1. Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, UK
2. School of Information Science and Technology, Dalian Maritime University, Dalian, China
3. Physics Department, Lancaster University, Lancaster, LA1 4YB, UK
4. Department of Physics, College of Education for Pure Science, Tikrit University, Tikrit, Iraq
5. Department of Physics, College of Science, Taif-University, Taif, Saudi Arabia
6. Department of Physics, College of Science, University of Anbar, Anbar, Iraq
7. Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK