Freeze Out and the Boltzmann Transport Equation
  Recently several works have appeared in the literature that addressed the problem of Freeze Out in energetic heavy ion reaction and aimed for a description based on the Boltzmann Transport Equation (BTE). In this paper we develop a dynamical Freeze-Out description, starting from the BTE, pointing out the basic limitations of the BTE approach, and the points where the BTE approach should be modified. 
L.P. Csernai, V.K. Magas, E. Molnar, A. Nyiri and K. Tamosiunas