Graft copolymerization onto rubber. VII. Graft copolymerization of methyl methacrylate onto rubber using potassium peroxydisulfate catalyzed by silver ion

The graft copolymerization of methyl methacrylate onto natural rubber (NR) was carried out varying the concentration of monomer, initiator, thiourea, and silver nitrate over a wide range. The grafting reaction was temperature-dependent. From the Arrhenius plot, the overall energy of activation was computed. A suitable reaction scheme and rate expression for the rate of polymerization was suggested.     

Long-term transients in a reactor under forced concentration cycling

In the approach to a cycle-invariant state in the forced feed concentration cycling of the CO oxidation over a NiO catalyst, a very long transient has been observed lasting 80 ks or more. This transient appears to be associated only with CO pretreatment of the catalyst and is not a general phenomenon. The slow convergence to the cycle-invariant state reported in certain modelling calculations in the literature appears to have a different cause.     

Retention of Escherichia coli in municipal sewage by means of planted soil filters in two-stage pilot plant systems.

Different types of constructed wetlands in a pilot-plant system were fed with identical municipal waste water to compare the sanitisation process in two-stage systems. With combinations of a vertical and a horizontal flow filter an E. coli reduction of 5 log10 with an E. coli influent concentration of 10(7) MPN/100 ml was achieved. Using different filter materials in each stage the total performance of the two-stage system was independent from the sequence of these materials. However, using coarser filter material in the first stage makes the filter less prone to clogging and is thus the preferential option with regard to operational reliability.     

Managing rivers for fisheries and livelihoods: how can we do it better?

The growing attention being given to improving water productivity at the catchment level has given rise to increased interest in the contribution of aquatic ecosystems and in particular fisheries to reducing rural poverty and improving food security. There is growing recognition that these natural resources have an important role to play in pro-poor water management in many of the world's river basins, but that capacity to optimize these benefits is constrained by a lack of appropriate technologies and tools to do so. The present paper provides an overview of the current state of understanding of these issues and identifies a number of challenges to be addressed, namely the need to: (i) build wider understanding of the value of river fisheries; (ii) understand the water requirements for sustaining river fisheries; and (iii) develop governance arrangements that bring fisheries to the decision-making table. It concludes by distilling from recent reviews of river fisheries valuation, environmental flows, and governance, a set of specific directions that need to be taken in order to meet these challenges.     

Effect of temperature and cyclic heating on the structure and strength of glass textolite

The article established the regularities of change of the physicomechanical characteristics and strength of glass textolites in single and repeated thermal loading. It shows that under multiple loading the intense loss of strength of the investigated materials is due to increased porosity on account of the large number of microcracks appearing in the structure. A correlation is obtained between the elastic and strength characteristics and porosity in dependence on the temperature of multiple heating which in the first approximation is described by a polynomial of second degree with respect to temperature, multiplied by the reciprocal of porosity.Translated from Problemy Prochnosti, No. 6, pp. 53–58, June, 1991.     

Comfort limits for asymmetric thermal radiation

Groups of 32 and 16 subjects of both sexes were exposed in an environmental chamber to radiant asymmetry caused by a cool wall, a warm wall, and a cool ceiling. Each subject was tested individually while seated and clothed at 0.6 clo. During each 3.5-hour experiment the subject was exposed to six radiant temperature asymmetries. He was asked whether and where he experienced any local cool or warm sensation, and whether it was felt to be uncomfortable. During the entire experiment he was kept thermally neutral by changing the air temperature according to his wishes.For cool walls, warm walls, and cool ceilings curves have been established showing the percentage of dissatisfied subjects as a function of the radiant asymmetry. Radiant asymmetry at a warm wall caused less discomfort than a cool wall. A cool ceiling caused less discomfort than a warm ceiling. Accepting that 5% of the subjects may feel uncomfortable. a radiant temperature asymmetry of 10°C is allowable at a cool wall, 23°C at a warm wall, and 14°C under a cool ceiling. A previous study showed that 4°C is allowable under a warm ceiling. Radiant asymmetry had no significant impact on the operative temperatures preferred by the subjects. No significant differences were observed between the responses of men and women exposed to radiant asymmetry.     

Criteria for evaluation of the hardening factor of machine parts

V. Ya. Chubar' Zaporozhe Machine Building Institute. Translated from Problemy Prochnosti, No. 3, pp. 62–65, March, 1989.     

Toughening of Dental Porcelain by Tetragonal ZrO2 Additions

The effect on mechanical behavior of ZrO₂ additions to a dental porcelain was investigated. The ZrO₂ was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO₂ was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance.