Portail "HAL-Francophonie Afrique et Océan Indien"
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Maqamat al-Ishq / Stations of Passion
No full textInternational audiencePrésentation des oeuvres picturales et poétiques de Himat et d'Adonis pour l'exposition de Himat Mohamed Ali à la Foire Internationale de l'art du Caire au Grand Musée Egyptien
A window on the amalgamation of Western Gondwana: Geological history of the Ouaddaï massif (E. Chad)
No full textInternational audienceThe Saharan metacraton was assembled during pre-Neoproterozoic to Neoproterozoic times and was strongly remobilised during the Pan African orogeny. The Ouaddaï massif in eastern Chad represents the core of the Saharan metacraton, yet its geological history remains poorly documented. In this study, we combine of field observations, petrological analysis of metamorphic rocks, and geochemical and geochronological constraints to reconstruct the tectono-metamorphic evolution of the Ouaddaï massif. The study area is dominated by collision-related plutonic rocks and migmatitic gneisses, within which inliers of older basement occur. Geochemical data indicate a transition from active-margin to collisional magmatism, with a compositional evolution from diorite to granite. This suite is cross-cut by syenogranites and alkaline granites with shoshonitic affinities, interpreted as post-collisional granitoids derived from tonalitic rocks to sedimentary protoliths. Geochronological data (U-Pb on zircon and monazite) point to a ca. 1000 Ma age for orthogneisses inliers. Granitoids of the Ouaddaï massif record emplacement ages from 620 to 590 Ma, coeval with high-temperature metamorphism characterized by peak pressure–temperature conditions of 1.2 GPa and 850 °C (mafic granulite) and around 0.8 GPa and 700 °C (sillimanite-garnet bearing migmatites). Integrating our new results with regional data, we discuss the existence and geodynamic evolution of the Saharan Metacraton. Our findings emphasize the significance of the Saharan Metacraton as a key region for understanding the extensive reworking of cratonic lithosphere during both a Tonian magmatic phase prior and the assembly of Gondwan
Improving penalty shoot-out performance in skilled youth soccer players: An imagery modality-based approach
No full textInternational audienceBackground: Since their introduction in professional football, penalty shoot-outs represent key moments in matches. Motor imagery (MI) can improve soccer performance, but different MI modalities can be used to mentally simulate motor actions. This study aimed to evaluate whether the MI modality used by the players would influence their penalty shoot-out performance. Methods: Twenty youth skilled football players from the Elite Center of the French Regions of America (CERFA) voluntarily participated in this experiment (M age = 16.4 years). After an assessment of their MI ability, the participants completed 4 counterbalanced experimental sessions spread over 4 weeks, each including the completion of 5 penalty shoot-outs. The sessions consisted of a control condition (count-down and actual execution) and 3 MI conditions during which the players had to mentally imagine themselves performing a penalty shoot-out according to one of the MI modalities: Internal Visual Imagery (IVI), External Visual Imagery (EVI), or Kinesthetic Imagery (KI), before kicking. Number of goals scored, shooting accuracy and ball speed were measured and served as dependent variables. Results: The soccer players benefited from MI. Indeed, in both the IVI and KI conditions, their performances were significantly higher than in the no-MI (i.e., control) condition with respect to the total number of goals scored and shooting accuracy variables
Canavalia ensiformis intercrop to reduce weeds and stalk borer damage in sugarcane
No full textThe aim of this study was to assess the efficiency of two intercrop species, Canavalia ensiformis and Desmodium intortum , to reduce weed growth, herbicide use and damage by the stalk borer Chilo sacchariphagus in sugarcane cropping system in Reunion. We compared six inter-row management techniques: four treatments combined the two intercrops Canavalia ensiformis or Desmodium intortum sown either early (between 0 and 2.1 months after sugarcane emergence) or late (between 1.3 and 3.7 months after sugarcane emergence), a treatment where no weeding was carried out on the inter-row, and a treatment with chemical weeding of the inter-row (CcWp). In all treatments, the sugarcane row was weeded chemically and manually. The six treatments were compared in a multilocal randomized block design with three localities, during one or two crop cycles depending on the locality. Desmodium intortum produced poor ground coverage in half of the trial x crop cycles and was therefore found unsuitable for use as an intercrop of sugarcane in our conditions. On the opposite, Canavalia ensiformis quickly covered the inter-rows, regardless of the sowing date. The Canavalia ensiformis intercrops allowed a reduction of herbicide consumption by 63% when sown early and by 28% when sown late, compared to the CcWp control treatment. Both Canavalia ensiformis intercrops caused a reduction of weed coverage on the inter-row similar or better than the chemical control. However, the early sown Canavalia ensiformis intercrop caused a 18.6 t.ha-1 yield loss compared the chemical control. No yield loss was detected with the late sown intercrop. A significant reduction of stalk damage by a 0.8-fold factor was observed in the early sown Canavalia ensiformis treatment
ForestScan: a unique multiscale dataset of tropical forest structure across 3 continents including terrestrial, UAV and airborne LiDAR and in-situ forest census data
No full textInternational audienceThe ForestScan project was conceived to evaluate new technologies for characterising forest structure and biomass at Forest Biomass Reference Measurement Sites (FBRMS). It is closely aligned with other international initiatives, particularly the Committee on Earth Observation Satellites (CEOS) Working Group on Calibration & Validation (WGCV) AGB cal/val protocols, and is part of GEO-TREES, an international consortium dedicated to establishing a global network of Forest Biomass Reference Measurement Sites (FBRMS) to support EO and encourage investment in relevant field-based observations and science. ForestScan is the first demonstration of what can be achieved more broadly under GEO-TREES, which would significantly expand and enhance the use of EO-derived AGB estimates.We present data from the ForestScan project, a unique multiscale dataset of tropical forest 3D structural measurements, including terrestrial LiDAR scanning (TLS), unmanned aerial vehicle LiDAR scanning (UAV-LS), airborne LiDAR scanning (ALS), and in-situ tree census and ancillary data. These data are critical for the calibration and validation of earth observation (EO) estimates of forest biomass, as well as providing broader insights into tropical forest structure. Data are presented for three FBRMS: FBRMS-01: Paracou, French Guiana; FBRMS-02: Lopé, Gabon; and FBRMS-03: Kabili-Sepilok, Malaysia. Field data for each site include new 3D LiDAR measurements combined with plot tree census and ancillary data, at a multi-hectare scale. Not all data types were collected at all sites, reflecting the practical challenges of field data collection. We also provide detailed data collection protocols and recommendations for TLS, UAV-LS, and plot census measurements for each site, along with requirements for ancillary data to enable integration with ALS data (where possible) and upscaling to EO estimates. We outline the requirements and challenges for field data collection for each data type and discuss the practical considerations for establishing new FBRMS or upgrading existing sites to FBRMS standard, including insights into the associated costs and benefits.</p
Rapport sur les services climatiques réussis dans le monde et leurs critères de succès: Livrable commun au Projet ciblé TRACCS-PC1-DIALOG (D5.3) et au Projet Ciblé TRACCS-PC3-DEMOCLIMA (D1)
No full textThe socio-economic challenges associated with the effects of global warming are such that a growing demand for tailored climate information—intended to support the implementation of mitigation and/or adaptation strategies—is clearly expressed by economic sectors (e.g., agriculture, energy, tourism, land or maritime infrastructure, etc.) as well as by territories and regions that are fully aware of their vulnerabilities. In response to these demands, numerous national, European, and international research projects have enabled the funding of “climate services”. Several national and European operational actors are developing and providing “climate services” through platforms that are often freely accessible. In addition, consultancy firms are emerging on the market, whose commercial activities focus on developing customized “climate services” tailored to client needs.The current offering of “climate services” is therefore multifaceted, both in terms of the information provided (basic climate data, indicators, decision-support tools) and in terms of development approaches. Faced with this diversity, the key challenges are to document and understand the current landscape of climate services, to highlight existing needs, and to develop means to characterize the success of climate services, in order to assess what already exists and guide the development of new projects.Conducted jointly by the targeted projects DIALOG (PC1) and DEMOCLIMA (PC3) of the PEPR TRACCS program, this study pursues four objectives:i) To document the current landscape of climate services (Section 2) in France and worldwide (as identified by the TRACCS community), by presenting them according to their uses and target audiences;ii) To identify unmet needs with regard to climate services (Section 4);iii) To identify a set of success criteria for climate services in order to evaluate them (Section 5);iv) To propose best practices for achieving these success criteria (Section 6); these elements will guide the choices of future demonstrators to be designed and developed within DEMOCLIMA.This work is based on a combination of collaborative desk research and the collection of stakeholder input from actors involved in “climate services.” The methods used (surveys and semi-structured interviews) are described in Section 3.Les enjeux socio-économiques liés aux effets du réchauffement climatique sont tels qu’une demande croissante d’informations climatiques adaptées pour la mise en place de stratégies d’atténuation et/ou d’adaptation est clairement exprimée par les secteurs économiques (e.g. agriculture, énergie, tourisme, infrastructures terrestres ou maritimes, etc…) et par les territoires/régions qui mesurent pleinement leurs vulnérabilités. En réponse à ces demandes, de nombreux projets de recherche nationaux, européens ou internationaux ont permis le financement de « services climatiques ». Plusieurs acteurs opérationnels nationaux et européens développent et mettent à disposition des « services climatiques » via des plateformes souvent libres d’accès et enfin, apparaissent sur le marché des bureaux d’études dont l’activité commerciale vise le développement de « services climatiques » à la carte et adaptés aux demandes des clients.L’offre pour les « services climatiques » est donc aujourd’hui multiforme par l’information fournie (données climatiques « simples », indicateurs, outils d’aide à la décision) et par son mode de développement. Face à cette diversité, les enjeux sont de documenter et comprendre le paysage des services climatiques actuels, de faire ressortir les besoins, et de se munir de moyens pour caractériser la réussite des services climatiques, pour évaluer l'existant et guider le développement de nouveaux projets. Menée conjointement par les projets ciblés DIALOG (PC1) et DEMOCLIMA (PC3) du PEPR TRACCS, cette étude vise quatre objectifs :i)Documenter le paysage actuel des services climatiques (section 2) en France et dans le monde (identifiés par la communauté TRACCS) en les présentant par usages et cibles ;ii)Identifier des besoins non satisfaits vis-à-vis des services climatiques (section 4) ;iii)Identifier un ensemble de critères de réussite d'un service climatique pour les évaluer (section 5) ;iv)Proposer des bonnes pratiques pour atteindre ces critères de réussite (section 6); ces éléments guideront les choix des futurs démonstrateurs qui seront conçus et développés au sein de DEMOCLIMA.Notre travail repose sur une combinaison de travail collaboratif de bureau, et de recueil de dires d'acteurs des "services climatiques". Les méthodes utilisées (enquêtes et entretiens semi-directifs) sont décrites dans la section 3
Investigating vertical gravity wave spectra to calibrate a gravity wave perturbation model: comparison with ERA5 reanalysis products and application to infrasound propagation simulations
No full textInternational audienceInfrasound technology is used to monitor the atmosphere and to verify compliance with the Comprehensive Nuclear Test-Ban-Treaty. Acoustic signals recorded by the International Monitoring System allow to characterize sources of interest.Fine-scale atmospheric perturbations of the order of a few kilometers to a few hundred meters in vertical wavelength are necessary to explain the duration and amplitude of acoustic signals. Such internal gravity wave (GW) perturbations must be added to atmospheric specifications for propagation simulations. Indeed, operational meteorological products underestimate or miss that part of the GW spectrum. The GW universal spectrum approach provides a convenient framework to quickly derive vertical perturbation profiles of GW using inverse Fourier transform along the atmospheric column.Using radiosonde and lidar measurements from the Observatoire De Haute-Provence in South of France (43° 55′ 51″ N, 5° 42′ 48″ E) and from La Réunion Island (21° 04′ 47″ S, 55° 22′ 59″ E) across many years, we characterize monthly GW vertical wavenumber spectra in different altitude layers. We fit those spectra using the modified Desaubies analytical model in order to retrieve relevant parameters (namely the maximum amplitude of the spectrum and the characteristic wavenumber m*). We also compare the observed spectra and their related parameters and quantities, notably kinetic and potential energies, to those derived from ERA5 products.Using the calibrated parameters of the GW spectra, we derive the associated ensemble perturbation profiles in a stochastic approach using bootstrap techniques. The goal is to be representative of the observed vertical distribution of the spectra. The ensembles of perturbation profiles are then used as input to infrasound propagation simulations. We discuss how waveform simulations used in operational monitoring can benefit from these better-constrained atmospheric fine-scale uncertainties
Geodynamo simulations spanning millennia in the physical conditions of Earth's core
No full textInternational audienceA geodynamo simulation is presented where the Earth's core density, rotation rate, convective power and electrical conductivity are matched, while viscous losses are maintained minor in the force balance and power budget. Improving over earlier preliminary calculations, the simulation is integrated over near 1700 years in physical time, and realistically renders the time scale range between interannual hydromagnetic waves and secular convective motions. The solution has been obtained by gradually approaching these conditions along a path in model parameter space. A quasi-geostrophic, magneto-Archimedes-Coriolis (QG-MAC) force balance is confirmed, with the characteristic length scale of the system remaining near the planetary scale. Without the need for extrapolation, the morphology, variations and dynamics of the velocity, convective density anomaly and magnetic fields are in excellent quantitative agreement with geomagnetic and geodetic observations supplied over the past centuries by navigation, observatories and satellites. In particular, the simulation reveals the contribution of interdecadal magneto-Coriolis waves to geomagnetic variations in the vicinity of 60-yr periods. This direct validation of the convective geodynamo paradigm additionally offers a quantitative and first principle-based physical link between the observable signals and deep Earth geodynamic parameters. The model confirms that a convective power (or Ohmic dissipation) level near 3 TW is needed to account for the observed geomagnetic variations, and that the top of the core should be convectively neutral or unstable. Explaining the core-originated interannual to decadal variations of the length of day through electromagnetic core-mantle coupling requires a lower mantle conductance on the order of 10^9 S. It may also become possible to constrain the outer core electrical conductivity from the observed patterns of interannual magneto-Coriolis waves. Finally, the simulation can be considered a reliable source of prior information for solving geomagnetic inverse and prediction problems
Technological Bibliography Study on UAV and IoT Wireless Communication Specification Through 5G Cellular Networks
No full textInternational audienceThe growth of Information and Communication Technologies (ICTs) involvement in our daily life elicits currently a reliable network connection at anytime and anywhere. Robust cellular network is required for the approval of demand users' demand. In the late of last century, noticeable studies were invested in the ICT infrastructure development to meet the public and industrial needs. The evolution of mobile telecommunication has transitioned through multiple phases, from early voice-centric First-Generation (1G) systems to the data-heavy Fourth-Generation (4G) era. Currently, Fifth-Generation (5G) technology has emerged as a superior standard, prioritizing enhanced security protocols and high-speed data transmission according to nomad users. The global rollout of 5G frameworks is inherently linked to the integration of Internet-of-Things (IoT) ecosystems. Then, the design of relevant Base Stations (BSs) for communication during the urban social events constitutes a challenging problem of IoT infrastructures. Scholars have identified Unmanned Aerial Vehicles (UAVs) as a versatile solution for supplementing BS infrastructure, particularly for broadening the reach and throughput of 5G deployments. In scenarios involving public safety, UAV-integrated networks function as airborne base stations, facilitating advanced technologies such as millimeter-wave signaling, IoT connectivity, and 3D Multiple-Input-Multiple-Output (MIMO) arrays. The review on UAV-based wireless communication system modelling by taking into account the different classes and specification with respect to the regulation of technology is synthesized. The synthesis review of UAV cellular network planning for the urban cities is reported by stating about the experiment and performance evaluation. The research works highlight the technical challenge on the UAV-BS deployed for urban social events. It can be emphasized that the study of the UAV wireless communication necessitates the modeling consideration of channel from air transmission to ground BS reception, optimal deployment and the optimization of trajectory.</div