Rotational Surfaces with Constant Mean Curvature in Pseudo-Euclidean   4-Space with Neutral Metric
  We give the classification of constant mean curvature rotational surfaces of elliptic, hyperbolic, and parabolic type in the four-dimensional pseudo-Euclidean space with neutral metric. 
Yana Aleksieva, Velichka Milousheva
math.DG