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A dynamic H2 system with multi-source methane in chromitite-rich ophiolitic settings
No full textInternational audienceThe generation and migration of hydrogen and methane in serpentinizing environments represent fundamental processes with implications for deep carbon cycling, the origin of life, and emerging carbon-free energy resources. Here we present an integrated geochemical study of gas emissions from the Bulqizë chromite mine in Albania, where exceptional underground access to depths exceeding 1000 m enables direct investigation of one of Earth's most intense natural hydrogen systems (~200 tones H₂/year). Through a comprehensive analysis of bulk and clumped isotopes, noble gases, molecular compositions, and structural controls, we report a novel occurrence of radiocarbon-bearing methane (3.76 ± 0.06 pMC; ~26 ka) in any ophiolite globally. This discovery, combined with modern water ages (³H = 3.5 TU; ¹⁴C-DIC = 95.8 pMC) yet ancient gas signatures, reveals a dramatically decoupled fluid systems where meteoric water circulates rapidly within the mine while gas migrates slowly from depth. Methane clumped isotopes (Δ¹³CH₃D = 2.52 ± 0.26‰; Δ¹²CH₂D₂ = 9.95 ± 1.6‰) indicate a lack of isotopic equilibrium with H₂ (δD-H₂ = -743.5 ± 1.1‰; ΔDD = 255 ± 35‰) and suggest formation from a single hydrogen source. They also show positive Δ¹²CH₂D₂ deviations likely due to diffusion or mixing, and point to a microbial origin probability of less than 10%. High δ¹³C-CH₄ values (-12.3‰), complete isotopic reversal in C₂-C₄ alkanes, and Volatile Organic Compounds signatures further support a predominantly abiotic synthesis. Noble gas and nitrogen isotopes reveal mixing between atmospheric (80-85%) and crustal (15-20%
Vers l'organiser incarné : une enquête sur l'incarnation et les organisations
No full textThis dissertation explores the notion of embodiment and its relations with organizing. Specifically, it inquires about how forms of embodiment are created and modified. The dissertation comprises three chapters. Firstly, chapter 1 builds a theoretical contribution regarding how bodies engage with organizational boundaries. Exploring the body-organization literature, which suggests that organizational rules impose themselves as norms to which bodies abide while half-apprehended, the article proposes the concept of embodied organizational boundaries, through a performative lens, to conceive of other forms of embodiment. The two subsequent chapters explore modes of organizing that escape dominant embodiment modes or otherwise shed light on possible alternatives. Secondly, chapter 2 uses data from an organizational ethnography conducted at a permacultural community garden to suggest how affective dynamics take place and influence organizational members' embodiment as well as organizational democracy, drawing from alternative organization and post-structuralist literature. Finally, chapter 3 explores the repositioning of non-human animals into non-utilitarian relations by means of an organizational ethnography conducted at an animal sanctuary, as embodiment is also intimately related to the non-human. Together, the three papers of this dissertation contribute to an understanding of relations among embodiment and socio-environmental impact that is necessary for democratic organizing and for sustainable and ethical futures at large. Specifically, the thesis draws on such relations focusing on the promises and limitations of existing organized alternative practices.Cette thèse explore la notion d'incarnation et ses relations avec l'organisation. Plus précisément, elle s'interroge sur la manière dont les formes d'incarnation sont créées et modifiées. La thèse comprend trois chapitres. Tout d'abord, le chapitre 1 apporte une contribution théorique sur la manière dont les corps s'engagent dans les limites de l'organisation. En explorant la littérature sur le corps et l'organisation, qui suggère que les règles organisationnelles s'imposent comme des normes auxquelles les corps se conforment tout en les appréhendant à moitié, l'article propose le concept de frontières organisationnelles incarnées, dans une optique performative, pour concevoir d'autres formes d'incarnation. Les deux chapitres suivants explorent des modes d'organisation qui échappent aux modes d'incarnation dominants ou qui mettent en lumière des alternatives possibles. Ensuite, le chapitre 2 utilise les données d'une ethnographie organisationnelle menée dans un jardin communautaire permaculturel pour suggérer comment les dynamiques affectives se produisent et influencent l'incarnation des membres de l'organisation ainsi que la démocratie organisationnelle, en s'inspirant de la littérature sur l'organisation alternative et le post-structuralisme. Enfin, le chapitre 3 explore le repositionnement des animaux non humains dans des relations non utilitaires au moyen d'une ethnographie organisationnelle menée dans un refuge animal, l'incarnation étant également intimement liée au non humain. Ensemble, les trois articles de cette thèse contribuent à une compréhension des relations entre l'incarnation et l'impact socio-environnemental qui est nécessaire pour l'organisation démocratique et pour des avenirs durables et éthiques en général. Plus précisément, la thèse s'appuie sur ces relations en se concentrant sur les promesses et les limites des pratiques alternatives organisées existantes
Superpolynomial Lower Bounds Against Low-Depth Algebraic Circuits
No full textInternational audienceAn Algebraic Circuit for a polynomial P is a computational model for constructing the polynomial P using only additions and multiplications. It is a syntactic model of computation, as opposed to the Boolean Circuit model, and hence lower bounds for this model are widely expected to be easier to prove than lower bounds for Boolean circuits. Despite this, we do not have superpolynomial lower bounds against general algebraic circuits of depth 3 (except over constant-sized finite fields) and depth 4 (over fields other than F2), while constant-depth Boolean circuit lower bounds have been known since the early 1980s. In this paper, we prove the first superpolynomial lower bounds against general algebraic circuits of all constant depths over all fields of characteristic 0 (or large). We also prove the first lower bounds against homogeneous algebraic circuits of constant depth over any field. Our approach is surprisingly simple. We first prove superpolynomial lower bounds for constant-depth Set-Multilinear circuits. While strong lower bounds were already known against such circuits, most previous lower bounds were of the form f(d)poly(N), where d denotes the degree of the polynomial. In analogy with Parameterized complexity, we call this an FPT lower bound. We extend a well-known technique of Nisan and Wigderson (FOCS 1995) to prove non-FPT lower bounds against constant-depth set-multilinear circuits computing the Iterated Matrix Multiplication polynomial IMM(n,d) (which computes a fixed entry of the product of d n*n matrices). More precisely, we prove that any set-multilinear circuit of depth ∆ computing IMM(n,d) must have size at least n^d^(exp(O(-∆))). This result holds over any field, as long as d = O(log n). We then show how to convert any constant-depth algebraic circuit of size s to a constant-depth set-multilinear circuit with a blow-up in size that is exponential in d but only polynomial in s over fields of characteristic 0. (For depths greater than 3, previous results of this form increased the depth of the resulting circuit to Ω(log s).) This implies our constant-depth circuit lower bounds. We can also use these lower bounds to prove a Depth Hierarchy theorem for constant-depth circuits. We show that for every depth Γ, there is an explicit polynomial which can be computed by a depth Γ circuit of size s, but requires circuits of size s = ω(1) if the depth is Γ-1. Finally, we observe that our superpolynomial lower bound for constant-depth circuits implies the first deterministic sub-exponential time algorithm for solving the Polynomial Identity Testing (PIT) problem for all small depth circuits using the known connection between algebraic hardness and randomness
The Limited Legacy of Post-Glacial Recolonization in the Floristic Patterns of the European Alps
No full textInternational audiencePast glacial periods were highly disruptive to plant species distributions in mid-latitude mountain belts, such as the European Alps, and drove many species to survive in peripheral or nunatak refugia. Progressive glacial retreat during the late Pleistocene and Holocene is thought to have triggered a mass recolonization event in the European Alps. Here, we asked whether this recolonization event has left a spatial legacy in the floristic patterns of the extant Alpine flora, and if so, how strongly this determines floristic patterns in comparison to present-day landscape and climatic drivers. We built on approximately 6 million data points sourced from the Global Biodiversity Information Facility and herbaria to build plant species ranges within a 10 × 10 km grid system laid across the European Alps, and then calculated species assemblage turnover across the grid. Additionally, we used a recent species-level molecular phylogeny encompassing over 80% of the Alpine flora to calculate standardized phylogenetic diversity, phylogenetic endemism, and phylogenetic turnover between grid cells. Using spatial autoregressive and generalised dissimilarity modelling, we showed that all floristic measures vary significantly, albeit weakly, with three key post-glacial variables: climate change velocity, time since deglaciation, and distance from the nearest refugium. Unexpectedly, differences in species’ dispersal ability did not explain these patterns. The post-glacial variables have little explanatory power relative to contemporary climate and landscape drivers. We conclude that post-glacial recolonization of the Alps is largely complete for the flora as a whole, and that the spatial structure of the extant flora is primarily driven by the contemporary environmental conditions
A Global-scale Database of Seismic Phases from Cloud-based Picking at Petabyte Scale
No full textInternational audienceWe present the first global-scale database of 4.3 billion P- and S-wave picks extracted from 1.3 PB continuous seismic data via a cloud-native workflow. Using cloud computing services on Amazon Web Services, we launched ~145,000 containerized jobs on continuous records from 47,354 stations spanning 2002-2025, completing in under three days. Phase arrivals were identified with a deep learning model, PhaseNet, through an open-source Python ecosystem for deep learning, SeisBench. To visualize and gain a global understanding of these picks, we present preliminary results about pick time series revealing Omori-law aftershock decay, seasonal variations linked to noise levels, and dense regional coverage that will enhance earthquake catalogs and machine-learning datasets. We provide all picks in a publicly queryable database, providing a powerful resource for researchers studying seismicity around the world. This report provides insights into the database and the underlying workflow, demonstrating the feasibility of petabyte-scale seismic data mining on the cloud and of providing intelligent data products to the community in an automated manner
Targeting visual-sensory and cognitive impairments following lateral ankle sprains: a practical framework for functional assessment across the return-to-sport continuum—Part 1. Sensory reweighting and cognitive impairments: what are we really talking about and why clinicians should consider central alterations in return to sport criteria
No full textInternational audienceLateral ankle sprain (LAS) is the most common traumatic injury, with a high recurrence rate and chronic ankle instability (CAI) developing in ∼40% of cases. LAS leads to patho-mechanical, sensory-perceptual and motor-behavioral deficits. Poor management of the return-to-sport (RTS) is now considered a major cause of re-injury and development of CAI, particularly due to the lack of validated tests and the failure of existing ones to account for those central deficits. The first part of this topic aimed to clarify concepts of cognitive constructs and sensory reweighting and their association with CAI. We also aimed to identify objective RTS criteria and discuss their limits regarding their ability to encompass central impairments. Motor-cognitive deficits have been identified using computerized cognitive tasks and dual-task paradigms. More specifically, deficits in visual memory, processing speed or inhibitory control and attentional resource allocation have demonstrated reduced performance in CAI populations. In addition, altered sensory reweighting process towards visual input has also been observed. While objective criteria are crucial to prevent re-injury, current evaluations remain largely subjective and central impairments are unaccounted for in conventional RTS testing. The Ankle-GO TM score was recently developed to guide clinicians in decision making process. To date, it is the first validated score that could help to identify patients who will RTS at the same level, those at risk of recurrence and those who are more likely to become copers. Unfortunately, it does not target cognitive or sensory reweighting alterations, that are both relevant in sport to manage gameplay demands
What does heritage mean for local communities? The contributions of a participatory photovoice approach and Challenges of Transferring Methodologie Across Cultural Contexts
No full textInternational audienceThis presentation has a dual aim: (1) to report on a participatory approach developed in South Africa with local communities around the question of heritage; and (2) to critically reflect on the potential transferability of this approach to other cultural contexts.As part of the COSMO-ART research project (ANR-21-CE27-0011, https://cosmo-art.org/) on the preservation and valorisation of rock art in South Africa and Namibia, a photovoice methodology was implemented in 2022–2023 with members of two San communities—the !Xun and Khwe—living in Platfontein, near Kimberley (Northern Cape, South Africa). Displaced in the 1990s from Angola and Namibia, these communities have lived since 1997 near the Wildebeest Kuil rock art site. In the 2000s, this site was identified by the South African government as part of a cultural tourism strategy, notably because of its proximity to San communities, often identified—both academically and publicly—as being the authors of rock art. This spatial proximity offered the possibility of promoting a supposedly “authentic” tourism experience: come visit a rock art site with San people who live nearby. However, despite these seemingly favorable conditions, efforts to develop tourism in the area have struggled to take hold.Beyond institutional and academic narratives, to what extent does rock art hold meaning for these two communities? This question led to the development of the photovoice project, which used photography and interviews to explore what participants themselves consider as heritage. The project revealed a disconnect between institutional conceptions of heritage and the perspectives of young community members on what they identify as their own heritage.This presentation will first provide contextual background of the COSMO-ART project and this case study, then detail the photovoice methodology, and finally offer a critical reflection on the potential for adapting and applying this participatory approach in other cultural settings
P and S wave finite-frequency tomography reveals the impact of slab interference on mantle flow beneath the greater Alpine region
No full textInternational audienceThe Cenozoic evolution of the tortuous Adria-Europe plate boundary zone suggests potential interference between opposite-dipping slabs in the upper mantle, with potential perturbation of the surrounding mantle flow. However, compelling seismic evidence of slab interference beneath the greater Alpine region is still lacking. Here we use P-and the first S-wave velocity models based on the Finite-Frequency Tomography method to reveal the interactions between slabs imaged beneath the greater Alpine region and their relationships with prominent low-velocity anomalies in the upper mantle. We document high-velocity anomalies beneath the Alps, the Apennines and the northern Dinarides. Low-velocity anomalies are found to the west of the Alps, beneath the Po Plain, and on either side of the central-southern Apennines. Because of slab interference, low-velocity anomalies of different origins, either due to asthenospheric upwelling or slab fluids, coexist in nearby regions of the upper mantle. The lack of slab gaps between the Western Alps slab and the retreating Apenninic slab precludes potential toroidal flow around the northern tip of the Apenninic slab during slab rollback, with consequent activation of an asthenospheric counterflow and associated mantle upwelling to the west of the Alps. Beneath the Eastern Alps, the Alpine slab is torn and overturned by the NE-dipping Dinaric slab. The asthenospheric mantle beneath the Po Plain is confined by slabs and shows a prominent lowvelocity anomaly likely due to melting triggered by carbon-rich supercritical fluids generated above the Alpine slab. Toroidal flow may occur farther south around the Apenninic slab, in a region where the mantle flow is not affected by interaction between slabs. Similar complexities may characterize other plate-boundary zones where the interplay between opposite-dipping slabs is suggested by geophysical and geological data, such as Taiwan or the Hindu Kush -Pamir -Tianshan tectonic knot in Central Asia
Recent vegetation shifts in the French Alps with winners outnumbering losers
No full textInternational audienceQuantifying the impact of global change on biodiversity is a central focus of ecological research, essential for guiding policy decisions and conservation management strategies. Mountain ecosystems, recognized as early indicators of climate change impacts and centres of exceptional biodiversity, can provide critical insights into these biodiversity shifts. However, accurately assessing biodiversity changes remains challenging due to limitations in data quality, particularly regarding coverage over adequate temporal scales and fuzzy sampling strategies. Here, we analysed more than 11 million expert‐verified occurrence records of 4250 plant species from the French Alps collected over the past 30 years. Using a robust detection framework to statistically correct spatiotemporal biases, we quantified changes in species distributions, identifying winners (species expanding their range) and losers (species contracting their range). Our results indicate that approximately one‐third of alpine plant species have significantly expanded their distribution, while about 13% experienced range declines since the '90s. Although species responses did not strongly correlate with their floristic characteristics or IUCN status, expanding species were typically characterized by high colonization ability (ruderal), rapid growth (acquisitive strategies) and tolerance to higher temperatures (thermophilic). Despite a weak overall phylogenetic signal, winners or losers were disproportionately represented in some families and genera. Synthesis . This study advances our understanding of recent biodiversity changes in mountain ecosystems, laying the groundwork for identifying underlying drivers and supporting targeted future conservation initiatives.Quantifier l‘impact du changement climatique mondial sur la biodiversité est un objectif central de la recherche écologique et essentiel pour orienter les décisions politiques ainsi que les stratégies de gestion de la conservation. Les écosystèmes de montagne, reconnus comme des indicateurs précoces des impacts du changement climatique et accueillant une biodiversité exceptionnelle, peuvent fournir des informations cruciales sur les changements de biodiversité à venir. Cependant, évaluer avec précision ces changements reste difficile en raison des limites de la qualité des données, notamment en ce qui concerne la couverture sur des échelles temporelles adéquates et les stratégies d‘échantillonnage floues. Nous avons analysé ici plus de 11 millions de relevés vérifiés par des experts botaniques concernant 4250 espèces végétales des Alpes françaises, collectés au cours des 30 dernières années. À l‘aide d‘un cadre de détection robuste permettant de corriger statistiquement les biais spatio‐temporels, nous avons quantifié les changements dans la répartition des espèces, en identifiant les gagnantes (espèces qui étendent leur aire de répartition) et les perdantes (espèces qui réduisent leur aire de répartition). Nos résultats indiquent qu‘environ un tiers des espèces végétales alpines ont considérablement élargi leur aire de répartition, tandis qu‘environ 13 % ont connu un déclin depuis les années 1990. Bien que les réponses des espèces ne soient pas fortement corrélées à leurs caractéristiques floristiques ou à leur statut UICN, les espèces en expansion se caractérisent généralement par une forte capacité de colonisation (rudérales), une croissance rapide (stratégies acquisitives) et une tolérance aux températures élevées (thermophiles). Malgré un signal phylogénétique global faible, les espèces gagnantes ou perdantes étaient représentées de manière disproportionnée dans certaines familles et certains genres. Synthèse: Cette étude nous permet de mieux comprendre les changements récents en matière de biodiversité dans les écosystèmes montagneux, jetant ainsi les bases pour identifier les facteurs sous‐jacents et soutenir des initiatives de conservation ciblées à l‘avenir
Tuning the nature of iridium species supported on gadolinium-doped ceria for accelerating methane steam reforming
No full textInternational audienceSteam reforming of methane at 650 °C under water-deficient conditions was investigated over Ir/Ce0.9Gd0.1O2-x nanocatalysts (noted Ir/CGO hereafter) with very low Ir loading (0.1 wt.%). Our previous works have shown the promising performances of Ir/CGO for gradual internal reforming in solid-oxide fuel cells (SOFCs). However, it was observed that the high-temperature (900 °C) conditions of the catalyst pretreatment, as required by SOFC devices, lead to low initial catalytic activity when using a purely neutral gas feed, although a slow activation occurs on stream. Herein, we demonstrate that a pretreatment involving trace amount of O2 (10 ppm) maximizes the initial activity. In contrast, overoxidation appears detrimental. Systematic investigations by aberration-corrected transmission electron microscopies, X-ray photoelectron spectroscopy and synchrotron X-ray absorption spectroscopy at the Ir L3 edge, including operando XANES, allow us to explain the enhancement by identifying the key restructuring phenomena and active species. Whereas single Ir cations and metallic Ir nanoparticles are spectator species, oxidic Ir clusters exhibit high activity. Subtle changes in O2 concentration during the pretreatment dictate the initial nature of the Ir species as well as their evolution on stream through redox and clustering/redispersion phenomena. These results then suggest optimal conditions for the reforming process