Portail HAL ONERA
Not a member yet
12842 research outputs found
Sort by
Adaptive Optics Rolling Slit Ophthalmoscope: Combining cellular-resolution, high-speed and large field-of-view in a multimodal retinal imager
No full textAbstract Label-free optical imaging systems capable of monitoring dynamic biological processes over a large field-of-view (FOV) are essential for advancing our understanding of retinal and neurovascular health. However, existing imaging modalities often involve trade-offs between spatial resolution, contrast, FOV, and frame rate. In this study, we present the Adaptive Optics Rolling Slit Ophthalmoscope (AO-RSO), a novel imaging system that integrates the high-speed, wide-FOV capabilities of camera-based systems with the enhanced contrast and multimodal functionality of point-scanning techniques—without compromising resolution or speed. The AO-RSO utilizes line illumination synchronized with the rolling shutter of a high-speed sCMOS camera, enabling precise and dynamic spatial selection of detected photons: back-scattered photons for near-confocal bright-field imaging and forward-scattered photons for phase-contrast imaging of translucent retinal features. This system successfully visualizes diverse retinal structures, including cone and rod photoreceptors, nerve fiber bundles, red blood cells, vessel walls, and ganglion cells, across a wide retinal area (4.5°× 2.5°). With a large FOV and frame rates up to 200 Hz, the AO-RSO enables the quantification of blood flow, tracking of red blood cells within hundreds of capillaries, and evaluation of thousands of photoreceptors in the living human retina. This capability opens new opportunities for functional neuronal imaging, neurovascular coupling studies, and the early detection of retinal and neurodegenerative diseases
Monolithic Dual-Polarized Leaky-Wave Array with Off-Axis Pointing, 36 DBI Gain and Unbalanced Beamforming Networks for Radar Applications
No full textNational audienceThis paper proposes a compact, lightweight radiating panel for polarimetric radar, consisting of 32 dual-mode leaky waveguides fed by orthomode transducers and unbalanced beamforming networks. The array generates a high-gain pencil beam (46λ long) with low sidelobes, achieved through equi-phase non-uniform excitation and modulation of the waveguide perforations. The three-layer monolithic panel, 3D printed using selective laser melting, integrates two beamforming networks and the radiating elements. The prototype is well matched for both polarization, it presents high isolation and a high-gain beam with off-axis pointing. This work demonstrates the first monolithic large radiating aperture with such a performance, providing a solution for balancing compactness and complexity in high-gain antenna arrays
Physical structure and architecture evolution of PEEK under proton irradiation: Comparison with electron irradiation
No full textInternational audienceOrbiting satellites operate in a hostile environment characterized by a high vacuum of the order of 10−11 mbar, thermal cycling and particle irradiation. This study focusses on proton irradiation and their effects on the physical properties of poly(ether-ether-ketone) (PEEK). It is a high-performance thermoplastic, commonly used in space industry because of its low outgassing and good resistance to irradiations. 8 µm PEEK films were irradiated with 1 MeV protons to avoid any possible implantation and to obtain an homogeneous dose in the thickness. Four doses representative of the lifetime of a satellite in GEOstationary (GEO) orbit were carried out. Analysis of the physico-chemical structure revealed two main phenomena after irradiation : amorphization and crosslinking. The study of molecular mobility confirmed these evolutions. Correlation of the different analysis techniques highlighted a change in behaviour from 50 MGy : crosslinking prevails over amorphization and chain scission. Then, new pristine samples were irradiated with electrons at equivalent doses. The comparison showed no major difference between proton-irradiated and electron-irradiated PEEK, except crytsallization. Indeed, proton irradiation leads to a higher decrease of crystallization temperature and crystallinity degree that can be due to the creation of a greater number of defects in the crystalline phase
Caractérisation expérimentale de la soufflerie transsonique ONERA S3Ch
No full textInternational audienceThis paper presents the experimental data available of the flow in the aerodynamical circuit of the ONERA S3Ch transonic wind tunnel, located at ONERA Meudon research center. The S3Ch facility operates across the subsonic, transonic, and supersonic regimes, making it a valuable tool for studying flow physics, validating numerical simulation tools and supporting the developments needed by the industry. A key feature of the facility is its adaptive wall system, which minimizes wall interference and facilitates computational fluid dynamics (CFD) replication of the wind tunnel tests. The characterization dataset provides insights into the uniformity of the flow at different location of the circuit as well as turbulence levels.Cet article présente les données expérimentales disponibles sur l’écoulement dans le circuit aérodynamique de la soufflerie transsonique ONERA S3Ch, située au centre de recherche ONERA Meudon. L’installation S3Ch fonctionne dans les régimes subsonique, transsonique et supersonique, ce qui en fait un outil précieux pour étudier la physique des flux, valider les outils de simulation numérique et soutenir les développements nécessaires pour l’industrie. Une caractéristique clé de l’installation est son système de parois déformables, qui minimise les perturbations causées par les parois et facilite la restitution des essais en soufflerie par calcul (CFD). L’ensemble de données de caractérisation fournit des informations sur l’uniformité du flux à différents endroits du circuit ainsi que sur les niveaux de turbulence
Étude numérique de la transition laminaire-turbulent sur un engin hypersonique en conditions de vol et de soufflerie
No full textInternational audienc
A Pose-Based Visual Servoing strategy for the autonomous landing of an airliner using a YOLOv11 model for runway detection
No full textInternational audienceEnhancing autonomy and safety in civil aviation, particularly in GPS-denied contexts, can significantly benefit from exteroceptive sensors. Recent advances in vision-based solutions and computer vision using neural networks for detection and segmentation have shown promise in estimating aircraft pose relative to a desired runway. Additionally, dataset generation tools have recently been available, enabling the training of Neural Networks (NN) models for runway detection in images. In this paper, we propose an extension of our previously developed Pose-Based Visual Servoing (PBVS) solution for autonomous airliner landing. This enhancement involves incorporating Artificial Intelligence (AI)-based measurements into the estimation of the aircraft pose. Specifically, pixel coordinates of detected runway corners serve as AI-based measurements, leveraging their corresponding real-world positions available in the onboard navigation dataset. Our proposed control strategy draws inspiration from ILS, which estimate an aircraft's lateral and vertical deviations from the runway using visual measurements. This approach enables the utilization of existing ILS-certified autopilots. The paper initially presents the integration of AI-based measurements from image flows into the multi-sensor data fusion filter providing an estimation of lateral and longitudinal deviations of the aircraft from the runway of interest. Subsequently, it provides a detailed explanation of the pipeline deriving the AI-based measurements with a YOLOv11 model as well as some insights on the training process and choice of datatest. Then, the proposed PBVS is validated through multiple replayed and fully autonomous landings performed on a high level fidelity simulation platform
Full Pose Tracking via Robust Control for Over-Actuated Multirotors
No full textInternational audience— This paper presents a robust cascaded controlarchitecture for over-actuated multirotors. It extends the Incremental Nonlinear Dynamic Inversion (INDI) control, combined with structured H∞ control—originally proposed forunder-actuated multirotors in [12]—to a broader range ofmultirotor configurations. Furthermore, it reduces the controllaw’s dependency on the multirotor model compared to themethods in the literature by shifting it to the actuator model,thereby improving the closed-loop robustness to uncertainties.To achieve attitude and position tracking, we employ a weightedleast-squares geometric guidance control allocation method,formulated as a quadratic optimization problem, enabling fullpose tracking. The proposed approach effectively addresseskey challenges, such as preventing infeasible pose references,enhancing robustness to disturbances, and accounting for themultirotor’s actual physical limitations. Numerical simulationswith an over-actuated hexacopter validate the method’s effectiveness, demonstrating its adaptability to diverse missionscenarios and its potential for real-world aerial applications
Electronic structure and optical absorption of armchair graphene/boron nitride lateral heterostructures from first principles and models
No full textWe investigate the electronic and optical properties of lateral heterostructures made of alternated armchair ribbons of graphene and hexagonal boron nitride. We employ ab initio theories (DFT and the G0W0 method) as well as a tight-binding ladder model originally introduced to study the gapwidth of isolated nanoribbons. After investigating the charge distribution across the interface, we identify the nature of the states around the gap and scrutinize their evolution as a function of the characteristic dimensions of the system (the graphene ribbons' width N and the boron nitride ribbons' width L). We also disclose how the very interface between graphene and boron nitride changes the electronic properties of both materials with respect to the corresponding isolated nanoribbons. Finally we discuss the light absorption properties of these systems by deriving specific selection rules for the heterostructures and calculating spectra from first principles in the independent particle and the random phase approximation
Utilisation des approches bayésiennes pour l'identification des lois de probabilité des paramètres incertains dans les panneaux raidis en composite.
No full textInternational audienceUtilisation des approches bayésiennes pour l'identification des lois de probabilité des paramètres incertains dans les panneaux raidis en composite
