Rf. Curtain et Aj. Sasane, Compactness and nuclearity of the Hankel operator and internal stability of infinite-dimensional state linear systems, INT J CONTR, 74(12), 2001, pp. 1260-1270
We examine the relationships between the exponential (or strong) stability
of certain classes of regular linear systems and the compactness and nuclea
rity properties of the Hankel operator. New sufficient conditions for nucle
arity are given for exponentially stable regular linear systems with an ana
lytic semigroup.