Basic theory and some applications concerning the ratio of shear viscosity to entropy density in dense fluids

Much interest continues relating to the conjecture from string theory of an inequality satisfied by the ratio η/s in dense fluids, where η is the shear viscosity and s the entropy density. First, we summarise the models which have prompted the proposal of the inequality. Second, we consider a model equation of state which may be appropriate for the dense fluids NH₃ and H₂O, both of which satisfy the inequality.