Velocity Distributions of Granular Gases with Drag and with Long-Range   Interactions
  We study velocity statistics of electrostatically driven granular gases. For two different experiments: (i) non-magnetic particles in a viscous fluid and (ii) magnetic particles in air, the velocity distribution is non-Maxwellian, and its high-energy tail is exponential, P(v) ~ exp(-|v|). This behavior is consistent with kinetic theory of driven dissipative particles. For particles immersed in a fluid, viscous damping is responsible for the exponential tail, while for magnetic particles, long-range interactions cause the exponential tail. We conclude that velocity statistics of dissipative gases are sensitive to the fluid environment and to the form of the particle interaction. 
K. Kohlstedt, A. Snezhko, M.V. Sapozhnikov, I. S. Aranson, J. S.   Olafsen, E. Ben-Naim