Of Rice and Men: Jamming of inert and active matter
Dept. of Physics and Astronomy, Swarthmore College
Abstract. — Grain, sand, colloids, living cells and pedestrians can behave dramatically by suddenly solidifying into a disordered “jammed” structure. Much has been learned about jamming in last two decades. Our research asks what is new and different when these particles are in contact with a fixed framework, like a lattice of diminutive obstacles or “pins”. In a first project on inert matter, pins permit one to tune the location of the jamming phase transition, and modify the solid structure. Anomalously weak as well as unusually strong interparticle forces are supported by pins. Heatmaps reveal a rich local structure and a transition to orientational order. We are in the process of characterizing the topology of the stress state via persistent homology.
A second project involves active matter undergoing bidirectional flow through a narrow aperture. A tendency of one species to follow each other (seen in flocking, as well as crowd panic behavior) enhances the mobility of non-followers and simultaneously decreases the mobility of followers. This leads to a clogging/jamming transition, identified from power law tails in the lag time distribution for the intermittent flow. The ability of passive obstacles to modify the flow of active matter is well known, and motivates determining the role of pins in this transition.
Host: Harsh Mathur