Quasi-median hulls in Hamming space are Steiner hulls

A Hamming space Λⁿ consists of all sequences of length n over an alphabet Λ and is endowed with the Hamming distance. In particular, any set of aligned DNA sequences of fixed length constitutes a subspace of a Hamming space with respect to mismatch distance. The quasi-median operation returns for any three sequences u,v,w the sequence which in each coordinate attains either the majority coordinate from u,v,w or else (in the case of a tie) the coordinate of the first entry, u; for a subset of Λⁿ the iterative application of this operation stabilizes in its quasi-median hull. We show that for every finite tree interconnecting a given subset X of Λⁿ there exists a shortest realization within Λⁿ for which all interior nodes belong to the quasi-median hull of X. Hence the quasi-median hull serves as a Steiner hull for the Steiner problem in Hamming space.     

An ε-Minimax Theorem for Bi-Lower-Semicontinuous Set-Valued Mappings

In this article, an approximate minimax theorem for bi-lower-semicontinuous set-valued mapping was proved, relationships between semicontinuous set-valued mappings are discussed and the existence of approximate maxmin was given. The minimax theorem in this article is the first minimax theorem that doesn’t require the set-valued mappings to be continuous.     

开平面C上的亚纯函数与完备极小曲面的Gauss映射

设■:D→R~3确定了以等温参数表示的极小曲面M,其中D是全平面R~2的开子区域,那么极小曲面的Gauss映射g(z)是D上的亚纯函数.Xavier与Chao提出了一个尚未解决的问题:任意给定区域■上的亚纯函数g(z),它是否是某完备极小曲面的Gauss映射?本文证明了若开平面C上的亚纯函数g(z)的零点列或极点列的收敛指数小于1/2,则g(z)—定是某完备极小曲面的Gauss映射.     

Minimal volume invariants,topological sphere theorems and biorthogonal curvature on 4‐manifolds

The goal of this article is to establish estimates involving the Yamabe minimal volume, mixed minimal volume and some topological invariants on compact 4‐manifolds. In addition, we provide topological sphere theorems for compact submanifolds of spheres and Euclidean spaces, provided that the full norm of the second fundamental form is suitably bounded.     

二阶奇异椭圆方程的Dirichlet问题

对二阶奇异椭圆方程-△u 1/uα-λuP=0的Dirichlet问题(λ＞0,0＜P＜1)证明了当α≥1时无解存在,当0＜α＜1时存在极小解;并对较一般的奇异方程给出了一个存在性结果.     

张量积型Said-Ball曲面的预处理渐近迭代逼近法

为加快张量积型 Said-Ball曲面渐近迭代逼近法的收敛速度,探讨了张量积型Said-Ball曲面渐近迭代逼近法的预处理技术。首先利用对角补偿约化技术构造了预处理子,然后结合矩阵Kronecker积性质,采取预处理渐近迭代逼近法求解张量积型Said-Ball曲面。为进一步降低计算量并提高算法的稳定性,利用广义极小残差法求解预处理方程,得到预处理渐近迭代逼近法的非精确求解方法。分析了预处理渐近迭代逼近法及非精确求解方法的收敛性。最后用数值实例说明预处理子能大大减小迭代矩阵的谱半径,令预处理技术及其非精确求解方法的计算效率明显提高。此外,由于对角补偿预处理子能改善配置矩阵的谱分布,因此也可用于对广义极小残差法的预处理,以改善其收敛性。     

A periodical replacement model based on cumulative repair‐cost limit

This paper considers a periodical replacement model based on a cumulative repair‐cost limit, whose concept uses the information of all repair costs to decide whether the system is repaired or replaced. The failures of the system can be divided into two types. One is minor failure that is assumed to be corrected by minimal repair, while the other is serious failure where the system is damaged completely. When a minor failure occurs, the corresponding repair cost is evaluated and minimal repair is then executed if this accumulated repair cost is less than a pre‐determined limit L, otherwise, the system is replaced by a new one. The system is also replaced at scheduled time T or at serious failure. Long‐run expected cost per unit time is formulated and the optimal period T* minimizing that cost is also verified to be finite and unique under some specific conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimality Conditions for D.C. Vector Optimization Problems Under Reverse Convex Constraints

In this paper, we establish global necessary and sufficient optimality conditions for D.C. vector optimization problems under reverse convex constraints. An application to vector fractional mathematical programming is also given. Mathematics Subject Classifications (1991). Primary 90C29, Secondary 49K30.     

Lemniscates and inequalities for the logarithmic capacities of continua

It is shown that if P(z) = z ⁿ + ? is a polynomial with connected lemniscate E(P) = {z: ¦P(z)¦ ≤ 1} and m critical points, then, for any n? m+1 points on the lemniscate E(P), there exists a continuum γ ? E(P) of logarithmic capacity cap γ ≤ 2^?1/n which contains these points and all zeros and critical points of the polynomial. As corollaries, estimates for continua of minimum capacity containing given points are obtained.     

Commutative idempotent residuated lattices

We investigate the variety of residuated lattices with a commutative and idempotent monoid reduct.