Paper is at <a href="http://arxiv.org/abs/0912.0888" rel="nofollow">http://arxiv.org/abs/0912.0888</a> . The Boltzmann equation describes the motion of particles in a fluid. If I've understood the opening section of the paper correctly (which I may not have done), other people have found solutions of the Boltzmann equation under some rather unrealistic assumptions about the distribution of relative velocities when particles collide. (AIUI you're supposed to work out that distribution by doing some actual physics, then plug it into the equation; the solutions describe the behaviour of a fluid with the properties encoded in that distribution.) Specifically, past work has required the assumption that collisions at shallow glancing angles never happen, which is typically far from the truth. What's new in this paper is that they've got rid of those unrealistic assumptions. I think.