Mossbauer effect for dark solitons in Bose-Einstein condensates
  We show that the energetic instability of dark solitons is associated with particle-like motion, and present a simple equation of motion, based on the M\"ossbauer effect, for dark solitons propagating in inhomogeneous Thomas-Fermi clouds. Numerical simulations support our theory. We discuss some experimental approaches. 
Th. Busch and J.R. Anglin