1. Department of Mathematics, Virginia Peninsula Community College, Hampton, VA 23666, USA
2. Department of Mathematics & Statistics, Old Dominion University, Norfolk, VA 23529, USA
3. School of Community & Environmental Health, Old Dominion University, Norfolk, VA 23529, USA
4. Hampton Roads Biomedical Research Consortium Research, Virginia Modeling Analysis and Simulation Center, Old Dominion University, Suffolk, VA 23435, USA