260 research outputs found
Nonuniversal Critical Spreading in Two Dimensions
Continuous phase transitions are studied in a two dimensional nonequilibrium
model with an infinite number of absorbing configurations. Spreading from a
localized source is characterized by nonuniversal critical exponents, which
vary continuously with the density phi in the surrounding region. The exponent
delta changes by more than an order of magnitude, and eta changes sign. The
location of the critical point also depends on phi, which has important
implications for scaling. As expected on the basis of universality, the static
critical behavior belongs to the directed percolation class.Comment: 21 pages, REVTeX, figures available upon reques
Numerical Study of a Field Theory for Directed Percolation
A numerical method is devised for study of stochastic partial differential
equations describing directed percolation, the contact process, and other
models with a continuous transition to an absorbing state. Owing to the
heightened sensitivity to fluctuationsattending multiplicative noise in the
vicinity of an absorbing state, a useful method requires discretization of the
field variable as well as of space and time. When applied to the field theory
for directed percolation in 1+1 dimensions, the method yields critical
exponents which compare well against accepted values.Comment: 18 pages, LaTeX, 6 figures available upon request LC-CM-94-00
Interacting Monomer-Dimer Model with Infinitely Many Absorbing States
We study a modified version of the interacting monomer-dimer (IMD) model that
has infinitely many absorbing (IMA) states. Unlike all other previously studied
models with IMA states, the absorbing states can be divided into two equivalent
groups which are dynamically separated infinitely far apart. Monte Carlo
simulations show that this model belongs to the directed Ising universality
class like the ordinary IMD model with two equivalent absorbing states. This
model is the first model with IMA states which does not belong to the directed
percolation (DP) universality class. The DP universality class can be restored
in two ways, i.e., by connecting the two equivalent groups dynamically or by
introducing a symmetry-breaking field between the two groups.Comment: 5 pages, 5 figure
Criticality of natural absorbing states
We study a recently introduced ladder model which undergoes a transition
between an active and an infinitely degenerate absorbing phase. In some cases
the critical behaviour of the model is the same as that of the branching
annihilating random walk with species both with and without hard-core
interaction. We show that certain static characteristics of the so-called
natural absorbing states develop power law singularities which signal the
approach of the critical point. These results are also explained using random
walk arguments. In addition to that we show that when dynamics of our model is
considered as a minimum finding procedure, it has the best efficiency very
close to the critical point.Comment: 6 page
Nonequilibrium Critical Dynamics of a Three Species Monomer-Monomer Model
We study a three species monomer-monomer catalytic surface reaction model
with a reactive steady state bordered by three equivalent unreactive phases
where the surface is saturated with one species. The transition from the
reactive to a saturated phase shows directed percolation critical behavior.
Each pair of these reactive-saturated phase boundaries join at a bicritical
point where the universal behavior is in the even branching annihilating random
walk class. We find the crossover exponent from bicritical to critical behavior
and a new exponent associated with the bicritical interface dynamics.Comment: 4 pages RevTex. 4 eps figures included with psfig.sty. Uses
multicol.sty. Accepted for publication in PR
Damage spreading for one-dimensional, non-equilibrium models with parity conserving phase transitions
The damage spreading (DS) transitions of two one-dimensional stochastic
cellular automata suggested by Grassberger (A and B) and the kinetic Ising
model of Menyh\'ard (NEKIM) have been investigated on the level of kinks and
spins. On the level of spins the parity conservation is not satisfied and
therefore studying these models provides a convenient tool to understand the
dependence of DS properties on symmetries. For the model B the critical point
and the DS transition point is well separated and directed percolation damage
spreading transition universality was found for spin damage as well as for kink
damage in spite of the conservation of damage variables modulo 2 in the latter
case. For the A stochastic cellular automaton, and the NEKIM model the two
transition points coincide with drastic effects on the damage of spin and kink
variables showing different time dependent behaviours. While the kink DS
transition is continuous and shows regular PC class universality, the spin
damage exhibits a discontinuous phase transition with compact clusters and PC
like dynamical scaling (), () and () exponents whereas
the static exponents determined by FSS are consistent with that of the spins of
the NEKIM model at the PC transition point. The generalised hyper-scaling law
is satisfied.Comment: 11 pages, 20 figures embedded in the text, minor changes in the text,
a new table and new references are adde
One-dimensional Nonequilibrium Kinetic Ising Models with local spin-symmetry breaking: N-component branching annihilation transition at zero branching rate
The effects of locally broken spin symmetry are investigated in one
dimensional nonequilibrium kinetic Ising systems via computer simulations and
cluster mean field calculations. Besides a line of directed percolation
transitions, a line of transitions belonging to N-component, two-offspring
branching annihilating random-walk class (N-BARW2) is revealed in the phase
diagram at zero branching rate. In this way a spin model for N-BARW2
transitions is proposed for the first time.Comment: 6 pages, 5 figures included, 2 new tables added, to appear in PR
Critical phenomena of nonequilibrium dynamical systems with two absorbing states
We study nonequilibrium dynamical models with two absorbing states:
interacting monomer-dimer models, probabilistic cellular automata models,
nonequilibrium kinetic Ising models. These models exhibit a continuous phase
transition from an active phase into an absorbing phase which belongs to the
universality class of the models with the parity conservation. However, when we
break the symmetry between the absorbing states by introducing a
symmetry-breaking field, Monte Carlo simulations show that the system goes back
to the conventional directed percolation universality class. In terms of domain
wall language, the parity conservation is not affected by the presence of the
symmetry-breaking field. So the symmetry between the absorbing states rather
than the conservation laws plays an essential role in determining the
universality class. We also perform Monte Carlo simulations for the various
interface dynamics between different absorbing states, which yield new
universal dynamic exponents. With the symmetry-breaking field, the interface
moves, in average, with a constant velocity in the direction of the unpreferred
absorbing state and the dynamic scaling exponents apparently assume trivial
values. However, we find that the hyperscaling relation for the directed
percolation universality class is restored if one focuses on the dynamics of
the interface on the side of the preferred absorbing state only.Comment: 11 pages, 21 figures, Revtex, submitted to Phy. Rev.
Genetic Dominant Variants in STUB1, Segregating in Families with SCA48, Display In Vitro Functional Impairments Indistinctive from Recessive Variants Associated with SCAR16.
Variants in STUB1 cause both autosomal recessive (SCAR16) and dominant (SCA48) spinocerebellar ataxia. Reports from 18 STUB1 variants causing SCA48 show that the clinical picture includes later-onset ataxia with a cerebellar cognitive affective syndrome and varying clinical overlap with SCAR16. However, little is known about the molecular properties of dominant STUB1 variants. Here, we describe three SCA48 families with novel, dominantly inherited STUB1 variants (p.Arg51_Ile53delinsProAla, p.Lys143_Trp147del, and p.Gly249Val). All the patients developed symptoms from 30 years of age or later, all had cerebellar atrophy, and 4 had cognitive/psychiatric phenotypes. Investigation of the structural and functional consequences of the recombinant C-terminus of HSC70-interacting protein (CHIP) variants was performed in vitro using ubiquitin ligase activity assay, circular dichroism assay and native polyacrylamide gel electrophoresis. These studies revealed that dominantly and recessively inherited STUB1 variants showed similar biochemical defects, including impaired ubiquitin ligase activity and altered oligomerization properties of the CHIP. Our findings expand the molecular understanding of SCA48 but also mean that assumptions concerning unaffected carriers of recessive STUB1 variants in SCAR16 families must be re-evaluated. More investigations are needed to verify the disease status of SCAR16 heterozygotes and elucidate the molecular relationship between SCA48 and SCAR16 diseases
Mean-Field Analysis and Monte Carlo Study of an Interacting Two-Species Catalytic Surface Reaction Model
We study the phase diagram and critical behavior of an interacting one
dimensional two species monomer-monomer catalytic surface reaction model with a
reactive phase as well as two equivalent adsorbing phase where one of the
species saturates the system. A mean field analysis including correlations up
to triplets of sites fails to reproduce the phase diagram found by Monte Carlo
simulations. The three phases coexist at a bicritical point whose critical
behavior is described by the even branching annihilating random walk
universality class. This work confirms the hypothesis that the conservation
modulo 2 of the domain walls under the dynamics at the bicritical point is the
essential feature in producing critical behavior different from directed
percolation. The interfacial fluctuations show the same universal behavior seen
at the bicritical point in a three-species model, supporting the conjecture
that these fluctuations are a new universal characteristic of the model.Comment: 11 pages using RevTeX, plus 4 Postscript figures. Uses psfig.st
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