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International audience; Although dealing with interruptions in remote collaboration has been studied in general, few works have done this for Extended Reality (XR) collaboration. With the current explosion of interest in XR collaboration, we explore the negative impacts of interruptions in synchronous distributed XR environments and propose a novel concept for dealing with them: Absence Agents. We present their requirements analysis, design, and a prototype implementation. We believe that our concept and design of Absence Agents are important for practitioners and researchers alike, as they highlight avenues for future research.

International audience; Evidence theory, also called belief functions theory, provides an efficient tool to represent and combine uncertain information for pattern classification. Evidence combination can be interpreted, in some applications, as classifier fusion. The sources of evidence corresponding to multiple classifiers usually exhibit different classification qualities, and they are often discounted using different weights before combination. In order to achieve the best possible fusion performance, a new Credal Belief Redistribution (CBR) method is proposed to revise such evidence. The rationale of CBR consists in transferring belief from one class not just to other classes but also to the associated disjunctions of classes (i.e., meta-classes). As classification accuracy for different objects in a given classifier can also vary, the evidence is revised according to prior knowledge mined from its training neighbors. If the selected neighbors are relatively close to the evidence, a large amount of belief will be discounted for redistribution. Otherwise, only a small fraction of belief will enter the redistribution procedure. An imprecision matrix estimated based on these neighbors is employed to specifically redistribute the discounted beliefs. This matrix expresses the likelihood of misclassification (i.e., the probability of a test pattern belonging to a class different from the one assigned to it by the classifier). In CBR, the discounted beliefs are divided into two parts. One part is transferred between singleton classes, whereas the other is cautiously committed to the associated meta-classes. By doing this, one can efficiently reduce the chance of misclassification by modeling partial imprecision. The multiple revised pieces of evidence are finally combined by Dempster-Shafer rule to reduce uncertainty and further improve classification accuracy. The effectiveness of CBR is extensively validated on several real datasets from the UCI repository, and critically compared with that of other related fusion methods.

Nickel-base superalloys display cuboidal precipitates aligned along the cubic directions, which are the elastic soft directions. At high precipitate volume fraction, the microstructure is often described as a regular array of precipitates organized on a simple cubic macro-lattice. In the present work, we use a stability analysis and 3D phase field simulations to show that such a regular array is in fact unstable whatever the volume fraction of precipitates. The two main instability modes are the longitudinal [100] mode and the transverse [110] mode along the [ 1 1 ¯ 0 ] eigenvector. We argue that these instabilities lead to formation of configurational defects closely related to experimentally observed branches and herringbone patterns. The roles of elastic anisotropy and elastic homogeneity are also discussed.

International audience; Ultra-High Temperature Ceramics (UHTC) are good candidates to fulfil the harsh requirements of hypersonic applications. For more than a decade, ONERA has been actively involved in several programs to develop such materials for different applications (hypersonic flights, propulsion systems ...). In our laboratories, monolithic and composite materials have been investigated as well as several processing methods. In this paper, we present for example the ZrB2-SiC and HfB2-SiC compositions with TaSi2 or Y2O3 additions which have been especially studied in the European Projects ATLLAS and ATLLAS 2. Assessments of several prototypes in realistic environment are also described. Furthermore, based on these material developments, a specific study on the oxidation behaviour of such monoliths from 1200°C to 2400°C with a dedicated test bench using a 2 kW CO2 laser has been carried out (oxidation under air and water vapour atmospheres). Recently, some work on the manufacturing of Ultra-High Temperature Ceramic Matrix Composites (UHTCMC) has been initiated using slurry infiltration and pyrolysis. The behaviour and properties of these materials are encouraging.; Les céramiques ultraréfractaires (UHTC) sont de bons candidats pour répondre aux besoins sévères des applications liées à l'hypersonique. Depuis plus de dix ans, l'ONERA est impliquée activement dans plusieurs programme de recherche pour développer ce type de matériaux pour différentes applications (vols hypersonique, systèmes de propulsion ...). Au sein de nos laboratoires, des matériaux monolithiques et composites ont été étudiés ainsi que plusieurs méthodes d'élaboration. Dans cet article, nous présentons par exemple les compositions de type ZrB2-SiC et HfB2-SiC contenant des ajouts de TaSi2 ou Y2O3 qui ont été spécifiquement étudiées dans les projets européens ATLLAS et ATLLAS 2. L'évaluation de plusieurs prototypes dans des conditions réalistes est également présentée. Par ailleurs, en se basant sur ces développements matériaux, une étude spécifique sur le comportement à l'oxydation de tels monolithes entre 1200°C et 2300°C a été effectuée avec un moyen d'essai utilisant un laser CO2 de 2 kW (oxydation sous air et sous vapeur d'eau). Récemment, des travaux sur l'élaboration de composites à matrice ultraréfractaire (UHTCMC) ont été engagés en employant l'infiltration de suspension et leur pyrolyse. Le comportement et les propriétés de ces matériaux sont encourageants.

International audience; This paper presents aeroacoustic investigations on a full-scale Ultra High Bypass Ratio (UHBR) engine with inflow distortion at transonic conditions. Computational Fluid Dynamics (CFD) simulations are first realized to compute the shocks in the vicinity of the fan. These shocks are then radiated in the near-field thanks to Computational AeroAcoustics (CAA) simulations. The chaining between CFD and CAA simulations is done by injecting the shocks in terms of usual conservative variables using a non-reflecting boundary condition. The CAA solver is based on the non-linearized Euler equations which allows to define the CFD/CAA interface close to the fan where the propagation of shocks is highly non-linear. Both shock generation and propagation mechanisms are investigated and the effects of inflow distortion are highlighted by comparison with a baseline case without distortion. The flow distortion is shown to be responsible for a modification of shock amplitudes along the circumferential direction. Thus, azimuthal modes appear in addition to the rotor-locked mode present without distortion. A particular feature of the studied configuration is the presence of a supersonic flow region in the bottom part of the nacelle. This supersonic pocket blocks the shocks in the lower half of the nacelle and also modifies the angle at which they leave the nacelle in its upper half. Consequently, the far-field radiation (obtained using Kirchhoff’s integral method) is mainly oriented skywards and towards the side of descending blades. Acoustic power estimates are provided to quantify these effects.

International audience; The presented adaptive modelling approach aims to jointly control the level of refinement for each of the building-blocks employed in a typical chain of finite element approximations for stochas-tically parametrized systems, namely: (i) finite error approximation of the spatial fields (ii) surro-gate modelling to interpolate quantities of interest(s) in the parameter domain and (iii) Monte-Carlo sampling of associated probability distribution(s). The control strategy seeks accurate calculation of any statistical measure of the distributions at minimum cost, given an acceptable margin of error as only tunable parameter. At each stage of the greedy-based algorithm for spatial discreti-sation, the mesh is selectively refined in the subdomains with highest contribution to the error in the desired measure. The strictly incremental complexity of the surrogate model is controlled by enforcing preponderant discretisation error integrated across the parameter domain. Finally, the number of Monte-Carlo samples is chosen such that either (a) the overall precision of the chain of approximations can be ascertained with sufficient confidence, or (b) the fact that the computational model requires further mesh refinement is statistically established. The efficiency of the proposed approach is discussed for a frequency-domain vibration structural dynamics problem with forward uncertainty propagation. Results show that locally adapted finite element solutions converge faster than those obtained using uniformly refined grids.

Modelocked lasers constitute the fundamental source of optically-coherent ultrashort-pulsed radiation, with huge impact in science and technology. Their modeling largely rests on the master equation (ME) approach introduced in 1975 by Hermann A. Haus. However, that description fails when the medium dynamics is fast and, ultimately, when light-matter quantum coherence is relevant. Here we set a rigorous and general ME framework, the coherent ME (CME), that overcomes both limitations. The CME predicts strong deviations from Haus ME, which we substantiate through an amplitude-modulated semiconductor laser experiment. Accounting for coherent effects, like the Risken-Nummedal-Graham-Haken multimode instability, we envisage the usefulness of the CME for describing self-modelocking and spontaneous frequency comb formation in quantum-cascade and quantum-dot lasers. Furthermore, the CME paves the way for exploiting the rich phenomenology of coherent effects in laser design, which has been hampered so far by the lack of a coherent ME formalism., Modelocked lasers are typically modeled using the Haus master equation which, albeit powerful, provides only a limited description in certain parameter regimes. The authors introduce another master equation formalism to describe laser modelocking that accounts for coherent effects and overcomes these limitations.

International audience; Under the current global energy crisis the interests in developing a third generation of biofuels produced from non-food feedstock such as microalgae and cyanobacteria have clearly increased. Hydrodynamic stress, always present in cultivation process of these microorganisms, is an essential factor to ensure mixing inside bioreactors; however the importance of its intensity is usually ignored by applying a random agitation (energy consumption) which is unnecessarily overestimated. In this work, two types of agitation, stirring in agitated photobioreactors (APBR) and bubbling air in draft tube airlift photobioreactors (DPBR), are applied to study the effects of hydrodynamic stress on the growth and pigment content evolution of the cyanobacteria Synechocystis sp. PCC 6803, a self-propelled microorganism. The range of applied shear stress was between 0 and 400 mPa. Similar results are obtained for both agitation mechanisms, indicating that the effects of shear stress are limited to the breakdown of the cell colonies; once they are broken down any further increase in shear stress has no significant effect on their growth rate. Moreover, the variation in pigments concentration appeared to be linear with the cellular concentration and independent from shear intensity.

International audience; Speech technology plays an important role in our everyday life. Speech is, among others, used for human-computer interaction, including, for instance, information retrieval and on-line shopping. In the case of an unwritten language, however, speech technology is unfortunately difficult to create, because it cannot be created by the standard combination of pre-trained speech-to-text and text-to-speech subsystems. The research presented in this paper takes the first steps towards speech technology for unwritten languages. Specifically, the aim of this work was 1) to learn speech-to-meaning representations without using text as an intermediate representation, and 2) to test the sufficiency of the learned representations to regenerate speech or translated text, or to retrieve images that depict the meaning of an utterance in an unwritten language. The results suggest that building systems that go directly from speech-to-meaning and from meaning-to-speech, bypassing the need for text, is possible.

International audience; Coronagraphic imaging of exoplanets and circumstellar environments using ground-based instruments on large telescopes is intrinsically limited by speckles induced by uncorrected aberrations. These aberrations originate from the imperfect correction of the atmosphere by an extreme adaptive optics system; from static optical defects; or from small opto-mechanical variations due to changes in temperature, pressure, or gravity vector. More than the speckles themselves, the performance of high-contrast imagers is ultimately limited by their temporal stability, since most post-processing techniques rely on difference of images acquired at different points in time. Identifying the origin of the aberrations and the timescales involved is therefore crucial to understanding the fundamental limits of dedicated high-contrast instruments. In previous works we demonstrated the use of a Zernike wavefront sensor called ZELDA for sensing non-common path aberrations (NCPA) in the VLT/SPHERE instrument. We now use ZELDA to investigate the stability of the instrumental aberrations using five long sequences of measurements obtained at high cadence on the internal calibration source. Our study reveals two regimes of decorrelation of the NCPA. The first, with a characteristic timescale of a few seconds and an amplitude of a few nanometers, is induced by a fast internal turbulence within the enclosure. The second is a slow quasi-linear decorrelation on the order of a few 10−3 nmrms s−1 that acts on timescales from minutes to hours. We use coronagraphic image reconstruction to demonstrate that these two NCPA contributions have a measurable impact on differences of images, and that the fast internal turbulence is a dominating term over to the slow linear decorrelation. We also use dedicated sequences where the derotator and atmospheric dispersion compensators emulate a real observation to demonstrate the importance of performing observations symmetric around the meridian, which minimizes speckle decorrelation, and therefore maximizes the sensitivity to point sources in difference of images.

International audience; BACKGROUND: Deep brain stimulation of the sub-thalamic nucleus (DBS-STN) reduces symptoms in Parkinson’s disease (PD) patients with motor fluctuations. However, some patients may not feel ameliorated afterwards, despite an objective motor improvement. It is thus important to find new predictors of patients’ quality of life (QoL) amelioration after DBS-STN. We hypothesized that personality dimensions might affect QoL after DBS-STN. OBJECTIVE: To evaluate associations between personality dimensions and QoL improvement one year after DBS-STN. METHODS: DBS-STN-PD patients (n = 303) having answered the "Temperament and Character Inventory" (TCI) before surgery and the PDQ-39 before and one year after surgery were included, from the cohort study PREDI-STIM. Linear regression models were used to evaluate associations between TCI dimensions and change in PDQ-39 scores after DBS-STN. RESULTS: Novelty Seeking and Cooperativeness scores before surgery were positively associated with PDQ-39 scores improvement after DBS-STN (FDR-adjusted p < 0.01). Moreover, paradoxically unimproved patients with deterioration of their PDQ-39 scores after DBS-STN despite improvement of their MDS-UPDRS-IV scores had lower Cooperativeness scores, while paradoxically improved patients with amelioration of their PDQ-39 scores despite deterioration of their MDS-UPDRS-IV scores had higher Reward Dependence scores. CONCLUSION: Some presurgical personality dimensions were significantly associated with QoL amelioration and discrepancy between motor state and QoL changes after DBS-STN in PD. Educational programs before DBS-STN should take in account patient personality dimensions to better deal with their expectations.

Collective self-consumption (CSC) is often presented as an approach for better energy management. This paper proposes a multi-agent and multi-level model to analyze the impact of CSC in the residential sector. It considers human activity as the core of electricity consumption in the household. In addition to a co-simulation between a multi-agent model of human activity and a thermal model, we added a layer to simulate interactions within an association of households, together with collective means of production and storage. This model was used to perform various studies. First, CSC configurations with individual and collective storage were simulated. The results highlight the impact of individual and collective means of storage on the way energy is consumed, exchanged, charged or discharged in the group of households and within each household. Finally, a large structure including energy exchanges between a set of households (neighborhood) forming a CSC was modeled. The results clearly show the impact of energy exchange between neighborhoods on the overall CSC.

International audience

International audience; In this paper, an environmental barrier coating (EBC), which has undergone thermal cycling under spatiotemporal gradients, is inspected using active thermography. The technique considered herein is known as laser spot thermography. This study deals with the detection of a very thin crack network of unknown orientation. A numerical analysis is presented to investigate the sensitivity of experimental parameters on the detection. Image processing using a Laplacian operator combined with histogram equalisation to mitigate optical defects is then proposed to construct a cartography that is similar to scanning electron microscopy (SEM) observations despite the very adverse conditions.

International audience; Nanocrystal-based solar cell technologies currently have two materials competing for the highest performances: PbS and perovskites. These latter benefit from a defect-tolerant electronic structure, while PbS benefits from a mature diode fabrication technique and from its near-infrared absorption. Here we choose to revisit the potential of these PbS photodiodes for near-infrared detection and more precisely for active imaging. This mode of detection combines an eye invisible source with a detector. Such detection mode is used for surveillance, industrial sorting, LIDAR, etc. Here we use a state-of-the-art photodiode geometry and we reveal its potential for near-IR active detection at 940 nm. The diode can achieve a high photoresponse of 0.5 A.W-1, corresponding to an external quantum efficiency of 66% and a detectivity above 1012 Jones at room temperature. The time response which is often neglected for solar cells is found to be 10 ns for rise time and 1 µs for decay time. We demonstrate that long-distance (over 150 m) and time-gated active imaging can be conducted using this device.

Dempster-Shafer evidence theory, also called the theory of belief function, is widely used for uncertainty modeling and reasoning. However, when the size and number of focal elements are large, the evidence combination will bring a high computational complexity. To address this issue, various methods have been proposed including the implementation of more efficient combination rules and the simplifications or approximations of Basic Belief Assignments (BBAs). In this paper, a novel principle for approximating a BBA into a simpler one is proposed, which is based on the degree of non-redundancy for focal elements. More non-redundant focal elements are kept in the approximation while more redundant focal elements in the original BBA are removed first. Three types of degree of non-redundancy are defined based on three different definitions of focal element distance, respectively. Two different implementations of this principle for BBA approximations are proposed including a batch and an iterative type. Examples, experiments, comparisons and related analyses are provided to validate proposed approximation approaches. Keywords: BBA approximation, Belief functions, Evidence theory, Focal element, Non-redundancy

International audience; This paper presents the broadband noise analysis of a Counter Rotating Open Rotor (CROR) configuration. The numerical study is based on a hybrid approach: a Large Eddy Simulation (LES) code solves the near-flow field of the CROR configuration and the near-to-far-field propagation is then predicted by a Ffowcs Williams-Hawkings analogy either based on a solid or porous formulation. The LES solver uses a phase-lagged assumption with a proper orthogonal decomposition for the data storage. The numerical approach is validated against wind tunnel experimental data of a CROR configuration (AI-PX7) at three different operating points focused on the broadband noise. The analysis of the numerical simulations shows the predominant effect of the rear rotor suction side on the radiated broadband noise with an increasing contribution with span location. This source is related to the impingement of front rotor wakes and the development of leading edge vortices that induce large pressure fluctuations close to the leading edge on the suction side.

International audience; The understanding of hydrodynamic heat transport in finite-sized graphitic materials remains elusive due to the lack of an efficient methodology. In this paper, we develop a computational framework enabling an accurate description of heat transport in anisotropic graphite ribbons by a kinetic theory approach with full quantum mechanical first-principles input. A unified analysis of the size scaling of the thermal conductivity in the longitudinal and transverse directions of the system is made within the computational framework complemented with a macroscopic hydrodynamic approach. As a result, we demonstrate a strong end effect on the phonon Knudsen minimum, as a hallmark of the transition from ballistic to hydrodynamic heat transports, along a rectangular graphite ribbon with finite length and width. The phonon Knudsen minimum is found to take place only when the ribbon length is ∼5-10 times the upper limit of the width range in the hydrodynamic regime. This paper contributes to a unique methodology with high efficiency and a deeper understanding of the size effect on phonon hydrodynamics, which would open opportunities for its theoretical and experimental investigation in graphitic micro-and nanostructures.

International audience; The New Astrometric Reduction of Old Observations (NAROO) center can be found at the Paris Observatory in Meudon, and it is dedicated to the measurement of astrophotographic plates and the analysis of old observations. The NAROO digitizer consists of a granite-based Newport-Microcontrol open-frame air-bearing XY positioning table, a scientific sCMOS camera, and a telecentric optical system. The plate holder assembly is suited for mounting glass plates up to 350 mm squared. The machine positioning stability is better than 15 nm, and its repeatability is better than 40 nm. With real photographic plate data, we were able to produce measurements with an accuracy better than 65 nm. The renewed interest about photographic plates concerns the expansion of the database of transient objects evolving in time, since digitization now makes it possible to measure images with a high level of accuracy and to identify all the available objects. The information extracted from such materials can be of an astrometric, photometric, and spectroscopic nature, when not purely imaging, with consequences in planetology, near-Earth asteroid risk assessment, astrophysical phenomena, and general relativity, to mention but a few. Through our scientific program in the Gaia era, we detail examples of current and upcoming uses for the community. We invite researchers to use our facilities and digitize their collection by answering our call for proposals.

International audience

Identification of coherent structures is an essential step to describe and model turbulence generation mechanisms in wall-bounded flows. To this end, we present a clustering method based on latent Dirichlet allocation (LDA), a generative probabilistic model for collection of discrete data. The method is applied to a set of snapshots featuring the Reynolds stress (. Both two- and three-dimensional analysis show that LDA provides a robust and compact flow description in terms of a combination of motifs, which are latent variables inferred from the set of snapshots. We find that the characteristics of the motifs scale with the wall distance, in agreement with the wall-attached eddy hypothesis of Townsend (Physics of Fluids, 1961, pp. 97–120). Latent Dirichlet allocation motifs can be used to reconstruct fields with an efficiency that can be compared with the proper orthogonal decomposition (POD). Moreover, the LDA model makes it possible to generate a collection of synthetic fields that captures the intermittent characteristics of the original dataset more clearly than its POD-generated counterpart. These findings highlight the potential of LDA for turbulent flow analysis, efficient reconstruction of actual fields and production of a new field with suitable statistics.

Professional embodied conversational agents (ECAs) deployed in the market are dedicated to satisfying the digital customer relationship. However, ECAs still suffer from a lack of user adoption, in particular because most of them have few social skills. Inspired by social presence theories and based on the ergonomic components of user experience (CUE) model (Mahlke and Lindgaard, 2007), the paper focuses on one social skill, i.e., virtual intimacy, a 3-dimensional concept including honesty and genuineness, positivity and mutual comprehension. Virtual intimacy may be a way to reinforce the social dimension of human-agent interactions and to provide a better user experience. We therefore propose an interactive experiment that incorporates natural interactions between real tourists and an autonomously intimate virtual counselor who is an expert in tourism and able to express intimacy-related behaviors in verbal and nonverbal communication. The paper studies the impact of the agent’s expression of intimacy-related behaviors on the perception of virtual intimacy, social presence and the user experience. The results show that users adopt a social attitude toward the intimate counselor, and although they do not significantly perceive virtual intimacy, they clearly perceive the dimension of honesty and genuineness. Moreover, the agent’s expression of intimacy only enhances copresence, the first perceptive level of social presence. Except for user social status, which is enhanced, the user experience is also not significantly influenced by intimate expression. The study results further demonstrate that perceiving virtual intimacy is a good predictor of social presence and user experience, especially user emotional reactions. Perceiving virtual intimacy influences user experience independently of social presence, which thereby indicates that independent intimacy-related mechanisms, such as emotional contagion, may be involved. Mediation analyses also underline that perceiving virtual intimacy has a direct effect on user emotional reactions, but this finding is not supported by the CUE model. The findings in this study provide new evidence that perceiving virtual intimacy in human-agent interaction elicits emotions in users and enhances user experience. In line with this, we propose an outline for an ECA-adapted, user experience model based on the CUE model.

When humans infer underlying probabilities from stochastic observations, they exhibit biases and variability that cannot be explained on the basis of sound, Bayesian manipulations of probability. This is especially salient when beliefs are updated as a function of sequential observations. We introduce a theoretical framework in which biases and variability emerge from a trade-off between Bayesian inference and a cognitive cost of carrying out probabilistic computations. We consider two forms of the cost: a precision cost and an unpredictability cost; these penalize beliefs that are less entropic and less deterministic, respectively. We apply our framework to the case of a Bernoulli variable: the bias of a coin is inferred from a sequence of coin flips. Theoretical predictions are qualitatively different depending on the form of the cost. A precision cost induces overestimation of small probabilities on average and a limited memory of past observations, and, consequently, a fluctuating bias. An unpredictability cost induces underestimation of small probabilities and a fixed bias that remains appreciable even for nearly unbiased observations. The case of a fair (equiprobable) coin, however, is singular, with non-trivial and slow fluctuations of the inferred bias. The proposed framework of costly Bayesian inference illustrates the richness of a 'resource-rational' (or 'bounded-rational') picture of seemingly irrational human cognition., Comment: 17 pages, 4 figures

This paper investigates the large-scale flow reorientations of Rayleigh–Bénard convection in a cubic cell using proper orthogonal decomposition (POD) analysis and modelling. A direct numerical simulation is performed for air at a Rayleigh number of $10^{7}$ and shows that the flow is characterized by four quasi-stable states, corresponding to a large-scale circulation lying in one of the two diagonal planes of the cube with a clockwise or anticlockwise motion, with occasional brief reorientations. Proper orthogonal decomposition is applied to the joint velocity and temperature fields of an enriched database which captures the statistical symmetries of the flow. We found that each quasi-stable state consists of a superposition of four spatial modes representing three types of structures: (i) a mean-flow mode consisting of two stacked counter-rotating torus-like structures; (ii) two large-scale two-dimensional rolls (pair of degenerated modes) which form large-scale diagonal rolls when combined together; and (iii) an eight-roll mode that transports fluid from one corner to the other and strengthens the circulation along the diagonal. In addition, we identified three other modes that play a role in the reorientation process: two boundary-layer modes (pair of degenerated modes) that connect the core region with the horizontal boundary layers and one mode associated with corner rolls. The symmetries of the different POD modes are discussed, as well as their temporal dynamics. A description of the reorientation process in terms of POD modes is provided and compared with other modal approaches available in the literature. Finally, Galerkin projection is used to derive a POD-based reduced-order model. Unresolved modes are accounted for in the model by an extra dissipation term and the addition of noise. A seven-mode model is able to reproduce the low-frequency dynamics of the large-scale reorientations as well as the high-frequency dynamics associated with the large-scale circulation rotation. Linear stability analysis and sensitivity analysis confirm the role of the boundary-layer modes and the corner-rolls mode in the reorientation process.

International audience; Infrared applications remain too often a niche market due to their prohibitive cost. Nanocrystals offer an interesting alternative to reach cost disruption especially in the shortwave infrared (SWIR, λ

International audience; This paper presents recent advances on two dimensional length-extension mode (2D-LEM) quartz resonators providing high quality (Q) factor on resonances at a few MHz. The resonators have been collectively manufactured using one or two steps quartz deep reactive-ion etching (DRIE) processes. These resonators combine the intrinsic qualities of quartz in comparison to silicon (i.e. high Q factor, low temperature sensitivity and piezoelectricity) and the advantages of microelectromechanical systems (MEMS) resonators: small dimensions, low power consumption and collective processes. Samples vibrating at frequencies f of 2.2, 3 and 4.5 MHz have shown promising results with very high Q factor. Q factor as high as 180,000 for fundamental mode vibrating at 2.2 MHz and 89,000 for harmonic mode at 8.9 MHz were measured which lead to quality factor and resonance frequency products (Q·f) figure of merit near 10^12 Hz at the state of the art for 2D-LEM quartz resonators and the higher Q factor measured for DRIE made quartz resonators. Two designs, several dimensions and two processes have been investigated. Two main limiting damping mechanisms were identified and one of them is strongly linked to the technological limits of the etching process.; Ce document présente les avancées récentes sur les résonateurs à quartz en mode d'extension bidimensionnelle de la longueur (2D-LEM) qui fournissent facteur de haute qualité (Q) sur les résonances à quelques MHz. Les résonateurs ont été fabriqués collectivement en utilisant un ou deux étapes des processus de gravure profonde par ions réactifs du quartz (DRIE). Ces résonateurs combinent les qualités intrinsèques du quartz dans par rapport au silicium (facteur Q élevé, faible sensibilité à la température et piézoélectricité) et les avantages de la microélectromécanique les résonateurs des systèmes MEMS : petites dimensions, faible consommation d'énergie et processus collectifs.Des échantillons vibrant à des fréquences f de 2,2, 3 et 4,5 MHz ont donné des résultats prometteurs avec un facteur Q très élevé. Le facteur Q comme jusqu'à 180 000 pour le mode fondamental vibrant à 2,2 MHz et 89 000 pour le mode harmonique à 8,9 MHz ont été mesurés qui conduisent à un facteur de qualité et à des produits de fréquence de résonance (Qxf) d'un mérite proche de 10^12 Hz à l'état de l'art pourLes résonateurs à quartz 2D-LEM et le facteur Q plus élevé mesuré pour le MEIR ont fait des résonateurs à quartz. Deux modèles, plusieurs et deux processus ont été étudiés. Deux principaux mécanismes d'amortissement limitatifs ont été identifiés et l'un des est fortement liée aux limites technologiques du processus de gravure.

International audience; In this paper, a model-based prognosis method where the degradation cannot be directly measured but only detectable through the drift of a model parameter is considered. This parameter drift is viewed as an unknown input, whose reconstruction allows the estimation of the degradation state. Model-based prognosis is divided into a filtering step where the current degradation state is estimated, and an uncertainty propagation step where the future degradation state is predicted. During these two steps, model uncertainty and measurement uncertainty are taken into account within the set-membership framework using interval techniques. The filtering step is performed with an interval unknown input observer for linear time-invariant discrete systems. Then, based on a set-membership constraint satisfaction methodology , interval propagation is performed to estimate the bounds that include the future degradation state until some failure threshold is reached, allowing the deduction of the interval including the remaining useful life. In order to demonstrate the efficiency of the proposed model-based prognosis methodology, the degradation of a suspension system is studied.

International audience; In this letter, we consider the robustness of the mismatched filter in presence of off-grid target. Since for an off-grid target, the received sampled signal differs from the on-grid signal, the mismatched filter as optimized in the literature is not optimal anymore, and in particular may present a deteriorated sidelobe level. We propose here a general optimization program enabling to get an optimal mismatched filter-with respect to the Integrated Sidelobe Level (ISL)-within the resolution cell. We detail then the resulting solution in two particular radar cases, namely a Doppler steering vector and a linear chirp signal. In both cases, the proposed solution involves the Discrete Prolate Spheroidal Sequences. Simulation results show that this solution indeed provides the best ISL in the resolution cell.

Publication étudiante; International audience; Optronic sensors on board satellites are used for remote sensing and telecommunications, but are submitted to meteorological conditions and among them cloud cover and aerosols. Aerosol presence in the field of view could be one of the key factor limiting performances of these sensors. The goal of this study is to predict optical transmission of a satellite’s sensor due to aerosols with a Monte Carlo method. Geometrical and optical properties required to build the model are obtained from CloudAerosol Lidar with Orthogonal Polarization (CALIOP) measurements. Atmospheric scenes containing aerosols are generated and transmission spectra are obtained along the line-of-sight of a virtual satellite. To evaluate the impact of aerosols on the optical link, we computed the probability that the transmittance along the LOS is higher than a given threshold. Different areas are selected and relevant satellites configurations are investigated: geostationary, Low-Earth-Orbit, nadir view angle, or tilted view. Results’ discussion points out the impact of climates and environments but also the importance of the satellite instruments angle of view in the optical transmission between ground stations and satellites.; Les capteurs optroniques embarqués à bord des satellites sont utilisés pour la télédétection et les télécommunications, mais sont soumis aux conditions météorologiques et parmi elles, la couverture nuageuse et les aérosols. La présence d'aérosols sur la ligne de visée pourrait être l'un des facteurs clés limitant les performances de ces capteurs. L'objectif de cette étude est de prédire la transmission optique entre un satellite et le sol en présence d'aérosols avec une méthode de Monte Carlo. Les propriétés géométriques et optiques des aérosols nécessaires à la construction du modèle sont obtenues à partir des données du Lidar Caliop (Cloud-Aerosol Lidar with Orthogonal Polarization). Des scènes atmosphériques contenant des aérosols sont générées et la transmission est obtenue le long de la ligne de visée d'un satellite virtuel. Pour évaluer l'impact des aérosols sur la liaison optique, nous avons calculé la probabilité que la transmission le long de la LDV soit supérieure à un seuil donné. Différentes régions sont sélectionnées et les configurations satellites pertinentes sont étudiées : géostationnaire, orbite terrestre basse (LEO), vue nadir ou oblique. La discussion sur les résultats met en évidence l'impact des climats et des environnements, mais aussi l'importance de l'angle de vue des satellites sur la qualité de la transmission optique entre les stations au sol et les satellites.

Quasi-static aberrations in coronagraphic systems are the ultimate limitation to the capabilities of exoplanet imagers both ground-based and space-based. These aberrations - which can be due to various causes such as optics alignment or moving optical parts during the observing sequence - create light residuals called speckles in the focal plane that might be mistaken for a planets. For ground-based instruments, the presence of residual turbulent wavefront errors due to partial adaptive optics correction causes an additional difficulty to the challenge of measuring aberrations in the presence of a coronagraph. In this paper, we present an extension of COFFEE, the coronagraphic phase diversity, to the estimation of quasi-static aberrations in the presence of adaptive optics-corrected residual turbulence. We perform realistic numerical simulations to assess the performance that can be expected on an instrument of the current generation. We perform the first experimental validation in the laboratory which demonstrates that quasistatic aberrations can be corrected during the observations by means of coronagraphic phase diversity., Comment: This is a pre-copyedited, author-produced PDF of an article accepted for publication in the Monthly Notices of the Royal Astronomical Society following peer review

International audience; Cet article retrace la vie d'Abraham de Moivre, « ce fameux géomètre » qui vécut à la charnière du Grand Siècle et de celui des Lumières, natif de Vitry-le-François mais qui finit ses jours outre-Manche et « que la France a droit de revendiquer sur l'Angleterre », selon le mot de Fontenelle. De Moivre est malheureusement quelque peu oublié dans son pays d'origine, lacune que cette contribution veut s'employer à combler. Nous mettons également l'accent sur son œuvre, en rappelant que ses travaux sur les rentes viagères sont à l'origine de la création de la première assurance vie.

International audience; We discuss spatial selection techniques for three-dimensional datasets. Such 3D spatial selection is fundamental to exploratory data analysis. While 2D selection is efficient for datasets with explicit shapes and structures, it is less efficient for data without such properties. We first propose a new taxonomy of 3D selection techniques, focusing on the amount of control the user has to define the selection volume. We then describe the 3D spatial selection technique Tangible Brush, which gives manual control over the final selection volume. It combines 2D touch with 6-DOF 3D tangible input to allow users to perform 3D selections in volumetric data. We use touch input to draw a 2D lasso, extruding it to a 3D selection volume based on the motion of a tangible, spatially-aware tablet. We describe our approach and present its quantitative and qualitative comparison to state-of-the-art structure-dependent selection. Our results show that, in addition to being dataset-independent, Tangible Brush is more accurate than existing dataset-dependent techniques, thus providing a trade-off between precision and effort.

International audience; The first stage in any control system is to be able to accurately estimate the system's state. However, some types of measurements are ambiguous (non-injective) in terms of state. Existing algorithms for such problems, such as Monte Carlo methods, are computationally expensive or not robust to such ambiguity. We propose the Box Regularized Particle Filter (BRPF) to resolve these problems. Based on previous works on box particle filters, we present a more generic and accurate formulation of the algorithm, with two innovations: a generalized box resampling step and a kernel smoothing method, which is shown to be optimal in terms of Mean Integrated Square Error. Monte Carlo simulations demonstrate the efficiency of BRPF on a severely ambiguous and non-linear estimation problem, that of Terrain Aided Navigation. BRPF is compared to the Sequential Importance Resampling Particle Filter (SIR-PF), Monte Carlo Markov Chain (MCMC), and the original Box Particle Filter (BPF). The algorithm outperforms existing methods in terms of Root Mean Square Error (e.g., improvement up to 42% in geographical position estimation with respect to the BPF) for a large initial uncertainty. The BRPF reduces the computational load by 73% and 90% for SIR-PF and MCMC, respectively, with similar RMSE values. This work offers an accurate (in terms of RMSE) and robust (in terms of divergence rate) way to tackle state estimation from ambiguous measurements while requiring a significantly lower computational load than classic Monte Carlo and particle filtering methods.; The first stage in any control system is to be able to accurately estimate the system’s state. However, some types of measurements are ambiguous (non-injective) in terms of state. Existing algorithms for such problems, such as Monte Carlo methods, are computationally expensive or not robust to such ambiguity. We propose the Box Regularized Particle Filter (BRPF) to resolve these problems.Based on previous works on box particle filters, we present a more generic and accurate formulation of the algorithm, with two innovations: a generalized box resampling step and a kernel smoothing method, which is shown to be optimal in terms of Mean Integrated Square Error.Monte Carlo simulations demonstrate the efficiency of BRPF on a severely ambiguous and non-linear estimation problem, the Terrain Aided Navigation. BRPF is compared to the Sequential Importance Resampling Particle Filter (SIR-PF), the Markov Chain Monte Carlo approach (MCMC), and the original Box Particle Filter (BPF). The algorithm is demonstrated to outperform existing methods in terms of Root Mean Square Error (e.g., improvement up to 42% in geographical position estimation with respect to the BPF) for a large initial uncertainty.The BRPF yields a computational load reduction of 73% with respect to the SIR-PF and of 90% with respect to MCMC for similar RMSE orders of magnitude. The present work offers an accurate (in terms of RMSE) and robust (in terms of divergence rate) way to tackle state estimation from ambiguous measurements while requiring a significantly lower computational load than classic Monte Carlo and particle filtering methods.

International audience; Macroscopic properties of structural materials are strongly dependent on their microstructure. However, the modeling of their evolution is a complex task because of the mechanisms involved such as plasticity, recrystallization, and phase transformations, which are common processes taking place in metallic alloys. This complexity led to a growing interest in atomistic simulations formulated without any auxiliary hypotheses beyond the choice of interatomic potential. In this context, we propose here a model based on an overdamped stochastic evolution of particles interacting through inter-atomic forces. The model settles to the correct thermal equilibrium distribution in canonical and grand-canonical ensembles and is used to study the grain boundary migration. Finally, a comparison of our results with those obtained by molecular dynamics shows that our approach reproduces the complex atomic-scale dynamics of grain boundary migration correctly.

International audience; The main purpose of this survey paper is to review the field of convergence between the liquid-propellant rocket-propulsion and automatic-control disciplines. A comprehensive collection of academic works and some industrial developments are summarised and discussed, making the link to the current context of launcher reusability. The main control problem in liquid-propellant rocket engines (LPRE), the target of this survey, generally consists in tracking set-points in combustion-chamber pressure and mixture ratio, their main operating quantities. This goal is attained via the adjustment of flow-control valves while complying with operating constraints. Each aspect of control systems, ranging from modelling to the actual control techniques, is reviewed and subsequently related to the rest of aspects. The comparison of the different approaches points to the general use of linearised models about concrete operating points for deriving steady-state controllers, which in most cases are of PID type. Other more sophisticated approaches present in the literature, incorporating some nonlinear, hybrid or robust techniques, improve certain aspects of performance and robustness. Nevertheless, no fully nonlinear or hybrid frameworks, which may allow the control of a wider throttling domain, have been published. In addition, control during the thermally and structurally demanding transient phases is usually in open loop, and hence with low correction margins. This sort of control enhancements, probably together with more sophisticated monitoring architectures, would serve to extend the life of LPRE, a significant factor in their reusability. Therefore, this survey intends to draw a path for the future control design trends which will certainly be more suitable for reusable LPRE.

International audience; In this work, we consider the discretization of nonlinear hyperbolic systems in nonconservative form with the high-order discontinuous Galerkin spectral element method (DGSEM) based on collocation of quadrature and interpolation points (Kopriva and Gassner, J. Sci. Comput., 44 (2010), pp.136-155). We present a general framework for the design of such schemes that satisfy a semi-discrete entropy inequality for a given convex entropy function at any approximation order. The framework is closely related to the one introduced for conservation laws by Fisher and Carpenter (J. Comput. Phys., 252 (2013), pp. 518-557) and Gassner (SIAM J. Sci. Comput., 35 (2013), pp. A1233-A1253) and relies on the modification of the integral over discretization elements where we replace the physical fluxes by entropy conservative numerical fluxes from Castro et al. (SIAM J. Numer. Anal., 51 (2013), pp. 1371-1391), while entropy stable numerical fluxes are used at element interfaces. Time discretization is performed with strong-stability preserving Runge-Kutta schemes. The present method is first validated on the Burgers and Euler equations in nonconservative form. We then use this framework for the discretization of two-phase flow systems in one space-dimension: a 2 × 2 system with a nonconservative product associated to a linearly-degenerate field for which the DGSEM fails to capture the physically relevant solution, and the isentropic Baer-Nunziato model. For the latter, we derive conditions on the numerical parameters of the discrete scheme to further keep positivity of the partial densities and a maximum principle on the void fractions. Numerical experiments support the conclusions of the present analysis and highlight stability and robustness of the present schemes.

International audience; Highlights: (maximum 85 characters, including spaces, per bullet point).  Acid-based geopolymers display different processing-dependent working properties.  Acid-based geopolymers are mostly composed of Al-O-P and Si(OH)4 networks.  The quantities of Al-O-P and unreacted metakaolin govern the thermal resistance.  The increase of the Young's modulus is related to a higher thermal resistance.  Ordered structures and low amounts of physisobed water lead to water resistance.

International audience; Thrombus formation is one of the main issues in the development of blood-contacting medical devices. This article focuses on the modeling of one aspect of thrombosis, the coagulation cascade, which is initiated by the contact activation at the device surface and forms thrombin. Models exist representing the coagulation cascade by a series of reactions, usually solved in quiescent plasma. However, large parameter uncertainty involved in the kinetic models can affect the predictive capabilities of this approach. In addition, the large number of reactions of the kinetic models prevents their use in the simulation of complex flow configurations encountered in medical devices. In the current work, both issues are addressed to improve the applicability and fidelity of kinetic models. A sensitivity analysis is performed by two different techniques to identify the most sensitive parameters of an existing detailed kinetic model of the coagulation cascade. The results are used to select the form of a novel reduced model of the coagulation cascade which relies on eight chemical reactors only. Then, once its parameters have been calibrated thanks to the Bayesian inference, this model shows good predictive capabilities for different initial conditions.

International audience; Composite materials are finding increasing application, for example in commercial aircraft. Traditionally fiber angles are restricted to 0 • , ±45 • and 90 •. The current work exploits the possibility of using multiple 'non-conventional' laminates where either fiber steering ('variable stiff-ness'), ply drops ('variable thickness'), or a combination of both is used. This leads to varying mechanical properties which means the load is being redistributed, increasing the overall buckling load. A flat panel of 400 × 600 mm loaded in uni-axial compression is optimized in the current work. As a benchmark a conventional laminate is used. The non-conventional laminates are 15% lighter to emphasize the possible weight savings. Only using variable stiffness or variable thickness is experimentally shown to not be sufficient to match the buckling load of the benchmark panel. However, using a combination of both, a 10% increase in the buckling load was found for a panel that is 15% lighter. This highlights the potential of non-conventional laminates.

International audience; In order to make substantial progress in reducing the environmental impact of aircrafts, a key technology is the reduction of aircraft weight. This challenge requires the development and the assessment of new technologies and methodologies of load prediction and control. To achieve the investigation of the specific case of gust load, ONERA defined a dedicated research program based on both Wind Tunnel Test campaigns and high fidelity simulations.To reach the experimental objectives, a set-up was designed, manufactured and implemented within the ONERA S3Ch transonic Wind Tunnel Facility. The first component, called gust generator, consists of two oscillating airfoils installed upstream of the wind tunnel test section and allows to produce air flow deflections. The second component, the test model, is a 2D supercritical airfoil based on a two degrees-of-freedom aeroelastic model. A test campaign has been performed leading to the generation of databases for high fidelity tools validation. These databases have been used in order to assess the capabilities of the elsA code (ONERA-Airbus-Safran property) using its aeroelastic module and a gust model based on the “Field Velocity Method”. A validation process has been defined in order to move from experimental results obtained in the wind tunnel with wall boundaries to industrial modeling computed with farfield boundaries. The full process was applied to a transonic case and a sine gust signals.; Afin de réaliser des progrès substantiels dans la réduction de l'impact environnemental des aéronefs, une technologie clé est la réduction de la masse de l'aéronef. Ce défi nécessite le développement et l'évaluation de nouvelles technologies et méthodologies de prévision et de contrôle de la charge. Pour mener à bien l’étude du cas particulier de rafale, l’ONERA a défini un programme de recherche dédié reposant à la fois sur des campagnes d’essais en soufflerie et sur des simulations haute fidélité.Pour atteindre les objectifs expérimentaux, une installation a été conçue, fabriquée et mise en œuvre au sein de de la soufflerie transsonique ONERA S3Ch. Le premier composant, appelé générateur de rafale, se compose de deux pales oscillantes installées en amont de la section d’essai en soufflerie et permettant de produire des variations longitudinales de l’écoulement d’air. Le deuxième composant, la maquette, est un modèle aéroélastique à deux degrés de liberté d'un profil aérodynamique supercritique. Une campagne de test a été réalisée qui a abouti à la création de bases de données pour la validation d’outils haute fidélité.Ces bases de données ont été utilisées pour évaluer les capacités du code elsA (propriété ONERA-Airbus-Safran) avec son module aéroélastique et un modèle de rafale basé sur la méthode Field velocity Method. Un processus de validation a été mis en place afin de passer des résultats expérimentaux obtenus en soufflerie avec des conditions aux limites de parois à une modélisation industrielle calculée à l'aide de conditions aux limites de champ lointain. Le processus complet a été appliqué à un cas transsonique avec des signaux d'excitation sinusoïdal.

International audience; Turbulent combustion models for Large Eddy Simulation (LES) aims at predicting the flame dynamics. So far, they have been proven to predict correctly the mean flow and flame properties in a wide range of configurations. A way to challenge these models in unsteady situations is to test their ability to recover turbulent flames submitted to harmonic flow modulations. In this study, the Flame Transfer Function (FTF) of a CH4/H2/air premixed swirled-stabilized flame submitted to harmonic flowrate modulations in a non-adiabatic combustor is compared to the response computed using the Filtered TAbulated Chemistry for LES (F-TACLES) formalism. Phase averaged analysis of the perturbed flow field and flame response reveal that the velocity field determined with Particle Image Velocimetry measurements, the heat release distribution inferred from OH* images and the probability of presence of burnt gases deduced from OH-Planar Laser Induced Fluorescence measure- ments are qualitatively well reproduced by the simulations. However, noticeable differences between experiments and simulations are also observed in a narrow frequency range. A detailed close-up view of the flow field highlight differences in experimental OH* and numerical volumetric heat release rate distributions which are at the origin of the differences observed between the numerical and experimental FTF. These differences mainly originate from the outer shear layer of the swirling jet where a residual reaction layer takes place in the simulations which is absent in the experiments. Consequences for turbulent combustion modeling are suggested by examining the evolution of the perturbed flame brush envelope along the downstream distance of the perturbed flames. It is shown that changing the grid resolution and the flame subgrid scale wrinkling factor in these regions does not alter the numerical results. It is finally concluded that the combined effects of strain rate and enthalpy defect due to heat losses are the main factors leading to small but sizable differences of the flame response to coherent structures synchronized by the acoustic forcing in the outer shear layer of the swirling flow. These small differences in flame response lead in turn to a misprediction of the FTF at specific forcing frequencies.

International audience; The direct measurement of Earth's energy imbalance (EEI) is one of the greatest challenges in climate research. The global mean EEI represents the integrated value of global warming and is tightly linked to changes in hydrological cycle and the habitability of our planet. Current space-born radiometers measure the individual radiative components of the energy balance with unprecedented stability, but with calibration errors too large to determine the absolute magnitude of global mean EEI as the components' residual. Best estimates of long-term EEI are currently derived from temporal changes in ocean heat content at ~0.7 Wm-2. To monitor EEI directly from space, we propose an independent approach based on accelerometry that measures non-gravitational forces, such as radiation pressure, acting on Earth orbiting spacecrafts. The concept of deriving EEI from radiation pressure has been considered in the past, and we provide analysis that shows today's capabilities are sufficiently accurate to answer the question: At what rate is our planet warming? To measure global mean EEI to within at least ±0.3 Wm-2 requires spacecraft(s) of near-spherical shape and well-characterized surface properties to reduce confounding effects. The proposed concept may provide the basis for a data record of global and zonal mean EEI on annual and potentially monthly time scales. It is not meant to replace existing concepts designed to measure energy balance components or ocean heat storage, but to complement these by providing an independent estimate of EEI for comparison and to anchor data products and climate models that lack energy balance closure.; La mesure directe du bilan énergétique de la Terre (EEI : Earth's Energy Imbalance) est l'un des plus grands défis de la recherche climatique. L'EEI moyen mondial représente la valeur intégrée du réchauffement climatique; sa variabilité spatiale et temporelle reflète la nature des transport de chaleur à travers le système climatique et les modes climatiques internes tels que l'ENSO. Ces transports de chaleur contrôlent les circulations atmosphériques et océaniques, et désormais le cycle de l'eau et l'habitabilité de notre planète. Les systèmes spatiaux actuels mesurent les composantes radiatives individuelles du bilan énergétique avec une précision et une stabilité sans précédent, mais les limites d'erreur sont trop grossières pour déterminer l'amplitude absolue de l'EEI moyen global ainsi que les résidus des contributeurs. Les meilleures estimations de l'IEE à long terme sont actuellement dérivées des changements de la teneur en chaleur des océans telle que mesurée in situ, mais sont affectées par des erreurs d'échantillonnage. Des méthodes alternatives sont nécessaires pour éviter l'imprécision de l'étalonnage radiométrique et l'échantillonnage incomplet in situ de l'océan. Pour suivre la valeur intégrée de l'EEI à partir de l'espace, nous proposons une approche basée sur l'accélérométrie qui mesure les forces non gravitationnelles, telles que la pression de radiation, agissant sur les satellites en orbite autour de la Terre. Le concept pour déduire l'EEI de la pression de radiation a été considéré dans le passé, et nous fournissons une analyse qui montre que les instruments d'aujourd'hui sont suffisamment précises pour enfin répondre à la question: à quel rythme notre planète se réchauffe-t-elle? Le concept proposé ne vise pas à remplacer les concepts existants conçus pour mesurer les composantes du bilan énergétique, mais à les compléter en fournissant une mesure directe de l'EEI responsable des changements climatiques de notre planète.

International audience; In order to investigate the influence of combustion-induced thermal expansion on turbulent flow within a premixed flame brush, a new method is introduced. The method consists in analyzing structure functions of the velocity field, which characterize velocity difference in two points A and B, with the structure functions being conditioned to various events; (i) unburned reactants in both points, (ii) combustion products in both points, (iii) intermediate states of the mixture in both points, (iv) the reactants in one point and the products in another point, (v) the reactants in one point and an intermediate state in another point, and (vi) the products in one point and an intermediate state in another point. Such structure functions and relevant probabilities are defined in the paper. Subsequently, the structure functions and the probabilities are extracted from Direct Numerical Simulation (DNS) data obtained from two statistically 1D, planar, fully-developed, weakly turbulent, premixed flames characterized by two significantly different (7.53 and 2.50) density ratios, with all other things being approximately equal. Obtained results indicate that (i) the conditioned structure functions differ significantly from the mean structure functions and (ii) the newly introduced approach could convey information important for understanding fundamentals of flame-turbulence interaction and finding issues that require further research. In particular, application of the approach to the aforementioned DNS data shows that the combustion-induced thermal expansion substantially affects small-scale two-point velocity statistics in the incoming constant-density turbulent flow of unburned reactants within a premixed flame brush.

We present an example of Bérenger's method for a problem with variable coefficients at the interface showing that the method is not perfectly matched. The reflections are revealed by constructing an infinitely accurate geometric optics approximation. They are also revealed in numerical simulations that confirm the dependence on wavelength from the asymptotic expansions.

International audience; Molecular dynamics simulations using two empirical potentials Cooper and MOX-07 are carried out to assess the mechanical properties of U$_x$Pu${1-x}$O$_2$ solid solution as a function of irradiation dose.The structural damage evolution with dose is modelled with the accumulation of Frenkel pairs method.The structural change follows classical steps with increasing dose first accumulation of point defects that cluster and form dislocation loops which transform in turn to dislocation lines. Elastic properties such as the bulk modulus and the anisotropic factor via the Zener's ratio are evaluated for each steps.Overall, bulk moduli decrease with increasing dose while anisotropic factor behaviour depends on the potential used.It is also found that point defects play a major role in these evolution.Traction-separation curves used in cohesive zone models are also calculated for different irradiation doses.From these curves we extract the tensile strengths and the energy release rates as well as the fracture toughness.Fracture toughness is found to increase steadily with dose whereas tensile strengths displays v-shape curves which decreases for low doses and raises for high doses.For all these mechanical properties, point defects seem to play a major role while the impact of the dislocations is rather minor.

This work investigates the evolution of the microstructure of an Nb-23Ti-20Si (at.%) based alloy, from the primary plasma-melted material that is gas-atomized towards the consolidated material (here using SPS). The nature, morphology and size of the solid solution and the various silicides are followed by SEM, EDS and EBSD. Homogenous and fine microstructures are obtained after the SPS step and are improved by a subsequent heat treatment (1500°C, 100 h). However blocky silicides, already present in the powder particles, cannot be eliminated. A better control of the primary material’s microstructure would improve the microstructure of the final material.

International audience; Cyber security system could benefit from the deep learning breakthrough.However, there are, today, critical issues with deep learning.The major issue is the lack of robustness of classical deep networks.This lack of robustness allows to compute well documented adversarial examples: confusing a network with just the addition of a low amplitude perturbation.Here, I show that this lack of robustness also allows adversarial model: possibility to change the global model behaviour with just the addition of a low amplitude perturbation to the train set.This property could be a real security faults for continuously trained system.Evaluation of the efficiency of adversarial model is provided on image classification datasets.

International audience; This paper investigates by means of computational fluid dynamics (CFD) and acoustic analogy the influence of blade deformations on open-rotor aerodynamics and aeroacoustics for three key operating points: cruise, takeoff, and approach conditions. For each operating point, simulation results obtained with unrunning blade shapes and running blade shapes are compared with wind tunnel test measurements. Experiments show that blade deformations affect mostly the front rotor, with twist deviations at tip varying within a range of ±2 deg and of opposite sign between cruise and takeoff conditions. Although blade deformations are low for the rear rotor, aerodynamic performance exhibits significant variations due to the modifications of the front rotor wash. Numerical results show that accounting for blade deformations increases or decreases the thrust or power depending on the operating point and leads to a much better prediction of the open-rotor aerodynamic performance. The same comments apply for the noise prediction although differences on self-noise and interaction noise directivities are rather low.; Cet article étudie par simulation numérique influence des déformations de pale sur l'aérodynamique et l'aéroacoustique d'un doublet d'hélices contrarotatives pour trois points de fonctionnement différents: conditions de croisière, de décollage et d'approche. Pour chaque point de fonctionnement, les résultats des simulations obtenus avec des formes de pales à froid et à chaud sont comparés aux mesures effectuées sur la configuration générique Open-Rotor AI-PX7 d'Airbus Clean Sky dans la soufflerie transsonique S1MA de l'ONERA.

This article presents the prospects of measurement systems for wind hazards and turbulence at airports, which have been explored in the Ultrafast Wind Sensors (UFO) project. At France’s Toulouse–Blagnac Airport, in situ, profiling, and scanning sensors have been used to collect measurements, from which wind vectors and turbulence intensities are estimated. A scanning 1.5-µm coherent Doppler lidar and a solid state X-band Doppler radar have been developed with improved update rates, spatial resolution, and coverage. In addition, Mode-S data downlinks have been collected for data analysis. Wind vector and turbulence intensity retrieval techniques are applied to demonstrate the capabilities of these measurement systems. An optimal combination of remote measurement systems is defined for all weather monitoring at airports. In this combination, lidar and radar systems are complementary for clear-air and rainy conditions, which are formulated in terms of visibility and rain rate. The added value of the measurement systems for high-resolution numerical weather prediction models is estimated by an observing system experiment, and a positive impact on the local wind forecast is demonstrated.

International audience; We are developing a virtual agent based on the Motivational Interviewing method to help elderly and inactive individuals change their behavior. The agent engages users in a conversation that aims to highlight reasons why they might want to increase their level of physical activity. In this work, we describe our approach to computerized adaptation of Motivational Interviewing. A study evaluates the outcome of this approach and the system as a whole. CCS CONCEPTS • Human-centered computing → Interaction design; User studies.; Nous développons un agent virtuel qui s’inspire de la méthode de l’Entretien Motivationnel pour soutenir des individus âgés et inactifs dans un changement de comportement positif. L’agent engage les utilisateurs dans une conversation qui a pour objectif de mettre en évidence les raisons qui pourraient les inciter à augmenter leur niveau d’activité physique. Dans ce travail, nous décrivons notre approche pour effectuer une adaptation informatisée de l’Entretien Motivationnel. Une étude évalue le résultat de cette démarche et le système dans son ensemble.