1. Laboratoire de Physique Appliquée, Faculté des Sciences, Université de Sfax, 3000 Sfax, Tunisia
2. University of Coimbra, CEMMPRE, Mechanical Engineering Department, Rua Luis Reis Santos, P-3030-788 Coimbra, Portugal
3. University of Coimbra, CFisUC, Physics Department, P-3004-516 Coimbra, Portugal