Generalized models of unification of dark matter and dark energy
  A model of unification of dark matter and dark energy based on the modeling
of the speed of sound as a function of the parameter of the equation of state
is introduced. It is found that the model in which the speed of sound depends
on the power of the parameter of the equation of state, $c_s^2=\alpha
(-w)^{\gamma}$, contains the generalized Chaplygin gas models as its subclass.
An effective scalar field description of the model is obtained in a parametric
form which in some cases can be translated into a closed form solution for the
scalar field potential. A constraint on model parameters is obtained using the
observational data on the Hubble parameter at different redshifts.
