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All-Optical Three-Input “AND” Gate Dependent on a Differential Modulation Architecture
No full textInternational audienceThis gazette focuses on simulation and experimental studies for all-optical three-input “AND” gate schemes. The proposed gate exploits the semiconductor optical amplifier Mach-Zehnder Interferometer (SOA-MZI) nonlinearities, particularly the cross-phase modulation (XPM) corollary in addition to the cross-gain modulation (XGM) corollary, which originates from a SOA-MZI differential modulation concept. Further, the system performance is analyzed and examined through actual and simulated results to evaluate the obtained “AND” gate signal. Dependent on the nonlinearity of SOAs, the all-optical “AND” gate can operate with three signals driven by a 2 picoseconds (ps) optical pulse source (OPS). We noticed that our experimental results are perfectly matched to the simulated results. The output “AND” signal is acquired at higher common harmonics up to 200 GHz in the simulation study and the optical “AND”, which can vastly be used in optical networking, is evaluated through many parameters, such as error vector magnitude (EVM), extinction ratio (ER), and gain. As a result, the pinnacle bit rate for the 16-QAM (Quadrature Amplitude Modulation) and 256-QAM “AND” signal reaches 100 and 200 Gbit/s, respectively, at the 100 GHz common harmonic frequency
Méthodes d'échantillonnage linéaire généralisées pour des couches périodiques localement perturbées
No full textWe are interested in this PhD thesis in studying the inverse scattering problem for the reconstruction of defects in unbounded periodic structures, without a knowledge of the periodic background, and without assuming that the defect is also periodic. We first study the inverse problem using quasi-periodic incident waves. More precisely we employ the GLSM to solve the inverse problem for a single Floquet-Bloch mode. We then consider the case where non-quasi periodic incident sources are applied, and we employ the GLSM to define an indicator function for the full domain. Based on these two results, we apply the differential imaging to construct an indicator function allowing us to directly construct the defect. We give some numerical examples for the reconstruction obtained using the indicator function associated with the single Floquet-Bloch mode. We finally give a study for the well-posedness of the interior transmission problem by considering the cases when the perturbation is included in the periodic background. The study is based on the application of the Floquet-Bloch transform, a discretization with respect to the Floquet-Bloch variable and a convergence analysis to construct a solution for the Interior Transmission Problem.Nous nous intéressons dans cette thèse à l'étude du problème inverse de diffraction pour la reconstruction de défauts dans des structures périodiques non bornées, sans connaissance du domaine périodique, et sans supposer que le défaut est également périodique. Nous étudions d'abord le problème inverse utilisant des ondes incidentes quasi-périodiques. Plus précisément, nous appliquons le GLSM pour résoudre le problème inverse pour un seul mode Floquet-Bloch. Nous considérons ensuite le cas où des sources incidentes non quasi-périodiques sont appliquées, et nous utilisons le GLSM pour définir une fonction indicatrice pour tout le domaine. En se basant sur ces deux résultats, nous appliquons l’imagerie différentielle pour construire une fonction indicatrice permettant de construire directement le défaut. Nous donnons quelques exemples numériques de reconstruction obtenue à l'aide de la fonction indicatrice associée au seul mode Floquet-Bloch. Nous donnons enfin une étude du caractère bien posé du problème de transmission intérieure en considérant le cas où la perturbation est incluse dans le domaine périodique. L'étude est basée sur l'application de la transformation de Floquet-Bloch, une discrétisation par rapport à la variable Floquet-Bloch et une analyse de convergence pour construire une solution au problème de transmission intérieure
Structural characterization of N-acyl-homoserine lactones implied in bacterial quorum sensing using LC-MS/MS or/and SFC-MS/MS after in-solution derivatization by a Paternò-Büchi reaction
No full textInternational audienc
Statistical characterization of microcellular polyurethane foams microstructure based on 2D and 3D image analysis
No full textInternational audience This paper presents protocols developed to quantitatively characterize the cellular microstructure of microcellular polyurethane foams, from scanning electron microscopy (2D) and X-ray micro-computed tomography (2D and 3D) data. The objectives are to provide, for both techniques: (i) a detailed description of the analysis steps based on open source Python algorithms; (ii) a method for automatic, robust and objective detection of the cells to limit user’s biases; (iii) a statistical description of fraction, size, shape and spatial distribution of cells. The study considers 12 samples with densities ranging from about 400 to 600 kg m−3 and pore sizes from a few micrometers to several hundred micrometers. In addition, the database obtained is used to investigate the reliability of 2D measurements to describe the cellular microstructure statistics. </jats:p
Prerequisite Structure Discovery in Intelligent Tutoring Systems
No full textInternational audienceThis paper addresses the importance of Knowledge Structure (KS) and Knowledge Tracing (KT) in improving the recommendation of educational content in intelligent tutoring systems. The KS represents the relations between different Knowledge Components (KCs), while KT predicts a learner's success based on her past history. The contribution of this research includes proposing a KT model that incorporates the KS as a learnable parameter, enabling the discovery of the underlying KS from learner trajectories. The quality of the uncovered KS is assessed by using it to recommend content and evaluating the recommendation algorithm with simulated students
Caractérisation en fatigue à grand nombre de cycles par mesures d’auto-échauffement des aciers d’arbres de transmission pour application navale sous chargements cycliques complexes
No full textMarine shaft lines undergo complex cyclic loadings. In order to characterize these structures in fatigue, two complementary objectives are achieved. Firstly, the marine shaft’s loads are characterized in order to identify relevant fatigue cycles. During this step, an original parametric fatigue design method is implemented. This method is based on the definition of an equivalent load considering multiaxiality, variability, non-proportionality and mean stress. This method allows to distinguish two damage modes with a mode associated with the established cyclic regime of rotary bending and a mode associated with the ship’s maneuvers. Secondly, a rapid characterization method is implemented to characterize in fatigue the marine shafts’ steels for a large number of loading configurations. The method is based on a model which enables fatigue identification behaviors from self-heating measurements. The steels of the study are characterized in tension-torsion for various configurations of mean stress and nonproportionality of the loading. In this context, the notion of iso-self-heating surfaces is introduced. It allows, for a specimen, to model the elastoplastic and dissipative behavior of the material in the dedicated stress space. Their use makes it possible to define a multiscale fatigue criterion based on the invariants of the stress tensor. In the study, a modeling of the behavior of the material is proposed for very low amplitude loads (VHCF) exhibiting a strong difference in dissipation compared to the regime of higher amplitudes (i.e. HCF domain).Les lignes d’arbres de transmission navale sont soumises à des chargements cycliques complexes. Afin de caractériser en fatigue ces lignes d’arbres, deux objectifs complémentaires sont achevés. Dans un premier temps, les chargements des lignes d’arbres sont caractérisés afin d’identifier des cycles de fatigue pertinents. Lors de cette étape, une méthode paramétrique originale de dimensionnement en fatigue est mise en place. Cette méthode repose sur une modélisation des chargements avec une prise en compte de leur variabilité, de la contrainte moyenne et de la non-proportionnalité. Cette méthode montre qu’il existe deux modes d’endommagement avec un mode associé au régime cyclique établi de la flexion rotative et un mode associé aux manoeuvres du navire. Dans un second temps, une méthode de caractérisation rapide est mise en place afin d’étudier le comportement des aciers des lignes d’arbres en fatigue pour un grand nombre de configurations de chargements. Un modèle permettant d’identifier le comportement en fatigue à grand nombre de cycles, à partir des mesures d’autoéchauffements, est employé. Les aciers de l’étude sont caractérisés en traction-torsion pour diverses configurations de contraintes moyennes et de non-proportionnalité du chargement. Dans ce cadre, la notion de surface d’iso-auto-échauffement est introduite. Elle permet, pour une éprouvette, de modéliser le comportement élastoplastique et dissipatif du matériau dans l’espace dédié des contraintes. Leur utilisation permet de définir un critère de fatigue multiéchelle basé sur les invariants du tenseur des contraintes. Dans l’étude, une modélisation du comportement du matériau est proposée pour les chargements de très faible amplitude (fatigue à très grand nombre de cycles VHCF) montrant une différence forte de dissipation par rapport au régime d’amplitudes plus importantes (i.e. le domaine de la fatigue à grand nombre de cycles HCF)
Compatibility effect on stress-free two-way memory of Ni-Mn-Ga single crystal
No full textInternational audienc
GuaNary: Efficient Buffer Overflow Detection In Virtualized Clouds Using Intel EPT-based Sub-Page Write Protection Support
No full textInternational audienceWrite buffer overflow is a widespread and prevalent memory safety violation in C/C++, reported as the top vulnerability in 2022 and 2023. Secure memory allocators are generally used to protect systems against attacks that may exploit buffer overflows. Existing allocators mainly rely on two types of countermeasures to prevent or detect write overflows: canaries and guard pages, each with pros and cons in terms of detection latency and memory footprint. For virtualized cloud applications, this paper follows the Out of Hypervisor (OoH) trend and introduces GuaNary, a safety guard against write overflows, allowing synchronous detection at a low memory footprint cost. OoH is a new virtualization research axis introduced in 2022 advocating the exposure of hardware features for virtualization to the guest OS so that its processes can take advantage of them. Based on the OoH principle, GuaNary leverages Intel Sub-Page write Permission (SPP), a recent hardware virtualization feature that allows to write-protect guest memory at the granularity of 128B (namely, sub-page) instead of 4KB. We implement a software stack, LeanGuard, which promotes the utilization of SPP from inside virtual machines by new secure allocators that use GuaNary. Our evaluation shows that for the same number of protected buffers, LeanGuard consumes 8.3× less memory than SlimGuard, a recent state-of-art secure allocator. Further, for the same memory consumption, LeanGuard allows protecting 25× more buffers than SlimGuard
Deep water focused breaking wave loads on a fixed cylinder
No full textInternational audienceThis paper presents new results regarding numerical simulations of breaking wave impacts on a surface-piercing cylinder. The computational fluid dynamics solver, code_saturne, using the volume of fluid approach, is presented and used for offshore hydrodynamics. Phase-focused waves are generated to recreate singular breaking events under relatively controlled conditions. The numerical results compare favourably with a recent experimental campaign for the same conditions, although there is better agreement over the force impulse than the maximum force. The fluid shape and kinematics are described during the breaking process and the load produced by a plunging breaker on a rigid cylinder is investigated
Closed-form solutions for the elastic–plastic buckling design of shell structures under external pressure
No full textInternational audienceThis paper deals with the elastoplastic buckling analysis of shell geometries traditionally encountered in pressure vessels subjected to external pressure loading. The objective is to propose in a unified way original analytical closed-form solutions giving rise to reliable results, with a good accuracy and a wide range of applications in a straightforward and low time-consuming way, for efficient dimensioning purposes. The present study is based on the plastic bifurcation theory, classically used in the context of conservative systems, where additional terms are incorporated here due to the follower external pressure acting normally to the deformed surface of the shell still after buckling. Cylindrical shells are first considered, which certainly represent the most fundamental components of pressure vessels in practice. Owing to the external pressure also acting on the closure ends of a cylinder, the influence of the induced axial compression is investigated thereafter. It appears to be non-negligible for short cylinders in elasticity and it becomes very significant in the case of plastic buckling. Then, closed-form solutions for the critical external pressure of a complete sphere are also obtained, both in elasticity and plasticity. Finally, all these new closed-form solutions are validated against reference numerical results obtained through finite element computations, and compared to current design rules