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Twin positive periodic solutions of second order singular differential systems
(Uniwersytet Mikolaja Kopernika/Nicolaus Copernicus University, 2005-06-01)
In this paper, we study positive periodic solutions to singular second order differential systems. It is proved that such a problem has at least two positive periodic solutions. The proof relies on a nonlinear alternative ...
Multiplicity of positive periodic solutions to second order differential equations
(Cambridge University Press (CUP), 2006-04-01)
In this paper, we study the existence of positive periodic solutions to the equation x" = f (t, x). It is proved that such a equation has more than one positive periodic solution when the nonlinearity changes sign. ...