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Submarine ash megabed fed by far-traveled, shoreline-crossing pyroclastic currents from a large explosive volcanic eruption
No full textInternational audienceLarge explosive volcanic eruptions from island volcanoes deliver vast quantities of ash to the marine environment. While many of the transport pathways are understood, those from shoreline-crossing or submarine pyroclastic currents, and their transformation into water-supported gravity flows, remain poorly constrained. We report the discovery by International Ocean Discovery Program (IODP) deep drilling of a 200-meter-thick ash megabed buried in rift basins of the South Aegean Volcanic Arc. The >73–cubic kilometer ash deposit originates from the Kos Plateau Tuff caldera-forming eruption, which occurred 161 thousand years ago, >120 kilometers to the east. The ash forms a chemically uniform, graded megabed lacking bioturbation, interpreted as having been emplaced by a stream of eruption-fed turbidity currents. Bioclastic debris within the ash provides evidence of widespread destruction of marine ecosystems. Large volcanic eruptions can remodel the seafloor landscape, deposit thick ash turbidites, and destroy marine biota on island arc–wide scales in short-lived, catastrophic events
Modeling and simulation of coupled biochemical and two-phase compositional flow in underground hydrogen storage
No full textInternational audienceIntegrating microbial activity into underground hydrogen storage models is crucial for simulating long-term reservoir behavior. In this work, we present a coupled framework that incorporates bio-geochemical reactions and compositional flow models within the Matlab Reservoir Simulation Toolbox (MRST). Microbial growth and decay are modeled using a double Monod formulation, with populations influenced by hydrogen and carbon dioxide availability. First, a refined Equation of State (EoS) is employed to accurately capture hydrogen dissolution, thereby improving phase behavior and modeling of microbial activity. The model is then discretized using a cell-centered finite-volume method with implicit Euler time discretization. A fully coupled fully implicit strategy is considered. Our implementation builds upon MRST’s compositional module by incorporating the Søreide–Whitson EoS, microbial reaction kinetics, and specific effects such as bio-clogging and molecular diffusion. Through a series of 1D, 2D and 3D simulations, we analyze the effects of microbial-induced bio-geochemical transformations on underground hydrogen storage in porous media.These results highlight that accounting for bio-geochemical effects can substantially impact hydrogen loss, purity, and overall storage performance
Mismatches in exposure, sensitivity, and adaptive capacity to global change lead to contrasting vulnerability profiles for insular vertebrates: Vulnerability of insular vertebrates
No full textIsland biota is currently threatened by global anthropogenic pressures. The limited ability of island species to track suitable conditions, combined with their inherent sensitivity to human pressures, makes insular biota highly vulnerable. While vulnerability assessments have been conducted for climate change or biological invasions individually, the vulnerability of island faunas to multiple global change drivers has not been assessed to date, preventing their inclusion in most global biodiversity policy. Here, we evaluate the relative vulnerability of 266 insular bird and mammal species from 45 islands located in six archipelagos worldwide to multiple threats. We first quantified the current exposure of islands to climate change, land-use change, and biological invasions. We then calculated insular assemblage sensitivity based on species’ ecological characteristics and integrated both biotic and abiotic features to assess the adaptive capacity of insular species in response to these threats. We found a strong variability of exposure and adaptive capacity markers among the six archipelagos, but the mean sensitivity of vertebrate assemblages was similar across islands. High vulnerability scores were found for Hawai’i, the Azores, and the Mascarenes. Climate change and biological invasions were dominant in Hawai’i, while land-use change was dominant in the Mascarenes, the Azores, and the Canaries. In contrast, vertebrate assemblages from the Galapagos and Tristan da Cunha had lower vulnerability to current threats. These contrasting profiles in island vulnerability result in different conservation needs for protecting their biodiversity. Our framework provides a more comprehensive and nuanced understanding of the mechanisms behind the vulnerability of insular biota under global change, a necessary step to effectively preserve island biodiversity and its associated benefits for human societies
Identifying the Activated Carbon Electrode Aging Pathways in Lithium-Ion Hybrid Capacitors
No full textInternational audienceThis paper reports on several mechanisms of carbon aging in a hybrid lithium-ion capacitor operating with 1 mol L -1 LiPF6 in an ethylene carbonate/dimethyl carbonate 1:1 vol/vol electrolyte. Carbon electrodes were subjected to a constant polarization protocol (i.e., floating) at various voltages and analyzed postmortem via several complementary techniques. The selected protocol was able to simulate the behavior of the real system. Due to the use of metallic lithium as the counter electrode, the influence of battery-like aging mechanisms was assumed to be limited. Our approach focused on the aging mechanisms related to the carbon electrode and determined the structural and chemical changes leading to energy fading in lithium-ion hybrid capacitors. It was shown that an increase in applied voltage not only results in faster system degradation but directs the aging chemistry to different pathways: at moderate voltage values, both capacitance loss and simultaneous increase in resistance predominate. This could be associated with the decrease in carbon surface area and possible pore clogging with by-products of electrolyte degradation and carbon oxidation, disrupting the C sp 2 network. When high voltage is applied, further oxidation of carbon occurs with an increase in measured resistance that leads to the relevant end-of-life criterion to be reached. Detailed postmortem analysis results attributed it to the formation of phenol and ether groups together with electrolyte decomposition products, higher oxidation levels, and structure degradation. It was evidenced that the decrease in the overall carbon conductivity and, in certain cases, modification of the textural properties ultimately aggravates the capacitor performance
Séance 6 du jeudi 06 février 2025 Thème 3 : Les littératures africaines francophones (séance 6)
No full textMasterPour cette sixième et dernière séance des cours consacrée auxlittératures africaines francophones, je vais aborder quelques thématiquesmettant en relief la place de l’imaginaire et de la narration historique dansles œuvres romanesques. Les auteurs des romans et des contes de lalittérature africaine francophone mêlent souvent dans leurs répertoires, desévénements et des scènes qui sont le fruit à la fois de l’imagination et de lacréativité. La narration dans les œuvres romanesques et les évocations descontes africains recourent souvent à l’image, aux symboles, auxmétaphores, aux structures cycliques et aux différents régimes del’imaginaire (notamment les régimes diurnes et nocturnes) pour relater unévénement, transposer un vécu et ré-inventer le monde de manière idéelle.Dans la mesure où le roman et le conte dans la littérature africainefrancophone écrite mêlent l’imaginaire, l’histoire et la fiction, quel seraitalors le lieu de jonction ou de disjonction entre le réel et l’imaginaire dans ladésignation des personnages, des lieux, des villes, des campagnes, desespaces habités, ainsi que dans le recours aux images ? Comment à traversle conte et le roman par exemple, appréhender l’indice de lisibilité desreprésentations imaginaires ainsi que les relations entre autonomie ethétéronomie dans le champ de la littérature africaine francophone ? On faitl'hypothèse d’après laquelle, la littérature africaine francophone est leproduit d'un travail intellectuel élaboré, articulant à travers détours etparadoxes, des formes d'expression variées où l’imaginaire est sans cesseconvoquée en session discursive
La housse partie 1 - Édité d'après le ms. BnF fr. 837
No full textLa housse partie 1 - Édité d'après le ms. BnF fr. 83
Les deus bordeors ribauz (pièce 3 La contrejengle) - Édité d'après le ms. BnF fr. 837
No full textLes deus bordeors ribauz (pièce 3 La contrejengle) - Édité d'après le ms. BnF fr. 83
Les deus bordeors ribauz (pièce 2) - Édité d'après le ms. BnF fr. 19152
No full textLes deus bordeors ribauz (pièce 2) - Édité d'après le ms. BnF fr. 1915
Synthesis and Study of the Application of Iron, Nitrogen-Doped High-Surface-Area Carbon for Li–S Batteries
No full textInternational audienceDespite their promising theoretical performance, lithium-sulfur (Li-S) batteries are often limited by low efficiency, primarily due to the solubility of lithium polysulfides and the low conductivity of sulfur electrodes. Enhancing the incorporation of sulfur into porous carbon with improved polarity could significantly boost Li-S battery performance. In this study, we doped carbon xerogels with nitrogen atoms and decorated them with iron-based nanostructures using a straightforward and scalable method. The decomposition of nitrogen-containing additives at varying temperatures—specifically 750°C (FeNC-750) and 950°C (FeNC-950) resulted in alterations to the porosity of the xerogel compared to the pristine structure. After impregnating these structures with sulfur to develop the sulfur electrode, we assessed the electrochemical performance of FeNC-750@S and FeNC-950@S, varying the sulfur content and the electrolyte-to-sulfur (E/S) ratio. Our results indicated that the electrochemical performance of the sulfur electrode with high sulfur content was significantly influenced by both the E/S ratio and the porosity of the host materials. Notably, the sulfur electrode with over 80% sulfur content, designated FeNC-950@S80, achieved a discharge capacity of 600 mAh g⁻¹ with an E/S ratio of 7.5 mL g⁻¹ and an electrode loading of 3.5 g cm⁻², demonstrating excellent capacity retention of 96% over 100 cycles at a rate of 0.1 C
Evidence from Tinshemet Cave in Israel suggests behavioural uniformity across Homo groups in the Levantine mid-Middle Palaeolithic circa 130,000–80,000 years ago
No full textInternational audienceThe south Levantine mid-Middle Palaeolithic (mid-MP; ~130-80 thousand years ago (ka)) is remarkable for its exceptional evidence of human morphological variability, w it h c on te mp or aneous fossils of Homo sapiens and Neanderthal-like hominins. Yet, it remains unclear whether these hominins adhered to discrete behavioural sets or whether r eg io na l-scale intergroup interactions could have homogenized mid-MP behaviour. Here we report on our discoveries at Tinshemet Cave, Israel. The site yielded articulated Homo remains in association with rich assemblages of ochre, fauna and stone tools dated to ~100 ka. Viewed from the perspective of other key regional sites of this period, our findings indicate consolidation of a uniform behavioural set in the Levantine mid-MP, consisting of similar lithic technology, an increased reliance on large-game hunting and a range of socially elaborated behaviours, comprising intentional human burial and the use of ochre in burial contexts. We suggest that the development of this behavioural uniformity is due to intensified inter-population interactions and admixture between Homo groups ~130-80 ka.Studies on the mid-Middle Palaeolithic (mid-MP; ~130-80 thousand years ago (ka)) document an increased pace of out-of-Africa hominin dispersals and provide a growing body of evidence that southwest Asia was the stepping stone for an Asia-wide expansion of Homo sapiens 1,2 . The Levant during this period is marked by exceptional evidence of synchronous human morphological variability within the region, including fossil evidence of highly variable populations 3-6 . This variability is expressed on the inter-site level with archaic Neanderthal-like fossils reported at Nesher Ramla 5 and H. sapiens-like fossils at Skhul and Qafzeh caves 3,4,7 , between the Skhul and Qafzeh fossils 8-11 , and on the intra-site level within the Qafzeh human fossil assemblage 6-8,11-14 . This variability has been a source of major debate about the anatomical affinities of Levantine mid-MP hominins. Skhul and Qafzeh hominins have been variously seen as variable populations of archaic H. sapiens 7,15-17 , distinct human types or hybrids 3,</div