Behavior of a boundary of moving volume inside of a smooth flow of   compressible liquid
  The question on expansion of moving volume inside of a smooth flow of the compressible liquid is under consideration. We find a condition on initial data such that if it holds, then within a finite time either the boundary of the moving volume attains a given neighborhood of a certain point (that do not belong to the volume initially), or some a priori estimate for the pressure on the boundary of volume fails. 
Olga Rozanova