1. J.R., D.J. Vaughan and B.J. Skinner, Resources of the Earth, Prentice Hall, Upper Saddle River, NY, USA, (2001).
2. Joseph. carpenter@ee. doe. gov or jjackman@nrcan. gc. ca.
3. www. nap. edu (search on PNGV, ) or www. uscar. org.
4. www. eere. energy. gov.
5. www. science. doe. gov/sbir.