  We study heavy quark energy loss and thermalization in hot and dense nuclear
medium. The diffusion of heavy quarks is calculated via a Langevin equation,
both for a static medium as well as for a quark-gluon plasma (QGP) medium
generated by a (3+1)-dimensional hydrodynamic model. We investigate how the
initial configuration of the QGP and its properties affect the final state
spectra and elliptic flow of heavy flavor mesons and non-photonic electrons. It
is observed that both the geometric anisotropy of the initial profile and the
flow profile of the hydrodynamic medium play important roles in the heavy quark
energy loss process and the development of elliptic flow. Within our definition
of the thermalization criterion and for reasonable values of the diffusion
constant, we observe thermalization times that are longer than the lifetime of
the QGP phase.
