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Autonomisation politique des femmes et instabilité politique dans les pays d’Afrique subsaharienne
No full textInternational audienceDespite the widespread recognition of political instability as a major constraint to economic development in sub-Saharan Africa, our understanding of the key factors influencing these countries’ ability to achieve a more stable political environment remains limited. Drawing on a sample of thirty-four sub-Saharan African countries, this study provides robust evidence of the importance of women’s political empowerment in reducing political instability. This finding is supported by accounting for potential biases, including reverse causality, the effect of observed or unobserved confounders on this relationship, and measurement errors. In-depth analyses reveal that reductions in military expenditures and improvements in democratic governance serve as key mechanisms through which women’s political empowerment influences political instability. These findings strengthen the case for policies promoting women’s political empowerment as a means of fostering political stability in sub-Saharan Africa.Malgré la reconnaissance globale de l’instabilité politique comme une contrainte majeure au développement économique en Afrique subsaharienne, nos connaissances demeurent limitées quant aux facteurs clés influençant la capacité de ces pays à établir un environnement politique plus stable. A partir d’un échantillon de 34 pays d’Afrique subsaharienne, cette étude offre une démonstration solide de l’importance de l’autonomisation politique des femmes dans la réduction de l’instabilité politique. Ce résultat est étayé par la prise en compte des biais potentiels, notamment la causalité inverse, l’effet des facteurs de confusion observés ou non sur cette relation, ainsi que les erreurs de mesure. Des analyses approfondies révèlent que la réduction des dépenses militaires ainsi l’amélioration de la démocratie constituent des mécanismes par lesquels l’autonomisation politique des femmes influe sur l’instabilité politique. Ces conclusions renforcent l’argument en faveur de politiques visant à promouvoir l’autonomisation politique des femmes pour la stabilité politique en Afrique subsaharienne
Experimental investigation of the oscillating flow characteristics at the exit of a thermally stratified porous medium for thermoacoustic applications
No full textInternational audienceThe focus of the current study is to investigate the effects of temperature on the flow characteristics at the extremity of a porous medium exposed to an oscillating flow. The flow velocity fields at different phases over the oscillating cycle are measured using a Particle Image Velocimetry (PIV) system for different temperature gradients across a porous medium. It is observed that a change in the temperature gradient does not lead to a significant change in the vorticity field during the acceleration part of the flow ejection, whereas it is associated with stronger and larger structures when the flow decelerates. The spatial decay of the intensity of fluctuation at the exit of the porous medium follows an exponential function. It is found that the constant of the exponential function is proportional to the flow temperature. By correcting this constant based on the measured temperature, a good agreement between the measured intensity of fluctuations of decay and the predicted values is obtained
Observation numérique d'une instabilité au-dessus d’un matériau acoustique constitué de quarts d'onde sous écoulement rasant
No full textAéroacoustique guidée : modélisation, mesure et traitements acoustiques; GAHA - Aéro et Hydro-AcoustiqueNational audienceLes ondes acoustiques se propageant dans des conduites sont atténuées par des matériaux absorbants généralement constitués de cavités résonantes. Dans la littérature, il a pu être observé expérimentalement qu'en présence d'écoulement ces matériaux peuvent devenir instables lorsque leur résistance acoustique est faible. Des simulations numériques avec des matériaux modélisés par des impédances pariétales ont également observé ces comportements. Dans le présent travail, on effectue une simulation numérique bidimensionnelle d'une série de résonateurs quart d'onde soumise à un écoulement rasant et à des ondes acoustiques incidentes. Ces simulations se basent sur les équations de Navier-Stokes simulées par la méthode des différences finies, et la géométrie des cavités est prise en compte avec la méthode des frontières immergées. Des structures périodiques de grande échelle par rapport à la dimension des cavités sont observées, qui ont les caractéristiques d’une instabilité. On cherchera à voir si ces instabilités sont à l'origine d'une émission acoustique
Formation of skin-core structure in filled room-temperature vulcanized polydimethylsiloxane after long exposure to moderate temperatures
No full textInternational audienceThis study highlights the formation of a skin-core effect inside a filled silicone rubber exposed to air for durations up to 600 days at temperatures between 30 • C and 70 • C. Coupling mechanical and physico-chemical characterisations reveal that the volatile components, such as crosslinking by-products and oligomers, evaporate from the elastomeric network during the exposure, resulting in the shrinkage of the sample. This phenomenon gives rise to the formation of a composition gradient from the sample's surface towards its core. All the samples become more brittle with ageing, but the tensile modulus increase only slightly at the longest durations and highest temperatures. More fillers are found on the outer surface while the infrared spectra in the core of the sample remain unaffected by neither the temperature nor the duration. The nanoindentation highlights gradients of elastic modulus on the cross-section and provides an estimation of the skin thickness. By wrapping the samples in aluminum foil, the evaporation of volatile components is prevented. The measured properties remain constant with the duration of thermal exposure even at the highest temperature
Flow field reconstruction of rocket engine turbine on sparse sensors
No full textInternational audienceFlow field reconstruction from spatially sparse sensors provides a means to identify global flow behavior and analyze the propagation of dynamic flow phenomena. This approach is particularly valuable for applications with limited accessibility, a restricted number of sensors, and challenging operating conditions, such as turbomachinery instrumentation. Detecting early-stage flow separation in turbines enables intelligent control strategies to mitigate the growth of this phenomenon and minimize its adverse effects on performance. This paper presents a method for reconstructing the flow field of a turbine-inlet manifold using an Autoencoder (AE) trained on computational fluid dynamic (CFD) simulation data. Figure 1 illustrates the extraction of a horizontal 2D flow field of interest from the toroidal manifold. Flow separation in the torus, visible in the upper-right region of the flow field, significantly affects the inflow into the downstream convergent-divergent stator channels, ultimately impacting the overall turbine performance.The AE, trained on CFD data, is validated using experimental data. The described methodology is applied to the impulse turbine of a rocket-engine turbo pump. Identifying early-stage flow separation in the reconstructed flow field can enable intelligent data-driven turbine control, avoiding critical operational points, optimizing performance, and reducing lifetime degrading effects. Figure 1turbine manifold, left: 3D velocity flow field, middle: 2D velocity arrows, right:</div
Whole-body cryostimulation exposures effectively alleviates menstrual-related pain and associated sleep disturbances in young women: a randomized controlled trial
No full textInternational audienceIntroduction Menstrual-related pain and sleep disturbances are widespread in women experiencing premenstrual syndrome and primary dysmenorrhea. Such disturbances could be alleviated through repeated whole-body cryostimulation (WBC) sessions. Therefore, this study aimed to assess the effect of menstrual-related pain on sleep parameters, and the impact of WBC exposures on pain and sleep. Materials and methods Pain and sleep were evaluated for two 5-day periods under different conditions (control vs. WBC), randomly assigned across two consecutive menstrual cycles. Measurements began when the first pain/symptom indicating the onset of the menstrual phase was experienced. Pain was rated using a scale, while sleep was assessed using accelerometers and questionnaires. Throughout the 5-day WBC exposure, women underwent 3-min exposure to intense ventilated cold air each evening. After data collection, participants were categorized into high (HP) or low/no pain (LP) groups based on control pain scores. Results Twenty-nine naturally menstruating women were assessed. Perceived sleep quality was lower in the HP group compared to the LP group during the control condition (Spiegel score: 20.1 ± 2.3 vs. 22.3 ± 1.9, respectively; Cohen's d = 1.1). Across both groups, perceived sleep quality improved with the number of WBC exposures (night1: 19.5 ± 3.2 vs. night5: 23.5 ± 3.8; Hedge's g = 1.10). In the HP group, pain was reduced in the WBC condition compared to the control condition. Changes in pain and perceived sleep quality following WBC were correlated ( r = −0.86). Discussion Women experiencing higher menstrual-related pain reported poorer perceived sleep quality. Their pain was reduced by WBC exposures. This improvement was highly associated with the enhancement in sleep quality
Drivers of the mammalian Grande Coupure in Western Europe at the Eocene-Oligocene transition
No full textInternational audienceOne of the main focuses of evolutionary biology studies today is investigating the evolutionary and ecological processes responsible for the diversification and decline of clades. The ‘Grande Coupure’ corresponds to a major turnover in the European fauna during the severe biological and climatic crisis of the Eocene–Oligocene transition (EOT), 33.9 million years ago (Ma). In Western Europe, this biological event is characterized by the dramatic extinction of insular European mammals, coupled with the massive arrival of modern Asian clades. Several hypotheses have been proposed to explain this extinction, including abiotic factors such as temperature, sea level, and seasonality, as well as biotic factors such as competitive interactions. However, these hypotheses have never been formally tested. Here, we examined the diversification of Western European mammals to determine the primary drivers of the Grande Coupure and to understand how the modern mammal fauna became established in Western Europe 34 Ma. Using Bayesian birth-death models considering the preservation bias of the fossil record, we analyzed a high-resolution fossil occurrence dataset (578 species, >3,300 occurrences) from Southern France spanning the late Eocene-Oligocene interval and estimated the regional diversification and diversity dynamics of endemic and immigrant European mammals. Our results show that a combination of multiple abiotic factors played a significant role in the diversification of European endemic mammals and that the major environmental changes at the EOT were responsible for the extinction of 65% of species. Importantly, our results do not support the hypothesis of competitive interactions between endemic and immigrant taxa. Instead, our results suggest that immigrant species opportunistically replaced endemic species after the EOT by colonizing new ecological niches left vacant. Interestingly, the diversity recovery of European mammals during the early Oligocene was not rapid, but occurred over three million years, indicating a gradual arrival of immigrant mammals in multiple migratory waves
Tracer la provenance du bois de sapin (Abies alba Mill.) : défis dendrochronologiques et apports à la compréhension des dynamiques passées d’exploitation des forêts montagnardes
No full textInternational audienceLe projet régional Bosca du Défi Clé Occitanie ‘Sciences du Passé’, vise à détailler les différentes étapes de la production, du transport et de l’utilisation du bois en région Occitanie durant les périodes médiévale et moderne. Il s’intéresse notamment aux modes de gestion et d’exploitation des forêts à ces époques, dans le but de sensibiliser à l’importance de ces écosystèmes pour la préservation de la biodiversité. L’un des objectifs majeurs du projet consiste à poursuivre les recherches dendrochronologiques dans cette région, en exploitant les cernes de croissance pour déterminer l’origine du bois d’œuvre historique. En complément des chênes caducifoliés (Quercus robur L. et Quercus petraea (Matt.) Liebl.), le sapin (Abies alba Mill.) a été retenu comme l’une des essences principales de notre étude en raison de son importance dans la filière bois passée en Occitanie.Après deux années d’investigations, le projet a permis des avancées notables dans la compréhension de l’usage du sapin dans la région. En confrontant les données issues de bois présents dans des bâtiments de l’époque moderne avec celles provenant d’arbres vivants, nous avons pu révéler la complexité des études de dendroprovenance liées à cette essence. En effet, des recherches antérieures ont démontré que des arbres de sapin situés à des distances considérables mais à une altitude équivalente produisent de variations de croissance très similaires. Ainsi, bien que les largeurs de cernes permettent une caractérisation altitudinale, les méthodes classiques de dendroprovenance – qui utilisent le coefficient de corrélation de Pearson (R) et le test de Student (T) – ne permettent pas de localiser précisément la provenance géographique du bois de sapin. Cela souligne la nécessité d’une évaluation rigoureuse des approches statistiques employées, et l’importance d’étudier les séries issues d’arbres vivants pour identifier les méthodes les plus fiables dans l’analyse de provenance des bois anciens.Pour cela, nous avons d’abord testé des méthodes statistiques, telles que l’analyse de la corrélation spatiale des résidus, sur un corpus d’arbres vivants provenant des Pyrénées centrales, du Massif central et des Alpes. L’étude de provenance s’est ensuite focalisée sur la zone de confluence entre les rivières Tarn et Garonne, avec une attention particulière portée à la ville de Montauban et à sa cathédrale, qui constitue un cas d’étude emblématique. L’édifice présente deux principales phases de construction. Les bois datés des XVIIe / XVIIIe siècles montrent des signes évidents de flottage ainsi que des marques de marchands originaires des Pyrénées, révélant l’existence de circuits d’approvisionnement bien établis. En revanche, les bois utilisés au XIXe siècle présentent des caractéristiques techniques et typologiques distinctes, témoignant d’un changement des modes de transport et vraisemblablement des aires d’approvisionnement en bois. L’ensemble de ces observations met en lumière une chaîne opératoire complexe, dont les dynamiques ont pu être précisées grâce à l’analyse dendrochronologique et à l’utilisation de méthodes statistiques d’abord testés sur nos référentiels d’arbres vivants
Comparative Analysis of Flax Fiber-Reinforced Composites and Hybrid Configurations for Enhanced Low Energy Impact Performance
No full textInternational audienceIn this study, the low energy impact properties of flax/epoxy, glass/epoxy and hybrid flax-glass/epoxy laminates are evaluated for two different stacking sequences: a unidirectional [0]8 and a cross-ply [0/90]2s. For flax laminates, the base reinforcement is made of the combination of a unidirectional flax layer and a flax mat layer, where the mat phase consisted of short flax fibers used as a binder for the unidirectional phase. All laminates were tested under uniaxial tension both before and after impact and were molded at a fiber volume fraction of 40%. The results indicate that the specific stiffness of the flax fiber composite is approximately 7% higher than that of the glass fiber composite, regardless of the stacking sequence used. Concerning low-energy impact resistance, the cross-ply laminate demonstrates superior performance with higher impact resistance and less permanent deformation compared to the unidirectional laminate. The study also explores the hybridization of flax and glass fibers, suggesting a promising approach that leverages the synergistic effects of employing two different types of fibers in the composite. The comparison of energy absorption during impact shows that the hybrid fibers/epoxy composite has a higher energy absorption capacity than the glass fiber/epoxy composite. Additionally, hybridization helps mitigate the degradation of tensile properties caused by impact, representing an effective strategy to enhance the mechanical properties of the flax fiber composite post-impact
