Field Theory of Critical Behavior in Driven Diffusive Systems with Quenched Disorder

We present a field-theoretic renormalization-group study for the critical behavior of a uniformly driven diffusive system with quenched disorder, which is modeled by different kinds of potential barriers between sites. Due to their symmetry properties, these different realizations of the random potential barriers lead to three different models for the phase transition to transverse order and to one model for the phase transition to longitudinal order all belonging to distinct universality classes. In these four models, which have different upper critical dimensions d _c, we find the critical scaling behavior of the vertex functions in spatial dimensions d<d _c. The deviation from purely diffusive behavior is characterized by the anomaly exponent , which we calculate at first and second order, respectively, in =d _c–d. In each model turns out to be positive, which means superdiffusive spread of density fluctuations in the driving force direction.     

Lattice Boltzmann simulation of a binary fluid with different phase viscosities and its application to fingering in two dimensions

A thermodynamically consistent lattice Boltzmann scheme for simulating the flow of a binary fluid is extended to allow the fluid components to have different viscosities. The approach is tested for the shear and Poiseuille flow of layered immiscible fluids and for the dispersion relation and the damping of a capillary wave. We then consider the fingering that results when a fluid is displaced by a less viscous fluid in a two-dimensional channel. The finger widths obtained match the results of Reinelt and Saffman [#!Reinelt85!#], but differ somewhat from those of Halpern and Gaver [#!Halpern94!#] for capillary numbers above 2. A limiting finger width close to 1/2 is obtained for high capillary numbers and high viscosity ratios. Received 25 May 1999 and Received in final form 19 November 1999     

一类具有修正Leslie-Gower功能性反应的扩散捕食系统的持久性与绝灭性

本文研究了一类具有修正Leslie-Gower功能性反应的捕食者-食饵模型.利用比较原理以及一些引理的方法,获得了保证食饵绝灭的充分条件以及保证捕食者和食饵永久持续生存的充分必要条件,所得结论完善和补充了前人的结果.     

Structural stability for the Brinkman equations of flow in double diffusive convection

This paper continues the investigation of structural stability for the Brinkman equations modeling the double diffusive convection for flow in a porous medium. It supplements earlier results of Straughan and Hutter [B. Straughan, K. Hutter, A priori bounds and structural stability for double diffusive convection incorporating the Soret effect, Proc. R. Soc. Lond. Ser. A 455 (1999) 767-777].     

忆阻器及其阻变机理研究进展

忆阻器是除电阻、电容、电感之外的第四种电路元件,在信息存储、逻辑运算和神经网络等研究领域具有重要的应用前景.本文综述了忆阻器以及忆阻器材料的研究进展,主要介绍了忆阻器的内涵与特征、阻变机理、材料类型以及应用前景,指出了目前忆阻器研究中需要关注的主要问题,并对以后的发展趋势进行了展望.     

2004～2009年深圳空气质量及其污染物扩散条件分析

利用2004～2009年深圳市空气监测网络的监测结果,对深圳地区近6年空气质量及污染物浓度进行了统计分析,并利用2005～2008年深圳常规地面气象观测资料对污染物扩散条件及其成因机理进行了研究。同时对2008年12月15日到2008年12月20日深圳空气污染系数连续偏高的现象进行了特征分析。分析研究表明:深圳近6年首要污染物为可吸入颗粒物,次要污染物为NO2;南山、宝安空气质量较其它区域差;深圳大气污染物的扩散与温度、降水量呈正相关,与气压、静风频次呈显著的负相关,而与日照相关性相对较小;2004～2009年深圳空气质量状况总的来说良好,环境空气污染指数(API)值呈下降趋势。     

用Weiss分子场理论对有外电场时铁电体系相变特征的研究

Weiss分子场理论(WMFT)对晶体中顺磁-铁磁和顺电-铁电相变特征的定量描述是相当成功的. 由于是平均场理论,又可作为初步分析结构无序体系和复杂组分体系相变行为的理论依据. 但是迄今为止,并没有对有外场时WMFT的相变特征进行详细研究. 而对铁电体系,仅仅对分子取向为两个状态时WMFT的相变特征进行了研究. 另外,虽然铁磁与铁电体系的WMFT描述极为相似,但是由于两种体系中微观磁化和极化的单元不同,导致相应的数学描述与结果也有所不同. 本文首先对外电场中分子取向包含任意状态的铁电体系的WMFT相变特征, 包括自发极化、内能和比热以及静态极化率随温度变化进行严格推导, 然后对相变特征随外电场的演变进行了研究.结果表明: 1)无外场时,体系发生二级顺电-铁电相变,且随状态数的增加,相变温度减小, 这是与铁磁体系不同的地方,同时单分子的平均极化强度减小,而内能、比热和极化率增大; 2)外场的存在,使得体系原有的二级相变转化为弥散相变,且外场越强,弥散温区越大. 上述结果对深入研究铁电体系的相变,特别是弥散相变无疑是有益的.     

Asymptotic analysis of unsteady neutron transport equation

Consider the unsteady neutron transport equation with diffusive boundary condition in 2D convex domains. We establish the diffusive limit with both initial layer and boundary layer corrections. The major difficulty is the lack of regularity in the boundary layer with geometric correction. Our contribution relies on a detailed analysis of asymptotic expansions inspired by the compatibility condition and an intricate L^2m ? L^∞ framework, which yields stronger remainder estimates.     

Influence of different mixing ratios of Mg and B powder on structural and superconducting properties in MgB2

We fabricated MgB₂ bulks by an in situ Mg diffusive reaction method from compacted B and compacted mixtures of Mg and B respectively. All samples were sintered at 1100 °C for 2 h. MgO impurity phase, density, and critical current density (J_c) were found to be dependent of the starting amount of mixing Mg powder. We also found that the MgO formation in MgB₂ matrix was not mainly attributed to the starting amount of additional Mg powder for Mg diffusive reaction. This indicates that MgO presented in the starting Mg powder is hardly diffused into compacted B.     

Interfacial growth in driven Ginzburg-Landau models: Short and long-time dynamics

Interfacial growth in driven systems is studied from the initial stage to the longtime regime. Numerical integrations of a Ginzburg-Landan type equation with a new flux term introduced by an external field are presented. The interfacial instabilities are induced by the external field. From the numerical results, we obtain the dispersion relation for the initial growth. During the intermediate temporal regime, fingers of a characteristic triangular shape could grow. Depending on the boundary conditions, the final state corresponds to strips, multifinger states, or a one-finger state. The results for the initial growth are interpreted by means of surface-driven and Mullins-Sekerka instabilities. The shape of the one-finger state is explained in terms of the characteristic length introduced by the external field.