Pion abundance and entropy in the hydrodynamical description of   relativistic nuclear collisions
  We show that a hydrodynamical model with continuous particle emission instead of sudden freeze out can explain both the strange particle abundances and pion abundance from NA35 without extra assumption (e.g., sequential freeze out, modified equation of state, sudden plasma hadronization,...). In this scenario, the observation of a larger pion abundance is natural and does not imply a higher initial entropy and early plasma phase. 
F. Grassi and O. Socolowski Jr