The transient start-up response of a universal exhaust gas oxygen sensor to investigate the Nernst equation in platinum/zirconia cells

The universal exhaust gas oxygen sensor (UEGO) is a device used to infer the combustion air-to-fuel ratio of an internal combustion engine by sampling the exhaust gas. The sensor operates using a feedback system to maintain a specified internal condition, and measures the oxygen current required for this. While the steady state operation of the sensor is reasonably well-understood - dominated as it is by the diffusion of gas species - the factors influencing the transient response are not so clear. In this paper a numerical model of a sensor is compared to experimental data. By examining the effect of the inclusion of different aspects into the model, it becomes clear that it is necessary to account for the influence of gaseous species adsorping onto surfaces, as well as the more traditional approach based on oxygen partial pressure, to correctly capture the transient response of a sensor containing a Pt|YSZ|Pt cell.The work undertaken was funded by the Engineering and Physical Sciences Research Council.This is the final version. It was first published by Elsevier at http://www.sciencedirect.com/science/journal/aip/09254005

Exploring the complexities of gender roles and psychological wellbeing in farm-families: implications for agricultural extension, management and research

Premised on the recognition that psychological wellbeing is a vital component of optimal productivity, and the need for agricultural extension to enhance farmers' welfare, the study was motivated by a dearth of research on the construction and determinants of psychological wellbeing and gender roles in farm-families. The intention was to gain insight and understanding of the farmers' life experiences, peculiar needs, problems and aspirations, in their unique socio-historical and cultural contexts. The study explored the complexities of the socio-cultural construction of gender roles and psychological wellbeing in farm-families of Ogun state Nigeria. The study is interdisciplinary in nature, drawing from and contributing to the bodies of knowledge in gender-based research, social psychology, family studies, and agricultural extension. Findings reveal a need for the development of gender-sensitive and culture-specific strategies in the agricultural extension system, aimed at improving psychological wellbeing and livelihood security of farm-families and ultimately enhancing sustainable agricultural and national development. Keywords: gender, farm-families, implications for extension, Nigeria South African Journal of Agricultural Extension Vol. 34(1) 2005: 122-13

Stability, Inter-Strand Contact Resistance and AC Losses in YBCO Roebel Cables

A dc transport current was applied to the strands of a Roebel cable at 77 K in liquid nitrogen bath. The inter-strand contact resistance was measured. It was modified either by applying a pressure on the cable at 77 K in liquid nitrogen bath or using different soldering patterns between the strands of the cable. Magnetization ac losses were measured in frequency range 50 – 200 Hz in applied magnetic field 4 – 70 mT perpendicular to the broader face of the cable to test the inter-strand contact resistance effect. High stability and very low level of coupling losses was observed in the cables even with the lowest interstrand resistances.This work was supported by the U.S. Department of Energy, grant DE-FG02-07ER84913.In an effort of aiming current sharing between the strands in Roebel cables we studied experimentally the effect of different kinds of inter-strand connections on inter-strand resistances. Just applying a pressure of 8 kPa gives a maximum interstrand resistance of 105 mΩ. Using a tin foil placed on top of the Roebel cable gives the maximum inter-strand resistance of 31.5 mΩ under a pressure of 8 kPa. The lowest maximum inter-strand resistance of 0.1 mΩ was achieved by soldering copper shunts (strips 5 mm wide and 0.1 mm thick). Even such a low inter-strand resistance value does not cause any significant coupling loss increase up to 200 Hz. However, on the other hand it will allow some current sharing between the strands of the Roebel cables. Detailed experimental results on this subject will be published elsewhere

Significance of gasification during oxy-fuel combustion of a lignite char in a fluidised bed using a fast UEGO sensor

In oxy-fuel combustion, fuel is combusted in a mixture of O₂ and recycled flue gas, i.e. the N₂ is replaced by CO₂ with the O₂ supplied from an air separation unit. The resulting gas consists largely of steam and CO2, which would be ready for sequestration when dried. In this work, the rate of reaction of particles of lignite char, typically 1200 μm diameter, in a fluidised bed reactor was determined using mixtures of O₂ with either CO₂ (“oxy-fuel”) or N₂. A universal exhaust-gas oxygen (UEGO) sensor enabled rapid measurements of the oxygen partial pressures in the off-gas, representing a novel application of this type of sensor. It was found that the rate of combustion of the particles in oxy-fuel is much more sensitive to temperature than in the equivalent O₂ and N₂ mixture. This is because for bed temperatures >∼1000 K particle combustion in mixtures of N₂ and O₂ is rate controlled by external mass transfer, which does not increase significantly with temperature. In contrast, using oxy-fuel, as the temperature increases, gasification by the high concentrations of CO₂ present becomes increasingly significant. At low temperatures, e.g. ∼1000 K, rates of combustion in oxy-fuel were lower than those in mixtures of O₂ and N₂ containing the same mole fraction of O₂ owing, primarily, to the lower diffusivities of O2 in CO₂ compared to O₂ in N₂ under conditions at which external mass transfer is still a significant factor in controlling the rate of reaction. At higher temperatures, e.g. 1223 K, oxy-fuel combustion rates were significantly higher than those in O₂ and N₂. The point at which oxy-fuel combustion becomes more rapid than in mixtures of O₂ and N₂ depends not only on temperature but also on the ratio of O₂ to CO₂ or N₂, respectively. A numerical model was developed to account for external mass transfer, changes in the temperature of the particle and for the effect of gasification under oxy-fuel conditions. The model confirmed that, at high temperatures, the high concentration of CO₂ at the surface of the burning particle in the oxy-fuel mixture led to an increase in the overall rate of carbon conversion via CO₂ + C → 2CO, whilst the rate of reaction with O₂ was limited by mass transfer. Good agreement was observed between the rates predicted by the numerical model and those observed experimentally.Financial support from the Engineering and Physical Sciences Research Council (Grant reference number: EP/G063265/1) and the Consejo Nacional de Ciencia y Tecnología (CONACYT) is also acknowledged.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.fuel.2014.10.02

Infrared spectroscopy of solid CO-CO2 mixtures and layers

The spectra of pure, mixed and layered CO and CO2 ices have been studied systematically under laboratory conditions using infrared spectroscopy. This work provides improved resolution spectra (0.5 cm-1) of the CO2 bending and asymmetric stretching mode, as well as the CO stretching mode, extending the existing Leiden database of laboratory spectra to match the spectral resolution reached by modern telescopes and to support the interpretation of the most recent data from Spitzer. It is shown that mixed and layered CO and CO2 ices exhibit very different spectral characteristics, which depend critically on thermal annealing and can be used to distinguish between mixed, layered and thermally annealed CO-CO2 ices. CO only affects the CO2 bending mode spectra in mixed ices below 50K under the current experimental conditions, where it exhibits a single asymmetric band profile in intimate mixtures. In all other ice morphologies the CO2 bending mode shows a double peaked profile, similar to that observed for pure solid CO2. Conversely, CO2 induces a blue-shift in the peak-position of the CO stretching vibration, to a maximum of 2142 cm-1 in mixed ices, and 2140-2146 cm-1 in layered ices. As such, the CO2 bending mode puts clear constraints on the ice morphology below 50K, whereas beyond this temperature the CO2 stretching vibration can distinguish between initially mixed and layered ices. This is illustrated for the low-mass YSO HH46, where the laboratory spectra are used to analyse the observed CO and CO2 band profiles and try to constrain the formation scenarios of CO2.Comment: Accepted in A&

Self-Organized Assemblies Of Colloidal Particles Obtained From An Aligned Chromonic Liquid Crystal Dispersion

The behavior of mono-disperse colloidal particles in a chromonic liquid crystal was investigated. Poly(methyl methacrylate) spherical particles with three different functionalizations, with and without surface charges, were utilized in the nematic and columnar phases of disodium cromoglycate solutions. The nematic phase was completely aligned parallel to the glass substrates by a simple rubbing technique, and the columnar phase showed regions of similar alignment. The behavior of the colloidal particles in the chromonic liquid crystal depended critically on the functionality, with bromine functionalized particles not dispersing at all, and cationic trimethylammonium and epoxy functionalized particles dispersing well in the isotropic phase of the liquid crystal. At the transition to the nematic and especially the columnar phase, the colloidal particles were expelled into the remaining isotropic phase. Since the columnar phase grew in parallel ribbons, the colloidal particles ended up in chain-like assemblies. Such behavior opens the possibility of producing patterned assemblies of colloidal particles by taking advantage of the self-organized structure of chromonic liquid crystals

The effect of training for field-independence on formal operations : The consequences for general ability and the effectiveness of developing an associated meta-cognitive language in combination with the training procedures

After conducting a number of pilot studies pre- and post-tests were given to three experimental classes of 11 to 13 year old early adolescents, one taken by Collings, and the two others by an inexperienced teacher. With one class the latter used materials designed to develop Field-independence only, with the other the teacher followed a similar pattern to Collings who incorporated a meta-cognitive aspect by encouraging students to analyse their own thinking strategies and to 'bridge' between the Field-independence lessons and the contexts of science. There were two control classes, and the overall period of the intervention was one school year with about 20% of the science teaching time used for the intervention. The tests used were the Group embedded Figures Test (GHFT) for Field-independence, and Volume and Heaviness (SRTII), NFER (1979) for Piagetian operations. In the pre- post-test Comparisons between experimental and Control groups all the differences between the differences were statistically significant. Collings' own class showed an effect-size of 1.53 σ on GBFT over the controls, and 0.92 σ on SRTII. The inexperienced teacher's class with Field-independence training only, showed an effect-size of 1.09 σ on GHFT and 0.36 on SRTII whereas his class with meta cognition added showed an effect-size of 1.13 σ on GEFT, and 0.63 σ on SRTII. There was no statistical difference between the 1.09 and 1.13 σ on GEFT and this inferred that the Field-independence materials were fairly robust to teacher effects. The difference between 0.36 and 0.68 σ on SRTII was significantly different, and this was interpreted as showing that the meta-cognitive aspect assisted transfer of training to Formal Operations

Prospects for Improving the Intrinsic and Extrinsic Properties of Magnesium Diboride Superconducting Strands

The magnetic and transport properties of magnesium diboride films represent performance goals yet to be attained by powder-processed bulk samples and conductors. Such performance limits are still out of the reach of even the best magnesium diboride magnet wire. In discussing the present status and prospects for improving the performance of powder-based wire we focus attention on (1) the intrinsic (intragrain) superconducting properties of magnesium diboride, Hc2 and flux pinning, (2) factors that control the efficiency with which current is transported from grain-to-grain in the conductor, an extrinsic (intergrain) property. With regard to Item-(1), the role of dopants in Hc2 enhancement is discussed and examples presented. On the other hand their roles in increasing Jc, both via Hc2 enhancement as well as direct fluxoid/pining-center interaction, are discussed and a comprehensive survey of Hc2 dopants and flux-pinning additives is presented. Current transport through the powder-processed wire (an extrinsic property) is partially blocked by the inherent granularity of the material itself and the chemical or other properties of the intergrain surfaces. These and other such results indicate that in many cases less than 15% of the conductor's cross sectional area is able to carry transport current. It is pointed out that densification in association with the elimination of grain-boundary blocking phases would yield five-to ten-fold increases in Jc in relevant regimes, enabling the performance of magnesium diboride in selected applications to compete with that of Nb-Sn