99th iCeMS Seminar: Takuma Akimoto PhD
Subdiffusion, where the mean square displacement (MSD) grows sublinearly with time, has been reported in biological transports, such as two-dimensional diffusion in the plasma membrane and three-dimensional diffusion in the cytoplasm. In particular, mRNA molecules in E. coli cells shows subdiffusion in time-averaged MSDs (TAMSDs) obtained from single-molecule tracking experiments. Moreover, the diffusion coefficients are distributed randomly depending on trajectories [1]. These random behaviors could be a manifestation of ergodicity breaking because time averages should converge to a constant if the system is ergodic.
In this presentation, I will talk about anomalous diffusion properties in biological transports. First, I consider the continuous time random walk (CTRW), which is a model of biological diffusion with binding sites. In CTRWs, the TAMSDs exhibit normal diffusion, whereas the MSD exhibits subdiffusion. Moreover, diffusion coefficients in TAMSDs are distributed according to the Mittag-Leffler distribution. In random walks with static disorder (CTRW is a kind of mean field approximations of this model), the distribution of diffusion coefficients is different from the Mittag-Leffler distribution (the modified Mittag-Leffler distribution) if the system is one-dimensional [2]. Next, I will consider an effect of cutoff in trapping-time distributions, which is a result of finite size of binding sites, in CTRWs. This cutoff provides a novel crossover from the distributional behavior to the ordinary ergodic behavior [3].
Finally, using molecular dynamics simulation of a lipid bilayer, I will present that a lipid bilayer is not only viscoelastic but also has a power-law in the trapping-time distribution. Furthermore, I will report that water molecules near the membrane are stickier than those in bulk.
References.
[1] I. Golding and E. C. Cox, Phys. Rev. Lett. 96, 098102 (2006)
[2] T. Miyaguchi and T. Akimoto, Phys. Rev. E 83, 031926 (2011)
[3] T. Miyaguchi and T. Akimoto, Phys. Rev. E 83, 062101 (2011)
[4] T. Akimoto, E. Yamamoto, K. Yasuoka, Y. Hirano and M. Yasui, Phys. Rev. Lett. 107, 178103 (2011)
| Lecturer Title |
Takuma Akimoto, PhD Department of Mechanical Engineering, Keio University Title: Anomalous Diffusion Properties in Biological Transports |
|---|---|
| Date / Time | January 12, 2012 / 13:30-15:00 |
| Venue | 2nd floor Seminar Room (#A207), Main Building iCeMS Complex 1, Kyoto University Directions |
| Flyer |  PDF (113KB) |
| Host | Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University |
| Co-Host | Center for Frontier Medicine, Global COE Program, Kyoto University |
| Contact | iCeMS Kalay Group kalay-g@icems.kyoto-u.ac.jp |