1. Department of Computing, Imperial College London, London, U.K.
2. IBM T.J. Watson Research Center, Yorktown Heights, NY, USA
3. Institute for Network Science & Electrical Engineering Department, Yale University, New Haven, CT, USA
4. Army Research Directorate, DEVCOM Army Research Laboratory, Adelphi, MD, USA
5. Department of Computer Science, University of Massachusetts, Amherst, MA, USA