1. UR Analysis and Control of Pde, UR 13ES64, Department of Mathematics, Faculty of Sciences of Monastir, University of Monastir, Monastir, Tunisia
2. LAMAV, FR CNRS 2956, Université de Valenciennes et du Hainaut Cambrésis, Valenciennes Cedex, France
3. Dipartimento di Ingegneria e Scienze dell’Informazione e Matematica, Università di L’Aquila, L’Aquila, Italy