavy amplitude damping noise, and
can perfectly protect some specific nonorthogonal states in an almost
deterministic way, which might be found some applications in current quantum
communication technology. And it is most important that our scheme is
experimentally available with current technology.",1402.4921v2
2014-02-25,Elastic Anomalies Associated with the Antiferroelectric Phase Transitions of PbHfO3 Single Crystals,"The temperature dependence of the elastic properties of antiferroelectric
PbHfO3 was investigated by Brillouin scattering. The two structural phase
transitions of antiferroelectric-antiferroelectric-paraelectric phases were
clearly identified by discontinuous changes in the acoustic mode frequencies
and the hypersonic damping. The substantial softening of the mode frequency
along with the remarkable increase in the acoustic damping observed in the
paraelectric phase indicated the formation of precursor noncentrosymmetric
(polar) clusters and their coupling to the acoustic waves. This was
corroborated by the observation of quasi-elastic central peaks, the intensity
of which grew upon cooling toward the Curie point. The obtained relaxation time
exhibited a slowing-down behavior, suggesting that the dynamics of precursor
clusters becomes more sluggish on approaching the phase transition temperature.",1402.6175v1
2014-03-05,Short-period pulsar oscillations following a glitch,"Following a glitch, the crust and magnetized plasma in the outer core of a
neutron star are believed to rapidly establish a state of co-rotation within a
few seconds by process analogous to classical Ekman pumping. However, in ideal
magnetohydrodynamics, a final state of co-rotation is inconsistent with
conservation of energy of the system. We demonstrate that, after the Ekman-like
spin up is completed, magneto-inertial waves continue to propagate throughout
the star, exciting torsional oscillations in the crust and plasma. The crust
oscillation is irregular and quasi-periodic, with a dominant frequency of the
order of seconds. Crust oscillations commence after an Alfv\'en crossing time,
approximately half a minute at the magnetic pole, and are subsequently damped
by the electron viscosity over approximately an hour. In rapidly rotating
stars, the magneto-inertial spectrum in the core approaches a continuum, and
crust oscillations are damped by resonant absorption analogous to
quasi-periodic oscillations in magnetars. The oscillations predicted are
unlikely to be observed in timing data from existing radio telescopes, but may
be visible to next generation telescope arrays.",1403.1046v2
2014-03-06,On the damped oscillations of an elastic quasi-circular membrane in a two-dimensional incompressible fluid,"We propose a procedure - partly analytical and partly numerical - to find the
frequency and the damping rate of the small-amplitude oscillations of a
massless elastic capsule immersed in a two-dimensional viscous incompressible
fluid. The unsteady Stokes equations for the stream function are decomposed
onto normal modes for the angular and temporal variables, leading to a
fourth-order linear ordinary differential equation in the radial variable. The
forcing terms are dictated by the properties of the membrane, and result into
jump conditions at the interface between the internal and external media. The
equation can be solved numerically, and an excellent agreement is found with a
fully-computational approach we developed in parallel. Comparisons are also
shown with the results available in the scientific literature for drops, and a
model based on the concept of embarked fluid is presented, which allows for a
good representation of the results and a consistent interpretation of the
underlying physics.",1403.1423v1
2014-03-07,The silicon matrix for the prototype for the Dark Matter Particle Explorer,"A new generation detector for the high energy cosmic ray - the DAMPE(DArk
Matter Particle Explorer) is a satellite based project. Its main object is the
measurement of energy spectrum of cosmic ray nuclei from 100GeV to 100TeV, the
high energy electrons and gamma ray from 5GeV to 10TeV. A silicon matrix
detector described in this paper, is employed for the sea level cosmic ray
energy and position detection while the prototype testing of the DAMPE. This
matrix is composed by the 180 silicon PIN detectors, which covers an area of
32*20 cm2. The primary testing results are shown including MIPs energy spectrum
and the position sensitive map.",1403.1679v2
2014-04-01,Anomalies in the specific heat of a free damped particle: The role of the cutoff in the spectral density of the coupling,"The properties of a dissipative system depend on the spectral density of the
coupling to the environment. Mostly, the dependence on the low-frequency
behavior is in the focus of interest. However, in order to avoid divergencies,
it is also necessary to suppress the spectral density of the coupling at high
frequencies. Interestingly, the very existence of this cutoff may lead to a
mass renormalization which can have drastic consequences for the thermodynamic
properties of the dissipative system. Here, we explore the role which the
cutoff in the spectral density of the coupling plays for a free damped particle
and we compare the effect of an algebraic cutoff with that of a sharp cutoff.",1404.0254v1
2014-04-09,Directly imaging damped Ly-alpha galaxies at z>2. II: Imaging and spectroscopic observations of 32 quasar fields,"Damped Ly-alpha absorbers (DLAs) are a well-studied class of absorption line
systems, and yet the properties of their host galaxies remain largely unknown.
To investigate the origin of these systems, we have conducted an imaging survey
of 32 quasar fields with intervening DLAs between z~1.9-3.8, leveraging a
technique that allows us to image galaxies at any small angular separation from
the background quasars. In this paper, we present the properties of the
targeted DLA sample, new imaging observations of the quasar fields, and the
analysis of new and archival spectra of the background quasars.",1404.2599v2
2014-04-13,Homotopy invariants methods in the global dynamics of strongly damped wave equation,"We are interested in the following differential equation $\ddot u(t) = -A
u(t) - c A \dot u(t) + \lambda u(t) + F(u(t))$ where $c > 0$ is a damping
factor, $A$ is a sectorial operator and $F$ is a continuous map. We consider
the situation where the equation is at resonance at infinity, which means that
$\lambda$ is an eigenvalue of $A$ and $F$ is a bounded map. We provide
geometrical conditions for the nonlinearity $F$ and determine the Conley index
of the set $K_\infty$, that is the union of the bounded orbits of this
equation.",1404.3429v3
2014-04-14,Low-distance Surface Codes under Realistic Quantum Noise,"We study the performance of distance-three surface code layouts under
realistic multi-parameter noise models. We first calculate their thresholds
under depolarizing noise. We then compare a Pauli-twirl approximation of
amplitude and phase damping to amplitude and phase damping. We find the
approximate channel results in a pessimistic estimate of the logical error
rate, indicating the realistic threshold may be higher than previously
estimated. From Monte-Carlo simulations, we identify experimental parameters
for which these layouts admit reliable computation. Due to its low resource
cost and superior performance, we conclude that the 17-qubit layout should be
targeted in early experimental implementations of the surface code. We find
that architectures with gate times in the 5-40 ns range and T1 times of at
least 1-2 us range will exhibit improved logical error rates with a 17-qubit
surface code encoding.",1404.3747v3
2014-04-21,Phase conversion dissipation in multicomponent compact stars,"We propose a mechanism for the damping of density oscillations in
multicomponent compact stars. The mechanism is the periodic conversion between
different phases, i.e., the movement of the interface between them, induced by
pressure oscillations in the star. The damping grows nonlinearly with the
amplitude of the oscillation. We study in detail the case of r-modes in a
hybrid star with a sharp interface, and we find that this mechanism is powerful
enough to saturate the r-mode at very low saturation amplitude, of order
$10^{-10}$, and is therefore likely to be the dominant r-mode saturation
mechanism in hybrid stars with a sharp interface.",1404.5279v4
2014-04-25,Nonlinear and Linear Timescales near Kinetic Scales in Solar Wind Turbulence,"The application of linear kinetic treatments to plasma waves, damping, and
instability requires favorable inequalities between the associated linear
timescales and timescales for nonlinear (e.g., turbulence) evolution. In the
solar wind these two types of timescales may be directly compared using
standard Kolmogorov-style analysis and observational data. The estimated local
nonlinear magnetohydrodynamic cascade times, evaluated as relevant kinetic
scales are approached, remain slower than the cyclotron period, but comparable
to, or faster than, the typical timescales of instabilities, anisotropic waves,
and wave damping. The variation with length scale of the turbulence timescales
is supported by observations and simulations. On this basis the use of linear
theory - which assumes constant parameters to calculate the associated kinetic
rates - may be questioned. It is suggested that the product of proton
gyrofrequency and nonlinear time at the ion gyroscales provides a simple
measure of turbulence influence on proton kinetic behavior.",1404.6569v1
2014-04-29,Quasi-normal modes of superfluid neutron stars,"We study non-radial oscillations of neutron stars with superfluid baryons, in
a general relativistic framework, including finite temperature effects. Using a
perturbative approach, we derive the equations describing stellar oscillations,
which we solve by numerical integration, employing different models of nucleon
superfluidity, and determining frequencies and gravitational damping times of
the quasi-normal modes. As expected by previous results, we find two classes of
modes, associated to superfluid and non-superfluid degrees of freedom,
respectively. We study the temperature dependence of the modes, finding that at
specific values of the temperature, the frequencies of the two classes of
quasi-normal modes show avoided crossings, and their damping times become
comparable. We also show that, when the temperature is not close to the avoided
crossings, the frequencies of the modes can be accurately computed by
neglecting the coupling between normal and superfluid degrees of freedom. Our
results have potential implications on the gravitational wave emission from
neutron stars.",1404.7512v1
2014-05-27,Nonequilibrium dynamical mean-field theory for bosonic lattice models,"We develop the nonequilibrium extension of bosonic dynamical mean field
theory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity
solver. In contrast to Gutzwiller mean-field theory and strong coupling
perturbative approaches, nonequilibrium BDMFT captures not only dynamical
transitions, but also damping and thermalization effects at finite temperature.
We apply the formalism to quenches in the Bose-Hubbard model, starting both
from the normal and Bose-condensed phases. Depending on the parameter regime,
one observes qualitatively different dynamical properties, such as rapid
thermalization, trapping in metastable superfluid or normal states, as well as
long-lived or strongly damped amplitude oscillations. We summarize our results
in non-equilibrium ""phase diagrams"" which map out the different dynamical
regimes.",1405.6941v2
2014-05-28,Electronic control of the spin-wave damping in a magnetic insulator,"It is demonstrated that the decay time of spin-wave modes existing in a
magnetic insulator can be reduced or enhanced by injecting an in-plane dc
current, $I_\text{dc}$, in an adjacent normal metal with strong spin-orbit
interaction. The demonstration rests upon the measurement of the ferromagnetic
resonance linewidth as a function of $I_\text{dc}$ in a 5~$\mu$m diameter
YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope
(MRFM). Complete compensation of the damping of the fundamental mode is
obtained for a current density of $\sim 3 \cdot 10^{11}\text{A.m}^{-2}$, in
agreement with theoretical predictions. At this critical threshold the MRFM
detects a small change of static magnetization, a behavior consistent with the
onset of an auto-oscillation regime.",1405.7415v1
2014-06-16,Study on FPGA SEU Mitigation for Readout Electronics of DAMPE BGO Calorimeter,"The BGO calorimeter, which provides a wide measurement range of the primary
cosmic ray spectrum, is a key sub-detector of Dark Matter Particle Explorer
(DAMPE). The readout electronics of calorimeter consists of 16 pieces of Actel
ProASIC Plus FLASH-based FPGA, of which the design-level flip-flops and
embedded block RAMs are single event upset (SEU) sensitive in the harsh space
environment. Therefore to comply with radiation hardness assurance (RHA), SEU
mitigation methods, including partial triple modular redundancy (TMR), CRC
checksum, and multi-domain reset are analyzed and tested by the heavy-ion beam
test. Composed of multi-level redundancy, a FPGA design with the
characteristics of SEU tolerance and low resource consumption is implemented
for the readout electronics.",1406.3928v1
2014-06-18,Damping of glacial-interglacial cycles from anthropogenic forcing,"Climate variability over the past million years shows a strong
glacial-interglacial cycle of ~100,000 years as a combined result of
Milankovitch orbital forcing and climatic resonance. It has been suggested that
anthropogenic contributions to radiative forcing may extend the length of the
present interglacial, but the effects of anthropogenic forcing on the
periodicity of glacial-interglacial cycles has received little attention. Here
I demonstrate that moderate anthropogenic forcing can act to damp this 100,000
year cycle and reduce climate variability from orbital forcing. Future changes
in solar insolation alone will continue to drive a 100,000 year climate cycle
over the next million years, but the presence of anthropogenic warming can
force the climate into an ice-free state that only weakly responds to orbital
forcing. Sufficiently strong anthropogenic forcing that eliminates the
glacial-interglacial cycle may serve as an indication of an epoch transition
from the Pleistocene to the Anthropocene.",1406.4728v1
2014-06-27,Magnetoplasmons of the tilted-anisotropic Dirac cone material $α-$(BEDT-TTF)$_2$I$_3$,"We study the collective modes of a low-energy continuum model of the
quasi-two-dimensional electron liquid in a layer of the organic compound
$\alpha-$(BEDT-TTF)$_2$I$_3$ in a perpendicular magnetic field. As testified by
zero magnetic field transport experiments and \textit{ab initio} theory, this
material hosts both massless and massive low-energy carriers, the former being
described by tilted and anisotropic Dirac cones. The polarizability of these
cones is anisotropic, and two sets of magnetoplasmon modes occur between any
two cyclotron resonances. We show that the tilt of the cones causes a unique
intervalley damping effect: the upper hybrid mode of one cone is damped by the
particle-hole continuum of the other cone in generic directions. We analyse how
the presence of massive carriers affects the response of the system, and
demonstrate how doping can tune $\alpha-$(BEDT-TTF)$_2$I$_3$ between regimes of
isotropic and anisotropic screening.",1406.7081v2
2014-06-30,Collective Coordinates Theory for Discrete Soliton Ratchets in the sine-Gordon Model,"A collective coordinate theory is develop for soliton ratchets in the damped
discrete sine-Gordon model driven by a biharmonic force. An ansatz with two
collective coordinates, namely the center and the width of the soliton, is
assumed as an approximated solution of the discrete non-linear equation. The
evolution of these two collective coordinates, obtained by means of the
Generalized Travelling Wave Method, explains the mechanism underlying the
soliton ratchet and captures qualitatively all the main features of this
phenomenon. The theory accounts for the existence of a non-zero depinning
threshold, the non-sinusoidal behaviour of the average velocity as a function
of the difference phase between the harmonics of the driver, the non-monotonic
dependence of the average velocity on the damping and the existence of
non-transporting regimes beyond the depinning threshold. In particular it
provides a good description of the intriguing and complex pattern of subspaces
corresponding to different dynamical regimes in parameter space.",1406.7656v1
2014-07-04,Temperature Dependent Ferromagnetic Resonance via the Landau-Lifshitz-Bloch Equation: Application to FePt,"Using the Landau-Lifshitz-Bloch (LLB) equation for ferromagnetic materials,
we derive analytic expressions for temperature dependent absorption spectra as
probed by ferromagnetic resonance (FMR). By analysing the resulting
expressions, we can predict the variation of the resonance frequency and
damping with temperature and coupling to the thermal bath. We base our
calculations on the technologically relevant L1$_0$ FePt, parameterised from
atomistic spin dynamics simulations, with the Hamiltonian mapped from ab-initio
parameters. By constructing a multi-macrospin model based on the LLB equation
and exploiting GPU acceleration we extend the study to investigate the effects
on the damping and resonance frequency in ${\mu}$m sized structures.",1407.1174v1
2014-07-07,Composition variation and underdamped mechanics near membrane proteins and coats,"We study the effect of membrane proteins on the shape, composition and
thermodynamic stability of the surrounding membrane. When the coupling between
membrane composition and curvature is strong enough the nearby composition and
shape both undergo a transition from over-damped to under-damped spatial
variation, well before the membrane becomes unstable in the bulk. This
transition is associated with a change in the sign of the thermodynamic energy
and hence has the unusual features that it can favour the early stages of coat
assembly necessary for vesiculation (budding), while suppressing the activity
of mechanosensitive membrane channels and transporters. Our results also
suggest an approach to obtain physical parameters that are otherwise difficult
to measure.",1407.1672v2
2014-07-11,Evidence for Wave Heating of the Quiet Sun Corona,"We have measured the energy and dissipation of Alfvenic waves in the quiet
Sun. A magnetic field was used to infer the location and orientation of the
magnetic field lines along which the waves are expected to travel. The waves
were measured using spectral lines to infer the wave amplitude. The waves cause
a non-thermal broadening of the spectral lines, which can be expressed as a
non-thermal velocity v_nt. By combining the spectroscopic measurements with
this magnetic field model we were able to trace the variation of v_nt along the
magnetic field. At the footpoints of the quiet Sun loops we find that waves
inject an energy flux in the range of 1.2-5.2 x 10^5 erg cm^-2 s^-1. At the
minimum of this range, this amounts to more than 80% of the energy needed to
heat the quiet Sun. We also find that these waves are dissipated over a region
centered on the top of the loops. The position along the loop where the damping
begins is strongly correlated with the length of the loop, implying that the
damping mechanism depends on the global loop properties rather than on local
collisional dissipation.",1407.3250v1
2014-07-16,Nonresonant high frequency excitation of mechanical vibrations in graphene based nanoresonator,"We theoretically analyse the dynamics of a suspended graphene membrane which
is in tunnel contact with grounded metallic electrodes and subjected to
ac-electrostatic potential induced by a gate electrode. It is shown that for
such system the retardation effects in the electronic subsystem generate an
effective pumping for the relatively slow mechanical vibrations if the driving
frequency exceeds the inverse charge relax- ation time. Under this condition
there is a critical value of the driving voltage ampli- tude above which the
pumping overcomes the intrinsic damping of the mechanical resonator leading to
a mechanical instability. This nonresonant instability is saturated by
nonlinear damping and the system exhibits self-sustained oscillations of
relatively large amplitude.",1407.4278v2
2014-07-21,Non-Markovian dynamics of open quantum systems without rotating wave approximation,"We study the non-Markovian dynamics of a damped oscillator coupled with a
reservoir. We present exact formulas for the oscillator's evolution directly
from the BCH formula by series expansion with neither Markovian nor rotating
wave approximation (RWA). Based on these, we show the existence of the
non-Markovian feature of the system's evolution for the damped oscillator. By
numerical simulation we find that the non-Markovian feature exists within a
wide range of the coupling strength, even when the coupling strength is very
small. To this problem, prior art results have assumed RWA and the existence of
non-Markovian feature was found when the system-reservoir coupling is strong
enough. However, as we show, given such a strong coupling, the original
Hamiltonian without RWA is actually not physical. Therefore, our exact study
here has thoroughly concluded the issue of non-Markovian feature.",1407.5359v2
2014-07-23,Global Existence of Smooth Solutions and Convergence to Barenblatt Solutions for the Physical Vacuum Free Boundary Problem of Compressible Euler Equations with Damping,"For the physical vacuum free boundary problem with the sound speed being
$C^{{1}/{2}}$-H$\ddot{\rm o}$lder continuous near vacuum boundaries of the
one-dimensional compressible Euler equations with damping, the global existence
of the smooth solution is proved, which is shown to converge to the Barenblatt
self-similar solution for the the porous media equation with the same total
mass when the initial data is a small perturbation of the Barenblatt solution.
The pointwise convergence with a rate of density, the convergence rate of
velocity in supereme norm and the precise expanding rate of the physical vacuum
boundaries are also given. The proof is based on a construction of higher-order
weighted functionals with both space and time weights capturing the behavior of
solutions both near vacuum states and in large time, an introduction of a new
ansatz, higher-order nonlinear energy estimates and elliptic estimates.",1407.6111v2
2014-07-24,Decay of dark and bright plasmonic modes in a metallic nanoparticle dimer,"We develop a general quantum theory of the coupled plasmonic modes resulting
from the near-field interaction between localized surface plasmons in a
heterogeneous metallic nanoparticle dimer. In particular, we provide analytical
expressions for the frequencies and decay rates of the bright and dark
plasmonic modes. We show that, for sufficiently small nanoparticles, the main
decay channel for the dark plasmonic mode, which is weakly coupled to light
and, hence, immune to radiation damping, is of nonradiative origin and
corresponds to Landau damping, i.e., decay into electron-hole pairs.",1407.6569v2
2014-07-29,Reproducing the Kinematics of Damped Lyman-alpha Systems,"We examine the kinematic structure of Damped Lyman-alpha Systems (DLAs) in a
series of cosmological hydrodynamic simulations using the AREPO code. We are
able to match the distribution of velocity widths of associated low ionisation
metal absorbers substantially better than earlier work. Our simulations produce
a population of DLAs dominated by halos with virial velocities around 70 km/s,
consistent with a picture of relatively small, faint objects. In addition, we
reproduce the observed correlation between velocity width and metallicity and
the equivalent width distribution of SiII. Some discrepancies of moderate
statistical significance remain; too many of our spectra show absorption
concentrated at the edge of the profile and there are slight differences in the
exact shape of the velocity width distribution. We show that the improvement
over previous work is mostly due to our strong feedback from star formation and
our detailed modelling of the metal ionisation state.",1407.7858v2
2014-07-31,Plasmons in finite spherical ionic systems,"The challenging question on possible plasmon type excitations in finite ionic
systems is discussed. The related theoretical model is formulated and developed
in order to describe surface and volume plasmons of ion liquid in finite
electrolyte systems. The irradiation of ionic surface plasmon fluctuations is
studied in terms of the Lorentz friction of oscillating charges. The
attenuation of surface plasmons in the ionic sphere is calculated and minimized
with respect to the sphere size. Various regimes of approximation for
description of size effect for damping of ionic plasmons are determined and a
cross-over in damping size-dependence is demonstrated. The most convenient
dimension of finite electrolyte system for energy and information transfer by
usage of ionic dipole plasmons is determined. The overall shift of size effect
to micrometer scale for ions in comparison to nanometer scale for electrons in
metals is found and by several orders red shift of plasmonic resonances in ion
systems is predicted in a wide range of variation depending of ion system
parameters. This convenient opportunity of tuning of resonances differs ionic
plasmons from plasmons in metals where electron concentration was firmly fixed.",1407.8369v2
2014-08-04,Collective Dynamics of Interacting Particles in Unsteady Flows,"We use the Fokker-Planck equation and its moment equations to study the
collective behavior of interacting particles in unsteady one-dimensional flows.
Particles interact according to a long-range attractive and a short-range
repulsive potential field known as Morse potential. We assume Stokesian drag
force between particles and their carrier fluid, and find analytic
single-peaked traveling solutions for the spatial density of particles in the
catastrophic phase. In steady flow conditions the streaming velocity of
particles is identical to their carrier fluid, but we show that particle
streaming is asynchronous with an unsteady carrier fluid. Using linear
perturbation analysis, the stability of traveling solutions is investigated in
unsteady conditions. It is shown that the resulting dispersion relation is an
integral equation of the Fredholm type, and yields two general families of
stable modes: singular modes whose eigenvalues form a continuous spectrum, and
a finite number of discrete global modes. Depending on the value of drag
coefficient, stable modes can be over-damped, critically damped, or decaying
oscillatory waves. The results of linear perturbation analysis are confirmed
through the numerical solution of the fully nonlinear Fokker-Planck equation.",1408.0558v1
2014-08-13,Correlated decay of triplet excitations in the Shastry-Sutherland compound SrCu$_2$(BO$_3$)$_2$,"The temperature dependence of the gapped triplet excitations (triplons) in
the 2D Shastry-Sutherland quantum magnet SrCu$_2$(BO$_3$)$_2$ is studied by
means of inelastic neutron scattering. The excitation amplitude rapidly
decreases as a function of temperature while the integrated spectral weight can
be explained by an isolated dimer model up to 10~K. Analyzing this anomalous
spectral line-shape in terms of damped harmonic oscillators shows that the
observed damping is due to a two-component process: one component remains sharp
and resolution limited while the second broadens. We explain the underlying
mechanism through a simple yet quantitatively accurate model of correlated
decay of triplons: an excited triplon is long-lived if no thermally populated
triplons are near-by but decays quickly if there are. The phenomenon is a
direct consequence of frustration induced triplon localization in the
Shastry--Sutherland lattice.",1408.3135v1
2014-08-20,Enhanced dissipation and inviscid damping in the inviscid limit of the Navier-Stokes equations near the 2D Couette flow,"In this work we study the long time, inviscid limit of the 2D Navier-Stokes
equations near the periodic Couette flow, and in particular, we confirm at the
nonlinear level the qualitative behavior predicted by Kelvin's 1887 linear
analysis. At high Reynolds number Re, we prove that the solution behaves
qualitatively like 2D Euler for times t \lesssim Re^(1/3), and in particular
exhibits inviscid damping (e.g. the vorticity weakly approaches a shear flow).
For times t \gtrsim Re^(1/3), which is sooner than the natural dissipative time
scale O(Re), the viscosity becomes dominant and the streamwise dependence of
the vorticity is rapidly eliminated by an enhanced dissipation effect.
Afterward, the remaining shear flow decays on very long time scales t \gtrsim
Re back to the Couette flow. When properly defined, the dissipative
length-scale in this setting is L_D \sim Re^(-1/3), larger than the scale L_D
\sim Re^(-1/2) predicted in classical Batchelor-Kraichnan 2D turbulence theory.
The class of initial data we study is the sum of a sufficiently smooth function
and a small (with respect to Re^(-1)) $L^2$ function.",1408.4754v1
2014-08-20,Building accurate initial models using gain functions for waveform inversion in the Laplace domain,"We suggest an initial model building technique using time gain functions in
the Laplace domain. Applying the gain expressed as a power of time is
equivalent to taking the partial derivative of the Laplace-domain wavefield
with respect to a damping constant. We construct an objective function, which
minimizes the logarithmic differences between the gained field data and the
partial derivative of the modeled data with respect to the damping constant. We
calculate the modeled wavefield, the partial derivative wavefield, and the
gradient direction in the Laplace domain using the analytic Green's function
starting from a constant velocity model. This is an efficient method to
generate an accurate initial model for a following Laplace-domain inversion.
Numerical examples using two marine field datasets confirm that a starting
model updated once from a scratch using the gradient direction calculated with
the proposed method can be successfully used for a subsequent Laplace-domain
inversion.",1408.5872v1
2014-09-01,Dynamical symmetries and crossovers in a three-spin system with collective dissipation,"We consider the non-equilibrium dynamics of a simple system consisting of
interacting spin-$1/2$ particles subjected to a collective damping. The model
is close to situations that can be engineered in hybrid electro/opto-mechanical
settings. Making use of large-deviation theory, we find a Gallavotti-Cohen
symmetry in the dynamics of the system as well as evidence for the coexistence
of two dynamical phases with different activity levels. We show that additional
damping processes smoothen out this behavior. Our analytical results are backed
up by Monte Carlo simulations that reveal the nature of the trajectories
contributing to the different dynamical phases.",1409.0422v2
2014-09-01,Damping of Bloch oscillations: Variational solutions of the Boltzmann equation beyond linear response,"Variational solutions of the Boltzmann equation usually rely on the concept
of linear response. We extend the variational approach for tight-binding models
at high entropies to a regime far beyond linear response. We analyze both
weakly interacting fermions and incoherent bosons on a lattice. We consider a
case where the particles are driven by a constant force, leading to the
well-known Bloch oscillations, and we consider interactions that are weak
enough not to overdamp these oscillations. This regime is computationally
demanding and relevant for ultracold atoms in optical lattices. We derive a
simple theory in terms of coupled dynamic equations for the particle density,
energy density, current and heat current, allowing for analytic solutions. As
an application, we identify damping coefficients for Bloch oscillations in the
Hubbard model at weak interactions and compute them for a one-dimensional toy
model. We also approximately solve the long-time dynamics of a weakly
interacting, strongly Bloch-oscillating cloud of fermionic particles in a
tilted lattice, leading to a subdiffusive scaling exponent.",1409.0560v2
2014-09-02,Controlled bidirectional remote state preparation in noisy environment: A generalized view,"It is shown that a realistic, controlled bidirectional remote state
preparation is possible using a large class of entangled quantum states having
a particular structure. Existing protocols of probabilistic, deterministic and
joint remote state preparation are generalized to obtain the corresponding
protocols of controlled bidirectional remote state preparation (CBRSP). A
general way of incorporating the effects of two well known noise processes, the
amplitude-damping and phase-damping noise, on the probabilistic CBRSP process
is studied in detail by considering that noise only affects the travel qubits
of the quantum channel used for the probabilistic CBRSP process. Also indicated
is how to account for the effect of these noise channels on deterministic and
joint remote state CBRSP protocols.",1409.0833v1
2014-09-07,The Effects of Long Pulse Durations and Radiation Damping in Selective Inversion Recovery Experiments,"Long pulse durations necessary in selective inversion recovery (SIR)
experiments along with radiation damping (RD) introduce difficulties in
quantitative nuclear magnetic resonance measurements, such as those that allow
for the determination of a sample's characteristics, including the rates that
govern magnetization transfer. Because of these influences, the assumption of
perfect inversion is invalid. In this work, we present data that demonstrates
that long pulse durations as well as RD cause difficulties in SIR experiments
performed on simple one-spin systems, indicating that they will be problematic
for multiple-spin systems as well. These results emphasize the importance of
understanding the evolution of magnetization for all time points throughout an
experiment used in quantitative NMR measurements. Furthermore, experimental
parameters must be chosen carefully and understood completely.",1409.2136v2
2014-09-19,Angular dependence of spin-orbit spin transfer torques,"In ferromagnet/heavy metal bilayers, an in-plane current gives rise to
spin-orbit spin transfer torque which is usually decomposed into field-like and
damping-like torques. For two-dimensional free-electron and tight-binding
models with Rashba spin-orbit coupling, the field-like torque acquires
nontrivial dependence on the magnetization direction when the Rashba spin-orbit
coupling becomes comparable to the exchange interaction. This nontrivial
angular dependence of the field-like torque is related to the Fermi surface
distortion, determined by the ratio of the Rashba spin-orbit coupling to the
exchange interaction. On the other hand, the damping-like torque acquires
nontrivial angular dependence when the Rashba spin-orbit coupling is comparable
to or stronger than the exchange interaction. It is related to the combined
effects of the Fermi surface distortion and the Fermi sea contribution. The
angular dependence is consistent with experimental observations and can be
important to understand magnetization dynamics induced by spin-orbit spin
transfer torques",1409.5600v1
2014-10-01,Non-linear collisionless damping of Weibel turbulence in relativistic blast waves,"The Weibel/filamentation instability is known to play a key role in the
physics of weakly magnetized collisionless shock waves. From the point of view
of high energy astrophysics, this instability also plays a crucial role because
its development in the shock precursor populates the downstream with a
small-scale magneto-static turbulence which shapes the acceleration and
radiative processes of suprathermal particles. The present work discusses the
physics of the dissipation of this Weibel-generated turbulence downstream of
relativistic collisionless shock waves. It calculates explicitly the
first-order non-linear terms associated to the diffusive nature of the particle
trajectories. These corrections are found to systematically increase the
damping rate, assuming that the scattering length remains larger than the
coherence length of the magnetic fluctuations. The relevance of such
corrections is discussed in a broader astrophysical perspective, in particular
regarding the physics of the external relativistic shock wave of a gamma-ray
burst.",1410.0146v1
2014-10-10,The Fate of Scattered Planets,"As gas giant planets evolve, they may scatter other planets far from their
original orbits to produce hot Jupiters or rogue planets that are not
gravitationally bound to any star. Here, we consider planets cast out to large
orbital distances on eccentric, bound orbits through a gaseous disk. With
simple numerical models, we show that super-Earths can interact with the gas
through dynamical friction to settle in the remote outer regions of a planetary
system. Outcomes depend on planet mass, the initial scattered orbit, and the
evolution of the time-dependent disk. Efficient orbital damping by dynamical
friction requires planets at least as massive as the Earth. More massive,
longer-lived disks damp eccentricities more efficiently than less massive,
short-lived ones. Transition disks with an expanding inner cavity can
circularize orbits at larger distances than disks that experience a global
(homologous) decay in surface density. Thus, orbits of remote planets may
reveal the evolutionary history of their primordial gas disks. A remote planet
with an orbital distance ~100 AU from the Sun is plausible and might explain
correlations in the orbital parameters of several distant trans-Neptunian
objects.",1410.2816v1
2014-10-13,Unified Theory of Inertial Granular Flows and Non-Brownian Suspensions,"Rheological properties of dense flows of hard particles are singular as one
approaches the jamming threshold where flow ceases, both for aerial granular
flows dominated by inertia, and for over-damped suspensions. Concomitantly, the
lengthscale characterizing velocity correlations appears to diverge at jamming.
Here we introduce a theoretical framework that proposes a tentative, but
potentially complete scaling description of stationary flows. Our analysis,
which focuses on frictionless particles, applies {\it both} to suspensions and
inertial flows of hard particles. We compare our predictions with the empirical
literature, as well as with novel numerical data. Overall we find a very good
agreement between theory and observations, except for frictional inertial flows
whose scaling properties clearly differ from frictionless systems. For
over-damped flows, more observations are needed to decide if friction is a
relevant perturbation or not. Our analysis makes several new predictions on
microscopic dynamical quantities that should be accessible experimentally.",1410.3535v3
2014-10-22,Landau damping in the Kuramoto model,"We consider the Kuramoto model of globally coupled phase oscillators in its
continuum limit, with individual frequencies drawn from a distribution with
density of class $C^n$ ($n\geq 4$). A criterion for linear stability of the
uniform stationary state is established which, for basic examples of frequency
distributions, is equivalent to the standard condition on the coupling strength
in the literature. We prove that, under this criterion, the Kuramoto order
parameter, when evolved under the full nonlinear dynamics, asymptotically
vanishes (with polynomial rate $n$) for every trajectory issued from
sufficiently small $C^n$ perturbation. The proof uses techniques from the
Analysis of PDEs and closely follows recent proofs of the nonlinear Landau
damping in the Vlasov equation and Vlasov-HMF model.",1410.6006v1
2014-10-30,Global Solutions to the Gas-Vacuum Interface Problem of Isentropic Compressible Inviscid Flows with Damping in Spherically Symmetric Motions and Physical Vacuum,"For the physical vacuum free boundary problem with the sound speed being
$C^{{1}/{2}}$-H$\ddot{\rm o}$lder continuous near vacuum boundaries of the
three-dimensional compressible Euler equations with damping, the global
existence of spherically symmetric smooth solutions is proved, which are shown
to converge to Barenblatt self-similar solutions of the porous media equation
with the same total masses when initial data are small perturbations of
Barenblatt solutions. The pointwise convergence with a rate of density, the
convergence rate of velocity in supreme norm and the precise expanding rate of
physical vacuum boundaries are also given by constructing nonlinear functionals
with space-time weights featuring the behavior of solutions in large time and
near the vacuum boundary and the center of symmetry, the nonlinear energy
estimates and elliptic estimates.",1410.8471v1
2014-11-03,Monami as an oscillatory hydrodynamic instability in a submerged sea grass bed,"The onset of monami ~-- the synchronous waving of sea grass beds driven by a
steady flow -- is modeled as a linear instability of the flow. Unlike previous
works, our model considers the drag exerted by the grass in establishing the
steady flow profile, and in damping out perturbations to it. We find two
distinct modes of instability, which we label Mode 1 and Mode 2. Mode 1 is
closely related to Kelvin-Helmholtz instability modified by vegetation drag,
whereas Mode 2 is unrelated to Kelvin-Helmholtz and arises from an interaction
between the flow in the vegetated and unvegetated layers. The vegetation
damping, according to our model, leads to a finite threshold flow for both
these modes. Experimental observations for the onset and frequency of waving
compare well with model predictions for the instability onset criteria and the
imaginary part of the complex growth rate respectively, but experiments lie in
a parameter regime where the two modes can not be distinguished. % The
inclusion of vegetation drag differentiates our mechanism from the previous
linear stability analyses of monami.",1411.0365v2
2014-11-12,Dependence of the Efficiency of Spin Hall Torque on the Transparency of Pt-Ferromagnetic Layer Interfaces,"We report that spin current transport across Pt-ferromagnet (FM) interfaces
is strongly dependent on the type and the thickness of the FM layer and on
post-deposition processing protocols. By employing both harmonic voltage
measurements and spin-torque ferromagnetic resonance measurements, we find that
the efficiency of the Pt spin Hall effect in exerting a damping-like spin
torque on the FM ranges from < 0.05 to > 0.10 under different interfacial
conditions. We also show that the temperature dependence of the spin torque
efficiencies for both the damping-like torque and field-like torque is
dependent upon the details of the Pt-FM interface. The ""internal"" spin Hall
angle of the Pt thin films used in this study, after taking the interfacial
spin transmission factor into account, is estimated to be ~ 0.20. This suggests
that a careful engineering of Pt-FM interfaces can improve the spin-Hall-torque
efficiency of Pt-based spintronic devices.",1411.3379v1
2014-11-13,Transverse dynamical magnetic susceptibilities from regular static density functional theory: Evaluation of damping and g-shifts of spin-excitations,"The dynamical transverse magnetic Kohn-Sham susceptibility calculated within
time-dependent density functional theory shows a fairly linear behavior for a
finite energy window. This observation is used to propose a scheme where the
computation of this quantity is greatly simplified. Regular simulations based
on static density functional theory can be used to extract the dynamical
behavior of the magnetic response function. Besides the ability to calculate
elegantly damping of magnetic excitations, we derive along the way useful
equations giving the main characteristics of these excitations: effective
$g$-factors and the resonance frequencies that can be accessed experimentally
using inelastic scanning tunneling spectroscopy or spin-polarized electron
energy loss spectroscopy.",1411.3630v1
2014-11-17,Decoherence Effects on the Non-locality of Symmetric States,"The observation of the non-local properties of multipartite entangled states
is of great importance for quantum information protocols. Such properties,
however, are fragile and may not be observed in the presence of decoherence
exhibited by practical physical systems. In this work, we investigate the
robustness of the non-locality of symmetric states experiencing phase and
amplitude damping, using suitable Bell inequalities based on an extended
version of Hardy's paradox. We derive thresholds for observing non-locality in
terms of experimental noise parameters, and demonstrate the importance of the
choice of the measurement bases for optimizing the robustness. For $W$ states,
in the phase damping case, we show that this choice can lead to a trade-off
between obtaining a high violation of the non-local test and optimal robustness
thresholds; we also show that in this setting the non-locality of $W$ states is
particularly robust for a large number of qubits. Furthermore, we apply our
techniques to the discrimination of symmetric states belonging to different
entanglement classes, thus illustrating their usefulness for a wide range of
practical quantum information applications.",1411.4489v1
2014-11-22,Quantification of the spin-Hall anti-damping torque with a resonance spectrometer,"We present a simple technique using a cavity-based resonance spectrometer to
quantify the anti-damping torque due to the spin Hall effect. Modification of
ferromagnetic resonance is observed as a function of small DC current in
sub-mm-wide strips of bilayers, consisting of magnetically soft FeGaB and
strong spin-Hall metal Ta. From the detected current-induced linewidth change,
we obtain an effective spin Hall angle of 0.08-0.09 independent of the magnetic
layer thickness. Our results demonstrate that a sensitive resonance
spectrometer can be a general tool to investigate spin Hall effects in various
material systems, even those with vanishingly low conductivity and
magnetoresistance.",1411.6166v1
2014-11-28,Quantifying entanglement of a two-qubit system via measurable and invariant moments of its partially transposed density matrix,"We describe a direct method to determine the negativity of an arbitrary
two-qubit state in experiments. The method is derived by analyzing the relation
between the purity, negativity, and a universal entanglement witness for
two-qubit entanglement. We show how the negativity of a two-qubit state can be
calculated from just three experimentally accessible moments of the partially
transposed density matrix of a two-photon state. Moreover, we show that the
negativity can be given as a function of only six invariants, which are linear
combinations of nine invariants from the complete set of 21 fundamental and
independent two-qubit invariants. We analyze the relation between these moments
and the concurrence for some classes of two-qubit states (including the X
states, as well as pure states affected by the amplitude-damping and
phase-damping channels). We also discuss the possibility of using the universal
entanglement witness as an entanglement measure for various classes of
two-qubit states. Moreover, we analyze how noise affects the estimation of
entanglement via this witness.",1411.7977v2
2014-12-05,Adaptive Damping and Mean Removal for the Generalized Approximate Message Passing Algorithm,"The generalized approximate message passing (GAMP) algorithm is an efficient
method of MAP or approximate-MMSE estimation of $x$ observed from a noisy
version of the transform coefficients $z = Ax$. In fact, for large zero-mean
i.i.d sub-Gaussian $A$, GAMP is characterized by a state evolution whose fixed
points, when unique, are optimal. For generic $A$, however, GAMP may diverge.
In this paper, we propose adaptive damping and mean-removal strategies that aim
to prevent divergence. Numerical results demonstrate significantly enhanced
robustness to non-zero-mean, rank-deficient, column-correlated, and
ill-conditioned $A$.",1412.2005v1
2014-12-14,An adaptive selective frequency damping method,"The selective frequency damping (SFD) method is an alternative to classical
Newton's method to obtain unstable steady-state solutions of dynamical systems.
However this method has two main limitations: it does not converge for
arbitrary control parameters; and when it does converge, the time necessary to
reach the steady-state solution may be very long. In this paper we present an
adaptive algorithm to address these two issues. We show that by evaluating the
dominant eigenvalue of a ""partially converged"" steady flow, we can select a
control coefficient and a filter width that ensure an optimum convergence of
the SFD method. We apply this adaptive method to several classical test cases
of computational fluid dynamics and we show that a steady-state solution can be
obtained without any a priori knowledge of the flow stability properties.",1412.4372v1
2014-12-23,Photoacoustic elastic oscillation and characterization,"Photoacoustic imaging and sensing have been studied extensively to probe the
optical absorption of biological tissue in multiple scales ranging from large
organs to small molecules. However, its elastic oscillation characterization is
rarely studied and has been an untapped area to be explored. In literature,
photoacoustic signal induced by pulsed laser is commonly modelled as a bipolar
""N-shape"" pulse from an optical absorber. In this paper, the photoacoustic
damped oscillation is predicted and modelled by an equivalent mass-spring
system by treating the optical absorber as an elastic oscillator. The
photoacoustic simulation incorporating the proposed oscillation model shows
better agreement with the measured signal from an elastic phantom, than
conventional photoacoustic simulation model. More interestingly, the
photoacoustic damping oscillation effect could potentially be a useful
characterization approach to evaluate biological tissue's mechanical properties
in terms of relaxation time, peak number and ratio beyond optical absorption
only, which is experimentally demonstrated in this paper.",1412.7284v1
2015-01-08,Landau Damping of Geodesic Acoustic Mode in Toroidally Rotating Tokamaks,"Geodesic acoustic mode (GAM) is analyzed by using modified gyro-kinetic (MGK)
equation applicable to low-frequency microinstabilities in a rotating
axisymmetric plasma. Dispersion relation of GAM in the presence of arbitrary
Mach number is analytically derived. Toroidal rotation plays the same effects
on the GAM regardless of the orientation of equilibrium flow. It is shown that
the toroidal Mach number $M$ increases the GAM frequency and dramatically
decreases the Landau damping rate. The valid of classical gyro-kinetic (CGK)
equation is also examined. For zero electron temperature, CGK is identical with
MGK. For non-zero electron temperature, CGK gives the same real frequency of
GAM as MGK but induces an instability with a growth rate proportional to
$M^3/q$, where $q$ is the safety factor.",1501.01750v2
2015-01-17,Applications of quantum cryptographic switch: Various tasks related to controlled quantum communication can be performed using Bell states and permutation of particles,"Recently, several aspects of controlled quantum communication (e.g.,
bidirectional controlled state teleportation, controlled quantum secure direct
communication, controlled quantum dialogue, etc.) have been studied using
$n$-qubit ($n\geq3$) entanglement. Specially, a large number of schemes for
bidirectional controlled state teleportation are proposed using $m$-qubit
entanglement ($m\in\{5,6,7\}$). Here, we propose a set of protocols to
illustrate that it is possible to realize all these tasks related to controlled
quantum communication using only Bell states and permutation of particles
(PoP). As the generation and maintenance of a Bell state is much easier than a
multi-partite entanglement, the proposed strategy has a clear advantage over
the existing proposals. Further, it is shown that all the schemes proposed here
may be viewed as applications of the concept of quantum cryptographic switch
which was recently introduced by some of us. The performances of the proposed
protocols as subjected to the amplitude damping and phase damping noise on the
channels are also discussed.",1501.04187v1
2015-02-06,pQCD approach to Charmonium regeneration in QGP at the LHC,"We analyze the applicability of perturbative QCD (pQCD) approach to the issue
of $J/\psi$ recombination at the Large Hadron Collider (LHC), and calculate the
recombination cross section for $c\bar{c}$ recombination to form $J/\psi$ as a
function of temperature. The charmonium wavefunction is obtained by employing a
temperature dependent phenomenological potential between the $c\bar{c}$ pair.
The temperature dependent formation time of charmonium is also employed in the
current work. A set of coupled rate equations is established which incorporates
color screening, gluonic dissociation, collisional damping and recombination of
uncorrelated $c\bar{c}$ pair in the quark-gluon plasma (QGP) medium. The final
$J/\psi$ suppression, thus determined as a function of centrality is compared
with the ALICE experimental data at both mid and forward rapidity and CMS
experimental data at mid rapidity obtained from the Large Hadron Collider (LHC)
at center of mass energy $\sqrt{s_{NN}} = 2.76$ TeV.
  Keywords : Color screening, Recombination, Gluonic dissociation, Collisional
damping, Survival probability, pQCD, Charmonium
  PACS numbers : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa",1502.01790v2
2015-02-06,"Biological control via ""ecological"" damping: An approach that attenuates non-target effects","In this work we develop and analyze a mathematical model of biological
control to prevent or attenuate the explosive increase of an invasive species
population in a three-species food chain. We allow for finite time blow-up in
the model as a mathematical construct to mimic the explosive increase in
population, enabling the species to reach ""disastrous"" levels, in a finite
time. We next propose various controls to drive down the invasive population
growth and, in certain cases, eliminate blow-up. The controls avoid chemical
treatments and/or natural enemy introduction, thus eliminating various
non-target effects associated with such classical methods. We refer to these
new controls as ""ecological damping"", as their inclusion dampens the invasive
species population growth. Further, we improve prior results on the regularity
and Turing instability of the three-species model that were derived in earlier
work. Lastly, we confirm the existence of spatio-temporal chaos.",1502.02010v1
2015-02-11,On the mass determination in liquid utilizing measurement of only the fundamental flexural resonances of the micro-/nanomechanical based mass sensors,"Micro-/nanomechanical mass sensors are capable to quantitatively determine
molecule mass from only first three (two) measured cantilever (bridge) resonant
frequencies. However, in liquid solutions that are relevant to most of the
biological systems, the mass determination is challenging because the Q-factor
due to fluid damping decreases and, as a result, usually just the fundamental
resonant frequencies can be correctly identified. Moreover, for higher modes
the resonance coupling, noise and internal damping have been proven to strongly
affect the measured resonant frequencies and, correspondingly, the accuracy of
the estimated masses. Here, we derive the easy accessible expressions enabling
the quantitative mass(es) determination just from the fundamental resonant
frequencies of the micro/nanomechanical mass sensor under intentionally applied
axial tension, which can be easily created and controlled by the electrostatic
or magnetostatic forces. We also show that typically achievable force
resolution has a negligible impact on the mass determination and the mass
sensitivity.",1502.03232v1
2015-02-13,A Dynamical Model of Plasma Turbulence in the Solar Wind,"A dynamical approach, rather than the usual statistical approach, is taken to
explore the physical mechanisms underlying the nonlinear transfer of energy,
the damping of the turbulent fluctuations, and the development of coherent
structures in kinetic plasma turbulence. It is argued that the linear and
nonlinear dynamics of Alfven waves are responsible, at a very fundamental
level, for some of the key qualitative features of plasma turbulence that
distinguish it from hydrodynamic turbulence, including the anisotropic cascade
of energy and the development of current sheets at small scales. The first
dynamical model of kinetic turbulence in the weakly collisional solar wind
plasma that combines self-consistently the physics of Alfven waves with the
development of small-scale current sheets is presented and its physical
implications are discussed. This model leads to a simplified perspective on the
nature of turbulence in a weakly collisional plasma: the nonlinear interactions
responsible for the turbulent cascade of energy and the formation of current
sheets are essentially fluid in nature, while the collisionless damping of the
turbulent fluctuations and the energy injection by kinetic instabilities are
essentially kinetic in nature.",1502.04109v1
2015-03-19,Vertical Oscillations of Fluid and Stellar Disks,"A satellite galaxy or dark matter subhalo that passes through a stellar disk
may excite coherent oscillations in the disk perpendicular to its plane. We
determine the properties of these modes for various self-gravitating plane
symmetric systems (Spitzer sheets) using the matrix method of Kalnajs. In
particular, we find an infinite series of modes for the case of a barotropic
fluid. In general, for a collisionless system, there is a double series of
modes, which include normal modes and/or Landau-damped oscillations depending
on the phase space distribution function of the stars. Even Landau-damped
oscillations may decay slowly enough to persist for several hundred Myr. We
discuss the implications of these results for the recently discovered vertical
perturbations in the kinematics of solar neighborhood stars and for broader
questions surrounding secular phenomena such as spiral structure in disk
galaxies.",1503.05741v1
2015-03-24,Linearized nonequilibrium dynamics in nonconformal plasma,"We investigate the behaviour of the lowest nonhydrodynamic modes in a class
of holographic models which exhibit an equation of state closely mimicking the
one determined from lattice QCD. We calculate the lowest quasinormal mode
frequencies for a range of scalar self-interaction potentials and find that the
damping of the quasinormal modes at the phase transition/crossover falls off by
a factor of around two from conformality after factoring out standard conformal
temperature dependence. The damping encoded in the imaginary part of the
frequencies turns out to be correlated with the speed of sound and is basically
independent of the UV details of the model. We also find that the dynamics of
the nonhydrodynamic degrees of freedom remains ultralocal, even to a higher
degree, as we deviate from conformality. These results indicate that the role
of nonhydrodynamic degrees of freedom in the vicinity of the crossover
transition may be enhanced.",1503.07149v1
2015-03-25,"The Conversion of CESR to Operate as the Test Accelerator, CesrTA, Part 1: Overview","Cornell's electron/positron storage ring (CESR) was modified over a series of
accelerator shutdowns beginning in May 2008, which substantially improves its
capability for research and development for particle accelerators. CESR's
energy span from 1.8 to 5.6 GeV with both electrons and positrons makes it
ideal for the study of a wide spectrum of accelerator physics issues and
instrumentation related to present light sources and future lepton damping
rings. Additionally a number of these are also relevant for the beam physics of
proton accelerators. This paper outlines the motivation, design and conversion
of CESR to a test accelerator, CesrTA, enhanced to study such subjects as low
emittance tuning methods, electron cloud (EC) effects, intra-beam scattering,
fast ion instabilities as well as general improvements to beam instrumentation.
While the initial studies of CesrTA focussed on questions related to the
International Linear Collider (ILC) damping ring design, CesrTA is a very
flexible storage ring, capable of studying a wide range of accelerator physics
and instrumentation questions. This paper contains the outline and the basis
for a set of papers documenting the reconfiguration of the storage ring and the
associated instrumentation required for the studies described above. Further
details may be found in these papers.",1503.07451v2
2015-04-10,"Fission barrier, damping of shell correction and neutron emission in the fission of A$\sim$200","Decay of $^{210}$Po compound nucleus formed in light and heavy-ion induced
fusion reactions has been analyzed simultaneously using a consistent
prescription for fission barrier and nuclear level density incorporating shell
correction and its damping with excitation energy. Good description of all the
excitation functions have been achieved with a fission barrier of 21.9 $\pm$
0.2 MeV. For this barrier height, the predicted statistical pre-fission
neutrons in heavy-ion fusion-fission are much smaller than the experimental
values, implying the presence of dynamical neutrons due to dissipation even at
these low excitation energies ($\sim$ 50~MeV) in the mass region A $\sim$ 200.
When only heavy-ion induced fission excitation functions and the pre-fission
neutron multiplicities are included in the fits, the deduced best fit fission
barrier depends on the assumed fission delay time during which dynamical
neutrons can be emitted. A fission delay of (0.8 $\pm$ 0.1 )$\times 10^{-19}$ s
has been estimated corresponding to the above fission barrier height assuming
that the entire excess neutrons over and above the statistical model
predictions are due to the dynamics. The present observation has implication on
the study of fission time scale/ nuclear viscosity using neutron emission as a
probe.",1504.02599v1
2015-04-10,Enhancement of the Anti-Damping Spin Torque Efficacy of Platinum by Interface Modification,"We report a strong enhancement of the efficacy of the spin Hall effect (SHE)
of Pt for exerting anti-damping spin torque on an adjacent ferromagnetic layer
by the insertion of $\approx$ 0.5 nm layer of Hf between a Pt film and a thin,
< 2 nm, Fe$_{60}$Co$_{20}$B$_{20}$ ferromagnetic layer. This enhancement is
quantified by measurement of the switching current density when the
ferromagnetic layer is the free electrode in a magnetic tunnel junction. The
results are explained as the suppression of spin pumping through a substantial
decrease in the effective spin-mixing conductance of the interface, but without
a concomitant reduction of the ferromagnet\' s absorption of the SHE generated
spin current.",1504.02806v1
2015-04-21,Effect of assortative mixing in the second-order Kuramoto model,"In this paper we analyze the second-order Kuramoto model presenting a
positive correlation between the heterogeneity of the connections and the
natural frequencies in scale-free networks. We numerically show that
discontinuous transitions emerge not just in disassortative but also in
assortative networks, in contrast with the first-order model. We also find that
the effect of assortativity on network synchronization can be compensated by
adjusting the phase damping. Our results show that it is possible to control
collective behavior of damped Kuramoto oscillators by tuning the network
structure or by adjusting the dissipation related to the phases movement.",1504.05447v1
2015-04-27,Controlled merging and annihilation of localized dissipative structures in an AC-driven damped nonlinear Schrödinger system,"We report studies of controlled interactions of localized dissipative
structures in a system described by the AC-driven damped nonlinear
Schr\""odinger equation. Extensive numerical simulations reveal a diversity of
interaction scenarios that are governed by the properties of the system driver.
In our experiments, performed with a nonlinear optical Kerr resonator, the
phase profile of the driver is used to induce interactions on demand. We
observe both merging and annihilation of localized structures, i.e.,
interactions governed by the dissipative, out-of-equilibrium nature of the
system.",1504.07231v1
2015-04-29,Wide-Range Tunable Dynamic Property of Carbon Nanotube-Based Fibers,"Carbon nanotube (CNT) fiber is formed by assembling millions of individual
tubes. The assembly feature provides the fiber with rich interface structures
and thus various ways of energy dissipation, as reflected by the non-zero loss
tangent (>0.028--0.045) at low vibration frequencies. A fiber containing
entangled CNTs possesses higher loss tangents than a fiber spun from aligned
CNTs. Liquid densification and polymer infiltration, the two common ways to
increase the interfacial friction and thus the fiber's tensile strength and
modulus, are found to efficiently reduce the damping coefficient. This is
because the sliding tendency between CNT bundles can also be well suppressed by
the high packing density and the formation of covalent polymer cross-links
within the fiber. The CNT/bismaleimide composite fiber exhibited the smallest
loss tangent, nearly as the same as that of carbon fibers. At a higher level of
the assembly structure, namely a multi-ply CNT yarn, the inter-fiber friction
and sliding tendency obviously influence the yarn's damping performance, and
the loss tangent can be tuned within a wide range, as similar to carbon fibers,
nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow
new applications ranging from high quality factor materials to dissipative
systems.",1504.07881v1
2015-05-10,Effects of electron drift on the collisionless damping of kinetic Alfvén waves in the solar wind,"The collisionless dissipation of anisotropic Alfv\'enic turbulence is a
promising candidate to solve the solar wind heating problem. Extensive studies
examined the kinetic properties of Alfv\'en waves in simple Maxwellian or
bi-Maxwellian plasmas. However, the observed electron velocity distribution
functions in the solar wind are more complex. In this study, we analyze the
properties of kinetic Alfv\'en waves in a plasma with two drifting electron
populations. We numerically solve the linearized Maxwell-Vlasov equations and
find that the damping rate and the proton-electron energy partition for kinetic
Alfv\'en waves are significantly modified in such plasmas, compared to plasmas
without electron drifts. We suggest that electron drift is an important factor
to take into account when considering the dissipation of Alfv\'enic turbulence
in the solar wind or other $\beta \sim 1$ astrophysical plasmas.",1505.02328v1
2015-05-13,The effect of a reversible shear transformation on plastic deformation of an amorphous solid,"Molecular dynamics simulations are performed to investigate the plastic
response of a model glass to a local shear transformation in a quiescent
system. The deformation of the material is induced by a spherical inclusion
that is gradually strained into an ellipsoid of the same volume and then
reverted back into the sphere. We show that the number of cage-breaking events
increases with increasing strain amplitude of the shear transformation. The
results of numerical simulations indicate that the density of cage jumps is
larger in the cases of weak damping or slow shear transformation. Remarkably,
we also found that, for a given strain amplitude, the peak value of the density
profiles is a function of the ratio of the damping coefficient and the time
scale of the shear transformation.",1505.03488v1
2015-05-14,Local large deviations principle for occupation measures of the damped nonlinear wave equation perturbed by a white noise,"We consider the damped nonlinear wave (NLW) equation driven by a spatially
regular white noise. Assuming that the noise is non-degenerate in all Fourier
modes, we establish a large deviations principle (LDP) for the occupation
measures of the trajectories. The lower bound in the LDP is of a local type,
which is related to the weakly dissipative nature of the equation and seems to
be new in the context of randomly forced PDE's. The proof is based on an
extension of methods developed in \cite{JNPS-2012} and \cite{JNPS-2014} in the
case of kick forced dissipative PDE's with parabolic regularisation property
such as, for example, the Navier-Stokes system and the complex Ginzburg-Landau
equations. We also show that a high concentration towards the stationary
measure is impossible, by proving that the rate function that governs the LDP
cannot have the trivial form (i.e., vanish on the stationary measure and be
infinite elsewhere).",1505.03686v1
2015-05-19,Undamped nonequilibrium dynamics of a nondegenerate Bose gas in a 3D isotropic trap,"We investigate anomalous damping of the monopole mode of a non-degenerate 3D
Bose gas under isotropic harmonic confinement as recently reported by the JILA
TOP trap experiment [D. S. Lob- ser, A. E. S. Barentine, E. A. Cornell, and H.
J. Lewandowski (in preparation)]. Given a realistic confining potential, we
develop a model for studying collective modes that includes the effects of
anharmonic corrections to a harmonic potential. By studying the influence of
these trap anharmonicities throughout a range of temperatures and collisional
regimes, we find that the damping is caused by the joint mechanisms of
dephasing and collisional relaxation. Furthermore, the model is complimented by
Monte Carlo simulations which are in fair agreement with data from the JILA
experiment.",1505.04841v1
2015-05-21,Control and stabilization of degenerate wave equations,"We study a wave equation in one space dimension with a general diffusion
coefficient which degenerates on part of the boundary. Degeneracy is measured
by a real parameter $\mu_a>0$. We establish observability inequalities for
weakly (when $\mu_a \in [0,1[$) as well as strongly (when $\mu_a \in [1,2[$)
degenerate equations. We also prove a negative result when the diffusion
coefficient degenerates too violently (i.e. when $\mu_a>2$) and the blow-up of
the observability time when $\mu_a$ converges to $2$ from below. Thus, using
the HUM method we deduce the exact controllability of the corresponding
degenerate control problem when $\mu_a \in [0,2[$. We conclude the paper by
studying the boundary stabilization of the degenerate linearly damped wave
equation and show that a suitable boundary feedback stabilizes the system
exponentially. We extend this stability analysis to the degenerate nonlinearly
boundary damped wave equation, for an arbitrarily growing nonlinear feedback
close to the origin. This analysis proves that the degeneracy does not affect
the optimal energy decay rates at large time. We apply the optimal-weight
convexity method of \cite{alaamo2005, alajde2010} together with the results of
the previous section, to perform this stability analysis.",1505.05720v1
2015-05-23,"Existence, blow-up and exponential decay of solutions for a porous-elastic system with damping and source terms","In this paper we consider a porous-elastic system consisting of nonlinear
boundary/interior damping and nonlinear boundary/interior sources. Our interest
lies in the theoretical understanding of the existence, finite time blow-up of
solutions and their exponential decay using non-trivial adaptations of
well-known techniques. First, we apply the conventional Faedo-Galerkin method
with standard arguments of density on the regularity of initial conditions to
establish two local existence theorems of weak solutions. Moreover, we detail
the uniqueness result in some specific cases. In the second theme, we prove
that any weak solution possessing negative initial energy has the latent
blow-up in finite time. Finally, we obtain the so-called exponential decay
estimates for the global solution under the construction of a suitable Lyapunov
functional. In order to corroborate our theoretical decay, a numerical example
is provided.",1505.06373v2
2015-05-26,Quantum Particle Motion in Absorbing Harmonic Trap,"The motivation of this work is to get an additional insight into the
irreversible energy dissipation on the quantum level. The presented examination
procedure is based on the Feynman path integral method that is applied and
widened towards the calculation of the kernel of a quantum mechanical damped
oscillator. Here, it is shown that the energy loss of the oscillator can be
generated by the introduced harmonic complex potential. The related damped wave
function, however, does not pertain to the probability meaning as it is usual
in the case of complex absorbing potentials. This decrease of the wave function
is evaluated, moreover, the energy dissipation and the measure the
irreversibility are expressed.",1505.06874v1
2015-06-03,Non-uniqueness of Admissible Weak Solutions to Compressible Euler Systems with Source Terms,"We consider admissible weak solutions to the compressible Euler system with
source terms, which include rotating shallow water system and the Euler system
with damping as special examples. In the case of anti-symmetric sources such as
rotations, for general piecewise Lipschitz initial densities and some suitably
constructed initial momentum, we obtain infinitely many global admissible weak
solutions. Furthermore, we construct a class of finite-states admissible weak
solutions to the Euler system with anti-symmetric sources. Under the additional
smallness assumption on the initial densities, we also obtain multiple
global-in-time admissible weak solutions for more general sources including
damping. The basic framework are based on the convex integration method
developed by De~Lellis and Sz\'{e}kelyhidi \cite{dLSz1,dLSz2} for the Euler
system. One of the main ingredients of this paper is the construction of
specified localized plane wave perturbations which are compatible with a given
source term.",1506.01103v1
2015-06-03,The effect of perpendicular electric field on Temperature-induced plasmon excitations for intrinsic silicene,"We use the tight-binding model and the random-phase approximation to
investigate the intrinsic plasmon in silicene. At finite temperatures, an
undamped plasmon is generated from the interplay between the intraband and the
interband-gap transitions. The extent of the plasmon existence range in terms
of momentum and temperature, which is dependent on the size of
single-particle-excitation gap, is further tuned by applying a perpendicular
electric field. The plasmon becomes damped in the interband-excitation region.
A low damped zone is created by the field-induced spin split. The
field-dependent plasmon spectrum shows a strong tunability in plasmon intensity
and spectral bandwidth. This could make silicene a very suitable candidate for
plasmonic applications.",1506.01140v1
2015-06-09,Transport Barrier generation at the interface of regions with different zonal flows dynamics,"A novel and generic understanding of spontaneous generation of transport
barriers and zonation regimes in turbulent self-organization is presented. It
associates the barrier onset to the development of a spectral gap between large
scale flows and turbulence modes leading to a zonation regime. A robust barrier
builds-up at the interface of such a region and a neighboring one with reduced
zonal flow generation. This more complex and generic transition paradigm could
fit the numerous and sometimes conflicting observations as in fusion plasma
experiments. Barrier relaxation by bursts of turbulence regenerate the zonal
flows that are eroded by viscous (collisional-like) damping. The duration of
the quiescent phase between the quasi-periodic relaxation events is governed by
this damping process, hence the barrier collision frequency for fusion plasmas.",1506.02942v2
2015-06-11,Fighting noise with noise in realistic quantum teleportation,"We investigate how the efficiency of the quantum teleportation protocol is
affected when the qubits involved in the protocol are subjected to noise or
decoherence. We study all types of noise usually encountered in real world
implementations of quantum communication protocols, namely, the bit flip, phase
flip (phase damping), depolarizing, and amplitude damping noise. Several
realistic scenarios are studied in which a part or all of the qubits employed
in the execution of the quantum teleportation protocol are subjected to the
same or different types of noise. We find noise scenarios not yet known in
which more noise or less entanglement lead to more efficiency. Furthermore, we
show that if noise is unavoidable it is better to subject the qubits to
different noise channels in order to obtain an increase in the efficiency of
the protocol.",1506.03803v2
2015-07-08,Low-Dimensional Stochastic Projected Gross-Pitaevskii Equation,"We present reduced-dimensional stochastic projected Gross-Pitaevskii
equations describing regimes of confinement and temperature where a 1D or 2D
superfluid is immersed in a 3D thermal cloud. The projection formalism provides
both a formally rigorous and physically natural way to effect the dimensional
reduction. The 3D form of the number-damping (growth) terms is unchanged by the
dimensional reduction. Projection of the energy-damping (scattering) terms
leads to modified stochastic equations of motion describing energy exchange
with the thermal reservoir. The regime of validity of the dimensional reduction
is investigated via variational analysis. Paying particular attention to 1D, we
validate our variational treatment by comparing numerical simulations of a
trapped oblate system in 3D with the 1D theory, and establish a consistent
choice of cutoff for the 1D theory. We briefly discuss the scenario involving
two-components with different degeneracy, suggesting that a wider regime of
validity exists for systems in contact with a buffer-gas reservoir.",1507.02023v2
2015-07-08,Low-emittance storage rings,"The effects of synchrotron radiation on particle motion in storage rings are
discussed. In the absence of radiation, particle motion is symplectic, and the
beam emittances are conserved. The inclusion of radiation effects in a
classical approximation leads to emittance damping: expressions for the damping
times are derived. Then, it is shown that quantum radiation effects lead to
excitation of the beam emittances. General expressions for the equilibrium
longitudinal and horizontal (natural) emittances are derived. The impact of
lattice design on the natural emittance is discussed, with particular attention
to the special cases of FODO, achromat, and TME style lattices. Finally, the
effects of betatron coupling and vertical dispersion (generated by magnet
alignment and lattice tuning errors) on the vertical emittance are considered.",1507.02213v1
2015-07-09,Controlling the stability of steady states in continuous variable quantum systems,"For the paradigmatic case of the damped quantum harmonic oscillator we
present two measurement-based feedback schemes to control the stability of its
fixed point. The first scheme feeds back a Pyragas-like time-delayed reference
signal and the second uses a predetermined instead of time-delayed reference
signal. We show that both schemes can reverse the effect of the damping by
turning the stable fixed point into an unstable one. Finally, by taking the
classical limit $\hbar\rightarrow0$ we explicitly distinguish between inherent
quantum effects and effects, which would be also present in a classical noisy
feedback loop. In particular, we point out that the correct description of a
classical particle conditioned on a noisy measurement record is given by a
non-linear stochastic Fokker-Planck equation and not a Langevin equation, which
has observable consequences on average as soon as feedback is considered.",1507.02538v1
2015-07-14,WIMP isocurvature perturbation and small scale structure,"The adiabatic perturbation of dark matter is damped during the kinetic
decoupling due to the collision with relativistic component on sub-horizon
scales. However the isocurvature part is free from damping and could be large
enough to make a substantial contribution to the formation of small scale
structure. We explicitly study the weakly interacting massive particles as dark
matter with an early mater dominated period before radiation domination and
show that the isocurvature perturbation is generated during the phase
transition and leaves imprint in the observable signatures for small scale
structure.",1507.03871v2
2015-07-17,Pairwise quantum discord for a symmetric multi-qubit system in different types of noisy channels,"We study the pairwise quantum discord (QD) for a symmetric multi-qubit system
in different types of noisy channels, such as phase-flip, amplitude damping,
phase-damping, and depolarizing channels. Using the QD and geometric measure of
quantum discord (GMQD) to quantify quantum correlations, some analytical or
numerical results are presented. The results show that, the dynamics of the
pairwise QD is related to the number of spin particles $N$ as well as initial
parameter $\theta$ of the one-axis twisting collective state. With the number
of spin particles $N$ increasing, the amount of the pairwise QD increases.
However, when the amount of the pairwise QD arrives at a stable maximal value,
the pairwise QD is independence of the number of spin particles $N$ increasing.
The behavior of the pairwise QD is symmetrical during a period $0\leq \theta
\leq 2\pi$. Moreover, we compare the pairwise QD dynamics with the GMQD for a
symmetric multi-qubit system in different types of noisy channels.",1507.04826v1
2015-07-20,Landau damping effects in the synchronization of conformist and contrarian oscillators,"Two decades ago, a phenomenon resembling Landau damping was described in the
synchronization of globally coupled oscillators: the evidence of a regime where
the order parameter decays when linear theory predicts neutral stability for
the incoherent state. We here show that such an effect is far more generic, as
soon as phase oscillators couple to their mean field according to their natural
frequencies, being then grouped into two distinct populations of conformists
and contrarians. We report the analytical solution of this latter situation,
which allows determining the critical coupling strength and the stability of
the incoherent state, together with extensive numerical simulations that fully
support all theoretical predictions. The relevance of our results is discussed
in relationship to collective phenomena occurring in polarized social systems.",1507.05383v1
2015-07-28,Attractors for Strongly Damped Wave Equations with Nonlinear Hyperbolic Dynamic Boundary Conditions,"We establish the well-posedness of a strongly damped semilinear wave equation
equipped with nonlinear hyperbolic dynamic boundary conditions. Results are
carried out with the presence of a parameter distinguishing whether the
underlying operator is analytic, $\alpha>0$, or only of Gevrey class,
$\alpha=0$. We establish the existence of a global attractor for each
$\alpha\in[0,1],$ and we show that the family of global attractors is
upper-semicontinuous as $\alpha\rightarrow0.$ Furthermore, for each
$\alpha\in[0,1]$, we show the existence of a weak exponential attractor. A weak
exponential attractor is a finite dimensional compact set in the weak topology
of the phase space. This result insures the corresponding global attractor also
possess finite fractal dimension in the weak topology; moreover, the dimension
is independent of the perturbation parameter $\alpha$. In both settings,
attractors are found under minimal assumptions on the nonlinear terms.",1507.07971v1
2015-07-29,Neimark--Sacker bifurcation and evidence of chaos in a discrete dynamical model of walkers,"Bouncing droplets on a vibrating fluid bath can exhibit wave-particle
behavior, such as being propelled by interacting with its own wave field. These
droplets seem to walk across the bath, and thus are dubbed walkers. Experiments
have shown that walkers can exhibit exotic dynamical behavior indicative of
chaos. While the integro-differential models developed for these systems agree
well with the experiments, they are difficult to analyze mathematically. In
recent years, simpler discrete dynamical models have been derived and studied
numerically. The numerical simulations of these models show evidence of exotic
dynamics such as period doubling bifurcations, Neimark--Sacker (N--S)
bifurcations, and even chaos. For example, in [Gilet, PRE 2014], based on
simulations Gilet conjectured the existence of a supercritical N-S bifurcation
as the damping factor in his one-dimensional path model. We prove Gilet's
conjecture and more; in fact, both supercritical and subcritical (N-S)
bifurcations are produced by separately varying the damping factor and
wave-particle coupling for all eigenmode shapes. Then we compare our
theoretical results with some previous and new numerical simulations, and find
complete qualitative agreement. Furthermore, evidence of chaos is shown by
numerically studying a global bifurcation.",1507.08057v2
2015-07-30,Beliaev damping of the Goldstone mode in atomic Fermi superfluids,"Beliaev damping in a superfluid is the decay of a collective excitation into
two lower frequency collective excitations; it represents the only decay mode
for a bosonic collective excitation in a superfluid at T = 0. The standard
treatment for this decay assumes a linear spectrum, which in turn implies that
the final state momenta must be collinear to the initial state. We extend this
treatment, showing that the inclusion of a gradient term in the Hamiltonian
yields a realistic spectrum for the bosonic excitations; we then derive a
formula for the decay rate of such excitations, and show that even moderate
nonlinearities in the spectrum can yield substantial deviations from the
standard result. We apply our result to an attractive Fermi gas in the BCS-BEC
crossover: here the low-energy bosonic collective excitations are density
oscillations driven by the phase of the pairing order field. These collective
excitations, which are gapless modes as a consequence of the Goldstone
mechanism, have a spectrum which is well established both theoretically and
experimentally, and whose linewidth, we show, is determined at low temperatures
by the Beliaev decay mechanism.",1507.08535v1
2015-08-09,"Small quantum absorption refrigerator in the transient regime: time scales, enhanced cooling and entanglement","A small quantum absorption refrigerator, consisting of three qubits, is
discussed in the transient regime. We discuss time scales for coherent
dynamics, damping, and approach to the steady state, and we study cooling and
entanglement. We observe that cooling can be enhanced in the transient regime,
in the sense that lower temperatures can be achieved compared to the
steady-state regime. This is a consequence of coherent dynamics, but can occur
even when this dynamics is strongly damped by the dissipative thermal
environment, and we note that precise control over couplings or timing is not
needed to achieve enhanced cooling. We also show that the amount of
entanglement present in the refrigerator can be much larger in the transient
regime compared to the steady-state. These results are of relevance to future
implementations of quantum thermal machines.",1508.02025v2
2015-08-13,Hybridization of Higgs modes in a bond-density-wave state in cuprates,"Recently, several groups have reported observations of collective modes of
the charge order present in underdoped cuprates. Motivated by these
experiments, we study theoretically the oscillations of the order parameters,
both in the case of pure charge order, and for charge order coexisting with
superconductivity. Using a hot-spot approximation we find in the coexistence
regime two Higgs modes arising from hybridization of the amplitude oscillations
of the different order parameters. One of them has a minimum frequency that is
within the single particle energy gap and which is a non-monotonic function of
temperature. The other -- high-frequency -- mode is smoothly connected to the
Higgs mode in the single-order-parameter region, but quickly becomes overdamped
in the case of coexistence. We explore an unusual low-energy damping channel
for the collective modes, which relies on the band reconstruction caused by the
coexistence of the two orders. For completeness, we also consider the damping
of the collective modes originating from the nodal quasiparticles. At the end
we discuss some experimental consequences of our results.",1508.03335v1
2015-08-18,Negative nonlinear damping of a graphene mechanical resonator,"We experimentally investigate the nonlinear response of a multilayer graphene
resonator using a superconducting microwave cavity to detect its motion. The
radiation pressure force is used to drive the mechanical resonator in an
optomechanically induced transparency configuration. By varying the amplitudes
of drive and probe tones, the mechanical resonator can be brought into a
nonlinear limit. Using the calibration of the optomechanical coupling, we
quantify the mechanical Duffing nonlinearity. By increasing the drive force, we
observe a decrease in the mechanical dissipation rate at large amplitudes,
suggesting a negative nonlinear damping mechanism in the graphene resonator.
Increasing the optomechanical backaction, we observe a nonlinear regime not
described by a Duffing response that includes new instabilities of the
mechanical response.",1508.04298v1
2015-08-21,Formulation and solutions of fractional continuously variable order mass spring damper systems controlled by viscoelastic and viscous-viscoelastic dampers,"The article presents the formulation and a new approach to find analytic
solutions for fractional continuously variable order dynamic models viz.
Fractional continuously variable order mass-spring damper systems. Here, we use
the viscoelastic and viscous-viscoelastic dampers for describing the damping
nature of the oscillating systems, where the order of fractional derivative
varies continuously. Here, we handle the continuous changing nature of
fractional order derivative for dynamic systems, which has not been studied
yet. By successive iteration method, here we find the solution of fractional
continuously variable order mass-spring damper systems, and then give a close
form solution. We then present and discuss the solutions obtained in the cases
with continuously variable order of damping for this oscillator with graphical
plots.",1508.06202v1
2015-08-25,Simultaneous cooling of coupled mechanical oscillators using whispering gallery mode resonances,"We demonstrate simultaneous center-of-mass cooling of two coupled
oscillators, consisting of a microsphere-cantilever and a tapered optical
fiber. Excitation of a whispering gallery mode (WGM) of the microsphere, via
the evanescent field of the taper, provides a transduction signal that
continuously monitors the relative motion between these two microgram objects
with a sensitivity of 3 pm. The cavity enhanced optical dipole force is used to
provide feedback damping on the motion of the micron-diameter taper, whereas a
piezo stack is used to damp the motion of the much larger (up to $180\,\mu$m in
diameter), heavier (up to $1.5\times 10^{-7}\,$kg) and stiffer
microsphere-cantilever. In each feedback scheme multiple mechanical modes of
each oscillator can be cooled, and mode temperatures below 10 K are reached for
the dominant mode, consistent with limits determined by the measurement noise
of our system. This represents stabilization on the picometer level and is the
first demonstration of using WGM resonances to cool the mechanical modes of
both the WGM resonator and its coupling waveguide.",1508.06217v2
2015-08-31,Damping of a system of linear oscillators using the generalized dry friction,"The problem of damping a system of linear oscillators is considered. The
problem is solved by using a control in the form of dry friction. The motion of
the system under the control is governed by a system of differential equations
with discontinuous right-hand side. A uniqueness and continuity theorem is
proved for the phase flow of this system. Thus, the control in the form of
generalized dry friction defines the motion of the system of oscillators
uniquely.",1508.07775v2
2015-09-02,Smoothing and Global Attractors for the Majda-Biello System on the Torus,"In this paper, we consider the Majda-Biello system, a coupled KdV-type
system, on the torus. In the first part of the paper, it is shown that, given
initial data in a Sobolev space, the difference between the linear and the
nonlinear evolution almost always resides in a smoother space. The smoothing
index depends on number-theoretic properties of the coupling parameter in the
system which control the behavior of the resonant sets. In the second part of
the paper, we consider the forced and damped version of the system and obtain
similar smoothing estimates. These estimates are used to show the existence of
a global attractor in the energy space. We also show that when the damping is
large in relation to the forcing terms, the attractor is trivial.",1509.00776v1
2015-09-07,Non-linear Cosmic Ray propagation close to the acceleration site,"Recent advances on gamma-ray observations from SuperNova Remnants and
Molecular Clouds offer the possibility to study in detail the properties of the
propagation of escaping Cosmic Rays (CR). However, a complete theory for CR
transport outside the acceleration site has not been developed yet. Two
physical processes are thought to be relevant to regulate the transport: the
growth of waves caused by streaming instability, and possible wave damping
mechanisms that reduce the growth of the turbulence. Only a few attempts have
been made so far to incorporate these mechanisms in the theory of CR diffusion.
In this work we present recent advances in this subject. In particular, we show
results obtained by solving the coupled equations for the diffusion of CRs and
the evolution of Alfven waves. We discuss the importance of streaming
instabilities and wave damping in different ISM phases.",1509.02174v1
2015-09-10,Strain-dependent damping in nanomechanical resonators from thin $\mathrm{MoS_2}$ crystals,"We investigate the effect of mechanical strain on the dynamics of thin
$\mathrm{MoS_2}$ nanodrum resonators. Using a piezoelectric crystal,
compressive and tensile biaxial strain is induced in initially flat and buckled
devices. In the flat device, we observe a remarkable strain-dependence of the
resonance line width, while the change in the resonance frequency is relatively
small. In the buckled device, the strain-dependence of the damping is less
pronounced, and a clear hysteresis is observed. The experiment suggests that
geometric imperfections, such as microscopic wrinkles, could play a role in the
strong dissipation observed in nanoresonators fabricated from 2-D materials.",1509.03080v1
2015-09-16,Variational principle for magnetisation dynamics in a temperature gradient,"By applying a variational principle on a magnetic system within the framework
of extended irreversible thermodynamics, we find that the presence of a
temperature gradient in a ferromagnet leads to a generalisation of the
Landau-Lifshitz equation with an additional magnetic induction field
proportional to the temperature gradient. This field modulates the damping of
the magnetic excitation. It can increase or decrease the damping, depending on
the orientation of the magnetisation wave-vector with respect to the
temperature gradient. This variational approach confirms the existence of the
Magnetic Seebeck effect which was derived from thermodynamics and provides a
quantitative estimate of the strength of this effect.",1509.04825v2
2015-10-01,Dilapidation of nonlocal correlations of two qubit states in noisy environment,"Composite quantum systems exhibit non-local correlations. These counter
intuitive correlations form a resource for quantum information processing and
quantum computation. In our previous work on two qubit maximally entangled
mixed states, we observed that entangled states, states that can be used for
quantum teleportaion, states that violate Bell-CHSH inequality and states that
do not admit local hidden variable description is the hierarchy in terms of the
order of nonlocal correlations. In order to establish this hierarchy, in the
present work, we investigate the effect of noise on two quibt states that
exhibit higher order nonlocal correlations. We find that dilapidation of
nonlocal correlations in the presence of noise follow the same hierarchy, that
is, higher order nonlocal correlation disappears for small strength of noise,
where as lower order nonlocal correlations survive strong noisy environment. We
show the results for decoherence due to amplitude damping channel on various
quantum states. However, we observe that same hierarchy is followed by states
undergoing decoherence due to phase damping as well as depolarizing channels.",1510.00119v1
2015-10-01,Production of charged Higgs boson pairs in the $pp \to ppH^{+}H^{-}$ reaction at the LHC and FCC,"We present differential cross sections for the $pp \to ppH^{+}H^{-}$ reaction
via photon-photon fusion with exact kinematics. We show predictions for
$\sqrt{s}$ = 14 TeV (LHC) and at the Future Circular Collider (FCC) for
$\sqrt{s}$ = 100 TeV. The integrated cross section for $\sqrt{s}$ = 14~TeV
(LHC) is about 0.1~fb and about 0.9~fb at the FCC for $\sqrt{s}$ = 100~TeV when
assuming $m_{H^{\pm}} = 150$~GeV. We present distributions in diHiggs boson
invariant mass. The results are compared with those obtained within
equivalent-photon approximation. We discuss also first calculations of cross
section for exclusive diffractive pQCD mechanism with estimated limits on the
$g_{hH^{+}H^{-}}$ coupling constant within 2HDM based on the LHC experimental
data. The diffractive contribution is much smaller than the $\gamma \gamma$
one. Absorption corrections are calculated differentially for various
distributions. In general, they lead to a damping of the cross section. The
damping depends on $M_{H^{+}H^{-}}$ invariant mass and on four-momentum
transfers squared in the proton line. We discuss a possibility to measure the
exclusive production of $H^{\pm}$ bosons.",1510.00171v1
2015-10-05,Universality in antiferromagnetic strange metals,"We propose a theory of metals at the spin-density wave quantum critical point
in spatial dimension $d=2$. We provide a first estimate of the full set of
critical exponents (dynamical exponent $z=2.13$, correlation length $\nu
=1.02$, spin susceptibility $\gamma = 0.96$, electronic non-Fermi liquid
$\eta^f_\tau = 0.53$, spin-wave Landau damping $\eta^b_\tau = 1.06$), which
determine the universal power-laws in thermodynamics and response functions in
the quantum-critical regime relevant for experiments in heavy-fermion systems
and iron pnictides. We present approximate numerical and analytical solutions
of Polchinski-Wetterich type flow equations with soft frequency regulators for
an effective action of electrons coupled to spin-wave bosons. Performing the
renormalization group in frequency -instead of momentum- space allows to track
changes of the Fermi surface shape and to capture Landau damping during the
flow. The technique is easily generalizable from models retaining only patches
of the Fermi surface to full, compact Fermi surfaces.",1510.01331v3
2015-10-09,Spin-orbit torque in Pt/CoNiCo/Pt symmetric devices,"Current induced magnetization switching by spin-orbit torques offers an
energy-efficient means of writing information in heavy metal/ferromagnet (FM)
multilayer systems. The relative contributions of field-like torques and
damping-like torques to the magnetization switching induced by the electrical
current are still under debate. Here, we describe a device based on a symmetric
Pt/FM/Pt structure, in which we demonstrate a strong damping-like torque from
the spin Hall effect and unmeasurable field-like torque from Rashba effect. The
spin-orbit effective fields due to the spin Hall effect were investigated
quantitatively and were found to be consistent with the switching effective
fields after accounting for the switching current reduction due to thermal
fluctuations from the current pulse. A non-linear dependence of deterministic
switching of average Mz on the in-plane magnetic field was revealed, which
could be explained and understood by micromagnetic simulation.",1510.02555v1
2015-10-15,On the global existence and blowup of smooth solutions of 3-D compressible Euler equations with time-depending damping,"In this paper, we are concerned with the global existence and blowup of
smooth solutions of the 3-D compressible Euler equation with time-depending
damping $$
  \partial_t\rho+\operatorname{div}(\rho u)=0, \quad
  \partial_t(\rho u)+\operatorname{div}\left(\rho u\otimes
  u+p\,I_{3}\right)=-\,\frac{\mu}{(1+t)^{\lambda}}\,\rho u, \quad
  \rho(0,x)=\bar \rho+\varepsilon\rho_0(x),\quad u(0,x)=\varepsilon u_0(x), $$
where $x\in\mathbb R^3$, $\mu>0$, $\lambda\geq 0$, and $\bar\rho>0$ are
constants, $\rho_0,\, u_0\in C_0^{\infty}(\mathbb R^3)$, $(\rho_0,
u_0)\not\equiv 0$, $\rho(0,\cdot)>0$, and $\varepsilon>0$ is sufficiently
small. For $0\leq\lambda\leq1$, we show that there exists a global smooth
solution $(\rho, u)$ when $\operatorname{curl} u_0\equiv 0$, while for
$\lambda>1$, in general, the solution $(\rho, u)$ will blow up in finite time.
Therefore, $\lambda=1$ appears to be the critical value for the global
existence of small amplitude smooth solutions.",1510.04613v1
2015-10-17,Direct evidence for minority spin gap in the Co2MnSi Heusler alloy,"Half Metal Magnets are of great interest in the field of spintronics because
of their potential full spin-polarization at the Fermi level and low
magnetization damping. The high Curie temperature and predicted 0.7eV minority
spin gap make the Heusler alloy Co2MnSi very promising for applications.We
investigated the half-metallic magnetic character of this alloy using
spin-resolved photoemission, ab initio calculation and ferromagnetic resonance.
At the surface of Co2MnSi, a gap in the minority spin channel is observed,
leading to 100% spin polarization. However, this gap is 0.3 eV below the Fermi
level and a minority spin state is observed at the Fermi level. We show that a
minority spin gap at the Fermi energy can nevertheless be recovered either by
changing the stoichiometry of the alloy or by covering the surface by Mn, MnSi
or MgO. This results in extremely small damping coefficients reaching values as
low as 7x 10-4.",1510.05085v1
2015-10-18,Information transmission over an amplitude damping channel with an arbitrary degree of memory,"We study the performance of a partially correlated amplitude damping channel
acting on two qubits. We derive lower bounds for the single-shot classical
capacity by studying two kinds of quantum ensembles, one which allows to
maximize the Holevo quantity for the memoryless channel and the other allowing
the same task but for the full-memory channel. In these two cases, we also show
the amount of entanglement which is involved in achieving the maximum of the
Holevo quantity. For the single-shot quantum capacity we discuss both a lower
and an upper bound, achieving a good estimate for high values of the channel
transmissivity. We finally compute the entanglement-assisted classical channel
capacity.",1510.05313v1
2015-10-29,A Semismooth Newton Method for Tensor Eigenvalue Complementarity Problem,"In this paper, we consider the tensor eigenvalue complementarity problem
which is closely related to the optimality conditions for polynomial
optimization, as well as a class of differential inclusions with nonconvex
processes. By introducing an NCP-function, we reformulate the tensor eigenvalue
complementarity problem as a system of nonlinear equations. We show that this
function is strongly semismooth but not differentiable, in which case the
classical smoothing methods cannot apply. Furthermore, we propose a damped
semismooth Newton method for tensor eigenvalue complementarity problem. A new
procedure to evaluate an element of the generalized Jocobian is given, which
turns out to be an element of the B-subdifferential under mild assumptions. As
a result, the convergence of the damped semismooth Newton method is guaranteed
by existing results. The numerical experiments also show that our method is
efficient and promising.",1510.08570v1
2015-11-15,Mode coupling in solar spicule oscillations,"In a real medium which has oscillations, the perturbations can cause the
energy transfer between different modes. The perturbation interpreted as an
interaction between the modes is inferred as mode coupling. Mode coupling
process in an inhomogeneous medium such as solar spicules may lead to the
coupling of kink waves to local Alfven waves. This coupling occurs practically
in any conditions when there is smooth variation in density in the radial
direction. This process is seen as the decay of transverse kink waves in the
medium. To study the damping of kink waves due to mode coupling, a
2.5-dimensional numerical simulation of the initial wave is considered in
spicules. The initial perturbation is assumed to be in a plane perpendicular to
the spicule axis. The considered kink wave is a standing wave which shows an
exponential damping in the inhomogeneous layer after occurrence of the mode
coupling.",1511.05135v1
2015-11-19,Resurgence in Extended Hydrodynamics,"It has recently been understood that the hydrodynamic series generated by the
M\""uller-Israel-Stewart theory is divergent, and that this large order
behaviour is consistent with the theory of resurgence. Furthermore, it was
observed, that the physical origin of this is the presence of a purely damped
nonhydrodynamic mode. It is very interesting to ask whether this picture
persists in cases where the spectrum of nonhydrodynamic modes is richer. We
take the first step in this direction by considering the simplest hydrodynamic
theory which, instead of the purely damped mode, contains a pair of
nonhydrodynamic modes of complex conjugate frequencies. This mimics the pattern
of black brane quasinormal modes which appear on the gravity side of the
AdS/CFT description of \symm\ plasma. We find that the resulting hydrodynamic
series is divergent in a way consistent with resurgence and precisely encodes
information about the nonhydrodynamic modes of the theory.",1511.06358v2
2015-12-02,Flow of colloidal solids and fluids through constrictions: dynamical density functional theory versus simulation,"Using both dynamical density functional theory and particle-resolved Brownian
dynamics simulations, we explore the flow of two-dimensional colloidal solids
and fluids driven through a linear channel with a geometric constriction. The
flow is generated by a constant external force acting on all colloids. The
initial configuration is equilibrated in the absence of flow and then the
external force is switched on instantaneously. Upon starting the flow, we
observe four different scenarios: a complete blockade, a monotonic decay to a
constant particle flux (typical for a fluid), a damped oscillatory behaviour in
the particle flux, and a long-lived stop-and-go behaviour in the flow (typical
for a solid). The dynamical density functional theory describes all four
situations but predicts infinitely long undamped oscillations in the flow which
are always damped in the simulations. We attribute the mechanisms of the
underlying stop-and-go flow to symmetry conditions on the flowing solid. Our
predictions are verifiable in real-space experiments on magnetic colloidal
monolayers which are driven through structured microchannels and can be
exploited to steer the flow throughput in microfluidics.",1512.00751v1
2015-12-04,Numerical solution of the stationary multicomponent nonlinear Schrödinger equation with a constraint on the angular momentum,"We formulate a damped oscillating particle method to solve the stationary
nonlinear Schr\""{o}dinger equation (NLSE). The ground state solutions are found
by a converging damped oscillating evolution equation that can be discretized
with symplectic numerical techniques. The method is demonstrated for three
different cases: for the single-component NLSE with an attractive
self-interaction, for the single-component NLSE with a repulsive self
interaction and a constraint on the angular momentum, and for the two-component
NLSE with a constraint on the total angular momentum. We reproduce the so
called yrast curve for the single-component case, described in [A. D. Jackson
et al., Europhys. Lett. 95, 30002 (2011)], and produce for the first time an
analogous curve for the two-component NLSE. The numerical results are compared
with analytic solutions and competing numerical methods. Our method is well
suited to handle a large class of equations and can easily be adapted to
further constraints and components.",1512.01441v2
2015-12-08,Influence of kinetic effects on the spectrum of a parallel electrode probe,"Active Plasma Resonance Spectroscopy (APRS) denotes a class of diagnostic
techniques which utilize the natural ability of plasmas to resonate on or near
the electron plasma frequency. One particular class of APRS can be described in
an abstract notation based on functional analytic methods in electrostatic
approximation. These methods allow for a general solution of the kinetic model
in arbitrary geometry. This solution is given as the response function of the
probe-plasma system and is defined by the resolvent of an appropriate dynamical
operator. The general response predicts an additional damping due to kinetic
effects. This manuscript provides the derivation of an explicit response
function of the kinetic APRS model in a simple geometry. Therefore, the
resolvent is determined by its matrix representation based on an expansion in
orthogonal basis functions. This allows to compute an approximated response
function. The resulting spectra show clearly a stronger damping due to kinetic
effects.",1512.02450v1
2015-12-09,Long time behaviors for 3D cubic damped Klein-Gordon equations in inhomogeneous mediums,"In this paper, we study the asymptotic dynamics of global solutions to damped
Klein-Gordon equations in inhomogeneous mediums (KGI). In the defocusing case,
we prove for any initial data, the solution is globally define in forward time
and it will converge to an equilibrium. In the focusing case, for global
solutions, we prove the solutions converge to the superposition of equilibriums
among which there exists at most one equilibrium to KGI and the other
equilibriums are solutions to stationary nonlinear Klein-Gordon equations. The
core ingredients of our proof are the existence of the ""concentration-compact
attractor"" and the gradient system theory.",1512.02755v3
2015-12-10,Strong Frequency Dependence in Over-damped Systems,"Strong frequency dependence is unlikely in diffusive or over-damped systems.
When exceptions do occur, such as in the case of stochastic resonance, it
signals an interesting underlying phenomenon. We find that such a case appears
in the motion of a particle in a diffusive environment under the effect of
periodically oscillating retarded force emanating from the boundaries. The
amplitude for the expectation value of position has an oscillating frequency
dependence, quite unlike a typical resonance. We first present an analysis of
the associated Fokker-Planck equation, then report the results of a Monte Carlo
simulation of the effect of a periodic perturbation on a totally asymmetric
simple exclusion process (TASEP) model with single species. This model is known
to exhibit a randomly moving shock profile, dynamics of which is a discrete
realization of the Fokker-Planck equation. Comparison of relevant quantities
from the two analyses indicate that the same phenomenon is apparent in both
systems.",1512.03187v1
2015-12-16,Back to Maupertuis' least action principle for dissipative systems: not all motions in Nature are most energy economical,"It is shown that an oldest form of variational calculus of mechanics, the
Maupertuis least action principle, can be used as a simple and powerful
approach for the formulation of the variational principle for damped motions,
allowing a simple derivation of the Lagrangian mechanics for any dissipative
systems and an a connection of the optimization of energy dissipation to the
least action principles. On this basis, it is shown that not all motions of
classical mechanics obey the rule of least energy dissipation or follow the
path of least resistance, and that the least action is equivalent to least
dissipation for two kinds of motions : all stationary motions with constant
velocity and all motions damped by Stokes drag.",1512.05339v1
2016-01-11,Damping of Landau levels in neutral graphene at low magnetic fields: A phonon Raman scattering study,"Landau level broadening mechanisms in electrically neutral and quasineutral
graphene were investigated through micro-magneto-Raman experiments in three
different samples, namely, a natural single-layer graphene flake and a
back-gated single-layer device, both deposited over Si/SiO2 substrates, and a
multilayer epitaxial graphene employed as a reference sample. Interband Landau
level transition widths were estimated through a quantitative analysis of the
magnetophonon resonances associated with optically active Landau level
transitions crossing the energy of the E_2g Raman-active phonon. Contrary to
multilayer graphene, the single-layer graphene samples show a strong damping of
the low-field resonances, consistent with an additional broadening contribution
of the Landau level energies arising from a random strain field. This extra
contribution is properly quantified in terms of a pseudomagnetic field
distribution Delta_B = 1.0-1.7 T in our single-layer samples.",1601.02663v3
2016-01-21,Negative frequencies in wave propagation: a microscopic model,"A change in the sign of the frequency of a wave between two inertial
reference frames corresponds to a reversal of the phase velocity. Yet from the
point of view of the relation $E=\hbar\omega$, a positive quantum of energy
apparently becomes a negative energy one. This is physically distinct from a
change in the sign of the wave-vector, and has been associated with various
effects such as Cherenkov radiation, quantum friction, and the Hawking effect.
In this work we provide a more detailed understanding of these negative
frequency modes based on a simple microscopic model of a dielectric medium as a
lattice of scatterers. We calculate the classical and quantum mechanical
radiation damping of an oscillator moving through such a lattice and find that
the modes where the frequency has changed sign contribute negatively. In terms
of the lattice of scatterers we find that this negative radiation damping
arises due to phase of the periodic force experienced by the oscillator due to
the relative motion of the lattice.",1601.05636v1
2016-01-26,"On the wave equation with hyperbolic dynamical boundary conditions, interior and boundary damping and supercritical sources","The aim of the paper is to study the problem $$ \begin{cases} u_{tt}-\Delta
u+P(x,u_t)=f(x,u) \qquad &\text{in $(0,\infty)\times\Omega$,} u=0 &\text{on
$(0,\infty)\times \Gamma_0$,} u_{tt}+\partial_\nu u-\Delta_\Gamma
u+Q(x,u_t)=g(x,u)\qquad &\text{on $(0,\infty)\times \Gamma_1$,}
u(0,x)=u_0(x),\quad u_t(0,x)=u_1(x) & \text{in $\bar{\Omega}$,} \end{cases}$$
where $\Omega$ is a bounded open $C^1$ subset of $\mathbb{R}^N$, $N\ge 2$,
$\Gamma=\partial\Omega$, $(\Gamma_0,\Gamma_1)$ is a measurable partition of
$\Gamma$, $\Delta_\Gamma$ denotes the Laplace--Beltrami operator on $\Gamma$,
$\nu$ is the outward normal to $\Omega$, and the terms $P$ and $Q$ represent
nonlinear damping terms, while $f$ and $g$ are nonlinear source, or sink,
terms.
  In the paper we establish local and existence, uniqueness and Hadamard
well--posedness results when source terms can be supercritical or
super-supercritical.",1601.07075v3
2016-01-29,Numerical Simulation of Tidal Evolution of a Viscoelastic Body Modelled with a Mass-Spring Network,"We use a damped mass-spring model within an N-body code to simulate the tidal
evolution of the spin and orbit of a self-gravitating viscoelastic spherical
body moving around a point-mass perturber. The damped mass-spring model
represents a Kelvin-Voigt viscoelastic solid. We measure the tidal quality
function (the dynamical Love number $\,k_2\,$ divided by the tidal quality
factor $\,Q\,$) from the numerically computed tidal drift of the semimajor axis
of the binary. The shape of $\,k_2/Q\,$, as a function of the principal tidal
frequency, reproduces the kink shape predicted by Efroimsky (2012a; CeMDA
112$\,:\,$283) for the tidal response of near-spherical homogeneous
viscoelastic rotators. We demonstrate that we can directly simulate the tidal
evolution of spinning viscoelastic objects. In future, the mass-spring N-body
model can be generalised to inhomogeneous and/or non-spherical bodies.",1601.08222v2
2016-02-04,Highly efficient two photon generation from a coherently pumped quantum dot embedded in a microcavity,"We propose a scheme to realize a highly efficient solid state source of
photon pairs using cavity-assisted stimulated Raman adiabatic passage (STIRAP)
in a single quantum dot, where a single photon from pump pulse and two stokes
photons from cavity mode drives the Raman transition. The Autler-Townes
doublet, generated by using a resonant continuous wave laser between biexciton
and exciton states, and two-photon-resonant transition through strongly coupled
cavity mode are utilized to facilitate (1+2)type Raman transition in the
quantum dot. We show in the case of weak pump although the probability of
generating two photons in cavity mode is small without cavity damping but
two-photon-resonant emission is enhanced by cavity damping within strong
coupling regime. We also discuss spectrum of the generated photon pair and
photon-photon correlations in the generated photon pair. The efficiency of two
photon source could be more than 80\% in current experimental conditions.",1602.01562v1
2016-02-09,Preservation of quantum key rate in the presence of decoherence,"It is well known that the interaction of quantum systems with the environment
reduces the inherent quantum correlations. Under special circumstances the
effect of decoherence can be reversed, for example, the interaction modeled by
an amplitude damping channel can boost the teleportation fidelity from the
classical to the quantum region for a bipartite quantum state. Here, we first
show that this phenomena fails in the case of a quantum key distribution
protocol. We further show that the technique of weak measurement can be used to
slow down the process of decoherence, thereby helping to preserve the quantum
key rate when one or both systems are interacting with the environment via an
amplitude damping channel. Most interestingly, in certain cases weak
measurement with post-selection where one considers both success and failure of
the technique is shown to be more useful than without it when both systems
interact with the environment.",1602.02903v1
2016-02-19,An accelerated exponential time integrator for semi-linear stochastic strongly damped wave equation with additive noise,"This paper is concerned with the strong approximation of a semi-linear
stochastic wave equation with strong damping, driven by additive noise. Based
on a spatial discretization performed by a spectral Galerkin method, we
introduce a kind of accelerated exponential time integrator involving linear
functionals of the noise. Under appropriate assumptions, we provide error
bounds for the proposed full-discrete scheme. It is shown that the scheme
achieves higher strong order in time direction than the order of temporal
regularity of the underlying problem, which allows for higher convergence rate
than usual time-stepping schemes. For the space-time white noise case in two or
three spatial dimensions, the scheme still exhibits a good convergence
performance. Another striking finding is that, even for the velocity with low
regularity the scheme always promises first order strong convergence in time.
Numerical examples are finally reported to confirm our theoretical findings.",1602.06050v1
2016-02-23,The calibration and electron energy reconstruction of the BGO ECAL of the DAMPE detector,"The DArk Matter Particle Explorer (DAMPE) is a space experiment designed to
search for dark matter indirectly by measuring the spectra of photons,
electrons, and positrons up to 10 TeV. The BGO electromagnetic calorimeter
(ECAL) is its main sub-detector for energy measurement. In this paper, the
instrumentation and development of the BGO ECAL is briefly described. The
calibration on the ground, including the pedestal, minimum ionizing particle
(MIP) peak, dynode ratio, and attenuation length with the cosmic rays and beam
particles is discussed in detail. Also, the energy reconstruction results of
the electrons from the beam test are presented.",1602.07015v1
2016-02-25,Order-disorder transition in repulsive self-propelled particle systems,"We study the collective dynamics of repulsive self-propelled particles. The
particles are governed by coupled equations of motion that include polar
self-propulsion, damping of velocity and of polarity, repulsive
particle-particle interaction, and deterministic dynamics. Particle dynamics
simulations show that the collective coherent motion with large density
fluctuations spontaneously emerges from a disordered, isotropic state. In the
parameter region where the rotational damping of polarity is strong, the
systems undergoes an abrupt shift to the absorbing ordered state after a
waiting period in the metastable disordered state. In order to obtain a simple
understanding of the mechanism underlying the collective behavior, we analyze
binary particle scattering process. We show that this approach correctly
predicts the order-disorder transition at dilute limit. The same approach is
expanded for finite densities, although it disagrees with the result from
many-particle simulations due to many-body correlations and density
fluctuations.",1602.07971v2
2016-03-01,Ferromagnetic resonance and magnetic damping in C-doped Mn5Ge3,"Ferromagnetic resonance (FMR) was used to investigate the static and dynamic
magnetic properties of carbon-doped Mn5Ge3 (C$_{0.1}$ and C$_{0.2}$) thin films
grown on Ge(111). The temperature dependence of magnetic anisotropy shows an
increased perpendicular magneto-crystalline contribution at 80K with an
in-plane easy axis due to the large shape contribution. We find that our
samples show a small FMR linewidth (corresponding to an intrinsic magnetic
damping parameter $\alpha$=0.005), which is a measure of the spin relaxation
and directly related with the magnetic and structural quality of the material.
In the perpendicular-to-plane geometry, the FMR linewidth shows a minimum at
around 200K for all the samples, which seems to be not correlated to the
C-doping. The magnetic relaxation parameters have been determined and indicate
the two-magnon scattering as the main extrinsic contribution. We observe a
change in the main contribution from scattering centres in Mn5Ge3C0.2 at low
temperatures, which could be related to the minimum in linewidth.",1603.00190v1
2016-03-01,Probing superfluidity in a quasi two-dimensional Bose gas through its local dynamics,"We report direct evidence of superfluidity in a quasi two-dimensional Bose
gas by observing its dynamical response to a collective excitation. Relying on
a novel local correlation analysis, we are able to probe inhomogeneous clouds
and reveal their local dynamics. We identify in this way the superfluid and
thermal phases inside the gas and locate the boundary at which the
Berezinskii--Kosterlitz--Thouless crossover occurs. This new analysis also
allows to evidence the coupling of the two fluids which induces at finite
temperatures damping rates larger than the usual Landau damping.",1603.00434v2
2016-03-03,Backreaction Effects on Nonequilibrium Spectral Function,"We show how to compute the spectral function for a scalar theory in two
different scenarios: one which disregards back-reaction i.e. the response of
the environment to the external particle, and the other one where back-reaction
is considered. The calculation was performed using the Kadanoff-Baym equation
through the Keldysh formalism. When back-reaction is neglected, the spectral
function is equal to the equilibrium one, which can be represented as a
Breit-Wigner distribution. When back-reaction is introduced we observed a
damping in the spectral function of the thermal bath. Such behavior modifies
the damping rate for particles created within the bath. This certainly implies
phenomenological consequences right after the Big-Bang, when the primordial
bath was created.",1603.01118v1
2016-04-06,Brownian motion of a matter-wave bright soliton: realizing a quantum pollen grain,"Taking an open quantum systems approach, we derive a collective equation of
motion for the dynamics of a matter-wave bright soliton moving through a
thermal cloud of a distinct atomic species. The reservoir interaction involves
energy transfer without particle transfer between the soliton and thermal
cloud, thus damping the soliton motion without altering its stability against
collapse. We derive a Langevin equation for the soliton centre of mass velocity
in the form of an Ornstein-Uhlenbeck process with analytical drift and
diffusion coefficients. This collective motion is confirmed by simulations of
the full stochastic projected Gross-Pitaevskii equation for the matter-wave
field. The system offers a pathway for experimentally observing the elusive
energy-damping reservoir interaction, and a clear realization of collective
Brownian motion for a mesoscopic superfluid droplet.",1604.01487v1
2016-04-06,Quantum backaction and noise interference in asymmetric two-cavity optomechanical systems,"We study the effect of cavity damping asymmetries on backaction in a
""membrane-in-the-middle"" optomechanical system, where a mechanical mode
modulates the coupling between two photonic modes. We show that in the
adiabatic limit, this system generically realizes a dissipative optomechanical
coupling, with an effective position-dependent photonic damping rate. The
resulting quantum noise interference can be used to ground-state cool a
mechanical resonator in the unresolved sideband regime. We explicitly
demonstrate how quantum noise interference controls linear backaction effects,
and show that this interference persists even outside the adiabatic limit. For
a one-port cavity in the extreme bad-cavity limit, the interference allows one
to cancel all linear backaction effects. This allows continuous measurements of
position-squared, with no stringent constraints on the single-photon
optomechanical coupling strength. In contrast, such a complete cancellation is
not possible in the good cavity limit. This places strict bounds on the
optomechanical coupling required for quantum non-demolition measurements of
mechanical energy, even in a one-port device.",1604.01703v1
2016-04-08,Discrete Breathers and Multi-Breathers in Finite Vibro-Impact Chain,"We explore dynamics of discrete breathers and multi-breathers in finite
one-dimensional chain. The model involves parabolic on-site potential with
rigid constraints and linear nearest-neighbor coupling. The rigid non-ideal
impact constraints are the only source of nonlinearity and damping in the
model. The model allows derivation of exact analytic solutions for the
breathers and multi-breathers with arbitrary set of localization sites, both in
conservative and forced-damped settings. We choose periodic boundary
conditions; exact solutions for other types of the boundary conditions are also
possible. Local character of the nonlinearity allows explicit derivation of a
monodromy matrix for the breather solutions. Consequently, a stability of the
derived breather and multi-breather solutions can be efficiently studied in the
framework of simple methods of linear algebra, and with rather moderate
computational efforts. We demonstrate that finitness of the chain fragment and
proximity of the localization sites strongly effect existence and stability
patterns of these localized solutions.",1604.02296v1
2016-04-22,A Liapunov function approach to the stabilization of second order coupled systems,"In 2002, Fatiha Alabau, Piermarco Cannarsa and Vilmos Komornik investigated
the extent of asymptotic stability of the null solution for weakly coupled
partially damped equations of the second order in time. The main point is that
the damping operator acts only on the first component and, whenever it is
bounded, the coupling is not strong enough to produce an exponential decay in
the energy space associated to the conservative part of the system. As a
consequence, for initial data in the energy space, the rate of decay is not
exponential. Due to the nature of the result it seems at first sight impossible
to obtain the asymptotic stability result by the classical Liapunov method.
Surprisingly enough, this turns out to be possible and we exhibit, under some
compatibility conditions on the operators, an explicit class of Liapunov
functions which allows to do 3 different things: 1) When the problem is reduced
to a stable finite dimensional space, we recover the exponential decay by a
single differential inequality and we estimate the logarithmic decrement of the
solutions with worst (slowest) decay. The estimate is optimal at least for some
values of the parameters.",1604.06547v1
2016-04-28,Temperature Dependence of Viscosity in Normal Fluid $^3$He Below 800mK Determined by a Micro-electro-mechanical Oscillator,"A micro-electro-mechanical system vibrating in its shear mode was used to
study the viscosity of normal liquid $^3$He from 20mK to 770mK at 3bar, 21bar,
and 29bar. The damping coefficient of the oscillator was determined by
frequency sweeps through its resonance at each temperature. Using a slide film
damping model, the viscosity of the fluid was obtained. Our viscosity values
are compared with previous measurements and with calculated values from Fermi
liquid theory. The crossover from the classical to the Fermi liquid regime is
manifest in the temperature dependence of viscosity. In the Fermi liquid
regime, the temperature dependence of viscosity changes from $T^{-1}$ to
$T^{-2}$ on cooling, indicating a transition from the Stokes flow to the
Couette flow regime.",1604.08554v1
2016-05-01,"Optical trapping by Laguerre-Gaussian beams: Symmetries, stability and equilibria","We use the T-matrix formalism in combination with the method of far-field
matching to evaluate the optical force exerted by Laguerre-Gaussian (LG) light
beams on a spherical (Mie) particle. For both non-vortex and optical vortex LG
beams, the theoretical results are used to analyze the optical-force-induced
dynamics of the scatterer near the trapping points represented by the
equilibrium (zero-force) positions. The regimes of linearized dynamics are
described in terms of the stiffness matrix spectrum and the damping constant of
the ambient medium. For the purely azimuthal LG beams, the dynamics is found to
be locally non-conservative and is characterized by the presence of
conditionally stable equilibria (unstable zero-force points that can be
stabilized by the ambient damping). The effects related to the Mie resonances
that under certain conditions manifest themselves as the points changing the
trapping properties of the particles are discussed.",1605.00243v2
2016-05-03,Including atomic vibrations in XANES calculations: polarization-dependent damping of the fine structure at the Cu K edge of (creat)$_{2}$CuCl$_{4}$,"Atomic vibrations are usually not taken into account when analyzing x-ray
absorption near edge structure (XANES) spectra. One of the reasons is that
including the vibrations in a formally exact way is quite complicated while the
effect of vibrations is supposed to be small in the XANES region. By analyzing
polarized Cu K edge x-ray absorption spectra of creatinium tetrachlorocuprate
[(creat)$_{2}$CuCl$_{4}$], we demonstrate that a technically simple method,
consisting in calculating the XANES via the same formula as for static systems
but with a modified free-electron propagator which accounts for fluctuations of
interatomic distances, may substantially help in understanding XANES of some
layered systems. In particular we show that the difference in the damping of
the x-ray absorption fine structure oscillations for different polarisations of
the incoming x-rays cannot be reproduced by calculations which rely on a static
lattice but it can be described if atomic vibrations are accounted for in such
a way that individual creatinium and CuCl$_{4}$ molecular blocks are treated as
semi-rigid entities while the mutual positions of these blocks are subject to
large mean relative displacements.",1605.00861v1
2016-05-05,Relaxation of Ferroelectric States in 2D Distributions of quantum Dots:EELS Simulation,"The relaxation time of collective electronic states in a 2D distribution of
quantum dots is investigated theoretically by simulating EELS experiments. From
the numerical calculation of the probability of energy loss of an electron
beam, traveling parallel to the distribution, it is possible to estimate the
damping time of ferroelectric-like states. We generate this collective response
of the distribution by introducing a mean field interaction among the quantum
dots, and then, the model is extended incorporating effects of long-range
correlations through a Bragg-Williams approximation. The behavior of the
dielectric function, the energy loss function, and the relaxation time of
ferroelectric-like states is then investigated as a function of the temperature
of the distribution and the damping constant of the electronic states in the
single quantum dots. The robustness of the trends and tendencies of our results
indicate that this scheme of analysis can guide experimentalists to develop
tailored quantum dots distributions for specific applications.",1605.01642v1
2016-05-10,Damped wave systems on networks: Exponential stability and uniform approximations,"We consider a damped linear hyperbolic system modelling the propagation of
pressure waves in a network of pipes. Well-posedness is established via
semi-group theory and the existence of a unique steady state is proven in the
absence of driving forces. Under mild assumptions on the network topology and
the model parameters, we show exponential stability and convergence to
equilibrium. This generalizes related results for single pipes and
multi-dimensional domains to the network context. Our proof of the exponential
stability estimate is based on a variational formulation of the problem, some
graph theoretic results, and appropriate energy estimates. The main arguments
are rather generic and can be applied also for the analysis of Galerkin
approximations. Uniform exponential stability can be guaranteed for the
resulting semi-discretizations under mild compatibility conditions on the
approximation spaces. A particular realization by mixed finite elements is
discussed and the theoretical results are illustrated by numerical tests in
which also bounds for the decay rate are investigated.",1605.03066v1
2016-05-14,The damped oscillating propagation of the compensating self-accelerating beams,"We report a new form of compensating accelerating beam generated by amplitude
modulation of the symmetric Airy beam (SAB) caustics with an exponential
apodization mask. Our numerical study manifests that the compensating beam is
with one main-lobe beam structure and can maintain the mean-intensity invariant
both in the free space and loss media. Specially, the beam inherits the
beamlets structure from the SAB and owns a novel damped oscillating propagation
property. We also conduct a comparative study of its propagation property with
that of the Airy beam theoretically. And by altering the signs of 2D masks, the
main lobe of the compensating beam can be modulated to orientate in four
different quadrants flexibly. The proposed compensating accelerating beam is
anticipated to get special applications in particle manipulation or plasmas
regions.",1605.04392v1
2016-05-14,Detecting Damped Lyman-$α$ Absorbers with Gaussian Processes,"We develop an automated technique for detecting damped Lyman-$\alpha$
absorbers (DLAs) along spectroscopic lines of sight to quasi-stellar objects
(QSOs or quasars). The detection of DLAs in large-scale spectroscopic surveys
such as SDSS-III sheds light on galaxy formation at high redshift, showing the
nucleation of galaxies from diffuse gas. We use nearly 50 000 QSO spectra to
learn a novel tailored Gaussian process model for quasar emission spectra,
which we apply to the DLA detection problem via Bayesian model selection. We
propose models for identifying an arbitrary number of DLAs along a given line
of sight. We demonstrate our method's effectiveness using a large-scale
validation experiment, with excellent performance. We also provide a catalog of
our results applied to 162 858 spectra from SDSS-III data release 12.",1605.04460v2
2016-05-17,Direct observation of dynamic modes excited in a magnetic insulator by pure spin current,"Excitation of magnetization dynamics by pure spin currents has been recently
recognized as an enabling mechanism for spintronics and magnonics, which allows
implementation of spin-torque devices based on low-damping insulating magnetic
materials. Here we report the first spatially-resolved study of the dynamic
modes excited by pure spin current in nanometer-thick microscopic insulating
Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear
self-broadening preventing the formation of the self-localized magnetic bullet,
which plays a crucial role in the stabilization of the single-mode
magnetization oscillations in all-metallic systems. This peculiarity associated
with the efficient nonlinear mode coupling in low-damping materials can be
among the main factors governing the interaction of pure spin currents with the
dynamic magnetization in high-quality magnetic insulators.",1605.05211v1
2016-05-18,Damped Arrow-Hurwicz algorithm for sphere packing,"We consider algorithms that, from an arbitrarily sampling of $N$ spheres
(possibly overlapping), find a close packed configuration without overlapping.
These problems can be formulated as minimization problems with non-convex
constraints. For such packing problems, we observe that the classical iterative
Arrow-Hurwicz algorithm does not converge. We derive a novel algorithm from a
multi-step variant of the Arrow-Hurwicz scheme with damping. We compare this
algorithm with classical algorithms belonging to the class of linearly
constrained Lagrangian methods and show that it performs better. We provide an
analysis of the convergence of these algorithms in the simple case of two
spheres in one spatial dimension. Finally, we investigate the behaviour of our
algorithm when the number of spheres is large.",1605.05473v1
2016-05-17,Dynamics of sessile drops. Part 3. Theory of forced oscillations,"A partially-wetting sessile drop is driven by a sinusoidal pressure field
that produces capillary waves on the liquid/gas interface. The analysis
presented in Part 1 of this series (Bostwick & Steen 2014) is extended by
computing response diagrams and phase shifts for the viscous droplet, whose
three phase contact-line moves with contact-angle that is a smooth function of
the contact line speed. Viscous dissipation is incorporated through the viscous
potential flow approximation and the critical Ohnesorge number bounding regions
beyond which a given mode becomes over-damped is computed. Davis dissipation
originating from the contact-line speed condition leads to damped oscillations
for drops with finite contact-line mobility, even for inviscid fluids. The
critical mobility and associated driving frequency to generate the largest
Davis dissipation is computed. Lastly, regions of modal coexistence where two
modes can be simultaneously excited by a single forcing frequency are
identified. Predictions compare favorably to related experiments on vibrated
drops.",1605.05533v1
2016-05-18,Electrical control over perpendicular magnetization switching driven by spin-orbit torques,"Flexible control of magnetization switching by electrical manners is crucial
for applications of spin-orbitronics. Besides of a switching current that is
parallel to an applied field, a bias current that is normal to the switching
current is introduced to tune the magnitude of effective damping-like and
field-like torques and further to electrically control magnetization switching.
Symmetrical and asymmetrical control over the critical switching current by the
bias current with opposite polarities is both realized in Pt/Co/MgO and
$\alpha$-Ta/CoFeB/MgO systems, respectively. This research not only identifies
the influences of field-like and damping-like torques on switching process but
also demonstrates an electrical method to control it.",1605.05569v1
2016-05-25,Quadratic band touching with long range interactions in and out of equilibrium,"Motivated by recent advances in cold atomic systems, we study the equilibrium
and quench properties of two dimensional fermions with quadratic band touching
at the Fermi level, in the presence of infinitely long range interactions.
Unlike when only short range interactions are present, both nematic and quantum
anomalous Hall (QAH) states state appear at weak interactions, separated by a
narrow coexistence region, whose boundaries mark second and third order quantum
phase transitions. After an interaction quench, the QAH order exhibits three
distinct regions: persistent or damped oscillations and exponential decay to
zero. In contrast, the nematic order always reaches a non-zero stationary value
through power law damped oscillations, due to the interplay of the symmetry of
the interaction and the specific topology of the quadratic band touching.",1605.07932v1
2016-05-26,Asymmetric Quantum Dialogue in Noisy Environment,"A notion of asymmetric quantum dialogue (AQD) is introduced. Conventional
protocols of quantum dialogue are essentially symmetric as both the users
(Alice and Bob) can encode the same amount of classical information. In
contrast, the scheme for AQD introduced here provides different amount of
communication powers to Alice and Bob. The proposed scheme, offers an
architecture, where the entangled state and the encoding scheme to be shared
between Alice and Bob depends on the amount of classical information they want
to exchange with each other. The general structure for the AQD scheme has been
obtained using a group theoretic structure of the operators introduced in
(Shukla et al., Phys. Lett. A, 377 (2013) 518). The effect of different types
of noises (e.g., amplitude damping and phase damping noise) on the proposed
scheme is investigated, and it is shown that the proposed AQD is robust and
uses optimized amount of quantum resources.",1605.08363v1
2016-06-11,Parameter identification in a semilinear hyperbolic system,"We consider the identification of a nonlinear friction law in a
one-dimensional damped wave equation from additional boundary measurements.
Well-posedness of the governing semilinear hyperbolic system is established via
semigroup theory and contraction arguments. We then investigte the inverse
problem of recovering the unknown nonlinear damping law from additional
boundary measurements of the pressure drop along the pipe. This coefficient
inverse problem is shown to be ill-posed and a variational regularization
method is considered for its stable solution. We prove existence of minimizers
for the Tikhonov functional and discuss the convergence of the regularized
solutions under an approximate source condition. The meaning of this condition
and some arguments for its validity are discussed in detail and numerical
results are presented for illustration of the theoretical findings.",1606.03580v1
2016-06-16,Design of the readout electronics for the DAMPE Silicon Tracker detector,"The Silicon Tracker (STK) is a detector of the DAMPE satellite to measure the
incidence direction of high energy cosmic ray. It consists of 6 X-Y double
layers of silicon micro-strip detectors with 73,728 readout channels. It's a
great challenge to readout the channels and process the huge volume of data in
the critical space environment. 1152 Application Specific Integrated Circuits
(ASIC) and 384 ADCs are adopted to readout the detector channels. The 192
Tracker Front-end Hybrid (TFH) modules and 8 identical Tracker Readout Board
(TRB) modules are designed to control and digitalize the front signals. In this
paper, the design of the readout electronics for STK and its performance will
be presented in detail.",1606.05080v1
2016-06-20,Classical analogue of the continuous transition between the Weisskopf-Wigner exponential decay and the Rabi oscillation,"When a discrete state is coupled to a continuum, the dynamics can be
described either by the Weisskopf-Wigner exponential decay or by the Rabi
oscillation, depending on the relative magnitudes of the continuum width and of
the Rabi frequency. A continuous transition between these two regimes exists,
as demonstrated in 1977 by C. Cohen-Tannoudji and P. Avan. Here, we describe a
fully analogous transition in classical mechanics, by studying the dynamics of
two coupled mechanical oscillators in the presence of damping. By varying the
relative magnitudes of the damping and coupling terms, we observe a continuous
transition between a regime analogous to the Rabi oscillation and a regime
analogous to the Weisskopf-Wigner exponential decay.",1606.06153v1
2016-07-05,Quantum Zeno and Anti-Zeno Effects on the Entanglement Dynamics of Qubits Dissipating into a Common and non-Markovian Environment,"We investigate the quantum Zeno and anti-Zeno effects on pairwise
entanglement dynamics of a collective of non-interacting qubits which have been
initially prepared in a Werner state and are off-resonantly coupled to a common
and non-Markovian environment. We obtain the analytical expression of the
concurrence in the absence and presence of the non-selective measurements. In
particular, we express our results in the strong and weak coupling regimes and
examine the role of the system size, and the effect of the detuning from the
cavity field frequency on the temporal behaviour of the pairwise entanglement.
We show that, the detuning parameter has a positive role in the protection of
entanglement in the absence of the measurement for weak coupling regime. We
find that for the values of detuning parameter less than the cavity damping
rate, the quantum Zeno effect is always dominant, while for the values greater
than the cavity damping rate, both Zeno and anti-Zeno effects can occur,
depending on the measurement intervals. We also find that the anti-Zeno effect
can occur in the pairwise entanglement dynamics in the absence and presence of
the detuning in the strong coupling regime.",1607.01160v1
2016-07-27,Linear and nonlinear viscoelastic arterial wall models: application on animals,"This work deals with the viscoelasticity of the arterial wall and its
influence on the pulse waves. We describe the viscoelasticity by a non-linear
Kelvin-Voigt model in which the coefficients are fitted using experimental time
series of pressure and radius measured on a sheep's arterial network. We
obtained a good agreement between the results of the nonlinear Kelvin-Voigt
model and the experimental measurements. We found that the viscoelastic
relaxation time-defined by the ratio between the viscoelastic coefficient and
the Young's modulus-is nearly constant throughout the network. Therefore, as it
is well known that smaller arteries are stiffer, the viscoelastic coefficient
rises when approaching the peripheral sites to compensate the rise of the
Young's modulus, resulting in a higher damping effect. We incorporated the
fitted viscoelastic coefficients in a nonlinear 1D fluid model to compute the
pulse waves in the network. The damping effect of viscoelasticity on the high
frequency waves is clear especially at the peripheral sites.",1607.07973v1
2016-08-03,Ultra-Low Dissipation Superfluid Micromechanical Resonator,"Micro and nanomechanical resonators with ultra-low dissipation have great
potential as useful quantum resources. The superfluid micromechanical
resonators presented here possess several advantageous characteristics:
straightforward thermalization, dissipationless flow, and in situ tunability.
We identify and quantitatively model the various dissipation mechanisms in two
resonators, one fabricated from borosilicate glass and one from single crystal
quartz. As the resonators are cryogenically cooled into the superfluid state,
the damping from thermal effects and from the normal fluid component are
strongly suppressed. At our lowest temperatures, damping is limited solely by
internal dissipation in the substrate materials, and reach quality factors up
to 913,000 at 13 mK. By lifting this limitation through substrate material
choice and resonator design, modelling suggests that the resonators should
reach quality factors as high as 10$^8$ at 100 mK, putting this architecture in
an ideal position to harness mechanical quantum effects.",1608.01380v1
2016-08-14,A second order dynamical system with Hessian-driven damping and penalty term associated to variational inequalities,"We consider the minimization of a convex objective function subject to the
set of minima of another convex function, under the assumption that both
functions are twice continuously differentiable. We approach this optimization
problem from a continuous perspective by means of a second order dynamical
system with Hessian-driven damping and a penalty term corresponding to the
constrained function. By constructing appropriate energy functionals, we prove
weak convergence of the trajectories generated by this differential equation to
a minimizer of the optimization problem as well as convergence for the
objective function values along the trajectories. The performed investigations
rely on Lyapunov analysis in combination with the continuous version of the
Opial Lemma. In case the objective function is strongly convex, we can even
show strong convergence of the trajectories.",1608.04137v1
2016-08-15,Power requirements for cosmic ray propagation models involving diffusive reacceleration; estimates and implications for the damping of interstellar turbulence,"We make quantitative estimates of the power supplied to the Galactic cosmic
ray population by second-order Fermi acceleration in the interstellar medium,
or as it is usually termed in cosmic ray propagation studies, diffusive
reacceleration. Using recent results on the local interstellar spectrum from
the Voyager missions we show that for parameter values, in particular the
Alfv\'en speed, typically used in propagation codes such as Galprop to fit the
B/C ratio, the power contributed by diffusive reacceleration is significant and
can be of order 50\% of the total Galactic cosmic ray power. The implications
for the damping of interstellar turbulence are briefly considered.",1608.04227v2
2016-08-19,Cooling a harmonic oscillator by optomechanical modification of its bath,"Optomechanical systems show tremendous promise for high sensitivity sensing
of forces and modification of mechanical properties via light. For example,
similar to neutral atoms and trapped ions, laser cooling of mechanical motion
by radiation pressure can take single mechanical modes to their ground state.
Conventional optomechanical cooling is able to introduce additional damping
channel to mechanical motion, while keeping its thermal noise at the same
level, and as a consequence, the effective temperature of the mechanical mode
is lowered. However, the ratio of temperature to quality factor remains roughly
constant, preventing dramatic advances in quantum sensing using this approach.
Here we propose an approach for simultaneously reducing the thermal load on a
mechanical resonator while improving its quality factor. In essence, we use the
optical interaction to dynamically modify the dominant damping mechanism,
providing an optomechanically-induced effect analogous to a phononic band gap.
The mechanical mode of interest is assumed to be weakly coupled to its heat
bath but strongly coupled to a second mechanical mode, which is cooled by
radiation pressure coupling to a red detuned cavity field. We also identify a
realistic optomechanical design that has the potential to realize this novel
cooling scheme.",1608.05717v1
2016-09-01,Observation of oscillatory radial electric field relaxation in a helical plasma,"Measurements of the relaxation of a zonal electrostatic potential
perturbation in a non-axisymmetric magnetically confined plasma are presented.
A sudden perturbation of the plasma equilibrium is induced by the injection of
a cryogenic hydrogen pellet in the TJ-II stellarator, which is observed to be
followed by a damped oscillation in the electrostatic potential. The waveform
of the relaxation is consistent with theoretical calculations of zonal
potential relaxation in a non-axisymmetric magnetic geometry. The turbulent
transport properties of a magnetic confinement configuration are expected to
depend on the features of the collisionless damping of zonal flows, of which
the present letter is the first direct observation.",1609.00281v1
2016-09-10,Stochastic Sampling for Structural Topology Optimization with Many Load Cases: Density-Based and Ground Structure Approaches,"We propose an efficient probabilistic method to solve a deterministic problem
-- we present a randomized optimization approach that drastically reduces the
enormous computational cost of optimizing designs under many load cases for
both continuum and truss topology optimization. Practical structural designs by
topology optimization typically involve many load cases, possibly hundreds or
more. The optimal design minimizes a, possibly weighted, average of the
compliance under each load case (or some other objective). This means that in
each optimization step a large finite element problem must be solved for each
load case, leading to an enormous computational effort. On the contrary, the
proposed randomized optimization method with stochastic sampling requires the
solution of only a few (e.g., 5 or 6) finite element problems (large linear
systems) per optimization step. Based on simulated annealing, we introduce a
damping scheme for the randomized approach. Through numerical examples in two
and three dimensions, we demonstrate that the stochastic algorithm drastically
reduces computational cost to obtain similar final topologies and results
(e.g., compliance) compared with the standard algorithms. The results indicate
that the damping scheme is effective and leads to rapid convergence of the
proposed algorithm.",1609.03099v1
2016-09-15,Low-damping sub-10-nm thin films of lutetium iron garnet grown by molecular-beam epitaxy,"We analyze the structural and magnetic characteristics of (111)-oriented
lutetium iron garnet (Lu$_3$Fe$_5$O$_{12}$) films grown by molecular-beam
epitaxy, for films as thin as 2.8 nm. Thickness-dependent measurements of the
in- and out-of-plane ferromagnetic resonance allow us to quantify the effects
of two-magnon scattering, along with the surface anisotropy and the saturation
magnetization. We achieve effective damping coefficients of $11.1(9) \times
10^{-4}$ for 5.3 nm films and $32(3) \times 10^{-4}$ for 2.8 nm films, among
the lowest values reported to date for any insulating ferrimagnetic sample of
comparable thickness.",1609.04753v1
2016-09-18,Inertia effects in the real-time dynamics of a quantum spin coupled to a Fermi sea,"Spin dynamics in the Kondo impurity model, initiated by suddenly switching
the direction of a local magnetic field, is studied by means of the
time-dependent density-matrix renormalization group. Quantum effects are
identified by systematic computations for different spin quantum numbers $S$
and by comparing with tight-binding spin-dynamics theory for the classical-spin
Kondo model. We demonstrate that, besides the conventional precessional motion
and relaxation, the quantum-spin dynamics shows nutation, similar to a spinning
top. Opposed to semiclassical theory, however, the nutation is efficiently
damped on an extremely short time scale. The effect is explained in the
large-$S$ limit as quantum dephasing of the eigenmodes in an emergent two-spin
model that is weakly entangled with the bulk of the system. We argue that,
apart from the Kondo effect, the damping of nutational motion is essentially
the only characteristics of the quantum nature of the spin. Qualitative
agreement between quantum and semiclassical spin dynamics is found down to
$S=1/2$.",1609.05526v1
2016-09-21,Force sensitivity of multilayer graphene optomechanical devices,"Mechanical resonators based on low-dimensional materials are promising for
force and mass sensing experiments. The force sensitivity in these ultra-light
resonators is often limited by the imprecision in the measurement of the
vibrations, the fluctuations of the mechanical resonant frequency, and the
heating induced by the measurement. Here, we strongly couple multilayer
graphene resonators to superconducting cavities in order to achieve a
displacement sensitivity of $1.3$ fm Hz$^{-1/2}$. This coupling also allows us
to damp the resonator to an average phonon occupation of $7.2$. Our best force
sensitivity, $390$ zN Hz$^{-1/2}$ with a bandwidth of $200$ Hz, is achieved by
balancing measurement imprecision, optomechanical damping, and heating. Our
results hold promise for studying the quantum capacitance of graphene, its
magnetization, and the electron and nuclear spins of molecules adsorbed on its
surface.",1609.06517v1
2016-09-26,Ferromagnetic resonance study of composite Co/Ni - FeCoB free layers with perpendicular anisotropy,"We study the properties of composite free layers with perpendicular
anisotropy. The free layers are made of a soft FeCoB layer ferromagnetically
coupled by a variable spacer (Ta, W, Mo) to a very anisotropic [Co/Ni]
multilayer embodied in a magnetic tunnel junction meant for spin torque memory
applications. For this we use broadband ferromagnetic resonance to follow the
field dependence of the acoustical and optical excitation of the composite free
layer in both in-plane and out-of-plane applied fields. The modeling provides
the interlayer exchange coupling, the anisotropies and the damping factors. The
popular Ta spacer are outperformed by W and even more by Mo, which combines the
strongest interlayer exchange coupling without sacrificing anisotropies,
damping factors and transport properties.",1609.07863v1
2016-09-30,Origin of the effective mobility in non-linear active micro-rheology,"The distinction between the damping coefficient and the effective non-linear
mobility of driven particles in active micro-rheology of supercooled liquids is
explained in terms of individual and collective dynamics. The effective
mobility arises as a collective effect which gives insight into the energy
landscape of the system. On the other hand, the damping coefficient is a
constant that modulates the effect of external forces over the thermal energy
which particles have at their disposition to perform Brownian motion. For long
times, these thermal fluctuations become characterized in terms of an effective
temperature that is a consequence of the dynamic coupling between kinetic and
configurational degrees of freedom induced by the presence of the strong
external force. The interplay between collective mobility and effective
temperature allows to formulate a generalized Stokes-Einstein relation that may
be used to determine the collective diffusion coefficient. The explicit
relations we deduce reproduce simulation data remarkably well.",1609.09853v1
2016-10-03,Inertia and universality of avalanche statistics: The case of slowly deformed amorphous solids,"By means of a finite elements technique we solve numerically the dynamics of
an amorphous solid under deformation in the quasistatic driving limit. We study
the noise statistics of the stress-strain signal in the steady state plastic
flow, focusing on systems with low internal dissipation. We analyze the
distributions of avalanche sizes and durations and the density of shear
transformations when varying the damping strength. In contrast to avalanches in
the overdamped case, dominated by the yielding point universal exponents,
inertial avalanches are controlled by a non-universal damping dependent
feedback mechanism; eventually turning negligible the role of correlations.
Still, some general properties of avalanches persist and new scaling relations
can be proposed.",1610.00533v2
2016-10-04,Statistical properties of damped Lyman-alpha systems from Sloan Digital Sky Survey DR12,"We present new estimates for the statistical properties of damped
Lyman-$\alpha$ absorbers (DLAs). We compute the column density distribution
function at $z>2$, the line density, $\mathrm{d}N/\mathrm{d}X$, and the neutral
hydrogen density, $\Omega_\mathrm{DLA}$. Our estimates are derived from the DLA
catalogue of Garnett 2016, which uses the SDSS-III DR12 quasar spectroscopic
survey. This catalogue provides a probability that a given spectrum contains a
DLA, allowing us to use even the noisiest data without biasing our results and
thus substantially increase our sample size. We measure a non-zero column
density distribution function at $95\%$ confidence for all column densities
$N_\mathrm{HI} < 5\times 10^{22}$ cm$^{-2}$. We make the first measurements
from SDSS of $\mathrm{d}N/\mathrm{d}X$ and $\Omega_\mathrm{DLA}$ at $z>4$. We
show that our results are insensitive to the signal-to-noise ratio of the
spectra, but that there is a residual dependence on quasar redshift for
$z<2.5$, which may be due to remaining systematics in our analysis.",1610.01165v2
2016-10-05,Higher-Harmonic Collective Modes in a Trapped Gas from Second-Order Hydrodynamics,"Utilizing a second-order hydrodynamics formalism, the dispersion relations
for the frequencies and damping rates of collective oscillations as well as
spatial structure of these modes up to the decapole oscillation in both two-
and three- dimensional gas geometries are calculated. In addition to
higher-order modes, the formalism also gives rise to purely damped
""non-hydrodynamic"" modes. We calculate the amplitude of the various modes for
both symmetric and asymmetric trap quenches, finding excellent agreement with
an exact quantum mechanical calculation. We find that higher-order hydrodynamic
modes are more sensitive to the value of shear viscosity, which may be of
interest for the precision extraction of transport coefficients in Fermi gas
systems.",1610.01611v2
2016-10-10,Robust force sensing for a free particle in a dissipative optomechanical system with a parametric amplifier,"We theoretically investigate optical detection of a weak classical force
acting on a free particle in a dissipative coupling optomechanical system with
a degenerate parametric amplifier (PA). We show that the PA allows one to
achieve the force sensitivity far better than the standard quantum limit (SQL)
over a broad range of the detection frequencies. The improvement depends on the
parametric gain and the driving power. Moreover, we discuss the effects of the
mechanical damping and the thermal noise on the force sensitivity. We find that
the robustness of the force sensitivity much better than the SQL against the
mechanical damping and the thermal noise is achievable in the presence of the
PA with a high parametric gain. For the temperature $T = 1$ K, the improvement
in sensitivity is better by a factor of about 7 when the driving power is set
at a value corresponding to the SQL with no PA.",1610.02761v2
2016-10-12,Stabilization of the Gear-Grimshaw system with weak damping,"The aim of this work is to consider the internal stabilization of a nonlinear
coupled system of two Korteweg--de Vries equations in a finite interval under
the effect of a very weak localized damping. The system was introduced by Gear
and Grimshaw to model the interactions of two-dimensional, long, internal
gravity waves propagation in a stratified fluid. Considering feedback controls
laws and using Compactness--Uniqueness Argument, which reduce the problem to
use a unique continuation property, we establish the exponential stability of
the weak solutions when the exponent in the nonlinear term ranges over the
interval $[1,4)$.",1610.03829v4
2016-10-16,Pulse-noise approach for classical spin systems,"For systems of classical spins interacting with the bath via damping and
thermal noise, the approach is suggested to replace the white noise by a pulse
noise acting at regular time intervals $\Delta t$, within which the system
evolves conservatively. The method is working well in the typical case of a
small dimensionless damping constant $\lambda$ and allows a considerable
speed-up of computations by using high-order numerical integrators with a large
time step $\delta t$ (up to a fraction of the precession period), while keeping
$\delta t\ll\Delta t$ to reduce the relative contribution of noise-related
operations. In cases when precession can be discarded, $\delta t$ can be
increased up to a fraction of the relaxation time $\propto1/\lambda$ that leads
to a further speed-up. This makes equilibration speed comparable with that of
Metropolis Monte Carlo. The pulse-noise approach is tested on single-spin and
multi-spin models.",1610.04914v2
2016-10-19,Heavy-tailed response of structural systems subjected to stochastic excitation containing extreme forcing events,"We characterize the complex, heavy-tailed probability distribution functions
(pdf) describing the response and its local extrema for structural systems
subjected to random forcing that includes extreme events. Our approach is based
on the recent probabilistic decomposition-synthesis technique, where we
decouple rare events regimes from the background fluctuations. The result of
the analysis has the form of a semi-analytical approximation formula for the
pdf of the response (displacement, velocity, and acceleration) and the pdf of
the local extrema. For special limiting cases (lightly damped or heavily damped
systems) our analysis provides fully analytical approximations. We also
demonstrate how the method can be applied to high dimensional structural
systems through a two-degrees-of-freedom structural system undergoing rare
events due to intermittent forcing. The derived formulas can be evaluated with
very small computational cost and are shown to accurately capture the
complicated heavy-tailed and asymmetrical features in the probability
distribution many standard deviations away from the mean, through comparisons
with expensive Monte-Carlo simulations.",1610.06110v3
2016-10-27,Thermally activated phase slips of one-dimensional Bose gases in shallow optical lattices,"We study the decay of superflow via thermally activated phase slips in
one-dimensional Bose gases in a shallow optical lattice. By using the Kramers
formula, we numerically calculate the nucleation rate of a thermally activated
phase slip for various values of the filling factor and flow velocity in the
absence of a harmonic trapping potential. Within the local density
approximation, we derive a formula connecting the phase-slip nucleation rate
with the damping rate of a dipole oscillation of the Bose gas in the presence
of a harmonic trap. We use the derived formula to directly compare our theory
with the recent experiment done by the LENS group [L. Tanzi, et al., Sci. Rep.
{\bf 6}, 25965 (2016)]. From the comparison, the observed damping of dipole
oscillations in a weakly correlated and small velocity regime is attributed
dominantly to thermally activated phase slips rather than quantum phase slips.",1610.08982v3
2016-10-28,Damping-free collective oscillations of a driven two-component Bose gas in optical lattices,"We explore quantum many-body physics of a driven Bose-Einstein condensate in
optical lattices. The laser field induces a gap in the generalized Bogoliubov
spectrum proportional to the effective Rabi frequency. The lowest lying modes
in a driven condensate are characterized by zero group velocity and non-zero
current. Thus, the laser field induces roton modes, which carry interaction in
a driven condensate. We show that collective excitations below the energy of
the laser-induced gap remain undamped, while above the gap they are
characterized by a significantly suppressed Landau damping rate.",1610.09076v5
2016-11-02,An extension of Bakhvalov's theorem for systems of conservation laws with damping,"For $2\X2$ systems of conservation laws satisfying Bakhvalov conditions, we
present a class of damping terms that still yield the existence of global
solutions with periodic initial data of possibly large bounded total variation
per period. We also address the question of the decay of the periodic solution.
As applications we consider the systems of isentropic gas dynamics, with
pressure obeying a $\gamma$-law, for the physical range $\gamma\ge1$, and also
for the ""non-physical"" range $0<\gamma<1$, both in the classical Lagrangian and
Eulerian formulation, and in the relativistic setting. We give complete details
for the case $\gamma=1$, and also analyze the general case when $|\gamma-1|$ is
small. Further, our main result also establishes the decay of the periodic
solution.",1611.00698v1
2016-11-15,The damped stochastic wave equation on p.c.f. fractals,"A p.c.f. fractal with a regular harmonic structure admits an associated
Dirichlet form, which is itself associated with a Laplacian. This Laplacian
enables us to give an analogue of the damped stochastic wave equation on the
fractal. We show that a unique function-valued solution exists, which has an
explicit formulation in terms of the spectral decomposition of the Laplacian.
We then use a Kolmogorov-type continuity theorem to derive the spatial and
temporal H\""older exponents of the solution. Our results extend the analogous
results on the stochastic wave equation in one-dimensional Euclidean space. It
is known that no function-valued solution to the stochastic wave equation can
exist in Euclidean dimension two or higher. The fractal spaces that we work
with always have spectral dimension less than two, and show that this is the
right analogue of dimension to express the ""curse of dimensionality"" of the
stochastic wave equation. Finally we prove some results on the convergence to
equilibrium of the solutions.",1611.04874v3
2016-11-29,Phase mixing importance for both Landau instability and damping,"We discuss the self-consistent dynamics of plasmas by means of hamiltonian
formalism for a system of $N$ near-resonant electrons interacting with a single
Langmuir wave. The connection with the Vlasov description is revisited through
the numerical calculation of the van Kampen-like eigenfrequencies of the
linearized dynamics for many degrees of freedom. Both the exponential-like
growth as well as damping of the Langmuir wave are shown to emerge from a phase
mixing effect among beam modes, revealing unexpected similarities between the
stable and unstable regimes.",1611.09596v3
2016-11-29,Dark matter annihilation and jet quenching phenomena in the early universe,"Dark-matter particles like neutralinos should decouple from the hot cosmic
plasma at temperatures of about 40 GeV. Later they can annihilate each other
into standard-model particles, which are injected into the dense primordial
plasma and quickly loose energy. This process is similar to jet quenching in
ultrarelativistic heavy-ion collisions, actively studied in RHIC and LHC
experiments. Using empirical information from heavy-ion experiments I show that
the cosmological (anti)quark and gluon jets are damped very quickly until the
plasma remains in the deconfined phase. The charged hadron and lepton jets are
strongly damped until the recombination of electrons and protons. The
consequences of energy transfer by the annihilation products to the cosmic
matter are discussed.",1611.09662v1
2016-11-30,Perspective on the cosmic-ray electron spectrum above TeV,"The AMS-02 has measured the cosmic ray electron (plus positron) spectrum up
to ~TeV with an unprecedent precision. The spectrum can be well described by a
power law without any obvious features above 10 GeV. The satellite instrument
Dark Matter Particle Explorer (DAMPE), which was launched a year ago, will
measure the electron spectrum up to 10 TeV with a high energy resolution. The
cosmic electrons beyond TeV may be attributed to few local cosmic ray sources,
such as supernova remnants. Therefore, spectral features, such as cutoff and
bumps, can be expected at high energies. In this work we give a careful study
on the perspective of the electron spectrum beyond TeV. We first examine our
astrophysical source models on the latest leptonic data of AMS-02 to give a
self-consistent picture. Then we focus on the discussion about the candidate
sources which could be electron contributors above TeV. Depending on the
properties of the local sources (especially on the nature of Vela), DAMPE may
detect interesting features in the electron spectrum above TeV in the future.",1611.10292v1
2016-12-01,Field- and damping-like spin-transfer torque in magnetic multilayers,"We investigate the spin-transfer torque in a magnetic multilayer structure by
means of a spin-diffusion model. The torque in the considered system,
consisting of two magnetic layers separated by a conducting layer, is caused by
a perpendicular-to-plane current. We compute the strength of the field-like and
the damping-like torque for different material parameters and geometries. Our
studies suggest that the field-like torque highly depends on the exchange
coupling strength of the itinerant electrons with the magnetization both in the
pinned and the free layer. While a low coupling leads to very high field-like
torques, a high coupling leads to low or even negative field-like torques. The
dependence of the different torque terms on system parameters is considered
very important for the development of applications such as STT MRAM and
spin-torque oscillators.",1612.00194v1
2016-12-04,Vector Approximate Message Passing for the Generalized Linear Model,"The generalized linear model (GLM), where a random vector $\boldsymbol{x}$ is
observed through a noisy, possibly nonlinear, function of a linear transform
output $\boldsymbol{z}=\boldsymbol{Ax}$, arises in a range of applications such
as robust regression, binary classification, quantized compressed sensing,
phase retrieval, photon-limited imaging, and inference from neural spike
trains. When $\boldsymbol{A}$ is large and i.i.d. Gaussian, the generalized
approximate message passing (GAMP) algorithm is an efficient means of MAP or
marginal inference, and its performance can be rigorously characterized by a
scalar state evolution. For general $\boldsymbol{A}$, though, GAMP can
misbehave. Damping and sequential-updating help to robustify GAMP, but their
effects are limited. Recently, a ""vector AMP"" (VAMP) algorithm was proposed for
additive white Gaussian noise channels. VAMP extends AMP's guarantees from
i.i.d. Gaussian $\boldsymbol{A}$ to the larger class of rotationally invariant
$\boldsymbol{A}$. In this paper, we show how VAMP can be extended to the GLM.
Numerical experiments show that the proposed GLM-VAMP is much more robust to
ill-conditioning in $\boldsymbol{A}$ than damped GAMP.",1612.01186v1
2016-12-06,Quantum Dynamics of Skyrmions in Chiral Magnets,"We study the quantum propagation of a Skyrmion in chiral magnetic insulators
by generalizing the micromagnetic equations of motion to a finite-temperature
path integral formalism, using field theoretic tools. Promoting the center of
the Skyrmion to a dynamic quantity, the fluctuations around the Skyrmionic
configuration give rise to a time-dependent damping of the Skyrmion motion.
From the frequency dependence of the damping kernel, we are able to identify
the Skyrmion mass, thus providing a microscopic description of the kinematic
properties of Skyrmions. When defects are present or a magnetic trap is
applied, the Skyrmion mass acquires a finite value proportional to the
effective spin, even at vanishingly small temperature. We demonstrate that a
Skyrmion in a confined geometry provided by a magnetic trap behaves as a
massive particle owing to its quasi-one-dimensional confinement. An additional
quantum mass term is predicted, independent of the effective spin, with an
explicit temperature dependence which remains finite even at zero temperature.",1612.01885v2
2016-12-06,Increased low-temperature damping in yttrium iron garnet thin films,"We report measurements of the frequency and temperature dependence of
ferromagnetic resonance (FMR) for a 15-nm-thick yttrium iron garnet (YIG) film
grown by off-axis sputtering. Although the FMR linewidth is narrow at room
temperature (corresponding to a damping coefficient $\alpha$ = (9.0 $\pm$ 0.2)
$\times 10^{-4}$), comparable to previous results for high-quality YIG films of
similar thickness, the linewidth increases strongly at low temperatures, by a
factor of almost 30. This increase cannot be explained as due to two-magnon
scattering from defects at the sample interfaces. We argue that the increased
low-temperature linewidth is due to impurity relaxation mechanisms that have
been investigated previously in bulk YIG samples. We suggest that the
low-temperature linewidth is a useful figure of merit to guide the optimization
of thin-film growth protocols because it is a particularly sensitive indicator
of impurities.",1612.01954v1
2016-12-09,Slow motion for one-dimensional nonlinear damped hyperbolic Allen-Cahn systems,"We consider a nonlinear damped hyperbolic reaction-diffusion system in a
bounded interval of the real line with homogeneous Neumann boundary conditions
and we study the metastable dynamics of the solutions. Using an ""energy
approach"" introduced by Bronsard and Kohn [CPAM 1990] to study slow motion for
Allen-Cahn equation and improved by Grant [SIAM J. Math. Anal. 1995] in the
study of Cahn-Morral systems, we improve and extend to the case of systems the
results valid for the hyperbolic Allen-Cahn equation. In particular, we study
the limiting behavior of the solutions as $\varepsilon\to0^+$, where
$\varepsilon^2$ is the diffusion coefficient, and we prove existence and
persistence of metastable states for a time
$T_\varepsilon>\exp(A/\varepsilon)$. Such metastable states have a transition
layer structure and the transition layers move with exponentially small
velocity.",1612.03203v5
2016-12-18,Entropically Damped Artificial Compressibility for SPH,"In this paper, the Entropically Damped Artificial Compressibility (EDAC)
formulation of Clausen (2013) is used in the context of the Smoothed Particle
Hydrodynamics (SPH) method for the simulation of incompressible fluids.
Traditionally, weakly-compressible SPH (WCSPH) formulations have employed
artificial compressiblity to simulate incompressible fluids. EDAC is an
alternative to the artificial compressiblity scheme wherein a pressure
evolution equation is solved in lieu of coupling the fluid density to the
pressure by an equation of state. The method is explicit and is easy to
incorporate into existing SPH solvers using the WCSPH formulation. This is
demonstrated by coupling the EDAC scheme with the recently proposed Transport
Velocity Formulation (TVF) of Adami et al. (2013). The method works for both
internal flows and for flows with a free surface (a drawback of the TVF
scheme). Several benchmark problems are considered to evaluate the proposed
scheme and it is found that the EDAC scheme gives results that are as good or
sometimes better than those produced by the TVF or standard WCSPH. The scheme
is robust and produces smooth pressure distributions and does not require the
use of an artificial viscosity in the momentum equation although using some
artificial viscosity is beneficial.",1612.05901v2
2016-12-19,Kinetic-simulation study of propagation of Langmuir-like ionic waves in dusty plasma,"The propagation of ionic perturbations in a dusty plasma is considered
through a three-species kinetic simulation approach, in which the temporal
evolution of all three elements i.e. electrons, ions and dust particles are
followed based on the Vlasov equation coupled with the Poisson equation. Two
cases are focused upon: firstly a fully electron depleted dusty plasma, i.e., a
plasma consisting of ions and dust-particles. The second case includes dusty
plasmas with large electron-to-ion temperature ratios. The main features of the
ionic waves in these two settings including the dispersion relation and the
Landau damping rate are studied. It is shown that the dispersion relation of
the ionic waves perfectly matches the dispersion relation of Langmuir waves and
hence are called Langmuir-like ionic waves and can be considered as
ion-Langmuir waves. These waves can be theoretically predicted by the
dispersion relation of the dust-ion-acoustic waves. The transition of ionic
waves from dust-ion-acoustic to Langmuir-like waves are shown to be
sharp/smooth in first/second case. The Landau damping rates based on simulation
results are presented and compared with theoretical predictions wherever
possible.",1612.06182v1
2016-12-21,Environment generated quantum correlations in bipartite qubit-qutrit systems,"The dynamics of entanglement and quantum discord for qubit-qutrit systems are
studied in the presence of phase damping and amplitude damping noises. Both one
way and two couplings of the marginal systems with the environments are
considered. Entanglement sudden death is unavoidable under any setup, however,
the required time span depends on the way of coupling. On the other hand, the
dynamics of quantum discord strongly depends both on the nature of environment
and on the number of dimensions of the Hilbert space of the coupled marginal
system. We show that freezing and invariance of quantum discord, as previously
reported in the literature, are limited to some special cases. Most
importantly, it is noted that under some particular coupling the existence of
environment can guarantee the generation of nonclassical correlations.",1612.06981v1
2016-12-28,Stretching and Kibble scaling regimes for Hubble-damped defect networks,"The cosmological evolution of topological defect networks can broadly be
divided into two stages. At early times they are friction-dominated due to
particle scattering and therefore non-relativistic, and may either be
conformally stretched or evolve in the Kibble regime. At late times they are
relativistic and evolve in the well known linear scaling regime. In this work
we show that a sufficiently large Hubble damping (that is a sufficiently fast
expansion rate) leads to a linear scaling regime where the network is
non-relativistic. This is therefore another realization of a Kibble scaling
regime, and also has a conformal stretching regime counterpart which we
characterize for the first time. We describe these regimes using analytic
arguments in the context of the velocity-dependent one-scale model, and we
confirm them using high-resolution $4096^3$ field theory simulations of domain
wall networks. We also use these simulations to improve the calibration of this
analytic model for the case of domain walls.",1612.08863v1
2016-12-29,Laser Pulse Compression Using Magnetized Plasmas,"Proposals to reach the next generation of laser intensities through Raman or
Brillouin backscattering have centered on optical frequencies. Higher
frequencies are beyond the range of such methods mainly due to the wave damping
that accompanies the higher density plasmas necessary for compressing higher
frequency lasers. However, we find that an external magnetic field transverse
to the direction of laser propagation can reduce the required plasma density.
Using parametric interactions in magnetized plasmas to mediate pulse
compression both reduces the wave damping and alleviates instabilities, thereby
enabling higher frequency or lower intensity pumps to produce pulses at higher
intensity and longer duration. In addition to these theoretical advantages, our
new method, in which strong uniform magnetic fields lessen the need for
high-density uniform plasmas, also lessens key engineering challenges, or at
least exchanges them for different challenges.",1612.09214v1
2017-01-05,Liquid-like thermal conduction in a crystalline solid,"A solid conducts heat through both transverse and longitudinal acoustic
phonons, but a liquid employs only longitudinal vibrations. Here, we report
that the crystalline solid AgCrSe2 has liquid-like thermal conduction. In this
compound, Ag atoms exhibit a dynamic duality that they are exclusively involved
in intense low-lying transverse acoustic phonons while they also undergo local
fluctuations inherent in an order-to-disorder transition occurring at 450 K. As
a consequence of this extreme disorder-phonon coupling, transverse acoustic
phonons become damped as approaching the transition temperature, above which
they are not defined anymore because their lifetime is shorter than the
relaxation time of local fluctuations. Nevertheless, the damped longitudinal
acoustic phonon survives for thermal transport. This microscopic insight might
reshape the fundamental idea on thermal transport properties of matter and
facilitates the optimization of thermoelectrics.",1701.01192v1
2017-01-09,Oscillations and damping in the fractional Maxwell materials,"This paper examines the oscillatory behaviour of complex viscoelastic systems
with power law-like relaxation behaviour. Specifically, we use the fractional
Maxwell model, consisting of a spring and fractional dashpot in series, which
produces a power-law creep behaviour and a relaxation law following the
Mittag-Leffler function. The fractional dashpot is characterised by a parameter
beta, continuously moving from the pure viscous behaviour when beta=1 to the
purely elastic response when beta=0. In this work, we study the general
response function and focus on the oscillatory behaviour of a fractional
Maxwell system in four regimes: stress impulse, strain impulse, step stress,
and driven oscillations. The solutions are presented in a format analogous to
the classical oscillator, showing how the fractional nature of relaxation
changes the long-time equilibrium behaviour and the short-time transient
solutions. We specifically test the critical damping conditions in the
fractional regime, since these have a particular relevance in biomechanics.",1701.02155v2
2017-01-11,Localization in finite asymmetric vibro-impact chains,"We explore the dynamics of strongly localized periodic solutions (discrete
solitons, or discrete breathers) in a finite one-dimensional chain of
asymmetric vibro-impact oscillators. The model involves a parabolic on-site
potential with asymmetric rigid constraints (the displacement domain of each
particle is finite), and a linear nearest-neighbor coupling. When the particle
approaches the constraint, it undergoes an impact (not necessarily elastic),
that satisfies Newton impact law. Nonlinearity of the system stems from the
impacts; their possible non-elasticity is the sole source of damping in the
system. We demonstrate that this vibro-impact model allows derivation of exact
analytic solutions for the asymmetric discrete breathers, both in conservative
and forced-damped settings. The asymmetry makes two types of breathers
possible: breathers that impact both or only one constraint. Transition between
these two types of the breathers corresponds to a grazing bifurcation. Special
character of the nonlinearity permits explicit derivation of a monodromy
matrix. Therefore, the stability of the obtained breather solutions can be
exactly studied in the framework of simple methods of linear algebra, and with
rather moderate computational efforts. All three generic scenarios of the loss
of stability (pitchfork, Neimark-Sacker and period doubling bifurcations) are
observed.",1701.03055v1
2017-01-13,Characterizing Fluid and Kinetic Instabilities using Field-Particle Correlations on Single-Point Time Series,"A recently proposed technique correlating electric fields and particle
velocity distributions is applied to single-point time series extracted from
linearly unstable, electrostatic numerical simulations. The form of the
correlation, which measures the transfer of phase-space energy density between
the electric field and plasma distributions and had previously been applied to
damped electrostatic systems, is modified to include the effects of drifting
equilibrium distributions of the type that drive counter-streaming and
bump-on-tail instabilities. By using single-point time series, the correlation
is ideal for diagnosing dynamics in systems where access to integrated
quantities, such as energy, is observationally infeasible. The velocity-space
structure of the field-particle correlation is shown to characterize the
underlying physical mechanisms driving unstable systems. The use of this
correlation in simple systems will assist in its eventual application to
turbulent, magnetized plasmas, with the ultimate goal of characterizing the
nature of mechanisms that damp turbulent fluctuations in the solar wind.",1701.03687v1
2017-01-17,Backward Raman Amplification in the Long-wavelength Infrared,"The wealth of work in backward Raman amplification in plasma has focused on
the extreme intensity limit, however backward Raman amplification may also
provide an effective and practical mechanism for generating intense, broad
bandwidth, long-wavelength infrared radiation (LWIR). An electromagnetic
simulation coupled with a relativistic cold fluid plasma model is used to
demonstrate the generation of picosecond pulses at a wavelength of 10 microns
with terawatt powers through backward Raman amplification. The effects of
collisional damping, Landau damping, pump depletion, and wave breaking are
examined, as well as the resulting design considerations for a LWIR Raman
amplifier.",1701.04879v2
2017-02-14,Electron-nuclear coherent spin oscillations probed by spin dependent recombination,"We demonstrate the detection of coherent electron-nuclear spin oscillations
related to the hyperfine interaction and revealed by the band-to-band
photoluminescence (PL) in zero external magnetic field. On the base of a
pump-probe PL experiment we measure, directly in the temporal domain, the
hyperfine constant of an electron coupled to a gallium defect in GaAsN by
tracing the dynamical behavior of the conduction electron spin-dependent
recombination to the defect site. The hyperfine constants and the relative
abundance of the nuclei isotopes involved can be determined without the need of
electron spin resonance technique and in the absence of any magnetic field.
Information on the nuclear and electron spin relaxation damping parameters can
also be estimated from the oscillations damping and the long delay behavior.",1702.04129v1
2017-02-14,Calibrating damping rates with LEGACY linewidths,"Linear damping rates of radial oscillation modes in selected $Kepler$ stars
are estimated with the help of a nonadiabatic stability analysis. The
convective fluxes are obtained from a nonlocal, time-dependent convection
model. The mixing-length parameter is calibrated to the surface-convection-zone
depth of a stellar model obtained from fitting adiabatic frequencies to the
LEGACY observations, and two of the three nonlocal convection parameters are
calibrated to the corresponding LEGACY linewidth measurements. The atmospheric
structure in the 1D stability analysis adopts a temperature-optical-depth
relation derived from 3D hydrodynamical simulations. Results from 3D
simulations are also used to calibrate the turbulent pressure and to guide the
functional form of the depth-dependence of the anisotropy of the turbulent
velocity field in the 1D stability computations.",1702.04251v1
2017-02-20,Resonant Scattering Characteristics of Homogeneous Dielectric Sphere,"In the present article the classical problem of electromagnetic scattering by
a single homogeneous sphere is revisited. Main focus is the study of the
scattering behavior as a function of the material contrast and the size
parameters for all electric and magnetic resonances of a dielectric sphere.
Specifically, the Pad\'e approximants are introduced and utilized as an
alternative system expansion of the Mie coefficients. Low order Pad\'e
approximants can give compact and physically insightful expressions for the
scattering system and the enabled dynamic mechanisms. Higher order approximants
are used for predicting accurately the resonant pole spectrum. These results
are summarized into general pole formulae, covering up to fifth order magnetic
and forth order electric resonances of a small dielectric sphere. Additionally,
the connection between the radiative damping process and the resonant linewidth
is investigated. The results obtained reveal the fundamental connection of the
radiative damping mechanism with the maximum width occurring for each
resonance. Finally, the suggested system ansatz is used for studying the
resonant absorption maximum through a circuit-inspired perspective.",1702.05883v1
2017-02-22,A Retrofitting-based Supplementary Controller Design for Enhancing Damping Performance of Wind Power Systems,"In this paper we address the growing concerns of wind power integration from
the perspective of power system dynamics and stability. We propose a new
retrofit control technique where an additional controller is designed at the
doubly-fed induction generator site inside the wind power plant. This
controller cancels the adverse impacts of the power flow from the wind side to
the grid side on the dynamics of the overall power system. The main advantage
of this controller is that it can be implemented by feeding back only the wind
states and wind bus voltage without depending on any of the other synchronous
machines in the rest of the system. Through simulations of a 4-machine Kundur
power system model we show that the retrofit can efficiently enhance the
damping performance of the system variable despite very high values of wind
penetration.",1702.06695v1
2017-02-23,Plasmon modes of bilayer molybdenum disulfide: A density functional study,"We explore the collective electronic excitations of bilayer molybdenum
disulfide (MoS$_2$) using the density functional theory together with the
random phase approximation. The many-body dielectric function and electron
energy-loss spectra are calculated using an {\it ab initio} based model
involving material-realistic physical properties. The electron energy-loss
function of bilayer MoS$_2$ system is found to be sensitive to either electron
or hole doping and it is owing to the fact that the Kohn-Sham band dispersions
are not symmetric for energies above and below the zero Fermi level. Three
plasmon modes are predicted. A damped high-energy mode, one optical mode
(in-phase mode) for which the plasmon dispersion exhibits $\sqrt q $ in the
long wavelength limit originating from low-energy electron scattering and
finally a highly damped acoustic mode (out-of-phase mode).",1702.07170v2
2017-02-25,Low-energy photoelectron transmission through aerosol overlayers,"The transmission of low-energy (<1.8eV) photoelectrons through the shell of
core-shell aerosol particles is studied for liquid squalane, squalene, and DEHS
shells. The photoelectrons are exclusively formed in the core of the particles
by two-photon ionization. The total photoelectron yield recorded as a function
of shell thickness (1-80nm) shows a bi-exponential attenuation. For all
substances, the damping parameter for shell thicknesses below 15nm lies between
8 and 9nm, and is tentatively assigned to the electron attenuation length at
electron kinetic energies of ~0.5-1eV. The significantly larger damping
parameters for thick shells (> 20nm) are presumably a consequence of distorted
core-shell structures. A first comparison of aerosol and traditional thin film
overlayer methods is provided.",1702.07865v1
2017-02-26,Magnon-photon coupling in antiferromagnets,"Magnon-photon coupling in antiferromagnets has many attractive features that
do not exist in ferro- or ferrimagnets. We show quantum-mechanically that, in
the absence of an external field, one of the two degenerated spin wave bands
couples with photons while the other does not. The photon mode anticrosses with
the coupled spin waves when their frequencies are close to each other. Similar
to its ferromagnetic counterpart, the magnon-photon coupling strength is
proportional to the square root of number of spins $\sqrt{N}$ in
antiferromagnets. An external field removes the spin wave degeneracy and both
spin wave bands couple to the photons, resulting in two anticrossings between
the magnons and photons. Two transmission peaks were observed near the
anticrossing frequency. The maximum damping that allows clear discrimination of
the two transmission peaks is proportional to $\sqrt{N}$ and it's well below
the damping of antiferromagnetic insulators. Therefore the strong magnon-photon
coupling can be realized in antiferromagnets and the coherent information
transfer between the photons and magnons is possible.",1702.07977v1
2017-03-03,Global behaviour of bistable solutions for hyperbolic gradient systems in one unbounded spatial dimension,"This paper is concerned with damped hyperbolic gradient systems of the form
\[ \alpha u_{tt} + u_t = -\nabla V(u) + u_{xx}\,, \] where the spatial domain
is the whole real line, the state variable $u$ is multidimensional, $\alpha$ is
a positive quantity, and the potential $V$ is coercive at infinity. For such
systems, under generic assumptions on the potential, the asymptotic behaviour
of every bistable solution (that is, every solution close at both ends of space
to stable homogeneous equilibria) is described. Every such solution approaches,
far to the left in space a stacked family of bistable fronts travelling to the
left, far to the right in space a stacked family of bistable fronts travelling
to the right, and in between a pattern of profiles of stationary solutions
homoclinic or heteroclinic to stable homogeneous equilibria, going slowly away
from one another. In the absence of maximum principle, the arguments are purely
variational. This extends previous results obtained in companion papers for
damped wave equations or parabolic gradient systems, in the spirit of the
program initiated in the late seventies by Fife and McLeod on the global
asymptotic behaviour of bistable solutions for parabolic equations.",1703.01221v2
2017-03-06,Polynomial Stabilization of Solutions to a Class of Damped Wave Equations,"We consider a class of wave equations of the type $\partial_{tt} u + Lu +
B\partial_{t} u = 0$, with a self-adjoint operator $L$, and various types of
local damping represented by $B$. By establishing appropriate and raher precise
estimates on the resolvent of an associated operator $A$ on the imaginary axis
of ${{\Bbb C}}$, we prove polynomial decay of the semigroup $\exp(-tA)$
generated by that operator. We point out that the rate of decay depends
strongly on the concentration of eigenvalues and that of the eigenfunctions of
the operator $L$. We give several examples of application of our abstract
result, showing in particular that for a rectangle $\Omega := (0,L_{1})\times
(0,L_{2})$ the decay rate of the energy is different depending on whether the
ratio $L_{1}^2/L_{2}^2$ is rational, or irrational but algebraic.",1703.01735v1
2017-03-08,System-Theoretic Performance Metrics for Low-Inertia Stability of Power Networks,"As bulk synchronous generators in the power grid are replaced by distributed
generation interfaced through power electronics, inertia is removed from the
system, prompting concerns over grid stability. Different metrics are available
for quantifying grid stability and performance; however, no theoretical results
are available comparing and contrasting these metrics. This paper presents a
rigorous system-theoretic study of performance metrics for low-inertia
stability. For networks with uniform parameters, we derive explicit expressions
for the eigenvalue damping ratios, and for the $\mathcal{H}_{2}$ and
$\mathcal{H}_{\infty}$ norms of the linearized swing dynamics, from external
power disturbances to different phase/frequency performance outputs.These
expressions show the dependence of system performance on inertia constants,
damping constants, and on the grid topology. Surprisingly, we find that the
$\mathcal{H}_2$ and $\mathcal{H}_{\infty}$ norms can display contradictory
behavior as functions of the system inertia, indicating that low-inertia
performance depends strongly on the chosen performance metric.",1703.02646v1
2017-03-20,A quantum correlated twin atom laser from a Bose-Hubbard system,"We propose and evaluate a method to construct a quantum correlated twin atom
laser using a pumped and damped Bose-Hubbard inline trimer which can operate in
a stationary regime. With pumping via a source condensate filling the middle
well and damping using either an electron beam or optical means at the two end
wells, we show that bipartite quantum correlations build up between the ends of
the chain, and that these can be measured either in situ or in the outcoupled
beams. While nothing similar to our system has yet been achieved
experimentally, recent advances mean that it should be practically realisable
in the near future.",1703.06607v2
2017-03-20,Non-universal velocity probability densities in two-dimensional turbulence: the effect of large-scale dissipation,"We show that some statistical properties of forced two-dimensional turbulence
have an important sensitivity to the form of large-scale dissipation which is
required to damp the inverse cascade. We consider three models of large-scale
dissipation: linear ""Ekman"" drag, non-linear quadratic drag, and scale
selective hypo-drag that damps only low-wavenumber modes. In all cases, the
statistically steady vorticity field is dominated by almost axisymmetric
vortices, and the probability density function of vorticity is non-Gaussian.
However, in the case of linear and quadratic drag, we find that the velocity
statistics is close to Gaussian, with non-negligible contribution coming from
the background turbulent flow. On the other hand, with hypo-drag, the
probability density function of velocity is non-Gaussian and is predominantly
determined by the properties of the vortices. With hypo-drag, the relative
positions of the vortices and the exponential distribution of the vortex
extremum are important factors responsible for the non-Gaussian velocity
statistics.",1703.07000v1
2017-03-21,Numerical Range and Quadratic Numerical Range for Damped Systems,"We prove new enclosures for the spectrum of non-selfadjoint operator matrices
associated with second order linear differential equations $\ddot{z}(t) + D
\dot{z} (t) + A_0 z(t) = 0$ in a Hilbert space. Our main tool is the quadratic
numerical range for which we establish the spectral inclusion property under
weak assumptions on the operators involved; in particular, the damping operator
only needs to be accretive and may have the same strength as $A_0$. By means of
the quadratic numerical range, we establish tight spectral estimates in terms
of the unbounded operator coefficients $A_0$ and $D$ which improve earlier
results for sectorial and selfadjoint $D$; in contrast to numerical range
bounds, our enclosures may even provide bounded imaginary part of the spectrum
or a spectral free vertical strip. An application to small transverse
oscillations of a horizontal pipe carrying a steady-state flow of an ideal
incompressible fluid illustrates that our new bounds are explicit.",1703.07447v1
2017-03-22,Kinetic simulations of ladder climbing by electron plasma waves,"The energy of plasma waves can be moved up and down the spectrum using
chirped modulations of plasma parameters, which can be driven by external
fields. Depending on whether the wave spectrum is discrete (bounded plasma) or
continuous (boundless plasma), this phenomenon is called ladder climbing (LC)
or autoresonant acceleration of plasmons. It was first proposed by Barth
\textit{et al.} [PRL \textbf{115}, 075001 (2015)] based on a linear fluid
model. In this paper, LC of electron plasma waves is investigated using fully
nonlinear Vlasov-Poisson simulations of collisionless bounded plasma. It is
shown that, in agreement with the basic theory, plasmons survive substantial
transformations of the spectrum and are destroyed only when their wave numbers
become large enough to trigger Landau damping. Since nonlinear effects decrease
the damping rate, LC is even more efficient when practiced on structures like
quasiperiodic Bernstein-Greene-Kruskal (BGK) waves rather than on Langmuir
waves \textit{per~se}.",1703.07694v1
2017-03-22,"New versions of Newton method: step-size choice, convergence domain and under-determined equations","Newton method is one of the most powerful methods for finding solutions of
nonlinear equations and for proving their existence. In its ""pure"" form it has
fast convergence near the solution, but small convergence domain. On the other
hand damped Newton method has slower convergence rate, but weaker conditions on
the initial point. We provide new versions of Newton-like algorithms, resulting
in combinations of Newton and damped Newton method with special step-size
choice, and estimate its convergence domain. Under some assumptions the
convergence is global. Explicit complexity results are also addressed. The
adaptive version of the algorithm (with no a priori constants knowledge) is
presented. The method is applicable for under-determined equations (with $m<n$,
$m$ being the number of equations and $n$ being the number of variables). The
results are specified for systems of quadratic equations, for composite
mappings and for one-dimensional equations and inequalities.",1703.07810v2
2017-03-30,Study of spin pumping in Co thin film vis-a-vis seed and capping layer using ferromagnetic resonance spectroscopy,"We investigated the dependence of the seed [Ta/Pt, Ta/Au] and capping [Pt/Ta,
Au/Ta] layers on spin pumping effect in the ferromagnetic 3 nm thick Co thin
film using ferromagnetic resonance spectroscopy. The data is fitted with Kittel
equation to evaluate damping constant and g-factor. A strong dependence of seed
and capping layers on spin pumping has been discussed. The value of damping
constant {alpha} is found to be relatively large i.e. 0.0326 for the
Ta{3}/Pt{3}/Co{3}/Pt{3}/Ta{3} {nm} multi-layer structure, while it is 0.0104
for Ta{3}/Co{3}/Ta{3} {nm}. Increase in {alpha} is observed due to Pt layer
that works as a good sink for spins due to high spin orbit coupling. In
addition, we measured the effective spin conductance = 2.0e18 m-2 for the
trilayer structure Pt{3}/Co{3}/Pt{3} {nm} as a result of the enhancement in
{alpha} relative to its bulk value. We observed that the evaluated g-factor
decreases as effective demagnetizing magnetic field increases in all the
studied samples. The azimuthal dependence of magnetic resonance field and line
width showed relatively high anisotropy in the trilayer Ta{3}/Co{3}/Ta{3} {nm}
structure.",1703.10630v1
2017-04-03,Sensing Coherent Phonons with Two-photon Interference,"Detecting coherent phonons pose different challenges compared to coherent
photons due to the much stronger interaction between phonons and matter. This
is especially true for high frequency heat carrying phonons, which are
intrinsic lattice vibrations experiencing many decoherence events with the
environment, and are thus generally assumed to be incoherent. Two photon
interference techniques, especially coherent population trapping (CPT) and
electromagnetically induced transparency (EIT), have led to extremely sensitive
detection, spectroscopy and metrology. Here, we propose the use of two photon
interference in a three level system to sense coherent phonons. Unlike prior
works which have treated phonon coupling as damping, we account for coherent
phonon coupling using a full quantum-mechanical treatment. We observe strong
asymmetry in absorption spectrum in CPT and negative dispersion in EIT
susceptibility in the presence of coherent phonon coupling which cannot be
accounted for if only pure phonon damping is considered. Our proposal has
application in sensing heat carrying coherent phonons effects and understanding
coherent bosonic multi-pathway interference effects in three coupled oscillator
systems.",1704.00446v1
2017-04-03,Simulating spin-boson models with trapped ions,"We propose a method to simulate the dynamics of spin-boson models with small
crystals of trapped ions where the electronic degree of freedom of one ion is
used to encode the spin while the collective vibrational degrees of freedom are
employed to form an effective harmonic environment. The key idea of our
approach is that a single damped mode can be used to provide a harmonic
environment with Lorentzian spectral density. More complex spectral functions
can be tailored by combining several individually damped modes. We propose to
work with mixed-species crystals such that one species serves to encode the
spin while the other species is used to cool the vibrational degrees of freedom
to engineer the environment. The strength of the dissipation on the spin can be
controlled by tuning the coupling between spin and vibrational degrees of
freedom. In this way the dynamics of spin-boson models with macroscopic and
non-Markovian environments can be simulated using only a few ions. We
illustrate the approach by simulating an experiment with realistic parameters
and show by computing quantitative measures that the dynamics is genuinely
non-Markovian.",1704.00629v1
2017-04-07,Coherent-induced state ordering with fixed mixedness,"In this paper, we study coherence-induced state ordering with Tsallis
relative entropy of coherence, relative entropy of coherence and $l_{1}$ norm
of coherence. Firstly, we show that these measures give the same ordering for
single-qubit states with a fixed mixedness or a fixed length along the
direction $\sigma_{z}$. Secondly, we consider some special cases of high
dimensional states, we show that these measures generate the same ordering for
the set of high dimensional pure states if any two states of the set satisfy
majorization relation. Moreover, these three measures generate the same
ordering for all $X$ states with a fixed mixedness. Finally, we discuss
dynamics of coherence-induced state ordering under Markovian channels. We find
phase damping channel don't change the coherence-induced state ordering for
some single-qubit states with fixed mixedness, instead amplitude damping
channel change the coherence-induced ordering even though for single-qubit
states with fixed mixedness.",1704.02244v1
2017-04-13,A possible connection between the spin temperature of damped Lyman-alpha absorption systems and star formation history,"We present a comprehensive analysis of the spin temperature/covering factor
degeneracy, T/f, in damped Lyman-alpha absorption systems. By normalising the
upper limits and including these via a survival analysis, there is, as
previously claimed, an apparent increase in T/f with redshift at z > 1.
However, when we account for the geometry effects of an expanding Universe,
neglected by the previous studies, this increase in T/f at z > 1 is preceded by
a decrease at z < 1. Using high resolution radio images of the background
continuum sources, we can transform the T/f degeneracy to T/d^2, where d is the
projected linear size of the absorber. Again, there is no overall increase with
redshift, although a dip at z ~ 2 persists. Furthermore, we find d^2/T to
follow a similar variation with redshift as the star formation rate. This
suggests that, although the total hydrogen column density shows little relation
to the SFR, the fraction of the cold neutral medium may. Therefore, further
efforts to link the neutral gas with the star formation history should also
consider the cool component of the gas.",1704.04294v2
2017-04-17,Magnetic field line random walk in two-dimensional dynamical turbulence,"The field line random walk (FLRW) of magnetic turbulence is one of the
important topics in plasma physics and astrophysics. In this article by using
the field line tracing method mean square displacements (MSD) of FLRW is
calculated in all possible length scales for pure two-dimensional turbulence
with damping dynamical model. We demonstrate that in order to describe FLRW
with damping dynamical model a new dimensionless quantity $R$ is needed to be
introduced. In different length scales dimensionless MSD shows different
relationship with the dimensionless quantity $R$. Although temporal effect
impacts MSD of FLRW and even changes regimes of FLRW, it dose not affect the
relationship between the dimensionless MSD and dimensionless quantity $R$ in
all possible length scales.",1704.05059v3
2017-04-19,Quantum simulation of quantum channels in nuclear magnetic resonance,"We propose and experimentally demonstrate an efficient framework for the
quantum simulation of quantum channels in NMR. Our approach relies on the
suitable decomposition of non-unitary operators in a linear combination of $d$
unitary ones, which can be then experimentally implemented with the assistance
of a number of ancillary qubits that grows logarithmically in $d$. As a
proof-of-principle demonstration, we realize the quantum simulation of three
quantum channels for a single-qubit: phase damping (PD), amplitude damping
(AD), and depolarizing (DEP) channels. For these paradigmatic cases, we measure
key features, such as the fidelity of the initial state and the associated von
Neuman entropy for a qubit evolving through these channels. Our experiments are
carried out using nuclear spins in a liquid sample and NMR control techniques.",1704.05593v2
2017-04-24,Beating the Classical Limits of Information Transmission using a Quantum Decoder,"Encoding schemes and error-correcting codes are widely used in information
technology to improve the reliability of data transmission over real-world
communication channels. Quantum information protocols can further enhance the
performance in data transmission by encoding a message in quantum states,
however, most proposals to date have focused on the regime of a large number of
uses of the noisy channel, which is unfeasible with current quantum technology.
We experimentally demonstrate quantum enhanced communication over an amplitude
damping noisy channel with only two uses of the channel per bit and a single
entangling gate at the decoder. By simulating the channel using a photonic
interferometric setup, we experimentally increase the reliability of
transmitting a data bit by greater than 20% for a certain damping range over
classically sending the message twice. We show how our methodology can be
extended to larger systems by simulating the transmission of a single bit with
up to eight uses of the channel and a two-bit message with three uses of the
channel, predicting a quantum enhancement in all cases.",1704.07036v2
2017-04-24,Quasilinear diffusion coefficients in a finite Larmor radius expansion for ion cyclotron heated plasmas,"In this paper, a reduced model of quasilinear diffusion by a small Larmor
radius approximation is derived to couple the Maxwell's equations and the
Fokker-Planck equation self-consistently for ion cyclotron range of frequency
waves in a tokamak. The reduced model ensures the important properties of the
full model by Kennel-Engelmann diffusion, such as diffusion directions, wave
polarizations, and H-theorem. The kinetic energy change (W-dot) is used to
derive the reduced model diffusion coefficients for the fundamental damping and
the second harmonic damping to the lowest order of the finite Larmor radius
expansion. The quasilinear diffusion coefficients are implemented in a coupled
code (TORIC-CQL3D) with the equivalent reduced model of dielectric tensor. We
also present the simulations of the ITER minority heating scenario, in which
the reduced model is verified within the allowable errors from the full model
results.",1704.07283v1
2017-04-27,Chirality-induced Antisymmetry in Magnetic Domain-Wall Speed,"In chiral magnetic materials, numerous intriguing phenomena such as built in
chiral magnetic domain walls (DWs) and skyrmions are generated by the
Dzyaloshinskii Moriya interaction (DMI). The DMI also results in asymmetric DW
speed under in plane magnetic field, which provides a useful scheme to measure
the DMI strengths. However, recent findings of additional asymmetries such as
chiral damping have disenabled unambiguous DMI determination and the underlying
mechanism of overall asymmetries becomes under debate. By extracting the
DMI-induced symmetric contribution, here we experimentally investigated the
nature of the additional asymmetry. The results revealed that the additional
asymmetry has a truly antisymmetric nature with the typical behavior governed
by the DW chirality. In addition, the antisymmetric contribution changes the DW
speed more than 100 times, which cannot be solely explained by the chiral
damping scenario. By calibrating such antisymmetric contributions, experimental
inaccuracies can be largely removed, enabling again the DMI measurement scheme.",1704.08751v1
2017-05-02,The response of a Unruh-deWitt particle detector in a thin-shell wormhole spacetime,"We investigate the transition probability of a Unruh-deWitt particle detector
evolving in flat space and in a wormhole spacetime, in various scenarios. In
Minkowski space, we look at the response of the detector on trajectories having
discontinuities and rapid variations, as well as the effect of finite-time
coupling. It is found that these features induce spurious oscillations in the
probability and rate of transition. At large times the oscillations are damped
and the probability tends to a constant value. Next, we look at the response of
an inertial detector on a radial trajectory that passes through a thin-shell
wormhole. After finding the appropriate modes, we look at the renormalized
detector response, defined by subtracting the flat space analogues from the
partial probabilities. The resulting curve has a peak around the wormhole
throat followed by a period of damped oscillations, before stabilizing to a
constant value. This is very similar to the flat space results, which is
surprising given that in this case the trajectory is continuous. The features
of the transition probability are due entirely to the nontrivial topology
induced by the wormhole.",1705.00890v1
2017-05-04,"Phase-space mixing in dynamically unstable, integrable few-mode quantum systems","Quenches in isolated quantum systems are currently a subject of intense
study. Here, we consider quantum few-mode systems that are integrable in their
classical mean-field limit and become dynamically unstable after a quench of a
system parameter. Specifically, we study a Bose-Einstein condensate (BEC) in a
double-well potential and an antiferromagnetic spinor BEC constrained to a
single spatial mode. We study the time dynamics after the quench within the
truncated Wigner approximation (TWA) and find that system relaxes to a steady
state due to phase-space mixing. Using the action-angle formalism and a
pendulum as an illustration, we derive general analytical expressions for the
time evolution of expectation values of observables and their long-time limits.
We find that the deviation of the long-time expectation value from its
classical value scales as $1/O(\ln N )$, where $N$ is the number of atoms in
the condensate. Furthermore, the relaxation of an observable to its steady
state value is a damped oscillation and the damping is Gaussian in time. We
confirm our results with numerical TWA simulations.",1705.01702v1
2017-05-11,Quantum Correlations and Bell Inequality Violation under Decoherence,"Quantum Correlations are studied extensively in quantum information domain.
Entanglement Measures and Quantum Discord are good examples of these actively
studied correlations. Detection of violation in Bell inequalities is also a
widely active area in quantum information theory world. In this work, we
revisit the problem of analyzing the behavior of quantum correlations and
violation of Bell inequalities in noisy channels. We extend the problem defined
in [1] by observing the changes in negativity measure, quantum discord and a
modified version of Horodecki measure for violation of Bell inequalities under
amplitude damping, phase damping and depolarizing channels. We report different
interesting results for each of these correlations and measures. All these
correlations and measures decrease under decoherence channels, but some changes
are very dramatical comparing to others. We investigate also separability
conditions of example studied states.",1705.03882v2
2017-05-18,Local and global existence of solutions to a strongly damped wave equation of the $p$-Laplacian type,"This article focuses on a quasilinear wave equation of $p$-Laplacian type: $$
u_{tt} - \Delta_p u - \Delta u_t=0$$ in a bounded domain
$\Omega\subset\mathbb{R}^3$ with a sufficiently smooth boundary
$\Gamma=\partial\Omega$ subject to a generalized Robin boundary condition
featuring boundary damping and a nonlinear source term. The operator
$\Delta_p$, $2 < p < 3$, denotes the classical $p$-Laplacian. The nonlinear
boundary term $f (u)$ is a source feedback that is allowed to have a
supercritical exponent, in the sense that the associated Nemytskii operator is
not locally Lipschitz from $W^{1,p}(\Omega)$ into $L^2(\Gamma)$. Under suitable
assumptions on the parameters we provide a rigorous proof of existence of a
local weak solution which can be extended globally in time provided the source
term satisfies an appropriate growth condition.",1705.06696v2
2017-05-21,Plasmon modes in graphene-GaAs heterostructures,"We investigate the plasmon dispersion relation and damping rate of collective
excitations in a double-layer system consisting of bilayer graphene and GaAs
quantum well, separated by a distance, at zero temperature with no interlayer
tunneling. We use the random-phase-approximation dielectric function and take
into account the nonhomogeneity of the dielectric background of the system. We
show that the plasmon frequencies and damping rates depend considerably on
interlayer correlation parameters, electron densities and dielectric constants
of the contacting media.",1705.07389v1
2017-05-23,Unifying description of the damping regimes of a stochastic particle in a periodic potential,"We analyze the classical problem of the stochastic dynamics of a particle
confined in a periodic potential, through the so called Il'in and Khasminskii
model, with a novel semi-analytical approach. Our approach gives access to the
transient and the asymptotic dynamics in all damping regimes, which are
difficult to investigate in the usual Brownian model. We show that the
crossover from the overdamped to the underdamped regime is associated with the
loss of a typical time scale and of a typical length scale, as signaled by the
divergence of the probability distribution of a certain dynamical event. In the
underdamped regime, normal diffusion coexists with a non Gaussian displacement
probability distribution for a long transient, as recently observed in a
variety of different systems. We rationalize the microscopic physical processes
leading to the non-Gaussian behavior, as well as the timescale to recover the
Gaussian statistics. The theoretical results are supported by numerical
calculations and are compared to those obtained for the Brownian model.",1705.08083v2
2017-05-27,Experimental Observation of Electron-Acoustic Wave Propagation in Laboratory Plasma,"In the field of fundamental plasma waves, direct observation of
electron-acoustic wave (EAW) propagation in laboratory plasmas remains a
challenging problem, mainly because of heavy damping. In the MaPLE device, the
wave is observed and seen to propagate with phase velocity $\sim1.8$ times the
electron thermal velocity. A small amount of cold, drifting electrons, with
moderate bulk to cold temperature ratio ($\approx 2 - 3$), is present in the
device. It plays a crucial role in reducing the damping. Our calculation
reveals that the drift relaxes the stringent condition on the temperature ratio
for wave destabilization. Growth rate becomes positive above a certain drift
velocity even if the temperature ratio is moderate. The observed phase velocity
agrees well with the theoretical estimate. Experimental realization of the mode
may open up a new avenue in EAW research.",1705.09806v1
2017-06-08,Superconductivity around nematic quantum critical point in two-dimensional metals,"We study the properties of $s$-wave superconductivity induced around a
nematic quantum critical point in two-dimensional metals. The strong Landau
damping and the Cooper pairing between incoherent fermions have dramatic mutual
influence on each other, and hence should be treated on an equal footing. This
problem is addressed by analyzing the self-consistent Dyson-Schwinger equations
for the superconducting gap and Landau damping rate. We solve the equations at
zero temperature without making any linearization, and show that the
superconducting gap is maximized at the quantum critical point and decreases
rapidly as the system departs from this point. The interplay between nematic
fluctuation and an additional pairing interaction, caused by phonon or other
boson mode, is also investigated. The total superconducting gap generated by
such interplay can be several times larger than the direct sum of the gaps
separately induced by these two pairing interactions. This provides a promising
way to achieve remarkable enhancement of superconductivity.",1706.02583v2
2017-06-16,Simulation of non-Pauli Channels,"We consider the simulation of a quantum channel by two parties who share a
resource state and may apply local operations assisted by classical
communication (LOCC). One specific type of such LOCC is standard teleportation,
which is however limited to the simulation of Pauli channels. Here we show how
we can easily enlarge this class by means of a minimal perturbation of the
teleportation protocol, where we introduce noise in the classical communication
channel between the remote parties. By adopting this noisy protocol, we provide
a necessary condition for simulating a non-Pauli channel. In particular, we
characterize the set of channels that are generated assuming the Choi matrix of
an amplitude damping channel as a resource state. Within this set, we identify
a class of Pauli-damping channels for which we bound the two-way quantum and
private capacities.",1706.05384v2
2017-06-17,\emph{Ab initio} calculation of spin-orbit coupling for NV center in diamond exhibiting dynamic Jahn-Teller effect,"Point defects in solids may realize solid state quantum bits. The spin-orbit
coupling in these point defects plays a key role in the magneto-optical
properties that determine the conditions of quantum bit operation. However,
experimental data and methods do not directly yield this highly important data,
particularly, for such complex systems where dynamic Jahn-Teller (DJT) effect
damps the spin-orbit interaction. Here, we show for an exemplary quantum bit,
nitrogen-vacancy (NV) center in diamond, that \emph{ab initio} supercell
density functional theory provide quantitative prediction for the spin-orbit
coupling damped by DJT. We show that DJT is responsible for the multiple
intersystem crossing rates of NV center at cryogenic temperatures. Our results
pave the way toward optimizing solid state quantum bits for quantum information
processing and metrology applications.",1706.05523v2
2017-06-20,Decoherence induced spin squeezing signatures in Greenberger-Horne-Zeilinger and W states,"We reckon the behaviour of spin squeezing in tripartite unsqueezed maximally
entangled Green- berger-Horne-Zeilinger (GHZ) and W states under various
decoherence channels with Kitagawa- Ueda (KU) criteria. In order to search spin
squeezing sudden death (SSSD) and signatures of spin squeezing production we
use bit flip, phase flip, bit-phase-flip, amplitude damping, phase damping and
depolarization channels in the present study. In literature, the influence of
decoherence has been studied as a destroying element. On the contrary here we
investigate the positive aspect of decoherence, which produce spin squeezing in
unsqueezed GHZ and W states under certain channels. Our meticulous study shows
that GHZ state remain unsqueezed under aforementioned channels except
bit-phase-flip and depolarization channels. While all the decoherence channels
produce spin squeezing in W state. So we find, GHZ is more robust in comparison
to W state in the sense of spin squeezing production under decoherence. Most
importantly we find that none of the decoherence channel produce SSSD in any
one of the state.",1706.06273v2
2017-06-22,Adaptive recurrence quantum entanglement distillation for two-Kraus-operator channels,"Quantum entanglement serves as a valuable resource for many important quantum
operations. A pair of entangled qubits can be shared between two agents by
first preparing a maximally entangled qubit pair at one agent, and then sending
one of the qubits to the other agent through a quantum channel. In this
process, the deterioration of entanglement is inevitable since the noise
inherent in the channel contaminates the qubit. To address this challenge,
various quantum entanglement distillation (QED) algorithms have been developed.
Among them, recurrence algorithms have advantages in terms of implementability
and robustness. However, the efficiency of recurrence QED algorithms has not
been investigated thoroughly in the literature. This paper put forth two
recurrence QED algorithms that adapt to the quantum channel to tackle the
efficiency issue. The proposed algorithms have guaranteed convergence for
quantum channels with two Kraus operators, which include phase-damping and
amplitude-damping channels. Analytical results show that the convergence speed
of these algorithms is improved from linear to quadratic and one of the
algorithms achieves the optimal speed. Numerical results confirm that the
proposed algorithms significantly improve the efficiency of QED.",1706.07461v1
2017-06-26,Landau Damping of Beam Instabilities by Electron Lenses,"Modern and future particle accelerators employ increasingly higher intensity
and brighter beams of charged particles and become operationally limited by
coherent beam instabilities. Usual methods to control the instabilities, such
as octupole magnets, beam feedback dampers and use of chromatic effects, become
less effective and insufficient. We show that, in contrast, Lorentz forces of a
low-energy, a magnetically stabilized electron beam, or ""electron lens"", easily
introduces transverse nonlinear focusing sufficient for Landau damping of
transverse beam instabilities in accelerators. It is also important that,
unlike other nonlinear elements, the electron lens provides the frequency
spread mainly at the beam core, thus allowing much higher frequency spread
without lifetime degradation. For the parameters of the Future Circular
Collider, a single conventional electron lens a few meters long would provide
stabilization superior to tens of thousands of superconducting octupole
magnets.",1706.08477v1
2017-07-01,Amending entanglement-breaking channels via intermediate unitary operations,"We report a bulk optics experiment demonstrating the possibility of restoring
the entanglement distribution through noisy quantum channels by inserting a
suitable unitary operation (filter) in the middle of the transmission process.
We focus on two relevant classes of single-qubit channels consisting in
repeated applications of rotated phase damping or rotated amplitude damping
maps, both modeling the combined Hamiltonian and dissipative dynamics of the
polarization state of single photons. Our results show that interposing a
unitary filter between two noisy channels can significantly improve
entanglement transmission. This proof-of-principle demonstration could be
generalized to many other physical scenarios where entanglement-breaking
communication lines may be amended by unitary filters.",1707.00161v1
2017-06-30,Damped oscillations of the energy of a bosonic bath due to spectral gaps and special initial correlations,"The energy of the bosonic bath and the flow of quantum information are
analyzed over short and long times in local dephasing channels for special
correlated or factorized initial conditions, respectively, which involve
thermal states. The continuous distribution of frequency modes of the bosonic
bath exhibits a spectral gap over low frequencies. The bath energy shows
oscillatory behaviors around the asymptotic value and information is
alternatively lost and gained by the open system. Due to the low-frequency gap,
the damped oscillations become regular over long times and the frequency of the
oscillations coincides with the upper cut-off frequency of the spectral gap.
Sequences of long-time intervals are obtained over which the bath energy
increases (decreases), for the correlated initial conditions, and information
is lost (gained) by the open system, for the factorized initial configurations,
even at different temperatures. Such long-time correspondence between the
variations of the bath energy and of the information is reversed if compared to
the one obtained without the low-frequency gap. The correspondence fails if the
spectral density is tailored according to power laws with odd natural powers
near the upper cut-off frequency of the spectral gap.",1707.00604v1
2017-07-11,Andreev reflection assisted lasing in an electromagnetic resonator coupled to a hybrid-quantum-dot,"A single mode electromagnetic resonator coupled to a two-level
hybrid-quantum-dot(hQD) is studied theoretically as a laser(maser), when the
hQD is driven out of equilibrium with external applied d.c. bias voltage. Using
the formalism of the non-equilibrium Green's functions for the hQD and the
semi-classical laser equations, we determine the relevant physical quantities
of the system. We find that due to the resonant Andreev reflections and the
formation of the Floquet-Andreev side-resonances in the sub-gap region, at
appropriate gate voltages and above a certain threshold bias voltage and
damping factor of the resonator, the two-level QD has non-zero gain spectrum
and lasing can happen in the system in the frequency range of superconducting
gap. Furthermore, our results show that depending on the damping factor of the
resonator and above a specific threshold bias voltages, the lasing can be
either due to single electron transitions or cascaded electron transitions
between the Andreev resonances and Floquet-Andreev side-resonances.",1707.03219v2
2017-07-13,The sharp estimate of the lifespan for the semilinear wave equation with time-dependent damping,"We consider the following semilinear wave equation with time-dependent
damping. \begin{align} \tag{NLDW} \left\{ \begin{array}{ll} \partial_t^2 u -
\Delta u + b(t)\partial_t u = |u|^{p}, & (t,x) \in [0,T) \times \mathbb{R}^n,
\\ u(0,x)=\varepsilon u_0(x), u_t(0,x)=\varepsilon u_1(x), & x \in
\mathbb{R}^n, \end{array} \right. \end{align} where $n \in \mathbb{N}$, $p>1$,
$\varepsilon>0$, and $b(t)\thickapprox (t+1)^{-\beta}$ with $\beta \in [-1,1)$.
It is known that small data blow-up occurs when $1<p< p_F$ and, on the other
hand, small data global existence holds when $p>p_F$, where $p_F:=1+2/n$ is the
Fujita exponent. The sharp estimate of the lifespan was well studied when $1<p<
p_F$. In the critical case $p=p_F$, the lower estimate of the lifespan was also
investigated. Recently, Lai and Zhou obtained the sharp upper estimate of the
lifespan when $p=p_F$ and $b(t)=1$. In the present paper, we give the sharp
upper estimate of the lifespan when $p=p_F$ and $b(t)\thickapprox
(t+1)^{-\beta}$ with $\beta \in [-1,1)$ by the Lai--Zhou method.",1707.03950v1
2017-07-17,Candidate dust structures for starlight polarization,"Rotation damping and alignment are discussed as prerequisites for
polarization power. An expression is derived from first principles, for the
damping time of the rotation of a particle in a magnetic field, under the
Faraday braking torque, provided its electrical properties are known. This
makes it possible to describe mathematically, in great detail, the motion of
the particle and determine its ultimate state of motion, if a steady state is
possible at all. This work defines, first, the necessary condition for the
Faraday braking to be effective: a) the net electronic charge distribution
should not be uniform throughout; b) the number of vibration modes should
exceed a few tens. Resonance of rotation frequency with any of these modes is
not a requirement. For alignment to be possible, the ratio of gyroscopic and
conservative magnetic to non-conservative (retarding) magnetic torques must be
low. Either dia-, para- or ferro-magnetism can do, and a small susceptibility
is enough and even preferable. This opens up a wide spectrum of possible
candidates. A few examples are given.",1707.05247v1
2017-07-21,Quasinormal ringing of black holes in Einstein aether theory,"The gravitational consequence of local Lorentz violation (LV) should show
itself in derivation of the characteristic quasinormal ringing of black hole
mergers from their general relativity case. In this paper, we study quasinormal
modes (QNMs) of the scalar and electromagnetic field perturbations to Einstein
aether black holes. We find that quasinormal ringing of the first kind aether
black hole is similar to that of another Lorentz violation model---the
QED-extension limit of standard model extension. These similarities between
completely different backgrounds may imply that LV in gravity sector and LV in
matter sector have some connections between themself: damping quasinormal
ringing of black holes more rapidly and prolonging its oscillation period. By
compared to Schwarzschild black hole, both the first and the second kind aether
black holes have larger damping rate and smaller real oscillation frequency of
QNMs. And the differences are from 0.7 percent to 35 percents, those could be
detected by new generation of gravitational antennas.",1707.06747v2
2017-07-24,Self-concordant inclusions: A unified framework for path-following generalized Newton-type algorithms,"We study a class of monotone inclusions called ""self-concordant inclusion""
which covers three fundamental convex optimization formulations as special
cases. We develop a new generalized Newton-type framework to solve this
inclusion. Our framework subsumes three schemes: full-step, damped-step and
path-following methods as specific instances, while allows one to use inexact
computation to form generalized Newton directions. We prove a local quadratic
convergence of both the full-step and damped-step algorithms. Then, we propose
a new two-phase inexact path-following scheme for solving this monotone
inclusion which possesses an
$\mathcal{O}\left(\sqrt{\nu}\log(1/\varepsilon)\right)$-worst-case
iteration-complexity to achieve an $\varepsilon$-solution, where $\nu$ is the
barrier parameter and $\varepsilon$ is a desired accuracy. As byproducts, we
customize our scheme to solve three convex problems: convex-concave
saddle-point, nonsmooth constrained convex program, and nonsmooth convex
program with linear constraints. We also provide three numerical examples to
illustrate our theory and compare with existing methods.",1707.07403v1
2017-07-28,Finding stability domains and escape rates in kicked Hamiltonians,"We use an effective Hamiltonian to characterize particle dynamics and find
escape rates in a periodically kicked Hamiltonian. We study a model of
particles in storage rings that is described by a chaotic symplectic map.
Ignoring the resonances, the dynamics typically has a finite region in phase
space where it is stable. Inherent noise in the system leads to particle loss
from this stable region. The competition of this noise with radiation damping,
which increases stability, determines the escape rate. Determining this
`aperture' and finding escape rates is therefore an important physical problem.
We compare the results of two different perturbation theories and a variational
method to estimate this stable region. Including noise, we derive analytical
estimates for the steady-state populations (and the resulting beam emittance),
for the escape rate in the small damping regime, and compare them with
numerical simulations.",1707.09336v1
2017-07-29,Empirical Bayes approaches to PageRank type algorithms for rating scientific journals,"Following criticisms against the journal Impact Factor, new journal influence
scores have been developed such as the Eigenfactor or the Prestige Scimago
Journal Rank. They are based on PageRank type algorithms on the cross-citations
transition matrix of the citing-cited network. The PageRank algorithm performs
a smoothing of the transition matrix combining a random walk on the data
network and a teleportation to all possible nodes with fixed probabilities (the
damping factor being $\alpha= 0.85$). We reinterpret this smoothing matrix as
the mean of a posterior distribution of a Dirichlet-multinomial model in an
empirical Bayes perspective. We suggest a simple yet efficient way to make a
clear distinction between structural and sampling zeroes. This allows us to
contrast cases with self-citations included or excluded to avoid overvalued
journal bias. We estimate the model parameters by maximizing the marginal
likelihood with a Majorize-Minimize algorithm. The procedure ends up with a
score similar to the PageRank ones but with a damping factor depending on each
journal. The procedures are illustrated with an example about cross-citations
among 47 statistical journals studied by Varin et. al. (2016).",1707.09508v2
2017-08-02,Global existence of solutions for semi-linear wave equation with scale-invariant damping and mass in exponentially weighted spaces,"In this paper we consider the following Cauchy problem for the semi-linear
wave equation with scale-invariant dissipation and mass and power
non-linearity: \begin{align}\label{CP abstract} \begin{cases} u_{tt}-\Delta
u+\dfrac{\mu_1}{1+t} u_t+\dfrac{\mu_2^2}{(1+t)^2}u=|u|^p, \\ u(0,x)=u_0(x),
\,\, u_t(0,x)=u_1(x), \end{cases}\tag{$\star$} \end{align} where $\mu_1,
\mu_2^2$ are nonnegative constants and $p>1$. On the one hand we will prove a
global (in time) existence result for \eqref{CP abstract} under suitable
assumptions on the coefficients $\mu_1, \mu_2^2$ of the damping and the mass
term and on the exponent $p$, assuming the smallness of data in exponentially
weighted energy spaces. On the other hand a blow-up result for \eqref{CP
abstract} is proved for values of $p$ below a certain threshold, provided that
the data satisfy some integral sign conditions. Combining these results we find
the critical exponent for \eqref{CP abstract} in all space dimensions under
certain assumptions on $\mu_1$ and $\mu_2^2$. Moreover, since the global
existence result is based on a contradiction argument, it will be shown firstly
a local (in time) existence result.",1708.00738v1
2017-08-09,Stable and unstable roots of ion temperature gradient driven mode using curvature modified plasma dispersion functions,"Basic, local kinetic theory of ion temperature gradient driven (ITG) mode,
with adiabatic electrons is reconsidered. Standard unstable, purely oscillating
as well as damped solutions of the local dispersion relation are obtained using
a bracketing technique that uses the argument principle. This method requires
computing the plasma dielectric function and its derivatives, which are
implemented here using modified plasma dispersion functions with curvature and
their derivatives, and allows bracketing/following the zeros of the plasma
dielectric function which corresponds to different roots of the ITG dispersion
relation. We provide an open source implementation of the derivatives of
modified plasma dispersion functions with curvature, which are used in this
formulation. Studying the local ITG dispersion, we find that near the threshold
of instability the unstable branch is rather asymmetric with oscillating
solutions towards lower wave numbers (i.e. drift waves), and damped solutions
toward higher wave numbers. This suggests a process akin to inverse cascade by
coupling to the oscillating branch towards lower wave numbers may play a role
in the nonlinear evolution of the ITG, near the instability threshold. Also,
using the algorithm, the linear wave diffusion is estimated for the marginally
stable ITG mode.",1708.03026v1
2017-08-11,On the Small Mass Limit of Quantum Brownian Motion with Inhomogeneous Damping and Diffusion,"We study the small mass limit (or: the Smoluchowski-Kramers limit) of a class
of quantum Brownian motions with inhomogeneous damping and diffusion. For Ohmic
bath spectral density with a Lorentz-Drude cutoff, we derive the
Heisenberg-Langevin equations for the particle's observables using a quantum
stochastic calculus approach. We set the mass of the particle to equal $m =
m_{0} \epsilon$, the reduced Planck constant to equal $\hbar = \epsilon$ and
the cutoff frequency to equal $\Lambda = E_{\Lambda}/\epsilon$, where $m_0$ and
$E_{\Lambda}$ are positive constants, so that the particle's de Broglie
wavelength and the largest energy scale of the bath are fixed as $\epsilon \to
0$. We study the limit as $\epsilon \to 0$ of the rescaled model and derive a
limiting equation for the (slow) particle's position variable. We find that the
limiting equation contains several drift correction terms, the quantum
noise-induced drifts, including terms of purely quantum nature, with no
classical counterparts.",1708.03685v1
2017-08-13,Observation of Spin Superfluidity in a Bose Gas Mixture,"The spin dynamics of a harmonically trapped Bose-Einstein condensed binary
mixture of sodium atoms is experimentally investigated at finite temperature.
In the collisional regime the motion of the thermal component is shown to be
damped because of spin drag, while the two condensates exhibit a counter flow
oscillation without friction, thereby providing direct evidence for spin
superfluidity. Results are also reported in the collisionless regime where the
spin components of both the condensate and thermal part oscillate without
damping, their relative motion being driven by a mean field effect. We also
measure the static polarizability of the condensed and thermal parts and we
find a large increase of the condensate polarizability with respect to the T=0
value, in agreement with the predictions of theory.",1708.03923v2
2017-08-16,Multi-component plasmons in monolayer MoS$_2$ with circularly polarized optical pumping,"By making use of circularly polarized light and electrostatic gating,
monolayer molybdenum disulfide (ML-MoS$_2$) can form a platform supporting
multiple types of charge carriers. They can be discriminated by their spin,
valley index or whether they're electrons or holes. We investigate the
collective properties of those charge carriers and are able to identify new
distinct plasmon modes. We analyze the corresponding dispersion relation,
lifetime and oscillator strength, and calculate the phase relation between the
oscillations in the different components of the plasmon modes. All platforms in
ML-MoS$_2$ support a long-wavelength $\sqrt{q}$ plasmon branch at zero Kelvin.
In addition to this, for an $n$-component system, $n-1$ distinct plasmon modes
appear as acoustic modes with linear dispersion in the long-wavelength limit.
These modes correspond to out-of-phase oscillations in the different Fermion
liquids and have, although being damped, a relatively long lifetime.
Additionally, we also find new distinct modes at large wave vector that are
stronger damped by intra-band processes.",1708.04940v1
2017-08-17,Viscous forces and bulk viscoelasticity near jamming,"When weakly jammed packings of soft, viscous, non-Brownian spheres are probed
mechanically, they respond with a complex admixture of elastic and viscous
effects. While many of these effects are understood for specific, approximate
models of the particles' interactions, there are a number of proposed force
laws in the literature, especially for viscous interactions. We numerically
measure the complex shear modulus $G^*$ of jammed packings for various viscous
force laws that damp relative velocities between pairs of contacting particles
or between a particle and the continuous fluid phase. We find a surprising
sensitive dependence of $G^*$ on the viscous force law: the system may or may
not display dynamic critical scaling, and the exponents describing how $G^*$
scales with frequency can change. We show that this sensitivity is closely
linked to manner in which viscous damping couples to floppy-like, non-affine
motion, which is prominent near jamming.",1708.05241v2
2017-08-21,"Diverging, but negligible power at Carnot efficiency: theory and experiment","We discuss the possibility of reaching the Carnot efficiency by heat engines
(HEs) out of quasi-static conditions at nonzero power output. We focus on
several models widely used to describe the performance of actual HEs. These
models comprise quantum thermoelectric devices, linear irreversible HEs,
minimally nonlinear irreversible HEs, HEs working in the regime of low
dissipation, over-damped stochastic HEs and an under-damped stochastic HE.
Although some of these HEs can reach the Carnot efficiency at nonzero and even
diverging power, the magnitude of this power is always negligible compared to
the maximum power attainable in these systems. We provide conditions for
attaining the Carnot efficiency in the individual models and explain practical
aspects connected with reaching the Carnot efficiency at large power output.
Furthermore, we show how our findings can be tested in practice using a
standard Brownian HE realizable with available micromanipulation techniques.",1708.06261v4
2017-08-21,Solar Line Asymmetries: Modelling the Effect of Granulation on the Solar Spectrum,"A parametric model of granulation employing a small number of parameters was
developed. Synthetic spectra calculated using this model closely match observed
spectra and, in particular, reproduce the asymmetries observed in spectral
lines. Both the microturbulent motions and the large-scale flow velocity
decrease exponentially with a scale height of 368 km as the height within the
photosphere increases. The model agrees with observations of the solar
granulation (from which it was derived).
  The horizontal motions associated with granulation were found and used to
calculate spectra emergent away from disk centre. These calculated spectra were
compared to observed spectra, with the agreement supporting the accuracy of the
granular model.
  Also in the course of this work, the Brueckner-O'Mara damping theory was
found to predict damping constants accurately. The photospheric abundances of a
number of elements were determined. The abundance obtained for iron agrees with
the meteoric iron abundance. Astrophysical f-values for some lines were also
determined.",1708.06408v1
2017-08-24,The influence of small-scale magnetic field on the evolution of inclination angle and precession damping in the framework of 3-component model of neutron star,"The evolution of inclination angle and precession damping of radio pulsars is
considered. It is assumed that the neutron star consists of 3 ""freely"" rotating
components: the crust and two core components, one of which contains pinned
superfluid vortices. We suppose that each component rotates as a rigid body.
Also the influence of the small-scale magnetic field on the star's braking
process is examined. Within the framework of this model the star simultaneously
can have glitch-like events combined with long-period precession (with periods
$10-10^{4}$ years). It is shown that the case of the small quantity of pinned
superfluid vortices seems to be more consistent with observations.",1708.07505v1
2017-08-25,On the ultimate energy bound of solutions to some forced second order evolution equations with a general nonlinear damping operator,"Under suitable growth and coercivity conditions on the nonlinear damping
operator $g$ which ensure non-resonance, we estimate the ultimate bound of the
energy of the general solution to the equation $\ddot{u}(t) + Au(t) +
g(\dot{u}(t))=h(t),\quad t\in\mathbb{R}^+ ,$ where $A$ is a positive
selfadjoint operator on a Hilbert space $H$ and $h$ is a bounded forcing term
with values in $H$. In general the bound is of the form $ C(1+ ||h||^4)$ where
$||h||$ stands for the $L^\infty$ norm of $h$ with values in $H$ and the growth
of $g$ does not seem to play any role. If $g$ behaves lie a power for large
values of the velocity, the ultimate bound has a quadratic growth with respect
to $||h||$ and this result is optimal. If $h$ is anti periodic, we obtain a
much lower growth bound and again the result is shown to be optimal even for
scalar ODEs.",1708.07639v1
2017-08-25,On annihilation of the relativistic electron vortex pair in collisionless plasmas,"In contrast to hydrodynamic vortices, vortices in plasma contain an electric
current circulating around the center of the vortex, which generates a magnetic
field localized inside. Using computer simulations, we demonstrate that the
magnetic field associated with the vortex gives rise to a mechanism of
dissipation of the vortex pair in a collisionless plasma, leading to fast
annihilation of the magnetic field with its energy transforming into the energy
of fast electrons, secondary vortices, and plasma waves. Two major contributors
to the energy damping of double vortex system, namely, magnetic field
annihilation and secondary vortex formation, are regulated by the size of the
vortex with respect to the electron skin depth, which scales with the electron
gamma-factor, $\gamma_e$, as $R/d_e \propto \gamma_e^{1/2}$. Magnetic field
annihilation appears to be dominant in mildly relativistic vortices, while for
the ultrarelativistic case, secondary vortex formation is the main channel for
damping of the initial double vortex system.",1708.07803v2
2017-08-30,Finite-temperature behavior of the Bose polaron,"We consider a mobile impurity immersed in a Bose gas at finite temperature.
Using perturbation theory valid for weak coupling between the impurity and the
bosons, we derive analytical results for the energy and damping of the impurity
for low and high temperatures, as well as for temperatures close to the
critical temperature $T_c$ for Bose-Einstein condensation. These results show
that the properties of the impurity vary strongly with temperature. In
particular, the energy exhibits a non-monotonic behavior close to $T_c$, and
the damping rises sharply close to $T_c$. We argue that this behaviour is
generic for impurities immersed in an environment undergoing a phase transition
that breaks a continuous symmetry. Finally, we discuss how these effects can be
detected experimentally.",1708.09172v2
2017-09-01,Quantum reservoir engineering through quadratic optomechanical interaction in the reversed dissipation regime,"We explore the electromagnetic field coupled to a mechanical resonator via
quadratic optomechanical interaction in the reversed dissipation regime where
the mechanical damping rate is much larger than the cavity field dissipation
rate. It is shown that in this regime, the cavity field effectively acquires an
additional reservoir which is conditioned by the temperature of the mechanical
bath as well as the mechanical damping rate. We analytically find the
steady-state mean photon number and the critical temperature of the mechanical
oscillator to cool or heat the coupled electromagnetic field. We also show that
in the case of quadratic coupling, the temperature of the mechanical oscillator
can be estimated in the quantum regime by observing the noise spectrum of the
cavity field.",1709.00279v1
2017-09-13,Life-span of solutions to semilinear wave equation with time-dependent critical damping for specially localized initial data,"This paper is concerned with the blowup phenomena for initial value problem
of semilinear wave equation with critical time-dependent damping term (DW). The
result is the sharp upper bound of lifespan of solution with respect to the
small parameter $\ep$ when $p_F(N)\leq p\leq p_0(N+\mu)$, where $p_F(N)$
denotes the Fujita exponent for the nonlinear heat equations and $p_0(n)$
denotes the Strauss exponent for nonlinear wave equation in $n$-dimension with
$\mu=0$. Consequently, by connecting the result of D'Abbicco--Lucente--Reissig
2015, our result clarifies the threshold exponent $p_0(N+\mu)$ for dividing
blowup phenomena and global existence of small solutions when $N=3$. The
crucial idea is to construct suitable test functions satisfying the conjugate
linear equation $\pa_t^2\Phi-\Delta \Phi-\pa_t(\frac{\mu}{1+t}\Phi)=0$ of (DW)
including the Gauss hypergeometric functions; note that the construction of
test functions is different from Zhou--Han in 2014.",1709.04406v1
2017-09-18,Optimal Energy Growth in Current Sheets,"In this paper, we investigate the possibility of transient growth in the
linear perturbation of current sheets. The resistive magnetohydrodynamic (MHD)
operator for a background field consisting of a current sheet is non-normal,
meaning that associated eigenvalues and eigenmodes can be very sensitive to
perturbation. In a linear stability analysis of a tearing current sheet, we
show that modes that are damped as $t\rightarrow\infty$ can produce transient
energy growth, contributing faster growth rates and higher energy attainment
(within a fixed finite time) than the unstable tearing mode found from
normal-mode analysis. We determine the transient growth for tearing-stable and
tearing-unstable regimes and discuss the consequences of our results for
processes in the solar atmosphere, such as flares and coronal heating. Our
results have significant potential impact on how fast current sheets can be
disrupted. In particular, transient energy growth due to (asymptotically)
damped modes may lead to accelerated current sheet thinning and, hence, a
faster onset of the plasmoid instability, compared to the rate determined by
the tearing mode alone.",1709.05858v1
2017-09-20,Spin-rotation mode in a quantum Hall ferromagnet,"A spin-rotation mode emerging in a quantum Hall ferromagnet due to laser
pulse excitation is studied. This state, macroscopically representing a
rotation of the entire electron spin-system to a certain angle, is not
microscopically equivalent to a coherent turn of all spins as a single-whole
and is presented in the form of a combination of eigen quantum states
corresponding to all possible S_z spin numbers. The motion of the macroscopic
quantum state is studied microscopically by solving a non-stationary
Schroedinger equation and by means of a kinetic approach where damping of the
spin-rotation mode is related to an elementary process, namely, transformation
of a `Goldstone spin exciton' to a `spin-wave exciton'. The system exhibits a
spin stochastizationa mechanism (determined by spatial fluctuations of the
Land'e g-factor) ensuring damping, transverse spin relaxation, but irrelevant
to decay of spin-wave excitons and thus not involving longitudinal relaxation,
i.e., recovery of the S_z number to its equilibrium value.",1709.06811v2
2017-09-22,Muon spin rotation study of the topological superconductor SrxBi2Se3,"We report transverse-field (TF) muon spin rotation experiments on single
crystals of the topological superconductor Sr$_x$Bi$_2$Se$_3$ with nominal
concentrations $x=0.15$ and $0.18$ ($T_c \sim 3$ K). The TF spectra ($B= 10$
mT), measured after cooling to below $T_c$ in field, did not show any
additional damping of the muon precession signal due to the flux line lattice
within the experimental uncertainty. This puts a lower bound on the magnetic
penetration depth $\lambda \geq 2.3 ~\mu$m. However, when we induce disorder in
the vortex lattice by changing the magnetic field below $T_c$ a sizeable
damping rate is obtained for $T \rightarrow 0$. The data provide microscopic
evidence for a superconducting volume fraction of $\sim 70~ \%$ in the $x=0.18$
crystal and thus bulk superconductivity.",1709.07547v1
2017-09-22,Slowly damped quasinormal modes of the massive Dirac field in d-dimensional Tangherlini spacetime,"We consider quasinormal modes of the massive Dirac field in the background of
a Schwarzschild- Tangherlini black hole. Different dimensions of the spacetime
are considered, from d = 4 to d = 9. The quasinormal modes are calculated using
two independent methods: WKB and continued fraction. We obtain the spectrum of
quasinormal modes for different values of the overtone number and angular
quantum number. An analytical approximation of the spectrum valid in the case
of large values of the angular quantum number and mass is calculated. Although
we don't find unstable modes in the spectrum, we show that for large values of
the mass, the quasinormal modes can become very slowly damped, giving rise to
quasistationary perturbations.",1709.07864v3
2017-09-20,Non-Adiabatic Vibrational Damping of Molecular Adsorbates: Insights into Electronic Friction and the Role of Electronic Coherence,"We present a perturbation approach rooted in time-dependent
density-functional theory to calculate electron hole (eh)-pair excitation
spectra during the non-adiabatic vibrational damping of adsorbates on metal
surfaces. Our analysis for the benchmark systems CO on Cu(100) and Pt(111)
elucidates the surprisingly strong influence of rather short electronic
coherence times. We demonstrate how in the limit of short electronic coherence
times, as implicitly assumed in prevalent quantum nuclear theories for the
vibrational lifetimes as well as electronic friction, band structure effects
are washed out. Our results suggest that more accurate lifetime or
chemicurrent-like experimental measurements could characterize the electronic
coherence.",1709.08003v1
2017-09-28,Phenomenological model for predicting stationary and non-stationary spectra of wave turbulence in vibrating plates,"A phenomenological model describing the time-frequency dependence of the
power spectrum of thin plates vibrating in a wave turbulence regime, is
introduced. The model equation contains as basic solutions the Rayleigh-Jeans
equipartition of energy, as well as the Kolmogorov-Zakharov spectrum of wave
turbulence. In the Wave Turbulence Theory framework, the model is used to
investigate the self-similar, non-stationary solutions of forced and free
turbulent vibrations. Frequency-dependent damping laws can easily be accounted
for. Their effects on the characteristics of the stationary spectra of
turbulence are then investigated. Thanks to this analysis, self-similar
universal solutions are given, relating the power spectrum to both the injected
power and the damping law.",1709.09884v1
2017-09-13,Effects of pressure on suspended micromechanical membrane arrays,"The effects of pressure on micromechanical air-filled cavities made by a pair
of suspended, parallel silicon nitride membranes are investigated in the free
molecular and quasi-molecular regimes. Variations of the fundamental drummode
mechanical resonant frequencies and damping with air pressure are determined by
means of optical interferometry. A kinetic damping linear friction force and a
positive resonant frequency shift due to the compression of the fluid between
the membranes are observed to be proportional with pressure in the range
0.01-10 mbars. For resonators with near-degenerate modes hybridization of the
modes due to this squeeze film effect is also observed and well accounted for
by a simple spring-coupled oscillator model.",1710.00043v2
2017-10-11,Parametric Decay Instability and Dissipation of Low-frequency Alfvén Waves in Low-beta Turbulent Plasmas,"Evolution of the parametric decay instability (PDI) of a circularly polarized
Aflv\'en wave in a turbulent low-beta plasma background is investigated using
3D hybrid simulations. It is shown that the turbulence reduces the growth rate
of PDI as compared to the linear theory predictions, but PDI can still exist.
Interestingly, the damping rate of ion acoustic mode (as the product of PDI) is
also reduced as compared to the linear Vlasov predictions. Nonetheless,
significant heating of ions in the direction parallel to the background
magnetic field is observed due to resonant Landau damping of the ion acoustic
waves. In low-beta turbulent plasmas, PDI can provide an important channel for
energy dissipation of low-frequency Alfv\'en waves at a scale much larger than
the ion kinetic scales, different from the traditional turbulence dissipation
models.",1710.04149v3
2017-10-14,Doubly Damped Stochastic Parallel Translations and Hessian Formulas,"We study the Hessian of the solutions of time-independent Schr\""odinger
equations, aiming to obtain as large a class as possible of complete Riemannian
manifolds for which the estimate $C(\frac 1 t +\frac {d^2}{t^2})$ holds. For
this purpose we introduce the doubly damped stochastic parallel transport
equation, study them and make exponential estimates on them, deduce a second
order Feynman-Kac formula and obtain the desired estimates. Our aim here is to
explain the intuition, the basic techniques, and the formulas which might be
useful in other studies.",1710.05169v1
2017-10-20,Magnetic field amplification in supernova remnants,"Based on the new findings on the turbulent dynamo in \citet{XL16}, we examine
the magnetic field amplification in the context of supernova remnants. Due to
the strong ion-neutral collisional damping in the weakly-ionized interstellar
medium, the dynamo in the preshock turbulence remains in the damping kinematic
regime, which leads to {\it a linear-in-time growth of the magnetic field
strength}. The resultant magnetic field structure enables effective diffusion
upstream and shock acceleration of cosmic rays to energies above the ""knee"".
Differently, the nonlinear dynamo in the postshock turbulence leads to {\it a
linear-in-time growth of the magnetic energy} due to the turbulent magnetic
diffusion. Given a weak initial field strength in the postshock region, the
magnetic field saturates at a significant distance from the shock front as a
result of the inefficiency of the nonlinear dynamo. This result is in a good
agreement with existing numerical simulations and well explains the X-ray spots
detected far behind the shock front.",1710.07717v1
2017-10-26,Coarse-graining in the derivation of Markovian master equations and its significance in quantum thermodynamics,"The coarse-graining approach to deriving the quantum Markovian master
equation is revisited, with close attention given to the underlying
approximations. It is further argued that the time interval over which the
coarse-graining is performed is a free parameter that can be given a physical
measurement-based interpretation. In the case of the damping of composite
systems to reservoirs of different temperatures, currently of much interest in
the study of quantum thermal machines with regard to the validity of `local'
and `global' forms of these equations, the coupling of the subsystems leads to
a further timescale with respect to which the coarse-graining time interval can
be chosen. Different choices lead to different master equations that correspond
to the local and global forms. These can be then understood as having different
physical interpretations based on the role of the coarse-graining, as well as
different limitations in application.",1710.09939v2
2017-10-27,The Marangoni effect on small-amplitude capillary waves in viscous fluids,"We derive a general integrodifferential equation for the transient behaviour
of small-amplitude capillary waves on the planar surface of a viscous fluid in
the presence of the Marangoni effect. The equation is solved for an insoluble
surfactant solution in concentration below the critical micelle concentration
(cmc) undergoing convective-diffusive surface transport. The special case of a
diffusion-driven surfactant is considered near the the critical damping
wavelength. The Marangoni effect is shown to contribute to the overall damping
mechanism and a first-order term correction to the critical wavelength with
respect to the surfactant concentration difference and the Schmidt number is
proposed.",1710.10137v1
2017-11-01,Plasmon modes in bilayer-monolayer graphene heterostructures,"We investigate the dispersion relation and damping of plasmon modes in a
bilayer-monolayer graphene heterostructure with carrier densities and at zero
temperature within the random-phase-approximation taking into account the
nonhomogeneity of the dielectric background of the system. We derive analytical
expressions for plasmon frequencies by using long wavelength expansion of
response and bare Coulomb interaction functions. We show that optical plasmon
dispersion curve of the bilayer-monolayer system lies slightly below that of
double-layer graphene (DLG) and the acoustic one lies much lower than that of
DLG. We find that while decay rates of acoustic modes of the system and DLG are
remarkably different, those of optical modes in both double-layer systems are
similar. Except the damping rate of acoustic mode, properties of plasmon
excitations in considered system depend remarkably on the interlayer distance,
inhomogeneity of the background, density ratio and spacer dielectric constant,
especially at large wave-vectors.",1711.00334v1
2017-11-03,Remark on upper bound for lifespan of solutions to semilinear evolution equations in a two-dimensional exterior domain,"In this paper we consider the initial-boundary value problem for the heat,
damped wave, complex-Ginzburg-Landau and Schr""odinger equations with the power
type nonlinearity $|u|^p$ with $p in (1,2]$ in a two-dimensional exterior
domain. Remark that $2=1+2/N$ is well-known as the Fujita exponent. If $p>2$,
then there exists a small global-in-time solution of the damped wave equation
for some initial data small enough (see Ikehata'05), and if $p<2$, then
global-in-time solutions cannot exist for any positive initial data (see
Ogawa-Takeda'09 and Lai-Yin'17). The result is that for given initial data
$(f,tau g)in H^1_0(Omega)times L^2(Omega)$ satisfying $(f+tau g)log |x|in
L^1(Omega)$ with some requirement, the solution blows up at finite time, and
moreover, the upper bound for lifespan of solutions to the problem is given as
the following {it double exponential type} when $p=2$: [ lifespan(u) leq
exp[exp(Cep^{-1})] . ] The crucial idea is to use test functions which
approximates the harmonic function $log |x|$ satisfying Dirichlet boundary
condition and the technique for derivation of lifespan estimate in
Ikeda-Sobajima(arXiv:1710.06780).",1711.00994v1
2017-11-03,A flowing pair of particles in inertial microfluidics,"A flowing pair of particles in inertial microfluidics gives important
insights into understanding and controlling the collective dynamics of
particles like cells or droplets in microfluidic devices. They are applied in
medical cell analysis and engineering. We study the dynamics of a pair of solid
particles flowing through a rectangular microchannel using lattice Boltzmann
simulations. We determine the inertial lift force profiles as a function of the
two particle positions, their axial distance, and the Reynolds number.
Generally, the profiles strongly differ between particles leading and lagging
in flow and the lift forces are enhanced due to the presence of a second
particle. At small axial distances, they are determined by viscous forces,
while inertial forces dominate at large separations. Depending on the initial
conditions, the two-particle lift forces in combination with the Poiseuille
flow give rise to three types of unbound particle trajectories, called
moving-apart, passing, and swapping, and one type of bound trajectories, where
the particles perform damped oscillations. The damping rate scales with
Reynolds number squared, since inertial forces are responsible for driving the
particles to their steady-state positions.",1711.01148v2
2017-11-07,Application of the coupled classical oscillators model to the Fano resonance build-up in a plasmonic nanosystem,"We study the excitation dynamics of Fano resonance within the classical model
framework of two linear coupled oscillators. An exact solution for the model
with a damped harmonic force is obtained. The details of growth a Fano profile
under the harmonic excitation is shown. For incident ultra-wideband pulse, the
reaction of a system becomes universal and coincides with the time-dependent
response function. The results of numerical calculations clarify two
alternative ways for experimental measurement of the complete characteristics
of a system: direct observation of the system response to a monochromatic force
by frequency scanning or recording of time-dependent response to the
delta-pulse. As a specific example, time-dependent excitation in a system
consisting of a quantum dot and a metal nanoparticle is calculated. Then it is
shown the applicability of the extended model of damped oscillators with
radiative correction to describe the build-up a plasmon Fano resonance in a
scattering of a femtosecond laser pulse by nanoantenna.",1711.02498v2
2017-11-11,Quantum Thermodynamics for Driven Dissipative Bosonic Systems,"We investigate two prototypical dissipative bosonic systems under slow
driving and arbitrary system-bath coupling strength, recovering their dynamic
evolution as well as the heat and work rates, and we verify that thermodynamic
laws are respected. Specifically, we look at the damped harmonic oscillator and
the damped two-level system. For the former, we study independently the slow
time- dependent perturbation in the oscillator frequency and in the coupling
strength. For the latter, we concentrate on the slow modulation of the energy
gap between the two levels. Importantly, we are able to find the entropy
production rates for each case without explicitly defining nonequilibrium
extensions for the entropy functional. This analysis also permits the
definition of phenomenological friction coefficients in terms of structural
properties of the system-bath composite.",1711.04077v1
2017-11-29,Constraints on box-shaped cosmic ray electron feature from dark matter annihilation with the AMS-02 and DAMPE data,"Precise measurements of spectra of cosmic ray electrons and positrons can
effectively probe the nature of dark matter (DM) particles. In a class of
models where DM particles initially annihilate into a pair of intermediate
particles which then decay into standard model particles, box-shaped spectra
can be generated. Such a kind of spectra are distinct from astrophysical
backgrounds, and can probably be regarded as characteristic features of the DM
annihilation. In this work, we search for such a feature in the total electron
plus positron spectrum measured by AMS-02 and DAMPE. No significant evidence
for such a DM annihilation component has been found. The 95\% confidence level
upper limits of the velocity-weighted annihilation cross section are derived,
which range from $\sim 10^{-26}~{\rm cm^3~s^{-1}}$ for DM mass of 50 GeV to
$\sim 10^{-23}~{\rm cm^3~s^{-1}}$ for DM mass of 10 TeV.",1711.11052v2
2017-11-30,TeV dark matter and the DAMPE electron excess,"The recent high energy electron and positron flux observed by the DAMPE
experiment indicates possible excess events near 1.4 TeV. Such an excess may be
evidence of dark matter annihilations or decays in a dark matter subhalo that
is located close to the solar system. We give here an analysis of this excess
from annihilations of Dirac fermion dark matter which is charged under a new
$U(1)_X$ gauge symmetry. The interactions between dark matter and the standard
model particles are mediated the $U(1)_X$ gauge boson. We show that dark matter
annihilations from a local subhalo can explain the excess with the canonical
thermal annihilation cross section. We further discuss the constraints from the
relic density, from the dark matter direct detection, from the dark matter
indirect detection, from the cosmic microwave background, and from the particle
colliders.",1711.11579v1
2017-12-04,"Quasi-degenerate dark matter for DAMPE excess and $3.5\,\textrm{keV}$ line","We propose a quasi-degenerate dark matter scenario to simultaneously explain
the $1.4\,\textrm{TeV}$ peak in the high-energy cosmic-ray electron-positron
spectrum reported by the DAMPE collaboration very recently and the
$3.5\,\textrm{keV}$ X-ray line observed in galaxies clusters and from the
Galactic centre and confirmed by the Chandra and NuSTAR satellites. We consider
a dark $SU(2)'\times U(1)'$ gauge symmetry under which the dark matter is a
Dirac fermion doublet composed of two $SU(2)'$ doublets with non-trivial
$U(1)'$ charges. At one-loop level the two dark fermion components can have a
mass split as a result of the dark gauge symmetry breaking. Through the
exchange of a mediator scalar doublet the two quasi-degenerate dark fermions
can mostly annihilate into the electron-positron pairs at tree level for
explaining the $1.4\,\textrm{TeV}$ positron anomaly, meanwhile, the heavy dark
fermion can very slowly decay into the light dark fermion with a photon at
one-loop level for explaining the $3.5\,\textrm{keV}$ X-ray line. Our dark
fermions can be also verified in the direct detection experiments.",1712.00922v1
2017-12-06,Collective modes of an imbalanced unitary Fermi gas,"We study theoretically the collective mode spectrum of a strongly imbalanced
two-component unitary Fermi gas in a cigar-shaped trap, where the minority
species forms a gas of polarons. We describe the collective breathing mode of
the gas in terms of the Fermi liquid kinetic equation taking collisions into
account using the method of moments. Our results for the frequency and damping
of the longitudinal in-phase breathing mode are in good quantitative agreement
with an experiment by Nascimb\`ene et al. [Phys. Rev. Lett. 103, 170402 (2009)]
and interpolate between a hydrodynamic and a collisionless regime as the
polarization is increased. A separate out-of phase breathing mode, which for a
collisionless gas is sensitive to the effective mass of the polaron, however,
is strongly damped at finite temperature, whereas the experiment observes a
well-defined oscillation.",1712.02181v1
2017-12-07,Bias of Damped Lyman-$α$ systems from their cross-correlation with CMB lensing,"We cross-correlate the positions of damped Lyman-$\alpha$ systems (DLAs) and
their parent quasar catalog with a convergence map derived from the Planck
cosmic microwave background (CMB) temperature data. We make consistent
measurements of the lensing signal of both samples in both Fourier and
configuration space. By interpreting the excess signal present in the DLA
catalog with respect to the parent quasar catalog as caused by the large scale
structure traced by DLAs, we are able to infer the bias of these objects:
$b_{\rm DLA}=2.6\pm0.9$. These results are consistent with previous
measurements made in cross-correlation with the Lyman-$\alpha$ forest, although
the current noise in the lensing data and the low number density of DLAs limits
the constraining power of this measurement. We discuss the robustness of the
analysis with respect to a number different systematic effects and forecast
prospects of carrying out this measurement with data from future experiments.",1712.02738v2
2017-12-08,Viscoelastic optical nonlocality of low-loss epsilon-near-zero nanofilms,"Optical nonlocalities are elusive and hardly observable in traditional
plasmonic materials like noble and alkali metals. Here we report experimental
observation of viscoelastic nonlocalities in the infrared optical response of
doped cadmium-oxide, epsilon-near-zero nanofilms. The nonlocality is detectable
thanks to the low damping rate of conduction electrons and the virtual absence
of interband transitions at infrared wavelengths. We describe the motion of
conduction electrons using a hydrodynamic model for a viscoelastic fluid, and
find excellent agreement with experimental results. The electrons elasticity
blue-shifts the infrared plasmonic resonance associated with the main
epsilon-near-zero mode, and triggers the onset of higher-order resonances due
to the excitation of electron-pressure modes above the bulk plasma frequency.
We also provide evidence of the existence of nonlocal damping, i.e., viscosity,
in the motion of optically-excited conduction electrons using a combination of
spectroscopic ellipsometry data and predictions based on the viscoelastic
hydrodynamic model.",1712.03169v2
2017-12-08,A Strong Test of the Dark Matter Origin of the 1.4 TeV DAMPE Signal Using IceCube Neutrinos,"A tentative excess in the electron spectrum at 1.4 TeV was recently reported
by the DArk Matter Particle Explorer (DAMPE). A non-astrophysical scenario in
which dark matter particles annihilate or decay in a local clump has been
invoked to explain the excess. If $e^\pm$ annihilation channels in the final
states are mediated by left-handed leptons as a component in the $SU(2)_L$
doublet, neutrinos with similar energies should have been simultaneously
produced. We demonstrate that generic dark matter models can be decisively
tested by the existing IceCube data. In case of a non-detection, such models
would be excluded at the $5\sigma$ level by the five-year data for a point-like
source and by the ten-year data for an extended source of dark matter particles
with left-handed leptons.",1712.03210v2
2017-12-11,Prospects of type-II seesaw at future colliders in light of the DAMPE $e^+ e^-$ excess,"The DAMPE $e^+ e^-$ excess at around 1.4 TeV could be explained in the
type-II seesaw model with a scalar dark mater $D$ which is stabilized by a
discrete $Z_2$ symmetry. The simplest scenario is the annihilation $DD \to
H^{++} H^{--}$ followed by the subsequent decay $H^{\pm\pm} \to e^\pm e^\pm$,
with both the DM and triplet scalars roughly 3 TeV with a small mass splitting.
In addition to the Drell-Yan process at future 100 TeV hadron colliders, the
doubly-charged components could also be produced at lepton colliders like ILC
and CLIC in the off-shell mode, and mediate lepton flavor violating processes
$e^+ e^- \to \ell_i^\pm \ell_j^\mp$ (with $i \neq j$). A wide range of
parameter space of the type-II seesaw could be probed, which are well below the
current stringent lepton flavor constraints.",1712.03642v3
2017-12-12,Thermal decoherence in a strongly correlated Bose liquid,"We compute the single particle spectral function of a Bose liquid on a
lattice, at integer filling, close to the superfluid-Mott transition. We use a
`static path approximation' that retains all the classical thermal fluctuations
in the problem, and a real space implementation of the random phase
approximation (RPA) for the Green's functions on the thermally fluctuating
backgrounds. This leads to the standard RPA answers in the ground state but
captures the progressive damping of the excitations with increasing
temperature. We focus on the momentum resolved lineshape across the superfluid
to Bose liquid thermal transition. In the superfluid regime we observe a gapped
`amplitude' mode, and gapless `phase' modes of positive and negative energy.
The dispersion and weight of these modes changes with interaction but are
almost temperature independent, even into the normal state, except near
critical coupling. The damping of the modes varies roughly as $T^{\alpha}
f_{\bf k}$, where $T$ is the temperature and ${\bf k}$ the momentum, with
$\alpha \sim 0.5$ and $f_{\bf k}$ having non trivial momentum dependence. The
Mott phase has gapped dispersive spectra. Near critical coupling the thermal
Bose `liquid' is gapped, with progressive widening of the gap with increasing
temperature, a feature that it shares with the Mott insulator.",1712.04433v1
2017-12-17,Oscillation energy based sensitivity analysis and control for multi-mode oscillation systems,"This paper describes a novel approach to analyze and control systems with
multi-mode oscillation problems. Traditional single dominant mode analysis
fails to provide effective control actions when several modes have similar low
damping ratios. This work addresses this problem by considering all modes in
the formulation of the system kinetic oscillation energy. The integral of
energy over time defines the total action as a measure of dynamic performance,
and its sensitivity allows comparing the performance of different
actuators/locations in the system to select the most effective one to damp the
oscillation energy. Time domain simulations in the IEEE 9-bus system and IEEE
39-bus system verify the findings obtained by the oscillation energy based
analysis. Applications of the proposed method in control and system planning
are discussed.",1712.06157v1
2017-12-19,Nonequilibrium quantum solvation with a time-dependent Onsager cavity,"We formulate a theory of nonequilibrium quantum solvation in which parameters
of the solvent are explicitly depending on time. We assume in a simplest
approach a spherical molecular Onsager cavity with a time-dependent radius. We
analyze the relaxation properties of a test molecular point dipole in a
dielectric solvent and consider two cases: (i) a shrinking Onsager sphere, and,
(ii) a breathing Onsager sphere. Due to the time-dependent solvent, the
frequency-dependent response function of the dipole becomes time-dependent. For
a shrinking Onsager sphere, the dipole relaxation is in general enhanced. This
is reflected in a temporally increasing line width of the absorptive part of
the response. Furthermore, the effective frequency-dependent response function
shows two peaks in the absorptive part which are symmetrically shifted around
the eigenfrequency. In contrast, a breathing sphere reduces damping as compared
to the static sphere. Interestingly, we find a non-monotonous dependence of the
relaxation rate on the breathing rate and a resonant suppression of damping
when both rates are comparable. Moreover, the line width of the absorptive part
of the response function is strongly reduced for times when the breathing
sphere reaches its maximal extension.",1712.06973v2
2017-12-26,Newton's equation of motion with quadratic drag force and Toda's potential as a solvable one,"The family of exactly solvable potentials for Newton's equation of motion in
the one-dimensional system with quadratic drag force has been determined
completely. The determination is based on the implicit inverse-function
solution valid for any potential shape, and hence exhaustive. This solvable
family includes the exponential potential appearing in the Toda lattice as a
special limit. The global solution is constructed by matching the solutions
applicable for positive and negative velocity, yielding the piecewise analytic
function with a cusp in the third-order derivative, i.e., the jerk. These
procedures and features can be regarded as a generalization of Gorder's
construction [Phys. Scr. 2015, {\bf 90}, 085208] to the energy-dissipating
damped oscillators. We also derive the asymptotic formulae by solving the
matching equation, and prove that the damping of the oscillation amplitude is
proportional to $ t^{-1} $.",1712.09189v4
2017-12-23,Density Fluctuations in the Solar Wind Driven by Alfvén Wave Parametric Decay,"Measurements and simulations of inertial compressive turbulence in the solar
wind are characterized by anti-correlated magnetic fluctuations parallel to the
mean field and density structures. This signature has been interpreted as
observational evidence for non-propagating pressure balanced structures (PBS),
kinetic ion acoustic waves, as well as the MHD slow-mode. Given the high
damping rates of parallel propagating compressive fluctuations, their ubiquity
in satellite observations is surprising, and suggestive of a local driving
process. One possible candidate for the generation of compressive fluctuations
in the solar wind is Alfv\'en wave parametric instability. Here we test the
parametric decay process as a source of compressive waves in the solar wind by
comparing the collisionless damping rates of compressive fluctuations with the
growth rates of the parametric decay instability daughter waves. Our results
suggest that generation of compressive waves through parametric decay is
overdamped at 1 AU, but that the presence of slow-mode like density
fluctuations is correlated with the parametric decay of Alfv\'en waves.",1712.09336v2
2018-01-15,A radiative neutrino mass model in light of DAMPE excess with hidden gauged $U(1)$ symmetry,"We propose a one-loop induced neutrino mass model with hidden $U(1)$ gauge
symmetry, in which we successfully involve a bosonic dark matter (DM) candidate
propagating inside a loop diagram in neutrino mass generation to explain the
$e^+e^-$ excess recently reported by the DArk Matter Particle Explorer (DAMPE)
experiment. In our scenario dark matter annihilates into four leptons through
$Z'$ boson as DM DM $\to Z' Z' (Z' \to \ell^+ \ell^-)$ and $Z'$ decays into
leptons via one-loop effect. We then investigate branching ratios of $Z'$
taking into account lepton flavor violations and neutrino oscillation data.",1801.04729v2
2018-01-22,A port-Hamiltonian approach to the control of nonholonomic systems,"In this paper a method of controlling nonholonomic systems within the
port-Hamiltonian (pH) framework is presented. It is well known that
nonholonomic systems can be represented as pH systems without Lagrange
multipliers by considering a reduced momentum space. Here, we revisit the
modelling of these systems for the purpose of identifying the role that
physical damping plays. Using this representation, a geometric structure
generalising the well known chained form is identified as \textit{chained
structure}. A discontinuous control law is then proposed for pH systems with
chained structure such that the configuration of the system asymptotically
approaches the origin. The proposed control law is robust against the damping
and inertial of the open-loop system. The results are then demonstrated
numerically on a car-like vehicle.",1801.06954v1
2018-01-23,Temperature gradient driven heat flux closure in fluid simulations of collisionless reconnection,"Recent efforts to include kinetic effects in fluid simulations of plasmas
have been very promising. Concerning collisionless magnetic reconnection, it
has been found before that damping of the pressure tensor to isotropy leads to
good agreement with kinetic runs in certain scenarios. An accurate
representation of kinetic effects in reconnection was achieved in a study by
Wang et al. (Phys. Plasmas, volume 22, 2015, 012108) with a closure derived
from earlier work by Hammett and Perkins (PRL, volume 64, 1990, 3019). Here,
their approach is analyzed on the basis of heat flux data from a Vlasov
simulation. As a result, we propose a new local closure in which heat flux is
driven by temperature gradients. That way, a more realistic approximation of
Landau damping in the collisionless regime is achieved. Previous issues are
addressed and the agreement with kinetic simulations in different reconnection
setups is improved significantly. To the authors' knowledge, the new fluid
model is the first to perform well in simulations of the coalescence of large
magnetic islands.",1801.07628v1
2018-01-29,Oscillatory relaxation of zonal flows in a multi-species stellarator plasma,"The low frequency oscillatory relaxation of zonal potential perturbations is
studied numerically in the TJ-II stellarator (where it was experimentally
detected for the first time). It is studied in full global gyrokinetic
simulations of multi-species plasmas. The oscillation frequency obtained is
compared with predictions based on single-species simulations using simplified
analytical relations. It is shown that the frequency of this oscillation for a
multi-species plasma can be accurately obtained from single-species
calculations using extrapolation formulas. The damping of the oscillation and
the influence of the different inter-species collisions is studied in detail.
It is concluded that taking into account multiple kinetic ions and electrons
with impurity concentrations realistic for TJ-II plasmas allows to account for
the values of frequency and damping rate in zonal flows relaxations observed
experimentally.",1801.09495v1
2018-01-30,Input / Output Stability of a Damped String Equation coupled with Ordinary Differential System,"The input/output stability of an interconnected system composed of an
ordinary differential equation and a damped string equation is studied. Issued
from the literature on time-delay systems, an exact stability result is firstly
derived using pole locations. Then, based on the Small-Gain theorem and on the
Quadratic Separation framework, some robust stability criteria are provided.
The latter follows from a projection of the infinite dimensional state on an
orthogonal basis of Legendre polynomials. Numerical examples comparing these
results with the ones in the literature are proposed and a comparison of its
efficiency is made.",1801.09916v2
2018-02-05,Intrinsic spin-orbit torque arising from Berry curvature in metallic-magnet/Cu-oxide interface,"We report the observation of the intrinsic damping-like spin-orbit torque
(SOT) arising from the Berry curvature in metallic-magnet/CuO$_x$
heterostructures. We show that a robust damping-like SOT, an order of magnitude
larger than a field-like SOT, is generated in the heterostructure despite the
absence of the bulk spin-orbit effect in the CuO$_x$ layer. Furthermore, by
tuning the interface oxidation level, we demonstrate that the field-like SOT
changes drastically and even switches its sign, which originates from oxygen
modulated spin-dependent disorder. These results provide an important
information for fundamental understanding of the physics of the SOTs.",1802.01285v2
2018-02-12,Selective Phonon Damping in Topological Semimetals,"Topological semimetals are characterized by their intriguing Fermi surfaces
(FSs) such as Weyl and Dirac points, or nodal FS, and their associated surface
states. Among them, topological crystalline semimetals, in the presence of
strong spin-orbit coupling, possess a nodal FS protected by non-symmorphic
lattice symmetries. In particular, it was theoretically proposed that
$\mathrm{SrIrO}_{3}$ exhibits a bulk nodal ring due to glide symmetries, as
well as flat two-dimensional surface states related to chiral and mirror
symmetries. However, due to the semimetallic nature of the bulk, direct
observation of these surface states is difficult. Here we study the effect of
flat-surface states on phonon modes for $\mathrm{SrIrO}_{3}$ side surfaces. We
show that particular phonon modes, based on mirror symmetry, have qualitatively
different damping mechanisms due to the surface states which could be used to
infer their existence. Experimental techniques for such measurements are also
discussed.",1802.04300v2
2018-02-14,Motion of interfaces for a damped hyperbolic Allen-Cahn equation,"Consider the Allen-Cahn equation $u_t=\varepsilon^2\Delta u-F'(u)$, where $F$
is a double well potential with wells of equal depth, located at $\pm1$. There
are a lot of papers devoted to the study of the limiting behavior of the
solutions as the diffusion coefficient $\varepsilon\to0^+$, and it is well
known that, if the initial datum $u(\cdot,0)$ takes the values $+1$ and $-1$ in
the regions $\Omega_+$ and $\Omega_-$, then the ""interface"" connecting
$\Omega_+$ and $\Omega_-$ moves with normal velocity equal to the sum of its
principal curvatures, i.e. the interface moves by mean curvature flow.
  This paper concerns with the motion of the inteface for a damped hyperbolic
Allen-Cahn equation, in a bounded domain of $\mathbb{R}^n$, for $n=2$ or $n=3$.
In particular, we focus the attention on radially simmetric solutions, studying
in detail the differences with the classic parabolic case, and we prove that,
under appropriate assumptions on the initial data $u(\cdot,0)$ and
$u_t(\cdot,0)$, the interface moves by mean curvature as $\varepsilon\to0^+$
also in the hyperbolic framework.",1802.05038v1
2018-02-23,Blow up of solutions for semilinear wave equations with noneffective damping,"In this paper, we study the finite-time blow up of solutions to the following
semilinear wave equation with time-dependent damping \[ \partial_t^2u-\Delta
u+\frac{\mu}{1+t}\partial_tu=|u|^p \] in $\mathbb{R}_{+}\times\mathbb{R}^n$.
More precisely, for $0\leq\mu\leq 2,\mu \neq1$ and $n\geq 2$, there is no
global solution for $1<p<p_S(n+\mu)$, where $p_S(k)$ is the $k$-dimensional
Strauss exponent and a life-span of the blow up solution will be obtained. Our
work is an extension of \cite{IS}, where the authors proved a similar blow up
result with a larger range of $\mu$. However, we obtain a better life-span
estimate when $\mu\in(0,1)\cup(1,2)$ by using a different method.",1802.08403v2
2018-03-06,A comparison of semi-Lagrangian discontinuous Galerkin and spline based Vlasov solvers in four dimensions,"The purpose of the present paper is to compare two semi-Lagrangian methods in
the context of the four-dimensional Vlasov--Poisson equation. More
specifically, our goal is to compare the performance of the more recently
developed semi-Lagrangian discontinuous Galerkin scheme with the de facto
standard in Eulerian Vlasov simulation (i.e. using cubic spline interpolation).
To that end, we perform simulations for nonlinear Landau damping and a
two-stream instability and provide benchmarks for the SeLaLib and sldg codes
(both on a workstation and using MPI on a cluster).
  We find that the semi-Lagrangian discontinuous Galerkin scheme shows a
moderate improvement in run time for nonlinear Landau damping and a substantial
improvement for the two-stream instability. It should be emphasized that these
results are markedly different from results obtained in the asymptotic regime
(which favor spline interpolation). Thus, we conclude that the traditional
approach of evaluating numerical methods is misleading, even for short time
simulations. In addition, the absence of any All-to-All communication in the
semi-Lagrangian discontinuous Galerkin method gives it a decisive advantage for
scaling to more than 256 cores.",1803.02143v1
2018-03-06,Kak's three-stage protocol of secure quantum communication revisited: Hitherto unknown strengths and weaknesses of the protocol,"Kak's three-stage protocol for quantum key distribution is revisited with
special focus on its hitherto unknown strengths and weaknesses. It is shown
that this protocol can be used for secure direct quantum communication.
Further, the implementability of this protocol in the realistic situation is
analyzed by considering various Markovian noise models. It is found that the
Kak's protocol and its variants in their original form can be implemented only
in a restricted class of noisy channels, where the protocols can be transformed
to corresponding protocols based on logical qubits in decoherence free
subspace. Specifically, it is observed that Kak's protocol can be implemented
in the presence of collective rotation and collective dephasing noise, but
cannot be implemented in its original form in the presence of other types of
noise, like amplitude damping and phase damping noise. Further, the performance
of the protocol in the noisy environment is quantified by computing average
fidelity under various noise models, and subsequently a set of preferred states
for secure communication in noisy environment have also been identified.",1803.02157v1
2018-03-09,Dynamical evolutions in non-Hermitian triple-well system with complex potential,"We investigate the dynamical properties for non-Hermitian triple-well system
with a loss in the middle well. When chemical potentials in two end wells are
uniform and nonlinear interactions are neglected, there always exists a dark
state, whose eigenenergy becomes zero, and the projections onto which do not
change over time and the loss factor. The increasing of loss factor only makes
the damping form from the oscillating decay to over-damping decay. However,
when the nonlinear interaction is introduced, even interactions in the two end
wells are also uniform, the projection of the dark state will be obviously
diminished. Simultaneously the increasing of loss factor will also aggravate
the loss. In this process the interaction in the middle well plays no role.
When two chemical potentials or interactions in two end wells are not uniform
all disappear with time. In addition, when we extend the triple-well system to
a general (2n + 1)-well, the loss is reduced greatly by the factor 1=2n in the
absence of the nonlinear interaction.",1803.03360v1
2018-03-11,Graph Laplacian Spectrum and Primary Frequency Regulation,"We present a framework based on spectral graph theory that captures the
interplay among network topology, system inertia, and generator and load
damping in determining the overall grid behavior and performance. Specifically,
we show that the impact of network topology on a power system can be quantified
through the network Laplacian eigenvalues, and such eigenvalues determine the
grid robustness against low frequency disturbances. Moreover, we can explicitly
decompose the frequency signal along scaled Laplacian eigenvectors when
damping-inertia ratios are uniform across buses. The insight revealed by this
framework partially explains why load-side participation in frequency
regulation not only makes the system respond faster, but also helps lower the
system nadir after a disturbance. Finally, by presenting a new controller
specifically tailored to suppress high frequency disturbances, we demonstrate
that our results can provide useful guidelines in the controller design for
load-side primary frequency regulation. This improved controller is simulated
on the IEEE 39-bus New England interconnection system to illustrate its
robustness against high frequency oscillations compared to both the
conventional droop control and a recent controller design.",1803.03905v3
2018-03-15,Control Inversion: A Clustering-Based Method for Distributed Wide-Area Control of Power Systems,"Wide-area control (WAC) has been shown to be an effective tool for damping
low-frequency oscillations in power systems. In the current state of art, WAC
is challenged by two main factors - namely, scalability of design and
complexity of implementation. In this paper we present a control design called
control inversion that bypasses both of these challenges using the idea of
clustering. The basic philosophy behind this method is to project the original
power system model into a lower-dimensional state-space through clustering and
aggregation of generator states, and then designing an LQR controller for the
lower-dimensional model. This controller is finally projected back to the
original coordinates for wide-area implementation. The main problem is,
therefore, posed as finding the projection which best matches the closed-loop
performance of the WAC controller with that of a reference LQR controller for
damping low-frequency oscillations. We verify the effectiveness of the proposed
design using the NPCC 48-machine power system model.",1803.05947v1
2018-03-18,Damped Anderson acceleration with restarts and monotonicity control for accelerating EM and EM-like algorithms,"The expectation-maximization (EM) algorithm is a well-known iterative method
for computing maximum likelihood estimates from incomplete data. Despite its
numerous advantages, a main drawback of the EM algorithm is its frequently
observed slow convergence which often hinders the application of EM algorithms
in high-dimensional problems or in other complex settings.To address the need
for more rapidly convergent EM algorithms, we describe a new class of
acceleration schemes that build on the Anderson acceleration technique for
speeding fixed-point iterations. Our approach is effective at greatly
accelerating the convergence of EM algorithms and is automatically scalable to
high dimensional settings. Through the introduction of periodic algorithm
restarts and a damping factor, our acceleration scheme provides faster and more
robust convergence when compared to un-modified Anderson acceleration while
also improving global convergence. Crucially, our method works as an
""off-the-shelf"" method in that it may be directly used to accelerate any EM
algorithm without relying on the use of any model-specific features or
insights. Through a series of simulation studies involving five representative
problems, we show that our algorithm is substantially faster than the existing
state-of-art acceleration schemes.",1803.06673v2
2018-03-21,Connectivity-Preserving Coordination Control of Multi-Agent Systems with Time-Varying Delays,"This paper presents a distributed position synchronization strategy that also
preserves the initial communication links for single-integrator multi-agent
systems with time-varying delays. The strategy employs a coordinating
proportional control derived from a specific type of potential energy,
augmented with damping injected through a dynamic filter. The injected damping
maintains all agents within the communication distances of their neighbours,
and asymptotically stabilizes the multi-agent system, in the presence of time
delays. Regarding the closed-loop single-integrator multi-agent system as a
double-integrator system suggests an extension of the proposed strategy to
connectivity-preserving coordination of Euler-Lagrange networks with
time-varying delays. Lyapunov stability analysis and simulation results
validate the two designs.",1803.08152v1
2018-03-23,A Novel Approach to Resonant Absorption of the Fast MHD Eigenmodes of a Coronal Arcade,"The arched field lines forming coronal arcades are often observed to undulate
as magnetohydrodynamic (MHD) waves propagate both across and along the magnetic
field. These waves are most likely a combination of resonantly coupled fast
magnetoacoustic waves and Alfv\'en waves. The coupling results in resonant
absorption of the fast waves, converting fast wave energy into Alfv\'en waves.
The fast eigenmodes of the arcade have proven difficult to compute or derive
analytically, largely because of the mathematical complexity that the coupling
introduces. When a traditional spectral decomposition is employed, the discrete
spectrum associated with the fast eigenmodes is often subsumed into the
continuous Alfv\'en spectrum. Thus fast eigenmodes, become collective modes or
quasi-modes. Here we present a spectral decomposition that treats the
eigenmodes as having real frequencies but complex wavenumbers. Using this
procedure we derive dispersion relations, spatial damping rates, and
eigenfunctions for the resonant, fast eigenmodes of the arcade. We demonstrate
that resonant absorption introduces a fast mode that would not exist otherwise.
This new mode is heavily damped by resonant absorption, only travelling a few
wavelengths before losing most of its energy.",1803.08948v1
2018-03-25,Parareal exponential $θ$-scheme for longtime simulation of stochastic Schrödinger equations with weak damping,"A parareal algorithm based on an exponential $\theta$-scheme is proposed for
the stochastic Schr\""odinger equation with weak damping and additive noise. It
proceeds as a two-level temporal parallelizable integrator with the exponential
$\theta$-scheme as the propagator on the coarse grid. The proposed algorithm in
the linear case increases the convergence order from one to $k$ for
$\theta\in[0,1]\setminus\{\frac12\}$. In particular, the convergence order
increases to $2k$ when $\theta=\frac12$ due to the symmetry of the algorithm.
Furthermore, the algorithm is proved to be suitable for longtime simulation
based on the analysis of the invariant distributions for the exponential
$\theta$-scheme. The convergence condition for longtime simulation is also
established for the proposed algorithm in the nonlinear case, which indicates
the superiority of implicit schemes. Numerical experiments are dedicated to
illustrate the best choice of the iteration number $k$, as well as the
convergence order of the algorithm for different choices of $\theta$.",1803.09188v1
2018-04-01,Aggregated Momentum: Stability Through Passive Damping,"Momentum is a simple and widely used trick which allows gradient-based
optimizers to pick up speed along low curvature directions. Its performance
depends crucially on a damping coefficient $\beta$. Large $\beta$ values can
potentially deliver much larger speedups, but are prone to oscillations and
instability; hence one typically resorts to small values such as 0.5 or 0.9. We
propose Aggregated Momentum (AggMo), a variant of momentum which combines
multiple velocity vectors with different $\beta$ parameters. AggMo is trivial
to implement, but significantly dampens oscillations, enabling it to remain
stable even for aggressive $\beta$ values such as 0.999. We reinterpret
Nesterov's accelerated gradient descent as a special case of AggMo and analyze
rates of convergence for quadratic objectives. Empirically, we find that AggMo
is a suitable drop-in replacement for other momentum methods, and frequently
delivers faster convergence.",1804.00325v3
2018-04-03,Damped perturbations in the no-boundary state,"We evaluate the no-boundary path integral exactly in a Bianchi IX
minisuperspace with two scale factors. In this model the no-boundary proposal
can be implemented by requiring one scale factor to be zero initially together
with a judiciously chosen regularity condition on the momentum conjugate to the
second scale factor. Taking into account the non-linear backreaction of the
perturbations we recover the predictions of the original semiclassical
no-boundary proposal. In particular we find that large perturbations are
strongly damped, consistent with vacuum state wave functions.",1804.01102v2
2018-04-04,Stabilizable Gaussian states,"The unavoidable interaction of quantum systems with their environment usually
results in the loss of desired quantum resources. Suitably chosen system
Hamiltonians, however, can, to some extent, counteract such detrimental decay,
giving rise to the set of stabilizable states. Here, we discuss the possibility
to stabilize Gaussian states in continuous-variable systems. We identify
necessary and sufficient conditions for such stabilizability and elaborate
these on two benchmark examples, a single, damped mode and two locally damped
modes. The obtained stabilizability conditions, which are formulated in terms
of the states' covariance matrices, are, more generally, also applicable to
non-Gaussian states, where they may similarly help to, e.g., discuss
entanglement preservation and/or detection up to the second moments.",1804.01315v2
2018-04-11,Collisionless sound in a uniform two-dimensional Bose gas,"Using linear response theory within the Random Phase Approximation, we
investigate the propagation of sound in a uniform two dimensional (2D) Bose gas
in the collisionless regime. We show that the sudden removal of a static
density perturbation produces a damped oscillatory behavior revealing that
sound can propagate also in the absence of collisions, due to mean-field
interaction effects. Our analysis points out the crucial role played by Landau
damping. We support our predictions by performing numerical simulations with
the stochastic (projected) Gross-Pitaevskii equation. The results are
consistent with the recent experimental observation of sound in a weakly
interacting 2D Bose gas both below and above the superfluid
Berezinskii-Kosterlitz-Thouless transition.",1804.04032v2
2018-04-11,Sound propagation in a uniform superfluid two-dimensional Bose gas,"In superfluid systems several sound modes can be excited, as for example
first and second sound in liquid helium. Here, we excite propagating and
standing waves in a uniform two-dimensional Bose gas and we characterize the
propagation of sound in both the superfluid and normal regime. In the
superfluid phase, the measured speed of sound is well described by a two-fluid
hydrodynamic model, and the weak damping rate is well explained by the
scattering with thermal excitations. In the normal phase the sound becomes
strongly damped due to a departure from hydrodynamic behavior.",1804.04037v1
2018-04-14,Theory of plasmon reflection by a 1D junction,"We present a comprehensive study of the reflection of normally incident
plasmon waves from a low-conductivity 1D junction in a 2D conductive sheet.
Rigorous analytical results are derived in the limits of wide and narrow
junctions. Two types of phenomena determine the reflectance, the cavity
resonances within the junction and the capacitive coupling between the leads.
The resonances give rise to alternating strong and weak reflection but are
vulnerable to plasmonic damping. The capacitive coupling, which is immune to
damping, induces a near perfect plasmon reflection in junctions narrower than
$1/10$ of the plasmon wavelength. Our results are important for infrared 2D
plasmonic circuits utilizing slot antennas, split gates or nanowire gates. They
are also relevant for the implementation of nanoscale terahertz detectors,
where optimal light absorption coincides with the maximal junction reflectance.",1804.05256v1
2018-03-25,Nonlinear effect of forced harmonic oscillator subject to sliding friction and simulation by a simple nonlinear circuit,"We study the nonlinear behaviors of mass-spring systems damped by dry
friction using simulation by a nonlinear LC circuit damped by anti-parallel
diodes. We show that the differential equation for the electric oscillator is
equivalent to the mechanical one's when a piecewise linear model is used to
simplify the diodes I-V curve. We derive series solutions to the differential
equation under weak nonlinear approximation which can describe the resonant
response as well as amplitudes of superharmonic components. Experimental
results are consistent with series solutions. We also present the phenomenon of
hysteresis. Theoretical analysis along with numerical simulations are conducted
to explore the stick-slip boundary.
  The correspondence between the mechanical and electric oscillators makes it
easy to demonstrate the behaviors of this nonlinear oscillator on a digital
oscilloscope. It can be used to extend the linear RLC experiment at the
undergraduate level.",1804.05762v1
2018-04-17,Asymmetric fitting function for condensed-phase Raman spectroscopy,"Asymmetric lineshapes are experimentally observed in Raman spectra of
different classes of condensed matter. Determination of the peak parameters,
typically done with symmetric pseudo-Voigt functions, in such situations yields
unreliable results. While wide choice of asymmetric fitting functions is
possible, for the function to be practically useful, it should satisfy several
criteria: simple analytic form, minimum of parameters, description of the
symmetric shape as ""zero case"", estimation of the desired peak parameters in a
straightforward way and, above all, adequate description of the experimental
data. In this work we formulate the asymmetric pseudo-Voigt function by damped
perturbation of the original symmetric shapes with one asymmetry-related
parameter. The damped character of the perturbation ensures by construction the
consistent behavior of the line tails. We test the asymmetric function by
fitting the experimental Raman spectra. The results show that the function is
able to describe a wide range of experimentally observed asymmetries for
different nature of asymmetric broadening, including 3D and 2D crystals,
nanoparticles, polymer, molecular solid and liquid.",1804.06083v2
2018-04-23,Linear inviscid damping and enhanced viscous dissipation of shear flows by using the conjugate operator method,"We study the large time behavior of solutions to two-dimensional Euler and
Navier-Stokes equations linearized about shear flows of the mixing layer type
in the unbounded channel $\mathbb{T} \times \mathbb{R}$. Under a simple
spectral stability assumption on a self-adjoint operator, we prove a local form
of the linear inviscid damping that is uniform with respect to small viscosity.
We also prove a local form of the enhanced viscous dissipation that takes place
at times of order $\nu^{-1/3}$, $\nu$ being the small viscosity. To prove these
results, we use a Hamiltonian approach, following the conjugate operator method
developed in the study of Schr\""odinger operators, combined with a
hypocoercivity argument to handle the viscous case.",1804.08291v1
2018-04-23,Capillary waves with surface viscosity,"Experiments over the last 50 years have suggested a tentative correlation
between the surface (shear) viscosity and the stability of a foam or emulsion.
We examine this link theoretically using small-amplitude capillary waves in the
presence of a surfactant solution of dilute concentrations where the associated
Marangoni and surface viscosity effects are modelled via the Boussinesq-Scriven
formulation. The resulting integro-differential initial value problem is solved
analytically and surface viscosity is found to contribute an overall damping
effect on the amplitude of the capillary wave with varying degrees depending on
the lengthscale of the system. Numerically, we find the critical damping
wavelength to increase for increasing surface concentration but the rate of
increase remains different for both the surface viscosity and the Marangoni
effect.",1804.08389v1
2018-04-23,The Multidimensional Damped Wave Equation: Maximal Weak Solutions for Nonlinear Forcing via Semigroups and Approximation,"The damped nonlinear wave equation, also known as the nonlinear telegraph
equation, is studied within the framework of semigroups and eigenfunction
approximation. The linear semigroup assumes a central role: it is bounded on
the domain of its generator for all time t > 0. This permits eigenfunction
approximation within the semigroup framework as a tool for the study of weak
solutions. The semigroup convolution formula, known to be rigorous on the
generator domain, is extended to the interpretation of weak solution on an
arbitrary time interval. A separate approximation theory can be developed by
using the invariance of the semigroup on eigenspaces of the Laplacian as the
system evolves. For (locally) bounded continuous L^2 forcing, this permits a
natural derivation of a maximal solution, which can logically include a
constraint on the solution as well. Operator forcing allows for the
incorporation of concurrent physical processes. A significant feature of the
proof in the nonlinear case is verification of successive approximation without
standard fixed point analysis.",1804.08394v3
2018-04-24,Bidirectional Controlled Quantum Teleportation Using Eight-Qubit Quantum Channel in Noisy Environments,"In this work, a novel protocol is proposed for bidirectional controlled
quantum teleportation (BCQT) in which a quantum channel is used with the
eight-qubit entangled state. Using the protocol, two users can teleport an
arbitrary entangled state and a pure two-qubit state (QBS) to each other
simultaneously under the permission of a third party in the role of controller.
This protocol is based on the controlled-not operation, appropriate
single-qubit (SIQ) UOs and SIQ measurements in the Z and X-basis. Reduction of
the predictability of the controller's qubit (QB) by the eavesdropper and also,
an increasing degree of freedom of controller for controlling one of the users
or both are other features of this protocol. Then, the proposed protocol is
investigated in two typical noisy channels include the amplitude-damping noise
(ADN) and the phase-damping noise (PDN). And finally, analysis of the protocol
shows that it only depends on the amplitude of the initial state and the
decoherence noisy rate (DR).",1804.08876v3
2018-04-25,"Type II Seesaw with scalar dark matter in light of AMS-02, DAMPE and Fermi-LAT","The Standard Model (SM) supplemented by Type II Seesaw and a SM gauge-singlet
scalar dark matter (DM) is a very simple framework to incorporate the observed
neutrino oscillations and provide a plausible DM candidate. In this framework,
the scalar DM naturally has a leptophilic nature with a pair annihilating
mainly into the SM SU(2)$_L$ triplet Higgs scalar of Type II Seesaw which, in
turn, decay into leptons. In this work, we consider indirect signatures of this
leptophilic DM and examine the spectrum of the cosmic ray electron/positron
flux from DM pair annihilations in the Galactic halo. Given an astrophysical
background spectrum of the cosmic ray electron/positron flux, we find that the
contributions from DM annihilations can nicely fit the observed data from the
AMS-02, DAMPE and Fermi-LAT collaborations, with a multi-TeV range of DM mass
and a boost factor for the DM annihilation cross section of ${\cal O}(1000)$.
The boost factor has a slight tension with the Fermi-LAT data for gamma-ray
from dwarf spheroidal galaxies, which can be ameliorated with an enhanced local
DM density by a factor of about 2.",1804.09835v1
2018-05-17,Viscous damping of gravity-capillary waves: Dispersion relations and nonlinear corrections,"We discuss the impact of viscosity on nonlinear propagation of surface waves
at the interface of air and a fluid of large depth. After a survey of the
available approximations of the dispersion relation, we propose to modify the
hydrodynamic boundary conditions to model both short and long waves. From them,
we derive a nonlinear Schr\""odinger equation where both linear and nonlinear
parts are modified by dissipation and show that the former plays the main role
in both gravity and capillary-gravity waves while, in most situations, the
latter represents only small corrections. This provides a justification of the
conventional approaches to damped propagation found in the literature.",1805.06777v2
2018-05-25,"Calculating the transport properties of magnetic materials from first-principles including thermal and alloy disorder, non-collinearity and spin-orbit coupling","A density functional theory based two-terminal scattering formalism that
includes spin-orbit coupling and spin non-collinearity is described. An
implementation using tight-binding muffin-tin orbitals combined with extensive
use of sparse matrix techniques allows a wide variety of inhomogeneous
structures to be flexibly modelled with various types of disorder including
temperature induced lattice and spin disorder. The methodology is illustrated
with calculations of the temperature dependent resistivity and magnetization
damping for the important substitutional disordered magnetic alloy Permalloy
(Py), Ni$_{80}$Fe$_{20}$. Comparison of calculated results with recent
experimental measurements of the damping (including its temperature dependence)
indicates that the scattering approach captures the most important
contributions to this important property.",1805.10062v1
2018-05-28,The linearized Vlasov and Vlasov-Fokker-Planck equations in a uniform magnetic field,"We study the linearized Vlasov equations and the linearized
Vlasov-Fokker-Planck equations in the weakly collisional limit in a uniform
magnetic field. In both cases, we consider periodic confinement and Maxwellian
(or close to Maxwellian) backgrounds. In the collisionless case, for modes
transverse to the magnetic field, we provide a precise decomposition into a
countably infinite family of standing waves for each spatial mode. These are
known as Bernstein modes in the physics literature, though the decomposition is
not an obvious consequence of any existing arguments that we are aware of. We
show that other modes undergo Landau damping. In the presence of collisions
with collision frequency $\nu \ll 1$, we show that these modes undergo
uniform-in-$\nu$ Landau damping and enhanced collisional relaxation at the
time-scale $O(\nu^{-1/3})$. The modes transverse to the field are uniformly
stable and exponentially thermalize on the time-scale $O(\nu^{-1})$. Most of
the results are proved using Laplace transform analysis of the associated
Volterra equations, whereas a simple case of Yan Guo's energy method for
hypocoercivity of collision operators is applied for stability in the
collisional case.",1805.10756v1
2018-06-08,Can Star Products be Augmented by Classical Physics?,"It has been suggested that star products in phase-space quantization may be
augmented to describe additional, classical effects. That proposal is examined
critically here. Two known star products that introduce classical effects are:
the generalized Husimi product of coarse-grained quantization, and a
non-Hermitian damped star product for the harmonic oscillator. Following these
examples, we consider products related by transition differential operators to
the classic Moyal star product. We restrict to Hermitian star products,
avoiding problems already pointed out for the original damped product. It is
shown, however, that with such star products, augmented quantization is
impossible, since an appropriate classical limit does not result.
  For a more complete study, we then also consider generalized, or local,
transition operators, that depend on the local phase-space coordinates, as well
as their derivatives. In this framework, one example of possible physical
interest is constructed. Because of its limited validity and complicated form,
however, it cannot be concluded that augmented quantization with local
transition operators is practical.",1806.03309v2
2018-06-20,Large-Scale Demonstration of Precise Demand Response Provided by Residential Heating Systems,"Being able to adjust the demand of electricity can be an effective means for
power system operators to compensate fluctuating renewable generation, to avoid
grid congestion, and to cope with other contingencies. Electric heating and
cooling systems of buildings can provide different demand response services
because their electricity consumption is inherently flexible because of their
thermal inertia. This paper reports on the results of a large-scale demand
response demonstration involving a population of more than 300 residential
buildings with heat pump installations. We show how the energetic behavior and
flexibility of individual systems can be identified autonomously based only on
energy meter data and outdoor air temperature measurements, and how the
aggregate demand response potential of the population can be quantified.
Various load reduction and rebound damping experiments illustrate the
effectiveness of the approach: the load reductions can be predicted precisely
and amount to 40-65% of the aggregate load, and the rebound can be damped
efficiently.",1806.07670v1
2018-06-22,Weakly coupled systems of semi-linear elastic waves with different damping mechanisms in 3D,"We consider the following Cauchy problem for weakly coupled systems of
semi-linear damped elastic waves with a power source non-linearity in
three-dimensions: \begin{equation*}
  U_{tt}-a^2\Delta U-\big(b^2-a^2\big)\nabla\text{div }
U+(-\Delta)^{\theta}U_t=F(U),\,\, (t,x)\in[0,\infty)\times\mathbb{R}^3,
\end{equation*} where
$U=U(t,x)=\big(U^{(1)}(t,x),U^{(2)}(t,x),U^{(3)}(t,x)\big)^{\mathrm{T}}$ with
$b^2>a^2>0$ and $\theta\in[0,1]$. Our interests are some qualitative properties
of solutions to the corresponding linear model with vanishing right-hand side
and the influence of the value of $\theta$ on the exponents $p_1,p_2,p_3$ in
$F(U)=\big(|U^{(3)}|^{p_1},|U^{(1)}|^{p_2},|U^{(2)}|^{p_3}\big)^{\mathrm{T}}$
to get results for the global (in time) existence of small data solutions.",1806.08543v2
2018-07-02,Global Existence of Solutions to the Compressible Euler Equations with Time-dependent Damping and Logarithmic State Equation,"In mathematical physics, the pressure function is determined by the equation
of state. There are two existing barotropic state equations: the state equation
for polytropic gas with adiabatic index greater than or equal to 1 and the
state equation for generalized Chaplygin gas in cosmology. In this paper, a
logarithmic pressure is derived naturally with the coexistence of the two
existing state equations through an equivalent symmetric hyperbolic
transformation. On the study of the logarithmic pressure, global existence of
solutions with small initial data to the one-dimensional compressible Euler
equations with time-dependent damping is established.",1807.00550v2
2018-07-02,On wave equations of the $p$-Laplacian type with supercritical nonlinearities,"This article focuses on a quasilinear wave equation of $p$-Laplacian type: \[
u_{tt} - \Delta_p u -\Delta u_t = f(u) \] in a bounded domain $\Omega \subset
\mathbb{R}^3$ with a sufficiently smooth boundary $\Gamma=\partial \Omega$
subject to a generalized Robin boundary condition featuring boundary damping
and a nonlinear source term. The operator $\Delta_p$, $2<p<3$, denotes the
classical $p$-Laplacian. The interior and boundary terms $f(u)$, $h(u)$ are
sources that are allowed to have a supercritical exponent, in the sense that
their associated Nemytskii operators are not locally Lipschitz from
$W^{1,p}(\Omega)$ into $L^2(\Omega)$ or $L^2(\Gamma)$. Under suitable
assumptions on the parameters we provide a rigorous proof of existence of a
local weak solution which can be extended globally in time, provided the
damping terms dominates the corresponding sources in an appropriate sense.
Moreover, a blow-up result is proved for solutions with negative initial total
energy.",1807.00650v1
2018-06-30,Efficient $p$-multigrid method based on an exponential time discretization for compressible steady flows,"An efficient multigrid framework is developed for the time marching of
steady-state compressible flows with a spatially high-order ($p$-order
polynomial) modal discontinuous Galerkin method. The core algorithm that based
on a global coupling, exponential time integration scheme provides strong
damping effects to accelerate the convergence towards the steady state, while
high-frequency, high-order spatial error modes are smoothed out with a
$s$-stage preconditioned Runge-Kutta method. Numerical studies show that the
exponential time integration substantially improves the damping and propagative
efficiency of Runge-Kutta time-stepping for use with the $p$-multigrid method,
yielding rapid and $p$-independent convergences to steady flows in both two and
three dimensions.",1807.01151v1
2018-07-04,Structural crossover in a model fluid exhibiting two length scales: repercussions for quasicrystal formation,"We investigate the liquid state structure of the two-dimensional (2D) model
introduced by Barkan et al. [Phys. Rev. Lett. 113, 098304 (2014)], which
exhibits quasicrystalline and other unusual solid phases, focussing on the
radial distribution function $g(r)$ and its asymptotic decay $r\to\infty$. For
this particular model system, we find that as the density is increased there is
a structural crossover from damped oscillatory asymptotic decay with one
wavelength to damped oscillatory asymptotic decay with another distinct
wavelength. The ratio of these wavelengths is $\approx1.932$. Following the
locus in the phase diagram of this structural crossover leads directly to the
region where quasicrystals are found. We argue that identifying and following
such a crossover line in the phase diagram towards higher densities where the
solid phase(s) occur is a good strategy for finding quasicrystals in a wide
variety of systems. We also show how the pole analysis of the asymptotic decay
of equilibrium fluid correlations is intimately connected with the
non-equilibrium growth or decay of small amplitude density fluctuations in a
bulk fluid.",1807.01467v1
2018-07-04,Dirac's Method for the Two-Dimensional Damped Harmonic Oscillator in the Extended Phase Space,"The system of two-dimensional damped harmonic oscillator is revisited in the
extended phase space. It is an old problem already addressed by many authors
that we present here in some fresh points of view and carry on smoothly a whole
discussion. We show that the system is singular. The classical Hamiltonian is
proportional to the first-class constraint. We pursue with the Dirac's
canonical quantization procedure by fixing the gauge and provide a reduced
phase space description of the system. As result the quantum system is simply
modeled by the original quantum Hamiltonian.",1807.01539v2
2018-07-05,Decay of approximate solutions for the damped semilinear wave equation on a bounded 1d domain,"In this paper we study the long time behavior for a semilinear wave equation
with space-dependent and nonlinear damping term. After rewriting the equation
as a first order system, we define a class of approximate solutions that employ
tipical tools of hyperbolic systems of conservation laws, such as the Riemann
problem. By recasting the problem as a discrete-time nonhomogeneous system,
which is related to a probabilistic interpretation of the solution, we provide
a strategy to study its long-time behavior uniformly with respect to the mesh
size parameter $\Delta x=1/N\to 0$. The proof makes use of the Birkhoff
decomposition of doubly stochastic matrices and of accurate estimates on the
iteration system as $N\to\infty$.
  Under appropriate assumptions on the nonlinearity, we prove the exponential
convergence in $L^\infty$ of the solution to the first order system towards a
stationary solution, as $t\to+\infty$, as well as uniform error estimates for
the approximate solutions.",1807.01968v3
2018-07-07,Axial Quasi-Normal Modes of Scalarized Neutron Stars with Realistic Equations of State,"We compute the axial quasi-normal modes of static neutron stars in scalar
tensor theory. In particular, we employ various realistic equations of state
including nuclear, hyperonic and hybrid matter. We investigate the fundamental
curvature mode and compare the results with those of General Relativity. We
find that the frequency of the modes and the damping time are reduced for the
scalarized neutron stars. In addition, we confirm and extend the universal
relations for quasi-normal modes known in General Relativity to this wide range
of realistic equations of state for scalarized neutron stars and confirm the
universality of the scaled frequency and damping time in terms of the scaled
moment of inertia as well as compactness for neutron stars with and without
scalarization.",1807.02598v1
2018-07-09,DLA and sub-DLA metallicity evolution: A case study of absorbers towards Q0338-0005,"The damped and sub-damped Lyman alpha systems (DLAs and sub-DLAs) traced in
absorption against bright background quasars represent the main reserve of
neutral hydrogen at high redshifts. We used the archival Very Large Telescope
(VLT) instrument Ultraviolet and Visual Echelle Spectrograph (UVES)
high-resolution data of Q0338-0005 (zem = 3.049) to study abundances of the DLA
(zabs = 2.2298) and sub-DLA (zabs =2.7457) along the line of sight. We
estimated column densities of HI and various elements present in the DLA and
sub-DLA through Voigt profile fitting. The DLA trough shows the Lyman alpha
emission from its host galaxy. We derive the metallicities of the DLA and
sub-DLA with [Zn/H] = -0.67 +/- 0.18 and [S/H] = -1.45 +/-0.17, respectively.
We compared our abundances of the DLA and sub-DLA with other high resolution
DLA and sub-DLA metallicities and find that both populations show an overall
increase of metallicity with decreasing redshift. However, sub-DLAs usually
have higher metallicities than the DLAs.",1807.04189v1
2018-07-15,Asymptotic profile of solutions for semilinear wave equations with structural damping,"This paper is concerned with the initial value problem for semilinear wave
equation with structural damping $u_{tt}+(-\Delta)^{\sigma}u_t -\Delta u
=f(u)$, where $\sigma \in (0,\frac{1}{2})$ and $f(u) \sim |u|^p$ or $u
|u|^{p-1}$ with $p> 1 + {2}/(n - 2 \sigma)$. We first show the global existence
for initial data small in some weighted Sobolev spaces on $\mathcal R^n$ ($n
\ge 2$). Next, we show that the asymptotic profile of the solution above is
given by a constant multiple of the fundamental solution of the corresponding
parabolic equation, provided the initial data belong to weighted $L^1$ spaces.",1807.05509v3
2018-07-19,Vibrational damping effects on electronic energy relaxation in molecular aggregates,"Representation of molecular vibrational degrees of freedom by independent
harmonic oscillators, when describing electronic spectra or electronic
excitation energy transport, raises unfavourable effects as vibrational energy
relaxation becomes inaccessible. A standard theoretical description is extended
in this paper by including both electronic-phonon and vibrational-phonon
couplings. Using this approach we have simulated a model pigment-protein system
and have shown that intermode coupling leads to the quenching of pigment
vibrational modes, and to the redistribution of fluctuation spectral density
with respect to the electronic excitations. Moreover, new energy relaxation
pathways, opened by the vibrational-phonon interaction, allow to reach the
electronic excited state equilibrium quicker in the naturally occurring water
soluble chlorophyll binding protein (WSCP) aggregate, demonstrating the
significance that the damping of molecular vibrations has for the
intrarmolecular energy relaxation process rate.",1807.07314v1
2018-07-24,Role of stable modes in driven shear-flow turbulence,"A linearly unstable, sinusoidal $E \times B$ shear flow is examined in the
gyrokinetic framework in both the linear and nonlinear regimes. In the linear
regime, it is shown that the eigenmode spectrum is nearly identical to
hydrodynamic shear flows, with a conjugate stable mode found at every unstable
wavenumber. In the nonlinear regime, turbulent saturation of the instability is
examined with and without the inclusion of a driving term that prevents
nonlinear flattening of the mean flow, and a scale-independent radiative
damping term that suppresses the excitation of conjugate stable modes. A simple
fluid model for how momentum transport and partial flattening of the mean flow
scale with the driving term is constructed, from which it is shown that, except
at high radiative damping, stable modes play an important role in the turbulent
state and yield significantly improved quantitative predictions when compared
with corresponding models neglecting stable modes.",1807.09280v1
2018-08-08,An application of $L^1$ estimates for oscillating integrals to parabolic like semi-linear structurally damped $σ$-evolution models,"We study the following Cauchy problems for semi-linear structurally damped
$\sigma$-evolution models: \begin{equation*} u_{tt}+ (-\Delta)^\sigma u+ \mu
(-\Delta)^\delta u_t = f(u,u_t),\, u(0,x)= u_0(x),\, u_t(0,x)=u_1(x)
\end{equation*} with $\sigma \ge 1$, $\mu>0$ and $\delta \in
(0,\frac{\sigma}{2})$. Here the function $f(u,u_t)$ stands for the power
nonlinearities $|u|^{p}$ and $|u_t|^{p}$ with a given number $p>1$. We are
interested in investigating $L^{1}$ estimates for oscillating integrals in the
presentation of the solutions to the corresponding linear models with vanishing
right-hand sides by applying the theory of modified Bessel functions and
Fa\`{a} di Bruno's formula. By assuming additional $L^{m}$ regularity on the
initial data, we use $(L^{m}\cap L^{q})- L^{q}$ and $L^{q}- L^{q}$ estimates
with $q\in (1,\infty)$ and $m\in [1,q)$, to prove the global (in time)
existence of small data Sobolev solutions to the above semi-linear models from
suitable function spaces basing on $L^q$ spaces.",1808.02706v2
2018-08-09,Two-qubit state recovery from amplitude damping based on weak measurement,"In the quantum control process, arbitrary pure or mixed initial states need
to be protected from amplitude damping through the noise channel using
measurements and quantum control. However, how to achieve it on a two-qubit
quantum system remains a challenge. In this paper, we propose a feed-forward
control approach to protect arbitrary two-qubit pure or mixed initial states
using the weak measurement. A feed-forward operation and measurements are used
before the noise channel, and afterwards a reversed operation and measurements
are applied to recover the state back to its initial state. In the case of
two-qubit pure states, we use the unravelling trick to describe the state of
the system in each step of the control procedure. For two-qubit mixed states, a
completely-positive trace-preserving (CPTP) map is implemented. Finally, the
fidelity and success probability are used to evaluate the effect of protection.
The complete recovery conditions for the measurement strengths are derived,
under which we achieve the optimal fidelity and the success probability of
recovering the initial pure or mixed states.",1808.03094v1
2018-08-10,Dynamical polarization and the optical response of silicene and related materials,"We discuss the dynamical polarization, optical response in low-frequency
regime under in-plane polarized driving field of the silicene. The dynamical
polarization, dielectric function, and absorption of radiation in infrared
region are obtained and shown in the ${\bf q}\sim\omega$ space, and they are
distinguishing for the cases of chemical potential larger than the band gap and
smaller than the band gap. The optical properties of silicene and the related
group-V and group-VI materials: MoS$_{2}$ and black phosphorus are explored
through the first-principle study. The plasmon which damped into the
electron-hole pair in the single-particle excitation regime is also mentioned.
The spin/valley polarized electron-hole pairs can be formed through that way,
especially for the high-energy $\pi$-plasmon which begin to damp at the small
${\bf q}$-limit. The anisotropic effects induced by the warping structure or
charged impurity, and the anisotropic polarization induced by the polarized
incident light are also discussed. Our result exhibits the great potential in
the optoelectronic applications of the materials we discussed.",1808.03442v1
2018-08-19,Reconstruction algorithms for photoacoustic tomography in heterogenous damping media,"In this article, we study several reconstruction methods for the inverse
source problem of photoacoustic tomography (PAT) with spatially variable sound
speed and damping. The backbone of these methods is the adjoint operators,
which we thoroughly analyze in both the $L^2$- and $H^1$-settings. They are
casted in the form of a nonstandard wave equation. We derive the well-pawedness
of the aforementioned wave equation in a natural functional space, and also
prove the finite speed of propagation. Under the uniqueness and visibility
condition, our formulations of the standard iterative reconstruction methods,
such as Landweber's and conjugate gradients (CG), achieve a linear rate of
convergence in either $L^2$- or $H^1$-norm. When the visibility condition is
not satisfied, the problem is severely ill-posed and one must apply a
regularization technique to stabilize the solutions. To that end, we study two
classes of regularization methods: (i) iterative, and (ii) variational
regularization. In the case of full data, our simulations show that the CG
method works best; it is very fast and robust. In the ill-posed case, the CG
method behaves unstably. Total variation regularization method (TV), in this
case, significantly improves the reconstruction quality.",1808.06176v1
2018-08-27,Landau damping of Alfvénic modes in stellarators,"It is found that the presence of the so-called non-axisymmetric resonances of
wave-particle interaction in stellarators [which are associated with the lack
of axial symmetry of the magnetic configuration, Kolesnichenko et al., Phys.
Plasmas 9 (2002) 517] may have a strong stabilizing influence through Landau
mechanism on the Toroidicity-induced Alfv\'en Eigenmodes (TAE) and isomon modes
(Alfv\'enic modes with equal poloidal and toroidal mode numbers and frequencies
in the continuum region) destabilized by the energetic ions. These resonances
involve largest harmonics of the equilibrium magnetic field of stellarators and
lead to absorption of the mode energy by thermal ions in medium pressure
plasma, in which case the effect is large. On the other hand, at the high
pressure attributed to, e.g., a Helias reactor, thermal ions can interact also
with high frequency Alfv\'en gap modes [Helicity-induced Alfv\'en Eigenmodes
(HAE) and mirror-induced Alfv\'en Eigenmodes (MAE)], leading to a considerable
damping of these modes. Only resonances with passing particles are considered.
The developed theory is applied to various modes in the Wendelstein 7-X
stellarator and a Helias reactor, and to two TAE modes in the LHD helical
device.",1808.08862v1
2018-09-04,Linear Wave Propagation for Resistive Relativistic Magnetohydrodynamics,"We present a linear mode analysis of the relativistic MHD equations in the
presence of finite electrical conductivity. Starting from the fully
relativistic covariant formulation, we derive the dispersion relation in the
limit of small linear perturbations. It is found that the system supports ten
wave modes which can be easily identified in the limits of small or large
conductivities. In the resistive limit, matter and electromagnetic fields
decouple and solution modes approach pairs of light and acoustic waves as well
as a number of purely damped (non-propagating) modes. In the opposite (ideal)
limit, the frozen-in condition applies and the modes of propagation coincide
with a pair of fast magnetosonic, a pair of slow and Alfv\'en modes, as
expected. In addition, the contact mode is always present and it is unaffected
by the conductivity. For finite values of the conductivity, the dispersion
relation gives rise to either pairs of opposite complex conjugate roots or
purely imaginary (damped) modes. In all cases, the system is dissipative and
also dispersive as the phase velocity depends nonlineary on the wavenumber.
Occasionally, the group velocity may exceed the speed of light although this
does not lead to superluminal signal propagation.",1809.01115v1
2018-09-05,NMR-like effect on Anisotropic Magnetic Moment of Surface Bound States in Topological Superfluid $^3$He-B,"We present experimental observation of a new phenomenon, that we interpret as
NMR-like effect on anisotropic magnetic moment of the surface Andreev bound
states in topological superfluid $^3$He-B at zero temperature limit. We show
that an anisotropic magnetic moment formed near the horizontal surface of a
mechanical resonator due to symmetry violation of the superfluid $^3$He-B order
parameter by the resonator's surface may lead to anomalous damping of the
resonator motion in magnetic field. In difference to classical NMR technique,
here NMR was excited using own harmonic motion of the mechanical resonator, and
nuclear magnetic resonance was detected as a maximum in damping when
resonator's angular frequency satisfied the Larmor resonance condition.",1809.01402v3
2018-09-11,Optomechanical damping basis,"We present a closed-form analytical solution to the eigenvalue problem of the
Liouville operator generating the dissipative dynamics of the standard
optomechanical system. The corresponding Lindblad master equation describes the
dynamics of a single-mode field inside an optical cavity coupled by radiation
pressure to its moving mirror. The optical field and the mirror are in contact
with separate environments, which are assumed at zero and finite temperature,
respectively. The optomechanical damping basis refers to the exact set of
eigenvectors of the generator that, together with the exact eigenvalues, are
explicitly derived. Both the weak- and the strong-coupling regime, which
includes combined decay mechanisms, are solved in this work.",1809.03693v2
2018-09-13,Active Damping of a DC Network with a Constant Power Load: An Adaptive Passivity-based Control Approach,"This paper proposes a nonlinear, adaptive controller to increase the
stability margin of a direct-current (DC) small-scale electrical network
containing a constant power load, whose value is unknown. Due to their negative
incremental impedance, constant power loads are known to reduce the effective
damping of a network, leading to voltage oscillations and even to network
collapse. To tackle this problem, we consider the incorporation of a controlled
DC-DC power converter between the feeder and the constant power load. The
design of the control law for the converter is based on the use of standard
Passivity-Based Control and Immersion and Invariance theories. The good
performance of the controller is evaluated with numerical simulations.",1809.04920v1
2018-09-14,Nonequilibrium polariton dynamics in a Bose-Einstein condensate coupled to an optical cavity,"We study quasiparticle scattering effects on the dynamics of a homogeneous
Bose-Einstein condensate of ultracold atoms coupled to a single mode of an
optical cavity. The relevant excitations, which are polariton-like mixed
excitations of photonic and atomic density-wave modes, are identified. All the
first-order correlation functions are presented by means of the Keldysh Green's
function technique. Beyond confirming the existence of the resonant enhancement
of Beliaev damping, we find a very structured spectrum of fluctuations. There
is a spectral hole burning at half of the recoil frequency reflecting the
singularity of the Beliaev scattering process. The effects of the photon-loss
dissipation channel and that of the Beliaev damping due to atom-atom collisions
can be well separated. We show that the Beliaev process does not influence the
properties of the self-organization criticality.",1809.05427v2
2018-09-26,The influence of oscillations on energy estimates for damped wave models with time-dependent propagation speed and dissipation,"The aim of this paper is to derive higher order energy estimates for
solutions to the Cauchy problem for damped wave models with time-dependent
propagation speed and dissipation. The model of interest is \begin{equation*}
u_{tt}-\lambda^2(t)\omega^2(t)\Delta u +\rho(t)\omega(t)u_t=0, \quad
u(0,x)=u_0(x), \,\, u_t(0,x)=u_1(x). \end{equation*} The coefficients
$\lambda=\lambda(t)$ and $\rho=\rho(t)$ are shape functions and
$\omega=\omega(t)$ is an oscillating function. If $\omega(t)\equiv1$ and
$\rho(t)u_t$ is an ""effective"" dissipation term, then $L^2-L^2$ energy
estimates are proved in [2]. In contrast, the main goal of the present paper is
to generalize the previous results to coefficients including an oscillating
function in the time-dependent coefficients. We will explain how the interplay
between the shape functions and oscillating behavior of the coefficient will
influence energy estimates.",1809.10179v2
2018-09-27,Non-equilibrium Quantum Langevin dynamics of orbital diamagnetic moment,"We investigate the time dependent orbital diamagnetic moment of a charged
particle in a magnetic field in a viscous medium via the Quantum Langevin
Equation. We study how the interplay between the cyclotron frequency and the
viscous damping rate governs the dynamics of the orbital magnetic moment in the
high temperature classical domain and the low temperature quantum domain for an
Ohmic bath. These predictions can be tested via state of the art cold atom
experiments with hybrid traps for ions and neutral atoms. We also study the
effect of a confining potential on the dynamics of the magnetic moment. We
obtain the expected Bohr Van Leeuwen limit in the high temperature, asymptotic
time ($ \gamma t\longrightarrow \infty$, where $ \gamma $ is the viscous
damping coefficient) limit.",1809.10370v1
2018-09-29,Uniform stabilization for the Klein-Gordon system in a inhomogeneous medium with locally distributed damping,"We consider the Klein-Gordon system posed in an inhomogeneous medium with
smooth boundary subject to a local viscoelastic damping distributed around a
neighborhoodof the boundary according to the Geometric Control Condition. We
show that the energy of the system goes uniformly and exponentially to zero for
all initial data of finite energy taken in bounded sets of finite energy
phase-space. For this purpose, refined microlocal analysis arguments are
considered by exploiting ideas due to Burq and Gerard . By using sharp Carleman
estimates we prove a unique continuation property for coupled systems.",1810.00247v1
2018-10-09,Lévy-walk-like Langevin dynamics,"Continuous time random walks and Langevin equations are two classes of
stochastic models for describing the dynamics of particles in the natural
world. While some of the processes can be conveniently characterized by both of
them, more often one model has significant advantages (or has to be used)
compared with the other one. In this paper, we consider the weakly damped
Langevin system coupled with a new subordinator|$\alpha$-dependent subordinator
with $1<\alpha<2$. We pay attention to the diffusion behaviour of the
stochastic process described by this coupled Langevin system, and find the
super-ballistic diffusion phenomena for the system with an unconfined potential
on velocity but sub-ballistic superdiffusion phenomenon with a confined
potential, which is like L\'{e}vy walk for long times. One can further note
that the two-point distribution of inverse subordinator affects mean square
displacement of this coupled weakly damped Langevin system in essential.",1810.04332v1
2018-10-18,Analysis of the controllability from the exterior of strong damping nonlocal wave equations,"We make a complete analysis of the controllability properties from the
exterior of the (possible) strong damping wave equation with the fractional
Laplace operator subject to the nonhomogeneous Dirichlet type exterior
condition. In the first part, we show that if $0<s<1$, $\Omega\subset\RR^N$
($N\ge 1$) is a bounded Lipschitz domain and the parameter $\delta> 0$, then
there is no control function $g$ such that the following system
\begin{equation*} \begin{cases} u_{tt} + (-\Delta)^{s} u + \delta(-\Delta)^{s}
u_{t}=0 & \mbox{ in }\; \Omega\times(0,T),\\ u=g\chi_{\mathcal O\times (0,T)}
&\mbox{ in }\; (\Omc)\times (0,T) ,\\ u(\cdot,0) = u_0, u_t(\cdot,0) = u_1
&\mbox{ in }\; \Omega, \end{cases} \end{equation*} is exact or null
controllable at time $T>0$. In the second part, we prove that for every
$\delta\ge 0$ and $0<s<1$, the system is indeed approximately controllable for
any $T>0$ and $g\in \mathcal D(\mathcal O\times(0,T))$, where $\mathcal
O\subset\Omc$ is any non-empty open set.",1810.08060v1
2018-10-20,Memory-based mediated interactions between rigid particulate inclusions in viscoelastic environments,"Many practically relevant materials combine properties of viscous fluids and
elastic solids to viscoelastic behavior. Our focus is on the induced dynamic
behavior of damped finite-sized particulate inclusions in such substances. We
explicitly describe history-dependent interactions that emerge between the
embedded particles. These interactions are mediated by the viscoelastic
surroundings. They result from the flows and distortions of the viscoelastic
medium when induced by the rigid inclusions. Both, viscoelastic environments of
terminal fluid-like flow or of completely reversible damped elastic behavior,
are covered. For illustration and to highlight the role of the formalism in
potential applications, we briefly address the relevant examples of dragging a
rigid sphere through a viscoelastic environment together with subsequent
relaxation dynamics, the switching dynamics of magnetic fillers in elastic gel
matrices, and the swimming behavior of active microswimmers in viscoelastic
solutions. The approach provides a basis for more quantitative and extended
investigations of these and related systems in the future.",1810.08832v1
2018-10-22,Dynamical instability towards finite-momentum pairing in quenched BCS superconducting phases,"In this work we numerically investigate the fate of the
Bardeen-Cooper-Schrieffer (BCS) pairing in the presence of quenched phase under
Peierls substitution using time-dependent real space and momentum space
Bogoliubov-de Gennes equation methods and Anderson pseudospin representation
method. This kind of phase imprint can be realized by modulating electric field
in ultracold atoms and illumining of THz optical pump pulse in solids with
conventional and unconventional superconductors. In the case of weak phase
imprint, the BCS pairing is stable; while in the strong phase imprint,
instability towards finite-momentum pairing is allowed, in which the real space
and momentum space methods yield different results. In the pulsed gauge
potential, we find that this instability will not happen even with much
stronger vector potential. We also show that the uniform and staggered gauge
potentials yield different behaviors. While the staggered potential induces
transition from the BCS pairing to over-damped phase, the uniform gauge may
enhance the pairing and will not induce to the over-damped phase. These result
may shade light on the realization of finite momentum pairing, such as
Fulde-Ferrell-Larkin-Ovchinnikov phase with dynamical modulation.",1810.09125v1
2018-10-21,A note on a weakly coupled system of semi-linear visco-elastic damped $σ$-evolution models with different power nonlinearities and different $σ$ values,"In this article, we prove the global (in time) existence of small data
solutions from energy spaces basing on $L^q$ spaces, with $q \in (1,\infty)$,
to the Cauchy problems for a weakly coupled system of semi-linear visco-elastic
damped $\sigma$-evolution models. Here we consider different power
nonlinearities and different $\sigma$ values in the comparison between two
single equations. To do this, we use $(L^m \cap L^q)- L^q$ and $L^q- L^q$
estimates, i.e., by mixing additional $L^m$ regularity for the data on the
basis of $L^q- L^q$ estimates for solutions, with $m \in [1,q)$, to the
corresponding linear Cauchy problems. In addition, allowing loss of decay and
the flexible choice of parameters $\sigma$, $m$ and $q$ bring some benefits to
relax the restrictions to the admissible exponents $p$.",1810.09664v1
2018-10-25,First-principles calculation of spin-orbit torque in a Co/Pt bilayer,"The angular dependence of spin-orbit torque in a disordered Co/Pt bilayer is
calculated using a first-principles non-equilibrium Green's function formalism
with an explicit supercell averaging over Anderson disorder. In addition to the
usual dampinglike and fieldlike terms, the odd torque contains a sizeable
planar Hall-like term $(\mathbf{m\cdot
E})\mathbf{m}\times(\mathbf{z}\times\mathbf{m})$ whose contribution to
current-induced damping is consistent with experimental observations. The
dampinglike and planar Hall-like torquances depend weakly on disorder strength,
while the fieldlike torquance declines with increasing disorder. The torques
that contribute to damping are almost entirely due to spin-orbit coupling on
the Pt atoms, but the fieldlike torque does not require it.",1810.11003v2
2018-10-29,Optimal identification of non-Markovian environments for spin chains,"Correlations of an environment are crucial for the dynamics of non-Markovian
quantum systems, which may not be known in advance. In this paper, we propose a
gradient algorithm for identifying the correlations in terms of time-varying
damping rate functions in a time-convolution-less master equation for spin
chains. By measuring time trace observables of the system, the identification
procedure can be formulated as an optimization problem. The gradient algorithm
is designed based on a calculation of the derivative of an objective function
with respect to the damping rate functions, whose effectiveness is shown in a
comparison to a differential approach for a two-qubit spin chain.",1810.11923v1
2018-10-29,Existence and uniqueness of dynamic evolutions for a one-dimensional debonding model with damping,"In this paper we analyse a one-dimensional debonding model for a thin film
peeled from a substrate when viscosity is taken into account. It is described
by the weakly damped wave equation whose domain, the debonded region, grows
according to a Griffith's criterion. Firstly we prove that the equation admits
a unique solution when the evolution of the debonding front is assigned.
Finally we provide an existence and uniqueness result for the coupled problem
given by the wave equation together with Griffith's criterion.",1810.12006v3
2018-10-29,A Graceful Exit for the Cosmological Constant Damping Scenario,"We present a broad and simple class of scalar-tensor scenarios that
successfully realize dynamical damping of the effective cosmological constant,
therefore providing a viable dynamical solution to the fine-tuning or ""old""
cosmological constant problem. In contrast to early versions of this approach,
pioneered in the works of A. Dolgov in the 1980es, these do not suffer from
unacceptable variations of Newton's constant, as one aims at a small but
strictly positive (rather than zero) late-time curvature. In our approach, the
original fine-tuning issue is traded for a hierarchy of couplings, and we
further suggest a way to naturally generate this hierarchy based on fermion
condensation and softly broken field shift symmetry.",1810.12336v2
2018-10-31,AGN Variability Analysis Handbook,"This work develops application techniques for stochastic modelling of Active
Galactic Nuclei (AGN) variability as a probe of accretion disk physics.
Stochastic models, specifically Continuous Auto-Regressive Moving Average
(CARMA) models, characterize lightcurves by estimating delay timescales that
describe movements away from and toward equilibrium (mean flux) as well as an
amplitude and frequency of intrinsic perturbations to the AGN flux. We begin
this tutorial by reviewing discrete auto-regressive (AR) and moving-average
(MA) processes, we bridge these components to their continuous analogs, and
lastly we investigate the significance of timescales from direct stochastic
modelling of a lightcurve projected in power spectrum (PSD) and structure
function (SF) space. We determine that higher order CARMA models, for example
the Damped Harmonic Oscillator (DHO or CARMA(2,1)) are more sensitive to
deviations from a single-slope power-law description of AGN variability; unlike
Damped Random Walks (DRW or CAR(1)) where the PSD slope is fixed, the DHO slope
is not. Higher complexity stochastic models than the DRW capture additional
covariance in data and output additional characteristic timescales that probe
the driving mechanisms of variability.",1811.00154v1
2018-11-15,Unique ergodicity for a class of stochastic hyperbolic equations with additive space-time white noise,"In this paper, we consider a certain class of second order nonlinear PDEs
with damping and space-time white noise forcing, posed on the $d$-dimensional
torus. This class includes the wave equation for $d=1$ and the beam equation
for $d\le 3$. We show that the Gibbs measure of the equation without forcing
and damping is the unique invariant measure for the flow of this system. Since
the flow does not satisfy the Strong Feller property, we introduce a new
technique for showing unique ergodicity. This approach may be also useful in
situations in which finite-time blowup is possible.",1811.06294v4
2018-12-04,Optical excitation of single- and multi-mode magnetization precession in Galfenol nanolayers,"We demonstrate a variety of precessional responses of the magnetization to
ultrafast optical excitation in nanolayers of Galfenol (Fe,Ga), which is a
ferromagnetic material with large saturation magnetization and enhanced
magnetostriction. The particular properties of Galfenol, including cubic
magnetic anisotropy and weak damping, allow us to detect up to 6 magnon modes
in a 120-nm layer, and a single mode with effective damping ${\alpha}_{eff}$ =
0.005 and frequency up to 100 GHz in a 4-nm layer. This is the highest
frequency observed to date in time-resolved experiments with metallic
ferromagnets. We predict that detection of magnetization precession approaching
THz frequencies should be possible with Galfenol nanolayers.",1812.01237v1
2018-12-10,Assessment of skin-friction-reduction techniques on a turbulent wing section,"The scope of the present project is to quantify the effects of uniform
blowing and body-force damping on turbulent boundary layers subjected to a
non-uniform adverse-pressure-gradient distribution. To this end, well-resolved
large-eddy simulations are employed to describe the flow around the NACA4412
airfoil at moderate Reynolds number 200, 000 based on freestream velocity and
chord length. In the present paper we focus on uniform blowing and the
conference presentation will include a comparison with body-force damping
applied in the same region. The inner-scaled profiles of the mean velocity and
of selected components of the Reynolds-stress tensor are examined and compared
with the uncontrolled cases. It is known that uniform blowing and
adverse-pressure gradients share some similarities in their effect on the
boundary layers, and our results will show that these effects are not
independent. The behaviour of the skin-friction coefficient is analyzed through
the FIK decomposition, and the impact of this control strategy on the
aerodynamic efficiency of the airfoil is discussed.",1812.03762v1
2018-12-18,Gravitational quasinormal modes of black holes in Einstein-aether theory,"The local Lorentz violation (LV) in gravity sector should show itself in
derivation of the characteristic quasinormal modes (QNMs) of black hole mergers
from their general relativity case. In this paper, I study QNMs of the
gravitational field perturbations to Einstein-aether black holes and, at first
compare them to those in Schwarzschild black hole, and then some other known LV
gravity theories. By comparing to Schwarzschild black hole, the first kind
aether black holes have larger damping rate and the second ones have lower
damping rate. And they all have smaller real oscillation frequency of QNMs. By
comparing to some other LV theories, the QNMs of the first kind aether black
hole are similar to that of the QED-extension limit of standard model
extension, non-minimal coupling to Einstein's tensor and massive gravity
theories. While as to the second kind aether black hole, they are similar to
those of the noncommutative gravity theories and Einstein-Born-Infeld theories.
These similarities may imply that LV in gravity sector and LV in matter sector
have some intrinsic connections.",1812.07994v1
2018-12-19,Rain Calms the Sea - The Impact of Entrained Air,"We propose a mechanism for the damping of short ocean gravity waves during
rainstorms associated with the injection of air bubbles by rain drops. The
mechanism is proposed as one of the possible explanations that ascribe to rain
a calming effect on ocean surface waves. A model is developed that shows how
wave attenuation increases with the presence of air bubbles in the upper
reaches of the ocean. The model makes predictions of the effective wave
dissipation coefficient, as a function of the volumetric ratio of air to water,
as well as to the rainfall rate. The model predicts dissipation rates that are
in line with experimental estimates of the effective wave damping rate.",1812.08200v2
2018-12-25,Blow-up for a weakly coupled system of semilinear damped wave equations in the scattering case with power nonlinearities,"In this work we study the blow-up of solutions of a weakly coupled system of
damped semilinear wave equations in the scattering case with power
nonlinearities. We apply an iteration method to study both the subcritical case
and the critical case. In the subcritical case our approach is based on lower
bounds for the space averages of the components of local solutions. In the
critical case we use the slicing method and a couple of auxiliary functions,
recently introduced by Wakasa-Yordanov, to modify the definition of the
functionals with the introduction of weight terms. In particular, we find as
critical curve for the pair (p, q) of the exponents in the nonlinear terms the
same one as for the weakly coupled system of semilinear wave equations with
power nonlinearities.",1812.10086v1
2018-12-27,Global existence of solutions to semilinear damped wave equation with slowly decaying inital data in exterior domain,"In this paper, we discuss the global existence of weak solutions to the
semilinear damped wave equation \begin{equation*} \begin{cases}
\partial_t^2u-\Delta u + \partial_tu = f(u) & \text{in}\ \Omega\times (0,T), \\
u=0 & \text{on}\ \partial\Omega\times (0,T), \\ u(0)=u_0, \partial_tu(0)=u_1 &
\text{in}\ \Omega, \end{cases} \end{equation*} in an exterior domain $\Omega$
in $\mathbb{R}^N$ $(N\geq 2)$, where $f:\mathbb{R}\to \mathbb{R}$ is a smooth
function behaves like $f(u)\sim |u|^p$. From the view point of weighted energy
estimates given by Sobajima--Wakasugi \cite{SoWa4}, the existence of
global-in-time solutions with small initial data in the sense of
$(1+|x|^2)^{\lambda/2}u_0$, $(1+|x|^2)^{\lambda/2}\nabla u_0$,
$(1+|x|^2)^{\lambda/2}u_1\in L^2(\Omega)$ with $\lambda\in (0,\frac{N}{2})$ is
shown under the condition $p\geq 1+\frac{4}{N+2\lambda}$. The sharp lower bound
for the lifespan of blowup solutions with small initial data $(\varepsilon
u_0,\varepsilon u_1)$ is also given.",1812.10664v1
2018-12-28,Axion Misalignment Driven to the Bottom,"Several theoretical motivations point to ultralight QCD axions with large
decay constants $f_a \simeq \mathcal{O}(10^{16}-10^{17})$ GeV, to which
experimental proposals are dedicated. This regime is known to face the problem
of overproduction of axion dark matter from the misalignment mechanism unless
the misalignment angle $\theta_{\rm mis}$ is as small as
$\mathcal{O}(10^{-3}-10^{-4})$, which is generally considered a fine-tuning
problem. We investigate a dynamical explanation for a small $\theta_{\rm mis}$.
The axion mass arises from strong dynamics and may be sufficiently enhanced by
early dynamics so as to overcome Hubble friction and drive the field value to
the bottom of the potential long before the QCD phase transition. Together with
an approximate CP symmetry in the theory, this minimum is very closely related
to today's value and thus $\theta_{\rm mis}$ can automatically be well under
unity. Owing to such efficient relaxation, the isocurvature perturbations are
essentially damped. As an existence proof, using supersymmetric theories we
illustrate that the Higgs coupling with the inflaton energy can successfully
achieve this axion damping in a consistent inflationary cosmology.",1812.11186v2
2019-01-03,Calibration and Status of the 3D Imaging Calorimeter of DAMPE for Cosmic Ray Physics on Orbit,"The DArk Matter Particle Explorer (DAMPE) developed in China was designed to
search for evidence of dark matter particles by observing primary cosmic rays
and gamma rays in the energy range from 5 GeV to 10 TeV. Since its launch in
December 2015, a large quantity of data has been recorded. With the data set
acquired during more than a year of operation in space, a precise
time-dependent calibration for the energy measured by the BGO ECAL has been
developed. In this report, the instrumentation and development of the BGO
Electromagnetic Calorimeter (BGO ECAL) are briefly described. The calibration
on orbit, including that of the pedestal, attenuation length, minimum ionizing
particle peak, and dynode ratio, is discussed, and additional details about the
calibration methods and performance in space are presented.",1901.00734v1
2019-01-08,Atom-only descriptions of the driven-dissipative Dicke model,"We investigate how to describe the dissipative spin dynamics of the
driven-dissipative Dicke model, describing $N$ two-level atoms coupled to a
cavity mode, after adiabatic elimination of the cavity mode. To this end, we
derive a Redfield master equation which goes beyond the standard secular
approximation and large detuning limits. We show that the secular (or rotating
wave) approximation and the large detuning approximation both lead to
inadequate master equations, that fail to predict the Dicke transition or the
damping rates of the atomic dynamics. In contrast, the full Redfield theory
correctly predicts the phase transition and the effective atomic damping rates.
Our work provides a reliable framework to study the full quantum dynamics of
atoms in a multimode cavity, where a quantum description of the full model
becomes intractable.",1901.02473v2
2019-01-10,Stability and Controllability results for a Timoshenko system,"In this paper, we study the indirect boundary stability and exact
controllability of a one-dimensional Timoshenko system. In the first part of
the paper, we consider the Timoshenko system with only one boundary fractional
damping. We first show that the system is strongly stable but not uniformly
stable. Hence, we look for a polynomial decay rate for smooth initial data.
Using frequency domain arguments combined with the multiplier method, we prove
that the energy decay rate depends on coefficients appearing in the PDE and on
the order of the fractional damping. Moreover, under the equal speed
propagation condition, we obtain the optimal polynomial energy decay rate. In
the second part of this paper, we study the indirect boundary exact
controllability of the Timoshenko system with mixed Dirichlet-Neumann boundary
conditions and boundary control. Using non-harmonic analysis, we first
establish a weak observability inequality, which depends on the ratio of the
waves propagation speeds. Next, using the HUM method, we prove that the system
is exactly controllable in appropriate spaces and that the control time can be
small.",1901.03303v2
2019-01-13,Dueling Dynamical Backaction in a Cryogenic Optomechanical Cavity,"Dynamical backaction has proven to be a versatile tool in cavity
optomechanics, allowing for precise manipulation of a mechanical resonator's
motion using confined optical photons. In this work, we present measurements of
a silicon whispering-gallery-mode optomechanical cavity where backaction
originates from opposing radiation pressure and photothermal forces, with the
former dictating the optomechanical spring effect and the latter governing the
optomechanical damping. At high enough optical input powers, we show that the
photothermal force drives the mechanical resonator into self-oscillations for a
pump beam detuned to the lower-frequency side of the optical resonance,
contrary to what one would expect for a radiation-pressure-dominated
optomechanical device. Using a fully nonlinear model, we fit the hysteretic
response of the optomechanical cavity to extract its properties, demonstrating
that this non-sideband-resolved device exists in a regime where photothermal
damping could be used to cool its motion to the quantum ground state.",1901.03950v1
2019-01-22,Coupling between superfluid neutrons and superfluid protons in the elementary excitations of neutron star matter,"Several phenomena occurring in neutron stars are affected by the elementary
excitations that characterize the stellar matter. In particular, low-energy
excitations can play a major role in the emission and propagation of neutrinos,
neutron star cooling and transport processes. In this paper, we consider the
elementary modes in the star region where both proton and neutron components
are superfluid.
  We study the overall spectral functions of protons, neutrons and electrons on
the basis of the Coulomb and nuclear interactions.
  This study is performed in the framework of the Random Phase Approximation,
generalized to superfluid systems. The formalism we use ensures that the
Generalized Ward's Identities are satisfied. We focus on the coupling between
neutrons and protons. On one hand this coupling results in collective modes
that involve simultaneously neutrons and protons, on the other hand it produces
a damping of the excitations. Both effects are especially visible in the
spectral functions of the different components of the matter. At high density
while the neutrons and protons tend to develop independent excitations, as
indicated by the spectral functions, the neutron-proton coupling still produces
a strong damping of the modes.",1901.07550v1
2019-02-08,Milky Way Halo Vibrations and Incommensurate Stream Velocities,"Collisionless dark matter galactic halos are expected to exhibit damped
oscillations as a result of ongoing late time accretion. An n-body model of the
cosmological assembly of a Milky Way-like halo is used to quantify the time
dependence of its gravitational field. The simulation contains stellar streams
whose incommensurate perpendicular velocities are found to have an
approximately exponential distribution with a scale of 10-20\kms, depending on
how the stars are selected, comparable to those reported for the Orphan stream.
The fluctuations in the quadrupole moment of the dark matter halo are
sufficient to largely explain the tangential velocities. If velocity
measurements of a larger sample of Milky Way streams finds (or does not find)
the expected distribution of transverse velocities it will lead to limits on
the cross-section of self-interacting dark matter, in which kinetic viscosity
can damp the oscillations more rapidly than the mixing processes of
collisionless dark matter alone.",1902.03275v2
2019-02-20,Dark matter gets DAMPE at high energies,"The DArk Matter Particle Explorer (DAMPE) mission revealed a break in the
spectrum of cosmic-ray electons and positrons. This is associated with an
excess above the expected backgrounds at energies around 1 TeV. Several authors
have argued that such an excess can be explained in terms of dark matter models
that feature heavy leptophilic WIMPs. These models, however, require some form
annihilation enchancement above that expected from the Milky-Way galactic
centre. This can take the form of either a local over-density near to our solar
system or some form of Sommerfeld enhancement of the annihilation rate. In this
work we will explore the detectability of local over-densities using gamma-ray
and neutrino observatories. We conclude that KM3NET may be the only up-coming
high-energy instrument capable of ruling out the presence of such objects.
However, in the case where the local over-density is an Ultra-Compact Mini
Halo, CTA can also explore the parameter space of these proposed dark matter
models.",1902.07468v1
2019-02-23,General symmetry in the reduced dynamics of two-level system,"We study general transformation on the density matrix of two-level system
that keeps the expectation value of observable invariant. We introduce a set of
generators that yields hermiticity and trace preserving general transformation
which casts the transformation into simple form. The general transformation is
in general not factorized and not completely positive. Consequently, either the
parameter of transformation or the density matrix it acts on needs to be
restricted. It can transform the system in the forward and backward direction
with regard to its parameter, not as a semigroup in the time translation
symmetry of dynamical maps. The general transformation can rotate the Bloch
vector circularly or hyperbolically, dilate it or translate it. We apply the
general transformation to study the general symmetry of amplitude damping and
phase damping in two-level system. We generalize the generators to higher level
systems.",1902.08714v2
2019-02-25,Interpretation of the cosmic ray positron and electron excesses with an annihilating-decaying dark matter scenario,"The precise measurements of energy spectra of cosmic ray positrons and/or
electrons by recent experiments show clear excesses above 10 GeV. Moreover, a
potential sharp spectral feature was suggested by the Dark Matter Particle
Explorer (DAMPE) data. These results inspire quite a number of discussions on
the connection with either the annihilation/decay of dark matter (DM) or the
astrophysical origins. Here we discuss a DM scenario in which DM particles
could annihilate and decay into standard model particle pairs simultaneously.
In this model, the peak structure is due to the DM annihilation in a nearby
subhalo and the broad positron/electron excesses are due to the decay of DM in
the Milky Way. This model can reasonably explain the DAMPE and AMS-02 data of
the total $e^+e^-$ spectra and the positron fraction, with model parameters
being consistent with existing constraints. A simple realization of such a DM
model is the spin-1 vector DM model.",1902.09235v2
2019-02-27,Necessary and Sufficient Conditions for Passivity of Velocity-Sourced Impedance Control of Series Elastic Actuators,"Series Elastic Actuation (SEA) has become prevalent in applications involving
physical human-robot interaction as it provides considerable advantages over
traditional stiff actuators in terms of stability robustness and fidelity of
force control. Several impedance control architectures have been proposed for
SEA. Among these alternatives, the cascaded controller with an inner-most
velocity loop, an intermediate torque loop and an outer-most impedance loop is
particularly favoured for its simplicity, robustness, and performance. In this
paper, we derive the \emph{necessary and sufficient conditions} to ensure the
passivity of this cascade-controller architecture for rendering two most common
virtual impedance models. Based on the newly established passivity conditions,
we provide non-conservative design guidelines to haptically display a null
impedance and a pure spring while ensuring the passivity of interaction. We
also demonstrate the importance of including physical damping in the actuator
model during derivation of passivity conditions, when integral controllers are
utilized. In particular, we show the adversary effect of physical damping on
system passivity.",1902.10607v2
2019-03-01,"Response to: [Comment on Quantization of the damped harmonic oscillator [Serhan et al, J. Math. Phys. 59, 082105 (2018)]]","This is a response to a recently reported comment [1] on paper [J. Math.
Phys.59, 082105 (2018)] regarding the quantization of damped harmonic
oscillator using a non-Hermitian Hamiltonian with real energy eigenvalues. We
assert here that the calculation of Eq. (29) of [2] is incorrect, and thus the
subsequent steps via the Nikiforov-Uvarov method are affected, and the energy
eigenvalues should have been complex. However, we show here that the
Hermiticity of the Hamiltonian should be firstly achieved to make the correct
transition from classical Hamiltonian to quantum counterpart, and this can be
reached using the symmetrization rule. Applying the canonical quantization on
the resulted Hermitian Hamiltonian and then using the Nikiforov-Uvarov method
correctly, the energy eigenvalues will be real and exactly as given by Eq. (35)
of [2].",1903.00352v2
2019-03-08,Protecting quantum correlations in presence of generalised amplitude damping channel: the two-qubit case,"Any kind of quantum resource useful in different information processing tasks
is vulnerable to several types of environmental noise. Here we study the
behaviour of quantum correlations such as entanglement and steering in
two-qubit systems under the application of the generalised amplitude damping
channel and propose some protocols towards preserving them under this type of
noise. First, we employ the technique of weak measurement and reversal for the
purpose of preservation of correlations. We then show how the evolution under
the channel action can be seen as an unitary process. We use the technique of
weak measurement and most general form of selective positive operator valued
measure (POVM) to achieve preservation of correlations for a significantly
large range of parameter values.",1903.03550v2
2019-03-17,"Generalized Euler, Smoluchowski and Schrödinger equations admitting self-similar solutions with a Tsallis invariant profile","The damped isothermal Euler equations, the Smoluchowski equation and the
damped logarithmic Schr\""odinger equation with a harmonic potential admit
stationary and self-similar solutions with a Gaussian profile. They satisfy an
$H$-theorem for a free energy functional involving the von Weizs\""acker
functional and the Boltzmann functional. We derive generalized forms of these
equations in order to obtain stationary and self-similar solutions with a
Tsallis profile. In particular, we introduce a nonlinear Schr\""odinger equation
involving a generalized kinetic term characterized by an index $q$ and a
power-law nonlinearity characterized by an index $\gamma$. We derive an
$H$-theorem satisfied by a generalized free energy functional involving a
generalized von Weizs\""acker functional (associated with $q$) and a Tsallis
functional (associated with $\gamma$). This leads to a notion of generalized
quantum mechanics and generalized thermodynamics. When $q=2\gamma-1$, our
nonlinear Schr\""odinger equation admits an exact self-similar solution with a
Tsallis invariant profile. Standard quantum mechanics (Schr\""odinger) and
standard thermodynamics (Boltzmann) are recovered for $q=\gamma=1$.",1903.07111v1
2019-03-21,Creating localized plasma wave by ionization of doped semiconductors,"Localized plasma waves can be generated by suddenly ionizing extrinsic
semiconductors with spatially periodic dopant densities. The built-in
electrostatic potentials at the metallurgical junctions, combined with electron
density ripples, offer the exact initial condition for exciting long-lasting
plasma waves upon ionization. This method can create plasma waves with a
frequency between a few terahertz to sub-petahertz without substantial damping.
The lingering plasma waves can seed backward Raman amplification in a wide
range of resonance frequencies up to the extreme ultraviolet regime. Chirped
wavevectors and curved wavefronts allow focusing the amplified beam in both
longitudinal and transverse dimensions. The main limitation to this method
appears to be obtaining sufficiently low plasma density from solid-state
materials to avoid collisional damping.",1903.09013v2
2019-03-22,Noncommutative approach to diagnose degenerate Higgs bosons at 125 GeV,"We propose a noncommutative (NC) version for a global O(2) scalar field
theory, whose damping feature is introduced into the scalar field theory
through the NC parameter. In this context, we investigate how noncommutative
drives spontaneous symmetry breaking (SSB) and Higgs-Kibble mechanisms and how
the damping feature workout. Indeed, we show that the noncommutativity plays an
important role in such mechanisms, i.e., the Higgs mass and VEV dependent on NC
parameter. After that, it is explored the consequences of noncommutativity
dependence of Higgs mass and VEV: for the first, it is shown that there are a
mass-degenerate Higgs bosons near 126.5 GeV, parametrized by the
noncommutativity; for the second, the gauge fields gain masses that present a
noncommutativity contribution.",1903.09727v2
2019-03-30,Uncertainty damping in kinetic traffic models by driver-assist controls,"In this paper, we propose a kinetic model of traffic flow with uncertain
binary interactions, which explains the scattering of the fundamental diagram
in terms of the macroscopic variability of aggregate quantities, such as the
mean speed and the flux of the vehicles, produced by the microscopic
uncertainty. Moreover, we design control strategies at the level of the
microscopic interactions among the vehicles, by which we prove that it is
possible to dampen the propagation of such an uncertainty across the scales.
Our analytical and numerical results suggest that the aggregate traffic flow
may be made more ordered, hence predictable, by implementing such control
protocols in driver-assist vehicles. Remarkably, they also provide a precise
relationship between a measure of the macroscopic damping of the uncertainty
and the penetration rate of the driver-assist technology in the traffic stream.",1904.00257v2
2019-04-01,Reduction of Kinetic Equations to Liénard-Levinson-Smith Form: Counting Limit Cycles,"We have presented an unified scheme to express a class of system of equations
in two variables into a Li\'enard-Levinson-Smith (LLS) oscillator form. We have
derived the condition for limit cycle with special reference to Rayleigh and
Li\'enard systems for arbitrary polynomial functions of damping and restoring
force. Krylov-Boguliubov (K-B) method is implemented to determine the maximum
number of limit cycles admissible for a LLS oscillator atleast in the weak
damping limit. Scheme is illustrated by a number of model systems with single
cycle as well as the multiple cycle cases.",1904.00604v2
2019-04-02,Stability of the interface of an isotropic active fluid,"We study the linear stability of an isotropic active fluid in three different
geometries: a film of active fluid on a rigid substrate, a cylindrical thread
of fluid, and a spherical fluid droplet. The active fluid is modeled by the
hydrodynamic theory of an active nematic liquid crystal in the isotropic phase.
In each geometry, we calculate the growth rate of sinusoidal modes of
deformation of the interface. There are two distinct branches of growth rates;
at long wavelength, one corresponds to the deformation of the interface, and
one corresponds to the evolution of the liquid crystalline degrees of freedom.
The passive cases of the film and the spherical droplet are always stable. For
these geometries, a sufficiently large activity leads to instability. Activity
also leads to propagating damped or growing modes. The passive cylindrical
thread is unstable for perturbations with wavelength longer than the
circumference. A sufficiently large activity can make any wavelength unstable,
and again leads to propagating damped or growing modes.",1904.01558v1
2019-04-04,Shear viscosity of classical fields in scalar theory,"We investigate the shear viscosity of massless classical scalar fields in the
$\phi^4$ theory on a lattice by using the Green-Kubo formula. Based on the
scaling property of the classical field, the shear viscosity is represented
using a scaling function. Equilibrium expectation value of the time-correlation
function of the energy-momentum tensor is evaluated as the ensemble average of
the classical field configurations, whose time evolution is obtained by solving
the classical equation of motion starting from the initial condition in thermal
equilibrium. It is found that there are two distinct damping time scales in the
time-correlation function, which is found to show damped oscillation behavior
in the early stage around a slow monotonous decay with an exponential form, and
the slow decay part is found to dominate the shear viscosity in the massless
classical field theory. This kind of slow decay is also known to exist in the
molecular dynamics simulation, then it may be a generic feature of dense
matter.",1904.02419v3
2019-04-08,Study of Decoherence in Quantum Computers: A Circuit-Design Perspective,"Decoherence of quantum states is a major hurdle towards scalable and reliable
quantum computing. Lower decoherence (i.e., higher fidelity) can alleviate the
error correction overhead and obviate the need for energy-intensive noise
reduction techniques e.g., cryogenic cooling. In this paper, we performed a
noise-induced decoherence analysis of single and multi-qubit quantum gates
using physics-based simulations. The analysis indicates that (i) decoherence
depends on the input state and the gate type. Larger number of $|1\rangle$
states worsen the decoherence; (ii) amplitude damping is more detrimental than
phase damping; (iii) shorter depth implementation of a quantum function can
achieve lower decoherence. Simulations indicate 20\% improvement in the
fidelity of a quantum adder when realized using lower depth topology. The
insights developed in this paper can be exploited by the circuit designer to
choose the right gates and logic implementation to optimize the system-level
fidelity.",1904.04323v1
2019-04-09,Ferromagnetic Resonance Studies of Strain tuned Bi:YIG Films,"Bismuth-doped Yttrium iron garnet (Bi:YIG) thin films known for large
Magneto-optical activity with low losses still needs to get probed for its
magnetization dynamics. We demonstrate a controlled tuning of
magnetocrystalline anisotropy in Bi-doped Y_3 Fe_5 O_12 (Bi:YIG) films of high
crystalline quality using growth induced epitaxial strain on [111]-oriented
Gd_3 Ga_5 O_12 (GGG) substrate. We optimize a growth protocol to get thick
highly-strained epitaxial films showing large magneto-crystalline anisotropy,
compare to thin films prepared using a different protocol. Ferromagnetic
resonance measurements establish a linear dependence of the out-of-plane
uniaxial anisotropy on the strain induced rhombohedral distortion of Bi:YIG
lattice. Interestingly, the enhancement in the magnetoelastic constant due to
an optimum substitution of Bi^(3+) ions with strong spin orbit coupling does
not strongly affect the precessional damping (~2x10^(-3) ). Large
magneto-optical activity, reasonably low damping, large magnetocrystalline
anisotropy and large magnetoelastic coupling in BiYIG are the properties that
may help BiYIG emerge as a possible material for photo-magnonics and other
spintronics applications.",1904.04800v2
2019-04-23,A novel undamped gapless plasmon mode in tilted type-II Dirac semimetal,"We predict the existence of a novel long-lived gapless plasmon mode in a
type-II Dirac semimetal (DSM). This gapless mode arises from the out-of-phase
oscillations of the density fluctuations in the electron and the hole pockets
of a type-II DSM. It originates beyond a critical wave-vector along the
direction of the tilt axis, owing to the momentum separation of the electron
and hole pockets. A similar out-of-phase plasmon mode arises in other
multi-component charged fluids as well, but generally it is Landau damped and
lies within the particle-hole continuum. In the case of a type-II DSM, the open
Fermi surface prohibits low-energy finite momentum single-particle excitations,
creating a `gap' in the particle-hole continuum. The gapless plasmon mode lies
within this particle-hole continuum gap and, thus, it is protected from Landau
damping.",1904.10137v1
2019-04-25,Interplay between nonclassicality and $\mathcal{PT}$ symmetry in an effective two level system with open system effects,"A three level atom in $\Lambda$ configuration is reduced to an effective two
level system, under appropriate conditions, and its $\mathcal{PT}$ symmetric
properties are investigated. This effective qubit system when subjected to a
beam-splitter type of interaction, it provides the scope of directly
(indirectly) probing the nonclassical properties of the output (input) state.
Here, we study nonclassical properties of the output state by using some well
known measures of nonclassical correlations like the measurement induced
disturbance, concurrence and negativity. The nonclassical features are found to
enhance in the $\mathcal{PT}$ symmetric (PTS) phase compared to the
$\mathcal{PT}$ symmetry broken (PTSB) phase. Further, the output ports of the
beam-splitter are subjected to different quantum noise channels, both
non-Markovian, e.g., random telegraph noise as well as Markovian, e.g., phase
damping, and amplitude damping noise. The application of noise channels is
found to decrease the degree of nonclassicality, though continuing to exhibit
distinct behavior in PTS and PTSB phases, with the dominant behavior appearing
in the former case.",1904.11181v1
2019-04-25,Low damping magnetic properties and perpendicular magnetic anisotropy with strong volume contribution in the Heusler alloy Fe1.5CoGe,"We present a study of the dynamic magnetic properties of TiN-buffered
epitaxial thin films of the Heusler alloy Fe$_{1.5}$CoGe. Thickness series
annealed at different temperatures are prepared and the magnetic damping is
measured, a lowest value of $\alpha=2.18\times 10^{-3}$ is obtained. The
perpendicular magnetic anisotropy properties in Fe$_{1.5}$CoGe/MgO are also
characterized. The evolution of the interfacial perpendicular anisotropy
constant $K^{\perp}_{\rm S}$ with the annealing temperature is shown and
compared with the widely used CoFeB/MgO interface. A large volume contribution
to the perpendicular anisotropy of $(4.3\pm0.5)\times 10^{5}$ $\rm J/m^3$ is
also found, in contrast with vanishing bulk contribution in common Co- and
Fe-based Heusler alloys.",1904.11247v1
2019-04-26,Terahertz spin dynamics driven by a field-derivative torque,"Efficient manipulation of magnetization at ultrashort time scales is of
particular interest for future technology. Here, we numerically investigate the
influence of the so-called field-derivative torque, which was derived earlier
based on relativistic Dirac theory [Mondal et al., Phys. Rev. B 94, 144419
(2016)], on the spin dynamics triggered by ultrashort laser pulses. We find
that only considering the THz Zeeman field can underestimate the spin
excitation in antiferromagnetic oxide systems as, e.g., NiO and CoO. However,
accounting for both, the THz Zeeman torque and the field-derivative torque, the
amplitude of the spin excitation increases significantly. Studying the damping
dependence of field-derivative torque we observe larger effects for materials
having larger damping constants.",1904.11768v2
2019-04-30,A Self-Adaptive Contractive Algorithm for Enhanced Dynamic Phasor Estimation,"In this paper, a self-adaptive contractive (SAC) algorithm is proposed for
enhanced dynamic phasor estimation in the diverse operating conditions of
modern power systems. At a high-level, the method is composed of three stages:
parameter shifting, filtering and parameter unshifting. The goal of the first
stage is to transform the input signal phasor so that it is approximately
mapped to nominal conditions. The second stage provides estimates of the
phasor, frequency, rate of change of frequency (ROCOF), damping and rate of
change of damping (ROCOD) of the parameter shifted phasor by using a
differentiator filter bank (DFB). The final stage recovers the original signal
phasor parameters while rejecting misleading estimates. The most important
features of the algorithm are that it offers convergence guarantees in a set of
desired conditions, and also great harmonic rejection. Numerical examples,
including the IEEE C37.118.1 standard tests with realistic noise levels, as
well as fault conditions, validate the proposed algorithm.",1904.13328v1
2019-05-02,The floatability of aerosols and waves damping on Titan's seas,"Titan, Saturn's largest moon, has a dense atmosphere, together with lakes and
seas of liquid hydrocarbons. These liquid bodies, which are in polar regions
and up to several hundred kilometres in diameter, generally have smooth
surfaces despite evidence of near-surface winds. Photochemically generated
organic aerosols form a haze that can settle and potentially interact with the
liquid surface. Here we investigate the floatability of these aerosols on
Titan's seas and their potential to dampen waves. We find that the majority of
aerosols are denser than the liquid hydrocarbons, but that some could have
liquid-repelling properties. From calculation of the capillary forces, we
propose that these 'liquidophobic' aerosols could float and form a persistent
film on Titan's seas. We numerically model the wave damping efficiency of such
a film under the conditions on Titan, demonstrating that even a film one
molecule thick may inhibit formation of waves larger than a few centimetres in
wavelength. We conclude that the presence of a floating film of aerosols
deposited on Titan's lakes and seas could explain the remarkable smoothness of
their surfaces.",1905.00760v1
2019-05-02,Holographic Plasmon Relaxation with and without Broken Translations,"We study the dynamics and the relaxation of bulk plasmons in strongly coupled
and quantum critical systems using the holographic framework. We analyze the
dispersion relation of the plasmonic modes in detail for an illustrative class
of holographic bottom-up models. Comparing to a simple hydrodynamic formula, we
entangle the complicated interplay between the three least damped modes and
shed light on the underlying physical processes. Such as the dependence of the
plasma frequency and the effective relaxation time in terms of the
electromagnetic coupling, the charge and the temperature of the system.
Introducing momentum dissipation, we then identify its additional contribution
to the damping. Finally, we consider the spontaneous symmetry breaking (SSB) of
translational invariance. Upon dialing the strength of the SSB, we observe an
increase of the longitudinal sound speed controlled by the elastic moduli and a
decrease in the plasma frequency of the gapped plasmon. We comment on the
condensed matter interpretation of this mechanism.",1905.00804v2
2019-05-05,Effective spin-mixing conductance of heavy-metal-ferromagnet interfaces,"The effective spin-mixing conductance (G_eff) of a heavy metal/ferromagnet
(HM/FM) interface characterizes the efficiency of the interfacial spin
transport.Accurately determining G_eff is critical to the quantitative
understanding of measurements of direct and inverse spin Hall effects. G_eff is
typically ascertained from the inverse dependence of magnetic damping on the FM
thickness under the assumption that spin pumping is the dominant mechanism
affecting this dependence.Here we report that, this assumption fails badly in
many in-plane magnetized prototypical HM/FM systems in the nm-scale thickness
regime. Instead, the majority of the damping is from two-magnon scattering at
the FM interface, while spin-memory-loss scattering at the interface can also
be significant.If these two effects are neglected, the results will be an
unphysical ""giant"" apparent G_eff and hence considerable underestimation of
both the spin Hall ratio and the spin Hall conductivity in inverse/direct spin
Hall experiments.",1905.01577v2
2019-05-07,Integral representation formulae for the solution of a wave equation with time-dependent damping and mass in the scale-invariant case,"This paper is devoted to derive integral representation formulae for the
solution of an inhomogeneous linear wave equation with time-dependent damping
and mass terms, that are scale-invariant with respect to the so-called
hyperbolic scaling. Yagdjian's integral transform approach is employed for this
purpose. The main step in our argument consists in determining the kernel
functions for the different integral terms, which are related to the source
term and to initial data. We will start with the one dimensional case (in
space). We point out that we may not apply in a straightforward way Duhamel's
principle to deal with the source term since the coefficients of lower order
terms make our model not invariant by time translation. On the contrary, we
shall begin with the representation formula for the inhomogeneous equation with
vanishing data by using a revised Duhamel's principle. Then, we will derive the
representation of the solution in the homogeneous case with nontrivial data.
After deriving the formula in the one dimensional case, the classical approach
by spherical means is used in order to deal with the odd dimensional case.
Finally, using the method of descent, the representation formula in the even
dimensional case is proved.",1905.02408v1
2019-05-07,Optimal decay for the $n$-dimensional incompressible Oldroyd-B model without damping mechanism,"By a new energy approach involved in the high frequencies and low frequencies
decomposition in the Besov spaces, we obtain the optimal decay for the
incompressible Oldroyd-B model without damping mechanism in $\mathbb{R}^n$
($n\ge 2$). More precisely, let $(u,\tau)$ be the global small solutions
constructed in [18],
  we prove for any $(u_0,\tau_0)\in{\dot{B}_{2,1}^{-s}}(\mathbb{R}^n)$ that
\begin{eqnarray*}
\big\|\Lambda^{\alpha}(u,\Lambda^{-1}\mathbb{P}\mathrm{div}\tau)\big\|_{L^q}
\le C (1+t)^{-\frac n4-\frac {(\alpha+s)q-n}{2q}},
\quad\Lambda\stackrel{\mathrm{def}}{=}\sqrt{-\Delta}, \end{eqnarray*}
  with $\frac n2-1<s<\frac np, $ $2\leq p \leq \min(4,{2n}/({n-2})),\ p\not=4\
\hbox{ if }\ n=2,$ and $p\leq q\leq\infty$, $\frac nq-\frac np-s<\alpha
\leq\frac nq-1$. The proof relies heavily on the special dissipative structure
of the equations and some commutator estimates and various interpolations
between Besov type spaces. The method also works for other parabolic-hyperbolic
systems in which the Fourier splitting technique is invalid.",1905.02604v1
2019-05-12,Transport and Phonon Damping in $^{\bf 4}$He,"The dynamic structure function $S(k,\omega)$ informs about the dispersion and
damping of excitations. We have recently (Phys. Rev. B {\bf 97}, 184520 (2018))
compared experimental results for $S(k,\omega)$ from high-precision neutron
scattering experiment and theoretical results using the ``dynamic many-body
theory'' (DMBT), showing excellent agreement over the whole experimentally
accessible pressure regime. This paper focuses on the specific aspect of the
propagation of low-energy phonons. We report calculations of the phonon
mean-free path and phonon life time in liquid \he4 as a function of wave length
and pressure. Historically, the question was of interest for experiments of
quantum evaporation. More recently, there is interest in the potential use of
$^4$He as a detector for low-energy dark matter (K. Schulz and Kathryn M.
Zurek, Phys. Rev. Lett. {\bf 117}, 121302 (2016)). While the mean free path of
long wave length phonons is large, phonons of intermediate energy can have a
short mean free path of the order of $\mu$m. Comparison of different levels of
theory indicate that reliable predictions of the phonon mean free path can be
made only by using the most advanced many--body method available, namely, DMBT.",1905.04759v1
2019-05-15,Nearly Markovian maps and entanglement-based bound on corresponding non-Markovianity,"We identify a set of dynamical maps of open quantum system, and refer to them
as ""$ \epsilon $-Markovian"" maps. It is constituted of maps which, in a higher
dimensional system-environment Hilbert space, possibly violate Born
approximation but only a ""little"". We characterize the
""$\epsilon$-nonmarkovianity"" of a general dynamical map by the minimum distance
of that map from the set of $\epsilon$-Markovian maps. We analytically derive
an inequality which gives a bound on the $ \epsilon$-nonmarkovianity of the
dynamical map, in terms of an entanglement-like resource generated between the
system and its ""immediate"" environment. In the special case of a vanishing
$\epsilon$, this inequality gives a relation between the
$\epsilon$-nonmarkovianity of the reduced dynamical map on the system and the
entanglement generated between the system and its immediate environment. We
numerically investigate the behavior of the similar distant based measures of
non-Markovianity for classes of amplitude damping and phase damping channels.",1905.06198v3
2019-05-15,A remark on triviality for the two-dimensional stochastic nonlinear wave equation,"We consider the two-dimensional stochastic damped nonlinear wave equation
(SdNLW) with the cubic nonlinearity, forced by a space-time white noise. In
particular, we investigate the limiting behavior of solutions to SdNLW with
regularized noises and establish triviality results in the spirit of the work
by Hairer, Ryser, and Weber (2012). More precisely, without renormalization of
the nonlinearity, we establish the following two limiting behaviors; (i) in the
strong noise regime, we show that solutions to SdNLW with regularized noises
tend to 0 as the regularization is removed and (ii) in the weak noise regime,
we show that solutions to SdNLW with regularized noises converge to a solution
to a deterministic damped nonlinear wave equation with an additional mass term.",1905.06278v3
2019-05-17,Chiral p-wave superconductors have complex coherence and magnetic field penetration lengths,"We show that in superconductors that break time reversal symmetry and have
anisotropy, such as p+ip materials, all order parameters and magnetic modes are
mixed. Excitation of the gap fields produces an excitation of the magnetic
field and vice versa. Correspondingly the long-range decay of the magnetic
field and order parameter are in general given by the same exponent. Thus one
cannot characterize p+ip superconductors by the usual coherence and magnetic
field penetration lengths. Instead the system has normal modes that are
associated with linear combinations of magnetic fields, moduli of and phases of
the order parameter components. Each such normal mode has its own decay length
that plays the role of a hybridized coherence/magnetic field penetration
length. On a large part of the parameter space these exponents are complex.
Therefore the system in general has damped oscillatory decay of the magnetic
field accompanied by damped oscillatory variation of the order parameter
fields.",1905.07296v2
2019-05-20,Short time blow-up by negative mass term for semilinear wave equations with small data and scattering damping,"In this paper we study blow-up and lifespan estimate for solutions to the
Cauchy problem with small data for semilinear wave equations with scattering
damping and negative mass term. We show that the negative mass term will play a
dominant role when the decay of its coefficients is not so fast, thus the
solutions will blow up in a finite time. What is more, we establish a lifespan
estimate from above which is much shorter than the usual one.",1905.08100v1
2019-05-21,Low-pass-filter-based shock response spectrum and the evaluation method of transmissibility between equipment and sensitive components interfaces,"According to the features of the sources of pyroshock and ballistic shock,
this study considers the pyroshock and ballistic shock generated by their
respective impulsive sources as damped harmonic waves with different
frequencies. According to the linear superposition assumption of damped
harmonic waves in a linear elastic structure, a shock analysis method based on
low-pass-filtered shock signals and their corresponding shock response spectrum
(SRS), termed as low-pass-filter-based shock response spectrum (LPSRS), is
proposed. LPSRS contains rich information of the frequency distribution of the
shock excitation signal. A method to calculate shock transmissibility is
proposed based on LPSRS and basic modal information of the equipment structure.
LPSRS and SRS curves can be predicted at any given position of the equipment
structure. The prediction method is validated by finite element method (FEM)
simulation.",1905.10190v1
2019-05-24,Sound damping in glasses: interplay between anharmonicities and elastic heterogeneities,"Some facets of the way sound waves travel through glasses are still unclear.
Recent works have shown that in the low-temperature harmonic limit a crucial
role in controlling sound damping is played by local elastic heterogeneity.
Sound waves propagation has been demonstrated to be strongly affected by
inhomogeneous mechanical features of the materials, which add to the anharmonic
couplings at finite temperatures. We describe the interplay between these two
effects by molecular dynamics simulation of a model glass. In particular, we
focus on the transverse components of the vibrational excitations in terms of
dynamic structure factors, and characterize the temperature dependence of sound
attenuation rates in an extended frequency range. We provide a complete picture
of all phenomena, in terms encompassing both theory and experiments.",1905.10235v2
2019-05-27,A blow-up result for a semilinear wave equation with scale-invariant damping and mass and nonlinearity of derivative type,"In this note, we prove blow-up results for semilinear wave models with
damping and mass in the scale-invariant case and with nonlinear terms of
derivative type. We consider the single equation and the weakly coupled system.
In the first case we get a blow-up result for exponents below a certain shift
of the Glassey exponent. For the weakly coupled system we find as critical
curve a shift of the corresponding curve for the weakly coupled system of
semilinear wave equations with the same kind of nonlinearities. Our approach
follows the one for the respective classical wave equation by Zhou Yi. In
particular, an explicit integral representation formula for a solution of the
corresponding linear scale-invariant wave equation, which is derived by using
Yagdjian's integral transform approach, is employed in the blow-up argument.
While in the case of the single equation we may use a comparison argument, for
the weakly coupled system an iteration argument is applied.",1905.11025v2
2019-05-28,Stationary states for underdamped anharmonic oscillators driven by Cauchy noise,"Using methods of stochastic dynamics, we have studied stationary states in
the underdamped anharmonic stochastic oscillators driven by Cauchy noise. Shape
of stationary states depend both on the potential type and the damping. If the
damping is strong enough, for potential wells which in the overdamped regime
produce multimodal stationary states, stationary states in the underdamped
regime can be multimodal with the same number of modes like in the overdamped
regime. For the parabolic potential, the stationary density is always unimodal
and it is given by the two dimensional $\alpha$-stable density. For the mixture
of quartic and parabolic single-well potentials the stationary density can be
bimodal. Nevertheless, the parabolic addition, which is strong enough, can
destroy bimodlity of the stationary state.",1905.12078v2
2019-05-30,Intrinsically Undamped Plasmon Modes in Narrow Electron Bands,"Surface plasmons in 2-dimensional electron systems with narrow Bloch bands
feature an interesting regime in which Landau damping (dissipation via
electron-hole pair excitation) is completely quenched. This surprising behavior
is made possible by strong coupling in narrow-band systems characterized by
large values of the ""fine structure"" constant $\alpha=e^2/\hbar \kappa v_{\rm
F}$. Dissipation quenching occurs when dispersing plasmon modes rise above the
particle-hole continuum, extending into the forbidden energy gap that is free
from particle-hole excitations. The effect is predicted to be prominent in
moir\'e graphene, where at magic twist-angle values, flat bands feature
$\alpha\gg1$. The extinction of Landau damping enhances spatial optical
coherence. Speckle-like interference, arising in the presence of disorder
scattering, can serve as a telltale signature of undamped plasmons directly
accessible in near-field imaging experiments.",1905.13088v2
2019-06-04,High frequency voltage-induced ferromagnetic resonance in magnetic tunnel junctions,"Voltage-induced ferromagnetic resonance (V-FMR) in magnetic tunnel junctions
(MTJs) with a W buffer is investigated. Perpendicular magnetic anisotropy (PMA)
energy is controlled by both thickness of a CoFeB free layer deposited directly
on the W buffer and a post-annealing process at different temperatures. The PMA
energy as well as the magnetization damping are determined by analysing
field-dependent FMR signals in different field geometries. An optimized MTJ
structure enabled excitation of V-FMR at frequencies exceeding 30 GHz. The
macrospin modelling is used to analyse the field- and angular-dependence of the
V-FMR signal and to support experimental magnetization damping extraction.",1906.01301v1
2019-06-04,Late time approach to Hawking radiation: terms beyond leading order,"Black hole evaporation is studied using wave packets for the modes. These
allow for approximate frequency and time resolution. The leading order late
time behavior gives the well known Hawking radiation that is independent of how
the black hole formed. The focus here is on the higher order terms and the rate
at which they damp at late times. Some of these terms carry information about
how the black hole formed. A general argument is given which shows that the
damping is significantly slower (power law) than what might be naively expected
from a stationary phase approximation (exponential). This result is verified by
numerical calculations in the cases of 2D and 4D black holes that form from the
collapse of a null shell.",1906.01735v2
2019-06-20,Time-sliced perturbation theory with primordial non-Gaussianity and effects of large bulk flows on inflationary oscillating features,"We extend the formalism of time-sliced perturbation theory (TSPT) for
cosmological large-scale structure to include non-Gaussian initial conditions.
We show that in such a case the TSPT interaction vertices acquire new
contributions whose time-dependence factorizes for the Einstein-de Sitter
cosmology. The new formulation is free from spurious infrared (IR) enhancements
and reveals a clear IR structure of non-Gaussian vertices. We use the new
technique to study the evolution of oscillating features in primordial
statistics and show that they are damped due to non-linear effects of large
bulk flows. We derive the damping factors for the oscillating primordial power
spectrum and bispectrum by means of a systematic IR resummation of relevant
Feynman diagrams.",1906.08697v2
2019-06-21,Control of eigenfunctions on surfaces of variable curvature,"We prove a microlocal lower bound on the mass of high energy eigenfunctions
of the Laplacian on compact surfaces of negative curvature, and more generally
on surfaces with Anosov geodesic flows. This implies controllability for the
Schr\""odinger equation by any nonempty open set, and shows that every
semiclassical measure has full support. We also prove exponential energy decay
for solutions to the damped wave equation on such surfaces, for any nontrivial
damping coefficient. These results extend previous works [arXiv:1705.05019],
[arXiv:1712.02692], which considered the setting of surfaces of constant
negative curvature.
  The proofs use the strategy of [arXiv:1705.05019], [arXiv:1712.02692] and
rely on the fractal uncertainty principle of [arXiv:1612.09040]. However, in
the variable curvature case the stable/unstable foliations are not smooth, so
we can no longer associate to these foliations a pseudodifferential calculus of
the type used in [arXiv:1504.06589]. Instead, our argument uses Egorov's
Theorem up to local Ehrenfest time and the hyperbolic parametrix of
[arXiv:0706.3242], together with the $C^{1+}$ regularity of the stable/unstable
foliations.",1906.08923v2
2019-06-21,Exponential damping induced by random and realistic perturbations,"Given a quantum many-body system and the expectation-value dynamics of some
operator, we study how this reference dynamics is altered due to a perturbation
of the system's Hamiltonian. Based on projection operator techniques, we unveil
that if the perturbation exhibits a random-matrix structure in the eigenbasis
of the unperturbed Hamiltonian, then this perturbation effectively leads to an
exponential damping of the original dynamics. Employing a combination of
dynamical quantum typicality and numerical linked cluster expansions, we
demonstrate that our theoretical findings for random matrices can, in some
cases, be relevant for the dynamics of realistic quantum many-body models as
well. Specifically, we study the decay of current autocorrelation functions in
spin-$1/2$ ladder systems, where the rungs of the ladder are treated as a
perturbation to the otherwise uncoupled legs. We find a convincing agreement
between the exact dynamics and the lowest-order prediction over a wide range of
interchain couplings.",1906.09268v2
2019-06-27,Fast control of dissipation in a superconducting resonator,"We report on fast tunability of an electromagnetic environment coupled to a
superconducting coplanar waveguide resonator. Namely, we utilize a
recently-developed quantum-circuit refrigerator (QCR) to experimentally
demonstrate a dynamic tunability in the total damping rate of the resonator up
to almost two orders of magnitude. Based on the theory it corresponds to a
change in the internal damping rate by nearly four orders of magnitude. The
control of the QCR is fully electrical, with the shortest implemented operation
times in the range of 10 ns. This experiment constitutes a fast active reset of
a superconducting quantum circuit. In the future, a similar scheme can
potentially be used to initialize superconducting quantum bits.",1906.11519v1
2019-06-28,Ground-state cooling of an magnomechanical resonator induced by magnetic damping,"Quantum manipulation of mechanical resonators has been widely applied in
fundamental physics and quantum information processing. Among them, cooling the
mechanical system to its quantum ground state is regarded as a key step. In
this work, we propose a scheme which one can realize ground-state cooling of
resonator in a cavity magnomechanical system. The system consists of a
microwave cavity and a small ferromagnetic sphere, in which phonon-magnon
coupling and cavity photon-magnon coupling can be achieved via magnetostrictive
interaction and magnetic dipole interaction, respectively. After adiabatically
eliminating the cavity mode, an effective Hamiltonian which consists of magnon
and mechanical modes is obtained. Within experimentally feasible parameters, we
demonstrate that the ground-state cooling of the magnomechanical resonator can
be achieved by extra magnetic damping. Unlike optomechanical cooling,
magnomechanical interaction is utilized to realize the cooling of resonators.
We further illustrate the ground-state cooling can be effectively controlled by
the external magnetic field.",1906.12081v1
2019-06-30,"Non-linear spin torque, pumping and cooling in superconductor/ferromagnet systems","We study the effects of the coupling between magnetization dynamics and the
electronic degrees of freedom in a heterostructure of a metallic nanomagnet
with dynamic magnetization coupled with a superconductor containing a steady
spin-splitting field. We predict how this system exhibits a non-linear spin
torque, which can be driven either with a temperature difference or a voltage
across the interface. We generalize this notion to arbitrary magnetization
precession by deriving a Keldysh action for the interface, describing the
coupled charge, heat and spin transport in the presence of a precessing
magnetization. We characterize the effect of superconductivity on the
precession damping and the anti-damping torques. We also predict the full
non-linear characteristic of the Onsager counterparts of the torque, showing up
via pumped charge and heat currents. For the latter, we predict a spin-pumping
cooling effect, where the magnetization dynamics can cool either the nanomagnet
or the superconductor.",1907.00424v2
2019-07-03,Wave-ice interaction in the North-West Barents Sea,"The results of field work on drift ice during wave propagation are analyzed
and presented. The field work was performed in the Barents Sea, and the main
focus of the paper is on wave processes in the MIZ. A model of wave damping in
broken ice is formulated and applied to interpret the field work results. It is
confirmed that waves of higher frequencies are subjected to stronger damping
when they propagate below the ice. This reduces the frequency of most energetic
wave with increasing distance from the ice edge. Difference of wave spectra
measured in two relatively close locations within the MIZ is discussed. The
complicated geometry and dynamics of the MIZ in the North-West Barents Sea
allow waves from the Atlantic Ocean and south regions of the Barents Sea to
penetrate into different locations of the MIZ.",1907.02032v1
2019-07-05,Nesterov's acceleration and Polyak's heavy ball method in continuous time: convergence rate analysis under geometric conditions and perturbations,"In this article a family of second order ODEs associated to inertial gradient
descend is studied. These ODEs are widely used to build trajectories converging
to a minimizer $x^*$ of a function $F$, possibly convex. This family includes
the continuous version of the Nesterov inertial scheme and the continuous heavy
ball method. Several damping parameters, not necessarily vanishing, and a
perturbation term $g$ are thus considered. The damping parameter is linked to
the inertia of the associated inertial scheme and the perturbation term $g$ is
linked to the error that can be done on the gradient of the function $F$. This
article presents new asymptotic bounds on $F(x(t))-F(x^*)$ where $x$ is a
solution of the ODE, when $F$ is convex and satisfies local geometrical
properties such as {\L}ojasiewicz properties and under integrability conditions
on $g$. Even if geometrical properties and perturbations were already studied
for most ODEs of these families, it is the first time they are jointly studied.
All these results give an insight on the behavior of these inertial and
perturbed algorithms if $F$ satisfies some {\L}ojasiewicz properties especially
in the setting of stochastic algorithms.",1907.02710v1
2019-07-08,Role of Toll-Like Receptors in the interplay between pathogen and damage associated molecular patterns,"Various theoretical studies have been carried out to infer relevant
protein-protein interactions among pathogens and their hosts. Such studies are
generally based on preferential attachment of bacteria / virus to their human
receptor homologs. We have analyzed 17 pathogenic species mainly belonging to
bacterial and viral pathogenic classes, with the aim to identify the
interacting human proteins which are targeted by both bacteria and virus
specifically. Our study reveals that the TLRs play a crucial role between the
pathogen-associated molecular patterns (PAMPs) and the damage associated
molecular patterns (DAMPS). PAMPs include bacterial lipopolysaccharides (LPs),
endotoxins, bacterial flagellin, lipoteichoic acid, peptidoglycan in bacterial
organisms and nucleic acid variants associated with viral organisms, whereas
DAMPs are associated with host biomolecules that perpetuate non-infectious
inflammatory responses. We found out the presence of SOD1 and SOD2 (superoxide
dismutase) is crucial, as it acts as an anti-oxidant and helps in eliminating
oxidative stress by preventing damage from reactive oxygen species. Hence, such
strategies can be used as new therapies for anti-inflammatory diseases with
significant clinical outcomes.",1907.03512v1
2019-07-15,Alternating Direction Method of Multipliers (ADMMs) Based Distributed Approach For Wide-Area Control,"In this paper, an alternating direction method of multipliers based novel
distributed wide-area control architecture is proposed for damping the
interarea oscillations. In this approach, first, an interconnected power system
is divided into areas based on coherency grouping. Second, local processors are
assigned on each area that estimate a black-box transfer function model based
on Lagrange multipliers using measurements. These local area processors are
then used to estimate a global transfer function model of the power system
based on a consensus algorithm through a global processor. After convergence, a
transfer function residue corresponding to the interarea mode of interest is
derived, to determine optimal wide area control loop. Finally, a wide-area
damping controller is designed based on this information. The efficacy of the
controller is validated using two area and IEEE-39 bus test systems on
RTDS/RSCAD and MATLAB cosimulation platform.",1907.06340v1
2019-07-16,Coherency and Online Signal Selection Based Wide Area Control of Wind Integrated Power Grid,"This paper introduces a novel method of designing wide area control (WAC)
based on a discrete linear quadratic regulator and Kalman filtering based
state-estimation that can be applied for real-time damping of interarea
oscillations of wind integrated power grid. The main advantages of the proposed
method are that the architecture provides online coherency grouping that
properly characterizes real-time changes in the power grid and online wide-area
signal selection based on residue method for proper selection of the WAC
signals. The proposed architecture can, thus, accurately monitors changes in
the power grid and select the appropriate control signal for more effectively
damping the interarea oscillation when compared to the conventional local
signal based power system stabilizers or offline based WAC designs. The
architecture is tested on a wind integrated two-area system and the IEEE 39 bus
system in order to show the capability of the proposed method.",1907.06846v1
2019-07-20,Magnon Bose-Einstein condensate and supercurrents over a wide temperature range,"Magnon Bose-Einstein Condensates (BECs) and supercurrents are coherent
quantum phenomena, which appear on a macroscopic scale in parametrically
populated solid state spinsystems. One of the most fascinating and attractive
features of these processes is the possibility of magnon condensation and
supercurrent excitation even at room temperature. At the same time, valuable
information about a magnon BEC state, such as its lifetime, its formation
threshold, and coherency, is provided by experiments at various temperatures.
Here, we use Brillouin Light Scattering (BLS) spectroscopy for the
investigation of the magnon BEC dynamics in a single-crystal film of yttrium
iron garnet in a wide temperature range from 30 K to 380 K. By comparing the
BLS results with previous microwave measurements, we re-vealed the direct
relation between the damping of the condensed and the parametrically injected
magnons. The enhanced supercurrent dynamics was detected at 180 K near the
minimum of BEC damping.",1907.08805v1
2019-07-21,Explaining Retrocausality Phenomena in Quantum Mechanics using a Modified Variational Principle,"A modified lagrangian with causal and retrocausal momenta was used to derive
a first causal wave equation and a second retrocausal wave equation using the
principle of least action. The retrocausal wave function obtained through this
method was found to be equivalent to the complex conjugate of the causal wave
function, thus leading to the conclusion that a retrocausal effect is already
implicit in quantum mechanics through the means of complex conjugation of the
wave function when computing the probability density for a particle. Lastly,
the same variational principle was employed with a fractionary langriangian,
(that is, containing fractional Riemann derivatives) to obtain a pair of
modified wave equations, one causal and other retrocausal, both of which
correspond to the differential equation of a damped oscillator in the free
particle (potential energy V=0) case. The solutions of this damped wave
equations remain to be explored.",1907.09688v3
2019-07-23,Global wellposedness to the $n$-dimensional compressible Oldroyd-B model without damping mechanism,"The Cauchy problem of the compressible Oldroyd-B model without damping
mechanism in R^n$ with $n\ge2$ is considered. The lack of dissipation in
density and stress tensor in the model is compensated by exploiting an
intrinsic structure and introducing new quantities between density, velocity
and stress tensor. Therefore, global solutions to the system with small initial
data in critical Besov spaces are obtained. As a byproduct, optimal time decay
rates of the solutions are derived by using an energy estimation argument. The
results remain valid for the compressible viscoelastic system without the
`div-curl structure assumption and thus improve those given by Hu and Wang [ J.
Differential Equations, {\bf 250}, 1200--1231, 2011] and Qian and Zhang [Arch.
Ration. Mech. Anal., {\bf 198}, 835--868, 2010].",1907.09829v3
2019-08-01,The $J$-method for the Gross-Pitaevskii eigenvalue problem,"This paper studies the $J$-method of [E. Jarlebring, S. Kvaal, W. Michiels.
SIAM J. Sci. Comput. 36-4:A1978-A2001, 2014] for nonlinear eigenvector problems
in a general Hilbert space framework. This is the basis for variational
discretization techniques and a mesh-independent numerical analysis. A simple
modification of the method mimics an energy-decreasing discrete gradient flow.
In the case of the Gross-Pitaevskii eigenvalue problem, we prove global
convergence towards an eigenfunction for a damped version of the $J$-method.
More importantly, when the iterations are sufficiently close to an
eigenfunction, the damping can be switched off and we recover a local linear
convergence rate previously known from the discrete setting. This quantitative
convergence analysis is closely connected to the~$J$-method's unique feature of
sensitivity with respect to spectral shifts. Contrary to classical gradient
flows, this allows both the selective approximation of excited states as well
as the amplification of convergence beyond linear rates in the spirit of the
Rayleigh quotient iteration for linear eigenvalue problems. These advantageous
convergence properties are demonstrated in a series of numerical experiments
involving exponentially localized states under disorder potentials and vortex
lattices in rotating traps.",1908.00333v2
2019-08-02,How do Conservative Backbone Curves Perturb into Forced Responses? A Melnikov Function Analysis,"Weakly damped mechanical systems under small periodic forcing tend to exhibit
periodic response in a close vicinity of certain periodic orbits of their
conservative limit. Specifically, amplitude frequency plots for the
conservative limit have often been noted, both numerically and experimentally,
to serve as backbone curves for the near resonance peaks of the forced
response. In other cases, such a relationship between the unforced and forced
response was not observed. Here we provide a systematic mathematical analysis
that predicts which members of conservative periodic orbit families will serve
as backbone curves for the forced-damped response. We also obtain mathematical
conditions under which approximate numerical and experimental approaches, such
as energy balance and force appropriation, are justifiable. Finally, we derive
analytic criteria for the birth of isolated response branches (isolas) whose
identification is otherwise challenging from numerical continuation.",1908.00721v3
2019-08-05,Tunable strong coupling of two adjacent optical λ/2 Fabry-Pérot microresonators,"Optical half-wave microresonators enable to control the optical mode density
around a quantum system and thus to modify the temporal emission properties. If
the coupling rate exceeds the damping rate, strong coupling between a
microresonator and a quantum system can be achieved, leading to a coherent
energy exchange and the creation of new hybrid modes. Here, we investigate
strong coupling between two adjacent lambda/2 Fabry-P\'erot microresonators,
where the resonance of one microresonator can be actively tuned across the
resonance of the other microresonator. The transmission spectra of the coupled
microresonators show a clear anticrossing behavior, which proves that the two
cavity modes are strongly coupled. Additionally, we can vary the coupling rate
by changing the resonator geometry and thereby investigate the basic principles
of strong coupling with a well-defined model system. Finally, we will show that
such a coupled system can theoretically be modelled by coupled damped harmonic
oscillators.",1908.01566v1
2019-07-27,An extension of the second order dynamical system that models Nesterov's convex gradient method,"In this paper we deal with a general second order continuous dynamical system
associated to a convex minimization problem with a Fr\`echet differentiable
objective function. We show that inertial algorithms, such as Nesterov's
algorithm, can be obtained via the natural explicit discretization from our
dynamical system. Our dynamical system can be viewed as a perturbed version of
the heavy ball method with vanishing damping, however the perturbation is made
in the argument of the gradient of the objective function. This perturbation
seems to have a smoothing effect for the energy error and eliminates the
oscillations obtained for this error in the case of the heavy ball method with
vanishing damping, as some numerical experiments show. We prove that the value
of the objective function in a generated trajectory converges in order O(1/t^2)
to the global minimum of the objective function. Moreover, we obtain that a
trajectory generated by the dynamical system converges to a minimum point of
the objective function.",1908.02574v1
2019-08-07,Interfacial contributions to spin-orbit torque and magnetoresistance in ferromagnet/heavy-metal bilayers,"The thickness dependence of spin-orbit torque and magnetoresistance in
ferromagnet/heavy-metal bilayers is studied using the first-principles
non-equilibrium Green's function formalism combined with the Anderson disorder
model. A systematic expansion in orthogonal vector spherical harmonics is used
for the angular dependence of the torque. The damping-like torque in Co/Pt and
Co/Au bilayers can be described as a sum of the spin-Hall contribution, which
increases with thickness in agreement with the spin-diffusion model, and a
comparable interfacial contribution. The magnetoconductance in the plane
perpendicular to the current in Co/Pt bilayers is of the order of a conductance
quantum per interfacial atom, exceeding the prediction of the spin-Hall model
by more than an order of magnitude. This suggests that the ""spin-Hall
magnetoresistance,"" similarly to the damping-like torque, has a large
interfacial contribution unrelated to the spin-Hall effect.",1908.02680v2
2019-08-16,Dynamics of Hot Bose-Einstein Condensates: stochastic Ehrenfest relations for number and energy damping,"Describing partially-condensed Bose gases poses a long-standing theoretical
challenge. We present exact stochastic Ehrenfest relations for the stochastic
projected Gross-Pitaevskii equation, including both number and energy damping
mechanisms, and all projector terms that arise from the energy cutoff
separating system from reservoir. We test the theory by applying it to the
centre of mass fluctuations of a harmonically trapped prolate system, finding
close agreement between c-field simulations and analytical results. The
formalism lays the foundation to analytically explore experimentally accessible
hot Bose-Einstein condensates.",1908.05809v3
2019-08-12,On a simple derivation of the very low damping escape rate for classical spins by modifying the method of Kramers,"The original perturbative Kramers' method (starting from the phase space
coordinates) (Kramers, 1940) of determining the energy-controlled-diffusion
equation for Newtonian particles with separable and additive Hamiltonians is
generalized to yield the energy-controlled diffusion equation and thus the very
low damping (VLD) escape rate including spin-transfer torque for classical
giant magnetic spins with two degrees of freedom. These have dynamics governed
by the magnetic Langevin and Fokker-Planck equations and thus are generally
based on non-separable and non-additive Hamiltonians. The derivation of the VLD
escape rate directly from the (magnetic) Fokker-Planck equation for the surface
distribution of magnetization orientations in the configuration space of the
polar and azimuthal angles $(\vartheta, \varphi)$ is much simpler than those
previously used.",1908.06747v1
2019-08-22,Improving the dynamics of quantum sensors with reinforcement learning,"Recently proposed quantum-chaotic sensors achieve quantum enhancements in
measurement precision by applying nonlinear control pulses to the dynamics of
the quantum sensor while using classical initial states that are easy to
prepare. Here, we use the cross-entropy method of reinforcement learning to
optimize the strength and position of control pulses. Compared to the
quantum-chaotic sensors with periodic control pulses in the presence of
superradiant damping, we find that decoherence can be fought even better and
measurement precision can be enhanced further by optimizing the control. In
some examples, we find enhancements in sensitivity by more than an order of
magnitude. By visualizing the evolution of the quantum state, the mechanism
exploited by the reinforcement learning method is identified as a kind of
spin-squeezing strategy that is adapted to the superradiant damping.",1908.08416v2
2019-08-28,Spin functional renormalization group for quantum Heisenberg ferromagnets: Magnetization and magnon damping in two dimensions,"We use the spin functional renormalization group recently developed by two of
us [J. Krieg and P. Kopietz, Phys. Rev. B $\bf{99}$, 060403(R) (2019)] to
calculate the magnetization $M ( H , T )$ and the damping of magnons due to
classical longitudinal fluctuations of quantum Heisenberg ferromagnets. In
order to guarantee that for vanishing magnetic field $H \rightarrow 0$ the
magnon spectrum is gapless when the spin rotational invariance is spontaneously
broken, we use a Ward identity to express the magnon self-energy in terms of
the magnetization. In two dimensions our approach correctly predicts the
absence of long-range magnetic order for $H=0$ at finite temperature $T$. The
magnon spectrum then exhibits a gap from which we obtain the transverse
correlation length. We also calculate the wave-function renormalization factor
of the magnons. As a mathematical by-product, we derive a recursive form of the
generalized Wick theorem for spin operators in frequency space which
facilitates the calculation of arbitrary time-ordered connected correlation
functions of an isolated spin in a magnetic field.",1908.10753v2
2019-09-03,Learning Elastic Constitutive Material and Damping Models,"Commonly used linear and nonlinear constitutive material models in
deformation simulation contain many simplifications and only cover a tiny part
of possible material behavior. In this work we propose a framework for learning
customized models of deformable materials from example surface trajectories.
The key idea is to iteratively improve a correction to a nominal model of the
elastic and damping properties of the object, which allows new forward
simulations with the learned correction to more accurately predict the behavior
of a given soft object. Space-time optimization is employed to identify gentle
control forces with which we extract necessary data for model inference and to
finally encapsulate the material correction into a compact parametric form.
Furthermore, a patch based position constraint is proposed to tackle the
challenge of handling incomplete and noisy observations arising in real-world
examples. We demonstrate the effectiveness of our method with a set of
synthetic examples, as well with data captured from real world homogeneous
elastic objects.",1909.01875v2
2019-09-06,Effect of Tantalum spacer thickness and deposition conditions on the properties of MgO/CoFeB/Ta/CoFeB/MgO free layers,"To get stable perpendicularly magnetized tunnel junctions at small device
dimensions, composite free layers that comprise two MgO/FeCoB interfaces as
sources of interface anisotropy are generally used. Proper cristallisation and
annealing robustness is typically ensured by the insertion of a spacer layer of
the early transition metal series within the FeCoB layer. We study the
influence of the spacer thickness and growth condition on the switching metrics
of tunnel junctions thermally annealed at 400$^\circ$C for the case of 1-4
\r{A} Ta spacers. Thick Ta spacer results in a large anisotropies indicative of
a better defined top FeCoB/MgO interface, but this is achieved at the
systematic expense of a stronger damping. For the best anisotropy-damping
compromise, junctions of diameter 22 nm can still be stable and spin-torque
switched. Coercivity and inhomogeneous linewidth broadening, likely arising
from roughness at the FeCoB/Ta interface, can be reduced if a sacrificial Mg
layer is inserted before the Ta spacer deposition.",1909.02741v1
2019-09-19,Blow-up for Strauss type wave equation with damping and potential,"We study a kind of nonlinear wave equations with damping and potential, whose
coefficients are both critical in the sense of the scaling and depend only on
the spatial variables. Based on the earlier works, one may think there are two
kinds of blow-up phenomenons when the exponent of the nonlinear term is small.
It also means there are two kinds of law to determine the critical exponent. In
this paper, we obtain a blow-up result and get the estimate of the upper bound
of the lifespan in critical and sub-critical cases. All of the results support
such a conjecture, although for now, the existence part is still open.",1909.08885v3
2019-09-23,Inference of modes for linear stochastic processes,"For dynamical systems that can be modelled as asymptotically stable linear
systems forced by Gaussian noise, this paper develops methods to infer or
estimate their modes from observations in real time. The modes can be real or
complex. For a real mode, we wish to infer its damping rate and mode shape. For
a complex mode, we wish to infer its frequency, damping rate and (complex) mode
shape. Their amplitudes and correlations are encoded in a mode covariance
matrix. The work is motivated and illustrated by the problem of detection of
oscillations in power flow in AC electrical networks. Suggestions of other
applications are given.",1909.10247v2
2019-10-02,Exponential stability for the nonlinear Schrödinger equation with locally distributed damping,"In this paper, we study the defocusing nonlinear Schr\""{o}dinger equation
with a locally distributed damping on a smooth bounded domain as well as on the
whole space and on an exterior domain. We first construct approximate solutions
using the theory of monotone operators. We show that approximate solutions
decay exponentially fast in the $L^2$-sense by using the multiplier technique
and a unique continuation property. Then, we prove the global existence as well
as the $L^2$-decay of solutions for the original model by passing to the limit
and using a weak lower semicontinuity argument, respectively. The distinctive
feature of the paper is the monotonicity approach, which makes the analysis
independent from the commonly used Strichartz estimates and allows us to work
without artificial smoothing terms inserted into the main equation. We, in
addition, implement a precise and efficient algorithm for studying the
exponential decay established in the first part of the paper numerically. Our
simulations illustrate the efficacy of the proposed control design.",1910.00921v1
2019-10-07,Quantum mechanics at high redshift -- Modelling Damped Lyman-$α$ absorption systems,"For around 100 years, hydrogen spectral modelling has been based on Voigt
profile fitting. The semi-classical Voigt profile is based on a 2-level atom
approximation. Whilst the Voigt profile is excellent for many circumstances,
the accuracy is insufficient for very high column density damped Lyman-$\alpha$
absorption systems. We have adapted the quantum-mechanical Kramers-Heisenberg
model to include thermal broadening, producing a new profile, the KHT profile.
Interactions involving multiple discrete atomic levels and continuum terms, not
accounted for in the Voigt model, generate asymmetries in the Lyman line wings.
If not modelled, this can lead to significant systematics in parameter
estimation when modelling real data. There are important ramifications in
particular for measurements of the primordial deuterium abundance. However, the
KHT model is complicated. We therefore present a simplified formulation based
on Taylor series expansions and look-up tables, quantifying the impact of the
approximations made. The KHT profile has been implemented within the
widely-used VPFIT code.",1910.02913v2
2019-10-12,Almost Global Solutions to the Three-dimensional Isentropic Inviscid Flows with Damping in Physical Vacuum Around Barenlatt Solutions,"For the three-dimensional vacuum free boundary problem with physical
singularity that the sound speed is $C^{ {1}/{2}}$-H$\ddot{\rm o}$lder
continuous across the vacuum boundary of the compressible Euler equations with
damping, without any symmetry assumptions, we prove the almost global existence
of smooth solutions when the initial data are small perturbations of the
Barenblatt self-similar solutions to the corresponding porous media equations
simplified via Darcy's law. It is proved that if the initial perturbation is of
the size of $\epsilon$, then the existing time for smooth solutions is at least
of the order of $\exp(\epsilon^{-2/3})$. The key issue for the analysis is the
slow {\em sub-linear} growth of vacuum boundaries of the order of
$t^{1/(3\gamma-1)}$, where $\gamma>1$ is the adiabatic exponent for the gas.
This is in sharp contrast to the currently available global-in-time existence
theory of expanding solutions to the vacuum free boundary problems with
physical singularity of compressible Euler equations for which the expanding
rate of vacuum boundaries is linear. The results obtained in this paper is
closely related to the open question in multiple dimensions since T.-P. Liu's
construction of particular solutions in 1996 .",1910.05516v1
2019-10-15,Nonlocal quantum correlations under amplitude damping decoherence,"Different nonlocal quantum correlations of entanglement, steering and Bell
nonlocality are defined with the help of local hidden state (LHS) and local
hidden variable (LHV) models. Considering their unique roles in quantum
information processing, it is of importance to understand the individual
nonlocal quantum correlation as well as their relationship. Here, we
investigate the effects of amplitude damping decoherence on different nonlocal
quantum correlations. In particular, we have theoretically and experimentally
shown that the entanglement sudden death phenomenon is distinct from those of
steering and Bell nonlocality. In our scenario, we found that all the initial
states present sudden death of steering and Bell nonlocality, while only some
of the states show entanglement sudden death. These results suggest that the
environmental effect can be different for different nonlocal quantum
correlations, and thus, it provides distinct operational interpretations of
different quantum correlations.",1910.06483v1
2019-10-17,The linearly damped nonlinear Schrödinger equation with localized driving: spatiotemporal decay estimates and the emergence of extreme wave events,"We prove spatiotemporal algebraically decaying estimates for the density of
the solutions of the linearly damped nonlinear Schr\""odinger equation with
localized driving, when supplemented with vanishing boundary conditions. Their
derivation is made via a scheme, which incorporates suitable weighted Sobolev
spaces and a time-weighted energy method. Numerical simulations examining the
dynamics (in the presence of physically relevant examples of driver types and
driving amplitude/linear loss regimes), showcase that the suggested decaying
rates, are proved relevant in describing the transient dynamics of the
solutions, prior their decay: they support the emergence of waveforms
possessing an algebraic space-time localization (reminiscent of the Peregrine
soliton) as first events of the dynamics, but also effectively capture the
space-time asymptotics of the numerical solutions.",1910.08425v2
2019-10-24,Gapless and gapped holographic phonons,"We study a holographic model where translations are both spontaneously and
explicitly broken, leading to the presence of (pseudo)-phonons in the spectrum.
The weak explicit breaking is due to two independent mechanisms: a small source
for the condensate itself and additional linearly space-dependent marginal
operators. The low energy dynamics of the model is described by Wigner crystal
hydrodynamics. In absence of a source for the condensate, the phonons remain
gapless, but momentum is relaxed. Turning on a source for the condensate damps
and pins the phonons. Finally, we verify that the universal relation between
the phonon damping rate, mass and diffusivity reported in arXiv:1812.08118
continues to hold in this model for weak enough explicit breaking.",1910.11330v2
2019-11-06,High spin mixing conductance and spin interface transparency at $Co_2Fe_{0.4}Mn_{0.6}Si$ Heusler alloy and Pt interface,"Ferromagnetic materials exhibiting low magnetic damping ($\alpha$) and
moderately high saturation magnetization are required from the viewpoints of
generation, transmission and detection of spin wave. Since spin-to-charge
conversion efficiency is another important parameter, high spin mixing
conductance ($g_{r}^{\uparrow \downarrow}$) is the key for efficient
spin-to-charge conversion. Full Heusler alloys e.g. $Co_2Fe_{0.4}Mn_{0.6}Si$
(CFMS), which are predicted to be 100$\%$ spin polarized, possess low $\alpha$.
However, the $g_{r}^{\uparrow \downarrow}$ at the interface between CFMS and a
paramagnet has not fully been understood. Here, we report the investigations of
spin pumping and inverse spin Hall effect in $CFMS/Pt$ bilayers. Damping
analysis indicates the presence of significant spin pumping at the interface of
CFMS and Pt, which is also confirmed by the detection of inverse spin Hall
voltage. We show that in CFMS/Pt the $g_{r}^{\uparrow \downarrow}$
(1.77$\times$10$^{20}$m$^{-2}$) and interface transparency (84$\%$) are higher
compared to values reported for other ferromagnet/heavy metal systems.",1911.02230v1
2019-11-10,Influence of resonances on the noise performance of SQUID susceptometers,"Scanning Superconducting Quantum Interference Device (SQUID) Susceptometry
simultaneously images the local magnetic fields and susceptibilities above a
sample with sub-micron spatial resolution. Further development of this
technique requires a thorough understanding of the current, voltage, and flux
characteristics of scanning SQUID susceptometers. These sensors often have
striking anomalies in their current-voltage characteristics, which we believe
to be due to electromagnetic resonances. The effect of these resonances on the
performance of these SQUIDs is unknown. To explore the origin and impact of the
resonances, we have developed a model that qualitatively reproduces the
experimentally-determined current-voltage characteristics of our scanning SQUID
susceptometers. We use this model to calculate the noise characteristics of
SQUIDs of different designs. We find that the calculated ultimate flux noise is
better in susceptometers with damping resistors that diminish the resonances
than susceptometers without damping resistors. Such calculations will enable
the optimization of the signal-to-noise characteristics of scanning SQUID
susceptometers.",1911.03836v2
2019-11-13,Impact of the crystal orientation on spin-orbit torques in Fe/Pd bilayers,"Spin-orbit torques in ferromagnetic (FM)/non-magnetic (NM) heterostructures
offer more energy-efficient means to realize spin-logic devices; however, their
strengths are determined by the heterostructure interface. This work examines
crystal orientation impact on the spin-orbit torque efficiency in different
Fe/Pd bilayer systems. Spin torque ferromagnetic measurements evidence that the
damping-like torque efficiency is higher in epitaxial than in polycrystalline
bilayer structures while the field-like torque is negligible in all bilayer
structures. The strength of the damping-like torque decreases with
deterioration of the bilayer epitaxial quality. The present finding provides
fresh insight for the enhancement of spin-orbit torques in magnetic
heterostructures.",1911.05487v1
2019-12-02,Boundary input-to-state stabilization of a damped Euler-Bernoulli beam in the presence of a state-delay,"This paper is concerned with the point torque boundary feedback stabilization
of a damped Euler-Bernoulli beam model in the presence of a time-varying
state-delay. First, a finite-dimensional truncated model is derived by spectral
reduction. Then, for a given stabilizing state-feedback of the delay-free
truncated model, an LMI-based sufficient condition on the maximum amplitude of
the state-delay is employed to guarantee the stability of the closed-loop
state-delayed truncated model. Second, we assess the exponential stability of
the resulting closed-loop infinite-dimensional system under the assumption that
the number of modes of the original infinite-dimensional system captured by the
truncated model has been selected large enough. Finally, we consider in our
control design the possible presence of a distributed perturbation, as well as
additive boundary perturbations in the control inputs. In this case, we derive
for the closed-loop system an exponential input-to-state estimate with fading
memory of the distributed and boundary disturbances.",1912.01117v1
2019-12-03,The noise fluxes produced by the degree of first-order temporal coherence in a single mode class-A laser amplifier,"The noise feature of a single mode class-A laser is investigated in the
presence (amplifier) and absence (free-running) of an input signal. The
Maxwell-Bloch equations of motion have been solved after adding the cavity
Langevin force to calculate fluctuations that imposed to the atomic population
inversion and the amplitude and phase of cavity electric field. The correlation
function of these fluctuations is then used to derive the spontaneous emission,
amplitude, and phase noise fluxes in the below and above-threshold states. The
bandwidth of noise fluxes is not only adjusted by the amplitude and frequency
detuning of input signal, but also by the laser pumping and cavity damping
rates. On the other hand, the degree of first-order temporal coherence (DFOTC)
is turned out as the correlation function of the amplitude fluctuation so that
its Fourier transform led to the amplitude noise flux. The coherence time plays
a dual role in order that it is equal to the damping rate invers of DFOTC and
at the same time has an uncertainty relation with the bandwidth of amplitude
noise flux. Finally, the flux conservation requires a balance between the input
pumping noise flux and the output amplitude and spontaneous emission noise
fluxes.",1912.01485v1
2019-12-05,A Fast Implementation for the Canonical Polyadic Decomposition,"A new implementation of the canonical polyadic decomposition (CPD) is
presented. It features lower computational complexity and memory usage than the
available state of art implementations available. The CPD of tensors is a
challenging problem which has been approached in several manners. Alternating
least squares algorithms were used for a long time, but they convergence
properties are limited. Nonlinear least squares (NLS) algorithms - more
precisely, damped Gauss-Newton (dGN) algorithms - are much better in this
sense, but they require inverting large Hessians, and for this reason there is
just a few implementations using this approach. In this paper, we propose a
fast dGN implementation to compute the CPD. In this paper, we make the case to
always compress the tensor, and propose a fast damped Gauss-Newton
implementation to compute the canonical polyadic decomposition.",1912.02366v1
2019-12-05,Damping of spinful excitons in LaCoO$_3$ by thermal fluctuations: Theory and experiment,"We present Co $L_3$-edge resonant inelastic x-ray scattering (RIXS) of bulk
LaCoO$_3$ across the thermally-induced spin-state crossover around 100~K. Owing
to a high energy resolution of 25~meV, we observe unambiguously the dispersion
of the intermediate-spin (IS) excitations in the low temperature regime.
Approaching the intermediate temperature regime, the IS excitations are damped
and the bandwidth is reduced. The observed behavior can be well described by a
model of mobile IS excitons with strong attractive interaction, which we solve
using dynamical mean-field theory for hard-core bosons. Our results provide a
detailed mechanism of how high-spin (HS) and IS excitations interact to
establish the physical properties of cobaltite perovskites.",1912.02564v3
2019-12-09,High Frequency Sound in a Unitary Fermi Gas,"We present an experimental and theoretical study of the phonon mode in a
unitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation
spectra at a momentum of approximately half the Fermi momentum, both above and
below the superfluid critical temperature $T_\mathrm{c}$. Below $T_\mathrm{c}$,
the dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by
gradients in the phase of the superfluid order parameter. The temperature
dependence of the BA phonon is consistent with a theoretical model based on the
quasiparticle random phase approximation in which the dominant damping
mechanism is via collisions with thermally excited quasiparticles. As the
temperature is increased above $T_\mathrm{c}$, the phonon evolves into a
strongly damped collisional mode, accompanied by an abrupt increase in spectral
width. Our study reveals strong similarities between sound propagation in the
unitary Fermi gas and liquid helium.",1912.03830v1
2019-12-10,Stability of traveling waves in a driven Frenkel-Kontorova model,"In this work we revisit a classical problem of traveling waves in a damped
Frenkel-Kontorova lattice driven by a constant external force. We compute these
solutions as fixed points of a nonlinear map and obtain the corresponding
kinetic relation between the driving force and the velocity of the wave for
different values of the damping coefficient. We show that the kinetic curve can
become non-monotone at small velocities, due to resonances with linear modes,
and also at large velocities where the kinetic relation becomes multivalued.
Exploring the spectral stability of the obtained waveforms, we identify, at the
level of numerical accuracy of our computations, a precise criterion for
instability of the traveling wave solutions: monotonically decreasing portions
of the kinetic curve always bear an unstable eigendirection. We discuss why the
validity of this criterion in the {\it dissipative} setting is a rather
remarkable feature offering connections to the Hamiltonian variant of the model
and of lattice traveling waves more generally. Our stability results are
corroborated by direct numerical simulations which also reveal the possible
outcomes of dynamical instabilities.",1912.05052v2
2019-12-11,Quasinormal Modes of Charged Fields in Reissner-Nordstrom Backgrounds by Borel-Pade Summation of Bender-Wu Series,"We extend recent work of Hatsuda on the computation of quasinormal mode
frequencies via analytic continuation of bound state energies and Borel-Pade
resummation of the Bender-Wu perturbation series to the case of charged fields
in the background of Reissner-Nordstrom black holes. We compare the quasinormal
mode frequencies obtained in this manner to calculations using Leaver's method
of continued fractions, and find good agreement for damped modes (DMs) with
imaginary part remaining finite in the extremal limit. We also present
numerical evidence that the frequencies of certain zero-damped modes (ZDMs)
with imaginary part tending to zero in the extremal limit can be computed when
constructing the Bender-Wu expansion about a peak of the potential inside the
outer horizon of the black hole.",1912.05553v2
2019-12-19,On twin peak quasi-periodic oscillations resulting from the interaction between discoseismic modes and turbulence in accretion discs around black holes,"Given the peculiar and (in spite of many efforts) unexplained quasi-periodic
oscillation (QPO) twin peak phenomena in accretion disc PSD observations, the
present exploratory analytical article tries to inquire deeper into the
relationship between discoseismic modes and the underlying driving turbulence
in order to assess its importance. We employ a toy model in the form of a
Gaussian white noise driven damped harmonic oscillator with stochastic
frequency. This oscillator represents the discoseismic mode. (Stochastic
damping was also considered, but interestingly found to be less relevant for
the case at hand.) In the context of this model, we find that turbulence
interacts with disc oscillations in interesting ways. In particular, the
stochastic part in the oscillator frequency behaves as a separate driving
agent. This gives rise to 3:2 twin peaks for some values of the physical
parameters, which we find. We conclude with the suggestion that the study of
turbulence be brought to the forefront of disc oscillation dynamics, as opposed
to being a mere background feature. This change of perspective carries
immediate observable consequences, such as considerably shifting the values of
the (discoseismic) oscillator frequencies.",1912.09527v1
2019-12-28,Non-linear damping of superimposed primordial oscillations on the matter power spectrum in galaxy surveys,"Galaxy surveys are an important probe for superimposed oscillations on the
primordial power spectrum of curvature perturbations, which are predicted in
several theoretical models of inflation and its alternatives. In order to
exploit the full cosmological information in galaxy surveys it is necessary to
study the matter power spectrum to fully non-linear scales. We therefore study
the non-linear clustering in models with superimposed linear and logarithmic
oscillations to the primordial power spectrum by running high-resolution
dark-matter-only N-body simulations. We fit a Gaussian envelope for the
non-linear damping of superimposed oscillations in the matter power spectrum to
the results of the N-body simulations for $k \lesssim 0.6\ h/$Mpc at $0 \leq z
\leq 5$ with an accuracy below the percent. We finally use this fitting formula
to forecast the capabilities of future galaxy surveys, such as Euclid and
Subaru, to probe primordial oscillation down to non-linear scales alone and in
combination with the information contained in CMB anisotropies.",1912.12499v3
2020-01-04,Finite Difference/Galerkin Finite Element Simulation of the Semi-Linear Wave Equation with Scale-Invariant Damping and Mass and Power Non-Linearity,"This study is concern with the numerical solution of the initial boundary
value problem (IBVP) for the semilinear scale-invariant wave equation with
damping and mass and power non-linearity. Numerical results of the
aforementioned IBVP is obtained by using standart Galerkin finite element
method (GFEM) for the spatial variable and the temporal variable is discretized
with the finite difference method (FDM). The FDM is also used for the
discretization of the spatial variable for the accuracy of the numerical
results. The obtained numerical results with different numerical schemes are
observed compatible. Numerical simulation of the considered problem is given
for the different initial conditions.",2001.01075v2
2020-01-05,Quantifying quantum non-Markovianity based on quantum coherence via skew information,"Based on the nonincreasing property of quantum coherence via skew information
under incoherent completely positive and trace-preserving maps, we propose a
non-Markovianity measure for open quantum processes. As applications, by
applying the proposed measure to some typical noisy channels, we find that it
is equivalent to the three previous measures of non-Markovianity for phase
damping and amplitude damping channels, i.e., the measures based on the quantum
trace distance, dynamical divisibility, and quantum mutual information. For the
random unitary channel, it is equivalent to the non-Markovianity measure based
on $l_1$ norm of coherence for a class of output states and it is incompletely
equivalent to the measure based on dynamical divisibility. We also use the
modified Tsallis relative $\alpha$ entropy of coherence to detect the
non-Markovianity of dynamics of quantum open systems, the results show that the
modified Tsallis relative $\alpha$ entropy of coherence are more comfortable
than the original Tsallis relative $\alpha$ entropy of coherence for small
$\alpha$.",2001.01261v1
2020-01-07,von Neumann entropy and the entropy production of a damped harmonic oscillator,"In this paper we analyze the entropy and entropy production of a non-isolated
quantum system described within the quantum Brownian motion framework. This is
a very general and paradigmatic framework for describing non-isolated quantum
systems and can be used in any kind of coupling regime. We start by considering
the application of von Neumann entropy to an arbitrarily damped quantum system
making use of its reduced density operator. We argue that this application is
formally valid and develop a path integral method to evaluate that quantity
analytically. We apply this technique to a harmonic oscillator in contact with
a heat bath and obtain an exact form for its entropy. Then we study the entropy
production of this system and enlighten important characteristics of its
thermodynamical behavior on the pure quantum realm and also address their
transition to the classical limit.",2001.02261v1
2020-01-09,Photon correlation measurements of stochastic limit cycles emerging from high-$Q$ nonlinear silicon photonic crystal microcavities,"We performed measurements of photon correlation [$g^{(2)}(\tau)$] in driven
nonlinear high-$Q$ silicon (Si) photonic crystal (PhC) microcavities. The
measured $g^{(2)}(\tau)$ exhibits a damped oscillatory behavior when input pump
power exceeds a critical value. From comparison between experiments and
simulations, we attribute the measured oscillation of $g^{(2)}(\tau)$ to
self-pulsing (a limit cycle) emerging from an interplay between photon,
carrier, and thermal dynamics. Namely, the oscillation frequency of
$g^{(2)}(\tau)$ corresponds to the oscillation period of the limit cycle, while
its finite coherence (damping) time originates from the stochastic nature of
the limit cycle. From the standpoint of phase reduction theory, we interpret
the measured coherence time of $g^{(2)}(\tau)$ as the coherence (diffusion)
time of a generalized phase of the limit cycle. Furthermore, we show that an
increase in laser input power enhances the coherence time of $g^{(2)}(\tau)$ up
to the order of microseconds, which could be a demonstration of the
stabilization of a stochastic limit cycle through pumping.",2001.02838v2
2020-01-12,Linear programming bounds for quantum amplitude damping codes,"Given that approximate quantum error-correcting (AQEC) codes have a
potentially better performance than perfect quantum error correction codes, it
is pertinent to quantify their performance. While quantum weight enumerators
establish some of the best upper bounds on the minimum distance of quantum
error-correcting codes, these bounds do not directly apply to AQEC codes.
Herein, we introduce quantum weight enumerators for amplitude damping (AD)
errors and work within the framework of approximate quantum error correction.
In particular, we introduce an auxiliary exact weight enumerator that is
intrinsic to a code space and moreover, we establish a linear relationship
between the quantum weight enumerators for AD errors and this auxiliary exact
weight enumerator. This allows us to establish a linear program that is
infeasible only when AQEC AD codes with corresponding parameters do not exist.
To illustrate our linear program, we numerically rule out the existence of
three-qubit AD codes that are capable of correcting an arbitrary AD error.",2001.03976v1
2020-01-22,Small data blow-up for the wave equation with a time-dependent scale invariant damping and a cubic convolution for slowly decaying initial data,"In the present paper, we study the Cauchy problem for the wave equation with
a time-dependent scale invariant damping, i.e.$\frac{2}{1+t}\partial_t v$ and a
cubic convolution $(|x|^{-\gamma}*v^2)v$ with $\gamma\in (0,n)$, where
$v=v(x,t)$ is an unknown function on $\mathbb{R}^n\times[0,T)$. Our aim of the
present paper is to prove a small data blow-up result and show an upper
estimate of lifespan of the problem for slowly decaying positive initial data
$(v(x,0),\partial_t v(x,0))$ such as $\partial_t v(x,0)=O(|x|^{-(1+\nu)})$ as
$|x|\rightarrow\infty$. Here $\nu$ belongs to the scaling supercritical case
$\nu<\frac{n-\gamma}{2}$. Our main new contribution is to estimate the
convolution term in high spatial dimensions, i.e. $n\ge 4$. This paper is the
first blow-up result to treat wave equations with the cubic convolution in high
spatial dimensions ($n\ge 4$).",2001.07985v1
2020-01-22,Testing a Quantum Error-Correcting Code on Various Platforms,"Quantum error correction plays an important role in fault-tolerant quantum
information processing. It is usually difficult to experimentally realize
quantum error correction, as it requires multiple qubits and quantum gates with
high fidelity. Here we propose a simple quantum error-correcting code for the
detected amplitude damping channel. The code requires only two qubits. We
implement the encoding, the channel, and the recovery on an optical platform,
the IBM Q System, and a nuclear magnetic resonance system. For all of these
systems, the error correction advantage appears when the damping rate exceeds
some threshold. We compare the features of these quantum information processing
systems used and demonstrate the advantage of quantum error correction on
current quantum computing platforms.",2001.07998v1
2020-01-22,Dynamic state reconstruction of quantum systems subject to pure decoherence,"The article introduces efficient quantum state tomography schemes for qutrits
and entangled qubits subject to pure decoherence. We implement the dynamic
state reconstruction method for open systems sent through phase-damping
channels which was proposed in: Open Syst. Inf. Dyn. 23, 1650019 (2016). In the
current article we prove that two distinct observables measured at four
different time instants suffice to reconstruct the initial density matrix of a
qutrit with evolution given by a phase-damping channel. Furthermore, we
generalize the approach in order to determine the optimal criteria for quantum
tomography of entangled qubits. Finally, we prove two universal theorems
concerning the minimal number of distinct observables required for quantum
tomography of qudits. We believe that dynamic state reconstruction schemes
bring significant advancement and novelty to quantum tomography since they
allow to reduce the number of distinct measurements required to solve the
problem, which is important from the experimental point of view.",2001.08167v1
2020-01-28,Rate of Estimation for the Stationary Distribution of Stochastic Damping Hamiltonian Systems with Continuous Observations,"We study the problem of the non-parametric estimation for the density $\pi$
of the stationary distribution of a stochastic two-dimensional damping
Hamiltonian system $(Z_t)_{t\in[0,T]}=(X_t,Y_t)_{t \in [0,T]}$. From the
continuous observation of the sampling path on $[0,T]$, we study the rate of
estimation for $\pi(x_0,y_0)$ as $T \to \infty$. We show that kernel based
estimators can achieve the rate $T^{-v}$ for some explicit exponent $v \in
(0,1/2)$. One finding is that the rate of estimation depends on the smoothness
of $\pi$ and is completely different with the rate appearing in the standard
i.i.d.\ setting or in the case of two-dimensional non degenerate diffusion
processes. Especially, this rate depends also on $y_0$. Moreover, we obtain a
minimax lower bound on the $L^2$-risk for pointwise estimation, with the same
rate $T^{-v}$, up to $\log(T)$ terms.",2001.10423v1
2020-01-28,Image polaritons in boron nitride for extreme polariton confinement with low losses,"Polaritons in two-dimensional materials provide extreme light confinement
that is difficult to achieve with metal plasmonics. However, such tight
confinement inevitably increases optical losses through various damping
channels. Here we demonstrate that hyperbolic phonon polaritons in hexagonal
boron nitride can overcome this fundamental trade-off. Among two observed
polariton modes, featuring a symmetric and antisymmetric charge distribution,
the latter exhibits lower optical losses and tighter polariton confinement.
Far-field excitation and detection of this high-momenta mode becomes possible
with our resonator design that can boost the coupling efficiency via virtual
polariton modes with image charges that we dub image polaritons. Using these
image polaritons, we experimentally observe a record-high effective index of up
to 132 and quality factors as high as 501. Further, our phenomenological theory
suggests an important role of hyperbolic surface scattering in the damping
process of hyperbolic phonon polaritons.",2001.10583v2
2020-02-06,Fractional derivative order determination from harmonic oscillator damping factor,"This article analysis differential equations which represents damped and
fractional oscillators. First, it is shown that prior to using physical
quantities in fractional calculus, it is imperative that they are turned
dimensionless. Afterwards, approximated expressions that relate the two
equations parameters for the case that the fractional order is close to an
integer number are presented. Following, a numerical regression is made using
power series expansion, and, also from fractional calculus, the fact that both
equations cannot be equivalent is concluded. In the end, from the numerical
regression data, the analytical approximated expressions that relate the two
equations' parameters are refined.",2002.02479v1
2020-02-11,A numerical damped oscillator approach to constrained Schrödinger equations,"This article explains and illustrates the use of a set of coupled dynamical
equations, second order in a fictitious time, which converges to solutions of
stationary Schr\""{o}dinger equations with additional constraints. We include
three qualitative different numerical examples: the radial Schr\""{o}dinger
equation for the hydrogen atom; the two-dimensional harmonic oscillator with
degenerate excited states; and finally a non-linear Schr\""{o}dinger equation
for rotating states. The presented method is intuitive, with analogies in
classical mechanics for damped oscillators, and easy to implement, either in
own coding, or with software for dynamical systems. Hence, we find it suitable
to introduce it in a continuation course in quantum mechanics or generally in
applied mathematics courses which contain computational parts.",2002.04400v2
2020-02-12,Fast computation of optimal damping parameters for linear vibrational systems,"We formulate the quadratic eigenvalue problem underlying the mathematical
model of a linear vibrational system as an eigenvalue problem of a
diagonal-plus-low-rank matrix $A$. The eigenvector matrix of $A$ has a
Cauchy-like structure. Optimal viscosities are those for which $trace(X)$ is
minimal, where $X$ is the solution of the Lyapunov equation $AX+XA^{*}=GG^{*}$.
Here $G$ is a low-rank matrix which depends on the eigenfrequencies that need
to be damped. After initial eigenvalue decomposition of linearized problem
which requires $O(n^3)$ operations, our algorithm computes optimal viscosities
for each choice of external dampers in $O(n^2)$ operations, provided that the
number of dampers is small. Hence, the subsequent optimization is order of
magnitude faster than in the standard approach which solves Lyapunov equation
in each step, thus requiring $O(n^3)$ operations. Our algorithm is based on
$O(n^2)$ eigensolver for complex symmetric diagonal-plus-rank-one matrices and
fast $O(n^2)$ multiplication of linked Cauchy-like matrices.",2002.04917v2
2020-02-13,Low-loss two-dimensional plasmon modes in antimonene,"The effects of spin-orbit (SOC) and electron-phonon coupling on the
collective excitation of doped monolayer Sb$_2$ are investigated using density
functional and many-body perturbation theories. The spin-orbit coupling is
exclusively important for the monolayer Sb$_2$ and it leads to the
reconstruction of the electronic band structure. In particular, plasmon modes
of monolayer Sb$_2$ are quite sensitive to the SOC and are characterized by
very low damping rates owing to small electron-phonon scatterings. Our results
show plasmons in antimonene are significantly less damped compared to monolayer
graphene when plasmon energies are $\hbar \omega> 0.2$ eV due to smaller
plasmon-phonon coupling in the former material.",2002.05302v1
2020-02-13,Quantization of the damped harmonic oscillator based on a modified Bateman Lagrangian,"An approach to quantization of the damped harmonic oscillator (DHO) is
developed on the basis of a modified Bateman Lagrangian (MBL); thereby some
quantum mechanical aspects of the DHO are clarified. We treat the energy
operator for the DHO, in addition to the Hamiltonian operator that is
determined from the MBL and corresponds to the total energy of the system. It
is demonstrated that the energy eigenvalues of the DHO exponentially decrease
with time and that transitions between the energy eigenstates occur in
accordance with the Schr\""{o}dinger equation. Also, it is pointed out that a
new critical parameter discriminates different behaviours of transition
probabilities.",2002.05435v1
2020-02-17,Charge Transfer Through Redox Molecular Junctions in Non-Equilibrated Solvents,"Molecular conduction operating in dielectric solvent environments are often
described using kinetic rates based on Marcus theory of electron transfer at a
molecule-metal electrode interface. However, the successive nature of charge
transfer in such system implies that the solvent does not necessarily reach
equilibrium in such process. Here we generalize the theory to account for
solvent nonequilibrium and consider a molecular junction consisting of an
electronic donor-acceptor system coupled to two metallic electrodes and placed
in a polarizable solvent. We determine the nonequilbrium distribution of the
solvent by solving diffusion equations in the strong- and weak-friction limits
and calculate the charge current and its fluctuating behavior. In extreme
limits: the absence of the solvent or fast solvent relaxation, the charge
transfer statistics is Poissonian, while it becomes correlated by the dynamic
solvent in between these limits. A Kramers-like turnover of the nonequilibrium
current as a function of the solvent damping is found. Finally, we propose a
way to tune the solvent-induced damping using geometrical control of the
solvent dielectric response in nanostructured solvent channels.",2002.06932v1
2020-02-19,Diagnostics of plasma ionisation using torsional Alfén waves,"Using the recently observed torsional Alfv\'en waves in solar prominences, we
determine the ionisation state of the plasma by taking into account that
Alfv\'en waves propagate in a partially ionised prominence plasma. We derive
the evolutionary equation of waves and compare the analytical solutions to
observations to determine the number density of neutrals. Using a single fluid
plasma approximation, where the wave damping is provided by the Cowling
resistivity, we study the temporal evolution of waves. By comparing the
solution of equations with observational data (period, amplitude, propagation
speed), we determined the value of the Cowling resistivity that led us to draw
a conclusion on the amount of neutrals in the partially ionised plasma, a
quantity that cannot be measured directly or indirectly. Our results show that
damped torsional Alfv\'en waves are an ideal diagnostic tool for the ionisation
state of the plasma. Using a simple model, we find that at the observational
temperature of torsional Alfv\'en waves, the number of neutrals is of the order
of $5\times 10^{10}$ cm$^{-3}$.",2002.08441v1
2020-03-01,Optimal Oscillation Damping Control of cable-Suspended Aerial Manipulator with a Single IMU Sensor,"This paper presents a design of oscillation damping control for the
cable-Suspended Aerial Manipulator (SAM). The SAM is modeled as a double
pendulum, and it can generate a body wrench as a control action. The main
challenge is the fact that there is only one onboard IMU sensor which does not
provide full information on the system state. To overcome this difficulty, we
design a controller motivated by a simplified SAM model. The proposed
controller is very simple yet robust to model uncertainties. Moreover, we
propose a gain tuning rule by formulating the proposed controller in the form
of output feedback linear quadratic regulation problem. Consequently, it is
possible to quickly dampen oscillations with minimal energy consumption. The
proposed approach is validated through simulations and experiments.",2003.00472v1
2020-03-06,Accelerating the Convergence of Higher-Order Coupled Cluster Methods II: Coupled Cluster $Λ$ Equations and Dynamic Damping,"The method of sub-iteration, which was previously applied to the higher-order
coupled cluster amplitude equations, is extended to the case of the coupled
cluster $\Lambda$ equations. The sub-iteration procedure for the $\Lambda$
equations is found to be highly similar to that for the amplitude equations,
and to exhibit a similar improvement in rate of convergence relative to
extrapolation of all $\hat{T}$ or $\hat{\Lambda}$ amplitudes using DIIS. A
method of dynamic damping is also presented which is found to effectively
recover rapid convergence in the case of oscillatory behavior in the amplitude
or $\Lambda$ equations. Together, these techniques allow for the convergence of
both the amplitude and $\Lambda$ equations necessary for the calculation of
analytic gradients and properties of higher-order coupled cluster methods
without the high memory or disk I/O cost of full DIIS extrapolation.",2003.03455v1
2020-03-09,Forces between Silica Particles in Isopropanol Solutions of 1:1 Electrolytes,"Interactions between silica surfaces across isopropanol solutions are
measured with colloidal probe technique based on atomic force microscope. In
particular, the influence of 1:1 electrolytes on the interactions between
silica particles is investigated. A plethora of different forces are found in
these systems. Namely, van der Waals, double-layer, attractive non-DLVO,
repulsive solvation, and damped oscillatory interactions are observed. The
measured decay length of the double-layer repulsion is substantially larger
than Debye lengths calculated from nominal salt concentrations. These
deviations are caused by pronounced ion pairing in alcohol solutions. At
separation below 10 nm, additional attractive and repulsive non-DLVO forces are
observed. The former are possibly caused by charge heterogeneities induced by
strong ion adsorption, whereas the latter originate from structuring of
isopropanol molecules close to the surface. Finally, at increased
concentrations the transition from monotonic to damped oscillatory interactions
is uncovered.",2003.04058v2
2020-03-13,Energy localization and transfer in autoresonant weakly dissipative anharmonic chains,"In this work, we develop an analytical framework to explain the influence of
dissipation and detuning parameters on the emergence and stability of
autoresonance in a strongly nonlinear weakly damped chain subjected to harmonic
forcing with a slowly-varying frequency. Using the asymptotic procedures, we
construct the evolutionary equations, which describe the behavior of the array
under the condition of 1:1 resonance and then approximately compute the slow
amplitudes and phases as well as the duration of autoresonance. It is shown
that, in contrast to autoresonance in a non-dissipative chain with unbounded
growth of energy, the energy in a weakly damped array being initially at rest
is growing only in a bounded time interval up to an instant of simultaneous
escape from resonance of all autoresonant oscillators. Analytical conditions of
the emergence and stability of autoresonance are confirmed by numerical
simulations.",2003.06346v1
2020-03-13,Photon and Phonon Spectral-Functions for Continuum Quantum Optomechanics,"We study many-particle phenomena of propagating multi-mode photons and
phonons interacting through Brillouin scattering-type Hamiltonian in nanoscale
waveguides. We derive photon and phonon retarded Green's functions and extract
their spectral functions in applying the factorization approximation of the
mean-field theory. The real part of the self-energy provides renormalization
energy shifts for the photons and the phonons. Besides the conventional leaks,
the imaginary part gives effective photon and phonon damping rates induced due
to many-particle phenomena. The results extend the simple spectral functions of
quantum optomechanics into continuum quantum optomechanics. We present the
influence of thermal phonons on the photon effective damping rates, and
consider cases of specific photon fields to be excited within the waveguide and
which are of importance for phonon cooling scenarios.",2003.06355v1
2020-03-13,Surface waves in a collisional quark-gluon plasma,"Surface waves propagating in the semi-bounded collisional hot QCD medium
(quark-gluon plasma) are considered. To investigate the effect of collisions as
damping and non-ideality factor, the longitudinal and transverse dielectric
functions of the quark-gluon plasma are used within the Bhatnagar-Gross-Krook
(BGK) approach. The results were obtained both analytically and numerically in
the long wavelength limit. First of all, collisions lead to smaller values of
surface wave frequency and their stronger damping. Secondly, the results show
that non-ideality leads to the appearance of a new branch of surface waves
compared to the collisionless case. The relevance of the surface excitations
(waves) for the QGP realized in experiments is discussed.",2003.06373v2
2020-03-18,Finite time extinction for the strongly damped nonlinear Schr{ö}dinger equation in bounded domains,"We prove the \textit{finite time extinction property} $(u(t)\equiv 0$ on
$\Omega$ for any $t\ge T_\star,$ for some $T_\star>0)$ for solutions of the
nonlinear Schr\""{o}dinger problem ${\rm i} u_t+\Delta u+a|u|^{-(1-m)}u=f(t,x),$
on a bounded domain $\Omega$ of $\mathbb{R}^N,$ $N\le 3,$ $a\in\mathbb{C}$ with
$\Im(a)>0$ (the damping case) and under the crucial assumptions $0<m<1$ and the
dominating condition $2\sqrt m\,\Im(a)\ge(1-m)|\Re(a)|.$ We use an energy
method as well as several a priori estimates to prove the main conclusion. The
presence of the non-Lipschitz nonlinear term in the equation introduces a lack
of regularity of the solution requiring a study of the existence and uniqueness
of solutions satisfying the equation in some different senses according to the
regularity assumed on the data.",2003.08105v2
2020-03-19,Challenge for describing the cluster states starting with realistic interaction,"We aim to describe the cluster states of nuclear systems starting with a
realistic interaction, which is a challenge of modern nuclear theories. Here,
the short-range correlation of realistic interaction is treated by employing
the damping factor, and the resultant interaction can be applied to the cluster
structure of light nuclei. We start with a realistic interaction (G3RS) and
transform it in this way, and the $\alpha$-$\alpha$ energy curve is compared
with the results of phenomenological interactions. The attractive effect
between two $\alpha$'s is found to be not enough even with a damping factor for
the short-range repulsion, and the necessity of a finite-range three-body term
is discussed. With this three-body term, the resonance energy of the ground
state and the scattering phase shift of two $\alpha$'s can be reproduced. Also,
the binding energy of $^{16}$O from the four $\alpha$ threshold is reasonably
reproduced. The linear-chain structure of three and four $\alpha$ clusters in
$^{12}$C and $^{16}$O are calculated with this interaction and compared with
the results of the conventional approaches including the density functional
theories.",2003.08546v1
2020-03-20,Large Deflections of A Structurally Damped Panel in A Subsonic Flow,"The large deflections of panels in subsonic flow are considered.
Specifically, a fully clamped von Karman plate accounting for both rotational
inertia in plate filaments and structural damping of square root type is
considered. The panel is taken to be embedded in the boundary of a linear,
subsonic potential flow on the positive halfspace in $\mathbb R^3$. Solutions
are constructed via a semigroup approach despite the lack of natural
dissipativity associated to the generator of the linear dynamics. The
flow-plate dynamics are then reduced---via an explicit Neumann-to-Dirichlet
(downwash-to-pressure) solver for the flow---to a memory-type dynamical system
for the plate. For the non-conservative plate dynamics, a global attractor is
explicitly constructed via Lyapunov and quasi-stability methods. Finally, it is
shown that via the compactness of the attractor and finiteness of the
dissipation integral, that all trajectories converge strongly to the set of
stationary states.",2003.09232v1
2020-03-24,Pulsed RF Schemes for Tearing Mode Stabilization,"The RF stabilization of tearing modes with current condensation has the
potential to increase stabilization efficiency and loosen power localization
requirements. Such benefits stem from the cooperative feedback between the RF
deposition and resulting island temperature perturbation governed by diffusion.
A self consistent treatment of the damping of an rf ray as it traverses the
island shows that low damping scenarios can require unfavorably high powers to
overcome initial power leakage and effectively capitalize on the nonlinear
effect. In this work it is demonstrated that for such regimes,modulated
stabilization schemes can achieve significant improvements in heating and
current drive contributions to stabilization for the same average power as a
continuous wave scheme. The impact of modulation frequency and duty cycle on
the performance is explored, the results of which suggest modulation strategies
in which the pulsing periods are kept on the order of a diffusive time.",2003.10896v1
2020-03-24,Detecting Multiple DLAs per Spectrum in SDSS DR12 with Gaussian Processes,"We present a revised version of our automated technique using Gaussian
processes (GPs) to detect Damped Lyman-$\alpha$ absorbers (DLAs) along quasar
(QSO) sightlines. The main improvement is to allow our Gaussian process
pipeline to detect multiple DLAs along a single sightline. Our DLA detections
are regularised by an improved model for the absorption from the Lyman-$\alpha$
forest which improves performance at high redshift. We also introduce a model
for unresolved sub-DLAs which reduces mis-classifications of absorbers without
detectable damping wings. We compare our results to those of two different
large-scale DLA catalogues and provide a catalogue of the processed results of
our Gaussian process pipeline using 158 825 Lyman-$\alpha$ spectra from SDSS
data release 12. We present updated estimates for the statistical properties of
DLAs, including the column density distribution function (CDDF), line density
($dN/dX$), and neutral hydrogen density ($\Omega_{\textrm{DLA}}$).",2003.11036v2
2020-03-28,Quantum speed limit based on the bound of Bures angle,"In this paper, we investigate the unified bound of quantum speed limit time
in open systems based on the modified Bures angle. This bound is applied to the
damped Jaynes-Cummings model and the dephasing model, and the analytical
quantum speed limit time is obtained for both models. As an example, the
maximum coherent qubit state with white noise is chosen as the initial states
for the damped Jaynes-Cummings model. It is found that the quantum speed limit
time in both the non-Markovian and the Markovian regimes can be decreased by
the white noise compared with the pure state. In addition, for the dephasing
model, we find that the quantum speed limit time is not only related to the
coherence of initial state and non-Markovianity, but also dependent on the
population of initial excited state.",2003.12758v1
2020-03-31,First-principles study of ultrafast dynamics of Dirac plasmon in graphene,"Exploring low-loss two-dimensional plasmon modes is considered central for
achieving light manipulation at the nanoscale and applications in plasmonic
science and technology. In this context, pump-probe spectroscopy is a powerful
tool for investigating these collective modes and the corresponding energy
transfer processes. Here, I present a first-principles study on non-equilibrium
Dirac plasmon in graphene, wherein damping channels under ultrafast conditions
are still not fully explored. The laser-induced blueshift of plasmon energy is
explained in terms of thermal increase of the electron-hole pair concentration
in the intraband channel. Interestingly, while damping pathways of the
equilibrium graphene plasmon are entirely ruled by scatterings with acoustic
phonons, the photoinduced plasmon predominantly transfers its energy to the
strongly coupled hot optical phonons, which explains the
experimentally-observed tenfold increase of the plasmon linewidth. The present
study paves the way for an in-depth theoretical comprehension of plasmon
temporal dynamics in novel two-dimensional systems and heterostructures.",2003.14074v2
2020-03-31,Parametric analysis of COVID-19 expansion in European countries in the period of February to June 2020,"The data on number of registered cases of COVID-19 disease in twenty European
countries is analyzed by the least-squares fitting procedure with generic
analytic functions. Three regimes of the expansion of the disease are
identified and quantified -- early exponential expansion, damped exponential,
and linear expansion. Differences among countries in the early expansion period
are quantified. The velocity of the expansion in the exponential regime lies
within one standard deviation from the average value for 11 countries. The
number of infected individuals at the initial time is excessively high for
Italy, 7 standard deviations from the average value.
  Method for predicting the expansion based on extrapolation in the parametric
space is presented. One-week predictions based on extrapolations have average
precision of 18% and 29% during the later period of the damped exponential
expansion for the case of Italy and Czechia, respectively. The method based on
extrapolations in the parametric space may provide an elementary method to
quantify the impact of restrictive measures on the spreading of the disease.",2003.14283v2
2020-04-14,Stability results of an elastic/viscoelastic transmission problem of locally coupled waves with non smooth coefficients,"We investigate the stabilization of a locally coupled wave equations with
only one internal viscoelastic damping of Kelvin-Voigt type. The main novelty
in this paper is that both the damping and the coupling coefficients are non
smooth. First, using a general criteria of Arendt-Batty, combined with an
uniqueness result, we prove that our system is strongly stable. Next, using a
spectrum approach, we prove the non-exponential (uniform) stability of the
system. Finally, using a frequency domain approach, combined with a piecewise
multiplier technique and the construction of a new multiplier satisfying some
ordinary differential equations, we show that the energy of smooth solutions of
the system decays polynomially of type t^{-1}.",2004.06758v1
2020-04-16,Ergodicity effects on transport-diffusion equations with localized damping,"The main objective of this paper is to study the time decay of
transport-diffusion equation with inhomogeneous localized damping in the
multi-dimensional torus. The drift is governed by an autonomous Lipschitz
vector field and the diffusion by the standard heat equation with small
viscosity parameter $\nu$. In the first part we deal with the inviscid case and
show some results on the time decay of the energy using in a crucial way the
ergodicity and the unique ergodicity of the flow generated by the drift. In the
second part we analyze the same problem with small viscosity and provide quite
similar results on the exponential decay uniformly with respect to the
viscosity in some logarithmic time scaling of the \mbox{type $t\in
[0,C_0\ln(1/\nu)]$}.",2004.07712v1
2020-04-17,Majorization-Minimization-Based Levenberg--Marquardt Method for Constrained Nonlinear Least Squares,"A new Levenberg--Marquardt (LM) method for solving nonlinear least squares
problems with convex constraints is described. Various versions of the LM
method have been proposed, their main differences being in the choice of a
damping parameter. In this paper, we propose a new rule for updating the
parameter so as to achieve both global and local convergence even under the
presence of a convex constraint set. The key to our results is a new
perspective of the LM method from majorization-minimization methods.
Specifically, we show that if the damping parameter is set in a specific way,
the objective function of the standard subproblem in LM methods becomes an
upper bound on the original objective function under certain standard
assumptions.
  Our method solves a sequence of the subproblems approximately using an
(accelerated) projected gradient method. It finds an $\epsilon$-stationary
point after $O(\epsilon^{-2})$ computation and achieves local quadratic
convergence for zero-residual problems under a local error bound condition.
Numerical results on compressed sensing and matrix factorization show that our
method converges faster in many cases than existing methods.",2004.08259v3
2020-04-23,Many-body Decay of the Gapped Lowest Excitation of a Bose-Einstein Condensate,"We study the decay mechanism of the gapped lowest-lying excitation of a
quasi-pure box-trapped atomic Bose-Einstein condensate. Owing to the absence of
lower-energy modes, or direct coupling to an external bath, this excitation is
protected against one-body (linear) decay and the damping mechanism is
exclusively nonlinear. We develop a universal theoretical model that explains
this fundamental nonlinear damping as a process whereby two quanta of the
gapped lowest excitation mode couple to a higher-energy mode, which
subsequently decays into a continuum. We find quantitative agreement between
our experiments and the predictions of this model. Finally, by strongly driving
the system below its (lowest) resonant frequency we observe third-harmonic
generation, a hallmark of nonlinear behavior.",2004.11363v1
2020-05-05,Hydrodynamic memory can boost enormously driven nonlinear diffusion and transport,"Hydrodynamic memory force or Basset force is known since the 19th-century.
Its influence on Brownian motion remains, however, mostly unexplored. Here, we
investigate its role in nonlinear transport and diffusion within a paradigmatic
model of tilted washboard potential. In this model, a giant enhancement of
driven diffusion over its potential-free limit presents a well-established
paradoxical phenomenon. In the overdamped limit, it occurs at a critical tilt
of vanishing potential barriers. However, for weak damping, it takes place
surprisingly at another critical tilt, where the potential barriers are clearly
expressed. Recently we showed that Basset force could make such a diffusion
enhancement enormously large. In this paper, we discover that even for
moderately strong damping, where the overdamped theory works very well when the
memory effects are negligible, substantial hydrodynamic memory unexpectedly
makes a strong impact. First, the diffusion boost occurs at non-vanishing
potential barriers and can be orders of magnitude larger. Second, transient
anomalous diffusion regimes emerge over many time decades and potential
periods. Third, particles' mobility can also be dramatically enhanced, and a
long transient super-transport regime emerges.",2005.01984v2
2020-05-05,Diffraction losses of a Fabry-Perot cavity with nonidentical non-spherical mirrors,"Optical cavities with both optimized resonant conditions and high quality
factors are important metrological tools. In particular, they are used for
laser gravitational wave (GW) detectors. It is necessary to suppress the
parametric instability by damping the resonant conditions of harmful higher
order optical modes (HOOM) in order to have high cavity powers in GW detectors.
This can be achieved effectively by using non spherical mirrors in symmetric
Fabry-Perot (FP) cavities by increasing roundtrip losses of HOOMs. Fabry-Perot
cavities in most of the GW detectors have non-identical mirrors to optimize
clipping losses and reduce thermal noise by reducing the beam size on one side
of the cavity facing to the beam splitter and recycling cavities. We here
present a general method to design non spherical non-identical mirrors in
non-symmetric FP cavities to damp HOOMs. The proposed design allows to the
suppress the loss of the arm power caused by point absorbers on test masses.",2005.02033v1
2020-05-11,Sound Absorption in Partially Ionized Hydrogen Plasma and Heating Mechanism of Solar Chromosphere,"The temperature dependence of rates of electron impact ionization and two
electrons recombination are calculated using Wannier cross section of electron
impact ionization of neutral hydrogen atom. Entropy production and power
dissipation are derived for the case when the ionization degree deviates from
its equilibrium value. This is the special case of the obtained general formula
for entropy production accompanying chemical reactions. Damping rate of the
sound waves is calculated and the conditions when ionization processes dominate
are considered. A quasi-classical approximation for the heating mechanism of
solar chromosphere is proposed. Several analogous phenomena for damping rates
in liquids and crystals are shortly discussed, for example, deaf sound of a
glass of beer or English salt solution. An explicit expression for the second
or bulk (or volume) viscosity of hydrogen plasma is calculated from firsts
principles. For the first time some second viscosity is calculated from first
principles.",2005.05056v4
2020-05-12,Calculating RF current condensation with self-consistent ray-tracing,"By exploiting the nonlinear amplification of the power deposition of RF
waves, current condensation promises new pathways to the stabilisation of
magnetic islands. We present a numerical analysis of current condensation,
coupling a geometrical optics treatment of wave propagation and damping to a
thermal diffusion equation solver in the island. Taking into account the island
geometry and relativistic damping, previous analytical theory can be made more
precise and specific scenarios can be realistically predicted. With this more
precise description, bifurcations and associated hysteresis effects could be
obtained in an ITER-like scenario at realistic parameter values. Moreover, it
is shown that dynamically varying the RF wave launching angles can lead to
hysteresis and help to avoid the nonlinear shadowing effect.",2005.05997v1
2020-05-13,Sustaining a temperature difference,"We derive an expression for the minimal rate of entropy that sustains two
reservoirs at different temperatures $T_0$ and $T_\ell$. The law displays an
intuitive $\ell^{-1}$ dependency on the relative distance and a characterisic
$\log^2 (T_\ell/T_0)$ dependency on the boundary temperatures. First we give a
back-of-envelope argument based on the Fourier Law (FL) of conduction, showing
that the least-dissipation profile is exponential. Then we revisit a model of a
chain of oscillators, each coupled to a heat reservoir. In the limit of large
damping we reobtain the exponential and squared-log behaviors, providing a
self-consistent derivation of the FL. For small damping ""equipartition
frustration"" leads to a well-known balistic behaviour, whose incompatibility
with the FL posed a long-time challenge.",2005.06289v2
2020-05-13,Numerical simulations of unsteady viscous incompressible flows using general pressure equation,"In fluid dynamics, an important problem is linked to the knowledge of the
fluid pressure. Recently, another approach to study incompressible fluid flow
was suggested. It consists in using a general pressure equation (GPE) derived
from compressible Navier-Stokes equation. In this paper, GPE is considered and
compared with the Chorin's artificial compressibility method (ACM) and the
Entropically damped artificial compressibility (EDAC) method. The three methods
are discretized in a staggered grid system with second order centered schemes
in space and a third order Runge-Kutta scheme in time. Three test cases are
realized: two-dimensional Taylor-Green vortex flow, the traveling wave and the
doubly periodic shear layers. It is demonstrated that GPE is accurate and
efficient to capture the correct behavior for unsteady incompressible flows.
The numerical results obtained by GPE are in excellent agreement with those
obtained by ACM, EDAC and a classical finite volume method with a Poisson
equation. Furthermore, GPE convergence is better than ACM convergence. The
proposed general pressure equation (GPE) allows to solve general, time-accurate
, incompressible Navier-Stokes flows. Finally, the parametric study realized in
terms of Mach and Prandtl numbers shows that the velocity divergence can be
limited by an arbitrary maximum and that acoustic waves can be damped.",2005.06448v1
2020-05-15,Response of the BGO Calorimeter to Cosmic Ray Nuclei in the DAMPE Experiment on Orbit,"This paper is about a study on the response of the BGO calorimeter of DAMPE
experiment. Four elements in Cosmic Ray nuclei are used as sources for this
analysis. A feature resulting from the geomagnetic cutoff exhibits in the
energy spectrum, both in simulated and reconstructed data, and is compared
between them.",2005.07621v1
2020-05-18,Linear inviscid damping for shear flows near Couette in the 2D stably stratified regime,"We investigate the linear stability of shears near the Couette flow for a
class of 2D incompressible stably stratified fluids. Our main result consists
of nearly optimal decay rates for perturbations of stationary states whose
velocities are monotone shear flows $(U(y),0)$ and have an exponential density
profile. In the case of the Couette flow $U(y)=y$, we recover the rates
predicted by Hartman in 1975, by adopting an explicit point-wise approach in
frequency space. As a by-product, this implies optimal decay rates as well as
Lyapunov instability in $L^2$ for the vorticity. For the previously unexplored
case of more general shear flows close to Couette, the inviscid damping results
follow by a weighted energy estimate. Each outcome concerning the stably
stratified regime applies to the Boussinesq equations as well. Remarkably, our
results hold under the celebrated Miles-Howard criterion for stratified fluids.",2005.09058v2
2020-05-19,High-redshift Damped Ly-alpha Absorbing Galaxy Model Reproducing the N(HI)-Z Distribution,"We investigate how damped Lyman-$\alpha$ absorbers (DLAs) at z ~ 2-3,
detected in large optical spectroscopic surveys of quasars, trace the
population of star-forming galaxies. Building on previous results, we construct
a model based on observed and physically motivated scaling relations in order
to reproduce the bivariate distributions of metallicity, Z, and HI column
density, N(HI). Furthermore, the observed impact parameters for galaxies
associated to DLAs are in agreement with the model predictions. The model
strongly favours a metallicity gradient, which scales with the luminosity of
the host galaxy, with a value of $\gamma$* = -0.019 $\pm$ 0.008 dex kpc$^{-1}$
for L* galaxies that gets steeper for fainter galaxies. We find that DLAs trace
galaxies over a wide range of galaxy luminosities, however, the bulk of the DLA
cross-section arises in galaxies with L ~ 0.1 L* at z ~ 2.5 broadly consistent
with numerical simulations.",2005.09660v1
2020-05-20,Dynamical phase transitions in dissipative quantum dynamics with quantum optical realization,"We study dynamical phase transitions (DPT) in the driven and damped Dicke
model, realizable for example by a driven atomic ensemble collectively coupled
to a damped cavity mode. These DPTs are characterized by non-analyticities of
certain observables, primarily the overlap of time evolved and initial state.
Even though the dynamics is dissipative, this phenomenon occurs for a wide
range of parameters and no fine-tuning is required. Focusing on the state of
the 'atoms' in the limit of a bad cavity, we are able to asymptotically
evaluate an exact path integral representation of the relevant overlaps. The
DPTs then arise by minimization of a certain action function, which is related
to the large deviation theory of a classical stochastic process. From a more
general viewpoint, in the considered system, non-analyticities emerge
generically in a Fock space representation of the state. Finally, we present a
scheme which allows a measurement of the DPT in a cavity-QED setup.",2005.10013v2
2020-05-21,The critical exponent for nonlinear damped $σ$-evolution equations,"In this paper, we derive suitable optimal $L^p-L^q$ decay estimates, $1\leq
p\leq q\leq \infty$, for the solutions to the $\sigma$-evolution equation,
$\sigma>1$, with structural damping and power nonlinearity $|u|^{1+\alpha}$ or
$|u_t|^{1+\alpha}$, \[ u_{tt}+(-\Delta)^\sigma u +(-\Delta)^\theta
u_t=\begin{cases} |u|^{1+\alpha}, \\ |u_t|^{1+\alpha}, \end{cases}\] where
$t\geq0$ and $x\in\mathbb{R}^n$. Using these estimates, we can solve the
problem of finding the critical exponents for the two nonlinear problems above
in the so-called non-effective case, $\theta\in(\sigma/2,\sigma]$. This latter
is more difficult than the effective case $\theta\in[0,\sigma/2)$, since the
asymptotic profile of the solution involves a diffusive component and an
oscillating one. The novel idea in this paper consists in treating separately
the two components to neglect the loss of decay rate created by the interplay
of the two components. We deal with the oscillating component, by localizing
the low frequencies, where oscillations appear, in the extended phase space.
This strategy allows us to recover a quasi-scaling property which replaces the
lack of homogeneity of the equation.",2005.10946v1
2020-05-22,Particle pairs and trains in inertial microfluidics,"Staggered and linear multi-particle trains constitute characteristic
structures in inertial microfluidics. Using lattice-Boltzmann simulations, we
investigate their properties and stability, when flowing through microfluidic
channels. We confirm the stability of cross-streamline pairs by showing how
they contract or expand to their equilibrium axial distance. In contrast,
same-streamline pairs quickly expand to a characteristic separation but even at
long times slowly drift apart. We reproduce the distribution of particle
distances with its characteristic peak as measured in experiments.
  Staggered multi-particle trains initialized with an axial particle spacing
larger than the equilibrium distance contract non-uniformly due to collective
drag reduction. Linear particle trains, similar to pairs, rapidly expand
towards a value about twice the equilibrium distance of staggered trains and
then very slowly drift apart non-uniformly. Again, we reproduce the statistics
of particle distances and the characteristic peak observed in experiments.
Finally, we thoroughly analyze the damped displacement pulse traveling as a
microfluidic phonon through a staggered train and show how a defect strongly
damps its propagation.",2005.12701v2
2020-05-20,"Dynamic Peach-Koehler self-force, inertia, and radiation damping of a regularized dislocation","The elastodynamic Peach-Koehler force is computed for a fully-regularized
straight dislocation with isotropic core in continuum isotropic elastic
elasticity, in compact forms involving partial mass or impulsion functions
relative to shear and compressional waves. The force accounts for both dynamic
radiation damping and inertia. The expressions are valid indifferently for
subsonic or supersonic velocities. Results are compared with the case of a
flat-core dislocation of the Peierls-Eshelby type, for a motion of jump from
rest to constant velocity. In the steady-state limit, the Lagrangian function
relevant to expressing the force in the flat-core case must be replaced by a
related but different function for the regularized dislocation. However, by
suitably defining the regularizing dislocation width, the steady-state limits
of the force for the fully-regularized and flat-core dislocations can be
matched exactly.",2005.12704v2
2020-05-27,Experimental diagnostics of entanglement swapping by a collective entanglement test,"The paper reports on experimental diagnostics of entanglement swapping
protocol by means of collective entanglement witness. Our approach is suitable
to detect disturbances occurring in the preparation of quantum states, quantum
communication channel and imperfect Bell-state projection. More specifically we
demonstrate that our method can distinguish disturbances such as
depolarization, phase-damping, amplitude-damping and imperfect Bell-state
measurement by observing four probabilities and estimating collective
entanglement witness. Since entanglement swapping is a key procedure for
quantum repeaters, quantum relays, device-independent quantum communications or
entanglement assisted error correction, this can aid in faster and practical
resolution of quality-of-transmission related problems as our approach requires
less measurements then other means of diagnostics.",2005.13292v2
2020-05-27,Magnon antibunching in a nanomagnet,"We investigate the correlations of magnons inside a nanomagnet and identify a
regime of parameters where the magnons become antibunched, i.e., where there is
a large probability for occupation of the single-magnon state. This antibunched
state is very different from magnons at thermal equilibrium and
microwave-driven coherent magnons. We further obtain the steady state
analytically and describe the magnon dynamics numerically, and ascertain the
stability of such antibunched magnons over a large window of magnetic
anisotropy, damping and temperature. This means that the antibunched magnon
state is feasible in a wide class of low-damping magnetic nanoparticles. To
detect this quantum effect, we propose to transfer the quantum information of
magnons to photons by magnon-photon coupling and then measure the correlations
of photons to retrieve the magnon correlations. Our findings may provide a
promising platform to study quantum-classical transitions and for designing a
single magnon source.",2005.13637v1
2020-05-31,Existence and uniqueness of strong solutions for the system of interaction between a compressible Navier-Stokes-Fourier fluid and a damped plate equation,"The article is devoted to the mathematical analysis of a fluid-structure
interaction system where the fluid is compressible and heat conducting and
where the structure is deformable and located on a part of the boundary of the
fluid domain. The fluid motion is modeled by the compressible
Navier-Stokes-Fourier system and the structure displacement is described by a
structurally damped plate equation. Our main results are the existence of
strong solutions in an $L^p-L^q$ setting for small time or for small data.
Through a change of variables and a fixed point argument, the proof of the main
results is mainly based on the maximal regularity property of the corresponding
linear systems. For small time existence, this property is obtained by
decoupling the linear system into several standard linear systems whereas for
global existence and for small data, the maximal regularity property is proved
by showing that the corresponding linear coupled {\em fluid-structure} operator
is $\mathcal{R}-$sectorial.",2006.00488v1
2020-06-03,Giant voltage control of spin Hall nano-oscillator damping,"Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for
microwave signal generation and oscillator based neuromorphic computing
combining nano-scale footprint, fast and ultra-wide microwave frequency
tunability, CMOS compatibility, and strong non-linear properties providing
robust large-scale mutual synchronization in chains and two-dimensional arrays.
While SHNOs can be tuned via magnetic fields and the drive current, neither
approach is conducive for individual SHNO control in large arrays. Here, we
demonstrate electrically gated W/CoFeB/MgO nano-constrictions in which the
voltage-dependent perpendicular magnetic anisotropy, tunes the frequency and,
thanks to nano-constriction geometry, drastically modifies the spin-wave
localization in the constriction region resulting in a giant 42 % variation of
the effective damping over four volts. As a consequence, the SHNO threshold
current can be strongly tuned. Our demonstration adds key functionality to
nano-constriction SHNOs and paves the way for energy-efficient control of
individual oscillators in SHNO chains and arrays for neuromorphic computing.",2006.02151v1
2020-06-08,"Rogue wave, interaction solutions to the KMM system","In this paper, the consistent tanh expansion (CTE) method and the truncated
Painlev$\acute{\rm e}$ analysis are applied to the Kraenkel-Manna-Merle (KMM)
system, which describes propagation of short wave in ferromagnets. Two series
of analytic solutions of the original KMM system (free of damping effect) are
obtained via the CTE method. The interaction solutions contain an arbitrary
function, which provides a wide variety of choices to acquire new propagation
structures. Particularly, the breather soliton, periodic oscillation soliton
and multipole instanton are obtained. Furthermore, we obtain some exact
solutions of the damped-KMM equation at the first time. On the other hand, a
coupled equation containing quadri-linear form and tri-linear form for the
original KMM system is obtained by the truncated Painlev$\acute{\rm e}$
analysis, and the rogue wave solution and interaction solutions between rogue
wave and multi-soliton for the KMM system are discussed.",2006.04312v1
2020-06-10,Interpolation between Residual and Non-Residual Networks,"Although ordinary differential equations (ODEs) provide insights for
designing network architectures, its relationship with the non-residual
convolutional neural networks (CNNs) is still unclear. In this paper, we
present a novel ODE model by adding a damping term. It can be shown that the
proposed model can recover both a ResNet and a CNN by adjusting an
interpolation coefficient. Therefore, the damped ODE model provides a unified
framework for the interpretation of residual and non-residual networks. The
Lyapunov analysis reveals better stability of the proposed model, and thus
yields robustness improvement of the learned networks. Experiments on a number
of image classification benchmarks show that the proposed model substantially
improves the accuracy of ResNet and ResNeXt over the perturbed inputs from both
stochastic noise and adversarial attack methods. Moreover, the loss landscape
analysis demonstrates the improved robustness of our method along the attack
direction.",2006.05749v4
2020-06-15,Multimode cold-damping optomechanics with delayed feedback,"We investigate the role of time delay in cold-damping optomechanics with
multiple mechanical resonances. For instantaneous electronic response, it was
recently shown in \textit{Phys. Rev. Lett. \textbf{123}, 203605 (2019)}, that a
single feedback loop is sufficient to simultaneously remove thermal noise from
many mechanical modes. While the intrinsic delayed response of the electronics
can induce single mode and mutual heating between adjacent modes, we propose to
counteract such detrimental effects by introducing an additional time delay to
the feedback loop. For lossy cavities and broadband feedback, we derive
analytical results for the final occupancies of the mechanical modes within the
formalism of quantum Langevin equations. For modes that are frequency
degenerate collective effects dominate, mimicking behavior similar to Dicke
super- and subradiance. These analytical results, corroborated with numerical
simulations of both transient and steady state dynamics, allow to find suitable
conditions and strategies for efficient single or multimode feedback
optomechanics.",2006.08430v2
2020-06-12,Analytic solution of the SEIR epidemic model via asymptotic approximant,"An analytic solution is obtained to the SEIR Epidemic Model. The solution is
created by constructing a single second-order nonlinear differential equation
in $\ln S$ and analytically continuing its divergent power series solution such
that it matches the correct long-time exponential damping of the epidemic
model. This is achieved through an asymptotic approximant (Barlow et. al, 2017,
Q. Jl Mech. Appl. Math, 70 (1), 21-48) in the form of a modified symmetric
Pad\'e approximant that incorporates this damping. The utility of the
analytical form is demonstrated through its application to the COVID-19
pandemic.",2006.09818v2
2020-06-20,On The Energy Transfer To High Frequencies In The Damped/Driven Nonlinear Schrödinger Equation (Extended Version),"We consider a damped/driven nonlinear Schr\""odinger equation in an $n$-cube
$K^{n}\subset\mathbb{R}^n$, $n$ is arbitrary, under Dirichlet boundary
conditions \[ u_t-\nu\Delta u+i|u|^2u=\sqrt{\nu}\eta(t,x),\quad x\in
K^{n},\quad u|_{\partial K^{n}}=0, \quad \nu>0, \] where $\eta(t,x)$ is a
random force that is white in time and smooth in space. It is known that the
Sobolev norms of solutions satisfy $ \| u(t)\|_m^2 \le C\nu^{-m}, $ uniformly
in $t\ge0$ and $\nu>0$. In this work we prove that for small $\nu>0$ and any
initial data, with large probability the Sobolev norms $\|u(t,\cdot)\|_m$ of
the solutions with $m>2$ become large at least to the order of
$\nu^{-\kappa_{n,m}}$ with $\kappa_{n,m}>0$, on time intervals of order
$\mathcal{O}(\frac{1}{\nu})$.",2006.11518v2
2020-06-23,The Contour Method: a new approach to finding modes of non-adiabatic stellar pulsations,"The contour method is a new approach to calculating the non-adiabatic
pulsation frequencies of stars. These frequencies can be found by solving for
the complex roots of a characteristic equation constructed from the linear
non-adiabatic stellar pulsation equations. A complex-root solver requires an
initial trial frequency for each non adiabatic root. A standard method for
obtaining initial trial frequencies is to use a star's adiabatic pulsation
frequencies, but this method can fail to converge to non-adiabatic roots,
especially as the growth and/or damping rate of the pulsations becomes large.
The contour method provides an alternative way for obtaining initial trial
frequencies that robustly converges to non-adiabatic roots, even for stellar
models with extremely non-adiabatic pulsations and thus large growth/damping
rates. We describe the contour method implemented in the GYRE stellar pulsation
code and use it to calculate the non-adiabatic pulsation frequencies of
$10\,\rm{M_{\odot}}$ and $20\,\rm{M_{\odot}}$ $\beta$ Cephei star models, and
of a $0.9\,\rm{M_{\odot}}$ extreme helium star model.",2006.13223v2
2020-06-24,The Complex Permeability of Split-Ring Resonator Arrays Measured at Microwave Frequencies,"We have measured the relative permeability of split-ring resonator (SRR)
arrays used in metamaterials designed to have $\mu^\prime< 0$ over a narrow
range of microwave frequencies. The SRR arrays were loaded into the bore of a
loop-gap resonator (LGR) and reflection coefficient measurements were used to
determine both the real and imaginary parts of the array's effective
permeability. Data were collected as a function of array size and SRR spacing.
The results were compared to those obtained from continuous extended split-ring
resonators (ESRRs). The arrays of planar SRRs exhibited enhanced damping and a
narrower range of frequencies with $\mu^\prime<0$ when compared to the ESRRs.
The observed differences in damping, however, were diminished considerably when
the array size was expanded from a one-dimensional array of $N$ SRRs to a
$2\times 2\times N$ array. Our method can also be used to experimentally
determine the effective permeability of other metamaterial designs.",2006.13861v1
2020-06-25,Sharp decay estimates and asymptotic behaviour for 3D magneto-micropolar fluids,"We characterize the $L^2$ decay rate of solutions to the 3D
magneto-micropolar system in terms of the decay character of the initial datum.
Due to a linear damping term, the micro-rotational field has a faster decay
rate. We also address the asymptotic behaviour of solutions by comparing them
to solutions to the linear part. As a result of the linear damping, the
difference between the micro-rotational field and its linear part also decays
faster. As part of the proofs of these results, we prove estimates for the
derivatives of solutions which might be of independent interest.",2006.14427v2
2020-06-27,Measurement-Based Estimation of System State Matrix for AC Power Systems with Integrated VSCs,"In this paper, a wide-area measurement system (WAMS)-based method is proposed
to estimate the system state matrix for AC system with integrated voltage
source converters (VSCs) and identify the electromechanical modes. The proposed
method is purely model-free, requiring no knowledge of accurate network
topology and system parameters. Numerical studies in the IEEE 68-bus system
with integrated VSCs show that the proposed measurementbased method can
accurately identify the electromechanical modes and estimate the damping
ratios, the mode shapes, and the participation factors. The work may serve as a
basis for developing WAMS-based damping control using VSCs in the future.",2006.15244v1
2020-06-29,Collective excitations in spin-polarized bilayer graphene,"We calculate the plasmon frequency and damping rate of plasma oscillations in
a spin-polarized BLG system. Using the long wavelength approximation for
dynamical dielectric function, we obtain an analytical expression for plasmon
frequency showing that the degree of spin polarization P has negligible effect
on the long wavelength plasmon frequency. Numerical calculations demonstrate
that the degree of spin polarization affects slightly (strongly) plasmon
frequency at small (large) wave-vectors and the maximum value of damping rate
increases with increasing P. We also study the effects of carrier density and
substrate dielectric constant on plasmon properties for different value of spin
polarization. The numerically calculated critical wave-vector, at which the
plasmon dispersion curve hits the edge of electron-hole continuum, decreases
with P and can be used to determine experimentally the degree of spin
polarization.",2006.16042v2
2020-06-29,Quadratic optomechanical cooling of a cavity-levitated nanosphere,"We report on cooling the center-of-mass motion of a nanoparticle due to a
purely quadratic coupling between its motion and the optical field of a high
finesse cavity. The resulting interaction gives rise to a Van der Pol nonlinear
damping, which is analogous to conventional parametric feedback where the
cavity provides passive feedback without measurement. We show experimentally
that like feedback cooling the resulting energy distribution is strongly
nonthermal and can be controlled by the nonlinear damping of the cavity. As
quadratic coupling has a prominent role in proposed protocols to generate
deeply nonclassical states, our work represents a first step for producing such
states in a levitated system.",2006.16103v1
2020-07-01,Entanglement of quantum oscillators coupled to different heat baths,"We study the non-equilibrium dynamics of two coupled oscillators interacting
with their own heat baths of quantum scalar fields at different temperature
$T_1$ and $T_2$ with bilinear couplings between them. We particularly focus on
the entanglement or inseparability property of their quantum states. The
critical temperatures of two respective oscillators, $T_{1c}$ and $T_{2c}$,
higher than which the entanglement disappears, can be determined. It is found
that when two damping parameters are largely different, say $\gamma_1 \ll
\gamma_2$, the critical temperature $T_{1c}$ with respect to the frequency
$\Omega_+$, the higher frequency among two normal modes frequencies, can be
very large, $T_{1c} \gg \Omega_+$, while $T_{2c} \propto \Omega_+$ with the
possibility of hot entanglement. The entanglement of two oscillators with the
temperature-dependent damping parameters $\gamma_{1;2,T}$ from heat baths is
also discussed.",2007.00288v2
2020-07-01,Stabilization of the critical and subcritical semilinear inhomogeneous and anisotropic elastic wave equation,"{\bf Abstract} \,\,We prove exponential decay of the critical and subcritical
semilinear inhomogeneous and anisotropic elastic wave equation with locally
distributed damping on bounded domain. One novelty compared to previous
results, is to give a checkable condition of the inhomogeneous and anisotropic
medias. Another novelty is to establish a framework to study the stability of
the damped semilinear inhomogeneous and anisotropic elastic wave equation,
which is hard to apply Carleman estimates to deal with. We develop the Morawetz
estimates and the compactness-uniqueness arguments for the semiliear elastic
wave equation to prove the unique continuation, observability inequality and
stabilization result.
  It is pointing that our proof is different from the classical method (See
Dehman et al.\cite{ZYY11}, Joly et al.\cite{ZYY16} and Zuazua \cite{ZYY43}),
which succeeds for the subcritical semilinear wave equation and fails for the
critical semilinear wave equation.",2007.00813v1
2020-07-06,Collective excitations and universal broadening of cyclotron absorption in Dirac semimetals in a quantizing magnetic field,"The spectrum of electromagnetic collective excitations in Dirac semimetals
placed in a quantizing magnetic field is considered. We have found the Landau
damping regions using the energy and momentum conservation law for allowed
transitions between one-particle states of electron excitations. Analysis of
dispersion equations for longitudinal and transverse waves near the window
boundaries in the Landau damping regions reveals different types of collective
excitations. We also indicate the features of universal broadening of cyclotron
absorption for a magnetic field variation in systems with linear dispersion of
the electron spectrum. The use of the obtained spectrum also allows us to
predict a number of oscillation and resonance effects in the field of
magneto-optical phenomena.",2007.02979v1
2020-07-06,Fast convex optimization via a third-order in time evolution equation: TOGES-V an improved version of TOGES,"In a Hilbert space setting H, for convex optimization, we analyze the fast
convergence properties as t tends to infinity of the trajectories generated by
a third-order in time evolution system. The function f to minimize is supposed
to be convex, continuously differentiable, with a nonempty set of minimizers.
It enters into the dynamic through its gradient. Based on this new dynamical
system, we improve the results obtained by [Attouch, Chbani, Riahi: Fast convex
optimization via a third-order in time evolution equation, Optimization 2020].
As a main result, when the damping parameter $\alpha$ satisfies $\alpha > 3$,
we show that the convergence of the values at the order 1/t3 as t goes to
infinity, as well as the convergence of the trajectories. We complement these
results by introducing into the dynamic an Hessian driven damping term, which
reduces the oscillations. In the case of a strongly convex function f, we show
an autonomous evolution system of the third order in time with an exponential
rate of convergence. All these results have natural extensions to the case of a
convex lower semicontinuous function with extended real values. Just replace f
with its Moreau envelope.",2007.03062v1
2020-08-13,Using Machine Learning to Find Ghostly Damped Ly$α$ Systems in SDSS DR14,"We report the discovery of 59 new ghostly absorbers from the Sloan Digital
Sky Survey (SDSS) Data Release 14 (DR14). These absorbers, with $z_{\rm
abs}$$\sim$$z_{\rm QSO}$, reveal no Ly$\alpha$ absorption, and they are mainly
identified through the detection of strong metal absorption lines in the
spectra. The number of previously known such systems is 30. The new systems are
found with the aid of machine learning algorithms. The spectra of 41 (out of
total of 89) absorbers also cover the Ly$\beta$ spectral region. By fitting the
damping wings of the Ly$\beta$ absorption in the stacked spectrum of 21 (out of
41) absorbers with relatively stronger Ly$\beta$ absorption, we measured an HI
column density of log$N$(HI)=21.50. This column density is 0.5dex higher than
that of the previous work. We also found that the metal absorption lines in the
stacked spectrum of the 21 ghostly absorbers with stronger Ly$\beta$ absorption
have similar properties as those in the stacked spectrum of the remaining
systems. These circumstantial evidence strongly suggest that the majority of
our ghostly absorbers are indeed DLAs.",2008.05910v1
2020-08-14,Testing Dissipative Collapse Models with a Levitated Micromagnet,"We present experimental tests of dissipative extensions of spontaneous wave
function collapse models based on a levitated micromagnet with ultralow
dissipation. The spherical micromagnet, with radius $R=27$ $\mu$m, is levitated
by Meissner effect in a lead trap at $4.2$ K and its motion is detected by a
SQUID. We perform accurate ringdown measurements on the vertical translational
mode with frequency $57$ Hz, and infer the residual damping at vanishing
pressure $\gamma/2\pi<9$ $\mu$Hz. From this upper limit we derive improved
bounds on the dissipative versions of the CSL (continuous spontaneous
localization) and the DP (Di\'{o}si-Penrose) models with proper choices of the
reference mass. In particular, dissipative models give rise to an intrinsic
damping of an isolated system with the effect parameterized by a temperature
constant; the dissipative CSL model with temperatures below 1 nK is ruled out,
while the dissipative DP model is excluded for temperatures below $10^{-13}$ K.
Furthermore, we present the first bounds on dissipative effects in a more
recent model, which relates the wave function collapse to fluctuations of a
generalized complex-valued spacetime metric.",2008.06245v2
2020-08-15,$L^1$-convergence to generalized Barenblatt solution for compressible Euler equations with time-dependent damping,"The large time behavior of entropy solution to the compressible Euler
equations for polytropic gas (the pressure $p(\rho)=\kappa\rho^{\gamma},
\gamma>1$) with time dependent damping like $-\frac{1}{(1+t)^\lambda}\rho u$
($0<\lambda<1$) is investigated. By introducing an elaborate iterative method
and using the intensive entropy analysis, it is proved that the $L^\infty$
entropy solution of compressible Euler equations with finite initial mass
converges strongly in the natural $L^1$ topology to a fundamental solution of
porous media equation (PME) with time-dependent diffusion, called by
generalized Barenblatt solution. It is interesting that the $L^1$ decay rate is
getting faster and faster as $\lambda$ increases in $(0,
\frac{\gamma}{\gamma+2}]$, while is getting slower and slower in $[
\frac{\gamma}{\gamma+2}, 1)$.",2008.06704v1
2020-08-21,Structure preserving algorithms for simulation of linearly damped acoustic systems,"Energy methods for constructing time-stepping algorithms are of increased
interest in application to nonlinear problems, since numerical stability can be
inferred from the conservation of the system energy. Alternatively, symplectic
integrators may be constructed that preserve the symplectic form of the system.
This methodology has been established for Hamiltonian systems, with numerous
applications in engineering problems. In this paper an extension of such
methods to non-conservative acoustic systems is presented. Discrete
conservation laws, equivalent to that of energy-conserving schemes, are derived
for systems with linear damping, incorporating the action of external forces.
Furthermore the evolution of the symplectic structure is analysed in the
continuous and the discrete case. Existing methods are examined and novel
methods are designed using a lumped oscillator as an elemental model. The
proposed methodology is extended to the case of distributed systems and
exemplified through a case study of a vibrating string bouncing against a rigid
obstacle.",2008.09479v1
2020-08-24,The move from Fujita to Kato type exponent for a class of semilinear evolution equations with time-dependent damping,"In this paper, we derive suitable optimal $L^p-L^q$ decay estimates, $1\leq
p\leq 2\leq q\leq \infty$, for the solutions to the $\sigma$-evolution
equation, $\sigma>1$, with scale-invariant time-dependent damping and power
nonlinearity~$|u|^p$, \[ u_{tt}+(-\Delta)^\sigma u + \frac{\mu}{1+t} u_t=
|u|^{p}, \] where $\mu>0$, $p>1$. The critical exponent $p=p_c$ for the global
(in time) existence of small data solutions to the Cauchy problem is related to
the long time behavior of solutions, which changes accordingly $\mu \in (0, 1)$
or $\mu>1$. Under the assumption of small initial data in $L^1\cap L^2$, we
find the critical exponent \[ p_c=1+ \max
\left\{\frac{2\sigma}{[n-\sigma+\sigma\mu]_+}, \frac{2\sigma}{n} \right\}
=\begin{cases} 1+ \frac{2\sigma}{[n-\sigma+\sigma\mu]_+}, \quad \mu \in (0,
1)\\ 1+ \frac{2\sigma}{n}, \quad \mu>1. \end{cases} \]
  For $\mu>1$ it is well known as Fujita type exponent, whereas for $\mu \in
(0, 1)$ one can read it as a shift of Kato exponent.",2008.10374v1
2020-09-01,"On the decay in $W^{1,\infty}$ for the 1D semilinear damped wave equation on a bounded domain","In this paper we study a semilinear wave equation with nonlinear,
time-dependent damping in one space dimension. For this problem, we prove a
well-posedness result in $W^{1,\infty}$ in the space-time domain $(0,1)\times
[0,+\infty)$. Then we address the problem of the time-asymptotic stability of
the zero solution and show that, under appropriate conditions, the solution
decays to zero at an exponential rate in the space $W^{1,\infty}$. The proofs
are based on the analysis of the corresponding semilinear system for the first
order derivatives, for which we show a contractive property of the invariant
domain.",2009.00731v2
2020-09-08,Nanomechanical damping via electron-assisted relaxation of two-level systems,"We report on measurements of dissipation and frequency noise at millikelvin
temperatures of nanomechanical devices covered with aluminum. A clear excess
damping is observed after switching the metallic layer from superconducting to
the normal state with a magnetic field. Beyond the standard model of internal
tunneling systems coupled to the phonon bath, here we consider the relaxation
to the conduction electrons together with the nature of the mechanical
dispersion laws for stressed/unstressed devices. With these key ingredients, a
model describing the relaxation of two-level systems inside the structure due
to interactions with electrons and phonons with well separated timescales
captures the data. In addition, we measure an excess 1/f-type frequency noise
in the normal state, which further emphasizes the impact of conduction
electrons.",2009.03804v3
2020-09-10,Inclination damping on Callisto,"Callisto is thought to possess a subsurface ocean, which will dissipate
energy due to obliquity tides. This dissipation should have damped any
primordial inclination within 1 Gyr - and yet Callisto retains a present-day
inclination. We argue that Callisto's inclination and eccentricity were both
excited in the relatively recent past (~0.3 Gyr). This excitation occurred as
Callisto migrated outwards according to the ""resonance-locking"" model and
passed through a 2:1 mean-motion resonance with Ganymede. Ganymede's orbital
elements were likewise excited by the same event. To explain the present-day
orbital elements we deduce a solid-body tidal k2/Q~0.05 for Callisto and a
significantly lower value for Ganymede.",2009.05002v1
2020-09-25,Sound in a system of chiral one-dimensional fermions,"We consider a system of one-dimensional fermions moving in one direction,
such as electrons at the edge of a quantum Hall system. At sufficiently long
time scales the system is brought to equilibrium by weak interactions between
the particles, which conserve their total number, energy, and momentum. Time
evolution of the system near equilibrium is described by hydrodynamics based on
the three conservation laws. We find that the system supports three sound
modes. In the low temperature limit one mode is a pure oscillation of particle
density, analogous to the ordinary sound. The other two modes involve
oscillations of both particle and entropy densities. In the presence of
disorder, the first sound mode is strongly damped at frequencies below the
momentum relaxation rate, whereas the other two modes remain weakly damped.",2009.12364v1
2020-09-30,Dynamical properties of a driven dissipative dimerized $S = 1/2$ chain,"We consider the dynamical properties of a gapped quantum spin system coupled
to the electric field of a laser, which drives the resonant excitation of
specific phonon modes that modulate the magnetic interactions. We deduce the
quantum master equations governing the time-evolution of both the lattice and
spin sectors, by developing a Lindblad formalism with bath operators providing
an explicit description of their respective phonon-mediated damping terms. We
investigate the nonequilibrium steady states (NESS) of the spin system
established by a continuous driving, delineating parameter regimes in driving
frequency, damping, and spin-phonon coupling for the establishment of
physically meaningful NESS and their related non-trivial properties. Focusing
on the regime of generic weak spin-phonon coupling, we characterize the NESS by
their frequency and wave-vector content, explore their transient and relaxation
behavior, and discuss the energy flow, the system temperature, and the critical
role of the type of bath adopted. Our study lays a foundation for the
quantitative modelling of experiments currently being designed to control
coherent many-body spin states in quantum magnetic materials.",2009.14805v2
2020-10-01,Avoiding coherent errors with rotated concatenated stabilizer codes,"Coherent errors, which arise from collective couplings, are a dominant form
of noise in many realistic quantum systems, and are more damaging than oft
considered stochastic errors. Here, we propose integrating stabilizer codes
with constant-excitation codes by code concatenation. Namely, by concatenating
an $[[n,k,d]]$ stabilizer outer code with dual-rail inner codes, we obtain a
$[[2n,k,d]]$ constant-excitation code immune from coherent phase errors and
also equivalent to a Pauli-rotated stabilizer code. When the stabilizer outer
code is fault-tolerant, the constant-excitation code has a positive
fault-tolerant threshold against stochastic errors. Setting the outer code as a
four-qubit amplitude damping code yields an eight-qubit constant-excitation
code that corrects a single amplitude damping error, and we analyze this code's
potential as a quantum memory.",2010.00538v2
2020-10-02,Parametric instability in a free evolving warped protoplanetary disc,"Warped accretion discs of low viscosity are prone to hydrodynamic instability
due to parametric resonance of inertial waves as confirmed by local
simulations. Global simulations of warped discs, using either smoothed particle
hydrodynamics (SPH) or grid-based codes, are ubiquitous but no such instability
has been seen. Here we utilize a hybrid Godunov-type Lagrangian method to study
parametric instability in global simulations of warped Keplerian discs at
unprecedentedly high resolution (up to 120 million particles). In the global
simulations, the propagation of the warp is well described by the linear
bending-wave equations before the instability sets in. The ensuing turbulence,
captured for the first time in a global simulation, damps relative orbital
inclinations and leads to a decrease in the angular momentum deficit. As a
result, the warp undergoes significant damping within one bending-wave crossing
time. Observed protoplanetary disc warps are likely maintained by companions or
aftermath of disc breaking.",2010.00862v2
2020-10-15,Dephasing in strongly disordered interacting quantum wires,"Many-body localization is a fascinating theoretical concept describing the
intricate interplay of quantum interference, i.e. localization, with many-body
interaction induced dephasing. Numerous computational tests and also several
experiments have been put forward to support the basic concept. Typically,
averages of time-dependent global observables have been considered, such as the
charge imbalance. We here investigate within the disordered spin-less Hubbard
($t-V$) model how dephasing manifests in time dependent variances of
observables. We find that after quenching a N\'eel state the local charge
density exhibits strong temporal fluctuations with a damping that is sensitive
to disorder $W$: variances decay in a power law manner, $t^{-\zeta}$, with an
exponent $\zeta(W)$ strongly varying with $W$. A heuristic argument suggests
the form, $\zeta\approx\alpha(W)\xi_\text{sp}$, where $\xi_\text{sp}(W)$
denotes the noninteracting localization length and $\alpha(W)$ characterizes
the multifractal structure of the dynamically active volume fraction of the
many-body Hilbert space. In order to elucidate correlations underlying the
damping mechanism, exact computations are compared with results from the
time-dependent Hartree-Fock approximation. Implications for experimentally
relevant observables, such as the imbalance, will be discussed.",2010.07919v1
2020-10-19,Modified EP MIMO Detection Algorithm with Deep Learning Parameters Selection,"Expectation Propagation (EP)-based Multiple-Input Multiple-Output (MIMO)
detector is regarded as a state-of-the-art MIMO detector because of its
exceptional performance. However, we find that the EP MIMO detector cannot
guarantee to achieve the optimal performance due to the empirical parameter
selection, including initial variance and damping factors. According to the
influence of the moment matching and parameter selection for the performance of
the EP MIMO detector, we propose a modified EP MIMO detector (MEPD). In order
to obtain the optimal initial variance and damping factors, we adopt a deep
learning scheme, in which we unfold the iterative processing of MEPD to
establish MEPNet for parameters training. The simulation results show that MEPD
with off-line trained parameters outperforms the original one in various MIMO
scenarios. Besides, the proposed MEPD with deep learning parameters selection
is more robust than EPD in practical scenarios.",2010.09183v2
2020-10-23,A damped point-vortex model for polar-core spin vortices in a ferromagnetic spin-1 Bose-Einstein condensate,"Ferromagnetic spin-1 Bose-Einstein condensates in the broken-axisymmetric
phase support polar-core spin vortices (PCVs), which are intimately linked to
the nonequilibrium dynamics of the system. For a purely transversely magnetized
system, the Turner point-vortex model predicts that PCVs behave like massive
charged particles interacting via a two-dimensional Coulomb potential. We test
the accuracy of the Turner model for two oppositely charged PCVs, via
comparisons with numerical simulations. While the bare Turner model shows
discrepancies with our numerical results, we find that a simple rescaling of
the PCV mass gives much better agreement. This can be explained via a
phenomenological damping arising from coupling to modes extrinsic to the
point-vortex phase space. We also identify the excitations produced following
PCV annihilation, which help elucidate recent phase ordering results. We extend
the Turner model to cases where the system is magnetized both transversally and
axially, identifying a crossover to scalar vortex dynamics for increasing
external Zeeman field.",2010.12154v1
2020-10-26,Viscous damping of chiral dynamos in the early universe,"Chiral dynamo converting asymmetry between right and left-handed leptons in
the early universe into helical magnetic field has been proposed as a possible
cosmological magnetogenesis scenario. We show that this mechanism is strongly
affected by viscous damping of primordial plasma motions excited by the dynamo.
This effect modifies the expected range of strength and correlation length of
the chiral dynamo field which could have survived till present epoch in the
voids of the Large Scale Structure. We show the range of parameters of chiral
dynamo field that may have survived in the voids is still consistent with
existing lower bounds on intergalactic magnetic field from gamma-ray
observations, but only if the right-left lepton asymmetry at the temperature
T~80 TeV is very high, close to the maximal possible value.",2010.13571v1
2020-10-28,Construction of quasimodes for non-selfadjoint operators via propagation of Hagedorn wave-packets,"We construct quasimodes for some non-selfadjoint semiclassical operators at
the boundary of the pseudo-spectrum using propagation of Hagedorn wave-packets.
Assuming that the imaginary part of the principal symbol of the operator is
non-negative and vanishes on certain points of the phase-space satisfying a
subelliptic finite-type condition, we construct quasimodes that concentrate on
these non-damped points. More generally, we apply this technique to construct
quasimodes for non-selfadjoint semiclassical perturbations of the harmonic
oscillator that concentrate on non-damped periodic orbits or invariant tori
satisfying a weak-geometric-control condition",2010.14967v5
2020-10-28,Spin-valley collective modes of the electron liquid in graphene,"We develop the theory of collective modes supported by a Fermi liquid of
electrons in pristine graphene. Under reasonable assumptions regarding the
electron-electron interaction, all the modes but the plasmon are over-damped.
In addition to the $SU(2)$ symmetric spin mode, these include also the valley
imbalance modes obeying a $U(1)$ symmetry, and a $U(2)$ symmetric valley spin
imbalance mode. We derive the interactions and diffusion constants
characterizing the over-damped modes. The corresponding relaxation rates set
fundamental constraints on graphene valley- and spintronics applications.",2010.15154v2
2020-10-29,Collisionless sound of bosonic superfluids in lower dimensions,"The superfluidity of low-temperature bosons is well established in the
collisional regime. In the collisionless regime, however, the presence of
superfluidity is not yet fully clarified, in particular in lower spatial
dimensions. Here we compare the Vlasov-Landau equation, which does not take
into account the superfluid nature of the bosonic system, with the
Andreev-Khalatnikov equations, which instead explicitly contain a superfluid
velocity. We show that recent experimental data of the sound mode in a
two-dimensional collisionless Bose gas of $^{87}$Rb atoms are in good agreement
with both theories but the sound damping is better reproduced by the Andreev
-Khalatnikov equations below the Berezinskii-Kosterlitz-Thouless critical
temperature $T_c$ while above $T_c$ the Vlasov-Landau results are closer to the
experimental ones. For one dimensional bosonic fluids, where experimental data
are not yet available, we find larger differences between the sound velocities
predicted by the two transport theories and, also in this case, the existence
of a superfluid velocity reduces the sound damping.",2010.15724v3
2020-11-02,Constraining the Halo Mass of Damped Ly$α$ Absorption Systems (DLAs) at $z=2-3.5$ using the Quasar-CMB Lensing Cross-correlation,"We study the cross correlation of damped Ly$\alpha$ systems (DLAs) and their
background quasars, using the most updated DLA catalog and the Planck 2018 CMB
lensing convergence field. Our measurement suggests that the DLA bias $b_{\rm
DLA}$ is smaller than $3.1$, corresponding to $\log(M/M_\odot h^{-1})\leq 12.3$
at a confidence of $90\%$. These constraints are broadly consistent with Alonso
et al. (2018) and previous measurements by cross-correlation between DLAs and
the Ly$\alpha$ forest (e.g. Font-Ribera et al. 2012; Perez-Rafols et al. 2018).
Further, our results demonstrate the potential of obtaining a more precise
measurement of the halo mass of high-redshift sources using next generation CMB
experiments with a higher angular resolution. The python-based codes and data
products of our analysis are available at
https://github.com/LittleLin1999/CMB-lensingxDLA.",2011.01234v1
2020-11-07,"Bresse-Timoshenko type systems with thermodiffusion effects: Well-possedness, stability and numerical results","Bresse-Timoshenko beam model with thermal, mass diffusion and theormoelastic
effects is studied. We state and prove the well-posedness of problem. The
global existence and uniqueness of the solution is proved by using the
classical Faedo-Galerkin approximations along with two a priori estimates. We
prove an exponential stability estimate for problem under an unusual
assumption, and by using a multiplier technique in two different cases, with
frictional damping in the angular rotation and with frictional damping in the
vertical displacement. In numerical parts, we first obtained a numerical scheme
for problem by $P_1$-finite element method for space discretization and
implicit Euler scheme for time discretization. Then, we showed that the
discrete energy decays, later a priori error estimates are established. Finally
, some numerical simulations are presented.",2011.03680v2
2020-11-09,Impedance Optimization for Uncertain Contact Interactions Through Risk Sensitive Optimal Control,"This paper addresses the problem of computing optimal impedance schedules for
legged locomotion tasks involving complex contact interactions. We formulate
the problem of impedance regulation as a trade-off between disturbance
rejection and measurement uncertainty. We extend a stochastic optimal control
algorithm known as Risk Sensitive Control to take into account measurement
uncertainty and propose a formal way to include such uncertainty for unknown
contact locations. The approach can efficiently generate optimal state and
control trajectories along with local feedback control gains, i.e. impedance
schedules. Extensive simulations demonstrate the capabilities of the approach
in generating meaningful stiffness and damping modulation patterns before and
after contact interaction. For example, contact forces are reduced during early
contacts, damping increases to anticipate a high impact event and tracking is
automatically traded-off for increased stability. In particular, we show a
significant improvement in performance during jumping and trotting tasks with a
simulated quadruped robot.",2011.04684v2
2020-11-12,A priori bounds for rough differential equations with a non-linear damping term,"We consider a rough differential equation with a non-linear damping drift
term: \begin{align*} dY(t) = - |Y|^{m-1} Y(t) dt + \sigma(Y(t)) dX(t),
\end{align*} where $X$ is a branched rough path of arbitrary regularity $\alpha
>0$, $m>1$ and where $\sigma$ is smooth and satisfies an $m$ and
$\alpha$-dependent growth property. We show a strong a priori bound for $Y$,
which includes the ""coming down from infinity"" property, i.e. the bound on
$Y(t)$ for a fixed $t>0$ holds uniformly over all choices of initial datum
$Y(0)$. The method of proof builds on recent work by Chandra, Moinat and Weber
on a priori bounds for the $\phi^4$ SPDE in arbitrary subcritical dimension. A
key new ingredient is an extension of the algebraic framework which permits to
derive an estimate on higher order conditions of a coherent controlled rough
path in terms of the regularity condition at lowest level.",2011.06645v4
2020-11-14,Oscillating charge currents of one-dimensional Hubbard model in an electric field,"The time evolution properties of charge current for the one-dimensional
Hubbard model in an electric field have been studied in a rigorous manner. We
find that there is a complete and orthonormal set of time-evolution states for
which the charge current can only keep zero or oscillate constantly, differing
from the possible picture of damped or over-damped Bloch oscillations due to
strong correlations. It is also found that, associated with these states, there
is a set of constant phase factors, which are uniquely determined and are very
useful on discussing the long-time evolution behaviors of the system.",2011.07220v2
2020-12-07,Damped Neutrino Oscillations in a Conformal Coupling Model,"Flavor transitions of Neutrinos with a nonstandard interaction are studied. A
scalar field is conformally coupled to matter and neutrinos. This interaction
alters the neutrino effective mass and its wavefunction leading to a damping
factor, causing deficits in the probability densities and affecting the
oscillation phase. As the matter density determines the scalar field's
behavior, we also have an indirect matter density effect on the flavor
conversion. We explain our results in the context of screening models and study
the deficit in the total flux of electron-neutrinos produced in the Sun through
the decay process and confront our results with observational data.",2012.03633v3
2020-12-10,Wakefield decay in a radially bounded plasma due to formation of electron halo,"There is a new effect that can limit the lifetime of a weakly nonlinear
wakefield in a radially bounded plasma. If the drive beam is narrow, some of
the plasma electrons fall out of the collective motion and leave the plasma
radially, forming a negatively charged halo around it. These electrons
repeatedly return to the plasma under the action of the charge separation
field, interact with the plasma wave and cause its damping. The lowest-energy
halo electrons take the energy from the wave more efficiently, because their
trajectories are bent by the plasma wave towards the regions of the strongest
acceleration. For correct accounting of the wave damping in simulations, it is
necessary and sufficient to take the simulation window twice as wide as the
plasma.",2012.05676v1
2020-12-17,Magnetic equivalent of electric superradiance: radiative damping in yttrium-iron-garnet films,"A dense system of independent oscillators, connected only by their
interaction with the same cavity excitation mode, will radiate coherently,
which effect is termed superradiance. In several cases, especially if the
density of oscillators is high, the superradiance may dominate the intrinsic
relaxation processes. This limit can be achieved, e.g., with cyclotron
resonance in two-dimensional electron gases. In those experiments, the
cyclotron resonance is coupled to the electric field of light, while the
oscillator density can be easily controlled by varying the gate voltage.
However, in the case of magnetic oscillators, to achieve the dominance of
superradiance is more tricky, as material parameters limit the oscillator
density, and the magnetic coupling to the light wave is rather small. Here we
present quasi-optical magnetic resonance experiments on thin films of yttrium
iron garnet. Due to the simplicity of experimental geometry, the intrinsic
damping and the superradiance can be easily separated in the transmission
spectra. We show that with increasing film thickness, the losses due to
coherent radiation prevail the system's internal broadening.",2012.09440v1
2020-12-21,Dissipation-driven strange metal behavior,"Anomalous metallic properties are often observed in the proximity of quantum
critical points (QCPs), with violation of the Fermi Liquid paradigm. We propose
a scenario where, due to the presence of a nearby QCP, dynamical fluctuations
of the order parameter with finite correlation length mediate a nearly
isotropic scattering among the quasiparticles over the entire Fermi surface.
This scattering produces an anomalous metallic behavior, which is extended to
the lowest temperatures by an increase of the damping of the fluctuations. We
phenomenologically identify one single parameter ruling this increasing damping
when the temperature decreases, accounting for both the linear-in-temperature
resistivity and the seemingly divergent specific heat observed, e.g., in
high-temperature superconducting cuprates and some heavy-fermion metals.",2012.11697v1
2020-12-22,Damped perturbations of systems with centre-saddle bifurcation,"An autonomous system of ordinary differential equations in the plane with a
centre-saddle bifurcation is considered. The influence of time damped
perturbations with power-law asymptotics is investigated. The particular
solutions tending at infinity to the fixed points of the limiting system are
considered. The stability of these solutions is analyzed when the bifurcation
parameter of the unperturbed system takes critical and non-critical values.
Conditions that ensure the persistence of the bifurcation in the perturbed
system are described. When the bifurcation is broken, a pair of solutions
tending to a degenerate fixed point of the limiting system appears in the
critical case. It is shown that, depending on the structure and the parameters
of the perturbations, one of these solutions can be stable, metastable or
unstable, while the other solution is always unstable.",2012.12116v1
2020-12-22,Mechanical parametric feedback-cooling for pendulum-based gravity experiments,"Gravitational forces that oscillate at audio-band frequencies are measured
with masses suspended as pendulums that have resonance frequencies even lower.
If the pendulum is excited by thermal energy or by seismic motion of the
environment, the measurement sensitivity is reduced. Conventionally, this
problem is mitigated by seismic isolation and linear damping, potentially
combined with cryogenic cooling. Here, we propose mechanical parametric cooling
of the pendulum motion during the gravitational field measurement. We report a
proof of principle demonstration in the seismic noise dominated regime and
achieve a damping factor of the pendulum motion of 5.7. We find a model system
for which mechanical parametric feedback cooling reaches the quantum mechanical
regime near the ground state. More feasible applications we anticipate in
gravitational-wave detectors.",2012.12158v2
2020-12-23,The fate of nonlinear perturbations near the QCD critical point,"The impact of the QCD critical point on the propagation of nonlinear waves
has been studied. The effects have been investigated within the scope of
second-order causal dissipative hydrodynamics by incorporating the critical
point into the equation of state, and the scaling behaviour of transport
coefficients and of thermodynamic response functions. Near the critical point,
the nonlinear waves are found to be significantly damped which may result in
the disappearance of the Mach cone effects of the away side jet. Such damping
may lead to enhancement in the fluctuations of elliptic and higher flow
coefficients. Therefore, the disappearance of Mach cone effects and the
enhancement of fluctuations in flow harmonics in the event-by-event analysis
may be considered as signals of the critical endpoint.",2012.12668v3
2020-12-28,A weakly nonlinear wave equation for damped acoustic waves with thermodynamic non-equilibrium effects,"The problem of propagating nonlinear acoustic waves is considered; the
solution to which, both with and without damping, having been obtained to-date
starting from the Navier-Stokes-Duhem equations together with the continuity
and thermal conduction equation. The novel approach reported here adopts
instead, a discontinuous Lagrangian approach, i.e. from Hamilton's principle
together with a discontinuous Lagrangian for the case of a general viscous
flow. It is shown that ensemble averaging of the equation of motion resulting
from the Euler-Lagrange equations, under the assumption of irrotational flow,
leads to a weakly nonlinear wave equation for the velocity potential: in effect
a generalisation of Kuznetsov's well known equation with an additional term due
to thermodynamic non-equilibrium effects.",2012.14399v2
2020-12-28,Reliability optimization of friction-damped systems using nonlinear modes,"A novel probabilistic approach for the design of mechanical structures with
friction interfaces is proposed. The objective function is defined as the
probability that a specified performance measure of the forced vibration
response is achieved subject to parameter uncertainties. The practicability of
the approach regarding the extensive amount of required design evaluations is
strictly related to the computational efficiency of the nonlinear dynamic
analysis. Therefore, it is proposed to employ a recently developed parametric
reduced order model (ROM) based on nonlinear modes of vibration, which can
facilitate a decrease of the computational burden by several orders of
magnitude. The approach was applied to a rotationally periodic assembly of a
bladed disk with underplatform friction dampers. The robustness of the optimum
damper design was significantly improved compared to the deterministic
approach, taking into account uncertainties in the friction coefficient, the
excitation level and the linear damping. Moreover, a scale invariance for
piecewise linear contact constraints is proven, which can be very useful for
the reduction of the numerical effort for the analysis of such systems.",2012.14466v1
2021-01-04,Fast flavor oscillations in dense neutrino media with collisions,"We investigate the impact of the nonzero neutrino splitting and elastic
neutrino-nucleon collisions on fast neutrino oscillations. Our calculations
confirm that a small neutrino mass splitting and the neutrino mass hierarchy
have very little effect on fast oscillation waves. We also demonstrate
explicitly that fast oscillations remain largely unaffected for the
time/distance scales that are much smaller than the neutrino mean free path but
are damped on larger scales. This damping originates from both the direct
modification of the dispersion relation of the oscillation waves in the
neutrino medium and the flattening of the neutrino angular distributions over
time. Our work suggests that fast neutrino oscillation waves produced near the
neutrino sphere can propagate essentially unimpeded which may have
ramifications in various aspects of the supernova physics.",2101.01278v2
2021-01-15,Efficient Spin-Orbit Torque Generation in Semiconducting WTe2 with Hopping Transport,"Spin-orbit torques (SOTs) from transition metal dichalcogenides systems
(TMDs) in conjunction with ferromagnetic materials are recently attractive in
spintronics for their versatile features. However, most of the previously
studied crystalline TMDs are prepared by mechanical exfoliation, which limits
their potentials for industrial applications. Here we show that amorphous WTe2
heterostructures deposited by magnetron sputtering possess a sizable
damping-like SOT efficiency {\xi}_DL^WTe2 ~ 0.20 and low damping constant
{\alpha} = 0.009/pm0.001. Only an extremely low critical switching current
density J_c ~ 7.05\times10^9 A/m^2 is required to achieve SOT-driven
magnetization switching. The SOT efficiency is further proved to depend on the
W and Te relative compositions in the co-sputtered W_100-xTe_x samples, from
which a sign change of {\xi}_DL^WTe2 is observed. Besides, the electronic
transport in amorphous WTe2 is found to be semiconducting and is governed by a
hopping mechanism. With the above advantages and rich tunability, amorphous and
semiconducting WTe2 serves as a unique SOT source for future spintronics
applications.",2101.06047v1
2021-01-25,A modified Kačanov iteration scheme with application to quasilinear diffusion models,"The classical Ka\v{c}anov scheme for the solution of nonlinear variational
problems can be interpreted as a fixed point iteration method that updates a
given approximation by solving a linear problem in each step. Based on this
observation, we introduce a modified Ka\v{c}anov method, which allows for
(adaptive) damping, and, thereby, to derive a new convergence analysis under
more general assumptions and for a wider range of applications. For instance,
in the specific context of quasilinear diffusion models, our new approach does
no longer require a standard monotonicity condition on the nonlinear diffusion
coefficient to hold. Moreover, we propose two different adaptive strategies for
the practical selection of the damping parameters involved.",2101.10137v3
2021-01-29,One-parameter robust global frequency estimator for slowly varying amplitude and noisy oscillations,"Robust online estimation of oscillation frequency belongs to classical
problems of system identification and adaptive control. The given harmonic
signal can be noisy and with varying amplitude at the same time, as in the case
of damped vibrations. A novel robust frequency-estimation algorithm is proposed
here, motivated by the existing globally convergent frequency estimator. The
advantage of the proposed estimator is in requiring one design parameter only
and being robust against measurement noise and initial conditions. The proven
global convergence also allows for slowly varying amplitudes, which is useful
for applications with damped oscillations or additionally shaped harmonic
signals. The proposed analysis is simple and relies on an averaging theory of
the periodic signals. Our results show an exponential convergence rate, which
depends, analytically, on the sought frequency, adaptation gain and oscillation
amplitude. Numerical and experimental examples demonstrate the robustness and
efficiency of the proposed estimator for signals with slowly varying amplitude
and noise.",2101.12497v3
2021-01-29,Quarter and Full Car Models Optimisation of Passive and Active Suspension System Using Genetic Algorithm,"This study evaluates a suspension design of a passenger car to obtain maximum
rider's comfort when the vehicle is subjected to different road profile or road
surface condition. The challenge will be on finding a balance between the
rider's comfort and vehicle handling to optimize design parameters. The study
uses a simple passive suspension system and an active suspension model
integrated with a pneumatic actuator controlled by proportional integral
derivative (PID) controller in both quarter car and full car models having a
different degree of freedoms (DOF) and increasing degrees of complexities. The
quarter car considered as a 2-DOF model, while the full car model is a 7-DOF
model. The design process set to optimise the spring stiffnesses, damping
coefficients and actuator PID controller gains. For optimisation, the research
featured genetic algorithm optimisation technique to obtain a balanced response
of the vehicle as evaluated from the displacement, velocity and acceleration of
sprung and unsprung masses along with different human comfort and vehicle
performance criteria. The results revealed that the active suspension system
with optimised spring stiffness, damping coefficients and PID gains
demonstrated the superior riding comfort and road holding compared to a passive
suspension system.",2101.12629v1
2021-02-01,Performance and limits of feedback cooling methods for levitated oscillators: a direct comparison,"Cooling the centre-of-mass motion is an important tool for levitated
optomechanical systems, but it is often not clear which method can practically
reach lower temperatures for a particular experiment. We directly compare the
parametric and velocity feedback damping methods, which are used extensively
for cooling the motion of single trapped particles in a range of traps. By
performing experiments on the same particle, and with the same detection
system, we demonstrate that velocity damping cools the oscillator to lower
temperatures and is more resilient to imperfect experimental conditions. We
show that these results are consistent with analytical limits as well as
numerical simulations that include experimental noise.",2102.01060v3
2021-02-16,A homogenized damping model for the propagation of elastic wave in a porous solid,"This paper develops an averaging technique based on the combination of the
eigenfunction expansion method and the collaboration method to investigate the
multiple scattering effect of the SH wave propagation in a porous medium. The
semi-analytical averaging technique is conducted using Monto Carlo method to
understand the macroscopic dispersion and attenuation phenomena of the stress
wave propagation in a porous solid caused by the multiple scattering effects.
The averaging technique is verified by finite element analysis. Finally, a
simple homogenized elastic model with damping is proposed to describe the
macroscopic dispersion and attenuation effects of SH waves in porous media.",2102.08334v1
2021-02-11,Semi-linear Poisson-mediated Flocking in a Cucker-Smale Model,"We propose a family of compactly supported parametric interaction functions
in the general Cucker-Smale flocking dynamics such that the mean-field
macroscopic system of mass and momentum balance equations with non-local
damping terms can be converted from a system of partial integro-differential
equations to an augmented system of partial differential equations in a compact
set. We treat the interaction functions as Green's functions for an operator
corresponding to a semi-linear Poisson equation and compute the density and
momentum in a translating reference frame, i.e. one that is taken in reference
to the flock's centroid. This allows us to consider the dynamics in a fixed,
flock-centered compact set without loss of generality. We approach the
computation of the non-local damping using the standard finite difference
treatment of the chosen differential operator, resulting in a tridiagonal
system which can be solved quickly.",2102.08772v1
2021-02-22,Robust formation of nanoscale magnetic skyrmions in easy-plane thin film multilayers with low damping,"We experimentally demonstrate the formation of room-temperature skyrmions
with radii of about 25\,nm in easy-plane anisotropy multilayers with
interfacial Dzyaloshinskii-Moriya interaction (DMI). We detect the formation of
individual magnetic skyrmions by magnetic force microscopy and find that the
skyrmions are stable in out-of-plane fields up to about 200 mT. We determine
the interlayer exchange coupling as well as the strength of the interfacial
DMI. Additionally, we investigate the dynamic microwave spin excitations by
broadband magnetic resonance spectroscopy. From the uniform Kittel mode we
determine the magnetic anisotropy and low damping $\alpha_{\mathrm{G}} < 0.04$.
We also find clear magnetic resonance signatures in the non-uniform (skyrmion)
state. Our findings demonstrate that skyrmions in easy-plane multilayers are
promising for spin-dynamical applications.",2102.11117v1
2021-02-22,Asymptotics of solutions with a compactness property for the nonlinear damped Klein-Gordon equation,"We consider the nonlinear damped Klein-Gordon equation \[
\partial_{tt}u+2\alpha\partial_{t}u-\Delta u+u-|u|^{p-1}u=0 \quad \text{on} \ \
[0,\infty)\times \mathbb{R}^N \] with $\alpha>0$, $2 \le N\le 5$ and energy
subcritical exponents $p>2$. We study the behavior of solutions for which it is
supposed that only one nonlinear object appears asymptotically for large times,
at least for a sequence of times.
  We first prove that the nonlinear object is necessarily a bound state. Next,
we show that when the nonlinear object is a non-degenerate state or a
degenerate excited state satisfying a simplicity condition, the convergence
holds for all positive times, with an exponential or algebraic rate
respectively. Last, we provide an example where the solution converges exactly
at the rate $t^{-1}$ to the excited state.",2102.11178v1
2021-02-23,The tipping effect of delayed interventions on the evolution of COVID-19 incidence,"We combine infectious disease transmission and the non-pharmaceutical
intervention (NPI) response to disease incidence into one closed model
consisting of two coupled delay differential equations for the incidence rate
and the time-dependent reproduction number. The model contains three free
parameters, the initial reproduction number, the intervention strength, and the
response delay relative to the time of infection. The NPI response is modeled
by assuming that the rate of change of the reproduction number is proportional
to the negative deviation of the incidence rate from an intervention threshold.
This delay dynamical system exhibits damped oscillations in one part of the
parameter space, and growing oscillations in another, and these are separated
by a surface where the solution is a strictly periodic nonlinear oscillation.
For parameters relevant for the COVID-19 pandemic, the tipping transition from
damped to growing oscillations occurs for response delays of the order of one
week, and suggests that effective control and mitigation of successive epidemic
waves cannot be achieved unless NPIs are implemented in a precautionary manner,
rather than merely as a response to the present incidence rate.",2102.11750v1
2021-03-01,Dynamics of a ring of three unidirectionally coupled Duffing oscillators with time-dependent damping,"We study dynamics of a ring of three unidirectionally coupled double-well
Duffing oscillators for three different values of the damping coefficient:
fixed dumping, proportional to time, and inversely proportional to time. The
dynamics in all cases is analyzed through time series, Fourier and Hilbert
transforms, Poincar\'e sections, as well as bifurcation diagrams and Lyapunov
exponents with respect to the coupling strength. In the first case, we observe
a well-known route from a stable steady state to hyperchaos through Hopf
bifurcation and a series of torus bifurcations, as the coupling strength is
increased. In the second case, the system is highly dissipative and converges
into one of stable equilibria. Finally, in the third case, transient toroidal
hyperchaos takes place.",2103.01297v1
2021-03-06,Deep learning stochastic processes with QCD phase transition,"It is non-trivial to recognize phase transitions and track dynamics inside a
stochastic process because of its intrinsic stochasticity. In this paper, we
employ the deep learning method to classify the phase orders and predict the
damping coefficient of fluctuating systems under Langevin's description. As a
concrete set-up, we demonstrate this paradigm for the scalar condensation in
QCD matter near the critical point, in which the order parameter of chiral
phase transition can be characterized in a $1+1$-dimensional Langevin equation
for $\sigma$ field. In a supervised learning manner, the Convolutional Neural
Networks(CNNs) accurately classify the first-order phase transition and
crossover based on $\sigma$ field configurations with fluctuations. Noise in
the stochastic process does not significantly hinder the performance of the
well-trained neural network for phase order recognition. For mixed dynamics
with diverse dynamical parameters, we further devise and train the machine to
predict the damping coefficients $\eta$ in a broad range. The results show that
it is robust to extract the dynamics from the bumpy field configurations.",2103.04090v1
2021-03-12,Longitudinal Modes of Bunched Beams with Weak Space Charge,"Longitudinal collective modes of a bunched beam with a repulsive inductive
impedance (the space charge below transition or the chamber inductance above
it) are analytically described by means of reduction of the linearized Vlasov
equation to a parameter-less integral equation. For any multipolarity, the
discrete part of the spectrum is found to consist of infinite number of modes
with real tunes, which limit point is the incoherent zero-amplitude frequency.
In other words, notwithstanding the RF bucket nonlinearity and potential well
distortion, the Landau damping is lost. Hence, even a tiny coupled-bunch
interaction makes the beam unstable; such growth rates for all the modes are
analytically obtained for arbitrary multipolarity. In practice, however, the
finite threshold of this loss of Landau damping is set either by the
high-frequency impedance roll-off or intrabeam scattering. Above the threshold,
growth of the leading collective mode should result in persistent nonlinear
oscillations.",2103.07523v4
2021-03-13,Microscopic Calculation of Spin Torques in Textured Antiferromagnets,"A microscopic calculation is presented for the spin-transfer torques (STT)
and damping torques in metallic antiferromagnets (AF). It is found that the
sign of the STT is opposite to that in ferromagnets because of the AF transport
character, and the current-to-STT conversion factor is enhanced near the AF gap
edge. The dissipative torque parameter $\beta_n$ and the damping parameter
$\alpha_n$ for the N\'eel vector arise from spin relaxation of electrons.
Physical consequences are demonstrated for the AF domain wall motion using
collective coordinates, and some similarities to the ferromagnetic case are
pointed out such as intrinsic pinning and the specialty of $\alpha_n =
\beta_n$. A recent experiment on a ferrimagnetic GdFeCo near its
angular-momentum compensation temperature is discussed.",2103.07634v1
2021-03-13,"Dissipative structures in a parametrically driven dissipative lattice: chimera, localized disorder, continuous-wave, and staggered state","Discrete dissipative coupled systems exhibit complex behavior such as chaos,
spatiotemporal intermittence, chimera among others. We construct and
investigate chimera states, in the form of confined stationary and dynamical
states in a chain of parametrically driven sites with onsite damping and cubic
nonlinearity. The system is modeled by the respective discrete parametrically
driven damped nonlinear Schrodinger equation. Chimeras feature quasi-periodic
or chaotic dynamic in the filled area, quantified by time dependence of the
total norm (along with its power spectrum), and by the largest Lyapunov
exponent. Systematic numerical simulations, in combination with some analytical
results, reveal regions in the parameter space populated by stable localized
states of different types. A phase transition from the stationary disorder
states to spatially confined dynamical chaotic one is identified. Essential
parameters of the system are the strength and detuning of the forcing, as well
as the lattice's coupling constant.",2103.07748v1
2021-03-16,On an inverse problem of nonlinear imaging with fractional damping,"This paper considers the attenuated Westervelt equation in pressure
formulation. The attenuation is by various models proposed in the literature
and characterised by the inclusion of non-local operators that give power law
damping as opposed to the exponential of classical models. The goal is the
inverse problem of recovering a spatially dependent coefficient in the
equation, the parameter of nonlinearity $\kappa(x)$, in what becomes a
nonlinear hyperbolic equation with nonlocal terms. The overposed measured data
is a time trace taken on a subset of the domain or its boundary. We shall show
injectivity of the linearised map from $\kappa$ to the overposed data used to
recover it and from this basis develop and analyse Newton-type schemes for its
effective recovery.",2103.08965v1
2021-03-17,Tunable exciton-optomechanical coupling in suspended monolayer MoSe2,"The strong excitonic effect in monolayer transition metal dichalcogenide
(TMD) semiconductors has enabled many fascinating light-matter interaction
phenomena. Examples include strongly coupled exciton-polaritons and nearly
perfect atomic monolayer mirrors. The strong light-matter interaction also
opens the door for dynamical control of mechanical motion through the exciton
resonance of monolayer TMDs. Here we report the observation of
exciton-optomechanical coupling in a suspended monolayer MoSe2 mechanical
resonator. By moderate optical pumping near the MoSe2 exciton resonance, we
have observed optical damping and anti-damping of mechanical vibrations as well
as the optical spring effect. The exciton-optomechanical coupling strength is
also gate-tunable. Our observations can be understood in a model based on
photothermal backaction and gate-induced mirror symmetry breaking in the device
structure. The observation of gate-tunable exciton-optomechanical coupling in a
monolayer semiconductor may find applications in nanoelectromechanical systems
(NEMS) and in exciton-optomechanics.",2103.09897v2
2021-03-18,Perturbation theory for solitons of the Fokas--Lenells equation : Inverse scattering transform approach,"We present perturbation theory based on the inverse scattering transform
method for solitons described by an equation with the inverse linear dispersion
law $\omega\sim 1/k$, where $\omega$ is the frequency and $k$ is the wave
number, and cubic nonlinearity. This equation, first suggested by Davydova and
Lashkin for describing dynamics of nonlinear short-wavelength ion-cyclotron
waves in plasmas and later known as the Fokas--Lenells equation, arises from
the first negative flow of the Kaup--Newell hierarchy. Local and nonlocal
integrals of motion, in particular the energy and momentum of nonlinear
ion-cyclotron waves, are explicitly expressed in terms of the discrete
(solitonic) and continuous (radiative) scattering data. Evolution equations for
the scattering data in the presence of a perturbation are presented. Spectral
distributions in the wave number domain of the energy emitted by the soliton in
the presence of a perturbation are calculated analytically for two cases: (i)
linear damping that corresponds to Landau damping of plasma waves, and (ii)
multiplicative noise which corresponds to thermodynamic fluctuations of the
external magnetic field (thermal noise) and/or the presence of a weak plasma
turbulence.",2103.10090v1
2021-04-07,Indirect stability of a multidimensional coupled wave equations with one locally boundary fractional damping,"In this work, we consider a system of multidimensional wave equations coupled
by velocities with one localized fractional boundary damping. First, using a
general criteria of Arendt- Batty, by assuming that the boundary control region
satisfy some geometric conditions, under the equality speed propagation and the
coupling parameter of the two equations is small enough, we show the strong
stability of our system in the absence of the compactness of the resolvent. Our
system is not uniformly stable in general since it is the case of the interval.
Hence, we look for a polynomial decay rate for smooth initial data for our
system by applying a frequency domain approach combining with a multiplier
method. Indeed, by assuming that the boundary control region satisfy some
geometric conditions and the waves propagate with equal speed and the coupling
parameter term is small enough, we establish a polynomial energy decay rate for
smooth solutions, which depends on the order of the fractional derivative.",2104.03389v1
2021-04-10,Free and forced vibrations of damped locally-resonant sandwich beams,"This paper addresses the dynamics of locally-resonant sandwich beams, where
multi-degree-of-freedom viscously-damped resonators are periodically
distributed within the core matrix. Using an equivalent single-layer Timoshenko
beam model coupled with mass-spring-dashpot subsystems representing the
resonators, two solution methods are presented. The first is a direct
integration method providing the exact frequency response under arbitrary
loads. The second is a complex modal analysis approach obtaining exact modal
impulse and frequency response functions, upon deriving appropriate
orthogonality conditions for the complex modes. The challenging issue of
calculating all eigenvalues, without missing anyone, is solved applying a
recently-introduced contour-integral algorithm to a characteristic equation
built as determinant of an exact frequency-response matrix, whose size is $4
\times 4$ regardless of the number of resonators. Numerical applications prove
exactness and robustness of the proposed solutions.",2104.04870v1
2021-04-15,Flexural wave modulation and mitigation in airfoils using acoustic black holes,"This study introduces a framework for the design and implementation of
acoustic black holes (ABHs) in airfoils. A generalized multi-parameter
damped-ABH generation function is mapped onto NACA series airfoils.
Representative geometries and a uniformly distributed baseline, all with the
same mass of structure and damping are fabricated using multi-material PolyJet
3D printing. Laser Doppler vibrometer measurements along the airfoil chord in
response to a broadband 0.1 - 12 kHz excitation show a decrease in trailing
edge vibrations by as much as 10 dB, a broadband 5 dB reduction across the
entire chord as well as substantial spatial and temporal modulation of flexural
waves by ABH-embedded foils. Finite element analysis (FEA) models are developed
and validated based on the measured data. Furthermore, a parametric FEA study
is performed on a set of comparable designs to elucidate the scope of
modulation achievable. These findings are applicable to trailing-edge noise
reduction, flow control, structural enhancement and energy harvesting for
airfoils.",2104.07374v1
2021-04-20,Entanglement robustness via spatial deformation of identical particle wave functions,"We address the problem of entanglement protection against surrounding noise
by a procedure suitably exploiting spatial indistinguishability of identical
subsystems. To this purpose, we take two initially separated and entangled
identical qubits interacting with two independent noisy environments. Three
typical models of environments are considered: amplitude damping channel, phase
damping channel and depolarizing channel. After the interaction, we deform the
wave functions of the two qubits to make them spatially overlap before
performing spatially localized operations and classical communication (sLOCC)
and eventually computing the entanglement of the resulting state. This way, we
show that spatial indistinguishability of identical qubits can be utilized
within the sLOCC operational framework to partially recover the quantum
correlations spoiled by the environment. A general behavior emerges: the higher
the spatial indistinguishability achieved via deformation, the larger the
amount of recovered entanglement.",2104.09714v1
2021-04-22,Dissipation and fluctuations in elongated bosonic Josephson junctions,"We investigate the dynamics of bosonic atoms in elongated Josephson
junctions. We find that these systems are characterized by an intrinsic
coupling between the Josephson mode of macroscopic quantum tunneling and the
sound modes. This coupling of Josephson and sound modes gives rise to a damped
and stochastic Langevin dynamics for the Josephson degree of freedom. From a
microscopic Lagrangian, we deduce and investigate the damping coefficient and
the stochastic noise, which includes thermal and quantum fluctuations. Finally,
we study the time evolution of relative-phase and population-imbalance
fluctuations of the Josephson mode and their oscillating thermalization to
equilibrium.",2104.11259v2
2021-04-24,The large-period limit for equations of discrete turbulence,"We consider the damped/driven cubic NLS equation on the torus of a large
period $L$ with a small nonlinearity of size $\lambda$, a properly scaled
random forcing and dissipation. We examine its solutions under the subsequent
limit when first $\lambda\to 0$ and then $L\to \infty$. The first limit, called
the limit of discrete turbulence, is known to exist, and in this work we study
the second limit $L\to\infty$ for solutions to the equations of discrete
turbulence. Namely, we decompose the solutions to formal series in amplitude
and study the second order truncation of this series. We prove that the energy
spectrum of the truncated solutions becomes close to solutions of a
damped/driven nonlinear wave kinetic equation. Kinetic nonlinearity of the
latter is similar to that which usually appears in works on wave turbulence,
but is different from it (in particular, it is non-autonomous). Apart from
tools from analysis and stochastic analysis, our work uses two powerful results
from the number theory.",2104.11967v2
2021-05-13,Global Solutions of Three-dimensional Inviscid MHD Fluids with Velocity Damping in Horizontally Periodic Domains,"The \emph{two-dimensional} (2D) existence result of global(-in-time)
solutions for the motion equations of incompressible, inviscid, non-resistive
magnetohydrodynamic (MHD) fluids with velocity damping had been established in
[Wu--Wu--Xu, SIAM J. Math. Anal. 47 (2013), 2630--2656]. This paper further
studies the existence of global solutions for the \emph{three-dimensional} (a
dimension of real world) initial-boundary value problem in a horizontally
periodic domain with finite height. Motivated by the multi-layers energy method
introduced in [Guo--Tice, Arch. Ration. Mech. Anal. 207 (2013), 459--531], we
develop a new type of two-layer energy structure to overcome the difficulty
arising from three-dimensional nonlinear terms in the MHD equations, and thus
prove the initial-boundary value problem admits a unique global solution.
Moreover the solution has the exponential decay-in-time around some rest state.
Our two-layer energy structure enjoys two features: (1) the lower-order energy
(functional) can not be controlled by the higher-order energy. (2) under the
\emph{a priori} smallness assumption of lower-order energy, we first close the
higher-order energy estimates, and then further close the lower-energy
estimates in turn.",2105.06080v1
2021-05-13,On Inhibition of Rayleigh--Taylor Instability by Horizontal Magnetic Field in an Inviscid MHD Fluid with Velocity Damping,"It is still an open problem whether the inhibition phenomenon of
Rayleigh--Taylor (RT) instability by horizontal magnetic field can be
mathematically proved in a non-resistive magnetohydrodynamic (MHD) fluid in a
two-dimensional (2D) horizontal slab domain, since it had been roughly verified
by a 2D linearized motion equations in 2012 \cite{WYC}. In this paper, we find
that this inhibition phenomenon can be rigorously verified in the
inhomogeneous, incompressible, inviscid case with velocity damping. More
precisely, there exists a critical number $m_{\rm{C}}$ such that if the
strength $|m|$ of horizontal magnetic field is bigger than $m_{\rm{C}}$, then
the small perturbation solution around the magnetic RT equilibrium state is
exponentially stable in time. Our result is also the first mathematical one
based on the nonlinear motion equations for the proof of inhibition of flow
instabilities by a horizontal magnetic field in a horizontal slab domain. In
addition, we also provide a nonlinear instability result for the case $|m|\in
[0,m_{\rm{C}})$. Our instability result presents that horizontal magnetic field
can not inhibit the RT instability, if it's strength is to small.",2105.06472v1
2021-05-14,"Quantum Langevin dynamics of a charged particle in a magnetic field : Response function, position-velocity and velocity autocorrelation functions","We use the Quantum Langevin equation as a starting point to study the
response function, the position-velocity correlation function and the velocity
autocorrelation function of a charged Quantum Brownian particle in the presence
of a magnetic field and linearly coupled to a heat bath via position
coordinate. We study two bath models -- the Ohmic bath model and the Drude bath
model -- and make a detailed comparison in various time-temperature regimes.
For both bath models there is a competition between the cyclotron frequency and
the viscous damping rate giving rise to a transition from an oscillatory to a
monotonic behaviour as the damping rate is increased. In the zero point
fluctuation dominated low temperature regime, non-trivial noise correlations
lead to some interesting features in this transition. We study the role of the
memory time scale which comes into play in the Drude model and study the effect
of this additional time scale. We discuss the experimental implications of our
analysis in the context of experiments in cold ions.",2105.07036v2
2021-05-18,Partially dissipative hyperbolic systems in the critical regularity setting : The multi-dimensional case,"We are concerned with quasilinear symmetrizable partially dissipative
hyperbolic systems in the whole space $\mathbb{R}^d$ with $d\geq2$. Following
our recent work [10] dedicated to the one-dimensional case, we establish the
existence of global strong solutions and decay estimates in the critical
regularity setting whenever the system under consideration satisfies the
so-called (SK) (for Shizuta-Kawashima) condition. Our results in particular
apply to the compressible Euler system with damping in the velocity equation.
Compared to the papers by Kawashima and Xu [27, 28] devoted to similar issues,
our use of hybrid Besov norms with different regularity exponents in low and
high frequency enable us to pinpoint optimal smallness conditions for global
well-posedness and to get more accurate information on the qualitative
properties of the constructed solutions. A great part of our analysis relies on
the study of a Lyapunov functional in the spirit of that of Beauchard and
Zuazua in [2]. Exhibiting a damped mode with faster time decay than the whole
solution also plays a key role.",2105.08333v1
2021-05-24,Response Dynamics of Alkali Metal-Noble Gas Hybrid Trispin System,"With numerical calculation of coupled Bloch equations, we have simulated the
spin dynamics of nuclear magnetic resonance gyroscope based on alkali
metal-noble gas hybrid trispin system. From the perspective of damping harmonic
oscillator, a thorough analysis of the response dynamics is demonstrated. The
simulation results shows a linear increasing response of gyroscope signal while
the noblge gas nuclear spin magnetization and alkali atomic spin lifetime
parameters are at the over damping condition. An upper limit of response is
imposed on the NMR gyroscope signal due to the inherent dynamics of the hybrid
trispin system. The results agrees with present available experimental results
and provide useful guidings for future experiments.",2105.11124v2
2021-05-26,Temperature Damping of Magneto-Intersubband Resistance Oscillations in Magnetically Entangled Subbands,"Magneto-intersubband resistance oscillations (MISO) of highly mobile 2D
electrons in symmetric GaAs quantum wells with two populated subbands are
studied in magnetic fields tilted from the normal to the 2D electron layer at
different temperatures $T$. Decrease of MISO amplitude with temperature
increase is observed. At moderate tilts the temperature decrease of MISO
amplitude is consistent with decrease of Dingle factor due to reduction of
quantum electron lifetime at high temperatures. At large tilts new regime of
strong MISO suppression with the temperature is observed. Proposed model
relates this suppression to magnetic entanglement between subbands, leading to
beating in oscillating density of states. The model yields corresponding
temperature damping factor: $A_{MISO}(T)=X/\sinh(X)$, where $X=2\pi^2kT\delta
f$ and $\delta f$ is difference frequency of oscillations of density of states
in two subbands. This factor is in agreement with experiment. Fermi liquid
enhancement of MISO amplitude is observed.",2105.12263v1
2021-05-26,A statistical study of propagating MHD kink waves in the quiescent corona,"The Coronal Multi-channel Polarimeter (CoMP) has opened up exciting
opportunities to probe transverse MHD waves in the Sun's corona. The archive of
CoMP data is utilised to generate a catalogue of quiescent coronal loops that
can be used for studying propagating kink waves. The catalogue contains 120
loops observed between 2012-2014. This catalogue is further used to undertake a
statistical study of propagating kink waves in the quiet regions of the solar
corona, investigating phase speeds, loop lengths, footpoint power ratio and
equilibrium parameter values. The statistical study enables us to establish the
presence of a relationship between the rate of damping and the length of the
coronal loop, with longer coronal loops displaying weaker wave damping. We
suggest the reason for this behaviour is related to a decreasing average
density contrast between the loop and ambient plasma as loop length increases.
The catalogue presented here will provide the community with the foundation for
the further study of propagating kink waves in the quiet solar corona.",2105.12451v1
2021-05-31,Machine-Learning Non-Conservative Dynamics for New-Physics Detection,"Energy conservation is a basic physics principle, the breakdown of which
often implies new physics. This paper presents a method for data-driven ""new
physics"" discovery. Specifically, given a trajectory governed by unknown
forces, our Neural New-Physics Detector (NNPhD) aims to detect new physics by
decomposing the force field into conservative and non-conservative components,
which are represented by a Lagrangian Neural Network (LNN) and a universal
approximator network (UAN), respectively, trained to minimize the force
recovery error plus a constant $\lambda$ times the magnitude of the predicted
non-conservative force. We show that a phase transition occurs at $\lambda$=1,
universally for arbitrary forces. We demonstrate that NNPhD successfully
discovers new physics in toy numerical experiments, rediscovering friction
(1493) from a damped double pendulum, Neptune from Uranus' orbit (1846) and
gravitational waves (2017) from an inspiraling orbit. We also show how NNPhD
coupled with an integrator outperforms previous methods for predicting the
future of a damped double pendulum.",2106.00026v2
2021-06-06,Non-delay limit in the energy space from the nonlinear damped wave equation to the nonlinear heat equation,"We consider a singular limit problem from the damped wave equation with a
power type nonlinearity to the corresponding heat equation. We call our
singular limit problem non-delay limit. Our proofs are based on the argument
for non-relativistic limit from the nonlinear Klein-Gordon equation to the
nonlinear Schr\""{o}dinger equation by the second author, Nakanishi, and Ozawa
(2002), Nakanishi (2002), and Masmoudi and Nakanishi (2002). We can obtain
better results for the non-delay limit problem than that for the
non-relativistic limit problem due to the dissipation property. More precisely,
we get the better convergence rate of the $L^2$-norm and we also obtain the
global-in-time uniform convergence of the non-delay limit in the
$L^2$-supercritical case.",2106.03030v1
2021-06-10,Symmetrical emergence of extreme events at multiple regions in a damped and driven velocity-dependent mechanical system,"In this work, we report the emergence of extreme events in a damped and
driven velocity-dependent mechanical system. We observe that the extreme events
emerge at multiple points. We further notice that the extreme events occur
symmetrically in both positive and negative values at all the points of
emergence. We statistically confirm the emergence of extreme events by plotting
the probability distribution function of peaks and interevent intervals. We
also determine the mechanism behind the emergence of extreme events at all the
points and classify these points into two categories depending on the region at
which the extreme events emerge. Finally, we plot the two parameter diagram in
order to have a complete overview of the system.",2106.05510v2
2021-06-11,On global existence for semilinear wave equations with spacedependent critical damping,"The global existence for semilinear wave equations with space-dependent
critical damping $\partial_t^2u-\Delta u+\frac{V_0}{|x|}\partial_t u=f(u)$ in
an exterior domain is dealt with, where $f(u)=|u|^{p-1}u$ and $f(u)=|u|^p$ are
in mind. Existence and non-existence of global-in-time solutions are discussed.
To obtain global existence, a weighted energy estimate for the linear problem
is crucial. The proof of such a weighted energy estimate contains an
alternative proof of energy estimates established by
Ikehata--Todorova--Yordanov [J.\ Math.\ Soc.\ Japan (2013), 183--236] but this
clarifies the precise independence of the location of the support of initial
data. The blowup phenomena is verified by using a test function method with
positive harmonic functions satisfying the Dirichlet boundary condition.",2106.06107v1
2021-06-13,Invariant measures for a stochastic nonlinear and damped 2D Schrödinger equation,"We consider a stochastic nonlinear defocusing Schr\""{o}dinger equation with
zero-order linear damping, where the stochastic forcing term is given by a
combination of a linear multiplicative noise in the Stratonovich form and a
nonlinear noise in the It\^o form. We work at the same time on compact
Riemannian manifolds without boundary and on relatively compact smooth domains
with either the Dirichlet or the Neumann boundary conditions, always in
dimension 2. We construct a martingale solution using a modified
Faedo-Galerkin's method, following arXiv:1707.05610. Then by means of the
Strichartz estimates deduced from arXiv:math/0609455 but modified for our
stochastic setting we show the pathwise uniqueness of solutions. Finally, we
prove the existence of an invariant measure by means of a version of the
Krylov-Bogoliubov method, which involves the weak topology, as proposed by
Maslowski and Seidler. This is the first result of this type for stochastic NLS
on compact Riemannian manifolds without boundary and on relatively compact
smooth domains even for an additive noise. Some remarks on the uniqueness in a
particular case are provided as well.",2106.07043v4
2021-06-13,Blow-up and lifespan estimates for solutions to the weakly coupled system of nonlinear damped wave equations outside a ball,"In this paper, we consider the initial-boundary value problems with several
fundamental boundary conditions (the Dirichlet/Neumann/Robin boundary
condition) for the multi-component system of semi-linear classical damped wave
equations outside a ball. By applying a test function approach with a judicious
choice of test functions, which approximates the harmonic functions being
subject to these boundary conditions on $\partial \Omega$, simultaneously we
have succeeded in proving the blow-up result in a finite time as well as in
catching the sharp upper bound of lifespan estimates for small solutions in two
and higher spatial dimensions. Moreover, such kind of these results will be
discussed in one-dimensional case at the end of this work.",2106.07050v2
2021-06-14,An Overview of Energy-Optimal Impedance Control of Cooperative Robot Manipulators,"An impedance-based control scheme is introduced for cooperative manipulators
grasping a rigid load. The position and orientation of the load are to be
maintained close to a desired trajectory, trading off tracking accuracy by low
energy consumption and maintaining stability. To this end, the augmented
dynamics of the robots, their actuators and the load is formed, and an
impedance control is adopted. A virtual control strategy is used to decouple
torque control from actuator control. An optimization problem is then
formulated using energy balance equations. The optimization finds the damping
and stiffness gains of the impedance relation such that the energy consumption
is minimized. Furthermore, L2 stability techniques are used to allow for
time-varying damping and stiffness in the desired impedance. A numerical
example is provided to demonstrate the results.",2106.07491v1
2021-06-17,Adaptive Low-Rank Regularization with Damping Sequences to Restrict Lazy Weights in Deep Networks,"Overfitting is one of the critical problems in deep neural networks. Many
regularization schemes try to prevent overfitting blindly. However, they
decrease the convergence speed of training algorithms. Adaptive regularization
schemes can solve overfitting more intelligently. They usually do not affect
the entire network weights. This paper detects a subset of the weighting layers
that cause overfitting. The overfitting recognizes by matrix and tensor
condition numbers. An adaptive regularization scheme entitled Adaptive Low-Rank
(ALR) is proposed that converges a subset of the weighting layers to their
Low-Rank Factorization (LRF). It happens by minimizing a new Tikhonov-based
loss function. ALR also encourages lazy weights to contribute to the
regularization when epochs grow up. It uses a damping sequence to increment
layer selection likelihood in the last generations. Thus before falling the
training accuracy, ALR reduces the lazy weights and regularizes the network
substantially. The experimental results show that ALR regularizes the deep
networks well with high training speed and low resource usage.",2106.09677v1
2021-06-23,Effect of different additional $L^{m}$ regularity on semi-linear damped $σ$-evolution models,"The motivation of the present study is to discuss the global (in time)
existence of small data solutions to the following semi-linear structurally
damped $\sigma$-evolution models: \begin{equation*}
\partial_{tt}u+(-\Delta)^{\sigma}u+(-\Delta)^{\sigma/2}\partial_{t}u=\left|u\right|
^{p}, \ \sigma\geq 1, \ \ p>1, \end{equation*} where the Cauchy data $(u(0,x),
\partial_{t}u(0,x))$ will be chosen from energy space on the base of $L^{q}$
with different additional $L^{m}$ regularity, namely \begin{equation*}
u(0,x)\in H^{\sigma,q}(\mathbb{R}^{n})\cap L^{m_{1}}(\mathbb{R}^{n}) , \ \
\partial_{t}u(0,x)\in L^{q}(\mathbb{R}^{n})\cap L^{m_{2}}(\mathbb{R}^{n}), \ \
q\in(1,\infty),\ \ m_{1}, m_{2}\in [1,q). \end{equation*} Our new results will
show that the critical exponent which guarantees the global (in time) existence
is really affected by these different additional regularities and will take
\textit{two different values} under some restrictions on $m_{1}, m_{2}$, $q$,
$\sigma$ and the space dimension $n\geq1$. Moreover, in each case, we have no
loss of decay estimates of the unique solution with respect to the
corresponding linear models.",2106.12286v1
2021-06-29,Damping effect in innovation processes: case studies from Twitter,"Understanding the innovation process, that is the underlying mechanisms
through which novelties emerge, diffuse and trigger further novelties is
undoubtedly of fundamental importance in many areas (biology, linguistics,
social science and others). The models introduced so far satisfy the Heaps'
law, regarding the rate at which novelties appear, and the Zipf's law, that
states a power law behavior for the frequency distribution of the elements.
However, there are empirical cases far from showing a pure power law behavior
and such a deviation is present for elements with high frequencies. We explain
this phenomenon by means of a suitable ""damping"" effect in the probability of a
repetition of an old element. While the proposed model is extremely general and
may be also employed in other contexts, it has been tested on some Twitter data
sets and demonstrated great performances with respect to Heaps' law and, above
all, with respect to the fitting of the frequency-rank plots for low and high
frequencies.",2106.15528v1
2021-07-01,Local available quantum correlations of X states: The symmetric and anti-symmetric cases,"Local available quantum correlations (LAQC), as defined by Mundarain et al.,
are analyzed for 2-qubit X states with local Bloch vectors of equal magnitude.
Symmetric X-states are invariant under the exchange of subsystems, hence having
the same {local} Bloch vector. On the other hand, anti-symmetric X states have
{local} Bloch vectors with an equal magnitude but opposite direction
{(anti-parallel)}. In both cases, we obtain exact analytical expressions for
their LAQC quantifier. We present some examples and compare this quantum
correlation to concurrence and quantum discord. We have also included Markovian
decoherence, with Werner states under amplitude damping decoherence. As is the
case for depolarization and phase damping, no sudden death behavior occurs for
the LAQC of these states with this quantum channel.",2107.00158v3
2021-07-06,Dynamical System Parameter Identification using Deep Recurrent Cell Networks,"In this paper, we investigate the parameter identification problem in
dynamical systems through a deep learning approach. Focusing mainly on
second-order, linear time-invariant dynamical systems, the topic of damping
factor identification is studied. By utilizing a six-layer deep neural network
with different recurrent cells, namely GRUs, LSTMs or BiLSTMs; and by feeding
input-output sequence pairs captured from a dynamical system simulator, we
search for an effective deep recurrent architecture in order to resolve damping
factor identification problem. Our study results show that, although previously
not utilized for this task in the literature, bidirectional gated recurrent
cells (BiLSTMs) provide better parameter identification results when compared
to unidirectional gated recurrent memory cells such as GRUs and LSTM. Thus,
indicating that an input-output sequence pair of finite length, collected from
a dynamical system and when observed anachronistically, may carry information
in both time directions for prediction of a dynamical systems parameter.",2107.02427v1
2021-07-14,Explaining the pseudogap through damping and antidamping on the Fermi surface by imaginary spin scattering,"The mechanism of the pseudogap observed in hole-doped cuprates remains one of
the central puzzles in condensed matter physics. We analyze this phenomenon via
a Feynman-diagrammatic inspection of the Hubbard model. Our approach captures
the pivotal interplay between Mott localization and Fermi surface topology
beyond weak-coupling spin fluctuations, which would open a spectral gap near
hot spots. We show that strong coupling and particle-hole asymmetry trigger a
very different mechanism: a large imaginary part of the spin-fermion vertex
promotes damping of antinodal fermions and, at the same time, protects the
nodal Fermi arcs (antidamping). Our analysis naturally explains puzzling
features of the pseudogap observed in experiments, such as Fermi arcs being cut
off at the antiferromagnetic zone boundary and the subordinate role of hot
spots.",2107.06529v2
2021-07-17,"Blow--up for the wave equation with hyperbolic dynamical boundary conditions, interior and boundary nonlinear damping and sources","The aim of this paper is to give global nonexistence and blow--up results for
the problem $$ \begin{cases} u_{tt}-\Delta u+P(x,u_t)=f(x,u) \qquad &\text{in
$(0,\infty)\times\Omega$,}\\ u=0 &\text{on $(0,\infty)\times \Gamma_0$,}\\
u_{tt}+\partial_\nu u-\Delta_\Gamma u+Q(x,u_t)=g(x,u)\qquad &\text{on
$(0,\infty)\times \Gamma_1$,}\\ u(0,x)=u_0(x),\quad u_t(0,x)=u_1(x) &
  \text{in $\overline{\Omega}$,} \end{cases}$$ where $\Omega$ is a bounded open
$C^1$ subset of $\mathbb{R}^N$, $N\ge 2$, $\Gamma=\partial\Omega$,
$(\Gamma_0,\Gamma_1)$ is a partition of $\Gamma$, $\Gamma_1\not=\emptyset$
being relatively open in $\Gamma$, $\Delta_\Gamma$ denotes the
Laplace--Beltrami operator on $\Gamma$, $\nu$ is the outward normal to
$\Omega$, and the terms $P$ and $Q$ represent nonlinear damping terms, while
$f$ and $g$ are nonlinear source terms. These results complement the analysis
of the problem given by the author in two recent papers, dealing with local and
global existence, uniqueness and well--posedness.",2107.08213v2
2021-07-22,Collisional Growth Within the Solar System's Primordial Planetesimal Disk and the Timing of the Giant Planet Instability,"The large scale structure of the Solar System has been shaped by a transient
dynamical instability that may have been triggered by the interaction of the
giants planets with a massive primordial disk of icy debris. In this work, we
investigate the conditions under which this primordial disk could have
coalesced into planets using analytic and numerical calculations. In
particular, we perform numerical simulations of the Solar System's early
dynamical evolution that account for the viscous stirring and collisional
damping within the disk. We demonstrate that if collisional damping would have
been sufficient to maintain a temperate velocity dispersion, Earth mass
trans-Neptunian planets could have emerged within a timescale of 10 Myr.
Therefore, our results favor a scenario wherein the dynamical instability of
the outer Solar System began immediately upon the dissipation of the gaseous
nebula to avoid the overproduction of Earth mass planets in the outer Solar
System.",2107.10403v1
2021-07-29,"$n$-dimensional PDM-damped harmonic oscillators: Linearizability, and exact solvability","We consider position-dependent mass (PDM) Lagrangians/Hamiltonians in their
standard textbook form, where the long-standing \emph{gain-loss balance}
between the kinetic and potential energies is kept intact to allow conservation
of total energy (i.e., $L=T-V$, $H=T+V$, and $dH/dt=dE/dt=0$). Under such
standard settings, we discuss and report on $n$-dimensional PDM damped harmonic
oscillators (DHO). We use some $n$-dimensional point canonical transformation
to facilitate the linearizability of their $n$-PDM dynamical equations into
some $n$-linear DHOs' dynamical equations for constant mass setting.
Consequently, the well know exact solutions for the linear DHOs are mapped,
with ease, onto the exact solutions for PDM DHOs. A set of one-dimensional and
a set of $n$-dimensional PDM-DHO illustrative examples are reported along with
their phase-space trajectories.",2107.14617v1
2021-08-02,Interplay of periodic dynamics and noise: insights from a simple adaptive system,"We study the dynamics of a simple adaptive system in the presence of noise
and periodic damping. The system is composed by two paths connecting a source
and a sink, the dynamics is governed by equations that usually describe food
search of the paradigmatic Physarum polycephalum. In this work we assume that
the two paths undergo damping whose relative strength is periodically modulated
in time and analyse the dynamics in the presence of stochastic forces
simulating Gaussian noise. We identify different responses depending on the
modulation frequency and on the noise amplitude. At frequencies smaller than
the mean dissipation rate, the system tends to switch to the path which
minimizes dissipation. Synchronous switching occurs at an optimal noise
amplitude which depends on the modulation frequency. This behaviour disappears
at larger frequencies, where the dynamics can be described by the time-averaged
equations. Here, we find metastable patterns that exhibit the features of
noise-induced resonances.",2108.01451v3
2021-08-06,Adjusting PageRank parameters and Comparing results,"The effect of adjusting damping factor {\alpha} and tolerance {\tau} on
iterations needed for PageRank computation is studied here. Relative
performance of PageRank computation with L1, L2, and L{\infty} norms used as
convergence check, are also compared with six possible mean ratios. It is
observed that increasing the damping factor {\alpha} linearly increases the
iterations needed almost exponentially. On the other hand, decreasing the
tolerance {\tau} exponentially decreases the iterations needed almost
exponentially. On average, PageRank with L{\infty} norm as convergence check is
the fastest, quickly followed by L2 norm, and then L1 norm. For large graphs,
above certain tolerance {\tau} values, convergence can occur in a single
iteration. On the contrary, below certain tolerance {\tau} values, sensitivity
issues can begin to appear, causing computation to halt at maximum iteration
limit without convergence. The six mean ratios for relative performance
comparison are based on arithmetic, geometric, and harmonic mean, as well as
the order of ratio calculation. Among them GM-RATIO, geometric mean followed by
ratio calculation, is found to be most stable, followed by AM-RATIO.",2108.02997v1
2021-08-06,Magnon transport in $\mathrm{\mathbf{Y_3Fe_5O_{12}}}$/Pt nanostructures with reduced effective magnetization,"For applications making use of magnonic spin currents damping effects, which
decrease the spin conductivity, have to be minimized. We here investigate the
magnon transport in an yttrium iron garnet thin film with strongly reduced
effective magnetization. We show that in a three-terminal device the effective
magnon conductivity can be increased by a factor of up to six by a current
applied to a modulator electrode, which generates damping compensation above a
threshold current. Moreover, we find a linear dependence of this threshold
current on the applied magnetic field. We can explain this behavior by the
reduced effective magnetization and the associated nearly circular
magnetization precession.",2108.03263v1
2021-08-12,On the critical exponent and sharp lifespan estimates for semilinear damped wave equations with data from Sobolev spaces of negative order,"We study semilinear damped wave equations with power nonlinearity $|u|^p$ and
initial data belonging to Sobolev spaces of negative order $\dot{H}^{-\gamma}$.
In the present paper, we obtain a new critical exponent
$p=p_{\mathrm{crit}}(n,\gamma):=1+\frac{4}{n+2\gamma}$ for some
$\gamma\in(0,\frac{n}{2})$ and low dimensions in the framework of Soblev spaces
of negative order. Precisely, global (in time) existence of small data Sobolev
solutions of lower regularity is proved for $p>p_{\mathrm{crit}}(n,\gamma)$,
and blow-up of weak solutions in finite time even for small data if
$1<p<p_{\mathrm{crit}}(n,\gamma)$. Furthermore, in order to more accurately
describe the blow-up time, we investigate sharp upper bound and lower bound
estimates for the lifespan in the subcritical case.",2108.05667v1
2021-08-25,Numerical investigation of non-condensable gas effect on vapor bubble collapse,"We numerically investigate the effect of non-condensable gas inside a vapor
bubble on bubble dynamics, collapse pressure and pressure impact of spherical
and aspherical bubble collapses. Free gas inside a vapor bubble has a damping
effect that can weaken the pressure wave and enhance the bubble rebound. To
estimate this effect numerically, we derive and validate a multi-component
model for vapor bubbles containing gas. For the cavitating liquid and the
non-condensable gas, we employ a homogeneous mixture model with a coupled
equation of state for all components. The cavitation model for the cavitating
liquid is a barotropic thermodynamic equilibrium model. Compressibility of all
phases is considered in order to capture the shock wave of the bubble collapse.
After validating the model with an analytical energy partitioning model,
simulations of collapsing wall-attached bubbles with different stand-off
distances are performed. The effect of the non-condensable gas on rebound and
damping of the emitted shock wave is well captured.",2108.11297v1
2021-08-23,"PDM damped-driven oscillators: exact solvability, classical states crossings, and self-crossings","Within the standard Lagrangian and Hamiltonian setting, we consider a
position-dependent mass (PDM) classical particle performing a damped driven
oscillatory (DDO) motion under the influence of a conservative harmonic
oscillator force field $V\left( x\right) =\frac{1}{2}\omega ^{2}Q\left(
x\right) x^{2}$ and subjected to a Rayleigh dissipative force field
$\mathcal{R}\left( x,\dot{x}\right) =\frac{1}{2}b\,m\left( x\right)
\dot{x}^{2}$ in the presence of an external periodic (non-autonomous) force
$F\left( t\right) =F_{\circ }\,\cos \left( \Omega t\right) $. Where, the
correlation between the coordinate deformation $\sqrt{Q(x)}$ and the velocity
deformation $\sqrt{m(x)}$ is governed by a point canonical transformation
$q\left( x\right) =\int \sqrt{m\left( x\right) }dx=\sqrt{% Q\left( x\right)
}x$. Two illustrative examples are used: a non-singular PDM-DDO, and a
power-law PDM-DDO models. Classical-states $\{x(t),p(t)\}$ crossings are
analysed and reported. Yet, we observed/reported that as a classical state
$\{x_{i}(t),p_{i}(t)\}$ evolves in time it may cross itself at an earlier
and/or a latter time/s.",2108.13924v1
2021-09-06,A well-balanced oscillation-free discontinuous Galerkin method for shallow water equations,"In this paper, we develop a well-balanced oscillation-free discontinuous
Galerkin (OFDG) method for solving the shallow water equations with a non-flat
bottom topography. One notable feature of the constructed scheme is the
well-balanced property, which preserves exactly the hydrostatic equilibrium
solutions up to machine error. Another feature is the non-oscillatory property,
which is very important in the numerical simulation when there exist some shock
discontinuities. To control the spurious oscillations, we construct an OFDG
method with an extra damping term to the existing well-balanced DG schemes
proposed in [Y. Xing and C.-W. Shu, CICP, 1(2006), 100-134.]. With a careful
construction of the damping term, the proposed method achieves both the
well-balanced property and non-oscillatory property simultaneously without
compromising any order of accuracy. We also present a detailed procedure for
the construction and a theoretical analysis for the preservation of the
well-balancedness property. Extensive numerical experiments including one- and
two-dimensional space demonstrate that the proposed methods possess the desired
properties without sacrificing any order of accuracy.",2109.02193v1
2021-09-16,Landau Modes are Eigenmodes of Stellar Systems in the Limit of Zero Collisions,"We consider the spectrum of eigenmodes in a stellar system dominated by
gravitational forces in the limit of zero collisions. We show analytically and
numerically using the Lenard-Bernstein collision operator that the Landau
modes, which are not true eigenmodes in a strictly collisionless system (except
for the Jeans unstable mode), become part of the true eigenmode spectrum in the
limit of zero collisions. Under these conditions, the continuous spectrum of
true eigenmodes in the collisionless system, also known as the Case-van Kampen
modes, is eliminated. Furthermore, since the background distribution function
in a weakly collisional system can exhibit significant deviations from a
Maxwellian distribution function over long times, we show that the spectrum of
Landau modes can change drastically even in the presence of slight deviations
from a Maxwellian, primarily through the appearance of weakly damped modes that
may be otherwise heavily damped for a Maxwellian distribution. Our results
provide important insights for developing statistical theories to describe
thermal fluctuations in a stellar system, which are currently a subject of
great interest for N-body simulations as well as observations of gravitational
systems.",2109.07806v2
2021-09-16,Stabilization of physical systems via saturated controllers with only partial state measurements,"This paper provides a constructive passivity-based control approach to solve
the set-point regulation problem for input-affine continuous nonlinear systems
while considering saturation in the inputs. As customarily in passivity-based
control, the methodology consists of two steps: energy shaping and damping
injection. In terms of applicability, the proposed controllers have two
advantages concerning other passivity-based control techniques: (i) the energy
shaping is carried out without solving partial differential equations, and (ii)
the damping injection is performed without measuring the passive output. The
proposed methodology is suitable to control a broad range of physical systems,
e.g., mechanical, electrical, and electro-mechanical systems. We illustrate the
applicability of the technique by designing controllers for systems in
different physical domains, where we validate the analytical results via
simulations and experiments.",2109.08111v2
2021-09-15,Universal relations between the quasinormal modes of neutron star and tidal deformability,"Universal relations independently of the equation of state (EOS) for neutron
star matter are valuable, if they exist, for extracting the neutron star
properties, which generally depend on the EOS. In this study, we newly derive
the universal relations predicting the gravitational wave frequencies for the
fundamental ($f$), the 1st pressure ($p_1$), and the 1st spacetime ($w_1$)
modes and the damping rate for the $f$- and $w_1$-modes as a function of the
dimensionless tidal deformability. In particular, with the universal relations
for the $f$-modes one can predict the frequencies and damping rate with less
than $1\%$ accuracy for canonical neutron stars.",2109.08145v2
2021-09-27,Estimating the characteristics of stochastic damping Hamiltonian systems from continuous observations,"We consider nonparametric invariant density and drift estimation for a class
of multidimensional degenerate resp. hypoelliptic diffusion processes,
so-called stochastic damping Hamiltonian systems or kinetic diffusions, under
anisotropic smoothness assumptions on the unknown functions. The analysis is
based on continuous observations of the process, and the estimators'
performance is measured in terms of the sup-norm loss. Regarding invariant
density estimation, we obtain highly nonclassical results for the rate of
convergence, which reflect the inhomogeneous variance structure of the process.
Concerning estimation of the drift vector, we suggest both non-adaptive and
fully data-driven procedures. All of the aforementioned results strongly rely
on tight uniform moment bounds for empirical processes associated to
deterministic and stochastic integrals of the investigated process, which are
also proven in this paper.",2109.13190v3
2021-10-04,Anomalous temperature dependence of phonon pumping by ferromagnetic resonance in Co/Pd multilayers with perpendicular anisotropy,"We demonstrate the pumping of phonons by ferromagnetic resonance in a series
of [Co(0.8 nm)/Pd(1.5 nm)]$_n$ multilayers ($n =$ 6, 11, 15, and 20) with large
magnetostriction and perpendicular magnetic anisotropy. The effect is shown
using broadband ferromagnetic resonance over a range of temperatures (10 to 300
K), where a resonant damping enhancement is observed at frequencies
corresponding to standing wave phonons across the multilayer. The strength of
this effect is enhanced by approximately a factor of 4 at 10 K compared to room
temperature, which is anomalous in the sense that the temperature dependence of
the magnetostriction predicts an enhancement that is less than a factor of 2.
Lastly, we demonstrate that the damping enhancement is correlated with a shift
in the ferromagnetic resonance field as predicted quantitatively from linear
response theory.",2110.01714v1
2021-10-05,A BSDEs approach to pathwise uniqueness for stochastic evolution equations,"We prove strong well-posedness for a class of stochastic evolution equations
in Hilbert spaces H when the drift term is Holder continuous. This class
includes examples of semilinear stochastic damped wave equations which describe
elastic systems with structural damping (for such equations even existence of
solutions in the linear case is a delicate issue) and semilinear stochastic 3D
heat equations. In the deterministic case, there are examples of non-uniqueness
in our framework. Strong (or pathwise) uniqueness is restored by means of a
suitable additive Wiener noise. The proof of uniqueness relies on the study of
related systems of infinite dimensional forward-backward SDEs (FBSDEs). This is
a different approach with respect to the well-known method based on the Ito
formula and the associated Kolmogorov equation (the so-called Zvonkin
transformation or Ito-Tanaka trick). We deal with approximating FBSDEs in which
the linear part generates a group of bounded linear operators in H; such
approximations depend on the type of SPDEs we are considering. We also prove
Lipschitz dependence of solutions from their initial conditions.",2110.01994v2
2021-10-07,Quantum speed limit for the maximum coherent state under squeezed environment,"The quantum speed limit time for quantum system under squeezed environment is
studied. We consider two typical models, the damped Jaynes-Cummings model and
the dephasing model. For the damped Jaynes-Cummings model under squeezed
environment, we find that the quantum speed limit time becomes larger with the
squeezed parameter $r$ increasing and indicates symmetry about the phase
parameter value $\theta=\pi$. Meanwhile, the quantum speed limit time can also
be influenced by the coupling strength between the system and environment.
However, the quantum speed limit time for the dephasing model is determined by
the dephasing rate and the boundary of acceleration region that interacting
with vacuum reservoir can be broken when the squeezed environment parameters
are appropriately chosen.",2110.03132v1
2021-10-13,Effect of damped oscillations in the inflationary potential,"We investigate the effect of damped oscillations on a nearly flat
inflationary potential and the features they produce in the power-spectrum and
bi-spectrum. We compare the model with the Planck data using Plik unbinned and
CamSpec clean likelihood and we are able to obtain noticeable improvement in
fit compared to the power-law $\Lambda$CDM model. We are able to identify three
plausible candidates each for the two likelihoods used. We find that the
best-fit to Plik and CamSpec likelihoods match closely to each other. The
improvement comes from various possible outliers at the intermediate to small
scales. We also compute the bi-spectrum for the best-fits. At all limits, the
amplitude of bi-spectrum, $f_{NL}$ is oscillatory in nature and its peak value
is determined by the amplitude and frequency of the oscillations in the
potential, as expected. We find that the bi-spectrum consistency relation
strictly holds at all scales in all the best-fit candidates.",2110.06837v2
2021-10-14,Thermalization in a Spin-Orbit coupled Bose gas by enhanced spin Coulomb drag,"An important component of the structure of the atom, the effects of
spin-orbit coupling are present in many sub-fields of physics. Most of these
effects are present continuously. We present a detailed study of the dynamics
of changing the spin-orbit coupling in an ultra-cold Bose gas, coupling the
motion of the atoms to their spin. We find that the spin-orbit coupling greatly
increases the damping towards equilibrium. We interpret this damping as spin
drag, which is enhanced by spin-orbit coupling rate, scaled by a remarkable
factor of $8.9(6)$~s. We also find that spin-orbit coupling lowers the final
temperature of the Bose gas after thermalization.",2110.07094v3
2021-10-15,Superconducting dome in ferroelectric-type materials from soft mode instability,"We present a minimal theory of superconductivity enhancement in
ferroelectric-type materials. Simple expressions for the optical mode
responsible for the soft mode transition are assumed. A key role is played by
the anharmonic phonon damping which is modulated by an external control
parameter (electron doping or mechanical strain) causing the appearance of the
soft mode. It is shown that the enhancement in the superconducting critical
temperature $T_{c}$ upon approaching the ferroelectric transition from either
side is due to the Stokes electron-phonon scattering processes promoted by
strong phonon damping effects.",2110.08114v2
2021-10-20,Dimensional control of tunneling two level systems in nanoelectromechanical resonators,"Tunneling two level systems affect damping, noise and decoherence in a wide
range of devices, including nanoelectromechanical resonators, optomechanical
systems, and qubits. Theoretically this interaction is usually described within
the tunneling state model. The dimensions of such devices are often small
compared to the relevant phonon wavelengths at low temperatures, and extensions
of the theoretical description to reduced dimensions have been proposed, but
lack conclusive experimental verification. We have measured the intrinsic
damping and the frequency shift in magnetomotively driven aluminum
nanoelectromechanical resonators of various sizes at millikelvin temperatures.
We find good agreement of the experimental results with a model where the
tunneling two level systems couple to flexural phonons that are restricted to
one or two dimensions by geometry of the device. This model can thus be used as
an aid when optimizing the geometrical parameters of devices affected by
tunneling two level systems.",2110.10492v1
2021-10-27,Quantum oscillations in interaction-driven insulators,"In recent years it has become understood that quantum oscillations of the
magnetization as a function of magnetic field, long recognized as phenomena
intrinsic to metals, can also manifest in insulating systems. Theory has shown
that in certain simple band insulators, quantum oscillations can appear with a
frequency set by the area traced by the minimum gap in momentum space, and are
suppressed for weak fields by an intrinsic ""Dingle damping"" factor reflecting
the size of the bandgap. Here we examine quantum oscillations of the
magnetization in excitonic and Kondo insulators, for which interactions play a
crucial role. In models of these systems, self-consistent parameters themselves
oscillate with changing magnetic field, generating additional contributions to
quantum oscillations. In the low-temperature, weak-field regime, we find that
the lowest harmonic of quantum oscillations of the magnetization are
unaffected, so that the zero-field bandgap can still be extracted by measuring
the Dingle damping factor of this harmonic. However, these contributions
dominate quantum oscillations at all higher harmonics, thereby providing a
route to measure this interaction effect.",2110.14643v2
2021-11-01,Achieving increased Phasor POD performance by introducing a Control-Input Model,"In this paper, an enhancement to the well known Phasor Power Oscillation
Damper is proposed, aiming to increase its performance. Fundamental to the
functioning of this controller is the estimation of a phasor representing
oscillatory behaviour at a particular frequency in a measured signal. The
phasor is transformed to time domain and applied as a setpoint signal to a
controllable device. The contribution in this paper specifically targets the
estimation algorithm of the controller: It is found that increased estimation
accuracy and thereby enhanced damping performance can be achieved by
introducing a prediction-correction scheme for the estimator, in the form of a
Kalman Filter. The prediction of the phasor at the next step is performed based
on the control signal that is applied at the current step. This enables more
precise damping of the targeted mode.
  The presented results, which are obtained from simulations on a
Single-Machine Infinite Bus system and the IEEE 39-Bus system, indicate that
the proposed enhancement improves the performance of this type of controller.",2111.00968v2
2021-11-02,Escape kinetics of self-propelled particles from a circular cavity,"We numerically investigate the mean exit time of an inertial active Brownian
particle from a circular cavity with single or multiple exit windows. Our
simulation results witness distinct escape mechanisms depending upon the
relative amplitudes of the thermal length and self-propulsion length compared
to the cavity and pore sizes. For exceedingly large self-propulsion lengths,
overdamped active particles diffuse on the cavity surface, and rotational
dynamics solely governs the exit process. On the other hand, the escape
kinetics of a very weakly damped active particle is largely dictated by
bouncing effects on the cavity walls irrespective of the amplitude of
self-propulsion persistence lengths. We show that the exit rate can be
maximized for an optimal self-propulsion persistence length, which depends on
the damping strength, self-propulsion velocity, and cavity size. However, the
optimal persistence length is insensitive to the opening windows' size, number,
and arrangement. Numerical results have been interpreted analytically based on
qualitative arguments. The present analysis aims to understand the transport
controlling mechanism of active matter in confined structures.",2111.01324v1
2021-11-09,Quantum Control of the Time-Dependent Interaction between a Three-Level $Ξ$-Type Atom and a Two-Mode Field with Damping Term,"The purpose of this paper is to investigate some properties through a
three-level $\Xi$-type atom interacting with a two-mode field. We test this
system in the presence of the photon assisted atomic phase damping, detuning
parameter and Kerr nonlinearity. Also, the coupling parameter modulated to be
time-dependent. The problem solution of this model is given by using the
Schr\H{o}dinger equation when the atom and the field are initially prepared in
the excited state and coherent state, respectively. We used the results to
calculate some aspects such as atomic population inversion and concurrence. The
results show that the time-dependent coupling parameter and the detuning
parameter can be considered as a quantum control parameters of the atomic
population inversion and quantum entanglement in the considered model.",2111.05449v1
2021-11-10,On the Convergence of Orthogonal/Vector AMP: Long-Memory Message-Passing Strategy,"Orthogonal/vector approximate message-passing (AMP) is a powerful
message-passing (MP) algorithm for signal reconstruction in compressed sensing.
This paper proves the convergence of Bayes-optimal orthogonal/vector AMP in the
large system limit. The proof strategy is based on a novel long-memory (LM) MP
approach: A first step is a construction of LM-MP that is guaranteed to
converge systematically. A second step is a large-system analysis of LM-MP via
an existing framework of state evolution. A third step is to prove the
convergence of state evolution recursions for Bayes-optimal LM-MP via a new
statistical interpretation of existing LM damping. The last is an exact
reduction of the state evolution recursions for Bayes-optimal LM-MP to those
for Bayes-optimal orthogonal/vector AMP. The convergence of the state evolution
recursions for Bayes-optimal LM-MP implies that for Bayes-optimal
orthogonal/vector AMP. Numerical simulations are presented to show the
verification of state evolution results for damped orthogonal/vector AMP and a
negative aspect of LM-MP in finite-sized systems.",2111.05522v2
2021-11-15,Spectral analysis of a viscoelastic tube conveying fluid with generalised boundary conditions,"We study the spectral problem associated with the equation governing the
small transverse motions of a viscoelastic tube of finite length conveying an
ideal fluid. The boundary conditions considered are of general form, accounting
for a combination of elasticity and viscous damping acting on both the slopes
and the displacements of the ends of the tube. These include many standard
boundary conditions as special cases such as the clamped, free, hinged, and
guided conditions. We derive explicit asymptotic formulae for the eigenvalues
for the case of generalised boundary conditions and specialise these results to
the clamped case and the case in which damping acts on the slopes but not on
the displacements. In particular, the dependence of the eigenvalues on the
parameters of the problem is investigated and it is found that all eigenvalues
are located in certain sectorial sets in the complex plane.",2111.07697v5
2021-11-18,Confronting cosmic ray electron and positron excesses with hybrid triplet Higgs portal dark matter,"We perform a detailed study of scalar dark matter with triplet Higgs
extensions of the Standard Model in order to explain the cosmic ray electron
and positron excesses reported by AMS-02 and DAMPE. A detailed analysis of
AMS-02 positron excess reveals that for different orderings (normal, inverted
and quasi-degenerate) of neutrino mass, the hybrid triplet Higgs portal
framework is more favored with respect to the single triplet Higgs portal for
TeV scale dark matter. We also show that the resonant peak and continuous
excess in DAMPE cosmic ray data can be well explained with the hybrid triplet
Higgs portal dark matter when a dark matter sub-halo nearby is taken into
account.",2111.09559v3
2021-11-30,Damping via the hyperfine interaction of a spin-rotation mode in a two-dimensional strongly magnetized electron plasma,"We address damping of a Goldstone spin-rotation mode emerging in a quantum
Hall ferromagnet due to laser pulse excitation. Recent experimental data show
that the attenuation mechanism, dephasing of the observed Kerr precession, is
apparently related not only to spatial fluctuations of the electron Land\'e
factor in the quantum well, but to a hyperfine interaction with nuclei, because
local magnetization of GaAs nuclei should also experience spatial fluctuations.
The motion of the macroscopic spin-rotation state is studied microscopically by
solving a non-stationary Schr\""odinger equation. Comparison with the previously
studied channel of transverse spin relaxation (attenuation of Kerr oscilations)
shows that relaxation via nuclei involves a longer quadratic stage of
time-dependance of the transverse spin, and, accordingly, an elongated
transition to a linear stage, so that a linear time-dependance may not be
revealed.",2111.15433v1
2021-11-30,Heating of Magnetically Dominated Plasma by Alfvén-Wave Turbulence,"Magnetic energy around astrophysical compact objects can strongly dominate
over plasma rest mass. Emission observed from these systems may be fed by
dissipation of Alfv\'en wave turbulence, which cascades to small damping
scales, energizing the plasma. We use 3D kinetic simulations to investigate
this process. When the cascade is excited naturally, by colliding large-scale
Alfv\'en waves, we observe quasithermal heating with no nonthermal particle
acceleration. We also find that the particles are energized along the magnetic
field lines and so are poor producers of synchrotron radiation. At low plasma
densities, our simulations show the transition to ""charge-starved"" cascades,
with a distinct damping mechanism.",2111.15578v2
2021-12-06,Decay properties and asymptotic behaviors for a wave equation with general strong damping,"In this paper, we study the Cauchy problem for a wave equation with general
strong damping $-\mu(|D|)\Delta u_t$ motivated by [Tao, Anal. PDE (2009)] and
[Ebert-Girardi-Reissig, Math. Ann. (2020)]. By employing energy methods in the
Fourier space and WKB analysis, we derive decay estimates for solutions under a
large class of $\mu(|D|)$. In particularly, a threshold
$\lim\nolimits_{|\xi|\to\infty}\mu(|\xi|)=\infty$ is discovered for the
regularity-loss phenomenon, where $\mu(|\xi|)$ denotes the symbol of
$\mu(|D|)$. Furthermore, we investigate different asymptotic profiles of
solution with additionally $L^1$ initial data, where some refined estimates in
the sense of enhanced decay rate and reduced regularity are found. The derived
results almost cover the known results with sufficiently small loss.",2112.02795v1
2021-12-09,UV sensitivity of Casimir energy,"We quantitatively estimate the effect of the UV physics on the Casimir energy
in a five-dimensional (5D) model on $S^1/Z_2$. If the cutoff scale of the 5D
theory is not far from the compactification scale, the UV physics may affect
the low energy result. We work in the cutoff regularization scheme by
introducing two independent cutoff scales for the spatial momentum in the
non-compact space and for the Kaluza-Klein masses. The effects of the UV
physics are incorporated as a damping effect of the contributions to the vacuum
energy around the cutoff scales. We numerically calculate the Casimir energy
and evaluate the deviation from the result obtained in the zeta-function
regularization, which does not include information on the UV physics. We find
that the result well agrees with the latter for the Gaussian-type damping,
while it can deviate for the kink-type one.",2112.04708v3
2021-12-11,Landau damping in hybrid plasmonics,"Landau Damping (LD) mechanism of the Localized Surface Plasmon (LSP) decay is
studied for the hybrid nanoplasmonic (metal core/dielectric shell) structures.
It is shown that LD in hybrid structures is strongly affected by permittivity
and electron effective mass in the dielectric shell in accordance with previous
observations by Kreibig, and the strength of LD can be enhanced by an order of
magnitude for some combinations of permittivity and effective mass. The
physical reason for this effect is identified as electron spillover into the
dielectric where electric field is higher than in the metal and the presence of
quasi-discrete energy levels in the dielectric. The theory indicates that the
transition absorption at the interface metal-dielectric is a dominant
contribution to LD in such hybrid structures. Thus, by judicious selection of
dielectric material and its thickness one can engineer decay rates and hot
carrier production for important applications, such as photodetection and
photochemistry.",2112.06005v1
2021-12-12,Raman and infrared studies of CdSe/CdS core/shell nanoplatelets,"The vibrational spectroscopy of semiconductor nanostructures can provide
important information on their structure. In this work, experimental Raman and
infrared spectra are compared with vibrational spectra of CdSe/CdS core/shell
nanoplatelets calculated from first principles using the density functional
theory. The calculations confirm the two-mode behavior of phonon spectra of
nanostructures. An analysis of the experimental spectra reveals the absence of
modes with a high amplitude of vibrations of surface atoms, which indicates
their strong damping. Taking into account the difference in the damping of
different modes and their calculated intensities, all bands in the spectra are
unambiguously identified. It is found that the frequencies of longitudinal
optical modes in heterostructures are close to the frequencies of LO phonons in
bulk strained constituents, whereas the frequencies of transverse modes can
differ significantly from those of the corresponding TO phonons. It is shown
that an anomalous thickness dependence of CdS TO mode is due to a noticeable
surface relaxation of the outer Cd layer in the nanostructure.",2112.06326v1
2021-12-20,Long-time behavior of solutions to the M1 model with boundray effect,"In this paper, we are concerned with the asymptotic behavior of solutions of
M1 model on quadrant. From this model, combined with damped compressible Euler
equations, a more general system is introduced. We show that the solutions to
the initial boundary value problem of this system globally exist and tend
time-asymptotically to the corresponding nonlinear parabolic equation governed
by the related Darcy's law. Compared with previous results on compressible
Euler equations with damping obtained by Nishihara and Yang in [24], and
Marcati, Mei and Rubino in [16], the better convergence rates are obtained. The
approach adopted is based on the technical time-weighted energy estimates
together with the Green's function method.",2112.10392v1
2021-12-22,Quantum fisher information protection of N-qubit Greenberger-Horne-Zeilinger state from decoherence,"In this paper we study the protection of N-qubit Greenberger-Horne- Zeilinger
(GHZ) state and generalized N-qubit GHZ states in amplitude damping channel by
means of quantum weak measurement and flip operations. We derive the explicit
formulas of the performances of the protection scheme: average fidelity,
average probability and the average quantum fisher information (QFI). Moreover,
the analytical results for maximizing the average fidelity and probability are
obtained. We show that our scheme can effectively protect the average QFI of
phase for GHZ states and generalized GHZ states. The proposed scheme has the
merit of protecting GHZ state and the QFI of phase against heavy amplitude
damping noise. Further we show that for some generalize GHZ state, the proposed
scheme can protect the state with probability one and fidelity more than 99%.",2112.11590v1
2021-12-23,Theory of Harmonic Hall Responses of Spin-Torque Driven Antiferromagnets,"Harmonic analysis is a powerful tool to characterize and quantify
current-induced torques acting on magnetic materials, but so far it remains an
open question in studying antiferromagnets. Here we formulate a general theory
of harmonic Hall responses of collinear antiferromagnets driven by
current-induced torques including both field-like and damping-like components.
By scanning a magnetic field of variable strength in three orthogonal planes,
we are able to distinguish the contributions from field-like torque,
damping-like torque, and concomitant thermal effects by analyzing the second
harmonic signals in the Hall voltage. The analytical expressions of the first
and second harmonics as functions of the magnetic field direction and strength
are confirmed by numerical simulations with good agreement. We demonstrate our
predictions in two prototype antiferromagnets, $\alpha-$Fe$_{2}$O$_{3}$ and
NiO, providing direct and general guidance to current and future experiments.",2112.12772v2
2021-12-24,Total Energy Shaping with Neural Interconnection and Damping Assignment -- Passivity Based Control,"In this work we exploit the universal approximation property of Neural
Networks (NNs) to design interconnection and damping assignment (IDA)
passivity-based control (PBC) schemes for fully-actuated mechanical systems in
the port-Hamiltonian (pH) framework. To that end, we transform the IDA-PBC
method into a supervised learning problem that solves the partial differential
matching equations, and fulfills equilibrium assignment and Lyapunov stability
conditions. A main consequence of this, is that the output of the learning
algorithm has a clear control-theoretic interpretation in terms of passivity
and Lyapunov stability. The proposed control design methodology is validated
for mechanical systems of one and two degrees-of-freedom via numerical
simulations.",2112.12999v2
2021-12-24,Critical comparison of collisionless fluid models: Nonlinear simulations of parallel firehose instability,"Two different fluid models for collisionless plasmas are compared. One is
based on the classical Chew-Goldberger-Low (CGL) model that includes a finite
Larmor radius (FLR) correction and the Landau closure for the longitudinal
mode. Another one takes into account the effect of cyclotron resonance in
addition to Landau resonance, which is referred to as the cyclotron resonance
closure (CRC) model. While the linear property of the parallel firehose
instability is better described by the CGL model, the electromagnetic ion
cyclotron instability driven unstable by the cyclotron resonance is reproduced
only by the CRC model. Nonlinear simulation results for the parallel firehose
instability performed with the two models are also discussed. Although the
linear and quasilinear isotropization phases are consistent with theory in both
models, long-term behaviors may be substantially different. The final state
obtained by the CRC model may be reasonably understood in terms of the marginal
stability condition. In contrast, the lack of cyclotron damping in the CGL
model makes it rather difficult to predict the long-term behavior with a simple
physical argument. This suggests that incorporating the collisionless damping
both for longitudinal and transverse modes is crucial for a nonlinear fluid
simulation model of collisionless plasmas.",2112.13077v1
2022-01-04,Second order splitting dynamics with vanishing damping for additively structured monotone inclusions,"In the framework of a real Hilbert space, we address the problem of finding
the zeros of the sum of a maximally monotone operator $A$ and a cocoercive
operator $B$. We study the asymptotic behaviour of the trajectories generated
by a second order equation with vanishing damping, attached to this problem,
and governed by a time-dependent forward-backward-type operator. This is a
splitting system, as it only requires forward evaluations of $B$ and backward
evaluations of $A$. A proper tuning of the system parameters ensures the weak
convergence of the trajectories to the set of zeros of $A + B$, as well as fast
convergence of the velocities towards zero. A particular case of our system
allows to derive fast convergence rates for the problem of minimizing the sum
of a proper, convex and lower semicontinuous function and a smooth and convex
function with Lipschitz continuous gradient. We illustrate the theoretical
outcomes by numerical experiments.",2201.01017v1
2022-01-15,Some Lq(R)-norm decay estimates for two Cauchy systems of type Rao-Nakra sandwich beam with a frictional damping or an infinite memory,"In this paper, we consider two systems of type Rao-Nakra sandwich beam in the
whole line R with a frictional damping or an infinite memory acting on the
Euler-Bernoulli equation. When the speeds of propagation of the two wave
equations are equal, we show that the solutions do not converge to zero when
time goes to infinity. In the reverse situation, we prove some L2(R)-norm and
L1(R)-norm decay estimates of solutions and theirs higher order derivatives
with respect to the space variable. Thanks to interpolation inequalities and
Carlson inequality, these L2(R)-norm and L1(R)-norm decay estimates lead to
similar ones in the Lq(R)-norm, for any q>1. In our both L2(R)-norm and
L1(R)-norm decay estimates, we specify the decay rates in terms of the
regularity of the initial data and the nature of the control.",2201.05881v1
2022-01-24,Pseudospectral continuation for aeroelastic stability analysis,"This technical note is concerned with aeroelastic flutter problems: the
analysis of aeroelastic systems undergoing airspeed-dependent dynamic
instability. Existing continuation methods for parametric stability analysis
are based on marching along an airspeed parameter until the flutter point is
found - an approach which may waste computational effort on low-airspeed system
behavior, before a flutter point is located and characterized. Here, we
describe a pseudospectral continuation approach which instead marches outwards
from the system's flutter points, from points of instability to points of
increasing damping, allowing efficient characterization of the subcritical and
supercritical behavior of the system. This approach ties together aeroelastic
stability analysis and abstract linear algebra, and provides efficient methods
for computing practical aeroelastic stability properties - for instance, flight
envelopes based on maximum modal damping, and the location of borderline-stable
zones.",2201.09816v1
2022-01-26,Enhanced weak force sensing through atom-based coherent noise cancellation in a hybrid cavity optomechanical system,"We investigate weak force-sensing based on coherent quantum noise
cancellation in a nonlinear hybrid optomechanical system. The optomechanical
cavity contains a moveable mechanical mirror, a fixed semitransparent mirror,
an ensemble of ultracold atoms, and an optical parametric amplifier (OPA).
Using the coherent quantum noise cancellation (CQNC) process, one can eliminate
the back action noise at all frequencies. Also by tuning the OPA parameters,
one can suppress the quantum shot-noise at lower frequencies than the resonant
frequency. In the CQNC scheme, the damping rate of the mechanical oscillator
matches the damping rate of the atomic ensemble, which is experimentally
achievable even for a low-frequency mechanical oscillator with a high-quality
factor. Elimination of the back action noise and suppression of the shot noise
significantly enhance force sensing and thus overcome the standard quantum
limit of weak force sensing. This hybrid scheme can play an essential role in
the realization of quantum optomechanical sensors and quantum control.",2201.10805v1
2022-01-31,Indistinguishability-enhanced entanglement recovery by spatially localized operations and classical communication,"We extend a procedure exploiting spatial indistinguishability of identical
particles to recover the spoiled entanglement between two qubits interacting
with Markovian noisy environments. Here, the spatially localized operations and
classical communication (sLOCC) operational framework is used to activate the
entanglement restoration from the indistinguishable constituents. We consider
the realistic scenario where noise acts for the whole duration of the process.
Three standard types of noises are considered: a phase damping, a depolarizing,
and an amplitude damping channel. Within this general scenario, we find the
entanglement to be restored in an amount proportional to the degree of spatial
indistinguishability. These results elevate sLOCC to a practical framework for
accessing and utilizing quantum state protection within a quantum network of
spatially indistinguishable subsystems.",2201.13365v1
2022-02-01,Uniform synchronization of an abstract linear second order evolution system,"Although the mathematical study on the synchronization of wave equations at
finite horizon has been well developed, there was few results on the
synchronization of wave equations for long-time horizon. The aim of the paper
is to investigate the uniform synchronization at the infinite horizon for one
abstract linear second order evolution system in a Hilbert space.
  First, using the classical compact perturbation theory on the uniform
stability of semigroups of contractions, we will establish a lower bound on the
number of damping, necessary for the uniform synchronization of the considered
system. Then, under the minimum number of damping, we clarify the algebraic
structure of the system as well as the necessity of the conditions of
compatibility on the coupling matrices. We then establish the uniform
synchronization by the compact perturbation method and then give the dynamics
of the asymptotic orbit. Various applications are given for the system of wave
equations with boundary feedback or (and) locally distributed feedback, and for
the system of Kirchhoff plate with distributed feedback. Some open questions
are raised at the end of the paper for future development.
  The study is based on the synchronization theory and the compact perturbation
of semigroups.",2202.00771v1
2022-02-02,Electric field screening in pair discharges and generation of pulsar radio emission,"Pulsar radio emission may be generated in pair discharges which fill the
pulsar magnetosphere with plasma as an accelerating electric field is screened
by freshly created pairs. In this Letter we develop a simplified analytic
theory for the screening of the electric field in these pair discharges and use
it to estimate total radio luminosity and spectrum. The discharge has three
stages. First, the electric field is screened for the first time and starts to
oscillate. Next, a nonlinear phase occurs. In this phase, the amplitude of the
electric field experiences strong damping because the field dramatically
changes the momenta of newly created pairs. This strong damping ceases, and the
system enters a final linear phase, when the electric field can no longer
dramatically change pair momenta. Applied to pulsars, this theory may explain
several aspects of radio emission, including the observed luminosity,
$L_{\rm{rad}} \sim 10^{28} \rm{erg} \, \rm{s}^{-1}$, and the observed spectrum,
$S_\omega \sim \omega^{-1.4 \pm 1.0} $.",2202.01303v2
2022-01-22,Dynamics of a Charged Thomas Oscillator in an External Magnetic Field,"In this letter, we provide a detailed numerical examination of the dynamics
of a charged Thomas oscillator in an external magnetic field. We do so by
adopting and then modifying the cyclically symmetric Thomas oscillator to study
the dynamics of a charged particle in an external magnetic field. These
dynamical behaviours for weak and strong field strength parameters fall under
two categories; conservative and dissipative. The system shows a complex
quasi-periodic attractor whose topology depends on initial conditions for high
field strengths in the conservative regime. There is a transition from
adiabatic motion to chaos on decreasing the field strength parameter. In the
dissipative regime, the system is chaotic for weak field strength and weak
damping but shows a limit cycle for high field strengths. Such behaviour is due
to an additional negative feedback loop that comes into action at high field
strengths and forces the system dynamics to be stable in periodic oscillations.
For weak damping and weak field strength, the system dynamics mimic Brownian
motion via chaotic walks.",2202.02383v2
2022-02-15,Damped Online Newton Step for Portfolio Selection,"We revisit the classic online portfolio selection problem, where at each
round a learner selects a distribution over a set of portfolios to allocate its
wealth. It is known that for this problem a logarithmic regret with respect to
Cover's loss is achievable using the Universal Portfolio Selection algorithm,
for example. However, all existing algorithms that achieve a logarithmic regret
for this problem have per-round time and space complexities that scale
polynomially with the total number of rounds, making them impractical. In this
paper, we build on the recent work by Haipeng et al. 2018 and present the first
practical online portfolio selection algorithm with a logarithmic regret and
whose per-round time and space complexities depend only logarithmically on the
horizon. Behind our approach are two key technical novelties of independent
interest. We first show that the Damped Online Newton steps can approximate
mirror descent iterates well, even when dealing with time-varying regularizers.
Second, we present a new meta-algorithm that achieves an adaptive logarithmic
regret (i.e. a logarithmic regret on any sub-interval) for mixable losses.",2202.07574v1
2022-02-22,Modal Estimation on a Warped Frequency Axis for Linear System Modeling,"Linear systems such as room acoustics and string oscillations may be modeled
as the sum of mode responses, each characterized by a frequency, damping and
amplitude. Here, we consider finding the mode parameters from impulse response
measurements, and estimate the mode frequencies and decay rates as the
generalized eigenvalues of Hankel matrices of system response samples, similar
to ESPRIT. For greater resolution at low frequencies, such as desired in room
acoustics and musical instrument modeling, the estimation is done on a warped
frequency axis. The approach has the benefit of selecting the number of modes
to achieve a desired fidelity to the measured impulse response. An optimization
to further refine the frequency and damping parameters is presented. The method
is used to model coupled piano strings and room impulse responses, with its
performance comparing favorably to FZ-ARMA.",2202.11192v1
2022-02-28,Estimating the degree of non-Markovianity using variational quantum circuits,"Several applications of quantum machine learning (QML) rely on a quantum
measurement followed by training algorithms using the measurement outcomes.
However, recently developed QML models, such as variational quantum circuits
(VQCs), can be implemented directly on the state of the quantum system (quantum
data). Here, we propose to use a qubit as a probe to estimate the degree of
non-Markovianity of the environment. Using VQCs, we find an optimal sequence of
qubit-environment interactions that yield accurate estimations of the degree of
non-Markovianity for the amplitude damping, phase damping, and the combination
of both models. We introduce a problem-based ansatz that optimizes upon the
probe qubit and the interaction time with the environment. This work
contributes to practical quantum applications of VQCs and delivers a feasible
experimental procedure to estimate the degree of non-Markovianity.",2202.13964v3
2022-03-08,Interplay between nonlinear spectral shift and nonlinear damping of spin waves in ultrathin YIG waveguides,"We use the phase-resolved imaging to directly study the nonlinear
modification of the wavelength of spin waves propagating in 100-nm thick,
in-plane magnetized YIG waveguides. We show that, by using moderate microwave
powers, one can realize spin waves with large amplitudes corresponding to
precession angles in excess of 10 degrees and nonlinear wavelength variation of
up to 18 percent in this system. We also find that, at large precession angles,
the propagation of spin waves is strongly affected by the onset of nonlinear
damping, which results in a strong spatial dependence of the wavelength. This
effect leads to a spatially dependent controllability of the wavelength by the
microwave power. Furthermore, it leads to the saturation of nonlinear spectral
shift's effects several micrometers away from the excitation point. These
findings are important for the development of nonlinear, integrated spin-wave
signal processing devices and can be used to optimize their characteristics.",2203.04018v1
2022-03-08,The low energy excitation spectrum of magic-angle semimetals,"We theoretically study the excitation spectrum of a two-dimensional Dirac
semimetal in the presence of an incommensurate potential. Such models have been
shown to possess magic-angle critical points in the single particle
wavefunctions, signalled by a momentum space delocalization of plane wave
eigenstates and flat bands due to a vanishing Dirac cone velocity. Using the
kernel polynomial method, we compute the single particle Green's function to
extract the nature of the single particle excitation energy, damping rate, and
quasiparticle residue. As a result, we are able to clearly demonstrate the
redistribution of spectral weight due to quasiperiodicity-induced downfolding
of the Brillouin zone creating minibands with effective mini Brillouin zones
that correspond to emergent superlattices. By computing the damping rate we
show that the vanishing of the velocity and generation of finite density of
states at the magic-angle transition coincides with the development of an
imaginary part in the self energy and a suppression of the quasiparticle
residue that vanishes in a power law like fashion. Observing these effects with
ultracold atoms using momentum resolved radiofrequency spectroscopy is
discussed.",2203.04318v1
2022-03-09,Nonequilibrium Hole Dynamics in Antiferromagnets: Damped Strings and Polarons,"We develop a nonperturbative theory for hole dynamics in antiferromagnetic
spin lattices, as described by the $t$-$J$ model. This is achieved by
generalizing the selfconsistent Born approximation to nonequilibrium systems,
making it possible to calculate the full time-dependent many-body wave
function. Our approach reveals three distinct dynamical regimes, ultimately
leading to the formation of magnetic polarons. Following the initial ballistic
stage of the hole dynamics, coherent formation of string excitations gives rise
to characteristic oscillations in the hole density. Their damping eventually
leaves behind magnetic polarons that undergo ballistic motion with a greatly
reduced velocity. The developed theory provides a rigorous framework for
understanding nonequilibrium physics of defects in quantum magnets and
quantitatively explains recent observations from cold-atom quantum simulations
in the strong coupling regime.",2203.04789v2
2022-03-10,Dynamics of the collapse of a ferromagnetic skyrmion in a centrosymmetric lattice,"Time dependence of the size and chirality of a ferromagnetic skyrmion in a
Heisenberg model with the magnetic field on a square lattice has been studied
analytically and numerically. The lattice and the magnetic field generate
strong time dependence of the skyrmion chirality. Due to nonlinearity, the
lattice alone also generates strong intrinsic damping that leads to the
skyrmion collapse via the emission of spin waves. In the absence of the
magnetic field the collapse is slow for a large skyrmion but it becomes
exponentially fast in the presence of the Landau-Lifshitz damping when the
field is turned on. Magnons emitted by a collapsing skyrmion must have a
discrete spectrum due to the quantization of the skyrmion magnetic moment.",2203.05342v1
2022-03-22,Viscous and centrifugal instabilities of massive stars,"Massive stars exhibit a variety of instabilities, many of which are poorly
understood. We explore instabilities induced by centrifugal forces and angular
momentum transport in massive rotating stars. First, we derive and numerically
solve linearized oscillation equations for adiabatic radial modes in polytropic
stellar models. In the presence of differential rotation, we show that
centrifugal and Coriolis forces combined with viscous angular momentum
transport can excite stellar pulsation modes, under both low- or high-viscosity
conditions. In the low-viscosity limit, which is common in real stars, we
demonstrate how to compute mode growth/damping rates via a work integral.
Finally, we build realistic rotating $30\,M_\odot$ star models and show that
overstable (growing) radial modes are predicted to exist for most of the star's
life, in the absence of non-adiabatic effects. Peak growth rates are predicted
to occur while the star is crossing the Hertzsprung-Russell gap, though
non-adiabatic damping may dominate over viscous driving, depending on the
effective viscosity produced by convective and/or magnetic torques. Viscous
instability could be a new mechanism to drive massive star pulsations and is
possibly related to instabilities of luminous blue variable stars.",2203.11809v1
2022-03-27,Improvement on the blow-up for a weakly coupled wave equations with scale-invariant damping and mass and time derivative nonlinearity,"An improvement of [18] on the blow-up region and the lifespan estimate of a
weakly coupled system of wave equations with damping and mass in the
scale-invariant case and with time-derivative nonlinearity is obtained in this
article. Indeed, thanks to a better understanding of the dynamics of the
solutions, we give here a better characterization of the blow-up region.
Furthermore, the techniques used in this article may be extended to other
systems and interestingly they simplify the proof of the blow-up result in [3]
which is concerned with the single wave equation in the same context as in the
present work.",2203.14403v1
2022-03-24,Walking droplets as a damped-driven system,"We consider the dynamics of a droplet on a vibrating fluid bath. This
hydrodynamic quantum analog system is shown to elicit the canonical behavior of
damped-driven systems, including a period doubling route to chaos. By
approximating the system as a compositional map between the gain and loss
dynamics, the underlying nonlinear dynamics can be shown to be driven by energy
balances in the systems. The gain-loss iterative mapping is similar to a normal
form encoding for the pattern forming instabilities generated in such
spatially-extended system. Similar to mode-locked lasers and rotating
detonation engines, the underlying bifurcations persist for general forms of
the loss and gain, both of which admit explicit representations in our
approximation. Moreover, the resulting geometrical description of the
particle-wave interaction completely characterizes the instabilities observed
in experiments.",2203.14705v2
2022-04-07,Pseudo Numerical Ranges and Spectral Enclosures,"We introduce the new concepts of pseu\-do numerical range for operator
functions and families of sesquilinear forms as well as the pseu\-do block
numerical range for $n \times n$ operator matrix functions. While these notions
are new even in the bounded case, we cover operator polynomials with unbounded
coefficients, unbounded holomorphic form families of type (a) and associated
operator families of type (B). Our main results include spectral inclusion
properties of pseudo numerical ranges and pseudo block numerical ranges. For
diagonally dominant and off-diagonally dominant operator matrices they allow us
to prove spectral enclosures in terms of the pseudo numerical ranges of Schur
complements that no longer require dominance order $0$ and not even $<1$. As an
application, we establish a new type of spectral bounds for linearly damped
wave equations with possibly unbounded and/or singular damping.",2204.03584v1
2022-04-13,Primordial Gravitational Waves Predictions for GW170817-compatible Einstein-Gauss-Bonnet Theory,"In this work we shall calculate in detail the effect of an
GW170817-compatible Einstein-Gauss-Bonnet theory on the energy spectrum of the
primordial gravitational waves. The spectrum is affected by two
characteristics, the overall amplification/damping factor caused by the
GW170817-compatible Einstein-Gauss-Bonnet theory and by the tensor spectral
index and the tensor-to-scalar ratio. We shall present the formalism for
studying the inflationary dynamics and post-inflationary dynamics of
GW170817-compatible Einstein-Gauss-Bonnet theories for all redshifts starting
from the radiation era up to the dark energy era. We exemplify our formalism by
using two characteristic models, which produce viable inflationary and dark
energy eras. As we demonstrate, remarkably the overall damping/amplification
factor is of the order of unity, thus the GW170817-compatible
Einstein-Gauss-Bonnet models affect the primordial gravitational waves energy
spectrum only via their tensor spectral index and the tensor-to-scalar ratio.
Both models have a blue tilted tensor spectrum, and therefore the predicted
energy spectrum of the primordial gravity waves can be detectable by most of
the future gravitational waves experiments, for various reheating temperatures.",2204.06304v1
2022-04-14,Stability of Exponentially Damped Oscillations under Perturbations of the Mori-Chain,"There is an abundance of evidence that some relaxation dynamics, e.g.,
exponential decays, are much more common in nature than others. Recently, there
have been attempts to trace this dominance back to a certain stability of the
prevalent dynamics versus generic Hamiltonian perturbations. In the paper at
hand, we tackle this stability issue from yet another angle, namely in the
framework of the recursion method. We investigate the behavior of various
relaxation dynamics with respect to alterations of the so-called Lanczos
coefficients. All considered scenarios are set up in order to comply with the
""universal operator growth hypothesis"". Our numerical experiments suggest the
existence of stability in a larger class of relaxation dynamics consisting of
exponentially damped oscillations. Further, we propose a criterion to identify
""pathological"" perturbations that lead to uncommon dynamics.",2204.06903v1
2022-04-24,Integrated Local Energy Decay for the Damped Wave Equation on Stationary Space-Times,"We prove integrated local energy decay for the damped wave equation on
stationary, asymptotically flat space-times in (1 + 3) dimensions. Local energy
decay constitutes a powerful tool in the study of dispersive partial
differential equations on such geometric backgrounds. By utilizing the
geometric control condition to handle trapped trajectories, we are able to
recover high frequency estimates without any loss. We may then apply known
estimates from the work of Metcalfe, Sterbenz, and Tataru in the medium and low
frequency regimes in order to establish local energy decay. This generalizes
the integrated version of results established by Bouclet and Royer from the
setting of asymptotically Euclidean manifolds to the full Lorentzian case.",2204.11339v2
2022-04-26,Accelerated-gradient-based generalized Levenberg--Marquardt method with oracle complexity bound and local quadratic convergence,"Minimizing the sum of a convex function and a composite function appears in
various fields. The generalized Levenberg--Marquardt (LM) method, also known as
the prox-linear method, has been developed for such optimization problems. The
method iteratively solves strongly convex subproblems with a damping term. This
study proposes a new generalized LM method for solving the problem with a
smooth composite function. The method enjoys three theoretical guarantees:
iteration complexity bound, oracle complexity bound, and local convergence
under a H\""olderian growth condition. The local convergence results include
local quadratic convergence under the quadratic growth condition; this is the
first to extend the classical result for least-squares problems to a general
smooth composite function. In addition, this is the first LM method with both
an oracle complexity bound and local quadratic convergence under standard
assumptions. These results are achieved by carefully controlling the damping
parameter and solving the subproblems by the accelerated proximal gradient
method equipped with a particular termination condition. Experimental results
show that the proposed method performs well in practice for several instances,
including classification with a neural network and nonnegative matrix
factorization.",2204.12016v3
2022-05-02,Thermoacoustic shocks in complex plasmas,"The formation of thermoacoustic shocks is revealed in a fluid complex plasma.
The thermoacoustic wave mode can be damped (or anti-damped) when the
contribution from the thermoacoustic interaction is lower (or higher) than that
due to the particle collision and/or the kinematic viscosity. In the nonlinear
regime, the thermoacoustic wave, propagating with the acoustic speed, can
evolve into small amplitude shocks whose dynamics is governed by the
Bateman-Burgers equation with nonlocal nonlinearity. The latter can cause the
shock fronts to be stable (or unstable) depending on the collision frequency
remains below (or above) a critical value and the thermal feedback is positive.
The existence of different kinds of shocks and their characteristics are
analyzed with the system parameters that characterize the thermal feedback,
thermal diffusion, heat capacity per fluid particle, the particle collision and
the fluid viscosity. A good agreement between the analytical and numerical
results are also noticed.",2205.00896v1
2022-05-09,Mutual friction and diffusion of two-dimensional quantum vortices,"We present a microscopic open quantum systems theory of thermally-damped
vortex motion in oblate atomic superfluids that includes previously neglected
energy-damping interactions between superfluid and thermal atoms. This
mechanism couples strongly to vortex core motion and causes dissipation of
vortex energy due to mutual friction, as well as Brownian motion of vortices
due to thermal fluctuations. We derive an analytic expression for the
dimensionless mutual friction coefficient that gives excellent quantitative
agreement with experimentally measured values, without any fitted parameters.
Our work closes an existing two orders of magnitude gap between dissipation
theory and experiments, previously bridged by fitted parameters, and provides a
microscopic origin for the mutual friction and diffusion of quantized vortices
in two-dimensional atomic superfluids.",2205.04065v2
2022-05-09,Nonlinear Landau damping for the Vlasov-Poisson system in $\R^3$: the Poisson equilibrium,"We prove asymptotic stability of the Poisson homogeneous equilibrium among
solutions of the Vlassov-Poisson system in the Euclidean space $\mathbb{R}^3$.
More precisely, we show that small, smooth, and localized perturbations of the
Poisson equilibrium lead to global solutions of the Vlasov-Poisson system,
which scatter to linear solutions at a polynomial rate as $t\to\infty$.
  The Euclidean problem we consider here differs significantly from the
classical work on Landau damping in the periodic setting, in several ways. Most
importantly, the linearized problem cannot satisfy a ""Penrose condition"". As a
result, our system contains resonances (small divisors) and the electric field
is a superposition of an electrostatic component and a larger oscillatory
component, both with polynomially decaying rates.",2205.04540v2
2022-05-11,Domain wall damped harmonic oscillations induced by curvature gradients in elliptical magnetic nanowires,"Understanding the domain wall (DW) dynamics in magnetic nanowires (NW) is
crucial for spintronic-based applications demanding the use of DWs as
information carriers. This work focuses on the dynamics of a DW displacing
along a bent NW with an elliptical shape under the action of spin-polarized
electric currents and external magnetic fields. Our results evidence that a
curvature gradient induces an exchange-driven effective tangential field
responsible for pinning a DW near the maximum curvature point in a NW. The DW
equilibrium position depends on the competition between the torques produced by
the external stimuli and the curvature-induced effective fields. When the
external stimuli are below a certain threshold, the DW follows a damped
harmonic oscillation around the equilibrium position. Above this threshold, DW
displaces along the NW under an oscillatory translational motion.",2205.05716v1
2022-05-12,Global existence and stability of subsonic time-periodic solution to the damped compressible Euler equations in a bounded domain,"In this paper, we consider the one-dimensional isentropic compressible Euler
equations with source term $\beta(t,x)\rho|u|^{\alpha}u$ in a bounded domain,
which can be used to describe gas transmission in a nozzle.~The model is
imposed a subsonic time-periodic boundary condition.~Our main results reveal
that the time-periodic boundary can trigger an unique subsonic time-periodic
smooth solution and this unique periodic solution is stable under small
perturbations on initial and boundary data.~To get the existence of subsonic
time-periodic solution, we use the linear iterative skill and transfer the
boundary value problem into two initial value ones by using the hyperbolic
property of the system. Then the corresponding linearized system can be
decoupled.~The uniqueness is a direct by-product of the stability. There is no
small assumptions on the damping coefficient.",2205.05858v2
2022-05-23,"Global existence, uniqueness and $L^{\infty}$-bound of weak solutions of fractional time-space Keller-Segel system","This paper studies the properties of weak solutions to a class of space-time
fractional parabolic-elliptic Keller-Segel equations with logistic source terms
in $\mathbb{R}^{n}$, $n\geq 2$. The global existence and $L^{\infty}$-bound of
weak solutions are established. We mainly divide the damping coefficient into
two cases: (i) $b>1-\frac{\alpha}{n}$, for any initial value and birth rate;
(ii) $0<b\leq 1-\frac{\alpha}{n}$, for small initial value and small birth
rate. The existence result is obtained by verifying the existence of a solution
to the constructed regularization equation and incorporate the generalized
compactness criterion of time fractional partial differential equation. At the
same time, we get the $L^{\infty}$-bound of weak solutions by establishing the
fractional differential inequality and using the Moser iterative method.
Furthermore, we prove the uniqueness of weak solutions by using the
hyper-contractive estimates when the damping coefficient is strong. Finally, we
also propose a blow-up criterion for weak solutions, that is, if a weak
solution blows up in finite time, then for all $h>q$, the $L^{h}$-norms of the
weak solution blow up at the same time.",2205.11041v1
2022-05-23,Schur complement dominant operator matrices,"We propose a method for the spectral analysis of unbounded operator matrices
in a general setting which fully abstains from standard perturbative arguments.
Rather than requiring the matrix to act in a Hilbert space $\mathcal{H}$, we
extend its action to a suitable distributional triple $\mathcal{D} \subset
\mathcal{H} \subset \mathcal{D}_-$ and restrict it to its maximal domain in
$\mathcal{H}$. The crucial point in our approach is the choice of the spaces
$\mathcal{D}$ and $\mathcal{D}_-$ which are essentially determined by the Schur
complement of the matrix. We show spectral equivalence between the resulting
operator matrix in $\mathcal{H}$ and its Schur complement, which allows to pass
from a suitable representation of the Schur complement (e.g. by generalised
form methods) to a representation of the operator matrix. We thereby generalise
classical spectral equivalence results imposing standard dominance patterns.
  The abstract results are applied to damped wave equations with possibly
unbounded and/or singular damping, to Dirac operators with Coulomb-type
potentials, as well as to generic second order matrix differential operators.
By means of our methods, previous regularity assumptions can be weakened
substantially.",2205.11653v1
2022-05-24,Extensions and Analysis of an Iterative Solution of the Helmholtz Equation via the Wave Equation,"In this paper we extend analysis of the WaveHoltz iteration -- a time-domain
iterative method for the solution of the Helmholtz equation. We expand the
previous analysis of energy conserving problems and prove convergence of the
WaveHoltz iteration for problems with impedance boundary conditions in a single
spatial dimension. We then consider interior Dirichlet/Neumann problems with
damping in any spatial dimension, and show that for a sufficient level of
damping the WaveHoltz iteration converges in a number of iteration independent
of the frequency. Finally, we present a discrete analysis of the WaveHoltz
iteration for a family of higher order time-stepping schemes. We show that the
fixed-point of the discrete WaveHoltz iteration converges to the discrete
Helmholtz solution with the order of the time-stepper chosen. We present
numerical examples and demonstrate that it is possible to completely remove
time discretization error from the WaveHoltz solution through careful analysis
of the discrete iteration together with updated quadrature formulas.",2205.12349v1
2022-05-31,Phonon decay in 1D atomic Bose quasicondensates via Beliaev-Landau damping,"In a 1D Bose gas, there is no non-trivial scattering channel involving three
Bogoliubov quasiparticles that conserves both energy and momentum.
Nevertheless, we show that such 3-wave mixing processes (Beliaev and Landau
damping) account for their decay via interactions with thermal fluctuations.
Within an appropriate time window where the Fermi Golden Rule is expected to
apply, the occupation number of the initially occupied mode decays
exponentially and the rate takes a simple analytic form. The result is shown to
compare favorably with simulations based on the Truncated Wigner Approximation.
It is also shown that the same processes slow down the exponential growth of
phonons induced by a parametric oscillation.",2205.15826v2
2022-06-02,Bistability in dissipatively coupled cavity magnonics,"Dissipative coupling of resonators arising from their cooperative dampings to
a common reservoir induces intriguingly new physics such as energy level
attraction. In this study, we report the nonlinear properties in a
dissipatively coupled cavity magnonic system. A magnetic material YIG (yttrium
iron garnet) is placed at the magnetic field node of a Fabry-Perot-like
microwave cavity such that the magnons and cavity photons are dissipatively
coupled. Under high power excitation, a nonlinear effect is observed in the
transmission spectra, showing bistable behaviors. The observed bistabilities
are manifested as clockwise, counterclockwise, and butterfly-like hysteresis
loops with different frequency detuning. The experimental results are well
explained as a Duffing oscillator dissipatively coupled with a harmonic one and
the required trigger condition for bistability could be determined
quantitatively by the coupled oscillator model. Our results demonstrate that
the magnon damping has been suppressed by the dissipative interaction, which
thereby reduces the threshold for conventional magnon Kerr bistability. This
work sheds light upon potential applications in developing low power
nonlinearity devices, enhanced anharmonicity sensors and for exploring the
non-Hermitian physics of cavity magnonics in the nonlinear regime.",2206.01231v1
2022-06-02,Impact of Frequency Support by Wind Turbines on Small-Signal Stability of Power Systems,"Rising wind energy integration, accompanied by a decreasing level of system
inertia, requires additional sources of ancillary services. Wind turbines based
on doubly fed induction generators (DFIG) can provide inertial and primary
frequency support, when equipped with specific controls. This paper
investigates the effect of frequency support provision by DFIGs on the
small-signal stability of power systems. To this end, a modified version of the
Kundur two-area test system is employed to analyze different scenarios. Wind
energy generation is either added to the existing system or displaces part of
the synchronous generation. Simulations show that primary frequency support
tends to improve the damping of electromechanical oscillations and deteriorate
it for converter control-based ones. On the other hand, inertial response may
be either beneficial, detrimental or negligible to damping, depending on the
tuning of control parameters.",2206.01237v1
2022-06-03,An Assessment Of Full-Wave Effects On Maxwellian Lower-Hybrid Wave Damping,"Lower-hybrid current drive (LHCD) actuators are important components of
modern day fusion experiments as well as proposed fusion reactors. However,
simulations of LHCD often differ substantially from experimental results, and
from each other, especially in the inferred power deposition profile shape.
Here we investigate some possible causes of this discrepancy; ""full-wave""
effects such as interference and diffraction, which are omitted from standard
raytracing simulations and the breakdown of the raytracing near reflections and
caustics. We compare raytracing simulations to state-of-the-art full-wave
simulations using matched hot-plasma dielectric tensors in realistic tokamak
scenarios for the first time. We show that differences between full-wave
simulations and raytracing in previous work were primarily due to numerical and
physical inconsistencies in the simulations, and we demonstrate that good
agreement between raytracing and converged full-wave simulations can be
obtained in reactor relevant-scenarios with large ray caustics and in
situations with weak damping.",2206.01773v2
2022-06-06,Fermi spin polaron and dissipative Fermi-polaron Rabi dynamics,"We consider a spin impurity with multiple energy levels moving in a
non-interacting Fermi sea, and theoretically solve this Fermi spin polaron
problem at nonzero temperature by using a non-self-consistent many-body
$T$-matrix theory. We focus on the simplest case with spin half, where the two
energy states of the impurity are coupled by a Rabi flip term. At small Rabi
coupling, the impurity exhibits damped Rabi oscillations, where the decoherence
is caused by the interaction with the Fermi sea, as recently reported in Fermi
polaron experiments with ultracold atoms. We investigate the dependence of Rabi
oscillations on the Rabi coupling strength and examine the additional nonlinear
damping due to large Rabi coupling. At finite temperature and at nonzero
impurity concentration, the impurity can acquire a pronounced momentum
distribution. We show that the momentum/thermal average can sizably reduce the
visibility of Rabi oscillations. We compare our theoretical predictions to the
recent experimental data and find a good agreement without any adjustable
parameter.",2206.02317v4
2022-06-09,A deep learning method for the trajectory reconstruction of cosmic rays with the DAMPE mission,"A deep learning method for the particle trajectory reconstruction with the
DAMPE experiment is presented. The developed algorithms constitute the first
fully machine-learned track reconstruction pipeline for space astroparticle
missions. Significant performance improvements over the standard
hand-engineered algorithms are demonstrated. Thanks to the better accuracy, the
developed algorithms facilitate the identification of the particle absolute
charge with the tracker in the entire energy range, opening a door to the
measurements of cosmic-ray proton and helium spectra at extreme energies,
towards the PeV scale, hardly achievable with the standard track reconstruction
methods. In addition, the developed approach demonstrates an unprecedented
accuracy in the particle direction reconstruction with the calorimeter at high
deposited energies, above several hundred GeV for hadronic showers and above a
few tens of GeV for electromagnetic showers.",2206.04532v2
2022-06-09,Excitation-damping quantum channels,"We study a class of quantum channels describing a quantum system, split into
the direct sum of an excited and a ground sector, undergoing a one-way transfer
of population from the former to the latter; this construction, which provides
a generalization of the amplitude-damping qubit channel, can be regarded as a
way to upgrade a trace non-increasing quantum operation, defined on the excited
sector, to a possibly trace preserving operation on a larger Hilbert space. We
provide necessary and sufficient conditions for the complete positivity of such
channels, and we also show that complete positivity is equivalent to simple
positivity whenever the ground sector is one-dimensional. Finally, we examine
the time-dependent scenario and characterize all CP-divisible channels and
Markovian semigroups belonging to this class.",2206.04623v1
2022-06-16,"Modeling, robust control synthesis and worst-case analysis for an on-orbit servicing mission with large flexible spacecraft","This paper outlines a complete methodology for modeling an on-orbit servicing
mission scenario and designing a feedback control system for the attitude
dynamics that is guaranteed to robustly meet pointing requirements, despite
model uncertainties as well as large inertia and flexibility changes throughout
the mission scenario. A model of the uncertain plant was derived, which fully
captures the dynamics and couplings between all subsystems as well as the
decoupled/coupled configurations of the chaser/target system in a single linear
fractional representation (LFR). In addition, a new approach is proposed to
model and analyze a closed-loop kinematic chain formed by the chaser and the
target spacecraft through the chaser's robotic arm, which uses two local
spring-damper systems with uncertain damping and stiffness. This approach
offers the possibility to model the dynamical behaviour of a docking mechanism
with dynamic stiffness and damping. The controller was designed by taking into
account all the interactions between subsystems and uncertainties as well as
the time-varying and coupled flexible dynamics. Lastly, the robust stability
and worst-case performances were assessed by means of a structured singular
value analysis.",2206.08324v1
2022-06-23,Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe$_3$,"Spin and lattice are two fundamental degrees of freedom in a solid, and their
fluctuations about the equilibrium values in a magnetic ordered crystalline
lattice form quasiparticles termed magnons (spin waves) and phonons (lattice
waves), respectively. In most materials with strong spin-lattice coupling
(SLC), the interaction of spin and lattice induces energy gaps in the spin wave
dispersion at the nominal intersections of magnon and phonon modes. Here we use
neutron scattering to show that in the two-dimensional (2D) van der Waals
honeycomb lattice ferromagnetic CrGeTe3, spin waves propagating within the 2D
plane exhibit an anomalous dispersion, damping, and break-down of quasiparticle
conservation, while magnons along the c axis behave as expected for a local
moment ferromagnet. These results indicate the presence of dynamical SLC
arising from the zero-temperature quantum fluctuations in CrGeTe3, suggesting
that the observed in-plane spin waves are mixed spin and lattice quasiparticles
fundamentally different from pure magnons and phonons.",2206.11962v1
2022-06-28,Strongly damped wave equations with mass-like terms of the logarithmic-Laplacian,"We consider strongly damped wave equations with logarithmic mass-like terms
with a parameter $\theta \in (0; 1]$. This research is a part of a series of
wave equations that was initiated by Char\~ao-Ikehata [6],
Char\~ao-D'Abbicco-Ikehata considered in [5] depending on a parameter $\theta
\in (1/2,1)$ and Piske- Char\~ao-Ikehata [26] for small parameter $\theta \in
(0,1/2)$. We derive a leading term (as time goes to infinity) of the solution,
and by using it, a growth and a decay property of the solution itself can be
precisely studied in terms of L^2-norm. An interesting aspect appears in the
case of n = 1, roughly speaking, a small $\theta$ produces a diffusive
property, and a large $\theta$ gives a kind of singularity, expressed by growth
rates.",2206.13713v1
2022-07-07,Control of Oscillatory Temperature Field in a Building via Damping Assignment to Nonlinear Koopman Mode,"This paper addresses a control problem on air-conditioning systems in
buildings that is regarded as a control practice of nonlinear
distributed-parameter systems. Specifically, we consider the design of a
controller for suppressing an oscillatory response of in-room temperature
field. The main idea in this paper is to apply the emergent theory of Koopman
operator and Koopman mode decomposition for nonlinear systems, and to formulate
a technique of damping assignment to a nonlinear Koopman mode in a fully
data-driven manner. Its effectiveness is examined by numerical simulations
guided by measurement of a practical room space.",2207.03219v1
2022-07-07,New perspectives on transient stability between grid-following and grid-forming VSCs,"The grid-following and grid-forming controls in voltage-source converters are
considered as different operation modes and the synchronization mechanism of
them are studied separately. In this article, the intrinsic relationships
between gridfollowing and grid-forming controlled converters are established as
follows: 1) the proportional gain of PLL is in inverse proportion to damping;
2) the integral gain of PLL is similar to integral droop; 3) PLL has no
practical inertia but acts like grid-forming control in zero inertia cases.
Further, a general stability-enhanced method combining damping and inertia is
proposed, and the modified energy function is obtained to estimate the region
of attraction for the system. Finally, these findings are corroborated by
simulation tests with an intuitive conclusion.",2207.03273v1
2022-07-11,Rapid Stabilization of Timoshenko Beam by PDE Backstepping,"In this paper, we present a rapid boundary stabilization of a Timoshenko beam
with anti-damping and anti-stiffness at the uncontrolled boundary, by using PDE
backstepping. We introduce a transformation to map the Timoshenko beam states
into a (2+2) x (2+2) hyperbolic PIDE-ODE system. Then backstepping is applied
to obtain a control law guaranteeing closed-loop stability of the origin in the
H^1 sense. Arbitrarily rapid stabilization can be achieved by adjusting control
parameters. Finally, a numerical simulation shows that the proposed controller
can rapidly stabilize the Timoshenko beam. This result extends a previous work
which considered a slender Timoshenko beam with Kelvin-Voigt damping, allowing
destabilizing boundary conditions at the uncontrolled boundary and attaining an
arbitrarily rapid convergence rate.",2207.04746v1
2022-07-17,Locational Aspect of Fast Frequency Reserves in Low-Inertia Systems -- Control Performance Analysis,"This paper evaluates the frequency performance of an AC system when primary
frequency response is provided by inverter-based resources located at
remote-areas. Due to potentially larger wave propagation constants over longer
lines, fast active power response from inverter based resources may have a
negative impact on the system frequency response. Within this context, this
paper presents a control performance analysis is presented in order to identify
limitations for improving the frequency stability when inverter-based resources
in remote locations use local frequency measurements. Our results suggest that
there exists a trafeoff between disturbance rejection and stability robustness
when allocating primary frequency control. In particular, fast frequency
control can have a negative impact on the damping ratio of poorly damped
electromechanical modes.",2207.08188v1
2022-07-20,MsSpec-DFM (Dielectric function module): Towards a multiple scattering approach to plasmon description,"We present here the MsSpec Dielectric Function module (MsSpec-DFM), which
generates dielectric functions in an electron gas or a liquid, either isolated
or embedded into an environment. In addition to standard models such as the
plasmon pole and the RPA, this module also provides more involved methods
incorporating local field corrections (in order to account for correlations),
Boltzmann-Vlasov hydrodynamical methods, the relaxation-damped Mermin and the
diffusion-damped Hu-O'Connell methods, as well as moment-based methods using
either a Nevanlinna function or a memory function. Ultimately, through the use
of form factors, the MsSpec-DFM module will be able to address a wide range of
materials such as metals, semiconductors, including inversion layers,
hetero-structures, superconductors, quantum wells, quantum wires, quantum dots,
Dirac materials such as graphene, and liquids.",2207.09924v1
2022-07-25,Extreme bursting events via pulse-shaped explosion in mixed Rayleigh-Lienard nonlinear oscillator,"We study the dynamics of a parametrically and externally driven
Rayleigh-Lienard hybrid model and report the emergence of extreme bursting
events due to a novel pulse-shaped explosion mechanism. The system exhibits
complex periodic and chaotic bursting patterns amid small oscillations as a
function of excitation frequencies. In particular, the advent of rare and
recurrent chaotic bursts that emerged for certain parameter regions is
characterized as extreme events. We have identified that the appearance of a
sharp pulse-like transition that occurred in the equilibrium points of the
system is the underlying mechanism for the development of bursting events.
Further, the controlling aspect of extreme events is attempted by incorporating
a linear damping term, and we show that for sufficiently strong damping
strength, the extreme events are eliminated from the system, and only periodic
bursting is feasible.",2207.11916v1
2022-07-26,The Global Existence of Martingale Solutions to Stochastic Compressible Navier-Stokes Equations with Density-dependent Viscosity,"The global existence of martingale solutions to the compressible
Navier-Stokes equations driven by stochastic external forces, with
density-dependent viscosity and vacuum, is established in this paper. This work
can be regarded as a stochastic version of the deterministic Navier-Stokes
equations \cite{Vasseur-Yu2016} (Vasseur-Yu, Invent. Math., 206:935--974,
2016.), in which the global existence of weak solutions was established for
adiabatic exponent $\gamma > 1$. For the stochastic case, the regularity of
density and velocity is even worse for passing the limit in nonlinear terms. We
design a regularized system to approximate the original system. To make up for
the lack of regularity of velocity, we need to add an artificial Rayleigh
damping term besides the artificial viscosity and damping forces in
\cite{Vasseur-Yu-q2016,Vasseur-Yu2016}. Moreover, we have to send the
artificial terms to $0$ in a different order.",2207.12835v5
2022-08-10,Phonon renormalization effects accompanying the 6 K anomaly in the Quantum Spin Liquid Candidate $κ$-(BEDT-TTF)$_{2}$Cu$_{2}$(CN)$_{3}$,"The low-temperature state of the quantum spin liquid candidate
$\kappa$-(BEDT-TTF)$_{2}$Cu$_{2}$(CN)$_{3}$ emerges via an anomaly at
$T^{*}\sim6$ K. Although signatures of this anomaly have been revealed in
various quantities, its origin has remained unclear. Here we report inelastic
neutron scattering measurements on single crystals of
$\kappa$-(BEDT-TTF)$_{2}$Cu$_{2}$(CN)$_{3}$, aiming at studying phonon
renormalization effects at $T^{*}$. A drastic change was observed in the phonon
damping across $T^{*}$ for a breathing mode of BEDT-TTF dimers at $E=4.7$ meV.
The abrupt change in the phonon damping is attributed to a phase transition
into a valence bond solid state based on an effective model describing the
spin-charge coupling in this dimer-Mott system.",2208.05096v2
2022-08-16,Particle dynamics on torsional galilean spacetimes,"We study free particle motion on homogeneous kinematical spacetimes of
galilean type. The three well-known cases of Galilei and (A)dS--Galilei
spacetimes are included in our analysis, but our focus will be on the
previously unexplored torsional galilean spacetimes. We show how in well-chosen
coordinates free particle motion becomes equivalent to the dynamics of a damped
harmonic oscillator, with the damping set by the torsion. The realization of
the kinematical symmetry algebra in terms of conserved charges is subtle and
comes with some interesting surprises, such as a homothetic version of
hamiltonian vector fields and a corresponding generalization of the Poisson
bracket. We show that the Bargmann extension is universal to all galilean
kinematical symmetries, but also that it is no longer central for nonzero
torsion. We also present a geometric interpretation of this fact through the
Eisenhart lift of the dynamics.",2208.07611v2
2022-08-17,Linking fluctuation and dissipation in spatially extended out-of-equilibrium systems,"For systems in equilibrium at a temperature $T$, thermal noise and energy
damping are related to $T$ through the fluctuation-dissipation theorem (FDT).
We study here an extension of the FDT to an out of equilibrium steady state: a
microcantilever subject to a constant heat flux. The resulting thermal profile
in this spatially extended system interplays with the local energy dissipation
field to prescribe the amplitude of mechanical fluctuations. Using three
samples with different damping profiles (localized or distributed), we probe
this approach and experimentally demonstrate the link between fluctuations and
dissipation. The thermal noise can therefore be predicted a priori from the
measurement of the dissipation as a function of the maximum temperature of the
micro-oscillator.",2208.08356v2
2022-08-27,Quantum Langevin Equation of a spin in a magnetic field : an analysis,"We derive a quantum Langevin equation for a quantum spin in the presence of a
magnetic field and study its dynamics in the Markovian limit using the Ohmic
bath model. We extend our analysis to the Drude bath with a finite memory. We
study the time evolution of the expectation values of the magnetic moments. The
spin auto-correlation functions exhibit a damped oscillatory behaviour with the
randomization time being determined by the damping rate and also the memory
time for the Drude bath model. We also analyse the spin response function of
the system for the Ohmic bath model. Our results are consistent with findings
in cold atom experiments. In addition we make predictions which can be tested
in future ultra cold atom experiments.",2208.12989v1
2022-09-01,\textit{Ab initio} study on spin fluctuations of itinerant kagome magnet FeSn,"Kagome antiferromagnetic metal FeSn has become an attracting platform for the
exploration of novel electronic states, such as topological Dirac states and
the formation of flat bands by localized electrons. Apart from the electronic
properties, Dirac magnons and flat magnon bands have also been proposed by
applying simplified Heisenberg models to kagome magnetic systems.Inelastic
neutron scattering studies on FeSn found well defined magnon dispersions at low
energies,but magnons at high energies are strongly dampled, which can not be
explained by localized spin models. In this paper, we utilize both linear spin
wave theory and time-dependent density functional perturbation theory to
investigate spin fluctuations of FeSn. Through the comparison of calculated
spin wave spectra and Stoner continuum, we explicitly show that the damping of
magnons at high energies are due to the Landau damping, and the appearance of
high energy optical-magnon like branches at the M and K point are resulted by
relatively low Stoner excitation intensity at those regions.",2209.00187v1
2022-09-01,"Comment on ""Damping of neutrino oscillations, decoherence and the lengths of neutrino wave packets''","We point out three apparent inconsistencies in the treatment of oscillation
coherence from reactor neutrino and source neutrino experiments in recent paper
""Damping of neutrino oscillations, decoherence and the lengths of neutrino wave
packets''. First, that the dependence of the oscillation probability upon the
subsequent interactions of entangled recoil particles implies causality
violations and in some situations superluminal signaling; second, that
integrating over a non-orthogonal basis for the entangled recoil leads to
unphysical effects; and third, that the question of what interactions serve to
measure the position of the initial state particle remains ambiguous. These
points taken together appear to undermine the claim made therein that the
effects of wave packet separation must be strictly unobservable in reactor and
radioactive source based neutrino experiments.",2209.00561v1
2022-09-02,The thermal-orbital evolution of the Earth-Moon system with a subsurface magma ocean and fossil figure,"Various theories have been proposed to explain the Moon's current inclined
orbit. We test the viability of these theories by reconstructing the
thermal-orbital history of the Moon. We build on past thermal-orbital models
and incorporate the evolution of the lunar figure including a fossil figure
component. Obliquity tidal heating in the lunar magma ocean would have produced
rapid inclination damping, making it difficult for an early inclination to
survive to the present-day. An early inclination is preserved only if the
solid-body of the early Moon were less dissipative than at present. If
instabilities at the Laplace plane transition were the source of the
inclination, then the Moon had to recede slowly, which is consistent with
previous findings of a weakly dissipative early Earth. If collisionless
encounters with planetesimals up to 140 Myr after Moon formation excited the
inclination, then the Moon had to migrate quickly to pass through the Cassini
state transition at 33 Earth radii and reach a period of limited inclination
damping. The fossil figure was likely established before 16 Earth radii to
match the present-day degree-2 gravity field observations.",2209.00935v1
2022-09-05,A new T-compatibility condition and its application to the discretization of the damped time-harmonic Galbrun's equation,"We consider the approximation of weakly T-coercive operators. The main
property to ensure the convergence thereof is the regularity of the
approximation (in the vocabulary of discrete approximation schemes). In a
previous work the existence of discrete operators $T_n$ which converge to $T$
in a discrete norm was shown to be sufficient to obtain regularity. Although
this framework proved usefull for many applications for some instances the
former assumption is too strong. Thus in the present article we report a weaker
criterium for which the discrete operators $T_n$ only have to converge
point-wise, but in addition a weak T-coercivity condition has to be satisfied
on the discrete level. We apply the new framework to prove the convergence of
certain $H^1$-conforming finite element discretizations of the damped
time-harmonic Galbrun's equation, which is used to model the oscillations of
stars. A main ingredient in the latter analysis is the uniformly stable
invertibility of the divergence operator on certain spaces, which is related to
the topic of divergence free elements for the Stokes equation.",2209.01878v2
2022-09-06,Suppressing Amplitude Damping in Trapped Ions: Discrete Weak Measurements for a Non-unitary Probabilistic Noise Filter,"The idea of exploiting maximally-entangled states as a resource lies at the
core of several modalities of quantum information processing, including secure
quantum communication, quantum computation, and quantum sensing. However, due
to imperfections during or after the entangling gates used to prepare such
states, the amount of entanglement decreases and their quality as a resource
gets degraded. We introduce a low-overhead protocol to reverse this degradation
by partially filtering out a specific type of noise relevant to many quantum
technologies. We present two trapped-ion schemes for the implementation of a
non-unitary probabilistic filter against amplitude damping noise, which can
protect any maximally-entangled pair from spontaneous photon scattering during
or after the two-qubit trapped-ion entangling gates. This filter can be
understood as a protocol for single-copy quasi-distillation, as it uses only
local operations to realise a reversal operation that can be understood in
terms of weak measurements.",2209.02753v1
2022-09-07,Classical correlations for Generic States are Fragile under Decoherence,"Quantum correlations typically decrease with increasing noise, although
classical correlators (CCors) may rise for a particular class of states with
noise. To analyse the behavior of classical correlation (CC) in the presence of
local noise, we scrutinize the set of classical correlators, axiomatic CC
measures like classical discord, and local work for Haar uniformly generated
states. Like quantum correlation measures, we illustrate that when noise levels
rise, the average value of the CC measures for noisy output states obtained
from random input states decreases for most of the channels. We also
demonstrate a connection between the CCors of the noise-affected multipartite
states that are produced and the CCors of the initial states that exhibit
exponential, polynomial, and constant behavior as the noise level changes.
Moreover, based on CCors of the generalised N-qubit W state as input, we
determine a method to discriminate between the quantum channels, namely phase
damping, depolarizing, and amplitude damping channels. We also relate
classical, quantum, and total correlation measures that exhibit a comparable
reaction to decoherence for generic states.",2209.03334v1
2022-09-10,Bulk Viscosity of Relativistic $npeμ$ Matter in Neutron-Star Mergers,"We discuss the bulk viscosity of hot and dense $npe\mu$ matter arising from
weak-interaction direct Urca processes. We consider two regimes of interest:
(a) the neutrino-transparent regime with $T\leq T_{\rm tr}$ ($T_{\rm tr}\simeq
5\div 10$ MeV is the neutrino-trapping temperature); and (b) the
neutrino-trapped regime with $T\geq T_{\rm tr}$. Nuclear matter is modeled in
relativistic density functional approach with density-dependent parametrization
DDME2. The maximum of the bulk viscosity is achieved at temperatures $T \simeq
5\div 6$ MeV in the neutrino-transparent regime, then it drops rapidly at
higher temperatures where neutrino-trapping occurs. As an astrophysical
application, we estimate the damping timescales of density oscillations by the
bulk viscosity in neutron star mergers and find that, e.g., at the oscillation
frequency $f=10$ kHz, the damping will be very efficient at temperatures $4\leq
T\leq 7$ MeV where the bulk viscosity might affect the evolution of the
post-merger object.",2209.04717v1
2022-09-11,Approximation of Algebraic Riccati Equations with Generators of Noncompact Semigroups,"In this work, we demonstrate that the Bochner integral representation of the
Algebraic Riccati Equations (ARE) are well-posed without any compactness
assumptions on the coefficient and semigroup operators. From this result, we
then are able to determine that, under some assumptions, the solution to the
Galerkin approximations to these equations are convergent to the infinite
dimensional solution. Going further, we apply this general result to
demonstrate that the finite element approximation to the ARE are optimal for
weakly damped wave semigroup processes in the $H^1(\Omega) \times L^2(\Omega)$
norm. Optimal convergence rates of the functional gain for a weakly damped wave
optimal control system in both the $H^1(\Omega) \times L^2(\Omega)$ and
$L^2(\Omega)\times L^2(\Omega)$ norms are demonstrated in the numerical
examples.",2209.04769v5
2022-09-11,Toward a Framework for Adaptive Impedance Control of an Upper-limb Prosthesis,"Adapting upper-limb impedance (i.e., stiffness, damping, inertia) is
essential for humans interacting with dynamic environments for executing
grasping or manipulation tasks. On the other hand, control methods designed for
state-of-the-art upper-limb prostheses infer motor intent from surface
electromyography (sEMG) signals in terms of joint kinematics, but they fail to
infer and use the underlying impedance properties of the limb. We present a
framework that allows a human user to simultaneously control the kinematics,
stiffness, and damping of a simulated robot through wrist's flexion-extension.
The framework includes muscle-tendon units and a forward dynamics block to
estimate the motor intent from sEMG signals, and a variable impedance
controller that implements the estimated intent on the robot, allowing the user
to adapt the robot's kinematics and dynamics online. We evaluate our framework
with 8 able-bodied subjects and an amputee during reaching tasks performed in
free space, and in the presence of unexpected external perturbations that
require adaptation of the wrist impedance to ensure stable interaction with the
environment. We experimentally demonstrate that our approach outperforms a
data-driven baseline in terms of its ability to adapt to external
perturbations, overall controllability, and feedback from participants.",2209.04937v2
2022-09-14,Time rescaling of a primal-dual dynamical system with asymptotically vanishing damping,"In this work, we approach the minimization of a continuously differentiable
convex function under linear equality constraints by a second-order dynamical
system with an asymptotically vanishing damping term. The system under
consideration is a time rescaled version of another system previously found in
the literature. We show fast convergence of the primal-dual gap, the
feasibility measure, and the objective function value along the generated
trajectories. These convergence rates now depend on the rescaling parameter,
and thus can be improved by choosing said parameter appropriately. When the
objective function has a Lipschitz continuous gradient, we show that the
primal-dual trajectory asymptotically converges weakly to a primal-dual optimal
solution to the underlying minimization problem. We also exhibit improved rates
of convergence of the gradient along the primal trajectories and of the adjoint
of the corresponding linear operator along the dual trajectories. Even in the
unconstrained case, some trajectory convergence result seems to be new. We
illustrate the theoretical outcomes through numerical experiments.",2209.06438v1
2022-09-18,Numerical Approximations for the Null Controllers of Structurally Damped Plate Dynamics,"In this paper, we consider a structurally damped elastic equation under
hinged boundary conditions. Fully-discrete numerical approximation schemes are
generated for the null controllability of these parabolic-like PDEs. We mainly
use finite element method (FEM) and finite difference method (FDM)
approximations to show that the null controllers being approximated via FEM and
FDM exhibit exactly the same asymptotics of the associated minimal energy
function. For this, we appeal to the theory originally given by R. Triggiani
[20] for construction of null controllers of ODE systems. These null
controllers are also amenable to our numerical implementation in which we
discuss the aspects of FEM and FDM numerical approximations and compare both
methodologies. We justify our theoretical results with the numerical
experiments given for both approximation schemes.",2209.08486v1
2022-09-19,Calculating quasinormal modes of Schwarzschild anti-de Sitter black holes using the continued fraction method,"We investigate the scalar, gravitational, and electromagnetic quasinormal
mode spectra of Schwarzschild anti-de Sitter black holes using the numerical
continued fraction method. The spectra have similar, almost linear structures.
With a few exceptions, the low overtone quasinormal modes are consistent with
previously obtained results in the literature that use other numerical
techniques. The intermediate and high overtone quasinormal modes, in comparison
to the Schwarzschild case, converge very quickly to the asymptotic formulas
previously obtained by analytic monodromy techniques. In addition, we find a
connection between the analytic asymptotic formulas and the purely imaginary
modes. In particular, these formulas can be used to predict the bifurcation of
the lowest damped electromagnetic modes. Finally, we find no high overtone
quasinormal modes with high oscillation frequency and low damping, which had
been previously predicted.",2209.09324v3
2022-09-20,Study of the Global Alignment for the DAMPE Detector,"The Dark Matter Particle Explorer (DAMPE) is designed as a high energy
particle detector for probing cosmic-rays and $\gamma-$rays in a wide energy
range. The trajectory of the incident particle is mainly measured by the
Silicon-Tungsten tracKer-converter (STK) sub-detector, which heavily depends on
the precise internal alignment correction as well as the accuracy of the global
coordinate system. In this work, we carried out a global alignment method to
validate the potential displacement of these sub-detectors, and particularly
demonstrated that the track reconstruction of STK can well satisfy the required
objectives by means of comparing flight data and simulations.",2209.09440v1
2022-09-22,Open quantum system dynamics of $X$-states: Entanglement sudden death and sudden birth,"The origin of disentanglement for two specific sub-classes of $X$-states
namely maximally nonlocal mixed states (MNMSs) and maximally entangled mixed
states (MEMSs) is investigated analytically for a physical system consisting of
two spatially separated qubits interacting with a common vacuum bath. The
phenomena of entanglement sudden death (ESD) and the entanglement sudden birth
(ESB) are observed, but the characteristics of ESD and ESB are found to be
different for the case of two photon coherence and single photon coherence
states. The role played by initial coherence for the underlying entanglement
dynamics is investigated. Further, the entanglement dynamics of MNMSs and MEMSs
under different environmental noises namely phase damping, amplitude damping
and RTN noise with respect to the decay and revival of entanglement is
analyzed. It's observed that the single photon coherence states are more robust
against the sudden death of entanglement indicating the usability of such
states in the development of technologies for the practical implementation of
quantum information processing tasks.",2209.11190v1
2022-09-23,Kernel-based quantum regressor models learn non-Markovianity,"Quantum machine learning is a growing research field that aims to perform
machine learning tasks assisted by a quantum computer. Kernel-based quantum
machine learning models are paradigmatic examples where the kernel involves
quantum states, and the Gram matrix is calculated from the overlap between
these states. With the kernel at hand, a regular machine learning model is used
for the learning process. In this paper we investigate the quantum support
vector machine and quantum kernel ridge models to predict the degree of
non-Markovianity of a quantum system. We perform digital quantum simulation of
amplitude damping and phase damping channels to create our quantum dataset. We
elaborate on different kernel functions to map the data and kernel circuits to
compute the overlap between quantum states. We show that our models deliver
accurate predictions that are comparable with the fully classical models.",2209.11655v1
2022-09-24,Reflectionless Programmable Signal Routers,"We demonstrate experimentally that reflectionless scattering modes (RSMs), a
generalized version of coherent perfect absorption, can be functionalized to
perform reflectionless programmable signal routing. We achieve versatile
programmability both in terms of operating frequencies and routing
functionality with negligible reflection upon in-coupling, which avoids
unwanted signal-power echoes in radio-frequency or photonic networks. We report
in-situ observations of routing functionalities like wavelength demultiplexing,
including cases where multi-channel excitation requires adapted coherent input
wavefronts. All experiments are performed in the microwave domain based on the
same irregularly shaped cavity with strong modal overlap that is massively
parametrized by a 304-element programmable metasurface. RSMs in our highly
overdamped multi-resonance transport problem are fundamentally intriguing
because the simple critical-coupling picture for reflectionless excitation of
isolated resonances fails spectacularly. We show in simulation that the
distribution of damping rates of scattering singularities broadens under strong
absorption so that weakly damped zeros can be tuned toward functionalized RSMs.",2209.11991v1
2022-09-30,A simple analytical expression of quantum Fisher and Skew information and their dynamics under decoherence channels,"In statistical estimation theory, it has been shown previously that the
Wigner-Yanase skew information is bounded by the quantum Fisher information
associated with the phase parameter. Besides, the quantum Cram\'er-Rao
inequality is expressed in terms of skew information. Since these two
fundamental quantities are based on the concept of quantum uncertainty, we
derive here their analytical formulas for arbitrary two qubit $X$-states using
the same analytical procedures. A comparison of these two informational
quantifiers for two quasi-Werner states composed of two bipartite superposed
coherent states is examined. Moreover, we investigated the decoherence effects
on such quantities generated by the phase damping, depolarization and amplitude
damping channels. We showed that decoherence strongly influences the quantum
criteria during the evolution and these quantities exhibit similar dynamic
behaviors. This current work is characterized by the fact that these two
concepts play the same role and capture similar properties in quantum
estimation protocols.",2209.15593v2
2022-10-03,"Voltage control of frequency, effective damping and threshold current in nano-constriction-based spin Hall nano-oscillators","Using micromagnetic simulations, we study the interplay between strongly
voltage-controlled magnetic anisotropy (VCMA), $\Delta K = \pm$200 kJ/m$^3$,
and gate width, $w=$ 10--400 nm, in voltage-gated W/CoFeB/MgO based
nano-constriction spin Hall nano-oscillators. The VCMA modifies the local
magnetic properties such that the magnetodynamics transitions between regimes
of \emph{i}) confinement, \emph{ii}) tuning, and \emph{iii}) separation, with
qualitatively different behavior. We find that the strongest tuning is achieved
for gate widths of the same size as the the constriction width, for which the
effective damping can be increased an order of magnitude compared to its
intrinsic value. As a consequence, voltage control remains efficient over a
very large frequency range, and subsequent manufacturing advances could allow
SHNOs to be easily integrated into next-generation electronics for further
fundamental studies and industrial applications.",2210.01042v1
2022-10-18,Evidence of fresh cosmic ray in galactic plane based on DAMPE measurement of B/C and B/O ratios,"More and more experiments have identified that the energy spectra of both
primary and secondary cosmic-rays exhibit a hardening above $\sim 200$ GV. Most
recently, the DAMPE experiment has reported a hardening of boron-to-carbon
ratio at $200$ GV. These signs call for modifications of the conventional
cosmic-ray (CR) picture. In this work, we propose that the plethoric secondary
cosmic rays, for example, boron, antiprotons, originate from the hadronic
interactions of freshly accelerated cosmic rays with the interstellar gas near
the sources. We find that secondary-to-primary ratios, for example,
boron-to-carbon, boron-to-oxygen and antiproton-to-proton ratios, could be well
described. The measurements of electrons and positrons could also be accounted
for.",2210.09591v2
2022-10-19,Global well-posedness of the partially damped 2D MHD equations via a direct normal mode method for the anisotropic linear operator,"We prove the global well-posedness of the 2D incompressible non-resistive MHD
equations with a velocity damping term near the non-zero constant background
magnetic field. To this end, we newly design a normal mode method of
effectively leveraging the anisotropy of the linear propagator that encodes
both the partially dissipative nature of the non-resistive MHD system and the
stabilizing mechanism of the underlying magnetic field. Isolating new key
quantities and estimating them with themselves in an entangling way via the
eigenvalue analysis based on Duhamel's formulation, we establish the global
well-posedness for any initial data $(v_0,B_0)$ that is sufficiently small in a
space rougher than $H^{4}\cap L^1$. This improves the recent work in SIAM J.
Math. Anal. 47, 2630-2656 (2015) where the similar result was obtained provided
that $(v_0,B_0)$ was small enough in a space strictly embedded in $H^{20}\cap
W^{6,1}$.",2210.10283v1
2022-10-19,Design and Modeling of a PVDF-TrFe Flexible Wind Energy Harvester,"This study presents the simulation, experimentation, and design
considerations of a Poly(vinylidene fluoride co-trifluoroethylene)/
Polyethylene Terephthalate (PVDF-TrFe / PET), laser-cut, flexible piezoelectric
energy harvester. It is possible to obtain energy from the environment around
autonomous sensor systems, which can then be used to power various equipment.
This article investigates the actuation means of ambient vibration, which is a
good candidate for using piezoelectric energy harvester (PEH) devices. The
output voltage characteristics were analyzed in a wind test apparatus. Finite
element modeling (FEM) was done for von Mises stress and modal analysis.
Resonance frequency sweeps, quality factors, and damping ratios of the circular
plate were given numerically. For a PVDF-TrFe piezoelectric layer thickness of
18 $\mu$m and 1.5 mm radius, a damping ratio of 0.117 and a quality factor of
4.284 was calculated. $V_{max}$ was calculated as 984 mV from the wind setup
and compared with the FEM outputs.",2210.10540v1
2022-10-20,Parameter analysis in continuous data assimilation for three-dimensional Brinkman-Forchheimer-extended Darcy,"In this paper, we study analytically the long-time behavior of
three-dimensional Brinkman-Forchheimer-extended Darcy model, in the context
that the parameters related to the damping nonlinear term are unknown. This
work is inspired by the approach firstly introduced for two-dimensional
Navier-Stokes equations by Carlson, Hudson and Larios. We show estimates in L2
and H1 for large-time error between the true solution and the assimilated
solution, which is constructed with the unknown damping parameters and
observational measurements obtained continuously in time from a continuous data
assimilation technique proposed by Azouani, Olson and Titi.",2210.11432v1
2022-10-21,Breathers in lattices with alternating strain-hardening and strain-softening interactions,"This work focuses on the study of time-periodic solutions, including
breathers, in a nonlinear lattice consisting of elements whose contacts
alternate between strain-hardening and strain-softening. The existence,
stability, and bifurcation structure of such solutions, as well as the system
dynamics in the presence of damping and driving are studied systematically. It
is found that the linear resonant peaks in the system bend toward the frequency
gap in the presence of nonlinearity. The time-periodic solutions that lie
within the frequency gap compare well to Hamiltonian breathers if the damping
and driving are small. In the Hamiltonian limit of the problem, we use a
multiple scale analysis to derive a Nonlinear Schr\""odinger (NLS) equation to
construct both acoustic and optical breathers. The latter compare very well
with the numerically obtained breathers in the Hamiltonian limit.",2210.11690v1
2022-10-28,"Two novel families of multiscale staggered patch schemes efficiently simulate large-scale, weakly damped, linear waves","Many multiscale wave systems exhibit macroscale emergent behaviour, for
example, the fluid dynamics of floods and tsunamis. Resolving a large range of
spatial scales typically requires a prohibitively high computational cost. The
small dissipation in wave systems poses a significant challenge to further
developing multiscale modelling methods in multiple dimensions. This article
develops and evaluates two families of equation-free multiscale methods on
novel 2D staggered patch schemes, and demonstrates the power and utility of
these multiscale schemes for weakly damped linear waves. A detailed study of
sensitivity to numerical roundoff errors establishes the robustness of
developed staggered patch schemes. Comprehensive eigenvalue analysis over a
wide range of parameters establishes the stability, accuracy, and consistency
of the multiscale schemes. Analysis of the computational complexity shows that
the measured compute times of the multiscale schemes may be 10^5 times smaller
than the compute time for the corresponding full-domain computation. This work
provides the essential foundation for efficient large-scale simulation of
challenging nonlinear multiscale waves.",2210.15823v1
2022-11-07,On Vacuum Free Boundary Problem of the Spherically Symmetric Euler Equations with Damping and Solid Core,"In this paper, the global existence of smooth solution and the long-time
asymptotic stability of the equilibrium to vacuum free boundary problem of the
spherically symmetric Euler equations with damping and solid core have been
obtained for arbitrary finite positive gas constant $A$ in the state equation
$p=A \rho^\gamma$ with $p$ being the pressure and $\rho$ the density, provided
that $\gamma>4/3,$ initial perturbation is small and the radius of the
equilibrium $R$ is suitably larger than the radius of the solid core $r_0$.
Moreover, we obtain the pointwise convergence from the smooth solution to the
equilibrium in a surprisingly exponential time-decay rate. The proof is mainly
based on weighted energy method in Lagrangian coordinate.",2211.03347v2
2022-11-07,A role of potential on L^{2}-estimates for some evolution equations,"In this papwe we consider an effective role of the potential of the wave
equations with/without damping on the L^{2}-estimate of the solution itself. In
the free wave equation case it is known that the L^{2}-norm of the solution
itself generally grows to infinity (as time goes to infinity) in the one and
two dimensional cases, however, by adding the potential with quite generous
conditions one can controle the growth property to get the L^{2}-bounds. This
idea can be also applied to the damped wave equations with potential in order
to get fast energy and L^{2} decay results in the low dimensional case, which
are open for a long period. Applications to heat and plate equations with a
potential can be also studied. In this paper the low dimensional case is a main
target.",2211.03389v1
2022-11-08,Cost-optimal adaptive iterative linearized FEM for semilinear elliptic PDEs,"We consider scalar semilinear elliptic PDEs where the nonlinearity is
strongly monotone, but only locally Lipschitz continuous. We formulate an
adaptive iterative linearized finite element method (AILFEM) which steers the
local mesh refinement as well as the iterative linearization of the arising
nonlinear discrete equations. To this end, we employ a damped Zarantonello
iteration so that, in each step of the algorithm, only a linear Poisson-type
equation has to be solved. We prove that the proposed AILFEM strategy
guarantees convergence with optimal rates, where rates are understood with
respect to the overall computational complexity (i.e., the computational time).
Moreover, we formulate and test an adaptive algorithm where also the damping
parameter of the Zarantonello iteration is adaptively adjusted. Numerical
experiments underline the theoretical findings.",2211.04123v2
2022-11-11,Radiation reaction effects in relativistic plasmas -- the electrostatic limit,"We study the evolution of electrostatic plasma waves, using the relativistic
Vlasov equation extended by the Landau-Lifshitz radiation reaction, accounting
for the back-reaction due to the emission of single particle Larmor radiation.
In particular, the Langmuir wave damping is calculated as a function of
wavenumber, initial temperature, and initial electric field amplitude.
Moreover, the background distribution function loses energy in the process, and
we calculate the cooling rate as a function of initial temperature and initial
wave amplitude. Finally, we investigate how the relative magnitude of wave
damping and background cooling varies with the initial parameters. In
particular, it is found that the relative contribution to the energy loss
associated with background cooling decreases slowly with the initial wave
amplitude.",2211.06240v1
2022-11-15,Limits of the phonon quasi-particle picture at the cubic-to-tetragonal phase transition in halide perovskites,"The soft modes associated with continuous-order phase transitions are
associated with strong anharmonicity. This leads to the overdamped limit where
the phonon quasi-particle picture can breakdown. However, this limit is
commonly restricted to a narrow temperature range, making it difficult to
observe its signature feature, namely the breakdown of the inverse relationship
between the relaxation time and damping. Here we present a physically intuitive
picture based on the relaxation times of the mode coordinate and its conjugate
momentum, which at the instability approach infinity and the inverse damping
factor, respectively. We demonstrate this behavior for the cubic-to-tetragonal
phase transition of the inorganic halide perovskite CsPbBr$_3$ via molecular
dynamics, and show that the overdamped region extends almost 200 K above the
transition temperature. Further, we investigate how the dynamics of these soft
phonon modes change when crossing the phase transition.",2211.08197v2
2022-11-16,Endemic Oscillations for SARS-CoV-2 Omicron -- A SIRS model analysis,"The SIRS model with constant vaccination and immunity waning rates is well
known to show a transition from a disease-free to an endemic equilibrium as the
basic reproduction number $r_0$ is raised above threshold. It is shown that
this model maps to Hethcote's classic endemic model originally published in
1973. In this way one obtains unifying formulas for a whole class of models
showing endemic bifurcation. In particular, if the vaccination rate is smaller
than the recovery rate and $r_- < r_0 < r_+$ for certain upper and lower bounds
$r_\pm$, then trajectories spiral into the endemic equilibrium via damped
infection waves. Latest data of the SARS-CoV-2 Omicron variant suggest that
according to this simplified model continuous vaccination programs will not be
capable to escape the oscillating endemic phase. However, in view of the strong
damping factors predicted by the model, in reality these oscillations will
certainly be overruled by time-dependent contact behaviors.",2211.09005v2
2022-11-18,"Accelerated gradient methods with strong convergence to the minimum norm minimizer: a dynamic approach combining time scaling, averaging, and Tikhonov regularization","In a Hilbert framework, for convex differentiable optimization, we consider
accelerated gradient methods obtained by combining temporal scaling and
averaging techniques with Tikhonov regularization. We start from the continuous
steepest descent dynamic with an additional Tikhonov regularization term whose
coefficient vanishes asymptotically. We provide an extensive Lyapunov analysis
of this first-order evolution equation. Then we apply to this dynamic the
method of time scaling and averaging recently introduced by Attouch, Bot and
Nguyen. We thus obtain an inertial dynamic which involves viscous damping
associated with Nesterov's method, implicit Hessian damping and Tikhonov
regularization. Under an appropriate setting of the parameters, just using
Jensen's inequality, without the need for another Lyapunov analysis, we show
that the trajectories have at the same time several remarkable properties: they
provide a rapid convergence of values, fast convergence of the gradients to
zero, and strong convergence to the minimum norm minimizer. These results
complete and improve the previous results obtained by the authors.",2211.10140v1
2022-12-15,DAMP: Doubly Aligned Multilingual Parser for Task-Oriented Dialogue,"Modern virtual assistants use internal semantic parsing engines to convert
user utterances to actionable commands. However, prior work has demonstrated
that semantic parsing is a difficult multilingual transfer task with low
transfer efficiency compared to other tasks. In global markets such as India
and Latin America, this is a critical issue as switching between languages is
prevalent for bilingual users. In this work we dramatically improve the
zero-shot performance of a multilingual and codeswitched semantic parsing
system using two stages of multilingual alignment. First, we show that
constrastive alignment pretraining improves both English performance and
transfer efficiency. We then introduce a constrained optimization approach for
hyperparameter-free adversarial alignment during finetuning. Our Doubly Aligned
Multilingual Parser (DAMP) improves mBERT transfer performance by 3x, 6x, and
81x on the Spanglish, Hinglish and Multilingual Task Oriented Parsing
benchmarks respectively and outperforms XLM-R and mT5-Large using 3.2x fewer
parameters.",2212.08054v2
2022-12-21,Global existence and Blow-up for the 1D damped compressible Euler equations with time and space dependent perturbation,"In this paper, we consider the 1D Euler equation with time and space
dependent damping term $-a(t,x)v$. It has long been known that when $a(t,x)$ is
a positive constant or $0$, the solution exists globally in time or blows up in
finite time, respectively. We prove that those results are invariant with
respect to time and space dependent perturbations. We suppose that the
coefficient $a$ satisfies the following condition $$ |a(t,x)- \mu_0| \leq
a_1(t) + a_2 (x), $$ where $\mu_0 \geq 0$ and $a_1$ and $a_2$ are integrable
functions with $t$ and $x$. Under this condition, we show the global existence
and the blow-up with small initial data, when $\mu_0 >0$ and $\mu=0$
respectively.",2212.11072v2
2022-12-22,Bayesian Physics-Informed Neural Networks for Robust System Identification of Power Systems,"This paper introduces for the first time, to the best of our knowledge, the
Bayesian Physics-Informed Neural Networks for applications in power systems.
Bayesian Physics-Informed Neural Networks (BPINNs) combine the advantages of
Physics-Informed Neural Networks (PINNs), being robust to noise and missing
data, with Bayesian modeling, delivering a confidence measure for their output.
Such a confidence measure can be very valuable for the operation of safety
critical systems, such as power systems, as it offers a degree of
trustworthiness for the neural network output. This paper applies the BPINNs
for robust identification of the system inertia and damping, using a single
machine infinite bus system as the guiding example. The goal of this paper is
to introduce the concept and explore the strengths and weaknesses of BPINNs
compared to existing methods. We compare BPINNs with the PINNs and the recently
popular method for system identification, SINDy. We find that BPINNs and PINNs
are robust against all noise levels, delivering estimates of the system inertia
and damping with significantly lower error compared to SINDy, especially as the
noise levels increases.",2212.11911v1
2022-12-29,Scheduling of Software-Defined Microgrids for Optimal Frequency Regulation,"Integrated with a high share of Inverter-Based Resources (IBRs), microgrids
face increasing complexity of frequency dynamics, especially after
unintentional islanding from the maingrid. These IBRs, on the other hand,
provide more control flexibility to shape the frequency dynamics of microgrid
and together with advanced communication infrastructure offer new opportunities
in the future software-defined microgrids. To enhance the frequency stability
of microgrids with high IBR penetration, this paper proposes an optimal
scheduling framework for software-defined microgrids to maintain frequency
stability by utilizing the non-essential load shedding and dynamical
optimization of the virtual inertia and virtual damping from IBRs. Moreover,
side effects of these services, namely, the time delay associated with
non-essential load shedding and potential IBR control parameter update failure
are explicitly modeled to avoid underestimations of frequency deviation and
over-optimistic results. The effectiveness and significant economic value of
the proposed simultaneous and dynamic virtual inertia and damping provision
strategy are demonstrated based on case studies in the modified IEEE 33-bus
system.",2212.14250v3
2023-01-01,Blow-up of a structural acoustics model,"This article studies the finite time blow-up of weak solutions to a
structural acoustics model consisting of a semilinear wave equation defined on
a bounded domain $\Omega\subset\mathbb{R}^3$ which is strongly coupled with a
Berger plate equation acting on the elastic wall, namely, a flat portion of the
boundary. The system is influenced by several competing forces, including
boundary and interior source and damping terms. We stress that the power-type
source term acting on the wave equation is allowed to have a supercritical
exponent, in the sense that its associated Nemytskii operators is not locally
Lipschitz from $H^1$ into $L^2$. In this paper, we prove the blow-up results
for weak solutions when the source terms are stronger than damping terms, by
considering two scenarios of the initial data: (i) the initial total energy is
negative; (ii) the initial total energy is positive but small, while the
initial quadratic energy is sufficiently large. The most significant challenge
in this work arises from the coupling of the wave and plate equations on the
elastic wall.",2301.00485v1
2023-01-03,Spin-orbit torque for field-free switching in C_{3v} crystals,"Spin-orbit torques in noncentrosymmetric polycrystalline magnetic
heterostructures are usually described in terms of field-like and damping-like
torques. However, materials with a lower symmetry point group can exhibit
torques whose behavior substantially deviates from the conventional ones. In
particular, based on symmetry arguments it was recently proposed that systems
belonging to the C_{3v} point group display spin-orbit torques that can promote
field-free switching [Liu et al. Nature Nanotechnology 16, 277 (2021)]. In the
present work, we analyze the general form of the torques expected in C3v
crystals using the Invariant Theory. We uncover several new components that
arise from the coexistence of the three-fold rotation and mirror symmetries.
Using both tight binding model and first principles simulations, we show that
these unconventional torque components arise from the onset of trigonal warping
of the Fermi surface and can be as large as the damping-like torque. In other
words, the Fermi surface warping is a key indicator to the onset of field-free
switching in low symmetry crystals.",2301.01133v2
2023-01-06,A Deep Reinforcement Learning-Based Controller for Magnetorheological-Damped Vehicle Suspension,"This paper proposes a novel approach to controller design for MR-damped
vehicle suspension system. This approach is predicated on the premise that the
optimal control strategy can be learned through real-world or simulated
experiments utilizing a reinforcement learning algorithm with continuous
states/actions. The sensor data is fed into a Twin Delayed Deep Deterministic
Policy Gradient (TD3) algorithm, which generates the actuation voltage required
for the MR damper. The resulting suspension space (displacement), sprung mass
acceleration, and dynamic tire load are calculated using a quarter vehicle
model incorporating the modified Bouc-Wen MR damper model. Deep RL's reward
function is based on sprung mass acceleration. The proposed approach
outperforms traditional suspension control strategies regarding ride comfort
and stability, as demonstrated by multiple simulated experiments",2301.02714v2
2023-01-07,Quantization of the Bateman damping system with conformable derivative,"In this work, the conformable Bateman Lagrangian for the damped harmonic
oscillator system is proposed using the conformable derivative concept. In
other words, the integer derivatives are replaced by conformable derivatives of
order $\alpha$ with $0<\alpha\leq 1$. The corresponding conformable
Euler-Lagrange equations of motion and fractional Hamiltonian are then
obtained. The system is then canonically quantized and the conformable
Schrodinger equation is constructed. The fractional-order dependence of the
energy eigenvalues $E_n ^\alpha$ and eigenfunctions $\psi_n ^\alpha$ are
obtained using using suitable transformations and the extended fractional
Nikiforov-Uvarov method. The corresponding conformable continuity equation is
also derived and the probability density and probability current are thus
suitably defined. The probability density evolution as well as its dependence
on $\alpha$ is plotted and analyzed for various situations. It is found that
the energy eigenvalues are real and there are sort of gradual ordering in the
behavior of the probability densities.",2301.02769v1
2023-01-17,Taking advantage of noise in quantum reservoir computing,"The biggest challenge that quantum computing and quantum machine learning are
currently facing is the presence of noise in quantum devices. As a result, big
efforts have been put into correcting or mitigating the induced errors. But,
can these two fields benefit from noise? Surprisingly, we demonstrate that
under some circumstances, quantum noise can be used to improve the performance
of quantum reservoir computing, a prominent and recent quantum machine learning
algorithm. Our results show that the amplitude damping noise can be beneficial
to machine learning, while the depolarizing and phase damping noises should be
prioritized for correction. This critical result sheds new light into the
physical mechanisms underlying quantum devices, providing solid practical
prescriptions for a successful implementation of quantum information processing
in nowadays hardware.",2301.06814v3
2023-01-18,Damping versus oscillations for a gravitational Vlasov-Poisson system,"We consider a family of isolated inhomogeneous steady states to the
gravitational Vlasov-Poisson system with a point mass at the centre. They are
parametrised by the polytropic index $k>1/2$, so that the phase space density
of the steady state is $C^1$ at the vacuum boundary if and only if $k>1$. We
prove the following sharp dichotomy result: if $k>1$ the linear perturbations
Landau damp and if $1/2< k\le1$ they do not.
  The above dichotomy is a new phenomenon and highlights the importance of
steady state regularity at the vacuum boundary in the discussion of long-time
behaviour of the perturbations. Our proof of (nonquantitative) gravitational
relaxation around steady states with $k>1$ is the first such result for the
gravitational Vlasov-Poisson system. The key step in the proof is to show that
no embedded eigenvalues exist in the essential spectrum of the linearised
system.",2301.07662v1
2023-01-22,Magnon bundle in a strongly dissipative magnet,"Hybrid quantum systems based on magnetic platforms have witnessed the birth
and fast development of quantum spintronics. Until now, most of the studies
rely on magnetic excitations in low-damping magnetic insulators, particularly
yttrium iron garnet, while a large class of magnetic systems is ruled out in
this interdisciplinary field. Here we propose the generation of a magnon bundle
in a hybrid magnet-qubit system, where two or more magnons are emitted
simultaneously. By tuning the driving frequency of qubit to match the detuning
between magnon and qubit mode, one can effectively generate a magnon bundle via
super-Rabi oscillations. In contrast with general wisdom, magnetic dissipation
plays an enabling role in generating the magnon bundle, where the relaxation
time of magnons determines the typical time delay between two successive
magnons. The maximal damping that allows an antibunched magnon bundle can reach
the order of 0.1, which may break the monopoly of low-dissipation magnetic
insulators in quantum spintronics and enables a large class of magnetic
materials for quantum manipulation. Further, our finding may provide a scalable
and generic platform to study multi-magnon physics and benefit the design of
magnonic networks for quantum information processing.",2301.09095v1
2023-01-24,Effect of mesonic off-shell correlations in the PNJL equation of state,"We study the meson contribution to the equation of state of the 2-flavor PNJL
model, including the full momentum dependence of the meson polarization loops.
Within the Beth-Uhlenbeck approach, we demonstrate that the contribution from
the quark-antiquark continuum excitations in the spacelike region $\omega^2 -
q^2 < 0$, i.e. the Landau damping, leads to an increase of the pressure for
temperatures $\gtrsim 0.8\,T_c^\chi$ and a significant meson momentum cut-off
dependence in the mesonic pressure and the QCD trace anomaly. We investigate
the dependence of the results on the choice of the Polyakov-loop potential
parameter $T_0$. From the dependence of the mesonic pressure on the current
quark mass, by means of the Feynman-Hellmann theorem, we evaluate the
contribution of the pion quasiparticle gas and Landau damping to the chiral
condensate.",2301.09882v1
2023-01-28,A speed restart scheme for a dynamics with Hessian driven damping,"In this paper, we analyze a speed restarting scheme for the dynamical system
given by $$ \ddot{x}(t) + \dfrac{\alpha}{t}\dot{x}(t) + \nabla \phi(x(t)) +
\beta \nabla^2 \phi(x(t))\dot{x}(t)=0, $$ where $\alpha$ and $\beta$ are
positive parameters, and $\phi:\mathbb{R}^n \to \mathbb{R}$ is a smooth convex
function. If $\phi$ has quadratic growth, we establish a linear convergence
rate for the function values along the restarted trajectories. As a byproduct,
we improve the results obtained by Su, Boyd and Cand\`es
\cite{JMLR:v17:15-084}, obtained in the strongly convex case for $\alpha=3$ and
$\beta=0$. Preliminary numerical experiments suggest that both adding a
positive Hessian driven damping parameter $\beta$, and implementing the restart
scheme help improve the performance of the dynamics and corresponding iterative
algorithms as means to approximate minimizers of $\phi$.",2301.12240v1
2023-01-31,Force moment partitioning and scaling analysis of vortices shed by a 2D pitching wing in quiescent fluid,"We experimentally study the dynamics and strength of vortices shed from a
NACA 0012 wing undergoing sinusoidal pitching in quiescent water. We
characterize the temporal evolution of the vortex trajectory and circulation
over a range of pitching frequencies, amplitudes and pivot locations. By
employing a physics-based force and moment partitioning method (FMPM), we
estimate the vortex-induced aerodynamic moment from the velocity fields
measured using particle image velocimetry. The vortex circulation, formation
time and vorticity-induced moment are shown to follow scaling laws based on the
feeding shear-layer velocity. The vortex dynamics, together with the spatial
distribution of the vorticity-induced moment, provide quantitative explanations
for the nonlinear behaviors observed in the fluid damping (Zhu et al., J. Fluid
Mech., vol. 923, 2021, R2). The FMPM-estimated moment and damping are shown to
match well in trend with direct force measurements, despite a discrepancy in
magnitude. Our results demonstrate the powerful capability of the FMPM in
dissecting experimental flow field data and providing valuable insights into
the underlying flow physics.",2301.13373v2
2023-02-13,A damped elastodynamics system under the global injectivity condition: Local wellposedness in $L^p$-spaces,"The purpose of this paper is to model mathematically mechanical aspects of
cardiac tissues. The latter constitute an elastic domain whose total volume
remains constant. The time deformation of the heart tissue is modeled with the
elastodynamics equations dealing with the displacement field as main unknown.
These equations are coupled with a pressure whose variations characterize the
heart beat. This pressure variable corresponds to a Lagrange multiplier
associated with the so-called global injectivity condition. We derive the
corresponding coupled system with nonhomogeneous boundary conditions where the
pressure variable appears. For mathematical convenience a damping term is
added, and for a given class of strain energies we prove the existence of
local-in-time solutions in the context of the $L^p$-parabolic maximal
regularity.",2302.06327v2
2023-02-16,Energy decay for wave equations with a potential and a localized damping,"We consider the total energy decay together with L^2-bound of the solution
itself of the Cauchy problem for wave equations with a localized damping and a
short-range potential. We treat it in the one dimensional Euclidean space R. We
adopt a simple multiplier method to study them. In this case, it is essential
that the compactness of the support of the initial data is not assumed. Since
this problem is treated in the whole space, the Poincare and Hardy inequalities
are not available as is developed in the exterior domain case. For compensating
such a lack of useful tools, the potential plays an effective role. As an
application, the global existence of small data solution for a semilinear
problem is provided.",2302.08114v1
2023-02-24,An Oscillation-free Spectral Volume Method for Hyperbolic Conservation Laws,"In this paper, an oscillation-free spectral volume (OFSV) method is proposed
and studied for the hyperbolic conservation laws. The numerical scheme is
designed by introducing a damping term in the standard spectral volume method
for the purpose of controlling spurious oscillations near discontinuities.
Based on the construction of control volumes (CVs), two classes of OFSV schemes
are presented. A mathematical proof is provided to show that the proposed OFSV
is stable and has optimal convergence rate and some desired superconvergence
properties when applied to the linear scalar equations. Both analysis and
numerical experiments indicate that the damping term would not destroy the
order of accuracy of the original SV scheme and can control the oscillations
discontinuities effectively. Numerical experiments are presented to demonstrate
the accuracy and robustness of our scheme.",2302.12412v1
2023-03-01,Event-triggered boundary damping of a linear wave equation,"This article presents an analysis of the stabilization of a multidimensional
partial differential wave equation under a well designed event-triggering
mechanism that samples the boundary control input. The wave equation is set in
a bounded domain and the control is performed through a boundary classical
damping term, where the Neumann boundary condition is made proportional to the
velocity. First of all, existence and regularity of the solution to the
closed-loop system under the event-triggering mechanism of the control are
proven. Then, sufficient conditions based on the use of a specific Lyapunov
functional are proposed in order to ensure that the solutions converge into a
compact set containing the origin, that can be tuned by the designer.
Furthermore, as expected, any Zeno behavior of the closed-loop system is
avoided.",2303.00381v1
2023-03-05,Coupling of magnetism and Dirac fermions in YbMnSb2,"We report inelastic neutron scattering measurements of magnetic excitations
in YbMnSb2, a low-carrier-density Dirac semimetal in which the
antiferromagnetic Mn layers are interleaved with Sb layers that host Dirac
fermions. We observe a considerable broadening of spin waves, which is
consistent with substantial spin fermion coupling. The spin wave damping,
$\gamma$, in YbMnSb2 is roughly twice larger compared to that in a sister
material, YbMnBi2, where an indication of a small damping consistent with
theoretical analysis of the spin-fermion coupling was reported. The inter-plane
interaction between the Mn layers in YbMnSb2 is also much stronger, suggesting
that the interaction mechanism is rooted in the same spin-fermion coupling. Our
results establish the systematics of spin-fermion interactions in layered
magnetic Dirac materials.",2303.02587v2
2023-03-08,Initial value formulation of a quantum damped harmonic oscillator,"The in-in formalism and its influence functional generalization are widely
used to describe the out-of-equilibrium dynamics of unitary and open quantum
systems, respectively. In this paper, we build on these techniques to develop
an effective theory of a quantum damped harmonic oscillator and use it to study
initial state-dependence, decoherence, and thermalization. We first consider a
Gaussian initial state and quadratic influence functional and obtain general
equations for the Green's functions of the oscillator. We solve the equations
in the specific case of time-local dissipation and use the resulting Green's
functions to obtain the purity and unequal-time two-point correlations of the
oscillator. In particular, we find that the dynamics must include a
non-vanishing noise term to yield physical results. We show that the oscillator
decoheres in time such that the late-time density operator is thermal, and find
the parameter regime for which the fluctuation-dissipation relation is
satisfied. We next develop a double in-out path integral approach to go beyond
Gaussian initial states and show that our equal-time results are in fact
non-perturbative in the initial state.",2303.04829v1
2023-03-17,Stochastic wave equations with constraints: well-posedness and Smoluchowski-Kramers diffusion approximation,"We investigate the well-posedness of a class of stochastic second-order in
time damped evolution equations in Hilbert spaces, subject to the constraint
that the solution lie within the unitary sphere. Then, we focus on a specific
example, the stochastic damped wave equation in a bounded domain of a
$d$-dimensional Euclidean space, endowed with the Dirichlet boundary condition,
with the added constraint that the $L^2$-norm of the solution is equal to one.
We introduce a small mass $\mu>0$ in front of the second-order derivative in
time and examine the validity of a Smoluchowski-Kramers diffusion
approximation. We demonstrate that, in the small mass limit, the solution
converges to the solution of a stochastic parabolic equation subject to the
same constraint. We further show that an extra noise-induced drift emerges,
which in fact does not account for the Stratonovich-to-It\^{o} correction term.",2303.09717v2
2023-03-21,Entropically damped artificial compressibility for the discretization corrected particle strength exchange method in incompressible fluid mechanics,"We present a consistent mesh-free numerical scheme for solving the
incompressible Navier-Stokes equations. Our method is based on entropically
damped artificial compressibility for imposing the incompressibility constraint
explicitly, and the Discretization-Corrected Particle Strength Exchange
(DC-PSE) method to consistently discretize the differential operators on
mesh-free particles. We further couple our scheme with Brinkman penalization to
solve the Navier-Stokes equations in complex geometries. The method is
validated using the 3D Taylor-Green vortex flow and the lid-driven cavity flow
problem in 2D and 3D, where we also compare our method with hr-SPH and report
better accuracy for DC-PSE. In order to validate DC-PSE Brinkman penalization,
we study flow past obstacles, such as a cylinder, and report excellent
agreement with previous studies.",2303.11983v2
2023-03-30,Superfluid $^3$He-B Surface States in a Confined Geometry Probed by a Microelectromechanical Oscillator,"A microelectromechanical oscillator with a 0.73 $\mu$m gap structure is
employed to probe the surface Andreev bound states in superfluid $^3$He-B. The
surface specularity of the oscillator is increased by preplating it with 1.6
monolayers of $^4$He. In the linear regime, the temperature dependence of the
damping coefficient is measured at various pressures, and the normalized energy
gap is extracted. The damping coefficient increases after preplating at lower
pressures, which is attributed to the decreased energy minigap of the surface
bound states. The device is also driven into the nonlinear regime, where the
temperature independent critical velocity at each pressure is measured. The
critical velocity is observed to increase after preplating at all pressures,
which might be related to the increased average energy gap. The observed
behavior warrants a microscopic theory beyond a single parameter
characterization of the surface.",2303.17073v1
2023-04-04,A damped Kačanov scheme for the numerical solution of a relaxed p(x)-Poisson equation,"The focus of the present work is the (theoretical) approximation of a
solution of the p(x)-Poisson equation. To devise an iterative solver with
guaranteed convergence, we will consider a relaxation of the original problem
in terms of a truncation of the nonlinearity from below and from above by using
a pair of positive cut-off parameters. We will then verify that, for any such
pair, a damped Ka\v{c}anov scheme generates a sequence converging to a solution
of the relaxed equation. Subsequently, it will be shown that the solutions of
the relaxed problems converge to the solution of the original problem in the
discrete setting. Finally, the discrete solutions of the unrelaxed problem
converge to the continuous solution. Our work will finally be rounded up with
some numerical experiments that underline the analytical findings.",2304.01566v1
2023-04-05,Optomechanical coupling and damping of a carbon nanotube quantum dot,"Carbon nanotubes are excellent nano-electromechanical systems, combining high
resonance frequency, low mass, and large zero-point motion. At cryogenic
temperatures they display high mechanical quality factors. Equally they are
outstanding single electron devices with well-known quantum levels and have
been proposed for the implementation of charge or spin qubits. The integration
of these devices into microwave optomechanical circuits is however hindered by
a mismatch of scales, between typical microwave wavelengths, nanotube segment
lengths, and nanotube deflections. As experimentally demonstrated recently in
[Blien et al., Nat. Comm. 11, 1363 (2020)], coupling enhancement via the
quantum capacitance allows to circumvent this restriction. Here we extend the
discussion of this experiment. We present the subsystems of the device and
their interactions in detail. An alternative approach to the optomechanical
coupling is presented, allowing to estimate the mechanical zero point motion
scale. Further, the mechanical damping is discussed, hinting at hitherto
unknown interaction mechanisms.",2304.02748v3
2023-04-12,Micromagnetics simulations and phase transitions of ferromagnetics with Dzyaloshinskii-Moriya interaction,"Magnetic skyrmions widely exist in a diverse range of magnetic systems,
including chiral magnets with a non-centrosymmetric structure characterized by
Dzyaloshinkii-Moriya interaction~(DMI). In this study, we propose a generalized
semi-implicit backward differentiation formula projection method, enabling the
simulations of the Landau-Lifshitz~(LL) equation in chiral magnets in a typical
time step-size of $1$ ps, markedly exceeding the limit subjected by existing
numerical methods of typically $0.1$ ps. Using micromagnetics simulations, we
show that the LL equation with DMI reveals an intriguing dynamic instability in
magnetization configurations as the damping varies. Both the isolated
skyrmionium and skyrmionium clusters can be consequently produced using a
simple initialization strategy and a specific damping parameter. Assisted by
the string method, the transition path between skyrmion and skyrmionium, along
with the escape of a skyrmion from the skyrmion clusters, are then thoroughly
examined. The numerical methods developed in this work not only provide a
reliable paradigm to investigate the skyrmion-based textures and their
transition paths, but also facilitate the understandings for magnetization
dynamics in complex magnetic systems.",2304.05789v1
2023-04-12,Abstract damped wave equations: The optimal decay rate,"The exponential decay rate of the semigroup $S(t)=e^{t\mathbb{A}}$ generated
by the abstract damped wave equation $$\ddot u + 2f(A) \dot u +A u=0 $$ is here
addressed, where $A$ is a strictly positive operator. The continuous function
$f$, defined on the spectrum of $A$, is subject to the constraints $$\inf
f(s)>0\qquad\text{and}\qquad \sup f(s)/s <\infty$$ which are known to be
necessary and sufficient for exponential stability to occur. We prove that the
operator norm of the semigroup fulfills the estimate $$\|S(t)\|\leq
Ce^{\sigma_*t}$$ being $\sigma_*<0$ the supremum of the real part of the
spectrum of $\mathbb{A}$. This estimate always holds except in the resonant
cases, where the negative exponential $e^{\sigma_*t}$ turns out to be penalized
by a factor $(1+t)$. The decay rate is the best possible allowed by the theory.",2304.05816v1
2023-04-28,Primal-Dual Damping algorithms for optimization,"We propose an unconstrained optimization method based on the well-known
primal-dual hybrid gradient (PDHG) algorithm. We first formulate the optimality
condition of the unconstrained optimization problem as a saddle point problem.
We then compute the minimizer by applying generalized primal-dual hybrid
gradient algorithms. Theoretically, we demonstrate the continuous-time limit of
the proposed algorithm forms a class of second-order differential equations,
which contains and extends the heavy ball ODEs and Hessian-driven damping
dynamics. Following the Lyapunov analysis of the ODE system, we prove the
linear convergence of the algorithm for strongly convex functions.
Experimentally, we showcase the advantage of algorithms on several convex and
non-convex optimization problems by comparing the performance with other
well-known algorithms, such as Nesterov's accelerated gradient methods. In
particular, we demonstrate that our algorithm is efficient in training
two-layer and convolution neural networks in supervised learning problems.",2304.14574v2
2023-05-01,Global existence and optimal decay of solutions to the incompressible Oldroyd-B model with only stress tensor dissipation and without damping mechanism,"We study the $d$-dimensional ($d\geq2$) incompressible Oldroyd-B model with
only stress tensor diffusion and without velocity dissipation as well as the
damping mechanism on the stress tensor. Firstly, based upon some new
observations on the model, we develope the pure energy argument (independent of
spectral analysis) in general $L^p$ framework, and present a small initial data
global existence and uniqueness of solutions to the model. Our results yield
that the coupling and interaction of the velocity and the non-Newtonian stress
actually enhances the regularity of the system. Later, by adding some
additional $L^2$ type conditions on the low frequencies of the initial data
$(u_0,\tau_0)$, %but without any more smallness restrictions, we obtain the
optimal time-decay rates of the global solution $(u,\tau)$. Our result solves
the problem proposed in Wang, Wu, Xu and Zhong \cite{Wang-Wu-Xu-Zhong} ({\it J.
Funct. Anal.}, 282 (2022), 109332.).",2305.00839v3
2023-05-02,Non-Markovian quantum interconnect formed by a surface plasmon polariton waveguide,"Allowing the generation of effective interactions between distant quantum
emitters (QEs) via flying photons, quantum interconnect (QI) is essentially a
light-matter interface and acts as a building block in quantum technologies. A
surface plasmon polariton (SPP) supported by a metallic waveguide provides an
ideal interface to explore strong light-matter couplings and to realize QI.
However, the loss of SPP in metal makes the mediated entanglement of the QEs
damp with the increase of the distance and time, which hinders its
applications. We propose a scheme of non-Markovian QI formed by the SPP of a
metallic nanowire. A mechanism to make the generated entanglement of the QEs
persistent is discovered. We find that, as long as bound states are formed in
the energy spectrum of total QE-SPP system, the damping of the SPP-mediated
entanglement is overcome even in the presence of the metal absorption to the
SPP. Our finding enriches our understanding of light-matter couplings in
absorptive medium and paves the way for using the SPP in designing QI.",2305.01156v2
2023-05-17,Stationary solutions for the nonlinear Schrödinger equation,"We construct stationary statistical solutions of a deterministic unforced
nonlinear Schr\""odinger equation, by perturbing it by a linear damping $\gamma
u$ and a stochastic force whose intensity is proportional to $\sqrt \gamma$,
and then letting $\gamma\to 0^+$. We prove indeed that the family of stationary
solutions $\{U_\gamma\}_{\gamma>0}$ of the perturbed equation possesses an
accumulation point for any vanishing sequence $\gamma_j\to 0^+$ and this
stationary limit solves the deterministic unforced nonlinear Schr\""odinger
equation and is not the trivial zero solution. This technique has been
introduced in [KS04], using a different dissipation. However considering a
linear damping of zero order and weaker solutions we can deal with larger
ranges of the nonlinearity and of the spatial dimension; moreover we consider
the focusing equation and the defocusing equation as well.",2305.10393v1
2023-05-22,Sketch-and-Project Meets Newton Method: Global $\mathcal O(k^{-2})$ Convergence with Low-Rank Updates,"In this paper, we propose the first sketch-and-project Newton method with
fast $\mathcal O(k^{-2})$ global convergence rate for self-concordant
functions. Our method, SGN, can be viewed in three ways: i) as a
sketch-and-project algorithm projecting updates of Newton method, ii) as a
cubically regularized Newton ethod in sketched subspaces, and iii) as a damped
Newton method in sketched subspaces. SGN inherits best of all three worlds:
cheap iteration costs of sketch-and-project methods, state-of-the-art $\mathcal
O(k^{-2})$ global convergence rate of full-rank Newton-like methods and the
algorithm simplicity of damped Newton methods. Finally, we demonstrate its
comparable empirical performance to baseline algorithms.",2305.13082v2
2023-05-26,Energetic cost for speedy synchronization in non-Hermitian quantum dynamics,"Quantum synchronization is crucial for understanding complex dynamics and
holds potential applications in quantum computing and communication. Therefore,
assessing the thermodynamic resources required for finite-time synchronization
in continuous-variable systems is a critical challenge. In the present work, we
find these resources to be extensive for large systems. We also bound the speed
of quantum and classical synchronization in coupled damped oscillators with
non-Hermitian anti-PT-symmetric interactions, and show that the speed of
synchronization is limited by the interaction strength relative to the damping.
Compared to the classical limit, we find that quantum synchronization is slowed
by the non-commutativity of the Hermitian and anti-Hermitian terms. Our general
results could be tested experimentally and we suggest an implementation in
photonic systems.",2305.16560v1
2023-05-31,Viscous damping in weltering motion of trapped hydrodynamic dipolar Fermi gases,"We consider collective motion and damping of dipolar Fermi gases in the
hydrodynamic regime. We investigate the trajectories of collective oscillations
-- here dubbed ``weltering'' motions -- in cross-dimensional rethermalization
experiments via Monte Carlo simulations, where we find stark differences from
the dilute regime. These observations are interpreted within a semi-empirical
theory of viscous hydrodynamics for gases confined to anisotropic harmonic
potentials. The derived equations of motion provide a simple effective theory
that show favorable agreement with full numerical solutions. To do so, the
theory must carefully account for the size and shape of the effective volume
within which the gas' behavior is hydrodynamic. Although formulated for dipolar
molecules, our theoretical framework retains a flexibility to accommodate
arbitrary elastic cross sections.",2306.00250v1
2023-06-01,Interferometry of Efimov states in thermal gases by modulated magnetic fields,"We demonstrate that an interferometer based on modulated magnetic field
pulses enables precise characterization of the energies and lifetimes of Efimov
trimers irrespective of the magnitude and sign of the interactions in 85Rb
thermal gases. Despite thermal effects, interference fringes develop when the
dark time between the pulses is varied. This enables the selective excitation
of coherent superpositions of trimer, dimer and free atom states. The
interference patterns possess two distinct damping timescales at short and long
dark times that are either equal to or twice as long as the lifetime of Efimov
trimers, respectively. Specifically, this behavior at long dark times provides
an interpretation of the unusually large damping timescales reported in a
recent experiment with 7Li thermal gases [Phys. Rev. Lett. 122, 200402 (2019)].
Apart from that, our results constitute a stepping stone towards a high
precision few-body state interferometry for dense quantum gases.",2306.01199v3
2023-06-06,Convergence analysis of nonconform $H(\operatorname{div})$-finite elements for the damped time-harmonic Galbrun's equation,"We consider the damped time-harmonic Galbrun's equation, which is used to
model stellar oscillations. We introduce a discontinuous Galerkin finite
element method (DGFEM) with $H(\operatorname{div})$-elements, which is
nonconform with respect to the convection operator. We report a convergence
analysis, which is based on the frameworks of discrete approximation schemes
and T-compatibility. A novelty is that we show how to interprete a DGFEM as a
discrete approximation scheme and this approach enables us to apply compact
perturbation arguments in a DG-setting, and to circumvent any extra regularity
assumptions on the solution. The advantage of the proposed
$H(\operatorname{div})$-DGFEM compared to $H^1$-conforming methods is that we
do not require a minimal polynomial order or any special assumptions on the
mesh structure. The considered DGFEM is constructed without a stabilization
term, which considerably improves the assumption on the smallness of the Mach
number compared to other DG methods and $H^1$-conforming methods, and the
obtained bound is fairly explicit. In addition, the method is robust with
respect to the drastic changes of magnitude of the density and sound speed,
which occur in stars. The convergence of the method is obtained without
additional regularity assumptions on the solution, and for smooth solutions and
parameters convergence rates are derived.",2306.03496v1
2023-06-06,Plasmons for the Hartree equations with Coulomb interaction,"In this work, we establish the existence and decay of {\em plasmons}, the
quantum of Langmuir's oscillatory waves found in plasma physics, for the
linearized Hartree equations describing an interacting gas of infinitely many
fermions near general translation-invariant steady states, including compactly
supported Fermi gases at zero temperature, in the whole space $\RR^d$ for $d\ge
2$. Notably, these plasmons exist precisely due to the long-range pair
interaction between the particles. Next, we provide a survival threshold of
spatial frequencies, below which the plasmons purely oscillate and disperse
like a Klein-Gordon's wave, while at the threshold they are damped by {\em
Landau damping}, the classical decaying mechanism due to their resonant
interaction with the background fermions. The explicit rate of Landau damping
is provided for general radial homogenous equilibria. Above the threshold, the
density of the excited fermions is well approximated by that of the free gas
dynamics and thus decays rapidly fast for each Fourier mode via {\em phase
mixing}. Finally, pointwise bounds on the Green function and dispersive
estimates on the density are established.",2306.03800v1
2023-06-10,"Discrepant Approaches to Modeling Stellar Tides, and the Blurring of Pseudosynchronization","We examine the reasons for discrepancies between two alternative approaches
to modeling small-amplitude tides in binary systems. The 'direct solution' (DS)
approach solves the governing differential equations and boundary conditions
directly, while the 'modal decomposition' (MD) approach relies on a normal-mode
expansion. Applied to a model for the primary star in the heartbeat system
KOI-54, the two approaches predict quite different behavior of the secular
tidal torque. The MD approach exhibits the pseudosynchronization phenomenon,
where the torque due to the equilibrium tide changes sign at a single,
well-defined and theoretically predicted stellar rotation rate. The DS approach
instead shows 'blurred' pseudosynchronization, where positive and negative
torques intermingle over a range of rotation rates.
  We trace a major source of these differences to an incorrect damping
coefficient in the profile functions describing the frequency dependence of the
MD expansion coefficients. With this error corrected some differences between
the approaches remain; however, both are in agreement that
pseudosynchronization is blurred in the KOI-54 system. Our findings generalize
to any type of star for which the tidal damping depends explicitly or
implicitly on the forcing frequency.",2306.06429v1
2023-06-19,Spin transport and magnetic proximity effect in CoFeB/normal metal/Pt trilayers,"We present a study of the damping and spin pumping properties of CoFeB/X/Pt
systems with $\rm X=Al,Cr$ and $\rm Ta$. We show that the total damping of the
CoFeB/Pt systems is strongly reduced when an interlayer is introduced
independently of the material. Using a model that considers spin relaxation, we
identify the origin of this contribution in the magnetically polarized Pt
formed by the magnetic proximity effect (MPE), which is suppressed by the
introduction of the interlayer. The induced ferromagnetic order in the Pt layer
is confirmed by transverse magneto-optical Kerr spectroscopy at the M$_{2,3}$
and N$_7$ absorption edges as an element-sensitive probe. We discuss the impact
of the MPE on parameter extraction in the spin transport model.",2306.11009v2
2023-06-23,Energy-optimal control of adaptive structures,"Adaptive structures are equipped with sensors and actuators to actively
counteract external loads such as wind. This can significantly reduce resource
consumption and emissions during the life cycle compared to conventional
structures. A common approach for active damping is to derive a
port-Hamiltonian model and to employ linear-quadratic control. However, the
quadratic control penalization lacks physical interpretation and merely serves
as a regularization term. Rather, we propose a controller, which achieves the
goal of vibration damping while acting energy-optimal. Leveraging the
port-Hamiltonian structure, we show that the optimal control is uniquely
determined, even on singular arcs. Further, we prove a stable long-time
behavior of optimal trajectories by means of a turnpike property. Last, the
proposed controller's efficiency is evaluated in a numerical study.",2306.13331v2
2023-06-23,Low-Lying Collective Excitations of Superconductors and Charged Superfluids,"We investigate theoretically the momentum-dependent frequency and damping of
low-lying collective excitations of superconductors and charged superfluids in
the BCS-BEC crossover regime. The study is based on the Gaussian
pair-and-density fluctuation method for the propagator of Gaussian fluctuations
of the pair and density fields. Eigenfrequencies and damping rates are
determined in a mutually consistent nonperturbative way as complex poles of the
fluctuation propagator. Particular attention is paid to new features with
respect to preceding theoretical studies, which were devoted to collective
excitations of superconductors in the far BCS regime. We find that at a
sufficiently strong coupling, new branches of collective excitations appear,
which manifest different behavior as functions of the momentum and the
temperature.",2306.13393v1
2023-06-27,On Nonlinear Scattering of Drift Wave by Toroidal Alfven Eigenmode in Tokamak Plasmas,"Using electron drift wave (eDW) as a paradigm model, we have investigated
analytically direct wave-wave interactions between a test DW and ambient
toroidal Alfv\'en eigenmodes (TAE) in toroidal plasmas, and their effects on
the stability of the eDW. The nonlinear effects enter via scatterings to
short-wavelength electron Landau damped kinetic Alfv\'en waves (KAWs).
Specifically, it is found that scatterings to upper-sideband KAW lead to
stimulated absorption of eDW. Scatterings to the lower-sideband KAW, on the
contrary, lead to its spontaneous emission. As a consequence, for typical
parameters and fluctuation intensity, nonlinear scatterings by TAE have
negligible net effects on the eDW stability; in contrast to the ``reverse""
process investigated in Ref. [Nuclear Fusion {\bf 62}, 094001 (2022)], where it
is shown that nonlinear scattering by ambient eDW may lead to significant
damping of TAE.",2306.15238v1
2023-06-27,Ground-state cooling of a mechanical oscillator by heating,"Dissipation and the accompanying fluctuations are often seen as detrimental
for quantum systems, since they are associated with fast relaxation and loss of
phase coherence. However, it has been proposed that a pure state can be
prepared if external noise induces suitable downwards transitions, while
exciting transitions are blocked. We demonstrate such a refrigeration mechanism
in a cavity optomechanical system, where we prepare a mechanical oscillator in
its ground state by injecting strong electromagnetic noise at frequencies
around the red mechanical sideband of the cavity. The optimum cooling is
reached with a noise bandwidth smaller than, but on the order of the cavity
decay rate. At higher bandwidths, cooling is less efficient. In the opposite
regime where the noise bandwidth becomes comparable to the mechanical damping
rate, damping follows the noise amplitude adiabatically, and the cooling is
also suppressed.",2306.15746v1
2023-07-07,Tikhonov regularized second-order plus first-order primal-dual dynamical systems with asymptotically vanishing damping for linear equality constrained convex optimization problems,"In this paper, in the setting of Hilbert spaces, we consider a Tikhonov
regularized second-order plus first-order primal-dual dynamical system with
asymptotically vanishing damping for a linear equality constrained convex
optimization problem. The convergence properties of the proposed dynamical
system depend heavily upon the choice of the Tikhonov regularization parameter.
When the Tikhonov regularization parameter decreases rapidly to zero, we
establish the fast convergence rates of the primal-dual gap, the objective
function error, the feasibility measure, and the gradient norm of the objective
function along the trajectory generated by the system. When the Tikhonov
regularization parameter tends slowly to zero, we prove that the primal
trajectory of the Tikhonov regularized dynamical system converges strongly to
the minimal norm solution of the linear equality constrained convex
optimization problem. Numerical experiments are performed to illustrate the
efficiency of our approach.",2307.03612v1
2023-07-14,"The Effects of Viscosity on the Linear Stability of Damped Stokes Waves, Downshifting, and Rogue Wave Generation","We investigate a higher order nonlinear Schr\""odinger equation with linear
damping and weak viscosity, recently proposed as a model for deep water waves
exhibiting frequency downshifting. Through analysis and numerical simulations,
we discuss how the viscosity affects the linear stability of the Stokes wave
solution, enhances rogue wave formation, and leads to permanent downshift in
the spectral peak. The novel results in this work include the analysis of the
transition from the initial Benjamin-Feir instability to a predominantly
oscillatory behavior, which takes place in a time interval when most rogue wave
activity occurs. In addition, we propose new criteria for downshifting in the
spectral peak and determine the relation between the time of permanent
downshift and the location of the global minimum of the momentum and the
magnitude of its second derivative.",2307.07156v2
2023-07-17,Tidal excitation of the obliquity of Earth-like planets in the habitable zone of M-dwarf stars,"Close-in planets undergo strong tidal interactions with the parent star that
modify their spins and orbits. In the two-body problem, the final stage for
tidal evolution is the synchronisation of the rotation and orbital periods, and
the alignment of the planet spin axis with the normal to the orbit (zero planet
obliquity). The orbital eccentricity is also damped to zero, but over a much
longer timescale, that may exceed the lifetime of the system. For non-zero
eccentricities, the rotation rate can be trapped in spin-orbit resonances that
delay the evolution towards the synchronous state. Here we show that capture in
some spin-orbit resonances may also excite the obliquity to high values rather
than damp it to zero. Depending on the system parameters, obliquities of 60 to
80 degrees can be maintained throughout the entire lifetime of the planet. This
unexpected behaviour is particularly important for Earth-like planets in the
habitable zone of M-dwarf stars, as it may help to sustain temperate
environments and thus more favourable conditions for life.",2307.08770v1
2023-07-19,A spin-rotation mechanism of Einstein-de Haas effect based on a ferromagnetic disk,"Spin-rotation coupling (SRC) is a fundamental phenomenon that connects
electronic spins with the rotational motion of a medium. We elucidate the
Einstein-de Haas (EdH) effect and its inverse with SRC as the microscopic
mechanism using the dynamic spin-lattice equations derived by elasticity theory
and Lagrangian formalism. By applying the coupling equations to an iron disk in
a magnetic field, we exhibit the transfer of angular momentum and energy
between spins and lattice, with or without damping. The timescale of the
angular momentum transfer from spins to the entire lattice is estimated by our
theory to be on the order of 0.01 ns, for the disk with a radius of 100 nm.
Moreover, we discover a linear relationship between the magnetic field strength
and the rotation frequency, which is also enhanced by a higher ratio of Young's
modulus to Poisson's coefficient. In the presence of damping, we notice that
the spin-lattice relaxation time is nearly inversely proportional to the
magnetic field. Our explorations will contribute to a better understanding of
the EdH effect and provide valuable insights for magneto-mechanical
manufacturing.",2307.10390v1
2023-07-20,Interaction-mitigated Landau damping,"Bosonic collective modes are ubiquitous in metals, but over a wide range of
energy and momenta suffer from Landau damping, decaying into the continuum of
particle-hole excitations. Here we point out that interactions can suppress
this decay, protecting a finite fraction of the total spectral weight
associated with the collective mode, e.g. a plasmon. The underlying mechanism
is level repulsion between a discrete mode and the continuum. We demonstrate
the effect using a number of simplified models of strongly correlated
Fermi-liquid metals, including a ``solvable"" random flavor model in the
large$-N$ limit. We discuss in detail the possibility of observing such an
avoided decay for plasmons in (moir\'e) graphene-like systems.",2307.11169v2
2023-07-20,Electron-positron plasma in BBN: damped-dynamic screening,"We characterize in detail the very dense $e^- e^+ \gamma$ plasma present
during the Big-Bang Nucleosynthesis (BBN) and explore how it is perturbed
electromagnetically by \lq\lq impurities, {\it i.e.\/}, spatially dispersed
protons and light nuclei undergoing thermal motion. The internuclear
electromagnetic screened potential is obtained (analytically) using the linear
response approach, allowing for the dynamic motion of the electromagnetic field
sources and the damping effects due to plasma component scattering. We discuss
the limits of the linear response method and suggest additional work needed to
improve BBN reaction rates in the primordial Universe. Our theoretical methods
to describe the potential between charged dust particles align with previous
studies on planetary and space dusty plasma and could have significant impact
on interpretation of standard cosmological model results.",2307.11264v2
2023-07-22,Damping of strong GHz waves near magnetars and the origin of fast radio bursts,"We investigate how a GHz radio burst emitted near a magnetar propagates
through its magnetosphere at radii $r=10^7$-$10^9$ cm. Bursts propagating near
the magnetic equator behave as magnetohydrodynamic (MHD) waves if they have
luminosity $L\gg 10^{40}$ erg/s. The waves develop plasma shocks in each
oscillation and dissipate at $r\sim 3 \times 10^8 L_{42}^{-1/4}$ cm. GHz waves
with lower $L$ or propagation directions closer to the magnetic axis do not
obey MHD. Instead, they interact with individual particles, which requires a
kinetic description. The kinetic interaction quickly accelerates particles to
Lorentz factors $10^4$-$10^5$ at the expense of the wave energy, which again
results in strong damping of the wave. In either regime of wave propagation,
MHD or kinetic, the magnetosphere acts as a pillow absorbing the GHz burst and
re-radiating the absorbed energy in X-rays. We conclude that a GHz source
confined in the inner magnetosphere would be blocked by the outer magnetosphere
at practically all relevant luminosities and viewing angles. This result
constrains the origin of observed fast radio bursts (FRBs). We argue that
observed FRBs come from magnetospheric explosions ejecting powerful outflows.",2307.12182v1
2023-07-25,Computational Guarantees for Doubly Entropic Wasserstein Barycenters via Damped Sinkhorn Iterations,"We study the computation of doubly regularized Wasserstein barycenters, a
recently introduced family of entropic barycenters governed by inner and outer
regularization strengths. Previous research has demonstrated that various
regularization parameter choices unify several notions of entropy-penalized
barycenters while also revealing new ones, including a special case of debiased
barycenters. In this paper, we propose and analyze an algorithm for computing
doubly regularized Wasserstein barycenters. Our procedure builds on damped
Sinkhorn iterations followed by exact maximization/minimization steps and
guarantees convergence for any choice of regularization parameters. An inexact
variant of our algorithm, implementable using approximate Monte Carlo sampling,
offers the first non-asymptotic convergence guarantees for approximating
Wasserstein barycenters between discrete point clouds in the
free-support/grid-free setting.",2307.13370v1
2023-07-30,Energy transfer and radiation in Hamiltonian nonlinear Klein-Gordon equations: general case,"In this paper, we consider Klein-Gordon equations with cubic nonlinearity in
three spatial dimensions, which are Hamiltonian perturbations of the linear one
with potential. It is assumed that the corresponding Klein-Gordon operator $B =
\sqrt{-\Delta + V(x) + m^2} $ admits an arbitrary number of possibly degenerate
eigenvalues in $(0, m)$, and hence the unperturbed linear equation has multiple
time-periodic solutions known as bound states. In \cite{SW1999}, Soffer and
Weinstein discovered a mechanism called Fermi's Golden Rule for this nonlinear
system in the case of one simple but relatively large eigenvalue $\Omega\in
(\frac{m}{3}, m)$, by which energy is transferred from discrete to continuum
modes and the solution still decays in time. In particular, the exact energy
transfer rate is given. In \cite{LLY22}, we solved the general one simple
eigenvalue case. In this paper, we solve this problem in full generality:
multiple and simple or degenerate eigenvalues in $(0, m)$. The proof is based
on a kind of pseudo-one-dimensional cancellation structure in each eigenspace,
a renormalized damping mechanism, and an enhanced damping effect. It also
relies on a refined Birkhoff normal form transformation and an accurate
generalized Fermi's Golden Rule over those of Bambusi--Cuccagna \cite{BC}.",2307.16191v1
2023-08-01,On damping a control system with global aftereffect on quantum graphs,"The paper naturally connects theory of quantum graphs, optimal control theory
and theory of functional-differential equations, and gives a new look at
quantum graphs as temporal networks. This means that the variable
parameterizing the edges is associated with time, while each internal vertex
opens several scenarios for the process flow. Under such settings, we extend
the problem of damping a first-order control system of the retarded type, which
was studied before only on an interval, to an arbitrary tree graph by employing
the recently suggested concept of the global delay. The latter means that the
delay imposed starting from the initial moment of time, associated with the
root of the tree, propagates through all its internal vertices. By minimizing
the energy functional, we arrive at the corresponding variational problem and
then prove its equivalence to a self-adjoint boundary value problem on the tree
for some second-order equations involving both the global delay and the global
advance, whose unique solvability is also established. Noteworthy is that at
the internal vertices, the optimal trajectory obeys Kirchhoff-type conditions,
which are common also for various models dealing with spacial networks.",2308.00496v2
2023-08-03,Part II On strong and non uniform stability of locally damped Timoshenko beam: Mathematical corrections to the proof of Theorem 2.2 in the publication referenced as [1] in the bibliography,"In part I of the rebuttal (see [2] to the article [1] entitled ""Uniform
stabilization for the Timoshenko beam by a locally distributed damping""
published in 2003, in the journal Electronic Journal of Differential Equations,
we prove that Lemma 3.6 and Theorem 3.1 are unproved due to major flaws
(contradictory assumptions). We also show that Theorem 2.2 and its proofs of
strong stability, and non uniform stability in the case of different speeds of
propagation, contain several incorrect arguments and several gaps (including
missing functional frames). In this part II, we give the precise missing
functional frames, fill the gaps and correct several parts contained in the
proof of Theorem 2.2 in [1]. We also complete a missing argument (see Remark
4.23 and Remark 3.2) in the proof of Theorem A in [5] used by [1]. For this we
state and prove Proposition 4.4 (see also Proposition 4.6 for a general
formulation in Banach spaces). We also give the correct formulations, and
proofs of strong stability and non uniform stability (in case of different
speeds of propagation) for Timoshenko beams.",2308.01625v1
2023-08-05,The isometric immersion of surfaces with finite total curvature,"In this paper, we study the smooth isometric immersion of a complete simply
connected surface with a negative Gauss curvature in the three-dimensional
Euclidean space. For a surface with a finite total Gauss curvature and
appropriate oscillations of the Gauss curvature, we prove the global existence
of a smooth solution to the Gauss-Codazzi system and thus establish a global
smooth isometric immersion of the surface into the three-dimensional Euclidean
space. Based on a crucial observation that some linear combinations of the
Riemann invariants decay faster than others, we reformulate the Gauss-Codazzi
system as a symmetric hyperbolic system with a partial damping. Such a damping
effect and an energy approach permit us to derive global decay estimates and
meanwhile control the non-integrable coefficients of nonlinear terms.",2308.02832v2
2023-08-25,The time dimensional reduction method to determine the initial conditions without the knowledge of damping coefficients,"This paper aims to reconstruct the initial condition of a hyperbolic equation
with an unknown damping coefficient. Our approach involves approximating the
hyperbolic equation's solution by its truncated Fourier expansion in the time
domain and using a polynomial-exponential basis. This truncation process
facilitates the elimination of the time variable, consequently, yielding a
system of quasi-linear elliptic equations. To globally solve the system without
needing an accurate initial guess, we employ the Carleman contraction
principle. We provide several numerical examples to illustrate the efficacy of
our method. The method not only delivers precise solutions but also showcases
remarkable computational efficiency.",2308.13152v1
2023-08-25,A Game of Bundle Adjustment -- Learning Efficient Convergence,"Bundle adjustment is the common way to solve localization and mapping. It is
an iterative process in which a system of non-linear equations is solved using
two optimization methods, weighted by a damping factor. In the classic
approach, the latter is chosen heuristically by the Levenberg-Marquardt
algorithm on each iteration. This might take many iterations, making the
process computationally expensive, which might be harmful to real-time
applications. We propose to replace this heuristic by viewing the problem in a
holistic manner, as a game, and formulating it as a reinforcement-learning
task. We set an environment which solves the non-linear equations and train an
agent to choose the damping factor in a learned manner. We demonstrate that our
approach considerably reduces the number of iterations required to reach the
bundle adjustment's convergence, on both synthetic and real-life scenarios. We
show that this reduction benefits the classic approach and can be integrated
with other bundle adjustment acceleration methods.",2308.13270v1
2023-08-30,Stochastic Thermodynamics of Brownian motion in Temperature Gradient,"We study stochastic thermodynamics of a Brownian particle which is subjected
to a temperature gradient and is confined by an external potential. We first
formulate an over-damped Ito-Langevin theory in terms of local temperature,
friction coefficient, and steady state distribution, all of which are
experimentally measurable. We then study the associated stochastic
thermodynamics theory. We analyze the excess entropy production (EP) both at
trajectory level and at ensemble level, and derive the Clausius inequality as
well as the transient fluctuation theorem (FT). We also use molecular dynamics
to simulate a Brownian particle inside a Lennard-Jones fluid and verify the FT.
Remarkably we find that the FT remains valid even in the under-damped regime.
We explain the possible mechanism underlying this surprising result.",2308.15764v3
2023-09-04,Sphaleron damping and effects on vector and axial charge transport in high-temperature QCD plasmas,"We modify the anomalous hydrodynamic equations of motion to account for
dissipative effects due to QCD sphaleron transitions. By investigating the
linearized hydrodynamic equations, we show that sphaleron transitions lead to
nontrivial effects on vector and axial charge transport phenomena in the
presence of a magnetic field. Due to the dissipative effects of sphaleron
transitions, a wavenumber threshold $k_{\rm CMW}$ emerges characterizing the
onset of chiral magnetic waves. Sphaleron damping also significantly impacts
the time evolution of both axial and vector charge perturbations in a QCD
plasma in the presence of a magnetic field. Based on our analysis of the
linearized hydrodynamic equations, we also investigate the dependence of the
vector charge separation on the sphaleron transition rate, which may have
implications for the experimental search for the Chiral Magnetic Effect in
Heavy Ion Collisions.",2309.01726v1
2023-09-05,Signatures and characterization of dominating Kerr nonlinearity between two driven systems with application to a suspended magnetic beam,"We consider a model of two harmonically driven damped harmonic oscillators
that are coupled linearly and with a cross-Kerr coupling. We show how to
distinguish this combination of coupling types from the case where a coupling
of optomechanical type is present. This can be useful for the characterization
of various nonlinear systems, such as mechanical oscillators, qubits, and
hybrid systems. We then consider a hybrid system with linear and cross-Kerr
interactions and a relatively high damping in one of the modes. We derive a
quantum Hamiltonian of a doubly clamped magnetic beam, showing that the
cross-Kerr coupling is prominent there. We discuss, in the classical limit,
measurements of its linear response as well as the specific higher-harmonic
responses. These frequency-domain measurements can allow estimating the
magnitude of the cross-Kerr coupling or its magnon population.",2309.02204v2
2023-09-07,Strong coupling between WS$_2$ monolayer excitons and a hybrid plasmon polariton at room temperature,"Light-matter interactions in solid-state systems have attracted considerable
interest in recent years. Here, we report on a room-temperature study on the
interaction of tungsten disulfide (WS$_2$) monolayer excitons with a hybrid
plasmon polariton (HPP) mode supported by nanogroove grating structures milled
into single-crystalline silver flakes. By engineering the depth of the
nanogroove grating, we can modify the HPP mode at the A-exciton energy from
propagating surface plasmon polariton-like (SPP-like) to localized surface
plasmon resonance-like (LSPR-like). Using reflection spectroscopy, we
demonstrate strong coupling between the A-exciton mode and the lower branch of
the HPP for a SPP-like configuration with a Rabi splitting of 68 meV. In
contrast, only weak coupling between the constituents is observed for LSPR-like
configurations. These findings demonstrate the importance to consider both the
plasmonic near-field enhancement and the plasmonic damping during the design of
the composite structure since a possible benefit from increasing the coupling
strength can be easily foiled by larger damping.",2309.03560v1
2023-09-07,"Neutron spin echo is a ""quantum tale of two paths''","We describe an experiment that strongly supports a two-path interferometric
model in which the spin-up and spin-down components of each neutron propagate
coherently along spatially separated parallel paths in a typical neutron spin
echo small angle scattering (SESANS) experiment. Specifically, we show that the
usual semi-classical, single-path treatment of Larmor precession of a polarized
neutron in an external magnetic field predicts a damping as a function of the
spin echo length of the SESANS signal obtained with a periodic phase grating
when the transverse width of the neutron wave packet is finite. However, no
such damping is observed experimentally, implying either that the Larmor model
is incorrect or that the transverse extent of the wave packet is very large. In
contrast, we demonstrate theoretically that a quantum-mechanical
interferometric model in which the two mode-entangled (i.e. intraparticle
entangled) spin states of a single neutron are separated in space when they
interact with the grating accurately predicts the measured SESANS signal, which
is independent of the wave packet width.",2309.03987v2
2023-09-07,An explicit multi-time stepping algorithm for multi-time scale coupling problems in SPH,"Simulating physical problems involving multi-time scale coupling is
challenging due to the need of solving these multi-time scale processes
simultaneously. In response to this challenge, this paper proposed an explicit
multi-time step algorithm coupled with a solid dynamic relaxation scheme. The
explicit scheme simplifies the equation system in contrast to the implicit
scheme, while the multi-time step algorithm allows the equations of different
physical processes to be solved under different time step sizes. Furthermore,
an implicit viscous damping relaxation technique is applied to significantly
reduce computational iterations required to achieve equilibrium in the
comparatively fast solid response process. To validate the accuracy and
efficiency of the proposed algorithm, two distinct scenarios, i.e., a nonlinear
hardening bar stretching and a fluid diffusion coupled with Nafion membrane
flexure, are simulated. The results show good agreement with experimental data
and results from other numerical methods, and the simulation time is reduced
firstly by independently addressing different processes with the multi-time
step algorithm and secondly decreasing solid dynamic relaxation time through
the incorporation of damping techniques.",2309.04010v1
2023-09-15,Limiting absorption principles and linear inviscid damping in the Euler-Boussinesq system in the periodic channel,"We consider the long-time behavior of solutions to the two dimensional
non-homogeneous Euler equations under the Boussinesq approximation posed on a
periodic channel. We study the linearized system near a linearly stratified
Couette flow and prove inviscid damping of the perturbed density and velocity
field for any positive Richardson number, with optimal rates. Our methods are
based on time-decay properties of oscillatory integrals obtained using a
limiting absorption principle, and require a careful understanding of the
asymptotic expansion of the generalized eigenfunction near the critical layer.
As a by-product of our analysis, we provide a precise description of the
spectrum of the linearized operator, which, for sufficiently large Richardson
number, consists of an essential spectrum (as expected according to classical
hydrodynamic problems) as well as discrete neutral eigenvalues (giving rise to
oscillatory modes) accumulating towards the endpoints of the essential
spectrum.",2309.08445v2
2023-09-15,Breakdown of sound in superfluid helium,"Like elementary particles carry energy and momentum in the Universe,
quasiparticles are the elementary carriers of energy and momentum quanta in
condensed matter. And, like elementary particles, under certain conditions
quasiparticles can be unstable and decay, emitting pairs of less energetic
ones. Pitaevskii proposed that such processes exist in superfluid helium, a
quantum fluid where the very concept of quasiparticles was borne, and which
provided the first spectacular triumph of that concept. Pitaevskii's decays
have important consequences, including possible breakdown of a quasiparticle.
Here, we present neutron scattering experiments, which provide evidence that
such decays explain the collapsing lifetime (strong damping) of higher-energy
phonon-roton sound-wave quasiparticles in superfluid helium. This damping
develops when helium is pressurized towards crystallization or warmed towards
approaching the superfluid transition. Our results resolve a number of puzzles
posed by previous experiments and reveal the ubiquity of quasiparticle decays
and their importance for understanding quantum matter.",2309.08790v1
2023-09-18,Nonlinear dynamics and magneto-elasticity of nanodrums near the phase transition,"Nanomechanical resonances of two-dimensional (2D) materials are sensitive
probes for condensed-matter physics, offering new insights into magnetic and
electronic phase transitions. Despite extensive research, the influence of the
spin dynamics near a second-order phase transition on the nonlinear dynamics of
2D membranes has remained largely unexplored. Here, we investigate nonlinear
magneto-mechanical coupling to antiferromagnetic order in suspended
FePS$_3$-based heterostructure membranes. By monitoring the motion of these
membranes as a function of temperature, we observe characteristic features in
both nonlinear stiffness and damping close to the N\'{e}el temperature
$T_{\rm{N}}$. We account for these experimental observations with an analytical
magnetostriction model in which these nonlinearities emerge from a coupling
between mechanical and magnetic oscillations, demonstrating that
magneto-elasticity can lead to nonlinear damping. Our findings thus provide
insights into the thermodynamics and magneto-mechanical energy dissipation
mechanisms in nanomechanical resonators due to the material's phase change and
magnetic order relaxation.",2309.09672v1
2023-09-21,Quantum State Reconstruction in a Noisy Environment via Deep Learning,"Quantum noise is currently limiting efficient quantum information processing
and computation. In this work, we consider the tasks of reconstructing and
classifying quantum states corrupted by the action of an unknown noisy channel
using classical feedforward neural networks. By framing reconstruction as a
regression problem, we show how such an approach can be used to recover with
fidelities exceeding 99% the noiseless density matrices of quantum states of up
to three qubits undergoing noisy evolution, and we test its performance with
both single-qubit (bit-flip, phase-flip, depolarising, and amplitude damping)
and two-qubit quantum channels (correlated amplitude damping). Moreover, we
also consider the task of distinguishing between different quantum noisy
channels, and show how a neural network-based classifier is able to solve such
a classification problem with perfect accuracy.",2309.11949v1
2023-09-27,Exploring antisymmetric tensor effects on black hole shadows and quasinormal frequencies,"This study explores the impact of antisymmetric tensor effects on spherically
symmetric black holes, investigating photon spheres, shadows, emission rate and
quasinormal frequencies in relation to a parameter which triggers the Lorentz
symmetry breaking. We examine these configurations without and with the
presence of a cosmological constant. In the first scenario, the Lorentz
violation parameter, denoted as $\lambda$, plays a pivotal role in reducing
both the photon sphere and the shadow radius, while also leading to a damping
effect on quasinormal frequencies. Conversely, in the second scenario, as the
values of the cosmological constant ($\Lambda$) increase, we observe an
expansion in the shadow radius. Also, we provide the constraints of the shadows
based on the analysis observational data obtained from the Event Horizon
Telescope (EHT) focusing on Sagittarius $A^{*}$ shadow images. Additionally,
with the increasing $\Lambda$, the associated gravitational wave frequencies
exhibit reduced damping modes.",2309.15778v3
2023-10-20,Exponential weight averaging as damped harmonic motion,"The exponential moving average (EMA) is a commonly used statistic for
providing stable estimates of stochastic quantities in deep learning
optimization. Recently, EMA has seen considerable use in generative models,
where it is computed with respect to the model weights, and significantly
improves the stability of the inference model during and after training. While
the practice of weight averaging at the end of training is well-studied and
known to improve estimates of local optima, the benefits of EMA over the course
of training is less understood. In this paper, we derive an explicit connection
between EMA and a damped harmonic system between two particles, where one
particle (the EMA weights) is drawn to the other (the model weights) via an
idealized zero-length spring. We then leverage this physical analogy to analyze
the effectiveness of EMA, and propose an improved training algorithm, which we
call BELAY. Finally, we demonstrate theoretically and empirically several
advantages enjoyed by BELAY over standard EMA.",2310.13854v1
2023-10-23,Adam through a Second-Order Lens,"Research into optimisation for deep learning is characterised by a tension
between the computational efficiency of first-order, gradient-based methods
(such as SGD and Adam) and the theoretical efficiency of second-order,
curvature-based methods (such as quasi-Newton methods and K-FAC). We seek to
combine the benefits of both approaches into a single computationally-efficient
algorithm. Noting that second-order methods often depend on stabilising
heuristics (such as Levenberg-Marquardt damping), we propose AdamQLR: an
optimiser combining damping and learning rate selection techniques from K-FAC
(Martens and Grosse, 2015) with the update directions proposed by Adam,
inspired by considering Adam through a second-order lens. We evaluate AdamQLR
on a range of regression and classification tasks at various scales, achieving
competitive generalisation performance vs runtime.",2310.14963v1
2023-10-24,Observation of Damped Oscillations in Chemical-Quantum-Magnetic Interactions,"Fundamental interactions are the basis of the most diverse phenomena in
science that allow the dazzling of possible applications. In this work, we
report a new interaction, which we call chemical-quantum-magnetic interaction.
This interaction arises due to the difference in valence that the Fe3O4/PANI
nanostructure acquires under certain conditions. In this study, PANI activates
the chemical part of the oscillations, leaving the quantum and magnetic part
for the double valence effect and consequently for changing the number of spins
of the nanostructure sites. We also observed using interaction measurements
that chemical-quantum-magnetic interactions oscillate in a subcritical regime
satisfying the behavior of a damped harmonic oscillator.",2310.15775v1
2023-10-26,Do Graph Neural Networks Dream of Landau Damping? Insights from Kinetic Simulations of a Plasma Sheet Model,"We explore the possibility of fully replacing a plasma physics kinetic
simulator with a graph neural network-based simulator. We focus on this class
of surrogate models given the similarity between their message-passing update
mechanism and the traditional physics solver update, and the possibility of
enforcing known physical priors into the graph construction and update. We show
that our model learns the kinetic plasma dynamics of the one-dimensional plasma
model, a predecessor of contemporary kinetic plasma simulation codes, and
recovers a wide range of well-known kinetic plasma processes, including plasma
thermalization, electrostatic fluctuations about thermal equilibrium, and the
drag on a fast sheet and Landau damping. We compare the performance against the
original plasma model in terms of run-time, conservation laws, and temporal
evolution of key physical quantities. The limitations of the model are
presented and possible directions for higher-dimensional surrogate models for
kinetic plasmas are discussed.",2310.17646v2
2023-10-29,Impact of Medium Anisotropy on Quarkonium Dissociation and Regeneration,"Quarkonium production in ultra-relativistic collisions plays a crucial role
in probing the existence of hot QCD matter. This study explores quarkonia
states dissociation and regeneration in the hot QCD medium while considering
momentum anisotropy. The net quarkonia decay width ($\Gamma_{D}$) arises from
two essential processes: collisional damping and gluonic dissociation. The
quarkonia regeneration includes the transition from octet to singlet states
within the anisotropic medium. Our study utilizes a medium-modified potential
that incorporates anisotropy via particle distribution functions. This modified
potential gives rise to collisional damping for quarkonia due to the
surrounding medium, as well as the transition of quarkonia from singlet to
octet states due to interactions with gluons. Furthermore, we employ the
detailed balance approach to investigate the regeneration of quarkonia within
this medium. Our comprehensive analysis spans various temperature settings,
transverse momentum values, and anisotropic strengths. Notably, we find that,
in addition to medium temperatures and heavy quark transverse momentum,
anisotropy significantly influences the dissociation and regeneration of
various quarkonia states.",2310.18909v1
2023-10-31,Stability threshold of nearly-Couette shear flows with Navier boundary conditions in 2D,"In this work, we prove a threshold theorem for the 2D Navier-Stokes equations
posed on the periodic channel, $\mathbb{T} \times [-1,1]$, supplemented with
Navier boundary conditions $\omega|_{y = \pm 1} = 0$. Initial datum is taken to
be a perturbation of Couette in the following sense: the shear component of the
perturbation is assumed small (in an appropriate Sobolev space) but importantly
is independent of $\nu$. On the other hand, the nonzero modes are assumed size
$O(\nu^{\frac12})$ in an anisotropic Sobolev space. For such datum, we prove
nonlinear enhanced dissipation and inviscid damping for the resulting solution.
The principal innovation is to capture quantitatively the \textit{inviscid
damping}, for which we introduce a new Singular Integral Operator which is a
physical space analogue of the usual Fourier multipliers which are used to
prove damping. We then include this SIO in the context of a nonlinear
hypocoercivity framework.",2311.00141v1
2023-11-10,Moment expansion method for composite open quantum systems including a damped oscillator mode,"We consider a damped oscillator mode that is resonantly driven and is coupled
to an arbitrary target system via the position quadrature operator. For such a
composite open quantum system, we develop a numerical method to compute the
reduced density matrix of the target system and the low-order moments of the
quadrature operators. In this method, we solve the evolution equations for
quantities related to moments of the quadrature operators, rather than for the
density matrix elements as in the conventional approach. The application to an
optomechanical setting shows that the new method can compute the correlation
functions accurately with a significant reduction in the computational cost.
Since the method does not involve any approximation in its abstract formulation
itself, we investigate the numerical accuracy closely. This study reveals the
numerical sensitivity of the new approach in certain parameter regimes. We find
that this issue can be alleviated by using the position basis instead of the
commonly used Fock basis.",2311.06113v1
2023-11-22,Analytic formulas for the D-mode Robinson instability,"The passive superconducting harmonic cavity (PSHC) scheme is adopted by
several existing and future synchrotron light source storage rings, as it has a
relatively smaller R/Q and a relatively larger quality factor (Q), which can
effectively reduce the beam-loading effect and suppress the mode-one
instability. Based on the mode-zero Robinson instability equation of uniformly
filled rigid bunches and a search algorithm for minimum, we have revealed that
the PSHC fundamental mode with a large loaded-Q possibly triggers the D-mode
Robinson instability [T. He, et al., Mode-zero Robinson instability in the
presence of passive superconducting harmonic cavities, PRAB 26, 064403 (2023)].
This D-mode Robinson instability is unique because it is anti-damped by the
radiation-damping effect. In this paper, analytical formulas for the frequency
and growth rate of the D-mode Robinson instability are derived with several
appropriate approximations. These analytical formulas will facilitate analyzing
and understanding the D-mode Robinson instability. Most importantly, useful
formulas for the D-mode threshold detuning calculation have finally been found.",2311.13205v1
2023-11-27,Learning Reionization History from Quasars with Simulation-Based Inference,"Understanding the entire history of the ionization state of the intergalactic
medium (IGM) is at the frontier of astrophysics and cosmology. A promising
method to achieve this is by extracting the damping wing signal from the
neutral IGM. As hundreds of redshift $z>6$ quasars are observed, we anticipate
determining the detailed time evolution of the ionization fraction with
unprecedented fidelity. However, traditional approaches to parameter inference
are not sufficiently accurate. We assess the performance of a simulation-based
inference (SBI) method to infer the neutral fraction of the universe from
quasar spectra. The SBI method adeptly exploits the shape information of the
damping wing, enabling precise estimations of the neutral fraction
$\left<x_{\rm HI}\right>_{\rm v}$ and the wing position $w_p$. Importantly, the
SBI framework successfully breaks the degeneracy between these two parameters,
offering unbiased estimates of both. This makes the SBI superior to the
traditional method using a pseudo-likelihood function. We anticipate that SBI
will be essential to determine robustly the ionization history of the Universe
through joint inference from the hundreds of high-$z$ spectra we will observe.",2311.16238v1
2023-12-05,DemaFormer: Damped Exponential Moving Average Transformer with Energy-Based Modeling for Temporal Language Grounding,"Temporal Language Grounding seeks to localize video moments that semantically
correspond to a natural language query. Recent advances employ the attention
mechanism to learn the relations between video moments and the text query.
However, naive attention might not be able to appropriately capture such
relations, resulting in ineffective distributions where target video moments
are difficult to separate from the remaining ones. To resolve the issue, we
propose an energy-based model framework to explicitly learn moment-query
distributions. Moreover, we propose DemaFormer, a novel Transformer-based
architecture that utilizes exponential moving average with a learnable damping
factor to effectively encode moment-query inputs. Comprehensive experiments on
four public temporal language grounding datasets showcase the superiority of
our methods over the state-of-the-art baselines.",2312.02549v1
2023-12-05,THz-Driven Coherent Magnetization Dynamics in a Labyrinth Domain State,"Terahertz (THz) light pulses can be used for an ultrafast coherent
manipulation of the magnetization. Driving the magnetization at THz frequencies
is currently the fastest way of writing magnetic information in ferromagnets.
Using time-resolved resonant magnetic scattering, we gain new insights to the
THz-driven coherent magnetization dynamics on nanometer length scales. We
observe ultrafast demagnetization and coherent magnetization oscillations that
are governed by a time-dependent damping. This damping is determined by the
interplay of lattice heating and magnetic anisotropy reduction revealing an
upper speed limit for THz-induced magnetization switching. We show that in the
presence of nanometer-sized magnetic domains, the ultrafast magnetization
oscillations are associated with a correlated beating of the domain walls. The
overall domain structure thereby remains largely unaffected which highlights
the applicability of THz-induced switching on the nanoscale.",2312.02654v1
2023-12-07,Enhanced high-dimensional teleportation in correlated amplitude damping noise by weak measurement and environment-assisted measurement,"High-dimensional teleportation provides various benefits in quantum networks
and repeaters, but all these advantages rely on the high-quality distribution
of high-dimensional entanglement over a noisy channel. It is essential to
consider correlation effects when two entangled qutrits travel consecutively
through the same channel. In this paper, we present two strategies for
enhancing qutrit teleportation in correlated amplitude damping (CAD) noise by
weak measurement (WM) and environment-assisted measurement (EAM). The fidelity
of both approaches has been dramatically improved due to the probabilistic
nature of WM and EAM. We have observed that the correlation effects of CAD
noise result in an increase in the probability of success. A comparison has
demonstrated that the EAM scheme consistently outperforms the WM scheme in
regard to fidelity. Our research expands the capabilities of WM and EAM as
quantum techniques to combat CAD noise in qutrit teleportation, facilitating
the development of advanced quantum technologies in high-dimensional systems.",2312.03988v1
2023-12-11,Collisions and collective flavor conversion: Integrating out the fast dynamics,"In dense astrophysical environments, notably core-collapse supernovae and
neutron star mergers, neutrino-neutrino forward scattering can spawn flavor
conversion on very short scales. Scattering with the background medium can
impact collective flavor conversion in various ways, either damping
oscillations or possibly setting off novel collisional flavor instabilities
(CFIs). A key feature in this process is the slowness of collisions compared to
the much faster dynamics of neutrino-neutrino refraction. Assuming spatial
homogeneity, we leverage this hierarchy of scales to simplify the description
accounting only for the slow dynamics driven by collisions. We illustrate our
new approach both in the case of CFIs and in the case of fast instabilities
damped by collisions. In both cases, our strategy provides new equations, the
slow-dynamics equations, that simplify the description of flavor conversion and
allow us to qualitatively understand the final state of the system after the
instability, either collisional or fast, has saturated.",2312.07612v2
2023-12-15,"Position-momentum conditioning, relative entropy decomposition and convergence to equilibrium in stochastic Hamiltonian systems","This paper is concerned with a class of multivariable stochastic Hamiltonian
systems whose generalised position is related by an ordinary differential
equation to the momentum governed by an Ito stochastic differential equation.
The latter is driven by a standard Wiener process and involves both
conservative and viscous damping forces. With the mass, diffusion and damping
matrices being position-dependent, the resulting nonlinear model of Langevin
dynamics describes dissipative mechanical systems (possibly with rotational
degrees of freedom) or their electromechanical analogues subject to external
random forcing. We study the time evolution of the joint position-momentum
probability distribution for the system and its convergence to equilibrium by
decomposing the Fokker-Planck-Kolmogorov equation (FPKE) and the
Kullback-Leibler relative entropy with respect to the invariant measure into
those for the position distribution and the momentum distribution conditioned
on the position. This decomposition reveals a manifestation of the
Barbashin-Krasovskii-LaSalle principle and higher-order dissipation
inequalities for the relative entropy as a Lyapunov functional for the FPKE.",2312.09475v1
2023-12-16,Continuous Phase Transition in Anyonic-PT Symmetric Systems,"We reveal the continuous phase transition in anyonic-PT symmetric systems,
contrasting with the discontinuous phase transition corresponding to the
discrete (anti-) PT symmetry. The continuous phase transition originates from
the continuity of anyonic-PT symmetry. We find there are three
information-dynamics patterns for anyonic-PT symmetric systems: damped
oscillations with an overall decrease (increase) and asymptotically stable
damped oscillations, which are three-fold degenerate and distorted using the
Hermitian quantum R\'enyi entropy or distinguishability. It is the
normalization of the non-unitary evolved density matrix causes the degeneracy
and distortion. We give a justification for non-Hermitian quantum R\'enyi
entropy being negative. By exploring the mathematics and physical meaning of
the negative entropy in open quantum systems, we connect the negative
non-Hermitian quantum R\'enyi entropy and negative quantum conditional entropy,
opening up a new journey to rigorously investigate the negative entropy in open
quantum systems.",2312.10350v4
2023-12-20,Quadrature squeezing enhances Wigner negativity in a mechanical Duffing oscillator,"Generating macroscopic non-classical quantum states is a long-standing
challenge in physics. Anharmonic dynamics is an essential ingredient to
generate these states, but for large mechanical systems, the effect of the
anharmonicity tends to become negligible compared to decoherence. As a possible
solution to this challenge, we propose to use a motional squeezed state as a
resource to effectively enhance the anharmonicity. We analyze the production of
negativity in the Wigner distribution of a quantum anharmonic resonator
initially in a squeezed state. We find that initial squeezing enhances the rate
at which negativity is generated. We also analyze the effect of two common
sources of decoherence, namely energy damping and dephasing, and find that the
detrimental effects of energy damping are suppressed by strong squeezing. In
the limit of large squeezing, which is needed for state-of-the-art systems, we
find good approximations for the Wigner function. Our analysis is significant
for current experiments attempting to prepare macroscopic mechanical systems in
genuine quantum states. We provide an overview of several experimental
platforms featuring nonlinear behaviors and low levels of decoherence. In
particular, we discuss the feasibility of our proposal with carbon nanotubes
and levitated nanoparticles.",2312.12986v1
2023-12-21,Subsonic time-periodic solution to damped compressible Euler equations with large entropy,"In this paper, one-dimensional nonisentropic compressible Euler equations
with linear damping $\alpha(x)\rho u$ are analyzed.~We want to explore the
conditions under which a subsonic temporal periodic boundary can trigger a
time-periodic $C^{1}$ solution. To achieve this aim, we use a technically
constructed iteration scheme and give the sufficient conditions to guarantee
the existence, uniqueness and stability of the $C^{1}$ time-periodic solutions
on the perturbation of a subsonic Fanno flow.~It is worthy to be pointed out
that the entropy exhibits large amplitude under the assumption that the inflow
sound speed is small.~However, it is crucial to assume that the boundary
conditions possess a kind of dissipative structure at least on one side, which
is used to cancel the nonlinear accelerating effect in the system.~The results
indicate that the time-periodic feedback boundary control with dissipation can
stabilize the nonisentropic compressible Euler equations around the Fanno
flows.",2312.13546v1
2023-12-27,Universal orbital and magnetic structures in infinite-layer nickelates,"We conducted a comparative study of the rare-earth infinite-layer nickelates
films, RNiO2 (R = La, Pr, and Nd) using resonant inelastic X-ray scattering
(RIXS). We found that the gross features of the orbital configurations are
essentially the same, with minor variations in the detailed hybridization. For
low-energy excitations, we unambiguously confirm the presence of damped
magnetic excitations in all three compounds. By fitting to a linear spin-wave
theory, comparable spin exchange coupling strengths and damping coefficients
are extracted, indicating a universal magnetic structure in the infinite-layer
nickelates. Interestingly, while signatures of a charge order are observed in
LaNiO2 in the quasi-elastic region of the RIXS spectrum, it is absent in NdNiO2
and PrNiO2. This prompts further investigation into the universality and the
origins of charge order within the infinite-layer inickelates.",2312.16444v1
2024-01-05,Response solutions for beam equations with nonlocal nonlinear damping and Liouvillean frequencies,"Response solutions are quasi-periodic ones with the same frequency as the
forcing term. The present work is devoted to the construction of response
solutions for $d$-dimensional beam equations with nonlocal nonlinear damping,
which model frictional mechanisms affecting the bodies based on the average. By
considering $\epsilon$ in a domain that does not include the origin and
imposing a small quasi-periodic forcing with Liouvillean frequency vector,
which is weaker than the Diophantine or Brjuno one, we can show the existence
of the response solution for such a model. We present an alternative approach
to the contraction mapping principle (cf. [5,33]) through a combination of
reduction and the Nash--Moser iteration technique. The reason behind this
approach lies in the derivative losses caused by the nonlocal nonlinearity.",2401.02628v1
2024-01-10,Stochastic modelling of blob-like plasma filaments in the scrape-off layer: Continuous velocity distributions,"A stochastic model for a superposition of uncorrelated pulses with a random
distribution of amplitudes, sizes, and velocities is analyzed. The pulses are
assumed to move radially with fixed shape and amplitudes decreasing
exponentially in time due to linear damping. The pulse velocities are taken to
be time-independent but randomly distributed. The implications of a broad
distribution of pulse amplitudes and velocities, as well as correlations
between these, are investigated. Fast and large-amplitude pulses lead to broad
and flat average radial profiles with order unity relative fluctuations in the
scrape-off layer. For theoretically predicted blob velocity scaling relations,
the stochastic model reveals average radial profiles similar to the case of a
degenerate distribution of pulse velocities but with more intermittent
fluctuations. The average profile e-folding length is given by the product of
the average pulse velocity and the linear damping time due to losses along
magnetic field lines. The model describes numerous common features from
experimental measurements and underlines the role of large-amplitude
fluctuations for plasma-wall interactions in magnetically confined fusion
plasmas.",2401.05198v1
2024-01-11,Optical and acoustic plasmons in the layered material Sr$_2$RuO$_4$,"We use momentum-dependent electron energy-loss spectroscopy in transmission
to study collective charge excitations in the ""strange"" layer metal
Sr$_2$RuO$_4$. We cover a complete range between in-plane and out-of-plane
oscillations. Outside of the classical range of electron-hole excitations,
leading to a Landau damping, we observe well defined plasmons. The optical
(acoustic) plasmon due to an in-phase (out-of-phase) charge oscillation of
neighbouring layers exhibits a quadratic (linear) dispersion. Using a model for
the Coulomb interaction of the charges in a layered system, it is possible to
describe the complete range of plasmon excitations in a mean-field random phase
approximation without taking correlation effects into account. There are no
signs of over-damped plasmons predicted by holographic theories. This indicates
that long wavelength charge excitations are not influenced by local correlation
effects such as on-site Coulomb interaction and Hund's exchange interaction.",2401.05880v1
2024-01-12,Robust fully discrete error bounds for the Kuznetsov equation in the inviscid limit,"The Kuznetsov equation is a classical wave model of acoustics that
incorporates quadratic gradient nonlinearities. When its strong damping
vanishes, it undergoes a singular behavior change, switching from a
parabolic-like to a hyperbolic quasilinear evolution. In this work, we
establish for the first time the optimal error bounds for its finite element
approximation as well as a semi-implicit fully discrete approximation that are
robust with respect to the vanishing damping parameter. The core of the new
arguments lies in devising energy estimates directly for the error equation
where one can more easily exploit the polynomial structure of the
nonlinearities and compensate inverse estimates with smallness conditions on
the error. Numerical experiments are included to illustrate the theoretical
results.",2401.06492v1
2024-01-12,Semilinear damped wave equations on the Heisenberg group with initial data from Sobolev spaces of negative order,"In this paper, we focus on studying the Cauchy problem for semilinear damped
wave equations involving the sub-Laplacian $\mathcal{L}$ on the Heisenberg
group $\mathbb{H}^n$ with power type nonlinearity $|u|^p$ and initial data
taken from Sobolev spaces of negative order homogeneous Sobolev space $\dot
H^{-\gamma}_{\mathcal{L}}(\mathbb{H}^n), \gamma>0$, on $\mathbb{H}^n$. In
particular, in the framework of Sobolev spaces of negative order, we prove that
the critical exponent is the exponent $p_{\text{crit}}(Q,
\gamma)=1+\frac{4}{Q+2\gamma},$ for some $\gamma\in (0, \frac{Q}{2})$, where
$Q:=2n+2$ is the homogeneous dimension of $\mathbb{H}^n$. More precisely, we
establish
  a global-in-time existence of small data Sobolev solutions of lower
regularity for $p>p_{\text{crit}}(Q, \gamma)$ in the energy evolution space;
  a finite time blow-up of weak solutions for $1<p<p_{\text{crit}}(Q, \gamma)$
under certain conditions on the initial data by using the test function method.
  Furthermore, to precisely characterize the blow-up time, we derive sharp
upper bound and lower bound estimates for the lifespan in the subcritical case.",2401.06565v1
2024-01-12,Universal Modelling of Emergent Oscillations in Fractional Quantum Hall Fluids,"Density oscillations in quantum fluids can reveal their fundamental
characteristic features. In this work, we study the density oscillation of
incompressible fractional quantum Hall (FQH) fluids created by flux insertion.
For the model Laughlin state, we find that the complex oscillations seen in
various density profiles in real space can be universally captured by a simple
damped oscillator model in the occupation-number space. It requires only two
independent fitting parameters or characteristic length scales: the decay
length and the oscillation wave number. Realistic Coulomb quasiholes can be
viewed as Laughlin quasiholes dressed by magnetorotons which can be modeled by
a generalized damped oscillator model. Our work reveals the fundamental
connections between the oscillations seen in various aspects of FQH fluids such
as in the density of quasiholes, edge, and the pair correlation function. The
presented model is useful for the study of quasihole sizes for their control
and braiding in experiments and large-scale numerical computation of
variational energies.",2401.06856v1
2024-01-19,Quantum circuit model for discrete-time three-state quantum walks on Cayley graphs,"We develop qutrit circuit models for discrete-time three-state quantum walks
on Cayley graphs corresponding to Dihedral groups $D_N$ and the additive groups
of integers modulo any positive integer $N$. The proposed circuits comprise of
elementary qutrit gates such as qutrit rotation gates, qutrit-$X$ gates and
two-qutrit controlled-$X$ gates. First, we propose qutrit circuit
representation of special unitary matrices of order three, and the block
diagonal special unitary matrices with $3\times 3$ diagonal blocks, which
correspond to multi-controlled $X$ gates and permutations of qutrit Toffoli
gates. We show that one-layer qutrit circuit model need $O(3nN)$ two-qutrit
control gates and $O(3N)$ one-qutrit rotation gates for these quantum walks
when $N=3^n$. Finally, we numerically simulate these circuits to mimic its
performance such as time-averaged probability of finding the walker at any
vertex on noisy quantum computers. The simulated results for the time-averaged
probability distributions for noisy and noiseless walks are further compared
using KL-divergence and total variation distance. These results show that noise
in gates in the circuits significantly impacts the distributions than amplitude
damping or phase damping errors.",2401.11023v1
2024-01-22,Exact Normal Modes of Quantum Plasmas,"The normal modes, i.e., the eigen solutions to the dispersion relation
equation, are the most fundamental properties of a plasma, which also of key
importance to many nonlinear effects such as parametric and two-plasmon decay,
and Raman scattering. The real part indicates the intrinsic oscillation
frequency while the imaginary part the Landau damping rate. In most of the
literatures, the normal modes of quantum plasmas are obtained by means of small
damping approximation (SDA), which is invalid for high-$k$ modes. In this
paper, we solve the exact dispersion relations via the analytical continuation
(AC) scheme, and, due to the multi-value nature of the Fermi-Dirac
distribution, reformation of the complex Riemann surface is required. It is
found that the change of the topological shape of the root locus in quantum
plasmas is quite different from classical plasmas, in which both real and
imaginary frequencies of high-$k$ modes increase with $k$ in a steeper way than
the typical linear behaviour as appears in classical plasmas. As a result, the
temporal evolution of a high-$k$ perturbation in quantum plasmas is dominated
by the ballistic modes.",2401.11894v1
2024-01-23,On the stability and emittance growth of different particle phase-space distributions in a long magnetic quadrupole channel,"The behavior of K-V, waterbag, parabolic, conical and Gaussian distributions
in periodic quadrupole channels is studied by particle simulations. It is found
that all these different distributions exhibit the known K-V instabilities. But
the action of the K-V type modes becomes more and more damped in the order of
the types of distributions quoted above. This damping is so strong for the
Gaussian distribution that the emittance growth factor after a large number of
periods is considerably lower than in the case of an equivalent K-V
distribution. In addition, the non K-V distributions experience in only one
period of the channel a rapid initial emittance growth, which becomes very
significant at high beam intensities. This growth is attributed to the
homogenization of the space-charge density, resulting in a conversion of
electric-field energy into transverse kinetic and potential energy. Two simple
analytical formulae are derived to estimate the upper and lower boundary values
for this effect and are compared with the results obtained from particle
simulations.",2401.12595v1
2024-01-26,Double pulse all-optical coherent control of ultrafast spin-reorientation in antiferromagnetic rare-earth orthoferrite,"A pair of circularly polarized laser pulses of opposite helicities are shown
to control the route of spin reorientation phase transition in rare-earth
antiferromagnetic orthoferrite SmTbFeO$_3$. The route can be efficiently
controlled by the delay between the pulses and the sample temperature.
Simulations employing earlier published models of laserinduced spin dynamics in
orthoferrites failed to reproduce the experimental results. It is suggested
that the failure is due to neglected temperature dependence of the
antiferromagnetic resonance damping in the material. Taking into account the
experimentally deduced temperature dependence of the damping, we have been able
to obtain a good agreement between the simulations and the experimental
results.",2401.15009v1
2024-01-31,Observer-based Controller Design for Oscillation Damping of a Novel Suspended Underactuated Aerial Platform,"In this work, we present a novel actuation strategy for a suspended aerial
platform. By utilizing an underactuation approach, we demonstrate the
successful oscillation damping of the proposed platform, modeled as a spherical
double pendulum. A state estimator is designed in order to obtain the
deflection angles of the platform, which uses only onboard IMU measurements.
The state estimator is an extended Kalman filter (EKF) with intermittent
measurements obtained at different frequencies. An optimal state feedback
controller and a PD+ controller are designed in order to dampen the
oscillations of the platform in the joint space and task space respectively.
The proposed underactuated platform is found to be more energy-efficient than
an omnidirectional platform and requires fewer actuators. The effectiveness of
our proposed system is validated using both simulations and experimental
studies.",2401.17676v1
2024-02-02,Long-time dynamics of stochastic wave equation with dissipative damping and its full discretization: exponential ergodicity and strong law of large numbers,"For stochastic wave equation, when the dissipative damping is a non-globally
Lipschitz function of the velocity, there are few results on the long-time
dynamics, in particular, the exponential ergodicity and strong law of large
numbers, for the equation and its numerical discretization to our knowledge.
Focus on this issue, the main contributions of this paper are as follows.
First, based on constructing novel Lyapunov functionals, we show the unique
invariant measure and exponential ergodicity of the underlying equation and its
full discretization. Second, the error estimates of invariant measures both in
Wasserstein distance and in the weak sense are obtained. Third, the strong laws
of large numbers of the equation and the full discretization are obtained,
which states that the time averages of the exact and numerical solutions are
shown to converge to the ergodic limit almost surely.",2402.01137v1
2024-02-05,Symmetries and conservation laws of a fifth-order KdV equation with time-dependent coefficients and linear damping,"A fifth-order KdV equation with time dependent coefficients and linear
damping has been studied. Symmetry groups have several different applications
in the context of nonlinear differential equations. For instance, they can be
used to determine conservation laws. We obtain the symmetries of the model
applying Lie's classical method. The choice of some arbitrary functions of the
equation by the equivalence transformation enhances the study of Lie symmetries
of the equation. We have determined the subclasses of the equation which are
nonlinearly self-adjoint. This allow us to obtain conservation laws by using a
theorem proved by Ibragimov which is based on the concept of adjoint equation
for nonlinear differential equations.",2402.03265v1
2024-02-07,Curvature-Informed SGD via General Purpose Lie-Group Preconditioners,"We present a novel approach to accelerate stochastic gradient descent (SGD)
by utilizing curvature information obtained from Hessian-vector products or
finite differences of parameters and gradients, similar to the BFGS algorithm.
Our approach involves two preconditioners: a matrix-free preconditioner and a
low-rank approximation preconditioner. We update both preconditioners online
using a criterion that is robust to stochastic gradient noise and does not
require line search or damping. To preserve the corresponding symmetry or
invariance, our preconditioners are constrained to certain connected Lie
groups. The Lie group's equivariance property simplifies the preconditioner
fitting process, while its invariance property eliminates the need for damping,
which is commonly required in second-order optimizers. As a result, the
learning rate for parameter updating and the step size for preconditioner
fitting are naturally normalized, and their default values work well in most
scenarios. Our proposed approach offers a promising direction for improving the
convergence of SGD with low computational overhead. We demonstrate that
Preconditioned SGD (PSGD) outperforms SoTA on Vision, NLP, and RL tasks across
multiple modern deep-learning architectures. We have provided code for
reproducing toy and large scale experiments in this paper.",2402.04553v1
2024-02-08,A non-damped stabilization algorithm for multibody dynamics,"The stability of integrators dealing with high order Differential Algebraic
Equations (DAEs) is a major issue. The usual procedures give rise to
instabilities that are not predicted by the usual linear analysis, rendering
the common checks (developed for ODEs) unusable. The appearance of these
difficult-toexplain and unexpected problems leads to methods that arise heavy
numerical damping for avoiding them. This has the undesired consequences of
lack of convergence of the methods, along with a need of smaller stepsizes. In
this paper a new approach is presented. The algorithm presented here allows us
to avoid the interference of the constraints in the integration, thus allowing
the linear criteria to be applied. In order to do so, the integrator is applied
to a set of instantaneous minimal coordinates that are obtained through the
application of the null space. The new approach can be utilized along with any
integration method. Some experiments using the Newmark method have been carried
out, which validate the methodology and also show that the method behaves in a
predictable way if one considers linear stability criteria.",2402.05768v1
2024-02-09,Constraints on Quasinormal modes from Black Hole Shadows in regular non-minimal Einstein Yang-Mills Gravity,"This work deals with the scalar quasinormal modes using higher order WKB
method and black hole shadow in non-minimal Einstein Yang-Mills theory. To
validate the results of quasinormal modes, time domain profiles are also
investigated. We found that with an increase in the magnetic charge of the
black hole, the ring-down gravitational wave increases non-linearly and damping
rate decreases non-linearly. The presence of magnetic charge also results in a
decrease in the black hole shadow non-linearly. It is found that for large
values of the coupling parameter, the black hole changes to a solitonic
solution and the corresponding ring-down gravitational wave frequency increases
slowly with a decrease in the damping rate. For the solitonic solutions, the
shadow is also smaller. The constraints on the model parameters calculated
using shadow observations of M87* and Sgr A* and an approximate analytic
relation between quasinormal modes and shadow at the eikonal limit is
discussed.",2402.06186v1
2024-02-14,The impact of load placement on grid resonances during grid restoration,"As inverter-based generation is being massively deployed in the grid, these
type of units have to take over the current roles of conventional generation,
including the capability of restoring the grid. In this context, the resonances
of the grid during the first steps of a black start can be concerning, given
that the grid is lightly loaded. Especially relevant are the low frequency
resonances, that may be excited by the harmonic components of the inverter. A
typical strategy to avoid or minimize the effect of such resonances relies on
connecting load banks. This was fairly feasible with conventional generation,
but given the limited ratings of inverters, the amount of load that can be
connected at the beginning is very limited. In this paper we consider the
energization of a transmission line, and investigate the optimal location of a
load along a line in order to maximize the damping in the system. By analysing
the spectral properties as a function of the load location, we formally prove
that placing the load in the middle of the transmission line maximizes the
damping ratio of the first resonance of the system.",2402.09294v1
2024-02-19,Gravitational wave asteroseismology of dark matter hadronic stars,"The influence of the dark matter mass~($M_{\chi}$) and the Fermi
momentum~($k_{F}^{\dm}$) on the $f_0$-mode oscillation frequency, damping time
parameter, and tidal deformability of hadronic stars are studied by employing a
numerical integration of hydrostatic equilibrium, nonradial oscillation, and
tidal deformability equations. The matter inside the hadronic stars follows the
NL3* equation of state. We obtain that the influence of $M_{\chi}$ and
$k_F^{\dm}$ is observed in the $f_0$-mode, damping tome parameter, and tidal
deformability. Finally, the correlation between the tidal deformability of the
GW$170817$ event with $M_{\chi}$ and $k_F^{\dm}$ are also investigated.",2402.12600v1
2024-02-21,"Landau damping, collisionless limit, and stability threshold for the Vlasov-Poisson equation with nonlinear Fokker-Planck collisions","In this paper, we study the Vlasov-Poisson-Fokker-Planck (VPFP) equation with
a small collision frequency $0 < \nu \ll 1$, exploring the interplay between
the regularity and size of perturbations in the context of the asymptotic
stability of the global Maxwellian. Our main result establishes the Landau
damping and enhanced dissipation phenomena under the condition that the
perturbation of the global Maxwellian falls within the Gevrey-$\frac{1}{s}$
class and obtain that the stability threshold for the Gevrey-$\frac{1}{s}$
class with $s>s_{\mathrm{k}}$ can not be larger than
$\gamma=\frac{1-3s_{\mathrm{k}}}{3-3s_{\mathrm{k}}}$ for $s_{\mathrm{k}}\in
[0,\frac{1}{3}]$. Moreover, we show that for Gevrey-$\frac{1}{s}$ with $s>3$,
and for $t\ll \nu^{\frac13}$, the solution to VPFP converges to the solution to
Vlasov-Poisson equation without collision.",2402.14082v2
2024-02-22,Long-time asymptotics of the damped nonlinear Klein-Gordon equation with a delta potential,"We consider the damped nonlinear Klein-Gordon equation with a delta potential
\begin{align*} \partial_{t}^2u-\partial_{x}^2u+2\alpha \partial_{t}u+u-\gamma
{\delta}_0u-|u|^{p-1}u=0, \ & (t,x) \in \mathbb{R} \times \mathbb{R},
\end{align*} where $p>2$, $\alpha>0,\ \gamma<2$, and $\delta_0=\delta_0 (x)$
denotes the Dirac delta with the mass at the origin. When $\gamma=0$, C\^{o}te,
Martel and Yuan proved that any global solution either converges to 0 or to the
sum of $K\geq 1$ decoupled solitary waves which have alternative signs. In this
paper, we first prove that any global solution either converges to 0 or to the
sum of $K\geq 1$ decoupled solitary waves. Next we construct a single solitary
wave solution that moves away from the origin when $\gamma<0$ and construct an
even 2-solitary wave solution when $\gamma\leq -2$. Last we give single
solitary wave solutions and even 2-solitary wave solutions an upper bound for
the distance between the origin and the solitary wave.",2402.14381v2
2024-02-22,Low-frequency Resonances in Grid-Forming Converters: Causes and Damping Control,"Grid-forming voltage-source converter (GFM-VSC) may experience low-frequency
resonances, such as synchronous resonance (SR) and sub-synchronous resonance
(SSR), in the output power. This paper offers a comprehensive study on the root
causes of low-frequency resonances with GFM-VSC systems and the damping control
methods. The typical GFM control structures are introduced first, along with a
mapping between the resonances and control loops. Then, the causes of SR and
SSR are discussed, highlighting the impacts of control interactions on the
resonances. Further, the recent advancements in stabilizing control methods for
SR and SSR are critically reviewed with experimental tests of a GFM-VSC under
different grid conditions.",2402.14543v1
2024-02-27,Unified study of viscoelasticity and sound damping in hard and soft amorphous solids,"Recent research has made significant progress in understanding the non-phonon
vibrational states present in amorphous materials. It has been established that
their vibrational density of states follows non-Debye scaling laws. Here, we
show that the non-Debye scaling laws play a crucial role in determining
material properties of a broad range of amorphous solids, from ``hard""
amorphous solids like structural glasses to ``soft"" amorphous solids such as
foams and emulsions. We propose a unified framework of viscoelasticity and
sound damping for these materials. Although these properties differ
significantly between hard and soft amorphous solids, they are determined by
the non-Debye scaling laws. We also validate our framework using numerical
simulations.",2402.17335v1
2024-02-29,Quantum coherence and entanglement under the influence of decoherence,"In this work, we delve into the dynamic traits of the relative entropy of
quantum coherence (REQC) as the quantum system interacts with the different
noisy channels, drawing comparisons with entanglement (concurrence). The
research results demonstrate the broader prevalence and stronger robustness of
the REQC as opposed to concurrence. It's worth noting that the bit flip channel
cannot uphold a constant nonzero frozen the REQC, besides, the concurrence
follows a pattern of temporary reduction to zero, followed by recovery after a
certain time span. More importantly, the REQC maintains its presence
consistently until reaching a critical threshold, whereas concurrence
experiences completely attenuation to zero under the influence of phase damping
and amplitude damping channels.",2402.19055v1
2024-03-02,Diffusive Decay of Collective Quantum Excitations in Electron Gas,"In this work the multistream quasiparticle model of collective electron
excitations is used to study the energy-density distribution of collective
quantum excitations in an interacting electron gas with arbitrary degree of
degeneracy. Generalized relations for the probability current and energy
density distributions is obtained which reveals a new interesting quantum
phenomenon of diffusive decay of pure quasiparticle states at microscopic
level. The effects is studied for various cases of free quasiparticles,
quasiparticle in an infinite square-well potential and half-space collective
excitations. It is shown that plasmon excitations have the intrinsic tendency
to decay into equilibrium state with uniform energy density spacial
distribution. It is found that plasmon levels of quasipaticle in a square-well
potential are unstable decaying into equilibrium state due to the fundamental
property of collective excitations. The decay rates of pure plasmon states are
determined analytically. Moreover, for damped quasiparticle excitations the
non-vanishing probability current divergence leads to imaginary energy density
resulting in damping instability of energy density dynamic. The pronounced
energy density valley close to half-space boundary at low level excitations
predicts attractive force close to the surface. Current research can have
implications with applications in plasmonics and related fields. Current
analysis can be readily generalized to include external potential and magnetic
field effects.",2403.01099v1
2024-03-04,Successive quasienergy collapse and the driven Dicke phase transition in the few-emitter limit,"The emergent behavior that arises in many-body systems of increasing size
follows universal laws that become apparent in order-to-disorder transitions.
While this behavior has been traditionally explored for large numbers of
emitters, recent progress allows for the exploration of the few-emitter limit,
where correlations can be measured and connected to microscopic models to gain
further insight into order-to-disorder transitions. We explore this few-body
limit in the driven and damped Tavis--Cummings model, which describes a
collection of atoms interacting with a driven and damped cavity mode. Our
exploration revolves around the dressed states of the atomic ensemble and
field, whose energies are shown to collapse as the driving field is increased
to mark the onset of a dissipative quantum phase transition. The collapse
occurs in stages and is an effect of light-matter correlations that are
overlooked for single atoms and neglected in mean-field models. The
implications of these correlations over the macroscopic observables of the
system are presented. We encounter a shift in the expected transition point and
an increased number of parity-broken states to choose from once the ordered
phase is reached.",2403.02417v1
2024-03-05,Domain-Agnostic Mutual Prompting for Unsupervised Domain Adaptation,"Conventional Unsupervised Domain Adaptation (UDA) strives to minimize
distribution discrepancy between domains, which neglects to harness rich
semantics from data and struggles to handle complex domain shifts. A promising
technique is to leverage the knowledge of large-scale pre-trained
vision-language models for more guided adaptation. Despite some endeavors,
current methods often learn textual prompts to embed domain semantics for
source and target domains separately and perform classification within each
domain, limiting cross-domain knowledge transfer. Moreover, prompting only the
language branch lacks flexibility to adapt both modalities dynamically. To
bridge this gap, we propose Domain-Agnostic Mutual Prompting (DAMP) to exploit
domain-invariant semantics by mutually aligning visual and textual embeddings.
Specifically, the image contextual information is utilized to prompt the
language branch in a domain-agnostic and instance-conditioned way. Meanwhile,
visual prompts are imposed based on the domain-agnostic textual prompt to
elicit domain-invariant visual embeddings. These two branches of prompts are
learned mutually with a cross-attention module and regularized with a
semantic-consistency loss and an instance-discrimination contrastive loss.
Experiments on three UDA benchmarks demonstrate the superiority of DAMP over
state-of-the-art approaches.",2403.02899v1
2024-03-12,Spatially oscillating correlation functions in $\left(2+1\right)$-dimensional four-fermion models: The mixing of scalar and vector modes at finite density,"In this work, we demonstrate that the mixing of scalar and vector condensates
produces spatially oscillating, but exponentially damped correlation functions
in fermionic theories at finite density and temperature. We find a regime
exhibiting this oscillatory behavior in a Gross-Neveu-type model that also
features vector interactions within the mean-field approximation. The existence
of this regime aligns with expectations based on symmetry arguments, that are
also applicable to QCD at finite baryon density. We compute the phase diagram
including both homogeneous phases and regions with spatially oscillating,
exponentially damped correlation functions at finite temperature and chemical
potential for different strengths of the vector coupling. Furthermore, we find
that inhomogeneous condensates are disfavored compared to homogeneous ones akin
to previous findings without vector interactions. We show that our results are
valid for a broad class of $\left(2+1\right)$-dimensional models with local
four-fermion interactions.",2403.07430v1
2024-03-13,"Painlevé Analysis, Prelle-Singer Approach, Symmetries and Integrability of Damped Hénon-Heiles System","We consider a modified damped version of H\'enon-Heiles system and
investigate its integrability. By extending the Painlev\'e analysis of ordinary
differential equations we find that the modified H\'enon-Heiles system
possesses the Painlev\'e property for three distinct parametric restrictions.
For each of the identified cases, we construct two independent integrals of
motion using the well known Prelle-Singer method. We then derive a set of
nontrivial non-point symmetries for each of the identified integrable cases of
the modified H\'enon-Heiles system. We infer that the modified H\'enon-Heiles
system is integrable for three distinct parametric restrictions. Exact
solutions are given explicitly for two integrable cases.",2403.08410v1
2024-03-15,Delayed interactions in the noisy voter model through the periodic polling mechanism,"We investigate the effects of delayed interactions on the stationary
distribution of the noisy voter model. We assume that the delayed interactions
occur through the periodic polling mechanism and replace the original
instantaneous two-agent interactions. In our analysis, we require that the
polling period aligns with the delay in announcing poll outcomes. As expected,
when the polling period is relatively short, the model with delayed
interactions is effectively identical to the original model. As the polling
period increases, oscillatory behavior emerges, but the model with delayed
interactions still converges to stationary distribution. The stationary
distribution resembles a Beta-binomial distribution, with its shape parameters
scaling with the polling period. The observed scaling behavior is non-trivial.
As the polling period increases, fluctuation damping also intensifies, yet
there is a critical intermediate polling period for which fluctuation damping
reaches its maximum intensity.",2403.10277v1
2024-03-16,CETASim: A numerical tool for beam collective effect study in storage rings,"We developed a 6D multi-particle tracking program CETASim in C++ programming
language to simulate intensity-dependent effects in electron storage rings. The
program can simulate the beam collective effects due to short-range/long-range
wakefields for single/coupled-bunch instability studies. It also features to
simulate interactions among charged ions and the trains of electron bunches,
including both fast ion and ion trapping effects. The bunch-by-bunch feedback
is also included so that the user can simulate the damping of the unstable
motion when its growth rate is faster than the radiation damping rate. The
particle dynamics is based on the one-turn map, including the nonlinear effects
of amplitude-dependent tune shift, high-order chromaticity, and second-order
momentum compaction factor. A skew quadrupole can also be introduced by the
users, which is very useful for the emittance sharing and the emittance
exchange studies. This paper describes the code structure, the physics models,
and the algorithms used in CETASim. We also present the results of its
application to PETRA-IV storage ring.",2403.10973v1
2024-03-18,Mitigation of the Microbunching Instability Through Transverse Landau Damping,"The microbunching instability has been a long-standing issue for
high-brightness free-electron lasers (FELs), and is a significant show-stopper
to achieving full longitudinal coherence in the x-ray regime. This paper
reports the first experimental demonstration of microbunching instability
mitigation through transverse Landau damping, based on linear optics control in
a dispersive region. Analytical predictions for the microbunching content are
supported by numerical calculations of the instability gain and confirmed
through the experimental characterization of the spectral brightness of the
FERMI FEL under different transverse optics configurations of the transfer line
between the linear accelerator and the FEL.",2403.11594v1
2024-03-19,Calculating quasinormal modes of extremal and non-extremal Reissner-Nordström black holes with the continued fraction method,"We use the numerical continued fraction method to investigate quasinormal
mode spectra of extremal and non-extremal Reissner-Nordstr\""om black holes in
the low and intermediate damping regions. In the extremal case, we develop
techniques that significantly expand the calculated spectrum from what had
previously appeared in the literature. This allows us to determine the
asymptotic behavior of the extremal spectrum in the high damping limit, where
there are conflicting published results. Our investigation further supports the
idea that the extremal limit of the non-extremal case, where the charge
approaches the mass of the black hole in natural units, leads to the same
vibrational spectrum as in the extremal case despite the qualitative
differences in their topology. In addition, we numerically explore the
quasinormal mode spectrum for a Reissner-Nordstr\""om black hole in the small
charge limit.",2403.13074v1
2024-03-19,Uniform vorticity depletion and inviscid damping for periodic shear flows in the high Reynolds number regime,"We study the dynamics of the two dimensional Navier-Stokes equations
linearized around a shear flow on a (non-square) torus which possesses exactly
two non-degenerate critical points. We obtain linear inviscid damping and
vorticity depletion estimates for the linearized flow that are uniform with
respect to the viscosity, and enhanced dissipation type decay estimates. The
main task is to understand the associated Rayleigh and Orr-Sommerfeld
equations, under the natural assumption that the linearized operator around the
shear flow in the inviscid case has no discrete eigenvalues. The key difficulty
is to understand the behavior of the solution to Orr-Sommerfeld equations in
three distinct regimes depending on the spectral parameter: the non-degenerate
case when the spectral parameter is away from the critical values, the
intermediate case when the spectral parameter is close to but still separated
from the critical values, and the most singular case when the spectral
parameter is inside the viscous layer.",2403.13104v1
2024-03-26,Greybody Factors Imprinted on Black Hole Ringdowns. II. Merging Binary Black Holes,"The spectral amplitude of the merger-ringdown gravitational wave (GW) emitted
by a comparable mass-ratio black hole merger is modeled by the greybody factor
of the remnant black hole. Our model does not include fitting parameters except
for a single overall spectral amplitude. We perform the mass-spin inference
from the SXS data without introducing fitting parameters and without tuning the
data range of each SXS template. Also, we find that the exponential damping in
the ringdown spectral amplitude can be modeled well with the exponential
damping in the greybody factor at high frequencies. Based on the findings, we
propose a conjecture that the light ring of the remnant black hole, which
sources the ringdown, forms as early as during the merger stage. We discuss the
formation of the light ring in the static binary solution as a first step
towards the understanding of how the separation of merging black holes may
affect the formation of the light ring.",2403.17487v1
2024-03-27,Fractional variational integrators based on convolution quadrature,"Fractional dissipation is a powerful tool to study non-local physical
phenomena such as damping models. The design of geometric, in particular,
variational integrators for the numerical simulation of such systems relies on
a variational formulation of the model. In [19], a new approach is proposed to
deal with dissipative systems including fractionally damped systems in a
variational way for both, the continuous and discrete setting. It is based on
the doubling of variables and their fractional derivatives. The aim of this
work is to derive higher-order fractional variational integrators by means of
convolution quadrature (CQ) based on backward difference formulas. We then
provide numerical methods that are of order 2 improving a previous result in
[19]. The convergence properties of the fractional variational integrators and
saturation effects due to the approximation of the fractional derivatives by CQ
are studied numerically.",2403.18362v1
2024-04-02,High-energy neutrinos flavour composition as a probe of neutrino magnetic moments,"Neutrino propagation in the Galactic magnetic field is considered. To
describe neutrino flavour and spin oscillations on the galactic scale baselines
an approach using wave packets is developed. Evolution equations for the
neutrino wave packets in a uniform and non-uniform magnetic field are derived.
Analytical expressions for neutrino flavour and spin oscillations probabilities
accounting for damping due to wave packet separation are obtained for the case
of uniform magnetic field. It is shown that for oscillations on magnetic
frequencies $\omega_i^B = \mu_i B_\perp$ the coherence lengths that
characterizes the damping scale is proportional to the cube of neutrino average
momentum $p_0^3$. Probabilities of flavour and spin oscillations are calculated
numerically for neutrino interacting with the non-uniform Galactic magnetic
field. Flavour compositions of high-energy neutrino flux coming from the
Galactic centre are calculated accounting for neutrino interaction with the
magnetic field. It is shown that for neutrino magnetic moments $\sim 10^{-13}
\mu_B$ and larger these flavour compositions significantly differ from ones
predicted by the vacuum neutrino oscillations scenario.",2404.02027v1
2018-06-27,Deterministics descriptions of the turbulence in the Navier-Stokes equations,"This PhD thesis is devoted to deterministic study of the turbulence in the
Navier- Stokes equations. The thesis is divided in four independent
chapters.The first chapter involves a rigorous discussion about the energy's
dissipation law, proposed by theory of the turbulence K41, in the deterministic
setting of the homogeneous and incompressible Navier-Stokes equations, with a
stationary external force (the force only depends of the spatial variable) and
on the whole space R3. The energy's dissipation law, also called the
Kolmogorov's dissipation law, characterizes the energy's dissipation rate (in
the form of heat) of a turbulent fluid and this law was developed by A.N.
Kolmogorov in 1941. However, its deduction (which uses mainly tools of
statistics) is not fully understood until our days and then an active research
area consists in studying this law in the rigorous framework of the
Navier-Stokes equations which describe in a mathematical way the fluids motion
and in particular the movement of turbulent fluids. In this setting, the
purpose of this chapter is to highlight the fact that if we consider the
Navier-Stokes equations on R3 then certain physical quantities, necessary for
the study of the Kolmogorov's dissipation law, have no a rigorous definition
and then to give a sense to these quantities we suggest to consider the
Navier-Stokes equations with an additional damping term. In the framework of
these damped equations, we obtain some estimates for the energy's dissipation
rate according to the Kolmogorov's dissipation law.In the second chapter we are
interested in study the stationary solutions of the damped Navier- Stokes
introduced in the previous chapter. These stationary solutions are a particular
type of solutions which do not depend of the temporal variable and their study
is motivated by the fact that we always consider the Navier-Stokes equations
with a stationary external force. In this chapter we study two properties of
the stationary solutions : the first property concerns the stability of these
solutions where we prove that if we have a control on the external force then
all non stationary solution (with depends of both spatial and temporal
variables) converges toward a stationary solution. The second property concerns
the decay in spatial variable of the stationary solutions. These properties of
stationary solutions are a consequence of the damping term introduced in the
Navier-Stokes equations.In the third chapter we still study the stationary
solutions of Navier-Stokes equations but now we consider the classical
equations (without any additional damping term). The purpose of this chapter is
to study an other problem related to the deterministic description of the
turbulence : the frequency decay of the stationary solutions. Indeed, according
to the K41 theory, if the fluid is in a laminar setting then the stationary
solutions of the Navier-Stokes equations must exhibit a exponential frequency
decay which starts at lows frequencies. But, if the fluid is in a turbulent
setting then this exponential frequency decay must be observed only at highs
frequencies. In this chapter, using some Fourier analysis tools, we give a
precise description of this exponential frequency decay in the laminar and in
the turbulent setting.In the fourth and last chapter we return to the
stationary solutions of the classical Navier-Stokes equations and we study the
uniqueness of these solutions in the particular case without any external
force. Following some ideas of G. Seregin, we study the uniqueness of these
solutions first in the framework of Lebesgue spaces of and then in the a
general framework of Morrey spaces.",1806.10430v2
1996-10-28,QSO Absorbing Galaxies at z<~1: Deep Imaging and Spectroscopy in the Field of 3C 336,"We present very deep WFPC2 images and FOS spectroscopy from the Hubble Space
Telescope (HST) together with numerous supporting ground-based observations of
the field of the quasar 3C 336 ($z_{em}=0.927$). The observations are designed
to investigate the nature of galaxies producing metal line absorption systems
in the spectrum of the QSO. Along a single line of sight, we find at least 6
metal line absorption systems (of which 3 are newly discovered) ranging in
redshift from 0.317 to 0.892. Through an extensive program of optical and IR
imaging, QSO spectroscopy, and faint galaxy spectroscopy, we have identified 5
of the 6 metal line absorption systems with luminous (L_K > 0.1 L*_K) galaxies.
These have morphologies ranging from very late-type spiral to S0, and exhibit a
wide range of inclination and position angles with respect to the QSO
sightline. The only unidentified absorber, despite our intensive search, is a
damped Lyman $\alpha$ system at $z_{abs}=0.656$. Analysis of the absorption
spectrum suggests that the metal abundances ([Fe/H]$=-1.2$) in this system are
similar to those in damped systems at $z \sim 2$, and to the two other damped
systems for which abundances have been determined at $z <1$. We have found no
examples of intrinsically faint galaxies ($L < 0.1 L^{\ast}$) at small impact
parameters that might have been missed as absorber candidates in our previous
ground-based imaging and spectroscopic programs on MgII absorbing galaxies.
There are no bright galaxies (L > 0.1 L_K) within 50h^{-1} kpc which do not
produce detectable metal lines (of Mg II 2796, 2803 and/or C IV 1548, 1550) in
the QSO spectrum. All of these results generally support the inferences which
we have previously reached from a larger survey for absorption-selected
galaxies at $z\simlt 1$.",9610230v1
1996-11-05,The nature of intermediate-redshift damped Ly-alpha absorbers,"We present HST/WFPC2 high-spatial resolution images in the R and B bands of
the close environment of the sightlines to seven quasars which spectra show
either a damped Ly-alpha absorption line, 21cm absorption, or a very strong
MgII/FeII absorption system at intermediate redshifts (0.4 < z < 1). Objects
down to about 0.3"", or 2.0 kpc at z=0.6 (H0 = 50 kms/s/Mpc, q0=0), and to a
limiting magnitude m(702, lim)=25.9 could be detected for seven fields
comprising eight absorbers (one at higher redshift z=1.78 towards MC 1331+170)
with high HI column densities of at least 1x10^20 cm^-2. In each case, a
candidate absorber with absolute magnitude Mb =-19.0 or much brighter has been
detected. This small sample of gas-rich galaxies at intermediate redshifts
covers a wide range in morphological types. There are three spiral galaxies of
various sizes and luminosities (towards 3C 196, Q 1209+107 and MC 1331+170),
three compact objects (towards EX 0302-223, PKS 0454+039 and, at high redshift,
MC 1331+170), and two amorphous, low surface brightness galaxies (towards PKS
1229-021 and 3C 286). In the fields around 3C 196, PKS 1229-021 and Q 1209+107,
there is an excess of galaxies in the PC2 images, suggestive of the presence of
a group of galaxies associated with the damped Ly-alpha absorber, or maybe with
the quasar itself for the two z = 1.0 cases. For 3C 196 and 3C 286, the quasar
host galaxies have also tentatively been discovered.",9611031v1
1997-07-08,The Formation of Galactic Disks,"We study the population of galactic disks expected in current hierarchical
clustering models for structure formation. A rotationally supported disk with
exponential surface density profile is assumed to form with a mass and angular
momentum which are fixed fractions of those of its surrounding dark halo. We
assume that haloes respond adiabatically to disk formation, and that only
stable disks can correspond to real systems. With these assumptions the
predicted population can match both present-day disks and the damped Lyman
alpha absorbers in QSO spectra. Good agreement is found provided: (i) the
masses of disks are a few percent of those of their haloes; (ii) the specific
angular momenta of disks are similar to those of their haloes; (iii)
present-day disks were assembled recently (at z<1). In particular, the observed
scatter in the size-rotation velocity plane is reproduced, as is the slope and
scatter of the Tully-Fisher relation. The zero-point of the TF relation is
matched for a stellar mass-to-light ratio of 1 to 2 h in the I-band, consistent
with observational values derived from disk dynamics. High redshift disks are
predicted to be small and dense, and could plausibly merge together to form the
observed population of elliptical galaxies. In many (but not all) currently
popular cosmogonies, disks with rotation velocities exceeding 200 km/s can
account for a third or more of the observed damped Lyman alpha systems at
z=2.5. Half of the lines-of-sight to such systems are predicted to intersect
the absorber at r>3kpc/h and about 10% at r>10kpc/h. The cross-section for
absorption is strongly weighted towards disks with large angular momentum and
so large size for their mass. The galaxy population associated with damped
absorbers should thus be biased towards low surface brightness systems.",9707093v1
1997-09-26,No C+ emission from the z=3.137 damped Lyman-alpha absorber towards PC1643+4631A,"We describe a search for redshifted [C II] in a z=3.137 damped Ly-alpha
absorption system that has a large neutral hydrogen column density and which
was controversially reported to be a source of CO emission, indicative of rapid
star-formation (Frayer, Brown & Vanden Bout 1994; Braine, Downes & Guilloteau
1996). There is no sign of [C II] emission in our spectrum, which was obtained
during excellent observing conditions at the James Clerk Maxwell Telescope
(JCMT) and covers 1890 km/s. The upper limit we have placed on the integrated
line intensity (3 sigma(T_MB) < 5.9 K km/s for a profile akin to that of the CO
lines) constrains the [C II]/CO(1-0) line-intensity ratio to 3 sigma < 8300,
based on the line intensity reported by Frayer et al. (1994), or to 3 sigma <
58700 based on the data obtained by Braine et al. (1996). These limits are
consistent with values measured in the Galactic plane and for nearby starburst
nuclei; the former, however, is significantly lower than the ratio found in
low-metallicity systems such as the Large Magellanic Cloud (which might be
expected to have much in common with a damped Ly-alpha absorption system at
high redshift). This can be taken as evidence against the reality of the CO
line detections, with the proviso that a system significantly larger than
present-day disk galaxies would NOT have been fully covered by our small beam
whereas it WOULD have been properly sampled by the Frayer et al. observations.
Finally, we demonstate (as did Ivison et al. 1996) that knitting together
overlapping bands can generate erroneous results - specifically, an emission
feature that has a width, profile and central velocity consistent with the
controversial CO emission lines and which could have drawn us to entirely the
wrong conclusions.",9709266v1
1998-04-06,Three-dimensional waves generated at Lindblad resonances in thermally stratified disks,"We analyze the linear, 3D response to tidal forcing of a disk that is thin
and thermally stratified in the direction normal to the disk plane. We model
the vertical disk structure locally as a polytrope which represents a disk of
high optical depth. We solve the 3D gas-dynamic equations semi-analytically in
the neighborhood of a Lindblad resonance. These solutions match asymptotically
on to those valid away from resonances and provide solutions valid at all
radii. We obtain the following results. 1) A variety of waves are launched at
resonance. However, the f mode carries more than 95% of the torque exerted at
the resonance. 2) These 3D waves collectively transport exactly the amount of
angular momentum predicted by the 2D torque formula. 3) Near resonance, the f
mode occupies the full vertical extent of the disk. Away from resonance, the f
mode becomes confined near the surface of the disk, and, in the absence of
other dissipation mechanisms, damps via shocks. The radial length scale for
this process is roughly r_L/m (for resonant radius r_L and azimuthal wavenumber
m), independent of the disk thickness H. This wave channeling process is due to
the variations of physical quantities in r and is not due to wave refraction.
4) However, the inwardly propagating f mode launched from an m=2 inner Lindblad
resonance experiences relatively minor channeling.
  We conclude that for binary stars, tidally generated waves in highly
optically thick circumbinary disks are subject to strong nonlinear damping by
the channeling mechanism, while those in circumstellar accretion disks are
subject to weaker nonlinear effects. We also apply our results to waves excited
by young planets for which m is approximately r/H and conclude that the waves
are damped on the scale of a few H.",9804063v1
2000-11-23,Near-Infrared Integral Field Spectroscopy of Damped Lyman-alpha Systems,"We assess the feasibility of detecting star formation in damped Lyman-alpha
systems (DLAs) at z>1 through near-infrared spectroscopy using the forthcoming
integral field units on 8m-class telescopes. Although their relation to
galaxies is not well established, high-z DLAs contain most of the neutral gas
in the Universe, and this reservoir is depleted with time - presumably through
star formation. Line emission should be an indicator of star formation
activity, but searches based on Lyman-alpha are unreliable because of the
selective extinction of this resonant UV line. Using more robust lines such as
H-alpha forces a move to the near-infrared at z>1. For line emission searches,
spectroscopy is more sensitive than imaging, but previous long-slit
spectroscopic searches have been hampered by the likelihood that any star
forming region in the DLA galaxy disk would fall outside the narrow slit. The
new integral field units such as CIRPASS on Gemini will cover sufficient solid
angles to intercept these, even in the extreme case of large galactic disks at
high redshift. On an 8m-class telescope, star formation rates of <1M_sun/yr
will be reached at z~1.4 with H-alpha in the H-band. Such star formation rates
are well below L* for the high-z Lyman-break population, and are comparable
locally to the luminous giant HII complexes in M101. It appears that
instruments such as CIRPASS on Gemini will have both the sensitivity and the
survey area to measure star formation rates in z>1 DLAs. These observations
will probe the nature of damped Lyman-alpha systems and address their relation
to galaxies.",0011421v1
2001-08-07,Dynamics and Origin of the 2:1 Orbital Resonances of the GJ 876 Planets,"(Abridged) A dynamical fit has placed the two planets about the star GJ 876
in coplanar orbits deep in 3 resonances at the 2:1 mean-motion commensurability
with small libration amplitudes. The libration of both lowest order mean-motion
resonance variables, theta_1 and theta_2, and the secular resonance variable,
theta_3, about 0 deg. differs from the familiar geometry of the Io-Europa pair,
where theta_2 and theta_3 librate about 180 deg. By considering a condition for
stable simultaneous librations of theta_1 and theta_2, we show that the GJ 876
geometry results because of the large orbital eccentricities e_i, whereas the
very small e_i in the Io-Europa system lead to the latter's geometry.
Surprisingly, the GJ 876 resonance configuration remains stable for e_1 up to
0.86 and for amplitude of libration of theta_1 approaching 45 deg. with the
current e_i. We find that inward migration of the outer planet of the GJ 876
system results in certain capture into the observed resonances if initially e_1
<0.06 and e_2<0.03 and the migration rate |(da_2/dt)/a_2| < 0.03(a_2/AU)^{-3/2}
yr^{-1}. The bound on the migration rate is easily satisfied by migration due
to planet-nebula interaction. If there is no eccentricity damping, eccentricity
growth is rapid with continued migration within the resonance, with e_i
exceeding the observed values after a further reduction in the semi-major axes
a_i of only 7%. With eccentricity damping (de_i/dt)/e_i = -K|(da_i/dt)/a_i|,
the e_i reach equilibrium values that remain constant for arbitrarily long
migration within the resonances. The equilibrium e_i are close to the observed
e_i for K=100 (K=10) if there is migration and damping of the outer planet only
(of both planets). It is as yet unclear that planet-nebula interaction can
produce the large value of K required to obtain the observed eccentricities.",0108104v2
2001-12-03,"Euler, Jacobi, and Missions to Comets and Asteroids","Whenever a freely spinning body is found in a complex rotational state, this
means that either the body is a recent victim of an impact or a tidal
interaction, or is a fragment of a recently disrupted progenitor. Another
factor (relevant for comets) is outgassing. Due to impacts, tidal forces and
outgassing, the asteroidal and cometary precession must be a generic
phenomenon: while some rotators are in the state of visible tumbling, a much
larger amount of objects must be performing narrow-cone precession not so
easily observable from the Earth. The internal dissipation in a freely
precessing top leads to relaxation (gradual damping of the precession) and
sometimes to spontaneous changes in the rotation axis. Recently developed
theory of dissipative precession of a rigid body reveals that this is a highly
nonlinear process: while the body is precessing at an angular rate $ \omega$,
the precession-caused stresses and strains in the body contain components
oscillating at other frequencies. Dependent upon the spin state, those
frequencies may be higher or, most remarkably, lower than the precession rate.
In many states dissipation at the harmonics is comparable to or even exceeds
that at the principal frequency. For this and other reasons, in many spin
states the damping of asteroidal and cometary wobble happens faster, by several
orders, than believed previously. This makes it possible to measure the
precession-damping rate. The narrowing of the precession cone through the
period of about a year can be registered by the currently available
spacecraft-based observational means. However, in the near-separatrix spin
states a precessing rotator can considerably slow down its relaxation.",0112054v3
2002-06-17,The UCSD HIRES/KECK I Damped Lya Abundance Database: IV. Probing Galactic Enrichment Histories with Nitrogen,"We present 14 N^0 measurements from our HIRES/Keck database of damped Lya
abundances. These data are combined with measurements from the recent and past
literature to build an homogeneous, uniform set of observations. We examine
photoionization diagnostics like Fe^++ and Ar^0 in the majority of the complete
sample and assess the impact of ionization corrections on N/alpha and alpha/H
values derived from observed ionic column densities of N^0, Si^+, H^0, and S^+.
Our final sample of 19 N/alpha, alpha/H pairs appears bimodal; the majority of
systems show N/alpha values consistent with metal-poor emission regions in the
local universe but a small sub-sample exhibit significantly lower N/alpha
ratios. Contrary to previous studies of N/alpha in the damped systems, our
sample shows little scatter within each sub-sample. We consider various
scenarios to explain the presence of the low N/alpha sightlines and account for
the apparent bimodality. We favor a model where at least some galaxies undergo
an initial burst of star formation with suppressed formation of
intermediate-mass stars. We found a power-law IMF with slope 0.10 or a mass cut
of ~5-8 Msolar would successfully reproduce the observed LN-DLA values. If the
bimodal distribution is confirmed by a larger sample of measurements, this may
present the first observational evidence for a top heavy initial mass function
in some early stellar populations.",0206296v1
2003-08-11,The Nature of Damped Ly-alpha Absorbing Galaxies at z<=1--A Photometric Redshift Survey of Damped Ly-alpha Absorbers,"We study the nature of damped Lya absorption (DLA) systems at z<=1 using a
sample of 11 DLA galaxies, for which accurate redshift measurements are
available. We demonstrate that the precision of photometric redshifts is
sufficient for identifying DLA galaxies, because DLAs are rare and their
intrinsically high column density implies a small impact parameter of the host
galaxy to the QSO line of sight. We adopt this first large DLA galaxy sample to
study the neutral gas cross section of intermediate-redshift galaxies and
examine the optical properties of DLA galaxies at z<=1. The results of our
study are: (1) the extent of neutral gas around intermediate-redshift galaxies
scales with B-band luminosity as R/R_* = [L_B/L_{B_*}]^{\beta} with R_*=24-30
h^{-1} kpc and \beta = 0.26_{-0.06}^{+0.24} at N(HI)=10^{20} cm^{-2}; (2) the
observed incidence of the DLAs versus the B-band luminosity of the DLA galaxies
is consistent with models derived from adopting a known galaxy B-band
luminosity function and the best-fit scaling relation of the neutral gas cross
section at M_B - 5\log h <= -17; (3) comparison of the observed and predicted
number density of DLAs supports that luminous galaxies can explain most of the
DLAs found in QSO absorption line surveys and a large contribution of dwarfs
(M_B - 5\log h >= -17) to the total neutral gas cross section is not necessary;
(4) of the 11 DLAs studied, 45% are disk dominated, 22% are bulge dominated,
11% are irregular, and 22% are in galaxy groups, indicating that galaxies that
give rise to the DLAs span a wide range of morphological types and arise in a
variety of galaxy environment; (Abridged)",0308190v1
2004-07-21,Discovery of a Primitive Damped Lyman alpha Absorber Near an X-ray Bright Galaxy Group in the Virgo Cluster,"We present a new UV echelle spectrum of PG1216+069, obtained with HST+STIS,
which reveals damped Lya (DLA) absorption as well as O I, C II, Si II, and Fe
II absorption lines at z(abs) = 0.00632 near the NGC4261 group. The absorber
shows no evidence of highly-ionized gas, which places constraints on ""warm-hot""
missing baryons in the NGC4261 group. The well-developed damping wings of the
Lya line tightly constrain the H I column density; we find log N(H I) =
19.32+/-0.03. The metallicity of this sub-DLA is remarkably low, [O/H] =
-1.60^{+0.09}_{-0.11}, which is comparable to many analogous high-redshift
systems, and the iron abundance indicates that this absorber contains little or
no dust. Nitrogen is underabundant; we detect neither N I or N II, and we show
that this is not due to ionization effects but rather indicates that [N/O] <
-0.28 (3sigma). Despite the proximity to NGC4261 group, there are no bright
galaxies close to the sight line at the absorption redshift. The nearest known
galaxy is a sub-L* galaxy with a projected distance rho = 86 kpc; the closest
L* galaxy is NGC4260 at rho = 246 kpc. The low metallicity and [N/O] indicate
that this low-z sub-DLA is a relatively primitive gas cloud. We consider the
nature and origin of the sub-DLA, and we find several possibilities. The
properties of the sub-DLA are similar to those of the interstellar media in
blue compact dwarf galaxies and are also reminiscent of Milky Way HVCs. Or, the
object could simply be a small dark-matter halo, self-enriched by a small
amount of internal star formation but mostly undisturbed since its initial
formation. In this case, the small halo would likely be an ancient building
block of galaxy formation that formed before the epoch of reionization.",0407465v2
2004-08-27,Detection of 21 Centimeter HI Absorption at z = 0.78 in a Survey of Radio Continuum Sources,"We report the detection of a deep broad HI 21 cm absorption system at z =
0.78 toward the radio source [HB89] 2351+456 (4C+45.51) at z = 1.992. The HI
absorption was identified in a blind spectral line survey conducted at the
Green Bank Telescope spanning 0.63 < z < 1.10 toward a large sample of radio
continuum sources. The HI column density is N(HI) = 2.35 x 10^19 (T_s/f) cm^-2,
where T_s is the spin temperature and f is the continuum covering factor of the
absorbing gas. For T_s/f > 8.5 K, this system is by definition a damped Ly
alpha absorption system (N(HI) >= 2 x 10^20 cm^-2). The line is unusually
broad, with a FWHM of 53 km/s and a full span of 163 km/s, suggesting a
physically extended HI gas structure. Radio surveys identify damped Ly alpha
systems in a manner that bypasses many of the selection effects present in
optical/UV surveys, including dust extinction and the atmospheric cutoff for z
< 1.65. The smooth broad profile of this HI 21 cm absorption system is similar
to the z = 0.89 HI absorption toward PKS 1830-211, which suggests that the
absorber toward [HB89] 2351+456 is also a gravitational lens and a molecular
absorption system. However, very long baseline interferometry and Hubble Space
Telescope observations show little evidence for gravitational lensing, and BIMA
millimeter observations show no HCO+ (1-2) or HCN (1-2) absorption down to tau
= 0.15 (3 sigma) in 5 km/s channels. Although this radio damped Ly alpha
selection technique would include dusty, molecule-rich systems, [HB89] 2351+456
appears to be a ``vanilla'' HI 21 cm absorber.",0408531v1
2005-03-17,The first WIMPy halos,"Dark matter direct and indirect detection signals depend crucially on the
dark matter distribution. While the formation of large scale structure is
independent of the nature of the cold dark matter (CDM), the fate of
inhomogeneities on sub-galactic scales, and hence the present day CDM
distribution on these scales, depends on the micro-physics of the CDM
particles. We study the density contrast of Weakly Interacting Massive
Particles (WIMPs) on sub-galactic scales. We calculate the damping of the
primordial power spectrum due to collisional damping and free-streaming of
WIMPy CDM and show that free-streaming leads to a CDM power spectrum with a
sharp cut-off at about $10^{-6} M_\odot$. We also calculate the transfer
function for the growth of the inhomogeneities in the linear regime, taking
into account the suppression in the growth of the CDM density contrast after
matter-radiation equality due to baryons and show that our analytic results are
in good agreement with numerical calculations. Combining the transfer function
with the damping of the primordial fluctuations we produce a WMAP normalized
primordial CDM power spectrum, which can serve as an input for high resolution
CDM simulations. We find that the smallest inhomogeneities typically have
co-moving radius of about 1 pc and enter the non-linear regime at a redshift of
$60 \pm 20$. We study the effect of scale dependence of the primordial power
spectrum on these numbers and also use the spherical collapse model to make
simple estimates of the properties of the first generation of WIMP halos to
form. We find that the very first WIMPy halos may have a significant impact on
indirect dark matter searches.",0503387v2
2005-06-30,Molecular Hydrogen in the Damped Ly alpha Absorber of Q1331+170,"We used HST/STIS to obtain the spectrum of molecular hydrogen associated with
the damped Ly$\alpha$ system at $z_{\rm abs}=1.7765$ toward the quasar
Q1331+170 at $z_{\rm em}=2.084$. Strong ${\rm H}_2$ absorption was detected,
with a total ${\rm H}_2$ column density of $N({\rm H}_2)=(4.45\pm 0.36)\times
10^{19} {\rm cm^{-2}}$.The molecular hydrogen fraction is $f_{{\rm
H}_2}=\frac{2N_{\rm H_2}}{N_{\rm HI}+2N_{\rm H_2}}=(5.6\pm 0.7)%$, which is the
greatest value reported so far in any redshifted damped Ly$\alpha$ system. This
results from the combined effect of a relatively high dust-to-gas ratio, a low
gas temperature, and an extremely low ambient UV radiation field. Based on the
observed population of $J$ states, we estimate the photo-absorption rate to be
$R_{\rm abs}=(7.6\pm 2.4)\times 10^{-13} {\rm s^{-1}}$, corresponding to a
local UV radiation field of $J(1000{\rm \AA})\approx 2.1\times 10^{-3}
J_{1000{\rm \AA},\odot}$, where $J_{1000{\rm \AA},\odot}$ is the UV intensity
at $1000 \AA$ in the solar neighborhood. This is comparable with the
metagalactic UV background intensity at this redshift, and implies an extremely
low star formation rate in the absorber's environment. The observed CO-to-H$_2$
column density ratio is $\frac{N_{\rm CO}}{N_{\rm H_2}}<2.5\times 10^{-7}$,
which is similar to the value measured for diffuse molecular clouds in the
Galactic ISM. Finally, applying the inferred physical conditions to the
observed C I fine structure excitation (Songaila {\it et al.} 1994), we
estimate the cosmic microwave background temperature to be $T_{\rm CMB}=(7.2\pm
0.8) {\rm K}$ at $z=1.77654$, consistent with the predicted value of $7.566
{\rm K}$ from the standard cosmology.",0506766v1
1997-05-06,Resonant Raman Scattering in Antiferromagnets,"Two-magnon Raman scattering provides important information about electronic
correlations in the insulating parent compounds of high-$T_c$ materials. Recent
experiments have shown a strong dependence of the Raman signal in $B_{1g}$
geometry on the frequency of the incoming photon. We present an analytical and
numerical study of the Raman intensity in the resonant regime. It has been
previously argued by one of us (A.Ch) and D. Frenkel that the most relevant
contribution to the Raman vertex at resonance is given by the triple resonance
diagram. We derive an expression for the Raman intensity in which we
simultaneously include the enhancement due to the triple resonance and a final
state interaction. We compute the two-magnon peak height (TMPH) as a function
of incident frequency and find two maxima at $\omega^{(1)}_{res} \approx
2\Delta + 3J$ and $\omega^{(2)}_{res} \approx 2\Delta + 8J$. We argue that the
high-frequency maximum is cut only by a quasiparticle damping, while the
low-frequency maximum has a finite amplitude even in the absence of damping. We
also obtain an evolution of the Raman profile from an asymmetric form around
$\omega^{(1)}_{res}$ to a symmetric form around $\omega^{(2)}_{res}$. We
further show that the TMPH depends on the fermionic quasiparticle damping, the
next-nearest neighbor hopping term $t^{\prime}$ and the corrections to the
interaction vertex between light and the fermionic current. We discuss our
results in the context of recent experiments by Blumberg et al. on
$Sr_2CuO_2Cl_2$ and $YBa_2Cu_3O_{6.1}$ and R\""{u}bhausen et al. on
$PrBa_2Cu_3O_7$ and show that the triple resonance theory yields a qualitative
and to some extent also quantitative understanding of the experimental data.",9705051v1
1998-09-15,Solid friction at high sliding velocities: an explicit 3D dynamical SPH approach,"We present realistic 3D numerical simulations of elastic bodies sliding on
top of each other in a regime of velocities ranging from meters to tens of
meters per second using the so-called Smoothed Particle Hydrodynamics (SPH)
method. Our investigations are restricted to regimes of pressure and roughness
where only elastic deformations occur between asperities at the contact surface
between the slider block and the substrate. In this regime, solid friction is
due to the generation of vibrational radiations which are subsequently damped
out. We study periodic commensurate and incommensurate asperities and various
types of disordered surfaces. We report the evidence of a transition from zero
(or non-measurable $\mu < 0.001$) friction to a finite friction as the normal
pressure increases above about $10^6~Pa$. For larger normal pressures (up to
$10^9~Pa$), we find a remarkably universal value for the friction coefficient
$\mu \approx 0.06$, which is independent of the internal dissipation strength
over three order of magnitudes, and independent of the detailled nature of the
slider block-substrate interactions. We find that disorder may either decrease
or increase $\mu$ due to the competition between two effects: disorder detunes
the coherent vibrations of the asperties that occur in the periodic case,
leading to weaker acoustic radiation and thus weaker damping. On the other
hand, large disorder leads to stronger vibration amplitudes at local asperities
and thus stronger damping. Our simulations have confirmed the existence of
jumps over steps or asperities of the slider blocks occurring at the largest
velocities studied ($10~m/s$). These jumps lead to chaotic motions similar to
the bouncing-ball problem. We find a velocity strengthening with a doubling of
the friction coefficient as the velocity increases from $1~m/s$ to $10~m/s$.",9809213v1
2000-03-10,Competing orders and quantum criticality in doped antiferromagnets,"We use a number of large-N limits to explore the competition between ground
states of square lattice doped antiferromagnets which break electromagnetic
U(1), time-reversal, or square lattice space group symmetries. Among the states
we find are d-, (s+id)-, and (d+id)-wave superconductors, Wigner crystals,
Wigner crystals of hole pairs, orbital antiferromagnets (or staggered-flux
states), and states with spin-Peierls and bond-centered charge stripe order. In
the vicinity of second-order quantum phase transitions between the states, we
go beyond the large-N limit by identifying the universal quantum field theories
for the critical points, and computing the finite temperature, quantum-critical
damping of fermion spectral functions. We identify candidate critical points
for the recently observed quantum-critical behavior in photoemission
experiments on BSCCO by Valla et al. (Science 285, 2110 (1999)). These involve
onset of a charge density wave, or of broken time-reversal symmetry with (d+id)
or (s+id) pairing, in a d-wave superconductor. It is not required (although it
is allowed) that the stable state in the doped cuprates to be anything other
than the d-wave superconductor--the other states need only be stable nearby in
parameter space. At finite temperatures, fluctuations associated with these
nearby states lead to the observed fermion damping in the vicinity of the nodal
points in the Brillouin zone. The cases with broken time-reversal symmetry are
appealing because the order parameter is not required to satisfy any special
commensurability conditions. The observed absence of inelastic damping of
quasiparticles with momenta (pi,k), (k,pi) (with 0 < k < pi) also appears very
naturally for the case of a transition to (d+id) order.",0003163v7
2001-12-03,Theory of proximity effect in superconductor/ferromagnet heterostructures,"We present a microscopic theory of proximity effect in the
ferromagnet/superconductor/ferromagnet (F/S/F) nanostructures where S is s-wave
low-T_c superconductor and F's are layers of 3d transition ferromagnetic metal.
Our approach is based on the solution of Gor'kov equations for the normal and
anomalous Green's functions together with a self-consistent evaluation of the
superconducting order parameter. We take into account the elastic
spin-conserving scattering of the electrons assuming s-wave scattering in the S
layer and s-d scattering in the F layers. In accordance with the previous
quasiclassical theories, we found that due to exchange field in the ferromagnet
the anomalous Green's function F(z) exhibits the damping oscillations in the
F-layer as a function of distance z from the S/F interface. In the given model
a half of period of oscillations is determined by the length \xi_m^0 = \pi
v_F/E_ex, where v_F is the Fermi velocity and E_ex is the exchange field, while
damping is governed by the length l_0 = (1/l_{\uparrow} +
1/l_{\downarrow})^{-1} with l_{\uparrow} and l_{\downarrow} being
spin-dependent mean free paths in the ferromagnet. The superconducting
transition temperature T_c(d_F) of the F/S/F trilayer shows the damping
oscillations as a function of the F-layer thickness d_F with period \xi_F =
\pi/\sqrt{m E_ex}, where m is the effective electron mass. We show that strong
spin-conserving scattering either in the superconductor or in the ferromagnet
significantly suppresses these oscillations. The calculated T_c(d_F)
dependences are compared with existing experimental data for Fe/Nb/Fe trilayers
and Nb/Co multilayers.",0112034v3
2007-07-27,C IV absorption in damped and sub-damped Lyman-alpha systems: correlations with metallicity and implications for galactic winds at z~2-3,"We present a study of C IV absorption in a sample of 63 damped Lyman-alpha
(DLA) systems and 11 sub-DLAs in the redshift range 1.75<z_abs<3.61, using a
dataset of high-resolution (6.6 km/s FWHM), high signal-to-noise VLT/UVES
spectra. Narrow and broad C IV absorption line components indicate the presence
of both warm, photoionized and hot, collisionally ionized gas. We report new
correlations between the metallicity (measured in the neutral-phase) and each
of the C IV column density, the C IV total line width, and the maximum C IV
velocity. We explore the effect on these correlations of the sub-DLAs, the
proximate DLAs (defined as those within 5 000 km/s of the quasar), the
saturated absorbers, and the metal line used to measure the metallicity, and we
find the correlations to be robust. There is no evidence for any difference
between the measured properties of DLA C IV and sub-DLA C IV. In 25 DLAs and 4
sub-DLAs, covering 2.5 dex in [Z/H], we directly observe C IV moving above the
escape speed, where v_esc is derived from the total line width of the neutral
gas profiles. These high-velocity C IV clouds, unbound from the central
potential well, can be interpreted as highly ionized outflowing winds, which
are predicted by numerical simulations of galaxy feedback. The distribution of
C IV column density in DLAs and sub-DLAs is similar to the distribution in
Lyman Break galaxies, where winds are directly observed, supporting the idea
that supernova feedback creates the ionized gas in DLAs. The unbound C IV
absorbers show a median mass flow rate of ~22(r/40 kpc) solar masses per year,
where r is the characteristic C IV radius. Their kinetic energy fluxes are
large enough that a star formation rate (SFR) of ~2 solar masses per year is
required to power them.",0707.4065v2
2007-09-25,On the Structure of Dark Matter Halos at the Damping Scale of the Power Spectrum with and without Relict Velocities,"We report a series of high-resolution cosmological N-body simulations
designed to explore the formation and properties of dark matter halos with
masses close to the damping scale of the primordial power spectrum of density
fluctuations. We further investigate the effect that the addition of a random
component, v_rms, into the particle velocity field has on the structure of
halos. We adopted as a fiducial model the Lambda Warm Dark Matter cosmology
with a non-thermal sterile neutrino mass of 0.5 keV. The filtering mass
corresponds then to M_f = 2.6x10^12 M_sun/h. Halos of masses close to M_f were
simulated with several million of particles. The results show that, on one
hand, the inner density slope of these halos (at radii <~0.02 the virial radius
Rvir) is systematically steeper than the one corresponding to the NFW fit or to
the CDM counterpart. On the other hand, the overall density profile (radii
larger than 0.02Rvir) is less curved and less concentrated than the NFW fit,
with an outer slope shallower than -3. For simulations with v_rms, the inner
halo density profiles flatten significantly at radii smaller than 2-3 kpc/h
(<~0.010-0.015Rvir). A constant density core is not detected in our
simulations, with the exception of one halo for which the flat core radius is
~1 kpc/h. Nevertheless, if ``cored'' density profiles are used to fit the halo
profiles, the inferred core radii are ~0.1-0.8 kpc/h, in rough agreement with
theoretical predictions based on phase-space constrains, and on dynamical
models of warm gravitational collapse. A reduction of v_rms by a factor of 3
produces a modest decrease in core radii, less than a factor of 1.5. We discuss
the extension of our results into several contexts, for example, to the
structure of the cold DM micro-halos at the damping scale of this model.",0709.4027v1
2008-10-01,Corotational Instability of Inertial-Acoustic Modes in Black Hole Accretion Discs and Quasi-Periodic Oscillations,"We study the global stability of non-axisymmetric p-modes (also called
inertial-acoustic modes) trapped in the inner-most regions of accretion discs
around black holes. We show that the lowest-order (highest-frequency) p-modes,
with frequencies $\omega=(0.5-0.7) m\Omega_{\rm ISCO}$, can be overstable due
to general relativistic effects, according to which the radial epicyclic
frequency is a non-monotonic function of radius near the black hole. The mode
is trapped inside the corotation resonance radius and carries a negative
energy. The mode growth arises primarily from wave absorption at the corotation
resonance, and the sign of the wave absorption depends on the gradient of the
disc vortensity. When the mode frequency is sufficiently high, such that the
slope of the vortensity is positive at corotation positive wave energy is
absorbed at the resonance, leading to the growth of mode amplitude. We also
study how the rapid radial inflow at the inner edge of the disc affects the
mode trapping and growth. Our analysis of the behavior of the fluid
perturbations in the transonic flow near the ISCO indicates that, while the
inflow tends to damp the mode, the damping effect is sufficiently small under
some conditions so that net mode growth can still be achieved. We further
clarify the role of the Rossby wave instability and show that it does not
operate for black hole accretion discs with smooth-varying vortensity profiles.
Overstable non-axisymmetric p-modes driven by the corotational instability
provide a plausible explanation for the high-frequency (> 100 Hz)
quasi-periodic oscillations (HFQPOs) observed from a number of black-hole X-ray
binaries in the very high state. The absence of HFQPOs in the soft (thermal)
state may result from mode damping due to the radial infall at the ISCO.",0810.0203v2
2008-10-03,Stochastic excitation of nonradial modes II. Are solar asymptotic gravity modes detectable?,"Detection of solar gravity modes remains a major challenge to our
understanding of the innerparts of the Sun. Their frequencies would enable the
derivation of constraints on the core physical properties while their
amplitudes can put severe constraints on the properties of the inner convective
region. Our purpose is to determine accurate theoretical amplitudes of solar g
modes and estimate the SOHO observation duration for an unambiguous detection.
We investigate the stochastic excitation of modes by turbulent convection as
well as their damping. Input from a 3D global simulation of the solar
convective zone is used for the kinetic turbulent energy spectrum. Damping is
computed using a parametric description of the nonlocal time-dependent
convection-pulsation interaction. We then provide a theoretical estimation of
the intrinsic, as well as apparent, surface velocity. Asymptotic g-mode
velocity amplitudes are found to be orders of magnitude higher than previous
works. Using a 3D numerical simulation, from the ASH code, we attribute this to
the temporal-correlation between the modes and the turbulent eddies which is
found to follow a Lorentzian law rather than a Gaussian one as previously used.
We also find that damping rates of asymptotic gravity modes are dominated by
radiative losses, with a typical life-time of $3 \times 10^5$ years for the
$\ell=1$ mode at $\nu=60 \mu$Hz. The maximum velocity in the considered
frequency range (10-100 $\mu$Hz) is obtained for the $\ell=1$ mode at $\nu=60
\mu$Hz and for the $\ell=2$ at $\nu=100 \mu$Hz. Due to uncertainties in the
modeling, amplitudes at maximum i.e. for $\ell=1$ at 60 $\mu$Hz can range from
3 to 6 mm s$^{-1}$.",0810.0602v2
2008-10-20,The kinematic signature of damped Lyman alpha systems: Using the D-index to screen for high column density HI absorbers,"Using a sample of 21 damped Lyman alpha systems (DLAs) and 35 sub-DLAs, we
evaluate the D-index = EW / Delta v x 1000 from high resolution spectra of the
MgII lambda 2796 profile. This sample represents an increase in sub-DLA D-index
statistics by a factor of four over the sample used by Ellison (2006). We
investigate various techniques to define the velocity spread (Delta v) of the
MgII line to determine an optimal D-index for the identification of DLAs. The
success rate of DLA identification is 50 -- 55%, depending on the velocity
limits used, improving by a few percent when the column density of FeII is
included in the D-index calculation. We recommend the set of parameters that is
judged to be most robust, have a combination of high DLA identification rate
(57%) and low DLA miss rate (6%) and most cleanly separate the DLAs and
sub-DLAs (Kolmogorov-Smirnov probability 0.5%). These statistics demonstrate
that the D-index is the most efficient technique for selecting low redshift DLA
candidates: 65% more efficient than selecting DLAs based on the equivalent
widths of MgII and FeII alone. We also investigate the effect of resolution on
determining the N(HI) of sub-DLAs. We convolve echelle spectra of sub-DLA Lya
profiles with Gaussians typical of the spectral resolution of instruments on
the Hubble Space Telescope and compare the best fit N(HI) values at both
resolutions. We find that the fitted HI column density is systematically
over-estimated by ~ 0.1 dex in the moderate resolution spectra compared to the
best fits to the original echelle spectra. This offset is due to blending of
nearby Lya clouds that are included in the damping wing fit at low resolution.",0810.3700v1
2009-01-24,Dynamic migration of rotating neutron stars due to a phase transition instability,"Using numerical simulations based on solving the general relativistic
hydrodynamic equations, we study the dynamics of a phase transition in the
dense core of isolated rotating neutron stars, triggered by the back bending
instability reached via angular momentum loss. In particular, we investigate
the dynamics of a migration from an unstable configuration into a stable one,
which leads to a mini-collapse of the neutron star and excites sizeable
pulsations in its bulk until it acquires a new stable equilibrium state. We
consider equations of state with softening at high densities, a simple analytic
one with a mixed hadron-quark phase in an intermediate pressure interval and
pure quark matter at very high densities, and a microphysical one that has a
first-order phase transition, originating from kaon condensation. Although the
marginally stable initial models are rigidly rotating, we observe that during
the collapse (albeit little) differential rotation is created. We analyze the
emission of gravitational radiation, which in some models is amplified by mode
resonance effects, and assess its prospective detectability by interferometric
detectors. We expect that the most favorable conditions for dynamic migration
exist in very young magnetars. We find that the damping of the post-migration
pulsations strongly depends on the character of the equation of state
softening. The damping of pulsations in the models with the microphysical
equation of state is caused by dissipation associated with matter flowing
through the density jump at the edge of the dense core. If at work, this
mechanism dominates over all other types of dissipation, like bulk viscosity in
the exotic-phase core, gravitational radiation damping, or numerical viscosity.",0901.3819v2
2009-02-12,New Magellan Inamori Kyocera Echelle Observations of z<1.5 sub-damped Lyman-alpha systems,"The Damped and sub-Damped Lyman-alpha (DLA and sub-DLA) systems seen in the
spectra of QSOs offer a unique way to study the interstellar medium of high
redshift galaxies. In this paper we report on new abundance determinations in a
sample of 10 new systems, nine of the lesser studied sub-DLAs and one DLA,
along the line of sight to seven QSOs from spectra taken with the MIKE
spectrograph. Lines of Mg I, Mg II, Al II, Al III, Ca II, Mn II, Fe II, and Zn
II were detected. Here, we give the column densities and equivalent widths of
the observed absorption lines, as well as the abundances determined for these
systems. Zn, a relatively undepleted element in the local interstellar medium
(ISM) is detected in one system with a high metallicity of [Zn/H]=+0.27\pm0.18.
In one other system, a high abundance based on the more depleted element Fe is
seen with [Fe/H]=-0.37\pm0.13, although Zn is not detected. The N(HI)-weighted
mean metallicity of these sub-DLA systems based on Fe is <[Fe/H]>=-0.76\pm0.11,
nearly ~0.7 dex higher (a factor of 5) than what is seen in DLAs in this
redshift range. The relative abundance of [Mn/Fe] is also investigated. A clear
trend is visible for these systems as well as systems from the literature, with
[Mn/Fe] increasing with increasing metallicity in good agreement with with
Milky Way stellar abundances.",0902.2022v2
2009-04-16,Revisiting the origin of the high metallicities of sub-damped Lyman-alpha systems,"Sub-damped Lyman-alpha systems (sub-DLAs) have previously been found to
exhibit a steeper metallicity evolution than the classical damped Lyman-alpha
systems (DLAs), evolving to close to solar metallicity by z~1. From new
high-resolution spectra of 17 sub-DLAs we have increased the number of
measurements of [Fe/H] at z<1.7 by 25% and compiled the most complete
literature sample of sub-DLA and DLA abundances to date. We find that sub-DLAs
are indeed significantly more metal-rich than DLAs, but only at z<1.7; the
metallicity distributions of sub-DLAs and DLAs at z>1.7 are statistically
consistent. We also present the first evidence that sub-DLAs follow a velocity
width-metallicity correlation over the same velocity range as DLAs, but the
relation is offset to higher metallicities than the DLA relation. On the basis
of these results, we revisit the previous explanation that the systematically
higher metallicities observed in sub-DLAs are indicative of higher host galaxy
masses. We discuss the various problems that this interpretation encounters and
conclude that in general sub-DLAs are not uniquely synonymous with massive
galaxies. We rule out physically related sources of bias (dust, environment,
ionization effects) and examine systematics associated with the selection and
analysis of low-redshift sub-DLAs. We propose that the high metallicities of
sub-DLAs at z<1.7 that drives an apparently steep evolution may be due to the
selection of most low-redshift sub-DLAs based on their high MgII equivalent
widths.",0904.2531v1
2009-05-27,A MIKE + UVES survey of Sub-Damped Lyman-Alpha Systems at z<1.5,"We have combined the results from our recent observations of Damped and
sub-Damped Lyman-alpha systems with the MIKE and UVES spectrographs on the
Magellan Clay and VLT Kueyen telescopes with ones from the literature to
determine the N(HI)-weighted mean metallicity of these systems based both on
Fe, a depleted element in QSO absorbers and the local ISM, and Zn a relatively
undepleted element. In each case, the N(HI)-weighted mean metallicity is higher
and shows faster evolution in sub-DLAs than the classical DLA systems. Large
grids of photoionisation models over the sub-DLA \nhI range with CLOUDY show
that the ionisation corrections to the abundances are in general small, however
the fraction of ionized H can be up to ~90 per cent. The individual spectra
have been shifted to the rest frame of the absorber and averaged together to
determine the average properties of these systems at z<1.5. We find that the
average abundance pattern of the Sub-DLA systems is similar to the gas in the
halo of the Milky Way, with an offset of ~0.3 dex in the overall metallicity.
Both DLAs and Sub-DLAs show similar characteristics in their relative
abundances patterns, although the DLAs have smaller <[Mn/Zn]> as well as higher
<[Ti/Zn]> and <[Cr/Zn]>. We calculate the contribution of sub-DLAs to the metal
budget of the Universe, and find that the sub-DLA systems at z<1.5 contain a
comoving density of metals Omega_met (3.5-15.8)x10^{5} M_sun Mpc^{-3}, at least
twice the comoving density of metals in the DLA systems. The sub-DLAs do
however track global chemical evolution models much more closely than do the
DLAs, perhaps indicating that they are a less dust biased metallicity indicator
of galaxies at high redshifts than the DLA systems.",0905.4473v2
2009-11-18,Slow Diffusive Gravitational Instability Before Decoupling,"Radiative diffusion damps acoustic modes at large comoving wavenumber (k)
before decoupling (``Silk damping''). In a simple WKB analysis, neglecting
moments of the temperature distribution beyond the quadrupole, damping appears
in the acoustic mode as a term of order ik^2/(taudot) where taudot is the
scattering rate per unit conformal time. Although the Jeans instability is
stabilized on scales smaller than the adiabatic Jeans length, I show that the
medium is linearly unstable to first order in (1/taudot) to a slow diffusive
mode. At large comoving wavenumber, the characteristic growth rate becomes
independent of spatial scale and constant: (t_{KH}a)^-1 ~ (128 pi G/9 kappa_T
c)(rho_m/rho_b), where ""a"" is the scale factor, rho_m and rho_b are the matter
and baryon energy density, respectively, and kappa_T is the Thomson opacity.
This is the characteristic timescale for a fluid parcel to radiate away its
thermal energy content at the Eddington limit, analogous to the Kelvin-Helmholz
(KH) time for a massive star or the Salpeter time for black hole growth.
Although this mode grows at all times prior to decoupling and on scales smaller
than the horizon, the growth time is long, about 100 times the age of the
universe at decoupling. Thus, it modifies the density and temperature
perturbations on small scales only at the percent level. The physics of this
mode is already accounted for in the popular codes CMBFAST and CAMB, but is
typically neglected in analytic studies of the growth of primordial
perturbations. This work clarifies the physics of this instability in the epoch
before decoupling, and emphasizes that the universe is formally unstable on
scales below the horizon, even in the limit of large taudot. Analogous
instabilities at yet earlier epochs are also mentioned. (Abridged)",0911.3665v1
2009-12-14,Using 21cm Absorption in Small Impact Parameter Galaxy-QSO Pairs to Probe Low-Redshift Damped and Sub-Damped Lyman-alpha System,"To search for low-redshift damped Lyman-alpha (DLA) and sub-DLA quasar
absorbers, we have conducted a 21cm absorption survey of radio-loud quasars at
small impact parameters to foreground galaxies selected from the Sloan Digital
Sky Survey (SDSS). Here we present the first results from this survey based on
observations of SDSS J104257.58+074850.5 ($z_{QSO}$ = 2.66521), a quasar at an
angular separation from a foreground galaxy ($z_{gal}$ = 0.03321) of 2.5"" (1.7
kpc in projection). The foreground galaxy is a low-luminosity spiral with
on-going star formation (0.004 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$) and a
metallicity of $-0.27 \pm 0.05$ dex. We detect 21cm absorption from the galaxy
with the Green Bank Telescope (GBT), the Very Large Array (VLA), and the Very
Long Baseline Array (VLBA). The absorption appears to be quiescent disk gas
corotating with the galaxy and we do not find any evidence for outflowing cold
neutral gas. The width of the main absorption line indicates that the gas is
cold, $T_{k} < 283$ K, and the HI column is surprisingly low given the impact
parameter of 1.7 kpc; we find that N(HI) $\leq 9.6 \times 10^{19}$ cm$^{-2}$
(GBT) and N(HI) $\leq 1.5 \times 10^{20}$ cm$^{-2}$ (VLBA). VLBA marginally
resolves the continuum source and the absorber, and a lower limit of 27.1
$\times$ 13.9 pc is derived for the size of the absorbing cloud. In turn, this
indicates a low density for a cold cloud, n(HI) $<$ 3.5 cm$^{-3}$. We
hypothesize that this galaxy, which is relatively isolated, is becoming
depleted in HI because it is converting its interstellar matter into stars
without a replenishing source of gas, and we suggest future observations to
probe this and similar galaxies.",0912.2575v2
2010-04-02,Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk,"We model the time variability of ~9,000 spectroscopically confirmed quasars
in SDSS Stripe 82 as a damped random walk. Using 2.7 million photometric
measurements collected over 10 years, we confirm the results of Kelly et al.
(2009) and Koz{\l}owski et al. (2010) that this model can explain quasar light
curves at an impressive fidelity level (0.01-0.02 mag). The damped random walk
model provides a simple, fast [O(N) for N data points], and powerful
statistical description of quasar light curves by a characteristic time scale
(tau) and an asymptotic rms variability on long time scales (SF_inf). We
searched for correlations between these two variability parameters and physical
parameters such as luminosity and black hole mass, and rest-frame wavelength.
We find that tau increases with increasing wavelength with a power law index of
0.17, remains nearly constant with redshift and luminosity, and increases with
increasing black hole mass with power law index of 0.21+/-0.07. The amplitude
of variability is anti-correlated with the Eddington ratio, which suggests a
scenario where optical fluctuations are tied to variations in the accretion
rate. The radio-loudest quasars have systematically larger variability
amplitudes by about 30%, when corrected for the other observed trends, while
the distribution of their characteristic time scale is indistinguishable from
that of the full sample. We do not detect any statistically robust differences
in the characteristic time scale and variability amplitude between the full
sample and the small subsample of quasars detected by ROSAT. Our results
provide a simple quantitative framework for generating mock quasar light
curves, such as currently used in LSST image simulations. (abridged)",1004.0276v2
2010-04-21,"Kadanoff-Baym description of Hubbard clusters out of equilibrium: performance of many-body schemes, correlation-induced damping and multiple steady states","We present in detail a method we recently introduced (PRL. 103, 176404
(2009)) to describe finite systems in and out of equilibrium, where the
evolution in time is performed via the Kadanoff-Baym Equations (KBE) within
Many-Body Perturbation Theory (MBPT). The main property we analyze is the
time-dependent density. We also study is the exchange-correlation potential of
TDDFT, obtained via reverse engineering from the time-dependent density. Our
systems consist of small, strongly correlated clusters, described by a Hubbard
Hamiltonian within the Hartree-Fock, second Born, GW and T-matrix
approximations. We compare the results from the KBE dynamics to those from
exact numerical solutions. The outcome of our comparisons is that, among the
many-body schemes considered, the T-matrix approximation is overall superior at
all electron densities. Such comparisons permit a general assessment of the
whole idea of applying MBPT, in the KBE sense, to finite systems. A striking
outcome of our analysis is that when the system evolves under a strong external
field, the KBE develop a steady-state solution as a consequence of a
correlation-induced damping. This damping is present both in isolated (finite)
systems, where it is purely artificial, as well as in clusters contacted to
(infinite) macroscopic leads. To illustrate this point we present selected
results for a system coupled to contacts within the T-matrix and second Born
approximation. The extensive characterization we performed indicates that this
behavior is present whenever approximate self energies, based upon infinite
partial summations, are used. A second important result is that, for isolated
clusters, the steady state reached is not unique but depends on how one
switches on the external field. This may also true for clusters connected to
leads.",1004.3662v1
2010-05-22,Helical edge magnetoplasmon in the quantum Hall effect regime,"We present the microscopic treatment of edge magnetoplasmons (EMPs) for the
regime of not-too-low temperatures defined by the condition $\hbar
\omega_{c}\gg k_{B}T\gg \hbar v_{g}/2\ell_{0}$, where $v_{g}$ is the group
velocity of the edge states, $\ell_{0}=\sqrt{\hbar /m^{\ast}\omega_{c}}$ is the
magnetic length and $\omega_{c}$ is the cyclotron frequency. We find a weakly
damped symmetric mode, named helical edge magnetoplasmon, which is localized at
the edge states region for filling factors $\nu =1, 2$ and \textit{very strong
dissipation} $\eta_{T}=\xi /k_{x}\ell_{T}\agt\ln (1/k_{x}\ell_{T})\gg 1$, where
the characteristic length $\ell_{T}=k_{B}T\ell_{0}^{2}/\hbar v_{g}\gg
\ell_{0}/2$ with $\xi $ being the ratio of the local transverse conductivity to
the local Hall conductivity at the edge states and $k_{x}$ is the wave vector
along the edge; here other EMP modes are strongly damped. The spatial structure
of the helical edge magnetoplasmon, transverse to the edge, is strongly
modified as the wave propagates along the edge. In the regime of \textit{weak
dissipation}, $\eta_{T}\ll 1$, we obtain exactly the damping of the fundamental
mode as a function of $k_{x}$. For $\nu=4$ and weak dissipation we find that
the fundamental modes of $n=0$ and $n=1$ Landau levels (LLs) are strongly
renormalized due to the Coulomb coupling. Renormalization of all these EMPs
coming from a metal gate and air half-space is studied.",1005.4154v1
2010-06-02,Do Damped and Sub-damped Lyman-alpha Absorbers Arise in Galaxies of Different Masses?,"We consider the questions of whether the damped Lyman-alpha (DLA) and sub-DLA
absorbers in quasar spectra differ intrinsically in metallicity, and whether
they could arise in galaxies of different masses. Using the recent measurements
of the robust metallicity indicators Zn and S in DLAs and sub-DLAs, we confirm
that sub-DLAs have higher mean metallicities than DLAs, especially at $z
\lesssim 2$. We find that the intercept of the metallicity-redshift relation
derived from Zn and S is higher than that derived from Fe by 0.5-0.6 dex. We
also show that, while there is a correlation between the metallicity and the
rest equivalent width of Mg II $\lambda 2796$ or Fe II $\lambda 2599$ for DLAs,
no correlation is seen for sub-DLAs. Given this, and the similar Mg II or Fe II
selection criteria employed in the discovery of both types of systems at lower
redshifts, the difference between metallicities of DLAs and sub-DLAs appears to
be real and not an artefact of selection. This conclusion is supported by our
simulations of Mg II $\lambda 2796$ and Fe II $\lambda 2599$ lines for a wide
range of physical conditions. On examining the velocity spreads of the
absorbers, we find that sub-DLAs show somewhat higher mean and median velocity
spreads ($\Delta v$), and an excess of systems with $\Delta v > 150$ km
s$^{-1}$, than DLAs. Compared to DLAs, the [Mn/Fe] vs. [Zn/H] trend for
sub-DLAs appears to be steeper and closer to the trend for Galactic bulge and
thick disk stars, possibly suggesting different stellar populations. The
absorber data appear to be consistent with galaxy down-sizing. The data are
also consistent with the relative number densities of low-mass and high-mass
galaxies. It is thus plausible that sub-DLAs arise in more massive galaxies on
average than DLAs.",1006.0298v1
2010-08-31,A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - I. New Detections and Limits for Intervening and Associated Absorbers,"Detailed studies of Damped and sub-Damped Lyman-alpha systems (DLA), the
galaxies probed by the absorption they produce in the spectra of background
quasars, rely on identifying the galaxy responsible for the absorber with more
traditional methods. Integral field spectroscopy provides an efficient way of
detecting faint galaxies near bright quasars, further providing immediate
redshift confirmation. Here, we report the detection of H-alpha emission from a
DLA and a sub-DLA galaxy among a sample of 6 intervening quasar absorbers
targeted. We derive F(H-alpha)=7.7+/-2.7*10^-17 erg/s/cm^2 (SFR=1.8+/-0.6
M_sun/yr) at impact parameter b=25 kpc towards quasar Q0302-223 for the DLA at
z_abs=1.009 and F(H-alpha)=17.1+/-6.0*10^-17 erg/s/cm^2 (SFR=2.9+/-1.0
M_sun/yr) at b=39 kpc towards Q1009-0026 for the sub-DLA at z_abs=0.887. These
results are in line with low star formation rates previously reported in the
literature for quasar absorbers. We use the NII 6585/H-alpha ratio to derive
the HII emission metallicities and compare them with the neutral gas H I
absorption metallicities derived from high-resolution spectra. In one case, the
absorption metallicity is actually found to be higher than the emission line
metallicity. For the remaining objects, we achieve 3-sigma limiting fluxes of
the order F(H-alpha)~10^-17 erg/s/cm^2 (corresponding to SFR~ 0.1 M_sun/yr at
z~1 and ~1 M_sun/yr at z~2), i.e. among the lowest that have been possible with
ground-based observations. We also present two other galaxies associated with C
IV systems and serendipitously discovered in our data.",1009.0025v1
2010-12-22,Abstract Wave Equations and Associated Dirac-Type Operators,"We discuss the unitary equivalence of generators $G_{A,R}$ associated with
abstract damped wave equations of the type $\ddot{u} + R \dot{u} + A^*A u = 0$
in some Hilbert space $\mathcal{H}_1$ and certain non-self-adjoint Dirac-type
operators $Q_{A,R}$ (away from the nullspace of the latter) in $\mathcal{H}_1
\oplus \mathcal{H}_2$. The operator $Q_{A,R}$ represents a non-self-adjoint
perturbation of a supersymmetric self-adjoint Dirac-type operator. Special
emphasis is devoted to the case where 0 belongs to the continuous spectrum of
$A^*A$.
  In addition to the unitary equivalence results concerning $G_{A,R}$ and
$Q_{A,R}$, we provide a detailed study of the domain of the generator
$G_{A,R}$, consider spectral properties of the underlying quadratic operator
pencil $M(z) = |A|^2 - iz R - z^2 I_{\mathcal{H}_1}$, $z\in\mathbb{C}$, derive
a family of conserved quantities for abstract wave equations in the absence of
damping, and prove equipartition of energy for supersymmetric self-adjoint
Dirac-type operators.
  The special example where $R$ represents an appropriate function of $|A|$ is
treated in depth and the semigroup growth bound for this example is explicitly
computed and shown to coincide with the corresponding spectral bound for the
underlying generator and also with that of the corresponding Dirac-type
operator.
  The cases of undamped (R=0) and damped ($R \neq 0$) abstract wave equations
as well as the cases $A^* A \geq \epsilon I_{\mathcal{H}_1}$ for some $\epsilon
> 0$ and $0 \in \sigma (A^* A)$ (but 0 not an eigenvalue of $A^*A$) are
separately studied in detail.",1012.4927v2
2011-02-18,The First Observations of Low Redshift Damped Lyman-alpha Systems with the Cosmic Origins Spectrograph,"We report on the first Cosmic Origins Spectrograph (COS) observations of
damped and sub-damped Lyman-alpha (DLA) systems discovered in a new survey of
the gaseous halos of low-redshift galaxies. From observations of 37 sightlines,
we have discovered three DLAs and four sub-DLAs. We measure the neutral gas
density Omega(HI), and redshift density dN/dz, of DLA and sub-DLA systems at
z<0.35. We find dN/dz=0.25 and Omega(HI)=1.4x10^-3 for DLAs, and dN/dz=0.08
with Omega(HI)=4.2x10^-5 for sub-DLAs over a redshift path delta z=11.9. To
demonstrate the scientific potential of such systems, we present a detailed
analysis of the DLA at z=0.1140 in the spectrum of SDSS J1009+0713. Profile
fits to the absorption lines determine log N(H I)=20.68pm0.10 with a
metallicity determined from the undepleted element Sulfur of [S/H]=-0.62pm0.18.
The abundance pattern of this DLA is similar to that of higher z DLAs, showing
mild depletion of the refractory elements Fe and Ti with [S/Fe]=+0.24pm0.22 and
[S/Ti]=+0.28pm0.15. Nitrogen is underabundant in this system with
[N/H]=-1.40pm0.14, placing this DLA below the plateau of the [N/alpha]
measurements in the local Universe at similar metallicities. This DLA has a
simple kinematic structure with only two components required to fit the
profiles and a kinematic width of 52 km/s. Imaging of the QSO field with WFC3
reveals a spiral galaxy at very small impact parameter to the QSO and several
galaxies within 10"". Followup spectra with LRIS reveal that none of the nearby
galaxies are at the redshift of the DLA. The spiral galaxy is identified as the
host galaxy of the QSO based on the near perfect alignment of the nucleus and
disk of the galaxy as well as spectra of an H II region showing emission lines
at the QSO redshift. A small feature appears 0.70"" from the nucleus of the QSO
after PSF subtraction, providing another candidate for the host galaxy of the
DLA. (abb)",1102.3927v1
2011-05-23,BCS - BEC crossover and quantum hydrodynamics in p-wave superfluids with a symmetry of the A1 - phase,"We solve the Leggett equations for the BCS - BEC crossover in the three
dimension resonance p-wave superfluid with the symmetry of the A1 - phase. We
calculate the sound velocity, the normal density, and the specific heat for the
BCS-domain (\mu > 0), BEC-domain (\mu < 0), and close to important point \mu =
0 in 100% polarized case. We find the indications of quantum phase - transition
close to the point \mu(T = 0) = 0. Deep in the BCS and BEC-domains the
crossover ideas of Leggett and Nozieres, Schmitt-Rink work pretty well. We
discuss the spectrum of orbital waves, the paradox of intrinsic angular
momentum and complicated problem of chiral anomaly in the BCS A1 - phase at T =
0. We present two different approaches to a chiral anomaly: one based on
supersymmetric hydrodynamics, another one on the formal analogy with the Dirac
equation in quantum electrodynamics. We evaluate the damping of nodal fermions
due to different decay processes in superclean case at T = 0 and find that we
are in a ballistic regime \omega\tau >> 1. We propose to use aerogel or
nonmagnetic impurities to reach hydrodynamic regime \omega\tau<< 1 at T = 0. We
discuss the concept of the spectral flow and exact cancellations between
time-derivatives of anomalous and quasiparticle currents in the equation for
the total linear momentum conservation. We propose to derive and solve the
kinetic equation for the nodal quasiparticles both in the hydrodynamic and in
the ballistic regimes to demonstrate this cancellation explicitly. We briefly
discuss the role of the other residual interactions different from damping and
invite experimentalists to measure the spectrum and damping of orbital waves in
A-phase of 3He at low temperatures.",1105.4438v1
2011-07-12,Considerations on the accretion of Uranus and Neptune by mutual collisions of planetary embryos in the vicinity of Jupiter and Saturn,"Modeling the formation of the ice giants Uranus and Neptune is a long-lasting
problem in planetary science. Due to gas-drag, collisional damping, and
resonant shepherding, the planetary embryos repel the planetesimals away from
their reach and thus they stop growing (Levison et al. 2010). This problem
persists independently of whether the accretion took place at the current
locations of the ice giants or closer to the Sun. Instead of trying to push the
runaway/oligarchic growth of planetary embryos up to 10-15 Earth masses, we
envision the possibility that the planetesimal disk could generate a system of
planetary embryos of only 1-3 Earth masses. Then we investigate whether these
embryos could have collided with each other and grown enough to reach the
masses of current Uranus and Neptune. Our results point to two major problems.
First, there is typically a large difference in mass between the first and the
second most massive core formed and retained beyond Saturn. Second, in many
simulations the final planetary system has more than two objects beyond Saturn.
The growth of a major planet from a system of embryos requires strong damping
of eccentricities and inclinations from the disk of gas. But strong damping
also favors embryos and cores to find a stable resonant configuration, so that
systems with more than two surviving objects are found. In addition to these
problems, in order to have substantial mutual accretion among embryos, it is
necessary to assume that the surface density of the gas was several times
higher than that of the minimum-mass solar nebula. However this contrasts with
the common idea that Uranus and Neptune formed in a gas-starving disk, which is
suggested by the relatively small amount of hydrogen and helium contained in
the atmospheres of these planets. Only one of our simulations ""by chance""
successfully reproduced the structure of the outer Solar System.",1107.2235v2
2011-08-19,The ALFALFA HI Absorption Pilot Survey: A Wide-Area Blind Damped Lyman Alpha System Survey of the Local Universe,"We present the results of a pilot survey for neutral hydrogen (HI) 21 cm
absorption in the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFALFA)
Survey. This project is a wide-area ""blind"" search for HI absorption in the
local universe, spanning -650 km/s < cz < 17,500 km/s and covering 517.0 square
degrees (7% of the full ALFALFA survey). The survey is sensitive to HI
absorption lines stronger than 7.7 mJy (8983 radio sources) and is 90% complete
for lines stronger than 11.0 mJy (7296 sources). The total redshift interval
sensitive to all damped Lyman alpha (DLA) systems (N_HI >= 2x10^20 cm^-2) is
Delta z = 7.0 (129 objects, assuming T_s = 100 K and covering fraction unity);
for super-DLAs (N_HI >= 2x10^21 cm^-2) it is Delta z= 128.2 (2353 objects). We
re-detect the intrinsic HI absorption line in UGC 6081 but detect no
intervening absorption line systems. We compute a 95% confidence upper limit on
the column density frequency distribution function f(N_HI,X) spanning four
orders of magnitude in column density, 10^19 (T_s/100 K)(1/f) cm^-2 < N_HI <
10^23 (T_s/100 K)(1/f) cm^-2, that is consistent with previous redshifted
optical damped Ly alpha surveys and the aggregate HI 21 cm emission in the
local universe. The detection rate is in agreement with extant observations.
This pilot survey suggests that an absorption line search of the complete
ALFALFA survey --- or any higher redshift, larger bandwidth, or more sensitive
survey, such as those planned for Square Kilometer Array pathfinders or a low
frequency lunar array --- will either make numerous detections or will set a
strong statistical lower limit on the typical spin temperature of neutral
hydrogen gas.",1108.4011v1
2011-09-22,Tidal Dissipation in Planet-Hosting Stars: Damping of Spin-Orbit Misalignment and Survival of Hot Jupiters,"Observations of hot Jupiters around solar-type stars with very short orbital
periods (~day) suggest that tidal dissipation in such stars is not too
efficient so that these planets can survive against rapid orbital decay. This
is consistent with recent theoretical works, which indicate that the tidal Q of
planet-hosting stars can indeed be much larger than the values inferred from
stellar binaries. On the other hand, recent measurements of Rossiter-McLaughlin
effects in transiting hot Jupiter systems not only reveal that many such
systems have misaligned stellar spin with respect to the orbital axis, but also
show that systems with cooler host stars tend to have aligned spin and orbital
axes. Winn et al. suggested that this obliquity - temperature correlation may
be explained by efficient damping of stellar obliquity due to tidal dissipation
in the star. This explanation, however, is in apparent contradiction with the
survival of these short-period hot Jupiters. We show that in the solar-type
parent stars of close-in exoplanetary systems, the effective tidal Q governing
the damping of stellar obliquity can be much smaller than that governing
orbital decay. This is because for misaligned systems, the tidal potential
contains a Fourier component with frequency equal to the stellar spin frequency
(in the rotating frame of the star). This component can excite inertial waves
in the convective envelope of the star, and the dissipation of inertial waves
then leads to a spin-orbit alignment torque, but not orbital decay. By
contrast, for aligned systems, such inertial wave excitation is forbidden since
the tidal forcing frequency is much larger than the stellar spin frequency. We
derive a general effective tidal evolution theory for misaligned binaries,
taking account of different tidal responses and dissipation rates for different
tidal forcing components.",1109.4703v2
2011-10-20,The First Observations of Low-Redshift Damped Lyman-α Systems with the Cosmic Origins Spectrograph: Chemical Abundances and Affiliated Galaxies,"We present Cosmic Origins Spectrograph (COS) measurements of metal abundances
in eight 0.083<z<0.321 damped Lyman-\alpha (DLA) and sub-damped Ly-\alpha\
absorption systems serendipitously discovered in the COS-Halos survey. We find
that these systems show a large range in metallicities, with -1.10<[Z/H]<0.31,
similar to the spread found at higher redshifts. These low-redshift systems on
average have subsolar metallicities, but do show a rise in metallicity over
cosmic time when compared to higher-redshift systems. We find the average
sub-DLA metallicity is higher than the average DLA metallicity at all
redshifts. Nitrogen is underabundant with respect to \alpha-group elements in
all but perhaps one of the absorbers. In some cases, [N/\alpha] is
significantly below the lowest nitrogen measurements in nearby galaxies.
Systems for which depletion patterns can be studied show little, if any,
depletion, which is characteristic of Milky Way halo-type gas. We also identify
affiliated galaxies for 3 of the sub-DLAs using spectra obtained from
Keck/LRIS. None of these sub-DLAs arise in the stellar disks of luminous
galaxies; instead, these absorbers may exist in galaxy halos at impact
parameters ranging from 38 to 92 kpc. Multiple galaxies are present near two of
the sub-DLAs, and galaxy interactions may play a role in the dispersal of the
gas. Many of these low-redshift absorbers exhibit simple kinematics, but one
sub-DLA has a complicated mix of at least 13 components spread over 150 km/s.
We find three galaxies near this sub-DLA, which also suggests that galaxy
interactions roil the gas. This study reinforces the view that DLAs have a
variety of origins, and low-redshift studies are crucial for understanding
absorber-galaxy connections.",1110.4557v2
2011-11-01,On the misalignment of the directly imaged planet β Pictoris b with the system's warped inner disk,"The vertical warp in the debris disk Beta Pictoris -- an inclined inner disk
extending into a flat outer disk -- has long been interpreted as the signpost
of a planet on an inclined orbit. Direct images spanning 2004-2010 have
revealed Beta Pictoris b, a planet with a mass and orbital distance consistent
with this picture. However, it was recently reported that the orbit of planet b
is aligned with the flat outer disk, not the inclined inner disk, and thus
lacks the inclination to warp the disk. We explore three scenarios for
reconciling the apparent misalignment of the directly imaged planet Beta
Pictoris b with the warped inner disk of Beta Pictoris: observational
uncertainty, an additional planet, and damping of planet b's inclination. We
find that, at the extremes of the uncertainties, the orbit of Beta Pictoris b
has the inclination necessary to produce the observed warp. We also find that
if planet b were aligned with the flat outer disk, it would prevent another
planet from creating a warp with the observed properties; therefore planet b
itself must be responsible for the warp. Finally, planet b's inclination could
have been damped by dynamical friction and still produce the observed disk
morphology, but the feasibility of damping depends on disk properties and the
presence of other planets. More precise observations of the orbit of planet b
and the position angle of the outer disk will allow us to distinguish between
the first and third scenario.",1111.0297v2
2011-11-25,Application of a damped Locally Optimized Combination of Images method to the spectral characterization of faint companions using an Integral Field Spectrograph,"High-contrast imaging instruments are now being equipped with integral field
spectrographs (IFS) to facilitate the detection and characterization of faint
substellar companions. Algorithms currently envisioned to handle IFS data, such
as the Locally Optimized Combination of Images (LOCI) algorithm, rely upon
aggressive point-spread-function (PSF) subtraction, which is ideal for
initially identifying companions but results in significantly biased photometry
and spectroscopy due to unwanted mixing with residual starlight. This
spectro-photometric issue is further complicated by the fact that algorithmic
color response is a function of the companion's spectrum, making it difficult
to calibrate the effects of the reduction without using iterations involving a
series of injected synthetic companions. In this paper, we introduce a new PSF
calibration method, which we call ""damped LOCI"", that seeks to alleviate these
concerns. By modifying the cost function that determines the weighting
coefficients used to construct PSF reference images, and also forcing those
coefficients to be positive, it is possible to extract companion spectra with a
precision that is set by calibration of the instrument response and
transmission of the atmosphere, and not by post-processing. We demonstrate the
utility of this approach using on-sky data obtained with the Project 1640 IFS
at Palomar. Damped-LOCI does not require any iterations on the underlying
spectral type of the companion, nor does it rely upon priors involving the
chromatic and statistical properties of speckles. It is a general technique
that can readily be applied to other current and planned instruments that
employ IFS's.",1111.6102v1
2012-02-01,CMB at 2x2 order: the dissipation of primordial acoustic waves and the observable part of the associated energy release,"Silk damping of primordial small-scale perturbations in the photon-baryon
fluid due to diffusion of photons inevitably creates spectral distortions in
the CMB. With the proposed CMB experiment PIXIE it might become possible to
measure these distortions and thereby constrain the primordial power spectrum
at comoving wavenumbers 50 Mpc^{-1} < k < 10^4 Mpc^{-1}. Since primordial
fluctuations in the CMB on these scales are completely erased by Silk damping,
these distortions may provide the only way to shed light on otherwise
unobservable aspects of inflationary physics. A consistent treatment of the
primordial dissipation problem requires going to second order in perturbation
theory, while thermalization of these distortions necessitates consideration of
second order in Compton scattering energy transfer. Here we give a full 2x2
treatment for the creation and evolution of spectral distortions due to the
acoustic dissipation process, consistently including the effect of polarization
and photon mixing in the free streaming regime. We show that 1/3 of the total
energy (9/4 larger than previous estimates) stored in small-scale temperature
perturbations imprints observable spectral distortions, while the remaining 2/3
only raises the average CMB temperature, an effect that is unobservable. At
high redshift dissipation is mainly mediated through the quadrupole
anisotropies, while after recombination peculiar motions are most important.
During recombination the damping of the higher multipoles is also significant.
We compute the average distortion for several examples using CosmoTherm,
analyzing their dependence on parameters of the primordial power spectrum. For
one of the best fit WMAP7 cosmologies, with n_S=1.027 and n_run=-0.034, the
cooling of baryonic matter practically compensates the heating from acoustic
dissipation in the mu-era. (abridged)",1202.0057v2
2012-02-28,The Last Stages of Terrestrial Planet Formation: Dynamical Friction and the Late Veneer,"The final stage of terrestrial planet formation consists of the cleanup of
residual planetesimals after the giant impact phase. Dynamically, a residual
planetesimal population is needed to damp the high eccentricities of the
terrestrial planets after the giant impact stage. Geochemically, highly
siderophile element (HSE) abundance patterns inferred for the terrestrial
planets and the Moon suggest that a total of about 0.01 M_Earth of chondritic
material was delivered as `late veneer' by planetesimals to the terrestrial
planets after the end of giant impacts. Here we combine these two independent
lines of evidence for a leftover population of planetesimals and show that: 1)
A residual planetesimal population containing 0.01 M_Earth is able to damp the
eccentricities of the terrestrial planets after giant impacts to their observed
values. 2) At the same time, this planetesimal population can account for the
observed relative amounts of late veneer added to the Earth, Moon and Mars
provided that the majority of the late veneer was delivered by small
planetesimals with radii <10m. These small planetesimal sizes are required to
ensure efficient damping of the planetesimal's velocity dispersion by mutual
collisions, which in turn ensures that the planets' accretion cross sections
are significantly enhanced by gravitational focusing above their geometric
values. Specifically we find, in the limit that the relative velocity between
the terrestrial planets and the planetesimals is significantly less than the
terrestrial planets' escape velocities, that gravitational focusing yields an
accretion ratio Earth/Mars~17, which agrees well with the accretion ratio
inferred from HSEs of 12-23. For the Earth-Moon system, we find an accretion
ratio of ~200, which is consistent with estimates of 150-700 derived from HSE
abundances that include the lunar crust as well as mantle component. (Abridged)",1202.6372v2
2012-03-13,Trapping in three-planet resonances during gas-driven migration,"We study the establishment of three-planet resonances -similar to the Laplace
resonance in the Galilean satellites- and their effects on the mutual
inclinations of the orbital planes of the planets, assuming that the latter
undergo migration in a gaseous disc. In particular, we examine the resonance
relations that occur, by varying the physical and initial orbital parameters of
the planets (mass, initial semi-major axis and eccentricity) as well as the
parameters of the migration forces (migration rate and eccentricity damping
rate), which are modeled here through a simplified analytic prescription. We
find that, in general, for planetary masses below 1.5 M_J, multiple-planet
resonances of the form n3:n2:n1=1:2:4 and 1:3:6 are established, as the inner
planets, m1 and m2, get trapped in a 1:2 resonance and the outer planet m3
subsequently is captured in a 1:2 or 1:3 resonance with m2. For mild
eccentricity damping, the resonance pumps the eccentricities of all planets on
a relatively short time-scale, to the point where they enter an
inclination-type resonance (as in Libert & Tsiganis 2011); then mutual
inclinations can grow to ~35{\deg}, thus forming a ""3-D system"". On the other
hand, we find that trapping of m2 in a 2:3 resonance with m1 occurs very
rarely, for the range of masses used here, so only two cases of capture in a
respective three-planet resonance were found. Our results suggest that trapping
in a three-planet resonance can be common in exoplanetary systems, provided
that the planets are not very massive. Inclination pumping could then occur
relatively fast, provided that eccentricity damping is not very efficient so
that at least one of the inner planets acquires an orbital eccentricity higher
than e=0.3.",1203.2960v1
2012-10-04,Plasmonic Waves on a Chain of Metallic Nanoparticles: Effects of a Liquid Crystalline Host or an Applied Magnetic Field,"A chain of metallic particles, of sufficiently small diameter and spacing,
allows linearly polarized plasmonic waves to propagate along the chain. In this
paper, we consider how these waves are altered by an anisotropic host (such as
a nematic liquid crystal) or an applied magnetic field. In a liquid crystalline
host, with principal axis (director) oriented either parallel or perpendicular
to the chain, we find that the dispersion relations of both the longitudinal
($L$) and transverse ($T$) modes are significantly altered relative to those of
an isotropic host. Furthermore, when the director is perpendicular to the
chain, the doubly degenerate $T$ branch is split by the anisotropy of the host
material. With an applied magnetic field ${\bf B}$ parallel to the chain, the
propagating transverse modes are circularly polarized, and the left and right
circularly polarized branches have slightly different dispersion relations. As
a result, if a linearly polarized transverse wave is launched along the chain,
it undergoes Faraday rotation. For parameters approximating that of a typical
metal and for a field of 2T, the Faraday rotation is of order 1$^o$ per ten
interparticle spacings, even taking into account single-particle damping. If
${\bf B}$ is perpendicular to the chain, one of the $T$ branches mixes with the
$L$ branch to form two elliptically polarized branches. Our calculations
include single-particle damping and can, in principle, be generalized to
include radiation damping. The present work suggests that the dispersion
relations of plasmonic waves on chain of nanoparticles can be controlled by
immersing the chain in a nematic liquid crystal and varying the director axis,
or by applying a magnetic field.",1210.1509v1
2012-11-12,The explosion energy of early stellar populations: The Fe-peak element ratios in low metallicity damped Lyman-alpha systems,"The relative abundances of the Fe-peak elements (Ti-Zn) at the lowest
metallicities are intimately linked to the physics of core-collapse supernova
explosions. With a sample of 25 very metal-poor damped Lyman-alpha systems, we
investigate the trends of the Fe-peak element ratios with metallicity. For nine
of the 25 DLAs, a direct measurement (or useful upper limit) of one or more of
the Ti,Cr,Co,Ni,Zn/Fe abundance ratios could be determined from detected
absorption lines. For the remaining systems (without detections), we devised a
new form of spectral stacking to estimate the typical Fe-peak element ratios of
the DLA population in this metallicity regime. We compare these data to
analogous measurements in metal-poor stars of the Galactic halo and to detailed
calculations of explosive nucleosynthesis in metal-free stars. We conclude that
most of the DLAs in our sample were enriched by stars that released an energy
of < 1.2 x 10^51 erg when they exploded as core-collapse supernovae. Finally,
we discuss the exciting prospect of measuring Fe-peak element ratios in damped
Lyman-alpha systems with Fe/H < 1/1000 of solar when 30-m class telescopes
become available. Only then will we be able to pin down the energy that was
released by the supernovae of the first stars.",1211.2805v3
2012-12-07,Circumstellar disks can erase the effects of stellar fly-bys on planetary systems,"Most stars form in embedded clusters. Stellar flybys may affect the orbital
architecture of the systems by exciting the eccentricity and causing dynamical
instability. Since, incidentally, the timescale over which a cluster loses its
gaseous component and begins to disperse is comparable to the circumstellar
disk lifetime, we expect that closer, and more perturbing, stellar flybys occur
when the planets are still embedded in their birth disk. We investigate the
effects of the disk on the dynamics of planets after the stellar encounter to
test whether it can damp the eccentricity and return the planetary system to a
non-excited state. We use the hydrodynamical code FARGO to study the
disk+planet(s) system during and after the stellar encounter in the context of
evolved disk models whose superficial density is 10 times lower than that of
the Minimum Mass Solar Nebula. The numerical simulations show that the planet
eccentricity, excited during a close stellar flyby, is damped on a short
timescale (~ 10 Kyr) in spite of the disk low initial density and subsequent
tidal truncation. This damping is effective also for a system of 3 giant
planets and the effects of the dynamical instability induced by the passing
star are quickly absorbed. If the circumstellar disk is still present around
the star during a stellar flyby, a planet (or a planetary system) is returned
to a non-excited state on a short timescale. This does not mean that stellar
encounters do not affect the evolution of planets, but they do it in a subtle
way with a short period of agitated dynamical evolution. At the end of it, the
system resumes a quiet evolution and the planetary orbits are circularized by
the interaction with the disk.",1212.1561v1
2013-01-21,Mass-metallicity relation from z=5 to the present: Evidence for a transition in the mode of galaxy growth at z=2.6 due to the end of sustained primordial gas infall,"We analyze the redshift evolution of the mass-metallicity relation in a
sample of 110 Damped Ly$\alpha$ absorbers spanning the redshift range
$z=0.11-5.06$ and find that the zero-point of the correlation changes
significantly with redshift. The evolution is such that the zero-point is
constant at the early phases of galaxy growth (i.e. no evolution) but then
features a sharp break at $z=2.6\pm 0.2$ with a rapid incline towards lower
redshifts such that damped absorbers of identical masses are more metal rich at
later times than earlier. The slope of this mass metallicity correlation
evolution is $0.35 \pm 0.07$ dex per unit redshift.
  We compare this result to similar studies of the redshift evolution of
emission selected galaxy samples and find a remarkable agreement with the slope
of the evolution of galaxies of stellar mass log$(M_{*}/M_\odot) \approx 8.5$.
This allows us to form an observational tie between damped absorbers and
galaxies seen in emission.
  We use results from simulations to infer the virial mass of the dark matter
halo of a typical DLA galaxy and find a ratio $(M_{vir}/M_{*}) \approx 30$.
  We compare our results to those of several other studies that have reported
strong transition-like events at redshifts around $z=2.5-2.6$ and argue that
all those observations can be understood as the consequence of a transition
from a situation where galaxies were fed more unprocessed infalling gas than
they could easily consume to one where they suddenly become infall starved and
turn to mainly processing, or re-processing, of previously acquired gas.",1301.5013v2
2013-01-22,Effect of partial ionization on wave propagation in solar magnetic flux tubes,"Observations show that waves are ubiquitous in the solar atmosphere and may
play an important role for plasma heating. The study of waves in the solar
corona is usually based on linear ideal magnetohydrodynamics (MHD) for a fully
ionized plasma. However, the plasma in the photosphere and the chromosphere is
only partially ionized. Here we investigate theoretically the impact of partial
ionization on MHD wave propagation in cylindrical flux tubes in the two-fluid
model. We derive the general dispersion relation that takes into account the
effects of neutral-ion collisions and the neutral gas pressure. We take the
neutral-ion collision frequency as an arbitrary parameter. Particular results
for transverse kink modes and slow magnetoacoustic modes are shown. We find
that the wave frequencies only depend on the properties of the ionized fluid
when the neutral-ion collision frequency is much lower that the wave frequency.
For high collision frequencies realistic of the solar atmosphere ions and
neutrals behave as a single fluid with an effective density corresponding to
the sum of densities of both fluids and an effective sound velocity computed as
the average of the sound velocities of ions and neutrals. The MHD wave
frequencies are modified accordingly. The neutral gas pressure can be neglected
when studying transverse kink waves but it has to be taken into account for a
consistent description of slow magnetoacoustic waves. The MHD waves are damped
due to neutral-ion collisions. The damping is most efficient when the wave
frequency and the collision frequency are of the same order of magnitude. For
high collision frequencies slow magnetoacoustic waves are more efficiently
damped than transverse kink waves. In addition, we find the presence of
cut-offs for certain combinations of parameters that cause the waves to become
non-propagating.",1301.5214v1
2013-02-07,Secular Orbital Evolution of Compact Planet Systems,"Recent observations have shown that at least some close-in exoplanets
maintain eccentric orbits despite tidal circularization timescales that are
typically shorter than stellar ages. We explore gravitational interactions with
a distant planetary companion as a possible cause of these non-zero
eccentricities. For simplicity, we focus on the evolution of a planar
two-planet system subject to slow eccentricity damping and provide an intuitive
interpretation of the resulting long-term orbital evolution. We show that
dissipation shifts the two normal eigenmode frequencies and eccentricity ratios
of the standard secular theory slightly, and that each mode decays at its own
rate. Tidal damping of the eccentricities drives orbits to transition between
periods of pericenter circulation and libration, and the planetary system
settles into a locked state where the pericenters are nearly aligned or
anti-aligned. Once in the locked state, the eccentricities of the two orbits
decrease very slowly due to tides rather than at the much more rapid
single-planet rate, and thus eccentric orbits, even for close-in planets, can
often survive much longer than the age of the system. Assuming that an observed
close-in planet on an elliptical orbit is apsidally-locked to a more distant,
and perhaps unseen companion, we provide a constraint on the mass, semi-major
axis, and eccentricity of the companion. We find the observed two-planet system
HAT-P-13 might be in just such an apsidally-locked state, with parameters that
obey our constraint well. We also survey close-in single planets, and found
that none provide compelling evidence for unseen companions. Instead, we
suspect that (1) orbits are circular, (2) tidal damping rates are slower than
our assumption, or (3) a recent event has excited these eccentricities. Our
method should prove useful for interpreting the results of current and future
planet searches.",1302.1620v2
2013-02-13,Low mass planets in protoplanetary disks with net vertical magnetic fields: the Planetary Wake and Gap Opening,"We study wakes and gap opening by low mass planets in gaseous protoplanetary
disks threaded by net vertical magnetic fields which drive
magnetohydrodynamical (MHD) turbulence through the magnetorotational instabilty
(MRI), using three dimensional simulations in the unstratified local shearing
box approximation. The wakes, which are excited by the planets, are damped by
shocks similar to the wake damping in inviscid hydrodynamic (HD) disks. Angular
momentum deposition by shock damping opens gaps in both MHD turbulent disks and
inviscid HD disks even for low mass planets, in contradiction to the ""thermal
criterion"" for gap opening. To test the ""viscous criterion"", we compared gap
properties in MRI-turbulent disks to those in viscous HD disks having the same
stress, and found that the same mass planet opens a significantly deeper and
wider gap in net vertical flux MHD disks than in viscous HD disks. This
difference arises due to the efficient magnetic field transport into the gap
region in MRI disks, leading to a larger effective \alpha within the gap. Thus,
across the gap, the Maxwell stress profile is smoother than the gap density
profile, and a deeper gap is needed for the Maxwell stress gradient to balance
the planetary torque density. We also confirmed the large excess torque close
to the planet in MHD disks, and found that long-lived density features (termed
zonal flows) produced by the MRI can affect planet migration. The comparison
with previous results from net toroidal flux/zero flux MHD simulations
indicates that the magnetic field geometry plays an important role in the gap
opening process. Overall, our results suggest that gaps can be commonly
produced by low mass planets in realistic protoplanetary disks, and caution the
use of a constant \alpha-viscosity to model gaps in protoplanetary disks.",1302.3239v1
2013-05-10,Nonlinear Development of the R Mode Instability and the Maximum Rotation Rate of Neutron Stars,"We describe how the nonlinear development of the R mode instability of
neutron stars influences spin up to millisecond periods via accretion. Our
arguments are based on nearly-resonant interactions of the R mode with pairs of
""daughter modes"". The amplitude of the R mode saturates at the lowest value for
which parametric instability leads to significant excitation of a particular
pair of daughters. The lower bound on this limiting amplitude is proportional
to the damping rate of the daughter modes that are excited parametrically.
Based on this picture, we show that if modes damp because of dissipation in a
very thin boundary layer at the crust-core boundary then spin up to frequencies
larger than about 300 Hz does not occur. Within this conventional scenario the
R mode saturates at an amplitude that is too large for angular momentum gain
from accretion to overcome gravitational loss to gravitational radiation. We
conclude that lower dissipation is required for spin up to frequencies much
higher than 300 Hz. We conjecture that if the transition from the fluid core to
the crystalline crust occurs over a distance much longer than 1 cm then a sharp
viscous boundary layer fails to form. In this case, damping is due to shear
viscosity dissipation integrated over the entire star; the rate is slower than
if a viscous boundary layer forms. We use statistical arguments and scaling
relations to estimate the lowest parametric instability threshold from first
principles. The resulting saturation amplitudes are low enough to permit spin
up to higher frequencies. Further, we show that the requirement that the lowest
parametric instability amplitude be small enough to allow continued spin up
imposes an upper bound to the frequencies that may be attained via accretion
that may plausibly be about 750 Hz. Within this framework, the R mode is
unstable for all millisecond pulsars, whether accreting or not.",1305.2335v2
2013-07-28,Constraint damping of the conformal and covariant formulation of the Z4 system in simulations of binary neutron stars,"Following previous work in vacuum spacetimes, we investigate the
constraint-damping properties in the presence of matter of the recently
developed traceless, conformal and covariant Z4 (CCZ4) formulation of the
Einstein equations. First, we evolve an isolated neutron star with an ideal gas
equation of state and subject to a constraint-violating perturbation. We
compare the evolution of the constraints using the CCZ4 and
Baumgarte-Shibata-Shapiro-Nakamura-Oohara-Kojima (BSSNOK) systems. Second, we
study the collapse of an unstable spherical star to a black hole. Finally, we
evolve binary neutron star systems over several orbits until the merger, the
formation of a black hole, and up to the ringdown. We show that the CCZ4
formulation is stable in the presence of matter and that the constraint
violations are one or more orders of magnitude smaller than for the BSSNOK
formulation. Furthermore, by comparing the CCZ4 and the BSSNOK formulations
also for neutron star binaries with large initial constraint violations, we
investigate their influence on the errors on physical quantities. We also give
a new, simple and robust prescription for the damping parameter that removes
the instabilities found when using the fully covariant version of CCZ4 in the
evolution of black holes. Overall, we find that at essentially the same
computational costs the CCZ4 formulation provides solutions that are stable and
with a considerably smaller violation of the Hamiltonian constraint than the
BSSNOK formulation. We also find that the performance of the CCZ4 formulation
is very similar to another conformal and traceless, but noncovariant
formulation of the Z4 system, i.e. the Z4c formulation.",1307.7391v2
2013-08-05,"Peculiar Velocity Decomposition, Redshift Space Distortion and Velocity Reconstruction in Redshift Surveys. II. Dark Matter Velocity Statistics","Massive spectroscopic redshift surveys open a promising window to accurately
measure peculiar velocity at cosmological distances through redshift space
distortion (RSD). In paper I of this series of work we proposed to decompose
peculiar velocity into three eigen-modes (v_\delta, v_S and v_B) in order to
facilitate the RSD modeling and peculiar velocity reconstruction. In the
current paper we measure the dark matter RSD related statistics of the velocity
eigen-modes through a set of N-body simulations, including the velocity power
spectra, correlation functions, one-point probability distribution functions,
cumulants and the damping functions describing the Finger of God effect. (1)
The power spectrum measurement shows that these velocity components have
distinctly different spatial distribution and redshift evolution. In
particular, we measure the window function \tilde{W}(k,z), which describes the
impact of nonlinear evolution on the v_\delta-density relation. We confirm that
it can induce a significant systematic error of O(10%) in RSD cosmology. We
demonstrate that \tilde{W} can be accurately described by a simple fitting
formula with one or two free parameters. (2) The correlation function
measurement shows that the correlation length is O(100), O(10) and O(1) Mpc for
v_\delta, v_S and v_B respectively. These correlation lengths determine where
we can treat the velocity fields as spatially uncorrelated. (3) The velocity
PDFs and cumulants quantify non-Gaussianities of the velocity fields. We
confirm speculation in paper I that v_\delta is largely Gaussian, nevertheless
with non-negligible non-Gaussianity, v_B is significantly non-Gaussian. We also
measure the damping functions. Despite the observed non-Gaussianities, the
damping functions and hence the FOG effect are all well approximated as
Gaussian ones at scales of interest.",1308.0886v4
2013-10-25,A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - V. Neutral and Ionised Phase Metallicities,"The gas-phase and stellar metallicities have proven to be important
parameters to constrain the star formation history of galaxies. However, HII
regions associated with recent star-formation may not have abundances typical
for the galaxy as a whole and it is believed that the bulk of the metals may be
contained in the neutral gas. It is therefore important to directly probe the
metal abundances in the neutral gas, which can be done by using absorption
lines imprinted on a background quasar. Recently, we have presented studies of
the stellar content of a small sample of such quasar absorbers with HI column
densities measured to be in the sub-Damped Lyman-alpha to Damped Lyman-alpha
range. Here, we present observations covering 300 nm to 2.5 microns of emission
line spectra of three of these absorbing-galaxies using the long-slit
spectrograph X-Shooter on the VLT. This allows us to compare the neutral and
ionised phase metallicities in the same objects and relates these measures to
possible signature of low-metallicity gas accretion or outflows of gas enriched
by star formation. Our results suggest that the abundances derived in
absorption along the line-of-sight to background quasars are reliable measures
of the overall galaxy metallicities. In addition to a comparison of abundances
in different phases of the gas, a potential observational consequence of
differences in fueling mechanisms for disc galaxies is the internal
distribution of their chemical abundances. We present some evidence for small
negative metallicity gradients in the three systems. The flat slopes are in
line with the differences observed between the two phases of the gas. These
results suggest that a comparison of the HI and HII metallicities is a robust
indicator of abundance gradients in high-redshift galaxies and do not favour
the presence of infall of fresh gas in these objects.",1310.6865v1
2014-04-10,"Thirty-six New, High-Probability, Damped Ly-alpha Absorbers at Redshift 0.42 < z < 0.70","Quasar damped Ly-alpha (DLA) absorption line systems with redshifts z<1.65
are used to trace neutral gas over approximately 70 per cent of the most recent
history of the Universe. However, such systems fall in the UV and are rarely
found in blind UV spectroscopic surveys. Therefore, it has been difficult to
compile a moderate-sized sample of UV DLAs in any narrow cosmic time interval.
However, DLAs are easy to identify in low-resolution spectra because they have
large absorption rest equivalent widths. We have performed an efficient
strong-MgII-selected survey for UV DLAs at redshifts z=[0.42,0.70] using HST's
low-resolution ACS-HRC-PR200L prism. This redshift interval covers ~1.8 Gyr in
cosmic time, i.e., t~[7.2,9.0] Gyrs after the Big Bang. A total of 96 strong
MgII absorption-line systems identified in SDSS spectra were successfully
observed with the prism at the predicted UV wavelengths of Ly-alpha absorption.
We found that 35 of the 96 systems had a significant probability of being DLAs.
One additional observed system could be a very high N(HI) DLA (N(HI)~2x10^22
atoms cm^-2 or possibly higher), but since very high N(HI) systems are
extremely rare, it would be unusual for this system to be a DLA given the size
of our sample. Here we present information on our prism sample, including our
best estimates of N(HI) and errors for the 36 systems fitted with damped
Ly-alpha profiles. This list is valuable for future follow-up studies of
low-redshift DLAs in a small redshift interval, although such work would
clearly benefit from improved UV spectroscopy to more accurately determine
their neutral hydrogen column densities.",1404.2914v2
2014-05-03,3D MHD simulation of linearly polarised Alfven wave dynamics in Arnold-Beltrami-Childress magnetic field,"Previous studies [Malara et al ApJ, 533, 523 (2000)] considered
small-amplitude Alfven wave (AW) packets in Arnold-Beltrami-Childress (ABC)
magnetic field using WKB approximation. In this work linearly polarised Alfven
wave dynamics in ABC magnetic field via direct 3D MHD numerical simulation is
studied for the first time. Gaussian AW pulse with length-scale much shorter
than ABC domain length and harmonic AW with wavelength equal to ABC domain
length are studied for four different resistivities. While it is found that AWs
dissipate quickly in the ABC field, surprisingly, AW perturbation energy
increases in time. In the case of the harmonic AW perturbation energy growth is
transient in time, attaining peaks in both velocity and magnetic perturbation
energies within timescales much smaller than resistive time. In the case of the
Gaussian AW pulse velocity perturbation energy growth is still transient in
time, attaining a peak within few resistive times, while magnetic perturbation
energy continues to grow. It is also shown that the total magnetic energy
decreases in time and this is governed by the resistive evolution of the
background ABC magnetic field rather than AW damping. On contrary, when
background magnetic field is uniform, the total magnetic energy decrease is
prescribed by AW damping, because there is no resistive evolution of the
background. By considering runs with different amplitudes and by analysing
perturbation spectra, possible dynamo action by AW perturbation-induced
peristaltic flow and inverse cascade of magnetic energy have been excluded.
Therefore, the perturbation energy growth is attributed to a new instability.
The growth rate appears to be dependent on the value of the resistivity and
spatial scale of the AW disturbance. Thus, when going beyond WKB approximation,
AW damping, described by full MHD equations, does not guarantee decrease of
perturbation energy.",1405.0587v1
2014-11-25,Investigation of toroidal acceleration and potential acceleration forces in EAST and J-TEXT plasmas,"In order to produce intrinsic rotation, bulk plasmas must be collectively
accelerated by the net force exerted on them, which results from both driving
and damping forces. So, to study the possible mechanisms of intrinsic rotation
generation, it is only needed to understand characteristics of driving and
damping terms because the toroidal driving and damping forces induce net
acceleration which generates intrinsic rotation. Experiments were performed on
EAST and J-TEXT for ohmic plasmas with net counter- and co-current toroidal
acceleration generated by density ramping up and ramping down. Additionally on
EAST, net co-current toroidal acceleration was also formed by LHCD or ICRF. For
the current experimental results, toroidal acceleration was between - 50 km/s^2
in counter-current direction and 70 km/s^2 in co-current direction. According
to toroidal momentum equation, toroidal electric field (E\-(\g(f))),
electron-ion toroidal friction, and toroidal viscous force etc. may play roles
in the evolution of toroidal rotation. To evaluate contribution of each term,
we first analyze characteristics of E\-(\g(f)). E\-(\g(f)) is one of the
co-current toroidal forces that acts on the plasma as a whole and persists for
the entire discharge period. It was shown to drive the co-current toroidal
acceleration at a magnitude of 10^3 km/s^2, which was much larger than the
experimental toroidal acceleration observed on EAST and J-TEXT. So E\-(\g(f))
is one of co-current forces producing cocurrent intrinsic toroidal acceleration
and rotation. Meanwhile, it indicates that there must be a strong
counter-current toroidal acceleration resulting from counter-current toroidal
forces. Electron-ion toroidal friction is one of the counter-current toroidal
forces because global electrons move in the counter-current direction in order
to produce a toroidal plasma current.",1411.6744v1
2015-01-07,Understanding resonance graphs using Easy Java Simulations (EJS) and why we use EJS,"This paper reports a computer model- simulation created using Easy Java
Simulation (EJS) for learners to visualize how the steady-state amplitude of a
driven oscillating system varies with the frequency of the periodic driving
force. The simulation shows (N=100) identical spring-mass systems being
subjected to (1) periodic driving force of equal amplitude but different
driving frequencies and (2) different amount of damping. The simulation aims to
create a visually intuitive way of understanding how the series of amplitude
versus driving frequency graphs are obtained by showing how the displacement of
the system changes over time as it transits from the transient to the steady
state.
  A suggested how to use the model is added to help educators and students in
their teaching and learning, where we explained the theoretical steady state
equation, time conditions when the model starts allowing data recording of
maximum amplitudes to closely match the theoretical equation and steps to
collect different runs of degree of damping. We also discuss two design
features in our computer model: A) displaying the instantaneous oscillation
together with the achieved steady state amplitudes and B) explicit world view
overlay with scientific representation with different degrees of damping runs.
  Three advantages of using EJS include 1) Open Source Codes and Creative
Commons Attribution Licenses for scaling up of interactively engaging
educational practices 2) models made can run on almost any device including
Android and iOS and 3) allows for redefining physics educational practices
through computer modeling. 2015 resource:
http://iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/09-oscillations/88-shm24",1501.01535v4
2015-04-20,Forward Modeling of Reduced Power Spectra From Three-Dimensional k-Space,"We present results from a numerical forward model to evaluate one-dimensional
reduced power spectral densities (PSD) from arbitrary energy distributions in
$\mathbf{k}$-space. In this model, we can separately calculate the diagonal
elements of the spectral tensor for incompressible axisymmetric turbulence with
vanishing helicity. Given a critically balanced turbulent cascade with
$k_\|\sim k_\perp^\alpha$ and $\alpha<1$, we explore the implications on the
reduced PSD as a function of frequency. The spectra are obtained under the
assumption of Taylor's hypothesis. We further investigate the functional
dependence of the spectral index $\kappa$ on the field-to-flow angle $\theta$
between plasma flow and background magnetic field from MHD to electron kinetic
scales. We show that critically balanced turbulence asymptotically develops
toward $\theta$-independent spectra with a slope corresponding to the
perpendicular cascade. This occurs at a transition frequency
$f_{2D}(L,\alpha,\theta)$, which is analytically estimated and depends on outer
scale $L$, critical balance exponent $\alpha$ and field-to-flow angle $\theta$.
We discuss anisotropic damping terms acting on the $\mathbf{k}$-space
distribution of energy and their effects on the PSD. Further, we show that the
spectral anisotropies $\kappa(\theta)$ as found by Horbury et al. (2008) and
Chen et al. (2010) in the solar wind are in accordance with a damped critically
balanced cascade of kinetic Alfv\'en waves. We also model power spectra
obtained by von Papen et al. (2014) in Saturn's plasma sheet and find that the
change of spectral indices inside $9\,R_\mathrm{s}$ can be explained by damping
on electron scales.",1504.04995v2
2015-07-13,The role of low-energy phonons with mean-free-paths >0.8 um in heat conduction in silicon,"Despite recent progress in the first-principles calculations and measurements
of phonon mean-free-paths (MFPs), contribution of low-energy phonons to heat
conduction in silicon is still inconclusive, as exemplified by the
discrepancies between different first-principles calculations. Here we
investigate the contribution of low-energy phonons with MFP>0.8 um by
accurately measuring the cross-plane thermal conductivity of crystalline
silicon films by time-domain thermoreflectance (TDTR), over a wide range of
film thickness 1-10 um and temperature 100-300 K. We employ a dual-frequency
TDTR approach to improve the accuracy of our cross-plane thermal conductivity
measurements. We find from our cross-plane thermal conductivity measurements
that phonons with MFP>0.8 um contribute 53 W/m-K (37%) to heat conduction in Si
at 300 K while phonons with MFP>3 um contribute 523 W/m-K (61%) at 100 K, >20%
lower than the first-principles predictions by Lindsay et al. of 68 W/m-K (47%)
and 695 W/m-K (77%), respectively. Using a relaxation times approximation (RTA)
model, we demonstrate that macroscopic damping (e.g., Akhieser's damping)
eliminates the contribution of phonons with mean-free-paths >30 um at 300 K,
which contributes 15 W/m-K (10%) to heat conduction in Si according to Lindsay
et al. Thus we propose that omission of the macroscopic damping for low-energy
phonons in the first-principles calculations could be one of the possible
explanations for the observed discrepancy between our measurements and
calculations by Lindsay et al. Our work provides an important benchmark for
future measurements and calculations of the distribution of phonon
mean-free-paths in crystalline silicon.",1507.03422v4
2015-08-03,Using coronal seismology to estimate the magnetic field strength in a realistic coronal model,"Coronal seismology is extensively used to estimate properties of the corona,
e.g. the coronal magnetic field strength are derived from oscillations observed
in coronal loops. We present a three-dimensional coronal simulation including a
realistic energy balance in which we observe oscillations of a loop in
synthesised coronal emission. We use these results to test the inversions based
on coronal seismology.
  From the simulation of the corona above an active region we synthesise
extreme ultraviolet (EUV) emission from the model corona. From this we derive
maps of line intensity and Doppler shift providing synthetic data in the same
format as obtained from observations. We fit the (Doppler) oscillation of the
loop in the same fashion as done for observations to derive the oscillation
period and damping time.
  The loop oscillation seen in our model is similar to imaging and
spectroscopic observations of the Sun. The velocity disturbance of the kink
oscillation shows an oscillation period of 52.5s and a damping time of 125s,
both being consistent with the ranges of periods and damping times found in
observation. Using standard coronal seismology techniques, we find an average
magnetic field strength of $B_{\rm kink}=79$G for our loop in the simulation,
while in the loop the field strength drops from some 300G at the coronal base
to 50G at the apex. Using the data from our simulation we can infer what the
average magnetic field derived from coronal seismology actually means. It is
close to the magnetic field strength in a constant cross-section flux tube that
would give the same wave travel time through the loop.
  Our model produced not only a realistic looking loop-dominated corona, but
also provides realistic information on the oscillation properties that can be
used to calibrate and better understand the result from coronal seismology.",1508.00593v1
2015-08-27,Nonlinear Landau damping and modulation of electrostatic waves in a nonextensive electron-positron-pair plasma,"The nonlinear theory of amplitude modulation of electrostatic wave envelopes
in a collisionless electron-positron (EP) pair plasma is studied by using a set
of Vlasov-Poisson equations in the context of Tsallis' $q$-nonextensive
statistics. In particular, the previous linear theory of Langmuir oscillations
in EP plasmas [Phys. Rev. E {\bf87}, 053112 (2013)] is rectified and modified.
Applying the multiple scale technique (MST), it is shown that the evolution of
electrostatic wave envelopes is governed by a nonlinear Schr{\""o}dinger (NLS)
equation with a nonlocal nonlinear term $\propto
{\cal{P}}\int|\phi(\xi',\tau)|^2d\xi'\phi/(\xi-\xi') $ [where ${\cal P}$
denotes the Cauchy principal value, $\phi$ is the small-amplitude electrostatic
(complex) potential, and $\xi$ and $\tau$ are the stretched coordinates in MST]
which appears due to the wave-particle resonance. It is found that a subregion
$1/3<q\lesssim3/5$ of superextensivity $(q<1)$ exists where the carrier wave
frequency can turn over with the group velocity going to zero and then to
negative values. The effects of the nonlocal nonlinear term and the
nonextensive parameter $q$ are examined on the modulational instability (MI) of
wave envelopes as well as on the solitary wave solution of the NLS equation. It
is found that the modulated wave packet is always unstable (nonlinear Landau
damping) due to the nonlocal nonlinearity in the NLS equation. Furthermore, the
effect of the nonlinear Landau damping is to slow down the amplitude of the
wave envelope, and the corresponding decay rate can be faster the larger is the
number of superthermal particles in pair plasmas.",1508.06903v2
2015-10-03,Systematic investigations of deep sub-barrier fusion reactions using an adiabatic approach,"To describe fusion hindrance observed in fusion reactions at extremely low
incident energies, I propose a novel extension of the standard CC model by
introducing a damping factor that describes a smooth transition from sudden to
adiabatic processes. I demonstrate the performance of this model by
systematically investigating various deep sub-barrier fusion reactions. I
extend the standard CC model by introducing a damping factor into the coupling
matrix elements in the standard CC model. I adopt the Yukawa-plus-exponential
(YPE) model as a basic heavy ion-ion potential, which is advantageous for a
unified description of the one- and two-body potentials. For the purpose of
these systematic investigations, I approximate the one-body potential with a
third-order polynomial function based on the YPE model. Calculated fusion cross
sections for the medium-heavy mass systems of $^{64}$Ni + $^{64}$Ni, $^{58}$Ni
+ $^{58}$Ni, and $^{58}$Ni + $^{54}$Fe, the medium-light mass systems of
$^{40}$Ca + $^{40}$Ca, $^{48}$Ca + $^{48}$Ca, and $^{24}$Mg + $^{30}$Si, and
the mass-asymmetric systems of $^{48}$Ca + $^{96}$Zr and $^{16}$O + $^{208}$Pb
are consistent with the experimental data. The astrophysical S factor and
logarithmic derivative representations of these are also in good agreement with
the experimental data. Since the results calculated with the damping factor are
in excellent agreement with the experimental data in all systems, I conclude
that the smooth transition from the sudden to adiabatic processes occurs and
that a coordinate-dependent coupling strength is responsible for the fusion
hindrance. In all systems, the potential energies at the touching point $V_{\rm
Touch}$ strongly correlate with the incident threshold energies for which the
fusion hindrance starts to emerge, except for the medium-light mass systems.",1510.00806v1
2015-10-29,Numerical simulations of transverse oscillations in radiatively cooling coronal loops,"We aim to study the influence of radiative cooling on the standing kink
oscillations of a coronal loop. Using the FLASH code, we solved the 3D ideal
magnetohydrodynamic equations. Our model consists of a straight, density
enhanced and gravitationally stratified magnetic flux tube. We perturbed the
system initially, leading to a transverse oscillation of the structure, and
followed its evolution for a number of periods. A realistic radiative cooling
is implemented. Results are compared to available analytical theory. We find
that in the linear regime (i.e. low amplitude perturbation and slow cooling)
the obtained period and damping time are in good agreement with theory. The
cooling leads to an amplification of the oscillation amplitude. However, the
difference between the cooling and non-cooling cases is small (around 6% after
6 oscillations). In high amplitude runs with realistic cooling, instabilities
deform the loop, leading to increased damping. In this case, the difference
between cooling and non-cooling is still negligible at around 12%. A set of
simulations with higher density loops are also performed, to explore what
happens when the cooling takes place in a very short time (tcool = 100 s). We
strengthen the results of previous analytical studies that state that the
amplification due to cooling is ineffective, and its influence on the
oscillation characteristics is small, at least for the cases shown here.
Furthermore, the presence of a relatively strong damping in the high amplitude
runs even in the fast cooling case indicates that it is unlikely that cooling
could alone account for the observed, flare-related undamped oscillations of
coronal loops. These results may be significant in the field of coronal
seismology, allowing its application to coronal loop oscillations with observed
fading-out or cooling behaviour.",1510.08760v1
2016-04-28,Single-Particle Dynamics in a Nonlinear Accelerator Lattice: Attaining a Large Tune Spread with Octupoles in IOTA,"Fermilab is constructing the Integrable Optics Test Accelerator (IOTA) as the
centerpiece of the Accelerator R&D Program towards high-intensity circular
machines. One of the factors limiting the beam intensity in present circular
accelerators is collective instabilities, which can be suppressed by a spread
of betatron frequencies (tunes) through the Landau damping mechanism or by an
external damper, if the instability is slow enough. The spread is usually
created by octupole magnets, which introduce the tune dependence on the
amplitude and, in some cases, by a chromatic spread (tune dependence on
particle's momentum). The introduction of octupoles usually has both the
beneficial (improved Landau damping) and harmful properties, such as a resonant
behavior and a reduction of the dynamic aperture. One of the research goals at
the IOTA ring is to achieve a large betatron tune spread, while retaining a
large dynamic aperture, using conventional octupole magnets in a special but
realistic accelerator configuration. In this paper, we present results of
computer simulations of an electron beam in the IOTA by particle tracking and
the Frequency Map Analysis. The results show that the ring's octupole magnets
can be configured to provide a betatron tune shift of 0.08 (for particles at
large amplitudes) with the dynamical aperture of over 20 beam sigma for a
150-MeV electron beam. The influence of the synchrotron motion, lattice errors,
and magnet imperfections is insignificant for the parameters and levels of
tolerances set by the design of the ring. The described octupole insert could
be beneficial for enhancing Landau damping in high intensity machines.",1604.08565v4
2016-10-12,Dipole modes with depressed amplitudes in red giants are mixed modes,"Seismic observations have shown that a number of evolved stars exhibit
low-amplitude dipole modes, which are referred to as depressed modes. Recently,
these low amplitudes have been attributed to the presence of a strong magnetic
field in the stellar core of those stars.
  We intend to study the properties of depressed modes in evolved stars, which
is a necessary condition before concluding on the physical nature of the
mechanism responsible for the reduction of the dipole mode amplitudes.
  We perform a thorough characterization of the global seismic parameters of
depressed dipole modes and show that these modes have a mixed character. The
observation of stars showing dipole mixed modes that are depressed is
especially useful for deriving model-independent conclusions on the dipole mode
damping.
  Observations prove that depressed dipole modes in red giants are not pure
pressure modes but mixed modes. This result invalidates the hypothesis that the
depressed dipole modes result from the suppression of the oscillation in the
radiative core of the stars. Observations also show that, except for the
visibility, the seismic properties of the stars with depressed modes are
equivalent to those of normal stars.
  The mixed nature of the depressed modes in red giants and their unperturbed
global seismic parameters carry strong constraints on the physical mechanism
responsible for the damping of the oscillation in the core. This mechanism is
able to damp the oscillation in the core but cannot fully suppress it.
Moreover, it cannot modify the radiative cavity probed by the gravity component
of the mixed modes. The recent mechanism involving high magnetic field proposed
for explaining depressed modes is not compliant with the observations and
cannot be used to infer the strength and the prevalence of high magnetic fields
in red giants.",1610.03872v1
2016-11-07,Three-phonon and four-phonon interaction processes in a pair-condensed Fermi gas,"We study the interactions among phonons and the phonon lifetime in a
pair-condensed Fermi gas in the BEC-BCS crossover in the collisionless regime.
To compute the phonon-phonon coupling amplitudes we use a microscopic model
based on a generalized BCS Ansatz including moving pairs, which allows for a
systematic expansion around the mean field BCS approximation of the ground
state. We show that the quantum hydrodynamic expression of the amplitudes
obtained by Landau and Khalatnikov apply only on the energy shell, that is for
resonant processes that conserve energy. The microscopic model yields the same
excitation spectrum as the Random Phase Approximation, with a linear (phononic)
start and a concavity at low wave number that changes from upwards to downwards
in the BEC-BCS crossover. When the concavity of the dispersion relation is
upwards at low wave number, the leading damping mechanism at low temperature is
the Beliaev-Landau process 2 phonons $\leftrightarrow$ 1 phonon while, when the
concavity is downwards, it is the Landau-Khalatnikov process 2 phonons
$\leftrightarrow$ 2 phonons. In both cases, by rescaling the wave vectors to
absorb the dependence on the interaction strength, we obtain a universal
formula for the damping rate. This universal formula corrects and extends the
original analytic results of Landau and Khalatnikov [ZhETF {\bf 19}, 637
(1949)] for the $2\leftrightarrow2$ processes in the downward concavity case.
In the upward concavity case, for the Beliaev 1$\leftrightarrow$ 2 process for
the unitary gas at zero temperature, we calculate the damping rate of an
excitation with wave number $q$ including the first correction proportional to
$q^7$ to the $q^5$ hydrodynamic prediction, which was never done before in a
systematic way.",1611.01954v3
2016-11-20,Migration of Planets Into and Out of Mean Motion Resonances in Protoplanetary Disks: Analytical Theory of Second-Order Resonances,"Recent observations of Kepler multi-planet systems have revealed a number of
systems with planets very close to second-order mean motion resonances (MMRs,
with period ratio $1:3$, $3:5$, etc.) We present an analytic study of resonance
capture and its stability for planets migrating in gaseous disks. Resonance
capture requires slow convergent migration of the planets, with sufficiently
large eccentricity damping timescale $T_e$ and small pre-resonance
eccentricities. We quantify these requirements and find that they can be
satisfied for super-Earths under protoplanetary disk conditions. For planets
captured into resonance, an equilibrium state can be reached, in which
eccentricity excitation due to resonant planet-planet interaction balances
eccentricity damping due to planet-disk interaction. We show that this
""captured"" equilibrium can be overstable, leading to partial or permanent
escape of the planets from the resonance. In general, the stability of the
captured state depends on the inner to outer planet mass ratio $q=m_1/m_2$ and
the ratio of the eccentricity damping times. The overstability growth time is
of order $T_e$, but can be much larger for systems close to the stability
threshold. For low-mass planets undergoing type I (non-gap opening) migration,
convergent migration requires $q \lesssim 1$, while the stability of the
capture requires $q\gtrsim 1$. These results suggest that planet pairs stably
captured into second-order MMRs have comparable masses. This is in contrast to
first-order MMRs, where a larger parameter space exists for stable resonance
capture. We confirm and extend our analytical results with $N$-body
simulations, and show that for overstable capture, the escape time from the MMR
can be comparable to the time the planets spend migrating between resonances.",1611.06463v2
2016-11-29,Kinetic Field Theory: Effects of momentum correlations on the cosmic density-fluctuation power spectrum,"In earlier work, we have developed a Kinetic Field Theory (KFT) for
cosmological structure formation and showed that the non-linear
density-fluctuation power spectrum known from numerical simulations can be
reproduced quite well even if particle interactions are taken into account to
first order only. Besides approximating gravitational interactions, we had to
truncate the initial correlation hierarchy of particle momenta at the second
order. Here, we substantially simplify KFT. We show that its central object,
the free generating functional, can be factorized, taking the full hierarchy of
momentum correlations into account. The factors appearing in the generating
functional, which we identify as non-linearly evolved density-fluctuation power
spectra, have a universal form and can thus be tabulated for fast access in
perturbation schemes.
  In this paper, we focus on a complete evaluation of the free generating
functional of KFT, not including particle interactions yet. This implies that
the non-linearly evolved power spectra contain a damping term which reflects
that structures are being wiped out at late times by free streaming. Once
particle interactions will be taken into account, they will compensate this
damping. If we suppress this damping in a way suggested by the
fluctuation-dissipation relations of KFT, our results show that the complete
hierarchy of initial momentum correlations is responsible for a large part of
the characteristic non-linear deformation and the mode transport in the
density-fluctuation power spectrum. Without any adjustable parameters, KFT
accurately reproduces the scale at which non-linear evolution sets in.
  Finally, we further develop perturbation theory based on the factorization of
the generating functional and propose a diagrammatic scheme for the
perturbation terms.",1611.09503v2
2016-12-08,Highly inclined and eccentric massive planets. II. Planet-planet interactions during the disc phase,"We aim to investigate the influence of the eccentricity and inclination
damping due to planet-disc interactions on the final configurations of the
systems, generalizing previous studies on the combined action of the gas disc
and planet-planet scattering during the disc phase. Instead of the simplistic
$K$-prescription, our n-body simulations adopt the damping formulae for
eccentricity and inclination provided by the hydrodynamical simulations of our
companion paper. We follow the evolution of $11000$ numerical experiments of
three giant planets in the late stage of the gas disc, exploring different
initial configurations, planetary mass ratios and disc masses. The dynamical
evolutions of the planetary systems are studied along the simulations, with
emphasis on the resonance captures and inclination-growth mechanisms. Most of
the systems are found with small inclinations ($\le10^{\circ}$) at the
dispersal of the disc. Even though many systems enter an inclination-type
resonance during the migration, the disc usually damps the inclinations on a
short timescale. Although the majority of the multiple systems in our results
are quasi-coplanar, $\sim5\%$ of them end up with high mutual inclinations
($\ge10^{\circ}$). Half of these highly mutually inclined systems result from
two- or three-body MMR captures, the other half being produced by orbital
instability and/or planet-planet scattering. When considering the long-term
evolution over $100$ Myr, destabilization of the resonant systems is common,
and the percentage of highly mutually inclined systems still evolving in
resonance drops to $30\%$. Finally, the parameters of the final system
configurations are in very good agreement with the semi-major axis and
eccentricity distributions in the observations, showing that planet-planet
interactions during the disc phase could have played an important role in
sculpting planetary systems.",1612.02693v1
2017-02-22,A Model of Energetic Ion Effects on Pressure Driven Tearing Modes in Tokamaks,"The effects that energetic trapped ions have on linear resistive
magnetohydrodynamic (MHD) instabilities are studied in a reduced model that
captures the essential physics driving or damping the modes through variations
in the magnetic shear. The drift-kinetic orbital interaction of a slowing down
distribution of trapped energetic ions with a resistive MHD instability is
integrated to a scalar contribution to the perturbed pressure, and entered into
an asymptotic matching formalism for the resistive MHD dispersion relation.
Toroidal magnetic field line curvature is included to model trapping in the
particle distribution, in an otherwise cylindrical model. The focus is on a
configuration that is driven unstable to the m/n = 2/1 mode by increasing
pressure, where m is the poloidal mode number and n the toroidal. The particles
and pressure can affect the mode both in the core region where there can be low
and reversed shear and outside the resonant surface in significant positive
shear. The results show that the energetic ions damp and stabilize the mode
when orbiting in significant positive shear, increasing the marginal stability
boundary. However, the inner core region contribution with low and reversed
shear can drive the mode unstable. This effect of shear on the energetic ion
pressure contribution is found to be consistent with the literature. These
results explain the observation that the 2/1 mode was found to be damped and
stabilized by energetic ions in {\delta}f - MHD simulations of tokamak
experiments with positive shear throughout, while the 2/1 mode was found to be
driven unstable in simulations of experiments with weakly reversed shear in the
core. This is also found to be consistent with related experimental
observations of the stability of the 2/1 mode changing significantly with core
shear.",1702.06837v2
2017-06-16,"Damping of Rabi oscillations in intensity-dependent photon echoes from exciton complexes in a CdTe/(Cd,Mg)Te single quantum well","We study Rabi oscillations detected in the coherent optical response from
various exciton complexes in a 20~nm-thick CdTe/(Cd,Mg)Te quantum well using
time-resolved photon echoes. In order to evaluate the role of exciton
localization and inhomogeneous broadening we use selective excitation with
spectrally narrow ps-pulses. We demonstrate that the transient profile of the
photon echo from the localized trion (X$^-$) and the donor-bound exciton
(D$^0$X) transitions strongly depends on the strength of the first pulse. It
acquires a non-Gaussian shape and experiences significant advancement for pulse
areas larger than $\pi$ due to non-negligible inhomogeneity-induced dephasing
of the oscillators during the optical excitation. Next, we observe that an
increase of the area of either the first (excitation) or the second (rephasing)
pulse leads to a significant damping of the photon echo signal, which is
strongest for the neutral excitons and less pronounced for the donor-bound
exciton complex (D$^0$X). The measurements are analyzed using a theoretical
model based on the optical Bloch equations which accounts for the inhomogeneity
of optical transitions in order to reproduce the complex shape of the photon
echo transients. In addition, the spreading of Rabi frequencies within the
ensemble due to the spatial variation of the intensity of the focused Gaussian
beams and excitation-induced dephasing are required to explain the fading and
damping of Rabi oscillations. By analyzing the results of the simulation for
the X$^-$ and the D$^0$X complexes we are able to establish a correlation
between the degree of localization and the transition dipole moments determined
as $\mu($X$^-$)=73~D and $\mu($D$^0$X)=58~D.",1706.05327v1
2017-06-28,Generating Log-normal Mock Catalog of Galaxies in Redshift Space,"We present a public code to generate a mock galaxy catalog in redshift space
assuming a log-normal probability density function (PDF) of galaxy and matter
density fields. We draw galaxies by Poisson-sampling the log-normal field, and
calculate the velocity field from the linearised continuity equation of matter
fields, assuming zero vorticity. This procedure yields a PDF of the pairwise
velocity fields that is qualitatively similar to that of N-body simulations. We
check fidelity of the catalog, showing that the measured two-point correlation
function and power spectrum in real space agree with the input precisely. We
find that a linear bias relation in the power spectrum does not guarantee a
linear bias relation in the density contrasts, leading to a cross-correlation
coefficient of matter and galaxies deviating from unity on small scales. We
also find that linearising the Jacobian of the real-to-redshift space mapping
provides a poor model for the two-point statistics in redshift space. That is,
non-linear redshift-space distortion is dominated by non-linearity in the
Jacobian. The power spectrum in redshift space shows a damping on small scales
that is qualitatively similar to that of the well-known Fingers-of-God (FoG)
effect due to random velocities, except that the log-normal mock does not
include random velocities. This damping is a consequence of non-linearity in
the Jacobian, and thus attributing the damping of the power spectrum solely to
FoG, as commonly done in the literature, is misleading.",1706.09195v2
2017-07-31,Investigating quantum wireless multihop teleportation under decoherence,"This research work scrutinizes quantum routing protocol with multihop
teleportation for wireless mesh backbone networks, in amplitude and phase
damping channels. After analyzing the quantum multihop protocol, we select a
four-qubit cluster state as the quantum channel for the protocol. The quantum
channel linking the intermediate nodes has been established via entanglement
swapping based on four-qubit cluster state. Also, we established the classical
and the quantum route in a distributed manner. We show that from the source
node to the destination node, quantum information can be teleported hop-by-hop
through an amplitude damping channel. We show that the quantum teleportation
could be successful if the sender node performs Bell state measurements (BSM),
and the receiver introduces auxiliary particles, applies positive operative
value measure and then utilizes corresponding unitary transformation to recover
the transmitted state. We scrutinize the success probability of transferring
the quantum state through a noisy channel. We found that optimum probability
would be attained if decoherence rate of amplitude damping channel ($\xi_a$) is
zero or the number of hops ($N$) is above $75$. Our numerical results evince
susceptibility of success probability to $\xi_a$ and $N$. It has been shown
that as the decoherence increases, the fidelity exponentially decays until it
vanishes. This decay is as a consequence of information loss from the system to
the surrounding. However, the fidelity can be enhanced by considering fewer
hops.",1708.00087v6
2017-11-30,Origins of sharp cosmic-ray electron structures and the DAMPE excess,"Nearby sources may contribute to cosmic-ray electron (CRE) structures at high
energies. Recently, the first DAMPE results on the CRE flux hinted at a narrow
excess at energy ~1.4 TeV. We show that in general a spectral structure with a
narrow width appears in two scenarios: I) ""Spectrum broadening"" for the
continuous sources with a delta-function-like injection spectrum. In this
scenario, a finite width can develop after propagation through the Galaxy,
which can reveal the distance of the source. Well-motivated sources include
mini-spikes and subhalos formed by dark matter (DM) particles $\chi_{s}$ which
annihilate directly into e+e- pairs. II) ""Phase-space shrinking"" for burst-like
sources with a power-law-like injection spectrum. The spectrum after
propagation can shrink at a cooling-related cutoff energy and form a sharp
spectral peak. The peak can be more prominent due to the energy-dependent
diffusion. In this scenario, the width of the excess constrains both the power
index and the distance of the source. Possible such sources are pulsar wind
nebulae (PWNe) and supernova remnants (SNRs). We analysis the DAMPE excess and
find that the continuous DM sources should be fairly close within ~0.3 kpc, and
the annihilation cross sections are close to the thermal value. For the
burst-like source, the narrow width of the excess suggests that the injection
spectrum must be hard with power index significantly less than two, the
distance is within ~(3-4) kpc, and the age of the source is ~0.16 Myr. In both
scenarios, large anisotropies in the CRE flux are predicted. We identify
possible candidates of mini-spike (PWN) sources in the current Fermi-LAT 3FGL
(ATNF) catalog. The diffuse gamma-rays from these sources can be well below the
Galactic diffuse gamma-ray backgrounds and less constrained by the Ferm-LAT
data, if they are located at the low Galactic latitude regions.",1712.00005v2
2017-11-30,Bayesian analysis of the break in DAMPE lepton spectra,"Recently, DAMPE has released its first results on the high-energy cosmic-ray
electrons and positrons (CREs) from about $25$ GeV to $4.6$ TeV, which directly
detect a break at $\sim 1$ TeV. This result gives us an excellent opportunity
to study the source of the CREs excess. In this work, we used the data fo
proton and helium flux (from AMS-02 and CREAM), $\bar{\mathrm{p}}/\mathrm{p}$
ratio (from AMS-02), positron flux (from AMS-02) and CREs flux (from DAMPE
without the peak signal point at $\sim 1.4$ TeV) to do global fitting
simultaneously, which can account the influence from the propagation model, the
nuclei and electron primary source injection and the secondary lepton
production precisely. For extra source to interpret the excess in lepton
spectrum, we consider two separate scenarios (pulsar and dark matter
annihilation via leptonic channels) to construct the bump ($\gtrsim 100$ GeV)
and the break at $\sim 1$ TeV. The result shows: (i) in pulsar scenario, the
spectral index of the injection should be $\nu_{\mathrm{psr}} \sim 0.65$ and
the cut-off should be $R_{c} \sim 650$ GV; (ii) in dark matter scenario, the
dark matter particle's mass is $m_{\chi} \sim 1208$ GeV and the cross section
is $\langle \sigma v \rangle \sim 1.48 \times 10^{-23} \mathrm{cm}^{3}
\mathrm{s}^{-1}$. Moreover, in the dark matter scenario, the $\tau \bar{\tau}$
annihilation channel is highly suppressed, and a DM model is built to satisfy
the fitting results.",1712.00372v4
2017-12-07,Internal alignment and position resolution of the silicon tracker of DAMPE determined with orbit data,"The DArk Matter Particle Explorer (DAMPE) is a space-borne particle detector
designed to probe electrons and gamma-rays in the few GeV to 10 TeV energy
range, as well as cosmic-ray proton and nuclei components between 10 GeV and
100 TeV. The silicon-tungsten tracker-converter is a crucial component of
DAMPE. It allows the direction of incoming photons converting into
electron-positron pairs to be estimated, and the trajectory and charge (Z) of
cosmic-ray particles to be identified. It consists of 768 silicon micro-strip
sensors assembled in 6 double layers with a total active area of 6.6 m$^2$.
Silicon planes are interleaved with three layers of tungsten plates, resulting
in about one radiation length of material in the tracker. Internal alignment
parameters of the tracker have been determined on orbit, with non-showering
protons and helium nuclei. We describe the alignment procedure and present the
position resolution and alignment stability measurements.",1712.02739v2
2018-01-24,Modelling redshift-space distortion in the post-reionization ${\rm HI}$ 21-cm power spectrum,"The post-reionization ${\rm HI}$ 21-cm signal is an excellent candidate for
precision cosmology, this however requires accurate modelling of the expected
signal. Sarkar et al. (2016) have simulated the real space ${\rm HI}$ 21-cm
signal, and have modelled the ${\rm HI}$ power spectrum as $P_{{\rm HI}}(k)=b^2
P(k)$ where $P(k)$ is the dark matter power spectrum and $b(k)$ is a (possibly
complex) scale dependent bias for which fitting formulas have been provided.
This paper extends these simulations to incorporate redshift space distortion
and predict the expected redshift space ${\rm HI}$ 21-cm power spectrum
$P^s_{{\rm HI}}(k_{\perp},k_{\parallel})$ using two different prescriptions for
the ${\rm HI}$ distributions and peculiar velocities. We model $P^s_{{\rm
HI}}(k_{\perp},k_{\parallel})$ assuming that it is the product of $P_{{\rm
HI}}(k)=b^2 P(k)$ with a Kaiser enhancement term and a Finger of God (FoG)
damping which has $\sigma_p$ the pair velocity dispersion as a free parameter.
Considering several possibilities for the bias and the damping profile, we find
that the models with a scale dependent bias and a Lorentzian damping profile
best fit the simulated $P^s_{{\rm HI}}(k_{\perp},k_{\parallel})$ over the
entire range $1 \le z \le 6$. The best fit value of $\sigma_p$ falls
approximately as $(1+z)^{-m}$ with $m=2$ and $1.2$ respectively for the two
different prescriptions. The model predictions are consistent with the
simulations for $k < 0.3 \, {\rm Mpc}^{-1}$ over the entire $z$ range for the
monopole $P^s_0(k)$, and at $z \le 3$ for the quadrupole $P^s_2(k)$. At $z \ge
4$ the models underpredict $P^s_2(k)$ at large $k$, and the fit is restricted
to $k < 0.15 \, {\rm Mpc}^{-1}$.",1801.07868v1
2018-02-16,Quantitative Constraints on the Reionization History from the IGM Damping Wing Signature in Two Quasars at z > 7,"During reionization, neutral hydrogen in the intergalactic medium (IGM)
imprints a damping wing absorption feature on the spectrum of high-redshift
quasars. A detection of this signature provides compelling evidence for a
significantly neutral Universe, and enables measurements of the hydrogen
neutral fraction $x_{\rm HI}(z)$ at that epoch. Obtaining reliable quantitative
constraints from this technique, however, is challenging due to stochasticity
induced by the patchy inside-out topology of reionization, degeneracies with
quasar lifetime, and the unknown unabsorbed quasar spectrum close to rest-frame
Ly$\alpha$. We combine a large-volume semi-numerical simulation of reionization
topology with 1D radiative transfer through high-resolution hydrodynamical
simulations of the high-redshift Universe to construct models of quasar
transmission spectra during reionization. Our state-of-the-art approach
captures the distribution of damping wing strengths in biased quasar halos that
should have reionized earlier, as well as the erosion of neutral gas in the
quasar environment caused by its own ionizing radiation. Combining this
detailed model with our new technique for predicting the quasar continuum and
its associated uncertainty, we introduce a Bayesian statistical method to
jointly constrain the neutral fraction of the Universe and the quasar lifetime
from individual quasar spectra. We apply this methodology to the spectra of the
two highest redshift quasars known, ULAS J1120+0641 and ULAS J1342+0928, and
measured volume-averaged neutral fractions $\langle x_{\rm HI}
\rangle(z=7.09)=0.48^{+0.26}_{-0.26}$ and $\langle x_{\rm HI}
\rangle(z=7.54)=0.60^{+0.20}_{-0.23}$ (posterior medians and 68% credible
intervals) when marginalized over quasar lifetimes of $10^3 \leq t_{\rm q} \leq
10^8$ years.",1802.06066v1
2018-02-16,Landau Damping in a strong magnetic field: Dissociation of Quarkonia,"We have investigated the effects of strong magnetic field on the properties
of quarkonia immersed in a thermal medium of quarks and gluons and studied its
quasi-free dissociation due to the Landau-damping. Thermalizing the Schwinger
propagator in the lowest Landau levels for quarks and the Feynman propagator
for gluons in real-time formalism, we have calculated the resummed retarded and
symmetric propagators, which in turn give the real and imaginary components of
dielectric permittivity, respectively. The magnetic field affects the
large-distance interaction more than the short-distance interaction, as a
result, the real part of potential becomes more attractive and the magnitude of
imaginary part too becomes larger, compared to the thermal medium in absence of
strong magnetic field. As a consequence the average size of $J/\psi$'s and
$\psi^\prime$'s are increased but $\chi_c$'s get shrunk. Similarly the magnetic
field affects the binding of $J/\psi$'s and $\chi_c$'s discriminately, i.e. it
decreases the binding of $J/\psi$ and increases for $\chi_c$. However, the
further increase in magnetic field results in the decrease of binding energies.
On contrary the magnetic field increases the width of the resonances, unless
the temperature is sufficiently high. We have finally studied how the presence
of magnetic field affects the dissolution of quarkonia in a thermal medium due
to the Landau damping, where the dissociation temperatures are found to
increase compared to the thermal medium in absence of magnetic field. However,
further increase of magnetic field decreases the dissociation temperatures. For
example, $J/\psi$'s and $\chi_c$'s are dissociated at higher temperatures at 2
$T_c$ and 1.1 $T_c$ at a magnetic field $eB \approx 6~{\rm{and}}~4~m_\pi^2$,
respectively, compared to the values 1.60 $T_c$ and 0.8 $T_c$ in the absence of
magnetic field, respectively.",1802.06874v1
2018-05-09,Amplitude and lifetime of radial modes in red giant star spectra observed by Kepler,"Context: the space-borne missions CoRoT and Kepler have provided photometric
observations of unprecedented quality. The study of solar-like oscillations
observed in red giant stars by these satellites allows a better understanding
of the different physical processes occurring in their interiors. In
particular, the study of the mode excitation and damping is a promising way to
improve our understanding of stellar physics that has, so far, been performed
only on a limited number of targets. Aims: the recent asteroseismic
characterization of the evolutionary status for a large number of red giants
allows us to study the physical processes acting in the interior of red giants
and how they are modify during stellar evolution. In this work, we aim to
obtain information on the excitation and damping of pressure modes through the
measurement of the stars' pressure mode widths and amplitudes and to analyze
how they are modified with stellar evolution. The objective is to bring
observational constraints on the modeling of the physical processes behind mode
excitation and damping. Methods: we fit the frequency spectra of red giants
with well defined evolutionary status using Lorentzians functions to derive the
pressure mode widths and amplitudes. To strengthen our conclusions, we used two
different fitting techniques. Results: pressure mode widths and amplitudes were
determined for more than 5000 red giants. With a stellar sample two orders of
magnitude larger than previous results, we confirmed that the mode width
depends on stellar evolution and varies with stellar effective temperature. In
addition, we discovered that the mode width depends on stellar mass. We also
confirmed observationally the influence of the stellar metallicity on the mode
amplitudes, as predicted by models.",1805.03690v1
2018-05-31,Impact of bias and redshift-space modelling for the halo power spectrum: Testing the effective field theory of large-scale structure,"We study the impact of different bias and redshift-space models on the halo
power spectrum, quantifying their effect by comparing the fit to a subset of
realizations taken from the WizCOLA suite. These provide simulated power
spectrum measurements between $k_{\rm min}$ = 0.03 h/Mpc and $k_{\rm max}$ =
0.29 h/Mpc, constructed using the comoving Lagrangian acceleration method. For
the bias prescription we include (i) simple linear bias; (ii) the McDonald &
Roy model and (iii) its coevolution variant introduced by Saito et al.; and
(iv) a very general model including all terms up to one-loop and corrections
from advection. For the redshift-space modelling we include the Kaiser formula
with exponential damping and the power spectrum provided by (i) tree-level
perturbation theory and (ii) the Halofit prescription; (iii) one-loop
perturbation theory, also with exponential damping; and (iv) an effective field
theory description, also at one-loop, with damping represented by the EFT
subtractions. We quantify the improvement from each layer of modelling by
measuring the typical improvement in chi-square when fitting to a member of the
simulation suite. We attempt to detect overfitting by testing for compatibility
between the best-fit power spectrum per realization and the best-fit over the
entire WizCOLA suite. For both bias and the redshift-space map we find that
increasingly permissive models yield improvements in chi-square but with
diminishing returns. The most permissive models show modest evidence for
overfitting. Accounting for model complexity using the Bayesian Information
Criterion, we argue that standard perturbation theory up to one-loop, or a
related model such as that of Taruya, Nishimichi & Saito, coupled to the
coevolution bias model, is likely to provide a good compromise for near-future
galaxy surveys operating with comparable $k_{\rm max}$.",1805.12394v3
2018-06-10,Non-damping oscillations at flaring loops,"Context. QPPs are usually detected as spatial displacements of coronal loops
in imaging observations or as periodic shifts of line properties in
spectroscopic observations. They are often applied for remote diagnostics of
magnetic fields and plasma properties on the Sun. Aims. We combine imaging and
spectroscopic measurements of available space missions, and investigate the
properties of non-damping oscillations at flaring loops. Methods. We used the
IRIS to measure the spectrum over a narrow slit. The double-component Gaussian
fitting method was used to extract the line profile of Fe XXI 1354.08 A at ""O
I"" window. The quasi-periodicity of loop oscillations were identified in the
Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected
in the line properties of Fe XXI, HXR emissions in GOES 1-8 A derivative, and
Fermi 26-50 keV. The Doppler velocity and line width oscillate in phase, while
a phase shift of about Pi/2 is detected between the Doppler velocity and peak
intensity. The amplitudes of Doppler velocity and line width oscillation are
about 2.2 km/s and 1.9 km/s, respectively, while peak intensity oscillate with
amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period
of about 155 s is identified in the Doppler velocity and peak intensity of Fe
XXI, and AIA 131 A intensity. Conclusions. The oscillations at about 40 s are
not damped significantly during the observation, it might be linked to the
global kink modes of flaring loops. The periodicity at about 155 s is most
likely a signature of recurring downflows after chromospheric evaporation along
flaring loops. The magnetic field strengths of the flaring loops are estimated
to be about 120-170 G using the MHD seismology diagnostics, which are
consistent with the magnetic field modeling results using the flux rope
insertion method.",1806.03573v1
2018-07-04,Constraints on reionisation from the z=7.5 QSO ULASJ1342+0928,"The recent detection of ULASJ1342+0928, a bright QSO at $z=7.54$, provides a
powerful probe of the ionisation state of the intervening intergalactic medium,
potentially allowing us to set strong constraints on the epoch of reionisation
(EoR). Here we quantify the presence of Ly$\alpha$ damping wing absorption from
the EoR in the spectrum of ULASJ1342+0928. Our Bayesian framework
simultaneously accounts for uncertainties on: (i) the intrinsic QSO emission
(obtained from reconstructing the Ly$\alpha$ profile from a covariance matrix
of emission lines) and (ii) the distribution of HII regions during reionisation
(obtained from three different 1.6$^3$ Gpc$^3$ simulations spanning the range
of plausible EoR morphologies). Our analysis is complementary to that in the
discovery paper (Ba\~nados et al.) and the accompanying method paper (Davies et
al.) as it focuses solely on the damping wing imprint redward of Ly$\alpha$
($1218 < \lambda < 1230$\AA), and uses a different methodology for (i) and
(ii). We recover weak evidence for damping wing absorption. Our intermediate
EoR model yields a volume-weighted neutral hydrogen fraction at $z=7.5$ of
$\bar{x}_{\rm HI} = 0.21\substack{+0.17 \\ -0.19}$ (68 per cent). The
constraints depend weakly on the EoR morphology. Our limits are lower than
those presented previously, though they are consistent at ~1-1.5$\sigma$. We
attribute this difference to: (i) a lower amplitude intrinsic Ly$\alpha$
profile obtained from our reconstruction pipeline, driven by correlations with
other high-ionisation lines in the spectrum which are relatively weak; and (ii)
only considering transmission redward of Ly$\alpha$ when computing the
likelihood, which reduces the available constraining power but makes the
results less model-dependent. Our results are consistent with previous
estimates of the EoR history, and support the picture of a moderately extended
EoR.",1807.01593v1
2018-07-04,"Stellar masses, metallicity gradients and suppressed star formation revealed in a new sample of absorption selected galaxies","Context. Absorbing galaxies are selected via the detection of characteristic
absorption lines which their gas-rich media imprint in the spectra of distant
light-beacons. The proximity of the typically faint foreground absorbing
galaxies to bright background sources makes it challenging to robustly identify
these in emission, and hence to characterise their relation to the general
galaxy population. Aims. We search for emission to confirm and characterise ten
galaxies hosting damped, metal-rich quasar absorbers at redshift z < 1.
Methods. We identify the absorbing galaxies by matching spectroscopic
absorption -and emission redshifts and from projected separations. Combining
emission-line diagnostics with existing absorption spectroscopy and photometry
of quasar-fields hosting metal-rich, damped absorbers, we compare our new
detections with reference samples and place them on scaling relations. Results.
We spectroscopically confirm seven galaxies harbouring damped absorbers (a 70%
success-rate). Our results conform to the emerging picture that neutral gas on
scales of tens of kpc in galaxies is what causes the characteristic Hi
absorption. Our key results are: (I) Absorbing galaxies with $\log _{10}
[M_\star ~(M_\odot)] \gtrsim 10$ have star formation rates that are lower than
predicted for the main sequence of star formation. (II) The distribution of
impact parameter with Hi column density and with absorption-metallicity for
absorbing galaxies at $z\sim 2-3$ extends to $z\sim 0.7$ and to lower Hi column
densities. (III) A robust mean metallicity gradient of $\langle \Gamma \rangle
= 0.022 \pm 0.001~[dex~kpc^{-1}]$. (IV) By correcting absorption metallicities
for $\langle \Gamma \rangle$ and imposing a truncation-radius at
$12~\mathrm{kpc}$, absorbing galaxies fall on top of predicted mass-metallicity
relations, with a statistically significant decrease in scatter.",1807.01755v1
2018-07-05,Stationarity and energy transfer in out-of-equilibrium systems,"We define a characteristic energy density based on the measurement of the two
first moments of the extrinsic injected power smoothed over time. Using the
stationarity, we show that this definition characterizes an energy per degrees
freedom of the intrinsic dissipation. Our framework can be applied to systems
in contact with thermostats put out of equilibrium by an external driving but
it holds also for intrinsically dissipative macroscopic systems that go at rest
when the forcing is stopped. Moreover, we are not concerned about the
fluctuations around zero of the smoothed injected power that can be extremely
rare and difficult to catch experimentally. Then we show that the
characteristic energy density we defined, reduces to the kinetic energy of a
Brownian-like particle described by a set of Langevin equations with a viscous
damping term. The particle can be either in contact with a thermostat or
intrinsically dissipative and driven by a random force. In the first case, we
recover the result obtained in the framework of the fluctuation relation but
extended to a correlated thermal noise. Our characteristic energy density is
measured in an experimental system of nonlinear waves generated by a large
shaker in a thin elastic plate. A smaller shaker attached to the moving plate
is used as a probe to measure the energy exchanged with the plate excited by
the large shaker. For both, the proportionality of our characteristic energy
density with the kinetic energy is demonstrated. It is a consequence of the
viscous damping driving the dissipation in this system. Another system with
nonlinear frictional dissipation is investigated numerically model. In this
case, our definition of energy density deduced from fluctuations of injected
power still characterizes the dissipation but is no more proportional to the
kinetic energy because the dissipative process is not a viscous damping.",1807.01856v1
2018-09-05,Nonlinear Mixed Modes in Red Giants,"Turbulent motions in the convective envelope of red giants excite a rich
spectrum of solar-like oscillation modes. Observations by CoRoT and Kepler have
shown that the mode amplitudes increase dramatically as the stars ascend the
red giant branch, i.e., as the frequency of maximum power, $\nu_\mathrm{max}$,
decreases. Most studies nonetheless assume that the modes are well described by
the linearized fluid equations. We investigate to what extent the linear
approximation is justified as a function of stellar mass $M$ and
$\nu_\mathrm{max}$, focusing on dipole mixed modes with frequency near
$\nu_\mathrm{max}$. A useful measure of a mode's nonlinearity is the product of
its radial wavenumber and its radial displacement, $k_r \xi_r$ (i.e., its
shear). We show that $k_r \xi_r \propto \nu_\mathrm{max}^{-9/2}$, implying that
the nonlinearity of mixed modes increases significantly as a star evolves. The
modes are weakly nonlinear ($k_r \xi_r > 10^{-3}$) for $\nu_\mathrm{max}
\lesssim 150 \, \mu\mathrm{Hz}$ and strongly nonlinear ($k_r \xi_r > 1$) for
$\nu_\mathrm{max} \lesssim 30 \, \mu\mathrm{Hz}$, with only a mild dependence
on $M$ over the range we consider ($1.0 - 2.0 M_\odot$). A weakly nonlinear
mixed mode can excite secondary waves in the stellar core through the
parametric instability, resulting in enhanced, but partial, damping of the
mode. By contrast, a strongly nonlinear mode breaks as it propagates through
the core and is fully damped there. Evaluating the impact of nonlinear effects
on observables such as mode amplitudes and linewidths requires large mode
network simulations. We plan to carry out such calculations in the future and
investigate whether nonlinear damping can explain why some red giants exhibit
dipole modes with unusually small amplitudes, known as depressed modes.",1809.01727v2
2018-12-14,Probing neutron star structure via f-mode oscillations and damping in dynamical spacetime models,"Gravitational wave and electromagnetic observations can provide new insights
into the nature of matter at supra-nuclear densities inside neutron stars.
Improvements in electromagnetic and gravitational wave sensing instruments
continue to enhance the accuracy with which they can measure the masses, radii,
and tidal deformability of neutron stars. These better measurements place
tighter constraints on the equation of state of cold matter above nuclear
density. In this article, we discuss a complementary approach to get insights
into the structure of neutron stars by providing a model prediction for
non-linear fundamental eigenmodes (f-modes) and their decay over time, which
are thought to be induced by time-dependent tides in neutron star binaries.
Building on pioneering studies that relate the properties of f-modes to the
structure of neutron stars, we systematically study this link in the
non-perturbative regime using models that utilize numerical relativity. Using a
suite of fully relativistic numerical relativity simulations of oscillating TOV
stars, we establish blueprints for the numerical accuracy needed to accurately
compute the frequency and damping times of f-mode oscillations, which we expect
to be a good guide for the requirements in the binary case. We show that the
resulting f-mode frequencies match established results from linear perturbation
theory, but the damping times within numerical errors depart from linear
predictions. This work lays the foundation for upcoming studies aimed at a
comparison of theoretical models of f-mode signatures in gravitational waves,
and their uncertainties with actual gravitational wave data, searching for
neutron star binaries on highly eccentric orbits, and probing neutron star
structure at high densities.",1812.06126v1
2019-05-06,Proximate Molecular Quasar Absorbers: Excess of damped H2 systems at zabs~zQSO in SDSS DR14,"We present results from a search for strong H2 absorption systems proximate
to quasars (zabs~zem) in the Sloan Digital Sky Survey (SDSS) Data Release 14.
The search is based on the Lyman-Werner band signature of damped H2 absorption
lines without any prior on the associated metal or neutral hydrogen content.
This has resulted in the detection of 81 systems with log N(H2)~19-20 located
within a few thousand km/s from the quasar. Compared to a control sample of
intervening systems, this implies an excess of proximate H2 systems by about a
factor of 4 to 5. The incidence of H2 systems increases steeply with decreasing
relative velocity, reaching an order of magnitude higher than expected from
intervening statistics at Delta_v<1000 km/s. The most striking feature of the
proximate systems compared to the intervening ones is the presence of Ly-alpha
emission in the core of the associated damped HI absorption line in about half
of the sample. This puts constraints on the relative projected sizes of the
absorbing clouds to those of the quasar line emitting regions. Using the SDSS
spectra, we estimate the HI, metal and dust content of the systems, which are
found to have typical metallicities of one tenth Solar, albeit with a large
spread among individual systems. We observe trends between the fraction of
leaking Ly-alpha emission and the relative absorber-quasar velocity as well as
with the excitation of several metal species, similar to what has been seen in
metal-selected proximate DLAs. With the help of theoretical HI-H2 transition
relations, we show that the presence of H2 helps to break the degeneracy
between density and strength of the UV field as main sources of excitation and
hence provides unique constraints on the possible origin and location of the
absorbing clouds. We suggest that most of these systems originate from galaxies
in the quasar group. [truncated]",1905.02040v1
2019-07-17,Sub-damped Lyman alpha systems in the XQ-100 survey I -- Identification and contribution to the cosmological HI budget,"Sub-damped Lyman alpha systems (subDLAs; HI column densities of
19.0<=logN(HI)<20.3) are rarely included in the cosmic HI census performed at
redshifts z>=1.5, yet are expected to contribute significantly to the overall
HI mass budget of the Universe. In this paper, we present a blindly selected
sample of 155 subDLAs found along 100 quasar sightlines (with a redshift path
length X=475) in the XQ-100 survey to investigate the contribution of subDLAs
to the HI mass density of the Universe. The impact of X-Shooter's spectral
resolution on sub-DLA identification is evaluated, and found to be sufficient
for reliably finding absorbers with logN(HI)>=18.9. We compared the
implications of searching for subDLAs solely using HI absorption versus the use
of additional metal lines to confirm the identification, and found that
metal-selection techniques would have missed 75 subDLAs. Using a
bootstrap-Monte Carlo simulation, we computed the column density distribution
function (f(N,X)) and the cosmological HI mass density of subDLAs and compared
with our previous work based on the XQ-100 damped Lyman alpha systems. We do
not find any significant redshift evolution in f(N,X) or cosmological HI mass
density for subDLAs. However, subDLAs contribute 10-20 per cent of the total
cosmological HI mass density measured at redshifts 2<z<5 (agreeing with
previous measurements), and thus have a small but significant contribution to
the HI budget of the Universe.",1907.07703v1
2019-10-28,Investigating the damping rate of phase-mixed Alfven waves,"Context: This paper investigates the effectiveness of phase mixing as a
coronal heating mechanism. A key quantity is the wave damping rate, $\gamma$,
defined as the ratio of the heating rate to the wave energy.
  Aims: We investigate whether or not laminar phase-mixed Alfv\'en waves can
have a large enough value of $\gamma$ to heat the corona. We also investigate
the degree to which the $\gamma$ of standing Alfv\'en waves which have reached
steady-state can be approximated with a relatively simple equation. Further
foci of this study are the cause of the reduction of $\gamma$ in response to
leakage of waves out of a loop, the quantity of this reduction, and how
increasing the number of excited harmonics affects $\gamma$.
  Results: We find that at observed frequencies $\gamma$ is too small to heat
the corona by approximately three orders of magnitude. Therefore, we believe
that laminar phase mixing is not a viable stand-alone heating mechanism for
coronal loops. We show that $\gamma$ is largest at resonance. We find our
simple equation provides a good estimate for the damping rate (within
approximately 10% accuracy) for resonant field lines. However, away from
resonance, the equation provides a poor estimate, predicting $\gamma$ to be
orders of magnitude too large. We find that leakage acts to reduce $\gamma$ but
plays a negligible role if $\gamma$ is of the order required to heat the
corona. If the wave energy follows a power spectrum with slope -5/3 then
$\gamma$ grows logarithmically with the number of excited harmonics. If the
number of excited harmonics is increased by much more than 100, then the
heating is mainly caused by gradients that are parallel to the field rather
than perpendicular to it. Therefore, in this case, the system is not heated
mainly by phase mixing.",1910.12510v1
2019-11-12,Self Sustained Thermally Induced Gas-Damped Oscillations of Bimetal Cantilevers with Application to the Design of a New Pyroelectric Micro Energy Harvester,"Low efficiency is the main drawback of many MEMS thermal energy harvesters.
Recently, energy harvesting micro-devices that operate using the pyroelectric
effect gained attention due to their potential superior performance. Operation
of these devices is based on the cyclic motion of a pyroelectric capacitor that
operates between a high temperature and a low temperature reservoirs. In this
paper, we investigate the dynamics of oscillations of a pyroelectric capacitor
self sustained by thermally actuated bimetal micro-cantilevers, a topic which
is so far under investigated. In addition to highlighting key thermodynamic
aspects of the operation, we explore conditions for self-sustained oscillations
and discuss the viability of operation at the mechanical resonance frequency.
The analysis is presented for a new design inspired by the device proposed in
Refs.\cite{2011,2012}, where in contrast, our proposed design boasts the
following features: The pyroelectric capacitor remains parallel to the heat
reservoirs, by virtue of its symmetric support by two bimetallic cantilever
beams; In addition, the cyclic operation of the device does not require
physical contact, thus lowering the risk of mechanical failure; To adjust the
damping force imparted by the surrounding gas, the thermal reservoirs are
equipped with trenches. To study the dynamic operation of the device, we
developed a physically based reduced order, yet accurate, model that accounts
for the heat transfer between and within the different components, and for the
various forces including the gas damping force. The model is embedded within an
optimization algorithm to produce optimal designs over the range 26-38 C of
temperature difference between the two reservoirs. The corresponding range of
harvested power density is 0.4-0.65 mW/cm2.",1911.04823v1
2020-03-01,Positivity and nonadditivity of quantum capacities using generalized erasure channels,"We consider various forms of a process, which we call {\em gluing}, for
combining two or more complementary quantum channel pairs
$(\mathcal{B},\mathcal{C})$ to form a composite. One type of gluing combines a
perfect channel with a second channel to produce a \emph{generalized erasure
channel} pair $(\mathcal{B}_g,\mathcal{C}_g)$. We consider two cases in which
the second channel is (i) an amplitude-damping, or (ii) a phase-damping qubit
channel; (ii) is the \emph{dephrasure channel} of Leditzky et al. For both (i)
and (ii), $(\mathcal{B}_g,\mathcal{C}_g)$ depends on the damping parameter
$0\leq p\leq 1$ and a parameter $0 \leq \lambda \leq 1$ that characterizes the
gluing process. In both cases we study $Q^{(1)}(\mathcal{B}_g)$ and
$Q^{(1)}(\mathcal{C}_g)$, where $Q^{(1)}$ is the channel coherent information,
and determine the regions in the $(p,\lambda)$ plane where each is zero or
positive, confirming previous results for (ii). A somewhat surprising result
for which we lack any intuitive explanation is that $Q^{(1)}(\mathcal{C}_g)$ is
zero for $\lambda \leq 1/2$ when $p=0$, but is strictly positive (though
perhaps extremely small) for all values of $\lambda> 0$ when $p$ is positive by
even the smallest amount. In addition we study the nonadditivity of
$Q^{(1)}(\mathcal{B}_g)$ for two identical channels in parallel. It occurs in a
well-defined region of the $(p,\lambda)$ plane in case (i). In case (ii) we
have extended previous results for the dephrasure channel without, however,
identifying the full range of $(p,\lambda)$ values where nonadditivity occurs.
Again, an intuitive explanation is lacking.",2003.00583v2
2020-04-22,A Significantly Neutral Intergalactic Medium Around the Luminous z=7 Quasar J0252-0503,"Luminous $z\ge7$ quasars provide direct probes of the evolution of
supermassive black holes (SMBHs) and the intergalactic medium (IGM) during the
epoch of reionization (EoR). The Ly$\alpha$ damping wing absorption imprinted
by neutral hydrogen in the IGM can be detected in a single EoR quasar spectrum,
allowing the measurement of the IGM neutral fraction towards that line of
sight. However, damping wing features have only been detected in two $z>7$
quasars in previous studies. In this paper, we present new high quality optical
and near-infrared spectroscopy of the $z=7.00$ quasar DES J025216.64--050331.8
obtained with Keck/NIRES and Gemini/GMOS. By using the MgII single-epoch virial
method, we find that it hosts a $\rm (1.39\pm0.16) \times10^{9} ~M_\odot$ SMBH
accreting at an Eddington ratio of $\lambda_{\rm Edd}=0.7\pm0.1$, consistent
with the values seen in other luminous $z\sim 7$ quasars. Furthermore, the
Ly$\alpha$ region of the spectrum exhibits a strong damping wing absorption
feature. The lack of associated metal absorption in the quasar spectrum
indicates that this absorption is imprinted by a neutral IGM. Using a
state-of-the-art model developed by Davies et al., we measure a volume-averaged
neutral hydrogen fraction at $z=7$ of $\langle x_{\rm HI} \rangle =
0.70^{+0.20}_{-0.23} (^{+0.28}_{-0.48})$ within 68% (95%) confidence intervals
when marginalizing over quasar lifetimes of $10^3\le t_{\rm Q}\le10^8$ yr. This
is the highest IGM neutral fraction yet measured using reionization-era quasar
spectra.",2004.10877v1
2020-09-28,Comparison of proton shower developments in the BGO calorimeter of the Dark Matter Particle Explorer between GEANT4 and FLUKA simulations,"The DArk Matter Particle Explorer (DAMPE) is a satellite-borne detector for
high-energy cosmic rays and $\gamma$-rays. To fully understand the detector
performance and obtain reliable physical results, extensive simulations of the
detector are necessary. The simulations are particularly important for the data
analysis of cosmic ray nuclei, which relies closely on the hadronic and nuclear
interactions of particles in the detector material. Widely adopted simulation
softwares include the GEANT4 and FLUKA, both of which have been implemented for
the DAMPE simulation tool. Here we describe the simulation tool of DAMPE and
compare the results of proton shower properties in the calorimeter from the two
simulation softwares. Such a comparison gives an estimate of the most
significant uncertainties of our proton spectral analysis.",2009.13036v1
2021-01-19,Sub-damped Lyman alpha systems in the XQ-100 survey II -- Chemical evolution at 2.4<z<4.3,"We present the measured gas-phase metal column densities in 155 sub-damped
Lyman alpha systems (subDLAs) with the aim to investigate the contribution of
subDLAs to the chemical evolution of the Universe. The sample was identified
within the absorber-blind XQ-100 quasar spectroscopic survey over the redshift
range 2.4<=z<=4.3. Using all available column densities of the ionic species
investigated (mainly CIV, SiII, MgII, SiIV, AlII, FeII, CII, and OI; in order
of decreasing detection frequency), we estimate the ionization-corrected
gas-phase metallicity of each system using Markov Chain Monte Carlo techniques
to explore a large grid of Cloudy ionization models. Without accounting for
ionization and dust depletion effects, we find that the HI-weighted gas-phase
metallicity evolution of subDLAs are consistent with damped Lyman alpha systems
(DLAs). When ionization corrections are included, subDLAs are systematically
more metal-poor than DLAs (between ~0.5 sigma and ~3 sigma significance) by up
to ~1.0 dex over the redshift range 3<=z<=4.3. The correlation of gas-phase
[Si/Fe] with metallicity in subDLAs appears to be consistent with that of DLAs,
suggesting that the two classes of absorbers have a similar relative dust
depletion pattern. As previously seen for Lyman limit systems, the gas-phase
[C/O] in subDLAs remains constantly solar for all metallicities indicating that
both subDLAs and Lyman limit systems could trace carbon-rich ejecta,
potentially in circumgalactic environments.",2101.07821v1
2021-02-01,On a Possible Solution to the Tidal Realignment Problem for Hot Jupiters,"Hot stars with hot Jupiters have a wide range of obliquities, while cool
stars with hot Jupiters tend to have low obliquities. An enticing explanation
for this pattern is tidal realignment of the cool host stars, although this
explanation assumes that obliquity damping occurs faster than orbital decay, an
assumption that needs further exploration. Here we revisit this tidal
realignment problem, building on previous work identifying a low-frequency
component of the time-variable tidal potential that affects the obliquity but
not the orbital separation. We adopt a recent empirically-based model for the
stellar tidal quality factor and its sharp increase with forcing frequency.
This leads to enhanced dissipation at low frequencies, and efficient obliquity
damping. We model the tidal evolution of 46 observed hot Jupiters orbiting cool
stars. A key parameter is the stellar age, which we determine in a homogeneous
manner for the sample, taking advantage of Gaia DR2 data. We explore a variety
of tidal histories and futures for each system, finding in most cases that the
stellar obliquity is successfully damped before the planet is destroyed. A
testable prediction of our model is that hot-Jupiter hosts with orbital periods
shorter than 2--3 days should have obliquities much smaller than $1^\circ$.
With the possible exception of WASP-19b, the predicted future lifetimes of the
planets range from $10^8$\,yr to more than $10^{10}$\,yr. Thus, our model
implies that these hot Jupiters are probably not in immediate danger of being
devoured by their host stars while they are on the main sequence.",2102.01081v2
2021-02-22,Slow-Mode Magnetoacoustic Waves in Coronal Loops,"Rapidly decaying long-period oscillations often occur in hot coronal loops of
active regions associated with small (or micro-) flares. This kind of wave
activity was first discovered with the SOHO/SUMER spectrometer from Doppler
velocity measurements of hot emission lines, thus also often called ""SUMER""
oscillations. They were mainly interpreted as global (or fundamental mode)
standing slow magnetoacoustic waves. In addition, increasing evidence has
suggested that the decaying harmonic type of pulsations detected in light
curves of solar and stellar flares are likely caused by standing slow-mode
waves. The study of slow magnetoacoustic waves in coronal loops has become a
topic of particular interest in connection with coronal seismology. We review
recent results from SDO/AIA and Hinode/XRT observations that have detected both
standing and reflected intensity oscillations in hot flaring loops showing the
physical properties (e.g., oscillation periods, decay times, and triggers) in
accord with the SUMER oscillations. We also review recent advances in theory
and numerical modeling of slow-mode waves focusing on the wave excitation and
damping mechanisms. MHD simulations in 1D, 2D and 3D have been dedicated to
understanding the physical conditions for the generation of a reflected
propagating or a standing wave by impulsive heating. Various damping mechanisms
and their analysis methods are summarized. Calculations based on linear theory
suggest that the non-ideal MHD effects such as thermal conduction, compressive
viscosity, and optically thin radiation may dominate in damping of slow-mode
waves in coronal loops of different physical conditions. Finally, an overview
is given of several important seismological applications such as determination
of transport coefficients and heating function.",2102.11376v1
2021-04-24,Compressive oscillations in hot coronal loops: Are sloshing oscillations and standing slow waves independent?,"Employing high-resolution EUV imaging observations from SDO/AIA, we analyse a
compressive plasma oscillation in a hot coronal loop triggered by a C-class
flare near one of its foot points as first studied by Kumar et al. We
investigate the oscillation properties in both the 131{\,}{\AA} and 94{\,}{\AA}
channels and find that what appears as a pure sloshing oscillation in the
131{\,}{\AA} channel actually transforms into a standing wave in the
94{\,}{\AA} channel at a later time. This is the first clear evidence of such
transformation confirming the results of a recent numerical study which
suggests that these two oscillations are not independent phenomena. We
introduce a new analytical expression to properly fit the sloshing phase of an
oscillation and extract the oscillation properties. For the AIA 131{\,}{\AA}
channel, the obtained oscillation period and damping time are 608$\pm$4{\,}s
and 431$\pm$20{\,}s, respectively during the sloshing phase. The corresponding
values for the AIA 94{\,}{\AA} channel are 617$\pm$3{\,}s and 828$\pm$50{\,}s.
During the standing phase that is observed only in the AIA 94{\,}{\AA} channel,
the oscillation period and damping time have increased to 791$\pm$5{\,}s and
1598$\pm$138{\,}s, respectively. The plasma temperature obtained from the DEM
analysis indicates substantial cooling of the plasma during the oscillation.
Considering this, we show that the observed oscillation properties and the
associated changes are compatible with damping due to thermal conduction. We
further demonstrate that the absence of a standing phase in the 131{\,}{\AA}
channel is a consequence of cooling plasma besides the faster decay of
oscillation in this channel.",2104.12038v1
2021-08-05,Small-scale clumping at recombination and the Hubble tension,"Despite the success of the standard $\Lambda$CDM model of cosmology, recent
data improvements have made tensions emerge between low- and high-redshift
observables, most importantly in determinations of the Hubble constant $H_0$
and the (rescaled) clustering amplitude $S_8$. The high-redshift data, from the
cosmic microwave background (CMB), crucially relies on recombination physics
for its interpretation. Here we study how small-scale baryon inhomogeneities
(i.e., clumping) can affect recombination and consider whether they can relieve
both the $H_0$ and $S_8$ tensions. Such small-scale clumping, which may be
caused by primordial magnetic fields or baryon isocurvature below kpc scales,
enhances the recombination rate even when averaged over larger scales, shifting
recombination to earlier times. We introduce a flexible clumping model,
parametrized via three spatial zones with free densities and volume fractions,
and use it to study the impact of clumping on CMB observables. We find that
increasing $H_0$ decreases both $\Omega_m$ and $S_8$, which alleviates the
$S_8$ tension. On the other hand, the shift in $\Omega_m$ is disfavored by the
low-$z$ baryon-acoustic-oscillations measurements. We find that the clumping
parameters that can change the CMB sound horizon enough to explain the $H_0$
tension also alter the damping tail, so they are disfavored by current Planck
2018 data. We test how the CMB damping-tail information rules out changes to
recombination by first removing $\ell>1000$ multipoles in Planck data, where we
find that clumping could resolve the $H_0$ tension. Furthermore, we make
predictions for future CMB experiments, as their improved damping-tail
precision can better constrain departures from standard recombination. Both the
Simons Observatory and CMB-S4 will provide decisive evidence for or against
clumping as a resolution to the $H_0$ tension.",2108.02747v3
2021-08-09,Synchronization of Power Systems under Stochastic Disturbances,"The synchronization of power generators is an important condition for the
proper functioning of a power system, in which the fluctuations in frequency
and the phase angle differences between the generators are sufficiently small
when subjected to stochastic disturbances. Serious fluctuations can prompt
desynchronization, which may lead to widespread power outages. Here, we model
the stochastic disturbance by a Brownian motion process in the linearized
system of the non-linear power systems and characterize the fluctuations by the
variances of the frequency and the phase angle differences in the invariant
probability distribution. We propose a method to calculate the variances of the
frequency and the phase angle differences. For the system with uniform
disturbance-damping ratio, we derive explicit formulas for the variance
matrices of the frequency and the phase angle differences. It is shown that the
fluctuation of the frequency at a node depends on the disturbance-damping ratio
and the inertia at this node only, and the fluctuations of the phase angle
differences in the lines are independent of the inertia. In particular, the
synchronization stability is related to the cycle space of the network. We
reveal the influences of constructing new lines and increasing capacities of
lines on the fluctuations in the phase angle differences in the existing lines.
The results are illustrated for the transmission system of Shandong Province of
China. For the system with non-uniform disturbance-damping ratio, we further
obtain bounds of the variance matrices.",2108.04667v2
2021-10-12,Two-body collapse model for self-gravitating flow of dark matter and generalized stable clustering hypothesis for pairwise velocity,"Analytical tools are extremely hard to find for non-linear gravitational
collpase. Only a few simple but powerful tools exist so far. Two examples are
the spherical collapse model (SCM) and stable clustering hypothesis (SCH). We
present a new analytical tool, a two-body collapse model (TBCM), that plays the
same fundamental role as harmonic oscillator in dynamics. For convenience, TBCM
is formulated for gravity with any potential exponent $n$ in a static
background with a fixed damping ($n$=-1 for Newtonian gravity). The competition
between gravity, expanding background (or damping), and angular momentum
classifies two-body collapse into: 1) free fall collapse, where free fall time
is greater if same system starts to collapse at earlier time; 2) equilibrium
collapse that persists longer in time, whose perturbative solutions lead to
power-law evolution of system energy and momentum. Two critical values
$\beta_{s1}=1$ and $\beta_{s2}=1/3\pi$ are identified that quantifies the
competition between damping and gravity. Value $\beta_{s2}$ only exists for
discrete values of potential exponent $n=(2-6m)/(1+3m)=$ -1,-10/7... for
integer $m$. Critical density ratio ($\Delta_c=18\pi^2$) is obtained for $n$=-1
that is consistent with SCM. TBCM predicts angular velocity $\propto Hr^{-3/2}$
for two-body system of size $r$. The isothermal density is a result of
extremely fast mass accretion. TBCM is able to demonstrate SCH, i.e. mean
pairwise velocity (first moment) $\langle\Delta u\rangle=-Hr$. A generalized
SCH is developed for higher order moments $\langle\Delta
u^{2m+1}\rangle=-(2m+1)\langle\Delta u^{2m}\rangle Hr$ that is validated by
N-body simulation. Energy evolution in TBCM is independent of particle mass and
energy equipartition does not apply. TBCM can be considered as a non-radial
SCM. Both models predict the same critical density ratio, while TBCM contains
much richer information.",2110.05784v2
2021-10-25,Capillary gravity water waves linearized at monotone shear flows: eigenvalues and inviscid damping,"This paper is concerned with the eigenvalues and linear inviscid damping of
the 2D capillary gravity water waves of finite depth $x_2\in(-h,0)$ linearized
at a monotone shear flow $U(x_2)$. Unlike the linearized Euler equation in a
fixed channel where eigenvalues exist only in low horizontal wave number $k$,
we first prove the linearized capillary gravity wave has two branches of
eigenvalues $-ikc^\pm(k)$, where the wave speeds $c^\pm(k)=O(\sqrt{|k|})$ for
$|k|\gg1$ have the same asymptotics as the those of the linear irrotational
capillary gravity waves. Under the additional assumption of $U""\ne0$, we obtain
the complete continuation of these two branches, which are all the eigenvalues
in this (and some other) case(s). Particularly $-ikc^-(k)$ could bifurcate into
unstable eigenvalues at $c^-(k)=U(-h)$. The bifurcation of unstable eigenvalues
from inflection values of $U$ is also proved. Assuming no singular modes, i.e.
no embedded eigenvalues for any wave number $k$, linear solutions
$(v(t,x),\eta(t,x_1))$ are studieded in both periodic-in-$x_1$ and $x_1\in R$
cases, where $v$ is the velocity and $\eta$ the surface profile. Solutions can
be split into $(v^p,\eta^p)$ and $(v^c,\eta^c)$ whose $k$-th Fourier mode in
$x_1$ correspond to the eigenvalues and the continuous spectra of wave number
$k$, respectively. The component $(v^p,\eta^p)$ is governed by a (possibly
unstable) dispersion relation given by the eigenvalues, which are simply
$k\to-ikc^\pm(k)$ in the case of $x_1\in R$. The other component $(v^c,\eta^c)$
satisfies the inviscid damping as fast as
$|v_1^c|_{L_x^2},|\eta^c|_{L_x^2}=O(|t|^{-1})$ and $|v_2^c|_{L_x^2}=O(t^{-2})$
as $|t|\gg1$. Additional decay of $tv_1^c,t^2v_2^c$ in $L_x^2L_t^q$,
$q\in(2,\infty]$, is obtained after leading asymptotic terms are removed, which
are in the forms of $t$-dependent translations in $x_1$ of certain functions of
$x$.",2110.12604v3
2021-11-22,Recent Developments in Quantum-Circuit Refrigeration,"We review the recent progress in direct active cooling of the
quantum-electric degrees freedom in engineered circuits, or quantum-circuit
refrigeration. In 2017, the invention of a quantum-circuit refrigerator (QCR)
based on photon-assisted tunneling of quasiparticles through a
normal-metal--insulator--superconductor junction inspired a series of
experimental studies demonstrating the following main properties: (i) the
direct-current (dc) bias voltage of the junction can change the QCR-induced
damping rate of a superconducting microwave resonator by orders of magnitude
and give rise to non-trivial Lamb shifts, (ii) the damping rate can be
controlled in nanosecond time scales, and (iii) the dc bias can be replaced by
a microwave excitation, the amplitude of which controls the induced damping
rate. Theoretically, it is predicted that state-of-the-art superconducting
resonators and qubits can be reset with an infidelity lower than $10^{-4}$ in
tens of nanoseconds using experimentally feasible parameters. A QCR-equipped
resonator has also been demonstrated as an incoherent photon source with an
output temperature above one kelvin yet operating at millikelvin. This source
has been used to calibrate cryogenic amplification chains. In the future, the
QCR may be experimentally used to quickly reset superconducting qubits, and
hence assist in the great challenge of building a practical quantum computer.",2111.11234v1
2021-12-01,Damped Ly-alpha Absorbers in Star-forming Galaxies at z < 0.15 Detected with the Hubble Space Telescope and Implications for Galaxy Evolution,"We report {\it HST} COS spectroscopy of 10 quasars with foreground
star-forming galaxies at 0.02$<$$z$$<$ 0.14 within impact parameters of
$\sim$1-7 kpc. We detect damped/sub-damped Ly$\alpha$ absorption in 100$\%$ of
cases where no higher-redshift Lyman-limit systems extinguish the flux at the
expected wavelength of Ly$\alpha$ absorption, obtaining the largest targeted
sample of DLA/sub-DLAs in low-redshift galaxies. We present absorption
measurements of neutral hydrogen and metals. Additionally, we present GBT 21-cm
emission measurements for 5 of the galaxies (including 2 detections). Combining
our sample with the literature, we construct a sample of 115 galaxies
associated with DLA/sub-DLAs spanning 0$<$$z$$<$4.4, and examine trends between
gas and stellar properties, and with redshift. The H~I column density is
anti-correlated with impact parameter and stellar mass. More massive galaxies
appear to have gas-rich regions out to larger distances. The specific SFR
(sSFR) of absorbing galaxies increases with redshift and decreases with
$M^{\ast}$, consistent with evolution of the star-formation main sequence
(SFMS). However, $\sim$20$\%$ of absorbing galaxies lie below the SFMS,
indicating that some DLA/sub-DLAs trace galaxies with longer-than-typical
gas-depletion time-scales. Most DLA/sub-DLA galaxies with 21-cm emission have
higher H I masses than typical galaxies with comparable $M^{\ast}$. High
$M_{\rm H I}/M^{\ast}$ ratios and high sSFRs in DLA/sub-DLA galaxies with
$M^{\ast}$$<$$10^{9}$$M_{\odot}$ suggest these galaxies may be gas-rich because
of recent gas accretion rather than inefficient star formation. Our study
demonstrates the power of absorption and emission studies of DLA/sub-DLA
galaxies for extending galaxy-evolution studies to previously under-explored
regimes of low $M^{\ast}$ and low SFR.",2112.00870v1
2022-01-06,Parameter-free quantum hydrodynamic theory for plasmonics: Electron density-dependent damping rate and diffusion coefficient,"Plasmonics is a rapid growing field, which has enabled both fundamental
science and inventions of various quantum optoelectronic devices. An accurate
and efficient method to calculate the optical response of metallic structures
with feature size in the nanoscale plays an important role. Quantum
hydrodynamic theory (QHT) provides an efficient description of the
free-electron gas, where quantum effects of nonlocality and spill-out are taken
into account. In this work, we introduce a general QHT that includes diffusion
to account for the broadening, which is a key problem in practical applications
of surface plasmon. We will introduce a density-dependent diffusion coefficient
to give very accurate linewidth. It is a self-consistent method, in which both
the ground and excited states are solved by using the same energy functional,
with the kinetic energy described by the Thomas-Fermi and von Weizs\""{a}cker
(vW) formalisms. In addition, our QHT method is stable by introduction of an
electron density-dependent damping rate. For sodium nanosphere of various
sizes, the plasmon energy and broadening by our QHT method are in excellent
agreement with those by density functional theory and Kreibig formula. By
applying our QHT method to sodium jellium nanorods, we clearly show that our
method enables a parameter-free simulation, i.e. without resorting to any
empirical parameter, such as size-dependent damping rate and diffusing
coefficient. It is found that there exists a perfect linear relation between
the resonance wavelength and aspect radio. The width decreases with increasing
aspect ratio and height. The calculations show that our QHT method provides an
explicit and unified way to account for size-dependent frequency shifts and
broadening of arbitrarily shaped geometries. It is reliable and robust with
great predicability, and hence provides a general and efficient platform to
study plasmonics.",2201.03426v3
2022-01-12,Neutrino effective potential and damping in a fermion and scalar background in the resonance region,"We consider the propagation of a neutrino or an antineutrino in a medium
composed of fermions $f$ and scalars $\phi$ interacting via a Yukawa-type
coupling of the form $\bar f\nu\phi$, for neutrino energies at which the
processes like $\nu + \phi \leftrightarrow f$ or $\nu + \bar f \leftrightarrow
\bar\phi$, and the corresponding ones for the antineutrino, are kinematically
accessible. The relevant energy values are around $|m^2_\phi - m^2_f|/2m_\phi$
or $|m^2_\phi - m^2_f|/2m_f$, where $m_\phi$ and $m_f$ are the masses of $\phi$
and $f$, respectively. We refer to either one of these regions as a resonance
energy range. Near these points, the one-loop formula for the neutrino
self-energy has a singularity. From a technical point of view, that feature is
indicative that the self-energy acquires an imaginary part, which is associated
with damping effects and cannot be neglected, while the integral formula for
the real part must be evaluated using the principal value of the integral. We
carry out the calculations explicitly for some cases that allow us to give
analytic results. Writing the dispersion relation in the form $\omega = \kappa
+ V_{\text{eff}} - i\gamma/2$, we give the explicit formula for
$V_{\text{eff}}$ and $\gamma$ for the cases considered. When the neutrino
energy is either much larger or much smaller than the resonance energy,
$V_{\text{eff}}$ reduces to the effective potential that has been already
determined in the literature in the high or low momentum regime, respectively.
The virtue of the formula we give for $V_{\text{eff}}$ is that it is valid also
in the \emph{resonance energy range}, which is outside the two limits
mentioned. As a guide to possible applications we give the relevant formulas
for $V_{\text{eff}}$ and $\gamma$, and consider the solution to the oscillation
equations including the damping term, in a simple two-generation case.",2201.04661v2
2022-01-19,Transverse Coronal-Loop Oscillations Induced by the Non-radial Eruption of a Magnetic Flux Rope,"We investigate the transverse coronal-loop oscillations induced by the
eruption of a prominence-carrying flux rope on 7 December 2012. The flux rope
originating from NOAA Active Region (AR) 11621 was observed in EUV wavelengths
by the SDO/AIA and in H$\alpha$ line center by the ground-based telescope at
the BBSO. The early evolution of the flux rope is divided into two steps: a
slow rise phase at a speed of $\approx$230\,km\,s$^{-1}$ and a fast rise phase
at a speed of $\approx$706\,km\,s$^{-1}$. The eruption generates a C5.8 flare
and the onset of the fast rise is consistent with the HXR peak time of the
flare. The embedded prominence has a lower speed of $\approx$452\,km\,s$^{-1}$.
During the early eruption of the flux rope, the nearby coronal loops are
disturbed and experience independent kink-mode oscillations in the horizontal
and vertical directions. The oscillation in the horizontal direction has an
initial amplitude of $\approx$3.1\,Mm, a period of $\approx$294\,seconds, and a
damping time of $\approx$645\,seconds. It is most striking in 171\,{\AA} and
lasts for three to four cycles. The oscillations in the vertical directions are
observed mainly in 171, 193, and 211\,{\AA}. The initial amplitudes lie in the
range of 3.4\,--\,5.2\,Mm, with an average value of 4.5\,Mm. The periods are
between 407\,seconds and 441\,seconds, with an average value of 423\,seconds.
The oscillations are damping and last for nearly four cycles. The damping times
lie in the range of 570\,--\,1012\,seconds, with an average value of
741\,seconds. Assuming a semi-circular shape of the vertically oscillating
loops, we calculate the loop lengths according to their heights. Using the
observed periods, we carry out coronal seismology and estimate the internal
Alfv\'{e}n speeds (988\,--\,1145\,km\,s$^{-1}$) and the magnetic-field
strengths (12\,--\,43\,G) of the oscillating loops.",2201.07389v1
2022-03-16,Snowmass Whitepaper AF6: Plasma-Based Particle Sources,"High-brightness beams generated by particle sources based on advanced
accelerator concepts have the potential to become an essential part of future
accelerator technology. High-gradient accelerators can generate and rapidly
accelerate particle beams to relativistic energies while minimizing
irreversible detrimental effects to the beam brightness that occur at low beam
energies. Due to the high accelerating gradients, these novel accelerators are
also significantly more compact than conventional technology. The beam
parameters of these particle sources are largely determined by the injection
and subsequent acceleration processes. While there has been significant
progress crucial parameters that are required for a future collider or more
near-term applications, including X-ray free-electron lasers (XFELs), such as a
sufficiently small energy spread and small emittance for bunches with a high
charge and at high pulse repetition rate. Major research and development
efforts are required to realize these approaches for a front-end injector for a
future collider in order to address these limitations. In particular, this
includes methods to control and manipulate the phase-space and spin
degrees-of-freedom of ultrashort LWFA electron bunches with high accuracy,
methods that increase the laser-to-electron beam efficiency and increased
repetition rate. This also includes the development of high-resolution
diagnostics, such as full 6D phase-space measurements, beam polarimetry and
high-fidelity simulation tools. A further increase in beam luminosity can be
achieve through emittance damping. For future colliders, the damping rings
might be replaced by a substantially more compact plasma-based approach. Here,
plasma wigglers are used to achieve similar damping performance but over a two
orders of magnitude reduced length.",2203.08379v2
2022-04-04,Staring at the Shadows of Archaic Galaxies: Damped Ly$α$ and Metal Absorbers toward a Young $z \sim 6$ Weak-line Quasar,"We characterize the Ly$\alpha$ halo and absorption systems toward PSO
J083+11, a unique $z=6.3401$ weak-line quasar, using Gemini/GNIRS,
Magellan/FIRE, and VLT/MUSE data. Strong absorptions by hydrogen and several
metal lines (e.g., CII, MgII, and OI) are discovered in the spectrum, which
indicates the presence of: (i) a proximate sub-damped Ly$\alpha$ (sub-DLA)
system at $z=6.314$ and (ii) a MgII absorber at $z=2.2305$. To describe the
observed damping wing signal, we model the Ly$\alpha$ absorption with a
combination of a sub-DLA with the neutral hydrogen column density of $\log
N_\mathrm{HI} = 20.03 \pm 0.30$ cm$^{-2}$ and absorption from the intergalactic
medium with a neutral fraction of around 10 percent. The sub-DLA toward PSO
J083+11 has an abundance ratio of [C/O] $=-0.04 \pm 0.33$ and metallicity of
[O/H] $=-2.19 \pm 0.44$, similar to those of low-redshift metal-poor DLAs.
These measurements suggest that the sub-DLA might truncate PSO J083+11's
proximity zone size and complicate the quasar lifetime measurement. However,
this quasar shows no sign of a Ly$\alpha$ halo in the MUSE data cube, where the
estimated $1\sigma$ limit of surface brightness is $2.76 \times 10^{-18}$ erg
s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ at aperture size of 1 arcsecond, or equivalent
to a Ly$\alpha$ luminosity of $\leq 43.46$ erg s$^{-1}$. This non-detection,
while being only weak independent evidence on its own, is at least consistent
with a young quasar scenario, as expected for a quasar with a short accretion
timescale.",2204.01245v2
2022-04-28,Viscous inertial modes on a differentially rotating sphere: Comparison with solar observations,"In a previous paper we studied the effect of latitudinal rotation on solar
equatorial Rossby modes in the beta-plane approximation. Since then, a rich
spectrum of inertial modes has been observed on the Sun, which is not limited
to the equatorial Rossby modes and includes high-latitude modes.
  Here we extend the computation of toroidal modes in 2D to spherical geometry,
using realistic solar differential rotation and including viscous damping. The
aim is to compare the computed mode spectra with the observations and to study
mode stability.
  At fixed radius, we solve the eigenvalue problem numerically using a
spherical harmonics decomposition of the velocity stream function. Due to the
presence of viscous critical layers, the spectrum consists of four different
families: Rossby modes, high-latitude modes, critical-latitude modes, and
strongly damped modes. For each longitudinal wavenumber m<4, up to three
Rossby-like modes are present on the sphere, in contrast to the equatorial beta
plane where only the equatorial Rossby mode is present. The least damped modes
in the model have eigenfrequencies and eigenfunctions that resemble the
observed modes; the comparison improves when the radius is taken in the lower
half of the convection zone. For radii above 0.75R and Ekman numbers E<10^{-4},
at least one mode is unstable. For either m=1 or m=2, up to two Rossby modes
are unstable when the radial dependence of the Ekman number follows a quenched
diffusivity model (E=2. 10^{-5} at the base of the convection zone). For m=3,
up to two Rossby modes can be unstable, including the equatorial Rossby mode.
  Although the 2D model discussed here is highly simplified, the spectrum of
toroidal modes appears to include many of the observed solar inertial modes.
The self-excited modes in the model have frequencies close to those of the
observed modes with the largest amplitudes.",2204.13412v1
2022-05-29,Modeling the Dynamics of the Coronavirus SARS-CoV-2 Pandemic using Modified SIR Model with the 'Damped-Oscillator' Dynamics of the Effective Reproduction Number,"The COVID-19 pandemic has been a great catastrophe that upended human lives
and caused millions of deaths all over the world. The rapid spread of the
virus, with its early-stage exponential growth and subsequent 'waves', caught
many medical professionals and decision-makers unprepared. Even though
epidemiological models have been known for almost a century (since the 'Spanish
Influenza' pandemic of 1918-20), the real-life spread of the SARS-CoV-2 virus
often confounded the modelers. While the general framework of epidemiological
models like SEIR (susceptible-exposed-infected-recovered) or SIR
(susceptible-exposed-infected) was not in question, the behavior of model
parameters turned out to be unpredictable and complicated. In particular, while
the 'basic' reproduction number, R0, can be considered a constant (for the
original SARS-CoV-2 virus, prior to the emergence of variants, R0 is between
2.5 and 3.0), the 'effective' reproduction number, R(t), was a complex function
of time, influenced by human behavior in response to the pandemic (e.g.,
masking, lockdowns, transition to remote work, etc.) To better understand these
phenomena, we model the first year of the pandemic (between February 2020 and
February 2021) for a number of localities (fifty US states, as well as several
countries) using a simple SIR model. We show that the evolution of the pandemic
can be described quite successfully by assuming that R(t) behaves in a
'viscoelastic' manner, as a sum of two or three 'damped oscillators' with
different natural frequencies and damping coefficients. These oscillators
likely correspond to different sub-populations having different reactions to
proposed mitigation measures. The proposed approach can offer future data
modelers new ways to fit the reproduction number evolution with time (as
compared to the purely data-driven approaches most prevalent today).",2205.14747v1
2022-07-27,Determination of Thickness-dependent Damping Constant and Plasma Frequency for Ultrathin Ag and Au Films: Nanoscale Dielectric Function,"There is an ever increasing interest in the development of plasmonic 2D
nanomaterials, with widespread applications in optoelectronics, high resolution
microscopy, imaging and sensing, among others. With the current ability of
ultrathin noble metal film deposition down to a few monolayers in thickness,
there is a need for an analytical expression of the thickness dependent complex
dielectric function for predicting optical properties for arbitrary
thicknesses. The free and bound electron contributions to the dielectric
function are dealt with independently, since their influences affect separate
wavelengths ranges. The former is dealt within the Drude model framework for
large wavelengths with appropriately addressed damping constant and plasma
frequency parameters to account for thickness dependence. Applying our
previously developed method, we determine these parameters for specific film
thicknesses, based on refractive index experimental values for Ag and Au thin
films. Fitting separately each one of these parameters allowed us to find an
analytical expression for their dependence on arbitrary film thickness and
consequently for the free electron contribution. Concerning bound electrons, it
is seen that its contribution for small wavelengths is the same for all
analyzed thicknesses and may be set equal to the bulk bound contribution.
Taking all these facts into account, the complex dielectric function can be
rewritten analytically, in terms of the bulk dielectric function plus
corrective film thickness dependent terms. In particular, the fitting process
for the damping constant allows us to determine that the electron scattering at
the film boundary is mainly diffusive (inelastic) for both silver and gold thin
films. It is also shown that, in accordance with theoretical studies, plasma
frequency shows a red shift as the film thickness decreases.",2207.13580v1
2022-10-18,Magnetohydrodynamic instabilities in a self-gravitating rotating cosmic plasma,"The generation of magnetohydrodynamic (MHD) waves and their instabilities are
studied in galactic gaseous rotating plasmas with the effects of the magnetic
field, the self gravity, the diffusion-convection of cosmic rays as well as the
gas and cosmic-ray pressures. The coupling of the Jeans, Alfv{\'e}n and
magnetosonic waves, and the conditions of damping or instability are studied in
three different cases, namely when the propagation direction is perpendicular,
parallel and oblique to the static magnetic field, and are shown to be
significantly modified by the effects of the Coriolis force due to the rotation
of cosmic fluids and the cosmic-ray diffusion. The coupled modes can be damped
or anti-damped depending on the wave number is above or below the Jeans
critical wave number that is reduced by the effects of the Coriolis force and
the cosmic-ray pressure. It is found that the deviation of the axis of rotation
from the direction of the static magnetic field gives rise to the coupling
between the Alfv{\'e}n wave and the classical Jeans mode which otherwise
results into the modified slow and fast Alfv{\'e}n waves as well as the
modified classical Jeans modes. Furthermore, due to the effects of the cosmic
rays diffusion, there appears a new wave mode (may be called the fast Jeans
mode) in the intermediate frequency regimes of the slow and fast Alfv{\'e}n
waves, which seems to be dispersionless in the long-wavelength propagation and
has a lower growth rate of instability in the high density regimes of galaxies.
The dispersion properties and the instabilities of different kinds of MHD waves
reported here can play pivotal roles in the formation of various galactic
structures at different length scales.",2210.09595v1
2023-04-17,Theoretical study of the Alfven Eigenmode stability in CFETR steady state discharges,"The aim of this study is to analyze the stability of Alfven Eigenmodes (AE)
in the China Fusion Engineering Test Reactor (CFETR) plasma for steady state
operations. The analysis is done using the gyro-fluid code FAR3d including the
effect of the acoustic modes, EP Finite Larmor radius damping effects and
multiple energetic particle populations. Two high poloidal beta scenarios are
studied with respect to the location of the internal transport barrier (ITB) at
r/a = 0.45 (case A) and r/a = 0.6 (case B). Both operation scenarios show a
narrow TAE gap between the inner-middle plasma region and a wide EAE gap all
along the plasma radius. The AE stability of CFETR plasmas improves if the ITB
is located inwards, case A, showing AEs with lower growth rates with respect to
the case B. The AEs growth rate is smaller in the case A because the modes are
located in the inner-middle plasma region where the stabilizing effect of the
magnetic shear is stronger with respect to the case B. Multiple EP populations
effects (NBI driven EP + alpha articles) are negligible for the case A,
although the simulations for the case B show a stabilizing effect of the NBI EP
on the n=1 BAE caused by alpha particles during the thermalization process. If
the FLR damping effects are included in the simulations, the growth rate of the
EAE/NAE decreases up to 70 %, particularly for n > 3 toroidal families. Low n
AEs (n<6) show the largest growth rates. On the other hand, high $n$ modes (n=6
to 15) are triggered in the frequency range of the NAE, strongly damped by the
FLR effects.",2304.08412v1
2023-05-21,Small-amplitude Compressible Magnetohydrodynamic Turbulence Modulated by Collisionless Damping in Earth's Magnetosheath: Observation Matches Theory,"Plasma turbulence is a ubiquitous dynamical process that transfers energy
across many spatial and temporal scales and affects energetic particle
transport. Recent advances in the understanding of compressible
magnetohydrodynamic (MHD) turbulence demonstrate the important role of damping
in shaping energy distributions on small scales, yet its observational evidence
is still lacking. This study provides the first observational evidence of
substantial collisionless damping (CD) modulation on small-amplitude
compressible MHD turbulence cascade in Earth's magnetosheath using four Cluster
spacecraft. Based on an improved compressible MHD decomposition algorithm,
turbulence is decomposed into three eigenmodes: incompressible Alfv\'en modes,
and compressible slow and fast (magnetosonic) modes. Our observations
demonstrate that CD enhances the anisotropy of compressible MHD modes because
CD has a strong dependence on wave propagation angle. The wavenumber
distributions of slow modes are mainly stretched perpendicular to the
background magnetic field ($\mathbf{B_0}$) and weakly modulated by CD. In
contrast, fast modes are subjected to a more significant CD modulation. Fast
modes exhibit a weak, scale-independent anisotropy above the CD truncation
scale. Below the CD truncation scale, the anisotropy of fast modes enhances as
wavenumbers increase. As a result, fast mode fractions in the total energy of
compressible modes decrease with the increase of perpendicular wavenumber (to
$\mathbf{B_0}$) or wave propagation angle. Our findings reveal how the
turbulence cascade is shaped by CD and its consequences to anisotropies in the
space environment.",2305.12507v3
2023-07-14,PIC simulations of stable surface waves on a subcritical fast magnetosonic shock front,"We study with particle-in-cell (PIC) simulations the stability of fast
magnetosonic shocks. They expand across a collisionless plasma and an
orthogonal magnetic field that is aligned with one of the directions resolved
by the 2D simulations. The shock speed is 1.6 times the fast magnetosonic speed
when it enters a layer with a reduced density of mobile ions, which decreases
the shock speed by up to 15\% in 1D simulations. In the 2D simulations, the
density of mobile ions in the layer varies sinusoidally perpendicularly to the
shock normal. We resolve one sine period. This variation only leads to small
changes in the shock speed evidencing a restoring force that opposes a shock
deformation. As the shock propagates through the layer, the ion density becomes
increasingly spatially modulated along the shock front and the magnetic field
bulges out where the mobile ion density is lowest. The perturbed shock
eventually reaches a steady state. Once it leaves the layer, the perturbations
of the ion density and magnetic field oscillate along its front at a frequency
close to the lower-hybrid frequency; the shock is mediated by a standing wave
composed of obliquely propagating lower-hybrid waves. We perform three 2D
simulations with different box lengths along the shock front. The shock front
oscillations are aperiodically damped in the smallest box with the fastest
variation of the ion density, strongly damped in the intermediate one, and
weakly damped in the largest box. The shock front oscillations perturb the
magnetic field in a spatial interval that extends by several electron skin
depths upstream and downstream of the shock front and could give rise to
Whistler waves that propagate along the shock's magnetic field overshoot.
Similar waves were observed in hybrid and PIC simulations and by the MMS
satellite mission.",2307.07435v1
2023-08-03,"Part I: Rebuttal to ""Uniform stabilization for the Timoshenko beam by a locally distributed damping""","A paper, entitled ""Uniform stabilization for the Timoshenko beam by a locally
distributed damping"" was published in 2003, in the journal Electronic Journal
of Differential Equations. Its title concerns exclusively its Section 3,
devoted to the case of equal speeds of propagation and to its main theorem,
namely Theorem 3.1. It states that the solutions of the Timoshenko system (see
(1.3) in [1]) decays exponentially when the damping coefficient b is locally
distributed. The proof of Theorem 3.1 is crucially based on Lemma 3.6, which
states the existence of a strict Lyapunov function along which the solutions of
(1.3) decay when the speeds of propagation are equal. This rebuttal shows the
major gap and flaws in the proof of Lemma 3.6, which invalidate the proofs of
Lemma 3.6 and Theorem 3.1. Lemma 3.6 is stated at the top of page 12. The main
part of its proof is given in the pages 12 and 13. In the last eight lines of
page 13, eight inequalities are requested to hold together for the proof of
Lemma 3.6. They don't appear in the statements of Lemma 3.6. The subsequent
flaws come from the evidence that several of them are contradictory either
between them or with claims in the title of the article. We also point in this
rebuttal other flaws, or gaps in the proofs of Theorem 2.2 related to strong
stability and non uniform stability for the case of distinct speeds of
propagation. In [3], we correct and complete the proof of strong stability. We
also correct, set up the missing functional frames, fill the gaps in the proof
of non uniform stability in the cases of different speeds of propagation, and
complete a missing argument in the proof of Theorem A in [4] (see Remark 4.3),
the result of Theorem A being used in the paper [1] on which this rebuttal is
mainly devoted.",2308.01611v1
2023-08-05,Modulating Spin Current Induced Effective Damping in $β-W/Py$ Heterostructures by a Systematic Variation in Resistivity of the Sputtered Deposited $β-W$ films,"Utilizing the spin-induced pumping from a ferromagnet (FM) into a heavy metal
(HM) under the ferromagnetic resonance (FMR) condition, we report an
enhancement in effective damping in $\beta$- W/Py bilayers by systematically
varying resistivity ($\rho_{W}$) of $\beta$-W films. Different resistivity
ranging from 100 $\mu\Omega$-cm to 1400 $\mu\Omega$-cm with a thickness of 8 nm
can be achieved by varying the argon pressure ($P_{Ar}$) during the growth by
the method of sputtering. The coefficient of effective damping $\alpha_{eff}$
is observed to increase from 0.010 to 0.025 with $\rho_{W}$, which can be
modulated by $P_{Ar}$. We observe a modest dependence of $\alpha_{eff}$ on the
sputtering power ($p_{S}$) while keeping the $P_{Ar}$ constant. $\alpha_{eff}$
dependence on both $P_{Ar}$ and $p_{S}$ suggests that there exists a strong
correlation between $\alpha_{eff}$ and $\rho_{W}$. It is thus possible to
utilize $\rho_{W}$ as a tuning parameter to regulate the $\alpha_{eff}$, which
can be advantageous for faster magnetization dynamics switching. The thickness
dependence study of Py in the aforementioned bilayers manifests a higher spin
mixing conductance ($g^{\uparrow\downarrow}_{eff}$) which suggests a strong
spin pumping from Py into the $\beta$-W layer. The effective spin current
($J_{S(eff)}$) is also evaluated by considering the spin-back flow in this
process. Intrinsic spin mixing conductance ($g^{\uparrow\downarrow}_{W}$) and
spin diffusion length ($\lambda_{SD}$) of $\beta$-W are additionally
investigated using thickness variations in $\beta$-W. Furthermore, the
low-temperature study in $\beta$-W/Py reveals an intriguing temperature
dependence in $\alpha_{eff}$ which is quite different from $\alpha_{b}$ of
single Py layer and the enhancement in $\alpha_{eff}$ at low temperature can be
attributed to the spin-induced pumping from Py layer into $\beta$-W.",2308.02939v1
2023-09-01,f-mode oscillations of anisotropic neutron stars in full general relativity,"We investigate f-mode oscillations of static anisotropic stable neutron stars
within the framework of full general relativity. We present equations governing
unperturbed stellar structures and oscillations with an ansatz to account for
the anisotropy. We solve those equations for two different equations of states.
We see that, moderately anisotropic neutron stars with the tangential pressure
larger than the radial pressure can give more massive neutron stars than the
isotropic or very anisotropic ones. We find that the frequency of the f-mode
exhibits a linear relationship with the square root of the average density of
the stars and the slope of the fit depends on the anisotropic strength. For any
given value of the anisotropic strength, the frequency increases with the
increase of the mass of the neutron star, linearly for lower masses, and
rapidly at higher masses. However, this non-linear rise in the frequency with
the mass is not prominent when the radial pressure is larger than the
tangential pressure. For a fixed value of a small mass, higher anisotropy leads
to a larger value of the frequency, but when the fixed mass is above a
threshold value, higher anisotropy leads to a smaller value of the frequency.
The nature of the variation in the frequency with the change in the anisotropic
strength is similar for the two equations of state, but for a fixed mass and
the same amount of the anisotropy, the softer equations of state gives higher
frequency. We also find that the damping time of the f-mode oscillation
decreases as the mass of the neutron star increases for all values of the
anisotropic strength. For a fixed mass of the neutron star and for the same
amount of the anisotropy, the value of the damping time is lower for the softer
equation of state, but the nature of the variation in the damping time with the
change in the anisotropic strength is similar.",2309.00439v2
2023-09-10,Stability and Regularity for Double Wall Carbon Nanotubes Modeled as Timoshenko Beams with Thermoelastic Effects and Intermediate Damping,"This research studies two systems composed by the Timoshenko beam model for
double wall carbon nanotubes, coupled with the heat equation governed by
Fourier's law. For the first system, the coupling is given by the speed the
rotation of the vertical filament in the beam $\beta\psi_t$ from the first beam
of Tymoshenko and the Laplacian of temperature $\delta\theta_{xx}$, where we
also consider the damping terms fractionals
$\gamma_1(-\partial_{xx})^{\tau_1}\phi_t$, $\gamma_2(-\partial_{xx})^{\tau_2}
y_t$ and $\gamma_3(-\partial_{xx})^{\tau_3} z_t$, where $(\tau_1, \tau_2,
\tau_3) \in [0,1]^3$. For this first system we proved that the semigroup
$S_1(t)$ associated to system decays exponentially for all $(\tau_1 , \tau_2 ,
\tau_3 ) \in [0,1]^3$. The second system also has three fractional damping
$\gamma_1(-\partial_{xx})^{\beta_1}\phi_t$, $\gamma_2(-\partial_{xx})^{\beta_2}
y_t$ and $\gamma_3(-\partial_{xx})^{\beta_3} z_t$, with $(\beta_1, \beta_2,
\beta_3) \in [0,1]^3$. Furthermore, the couplings between the heat equation and
the Timoshenko beams of the double wall carbon nanotubes for the second system
is given by the Laplacian of the rotation speed of the vertical filament in the
beam $\beta\psi_{xxt}$ of the first beam of Timoshenko and the Lapacian of the
temperature $\delta\theta_{xx}$. For the second system, we prove the
exponential decay of $S_2(t)$ for $(\beta_1, \beta_2, \beta_3) \in [0,1]^3$ and
also show that $S_2(t)$ admits Gevrey classes $s>(\phi+1)/(2\phi)$ for
$\phi=\min\{\beta_1,\beta_2,\beta_3\}, \forall (\beta_1,\beta_2,\beta_3)\in
(0,1)^3$, and proving that $S_2(t)$ is analytic when the parameters $(\beta_1,
\beta_2, \beta_3) \in [1/2,1]^3$. One of the motivations for this research was
the work; Ramos et al. \cite{Ramos2023CNTs}, whose partial results are part of
our results obtained for the first system for $(\tau_1, \tau_2, \tau_3) = (0,
0, 0)$.",2309.04906v1
2023-11-03,"Probing the disc-jet coupling in S4 0954+65, PKS 0903-57, & 4C +01.02 with $γ$-rays","We present a comprehensive variability study on three blazars, S4 0954+65,
PKS 0903-57, and 4C +01.02 covering a mass range of log(M/M$_{\odot}$) = 8--9,
by using $\sim$15 years-long $\gamma$-ray light curves from \textit{Fermi}-LAT.
The variability level is characterized by the fractional variability amplitude
which is higher for $\gamma$-rays compared to optical/UV and X-rays emissions.
A power spectral density (PSD) study and damped random walk (DRW) modeling are
done to probe the characteristic timescale. The PSD is fitted with a single
power-law (PL) and bending power-law models and the corresponding success
fraction was estimated. In the case of PKS 0903-57, We observed a break in the
$\gamma$-ray PSD at 256 days which is comparable to the viscous timescale in
the accretion disc suggesting a possible disk-jet coupling. The non-thermal
damping timescale from the DRW modeling is compared with the thermal damping
timescale for AGNs including our three sources. Our sources lie on the best-fit
of the $\mathrm{\tau^{rest}_{damping}} - M_{BH}$ plot derived for AGN
suggesting a possible accretion disc-jet connection. If the jet's variability
is linked to the disc's variability, we expect a log-normal flux distribution,
often connected to the accretion disc's multiplicative processes. Our study
observed a double log-normal flux distribution, possibly linked to long and
short-term variability from the accretion disk and the jet. In summary, PSD and
DRW modeling results for these three sources combined with blazars and AGNs
studied in literature favor a disc-jet coupling scenario. However, more such
studies are needed to refine this understanding.",2311.01738v1
2023-11-30,Compton scattering of electrons in the intergalactic medium,"This paper investigates the distribution and implications of cosmic ray
electrons within the intergalactic medium (IGM). Utilizing a synthesis model of
the extragalactic background, we evolve the spectrum of Compton-included cosmic
rays. The energy density distribution of cosmic ray electrons peaks at redshift
$z \approx2$, and peaks in the $\sim$MeV range. The fractional contribution of
cosmic ray pressure to the general IGM pressure progressively increases toward
lower redshift. At mean density, the ratio of cosmic ray electron to thermal
pressure in the IGM $ P_{\rm CRe} / P_{\rm th}$ is 0.3% at $z=2$, rising to
1.0% at $z=1$, and 1.8% at $z=0.1$ (considering only the cosmic rays produced
locally by Compton scattering). We compute the linear Landau damping rate of
plasma oscillations in the IGM caused by the $\sim$MeV cosmic ray electrons,
and find it to be of order $\sim 10^{-6}\,\rm s^{-1}$ for wavenumbers
$1.2\lesssim ck/\omega_{\rm p}\lesssim 5$ at $z=2$ and mean density (where
$\omega_{\rm p}$ is the plasma frequency). This strongly affects the fate of
TeV $e^+e^-$ pair beams produced by blazars, which are potentially unstable to
oblique instabilities involving plasma oscillations with wavenumber
$ck/\omega_{\rm p}\approx\sec\theta$ ($\theta$ being the angle between the beam
and wave vector). Linear Landau damping is at least thousands of times faster
than either pair beam instability growth or collisional effects; it thus turns
off the pair beam instability except for modes with very small $\theta$
($ck/\omega_{\rm p}\rightarrow 1$, where linear Landau damping is kinematically
suppressed). This leaves open the question of whether the pair beam instability
is turned off entirely, or can still proceed via the small-$\theta$ modes.",2311.18721v2
2023-12-26,Observation of Magnon Damping Minimum Induced by Kondo Coupling in a van der Waals Ferromagnet Fe$_{3-x}$GeTe$_{2}$,"In heavy-fermion systems with $f$ electrons, there is an intricate interplay
between Kondo screening and magnetic correlations, which can give rise to
various exotic phases. Recently, similar interplay appears to also occur in
$d$-electron systems, but the underlying mechanism remains elusive. Here, using
inelastic neutron scattering, we investigate the temperature evolution of the
low-energy spin waves in a metallic van der Waals ferromagnet
Fe$_{3-x}$GeTe$_{2}$ (Curie temperature $T_{\rm C}\sim160$ K), where the
Kondo-lattice behavior emerges in the ferromagnetic phase below a
characteristic temperature $T^*\sim90$ K. We observe that the magnon damping
constant diverges at both low and high temperatures, exhibiting a minimum
coincidentally around $T^*$. Such an observation is analogous to the
resistivity minimum as due to the single-impurity Kondo effect. This unusual
behavior is described by a formula that combines logarithmic and power terms,
representing the dominant contributions from Kondo screening and thermal
fluctuations, respectively. Furthermore, we find that the magnon damping
increases with momentum below $T_{\rm C}$. These findings can be explained by
considering spin-flip electron-magnon scattering, which serves as a magnonic
analog of the Kondo-impurity scattering, and thus provides a measure of the
Kondo coupling through magnons. Our results provide critical insights into how
Kondo coupling manifests itself in a system with magnetic ordering and shed
light on the coexistence of and interplay between magnetic order and Kondo
effect in itinerant 3$d$-electron systems.",2312.15961v1
2024-01-18,Chronicling the reionization history at $6\lesssim z \lesssim 7$ with emergent quasar damping wings,"The spectra of high-redshift ($z\gtrsim 6$) quasars contain valuable
information on the progression of the Epoch of Reionization (EoR). At redshifts
$z<6$, the observed Lyman-series forest shows that the intergalactic medium
(IGM) is nearly ionized, while at $z>7$ the observed quasar damping wings
indicate high neutral gas fractions. However, there remains a gap in neutral
gas fraction constraints at $6\lesssim z \lesssim 7$ where the Lyman series
forest becomes saturated but damping wings have yet to fully emerge. In this
work, we use a sample of 18 quasar spectra at redshifts $6.0<z<7.1$ to close
this gap. We apply neural networks to reconstruct the quasars' continuum
emission around the partially absorbed Lyman $\alpha$ line to normalize their
spectra, and stack these continuum-normalized spectra in three redshift bins.
To increase the robustness of our results, we compare the stacks to a grid of
models from two hydrodynamical simulations, ATON and CROC, and we measure the
volume-averaged neutral gas fraction, $\bar{x}_{\rm HI}$, while jointly fitting
for the mean quasar lifetime, $t_{\rm Q}$, for each stacked spectrum. We
chronicle the evolution of neutral gas fraction using the ATON (CROC) models as
follows: $\bar{x}_{\rm HI} = 0.21_{-0.07}^{+0.17}$ ($\bar{x}_{\rm HI} =
0.10_{<10^{-4}}^{+0.73}$) at $\langle z \rangle =6.10$, $\bar{x}_{\rm HI} =
0.21_{-0.07}^{+0.33}$ ($\bar{x}_{\rm HI} =0.57_{-0.47}^{+0.26}$) at $\langle z
\rangle =6.46$, and $\bar{x}_{\rm HI} = 0.37_{-0.17}^{+0.17}$ ($\bar{x}_{\rm
HI} =0.57_{-0.21}^{+0.26}$) at $\langle z \rangle =6.87$. At the same time we
constrain the average quasar lifetime to be $t_{\rm Q} \lesssim 7\ {\rm Myr}$
across all redshift bins, in good agreement with previous studies.",2401.10328v1
2024-03-04,Exploring Standing and Reflected Slow-mode Waves in Flaring Coronal Loops: A Parametric Study Using 2.5D MHD Modeling,"Recent observations of reflected propagating and standing slow-mode waves in
hot flaring coronal loops have spurred our investigation into their underlying
excitation and damping mechanisms. To understand these processes, we conduct
2.5D magnetohydrodynamic (MHD) simulations using an arcade active region model
that includes a hot and dense loop. Our simulations allow for in-depth
parametric investigations complementing and expanding our previous 3D MHD
modeling results. We excite these waves in two distinct models as motivated by
observations from the SDO/AIA. Model 1 incorporates classical compressive
viscosity coefficient, while Model 2 adopts a 10-times enhanced viscosity
coefficient. We find that: (1) Our 2.5D MHD simulations reinforce previous
conclusions derived from 1D and 3D MHD models that significantly enhanced
viscosity is crucial for the rapid excitation of standing slow waves with
damping times consistent with observations by Wang et al. (2015). (2) We
uncover that nonlinearity in Model 1 delays the conversion of a reflected
propagating wave into a standing wave. In contrast, Model 2 exhibits a much
weak influence of nonlinearity. (3) Our results reveal that the transverse
temperature structure holds more influence on wave behavior than the density
structure. In Model 1, increased loop temperature contrast significantly
enhances wave trapping within the structure, mitigating the impact of
temperature-dependent viscous damping. Conversely, in Model 2, the impact of
temperature structure on wave behavior weakens in comparison to the effect of
viscosity. (4) Model 1 displays evident nonlinear coupling to the fast and kink
magnetoacoustic waves and pronounced wave leakage into the corona. However,
analyzing three observed wave events by SDO/AIA aligns with Model 2
predictions, providing further support for the substantial viscosity increase.",2403.02464v1
2000-02-17,Constraints on Cosmological Parameters from Future Galaxy Cluster Surveys,"We study the expected redshift evolution of galaxy cluster abundance between
0 < z < 3 in different cosmologies, including the effects of the cosmic
equation of state parameter w=p/rho. Using the halo mass function obtained in
recent large scale numerical simulations, we model the expected cluster yields
in a 12 deg^2 Sunyaev-Zeldovich Effect (SZE) survey and a deep 10^4 deg^2 X-ray
survey over a wide range of cosmological parameters. We quantify the
statistical differences among cosmologies using both the total number and
redshift distribution of clusters. Provided that the local cluster abundance is
known to a few percent accuracy, we find only mild degeneracies between w and
either Omega_m or h. As a result, both surveys will provide improved
constraints on Omega_m and w. The Omega_m-w degeneracy from both surveys is
complementary to those found either in studies of CMB anisotropies or of
high-redshift Supernovae (SNe). As a result, combining these surveys together
with either CMB or SNe studies can reduce the statistical uncertainty on both w
and Omega_m to levels below what could be obtained by combining only the latter
two data sets. Our results indicate a formal statistical uncertainty of about
3% (68% confidence) on both Omega_m and w when the SZE survey is combined with
either the CMB or SN data; the large number of clusters in the X-ray survey
further suppresses the degeneracy between w and both Omega_m and h. Systematics
and internal evolution of cluster structure at the present pose uncertainties
above these levels. We briefly discuss and quantify the relevant systematic
errors. By focusing on clusters with measured temperatures in the X-ray survey,
we reduce our sensitivity to systematics such as non-standard evolution of
internal cluster structure.",0002336v2
2000-03-03,J-Band Infrared Spectroscopy of a Sample of Brown Dwarfs Using Nirspec on Keck II,"Near-infrared spectroscopic observations of a sample of very cool, low-mass
objects are presented with higher spectral resolution than in any previous
studies. Six of the objects are L-dwarfs, ranging in spectral class from L2 to
L8/9, and the seventh is a methane or T-dwarf. These new observations were
obtained during commissioning of NIRSPEC, the first high-resolution
near-infrared cryogenic spectrograph for the Keck II 10-meter telescope on
Mauna Kea, Hawaii. Spectra with a resolving power of R=2500 from 1.135 to 1.360
microns (approximately J-band) are presented for each source. At this
resolution, a rich spectral structure is revealed, much of which is due to
blending of unresolved molecular transitions. Strong lines due to neutral
potassium (K I), and bands due to iron hydride (FeH) and steam (H2O) change
significantly throughout the L sequence. Iron hydride disappears between L5 and
L8, the steam bands deepen and the K I lines gradually become weaker but wider
due to pressure broadening. An unidentified feature occurs at 1.22 microns
which has a temperature dependence like FeH but has no counterpart in the
available FeH opacity data. Because these objects are 3-6 magnitudes brighter
in the near-infrared compared to the I-band, spectral classification is
efficient. One of the objects studied (2MASSW J1523+3014) is the coolest
L-dwarf discovered so far by the 2-Micron All-Sky Survey (2MASS), but its
spectrum is still significantly different from the methane-dominated objects
such as Gl229B or SDSS 1624+0029.",0003035v1
2001-07-19,The Altitude of an Infrared Bright Cloud Feature on Neptune from Near-Infrared Spectroscopy,"We present 2.03-2.30 micron near-infrared spectroscopy of Neptune taken 1999
June 2 (UT) with the W.M. Keck Observatory's near-infrared spectrometer
(NIRSPEC) during the commissioning of the instrument. The spectrum is dominated
by a bright cloud feature, possibly a storm or upwelling, in the southern
hemisphere at approximately 50 degrees S latitude. The spectrum also includes
light from a dimmer northern feature at approximately 30 degrees N latitude. We
compare our spectra (R ~ 2000) of these two features with a simple model of
Neptune's atmosphere. Given our model assumption that the clouds are flat
reflecting layers, we find that the top of the bright southern cloud feature
sat at a pressure level of 0.14 (+0.05, -0.03) bar, and thus this cloud did not
extend into the stratosphere (P < 0.1 bar). A similar analysis of the dimmer
northern feature gives a cloud-top pressure of 0.084 +/- 0.026 bar. This
suggests that the features we observed efficiently transport methane to the
base of the stratosphere, but do not directly transport methane to the upper
stratosphere (P < 0.01-0.001 bar) where photolysis occurs. Our observations do
not constrain how far these clouds penetrate down into the troposphere. We find
that our model fits to the data restrict the fraction of molecular hydrogen in
ortho/para thermodynamic equilibrium to greater than 0.8.",0107361v1
2002-03-20,Observation of X-ray variability in the BL Lac object 1ES1959+65,"This paper reports X-ray spectral observations of a relatively nearby z =
0.048 BL Lacertae (BL Lac) object 1ES1959+650, which is a potential TeV
emitter. The observations include 31 short pointings made by the Unconventional
Stellar Aspect (USA) Experiment on board the Advanced Research and Global
Observation Satellite (ARGOS), and 17 pointings by the PCA on board the Rossi
X-ray Timing Explorer (RXTE). Most of these observations were spaced by less
than 1 day. \es was detected by the ARGOS USA detector in the range 1-16 keV,
and by the PCA in the 2-16 keV range but at different times. During the closely
spaced RXTE observations beginning on 2000 July 28, an ending of one flare and
a start of another are visible, associated with spectral changes, where the
photon index Gamma ranges between ~ 1.4 and 1.7, and the spectrum is harder
when the source is brighter. This implies that 1ES1959 is an XBL-type blazar,
with the X-ray emission likely to originate via the synchrotron process. The
USA observations reveal another flare that peaked on 2000 November 14 and
doubled the flux within a few days, again associated with spectral changes of
the same form. The spectral variability correlated with the flux and timing
characteristics of this object that are similar to those of other nearby BL
Lacs, and suggest relativistic beaming with a Doppler factor delta > 1.6 and
magnetic fields of the order of a few mG. We also suggest that the steady
component of the X-ray emission -- present in this object as well as in other
XBLs -- may be due to the large-scale relativistic jet (such as measured by
Chandra in many radio-loud AGN), but pointing very closely to our line of
sight.",0203335v1
2002-06-18,Near-IR and Optical Morphology of Spiral Galaxies,"We announce the initial release of data from the Ohio State University Bright
Spiral Galaxy Survey, a BVRJHK imaging survey of a well-defined sample of 205
bright, nearby spiral galaxies. We present H-band morphological classification
on the Hubble sequence for the OSU Survey sample. We compare the H-band
classification to B-band classification from our own images and from standard
galaxy catalogs. Our B-band classifications match well with those of the
standard catalogs. On average, galaxies with optical classifications from Sa
through Scd appear about one T-type earlier in the H-band than in the B-band,
but with large scatter. This result does not support recent claims made in the
literature that the optical and near-IR morphologies of spiral galaxies are
uncorrelated. We present detailed descriptions of the H-band morphologies of
our entire sample, as well as B- and H-band images for a set of 17 galaxies
chosen as type examples, and BRH color-composite images of six galaxies chosen
to demonstrate the range in morphological variation as a function of
wavelength. Data from the survey are accessible at
http://www.astronomy.ohio-state.edu/~survey/",0206320v1
2003-02-20,The Reionization History at High Redshifts I: Physical Models and New Constraints from CMB Polarization,"The recent discovery of a high optical depth tau to Thomson scattering from
the WMAP data implies that significant reionization took place at redshifts
z~15. This discovery has important implications for the sources of
reionization, and allows, for the first time, constraints to be placed on
physical reionization scenarios out to redshift z~20. Using a new suite of
semi-analytic reionization models, we show that the high value of tau requires
a surprisingly high efficiency epsilon of the first generation of UV sources
for injecting ionizing photons into the intergalactic medium. We find that no
simple reionization model can be consistent with the combination of the WMAP
result with data from the z<6.5 universe. Satisfying both constraints requires
either of the following: (i) H_2 molecules form efficiently at z~20, survive
feedback processes, and allow UV sources in halos with virial temperatures
below Tvir=10^4 K to contribute substantially to reionization, or (ii) the
efficiency epsilon in halos with Tvir>10^4K decreased by a factor of ~ 30
between (z~20) and (z~6). We discuss the relevant physical issues to produce
either scenario, and argue that both options are viable, and allowed by current
data. In detailed models of the reionization history, we find that the
evolution of the ionized fractions in the two scenarios have distinctive
features that Planck can distinguish at 3 sigma significance. At the high WMAP
value for tau, Planck will also be able to provide tight statistical
constraints on reionization model parameters, and elucidate much of the physics
at the end of the Dark Ages. The sources responsible for the high optical depth
discovered by WMAP should be directly detectable out to z~15 by the James Webb
Space Telescope.",0302403v2
2004-06-07,Dynamics and Stellar Content of the Giant Southern Stream in M31. I. Keck Spectroscopy of Red Giant Stars,"We present results from a large spectroscopic survey of M31 red giants using
the Keck telescope/DEIMOS. Photometric pre-screening, based on the 100A-wide
DDO51 band centered on the Mgb/MgH feature, was used to select spectroscopic
targets. Red giant candidates were targeted in a small field on M31's giant
southern tidal stream at a projected distance of 31kpc from the galaxy center.
We isolate a clean sample of 68 giants by removing contaminants (foreground
Galactic dwarfs and background galaxies) using spectroscopic, imaging, and
photometric methods. About 65% of the M31 stars are found to be members of the
stream, while the rest appear to be members of the general halo population. The
mean (heliocentric) radial velocity of the stream in our field is -458 km/s, or
-158 km/s relative to M31's systemic velocity, in good agreement with recent
measurements at other stream locations. The intrinsic velocity dispersion of
the stream is constrained to be 15_{-15}^{+8} km/s (90% confidence limits). The
companion paper by Font et al. (2004, astro-ph/0406146) discusses possible
orbits, implications of the coldness of the stream, and progenitor satellite
properties. The kinematics (and perhaps [Fe/H] distribution) of our halo sample
indicate that it is different from other M31 halo samples; this may be an
indication of substructure in the halo. The stream seems to have a higher mean
[Fe/H] than the halo, -0.51 vs -0.74 dex, and a smaller [Fe/H] spread. The
stream's high metallicity implies that its progenitor must have been a luminous
dwarf galaxy. The CaII triplet strengths of the M31 giants are generally
consistent with photometric estimates of their metallicity (derived by fitting
RGB fiducials in the color-magnitude diagram). There is indirect evidence of
intermediate-age stars in the stream.",0406145v1
2004-07-14,Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database,"We present improved black hole masses for 35 active galactic nuclei (AGNs)
based on a complete and consistent reanalysis of broad emission-line
reverberation-mapping data. From objects with multiple line measurements, we
find that the highest precision measure of the virial product is obtained by
using the cross-correlation function centroid (as opposed to the
cross-correlation function peak) for the time delay and the line dispersion (as
opposed to full width half maximum) for the line width and by measuring the
line width in the variable part of the spectrum. Accurate line-width
measurement depends critically on avoiding contaminating features, in
particular the narrow components of the emission lines. We find that the
precision (or random component of the error) of reverberation-based black hole
mass measurements is typically around 30%, comparable to the precision attained
in measurement of black hole masses in quiescent galaxies by gas or stellar
dynamical methods. Based on results presented in a companion paper by Onken et
al., we provide a zero-point calibration for the reverberation-based black hole
mass scale by using the relationship between black hole mass and host-galaxy
bulge velocity dispersion. The scatter around this relationship implies that
the typical systematic uncertainties in reverberation-based black hole masses
are smaller than a factor of three. We present a preliminary version of a
mass-luminosity relationship that is much better defined than any previous
attempt. Scatter about the mass-luminosity relationship for these AGNs appears
to be real and could be correlated with either Eddington ratio or object
inclination.",0407299v1
2005-02-06,SINFONI in the Galactic Center: young stars and IR flares in the central light month,"We report 75 milli-arcsec resolution, near-IR imaging spectroscopy within the
central 30 light days of the Galactic Center [...]. To a limiting magnitude of
K~16, 9 of 10 stars in the central 0.4 arcsec, and 13 of 17 stars out to 0.7
arcsec from the central black hole have spectral properties of B0-B9, main
sequence stars. [...] all brighter early type stars have normal rotation
velocities, similar to solar neighborhood stars. We [...] derive improved 3d
stellar orbits for six of these S-stars in the central 0.5 arcsec. Their
orientations in space appear random. Their orbital planes are not co-aligned
with those of the two disks of massive young stars 1-10 arcsec from SgrA*. We
can thus exclude [...] that the S-stars as a group inhabit the inner regions of
these disks. They also cannot have been located/formed in these disks [...].
[...] we conclude that the S-stars were most likely brought into the central
light month by strong individual scattering events. The updated estimate of
distance to the Galactic center from the S2 orbit fit is Ro = 7.62 +/- 0.32
kpc, resulting in a central mass value of 3.61 +/- 0.32 x 10^6 Msun. We
happened to catch two smaller flaring events from SgrA* [...]. The 1.7-2.45 mum
spectral energy distributions of these flares are fit by a featureless, red
power law [...]. The observed spectral slope is in good agreement with
synchrotron models in which the infrared emission comes from [...] radiative
inefficient accretion flow in the central R~10 Rs region.",0502129v1
2005-02-18,Discovery of an extended halo of metal-poor stars in the Andromeda spiral galaxy,"Understanding galaxy formation involves look-back and fossil-record studies
of distant and nearby galaxies, respectively. Debris trails in our Galaxy's
spheroidal halo of old stars provide evidence of ""bottom-up"" formation via
tidal disruption/merging of dwarf satellite galaxies, but it is difficult to
study our Galaxy's large-scale structure from within. Studies of our
neighbouring Andromeda galaxy have concluded that its spheroid contains
chemically enriched (""metal-rich"") stars out to a radius of 30 kiloparsecs with
an exponential r^1/4 fall-off in density thereby resembling a galactic ""bulge"".
Were Andromeda's true halo to be found, our detailed yet global view of its
stellar dynamics, substructure, chemical abundance, and age distribution would
directly constrain hierarchical halo formation models. We report here on the
discovery of a hitherto elusive halo of metal-poor Andromeda stars, distinct
from its bulge, with a power-law brightness profile extending beyond r = 160
kiloparsecs. This is 3 - 5 times larger than any previously mapped Andromeda
spheroidal/disk component. Together, the Galactic and Andromeda halos span >1/3
of the distance between them, suggesting that stars occupy a substantial volume
fraction of our Local Group, and possibly most galaxy groups.",0502366v5
2005-04-12,Constrained Cluster Parameters from Sunyaev-Zel'dovich Observations,"Near-future SZ surveys such as ACT, SPT, APEX, and Planck will find thousands
of galaxy clusters. Multi-frequency arcminute-resolution SZ observations can,
in principle, determine each cluster's gas temperature (T_e), bulk velocity
(v_pec), and optical depth (tau). However, the frequency bands and detector
sensitivity employed by upcoming surveys will generally not be sufficient to
disentangle the degeneracy between these three cluster parameters, even in the
absence of SZ signal contamination from point sources and imperfect primary
microwave background subtraction. Assuming contaminants can be removed, we find
that near-future SZ surveys will be able to constrain well two cluster gas
parameters that are linear combinations of tau*T_e, tau*v_z, and tau*T_e^2.
Because the SZ intensity shift is nearly a linear function of tau*T_e, tau*v_z,
and tau*T_e^2, a correspondence exists between the two effective gas parameters
that SZ surveys can constrain and simple line-of-sight integrals through the
three dimensional cluster. We illustrate the parameter constraints and
correspondence to line-of-sight integrals using 3D Nbody + hydro cluster
simulations and a Markov chain Monte Carlo method. We show that adding an
independent T_e measurement to upcoming SZ data breaks the parameter
degeneracy. The cluster effective velocity thus constrained is approximately
the optical-depth-weighted velocity integrated along the cluster line of sight.
A temperature prior with an error as large as 2 keV still gives bulk velocity
errors < 100 km/sec, even for a more typical cluster with an electron
temperature of 3 keV, for ACT-like SZ observations in the absence of signal
contamination. The Markov chain constraints on v_pec and tau are more
encouraging and likely more accurate than those obtained from Fisher matrices.",0504274v3
2005-10-03,High Spectral Resolution Observations of the Massive Stars in the Galactic Center,"We present high-resolution near-infrared spectra, obtained with the NIRSPEC
spectrograph on the W. M. Keck II Telescope, of a collection of hot, massive
stars within the central 25 arcseconds of the Galactic center. We have
identified a total of twenty-one emission-line stars, seven of which are new
radial velocity detections with five of those being classified as He I
emission-line stars for the first time. These stars fall into two categories
based on their spectral properties: 1) those with narrow 2.112, 2.113 micron He
I doublet absorption lines, and 2) those with broad 2.058 micron He I emission
lines. These data have the highest spectral resolution ever obtained for these
sources and, as a result, both components of the absorption doublet are
separately resolved for the first time. We use these spectral features to
measure radial velocities. The majority of the measured radial velocities have
relative errors of 20 kms, smaller than those previously obtained with
proper-motion or radial velocity measurements for similar stellar samples in
the Galactic center. The radial velocities estimated from the He I absorption
doublet are more robust than those previously estimated from the 2.058 micron
emission line, since they do not suffer from confusion due to emission from the
surrounding ISM. Using this velocity information, we agree that the stars are
orbiting in a somewhat coherent manner but are not as defined into a disk or
disks as previously thought. Finally, multi-epoch radial velocity measurements
for IRS 16NE show a change in its velocity presumably due to an unseen stellar
companion.",0510028v2
2005-12-06,Kinematics and Metallicity of M31 Red Giants: The Giant Southern Stream and Discovery of a Second Cold Component at R = 20 kpc,"We present spectroscopic observations of red giant branch (RGB) stars in the
Andromeda spiral galaxy (M31), acquired with the DEIMOS instrument on the Keck
II 10-m telescope. The three fields targeted in this study are in the M31
spheroid, outer disk, and giant southern stream. In this paper, we focus on the
kinematics and chemical composition of RGB stars in the stream field located at
a projected distance of R = 20 kpc from M31's center. A mix of stellar
populations is found in this field. M31 RGB stars are isolated from Milky Way
dwarf star contaminants using a variety of spectral and photometric
diagnostics. The radial velocity distribution of RGB stars displays a clear
bimodality -- a primary peak centered at v = -513 km/s and a secondary one at v
= -417 km/s -- along with an underlying broad component that is presumably
representative of the smooth spheroid of M31. Both peaks are found to be
dynamically cold with intrinsic velocity dispersions of sigma(v) = 16 km/s. The
mean metallicity and metallicity dispersion of stars in the two peaks is also
found to be similar: [Fe/H] = -0.45 and sigma([Fe/H]) = 0.2. The observed
velocity of the primary peak is consistent with that predicted by dynamical
models for the stream, but there is no obvious explanation for the secondary
peak. The nature of the secondary cold population is unclear: it may represent:
(1) tidal debris from a satellite merger event that is superimposed on, but
unrelated to, the giant southern stream; (2) a wrapped around component of the
giant southern stream; (3) a warp or overdensity in M31's disk at R > 50 kpc
(this component is well above the outward extrapolation of the smooth
exponential disk brightness profile).",0512161v1
2006-02-28,Rejecting Astrophysical False Positives from the TrES Transiting Planet Survey: The Example of GSC 03885-00829,"Ground-based wide-field surveys for nearby transiting gas giants are yielding
far fewer true planets than astrophysical false positives, of which some are
difficult to reject. Recent experience has highlighted the need for careful
analysis to eliminate astronomical systems where light from a faint eclipsing
binary is blended with that from a bright star. During the course of the
Trans-atlantic Exoplanet Survey, we identified a system presenting a
transit-like periodic signal. We obtained the proper motion and infrared color
of this target (GSC 03885-00829) from publicly available catalogs, which
suggested this star is an F dwarf, supporting our transit hypothesis. This
spectral classification was confirmed using spectroscopic observations from
which we determined the stellar radial velocity. The star did not exhibit any
signs of a stellar mass companion. However, subsequent multi-color photometry
displayed a color-dependent transit depth, indicating that a blend was the
likely source of the eclipse. We successfully modeled our initial photometric
observations of GSC 03885-00829 as the light from a K dwarf binary system
superimposed on the light from a late F dwarf star. High-dispersion
spectroscopy confirmed the presence of light from a cool stellar photosphere in
the spectrum of this system. With this candidate, we demonstrate both the
difficulty in identifying certain types of false positives in a list of
candidate transiting planets and our procedure for rejecting these imposters,
which may be useful to other groups performing wide-field transit surveys.",0603005v1
2006-03-21,SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution,"We present 0.5"" resolution near-IR integral field spectroscopy of the Ha line
emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT.
The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected
over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved
velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of
the larger systems are consistent with orbital motions. Four galaxies are well
described by rotating disks with clumpy morphologies and we extract rotation
curves out to radii > ~10kpc. One or two galaxies exhibit signatures more
consistent with mergers. Analyzing all 14 galaxies in the framework of rotating
disks, we infer mean inclination- and beam-corrected maximum circular
velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun
within r_1/2. On average, the dynamical masses are consistent with photometric
stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun
Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to
those of local late-type galaxies. The specific angular momenta of their
baryons are comparable to those of their dark matter halos. Extrapolating from
the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in
our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases
implies a ratio of v_c to local velocity dispersion of order 2-4 and
accordingly a large geometric thickness. We argue that this suggests a mass
accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue
that if our BM/BX galaxies were initially gas rich, their clumpy disks will
subsequently lose their angular momentum and form compact bulges on a timescale
of ~1 Gyr. [ABRIDGED]",0603559v1
2006-05-06,The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31),"We present spectroscopic observations of red giant branch (RGB) stars over a
large expanse in the halo of the Andromeda spiral galaxy (M31), acquired with
the DEIMOS instrument on the Keck II 10-m telescope. Using a combination of
five photometric/spectroscopic diagnostics -- (1) radial velocity, (2)
intermediate-width DDO51 photometry, (3) Na I equivalent width (surface gravity
sensitive), (4) position in the color-magnitude diagram, and (5) comparison
between photometric and spectroscopic [Fe/H] estimates -- we isolate over 250
bona fide M31 bulge and halo RGB stars located in twelve fields ranging from R
= 12-165kpc from the center of M31 (47 of these stars are halo members with R >
60 kpc). We derive the photometric and spectroscopic metallicity distribution
function of M31 RGB stars in each of these fields. The mean of the resulting
M31 spheroid (bulge and halo) metallicity distribution is found to be
systematically more metal-poor with increasing radius, shifting from <[Fe/H]> =
-0.47+/-0.03 (sigma = 0.39) at R < 20 kpc to <[Fe/H]> = -0.94+/-0.06 (sigma =
0.60) at R ~ 30 kpc to <[Fe/H]> = -1.26+/-0.10 (sigma = 0.72) at R > 60 kpc,
assuming [alpha/Fe] = 0.0. These results indicate the presence of a metal-poor
RGB population at large radial distances out to at least R = 160 kpc, thereby
supporting our recent discovery of a stellar halo in M31: its halo and bulge
(defined as the structural components with R^{-2} power law and de Vaucouleurs
R^{1/4} law surface brightness profiles, respectively) are shown to have
distinct metallicity distributions. If we assume an alpha-enhancement of
[alpha/Fe] = +0.3 for M31's halo, we derive <[Fe/H]> = -1.5+/-0.1 (sigma =
0.7). Therefore, the mean metallicity and metallicity spread of this newly
found remote M31 RGB population are similar to those of the Milky Way halo.",0605170v1
2006-05-08,A New Method for Isolating M31 Red Giant Stars: The Discovery of Stars out to a Radial Distance of 165 Kiloparsecs,"We present a method for isolating a clean sample of red giant stars in the
outerregions of the Andromeda spiral galaxy (M31) from an ongoing spectroscopic
survey using the DEIMOS instrument on the Keck 10-m telescope. The survey aims
to study the kinematics, global structure, substructure, and metallicity of
M31's halo. Although most of our spectroscopic targets were photometrically
screened to reject foreground Milky Way dwarf star contaminants, the latter
class of objects still constitutes a substantial fraction of the observed
spectra in the sparse outer halo. Our likelihood-based method for isolating M31
red giants uses five criteria: (1) radial velocity, (2) photometry in the
intermediate-width DDO51 band to measure the strength of the MgH/Mgb absorption
features, (3) strength of the Na I 8190A absorption line doublet, (4) location
within an (I, V-I) color-magnitude diagram, and (5) comparison of photometric
(CMD-based) versus spectroscopic (Ca II 8500A triplet-based) metallicity
estimates. We also discuss K I and TiO diagnostics for giant/dwarf separation
that might be useful in future analyses. Training sets consisting of definite
M31 red giants and Galactic dwarf stars are used to derive empirical
probabilitydistribution functions for each diagnostic. These functions are used
to calculate the likelihood that a given star is a red giant in M31 versus a
Milky Way dwarf. By applying this diagnostic method to our spectroscopic data
set, we isolate 40 M31 red giants beyond a projected distance of R = 60 kpc
from the galaxy's center, including three out at R ~ 165 kpc. The ability to
identify individual M31 red giants gives us an unprecedented level of
sensitivity in studying the properties of the galaxy's outer halo.",0605171v2
2006-06-21,Extreme gas kinematics in the z=2.2 powerful radio galaxy MRC1138-262: Evidence for efficient AGN feedback in the early Universe?,"To explain the properties of the most massive low-redshift galaxies and the
shape of their mass function, recent models of galaxy evolution include strong
AGN feedback to complement starburst-driven feedback in massive galaxies. Using
the near-infrared integral-field spectrograph SPIFFI on the VLT, we searched
for direct evidence for such a feedback in the optical emission line gas around
the z=2.16 powerful radio galaxy MRC1138-262, likely a massive galaxy in
formation. The kpc-scale kinematics, with FWHMs and relative velocities <= 2400
km/s and nearly spherical spatial distribution, do not resemble large-scale
gravitational motion or starburst-driven winds. Order-of-magnitude timescale
and energy arguments favor the AGN as the only plausible candidate to
accelerate the gas, with a total energy injection of a few x 10^60 ergs or
more, necessary to power the outflow, and relatively efficient coupling between
radio jet and ISM. Observed outflow properties are in gross agreement with the
models, and suggest that AGN winds might have a similar, or perhaps larger,
cosmological significance than starburst-driven winds, if MRC1138-262 is indeed
archetypal. Moreover, the outflow has the potential to remove significant gas
fractions (<= 50%) from a >L* galaxy within a few 10 to 100 Myrs, fast enough
to preserve the observed [alpha/Fe] overabundance in massive galaxies at low
redshift. Using simple arguments, it appears that feedback like that observed
in MRC1138-262 may have sufficient energy to inhibit material from infalling
into the dark matter halo and thus regulate galaxy growth as required in some
recent models of hierarchical structure formation.",0606530v1
2006-05-02,Proton NMR measurements of the local magnetic field in the paramagnetic metal and antiferromagnetic insulator phases of $λ$-(BETS)$_{2}$FeCl$_{4}$,"Measurements of the $^{1}$H-NMR spectrum of a small ($\sim$ 4 $\mu$g) single
crystal of the organic conductor $\lambda$-(BETS)$_{2}$FeCl$_{4}$ are reported
with an applied magnetic field $\bf{B}$$_{0}$ = 9 T parallel to the a-axis in
the $ac$-plane over a temperature $(T)$ range 2.0 $-$ 180 K. They provide the
distribution of the static local magnetic field at the proton sites in the
paramagnetic metal (PM) and antiferromagnetic insulator (AFI) phases, along
with the changes that occur at the PM$-$AFI phase transition. The spectra have
six main peaks that are significantly broadened and shifted at low $T$. The
origin of these features is attributed to the large dipolar field from the 3d
Fe$^{3+}$ ion moments (spin $S_{\rm{d}}$ = 5/2). Their amplitude and
$T-$dependence are modeled using a modified Brillouin function that includes a
mean field approximation for the total exchange interaction ($J_{0}$) between
one Fe$^{3+}$ ion and its two nearest neighbors. A good fit is obtained using
$J_{0}$ = $-$ 1.7 K. At temperatures below the PM$-$AFI transition temperature
$T_{MI}$ = 3.5 K, an extra peak appears on the high frequency side of the
spectrum and the details of the spectrum become smeared. Also, the rms
linewidth and the frequency shift of the spectral distribution are
discontinuous, consistent with the transition being first-order. These
measurements verify that the dominant local magnetic field contribution is from
the Fe$^{3+}$ ions and indicate that there is a significant change in the
static local magnetic field distribution at the proton sites on traversing the
PM to AFI phase transition.",0605044v2
2006-09-07,$^{1}$H-NMR spin-echo measurements of the static and dynamic spin properties in $λ$-(BETS)$_{2}$FeCl$_{4}$,"$^{1}$H-NMR spin-echo measurements of the spin-echo decay $M(2\tau)$ with a
decay rate 1/$T_{2}$ and the frequency shift $\Delta\nu/\nu_{0}$ under applied
magnetic field $\mathbf{B}$$_{0}$ = 9 T along the a-axis over a temperature
range 2.0$-$180 K are reported for a single crystal of the organic conductor
$\lambda$-(BETS)$_{2}$FeCl$_{4}$. It provides the spin dynamic and static
properties in the paramagnetic metal (PM) and antiferromagnetic insulator (AFI)
states as well as across the PM$-$AFI phase transition. A large slow beat
structure in the spin-echo decay is observed with a typical beat frequency of
$f$ $\sim$ 7 kHz and it varies across the spectrum. Its origin is attributed to
the $^{1}$H$-$$^{1}$H dipole interactions rather than to the much larger
dipolar field contribution from the Fe$^{3+}$ electrons (spin $S$ = 5/2). A
simple phenomenological model provides an excellent fit to the data. The
dominant $^{1}$H-NMR frequency shift comes from the dipolar field from the 3d
Fe$^{3+}$ ions, and the Fe$^{3+}$ $-$ Fe$^{3+}$ exchange interactions ($J_{0}$)
($J_{0} $ includes the d$-$d exchange interactions through the $\pi-$electrons)
have a substantial effect to the local field at the proton sites expecially at
low temperatures. A good fit is obtained with $J_{0}$ = - 1.7 K. The data of
the spin-echo decay rate 1/$T_{2}$ indicates that there is a significant change
in the slow fluctuations of the local magnetic field at the $^{1}$H-sites on
traversing the PM to AFI phase. This evidence supports earlier reports that the
PM$-$AFI phase transition in $\lambda$-(BETS)$_{2}% $FeCl$_{4} $ is driven
magnetically and first order.",0609151v2
2007-05-14,"TrES-3: A Nearby, Massive, Transiting Hot Jupiter in a 31-Hour Orbit","We describe the discovery of a massive transiting hot Jupiter with a very
short orbital period (1.30619 d), which we name TrES-3. From spectroscopy of
the host star GSC 03089-00929, we measure T_eff = 5720 +- 150 K, logg=4.6 +-
0.3, and vsini < 2 km/s, and derive a stellar mass of 0.90 +- 0.15 M_sun. We
estimate a planetary mass of 1.92 +- 0.23 M_Jup, based on the sinusoidal
variation of our high-precision radial velocity measurements. This variation
has a period and phase consistent with our transit photometry. Our spectra show
no evidence of line bisector variations that would indicate a blended eclipsing
binary star. From detailed modeling of our B and z photometry of the 2.5%-deep
transits, we determine a stellar radius 0.802 +- 0.046 R_sun and a planetary
radius 1.295 +- 0.081 R_Jup. TrES-3 has one of the shortest orbital periods of
the known transiting exoplanets, facilitating studies of orbital decay and mass
loss due to evaporation, and making it an excellent target for future studies
of infrared emission and reflected starlight.",0705.2004v1
2007-08-06,TrES-4: A Transiting Hot Jupiter of Very Low Density,"We report the discovery of TrES-4, a hot Jupiter that transits the star GSC
02620-00648 every 3.55 days. From high-resolution spectroscopy of the star we
estimate a stellar effective temperature of Teff = 6100 +/- 150 K, and from
high-precision z and B photometry of the transit we constrain the ratio of the
semi-major axis and the stellar radius to be a/R = 6.03 +/- 0.13. We compare
these values to model stellar isochrones to constrain the stellar mass to be M*
= 1.22 +/- 0.17 Msun. Based on this estimate and the photometric time series,
we constrain the stellar radius to be R* = 1.738 +/- 0.092 Rsun and the planet
radius to be Rp = 1.674 +/- 0.094 RJup. We model our radial-velocity data
assuming a circular orbit and find a planetary mass of 0.84 +/- 0.10 MJup. Our
radial-velocity observations rule out line-bisector variations that would
indicate a specious detection resulting from a blend of an eclipsing binary
system. TrES-4 has the largest radius and lowest density of any of the known
transiting planets. It presents a challenge to current models of the physical
structure of hot Jupiters, and indicates that the diversity of physical
properties amongst the members of this class of exoplanets has yet to be fully
explored.",0708.0834v1
2007-08-30,Compact radio sources and jet-driven AGN feedback in the early Universe: Constraints from integral-field spectroscopy,"To investigate the impact of radio jets during the formation epoch of their
massive host galaxies, we present an analysis of two massive, log(M_stel/
M_sun)~10.6 and 11.3, compact radio galaxies at z=3.5, TNJ0205+2242 and
TNJ0121+1320. Their small radio sizes (R<= 10 kpc) are most likely a sign of
youth. We compare their radio properties and gas dynamics with those in well
extended radio galaxies at high redshift, which show strong evidence for
powerful, jet-driven outflows of significant gas masses (M 10^9-10 M_sun). Our
analysis combines rest-frame optical integral-field spectroscopy with existing
radio imaging, CO emission line spectra, and rest-frame UV spectroscopy.
[OIII]5007 line emission is compact in both galaxies and lies within the region
defined by the radio lobes. For TNJ0205+2242, the Ly-alpha profile narrows
significantly outside the jet radius, indicating the presence of a quiescent
halo. TNJ0121+1320 has two components separated by ~10 kpc and a velocity
offset of ~300 km s^-1. If motions are gravitational, this implies a dynamical
mass of 2x10^11 M_sun for the more massive, radio-loud component. The dynamical
mass, molecular gas mass measured from the CO line emission, and radio
luminosity of these two compact radio galaxies imply that compact radio sources
may well develop large-scale, energetic outflows as observed in extended radio
galaxies, with the potential of removing significant fractions of the ISM from
the host galaxy. The absence of luminous emission line gas extending beyond the
radio emission in these sources agrees with the observed timescales and outflow
rates in extended radio galaxies, and adds further evidence that the energetic,
large-scale outflows observed in extended radio sources (Nesvadba et al. 2006)
are indeed the result of influence of the radio jet.",0708.4150v1
2008-08-19,The Extended Star Formation History of the Andromeda Spheroid at 35 Kpc on the Minor Axis,"Using the HST ACS, we have obtained deep optical images reaching well below
the oldest main sequence turnoff in fields on the southeast minor-axis of the
Andromeda Galaxy, 35 kpc from the nucleus. These data probe the star formation
history in the extended halo of Andromeda -- that region beyond 30 kpc that
appears both chemically and morphologically distinct from the metal-rich,
highly-disturbed inner spheroid. The present data, together with our previous
data for fields at 11 and 21 kpc, do not show a simple trend toward older ages
and lower metallicities, as one might expect for populations further removed
from the obvious disturbances of the inner spheroid. Specifically, the mean
ages and [Fe/H] values at 11 kpc, 21 kpc, and 35 kpc are 9.7 Gyr and -0.65,
11.0 Gyr and -0.87, and 10.5 Gyr and -0.98, respectively. In the best-fit model
of the 35 kpc population, one third of the stars are younger than 10 Gyr, while
only ~10% of the stars are truly ancient and metal-poor. The extended halo thus
exhibits clear evidence of its hierarchical assembly, and the contribution from
any classical halo formed via early monolithic collapse must be small.",0808.2648v1
2008-09-30,"Evidence for powerful AGN winds at high redshift: Dynamics of galactic outflows in radio galaxies during the ""Quasar Era""","AGN feedback now appears as an attractive mechanism to resolve some of the
outstanding problems with the ""standard"" cosmological models, in particular
those related to massive galaxies. To directly constrain how this may influence
the formation of massive galaxies near the peak in the redshift distribution of
powerful quasars, z~2, we present an analysis of the emission-line kinematics
of 3 powerful radio galaxies at z~2-3 (HzRGs) based on rest-frame optical
integral-field spectroscopy obtained with SINFONI on the VLT. HzRGs are among
the most massive galaxies, so AGN feedback may have a particularly clear
signature. We find evidence for bipolar outflows in all HzRGs, with kinetic
energies that are equivalent to 0.2% of the rest-mass of the supermassive black
hole. Velocity offsets in the outflows are ~800-1000 km s^-1 between the
blueshifted and redshifted line emission, FWHMs ~1000 km s^-1 suggest strong
turbulence. Ionized gas masses estimated from the Ha luminosity are of order
10^10 M_s, similar to the molecular gas content of HzRGs, underlining that
these outflows may indicate a significant phase in the evolution of the host
galaxy. The total energy release of ~10^60 erg during a dynamical time of ~10^7
yrs corresponds to about the binding energy of a massive galaxy. Geometry,
timescales and energy injection rates of order 10% of the kinetic energy flux
of the jet suggest that the outflows are most likely driven by the radio
source. The global energy density release of ~10^57 erg s^-1 Mpc^-3 may also
influence the subsequent evolution of the HzRG by enhancing the entropy and
pressure in the surrounding halo and facilitating ram-pressure stripping of gas
in satellite galaxies that may contribute to the subsequent mass assembly of
the HzRG through low-dissipation ""dry"" mergers.",0809.5171v2
2009-02-16,The Role of Dwarf Galaxies in Building Large Stellar Halos,"The hierarchical theory of galaxy formation rests on the idea that smaller
galactic structures merge to form the galaxies that we see today. The past
decade has provided remarkable observational support for this scenario, driven
in part by advances in spectroscopic instrumentation. Multi-object spectroscopy
enabled the discovery of kinematically cold substructures around the Milky Way
and M31 that are likely the debris of disrupting satellites. Improvements in
high-resolution spectroscopy have produced key evidence that the abundance
patterns of the Milky Way halo and its dwarf satellites can be explained by
Galactic chemical evolution models based on hierarchical assembly.
  These breakthroughs have depended almost entirely on observations of nearby
stars in the Milky Way and luminous red giant stars in M31 and Local Group
dwarf satellites. In the next decade, extremely large telescopes will allow
observations far down the luminosity function in the known dwarf galaxies, and
they will enable observations of individual stars far out in the Galactic halo.
The chemical abundance census now available for the Milky Way will become
possible for our nearest neighbor, M31. Velocity dispersion measurements now
available in M31 will become possible for systems beyond the Local Group such
as Sculptor and M81 Group galaxies. Detailed studies of a greater number of
individual stars in a greater number of spiral galaxies and their satellites
will test hierarchical assembly in new ways because dynamical and chemical
evolution models predict different outcomes for halos of different masses in
different environments.",0902.2591v2
2009-06-12,Mass and radius determinations for five transiting M-dwarf stars,"We have derived masses and radii for both components in five short-period
single-lined eclipsing binary stars discovered by the TrES wide-angle
photometric survey for transiting planets. All these systems consist of a
visible F-star primary and an unseen M-star secondary (M_A > 0.8 M_sun, M_B <
0.45 M_sun). The spectroscopic orbital solution combined with a high precision
transit light curve for each system gives sufficient information to calculate
the density of the primary star and the surface gravity of the secondary. The
masses of the primary stars were obtained using stellar evolution models. The
solutions were compared with results obtained by calculating the radius of the
primary stars under the assumption of rotational synchronization with the
orbital period and alignment between their spin axis and the axis of the orbit.
Four systems show an acceptable match between the two sets of results, but one
system shows a clear mismatch between the two solutions, which may indicate the
absence of synchronization or a misalignment between the rotational and orbital
axis. When compared to low-mass stellar evolution models, the derived masses
and radii of the unseen M dwarfs are inconsistent (three only marginally) with
the predicted values, with all of the radii being larger than expected for
their masses. These results confirm the discrepancy shown in previous work
between the predicted and observed radii on low-mass binary stars. This work
also shows that reliance on the assumption of synchronization to derive the
mass and radius of stars in eclipsing single--lined F+M binaries is a useful
tool, but may not always be warranted and should be carefully tested against
stellar evolution models.",0906.2207v2
2009-06-23,"GJ 3236: a new bright, very low-mass eclipsing binary system discovered by the MEarth observatory","We report the detection of eclipses in GJ 3236, a bright (I = 11.6) very low
mass binary system with an orbital period of 0.77 days. Analysis of light- and
radial velocity curves of the system yielded component masses of 0.38 +/- 0.02
and 0.28 +/- 0.02 Msol. The central values for the stellar radii are larger
than the theoretical models predict for these masses, in agreement with the
results for existing eclipsing binaries, although the present 5% observational
uncertainties limit the significance of the larger radii to approximately 1
sigma. Degeneracies in the light curve models resulting from the unknown
configuration of surface spots on the components of GJ 3236 currently dominate
the uncertainties in the radii, and could be reduced by obtaining precise,
multi-band photometry covering the full orbital period. The system appears to
be tidally synchronized and shows signs of high activity levels as expected for
such a short orbital period, evidenced by strong Halpha emission lines in the
spectra of both components. These observations probe an important region of
mass-radius parameter space around the predicted transition to fully-convective
stellar interiors, where there are a limited number of precise measurements
available in the literature.",0906.4365v1
2009-07-03,The NGC 300 Transient: An Alternative Method For Measuring Progenitor Masses,"We present an alternative technique for measuring the precursor masses of
transient events in stars undergoing late stage stellar evolution. We use the
well-established techniques of stellar population modeling to age-date the
stars surrounding the site of the recent transient event in NGC 300 (NGC 300
OT2008-1). The surrounding stars must share a common turnoff mass with the
transient, since almost all stars form in stellar clusters that remain
physically associated for periods longer than the lifetime of the most massive
stars. We find that the precursor of NGC 300 OT2008-1 is surrounded by stars
that formed in a single burst between 8-13 Myr ago, with 70% confidence. The
transient was therefore likely to be due to a progenitor whose mass falls
between the main sequence turnoff mass (12 Msun) and the maximum stellar mass
(25 Msun) found for isochrones bounding this age range. We characterize the
general applicability of this technique in identifying precursor masses of
historic and future transients and supernovae (SNe), noting that it requires
neither precursor imaging nor sub-arcsecond accuracy in the position of the
transient. It is also based on the well-understood physics of the main
sequence, and thus may be a more reliable source of precursor masses than
fitting evolutionary tracks to precursor magnitudes. We speculate that if the
progenitor mass is close to 17 Msun, there may be a connection between optical
transients such as NGC 300 OT2008-1 and the missing type II-P SNe, known as the
""red supergiant problem.""",0907.0710v2
2009-08-03,"A binary engine fuelling HD87643' s complex circumstellar environment, using AMBER/VLTI","Context. The star HD 87643, exhibiting the ""B[e] phenomenon"", has one of the
most extreme infrared excesses for this object class. It harbours a large
amount of both hot and cold dust, and is surrounded by an extended reflection
nebula. Aims. One of our major goals was to investigate the presence of a
companion in HD87643. In addition, the presence of close dusty material was
tested through a combination of multi-wavelength high spatial 5Aresolution
observations. Methods. We observed HD 87643 with high spatial resolution
techniques, using the near-IR AMBER/VLTI interferometer with baselines ranging
from 60 m to 130 m and the mid-IR MIDI/VLTI interferometer with baselines
ranging from 25 m to 65 m. These observations are complemented by NACO/VLT
adaptive-optics-corrected images in the K and L-bands, ESO-2.2m optical
Wide-Field Imager large-scale images in the B, V and R-bands, Results. We
report the direct detection of a companion to HD 87643 by means of image
synthesis using the AMBER/VLTI instrument. The presence of the companion is
confirmed by the MIDI and NACO data, although with a lower confidence. The
companion is separated by ~ 34 mas with a roughly north-south orientation. The
period must be large (several tens of years) and hence the orbital parameters
are not determined yet. Binarity with high eccentricity might be the key to
interpreting the extreme characteristics of this system, namely a dusty
circumstellar envelope around the primary, a compact dust nebulosity around the
binary system and a complex extended nebula witnessing past violent ejections.",0908.0227v2
2009-08-12,"Refined stellar, orbital and planetary parameters of the eccentric HAT-P-2 planetary system","We present refined parameters for the extrasolar planetary system HAT-P-2
(also known as HD 147506), based on new radial velocity and photometric data.
HAT-P-2b is a transiting extrasolar planet that exhibits an eccentric orbit. We
present a detailed analysis of the planetary and stellar parameters, yielding
consistent results for the mass and radius of the star, better constraints on
the orbital eccentricity, and refined planetary parameters. The improved
parameters for the host star are M_star = 1.36 +/- 0.04 M_sun and R_star = 1.64
+/- 0.08 R_sun, while the planet has a mass of M_p = 9.09 +/- 0.24 M_Jup and
radius of R_p = 1.16 +/- 0.08 R_Jup. The refined transit epoch and period for
the planet are E = 2,454,387.49375 +/- 0.00074 (BJD) and P = 5.6334729 +/-
0.0000061 (days), and the orbital eccentricity and argument of periastron are e
= 0.5171 +/- 0.0033 and omega = 185.22 +/- 0.95 degrees. These orbital elements
allow us to predict the timings of secondary eclipses with a reasonable
accuracy of ~15 minutes. We also discuss the effects of this significant
eccentricity including the characterization of the asymmetry in the transit
light curve. Simple formulae are presented for the above, and these, in turn,
can be used to constrain the orbital eccentricity using purely photometric
data. These will be particularly useful for very high precision, space-borne
observations of transiting planets.",0908.1705v2
2009-09-17,"The SPLASH Survey: A Spectroscopic Analysis of the Metal-Poor, Low-Luminosity M31 dSph Satellite Andromeda X","Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal
galaxy (dSph) found by Zucker et al. (2007) in the Sloan Digital Sky Survey
(SDSS - York et al. 2000). In this paper, we present the first spectroscopic
study of individual red giant branch stars in And X, as a part of the SPLASH
Survey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo).
Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two
spectroscopic masks over the face of the galaxy and measure radial velocities
for ~100 stars with a median accuracy of sigma_v ~ 3 km/s. The velocity
histogram for this field confirms three populations of stars along the sight
line: foreground Milky Way dwarfs at small negative velocities, M31 halo red
giants over a broad range of velocities, and a very cold velocity ``spike''
consisting of 22 stars belonging to And X with v_rad = -163.8 +/- 1.2 km/s. By
carefully considering both the random and systematic velocity errors of these
stars (e.g., through duplicate star measurements), we derive an intrinsic
velocity dispersion of just sigma_v = 3.9 +/- 1.2 km/s for And X, which for its
size, implies a minimum mass-to-light ratio of M/L =37^{+26}_{-19} assuming the
mass traces the light. Based on the clean sample of member stars, we measure
the median metallicity of And X to be [Fe/H] = -1.93 +/- 0.11, with a slight
radial metallicity gradient. The dispersion in metallicity is large,
sigma([Fe/H]) = 0.48, possibly hinting that the galaxy retained much of its
chemical enrichment products. We discuss the potential for better understanding
the formation and evolution mechanisms for M31's system of dSphs through
(current) kinematic and chemical abundance studies, especially in relation to
the Milky Way sample. (abridged version)",0909.3298v1
2009-11-11,"The SPLASH Survey: Internal Kinematics, Chemical Abundances, and Masses of the Andromeda I, II, III, VII, X, and XIV dSphs","We present new Keck/DEIMOS spectroscopic observations of hundreds of
individual stars along the sightline to Andromeda's first three discovered
dwarf spheroidal galaxies (dSphs) - And I, II, and III, and leverage recent
observations by our team of three additional dSphs, And VII, X, and XIV, as a
part of the SPLASH Survey. Member stars of each dSph are isolated from
foreground Milky Way dwarf and M31 field contamination using a variety of
photometric and spectroscopic diagnostics. Our final spectroscopic sample of
member stars in each dSph, for which we measure accurate radial velocities with
a median uncertainty (random plus systematic errors) of 4 - 5 km/s, includes 80
red giants in And I, 95 in And II, 43 in And III, 18 in And VII, 22 in And X,
and 38 in And XIV. The sample of confirmed members in the six dSphs are used to
derive each system's mean radial velocity, intrinsic central velocity
dispersion, mean abundance, abundance spread, and dynamical mass. This combined
data set presents us with a unique opportunity to perform the first systematic
comparison of the global properties (e.g., metallicities, sizes, and dark
matter masses) of one-third of Andromeda's total known dSph population with
Milky Way counterparts of the same luminosity. We discuss both the
luminosity-metallicity relation and the luminosity-size relation of these
satellites, and find that the chemical evolution histories of each host's
satellites is similar. The dynamical mass estimates of M31's dSphs are similar
or smaller than Milky Way dSphs of the same luminosity despite their sizes
being similar or larger, suggesting M31 dSphs are less dense than Milky Way
counterparts. The implications of these results for general understanding of
galaxy formation and evolution is summarized. Abridged.",0911.1998v3
2009-11-19,Local Group Dwarf Elliptical Galaxies: II. Stellar Kinematics to Large Radii in NGC 147 and NGC 185,"We present kinematic and metallicity profiles for the M31 dwarf elliptical
(dE) satellite galaxies NGC 147 and NGC 185. The profiles represent the most
extensive spectroscopic radial coverage for any dE galaxy, extending to a
projected distance of eight half-light radii (8 r_eff = 14'). We achieve this
coverage via Keck/DEIMOS multislit spectroscopic observations of 520 and 442
member red giant branch stars in NGC 147 and NGC 185, respectively. In contrast
to previous studies, we find that both dEs have significant internal rotation.
We measure a maximum rotational velocity of 17+/-2 km/s for NGC 147 and 15+/-5
km/s for NGC 185. The velocity dispersions decrease gently with radius with an
average dispersion of 16+/-1 km/s for NGC 147 and 24+/-1 km/s for NGC 185. Both
dEs have internal metallicity dispersions of 0.5 dex, but show no evidence for
a radial metallicity gradient. We construct two-integral axisymmetric dynamical
models and find that the observed kinematical profiles cannot be explained
without modest amounts of non-baryonic dark matter. We measure central
mass-to-light ratios of ML_V = 4.2+/-0.6 and ML_V = 4.6+/-0.6 for NGC 147 and
NGC 185, respectively. Both dE galaxies are consistent with being primarily
flattened by their rotational motions, although some anisotropic velocity
dispersion is needed to fully explain their observed shapes. The velocity
profiles of all three Local Group dEs (NGC 147, NGC 185 and NGC 205) suggest
that rotation is more prevalent in the dE galaxy class than previously assumed,
but is often manifest only at several times the effective radius. Since all dEs
outside the Local Group have been probed to only inside the effective radius,
this opens the door for formation mechanisms in which dEs are transformed or
stripped versions of gas-rich rotating progenitor galaxies.",0911.3654v2
2009-11-20,The ACS Nearby Galaxy Survey Treasury IV. The Star Formation History of NGC 2976,"We present resolved stellar photometry of NGC 2976 obtained with the Advanced
Camera for Surveys (ACS) as part of the ACS Nearby Galaxy Survey Treasury
(ANGST) program. The data cover the radial extent of the major axis of the disk
out to 6 kpc, or ~6 scale lengths. The outer disk was imaged to a depth of
M_F606W ~ 1, and an inner field was imaged to the crowding limit at a depth of
M_F606W ~ -1. Through detailed analysis and modeling of these CMDs we have
reconstructed the star formation history of the stellar populations currently
residing in these portions of the galaxy, finding similar ancient populations
at all radii but significantly different young populations at increasing radii.
In particular, outside of the well-measured break in the disk surface
brightness profile, the age of the youngest population increases with distance
from the galaxy center, suggesting that star formation is shutting down from
the outside-in. We use our measured star formation history, along with H I
surface density measurements, to reconstruct the surface density profile of the
disk during previous epochs. Comparisons between the recovered star formation
rates and reconstructed gas densities at previous epochs are consistent with
star formation following the Schmidt law during the past 0.5 Gyrs, but with a
drop in star formation efficiency at low gas densities, as seen in local
galaxies at the present day. The current rate and gas density suggest that
rapid star formation in NGC 2976 is currently in the process of ceasing from
the outside-in due to gas depletion. This process of outer disk gas depletion
and inner disk star formation was likely triggered by an interaction with the
core of the M81 group >~1 Gyr ago that stripped the gas from the galaxy halo
and/or triggered gas inflow from the outer disk toward the galaxy center.",0911.4121v1
2009-12-07,OB Stars & Stellar Bowshocks in Cygnus-X: A Novel Laboratory Estimating Stellar Mass Loss Rates,"We use mid-IR images from the Spitzer Cygnus~X Legacy Survey to search for
stellar bowshocks, a signature of early type ""runaway"" stars with high space
velocities. We identify ten arc-shaped nebulae containing centrally located
stars as candidate bowshocks. New spectroscopic observations of five stars show
that all are late O to early B dwarfs. Our morphologically selected sample of
bowshock candidates encompasses diverse physical phenomena. Three of the stars
appear to be pre-main-sequence objects on the basis of rising SEDs in the
mid-IR, and their nebulae may be photon-dominated regions (PDRs). Four objects
have ambiguous classification. These may be partial dust shells or bubbles. We
conclude that three of the objects are probable bowshocks, based on their
morphological similarity to analytic prescriptions. Their nebular morphologies
reveal no systematic pattern of orientations that might indicate either a
population of stars ejected from or large-scale hydrodynamic outflows from Cyg
OB2. The fraction of runaways among OB stars near Cyg OB2 identified either by
radial velocity or bowshock techniques is ~0.5%, much smaller than the 8%
estimated among field OB stars. We also obtained a heliocentric radial velocity
for the previously known bowshock star, BD+43\degr3654, of -66.2+/-9.4 km/s,
solidifying its runaway status and implying a space velocity of 77+/-10 km/s.
We use the principles of momentum-driven bowshocks to arrive at a novel method
for estimating stellar mass loss rates. Derived mass loss rates range between
10^-7 and few x10^-6 solar masses/yr for the three O5V -- ~B2V stars identified
as generating bowshocks. These values are at the upper range of, but broadly
consistent with, estimates from other methods. (Abridged)",0912.1314v1
2010-01-27,Mass-radius relationships for exoplanets,"For planets other than Earth, interpretation of the composition and structure
depends largely on comparing the mass and radius with the composition expected
given their distance from the parent star. The composition implies a
mass-radius relation which relies heavily on equations of state calculated from
electronic structure theory and measured experimentally on Earth. We lay out a
method for deriving and testing equations of state, and deduce mass-radius and
mass-pressure relations for key materials whose equation of state is reasonably
well established, and for differentiated Fe/rock. We find that variations in
the equation of state, such as may arise when extrapolating from low pressure
data, can have significant effects on predicted mass- radius relations, and on
planetary pressure profiles. The relations are compared with the observed
masses and radii of planets and exoplanets. Kepler-10b is apparently 'Earth-
like,' likely with a proportionately larger core than Earth's, nominally 2/3 of
the mass of the planet. CoRoT-7b is consistent with a rocky mantle over an
Fe-based core which is likely to be proportionately smaller than Earth's. GJ
1214b lies between the mass-radius curves for H2O and CH4, suggesting an 'icy'
composition with a relatively large core or a relatively large proportion of
H2O. CoRoT-2b is less dense than the hydrogen relation, which could be
explained by an anomalously high degree of heating or by higher than assumed
atmospheric opacity. HAT-P-2b is slightly denser than the mass-radius relation
for hydrogen, suggesting the presence of a significant amount of matter of
higher atomic number. CoRoT-3b lies close to the hydrogen relation. The
pressure at the center of Kepler-10b is 1.5+1.2-1.0 TPa. The central pressure
in CoRoT-7b is probably close to 0.8TPa, though may be up to 2TPa.",1001.4851v3
2010-02-09,The ACS Nearby Galaxy Survey Treasury V. Radial Star Formation History of NGC 300,"We present new Hubble Space Telescope (HST) observations of NGC 300 taken as
part of the ACS Nearby Galaxy Survey Treasury (ANGST). Individual stars are
resolved in these images down to an absolute magnitude of M_F814W = 1.0 (below
the red clump). We determine the star formation history of the galaxy in 6
radial bins by comparing our observed color-magnitude diagrams (CMDs) with
synthetic CMDs based on theoretical isochrones. We find that the stellar disk
out to 5.4 kpc is primarily old, in contrast with the outwardly similar galaxy
M33. We determine the scale length as a function of age and find evidence for
inside-out growth of the stellar disk: the scale length has increased from 1.1
+/- 0.1 kpc 10 Gyr ago to 1.3 +/- 0.1 kpc at present, indicating a buildup in
the fraction of young stars at larger radii. As the scale length of M33 has
recently been shown to have increased much more dramatically with time, our
results demonstrate that two galaxies with similar sizes and morphologies can
have very different histories. With an N-body simulation of a galaxy designed
to be similar to NGC 300, we determine that the effects of radial migration
should be minimal. We trace the metallicity gradient as a function of time and
find a present day metallicity gradient consistent with that seen in previous
studies. Consistent results are obtained from archival images covering the same
radial extent but differing in placement and filter combination.",1002.1743v1
2010-04-28,The ACS Nearby Galaxy Survey Treasury VI. The Ancient Star Forming disk of NGC 404,"We present HST/WFPC2 observations across the disk of the nearby isolated
dwarf S0 galaxy NGC 404, which hosts an extended gas disk. Our deepest field
reaches the red clump and main-sequence stars with ages <500 Myr. Although we
detect trace amounts of star formation at times more recent than 10 Gyr for all
fields, the proportion of red giant stars to asymptotic giants and main
sequence stars suggests that the disk is dominated by an ancient (>10 Gyr)
population. Detailed modeling of the color-magnitude diagram suggests that ~70%
of the stellar mass in the NGC 404 disk formed by z~2 (10 Gyr ago) and at least
~90% formed prior to z~1 (8 Gyr ago). These results indicate that the stellar
populations of the NGC 404 disk are on average significantly older than those
of other nearby disk galaxies, suggesting that early and late type disks may
have different long-term evolutionary histories, not simply differences in
their recent star formation rates. Comparisons of the spatial distribution of
the young stellar mass and FUV emission in GALEX images show that the brightest
FUV regions contain the youngest stars, but that some young stars (<160 Myr)
lie outside of these regions. FUV luminosity appears to be strongly affected by
both age and stellar mass within individual regions. Finally, we use our
measurements to infer the relationship between the star formation rate and the
gas density of the disk at previous epochs. We find that most of the history of
the NGC 404 disk is consistent with star formation that has decreased with the
gas density according to the Schmidt law. However, 0.5-1 Gyr ago, the star
formation rate was unusually low for the inferred gas density, consistent with
the possibility that there was a gas accretion event that reignited star
formation ~0.5 Gyr ago. Such an event could explain why this S0 galaxy hosts an
extended gas disk.",1004.5135v1
2010-06-13,The 21 cm Signature of Cosmic String Wakes,"We discuss the signature of a cosmic string wake in 21cm redshift surveys.
Since 21cm surveys probe higher redshifts than optical large-scale structure
surveys, the signatures of cosmic strings are more manifest in 21cm maps than
they are in optical galaxy surveys. We find that, provided the tension of the
cosmic string exceeds a critical value (which depends on both the redshift when
the string wake is created and the redshift of observation), a cosmic string
wake will generate an emission signal with a brightness temperature which
approaches a limiting value which at a redshift of $z + 1 = 30$ is close to 400
mK in the limit of large string tension. The signal will have a specific
signature in position space: the excess 21cm radiation will be confined to a
wedge-shaped region whose tip corresponds to the position of the string, whose
planar dimensions are set by the planar dimensions of the string wake, and
whose thickness (in redshift direction) depends on the string tension. For
wakes created at $z_i + 1 = 10^3$, then at a redshift of $z + 1 = 30$ the
critical value of the string tension $\mu$ is $G \mu = 6 \times 10^{-7}$, and
it decreases linearly with redshift (for wakes created at the time of equal
matter and radiation, the critical value is a factor of two lower at the same
redshift). For smaller tensions, cosmic strings lead to an observable
absorption signal with the same wedge geometry.",1006.2514v3
2010-09-23,The ACS Nearby Galaxy Survey Treasury IX. Constraining asymptotic giant branch evolution with old metal-poor galaxies,"In an attempt to constrain evolutionary models of the asymptotic giant branch
(AGB) phase at the limit of low masses and low metallicities, we have examined
the luminosity functions and number ratio between AGB and red giant branch
(RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy
Survey Treasury (ANGST). This database provides HST optical photometry together
with maps of completeness, photometric errors, and star formation histories for
dozens of galaxies within 4 Mpc. We select 12 galaxies characterized by
predominantly metal-poor populations as indicated by a very steep and blue RGB,
and which do not present any indication of recent star formation in their
color--magnitude diagrams. Thousands of AGB stars brighter than the tip of the
RGB (TRGB) are present in the sample (between 60 and 400 per galaxy), hence the
Poisson noise has little impact in our measurements of the AGB/RGB ratio. We
model the photometric data with a few sets of thermally pulsing AGB (TP-AGB)
evolutionary models with different prescriptions for the mass loss. This
technique allows us to set stringent constraints to the TP-AGB models of
low-mass metal-poor stars (with M<1.5 Msun, [Fe/H]<~-1.0). Indeed, those which
satisfactorily reproduce the observed AGB/RGB ratios have TP-AGB lifetimes
between 1.2 and 1.8 Myr, and finish their nuclear burning lives with masses
between 0.51 and 0.55 Msun. This is also in good agreement with recent
observations of white dwarf masses in the M4 old globular cluster. These
constraints can be added to those already derived from Magellanic Cloud star
clusters as important mileposts in the arduous process of calibrating AGB
evolutionary models.",1009.4618v1
2010-11-08,Least Squares Ranking on Graphs,"Given a set of alternatives to be ranked, and some pairwise comparison data,
ranking is a least squares computation on a graph. The vertices are the
alternatives, and the edge values comprise the comparison data. The basic idea
is very simple and old: come up with values on vertices such that their
differences match the given edge data. Since an exact match will usually be
impossible, one settles for matching in a least squares sense. This formulation
was first described by Leake in 1976 for rankingfootball teams and appears as
an example in Professor Gilbert Strang's classic linear algebra textbook. If
one is willing to look into the residual a little further, then the problem
really comes alive, as shown effectively by the remarkable recent paper of
Jiang et al. With or without this twist, the humble least squares problem on
graphs has far-reaching connections with many current areas ofresearch. These
connections are to theoretical computer science (spectral graph theory, and
multilevel methods for graph Laplacian systems); numerical analysis (algebraic
multigrid, and finite element exterior calculus); other mathematics (Hodge
decomposition, and random clique complexes); and applications (arbitrage, and
ranking of sports teams). Not all of these connections are explored in this
paper, but many are. The underlying ideas are easy to explain, requiring only
the four fundamental subspaces from elementary linear algebra. One of our aims
is to explain these basic ideas and connections, to get researchers in many
fields interested in this topic. Another aim is to use our numerical
experiments for guidance on selecting methods and exposing the need for further
development.",1011.1716v4
2010-12-20,Integrable embeddings and foliations,"A k-submanifold L of an open n-manifold M is called weakly integrable (WI)
[resp. strongly integrable (SI)] if there exists a submersion \Phi:M\to R^{n-k}
such that L\subset \Phi^{-1}(0) [resp. L= \Phi^{-1}(0)]. In this work we study
the following problem, first stated in a particular case by Costa et al.
(Invent. Math. 1988): which submanifolds L of an open manifold M are WI or SI?
For general M, we explicitly solve the case k=n-1 and provide necessary and
sufficient conditions for submanifolds to be WI and SI in higher codimension.
As particular cases we recover the theorem of Bouma and Hector (Indagationes
Math. 1983) asserting that any open orientable surface is SI in R^3, and
Watanabe's and Miyoshi's theorems (Topology 1993 and 1995) claiming that any
link is WI in an open 3-manifold. In the case M=R^n we fully characterize WI
and SI submanifolds, we provide examples of 3- and 7-manifolds which are not WI
and we show that a theorem by Miyoshi (Topology 1995) which states that any
link in R^3 is SI does not hold in general. The right analogue to Miyoshi's
theorem is also proved, implying in particular the surprising result that no
knot in R^3 is SI. Our results applied to the theory of foliations of Euclidean
spaces give rise to some striking corollaries: using some topological
invariants we classify all the submanifolds of R^n which can be realized as
proper leaves of foliations; we prove that S^3 can be realized as a leaf of a
foliation of R^n, n\geq 7, but not in R^5 or R^6, which partially answers a
question by Vogt (Math. Ann. 1993); we construct open 3-manifolds which cannot
be leaves of a foliation of any compact 4-manifold but are proper leaves in
R^4. The theory of WI and SI submanifolds is a framework where many classical
tools of differential and algebraic topology play a prominent role:
h-principle, complete intersections and the theory of immersions and
embeddings.",1012.4312v1
2011-01-06,How Typical Are The Local Group Dwarf Galaxies?,"We compare the cumulative star formation histories (SFHs) of Local Group (LG)
dwarf galaxies with those in the volume-limited ACS Nearby Galaxy Survey
Treasury (ANGST) sample (D < 4 Mpc), in order to understand how typical the LG
dwarf galaxies are relative to those in the nearby universe. The SFHs were
derived in a uniform manner from high quality optical color-magnitude diagrams
constructed from Hubble Space Telescope imaging. We find that the {\it mean}
cumulative SFHs of the LG dwarfs are comparable to the mean cumulative SFHs of
the ANGST sample for the three different morphological types (dwarf
spheroidals/ellipticals: dSph/dE; dwarf irregulars: dI; transition dwarfs:
dTrans). We also discuss effects such as population gradients and systematic
uncertainties in the stellar models that may influence the derived SFHs. Both
the ANGST and Local Group dwarf galaxies show a consistent and strong
morphology-density relationship, emphasizing the importance of environment in
the evolution of dwarf galaxies. Specifically, we confirm that dIs are found at
lower densities and higher luminosities than dSphs, within this large sample.
We also find that dTrans are located in similar environments to those occupied
by dwarf irregular galaxies, but have systematically lower luminosities that
are more comparable to those of dwarf spheroidals. The similarity of the SFHs
and morphology-density relationships of the LG and ANGST dwarf galaxies
suggests that the LG dwarfs are a good representation of dwarf galaxies in the
local universe.",1101.1301v2
2011-01-18,HAT-P-27b: A hot Jupiter transiting a G star on a 3 day orbit,"We report the discovery of HAT-P-27b, an exoplanet transiting the moderately
bright G8 dwarf star GSC 0333-00351 (V=12.214). The orbital period is 3.039586
+/- 0.000012 d, the reference epoch of transit is 2455186.01879 +/- 0.00054
(BJD), and the transit duration is 0.0705 +/- 0.0019 d. The host star with its
effective temperature 5300 +/- 90 K is somewhat cooler than the Sun, and is
more metal-rich with a metallicity of +0.29 +/- 0.10. Its mass is 0.94 +/- 0.04
Msun and radius is 0.90 +/- 0.04 Rsun. For the planetary companion we determine
a mass of 0.660 +/- 0.033 MJ and radius of 1.038 +0.077 -0.058 RJ. For the 30
known transiting exoplanets between 0.3 MJ and 0.8 MJ, a negative correlation
between host star metallicity and planetary radius, and an additional
dependence of planetary radius on equilibrium temperature are confirmed at a
high level of statistical significance.",1101.3511v2
2011-03-31,The ACS Nearby Galaxy Survey Treasury VII. The NGC 4214 Starburst and the Effects of Star Formation History on Dwarf Morphology,"We present deep Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2)
optical observations obtained as part of the ACS Nearby Galaxy Survey Treasury
(ANGST) as well as early release Wide Field Camera 3 (WFC3) ultra-violet and
infrared observations of the nearby dwarf starbursting galaxy NGC 4214. Our
data provide a detailed example of how covering such a broad range in
wavelength provides a powerful tool for constraining the physical properties of
stellar populations. The deepest data reach the ancient red clump at M_F814W
-0.2. All of the optical data reach the main sequence turnoff for stars younger
than ~300 Myr, and the blue He burning sequence for stars younger than 500 Myr.
The full CMD-fitting analysis shows that all three fields in our data set are
consistent with ~75% of the stellar mass being older than 8 Gyr, in spite of
showing a wide range in star formation rates at the present day. Thus, our
results suggest that the scale length of NGC 4214 has remained relatively
constant for many Gyr. As previously noted by others, we also find the galaxy
has recently ramped up production, consistent with its bright UV luminosity and
its population of UV-bright massive stars. In the central field we find UV
point sources with F336W magnitudes as bright as -9.9. These are as bright as
stars with masses of at least 52-56 M_sun and ages near 4 Myr in stellar
evolution models. Assuming a standard IMF, our CMD is well-fitted by an
increase in star formation rate beginning 100 Myr ago. The stellar populations
of this late-type dwarf are compared with those of NGC 404, an early-type dwarf
that is also the most massive galaxy in its local environment. The late-type
dwarf appears to have a similar high fraction of ancient stars, suggesting that
these dominant galaxies may form at early epochs even if they have low total
mass and very different present-day morphologies.",1104.0033v1
2011-05-10,The Higgs Potential in the Type II Seesaw Model,"We perform in the type II seesaw setting, a detailed study of the dynamical
features of the corresponding general renormalizable doublet/triplet Higgs
potential that depends on five dimensionless couplings and two mass parameters
after spontaneous symmetry breaking, and highlight the implications for the
Higgs phenomenology. In particular, we determine i) the complete set of
tree-level unitarity constraints on the couplings of the potential and ii) the
exact tree-level {\sl all directions} boundedness from below constraints on
these couplings. When combined, these constraints delineate precisely the
theoretically allowed parameter space domain within our perturbative
approximation. Among the seven physical Higgs states of this model, the mass of
the lighter (heavier) CP-even state h0 (H0) will always satisfy a theoretical
upper (lower) bound that is reached for a critical value mu_c of mu (the mass
parameter controlling triple couplings among the doublet/triplet Higgses).
Saturating the unitarity bounds we find m_h0 < {\cal O}(0.7 - 1 TeV), while the
upper bound for the remaining Higgses lies in the several tens of TeV. However,
the actual masses can be much lighter. We identify two regimes corresponding to
mu > mu_c and mu < mu_c. In the first regime the Higgs sector is typically very
heavy and only h0 that becomes SM-like could be accessible to the LHC. In
contrast, in the second regime, somewhat overlooked in the literature, most of
the Higgs sector is light. In particular the heaviest state H0 becomes SM-like,
the lighter states being the CP-odd Higgs, the (doubly) charged Higgses and a
decoupled h0, possibly leading to a distinctive phenomenology at the colliders.",1105.1925v2
2011-06-17,The Luminosity Profile and Structural Parameters of the Andromeda Galaxy,"We have constructed an extended composite luminosity profile for the
Andromeda galaxy, M31, and have decomposed it into three basic luminous
structural components: a bulge, a disk and a halo. The dust-free Spitzer/IRAC
imaging and extended spatial coverage of ground-based optical imaging and deep
star counts allow us to map M31's structure from its center to 22 kpc along the
major axis. We apply different decomposition methods for the 1D luminosity
profiles and 2D images. These include non-linear least-squares and Bayesian
Monte-Carlo Markov-chain analyses. The basic photometric model for M31 has a
Sersic bulge with shape index n = 2.2 +/- 0.3 and effective radius R_e = 1.0
+/- 0.2 kpc, a dust-free exponential disk of scale length R_d = 5.3 +/- 0.5
kpc; the parameter errors reflect the range between various decomposition
methods. The bulge parameter, n, is rather insensitive to bandpass effects and
its value suggests a first rapid formation via mergers followed by secular
growth from the disk. The M31 halo has a 2D power-law index ~ -2.5 +/- 0.2. We
find that the M31 bulge light is mostly dominant over the range R_minor < 1.2
kpc. The disk takes over in the range 1.2 kpc < R_minor < 9 kpc, whereas the
halo dominates at R_minor > 9 kpc. The stellar nucleus, bulge, disk, and halo
components each contribute roughly 0.05%, 23%, 73% and 4% of the total light of
M31 out to 200 kpc along the minor axis. Nominal errors for the structural
parameters of the M31 bulge, disk and halo amount to 20%. If M31 and the Milky
Way are at all typical, faint stellar halos should be routinely detected in
galaxy surveys reaching below mu_i ~ 27 mag/arcsec^2. We stress that our
results rely on this photometric analysis alone. Structural parameters may
change when other fundamental constraints, such as those provided by abundance
gradients and stellar kinematics, are considered simultaneously (Abridged).",1106.3564v1
2011-08-24,The Canada-France Ecliptic Plane Survey - Full Data Release: The orbital structure of the Kuiper belt,"We report the orbital distribution of the trans-neptunian objects (TNOs)
discovered during the Canada-France Ecliptic Plane Survey, whose discovery
phase ran from early 2003 until early 2007. The follow-up observations started
just after the first discoveries and extended until late 2009. We obtained
characterized observations of 321 sq.deg. of sky to depths in the range g ~
23.5--24.4 AB mag. We provide a database of 169 TNOs with high-precision
dynamical classification and known discovery efficiency. Using this database,
we find that the classical belt is a complex region with sub-structures that go
beyond the usual splitting of inner (interior to 3:2 mean-motion resonance
[MMR]), outer (exterior to 2:1 MMR), and main (in between). The main classical
belt (a=40--47 AU) needs to be modeled with at least three components: the
`hot' component with a wide inclination distribution and two `cold' components
(stirred and kernel) with much narrower inclination distributions. The hot
component must have a significantly shallower absolute magnitude (Hg)
distribution than the other two components. With 95% confidence, there are
8000+1800-1600 objects in the main belt with Hg <= 8.0, of which 50% are from
the hot component, 40% from the stirred component and 10% from the kernel; the
hot component's fraction drops rapidly with increasing Hg. Because of this, the
apparent population fractions depend on the depth and ecliptic latitude of a
trans-neptunian survey. The stirred and kernel components are limited to only a
portion of the main belt, while we find that the hot component is consistent
with a smooth extension throughout the inner, main and outer regions of the
classical belt; the inner and outer belts are consistent with containing only
hot-component objects. The Hg <= 8.0 TNO population estimates are 400 for the
inner belt and 10,000 for the outer belt within a factor of two.",1108.4836v1
2011-09-09,LSPM J1112+7626: detection of a 41-day M-dwarf eclipsing binary from the MEarth transit survey,"We report the detection of eclipses in LSPM J1112+7626, which we find to be a
moderately bright (I_C = 12.14 +/- 0.05) very low-mass binary system with an
orbital period of 41.03236 +/- 0.00002 days, and component masses M_1 = 0.395
+/- 0.002 Msol and M_2 = 0.275 +/- 0.001 Msol in an eccentric (e = 0.239 +/-
0.002) orbit. A 65 day out of eclipse modulation of approximately 2%
peak-to-peak amplitude is seen in I-band, which is probably due to rotational
modulation of photospheric spots on one of the binary components. This paper
presents the discovery and characterization of the object, including radial
velocities sufficient to determine both component masses to better than 1%
precision, and a photometric solution. We find that the sum of the component
radii, which is much better-determined than the individual radii, is inflated
by 3.8 +0.9 -0.5 % compared to the theoretical model predictions, depending on
the age and metallicity assumed. These results demonstrate that the
difficulties in reproducing observed M-dwarf eclipsing binary radii with
theoretical models are not confined to systems with very short orbital periods.
This object promises to be a fruitful testing ground for the hypothesized link
between inflated radii in M-dwarfs and activity.",1109.2055v1
2011-09-15,Kepler-16: A Transiting Circumbinary Planet,"We report the detection of a planet whose orbit surrounds a pair of low-mass
stars. Data from the Kepler spacecraft reveal transits of the planet across
both stars, in addition to the mutual eclipses of the stars, giving precise
constraints on the absolute dimensions of all three bodies. The planet is
comparable to Saturn in mass and size, and is on a nearly circular 229-day
orbit around its two parent stars. The eclipsing stars are 20% and 69% as
massive as the sun, and have an eccentric 41-day orbit. The motions of all
three bodies are confined to within 0.5 degree of a single plane, suggesting
that the planet formed within a circumbinary disk.",1109.3432v1
2011-09-30,Resolved Near-Infrared Stellar Populations in Nearby Galaxies,"We present near-infrared (NIR) color-magnitude diagrams (CMDs) for the
resolved stellar populations within 26 fields of 23 nearby galaxies (<4 Mpc),
based on F110W and F160W images from Wide Field Camera 3 (WFC3) on the Hubble
Space Telescope (HST). The CMDs sample both old dormant and young star-forming
populations. We match key NIR CMD features with their counterparts in optical
CMDs, and identify the red core Helium burning (RHeB) sequence as a significant
contributor to the NIR flux in stellar populations younger than a few 100 Myrs
old, suggesting that star formation can drive surprisingly rapid variations in
the NIR mass-to-light ratio. The NIR luminosity of star forming galaxies is
therefore not necessarily proportional to the stellar mass. We note that these
individual bright RHeB stars may be misidentified as old stellar clusters in
low resolution imaging. We also discuss the CMD location of asymptotic giant
branch (AGB) stars, and the separation of AGB sub-populations using a
combination of optical and NIR colors. We empirically calibrate the NIR
magnitude of the tip of the red giant branch (TRGB) as a function of color,
allowing this widely adopted filter to be used for distance measurements. We
find a clear trend between NIR RGB color and metallicity. However, it appears
unlikely that the slope of the NIR RGB can be used as a metallicity indicator
in extragalactic systems with comparable data. Finally, we discuss scattered
light in the WFC3, which becomes significant for exposures taken close to a
bright earth limb.",1109.6893v1
2011-10-13,The First Stray Light Corrected EUV Images of Solar Coronal Holes,"Coronal holes are the source regions of the fast solar wind, which fills most
of the solar system volume near the cycle minimum. Removing stray light from
extreme ultraviolet (EUV) images of the Sun's corona is of high astrophysical
importance, as it is required to make meaningful determinations of temperatures
and densities of coronal holes. EUV images tend to be dominated by the
component of the stray light due to the long-range scatter caused by
microroughness of telescope mirror surfaces, and this component has proven very
difficult to measure in pre-flight characterization. In-flight characterization
heretofore has proven elusive due to the fact that the detected image is
simultaneously nonlinear in two unknown functions: the stray light pattern and
the true image which would be seen by an ideal telescope. Using a constrained
blind deconvolution technique that takes advantage of known zeros in the true
image provided by a fortuitous lunar transit, we have removed the stray light
from solar images seen by the EUVI instrument on STEREO-B in all four filter
bands (171, 195, 284, and 304 \AA). Uncertainty measures of the stray light
corrected images, which include the systematic error due to misestimation of
the scatter, are provided. It is shown that in EUVI, stray light contributes up
to 70% of the emission in coronal holes seen on the solar disk, which has
dramatic consequences for diagnostics of temperature and density and therefore
estimates of key plasma parameters such as the plasma $\beta$\ and ion-electron
collision rates.",1110.3052v2
2011-10-26,Qatar-2: A K dwarf orbited by a transiting hot Jupiter and a more massive companion in an outer orbit,"We report the discovery and initial characterization of Qatar-2b, a hot
Jupiter transiting a V = 13.3 mag K dwarf in a circular orbit with a short
period, P_ b = 1.34 days. The mass and radius of Qatar-2b are M_p = 2.49 M_j
and R_p = 1.14 R_j, respectively. Radial-velocity monitoring of Qatar-2 over a
span of 153 days revealed the presence of a second companion in an outer orbit.
The Systemic Console yielded plausible orbits for the outer companion, with
periods on the order of a year and a companion mass of at least several M_j.
Thus Qatar-2 joins the short but growing list of systems with a transiting hot
Jupiter and an outer companion with a much longer period. This system
architecture is in sharp contrast to that found by Kepler for multi-transiting
systems, which are dominated by objects smaller than Neptune, usually with
tightly spaced orbits that must be nearly coplanar.",1110.5912v1
2011-11-01,Cosmological evolution of warm dark matter fluctuations I: Efficient computational framework with Volterra integral equations,"We study the complete cosmological evolution of dark matter (DM) density
fluctuations for DM particles that decoupled being ultrarelativistic during the
radiation dominated era which is the case of keV scale warm DM (WDM). The new
framework presented here can be applied to other types of DM and in particular
we extend it to cold DM (CDM). The collisionless and linearized
Boltzmann-Vlasov equations (B-V) for WDM and neutrinos in the presence of
photons and coupled to the linearized Einstein equations are studied in detail
in the presence of anisotropic stress with the Newtonian potential generically
different from the spatial curvature perturbations. We recast this full system
of B-V equations for DM and neutrinos into a system of coupled Volterra
integral equations. These Volterra-type equations are valid both in the
radiation dominated (RD) and matter dominated (MD) eras during which the WDM
particles are ultrarelativistic and then nonrelativistic. This generalizes the
so-called Gilbert integral equation only valid for nonrelativistic particles in
the MD era. We succeed to reduce the system of four Volterra integral equations
for the density and anisotropic stress fluctuations of DM and neutrinos into a
system of only two coupled Volterra equations. The kernels and inhomogeneities
in these equations are explicitly given functions. Combining the
Boltzmann-Vlasov equations and the linearized Einstein equations constrain the
initial conditions on the distribution functions and gravitational potentials.
In the absence of neutrinos the anisotropic stress vanishes and the
Volterra-type equations reduce to a single integral equation. These Volterra
integral equations provide a useful and precise framework to compute the
primordial WDM fluctuations over a wide range of scales including small scales
up to k ~ 1/5 kpc.",1111.0290v2
2011-12-06,Towards resolution of the Fermi surface in underdoped high-Tc superconductors,"We survey recent experimental results including quantum oscillations and
complementary measurements probing the electronic structure of underdoped
cuprates, and theoretical proposals to explain them. We discuss quantum
oscillations measured at high magnetic fields in the underdoped cuprates that
reveal a small Fermi surface section comprising quasiparticles that obey
Fermi-Dirac statistics, unaccompanied by other states of comparable
thermodynamic mass at the Fermi level. The location of the observed Fermi
surface section at the nodes is indicated by a body of evidence including the
collapse in Fermi velocity measured by quantum oscillations, which is found to
be associated with the nodal density of states observed in angular resolved
photoemission, the persistence of quantum oscillations down to low fields in
the vortex state, the small value of density of states from heat capacity and
the multiple frequency quantum oscillation pattern consistent with nodal
magnetic breakdown of bilayer-split pockets. A nodal Fermi surface pocket is
further consistent with the observation of a density of states at the Fermi
level concentrated at the nodes in photoemission experiments, and the antinodal
pseudogap observed by photoemission, optical conductivity, nuclear magnetic
resonance Knight shift, as well as other complementary diffraction, transport
and thermodynamic measurements. One of the possibilities considered is that the
small Fermi surface pockets observed at high magnetic fields can be understood
in terms of Fermi surface reconstruction by a form of small wavevector charge
order, observed over long lengthscales in experiments such as nuclear magnetic
resonance and x-ray scattering, potentially accompanied by an additional
mechanism to gap the antinodal density of states.",1112.1373v2
2012-01-23,The Star Formation History of Leo T from Hubble Space Telescope Imaging,"We present the star formation history (SFH) of the faintest known
star-forming galaxy, Leo T, based on imaging taken with the Hubble Space
Telescope (HST) Wide Field Planetary Camera 2 (WFPC2). The HST/WFPC2
color-magnitude diagram (CMD) of Leo T is exquisitely deep, extending ~ 2
magnitudes below the oldest main sequence turnoff, permitting excellent
constraints on star formation at all ages. We use a maximum likelihood CMD
fitting technique to measure the SFH of Leo T assuming three different sets of
stellar evolution models: Padova (solar-scaled metallicity) and BaSTI (both
solar-scaled and alpha-enhanced metallicities). The resulting SFHs are
remarkably consistent at all ages, indicating that our derived SFH is robust to
the choice of stellar evolution model. From the lifetime SFH of Leo T, we find
that 50% of the total stellar mass formed prior to z ~ 1 (7.6 Gyr ago).
Subsequent to this epoch, the SFH of Leo T is roughly constant until the most
recent ~ 25 Myr, where the SFH shows an abrupt drop. This decrease could be due
to a cessation of star formation or stellar initial mass function sampling
effects, but we are unable to distinguish between the two scenarios. Overall,
our measured SFH is consistent with previously derived SFHs of Leo T. However,
the HST-based solution provides improved age resolution and reduced
uncertainties at all epochs. The SFH, baryonic gas fraction, and location of
Leo T are unlike any of the other recently discovered faint dwarf galaxies in
the Local Group, and instead bear strong resemblance to gas-rich dwarf galaxies
(irregular or transition), suggesting that gas-rich dwarf galaxies may share
common modes of star formation over a large range of stellar mass (~ 10^5-10^9
Msun).",1201.4859v1
2012-02-13,Internal Stellar Kinematics of M32 from the SPLASH Survey: Dark Halo Constraints and the Formation of Compact Elliptical Galaxies,"As part of the SPLASH survey of the Andromeda galaxy (M31) and its neighbors,
we have obtained Keck/DEIMOS spectra of the compact elliptical (cE) satellite
M32. This is the first resolved-star kinematical study of any cE galaxy. In
contrast to previous studies that extended out to r<30""~1Re~100pc, we measure
the rotation curve and velocity dispersion profile out to r~250"" and higher
order Gauss-Hermite moments out to r~70"". We achieve this by combining
integrated-light spectroscopy at small radii (where crowding/blending are
severe) with resolved stellar spectroscopy at larger radii, using spatial and
kinematical information to statistically account for M31 contamination. The
rotation curve and velocity dispersion profile extend well beyond the radius
(r~150"") where the isophotes are distorted. Unlike NGC 205, another close dwarf
companion of M31, M32's kinematic are regular and symmetric and do not show
obvious sharp gradients across the region of isophotal elongation and twists.
We interpret M32's kinematics using three-integral axisymmetric dynamical
equilibrium models constructed using Schwarzschild's orbit superposition
technique. Models with a constant M/L can fit the data remarkably well.
However, since such a model requires an increasing tangential anisotropy with
radius, invoking the presence of an extended dark halo may be more plausible.
Such an extended dark halo is definitely required to bind a half-dozen
fast-moving stars observed at the largest radii, but these stars may not be an
equilibrium component of M32. The observed regularity of the stellar
kinematics, as well as the possible detection of an extended dark halo, are
unexpected if M31 tides are significant at large radii. While these findings by
themselves do not rule out tidal models for cE formation, they suggest that
tidal stripping may not be as significant for shaping cE galaxies as has often
been argued.",1202.2897v3
2012-04-19,The SPLASH Survey: Kinematics of Andromeda's Inner Spheroid,"The combination of large size, high stellar density, high metallicity, and
Sersic surface brightness profile of the spheroidal component of the Andromeda
galaxy (M31) within R_proj ~ 20 kpc suggest that it is unlike any subcomponent
of the Milky Way. In this work we capitalize on our proximity to and external
view of M31 to probe the kinematical properties of this ""inner spheroid."" We
employ a Markov chain Monte Carlo (MCMC) analysis of resolved stellar
kinematics from Keck/DEIMOS spectra of 5651 red giant branch stars to
disentangle M31's inner spheroid from its stellar disk. We measure the mean
velocity and dispersion of the spheroid in each of five spatial bins after
accounting for a locally cold stellar disk as well as the Giant Southern Stream
and associated tidal debris. For the first time, we detect significant spheroid
rotation (v_rot ~ 50 km/s) beyond R_proj ~ 5 kpc. The velocity dispersion
decreases from about 140 km/s at R_proj = 7 kpc to 120 km/s at R_proj = 14 kpc,
consistent to 2 sigma with existing measurements and models. We calculate the
probability that a given star is a member of the spheroid and find that the
spheroid has a significant presence throughout the spatial extent of our
sample. Lastly, we show that the flattening of the spheroid is due to velocity
anisotropy in addition to rotation. Though this suggests that the inner
spheroid of M31 more closely resembles an elliptical galaxy than a typical
spiral galaxy bulge, it should be cautioned that our measurements are much
farther out (2 - 14 r_eff) than for the comparison samples.",1204.4455v1
2012-06-07,"KELT-1b: A Strongly Irradiated, Highly Inflated, Short Period, 27 Jupiter-mass Companion Transiting a mid-F Star","We present the discovery of KELT-1b, the first transiting low-mass companion
from the wide-field Kilodegree Extremely Little Telescope-North (KELT-North)
survey. The V=10.7 primary is a mildly evolved, solar-metallicity, mid-F star.
The companion is a low-mass brown dwarf or super-massive planet with mass of
27.23+/-0.50 MJ and radius of 1.110+0.037-0.024 RJ, on a very short period
(P=1.21750007) circular orbit. KELT-1b receives a large amount of stellar
insolation, with an equilibrium temperature assuming zero albedo and perfect
redistribution of 2422 K. Upper limits on the secondary eclipse depth indicate
that either the companion must have a non-zero albedo, or it must experience
some energy redistribution. Comparison with standard evolutionary models for
brown dwarfs suggests that the radius of KELT-1b is significantly inflated.
Adaptive optics imaging reveals a candidate stellar companion to KELT-1, which
is consistent with an M dwarf if bound. The projected spin-orbit alignment
angle is consistent with zero stellar obliquity, and the vsini of the primary
is consistent with tidal synchronization. Given the extreme parameters of the
KELT-1 system, we expect it to provide an important testbed for theories of the
emplacement and evolution of short-period companions, and theories of tidal
dissipation and irradiated brown dwarf atmospheres.",1206.1635v1
2012-06-12,A spectroscopic survey of Andromeda's Western Shelf,"The Andromeda galaxy (M31) shows many tidal features in its halo, including
the Giant Southern Stream (GSS) and a sharp ledge in surface density on its
western side (the W Shelf). Using DEIMOS on the Keck telescope, we obtain
radial velocities of M31's giant stars along its NW minor axis, in a radial
range covering the W Shelf and extending beyond its edge. In the space of
velocity versus radius, the sample shows the wedge pattern expected from a
radial shell, which is detected clearly here for the first time. This confirms
predictions from an earlier model of formation of the GSS, which proposed that
the W Shelf is a shell from the third orbital wrap of the same tidal debris
stream that produces the GSS, with the main body of the progenitor lying in the
second wrap. We calculate the distortions in the shelf wedge pattern expected
from its outward expansion and angular momentum, and show that these effects
are echoed in the data. In addition, a hot, relatively smooth spheroid
population is clearly present. We construct a bulge-disk-halo N-body model that
agrees with surface brightness and kinematic constraints, and combine it with a
simulation of the GSS. From the contrasting kinematic signatures of the hot
spheroid and shelf components, we decompose the observed stellar metallicity
distribution into contributions from each component using a non-parametric
mixture model. The shelf component's metallicity distribution matches previous
observations of the GSS superbly, further strengthening the evidence they are
connected and bolstering the case for a massive progenitor of this stream.",1206.2619v1
2012-09-10,Stellar Kinematics of the Andromeda II Dwarf Spheroidal Galaxy,"We present kinematical profiles and metallicity for the M31 dwarf spheroidal
(dSph) satellite galaxy Andromeda II (And II) based on Keck DEIMOS spectroscopy
of 531 red giant branch stars. Our kinematical sample is among the largest for
any M31 satellite and extends out to two effective radii (r_eff = 5.3' = 1.1
kpc). We find a mean systemic velocity of -192.4+-0.5 km/s and an average
velocity dispersion of sigma_v = 7.8+-1.1 km/s. While the rotation velocity
along the major axis of And II is nearly zero (<1 km/s), the rotation along the
minor axis is significant with a maximum rotational velocity of v_max=8.6+-1.8
km/s. We find a kinematical major axis, with a maximum rotational velocity of
v_max=10.9+-2.4 km/s, misaligned by 67 degrees to the isophotal major axis. And
II is thus the first dwarf galaxy with evidence for nearly prolate rotation
with a v_max/sigma_v = 1.1, although given its ellipticity of epsilon = 0.10,
this object may be triaxial. We measured metallicities for a subsample of our
data, finding a mean metallicity of [Fe/H] = -1.39+- 0.03 dex and an internal
metallicity dispersion of 0.72+-0.03 dex. We find a radial metallicity gradient
with metal-rich stars more centrally concentrated, but do not observe a
significant difference in the dynamics of two metallicity populations. And II
is the only known dwarf galaxy to show minor axis rotation making it a unique
system whose existence offers important clues on the processes responsible for
the formation of dSphs.",1209.2116v1
2012-09-11,The Panchromatic Hubble Andromeda Treasury II. Tracing the Inner M31 Halo with Blue Horizontal Branch Stars,"We attempt to constrain the shape of M31's inner stellar halo by tracing the
surface density of blue horizontal branch (BHB) stars at galactocentric
distances ranging from 2 kpc to 35 kpc. Our measurements make use of resolved
stellar photometry from a section of the Panchromatic Hubble Andromeda Treasury
(PHAT) survey, supplemented by several archival Hubble Space Telescope
observations. We find that the ratio of BHB to red giant stars is relatively
constant outside of 10 kpc, suggesting that the BHB is as reliable a tracer of
the halo population as the red giant branch. In the inner halo, we do not
expect BHB stars to be produced by the high metallicity bulge and disk, making
BHB stars a good candidate to be a reliable tracer of the stellar halo to much
smaller galactocentric distances. If we assume a power-law profile r^(-\alpha)
for the 2-D projected surface density BHB distribution, we obtain a
high-quality fit with a 2-D power-law index of \alpha=2.6^{+0.3}_{-0.2} outside
of 3 kpc, which flattens to \alpha<1.2 inside of 3 kpc. This slope is
consistent with previous measurements but is anchored to a radial baseline that
extends much farther inward. Finally, assuming azimuthal symmetry and a
constant mass-to-light ratio, the best-fitting profile yields a total halo
stellar mass of 2.1^{+1.7}_{-0.4} x 10^9 M_sun. These properties are comparable
with both simulations of stellar halo formation formed by satellite disruption
alone, and with simulations that include some in situ formation of halo stars.",1209.2416v1
2012-10-23,Supernova Remnant Progenitor Masses in M31,"Using HST photometry, we age-date 59 supernova remnants (SNRs) in the spiral
galaxy M31 and use these ages to estimate zero-age main sequence masses (MZAMS)
for their progenitors. To accomplish this, we create color-magnitude diagrams
(CMDs) and use CMD fitting to measure the recent star formation history (SFH)
of the regions surrounding cataloged SNR sites. We identify any young coeval
population that likely produced the progenitor star and assign an age and
uncertainty to that population. Application of stellar evolution models allows
us to infer the MZAMS from this age. Because our technique is not contingent on
precise location of the progenitor star, it can be applied to the location of
any known SNR. We identify significant young SF around 53 of the 59 SNRs and
assign progenitor masses to these, representing a factor of 2 increase over
currently measured progenitor masses. We consider the remaining 6 SNRs as
either probable Type Ia candidates or the result of core-collapse progenitors
that have escaped their birth sites. The distribution of recovered progenitor
masses is bottom heavy, showing a paucity of the most massive stars. If we
assume a single power law distribution, dN/dM proportional to M^alpha, we find
a distribution that is steeper than a Salpeter IMF (alpha=-2.35). In
particular, we find values of alpha outside the range -2.7 to -4.4 inconsistent
with our measured distribution at 95% confidence. If instead we assume a
distribution that follows a Salpeter IMF up to some maximum mass, we find that
values of M_max greater than 26 Msun are inconsistent with the measured
distribution at 95% confidence. In either scenario, the data suggest that some
fraction of massive stars may not explode. The result is preliminary and
requires more SNRs and further analysis. In addition, we use our distribution
to estimate a minimum mass for core collapse between 7.0 and 7.8 Msun.",1210.6353v1
2012-11-02,Sketched SVD: Recovering Spectral Features from Compressive Measurements,"We consider a streaming data model in which n sensors observe individual
streams of data, presented in a turnstile model. Our goal is to analyze the
singular value decomposition (SVD) of the matrix of data defined implicitly by
the stream of updates. Each column i of the data matrix is given by the stream
of updates seen at sensor i. Our approach is to sketch each column of the
matrix, forming a ""sketch matrix"" Y, and then to compute the SVD of the sketch
matrix. We show that the singular values and right singular vectors of Y are
close to those of X, with small relative error. We also believe that this bound
is of independent interest in non-streaming and non-distributed data collection
settings.
  Assuming that the data matrix X is of size Nxn, then with m linear
measurements of each column of X, we obtain a smaller matrix Y with dimensions
mxn. If m = O(k \epsilon^{-2} (log(1/\epsilon) + log(1/\delta)), where k
denotes the rank of X, then with probability at least 1-\delta, the singular
values \sigma'_j of Y satisfy the following relative error result
  (1-\epsilon)^(1/2)<= \sigma'_j/\sigma_j <= (1 + \epsilon)^(1/2) as compared
to the singular values \sigma_j of the original matrix X. Furthermore, the
right singular vectors v'_j of Y satisfy
  ||v_j-v_j'||_2 <= min(sqrt{2},
(\epsilon\sqrt{1+\epsilon})/(\sqrt{1-\epsilon}) max_{i\neq j}
(\sqrt{2}\sigma_i\sigma_j)/(min_{c\in[-1,1]}(|\sigma^2_i-\sigma^2_j(1+c\epsilon)|)))
as compared to the right singular vectors v_j of X. We apply this result to
obtain a streaming graph algorithm to approximate the eigenvalues and
eigenvectors of the graph Laplacian in the case where the graph has low rank
(many connected components).",1211.0361v1
2012-11-05,KELT-3b: A Hot Jupiter Transiting a V=9.8 Late-F Star,"We report the discovery of KELT-3b, a moderately inflated transiting hot
Jupiter with a mass of 1.477 (-0.067, +0.066) M_J, and radius of 1.345 +/-
0.072 R_J, with an orbital period of 2.7033904 +/- 0.000010 days. The host
star, KELT-3, is a V=9.8 late F star with M_* = 1.278 (-0.061, +0.063) M_sun,
R_* = 1.472 (-0.067, +0.065) R_sun, T_eff = 6306 (-49, +50) K, log(g) = 4.209
(-0.031, +0.033), and [Fe/H] = 0.044 (-0.082, +0.080), and has a likely proper
motion companion. KELT-3b is the third transiting exoplanet discovered by the
KELT survey, and is orbiting one of the 20 brightest known transiting planet
host stars, making it a promising candidate for detailed characterization
studies. Although we infer that KELT-3 is significantly evolved, a preliminary
analysis of the stellar and orbital evolution of the system suggests that the
planet has likely always received a level of incident flux above the
empirically-identified threshold for radius inflation suggested by Demory &
Seager (2011).",1211.1031v2
2013-01-16,Mandated data archiving greatly improves access to research data,"The data underlying scientific papers should be accessible to researchers
both now and in the future, but how best can we ensure that these data are
available? Here we examine the effectiveness of four approaches to data
archiving: no stated archiving policy, recommending (but not requiring)
archiving, and two versions of mandating data deposition at acceptance. We
control for differences between data types by trying to obtain data from papers
that use a single, widespread population genetic analysis, STRUCTURE. At one
extreme, we found that mandated data archiving policies that require the
inclusion of a data availability statement in the manuscript improve the odds
of finding the data online almost a thousand-fold compared to having no policy.
However, archiving rates at journals with less stringent policies were only
very slightly higher than those with no policy at all. At one extreme, we found
that mandated data archiving policies that require the inclusion of a data
availability statement in the manuscript improve the odds of finding the data
online almost a thousand fold compared to having no policy. However, archiving
rates at journals with less stringent policies were only very slightly higher
than those with no policy at all. We also assessed the effectiveness of asking
for data directly from authors and obtained over half of the requested
datasets, albeit with about 8 days delay and some disagreement with authors.
Given the long term benefits of data accessibility to the academic community,
we believe that journal based mandatory data archiving policies and mandatory
data availability statements should be more widely adopted.",1301.3744v1
2013-01-25,Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin,"The transiting planet WASP-12 b was identified as a potential target for
transit timing studies because a departure from a linear ephemeris was reported
in the literature. Such deviations could be caused by an additional planet in
the system. We attempt to confirm the existence of claimed variations in
transit timing and interpret its origin. We organised a multi-site campaign to
observe transits by WASP-12 b in three observing seasons, using 0.5-2.6-metre
telescopes. We obtained 61 transit light curves, many of them with
sub-millimagnitude precision. The simultaneous analysis of the best-quality
datasets allowed us to obtain refined system parameters, which agree with
values reported in previous studies. The residuals versus a linear ephemeris
reveal a possible periodic signal that may be approximated by a sinusoid with
an amplitude of 0.00068+/-0.00013 d and period of 500+/-20 orbital periods of
WASP-12 b. The joint analysis of timing data and published radial velocity
measurements results in a two-planet model which better explains observations
than single-planet scenarios. We hypothesize that WASP-12 b might be not the
only planet in the system and there might be the additional 0.1 M_Jup body on a
3.6-d eccentric orbit. A dynamical analysis indicates that the proposed
two-planet system is stable over long timescales.",1301.5976v1
2013-03-20,Genomic Sequence Diversity and Population Structure of Saccharomyces cerevisiae Assessed by RAD-seq,"The budding yeast Saccharomyces cerevisiae is important for human food
production and as a model organism for biological research. The genetic
diversity contained in the global population of yeast strains represents a
valuable resource for a number of fields, including genetics, bioengineering,
and studies of evolution and population structure. Here, we apply a
multiplexed, reduced genome sequencing strategy (known as RAD-seq) to genotype
a large collection of S. cerevisiae strains, isolated from a wide range of
geographical locations and environmental niches. The method permits the
sequencing of the same 1% of all genomes, producing a multiple sequence
alignment of 116,880 bases across 262 strains. We find diversity among these
strains is principally organized by geography, with European, North American,
Asian and African/S. E. Asian populations defining the major axes of genetic
variation. At a finer scale, small groups of strains from cacao, olives and
sake are defined by unique variants not present in other strains. One
population, containing strains from a variety of fermentations, exhibits high
levels of heterozygosity and mixtures of alleles from European and Asian
populations, indicating an admixed origin for this group. In the context of
this global diversity, we demonstrate that a collection of seven strains
commonly used in the laboratory encompasses only one quarter of the genetic
diversity present in the full collection of strains, underscoring the
relatively limited genetic diversity captured by the current set of lab
strains. We propose a model of geographic differentiation followed by
human-associated admixture, primarily between European and Asian populations
and more recently between European and North American populations. The large
collection of genotyped yeast strains characterized here will provide a useful
resource for the broad community of yeast researchers.",1303.4835v1
2013-04-02,Modeling Multi-Magnet Networks Interacting Via Spin Currents,"The significant experimental advances of the last few decades in dealing with
the interaction of spin currents and nanomagnets, at the device level, has
allowed envisioning a broad class of devices that propose to implement
information processing using spin currents and nanomagnets. To analyze such
spin-magnet logic circuits, in general, we have developed a coupled
spin-transport/ magnetization-dynamics simulation framework that could be
broadly applicable to various classes of spin-valve/ spin-torque devices.
Indeed, the primary purpose of this chapter is to describe in detail, the
overall approach we have developed to include a description of spin transport
coupled with magnetization dynamics and to show how it was benchmarked against
available data on experiments.
  We address non-collinear spin-transport in Section-2 using a lumped
""4-component spin-circuit formalism"" that describes the interaction of
non-collinear magnets (required for modeling spin torque), by computing
4-component currents and voltages at every node of a ""circuit"". For modeling
the magnetization dynamics, we use the standard Landau-Lifshitz-Gilbert (LLG)
equation with the Slonczewski and the field-like terms included for spin
torque. Section-3 describes how this LLG model is coupled with the spin
transport model to analyze spin-torque experiments and spin-magnet circuits in
general.
  We include MATLAB codes in the Appendix to facilitate a ""hands-on""
understanding of our model and hope it will enable interested readers to
conveniently analyze their own experiments, develop a deeper insight into
spin-magnet circuits or come up with their own creative designs.",1304.0742v3
2013-04-03,A Novel Frank-Wolfe Algorithm. Analysis and Applications to Large-Scale SVM Training,"Recently, there has been a renewed interest in the machine learning community
for variants of a sparse greedy approximation procedure for concave
optimization known as {the Frank-Wolfe (FW) method}. In particular, this
procedure has been successfully applied to train large-scale instances of
non-linear Support Vector Machines (SVMs). Specializing FW to SVM training has
allowed to obtain efficient algorithms but also important theoretical results,
including convergence analysis of training algorithms and new characterizations
of model sparsity.
  In this paper, we present and analyze a novel variant of the FW method based
on a new way to perform away steps, a classic strategy used to accelerate the
convergence of the basic FW procedure. Our formulation and analysis is focused
on a general concave maximization problem on the simplex. However, the
specialization of our algorithm to quadratic forms is strongly related to some
classic methods in computational geometry, namely the Gilbert and MDM
algorithms.
  On the theoretical side, we demonstrate that the method matches the
guarantees in terms of convergence rate and number of iterations obtained by
using classic away steps. In particular, the method enjoys a linear rate of
convergence, a result that has been recently proved for MDM on quadratic forms.
  On the practical side, we provide experiments on several classification
datasets, and evaluate the results using statistical tests. Experiments show
that our method is faster than the FW method with classic away steps, and works
well even in the cases in which classic away steps slow down the algorithm.
Furthermore, these improvements are obtained without sacrificing the predictive
accuracy of the obtained SVM model.",1304.1014v2
2013-07-10,Hard X-ray and ultraviolet emission during the 2011 June 7 solar flare,"The relationship between X-ray and UV emission during flares, particularly in
the context of quasi-periodic pulsations, remains unclear. To address this, we
study the impulsive X-ray and UV emission during the eruptive flare of 2011
June 7 utilising X-ray imaging from RHESSI and UV 1700A imaging from SDO/AIA.
This event is associated with quasi-periodic pulsations in X-ray and possibly
UV emission, as well as substantial parallel and perpendicular motion of the
hard X-ray footpoints.
  The motion of the footpoints parallel to the flare ribbons is unusual; it is
shown to reverse direction on at least two occasions. However, there is no
associated short-timescale motion of the UV bright regions. Additionally, we
find that the locations of the brightest X-ray and UV regions are different,
particularly during the early portion of the flare impulsive phase, despite
their integrated emission being strongly correlated in time. Correlation
analysis of measured flare properties, such as the footpoint separation, flare
shear, photospheric magnetic field and coronal reconnection rate, reveals that
- in the impulsive phase - the 25 - 50 keV hard X-ray flux is only weakly
correlated with these properties, in contrast to previous studies.
  We characterise this event in terms of long-term behaviour, where the X-ray
nonthermal, thermal, and UV emission sources appear temporally and spatially
consistent, and short-term behaviour, where the emission sources are
inconsistent and quasi-periodic pulsations are a dominant feature requiring
explanation. We suggest that the short timescale behaviour of hard X-ray
footpoints, and the nature of the observed quasi-periodic pulsations, is
determined by fundamental, as-yet unobserved properties of the reconnection
region and particle acceleration sites. This presents a challenge for current
three-dimensional flare reconnection models.",1307.2874v2
2013-07-11,Inferring the Andromeda Galaxy's mass from its giant southern stream with Bayesian simulation sampling,"M31 has a giant stream of stars extending far to the south and a great deal
of other tidal debris in its halo, much of which is thought to be directly
associated with the southern stream. We model this structure by means of
Bayesian sampling of parameter space, where each sample uses an N-body
simulation of a satellite disrupting in M31's potential. We combine constraints
on stellar surface densities from the Isaac Newton Telescope survey of M31 with
kinematic data and photometric distances. This combination of data tightly
constrains the model, indicating a stellar mass at last pericentric passage of
log(M_s / Msun) = 9.5+-0.1, comparable to the LMC. Any existing remnant of the
satellite is expected to lie in the NE Shelf region beside M31's disk, at
velocities more negative than M31's disk in this region. This rules out the
prominent satellites M32 or NGC 205 as the progenitor, but an overdensity
recently discovered in M31's NE disk sits at the edge of the progenitor
locations found in the model. M31's virial mass is constrained in this model to
be log(M200) = 12.3+-0.1, alleviating the previous tension between
observational virial mass estimates and expectations from the general galactic
population and the timing argument. The techniques used in this paper, which
should be more generally applicable, are a powerful method of extracting
physical inferences from observational data on tidal debris structures.",1307.3219v1
2013-07-31,Learning about SANS Instruments and Data Reduction from Round Robin Measurements on Samples of Polystyrene Latex,"Measurements of a well-characterised standard sample can verify the
performance of an instrument. Typically, small-angle neutron scattering
instruments are used to investigate a wide range of samples and may often be
used in a number of configurations. Appropriate standard samples are useful to
test different aspects of the performance of hardware as well as that of the
data reduction and analysis software. Measurements on a number of instruments
with different intrinsic characteristics and designs in a round robin can not
only better characterise the performance for a wider range of conditions but
also, perhaps more importantly, reveal the limits of the current state of the
art of small-angle scattering. The exercise, followed by detailed analysis,
tests the limits of current understanding as well as uncovers often forgotten
assumptions, simplifications and approximations that underpin the current
practice of the technique. This paper describes measurements of polystyrene
latex, radius 72 nm with a number of instruments. Scattering from monodisperse,
uniform spherical particles is simple to calculate and displays sharp minima.
Such data test the calibrations of intensity, wavelength and resolution as well
as the detector response. Smoothing due to resolution, multiple scattering and
polydispersity has been determined. Sources of uncertainty are often related to
systematic deviations and calibrations rather than random counting errors. The
study has prompted development of software to treat modest multiple scattering
and to better model the instrument resolution. These measurements also allow
checks of data reduction algorithms and have identified how they can be
improved. The reproducibility and the reliability of instruments and the
accuracy of parameters derived from the data are described.",1307.8296v1
2013-08-09,A Search for RR Lyrae Stars in Segue 2 and Segue 3,"We present an extensive search for RR Lyrae stars in and around the
ultra-faint Milky Way companions Segue 2 and Segue 3. The former (M_V = -2.5,
Belokurov et al. 2009) appears to be an extremely faint dwarf galaxy companion
of the Milky Way. The latter (M_V = 0.0, Fadely et al. 2011) is among the
faintest star clusters known. We use B and V band time-series imaging obtained
at the WIYN 0.9 meter telescope at Kitt Peak National Observatory to search for
RR Lyrae in these objects. In our Segue 2 observations, we present a previously
unknown fundamental mode (RRab) RR Lyrae star with a period of P_ab = 0.748
days. With this measurement, we revisit the inverse correlation between <P_ab>
and <[Fe/H]> established in the literature for Milky Way dwarf galaxies and
their RR Lyrae. In this context, the long period of Segue 2's RRab star as well
as the known significant spread in metallicity in this dwarf galaxy are
consistent with the observed trend in <P_ab> and <[Fe/H]>. We derive the first
robust distance to Segue 2, using both its RRab star and spectroscopically
confirmed blue horizontal branch stars. Using [Fe/H] = -2.16 and -2.44 dex, we
find d_RRL = 36.6 +2.5/-2.4 and 37.7 +/- 2.7 kpc; assuming [Fe/H] = -2.257 dex,
we find d_BHB = 34.4 +/- 2.6 kpc. Although no RR Lyrae were present in the
Segue 3 field, we found a candidate eclipsing binary star system.",1308.2227v1
2013-10-15,A New Approach to Detailed Structural Decomposition from the SPLASH and PHAT Surveys: Kicked-up Disk Stars in the Andromeda Galaxy?,"We characterize the bulge, disk, and halo subcomponents in the Andromeda
galaxy (M31) over the radial range 4 < R_proj < 225 kpc. The cospatial nature
of these subcomponents renders them difficult to disentangle using surface
brightness (SB) information alone, especially interior to ~20 kpc. Our new
decomposition technique combines information from the luminosity function (LF)
of over 1.5 million bright (20 < m_814W < 22) stars from the Panchromatic
Hubble Andromeda Treasury (PHAT) survey, radial velocities of over 5000 red
giant branch stars in the same magnitude range from the Spectroscopic and
Photometric Landscape of Andromeda's Stellar Halo (SPLASH) survey, and
integrated I-band SB profiles from various sources. We use an affine-invariant
Markov chain Monte Carlo algorithm to fit an appropriate toy model to these
three data sets. The bulge, disk, and halo SB profiles are modeled as a Sersic,
exponential, and cored power-law, respectively, and the LFs are modeled as
broken power-laws. We present probability distributions for each of 32
parameters describing the SB profiles and LFs of the three subcomponents. We
find that the number of stars with a disk-like LF is ~5% larger than the the
number with disk-like (dynamically cold) kinematics, suggesting that some stars
born in the disk have been dynamically heated to the point that they are
kinematically indistinguishable from halo members. This is the first
kinematical evidence for a ""kicked-up disk"" halo population in M31. The
fraction of kicked-up disk stars is consistent with that found in simulations.
We also find evidence for a radially varying disk LF, consistent with a
negative metallicity gradient in the stellar disk.",1310.4179v1
2013-12-11,The Nosoi commute: a spatial perspective on the rise of BSL-4 laboratories in cities,"Recent H5N1 influenza research has revived the debate on the storage and
manipulation of potentially harmful pathogens. In the last two decades, new
high biosafety (BSL-4) laboratories entered into operation, raising strong
concerns from the public. The probability of an accidental release of a
pathogen from a BSL-4 laboratory is extremely low, but the corresponding risk
-- defined as the probability of occurrence multiplied by its impact -- could
be significant depending on the pathogen specificities and the population
potentially affected. A list of BSL-4 laboratories throughout the world, with
their location and date of first activity, was established from publicly
available sources. This database was used to estimate the total population
living within a daily commuting distance of BSL-4 laboratories, and to quantify
how this figure changed over time. We show that from 1990 to present, the
population living within the commuting belt of BSL-4 laboratories increased by
a factor of 4 to reach up to 1.8% of the world population, owing to an increase
in the number of facilities and their installation in cities. Europe is
currently hosting the largest population living in the direct vicinity of BSL-4
laboratories, while the recent building of new facilities in Asia suggests that
an important increase of the population living close to BSL-4 laboratories will
be observed in the next decades. We discuss the potential implications in term
of global risk, and call for better pathogen-specific quantitative assessment
of the risk of outbreaks resulting from the accidental release of potentially
pandemic pathogens",1312.3283v2
2013-12-18,The thermal Sunyaev Zel'dovich effect power spectrum in light of Planck,"(Abridged) The amplitude of the thermal Sunyaev Zel'dovich effect (tSZ) power
spectrum is extremely sensitive to the abundance of galaxy clusters and
therefore to fundamental cosmological parameters that control their growth,
such as sigma_8 and Omega_m. Here we explore the sensitivity of the tSZ power
spectrum to important non-gravitational ('sub-grid') physics by employing the
cosmo-OWLS suite of large-volume cosmological hydrodynamical simulations, run
in both the Planck and WMAP7 best-fit cosmologies. On intermediate and small
angular scales (ell > ~1000, or theta < ~10 arcmin), accessible with the South
Pole Telescope and the Atacama Cosmology Telescope, the predicted tSZ power
spectrum is highly model dependent, with AGN feedback having a particularly
large effect. However, at large scales, observable with the Planck telescope,
the effects of sub-grid physics are minor. Comparing the simulations with
observations, we find a significant amplitude offset on all measured angular
scales (including large scales), if the Planck best-fit cosmology is assumed by
the simulations. This is shown to be a generic result for all current tSZ
models. By contrast, if the WMAP7 cosmology is adopted, there is full
consistency with the Planck power spectrum measurements on large scales and
agreement at the 2 sigma level with the SPT/ACT measurements at intermediate
scales for our fiducial AGN model, which Le Brun et al. (2014) have shown
reproduces the 'resolved' properties of the local cluster population remarkably
well. These findings strongly suggest that there are significantly fewer
massive galaxy clusters than expected for the Planck best-fit cosmology, which
is consistent with recent measurements of the tSZ number counts. Our findings
therefore pose a significant challenge to the cosmological parameter values
preferred (and/or the model adopted) by the Planck primary CMB analyses.",1312.5341v2
2014-02-21,How to Scale Exponential Backoff,"Randomized exponential backoff is a widely deployed technique for
coordinating access to a shared resource. A good backoff protocol should,
arguably, satisfy three natural properties: (i) it should provide constant
throughput, wasting as little time as possible; (ii) it should require few
failed access attempts, minimizing the amount of wasted effort; and (iii) it
should be robust, continuing to work efficiently even if some of the access
attempts fail for spurious reasons. Unfortunately, exponential backoff has some
well-known limitations in two of these areas: it provides poor (sub-constant)
throughput (in the worst case), and is not robust (to resource acquisition
failures).
  The goal of this paper is to ""fix"" exponential backoff by making it scalable,
particularly focusing on the case where processes arrive in an on-line,
worst-case fashion. We present a relatively simple backoff
protocol~Re-Backoff~that has, at its heart, a version of exponential backoff.
It guarantees expected constant throughput with dynamic process arrivals and
requires only an expected polylogarithmic number of access attempts per
process.
  Re-Backoff is also robust to periods where the shared resource is unavailable
for a period of time. If it is unavailable for $D$ time slots, Re-Backoff
provides the following guarantees. When the number of packets is a finite $n$,
the average expected number of access attempts for successfully sending a
packet is $O(\log^2( n + D))$. In the infinite case, the average expected
number of access attempts for successfully sending a packet is $O( \log^2(\eta)
+ \log^2(D) )$ where $\eta$ is the maximum number of processes that are ever in
the system concurrently.",1402.5207v4
2014-04-10,The Spitzer South Pole Telescope Deep Field Survey: Linking galaxies and halos at z=1.5,"We present an analysis of the clustering of high-redshift galaxies in the
recently completed 94 deg$^2$ Spitzer-SPT Deep Field survey. Applying flux and
color cuts to the mid-infrared photometry efficiently selects galaxies at
$z\sim1.5$ in the stellar mass range $10^{10}-10^{11}M_\odot$, making this
sample the largest used so far to study such a distant population. We measure
the angular correlation function in different flux-limited samples at scales
$>6^{\prime \prime}$ (corresponding to physical distances $>0.05$ Mpc) and
thereby map the one- and two-halo contributions to the clustering. We fit halo
occupation distributions and determine how the central galaxy's stellar mass
and satellite occupation depend on the halo mass. We measure a prominent peak
in the stellar-to-halo mass ratio at a halo mass of $\log(M_{\rm halo} /
M_\odot) = 12.44\pm0.08$, 4.5 times higher than the $z=0$ value. This supports
the idea of an evolving mass threshold above which star formation is quenched.
We estimate the large-scale bias in the range $b_g=2-4$ and the satellite
fraction to be $f_\mathrm{sat}\sim0.2$, showing a clear evolution compared to
$z=0$. We also find that, above a given stellar mass limit, the fraction of
galaxies that are in similar mass pairs is higher at $z=1.5$ than at $z=0$. In
addition, we measure that this fraction mildly increases with the stellar mass
limit at $z=1.5$, which is the opposite of the behavior seen at low-redshift.",1404.2930v2
2014-04-28,The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations,"We present uniformly measured star formation histories (SFHs) of 40 Local
Group dwarf galaxies based on color-magnitude diagram (CMD) analysis from
archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can
be recovered from CMDs that do not reach the oldest main sequence turn-off
(MSTO), but emphasize that the oldest MSTO is critical for precisely
constraining the earliest epochs of star formation. We find that: (1) the
average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an
exponentially declining SFH with $\tau$ $\sim$ 5 Gyr; (2) lower luminosity
dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the
average SFHs of dwarf irregulars (dIrrs), transition dwarfs (dTrans), and dwarf
ellipticals (dEs) can be approximated by the combination of an exponentially
declining SFH ($\tau$ $\sim$ 3-4 Gyr) for lookback ages $>$ 10-12 Gyr ago and a
constant SFH thereafter; (4) the observed fraction of stellar mass formed prior
to z=2 ranges considerably (80\% for galaxies with M $<$ 10$^5$ M$_{\odot}$ to
30\% for galaxies with M$>$10$^7$ M$_{\odot}$) and is largely explained by
environment; (5) the distinction between ""ultra-faint"" and ""classical"" dSphs is
arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass
prior to z=2 than the SDSS galaxies from Leiter 2012 and the SFHs from the
abundance matching models of Behroozi et al. 2013. This may indicate higher
than expected star-formation efficiencies at early times in low mass galaxies.
Finally, we provide all the SFHs in tabulated electronic format for use by the
community.",1404.7144v1
2014-06-26,"Spin Supercurrent, Magnetization Dynamics, and Phi-State in Spin-Textured Josephson Junctions","The prospect of combining the dissipationless nature of superconducting
currents with the spin-polarization of magnetic materials is interesting with
respect to exploring superconducting analogues of topics in spintronics. In
order to accomplish this aim, it is pivotal to understand how
spin-supercurrents interact dynamically with magnetization textures. We
investigate the appearance of a spin-supercurrent and the resulting
magnetization dynamics in a textured magnetic Josephson current by using three
experimentally relevant models: i) a S/F/S junction with spin-active
interfaces, ii) a S/F1/F2/F3/S Josephson junction with a ferromagnetic
trilayer, and iii) a Josephson junction containing a domain wall. In all of
these cases, the supercurrent is spin-polarized and exerts a spin-transfer
torque on the ferromagnetic interlayers which causes magnetization dynamics.
Using a scattering matrix formalism in the clean limit, we compute the
Andreev-bound states and free energy of the system which is used to solve the
Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous
magnetism influences the phase-dependence of the charge supercurrent as well as
the magnetization dynamics caused by the spin-supercurrent. Using a realistic
experimental parameter set, we find that the supercurrent can induce
magnetization switching that is controlled by the superconducting phase
difference. Moreover, we demonstrate that the combined effect of chiral spin
symmetry breaking and interface scattering causes the system to act as a phase
battery that may supply any superconducting phase difference phi in the ground
state. Such a phi junction is accompanied by an anomalous supercurrent
appearing even at zero phase difference, and we demonstrate that the flow
direction of this current is controlled by the chirality of the magnetization
configuration.",1406.7016v1
2014-07-11,Digital frequency domain multiplexing readout electronics for the next generation of millimeter telescopes,"Frequency domain multiplexing (fMux) is an established technique for the
readout of transition-edge sensor (TES) bolometers in millimeter-wavelength
astrophysical instrumentation. In fMux, the signals from multiple detectors are
read out on a single pair of wires reducing the total cryogenic thermal loading
as well as the cold component complexity and cost of a system. The current
digital fMux system, in use by POLARBEAR, EBEX, and the South Pole Telescope,
is limited to a multiplexing factor of 16 by the dynamic range of the
Superconducting Quantum Interference Device pre-amplifier and the total system
bandwidth. Increased multiplexing is key for the next generation of large
format TES cameras, such as SPT-3G and POLARBEAR2, which plan to have on the of
order 15,000 detectors.
  Here, we present the next generation fMux readout, focusing on the warm
electronics. In this system, the multiplexing factor increases to 64 channels
per module (2 wires) while maintaining low noise levels and detector stability.
This is achieved by increasing the system bandwidth, reducing the dynamic range
requirements though active feedback, and digital synthesis of voltage biases
with a novel polyphase filter algorithm. In addition, a version of the new fMux
readout includes features such as low power consumption and radiation-hard
components making it viable for future space-based millimeter telescopes such
as the LiteBIRD satellite.",1407.3161v1
2014-08-03,Bounded Real Lemma and structured singular value versus diagonal scaling: the free noncommutative setting,"The structured singular value $\mu$ was introduced independently by Doyle and
Safanov as a tool for analyzing robustness of system stability and performance
in the presence of structured uncertainty in the system parameters. While the
structured singular value provides a necessary and sufficient criterion for
robustness with respect to a structured ball of uncertainty, it is notoriously
difficult to actually compute. The method of diagonal (or simply ""D"") scaling,
on the other hand, provides an easily computable upper bound (which we call
$\hat \mu$) for the structured singular value, but provides an exact evaluation
of $\mu$ (or even a useful upper bound for $\mu$) only in special cases.
However it was discovered in the 1990s that a certain enhancement of the
uncertainty structure (i.e., letting the uncertainty parameters be freely
noncommuting linear operators on an infinite-dimensional separable Hilbert
space) resulted in the $D$-scaling procedure leading to an exact evaluation of
$\mu_{\text{enhanced}}$ ($\mu_{\text{enhanced}} = \hat \mu$), at least for the
tractable special cases which were analyzed in complete detail. On the one hand
this enhanced uncertainty has some appeal from the physical point of view: one
can allow the uncertainty in the plant parameters to be time-varying, or more
generally, one can catch the uncertainty caused by the designer's decision not
to model the more complex (e.g. nonlinear) dynamics of the true plant. On the
other hand, the precise mathematical formulation of this enhanced uncertainty
structure makes contact with developments in the growing theory of analytic
functions in freely noncommuting arguments and associated formal power series
in freely noncommuting indeterminates. In this article we obtain the
$\widetilde \mu = \hat \mu$ theorem for a more satisfactory general setting.",1408.0519v1
2014-09-02,The Panchromatic Hubble Andromeda Treasury X. Ultraviolet to Infrared Photometry of 117 Million Equidistant Stars,"We have measured stellar photometry with the Hubble Space Telescope (HST)
Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) in near
ultraviolet (F275W, F336W), optical (F475W, F814W), and near infrared (F110W,
F160W) bands for 117 million resolved stars in M31. As part of the Panchromatic
Hubble Andromeda Treasury (PHAT) survey, we measured photometry with
simultaneous point spread function fitting across all bands and at all source
positions after precise astrometric image alignment (<5-10 milliarcsecond
accuracy). In the outer disk, the photometry reaches a completeness-limited
depth of F475W~28, while in the crowded, high surface brightness bulge, the
photometry reaches F475W~25. We find that simultaneous photometry and optimized
measurement parameters significantly increase the detection limit of the lowest
resolution filters (WFC3/IR) providing color-magnitude diagrams that are up to
2.5 magnitudes deeper when compared with color-magnitude diagrams from WFC3/IR
photometry alone. We present extensive analysis of the data quality including
comparisons of luminosity functions and repeat measurements, and we use
artificial star tests to quantify photometric completeness, uncertainties and
biases. We find that largest sources of systematic error in the photometry are
due to spatial variations in the point spread function models and charge
transfer efficiency corrections. This stellar catalog is the largest ever
produced for equidistant sources, and is publicly available for download by the
community.",1409.0899v1
2014-09-30,The Supernova Progenitor Mass Distributions of M31 and M33: Further Evidence for an Upper Mass Limit,"Using Hubble Space Telescope (HST) photometry to measure star formation
histories, we age-date the stellar populations surrounding supernova remnants
(SNRs) in M31 and M33. We then apply stellar evolution models to the ages to
infer the corresponding masses for their supernova progenitor stars. We analyze
33 M33 SNR progenitors and 29 M31 SNR progenitors in this work. We then combine
these measurements with 53 previously published M31 SNR progenitor measurements
to bring our total number of progenitor mass estimates to 115. To quantify the
mass distributions, we fit power laws of the form $dN/dM \propto M^{-\alpha}$.
Our new, larger sample of M31 progenitors follows a distribution with $\alpha =
4.4\pm 0.4$, and the M33 sample follows a distribution with $\alpha =
3.8^{+0.4}_{-0.5}$. Thus both samples are consistent within the uncertainties,
and the full sample across both galaxies gives $\alpha = 4.2\pm 0.3$. Both the
individual and full distributions display a paucity of massive stars when
compared to a Salpeter initial mass function (IMF), which we would expect to
observe if all massive stars exploded as SN that leave behind observable SNR.
If we instead fix $\alpha = 2.35$ and treat the maximum mass as a free
parameter, we find $M_{max} \sim 35-45M_{sun}$, indicative of a potential
maximum cutoff mass for SN production. Our results suggest that either SNR
surveys are biased against finding objects in the youngest (<10 Myr old)
regions, or the highest mass stars do not produce SNe.",1410.0018v1
2014-10-17,Ferromagnetic resonance in $ε$-Co magnetic composites,"We investigate the electromagnetic properties of assemblies of nanoscale
$\epsilon$-cobalt crystals with size range between 5 nm to 35 nm, embedded in a
polystyrene (PS) matrix, at microwave (1-12 GHz) frequencies. We investigate
the samples by transmission electron microscopy (TEM) imaging, demonstrating
that the particles aggregate and form chains and clusters. By using a broadband
coaxial-line method, we extract the magnetic permeability in the frequency
range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance
with respect to an externally applied magnetic field. We find that the
zero-magnetic field ferromagnetic resonant peak shifts towards higher
frequencies at finite magnetic fields, and the magnitude of complex
permeability is reduced. At fields larger than 2.5 kOe the resonant frequency
changes linearly with the applied magnetic field, demonstrating the transition
to a state in which the nanoparticles become dynamically decoupled. In this
regime, the particles inside clusters can be treated as non-interacting, and
the peak position can be predicted from Kittel's ferromagnetic resonance theory
for non-interacting uniaxial spherical particles combined with the
Landau-Lifshitz-Gilbert (LLG) equation. In contrast, at low magnetic fields
this magnetic order breaks down and the resonant frequency in zero magnetic
field reaches a saturation value reflecting the interparticle interactions as
resulting from aggregation. Our results show that the electromagnetic
properties of these composite materials can be tuned by external magnetic
fields and by changes in the aggregation structure.",1410.4789v2
2014-12-28,The structure of solar radio noise storms,"The Nan\c{c}ay Radioheliograph (NRH) routinely produces snapshot images of
the full sun at frequencies between 150 and 450 MHz, with typical resolution 3
arcmin and time cadence 0.2 s. Combining visibilities from the NRH and from the
Giant Meterwave Radio Telescope (GMRT) allows us to produce images of the sun
at 236 or 327 MHz, with a large FOV, high resolution and time cadence. We seek
to investigate the structure of noise storms (the most common non-thermal solar
radio emission). We focus on the relation of position and altitude of noise
storms with the observing frequency and on the lower limit of their sizes. We
present results for noise storms on four days. The results consist of an
extended halo and of one or several compact cores with relative intensity
changing over a few seconds. We found that core sizes can be almost stable over
one hour, with a minimum in the range 31-35 arcsec (less than previously
reported) and can be stable over one hour. The heliocentric distances of noise
storms are $\sim 1.20$ and 1.35 $R_{\odot}$ at 432 and 150 MHz, respectively.
Regions where storms originate are thus much denser than the ambient corona and
their vertical extent is found to be less than expected from hydrostatic
equilibrium. The smallest observed sizes impose upper limits on broadening
effects due to scattering on density inhomogeneities in the low and medium
corona and constrain the level of density turbulence in the solar corona. It is
possible that scatter broadening has been overestimated in the past, and that
the observed sizes cannot only be attributed to scattering. The vertical
structure of the noise storms is difficult to reconcile with the classical
columnar model.",1412.8189v2
2014-12-28,Hopf Algebras and Markov Chains,"This thesis introduces a way to build Markov chains out of Hopf algebras. The
transition matrix of a ""Hopf-power Markov chain"" is (the transpose of) the
matrix of the coproduct-then-product operator on a combinatorial Hopf algebra
with respect to a suitable basis. These chains describe the
breaking-then-recombining of the combinatorial objects in the Hopf algebra. The
motivating example is the famous Gilbert-Shannon-Reeds model of
riffle-shuffling of a deck of cards, which arises in this manner from the
shuffle algebra.
  The primary reason for constructing Hopf-power Markov chains, or for
rephrasing familiar chains through this lens, is that much information about
them comes simply from translating well-known facts on the underlying Hopf
algebra. For example, there is an explicit formula for the stationary
distribution (Theorem 4.5.1), and constructing quotient algebras show that
certain statistics on a Hopf-power Markov chain are themselves Markov chains
(Theorem 4.7.1). Perhaps the pinnacle is Theorem 2.5.1, a collection of
algorithms for a full left and right eigenbasis in many common cases where the
underlying Hopf algebra is commutative or cocommutative. This arises from a
cocktail of the Poincare-Birkhoff-Witt theorem, the Cartier-Milnor-Moore
theorem, Reutenauer's structure theory of the free Lie algebra, and Patras's
Eulerian idempotent theory.
  Since Hopf-power Markov chains can exhibit very different behaviour depending
on the structure of the underlying Hopf algebra and its distinguished basis,
one must restrict attention to certain styles of Hopf algebras in order to
obtain stronger results. This thesis will focus respectively on a
free-commutative basis, which produces ""independent breaking"" chains, and a
cofree basis; there will be both general statements and in-depth examples.",1412.8221v2
2015-01-22,KELT-7b: A hot Jupiter transiting a bright V=8.54 rapidly rotating F-star,"We report the discovery of KELT-7b, a transiting hot Jupiter with a mass of
$1.28 \pm 0.18$ MJ, radius of $1.53_{-0.047}^{+0.046}$ RJ, and an orbital
period of $2.7347749 \pm 0.0000039$ days. The bright host star (HD33643;
KELT-7) is an F-star with $V=8.54$, Teff $=6789_{-49}^{+50}$ K, [Fe/H]
$=0.139_{-0.081}^{+0.075}$, and $\log{g}=4.149 \pm 0.019$. It has a mass of
$1.535_{-0.054}^{+0.066}$ Msun, a radius of $1.732_{-0.045}^{+0.043}$ Rsun, and
is the fifth most massive, fifth hottest, and the ninth brightest star known to
host a transiting planet. It is also the brightest star around which KELT has
discovered a transiting planet. Thus, KELT-7b is an ideal target for detailed
characterization given its relatively low surface gravity, high equilibrium
temperature, and bright host star. The rapid rotation of the star ($73 \pm 0.5$
km/s) results in a Rossiter-McLaughlin effect with an unusually large amplitude
of several hundred m/s. We find that the orbit normal of the planet is likely
to be well-aligned with the stellar spin axis, with a projected spin-orbit
alignment of $\lambda=9.7 \pm 5.2$ degrees. This is currently the second most
rapidly rotating star to have a reflex signal (and thus mass determination) due
to a planetary companion measured.",1501.05565v2
2015-01-27,Tracing the Metal-Poor M31 Stellar Halo with Blue Horizontal Branch Stars,"We have analyzed new HST/ACS and HST/WFC3 imaging in F475W and F814W of two
previously-unobserved fields along the M31 minor axis to confirm our previous
constraints on the shape of M31's inner stellar halo. Both of these new
datasets reach a depth of at least F814W$<$27 and clearly detect the blue
horizontal branch (BHB) of the field as a distinct feature of the
color-magnitude diagram. We measure the density of BHB stars and the ratio of
BHB to red giant branch stars in each field using identical techniques to our
previous work. We find excellent agreement with our previous measurement of a
power-law for the 2-D projected surface density with an index of
2.6$^{+0.3}_{-0.2}$ outside of 3 kpc, which flattens to $\alpha <$1.2 inside of
3 kpc. Our findings confirm our previous suggestion that the field BHB stars in
M31 are part of the halo population. However, the total halo profile is now
known to differ from this BHB profile, which suggests that we have isolated the
metal-poor component. This component appears to have an unbroken power-law
profile from 3-150 kpc but accounts for only about half of the total halo
stellar mass. Discrepancies between the BHB density profile and other
measurements of the inner halo are therefore likely due to the different
profile of the metal-rich halo component, which is not only steeper than the
profile of the met al-poor component, but also has a larger core radius. These
profile differences also help to explain the large ratio of BHB/RGB stars in
our observations.",1501.06631v1
2015-02-12,A clear age-velocity dispersion correlation in Andromeda's stellar disk,"The stellar kinematics of galactic disks are key to constraining disk
formation and evolution processes. In this paper, for the first time, we
measure the stellar age-velocity dispersion correlation in the inner 20 kpc
(3.5 disk scale lengths) of M31 and show that it is dramatically different from
that in the Milky Way. We use optical Hubble Space Telescope/Advanced Camera
for Surveys photometry of 5800 individual stars from the Panchromatic Hubble
Andromeda Treasury (PHAT) survey and Keck/DEIMOS radial velocity measurements
of the same stars from the Spectroscopic and Photometric Landscape of
Andromeda's Stellar Halo (SPLASH) survey. We show that the average
line-of-sight velocity dispersion is a steadily increasing function of stellar
age exterior to R=10 kpc, increasing from 30 km/s for the young upper main
sequence stars to 90 km/s for the old red giant branch stars. This monotonic
increase implies that a continuous or recurring process contributed to the
evolution of the disk. Both the slope and normalization of the dispersion vs.
age relation are significantly larger than in the Milky Way, allowing for the
possibility that the disk of M31 has had a more violent history than the disk
of the Milky Way, more in line with cosmological predictions. We also find
evidence for an inhomogeneous distribution of stars from a second kinematical
component in addition to the dominant disk component. One of the largest and
hottest high-dispersion patches is present in all age bins, and may be the
signature of the end of the long bar.",1502.03820v1
2015-03-17,The Star Formation Histories of Local Group Dwarf Galaxies III. Characterizing Quenching in Low-Mass Galaxies,"We explore the quenching of low-mass galaxies (10^4 < Mstar < 10^8 Msun) as a
function of lookback time using the star formation histories (SFHs) of 38 Local
Group dwarf galaxies. The SFHs were derived from analyzing color-magnitude
diagrams of resolved stellar populations in archival Hubble Space
Telescope/Wide Field Planetary Camera 2 imaging. We find: (1) Lower mass
galaxies quench earlier than higher mass galaxies; (2) Inside of virial radius
there is no correlation between a satellite's current proximity to a massive
host and its quenching epoch; (3) There are hints of systematic differences in
quenching times of M31 and Milky Way (MW) satellites, although the sample
sample size and uncertainties in the SFHs of M31 dwarfs prohibit definitive
conclusions. Combined with literature results, we qualitatively consider the
redshift evolution (z=0-1) of the quenched galaxy fraction over ~7 dex in
stellar mass (10^4 < Mstar < 10^11.5 Msun). The quenched fraction of all
galaxies generally increases toward the present, with both the lowest and
highest mass systems exhibiting the largest quenched fractions at all
redshifts. In contrast, galaxies between Mstar ~ 10^8-10^10 Msun have the
lowest quenched fractions. We suggest that such intermediate-mass galaxies are
the least efficient at quenching. Finally, we compare our quenching times with
predictions for infall times of low-mass galaxies associated with the MW. We
find that some of the lowest-mass satellites (e.g., CVn II, Leo IV) may have
been quenched before infall while higher mass satellites (e.g., Leo I, Fornax)
typically quench ~1-4 Gyr after infall.",1503.05195v1
2015-04-28,Nearly Optimal Deterministic Algorithm for Sparse Walsh-Hadamard Transform,"For every fixed constant $\alpha > 0$, we design an algorithm for computing
the $k$-sparse Walsh-Hadamard transform of an $N$-dimensional vector $x \in
\mathbb{R}^N$ in time $k^{1+\alpha} (\log N)^{O(1)}$. Specifically, the
algorithm is given query access to $x$ and computes a $k$-sparse $\tilde{x} \in
\mathbb{R}^N$ satisfying $\|\tilde{x} - \hat{x}\|_1 \leq c \|\hat{x} -
H_k(\hat{x})\|_1$, for an absolute constant $c > 0$, where $\hat{x}$ is the
transform of $x$ and $H_k(\hat{x})$ is its best $k$-sparse approximation. Our
algorithm is fully deterministic and only uses non-adaptive queries to $x$
(i.e., all queries are determined and performed in parallel when the algorithm
starts).
  An important technical tool that we use is a construction of nearly optimal
and linear lossless condensers which is a careful instantiation of the GUV
condenser (Guruswami, Umans, Vadhan, JACM 2009). Moreover, we design a
deterministic and non-adaptive $\ell_1/\ell_1$ compressed sensing scheme based
on general lossless condensers that is equipped with a fast reconstruction
algorithm running in time $k^{1+\alpha} (\log N)^{O(1)}$ (for the GUV-based
condenser) and is of independent interest. Our scheme significantly simplifies
and improves an earlier expander-based construction due to Berinde, Gilbert,
Indyk, Karloff, Strauss (Allerton 2008).
  Our methods use linear lossless condensers in a black box fashion; therefore,
any future improvement on explicit constructions of such condensers would
immediately translate to improved parameters in our framework (potentially
leading to $k (\log N)^{O(1)}$ reconstruction time with a reduced exponent in
the poly-logarithmic factor, and eliminating the extra parameter $\alpha$).
  Finally, by allowing the algorithm to use randomness, while still using
non-adaptive queries, the running time of the algorithm can be improved to
$\tilde{O}(k \log^3 N)$.",1504.07648v1
2015-06-26,Modeling and Simulation of Spin Transfer Torque Generated at Topological Insulator/Ferromagnetic Heterostructure,"Topological Insulator (TI) has recently emerged as an attractive candidate
for possible application to spintronic circuits because of its strong spin
orbit coupling. TIs are unique materials that have an insulating bulk but
conducting surface states due to band inversion and these surface states are
protected by time reversal symmetry. In this paper, we propose a physics-based
spin dynamics simulation framework for TI/Ferromagnet (TI/FM) bilayer
heterostructures that is able to capture the electronic band structure of a TI
while calculating the electron and spin transport properties. Our model differs
from TI/FM models proposed in the literature in that it is able to account for
the 3D band structure of TIs and the effect of exchange coupling and external
magnetic field on the band structure. Our proposed approach uses 2D surface
Hamiltonian for TIs that includes all necessary features for spin transport
calculations so as to properly model the characteristics of a TI/FM
heterostructure. Using this Hamiltonian and appropriate parameters, we show
that the effect of quantum confinement and exchange coupling are successfully
captured in the calculated surface band structure compared with the quantum
well band diagram of a 3D TI, and matches well with experimental data reported
in the literature. We then show how this calibrated Hamiltonian is used with
the self-consistent non equilibrium Green's functions (NEGF) formalism to
determine the charge and spin transport in TI/FM bilayer heterostructures. Our
calculations agree well with experimental data and capture the unique features
of a TI/FM heterostructure such as high spin Hall angle, high spin conductivity
etc. Finally, we show how the results obtained from NEGF calculations may be
incorporated into the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) formulation to
simulate the magnetization dynamics of an FM layer sitting on top of a TI.",1506.07932v2
2015-07-23,A Spectroscopic and Photometric Exploration of the C/M Ratio in the Disk of M31,"We explore the ratio (C/M) of carbon-rich to oxygen-rich thermally pulsing
asymptotic giant branch(TP-AGB) stars in the disk of M31 using a combination of
moderate-resolution optical spectroscopy from the Spectroscopic Landscape of
Andromeda's Stellar Halo (SPLASH) survey and six-filter Hubble Space Telescope
photometry from the Panchromatic Hubble Andromeda Treasury (PHAT) survey.Carbon
stars were identified spectroscopically. Oxygen-rich M-stars were identifed
using three different photometric definitions designed to mimic, and thus
evaluate, selection techniques common in the literature. We calculate the C/M
ratio as a function of galactocentric radius, present-day gas-phase oxygen
abundance, stellar metallicity, age (via proxy defined as the ratio of TP-AGB
stars to red giant branch, RGB, stars), and mean star formation rate over the
last 400 Myr. We find statistically significant correlations between log(C/M)
and all parameters. These trends are consistent across different M-star
selection methods, though the fiducial values change. Of particular note is our
observed relationship between log(C/M) and stellar metallicity, which is fully
consistent with the trend seen across Local Group satellite galaxies. The fact
that this trend persists in stellar populations with very different star
formation histories indicates that the C/M ratio is governed by stellar
properties alone.",1507.06687v1
2015-07-24,Discovery and Validation of Kepler-452b: A 1.6-Re Super Earth Exoplanet in the Habitable Zone of a G2 Star,"We report on the discovery and validation of Kepler-452b, a transiting planet
identified by a search through the 4 years of data collected by NASA's Kepler
Mission. This possibly rocky 1.63$^{+0.23}_{-0.20}$ R$_\oplus$ planet orbits
its G2 host star every 384.843$^{+0.007}_{0.012}$ days, the longest orbital
period for a small (R$_p$ < 2 R$_\oplus$) transiting exoplanet to date. The
likelihood that this planet has a rocky composition lies between 49% and 62%.
The star has an effective temperature of 5757$\pm$85 K and a log g of
4.32$\pm$0.09. At a mean orbital separation of 1.046$^{+0.019}_{-0.015}$ AU,
this small planet is well within the optimistic habitable zone of its star
(recent Venus/early Mars), experiencing only 10% more flux than Earth receives
from the Sun today, and slightly outside the conservative habitable zone
(runaway greenhouse/maximum greenhouse). The star is slightly larger and older
than the Sun, with a present radius of 1.11$^{+0.15}_{-0.09}$ R$_\odot$ and an
estimated age of 6 Gyr. Thus, Kepler-452b has likely always been in the
habitable zone and should remain there for another 3 Gyr.",1507.06723v1
2015-08-02,Optimal Radio Frequency Energy Harvesting with Limited Energy Arrival Knowledge,"In this paper, we develop optimal policies for deciding when a wireless node
with radio frequency (RF) energy harvesting (EH) capabilities should try and
harvest ambient RF energy. While the idea of RF-EH is appealing, it is not
always beneficial to attempt to harvest energy; in environments where the
ambient energy is low, nodes could consume more energy being awake with their
harvesting circuits turned on than what they can extract from the ambient radio
signals; it is then better to enter a sleep mode until the ambient RF energy
increases. Towards this end, we consider a scenario with intermittent energy
arrivals and a wireless node that wakes up for a period of time (herein called
the time-slot) and harvests energy. If enough energy is harvested during the
time-slot, then the harvesting is successful and excess energy is stored;
however, if there does not exist enough energy the harvesting is unsuccessful
and energy is lost.
  We assume that the ambient energy level is constant during the time-slot, and
changes at slot boundaries. The energy level dynamics are described by a
two-state Gilbert-Elliott Markov chain model, where the state of the Markov
chain can only be observed during the harvesting action, and not when in sleep
mode. Two scenarios are studied under this model. In the first scenario, we
assume that we have knowledge of the transition probabilities of the Markov
chain and formulate the problem as a Partially Observable Markov Decision
Process (POMDP), where we find a threshold-based optimal policy. In the second
scenario, we assume that we don't have any knowledge about these parameters and
formulate the problem as a Bayesian adaptive POMDP; to reduce the complexity of
the computations we also propose a heuristic posterior sampling algorithm. The
performance of our approaches is demonstrated via numerical examples.",1508.00285v1
2015-09-22,"The Panchromatic Hubble Andromeda Treasury VIII: A Wide-Area, High-Resolution Map of Dust Extinction in M31","We map the distribution of dust in M31 at 25pc resolution, using stellar
photometry from the Panchromatic Hubble Andromeda Treasury. We develop a new
mapping technique that models the NIR color-magnitude diagram (CMD) of red
giant branch (RGB) stars. The model CMDs combine an unreddened foreground of
RGB stars with a reddened background population viewed through a log-normal
column density distribution of dust. Fits to the model constrain the median
extinction, the width of the extinction distribution, and the fraction of
reddened stars. The resulting extinction map has >4 times better resolution
than maps of dust emission, while providing a more direct measurement of the
dust column. There is superb morphological agreement between the new map and
maps of the extinction inferred from dust emission by Draine et al. 2014.
However, the widely-used Draine & Li (2007) dust models overpredict the
observed extinction by a factor of ~2.5, suggesting that M31's true dust mass
is lower and that dust grains are significantly more emissive than assumed in
Draine et al. (2014). The discrepancy we identify is consistent with similar
findings in the Milky Way by the Planck Collaboration (2015), but has a more
complex dependence on parameters from the Draine & Li (2007) dust models. We
also show that the discrepancy with the Draine et al. (2014) map is lowest
where the interstellar radiation field has a harder spectrum than average. We
discuss possible improvements to the CMD dust mapping technique, and explore
further applications.",1509.06988v1
2016-01-07,Detection of lensing substructure using ALMA observations of the dusty galaxy SDP.81,"We study the abundance of substructure in the matter density near galaxies
using ALMA Science Verification observations of the strong lensing system
SDP.81. We present a method to measure the abundance of subhalos around
galaxies using interferometric observations of gravitational lenses. Using
simulated ALMA observations, we explore the effects of various systematics,
including antenna phase errors and source priors, and show how such errors may
be measured or marginalized. We apply our formalism to ALMA observations of
SDP.81. We find evidence for the presence of a $M=10^{8.96\pm 0.12} M_{\odot}$
subhalo near one of the images, with a significance of $6.9\sigma$ in a joint
fit to data from bands 6 and 7; the effect of the subhalo is also detected in
both bands individually. We also derive constraints on the abundance of dark
matter subhalos down to $M\sim 2\times 10^7 M_{\odot}$, pushing down to the
mass regime of the smallest detected satellites in the Local Group, where there
are significant discrepancies between the observed population of luminous
galaxies and predicted dark matter subhalos. We find hints of additional
substructure, warranting further study using the full SDP.81 dataset
(including, for example, the spectroscopic imaging of the lensed carbon
monoxide emission). We compare the results of this search to the predictions of
$\Lambda$CDM halos, and find that given current uncertainties in the host halo
properties of SDP.81, our measurements of substructure are consistent with
theoretical expectations. Observations of larger samples of gravitational
lenses with ALMA should be able to improve the constraints on the abundance of
galactic substructure.",1601.01388v1
2016-02-09,Isotropic at the Break? 3D Kinematics of Milky Way Halo Stars in the Foreground of M31,"We present the line-of-sight (LOS) velocities for 13 distant main sequence
Milky Way halo stars with published proper motions. The proper motions were
measured using long baseline (5-7 years) multi-epoch HST/ACS photometry, and
the LOS velocities were extracted from deep (5-6 hour integrations) Keck
II/DEIMOS spectra. We estimate the parameters of the velocity ellipsoid of the
stellar halo using a Markov chain Monte Carlo ensembler sampler method. The
velocity second moments in the directions of the Galactic $(l,b,$ LOS)
coordinate system are $\langle v^2_l \rangle^{1/2} = 138^{+43}_{-26}$ km/s,
$\langle v^2_b \rangle^{1/2} = 88^{+28}_{-17}$ km/s, and $\langle
v^2_{\rm{LOS}} \rangle^{1/2} = 91^{+27}_{-14}$ km/s. We use these ellipsoid
parameters to constrain the velocity anisotropy of the stellar halo. Ours is
the first measurement of the anisotropy parameter $\beta$ using 3D kinematics
outside of the solar neighborhood. We find $\beta=-0.3^{+0.4}_{-0.9}$,
consistent with isotropy and lower than solar neighborhood $\beta$ measurements
by 2$\sigma$ ($\beta_{SN} \sim 0.5-0.7$). We identify two stars in our sample
that are likely members of the known TriAnd substructure, and excluding these
objects from our sample increases our estimate of the anisotropy to
$\beta=0.1^{+0.4}_{-1.0}$, which is still lower than solar neighborhood
measurements by $1\sigma$. The potential decrease in $\beta$ with
Galactocentric radius is inconsistent with theoretical predictions, though
consistent with recent observational studies, and may indicate the presence of
large, shell-type structure (or structures) at $r \sim 25$ kpc. The methods
described in this paper will be applied to a much larger sample of stars with
3D kinematics observed through the ongoing HALO7D program.",1602.03180v1
2016-06-22,"Qatar Exoplanet Survey : Qatar-3b, Qatar-4b and Qatar-5b","We report the discovery of Qatar-3b, Qatar-4b, and Qatar-5b, three new
transiting planets identified by the Qatar Exoplanet Survey (QES). The three
planets belong to the hot Jupiter family, with orbital periods of
$P_{Q3b}$=2.50792 days, $P_{Q4b}$=1.80539 days, and $P_{Q5b}$=2.87923 days.
Follow-up spectroscopic observations reveal the masses of the planets to be
$M_{Q3b}$=4.31$\pm0.47$ $M_{\rm J}$, $M_{Q4b}$=6.10$ \pm0.54$ $M_{\rm J}$, and
$M_{Q5b}$ = 4.32$ \pm0.18$ $M_{\rm J}$, while model fits to the transit light
curves yield radii of $R_{Q3b}$ = 1.096$ \pm0.14$ $R_{\rm J}$, $R_{Q4b}$ =
1.135$ \pm0.11$ $R_{\rm J}$, and $R_{Q5b}$ = 1.107$ \pm0.064$ $R_{\rm J}$. The
host stars are low-mass main sequence stars with masses and radii $M_{Q3}$ =
1.145$ \pm0.064$ $M_{\odot}$, $M_{Q4}$ = 0.896$ \pm0.048$ $M_{\odot}$, $M_{Q5}$
= 1.128$ \pm0.056$ $M_{\odot}$ and $R_{Q3}$ = 1.272$ \pm0.14$ $R_{\odot}$,
$R_{Q4}$ = 0.849$\pm0.063$ $R_{\odot}$ and $R_{Q5}$ = 1.076$\pm0.051$
$R_{\odot}$ for Qatar-3, 4 and 5 respectively. The V magnitudes of the three
host stars are $V_{Q3}$=12.88, $V_{Q4}$=13.60, and $V_{Q5}$=12.82. All three
new planets can be classified as heavy hot Jupiters (M > 4 $M_{J}$).",1606.06882v5
2016-06-27,Five Planets Transiting a Ninth Magnitude Star,"The Kepler mission has revealed a great diversity of planetary systems and
architectures, but most of the planets discovered by Kepler orbit faint stars.
Using new data from the K2 mission, we present the discovery of a five planet
system transiting a bright (V = 8.9, K = 7.7) star called HIP 41378. HIP 41378
is a slightly metal-poor late F-type star with moderate rotation (v sin(i) = 7
km/s) and lies at a distance of 116 +/- 18 from Earth. We find that HIP 41378
hosts two sub-Neptune sized planets orbiting 3.5% outside a 2:1 period
commensurability in 15.6 and 31.7 day orbits. In addition, we detect three
planets which each transit once during the 75 days spanned by K2 observations.
One planet is Neptune sized in a likely ~160 day orbit, one is sub-Saturn sized
likely in a ~130 day orbit, and one is a Jupiter sized planet in a likely ~1
year orbit. We show that these estimates for the orbital periods can be made
more precise by taking into account dynamical stability considerations. We also
calculate the distribution of stellar reflex velocities expected for this
system, and show that it provides a good target for future radial velocity
observations. If a precise orbital period can be determined for the outer
Jovian planet through future observations, it will be an excellent candidate
for follow-up transit observations to study its atmosphere and measure its
oblateness.",1606.08441v1
2016-07-06,Holographic Beam Mapping of the CHIME Pathfinder Array,"The Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder radio
telescope is currently surveying the northern hemisphere between 400 and 800
MHz. By mapping the large scale structure of neutral hydrogen through its
redshifted 21 cm line emission between $z \sim 0.8-2.5$ CHIME will contribute
to our understanding of Dark Energy. Bright astrophysical foregrounds must be
separated from the neutral hydrogen signal, a task which requires precise
characterization of the polarized telescope beams. Using the DRAO John A. Galt
26 m telescope, we have developed a holography instrument and technique for
mapping the CHIME Pathfinder beams. We report the status of the instrument and
initial results of this effort.",1607.01473v1
2016-07-21,Long-Term Photometry of IC 348 with the YETI Network,"We present long-term photometric observations of the young open cluster IC
348 with a baseline time-scale of 2.4 yr. Our study was conducted with several
telescopes from the Young Exoplanet Transit Initiative (YETI) network in the
Bessel $R$ band to find periodic variability of young stars. We identified 87
stars in IC 348 to be periodically variable; 33 of them were unreported before.
Additionally, we detected 61 periodic non-members of which 41 are new
discoveries. Our wide field of view was the key to those numerous newly found
variable stars. The distribution of rotation periods in IC 348 has always been
of special interest. We investigate it further with our newly detected periods
but we cannot find a statistically significant bimodality. We also report the
detection of a close eclipsing binary in IC 348 composed of a low-mass stellar
component ($M \gtrsim 0.09\,\mathrm{M}_{\odot}$) and a K0 pre-main sequence
star ($M \approx 2.7\,\mathrm{M}_{\odot}$). Furthermore, we discovered three
detached binaries among the background stars in our field of view and confirmed
the period of a fourth one.",1607.06322v1
2016-08-02,Atomic-scale observation and manipulation of plaquette antiferromagnetic order in iron-based superconductor,"The symmetry requirement and the origin of magnetic orders coexisting with
superconductivity have been strongly debated issues of iron-based
superconductors (FeSCs). Observation of C$_4$-symmetric antiferromagnetism in
violation of the inter-band nesting condition of spin-density waves in
superconducting ground state will require significant change in our
understanding of the mechanism of FeSC. The superconducting material
Sr$_2$VO$_3$FeAs, a bulk version of monolayer FeSC in contact with a perovskite
layer with its magnetism (T$_N$ ~ 50 K) and superconductivity (T$_c$ ~ 37 K)
coexisting at parent state, has no reported structural orthorhombic distortion
and thus makes a perfect system to look for theoretically expected C$_4$
magnetisms. Based on variable temperature spin-polarized scanning tunneling
microscopy (SPSTM) with newly discovered imaging mechanism that removes the
static surface reconstruction (SR) pattern by fluctuating it rapidly with
spin-polarized tunneling current, we could visualize underlying C$_4$ symmetric
(2$\times$2) magnetic domains and its phase domain walls. We find that this
magnetic order is perfectly consistent with the plaquette antiferromagnetic
order in tetragonal Fe spin lattice expected from theories based on the
Heisenberg exchange interaction of local Fe moments and the quantum order by
disorder. The inconsistency of its modulation Q vectors from the nesting
condition also implies that the nesting-based C$_2$ symmetric magnetism is not
a unique prerequisite of high-T$_c$ FeSC. Furthermore, the plaquette
antiferromagnetic domain wall dynamics under the influence of small spin torque
effect of spin-polarized tunneling current are shown to be consistent with
theoretical simulation based on the extended Landau-Lifshitz-Gilbert equation.",1608.00884v3
2016-08-10,POLARBEAR-2: an instrument for CMB polarization measurements,"POLARBEAR-2 (PB-2) is a cosmic microwave background (CMB) polarization
experiment that will be located in the Atacama highland in Chile at an altitude
of 5200 m. Its science goals are to measure the CMB polarization signals
originating from both primordial gravitational waves and weak lensing. PB-2 is
designed to measure the tensor to scalar ratio, r, with precision {\sigma}(r) <
0.01, and the sum of neutrino masses, {\Sigma}m{\nu}, with
{\sigma}({\Sigma}m{\nu}) < 90 meV. To achieve these goals, PB-2 will employ
7588 transition-edge sensor bolometers at 95 GHz and 150 GHz, which will be
operated at the base temperature of 250 mK. Science observations will begin in
2017.",1608.03025v1
2016-08-15,ICE-based Custom Full-Mesh Network for the CHIME High Bandwidth Radio Astronomy Correlator,"New generation radio interferometers encode signals from thousands of antenna
feeds across large bandwidth. Channelizing and correlating this data requires
networking capabilities that can handle unprecedented data rates with
reasonable cost. The Canadian Hydrogen Intensity Mapping Experiment (CHIME)
correlator processes 8-bits from N=2048 digitizer inputs across 400~MHz of
bandwidth. Measured in $N^2~\times $ bandwidth, it is the largest radio
correlator that has been built. Its digital back-end must exchange and
reorganize the 6.6~terabit/s produced by its 128 digitizing and channelizing
nodes, and feed it to the 256-node spatial correlator in a way that each node
obtains data from all digitizer inputs but across a small fraction of the
bandwidth (i.e. `corner-turn'). In order to maximize performance and
reliability of the corner-turn system while minimizing cost, a custom
networking solution has been implemented. The system makes use of Field
Programmable Gate Array (FPGA) transceivers to implement direct, passive,
full-mesh, high speed serial connections between sixteen circuit boards in a
crate, to exchange data between crates, and to offload the data to a cluster of
256 graphics processing unit (GPU) nodes using standard 10~Gbit/s Ethernet
links. The GPU nodes complete the corner-turn by combining data from all crates
and then computing visibilities. Eye diagrams and frame error counters confirm
error-free operation of the corner-turn network in both the currently operating
CHIME Pathfinder telescope (a prototype for the full CHIME telescope) and a
representative fraction of the full CHIME hardware providing an end-to-end
system validation.
  An analysis of an equivalent corner-turn system built with Ethernet switches
instead of custom passive data links is provided.",1608.04347v1
2016-08-22,"ICE: a scalable, low-cost FPGA-based telescope signal processing and networking system","We present an overview of the 'ICE' hardware and software framework that
implements large arrays of interconnected FPGA-based data acquisition, signal
processing and networking nodes economically. The system was conceived for
application to radio, millimeter and sub-millimeter telescope readout systems
that have requirements beyond typical off-the-shelf processing systems, such as
careful control of interference signals produced by the digital electronics,
and clocking of all elements in the system from a single precise
observatory-derived oscillator. A new generation of telescopes operating at
these frequency bands and designed with a vastly increased emphasis on digital
signal processing to support their detector multiplexing technology or
high-bandwidth correlators---data rates exceeding a terabyte per second---are
becoming common. The ICE system is built around a custom FPGA motherboard that
makes use of an Xilinx Kintex-7 FPGA and ARM-based co-processor. The system is
specialized for specific applications through software, firmware, and custom
mezzanine daughter boards that interface to the FPGA through the
industry-standard FMC specifications. For high density applications, the
motherboards are packaged in 16-slot crates with ICE backplanes that implement
a low-cost passive full-mesh network between the motherboards in a crate, allow
high bandwidth interconnection between crates, and enable data offload to a
computer cluster. A Python-based control software library automatically detects
and operates the hardware in the array. Examples of specific telescope
applications of the ICE framework are presented, namely the
frequency-multiplexed bolometer readout systems used for the SPT and Simons
Array and the digitizer, F-engine, and networking engine for the CHIME and
HIRAX radio interferometers.",1608.06262v1
2016-09-14,Revised Stellar Properties of Kepler Targets for the Q1-17 (DR25) Transit Detection Run,"The determination of exoplanet properties and occurrence rates using Kepler
data critically depends on our knowledge of the fundamental properties (such as
temperature, radius and mass) of the observed stars. We present revised stellar
properties for 197,096 Kepler targets observed between Quarters 1-17 (Q1-17),
which were used for the final transiting planet search run by the Kepler
Mission (Data Release 25, DR25). Similar to the Q1--16 catalog by Huber et al.
the classifications are based on conditioning published atmospheric parameters
on a grid of Dartmouth isochrones, with significant improvements in the adopted
methodology and over 29,000 new sources for temperatures, surface gravities or
metallicities. In addition to fundamental stellar properties the new catalog
also includes distances and extinctions, and we provide posterior samples for
each stellar parameter of each star. Typical uncertainties are ~27% in radius,
~17% in mass, and ~51% in density, which is somewhat smaller than previous
catalogs due to the larger number of improved logg constraints and the
inclusion of isochrone weighting when deriving stellar posterior distributions.
On average, the catalog includes a significantly larger number of evolved
solar-type stars, with an increase of 43.5% in the number of subgiants. We
discuss the overall changes of radii and masses of Kepler targets as a function
of spectral type, with particular focus on exoplanet host stars.",1609.04128v2
2016-11-16,Low Barrier Nanomagnets as p-bits for Spin Logic,"It has recently been shown that a suitably interconnected network of tunable
telegraphic noise generators or ""p-bits"" can be used to perform even precise
arithmetic functions like a 32-bit adder. In this paper we use simulations
based on the stochastic Landau-Lifshitz-Gilbert (sLLG) equation to demonstrate
that similar impressive functions can be performed using unstable nanomagnets
with energy barriers as low as a fraction of a kT. This is surprising since the
magnetization of low barrier nanomagnets is not telegraphic with discrete
values of +1 and -1. Rather it fluctuates randomly among all values between -1
and +1, and the output magnets are read with a thresholding device that
translates all positive values to 1 and all negative values to zero. We present
sLLG-based simulations demonstrating the operation of a 32-bit adder with a
network of several hundred nanomagnets, exhibiting a remarkably precise
correlation: The input magnets {A} and {B} as well as the output magnets {S}
all fluctuate randomly and yet the quantity A+B-S is sharply peaked around
zero! If we fix {A} and {B}, the sum magnets {S} rapidly converge to a unique
state with S=A+B so that the system acts as an adder. But unlike standard
adders, the operation is invertible. If we fix {S} and {B}, the remaining
magnets {A} converge to the difference A=S-B. These examples suggest a new
direction for the field of nanomagnetics away from stable high barrier magnets
towards stochastic low barrier magnets which not only operate with lower
currents, but are also more promising for continued downscaling.",1611.05477v3
2016-11-19,"Slow links, fast links, and the cost of gossip","Consider the classical problem of information dissemination: one (or more)
nodes in a network have some information that they want to distribute to the
remainder of the network. In this paper, we study the cost of information
dissemination in networks where edges have latencies, i.e., sending a message
from one node to another takes some amount of time. We first generalize the
idea of conductance to weighted graphs by defining $\phi_*$ to be the ""critical
conductance"" and $\ell_*$ to be the ""critical latency"". One goal of this paper
is to argue that $\phi_*$ characterizes the connectivity of a weighted graph
with latencies in much the same way that conductance characterizes the
connectivity of unweighted graphs.
  We give near tight lower and upper bounds on the problem of information
dissemination, up to polylogarithmic factors. Specifically, we show that in a
graph with (weighted) diameter $D$ (with latencies as weights) and maximum
degree $\Delta$, any information dissemination algorithm requires at least
$\Omega(\min(D+\Delta, \ell_*/\phi_*))$ time % in the worst case. We show
several variants of the lower bound (e.g., for graphs with small diameter,
graphs with small max-degree, etc.) by reduction to a simple combinatorial
game.
  We then give nearly matching algorithms, showing that information
dissemination can be solved in $O(\min((D+\Delta)\log^3{n}, (\ell_*/\phi_*)\log
n)$ time. This is achieved by combining two cases. We show that the classical
push-pull algorithm is (near) optimal when the diameter or the maximum degree
is large. For the case where the diameter and the maximum degree are small, we
give an alternative strategy in which we first discover the latencies and then
use an algorithm for known latencies based on a weighted spanner construction.
(Our algorithms are within polylogarithmic factors of being tight both for
known and unknown latencies.)",1611.06343v4
2016-12-22,Eroding dipoles and vorticity growth for Euler flows in $ \scriptstyle{\mathbb{R}}^3$: The hairpin geometry as a model for finite-time blowup,"A theory of an eroding ""hairpin"" vortex dipole structure in three dimensions
is developed, extending our previous study of an axisymmetric eroding dipole
without swirl. The hairpin is here similarly proposed as a model to produce
large ""self-stretching"" of vorticity, with the possibility of finite-time
blow-up. We derive a system of partial differential equations of ""generalized""
form, involving contour averaging of a locally two-dimensional Euler flow. We
do not attempt here to solve the system exactly, but point out that
non-existence of physically acceptable solutions would most probably be a
result of the axial flow. Because of the axial flow the vorticity distribution
within the dipole eddies is no longer of the simple Sadovskii type (vorticity
constant over a cross-section) obtained in the axisymmetric problem. Thus the
solution of the system depends upon the existence of a larger class of
propagating two-dimensional dipoles.
  The hairpin model is obtained by formal asymptotic analysis. As in the
axisymmetric problem a local transformation to ""shrinking"" coordinates is
introduced, but now in a self-similar form appropriate to the study of a
possible finite-time singularity. We discuss some properties of the model,
including a study of the helicity and a first step in iterating toward a
solution from the Sadovskii structure. We also present examples of
two-dimensional propagating dipoles not previously studied, which have a
vorticity profile consistent with our model. Although no rigorous results can
be given, and analysis of the system is only partial, the formal calculations
are consistent with the possibility of a finite time blowup of vorticity at a
point of vanishing circulation of the dipole eddies, but depending upon the
existence of the necessary two-dimensional propagating dipole.",1612.07709v2
2017-06-22,Efficiency of magnetic hyperthermia in the presence of rotating and static fields,"Single-domain ferromagnetic nanoparticle systems can be used to transfer
energy from a time-dependent magnetic field into their environment. This local
heat generation, i.e., magnetic hyperthermia, receives applications in cancer
therapy which requires the enhancement of the energy loss. A possible way to
improve the efficiency is to chose a proper type of applied field, e.g., a
rotating instead of an oscillating one. The latter case is very well studied
and there is an increasing interest in the literature to investigate the former
although it is still unclear under which circumstances the rotating applied
field can be more favourable than the oscillating one. The goal of this work is
to incorporate the presence of a static field and to perform a systematic study
of the non-linear dynamics of the magnetisation in the framework of the
deterministic Landau-Lifshitz-Gilbert equation in order to calculate energy
losses. Two cases are considered: the static field is either assumed to be
perpendicular to the plane of rotation or situated in the plane of rotation. In
the latter case a significant increase in the energy loss/cycle is observed if
the magnitudes of the static and the rotating fields have a certain ratio (e.g.
it should be one for isotropic nanoparticles). It can be used to
""super-localise"" the heat transfer: in case of an inhomogeneous applied static
field, tissues are heated up only where the magnitudes of the static and
rotating fields reach the required ratio.",1706.07426v4
2017-07-05,"Measuring Reionization, Neutrino Mass, and Cosmic Inflation with BFORE","BFORE is a NASA high-altitude ultra-long-duration balloon mission proposed to
measure the cosmic microwave background (CMB) across half the sky during a
28-day mid-latitude flight launched from Wanaka, New Zealand. With the unique
access to large angular scales and high frequencies provided by the balloon
platform, BFORE will significantly improve measurements of the optical depth to
reionization tau, breaking parameter degeneracies needed for a measurement of
neutrino mass with the CMB. The large angular scale data will enable BFORE to
hunt for the large-scale gravitational wave B-mode signal, as well as the
degree-scale signal, each at the r~0.01 level. The balloon platform allows
BFORE to map Galactic dust foregrounds at frequencies where they dominate, in
order to robustly separate them from CMB signals measured by BFORE, in addition
to complementing data from ground-based telescopes. The combination of
frequencies will also lead to velocity measurements for thousands of galaxy
clusters, as well as probing how star-forming galaxies populate dark matter
halos. The mission will be the first near-space use of TES multichroic
detectors (150/217 GHz and 280/353 GHz bands) using highly-multiplexed mSQUID
microwave readout, raising the technical readiness level of both technologies.",1707.01488v1
2017-08-28,Three statistically validated K2 transiting warm Jupiter exoplanets confirmed as low-mass stars,"We have identified three K2 transiting star-planet systems, K2-51 (EPIC
202900527), K2-67 (EPIC 206155547), and K2-76 (EPIC 206432863), as stellar
binaries with low-mass stellar secondaries. The three systems were
statistically validated as transiting planets, and through measuring their
orbits by radial velocity monitoring we have derived the companion masses to be
$0.1459^{+0.0029}_{-0.0032}$ $M_{Sun}$ (EPIC 202900527 B),
$0.1612^{+0.0072}_{-0.0067}$ $M_{Sun}$ (EPIC 206155547 B), and $0.0942 \pm
0.0019$ $M_{Sun}$ (EPIC 206432863 B). Therefore they are not planets but small
stars, part of the small sample of low-mass stars with measured radius and
mass. The three systems are at an orbital period range of $12-24$ days, and the
secondaries have a radius within $0.9-1.9$ $R_J$, not inconsistent with the
properties of warm Jupiter planets. These systems illustrate some of the
existing challenges in the statistical validation approach. We point out a few
possible origins for the initial misclassification of these objects, including
poor characterization of the host star, the difficulty in detecting a secondary
eclipse in systems on an eccentric orbit, and the difficulty in distinguishing
between the smallest stars and gas giant planets as the two populations have
indistinguishable radius distributions. Our work emphasizes the need for
obtaining medium-precision radial velocity measurements to distinguish between
companions that are small stars, brown dwarfs, and gas giant planets.",1708.08455v2
2017-09-29,Zodiacal Exoplanets in Time (ZEIT) VI: a three-planet system in the Hyades cluster including an Earth-sized planet,"Planets in young clusters are powerful probes of the evolution of planetary
systems. Here we report the discovery of three planets transiting K2-136 (EPIC
247589423), a late K dwarf in the Hyades (~800 Myr) cluster, and robust
detection limits for additional planets in the system. The planets were
identified from their K2 light curves, as part of our survey of young clusters
and star forming regions. The smallest planet has a radius comparable to Earth
(0.99 +/- 0.05 Earth radii), making it one of the few Earth-sized planets with
a known, young age. The two larger planets are likely a mini-Neptune and a
super-Earth, with radii of 2.91+/-0.11 and 1.45+/-0.10 Earth radii,
respectively. The predicted radial velocity signals from these planets are
between 0.4 and 2 m/s, achievable with modern precision RV spectrographs.
Because the target star is bright (V=11.2) and has relatively low-amplitude
stellar variability for a young star (2-6 mmag), EPIC 247589423 hosts the best
planets known in a young open cluster for precise radial velocity follow-up,
enabling a robust test of earlier claims that young planets are less dense than
their older counterparts.",1709.10328v2
2017-12-11,Stellar Stream and Halo Structure in the Andromeda Galaxy From a Subaru/Hyper Suprime-Cam Survey,"We present wide and deep photometry of the northwest part of the halo of the
Andromeda galaxy (M31) using Hyper Suprime-Cam on the Subaru Telescope. The
survey covers 9.2 deg$^{2}$ field in the $g$, $i$, and $NB515$ bands and shows
a clear red giant branch (RGB) of M31's halo stars and a pronounced red clump
(RC) feature. The spatial distribution of RC stars shows a prominent stream
feature, the North Western (NW) Stream, and a diffuse substructure in the south
part of our survey field. We estimate the distances based on the RC method and
obtain $(m-M)$ = 24.63$\pm 0.191$(random)$\pm0.057$(systematic) and 24.29$\pm
0.211$(random)$\pm0.057$(systematic) mag for the NW stream and diffuse
substructure, respectively, implying that the NW Stream is located behind M31,
whereas the diffuse substructure is located in front. We also estimate
line-of-sight distances along the NW Stream and find that the south part of the
stream is $\sim$20 kpc closer to us relative to the north part. The distance to
the NW Stream inferred from the isochrone fitting to the color-magnitude
diagram favors the RC-based distance, but the TRGB-based distance estimated for
$NB515$-selected RGB stars does not agree with it. The surface number density
distribution of RC stars across the NW Stream is found to be approximately
Gaussian with a FWHM of $\sim$25 arcmin (5.7 kpc), with a slight skew to the
south-west side. That along the NW Stream shows a complicated structure
including variations in number density and a significant gap in the stream.",1712.03654v1
2018-02-15,Spin and charge pumping by steady or pulse current-driven magnetic domain wall: A self-consistent multiscale time-dependent-quantum/time-dependent-classical approach,"We introduce a multiscale framework which combines time-dependent
nonequilibrium Green function (TD-NEGF) algorithms, scaling linearly in the
number of time steps and describing quantum-mechanically conduction electrons
in the presence of time-dependent fields of arbitrary strength or frequency,
with classical time evolution of localized magnetic moments described by the
Landau-Lifshitz-Gilbert (LLG) equation. The TD-NEGF+LLG framework can be
applied to a variety of problems where current-driven spin torque induces
dynamics of magnetic moments as the key resource for next generation
spintronics. Using magnetic domain wall (DW) as an example, we predict that its
motion will pump time-dependent spin and charge currents (on the top of
unpolarized DC charge current injected through normal metal leads to drive the
DW motion). The conversion of AC components of spin current, whose amplitude
increases (decreases) as the DW approaches (distances from) the normal metal
lead, into AC voltage via the inverse spin Hall effect offers a tool to
precisely track the DW position along magnetic nanowire. We also quantify the
DW transient inertial displacement due to its acceleration and deceleration by
pulse current and the entailed spin and charge pumping. Finally, TD-NEGF+LLG as
a nonperturbative (i.e., numerically exact) framework allows us to establish
the limits of validity of the so-called spin-motive force (SMF) theory for
pumped charge current by time-dependent magnetic textures---the perturbative
analytical formula of SMF theory becomes inapplicable for large frequencies
(but unrealistic in magnetic system) and, more importantly, for increasing
noncollinearity when the angles between neighboring magnetic moments exceed
$\simeq 10^\circ$.",1802.05682v3
2018-03-21,Constraints for the Progenitor Masses of Historic Core-Collapse Supernovae,"We age-date the stellar populations associated with 12 historic nearby
core-collapse supernovae (CCSNe) and 2 supernova impostors, and from these
ages, we infer their initial masses and associated uncertainties. To do this,
we have obtained new HST imaging covering these CCSNe. Using these images, we
measure resolved stellar photometry for the stars surrounding the locations of
the SNe. We then fit the color-magnitude distributions of this photometry with
stellar evolution models to determine the ages of any young existing
populations present. From these age distributions, we infer the most likely
progenitor mass for all of the SNe in our sample. We find ages between 4 and 50
Myr, corresponding to masses from 7.5 to 59 solar masses. There were no SNe
that lacked a young population within 50~pc. Our sample contains 4 type Ib/c
SNe; their masses have a wide range of values, suggesting that the progenitors
of stripped-envelope SNe are binary systems. Both impostors have masses
constrained to be $\lesssim$7.5 solar masses. In cases with precursor imaging
measurements, we find that age-dating and precursor imaging give consistent
progenitor masses. This consistency implies that, although the uncertainties
for each technique are significantly different, the results of both are
reliable to the measured uncertainties. We combine these new measurements with
those from our previous work and find that the distribution of 25 core-collapse
SNe progenitor masses is consistent with a standard Salpeter power-law mass
function, no upper mass cutoff, and an assumed minimum mass for core-collapse
of 7.5~M$_{\odot}$.",1803.08112v1
2018-03-29,The CHIME Fast Radio Burst Project: System Overview,"The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a novel transit
radio telescope operating across the 400-800-MHz band. CHIME is comprised of
four 20-m x 100-m semi-cylindrical paraboloid reflectors, each of which has 256
dual-polarization feeds suspended along its axis, giving it a >200 square
degree field-of-view. This, combined with wide bandwidth, high sensitivity, and
a powerful correlator makes CHIME an excellent instrument for the detection of
Fast Radio Bursts (FRBs). The CHIME Fast Radio Burst Project (CHIME/FRB) will
search beam-formed, high time-and frequency-resolution data in real time for
FRBs in the CHIME field-of-view. Here we describe the CHIME/FRB backend,
including the real-time FRB search and detection software pipeline as well as
the planned offline analyses. We estimate a CHIME/FRB detection rate of 2-42
FRBs/sky/day normalizing to the rate estimated at 1.4-GHz by Vander Wiel et al.
(2016). Likely science outcomes of CHIME/FRB are also discussed. CHIME/FRB is
currently operational in a commissioning phase, with science operations
expected to commence in the latter half of 2018.",1803.11235v1
2018-05-15,Parallel Working-Set Search Structures,"In this paper we present two versions of a parallel working-set map on p
processors that supports searches, insertions and deletions. In both versions,
the total work of all operations when the map has size at least p is bounded by
the working-set bound, i.e., the cost of an item depends on how recently it was
accessed (for some linearization): accessing an item in the map with recency r
takes O(1+log r) work. In the simpler version each map operation has O((log
p)^2+log n) span (where n is the maximum size of the map). In the pipelined
version each map operation on an item with recency r has O((log p)^2+log r)
span. (Operations in parallel may have overlapping span; span is additive only
for operations in sequence.)
  Both data structures are designed to be used by a dynamic multithreading
parallel program that at each step executes a unit-time instruction or makes a
data structure call. To achieve the stated bounds, the pipelined data structure
requires a weak-priority scheduler, which supports a limited form of 2-level
prioritization. At the end we explain how the results translate to practical
implementations using work-stealing schedulers.
  To the best of our knowledge, this is the first parallel implementation of a
self-adjusting search structure where the cost of an operation adapts to the
access sequence. A corollary of the working-set bound is that it achieves work
static optimality: the total work is bounded by the access costs in an optimal
static search tree.",1805.05787v3
2018-05-28,Zodiacal Exoplanets in Time (ZEIT) VII: A Temperate Candidate Super-Earth in the Hyades Cluster,"Transiting exoplanets in young open clusters present opportunities to study
how exoplanets evolve over their lifetimes. Recently, significant progress
detecting transiting planets in young open clusters has been made with the K2
mission, but so far all of these transiting cluster planets orbit close to
their host stars, so planet evolution can only be studied in a high-irradiation
regime. Here, we report the discovery of a long-period planet candidate, called
HD 283869 b, orbiting a member of the Hyades cluster. Using data from the K2
mission, we detected a single transit of a super-Earth-sized (1.96 +/- 0.12
R_earth) planet candidate orbiting the K-dwarf HD 283869 with a period longer
than 72 days. Since we only detected a single transit event, we cannot validate
HD 283869 b with high confidence, but our analysis of the K2 images, archival
data, and follow-up observations suggests that the source of the event is
indeed a transiting planet. We estimated the candidate's orbital parameters and
find that if real, it has a period P~100 days and receives approximately
Earth-like incident flux, giving the candidate a 71% chance of falling within
the circumstellar habitable zone. If confirmed, HD 283869 b would have the
longest orbital period, lowest incident flux, and brightest host star of any
known transiting planet in an open cluster, making it uniquely important to
future studies of how stellar irradiation affects planetary evolution.",1805.11117v1
2018-06-07,Discovery of a Candidate Black Hole - Giant Star Binary System in the Galactic Field,"We report the discovery of the first likely black hole in a non-interacting
binary system with a field red giant. By combining radial velocity measurements
from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) with
photometric variability data from the All-Sky Automated Survey for Supernovae
(ASAS-SN), we identified the bright rapidly-rotating giant 2MASS
J05215658+4359220 as a binary system with a massive unseen companion.
Subsequent radial velocity measurements reveal a system with an orbital period
of 83 days and near-zero eccentricity. The photometric variability period of
the giant is consistent with the orbital period, indicative of star spots and
tidal synchronization. Constraints on the giant's mass and radius from its
luminosity, surface gravity, and temperature imply an unseen companion with
mass of $3.3^{+2.8}_{-0.7}$ M$_\odot$, indicating a low-mass black hole or an
exceedingly massive neutron star. Measurement of the astrometric binary motion
by {\it Gaia} will further characterize the system. This discovery demonstrates
the potential of massive spectroscopic surveys like APOGEE and all-sky,
high-cadence photometric surveys like ASAS-SN to revolutionize our
understanding of the compact object mass function, and to test theories of
binary star evolution and the supernova mechanism.",1806.02751v2
2018-06-08,A TESS Dress Rehearsal: Planetary Candidates and Variables from K2 Campaign 17,"We produce light curves for all ~34,000 targets observed with K2 in Campaign
17 (C17), identifying 34 planet candidates, 184 eclipsing binaries, and 222
other periodic variables. The location of the C17 field means follow-up can
begin immediately now that the campaign has concluded and interesting targets
have been identified. The C17 field has a large overlap with C6, so this latest
campaign also offers a rare opportunity to study a large number of targets
already observed in a previous K2 campaign. The timing of the C17 data release,
shortly before science operations begin with the Transiting Exoplanet Survey
Satellite (TESS), also lets us exercise some of the tools and methods developed
for identification and dissemination of planet candidates from TESS. We find
excellent agreement between these results and those identified using only
K2-based tools. Among our planet candidates are several planet candidates with
sizes < 4 R_E and orbiting stars with KepMag < 10 (indicating good RV targets
of the sort TESS hopes to find) and a Jupiter-sized single-transit event around
a star already hosting a 6 d planet candidate.",1806.03127v1
2018-08-31,Design and characterization of the SPT-3G receiver,"The SPT-3G receiver was commissioned in early 2017 on the 10-meter South Pole
Telescope (SPT) to map anisotropies in the cosmic microwave background (CMB).
New optics, detector, and readout technologies have yielded a multichroic,
high-resolution, low-noise camera with impressive throughput and sensitivity,
offering the potential to improve our understanding of inflationary physics,
astroparticle physics, and growth of structure. We highlight several key
features and design principles of the new receiver, and summarize its
performance to date.",1809.00032v1
2018-10-02,Project AMIGA: Distance and Metallicity Gradients Along Andromeda's Giant Southern Stream from the Red Clump,"The Giant Southern Stream (GSS) of M31, a keystone signature of a major
accretion event, yields crucial constraints on M31 formation and evolution
models. Currently, our understanding of the GSS, in terms of both its geometry
and its chemistry, results from either wide-field imaging probing only a few
magnitudes below the red giant branch tip, or deep imaging or spectroscopy of
isolated regions. Here, we take an alternative approach, using Hubble Space
Telescope (HST) imaging to characterize the horizontal branch red clump (RC)
using unbinned maximum likelihood fits to luminosity functions (LFs) from
observed color-magnitude diagrams (CMDs). Comparing the RC mean magnitude
across three fields at projected distances of 21, 52 and 80 kpc from M31, we
find a line of sight distance gradient identical to recent literature
measurements in fields along the core. We also find tentative evidence that the
line of sight distance dispersion increases with projected distance from M31.
Meanwhile, the metallicity in the 52 kpc field westward of the GSS core is at
least as high as that in the 21 kpc GSS core field, and the peak colors of the
RC in these two fields imply identical metallicities to within 0.2 dex. We
discuss implications for distance and metallicity gradients both along and
perpendicular to the GSS in the context of recent ground-based photometric and
spectroscopic results, including evidence for a dropoff in metallicity moving
westward from the GSS, as well as prospects for further constraining stellar
populations in the vicinity of the GSS.",1810.01525v1
2018-10-30,MAMMO: A Deep Learning Solution for Facilitating Radiologist-Machine Collaboration in Breast Cancer Diagnosis,"With an aging and growing population, the number of women requiring either
screening or symptomatic mammograms is increasing. To reduce the number of
mammograms that need to be read by a radiologist while keeping the diagnostic
accuracy the same or better than current clinical practice, we develop Man and
Machine Mammography Oracle (MAMMO) - a clinical decision support system capable
of triaging mammograms into those that can be confidently classified by a
machine and those that cannot be, thus requiring the reading of a radiologist.
The first component of MAMMO is a novel multi-view convolutional neural network
(CNN) with multi-task learning (MTL). MTL enables the CNN to learn the
radiological assessments known to be associated with cancer, such as breast
density, conspicuity, suspicion, etc., in addition to learning the primary task
of cancer diagnosis. We show that MTL has two advantages: 1) learning refined
feature representations associated with cancer improves the classification
performance of the diagnosis task and 2) issuing radiological assessments
provides an additional layer of model interpretability that a radiologist can
use to debug and scrutinize the diagnoses provided by the CNN. The second
component of MAMMO is a triage network, which takes as input the radiological
assessment and diagnostic predictions of the first network's MTL outputs and
determines which mammograms can be correctly and confidently diagnosed by the
CNN and which mammograms cannot, thus needing to be read by a radiologist.
Results obtained on a private dataset of 8,162 patients show that MAMMO reduced
the number of radiologist readings by 42.8% while improving the overall
diagnostic accuracy in comparison to readings done by radiologists alone. We
analyze the triage of patients decided by MAMMO to gain a better understanding
of what unique mammogram characteristics require radiologists' expertise.",1811.02661v1
2018-11-22,Elemental Abundances in M31: Alpha and Iron Element Abundances from Low-Resolution Resolved Stellar Spectroscopy in the Stellar Halo,"Measurements of [Fe/H] and [$\alpha$/Fe] can probe the minor merging history
of a galaxy, providing a direct way to test the hierarchical assembly paradigm.
While measurements of [$\alpha$/Fe] have been made in the stellar halo of the
Milky Way, little is known about detailed chemical abundances in the stellar
halo of M31. To make progress with existing telescopes, we apply spectral
synthesis to low-resolution DEIMOS spectroscopy (R $\sim$ 2500 at 7000
Angstroms) across a wide spectral range (4500 Angstroms $<$ $\lambda$ $<$ 9100
Angstroms). By applying our technique to low-resolution spectra of 170 giant
stars in 5 MW globular clusters, we demonstrate that our technique reproduces
previous measurements from higher resolution spectroscopy. Based on the
intrinsic dispersion in [Fe/H] and [$\alpha$/Fe] of individual stars in our
combined cluster sample, we estimate systematic uncertainties of $\sim$0.11 dex
and $\sim$0.09 dex in [Fe/H] and [$\alpha$/Fe], respectively. We apply our
method to deep, low-resolution spectra of 11 red giant branch stars in the
smooth halo of M31, resulting in higher signal-to-noise per spectral resolution
element compared to DEIMOS medium-resolution spectroscopy, given the same
exposure time and conditions. We find $\langle$[$\alpha$/Fe]$\rangle$ = 0.49
$\pm$ 0.29 dex and $\langle$[Fe/H]$\rangle$ = 1.59 $\pm$ 0.56 dex for our
sample. This implies that---much like the Milky Way---the smooth halo of M31 is
likely composed of disrupted dwarf galaxies with truncated star formation
histories that were accreted early in the halo's formation.",1811.09279v2
2018-12-14,$ε^\prime/ε$-2018: A Christmas Story,"I was supposed to review the status of $\epsilon^\prime/\epsilon$ both at the
CKM Workshop in September in Heidelberg and recently at the Discrete 2018
Conference in Vienna. Unfortunately I had to cancel both talks for family
reasons. My main goal in these talks was to congratulate NA48 and KTeV
collaborations for the discovery of new sources of CP violation through their
heroic efforts to measure the ratio $\epsilon^\prime/\epsilon$ in the 1980s and
1990s with final results presented roughly 16 years ago. As I will not attend
any other conferences this year I will reach this goal in this writing. In this
context I will give arguments, why I am convinced about the presence of new
physics in $\epsilon^\prime/\epsilon$ on the basis of my work with Jean-Marc
Gerard within the context of the Dual QCD (DQCD) approach and why RBC-UKQCD
collaboration and in particular Chiral Perturbation Theory practitioners are
still unable to reach this conclusion. I will demonstrate that even in the
presence of pion loops, as large as advocated recently by Gilbert and Pich, the
value of $\epsilon^\prime/\epsilon$ is significantly below the data, when the
main non-factorizable QCD dynamics at long distance scales, represented in DQCD
by {the meson evolution}, is taken into account. As appriopriate for a
Christmas story, I will prophesy the final value of $\epsilon^\prime/\epsilon$
within the SM, which should include in addition to the correct matching between
long and short distance contributions, isospin breaking effects, NNLO QCD
corrections to both QCD penguin and electroweak penguin contributions and final
state interactions. Such final SM result will probably be known from lattice
QCD only in the middle of 2020s, but already in 2019 we should be able to see
some signs of NP in the next result on $\epsilon^\prime/\epsilon$ from
RBC-UKQCD.",1812.06102v2
2018-12-20,Single-spin qubits in isotopically enriched silicon at low magnetic field,"Single-electron spin qubits employ magnetic fields on the order of 1 Tesla or
above to enable quantum state readout via spin-dependent-tunnelling. This
requires demanding microwave engineering for coherent spin resonance control
and significant on-chip real estate for electron reservoirs, both of which
limit the prospects for large scale multi-qubit systems. Alternatively,
singlet-triplet (ST) readout enables high-fidelity spin-state measurements in
much lower magnetic fields, without the need for reservoirs. Here, we
demonstrate low-field operation of metal-oxide-silicon (MOS) quantum dot qubits
by combining coherent single-spin control with high-fidelity, single-shot,
Pauli-spin-blockade-based ST readout. We discover that the qubits decohere
faster at low magnetic fields with $T_{2}^{Rabi}=18.6$~$\mu$s and
$T_2^*=1.4$~$\mu$s at 150~mT. Their coherence is limited by spin flips of
residual $^{29}$Si nuclei in the isotopically enriched $^{28}$Si host material,
which occur more frequently at lower fields. Our finding indicates that new
trade-offs will be required to ensure the frequency stabilization of spin
qubits and highlights the importance of isotopic enrichment of device
substrates for the realization of a scalable silicon-based quantum processor.",1812.08347v5
2019-01-17,Lithium-loaded Liquid Scintillator Production for the PROSPECT experiment,"This work reports the production and characterization of lithium-loaded
liquid scintillator (LiLS) for the Precision Reactor Oscillation and Spectrum
Experiment (PROSPECT). Fifty-nine 90 liter batches of LiLS (${}^6{\rm Li}$ mass
fraction 0.082%$\pm$0.001%) were produced and samples from all batches were
characterized by measuring their optical absorbance relative to air, light
yield relative to a pure liquid scintillator reference, and pulse shape
discrimination capability. Fifty-seven batches passed the quality assurance
criteria and were used for the PROSPECT experiment.",1901.05569v2
2019-01-31,Spirit: Multifunctional Framework for Atomistic Spin Simulations,"The \textit{Spirit} framework is designed for atomic scale spin simulations
of magnetic systems of arbitrary geometry and magnetic structure, providing a
graphical user interface with powerful visualizations and an easy to use
scripting interface. An extended Heisenberg type spin-lattice Hamiltonian
including competing exchange interactions between neighbors at arbitrary
distance, higher-order exchange, Dzyaloshinskii-Moriya and dipole-dipole
interactions is used to describe the energetics of a system of classical spins
localised at atom positions. A variety of common simulations methods are
implemented including Monte Carlo and various time evolution algorithms based
on the Landau-Lifshitz-Gilbert equation of motion, which can be used to
determine static ground state and metastable spin configurations, sample
equilibrium and finite temperature thermodynamical properties of magnetic
materials and nanostructures or calculate dynamical trajectories including spin
torques induced by stochastic temperature or electric current. Methods for
finding the mechanism and rate of thermally assisted transitions include the
geodesic nudged elastic band method, which can be applied when both initial and
final states are specified, and the minimum mode following method when only the
initial state is given. The lifetime of magnetic states and rate of transitions
can be evaluated within the harmonic approximation of transition-state theory.
The framework offers performant CPU and GPU parallelizations. All methods are
verified and applications to several systems, such as vortices, domain walls,
skyrmions and bobbers are described.",1901.11350v1
2019-02-24,"Latency, Capacity, and Distributed MST","We study the cost of distributed MST construction in the setting where each
edge has a latency and a capacity, along with the weight. Edge latencies
capture the delay on the links of the communication network, while capacity
captures their throughput (in this case, the rate at which messages can be
sent). Depending on how the edge latencies relate to the edge weights, we
provide several tight bounds on the time and messages required to construct an
MST.
  When edge weights exactly correspond with the latencies, we show that,
perhaps interestingly, the bottleneck parameter in determining the running time
of an algorithm is the total weight $W$ of the MST (rather than the total
number of nodes $n$, as in the standard CONGEST model). That is, we show a
tight bound of $\tilde{\Theta}(D + \sqrt{W/c})$ rounds, where $D$ refers to the
latency diameter of the graph, $W$ refers to the total weight of the
constructed MST and edges have capacity $c$. The proposed algorithm sends
$\tilde{O}(m+W)$ messages, where $m$, the total number of edges in the network
graph under consideration, is a known lower bound on message complexity for MST
construction. We also show that $\Omega(W)$ is a lower bound for fast MST
constructions.
  When the edge latencies and the corresponding edge weights are unrelated, and
either can take arbitrary values, we show that (unlike the sub-linear time
algorithms in the standard CONGEST model, on small diameter graphs), the best
time complexity that can be achieved is $\tilde{\Theta}(D+n/c)$. However, if we
restrict all edges to have equal latency $\ell$ and capacity $c$ while having
possibly different weights (weights could deviate arbitrarily from $\ell$), we
give an algorithm that constructs an MST in $\tilde{O}(D + \sqrt{n\ell/c})$
time. In each case, we provide nearly matching upper and lower bounds.",1902.08979v2
2019-03-20,"Qatar Exoplanet Survey: Qatar-8b, 9b and 10b --- A Hot Saturn and Two Hot Jupiters","In this paper we present three new extrasolar planets from the Qatar
Exoplanet Survey (QES). Qatar-8b is a hot Saturn, with Mpl = 0.37 Mjup and Rpl
= 1.3 Rjup, orbiting a solar-like star every Porb = 3.7 days. Qatar-9b is a hot
Jupiter with a mass of Mpl = 1.2 Mjup and a radius of Rpl = 1 Rjup, in a Porb =
1.5 days orbit around a low mass, Mstar = 0.7 Msun, mid-K main-sequence star.
Finally, Qatar-10b is a hot, Teq ~ 2000 K, sub-Jupiter mass planet, Mpl = 0.7
Mjup, with a radius of Rpl = 1.54 Rjup and an orbital period of Porb = 1.6
days, placing it on the edge of the sub-Jupiter desert.",1903.09258v4
2019-03-25,Identifying Exoplanets with Deep Learning II: Two New Super-Earths Uncovered by a Neural Network in K2 Data,"For years, scientists have used data from NASA's Kepler Space Telescope to
look for and discover thousands of transiting exoplanets. In its extended K2
mission, Kepler observed stars in various regions of sky all across the
ecliptic plane, and therefore in different galactic environments. Astronomers
want to learn how the population of exoplanets are different in these different
environments. However, this requires an automatic and unbiased way to identify
the exoplanets in these regions and rule out false positive signals that mimic
transiting planet signals. We present a method for classifying these exoplanet
signals using deep learning, a class of machine learning algorithms that have
become popular in fields ranging from medical science to linguistics. We
modified a neural network previously used to identify exoplanets in the Kepler
field to be able to identify exoplanets in different K2 campaigns, which range
in galactic environments. We train a convolutional neural network, called
AstroNet-K2, to predict whether a given possible exoplanet signal is really
caused by an exoplanet or a false positive. AstroNet-K2 is highly successful at
classifying exoplanets and false positives, with accuracy of 98% on our test
set. It is especially efficient at identifying and culling false positives, but
for now, still needs human supervision to create a complete and reliable planet
candidate sample. We use AstroNet-K2 to identify and validate two previously
unknown exoplanets. Our method is a step towards automatically identifying new
exoplanets in K2 data and learning how exoplanet populations depend on their
galactic birthplace.",1903.10507v1
2019-04-23,Spin injection and pumping generated by a direct current flowing through a magnetic tunnel junction,"A charge flow through a magnetic tunnel junction (MTJ) leads to the
generation of a spin-polarized current which exerts a spin-transfer torque
(STT) on the magnetization. When the density of applied direct current exceeds
some critical value, the STT excites high-frequency magnetization precession in
the ""free"" electrode of MTJ. Such precession gives rise to microwave output
voltage and, furthermore, can be employed for spin pumping into adjacent normal
metal or semiconductor. Here we describe theoretically the spin dynamics and
charge transport in the CoFeB/MgO/CoFeB/Au tunneling heterostructure connected
to a constant-current source. The magnetization dynamics in the free CoFeB
layer with weak perpendicular anisotropy is calculated by numerical integration
of the Landau-Lifshitz-Gilbert-Slonczewski equation accounting for both STT and
voltage controlled magnetic anisotropy associated with the CoFeB|MgO interface.
It is shown that a large-angle magnetization precession, resulting from
electrically induced dynamic spin reorientation transition, can be generated in
a certain range of relatively low current densities. An oscillating spin
current, which is pumped into the Au overlayer owing to such precession, is
then evaluated together with the injected spin current. Considering both the
driving spin-polarized charge current and the pumped spin current, we also
describe the charge transport in the CoFeB/Au bilayer with the account of
anomalous and inverse spin Hall effects. An electric potential difference
between the lateral sides of the CoFeB/Au bilayer is calculated as a function
of distance from the CoFeB|MgO interface. It is found that this transverse
voltage signal in Au is large enough for experimental detection, which
indicates significant efficiency of the proposed current-driven spin injector.",1904.10361v1
2019-04-26,"TOI-216b and TOI-216c: Two warm, large exoplanets in or slightly wide of the 2:1 orbital resonance","Warm, large exoplanets with 10-100 day orbital periods pose a major challenge
to our understanding of how planetary systems form and evolve. Although high
eccentricity tidal migration has been invoked to explain their proximity to
their host stars, a handful reside in or near orbital resonance with nearby
planets, suggesting a gentler history of in situ formation or disk migration.
Here we confirm and characterize a pair of warm, large exoplanets discovered by
the TESS Mission orbiting K-dwarf TOI-216. Our analysis includes additional
transits and transit exclusion windows observed via ground-based follow-up. We
find two families of solutions, one corresponding to a sub-Saturn-mass planet
accompanied by a Neptune-mass planet and the other to a Jupiter in resonance
with a sub-Saturn-mass planet. We prefer the second solution based on the
orbital period ratio, the planet radii, the lower free eccentricities, and
libration of the 2:1 resonant argument, but cannot rule out the first. The free
eccentricities and mutual inclination are compatible with stirring by other,
undetected planets in the system, particularly for the second solution. We
discuss prospects for better constraints on the planets' properties and orbits
through follow-up, including transits observed from the ground.",1904.11852v1
2019-04-28,Periodic Bandits and Wireless Network Selection,"Bandit-style algorithms have been studied extensively in stochastic and
adversarial settings. Such algorithms have been shown to be useful in
multiplayer settings, e.g. to solve the wireless network selection problem,
which can be formulated as an adversarial bandit problem. A leading bandit
algorithm for the adversarial setting is EXP3. However, network behavior is
often repetitive, where user density and network behavior follow regular
patterns. Bandit algorithms, like EXP3, fail to provide good guarantees for
periodic behaviors. A major reason is that these algorithms compete against
fixed-action policies, which is ineffective in a periodic setting.
  In this paper, we define a periodic bandit setting, and periodic regret as a
better performance measure for this type of setting. Instead of comparing an
algorithm's performance to fixed-action policies, we aim to be competitive with
policies that play arms under some set of possible periodic patterns $F$ (for
example, all possible periodic functions with periods $1,2,\cdots,P$). We
propose Periodic EXP4, a computationally efficient variant of the EXP4
algorithm for periodic settings. With $K$ arms, $T$ time steps, and where each
periodic pattern in $F$ is of length at most $P$, we show that the periodic
regret obtained by Periodic EXP4 is at most $O\big(\sqrt{PKT \log K + KT \log
|F|}\big)$. We also prove a lower bound of $\Omega\big(\sqrt{PKT + KT
\frac{\log |F|}{\log K}} \big)$ for the periodic setting, showing that this is
optimal within log-factors. As an example, we focus on the wireless network
selection problem. Through simulation, we show that Periodic EXP4 learns the
periodic pattern over time, adapts to changes in a dynamic environment, and far
outperforms EXP3.",1904.12355v1
2019-04-30,An Inpainting Approach to Tackle the Kinematic and Thermal SZ Induced Biases in CMB-Cluster Lensing Estimators,"A galaxy cluster's own Sunyaev-Zel{'}dovich (SZ) signal is known to be a
major contaminant when reconstructing the cluster's underlying lensing
potential using cosmic microwave background (CMB) temperature maps. In this
work, we develop a modified quadratic estimator (QE) that is designed to
mitigate the lensing biases due to the kinematic and thermal SZ effects. The
idea behind the approach is to use inpainting to eliminate the cluster's own
emission from the large-scale CMB gradient map. In this inpainted gradient map,
we fill the pixel values at the cluster location using a constrained Gaussian
realization based on the information from surrounding regions. We show that the
noise induced due to inpainting process is small compared to other noise
sources for upcoming surveys and has minimal impact on the final lensing
signal-to-noise. Without any foreground cleaning, we find a stacked mass
uncertainty of 6.5% for the CMB-S4 experiment on a cluster sample containing
5000 clusters with $M_{200c} = 2 \times 10^{14}\ M_{\odot}$ at z = 0.7. In
addition to the SZ-induced lensing biases, we also quantify the low mass bias
arising due to the contamination of the CMB gradient by the cluster
convergence. For the fiducial cluster sample considered in this work, we find
that bias is negligible compared to the statistical uncertainties for both the
standard and the modified QE even when modes up to $\sim 2700$ are used for the
gradient estimation. With more gradient modes, we demonstrate that the
sensitivity can be increased by 14% compared to the fiducial result above with
gradient modes up to $2000$",1904.13392v2
2019-05-31,Balancing spreads of influence in a social network,"The personalization of our news consumption on social media has a tendency to
reinforce our pre-existing beliefs instead of balancing our opinions. This
finding is a concern for the health of our democracies which rely on an access
to information providing diverse viewpoints. To tackle this issue from a
computational perspective, Garimella et al. (NIPS'17) modeled the spread of
these viewpoints, also called campaigns, using the well-known independent
cascade model and studied an optimization problem that aims at balancing
information exposure in a social network when two opposing campaigns propagate
in the network. The objective in their $NP$-hard optimization problem is to
maximize the number of people that are exposed to either both or none of the
viewpoints. For two different settings, one corresponding to a model where
campaigns spread in a correlated manner, and a second one, where the two
campaigns spread in a heterogeneous manner, they provide constant ratio
approximation algorithms. In this paper, we investigate a more general
formulation of this problem. That is, we assume that $\mu$ different campaigns
propagate in a social network and we aim to maximize the number of people that
are exposed to either $\nu$ or none of the campaigns, where $\mu\ge\nu\ge2$. We
provide dedicated approximation algorithms for both the correlated and
heterogeneous settings. Interestingly, for the heterogeneous setting with
$\nu\ge 3$, we give a reduction leading to several approximation hardness
results. Maybe most importantly, we obtain that the problem cannot be
approximated within a factor of $n^{-g(n)}$ for any $g(n)=o(1)$ assuming
Gap-ETH, denoting with $n$ the number of nodes in the social network. For $\nu
\ge 4$, there is no $n^{-\epsilon}$-approximation algorithm if a certain class
of one-way functions exists, where $\epsilon > 0$ is a given constant which
depends on $\nu$.",1906.00074v1
2019-06-17,The Radioactive Source Calibration System of the PROSPECT Reactor Antineutrino Detector,"The Precision Reactor Oscillation and Spectrum (PROSPECT) Experiment is a
reactor neutrino experiment designed to search for sterile neutrinos with a
mass on the order of 1 eV/c$^2$ and to measure the spectrum of electron
antineutrinos from a highly-enriched $^{235}$U nuclear reactor. The PROSPECT
detector consists of an 11 by 14 array of optical segments in $^{6}$Li-loaded
liquid scintillator at the High Flux Isotope Reactor in Oak Ridge National
Laboratory. Antineutrino events are identified via inverse beta decay and read
out by photomultiplier tubes located at the ends of each segment. The detector
response is characterized using a radioactive source calibration system. This
paper describes the design, operation, and performance of the PROSPECT source
calibration system.",1906.07244v2
2019-07-17,Topical Review on Skyrmions and Hall Transport,"We review recent progresses towards an understanding of the Skyrmion Hall
transport in insulating as well as conducting materials. First, we consider a
theoretical breakthrough based on the quantum field theory Ward identity, a
first principle analysis, relying on symmetries and conservation laws. Broken
parity (inversion) symmetry plays a crucial role in Skyrmion Hall transport. In
addition to the well known thermal and electric Hall conductivities, our
analysis has led us to the discovery of a new and unforeseen physical quantity,
Hall viscosity - an anti-symmetric part of the viscosity tensor. We propose a
simple way to confirm the existence of Hall viscosity in the measurements of
Hall conductivity as a function of momentum. We provide various background
materials to assist the readers to understand the quantum field theory Ward
identity.
  In the second part, we review recent theoretical and experimental
advancements of the Skyrmion Hall effects and the topological (Magnon) Hall
effects for conducting (insulting) magnets. For this purpose, we consider two
enveloping themes: spin torque and thermo-electromagnetic effect. First, we
overview various spin torques, such as spin transfer torque, spin-orbit torque,
and spin Hall torque, and generalized Landau-Lifshitz-Gilbert equations and
Thiele equations using a phenomenological approach. Second, we consider
irreversible thermodynamics to survey possible thermo-electromagnetic effects,
such as Seebeck, Peltier and Thompson effects in the presence of the electric
currents, along with the Hall effects in the presence of a background magnetic
field. Recently developed spin Seebeck effects are also a significant part of
the survey. We also accommodate extensive background materials to make this
review self-contained. Finally, we revisit the Skyrmion Hall transport from the
Ward identity view point.",1907.07696v1
2019-07-29,Research and Development for HI Intensity Mapping,"Development of the hardware, data analysis, and simulation techniques for
large compact radio arrays dedicated to mapping the 21 cm line of neutral
hydrogen gas has proven to be more difficult than imagined twenty years ago
when such telescopes were first proposed. Despite tremendous technical and
methodological advances, there are several outstanding questions on how to
optimally calibrate and analyze such data. On the positive side, it has become
clear that the outstanding issues are purely technical in nature and can be
solved with sufficient development activity. Such activity will enable science
across redshifts, from early galaxy evolution in the pre-reionization era to
dark energy evolution at low redshift.",1907.13090v1
2019-07-03,Deep Learning Based Energy Disaggregation and On/Off Detection of Household Appliances,"Energy disaggregation, a.k.a. Non-Intrusive Load Monitoring, aims to separate
the energy consumption of individual appliances from the readings of a mains
power meter measuring the total energy consumption of, e.g. a whole house.
Energy consumption of individual appliances can be useful in many applications,
e.g., providing appliance-level feedback to the end users to help them
understand their energy consumption and ultimately save energy. Recently, with
the availability of large-scale energy consumption datasets, various neural
network models such as convolutional neural networks and recurrent neural
networks have been investigated to solve the energy disaggregation problem.
Neural network models can learn complex patterns from large amounts of data and
have been shown to outperform the traditional machine learning methods such as
variants of hidden Markov models. However, current neural network methods for
energy disaggregation are either computational expensive or are not capable of
handling long-term dependencies. In this paper, we investigate the application
of the recently developed WaveNet models for the task of energy disaggregation.
Based on a real-world energy dataset collected from 20 households over two
years, we show that WaveNet models outperforms the state-of-the-art deep
learning methods proposed in the literature for energy disaggregation in terms
of both error measures and computational cost. On the basis of energy
disaggregation, we then investigate the performance of two deep-learning based
frameworks for the task of on/off detection which aims at estimating whether an
appliance is in operation or not. Based on the same dataset, we show that for
the task of on/off detection the second framework, i.e., directly training a
binary classifier, achieves better performance in terms of F1 score.",1908.00941v2
2019-08-07,Parallel Finger Search Structures,"In this paper we present two versions of a parallel finger structure FS on p
processors that supports searches, insertions and deletions, and has a finger
at each end. This is to our knowledge the first implementation of a parallel
search structure that is work-optimal with respect to the finger bound and yet
has very good parallelism (within a factor of O( (log p)^2 ) of optimal). We
utilize an extended implicit batching framework that transparently facilitates
the use of FS by any parallel program P that is modelled by a dynamically
generated DAG D where each node is either a unit-time instruction or a call to
FS.
  The total work done by either version of FS is bounded by the finger bound
F[L] (for some linearization L of D ), i.e. each operation on an item with
finger distance r takes O( log r + 1 ) amortized work; it is cheaper for items
closer to a finger. Running P using the simpler version takes O( ( T[1] + F[L]
) / p + T[inf] + d * ( (log p)^2 + log n ) ) time on a greedy scheduler, where
T[1],T[inf] are the size and span of D respectively, and n is the maximum
number of items in FS, and d is the maximum number of calls to FS along any
path in D. Using the faster version, this is reduced to O( ( T[1] + F[L] ) / p
+ T[inf] + d * (log p)^2 + s[L] ) time, where s[L] is the weighted span of D
where each call to FS is weighted by its cost according to F[L]. We also sketch
how to extend FS to support a fixed number of movable fingers.
  The data structures in our paper fit into the dynamic multithreading
paradigm, and their performance bounds are directly composable with other data
structures given in the same paradigm. Also, the results can be translated to
practical implementations using work-stealing schedulers.",1908.02741v4
2019-08-12,Percolation phase transitions for the SIR model with random powers,"This thesis considers three models which describe a multihop ad-hoc
telecommunication system. These systems consist of users sending messages,
which can jump to other users to reach the target user. The first two models
have already been examined extensively, whereas it is the first time the third
model is studied. In all these models our goal is to understand under which
conditions users situated far away from each other can communicate. This is the
fundamental question of continuum percolation, which was introduced by Gilbert
(1961), who established the Boolean model for Poisson point processes. In the
first part of this thesis we introduce this model and prove the existence of a
phase transition between a subcritical phase, where no infinite connected
component of users exists, and a supercritical phase, where such a component
exists. We also consider the case of random connection radii, following Meester
and Roy (1996). In the second part we study the SINR model for Cox point
processes in two or higher dimensions, following T\'obi\'as (2019). He proved
that there exists a phase transition under certain stabilization and
connectedness conditions on the intensity measure. The SINR model for
homogeneous Poisson point processes in $\mathbb R^2$ was introduced by Dousse
et al. (2005). In the third part we study percolation in the SINR model with
random powers for Poisson point processes in $\mathbb R^d$, $d \geq 2$. This
model was studied by Kong and Yeh (2007) for $d=2$ under strong boundedness
conditions on the random power. In this thesis we weaken these conditions and
only assume that the random power is nonnegative, integrable and not a.s. zero.
We show that there exists a subcritical phase if the path-loss function decays
fast enough. Further, we prove that a supercritical phase exists if random
power has a large enough essential supremum and some exponential moments.",1908.07375v1
2019-08-30,"Elemental Abundances in M31: A Comparative Analysis of Iron and Alpha Element Abundances in the Outer Disk, Giant Stellar Stream, and Inner Halo of M31","We measured [Fe/H] and [$\alpha$/Fe] using spectral synthesis of
low-resolution stellar spectroscopy for 70 individual red giant branch stars
across four fields spanning the outer disk, Giant Stellar Stream (GSS), and
inner halo of M31. Fields at M31-centric projected distances of 23 kpc in the
halo, 12 kpc in the halo, 22 kpc in the GSS, and 26 kpc in the outer disk are
$\alpha$-enhanced, with $\langle$[$\alpha$/Fe]$\rangle$ = 0.43, 0.50, 0.41, and
0.58, respectively. The 23 kpc and 12 kpc halo fields are relatively
metal-poor, with $\langle$[Fe/H]$\rangle$ = $-$1.54 and $-$1.30, whereas the 22
kpc GSS and 26 kpc outer disk fields are relatively metal-rich with
$\langle$[Fe/H]$\rangle$ = $-$0.84 and $-$0.92, respectively. For fields with
substructure, we separated the stellar populations into kinematically hot
stellar halo components and kinematically cold components. We did not find any
evidence of an [$\alpha$/Fe] gradient along the high surface brightness core of
the GSS between $\sim$17$-$22 kpc. However, we found tentative suggestions of a
negative [$\alpha$/Fe] gradient in the stellar halo, which may indicate that
different progenitor(s) or formation mechanisms contributed to the build up of
the inner versus outer halo. Additionally, the [$\alpha$/Fe] distribution of
the metal-rich ([Fe/H] $>$ $-$1.5), smooth inner stellar halo (r$_{\rm{proj}}$
$\lesssim$ 26 kpc) is inconsistent with having formed from the disruption of
progenitor(s) similar to present-day M31 satellite galaxies. The 26 kpc outer
disk is most likely associated with the extended disk of M31, where its high
$\alpha$-enhancement provides support for an episode of rapid star formation in
M31's disk, possibly induced by a major merger.",1909.00006v2
2019-09-25,Deep Learning for RF Signal Classification in Unknown and Dynamic Spectrum Environments,"Dynamic spectrum access (DSA) benefits from detection and classification of
interference sources including in-network users, out-network users, and jammers
that may all coexist in a wireless network. We present a deep learning based
signal (modulation) classification solution in a realistic wireless network
setting, where 1) signal types may change over time; 2) some signal types may
be unknown for which there is no training data; 3) signals may be spoofed such
as the smart jammers replaying other signal types; and 4) different signal
types may be superimposed due to the interference from concurrent
transmissions. For case 1, we apply continual learning and train a
Convolutional Neural Network (CNN) using an Elastic Weight Consolidation (EWC)
based loss. For case 2, we detect unknown signals via outlier detection applied
to the outputs of convolutional layers using Minimum Covariance Determinant
(MCD) and k-means clustering methods. For case 3, we extend the CNN structure
to capture phase shifts due to radio hardware effects to identify the spoofing
signal sources. For case 4, we apply blind source separation using Independent
Component Analysis (ICA) to separate interfering signals. We utilize the signal
classification results in a distributed scheduling protocol, where in-network
(secondary) users employ signal classification scores to make channel access
decisions and share the spectrum with each other while avoiding interference
with out-network (primary) users and jammers. Compared with benchmark
TDMA-based schemes, we show that distributed scheduling constructed upon signal
classification results provides major improvements to in-network user
throughput and out-network user success ratio.",1909.11800v1
2019-09-30,First-principles theory of proximity spin-orbit torque on a two-dimensional magnet: Current-driven antiferromagnet-to-ferromagnet reversible transition in bilayer CrI$_3$,"The recently discovered two-dimensional (2D) magnetic insulator CrI$_3$ is an
intriguing case for basic research and spintronic applications since it is a
ferromagnet in the bulk, but an antiferromagnet in bilayer form, with its
magnetic ordering amenable to external manipulations. Using first-principles
quantum transport approach, we predict that injecting unpolarized charge
current parallel to the interface of bilayer-CrI$_3$/monolayer-TaSe$_2$ van der
Waals heterostructure will induce spin-orbit torque (SOT) and thereby driven
dynamics of magnetization on the first monolayer of CrI$_3$ in direct contact
with TaSe$_2$. By combining calculated complex angular dependence of SOT with
the Landau-Lifshitz-Gilbert equation for classical dynamics of magnetization,
we demonstrate that current pulses can switch the direction of magnetization on
the first monolayer to become parallel to that of the second monolayer, thereby
converting CrI$_3$ from antiferromagnet to ferromagnet while not requiring any
external magnetic field. We explain the mechanism of this reversible
current-driven nonequilibrium phase transition by showing that first monolayer
of CrI$_3$ carries current due to evanescent wavefunctions injected by metallic
transition metal dichalcogenide TaSe$_2$, while concurrently acquiring strong
spin-orbit coupling (SOC) via such proximity effect, whereas the second
monolayer of CrI$_3$ remains insulating. The transition can be detected by
passing vertical read current through the vdW heterostructure, encapsulated by
bilayer of hexagonal boron nitride and sandwiched between graphite electrodes,
where we find tunneling magnetoresistance of $\simeq 240$%.",1909.13876v2
2019-10-14,"An Extreme-mass Ratio, Short-period Eclipsing Binary Consisting of a B Dwarf Primary and a Pre-main Sequence M Star Companion Discovered by KELT","We present the discovery of \thisstar\ (HD 58730), a very low mass ratio ($q
\equiv M_2/M_1 \approx 0.07$) eclipsing binary (EB) identified by the
Kilodegree Extremely Little Telescope (KELT) survey. We present the discovery
light curve and perform a global analysis of four high-precision ground-based
light curves, the Transiting Exoplanets Survey Satellite (TESS) light curve,
radial velocity (RV) measurements, Doppler Tomography (DT) measurements, and
the broad-band spectral energy distribution (SED). Results from the global
analysis are consistent with a fully convective ($M_2 = 0.22 \pm 0.02\
M_{\odot})$ M star transiting a late-B primary ($M_1 = 3.34^{+0.07}_{-0.09}\
M_{\odot};\ T_{\rm eff,1} = 11960^{+430}_{-520}\ {\rm K}$). We infer that the
primary star is $183_{-30}^{+33}$ Myr old and that the companion star's radius
is inflated by $26 \pm 8\%$ relative to the predicted value from a low-mass
isochrone of similar age. We separately and analytically fit for the
variability in the out-of-eclipse TESS phase curve, finding good agreement
between the resulting stellar parameters and those from the global fit. Such
systems are valuable for testing theories of binary star formation and
understanding how the environment of a star in a close-but-detached binary
affects its physical properties. In particular, we examine how a star's
properties in such a binary might differ from the properties it would have in
isolation.",1910.06212v2
2019-10-28,"A detailed study of Andromeda XIX, an extreme local analogue of ultra diffuse galaxies","With a central surface brightness of $\mu_0=29.3$ mag. per sq. arcsec, and
half-light radius of $r_{\rm half}=3.1^{+0.9}_{-1.1}$~kpc, Andromeda XIX (And
XIX) is an extremely diffuse satellite of Andromeda. We present spectra for
$\sim100$ red giant branch stars in this galaxy, plus 16 stars in a nearby
stellar stream. With this exquisite dataset, we re-derive the properties of And
XIX, measuring a systemic velocity of $v_r=-109.0\pm1.6$ km/s and a velocity
dispersion of $\sigma_v = 7.8^{+1.7}_{-1.5}$ km/s (higher than derived in our
previous work). We marginally detect a velocity gradient along the major axis
of ${\rm d}v/{\rm d}r = -2.1\pm1.8$ km/s kpc$^{-1}$. We find its mass-to-light
ratio is higher than galaxies of comparable stellar mass ($[M/L]_{\rm half} =
278^{+146}_{-198}M_\odot/L_\odot$), but its dynamics place it in a halo with a
similar total mass to these galaxies. This could suggest that And XIX is a
""puffed up"" dwarf galaxy, whose properties have been altered by tidal
processes, similar to its Milky Way counterpart, Antlia II. For the nearby
stream, we measure $v_r=-279.2\pm3.7$ km/s, and $\sigma_v=13.8^{+3.5}_{-2.6}$
km/s. We measure its metallicity, and find it to be more metal rich than And
XIX, implying that the two features are unrelated. Finally, And XIX's dynamical
and structural properties imply it is a local analogue to ultra diffuse
galaxies (UDGs). Its complex dynamics suggest that the masses of distant UDGs
measured from velocity dispersions alone should be carefully interpreted",1910.12879v2
2019-10-28,Added Value of Intraoperative Data for Predicting Postoperative Complications: Development and Validation of a MySurgeryRisk Extension,"To test the hypothesis that accuracy, discrimination, and precision in
predicting postoperative complications improve when using both preoperative and
intraoperative data input features versus preoperative data alone. Models that
predict postoperative complications often ignore important intraoperative
physiological changes. Incorporation of intraoperative physiological data may
improve model performance. This retrospective cohort analysis included 52,529
inpatient surgeries at a single institution during a 5 year period. Random
forest machine learning models in the validated MySurgeryRisk platform made
patient-level predictions for three postoperative complications and mortality
during hospital admission using electronic health record data and patient
neighborhood characteristics. For each outcome, one model trained with
preoperative data alone and one model trained with both preoperative and
intraoperative data. Models were compared by accuracy, discrimination
(expressed as AUROC), precision (expressed as AUPRC), and reclassification
indices (NRI). Machine learning models incorporating both preoperative and
intraoperative data had greater accuracy, discrimination, and precision than
models using preoperative data alone for predicting all three postoperative
complications (intensive care unit length of stay >48 hours, mechanical
ventilation >48 hours, and neurological complications including delirium) and
in-hospital mortality (accuracy: 88% vs. 77%, AUROC: 0.93 vs. 0.87, AUPRC: 0.21
vs. 0.15). Overall reclassification improvement was 2.9-10.0% for complications
and 11.2% for in-hospital mortality. Incorporating both preoperative and
intraoperative data significantly increased accuracy, discrimination, and
precision for machine learning models predicting postoperative complications.",1910.12895v2
2019-12-04,Elemental Abundances in M31: The Kinematics and Chemical Evolution of Dwarf Spheroidal Satellite Galaxies,"We present deep spectroscopy from Keck/DEIMOS of Andromeda I, III, V, VII,
and X, all of which are dwarf spheroidal satellites of M31. The sample includes
256 spectroscopic members across all five dSphs. We confirm previous
measurements of the velocity dispersions and dynamical masses, and we provide
upper limits on bulk rotation. Our measurements confirm that M31 satellites
obey the same relation between stellar mass and stellar metallicity as Milky
Way (MW) satellites and other dwarf galaxies in the Local Group. The
metallicity distributions show similar trends with stellar mass as MW
satellites, including evidence in massive satellites for external influence,
like pre-enrichment or gas accretion. We present the first measurements of
individual element ratios, like [Si/Fe], in the M31 system, as well as
measurements of the average [alpha/Fe] ratio. The trends of [alpha/Fe] with
[Fe/H] also follow the same galaxy mass-dependent patterns as MW satellites.
Less massive galaxies have more steeply declining slopes of [alpha/Fe] that
begin at lower [Fe/H]. Finally, we compare the chemical evolution of M31
satellites to M31's Giant Stellar Stream and smooth halo. The properties of the
M31 system support the theoretical prediction that the inner halo is composed
primarily of massive galaxies that were accreted early. As a result, the inner
halo exhibits higher [Fe/H] and [alpha/Fe] than surviving satellite galaxies.",1912.02186v1
2020-01-03,The First Habitable Zone Earth-sized Planet from TESS. III: Climate States and Characterization Prospects for TOI-700 d,"We present self-consistent three-dimensional climate simulations of possible
habitable states for the newly discovered Habitable Zone Earth-sized planet,
TOI-700 d. We explore a variety of atmospheric compositions, pressures, and
rotation states for both ocean-covered and completely desiccated planets in
order to assess the planet's potential for habitability. For all 20 of our
simulated cases, we use our climate model outputs to synthesize transmission
spectra, combined-light spectra, and integrated broadband phase curves. These
climatologically-informed observables will help the community assess the
technological capabilities necessary for future characterization of this planet
- as well as similar transiting planets discovered in the future - and will
provide a guide for distinguishing possible climate states if one day we do
obtain sensitive spectral observations of a habitable planet around a M-star.
We find that TOI-700 d is a strong candidate for a habitable world and can
potentially maintain temperate surface conditions under a wide variety of
atmospheric compositions. Unfortunately, the spectral feature depths from the
resulting transmission spectra and the peak flux and variations from our
synthesized phase curves for TOI-700 d do not exceed 10 ppm. This will likely
prohibit the James Webb Space Telescope (JWST) from characterizing its
atmosphere; however, this motivates the community to invest in future
instrumentation that perhaps can one day reveal the true nature of TOI-700 d,
and to continue to search for similar planets around less distant stars.",2001.00955v2
2020-01-07,X-ray Observations of the Peculiar Cepheid V473 Lyr Identify A Low-Mass Companion,"V473 Lyr is a classical Cepheid which is unique in having substantial
amplitude variations with a period of approximately 3.3 years, thought to be
similar to the Blazhko variations in RR Lyrae stars. We obtained an {\it
XMM-Newton} observation of this star to followup a previous detection in
X-rays. Rather than the X-ray burst and rapid decline near maximum radius seen
in $\delta$ Cephei itself, the X-ray flux in V473 Lyr remained constant for a
third of the pulsation cycle covered by the observation. Thus the X-rays are
most probably not produced by the changes around the pulsation cycle. The X-ray
spectrum is soft (kT = 0.6 keV), with
  X-ray properties which are consistent with a young low mass companion.
Previously there was no evidence of a companion in radial velocities or in {\it
Gaia} and {\it Hipparcos} proper motions. While this rules out companions which
are very close or very distant, a binary companion at a separation between 30
and 300 AU is possible. This is an example of an X-ray observation revealing
evidence of a low mass companion, which is important in completing the mass
ratio statistics of binary Cepheids. Furthermore, the detection of a young
X-ray bright companion is a further indication that the Cepheid (primary) is a
Population I star, even though its pulsation behavior differs from other
classical Cepheids.",2001.02253v1
2020-02-11,Spintronics meets density matrix renormalization group: Quantum spin torque driven nonclassical magnetization reversal and dynamical buildup of long-range entanglement,"We introduce time-dependent density matrix renormalization group (tDMRG) as a
solution to long standing problem in spintronics -- how to describe
spin-transfer torque (STT) between flowing spins of conduction electrons and
localized spins within a magnetic material by treating the dynamics of both
spin species fully quantum-mechanically. In contrast to conventional
Slonczewski-Berger STT, where the localized spins are viewed as classical
vectors obeying the Landau-Lifshitz-Gilbert equation and where their STT-driven
dynamics is initiated only when the spin-polarization of flowing electrons and
localized spins are noncollinear, quantum STT can occur when these vectors are
collinear but antiparallel. Using tDMRG, we simulate the time evolution of a
many-body quantum state of electrons and localized spins, where the former are
injected as a spin-polarized current pulse while the latter comprise a quantum
Heisenberg ferromagnetic metallic (FM) spin-$\frac{1}{2}$ XXZ chain initially
in the ground state with spin-polarization antiparallel to that of injected
electrons. The quantum STT reverses the direction of localized spins, but
without rotation from the initial orientation, when the number of injected
electrons exceeds the number of localized spins. Such nonclassical reversal,
which is absent from LLG dynamics, is strikingly inhomogeneous across the FM
chain and it can be accompanied by reduction of the magnetization associated
with localized spins, even to zero at specific locations. This is because
quantum STT generates a highly entangled nonequilibrium many-body state of all
flowing and localized spins, despite starting from the initially unentangled
ground state of a mundane FM. Furthermore, the mutual information between
localized spins at the FM edges remains nonzero even at infinite separation as
the signature of dynamical buildup of long-range entanglement.",2002.04655v4
2020-02-27,Les Houches 2019 Physics at TeV Colliders: New Physics Working Group Report,"This report presents the activities of the `New Physics' working group for
the `Physics at TeV Colliders' workshop (Les Houches, France, 10--28 June,
2019). These activities include studies of direct searches for new physics,
approaches to exploit published data to constrain new physics, as well as the
development of tools to further facilitate these investigations. Benefits of
machine learning for both the search for new physics and the interpretation of
these searches are also presented.",2002.12220v1
2020-03-19,Realizing an Isotropically Coercive Magnetic Layer for Memristive Applications by Analogy to Dry Friction,"We investigate the possibility of realizing a spintronic memristive device
based on the dependence of the tunnel conductance on the relative angle between
the magnetization of the two magnetic electrodes in in-plane magnetized tunnel
junctions. For this, it is necessary to design a free layer whose magnetization
can be stabilized along several or even any in-plane direction between the
parallel and the antiparallel magnetic configurations. We experimentally show
that this can be achieved by exploiting antiferromagnet-ferromagnet exchange
interactions in a regime where the antiferromagnet is thin enough to induce
enhanced coercivity and no exchange bias. The frustration of exchange
interactions at the interfaces due to competing ferro- and antiferromagnetic
interactions is at the origin of an isotropic dissipation mechanism yielding
isotropic coercivity. From a modeling point of view, it is shown that this
isotropic dissipation can be described by a dry friction term in the
Landau-Lifshitz-Gilbert equation. The influence of this dry friction term on
the magnetization dynamics of an in-plane magnetized layer submitted to a
rotating in-plane field is investigated both analytically and numerically. The
possibility to control the free layer magnetization orientation in an in-plane
magnetized magnetic tunnel junction by using the spin transfer torque from an
additional perpendicular polarizer is also investigated through macrospin
simulation. It is shown that the memristor function can be achieved by the
injection of current pulses through the stack in the presence of an in-plane
static field transverse to the reference layer magnetization, the aim of which
is to limit the magnetization rotation between 0{\deg} and 180{\deg}.",2003.08850v1
2020-04-07,Elemental abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra,"We present chemical abundances of red giant branch (RGB) stars in the dwarf
spheroidal (dSph) satellite system of Andromeda (M31), using spectral synthesis
of medium resolution (R $\sim 6000$) spectra obtained with the Keck II
telescope and DEIMOS spectrograph via the Spectroscopic and Photometric
Landscape of Andromeda's Stellar Halo (SPLASH) survey. We coadd stars according
to their similarity in photometric metallicity or effective temperature to
obtain a signal-to-noise ratio (S/N) high enough to measure average [Fe/H] and
[$\alpha$/Fe] abundances. We validate our method using high S/N spectra of RGB
stars in Milky Way globular clusters as well as deep observations for a subset
of the M31 dSphs in our sample. For this set of validation coadds, we compare
the weighted average abundance of the individual stars with the abundance
determined from the coadd. We present individual and coadded measurements of
[Fe/H] and [$\alpha$/Fe] for stars in ten M31 dSphs, including the first
[$\alpha$/Fe] measurements for And IX, XIV, XV, and XVIII. These fainter, less
massive dSphs show declining [$\alpha$/Fe] relative to [Fe/H], implying an
extended star formation history. In addition, these dSphs also follow the same
mass-metallicity relation found in other Local Group satellites. The
conclusions we infer from coadded spectra agree with those from previous
measurements in brighter M31 dSphs with individual abundance measurements, as
well as conclusions from photometric studies. These abundances greatly increase
the number of spectroscopic measurements of the chemical composition of M31's
less massive dwarf satellites, which are crucial to understanding their star
formation history and interaction with the M31 system.",2004.03425v1
2020-04-15,Toward Trustworthy AI Development: Mechanisms for Supporting Verifiable Claims,"With the recent wave of progress in artificial intelligence (AI) has come a
growing awareness of the large-scale impacts of AI systems, and recognition
that existing regulations and norms in industry and academia are insufficient
to ensure responsible AI development. In order for AI developers to earn trust
from system users, customers, civil society, governments, and other
stakeholders that they are building AI responsibly, they will need to make
verifiable claims to which they can be held accountable. Those outside of a
given organization also need effective means of scrutinizing such claims. This
report suggests various steps that different stakeholders can take to improve
the verifiability of claims made about AI systems and their associated
development processes, with a focus on providing evidence about the safety,
security, fairness, and privacy protection of AI systems. We analyze ten
mechanisms for this purpose--spanning institutions, software, and hardware--and
make recommendations aimed at implementing, exploring, or improving those
mechanisms.",2004.07213v2
2020-04-22,"Impurity-dependent gyrotropic motion, deflection and pinning of current-driven ultrasmall skyrmions in PdFe/Ir(111) surface","Resting on multi-scale modelling simulations, we explore dynamical aspects
characterizing skyrmions driven by spin-transfer-torque towards repulsive and
pinning 3d and 4d single atomic defects embedded in a Pd layer deposited on the
Fe/Ir(111) surface. The latter is known to host sub-10 nm skyrmions which are
of great interest in information technology. The Landau-Lifshitz-Gilbert
equation is parametrized with magnetic exchange interactions extracted from
first-principles. Depending on the nature of the defect and the magnitude of
the applied magnetic field, the skyrmion deforms by either shrinking or
increasing in size, experiencing thereby elliptical distortions. After applying
a magnetic field of 10 Tesla, ultrasmall skyrmions are driven along a straight
line towards the various defects which permits a simple analysis of the impact
of the impurities. Independently from the nature of the skyrmion-defect complex
interaction a gyrotropic motion is observed. A repulsive force leads to a
skyrmion trajectory similar to the one induced by an attractive one. We unveil
that the circular motion is clockwise around pinning impurities but counter
clockwise around the repulsive ones, which can be used to identify the
interaction nature of the defects by observing the skyrmions trajectories.
Moreover, and as expected, the skyrmion always escapes the repulsive defects in
contrast to the pinning defects, which require a minimal depinning current to
observe impurity avoidance. This unveils the richness of the motion regimes of
skyrmions. We discuss the results of the simulations in terms of the Thiele
equation, which provides a reasonable qualitative description of the observed
phenomena. Finally, we show an example of a double track made of pinning
impurities, where the engineering of their mutual distance allows to control
the skyrmion motion with enhanced velocity.",2004.10509v1
2020-04-23,"Spectroscopic Orbits of Eleven Nearby, Mid-to-Late M Dwarf Binaries","We present the spectroscopic orbits of eleven nearby, mid-to-late M dwarf
binary systems in a variety of configurations: two single-lined binaries
(SB1s), seven double-lined binaries (SB2s), one double-lined triple (ST2), and
one triple-lined triple (ST3). Eight of these orbits are the first published
for these systems, while five are newly identified multiples. We obtained
multi-epoch, high-resolution spectra with the TRES instrument on the 1.5m
Tillinghast Reflector at the Fred Lawrence Whipple Observatory located on Mt.
Hopkins in AZ. Using the TiO molecular bands at 7065 -- 7165 Angstroms, we
calculated radial velocities for these systems, from which we derived their
orbits. We find LHS 1817 to have in a 7-hour period a companion that is likely
a white dwarf, due to the ellipsoidal modulation we see in our MEarth-North
light curve data. We find G 123-45 and LTT 11586 to host companions with
minimum masses of 41 M_Jup and 44 M_Jup with orbital periods of 35 and 15 days,
respectively. We find 2MA 0930+0227 to have a rapidly rotating stellar
companion in a 917-day orbital period. GJ 268, GJ 1029, LP 734-34, GJ 1182, G
258-17, and LTT 7077 are SB2s with stellar companions with orbital periods of
10, 96, 34, 154, 5, and 84 days; LP 655-43 is an ST3 with one companion in an
18-day orbital period and an outer component in a longer undetermined period.
In addition, we present radial velocities for both components of L 870-44AB and
for the outer components of LTT 11586 and LP 655-43.",2004.11225v2
2020-05-25,Recovering the city street lighting fraction from skyglow measurements in a large-scale municipal dimming experiment,"Anthropogenic skyglow dominates views of the natural night sky in most urban
settings, and the associated emission of artificial light at night (ALAN) into
the environment of cities involves a number of known and suspected negative
externalities. One approach to lowering consumption of ALAN in cities is
dimming or extinguishing publicly owned outdoor lighting during overnight
hours; however, there are few reports in the literature about the efficacy of
these programs. Here we report the results of one of the largest municipal
lighting dimming experiments to date, involving $\sim$20,000 roadway luminaires
owned and operated by the City of Tucson, Arizona, U.S. We analyzed both
single-channel and spatially resolved ground-based measurements of broadband
night sky radiance obtained during the tests, determining that the zenith sky
brightness during the tests decreased by ($-5.4\pm0.9$)% near the city center
and ($-3.6\pm0.9$)% at an adjacent suburban location on nights when the output
of the street lighting system was dimmed from 90% of its full power draw to 30%
after local midnight. Modeling these changes with a radiative transfer code
yields results suggesting that street lights account for about ($14\pm1$)% of
light emissions resulting in skyglow seen over the city. A separate derivation
from first principles implies that street lighting contributes only 2-3% of
light seen at the zenith over Tucson. We discuss this inconsistency and suggest
routes for future work.",2005.12357v1
2020-05-31,"Ontology-based systematic classification and analysis of coronaviruses, hosts, and host-coronavirus interactions towards deep understanding of COVID-19","Given the existing COVID-19 pandemic worldwide, it is critical to
systematically study the interactions between hosts and coronaviruses including
SARS-Cov, MERS-Cov, and SARS-CoV-2 (cause of COVID-19). We first created four
host-pathogen interaction (HPI)-Outcome postulates, and generated a HPI-Outcome
model as the basis for understanding host-coronavirus interactions (HCI) and
their relations with the disease outcomes. We hypothesized that ontology can be
used as an integrative platform to classify and analyze HCI and disease
outcomes. Accordingly, we annotated and categorized different coronaviruses,
hosts, and phenotypes using ontologies and identified their relations. Various
COVID-19 phenotypes are hypothesized to be caused by the backend HCI
mechanisms. To further identify the causal HCI-outcome relations, we collected
35 experimentally-verified HCI protein-protein interactions (PPIs), and applied
literature mining to identify additional host PPIs in response to coronavirus
infections. The results were formulated in a logical ontology representation
for integrative HCI-outcome understanding. Using known PPIs as baits, we also
developed and applied a domain-inferred prediction method to predict new PPIs
and identified their pathological targets on multiple organs. Overall, our
proposed ontology-based integrative framework combined with computational
predictions can be used to support fundamental understanding of the intricate
interactions between human patients and coronaviruses (including SARS-CoV-2)
and their association with various disease outcomes.",2006.00639v1
2020-06-23,Simultaneous compression and opacity data from time-series radiography with a Lagrangian marker,"Time-resolved radiography can be used to obtain absolute shock Hugoniot
states by simultaneously measuring at least two mechanical parameters of the
shock, and this technique is particularly suitable for one-dimensional
converging shocks where a single experiment probes a range of pressures as the
converging shock strengthens. However, at sufficiently high pressures, the
shocked material becomes hot enough that the x-ray opacity falls significantly.
If the system includes a Lagrangian marker, such that the mass within the
marker is known, this additional information can be used to constrain the
opacity as well as the Hugoniot state. In the limit that the opacity changes
only on shock heating, and not significantly on subsequent isentropic
compression, the opacity of shocked material can be determined uniquely. More
generally, it is necessary to assume the form of the variation of opacity with
isentropic compression, or to introduce multiple marker layers. Alternatively,
assuming either the equation of state or the opacity, the presence of a marker
layer in such experiments enables the non-assumed property to be deduced more
accurately than from the radiographic density reconstruction alone. An example
analysis is shown for measurements of a converging shock wave in polystyrene,
at the National Ignition Facility.",2006.13342v3
2020-06-30,EndoSLAM Dataset and An Unsupervised Monocular Visual Odometry and Depth Estimation Approach for Endoscopic Videos: Endo-SfMLearner,"Deep learning techniques hold promise to develop dense topography
reconstruction and pose estimation methods for endoscopic videos. However,
currently available datasets do not support effective quantitative
benchmarking. In this paper, we introduce a comprehensive endoscopic SLAM
dataset consisting of 3D point cloud data for six porcine organs, capsule and
standard endoscopy recordings as well as synthetically generated data. A Panda
robotic arm, two commercially available capsule endoscopes, two conventional
endoscopes with different camera properties, and two high precision 3D scanners
were employed to collect data from 8 ex-vivo porcine gastrointestinal
(GI)-tract organs. In total, 35 sub-datasets are provided with 6D pose ground
truth for the ex-vivo part: 18 sub-dataset for colon, 12 sub-datasets for
stomach and 5 sub-datasets for small intestine, while four of these contain
polyp-mimicking elevations carried out by an expert gastroenterologist.
Synthetic capsule endoscopy frames from GI-tract with both depth and pose
annotations are included to facilitate the study of simulation-to-real transfer
learning algorithms. Additionally, we propound Endo-SfMLearner, an unsupervised
monocular depth and pose estimation method that combines residual networks with
spatial attention module in order to dictate the network to focus on
distinguishable and highly textured tissue regions. The proposed approach makes
use of a brightness-aware photometric loss to improve the robustness under fast
frame-to-frame illumination changes. To exemplify the use-case of the EndoSLAM
dataset, the performance of Endo-SfMLearner is extensively compared with the
state-of-the-art. The codes and the link for the dataset are publicly available
at https://github.com/CapsuleEndoscope/EndoSLAM. A video demonstrating the
experimental setup and procedure is accessible through
https://www.youtube.com/watch?v=G_LCe0aWWdQ.",2006.16670v3
2020-08-06,Magnon versus electron mediated spin-transfer torque exerted by spin currents across antiferromagnetic insulator to switch magnetization of adjacent ferromagnetic metal,"The recent experiment [Y. Wang et al., Science 366, 1125 (2019)] on
magnon-mediated spin-transfer torque (MSTT) was interpreted in terms of a
picture where magnons are excited within an antiferromagnetic insulator (AFI),
by applying nonequilibrium electronic spin density at one of its surfaces, so
that their propagation across AFI deprived of conduction electrons eventually
leads to reversal of magnetization of a ferromagnetic metal (FM) attached to
the opposite surface of AFI. We employ a recently developed time-dependent
nonequilibrium Green functions combined with the Landau-Lifshitz-Gilbert
equation (TDNEGF+LLG) formalism to evolve conduction electrons
quantum-mechanically while they interact via self-consistent back-action with
localized magnetic moments described classically by atomistic spin dynamics
solving a system of LLG equations. Upon injection of square current pulse as
the initial condition, TDNEGF+LLG simulations of FM-polarizer/AFI/FM-analyzer
junctions show that reversal of localized magnetic moments within FM-analyzer
is less efficient, in the sense of requiring larger pulse height and its longer
duration, than conventional electron-mediated STT (ESTT) driving magnetization
switching in standard FM-polarizer/normal-metal/FM-analyzer spin valve. Since
both electronic, generated by spin pumping from AFI, and magnonic, generated by
direct transmission from AFI, spin currents are injected into the FM-analyzer,
its localized magnetic moments will experience combined MSTT and ESTT.
Nevertheless, by artificially turning off ESTT we demonstrate that MSTT plays a
dominant role whose understanding, therefore, paves the way for
all-magnon-driven magnetization switching devices with no electronic parts.",2008.02794v3
2020-08-29,VR-Caps: A Virtual Environment for Capsule Endoscopy,"Current capsule endoscopes and next-generation robotic capsules for diagnosis
and treatment of gastrointestinal diseases are complex cyber-physical platforms
that must orchestrate complex software and hardware functions. The desired
tasks for these systems include visual localization, depth estimation, 3D
mapping, disease detection and segmentation, automated navigation, active
control, path realization and optional therapeutic modules such as targeted
drug delivery and biopsy sampling. Data-driven algorithms promise to enable
many advanced functionalities for capsule endoscopes, but real-world data is
challenging to obtain. Physically-realistic simulations providing synthetic
data have emerged as a solution to the development of data-driven algorithms.
In this work, we present a comprehensive simulation platform for capsule
endoscopy operations and introduce VR-Caps, a virtual active capsule
environment that simulates a range of normal and abnormal tissue conditions
(e.g., inflated, dry, wet etc.) and varied organ types, capsule endoscope
designs (e.g., mono, stereo, dual and 360{\deg}camera), and the type, number,
strength, and placement of internal and external magnetic sources that enable
active locomotion. VR-Caps makes it possible to both independently or jointly
develop, optimize, and test medical imaging and analysis software for the
current and next-generation endoscopic capsule systems. To validate this
approach, we train state-of-the-art deep neural networks to accomplish various
medical image analysis tasks using simulated data from VR-Caps and evaluate the
performance of these models on real medical data. Results demonstrate the
usefulness and effectiveness of the proposed virtual platform in developing
algorithms that quantify fractional coverage, camera trajectory, 3D map
reconstruction, and disease classification.",2008.12949v2
2020-09-01,Elemental Abundances in M31: Properties of the Inner Stellar Halo,"We present measurements of [Fe/H] and [$\alpha$/Fe] for 128 individual red
giant branch stars (RGB) in the stellar halo of M31, including its Giant
Stellar Stream (GSS), obtained using spectral synthesis of low- and
medium-resolution Keck/DEIMOS spectroscopy ($R \sim 3000$ and 6000,
respectively). We observed four fields in M31's stellar halo (at projected
radii of 9, 18, 23, and 31 kpc), as well as two fields in the GSS (at 33 kpc).
In combination with existing literature measurements, we have increased the
sample size of [Fe/H] and [$\alpha$/Fe] measurements from 101 to a total of 229
individual M31 RGB stars. From this sample, we investigate the chemical
abundance properties of M31's inner halo, finding $\langle$[Fe/H]$\rangle$ =
$-$1.08 $\pm$ 0.04 and $\langle$[$\alpha$/Fe]$\rangle$ = 0.40 $\pm$ 0.03.
Between 8--34 kpc, the inner halo has a steep [Fe/H] gradient ($-$0.025 $\pm$
0.002 dex kpc$^{-1}$) and negligible [$\alpha$/Fe] gradient, where substructure
in the inner halo is systematically more metal-rich than the smooth component
of the halo at a given projected distance. Although the chemical abundances of
the inner stellar halo are largely inconsistent with that of present-day dwarf
spheroidal (dSph) satellite galaxies of M31, we identified 22 RGB stars
kinematically associated with the smooth component of the stellar halo that
have chemical abundance patterns similar to M31 dSphs. We discuss formation
scenarios for M31's halo, concluding that these dSph-like stars may have been
accreted from galaxies of similar stellar mass and star formation history, or
of higher stellar mass and similar star formation efficiency.",2009.00529v1
2020-09-02,The Solar Orbiter mission -- Science overview,"Solar Orbiter, the first mission of ESA's Cosmic Vision 2015-2025 programme
and a mission of international collaboration between ESA and NASA, will explore
the Sun and heliosphere from close up and out of the ecliptic plane. It was
launched on 10 February 2020 04:03 UTC from Cape Canaveral and aims to address
key questions of solar and heliospheric physics pertaining to how the Sun
creates and controls the Heliosphere, and why solar activity changes with time.
To answer these, the mission carries six remote-sensing instruments to observe
the Sun and the solar corona, and four in-situ instruments to measure the solar
wind, energetic particles, and electromagnetic fields. In this paper, we
describe the science objectives of the mission, and how these will be addressed
by the joint observations of the instruments onboard. The paper first
summarises the mission-level science objectives, followed by an overview of the
spacecraft and payload. We report the observables and performance figures of
each instrument, as well as the trajectory design. This is followed by a
summary of the science operations concept. The paper concludes with a more
detailed description of the science objectives. Solar Orbiter will combine
in-situ measurements in the heliosphere with high-resolution remote-sensing
observations of the Sun to address fundamental questions of solar and
heliospheric physics. The performance of the Solar Orbiter payload meets the
requirements derived from the mission's science objectives. Its science return
will be augmented further by coordinated observations with other space missions
and ground-based observatories.",2009.00861v1
2020-09-03,Mapping the Escape Fraction of Ionizing Photons Using Resolved Stars: A Much Higher Escape Fraction for NGC 4214,"We demonstrate a new method for measuring the escape fraction of ionizing
photons using Hubble Space Telescope imaging of resolved stars in NGC 4214, a
local analog of high-redshift starburst galaxies that are thought to be
responsible for cosmic reionization. Specifically, we forward model the UV
through near-IR spectral energy distributions of $\sim$83,000 resolved stars to
infer their individual ionizing flux outputs. We constrain the local escape
fraction by comparing the number of ionizing photons produced by stars to the
number that are either absorbed by dust or consumed by ionizing the surrounding
neutral hydrogen in individual star-forming regions. We find substantial
spatial variation in the escape fraction (0-40%). Integrating over the entire
galaxy yields a global escape fraction of 25% (+16%/-15%). This value is much
higher than previous escape fractions of zero reported for this galaxy. We
discuss sources of this apparent tension, and demonstrate that the viewing
angle and the 3D ISM geometric effects are the cause. If we assume the NGC 4214
has no internal dust, like many high-redshift galaxies, we find an escape
fraction of 59% (an upper-limit for NGC 4214). This is the first non-zero
escape fraction measurement for UV-faint (M$_{\rm FUV}$ = -15.9) galaxies at
any redshift, and supports the idea that starburst UV-faint dwarf galaxies can
provide a sufficient amount of ionizing photons to the intergalactic medium.",2009.01844v1
2020-09-16,Reflection-mode virtual histology using photoacoustic remote sensing microscopy,"Histological visualizations are critical to clinical disease management and
are fundamental to biological understanding. However, current approaches that
rely on bright-field microscopy require extensive tissue preparation prior to
imaging. These processes are labor intensive and contribute to delays in
clinical feedback that can extend to two to three weeks for standard
paraffin-embedded tissue preparation and interpretation. Here, we present a
label-free reflection-mode imaging modality that reveals cellular-scale
morphology by detecting intrinsic endogenous contrast. We accomplish this with
the novel photoacoustic remote sensing (PARS) detection system that permits
non-contact optical absorption contrast to be extracted from thick and opaque
biological targets with optical resolution. PARS was examined both as a rapid
assessment tool that is capable of managing large samples (>1 cm2) in under 10
minutes, and as a high contrast imaging modality capable of extracting specific
biological contrast to simulate conventional histological stains such as
hematoxylin and eosin (H&E). The capabilities of the proposed method are
demonstrated in a variety of human tissue preparations including formalin-fixed
paraffin-embedded tissue blocks and unstained slides sectioned from these
blocks, including normal and neoplastic human brain, and breast epithelium
involved with breast cancer. Similarly, PARS images of human skin prepared by
frozen section clearly demonstrated basal cell carcinoma and normal human skin
tissue. Finally, we imaged unprocessed murine kidney and achieved
histologically relevant subcellular morphology in fresh tissue. This represents
a vital step towards an effective real-time clinical microscope that overcomes
the limitations of standard histopathologic tissue preparations and enables
real-time pathology assessment.",2009.10010v1
2020-09-24,Quantum spin torque driven transmutation of antiferromagnetic Mott insulator,"The standard model of spin-transfer torque (STT) in antiferromagnetic
spintronics considers exchange of angular momentum between quantum spins of
flowing electrons and noncollinear-to-them localized spins treated as classical
vectors. These vectors are assumed to realize N\'{e}el order in equilibrium,
$\uparrow \downarrow \ldots \uparrow \downarrow$, and their STT-driven dynamics
is described by the Landau-Lifshitz-Gilbert (LLG) equation. However, many
experimentally employed materials (such as archetypal NiO) are strongly
electron-correlated antiferromagnetic Mott insulators (AFMI) where localized
spins form a ground state quite different from the unentangled N\'{e}el state
$|\!\! \uparrow \downarrow \ldots \uparrow \downarrow \rangle$. The true ground
state is entangled by quantum spin fluctuations, leading to expectation value
of all localized spins being zero, so that LLG dynamics of classical vectors of
fixed length rotating due to STT cannot even be initiated. Instead, a fully
quantum treatment of both conduction electrons and localized spins is necessary
to capture exchange of spin angular momentum between them, denoted as quantum
STT. We use a recently developed time-dependent density matrix renormalization
group approach to quantum STT to predict how injection of a spin-polarized
current pulse into a normal metal layer coupled to AFMI overlayer via exchange
interaction and possibly small interlayer hopping -- which mimics, e.g.,
topological-insulator/NiO bilayer employed experimentally -- will induce
nonzero expectation value of AFMI localized spins. This new nonequilibrium
phase is a spatially inhomogeneous ferromagnet with zigzag profile of localized
spins. The total spin absorbed by AFMI increases with electron-electron
repulsion in AFMI, as well as when the two layers do not exchange any charge.",2009.11833v3
2020-09-29,The Terahertz Intensity Mapper (TIM): a Next-Generation Experiment for Galaxy Evolution Studies,"Understanding the formation and evolution of galaxies over cosmic time is one
of the foremost goals of astrophysics and cosmology today. The cosmic star
formation rate has undergone a dramatic evolution over the course of the last
14 billion years, and dust obscured star forming galaxies (DSFGs) are a crucial
component of this evolution. A variety of important, bright, and unextincted
diagnostic lines are present in the far-infrared (FIR) which can provide
crucial insight into the physical conditions of galaxy evolution, including the
instantaneous star formation rate, the effect of AGN feedback on star
formation, the mass function of the stars, metallicities, and the spectrum of
their ionizing radiation. FIR spectroscopy is technically difficult but
scientifically crucial. Stratospheric balloons offer a platform which can
outperform current instrument sensitivities and are the only way to provide
large-area, wide bandwidth spatial/spectral mapping at FIR wavelengths. NASA
recently selected TIM, the Terahertz Intensity Mapper, with the goal of
demonstrating the key technical milestones necessary for FIR spectroscopy. The
TIM instrument consists of an integral-field spectrometer from 240-420 microns
with 3600 kinetic-inductance detectors (KIDs) coupled to a 2-meter
low-emissivity carbon fiber telescope. In this paper, we will summarize plans
for the TIM experiment's development, test and deployment for a planned flight
from Antarctica.",2009.14340v1
2020-10-07,Fairness in Influence Maximization through Randomization,"The influence maximization paradigm has been used by researchers in various
fields in order to study how information spreads in social networks. While
previously the attention was mostly on efficiency, more recently fairness
issues have been taken into account in this scope. In this paper, we propose to
use randomization as a mean for achieving fairness. Similar to previous works
like Fish et al. (WWW '19) and Tsang et al. (IJCAI '19), we study the maximin
criterion for (group) fairness. In contrast to their work however, we model the
problem in such a way that, when choosing the seed sets, probabilistic
strategies are possible rather than only deterministic ones. We introduce two
different variants of this probabilistic problem, one that entails
probabilistic strategies over nodes (node-based problem) and a second one that
entails probabilistic strategies over sets of nodes (set-based problem). While
the original deterministic problem involving the maximin criterion has been
shown to be inapproximable, interestingly, we show that both probabilistic
variants permit approximation algorithms that achieve a constant multiplicative
factor of 1-1/e plus an additive arbitrarily small error that is due to the
simulation of the information spread. For an experimental study, we provide
implementations of multiplicative-weight routines for both problems and compare
the achieved fairness values to existing methods. Maybe non-surprisingly, we
show that the ex-ante values of the computed probabilistic strategies are
significantly larger than the (ex-post) fairness values of previous methods.
This indicates that studying fairness via randomization is a worthwhile path to
follow. Interestingly and maybe more surprisingly, we observe that even the
ex-post fairness values computed by our routines, dominate over the fairness
achieved by previous methods on most of the instances tested.",2010.03438v4
2020-10-10,Multi-path Neural Networks for On-device Multi-domain Visual Classification,"Learning multiple domains/tasks with a single model is important for
improving data efficiency and lowering inference cost for numerous vision
tasks, especially on resource-constrained mobile devices. However,
hand-crafting a multi-domain/task model can be both tedious and challenging.
This paper proposes a novel approach to automatically learn a multi-path
network for multi-domain visual classification on mobile devices. The proposed
multi-path network is learned from neural architecture search by applying one
reinforcement learning controller for each domain to select the best path in
the super-network created from a MobileNetV3-like search space. An adaptive
balanced domain prioritization algorithm is proposed to balance optimizing the
joint model on multiple domains simultaneously. The determined multi-path model
selectively shares parameters across domains in shared nodes while keeping
domain-specific parameters within non-shared nodes in individual domain paths.
This approach effectively reduces the total number of parameters and FLOPS,
encouraging positive knowledge transfer while mitigating negative interference
across domains. Extensive evaluations on the Visual Decathlon dataset
demonstrate that the proposed multi-path model achieves state-of-the-art
performance in terms of accuracy, model size, and FLOPS against other
approaches using MobileNetV3-like architectures. Furthermore, the proposed
method improves average accuracy over learning single-domain models
individually, and reduces the total number of parameters and FLOPS by 78% and
32% respectively, compared to the approach that simply bundles single-domain
models for multi-domain learning.",2010.04904v2
2020-10-29,Group-Harmonic and Group-Closeness Maximization -- Approximation and Engineering,"Centrality measures characterize important nodes in networks. Efficiently
computing such nodes has received a lot of attention. When considering the
generalization of computing central groups of nodes, challenging optimization
problems occur. In this work, we study two such problems, group-harmonic
maximization and group-closeness maximization both from a theoretical and from
an algorithm engineering perspective.
  On the theoretical side, we obtain the following results. For group-harmonic
maximization, unless $P=NP$, there is no polynomial-time algorithm that
achieves an approximation factor better than $1-1/e$ (directed) and $1-1/(4e)$
(undirected), even for unweighted graphs. On the positive side, we show that a
greedy algorithm achieves an approximation factor of $\lambda(1-2/e)$
(directed) and $\lambda(1-1/e)/2$ (undirected), where $\lambda$ is the ratio of
minimal and maximal edge weights. For group-closeness maximization, the
undirected case is $NP$-hard to be approximated to within a factor better than
$1-1/(e+1)$ and a constant approximation factor is achieved by a local-search
algorithm. For the directed case, however, we show that, for any
$\epsilon<1/2$, the problem is $NP$-hard to be approximated within a factor of
$4|V|^{-\epsilon}$.
  From the algorithm engineering perspective, we provide efficient
implementations of the above greedy and local search algorithms. In our
experimental study we show that, on small instances where an optimum solution
can be computed in reasonable time, the quality of both the greedy and the
local search algorithms come very close to the optimum. On larger instances,
our local search algorithms yield results with superior quality compared to
existing greedy and local search solutions, at the cost of additional running
time. We thus advocate local search for scenarios where solution quality is of
highest concern.",2010.15435v1
2020-11-19,A novel in vitro device to deliver induced electromagnetic fields to cell and tissue cultures,"We have developed a novel in vitro instrument that can deliver intermediate
frequency (100 - 400 kHz), moderate intensity (up to and exceeding 6.5 V/cm
pk-pk) electric fields (EFs) to cell and tissue cultures generated using
induced electromagnetic fields (EMFs) in a solenoid coil. A major application
of these EFs is as an emerging cancer treatment modality. In vitro studies by
Novocure Ltd. reported that intermediate frequency (100 - 300 kHz), low
amplitude (1 - 3 V/cm) EFs, which they called ""Tumor Treating Fields""
(TTFields), had an anti-mitotic effect on glioblastoma multiforme (GBM) cells.
The effect was found to increase with increasing EF amplitude. Despite
continued theoretical, preclinical, and clinical study, the mechanism of action
remains incompletely understood. Previous in vitro studies of ""TTFields"" have
used attached, capacitively coupled electrodes to deliver alternating EFs to
cell and tissue cultures. This contacting delivery method suffers from a poorly
characterized EF profile and conductive heating that limits the duration and
amplitude of the applied EFs. In contrast, our device delivers EFs with a
well-characterized radial profile in a non-contacting manner, eliminating
conductive heating and enabling thermally regulated EF delivery. To test and
demonstrate our system, we generated continuous 200 kHz EMF with an EF
amplitude profile spanning 0 - 6.5 V/cm pk-pk and applied them to human thyroid
cell cultures for 72 hours. We observed moderate reduction in cell density (<
10%) at low EF amplitudes (< 4 V/cm) and a greater reduction in cell density of
up to 25% at higher amplitudes (4 - 6.5 V/cm). Our device can be extended to
other EF frequency and amplitude regimes. Future studies with this device
should contribute to the ongoing debate about the efficacy and mechanism(s) of
action of ""TTFields"" by better isolating the effects of EFs.",2011.09698v1
2020-11-23,Revealing defect-induced spin disorder in nanocrystalline Ni,"We combine magnetometry and magnetic small-angle neutron scattering to study
the influence of the microstructure on the macroscopic magnetic properties of a
nanocrystalline Ni bulk sample, which was prepared by straining via
high-pressure torsion. As seen by magnetometry, the mechanical deformation
leads to a significant increase of the coercivity compared to nondeformed
polycrystalline Ni. The neutron data reveal a significant spin-misalignment
scattering caused by the high density of crystal defects inside the sample,
which were created by the severe plastic deformation during the sample
preparation. The corresponding magnetic correlation length, which characterizes
the spatial magnetization fluctuations in real space, indicates an average
defect size of 11 nm, which is smaller than the average crystallite size of 60
nm. In the remanent state, the strain fields around the defects cause spin
disorder in the surrounding ferromagnetic bulk, with a penetration depth of
around 22 nm. The range and amplitude of the disorder is systematically
suppressed by an increasing external magnetic field. Our findings are supported
and illustrated by micromagnetic simulations, which, for the particular case of
nonmagnetic defects (holes) embedded in a ferromagnetic Ni phase, further
highlight the role of localized spin perturbations for the magnetic
microstructure of defect-rich magnets such as high-pressure torsion materials.",2011.11318v4
2021-01-05,The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) I. Ultraviolet to Infrared Photometry of 22 Million Stars in M33,"We present panchromatic resolved stellar photometry for 22 million stars in
the Local Group dwarf spiral Triangulum (M33), derived from Hubble Space
Telescope (HST) observations with the Advanced Camera for Surveys (ACS) in the
optical (F475W, F814W), and the Wide Field Camera 3 (WFC3) in the near
ultraviolet (F275W, F336W) and near-infrared (F110W, F160W) bands. The large,
contiguous survey area covers $\sim$14 square kpc and extends to 3.5 kpc (14
arcmin, or 1.5-2 scale lengths) from the center of M33. The PHATTER observing
strategy and photometry technique closely mimic those of the Panchromatic
Hubble Andromeda Treasury (PHAT), but with updated photometry techniques that
take full advantage of all overlapping pointings (aligned to within $<$5-10
milliarcseconds) and improved treatment of spatially-varying point spread
functions. The photometry reaches a completeness-limited depth of
F475W$\sim$28.5 in the lowest surface density regions observed in M33 and
F475W$\sim$26.5 in the most crowded regions found near the center of M33. We
find the young populations trace several relatively tight arms, while the old
populations show a clear, looser two-armed structure. We present extensive
analysis of the data quality including artificial star tests to quantify
completeness, photometric uncertainties, and flux biases. This stellar catalog
is the largest ever produced for M33, and is publicly available for download by
the community.",2101.01293v1
2021-01-20,Beyond Fine-tuning: Classifying High Resolution Mammograms using Function-Preserving Transformations,"The task of classifying mammograms is very challenging because the lesion is
usually small in the high resolution image. The current state-of-the-art
approaches for medical image classification rely on using the de-facto method
for ConvNets - fine-tuning. However, there are fundamental differences between
natural images and medical images, which based on existing evidence from the
literature, limits the overall performance gain when designed with algorithmic
approaches. In this paper, we propose to go beyond fine-tuning by introducing a
novel framework called MorphHR, in which we highlight a new transfer learning
scheme. The idea behind the proposed framework is to integrate
function-preserving transformations, for any continuous non-linear activation
neurons, to internally regularise the network for improving mammograms
classification. The proposed solution offers two major advantages over the
existing techniques. Firstly and unlike fine-tuning, the proposed approach
allows for modifying not only the last few layers but also several of the first
ones on a deep ConvNet. By doing this, we can design the network front to be
suitable for learning domain specific features. Secondly, the proposed scheme
is scalable to hardware. Therefore, one can fit high resolution images on
standard GPU memory. We show that by using high resolution images, one prevents
losing relevant information. We demonstrate, through numerical and visual
experiments, that the proposed approach yields to a significant improvement in
the classification performance over state-of-the-art techniques, and is indeed
on a par with radiology experts. Moreover and for generalisation purposes, we
show the effectiveness of the proposed learning scheme on another large
dataset, the ChestX-ray14, surpassing current state-of-the-art techniques.",2101.07945v1
2021-01-21,A decade of radial-velocity monitoring of Vega and new limits on the presence of planets,"We present an analysis of 1524 spectra of Vega spanning 10 years, in which we
search for periodic radial velocity variations. A signal with a periodicity of
0.676 days and a semi-amplitude of ~10 m/s is consistent with the rotation
period measured over much shorter time spans by previous spectroscopic and
spectropolarimetric studies, confirming the presence of surface features on
this A0 star. The timescale of evolution of these features can provide insight
into the mechanism that sustains the weak magnetic fields in normal A type
stars. Modeling the radial velocities with a Gaussian process using a
quasi-periodic kernel suggests that the characteristic spot evolution timescale
is ~180 days, though we cannot exclude the possibility that it is much longer.
Such long timescales may indicate the presence of failed fossil magnetic fields
on Vega. TESS data reveal Vega's photometric rotational modulation for the
first time, with a total amplitude of only 10 ppm, and a comparison of the
spectroscopic and photometric amplitudes suggest the surface features may be
dominated by bright plages rather than dark spots. For the shortest orbital
periods, transit and radial velocity injection recovery tests exclude the
presence of transiting planets larger than 2 Earth radii and most
non-transiting giant planets. At long periods, we combine our radial velocities
with direct imaging from the literature to produce detection limits for Vegan
planets and brown dwarfs out to distances of 15 au. Finally, we detect a
candidate radial velocity signal with a period of 2.43 days and a
semi-amplitude of 6 m/s. If caused by an orbiting companion, its minimum mass
would be ~20 Earth masses; because of Vega's pole-on orientation, this would
correspond to a Jovian planet if the orbit is aligned with the stellar spin. We
discuss the prospects for confirmation of this candidate planet.",2101.08801v1
2021-02-04,Magnon-spinon dichotomy in the Kitaev hyperhoneycomb $β$-Li$_2$IrO$_3$,"The family of edge-sharing tri-coordinated iridates and ruthenates has
emerged in recent years as a major platform for Kitaev spin liquid physics,
where spins fractionalize into emergent magnetic fluxes and Majorana fermions
with Dirac-like dispersions. While such exotic states are usually pre-empted by
long-range magnetic order at low temperatures, signatures of Majorana fermions
with long coherent times have been predicted to manifest at intermediate and
higher energy scales, similar to the observation of spinons in quasi-1D spin
chains. Here we present a Resonant Inelastic X-ray Scattering study of the
magnetic excitations of the hyperhoneycomb iridate $\beta$-Li$_2$IrO$_3$ under
a magnetic field with a record-high-resolution spectrometer. At
low-temperatures, dispersing spin waves can be resolved around the predicted
intertwined incommensurate spiral and field-induced zigzag orders, whose
excitation energy reaches a maximum of 16meV. A 2T magnetic field softens the
dispersion around ${\bf Q}=0$. The behavior of the spin waves under magnetic
field is consistent with our semiclassical calculations for the ground state
and the dynamical spin structure factor, which further predicts that the ensued
intertwined uniform states remain robust up to very high fields (100 T). Most
saliently, the low-energy magnon-like mode is superimposed by a broad continuum
of excitations, centered around 35meV and extending up to 100meV. This
high-energy continuum survives up to at least 300K -- well above the ordering
temperature of 38K -- and gives evidence for pairs of long-lived Majorana
fermions of the proximate Kitaev spin liquid.",2102.02714v2