Boundary Value Problems
Volume 2009 (2009), Article ID 540863, 20 pages
doi:10.1155/2009/540863
Research Article

Recent Existence Results for Second-Order Singular Periodic Differential Equations

Jifeng Chu1,2 and Juan J. Nieto3

1Department of Mathematics, College of Science, Hohai University, Nanjing 210098, China
2Department of Mathematics, Pusan National University, Busan 609-735, South Korea
3Departamento de Análisis Matemático, Facultad de Matemáticas, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain

Received 12 February 2009; Accepted 29 April 2009

Academic Editor: Donal O'Regan

Copyright © 2009 Jifeng Chu and Juan J. Nieto. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We present some recent existence results for second-order singular periodic differential equations. A nonlinear alternative principle of Leray-Schauder type, a well-known fixed point theorem in cones, and Schauder's fixed point theorem are used in the proof. The results shed some light on the differences between a strong singularity and a weak singularity.