1. Ecole Normale Supérieure d’Enseignement Technologique, Azzaba, Skikda, Algeria
2. Department of Mathematics, Laboratory of Analysis and Control of Differential Equations, Faculty of MISM, University 8 May 1945, Guelma, Algeria
3. University Badji Mokhtar, P.O. Box 12, 23000 Annaba, Algeria
4. Souk Ahras University, B.P. 1553, Souk Ahrass 41000, Algeria
5. University 20 August 1955, BP 26, Route d’El Hadaiek, Skikda 21000, Algeria