586 research outputs found
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
Heat Conduction in two-dimensional harmonic crystal with disorder
We study the problem of heat conduction in a mass-disordered two-dimensional
harmonic crystal. Using two different stochastic heat baths, we perform
simulations to determine the system size (L) dependence of the heat current
(J). For white noise heat baths we find that J ~ 1/L^a with
while correlated noise heat baths gives . A special case with
correlated disorder is studied analytically and gives a=3/2 which agrees also
with results from exact numerics.Comment: Revised version. 4 pages, 3 figure
Local Temperature and Universal Heat Conduction in FPU chains
It is shown numerically that for Fermi Pasta Ulam (FPU) chains with
alternating masses and heat baths at slightly different temperatures at the
ends, the local temperature (LT) on small scales behaves paradoxically in
steady state. This expands the long established problem of equilibration of FPU
chains. A well-behaved LT appears to be achieved for equal mass chains; the
thermal conductivity is shown to diverge with chain length N as N^(1/3),
relevant for the much debated question of the universality of one dimensional
heat conduction. The reason why earlier simulations have obtained
systematically higher exponents is explained.Comment: 4 pages, 3 figures, revised published versio
Universality of One-Dimensional Heat Conductivity
We show analytically that the heat conductivity of oscillator chains diverges
with system size N as N^{1/3}, which is the same as for one-dimensional fluids.
For long cylinders, we use the hydrodynamic equations for a crystal in one
dimension. This is appropriate for stiff systems such as nanotubes, where the
eventual crossover to a fluid only sets in at unrealistically large N. Despite
the extra equation compared to a fluid, the scaling of the heat conductivity is
unchanged. For strictly one-dimensional chains, we show that the dynamic
equations are those of a fluid at all length scales even if the static order
extends to very large N. The discrepancy between our results and numerical
simulations on Fermi-Pasta-Ulam chains is discussed.Comment: 7 pages, 2 figure
Intriguing Heat Conduction of a Polymer Chain
We study heat conduction in a one-dimensional chain of particles with
longitudinal as well as transverse motions. The particles are connected by
two-dimensional harmonic springs together with bending angle interactions.
Using equilibrium and nonequilibrium molecular dynamics, three types of thermal
conducting behaviors are found: a logarithmic divergence with system sizes for
large transverse coupling, 1/3 power-law at intermediate coupling, and 2/5
power-law at low temperatures and weak coupling. The results are consistent
with a simple mode-coupling analysis of the same model. The 1/3 power-law
divergence should be a generic feature for models with transverse motions.Comment: 4 page
Analyticity of the SRB measure for a class of simple Anosov flows
We consider perturbations of the Hamiltonian flow associated with the
geodesic flow on a surface of constant negative curvature. We prove that, under
a small perturbation, not necessarely of Hamiltonian character, the SRB measure
associated to the flow exists and is analytic in the strength of the
perturbation. An explicit example of "thermostatted" dissipative dynamics is
constructed.Comment: 23 pages, corrected typo
Fluctuation relation for a L\'evy particle
We study the work fluctuations of a particle subjected to a deterministic
drag force plus a random forcing whose statistics is of the L\'evy type. In the
stationary regime, the probability density of the work is found to have ``fat''
power-law tails which assign a relatively high probability to large
fluctuations compared with the case where the random forcing is Gaussian. These
tails lead to a strong violation of existing fluctuation theorems, as the ratio
of the probabilities of positive and negative work fluctuations of equal
magnitude behaves in a non-monotonic way. Possible experiments that could probe
these features are proposed.Comment: 5 pages, 2 figures, RevTeX4; v2: minor corrections and references
added; v3: typos corrected, new conclusion, close to published versio
New application of open source data and Rock Engineering System for debris flow susceptibility analysis
This research describes a quantitative, rapid, and low-cost methodology for debris flow susceptibility evaluation at the basin scale using open-access data and geodatabases. The proposed approach can aid decision makers in land management and territorial planning, by first screening for areas with a higher debris flow susceptibility. Five environmental predisposing factors, namely, bedrock lithology, fracture network, quaternary deposits, slope inclination, and hydrographic network, were selected as independent parameters and their mutual interactions were described and quantified using the Rock Engineering System (RES) methodology. For each parameter, specific indexes were proposed, aiming to provide a final synthetic and representative index of debris flow susceptibility at the basin scale. The methodology was tested in four basins located in the Upper Susa Valley (NW Italian Alps) where debris flow events are the predominant natural hazard. The proposed matrix can represent a useful standardized tool, universally applicable, since it is independent of type and characteristic of the basin
Temperature Profiles in Hamiltonian Heat Conduction
We study heat transport in the context of Hamiltonian and related stochastic
models with nearest-neighbor coupling, and derive a universal law for the
temperature profiles of a large class of such models. This law contains a
parameter , and is linear only when . The value of
depends on energy-exchange mechanisms, including the range of motion of tracer
particles and their times of flight.Comment: Revised text, same results Second revisio
- …