Existence of positive periodic solutions to nonlinear second order differential equations

Abstract: In this paper, we discuss the existence of positive periodic solutions to the nonlinear differential equation where is an -periodic continuous function with , is continuous and is also an -periodic function for each . Using the fixed point index theory in a cone, we get an essential existence result because of its involving the first positive eigenvalue of the linear equation with regard to the above equation. [Copyright &y& Elsevier]