1. Department of Computer Science and Engineering, University of California,
San Diego, La Jolla, California, U.S.A.
2. National Center for Supercomputing Applications, University of Illinois
at Urbana-Champaign, Urbana, Illinois, U.S.A.
3. Dipartimento di Informatica e Sistemistica, Università di
Napoli “Federico II,” Napoli, Italy
4. Department of Computer Science, University of Illinois at
Urbana-Champaign, Urbana, Illinois, U.S.A.