A channel Brownian pump powered by an unbiased external force.

A Brownian pump of particles in an asymmetric finite tube is investigated in the presence of an unbiased external force. The pumping system is bounded by two particle reservoirs. It is found that the particles can be pumped through the tube from a reservoir at low concentration to one at the same or higher concentration. There exists an optimized value of temperature (or the amplitude of the external force) at which the pumping capacity takes its maximum value. The pumping capacity decreases with increasing radius at the bottleneck of the tube.