Invariant curves of almost periodic twist mappings
  In this paper we are concerned with the existence of invariant curves of planar twist mappings which are almost periodic in a spatial variable. As an application of this result to differential equations we will discuss the existence of almost periodic solutions and the boundedness of all solutions for superlinear Duffing's equation with an almost periodic external force. 
Peng Huang, Xiong Li, Bin Liu
math.DS