A Langevin simulation for active transport

A nonequilibrium state is studied by a Langevin equation with an additional boundary condition. The active transport across the membrane is studied as an example of a nonequilibrium state. The electric potential is normally positive outside the cell membrane owing to the active transport of ions. A probabilistic boundary condition plays a role of pumping for ions in the Langevin simulation. The mathematical model can be solved using an averaged Fokker-Planck equation, and the solution is compared with the Langevin simulation.