On the existence and multiplicity of positive periodic solutions of a nonlinear third-order equation

In this paper, we are concerned with the existence and multiplicity of positive 2π2π-periodic solutions for the following nonlinear third-order problem u‴(t)+αu″(t)+βu′(t)=f(t,u(t)).u‴(t)+αu″(t)+βu′(t)=f(t,u(t)). Here α,βα,β are two positive constants, f(t,u)∈C(R×R,R),f(t+2π,u)=f(t,u)f(t,u)∈C(R×R,R),f(t+2π,u)=f(t,u). The proof relies on a fixed point theorem on cones.