We consider the problem of multiplicity and uniqueness of radial solutions of a nonlinear elliptic equation of the form where f is a prescribed function, satisfying appropriate conditions. This paper is a review of recent ...

Using Leray-Schauder degree theory and the method of upper andlower solutions we establish existence and multiplicity of solutions for problemsof the form(ϕ(u0))0 = f(t, u, u0)u(0) = u(T) = u0(0),where ϕ is an increasing ...

We consider an elliptic system with linear part depending on two parameters and a sublinear perturbation. We obtain the existence of at least two solutions when the linear part is near resonance. The system is associated ...

Small non-autonomous perturbations around an equilibrium of a nonlinear delayed system are studied. Under appropriate assumptions, it is shown that the number of T-periodic solutions lying inside a bounded domain Ω ⊂ R N ...