Vorticity and entropy production in tilted Szekeres spacetimes
  We analyze the properties of the tilted Szekeres spacetime, i.e. the version
of such spacetime as seen by a congruence of observers with respect to which
the fluid is moving. The imperfect fluid and the kinematical variables
associated to the four-velocity of the fluid assigned by tilted observers are
studied in detail. As it happens for the case of the Lemaitre--Tolman--Bondi
spacetime, the fluid evolves nonreversibly (with nonvanishing entropy
production) and is nongeodesic. However unlike that later case, the tilted
observer detects vorticity in the congruence of the fluid world lines. Also, as
for the nontilted congruence the magnetic part of the Weyl tensor vanishes,
reinforcing the nonradiative character of this kind of spacetime. Possible
physical implications of these results are discussed.
