1. CNRS, University of Bordeaux, ICMCB, UMR 5026, F-33600 Pessac, France
2. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511, United States
3. CNRS, University of Bordeaux, I2M, UMR 5295, F-33400 Talence, France