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arXiv 0710.2819cond-mat.stat-mech
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年龄和平衡随机游动的分数阶扩散方程

Fractional diffusion equation for aging and equilibrated random walks

V. Yu. Zaburdaev, I. M. Sokolov

摘要:

我们考虑连续时间随机游走(CTRW),并讨论有关老化的情况。这些对应于系统的初始状态不是在准备时(在$t=0$)而是在稍后的时刻$t_1>0$(中间时间初始条件)已知的情况。我们推导出这种情况下的广义老化扩散方程,并表示它通过一个单一的记忆核。所得到的结果适用于实际相关的情况下的平衡随机游动。此外,我们讨论了一些微妙的设置中的老化亚扩散问题,并表明该系统的行为取决于什么被视为中间时间的初始条件:无论是一个粒子的坐标测量或整个概率分布。这两种设置导致对系统演化的不同预测。这一事实突出表明,有必要对老龄化统计总体作出准确的定义。

英文摘要:

We consider continuous time random walks (CTRW) and discuss situations pertinent to aging. These correspond to the case when the initial state of the system is known not at preparation (at $t=0$) but at the later instant of time $t_1>0$ (intermediate-time initial condition). We derive the generalized aging diffusion equation for this case and express it through a single memory kernel. The results obtained are applied to the practically relevant case of the equilibrated random walks. We moreover discuss some subtleties in the setup of the aging subdiffusion problem and show that the behavior of the system depends on what was taken as the intermediate-time initial condition: whether it was coordinate of one particle given by measurement or the whole probability distribution. The two setups lead to different predictions for the evolution of a system. This fact stresses the necessity of a precise definition of aging statistical ensembles.

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