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International audience; The adaptive optics systems of future Extremely Large Telescopes (ELTs) will be assisted with laser guide stars (LGS) which will be created in the sodium layer at a height of ≈90 km above the telescopes. In a Shack–Hartmann wavefront sensor, the long elongation of LGS spots on the sub-pupils far apart from the laser beam axis constraints the design of the wavefront sensor (WFS) which must be able to fully sample the elongated spots without undersampling the non-elongated spots. To fulfill these requirements, a newly released large complementary metal oxide semiconductor sensor with 1100 × 1600 pixels and 9 μm pixel pitch could be employed. Here, we report on the characterization of such a sensor in terms of noise and linearity, and we evaluate its performance for wavefront sensing based on the spot centroid variations. We then illustrate how this new detector can be integrated into a full LGS WFS for both the European Southern Observatory’s ELT and the Thirty Meter Telescope.; Les systèmes d'optique adaptative des futurs Extremely Large Telescopes (ELT) seront assistés par des étoiles guides laser (LGS) qui seront créées dans la couche de sodium à une hauteur de ≈90 km au-dessus des télescopes. Dans un capteur de front d'onde de Shack-Hartmann, la longue élongation des taches LGS sur les sous-pupilles éloignées de l'axe du faisceau laser contraint la conception du capteur de front d'onde (WFS) qui doit être capable d'échantillonner entièrement les taches allongées sans sous-échantillonner les taches non allongées. Pour répondre à ces exigences, un grand capteur à semi-conducteurs d'oxyde de métal complémentaire récemment commercialisé avec 1100 × 1600 pixels et un pas de pixel de 9 μm pourrait être employé. Nous présentons ici la caractérisation d'un tel capteur en termes de bruit et de linéarité, et nous évaluons ses performances pour la détection du front d'onde en fonction des variations du centroïde du spot. Nous illustrons ensuite comment ce nouveau détecteur peut être intégré dans un WFS LGS complet pour l'ELT de l'Observatoire européen austral et le télescope de trente mètres.

We introduce one- and two-dimensional `exponential shapelets': orthonormal basis functions that efficiently model isolated features in data. They are built from eigenfunctions of the quantum mechanical hydrogen atom, and inherit mathematics with elegant properties under Fourier transform, and hence (de)convolution. For a wide variety of data, exponential shapelets compress information better than Gauss-Hermite/Gauss-Laguerre (`shapelet') decomposition, and generalise previous attempts that were limited to 1D or circularly symmetric basis functions. We discuss example applications in astronomy, fundamental physics and space geodesy., Comment: Accepted for publication in MNRAS. 13+4 pages

MICROSCOPE's space test of the weak equivalence principle (WEP) is based on the minute measurement of the difference of accelerations experienced by two test masses as they orbit the Earth. A detection of a violation of the WEP would appear at a well-known frequency $f_{\rm EP}$ depending on the satellite's orbital and spinning frequencies. Consequently, the experiment was optimised to miminise systematic errors at $f_{\rm EP}$. Glitches are short-lived events visible in the test masses' measured acceleration, most likely originating in cracks of the satellite's coating. In this paper, we characterise their shape and time distribution. Although intrinsically random, their time of arrival distribution is modulated by the orbital and spinning periods. They have an impact on the WEP test that must be quantified. However, the data available prevents us from unequivocally tackling this task. We show that glitches affect the test of the WEP, up to an a priori unknown level. Discarding the perturbed data is thus the best way to reduce their effect., Comment: References updated

This paper focus on the description of the design and performance of the MICROSCOPE satellite and its Drag-Free and Attitude Control System (DFACS). The satellite is derived from CNES' Myriade platform family, albeit with significant upgrades dictated by the unprecedented MICROSCOPE's mission requirements. The 300kg drag-free microsatellite has completed its 2-year flight with higher-than-expected performances. Its passive thermal concept allowed for variations smaller than 1 $\mu$K at the measurement frequency $f_{\rm{EP}}$. The propulsion system provided a 6 axis continuous and very low noise thrust from zero to some hundreds of micronewtons. Finally, the performance of its DFACS (aimed at compensating the disturbing forces and torques applied to the satellite) is the finest ever achieved in low Earth orbit, with residual accelerations along the three axes are lower than $10^{-12} {\rm m/s}^2$ at $f_{\rm{EP}}$ over 8 days., Comment: References updated

This article describes the dynamics of a charge particle in a electromagnetic field in presence of a scalar fifth force. Focusing to the fifth force that would be induced by a chameleon field, the profile of which can be designed properly in the laboratory, it draws its physical effects on the cyclotron motion of a particle in a static and uniform magnetic field. The fifth force induces a drift of the trajectory that is estimated analytically and compared to numerical computations for profiles motivated by the ones of a chameleon field within two nested cylinders. The magnitude of the effect and the detectability of this drift are discussed to argue that this may offer a new experimental design to test small fifth force in the laboratory. More important, at the macroscopic level it induces a current that can in principle also be measured, and would even allow one to access the transverse profile of the scalar field within the cavity. In both cases, aligning the magnetic field with the local gravity field suppresses the effects of Newtonian gravity that would be several order larger than the ones of the fifth force otherwise and the Newtonian gravity of the cavity on the particle is also argued to be negligible. Given this insight, this experimental set-up, with its two effects -- on a single particle and at the macroscopic level -- may require attention to demonstrate its actual feasability in the laboratory., 16 pages, 21 figures

International audience; Measuring gravity from an aircraft is essential in geodesy, geophysics and exploration. It fills a gap between satellite techniques which have a low spatial resolution and traditional ground measurements which can only be performed on ground in accessible areas. Today, only relative sensors are available for airborne gravimetry. This is a major drawback because of the calibration and drift estimation procedures which lead to important operational constraints and measurement errors. Here, we report an absolute airborne gravimeter based on atom interferometry. This instrument has been first tested on a motion simulator leading to gravity measurements noise of 0.3 mGal for 75 s filtering time constant. Then, we realized an airborne campaign across Iceland in April 2017. From repeated line and crossing points, we obtain gravity measurements with an estimated error between 1.7 and 3.9 mGal. The airborne measurements have also been compared to upward continued ground gravity data and show differences with a standard deviation ranging from 3.3 to 6.2 mGal and a mean value ranging from − 0.7 to − 1.9 mGal.

This article investigates the properties of a scalar fifth force that arises in a scalar tensor-theory with a chameleon screening mechanism in the context of gravity space missions like the MICROSCOPE experiment. In such an experiment, the propagation of the chameleon field inside the nested cylinders of the experiment causes a fifth force when the cylinders are not perfectly co-axial. We propose a semi-analytic method to compute the field distribution and the induced fifth force and compare it to a full numerical simulation, in settings where the cylindrical symmetry is broken. The scaling of the fifth force with both the parameters of the model and the geometry of the experiment is discussed. We show that the fifth force is repulsive, hence adds a destabilizing stiffness that should be included in the force budget acting on the detector. This opens the way to a new method to constrain a scalar fifth force in screened models., Comment: Submitted to Phys. Rev. D

International audience; We consider the Finite Volume Method on irregular grids for conservation laws with a particular polynomial reconstruction. This reconstruction is based on a least squares approach to compute consistent approximations of the first, second and third order derivatives. The resulting reconstruction is cubic. It is called the Coupled Least Squares reconstruction. It is obtained by a three stages iteration. At each iteration, only data located in a compact stencil, and not beyond, are accessed. A linear stability analysis is given in the case of regular and irregular one-dimensional grids. Numerical results for various problems, including shock tubes, vortex and accoustic wave propagation, support the interest of this approach. The reconstruction algorithm is presented in detail in the one dimensional case. An outline of the multidimensional case in also given. This work was announced in [14].; Nous examinons la méthode des volumes finis sur des maillages non structurés pour des lois de conservation avec une reconstruction polynomiale particulière. La reconstruction se base sur une approche des moindres carrés pour calculer des approximations consistantes des dérivées premières, deuxièmes et troisièmes. La reconstruction qui en résulte est cubique. Elle est appelée la reconstruction par moindres carrés couplés et s'obtient de façon itérative en trois étapes. Chaque itération accède aux données dans un petit voisinage compact de la cellule et n'a pas besoin de données situées en dehors de ce voisinage. Une analyse de stabilité linéaire est présentée pour le cas de maillages unidimensionnels réguliers et irréguliers. Des résultats numériques pour des problème variés comme les tubes de choc, l'advection de tourbillons et la propagation d'ondes montrent l'intérêt de la présente approche. L'algorithme de reconstruction est présenté en détail pour le cas unidimensionnel, le cas multi-dimensionnel est esquissé dans ses grandes lignes.

International audience; The paper presents a new methodology for the numerical estimation of the Green's functions in complex external aeroacoustic configurations. Computational aeroacoustics is used to propagate multi-frequency signals from focus points to microphones. The method takes advantage of the sparsity of the Green's functions in the time-domain to minimize the simulation time. It leads to a complex sparse linear regression problem. To solve it, the Orthogonal Matching Pursuit algorithm is adapted. The method is first applied on the case of the diffraction by a rigid sphere. Results are studied both in terms of Green's function estimation and aeroacoustic beamforming. They show that the Green's functions are obtained with a good accuracy and enable to localize acoustic sources placed behind the diffracting object. The methodology is then applied on a NACA0012 2D wing in a potential flow for which the Green's function is not known analytically. The use of the reverse-flow reciprocity principle enables to reduce the complexity of the estimation problem when there are more scan points than microphones. It is shown that it is possible to take advantage of the presence of diffracting objects to improve the capability of detection of a sensor array.

This work deals with the application of a high-order discontinuous Galerkin (DG) method to predict the noise generated by a subsonic free jet at high Reynolds number R e D = 10 6 , based on the nozzle diameter. The large-eddy simulation (LES) technique is used to compute the turbulent flow dynamics and acoustics in the near field. The estimation of the far-field noise is made by means of the Ffowcs Williams and Hawkings surface integral formulation. A fourth-order DG simulation of this jet configuration is presented in this paper. The DG simulation is based on the Smagorinsky model and the computational grid employed is fully tetrahedral. This DG simulation is compared to an LES computation performed in previous work by means of a second-order finite-volume (FV) solver using a similar type of grid and SGS model. The results from the DG and FV computations are also compared to the available experimental data. It appears from this study that the DG computation is able to resolve higher-frequency components close to the nozzle exit, which is related to the better match found with the experimental data in the far field.

9 figures, 2 tables, MNRAS accepted; International audience; Wide Field Adaptive Optics (WFAO) systems are among the most sophisticated AO systems available today on large telescopes. The knowledge of the vertical spatio-temporal distribution of the wind speed (WS) and direction (WD) are fundamental to optimize the performance of such systems. Previous studies already proved that the Gemini Multi-Conjugated AO system (GeMS) is able to retrieve measurements of the WS and WD stratification using the SLODAR technique and to store measurements in the telemetry data. In order to assess the reliability of these estimates and of the SLODAR technique applied to such a kind of complex AO systems, in this study we compared WS and WD retrieved from GeMS with those obtained with the atmospherical model Meso-Nh on a rich statistical sample of nights. It has been previously proved that, the latter technique, provided an excellent agreement with a large sample of radiosoundings both, in statistical terms and on individual flights. It can be considered, therefore, as an independent reference. The excellent agreement between GeMS measurements and the model that we find in this study, proves the robustness of the SLODAR approach. To by-pass the complex procedures necessary to achieve automatic measurements of the wind with GeMS, we propose a simple automatic method to monitor nightly WS and WD using the Meso-Nh model estimates. Such a method can be applied to whatever present or new generation facilities supported by WFAO systems. The interest of this study is, therefore, well beyond the optimization of GeMS performance.

Colloidal particles based on self-assembled Cu2+ coordination polymers were fabricated following a one-step process. These particles were shown to be stimuli-responsive. In particular they can be readily disassembled in acidic conditions. This effect originates from a pH-induced fragmentation of the polymer chains into dinuclear Cu2+ complexes.

The purpose of this article is to assess the adaptive multipreconditioned FETI solvers (AMPFETI) on real industrial problems and hardware. The multipreconditioned FETI algorithm (first introduced as Simultaneous FETI (Gosselet et al., 2015) is a non-overlapping domain decomposition method which exhibits good robustness properties without requiring the explicit knowledge of the original partial differential equation, or any a priori analysis of the algebraic system through eigenvalues problems. Multipreconditioned FETI solves critical problems in significantly fewer iterations than classical FETI but each iteration involves a larger computational effort. An adaptive strategy (known as the adaptive multipreconditioned conjugate gradient algorithm (Spillane, 2016) has been proposed to achieve balance between robustness and efficiency and we will observe that it provides an efficient solver for the problems considered here.

International audience; We propose a new experimental method using a Hassler cell and air injection to measure the permeability of fiber preform while avoiding a race tracking effect. This method was proven to be particularly efficient to measure very low through-thickness permeability of preform fabricated by automated dry fiber placement. To validate the reliability of the permeability measurement, the experiments of viscous liquid infusion into the preform with or without a distribution medium were performed. The experimental data of flow front advancement was compared with the numerical simulation result using the permeability values obtained by the Hassler cell permeability measurement set-up as well as by the liquid infusion experiments. To address the computational cost issue, the model for the equivalent permeability of distribution medium was employed in the numerical simulation of liquid flow. The new concept using air injection and Hassler cell for the fiber preform permeability measurement was shown to be reliable and efficient.; Nous proposons une nouvelle méthode expérimentale utilisant une cellule de Hassler et une injection d'air mesurer la perméabilité de la préforme fibreuse qi permet d'éviter les effets de bord. Cette méthode a été validée pour mesurer les très faibles perméabilités de préforme fabriquée par placement automatisée de fibres sèches. Pour valider le la fiabilité de cette mesure, les expériences d'infusion de préforme avec ou sans un milieu de distribution ont été réalisées. les données expérimentales de l'avancement du front d'écoulement a été comparé avec les résultats de simulation en utilisant les valeurs de perméabilité obtenues par la méthode de Hassler.

International audience; A Zonal Detached Eddy Simulation (ZDES) has been performed on the simplified LAGOON nose landing gear geometry using a Navier-Stokes solver on a fully unstructured grid. The attached boundary layers have been finely resolved using Y + values in the order of unity, while the high curvature zones have been intensively meshed in order to accurately solving adverse pressure gradients present in these regions. The mean and fluctuating flow fields have been compared with the experimental results, proving that both the mean flow field and the spectral content recorded at the wall are accurately reproduced. Following these comparisons, a detailed analysis of the topology of the flow has been carried out through the analysis of the skin friction coefficient and friction lines, coupled with three dimensional visualizations of the landing gear wake. The far-field acoustics, computed through the Ffowcs-Williams and Hawkings (FW-H) equation from the computed pressure on the landing gear skin, has been compared with the experimental results, obtaining a very good agreement for the different microphones and directions. Finally, the CFD methodology presented in this study proves to be a moderate cost approach, enabling an accurate flow and noise prediction for bluff bodies such as landing gears.

International audience; This review presents the state of the art of hybrid RANS/LES modeling for thesimulation of turbulent flows. After recalling the modeling used in RANS and LES methodologies,we propose in a first step a theoretical formalism developed in the spectral spacethat allows to unify the RANS and LES methods from a physical standpoint. In a secondstep, we discuss the principle of the hybrid RANS/LES methods capable of representing aRANS-type behavior in the vicinity of a solid boundary and an LES-type behavior far awayfrom the wall boundary. Then, we analyze the principal hybrid RANS/LES methods usuallyused to perform numerical simulation of turbulent flows encountered in engineering applications.In particular, we investigate the very large eddy simulation (VLES), the detachededdy simulation (DES), the partially integrated transport modeling (PITM) method, thepartially averaged Navier-Stokes (PANS) method, and the scale adaptive simulation (SAS)from a physical point of view. Finally, we establish the connection between these methodsand more precisely, the link between PITM and PANS as well as DES and PITMshowing that these methods that have been built by different ways, practical or theoreticalmanners have common points of comparison. It is the opinion of the author to considerthat the most appropriate method for a particular application will depend on the expectationsof the engineer and the computational resources the user is prepared to expend on theproblem.; Cet article d’expertise présente l’état de l’art de la modélisation hybride RANS/LES pour la simulation des écoulements turbulents. Après avoir rappelé la modélisation des méthodologies RANS et LES, nous proposons dans une première étape un formalisme théorique développée dans l’espace spectral qui permet d’unifier les méthodes RANS et LES sur la base d’arguments physiques. Dans une seconde étape, nous étudions les principes des méthodes hybrides RANS et LES, capables de reproduire un comportement de type RANS à proximité des zones de paroi et de type LES plus au loin des parois. Nous analysons ensuite les principales méthodes RANS/LES utilisées pour simuler les écoulements turbulents rencontrées dans les applications d’ingénieur. En particulier, nous abordons les méthodes “very large eddy simulation ”(VLES), “detached eddy simulation ”(DES), “partially integrated transport modeling ”(PITM), “partially averaged Navier-Stokes ”(PANS), et “scale adaptive simulation ”(SAS). Finalement, nous établissons les connexions entre ces différentes méthodes et plus précisement le lien entre les méthodes PITM et PANS ainsi que le lien entre les méthodes DES et PITM, montrant que ces méthodes qui ont été construites par différentes voies, pratique ou théorique, ont des points communs de comparaison. C’est l’opinion de l’auteur de considérer que la méthode la plus approprée pour une application donnée dépendra des attentes de l’ingénieur et des ressources informatiques que l’utilisateur est pret à consacrer sur le problème.

International audience; This work exploits the ONERA 7A rotor wind tunnel test for comparison with concurrent simulations at the U.S. Army and ONERA. Rotor airloads and structural loads are predicted by coupling computational fluid dynamics (CFD) with rotorcraft comprehensive analysis (CA). Two test points are examined: a high-speed point and a high-thrust point featuring dynamic stall. The contributions of experimental data processing and wind tunnel test stand to improved agreement are shown. Comparisons are shown for airloads, structural loads, surface pressures, rotor controls, and power. The use of state-of-theart CFD/CA coupled tools provides dramatic improvements in agreement with experiment, compared to previous work. The Helios/RCAS coupling used by the U.S. Army has been validated on the 7A rotor, adding to prior published validations on the UH-60A and HART-II rotors. The elsA/HOST (Helicopter Overall Simulation Tool) coupling used by ONERA has had its latest developments validated as well.

International audience; The present study was aimed at determining the mechanical behaviour of a weak matrix oxide/oxide CMC subjected to tensile and compressive loadings in the fibre direction and at identifying the damage mechanisms. The material consisted of Nextel™610 fibres (8 HSW) embedded in an alumina matrix, with a 49 % fibre volume fraction and 24 ± 2 % total porosity. The average ultimate tensile stress and strain of the material were, respectively, 260 ± 37 MPa and 0.3 ± 0.09 % under tensile loading and −261 ± 69 MPa and −0.19 ± 0.04 % under compressive loading. Three types of pores were differentiated within the material: nanopores (13 ± 1 %), micropores (6 ± 2 %) and macropores (5 ± 1 %). The latter appear to be the most detrimental for the material, enhancing delamination. The damage mechanisms of the material were assessed through SEM examination and in situ tensile tests.

International audience; Aconitum karacolicum from northern Kyrgyzstan (Alatau area) contains about 0.8-1% aconitine as well as other aconite derivatives that have already been identified. In this paper, we compare several methods for the further purification of an Aconitum karacolicum extract initially containing 80% of aconitine. Reverse-phase flash chromatography, reverse-phase semi-preparative HPLC, centrifugal partition chromatography (CPC) and re crystallization techniques were evaluated regarding first their efficiency to get the highest purity of aconitine (over 96%) and secondly their applicability in a semi-industrial scale purification process (in our case, 150 g of plant extract). Even if the CPC technique shows the highest purification yield (63%), the recrystallization remains the method of choice to purify a large amount of aconitine as i) it can be easily carried out in safe conditions; ii) an aprotic solvent is used, avoiding aconitine degradation. Moreover, this study led us to the identification of lappaconitine in Aconitwn karacolicum, a well-known alkaloid never found in this Aconttum species.

International audience; The specific problems of DSECs mechanical testing result from the particularities of these 3-D interconnected eutectic ceramics. First of all, 4-point bending tests ensure pure bending loading, whereas 3 PB tests only lead to a tensile and shear stress combination. Consequently, due to the 3-D microstructure of DSECs, interfaces between the various phases are subjected to a mixed (tensile and shear) loading which makes the interpretation of the results (strength) and of the fracture surfaces, rather difficult. For usual ceramics, biaxial flexure testing offers many advantages over 3- or 4-point beam-bending testing. The coaxial-ring test is free of edge influences (flaws): cracks initiate in the central area and propagate outwardly. However, in the case of DSECs, due to the presence of high internal thermal stresses (especially for ternary eutectics), interfaces can be subjected to a strong radial tensile and shear (near the free surface) stress combination. In the presence of the radial tensile stress resulting from biaxial loading, this internal thermal stress combination can lead to premature crack initiation leading to failure. Specimen machining through grinding leads to the formation of a strongly damaged layer. Annealing of this layer leads to the formation of a rough surface: slightly protruding phases and stress concentrations at the interfaces. The measured strength is ≈20% lower after annealing than that directly after grinding. Concerning the effect of the microstructure size, four representative sizes have been selected in the ≈10 µm to submicrometre range. A classical crack propagation criterion has allowed explaining the corresponding strength values.; Les problèmes posés par la caractérisation mécanique des composites céramiques eutectiques obtenus par solidification dirigée résultent des particularités de la microstructure 3-D interconnectée de ces matériaux. Tout d'abord, les essais de flexion 4 points (4PB) assurent un chargement de flexion pure, alors que les essais de flexion 3 points (3PB) conduisent à une combinaison de traction/compression et de contraintes de cisaillement. Par conséquent, de par la microstructure 3D de ces céramiques eutectiques, les interfaces entre les différentes phases sont soumises à un chargement mixte (traction et cisaillement) qui rend l'interprétation des résultats (résistance en flexion) et des surfaces de rupture, particulièrement difficile. Pour les céramiques courantes, les essais de flexion biaxiale offrent de nombreux avantages par rapport à des essais de flexion 3 ou 4 points. L’essai de flexion biaxiale est indépendant des effets de bord (défauts): les fissures sont amorcées dans la zone centrale et se propagent vers l'extérieur. Cependant, dans le cas des composites céramiques eutectiques obtenus par solidification dirigée, en raison de la présence de fortes contraintes internes d’origine thermique (en particulier pour les eutectiques ternaires), les phases peuvent être soumises à une traction radiale et une cission (singularité en surface libre) très élevées. En présence de la contrainte de traction radiale résultant du chargement biaxial, cette combinaison de contraintes internes d’origine thermique peut conduire à un amorçage prématuré de fissures conduisant à la rupture. L’usinage des éprouvettes par rectification conduit à la formation d'une couche écrouie fortement endommagée. Le recuit de cette couche entraîne la formation d'une surface à fort relief: phases très convexes et concentrations de contraintes au niveau des interfaces. La charge de rupture mesurée est de ≈ 30% plus faible après recuit que directement après rectification. En ce qui concerne l'effet de la taille de la microstructure, trois tailles représentatives ont été sélectionnées dans la gamme : ≈ 10 µm à submicronique. Un critère de propagation de fissure classique a permis d'expliquer les valeurs des résistances à la rupture correspondantes.

International audience; Partitioned approaches for the simulation of coupled conjugate heat transfer are gaining popularity in fields that require accurate thermal predictions. Considerable efforts have been put into determining stable coupling schemes, but performance enhancements have been neglected. This paper presents, for the first time, a detailed and comprehensive study of the numerical properties of Dirichlet-Robin coupling procedures, used in conjugate heat transfer simulation, with emphasis put on the optimal local coupling formulation that was recently derived from a stability analysis. This all-new optimal coupling approach provides local adaptability and has never been tested on a complex setup. This investigation looks to determine the relevance and the limitations of the theory when applied to complex conjugate heat transfer setups. The stability theory of the optimal Dirichlet-Robin coupling scheme is first recalled, then, a realistic 3D application, with complex geometry and flow structures, is used to evaluate the performance and sensitivity of Dirichlet-Robin couplings, with respect to various numerical parameters. This detailed study allows, for the first time, to evaluate the advantages and limitations of the recently proposed optimal procedure, when used on realistic 3D CHT problems. It turns out that the local optimal Dirichlet-Robin formulation outperforms all what is found in literature, and insures unconditional stability with monotone convergence for all considered setups of the 3D model.

International audience; This paper presents models developed through analytical or numerical computation and finite element analysis to improve the resolution of a new kind of vibrating magnetometers. This peculiar magnetometer uses the piezoelectric transduction to actuate a quartz resonator at its resonance frequency taking advantage of the high Q factor of a quartz resonator to achieve high resolution. The magnetic sensitive element is a thin ferromagnetic film of Nickel-Cobalt which is sputtered on the moving beams of the resonator. This magnetic thin film applies a periodic torque on the resonator, shifting its resonance frequency. This torque depends on the magnetic field applied; therefore the value of the magnetic field can be deduced from the frequency shift measurement. The aim of this paper is to develop and improve sensitivity models which will be useful tools in a future work to establish the optimal geometry for a resonator and the best position of the magnetic thin film on it in order to improve the sensitivity and resolution of the global sensor.

International audience; This study summarizes a rotor blade shape optimization exercise with an emphasis on the risk of off-design performance degradation. After optimizing by comprehensive analysis twist and anhedral with respect to rotor shaft power in a highspeed, high-load forward flight condition, benchmarks against the reference blade were performed on vibratory levels, acoustics in descent flight, and aerodynamic performance. Performance in forward flight and in hover is validated by coupling comprehensive analysis with computational fluid dynamics. In forward flight, the coupled evaluations confirm the comprehensive code predictions of moderate shaft power reduction. In hover, the optimized-for-forward-flight rotor underperforms the reference. Also, higher blade–vortex interaction noise levels occur in descent flight. Next, as a step to evolve toward increasingly feasible optimized designs, a method to update blade structural properties as a function of variations in blade shape is proposed. The method is first evaluated between two real blades of known properties. Second, the method is implemented in a shape optimization loop and assessed for two optimization cases. It is shown that accounting for structural data modifications smoothes the optimal shape and produces more realistic designs, albeit at the cost of a smaller margin in power reduction.

International audience; A method to separate entropy induced noise from an acoustic pressure wave in an harmonically perturbed flow through a nozzle is presented. It is tested on an original experimental setup generating simultaneously acoustic and temperature fluctuations in an air flow that is accelerated by a convergent nozzle. The setup mimics the direct and indirect noise contributions to the acoustic pressure field in a confined combustion chamber by producing synchronized acoustic and temperature fluctuations, without dealing with the complexity of the combustion process. It allows generating temperature fluctuations with amplitude up to 10K in the frequency range from 10 to 100Hz. The noise separation technique uses experiments with and without temperature fluctuations to determine the relative level of acoustic and entropy fluctuations in the system and to identify the nozzle response to these forcing waves. It requires multi-point measurements of acoustic pressure and temperature. The separation method is first validated with direct numerical simulations of the nonlinear Euler equations. These simulations are used to investigate the conditions for which the separation technique is valid and yield similar trends as the experiments for the investigated flow operating conditions. The separation method then gives successfully the acoustic reflection coefficient but does not recover the same entropy reflection coefficient as predicted by the compact nozzle theory due to the sensitivity of the method to signal noises in the explored experimental conditions. This methodology provides a framework for experimental investigation of direct and indirect combustion noises originating from synchronized perturbations.; Cet article présente une méthode pour extraire la contribution d'origine entropique d'une onde de pression acoustique dans un écoulement de tuyère perturbé de façon harmonique. Cette méthode est testée sur un dispositif expérimental original générant simultanément des fluctuations acoustiques et de température dans un écoulement d'air accéléré par une tuyère convergente. L'installation reproduit les contributions du bruit direct et du bruit indirect au champ de pression acoustique dans une chambre de combustion confinée en produisant des fluctuations acoustiques et de température synchronisées, sans la complexité du processus de combustion. Elle permet de générer des fluctuations de température d'une amplitude de 10K pour des fréquences allant de 10 à 100 Hz. La méthode de séparation des bruits utilise les mesures sans et avec fluctuations de température pour déterminer les niveaux relatifs de fluctuations acoustiques et entropiques dans le système et pour identifier la réponse de la tuyère à ces forçages. Elle nécessite des mesures de pression acoustique et de température à plusieurs positions. La méthode de séparation est d'abord validée par résolution numérique des équations d'Euler non linéaires. Ces simulations sont utilisées afin d'étudier les conditions pour lesquelles la méthode de séparation est valide. Les résultats obtenus présentent les mêmes tendances que les mesures pour les points de fonctionnement étudiés. La méthode de séparation permet de retrouver le coefficient de réflexion acoustique mais le coefficient de réflexion entropique diffère de celui prédit par la théorie pour les tuyères compactes à cause de la sensibilité de la méthode au bruit du signal, pour les conditions expérimentales étudiées. Cette méthodologie fournit un cadre pour l'étude expérimentale des bruit de combustion direct et indirect issus de perturbations synchronisées.

International audience; Vacuum-assisted resin transfer molding (VARTM) is a very suitable solution for composite manufacturing industry. It allows the manufacturing of large and complex shape parts at low costs. However, the simulation of this process is complicated due to myriad physical phenomena involved, specifically the strong coupling between the resin flow and the preform compressibility, i.e. hydro-mechanical coupling. Moreover, the use of the distribution medium involves two types of flow: Planar flow and through-the-thickness flow. These flows cannot be considered together by a 2D model. On the other hand, 3D models require an important amount of computation time. This article presents a VARTM modeling approach that takes into account the hydro-mechanical coupling and the coexistence of planar and transverse flows. The proposed modeling approach allows the simulation of the infusion process in the case of multilayer preform with different materials and orientations, including the distribution medium. This model is validated experimentally based on several infusions.

International audience; 3D woven composite materials have been recently used to design some engine structures in order to improve their impact resistance. The aim of this work is to study experimentally and numerically low-velocity/energy impact damage in such recent composites. Impact tests at different energy levels have been performed and analysed using microscopic observations and X-ray tomography in order to understand damage mechanisms occurring in this material. Finite element simulations have been performed using the continuum damage model, ODM-PMC, developed at Onera for 3D woven composites under static loadings. Through comparisons with the available experimental data, it has been demonstrated that the damage mechanisms are described correctly by the present model. Moreover, the residual depth after impact is also accurately predicted, allowing to generate, numerically, relations between impact energy, damaged area and residual depth, currently determined experimentally in aeronautical industries.

International audience; The perceived unpleasantness due to aircraft flyover noise is mostly explained by a) non-acoustical factors, and b) the noise level, on which future progress will be prospectively hard and expensive to obtain. However, the literature suggests that sound-quality approaches may provide new solutions for reducing the perceived unpleasantness. The study reported here investigates the effects of the temporal parameters of single aircraft flyover sound signatures on the unpleasantness experienced by people outside the aircraft. Two listening tests (semantic differential, synthesised stimuli) were conducted. In the first test the stimuli were equalised according to the EPNL in order to concentrate on the slope, duration and amount of fluctuation of the sound signatures. In the second test the influences of the temporal aspects and of the noise level were compared. Statistical analyses were performed. Although slope and duration were made independent, their perceptions remain correlated. Descriptors are proposed for assessing the duration and the amount of fluctuation. For both configurations (stimuli equalised or not), a model is proposed, in which the unpleasantness is explained by the duration, the amount of fluctuation and the noise level. Unsurprisingly the noise level is the most influential factor for the unpleasantness, but the temporal factors are also important. The amount of fluctuation strongly correlates with the unpleasantness. The duration has a two-sided effect: short flyover noises exhibit higher peak levels and so increase the unpleasantness; long flyover noises maximise the length of sound exposure and also increase the unpleasantness.

The elsA CFD software developed at ONERA is both a software package capitalizing the innovative results of research over time and a multipurpose tool for applied CFD and for multi-physics. elsA is intensively used by the Safran and Airbus groups and ONERA, as well as other industrial groups and research partners. This paper presents the main capabilities of elsA and recent numerical simulations using elsA for a wide range of challenging turbomachinery applications. The simulations address aerodynamics computations as well as aero-structure and aeroacoustics ones. Each simulation enables to underline differentiating modelling and numerical methods implemented within elsA and shows that this software has reached a very high level of maturity and reliability., Le code elsA de mécanique des fluide numérique développé à l'ONERA est à la fois un ensemble logiciel capitalisant les résultats innovants de la recherche dans le temps et un outil polyvalent pour l'aérodynamique numérique appliquée et la multi-physique. elsA est largement utilisé à l'ONERA, par les groupes Safran et Airbus, ainsi que par d'autres groupes industriels et des partenaires de recherche. Cet article présente les principales fonctionnalités d'elsA et les simulations numériques récentes utilisant elsA pour un large éventail d'applications dans les turbomachines difficiles. Les simulations portent sur des calculs aérodynamiques ainsi que des calculs aéroacoustiques et aéroélastiques. Chaque simulation permet de mettre en relief la modélisation et les méthodes numériques discriminantes mises en œuvre au sein d'elsA et montre que ce logiciel a atteint un très haut niveau de maturité et de fiabilité.

We speculate on the development and availability of new innovative propulsion techniques in the 2040s, that will allow us to fly a spacecraft outside the Solar System (at 150 AU and more) in a reasonable amount of time, in order to directly probe our (gravitational) Solar System neighborhood and answer pressing questions regarding the dark sector (dark energy and dark matter). We identify two closely related main science goals, as well as secondary objectives that could be fulfilled by a mission dedicated to probing the local dark sector: (i) begin the exploration of gravitation's low-acceleration regime with a man-made spacecraft and (ii) improve our knowledge of the local dark matter and baryon densities. Those questions can be answered by directly measuring the gravitational potential with an atomic clock on-board a spacecraft on an outbound Solar System orbit, and by comparing the spacecraft's trajectory with that predicted by General Relativity through the combination of ranging data and the in-situ measurement (and correction) of non-gravitational accelerations with an on-board accelerometer. Despite a wealth of new experiments getting online in the near future, that will bring new knowledge about the dark sector, it is very unlikely that those science questions will be closed in the next two decades. More importantly, it is likely that it will be even more urgent than currently to answer them. Tracking a spacecraft carrying a clock and an accelerometer as it leaves the Solar System may well be the easiest and fastest way to directly probe our dark environment., White Paper submitted to ESA's Voyage 2050 call for papers. Reference updated

Single-phase multi-component alloys exist for a very wide range of composition, which is still mostly unexplored. To determine the mechanical properties of one new medium entropy alloy (MEA) and to assess the potential of an accelerated testing strategy, the compositions CoCrFeMnNi, (CoCrFeMn)40Ni60 and (CoCrFeMn)8Ni92 were studied. They were processed in homogenized and recrystallized states, characterized by scanning electron microscopy coupled with electron backscattered diffraction and mechanically tested by tensile tests and nanoindentation. It was shown that the (CoCrFeMn)40Ni60 MEA exhibits as high tensile properties as the CoCrFeMnNi high entropy alloy. Not only the mechanical strength but also the ductility are the same in both alloys. Moreover, the uncertainty when comparing nanoindentation on homogenized samples with tensile yield strength was quantified. Knowing that, nanoindentation on homogenized HEA was identified as a powerful tool for fast exploring of chemical compositions and pre-selection of the most promising ones.

The elsA CFD software developed at ONERA is both a software package capitalizing the innovative results of research over time and a multipurpose tool for applied CFD and for multi-physics. elsA is used intensively by the Safran and Airbus groups and ONERA, as well as other industrial groups and research partners. This paper presents the main capabilities of elsA and recent numerical simulations using elsA for a wide range of challenging aeronautic applications. The simulations address aerodynamics computations as well as aero-structure and aeroacoustics ones. Each simulation enables to underline differentiating modelling and numerical methods implemented within elsA and shows that this software has reached a very high level of maturity and reliability., Le code elsA de mécanique des fluide numérique développé à l'ONERA est à la fois un ensemble logiciel capitalisant les résultats innovants de la recherche dans le temps et un outil polyvalent pour l'aérodynamique numérique appliquée et la multi-physique. elsA est largement utilisé à l'ONERA, par les groupes Safran et Airbus, ainsi que par d'autres groupes industriels et des partenaires de recherche. Cet article présente les principales fonctionnalités d'elsA et les simulations numériques récentes utilisant elsA pour un large éventail d'applications aéronautiques difficiles. Les simulations portent sur des calculs aérodynamiques ainsi que des calculs aéroacoustiques et aéroélastiques. Chaque simulation permet de mettre en relief la modélisation et les méthodes numériques discriminantes mises en œuvre au sein d'elsA et montre que ce logiciel a atteint un très haut niveau de maturité et de fiabilité.

International audience; Solving highly heterogeneous structural mechanic problems with a large number of degrees of freedom (HPC simulations) is a real issue in engineering work, because of the required time and memory. Non overlapping domain decomposition methods such as the Finite Element Tearing and Interconnecting (FETI) or Balanced Domain Decomposition (BDD) methods have been developed in order to allocate the problems on distributed memory clusters with a large number of processors and to make mechanical calculations parallel. Two difficulties are encountered when applying domain decomposition methods. First, the mesh generation is most often a sequential process applied to the full domain. Second, the linear system resulting from the partitioning of the mesh may be poorly conditioned, leading to slow convergence. Recently developed techniques such as adapted coarse spaces (e.g. FETI-GenEO) or multipreconditioning (e.g. AMPFETI) enable to restore good convergence rate, at the cost of extra computations. In this study, we try to mitigate these two difficulties by proposing a new hierarchical substructuring method which aims at making the mesh preprocessing step parallel and at improving the condition number of the linear system to be solved by generating regular interfaces adapted to the heterogeneity.

In this work we perform a-priori analyses of the Discontinuous Galerkin (DG) Variational Multiscale (VMS) method for Large Eddy Simulation (LES). An analytical framework is introduced to study the ideal energy transfer between resolved and unresolved scales. The proposed framework is consistent with the discretization employed for the DG-LES simulations. The concept of modal eddy viscosity is also introduced which can be employed for the a-priori analysis of the DG-VMS method or spectral vanishing viscosity approaches. The developed framework is then applied to the analysis of the energy transfer in DG-LES by employing a DNS database of the Taylor-Green Vortex (TGV) at Re = 5 000, 20 000 and 40 000. A-priori analyses are carried out for three variants of the DG-VMS approach: the small-small [1], Vreman [2], and all-all variants [3]. The performed analysis demonstrates that when the DG-LES resolution limit falls at the beginning of the dissipation range the assumption of large scales free of interaction with the unresolved scales is valid and the DG-VMS approach can replicate the ideal SGS dissipation spectrum. For coarser resolutions, typical of LES at high Reynolds numbers, the DG-VMS approach is unable to replicate the ideal energy transfer mechanism at the large-resolved scales. It is shown, a-priori, that a more accurate agreement can be obtained by employing a mixed Smagorinsky and DG-VMS approach with a fixed value of the scale-fraction parameter.

Introduction L’arterite a cellules geantes (ACG) est une vascularite systemique touchant les gros vaisseaux. Le diagnostic repose sur la biopsie de l’artere temporale (BAT) qui montre une infiltration arterielle segmentaire et focale composee de lymphocytes T CD4 et de macrophages. Elle s’accompagne d’une destruction de la limite elastique interne de la media et d’une hyperplasie de la couche la plus interne, l’intima par proliferation de myofibroblastes (Weyand). L’origine de ces myofibroblastes est controversee (Ly). Des donnees suggerent qu’ils proviendraient, en partie, de l’activation des fibroblastes de l’adventice, tunique la plus externe (Stenmark). L’objectif de cette etude etait de determiner si les fibroblastes adventitiels migrent vers l’intima et contribuent ainsi a l’hyperplasie intimale au cours de l’ACG. Materiels et methodes Des coupes arterielles provenant de BAT de patients ACG (n = 24) et de sujets controles (n = 24) ont ete analysees. Une analyse immunohistochimique a ete realisee pour chaque patient a l’aide d’anticorps diriges contre les fibroblastes (CD90, vimentine), les myofibroblastes (actine de muscle lisse alpha {ASMA}) et les cellules musculaires lisses vasculaires (CMLV) (desmine). Des marquages de la prolyl-4-hydroxylase (P4H) et de la myosine ont aussi ete effectues. Les differents marquages ont ete quantifies a l’aide du logiciel ODPviewer® (Kamax Innovative System, France) par deux observateurs en double aveugle. Par ailleurs la co-expression du CD90 a differentes cibles (ASMA, myosine et P4H) a ete realisee en immunohistochimie egalement. Des tests fonctionnels ont ete realises en utilisant des cellules de culture obtenues a partir de BAT d’ACG (n = 4) et de controles (n = 4). Les BAT ont ete dissequees pour separer l’adventice des deux autres couches (media et intima). Chaque fragment a ete ensemence separement. Les cellules en culture ont ete identifiees par immunocytochimie et western-blot en utilisant des anticorps anti-CD90 ainsi que des marqueurs d’activite tels que la myosine (contraction cellulaire) et la P4H (secretion de collagene). L’etude de la proliferation a ete realisee en utilisant un test d’incorporation de la bromodesoxyuridine dans differentes conditions : DMEM, serum de veau foetal (SVF) a 10 %, PDGF a 40 ng/mL (controle positif) et surnageants des cellules en culture. L’etude de la migration a ete realisee a l’aide d’un test de type cicatrice manuelle dans les memes conditions. Resultats Le marquage pour le CD90 (fibroblastes) etait significativement plus eleve chez les ACG que chez les temoins dans l’adventice et l’intima. La vimentine (fibroblastes) et l’ASMA (myofibroblastes) etaient significativement plus elevees dans les 3 tuniques pour les ACG. L’expression de la desmine (CMLV) n’etait presente que dans les medias pour les deux groupes sans difference. Le marquage pour la P4H etait present au niveau des adventices et intimas sans differences significatives entre les deux groupes. Les cellules CD90+ de l’adventice et de l’intima co-exprimaient la P4H, l’ASMA et la myosine de facon plus importante au cours de l’ACG. Les cellules en culture issues d’adventices de BAT exprimaient le CD90 et n’exprimaient pas la desmine en immunocytochimie. Par ailleurs ces cellules avaient un marquage pour la myosine plus important pour les ACG. Les cellules de l’adventice avaient des capacites de proliferation augmentees au cours de l’ACG par rapport aux controles de facon significative en presence de SVF, de PDGF et de surnageants de fibroblastes de patients temoins ou ACG. Les vitesses de migration de ces cellules etaient egalement significativement augmentees au cours de l’ACG en presence de SVF et de PDGF. Conclusion Le remodelage vasculaire de l’ACG commencerait dans la couche externe adventitielle avec un role cle des fibroblastes. En effet, les fibroblastes adventitiels pourraient s’activer en myofibroblastes et acquerir des capacites proliferatives et migratoires. Ils participeraient ainsi a l’hyperplasie intimale responsable des complications ischemiques de la maladie. Leur inhibition pourrait etre une piste therapeutique afin de limiter les risques ischemiques. Enfin, le signal activateur des fibroblastes adventitiels en myofibroblastes n’est pas encore connu au cours de l’ACG et necessite d’autres etudes.

This paper discusses change detection in SAR time-series. Firstly, several statistical properties of the coefficient of variation highlight its pertinence for change detection. Then several criteria are proposed. The coefficient of variation is suggested to detect any kind of change. Then other criteria based on ratios of coefficients of variations are proposed to detect long events such as construction test sites, or point-event such as vehicles. These detection methods are evaluated first on theoretical statistical simulations to determine the scenarios where they can deliver the best results. Then detection performance is assessed on real data for different types of scenes and sensors (Sentinel-1, UAVSAR). In particular, a quantitative evaluation is performed with a comparison of our solutions with state-of-the-art methods.

Wavefront sensors encode phase information of an incoming wavefront into an intensity pattern that can be measured on a camera. Several kinds of wavefront sensors (WFS) are used in astronomical adaptive optics. Amongst them, Fourier-based wavefront sensors perform a filtering operation on the wavefront in the focal plane. The most well known example of a WFS of this kind is the Zernike wavefront sensor, and the pyramid wavefront sensor (PWFS) also belongs to this class. Based on this same principle, new WFSs can be proposed such as the n-faced pyramid (which ultimately becomes an axicone) or the flattened pyramid, depending on whether the image formation is incoherent or coherent. In order to test such novel concepts, the LOOPS adaptive optics testbed hosted at the Laboratoire d'Astrophysique de Marseille has been upgraded by adding a Spatial Light Modulator (SLM). This device, placed in a focal plane produces high-definition phase masks that mimic otherwise bulk optic devices. In this paper, we first present the optical design and upgrades made to the experimental setup of the LOOPS bench. Then, we focus on the generation of the phase masks with the SLM and the implications of having such a device in a focal plane. Finally, we present the first closed-loop results in either static or dynamic mode with different WFS applied on the SLM., 14 pages, 9 figures, submitted to JATIS

International audience; Radiative heat normally flows from hot to cold bodies. Inverting the direction of heat is possible by tuning the chemical potential of light in a photodiode. This provides a new way for solid-state refrigeration. Radiative heat transfer is interesting for applications requiring contactless cooling. It is generally taken for granted that two macroscopic bodies at different temperatures will transfer heat with a flux directed from hot to cold. When the distance between the bodies is larger than the dominant thermal wavelength (around 10 µm at room temperature) the upper limit of this flux coincides with the fundamental blackbody limit given by Stefan-Boltzmann's law. On page 000 of this issue, Zhu et al. (1) show that a photodiode is able to cool a yet colder calorimeter located in the near-field, that is at a distance well below the thermal wavelength. To obtain the desired cooling effect, the photodiode, which is a directional device, must be operated in reverse voltage. The demonstration of radiative cooling using incoherent thermal light with an active device is potentially as impactful as thermoelectricity for applications in the fields of cooling and heat management. Optical refrigeration of solids had so far only been achieved with coherent laser light, using blue-shifted fluorescence from a solid state sample to lower the thermal energy of lattice vibrations, called phonons (2). In a way similar to what was initially invented to produce ultra-cold atoms and ions, photons from a monochromatic laser source are absorbed slightly

BACKGROUND Data on dermatological manifestations of Noonan syndrome (NS) remain heterogeneous and are based on limited dermatological expertise. OBJECTIVES To describe the dermatological manifestations of NS, compare them with the literature findings, and test for dermatological phenotype-genotype correlations with or without the presence of PTPN11 mutations. METHODS We performed a large 4-year, prospective, multicentric, collaborative dermatological and genetic study. RESULTS Overall, 129 patients with NS were enrolled, including 65 patients with PTPN11-NS, 34 patients with PTPN11-NS with multiple lentigines (NSML), and 30 patients with NS who had a mutation other than PTPN11. Easy bruising was the most frequent dermatological finding in PTPN11-NS, present in 53·8% of patients. Multiple lentigines and cafe-au-lait macules (n ≥ 3) were present in 94% and 80% of cases of NSML linked to specific mutations of PTPN11, respectively. Atypical forms of NSML could be associated with NS with RAF1 or NRAS mutations. In univariate analysis, patients without a PTPN11 mutation showed (i) a significantly higher frequency of keratinization disorders (P = 0·001), including keratosis pilaris (P = 0·005), ulerythema ophryogenes (P = 0·0001) and palmar and/or plantar hyperkeratosis (P = 0·06, trend association), and (ii) a significantly higher frequency of scarce scalp hair (P = 0·035) and scarce or absent eyelashes (P = 0·06, trend association) than those with PTPN11 mutations. CONCLUSIONS The cutaneous phenotype of NS with a PTPN11 mutation is generally mild and nonspecific, whereas the absence of a PTPN11 mutation is associated with a high frequency of keratinization disorders and hair abnormalities.

Whereas direct numerical simulation (DNS) have reached a high level of description in the field of atomization processes, they are not yet able to cope with industrial needs since they lack resolution and are too costly. Predictive simulations relying on reduced order modeling have become mandatory for applications ranging from cryotechnic to aeronautic combustion chamber liquid injection. Two-fluid models provide a good basis in order to conduct such simulations, even if recent advances allow to refine subscale modeling using geometrical variables in order to reach a unified model including separate phases and disperse phase descriptions based on high order moment methods. The simulation of such models has to rely on dedicated numerical methods and still lacks assessment of its predictive capabilities. The present paper constitutes a building block of the investigation of a hierarchy of test-cases designed to be amenable to DNS while close enough to industrial configurations, for which we propose a comparison of two-fluid compressible simulations with DNS data-bases. We focus in the present contribution on an air-assisted water atomization using a planar liquid sheet injector. Qualitative and quantitative comparisons with incompressible DNS allow us to identify and analyze strength and weaknesses of the reduced-order modeling and numerical approach in this specific configuration and set a framework for more refined models since they already provide a very interesting level of comparison on averaged quantities., Comment: Flow, Turbulence and Combustion, Springer Verlag (Germany), In press

Atom interferometry using stimulated Raman transitions in a retroreflected configuration is the first choice in high precision measurements because it provides low phase noise, high quality Raman wavefront and simple experimental setup. However, it cannot be used for atoms at zero velocity because two pairs of Raman lasers are simultaneously resonant. Here we report a method which allows to lift this degeneracy by using a frequency chirp on the Raman lasers. Using this technique, we realize a Mach-Zehnder atom interferometer hybridized with a force balanced accelerometer which provides horizontal acceleration measurements with a short-term sensitivity of $3.2\times 10^{-5}$ m.s$^{-2}$/$\sqrt{Hz}$. We check at the level of precision of our experiment the absence of bias induced by this method. This technique could be used for multiaxis inertial sensors, tiltmeters or atom interferometry in a microgravity environment., Comment: 7 pages, 9 figures

Chordoid glioma (ChG) is a characteristic, slow growing, and well-circumscribed diencephalic tumor, whose mutational landscape is unknown. Here we report the analysis of 16 ChG by whole-exome and RNA-sequencing. We found that 15 ChG harbor the same PRKCA D463H mutation. PRKCA encodes the Protein kinase C (PKC) isozyme alpha (PKCα) and is mutated in a wide range of human cancers. However the hot spot PRKCA D463H mutation was not described in other tumors. PRKCA D463H is strongly associated with the activation of protein translation initiation (EIF2) pathway. PKCαD463H mRNA levels are more abundant than wild-type PKCα transcripts, while PKCαD463H is less stable than the PCKαWT protein. Compared to PCKαWT, the PKCαD463H protein is depleted from the cell membrane. The PKCαD463H mutant enhances proliferation of astrocytes and tanycytes, the cells of origin of ChG. In conclusion, our study identifies the hallmark mutation for chordoid gliomas and provides mechanistic insights on ChG oncogenesis.

International audience; With the introduction of TiAl in aircraft jet engines, there is an increasing demand for the evaluation of novel processing routes for gamma titanium aluminides such as additive manufacturing (AM). A Ti-47Al-2Cr-2Nb powder material has been used as feedstock for laser fabrication of 3D samples by means of “Selective Laser Melting” (SLM) and “Direct Metal Deposition” (DMD). A number of processing parameters including laser power, laser scan rate, powder feed rate, have been varied to evaluate their effects on the material soundness. Optimised conditions can significantly reduce the crack sensitivity for this relatively low ductility material. In particular, crack-free experimental conditions have been identified by using additional heating strategies, thus limiting built-up residual stresses during fast cooling. The different samples have been examined using optical and scanning electron microscopy in the as-built condition. The non-equilibrium cooling conditions generate ultrafine and metastable structures exhibiting high microhardness values. A range of post-heat treatments have been performed to relieve the residual stresses and to tailor more uniform microstructures. Conventional heat treatments in the α + γ two-phase domain or in the a single phase domain have been successfully used to fully restore homogeneous microstructures either duplex or fully lamellar. A comparison is made with microstructures of both laser treated materials and of conventionally processed materials.

International audience; This paper is the first part of a set of two papers dedicated to the mechanical behavior of cellular materials at high temperatures. For that purpose, cellular materials made of brazed tube stacking cores have been considered here. This paper addresses the characterization of the elasto-viscoplastic properties of the constitutive material of the tubes, Inconel 600, by means of tensile tests. Various temperatures and strain rates were investigated, from room temperature to 800°C, in order to study the influence of both the brazing heat treatment and the test temperature on the mechanical properties of Inconel 600. Whereas the heat treatment drastically decreases the strength of the tubes, a significant viscous effect is revealed at 800°C. Electron backscattered diffraction analyses carried out post-mortem on samples showed that both dynamic recrystallization and recovery occurred during tensile tests performed at 800°C, especially at lower strain rates. In contrast, a highly deformed and textured microstructure was observed for the tubes loaded at lower temperatures.

International audience; Dwell-fatigue tests and variable strain rate tensile tests followed by cycling tests were performed using 〈0 0 1〉-oriented specimens made of a first-generation Ni-based single crystal superalloy. A short thermal jump from the nominal temperature of 1050 to 1200 °C was introduced along the lifetime of dwell-fatigue experiments and at the beginning of tensile tests. A fine γ′ precipitation occurred in the γ matrix upon such event which induced a large transient strengthening effect on the mechanical properties. In fact, a transient decrease of the plastic strain rate, corresponding to a reduced magnitude in the hysteresis loops, was measured after the temperature peak during the dwell-fatigue experiments. In addition, a temperature peak produced a large hardening effect and a mechanical behavior change during the tensile tests since a hardening of 160 MPa was recorded and a perfectly plastic behavior was obtained. These transient phenomena were due to a temporary additional strengthening provided by fine γ′ precipitates lasting for the time necessary to not hinder dislocation motions anymore. Furthermore, the experimental results were also used to determine how fine γ′ precipitates modified the magnitude and the saturation speed of the isotropic and kinematic hardenings.

International audience; The scattering of an acoustic wave by a 3D spatially-developing plane turbulent mixing layer is investigated by means of a Large Eddy Simulation (LES). First, a plane turbulent mixing layer of initial Reynolds number Reω, 0 ≈ 1200 and convective Mach number Mc ≈ 0.12 is computed and its characteristics are validated by comparisons to experimental and numerical studies. Then, an acoustic source is introduced in the computational domain and the LES of both the turbulent mixing layer and the acoustic field is carried out, allowing the direct computation of the scattered pressure field. Computational Aero Acoustics (CAA) methods have been implemented to minimize spurious pressure fluctuations created while the turbulent structures leave the computational domain. The side-lobes of the scattered pressure power spectral density are recovered and a parametric study, involving the convection velocity of the large turbulent structures, the amplitude and the tonal frequency of the source is carried out. The part of scattered energy, the frequency shift of the side-lobes and the spectra decrease are found to be correctly estimated. Analysis of directivity at the side-lobes frequencies show a progressive re-distribution of the acoustic energy, as the acoustic wave propagates through the turbulent shear layer.

Large uncertainties in land surface models (LSMs) simulations still arise from inaccurate forcing, poor description of land surface heterogeneity (soil and vegetation properties), incorrect model parameter values and incomplete representation of biogeochemical processes. The recent increase in the number and type of carbon cycle-related observations, including both in situ and remote sensing measurements, has opened a new road to optimize model parameters via robust statistical model–data integration techniques, in order to reduce the uncertainties of simulated carbon fluxes and stocks. In this study we present a carbon cycle data assimilation system that assimilates three major data streams, namely the Moderate Resolution Imaging Spectroradiometer (MODIS)-Normalized Difference Vegetation Index (NDVI) observations of vegetation activity, net ecosystem exchange (NEE) and latent heat (LE) flux measurements at more than 70 sites (FLUXNET), as well as atmospheric CO2 concentrations at 53 surface stations, in order to optimize the main parameters (around 180 parameters in total) of the Organizing Carbon and Hydrology in Dynamics Ecosystems (ORCHIDEE) LSM (version 1.9.5 used for the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations). The system relies on a stepwise approach that assimilates each data stream in turn, propagating the information gained on the parameters from one step to the next. Overall, the ORCHIDEE model is able to achieve a consistent fit to all three data streams, which suggests that current LSMs have reached the level of development to assimilate these observations. The assimilation of MODIS-NDVI (step 1) reduced the growing season length in ORCHIDEE for temperate and boreal ecosystems, thus decreasing the global mean annual gross primary production (GPP). Using FLUXNET data (step 2) led to large improvements in the seasonal cycle of the NEE and LE fluxes for all ecosystems (i.e., increased amplitude for temperate ecosystems). The assimilation of atmospheric CO2, using the general circulation model (GCM) of the Laboratoire de Météorologie Dynamique (LMDz; step 3), provides an overall constraint (i.e., constraint on large-scale net CO2 fluxes), resulting in an improvement of the fit to the observed atmospheric CO2 growth rate. Thus, the optimized model predicts a land C (carbon) sink of around 2.2 PgC yr−1 (for the 2000–2009 period), which is more compatible with current estimates from the Global Carbon Project (GCP) than the prior value. The consistency of the stepwise approach is evaluated with back-compatibility checks. The final optimized model (after step 3) does not significantly degrade the fit to MODIS-NDVI and FLUXNET data that were assimilated in the first two steps, suggesting that a stepwise approach can be used instead of the more “challenging” implementation of a simultaneous optimization in which all data streams are assimilated together. Most parameters, including the scalar of the initial soil carbon pool size, changed during the optimization with a large error reduction. This work opens new perspectives for better predictions of the land carbon budgets.

Purpose The purpose of this paper is to investigate a new cooling process of a heated cylinder with confined impacting air jet. Design/methodology/approach To do this the authors used experience-numerical and numerical-numerical comparisons. The experimental facility, designed and built at the Pau University, consists in air jets impacting around a heated circular cylinder. As the inlet velocity magnitude is low (Vin=4.37 m/s – Machin=0.0125), using a compressible solver for numerical simulations presents a number of difficulties. For this low Mach number configuration, the authors compare the performance of three different solvers in this paper. Two of them are compressible, one based on the finite volume approach and the other on a discontinuous Galerkin method, and the third one is an incompressible solver. Some of the numerical results are compared to experimental data. Findings Comparisons between the results from 3D and 2D computations support the relevance of 2D models. Some of the numerical results are compared to experimental data. Research limitations/implications The confined aspect of the set-up reduces experimental measurement to intrusive measures. It should be noted that the temperature measurement given by thermocouples is always considered as “global” or “average”. Originality/value Future aircraft technology will increasingly rely on electrical power. The substitution of mechanical energy by electrical energy will lead to an increasing amount of heat power that need be evacuated. Innovative cooling processes have to be set up according to constraints imposed by the technological design.

This paper introduces a variational multiscale simulation (VMS) approach in the context of high-order discontinuous Galerkin (DG) discretizations. First, a new calibration of the Smagorinsky model parameter ( C S Δ ) is proposed in terms of the DG discretization (grid size, h , and polynomial order, p ) and the selected VMS scale partition. Second, an efficient and simple implementation of the VMS version of the Smagorinsky model is presented. The dissipation properties of the DG discretizations for different values of h and p are then analysed based on Taylor–Green vortex computations in the limit of inviscid flow. The low levels of dissipation found for high-order DG discretizations emphasize the suitability of this type of discretization for LES. The performance of the presented approach is demonstrated by comparing DG/VMS computations of the Taylor–Green vortex at R e = 3000 with a reference spectral DNS.

International audience; Properties of resin and composite, especially anisotropic coefficients of thermal expansion, are very crucial to precisely determine residual stress generated in a composite part. No comprehensive study is available in the literature to determine these properties for woven composites and then its application to model residual stress in woven carbon epoxy composite parts. In the present article, experimental results on thermal coefficients of RTM6 epoxy resin as well carbon/epoxy woven composites obtained using different experimental techniques are compared with homogenised coefficients of thermal expansion results. Evolution of spring-in angle of L-shaped carbon/epoxy woven composite (during and after cure) with three different thicknesses is modelled by simultaneously solving the thermal-kinetics and thermal-chemical-mechanics coupling by using finite element code COMSOL Multiphysics. Objective was to quantify the contribution of curing and cooling to the formation of residual stress. Anisotropic properties of composite, during and after cure, required for numerical simulation are obtained using an analytical method. Variation in properties with degree of cure and thermal gradients induced in the part during fabrication are considered while modelling. Modelled properties of cured composites were compared with experimental values and were found in agreement. The spring-in angle values obtained by numerical simulation are compared with the results of the analytical model as well as experiments. Effect of variation of fibre volume fraction and presence of thermal gradients on spring-in was studied as well.

International audience; This study deals with the development of a partitioned coupling strategy at the fluid–solid interface for weakly transient heat transfer problems. The thermal coupling is carried out by an iterative procedure (strong coupling) between a transient solid and a sequence of steady states in the fluid. Continuity of temperature and heat flux is ensured at each coupling time step. Emphasis is put on the choice of interface conditions at the fluid–solid interface. Two fluid–solid transmission procedures are considered in this paper: Dirichlet–Robin and Neumann–Robin conditions. These conditions are theoretically examined and it is shown that the Biot number is a key parameter for determining relevant interface conditions. Stability diagrams are provided in each case and the most effective coupling coefficients are highlighted and expressed. Numerical thermal computations are then performed for two different Biot numbers. They confirm the efficiency of the interface conditions in terms of accuracy, stability and convergence. At the end of this paper a comparison between a partitioned and a monolithic approach is presented.