  We use quasiparticle description of deconfined matter in nuclear collisions
at finite temperature and chemical potential. We assume that evolution of
expanding system is isentropic. Using theoretical formulas and experimental
meaning for the average multiplicity of charged and neutral particles and also
of net nucleons ($N-\bar{N}$) per unit central rapidity, we calculate the
initial temperature $T_0$, and the volume $V_0$ for the collisions of heavy
nuclei ($Pb+Pb$ and $Au+Au$) at SPS and RHIC energies. At calculations we use
the conservation of entropy and of number net nucleons in initial plasma stage
and on the stage of phase transition at temperature $T_c$, where we take into
account the phase of constituent quarks $m_q$ and $m_s$. The spectra of baryons
and mesons are calculated at temperature of thermal freeze-out $T_f = 120$ MeV.
The quantitative characteristic of these spectra (for example, the
normalization for baryons and mesons) are determined in the present model by
initial state - quark-gluon plasma.
