Mean-field solution of the parity-conserving kinetic phase transition in one dimension

A two-offspring branching annihilating random walk model, with finite reaction rates, is studied in one-dimension. The model exhibits a transition from an active to an absorbing phase, expected to belong to the $DP2$ universality class embracing systems that possess two symmetric absorbing states, which in one-dimensional systems, is in many cases equivalent to parity conservation. The phase transition is studied analytically through a mean-field like modification of the so-called {\it parity interval method}. The original method of parity intervals allows for an exact analysis of the diffusion-controlled limit of infinite reaction rate, where there is no active phase and hence no phase transition. For finite rates, we obtain a surprisingly good description of the transition which compares favorably with the outcome of Monte Carlo simulations. This provides one of the first analytical attempts to deal with the broadly studied DP2 universality class.Comment: 4 Figures. 9 Pages. revtex4. Some comments have been improve

Large-Scale Simulations of Diffusion-Limited n-Species Annihilation

We present results from computer simulations for diffusion-limited $n$-species annihilation, $A_i+A_j\to0$ $(i,j=1,2,...,n;i\neq j)$, on the line, for lattices of up to $2^{28}$ sites, and where the process proceeds to completion (no further reactions possible), involving up to $10^{15}$ time steps. These enormous simulations are made possible by the renormalized reaction-cell method (RRC). Our results suggest that the concentration decay exponent for $n$ species is \a(n)=(n-1)/2n instead of $(2n-3)/(4n-4)$, as previously believed, and are in agreement with recent theoretical arguments \cite{tauber}. We also propose a scaling relation for $\Delta$, the correction-to-scaling exponent for the concentration decay; c(t)\sim t^{-\a}(A+Bt^{-\Delta})

Diffusion-Limited Coalescence with Finite Reaction Rates in One Dimension

We study the diffusion-limited process $A+A\to A$ in one dimension, with finite reaction rates. We develop an approximation scheme based on the method of Inter-Particle Distribution Functions (IPDF), which was formerly used for the exact solution of the same process with infinite reaction rate. The approximation becomes exact in the very early time regime (or the reaction-controlled limit) and in the long time (diffusion-controlled) asymptotic limit. For the intermediate time regime, we obtain a simple interpolative behavior between these two limits. We also study the coalescence process (with finite reaction rates) with the back reaction $A\to A+A$, and in the presence of particle input. In each of these cases the system reaches a non-trivial steady state with a finite concentration of particles. Theoretical predictions for the concentration time dependence and for the IPDF are compared to computer simulations. P. A. C. S. Numbers: 82.20.Mj 02.50.+s 05.40.+j 05.70.LnComment: 13 pages (and 4 figures), plain TeX, SISSA-94-0

Universality Class of Two-Offspring Branching Annihilating Random Walks

We analyze a two-offspring Branching Annihilating Random Walk ($n=2$ BAW) model, with finite annihilation rate. The finite annihilation rate allows for a dynamical phase transition between a vacuum, absorbing state and a non-empty, active steady state. We find numerically that this transition belongs to the same universality class as BAW's with an even number of offspring, $n\geq 4$, and that of other models whose dynamic rules conserve the parity of the particles locally. The simplicity of the model is exploited in computer simulations to obtain various critical exponents with a high level of accuracy.Comment: 10 pages, tex, 4 figures uuencoded, also available upon reques

Two-Species Annihilation with Drift: A Model with Continuous Concentration-Decay Exponents

We propose a model for diffusion-limited annihilation of two species, $A+B\to A$ or $B$, where the motion of the particles is subject to a drift. For equal initial concentrations of the two species, the density follows a power-law decay for large times. However, the decay exponent varies continuously as a function of the probability of which particle, the hopping one or the target, survives in the reaction. These results suggest that diffusion-limited reactions subject to drift do not fall into a limited number of universality classes.Comment: 10 pages, tex, 3 figures, also available upon reques

Conversion of wood flour/SiO2/phenolic composite to porous SiC ceramic containing SiC whiskers

A novel wood flour/SiO2/phenolic composite was chosen to be converted into porous SiC ceramic containing SiC whiskers via carbothermal reduction. At 1550°C the composite is converted into porous SiC ceramic with pore diameters of 10~40μm, and consisting of β-SiC located at the position of former wood cell walls. β-SiC wire-like whiskers of less than 50 nm in diameter and several tens to over 100 μm in length form within the pores. The surface of the resulting ceramic is coated with β-SiC necklace-like whiskers with diameters of 1~2μm

Study on the Physiological, Cellular, and Morphological Aspects of the Postharvest Development of Cut Lily Flowers

It is of great practical significance to study the development process of cut lily for regulating flowering and preservation. In this study, the developmental process of lily cut flower was explored from cellular, morphological, and physiological aspects. From a morphological aspect, the tepal edge grows faster than the midrib. The midrib groove of the flowering stage is wider than that of bud stage. The fast-growing edge of the petals results in the midrib bending outward. Moreover, the rapid growth of the stamens and stigmas also contributes to bud cracking. From the cellular aspect, in the bud stage there were more wrinkles in the outer epidermal cell wall of the tepal than those in the inner epidermal cell wall, indicating that asymmetric structural differences exist from the beginning of lily development. From a physiological aspect, from the bud cracking stage to the senescence stage, a variety of substances in the tepal cells gradually decreased, including total nitrogen, total phosphorus, total potassium, total calcium, starch, soluble sugar, and soluble protein, but not malondialdehyde. These results indicate that the asymmetric growth caused by this structural difference is responsible for flowering. The wrinkles in the cell wall can be regarded as indicators of senescent cells and are caused by the degradation of the cell wall and the loss of intracellular turgor pressure. The differences in the epidermal cells between the inner and outer tepal indicated ultrastructural changes in the tepal cells. The bud and flowering stages are maintained by the tepals acting as a sink. After flowering, the tepals gradually change from a sink to a source organ. Senescence of the cut lily flowers was caused by the decomposition of intracellular compounds in the tepals and the remobilization of nutrients from the tepals to the developing organs

Geographic Named Entity Recognition by Employing Natural Language Processing and an Improved BERT Model

Toponym recognition, or the challenge of detecting place names that have a similar referent, is involved in a number of activities connected to geographical information retrieval and geographical information sciences. This research focuses on recognizing Chinese toponyms from social media communications. While broad named entity recognition methods are frequently used to locate places, their accuracy is hampered by the many linguistic abnormalities seen in social media posts, such as informal sentence constructions, name abbreviations, and misspellings. In this study, we describe a Chinese toponym identification model based on a hybrid neural network that was created with these linguistic inconsistencies in mind. Our method adds a number of improvements to a standard bidirectional recurrent neural network model to help with location detection in social media messages. We demonstrate the results of a wide-ranging evaluation of the performance of different supervised machine learning methods, which have the natural advantage of avoiding human design features. A set of controlled experiments with four test datasets (one constructed and three public datasets) demonstrates the performance of supervised machine learning that can achieve good results on the task, significantly outperforming seven baseline models