Regensburg 2010 – wissenschaftliches Programm

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SYAT: Symposium Anomalous Transport in Heterogeneous Media - from Porous Materials to Cellular Crowding

SYAT 2: Anomalous Transport in Heterogeneous Media II

SYAT 2.2: Hauptvortrag

Mittwoch, 24. März 2010, 17:00–17:30, H1

Viscoelastic subdiffusion: from anomalous to normal — •Igor Goychuk — Institut für Physik, Universität Augsburg, Germany

The subdiffusional search can bring certain advantages for the cell functioning. However, it can also entail fatal consequences by leading to vanishing effective rates of the subdiffusion-limited binding reactions. Yet there is an increasing body of evidence for the occurrence of subdiffusion in healthy biological cells. Which is the physical mechanism for it and why it can be beneficial? Different answers are currently given. I will discuss one physical mechanism based on the viscoelasticity of complex crowded media within a generalized Langevin equation description. It will be shown that: (i) this mechanism is ergodic, (ii) it does not entail a quasi-infinite mean residence time in a finite spatial domain, and therefore (iii) the subdiffusion-limited binding rate is finite. The escape kinetics out of a potential well follows asymptotically a stretched-exponential law. However, in the limit of high barriers it becomes ever more normal and described by the non-Markovian rate theory. This limit of exponential kinetics can be practically achievable or not, depending on the subdiffusion exponent, memory cutoff, potential height and temperature. Surprisingly, in periodic potentials such a viscoelastic subdiffusion is asymptotically not sensitive to the presence of potential. However, the transient regime with a slowly changing subdiffusion exponent can last very long and initially resemble normal diffusion. Such a combination of anomalous and normal features selects viscoelastic mechanism as biologically most relevant [1].

[1] I. Goychuk, Phys. Rev. E 80, 046125 (2009).