Effects of mastication on the distribution of molecular weights and on the mechanical properties of native and commercial dental gutta percha (trans-polyisoprene)

Mastication of gutta percha (trans-polyisoprene) resulted in the selective scission of molecules, producing a narrower distribution of lower molecular weights. The mechanical properties of the samples also underwent a significant change due to mastication. The greater the content of incompatible substances (salts and oxides) in commercial gutta percha. the more substantial were these effects. The atmosphere (air, N₂, O₂) in which the experiments were conducted yielded significantly different results. The decrease in molecular weight was far greater in an O₂ atmosphere than under a current of nitrogen or air, owing to the combination of double bonds with O₂.     

Technological basis of SHS extrusion

The results of the development of the SHS extrusion process, including creation of the equipment, studies of the production conditions and product quality are presented. The concepts of the ability of different composite refractory materials to plastic deformation are formulated. Examples of practical applications of the method developed are given.Institute for Structural Microkinetics, Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 5, pp. 525–537, November, 1992.     

Inbreeding in Swiss Braunvieh and its influence on breeding values predicted from a repeatability animal model.

Inbreeding coefficients were computed for 910,444 animals of the Swiss Braunvieh population. Of the animals born in 1984, 71.5% were inbred with 67.9, 3.4, and .2% having inbreeding coefficients between greater than 0 and 5%, greater than 5 to 10%, and greater than 10%, respectively. The average inbreeding coefficient was 1.14% but, for animals with both parents and at least one grandparent known, it was 1.67%. Breeding values for total milk, fat, and protein yields and for fat and protein percentages were predicted using a repeatability animal model including a regression on the inbreeding coefficient. Phenotypic performance was sizeably depressed for milk yield only (-26 kg/% of inbreeding or 2.4% of the phenotypic standard deviation). Adjusting for inbreeding increased the estimated genetic trend slightly. Inbreeding is only partially accounted for when it is ignored in the construction of the inverse of the numerator relationship matrix. This effect was investigated by comparing predicted breeding values from a model including the complete matrix with predicted breeding values from a model including a matrix constructed with inbreeding ignored. Only .8% of all predicted breeding values were affected by more than +/- 5.5 kg. The maximum difference observed was 55.3 kg. The observed average absolute differences between the breeding values of offspring predicted with the two models increased with inbreeding of parents.