Indefinite Affine Umbilical Surfaces in R^4

We study surfaces M ² in the four-dimensional affine space equipped with its usual torsion-free connection D and parallel volume form given by the determinant.     

`CH~2中齐性曲面的分类(英文)

ＣＨ~２中的曲面 Ｍ称为（局部）齐性的,如果对任何一对点 ｐ,ｑ,存在变换。 σ　Ｕ（１,２）把含ｐ的一个邻域变为含ｑ的邻域,且把ｑ变为ｑ．本文给出ＣＨ２中齐性曲面的完全分类．     

中间逻辑中的良构范式

本文在中间逻辑中引入了良构范式的概念,为该类范式的研究提出了一个通用方法,并应用该方法证明了HT逻辑是存在一般蕴含范式的最弱中间逻辑,经典命题逻辑CPL是存在限制蕴含范式的仅有中间逻辑.     

Affine Locally Symmetric Surfaces in R~4

The nondegenerate affine locally symmetric surfaces in R^4 with the transversal bundle defined by Nomizu and Vrancken have been studied and a complete classification of the locally symmetric surfaces with flat normal bundle has been given.     

Sn中Moebius形式平行的曲面

证明了如下结果：设x：M^2→S^n(n≥3)是不含脐点的曲面，若x的法丛平坦，则x的Moebius形式φ平行(△↓φ=O)当且仅当φ=0．     

Differential Posets and Smith Normal Forms

We conjecture a strong property for the up and down maps U and D in an r-differential poset: DU + tI and UD + tI have Smith normal forms over . In particular, this would determine the integral structure of the maps U, D, UD, DU, including their ranks in any characteristic. As evidence, we prove the conjecture for the Young-Fibonacci lattice Y F studied by Okada and its r-differential generalizations Z(r), as well as verifying many of its consequences for Young’s lattice Y and the r-differential Cartesian products Y ^r .     

On Ruled Real Hypersurfaces in Complex Space Forms

Ruled real hypersurfaces of complex space forms are investigated by using the fact that such hypersurfaces can be constructed by moving a 1-codimensional complex totally geodesic submanifold of the ambient space along a curve. Among other results, a classification of minimal ruled real hypersurfaces and an example of a homogeneous ruled real hypersurface are given.     

矩阵对的相似标准形

设A,B,C,D都是n阶方阵,矩阵对(A,B)相似于矩阵对(C,D),如果存在n阶可逆矩阵P,使得P-1AP=C,P-1BP=D.本文借助Belitskii约化算法,提供一种在相似变化下化任一n阶矩阵对为标准形的有效方法,该方法可以看作Jordan标准形的推广.     

一类网络成本分配函数的规范性质

该文以数学方法论证了一类网络成本分配函数的性质,证明了成本分配函数具有规范形式的充要条件是它满足无记名性,可加性和等价性。并进一步论证了若成本分配函数还具有对成员数的单调递减性,它必是下游均等分配函数。     

Flat Affine Surfaces in \mathbb{R}^4 with Flat Normal Connection

In this paper we study nondegenerate affine surfaces in the 4-dimensional affine space . We assume that both the connection and the normal connection induced by the canonical equiaffine transversal bundle are flat. Surfaces with constant equiaffine transversal bundle are trivial examples of such surfaces. Here, we obtain a complete classification of all such surfaces which do not have constant equiaffine normal bundle.     

单位球中的极小曲面

Let M be a closed surface with positive Gauss curvature minimally immersed in a standard Euclidean unit sphere S~n.In this paper,we choose a local orthonormal frame field on M,under which the shape operators have very convenient form.We also give some applications of this kind of frame field.     

Further Reduction of Normal Forms for Vector Fields

We study Lie's method in the way of Ushiki for further reduction of normal forms for vector fields with singularity at the origin. We give further reduction of normal forms in two typical cases for vector fields in dimension 2: one with a rotation as its linear part and the other with a nilpotent linear part.     

Koszul Complexes and Symmetric Forms over the Punctured Affine Space

Let X be a regular separated scheme of finite Krull dimensionand let be the punctured affine n-space over X. We show that the total graded Witt ring of is a free graded module over the totalgraded Witt ring of X with two generators 1 and . The secondgenerator satisfies the equation ² = 1 when n = 1 and ² = 0when n 2. 2000 Mathematics Subject Classification 11E81, 19G12.     

关于常系数齐次线性微分方程组的解法研究

利用凯莱-哈密顿定理给出矩阵指数函数eAt的简洁计算方法;同时利用约当标准形推导出求常系数齐次线性微分方程组通解的循环公式.     

A Determinant Representation for the Distribution of Quadratic Forms in Complex Normal Vectors

Let the column vectors of X:: M×N, M<N, be distributed as independent complex normal vectors with the same covariance matrix Σ. Then the usual quadratic form in the complex normal vectors is denoted by Z=XLX^H where L: N×N is a positive definite hermitian matrix. This paper deals with a representation for the density function of Z in terms of a ratio of determinants. This representation also yields a compact form for the distribution of the generalized variance |Z|.     

On the Embedding of an Affine Space into a Projective Space

Let k, K be fields, and assume that |k| 4 and n, m 2, or |k| = 3 and n 3, m 2. Then, for any embedding of AG(n, k) into PG(m, K), there exists an isomorphism from k into K and an (n+1) × (m+1) matrix B with entries in K such that can be expressed as (x₁,x₂,...,x_n) = [(1,x₁ ,x₂ ,...,x_n )B], where the right-hand side is the equivalence class of (1,x₁ ,x₂ ,...,x_n )B. Moreover, in this expression, is uniquely determined, and B is uniquely determined up to a multiplication of element of K*. Let l 1, and suppose that there exists an embedding of AG(m+l, k) into PG(m, K) which has the above expression. If we put r = dim _k K, then we have r 3 and m > 2 l-1)/(r-2). Conversely, there exists an embedding of AG(l+m, k) into PG(m, K) with the above expression if K is a cyclic extension of k with dim _k K=r 3, and if m 2l/(r-2) with m even or if m 2l/(r-2) +1 with m odd.     

Normal Forms of Maps: Formal and Algebraic Aspects

We survey and discuss Poincaré–Dulac normal forms of maps near a fixed point. The presentation is accessible with no particular prerequisites. After some introductory material and general results (mostly known facts) we turn to further normalization in the simple resonance case and to formal and analytic infinitesimal symmetries.Mathematics Subject Classifications (2000) 37G05, 39A11.Todor Gramchev: The author is supported by a NATO grant PST.CLG.979347 and GNAMPA–INDAM, Italy.     

Classification of Quadratic Homogeneous Automorphisms in Dimension Five

In this paper, we present a classification of quadratic homogeneous automorphisms in dimension 5 up to linear conjugation. As a consequence, we give an affirmative answer to the Rusek Conjecture in dimension 5.     

On the Construction of Affine Extractors

In this paper, we address the problem of explicit construction of so-called ‘affine extractors’ of δ-entropy ratio, when δ ≤ 1/2 (for δ > 1/2, there is a well-known and easy example based on the Hadamard function). We first give examples for δ slightly below 1/2 and produce then a construction for arbitrary given δ > 0. All these examples are again of a simple algebraic nature. The mathematics involved includes recent developments in the sum-product theory in finite fields and certain new bounds on multilinear exponential sums. Supported in part by NSF grant DMS 0322370. Submitted: May 2005 Accepted: February 2006