[1] New Jersey Inst Technol, Dept Math Sci, Martin Luther King Blvd, Newark, NJ 07102 USA
[2] Univ Arizona, Dept Psychol & Biomed Engn, 1503 E Univ, Tucson, AZ 85721 USA
[3] Case Western Reserve Univ, Dept Math Appl Math & Stat, 10900 Euclid Ave, Cleveland, OH 44106 USA
[4] Humboldt Univ, Dept Phys, Newtonstr 15, D-12489 Berlin, Germany