1. Mechanical Engineering Department, University of New Mexico 1 , Albuquerque, New Mexico 87131, USA
2. Electrical, Computer and Biomedical Engineering Department, Union College 2 , Schenectady, New York 12309, USA
3. Department of Physics and Vitreous State Laboratory, The Catholic University of America 3 , Washington, DC 20064, USA
4. US Naval Research Laboratory 4 , Washington, DC 20375, USA