Exact null controllability, complete stabilizability and exact final   observability: the case of neutral type systems
  For abstract linear systems in Hilbert spaces we revisit the problems of exact controllability and complete stabilizability (stabilizability with an arbitrary decay rate), the latter property is equivalent to exact null controllability. We extend this result to the case when the feedback is not bounded. This enables the characterization of exact null controllability and complete stabilizability for neutral type systems. By duality, we obtain a result about continuous final observability.Illustrative examples are given. 
Rabah Rabah, Grigory Sklyar, Pavel Yu. Barkhayev, Pavel Barkhayev,   Grzegorz Szkibiel
math.OC math.DS