On the Existence of Periodic Solutions to Certain Impulsive Differential 
Equations 

C. Cooke and J. Kroll 

The authors study here an impulsive differential systems which appears to
have no periodic solutions. Continuous manifolds of initial vectors are found
for which it is proven that the trajectory emanating from each initial vector
is unstable; hence, non-periodic. It is also established that a particular
type of impulsive periodic solution, the so-called simple periodic motion,
can not exist.