关于k—消去图的若干新结果

设G是一个图．k是自然数．图G的一个k-正则支撑子图称为G的一个k-因子．若对于G的每条边e．G—e都存在一个k-因子，则称G是一个k-消去图．该文得到了一个图是k-消去图的若干充分条件，推广了文［2—4］中有关结论．     

图的分数κ-因子

给定图Ｇ＝（Ｖ,Ｅ）．设ａ和ｂ是两个非负整数．是一个函数．如果对所有的均成立,称 ｆ为 Ｇ的一个分数［ａ,ｂ］－ 因子． ａ＝ ｂ＝ κ时,称ｆ为 Ｇ的一个分数 ｋ＝因子．本文给出了一个图有分数 ｋ－因子的充分必要条件．     

关于k－复盖图的几个条件

设Ｇ是一个图，ｋ为正整数．图Ｇ的一个ｋ－正则支撑子图Ｆ称做图Ｇ的一个ｋ－因子．若图Ｇ的每一条边ｅ都属于Ｇ的一个ｋ－因子，则称Ｇ是一个ｋ－复盖图．本文给出了一个图Ｇ是ｋ－复盖图的几个充分条件．     

Stefan－Signorini问题的均匀化

本文讨论了一维Ｓｔｅｆａｎ－Ｓｉｇｎｏｒｉｎｉ问题的均匀化．利用一个关于未知函数的变换，将原问题转化为一个等价问题，然后利用一些估计和分析技巧对后者进行均匀化．这部分地回答Ｊ．Ｒ．Ｒｏｄｒｉｓｕｅｓ提出的一个问题．     

周期多尺度分析的特征及它的一个应用

在这篇文章里，我们研究了周期多尺度分析的性质，给出了尺度函数序列的一个特征．这个特征能够使我们从一个尺度函数序列得到另一个尺度函数序列．最后，我们给出了主要结果的一个应用．     

二阶差分方程非振动解的渐近性态

把二阶线性差分方程（１．１）看成非振动方程（１．２）的扰动,其中是向前差分算子,是实数序列．假设（１．２）非振动,则（１．２）有一个主解及副解．本文给出充分条件或必要条件使（１．１）也有一个主解ｘｎ和一个副解ｘｎ满足且这种渐近表示式以三种不同形式给出．     

学会调整思维触角

同学们知道,数学是思维的体操．解决任何一个数学问题,都需要伸出你思维的触角,而思维的触角可以是多方位的,找出最佳的思维触角常常有一个不断调整的过程．所以,解决一个数学问题（尤其是有一定难度的数学问题）的过程,就是一个不断调整思维触角的过程．下面,我们通过对一个具体的问题的思维历程加以说明,供同学们参考．     

如何做实证:路径分析北大核心

在回归模型中,可以包括多个自变量,但只能包括一个因变量．而许多因果效应问题,因变量往往不止一个．回归分析还有一个局限就是只能分析直接效应,不能分析间接效应．事实上,许多变量之间可能有直接关系,也可能受到中介变量的影响而产生间接效应．路径分析就是解决这类问题的方法．     

一道例题的答案给我的启示

针对某考研资料中的一道极限题目给出了两个解答．第一个依赖偏导数的定义,第二个依赖两个重要极限之一．且第二个解答的获得源于第一个解答所算出的答案．此外,还证明了有关等价无穷小代换的一个结论,扩大了其解决问题的范围．     

用平面函数构造仿射几何

短文证明了可以从n阶循环群到它自身的平面函数来构造一类仿射几何．作为推论，证明了礼必须是奇素数幂．从而证明了如果存在一个射影平面，它具有一个n^2阶的自同构群，那么扎必须是素数幂．这是“素幂猜想”的一个特殊情形．     

Decay mode solution of nonlinear boundary–initial value problems for the cylindrical (spherical) Boussinesq–Burgers equations

The major target of this paper is to construct new nonlinear boundary–initial value problems for Boussinesq–Burgers Equations, and derive the solutions of these nonlinear boundary–initial value problems by the simplified homogeneous balance method. The nonlinear transformation and its inversion between the Boussinesq–Burgers Equations and the linear heat conduction equation are firstly derived; then a new nonlinear boundary–initial value problem for the Boussinesq–Burgers equations with variable damping on the half infinite straight line is put forward for the first time, and the solution of this nonlinear boundary–initial value problem is obtained, especially, the decay mode solution of nonlinear boundary–initial value problem for the cylindrical (spherical) Boussinesq–Burgers equations is obtained.     

广义双正则函数的非线性带位移边值问题

本文研究Ｃｌｉｆｆｏｒｄ分析中的广义双正则函数及其一类非线性带Ｈａｓｅｍａｎ位移的边 值问题．通过积分变换将边值问题转化成积分方程问题，借助于积分方程理论和不动点 定理证明了边值问题解的存在性并给出了解的积分表示式．     

A free boundary problem of elliptic equation arising in supersonic flow past a conical body

We study free boundary value problems of elliptic equation caused by a supersonic flow past a non-symmetric conical body. The flow is described by the potential flow equation. In the self-similar coordinate system the problem can be reduced to a boundary value problem of second order nonlinear elliptic equation with a free boundary. Applying the partial hodograph transformation and the method of nonlinear alternative iteration we proved the existence of solution to this boundary value problem. Consequently, we also proved the conclusion that for the problem of supersonic flow past a conical body, if the conical body is slightly different from a circular cone with its vertex angle less than a given value determined by the parameters of the coming flow, then there exists a weak entropy solution with an attached conical shock.     

Hopf-Cole transformation to some systems of partial differential equations

In this paper we study a system of nonlinear partial differential equations which we write as a Burgers equation for matrix and use the Hopf-Cole transformation to linearize it. Using this method we solve initial value problem and initial boundary value problems for some systems of parabolic partial differential equations. Also we study an initial value problem for a system of nonlinear partial differential equations of first order which does not have solution in the standard distribution sense and construct an explicit solution in the algebra of generalized functions of Colombeau. Received November 1999     

Evolution of methacrylate distribution during wood saturation

It is established that a nonlinear model for the evolution of methacrylate in wood may be reduced via a reciprocal transformation to a moving boundary problem amenable to analytic treatment. Therein, the nonlinearity in the original problem is removed to the boundary. A recently developed method for the analysis of initial-boundary value problems is then used to obtain a single integral equation for the temporal evolution of the moving boundary in the canonical problem.     

Existence and Ulam's type stability results for a class of fractional boundary value problems on a star graph

This paper is concerned with a nonlinear fractional boundary value problem on a star graph. By using a transformation, the suggested problem is converted into an equivalent system of fractional boundary value problem. Schaefer's fixed point theorem and Banach's contraction principle is used to establish its existence and uniqueness results. Further, different kinds of Ulam's type stability results for the proposed problem have been discussed. Finally, two examples are presented to illustrate the application of the obtained results.     

圆薄板非对称大变形弯曲问题

本文首先导出圆薄板非轴对称大变形问题的位移基本方程及边界条件.利用变换和摄动法将非线性位移方程线性化,得到了近似边值问题.作为算例,文中研究了圆薄板在较复杂载荷作用下的非线性弯曲问题.     

A Class of Quadratic Integral-Differential Equations

A nonlinear integro-ordinary differential equation built up by a linear ordinary differential operator of n th order with constant coefficients and a quadratic integral term is dealt with. The integral term represents the so-called autocorrelation of the unknown function. Applying the Fourier cosine transformation, the integral-differential equation is reduced to a quadratic boundary value problem for the complex Fourier transform of the solution in the upper half-plane. This problem in turn is reduced to a linear boundary value problem which can be solved in closed form. There are infinitely many solutions of the integral-differential equation depending on the prescribed zeros of a function related to the complex Fourier transform.     

具有双参数的弱非线性方程的奇摄动解

讨论了一四阶具有双参数的弱非线性方程在有限区间上的奇摄动边值问题．在一定的假设下,首先,利用幂级数形式展开方法,构造了原问题的外部解A·D2其次,利用伸长变量,在左端点附近构造问题解的第一边界层校正项．然后,利用更强的伸长变量,仍然在左端点附近构造问题解的第二边界层校正项．第二边界层的厚度比第一边界层的厚度更小,形成在左端点附近的边界层的套层．最后利用微分不等式理论,证明了边值问题解的存在性、和在整个区间内一致有效性和渐近性态,得到了满意的结果．     

含有广义p-Laplace算子的非线性边值问题解的存在性的研究

该文研究了两类含有广义p-Laplace算子的非线性边值问题. 首先, 利用变分不等式解的存在性的结果, 证明了含有广义p-Laplace算子的非线性Dirichlet边值问题解的存在性. 然后, 提出了一类含有广义p-Laplace算子的非线性Neumann边值问题. 通过深入挖掘这两类非线性边值问题间的关系, 借助于极大单调算子值域的一个扰动结果, 证明了含有广义p-Laplace算子的非线性Neumann边值问题解的存在性. 文中采用了一些新的证明技巧,推广和补充了作者以往的一些研究工作.