Do potential methylation rates reflect accumulated methyl mercury in contaminated sediments?

Relationships between the short-term mono-methyl mercury (MeHg) production, determined as the specific, potential methylation rate constant Km (day(-1)) after 48 h of incubation with isotope-enriched 201Hg(II) at 23 degrees C, and the long-term accumulation of ambient MeHg, were investigated in contaminated sediments. The sediments covered a range of environments from small freshwater lakes to large brackish water estuaries and differed with respect to source and concentration of Hg, salinity, primary productivity, quantity and quality of organic matter, and temperature climate. Significant (p < 0.001), positive relationships were observed between Km (day(-1)) and the concentration of MeHg normalized to total Hg (%MeHg) for surface sediments (0-10, 0-15, and in one case 0-20 cm) across all environments, and across subsets of organic and minerogenic freshwaters. This suggests that the methylation process (MeHg production) overruled demethylation and net transport processes in the surface sediments. The lack of a relationship between Km and %MeHg in two brackish water sediment depth profiles (0-100 cm) indicates that demethylation and the net effect of input-output are relatively more important at greater depths. Differences in the primary production and subsequent availability of easily degradable organic matter (serving as electron donor for methylating bacteria) was indicated to be the most important factor behind observed differences in %MeHg and Km among sites. In contrast, concentrations of sulfate were not correlated to Km, %MeHg, or absolute concentrations of MeHg. We conclude that total concentrations of Hg are of importance for the long-term accumulation of MeHg, and that %MeHg in surface sediments can be used as a proxy for the rate of methylation, across a range of sites from different environments.     

Global emission and production of mercury during the pyrometallurgical extraction of nonferrous sulfide ores

The contribution of the milling, smelting, and refining of sulfide ores to Hg emissions and to Hg byproduction is not adequately quantified in a global context. In this study, we estimate Hg emissions from the pyrometallurgical treatment of Cu, Pb, and Zn sulfide ores. We base our calculations on quantities processed and Hg content in Cu, Pb, and Zn concentrates, derived from unique global databases on smelter feed and production. In 2005, about 275 tons of Hg were emitted globally to the atmosphere from Cu, Pb, and Zn smelters. Nearly one-half was emitted from Zn smelters and the other half equally divided between Cu and Pb smelters. Most Hg was emitted in China, followed by the Russian Federation, India, and South Korea. Global emission factors were 5.81, 15.71, and 12.09 g of Hg ton(-1) of metal for Cu, Pb, and Zn smelters, respectively. Calculations indicate that Hg abatementtechnologies applied to flue gases may have recovered 8.8 tons and 228 tons Hg from Pb and Zn smelters, respectively, most of which was probably sold as a byproduct. In conclusion, Hg emitted from processing copper, lead, and zinc ores has been largely underestimated in Hg emission inventories. Reducing these emissions may be one of the most economical measures to reduce global Hg emissions.     

Wide area system monitoring and control - terminology, phenomena, and solution implementation strategies

This article describes the transition from phasor-based wide area measurement to real time monitoring, control, and protection. The power system phenomena to deal with are reviewed, and key concepts in control and protection are addressed along with different design principles and architectures. Examples of analysis tools, monitoring tools and concepts for control and protection are given. The use of PMU improved the observability of the power system dynamics.     

A new reference for wind power forecasting

In recent years some research towards developing forecasting models for wind power or energy has been carried out. In order to evaluate the prediction ability of these models, the forecasts are usually compared with those of the persistence forecast model. As shown in this article, however, it is not reasonable to use the persistence model when the forecast length is more than a few hours. Instead, a new statistical reference for predicting wind power, which basically is a weighting between the persistence and the mean of the power, is proposed. This reference forecast model is adequate for all forecast lengths and, like the persistence model, requires only measured time series as input. Copyright © 1998 John Wiley & Sons, Ltd.     

Laboratory-derived temperature preference and effect on the feeding rate and survival of juvenile Hemimysis anomala

Hemimysis anomala is a warm-water mysid that invaded the Great Lakes region in 2006 and has since rapidly spread throughout the basin. We conducted three laboratory experiments to better define the temperature preference, tolerance limits, and temperature effects on feeding rates of juvenile Hemimysis, using individuals acclimated to mid (16 °C) and upper (22 °C) preferred temperature values previously reported for the species. For temperature preference, we fit a two-parameter Gaussian (μ, σ) function to the experimental data, and found that the peak values (μ, interpreted as the preference temperature) were 22.0 °C (SE 0.25) when acclimated to 16 and 21.9 °C (SE 0.38) when acclimated to 22 °C, with the σ-values of the curves at 2.6 and 2.5 °C, respectively. No mysids were observed in temperatures below 10 or above 28 °C in these preference experiments. In short-term tolerance experiments for temperatures between 4 and 32 °C, all mysids died within 8 h at 30.2 °C for 16 °C acclimated mysids, and at 31.8 °C for 22 °C acclimated mysids. No lower lethal limit was found. Feeding rates increased with temperature from an average of 4 Bosmina eaten per hour at 5 °C to 19 Bosmina eaten per hour at 27 °C. The results of our experiments indicate an optimal temperature for Hemimysis between 21 and 27 °C, which corresponds with temperatures during periods of high population growth in the field. These results contribute a better understanding of this species' biological response to temperature that will help guide field studies and inform bioenergetics modeling.     

Temperature‐dependent Hall‐effect measurements of p‐type multicrystalline compensated solar grade silicon

In this study, we have investigated the Hall majority carrier mobility of p‐type, compensated multicrystalline solar grade silicon (SoG‐Si) wafers for solar cells in the temperature range 70–373 K. At low temperature (~70 K) the difference in the mobilities measured for the compensated and the uncompensated reference samples is the highest, and the measured mobility shows dependence on the compensation ratio. Mobilities decrease with increasing temperature, and towards room temperature, the mobilities of the different samples are in the same range. The measurements show that, for these samples, the contribution from lattice scattering is dominating over ionized impurity scattering at room temperature. In the range of interest for silicon solar cells (above room temperature), the trend in carrier mobility is similar for all the samples, and the measured value for the sample with low compensation ratio and low doping density is comparable to the uncompensated references. A comparison of resistivity and majority carrier density measured by the Hall setup at room temperature and by four‐point probe and glow discharge mass spectroscopy, respectively, is reported as well. Copyright © 2012 John Wiley & Sons, Ltd.     

The influence of complexing agents on the solubility and absorption of aluminium in rats exposed to aluminium in water

The influence of citrate (0-31mm), fluoride (0 or 2.6mM) and silicate (0 or 2.6mM) on the absorption of Al (0-18mM) was studied in rats. We tested the hypothesis that the solubility and absorption of Al increases in the gastrointestinal (GI) tract in the presence of the complexing agents. Male rats were exposed for 6 or 7 weeks to soluble Al in acidic drinking water (pH 2.5-3.0) with or without the complexing agents. At the end of exposure Al was fractionated in the stomach content, in order to study if the solubility of Al was changed after ingestion. Al absorption was estimated by Al analysis of the right femur bone. Speciation calculations indicated that citrate and fluoride caused formation of soluble Al-citrate (97%) and -fluoride (>60%) complexes in the water. Silicate did not affect the theoretical speciation. In all cases, a large fraction of soluble Al became insoluble in the stomach after ingestion. The concentration of soluble Al increased only in the presence of citrate or a mixture of fluoride and silicate, but citrate was the only complexing agent that influenced the absorption of Al in the rat. This indicates that the form of Al may be changed in the GI tract when soluble drinking-water Al is ingested, and that the solubility of Al in drinking water and GI tract may not be good predictors of the bioavailability of Al even when chelating agents are present.     

Experimental difficulties associated with permeability measurements in aluminum alloys

The general principles and experimental difficulties associated with the measurement of permeability in aluminum alloys have been discussed, in order to ease the further development of experimental methods suitable for such measurements. In order to avoid the surface-tension effects associated with liquid/gas interfaces in the narrow channels of the mushy zone, a flux melt can be used at the inlet of the permeameter. Electron-beam (EB) welding has been shown to be a suitable method for ensuring a complete wetting between the sample and flux after remelting to the test temperature. Moreover, the influence of the permeameter design and the experimental procedure on grain detachment, preferred-flow channel formation, and coarsening have been revealed through microstructural images.     

The issue of gender within computing: reflections from the UK and Scandinavia

Abstract. Thispaper explores some of the reasons that may underlie the gender segregation and declining levels of female participation within the field of computing in Europe during the 1990s in both the professional (industrial) and academic spheres. The interrelationships between three areas – communicative processes, social networks and legitimizing claims to knowledge overlaid by gendered-power relations – are used to analyse and explain the existing situation. The paper draws upon statistical data to explore the extent of gender segregation and then focuses on the authors' own experiences within the UK and Scandinavia in order to explore some of the underlying causes. While direct discrimination does still occur, the paper suggests that indirect, deep-rooted discrimination is the major reason for the situation that currently exists. Drawing upon our own experiences in academia and business and acknowledging the importance of the institutional context, the paper offers a number of recommendations as to how the current situation may be improved. We suggest first that consideration is given to the pedagogical design and marketing of computing courses so that individuals are initially attracted to computing from far more diverse backgrounds, approaches and interests than at present. Second, we suggest that those with influence in the field reflect upon the constitution and behaviours of the informal networks in which they are involved and seek to include female researchers more actively here. Finally we suggest that consideration is given in more general terms to how the field may become more gender neutral and, thus, more inclusive in the future. Masculine discourses and 'hard' skills have dominated within computing for too long and contribute significantly to the declining participation of women within computing.