  A model of an autonomous isothermal Brownian motor with an internal
propulsion mechanism is considered. The motor is a Brownian particle which is
semi-transparent for molecules of surrounding ideal gas. Molecular passage
through the particle is controlled by a potential similar to that in the
transition rate theory, i.e. characterized by two stationary states with a
finite energy difference separated by a potential barrier. The internal
potential drop maintains the diode-like asymmetry of molecular fluxes through
the particle, which results in the particle's stationary drift.
