  We study the flux of totally asymmetric simple exclusion processes (TASEPs)
on a twin co-axial square tracks. In this biologically motivated model the
particles in each track act as mobile bottlenecks against the movement of the
particles in the other although the particle are not allowed to move out of
their respective tracks. So far as the outer track is concerned, the particles
on the inner track act as bottlenecks only over a set of fixed segments of the
outer track, in contrast to site-associated and particle-associated quenched
randomness in the earlier models of disordered TASEP. In a special limiting
situation the movement of particles in the outer track mimic a TASEP with a
"point-like" immobile (i.e., quenched) defect where phase segregation of the
particles is known to take place. The length of the inner track as well as the
strength and number density of the mobile bottlenecks moving on it are the
control parameters that determine the nature of spatio-temporal organization of
particles on the outer track. Variation of these control parameters allow
variation of the width of the phase-coexistence region on the flux-density
plane of the outer track. Some of these phenomena are likely to survive even in
the future extensions intended for studying traffic-like collective phenomena
of polymerase motors on double-stranded DNA.
