Fig. 1: Tracer dynamics in a (non-)equilibrium environment.
From: Emergent memory from tapping collisions in active granular matter
Tracer and bath particles are represented by large and small disks, respectively. a The equilibrium scenario is characterized by elastic collisions that conserve energy and momentum. After a collision with the environmental particle, the tracer behaves as a passive unit subject to Brownian motion and dissipation. b The non-equilibrium environment formed by active vibrobots does not conserve energy, which is continuously injected into the system by the active force. Particles of the environment display tapping collisions, i.e., collisions are persistent and the particles of the environment align around the tracer. As a result, the tracer performs an effective active motion. Note that, in general, collisions of granular particles are partially inelastic. However, this does not alter the present picture.
