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arXiv cond-mat/0108024cond-mat.stat-mech
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分数阶扩散方程的CTRW途径

CTRW Pathways to the Fractional Diffusion Equation

Eli Barkai

摘要:

基于耦合和解耦连续时间随机游动(CTRW),研究了分数阶扩散方程的基础。为了这个目的,我们找到一个精确的解的去耦CTRW,在一个无限的稳定的概率密度的总和。这个精确的解决方案,然后用来理解分数扩散方程的意义和域的有效性。讨论了耦合存储器(即,Lévy walks).随机游走的矩表现出强烈的反常扩散,表明(以一种天真的方式)简单标度行为的崩溃,因此分数近似。分数阶扩散方程仍然能很好地描述格林函数$P(x,t)$的长时间极限。

英文摘要:

The foundations of the fractional diffusion equation are investigated based on coupled and decoupled continuous time random walks (CTRW). For this aim we find an exact solution of the decoupled CTRW, in terms of an infinite sum of stable probability densities. This exact solution is then used to understand the meaning and domain of validity of the fractional diffusion equation. An interesting behavior is discussed for coupled memories (i.e., Lévy walks). The moments of the random walk exhibit strong anomalous diffusion, indicating (in a naive way) the breakdown of simple scaling behavior and hence of the fractional approximation. Still the Green function $P(x,t)$ is described well by the fractional diffusion equation, in the long time limit.

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