Positive periodic solutions for fully third-order ordinary differential equations

In this paper the existence results of positive !-periodic solutions are obtained for the fully third-order ordinary differential equation u000.t/ D f .t; u.t/; u0.t/; u00.t//; t 2 R where f 2 C.R .0;1/ R R; R/ is !-periodic in t, and f .t; u; v;w/ may be singular at u D 0. The discussion is based on a fixed point theorem in cones.