1. Department of Physics, Anna University, Chennai 600 025, India
2. Institute of Mathematical Sciences, C.I.T. Campus, Taramani, Chennai 600 113, India
3. Control Dynamics Inc., 1662 102nd Place SE, Bellevue, WA 98004, USA
4. Biomedical Engineering Department, University of Florida, Gainesville, FL 32611-6131, USA