Worldwatch Institute. 1999. Vital Signs 1999: The Environmental Trends That Are Shaping Our Future. London: W.W. Norton.
Yang, J., A. Banerjee, and S. Guha. 1997. “Triple-Junction Amorphous Silicon Alloy Solar Cells with 14.6% Initial and 13.0% Stable Conversion Efficiencies.” Applied Physics Letters, Vol. 70, No. 22, June 2, pp. 2975–2977.
Yildiz, B., and M. Kazimi. 2003. Nuclear Options for Hydrogen and Hydrogen-Based Liquid Fuels Production. MIT-NES-TR-001. Center for Advanced Nuclear Energy Systems, Cambridge, Mass.: Massachusetts Institute of Technology.