1. Mathematics Department, The University of Georgia, 240A Riverbend Rd, Athens GA 30602, USA
2. Department of Mathematics, Clarkson University, Potsdam, New York 13699, USA
3. Pacific Source Health Plans, Springfield, Oregon 97477, USA
4. Department of Basic Teaching and Research, Yango University, Fuzhou, Fujian 350015, P. R. China
5. Department of Applied Mathematics, Indian Institute of Technology (ISM), Dhanbad 826004, Jharkhand, India