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Self-written high-efficiency single-mode optical link using a single near-infrared photopolymerization step
No full textAccepté pour publication dans J. Lightwave Tech.International audienceWe present a method for fabricating a self-written waveguide (SWW) between two optical fibers that are single-mode (SM) at 850 nm (780HP/ core diameter: 4.4 µm). The basic principle consists in exposing an acrylic photopolymer formulation sensitive in the near-infrared range (NIR) to a laser beam transmitted simultaneously from both fibers placed face to face, to build a continuous, flexible and self-aligned optical link. The specificity of the presented process (NIR-SM-SWW) lies in the use of a writing wavelength identical to that intended for singlemode propagation in the fibers. This enables the creation in a single step of a SWW directly adapted to the fundamental mode to be transmitted. A precise pre-positioning stage is used to optimize the process. For best photochemical conditions, a coupling efficiency as high as 82 % (-0.86 dB loss) is demonstrated for a 300 µm-long link. The effect of fiber-to-fiber axial and lateral distances is also investigated to estimate the propagation loss and misalignment tolerance, respectively. In addition, measurements performed by quantitative phase optical microscopy indicate a homogeneous index profile in the guide. Using these data, optical modeling is performed and compared to experiments, confirming that a high efficiency SM link is actually fabricated, without the need for further fabrication of an external cladding. This method could therefore be easily applied to the SM connection of a SM VCSEL (vertical-cavity surface-emitting laser) to a SM fiber, which is of major interest for the development of compact optical communications and instrumentation systems
Improving the geotechnical and mechanical characteristics of a lateritic clay in sustainable road construction: Optimised incorporation of dolomitic lime and metakaolin
No full textInternational audienc
The ARMAGNHAC database: A Ratio-based Molecular Analyzer and Generator of Numerous Hydrogenated Amorphous Carbons
No full textInternational audienceHydrogenated amorphous carbons (HACs) are complex disordered forms of carbons that are of interest in various scientific fields, such as the study of air pollution from soot particles and astrochemistry. A new stochastic, structurally-guided algorithm, is presented for large-scale generation of atomistic models of HACs. It consists of a two-step procedure: (i) the randomized generation of 2D structures, using the SMILES (Simplified Molecular Input Line Entry System) description, respecting user predefined chemical constraints; (ii) the subsequent generation of 3D structures, making use of a stochastic sampling algorithm combined with local optimizations at the DFTB (density functional based tight binding) level. The method was used to generate the ARMAGNHAC database (website: https://armagnhac.laas.fr/) which provides structural (cartesian coordinates, functional group ratios, Hill-Wheeler parameters and aromaticity descriptors), energetic (HOMO-LUMO gap, ionization energy and electronic affinity) and spectroscopic properties of 4366 HACs. Correlation plots between these descriptors can be generated on the website, as well as IR spectra, possibly including their evolution as a function of a given property. Several illustrations are given, such as the dependence of the ionization potentials and electronic affinities on the size of the largest aromatic island of the HACs. The database (structures and properties) can be downloaded by the users. This work paves the way for future studie
Machine Learning et Interfaces 2D/3D pour automatiser,interagir avec et visualiser la configuration d'un MicroscopeÉlectronique en Transmission.
No full textThe aim of this thesis is to respond to the need for automation and understanding of the electron microscope by its operator. Indeed, a transmission electron microscope is a complex instrument to operate, which is also difficult to get a coherent mental representation of, especially for a novice microscopist. To address this issue of electron microscope accessibility, this thesis focuses on automating microscope alignment using new machine learning techniques such as CNN or RL. On the other hand, we are interested in the use of interactive and immersive visualization interfaces to enable the operator to visualize how modifications to the TEM configuration impact the electron beam within it, and thus facilitate the construction of a mental model of the microscope. the construction of a mental model of the tool that is consistent with reality and more direct than the changes visible on the image. To this end, we have developed a modular TEM simulation and two visualization interfaces, one 2D and one 3D for (Meta Quest, Android and Microscoft Hololens).L'objectif de cette thèse est de répondre au besoin d'automatisation et de compréhension du microscope électronique par son opérateur. En effet, un microscope électronique à transmission est un instrument complexe à utiliser, dont il est également difficile d'avoir une représentation mentale cohérente, en particulier pour un microscopiste novice. Pour répondre à ce problème d'accessibilité du microscope électronique, cette thèse se concentre sur l'automatisation de l'alignement des microscopes en utilisant de nouvelles techniques d'apprentissage automatique telles que CNN ou RL. D'autre part, nous nous intéressons à l'utilisation d'interfaces de visualisation interactives et immersives pour permettre à l'opérateur de visualiser l'impact des modifications de la configuration du TEM sur le faisceau d'électrons qui s'y trouve, et ainsi faciliter la construction d'un modèle mental du microscope. La construction d'un modèle mental de l'outil cohérent avec la réalité et plus direct que les changements visibles sur l'image. Pour ce faire, nous avons développé une simulation modulaire du MET et deux interfaces de visualisation, l'une 2D et l'autre 3D pour (Meta Quest, Android et Microscoft Hololens
Biomechanically consistent real-time action recognition for human-robot interaction
No full textThis paper presents a novel framework for real-time human action recognition in industrial contexts, using standard 2D cameras. We introduce a complete pipeline for robust and real-time estimation of human joint kinematics, input to a temporally smoothed Transformer-based network,for action recognition. We rely on a new dataset including 11 subjects performing various actions, to evaluate our approach. Unlike most of the literature that relies on joint center positions (JCP) and is offline, ours uses biomechanical prior, eg. joint angles, for fast and robust real-time recognition. Besides, joint angles make the proposed method agnostic to sensor and subject poses as well as to anthropometric differences, and ensure robustness across environments and subjects. Our proposed learning model outperforms the best baseline model, running also in real-time, along various metrics. It achieves 88% accuracy and shows great generalization ability, for subjects not facing the cameras. Finally, we demonstrate the robustness and usefulness of our technique, through an online interaction experiment, with a simulated robot controlled in real-time viathe recognized actions
Investigating the Nanoscale Dynamics of Chlorella vulgaris Flocculation with Pyridinium-Modified Cellulose Nanocrystals
No full textInternational audienceMicroalgae show significant potential as a sustainable resource for the production of food, animal feed, biofuels, and several high-value products. However, the lack of effective harvesting techniques limits the large-scale production of microalgae. A strategy to enhance the separation of microalgae from their growth medium is to flocculate the microalgae cells into larger particles that can then be separated from water by sedimentation or flotation. Understanding the flocculation mechanism is crucial for developing a more efficient separation methodology. To this end, we applied Atomic Force Microscopy (AFM) to probe and localize the interactions between negatively charged AFM tips and the surface of cells in contact with varying concentrations of flocculants. We used cationic cellulose nanocrystals (CNCs) as a flocculant and Chlorella vulgaris as a model microalgae species. Cationic CNCs are a novel type of biobased flocculants consisting of nanoparticles and, hence, the flocculation mechanism is poorly understood. AFM force spectroscopy experiments allowed us to detect at high resolution the presence of cationic nanoparticles on the cell surface. Flocculation occurs when the CNCs form cationic patches on an otherwise homogeneous anionic cell surface. Taken together, our observations provide evidence that cationic CNCs induce flocculation by a patch mechanism. This study demonstrates that AFM can be a powerful tool to understand the molecular mechanisms underlying flocculation
Planetary boundaries and regional justice: Rethinking aviation transitions through AESA
No full textInternational audienceDespite growing scrutiny of aviation’s environmental footprint, no study to date has assessed future aviation pathways through the lens of the Planetary Boundaries framework. Our team conducted the first absolute environmental sustainability assessment (AESA) of global civil aviation futures, revealing that even ambitious decarbonization scenarios transgress core planetary boundaries (climate change and biosphere integrity) when assessed against an ethically grounded share of safe operating space.Building on this foundation, the present work extends AESA to the regional scale, addressing the need to consider divergent regional capacities and responsibilities in sustainability transitions. We evaluate region-specific aviation scenarios sourced from institutional, industrial, and academic literature, using prospective life-cycle assessment combined with Integrated Assessment Model projections via the premise package.We integrate key sources of regional differentiation, including electricity mix evolution, biomass availability, and historical contributions to global impacts, and we explore multiple ethical-based allocation principles to operationalize fair regional planetary boundaries budgets.Our results reveal sharp contrasts between regions: some face tighter sustainability constraints due to high historical impacts and limited renewable resources, while others may pursue lower-impact pathways. These differences are masked in global assessments, but essential for designing just and effective transition strategies.This work advances aviation AESA by embedding regional granularity and ethical considerations, offering actionable insights for sustainable aviation futures
Integration theory of lie-graph algebras
No full textWe develop the Lie theory of Lie-admissible algebras whose product is enriched with higher operations modeled on directed graphs with a view to apply it to the deformation theories controlled by this kind of Lie algebras. We produce effective formulas for their exponential map, their gauge group structure and the action on Maurer-Cartan elements. The main motivation and range of applications lies in the deformation theory of types of bialgebras which is done in a sequel article. This work extends the case of pre-Lie algebra structures which appear in the deformation theory of operadic algebras
Prediction of crack initiation location and direction in fretting fatigue considering cylindrical contact
No full textInternational audienceFretting phenomenon results in severe contact stresses that develop on the surface near the trailing edge of the contact, which can lead to the formation of microcracks. Combined with fatigue stresses, these cracks may propagate and cause catastrophic specimen failure. Referred to as fretting fatigue, this phenomenon is characterized by both multiaxial and steep stress gradients. Multiaxiality is addressed using various fatigue parameters based on stresses and strains computed along the contact surface. The severity of stress gradients and the contact size are accounted for using process volume averaging methods. Therefore, combining fatigue criteria with averaging methods provides an advantage in better predicting crack nucleation conditions. In this study, salient features of the experimental crack nucleation condition are considered in the finite element analysis. The SWT critical-plane-based multiaxial fatigue criterion, based on the computed stresses and strains at the contact surface, is then employed to predict crack nucleation risk, location, and orientation. Recent analytical expressions derived from the Muskhelishvili potential are used to calculate the stresses. The predicted results are compared with experimental data reported in the literature. Finally, applying an averaging strategy to the localized parameter values within the process volume improved the results and enhanced the accuracy of the predictions