Meridian Surfaces with Constant Mean Curvature in Pseudo-Euclidean   4-space with Neutral Metric
  In the present paper we consider a special class of Lorentz surfaces in the four-dimensional pseudo-Euclidean space with neutral metric which are one-parameter systems of meridians of rotational hypersurfaces with timelike or spacelike axis and call them meridian surfaces. We give the complete classification of minimal and quasi-minimal meridian surfaces. We also classify the meridian surfaces with non-zero constant mean curvature. 
Betul Bulca and Velichka Milousheva
math.DG