E Gershnabel, Katz, N, Ozeri, R, Rowen, E , Steinhauer, J , and Davidson, N . 2004. “Echo Spectroscopy Of Bulk Bogoliubov Excitations In Trapped Bose-Einstein Condensates”. Physical Review A, 69, Pp. 041604. doi:10.1103/PhysRevA.69.041604.