SH波对多个凸起与凹陷相连地形的散射问题研究

以双等腰三角形凸起与半圆形凹陷相连地形为例,研究了SH波对复杂地形的散射问题．利用分区求解的方法,把求解模型分割成3个区域,利用复变函数和多极坐标的方法分别构造各个区域内满足边界条件的波函数,根据公共边界上的位移和应力连续条件建立方程组,求解方程组得到各未知系数．最后给出复杂地形的地表位移,并分析了波数、入射角等不同因素对复杂地形造成的散射影响．     

各向异性介质中SH波对有衬砌的任意形半凹陷地形的散射

本文研究各向异性介质中具有衬砌的凹陷地形对SH波的散射.采用保角映射法[1]求解了有衬砌的凹陷地形对SH波的散射和它的地面位移.利用富氏级数展开方法,将待解的问题归结为一组无穷代数方程组的求解问题.由算例知,在衬砌和凹陷地形附近的地表上.位移幅值的变化是激烈的.当入射波的频率增加时,尤为显著.     

任意形状凸起地形对平面SH波的散射

将具有任意形状的凸起地形对称态SH波散射问题转换为契合问题加以研究,利用求解弹性波动问题的复变函数与保角映射方法,在包括任意形状凸起边界在内的一个区域中,构造一个在凸起边界上应力自由,其他部分位移和应力均为任意的驻波解,然后再将这个驻波解与其余下的区域中的散射波解在两个区域结合面上完成契合过程,由此决定出这两个区域中的驻波和散射波解答,最后对圆弧形和半椭圆形凸起进行了数值计算,并将计算结果与有限元法的数值解进行了比较。     

直角平面内圆孔对稳态SH波的散射

利用复变函数方法和多极坐标移动技术，研究了直角平面内圆孔在直边分布有反平面稳态载荷时的sH波散射问题．首先构造出直角平面内不含有圆孔时满足边界应力条件的Green函数解；其次提出直角平面内存在圆孔时满足边界应力自由条件的散射波解，并利用叠加原理写出问题的位移总波场．借助于多极坐标移动技术和圆孔边界处应力自由条件，列出求解散射波解中未知系数的无穷代数方程组，在满足计算精度的前提下，通过有限项截断进行求解．作为算例，具体讨论了圆孔边界处的环向动应力随不同波数、圆孔位置及载荷分布位置和分布范围大小的变化情况，算例结果说明了算法的有效实用性．     

横观各向同性电磁弹性介质中裂纹对SH波的散射

研究横观各向同性电磁弹性介质中裂纹和反平面剪切波之间的相互作用．根据电磁弹性介质的平衡运动微分方程、电位移和磁感应强度微分方程,得到SH波传播的控制场方程．引入线性变换,将控制场方程简化为Helmholtz方程和两个Laplace方程A·D2通过Fourier变换,并采用非电磁渗透型裂面边界条件,得到了柯西奇异积分方程组．利用Chebyshev多项式求解积分方程,得到应力场、电场和磁场以及动应力强度因子的表达,并给出了数值算例．     

相邻多个浅圆弧凹陷地形对平面SH波散射的级数解

本文采用解析法研究相邻多个线圆弧凹陷地形对平面SH波散射问题。文中由分离变量法把相邻多个圆弧凹陷对平面SH波的多重散射表示为各局部坐标中的级数之和,再利用Graf加法公式的内域和外域表达式进一步表示某个局部坐标中的双重无穷级数形式。问题最后可归结为求解一组无穷型的线性代数方程。文末给出了相邻两个等直径浅圆弧凹陷地形的多种深宽比对地面运动的影响的计算结果,并讨论了浅圆凹陷地形对波的屏蔽及它们之间的相互作用。     

SH波对界面含有半圆形脱胶的圆柱形弹性夹杂的散射的近似分析

采用Green函数法、复变函数法研究了SH波对界面附近含有半圆形脱胶的圆柱形弹性夹杂的散射,并给出了动应力集中系数的数值结果．首先,界面将整个空间分成上下两部分．在下半空间,给出在含有半圆形凸起的圆柱形弹性夹杂的弹性半空间中,水平表面上任意一点承受时间谐和的出平面线源荷载作用时的位移函数．其次,取该位移函数作为Green函数．上下空间连接时在界面处满足连续性条件,构造出半圆形脱胶裂纹,进而求出应力和位移的表达式．最后作为算例,给出了动应力集中系数的数值结果,分析了介质参数和入射波参数对动应力集中的影响情况．     

表面局部开裂圆柱夹塞物对SH型导波的散射

建立了平板波导中表面局部开裂圆柱夹塞物对SH型导波散射问题的解.用两个垂直于波导表面的虚拟平面将波导分割为3个区域.在包含夹塞物的中间区域,将波场展开为柱面波模式和Chebyshev多项式的叠加;在不含夹塞物的其余两个区域,将波场展开为导波模式的叠加.根据波导表面上应力自由的边界条件及虚拟平面上应力和位移连续的边界条件得到了待求解问题的基础方程组.利用模式匹配技术构造数值计算所需的矩阵方程,从而得到反射及透射系数随圆柱体归一化半径和脱黏区域大小变化的关系曲线.对圆柱表面完好黏结和脱黏区段不同大小的情况作了对比,对结果作了讨论.     

球壳中球形夹杂对SH波的三维散射与动应力集中

研究了一般情况下球壳中球形夹杂(包括孔洞)引起的SH波三维散射与动应力集中现象.根据球壳与夹杂的几何特点,分别以球壳和夹杂中心建立球坐标,用于描述球壳中的入射波、散射波和夹杂中的驻波势函数,并采用球波函数的加法公式,实现了不同坐标下球波函数的变换,推导出位移、应力分量的解析解.结合球壳的边界条件和夹杂界面的连续条件,求解了不同材料属性夹杂,以及空洞情况下弹性波的散射和动应力集中因子分布情况,并分析了频率以及夹杂中心位置对动应力集中因子的影响.文中的研究为球壳结构的力学性能分析以及无损检测提供了理论支持.     

压电材料中两平行不相等界面裂纹的动态特性研究

利用Schmidt方法,研究了压电材料中两个平行不相等的可导通界面裂纹对简谐反平面剪切波的散射问题．利用Fourier变换,使问题的求解转换为对两对以裂纹面张开位移为未知变量的对偶积分方程的求解．数值计算结果表明,动态应力强度因子及电位移强度因子受裂纹的几何参数、入射波频率的影响．在特殊情况下,与已有结果进行了比较分析．同时,电位移强度因子远小于不可导通电边界条件下相应问题的结果．     

Fractal functions with continuous Weil-type derivatives of variable order in control of distributed systems

Properties of fractal functions which are not differentiable in the classical sense but have continuous Weil-type derivatives of variable order at each point are studied. It is shown that the Weierstrass, Takagi, and Besicovitch classical fractal functions have such derivatives. An example of an oscillatory system controlling which requires constructing a fractal control function having a Weil-type derivative of variable order at each point is considered.     

Statistical aspects of random fragmentations

Three random fragmentation of an interval processes are investigated. For each of them, there is a splitting probability and a probability not to split at each step of the fragmentation process whose overall effect is to stabilize the global number of splitting events. Some of their statistical features are studied in each case among which fragments’ size distribution, partition function, structure of the underlying random fragmentation tree, occurrence of a phase transition. In the first homogeneous model, splitting probability does not depend on fragments’ size at each step. In the next two fragmentation models, splitting probability is fragments’ length dependent. In the first such models, fragments further split with probability one if their sizes exceed some cutoff value only; in a second model considered, splitting probability of finite-size objects is assumed to increase algebraically with fragments’ size at each step. The impact of these dependencies on statistical properties of the resulting random partitions are studied. Several examples are supplied.     

Nested splitting CG-like iterative method for solving the continuous Sylvester equation and preconditioning

We present a nested splitting conjugate gradient iteration method for solving large sparse continuous Sylvester equation, in which both coefficient matrices are (non-Hermitian) positive semi-definite, and at least one of them is positive definite. This method is actually inner/outer iterations, which employs the Sylvester conjugate gradient method as inner iteration to approximate each outer iterate, while each outer iteration is induced by a convergent and Hermitian positive definite splitting of the coefficient matrices. Convergence conditions of this method are studied and numerical experiments show the efficiency of this method. In addition, we show that the quasi-Hermitian splitting can induce accurate, robust and effective preconditioned Krylov subspace methods.     

一类抛物型方程组的特征修正区域分解有限元方法

在实际生产和科学研究中,有许多物理问题的数学模型为抛物型方程组问题,如可压缩核废料污染问题,地下水资源问题,杨青提出了差分格式和有限元格式,应用先验估计得到了最优的l^2和L^2模误差估计,江城顺等利用交替方向有限元方法得到了H^1模和L^2模误差估计．杨国强等采用显式可解的三层差分格式求解二维方程组得到了H^1模误差估计．     

Measuring teaching efficiency in higher education: An application of data envelopment analysis to economics graduates from UK Universities 1993

Data envelopment analysis (DEA) is applied to 2547 Economics graduates from UK Universities in 1993 in order to assess teaching efficiency. Following a methodology developed by [Education Economics 10(2) (2002) 183–207], each individual’s efficiency is decomposed into two components: one attributable to the university at which the student studied, and the other attributable to the student himself. From the former component, a measure of each institution’s teaching efficiency is derived and compared to efficiency scores derived from a conventional DEA applied using each Economics department as a decision making unit (DMU). The results suggest that efficiencies derived from DEAs performed at an aggregate level include both institution and individual components, and are therefore misleading. Thus the unit of analysis in a DEA is highly important. Moreover, an analysis at the individual level can give institutions insight into whether it is the students’ own efforts or the institution’s efficiency which are a constraint on increased efficiency. This has implications for the choice of strategy for improving efficiency.     

A generalization of edge-coloring in graphs

Bounds are given on the number of colors required to color the edges of a graph (multigraph) such that each color appears at each vertex v at most m(ν) times. The known results and proofs generalize in natural ways. Certain new edge-coloring problems, which have no counterparts when m(ν) = 1 for all ν ? V, are studied.     

Quasi-invariant domain constants

Five domain constants are studied in our paper, all related to the hyperbolic geometry in hyperbolic plane regions which are uniformly perfect (in Pommerenke’s terminology). Relations among these domain constants are obtained, from which bounds are derived for the variance ratio of each constant under conformal mappings of the regions, and we also show that each constant may be used to characterize uniformly perfect regions. The authors wish to thank the University of California, San Diego for its hospitality during the 1988–89 academic year when this research was begun. Supported by the Landau Center for Mathematical Research in Analysis. Research partially supported by NSF Grant No. DMS-8801439.     

The Egalitarian Solution for Multichoice Games

In a multichoice game a coalition is characterized by the level at which each player is acting, and to each coalition a real number is assigned. A multichoice solution assigns, for each multichoice game, a numerical value to each possible activity level of each player, intended to measure the contribution of each such level to reaching the grand coalition in which each player is active at the maximal level. The paper focuses on the egalitarian multichoice solution, characterized by the properties of Efficiency, Zero Contribution, Additivity, Anonymity, and Level Symmetry. The egalitarian solution is also shown to satisfy the property of marginalism: it measures the effect of lowering, ceteris paribus, a certain activity level by one. The solution is compared to a multichoice solution studied in Klijn, Slikker, and Zarzuelo (1999). Finally, it is discussed how the formalism of this paper can be applied to the different framework of multi-attribute utilities.     

复杂金融网络收益率加权和的不变性研究

对包含两个子网络的复杂金融网络进行了分析,研究了网络中各节点收益率与资金流通量之间的关系.通过建立数学模型,证明了网络中各节点收益率加权和的不变性.     

New differentiated consensus problem with topology cost constraints

A new differentiated consensus problem is studied. The problem is, given a system with multiple classes, consensus is targeted for each class and the consensus values can be different among the classes. Specifically, differentiated consensus is studied in a distributed stochastic network of nodes (or agents), where tasks assigned with different priorities are serviced. The network is assumed to have a switching topology and involves noises, delays in measurements, and topology cost constraints. The goal is to reach a balanced load (i.e., consensus) across the network and, at the same time, to satisfy the topology cost constraint, both for each priority class. A new control protocol is proposed, with which the network resources are allocated in a randomized way with a probability assigned to each priority class. It is shown that the control protocol meets the topology cost constraint and can be used to reach an approximate consensus for each of the priority classes in the network.