Onsager relations and Eulerian hydrodynamics for systems with several   conservation laws
  We present the derivation of the hydrodynamic limit under Eulerian scaling for a general class of one-dimensional interacting particle systems with two or more conservation laws. Following Yau's relative entropy method it turns out that in case of more than one conservation laws, in order that the system exhibit hydrodynamic behaviour, some particular identities reminiscent of Onsager's reciprocity relations must hold. We check validity of these identities for a wide class of models. It also follows that, as a general rule, the equilibrium thermodynamic entropy (as function of the densities of the conserved variables) is a globally convex Lax entropy of the hyperbolic systems of conservation laws arising as hydrodynamic limit. The Onsager relations arising in this context and its consequences seem to be novel. As concrete examples we also present a number of models modeling deposition (or domain growth) phenomena. 
Balint Toth, Benedek Valko