[1] SUNY Stony Brook, CN Yang Inst Theoret Phys, Stony Brook, NY 11794 USA
[2] Univ Blida, LPTHIRM, Blida, Algeria
[3] Univ Blida, Dept Aeronaut, Blida, Algeria
[4] Ctr Rech Nucl Alger, Algiers, Algeria
[5] Univ Paris 06, LPTMC, F-75252 Paris 05, France
[6] Indiana Univ, Dept Math, Bloomington, IN 47405 USA