Existence and multiplicity of nonzero periodic solution with saddle point character for some nonautonomous second order systems

Abstract: The purpose of this paper is to study the existence and multiplicity of nonzero periodic solutions with saddle point character for the following nonautonomous second order systems: Some new existence and multiplicity theorems are obtained by using saddle point reduction method and a three-critical-point theorem proposed by Brezis and Nirenberg. [Copyright &y& Elsevier]