Portail "HAL-Francophonie Afrique et Océan Indien"
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Confiance dans les chefs religieux et réglementation du marché des services religieux en Afrique
No full textInternational audienceThis paper aims to examine the effect of trust in religious leaders on preferences for religious services market regulation in Africa. The analysis is based on a sample of 46,585 people living in Africa, drawn from data collected by Afrobarometer (2023). The econometric results show that trust in religious leaders increases the preference for religious services market regulation in Africa. This result can be explained by the corruption of religious leaders. On the other hand, in a context characterized by government corruption, the trust in religious leaders reduces the preference for the religious services market regulation. Moreover, some differences emerge when the analysis is conducted within each religious group.Cet article vise à examiner l'effet de la confiance envers les chefs religieux sur les préférences en matière de réglementation du marché des services religieux en Afrique. L'analyse repose sur un échantillon de 46 585 personnes vivant en Afrique, tiré des données collectées par Afrobarometer (2023). Les résultats économétriques montrent que la confiance envers les chefs religieux augmente la préférence pour la réglementation du marché des services religieux en Afrique. Ce résultat s'explique par la corruption des chefs religieux. En revanche, dans un contexte caractérisé par la corruption du gouvernement, la confiance envers les chefs religieux réduit la préférence pour la réglementation du marché des services religieux. De plus, certaines différences apparaissent lorsque l'analyse est menée au sein de chaque groupe religieux
A multi-methods analysis to assess the challenges of pineapple cultivation in Moorea and the capability of taro to mitigate impacts on human and environmental health
No full textAbstract Resulting from a collaboration between the CRIOBE (Centre de Recherches Insulaires et Observatoire de l’Environnement), and ChimEco, this article examines the cultural and ecological importance of taro cultivation in the context of a socio-ecological transition on Moorea since the 1950s. The methods used are based on individual, non-directive, participatory surveys in Moorea and the urban area of Faaa (Tahiti) among government agencies, the private and public sectors, the general public, and civil society. These surveys and analyses highlight the controversial nature and sources of tension related to the socio-ecological transition on Moorea. They highlight the lack of negotiation and inclusiveness in the management of the "land-sea continuum" and the contemporary role attributed to taro as a possible solution to the challenges of the transition. Finally, this article discusses the characteristics of the "land-sea continuum" from a Polynesian perspective, with a view to management by the socio-ecosystem, from the mountain to the reef
Chilling injury to algal symbionts induces host starvation and metabolic reorganization in a temperate cnidarian
No full text● Global temperature anomalies increasingly disrupt the cnidarian-algal symbiosis through a phenomenon coined bleaching. In contrast to heat stress, the mechanisms underlying symbiotic breakdown under cold stress remain largely unknown. ● Combining physiological and metabolomic measurements, we investigated the response of the photosymbiotic sea anemone holobiont Aiptasia couchii to an experiment mimicking a cold spell in the Mediterranean Sea. ● Within four weeks, we observed the onset of symbiotic breakdown reflected in reduced algal endosymbiont density and chlorophyll a content. While photosynthetic efficiency remained largely unaffected, no gross photosynthesis was detectable in cold-stressed anemones and decreases in glycosyldiacylglycerols and fatty acyl glycosides indicated chloroplast lipid remobilization. This breakdown of symbiotic carbon cycling was reflected in increased dipeptide and ceramide levels suggesting anemones catabolized protein reserves and induced pre-apoptotic pathways. ● Taken together, these responses suggest a decoupling of light and dark reactions of photosynthesis in cold-stressed endosymbionts, resembling chilling injury in higher plants and free-living microalgae. This chilling-induced collapse of symbiotic nutrient cycling eventually leads to host starvation in cold-stressed Cnidaria. Hence, while cold and heat stress may invoke contrasting physiological effects on endosymbionts, our results suggest that both stressors destabilize the symbiosis through similar mechanisms rooted in host starvation
The Drain of Scientific Publishing
No full textCorrections: Version 1 of this paper (released 6th Nov 2025) stated that publisher profits were over 14.7bn. We also under-estimated the NSERC budget. This second version was released on 17th November 2025.The domination of scientific publishing in the Global North by major commercial publishers is harmful to science; we need the most powerful members of the research community -funders, governments and Universities -to lead the drive to re-communalise publishing to serve science not the market.</div
Le service énergétique comme concept intégrateur des enjeux sociaux dans les modèles : le cas de la boulangerie solaire
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Gradients d'oxydo-réduction, biofilms microbiens, et grands cycles biogéochimiques dans la zone critique
No full textMicroorganisms are ubiquitous in terrestrial surface and subsurface environments. With an estimated population of ~10^30 cells, and prokaryotes alone accounting for ~15% of total biomass, microorganisms are considered a major environmental compartment. In particular, they influence the fate of metals and metalloids in natural systems through processes such as biosorption and bioprecipitation. They can also modify the speciation of metallic elements via direct or indirect electron exchange. These interactions can thus affect the toxicity and bioavailability of chemical elements. However, quantification of the control exerted by microorganisms on biogeochemical cycles remains insufficient, due to limited understanding of the mechanisms governing microbe-metal interactions. In particular, microorganisms are mainly organized in the form of biofilms on Earth, which are three-dimensional structures composed of microbial cells embedded in a self-secreted extracellular matrix of exopolymers. These biofilms, characterized by limited nutrient transport and intense metabolic activity, are made up of specific, reactive microenvironments that largely determine their interaction with organic and inorganic molecules. This PhD work therefore focused on the study of interaction mechanisms between biofilms and metals, from the watershed to the micrometer scale. Particular attention was paid to manganese (Mn), a central element in biogeochemical cycles. Indeed, Mn oxides are among the strongest oxidants, controlling the fate of many redox-sensitive metals. In this context, an environmental study carried out on biofilms in the Seine basin revealed a high accumulation of iron and manganese in biofilms compared to the water column. The speciation of these two elements, studied by X-ray absorption spectroscopy, highlights the complementarity of strongly oxidizing and reducing zones within the same biofilms, without necessarily forming a vertical gradient. This illustrates the potential for biofilms to exert strong control over the cycling of chemical elements with multiple redox levels. To investigate the mechanisms underlying this accumulation, experiments under controlled conditions were carried out on Escherichia coli model biofilms. This work enabled us to study the kinetics of Mn accumulation and the associated thermodynamic processes, demonstrating that Mn accumulation in biofilms can be modelled by a surface complexation model. In addition, the production of reactive oxygen species (ROS) by bacteria in biofilms has been explored, due to their strong oxidative capacity to oxidize manganese. These redox microenvironments were imaged using confocal laser scanning microscopy (CLSM), a technique that enables 3D imaging of biofilms using appropriate probes, while preserving biofilm structure. In particular, this work revealed the redox microenvironments linked to this ROS production in biofilms, and their distribution in the structure.Les microorganismes sont omniprésents dans les environnements de surface et de subsurface terrestres. Avec une population estimée à ~10^30 cellules, et les procaryotes représentant à eux seuls ~15 % de la biomasse totale, les microorganismes sont considérés comme un compartiment environnemental majeur. En particulier, ils influencent le devenir des métaux et métalloïdes dans les systèmes naturels par des processus tels que la biosorption et la bioprécipitation. Ils peuvent également modifier la spéciation des éléments métalliques via des échanges d'électrons, directs ou indirects. Ces interactions peuvent ainsi affecter la toxicité et la biodisponibilité des éléments chimiques. Cependant, la quantification du contrôle exercé par les microorganismes sur les cycles biogéochimiques reste insuffisante, notamment en raison d'une compréhension limitée des mécanismes contrôlant ces interactions. En particulier, les microorganismes sont principalement organisés sous la forme de biofilms sur Terre, qui sont des structures tridimensionnelles composées de cellules microbiennes dans une matrice extracellulaire auto-produite d'exopolymères. Ces biofilms, caractérisés par un transport limité des nutriments et une activité métabolique intense, sont constitués de microenvironnements spécifiques et réactifs qui déterminent en grande partie leur interaction avec les molécules organiques et inorganiques. Ce travail de thèse s'est ainsi concentré sur l'étude des mécanismes d'interaction entre les biofilms et les métaux, depuis l'échelle d'un bassin versant jusqu'à celle du micromètre. Une attention particulière a été portée au manganèse (Mn), un élément central des cycles biogéochimiques. En effet les oxydes de Mn figurent parmi les oxydants les plus forts, contrôlant le devenir de nombreux métaux redox-sensibles. Dans ce contexte, une étude environnementale menée sur des biofilms du bassin de la Seine a permis de révéler une forte accumulation du fer et du manganèse dans les biofilms comparés à la colonne d'eau. La spéciation de ces deux éléments, étudiée par spectroscopie d'absorption des rayons X, met en évidence une complémentarité des zones fortement oxydantes et réductrices au sein de mêmes biofilms, sans nécessairement former un gradient vertical. Cela illustre donc le potentiel de contrôle fort exercé par les biofilms sur le cycle d'éléments chimiques présentant plusieurs niveaux d'oxydoréduction. Pour approfondir les mécanismes sous-jacents à cette accumulation, des expériences en conditions contrôlées ont été menées sur des biofilms modèles d'Escherichia coli. Ces travaux ont permis d'étudier la cinétique d'accumulation du Mn et les processus thermodynamiques associés, démontrant que l'accumulation de Mn dans les biofilms peut être modélisée par un modèle de complexation de surface. Par ailleurs, la production d'espèces réactives de l'oxygène (ROS) par les bactéries en biofilm a été explorée, en raison de leur pouvoir oxydatif très fort, capable d'oxyder le manganèse. Ces microenvironnements redox ont été imagés par microscopie confocale à balayage laser (CLSM), une technique permettant d'imager en 3D les biofilms par utilisation de sondes appropriées, tout en préservant la structure des biofilms. Ce travail a notamment permis de révéler les microenvironnements redox liés à cette production de ROS dans les biofilms, et leur répartition dans la structure
Bifurcation analysis and optimal control of an infection age-structured epidemic model with vaccination and treatment
No full textInternational audienceThis paper addresses the problem of bifurcation analysis and optimal control of an age-structured epidemic model. We first develop and analyze a deterministic epidemiological model for the transmission of an infectious disease described by a susceptible-vaccinated-infected (SVI). The model takes into account the age structure of the infection, imperfect vaccination and treatment of infected people who become susceptible again. The model without intervention strategies is completely analyzed. We compute the disease-free equilibrium and derive the basic reproduction number and Rscr;(0). The analysis of the model reveals the existence of the phenomenon of backward bifurcation, where a stable disease-free equilibrium coexists with one or more stable endemic equilibria when the associated basic reproduction number is less than unity. In this case, controlling this infectious disease remains extremely difficult. Therefore, based on this continuous model, a control is formulated and solved as an optimal control theory problem, indicating how control terms on vaccination and treatment should be introduced in the population to minimize the number of infected individuals as well as the cost of applying controls. We establish the first-order necessary conditions for optimality and characterize optimal controls. The theory is supported by numerical simulations, which further suggest that the combination of intervention measures can significantly reduce the transmission dynamics of infectious diseases by keeping the population of infected individuals relatively low
Apports expérimentaux sur le cycle profond du carbone organique lors de la subduction
No full textRecent thermodynamic and experimental studies have suggested that organic compounds may represent a significant carbon fraction in subduction zones. Beyond these analogical studies, the observation of solid organic compounds associated with high-pressure-high-temperature minerals, inherited from oceanic hydrothermal circulation or neo-formed during the destabilization of solid carbonates during subduction, attests to the existence of a deep organic carbon cycle in subduction zones. To further our understanding of carbon dynamics during subduction, we carried out piston-cylinder and multi-anvil press experiments involving natural serpentine (antigorite) associated with synthetic polycyclic aromatic hydrocarbons or solid carbonates (calcite, ankerite). A wide range of pressures (3-7 GPa) and temperatures (500-1000°C) were explored, as well as different redox conditions imposed in situ by silicon metal or via the use of double capsules. The aim of these experiments was to characterize the interactions between oxidized solid carbonates, reduced organic carbon and ferrous iron-bearing mineral phases (which have a strong reducing power in these environments) during two key reactions in subduction zones: the dehydration of antigorite and chlorite. The composition and structure of the produced organic phases were characterized at the micro- and nanometric scales using high-resolution spectroscopy and imaging techniques (SEM-EDS, Raman, ToF-SIMS, Orbi-SIMS). The results reveal that redox conditions play a critical role in the formation and stability of solid organic phases. These conditions therefore have a significant influence on the mobility and fate of carbon in subduction zones, offering new perspectives for constraining the deep carbon cycle.De récentes études thermodynamiques et expérimentales ont suggéré que les composés organiques pouvaient représenter une fraction importante du carbone dans les zones de subduction. Au-delà de ces études analogiques, l'observation de composés organiques solides associés aux minéraux de haute pression-haute température, hérités de la circulation hydrothermale océanique ou néoformés lors de la déstabilisation des carbonates pendant la subduction, atteste de l'existence d'un cycle du carbone organique profond en zones de subduction. Pour progresser dans notre compréhension de la dynamique du carbone au cours de la subduction, nous avons réalisé des expériences en piston cylindre et presse multi-enclumes mettant en jeu de la serpentine naturelle (antigorite) associée à des hydrocarbures polycycliques aromatiques synthétiques ou à des carbonates solides (calcite, ankérite). Une large gamme de pression (3-7 GPa) et de température (500-1000°C) a été explorée ainsi que différentes conditions d'oxydoréduction imposées in situ par du silicium métal ou via l'utilisation de double capsules. Ces expériences visaient à caractériser les interactions entre les carbonates solides oxydés, le carbone organique réduit et les phases minérales porteuses de fer ferreux (qui ont un fort pouvoir réducteur dans ces environnements) au cours de deux réactions clés dans les zones de subduction : la déshydratation de l'antigorite et de la chlorite. La composition et la structure des phases organiques dans les produits expérimentaux ont été caractérisées à l'échelle micro- et nanométrique via des techniques de spectroscopie et d'imagerie à haute résolution (SEM-EDS, Raman, TOF-SIMS, Orbi-SIMS). Les résultats révèlent que les conditions d'oxydoréduction jouent un rôle déterminant dans la formation et la stabilité des phases organiques solides. Ces conditions influencent donc de manière significative la mobilité et le devenir du carbone dans les zones de subduction, offrant ainsi de nouvelles perspectives pour contraindre le cycle du carbone profond
Spatial and Temporal Wave Climate Variability and Trends in Fiji: Insights from Four Decades of Hindcast Data
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Oridonin: A natural terpenoid having the potential to modulate apoptosis and survival signaling in cancer
No full textInternational audienceBackground: Oridonin, a diterpenoid lactone derived from medicinal plants, has drawn considerable attention due to its therapeutic potential, particularly its anticancer properties. It demonstrates efficacy in inducing apoptosis, suppressing cancer cell proliferation, and sensitizing cells to conventional chemotherapeutics by modulating key signaling pathways like PI3K/AKT, MAPKs, and NF-κB. Purpose: This article investigates the apoptotic mechanisms and anticancer potential of oridonin, including its modulatory effects on signaling pathways and its derivatives' enhanced efficacy against drug-resistant cancer cells. Methods: A systematic literature search was conducted using Scopus, PubMed, SpringerLink, ScienceDirect, Wiley Online, and Web of Science databases, covering the period from 2007 to 2024. Keywords such as "Oridonin," "Apoptosis," "Cancer Cell Signaling Pathways," "PI3K/AKT," "ROS," and "Nanotechnology" were used, yielding 96 relevant studies. Results: Oridonin induces apoptosis through intrinsic and extrinsic pathways, involving ROS amplification and mitochondrial membrane potential regulation. It modulates proteins like Bax, Bcl-2, cytochrome c, and caspases, leading to DNA fragmentation. Its derivatives, such as 13p, exhibit enhanced potency by arresting the G2/M phase and targeting drug-resistant cells with minimal toxicity. Advanced nano-delivery systems and combination therapies further enhance oridonin's therapeutic potential. Conclusion: Oridonin demonstrates robust anticancer activity by modulating signaling pathways and inducing apoptosis. Its derivatives and novel delivery systems offer promising avenues for overcoming drug resistance and optimizing its therapeutic efficacy. Further research, including clinical trials, is necessary to fully harness its potential as a cancer treatment alternative