The resistance of 20Cr/25Ni steels to carbon deposition. III. Cold work and selective pre-oxidation

Specimens of annealed 20 Cr/25Ni/Nb, selectively pre-oxidised 20Cr/25Ni/Nb, cold worked 20Cr/25Ni/Nb and TiN-strengthened 20Cr-25Ni steels have been exposed to a 75% CO/CO₂ gas atmosphere for periods up to 2000 hrs at 923 K (650°C). Whereas the cold-worked and TiN-strengthened steels show high resistance to this environment, the annealed Nb-stabilised alloy exhibited large amounts of carbon deposition. Associated with these were extensive regions of oxide pitting and gross carburisation of the substrate. By contrast, the selectively preoxidised specimens suffered much less deposition and no evidence for carburisation was found. It was also shown that small quantities of defects in the original preoxidised layer increased the propensity for deposition but did not result in local carburisation.     

Growth dilution of metals in microalgal biofilms

Despite the key role microalgae play in introducing toxicants into aquatic food webs, little is known about the effects of environmental factors on metal accumulation by these primary producers. Environmental factors such as light and nutrients alter growth rates and may consequently influence metal concentrations in microalgae through growth dilution. Laboratory experiments suggested that metal uptake and elimination by microalgal biofilms were gradual enough to enable dilution of metals within the biofilms by photosynthetically accrued carbon, and a simple kinetic model of metal accumulation predicted significant variation in metal content due to growth dilution over the natural range of microalgal growth rates. The ratio of metal uptake to carbon uptake by microalgal biofilms decreased exponentially with increasing light in short-term laboratory experiments because photosynthesis was much more sensitive to a light gradient than was metal uptake. The effect of light on biofilm metal concentrations was confirmed in situ with a long-term experiment in which experimental shading of biofilms in a metal-contaminated stream decreased biofilm growth rates and caused a 3x increase in biofilm concentrations of twelve metals, including methylmercury. Slow growth at the primary producer level is a likely contributor to higher biotic metal concentrations in shaded, oligotrophic, or cold ecosystems.     

Dental caries, tooth trauma, malocclusion, fluoride usage, toothbrushing and dietary habits in 4-year-old Swedish children: changes between 1967 and 1992

The dental health of 4-year-old children in the city of Ume?, northern Sweden, has been followed in cross-sectional studies conducted in 1967, 1971, 1976, 1980, 1987 and 1992. Similar methods and criteria were used. Dental caries and background factors (fluoride usage, toothbrushing frequency and diet) were recorded. In 1971, 1987 and 1992 signs of tooth trauma and presence of malocclusion were also recorded, the latter also in 1976. The present paper summarizes the results of these studies. Between 1967 and 1992 the mean dmfs values declined from 7-8 to 1-8. The decline was greatest between 1967 and 1980 and then levelled off. Toothbrushing frequency was similar over the years, but parental help with brushing was more common in the more recent studies. The use of fluoride toothpaste increased. About 30% of the children had experienced tooth trauma. A unilateral crossbite was recorded in 18% and 16% of the children in 1971 and 1992, respectively, and an anterior open bite in about 35% and 41%, respectively; both types of malocclusion were related to a dummy- or finger-sucking habit.     

Building thermal analyses: What the industry needs: The Architect''s perspective

Drawing on experience as a practitioner, the author argues that a static need definition is necessarily inferior to a dynamic need definition attained by a feed-back and feed-forward procedure built on general systems theory. The designer's approach, working from the whole towards the detail, is contrasted with the way analytical models are typically structured. Recent advances, problems and future work are identified.     

Hand injuries in the users of hydraulic wood-cutters

This study has been carried out in order to suggest possible prophylactic recommendations. We investigated the type of injuries, the type of logsplitter used, the injury circumstances and the safety measures. Fifty-two patients were included. There were a total of 21 crushing injuries with amputations of fingers, hand, on forearm. Nine replantations, two revascularisations and seven amputations were carried out. Eighty-eight percent of the patients had their hand in the splitting area. Sixty-seven percent had not received any instructions on how to operate the machinery. In 58% of the cases two or more persons were operating the logsplitter and 40% of the machines had no emergency stop button. The hazards mentioned above influenced the injury frequence and severity. We therefore recommend improved prophylactic measures and precautions to be considered. For the old machines a campaign will be necessary, and for new logsplitters we recommend implementation of new standards.