A note on partial numberings

The different behaviour of total and partial numberings with respect to the reducibility preorder is investigated. Partial numberings appear quite naturally in computability studies for topological spaces. The degrees of partial numberings form a distributive lattice which in the case of an infinite numbered set is neither complete nor contains a least element. Friedberg numberings are no longer minimal in this situation. Indeed, there is an infinite descending chain of non‐equivalent Friedberg numberings below every given numbering, as well as an uncountable antichain. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

集值离散系统的某些动力性质

A discrete dynamical system can be expressed as xn 1 =f(xn), n=0,1, 2,... where X isa metric space and f : X→X is a continuous map. The study of it tells us how the points in the base space X moved. Nevertheless, this is not enough for the researches of biological species, demography, numerical simulation and attractors (see [1], [2]).     

On homeomorphism groups of Menger continua

It is shown that the homeomorphism groups of the (generalized) Sierpinski carpet and the universal Menger continua are not zero-dimensional. These results were corollaries to a 1966 theorem of Brechner. New proofs were needed because we also show that Brechner's proof is inadequate. The method by which we obtain our results, the construction of closed imbeddings of complete Erdos space in the homeomorphism groups, is of independent interest.

     

关于随机算子方程的随机解

本文研究了随机算子方程（Ａ（ω，ｘ）＝μｘ，（ω，ｘ）∈Ω×Ｄ，μ１）的随机解，得到了若干新的结果，同时，我们推广了著名的Ａｌｔｍａｎ定理．     

Topological Aspects of Entropy and Phase Transition of Kerr Black Holest

In the light of topological current and the relationship between the entropy and the Euler characteristic, the topological aspects of entropy and phase transition of Kerr black holes are studied. From Gauss-Bonnet-Chern theorem, it is shown that the entropy of Kerr black holes is determined by the singularities of the Killing vector field of spacetime. By calculating the Hopf indices and Brouwer degrees of the Killing vector field at the singularities, the entropy S = A/4 for nonextreme Kerr black holes and S = 0 for extreme ones are obtained, respectively. It is also discussed that, with the change of the ratio of mass to angular momentum for unit mass, the Euler characteristic and the entropy of Kerr black holes will change discontinuously when the singularities on Cauchy horizon merge with the singularities on event horizon, which will lead to the first-order phase transition of Kerr black holes.     

一类具复杂偏差变元的中立型微分方程的周期解

本文研究了一类具复杂偏差变元的中立型泛函微分方程■(t)=θ■(t-r) α(t)f(x(t)) β(t)g(x(x(t))) p(t)的周期解的存在性,得到了周期解存在的充分条件,并给出了所得结论的几个简单应用．     

Algebraic Entropy of Elementary Amenable Groups

We prove that any finitely generated elementary amenable group of zero (algebraic) entropy contains a nilpotent subgroup of finite index or, equivalently, any finitely generated elementary amenable group of exponential growth is of uniformly exponential growth. We also show that 0 is an accumulation point of the set of entropies of elementary amenable groups.     

Subdivisions of large complete bipartite graphs and long induced paths in k‐connected graphs

It is proved that for every positive integers k, r and s there exists an integer n = n(k,r,s) such that every k‐connected graph of order at least n contains either an induced path of length s or a subdivision of the complete bipartite graph K_k,r. © 2004 Wiley Periodicals, Inc. J Graph Theory 45: 270–274, 2004     

不变平均和拓扑不变平均

设G为局部紧群，在一致连续函数空间U(G)上，用两种方法证明左不变平均和拓扑左不变的等价性．当G是交换群时．给出一种证明其顺从的方法．     

Pasting topological spaces at one point

Let {X _α } _α∈Λ be a family of topological spaces and x _α ∈ X _α , for every α ∈ Λ. Suppose X is the quotient space of the disjoint union of X _α ’s by identifying x _α ’s as one point σ. We try to characterize ideals of C(X) according to the same ideals of C(X _α )’s. In addition we generalize the concept of rank of a point, see [9], and then answer the following two algebraic questions. Let m be an infinite cardinal. (1) Is there any ring R and I an ideal in R such that I is an irreducible intersection of m prime ideals? (2) Is there any set of prime ideals of cardinality m in a ring R such that the intersection of these prime ideals can not be obtained as an intersection of fewer than m prime ideals in R? Finally, we answer an open question in [11].