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0704.1501 | Surface Structure Analysis of Atomically Smooth BaBiO$_3$ Films | Using low energy Time-of-Flight Scattering and Recoil Spectroscopy (TOF-SARS)
and Mass Spectroscopy of Recoiled Ions (MSRI) we analyze the surface structure
of an atomically smooth BaBiO$_3$ film grown by molecular beam epitaxy. We
demonstrate high sensitivity of the TOF-SARS and MSRI spectra to slight changes
in the orientation of the ion scattering plane with respect to the
crystallographic axes. The observed angle dependence allows us to clearly
identify the termination layer as BiO$_2$. Our data also indicate that
angle-resolved MSRI data can be used for high resolution studies of surface
structure of complex oxide thin films.
| cond-mat.other |
0704.1502 | Evolution of Magnetic Fields in Stars Across the Upper Main Sequence:
II. Observed distribution of the magnetic field geometry | We re-discuss the evolutionary state of upper main sequence magnetic stars
using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and
definitely determined longitudinal magnetic fields. We confirm our previous
results obtained from the study of Ap and Bp stars with accurate measurements
of the mean magnetic field modulus and mean quadratic magnetic fields that
magnetic stars of mass M < 3 M_sun are concentrated towards the centre of the
main-sequence band. In contrast, stars with masses M > 3 M_sun seem to be
concentrated closer to the ZAMS. The study of a few known members of nearby
open clusters with accurate Hipparcos parallaxes confirms these conclusions.
Stronger magnetic fields tend to be found in hotter, younger and more massive
stars, as well as in stars with shorter rotation periods. No evidence is found
for any loss of angular momentum during the main-sequence life. The magnetic
flux remains constant over the stellar life time on the main sequence. An
excess of stars with large obliquities beta is detected in both higher and
lower mass stars. The obliquity angle distribution as inferred from the
distribution of r-values appears random at the time magnetic stars become
observable on the H-R diagram. After quite a short time spent on the main
sequence, the obliquity angle beta tends to reach values close to either 90 deg
or 0 deg for M < 3 M_sun. The evolution of the obliquity angle beta seems to be
somewhat different for low and high mass stars. While we find a strong hint for
an increase of beta with the elapsed time on the main sequence for stars with M
> 3 M_sun, no similar trend is found for stars with M < 3 M_sun. However, the
predominance of high values of beta at advanced ages in these stars is notable.
| astro-ph |
0704.1503 | A Diagrammatic Category for the Representation Theory of U_q(sl_n) | This thesis provides a partial answer to a question posed by Greg Kuperberg
in q-alg/9712003 and again by Justin Roberts as problem 12.18 in "Problems on
invariants of knots and 3-manifolds", math.GT/0406190, essentially: "Can one
describe the category of representations of the quantum group U_q(sl_n)
(thought of as a spherical category) via generators and relations?"
For each n \geq 0, I define a certain tensor category of trivalent graphs,
modulo isotopy, and construct a functor from this category onto (a full
subcategory of) the category of representations of the quantum group U_q(sl_n).
One would like to describe completely the kernel of this functor, by providing
generators. The resulting quotient of the diagrammatic category would then be a
category equivalent to the representation category of U_q(sl_n).
I make significant progress towards this, describing certain generators of
the kernel, and some obstructions to further elements. It remains a conjecture
that these relations generate the kernel. My results extend those of
q-alg/9712003, MR1659228, math.QA/0310143 and math.GT/0506403.
The argument is essentially by constructing a diagrammatic version of the
forgetful functor coming from the inclusion of U_q(sl_{n-1}) in U_q(sl_n}. We
know this functor is faithful, so a diagram is in the kernel for n exactly if
its image under the diagrammatic forgetful functor is in the kernel for n-1.
This allows us to perform inductive calculations, both establishing families of
elements of the kernel, and finding obstructions.
| math.QA math.RT |
0704.1504 | The Formation of Lake Stars | Star patterns, reminiscent of a wide range of diffusively controlled growth
forms from snowflakes to Saffman-Taylor fingers, are ubiquitous features of ice
covered lakes. Despite the commonality and beauty of these ``lake stars'' the
underlying physical processes that produce them have not been explained in a
coherent theoretical framework. Here we describe a simple mathematical model
that captures the principal features of lake-star formation; radial fingers of
(relatively warm) water-rich regions grow from a central source and evolve
through a competition between thermal and porous media flow effects in a
saturated snow layer covering the lake. The number of star arms emerges from a
stability analysis of this competition and the qualitative features of this
meter-scale natural phenomena are captured in laboratory experiments.
| physics.geo-ph physics.flu-dyn |
0704.1505 | A Higgs-Higgs bound state due to New Physics at a TeV | We examine the effects of new physics effecting the Higgs sector of the
standard model, focusing on the effects on the Higgs self couplings. We
demonstrate that a low mass higgs, m_h < 2 m_t, can have a strong effective
self coupling due to the effects of a new interaction at a TeV. We investigate
the possibility that the first evidence of such an interaction could be a
higgs-higgs bound state. To this end, we construct an effective field theory
formalism to examine the physics of such a low mass higgs boson. We explore the
possibility of a non relativistic bound state of the higgs field (Higgsium) at
LHC and construct a non relativistic effective field theory of the higgs sector
that is appropriate for such studies (NRHET).
| hep-ph |
0704.1506 | Measuring two-photon orbital angular momentum entanglement | We put forward an approach to estimate the amount of bipartite spatial
entanglement of down-converted photon states correlated in orbital angular
momentum and the magnitude of the transverse (radial) wave vectors. Both
degrees of freedom are properly considered in our framework, which only
requires azimuthal local linear optical transformations and mode selection
analysis with two fiber detectors. The coincidence distributions predicted by
our approach give an excellent fit to the distributions measured in a recent
experiment aimed to show the very high-dimensional transverse entanglement of
twin photons from a down-conversion source. Our estimate for the Schmidt number
is substantially lower but still confirms the presence of high-dimensional
entanglement.
| quant-ph physics.optics |
0704.1507 | HST/ACS Coronagraphic Observations of the Dust Surrounding HD 100546 | We present ACS/HST coronagraphic observations of HD 100546, a B9.5 star, 103
pc away from the sun, taken in the F435W, F606W, and F814W bands. Scattered
light is detected up to 14'' from the star. The observations are consistent
with the presence of an extended flattened nebula with the same inclination as
the inner disk. The well-known ``spiral arms'' are clearly observed and they
trail the rotating disk material. Weaker arms never before reported are also
seen. The inter-arm space becomes brighter, but the structures become more
neutral in color at longer wavelengths, which is not consistent with models
that assume that they are due to the effects of a warped disk. Along the major
disk axis, the colors of the scattered-light relative to the star are \Delta
(F435W-F606W) ~ 0.0--0.2 mags and \Delta (F435W-F814W)~0.5--1 mags. To explain
these colors, we explore the role of asymmetric scattering, reddening, and
large minimum sizes on ISM-like grains. We conclude each of these hypotheses by
itself cannot explain the colors. The disk colors are similar to those derived
for Kuiper Belt objects, suggesting that the same processes responsible for
their colors may be at work here. We argue that we are observing only the
geometrically thick, optically thin envelope of the disk, while the optically
thick disk responsible for the far-IR emission is undetected. The observed
spiral arms are then structures on this envelope. The colors indicate that the
extended nebulosity is not a remnant of the infalling envelope but reprocessed
disk material.
| astro-ph |
0704.1508 | Anomalous diffusion and stretched exponentials in heterogeneous
glass-forming liquids: Low-temperature behavior | We propose a model of a heterogeneous glass forming liquid and compute the
low-temperature behavior of a tagged molecule moving within it. This model
exhibits stretched-exponential decay of the wavenumber-dependent, self
intermediate scattering function in the limit of long times. At temperatures
close to the glass transition, where the heterogeneities are much larger in
extent than the molecular spacing, the time dependence of the scattering
function crosses over from stretched-exponential decay with an index $b=1/2$ at
large wave numbers to normal, diffusive behavior with $b = 1$ at small
wavenumbers. There is a clear separation between early-stage, cage-breaking
$\beta$ relaxation and late-stage $\alpha$ relaxation. The spatial
representation of the scattering function exhibits an anomalously broad
exponential (non-Gaussian) tail for sufficiently large values of the molecular
displacement at all finite times.
| cond-mat.mtrl-sci |
0704.1509 | Modeling the Solar Chromosphere | Spectral diagnostic features formed in the solar chromosphere are few and
difficult to interpret -- they are neither formed in the optically thin regime
nor in local thermodynamic equilibrium (LTE). To probe the state of the
chromosphere, both from observations and theory, it is therefore necessary with
modeling. I discuss both traditional semi-empirical modeling, numerical
experiments illustrating important ingredients necessary for a self-consistent
theoretical modeling of the solar chromosphere and the first results of such
models.
| astro-ph |
0704.1510 | A compact star rotating at 1122 Hz and the r-mode instability | We show that r-mode instabilities severely constraint the composition of a
compact star rotating at a submillisecond period. In particular, the only
viable astrophysical scenario for such an object, present inside the Low Mass
X-ray Binary associated with the x-ray transient XTE J1739-285, is that it has
a strangeness content. Since previous analysis indicate that hyperonic stars or
stars containing a kaon condensate are not good candidates, the only remaining
possibility is that such an object is either a strange quark star or a hybrid
quark-hadron star. We also discuss under which conditions sub-millisecond
pulsars are rare.
| astro-ph gr-qc hep-ph nucl-th |
0704.1511 | 3d Numerical Models of the Chromosphere, Transition Region, and Corona | A major goal in solar physics has during the last five decades been to find
how energy flux generated in the solar convection zone is transported and
dissipated in the outer solar layers. Progress in this field has been slow and
painstaking. However, advances in computer hardware and numerical methods,
vastly increased observational capabilities and growing physical insight seem
finally to be leading towards understanding. Here we present exploratory
numerical MHD models that span the entire solar atmosphere from the upper
convection zone to the lower corona. These models include non-grey, non-LTE
radiative transport in the photosphere and chromosphere, optically thin
radiative losses as well as magnetic field-aligned heat conduction in the
transition region and corona.
| astro-ph |
0704.1512 | Gauge Invariant Factorisation and Canonical Quantisation of
Topologically Massive Gauge Theories in Any Dimension | Abelian topologically massive gauge theories (TMGT) provide a topological
mechanism to generate mass for a bosonic p-tensor field in any spacetime
dimension. These theories include the 2+1 dimensional Maxwell-Chern-Simons and
3+1 dimensional Cremmer-Scherk actions as particular cases. Within the
Hamiltonian formulation, the embedded topological field theory (TFT) sector
related to the topological mass term is not manifest in the original phase
space. However through an appropriate canonical transformation, a gauge
invariant factorisation of phase space into two orthogonal sectors is feasible.
The first of these sectors includes canonically conjugate gauge invariant
variables with free massive excitations. The second sector, which decouples
from the total Hamiltonian, is equivalent to the phase space description of the
associated non dynamical pure TFT. Within canonical quantisation, a likewise
factorisation of quantum states thus arises for the full spectrum of TMGT in
any dimension. This new factorisation scheme also enables a definition of the
usual projection from TMGT onto topological quantum field theories in a most
natural and transparent way. None of these results rely on any gauge fixing
procedure whatsoever.
| hep-th |
0704.1513 | Compensation of loss in propagating surface plasmon polariton by gain in
adjacent dielectric medium | We report the suppression of loss of surface plasmon polariton propagating at
the interface between silver film and optically pumped polymer with dye. Large
magnitude of the effect enables a variety of applications of "active"
nanoplasmonics. The experimental study is accompanied by the development of the
analytical description of the phenomenon and the solution of the controversy
regarding the direction of the wavevector of a wave with a strong evanescent
component in an active medium.
| physics.optics |
0704.1514 | Towards Functional Flows for Hierarchical Models | The recursion relations of hierarchical models are studied and contrasted
with functional renormalisation group equations in corresponding
approximations. The formalisms are compared quantitatively for the Ising
universality class, where the spectrum of universal eigenvalues at criticality
is studied. A significant correlation amongst scaling exponents is pointed out
and analysed in view of an underlying optimisation. Functional flows are
provided which match with high accuracy all known scaling exponents from
Dyson's hierarchical model for discrete block-spin transformations.
Implications of the results are discussed.
| hep-th cond-mat.stat-mech hep-ph |
0704.1515 | High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes | We present the results of high precision measurements of the thermal
expansion of the sintered SiC, SiC-100, intended for use in cryogenic
space-telescopes, in which minimization of thermal deformation of the mirror is
critical and precise information of the thermal expansion is needed for the
telescope design. The temperature range of the measurements extends from room
temperature down to $\sim$ 10 K. Three samples, #1, #2, and #3 were
manufactured from blocks of SiC produced in different lots. The thermal
expansion of the samples was measured with a cryogenic dilatometer, consisting
of a laser interferometer, a cryostat, and a mechanical cooler. The typical
thermal expansion curve is presented using the 8th order polynomial of the
temperature. For the three samples, the coefficients of thermal expansion
(CTE), $\bar{\alpha}_{#1}$, $\bar{\alpha}_{#2}$, and $\bar{\alpha}_{#3}$ were
derived for temperatures between 293 K and 10 K. The average and the dispersion
(1 $\sigma$ rms) of these three CTEs are 0.816 and 0.002 ($\times 10^{-6}$/K),
respectively. No significant difference was detected in the CTE of the three
samples from the different lots. Neither inhomogeneity nor anisotropy of the
CTE was observed. Based on the obtained CTE dispersion, we performed an
finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m
diameter cryogenic mirror made of six SiC-100 segments. It was shown that the
present CTE measurement has a sufficient accuracy well enough for the design of
the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope
for Cosmology and Astrophysics (SPICA).
| astro-ph |
0704.1516 | Compton Scattering of Fe K alpha Lines in Magnetic Cataclysmic Variables | Compton scattering of X-rays in the bulk flow of the accretion column in
magnetic cataclysmic variables (mCVs) can significantly shift photon energies.
We present Monte Carlo simulations based on a nonlinear algorithm demonstrating
the effects of Compton scattering on the H-like, He-like and neutral Fe K alpha
lines produced in the post-shock region of the accretion column. The peak line
emissivities of the photons in the post-shock flow are taken into consideration
and frequency shifts due to Doppler effects are also included. We find that
line profiles are most distorted by Compton scattering effects in strongly
magnetized mCVs with a low white dwarf mass and high mass accretion rate and
which are viewed at an oblique angle with respect to the accretion column. The
resulting line profiles are most sensitive to the inclination angle. We have
also explored the effects of modifying the accretion column width and using a
realistic emissivity profile. We find that these do not have a significant
overall effect on the resulting line profiles. A comparison of our simulated
line spectra with high resolution Chandra/HETGS observations of the mCV GK Per
indicates that a wing feature redward of the 6.4 keV line may result from
Compton recoil near the base of the accretion column.
| astro-ph |
0704.1517 | The Limits of Special Relativity | The Special Theory of Relativity and the Theory of the Electron have had an
interesting history together. Originally the electron was studied in a non
relativistic context and this opened up the interesting possibility that lead
to the conclusion that the mass of the electron could be thought of entirely in
electromagnetic terms without introducing inertial considerations. However the
application of Special Relativity lead to several problems, both for an
extended electron and the point electron. These inconsistencies have, contrary
to popular belief not been resolved satisfactorily today, even within the
context of Quantum Theory. Nevertheless these and subsequent studies bring out
the interesting result that Special Relativity breaks down within the Compton
scale or when the Compton scale is not neglected. This again runs contrary to
an uncritical notion that Special Relativity is valid for point particles.
| physics.gen-ph |
0704.1518 | Crystalline silicates and dust processing in the protoplanetary disks of
the Taurus young cluster | We characterize the crystalline silicate content and spatial distribution of
small dust grains in a large sample of protoplanetary disks in the
Taurus-Auriga young cluster, using Spitzer Space Telescope mid-infrared
spectra. In turn we use the results to analyze the evolution of structure and
composition of these 1-2 Myr-old disks around Solar- and later-type young
stars, and test the standard models of dust processing which result in the
conversion of originally amorphous dust into minerals. We find strong evidence
of evolution of the dust crystalline mass fraction in parallel with that of the
structure of the disks, in the sense that increasing crystalline mass fraction
is strongly linked to dust settling to the disk midplane. We also confirm that
the crystalline silicates are confined to small radii, r < 10 AU. However, we
see no significant correlation of crystalline mass fraction with stellar mass
or luminosity, stellar accretion rate, disk mass, or disk/star mass ratio, as
would be expected in the standard models of dust processing based upon
photo-evaporation and condensation close to the central star,
accretion-heating-driven annealing at r < 1 AU, or spiral-shock heating at r <
10 AU, with or without effective radial mixing mechanisms. Either another
grain-crystallizing mechanism dominates over these, or another process must be
at work within the disks to erase the correlations they produce. We propose one
of each sort that seem to be worth further investigation, namely X-ray heating
and annealing of dust grains, and modulation of disk structure by
giant-planetary formation and migration.
| astro-ph |
0704.1519 | Comprehensive simulations of superhumps | (Abridged) We use 3D SPH calculations with higher resolution, as well as with
more realistic viscosity and sound-speed prescriptions than previous work to
examine the eccentric instability which underlies the superhump phenomenon in
semi-detached binaries. We illustrate the importance of the two-armed spiral
mode in the generation of superhumps. Differential motions in the fluid disc
cause converging flows which lead to strong spiral shocks once each superhump
cycle. The dissipation associated with these shocks powers the superhump. We
compare 2D and 3D results, and conclude that 3D simulations are necessary to
faithfully simulate the disc dynamics. We ran our simulations for unprecedented
durations, so that an eccentric equilibrium is established except at high mass
ratios where the growth rate of the instability is very low. Our improved
simulations give a closer match to the observed relationship between superhump
period excess and binary mass ratio than previous numerical work. The observed
black hole X-ray transient superhumpers appear to have systematically lower
disc precession rates than the cataclysmic variables. This could be due to
higher disc temperatures and thicknesses. The modulation in total viscous
dissipation on the superhump period is overwhelmingly from the region of the
disc within the 3:1 resonance radius. As the eccentric instability develops,
the viscous torques are enhanced, and the disc consequently adjusts to a new
equilibrium state, as suggested in the thermal-tidal instability model. We
quantify this enhancement in the viscosity, which is ~10 per cent for q=0.08.
We characterise the eccentricity distributions in our accretion discs, and show
that the entire body of the disc partakes in the eccentricity.
| astro-ph |
0704.1520 | Singular Energy Distributions in Granular Media | We study the kinetic theory of driven granular gases, taking into account
both translational and rotational degrees of freedom. We obtain the high-energy
tail of the stationary bivariate energy distribution, depending on the total
energy E and the ratio x=sqrt{E_w/E} of rotational energy E_w to total energy.
Extremely energetic particles have a unique and well-defined distribution f(x)
which has several remarkable features: x is not uniformly distributed as in
molecular gases; f(x) is not smooth but has multiple singularities. The latter
behavior is sensitive to material properties such as the collision parameters,
the moment of inertia and the collision rate. Interestingly, there are
preferred ratios of rotational-to-total energy. In general, f(x) is strongly
correlated with energy and the deviations from a uniform distribution grow with
energy. We also solve for the energy distribution of freely cooling Maxwell
Molecules and find qualitatively similar behavior.
| cond-mat.soft cond-mat.stat-mech |
0704.1521 | Cosmological Shock Waves in the Large Scale Structure of the Universe:
Non-gravitational Effects | Cosmological shock waves result from supersonic flow motions induced by
hierarchical clustering of nonlinear structures in the universe. These shocks
govern the nature of cosmic plasma through thermalization of gas and
acceleration of nonthermal, cosmic-ray (CR) particles. We study the statistics
and energetics of shocks formed in cosmological simulations of a concordance
$\Lambda$CDM universe, with a special emphasis on the effects of
non-gravitational processes such as radiative cooling, photoionization/heating,
and galactic superwind feedbacks. Adopting an improved model for gas
thermalization and CR acceleration efficiencies based on nonlinear diffusive
shock acceleration calculations, we then estimate the gas thermal energy and
the CR energy dissipated at shocks through the history of the universe. Since
shocks can serve as sites for generation of vorticity, we also examine the
vorticity that should have been generated mostly at curved shocks in
cosmological simulations. We find that the dynamics and energetics of shocks
are governed primarily by the gravity of matter, so other non-gravitational
processes do not affect significantly the global energy dissipation and
vorticity generation at cosmological shocks. Our results reinforce scenarios in
which the intracluster medium and warm-hot intergalactic medium contain
energetically significant populations of nonthermal particles and turbulent
flow motions.
| astro-ph |
0704.1522 | Outstanding Issues in Our Understanding of L, T, and Y Dwarfs | Since the discovery of the first L dwarf 19 years ago and the discovery of
the first T dwarf 7 years after that, we have amassed a large list of these
objects, now numbering almost six hundred. Despite making headway in
understanding the physical chemistry of their atmospheres, some important
issues remain unexplained. Three of these are the subject of this paper: (1)
What is the role of "second parameters" such as gravity and metallicity in
shaping the emergent spectra of L and T dwarfs? Can we establish a robust
classification scheme so that objects with unusual values of log(g) or [M/H],
unusual dust content, or unresolved binarity are easily recognized? (2) Which
physical processes drive the unusual behavior at the L/T transition? Which
observations can be obtained to better confine the problem? (3) What will
objects cooler than T8 look like? How will we know a Y dwarf when we first
observe one?
| astro-ph |
0704.1523 | The orbit, mass, size, albedo, and density of (65489) Ceto/Phorcys: A
tidally-evolved binary Centaur | Hubble Space Telescope observations of Uranus- and Neptune-crossing object
(65489) Ceto/Phorcys (provisionally designated 2003 FX128) reveal it to be a
close binary system. The mutual orbit has a period of 9.554 +/- 0.011 days and
a semimajor axis of 1840 +/- 48 km. These values enable computation of a system
mass of (5.41 +/- 0.42) 10^18 kg. Spitzer Space Telescope observations of
thermal emission at 24 and 70 microns are combined with visible photometry to
constrain the system's effective radius (109 +10/-11 km) and geometric albedo
(0.084 +0.021/-0.014). We estimate the average bulk density to be 1.37
+0.66/-0.32 g cm^-3, consistent with ice plus rocky and/or carbonaceous
materials. This density contrasts with lower densities recently measured with
the same technique for three other comparably-sized outer Solar System binaries
(617) Patroclus, (26308) 1998 SM165, and (47171) 1999 TC36, and is closer to
the density of the saturnian irregular satellite Phoebe. The mutual orbit of
Ceto and Phorcys is nearly circular, with an eccentricity <= 0.015. This
observation is consistent with calculations suggesting that the system should
tidally evolve on a timescale shorter than the age of the solar system.
| astro-ph |
0704.1524 | GLRT-Optimal Noncoherent Lattice Decoding | This paper presents new low-complexity lattice-decoding algorithms for
noncoherent block detection of QAM and PAM signals over complex-valued fading
channels. The algorithms are optimal in terms of the generalized likelihood
ratio test (GLRT). The computational complexity is polynomial in the block
length; making GLRT-optimal noncoherent detection feasible for implementation.
We also provide even lower complexity suboptimal algorithms. Simulations show
that the suboptimal algorithms have performance indistinguishable from the
optimal algorithms. Finally, we consider block based transmission, and propose
to use noncoherent detection as an alternative to pilot assisted transmission
(PAT). The new technique is shown to outperform PAT.
| cs.IT math.IT |
0704.1525 | Distributions of H2O and CO2 ices on Ariel, Umbriel, Titania, and Oberon
from IRTF/SpeX observations | We present 0.8 to 2.4 micron spectral observations of uranian satellites,
obtained at IRTF/SpeX on 17 nights during 2001-2005. The spectra reveal for the
first time the presence of CO2 ice on the surfaces of Umbriel and Titania, by
means of 3 narrow absorption bands near 2 microns. Several additional, weaker
CO2 ice absorptions have also been detected. No CO2 absorption is seen in
Oberon spectra, and the strengths of the CO2 ice bands decline with
planetocentric distance from Ariel through Titania. We use the CO2 absorptions
to map the longitudinal distribution of CO2 ice on Ariel, Umbriel, and Titania,
showing that it is most abundant on their trailing hemispheres. We also examine
H2O ice absorptions in the spectra, finding deeper H2O bands on the leading
hemispheres of Ariel, Umbriel, and Titania, but the opposite pattern on Oberon.
Potential mechanisms to produce the observed longitudinal and planetocentric
distributions of the two ices are considered.
| astro-ph |
0704.1526 | Proof of the Labastida-Marino-Ooguri-Vafa Conjecture | Based on large N Chern-Simons/topological string duality, in a series of
papers, J.M.F. Labastida, M. Marino, H. Ooguri and C. Vafa conjectured certain
remarkable new algebraic structure of link invariants and the existence of
infinite series of new integer invariants. In this paper, we provide a proof of
this conjecture. Moreover, we also show these new integer invariants vanish at
large genera.
| math.QA hep-th |
0704.1527 | Study of exotic hadrons in s-wave chiral dynamics | We study the exotic hadrons in s-wave scattering of the Nambu-Goldstone boson
with a target hadron based on chiral dynamics. Utilizing the low energy theorem
of chiral symmetry, we show that the s-wave interaction is not strong enough to
generate bound states in exotic channels in flavor SU(3) symmetric limit,
although the interaction is responsible for generating some nonexotic hadron
resonances dynamically. We discuss the renormalization condition adopted in
this analysis.
| hep-ph nucl-th |
0704.1528 | Extremely strong-coupling superconductivity and anomalous lattice
properties in the beta-pyrochlore oxide KOs2O6 | Superconducting and normal-state properties of the beta-pyrochlore oxide
KOs2O6 are studied by means of thermodynamic and transport measurements. It is
shown that the superconductivity is of conventional s-wave type and lies in the
extremely strong-coupling regime. Specific heat and resistivity measurements
reveal that there are characteristic low-energy phonons that give rise to
unusual scattering of carriers due to strong electron-phonon interactions. The
entity of the low-energy phonons is ascribed to the heavy rattling of the K ion
confined in an oversized cage made of OsO6 octahedra. It is suggested that this
electron-rattler coupling mediates the Cooper pairing, resulting in the
extremely strong-coupling superconductivity.
| cond-mat.supr-con |
0704.1529 | Analysis of low energy pion spectra | The transverse mass spectra and the rapidity distributions of $\pi^+$ and
$\pi^-$ in Au-Au collisions at 2, 4, 6, and 8 GeV$\cdot$A by E895 collaboration
are fitted using an elliptically expanding fireball model with the contribution
from the resonance decays and the final state Coulomb interaction. The ratio of
the total number of produced $\pi^-$ and $\pi^+$ is used to fit the data. The
resulting freeze-out temperature is rather low($T_f < 60$ MeV) with large
transverse flow and thus resonance contribution is very small. The difference
in the shape of $m_t$ spectra of the oppositely charged pions are found to be
due to the Coulomb interaction of the pions.
| nucl-th |
0704.1530 | A study of the $p d \to p d \eta$ reaction | A study of the $p d \to p d \eta$ reaction in the energy range where the
recent data from Uppsala are available, is done in the two-step model of $\eta$
production including the final state interaction. The $\eta -d$ final state
interaction is incorporated through the solution of the Lippmann Schwinger
equation using an elastic scattering matrix element, $T_{\eta d \to \eta d}$,
which is required to be half off-shell. It is written in a factorized form,
with an off-shell form factor multiplying an on-shell part given by an
effective range expansion up to the fourth power in momentum. The parameters of
this expansion have been taken from an existing recent relativistic Faddeev
equation solution for the $\eta NN$ system corresponding to different $\eta-N$
scattering amplitudes. Calculations have also been done using few body
equations within a finite rank approximation (FRA) to generate $T_{\eta d \to
\eta d}$. The $p-d$ final state interaction is included in the spirit of the
Watson-Migdal prescription by multiplying the matrix element by the inverse of
the Jost function. The $\eta-d$ interaction is found to be dominant in the
region of small invariant $\eta -d$ mass, $M_{\eta d}$. The $p-d$ interaction
enhances the cross section in the whole region of $M_{\eta d}$, but is larger
for large $M_{\eta d}$. We find nearly isotropic angular distributions of the
proton and the deuteron in the final state. All the above observations are in
agreement with data. The production mechanism for the entire range of the
existing data on the $p d \to p d \eta$ reaction seems to be dominated by the
two-step model of $\eta$ production.
| nucl-th nucl-ex |
0704.1531 | On the exact formula for neutrino oscillation probability by Kimura,
Takamura and Yokomakura | The exact formula for the neutrino oscillation probability in matter with
constant density, which was discovered by Kimura, Takamura and Yokomakura, has
been applied mostly to the standard case with three flavor neutrino so far. In
this paper applications of their formula to more general cases are discussed.
It is shown that this formalism can be generalized to various cases where the
matter potential have off-diagonal components, and the two non-trivial examples
are given: the case with magnetic moments and a magnetic field and the case
with non-standard interactions. It is pointed out that their formalism can be
applied also to the case in the long baseline limit with matter whose density
varies adiabatically as in the case of solar neutrino.
| hep-ph |
0704.1532 | Absolute measurement of the nitrogen fluorescence yield in air between
300 and 430 nm | The nitrogen fluorescence induced in air is used to detect ultra-high energy
cosmic rays and to measure their energy. The precise knowledge of the absolute
fluorescence yield is the key quantity to improve the accuracy on the cosmic
ray energy. The total yield has been measured in dry air using a 90Sr source
and a [300-430 nm] filter. The fluorescence yield in air is 4.23 $\pm$ 0.20
photons per meter when normalized to 760 mmHg, 15 degrees C and with an
electron energy of 0.85 MeV. This result is consistent with previous
experiments made at various energies, but with an accuracy improved by a factor
of about 3. For the first time, the absolute continuous spectrum of nitrogen
excited by 90Sr electrons has also been measured with a spectrometer. Details
of this experiment are given in one of the author's PhD thesis [32].
| astro-ph |
0704.1533 | Concrete Classification and Centralizers of Certain $\mathbb{Z}^2
\rtimes {\rm SL}(2,\mathbb{Z})$-actions | We introduce a new class of actions of the group $\G$ on finite von Neumann
algebras and call them twisted Bernoulli shift actions. We classify these
actions up to conjugacy and give an explicit description of their centralizers.
We also distinguish many of those actions on the AFD $\mathrm{II}_1$ factor in
view of outer conjugacy.
| math.OA |
0704.1534 | The Phase-resolved High Energy Spectrum of the Crab Pulsar | We present a modified outer gap model to study the phase-resolved spectra of
the Crab pulsar. A theoretical double peak profile of the light curve
containing the whole phase is shown to be consistent with the observed light
curve of the Crab pulsar by shifting the inner boundary of the outer gap
inwardly to $\sim 10$ stellar radii above the neutron star surface. In this
model, the radial distances of the photons corresponding to different phases
can be determined in the numerical calculation. Also the local electrodynamics,
such as the accelerating electric field, the curvature radius of the magnetic
field line and the soft photon energy, are sensitive to the radial distances to
the neutron star. Using a synchrotron self-Compton mechanism, the
phase-resolved spectra with the energy range from 100 eV to 3 GeV of the Crab
pulsar can also be explained.
| astro-ph |
0704.1535 | Massive N=1 supermultiplets with arbitrary superspins | In this paper we give explicit construction of massive N=1 supermultiplets in
flat d=4 Minkowski space-time. We work in a component on-shell formalism based
on gauge invariant description of massive integer and half-integer spin
particles where massive supermultiplets are constructed out of appropriate set
of massless ones.
| hep-th |
0704.1536 | Critical Current of Type-II Superconductors in a Broken Bose Glass State | The tilt modulus of a defective Abrikosov vortex lattice pinned by material
line defects is computed using the boson analogy. It tends to infinity at long
wavelength, which yields a Bose glass state that is robust to the addition of
weak point-pinning centers, and which implies a restoring force per vortex line
for rigid translations about mechanical equilibrium that is independent of
magnetic field. It also indicates that the Bose glass state breaks into pieces
along the direction of the correlated pinning centers if the latter have finite
length. The critical current is predicted to crossover from two dimensional to
three dimensional behavior as a function of sample thickness along the
correlated pinning centers in such case. That crossover notably can occur at a
film thickness that is much larger than that expected from point pins of
comparable strength. The above is compared to the dependence on thickness shown
by the critical current in certain films of high-temperature superconductors
currently being developed for wire technology.
| cond-mat.supr-con |
0704.1537 | Estimates for singular integrals and extrapolation | We prove a sharp Lp estimate for a singular Radon transform according to a
size condition of its kernel, which is useful for extrapolation.
| math.CA |
0704.1538 | Rounding of first-order phase transitions and optimal cooperation in
scale-free networks | We consider the ferromagnetic large-$q$ state Potts model in complex evolving
networks, which is equivalent to an optimal cooperation problem, in which the
agents try to optimize the total sum of pair cooperation benefits and the
supports of independent projects. The agents are found to be typically of two
kinds: a fraction of $m$ (being the magnetization of the Potts model) belongs
to a large cooperating cluster, whereas the others are isolated one man's
projects. It is shown rigorously that the homogeneous model has a strongly
first-order phase transition, which turns to second-order for random
interactions (benefits), the properties of which are studied numerically on the
Barab\'asi-Albert network. The distribution of finite-size transition points is
characterized by a shift exponent, $1/\tilde{\nu}'=.26(1)$, and by a different
width exponent, $1/\nu'=.18(1)$, whereas the magnetization at the transition
point scales with the size of the network, $N$, as: $m\sim N^{-x}$, with
$x=.66(1)$.
| cond-mat.stat-mech cond-mat.dis-nn physics.soc-ph |
0704.1539 | A New Monte Carlo Method and Its Implications for Generalized Cluster
Algorithms | We describe a novel switching algorithm based on a ``reverse'' Monte Carlo
method, in which the potential is stochastically modified before the system
configuration is moved. This new algorithm facilitates a generalized
formulation of cluster-type Monte Carlo methods, and the generalization makes
it possible to derive cluster algorithms for systems with both discrete and
continuous degrees of freedom. The roughening transition in the sine-Gordon
model has been studied with this method, and high-accuracy simulations for
system sizes up to $1024^2$ were carried out to examine the logarithmic
divergence of the surface roughness above the transition temperature, revealing
clear evidence for universal scaling of the Kosterlitz-Thouless type.
| cond-mat.soft cond-mat.stat-mech |
0704.1540 | The Orbifolds of Permutation-Type as Physical String Systems at
Multiples of $c=26$ III. The Spectra of $\hat{c}=52$ Strings | In the second paper of this series, I obtained the twisted BRST systems and
extended physical-state conditions of all twisted open and closed $\hat{c} =
52$ strings. In this paper, I supplement the extended physical-state conditions
with the explicit form of the extended (twisted) Virasoro generators of all
$\hat{c} = 52$ strings, which allows us to discuss the physical spectra of
these systems. Surprisingly, all the $\hat{c}=52$ spectra admit an equivalent
description in terms of generically-unconventional Virasoro generators at
$c=26$. This description strongly supports our prior conjecture that the
$\hat{c}=52$ strings are free of negative-norm states, and moreover shows that
the spectra of some of the simpler cases are equivalent to those of ordinary
untwisted open and closed $c=26$ strings.
| hep-th math-ph math.MP |
0704.1541 | Riemannian and Lorentzian structures on the non symmetric space
SO(2m)/Sp(m) | In this work, we are interested in a non symmetric homogeneous space, namely
$SO(2m)/Sp(m)$. We show that this space admits a structure of $Z_2^2$-symmetric
space. We describe all the non degenerated metrics and classify the Riemannian
and Lorentzian ones.
| math.DG math.RA |
0704.1542 | Quasiparticles in Neon using the Faddeev Random Phase Approximation | The spectral function of the closed-shell Neon atom is computed by expanding
the electron self-energy through a set of Faddeev equations. This method
describes the coupling of single-particle degrees of freedom with correlated
two-electron, two-hole, and electron-hole pairs. The excitation spectra are
obtained using the Random Phase Approximation, rather than the Tamm-Dancoff
framework employed in the third-order algebraic diagrammatic contruction
[ADC(3)] method. The difference between these two approaches is studied, as
well as the interplay between ladder and ring diagrams in the self-energy.
Satisfactory results are obtained for the ionization energies as well as the
energy of the ground state with the Faddeev-RPA scheme that is also appropriate
for the high-density electron gas.
| physics.chem-ph nucl-th |
0704.1543 | Discrete Nonholonomic Lagrangian Systems on Lie Groupoids | This paper studies the construction of geometric integrators for nonholonomic
systems. We derive the nonholonomic discrete Euler-Lagrange equations in a
setting which permits to deduce geometric integrators for continuous
nonholonomic systems (reduced or not). The formalism is given in terms of Lie
groupoids, specifying a discrete Lagrangian and a constraint submanifold on it.
Additionally, it is necessary to fix a vector subbundle of the Lie algebroid
associated to the Lie groupoid. We also discuss the existence of nonholonomic
evolution operators in terms of the discrete nonholonomic Legendre
transformations and in terms of adequate decompositions of the prolongation of
the Lie groupoid. The characterization of the reversibility of the evolution
operator and the discrete nonholonomic momentum equation are also considered.
Finally, we illustrate with several classical examples the wide range of
application of the theory (the discrete nonholonomic constrained particle, the
Suslov system, the Chaplygin sleigh, the Veselova system, the rolling ball on a
rotating table and the two wheeled planar mobile robot).
| math.DG |
0704.1544 | Pseudogap and charge density waves in two dimensions | An interaction between electrons and lattice vibrations (phonons) results in
two fundamental quantum phenomena in solids: in three dimensions it can turn a
metal into a superconductor whereas in one dimension it can turn a metal into
an insulator. In two dimensions (2D) both superconductivity and charge-density
waves (CDW) are believed to be anomalous. In superconducting cuprates, critical
transition temperatures are unusually high and the energy gap may stay unclosed
even above these temperatures (pseudogap). In CDW-bearing dichalcogenides the
resistivity below the transition can decrease with temperature even faster than
in the normal phase and a basic prerequisite for the CDW, the favourable
nesting conditions (when some sections of the Fermi surface appear shifted by
the same vector), seems to be absent. Notwithstanding the existence of
alternatives to conventional theories, both phenomena in 2D still remain the
most fascinating puzzles in condensed matter physics. Using the latest
developments in high-resolution angle-resolved photoemission spectroscopy
(ARPES) here we show that the normal-state pseudogap also exists in one of the
most studied 2D examples, dichalcogenide 2H-TaSe2, and the formation of CDW is
driven by a conventional nesting instability, which is masked by the pseudogap.
Our findings reconcile and explain a number of unusual, as previously believed,
experimental responses as well as disprove many alternative theoretical
approaches. The magnitude, character and anisotropy of the 2D-CDW pseudogap are
intriguingly similar to those seen in superconducting cuprates.
| cond-mat.supr-con cond-mat.str-el |
0704.1545 | Supersymmetric Field Theory Based on Generalized Uncertainty Principle | We construct a quantum theory of free fermion field based on the generalized
uncertainty principle using supersymmetry as a guiding principle. A
supersymmetric field theory with a real scalar field and a Majorana fermion
field is given explicitly and we also find that the supersymmetry algebra is
deformed from an usual one.
| hep-th math-ph math.MP |
0704.1546 | Optimal flexibility for conformational transitions in macromolecules | Conformational transitions in macromolecular complexes often involve the
reorientation of lever-like structures. Using a simple theoretical model, we
show that the rate of such transitions is drastically enhanced if the lever is
bendable, e.g. at a localized "hinge''. Surprisingly, the transition is fastest
with an intermediate flexibility of the hinge. In this intermediate regime, the
transition rate is also least sensitive to the amount of "cargo'' attached to
the lever arm, which could be exploited by molecular motors. To explain this
effect, we generalize the Kramers-Langer theory for multi-dimensional barrier
crossing to configuration dependent mobility matrices.
| q-bio.BM |
0704.1547 | AFM Imaging of SWI/SNF action: mapping the nucleosome remodeling and
sliding | We propose a combined experimental (Atomic Force Microscopy) and theoretical
study of the structural and dynamical properties of nucleosomes. In contrast to
biochemical approaches, this method allows to determine simultaneously the DNA
complexed length distribution and nucleosome position in various contexts.
First, we show that differences in the nucleo-proteic structure observed
between conventional H2A and H2A.Bbd variant nucleosomes induce quantitative
changes in the in the length distribution of DNA complexed with histones. Then,
the sliding action of remodeling complex SWI/SNF is characterized through the
evolution of the nucleosome position and wrapped DNA length mapping. Using a
linear energetic model for the distribution of DNA complexed length, we extract
the net wrapping energy of DNA onto the histone octamer, and compare it to
previous studies.
| physics.bio-ph cond-mat.soft q-bio.BM |
0704.1548 | When the orbit algebra of group is an integral domain? Proof of a
conjecture of P.J. Cameron | P.J.Cameron introduced the orbit algebra of a permutation group and
conjectured that this algebra is an integral domain if and only if the group
has no finite orbit. We prove that this conjecture holds and in fact that the
age algebra of a relational structure $R$ is an integral domain if and only if
$R$ is age-inexhaustible. We deduce these results from a combinatorial lemma
asserting that if a product of two non-zero elements of a set algebra is zero
then there is a finite common tranversal of their supports. The proof is built
on Ramsey theorem and the integrity of a shuffle algebra.
| math.CO math.AC |
0704.1549 | Saturated actions by finite dimensional Hopf *-algebras on C*-algebras | If a finite group action $\alpha$ on a unital $C^*$-algebra $M$ is saturated,
the canonical conditional expectation $E:M\to M^\alpha$ onto the fixed point
algebra is known to be of index finite type with $Index(E)=|G|$ in the sense of
Watatani. More generally if a finite dimensional Hopf $*$-algebra $A$ acts on
$M$ and the action is saturated, the same is true with $Index (E)=\dim(A)$. In
this paper we prove that the converse is true. Especially in case $M$ is a
commutative $C^*$-algebra $C(X)$ and $\alpha$ is a finite group action, we give
an equivalent condition in order that the expectation $E:C(X)\to C(X)^\alpha$
is of index finite type, from which we obtain that $\alpha$ is saturated if and
only if $G$ acts freely on $X$.
Actions by compact groups are also considered to show that the gauge action
$\gamma$ on a graph $C^*$-algebra $C^*(E)$ associated with a locally finite
directed graph $E$ is saturated.
| math.OA |
0704.1550 | The electronic structures, the equilibrium geometries and finite
temperature properties of Na_n (n=39-55) | Density-functional theory has been applied to investigate systematics of
sodium clusters Na_n in the size range of n= 39-55. A clear evolutionary trend
in the growth of their ground-state geometries emerges. The clusters at the
beginning of the series (n=39-43) are symmetric and have partial icosahedral
(two-shell) structure. The growth then goes through a series of disordered
clusters (n=44-52) where the icosahedral core is lost. However, for n>52 a
three shell icosahedral structure emerges. This change in the nature of the
geometry is abrupt. In addition, density-functional molecular dynamics has been
used to calculate the specific heat curves for the representative sizes n= 43,
45, 48 and 52. These results along with already available thermodynamic
calculations for n= 40, 50, and 55 enable us to carry out a detailed comparison
of the heat capacity curves with their respective geometries for the entire
series. Our results clearly bring out strong correlation between the evolution
of the geometries and the nature of the shape of the heat capacities. The
results also firmly establish the size-sensitive nature of the heat capacities
in sodium clusters.
| physics.atm-clus physics.comp-ph |
0704.1551 | Quantum Zeno Effect in the Decoherent Histories | The quantum Zeno effect arises due to frequent observation. That implies the
existence of some experimenter and its interaction with the system. In this
contribution, we examine what happens for a closed system if one considers a
quantum Zeno type of question, namely: "what is the probability of a system,
remaining always in a particular subspace". This has implications to the
arrival time problem that is also discussed. We employ the decoherent histories
approach to quantum theory, as this is the better developed formulation of
closed system quantum mechanics, and in particular, dealing with questions that
involve time in a non-trivial way. We get a very restrictive decoherence
condition, that implies that even if we do introduce an environment, there will
be very few cases that we can assign probabilities to these histories, but in
those cases, the quantum Zeno effect is still present.
| quant-ph |
0704.1552 | Green function theory versus Quantum Monte Carlo calculations for thin
magnetic films | In this work we compare numerically exact Quantum Monte Carlo (QMC)
calculations and Green function theory (GFT) calculations of thin ferromagnetic
films including second order anisotropies. Thereby we concentrate on easy plane
systems, i.e. systems for which the anisotropy favors a magnetization parallel
to the film plane. We discuss these systems in perpendicular external field,
i.e. B parallel to the film normal. GFT results are in good agreement with QMC
for high enough fields and temperatures. Below a critical field or a critical
temperature no collinear stable magnetization exists in GFT. On the other hand
QMC gives finite magnetization even below those critical values. This indicates
that there occurs a transition from non-collinear to collinear configurations
with increasing field or temperature. For slightly tilted external fields a
rotation of magnetization from out-of-plane to in-plane orientation is found
with decreasing temperature.
| cond-mat.str-el |
0704.1553 | Matrix Ordered Operator Algebras | We study the question when for a given *-algebra $\mathcal{A}$ a sequence of
cones $C_n\in M_n(\mathcal{A})$ can be realized as cones of positive operators
in a faithful *-representation of $\mathcal{A}$ on a Hilbert space. A
characterization of operator algebras which are completely boundedly isomorphic
to $C\sp*$-algebras is presented.
| math.OA math.FA math.RT |
0704.1554 | Properly infinite C(X)-algebras and K_1-injectivity | We investigate if a unital C(X)-algebra is properly infinite when all its
fibres are properly infinite. We show that this question can be rephrased in
several different ways, including the question if every unital properly
infinite C*-algebra is K_1-injective. We provide partial answers to these
questions, and we show that the general question on proper infiniteness of
C(X)-algebras can be reduced to establishing proper infiniteness of a specific
C([0,1])-algebra with properly infinite fibres.
| math.OA |
0704.1555 | An information-based traffic control in a public conveyance system:
reduced clustering and enhanced efficiency | A new public conveyance model applicable to buses and trains is proposed in
this paper by using stochastic cellular automaton. We have found the optimal
density of vehicles, at which the average velocity becomes maximum,
significantly depends on the number of stops and passengers behavior of getting
on a vehicle at stops. The efficiency of the hail-and-ride system is also
discussed by comparing the different behavior of passengers. Moreover, we have
found that a big cluster of vehicles is divided into small clusters, by
incorporating information of the number of vehicles between successive stops.
| physics.soc-ph cond-mat.stat-mech |
0704.1556 | A separable deformation of the quaternion group algebra | The Donald-Flanigan conjecture asserts that for any finite group and for any
field, the corresponding group algebra can be deformed to a separable algebra.
The minimal unsolved instance, namely the quaternion group over a field of
characteristic 2 was considered as a counterexample. We present here a
separable deformation of the quaternion group algebra. In a sense, the
conjecture for any finite group is open again.
| math.RA |
0704.1557 | On the residue fields of Henselian valued stable fields, II | Let $E$ be a primarily quasilocal field, $M/E$ a finite Galois extension and
$D$ a central division $E$-algebra of index divisible by $[M\colon E]$. In
addition to the main result of Part I, this part of the paper shows that if the
Galois group $G(M/E)$ is not nilpotent, then $M$ does not necessarily embed in
$D$ as an $E$-subalgebra. When $E$ is quasilocal, we find the structure of the
character group of its absolute Galois group; this enables us to prove that if
$E$ is strictly quasilocal and almost perfect, then the divisible part of the
multiplicative group $E ^{\ast}$ equals the intersection of the norm groups of
finite Galois extensions of $E$.
| math.RA |
0704.1558 | Chromospheric Cloud-Model Inversion Techniques | Spectral inversion techniques based on the cloud model are extremely useful
for the study of properties and dynamics of various chromospheric cloud-like
structures. Several inversion techniques are reviewed based on simple (constant
source function) and more elaborated cloud models, as well as on grids of
synthetic line profiles produced for a wide range of physical parameters by
different NLTE codes. Several examples are shown of how such techniques can be
used in different chromospheric lines, for the study of structures of the quiet
chromosphere, such as mottles/spicules, as well as for active region structures
such as fibrils, arch filament systems (AFS), filaments and flares.
| astro-ph |
0704.1559 | Dust covering factor, silicate emission and star formation in luminous
QSOs | We present Spitzer IRS low resolution, mid-IR spectra of a sample of 25 high
luminosity QSOs at 2<z<3.5. When combined with archival IRS observations of
local, low luminosity type-I AGNs, the sample spans five orders of magnitude in
luminosity. We find that the continuum dust thermal emission at
lambda(rest)=6.7um is correlated with the optical luminosity, following the
non-linear relation L(6.7um) propto L(5100A)^0.82. We also find an anti
correlation between the ratio L(6.7um)/L(5100A) and the [OIII]5007A line
luminosity. These effects are interpreted as a decreasing covering factor of
the circumnuclear dust as a function of luminosity. Such a result is in
agreement with the decreasing fraction of absorbed AGNs as a function of
luminosity recently found in various surveys. We clearly detect the silicate
emission feature in the average spectrum, but also in four individual objects.
These are the Silicate emission in the most luminous objects obtained so far.
When combined with the silicate emission observed in local, low luminosity
type-I AGNs, we find that the silicate emission strength is correlated with
luminosity.
The silicate strength of all type-I AGNs also follows a positive correlation
with the black hole mass and with the accretion rate. The Polycyclic Aromatic
Hydrocarbon (PAH) emission features, expected from starburst activity, are not
detected in the average spectrum of luminous, high-z QSOs. The upper limit
inferred from the average spectrum points to a ratio between PAH luminosity and
QSO optical luminosity significantly lower than observed in lower luminosity
AGNs, implying that the correlation between star formation rate and AGN power
saturates at high luminosities.
| astro-ph |
0704.1560 | Generating entanglement of photon-number states with coherent light via
cross-Kerr nonlinearity | We propose a scheme for generating entangled states of light fields. This
scheme only requires the cross-Kerr nonlinear interaction between coherent
light-beams, followed by a homodyne detection. Therefore, this scheme is within
the reach of current technology. We study in detail the generation of the
entangled states between two modes, and that among three modes. In addition to
the Bell states between two modes and the W states among three modes, we find
plentiful new kinds of entangled states. Finally, the scheme can be extend to
generate the entangled states among more than three modes.
| quant-ph |
0704.1561 | A parachute for the degree of a polynomial in algebraically independent
ones | We give a simpler proof as well as a generalization of the main result of an
article of Shestakov and Umirbaev. This latter article being the first of two
that solve a long-standing conjecture about the non-tameness, or "wildness", of
Nagata's automorphism. As corollaries we get interesting informations about the
leading terms of polynomials forming an automorphism in any dimension and
reprove the tameness of automorphisms in dimension two.
| math.AC math.AG |
0704.1562 | Galaxy evolution in the infra-red: comparison of a hierarchical galaxy
formation model with SPITZER data | We present predictions for the evolution of the galaxy luminosity function,
number counts and redshift distributions in the IR based on the Lambda-CDM
cosmological model. We use the combined GALFORM semi-analytical galaxy
formation model and GRASIL spectrophotometric code to compute galaxy SEDs
including the reprocessing of radiation by dust. The model, which is the same
as that in Baugh et al (2005), assumes two different IMFs: a normal solar
neighbourhood IMF for quiescent star formation in disks, and a very top-heavy
IMF in starbursts triggered by galaxy mergers. We have shown previously that
the top-heavy IMF seems to be necessary to explain the number counts of faint
sub-mm galaxies. We compare the model with observational data from the SPITZER
Space Telescope, with the model parameters fixed at values chosen before
SPITZER data became available. We find that the model matches the observed
evolution in the IR remarkably well over the whole range of wavelengths probed
by SPITZER. In particular, the SPITZER data show that there is strong evolution
in the mid-IR galaxy luminosity function over the redshift range z ~ 0-2, and
this is reproduced by our model without requiring any adjustment of parameters.
On the other hand, a model with a normal IMF in starbursts predicts far too
little evolution in the mid-IR luminosity function, and is therefore excluded.
| astro-ph |
0704.1563 | Use of Triangular Elements for Nearly Exact BEM Solutions | A library of C functions yielding exact solutions of potential and flux
influences due to uniform surface distribution of singularities on flat
triangular and rectangular elements has been developed. This library, ISLES,
has been used to develop the neBEM solver that is both precise and fast in
solving a wide range of problems of scientific and technological interest. Here
we present the exact expressions proposed for computing the influence of
uniform singularity distributions on triangular elements and illustrate their
accuracy. We also present a study concerning the time taken to evaluate these
long and complicated expressions \textit{vis a vis} that spent in carrying out
simple quadratures. Finally, we solve a classic benchmark problem in
electrostatics, namely, estimation of the capacitance of a unit square plate
raised to unit volt. For this problem, we present the estimated values of
capacitance and compare them successfully with some of the most accurate
results available in the literature. In addition, we present the variation of
the charge density close to the corner of the plate for various degrees of
discretization. The variations are found to be smooth and converging. This is
in clear contrast to the criticism commonly leveled against usual BEM solvers.
| math.NA math-ph math.MP physics.comp-ph |
0704.1564 | Entropy of eigenfunctions | We study the high--energy limit for eigenfunctions of the laplacian, on a
compact negatively curved manifold. We review the recent result of
Anantharaman-Nonnenmacher giving a lower bound on the Kolmogorov-Sinai entropy
of semiclassical measures, and improve this lower bound in the case of variable
negative curvature.
| math-ph math.DS math.MP nlin.CD |
0704.1565 | Vector meson production from a polarized nucleon | We provide a framework to analyze the electroproduction process ep -> ep rho
with a polarized target, writing the angular distribution of the rho decay
products in terms of spin density matrix elements that parameterize the
hadronic subprocess gamma* p -> rho p. Using the helicity basis for both photon
and meson, we find a representation in which the expressions for a polarized
and unpolarized target are related by simple substitution rules.
| hep-ph |
0704.1566 | The effect of the solar corona on the attenuation of small-amplitude
prominence oscillations. I. Longitudinal magnetic field | Context. One of the typical features shown by observations of solar
prominence oscillations is that they are damped in time and that the values of
the damping times are usually between one and three times the corresponding
oscillatory period. However, the mechanism responsible for the attenuation is
still not well-known. Aims. Thermal conduction, optically thin or thick
radiation and heating are taken into account in the energy equation, and their
role on the attenuation of prominence oscillations is evaluated. Methods. The
dispersion relation for linear non-adiabatic magnetoacoustic waves is derived
considering an equilibrium made of a prominence plasma slab embedded in an
unbounded corona. The magnetic field is orientated along the direction parallel
to the slab axis and has the same strength in all regions. By solving the
dispersion relation for a fixed wavenumber, a complex oscillatory frequency is
obtained, and the period and the damping time are computed. Results. The effect
of conduction and radiation losses is different for each magnetoacoustic mode
and depends on the wavenumber. In the observed range of wavelengths the
internal slow mode is attenuated by radiation from the prominence plasma, the
fast mode by the combination of prominence radiation and coronal conduction and
the external slow mode by coronal conduction. The consideration of the external
corona is of paramount importance in the case of the fast and external slow
modes, whereas it does not affect the internal slow modes at all. Conclusions.
Non-adiabatic effects are efficient damping mechanisms for magnetoacoustic
modes, and the values of the obtained damping times are compatible with those
observed.
| astro-ph |
0704.1567 | Energy and Momentum Distributions of Kantowski and Sachs Space-time | We use the Einstein, Bergmann-Thomson, Landau-Lifshitz and Papapetrou
energy-momentum complexes to calculate the energy and momentum distributions of
Kantowski and Sachs space-time. We show that the Einstein and Bergmann-Thomson
definitions furnish a consistent result for the energy distribution, but the
definition of Landau-Lifshitz do not agree with them. We show that a signature
switch should affect about everything including energy distribution in the case
of Einstein and Papapetrou prescriptions but not in Bergmann-Thomson and
Landau-Lifshitz prescriptions.
| gr-qc |
0704.1568 | Green functions and nonlinear systems: Short time expansion | We show that Green function methods can be straightforwardly applied to
nonlinear equations appearing as the leading order of a short time expansion.
Higher order corrections can be then computed giving a satisfactory agreement
with numerical results. The relevance of these results relies on the
possibility of fully exploiting a gradient expansion in both classical and
quantum field theory granting the existence of a strong coupling expansion.
Having a Green function in this regime in quantum field theory amounts to
obtain the corresponding spectrum of the theory.
| hep-th hep-ph math-ph math.MP |
0704.1569 | One-way permutations, computational asymmetry and distortion | Computational asymmetry, i.e., the discrepancy between the complexity of
transformations and the complexity of their inverses, is at the core of one-way
transformations. We introduce a computational asymmetry function that measures
the amount of one-wayness of permutations. We also introduce the word-length
asymmetry function for groups, which is an algebraic analogue of computational
asymmetry. We relate boolean circuits to words in a Thompson monoid, over a
fixed generating set, in such a way that circuit size is equal to word-length.
Moreover, boolean circuits have a representation in terms of elements of a
Thompson group, in such a way that circuit size is polynomially equivalent to
word-length. We show that circuits built with gates that are not constrained to
have fixed-length inputs and outputs, are at most quadratically more compact
than circuits built from traditional gates (with fixed-length inputs and
outputs). Finally, we show that the computational asymmetry function is closely
related to certain distortion functions: The computational asymmetry function
is polynomially equivalent to the distortion of the path length in Schreier
graphs of certain Thompson groups, compared to the path length in Cayley graphs
of certain Thompson monoids. We also show that the results of Razborov and
others on monotone circuit complexity lead to exponential lower bounds on
certain distortions.
| math.GR |
0704.1570 | A method for the direct determination of the surface gravities of
transiting extrasolar planets | We show that the surface gravity of a transiting extrasolar planet can be
calculated from only the spectroscopic orbit of its parent star and the
analysis of its transit light curve. This does not require additional
constraints, such as are often inferred from theoretical stellar models or
model atmospheres. The planet's surface gravity can therefore be measured
precisely and from only directly observable quantities. We outline the method
and apply it to the case of the first known transiting extrasolar planet, HD
209458b. We find a surface gravity of g_p = 9.28 +/- 0.15 m/s, which is an
order of magnitude more precise than the best available measurements of its
mass, radius and density. This confirms that the planet has a much lower
surface gravity that that predicted by published theoretical models of gas
giant planets. We apply our method to all fourteen known transiting extrasolar
planets and find a significant correlation between surface gravity and orbital
period, which is related to the known correlation between mass and period. This
correlation may be the underlying effect as surface gravity is a fundamental
parameter in the evaporation of planetary atmospheres.
| astro-ph |
0704.1571 | On restrictions of balanced 2-interval graphs | The class of 2-interval graphs has been introduced for modelling scheduling
and allocation problems, and more recently for specific bioinformatic problems.
Some of those applications imply restrictions on the 2-interval graphs, and
justify the introduction of a hierarchy of subclasses of 2-interval graphs that
generalize line graphs: balanced 2-interval graphs, unit 2-interval graphs, and
(x,x)-interval graphs. We provide instances that show that all the inclusions
are strict. We extend the NP-completeness proof of recognizing 2-interval
graphs to the recognition of balanced 2-interval graphs. Finally we give hints
on the complexity of unit 2-interval graphs recognition, by studying
relationships with other graph classes: proper circular-arc, quasi-line graphs,
K_{1,5}-free graphs, ...
| cs.DM q-bio.QM |
0704.1572 | Exchange parameters from approximate self-interaction correction scheme | The approximate atomic self-interaction corrections (ASIC) method to density
functional theory is put to the test by calculating the exchange interaction
for a number of prototypical materials, critical to local exchange and
correlation functionals. ASIC total energy calculations are mapped onto an
Heisenberg pair-wise interaction and the exchange constants J are compared to
those obtained with other methods. In general the ASIC scheme drastically
improves the bandstructure, which for almost all the cases investigated
resemble closely available photo-emission data. In contrast the results for the
exchange parameters are less satisfactory. Although ASIC performs reasonably
well for systems where the magnetism originates from half-filled bands, it
suffers from similar problems than those of LDA for other situations. In
particular the exchange constants are still overestimated. This reflects a
subtle interplay between exchange and correlation energy, not captured by the
ASIC.
| cond-mat.mtrl-sci |
0704.1573 | Generalized sqrt(epsilon)-law. The role of unphysical source terms in
resonance line polarization transfer and its importance as an additional test
of NLTE radiative transfer codes | Context. A derivation of a generalized sqrt(epsilon)-law for nonthermal
collisional rates of excitation by charged perturbers is presented. Aims. Aim
of this paper is to find a more general analytical expression for a surface
value of the source function which can be used as an addtional tool for
verification of the non-LTE radiative transfer codes. Methods. Under the impact
approximation hypothesis, static, one-dimensional, plane-parallel atmosphere,
constant magnetic field of arbitrary strength and direction, two-level atom
model with unpolarized lower level and stimulated emission neglected, we
introduce the unphysical terms into the equations of statistical equilibrium
and solve the appropriate non-LTE integral equations. Results. We derive a new
analytical condition for the surface values of the source function components
expressed in the basis of irreducible spherical tensors.
| astro-ph |
0704.1574 | Retarded electric and magnetic fields of a moving charge: Feynman's
derivation of Li\'enard-Wiechert potentials revisited | Retarded electromagnetic potentials are derived from Maxwell's equations and
the Lorenz condition. The difference found between these potentials and the
conventional Li\'{e}nard-Wiechert ones is explained by neglect, for the latter,
of the motion-dependence of the effective charge density. The corresponding
retarded fields of a point-like charge in arbitary motion are compared with
those given by the formulae of Heaviside, Feynman, Jefimenko and other authors.
The fields of an accelerated charge given by the Feynman are the same as those
derived from the Li\'{e}nard-Wiechert potentials but not those given by the
Jefimenko formulae. A mathematical error concerning partial space and time
derivatives in the derivation of the Jefimenko equations is pointed out.
| physics.class-ph |
0704.1575 | On the characterization of isotropic Gaussian fields on homogeneous
spaces of compact groups | Let T be a random field invariant under the action of a compact group G We
give conditions ensuring that independence of the random Fourier coefficients
is equivalent to Gaussianity. As a consequence, in general it is not possible
to simulate a non-Gaussian invariant random field through its Fourier expansion
using independent coefficients.
| math.PR math.RT |
0704.1576 | A Catalog of Star Cluster Candidates in M33 | We present a new catalog of star cluster candidates in the nearby spiral
galaxy M33. It is based on eight existing catalogs wherein we have
cross-referenced identifications and endeavored to resolve inconsistencies
between them. Our catalog contains 451 candidates of which 255 are confirmed
clusters based on HST and high resolution ground-based imaging. The catalog
contains precise cluster positions (RA and Dec), magnitudes and colors in the
UBVRIJHKs filters, metallicities, radial velocities, masses and ages, where
available, and galactocentric distances for each cluster. The color
distribution of the M33 clusters appears to be similar to those in the Large
Magellanic Cloud with major peaks at (B-V)o~0.15, and (B-V)o~0.65. The
intrinsic colors are correlated with cluster ages, which range from 10^{7.5} to
10^{10.3} years. The age distribution of the star clusters supports the notion
of rapid cluster disruption with a slope of alpha=-1.09 +/- 0.07 in the
dN_{cluster}/dt ~ t^{alpha} relation. In addition, comparison to theoretical
single stellar population models suggests the presence of an age-metallicity
relation among these clusters with younger clusters being more metal-rich.
Analysis of the radial distribution of the clusters yields some evidence that
younger clusters (age <~ 1 Gyr) may be more concentrated toward the center of
M33 than older ones. A similar comparison with the radial profile of the M33
field stars shows the clusters to be more centrally concentrated at the greater
than 99.9% confidence level. Possible reasons for this are presented and
discussed; however, the overwhelming conclusion seems to be that a more
complete and thorough cluster search is needed covering at least 4 square
degrees centered on M33.
| astro-ph |
0704.1577 | Sharp dark-mode resonances in planar metamaterials with broken
structural symmetry | We report that resonant response with a very high quality factor can be
achieved in a planar metamaterial by introducing symmetry breaking in the shape
of its structural elements, which enables excitation of dark modes, i.e. modes
that are weakly coupled to free space.
| physics.optics |
0704.1578 | Proper motion L and T dwarf candidate members of the Pleiades | We present the results of a deep optical-near-infrared multi-epoch survey
covering 2.5 square degrees of the Pleiades open star cluster to search for new
very-low-mass brown dwarf members. A significant (~ 5 year) epoch difference
exists between the optical (CFH12k I-, Z-band) and near infrared (UKIRT WFCAM
J-band) observations. We construct I,I-Z and Z,Z-J colour magnitude diagrams to
select candidate cluster members. Proper motions are computed for all candidate
members and compared to the background field objects to further refine the
sample. We recover all known cluster members within the area of our survey. In
addition, we have discovered 9 new candidate brown dwarf cluster members. The 7
faintest candidates have red Z-J colours and show blue near-infrared colours.
These are consistent with being L and T-type Pleiads. Theoretical models
predict their masses to be around 11 Jupiter masses.
There is 1 errata for this paper
| astro-ph |
0704.1579 | A Study of Catalogued Nearby Galaxy Clusters in the SDSS-DR4: I. Cluster
Global Properties | We have selected a sample of 88 nearby (z<0.1) galaxy clusters from the
SDSS-DR4 with redshift information for the cluster members. We have derived
global properties for each cluster, such as their mean recessional velocity,
velocity dispersion, and virial radii. Cluster galaxies have been grouped in
two families according to their $u-r$ colours. The total sample consists of
10865 galaxies. As expected, the highest fraction of galaxies (62%) turned to
be early-type (red) ones, being located at smaller distances from the cluster
centre and showing lower velocity dispersions than late-type (blue) ones. The
brightest cluster galaxies are located in the innermost regions and show the
smallest velocity dispersions. Early-type galaxies also show constant velocity
dispersion profiles inside the virial radius and a mild decline in the
outermost regions. In contrast, late-type galaxies show always decreasing
velocity dispersions profiles. No correlation has been found between the
fraction of blue galaxies and cluster global properties, such as cluster
velocity dispersion and galaxy concentration. In contrast, we found correlation
between the X-ray luminosity and the fraction of blue galaxies. These results
indicate that early- and late-type galaxies may have had different evolution.
Thus, blue galaxies are located in more anisotropic and radial orbits than
early-type ones. Their star formation seems to be independent of the cluster
global properties in low mass clusters, but not for the most massive ones.
These observational results suggest that the global environment could be
important for driving the evolution of galaxies in the most massive cluster
($\sigma > 800$ km s$^{-1}$). However, the local environment could play a key
role in galaxy evolution for low mass clusters.
| astro-ph |
0704.1580 | Optical implementation and entanglement distribution in Gaussian valence
bond states | We study Gaussian valence bond states of continuous variable systems,
obtained as the outputs of projection operations from an ancillary space of M
infinitely entangled bonds connecting neighboring sites, applied at each of $N$
sites of an harmonic chain. The entanglement distribution in Gaussian valence
bond states can be controlled by varying the input amount of entanglement
engineered in a (2M+1)-mode Gaussian state known as the building block, which
is isomorphic to the projector applied at a given site. We show how this
mechanism can be interpreted in terms of multiple entanglement swapping from
the chain of ancillary bonds, through the building blocks. We provide optical
schemes to produce bisymmetric three-mode Gaussian building blocks (which
correspond to a single bond, M=1), and study the entanglement structure in the
output Gaussian valence bond states. The usefulness of such states for quantum
communication protocols with continuous variables, like telecloning and
teleportation networks, is finally discussed.
| quant-ph cond-mat.other physics.optics |
0704.1581 | Rich magnetic phase diagram in the Kagome-staircase compound Mn3V2O8 | Mn3V2O8 is a magnetic system in which S = 5/2 Mn2+ is found in the kagome
staircase lattice. Here we report the magnetic phase diagram for temperatures
above 2 K and applied magnetic fields below 9 T, characterized by measurements
of the magnetization and specific heat with field along the three unique
lattice directions. At low applied magnetic fields, the system first orders
magnetically below Tm1 ~ 21 K, and then shows a second magnetic phase
transition at Tm2 ~ 15 K. In addition, a phase transition that is apparent in
specific heat but not seen in magnetization is found for all three applied
field orientations, converging towards Tm2 as H -> 0. The magnetic behavior is
highly anisotropic, with critical fields for magnetic phase boundaries much
higher when the field is applied perpendicular to the Kagome staircase plane
than when applied in-plane. The field-temperature (H - T) phase diagrams are
quite rich, with 7 distinct phases observed.
| cond-mat.str-el |
0704.1582 | L^2-Betti numbers of coamenable quantum groups | We prove that a compact quantum group is coamenable if and only if its
corepresentation ring is amenable. We further propose a Foelner condition for
compact quantum groups and prove it to be equivalent to coamenability. Using
this Foelner condition, we prove that for a coamenable compact quantum group
with tracial Haar state, the enveloping von Neumann algebra is dimension flat
over the Hopf algebra of matrix coefficients. This generalizes a theorem of
Lueck from the group case to the quantum group case, and provides examples of
compact quantum groups with vanishing L^2-Betti numbers.
| math.OA math.QA |
0704.1583 | OPserver: interactive online-computations of opacities and radiative
accelerations | Codes to compute mean opacities and radiative accelerations for arbitrary
chemical mixtures using the Opacity Project recently revised data have been
restructured in a client--server architecture and transcribed as a subroutine
library. This implementation increases efficiency in stellar modelling where
element stratification due to diffusion processes is depth dependent, and thus
requires repeated fast opacity reestimates. Three user modes are provided to
fit different computing environments, namely a web browser, a local workstation
and a distributed grid.
| astro-ph |
0704.1584 | Can One Estimate The Unconditional Distribution of Post-Model-Selection
Estimators? | We consider the problem of estimating the unconditional distribution of a
post-model-selection estimator. The notion of a post-model-selection estimator
here refers to the combined procedure resulting from first selecting a model
(e.g., by a model selection criterion like AIC or by a hypothesis testing
procedure) and then estimating the parameters in the selected model (e.g., by
least-squares or maximum likelihood), all based on the same data set. We show
that it is impossible to estimate the unconditional distribution with
reasonable accuracy even asymptotically. In particular, we show that no
estimator for this distribution can be uniformly consistent (not even locally).
This follows as a corollary to (local) minimax lower bounds on the performance
of estimators for the distribution; performance is here measured by the
probability that the estimation error exceeds a given threshold. These lower
bounds are shown to approach 1/2 or even 1 in large samples, depending on the
situation considered. Similar impossibility results are also obtained for the
distribution of linear functions (e.g., predictors) of the post-model-selection
estimator.
| math.ST stat.ME stat.TH |
0704.1585 | Fixed Phase Quantum Search Algorithm | Building quantum devices using fixed operators is a must to simplify the
hardware construction. Quantum search engine is not an exception. In this
paper, a fixed phase quantum search algorithm that searches for M matches in an
unstructured search space of size N will be presented. Selecting phase shifts
of 1.91684\pi in the standard amplitude amplification will make the technique
perform better so as to get probability of success at least 99.58% in
O(sqrt(N/M)) better than any know fixed operator quantum search algorithms. The
algorithm will be able to handle either a single match or multiple matches in
the search space. The algorithm will find a match in O(sqrt(N/M)) whether the
number of matches is known or not in advance.
| quant-ph |
0704.1586 | Core excitation in the elastic scattering and breakup of $^{11}$Be on
protons | The elastic scattering and breakup of $^{11}$Be from a proton target at
intermediate energies is studied. We explore the role of core excitation in the
reaction mechanism. Comparison with the data suggests that there is still
missing physics in the description.
| nucl-th |
0704.1587 | Possible X-ray diagnostic for jet/disk dominance in Type 1 AGN | Using Rossi X-ray Timing Explorer Seyfert 1 and 1.2 data spanning 9 years, we
study correlations between X-ray spectral features. The sample consists of 350
time-resolved spectra from 12 Seyfert 1 and 1.2 galaxies. Each spectrum is
fitted to a model with an intrinsic powerlaw X-ray spectrum produced close to
the central black hole that is reprocessed and absorbed by material around the
black hole. To test the robustness of our results, we performed Monte Carlo
simulations of the spectral sample. We find a complex relationship between the
iron line equivalent width (EW) and the underlying power law index (Gamma). The
data reveal a correlation between Gamma and EW which turns over at Gamma <~ 2,
but finds a weak anti-correlation for steeper photon indices. We propose that
this relationship is driven by dilution of a disk spectrum (which includes the
narrow iron line) by a beamed jet component and, hence, could be used as a
diagnostic of jet-dominance. In addition, our sample shows a strong correlation
between the reflection fraction (R) and Gamma, but we find that it is likely
the result of modeling degeneracies. We also see the X-ray Baldwin effect (an
anti-correlation between the 2-10 keV X-ray luminosity and EW) for the sample
as a whole, but not for the individual galaxies and galaxy types.
| astro-ph |
0704.1588 | On algebraic automorphisms and their rational invariants | Let X be an affine irreducible variety over an algebraically closed field k
of characteristic zero. Given an automorphism F, we denote by k(X)^F its field
of invariants, i.e. the set of rational functions f on X such that f(F)=f. Let
n(F) be the transcendence degree of k(X)^F over k. In this paper, we study the
class of automorphisms F of X for which n(F)= dim X - 1. More precisely, we
show that under some conditions on X, every such automorphism is of the form
F=A_g, where A is an algebraic action of a linear algebraic group G of
dimension 1 on X, and where g belongs to G. As an application, we determine the
conjugacy classes of automorphisms of the plane for which n(F)=1.
| math.AG |
0704.1589 | Improving immunization strategies | We introduce an immunization method where the percentage of required
vaccinations for immunity are close to the optimal value of a targeted
immunization scheme of highest degree nodes. Our strategy retains the advantage
of being purely local, without the need of knowledge on the global network
structure or identification of the highest degree nodes. The method consists of
selecting a random node and asking for a neighbor that has more links than
himself or more than a given threshold and immunizing him. We compare this
method to other efficient strategies on three real social networks and on a
scale-free network model, and find it to be significantly more effective.
| physics.soc-ph |
0704.1590 | Constraints on the Very Early Universe from Thermal WIMP Dark Matter | We investigate the relic density n_\chi of non-relativistic long-lived or
stable particles \chi in non-standard cosmological scenarios. We calculate the
relic abundance starting from arbitrary initial temperatures of the
radiation-dominated epoch, and derive the lower bound on the initial
temperature T_0 \geq m_\chi/23, assuming that thermally produced \chi particles
account for the dark matter energy density in the universe; this bound holds
for all \chi annihilation cross sections. We also investigate cosmological
scenarios with modified expansion rate. Even in this case an approximate
formula similar to the standard one is capable of predicting the final relic
abundance correctly. Choosing the \chi annihilation cross section such that the
observed cold dark matter abundance is reproduced in standard cosmology, we
constrain possible modifications of the expansion rate at T \sim m_\chi/20,
well before Big Bang nucleosynthesis.
| hep-ph astro-ph |
0704.1591 | Flavour-Dependent Type II Leptogenesis | We reanalyse leptogenesis via the out-of-equilibrium decay of the lightest
right-handed neutrino in type II seesaw scenarios, taking into account
flavour-dependent effects. In the type II seesaw mechanism, in addition to the
type I seesaw contribution, an additional direct mass term for the light
neutrinos is present. We consider type II seesaw scenarios where this
additional contribution arises from the vacuum expectation value of a Higgs
triplet, and furthermore an effective model-independent approach. We
investigate bounds on the flavour-specific decay asymmetries, on the mass of
the lightest right-handed neutrino and on the reheat temperature of the early
universe, and compare them to the corresponding bounds in the type I seesaw
framework. We show that while flavour-dependent thermal type II leptogenesis
becomes more efficient for larger mass scale of the light neutrinos, and the
bounds become relaxed, the type I seesaw scenario for leptogenesis becomes more
constrained. We also argue that in general, flavour-dependent effects cannot be
ignored when dealing with leptogenesis in type II seesaw models.
| hep-ph |
0704.1592 | Multi-wavelength Analysis of a Quiet Solar Region | We present observations of a solar quiet region obtained by the ground-based
Dutch Open Telescope (DOT), and by instruments on the spacecraft SOHO and
TRACE. The observations were obtained during a coordinated observing campaign
on October 2005. The aim of this work is to present the rich diversity of
fine-scale structures that are found at the network boundaries and their
appearance in different instruments and different spectral lines that span the
photosphere to the corona. Detailed studies of these structures are crucial to
understanding their dynamics in different solar layers, as well as the role
such structures play in the mass balance and heating of the solar atmosphere.
| astro-ph |
0704.1593 | Orbital currents in the Colle-Salvetti correlation energy functional and
the degeneracy problem | Popular density functionals for the exchange-correlation energy typically
fail to reproduce the degeneracy of different ground states of open-shell
atoms. As a remedy, functionals which explicitly depend on the current density
have been suggested. We present an analysis of this problem by investigating
functionals that explicitly depend on the Kohn-Sham orbitals. Going beyond the
exact-exchange approximation by adding correlation in the form of the
Colle-Salvetti functional we show how current-dependent terms enter the
Colle-Salvetti expression and their relevance is evaluated. A very good
description of the degeneracy of ground-states for atoms of the first and
second row of the periodic table is obtained.
| cond-mat.mtrl-sci |
0704.1594 | Cooper pairs in atomic nuclei | We consider the development of Cooper pairs in a self-consistent Hartree Fock
mean field for the even Sm isotopes. Results are presented at the level of a
BCS treatment, a number-projected BCS treatment and an exact treatment using
the Richardson ansatz. While projected BCS captures much of the pairing
correlation energy that is absent from BCS, it still misses a sizable
correlation energy, typically of order $1 MeV$. Furthermore, because it does
not average over the properties of the fermion pairs, the exact Richardson
solution permits a more meaningful definition of the Cooper wave function and
of the fraction of pairs that are collective.
| nucl-th |
0704.1595 | An adaptive numerical method for the Vlasov equation based on a
multiresolution analysis | In this paper, we present very first results for the adaptive solution on a
grid of the phase space of the Vlasov equation arising in particles accelarator
and plasma physics. The numerical algorithm is based on a semi-Lagrangian
method while adaptivity is obtained using multiresolution analysis.
| math.NA |
0704.1596 | Turbulence and the Navier-Stokes equations | The concept of continuous topological evolution, based upon Cartan's methods
of exterior differential systems, is used to develop a topological theory of
non-equilibrium thermodynamics, within which there exist processes that exhibit
continuous topological change and thermodynamic irreversibility. The technique
furnishes a universal, topological foundation for the partial differential
equations of hydrodynamics and electrodynamics; the technique does not depend
upon a metric, connection or a variational principle. Certain topological
classes of solutions to the Navier-Stokes equations are shown to be equivalent
to thermodynamically irreversible processes.
| math-ph math.MP |
0704.1597 | Numerical estimation of critical parameters using the Bond entropy | Using a model of spinless fermions in a lattice with nearest neighbor and
next-nearest neighbor interaction we show that the entropy of the reduced two
site density matrix (the bond entropy) can be used as an extremely accurate and
easy to calculate numerical indicator for the critical parameters of the
quantum phase transition when the basic ordering pattern has a two-site
periodicity. The actual behavior of the bond entropy depends on the particular
characteristics of the transition under study. For the Kosterlitz-Thouless type
phase transition from a Luttinger liquid phase to a charge density wave state
the bond entropy has a local maximum while in the transition from the Luttinger
liquid to the phase separated state the derivative of the bond entropy has a
divergence due to the cancelation of the third eigenvalue of the two-site
reduced density matrix.
| cond-mat.str-el cond-mat.mes-hall |
0704.1598 | Radiative transitions of the helium atom in highly magnetized neutron
star atmospheres | Recent observations of thermally emitting isolated neutron stars revealed
spectral features that could be interpreted as radiative transitions of He in a
magnetized neutron star atmosphere. We present Hartree-Fock calculations of the
polarization-dependent photoionization cross sections of the He atom in strong
magnetic fields ranging from 10^12 G to 10^14 G. Convenient fitting formulae
for the cross sections are given as well as related oscillator strengths for
various bound-bound transitions. The effects of finite nucleus mass on the
radiative absorption cross sections are examined using perturbation theory.
| astro-ph |
0704.1599 | Critical points for surface maps and the Benedicks-Carleson theorem | We give an alternative proof of the Benedicks-Carleson theorem on the
existence of strange attractors in H\'enon-like families in the plane. To
bypass a huge inductive argument, we introduce an induction-free explicit
definition of dynamically critical points. The argument is sufficiently general
and in particular applies to the case of non-invertible maps as well. It
naturally raises the question of an intrinsic characterization of dynamically
critical points for dissipative surface maps.
| math.DS |
0704.1600 | The VIMOS VLT Deep Survey. The Assembly History of the Stellar Mass in
Galaxies: from the Young to the Old Universe | We present a detailed analysis of the Galaxy Stellar Mass Function of
galaxies up to z=2.5 as obtained from the VVDS. We estimate the stellar mass
from broad-band photometry using 2 different assumptions on the galaxy star
formation history and show that the addition of secondary bursts to a
continuous star formation history produces systematically higher (up to 40%)
stellar masses. At low redshift (z=0.2) we find a substantial population of
low-mass galaxies (<10^9 Msun) composed by faint blue galaxies (M_I-M_K=0.3).
In general the stellar mass function evolves slowly up to z=0.9 and more
significantly above this redshift. Conversely, a massive tail is present up to
z=2.5 and have extremely red colours (M_I-M_K=0.7-0.8). We find a decline with
redshift of the overall number density of galaxies for all masses (59+-5% for
M>10^8 Msun at z=1), and a mild mass-dependent average evolution
(`mass-downsizing'). In particular our data are consistent with mild/negligible
(<30%) evolution up to z=0.7 for massive galaxies (>6x10^10 Msun). For less
massive systems the no-evolution scenario is excluded. A large fraction (>=50%)
of massive galaxies have been already assembled and converted most of their gas
into stars at z=1, ruling out the `dry mergers' as the major mechanism of their
assembly history below z=1. This fraction decreases to 33% at z=2. Low-mass
systems have decreased continuously in number and mass density (by a factor up
to 4) from the present age to z=2, consistently with a prolonged mass assembly
also at z<1.
| astro-ph |
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