1. Unkrüer, W., Ph. D. Thesis, Techn. Univ. Aachen (1970).
2. Chong, J. S. J. Appl. Pol. Sci.12, 191 (1968).
3. Bergen, J. T., G. W. Scott andP. Lancaster J. Appl. Mech.73, 101 (1951).
4. Perlberg, S. E. andR. C. Seanor SPE Journal22, 57 (1966).
5. Pearson, J. R. A., Mechanical Principles of Polymer Melt Processing, p. 68 (Oxford 1966).