Narrow Results

We consider the problem of transitions between states of a bistable mechanical system induced by a harmonically, and a randomly oscillating barrier. We study the problem both experimentally and numerically. The system consists of a mass attached to a rotating disk, nonlinearly coupled to a spring subject to an external force. For periodically driven external forces, the transition rate across the barrier increases linearly with the frequency of the driving force until the system reaches the boundary of a chaotic region. Beyond this boundary, the rate drops sharply until it is fully suppressed at the end of this region. When the driving force is stochastic we find that the transition rate also has a maximum, and that its position depends on the rate of switching of the random force.

We present a nonequilibrium reaction rate model of the ionic transition through an open ion channel, taking account of the interaction between an ion at the entrance of the channel and an ion at the binding site in a self-consistent way. The electrostatic potential is calculated by solution of the Poisson equation for a channel modeled as a cylindrical tube. The transition rate, and the binding site occupancy as a function of the left bulk concentration are compared to 1D Brownian dynamics simulations. The analysis is performed for a single binding site of high-affinity, with the exit rate influenced by barrier fluctuations at the channel exit. The results are compared with experimental data for the permeation of the Na⁺ ion through the Gramicidin A channel, with which they are shown to be in good agreement.

We present a nonequilibrium reaction rate model of the ionic transition through an open ion channel, taking account of the interaction between an ion at the entrance of the channel and an ion at the binding site in a self-consistent way. The electrostatic potential is calculated by solution of the Poisson equation for a channel modeled as a cylindrical tube. The transition rate, and the binding site occupancy as a function of the left bulk concentration are compared to 1D Brownian dynamics simulations. The analysis is performed for a single binding site of high-affinity, with the exit rate influenced by barrier fluctuations at the channel exit. The results are compared with experimental data for the permeation of the Na⁺ ion through the Gramicidin A channel, with which they are shown to be in good agreement.