1. Laboratoire de Dynamique des Fluides Complexes, 4 rue Blaise Pascal, Unité Mixte de Recherche No. 7506, Université Louis Pasteur, Centre National de la Recherche Scientifique, 4 rue Blaise Pascal, 67070 Strasbourg Cedex, France, Department of Physics, R. J. College, Ghatkopar, Mumbai 400 086, India, Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India, and Chemistry Department, University Department of Chemical Technology, Matunga, Mumbai 400 019, India