U. Schultze et al., WIND-TREE MODEL IN 2 DIMENSIONS WITH INTERNAL DEGREES OF FREEDOM - EXACT SOLUTION, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 47(6), 1993, pp. 4589-4592
The two-dimensional wind-tree model with particles with four allowed v
elocities, which can scatter off obstacles with internal degrees of fr
eedom, is solved exactly. Depending on initial conditions the distribu
tion functions and entropy of obstacles can display a nonmonotonic tim
e dependence with over- and underpopulations followed by transient rel
axation.