L-保序算子空间的ω-紧性

研究了L-保序算子空间的ω-紧性．借助于Hα-ω-开覆盖,定义了L-保序算子空间的ω-紧性,证明了ω-紧集和ω-闭集之交是ω-紧的,ω-紧性被连续的广义Zadeh型函数所保持,ω-紧性是L-好的推广,Tychonoff乘积定理成立．此外,给出了ω-紧性的网式刻画．     

Flows, flow-pair covers and cycle double covers

In this paper, some earlier results by Fleischner [H. Fleischner, Bipartizing matchings and Sabidussi’s compatibility conjecture, Discrete Math. 244 (2002) 77-82] about edge-disjoint bipartizing matchings of a cubic graph with a dominating circuit are generalized for graphs without the assumption of the existence of a dominating circuit and 3-regularity. A pair of integer flows (D,f₁) and (D,f₂) is an (h,k)-flow parity-pair-cover of G if the union of their supports covers the entire graph; f₁ is an h-flow and f₂ is a k-flow, and . Then G admits a nowhere-zero 6-flow if and only if G admits a (4,3)-flow parity-pair-cover; and G admits a nowhere-zero 5-flow if G admits a (3,3)-flow parity-pair-cover. A pair of integer flows (D,f₁) and (D,f₂) is an (h,k)-flow even-disjoint-pair-cover of G if the union of their supports covers the entire graph, f₁ is an h-flow and f₂ is a k-flow, and for each {i,j}={1,2}. Then G has a 5-cycle double cover if G admits a (4,4)-flow even-disjoint-pair-cover; and G admits a (3,3)-flow parity-pair-cover if G has an orientable 5-cycle double cover.     

Symplectic group actions and covering spaces

For symplectic group actions which are not Hamiltonian there are two ways to define reduction. Firstly using the cylinder-valued momentum map and secondly lifting the action to any Hamiltonian cover (such as the universal cover), and then performing symplectic reduction in the usual way. We show that provided the action is free and proper, and the Hamiltonian holonomy associated to the action is closed, the natural projection from the latter to the former is a symplectic cover. At the same time we give a classification of all Hamiltonian covers of a given symplectic group action. The main properties of the lifting of a group action to a cover are studied.     

Applying a combinatorial determinant to count weighted cycle systems in a directed graph

One method for counting weighted cycle systems in a graph entails taking the determinant of the identity matrix minus the adjacency matrix of the graph. The result of this operation is the sum over cycle systems of −1 to the power of the number of disjoint cycles times the weight of the cycle system. We use this fact to reprove that the determinant of a matrix of much smaller order can be computed to calculate the number of cycle systems in a hamburger graph.     

自旋冰材料R2Ti2O7（R=Dy，Ho）的单晶生长和低温物性研究

本文首先对R2Ti2O7（R=Dy,Ho）单晶的生长条件进行了探索,经过多次尝试,得到了较理想的生长条件,并获得了高品质的单晶．磁化率和比热测量证实了这些单晶材料具有自旋冰基态．另外,通过对不同条件下退火的Dy2Ti2O7单晶低温热传导的深入研究,发现R2Ti2O7单晶具有较小的声子峰,并且退火条件的变化对峰值的影响很...     

Lω-空间的ωδ-紧性

在Lω-空间中借助βα-ωδ-开覆盖,定义了Lω-空间的ωδ-紧性,ωδ-基与ωδ-子基,并证明了ωδ-紧性被连续的Zadeh型函数所保持,Tychonoff乘积定理也成立.     

A question on partial CAP-subgroups of finite groups

A subgroup H of a finite group G is a partial CAP-subgroup of G if there is a chief series of G such that H either covers or avoids every chief factor of the series.The structural impact of the partial cover and avoidance property of some distinguished subgroups of a group has been studied by many authors.However,there are still some open questions which deserve an answer.The purpose of the present paper is to give a complete answer to one of these questions.     

基于流形覆盖思想的无网格方法的研究

本语言基于流形思想,利用有限覆盖,单位分解等概念,引入建立在覆盖上的覆盖函数和具有紧支撑特性的单位分解函数,建立场逼近的近似表达,由弱形式的Galerkin变分得到数值分析模型,结合边界条件用于边值问题的求解,由此建立了一类新的无网格数值方法,论文采用这种方法分析了平面弹性问题,分析了体积闭锁现象,h、p型收敛性等,提出了一种选择覆盖大小的方案,且对狭长城采用了椭圆覆盖形式,取得了比较好的效果。     

Using Homogeneous Weights for Approximating the Partial Cover Problem

In this paper we consider the natural generalizations of two fundamental problems, the Set-Cover problem and the Min-Knapsack problem. We are given a hypergraph, each vertex of which has a nonnegative weight, and each edge of which has a nonnegative length. For a given threshold , our objective is to find a subset of the vertices with minimum total cost, such that at least a length of of the edges is covered. This problem is called the partial set cover problem. We present an O(|V|² + |H|)-time, Δ_E-approximation algorithm for this problem, where Δ_E ≥ 2 is an upper bound on the edge cardinality of the hypergraph and |H| is the size of the hypergraph (i.e., the sum of all its edges cardinalities). The special case where Δ_E = 2 is called the partial vertex cover problem. For this problem a 2-approximation was previously known, however, the time complexity of our solution, i.e., O(|V|²), is a dramatic improvement.We show that if the weights are homogeneous (i.e., proportional to the potential coverage of the sets) then any minimal cover is a good approximation. Now, using the local-ratio technique, it is sufficient to repeatedly subtract a homogeneous weight function from the given weight function.     

A short proof that hyperspaces of Peano continua are absolute retracts

We give a short proof of Wojdyslawski's famous theorem.