Central Extensions of the Quasi-orthogonal Lie algebras
  We determine the central extensions of a whole family of Lie algebras, obtained by the method of graded contractions from so(N+1), N arbitrary. All the inhomogeneous orthogonal and pseudo-orthogonal algebras are members of this family, as well as a large number of other non-semisimple algebras, all of which have at least a semidirect structure (in some cases two or more). The dimensions of their second cohomology groups H^2(G,R) and the explicit expression of their central extensions are given. 
J. A. de Azcarraga, F. J. Herranz, J. C. Perez Bueno and M. Santander