[1] Consumer Product Safety Planning Division, Product Safety Technology Center, National Institute of Testing and Evaluation, 49-10, Nishihara 2-chome, Shibuya-ku, Tokyo 151-0066, Japan
[2] Institute for Human Science and Biomedical Engineering, 2-1, Namiki 1-chome, Tsukuba-shi, Ibaraki 305- 8564, Japan