重积分坐标变换的应用

本文系统给出了重积分坐标变换的相关应用公式及典型例题,特别是对近几年全国大学生数学竞赛题中出现的应用到重积分坐标变换的典型题目及其中的技巧给出详细的分析和阐述.     

积分微元变换的一种解释

<正> 本文将对重积分坐标变换时的积分微元变换作出一种新的解释。比如,众所周知,对二重积分,在直角坐标系下,积分微元ds=dxdy,在直角坐标系下,积分微元ds=dxdy,在极坐标系下,ds=rdrdφ。后者的证法常见有三     

一类重积分解法的探讨

从一道考研试题入手,给出了当二重积分的被积函数或积分区域边界含x2-y2时的"双曲坐标变换"法.通过实例,对比说明该方法能够解决一类用直角坐标不易计算或不能计算的二重积分问题,并且可以运用到三重积分的计算上.     

积分变量变换公式的类比和应用

利用类比思想,通过对定积分和二重积分的变量变换公式进行比较、分析、联想,然后推出n重积分的变量变换公式,有助于简单快速地理解和掌握不同维数的积分变量变换公式.举例说明如何借助极坐标变换来构造一类重积分计算的有效变换.     

球面坐标系中三重积分体积微元的分析

三重积分是高等数学教学中的一个重要知识点,特别是球面坐标系下的三重积分的计算.球面坐标系下三重积分的一个教学难点是如何清晰直观的理解体积微元.不同于坐标变换这种抽象的理论分析方式,从体积增量的角度出发,并通过MATLAB绘图,直观形象地给出球面坐标系下三重积分体积微元公式的分析过程.     

计算重积分的代数定限法

为避免确定累次积分的积分限之困难,介绍一种实用方法———代数定限法:利用不等式同解变换的办法将重积分的积分区域表示成累次积分所需要的形状     

正态定限（Orthant）概率

本文采用不同以往的方法；对正态定限（Ｏｒｔｈａｎｔ）概率积分施行线性变换与极坐标变换；得到了一个新的递推公式，使积分重数至少降低了３重；并推导了四维正态定限概率的表达式，这对进行数值计算是十分有意义的．     

曲线曲面积分的对称性质

在本文中先给出了弧元素、面元素在坐标变换下的变换公式，然后给出了曲线、曲面积分在坐标变换下的变换公式，最后利用上述坐标变换公式推出了曲线曲面积分的对称性质．     

曲线曲面积分的对称性质

在本文中先给出了弧元素、面元索在坐标变换下的变换公式，然后给出了曲线、曲面积分在坐标变换下的变换公式，最后利用上述坐标变换公式推出了曲线曲面积分的对称性质．     

一类曲面积分的简单计算与推广

第一类曲面积分的积分表达式具有如下特点时:(1)积分曲面是可求曲面面积的曲面;(2)被积函数是单变量函数或可化为单变量函数的函数,利用积分元素法,能将其直接化为定积分计算,这种简单的算法还可以推广到计算具有类似特征的三重积分.     

Heterotic string space-time from probability theory

This note shows how the 10 dimensions of heterotic strings arise naturally from the probabilistic character of the geometry of micro-space as the result of the standard deviation of the expectation value of an infinite-dimensional space using χ(n) and exponential statistical distribution.     

Large deviation on a covering graph with group of polynomial growth

We discuss a large deviation principle of a periodic random walk on a covering graph with its transformation group of polynomial volume growth in view of geometry. As we shall observe, the behavior of a random walk at infinity is closely related to the Gromov?CHausdorff limit of an infinite graph and in the case where the graph admits an action of a group of polynomial volume growth, the Carnot-Carathéodory metric shows up in its limit space.     

颗粒增强复合材料相界面的动态应力分析

针对硬微粒填充高聚物复合材料因相界面脱粘开裂生成微孔洞的微损伤成核机制,取材料的代表体积单元进行动力分析,通过对粘弹性基体本构关系作Laplace变换建立了基本方程,并引入Hankel变换,得到了球对称动荷载作用下相界面应力变化规律的解析解,据此分析了惯性效应和粘性效应对界面脱粘的影响。     

关于型III对称空间的热核构造

引进了第III类典型域上的内切超圆坐标;计算出了矩阵极坐标下相应于不变度量的体积元素;利用积分变换构造出了不变度量的Laplace-Beltrami算子的热核.     

A computational two scaled model for the simulation of micro-heterogeneous low-alloyed TRIP steels

In transformation induced plasticity (TRIP) steel a diffusionless austenitic-martensitic phase transformation induced by plastic deformation can be observed, resulting in excellent macroscopic properties. In particular low-alloyed TRIP steels, which can be obtained at lower production costs than high-alloyed TRIP steel, combine this mechanism with a heterogeneous arrangement of different phases at the microscale, namely ferrite, bainite, and retained austenite. The macroscopic behavior is governed by a complex interaction of the phases at the micro-level and the inelastic phase transformation from retained austenite to martensite. A reliable model for low-alloyed TRIP steel should therefore account for these microstructural processes to achieve an accurate macroscopic prediction. To enable this, we focus on a multiscale method often referred to as FE² approach, see [6]. In order to obtain a reasonable representative volume element, a three-dimensional statistically similar representative volume element (SSRVE) [1] can be used. Thereby, also computational costs associated with FE² calculations can be significantly reduced at a comparable prediction quality. The material model used here to capture the above mentioned microstructural phase transformation is based on [3] which was proposed for high alloyed TRIP steels, see also e.g. [8]. Computations based on the proposed two-scale approach are presented here for a three dimensional boundary value problem to show the evolution of phase transformation at the microscale and its effects on the macroscopic properties. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A constitutive model for a high alloyed cast CrMnNi TRIP-steel

The macroscopic material model, proposed by Papatriantafillou [1], is adopted to describe the rate dependent flow behaviour and the temperature and stress state dependent γ-α′ phase transformation of a newly developed cast TRIP-steel. Simple test of the implemented model revealed that the evolution of the martensite volume fraction is not predicted correctly in case of inelastic deformation and subsequent unloading. Therefore, we present an improved model for the γ-α′ phase transformation and show that these predictions are due to the choice of the corresponding thermodynamical driving force. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reduction of Volume—preserving Flows on an n—dimensional Manifold

A geometric reduction procedure for volume-preserving flows with a volume-preserving symme-try on an n-dimensional manifold is obtained.Instead of the coordinate-dependent theory and the concrete coordinate transformation,we xhow that a volume-preserving flow with a one-parameter volume-preserving symmetry on an n-dimensional manifold can be reduced to a volume-preserving flow on the corresponding (n-1)-dimensional quotient space.More generally,if it admits an r-parameter volume-preserving commutable symmetry,then the reduced folw preserves the corresponding (n-r)-dimensional volume form.     

Extremal Eigenvalues of the Sturm-Liouville Problems with Discontinuous Coefficients

In this paper, an extremal eigenvalue problem to the Sturm-Liouville equations with discontinuous coefficients and volume constraint is investigated. Liouville transformation is applied to change the problem into an equivalent minimization problem. Finite element method is proposed and the convergence for the finite element solution is established. A monotonic decreasing algorithm is presented to solve the extremal eigenvalue problem. A global convergence for the algorithm in the continuous case is proved. A few numerical results are given to depict the efficiency of the method.     

Nonlinear Deformational Properties of Dispersely Strengthened Materials

A method and an algorithm for determining the effective deformational properties of dispersely strengthened materials with a physically nonlinear matrix and quasi-spheroidal linearly elastic inclusions are elaborated based on the stochastic differential equations of the physically nonlinear theory of elasticity. Their transformation to integral equations and the application of the method of conditional moments reduce the problem to a system of nonlinear algebraic equations, whose solution is constructed by the iteration method. The deformation diagrams as functions of the volume content of inclusions are investigated.     

Nucleation Barriers for the Cubic‐to‐Tetragonal Phase Transformation

We are interested in the phase transformation from austenite to martensite. This transformation is typically accompanied by the generation and growth of small inclusions of martensite. We consider a model from geometrically linear elasticity with sharp energy penalization for phase boundaries. Focusing on a cubic‐to‐tetragonal phase transformation, we show that the minimal energy for an inclusion of martensite scales like $\max \{ V^{2/3}, V^{9/11} \}$ in terms of the volume V. Moreover, our arguments illustrate the importance of self‐accommodation for achieving the minimal scaling of the energy. The analysis is based on Fourier representation of the elastic energy. © 2012 Wiley Periodicals, Inc.