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has been cited by the following article:

• TITLE: Periodic Solutions to Non-Autonomous Second-Order Dynamical Systems

  AUTHORS: An-Min Mao, Miao-Miao Yang

  KEYWORDS: Critical Point, Invariant Sets of Descending Flow, (PS) Condition

  JOURNAL NAME: Advances in Pure Mathematics, Vol.1 No.3, June 3, 2011

  ABSTRACT: We study the multiple existence of periodic solutions for a second-order non-autonomous dynamical systems (1). Using the method of invariant sets of descending flow and chain of rings theorem, we obtain the existence of seven -periodic solutions.