b-tau unification and large atmospheric mixing: a case for non-canonical   see-saw
  We study the second and third generation masses in the context of the minimal renormalizable SO(10) theory. We show that if the see-saw takes the non-canonical (type II) form, large atmospheric neutrino mixing angle requires b-tau unification. 
Borut Bajc, Goran Senjanovic, and Francesco Vissani