Penrose limits and maximal supersymmetry
  We show that the maximally supersymmetric pp-waves of IIB superstring and M-theories can be obtained as a Penrose limit of the supersymmetric AdS x S solutions. In addition we find that in a certain large tension limit, the geometry seen by a brane probe in an AdS x S background is either Minkowski space or a maximally supersymmetric pp-wave. 
Matthias Blau, Jose Figueroa-O'Farrill, Christopher Hull, George   Papadopoulos