Tilted Lemaitre-Tolman-Bondi Spacetimes: Hydrodynamic and Thermodynamic
  Properties
  We consider Lemaitre-Tolman-Bondi spacetimes from the point of view of a
tilted observer, i.e. one with respect to which the fluid is radially moving.
The imperfect fluid and the congruence described by its four-velocity, as seen
by the tilted observer is studied in detail. It is shown that from the point of
view of such tilted observer the fluid evolves non-reversibly (i.e. with
non-vanishing rate of entropy production). The non-geodesic character of the
tilted congruence is related to the non-vanishing of the divergence of the
4-vector entropy flow. We determine the factor related to the existence of
energy-density inhomogeneities and describe its evolution, these results are
compared with those obtained for the non-tilted observer. Finally, we exhibit a
peculiar situation where the non-tilted congruence might be unstable.
