26 research outputs found
The phase transition of triplet reaction-diffusion models
The phase transitions classes of reaction-diffusion systems with
multi-particle reactions is an open challenging problem. Large scale
simulations are applied for the 3A -> 4A, 3A -> 2A and the 3A -> 4A, 3A->0
triplet reaction models with site occupation restriction in one dimension.
Static and dynamic mean-field scaling is observed with signs of logarithmic
corrections suggesting d_c=1 upper critical dimension for this family of
models.Comment: 4 pages, 4 figures, updated version prior publication in PR
One-dimensional spin-anisotropic kinetic Ising model subject to quenched disorder
Large-scale Monte Carlo simulations are used to explore the effect of
quenched disorder on one dimensional, non-equilibrium kinetic Ising models with
locally broken spin symmetry, at zero temperature (the symmetry is broken
through spin-flip rates that differ for '+' and '-' spins). The model is found
to exhibit a continuous phase transition to an absorbing state. The associated
critical behavior is studied at zero branching rate of kinks, through analysis
spreading of '+' and '-' spins and, of the kink density. Impurities exert a
strong effect on the critical behavior only for a particular choice of
parameters, corresponding to the strongly spin-anisotropic kinetic Ising model
introduced by Majumdar et al. Typically, disorder effects become evident for
impurity strengths such that diffusion is nearly blocked. In this regime, the
critical behavior is similar to that arising, for example, in the
one-dimensional diluted contact process, with Griffiths-like behavior for the
kink density. We find variable cluster exponents, which obey a hyperscaling
relation, and are similar to those reported by Cafiero et al. We also show that
the isotropic two-component AB -> 0 model is insensitive to reaction-disorder,
and that only logarithmic corrections arise, induced by strong disorder in the
diffusion rate.Comment: 10 pages, 13 figures. Final, accepted form in PRE, including a new
table summarizing the molde
Critical wetting of a class of nonequilibrium interfaces: A mean-field picture
A self-consistent mean-field method is used to study critical wetting
transitions under nonequilibrium conditions by analyzing Kardar-Parisi-Zhang
(KPZ) interfaces in the presence of a bounding substrate. In the case of
positive KPZ nonlinearity a single (Gaussian) regime is found. On the contrary,
interfaces corresponding to negative nonlinearities lead to three different
regimes of critical behavior for the surface order-parameter: (i) a trivial
Gaussian regime, (ii) a weak-fluctuation regime with a trivially located
critical point and nontrivial exponents, and (iii) a highly non-trivial
strong-fluctuation regime, for which we provide a full solution by finding the
zeros of parabolic-cylinder functions. These analytical results are also
verified by solving numerically the self-consistent equation in each case.
Analogies with and differences from equilibrium critical wetting as well as
nonequilibrium complete wetting are also discussed.Comment: 11 pages, 2 figure
Anisotropic model of kinetic roughening:he strong-coupling regime
We study the strong coupling (SC) limit of the anisotropic Kardar-Parisi-Zhang (KPZ) model. A systematic mapping of the continuum model to its lattice equivalent shows that in the SC limit, anisotropic perturbations destroy all spatial correlations but retain a temporal scaling which shows a remarkable crossover along one of the two spatial directions, the choice of direction depending on the relative strength of anisotropicity. The results agree with exact numerics and are expected to settle the long-standing SC problem of a KPZ model in the infinite range limit. © 2007 The American Physical Society
Reaction-diffusion processes in zero transverse dimensions as toy models for high-energy QCD
We examine numerically different zero-dimensional reaction-diffusion
processes as candidate toy models for high-energy QCD evolution. Of the models
examined -- Reggeon Field Theory, Directed Percolation and Reversible Processes
-- only the latter shows the behaviour commonly expected, namely an increase of
the scattering amplitude with increasing rapidity. Further, we find that
increasing recombination terms, quantum loops and the heuristic inclusion of a
running of the couplings, generically slow down the evolution.Comment: 17 pages, 7 figure
Mean-field analysis of the q-voter model on networks
We present a detailed investigation of the behavior of the nonlinear q-voter
model for opinion dynamics. At the mean-field level we derive analytically, for
any value of the number q of agents involved in the elementary update, the
phase diagram, the exit probability and the consensus time at the transition
point. The mean-field formalism is extended to the case that the interaction
pattern is given by generic heterogeneous networks. We finally discuss the case
of random regular networks and compare analytical results with simulations.Comment: 20 pages, 10 figure
Womenâs health and well-being in low-income formal and informal neighbourhoods on the eve of the armed conflict in Aleppo
Objectives
To explore how married women living in low-income formal and informal neighbourhoods in Aleppo, Syria, perceived the effects of neighbourhood on their health and well-being, and the relevance of these findings to future urban rebuilding policies post-conflict.
Methods
Semi-structured interviews were undertaken with eighteen married women living in informal or socioeconomically disadvantaged formal neighbourhoods in Aleppo in 2011, a year before the armed conflict caused massive destruction in all these neighbourhoods.
Results
Our findings suggest that the experience of neighbourhood social characteristics is even more critical to womenâs sense of well-being than environmental conditions and physical infrastructure. Most prominent was the positive influence of social support on well-being.
Conclusions
The significance of this study lies, first, in its timing, before the widespread destruction of both formal and informal neighbourhoods in Aleppo and, second, and in its indication of the views of women who lived in marginalised communities on what neighbourhood characteristics mattered to them. Further research post-conflict needs to explore how decisions on urban rebuilding are made and their likely influence on health and well-being
Nonequilibrium wetting
When a nonequilibrium growing interface in the presence of a wall is
considered a nonequilibrium wetting transition may take place. This transition
can be studied trough Langevin equations or discrete growth models. In the
first case, the Kardar-Parisi-Zhang equation, which defines a very robust
universality class for nonequilibrium moving interfaces, with a soft-wall
potential is considered. While in the second, microscopic models, in the
corresponding universality class, with evaporation and deposition of particles
in the presence of hard-wall are studied. Equilibrium wetting is related to a
particular case of the problem, it corresponds to the Edwards-Wilkinson
equation with a potential in the continuum approach or to the fulfillment of
detailed balance in the microscopic models. In this review we present the
analytical and numerical methods used to investigate the problem and the very
rich behavior that is observed with them.Comment: Review, 36 pages, 16 figure
Applications of Field-Theoretic Renormalization Group Methods to Reaction-Diffusion Problems
We review the application of field-theoretic renormalization group (RG)
methods to the study of fluctuations in reaction-diffusion problems. We first
investigate the physical origin of universality in these systems, before
comparing RG methods to other available analytic techniques, including exact
solutions and Smoluchowski-type approximations. Starting from the microscopic
reaction-diffusion master equation, we then pedagogically detail the mapping to
a field theory for the single-species reaction k A -> l A (l < k). We employ
this particularly simple but non-trivial system to introduce the
field-theoretic RG tools, including the diagrammatic perturbation expansion,
renormalization, and Callan-Symanzik RG flow equation. We demonstrate how these
techniques permit the calculation of universal quantities such as density decay
exponents and amplitudes via perturbative eps = d_c - d expansions with respect
to the upper critical dimension d_c. With these basics established, we then
provide an overview of more sophisticated applications to multiple species
reactions, disorder effects, L'evy flights, persistence problems, and the
influence of spatial boundaries. We also analyze field-theoretic approaches to
nonequilibrium phase transitions separating active from absorbing states. We
focus particularly on the generic directed percolation universality class, as
well as on the most prominent exception to this class: even-offspring branching
and annihilating random walks. Finally, we summarize the state of the field and
present our perspective on outstanding problems for the future.Comment: 10 figures include