广义零程无穷质点过程的不变测度

本文研究了一类广义零程无穷质点马氏过程。给出了此类过程的一类不变测度;在平移不变情形下,构造了平移不变的不变测度集;而在重随机、常返的情形下,构造了不变测度集。这些结果自然推广了[3]的结果。     

随机环境中的马氏链的不变测度与遍历性

本文考虑了一类特殊的随机环境的马氏链。假设随机“Doeblin”条件成立，我们证明了随机环境的马氏链的不变测度存在，且任何初始分布以指数收敛速度到些不变测度。进一步的，存在关于绕积算子遍历的不变测度。最后，我们得到了随机马氏链的强大数定律。     

统计自相似集与随机不变测度

设犡是一完备可分度量空间，犓（ω）为Ｇｒａｆ随机模型下的随机递归集．该文构造了一列随机不变测度μ狀（狀≥１），它们是Ｈｕｔｃｈｉｎｓｏｎ确定模型下不变测度的推广；证明了存在一随机概率测度μ ，使得Ｓｕｐｐμ ＝犓（ω）且μ狀→μ （狀→∞）（弱收敛）；得到了μ狀的一些局部性质．     

Gauss噪声扰动下的FitzHugh-Nagumo系统的随机稳定性

在Gauss噪声扰动下FitzHugh-Nagumo系统的随机稳定性是该文的研究目的．通过研究随机FitzHugh-Nagumo系统的动力学行为, 证明其存在唯一的、具有指数混合速度的不变测度．最后, 考察当噪声趋于0时不变测度的渐近行为．     

随机环境中耦合空间的不变测度存在性

本文研究了随机环境中耦合空间上不变测度存在性问题，证明了一些存在性定理．     

带小扰动的随机发展方程的不变测度

本文考虑带小扰动的随机发展方程,证明如何建立此方程的耦合解.作为应用,我们证明解的Feller连续性和不变测度的存在唯一性.还进一步建立了当扰动趋于零时,关于这族不变测度的大偏差原理.     

带有双噪声的随机SI传染病模型的稳定性与分岔

建立一个带有双噪声的随机SI传染病模型,运用随机平均法及非线性动力学理论对模型进行化简．通过Lyapunov指数和奇异边界理论,得到模型的局部随机稳定性和全局随机稳定性的条件．根据不变测度的Lyapunov指数和平稳概率密度,分析模型的随机分岔．结果表明,系统在随机因素作用下变得更敏感、更不稳定.     

具有拟不变测度的交换拓扑群上的正定函数

<正> §1.引言如所周知,拓扑群上的正定函数是研究拓扑群的酉表示的重要工具.对于交换的、具有平移不变测度(即 Haar 测度)的拓扑群,例如局部紧的拓扑群,群上的连续正定函数可以用连续特征标关于对偶群上某个测度的积分表示.对于不具有平移不变测度的交换拓扑群,并不是每个连续正定函数都可以用上述积分表示.因而对于不具有平移不变的交换拓扑群,对群上的连续正定函数较难研究,关于抽象调和分析中其余的问题也有类似情     

紧距离空间上随机连续的Feller过程不变测度集的构造

设P(t,x,A)为紧距离空间上随机连续的Feller过程,本文定义了P(t,x,A)的弱遍历测度及概率核(?)(x,A),并证明了P(t,x,A)的弱遍历测度集、集{(?)(x,·):x∈X}和不变测度集的极点集是重合的。     

随机能源Logistic反馈控制系统的分岔研究

建立了非线性随机动力模型—带噪声的能源Logistic反馈控制模型,应用随机平均法对随机动力模型进行了简化,得到了一个二维的扩散过程.二维过程满足Ito型随机微分方程,应用不变测度理论研究了该模型的随机分岔.最后,给出了数值实验验证了相应的结论.     

The number of extremal components of a rigid measure

The Littlewood-Richardson rule can be expressed in terms of measures, and the fact that the Littlewood-Richardson coefficient is one amounts to a rigidity property of some measure. We show that the number of extremal components of such a rigid measure can be related to easily calculated geometric data. We recover, in particular, a characterization of those extremal measures whose (appropriately defined) duals are extremal as well. This result is instrumental in writing explicit solutions of Schubert intersection problems in the rigid case.     

Diophantine approximation and self-conformal measures

It is proved that the Hausdorff measure on the limit set of a finite conformal iterated function system is strongly extremal, meaning that almost all points with respect to this measure are not multiplicatively very well approximable. This proves Conjecture 10.6 from (on fractal measures and Diophantine approximation, preprint, 2003). The strong extremality of all (S,P)-invariant measures is established, where S is a finite conformal iterated function system and P is a probability vector. Both above results are consequences of the much more general Theorem 1.5 concerning Gibbs states of Hölder families of functions.     

Extremal dilations and their associated extremal measures

If μ and λ are probability measures on a metrisable compact convex set with μ < λ in the Choquet sense, then the main object of this paper is the study of the extremal structure of the convex set of all dilations carrying μ to λ. The extremal dilations are characterized and the relationships between these dilations and the extremal measures they induce are investigated. Several examples of extremal dilations with special properties are given to illustrate their behavior. Also given is a systematic characterization of measures which are extreme in the convex set of all measures dominating μ in the Choquet ordering.     

Tail dependence between order statistics

In this work, we introduce the s,k-extremal coefficients for studying the tail dependence between the s-th lower and k-th upper order statistics of a normalized random vector. If its margins have tail dependence then so do their order statistics, with the strength of bivariate tail dependence decreasing as two order statistics become farther apart. Some general properties are derived for these dependence measures which can be expressed via copulas of random vectors. Its relations with other extremal dependence measures used in the literature are discussed, such as multivariate tail dependence coefficients, the coefficient η of tail dependence, coefficients based on tail dependence functions, the extremal coefficient ?, the multivariate extremal index and an extremal coefficient for min-stable distributions. Several examples are presented to illustrate the results, including multivariate exponential and multivariate Gumbel distributions widely used in applications.     

Analysis of triangle quality measures

Several of the more commonly used triangle quality measures are analyzed and compared. Proofs are provided to verify that they do exhibit the expected extremal properties. The asymptotic behavior of these measures is investigated and a number of useful results are derived. It is shown that some of the quality measures are equivalent, in the sense of displaying the same extremal and asymptotic behavior, and that it is therefore possible to achieve a concise classification of triangle quality measures.

     

Potential and Discrepancy Estimates for Weighted Extremal Points

We derive estimates for Green and logarithmic potentials of measures associated with extremal points. These results are applied to obtain discrepancy estimates for weighted Fekete and Tsuji points on quasiconformal arcs or curves. September 21, 1998. Date revised: July 6, 1999. Date accepted: September 22, 1999.     

On a class of extremal problems

In the paper we introduce a class of trigonometrical polynomial extremal problems depending on a continuous parameter 0≤r≤1. It turns out that the two border cases r=0 and r=1 are known problems investigated earlier by Kamae, Mendes-France, Ruzsa and the present author. We also introduce another set of extremal problems for measures with similar parametrization, and prove a duality relationship between the two type of extremal quantities. The proof relies on a minimax theorem proved earlier by the author. The known duality results are proved as corollaries. 1980 MS Classification. Primary 42A05; Secondary 46B25, 46N05.     

Shift ergodicity for stationary Markov processes

In this paper shift ergodicity and related topics are studied for certain stationary processes. We first present a simple proof of the conclusion that every stationary Markov process is a generalized convex combination of stationary ergodic Markov processes. A direct consequence is that a stationary distribution of a Markov process is extremal if and only if the corresponding stationary Markov process is time ergodic and every stationary distribution is a generalized convex combination of such extremal ones. We then consider space ergodicity for spin flip particle systems. We prove space shift ergodicity and mixing for certain extremal invariant measures for a class of spin systems, in which most of the typical models, such as the Voter Models and the Contact Models, are included. As a consequence of these results we see that for such systems, under each of those extremal invariant measures, the space and time means of an observable coincide, an important phenomenon in statistical physics. Our results provide partial answers to certain interesting problems in spin systems.     

Haudorff测度与等径不等式

对于:Hausdorff维数为s>0的满足开集条件的自相似集E(?)Rn(n>1),我们引入等径不等式Hs|E(X)≤|X|s,以及使该不等式等号成立而直径大于0的极限集U(?)Rn.这里,Hs|E(·)是限制到集合E上的s维Hausdorff测度,而|X|指集合X在欧氏度量下的直径.当s=n时,n维球是唯一的极限集;当s∈(1,n)时,除去一些反面例子以外,我们对上述等径不等式的极限集的基本性质所知甚少.可以看出,这些不等式与Hs(E)的准确值的计算有密切联系.作为特例,我们将考虑Sierpinski垫片,指出计算这一典型自相似集的In2/In3维Hausdorff测度准确值的困难何在.由此可以大致推想,为什么除去平凡情形以外,至今还没有一个具体的满足开集条件而维数大于1的自相似集的:Hausdorff测度准确值被计算出来.