1. 1) H. Okumura: Nippon Steel Tech. Rep., 61 (1994), 9.
2. 2) M. Iwasaki and M. Matsuo: Nippon Steel Tech. Rep., 101 (2012), 89.
3. 3) K. Yoneyama: The Economic Studies, 30 (1980), No. 3, 97, http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/31509/1/30%283%29_P97-156.pdf, (accessed 2015-03-16).
4. 4) S. Tsuru, Y. Nomiyama and K. Nishioka: Nippon Steel Tech. Rep., 75 (1997), 1.
5. 5) J. X. Fu, C. Zhang, W. S. Hwang, Y. T. Liau and Y. T. Lin: Int. J. Green Gas Con., 8 (2012), 143.