Euler-type equations and commutators in singular and hyperbolic limits   of kinetic Cucker-Smale models
  This paper deals with the derivation and analysis of a compressible Euler-type equation with singular commutator, which is derived from a hyperbolic limit of the kinetic description to the Cucker-Smale model of interacting individuals 
David Poyato, Juan Soler
math.AP