1. College of Sciences, King Saud University , Saudi Arabia.
2. Faculté des Sciences de Sfax, Départment de Mathématiques, Université de Sfax , Tunisia.
3. Faculty of Sciences of Tunis, LR03ES04 partial differential equations and applications, University of Tunis El Manar , Tunis, Tunisia.
4. California State University , Los Angeles, CA, USA.