  The damping effect to the DNA bubble is investigated within the
Peyrard-Bishop model. In the continuum limit, the dynamics of the bubble of DNA
is described by the damped nonlinear Schrodinger equation and studied by means
of variational method. It is shown that the propagation of solitary wave
pattern is not vanishing in a non-viscous system. Inversely, the solitary wave
vanishes soon as the viscous force is introduced.
