Statistical Ensembles with Volume Fluctuations
  The volume fluctuations in statistical mechanics are discussed. First, the volume fluctuations in ensembles with a fixed external pressure, the so called pressure ensembles, are considered. Second, a generalization of the pressure ensembles is suggested. Namely, the statistical ensembles with the volume fluctuating according to externally given distributions are considered. Several examples and possible applications in statistical models of hadron production are discussed. 
Mark I. Gorenstein