  Geometric stochastic resonance of particles diffusing across a porous
membrane subject to oscillating forces is characterized as a synchronization
process. Noninteracting particle currents through a symmetric membrane pore are
driven either perpendicular or parallel to the membrane, whereas
harmonic-mixing spectral current components are generated by the combined
action of perpendicular and parallel drives. In view of potential applications
to the transport of colloids and biological molecules through narrow pores, we
also consider the role of particle repulsion as a controlling factor.
