Molecular weight distribution in cellulose triacetates and its effect on the mechanical properties of fibres

Conclusions 1. A precise method is defined for determination of the molecular-weight distribution of the original cellulose acetate by fractional precipitation of 1% methylene chloride solutions of the TAC in ethanol.2. A method is developed for quantitative determination of low-molecular fractions which is based on extraction of the polymer from a mixture of methylene chloride and ethanol at 25°C with addition of ammonium thiocyanate.3. The dependence of the physical and mechanical properties of triacetate fibres on the average molecular weight of the polymer is demonstrated.Tashkent Institute for Textiles and Light Industry; HIIKhTTs MKhP SSSR, Tashkent; Kaunas Factory. Translated from Khimicheskie Volokna, No. 5, pp. 48–50, September–October, 1969.     

Investigations of Ultrasound Propagation in Porous Impurity-Helium Solids

The velocity and attenuation of ultrasound passing through porous impurity-helium solids immersed in liquid ⁴He have been measured in the temperature range 1.1–2.3 K. These solids were formed by injecting a mixture of impurity (e.g. D₂, Ne, N₂ or Kr) and helium gases into superfluid ⁴He. The sound signal seemed to propagate mainly in the helium contained in the pores, rather than through the solid sample itself. We found that the speed of sound at low temperatures is close to and decreases more rapidly with temperature than first sound in bulk helium, similar to behavior observed in aerogel. The attenuation of sound in helium in the compressed impurity-helium solids is bigger than in bulk helium and increases rapidly with temperature up to 1.65 K, after which a crossover to a much weaker temperature dependence was observed.     

Relationship between lateral subluxation and widening of medial joint space in Legg-Calvé-Perthes disease

Fifty-five patients (61 affected hips and 49 unaffected hips) with Perthes disease were reviewed to evaluate the relationship between widening of medial joint space and lateral subluxation of the femoral head in radiographs. The components of the medial joint space were evaluated by using T1, T2, proton, and Gd-enhanced T1WI magnetic resonance images (MRI). The widened medial joint space in radiographs was filled with overgrown cartilage at the initial stage (27 hips) in MRI, with both overgrown cartilage and widened true medial joint space at the fragmentation stage (23 hips) and widened true medial joint space at the healing stage (11 hips). Between affected hips and unaffected hips, the mean difference of medial joint space in radiographs between hips at the initial stage and at the fragmentation stage was 2 and 4.5 mm, respectively; the mean difference in percentage of lack of coverage of the femoral head between hips at the initial stage and at the fragmentation stage was 3 and 15%, respectively. During the healing stage, widening of the medial joint space decreased or normalized because of ossification of overgrown cartilage despite the existence of lateral subluxation because of coxa magna. We concluded that widening of the medial joint space may be used as an index of lateral subluxation at only the fragmentation stage in Perthes disease.