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Resonant Infrasonic Disturbances in Total-Electron-Content During a Severe Thunderstorm on 23 October 2021
No full textInternational audienceDeep convective clouds and lightning activity during thunderstorms imprint Infrasonic ({ >} 3 mili Hertz) oscillations in the ionospheric density or Traveling Ionospheric Disturbances (TIDs). The wave characteristics of these oscillations and the coupling mechanisms remain a subject of investigation, noting that the coupling energetics may alter the spectral and propagation characteristics. Moreover, the availability of numerous convective dynamics time scales makes the oscillation detection time uncertain. To study these aspects, the present work examines the spatial-temporal lightning flash rate during a severe thunderstorm (cloud top temperature {< } ‑80°C) from the GOES16 infrared channel and the total electron content of the ionosphere from the GNSS network over the tropical Southern Hemisphere. The study finds TIDs amplification above the deep convective clouds. The strongest amplification occurs at the earliest, at 9 min, from the most intense lightning flash rate and propagates at the most probable speed of 400–1,100 m/s. In contrast to the spectral peak of the active storm, which is 1.2 mHz, the spectral peak of TIDs is 4.8 mHz. The results highlight the magnitude of coupling energetics to determine the wave propagation characteristics of infrasonic TIDs
Shear Strain Evolution Spanning the 2020 Mw6.8 Elazığ and 2023 Mw7.8/Mw7.6 Kahramanmaraş Earthquake Sequence Along the East Anatolian Fault Zone
No full textInternational audienceShallow creep along strike-slip faults is essential in releasing strain during earthquake cycles. However, its origin—whether inherent or triggered by earthquakes—remains debated. Using Interferometric Synthetic Aperture Radar phase-gradient data, we map shear-strain rates along the East Anatolian Fault Zone (EAFZ) before and after the 2020 Mw6.8 Elazığ and 2023 Mw7.8/Mw7.6 Kahramanmaraş earthquakes. The observed strain-rate distributions strongly correlate with coseismic slips in the EAFZ. The stress-driven afterslip model constrained by the phase-gradient time series reproduces distinct decaying patterns of newly activated creeping segments, showing that rapid afterslip may decay slowly and keep slipping for decades. Our results reveal that large earthquakes can accelerate, expand, and trigger shallow fault creep, highlighting the roles of fault frictional properties and stress changes caused by nearby earthquakes. These findings provide new insights into fault creep mechanisms and their linkage to large earthquakes, with implications for faulting behaviors
Introduction - Les territoires périphériques et ultrapériphériques face aux crises majeures
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Uncovering the xenon isotope composition of continental rift magmas: Insight from analysis of geothermal gases at Homa Hills, Kenya
No full textInternational audienceWe investigated geothermal gases from Homa Hills, a carbonatitic complex situated along an adjacent branch of the Kenyan rift system, using neon, argon, krypton, xenon and nitrogen isotopes. Large quantities of gas were sampled in Giggenbach-type bottles (Giggenbach, 1975) and analyzed by dynamic mass spectrometry to resolve isotopic variations at high precision (0.01-0.1‰; Seltzer and Bekaert, 2022; Bekaert et al., 2023; 2024). Neon and nitrogen isotope compositions are consistent with parental magmas being derived from the convecting mantle. Xenon isotopic data present ubiquitous enrichments (relative to air) of 129Xe from the decay of extinct 129I (T1/2 = 15.7 Myr) and 131-136Xef from fissions of 238U (T1/2 = 4.468 Myr) and/or 244Pu (T1/2 = 82 Myr). We also find slight excesses of 128Xe (relative to 130Xe and air), which could be due to subsurface isotopic fractionation during e.g., diffusive transport fractionation (DTF) and gravitational settling. However, the 128Xe excesses are not accompanied by correlated Kr isotope excesses and plot off the empirical fractionation line defined from several other locations worldwide (Bekaert et al., 2023). Instead, a detailed isotope deconvolution suggests the occurrence of either chondritic Xe (with mantle 130Xe consisting of up to 22 % of chondritic 130Xe) or recycled Xe from the Archean atmosphere could explain the observed Xe isotope signatures. The latter possibility would have profound implications for models of mantle-surface exchange throughout Earth history. The fission spectra indicate a predominantly 238U origin for fissiogenic Xe, with contribution of 244Pu-derived Xe being negligible within uncertainties, implying extensive mantle degassing during the Hadean and Archean eons. The 129Xe*/136Xe* ratio (where * indicates non-atmospheric excesses of Xe isotopes) of Homa Hills samples correlates with other tracers of mantle/crust contributions such as He, Ar and N isotopes. Variations in 129Xe*/136Xe* among the different gases sampled at Homa Hills is mainly the result of contribution from fissiogenic Xe produced in uranium-rich crustal material. Therefore, this ratio may constitute a robust tracer of mantle-crust interactions. Given available high precision data (Bekaert et al., 2023; 2024; this work) together with mantle-derived rock data, 129Xe*/136Xe* appears homogenous in the convecting mantle, and comparable to values observed at mantle plumes. Such homogeneity is in sharp contrast with light noble gas systematics and may call for whole mantle convection and a core origin for He and Ne.
Equilibrium Distance From Long-Range Dune Interactions
No full textInternational audienceFlow perturbations induced by dune topography affect sediment transport locally but can also be felt over long distances, altering the dynamics of isolated neighbouring dunes downstream. In order to work under optimal conditions that eliminate transverse flow components, collisions, and mass exchange between dunes, we study here these long-range interactions using a 2D numerical model where two equal-sized dunes lying on a non-erodible bed are exposed to a symmetric reversing flow. Depending on the initial spacing, dunes either attract or repel each other to eventually converge towards a steady-state spacing. This equilibrium distance decreases with flow strength and increases with the period of flow reorientation and dune size. It is mainly controlled by the reversing dune shape and the structure of the turbulent wake it generates, which continuously modulates the mean shear stress on the downstream dune. Under multi-directional wind regimes, these long-range flow perturbations offer an alternative mechanism for wavelength selection in linear dune fields with non-erodible interdune areas. Within these dune fields, estimates of mean shear stress could be used to assess the relative migration rate and the state of attraction or repulsion between neighbouring dunes
Editorial Note: Strategic engineering and functional mechanism elucidation of advanced materials in adsorption and catalysis for detoxification of contaminated water matrices
No full textInternational audienceUncontrolled anthropogenic activities have contaminated water resources with emerging contaminants such as pharmaceuticals, pesticides, microplastics, per- and poly-fluoroalkyl substances (PFAS), and heavy metals, making them unsuitable for living ecosystems. Emerging contaminants pose a severe threat to ecosystems. Hence water treatment methods through improved efficiencies are essential for removing these contaminants at ease of application and at low energy. However, further developments and insights are needed to improve selectivity and efficiency by specifically tuning the materials used in these processes. Advances in material chemistry have created research interest and opportunities to manage water matrices effectively. Novel materials like MXene, Metal-Organic Frameworks (MOFs), Covalent Organic Frameworks (COFs), Graphene, and Engineered Heteroatom biochars are being developed to remediate these contaminants. Material scientists currently focus on synthesizing novel materials for adsorption and catalytic applications. Still, there is a decreasing trend among the scientific community to discuss the chemistry behind these modifications in detail. To encourage the scientific community to focus on design and modification aspects, the special issue aims to focus on an in-depth analysis of novel material modification using advanced computational approaches and spectroscopic studies and applying the designed materials in emerging contaminant removal
Nanoparticules d'or stabilisées par des polyoxotungstates : comment passer d'une suspension aqueuse à CH3CN ?
No full textInternational audienceThe present study aims to evaluate available methods for preparing suspensions of gold nanoparticles stabilized by polyoxometalates (POMs@AuNPs) in CH3CN, a solvent commonly used in oxidation reactions. POMs@AuNPs are successfully synthesized in CH3CN using three different approaches: i) in situ generation of nanoparticles via chemical reduction of the HAuCl4 precursor with various reducing agents in CH3CN in the presence of POMs; ii) formation of POMs@AuNPs by reducing HAuCl4 with NaBH4 in the presence of [PW11O39]7− or [AsW9O33]9− in aqueous solution, followed by transfer into CH3CN after centrifugation; and iii) transfer of aqueous suspensions of Au0 nanoparticles, obtained by reducing HAuCl4 with NaBH4 and subsequent centrifugation, into CH3CN, followed by the addition of soluble organic salts of [PW12O40]3− or [AsW9O33{PO(CH2)2CO2H}2]5−. These strategies, inspired by literature, are used to assess their strengths and limitations regarding translation to CH3CN. The resulting suspensions are characterized by UV-Vis spectroscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy analysis, dynamic light scattering, and zeta potential measurements. The most stable suspensions are obtained by transferring an aqueous suspension initially stabilized with a mixture of citrate ions and tannic acid into acetonitrile. Subsequent exchange with polyoxometalates in CH3CN results in negligible changes in nanoparticle size or suspension stability
Quantifying the impacts of exogenous dust inputs to the critical zone using reactive transport modeling
No full textInternational audienceIn upland watersheds, depletion of essential nutrients due to physical erosion and chemical weathering can be compensated by exogenous inputs such as aeolian dust deposition. However, it remains an outstanding challenge to describe the impacts of dust on the reaction rates that produce weathering profiles and how this cascades into ecosystem function and water chemistry. As increasingly intense and episodic periods of drought and aridity are promoted by a warming climate, the role of dust production and deposition in Critical Zone structure and function requires improved modeling techniques to facilitate rigorous quantification and prediction. Here we present a newly developed process-based reactive transport framework by modifying the open-source CrunchTope software in order to quantitatively interpret the impacts of dust deposition and solubilization in stream water chemistry, regolith weathering rates, and ecosystem nutrient availability. We describe two simulations: (1) a generic model demonstrating a simplified system in which bedrock uplift and soil erosion occur in tandem with solid phase dust deposition at the land surface; (2) a case study based on a small (0.54 km2) upland Mediterranean watershed located on Mont Loz & egrave;re in the National Park of Les C & eacute;vennes, France. In the absence of an exogenous dust input, long-term field observations of calcium in stream water, rain, soil, and plant samples cannot be produced by reactive transport simulations of the weathering profile. By adding a carbonate-bearing depositional input consistent with the composition of Saharan dust, both stream water chemistry and elemental mass-transfer coefficients in the soil profile better align with field observations, suggesting that dust has become a significant input to this field site in the last similar to 10 ka. Over this period, the deposition of exogenous carbonates has introduced far more calcium into the system than what could be supplied by the Ca-poor granitic bedrock. This highly soluble carbonate also limits the reactive potential of infiltrating precipitation, ultimately inhibiting chemical weathering rates and hence the component of elemental export fluxes derived from local bedrock
Formulation and Numerical Verification of a New Rheological Model for Creep Behavior of Tropical Wood Species Based on Modified Variable-Order Fractional Element
No full textInternational audienceThis paper aims to develop a rheological model with fewer parameters that accurately describes the primary and secondary creep behavior of wood materials. The models studied are grounded in Riemann–Liouville fractional calculus theory. A comparison was conducted between the constant-order fractional Zener model and the variable-order fractional Maxwell model, with four parameters each. Using experimental creep data from four-point bending tests on two tropical wood species, along with an optimization algorithm, the variable-order fractional model demonstrated greater effectiveness. The selected fractional derivative order, modeled as a linearly increasing function of time, helped to elucidate the internal mechanisms in the wood structure during creep tests. Analyzing the parameters of this order function enabled an interpretation of their physical meanings, showing a direct link to the material’s mechanical properties. The Sobol indices have demonstrated that the slope of this function is the most influential factor in determining the model’s behavior. Furthermore, to enhance descriptive performance, this model was adjusted by incorporating stress non-linearity to account for the effects of the variation in constant loading level in wood. Consequently, this new formulation of rheological models, based on variable-order fractional derivatives, not only allows for a satisfactory simulation of the primary and secondary creep of wood but also provides deeper insights into the mechanisms driving the viscoelastic behavior of this material
Assessing the threat of Yersinia pestis harboring a multi-resistant IncC plasmid and the efficacy of an antibiotic targeting LpxC
No full textInternational audienceSelf-transmissible IncC plasmids rapidly spread multidrug resistance in many medically important pathogens worldwide. A large plasmid of this type (pIP1202, ~80 Kb) has been isolated in a clinical isolate of Yersinia pestis , the agent of plague. Here, we report that pIP1202 was highly stable in Y. pestis- infected mice and fleas and did not reduce Y. pestis virulence in these animals. Although pIP1202 inflicted a fitness cost in fleas (but not in mice) when the insects fed on blood containing a mixture of plasmid-free and plasmid-bearing strains, such a co-infection scenario has never been reported in nature, indicating that pIP1202 could persist in Y. pestis strains. Despite being resistant to commonly used antibiotic treatments, we show that plague caused by Y. pestis harboring the pIP1202 plasmid is effectively cured by LPC-233—a potent inhibitor of the essential LpxC enzyme in the lipid A biosynthetic pathway. Taken as a whole, our data highlight the alarming threat posed by Y. pestis harboring multidrug-resistant IncC plasmids that may persist in wild animals as a reservoir for long periods without antibiotic pressure and illuminate the impact of antibiotics with a novel mode of action against such a biothreat