On the modulational stability of Gross-Pitaevskii type equations in 1+1   dimensions
  The modulational stability of the nonlinear Schr{\"o}dinger (NLS) equation is examined in the case with a quadratic external potential. This study is motivated by recent experimental studies in the context of matter waves in Bose-Einstein condensates (BECs). The theoretical analysis invokes a lens-type transformation that converts the Gross-Pitaevskii into a regular NLS equation with an additional growth term. This analysis suggests the particular interest of a specific time-varying potential ((t+t*)^{-2}). We examine both this potential, as well as the time independent one numerically and conclude by suggesting experiments for the production of solitonic wave-trains in BEC. 
G. Theocharis, Z. Rapti, P.G. Kevrekidis, D.J. Frantzeskakis and V.V.   Konotop