Baranov D. B. Phonons and rotons of trapped atoms in gravitational field / D. B. Baranov, V. S. Yarunin // Физика низ. температур. - 2003. - 29, № 6. - С. 674-677. - Библиогр.: 7 назв. - англ.
The excitations of trapped atoms with a Bose - Einstein condensate in a trap are determined by the conservation of common phonon and roton numbers of atomic motion, and these properties depend on the presence of gravitational field.