  The nuclear stopping, the elliptic flow, and the HBT interferometry are
calculated by the UrQMD transport model, in which potentials for "pre-formed"
particles (string fragments) from color fluxtube fragmentation as well as for
confined particles are considered. This description provides stronger pressure
at the early stage and describes these observables better than the default
cascade mode (where the "pre-formed" particles from string fragmentation are
treated to be free-streaming). It should be stressed that the inclusion of
potential interactions pushes down the calculated HBT radius $R_O$ and pulls up
the $R_S$ so that the HBT time-related puzzle disappears throughout the
energies from AGS, SPS, to RHIC.
