1. Department of Mathematics; Faculty of Science; Banaras Hindu University; Varanasi 221 005 India
2. The University of New South Wales; NSW; 2052 Australia
3. C-MEND, 18, Navsheel Dham; Kanpur 208 017 India
4. BIT, BIIFR & D; Bhabha Group of Institutions; Kanpur (Rural) 209 204 India