1. Graduate School of Information Production and Systems Waseda University Kitakyushu 808‐0135 Japan
2. Politeknik Perkapalan Negeri Surabaya, Jalan Teknik Kimia, Kampus ITS Sukolilo Surabaya 60111 Indonesia
3. CAPER, Center of Advanced Power and Energy Research Universiti Putra Malaysia Serdang 43400 Malaysia