Rietveld refinement of amorphous SiO2 prepared via sol–gel method

Using the Rietveld refinement, we analyze the structural evolution under thermal treatment of silica xerogel samples prepared by the sol–gel method with molar ratio (R) of water to TEOS of R = 5 and R = 11.66. We refine the structure of compounds using the Maud program and we found the unit cell parameters and atomic positions of the refined silica amorphous atoms for whole samples. The results show us that the amorphous structure is quartz-like or low-cristobalite-like, depending on the molar ratio values and the heat-treatment of the samples. For R = 5 different quartz structures are obtained, whereas for R = 11.66 we obtain close structures in which a transformation of quartz-like amorphous to low-cristobalite amorphous phase occurs at about 600 °C. These results give some scopes to explain the partial crystallization of the silica at relatively low temperatures obtained when metallic species are present.     

An artificial neural network for fault detection in the assembly of thread-forming screws

This paper presents a method, based on a two-layer dynamic Elman neural network, for detecting faults in the assembly of thread-forming screws. Using torque measurements, the method provides a high degree of reliability in detecting assembly faults. The ability of neural networks to learn and to generalize creates an efficient detection system when there is limited or distorted information available about the assembly process.     

Utilization of the k-ε turbulence model in a free-convective turbulent boundary layer

A free-convective turbulent boundary layer on a vertical isothermal surface is examined. The influence of the buoyancy force on the kinetic energy of the turbulent fluctuations is analyzed. A modification is proposed for the turbulence model that takes account of the free-convective flow singularities.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 5, pp. 721–726, November, 1988.     

Succession of mutations in the Sabin strain of type 3 poliovirus replicating in the central nervous system of monkeys

Pentachlorophenol (PCP), which has been used as a wood preservative, was reported to be a liver carcinogen in mice. To investigate the initial effects of PCP administration under the same conditions of exposure as in the carcinogenic study, we examined oxidative stress and cell proliferation, along with other hepatotoxicological parameters, in the livers of B6C3F1 mice fed PCP in their diet at doses of 0.03, 0.06, and 0.12% for up to 4 weeks. We observed significant increases of 8-OHdG levels in hepatic nuclear DNA at doses of 0.03% and above at 2 and 4 weeks. Likewise, dose-dependent increases in the labeling index of cells were detected by counting those that had incorporated 5-bromo-2'-deoxyuridine throughout the experimental period. Also, we found significant elevations of the liver weights, concurrent with increases in hepatic DNA content in the treated mice, which again were dose-related. Serum aspartic transferase activity at doses of 0.06% and above were significantly increased despite these changes being slight. Also, histopathological examination provided no evidence of necrotic changes, but severe hepatocyte swelling in the treated mouse livers. These data indicate that PCP might be able to induce cell proliferation in the mouse liver, as well as induce oxidative DNA damage, suggesting both changes may play an important role in hepatocarcinogenesis.