Planar random walk in a stratified quasi-periodic environment

Random walk in a stratified medium

We study the recurrence properties of a random walk in a stratified medium.

Random walk in a stratified independent random environment

We study Markov chains on a lattice in a codimension-one stratified independent random environment, exploiting results established in [2]. First of all the random walk is transient in dimension at least three. Focusing on dimension two, both recurrence and transience can happen, but transience remains by far the most general situation. We identify the critical scale of the local drift along the strata corresponding to the frontier between the two regimes.

Recurrence of the twisted planar random walk

We show that the "twisted" planar random walk - which results by summing up stationary increments rotated by multiples of a fixed angle - is recurrent under diverse assumptions on the increment process. For example, if the increment process is alpha-mixing and of finite second moment, then the twisted random walk is recurrent for every angle fixed choice of the angle out of a set of full Lebesgue measure, no matter how slow the mixing coefficients decay.

Existence and stability of a limit cycle in the model of a planar passive biped walking down a slope

We consider the simplest model of a passive biped walking down a slope given by the equations of switched coupled pendula (McGeer, 1990). Following the fundamental work by Garcia et al (1998), we view the slope of the ground as a small parameter $γ\ge 0$. When $γ=0$ the system can be solved in closed form and the existence of a family of limit cycles (i.e. potential walking cycles) can be established explicitly. As observed in Garcia et al (1998), the family of limit cycles disappears when $γ$ increases and only isolated asymptotically stable cycles (walking cycles) persist. However, no rigoro…

随机游走与洛伦兹过程

Random walks and Lorentz processes

本文利用概率论方法研究洛伦兹过程，证明平面齐次随机游走的局部扰动不改变极限律，并得到有限视界平面洛伦兹过程局部扰动的概率结论，同时为Lenci的常返性结果提供新证明。

An asymptotic estimate of the variance of the self-intersections of a planar periodic Lorentz process

We consider a periodic planar Lorentz process with strictly convex obstacles and finite horizon. This process describes the displacement of a particle moving in the plane with unit speed and with elastic reflection on the obstacles. We call number of self-intersections of this Lorentz process the number V(n) of couples of integers (k,m) smaller than n such that the particle hits a same obstacle both at the k-th and at the m-th collision times. The aim of this paper is to prove that the variance of V(n) is equivalent to cn^2 (such a result has recently been proved for simple planar random walks…