301 research outputs found
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
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
Brownian-Vacancy Mediated Disordering Dynamics
The disordering of an initially phase segregated system of finite size,
induced by the presence of highly mobile vacancies, is shown to exhibit dynamic
scaling in its late stages.
A set of characteristic exponents is introduced and computed analytically, in
excellent agreement with Monte Carlo data. In particular, the characteristic
time scale, controlling the crossover between increasing disorder and
saturation, is found to depend on the exponent scaling the number of vacancies
in the sample.Comment: 6 pages, typeset using Euro-LaTex, 6 figures, compresse
Power Spectra of the Total Occupancy in the Totally Asymmetric Simple Exclusion Process
As a solvable and broadly applicable model system, the totally asymmetric
exclusion process enjoys iconic status in the theory of non-equilibrium phase
transitions. Here, we focus on the time dependence of the total number of
particles on a 1-dimensional open lattice, and its power spectrum. Using both
Monte Carlo simulations and analytic methods, we explore its behavior in
different characteristic regimes. In the maximal current phase and on the
coexistence line (between high/low density phases), the power spectrum displays
algebraic decay, with exponents -1.62 and -2.00, respectively. Deep within the
high/low density phases, we find pronounced \emph{oscillations}, which damp
into power laws. This behavior can be understood in terms of driven biased
diffusion with conserved noise in the bulk.Comment: 4 pages, 4 figure
Reversibility, heat dissipation and the importance of the thermal environment in stochastic models of nonequilibrium steady states
We examine stochastic processes that are used to model nonequilibrium
processes (e.g, pulling RNA or dragging colloids) and so deliberately violate
detailed balance. We argue that by combining an information-theoretic measure
of irreversibility with nonequilibrium work theorems, the thermal physics
implied by abstract dynamics can be determined. This measure is bounded above
by thermodynamic entropy production and so may quantify how well a stochastic
dynamics models reality. We also use our findings to critique various modeling
approaches and notions arising in steady-state thermodynamics.Comment: 8 pages, 2 figures, easy-to-read, single-column, large-print RevTeX4
format; version with modified abstract and additional discussion, references
to appear in Phys Rev Let
Effects of differential mobility on biased diffusion of two species
Using simulations and a simple mean-field theory, we investigate jamming
transitions in a two-species lattice gas under non-equilibrium steady-state
conditions. The two types of particles diffuse with different mobilities on a
square lattice, subject to an excluded volume constraint and biased in opposite
directions. Varying filling fraction, differential mobility, and drive, we map
out the phase diagram, identifying first order and continuous transitions
between a free-flowing disordered and a spatially inhomogeneous jammed phase.
Ordered structures are observed to drift, with a characteristic velocity, in
the direction of the more mobile species.Comment: 15 pages, 4 figure
Long Range Correlations in the Disordered Phase of a Simple Three State Lattice Gas
We investigate the dynamics of a three-state stochastic lattice gas,
consisting of holes and two oppositely "charged" species of particles, under
the influence of an "electric" field, at zero total charge. Interacting only
through an excluded volume constraint, particles can hop to nearest neighbour
empty sites. With increasing density and drive, the system orders into a
charge-segregated state. Using a combination of Langevin equations and Monte
Carlo simulations, we study the steady-state structure factors in the
disordered phase where homogeneous configurations are stable against small
harmonic perturbations. They show a discontinuity singularity at the origin
which in real space leads to an intricate crossover between power laws of
different kinds.Comment: 7 RevTeX pages, 1 postscript figure include
Dynamic instability transitions in 1D driven diffusive flow with nonlocal hopping
One-dimensional directed driven stochastic flow with competing nonlocal and
local hopping events has an instability threshold from a populated phase into
an empty-road (ER) phase. We implement this in the context of the asymmetric
exclusion process. The nonlocal skids promote strong clustering in the
stationary populated phase. Such clusters drive the dynamic phase transition
and determine its scaling properties. We numerically establish that the
instability transition into the ER phase is second order in the regime where
the entry point reservoir controls the current and first order in the regime
where the bulk is in control. The first order transition originates from a
turn-about of the cluster drift velocity. At the critical line, the current
remains analytic, the road density vanishes linearly, and fluctuations scale as
uncorrelated noise. A self-consistent cluster dynamics analysis explains why
these scaling properties remain that simple.Comment: 11 pages, 14 figures (25 eps files); revised as the publised versio
Will jams get worse when slow cars move over?
Motivated by an analogy with traffic, we simulate two species of particles
(`vehicles'), moving stochastically in opposite directions on a two-lane ring
road. Each species prefers one lane over the other, controlled by a parameter
such that corresponds to random lane choice and
to perfect `laning'. We find that the system displays one large cluster (`jam')
whose size increases with , contrary to intuition. Even more remarkably, the
lane `charge' (a measure for the number of particles in their preferred lane)
exhibits a region of negative response: even though vehicles experience a
stronger preference for the `right' lane, more of them find themselves in the
`wrong' one! For very close to 1, a sharp transition restores a homogeneous
state. Various characteristics of the system are computed analytically, in good
agreement with simulation data.Comment: 7 pages, 3 figures; to appear in Europhysics Letters (2005
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