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Scattered wavefield in the stochastic homogenization regime
No full textIn the context of providing a mathematical framework for the propagation of ultrasound waves in a random multiscale medium, we consider the scattering of classical waves (modeled by a divergence form scalar Helmholtz equation) by a bounded object with a random composite micro-structure embedded in an unbounded homogeneous background medium. Using quantitative stochastic homogenization techniques, we provide asymptotic expansions of the scattered field in the background medium with respect to a scaling parameter describing the spatial random oscillations of the micro-structure. Introducing a boundary layer corrector to compensate the breakdown of stationarity assumptions at the boundary of the scattering medium, we prove quantitative - and - error estimates for the asymptotic first-order expansion. The theoretical results are supported by numerical experiments
Combined field-only boundary integral equations for PEC electromagnetic scattering problem in spherical geometries
No full textInternational audienceWe analyze the well posedness of certain field-only boundary integral equations (BIE) for frequency domain electromagnetic scattering from perfectly conducting spheres. Starting from the observations that (1) the three components of the scattered electric field and (2) scalar quantity are radiative solutions of the Helmholtz equation, novel boundary integral equation formulations of electromagnetic scattering from perfectly conducting obstacles can be derived using Green's identities applied to the aforementioned quantities and the boundary conditions on the surface of the scatterer. The unknowns of these formulations are the normal derivatives of the three components of the scattered electric field and the normal component of the scattered electric field on the surface of the scatterer, and thus these formulations are referred to as field-only BIE. In this paper we use the Combined Field methodology of Burton and Miller within the field-only BIE approach and we derive new boundary integral formulations that feature only Helmholtz boundary integral operators, which we subsequently show to be well posed for all positive frequencies in the case of spherical scatterers. Relying on the spectral properties of Helmholtz boundary integral operators in spherical geometries, we show that the combined field-only boundary integral operators are diagonalizable in the case of spherical geometries and their eigenvalues are non zero for all frequencies. Furthermore, we show that for spherical geometries one of the field-only integral formulations considered in this paper exhibits eigenvalues clustering at one -- a property similar to second kind integral equations
Efficient linear reformulations for binary polynomial optimization problems
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Fusion of images and clinical features for the prediction of Pulmonary embolism in Ultrasound imaging
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SOA-MZI Differential Transformation Approach Applied on Simultaneous Electro-Optical Mixing
No full textInternational audienceWe experimentally incubate a ground-breaking design, for the first time, of concurrent electro-optical semiconductor optical amplifier Mach–Zehnder interferometer mixing (SOA-MZI) based on a differential transformation methodology. Projecting the simultaneous electro-optical mixing system and improving its efficiency and quality achievement in optical and electrical features is a crucial task due to the characteristics of an optical pulse source (OPS) operating with a repetition rate of f= 58.5 GHz and a pulse width duration of 1 picosecond (ps). The resultant of the contemporaneous electro-optical mixing exhibits exceptional passive power stability, reaching 0.8% RMS over a two-hour period. Furthermore, when the optical bandpass filter is controlled at the data wavelength of 1540 nm, we achieve up to 30 dBm of the overall mean output power with an optical conversion gain of 46 dB and an exceptionally high optical signal-to-noise ratio reaching 80 dB. Using orthogonal frequency division multiplexing (OFDM) signals, each data subcarrier is modulated using 128 quadratic amplitude modulation (128-QAM) at carrier frequencies fk and simultaneously up-mixed to high aim frequencies nf±fk at the SOA-MZI output. Additionally, the resulting OFDM_128-QAM up-mixed signal is examined using the specifications for the error vector magnitudes (EVMs) and the electrical conversion gains (ECGs). The SOA-MZI mixing experiment can handle high frequencies up to 120 GHz. Positive ECGs are followed by a sharp reduction over the entire band of the aim frequencies. The highest frequency range achieved during the realistic investigation is shown at 2f+f4= 120 GHz, where the EVM reaches 8% with a symbol rate of 15 GSymb/s. Furthermore, the concurrent OFDM_128-QAM up-mixed signal achieves an absolute maximum bit rate of 80.4 Gbit/s. The investigation into the simultaneous electro-optical mixing regime is finally supported by unmatched characterization improvements
Uncovering the toughening mechanisms of bonded joints through tailored CFRP layup
No full textInternational audienceAiming to increase damage tolerance of adhesively bonded joints, this work explores the influence of CFRP layup of the adherends on the crack onset and crack propagation of composite bonded joints under mode I loading. Quasi-static Double Cantilever Beam tests were performed using four different CFRP layups bonded with two adhesives. Parallel to the experimental program, finite element analyses were performed to aid in understanding and identifying the various damage mechanisms in each specimen type. The results show that the CFRP layup and adhesive fracture toughness significantly influence the joint fracture phenomena at crack onset and further crack propagation. An enhancement of the joint's mode I fracture toughness values at crack onset was observed in the specimens where a crack competition between the propagation within the bondline and the composite's layers was triggered. During crack propagation, the fracture toughness of the joint increases at crack deflections between the different plies of the CFRP layup until reaching the 0° ply, where sudden delamination occurs. It has been shown that CFRP layup tailoring is a promising toughening method that, when carefully designed, has the potential to increase the maximum effective fracture toughness up to 100% when compared to pure cohesive failure
Conception d'une application de soutien à la coéducation pour l'inclusion scolaire des élèves TSA
No full textNational audienceThe socio-educational environment of a student with Autism Spectrum Disorder (ASD) is mainly tripartite, involving the family, the school and the medical-social services. Each of these parties, the people involved and their interactions have a direct influence on the young person. Although formally instituted as a requirement for school inclusion, coeducation is rarely operational, and each of the parties reports difficulties in communicating and coordinating the pupil's projects due to the absence of a unit of time and space for exchange. To fill this gap, the TousEnsemble research project consisted in co-designing an interactive web application for collaboration between those involved in the school inclusion of students with ASD. A participatory design method was chosen to enable co-decision, civic engagement and ethical accountability of stakeholders in the design of the future tool. Users' needs were collected, and various prototypes were created by iteratively integrating their feedback, until a consensus was reached. The ergonomic inspection of the final tool satisfied the main initial needs, resulting in a tool to support coeducation centered on skills, educational solutions and the sharing of everyone's expertise for the benefit of the pupil.L'environnement socioéducatif d'un élève avec Trouble du Spectre de l'Autisme (TSA) est principalement tripartite avec : sa famille, l'école, et les services médico-sociaux. Chacune des parties, les personnes impliquées et leurs interactions ont une influence directe sur le jeune. Bien que formellement instituée comme requise pour favoriser l'inclusion scolaire, la coéducation est rarement opérationnelle, et chacune des parties rapportent des difficultés de communication et de coordination des projets de l'élève liées à l'absence d'unité de temps et d'espace pour échanger. Pour parfaire cette absence, l'action recherche TousEnsemble a consisté à coconcevoir une application web interactive pour la collaboration entre les acteurs de l'inclusion scolaire des élèves avec TSA. Une méthode de conception participative a été choisie pour permettre la codécision, l'engagement citoyen, et la responsabilisation éthique des parties prenantes à la conception du futur outil. Les besoins des utilisateurs ont été collectés, différents prototypes ont été créés en intégrant itérativement leurs retours, jusqu'à aboutir à un consensus. L'inspection ergonomique de l'outil final a satisfait les principaux besoins initiaux, aboutissant à un outil de soutien à la coéducation centrée sur les compétences, solutions éducatives et un partage de l'expertise de chacun au bénéfice de l'élève