by Tsamis, N.C., Woodard, R.P.
Published in Physics letters. B (11.03.1993)

by Cougo-Pinto, M. V., Farina, C., Segu -Santonja, Antonio J.
Published in Letters in mathematical physics (01.02.1994)

by Cougo-Pinto, M. V., Farina, C., Segu -Santonja, A. J.
Published in Letters in mathematical physics (01.08.1994)

by Zimmermann, Wolfhart
Published in Letters in mathematical physics (01.01.1994)

by Kijowski, J., Rudolph, G.
Published in Letters in mathematical physics (01.10.1993)

by Censor, D.
Published in Journal of electromagnetic waves and applications (01.01.1998)

by Vanyashin, Vladimir
Published in Letters in mathematical physics (01.06.1994)

by Steyerl, A, Malik, S.S
Published in Annals of physics (01.08.1992)

by KITAZAWA, Y.
Published in International journal of modern physics. A, Particles and fields, gravitation, cosmology (20.06.1992)

by URRUTIA, L. F., WAELBROECK, H., ZERTUCHE, F.
Published in Modern physics letters A (21.09.1992)

by Lin, G.L., Liu, J., Yao, Y.P.
Published in Modern physics letters A (20.05.1991)