On the Frequency Theorem for nonperiodic systems

with Roberta Fabbri and  Russell Johnson,
in: Dynamics, Bifurcations and Control, 233-241,
Lecture Notes in Control and Information Sciences 273,
ed: Fritz Colonius, Springer-Verlag, 2002.

Using methods of the theory of nonautonomous linear differential systems,
namely exponential dichotomies and rotation numbers, some aspects of
Yakubovich's Frequency Theorem from periodic control systems are
generalized to systems with bounded measurable coefficients