具有单参数空间对称群的向量场及其约化

对于保持某n-形式的n维向量场,应用Lie群的方法得到结论:当这类向量场有保持n-形式的空间单参数对称群时,可具体地构造出一个与该向量场无关的变换,它不仅使向量场约化掉一维,并且使得约化向量场保持相应的(n-1)-形式.特别,当n=3时,简单地得到了Mezie和Wiggins最近得到的重要结果.     

具有平行平均曲率向量场的子流形

本文改进了Ｓ．Ｔ．Ｙａｕ（文［１］）中关于单位球面中具有平行平均曲率向量场的子流形的一个结果。然而从截面曲率这一角度出发，给出了空间形式Ｒ＾ｎ＋ｐ（ｃ）（ｎ＞１，ｐ＞１）中具有平行平均曲率向量场的可定向闭子流形Ｍ＾ｎ的有关结果和积分不等式。     

布尔矩阵半群中的缺断区间及应用

本文证明了阶为ｎ（ｎ≥７）的布尔矩阵的行空间维数的一个缺断区间为〔２＾ｎ－２＋２ｎ－３＋２＾ｎ－４＋２＾ｎ－５＋２＾ｎ－６＋１，２＾ｎ＋１－１〕。这一结论扩展了关于布尔矩阵半群缺断区间的几个已有结果。作为应用，得到了布尔矩阵半群中一类偏序集的高度的一个新的上界，此外，还得到了关于有限拓扑维数分布的几个新结果。     

Hibert模形式与一类Dirichlet级数的特殊值

在文（２）中，Ｗ．Ｋｏｈｎｎ对权为Ｋ和Ｌ的任意二个岐点型模形式ｆ和ｇ（其变换群是全模群ＳＬ２（Ｚ）定义了一类Ｄｉｒｉｃｈｌｅｔ级数Ｌｆ，ｇ，ｎ（Ｓ），利用Ｌｆ，ｇ；ｎ（ｓ）（ｎ≥１为整数），可构造一个线性映射Ｗｇ：Ｓｋ→Ｓｋ－１，并且讨论了Ｌｆ，ｇ；ｎ的一些特征值，在本文中，我们将（２）中的结果推广到Ｈｉｂｅｒｔ模形式的情况，并得到类似的结论。     

Ⅲa＝0（－1＜n＜0，0＜l＜1）类二次系统存在极限环的充要条件

本文利用旋转向量场理论得到了系统ｘ＝－ｙ＋δｘ＋ｌｘ２＋ｍｘｙ＋ｎｙ２，ｙ＝ｘ（１＋ｙ），｛（－１＜ｎ＜０，０＜ｌ＜１）存在极限环的充要条件．     

R~n和RP~n上的多项式系统

本文讨论了ｎ维欧氏空间Ｒｎ（ｎ＞２）上的多项式向量场集合的系数拓扑不变量，可分为具有不同全局拓扑性质的两类不交的子集合；证明了Ｒｎ上的多项式向量场可连续地延拓成ｎ维射影空间ＲＰｎ上的连续多项式向量场的充要条件，反应了其次数与系数相关的拓扑性质；还证明了平面上的多项式向量场的赤道是闭轨线和不变集的充要条件．     

3-空间曲面上的一个重要向量场及相关结果

设 ｆ：Ｍ２（Ｃ）→ Ｎ３（ｃ）是 ２－维黎曼流形 Ｍ２到 ３维空间形式 Ｎ３（Ｃ）的等距浸入．找到一个由Ｍ２的第二基本形式确定的向量场 δ ，使得高斯曲率 Ｋ表为其散度 Ｋ＝ ｄｉｖ（δ）．在 Ｎ３（ｃ）＝ Ｅ３的情形，证明了ｆ可保持反定向高斯映射共形形变的充要条件是δ为闭向量场．对于可保持反定向高斯映射共形形变的曲面，本文给出了其形变象的表示公式     

施密特(Schmidt)正交化的几何意义

本文给出施密特（Ｓｃｈｍｉｄｔ）正交化方法的几何解释,以帮助学生弄懂施密特正交化方法的指导思想,以便于牢固掌握之．定理　从ｎ维欧氏空间Ｖ的任意一组基ａ１,ａ２,…,ａｎ出发,都可（经施密特正交化方法）得到Ｖ的一组标准正交基ｅ１,ｅ２,…,ｅｎ;施密特正交化方法为：首先由ｅ１＝ａ１｜ａ１｜来决定ｅ１,令ｂｉ＝ａｉ－（ａｉ,ｅ１）ｅ１－（ａｉ,ｅ２）ｅ２－…－（ａｉ,ｅｉ－１）ｅｉ－１,并令ｅｉ＝ｂｉ｜ｂｉ｜（ｉ＝２,３,…,ｎ）,于是便可得到Ｖ的一组标准正交基ｅ１,ｅ２,…,ｅｎ．当ｎ＝３时,上述…     

具有非退化亦型的Z—阶化李超代数

本文给出了Ｚ－阶化有限维单李超代数具有非退化亦型的一个必要条件。应用这一结果,我们可以得到Ｃａｒｔａｎ型李超代数Ｘ（ｎ）与Ｘ（ｍ,ｎ,ｔ）的Ｋｉｌｌｉｎｇ型是退化的。     

关于退化的拟正则映射

本文在ｎ维欧氏空间中刻划了一类退化的Ｋ－拟正则映射，其ｎ×ｎ阶Ｊａｃｏｂｉ矩阵的秩为ｌ：１ｌ＜ｎ；得到了其Ｌｐ可积性（ｐ（ｌ，ｎ，Ｋ）＞ｌ）和局部Ｈｌｄｅｒ连续性（ｌ＞ｎ（Ｋ－１）Ｋ）．     

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.     

球面空间单形的两个几何不等式（英文）

In this paper, by using the theory and method of distance geometry, we study the geometric inequality of a n-dimensional simplex in the spherical space and establish two geometric inequalities involving the edge-length and volume of one simplex and the volume,height and(n-1)-dimensional volume of the side of another simplex in the n-dimensional spherical space. They are the extensions of the results [10] in the n-dimensional Euclidean geometry to the n-dimensional spherical space.     

A Local Well-Posedness Result for the Quasilinear Wave Equation in ℝ2+1

Abstract

In this article we investigate the issue of local well-posedness for quasilinear wave equations in ?²⁺¹ with rough initial data. Our work extends the geometric methods pioneered by Klainerman and Klainerman-Rodniandski for similar problems in ?³⁺¹. The main new ingredient of the argument is the use of two new vectorfields, the scaling vectorfield S and the angular momentum vectorfield Ω, which complement the decay information provided by the Morawetz vectorfield K.     

Integration of differential forms on manifolds with locally-finite variations

It is well known that one can integrate any compactly supported, continuous, differential n-form over n-dimensional C¹-manifolds in ℝ^m (m ≥ n). For n = 1, the integral may be defined over any locally rectifiable curve. Another generalization is the theory of currents (linear functionals on the space of compactly supported C^∞-differential forms). The theme of the article is integration of measurable differential n-forms over n-dimensional n C⁰-manifolds in ℝ^m with locally-finite n-dimensional variations (a generalization of locally rectifiable curves to dimension n > 1). The main result states that any such manifold generates an n-dimensional current in ℝ^m (i.e., any compactly supported C^∞ n-form can be integrated over a manifold with the properties mentioned above). Bibliography: 8 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 327, 2005, pp. 168–206.     

n-2型黎曼空间的等距对应

<正> §1.导言一个正则的 n 维黎曼空间,若恰有 p 个函数独立的不变量,便称为 p 型的,这样的空间,我们将用 R(n,p)表之.此定义创自 T.Y.Thomas,他并详尽地研究了特殊情况:n=2,p=0,1,2.本文作者假定两个 R(n,n—2)具有结构相同的两组不变式 I_1,     

Covering lattice points by subspaces

We find tight estimates for the minimum number of proper subspaces needed to cover all lattice points in an n-dimensional convex body C , symmetric about the origin 0. This enables us to prove the following statement, which settles a problem of G. Halász. The maximum number of n-wise linearly independent lattice points in the n-dimensional ball r B n of radius r around 0 is O(rn/(n-1)). This bound cannot be improved. We also show that the order of magnitude of the number of diferent (n - 1)-dimensional subspaces induced by the lattice points in r&Bgr;n is rn/(n-1).     

Symmetry analysis of the two-dimensional diffusion equation with a source term

A symmetry analysis is performed on a (2+1)-dimensional linear diffusion equation with a nonlinear source term involving the dependent variable and its spatial derivatives. In the first part of the paper, we use the classical method to classify source terms where the original equation admits a nontrivial symmetry. In the second part of the paper, we use the nonclassical method and show that we simply recover the classical symmetries.     

多元FFT与FST的直接方法

一、多元变换矩阵与矩阵的张量积 矩阵的张量积(Kronecker乘积)是导出多元直接变换的主要工具,因此,这里首先列出张量积的定义及其简单性质. 定义.设A_n,B_m分别是n×n,m×m方阵,则A_n与B_m的张量积是一个(n·m)×(n·m)方阵:A_nB_m=[A_nb_(ij)],其中B_m=[b_(ij)].并记A~(k)=?.     

Integration of differential forms on manifolds with locally-finite variations. II

In part I of the paper, we have defined n-dimensional C⁰-manifolds in ℝⁿ(m ≥ n) with locally-finite n-dimensional variations (a generalization of locally-rectifiable curves to dimensionn > 1) and integration of measurable differential n-forms over such manifolds. The main result of part II states that an n-dimensional manifold that is C¹-embedded into ℝ^m has locally-finite variations and the integral of a measurable differential n-form defined in part I can be calculated by the well-known formula. Bibliography: 5 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 333, 2006, pp. 66–85.