  A new segregation criterion based on the inelastic Enskog kinetic equation is
derived to show the transition between the Brazil-nut effect (BNE) and the
reverse Brazil-nut effect (RBNE) by varying the different parameters of the
system. In contrast to previous theoretical attempts the approach is not
limited to the near-elastic case, takes into account the influence of both
thermal gradients and gravity and applies for moderate densities. The form of
the phase-diagrams for the BNE/RBNE transition depends sensitively on the value
of gravity relative to the thermal gradient, so that it is possible to switch
between both states for given values of the mass and size ratios, the
coefficients of restitution and the solid volume fraction. In particular, the
influence of collisional dissipation on segregation becomes more important when
the thermal gradient dominates over gravity than in the opposite limit. The
present analysis extends previous results derived in the dilute limit case and
is consistent with the findings of some recent experimental results.
