Michele V. Bartuccelli, Jonathan H.B. Deane, Guido Gentile, Luke Marsh
Invariant sets for the varactor equation
(1537K, pdf)

ABSTRACT.  The differential equation $\ddot{x} + \gamma \dot{x} + x^\mu = f(t)$ 
with $f(t)$ positive, periodic and continuous is studied. 
After describing some physical applications of this equation, 
we construct a variety of invariant sets for it, thereby partitioning 
the phase plane into regions in which solutions grow without bound 
and also those in which bounded periodic solutions exist.