140,697 research outputs found
Exchange Monte Carlo Method and Application to Spin Glass Simulations
We propose an efficient Monte Carlo algorithm for simulating a
``hardly-relaxing" system, in which many replicas with different temperatures
are simultaneously simulated and a virtual process exchanging configurations of
these replica is introduced. This exchange process is expected to let the
system at low temperatures escape from a local minimum. By using this algorithm
the three-dimensional Ising spin glass model is studied. The ergodicity
time in this method is found much smaller than that of the multi-canonical
method. In particular the time correlation function almost follows an
exponential decay whose relaxation time is comparable to the ergodicity time at
low temperatures. It suggests that the system relaxes very rapidly through the
exchange process even in the low temperature phase.Comment: 10 pages + uuencoded 5 Postscript figures, REVTe
Intermittency and the Slow Approach to Kolmogorov Scaling
From a simple path integral involving a variable volatility in the velocity
differences, we obtain velocity probability density functions with exponential
tails, resembling those observed in fully developed turbulence. The model
yields realistic scaling exponents and structure functions satisfying extended
self-similarity. But there is an additional small scale dependence for
quantities in the inertial range, which is linked to a slow approach to
Kolmogorov (1941) scaling occurring in the large distance limit.Comment: 10 pages, 5 figures, minor changes to mirror version to appear in PR
Creep motion of a domain wall in the two-dimensional random-field Ising model with a driving field
With Monte Carlo simulations, we study the creep motion of a domain wall in
the two-dimensional random-field Ising model with a driving field. We observe
the nonlinear fieldvelocity relation, and determine the creep exponent {\mu}.
To further investigate the universality class of the creep motion, we also
measure the roughness exponent {\zeta} and energy barrier exponent {\psi} from
the zero-field relaxation process. We find that all the exponents depend on the
strength of disorder.Comment: 5 pages, 4 figure
Radiative parton energy loss and jet quenching in high-energy heavy-ion collisions
We study within the light-cone path integral approach [3] the effect of the
induced gluon radiation on high-p_{T} hadrons in high-energy heavy-ion
collisions. The induced gluon spectrum is represented in a new form which is
convenient for numerical simulations. For the first time, computations are
performed with a realistic parametrization of the dipole cross section. The
results are in reasonable agreement with suppression of high-p_{T} hadrons in
Au+Au collisions at \sqrt{s}=200 GeV observed at RHIC.Comment: 12 pages, 3 epsi figures. Typos correcte
Non-Abelian Energy Loss at Finite Opacity
A systematic expansion in opacity, , is used to clarify the
non-linear behavior of induced gluon radiation in quark-gluon plasmas. The
inclusive differential gluon distribution is calculated up to second order in
opacity and compared to the zeroth order (factorization) limit. The opacity
expansion makes it possible to take finite kinematic constraints into account
that suppress jet quenching in nuclear collisions below RHIC (
AGeV) energies.Comment: 4 pages (revtex) with 3 eps figures, submitted to PR
Energy flux fluctuations in a finite volume of turbulent flow
The flux of turbulent kinetic energy from large to small spatial scales is
measured in a small domain B of varying size R. The probability distribution
function of the flux is obtained using a time-local version of Kolmogorov's
four-fifths law. The measurements, made at a moderate Reynolds number, show
frequent events where the flux is backscattered from small to large scales,
their frequency increasing as R is decreased. The observations are corroborated
by a numerical simulation based on the motion of many particles and on an
explicit form of the eddy damping.Comment: 10 Pages, 5 figures, 1 tabl
Sub-Kolmogorov-Scale Fluctuations in Fluid Turbulence
We relate the intermittent fluctuations of velocity gradients in turbulence
to a whole range of local dissipation scales generalizing the picture of a
single mean dissipation length. The statistical distribution of these local
dissipation scales as a function of Reynolds number is determined in numerical
simulations of forced homogeneous isotropic turbulence with a spectral
resolution never applied before which exceeds the standard one by at least a
factor of eight. The core of the scale distribution agrees well with a
theoretical prediction. Increasing Reynolds number causes the generation of
ever finer local dissipation scales. This is in line with a less steep decay of
the large-wavenumber energy spectra in the dissipation range. The energy
spectrum for the highest accessible Taylor microscale Reynolds number
R_lambda=107 does not show a bottleneck.Comment: 8 pages, 5 figures (Figs. 1 and 3 in reduced quality
Kolmogorov's law for two-dimensional electron-magnetohydrodynamic turbulence
The analogue of the Kolmogorov's four-fifths law is derived for
two-dimensional, homogeneous, isotropic EMHD turbulence in the energy cascade
inertial range. Direct numerical simulations for the freely decaying case show
that this relation holds true for different values of the adimensional electron
inertial length scale, . The energy spectrum is found to be close to the
expected Kolmogorov spectrum.Comment: 9 pages RevTeX, 3 PostScript figure
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