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Rate-dependent tensile response of Polyvinyl Chloride geomembranes
No full textInternational audienceOne of the challenge that face the effectiveness of Polyvinyl Chloride geomembranes (PVC GMs) as a hydraulic barrier is the capacity to withstand unexpected mechanical actions, particularly tensile forces, during installation and throughout their lifespan. These forces pose risks of premature failure and impermeability degradation. In this study, the characterization of the short and long-term mechanical response of PVC GMs to uniaxial tensile forces has been investigated. Uniaxial tensile test have been performed for tensile rates spanning several orders of magnitude. Analysis of the true stress-strain curves reveals a significant decrease in tensile modulus, strength, and strain at failure at low strain rates, which are relatively close to those applied in situ. Long-term investigations have been conducted as well, through relaxation tests. Our key results unveil two distinct characteristic times in stress relaxation, with the fast relaxation occurring over the first four hours. During this phase, the pre-relaxation loading rate affects the relaxation behavior. Beyond this phase, the relaxation behavior becomes independent from the pre-relaxation loading rate. Burger's rheological model is proposed to measure the stress relaxation at different rates. The model's results validate the existence of two characteristic times.L'un des défis qui affectent l'efficacité des géomembranes en polychlorure de vinyle (PVC GMs) en tant que barrière hydraulique réside dans leur capacité à résister aux actions mécaniques imprévues, en particulier les forces de traction, lors de leur installation et tout au long de leur durée de vie. Ces forces posent des risques de défaillance prématurée et de dégradation de l'imperméabilité. Dans cette étude, la caractérisation de la réponse mécanique à court et à long terme des géomembranes en PVC sous l'effet de forces de traction uniaxiales a été étudiée. Des essais de traction uniaxiale ont été réalisés pour des vitesses de traction couvrant plusieurs ordres de grandeur.L'analyse des courbes de contrainte-déformation révèle une diminution significative du module de traction, de la résistance et de la déformation à la rupture à des vitesses de déformation faibles, proches de celles appliquées in situ. Des évaaluations à long terme ont également été menées à travers des essais de relaxation. Nos résultats clés mettent en évidence deux temps caractéristiques distincts dans la relaxation des contraintes, avec une relaxation rapide se produisant au cours des quatre premières heures. Pendant cette phase, la vitesse de chargement avant relaxation influence le comportement de relaxation. Au-delà de cette phase, le comportement de relaxation devient indépendant de la vitesse de chargement préalable. Le modèle rhéologique de Burger est proposé pour mesurer la relaxation des contraintes à différentes vitesses. Les résultats du modèle valident l'existence de deux temps caractéristique
Probing QCD Axions or Axion-like Particles in three-body Decays
No full textInternational audienceTwo-body decays like rank among the most constraining collider probes for new, low-mass, feebly interacting pseudoscalar particles . We explore an alternative class of kaon decay modes, specifically three-body decays to or . The former occur at tree level, while the latter is loop-suppressed yet accidentally finite. These modes specifically leverage the accurate tracking capabilities at LHCb. We present an estimation approach for the sensitivity achievable in future searches within these channels. Our argument uses the current uncertainty in leading irreducible backgrounds identified for each channel. Our findings suggest that dedicated searches could probe scales between and TeV, highlighting their strong potential. A direct comparison with actual searches, only available in the channel, supports this conclusion. Finally, we show that, in these searches, reconstruction efficiency maps are such that large efficiencies are naturally aligned with regions of higher yields in Dalitz plots
Impact of dust and temperature on primary productivity in Late Miocene oceans
No full textInternational audienceMost of the primary productivity in the ocean comes from phytoplankton, and is impacted, among other things, by the amount of nutrients available, as well as by temperature. The Late Miocene and Pliocene were marked by global aridification, linked to the emergence of the large deserts, likely increasing the input of dust and thus nutrients into the ocean. There was also a global decrease in temperature during this period, linked to a decline in atmospheric CO2 concentration. The objective of this study is to explore the sensitivity to dust and pCO2 levels on primary productivity in the oceans under Late Miocene boundary conditions. Here we used simulations performed with the coupled ocean-atmosphere model IPSL-CM5A2 and its marine biogeochemistry component PISCES and a Late Miocene paleogeography. Our results show that an increase in dust input produces a quasi-generalized increase in primary productivity, associated with a decrease in nutrient limitation. This increase in productivity also leads to nutrient deficits in some areas, such as coastlines and the Eastern Equatorial Pacific. The decrease in pCO2 levels and the associated lower water temperatures lead to a reduction in primary productivity. This decrease is mainly due to a reduction in the supply of nutrients resulting from less intense remineralization. In addition, our results show that change in carbon export resulting from change in dust input and temperature are highly heterogeneous spatially. Simulations combined with sedimentary data suggesting a link between aridification, cooling and the Biogenic Bloom of the Late Miocene and Pliocene
Galactic transient sources with the Cherenkov Telescope Array
No full textInternational audienceA wide variety of Galactic sources show transient emission at soft and hard X-ray energies: low-mass and high-mass X-ray binaries containing compact objects (e.g., novae, microquasars, transitional millisecond pulsars, supergiant fast X-ray transients), isolated neutron stars exhibiting extreme variability as magnetars as well as pulsar wind nebulae. Although most of them can show emission up to MeV and/or GeV energies, many have not yet been detected in the TeV domain by Imaging Atmospheric Cherenkov Telescopes. In this paper, we explore the feasibility of detecting new Galactic transients with the Cherenkov Telescope Array (CTA) and the prospects for studying them with Target of Opportunity observations. We show that CTA will likely detect new sources in the TeV regime, such as the massive microquasars in the Cygnus region, low-mass X-ray binaries with low-viewing angle, flaring emission from the Crab pulsar-wind nebula or other novae explosions, among others. We also discuss the multi-wavelength synergies with other instruments and large astronomical facilities
Bloch-Floquet band gaps for water waves over a periodic bottom
No full textInternational audienceA central object in the analysis of the water wave problem is the Dirichlet-Neumann operator. This paper is devoted to the study of its spectrum in the context of the water wave system linearized near equilibrium in a domain with a variable bottom, assumed to be a periodic function. We use the analyticity of the Dirichlet-Neumann operator with respect to the bottom variation and combine it with general properties of elliptic systems and spectral theory for self-adjoint operators to develop a Bloch-Floquet theory and describe the structure of its spectrum. We find that under some conditions on the bottom variations, the spectrum is composed of bands separated by gaps, with explicit formulas for their sizes and locations
Observation of exotic resonances in diffractive processes in proton-proton collisions
No full textInternational audienceThe first study of production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb. The data disfavour a nonresonant production but are consistent with a resonant model including several resonant states observed previously only in decays. The state is observed with a significance over and the is confirmed with a significance of more than
Euclid. I. Overview of the Euclid mission
No full textInternational audienceThe current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance
A multi-tagged SAR ocean image dataset identifying atmospheric boundary layer structure in winter tradewind conditions
No full textInternational audienceA dataset of multi-tagged sea surface roughness synthetic aperture radar (SAR) satellite images was established near Barbados from January to June 2016 to 2019. It is an advancement of the Sentinel-1 Wave Mode TenGeoP-SARwv (a labelled SAR imagery dataset of 10 geophysical phenomena from Sentinel-1 wave mode) dataset that targets SAR marine atmospheric boundary layer (MABL) coherent structures. Twelve tags define roll vortices, convective cells, mixed rolls and convective cells, fronts, rain cells, cold pools and low winds. Examples are provided for each signature. The final dataset is comprised of 2100 Sentinel-1 wave mode SAR images acquired at 36 incidence angle over an 8° × 8°region centered at 51° W, 15° N. Each image is tagged with one or multiple phenomena by five experts. This strategy extends the TenGeoP-SARwv by identifying coexisting phenomena within a single SAR image and by the addition of mixed roll/cell states and cold pools. The dataset includes PNG-formatted SAR image files along with two text files containing the file name, the central latitude/longitude, expert tags for each image, and all dataset metadata. There is a high degree of consensus among expert tags. The dataset complements existing hand-labelled ocean SAR image datasets and offers the potential for new deep-learning SAR image classification model developments. Future use is also expected to yield new insights into the tradewind MABL processes such as structure transitions and their relation to the stratification
Probing the general axion-nucleon interaction in water Cherenkov experiments
No full textInternational audienceWe consider an axion flux on Earth consistent with emission from the Supernova explosion SN 1987A. Using Chiral Perturbation Theory augmented with an axion, we calculate the energy spectrum of as well as , where denotes a nucleon in a water tank, such as the one planned for the Hyper-Kamiokande neutrino detection facility. Our calculations assume the most general axion-quark interactions, with couplings constrained either solely by experimental data, or by specific theory scenarios. We find that even for the QCD axion -- whose interaction strength with matter is at its weakest as compared with axion-like particles -- the expected Čherenkov-light spectrum from neutrino-nucleon interactions is modified in a potentially detectable way. Furthermore, detectability appears significantly more promising for the final state, as its spectrum peaks an order of magnitude higher and at energies twice as large compared to the counterpart. Given the rarity of SN events where both the neutrino and the hypothetical axion burst are detectable, we emphasize the importance of identifying additional mechanisms that could enhance such signals
Cognitive flexibility in autism: How task predictability and sex influence performances
No full textInternational audienceAbstract While cognitive flexibility challenges are frequently reported in autistic individuals, inconsistencies in the findings prompt further investigation into the factors influencing this flexibility. We suggest that unique aspects of the predictive brain in autistic individuals might contribute to these challenges, potentially varying by sex. Our study aimed to test these hypotheses by examining cognitive flexibility under different predictability conditions in a sample including a similar number of males and females. We conducted an online study with 263 adults (127 with an autism diagnosis), where participants completed a flexibility task under varying levels of predictability (unpredictable, moderately predictable, and predictable). Our results indicate that as task predictability increases, performance improves; however, the response time gap between autistic and non‐autistic individuals also widens. Moreover, we observe significant differences between autistic males and females, which differ from non‐autistic individuals, highlighting the need to consider sex differences in research related to the cognition of autistic individuals. Overall, our findings contribute to a better understanding of cognitive flexibility and sex differences in autism in light of predictive brain theories and suggest avenues for further research