Existence and multiplicity of radial solutions for an elliptic boundary value problem on an annulus

This paper deals with the study of the existence and multiplicity of radial solutions for the problem -Delta u(x) = f(u(x)) when x is an element of Omega and u(x) = 0 when x is an element of Omega, where Omega = {x is an element of R-N; a < vertical bar x vertical bar < b} with 0 < a < b is an annulus in R-N and f : R --> R is a continuous function. We use as main tools Schaeffer's fixed point theorem and Leggett-Williams fixed point theorem in order to obtain radial solutions for the above problem.