1. Department of Physics, Catholic University, Washington, DC 20064
2. Laboratoire de Me´canique Physique, University Bordeaux I, 33405 Talence, France
3. Electrical Engineering-Systems Department, University of Southern California, Los Angeles, CA 90089-2563
4. LAUE, URA-CNRS 1373, University of Le Havre, place Robert Schuman, 76610 Le Havre, France
5. Institut National des Industries Manufacturie`res, 35000 Boumerdes, Algeria
6. Department of Mechanical Engineering, Auburn University, Auburn, AL 36849