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Electromagnetic phenomena associated with dust particle dynamics in a simulated Martian atmosphere: an experimental study
No full textInternational audienceElectromagnetic phenomena associated with dust particle collisions contribute to the local electrostatic processes within Martian dust storms, impacting surface interactions and posing potential risks to spacecraft and instruments. This study investigates the generation and characteristics of electromagnetic discharges under controlled laboratory conditions designed to approximate key aspects of the Martian atmosphere. Experiments were conducted in a vacuum chamber, replicating Martian atmospheric conditions with CO2 at low pressure. A 3D-printed dust chamber was used to create dust vortices with several materials including sand particles, and Martian regolith analogs of varying particle sizes. Electromagnetic signals generated during dust collisions were measured using the Dust Complex module developed for the ExoMars-2022 landing mission. Results of the laboratory experiments demonstrate distinct discharge characteristics across different materials, influenced by particle size, composition, and morphology. Signals exhibited variations in amplitude, frequency, and waveform, reflecting the complex interactions between dust particles in a CO2 environment under low-pressure conditions. Comparative analysis with prior studies under earth conditions highlights the role of the Martian atmosphere in enhancing charge transfer processes. These findings provide new insights into the electrostatic environment of Martian dust storms and contribute to understanding electromagnetic interference risks for future exploration missions
Prediction of temperature-dependent nucleation and growth in pure FeCr alloy via a self-consistent Phase Field approach
No full textInternational audienceIn a nucleation and growth process, the nucleation rate dictating the decomposition kinetics is generally modeled using the classical nucleation theory approach, which is only valid near the solubility limit where experiments are very difficult to perform. An alternative to this difficulty is to describe the exact dynamics associated with the decomposition from the metastable state to the stable state. This dynamics depends on the system under consideration and is complex to calculate. The approach presented in this work circumvents these two difficulties. The nucleation rate is calculated using only the knowledge of an effective Hamiltonian within a phase field approach. It then does not require the exact knowledge of the dynamics. The key point of this generic work is to show that only two time scales are sufficient to describe the complex interactions between the nucleation, growth, and coarsening processes. Comparing these scales makes it then possible to simulate microstructures by considering the nucleation process either as an initial condition or as a source term in the phase field equations. This approach is validated by the very good agreement between the simulated and measured 3D microstructures at different times on ultra-pure samples of FeCr, a textbook case of a nucleation-growth process
Automated event generation for S-wave quarkonium and leptonium production in NRQCD and NRQED
No full textInternational audienceWe present an extension of the MadGraph5_aMC@NLO framework that enables the automated calculation of leading-order cross sections for S-wave quarkonium and leptonium production within the non-relativistic QCD (NRQCD) and non-relativistic QED (NRQED) factorisation formalisms. The framework has been validated against a variety of benchmark processes, demonstrating robustness and flexibility for phenomenological studies. A key advantage of this implementation is its seamless integration with existing MadGraph5_aMC@NLO features, allowing computations not only within the Standard Model but also in a wide range of Beyond the Standard Model or Effective Field Theory scenarios via a modified Universal Feynman Output (UFO) interface. Furthermore, the framework maintains compatibility with standard Monte Carlo event generators for parton showering and hadronisation. Through numerous examples, we highlight that theoretical studies of quarkonium processes require careful consideration: the impact of subleading contributions is often difficult to predict using simple counting arguments based solely on the hierarchy of couplings and velocity-scaling rules
Reconstruct Anything Model: a lightweight foundation model for computational imaging
No full textInternational audienceMost existing learning-based methods for solving imaging inverse problems can be roughly divided into two classes: iterative algorithms, such as plug-and-play and diffusion methods leveraging pretrained denoisers, and unrolled architectures that are trained end-to-end for specific imaging problems. Iterative methods in the first class are computationally costly and often yield suboptimal reconstruction performance, whereas unrolled architectures are generally problem-specific and require expensive training. In this work, we propose a novel non-iterative, lightweight architecture that incorporates knowledge about the forward operator (acquisition physics and noise parameters) without relying on unrolling. Our model is trained to solve a wide range of inverse problems, such as deblurring, magnetic resonance imaging, computed tomography, inpainting, and super-resolution, and handles arbitrary image sizes and channels, such as grayscale, complex, and color data. The proposed model can be easily adapted to unseen inverse problems or datasets with a few fine-tuning steps (up to a few images) in a self-supervised way, without ground-truth references. Throughout a series of experiments, we demonstrate state-of-the-art performance from medical imaging to low-photon imaging and microscopy. Our code is available at https://github.com/matthieutrs/ram
Clustering analysis of medium-band selected high-redshift galaxies
No full textInternational audienceNext-generation large-scale structure spectroscopic surveys will probe cosmology at high redshifts , relying on abundant galaxy tracers such as Ly emitters (LAEs) and Lyman break galaxies (LBGs). Medium-band photometry has emerged as a potential technique for efficiently selecting these high-redshift galaxies. In this work, we present clustering analysis of medium-band selected galaxies at high redshift, utilizing photometric data from the Intermediate Band Imaging Survey (IBIS) and spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI). We interpret the clustering of such samples using both Halo Occupation Distribution (HOD) modeling and a perturbation theory description of large-scale structure. Our modeling indicates that the current target sample is composed from an overlapping mixture of LAEs and LBGs with emission lines. Despite differences in target selection, we find that the clustering properties are consistent with previous studies, with correlation lengths Mpc and a linear bias of . Finally, we discuss the simulation requirements implied by these measurements and demonstrate that the properties of the samples would make them excellent targets to enhance our understanding of the high- universe
Identification of low-energy kaons in the ProtoDUNE-SP detector
No full textInternational audienceThe Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment with a rich physics program that includes searches for the hypothetical phenomenon of proton decay. Utilizing liquid-argon time-projection chamber technology, DUNE is expected to achieve world-leading sensitivity in the proton decay channels that involve charged kaons in their final states. The first DUNE demonstrator, ProtoDUNE Single-Phase, was a 0.77 kt detector that operated from 2018 to 2020 at the CERN Neutrino Platform, exposed to a mixed hadron and electron test-beam with momenta ranging from 0.3 to 7 GeV/c. We present a selection of low-energy kaons among the secondary particles produced in hadronic reactions, using data from the 6 and 7 GeV/c beam runs. The selection efficiency is 1% and the sample purity 92%. The initial energies of the selected kaon candidates encompass the expected energy range of kaons originating from proton decay events in DUNE (below 200 MeV). In addition, we demonstrate the capability of this detector technology to discriminate between kaons and other particles such as protons and muons, and provide a comprehensive description of their energy loss in liquid argon, which shows good agreement with the simulation. These results pave the way for future proton decay searches at DUNE
Theoretical filters for shift-symmetric Horndeski gravities
No full textInternational audienceWe investigate the structure of nontrivial maximally symmetric vacua and compact-object solutions in shift-symmetric scalar-tensor theories. Focusing on Horndeski gravity, we derive consistency conditions directly from the field equations to identify the subclasses that admit Minkowski and de Sitter vacua with a nontrivial scalar field. In doing so, we obtain a filtering mechanism that operates independently of observational data. In this context, we introduce the notion of stealth vacua, where the scalar field remains active without altering the vacuum. Following this, we examine the theoretical framework of Horndeski theories that admit homogeneous geometries and we extract the implicit form of the solution pertaining to the entire family of theories. Building upon these frameworks, we construct exact solutions in beyond-Horndeski gravity by applying a linear disformal transformation to the regularized Einstein-Gauss-Bonnet black hole. This procedure yields solitonic spacetimes with scalar hair as well as black holes carrying primary scalar hair, demonstrating how disformal maps can qualitatively modify solution properties. We delineate the parameter space in which the transformation is well-defined and analyze the solutions. Our results provide both a principled criterion for selecting viable Horndeski models and a framework for exploring rich solution spaces in beyond-Horndeski gravity
Effect of current intensity and polarity on the electrical performances of slip ring contacts
No full textInternational audienceIn this investigation, the effect of current has been studied on sliding electrical contacts between bulk gold-alloy wires and gold-alloy plated rings. Two parameters have been examined: current intensity, and direction of current. For this purpose, a model slip ring has been used which includes 4 electrically independent groups of 4 rings. For each group, the electrical diagram requires the current to flow alternately from the wires to the ring (cathode ring) and from the ring to the wires (anode ring). The contact voltage has been measured with an equivalent 4-probes method, and the morphology of the worn surfaces has been observed by means of an optical microscope and a Scanning Electron Microscope (SEM); its composition has been characterized by Energy Dispersive X-ray spectroscopy (EDX). First, the results show that the current allows to reduce the contact voltage and the wear of surfaces. Secondly, the results show an influence of the polarity of the current: the anode rings present much higher contact voltage, and a greater loss of the gold-plating compared to the cathode rings. In this paper, the results obtained are presented and a hypothesis is proposed to explain the polarity effect on the contacts
Parameter influence analysis in a 3D TBM model via sensitivity analysis and GP metamodels
No full textInternational audienceUrban tunnel excavation with tunnel boring machines induces ground movements that can affect nearby structures. Three-dimensional finite element models (FEM) are widely used to predict these settlements, but their high computational cost limits direct exploration of parameter influence. This work presents a 3D FEM simulator of mechanized tunneling and a methodology to quantify the impact of both numerical and physical inputs on settlement predictions. First, an accuracy-cost model reduction study evaluates the effect of domain dimensions and mesh densities on a small number of scalar quantities of interest extracted from simulated settlement fields. Empirical error models are fitted and used to select a reduced configuration that balances accuracy and runtime. Second, Gaussian process models are trained on simulation data from the reduced configuration and validated using exact leave-one-out cross-validation. These metamodels enable the computation of Sobol’ sensitivity indices with quantified uncertainty, identifying the most influential geological, operational, and loading parameters. The proposed framework reduces the cost of sensitivity analysis for computationally intensive 3D tunneling simulations, supporting input screening and dimensionality reduction for design and calibration
LiteBIRD Science Goals and Forecasts. -mode Anomalies
No full textInternational audienceVarious so-called anomalies have been found in both the WMAP and Planck cosmic microwave background (CMB) temperature data that exert a mild tension against the highly successful best-fit 6 parameter cosmological model, potentially providing hints of new physics to be explored. That these are real features on the sky is uncontested. However, given their modest significance, whether they are indicative of true departures from the standard cosmology or simply statistical excursions, due to a mildly unusual configuration of temperature anisotropies on the sky which we refer to as the "fluke hypothesis", cannot be addressed further without new information. No theoretical model of primordial perturbations has to date been constructed that can explain all of the temperature anomalies. Therefore, we focus in this paper on testing the fluke hypothesis, based on the partial correlation between the temperature and -mode CMB polarisation signal. In particular, we compare the properties of specific statistics in polarisation, built from unconstrained realisations of the CDM cosmological model as might be observed by the LiteBIRD satellite, with those determined from constrained simulations, where the part of the -mode anisotropy correlated with temperature is constrained by observations of the latter. Specifically, we use inpainted Planck 2018 SMICA temperature data to constrain the -mode realisations. Subsequent analysis makes use of masks defined to minimise the impact of the inpainting procedure on the -mode map statistics. We find that statistical assessments of the -mode data alone do not provide any evidence for or against the fluke hypothesis. However, tests based on cross-statistical measures determined from temperature and modes can allow this hypothesis to be rejected with a moderate level of probability