Department of Mathematics and Applied Mathematics, Virginia Commonwealth University, Richmond, Virginia, United States of America.|Department of Internal Medicine, Virginia Commonwealth University, Richmond, Virginia, United States of America.|Hunter Holmes McGuire VA Medical Center, Richmond, Virginia, United States of America.|Department of Internal Medicine, Virginia Commonwealth University, Richmond, Virginia, United States of America.|Department of Mathematics and Applied Mathematics, Virginia Commonwealth University, Richmond, Virginia, United States of America.|Department of Mathematics and Applied Mathematics, Virginia Commonwealth University, Richmond, Virginia, United States of America.