1. a Department of Physics , Calcutta University , 92, A. P. C. Road, Calcutta , 700 009 , India
2. b R. K. Mission Vidyamandira , Belur Math, Howrah , 711202 , India
3. c Scottish Church College , Calcutta , 700006 , India
4. d Saha Institute of Nuclear Physics , Calcutta , 700064 , India