HAL Université de Savoie
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SFIxM : Flexible LoRa Modulations for Elastic Resource Allocation
No full textInternational audienceThis paper presents SFIxM , a flexible evolution of the LoRa modulation scheme designed to facilitate the allocation of transmission parameters across nodes within a gateway's coverage area. SFIxM increases the number of available quasiorthogonal channels and, unlike standard LoRa, offers tunable robustness to noise and interference. Because SFIxM introduces a new requirement for time-axis alignment between transmitter and receiver, we present a practical procedure to achieve this synchronisation, along with an analytical estimate of its failure probability, which we find negligible. Based on this foundation, we show that SFIxM provides traffic capacity gains of 40 to 55%, comparable to the gains obtained with receiver diversity, a well-known approach to improving coverage and range, which also turns out to combine well with SFIxM
Poursuite des acquisitions topographiques 3D à La Chaise-de-Vouthon, et construction d’une base de données SIG
No full textSimulation de l'injection de porteurs dans les LED GaN à nanofils axiales
No full textInternational audienceMicro Light‐Emitting Diodes (MicroLEDs) are expected to penetrate the display market and allow for the development of augmented reality (AR) or virtual reality (VR) technologies. InGaN/GaN nanowires are very promising for these applications, thanks to their high luminescence and emission directivity. However, there is still room for significant improvement of the efficiency of these 3D nanostructures. This study presents a numerical simulation of multiple quantum well (MQW) nanowires in Light‐Emitting Diodes (LEDs). Using a Poisson‐drift‐diffusion solver, the tuning of the injection efficiency for multiple geometries and material variations will be presented. It is found that the injection of holes through the multiple planes of nanowires always follows a lateral injection through the semi‐polar planes into polar quantum wells, that needs to be optimized to ensure radiative recombination in the first quantum wells. The ratio of polar/semi‐polar plane quantum wells length is a key factor in the design of nanowires, and the Wall‐Plug Efficiency (WPE) significantly varies with the size of semi‐polar quantum wells. Furthermore, the impact of degraded recombination area at the top and bottom of the nanowire confirms that a careful choice in the quantum well number must be carried out. The design of optimal and efficient InGaN/GaN nanowires, hence, reveals complex trade‐offs, adjustable through controlled epitaxial growth.Les micro‐diodes électroluminescentes (MicroLEDs) devraient pénétrer le marché des écrans et permettre le développement de technologies de réalité augmentée (RA) ou de réalité virtuelle (RV). Les nanofils InGaN/GaN sont très prometteurs pour ces applications, grâce à leur forte luminiscence et à la directivité de leur émission. Cependant, il reste encore une marge importante d'amélioration de l'efficacité de ces nanostructures 3D. Cette étude présente une simulation numérique de nanofils à puits quantiques multiples (MQW) dans des diodes électroluminescentes (LED). À l'aide d'un solveur Poisson‐drift‐diffusion, l'optimisation de l'efficacité d'injection pour différentes géométries et variations de matériaux sera présentée. Il a été observé que l'injection de trous à travers les multiples plans des nanofils suit toujours une injection latérale à travers les plans semi-polaires vers les puits quantiques polaires, qui doit être optimisée pour assurer la recombinaison radiative dans les premiers puits quantiques.Le rapport de longueur des puits quantiques plans polaires/ semi-polaires est un facteur clé dans la conception des nanofils, et l'efficacité Wall-Plug (WPE) varie considérablement en fonction de la taille des puits quantiques semi-polaires. De plus, l'impact de la zone de recombinaison dégradée au sommet et à la base du nanofil confirme qu'un choix attentif du nombre de puits quantiques doit être effectué. La conception de nanofils InGaN/GaN optimaux et efficaces révèle donc des compromis complexes, ajustables grâce à une croissance épitaxiale contrôlée
Stratégies multiéchelles de recyclage de déchets riches en métaux: du réacteur de laboratoire au pilote de terrain
No full textNational audienceTo meet the ever-growing global demand for metals, the main consequence of which is the criticality of many metals, the exploitation of primary resources continues to increase, as does the production of waste that poses health and ecological hazards. To limit their impact, an innovative approach consists of considering this waste as secondary resources, in line with the concept of the circular economy. The aim of the European projects REVIVING and DESIRE4EU is to develop an efficient recycling process for metals of interest from tungsten-rich mining waste (Panasqueira, Portugal) and recyclable and degradable electronic cards, respectively. As part of the REVIVING project, we operated a series of laboratory bioreactors at increasing experimental scales (10g batch reactors; x200: 2kg continuous flow column reactors) before scaling up the process in situ (x100: 200kg continuous flow column reactor). The physico-chemical and biological parameters (pH, O2, metal concentrations, DNA metabarcoding, etc.) were monitored in the various reactors. A similar approach was adopted for the DESIRE4EU project. The understanding and optimisation of metal bioleaching from electronic cards in micro-reactors is currently being optimised. All of our results will contribute to consolidating our knowledge in order to meet circular economy objectives by recovering waste through the secondary production of critical metals from waste.Pour satisfaire la demande mondiale en métaux en croissance constante et dont la principale conséquence est la criticité de nombreux métaux, l’exploitation des ressources primaires ne cesse d’augmenter ainsi que la production de déchets qui représentent des dangers sanitaire et écologique. Pour limiter leurs impacts, une approche innovante consiste à considérer ces déchets, comme des ressources secondaires, selon un concept d'économie circulaire. L'objectif des projets européens REVIVING et DESIRE4EU est de développer un procédé de recyclage efficace des métaux d'intérêt à partir de déchets miniers riches en tungstène (Panasqueira, Portugal) et de cartes électroniques recyclables et dégradables, respectivement. Dans le cadre du projet REVIVING, nous avons exploité une série de bioréacteurs de laboratoire à des échelles expérimentales croissantes (réacteurs batch de 10g ; x200 : réacteurs colonnes à flux continu de 2 Kg) avant une mise à l'échelle du procédé in situ (x100 : réacteur colonne à flux continu de 200 Kg). Un suivi des paramètres physico-chimiques et biologiques (pH, O2, concentrations des métaux, DNA-metabarcoding …) a été effectué sur les différents réacteurs. Une approche similaire a été adoptée pour le projet DESIRE4EU. La compréhension et l’optimisation en micro-réacteurs de la biolixiviation des métaux à partir de cartes électroniques est en cours d’optimisation. L'ensemble de nos résultats contribueront à consolider nos connaissances pour répondre à des objectifs de l'économie circulaire en valorisant les déchets par la production secondaire de métaux critiques à partir de déchets
Quelle(s) place(s) de la science dans le débat démocratique et la vie publique ?
No full textInternational audienceTable ronde pour interroger la place des scientifiques dans le débat démocratique et la vie publique, en donnant la parole à plusieurs chercheur.ses témoignant de diverses formes d’engagement (Sébastien Lavergne, Sabine Girard, Carine Pachoud, Romain Couillet)
Rockfall detection using lidar point clouds: identification of geometric distortions during acquisition and proposed processing to enable a low detection threshold
No full textInternational audienceThe C2R-IA project (www.c2r-ia.fr) is aimed to better account for the influence of weather conditions on the level of rockfall hazards and to anticipate temporary increases in hazard levels during storms and other specific weather conditions, in order to implement risk mitigation systems (access restrictions, monitoring, mobilization of emergency kits, predictive maintenance). To achieve this, a database of rockfall events is built to train AI predictive models of rockfalls based on weather conditions. One of the monitoring technologies used is a terrestrial laser scanner with a RIEGL VZ-2000i long range 3D laser scanning system. Lidar point clouds are thus used to provide at several time intervals the 3D surface of the study site: the Saint-Eynard cliff, located northeast of Grenoble in the french Alps. From the lidar point cloud series, the goal is to compare the clouds to detect changes and identify rockfall events (Manceau et al, EGU 2025, oral presentaion). For a large and rich database, it is important to achieve very precise alignement between lidar point clouds to detect the smallest possible changes in our point clouds series (small rockfall volumes).In this context, a basic ICP (Iterative Closest Point) alignement reveals artefacts that need to be treated in a special way to achieve high-precision alignement. Geometric distortions are thus observed within the point clouds in the form of vertical strips. This phenomenon occurs at two scales:- Low frequency: observations of decimetric to multi-decimetric jumps with strip widths ranging from 10 to 100 meters during acquisitions from a tripod, a flexible support.- High frequency: observations of centimetric jumps with narrower strip widths (ranging from one to several meters) during acquisitions from a rigid base (reinforced concrete post).Several hypotheses are put forward and tested to explain the existence of these strips: machine-related mechanical issues, independent or dependent on time, interaction between the ground, support, and machine, changes in atmospheric conditions during the acquisition period (lasting 40 minutes), the geometry of the cliff and its local orientation relative to the lidar's line of sight.A processing method is proposed to overcome these geometric distortions during acquisition and maintain a low detection threshold when comparing two point clouds: this involves a new strip-based alignment of the two clouds before change detection. The first step is the extraction of strips from the compared cloud, then an independent alignment of each strip to the reference cloud is performed using the ICP method. Finally, the aligned strips are merged to form the new compared cloud : we reach a detection threshold of less than 10 cm (i.e. 10-4 times the measurement distance) whereas 40 cm has been previously used on the same site in the literature
