SCIENCE SEMINAR
Brownian Motion, Active Fluctuations, and Anomalous diffusion
Prof. Mehran Kardar
Massachusetts Institute of Technology
Monday, February 18, 2008
11:30 a.m.
Nicolls 2
Brownian motion plays an important role in the framework for analyzing fluctuations and diffusion. I shall discuss two examples, inspired by biological systems, where this framework has to be applied with caution:
- Locomotion of bacteria by actin polymerization, and in vitro motion of spherical beads coated with a protein catalyzing polymerization, are examples of active motility. Starting from a simple model of forces locally normal to the surface of a bead, we construct a phenomenological equation for its motion. The singularities at a continuous transition between moving and stationary beads are shown to be related to the symmetries of its shape. The fluctuations of such an actively energy consuming system are shown to be quite different from those of a passive Brownian particle.
- The passage of a polymer (e.g. a nucleic acid) through a membrane pore is characterized by several scaling laws. In particular, the dynamics of the process is shown to be anomalous (non-diffusive).
