[1] Univ Maryland, College Pk, MD 20742 USA
[2] Osaka Univ, Osaka, Japan
[3] Northwestern Univ, Evanston, IL USA
[4] Princeton Univ, Princeton, NJ 08544 USA
[5] AT&T Labs Res, Holmdel, NJ USA
[6] USA, Res Lab, Adelphi, MD USA
[7] MIT, Cambridge, MA 02139 USA