1. Functional Polymer Research Project Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology (QST) 1233 Watanuki, Takasaki Gunma 370‐1292 Japan
2. Graduate School of Engineering, Gunma University 1‐5‐1 Tenjin‐cho, Kiryu Gunma 376‐8515 Japan
3. Daihatsu Motor Co., Ltd. 2910 Ohaza Yamanoue, Ryuo, Gamo Shiga 520‐2593 Japan