  A radiative transport model is used to study kinetic equilibration during the
early stage of a relativistic heavy ion collision. The parton system is found
to be able to overcome expansion and move toward thermalization via parton
collisions. Scaling behaviors show up in both the pressure anisotropy and the
energy density evolutions. In particular, the pressure anisotropy evolution
shows an approximate alpha_s scaling when radiative processes are included. It
approaches an asymptotic time evolution on a time scale of 1 to 2 fm/c. The
energy density evolution shows an asymptotic time evolution that decreases
slower than the ideal hydro evolution. These observations indicate that partial
thermalization can be achieved and viscosity is important for the evolution
during the early longitudinal expansion stage of a relativistic heavy ion
collision.
