1. John D, Richmond Va. US Patent 3386449, (1968).
2. John D Hooper, Keynsham, John F Britton. US Patent 4337783, (1982).
3. Liu jianfu. EP 1872670 A1, (2008).
4. Wanna, joseph T, Alpharetta, Georgia. EP 1781124 B1, (2009).
5. Edward J, Stephen Sohn. US Patent 5143097, (1992).