449 research outputs found
Steady States of a Nonequilibrium Lattice Gas
We present a Monte Carlo study of a lattice gas driven out of equilibrium by
a local hopping bias. Sites can be empty or occupied by one of two types of
particles, which are distinguished by their response to the hopping bias. All
particles interact via excluded volume and a nearest-neighbor attractive force.
The main result is a phase diagram with three phases: a homogeneous phase, and
two distinct ordered phases. Continuous boundaries separate the homogeneous
phase from the ordered phases, and a first-order line separates the two ordered
phases. The three lines merge in a nonequilibrium bicritical point.Comment: 14 pages, 24 figure
Anomalous nucleation far from equilibrium
We present precision Monte Carlo data and analytic arguments for an
asymmetric exclusion process, involving two species of particles driven in
opposite directions on a lattice. We propose a scenario which
resolves a stark discrepancy between earlier simulation data, suggesting the
existence of an ordered phase, and an analytic conjecture according to which
the system should revert to a disordered state in the thermodynamic limit. By
analyzing the finite size effects in detail, we argue that the presence of a
single, seemingly macroscopic, cluster is an intermediate stage of a complex
nucleation process: In smaller systems, this cluster is destabilized while
larger systems allow the formation of multiple clusters. Both limits lead to
exponential cluster size distributions which are, however, controlled by very
different length scales.Comment: 5 pages, 3 figures, one colum
Stationary correlations for a far-from-equilibrium spin chain
A kinetic one-dimensional Ising model on a ring evolves according to a
generalization of Glauber rates, such that spins at even (odd) lattice sites
experience a temperature (). Detailed balance is violated so
that the spin chain settles into a non-equilibrium stationary state,
characterized by multiple interactions of increasing range and spin order. We
derive the equations of motion for arbitrary correlation functions and solve
them to obtain an exact representation of the steady state. Two nontrivial
amplitudes reflect the sublattice symmetries; otherwise, correlations decay
exponentially, modulo the periodicity of the ring. In the long chain limit,
they factorize into products of two-point functions, in precise analogy to the
equilibrium Ising chain. The exact solution confirms the expectation, based on
simulations and renormalization group arguments, that the long-time,
long-distance behavior of this two-temperature model is Ising-like, in spite of
the apparent complexity of the stationary distribution.Comment: 9 page
Novel Quenched Disorder Fixed Point in a Two-Temperature Lattice Gas
We investigate the effects of quenched randomness on the universal properties
of a two-temperature lattice gas. The disorder modifies the dynamical
transition rates of the system in an anisotropic fashion, giving rise to a new
fixed point. We determine the associated scaling form of the structure factor,
quoting critical exponents to two-loop order in an expansion around the upper
critical dimension d. The close relationship with another quenched
disorder fixed point, discovered recently in this model, is discussed.Comment: 11 pages, no figures, RevTe
Driven Diffusive Systems: An Introduction and Recent Developments
Nonequilibrium steady states in driven diffusive systems exhibit many
features which are surprising or counterintuitive, given our experience with
equilibrium systems. We introduce the prototype model and review its unusual
behavior in different temperature regimes, from both a simulational and
analytic view point. We then present some recent work, focusing on the phase
diagrams of driven bi-layer systems and two-species lattice gases. Several
unresolved puzzles are posed.Comment: 25 pages, 5 figures, to appear in Physics Reports vol. 299, June 199
Coarsening of "clouds" and dynamic scaling in a far-from-equilibrium model system
A two-dimensional lattice gas of two species, driven in opposite directions
by an external force, undergoes a jamming transition if the filling fraction is
sufficiently high. Using Monte Carlo simulations, we investigate the growth of
these jams ("clouds"), as the system approaches a non-equilibrium steady state
from a disordered initial state. We monitor the dynamic structure factor
and find that the component exhibits dynamic scaling, of
the form . Over a significant range
of times, we observe excellent data collapse with and .
The effects of varying filling fraction and driving force are discussed
``Weather'' Records: Musings on Cold Days after a Long Hot Indian Summer
We present a simple, pedagogical introduction to the statistics of extreme
values. Motivated by a string of record high temperatures in December 1998, we
consider the distribution, averages and lifetimes for a simplified model of
such ``records.'' Our ``data'' are sequences of independent random numbers all
of which are generated from the same probability distribution. A remarkable
universality emerges: a number of results, including the lifetime histogram,
are universal, that is, independent of the underlying distribution.Comment: 14 pages, 3 figures. Invited paper for American Journal of Physic
Controlling surface morphologies by time-delayed feedback
We propose a new method to control the roughness of a growing surface, via a
time-delayed feedback scheme. As an illustration, we apply this method to the
Kardar-Parisi-Zhang equation in 1+1 dimensions and show that the effective
growth exponent of the surface width can be stabilized at any desired value in
the interval [0.25,0.33], for a significant length of time. The method is quite
general and can be applied to a wide range of growth phenomena. A possible
experimental realization is suggested.Comment: 4 pages, 3 figure
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