746 research outputs found
Crossover from ballistic to diffusive thermal transport in quantum Langevin dynamics study of a harmonic chain connected to self-consistent reservoirs
Through an exact analysis using quantum Langevin dynamics, we demonstrate the
crossover from ballistic to diffusive thermal transport in a harmonic chain
with each site connected to Ohmic heat reservoirs. The temperatures of the two
heat baths at the boundaries are specified from before whereas the temperatures
of the interior heat reservoirs are determined self-consistently by demanding
that in the steady state, on average, there is no heat current between any such
(self-consistent) reservoir and the harmonic chain. Essence of our study is
that the effective mean free path separating the ballistic regime of transport
from the diffusive one emerges naturally.Comment: 4 pages, 2 figur
Reversibility, coarse graining and the chaoticity principle
We describe a way of interpreting the chaotic principle of (ref. [GC1]) more
extensively than it was meant in the original works. Mathematically the
analysis is based on the dynamical notions of Axiom A and Axiom B and on the
notion of Axiom C, that we introduce arguing that it is suggested by the
results of an experiment (ref. [BGG]) on chaotic motions. Physically we
interpret a breakdown of the Anosov property of a time reversible attractor
(replaced, as a control parameter changes, by an Axiom A property) as a
spontaneous breakdown of the time reversal symmetry: the relation between time
reversal and the symmetry that remains after the breakdown is analogous to the
breakdown of -invariance while still holds.Comment: 15 pages, plain TeX, no figure
Fluctuation theorem for non-equilibrium relaxational systems driven by external forces
We discuss an extension of the fluctuation theorem to stochastic models that,
in the limit of zero external drive, are not able to equilibrate with their
environment, extending results presented by Sellitto (cond-mat/9809186). We
show that if the entropy production rate is suitably defined, its probability
distribution function verifies the Fluctuation Relation with the ambient
temperature replaced by a (frequency-dependent) effective temperature. We
derive modified Green-Kubo relations. We illustrate these results with the
simple example of an oscillator coupled to a nonequilibrium bath driven by an
external force. We discuss the relevance of our results for driven glasses and
the diffusion of Brownian particles in out of equilibrium media and propose a
concrete experimental strategy to measure the low frequency value of the
effective temperature using the fluctuations of the work done by an ac
conservative field. We compare our results to related ones that appeared in the
literature recently.Comment: 39 pages, 6 figure
Fluctuations relation and external thermostats: an application to granular materials
In this note we discuss a paradigmatic example of interacting particles
subject to non conservative external forces and to the action of thermostats
consisting of external (finite) reservoirs of particles. We then consider a
model of granular materials of interest for experimental tests that had
recently attracted lot of attentions. This model can be reduced to the
previously discussed example under a number of assumptions, in particular that
inelasticity due to internal collisions can be neglected for the purpose of
measuring the large deviation functional for entropy production rate. We show
that if the restitution coefficient in the granular material model is close to
one, then the required assuptions are verified on a specific time scale and we
predict a fluctuation relation for the entropy production rate measured on the
same time scale.Comment: 7 pages; updated to take into account comments received on the first
version; to appear on J.Stat.Mech.(2006
Spatial Structure of Stationary Nonequilibrium States in the Thermostatted Periodic Lorentz Gas
We investigate analytically and numerically the spatial structure of the
non-equilibrium stationary states (NESS) of a point particle moving in a two
dimensional periodic Lorentz gas (Sinai Billiard). The particle is subject to a
constant external electric field E as well as a Gaussian thermostat which keeps
the speed |v| constant. We show that despite the singular nature of the SRB
measure its projections on the space coordinates are absolutely continuous. We
further show that these projections satisfy linear response laws for small E.
Some of them are computed numerically. We compare these results with those
obtained from simple models in which the collisions with the obstacles are
replaced by random collisions.Similarities and differences are noted.Comment: 24 pages with 9 figure
Crossover from Fermi-Pasta-Ulam to normal diffusive behaviour in heat conduction through open anharmonic lattices
We study heat conduction in one, two and three dimensional anharmonic
lattices connected to stochastic Langevin heat baths. The inter-atomic
potential of the lattices is double-well type, i.e., with . We observe two different
temperature regimes of transport: a high-temperature regime where asymptotic
length dependence of nonequilibrium steady state heat current is similar to the
well-known Fermi-Pasta-Ulam lattices with an inter-atomic potential, with . A low temperature regime where
heat conduction is diffusive normal satisfying Fourier's law. We present our
simulation results at different temperature regimes in all dimensions.Comment: 5 pages, 7 figure
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