1. Bekenstein, J.D.: 1977,Phys. Rev. D 15, 1548.
2. Canuto, V.et al.: 1977,Phys. Rev. D 15, 1643.
3. Carvalho, J.C. and Lima, J.A.S.: 1992,Gen. Rel. Grav. 24, 171.
4. Carvalho, J.C., Lima, J.A.S. and Nelson, O.R.: 1994, Astrophys. Space Sci., (in press).
5. Chatterjee, S.: 1987,Astron. Astrophys. 179, 1.