Bose-Einstein condensates with attractive interactions on a ring
  Considering an effectively attractive quasi-one-dimensional Bose-Einstein condensate of atoms confined in a toroidal trap, we find that the system undergoes a phase transition from a uniform to a localized state, as the magnitude of the coupling constant increases. Both the mean-field approximation, as well as a diagonalization scheme are used to attack the problem. 
G. M. Kavoulakis (LTH, Lund, Sweden)