36 research outputs found
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Impact of Atlantic multidecadal variability on rainfall intensity distribution and timing of the West African monsoon
Previous studies agree on an impact of the Atlantic multidecadal variability (AMV) on the total seasonal rainfall amounts over the Sahel. However, whether and how the AMV affects the distribution of rainfall or the timing of the West African monsoon is not well known. Here we seek to explore these impacts by analyzing daily rainfall outputs from climate model simulations with an idealized AMV forcing imposed in the North Atlantic, which is representative of the observed one. The setup follows a protocol largely consistent with the one proposed by the Component C of the Decadal Climate Prediction Project (DCPP-C). We start by evaluating model's performance in simulating precipitation, showing that models underestimate it over the Sahel, where the mean intensity is consistently smaller than observations. Conversely, models overestimate precipitation over the Guinea coast, where too many rainy days are simulated. In addition, most models underestimate the average length of the rainy season over the Sahel; some are due to a monsoon onset that is too late and others due to a cessation that is too early. In response to a persistent positive AMV pattern, models show an enhancement in total summer rainfall over continental West Africa, including the Sahel. Under a positive AMV phase, the number of wet days and the intensity of daily rainfall events are also enhanced over the Sahel. The former explains most of the changes in seasonal rainfall in the northern fringe, while the latter is more relevant in the southern region, where higher rainfall anomalies occur. This dominance is connected to the changes in the number of days per type of event; the frequency of both moderate and heavy events increases over the Sahel's northern fringe. Conversely, over the southern limit, it is mostly the frequency of heavy events which is enhanced, thus affecting the mean rainfall intensity there. Extreme rainfall events are also enhanced over the whole Sahel in response to a positive phase of the AMV. Over the Sahel, models with stronger negative biases in rainfall amounts compared to observations show weaker changes in response to AMV, suggesting that systematic biases could affect the simulated responses. The monsoon onset over the Sahel shows no clear response to AMV, while the demise tends to be delayed, and the overall length of the monsoon season enhanced between 2 and 5âd with the positive AMV pattern. The effect of AMV on the seasonality of the monsoon is more consistent to the west of 10ââW, with all models showing a statistically significant earlier onset, later demise, and enhanced monsoon season with the positive phase of the AMV. Our results suggest a potential for the decadal prediction of changes in the intraseasonal characteristics of rainfall over the Sahel, including the occurrence of extreme events.</p
Agroforesterie et services écosystémiques en zone tropicale
Respectueux de lâenvironnement et garantissant une sĂ©curitĂ© alimentaire soutenue par la diversification des productions et des revenus quâils procurent, les systĂšmes agroforestiers apparaissent comme un modĂšle prometteur dâagriculture durable dans les pays du Sud les plus vulnĂ©rables aux changements globaux. Cependant, ces systĂšmes agroforestiers ne peuvent ĂȘtre optimisĂ©s quâĂ condition de mieux comprendre et de mieux maĂźtriser les facteurs de leurs productions. Lâouvrage prĂ©sente un ensemble de connaissances rĂ©centes sur les mĂ©canismes biophysiques et socio-Ă©conomiques qui sous-tendent le fonctionnement et la dynamique des systĂšmes agroforestiers. Il concerne, dâune part les systĂšmes agroforestiers Ă base de cultures pĂ©rennes, telles que cacaoyers et cafĂ©iers, de rĂ©gions tropicales humides en AmĂ©rique du Sud, en Afrique de lâEst et du Centre, dâautre part les parcs arborĂ©s et arbustifs Ă base de cultures vivriĂšres, principalement de cĂ©rĂ©ales, de la rĂ©gion semi-aride subsaharienne dâAfrique de lâOuest. Il synthĂ©tise les derniĂšres avancĂ©es acquises grĂące Ă plusieurs projets associant le Cirad, lâIRD et leurs partenaires du Sud qui ont Ă©tĂ© conduits entre 2012 et 2016 dans ces rĂ©gions. Lâensemble de ces projets sâarticulent autour des dynamiques des systĂšmes agroforestiers et des compromis entre les services de production et les autres services socio-Ă©cosystĂ©miques que ces systĂšmes fournissent
Promotion de lâenseignement de la gymnastique a lâĂ©cole Ă©lĂ©mentaire au SĂ©nĂ©gal: Promotion of gymnastics teaching at elementary school in Senegal
Depuis l'antiquitĂ© grecque, l'Ă©ducation par les activitĂ©s physiques trouve sa place dans l'Ă©ducation gĂ©nĂ©rale des jeunes. Lâenseignement Ă©lĂ©mentaire au SĂ©nĂ©gal vise Ă assurer Ă tous les enfants et particuliĂšrement ceux en difficultĂ© ou appartenant Ă des minoritĂ©s ethniques la possibilitĂ© dâaccĂ©der Ă un enseignement obligatoire, gratuit, de qualitĂ© et de le suivre jusquâĂ son terme. La gymnastique occupant une place importante dans le dĂ©veloppement psychomoteur de lâenfant, son absence dans lâenseignement des activitĂ©s physiques et sportives dans le cycle Ă©lĂ©mentaire ne sâexplique pas. Ce fait nous a poussĂ© Ă initier une recherche sur la problĂ©matique de lâintĂ©gration de lâenseignement de la gymnastique Ă lâĂ©cole Ă©lĂ©mentaire au SĂ©nĂ©gal. Notre problĂšme de recherche porte sur les modalitĂ©s et dispositions quâil faudrait mettre en place pour que la gymnastique soit intĂ©grĂ©e parmi les activitĂ©s physiques et sportives qui sont enseignĂ©es Ă lâĂ©cole Ă©lĂ©mentaire. Cette recherche sâinscrit dans le cadre dâune Ă©tude qualitative descriptive. Nous nous proposons de dĂ©crire les milieux de pratique de lâenseignement Ă©lĂ©mentaire ainsi que les parcours de formation des enseignants. Le programme dâenseignement des activitĂ©s physiques et sportives et la perception de la gymnastique par les intervenants sont aussi explorĂ©s. Notre Ă©chantillon est composĂ© de 85 enseignants issus des Ă©coles Ă©lĂ©mentaires privĂ©es et publiques. Le questionnaire a Ă©tĂ© utilisĂ© comme outil de collecte de donnĂ©es.
ABSTRACTEducation through physical activity has since ancient Greece been part of the youthâs general education. Elementary education in Senegal aims to ensure that all children, particularly those in difficulty or belonging to ethnic minorities, have access to complete, compulsory and free quality education. Since gymnastics plays an important role in the child's psychomotor development, there is no explanation for its absence in the teaching of physical and sports activities in the elementary cycle. This fact prompted us to initiate research on the issue of the integration of gymnastics teaching into elementary school in Senegal. Our research problem concerns the modalities and provisions that should be put in place to ensure that gymnastics is integrated into physical and sports activities that are taught in elementary schools. This research is part of a descriptive qualitative study. We propose to describe the practice environments of elementary education as well as the teacher training specializations. The physical and sports activities teaching program, and the perception of gymnastics by the participants are also explored. Our sample consists of 85 teachers from private and public elementary schools. The questionnaire was used as a data collection tool
Les subsahariens en Chine : solidarité inter migrants face à une politique migratoire chinoise complexe : étude des cas des Africains de Guangzhou (Chine) dans ETHOS
International audienc
Les subsahariens en Chine : solidarité inter migrants face à une politique migratoire chinoise complexe : étude des cas des Africains de Guangzhou (Chine) dans ETHOS
International audienc
Potential contribution of climate conditions on COVID-19 pandemic transmission over West and North African countries
COVID-19, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), is a very contagious disease that has killed many people worldwide. According to data from the World Health Organization (WHO), the spread of the disease appears to be slower in Africa. Although several studies have been published on the relationship between meteorological parameters and COVID-19 transmission, the effects of climate conditions on COVID-19 remain largely unexplored and without consensus. However, the transmission of COVID-19 and sensitivity to climate conditions are also not fully understood in Africa. Here, using available epidemiological data over 275 days (i.e., from 1 March to 30 November 2020) taken from the European Center for Disease Prevention and Control of the European Union database and daily data of surface air temperature specific humidity and water vapor from the National Center for Environmental Prediction (NCEP), this paper investigates the potential contribution of climate conditions on COVID-19 transmission over 16 selected countries throughout three climatic regions of Africa (i.e., Sahel, Maghreb, and Gulf of Guinea). The results highlight statistically significant inverse correlations between COVID-19 cases and temperature over the Maghreb and the Gulf of Guinea regions. In contrast, positive correlations are found over the Sahel area, especially in the central part, including Niger and Mali. Correlations with specific humidity and water vapor parameters display significant and positive values over the Sahelian and the Gulf of Guinea countries and negative values over the Maghreb countries. Then, the COVID-19 pandemic transmission is influenced differently across the three climatic regions: (i) cold and dry environmental conditions over the Maghreb; (ii) warm and humid conditions over the Sahel; and (iii) cold and humid conditions over the Gulf of Guinea. In addition, for all three climatic regions, even though the climate impact has been found to be significant, its effect appears to display a secondary role based on the explanatory power variance compared to non-climatic factors assumed to be dominated by socio-economic factors and early strong public health measures
An efficient strategy for 3D numerical simulation of friction stir welding process of pure copper plates
International audienceCopper and its alloys have a wide spectrum of engineering applications such as heat exchangers, hot water tanks or nuclear pressure vessels. Most of these structures are obtained by welding. Unfortunately, the use of conventional arc welding process is affected by several factors such as the thermal conductivity of the alloy being welded, the shielding gas, the joint design, the welding position, and the surface condition and its cleanliness. Friction stir welding process could be an interesting alternative as it can be performed without melting the material, it involves a non-consumable tool, and provides good mechanical properties. To understand in depth both the physical and the thermal mechanisms involved in this process, numerical modelling is essential. The aim of this paper is to propose an efficient simulation strategy based on the coupled Eulerian Lagrangian finite element method. The mass scaling procedure, which is used to decrease the computation time will be presented, as well as its effect on the temperature field distribution and on the down force. This model will then be used for a parametric study in order to improve the friction welding process's parameters. Published under licence by IOP Publishing Lt
Measurement of three-dimensional volumetric displacement fields in structural porous adhesive joints, under tensile and tensile-shear load, by means of in-situ X-ray microtomography
International audienceNowadays, structural bonding is increasingly used for its advantages over conventional joining methods such as riveting or welding. Bonding defects (incomplete polymerization, gradient of mechanical properties, and presence of pores, among others.) can significantly impact the mechanical behavior of these assemblies. Among these defects, the presence of pores, detectable by means of X-ray microtomography measurements, could have a significant influence on the mechanical strength of a bonded structure (reduction of the useful section, questioning of the continuity of the joint, and stress concentration, among others). The study of these pores populations by means of microtomographic measurements, as well as their evolution under mechanical stress, can therefore provide valuable information regarding the mechanical behavior. These data can provide information on (i) the mechanical behavior on a microscopic scale, (ii) the identification of mechanisms of damage and failure of the adhesive joint, or (iii) the measurement of volume displacement fields. In this work, a method for calculating volume displacement fields in an adhesive joint is presented, using the detected pores as markers. The robustness, limits, and effects of different parameters (noise, voxelization, among others.) on this algorithm are identified on synthetic data representative of an adhesive joint. Finally, the validation of the method is based on interrupted tests on relatively small bonded specimens (called mini-Scarf) under tensile and tensile-shear loads