Bidirectional flow of confined active matter through an aperture: same-species Following and Obstacles

Collective movement of many-body systems like flocks of animals, swarms of robots or inert active matter is an out-of-equilibrium situation with a rich character that includes heterogeneous dynamics, pattern formation, and jamming/clogging. We simulate bidirectional flow of active matter, in which two species confined in a 2d channel are driven in opposite directions through a narrow aperture. Our interest is in the role of individual behavioral rules on transport, under the Helbing-Molnár-Farkas-Vicsek model. This active matter model includes psychosocial and granular material forces. We ask how the individual tendency to follow other particles of the same species affects passage through a rate-limiting aperture. We calculate the time averaged current, burst size and time lag statistics. One finds power-law tailed PDFs of lag times just as in cases of constricted unidirectional flow. The power-law exponent locates a clogging phase transition as a function of the tendency to follow. We repeat this analysis in the presence of small, randomly placed, inert-matter obstacles. Fixed obstacles have been known to affect passage through an aperture and modify collective behavior (for example, shift the location of phase transitions) in non-active and active matter systems.