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Vertex-oriented Metaheuristic for Radar Lobe Detection in Electronic Warfare Context
No full textInternational audienceDeinterleaving is the task in electronic warfare aim-ing to sort pulses emitted by multiple radars. Most deinterleavingmethods search temporal patterns or cluster pulses according totheir primary parameters, yet rarely exploit pulse amplitude.In this article, we propose a lobe detection method for noisyobserved scenes. It is useful for deinterleaving because it providesinformation about a subset of pulses, i.e. pulses from the samelobe have likely the same emitter. Our method first estimates alobe vertex, then uses simulated annealing optimization to findthe best parabola fitting the lobe. It is evaluated on some realobserved scenes, and results show it successfully performs lobedetection even in case of a high outlier rate
Fatigue study of twisted polyamide sub-rope for floating wind turbines: Fast evaluation with heat build-up protocol and tomography study of mechanisms
No full textInternational audiencePolyamide 6 fibre ropes are of interest for floating offshore wind turbine mooring lines but their fatigue durability represents a key aspect to characterize and validate on the new constructions and coatings developed for this long term application. This paper presents a fatigue study on laboratory scale polyamide 6 sub-ropes which were wetted before testing. A T-N curve describing ranges of [2%, 70%] of MBL and [102,105] is obtained. An investigation of the damage mechanisms, using X-ray tomography analysis and SEM images, is performed and highlights the complexity of the mechanical response of twisted ropes, due to their hierarchical multi-scale construction. Cyclic loading changes significantly the sub-rope aspect and architecture. Finally, this study describes the use of a heat build-up measurement protocol, for a rapid evaluation of the fatigue properties of ropes. The cyclic dissipated energy was determined from temperature measurements by an infrared camera. A first prediction using this method is proposed and shows that it could provide a powerful solution, to overcome the very long testing times required for fatigue studies on synthetic sub-ropes
Revealing degradation mechanisms of archaeological flax textiles through the evolution of fibres’ parietal polymers by synchrotron deep-UV fluorescence
No full textInternational audienceAutofluorescence generated by plant cells and tissues provides a label-free method for investigating them without altering their structure and biochemistry. While in the literature, research mainly focuses on investigating fresh plant tissues, this study examines flax yarns from five archaeological artefacts to understand how cell wall fibres degrade and how their biochemical composition is modified after natural ageing over millennia. Using Synchrotron-based deep UV fluorescence (S-DUV), we aim to correlate fibre autofluorescence with the environmental conditions of discovery (clothes of votive statuettes buried in a sanctuary or shrouds and bandages for mummification rituals found in tombs) or their intended purposes (fishing net, which underwent wet-dry cycles during its use). Out of the five archaeological objects studied, the two yarns sampled from the buried fabrics were found encrusted with minerals, but with significant differences in the fibres’ degradation. The yarn sampled from the fishing net displayed a great variability of the dataset, with some fibres biochemically similar to the buried samples while others were closer to the funerary linen shrouds. Lignin's predominant presence at 480 nm in the fishing net suggests extensive cellulose-enriched cell wall layer degradation while the lignin-enriched layer is still preserved. Additionally, second harmonic generation imaging microscopy (SHG) and 2-photon excitation fluorescence (2PEF) were used alongside S-DUV analyses to evaluate the flax fibres’ ultrastructure. SHG confirmed S-DUV findings and indicated poor crystalline cellulose preservation in one linen shroud, explaining the yarn's brittleness
SpinDoctor-IVIM: A virtual imaging framework for intravoxel incoherent motion MRI
No full textInternational audienceIntravoxel incoherent motion (IVIM) imaging is increasingly recognised as an important tool in clinical MRI, where tissue perfusion and diffusion information can aid disease diagnosis, monitoring of patient recovery, and treatment outcome assessment. Currently, the discovery of biomarkers based on IVIM imaging, similar to other medical imaging modalities, is dependent on long preclinical and clinical validation pathways to link observable markers derived from images with the underlying pathophysiological mechanisms. To speed up this process, virtual IVIM imaging is proposed. This approach provides an efficient virtual imaging tool to design, evaluate, and optimise novel approaches for IVIM imaging. In this work, virtual IVIM imaging is developed through a new finite element solver, SpinDoctor-IVIM, which extends SpinDoctor, a diffusion MRI simulation toolbox. SpinDoctor-IVIM simulates IVIM imaging signals by solving the generalised Bloch-Torrey partial differential equation. The input velocity to SpinDoctor-IVIM is computed using HemeLB, an established Lattice Boltzmann blood flow simulator. Contrary to previous approaches, SpinDoctor-IVIM accounts for volumetric microvasculature during blood flow simulations, incorporates diffusion phenomena in the intravascular space, and accounts for the permeability between the intravascular and extravascular spaces. The above-mentioned features of the proposed framework are illustrated with simulations on a realistic microvasculature model.</div
Propagation des ultrasons dans des milieux aléatoires multi-échelles et estimation de vitesses effectives
No full textUltrasounds are widely used in medical imaging modalities. Originally, the ultrasound devices were built to image the internal structure of the tissues. In recent years, a change of paradigm operated and the goal is now also to assess physical parameters that can be used for medical diagnosis.The speed of acoustic waves inside soft tissues can be used for diagnosis of breast cancers or hepatic steatosis. Moreover, it determines the quality of the tomographic reconstruction of the tissues. Indeed, the images are usually computed by backpropagating the measured echoes at the speed of sound in water. However, the discrepancy between the speed of sound in water and the actual speed of sound inside the tissues results in nonphysical artifacts on the image.In order to establish a quantitative estimator of the propagation speed of sound inside the soft tissues, it is necessary to deeply understand the scattering of the medium. It is commonly admitted that the backscattered echoes are produced by numerous unresolved scatterers inside the medium (cell nuclei, mitochondria...). The scattering is then often modeled by the Born approximation. However, this model does not capture the variation of the effective speed of sound inside the tissue due to the unresolved scatterers. The goal of this thesis is thus to establish a propagation model that takes into account the variations of the effective speed of sound inside the tissues. Then, we will theoretically study the estimators previously introduced by Alexandre Aubry in his work.The tissue is here modeled as a bounded homogeneous mediumin which lie unresolved scatterers. As their distribution is unknown and inaccessible, their number and position is modeled as a random process. To obtain a simple form of the backscattered field, the techniques and tools developed for the quantitative stochastic homogenization theory will be used and a high-order asymptotic expansion will be proven.An asymptotic analysis of the imaging functional is carried out by using the high-order asymptotic expansion. Furthermore, the theoretical study of the estimators introduced by Alexandre Aubry and his team confirms and justifies some of the experimental results. In particular, it is possible to recover the effective speed of sound by a local spatial average of the imaging function.Numerical simulation supports each and every major result proven in this thesis.L'échographie est une méthode d'imagerie médicale très répandue. Son objectif principal est de fournir des images structurelles précises des tissus biologiques. Ces dernières années, un changement de paradigme s'est opéré, et le but est maintenant aussi d'obtenir des informations quantitatives sur les paramètres physiques des tissus, qui peuvent ensuite être utilisées pour le diagnostic.La vitesse de propagation des ondes acoustiques dans les tissus mous joue un double rôle, puisque sa bonne estimation peut être utilisée pour le diagnostic de cancer du sein ou de la stéatose hépatique, mais elle détermine aussi la qualité de la reconstruction structurelle. En effet, l'image est traditionnellement produite en repropageant numériquement les échos mesurés, à la vitesse du son dans l'eau. Cependant, lorsque la vitesse du son à l'intérieur des tissus n'est pas exactement celle de l'eau, des artéfacts non physiques apparaissent sur les images.Afin d'établir un estimateur quantitatif de cette vitesse de propagation, il est important de comprendre théoriquement la propagation des ondes acoustiques dans les tissus. Il est admis que les échos sont générés par les petites et nombreuses hétérogénéités à l'intérieur des tissus (noyaux de cellules, mitochondries...). Bien que le modèle de Born soit couramment utilisé, il ne prend pas en compte les effets des variations de vitesse effective dues aux hétérogénéités sous-résolues. L'objectif de cette thèse est donc d'établir un modèle de propagation d'onde plus sophistiqué, capable de représenter les variations de vitesse effectives dans les différents tissus. Dans un second temps, on s'attachera à étudier des estimateurs de la vitesse du son introduits précédemment par Alexandre Aubry dans ses travaux.Nous considérons donc un milieu homogène dans lequel se trouvent de nombreuses hétérogénéités microscopiques. Les hétérogénéités étant sous-résolues et leur distribution inconnue et inaccessible, on modélisera leur nombre et leur position de manière aléatoire. Afin d’obtenir une représentation simple du champ diffusé par le milieu, le formalisme et les techniques d'homogénéisation stochastique quantitative sont employés. En particulier, une asymptotique d’ordre élevé est obtenue.Nous poursuivons ensuite une analyse asymptotique de la fonctionnelle d'imagerie à partir du modèle d’ordre élevé précédemment obtenu. De plus, l'étude théorique des estimateurs introduits par Alexandre Aubry et de son équipe est menée permet de confirmer et de retrouver une partie des résultats expérimentaux. En particulier, il est possible de retrouver la vitesse effective des tissus à partir d'une moyenne spatiale locale de la fonctionnelle d'imagerie. Des simulations numériques attestent de chacun des résultats théoriques majeurs prouvés dans cette thèse
PhysioFormer: A Spatio-Temporal Transformer for Physical Rehabilitation Assessment
No full textInternational audienceStudies indicate that physical rehabilitation exercises recommended by healthcare professionals can enhance physical function,improve quality of life, and promote independence for physically disabled individuals. In response to the lack of immediate expert feedbackon performed actions, developing an automated system for monitoringsuch actions and providing feedback is very much needed. In this work,we focus on skeleton-based exercise assessment, which uses skeleton datato evaluate human motion and provide a score on how well a patientperformed a movement. There are several approaches to this issue, withSpatio Temporal Graph Convolutional Networks (GCN) being amongthe most recent. GCNs model skeleton data as graphs and utilize temporal and spatial convolutions to capture relationships between jointsmore effectively than previous methods. In this research, we propose anew Transformer based model, PhysioFormer. It is inspired by Skate-Former method for human action recognition, with enhanced structureto fit the task of physical rehabilitation assessment. The model leveragesskeletal-temporal self-attention across different groups based on relationsbetween joints. The evaluation is done on the KIMORE, UI-PRMD, andKERAAL datasets, benchmark datasets that provide skeleton data captured by Kinect motion system. Our model is surpassing state-of-the-artmethods significantly
Multi-modèles et apprentissage automatique pour l’optimisation et le contrôle du pas d’un propulseur cycloïdal
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Considering adjacent sets for computing the visibility region
No full textInternational audienceThis paper explores the problem of the paving of the union of adjacent contractors. The focus is first put on the analysis of the topology of a set operator, which can be stable or not stable. Then, depending on the stability of the union operator, solutions are proposed to avoid fake boundaries in stable and non-stable union of sets. For stable union of sets, a boundary preserving form will be developed to add a set overlapping the fake boundary in the expression of the union, whereas for non-stable union of sets, a boundary approach will be developed to avoid fake boundaries. Some problem specific solutions are also developed to avoid fake boundaries. As an example, an enhancement of the separator on the visibility constraint is proposed. This avoids fake boundaries while characterizing the set of non-visible points from an observation point relative to a polygon
Exploring the dynamic compression behavior of glass/epoxy composite through cutting-edge numerical modeling techniques
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Numerical analysis of an enriched beam model
No full textNational audienceThe finite element for a thin-walled tube developped in [1] is considered. A classical EulerBernoulli beam element has been enriched in order to take into account the influence of the rotations of the mid-surface on the local deformations of the tube cross-sections. The latter is a semi-analytical model using a Fourier expansion based on the circumferential variable. A grid convergence study of the enriched model is carried out for different mesh discretisations. Next, the stability of the explicit time integration is studied using the lumped mass matrix and the critical time steps associated to the mass matrix lumping are estimated