[1] Oak Ridge Natl Lab, Ctr Nanophase Mat Sci, Oak Ridge, TN 37831 USA
[2] New Jersey Inst Technol, Ctr Appl Math & Stat, Dept Math Sci, Newark, NJ 07102 USA
[3] Univ Nacl Ctr Prov Buenos Aires Pinto 399, Inst Fis Arroyo Seco, Fac Ciencias Exactas, RA-7000 Tandil, Argentina
[4] Univ Tennessee, Dept Mat Sci & Engn, Knoxville, TN 37996 USA