  The problem of constructing a necessary and sufficient condition for
establishing the separability of continuous variable systems is revisited.
Simon [R. Simon, Phys. Rev. Lett. 84, 2726 (2000)] pointed out that such a
criterion may be constructed by drawing a parallel between the Peres' partial
transpose criterion for finite dimensional systems and partial time reversal
transformation for continuous variable systems. We generalize the partial time
reversal transformation to a partial scaling transformation and re-examine the
problem using a tomographic description of the continuous variable quantum
system. The limits of applicability of the entanglement criteria obtained from
partial scaling and partial time reversal are explored.
