1. Hatton, L.R., Buntain, I.G., Hawkins, D.W., Parnell, E.W., Pearson, C.J., and Roberts, D.A., US Patent no. 5232940, 1993.
2. Buntain, I.G., Hatton, L.R., Hawkins, D.W., Pearson, C.J., and Roberts, D.A., EP Patent no. 0295117, 1988.
3. Okui, S., Kyomura, N., Fukuchi, T., Tanaka, K., Katsurada, M., Okano, K., Sumitani, N., Miyauchi, A., and Yabe, A., US Patent no. 6849633, 2005.
4. Lindig, M. and Becker, B., US Patent no. 4822810, 1989.
5. Wu, T., Chene, A., Manning, D.T., Newsome, P.W., Ray, N.C., Phillips, J.L., and Lowder, P.D., US Patent no. 6350771, 2002.