3,480 research outputs found
Finite Temperature Spectral Densities of Momentum and R-Charge Correlators in Yang Mills Theory
We compute spectral densities of momentum and R-charge correlators in thermal
Yang Mills at strong coupling using the AdS/CFT correspondence. For
and smaller, the spectral density differs markedly from
perturbation theory; there is no kinetic theory peak. For large , the
spectral density oscillates around the zero-temperature result with an
exponentially decreasing amplitude. Contrast this with QCD where the spectral
density of the current-current correlator approaches the zero temperature
result like . Despite these marked differences with perturbation
theory, in Euclidean space-time the correlators differ by only from
the free result. The implications for Lattice QCD measurements of transport are
discussed.Comment: 18 pages, 3 figure
Macroscopic evidence of microscopic dynamics in the Fermi-Pasta-Ulam oscillator chain from nonlinear time series analysis
The problem of detecting specific features of microscopic dynamics in the
macroscopic behavior of a many-degrees-of-freedom system is investigated by
analyzing the position and momentum time series of a heavy impurity embedded in
a chain of nearest-neighbor anharmonic Fermi-Pasta-Ulam oscillators. Results
obtained in a previous work [M. Romero-Bastida, Phys. Rev. E {\bf69}, 056204
(2004)] suggest that the impurity does not contribute significantly to the
dynamics of the chain and can be considered as a probe for the dynamics of the
system to which the impurity is coupled. The () entropy, which measures
the amount of information generated by unit time at different scales of
time and of the observable, is numerically computed by methods of nonlinear
time-series analysis using the position and momentum signals of the heavy
impurity for various values of the energy density (energy per degree
of freedom) of the system and some values of the impurity mass . Results
obtained from these two time series are compared and discussed.Comment: 7 pages, 5 figures, RevTeX4 PRE format; to be published in Phys. Rev.
Xray Tomographic Microscopic Studies a Resin Embedded Paint Sample from a Mechanical Failing Area in the Floor Tiles of The Art of Painting by Johannes Vermeer (1632-1675)
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 - August 5, 201
-Scale Decoupling of the Mechanical Relaxation and Diverging Shear Wave Propagation Lengthscale in Triphenylphosphite
We have performed depolarized Impulsive Stimulated Scattering experiments to
observe shear acoustic phonons in supercooled triphenylphosphite (TPP) from
10 - 500 MHz. These measurements, in tandem with previously performed
longitudinal and shear measurements, permit further analyses of the relaxation
dynamics of TPP within the framework of the mode coupling theory (MCT). Our
results provide evidence of coupling between the shear and
longitudinal degrees of freedom up to a decoupling temperature = 231 K. A
lower bound length scale of shear wave propagation in liquids verified the
exponent predicted by theory in the vicinity of the decoupling temperature
Dynamic correlations in stochastic rotation dynamics
The dynamic structure factor, vorticity and entropy density dynamic
correlation functions are measured for Stochastic Rotation Dynamics (SRD), a
particle based algorithm for fluctuating fluids. This allows us to obtain
unbiased values for the longitudinal transport coefficients such as thermal
diffusivity and bulk viscosity. The results are in good agreement with earlier
numerical and theoretical results, and it is shown for the first time that the
bulk viscosity is indeed zero for this algorithm. In addition, corrections to
the self-diffusion coefficient and shear viscosity arising from the breakdown
of the molecular chaos approximation at small mean free paths are analyzed. In
addition to deriving the form of the leading correlation corrections to these
transport coefficients, the probabilities that two and three particles remain
collision partners for consecutive time steps are derived analytically in the
limit of small mean free path. The results of this paper verify that we have an
excellent understanding of the SRD algorithm at the kinetic level and that
analytic expressions for the transport coefficients derived elsewhere do indeed
provide a very accurate description of the SRD fluid.Comment: 33 pages including 16 figure
Thermodiffusion in model nanofluids by molecular dynamics simulations
In this work, a new algorithm is proposed to compute single particle
(infinite dilution) thermodiffusion using Non-Equilibrium Molecular Dynamics
simulations through the estimation of the thermophoretic force that applies on
a solute particle. This scheme is shown to provide consistent results for
simple Lennard-Jones fluids and for model nanofluids (spherical non-metallic
nanoparticles + Lennard-Jones fluid) where it appears that thermodiffusion
amplitude, as well as thermal conductivity, decrease with nanoparticles
concentration. Then, in nanofluids in the liquid state, by changing the nature
of the nanoparticle (size, mass and internal stiffness) and of the solvent
(quality and viscosity) various trends are exhibited. In all cases the single
particle thermodiffusion is positive, i.e. the nanoparticle tends to migrate
toward the cold area. The single particle thermal diffusion 2 coefficient is
shown to be independent of the size of the nanoparticle (diameter of 0.8 to 4
nm), whereas it increases with the quality of the solvent and is inversely
proportional to the viscosity of the fluid. In addition, this coefficient is
shown to be independent of the mass of the nanoparticle and to increase with
the stiffness of the nanoparticle internal bonds. Besides, for these
configurations, the mass diffusion coefficient behavior appears to be
consistent with a Stokes-Einstein like law
Multi-Resolution Analysis and Fractional Quantum Hall Effect: an Equivalence Result
In this paper we prove that any multi-resolution analysis of \Lc^2(\R)
produces, for some values of the filling factor, a single-electron wave
function of the lowest Landau level (LLL) which, together with its (magnetic)
translated, gives rise to an orthonormal set in the LLL. We also give the
inverse construction. Moreover, we extend this procedure to the higher Landau
levels and we discuss the analogies and the differences between this procedure
and the one previously proposed by J.-P. Antoine and the author.Comment: Submitted to Journal Mathematical Physisc
Fluctuating hydrodynamic modelling of fluids at the nanoscale
A good representation of mesoscopic fluids is required to combine with
molecular simulations at larger length and time scales (De Fabritiis {\it et.
al}, Phys. Rev. Lett. 97, 134501 (2006)). However, accurate computational
models of the hydrodynamics of nanoscale molecular assemblies are lacking, at
least in part because of the stochastic character of the underlying fluctuating
hydrodynamic equations. Here we derive a finite volume discretization of the
compressible isothermal fluctuating hydrodynamic equations over a regular grid
in the Eulerian reference system. We apply it to fluids such as argon at
arbitrary densities and water under ambient conditions. To that end, molecular
dynamics simulations are used to derive the required fluid properties. The
equilibrium state of the model is shown to be thermodynamically consistent and
correctly reproduces linear hydrodynamics including relaxation of sound and
shear modes. We also consider non-equilibrium states involving diffusion and
convection in cavities with no-slip boundary conditions
Sound-propagation gap in fluid mixtures
We discuss the behavior of the extended sound modes of a dense binary
hard-sphere mixture. In a dense simple hard-sphere fluid the Enskog theory
predicts a gap in the sound propagation at large wave vectors. In a binary
mixture the gap is only present for low concentrations of one of the two
species. At intermediate concentrations sound modes are always propagating.
This behavior is not affected by the mass difference of the two species, but it
only depends on the packing fractions. The gap is absent when the packing
fractions are comparable and the mixture structurally resembles a metallic
glass.Comment: Published; withdrawn since ordering in archive gives misleading
impression of new publicatio
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