波动方程解的Poisson公式的降维问题

利用微元法从三维和二维波动方程的Cauchy问题的Poisson公式解得到一维波动方程的Cauchy问题的D’Alembert公式解.     

Stokes问题有限元逼近中求导数的提取法

1.引言 我们知道Poisson方程和平面弹性问题的解的导数的近似值可以通过所谓提取公式得到,而不必对近似解直接求导数.这样我们可以得到具有与近似解本身同阶精度的导数的近似值.这一方法已被用于基于插值误差的后验误差估计及相应的自适应有限元方法中本文将这一方法应用于Stokes问题的有限元逼近,从Stokes方程的解的     

不通过Poisson公式解调和方程在球上的一类Dirichlet问题

得到了一个解调和方程在球上的一类Dirichlet问题的简单方法,即不通过Poisson公式而实际上只解一个Euler方程,从而较容易地求出其解.     

重调和椭圆边值问题的正则积分方程

我们熟知,利用位势理论或由Green公式及基本解出发区域内调和及重调和边值问题可归化为边界上的积分方程。近年来冯康又提出一种更自然而直接的归化,即从Green公式及Green函数出发将微分方程边值问题化为边界上的含有广义函数意义下发散积分有限部分的奇异积分方程,这种归化在各种边界归化中占有特殊地位,被称为正则边界归化,本文将这一理论应用于重调和椭圆边值问题,研究了其正则归化的性质,并通过利用Green函数、Fourier分析及复变函数论方法等不同途径求出了在上半平面、单位圆内部、单位圆外部三种区域的Poisson积分公式及正则积分方程,其离散化可用于实际计算。 本文是在导师冯康教授指导下完成的,作者谨在此对他表示衷心的感谢。     

SG~4上Poisson方程的Dirichlet问题

考察具有D-4对称性的立体Sierpinski垫片,定义其上的Laplacian,给出Green函数,从而解决了立体Sierpinski垫片上的Poisson方程的Dirichlet问题.     

Poisson方程的一维最优系统和不变解

本文研究了Poisson方程的一维最优系统及其不变解问题.利用吴-微分特征列集算法,借助于Mathematica软件,计算了Poisson方程的古典对称,并构建了Lie代数的一维最优系统.同时,利用不变量法,获得了一维最优系统中一个元素对应的Poisson方程的不变解.得到的结果推广了Poisson方程的精确解.     

一类Kuramoto Sivashinsky方程的显式解

本文研究了一类KS方程的初边值问题.利用一致变换方法,并结合Green公式和Jordan引理,在半直线上得到了这类方程的显式解公式.所得结论将为该类方程适定性和数值计算的研究提供新的思路.     

Winkler地基上固支薄板自由振动问题的准Green函数方法

将准Green函数方法应用于求解Winkler地基上固支薄板的自由振动问题.即利用问题的基本解和边界方程构造一个准Green函数,这个函数满足了问题的齐次边界条件.采用Green公式,将Winkler地基上固支薄板自由振动问题的振型控制微分方程化为第二类Fredholm积分方程.通过边界方程的适当选择,积分方程核的奇异性被克服了.数值算例表明,该方法具有较高的精度,是一种有效的数学方法.     

双解析函数、双调和函数和平面弹性问题

通过考虑双解析函数和双调和函数的关系,对单连通区域上平面弹性问题中只有重力体力作用的应力函数建立了唯一性和存在性结果;并对单位圆区域得到了类似于Poisson公式解的积分表示式。     

Mbius变换和正则函数的Poisson积分表示

首先,给出了R³中平面和球面方程的超复形式,接着提出了R3中平面和球面方程的超复形式,接着提出了R³中关于平面和球面对称点的概念,并给出了关于平面和球面对称点所满足的等价方程.我们考虑了超复空间Cl_3中的一些特殊的Mbius变换,并给出了其一些性质,比如:保持球面或平面不变性,保持关于平面和球面对称性不变性,保持交比不变性等.文中给出了正则函数和Mbius变换的关系.其次,证明了R3中关于平面和球面对称点的概念,并给出了关于平面和球面对称点所满足的等价方程.我们考虑了超复空间Cl_3中的一些特殊的Mbius变换,并给出了其一些性质,比如:保持球面或平面不变性,保持关于平面和球面对称性不变性,保持交比不变性等.文中给出了正则函数和Mbius变换的关系.其次,证明了R³中球内正则函数的推广的Cauchy定理和Cauchy积分公式.借助于上述正则函数的Cauchy积分公式和其对称点的积分表示,给出了正则函数的Poisson积分表示.最后,在Mbius变换的性质基础上,给出了Mbius变换下曲面积分的变量替换公式.     

Green's functions for elliptic and parabolic equations with random coefficients II

This paper is concerned with linear parabolic partial differential equations in divergence form and their discrete analogues. It is assumed that the coefficients of the equation are stationary random variables, random in both space and time. The Green's functions for the equations are then random variables. Regularity properties for expectation values of Green's functions are obtained. In particular, it is shown that the expectation value is a continuously differentiable function in the space variable whose derivatives are bounded by the corresponding derivatives of the Green's function for the heat equation. Similar results are obtained for the related finite difference equations. This paper generalises results of a previous paper which considered the case when the coefficients are constant in time but random in space.

     

EIGENFUNCTION EXPANSION FOR STURM-LIOUVILLE PROBLEMS WITH TRANSMISSION CONDITIONS AT ONE INTERIOR POINT

The purpose of this article is to extend some spectral properties of regular SturmLiouville problems to the special type discontinuous boundaxy-value problem,which consists of a Sturm-Liouville equation together with eigenparameter-dependent boundary conditions and two supplementary transmission conditions.We construct the resolvent operator and Green's function and prove theorems about expansions in terms of eigenfunctions in modified Hilbert space L_2[a,b].     

On the conjugate boundary value problem

We study the conjugate boundary-value problem with boundary conditions whose orders can be as large as the order of the differential equation or larger. We construct the Green's function of the problem over the entire space when the separating surface is a hyperplane, and we describe its properties. Bibliography: 6 titles.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 30, 1989, pp. 20–24.     

On variations in the solutions of integro-differential equations of mixed problems of elasticity theory for domain variations

The behaviour of the solution of the boundary value problem for a pseudodifferential equation (PDE), Green's function of this problem, and also some of their local and global characteristics, during variation of the domain is investigated. Formulas are proposed that enable the solution of a broad class of PDE in a domain to be expressed in terms of the solution in the near domain. Local characteristics of the solution are expressed in terms of the local characteristics of the solution in the near domain. A double asymptotic form of Green's function for both arguments tending to the domain boundary occurs in the variation formula. The variation of this double asymptotic form as the domain varies is expressed in terms of this same asymptotic form. The system of variation formulas obtained is closed. It enables the PDE solution in the domain to be reduced to the solution of an ordinary differential equation in functional space. The local characteristics of the solution can also be found by this method without calculating the solution itself. If there is sufficient symmetry in the initial operator, then conservation laws in the Noether sense are obtained for its Green's function and its asymptotic form. The behaviour of the quantities under investigation is studied under inversion.

The investigation of variations of the solutions of problems for the variation of the domain occurs in the paper by Hadamard /1/, who studied the variation in conformal mapping and obtained a formula similar to (1.4). The formula for the variation of the solution of the boundary value problem for an elliptic differential equation is obtained in /2/. Variation formulas for the case of the operator of the problem about a crack and a circular domain are obtained in /3, 4/. The Irwin formula /5/ is obtained from formulas (1.4) and (1.21) by substitution.     

Integral Equations without a Unique Solution can be made Useful for Solving some Plane Harmonic Problems

Using Green's third identity an integral equation for a twodimensional harmonic problem is derived. For a particular exceptionalgeometry the integral equation does not have a unique solutionbut by applying Green's third identify a supplementary integralcondition is derived. When the integral equation and the integralcondition are solved simultaneously we obtain always a uniquesolution. The procedure is demonstrated by some numerical examples.     

Green's function of the Brinkman equation in a 2D anisotropic case

The purpose of this paper is to obtain the Green's functionof the Brinkman equation in a 2D case of hydrodynamic anisotropywith respect to the permeability. The anisotropic nature ofthe permeability is assumed to be not space or time dependent.We use the method of Fourier transform which reduces the computationof the Green's function to the computation of the fundamentalsolution of a fourth-order partial differential equation. Thisresearch work has several applications in engineering and medicineto the motion of bodies in anisotropic porous media.     

Blowing-up semilinear wave equation with exponential nonlinearity in two space dimensions

We investigate the initial value problem for some semi-linear wave equation in two space dimensions with exponential nonlinearity growth.     

Optimal institutional advertising: Minimum-time problem

This paper considers the problem of optimizing the institutional advertising expenditure for a firm which produces two products. The problem is formulated as a minimum-time control problem for the dynamics of an extended Vidale-Wolfe advertising model, the optimal control being the rate of institutional advertising that minimizes the time to attain the specified target market shares for the two products. The attainable set and the optimal control are obtained by applying the recent theory developed by Hermes and Haynes extending the Green's theorem approach to higher dimensions. It is shown that the optimal control is a strict bang-bang control. An interesting side result is that the singular arc obtained by the Green's theorem application turns out to be a maximum-time solution over the set of all feasible controls. The result clarifies the connection between the Green's theorem approach and the maximum principle approach.     

双空间指示函数方法在三维柱面对称波导中电磁波的反散射问题的推广

给出了双空间指示函数方法在三维柱面对称波导中电磁波的反散射问题的推广.基于这个观察:当Green函数的点源在障碍物内部时,那么远域数据的赋权积分可以很好地近似估计Green函数,但是当Green函数的点源在障碍物外部时,那么远域数据的赋权积分就不能很好地近似估计Green函数.建立一个积分方程:它的右边是点源在所重构区域的Green函数,那么我们可以知道这个积分方程的解的范数在未知障碍物的内部有极大值,而这些取得极大值的点所围成的区域恰好就是所重构的障碍物区域.方法最显著的优势在于它不依赖于未知障碍物的边界条件.     

Global well‐posedness of a damped Schrödinger equation in two space dimensions

We investigate the initial value problem for a semilinear damped Schrödinger equation with exponential growth nonlinearity in two space dimensions. We obtain global well‐posedness in the energy space. Copyright © 2013 John Wiley & Sons, Ltd.