Thermodynamic hierarchies of evolution equations
  Non-equilibrium thermodynamics with internal variables introduces a natural hierarchical arrangement of evolution equations. Three examples are shown: a hierarchy of linear constitutive equations in thermodynamic rhelogy with a single internal variable, a hierarchy of wave equations in the theory of generalized continua with dual internal variables and a hierarchical arrangement of the Fourier equation in the theory of heat conduction with current multipliers. 
P. V\'an, R. Kov\'acs and T. F\"ul\"op
cond-mat.stat-mech