Weak asymptotic method for the study of propagation and interaction of infinitely narrow δ -solitons. Danilov, Vladimir G., Omel'yanov, Georgii A. (2003) Electronic Journal of Differential Equations (EJDE) [electronic only]
WKB analysis for the Gross-Pitaevskii equation with non-trivial boundary conditions at infinity Thomas Alazard, Rémi Carles (2009) Annales de l'I.H.P. Analyse non linéaire