1. Department of Mathematics, Faculty of Applied Sciences, Umm Al-Qura University, Mecca, Saudi Arabia
2. Department of Mathematics, Rustaq College of Education, Ministry of Higher Education, Rustaq, Oman
3. Department of Mathematics, Faculty of Science, Fayoum University, Faiyum, Egypt
4. School of Neurology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, USA