Thermo Field Dynamics and quantum algebras
  The algebraic structure of Thermo Field Dynamics lies in the $q$-deformation of the algebra of creation and annihilation operators. Doubling of the degrees of freedom, tilde-conjugation rules, and Bogoliubov transformation for bosons and fermions are recognized as algebraic properties of $h_{q}(1)$ and of $h_{q}(1|1)$, respectively. 
E.Celeghini, S.De Martino, S.De Siena, A.Iorio, M.Rasetti and   G.Vitiello