Diffusion phenomena for the wave equation with space-dependent damping   in an exterior domain
  In this paper, we consider the asymptotic behavior of solutions to the wave equation with space-dependent damping in an exterior domain. We prove that when the damping is effective, the solution is approximated by that of the corresponding heat equation as time tends to infinity. Our proof is based on semigroup estimates for the corresponding heat equation and weighted energy estimates for the damped wave equation. The optimality of the decay late for solutions is also established. 
Motohiro Sobajima, Yuta Wakasugi
math.AP