“…Theoretical analysis and developments (Sarkar and Nandy, 2000;Nandy et al, 1999;Dhar et al, 2003b;Maity et al, 2005;Tripathy et al, 2007Tripathy et al, , 2009 in this field of research are also reviewed. In doing the review, emphasis is given to the work carried out in India and, consequently, a summary of important observations and conclusions drawn are indicated.…”