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

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

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

The phonology of modern South Arabian Harsusi of Oman

Harsusi is one of the five Modern South Arabian (MSA) languages spoken in the Sultanate of Oman. It is one of the least studied and known about languages in this group of Semitic languages. It is considered as a shifting language by the Ethnologue (Simons, G. F. & Charles, D. F., 2018) with around 6000 speakers. Being spoken in the desert, in the middle of Oman, Harsusi enjoyed a relative isolation for some time from the other surrounding languages including Arabic; however, after 1970 Harsusi became into direct contact with Arabic. This direct contact, in addition to not being systematically taught and learned in official contexts, pose threats at the situation of Harsusi in Oman. Moreover, there is a scarcity of thorough linguistic studies on Harsusi and such studies can help in both preserving Harsusi, and understanding the features of the (MSA) group as a whole. This report will provide an overview of the (MSA) language group. It will investigate the phonological structure of Harsusi in detail and provide a descriptive analysis of it. The main goal of this report is to explore the distribution of the sounds in Harsusi. It will explore the phonemic realizations in addition to the allophonic variations and the rules governing their occurrence in different environments. Moreover, it will look at the syllable structure and the stress patterns in Harsusi. Understanding the phonological structure of Harsusi is very important for any future studies on the morphology, syntax or semantics of HarsusiLinguistic

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

Simplified Langevin approach to the Peyrard-Bishop-Dauxois model of DNA

A simple Langevin approach is used to study stationary properties of the Peyrard-Bishop-Dauxois model for DNA, allowing known properties to be recovered in an easy way. Results are shown for the denaturation transition in homogeneous samples, for which some implications, so far overlooked, of an analogy with equilibrium wetting transitions are highlighted. This analogy implies that the order-parameter, asymptotically, exhibits a second order transition even if it may be very abrupt for non-zero values of the stiffness parameter. Not surprisingly, we also find that for heterogeneous DNA, within this model the largest bubbles in the pre-melting stage appear in adenine-thymine rich regions, while we suggest the possibility of some sort of not strictly local effects owing to the merging of bubbles.Comment: 4 pages, 2 figure

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

When can species abundance data reveal non-neutrality?

Species abundance distributions (SAD) are probably ecology's most well-known empirical pattern, and over the last decades many models have been proposed to explain their shape. There is no consensus over which model is correct, because the degree to which different processes can be discerned from SAD patterns has not yet been rigorously quantified. We present a power calculation to quantify our ability to detect deviations from neutrality using species abundance data. We study non-neutral stochastic community models, and show that the presence of non-neutral processes is detectable if sample size is large enough and/or the amplitude of the effect is strong enough. Our framework can be used for any candidate community model that can be simulated on a computer, and determines both the sampling effort required to distinguish between alternative processes, and a range for the strength of non-neutral processes in communities whose patterns are statistically consistent with neutral theory. We find that even data sets of the scale of the 50 Ha forest plot on Barro Colorado Island, Panama, are unlikely to be large enough to detect deviations from neutrality caused by competitive interactions alone, though the presence of multiple non-neutral processes with contrasting effects on abundance distributions may be detectable