  We develop a transport approach for heavy quarks in a quark-gluon plasma,
which is based on improved binary collision rates taking into account quantum
statistics, the running of the QCD coupling and an effective screening mass
adjusted to hard-thermal loop calculations. We quantify the effects of
in-medium collisions by calculating the heavy flavor nuclear modification
factor and the elliptic flow for RHIC energies, which are comparable to
radiative effects. We also derive an analytic formula for the mean collisional
energy loss of an energetic heavy quark in a streaming quark gluon plasma.
