A FRW dark fluid with a non-linear inhomogeneous equation of state I. Brevik, E. Elizalde, O. Gorbunova and A.V. Timoshkin Eur. Phys. J. C, 52 1 (2007) 223-228 Published online: 17 July 2007 DOI: 10.1140/epjc/s10052-007-0357-9