HAL-Polytechnique
Not a member yet
51406 research outputs found
Sort by
Toward characterization of organic matter rich in aromatic compounds by spectral-induced polarization: preliminary investigation and perspectives
No full textInternational audienceSpectral induced polarization (SIP) has been suggested as a non-invasive and cost-effective tool to detect and monitor aromatic rich organic matter such as biochar. In our study, we show that SIP can track biochar concentration up to 10 per cent (wt.) in a soil with a clay content of 20 per cent. Assessment of changes in the concentration of biochar was conducted according to double Pelton parameters and the maximal phase determined at 11.7 Hz, a frequency at which a polarization peak is observed in the presence of biochar. All SIP-derived parameters were correlated with the biochar content, with the exception of the relaxation time of the polarization peak occurring at 11.7 Hz, which was related to soil water saturation in previous investigations. Among studied parameters, the phase value that we measured at 11.7 Hz may therefore consist in a simple and reliable methodology to evaluate the biochar content on SIP in our experiment. Several steps are still necessary before a widespread field application notably by considering how modifications in the chemistry of biochar with time can interact with biochar concentration and water saturation to modify polarization processes shaping SIP curves. Beyond the scope of tracking changes in the content of highly aromatic OM—such as biochar—in soils, this study suggests that the degree of aromaticity of OM can play a key role in the SIP response paving the way for wider use of SIP in soil science
Cross sections of mesons in collisions at forward rapidity at GeV and central rapidity at GeV
No full textInternational audienceWe present the first measurements of the forward and midrapidity -meson cross sections from collisions at and ~GeV, respectively. We also report the midrapidity ratio at 510 GeV. The forward cross section is measured differentially in -meson transverse momentum () from 1.0 to 6.5~GeV/ for pseudorapidity . The midrapidity cross section is measured from 3.5 to 44 GeV/ for pseudorapidity . Both cross sections serve as critical inputs to an updated global analysis of the -meson fragmentation functions
Refining the modeling strategy for anomalous electron transport in fluid simulations of Hall thrusters via insights from PIC simulations
No full textInternational audienceModeling anomalous transport in fluid simulations is a fundamental challenge for developing efficient and robust fluid simulation tools for Hall thrusters. This paper investigates optimal strategies for modeling anomalous transport in such simulations. Using the particle-in-cell (PIC) benchmark (BM) setup of Charoy et al., we demonstrate that various terms in the electron momentum equation can be readily identified. In particular, we show that the assumption of expressing the rate of change of the electron momentum due to instability as proportional to the momentum itself does not hold under these simulation conditions. Subsequently, we present two fluid simulations that replicate the conditions of the PIC BM setup. The first employs the conventional empirical anomalous collision frequency approach. While this model provides generally satisfactory results, it fails to capture specific plasma characteristics. The second fluid model adopts a data-driven approach to represent the anomalous force terms in the momentum equation. This approach furnishes significantly improved results, suggesting that although the anomalous collisionality framework provides meaningful outcomes, it can be effectively replaced by more advanced techniques
Diurnal Cycle of Non‐Orographic Gravity Waves' Source Altitudes and Its Impacts: Tests With Mars Planetary Climate Model
No full textInternational audienceThe transfer of momentum due to non‐orographic Gravity Waves (GWs) significantly regulates the Martian middle‐upper atmospheric dynamics. Thus, these waves influence the transport of tracers and escape in the thermosphere. However, models assume that the non‐orographic GWs are emitted from a constant source level that approximates the averaged Planetary Boundary Layer (PBL). We move on to impose that the emission of the waves follows the top of a real‐time evaluated PBL to account for the diurnal cycle of the waves' source altitudes and implement this improvement in the Mars Planetary Climate Model (Mars PCM). In the absence of the PBL during the night, the non‐orographic GWs are assumed to be launched at altitudes near the surface following Hinson and Wilson (2023, https://doi.org/10.1016/j.icarus.2022.115420 )'s results. Sensitivity tests with the Mars PCM show that non‐orographic GWs are built up efficiently during the (polar) night. With the new scheme, the angular momentum in the upper atmosphere is enhanced. Additionally, simulations recover the “cold pockets” in temperature observed by the Mars Climate Sounder at 80–100 km and capture “deep drops” of the atmospheric species recorded by the Neutral Gas and Ion Mass Spectrometer in the polar night.Le transfert de moment dû aux ondes de gravité non orographiques (OGs) régule de manière significative la dynamique de l'atmosphère moyenne et supérieure de Mars. Ces ondes influencent ainsi le transport des traceurs et l’échappement atmosphérique dans la thermosphère. Toutefois, les modèles supposent généralement que les OGs non orographiques sont émises depuis un niveau source constant représentant une moyenne de la couche limite planétaire (PBL). Nous proposons ici de faire évoluer ce schéma en imposant que l’émission des ondes suive le sommet d’une PBL évaluée en temps réel, afin de prendre en compte le cycle diurne des altitudes sources des ondes, et implémentons cette amélioration dans le Modèle Climatique Planétaire de Mars (Mars PCM). En l’absence de PBL durant la nuit, les OGs non orographiques sont supposées être émises à des altitudes proches de la surface, conformément aux résultats de Hinson et Wilson (2023, https://doi.org/10.1016/j.icarus.2022.115420). Des tests de sensibilité avec le Mars PCM montrent que les OGs non orographiques se développent efficacement pendant la nuit (polaire). Avec ce nouveau schéma, le moment angulaire dans la haute atmosphère est renforcé. De plus, les simulations reproduisent les « poches froides » observées par le Mars Climate Sounder à 80–100 km, ainsi que les « chutes profondes » des espèces atmosphériques enregistrées par le Neutral Gas and Ion Mass Spectrometer durant la nuit polaire
Marine snow morphology drives sinking and attenuation in the ocean interior
No full textInternational audienceSimultaneous measurements of marine snow (particles larger than 600 µm) morphologies, estimates of their in situ sinking speeds, and midwater attenuation in export plumes were performed for the first time using a biogeochemical (BGC)-Argo float equipped with optical and imaging sensors. The float was deployed and recovered after drifting for 1 year in the sluggish-flow regime of the Angola Basin. Six consecutive chlorophyll a and particulate matter accumulation events were recorded at the surface, each followed by an export plume of sinking aggregates. Objects larger than 600 µm were classified using machine learning recognition and clustered into four morphological categories of marine aggregates. Plankton images were validated by an expert in a few broad categories. Results show that different types of aggregates were produced and exported from the different blooms. The different morphological categories of marine snow had different sinking speeds and attenuation for a similar size, indicating the effect of morphology on sinking speed. However, a typical size-to-sinking relationship for two of the categories and over the larger observed size range (100 µm to a few millimeters) was also observed, indicating the importance of size for sinking. Surprisingly, in situ-calculated sinking speeds were constantly in the lower range of known values usually assessed ex situ, suggesting a methodological effect, which is discussed. Moving away from purely size-based velocity relationships and incorporating these additional morphological aggregate properties will help to improve the mechanistic understanding of particle sinking and provide more accurate flux estimates. When used from autonomous platforms at high frequency, they will also provide increased spatio-temporal resolution for the observation of intermittent export events naturally occurring or induced by human activities
The Yukawa potential of a non-homogeneous sphere, with new limits on an ultralight boson
No full textInternational audienceExtremely weak long-range forces may lead to apparent violations of the Equivalence Principle. The final MICROSCOPE result, leading at 95 % c.l. to or for a positive or negative Eötvös parameter , requires taking into account the spin of the mediator, and the sign of ( denoting the new charge involved). A coupling to or should verify or , for a spin-1 mediator of mass eV, with slightly different limits of or in the spin-0 case. The limits increase with , in a way which depends on the density distribution within the Earth. This involves an hyperbolic form factor, expressed through a bilateral Laplace transform as , related by analytic continuation to the Earth form factor . It may be expressed as , where is an effective density, decreasing from the average at down to the density at the periphery. We give general integral or multishell expressions of , evaluating it, and , in a simplified 5-shell model. may be expanded as , absolutely convergent for all and potentially useful up to . The coupling limits increase at large like ( being the satellite altitude), getting multiplied by , or , for or eV, respectively
Pre-flight performance of the ion energy mass spectrum analyzer for the Martian Moons eXploration (MMX) mission
No full textInternational audienceAbstract An ion energy mass spectrum analyzer was developed for the Martian Moons eXploration (MMX) mission to measure the three-dimensional velocity distribution function and mass profile of low-energy ions around the Mars-Moon system. The hemispheric field-of-view (FOV) is acquired by a pair of angular scanning deflectors, and the energy/charge and mass/charge are determined for each ion by an electrostatic analyzer and a linear-electric-field (LEF) time-of-flight (TOF) analyzer, respectively, with an enhanced mass resolution of m / Δ m ∼ 100 . The ion analyzer, together with magnetometers, constitutes the mass spectrum analyzer (MSA), one of the scientific instruments on board the MMX spacecraft. This paper describes the instrumentation of the ion analyzer, and results of the performance tests of its flight model (FM)
Eyring theory for plasticity in amorphous polymers violates Curie's principle
No full textInternational audienc
Holistic approach and Advanced Color Singlet Identification for physics measurements at high energy frontier
No full textInternational audienceTo enhance the discovery power of high-energy colliders, we propose a holistic approach and Advanced Color Singlet Identification (ACSI), both of which utilize inclusive reconstructed information as input. The holistic approach is designed to simultaneously classify physics events, while ACSI focuses on associating final-state particles with their parent massive bosons. Implemented using state-of-the-art artificial intelligence architectures and applied to benchmark analyses with simulated data from a future Higgs factory, these new concepts significantly improve the accuracy of H->bb/cc/ss/gg measurements by up to a factor of two to six
Statistical properties of beam-driven upper-hybrid wave turbulence in the solar wind
No full textInternational audienceWe studied the statistical properties of beam-driven upper-hybrid wave turbulence in the solar wind by focusing on the probability density functions (PDFs) of electric field amplitudes, |E|. We used, for the first time, high-resolution and long-term 2D particle-in-cell simulations of the interaction of an electron beam with a magnetized plasma to calculate and analyse the skewness (degree of anisotropy) and the kurtosis (degree of flatness) of the PDFs of |E| and log|E|2 for various intensities of plasma magnetization (Ω = ωc/ωp) and average levels of random density fluctuations (ΔN). Using the Pearson classification, we show that the PDFs of log|E|2 predominantly align with Type VI Pearson distributions, with a shift towards Type I at high plasma magnetizations. In contrast, the PDFs of |E| are Type I Pearson distributions regardless of the Ω and ΔN values. Comparisons between simulation results and observations by the Solar Orbiter’s Time Domain Sampler instrument show a good agreement. This study also offers a promising method for understanding the dynamics of wave turbulence and indirectly estimating plasma magnetization