纳米结构链的hopping电导实空间重正化群方法

基于Miller-Abrahams理论,发展了一种重正化群方法,研究了一维纳米结构体系的hopping电导.研究表明在纳米结构体系中晶粒种类、晶粒尺寸对hopping电导有显著的调制作用,界面结构及晶格畸变等对hopping电导也有不同程度的影响.     

采用正方元胞的Ising模型实空间重正化群解

在二维正方形晶格上,将元胞取为4格点正方形,采用3种不同的规则定义块自旋状态,进行了重正化群计算,得出了更为精确的结果;解决了元胞内格点数为偶数的重正化群计算问题.     

一种推广伊辛自旋模型的实空间重正化群理论

本文提出了一种推广的伊辛自旋模型。它包括了伊辛自旋模型、Schofield和Bowers提出的混合自旋模型以及一种特殊的格点稀释伊辛自旋模型作为特例。运用实空间重正化群得到了这个推广模型的相变流图和三个非平庸不动点(一个伊辛不动点,一个三相不动点和一个一级相变不动点)。结果表明:混合自旋模型和伊辛模型属于同一普适类。证实了Schofield和Bowers通过直接对混合自旋模型临界指数的计算所做的结论。关键词：     

二维超晶格伊辛模型的实空间重正化群计算

我们在Mignal-Kadanoff重正化群近似下运用非整数标度变换来计算二维超晶格伊辛系统的临界性质。我们发现存在两个临界温度和三个相,并讨论了与各向异性参量有关的临界指数。     

畸变对hopping电导的影响：Thue Morse纳米结构模型

发展实空间重正化群方法,研究了一维非周期Thue Morse纳米结构链的hopping电导率.计算表明Thue Morse纳米结构体系的晶粒种类、晶粒尺寸对hopping电导有显著的调制作用,界面结构和晶格畸变对hopping电导也有不同程度的影响.从无序度对hopping电导的影响来看,Thue Morse纳米结构链的无序度介于Fibonacci链和周期链之间.关键词：Thue Morse纳米结构链重正化群方法hopping电导尺寸效应界面效应     

A-15化合物结构相变的重正化群分析

对A-15化合物的结构相变,讨论了空间群O_h~3的M点不稳定性的模型,提出一个O_h~3空间群的Г点不可约表示E_g和T_1(?)相耦合的模型并对它进行了重整化群的分析,用(?)-展开的方法,我们发现存在一个不平凡的稳定的固定点,它的临界指数v=0.65.     

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。     

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。     

量子多体系统的线性张量重正化群方法

文章简述了数值重正化群方法的历史发展,包括威耳逊（Wilson）的数值重正化群算法,S.R.White的密度矩阵重正化群方法,以及近 期迅速发展的处理强关联量子系统的几种张量网络态与张量网络算法.在此基础上,文章重点介绍了作者最近提出的用于研究量子多体系统热 力学性质的线性张量重正化群方法,以及该方法在一维和二维量子系统中的应用.     

准周期层状铁磁超晶格的实空间重整化群方法

本文用实空间重整化群方法讨论了准周期层状铁磁超晶格的磁自旋波,用Reduce语言推导了decimation变换公式,从而求得了局域格林函数、局域态密度和约化磁矩。发现局域态密度的带宽和约化磁矩与最近邻相互作用J₁、J₂及格点自旋s_a、s_b密切相关。     

提高重整化群精度的一个尝试

以热逾渗分析散粒体导热率时,利用重整化群方法改变粗视化程度来定量地获得导热率的变化。实践表明这只有设法提高重整化群的精度才会有较好的结果。本文以逾渗转变为例,针对b=2的相关尺度变化方式,分别对二维和三维实空间的重整化变换进行了修正,导出了相应的重整化方程。计算精度有明显提高,计算结果与实验值更接近。     

AN APPROACH TO RAYLEIGH MODEL OF EFFECTIVE CONDUCTIVITY TENSOR OF COMPOSITE

Using a new approach to Rayleigh model of composite, we obtain the complete solutions for many systems of orthorhombic., The evaluation of the effective conductivity tensor of the composite with anisotropic,structure,is also discussed in detail for the first time.     

A GROUP THEORETIC APPROACH TO THE LINEAR FREE VIBRATION ANALYSIS OF SHELLS WITH DIHEDRAL SYMMETRY

This paper deals with a group theoretic approach to the finite element analysis of linear free vibrations of shells with dihedral symmetry. Examples of such shell structures are cylindrical shells, conical shells, shells with circumferential stiffeners, corrugated shells, spherical shells, etc. The group theoretic approach is used to exploit the inherent symmetry in the problem. For vibration analysis, the group theoretic results give the correct symmetry-adapted basis for the displacement field. The stiffness matrix K and the mass matrix M are identically block diagonalized in this basis. The generalized linear eigenvalue problem of free vibration gets split into independent subproblems due to this block diagonalization. The Simo element is used in the finite element formulation of the shell equilibrium equations. Numerical results for natural frequencies and natural modes of vibration of several dihedral shell structures are presented. The results are shown to be in very good agreement with those reported in the literature. The computational advantages and physical insights due to the group theoretic approach are also discussed.     

CONDITIONAL SIMILARITY REDUCTION APPROACH: JIMBO－MIWA EQUATION

The direct method developed by Clarkson and Kruskal (1989 J. Math. Phys. 30 2201) for finding the symmetry reductions of a nonlinear system is extended to find the conditional similarity solutions. Using the method of the Jimbo－Miwa (JM) equation, we find that three well-known (2+1)-dimensional models－the asymmetric Nizhnik--Novikov－Veselov equation, the breaking soliton equation and the Kadomtsev-Petviashvili equation－can all be obtained as the conditional similarity reductions of the JM equation.     

导热优化:热耗散与最优导热系数场

本文讨论了通过重新布置场内的导热系数分布来强化热传导的导热优化问题。针对边界上传热量一定的任意几何区域的稳态导热,在全场的导热系数积分为定值的条件下,以最小热耗散作为目标,利用变分方法导出了导热优化的基本准则;导热系数与局部热流密度成正比。该准则指导下的导热优化过程可获得热耗散最小的导热系数分布。实例证明了该方法是有效且合理的。     

ELECTROSTATIC POTENTIAL OF STRONGLY NONLINEAR COMPOSITES: HOMOTOPY CONTINUATION APPROACH

The homotopy continuation method is used to solve the electrostatic boundary-value problems of strongly nonlinear composite media, which obey a current-field relation of J=σ E+χ|E|²E. With the mode expansion, the approximate analytical solutions of electric potential in host and inclusion regions are obtained by solving a set of nonlinear ordinary different equations, which are derived from the original equations with homotopy method. As an example in dimension two, we apply the method to deal with a nonlinear cylindrical inclusion embedded in a host. Comparing the approximate analytical solution of the potential obtained by homotopy method with that of numerical method, we can obverse that the homotopy method is valid for solving boundary-value problems of weakly and strongly nonlinear media.     

HYDRODYNAMIC AND THERMAL CHARACTERISTICS OF CORRUGATED CHANNELS: EXPERIMENTAL APPROACH

Corrugated channels in a plate heat exchanger have probably the most complicated geometry of all flow ducts. To understand the hydrodynamic and thermal characteristics of corrugated channels, a proper balance of theoretical, computational, and experimental approaches is essential. The theoretical approach, which involves the simultaneous solution of the governing equations of fluid dynamics, becomes so complex as to be impractical, except for some special cases and with many simplifying assumptions. The computational approach includes using computers to solve discretized versions of the governing equations of fluid dynamics. This article is focused on an experimental approach which concerns local pressure and local temperature measurements.     

DIFFERENTIALLY MOVING MEDIA WITH MANY SPECTRAL LINES: STOCHASTIC APPROACH

Based upon the analytical solution of the radiative transfer equation for a given source function and a new approach to account for very many spectral lines contributing to the extinction, the connection between line properties and the emergent intensity is derived under the assumption that the wavelengths of the line centers follow a Poisson point process, whereas the other line parameters may have arbitrary distribution functions.A comparison with the widely used list of Kurucz shows that the Poisson distribution well describes deterministic “real” lines. The presentation by a Poisson point process requires only a modest number of parameters and is very flexible. It allows most operations to be carried out analytically and hence is very suitable to study the intricate influence of many lines on radiation fields in differentially moving media.We consider a simplified case of the solution of the radiative transfer equation in order to demonstrate the basic effects of the velocity field upon the emerging radiation field. Expressions for the expectation value of the intensity are derived, and examples are given for Lorentz line profiles and infinitely sharp lines, in particular as functions of the velocity gradient and the mean line density.