1. Department of Mathematics and Computer Science, Transilvania University of Brasov, Brasov, Romania
2. Department of Mathematics, Faculty of Science, Zagazig University, Zagazig, Egypt
3. Mathematics Department, Faculty of Science, Taibah University, Al-Madinah Al-Munawarah, Saudi Arabia
4. Department of Air Surveillance and Defense, “Henry Coanda” Air Force Academy, Brasov, Romania