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Development of a mechanical frame adapted to Arcan tests to identify the creep behaviour of adhesive joints
No full textInternational audienceThe use of structural adhesive bonding is increasing in the structural assembly field. It has indeed several advantages compared to other assembly techniques such as welding and riveting: uniform stress distribution, assembly of materials with different natures, no heat production. Creep is an important long-term phenomenon that needs to be considered for adhesive joints. To investigate this aspect, a study at the scale of the adhesive joint is required. At this scale, Arcan test presents several advantages compared to other existing tests (analysis of different loads, limited edge effects). Consequently, Arcan test was chosen for an ongoing creep study aimed at studying bonded fasteners. A mechanically operated creep testing machine for adhesive joints and adapted to this test was developed. To study the local strain of the adhesive, two LVDT sensors measure the displacements according to two directions: normal and tangential to the bonded surface. These sensors are placed in a support, which is fixed at the beaks of the sample. This mechanically welded frame enables investigating the creep behaviour of adhesive joints according to a lot of parameters (load levels, type of load, temperature, adhesive thickness). The analysis of the behaviour allowed suggesting some design tools adapted for the use of the bonded fasteners under creep loads.Le collage structural est une méthode d’assemblage de plus en plus utilisée. En effet, cette solution présente plusieurs avantages par rapport à d’autres techniques comme le rivetage et le soudage : distribution uniforme de contraintes, assemblage de matériaux de nature différente, pas de production de chaleur. Le fluage est un phénomène important à prendre en compte en termes de durabilité lors de la conception d’un assemblage collé. Pour étudier ce phénomène, une analyse à l’échelle du joint mince est nécessaire. L’essai Arcan dispose de plusieurs avantages par rapport à d’autres méthodes expérimentales à l’échelle du joint de colle (plusieurs types de chargement possibles, effets de bord limités). Par conséquent, cet essai a été choisi dans le cadre d’un projet s’intéressant au fluage de connecteurs collés. Pour utiliser cette géométrie, un bâti de fluage spécifique a été conçu. Pour analyser la déformation locale au niveau de la couche d’adhésif, deux capteurs LVDT mesurent le déplacement selon deux directions (normale et tangente à la surface collée). L’ensemble de ce dispositif expérimental permet d’étudier le comportement en fluage selon plusieurs paramètres : niveau de chargement, type de chargement, température, réversibilité du fluage. L’analyse des résultats de ces investigations expérimentales permet d’appréhender au mieux le comportement l’utilisation de l’assemblage collé vis-à-vis de son utilisation
Contrôle optimal et robuste pour le guidage de véhicules autonomes
No full textThe guidance of a reusable launcher is a control problem that requires both precision and robustness: one must compute a trajectory and a control such that the system reaches the landing zone, without crashing into it or exploding mid-flight, all while using as little fuel as possible. Optimal control methods based on Pontryagin's Maximum Principle can compute an optimal trajectory with great precision, but uncertainties, the discrepancies between estimated values of the initial state and parameters and actual values, cause the actual trajectory to deviate, which can be dangerous. In parallel, set-based methods and notably validated simulation can enclose all trajectories of a system with uncertainties.This thesis combines those two approaches to enclose sets of optimal trajectories of a problem with uncertainties to guarantee the robustness of the guidance of autonomous vehicles.We start by defining sets of optimal trajectories for systems with uncertainties, first for mathematically perfect trajectories, then for the trajectory of a vehicle subject to estimation errors that can use, or not use, sensor information to compute a new trajectory online. Pontryagin's principle characterizes those sets as solutions of a boundary value problem with dynamics subject to uncertainties. We develop algorithms that enclose all solutions of these boundary value problem using validated simulation, interval arithmetic and contractor theory. However, validated simulation with intervals is subject to significant over-approximation that limits our methods. To remedy that we replace intervals by constrained symbolic zonotopes. We use those zonotopes to simulate hybrid systems, enclose the solutions of boundary value problems and build an inner-approximation to complement the classical outer-approximation. Finally, we combine all our methods to compute sets of trajectories for aerospace systems and use those sets to assess the robustness of a control.Le guidage d'un lanceur réutilisable est un problème de contrôle qui nécessite à la fois précision et robustesse : il faut calculer une trajectoire et un contrôle, de sorte que le lanceur atteigne la piste d'atterrissage, sans s'écraser ni exploser en vol, le tout en utilisant le moins de carburant possible.Les méthodes de Contrôle Optimal issu du Principe de Pontryagin calculent une trajectoire optimale avec grande précision, mais les incertitudes, soit les erreurs entre les estimations de l'état initial et des paramètres et leurs valeurs réelles, causent une déviation potentiellement dangereuse de la trajectoire réelle. En parallèle, les méthodes ensemblistes et notamment la simulation validée peuvent encadrer toutes les trajectoires possibles d'un système dynamique avec des incertitudes bornées.Cette thèse combine ces deux approches pour encadrer des ensembles de trajectoires optimales de systèmes avec incertitudes afin de garantir la robustesse du guidage d'un véhicule autonome.Nous commençons par définir des ensembles de trajectoires optimales pour des systèmes avec incertitudes, d'abord pour les trajectoires mathématiquement parfaites, puis pour les trajectoires d'un véhicule sujet à des erreurs d'estimation, mais qui utiliserait, ou non, les données des capteurs pour recalculer sa trajectoire en cours de route. Le principe de Pontryagin caractérise ces ensembles comme solutions de problèmes aux deux bouts avec des dynamiques avec incertitudes. Nous développons alors des algorithmes qui encadrent toutes les solutions de ces problèmes aux deux bouts en utilisant la simulation validée, l'arithmétique des intervalles et la théorie des contracteurs. Cependant, la simulation avec des intervalles occasionne une forte sur-approximation qui limite nos méthodes. Pour y remédier, nous remplaçons les intervalles par des zonotopes symboliques contraints. Nous utilisons notamment ces zonotopes pour simuler des systèmes hybrides, encadrer des solutions de problèmes aux deux bouts et construire des sous-approximations en complément de la sur-approximation classique. Enfin, nous combinons tout ceci pour calculer des ensembles de trajectoires de systèmes aérospatiaux et les utilisons pour évaluer la robustesse du contrôle
Cavell and Kuhn: Editorial Comment
No full textInternational audienceThe tenth issue of Conversations takes as its starting point the mutually expressed importance of the intellectual relationship and friendship between Stanley Cavell and the historian of science Thomas Kuhn. Their dialogue is all the more striking given that both thinkers were as concerned with difficulties of communication as with its achievement. Yet there is no hint of a struggle with incommensurability in Kuhn’s claim that Cavell was “the only person with whom I have been able to explore my ideas in incomplete sentences.” Cavell likewise explained, in The Claim of Reason, that the work owed much to having been “at times almost in possession of the something you might call an intellectual community” while working with Kuhn at Berkeley. This issue springs from these conversations between Cavell and Kuhn, exploring and extending their encounters through readings which cross Cavell with Kuhn and Kuhn with Cavell, and in so doing extending our understanding of each, while also illustrating the ways in which their work can still provide inspiration for grappling with science, art, and philosophy
Objective assessment of corneal transparency in the clinical setting: Identification and correction of acquisition artifacts in SD-OCT images
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Full-Field Optical Coherence Microscopy for Histology-Like Analysis of Stromal Features in Corneal Grafts
No full textInternational audienceCorneal transparency is essential to provide a clear view into and out of the eye, yet clinical means to assess such transparency are extremely limited and usually involve a subjective grading of visible opacities by means of slit-lamp biomicroscopy. Here, we describe an automated algorithm allowing extraction of quantitative corneal transparency parameters with standard clinical spectral-domain optical coherence tomography (SD-OCT). Our algorithm employs a novel pre-processing procedure to standardize SD-OCT image analysis and to numerically correct common instrumental artifacts before extracting mean intensity stromal-depth ( z ) profiles over a 6-mm-wide corneal area. The z -profiles are analyzed using our previously developed objective method that derives quantitative transparency parameters directly related to the physics of light propagation in tissues. Tissular heterogeneity is quantified by the Birge ratio B r and the photon mean-free path ( l s ) is determined for homogeneous tissues (i.e., B r ~1 ). SD-OCT images of 83 normal corneas (ages 22–50 years) from a standard SD-OCT device (RTVue-XR Avanti, Optovue Inc.) were processed to establish a normative dataset of transparency values. After confirming stromal homogeneity ( B r <10), we measured a median l s of 570 μm (interdecile range: 270–2400 μm). By also considering corneal thicknesses, this may be translated into a median fraction of transmitted (coherent) light T coh(stroma) of 51% (interdecile range: 22–83%). Excluding images with central saturation artifact raised our median T coh(stroma) to 73% (interdecile range: 34–84%). These transparency values are slightly lower than those previously reported, which we attribute to the detection configuration of SD-OCT with a relatively small and selective acceptance angle. No statistically significant correlation between transparency and age or thickness was found. In conclusion, our algorithm provides robust and quantitative measurements of corneal transparency from standard SD-OCT images with sufficient quality (such as ‘Line’ and ‘CrossLine’ B-scan modes without central saturation artifact) and addresses the demand for such an objective means in the clinical setting
Development of new strategies for the synthesis of aromatic polyketides: regioselective C-H functionalization of naphthalene derivatives
No full textNational audienc
Procédé de préparation de composés comportant une structure 2,5-dihydrobenzoxépine par réarrangement photochimique
No full textLa présente invention s’applique au domaine de la synthèse de composés chimiques possédant une structure dihydrobenzoxépine. En particulier, l’invention est relative à un procédé de préparation de composés chimiques comportant une structure 2,5-dihydro-1-benzoxépine par réarrangement photochimique à partir composés chimiques possédant une structure chromène. Figure à publier : aucune figur
Characterization of spatiotemporal couplings with far-field beamlet cross-correlation
No full textInternational audienceAbstract We present a novel, straightforward method for the characterization of spatiotemporal couplings in ultra-short laser pulses. The method employs far-field interferometry and inverse Fourier transform spectroscopy, built on the theoretical basis derived in this paper. It stands out in its simplicity: it requires few non-standard optical elements and simple analysis algorithms. This method was used to measure the space-time intensity of our 100 TW class laser and to test the efficacy of a refractive doublet as a suppressor of pulse front curvature (PFC). The measured low-order spatiotemporal couplings agreed with ray-tracing simulations. In addition, we demonstrate a one-shot measurement technique, derived from our central method, which allows for quick and precise alignment of the compressor by pulse front tilt (PFT) minimization and for optimal refractive doublet positioning for the suppression of PFC
Determination of the equivalent structural properties of a composite hydrofoil
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Quadrature amplitude modulation frequency up- and down-conversions using a positive-intrinsic-negative photodiode sampling mixer
No full textInternational audienceSimulation and experimental performance analysis of a positive-intrinsic-negative photodiode (PIN-PD) sampling mixer used as frequency up and down-converters are presented. Besides, a frequency mixing with a PIN-PD can operate in a frequency range up to 47.3 GHz for up-conversion and 38.5 GHz for down-conversion. The design and operating regime peculiarities of a PIN-PD as an up and down-converter in a radio over fiber (RoF) system are also discussed. The conversion gain of a PIN-PD sampling mixer is simulated and measured. We showed that the gain may decrease from 27 dB at a mixing frequency of 8.3 GHz to 3 dB at the one with 47.3 GHz in an up-conversion mode and from 26.5 dB at 31.7 GHz to 7 dB at 38.5 GHz in a down-conversion mode, when the PIN-PD bias voltage was 0 V. The conversion gain degrades with the decrease of the bias voltage from 0 to −5 V. Error vector magnitudes (EVMs) of the quadratic amplitude modulation (M-QAM) up and down-converted signals are investigated. Quadrature phase shift keying (QPSK) data at bit rates between 312.5 Mbit∕s and 5 Gbit∕s are frequency-converted. The EVM is used a performance index to assess the mixing system. Exploitable EVMs in the range of 15% up to 34.9% are reached for up-conversion of the mixing frequency. For down-conversion, the EVM varies from 20% to 34.9% at 5 Gbit∕s over the whole frequency range. The EVM of mixed signals is improved with 16-QAM and 64-QAM modulations