1. Department of Physics, Gurukula Kangri Vishwavidyalaya, Haridwar 249 404, India
2. Department of Physics, A.P.B. Government Post Graduate College, Agastyamuni 246 421, India
3. Fachbereich Physik, Universität Konstanz, M677, 78457 Konstanz, Germany
4. Department of Physics, HNB Garhwal University, Srinagar (Garhwal) 246 174, India