1. U.S. Patent 4,000,216 (12/28/76).
2. and U.S. Patent 4,526,926 (7/2/85).
3. and U.S. Patent 5,026,777 (6/25/91).
4. and European Patent 30106 (3/8/89).
5. and Melt Rheology and its Role in Plastics Processing?Theory and Practice, Ch. 8. Van Nostrand, New York (1990).