The phenomenon of two-soliton resonances of the Kadomtsev-Petviashvilli equation for the superfluid surface density fluctuation in He films is studied. The velocity of the resonant soliton is obtained.
J. Sreekumar and Dr. V . M. Nandakumaran, “Soliton resonances in helium films”, Physics Letters A, vol. 112, pp. 168–170, 1985.