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Cool-flame chemistry of the representative bio-hybrid fuel 1,3-dioxane
No full textInternational audienceThe low-temperature oxidation of 1,3-dioxane was systematically investigated in two atmospheric pressure jetstirred reactors (JSRs) at temperatures ranging from 450 to 850 K and equivalence ratios ranging from 0.25 to 0.5. A suite of oxidation intermediates, including carbonyl compounds, conjugated olefins, cyclic ethers, and reactive hydroperoxides, were identified and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC). The experiments reveal strong low-temperature reactivity and a pronounced negative temperature coefficient (NTC) behavior, that had not previously been reported for 1,3-dioxane to such an extent. A detailed kinetic model was developed to interpret the observed phenomena. Rate constants for hydrogen abstraction reactions by OH radicals, identified as the dominant fuel consumption pathways, are calculated using ab initio methods. The model also incorporates theoretically derived rate constants from the literature for key beta-scission ring-opening reactions and first-stage oxygen addition pathways of three 1,3-dioxanyl radicals. These inclusions improve the model's predictive capability and highlight the complex cool-flame chemistry associated with 1,3-dioxane. Model validation against experimental datasets from this study and literature-including JSR oxidation, flow reactor pyrolysis and oxidation, and ignition delay time (IDT) measurements-demonstrates good agreement. Mechanistic insights reveal that the ether group in the 1,3-dioxane ring facilitates hydrogen abstraction at the ortho positions (e.g., methylene bridge and ortho-CH2-) while suppressing abstraction at meta sites. These structural effects also influence intramolecular hydrogen shifts in ROO and OOQOOH radicals. Additionally, the presence of ring oxygen atoms weakens radical stabilization through inductive effects, promoting ring-opening reactions of R and QOOH species. Collectively, these factors contribute to the observed NTC behavior and the unique cool-flame characteristics of 1,3-dioxane
Spatial variability in nutrient and organic matter concentrations during hydrological fragmentation of an intermittent temperate catchment
No full textThis research was funded by the AQUA division of the Institut national de recherche pour l’agriculture, l’alimentation et l’environnement (INRAE), the Brittany region, and the Observatoire des sciences de l’environnement de Rennes (OSERen).International audienceIntermittent and ephemeral streams are watercourses that cease to flow and/or dry up during part of the year. Their seasonal drying is sometimes preceded by a stream fragmentation phase with formation of isolated pools where the biogeochemistry differs from that of perennial reaches. Our objective was to analyse how hydrological fragmentation alters the spatial variability in dissolved nutrient and organic matter concentrations in a temperate-oceanic and agriculture-impacted headwater stream, where nutrient loadings are high. We conducted repeated synoptic sampling campaigns at high spatial resolution (150–200 m) along the stream network of the Naizin catchment (7 km2) during the spring–summer-fall of 2023. We sampled 38 sites and analysed dissolved organic carbon (DOC) concentrations and fluorescence properties, dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) concentrations, during four sampling campaigns: stream recession, early and late fragmentation and reconnection. Our results showed an increase in the spatial variability of concentrations, with monotonic longitudinal gradients along the stream disappearing during hydrological fragmentation. Both DOC and SRP concentrations were higher in isolated pools than in flowing reaches, while DIN concentration was lower. The chemical composition of DIN and DOC also changed with stream fragmentation, with increasing proportions of nitrite and ammonium in DIN and humic-like organic matter in DOC. These results suggest that the main controlling processes in the isolated pools were streambed mobilisation of SRP and DOC, along with denitrification under anoxic conditions. We expect the observed spatio-temporal patterns in nutrient and DOC concentrations to become more widespread in the future as intermittent streams will become more frequent owing to climate change
Robust Detection of Synthetic Tabular Data under Schema Variability
No full textInternational audienceThe rise of powerful generative models has sparked concerns over data authenticity. While detection methods have been extensively developed for images and text, the case of tabular data, despite its ubiquity, has been largely overlooked. Yet, detecting synthetic tabular data is especially challenging due to its heterogeneous structure and unseen formats at test time. We address the underexplored task of detecting synthetic tabular data "in the wild'', i.e. when the detector is deployed on tables with variable and previously unseen schemas. We introduce a novel datum-wise transformer architecture that significantly outperforms the only previously published baseline, improving both AUC and accuracy by 7 points. By incorporating a table-adaptation component, our model gains an additional 7 accuracy points, demonstrating enhanced robustness. This work provides the first strong evidence that detecting synthetic tabular data in real-world conditions is feasible, and demonstrates substantial improvements over previous approaches. Following acceptance of the paper, we are finalizing the administrative and licensing procedures necessary for releasing the source code. This extended version will be updated as soon as the release is complete
Magneto-Optical Readout of a Chiral Single-Molecule Magnet at Telecom Wavelengths
No full textInternational audienceIn this work, the wavelength range of magneto-chiral dichroism (MChD) based optical readout of magnetic hysteresis is extended to the near-infrared (NIR) telecom communication range where optical fibers have the smallest transmission loss. To achieve this goal, we have prepared and investigated a new air-stable chiral single-molecule magnet (SMM) formulated as (S)- and (R)-[Dy(bbppn)Cl] (bbppn = N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-pyridylmethyl)-X-1,2-propanediamine, X = S, R). We demonstrate that the magnetic hysteresis of this SMM, despite exhibiting rapid quantum tunneling of magnetization (QTM) at zero field, can be optically detected using unpolarized light through MChD. Complementary to our seminal study limited to the visible spectral range, we demonstrate that the MChD-based readout is also effective for the Dy(III) f-f transitions in the NIR region, confirming the robustness of this method across a broader spectral window. These findings establish MChD as a generalizable optical readout method for molecular magnetic materials, reinforcing its potential for future applications in polarization-free optical data readout technologies and optical communication at telecom wavelengths
"Multi-scale climate analysis of two coastal wine terroirs in Uruguay: Adapting to climate change and heatwaves"
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« Politique, idéologie, morale : quels héritages contemporains de la pensée du roman de Kundera ? »
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Cartographic tools for evaluating land cover transitions: implications for landscape management and almond diversity conservation
No full textInternational audienceOver the past four decades, rapid urbanization has profoundly affected the sustainability of urban and peri-urban agriculture (UPA) as well as the diversity of native fruit tree ecotypes. Despite the ecological and agricultural importance of Tunisia’s coastal regions, few studies have addressed the impacts of urbanization on local fruit tree diversity and orchard dynamics. To fill this gap, the present study employs remote sensing to map and quantify the evolution of urban expansion and the degradation of almond orchards between 1980 and 2023. In addition, field surveys were conducted to complement the spatial analysis and to assess the economic, social, and ecological importance of UPA, here defined as all agricultural activities carried out within and around urban areas. These surveys also provided insights into the effects of urbanization on almond cultivation. Cartographic analyses reveal a marked transformation of the landscape under the pressure of urbanization. In Kalâa Kebira, tree crops decreased from 3,234.2 ha in 1980, with a loss of 621 ha by 2023, while urban areas expanded from 145 ha to 1,307.2 ha. In Bouficha, almond and olive plantations declined by 29.4% between 1980 and 2012 (from 11,927.32 ha to 8,420.9 ha), before recovering to 10,666.19 ha by 2023, despite urbanization reaching 1,130.69 ha. This regeneration can be attributed to the central economic role of agriculture (accounting for 80% of local income), government-supported irrigation projects, and the engagement of a new generation of farmers. Field surveys highlight the high genetic diversity and good conservation status of native almond ecotypes in the Kalâa Kebira region, reflecting traditional management practices that safeguard local genetic resources. This diversity represents an asset for adapting to climatic constraints, particularly drought. Conversely, in Bouficha, the expansion of orchards through the introduction of selected or imported almond varieties has led to a reduction in local genetic variability. This process has intensified genetic erosion, already exacerbated by rapid urbanization and recurrent droughts, threatening the resilience of these agroecosystems. These findings underscore the urgent need for concrete sustainable management policies for fruit trees particularly almonds to preserve this valuable native diversity. Recommended measures include ex situ conservation in gene banks, participatory selection, and in situ agroecological zoning. Furthermore, comprehensive analysis and the development of an in-situ conservation strategy are required. In the absence of such actions, this diversity risks being progressively replaced by uniform cultivars in the medium term and could disappear in the long term under drought stress, resulting in a significant loss of biodiversity at the national scale
Sortir de la grotte pour mieux y rentrer : à la recherche d’invariants
No full textInternational audienceBernard Lahire’s thinking is extremely motivating because it allows us to connect the social with the living, to identify “lines of force” and “laws” that permit the creation of a scientific language that transcends mere descriptions and protects us from general discourses too disconnected from reality. Is it possible to make a considerable leap forward in time and apply these ideas to periods without written records, about which we know practically nothing? This is a new path to explore, and we present here the first, undoubtedly still clumsy, strokes of the pruning knife.La pensée de Bernard Lahire est extrêmement motivante, car elle permet d’articuler le social avec le vivant, d’identifier des « lignes de force » et des « lois » qui autorisent la création d’un langage scientifique dépassant les simples descriptions et qui nous préserve des discours généraux trop déconnectés du réel. Est-il possible de faire un saut considérable dans le temps et de les appliquer à des époques sans trace écrite, dont nous ne connaissons pratiquement rien ? Voici un nouveau chemin à défricher, dont nous présentons ici les premiers coups de serpette, encore maladroits sans doute
The Greeks among the natives: Culture, ritual, and craftmanship in non-colonial spaces of the Southern Italy Iron Age
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Latitude affects continental acidity in the Smithian–Spathian boundary biotic crisis
No full textInternational audienceThe extent to which continental acidity during the Early Triassic varied with latitude remains insufficiently constrained, despite its relevance for understanding environmental stress and biotic recovery patterns across the Smithian–Spathian boundary (SSB). We examined the abundance, textures and compositions of strontium-rich hydrated aluminium phosphate–sulphate (APS) minerals in 179 continental samples spanning tropical to high paleolatitudes in both hemispheres. APS minerals display broadly comparable early-diagenetic features across sections, indicating formation shortly after deposition under acidic meteoric conditions. Their distribution suggests a latitudinal trend: APS contents commonly exceed 0.1 vol.% in equatorial western peri-Tethyan basins, where faunal and floral records are sparse during the SSB, whereas concentrations decrease towards higher latitudes and are rare beyond ∼40° in both hemispheres. This pattern does not appear to correlate with lithological or textural variability and may reflect spatial differences in the intensity or duration of acidification linked to Siberian Traps volcanism. Equatorial basins thus likely experienced more prolonged or recurrent acidic episodes, whereas higher-latitude areas may have been subject to comparatively attenuated effects, potentially contributing to earlier ecological recovery. These results provide a useful framework for evaluating continental acidification and its environmental implications during the interval following the end-Permian mass extinction (EPME)