Collective Motion and Phase Transitions of Symmetric Camphor Boats
  The motion of several self-propelled boats in a narrow channel displays spontaneous pattern formation and kinetic phase transitions. In contrast with previous studies on self-propelled particles, this model does not require stochastic fluctuations and it is experimentally accessible. By varying the viscosity in the system, it is possible to form either a stationary state, correlated or uncorrelated oscillations, or unidirectional flow. Here, we describe and analyze these self organized patterns and their transitions. 
Eric Heisler, Nobuhiko J. Suematsu, Akinori Awazu, Hiraku Nishimori
cond-mat.stat-mech