Affiliation: | 1. Faculty of Mechanical Engineering, Kraljice Marije 16, 11 000 Belgrade, Serbia;2. Ecole Supérieure des Sciences et Techniques de Tunis, Département de Mathématiques, 5, Avenue Taha Hussein-Tunis, B.P.:56, Bab Menara-1008, Tunisie;3. University of Palermo, Department of Mathematics and Informatics, Via Archirafi 34, 90123 Palermo, Italy |