Portail "HAL-Francophonie Afrique et Océan Indien"
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Dynamiques et enjeux contemporains de la communication. Mélanges offerts au Professeur Bertrand Cabedoche
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Recurrent neural network trained with the extended Kalman filter to forecast the geomagnetic secular variation for IGRF-14
No full textInternational audienceAbstract This study proposes a neural network approach for predicting the geomagnetic secular variation (SV) to improve the accuracy and efficiency of short-term geomagnetic forecasts. The International Geomagnetic Reference Field (IGRF), updated every five years, provides a standardized representation of Earth’s magnetic field, including a 5-year linear prediction of SV. Recent forecasting methods, which are reliant on computationally intensive geodynamo simulations, often struggle to capture sudden changes due to nonlinearity, such as the geomagnetic jerk. We have developed a novel recurrent neural network (RNN) framework trained using the extended Kalman filter (EKF), termed the EKF-RNN, to address these challenges. Unlike conventional backpropagation methods, the EKF dynamically updates the RNN weights by incorporating error covariance from training data, effectively mitigating overfitting while preserving computational efficiency. The EKF-RNN model is validated through hindcast experiments for epochs 2004.87 to 2014.62, utilizing geomagnetic field snapshots derived from satellite and ground magnetic observations. The results exhibit forecast errors below 85 nT for 5-year predictions, outperforming known data assimilation methods such as 4dEnVar. Additionally, the EKF-RNN method provides forecast error covariance matrices, offering enhanced interpretability and robustness compared to earlier neural network models. This research underscores the potential of EKF-RNN for reliable geomagnetic SV predictions, contributing to the accuracy of the 14th-generation IGRF and advancing data-driven approaches in geomagnetic field modeling. Graphical Abstrac
Quartz porosity in amorphous SiO2 of granitic shear bands
No full textInternational audienceAbstract Important porosity is commonly observed in quartz-rich rocks that viscously deformed at depths of the metamorphic continental crust. Although the presence of such pores – often occurring with angular, pyramidal shapes – has major implications for fluid circulation, mass transfer and rock strength, whether or not they are directly produced by deformation remains unclear. Here we provide detailed observations of plastically deformed, pure quartz aggregates decorated by (sub)micrometric pores in granitic shear bands (western granite, Naxos, Greece). Using electron microscopy, we demonstrate that pores (1) decorate both grain boundaries and intra-grain substructures, (2) do not necessarily align with substructures when decorating grain boundaries, and (3) interconnect through layers of amorphous SiO 2 . Transmission electron microscopy further reveals dislocation densities one (or two) order(s) of magnitude below the predictions based on the lattice curvature gradients, suggesting the occurrence of residual stress along pore-decorated, partly amorphized substructures. Challenging long-lasting hypotheses, these features are here proposed to result from stress concentration at grain and subgrain boundaries, followed by fluid exsolution into mechanically amorphized quartz. Although involving syn-kinematic processes that remain to be fully understood, our findings corroborate recent studies that emphasise stress-induced amorphization as a general process of lithospheric rock deformation
Sustainable acoustic metamaterials from recycled plastic bottles: A comprehensive review for circular noise control in the built environment
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Comment réduire les difficultés d’accès aux services d’éducation publique dans un contexte de corruption dans les écoles ?
No full textInternational audienceThis paper aims to examine how to reduce the difficulties of access to public education services in a context of corruption in schools in Africa. The econometric results show that corruption in schools increases the difficulty of accessing public school education services. People who face difficulties in accessing public education services are more inclined to practice corruption in schools. Moreover, difficulties in accessing public school education services decrease with the proximity of the school. People living near a school are less exposed to difficulties in accessing public education services in an environment characterized by corruption in schools. In addition, people who benefit from the government's equity and inclusion policy are less exposed to difficulties in accessing public education services in an environment characterized by corruption in schools.Cet article vise à examiner comment réduire les difficultés d'accès aux services d'éducation publique dans un contexte de corruption dans les écoles en Afrique. Les résultats économétriques montrent que la corruption dans les écoles augmente la difficulté d'accès aux services d'éducation publique. Les personnes qui rencontrent des difficultés pour accéder aux services d'éducation publique sont plus enclines à pratiquer la corruption dans les écoles. De plus, les difficultés d'accès aux services d'éducation publique diminuent avec la proximité de l'école. Les personnes vivant à proximité d'une école sont moins exposées aux difficultés d'accès aux services d'éducation publique dans un environnement caractérisé par la corruption dans les écoles. En outre, les personnes qui bénéficient de la politique d'équité et d'inclusion du gouvernement sont moins exposées aux difficultés d'accès aux services d'éducation publique
Diversity, distribution and conservation of Annonaceae (Magnoliales) in Madagascar
No full textInternational audienceMadagascar is a global biodiversity hotspot with extraordinary levels of plant endemism, but its unique ecosystems are increasingly threatened by deforestation and other human-induced activities. Annonaceae is a major pantropical plant family with approximately 2,500 species.Despite its ecological importance, the taxonomic diversity and distribution of the family in Madagascar have remained poorly studied, limiting conservation assessments and planning.Here, we provide a comprehensive analysis of diversity distribution patterns and undertake preliminary conservation assessments of Malagasy Annonaceae. A taxonomically verified database of 2,306 specimens representing 102 native species in nine genera was used to generate species richness patterns. Preliminary conservation status assessments were conducted following IUCN Red List Criteria A and B, and species exposure to human pressure was evaluated using deforestation layers and the anthrome framework. Annonaceae species richness is concentrated within the Eastern and Sambirano domains, corresponding to warm, humid climates. These regions also emerged as major centers of endemism and conservation concern. Based on Criterion B, 53.9% of species are preliminarily classified as threatened, while 25.5% are considered potentially threatened under Criterion A. Based on Madagascar anthromes, Annonaceae species are not restricted to intact habitats but persist across a wide range of human-modified and densely populated landscapes. Our findings highlight the need to integrate both natural and anthropogenic systems into conservation planning, especially in biodiversity hotspots undergoing rapid land-use change. These results provide a baseline for future biogeographic and evolutionary studies and support targeted conservation actions to reduce extinction risk in Madagascar's most biodiverse regions
Molecular Characterisation of Endangered White‐Clawed Crayfish Populations in Southern Switzerland
No full textInternational audienceThis study investigates the phylogeography of the endangered European White-Clawed Crayfish (WCC) Austropotamobius pallipes species complex in the main tributaries of the Po River basin in southern Switzerland and northern Italy, a diversity hotspot for this species. Because of various factors, including invasive species and pathogens, this keystone species experienced a significant decline. Conservation efforts should be taken to protect the species, but there is a lack of basic knowledge about the diversity and distribution of remaining WCC populations. We used mitochondrial (COI, 12S, 16S) and nuclear (28S) markers, generating, to our knowledge, the most comprehensive multiple-marker dataset for this species, an essential step toward resolving the taxonomic puzzle surrounding the WCC. All samples collected in Canton Ticino belonged to the subspecies A. f. fulcisianus, with 14 unique COI haplotypes, none of which were previously documented. Phylogenetic analyses revealed close genetic ties to Italian populations, supporting theories of northward expansion from the Italian peninsula. High haplotype diversity was observed in the southernmost area of Canton Ticino, where waters from three major tributaries of the Po River (Adda, Olona-Seveso-Lambro system and Ticino) flow near each other. In contrast, northern WCC populations showed reduced diversity, likely due to bottlenecks, habitat fragmentation, invasive species and pathogen pressures. Our findings highlight the need for cross-border management, habitat protection and genetic monitoring to safeguard this keystone species amid ongoing environmental threats. Hence, taking advantage of the local topography and insights gained from this study, we propose establishing ark sites in isolated headwater areas
Inventories of the Main Insect Pests of Stored Corn and Repellent and Insecticidal Effects of Sapwood and Heartwood Extracts from Wood Côte d'Ivoire against Sitophilus zeamais Motschulsky (Coleoptera, Curculionidae)
No full textInternational audienceBackground: Cereals play a central and important role globally in food security, nutrition and energy. Sitophilus zeamais Motschulsky is without doubt the most devastating insect pest of agricultural stocks and is resistant to synthetic chemical pesticides. The search for botanical products with low toxicity for the environment and for living beings has intensified considerably. Forestry operations produce large quantities of waste that remain under-exploited, posing a real environmental problem. Studies have shown that tropical tree species synthesis biomolecules in their heartwood that are responsible for their natural resistance and could be highly effective against insect pests.Objectives: The aim of this study was firstly to carry out an inventory of insect pests on stored maize and secondly to assess the repellent and insecticidal activity of hydroalcoholic extracts of Nauclea diderrichii, Mansonia altissima and Milicia excelsa against Sitophilus zeamais.Method: Stored maize samples were collected, insect pests were identified, and their relative abundance was calculated. Hydroalcoholic extracts of sapwood and heartwood were then tested, in comparison with a synthetic chemical insecticide, Protect DP (1.5% pyrimiphos-methyl and 0.1% deltamethrin), on S. zeamais to evaluate their insecticidal activity (mortality, LD₅₀, TL₅₀) and repellency at different concentrations, using a randomised experimental design with three replicates.Results: The inventory showed that S. zeamais with a Relative Abundance (Ra) of 51.06% (Ra ≥ 10%) and T. castanenum with an Ra of 43.61% were abundant species. Hydroalcoholic extracts of sapwood from N. diderrichii, M. altissima and M. excelsa resulted in mortality rates of 80-96.67%, 76.67-88.33% and 66.67-81.67% respectively. The mortality of heartwood extracts from these same woods varied respectively from 58.33 to 95%, from 66.67 to 95% and from 36.67 to 78.33%. The LD50 of sapwood extracts was between 0.0093 and 0.0289 and the TL50 ranged from 3.5 to 6.2 days. The LD50 of heartwood extracts was between 0.050 and 0.1435 g/mL and the TL50 varied from 1.8 to 0.5 days. The repellency rate ranged from 26.67 to 96.67% after 1 hour and from 50 to 93.37% after 2 hours' exposure to the extracts tested.Conclusions. The toxicity of the extracts is due to the presence of the main secondary compounds present in hydroalcoholic wood extracts. These results demonstrate the potential of wood extracts for controlling insect pests of stored foodstuffs
From alteration to avalanche: A 3D framework for exploring hydrothermal weakening of lava domes
No full textInternational audienceVolcanic domes are inherently unstable structures that form when lava is too viscous to flow away from the vent. Dome collapse poses a hazard via volcanic landslides and debris avalanches that can threaten nearby communities. Dome collapse can be promoted by hydrothermal alteration, which can weaken volcanic rock and is commonly concentrated in regions with high fluid flow, such as fractures and areas of high permeability within the dome. Here, we focus on understanding how alteration affects dome stability, collapse volumes and runout distances, using the case study of La Soufrière de Guadeloupe, in the Eastern Caribbean. We present new 3D models that combine geophysical and mechanical data to investigate different post-emplacement dome stability scenarios that incorporate hydrothermal alteration. Our results demonstrate that increased alteration-induced weakening (i.e., to 50% or 10% of the original rock strength) leads to greater displacements and causes dome destabilisation. Additionally, we show displacement and finite shear strain as a result of varying the spatial extent (the thickness and location) of the alteration zones. We also show that incorporating mechanical heterogeneity is crucial for accurate hazard modelling. We introduce a novel method using the La Soufrière de Guadeloupe dome to offer a comprehensive understanding of the alteration process from initiation to deposit. Our results indicate that hydrothermal alteration significantly increases collapse volumes and thus runout distances, which are critical for understanding the potential impact of dome collapse and a critical motivation for our 3D modelling approach. By capturing the full process from internal weakening to hazard potential, this method enhances our ability to anticipate future dome collapse events, and thus, mitigate their effects
