  Using computer simulations and a thermodynamically self consistent integral
equation we investigate the phase behaviour and thermodynamic anomalies of a
fluid composed of spherical particles interacting via a two-scale ramp
potential (a hard core plus a repulsive and an attractive ramp) and the
corresponding purely repulsive model. Both simulation and integral equation
results predict a liquid-liquid de-mixing when attractive forces are present,
in addition to a gas-liquid transition. Furthermore, a fluid-solid transition
emerges in the neighbourhood of the liquid-liquid transition region, leading to
a phase diagram with a somewhat complicated topology. This solidification at
moderate densities is also present in the repulsive ramp fluid, thus preventing
fluid-fluid separation.
