  New constraints for the nuclear equation of state at suprasaturation
densities have been obtained by measuring collective particle flows in
heavy-ion reactions at relativistic energies. Ratios and differences of neutron
and hydrogen flows in 197Au + 197Au collisions at 400 MeV/nucleon were used in
studies of the asymmetric-matter equation of state. The comparison with
predictions of transport models favors a moderately soft to linear density
dependence, consistent with ab-initio nuclear matter theories. Model
predictions suggest that comprehensive data sets collected at higher bombarding
energies will provide information on the asymmetric-matter equation of state in
the density range up to two or three times the saturation value.
