1. Department of Physics, National Chung Hsing University, Taichung, Taiwan
2. Math. Dept, Faculty of Science, Al-Azhar University, Assiut, Egypt
3. Math. Dept, Faculty of Science, Assiut University, Assiut, Egypt
4. Math. Dept, Faculty of Science, Aswan University, Aswan, Egypt
5. Department of Mathematics, College of Science, University of Bahrain, El-sakihur, Bahrain
6. Math. Dept, Faculty of Science, Al-Azhar University, Nasr City, Cairo, Egypt