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Upgrading SPHERE with the second stage AO system SAXO+: non-common path aberrations estimation and correction
No full textInternational audienceSAXO+ is a planned enhancement of the existing SAXO, the VLT/ SPHERE adaptive optics system, deployed on ESO’s Very Large Telescope. This upgrade is designed to significantly enhance the instrument’s capacity to detect and analyze young Jupiter-like planets. The pivotal addition in SAXO+ is a second-stage adaptive optics system featuring a dedicated near-infrared pyramid wavefront sensor and a second deformable mirror. This secondary stage is strategically integrated to address any residual wavefront errors persisting after the initial correction performed by the current primary AO loop, SAXO. However, several recent studies clearly showed that in good conditions, even in the current system SAXO, non-common path aberrations (NCPAs) are the limiting factor of the final normalized intensity in focal plane, which is the final metric for ground-based high-contrast instruments. This is likely to be even more so the case with the new AO system, with which the AO residuals will be minimized. Several techniques have already been extensively tested on SPHERE in internal source and/or on-sky and will be presented in this paper. However, the use of a new type of sensor for the second stage, a pyramid wavefront sensor, will likely complicate the correction of these aberrations. Using an end-to-end AO simulation tool, we conducted simulations to gauge the effect of measured SPHERE NCPAs in the coronagraphic image on the second loop system and their correction using focal plane wavefront sensing systems. We finally analyzed how the chosen position of SAXO+ in the beam will impact the evolution of the NCPAs in the new instrument
Electroluminescence and energy transfer mediated by hyperbolic polaritons
No full textData are publicly available on Zenodo at 10.5281/zenodo.10625437https://zenodo.org/records/14382617International audienceUnder high electrical current, some materials can emit electromagnetic radiation beyond incandescence. This phenomenon, referred to as electroluminescence, leads to the efficient emission of visible photons and is the basis of domestic lighting devices (for example, light-emitting diodes)1,2. In principle, electroluminescence can lead to mid-infrared emission of confined light–matter excitations called phonon polaritons3,4, resulting from the coupling of photons with crystal lattice vibrations (optical phonons). In particular, phonon polaritons arising in the van der Waals crystal hexagonal boron nitride (hBN) present hyperbolic dispersion, which enhances light–matter coupling5,6. For this reason, electroluminescence of hyperbolic phonon polaritons (HPhPs) has been proposed as an explanation for the peculiar radiative energy transfer within hBN-encapsulated graphene transistors7,8. However, as HPhPs are locally confined, they are inaccessible in the far field, and as such, any hint of electroluminescence has been based on indirect electronic signatures and has yet to be confirmed by direct observation. Here we demonstrate far-field mid-infrared (wavelength approximately 6.5 μm) electroluminescence of HPhPs excited by strongly biased high-mobility graphene within a van der Waals heterostructure, and we quantify the associated radiative energy transfer through the material. The presence of HPhPs is revealed by far-field mid-infrared spectroscopy owing to their elastic scattering at discontinuities in the heterostructure. The resulting radiative flux is quantified by mid-infrared pyrometry of the substrate receiving the energy. This radiative energy transfer is also shown to be reduced in hBN with nanoscale inhomogeneities, demonstrating the central role of the electromagnetic environment in this process
Aéroacoustique d'un turboréacteur avec un stator dentelé : conception, prédictions et comparaisons avec les mesures
No full textInternational audienceThis work is devoted to the design and evaluation of a low-noise outlet guide vane (OGV) aiming to reduce the rotor–stator interaction noise using leading-edge serrations and tested on the ECL5 ultrahigh-bypass-ratio model in the PHARE-2 rig at Ecole Centrale Lyon. First, a radially varying 2D design is proposed and evaluated by means of a fast analytical prediction tool and using a strip approach. Then, an iterative process combining 3D Reynolds-averaged Navier–Stokes (RANS) calculations with an in-house modeler is carried out to achieve a suitable 3D geometry while minimizing the aerodynamic penalties. Following this design process, high-fidelity simulations based on a lattice Boltzmann solver are performed to assess the sound power level reduction achieved by the serrated OGV (by comparison to the untreated baseline case primarily tested). Due to the low-compressibility assumptions of the present lattice Boltzmann method, simulations are limited to the reachable higher regime (45% of nominal rotational speed). Hence, available analytical and numerical predictions are compared to the experimental data in terms of both aerodynamic and acoustic performances. A rather good agreement is obtained with sound power level reductions up to 3 dB from broadband intake radiation and 6 dB in the bypass duct at the considered operating points. In addition, around 4 dB power reduction has been achieved at the most energetic blade passing frequency.Ce travail est consacré à la conception et l'évaluation d'un stator bas-bruit visant à réduire le bruit d'interaction rotor-stateur grâce à des serrations d'extrémité de bord d'attaque et testé sur le modèle de soufflante à très haut taux de dilution ECL5 dans la soufflerie PHARE-2 à l'Ecole Centrale Lyon. Tout d'abord, une conception 2D variable radialement est proposée et évaluée à l'aide d'un outil de prédiction analytique rapide et en utilisant une approche par bandes. Ensuite, un processus itératif combinant des calculs RANS 3D avec un outil de déformation géométrique développé en interne est réalisé pour obtenir une géométrie 3D appropriée, tout en minimisant les pénalités aérodynamiques. Suite à ce processus de conception, des simulations de haute fidélité basées sur un solveur lattice-Boltzmann sont effectuées pour évaluer la réduction du niveau de puissance sonore obtenue par le stator avec dentelures (par comparaison avec le cas de référence non traité principalement testé). En raison des hypothèses de faible compressibilité du présent code LBM, les simulations sont limitées au régime de 45% de la vitesse de rotation nominale. Par conséquent, les prédictions analytiques et numériques disponibles sont comparées aux données expérimentales, à la fois en termes de performances aérodynamiques et acoustiques. Un accord assez satisfaisant est obtenu avec des réductions du niveau de puissance sonore allant jusqu'à 3 dB pour le rayonnement à large bande à l'amont et 6 dB dans en conduit sur les points de fonctionnement considérés. De plus, une réduction de puissance d'environ 4 dB a été atteinte à la fréquence de passage de pale la plus énergétique
Evaluating the Posterior Sampling Ability of Plug&Play Diffusion Methods in Sparse-View CT
No full textInternational audiencePlug&Play (PnP) diffusion models are state-of-the-art methods in computed tomography (CT) reconstruction. Such methods usually consider applications where the sinogram contains a sufficient amount of information for the posterior distribution to be concentrated around a single mode, and consequently are evaluated using image-to-image metrics such as PSNR/SSIM. Instead, we are interested in reconstructing compressible flow images from sinograms having a small number of projections, which results in a posterior distribution no longer concentrated or even multimodal. Thus, in this paper, we aim at evaluating the approximate posterior of PnP diffusion models and introduce two posterior evaluation properties. We quantitatively evaluate three PnP diffusion methods on three different datasets for several numbers of projections. We surprisingly find that, for each method, the approximate posterior deviates from the true posterior when the number of projections decreases
Continuous Planning and Execution for a Mission Planning System Managing a Constellation of Earth Observation Satellites
No full textInternational audienceThis paper introduces a prototype of a future mission planning system managing a constellation of Earth observation satellites. This ground system receives observation requests and continuously performs unit planning operations to build plan fragments regularly sent to the satellites. The novelty is its ability to simultaneously handle heterogeneous requests (standard requests, urgent requests, periodic requests, stereoscopic requests, large area coverage requests, etc), heterogeneous orbits (inclined or not), heterogeneous events (request arrival, new weather forecast, image rejection due to clouds), decision horizons depending on the communication windows of each satellite, and to deal with the interleaving between planning and execution. These components are integrated in a simulator proving the feasibility of the concept
Étude numérique de l'amorçage et de la stabilisation assistée par plasma par un Q-DC arc glissant d'une combustion supersonique hydrogène-air dans la chambre de combustion LAERTE
No full textInternational audienceWe propose a new method for automatically identifying radiation belt electron enhancement events using Ca, a ground-based 1D surrogate index for the global dynamics of the electron radiation belts. Our method improves event identification by accurately determining start and end dates, considering intensification and return-to-equilibrium phases, and resolving ambiguity between single, longer-lasting events and multiple, successive events. The events detected after 1995, are automatically associated with possible physical driving causes, such as interplanetary coronal mass ejections and stream interaction regions. The resulting list of events is consistent with our understanding of how radiation belts respond to interplanetary drivers, in terms of event intensity, duration, and distribution over the solar cycle. The list of events from 1868 to 2021 is publicly available for statistical analyses of radiation belt climatology, constructing space weather forecasting models, and selecting periods of interest for studying physical processes
Real-time visual pose estimation: from BOP objects to custom drone — A journey
No full textInternational audiencePose estimation plays a crucial role in robotics for prehension tasks or in augmented-reality application, yet its application on real-world far-range estimation has not been thoroughly studied. This study aims to evaluate pose estimators on a custom drone at distances from 0.5 m to 10 m, which is beyond the scope of existing datasets, that only contain objects close to less than 2 m. We created synthetic and real databases specific to our drone and compared various RGB pose estimators, evaluating their performance across different distances. PViT-6D, being one of the SoTA methods on the classic [0,2] m interval, also outperforms others estimators at greater distances, and proves robust with respect to detection inaccuracy. The results demonstrate the potential of PViT-6D to be used on a real time application embedded in the drone platform. This work aims to evaluate the potential of pose estimators for mutual perception and communication within a drone swarm
Separation and transition on a cone-cylinder-flare: Experimental campaigns
No full textInternational audienceExperimental campaigns were conducted across three Mach 6 facilities on the hypersonic flow around a cone-cylinder-flare (CCF) geometry as part of the NATO STO Research Task Group AVT-346. Two conventional facilities (AFRL M6LT and ONERA R2Ch) and one quiet tunnel (Purdue BAM6QT) were used to test the same geometry and to study the instabilities in both the boundary layer and the shear layer above the axisymmetric separation bubble. Two nose tip radii (one nominally sharp and one blunt with a 5 mm radius) were tested. For the sharp nose tip case, there was excellent agreement between the measurements of both second-mode and shear-layer instabilities across the conventional facilities. However, the measured spectra for the blunt nose tip case showed more significant differences between the two conventional tunnels, potentially due to an alternate dominant instability mechanism coupled with the variations in the freestream noise spectra. The quiet facility resulted in a flow that remained laminar to much higher freestream unit Reynolds numbers, as well as in instability measurements that had more distinct spectral peaks for the sharp tip case and broadband rises for the blunt one. The instability mechanisms at play in the sharp quiet case were found to be the same as those in the conventional facilities
Multi-view 3D surface reconstruction from SAR images by inverse rendering
No full textInternational audience3D reconstruction of a scene from Synthetic Aperture Radar (SAR) images mainly relies on interferometric measurements, which involve strict constraints on the acquisition process. These last years, progress in deep learning has significantly advanced 3D reconstruction from multiple views in optical imaging, mainly through reconstruction-by-synthesis approaches popularized by Neural Radiance Fields. In this paper, we propose a new inverse rendering method for 3D reconstruction from a few incoherent SAR views, drawing inspiration from optical approaches. First, we introduce a new simplified differentiable SAR rendering model, able to synthetize images from a Digital Surface Model (DSM) and a radar backscattering coefficients map. Then, we introduce a coarse-to-fine strategy to reconstruct the DSM and the map of backscattering coefficients of a SAR scene starting only from a few SAR views. We use a neural field, i.e. a continuous parametric model based on a Multi-Layer Perceptron, to represent the SAR scene. Finally, we present preliminary results of DSM reconstruction from synthetic SAR images produced by ONERA's physically-based EMPRISE simulator, supporting the potential of applying inverse rendering approaches to SAR data in order to efficiently exploit geometric disparities in future applications such as multi-sensor data fusion
SkiNet: un outil orienté utilisateur pour l'analyse de skills robotiques par des réseaux de Petri
No full textInternational audienceDespite the rise in applications of formal methods for the design and analysis of robotic systems, their integration into existing frameworks remains a challenge. Part of the problem is due to the important changes in the software architecture of robotic design tools needed to accommodate for formal methods, but another challenge is the inherent difficulty for non-experts to use formal methods. In this work, we present SkiNet, a user-oriented tool which aims to assist in the design of skill-based robotic systems using a formal model based on Petri nets. The main idea for SkiNet is to interpret the user-written specifications and properties, into elements from the formal model, and vice versa. This allows the user to be more independent when diagnosing and validating the specified behavior, without having to directly manipulate the backend formal tools. An example of the verification process of robotic skills specifications using SkiNet is given to showcase this paradigm