A. P. Contogouris*
R. Gaskell and M. Svec†
K. V. Vasavada and L. J. Gutay
Phys. Rev. D 9 2563 (1974)
A.M.Harun-Ar Rashid
Annals of Physics 80 425 (1973)
Richard H. Capps
Phys. Rev. D 4 2997 (1971)