1. Department of Physics , , Addis Ababa 1000 , Ethiopia
2. Addis Ababa University , , Addis Ababa 1000 , Ethiopia
3. Department of Biology , , Murfreesboro, Tennessee 37132 , USA
4. Middle Tennessee State University , , Murfreesboro, Tennessee 37132 , USA
5. Department of Physics and Astronomy , , Murfreesboro, Tennessee 37132 , USA
6. Department of Physics , , Carson, California, 90747 , USA
7. California State University Dominguez Hills , , Carson, California, 90747 , USA