  As a model for molecular traffic control (MTC) we investigate the diffusion
of hard core particles in crossed single-file systems. We consider a square
lattice of single-files being connected to external reservoirs. The (vertical)
alpha-channels, carrying only A-particles, are connected to reservoirs with
constant density ra. B-particles move along the (horizontal) beta-channels,
which are connected to reservoirs of density rB. We allow the irreversible
transition A to B at intersections. We are interested in the stationary density
profile in the alpha- and beta- channels, which is the distribution of the
occupation probabilities over the lattice. We calculate the stationary currents
of the system and show that for sufficiently long channels the currents (as a
function of the reservoir densities) show in the limit of large transition
rates non analytic behavior. The results obtained by direct solution of the
master equation are verified by kinetic Monte Carlo simulations.
