This paper considers properties of nonlinear waves and solitons of
Korteweg-de Vries equation in the presence of external perturbation. For
time-periodic hamiltonian perturbation the width of the stochastic layer is
calculated. The conclusions about chaotic behaviour in long-period waves and
solitons are inferred. Obtained theoretical results find experimental
confirmation in experiments with the propagation of ion-acoustic waves in
plasma.Comment: 7 pages, LaTeX, 2 Postscript figures, submitted to Reports on
Mathematical Physic
