1. Department of Physics, Guru Nanak Dev University, Amritsar-143005, India
2. Department of Environmental
Engineering, College of Engineering, Sangmyung University, 300 Anseo-dong, Dongnam-gu, Cheonan, Chungnam Province, 330-720,
Republic of Korea
3. Department
of Physics, The University of the West Indies, St. Augustine, Trinidad
and Tobago