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Homogenization model for a dense elastic medium of cylindrical scatterers and based on a realistic pair correlation function
No full textInternational audienceMultiple scattering effects due to a random distribution of identical cylindrical inclusions in an elastic medium are investigated. The approach is based on the analysis proposed by Fikioris and Waterman. The solution of the developed modal equations yields the effective wavenumbers of elastic coherent waves. Attention is made in this paper to a more realistic description of scatterers’ distribution in the host medium: this distribution is taken into account in modeling by introducing the notion of pair correlation function. The existing Conoir and Norris approach has been established by using the Hole Correction as pair correlation function, which simplifies the description of scatterers’ distribution and may lead to unphysical results for dense media. New formulas for the effective wavenumbers are proposed here by generalization of the latter theory and enable the use of any pair correlation function for possible application to dense media. The new generalized analytical model coupled to a realistic pair correlation function is compared to the previous approach in different materials configurations and validated for concrete structures by comparison to numerical simulations
Cosmic Vine: High abundance of massive galaxies and dark matter halos in a forming cluster at z=3.44
No full textInternational audienceThe Cosmic Vine is a massive protocluster at z=3.44 in the JWST CEERS field, offering an ideal laboratory for studying the early phases of cluster formation. Using the data from the DAWN JWST Archive, we conduct a comprehensive study on the large-scale structure, stellar mass function (SMF), quiescent members, and dark matter halos in the Cosmic Vine. First, we spectroscopically confirm 136 galaxies in the Vine at z=3.44, and an additional 47 galaxies belonging to a diffuse foreground structure at z=3.34 which we dub the Leaf. We identify four subgroups comprising the Cosmic Vine and two subgroups within the Leaf. Second, we identified 11 quiescent members with log(M*/Msun)=9.5-11.0, the largest sample of quiescent galaxies in overdense environments at z>3, which gives an enhanced quiescent galaxy number density 2x10^(-4)cMpc^(-3) that is three times above the field level at log(M*/Msun) > 10. Notably, these quiescent members form a tight red sequence on the color-magnitude diagram, making it one of the earliest red sequences known to date. Third, by constructing the SMFs for both star-forming and quiescent members, we find that both SMFs are top-heavy, with a significantly enhanced quiescent fraction at log(M*/Msun)>10.5 compared to field counterparts. The stellar mass-size analysis reveals that star-forming members are more compact at higher masses than their field counterparts. Finally, we estimate a halo mass of log(Mh/Msun)=13.2+-0.3 for the protocluster core, and log(Mh/Msun)=11.9-12.4 for satellite subgroups. The phase-space analysis indicates that three subgroups are likely infalling to the core. This work reveals a high abundance of massive galaxies and dark matter halos in a forming cluster, demonstrating the accelerated assembly of massive galaxies in massive halos when the Universe was less than 2 billion years old
Advancing time-resolved spectroscopies with custom scanning units and event-based electron detection
No full textInternational audienceDirect electron detection is revolutionizing electron microscopy by offering lower noise, reduced point-spread function, and increased quantum efficiency. Among these advancements, the Timepix3 hybrid-pixel direct electron detector stands out for its unique ability to output temporal information about individual hits within its pixel array. Its event-based architecture enables data-driven detection, where individual events are immediately read out from the chip. While recent studies have demonstrated the potential of event-based detectors in various applications in the context of continuous-gun scanning transmission electron microscopes (STEM), the use of such detectors with standard scanning units remains underdeveloped. In this work, we present a custom-designed, Timepix3-compatible scanning unit specifically developed to leverage the advantages of event-based detection. We explore its performance in enabling spatially and temporally resolved experiments, as well as its seamless interfacing with other time-resolved instruments, such as pulsed lasers and electron beam blankers. Additionally, we examine the prospects for achieving enhanced temporal resolution in time-resolved experiments using continuous-gun electron microscopes, identifying key challenges and proposing solutions to improve performance. This combination of custom hardware with advanced detection technology promises to expand the capabilities of electron microscopy in both fundamental research and practical applications
libMeshb: a Simple, Fast and Versatile Library to Handle HPC Meshes and Solutions with a Dedicated File Format
No full textInternational audienceProblem statement: a full HPC toolchain is made of numerous pre/post-processing tools and solvers, all communicating with each other either through file-based I/O or in memory exchanges. The first solution is less invasive in terms of software development but requires lots of external libraries, components and knowledge to use them (i.e. MPIO, HDF5, GPFS, Lustre, CGNS). The latter is more invasive as internal data structures need to be adapted and exposed to the communication layer but is much faster both in terms of throughput and latency. Furthermore, most standard HPC I/O libraries and file formats have been developed in the time of spinning hard drives and fail to extract the full potential of today's SSDs.Solution: we propose a lightweight library made of a single C file, without external dependency aside the Linux kernel's async IO and pthreads, whose API is based on tables and scalars so it can be easily accessed from any kind of languages and that is inherently parallel and SSD-native
EMG-to-torque models for exoskeleton assistance: a framework for the evaluation of in situ calibration
No full textInternational audienceIn the field of robotic exoskeleton control, it is critical to accurately predict the intention of the user. While surface electromyography (EMG) holds the potential for such precision, current limitations arise from the absence of robust EMG-to-torque model calibration procedures and a universally accepted model. This paper introduces a practical framework for calibrating and evaluating upper-limb EMG-to-torque models, accompanied by a novel nonlinear model. The framework includes an in situ procedure that involves generating calibration trajectories and subsequently evaluating them using standardized criteria. A comprehensive assessment on a dataset with 17 participants, encompassing single-joint and multi-joint conditions, suggests that the novel model outperforms the others in terms of accuracy while conserving computational efficiency. This contribution introduces an efficient model and establishes a versatile framework for EMG-to-torque model calibration and evaluation, complemented by a dataset made available. This further lays the groundwork for future advancements in EMG-based exoskeleton control and human intent detection
The North Balearic Front as an ecological boundary: zooplankton fine-scale distribution patterns in late spring
No full textInternational audienceObservations, models and theory have suggested that ocean fronts are ecological hotspots, generally associated with higher diversity and biomass across many trophic levels. Nutrient injections are often associated with higher chlorophyll concentrations at fronts, but the response of the zooplankton community is still insufficiently understood. The present study investigates mesozooplankton stocks and composition during late spring, northeast of Menorca, along two north-south transects that crossed the North Balearic Front separating central waters of the Northwestern Mediterranean Sea gyre from peripheral waters originating from the Algerian basin. During the BioSWOT-Med campaign, vertical triple-net tows with 200 and 500 µm meshes were carried out at three depths (100, 200, and 400 m), and the samples were processed with ZooScan to classify organisms into eight taxonomic groups. Zooplankton distributions were analyzed for the surface layer (0–100 m), a mid-depth layer (100–200 m), and a deeper layer (200–400 m). The results did not show a significant increase in biomass in the front in any layers. The NBF appears to act as a boundary between communities rather than a pronounced area of active or passive zooplankton accumulation. Analyses of stratified vertical distributions of zooplankton highlighted distinct taxonomic compositions in the three layers, and a progressive homogenization of community structure with depth, reflecting a weaker impact of hydrological processes on deeper communities. The clearest impact of the front was within the upper 100 m, where the mesozooplanktonic taxonomic composition differed between the front and adjacent water masses, with a decrease in all taxonomic groups except Cnidaria, which increased dramatically. In the two deeper layers, the front also influenced community composition, although to a lesser extent, with marked increases in Foraminifera and Cnidaria. Moreover, the northern water mass and the front were dominated by large copepods, while the southern water mass exhibited higher zooplankton diversity and smaller-sized copepods. The results of this study highlight the complexity of processes shaping planktonic communities over time and space in the NBF zone and its adjacent waters. These processes include zooplankton stock reduction in the transitional post-bloom period, marked effect of diel variation linked to vertical migrations, and potentially the impact of storm-related mixing in the surface layer that can disrupt established ecological patterns
Chiral-sensitive frequency mixing in valley-excited two-dimensional semiconductors
No full textInternational audienceTwo-dimensional (2D) semiconductors endowed with valley degree of freedom offer potential applications in next-generation petahertz valleytronics and photonics for emerging quantum technologies. We experimentally and theoretically uncover striking signatures of nonperturbative nonlinear optical response in valley-selective photodoped monolayer molybdenum disulfide, highlighting the interplay between strong-field dynamics and valley polarization. The interplay of valley-assisted excitation and circularly polarized probe leads to chiral-sensitive sum and difference frequency mixing of the pump and probe photons, appearing as sidebands in the high-harmonic spectra. Interestingly, the sideband's strength depends on the photodoped valley's chirality and the weaker pump's helicity. Additionally, a circular dichroic signal results from valley-selective photodoping when the pumps's helicity is changed. Sensitivity of the sideband's strength on the pump–probe delay bears an imprint of the temporal aspect of the electron–hole coherence in 2D semiconductors
Error Exponents for Randomised List Decoding
No full textThis paper studies random-coding error exponents of randomised list decoding, in which the decoder randomly selects messages with probabilities proportional to the decoding metric of the codewords. The exponents (or bounds) are given for mismatched, and then particularised to matched and universal decoding metrics. Two regimes are studied: for fixed list size, we derive an ensemble-tight random-coding error exponent, and show that, for the matched metric, it does not improve the error exponent of ordinary decoding. For list sizes growing exponentially with the block-length, we provide a non-trivial lower bound to the error exponent that is tight at high rates under the matched metric
La présomption de blanchiment : réponses jurisprudentielles et évolutions législatives
No full textInternational audience(Crim. 4 déc. 2024, no 24-83.013, non publié ; Crim. 12 févr. 2025, no 24-84.828, non publié
