15 research outputs found
Critical behavior of a bounded Kardar-Parisi-Zhang equation
A host of spatially extended systems, both in physics and in other
disciplines, are well described at a coarse-grained scale by a Langevin
equation with multiplicative-noise. Such systems may exhibit non-equilibrium
phase transitions, which can be classified into universality classes. Here we
study in detail one of such classes that can be mapped into a
Kardar-Parisi-Zhang (KPZ) interface equation with a positive (negative)
non-linearity in the presence of a bounding lower (upper) wall. The wall limits
the possible values taken by the height variable, introducing a lower (upper)
cut-off, and induce a phase transition between a pinned (active) and a depinned
(absorbing) phase. This transition is studied here using mean field and field
theoretical arguments, as well as from a numerical point of view. Its main
properties and critical features, as well as some challenging theoretical
difficulties, are reported. The differences with other multiplicative noise and
bounded-KPZ universality classes are stressed, and the effects caused by the
introduction of ``attractive'' walls, relevant in some physical contexts, are
also analyzed.Comment: Invited paper to a special issue of the Brazilian J. of Physics. 5
eps Figures. 9 pagres. Revtex
Unequal Intra-layer Coupling in a Bilayer Driven Lattice Gas
The system under study is a twin-layered square lattice gas at half-filling,
being driven to non-equilibrium steady states by a large, finite `electric'
field. By making intra-layer couplings unequal we were able to extend the phase
diagram obtained by Hill, Zia and Schmittmann (1996) and found that the
tri-critical point, which separates the phase regions of the stripped (S) phase
(stable at positive interlayer interactions J_3), the filled-empty (FE) phase
(stable at negative J_3) and disorder (D), is shifted even further into the
negative J_3 region as the coupling traverse to the driving field increases.
Many transient phases to the S phase at the S-FE boundary were found to be
long-lived. We also attempted to test whether the universality class of D-FE
transitions under a drive is still Ising. Simulation results suggest a value of
1.75 for the exponent gamma but a value close to 2.0 for the ratio gamma/nu. We
speculate that the D-FE second order transition is different from Ising near
criticality, where observed first-order-like transitions between FE and its
"local minimum" cousin occur during each simulation run.Comment: 29 pages, 19 figure
Dynamic behavior of anisotropic non-equilibrium driving lattice gases
It is shown that intrinsically anisotropic non-equilibrium systems relaxing
by a dynamic process exhibit universal critical behavior during their evolution
toward non-equilibrium stationary states. An anisotropic scaling anzats for the
dynamics is proposed and tested numerically. Relevant critical exponents can be
evaluated self-consistently using both the short- and long-time dynamics
frameworks. The obtained results allow us to clarify a long-standing
controversy about the theoretical description, the universality and the origin
of the anisotropy of driven diffusive systems, showing that the standard field
theory does not hold and supporting a recently proposed alternative theory.Comment: 4 pages, 2 figure
Kinetic Ising model in an oscillating field: Finite-size scaling at the dynamic phase transition
We study hysteresis for a two-dimensional, spin-1/2, nearest-neighbor,
kinetic Ising ferromagnet in an oscillating field, using Monte Carlo
simulations. The period-averaged magnetization is the order parameter for a
proposed dynamic phase transition (DPT). To quantify the nature of this
transition, we present the first finite-size scaling study of the DPT for this
model. Evidence of a diverging correlation length is given, and we provide
estimates of the transition frequency and the critical indices ,
and .Comment: Accepted by Physical Review Letters. 9 page
Is the particle current a relevant feature in driven lattice gases?
By performing extensive MonteCarlo simulations we show that the infinitely
fast driven lattice gas (IDLG) shares its critical properties with the randomly
driven lattice gas (RDLG).
All the measured exponents, scaling functions and amplitudes are the same in
both cases. This strongly supports the idea that the main relevant
non-equilibrium effect in driven lattice gases is the anisotropy (present in
both IDLG and RDLG) and not the particle current (present only in the IDLG).
This result, at odds with the predictions from the standard theory for the
IDLG, supports a recently proposed alternative theory. The case of finite
driving fields is also briefly discussed.Comment: 4 pages. Slightly improved version. Journal Reference: To appear in
Phys. Rev. Let
Monte Carlo study of the interaction volume changes by the beam skirt in VP-SEM
In this work we present a new contribution for tracking the behavior of electron beam in gas and then in material placed in the chamber of a variable pressure scanning electron microscope using Monte Carlo simulation. Firstly our results for width and depth of interaction volume in high vacuum mode are compared and are consistent with those obtained by several relationships present in literature. Carbon and aluminum are considered as examples in order to establish the reliability of our approach and experimental data available from the literature. Then, we compared the evolution of width in both high (Re_{(HV)}) and low (Re_{(LV)}) vacuum modes with enlargement of skirt (R_{s}). The present work demonstrates that the best resolution conditions for energy, pressure and material, is given by R_{s}=Re_{(HV)}. Finally, the energy that must be used to get the best image resolution for given pressure and material is determined