1. Department of Mathematical Sciences, KAIST , Daejeon , Republic of Korea
2. Biomedical Mathematics Group, Institute for Basic Science , Daejeon , Republic of Korea
3. Graduate School of Clinical Nursing Science, Sungkyunkwan University , Seoul , Republic of Korea
4. Department of Mathematics, University of Wisconsin-Madison , Madison, WI , USA
5. Department of Neurology, Neuroscience Center, Samsung Medical Center, Samsung Biomedical Research Institute, School of Medicine, Sungkyunkwan University , Seoul , Republic of Korea