Blow up versus Global Boundedness of Solutions of Reaction Diffusion Equations with Nonlinear Boundary Conditions∗

In this paper we analyze the behavior of solutions of reaction-diffusion equations with nonlinear boundary conditions of the type (1.1). We show that if f(x, u) = −β0u and g(x, u) = uq in a neighborhood of a point x0 ∈ ΓN , then i) for the case q > 1, if p + 1 < 2q or if p + 1 = 2q and β0 < q, then blow up in finite time at x0 occurs. ii) for the case p > 1 if p + 1 > 2q or if p + 1 = 2q and β0 > q then any solution is globally bounded around the point x0.