International Journal of Agricultural Research, Innovation and Technology (IJARIT)
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Lower oceanic crust formed by in situ melt crystallization revealed by seismic layering
No full textInternational audienceOceanic crust forms at mid-ocean spreading centres through a combination of magmatic and tectonic processes, with the magmatic processes creating two distinct layers: the upper and the lower crust. While the upper crust is known to form from lava flows and basaltic dykes based on geophysical and drilling results, the formation of the gabbroic lower crust is still debated. Here we perform a full waveform inversion of wide-angle seismic data from relatively young (7-12-Myr-old) crust formed at the slow-spreading Mid-Atlantic Ridge. The seismic velocity model reveals alternating, 400-500 m thick, high- and low-velocity layers with ±200 m s−1 velocity variations, below ~2 km from the oceanic basement. The uppermost low-velocity layer is consistent with hydrothermal alteration, defining the base of extensive hydrothermal circulation near the ridge axis. The underlying layering supports that the lower crust is formed through the intrusion of melt as sills at different depths, which cool and crystallize in situ. The layering extends up to 5-15 km distance along the seismic profile, covering 300,000-800,000 years, suggesting that this form of lower crustal accretion is a stable process
A detailed magnetic record of Pleistocene climate and distal ash dispersal during the last 800 kyrs - The Suhia Kladenetz quarry loess-paleosol sequence near Pleven (Bulgaria)
No full textInternational audienceLoess-paleosol sequences (LPS) from the Lower Danube area are valuable terrestrial archives of environmental change in SE Europe during the Pleistocene. A twenty-seven meters thick sequence has been sampled in Central North Bulgaria near the city of Pleven within the Suhia Kladenetz (SK) quarry. The sedimentary sequence consists of seven loess units and six interbedded paleosol complexes covering the last 800 kyrs. The continuous 2 cm resolution sampling depth interval enabled the recovery of several cryptotephras in addition to a ~ 20 cm thick tephra deposit observed in the field within the L2 loess unit. All cryptotephras are clearly identified in laboratory analyses by their strong magnetic signal, particularly well expressed by concentration - dependent anhysteretic susceptibility (χARM), isothermal remanence (IRM), low field magnetic susceptibility (χlf) and in some cases by frequency dependent magnetic susceptibility (Δχ), coercivity of remanence (BCR), and hard isothermal remanence (HIRM2.0-0.3T). Complementary optical and scanning electron microscope analyses of single grains from the tephra deposit and cryptotephra intervals reveal the presence of volcanogenic grains with smooth glassy surfaces and vesicular internal structure; fluidal grains with bulbous surfaces and dense irregular grains. Grain size sensitive magnetic ratios χARM/χlf, ARM/IRM100mT, IRM2T/χlf are not always discriminative, suggesting that (crypto)tephras do not have a single uniform source. Preliminary correlative age models are used to estimate ages for the (crypto)tephras and propose likely associated volcanic eruptions. Finally, strong pedogenic magnetic enhancement of the younger paleosols (S4, S3, S2 and partly S1) contrasts with the smeared and low magnetic signal of the older paleosols (S6 and S5). Moreover, an enhanced content of low-coercivity hematite observed from the upper part of the S5 paleosol upwards to the present and a sharp increase in the concentration of maghemite at the expense of magnetite observed for the S3, S2 and S1 paleosols provides strong evidence for a significant paleoenvironmental change. The timing of this change, based on the SK LPS age models, is compatible with the mid-Brunhes climate transition
Patterns of food transfer in yellow-legged hornet nests revealed by heavy metal tracers
No full textInternational audienceA social insect colony can be seen as a superorganism in which nutrient collection and regulation is achieved through the collective action of workers. Here we investigated how workers of the yellow-legged hornet Vespa velutina, an invasive predator of honeybees and other insects in Europe, distribute the incoming food within their nests. Food transfer among colonies differing in composition of developmental stage and abundance of different castes was compared by feeding workers with protein and carbohydrate solutions labelled with non-radioactive heavy metals (rubidium and caesium) and measuring the heavy metal tracers??? occurrence in adults and larvae in the nests after 24h. Caesium labelled sucrose was more abundant in the adults (workers, males and the queen), while rubidium labelled proteins were more abundant in the larvae. The lightest larvae received more protein than the others. The lightest workers received more carbohydrate, and the largest workers more protein. Even if this work is exploratory, our results considerably improve our knowledge of hornet biology by showing how food distribution patterns may vary throughout the development cycle of colonies. They also provide new perspectives to understand how specific nutrients are distributed in nests, and may help develop Trojan horses biological control strategies based on food distribution
Imagerie mentale et tennis: revue, recommandation appliquées et perspectives de recherches
No full textInternational audienceMental Imagery (MI), which can be defined as the brain's ability to recreate motor experiences in the absence of actual actions, is a mental strategy frequently used by tennis players and coaches in the context of learning and performance. The purpose of this review was to examine the MI use, interventions and effects on the performance of tennis players. Preferred reporting items for reviews and meta-analyses guidelines were employed and research studies were collected via SCOPUS, PubMed, PsycINFO, Science Direct and Google Scholar, in English and French, from the earliest record up to August 2021. Forty-one studies met the inclusion criteria. This review (number 2020-05-87) resulted in a wide variety of MI use in tennis and its beneficial effects, whatever the level or age of the players. MI interventions generally improve motor performance, motivational or affective outcomes. Moreover, MI is frequently combined with other mental skills and integrated in preperformance routines including breathing, positive self-talk, and/or concentration. Future research is needed to better explore the gender effect in MI interventions in tennis. Overall, MI appears to be beneficial for players, whatever their age or level, and should be incorporated in training programs. Practical implications are discussed.L’imagerie mentale (IM), définie comme la capacité du cerveau à recréer des expériences motrices en l’absence d’actions réelles, est une stratégie mentale communément utilisée par les joueurs de tennis et les entraîneurs dans le cadre de l’apprentissage et de la performance. Le but de cette revue était d’examiner l’utilisation de l’IM et ses effets sur la performance des joueurs de tennis. La méthode PRISMA a été utilisée et les travaux de recherche ont été collectés via SCOPUS, PubMed, PsycINFO, Science Direct et Google Scholar, en anglais et en français, jusqu’en août 2021. Quarante-et-une études ont respecté les critères d’inclusion. Cette revue a révélé une grande variété d’utilisation de l’IM au tennis et des effets bénéfiques, quel que soit le niveau ou l’âge des joueurs sur les performances motrices, les affects et la motivation. De plus, l’IM est fréquemment associée à d’autres habiletés mentales et intégrée dans les routines de pré-performance. Cette étude a mis en évidence la faible représentation des joueuses de tennis, des recherches futures sont donc nécessaires pour explorer s’il existe un effet du genre en lien avec l’IM. Dans l’ensemble, l’IM semble être bénéfique pour les joueurs, indépendamment de leur âge ou de leur niveau et devrait être intégrée dans les programmes d’entraînement. Des recommandations pratiques sont proposées
What causes the persistent seismicity below the eastern flank of Piton de la Fournaise (Réunion Island)? Elasto-plastic models of magma inflation
No full textInternational audienceIdentifying the causes of flank destabilization of active volcanic edifices is key to prevent catastrophic events. The persistent seismicity recorded below the eastern flank of Piton de la Fournaise shield volcano (Réunion Island), both in between and during eruptive events, may give indications on the mechanical stability of this edifice. Whether this asymmetric "cup" shaped seismicity is linked to magma injections and whether it sparks a gravitational flank slide motivates this study. Here we model the elasto-plastic behavior of this volcanic edifice at crustal scale, with the 3D finite-element code Adeli. First, we test the influence of tensile failure, recently implemented in combination to a Drucker-Prager shear failure criterion; a pressurized cavity below a flat top surface triggers shear failure in general, with tensile failure restricted to the surface and cavity tip. Then we include the topography of Piton de la Fournaise in the gravity field. Considering first only elasticity, deviatoric stresses attain about 35 MPa below the volcanic edifice and displacements are maximum in the horizontal east-west direction, reaching 30 m near sea-level. Introducing plastic behavior produces a rather symmetric cup shape plastic domain around the volcano's summit, that extends at depth with reducing bedrock {\it effective} friction (which acts is a proxy for reduced standard friction due to pore fluid pressurization). An asymmetric listric shear zone develops down to -3 km (bsl) only if the tensile strength, cohesion and friction angle are set as low as 1.5 MPa, 3 MPa and 3°, respectively; these values hence provide a lower bound for the edifice's effective strength. The second part of this study explores the influence of an internal overpressure, which is either applied as a vertical inflation source located about 500 m below the surface of the eastern flank, simulating a distal dike, or from a deeper ellipsoid simulating the magma reservoir located at depth ca. 0 km (near sea level) below the summit. The resulting strain pattern forms a cup-shaped shear zone dipping down below the eastern flanks of the edifice, reaching depth -2 km ({\it bsl}) if effective friction angle is . Whereas the deep base of the dike and the eastern edge of the magma reservoir coincide geometrically in the models, the inflating dike produces a shear zone 1 km shallower than does the inflating magma reservoir, the latter coinciding better with the shape of the observed seismic cup. Hence, we propose that this structure is a mechanical consequence of continuous magma supply in the reservoir, coherent with previous interpretations. This means that at least originally it did not need to form as a pre-existing weak zone or a magma-filled structure. However, this shear zone delimits an underlying domain in dilatation relative to a constricted hanging-wall; it may thus promote magma sills. It also branches to the surface with planar radial shear zones comparable to some observed eruptive fissures. The 3D kinematics of this shear zone does not rule out the possibility of a giant flank slide, although it does not appear today as imminent
Relationships between Physico-Chemical Parameters and Taxonomic Structure of Benthic Macroinvertebrate Assemblages in Streams of West Cameroon
No full textInternational audienceTropical rivers are strongly influenced by stormwaters, pollutants and agro-pastoral activities. These systems are no longer able to maintain their native biota. Therefore, it seems important to understand how biological assemblages are driven by environmental gradients at different spatial scales. However, information on the relationships between the distribution of aquatic macroinvertebrates and environmental variables remains scarce in Cameroon. To improve our knowledge on the drivers of such distributions, a study was carried out at 11 contrasted sites from three catchments located in West Cameroon. This study aimed at understanding the spatio-temporal variations of 19 taxonomic metrics calculated for the benthic macroinvertebrate assemblages of these sites sampled during 13 months, concurrently with physico-chemical analyses of water quality. Two hundred and twelve taxa were caught. Diptera(rf-S), Shannon-Wiener diversity, 1–GOLD, total richness, Pielou evenness and Heteroptera(rf-S) revealed their high ability to respond to anthropogenic pressures or disturbances. Conductivity, water temperature, dissolved oxygen, nitrates, total hardness and alkalinity were identified as the main physico-chemical drivers of the taxonomic structure of benthic assemblages. These results will allow further exploration of the implementation of a tool for monitoring the ecological quality of West Cameroon rivers
Change of paradigm for breeding disease resistant cultivars robust to varying environments: estimators of the robustness of plant immunity and promising genes for the future
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Digestion anaérobie des épluchures de légumes : Évaluation de l'influence de prétraitements biologiques et de la co-digestion sur le potentiel méthanogène
No full textInternational audienceLa digestion anaérobie est une solution prometteuse pour la gestion des déchets organiques et la production d'énergie. Ce processus naturel de dégradation de la matière organique permet de valoriser les déchets avec la production d'un biogaz, riche en méthane, et d'un digestat, pouvant être utilisé comme amendement organique. Des inhibitions de la digestion anaérobie peuvent cependant être rencontrées, diminuant ainsi le rendement en méthane. À l'heure actuelle, diverses stratégies existent afin d'améliorer les performances de la digestion anaérobie, notamment le prétraitement et la co-digestion. Le présent article a pour premier objectif de présenter la méthodologie pour l'évaluation de l'influence du prétraitement aérobie sur la production de méthane optimale pouvant être obtenue avec la méthanisation des épluchures de légumes (carottes, chou et pommes de terre), autrement dit le potentiel méthanogène de ces déchets prétraités ou non. Le deuxième objectif est l'étude de l'impact de la co-digestion de ces trois types d'épluchures sur le potentiel méthanogène