247 research outputs found
Making time for what's important:what elements should we value when planning practice-based professional training?
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Is the poleward migration of tropical cyclone maximum intensity associated with a poleward migration of tropical cyclone genesis?
A recent study showed that the global average latitude where tropical cyclones achieve their lifetime-maximum intensity has been migrating poleward at a rate of about one-half degree of latitude per decade over the last 30 years in each hemisphere. However, it does not answer a critical question: is the poleward migration of tropical cyclone lifetime-maximum intensity associated with a poleward migration of tropical cyclone genesis? In this study we will examine this question. First we analyze changes in the environmental variables associated with tropical cyclone genesis, namely entropy deficit, potential intensity, vertical wind shear, vorticity, skin temperature and specific humidity at 500 hPa in reanalysis datasets between 1980 and 2013. Then, a selection of these variables is combined into two tropical cyclone genesis indices that empirically relate tropical cyclone genesis to large-scale variables. We find a shift toward greater (smaller) average potential number of genesis at higher (lower) latitudes over most regions of the Pacific Ocean, which is consistent with a migration of tropical cyclone genesis towards higher latitudes. We then examine the global best track archive and find coherent and significant poleward shifts in mean genesis position over the Pacific Ocean basins
Study of the microstructure resulting from brazed aluminium materials used in heat exchangers
Re-solidification of AA4343 cladding after brazing as well as the related precipitation in the modified AA3003 core material have been investigated. Analysis of the re-solidified material showed that partial dissolution of the core alloy occurs in both the brazing joints and away of them. Far from the brazing joints, the dissolution is, however, limited and diffusion of silicon from the liquid into the core material leads to solid-state precipitation in the so-called âband of dense precipitatesâ (BDP). On the contrary, the dissolution is enhanced in the brazing joint to such an extent that no BDP could be observed. The intermetallic phases present in the resolidified areas as well as in the core material have been analyzed and found to be mainly cubic alpha-Al(Mn,Fe)Si. These results were then compared to predictions made with available phase diagram information
Effect of Ce and Sb on Primary Graphite Growth in Cast Irons
It is well-known that if certain trace elements are present in cast iron melts the morphology of the graphite precipitates can be altered. In order to understand the effect of doping elements on primary growth of graphite, pure FeâSb alloys were prepared by induction melting. They were then placed in graphite crucibles and heated to a temperature above the FeâC eutectic so that the charge became saturated in carbon and melted. To obtain FeâCe alloys, metallic Ce was added at the bottom of a graphite crucible and covered with iron, and then heated as for the FeâSb charge. In both cases, the melt was then cooled and held slightly above the eutectic temperature so that primary graphite crystals, which had nucleated on the crucible walls and then detached from it, could grow freely in the melt. The influence of the added elements on graphite growth was revealed by the change in the shape and distribution of the crystals compared to those obtained in similar experiments carried out with pure Fe. The experiments were made in air and vacuum so as to point out possible interactions between the elements present in the melt and oxygen
High-resolution projections of ambient heat for major European cities using different heat metrics
Heat stress in cities is projected to strongly increase due to climate change. The associated health risks will be exacerbated by the high population density in cities and the urban heat island effect. However, impacts are still uncertain, which is among other factors due to the existence of multiple metrics for quantifying ambient heat and the typically rather coarse spatial resolution of climate models. Here we investigate projections of ambient heat for 36 major European cities based on a recently produced ensemble of regional climate model simulations for Europe (EURO-CORDEX) at 0.11â spatial resolution (âŒâ12.5âkm). The 0.11â EURO-CORDEX ensemble provides the best spatial resolution currently available from an ensemble of climate model projections for the whole of Europe and makes it possible to analyse the risk of temperature extremes and heat waves at the city level. We focus on three temperature-based heat metrics â yearly maximum temperature, number of days with temperatures exceeding 30ââC, and Heat Wave Magnitude Index daily (HWMId) â to analyse projections of ambient heat at 3ââC warming in Europe compared to 1981â2010 based on climate data from the EURO-CORDEX ensemble. The results show that southern European cities will be particularly affected by high levels of ambient heat, but depending on the considered metric, cities in central, eastern, and northern Europe may also experience substantial increases in ambient heat. In several cities, projections of ambient heat vary considerably across the three heat metrics, indicating that estimates based on a single metric might underestimate the potential for adverse health effects due to heat stress. Nighttime ambient heat, quantified based on daily minimum temperatures, shows similar spatial patterns to daytime conditions, albeit with substantially higher HWMId values. The identified spatial patterns of ambient heat are generally consistent with results from global Earth system models, though with substantial differences for individual cities. Our results emphasise the value of high-resolution climate model simulations for analysing climate extremes at the city level. At the same time, they highlight that improving the predominantly rather simple representations of urban areas in climate models would make their simulations even more valuable for planning adaptation measures in cities. Further, our results stress that using complementary metrics for projections of ambient heat gives important insights into the risk of future heat stress that might otherwise be missed.</p
Etablissement de la texture au cours du soudage TIG dâalliages austĂ©nitiques : soudures rĂ©elles et numĂ©riques
The structure prediction of metallic alloys during a welding or additive manufacturing process is the key point for the joiningâs properties. In addition to the welding parameters (or additive manufacturing), the base metal microstructure, chemical homogeneity and crystallographic structure are numerous factors playing an important role on the final microstructure and texture development. Few studies are available in this way. This work purposes a focus on the microstructure establishment during the welded zone solidification during Gas Tungsten Arc Welding. The materials investigated are nickel â chromium â iron austenitic alloys. The grain selection is tracked in a real weld and a texturation criteria is proposed. The following dataâs are compared to the properties of the numerical weld experience. The conclusion suggests that is necessary to improve the knowledges in the grain selection mechanism in order to produce numerical welding microstructure in good accordance with real microstructure welding.La prĂ©diction de la structure des alliages mĂ©talliques durant une Ă©tape de soudage ou de fabrication additive est un point clef du dĂ©veloppement de ces procĂ©dĂ©s et des propriĂ©tĂ©s des assemblages. En plus des paramĂštres de soudage (ou de fabrication additive), la microstructure du mĂ©tal de base, son homogĂ©nĂ©itĂ© chimique et sa nature cristallographique sont autant de facteur jouant un rĂŽle sur lâĂ©tablissement final des microstructures et des textures pour lesquels peu dâĂ©tudes dĂ©taillĂ©es sont disponibles. Une description prĂ©cise de lâĂ©tablissement des microstructures de solidification lors du soudage TIG dâalliage austĂ©nitique nickel-chrome-fer est rĂ©alisĂ©e dans ce travail. La sĂ©lection des grains dans la soudure est suivie dans une soudure rĂ©elle. Un critĂšre de texturation est proposĂ© et les donnĂ©es sont comparĂ©es aux textures simulĂ©es dâoĂč il ressort lâimportance dâaugmenter la connaissance des mĂ©canismes de sĂ©lection de grains pour espĂ©rer modĂ©liser encore plus fidĂšlement les propriĂ©tĂ©s microstructurales et de texture gĂ©nĂ©rĂ©es par le soudage
Cell arrest and cell death in mammalian preimplantation development
The causes, modes, biological role and prospective significance of cell death in preimplantation development in humans and other mammals are still poorly understood. Early bovine embryos represent a very attractive experimental model for the investigation of this fundamental and important issue.
To obtain reference data on the temporal and spatial occurrence of cell death in early bovine embryogenesis, three-dimensionally preserved embryos of different ages and stages of development up to hatched blastocysts were examined in toto by confocal laser scanning microscopy. In parallel, transcript abundance profiles for selected apoptosis-related genes were analyzed by real-time reverse transcriptase-polymerase chain reaction. Our study documents that in vitro as well as in vivo, the first four cleavage cycles are prone to a high failure rate including different types of permanent cell cycle arrest and subsequent non-apoptotic blastomere death. In vitro produced and in vivo derived blastocysts showed a significant incidence of cell death in the inner cell mass (ICM), but only in part with morphological features of apoptosis. Importantly, transcripts for CASP3, CASP9, CASP8 and FAS/FASLG were not detectable or found at very low abundances.
In vitro and in vivo, errors and failures of the first and the next three cleavage divisions frequently cause immediate embryo death or lead to aberrant subsequent development, and are the main source of developmental heterogeneity. A substantial occurrence of cell death in the ICM even in fast developing blastocysts strongly suggests a regular developmentally controlled elimination of cells, while the nature and mechanisms of ICM cell death are unclear. Morphological findings as well as transcript levels measured for important apoptosis-related genes are in conflict with the view that classical caspase-mediated apoptosis is the major cause of cell death in early bovine development
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Cluster analysis of downscaled and explicitly simulated North Atlantic tropical cyclone tracks
A realistic representation of the North Atlantic tropical cyclone tracks is crucial as it allows, for example, explaining potential changes in US landfalling systems. Here we present a tentative study, which examines the ability of recent climate models to represent North Atlantic tropical cyclone tracks. Tracks from two types of climate models are evaluated: explicit tracks are obtained from tropical cyclones simulated in regional or global climate models with moderate to high horizontal resolution (1° to 0.25°), and downscaled tracks are obtained using a downscaling technique with large-scale environmental fields from a subset of these models. For both configurations, tracks are objectively separated into four groups using a cluster technique, leading to a zonal and a meridional separation of the tracks. The meridional separation largely captures the separation between deep tropical and sub-tropical, hybrid or baroclinic cyclones, while the zonal separation segregates Gulf of Mexico and Cape Verde storms. The properties of the tracksâ seasonality, intensity and power dissipation index in each cluster are documented for both configurations. Our results show that except for the seasonality, the downscaled tracks better capture the observed characteristics of the clusters. We also use three different idealized scenarios to examine the possible future changes of tropical cyclone tracks under 1) warming sea surface temperature, 2) increasing carbon dioxide, and 3) a combination of the two. The response to each scenario is highly variable depending on the simulation considered. Finally, we examine the role of each cluster in these future changes and find no preponderant contribution of any single cluster over the others
Credentials, talent and cultural capital: a comparative study of educational elites in England and France
This article examines student accounts of credentials, talent and academic success, against a backdrop of the enduring liberal ideal of an education-based meritocracy. The article also examines Bourdieuâs account of academic qualifications as the dominant source of institutionalised cultural capital, and concludes that it does not adequately account for comparative differences in the social structure of competition and ideological shifts in class (re)production in different national contexts. This analysis is based on an empirical investigation of elite students at Oxford University and Sciences Po in Paris. We investigated how they understand the competition for a livelihood and whether they see themselves as more âtalentedâ than students from non-elite universities. This investigation revealed important similarities and differences between British and French students that have significant sociological implications for the (re)production and legitimation of educational and labour market inequalities
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