Monte Carlo重整化群方法计算逾渗模型的临界指数

本文运用Ｍｏｎｔｅ Ｃａｒｌｏ重整化群方法计算了点逾渗中次近邻正方格子的导通阈值和临界指数，得出与最近领正方格子属于同一普适类的结论。     

粒径均匀散体导热系数的分形描述

本文以分形理论为工具,采用填充率、散体颗粒直径等宏观易等测参数较准确地描述了颗粒散体的几何结构;运用导热与逾渗的类比,建立了均匀散体导热系数的逾渗模型,模型的预测值与实验测量结果基本一致。     

裂隙多孔介质双重逾渗模型的算法实现

简要介绍基于孔隙逾渗和裂隙逾渗叠加的双重逾渗模型,阐述模型的原理、算法及其实现过程.初步研究模型的分形特性,认为分形维数D是能够衡量模型连通性的重要参数.最后探讨模型的蒙特卡洛数值计算方法,兼顾计算精度与计算耗时,提出可操作的计算规模.     

炭黑橡胶复合材料导热逾渗行为

研究了导电炭黑40b2填充天然橡胶复合材料的导热性能和力学性能随炭黑体积分数的变化规律,并采用扫描电子显微镜观察了炭黑橡胶体系内部的炭黑分布状况.结果表明,导热性能随炭黑体积分数的变化规律存在类似于导电逾渗现象的导热逾渗现象,逾渗阈值在8.3%～13.63%之间.在逾渗阈值之后,复合材料的拉伸强度下降.炭黑橡胶复合材料...     

相依网络的条件依赖群逾渗

相依网络鲁棒性研究多集中于满足无反馈条件的一对一依赖,但现实网络节点往往依赖于多节点构成的依赖群,即使群内部分节点失效也不会导致依赖节点失效.针对此现象提出了一种相依网络的条件依赖群逾渗模型,该模型允许依赖群内节点失效比例不超过容忍度γ时,依赖节点仍可正常工作.通过理论分析给出了基于生成函数方法的模型巨分量方程,仿真结果表明方程理论解与相依网络模拟逾渗值相吻合,增大γ值和依赖群规模可提高相依网络鲁棒性.本文模型有助于更好地理解现实网络逾渗现象,对如何增强相依网络鲁棒性有一定指导作用.     

化整为零:聚合物/粘土纳米复合材料的微观结构和阻隔性能

在聚合物基体中掺入少量的层状硅酸盐所制备的聚合物／粘土纳米复合材料，其阻隔性能明显地优于纯聚合物及其传统的复合材料。实验及分析结果表明，聚合物／粘土纳米复合材料的微观结构和阻隔性能主要受控于粘土剥离后的径厚比．一简单的重整化群模型被用来评估粘土几何因素（诸如径厚比、取向、剥离程度等）对聚合物／粘土纳米复合材料阻隔性能的影响，所得到的逾渗阈值及最佳粘土含量与实验结果吻合。     

工程陶瓷崩碎损伤的声发射逾渗特征

为研究工程陶瓷崩碎损伤演化过程中的逾渗行为,揭示其损伤机理,以氧化铝陶瓷为研究对象,构建了工程陶瓷崩碎损伤实验系统,建立了基于声发射的逾渗理论模型。通过对崩碎损伤过程中声发射信号分析可得:声发射计数率/能量释放率能实时反映陶瓷崩碎损伤过程中裂纹激活率的逾渗行为;基于声发射累积计数/累积能量的破坏比率反映了损伤累积对材料内部性能的影响,可从损伤积累的角度描述陶瓷崩碎损伤过程中的逾渗行为;声发射持续时间反映了陶瓷崩碎过程中逾渗行为的团簇变化规律。研究结果表明:基于声发射的逾渗理论模型可较好的描述陶瓷崩碎损伤演化过程的逾渗特征。      

非局域Lai-Das Sarma-Villain方程动力学标度性质的研究

使用动力学重整化群和直接标度分析的方法研究了非局域Lai-Das Sarma-Villain方程的动力学标度性质.动力学重整化群分析表明非局域非线性项的存在能够导致新的固定点和连续变化的动力学标度指数的产生.使用直接标度分析方法则分别得到了在弱耦合和强耦合区内的标度指数值.在弱耦合区域内得到的标度指数与动力学重整化方法得到的标度指数值能很好地吻合. 关键词： 表面生长 动力学重整化群分析 标度分析     

基于有限元法的光子并矢格林函数重整化及其在自发辐射率和能级移动研究中的应用

任意微纳结构中量子点的自发辐射率和能级移动均可用并矢格林函数表达.当源点和场点在同一位置时,格林函数的实部是发散的.为解决这一发散问题,可采用重整化格林函数方法.本文提出一种计算重整化格林函数和散射格林函数的方法.该方法利用有限元,计算点电偶极子的辐射场,将其在量子点体积内做平均得到重整化的并矢格林函数,减去均匀空间中解析的重整化格林函数,得到重整化的散射格林函数.在均匀空间情况下,本方法所得数值结果与解析解一致.将该方法应用到银纳米球系统,以解析的散射格林函数作为参考,结果表明该方法能准确处理散射格林函数的重整化问题.将该方法应用到表面等离激元纳米腔中,发现有极大的自发辐射增强和能级移动,且该结果不依赖于量子点的体积.这些研究在光与物质相互作用领域具有积极的意义.     

热标量场等离子体激元阻尼率的临界行为

在闭合时间路径的实时温度场论的框架下,导出了热重整化群方程.热重整化群方程的数值解表明热标量场的耦合常数随温度跑动.将热重整化群方程应用到对称性自发破缺的φ4理论,我们考察了具有有限动量的等离子体激元阻尼率在自发破缺对称性恢复的相变温度下的临界行为.当温度趋于临界温度时,结果表明耦合常数随温度的跑动导致有限动量的等离子体激元阻尼率逐渐减小到零,与不考虑耦合常数随温度的跑动得到的趋势相反.解决了把耦合常数看成常量导致的与临界趋缓规律的矛盾.     

纳米石墨烯片-正十八烷复合相变材料制备及热物性研究

本文分别制备了纳米石墨烯片质量分数为0%, 0.5%, 1%, 1.5%, 2%的纳米石墨烯片-正十八烷复合相变材料,并通过扫描电镜测试、红外光谱分析、差示扫描量热实验及导热分析等实验对其形貌结构及热物性进行表征和研究.实验表明本文制备的纳米石墨烯-正十八烷复合相变材料具有很好的相变稳定性;当纳米石墨烯片的质量分数达到2%时,复合相变材料的导热系数相对于纯十八烷高出了89.4%.     

重正化群与渗流理论

本文由一系列讲演组成,内容包括:临界现象与渗流,标度理论,位置空间重正化群与渗流,位置空间重正化群用于热力学相变,动量空间重正化群与高斯模型和动量空间重正化群用于S~4模型。     

Stability of the smectic quantum hall state: a quantitative study

We present an effective elastic theory which quantitatively describes the stripe phase of the two-dimensional electron gas in high Landau levels ( N>/=2). The dynamical matrix is obtained with remarkably high precision using the time-dependent Hartree-Fock approximation. A renormalization group analysis shows that at T = 0, as the partial filling factor Deltanu identical withnu- left floornu right floor moves away from 1/2, the anisotropic conducting state may undergo quantum phase transitions: stripes may get pinned along their conducting direction by disorder, or may lock into one another to form a crystal. The transitions should be reflected in the temperature dependence of the dissipative conductivity.     

Real space renormalization group theory of the percolation model

A cluster expansion renormalization group method in real space is-developed to determine the critical properties of the percolation model. In contrast to previous renormalization group approaches, this method considers the cluster size distribution (free energy) rather than the site or bond probability distribution (coupling constants) and satisfies the basic renormalization group requirement of free energy conservation. In the construction of the renormalization group transformation, new couplings are generated which alter the topological structure of the clusters and which must be introduced in the original system. Predicted values of the critical exponents appear to converge to presumed exact values as higher orders in the expansion are considered. The method can in principle be extended to different lattice structures, as well as to different dimensions of space.This paper is dedicated to Prof. Philippe Choquard.     

铝基覆铜板导热系数测试系统设计研究

为了更加准确地测量铝基覆铜板的导热系数,设计实现了一种改进型铝基覆铜板导热系数测试系统。重点阐述了测试系统的设计原理和设计思想,并对测试系统的硬件和软件设计进行了详细介绍。实验结果表明,该测试系统具有测试速度快、精度高、操作方便等特点。在实际铝基覆铜板导热系数测试中具有很高的使用价值,并为铝基覆铜板导热系数测试标准的制定提供了设备和数据上的支持。     

On the universality of geometrical and transport exponents of rigidity percolation

We develop a three-parameter position-space renormalization group method and investigate the universality of geometrical and transport exponents of rigidity (vector) percolation in two dimensions. To do this, we study site-bond percolation in which sites and bonds are randomly and independently occupied with probabilitiess andb, respectively. The global flow diagram of the renormalization transformation is obtained which shows that thegeometrical exponents of the rigid clusters in both site and bond percolation belong to the same universality class, and possibly that of random (scalar) percolation. However, if we use the same renormalization transformation to calculate the critical exponents of the elastic moduli of the system in bond and site percolation, we find them to be very different (although the corresponding values of the correlation length exponent are the same). This indicates that the critical exponent of the elastic moduli of rigidity percolation may not be universal, which is consistent with some of the recent numerical simulations.     

Experimental study on enhanced heat transfer of nanocomposite phase change materials

Nanocomposite phase change materials (NCPCMs) containing different mass fractions (nanomaterial concentration) and different copper nanoparticle (CN)/multi-walled carbon nanotubes (MWCNT) mass ratios were prepared and experimentally studied. Latent heat and thermal conductivity of the NCPCMs were studied and calculated by using the T-history method. The results revealed that addition of CN or MWCNT to the phase change material (PCM) resulted in NCPCMs with enhanced thermal conductivity and charge rates, respectively. However, when both nanoparticle materials were added to the PCM simultaneously, the resulting NCPCMs improved their thermal performance below expectations as a result of agglomeration and sedimentation between the two additives. Thus, the NCPCMs containing only CN or MWCNT showed superior thermophysical properties than the pure PCM, while the NCPCM containing both CN and MWCNT did not improve the thermal characteristic of PCM significantly.     

The tensor renormalization group for pure and disordered two-dimensional lattice systems

The tensor renormalization group (TRG) is a powerful new approach for coarse-graining classical two-dimensional (2D) lattice Hamiltonians. It uses the intuitive framework of traditional position space renormalization group methods-analyzing flows in the space of Hamiltonian parameters-but can be systematically improved to yield thermodynamic properties at much higher precision. We present initial results demonstrating that the TRG can be generalized to quenched random systems, applying it to obtain the phase diagram of a bond-diluted triangular lattice Ising ferromagnet. This opens a variety of potential future applications, most prominently spin glasses.