Global action-angle coordinates for completely integrable systems with   noncompact invariant submanifolds
  The obstruction to the existence of global action-angle coordinates of Abelian and noncommutative (non-Abelian) completely integrable systems with compact invariant submanifolds has been studied. We extend this analysis to the case of noncompact invariant submanifolds. 
E.Fiorani, G.Sardanashvily