  Asymmetric exclusion processes for particles moving on parallel channels with
inhomogeneous coupling are investigated theoretically. Particles interact with
hard-core exclusion and move in the same direction on both lattices, while
transitions between the channels is allowed at one specific location in the
bulk of the system. An approximate theoretical approach that describes the
dynamics in the vertical link and horizontal lattice segments exactly but
neglects the correlation between the horizontal and vertical transport is
developed. It allows us to calculate stationary phase diagrams, particle
currents and densities for symmetric and asymmetric transitions between the
channels. It is shown that in the case of the symmetric coupling there are
three stationary phases, similarly to the case of single-channel totally
asymmetric exclusion processes with local inhomogeneity. However, the
asymmetric coupling between the lattices lead to a very complex phase diagram
with ten stationary-state regimes. Extensive Monte Carlo computer simulations
generally support theoretical predictions, although simulated stationary-state
properties slightly deviate from calculated in the mean-field approximation,
suggesting the importance of correlations in the system. Dynamic properties and
phase diagrams are discussed by analyzing constraints on the particle currents
across the channels.
