Collapse transition and cyclomatic number distribution of directed lattice animals

We computed the specific heat of directed lattice animals using a Monte Carlo method for various animals sizesN, withN up to 100 on the square andN up to 125 on the simple cubic lattices. The specific heat as a function of the temperature for various animal sizes exhibits peaks which seem to approach a collapse transition temperature monotonically from below with increasingN. A least square fit together with finite-size scaling then gives both the transition temperature T_c and the specific heat exponent for these two lattices. The cyclomatic number distributions for the number of animals with fixed animal sizeN are also calculated and these seem to obey a scaling law for largeN. On leave from Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, China.     

简立方格点自避行走所模拟的高分子链吸附和塌缩

采用复合Markov链法 ,针对简立方格点上的自避行走模型 ,研究了同时具有对壁的吸附作用ε1 和最近邻相互作用ε2 的高分子链的热力学性质 .相互作用能量参数ε1 和ε2 分别联系于参数α和 β .令链长N=10 0 ,由这种MonteCarlo方法可得出链的自由能FN(α ,β) ,热容2 FN(α ,β) /2 α和2 FN(α ,β) /2 β ,吸附点平均数〈m〉/N ,最近邻相互作用对平均数〈n〉/N和均方末端距对壁的垂直分量RZ2 .除已有方法由热容数据可绘出α β相图外 ,建议由结构参数〈m〉/N ,〈n〉/N和RZ2 绘制相图 ,并发现二者基本一致 .所得相图表明 ,存在 4个相区 ,分别是解吸 膨胀相 (DE) ,吸附 膨胀相 (AE) ,解吸 紧密相 (DC)和吸附 紧密相 (AC) .在伸展区和塌缩区 ,随着吸附作用的增强 ,会出现吸附相转变 .在解吸区和吸附区 ,随着自相互作用的增大 ,也将出现塌缩相转变 .相图出现了两个三相点 ,即AE AC DC三相点和AE DE DC三相点     

重庆小南海地震崩滑体的基本特征及形成机制研究

通过对重庆小南海地震崩滑堆积体进行野外地质调查和工程地质勘察等相关工作,阐述了该崩滑堆积体的基本特征和形成机制,认为其形成过程经历了“风化剥蚀→震荡抛射→崩滑堆积→堵江成湖”4个阶段,其岩体破坏形式为高度破裂或严重高度破裂状态,其岩体破坏过程以崩塌为主,滑动为辅。研究发现,小南海地震崩滑堆积体的最终形成是受地震构造运动及应力、岩体构造、地形地貌及地震波作用等因素综合作用的结果：(1)该区NE向黔江逆滑（右行）断裂与NNW向仰头山逆滑（左行）断层形成的“X”型地震构造组合及轴向呈NWW向的构造压应力使小南海断块内部发生张滑（左行）破裂而导致61/4级地震发生;(2)该区呈“X”形展布的3组主要构造节理是崩滑体发育的物质基础,大、小垮岩在地震波作用下最终发生了向山体临空面（约145°~155°方向）的各自崩滑;(3)从崩滑堆积体中发现的灰岩块石证明崩滑体原始地层中曾含二叠系栖霞组和茅口组灰岩,这为恢复崩滑前山体地形提供了直接证据;(4)崩滑体中堆积岩块直径分布区域沿约150°方向自WN到ES依次递减,间接证明了地震时崩滑体抛洒方向为约150°方向,且大、小垮岩分别形成堆积区,交叉堆积部分较少。     

激光等离子体中的强朗缪尔湍动谱分析

通过数值计算完全的萨哈罗夫方程,得到了朗缪尔波能量密度谱图。从一系列的谱图中可以看出,波的塌缩过程是沿着能量密度谱由小波数区域向大波数区域转移,朗缪尔波在塌缩过程中出现成丝现象。通过对获得的朗缪尔波平均能量密度谱进行拟合,得到了朗缪尔波能量密度谱函数。     

Collapse transitions of a supersized neutral chain due to irreversibly adsorbed small colloidal particles

 We performed Monte Carlo simulations to study the destabilization processes of large neutral and flexible polymer chains due to irreversibly adsorbed colloidal particles attached to the chains like beads on a necklace. The particles are modeled as charged spherical units which interact with each other via repulsive electrostatic and attractive van der Waals (vdW) potentials. The usual Monte Carlo search procedure is extended and carefully checked to completely sample the chain conformational space and achieve dense conformations in the limit of both strong attractive and repulsive interaction potentials. Configurational properties, such as the radius of gyration, the end-to-end length, and the Kuhn length, are calculated as a function of the intensity of the vdW interactions and ionic strength values. It is observed that chains exhibit a new range of possible conformations compared to the classical random walk and self avoiding walk chains or polyelectrolytes. In the limit of low salt concentration, by gradually increasing vdW interactions, chains undergo a cascade of transitions from extended structures to dumbbells, from dumbbells to pearl necklaces, and from pearl necklaces to collapsed coils. Because of strong competition between the vdW and electrostatic forces, the distance along the chain between the interacting particles, and the sampling limitations, these transitions are found to sample metastable domains and to depend on the initial conformations. To gain insight into the spatial organization of the collapsed conformations, the pair correlation functions of both monomers and particles are calculated. It is shown that collapsed conformations which are the result of strong particle–particle interactions exhibit two distinct parts: a hard core mainly composed of particles and a surrounding polymeric shell composed of loops and tails. Possible effects of such a collapsed transition on the kinetics of flocculation of a mixture containing large flexible chains and small adsorbing colloidal particles are discussed. Received: 26 July 1999 Accepted in revised form: 9 November 1999     

含高阶项Trapped离子振动态的崩塌-回复特性

解析分析了“捕陷”离子在驻波光场作用下的动力学。离子的量子平均能量随时间的变化呈现崩塌 -回复的特征 ,表明这个系统的振动态具有压缩效应。哈密顿量中的高阶项使得离子平均能量呈现不规则的崩塌 -回复 ,严重抑制离子的振动态的相干性。     

Gravitational Collapse of Null Strange Quark Fluid and Cosmic Censorship

We study the gravitational collapse of the general spherically symmetric null strange quark fluid having the equation of state, p = ( – 4B)/n, where B is the bag constant. It is an interesting feature that the initial data set giving rise to a naked singularity in the Vaidya collapse of null fluid gets covered due to the presence of the strange quark matter component. Its implication for the Cosmic Censorship Conjecture is discussed.     

Numerical simulation of liquefied fuel spills: I. Instantaneous release into a confined area

The shallow-water equations in radial symmetry are solved numerically to simulate the collapse of a cylindrical liquid column into an area surrounded by a concentric dike. The following three subcases of this problem are considered: a liquid column collapsing onto a layer of the same liquid, a liquid column collapsing onto a solid surface, and a column of lighter liquid collapsing onto a heavier liquid (i.e. liquefied natural gas (LNG) spilled onto water). The results for the three categories are compared and the differences and similarities between them are analysed.     

Spontaneous photon emission from a non-relativistic free charged particle in collapse models: A case study

We study the photon emission rate of a non-relativistic charged particle interacting with an external classical noise through its position. Both the particle and the electromagnetic field are quantized. Under only the dipole approximation, the equations of motion can be solved exactly for a free particle, or a particle bounded by an harmonic potential. The physical quantity we will be interested in is the spectrum of the radiation emitted by the particle, due to the interaction with the noise. We will highlight several properties of the spectrum and clarify some issues appearing in the literature, regarding the exact mathematical formula of a spectrum for a free particle.     

On collapse of wave maps

We derive the universal collapse law of degree 1 equivariant wave maps (solutions of the sigma model) from the 2+1 Minkowski space-time, to the 2-sphere. To this end, we introduce a nonlinear transformation from original variables to blowup ones. Our formal derivations are confirmed by numerical simulations.