Collective excitations of atomic Bose-Einstein condensates
  We apply linear-response analysis of the Gross-Pitaevskii equation to obtain the excitation frequencies of a Bose-Einstein condensate confined in a time-averaged orbiting potential trap. Our calculated values are in excellent agreement with those observed in a recent experiment. 
Mark Edwards (Georgia Southern University), P.A. Ruprecht and K.   Burnett (Oxford University), R.J. Dodd and Charles W. Cla...