1. a Department of Information and Communication Technologies, University of Trento, Via Sommarive 14, Trento 38050, Italy
2. b Schlumberger-Doll Research, 36 Old Quarry Road, Ridgefield CT-06877, USA
3. c Schlumberger-Doll Research, 36 Old Quarry Road, Ridgefield CT-06877, USA
4. d Department of Information and Communication Technologies, University of Trento, Via Sommarive 14, Trento 38050, Italy