1. Department of Materials Engineering; Indian Institute of Science; Bangalore-560012 Karnataka India
2. Indo-French Cell for Water Sciences; Indian Institute of Science; Bangalore-560012 Karnataka India
3. Institut de Physique du Globe de Paris &; Université Paris Diderot Paris 7; UMR CNRS 7154, 1, Rue Jussieu 75238 Paris cedex 05 France