1. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6493
2. Department of Mathematical Sciences, Center for Applied Mathematics and Statistics, New Jersey Institute of Technology, Newark, New Jersey 07102
3. Instituto de Fisica Arroyo Seco, Facultad de Ciencias Exactas, Universidad Nacional del Centro de la Provincia de Buenos Aires Pinto 399, 7000, Tandil, Argentina
4. Materials Science and Engineering Department, The University of Tennessee, Knoxville, Tennessee 37996-2200