504 research outputs found
Transport properties of a modified Lorentz gas
We present a detailed study of the first simple mechanical system that shows
fully realistic transport behavior while still being exactly solvable at the
level of equilibrium statistical mechanics. The system under consideration is a
Lorentz gas with fixed freely-rotating circular scatterers interacting with
point particles via perfectly rough collisions. Upon imposing a temperature
and/or a chemical potential gradient, a stationary state is attained for which
local thermal equilibrium holds for low values of the imposed gradients.
Transport in this system is normal, in the sense that the transport
coefficients which characterize the flow of heat and matter are finite in the
thermodynamic limit. Moreover, the two flows are non-trivially coupled,
satisfying Onsager's reciprocity relations to within numerical accuracy as well
as the Green-Kubo relations . We further show numerically that an applied
electric field causes the same currents as the corresponding chemical potential
gradient in first order of the applied field. Puzzling discrepancies in higher
order effects (Joule heating) are also observed. Finally, the role of entropy
production in this purely Hamiltonian system is shortly discussed.Comment: 16 pages, 16 figures, submitted to J. Stat. Phy
Nonequlibrium particle and energy currents in quantum chains connected to mesoscopic Fermi reservoirs
We propose a model of nonequilibrium quantum transport of particles and
energy in a system connected to mesoscopic Fermi reservoirs (meso-reservoir).
The meso-reservoirs are in turn thermalized to prescribed temperatures and
chemical potentials by a simple dissipative mechanism described by the Lindblad
equation. As an example, we study transport in monoatomic and diatomic chains
of non-interacting spinless fermions. We show numerically the breakdown of the
Onsager reciprocity relation due to the dissipative terms of the model.Comment: 5pages, 4 figure
Fourier's Law in a Quantum Spin Chain and the Onset of Quantum Chaos
We study heat transport in a nonequilibrium steady state of a quantum
interacting spin chain. We provide clear numerical evidence of the validity of
Fourier law. The regime of normal conductivity is shown to set in at the
transition to quantum chaos.Comment: 4 pages, 5 figures, RevTe
Nonequilibrium dynamics of a stochastic model of anomalous heat transport: numerical analysis
We study heat transport in a chain of harmonic oscillators with random
elastic collisions between nearest-neighbours. The equations of motion of the
covariance matrix are numerically solved for free and fixed boundary
conditions. In the thermodynamic limit, the shape of the temperature profile
and the value of the stationary heat flux depend on the choice of boundary
conditions. For free boundary conditions, they also depend on the coupling
strength with the heat baths. Moreover, we find a strong violation of local
equilibrium at the chain edges that determine two boundary layers of size
(where is the chain length), that are characterized by a
different scaling behaviour from the bulk. Finally, we investigate the
relaxation towards the stationary state, finding two long time scales: the
first corresponds to the relaxation of the hydrodynamic modes; the second is a
manifestation of the finiteness of the system.Comment: Submitted to Journal of Physics A, Mathematical and Theoretica
What is so special about wingsuit BASE jumpers? A comparative study of their psychological characteristics
For the general public, BASE jumping is considered the ultimate extreme activity. Among BASE jumpers, those using wingsuits are generally perceived as the most experienced but also as the most risk-taking. Starting from this observation, we wanted to know whether wingsuit users differed in their psychological characteristics from other BASE jumpers. More specifically, we hypothesized that wingsuit users would be characterized by higher levels of mental toughness and by lower levels of harm avoidance. We also expected them to use more mental training techniques than the other jumpers. To this end, we conducted a vast survey on a sample of 183 BASE jumpers. Contrary to our hypotheses, the results did not reveal any significant difference in psychological characteristics between wingsuit users and other BASE jumpers. This absence of significant differences is discussed and recommendations for the use of mixed or multi-methods in the study of extreme sports are proposed
Particle and Energy Transport in quantum disordered and quasi-periodic chains connected to mesoscopic Fermi reservoirs
We study a model of nonequilibrium quantum transport of particles and energy
in a many-body system connected to mesoscopic Fermi reservoirs (the so-called
meso-reservoirs). We discuss the conservation laws of particles and energy
within our setup as well as the transport properties of quasi-periodic and
disordered chains.Comment: 11pages, 4 figure
Current in coherent quantum systems connected to mesoscopic Fermi reservoirs
We study particle current in a recently proposed model for coherent quantum transport. In this model, a system connected to mesoscopic Fermi reservoirs (meso-reservoir) is driven out of equilibrium by the action of super-reservoirs thermalized to prescribed temperatures and chemical potentials by a simple dissipative mechanism described by the Lindblad equation. We compare exact (numerical) results with theoretical expectations based on the Landauer formula
Nonequilibrium dynamics of a stochastic model of anomalous heat transport
We study the dynamics of covariances in a chain of harmonic oscillators with
conservative noise in contact with two stochastic Langevin heat baths. The
noise amounts to random collisions between nearest-neighbour oscillators that
exchange their momenta. In a recent paper, [S Lepri et al. J. Phys. A: Math.
Theor. 42 (2009) 025001], we have studied the stationary state of this system
with fixed boundary conditions, finding analytical exact expressions for the
temperature profile and the heat current in the thermodynamic (continuum)
limit. In this paper we extend the analysis to the evolution of the covariance
matrix and to generic boundary conditions. Our main purpose is to construct a
hydrodynamic description of the relaxation to the stationary state, starting
from the exact equations governing the evolution of the correlation matrix. We
identify and adiabatically eliminate the fast variables, arriving at a
continuity equation for the temperature profile T(y,t), complemented by an
ordinary equation that accounts for the evolution in the bulk. Altogether, we
find that the evolution of T(y,t) is the result of fractional diffusion.Comment: Submitted to Journal of Physics A, Mathematical and Theoretica
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