用首次通过观测量探讨受限次扩散的微观起源
Probing microscopic origins of confined subdiffusion by first-passage observables
摘要：
示踪粒子在复杂拥挤环境中的亚扩散运动，如生物细胞，已被证明是广泛的。这种对布朗运动的偏离通常以均方位移（MSD）的次线性时间依赖性为特征。然而，亚扩散行为可以源于不同的微观场景，这不能仅仅通过MSD数据来识别。在本文中，我们提出了一个理论框架，允许计算分析第一次通过观测（平均第一次通过时间，分裂概率和占领时间分布）在无序介质中的任何尺寸。这种分析适用于两个代表性的微观模型的subdiffusion：连续时间随机游动与重尾等待时间，和分形扩散。我们的研究结果表明，第一次通过观测值提供的工具，明确区分两种可能的微观情况下的次扩散。此外，我们建议实验的基础上，第一次通过的观测，这可能有助于确定在复杂的媒体，如活细胞的亚扩散的起源，并讨论异常运输的影响，在细胞中的反应动力学。
英文摘要：
Subdiffusive motion of tracer particles in complex crowded environments, such as biological cells, has been shown to be widepsread. This deviation from brownian motion is usually characterized by a sublinear time dependence of the mean square displacement (MSD). However, subdiffusive behavior can stem from different microscopic scenarios, which can not be identified solely by the MSD data. In this paper we present a theoretical framework which permits to calculate analytically first-passage observables (mean first-passage times, splitting probabilities and occupation times distributions) in disordered media in any dimensions. This analysis is applied to two representative microscopic models of subdiffusion: continuous-time random walks with heavy tailed waiting times, and diffusion on fractals. Our results show that first-passage observables provide tools to unambiguously discriminate between the two possible microscopic scenarios of subdiffusion. Moreover we suggest experiments based on first-passage observables which could help in determining the origin of subdiffusion in complex media such as living cells, and discuss the implications of anomalous transport to reaction kinetics in cells.
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