Propagators and time-dependent diffusion coefficients for anomalous diffusion.
Propagators and time-dependent diffusion coefficients for anomalous diffusion.
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DOI：
10.1529/biophysj.107.121608
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发表时间：
2008-08
影响因子：
3.4
通讯作者：
Jianrong Wu;K. Berland
中科院分区：
文献类型：
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作者：
Jianrong Wu;K. Berland
当人们研究活细胞和其他复杂环境中大分子的流动性时，经常会观察到复杂的扩散动力学，但异常扩散的潜在物理或化学原因通常尚未完全理解，因此是正在进行的研究兴趣的主题。捕获异常动力学的理论模型被广泛用于分析来自荧光相关光谱和其他实验测量的迁移率数据，但这些模型存在明显的混乱，因为已发布的版本并不完全一致，并且在某些情况下似乎不满足扩散方程。拟合参数报告方式的变化导致了进一步的混乱。拟合参数及其物理意义的明确定义对于准确解释实验数据以及比较在不同实验条件下获得的不同研究结果至关重要。本文旨在阐明与常用拟合模型相关的随时间扩散系数的物理含义，以方便其用于研究异常扩散的根本原因。我们讨论了一种反常扩散的传播器，它捕获均方位移的幂律依赖性，并且可以证明严格满足扩展扩散方程，前提是正确定义了与时间相关的扩散系数。我们还明确阐明了荧光相关光谱中随时间扩散系数与拟合参数之间的关系。
Complex diffusive dynamics are often observed when one is investigating the mobility of macromolecules in living cells and other complex environments, yet the underlying physical or chemical causes of anomalous diffusion are often not fully understood and are thus a topic of ongoing research interest. Theoretical models capturing anomalous dynamics are widely used to analyze mobility data from fluorescence correlation spectroscopy and other experimental measurements, yet there is significant confusion regarding these models because published versions are not entirely consistent and in some cases do not appear to satisfy the diffusion equation. Further confusion is introduced through variations in how fitting parameters are reported. A clear definition of fitting parameters and their physical significance is essential for accurate interpretation of experimental data and comparison of results from different studies acquired under varied experimental conditions. This article aims to clarify the physical meaning of the time-dependent diffusion coefficients associated with commonly used fitting models to facilitate their use for investigating the underlying causes of anomalous diffusion. We discuss a propagator for anomalous diffusion that captures the power law dependence of the mean-square displacement and can be shown to rigorously satisfy the extended diffusion equation provided one correctly defines the time-dependent diffusion coefficient. We also clarify explicitly the relation between the time-dependent diffusion coefficient and fitting parameters in fluorescence correlation spectroscopy.