Nonlinear Coupling of Langmuir Wave and Dust-Acoustic Wave in Plasmas with the Variable-charge grains

Nonlinear interaction of the Langmuir wave and the dust-acoustic wave in plasmas with the variable-charge grains has been investigated.In the approximation of small amplitude,we find the solution of envelope soliton for the nonlinear Langmuir wave.The results show that the amplitude of envelope soliton increases with the increasing of dust grain density.