339 research outputs found
Assessment of ammonia as energy carrier in the use with reversible solid oxide cells
No full textAmmonia represents one of the most promising potential solutions as energy vector and hydrogen carrier, having a higher potential to transport energy than hydrogen itself in a pressurized form. Furthermore, solid oxide fuel cells (SOFCs) can directly be fed with ammonia, thus allowing for immediate electrical power and heat generation. This paper deals with the analysis of the dynamic behavior of commercial SOFCs when fueled with ammonia. Several measurements at different temperatures have been performed and performances are compared with hydrogen and a stoichiometrically equivalent mixture of H2 and N2 (3:1 M ratio). Higher temperature led to smaller drops in voltage for both fuels, thus providing higher efficiencies. Ammonia resulted slightly more performant (48% at 760 °C) than hydrogen (45% at 760 °C), in short stack tests. Moreover, different ammonia-to-air ratios have been investigated and the stack area-specific resistance has been studied in detail by comparing numerical modeling predictions and experimental values.SCI-STI-JVHThis is an Open Access article under the terms of the Creative Commons Attribution Licens
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Trini talk or the Queen's English? : navigating language varieties in the post-colonial, high stakes climate of "Standard Five" classrooms in Trinidad
No full texttextThis study was an exploration of the relationship between classroom discourse and a high-stakes, standardized test, the Secondary Entrance Assessment (SEA), administered to students in Trinidad in their final elementary school year ("Standard 5"), with scores used to determine placement into secondary school. Classroom discourse was measured as represented in the oral and written language modeled to students by teachers and textbooks, and compared to the written language expectations implicit in the instructions and items on the SEA. Students' SEA scores were analyzed in relation to their teachers' language to determine if achievement was related to exposure to local/non-standard features of Trinidadian English. One outcome of this analysis was the creation of a survey developed to measure teachers' propensity for speaking Trini (Creole/dialect) or Trinidadian Academic English (standard English) in class by having them respond to audio clips. The survey was found to have acceptable reliability and concurrent validity. For the oral language investigation, 13 teachers were recorded as they led their class in one lesson, and an index of Trini usage (number of Trini utterances per 100 words) was calculated for each teacher. This index was used in an HLM model to determine if teachers' language was a predictor of their students' SEA scores. The distribution of the Trini index was positively skewed, M=1.1 and SD=1.25, indicating low usage of Trini. Trini usage was not found to be a significant predictor of students' 2008 SEA scores, but was found to be a significant predictor of the variation in SEA scores when these were aggregated by class. Similarly, there were few instances of Trini features in the examined textbooks. However, on the SEA, the only influence of Trini was the presence of dialect options used as distractors on two "fill in the blank" items, suggesting a mismatch between the features used in instructional language and the language expectations on the exam. In general, the low exposure to local features did not account for students' achievement on the SEA, but was positively related to the consistency of scores within a class.Educational Psycholog
Characterization of wind meandering in low-wind-speed conditions
No full textInvestigation of low-wind cases observed during the Urban Turbulent Project campaign (Torino, Italy) and at the Santa Maria meteorological station (Santa Maria, Brazil) provides insight into the wind-meandering phenomenon, i.e. large, non-turbulent oscillations of horizontal wind speed and temperature. Meandering and non-meandering cases are identified through analysis of the Eulerian autocorrelation functions of the horizontal wind-velocity components and temperature. When all three autocorrelation functions oscillate, meandering is present. As with weak turbulence, meandering shows no dependence on stability but is influenced by presence of buildings and depends on wind speed. We show that, while the standard deviation of the horizontal velocity is always large in low-wind conditions, the standard deviation of the vertical velocity shows very different behaviour in meandering and non-meandering conditions. In particular, the value of the ratio of the standard deviations of the vertical and horizontal velocities typifies the meandering condition
A new high performance version of the Lagrangian particle dispersion model spray, some case studies
No full textEVALUATION OF THE POSSIBLE THREAT OF NAFTA ON U.S. CATFISH INDUSTRY USING A TRADITIONAL IMPORT DEMAND FUNCTION
No full textThe effects of increased exports from NAFTA member countries on the U.S. domestic catfish industry were evaluated. Results showed that the quantity of catfish imported will fall if the domestic price of catfish falls relative to the import price. Past imports have no effect on present imports. The income elasticity was negative indicating that imported catfish may be an inferior good. Doubling present levels of imports from NAFTA member countries is not a threat to the U.S. catfish industry.International Relations/Trade,
Comparison of microstructural evolution of fuel electrodes in solid oxide fuel cells and electrolysis cells
No full textSolid oxide cells are electrochemical devices used for the conversion of chemical energy to electrical energy (Solid Oxide Fuel Cells-SOFC) and vice versa (Solid Oxide Electrolysis Cells-SOEC). However, long-term performance degradation impedes the widespread commercialization of the technology. To investigate the effects of operation mode on the degradation of Ni/yttria-stabilized zirconia (YSZ) electrodes, two cells from the same production batch are tested for 1000 h at 800 °C; one as SOFC and the other as SOEC. The cells are fed with the same gas composition at the fuel inlet side (p(H2O)/p(H2) = 0.5/0.5) while the direction of the current (±1 A cm−2) is reversed. It is found that Ni coarsening occurs to a similar extent in both operation modes while Ni depletion is only observed in SOEC mode, in the region close to the electrode/electrolyte interface. Here, the Ni/(Ni + Zr + Y) atomic ratio decreases from ~0.49 before operating the cell to ~ 0.28 and the SOEC shows a pronounced decrease in percolating triple phase boundaries (TPBs). The wettability of Ni on YSZ is studied and hypotheses are presented to correlate the phenomena of Ni coarsening and Ni depletion with the cell operation mode
Low-frequency processes and turbulence structure in a perturbed boundary-layer
No full textAn analysis of the turbulence structure in a perturbed boundary layer and in low-wind regimes is presented. The study is based on 15 months of continuous wind and turbulence measurements gathered, within the framework of the Urban Turbulence Project, at three levels (5, 9 and 25 m) on a mast located in the outskirts of the city of Turin (Italy). The aim of the work is to investigate low-frequency processes in a perturbed boundary-layer. In fact, the urban canopy and the heat island, together with frequent low-wind conditions, interact with and modify the turbulence structure. In order to investigate this modification, the velocity Eulerian autocorrelation functions together with both the Eulerian and Lagrangian time-scales are shown and compared with the classical theory. The comparisons show that in low-wind cases the velocity autocorrelation functions are not simply exponential but present an oscillating behaviour. A method of normalization is proposed together with an analysis on the applicability of this function. The estimated Lagrangian time-scales are compared with two widely used parametrizations. It is found that the presence of the urban fabric influences the turbulence time-scales and suggests the development of new parametrizations. Finally, higher-order statistics are evaluated and the relationship between higher-order and lower-order moments are analysed, pointing out the effects due to the urban environment
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