Dynamics of a perfect fluid through velocity potentials with aplication   in quantum cosmology
  We review the Eulerian description of hidrodynamics using Seliger-Whitham's formalism (in classical case) and Schutz's formalism (in relativistic case). In these formalisms, the velocity field of a perfect fluid is described by scalar potentials. With this we can obtain the evolution equations of the fluid and its Hamiltonian. In the scenario of quantum cosmology the Schutz's formalism makes it possible to introduce phenomenologically a time variable in minisuperspace models. 
F. G. Alvarenga, R. Fracalossi, R. G. Furtado and S. V. B.   Gon\c{c}alves
gr-qc