乘积σ—代数的一种生成方法

本得到了有限及可数无限维乘积σ一代数的一种新的生成方法，并证明了可数无限维Borel城具有连续统的势。     

向量到子空间的距离及其应用

给出了向量到有限维子空间距离的定义及求法 ,并推广到向量到可数无限维子空间距离 .采用两种方法求距离并比较了它们的运算量 .揭示了 Cholesky分解法与 Schmidt正交化方法的内在联系 .最后利用向量到子空间距离给出了矛盾方程组最小二乘解的求法     

可数sofic群的等距线性作用的维数

我们对复Banach空间上的可数sofic群的等距线性作用提出了一种新的维数,推广了复Banach空间上的可数顺从群的等距线性作用的Voiculescu维数,并且在可数sofic群的情形回答了Gromov的一个问题.     

可数sofic群的等距线性作用的维数

我们对复Banach空间上的可数sofic群的等距线性作用提出了一种新的维数，推广了复Banach空间上的可数顺从群的等距线性作用的Voiculescu维数，并且在可数sofic群的情形回答了Gromov的一个问题.     

Boole代数中极大滤子的刻画与Cantor三分集

清楚地刻画出有限和由无限可数个基本元生成的Boole代数中极大滤子的具体结构,在全体极大滤子之集上通过自然的方式引入一种紧致的Hausdorff拓扑,证明了当Boole代数可由无限可数个基本元生成时所得的拓扑空间与Cantor三分集同胚.     

连续树映射的ω极限集与非游荡集

本文研究树上连续自映射ｆ的ω极限集Λ,非游荡集Ω的若干拓扑结构,主要证明了：不在周期点集闭包中的ω极限点都有无限轨迹;Ω－Ｐ,Ω－Γ为可数集,Λ－Γ,Ｐ－Γ或为空集或可数无限,其中Γ为ｆ的γ极限集．     

关于弱正则空间的闭扩充

在此文中我们分别给出了刻画第一可数弱正则一闭拓空间和第一可数弱正则一极小拓扑空间的等价性定理，同时我们还证明了第一个局部弱紧的第一可为九弱正则空间都存在一个第一可数弱正则一闭扩充，此定理在表达形式上数拟于Ｒ．Ｍ．Ｓｔｅｐｈｅｎｓｏｎ等人对ｐ＝第一可数完全正则，或第一可数Ｕｒｙｓｏｈｎ以及第一可数零维时的结果。     

关于内顺从群的一些性质

本文给出了离散群的可数内不变平均的具体的表达式．证明了由可数内不变平均生成的向量空间的维数等于极小内不变平均的基数，并得到了内顺从群的一些新的刻划．     

可数无限群作用子集的单纯Bowen拓扑熵 献给杨乐教授80华诞

本文研究紧度量空间上可数无限群作用给出的动力系统G■X.特别地,对于X的任何一个子集Z,定义这个群作用相对于子集Z的单纯(naive) Bowen拓扑熵h_(top)~(nv)(G, Z).进一步,本文研究这种熵的基本性质,并且对于非顺从的可数无限群,计算这种熵的取值范围.事实证明,这种单纯熵的取值真的很单纯,反映了动力系统复杂度的一种二分现象.     

无限集合上的一类映射与余有限子集

本文证明了文献［１］中Ｆｏｒｙｓ＇的结果对于任何无限集合都对，与半群结构和可数无限性无关。讨论了一般无限集上的（＊）一映时，在余有限拓扑的框架下讨论了（＊）一映射的连续性。     

Optimal control for infinite dimensional stochastic differential equations with infinite Markov jumps and multiplicative noise

In this paper we solve an infinite-horizon linear quadratic control problem for a class of differential equations with countably infinite Markov jumps and multiplicative noise. The global solvability of the associated differential Riccati-type equations is studied under detectability hypotheses. A nonstochastic, operatorial approach is used. Some properties of the linear stochastic systems, such as stability, stabilizability and detectability, are also discussed on the basis of a new solution representation result. A generalized Ito's formula which applies to infinite dimensional stochastic differential equations with countably infinite Markov jumps is also provided.     

Infinitely many reducts of homogeneous structures

It is shown that the countably infinite dimensional pointed vector space (the vector space equipped with a constant) over a finite field has infinitely many first order definable reducts. This implies that the countable homogeneous Boolean-algebra has infinitely many reducts.     

On group operations on homogeneous spaces

It is proved that every countably infinite homogeneous regular space admits a structure of any countably infinite group with continuous left shifts.

     

Free continuous actions on zero-dimensional spaces

We show that every countably infinite group admits a free, continuous action on the Cantor set having an invariant probability measure. We also show that every countably infinite group admits a free, continuous action on a non-homogeneous compact metric space and the action is minimal (that is to say, every orbit is dense). In answer to a question posed by Giordano, Putnam and Skau, we establish that there is a continuous, minimal action of a countably infinite group on the Cantor set such that no free continuous action of any group gives rise to the same equivalence relation.     

The lattice complexity of quasivarieties of graphs and endographs

We construct a countably infinite descending chain of Q-universal quasivarieties of graphs, starting with D, and show that its intersection has a distributive countably infinite lattice of subquasivarieties. It is also proved that the quasivariety of symmetric endographs is Q-universal. Translated fromAlgebra i Logika, Vol. 36, No. 3, pp. 273–281, May–June, 1997.     

Homomorphisms between Stone-Cech Homomorphisms into Stone-Cech Remainders of Countable Groups

We study properties of continuous homomorphisms from β S into T^* and from S^* into T^*, where S denotes a countably infinite semigroup and T denotes a countably infinite group. We show that they have striking algebraic properties if they do not arise as continuous extensions of homomorphisms from S to T.     

Causal modeling in impulsive systems: A new rigorous non-standard analysis approach

A new approach for modeling nonlinear impulsive system is suggested based on nonstandard analysis. Basic properties of the hyperreals in nonstandard analysis are revisited. Depending on the convergence rate of infinitesimals in hyperreals, a new extended real space is proposed, which extends the one dimensional real line to a countably infinite dimensional extended real space. Generalized functions are defined via a sequential approach on the extended space, which yields a class of Heaviside functions and singular functions. By using the extended functions, a causal way for characterizing jumps in discontinuous system follows. We illustrate the usefulness of the theoretical development by analyzing three simple cases of impulsive affine system: (1) scalar case, (2) multi-dimensional case, and (3) one dimensional horizontal bouncing ball. The results suggest not only the existence of such infinitesimal models within the jump but also how to detour the equilibrium point while connecting the discontinuous state at the impact.     

The existence of multiple positive solutions to boundary value problems of nonlinear delay differential equations with countably many singularities on infinite interval

In this paper, we consider the existence of countably many positive solutions to a boundary value problem of a nonlinear delay differential equation with countably many singularities on infinite interval

     

Super-replication and utility maximization in large financial markets

We study the problems of super-replication and utility maximization from terminal wealth in a semimartingale model with countably many assets. After introducing a suitable definition of admissible strategy, we characterize superreplicable contingent claims in terms of martingale measures. Utility maximization problems are then studied with the convex duality method, and we extend finite-dimensional results to this setting. The existence of an optimizer is proved in a suitable class of generalized strategies: this class has also the property that maximal expected utility is the limit of maximal expected utilities in finite-dimensional submarkets. Finally, we illustrate our results with some examples in infinite dimensional factor models.     

Infinite,highly connected digraphs with no two arc-disjoint spanning trees

We present a construction of countably infinite, highly connected graphs and digraphs, which shows that several basic connectivity results on finite graphs, including Edmondsapos;s branching theorem, cannot be extended to the infinite case.