Simultaneous diffusion and homogenization asymptotic for the linear   Boltzmann equation
  This article is on the simultaneous diffusion approximation and homogenization of the linear Boltzmann equation when both the mean free path $\varepsilon$ and the heterogeneity length scale $\eta$ vanish. No periodicity assumption is made on the scattering coefficient of the background material. There is an assumption made on the heterogeneity length scale $\eta$ that it scales as $\varepsilon^\beta$ for $\beta\in(0,\infty)$. In one space dimension, we prove that the solutions to the kinetic model converge to the solutions of an effective diffusion equation for any $\beta\le2$ in the $\varepsilon\to0$ limit. In any arbitrary phase space dimension, under a smallness assumption of a certain quotient involving the scattering coefficient in the $H^{-\frac{1}{2}}$ norm, we again prove that the solutions to the kinetic model converge to the solutions of an effective diffusion equation in the $\varepsilon\to0$ limit. 
Claude Bardos (Paris VII), Harsha Hutridurga (Imperial College)
math.AP