LARGE TIME BEHAVIOR FOR CONVECTION-DIFFUSION EQUATIONS IN RN

We describe the large time behavior of solutions of the convection-diffusion equation ut - Δu = a · ▽(|u|q - 1u) in (0, ∞) × RN with a ε{lunate} RN and q ≥ 1 + 1 N, N ≥ 1. When q = 1 + 1 N, we prove that the large time behavior of solutions with initial data in L1(RN) is given by a uniparametric family of self-similar solutions. The relevant parameter is the mass of the solution that is conserved for all t. Our result extends to dimensions N > 1 well known results on the large time behavior of solutions for viscous Burgers equations in one space dimension. The proof is based on La Salle's Invariance Principle applied to the equation written in its self-similarity variables. When q > 1 + 1 N the convection term is too weak and the large time behavior is given by the heat kernel. In this case, the result is easily proved applying standard estimates of the heat kernel on the integral equation related to the problem. © 1991.