Adaptive Observers as Nonlinear Internal Models
  This paper shows how the theory of nonlinear adaptive observers can be effectively used in the design of internal models for nonlinear output regulation. The theory substantially enhances the existing results in the context of {\em adaptive} output regulation, by allowing for not necessarily stable zero dynamics of the controlled plant and by weakening the standard assumption of having the steady state control input generated by a linear system. 
Francesco Delli Priscoli, Lorenzo Marconi, Alberto Isidori