Periodic solutions to differential systems with unbounded or periodic nonlinearities
The authors investigate the existence and multiplicity of periodic solutions to differential systems of Josephson type. They prove some variants of results obtained by K. C. Chang and others [see also \textit{A. Fonda} and \textit{J. Mawhin}, in: M. Themistocles Rassias (ed.), The Problem of Plateau: A tribute to J. Douglas and T. Rado. London: World Scientific Publishing Co. Pte. Ltd, 111--128 (1992; Zbl 0798.58028)]. The proofs use variational methods, and in particular the saddle point theorem with some of its generalizations.
scientific article; zbMATH DE number 5077904