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Revisiting irreversible capacity in lignin-derived hard carbons for sodium-ion batteries: The dominant role of surface functional groups over surface area
No full textInternational audienceHard carbons are promising materials as anode for sodium-ion batteries due to their good reversible capacities and the huge diversity of bio-based precursors available for their synthesis. Nevertheless, their low initial coulombic efficiency (ICE), often below 80% for bio-based hard carbons, is one of the main challenges for their commercial applications. In this work, the surface of lignin-based hard carbons is modified with a thin layer of soft carbon obtained from petroleum pitch. Soft carbon is known to have rich sp2-hybridized domains, with very few heteroatoms, leading to a surface with less defects. After pyrolysis at different temperatures (900 °C to 1400 °C), hard carbon materials were coated using an impregnation coating method. Structural, textural and surface analyses were carried out to understand the impact of soft carbon coating on the electrochemical performance. The composite carbon initially pyrolyzed at 1200 °C exhibited the best performance, achieving a reversible capacity of 310 mAh.g−1, and an excellent initial coulombic efficiency of 89%. Notably, this ICE is among the highest reported for lignin-based hard carbons, which highlights the effectiveness of surface engineering in enhancing their electrochemical properties for sodium-ion batteries
Shifting Drivers of Holocene Fire Regimes in Uzbekistan: From Natural Factors to Anthropogenic Impact
No full textInternational audienceIn the context of the current fire intensification associated to climate aridification, this study explores Holocene fire regimes in the foothills of the Pamir-Alai Range (Uzbekistan) through macro-charcoal analysis of sediment cores from Lake Fazilman and the Ogshagil wetland, spanning the past 11000 years. In addition to their novelty, the results reveal distinct fire phases driven by both climatic fluctuations and human activities. During the early Holocene (12000–5000 cal. yr BP), fire activity was primarily climate-driven, with higher frequencies during arid phases. A significant shift occurred around 4000 – 3000 cal. yr BP, with synchronous fire trends at both sites suggesting increased anthropogenic influence linked to agro-pastoral practices of the Oxus Civilization, the Andronovo Cultures and the Handmade Painted Ware Cultures. Fire frequency declined during periods of intensified agricultural practices but increased again in later centuries, likely influenced by shifts in land use and socio-economic dynamics. Over the past 500 years, a rise in fire activity and woody plant combustion, likely influenced by post-medieval pastoral land use and firewood transportation, suggests intensified human impact. This study provides new insights into the interplay between climate, vegetation, human activity and fire in shaping Central Asia's steppe landscapes
The political effects of X’s feed algorithm
No full textInternational audienceFeed algorithms are widely suspected to influence political attitudes. However, previous evidence from switching off the algorithm on Meta platforms found no political effects1. Here we present results from a 2023 field experiment on Elon Musk’s platform X shedding light on this puzzle. We assigned active US-based users randomly to either an algorithmic or a chronological feed for 7 weeks, measuring political attitudes and online behaviour. Switching from a chronological to an algorithmic feed increased engagement and shifted political opinion towards more conservative positions, particularly regarding policy priorities, perceptions of criminal investigations into Donald Trump and views on the war in Ukraine. In contrast, switching from the algorithmic to the chronological feed had no comparable effects. Neither switching the algorithm on nor switching it off significantly affected affective polarization or self-reported partisanship. To investigate the mechanism, we analysed users’ feed content and behaviour. We found that the algorithm promotes conservative content and demotes posts by traditional media. Exposure to algorithmic content leads users to follow conservative political activist accounts, which they continue to follow even after switching off the algorithm, helping explain the asymmetry in effects. These results suggest that initial exposure to X’s algorithm has persistent effects on users’ current political attitudes and account-following behaviour, even in the absence of a detectable effect on partisanship
Un modèle de gestion de l’eau en contexte sismique : le système d’irrigation de Sarazm (vallée du Zeravshan, Asie centrale) au tournant des 4e et 3e millénaires av. n. è.
No full textInternational audienceÉtabli dans la vallée semi-aride et tectoniquement active du Moyen-Zeravshan, au Tadjikistan, l’établissement proto-urbain de Sarazm (3500/2500 av. J-C) témoigne de savoir-faire de haute technicité dans l’architecture, les artisanats et les arts ; ainsi que d’une maîtrise précoce de l’irrigation gravitaire. Le plus ancien système d’irrigation daté à ce jour en Asie centrale, fonctionnel à la fin du 4e millénaire et à l’âge du Bronze ancien, était basé sur la dérivation d’écoulements nivoglaciaires plusieurs kilomètres à l’amont des secteurs irrigués par un canal en terre creusé en bordure de haute terrasse. L’étude des dépôts de ce canal à ciel ouvert, combinant une approche topographique, pédo-stratigraphique, sédimentologique et micromorphologique, révèle les modalités techniques et pratiques de la gestion de l’eau, qui s’exprime dans la maîtrise de la planimétrie, le dimensionnement de l’ouvrage (gabarit, profil), le contrôle des flux et la maintenance. Son histoire fonctionnelle inclut des phases de mise en eau, de fonctionnement courant, d’entretien à l’outil et de réparations associées à des secousses sismiques récurrentes qui ont endommagé l’ouvrage et perturbé la circulation de l’eau. A l’échelle microrégionale, l’impact des contraintes sismotectoniques sur la dynamique fluviale (barrages de débris, défluviations, incision) et sur la fonctionnalité du système hydraulique ont probablement joué un rôle dans l’apparition des galeries drainantes de type karez creusées dans les conglomérats de la terrasse à la fin de l’âge du Bronze, période marquant la fin de l’occupation de Sarazm
Vapor–Liquid Equilibrium Data Measurements and Modeling for the Methane + Perfluorohexane System from 293.39 to 333.38 K
No full textInternational audienceThis study presents vapor–liquid equilibrium (VLE) data for the methane + perfluorohexane system across five isotherms (293.39 to 333.38 K) with pressures up to 6.669 MPa. The experimental data were obtained via a “static-analytical” based setup incorporating a Rapid Online Sampler Injector (ROLSI) for sampling of equilibrium phases and a gas chromatograph (GC) for analyzing phase composition. Expanded uncertainties for temperature (T), pressure (P) and phase compositions (x, y) are estimated within 0.07 K, 0.011 MPa, and 0.020, 0.030, respectively. The experimental VLE data were regressed via the direct method using both the Peng–Robinson and the Soave–Redlich–Kwong equations of state. In each case, the Mathias–Copeman α function was employed, and the calculations were performed using either the Wong–Sandler or the predictive Soave-Redlich-Kwong mixing rule in combination with the nonrandom two-liquid activity coefficient model. The model parameters were refined using a simplex algorithm optimized through the flash calculation objective function. The calculated average absolute deviation (AADxy) and bias (Biasxy) values between the measured data and the models were both below 4%, indicating satisfactory data regression. Comparative analysis of the CO2 + C6F14, C2H6 + C6F14 and CH4 + C6F14 systems highlights C6F14’s strong selectivity as a physical solvent for C2H6 and CO2 over CH4
Large landslides and lake evolution in the semi-arid volcanic tableland of the Sarmiento Basin (Patagonia): when did the last major failures occur?
No full textInternational audienceLarge landslides are prominent geomorphic features on many arid tablelands, yet their absolute ages and links topaleoenvironmental conditions remain poorly constrained. This study investigates landslides along the volcanicplateaus adjacent to the Sarmiento Basin in eastern Patagonia, occupied by Lakes Musters and Colhúe Huapi, anarea characterized by significant Late Quaternary lake-level fluctuations. The region hosts extensive rotationaland flow-type landslides, including some of the largest documented in Patagonia, with lengths exceeding 16 km.Using geomorphic mapping, luminescence dating of paleoshorelines, cosmogenic 36Cl exposure dating of landslidescarps and deposits, and DInSAR analysis of recent ground deformation, we reconstruct a prolonged historyof slope failures spanning >3Ma to the Holocene. We provide the first absolute age constraints for paleolakeSarmiento, revealing highstands during the Last Glacial Maximum (LGM) and Early to Middle Holocene. Themost recent major phase of landsliding occurred after the younger lake highstand, suggesting that Early toMiddle Holocene flooding of the basin—likely linked to capture of the Río Senguer—together with wetter climaticconditions, may have triggered renewed slope instability. Pre-Holocene landslide ages remain less wellconstrained. However, failures from high mesas disconnected from modern lake shores yield significantly olderexposure ages (≥10^5 yr) compared to landslides along recent lake margins and valleys (~10^4 yr). We proposethat episodic wetter conditions and lake-level rises driven by enhanced Andean runoff or drainage reorganizations,periodically increased pore pressures in escarpments. This promoted slope failure within alandscape that has remained largely arid since at least the Pliocene
Exploring microbial and metabolite composition of the external mucus of wild Mediterranean sparids: is there a link with their monogenean ectoparasites?
No full textInternational audienceBackgroundExternal mucus forms a complex interface that constitutes the first line of defense in teleost fish. In addition to host-derived molecules, this mucus harbors bacterial communities capable of producing a wide range of bioactive compounds. The structure and function of these microbial and chemical assemblages remain to be characterized, particularly in wild populations. This is especially true in the context of fish-parasite interactions, as all components of the external mucus may act in concert to act on pathogen entrance.In this study, we investigated the microbial and chemical composition of the external mucus (skin and gills) from four wild Mediterranean sparid species using 16S rRNA gene amplicon sequencing and non-targeted LC-HRMS metabolomics. After assessing the effect of environmental and host-related factors on the structure and diversity of these assemblages, we focused on one of the species, Boops boops (bogue), which, unlike the other three sparid species studied, never exhibits infection by Lamellodiscus monogeneans. This systematic absence of Lamellodiscus infection in this species led us to investigate bacterial taxa and metabolites specifically associated with their external mucus, to identify potential anti-parasite bio-markers.ResultsThe present results suggest that while several factors influence mucus composition, host species seems to be the primary driver of both microbial and chemical assemblages, suggesting that intrinsic physiological factors primarily govern their structure, each compartment may influence the other. Although the potential impact of abiotic factors on the structure of the mucus microbiota could not be fully assessed in this study, since B. boops and other fish species were sampled at different times, a significant enrichment of an anaerobic bacterial taxon from the Cardiobacteriaceae family was detected in the gill mucus of B. boops. This taxon, rarely associated with oxygenated areas or with external teleost microbiota, could contribute to the exclusion of Lamellodiscus parasites. This protection may also be linked to the distinctive chemical composition of the external mucus of bogues, although establishing a direct link between the identified eicosanoid molecules in the gill mucus and protection against Lamellodiscus remains challenging.ConclusionsOverall, untargeted metabolomics and metabarcoding appear to be powerful tools for assessing global variations in the composition of external mucus in teleost fish. However, the identification of biomarkers remains more challenging with such approaches in wild populations, but suggests that the mucus of wild fish is likely an underexplored source of bioactive molecules, whose identity and role remain to be characterized
Plant-parasitic nematode microRNAs hijack plant AGO1 to induce host-cell reprogramming
No full textCross-kingdom RNA interference (ckRNAi) is emerging as a mode of inter-organismal gene regulation, yet mechanistic examples in plant-metazoan interactions remain limited. Here, we demonstrate miRNA-driven ckRNAi in the nematode-plant pathosystem. Root-knot nematodes are among the most destructive plant pathogens, reprogramming root tissues to develop into galls containing multinucleated, hypermetabolic giant feeding cells essential for parasitism. AGO1-associated small-RNA immunoprecipitation (AGO1-RIP) from tomato galls revealed the selective in planta loading of 10 M. incognita miRNAs into host AGO1.Integrating degradome profiling, target prediction, and dual-luciferase reporter assays, we validated miRNA-directed silencing of nine tomato transcripts by four secreted nematode miRNAs. These targets map to major pathway classes involved in immune signaling, metabolic regulation, and cellular reprogramming linked to feeding-site establishment.Functional analyses further show that the nematode-secreted miR-2b is enhances giant remix, or adapt.</p
L’influence des plateformes de pré-inscription sur les différences d’orientation et de réussite dans l’enseignement supérieur français
No full textThis thesis draws on comprehensive administrative data from the French higher education system to examine the influence of centralized college admission platforms on postsecondary trajectories. It analyzes three key stages in the transition from secondary to higher education: the decision toapply to a specific program, the consequences of admission to one’s preferred program, and the impact of postsecondary redirection.The French centralized college admission platform lists over 25,000 postsecondary programs. This vast array of options may hinder high school students from identifying pathways that are well-suited to their profiles, reinforcing disparities in postsecondary pathways and prospects for academic success.The first chapter of my thesis, co-authored with Gustave Kenedi (Paris Cergy University), investigates the factors that shape high school students’ decisions to apply to specific postsecondary programs. In particular, we examine the extent to which the college choices made by previous cohorts influence the application behavior of current students within the same high school. Leveraging cross-cohort administrative data on college applications, this chapter offers an innovative strategy to address the reflection problem—namely, the challenge of disentangling who influences whom—which is a central methodological hurdle in peer effects research. For each postsecondary program, we compare application patterns among high schools where at least one older schoolmate was admitted to the program in the previous admission cycle with those observed in high schools where no student gained entry. To isolate causal spillover effects, we implement a regression discontinuity design that compares application behaviors across high schools with similar characteristics, focusing on those where a former student narrowly received or missed an admission offer.Our findings reveal significant older schoolmate spillovers: students are 6 percentage points (+19%) more likely to apply to and 2 percentage points (+45%) more likely to enroll in the same degree as a marginally enrolled older schoolmate. We find that both teacher influence and homophily/role model effects mediate these cross-cohort spillovers. Finally, counterfactual simulations suggest that enhancing social diversity within high schools may reduce inequalities in access to the most selective programs across SES by around 10%, by broadening students’ exposure to diverse role models and information channels.Access to higher education is often constrained by limited capacity, forcing institutions to ration seats when demand exceeds supply. In France, these pressures are especially acute in popular university tracks such as psychology, law, and sports studies (called STAPS). Traditionally non-selective, universities relied on non-academic criteria such as place of residence to prioritize applicants and, when these rules proved insufficient, on random lotteries to determine admission.The second chapter, co-authored with Georgia Thebault (Paris Dauphine University), exploits this exceptional institutional feature as a natural experiment to identify the causal impact of being admitted to one’s top-ranked program on subsequent trajectories in higher education. Focusing on high school graduates who listed an oversubscribed university program as their first choice, we compare those admitted thanks to a favorable lottery draw with those rejected due to an unfavorable draw. The analysis shows that admission to the preferred program significantly increases the likelihood of enrolling in higher education (+10%), leads to more stable academic paths, and raises graduation rates (+7%). The effects are particularly strong for students with weaker academic preparation, including scholarship holders and vocational high school graduates, whose probability of entering higher education rises substantially when they secure admission to their first choice. The impact is also especially pronounced in STAPS programs, where unsuccessful applicants face limited alternatives. Overall, the findings indicate that accommodating students’ stated preferences is an effective way to foster persistence and success, while also highlighting the policy trade-off between academic selection and alignment with students’ choices.Once admitted to the first year of higher education, students may come to realize that their program of admission does not meet their expectations. While some respond by leaving higher education entirely, others attempt to realign their path through postsecondary redirection—submitting a new application to a different institution or program, which may involve restarting from the first year. There has been a sharp increase in postsecondary redirection in France over the past decade. By 2022, one in three students admitted through the centralized college admission platform submitted a new application the very next year.This third chapter provides the first causal evaluation of postsecondary redirection in higher education, using French administrative data on second-chance applications linked to matriculation and graduation records. To estimate these effects, I exploit a fuzzy regression discontinuity design based on the qualifying cutoff—that is, the lowest admission cutoff among the programs to which each student applied. This strategy enables comparisons between students with similar academic and sociodemographic profiles, and thus with comparable ex-ante probabilities of success in both their current program and the alternative one they would enter in case of successful redirection. For applicants just above the cutoff, admission to a new program increases matriculation and graduation rates by 38 and 23 percentage points, respectively (from 58% to 96% for matriculation and from 46% to 69% for graduation). The effects are strongest for students shifting to two-year vocational programs. Based on a cost–benefit analysis that compares the additional education costs generated by longer study durations among redirected students with the gains in graduation prospects, I show that redirection is essentially a cost-neutral corrective mechanism, allowing students to recover from early misalignments in their educational path. These findings challenge the prevailing view in public statistics, official reports, and policy debates, which often portray postsecondary redirection as socially costly and individually inefficient.L’objet principal de cette thèse est d'analyser les différences d’orientation et de réussite dans l’enseignement supérieur, et d'étudier dans quelle mesure les plateformes centralisées de pré-inscription y contribuent. Sans chercher à couvrir toutes les facettes d’un sujet aux ressorts multiples et complexes, l’étude s’attache à trois moments essentiels de la transition entre le secondaire et le supérieur : la décision de s'orienter vers une formation spécifique, les répercussions d'une admission à son vœu préféré, et l'impact d'une réorientation d'études supérieures.La plateforme Parcoursup compte aujourd'hui plus de 25 000 formations du supérieur. Cette myriade de possibilités peut induire des difficultés à identifier les formations les plus appropriées pour un projet d'études et être vectrice d'inégalités de parcours.Le premier chapitre, écrit en collaboration avec Gustave Kenedi (Université Paris Cergy), interroge les facteurs pouvant conduire les lycéens à s'orienter vers un cursus plutôt qu'un autre. Plus spécifiquement, ce chapitre examine dans quelle mesure les décisions d’orientation prises par les lycéens des cohortes précédentes influencent les candidatures et les choix d’admission des élèves actuels au sein d’un même établissement. Pour mesurer l'impact causal des admissions des anciens élèves sur l’orientation des cohortes suivantes, l’analyse consiste, pour chaque formation du supérieur, à considérer uniquement les lycées où un ancien élève avait postulé à la formation l’année précédente, qu’il ait été finalement admis ou non. C’est uniquement dans le sous-ensemble d’établissements où un ancien élève a finalement été admis qu’une influence peut s’exercer, en augmentant potentiellement les chances de s’orienter vers cette formation chez les générations d’élèves suivantes. Par une méthode de « régression sur discontinuité », cette influence est mesurée en comparant les comportements de candidature l’année suivante dans les lycées selon qu’un ancien élève a été admis de justesse à la formation (ce sont les lycées traités) ou refusé de justesse (ce sont les lycées du groupe témoin). Nos résultats montrent que l’admission d’un élève à une certaine formation du supérieur augmente significativement la probabilité qu’un lycéen du même établissement postule (+19 %) à cette formation l’année suivante ou soit admis (+45 %). Ces effets persistent au-delà d’un an. Des analyses d’hétérogénéité révèlent que l’influence de l’orientation d’un ancien élève sur les choix des lycéens des cohortes suivantes concerne essentiellement les élèves assignés au même professeur principal. Ce constat suggère que les professeurs principaux constituent le canal privilégié de transmission d’informations entre cohortes. Les analyses révèlent une forme d’homophilie dans les effets d’influence : ils sont plus marqués lorsque les lycéens partagent le même genre ou le même milieu social que l’ancien élève. Enfin, des simulations neutralisant les différences d’exposition aux filières sélectives liées aux anciens élèves suggèrent qu’une plus grande mixité sociale dans les lycées réduirait d’environ 10 % les écarts d’aspiration entre élèves socialement favorisés et défavorisés, à niveau scolaire équivalent.L’accès à l’enseignement supérieur est parfois conditionné par des contraintes de capacité, qui obligent les établissements à départager les candidatures lorsque la demande excède l’offre. En France, de fortes tensions existent sur les capacités d'accueil de certaines filières universitaires très prisées, comme la psychologie, le droit ou encore les Sciences et Techniques des Activités Physiques et Sportives (STAPS). Face à ces déséquilibres, les universités, traditionnellement non sélectives, ont eu recours à des règles de priorité fondées sur des critères indépendants du dossier scolaire, tels que le secteur géographique et, en dernier ressort, à un tirage au sort pour départager les candidats. Le deuxième chapitre, écrit en collaboration avec Georgia Thebault (Université Paris-Dauphine), exploite cette procédure exceptionnelle comme une expérience naturelle permettant d'analyser l’impact causal de l’admission à son premier vœu sur les trajectoires dans l’enseignement supérieur. En comparant les lycéens ayant inscrit en tête de leurs choix une licence en tension, l'étude montre que les candidats admis grâce à un tirage au sort favorable s'engagent plus souvent dans des études supérieures (+10 %), connaissent des parcours moins sinueux et disposent de meilleures chances d’obtenir un diplôme (+7 %). Ces effets apparaissent particulièrement marqués pour les élèves les plus fragiles scolairement, tels que les boursiers ou les titulaires d’un baccalauréat professionnel ou technologique, dont la probabilité de s’inscrire dans le supérieur et d'obtenir un diplôme augmente nettement à l’issue du tirage au sort. L’impact est aussi très fort dans les licences de STAPS, où les candidats refusés connaissent des parcours universitaires dégradés en raison de l’absence d’alternatives dans l’offre de formation. Ces résultats suggèrent que l’intégration des préférences déclarées des candidats constitue un levier efficace pour renforcer la persévérance et la réussite dans les études supérieures, et mettent en évidence la tension entre une logique de sélection académique et une logique d’accommodation des choix d’orientation.Certains étudiants, une fois admis en première année d'études supérieures, réalisent que la formation choisie ne correspond pas à leurs attentes. La réorientation, qui consiste à déposer une nouvelle candidature pour intégrer une autre formation, représente alors l’une des voies permettant de remédier à cette inadéquation. En France, ce phénomène est massif : en 2022, un lycéen sur trois admis dans le supérieur a formulé des vœux de réorientation dès la campagne d'affectation suivante, soit quelques mois après la première rentrée.Le troisième chapitre propose la première évaluation causale de l’impact d’une réorientation sur les trajectoires dans le supérieur, en comparant le devenir des étudiants ayant formulé des vœux de réorientation selon l’issue des affectations. Par une méthode de régression sur discontinuité, les candidats à une réorientation ayant été admis de justesse quelque part (ceux dont le rang est juste au-dessus du rang du dernier admis) sont comparés aux candidats à une réorientation marginalement refusés (ceux dont le rang est juste en-dessous du dernier admis). Cette approche permet de comparer des étudiants présentant des profils scolaires et socio-démographiques similaires et, à ce titre, les mêmes perspectives de réussite à la fois dans leur formation actuelle et dans celles inscrites dans leurs vœux de réorientation. Les résultats de ces analyses montrent que la réorientation induit une augmentation très nette des chances de rester inscrit dans le supérieur au terme des affectations (+38 points de pourcentage) et d'obtenir un diplôme du supérieur (+23 points de pourcentage). Ces effets sont particulièrement prononcés chez les étudiants se réorientant en Section de Technicien Supérieur (STS), filières post-bac professionnalisantes de deux ans. Plus spécifiquement, la réorientation induit une probabilité nettement accrue d’obtenir un diplôme de BTS (+25 points) ou de DUT (+7 points), excédant la légère diminution du taux de diplômés de licence générale (-6 points). Les avantages sont moindres lorsque la réorientation conduit vers un domaine trop éloigné ou, au contraire, trop similaire à la filière d’origine. Enfin, l'analyse coût-bénéfice réalisée dans ce chapitre montre que l’amélioration des chances d’obtenir un diplôme après une réorientation pourrait compenser les coûts éducatifs supplémentaires qu’elle génère, suggérant un impact budgétaire globalement neutre du phénomène et nuançant la perception dominante dans le débat public d’une réorientation coûteuse et inefficace
L'impact des licenciements sur les individus et les entreprises
No full textCe papier synthétise la recherche économique autour des impacts des licenciements, individuels et collectifs, sur les individus et les entreprises. Après avoir présenté un cadre conceptuel pour comprendre les mécanismes susceptibles de moduler les impacts des licenciements, il présente la recherche en France et à l'étranger sur leurs impacts, en s'appuyant sur des articles clés de la littérature économique. Il finit avec des propositions pour la recherche à l'avenir