  Heterogeneous media constitute random disordered environments where transport
is drastically hindered. Employing extensive molecular dynamics simulations, we
investigate the spatio-temporal dynamics of tracer particles in the Lorentz
model in the vicinity of the localization transition. There transport becomes
anomalous and non-gaussian due to the presence of self-similar spatial
structures, and dynamic scaling behavior is anticipated. The interplay of
different time and length scales is revealed by the intermediate scattering
functions, which are sensitive both to the underlying spatial fractal as well
as the anomalous transport. We compare our numerical results in the transition
regime to a mode-coupling approach, and find that certain aspects are
surprisingly well predicted.
