1. Dipartimento Interateneo di Fisica, Università e Politecnico di Bari, IFN-CNR UOS Bari, via Amendola 173, 70126 Bari, Italy
2. Department of Electrical and Computer Engineering, Rice University, 6100 Main Street, Houston, Texas 77005, USA
3. Institute of Electronic Systems, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warsaw, Poland