1. Internal Energy Outlook, Energy Information Administration, US Department of Energy, 1995.
2. H. Nagai, K. Uehara, Gas sensing by laser diode for environmental monitoring and preventive maintenance, in: Proceedings of the 10th International Conference on Solid-State Sensors and Actuators, Transducer’99, Tech. Digest, Sendai, Japan, 7–10 June 1999, pp.16–19.
3. Y.H. Hong, Methane gas sensor fabricated with SnO2/Pt fine powder added Ca for crystal growth suppression, PhD Thesis, Kyungpook National University, Korea, December 1995, pp. 29–42.
4. Altera Digital Library CD-ROM, Altera Corporation, USA, August 1999.