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International audience; Halide perovskites doped with magnetic impurities (such as the transition metals Mn2+, Co2+, Ni2+) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs2PbI2Cl2, we show that doping Mn2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn2+ does not replace the Pb2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl– and two I– atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.

International audience; The next generation of giant ground and space telescopes will have the light-collect-ing power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of the Giant Segment Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are opti-mized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance and, as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the innovative comprehensive adaptive optics and coronagraph test instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We describe the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. We detail the error budget of the CACTI system, review its operation and calibration procedures, and discuss its current status. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the raw intensity and slopes map signal processing methods. This experiment was repeated for a modulation radius of 1.6 and 3.25 λ∕D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.; La prochaine génération de télescopes terrestres et spatiaux géants aura la capacité de collecter la lumière pour détecter et caractériser des exoplanètes terrestres potentiellement habitables en utilisant pour la première fois une imagerie à contraste élevée. Cela ne sera réalisable que si les performances des systèmes d'optique adaptative extrême (ExAO) des télescopes à miroir à segmentés géants (GSMT) sont optimisées à leur plein potentiel. Un composant clé d'un système ExAO est le senseur de front d'onde (WFS), qui mesure les aberrations de la turbulence atmosphérique. Un choix courant dans les instruments actuels et de prochaine génération est le senseur de front d'onde pyramidal (PWFS). Les systèmes ExAO nécessitent un échantillonnage spatial et temporel élevé des fronts d'onde pour optimiser les performances et en conséquence nécessitent des détecteurs de grande taille pour le WFS. Nous présentons une démonstration de banc d'essai en boucle fermée d'un capteur de front d'onde pyramidal à trois côtés (3PWFS) comme alternative au capteur conventionnel de front d'onde pyramidal à quatre côtés (4PWFS) pour les applications GSMT-ExAO sur l'optique adaptative complète innovante et l'instrument de test coronographe ( CACTUS). Le 3PWFS est moins sensible au bruit de lecture que le 4PWFS car il utilise moins de pixels détecteurs. Le 3PWFS a un avantages supplémentaire : une optique pyramidale à trois côtés de haute qualité est plus facile à fabriquer qu'une pyramide à quatre côtés. Nous décrivons la conception des deux composants du système CACTI, le simulateur d'optique adaptative et le banc d'essai PWFS qui comprend à la fois un 3PWFS et un 4PWFS. Nous détaillons le budget d'erreur du système CACTI, passons en revue ses procédures de fonctionnement et d'étalonnage, et discutons de son état actuel. Une expérience préliminaire a été réalisée sur CACTI pour étudier les performances de la 3PWFS à la 4PWFS dans différentes forces de turbulence en utilisant à la fois l'intensité brute et les méthodes de traitement du signal de la carte des pentes. Cette expérience a été répétée pour un rayon de modulation de 1,6 et 3,25 λ∕D. Nous avons constaté que les performances des deux capteurs de front d'onde sont comparables si les gains de boucle modale sont réglés.

International audience; The Giant Segmented Mirror Telescopes (GSMTs) including the Giant Magellan Telescope (GMT), the Thirty Meter Telescope (TMT), and the European Extremely Large Telescope (E-ELT), all have extreme adaptive optics (ExAO) instruments planned that will use pyramid wavefront sensors (PWFS). The ExAO instruments all have common features: a high-actuator-count deformable mirror running at extreme speeds (>1 kHz); a high-performance wavefront sensor (WFS); and a high-contrast coronagraph. ExAO WFS performance is currently limited by the need for high spatial sampling of the wavefront which requires large detectors. For ExAO instruments for the next generation of telescopes, alternative architectures of WFS are under consideration because there is a trade-off between detector size, speed, and noise that reduces the performance of GSMT-ExAO wavefront control. One option under consideration for a GSMT-ExAO wavefront sensor is a three-sided PWFS (3PWFS). The 3PWFS creates three copies of the telescope pupil for wavefront sensing, compared to the conventional four-sided PWFS (4PWFS), which uses four pupils. The 3PWFS uses fewer detector pixels than the 4PWFS and should therefore be less sensitive to read noise. Here we develop a mathematical formalism based on the diffraction theory description of the Foucault knife-edge test that predicts the intensity pattern after the PWFS. Our formalism allows us to calculate the intensity in the pupil images formed by the PWFS in the presence of phase errors corresponding to arbitrary Fourier modes. We use these results to motivate how we process signals from a 3PWFS. We compare the raw intensity (RI) method, and derive the Slopes Maps (SM) calculation for the 3PWFS, which combines the three pupil images of the 3PWFS to obtain the X and Y slopes of the wavefront. We then use the Object Oriented MATLAB Adaptive Optics toolbox (OOMAO) to simulate an end-to-end model of an AO system using a PWFS with modulation and compare the performance of the 3PWFS to the 4PWFS. In the case of a low read noise detector, the Strehl ratios of the 3PWFS and 4PWFS are within 0.01. When we included higher read noise in the simulation, we found a Strehl ratio gain of 0.036 for the 3PWFS using RI over the 4PWFS using SM at a stellar magnitude of 10. At the same magnitude, the 4PWFS RI also outperformed the 4PWFS SM, but the gain was only 0.012 Strehl. This is significant because 4PWFS using SM is how the PWFS is conventionally used for AO wavefront sensing. We have found that the 3PWFS is a viable WFS that can fully reconstruct a wavefront and produce a stable closed-loop with correction comparable to that of a 4PWFS, with modestly better performance for high read-noise detectors.

Transients in plastic flow behavior and the kinetics of dynamic dissolution of α particles were established via isothermal, hot compression testing of Ti-6Al-4V (Ti64) and Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti6242S). For this purpose, samples were preheated at a low subtransus temperature at which the volume fraction of α was ~ 0.90, heated at a fixed rate to one of two higher temperatures, held for a time between 0 and 900 seconds, and then upset to a 2:1 reduction using a strain rate of 0.01, 0.1, or 1 s−1. For a given alloy, test temperature, and strain rate, the flow stress decreased with increasing hold time. The observations were interpreted in terms of various models of plastic flow and microstructure evolution. The plastic-flow behavior of the two-phase microstructures was analyzed using approaches based on isostrain (upper-bound), self-consistent (SC), and isostress (lower-bound) approaches coupled with the measured (transient/non-equilibrium) phase fractions/phase compositions. The isostrain and SC methods both provided reasonable estimates of the observed flow stresses; the isostress method greatly under-predicted the measurements. Microstructure models comprised diffusion-based analyses of the dissolution of α particles into the β matrix both statically (during heating to test temperature and holding prior to deformation) and dynamically (during deformation). Static dissolution predictions showed good agreement with measurements. A comparison of static and dynamic dissolution behaviors revealed that concurrent deformation led to an enhancement of diffusion rates by a factor of approximately 8 or 4 for Ti64 and Ti6242S, respectively.

International audience; Thermodynamic and mechanical properties of 15 single-phase and 11 multi-phase refractory complex concentrated alloys (RCCAs) are reported. Using the CALPHAD approach, phase diagrams for these alloys are calculated to identify the solidus (melting, Tm) temperatures and volume fractions of secondary phases. Correlations were identified between the strength drops at 1000 °C and 1200 °C and the alloy compositions, room temperature properties, melting temperatures and volume fractions of secondary phases. The influence of alloy density on the temperature dependence of specific yield strength was also explored. The conducted analysis suggests that the loss of high-temperature strength of single-phase BCC RCCAs is related to the activation of diffusion-controlled deformation mechanisms, which occurs at T ≥ 0.6 Tm, so that the alloys with higher Tm retain their strength to higher temperatures. On the other hand, a rapid decrease in strength of multi-phase RCCAs with increasing temperature above 1000 °C is probably due to dissolution of secondary phases.

Polar chiral structures have recently attracted much interest within the scientific community, as they pave the way towards innovative device concepts similar to the developments achieved in nanomagnetism. Despite the growing interest, many fundamental questions related to the mechanisms controlling the appearance and stability of ferroelectric topological structures remain open. In this context, ferroelectric nanoparticles provide a flexible playground for such investigations. Here, we present a theoretical study of ferroelectric polar textures in a cylindrical core-shell nanoparticle. The calculations reveal a chiral polarization structure containing two oppositely oriented diffuse axial domains located near the cylinder ends, separated by a region with a zero-axial polarization. We name this polarization configuration "flexon" to underline the flexoelectric nature of its axial polarization. Analytical calculations and numerical simulation results show that the flexon's chirality can be switched by reversing the sign of the flexoelectric coefficient. Furthermore, the anisotropy of the flexoelectric coupling is found to critically influence the polarization texture and domain morphology. The flexon rounded shape, combined with its distinct chiral properties and the localization nature near the surface, are reminiscent of Chiral Bobber structures in magnetism. In the azimuthal plane, the flexon displays the polarization state of a vortex with an axially polarized core region, i.e., a meron. The flexoelectric effect, which couples the electric polarization and elastic strain gradients, plays a determining role in the stabilization of these chiral states. We discuss similarities between this interaction and the recently predicted ferroelectric Dyzaloshinskii-Moriya interaction leading to chiral polarization states., Comment: 53 pages, 5 figures, supplementary materials on 31 pages

International audience

This data article presents a compilation of mechanical properties of 630 multi-principal element alloys (MPEAs). Built upon recently published MPEA databases, this article includes updated records from previous reviews (with minor error corrections) along with new data from articles that were published since 2019. The extracted properties include reported composition, processing method, microstructure, density, hardness, yield strength, ultimate tensile strength (or maximum compression strength), elongation (or maximum compression strain), and Young’s modulus. Additionally, descriptors (e.g. grain size) not included in previous reviews were also extracted for articles that reported them. The database is hosted and continually updated on an open data platform, Citrination. To promote interpretation, some data are graphically presented., Measurement(s) alloy • oxygen content • carbon content • nitrogen content • yield strength • elongation • ultimate strength • hardness • density • grain size • observed phases Technology Type(s) digital curation Factor Type(s) alloy processing method • test temperature • test type • alloy composition Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12804137

International audience; This data article presents the compilation of mechanical properties for 370 high entropy alloys (HEAs) and complex concentrated alloys (CCAs) reported in the period from 2004 to 2016. The data sheet includes alloy composition, type of microstructures, density, hardness, type of tests to measure the room temperature mechanical properties, yield strength, elongation, ultimate strength and Young׳s modulus. For 27 refractory HEAs (RHEAs), the yield stress and elongation are given as a function of the testing temperature. The data are stored in a database provided in Supplementary materials, and for practical use they are tabulated in the present paper. The database was used in recent publications by Miracle and Senkov [1], Gorsse et al. [2] and Senkov et al. [3].

International audience; The oxide/semiconductor structure is key to controlling current in electronic devices and HfO$_2$ is a common gate material in conventional electronic devices due to its favorable dielectric properties. Graphene devices also require insulating gates. We demonstrate a unique direct growth approach to obtain the bottom gate structure (graphene/HfO$_2$/n-SiC). The present approach involves transfer of graphene grown by chemical vapor deposition (CVD) on Cu to oxidized Si wafers, a complex process prone to low yield and reduced performance. Furthermore, HfO$_2$ is preferred to SiO$_2$ because of its superior properties. The proposed concept consists of the direct deposition of graphene by solid carbon molecular beam epitaxy on Hf metal coated n-type SiC, followed by oxygen intercalation to form HfO$_2$. The oxygen intercalation will then convert the underlying Hf into HfO$_2$ due to the strong affinity of Hf with oxygen. We identify the graphene/HfO 2 formation by Raman, X-ray photoelectron spectroscopy (XPS), Low energy electron diffraction (LEED), Low energy electron microscopy (LEEM) and electrical properties including Hall mobility and leakage current measurement.

International audience; Nature abounds with examples of animals which decrease their energy expenditure by gliding off the bow waves of large moving objects, riding thermals, or flying in efficient configurations. The past twenty years has seen significant advances in the scientific understanding and feasibility of large aircraft saving energy by flying in advantageous pair or triple geometries. Several recent flight tests demonstrated reductions in fuel burn for trailing aircraft of 10% or more. The energy savings can be converted into a variety of beneficial operational capabilities: extended range, increased loiter time, larger payload, cost savings, etc. The next looming challenge is operationalizing this practice. The discussion areas include: benefits, penalties, and trade-offs; operational modes; maneuvers; routing and scheduling; regulations; and the process of a deliberate, evolutionary approach in fielding this capability into existing aviation enterprises.

Ground-based observations of Mercury’s exosphere are intrinsically difficult due to its proximity to the Sun and must be made in daylight or during brief windows at twilight. While the dimmer twilight background is far preferred, high airmass seeing and haze through Earth’s atmosphere, windshake, and guiding all present formidable challenges toward spatially resolving the exosphere’s structure. This study explores how such effects can be mitigated using results from a new instrument for high cadence spectroscopy, the Rapid Imaging Planetary Spectrograph. While high cadence observations do not significantly improve upon the resolution floor imposed by atmospheric seeing, the method does mitigate obstacles such as telescope tracking inaccuracy, windshake, and flux calibration. Whereas daytime observing has been the predominant methodology in past exosphere studies, the twilight observations performed here easily resolve distinct brightness enhancements near 50°–60° latitude, just equatorward of magnetic cusp regions. The exosphere in these locations is diagnostic of space weather effects such as charged particle precipitation. The structure in the sodium exosphere generally appears both more extended and brighter over the southern cusp, which has a broader open magnetic field line region. However, a northern enhancement during one observation confirms that the exosphere responds dynamically to environmental drivers, presumably changes in the solar wind dynamic pressure and/or interplanetary magnetic field.

We perform a validation study of the latest version of the Alfv\'{e}n Wave Solar atmosphere Model (AWSoM) within the Space Weather Modeling Framework (SWMF). To do so, we compare the simulation results of the model with a comprehensive suite of observations for Carrington rotations representative of the solar minimum conditions extending from the solar corona to the heliosphere up to the Earth. In the low corona ($r < 1.25$ \Rs), we compare with EUV images from both STEREO-A/EUVI and SDO/AIA and to three-dimensional (3-D) tomographic reconstructions of the electron temperature and density based on these same data. We also compare the model to tomographic reconstructions of the electron density from SOHO/LASCO observations ($2.55 < r < 6.0$\Rs). In the heliosphere, we compare model predictions of solar wind speed with velocity reconstructions from InterPlanetary Scintillation (IPS) observations. For comparison with observations near the Earth, we use OMNI data. Our results show that the improved AWSoM model performs well in quantitative agreement with the observations between the inner corona and 1 AU. The model now reproduces the fast solar wind speed in the polar regions. Near the Earth, our model shows good agreement with observations of solar wind velocity, proton temperature and density. AWSoM offers an extensive application to study the solar corona and larger heliosphere in concert with current and future solar missions as well as being well suited for space weather predictions.

International audience; In the framework of NATO task group SET 226 on turbulence mitigation techniques for OA systems, a trial was conducted in the premises of RDDC-Valcartier, using indoor and outdoor facilities in September 2016. Images data sets were collected under various turbulence conditions, both controllable (indoor) and natural (outdoor). The imagery of this trial was used in the Grand Challenge, where different experts were asked to process identical input data with state-of-the-art algorithms. The trial also provided a database to validate theoretical and numerical models. The paper will give an overview of the experiment setup (target, sensors, turbulence screens generators…) and present some preliminary results obtained with the collected data in terms of effectiveness of image processing techniques, new methods for turbulence characterisation, modelling of laser beam propagation.; Augmenter la distance et/ou la résolution des systèmes optiques et laser devient de plus en plus difficile. La turbulence présente entre la cible et le senseur ou la source dégrade les performance des systèmes imageurs, des communications laser en espace libre, les systèmes de focalisation laser ou les armes à énergie dirigée. Des techniques permettant de réduire les effets induits pas la turbulence peuvent être utilisées. L'optique adaptative (OA) est plus efficaces pour des systèmes laser, tandis que le traitement du signal est plus approprié pour les systèmes imageurs. Cependant, plus la turbulence est importante moins ces techniques sont efficaces. Comprendre la turbulence et ses effets à travers des modèles et des simulations permet de développer des instruments et des algorithmes pour la mesurer et réduire ses effets. Dans le cadre du groupe OTAN SET 226 sur les techniques de mitigation de la turbulence pour les systèmes optiques, une expérimentation a été réalisée dans les locaux du RDDC Valcatier (Canada), en septembre 2016 en utilisant les équipements intérieurs et extérieurs. 8 nations ont été impliquées dans cette expérimentation. Des séquences d'images ont été enregistrées sous différentes conditions de turbulence, en environnement contrôlable (intérieur) et naturel (extérieur). Les images ont été utilisé dans le "Grand Challenge", pour lequel plusieurs experts ont mis en œuvre des algorithmes à l'état-de-l'art pour restaurer les images. Des données ont également été enregistrées pour valider les méthodes théoriques et numériques. Une autre sortie du groupe est la mise en œuvre d'instruments pour caractériser la turbulence ainsi que leur comparaison.Ce papier présente l'expérimentation (cibles, senseurs, écrans générateurs de turbulence...) et donne quelques résultats préliminaires obtenues avec les données collectées pour ce qui est de l'efficacité des techniques de traitement d'images, des méthodes de caractérisation de la turbulence, de la modélisation de la propagation laser.

International audience; In the framework of NATO task group SET 226 on turbulence mitigation techniques for OA systems, a trial was conducted in the premises of RDDC-Valcartier, using indoor and outdoor facilities in September 2016. Images data sets were collected under various turbulence conditions, both controllable (indoor) and natural (outdoor). The imagery of this trial was used in the Grand Challenge, where different experts were asked to process identical input data with state-of-the-art algorithms. The trial also provided a database to validate theoretical and numerical models. The paper will give an overview of the experiment setup (target, sensors, turbulence screens generators…) and present some preliminary results obtained with the collected data in terms of effectiveness of image processing techniques, new methods for turbulence characterisation, modelling of laser beam propagation.; Augmenter la distance et/ou la résolution des systèmes optiques et laser devient de plus en plus difficile. La turbulence présente entre la cible et le senseur ou la source dégrade les performance des systèmes imageurs, des communications laser en espace libre, les systèmes de focalisation laser ou les armes à énergie dirigée. Des techniques permettant de réduire les effets induits pas la turbulence peuvent être utilisées. L'optique adaptative (OA) est plus efficaces pour des systèmes laser, tandis que le traitement du signal est plus approprié pour les systèmes imageurs. Cependant, plus la turbulence est importante moins ces techniques sont efficaces. Comprendre la turbulence et ses effets à travers des modèles et des simulations permet de développer des instruments et des algorithmes pour la mesurer et réduire ses effets. Dans le cadre du groupe OTAN SET 226 sur les techniques de mitigation de la turbulence pour les systèmes optiques, une expérimentation a été réalisée dans les locaux du RDDC Valcatier (Canada), en septembre 2016 en utilisant les équipements intérieurs et extérieurs. 8 nations ont été impliquées dans cette expérimentation. Des séquences d'images ont été enregistrées sous différentes conditions de turbulence, en environnement contrôlable (intérieur) et naturel (extérieur). Les images ont été utilisé dans le "Grand Challenge", pour lequel plusieurs experts ont mis en œuvre des algorithmes à l'état-de-l'art pour restaurer les images. Des données ont également été enregistrées pour valider les méthodes théoriques et numériques. Une autre sortie du groupe est la mise en œuvre d'instruments pour caractériser la turbulence ainsi que leur comparaison.Ce papier présente l'expérimentation (cibles, senseurs, écrans générateurs de turbulence...) et donne quelques résultats préliminaires obtenues avec les données collectées pour ce qui est de l'efficacité des techniques de traitement d'images, des méthodes de caractérisation de la turbulence, de la modélisation de la propagation laser.

Part 7: Information Visualization; International audience; Interaction is the cornerstone of how people perform tasks and gain insight in visual analytics. However, people’s inherent cognitive biases impact their behavior and decision making during their interactive visual analytic process. Understanding how bias impacts the visual analytic process, how it can be measured, and how its negative effects can be mitigated is a complex problem space. Nonetheless, recent work has begun to approach this problem by proposing theoretical computational metrics that are applied to user interaction sequences to measure bias in real-time. In this paper, we implement and apply these computational metrics in the context of anchoring bias. We present the results of a formative study examining how the metrics can capture anchoring bias in real-time during a visual analytic task. We present lessons learned in the form of considerations for applying the metrics in a visual analytic tool. Our findings suggest that these computational metrics are a promising approach for characterizing bias in users’ interactive behaviors.

Electron attachment to phosphoryl chloride (phosphorus oxychloride) POCl 3 has been studied in the gas phase by mass spectrometry at several low temperatures (47.7, 74.5, 169.7 and 199.5 K) with the CRESU method. By measuring over this temperature range and data from [8] , we have demonstrated the inversion of the branching ratio between the exothermic non-dissociative exit channel POCl 3 − and the thermo-neutral dissociative exit channel POCl 2 − + Cl. A kinetic model in terms of statistical theory is used to fit the experimental data.

International audience; Zr-C thin films are grown on single-crystalline MgO(001) substrates via ultra-high vacuum dc magnetron sputtering of Zr target in 10 mTorr Ar-C$_2$H$_4$ gas mixtures with ethylene partial pressures ($P_{C2H4}$) between 2 × 10$^{−7}$ Torr and 2 × 10$^{−4}$ Torr at substrate temperature $T_s$ = 923 K and using $P_{C2H4}$ = 2 × 10$^{−6}$ Torr at 723 K ≤ $T_s$ ≤ 1123 K. The as-deposited layer microstructure and composition are determined using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. We find that the layers sputter-deposited at $T_s$ = 923 K using the lowest $P_{C2H4}$ = 2 × 10$^{−7}$ Torr are polycrystalline, close-packed hexagonal structured Zr:C solid solutions. At higher $P_{C2H4}$ = 2 × 10$^{−6}$ Torr and 2 × 10$^{−5}$ Torr, we obtain films composed of free‑carbon (C) and NaCl-structured ZrC$_x$, $x$ ≤ 1. The amount of C increases 104% with ten-fold increase in $P_{C2H4}$ from 2 × 10$^{−6}$ Torr to 2 × 10$^{−5}$ Torr. At the highest $P_{C2H4}$ = 2 × 10$^{−4}$ Torr, the layers are X-ray amorphous with $\sim$49 at.% C. Films grown at 723 K ≤ $T_s$ ≤ 1123 K using constant $P_{C2H4}$ = 2 × 10$^{−6}$ Torr exhibit qualitatively similar microstructures, irrespective of $T_s$, composed of dense columnar ZrC$_x$ grains surrounded by C and corrugated surfaces. Our results suggest that the compositional and microstructural evolution of Zr-C films during reactive sputter-deposition of Zr is highly sensitive to ethylene partial pressure, with as little as 0.02% of the total pressure sufficient at $T_s$ ≥ 723 K to obtain ZrC$_x$ films.

International audience; Active ionospheric experiments using high-power, high-frequency transmitters, “heaters”, to study plasma processes in the ionosphere and magnetosphere continue to provide new insights into understanding plasma and geophysical proceses. This review describes the heating facilities, past and present, and discusses scientific results from these facilities and associated space missions. Phenomena that have been observed with these facilities are reviewed along with theoretical explanations that have been proposed or are commonly accepted. Gaps or uncertainties in understanding of heating-initiated phenomena are discussed together with proposed science questions to be addressed in the future. Suggestions for improvements and additions to existing facilities are presented including important satellite missions which are necessary to answer the outstanding questions in this field.

Spatial structures in ionospheric electron density revealed in a tomographic image have been identified with auroral forms and related to their sources in precipitating particles observed by DMSP satellites. The observations of plasma enhancements relate to discrete auroral arcs seen in the post-noon sector, identified by both red- and green-line emissions measured by a meridional scanning photometer. The features lie within a very narrow latitudinal band on L-shells where the satellite detectors observed electron precipitation classified as from the boundary plasma sheet (BPS). The harder particles are identified with an E-region structure, while further north the precipitation is softer, resulting in a localised F-layer blob and 630.0 nm emissions. A steep gradient in plasma density represent a signature in the ionosphere of the central plasma sheet (CPS)/BPS boundary. A transition to a less-structured F-layer is found on crossing the convection reversal boundary..Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; polar ionosphere)

In two case studies we elaborate on spatial and temporal structures of the dayside aurora within 08:00-16:00 magnetic local time (MLT) and discuss the relationship of this structure to solar wind-magnetosphere interconnection topology and the different stages of evolution of open field lines in the Dungey convection cycle. The detailed 2-D auroral morphology is obtained from continuous ground observations at Ny Ålesund (76° magnetic latitude (MLAT)), Svalbard during two days when the interplanetary magnetic field (IMF) is directed southeast (By>0; Bz). The auroral activity consists of the successive activations of the following forms: (i) latitudinally separated, sunward moving, arcs/bands of dayside boundary plasma sheet (BPS) origin, in the prenoon (08:00-11:00MLT) and postnoon (12:00-16:00MLT) sectors, within 70-75° MLAT, (ii) poleward moving auroral forms (PMAFs) emanating from the pre- and postnoon brightening events, and (iii) a specific activity appearing in the 07:00-10:00MLT/75-80° MLAT during the prevailing IMF By>0 conditions. The pre- and postnoon activations are separated by a region of strongly attenuated auroral activity/intensity within the 11:00-12:00MLT sector, often referred to as the midday gap aurora. The latter aurora is attributed to the presence of component reconnection at the subsolar magnetopause where the stagnant magnetosheath flow lead to field-aligned currents (FACs) which are of only moderate intensity. The much more active and intense aurorae in the prenoon (07:00-11:00MLT) and postnoon (12:00-16:00MLT) sectors originate in magnetopause reconnection events that are initiated well away from the subsolar point. The high-latitude auroral activity in the prenoon sector (feature iii) is found to be accompanied by a convection channel at the polar cap boundary. The associated ground magnetic deflection (DPY) is a Svalgaard-Mansurov effect. The convection channel is attributed to effective momentum transfer from the solar wind-magnetosphere dynamo in the high-latitude boundary layer (HBL), on the downstream side of the cusp.

International audience; Virtual imaging through dielectric microspheres is shown to possess the resolution beyond the classical diffraction limit, but the factors responsible for such resolution are debated in the literature. In this work, we experimentally demonstrated an important role of spectral overlap between the emission band of a fluorescent (FL) object and the spectral peak of localized surface plasmon resonance (LSPR) in the underlying metallic periodic nanostructure. As an object, we used green and blue FL nanospheres placed at the top of Au and Al arrays with different periods. It is shown that the maximal resolution beyond the diffraction limit can be achieved in confocal microscopy of green (blue) FL nanospheres at the top of Au(Al) arrays. Our results provide the first direct evidence for the critically important role of resonant coupling of emission of point-like objects to LSPRs in the underlying nanostructure for achieving the super-resolution.

International audience; It is shown that the resolution of virtual images of dye-doped dielectric nanospheres obtained through dielectric microspheres can be increased beyond the classical diffraction limit by decreasing the period of nanoplasmonic array used for localized plasmonic structured illumination of these objects. In contrast to far-field superlens design, the superresolution is obtained without using metallic layers and gratings after superlens. In addition, it is shown that the postimaging processing, which represents an intrinsic part of SIM, is not required for achieving the super-resolved images. This observation is interpreted based on a concept that the radiation of objects placed at the surface of nanoplasmonic arrays with sufficiently short periods is initially provided into folded dispersions of nanoplamonic array, so that the diffraction orders responsible for super-resolution are more efficiently coupled to dielectric microspherical antenna compared to that for the propagating modes within the cutoff frequency.

International audience; Use of resonant light forces opens up a unique approach to high-volume sorting of microspherical resonators with 1/Q accuracy, where Q is the resonance quality factor. Based on a two-dimensional model, it is shown that the sorting can be realized by allowing spherical particles to traverse a focused beam. Under resonance with the whispering gallery modes (WGM), the particles acquire significant velocity along the laser beam which should allow sorting dielectric microspheres with almost identical positions of their WGM resonances. This is an enabling technology for developing super-low-loss coupled-cavity structures and devices.

This paper addresses how well and under what conditions the Rayleigh-Debye-Gans (RDG) approximation describes scattering and absorption of light by fractal aggregates (FA) including soot. The RDGFA theory, which is the prevailing, first order description of this problem, has two assumptions: the monomers, or primary particles, of the aggregate scatter and absorb in the Rayleigh regime, and the aggregate scatters in the diffraction limit weighted by this Rayleigh scattering and absorbs as a system of independent monomer particles. The aggregates studied here are formed via Diffusion Limited Cluster Aggregation (DLCA) and have a fractal dimension D = 1.78 ± 0.04 and prefactor of k0 = 1.35 ± 0.10. The aggregates are a collection of monodisperse spherical monomers with point contacts. Optical calculations were performed with the multiple sphere T-matrix (MSTM) and DDSCAT codes for incident light polarized perpendicular to the scattering plane. The scattering considered is the forward scattering intensity and the angular scattering as parameterized by the scattering wave vector. The total absorption cross section for aggregates is also calculated. This work stresses the systematic study of the effects of the variables of monomers per aggregate, which ranged from one to 502, two monomer size parameters of 0.157 and 0.314, and a wide range of refractive index real and imaginary parts. It also considers soot refractive indices with three representative dispersions. A summary of results for both scattering and absorption includes deviations from RDGFA theory ranging as large as 35% with positive deviations increasing with the real part of the refractive index and negative deviations growing with the imaginary part. These deviation from the RDG limit are shown to be similar to deviations for spheres.

International audience; We describe molecular beam epitaxy (MBE) growth conditions for self-assembled indium nanostructures, or islands, which allow for the tuning of the density and size of the indium nanostructures. How the plasmonic resonance of indium nanostructures is affected by the island density, size, distribution in sizes, and indium purity of the nanostructures is explored. These self-assembled nanostructures provide a platform for integration of resonant and non-resonant plasmonic structures within a few nm of quantum wells (QWs) or quantum dots (QDs) in a single process. A 4× increase in peak photoluminescence intensity is demonstrated for near-surface QDs resonantly coupled to indium nanostructures

International audience; Quantum cascade lasers (QCL) are semiconductor lasers based on ultrafast intersubband transitions with pi-cosecond timescale that have become the most suitable laser sources from the mid-infrared to the THz range, due to their compactness, efficiency and high room temperature performances. In particular, high-power QCLs are powerful sources for optical countermeasures, including night vision blinding and missile out steering. This work investigates the nonlinear dynamical features of coupling of linear arrays of emitters in the so-called Tal-bot configuration for phase-locking operation using broad area emitters. These initial results are of paramount importance for creating future bright infrared sources with Watt-level power.

We propose a concept of chiral photonic limiters utilising topologically protected localised midgap defect states in a photonic waveguide. The chiral symmetry alleviates the effects of structural imperfections and guaranties a high level of resonant transmission for low intensity radiation. At high intensity, the light-induced absorption can suppress the localised modes, along with the resonant transmission. In this case the entire photonic structure becomes highly reflective within a broad frequency range, thus increasing dramatically the damage threshold of the limiter. Here we demonstrate experimentally the principle of operation of such photonic structures using a waveguide consisting of coupled dielectric microwave resonators., Comment: 6 pages, 4 figures

Several fast solar wind streams and stream interaction regions (SIRs) were observed by the Parker Solar Probe (PSP) during its first orbit (2018 September–2019 January). During this time, several recurring SIRs were also seen at 1 au at both L1 (Advanced Composition Explorer (ACE) and Wind) and the location of the Solar Terrestrial Relations Observatory-Ahead (STEREO-A). In this paper, we compare four fast streams observed by PSP at different radial distances during its first orbit. For three of these fast stream events, measurements from L1 (ACE and Wind) and STEREO-A indicated that the fast streams were observed by both PSP and at least one of the 1 au monitors. Our associations are supported by simulations made by the ENLIL model driven by GONG-(ADAPT-)WSA, which allows us to contextualize the inner heliospheric conditions during the first orbit of PSP. Additionally, we determine which of these fast streams are associated with an SIR and characterize the SIR properties for these events. From these comparisons, we find that the compression region associated with the fast-speed streams overtaking the preceding solar wind can form at various radial distances from the Sun in the inner heliosphere inside 0.5 au, with the suprathermal ion population (energies between 30 and 586 keV) observed as isolated enhancements suggesting localized acceleration near the SIR stream interface at ∼0.3 au, which is unlike those seen at 1 au, where the suprathermal enhancements extend throughout and behind the SIR. This suprathermal enhancement extends further into the fast stream with increasing distance from the Sun.

International audience; The resolution of microsphere-based nanoscopy is studied using fluorescently labeled nanospheres and F-actin protein filaments with the emission coupled to the localized surface plasmon resonances in the underlying Au nanodisk arrays. Virtual imaging is performed through high-index microspheres embedded in plastic coverslips placed in contact with the nanoscale objects. For 150 and 200 nm periods of nanoplasmonic arrays, the imaging has a solid immersion lens-limited resolution, whereas for shorter periods of 80 and 100 nm, the resolution was found to increase up to ∼λ/7, where λ is the emission wavelength. The results cannot be interpreted within a framework of a regular localized plasmonic structured illumination microscopy since the array period was significantly shorter than the wavelength and postimaging processing was not used. It is hypothesized that the observed super-resolution is based on coupling of the emission of nanoscale objects to strongly localized near-field maxima in the adjacent plasmonic metasurfaces followed by evanescent coupling to high-index microspheres.

International audience; An experimental program was performed to determine the rheology and influence of niobium additions to high-purity nickel on dynamic-recrystallization behavior during hot working. Various high-purity alloys were prepared (pure Ni and Ni-0.01, 0.1, 1, 2, 5 and 10 wt% Nb) and deformed to high strains by hot torsion to characterize the mechanical behavior within the temperature range from 800 to 1000 degrees C at (von Mises equivalent) strain rates of 0.03, 0.1 and 03 s(-1). A simple analytical method was proposed for predicting the strain-hardening and dynamic-recovery parameters in the classical Yoshie-Laasraoui-Jonas equation. By the means, the effect of niobium solutes on plastic flow was determined, thus enabling a reasonable fit for the flow curves for the entire range of solid solution Ni-Nb alloys. (C) 2013 Elsevier B.V. All rights reserved.

A numerical method is demonstrated in which a simple flame temperature criterion of 2700 K is used to map out flammability diagrams as a function of total mixture pressure and equivalence ratio in the hypergolic system, MMH/NTO/He. The computed results are in good agreement with experimentally determined ignition diagrams for MMH/NTO/He. The method is used to predict the lower and upper hypergolicity limits of other mixtures known to be hypergolic at 298 K and 1 atm. Comparisons between available experimental data (mixing ratios) and calculated limits lead to the conclusion that the present numerical method may allow the screening of other fuel/oxidant systems potentially of interest for spacecraft propulsion as well as for the determination of the range of mixing ratios able to ensure auto-ignitibility (hypergolicity) in combustion devices. In the safety field, the same method allows for the rapid assessment of hazards in terms of hypergolicity.

International audience; LaB$_6$–ZrB$_2$ composites obtained by directional solidification at eutectic composition have been investigated by low-energy electron microscopy (LEEM) and thermal emission electron microscopy (ThEEM). The transitions from the mirror electron microscopy mode to the LEEM mode for the hexa- and diborides indicate lower work functions of the two phases when embedded in the composite compared to the corresponding single phases. In the composite, the work function of the ZrB2 fibers is similar to that of the matrix and ThEEM images display a brighter contrast for the fibers. This is explained by the thermally activated diffusion of La on the fiber surface.

International audience; The effects of pulse repetition frequency (PRF) and energy deposition was investigated using nanosecond repetitively pulsed discharges in a constant volume combustion chamber. Quiescent lean propane-air mixtures (equivalence ratio of 0.7) at 0.2 MPa were ignited using fixed total energy deposition and number of pulses across the range of PRF from 2 to 90 kHz. Individual pulse energies were measured by electrical probes, and the ignition time was quantified through the use of high-frame-rate intensified imaging of the chemiluminescence. For fixed inter-electrode gap and constant total energy, the ignition time was minimized at a certain pulsation frequency, with higher PRF being detrimental and resulting in longer ignition delay times. Decreasing the total energy deposited in the mixture shifted the minimum ignition time to higher PRF. On the contrary, increasing the gap distance at constant total energy allowed for the same minimum ignition time to be achieved at significantly lower PRF. The minimum ignition delay times for fixed inter-electrode gap distance were similar for a given amount of mean energy deposited per unit time. The effect of energy deposition, PRF, and inter-electrode gap was attributed to the competition between characteristic recirculation time from the discharge-induced flowfield and the inter-pulse time.

An examination of a compositionally graded Al x CuCrFeNi 2 high entropy alloy (HEA) or complex concentrated alloy (CCA), revealed that marginally increasing Al content from x = 0.8 to x = 1.0 (+ 6 at.%) changes the primary solidification phase from a simple disordered- fcc to a bcc -based ordered-B2 phase. Subsequently, a second solidification product forms, a disordered- bcc in case of x = 0.8 and a disordered- fcc in case of x = 1.0. Solid-state decomposition within these phases results in fcc + L1 2 and bcc + B2 products, accompanied by compositional partitioning. These results provide new insights into the influence of Al on the primary solidification product, and have been rationalized using a computational thermodynamic approach.

International audience; We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about On-Orbit Degradation of Solar and Space Weather Instruments that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions.

International audience; The onset of the coherence collapse (CC) regime, which is incompatible with data transmission, is investigated both theoretically and experimentally in a 1.55-um InAs/InP quantum dash semiconductor laser. It is numerically shown that the filling from the excited state produces an additional term, which accelerates the route to chaos. This contribution can be seen as a perturbation that reduces the overall CC threshold.

ISBN de l'édition originale : ISBN 978-1-118-94545-2; International audience; This is a collection of manuscripts presented at the 2nd International Congress on 3D MaterialsScience, a conference organized by The Minerals, Metals & Materials Society (TMS), the AdvancedCharacterization, Testing and Simulation Committee, and the six congress organizers, and held inAnnecy, France, on June 29–July 2, 2014.Building on the great success of the first event in 2012, the 2nd Congress on 3D Materials Scienceconvened researchers and engineers to assess the state-of-the-art in 3D materials science anddetermine paths to further the global advancement of this field. More than 150 presenters andattendees from all over the world contributed to this congress in the form of presentations, livelydiscussions, and manuscripts presented in this volume. The international advisory committeemembers, representing 11 different countries, actively participated in selecting the contributions,reviewing the manuscripts, and promoting the congress.The congress consisted of 2 keynote presentations from international experts, 96 contributedpresentations (in two parallel sessions), 75 poster presentations, and 1 panel discussion. From theposter sessions, outstanding posters were selected for awards, which were presented to the authorsat the congress dinner. The event concluded with a closing panel of experts focusing the discussionon the evolution of 3D materials science in the period between the two congresses and the futuredirections.The 20 papers presented in this proceedings publication are divided into 6 sections: (1) Acquisitionand Handling of 3D Data; (2) Microstructure/Property Relationship in 3D: Characterization andSimulation; (3) Microstructure/Property Relationship in 3D: Deformation and Damage; (4) NewExperimental Techniques; (5) Analysis at the Nanoscale; (6) Dynamic Processes. It is our hopethat the 2nd International Congress on 3D Materials Science and these proceedings will furtherthe implementation of three-dimensional materials science and broaden its variety of applications.