物理学报2016，Vol.65Issue(16)：160502-1-160502-7,7.DOI:10.7498/aps.65.160502
非线性阻尼驱动的莱维飞行动力学性质∗
Dynamical mechanism of Lévy flight driven by the nonlinear friction
摘要
Abstract
As a basic problem, anomalous diffusions in various fields of physics and related science have been studied for several decades. One of the topic problems of anomalous diffusion is Lévy flight, which is employed as the statistical model to solve the problems in various fields. Therefore, studying the dynamical mechanism of Lévy flight, especially in the existence of external potential, is of importance for relative theoretical and experimental research. In this paper, within the framework of dynamical continuous time random walk method, the Lévy flight diffusive behaviors and dynamical mechanisms driven by nonlinear friction are studied in the force-free potential and periodic potential. The nonlinear friction instead of Stokes friction is considered in each step of Lévy random walker through the dynamical continuous time random walk method. In the force-free potential, the nonlinear friction term can be considered to be inharmonic potential in the velocity space which can restrain the velocity of random walker, so the anomalous superdiffusion of Lévy flight turns into a behavior in the normal case because of the strong dissipative effect of the nonlinear friction. Due to the introduction of the nonlinear friction, the velocity steady probability density distribution behaves as transitions between bimodal shape and unimodal shape, which is detrmined by the Lévy index µ and the friction indexes γ0 andγ2. The bimodality is most pronounced at µ = 1, with µ increasing the bimodality becomes weaker, and vanishes at µ=2 which is the Gaussian case. Besides, there is a critical value γ0c =0.793701, which also determines the bimodal behaviors. Forγ0=0 the bimodality is most pronounced, asγ0 increases it smooths out and turns into a unimodal one forγ0>γ0c. In the existence of periodic potential, the Lévy random walker can be captured by the periodical potential due to the introduction of nonlinear friction, which behaves as the mean square displacement ⟨δx2(t)⟩ of the random walker and can reach a steady state quite quickly after a short lag time. However, the restraint is not equivalent to truncation procedures. Since the velocity of random walker obeys Lévy distribution, there is still extremely large jump length for random walker with extremely small probability. When the extremely large jump length is long enough and the barrier height U0 is not comparably high, the random walker can cross the barrier height of the periodic potential and jump out of the periodic potential, which behaves as the mean square displacement⟨δx2(t)⟩and a leap from a steady state to another one appears. However, the restraint on the random walker from the nonlinear friction always exists, so the random walker is captured again by the periodic potential, which means that the mean square displacement comes into a steady state again.关键词
动力学连续时间无规行走/非线性阻尼/莱维飞行/周期势场Key words
dynamical continuous time random walk/nonlinear friction/Lévy flights/periodic potential引用本文复制引用
刘剑,陈晓白,徐登辉,李熊,陈晓松,杨波..非线性阻尼驱动的莱维飞行动力学性质∗[J].物理学报,2016,65(16):160502-1-160502-7,7.基金项目
国家自然科学基金(批准号:11547231,61405003,11404013)资助的课题.* Project supported by the National Natural Science Foundation of China (Grant Nos.11547231,61405003,11404013) （批准号:11547231,61405003,11404013）
