A note on spatial uniformation for Fisher-KPP type equations with a concentration dependent diffusion

Abstract

We prove a pointwise gradient estimate for the solution of the Cauchy problem associated to the quasilinear Fisher-KPP type equation with a diffusion coefficient ϕ(u) satisfying that ϕ(0) = 0, ϕ(1) = 1 and a source term ψ(u) which is vanishing only for levels u = 0 and u = 1. As consequence we prove that the bounded weak solution becomes instantaneously a continuous function even if the initial datum is merely a bounded function.