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