Portail "HAL-Francophonie Afrique et Océan Indien"
Not a member yet
43052 research outputs found
Sort by
Culturable macroplastic-associated potential human pathogens in coral reef lagoons, Madagascar
No full textInternational audiencePotentially human pathogenic bacteria (PHPBs) have been detected in plastic-associated marine microbiomes, primarily through DNA-based methods. However, data on their culturability and concentrations on plastics remain limited, yet are essential to assess actual health risks. To address this gap, 70 floating macroplastic and 20 seawater samples were collected from two human-impacted reef lagoons in southwestern Madagascar (AtsimoAndrefana region). PHPBs were cultured from their microbiomes using selective media and quantified. Macroplastics were predominantly polypropylene (34 %) and polyamide (31 %). In increasing order of concentration, four culturable PHPBs, Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, and Vibrio Harveyi clade species, were identified on both macroplastics and in seawater, across all sites and polymer types. Notably, 52 % of macroplastic samples harbored two PHPB species simultaneously, while only 7 % were PHPB-free. Concentrations of all PHPBs were consistently and significantly higher on macroplastics than in seawater, regardless of the measurement unit or polymer type, with the Vibrio Harveyi clade being the most abundant. No significant correlations were observed among PHPB species concentrations, suggesting limited interaction and independent colonization. These findings indicate that floating macroplastics may serve as reservoirs and fomites for viable PHPBs. However, their potential impacts on ecosystems and human health should be interpreted cautiously. We emphasize the need to contextualize PHPB concentration data by considering factors such as exposure pathways, environmental persistence, and bacterial virulence, rather than relying solely on concentration-based comparisons, which may lead to misinterpretatio
Origin and evolution of giant comet marks along the North Atlantic Deep-Water flow on the Demerara plateau
No full textInternational audienceThe Demerara Plateau, located in the equatorial Atlantic, is particularly well-suited for recording the activity of the Deep Western Boundary Current (DWBC), which transports North Atlantic Deep Water (NADW) southward into the Atlantic basin. This current, active between 1500 and 3500 m depth, constitutes the deep part of the global thermohaline circulation and plays a crucial role in climate regulation. The Demerara Plateau is remarkable for the abundance and wide distribution of comet mark-type sedimentary structures, which can reach several kilometres in length. These hydrodynamic bedforms, interpreted as erosional features associated with strong bottom currents, are currently used as proxies for deep currents velocities, with minimum formation thresholds estimated between 0.60 and 0.75 m/s according to the literature (Rebesco et al., 2014; Werner et al., 1980). The DIADEM (Dive At DEMerara) oceanographic cruise (Basile and Loncke, 2023) enabled detailed investigation of one such structure using a combination of complementary tools with the aim of better understanding their functioning and evolution with in-situ observation, physical records, and sampling. Those new data were also combined with formerly acquired high-resolution seismic data, allowing a new vision of these bedforms their formation, and their evolution over time. The main findings are the following: (1) comet-marks localize on carbonate mass transported blocs outcropping on the seafloor; (2) Clearly show a polyphase evolution of the bedforms of comet mark presenting alternations of erosion and sedimentation phases. The bedforms therefore record long-term variations in bottom current activity with an alternation of intense hydrodynamic events (erosion) and quieter hydrodynamic periods (deposition) through time, reflecting a complex hydrodynamic history; (3) At present, comet-marks recorded a significant decrease in current velocity within the erosional zones located inside the comet tails associated with fined-grained sediments infill in this area, highlighting the need for cautious interpretation of such features as direct indicators of present-day current intensity; (4) Finally, a result that was not necessarily anticipated but documented by exploring those bedforms with the Nautile submersible, comet-marks host quite important benthic and epibenthic biodiversity with a wide variety of associated species
Shapley value to rank vulnerabilities on attack graphs: Applications to cyberdeception
No full textInternational audienc
Magnetite production in mesh texture during serpentinization, a marker of H diffusion
No full textInternational audienceThe detailed mineralogical study of serpentinized peridotites collected at 13 localities at mid-ocean ridges, in ophiolites and ultramafic bodies shows the formation of two alteration zones around olivine grains. At the olivine contact, a fine-grained mixture of serpentine, Fe-brucite ( molar ratio comprised between 0.66 and 0.82) and awaruite occurs (Reaction Zone 1). X-ray mapping indicates limited mass transfer during Reaction Zone 1 formation, suggesting isochemical serpentinization except for the addition of water. The measured distribution of Fe and Mg between serpentine and brucite in Reaction Zone 1 is well reproduced with thermodynamic modelling incorporating the latest data for the Fe(OH)2 endmember. Thermodynamic modelling also reveals that, at low water to rock ratio, awaruite formation limits H2 production to values more than one order of magnitude lower than previous estimates. The predicted H2,aq concentrations are comprised between 10−3 and 10−2 mol/kg, that is in the same range than the maximum values measured in fluids expelled at ultramafic-hosted hydrothermal sites. At a water to rock ratio of 1, the updated thermodynamic model only predicts magnetite formation after olivine at temperatures above 300 °C, that is above the temperature estimates for serpentinization based on published oxygen isotope data. Nevertheless, a second assemblage composed of Ni-bearing magnetite, serpentine and Mg-brucite ( molar ratio comprised between 0.83 and 0.98) can be found at the mesh rim (Reaction Zone 2). Reaction Zone 2 can display a symplectite microtexture. Transmission electron microscopy reveals the presence of porosity and Fe-brucite relics in the symplectite, suggesting Reaction Zone 2 formation after Reaction Zone 1 by dissolution-precipitation. Significant mass transfer is observed in Reaction Zone 2 at the mesh rim, probably associated with the solid volume decrease of 7 % during Reaction Zone 1 reaction to form Reaction Zone 2. The mineralogy and the composition of Reaction Zone 2 are reproduced with thermodynamic modelling of olivine serpentinization not by increasing the water to rock ratio but rather by removing H2 from the system. This indicates that H2 diffusion is the main driver for magnetite formation during serpentinization. The H2,aq concentrations at the equilibrium with Reaction Zone 2 fall in the 10−7-10−3 mol/kg range. The relative proportion of Reaction Zone 1 and Reaction Zone 2 in serpentinized peridotites has first-order impacts on H2 production
Unlocking new quality productive forces from biowaste valorization through the 5B initiative
No full textInternational audienceThe escalating anthropogenic biomass production leads to an unprecedented rise in biowaste generation, exceeding the decomposition capacity of natural microbial communities. This disturbance of global nutrient cycling substantially threatens the habitability and thriving of Earth's life system. To address this challenge, the newly launched 5B Initiative (Biowaste, Bioconversion, Bioproduct, Biosafety, and Bioeconomy) provides a global collaborative framework that drives a paradigm shift from waste to wealth by four synergistic objectives: characterizing biowaste generation, advancing bioconversion technology, enhancing biosafety, and facilitating the bioeconomy. Integrating above objectives, the 5B initiative plan to propose a BioCyclos model framework, that traces and optimizes biomass bioconversion processes in bioresource-biowaste-bioproduct chain to promote bioeconomy and ensure biosafety. This integrated platform positions biowaste-to-bioproduct conversion alongside nature-based solutions and thereby promotes the transition toward a circular, decarbonized, and sustainable bioeconomy while restoring and maintaining balance in Earth's nutrient cycles
Optimization of the representation of results in interval arithmetic
No full textInterval arithmetic enables rigorous bounding of rounding errors, but standard representations require storing two floating-point numbers per interval, which increases memory costs and data transfer in large-scale computations. We propose a compressed interval representation inspired by the FP-ANR format, encoding both the center and the radius within a single floating-point word while preserving the strict inclusion of the original interval. We present an efficient algorithm to convert center-radius intervals into this format with minimal over-approximation. Its applications to the interval matrix product and the interval Newton method demonstrate the practical benefits of this representation. Additionally, the proposed approach enables the integration of mixed-precision computations, paving the way for scalable and memory-efficient interval arithmetic in scientific computing
Bridging gaps in agro-ecosystem integration: a multi-level modelling study in semi-arid Burkina Faso
No full textInternational audienceHighlights: • Agent-based model tracked nutrient and resource flows in mixed farming systems. • Sensitivity analysis found key biophysical (e.g. nitrogen uptake) and social drivers. • Model captured emergent, nonlinear effects across 700 farms in Burkina Faso. • Scenarios revealed trade-offs between yields, income equity, and sustainability. • Results inform tailored management strategies (subsidies, legumes) in agroecosystems.Abstract: Mixed crop–livestock systems are central to livelihoods in semi-arid West Africa, yet they face persistent challenges related to low input efficiency, nutrient depletion, and food insecurity. These systems are characterized by complex social and biophysical interactions that produce nonlinear outcomes, complicating sustainable management.To unravel this complexity, we developed TENGA—an agent-based model (ABM) simulating the dynamics of 700 heterogeneous farms in semi-arid Burkina Faso. The model captured spatial and temporal interactions among crop and livestock management, nutrient flows, and farmers’ interactions. A Morris sensitivity analysis was used to identify key parameters influencing system behavior, and scenario analysis explored interventions to improve crop-livestock integration including legume intensification (increasing the functional contribution of nitrogen-fixing legumes), fertilizer subsidies, and intensified direct exchange of manure and crop residues.Nitrogen uptake efficiency, livestock feed parameters, manure management, and social interactions emerged as critical drivers of system outcomes. Sensitivity analysis revealed nonlinear feedbacks, particularly in the propagation of farm-level effects (e.g. income) to village-level dynamics (e.g. equity). Antagonistic responses among farm types reduced overall system gains, highlighting the interconnectedness of component interactions. Scenario results showed that while nitrogen-fixing legumes improved yields and reduced nutrient mining, they also reduced herd size and increased transhumance pressure. Fertilizer subsidies favored wealthier farms but did not address food insecurity among subsistence households. Intensified residue–manure exchanges enhanced nutrient recycling but had minimal impact at system level.This study demonstrates the utility of ABMs for exploring the multi-dimensional and multi-level dynamics of mixed farming systems of semi-arid West Africa
Fallow land simulations to fight against soil degradation: Engaging stakeholders with model exploration
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/616636/) * Autres projets (id;sigle;titre): AF 1802-001;DSCATT;(FRA) Dynamics of Soil Carbon Sequestration in Tropical and Temperate Agricultural systems//International audienceThis methodological paper forms part of a modelling approach conducted in the Senegalese groundnut basin. It addresses two key aspects: (1) the process of co-constructing the model with local stakeholders; and (2) the use of calibration to account for non-measurable elements, which stakeholders needed to describe and evaluate their system effectively. Thematically, the study examines the relationship between social solidarity and agro-pastoral systems in Diohine, a Senegalese village where communal fallow lands are a vital indicator of socio-ecological resilience. Using the co-constructed, agent-based "Me re Diam" model, we examine the dynamics of soil fertility, population growth and agricultural yields over a 25-year period, integrating local knowledge and ecological data. Our findings emphasise the pivotal role of social solidarity mechanisms, such as parcel lending and food sharing, in stabilising agro-pastoral systems amidst resource scarcity. Calibrating the model demonstrates its ability to reproduce historical dynamics and test alternative practices. Without these mechanisms, the system collapses, revealing their indispensable nature for long-term sustainability. This work emphasises the importance of collaborative modelling in bridging the gap between empirical data and local practices, providing actionable insights for addressing soil degradation and demographic pressures
Les défis olympiques de la luge : relations institutionnelles, représentativité internationale et standardisation des infrastructures (1964-2026)
No full textInternational audienceCe chapitre explore l’histoire olympique de la luge de course, entre 1964 et 2026. Discipline sportive au passé foisonnant quoique méconnu, la luge accède au milieu du XXe siècle aux honneurs olympiques pour ne plus quitter le programme de l’évènement quadriennal d’hiver. Restent des défis de taille pour asseoir sa place dans le microcosme olympique, parmi lesquels les relations institutionnelles entre la Fédération internationale de luge (FIL) et le CIO ; la question de la représentativité internationale de ce sport ; ou encore les évolutions techniques relatives à la confection des pistes dédiées (et bientôt « combinées » avec les pratiques du bobsleigh et du skeleton). En se reposant sur les archives du Centre d’études olympiques de Lausanne, l’analyse montre le chemin parcouru par le sport de luge jusqu’au cœur des Jeux d’hiver et du Mouvement olympique