Remarks on an S-shaped bifurcation curve

We study the non-negative solutions of the boundary value problem $\text{?Δu = λ}\text{exp}\text{αu}\text{(α + u)}\text{]; x ? Ω. u = 0; x ? ?Ω,}\text{where}\text{α > 0, λ ? 0, Ω ? R}{}^{\mathrm{n}}$ is bounded with smooth boundary ?Ω.This problem arises in the theory of combustion. We study the estimates on the supremum norm of the solutions and estimates on the critical values of λ.