Resonant pumping in nonlinear Klein-Gordon equation and solitary packets   of waves
  Solution of the nonlinear Klein-Gordon equation perturbed by small external force is investigated. The frequency of perturbation varies slowly and passes through a resonance. The resonance generates a solitary packets of waves. Full asymptotic description of this process is presented. 
O.M. Kiselev, S.G. Glebov, V.A. Lazarev