1. Department of Mathematics and Statistics, North Carolina A&T State University, Greensboro, North Carolina 27411, USA
2. Department of Mathematical Sciences, Indiana University-Purdue University Indianapolis, Indianapolis, Indiana 46202, USA
3. Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
4. Department of Mathematics, East Carolina University, Greenville, North Carolina 27858, USA