1. Department of Physics, Faculty of Mathematics
and Natural Sciences, Padjadjaran University, Jl. Raya Bandung-Sumedang KM 21, Jatinangor 45363, Indonesia
2. Department of Chemical Engineering,
Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi Hiroshima, Hiroshima 739-8527, Japan