Boundary Value Problems 
Volume 2006 (2006), Article ID 25104, 9 pages
doi:10.1155/BVP/2006/25104

Periodic solutions of second-order nonautonomous dynamical systems

Martin Schechter

 Department of Mathematics, University of California, Irvine 92697-3875, CA, USA
Received 13 March 2006; Revised 10 May 2006; Accepted 15 May 2006

Abstract

We study the existence of periodic solutions for second-order nonautonomous dynamical systems. We give four sets of hypotheses which guarantee the existence of solutions. We were able to weaken the hypotheses considerably from those used previously for such systems. We employ a new saddle point theorem using linking methods.