Physics Colloquium, April 25, 2006

A least dissipation principle for single molecule mechanics

R. Dean Astumian

The University of Maine

There has been much interest in applying the results of statistical mechanics to single molecule experiments. Recent work has highlighted nonequilibrium work-energy relations and fluctuation theorems that have an equilibrium-like (time independent) form. I give a simple heuristic example where an equilibrium result (the barometric law for colloidal particles) arises from describing the nonequilibrium behavior of a single colloidal particle falling due to gravity through the solution. This description arises from the fact that the particle, even while falling, is in mechanical equilibrium (the gravitational force equals the viscous drag force) at every instant. The results are generalized using Onsager's least dissipation approach for stochastic processes to derive time independent equations that hold for thermodynamically nonequilibrium (and even nonstationary) systems. The equations offer great possibilities for the rapid determination of thermodynamic parameters from single molecule experiments.

4:00 p.m., Physics Research Building (PRB), Room 1080

Reception at 3:45 p.m., Atrium, PRB