1. S.L. Ledis, T. Sena, H.R. Crews, J.H. Carter, II, US Patent 4,485,175 (1984).
2. J.H. Carter, S.L. Ledis, H.R. Crews, T. Sena, F.L. Larsen, US Patent 4,528,274 (1985).
3. F.L. Larsen, US Patent 4,529,705 (1985).
4. J.D. Lapicola, S.M. Edmondson, Jr., US Patent 4,745,071 (1988).
5. W.L. Ryan, US Patent 5,250,438 (1993).