Perturbations of Admissibility, Exact Controllability, Exact   Observability and Regularity
  This paper is concerned with the notions of admissibility, exact controllability, exact observability and regularity of linear systems in the Banach space setting. It is proved that admissible controllability, exact controllability, admissible observation, exact observability and regularity are invariant under some regular perturbations of the generators, such results are generalizations of some previous references. Moreover, the related boundary linear systems and some illustrative examples are presented. 
Zhan-Dong Mei and Ji-Gen Peng
math.FA math.OC