Extension of covariant derivative(Ⅲ): From classical gradient to shape gradient

This paper further extends the generalized covari ant derivative from the first covariant derivative to the sec ond one on curved surfaces. Through the linear transforma tion between the first generalized covariant derivative and the second one, the second covariant differential transformation group is set up. Under this transformation group, the sec ond class of differential invariants and integral invariants on curved surfaces is made clear. Besides, the symmetric struc ture of the tensor analysis on curved surfaces are revealed.

Extension of covariant derivative(Ⅰ): From component form to objective form

This paper extends the covariant derivative un der curved coordinate systems in 3D Euclid space. Based on the axiom of the covariant form invariability, the classical covariant derivative that can only act on components is ex tended to the generalized covariant derivative that can act on any geometric quantity including base vectors, vectors and tensors. Under the axiom, the algebra structure of the gen eralized covariant derivative is proved to be covariant dif ferential ring. Based on the powerful operation capabilities and simple analytical properties of the generalized covariant derivative, the tensor analysis in curved coordinate systems is simplified to a large extent.

Extension of covariant derivative(Ⅱ): From flat space to curved space

This paper extends the classical covariant deriva tive to the generalized covariant derivative on curved sur faces. The basement for the extension is similar to the pre vious paper, i.e., the axiom of the covariant form invariabil ity. Based on the generalized covariant derivative, a covari ant differential transformation group with orthogonal duality is set up. Through such orthogonal duality, tensor analy sis on curved surfaces is simplified intensively. Under the covariant differential transformation group, the differential invariabilities and integral invariabilities are constructed on curved surfaces.

Generalized Covariant Derivative with Respect to Time in Flat Space(Ⅰ):Eulerian Description

This paper reports a new derivative in the Eulerian description in flat space-the generalized covariant derivative with respect to time. The following contents are included:(a) the restricted covariant derivative with respect to time for Eulerian component is defined;(b) the postulate of the covariant form invariability in time field is set up;(c) the generalized covariant derivative with respect to time for generalized Eulerian component is defined;(d) the algebraic structure of the generalized covariant derivative with respect to time is made clear;(e) the covariant differential transformation group in time filed is derived. These progresses reveal the covariant form invariability of Eulerian space and time.

Generalized Covariant Derivative with Respect to Time in Flat Space(Ⅱ):Lagrangian Description

The previous paper reported a new derivative in the Eulerian description in flat space—the generalized covariant derivative of generalized Eulerian component with respect to time. This paper extends the thought from the Eulerian description to the Lagrangian description:on the basis of the postulate of covariant form invariability in time field, we define a new derivative in the Lagrangian description in flat space—the generalized covariant derivative of generalized Lagrangian component with respect to time. Besides, the covariant differential transformation group is set up. The covariant form invariability of Lagrangian space-time is ascertained.

自然基矢量的协变导数与广义协变性思想的演进

博士生在课堂上提出问题:'自然基矢量能否求协变导数?'。本文以此问题为引子,引入公理化思想,定义了广义分量和广义协变导数概念,并以新概念为基础,将经典协变性发展为广义协变性,将经典协变微分学发展为广义协变微分学。论文综述了探索中遇到的困难以及突破的途径,展示了广义协变导数概念的抽象过程和广义协变性思想的演进过程。

二维曲面理论引入数学物理方法的探讨

本文探讨如何将二维曲面理论引入到数学物理方法的教学当中,目的在于沟通从高等数学到一般微分几何知识之间的“鸿沟”。使得本科生在学习更抽象的微分几何前,具备一些直观的图像。文中主要利用嵌入到三维空间的曲面参数方程,计算给出二维曲面理论的第一、二基本形式,并且基于它们,建立起曲面上线元、面元、曲线夹角、曲率、测地线、平行移动的概念。运用这些概念,我们直接推导出在二维曲面上梯度、散度、旋度的数学表达式及对应的高斯、斯托克斯定理。这些式子经过简单推广便可以得到更高维曲线坐标系中梯度、散度、旋度的表达。作为曲面理论的一个直接应用,我们也讨论了如何将所得到曲面理论运用到肥皂膜上的流体,得到二维固定曲面上流体所满足的动力学方程,从而可以解释皂膜上的等厚干涉条纹的变化。最后我们介绍二维曲面理论到高维黎曼内蕴几何的推广以及在广义相对论上的应用。

一般道路空间中超曲面的基本方程

在本人原来研究的基础上,进一步探讨了一般道路空间中超曲面的基础方程式,推导出推广的高斯方程和柯达齐方程。

黎曼流形里满足:_LH_(ijp)=0的m维曲面

本文应用n维黎曼空间M^a中沿m维子空间M^m(m维曲面)的广义共变导数,探讨了黎曼流形里具有平行曲率的m维曲面,得到广义的Ricci公式,Weingarten公式和广义的Codazzi方程,Gauss方程的一种新的特殊形式。并应用这些公式和方程推导了几个定理,[2]中的平行曲率超曲面是本文的特殊情形。

一般道路空间中子空间的基本方程

本文进一步探讨了一般过路空间中子空间的基本方程。

Series Representation of Jointly S˛S Distribution via Symmetric Covariations

We introduce the notion of symmetric covariation,which is a new measure of dependence between two components of a symmetricα-stable random vector,where the stability parameterαmeasures the heavy-tailedness of its distribution.Unlike covariation that exists only whenα∈(1,2],symmetric covariation is well defined for allα∈(0,2].We show that symmetric covariation can be defined using the proposed generalized fractional derivative,which has broader usages than those involved in this work.Several properties of symmetric covariation have been derived.These are either similar to or more general than those of the covariance functions in the Gaussian case.The main contribution of this framework is the representation of the characteristic function of bivariate symmetricα-stable distribution via convergent series based on a sequence of symmetric covariations.This series representation extends the one of bivariate Gaussian.