1. G.E.S.N.L.A.-L.E.S.I.A. Institut National des Sciences Appliquées, Complexe Scientifique de Rangueil, 31077 Toulouse Cedex, France
2. Department of Electrical and Electronic Engineering, University of Tokushima, Minami-Josanjima Tokushima, Japan 770, Japan
3. Department of Mathematics, University of Tanta, Egypt