一类随机环境中的随机游动

在Solomn的模型的基础上对一类随机环境中随机游动进行了讨论，并得出了一个常返性准则和一些极限性质。     

一类随机环境中的随机游动

研究了在环境平稳遍历时,右半直线上可逗留的随机环境中的随机游动的常返性和非常返性,给出非常返、正常返、零常返的充要条件,并讨论了极限性质.作为推论,给出P独立同分布时的相应结论.     

Moments of Exit Times from Wedges for Non-homogeneous Random Walks with Asymptotically Zero Drifts

We study quantitative asymptotics of planar random walks that are spatially non-homogeneous but whose mean drifts have some regularity. Specifically, we study the first exit time τ _α from a wedge with apex at the origin and interior half-angle α by a non-homogeneous random walk on ?² with mean drift at x of magnitude O(∥x∥^?1) as ∥x∥→∞. This is the critical regime for the asymptotic behaviour: under mild conditions, a previous result of the authors stated that τ _α <∞ a.s. for any α. Here we study the more difficult problem of the existence and non-existence of moments ${\mathbb{E}}[ \tau_{\alpha}^{s}]$ , s>0. Assuming a uniform bound on the walk’s increments, we show that for α<π/2 there exists s ₀∈(0,∞) such that ${\mathbb{E}}[ \tau_{\alpha}^{s}]$ is finite for s<s ₀ but infinite for s>s ₀; under specific assumptions on the drift field, we show that we can attain ${\mathbb{E}}[ \tau_{\alpha}^{s}] = \infty$ for any s>1/2. We show that there is a phase transition between drifts of magnitude O(∥x∥^?1) (the critical regime) and o(∥x∥^?1) (the subcritical regime). In the subcritical regime, we obtain a non-homogeneous random walk analogue of a theorem for Brownian motion due to Spitzer, under considerably weaker conditions than those previously given (including work by Varopoulos) that assumed zero drift.     

一类随机徘徊的等待时间

以一种随机徘徊为例,说明由独立增量点过程的等待时间生成的两类随机量——点间间距、给定时刻前后两次事件出现的时间差——之间的关系.     

On the Local Times of Transient Random Walks

We study the properties of the local and occupation times of certain transient random walks. First, our recent results concerning simple symmetric random walk in higher dimension are surveyed, then we start to establish similar results for simple asymmetric random walk on the line.     

Central Limit Theorem for a Class of Nonhomogeneous Random Walks

A spatially nonhomogeneous random walk _t on the grid =^m X ⁿ is considered. Let _t ⁰ be a random walk homogeneous in time and space, and let _t be obtained from it by changing transition probabilities on the set A= X ⁿ, || < , so that the walk remains homogeneous only with respect to the subgroup ⁿ of the group . It is shown that if >m 2 or the drift is distinct from zero, then the central limit theorem holds for _t.     

On the Recurrence Set of Planar Markov Random Walks

In this paper, we investigate properties of recurrent planar Markov random walks. More precisely, we study the set of recurrence points with the use of local limit theorems. The Nagaev–Guivarc’h spectral method provides several examples for which these local limit theorems are satisfied as soon as some (standard or non-standard) central limit theorem and some non-sublattice assumption hold.     

一类非标准随机游动及其在风险理论中的应用

考虑一类非标准的随机游动Sn=X1 … Xn,其中Xi(i≥1)为一列独立的随机变量序列,X1的分布函数为G,Xi(i≥2)具有共同的分布函数F.本文主要研究了F与G属于S(γ)族时,非标准随机游动的尾等价式和局部等价式,并给出在风险理论中的一些应用.     

一类随机环境中半直线上的可逗留随机游动

该文对一类随机环境中的半直线上的可逗留随机游动进行了讨论，得出了一个常返性准则(正常返、零常返、瞬时); 并通过构造Lyapunov函数和利用鞅理论，求出该模型的一个重对数律和一个L_p收敛的结果.     

On Large Deviations of Multivariate Heavy-Tailed Random Walks

Let {S _n ;n=1,2,…} be a random walk in R ^d and E(S ₁)=(μ ₁,…,μ _d ). Let a _j >μ _j for j=1,…,d and A=(a ₁,∞)×⋅⋅⋅×(a _d ,∞). We are interested in the probability P(S _n /n∈A) for large n in the case where the components of S ₁ are heavy tailed. An objective is to associate an exact power with the aforementioned probability. We also derive sharper asymptotic bounds for the probability and show that in essence, the occurrence of the event {S _n /n∈A} is caused by large single increments of the components in a specific way.      

Random Walks on Trees and an Inequality of Means

We define trees generated by bi-infinite sequences, calculate their walk-invariant distribution and the speed of a biased random walk. We compare a simple random walk on a tree generated by a bi-infinite sequence with a simple random walk on an augmented Galton-Watson tree. We find that comparable simple random walks require the augmented Galton-Watson tree to be larger than the corresponding tree generated by a bi-infinite sequence. This is due to an inequality for random variables with values in [1, [ involving harmonic, geometric and arithmetic mean.     

直线上独立时间随机环境中随机游动的渐近行为

主要讨论直线上独立时间随机环境中随机游动的常返性和非常返性,以及该过程的中心极限定理.     

On Transience Conditions for Markov Chains and Random Walks

We prove a new transience criterion for Markov chains on an arbitrary state space and give a corollary for real-valued chains. We show by example that in the case of a homogeneous random walk with infinite mean the proposed sufficient conditions are close to those necessary. We give a new proof of the well-known criterion for finiteness of the supremum of a random walk.     

Random Walks On Finite Convex Sets Of Lattice Points

This paper examines the convergence of nearest-neighbor random walks on convex subsets of the lattices^d. The main result shows that for fixedd, O(²) steps are sufficient for a walk to get random, where is the diameter of the set. Toward this end a new definition of convexity is introduced for subsets of lattices, which has many important properties of the concept of convexity in Euclidean spaces.     

Fastest Coupling of Random Walks

A new coupling of one-dimensional random walks is describedwhich tries to control the coupling by keeping the separationof the two random walks of constant sign. It turns out thatamong such monotone couplings there is an optimal one-step couplingwhich maximises the second moment of the difference (assumingthis is finite), and this coupling is ‘fast’ inthe sense that for a random walk with a unimodal step distributionthe coupling time achieved by using the new coupling at eachstep is stochastically no larger than any other coupling. Thisis applied to the case of symmetric unimodal distributions.     

Survival of Branching Random Walks in Random Environment

We study survival of nearest-neighbor branching random walks in random environment (BRWRE) on ℤ. A priori there are three different regimes of survival: global survival, local survival, and strong local survival. We show that local and strong local survival regimes coincide for BRWRE and that they can be characterized with the spectral radius of the first moment matrix of the process. These results are generalizations of the classification of BRWRE in recurrent and transient regimes. Our main result is a characterization of global survival that is given in terms of Lyapunov exponents of an infinite product of i.i.d. 2×2 random matrices.     

First Exit Time from a Bounded Interval for a Certain Class of Additive Functionals of Brownian Motion

Let (B _t) _t0 be standard Brownian motion starting at y, X _t = x + ^t ₀ V(B _s) ds for x (a, b), with V(y) = y if y0, V(y)=–K(–y) if y0, where >0 and K is a given positive constant. Set _ab=inf{t>0: X _t(a, b)} and ₀=inf{t>0: B _t=0}. In this paper we give several informations about the random variable _ab. We namely evaluate the moments of the random variables , and also show how to calculate the expectations . Then, we explicitly determine the probability laws of the random variables as well as the probability by means of special functions.     

On the First Exit Time of a Completely Asymmetric Stable Process from a Finite Interval

We compute the Laplace transform of the distribution of thefirst exit time from a finite interval for a completely asymmetricstable process. The formula involves a Mittag-Leffler functionand its derivative. As an application, we determine the asymptotictail behaviour of the foregoing distribution, and deduce anextension of the law of the iterated logarithm of Chung.     

On a Fluctuation Identity for Random Walks and Levy Processes

In this paper, some identities in laws involving ladder processesfor random walks and Lévy processes are extended andunified. 2000 Mathematics Subject Classification 60G50, 60G51(primary), 60G17 (secondary).