1. Department of Physics, State University of New York at Buffalo, Buffalo, New York 14260-1500, USA
2. Centre for Mathematical Modelling and Computer Simulations, Bangalore 560017, India
3. Department of Chemical Engineering, Tennessee Technological University, Cookeville, Tennessee 38505, USA
4. Department of Physics, Duke University Durham, North Carolina 27708, USA
5. Departamento de Fisica, Universidad Autonoma, Metropolitana, Iztapalapa, Apdo 55 534, Mexico, DF, 09340, Mexico
6. Department of Mining Engineering, Colorado School of Mines, Golden, Colorado 80401, USA