Bose-Einstein condensation under external conditions
  We discuss the phenomenon of Bose-Einstein condensation under general external conditions using connections between partition sums and the heat-equation. Thermodynamical quantities like the critical temperature are given in terms of the heat-kernel coefficients of the associated Schr\"odinger equation. The general approach is applied to situations where the gas is confined by arbitrary potentials or by boxes of arbitrary shape. 
Klaus Kirsten and David J. Toms