Within an isospin- and momentum-dependent hadronic transport model it is shown that the recent FOPI data on the $pi^-/pi^+$ ratio in central heavy-ion collisions at SIS/GSI energies (Willy Reisdorf {it et al.}, NPA {bf 781}, 459 (2007)) provide circu
mstantial evidence suggesting a rather soft nuclear symmetry energy esym at $rhogeq 2rho_0$ compared to the Akmal-Pandharipande-Ravenhall prediction. Some astrophysical implications and the need for further experimental confirmations are discussed.
Pressure isotropization of an equilibrating quark-gluon plasma produced in relativistic heavy ion collisions is studied within the framework of a multi-phase transport model (AMPT). The time evolution of the bulk properties of the quark-gluon plasma
is found to depend on its expansion dynamics and hadronization scheme as well as the scattering cross sections among quarks and gluons. It is further found that the pressure isotropy of the produced quark-gluon plasma can only be achieved temporarily, indicating that there is only partial thermalization during the time evolution of the quark-gluon plasma.
Within the framework of a multi-phase transport model, we study the equation of state and pressure anisotropy of the hot dense matter produced in central relativistic heavy ion collisions. Both are found to depend on the hadronization scheme and scat
tering cross sections used in the model. Furthermore, only partial thermalization is achieved in the produced matter as a result of its fast expansion.
